Supervised peer-to-peer systems
Supervised Peer-to-Peer Systems
Kishore Kothapalli and Christian Scheideler?
Department of Computer Science
Johns Hopkins University
3400N.Charles Street
Baltimore,MD21218,USA
Email:{kishore,scheideler}@https://www.wendangku.net/doc/9d3805582.html,
April6,2006
Abstract
In this paper we present a general methodology for designing supervised peer-to-peer systems.A supervised peer-to-peer system is a system in which the overlay network is formed by a supervisor but in which all other activities can be performed on a peer-to-peer basis without involving the supervisor.It can therefore be seen as being between server-based systems and pure peer-to-peer systems.Though it appears that supervised peer-to-peer systems are limited in their scalability,we will argue that with our concept supervised peer-to-peer systems can scale to millions of peers without requiring the supervisor to be more powerful than just having a normal workstation with a100Mbit/s connection.In fact,the supervisor only has to store a constant amount of information about the system at any time and only needs to send a small constant number of messages to integrate or remove a peer in a constant amount of time.Thus,with a minimum amount of involvement from the supervisor,peer-to-peer systems can be maintained,for example,that can handle large distributed computing tasks as well as tasks such as ?le sharing and web crawling.Furthermore,our concept extends easily to multiple supervisors so that peers can join and leave the network massively in parallel.We also show how to extend the basic system to provide robustness guarantees under the presence of random faults and under adversarial join/leave attacks.Hence,with our approach,supervised peer-to-peer systems can share the bene?ts of server-based and pure peer-to-peer systems without inheriting their disadvantages.
1Introduction
Peer-to-peer systems have recently attracted a signi?cant amount of attention inside and outside of the research community.The advantage of peer-to-peer systems is that they can scale to millions of sites with low-cost hardware whereas the classical approach of using server-based systems does not scale well,unless powerful servers are provided.On the other hand,server-based systems can provide guarantees and are therefore preferable for critical applications that need a high level of reliability.The question is whether it is possible to marry the two approaches in order to share their bene?ts without sharing their disadvantages. We propose supervised peer-to-peer systems as a possible solution to this.
A supervised peer-to-peer system is a system in which the overlay network is formed by a supervisor but in which all other activities can be performed on a peer-to-peer basis without involving the supervisor. That is,all peers that want to join(or leave)the network have to contact the supervisor,and the supervisor will then initiate their integration into(or removal from)the network.All other operations,however,may be executed without involving the supervisor.In order for a supervised network to be highly scalable,we propose two central requirements that have to be ful?lled:
1.The supervisor needs to store at most a polylogarithmic amount of information about the system at
any time(i.e.if there are n peers in the system,storing contact information about O(log2n)of these peers would be?ne,for example),and
2.The supervisor needs at most a constant number of messages to include a new peer into,or exclude
an old peer,from the network.
The second condition makes sure that the work of the supervisor to include or exclude peers from the system is kept at a minimum.Still,one may certainly wonder whether supervised peer-to-peer systems are really as scalable as pure peer-to-peer systems on the one hand and as reliable as server-based systems on the other hand.In this paper,we argue that our approach can result in highly scalable and highly reliable systems.
1.1Motivation
First of all,remember that even pure peer-to-peer systems need some kind of a“rendezvous point”,such as a well-known host server[17]or a well-known web-address like https://www.wendangku.net/doc/9d3805582.html,,which allows new peers to join the system.The rendezvous point typically does not play any role in the overall topology of the network but just acts as a bridge between new nodes and the existing network.This means that nodes have to self-organize to form an overlay network with good topological properties such as diameter,degree and expansion.In such a scenario,(a)randomized constructions cannot guarantee a good expansion or diameter and(b)deterministic constructions involve complex balancing schemes[4]to arrive at a good topology.
We show that allowing the supervisor to oversee the topology of the overlay network,apart from working as the rendezvous point,tremendously simpli?es the problem of maintaining the above mentioned desirable properties of the peer-to-peer network.Hence,as long as the communication effort of a supervisor for including or excluding a peer is only a low constant,supervised designs should compete well with pure peer-to-peer systems.
Our approach has many interesting applications in the area of grid computing[20,23,9],WebTV,and massive multi-player online gaming[12],as outlined in Section5.A supervisor may also serve,for example, as a reliable anchor for code execution rollback,which is important for failure recovery mechanisms such as those used in the Time Warp system[10].This would make supervised peer-to-peer systems particularly interesting for grid computing[20].With our concept,supervised peer-to-peer systems can scale to millions of peers without requiring the supervisor to be more powerful than just having a normal workstation with a100Mbit/s connection.Also,it is much easier to recover from temporary network partitions with a
supervised system than a pure peer-to-peer system.This is useful for systems in which fast recovery is important due to real-time content,such as Internet radio or Internet TV.Finally,though supervised peer-to-peer systems are not as stable as server-based systems with powerful servers,their advantage is that because the supervisor only takes care of the topology but may not be involved at all in peer-to-peer activities,it is from a legal point of view a much safer design than the server-based design.
1.2Our Results
In Section2,we show how to combine known techniques proposed for peer-to-peer systems such as the hierarchical decomposition approach of CAN[18],and the continuous-discrete approach[16]in a novel way to obtain a general framework for the design of supervised peer-to-peer systems.Our approach requires the supervisor to store a constant amount of information about the system at any time and to only send and receive a low constant number of messages in order to integrate or remove a peer from the system.We demonstrate our approach by showing how to maintain a supervised hypercube network and a supervised de Bruijn network with it.Our scheme can also be extended to allow concurrent join/leave operations or allow multiple supervisors as outlined in Section3.In order to demonstrate that supervised systems can be made highly scalable,we propose solutions in Section3that allow a supervisor to serve many join and leave requests concurrently and then extend our basic design to allow multiple supervisors.Afterwards,in Section 4we look at robustness issues and discuss how our supervised design can be extended to handle random faults.We also present and analyze a simple scheme involving the supervisor so that the resulting network is robust even against adaptive adversarial join/leave attacks,a study recently initiated in[22].Finally,we discuss in Section5various applications of our supervised approach.
1.3Related work
Special cases of supervised peer-to-peer systems have already been formally investigated[17,21,20],but to the best of our knowledge a general framework for supervised peer-to-peer systems has not been presented yet.
In[17],the authors consider a special node called the host server that is contacted by all new peers that join the system.The overlay network maintained by the host server is close to a random-looking graph.As shown by the authors,under a stochastic model of join/leave requests the overlay network can,with high probability,guarantee connectivity,low diameter,and low degree.Alternative designs were later proposed in [21,20].In[21]it is shown how to maintain a tree topology using a supervisor for guaranteed broadcasting and in[20]it is shown how to maintain a supervised overlay network with de Bruijn graph topology for grid computing and load balancing.In this work,we propose a uni?ed model that enables one to create a large class of supervised overlay networks.
Most of the distributed systems are either server-based or peer-to-peer.For example,Napster is rather server-based because all peer requests are handled at a single location.Also systems like SETI@home[23], Folding@home[11],and https://www.wendangku.net/doc/9d3805582.html,[9]are heavily server-oriented because they do not allow peer-to-peer interactions.Other systems such as the IBM OptimalGrid allow communication between peers but it still uses a star topology and therefore is still closer to being server-based than supervised.Extensive research on computational grids is also done in the Globus Alliance but they do not appear to consider topological designs in their research.
The line of research that is probably closest to our approach is the work on overlay networks in the area of application-layer multicasting.Among them are SpreadIt[8],NICE[2],Overcast[13],and PRM[3],to name a few.However,these systems only focus on speci?c topologies such as trees,and they do not seem to be generalizable to a universal approach for supervised systems.Other protocols for application-layer multicasting such as Scribe[5],Bayeux[27],I3[24],Borg[26],SplitStream[6],and CAN-Multicast[19]
are rather extensions of a pure peer-to-peer system.For an evaluation of several of these protocols see [7],for example.
2A general framework for supervised peer-to-peer systems
Our general framework for supervised peer-to-peer systems needs several ingredients,including the hier-archical decomposition technique [18],the continuous-discrete technique [16],and the recursive labeling technique.After presenting these techniques we show how to put them together in an appropriate way so that we obtain a universal approach for supervised peer-to-peer systems.Afterwards,we give some ex-amples that demonstrate how to apply this approach to maintain a supervised hypercubic network and a supervised de Bruijn network.
2.1The hierarchical decomposition technique
Consider any d –dimensional space U =[0,1)d for some d ≥1.The decomposition tree T (U )of U is an in?nite binary tree in which the root represents U and for every node v representing the subcube U in U ,the children of v represent two subcubes U and U ,where U and U are the result of cutting U in the middle at the smallest dimension in which U has a maximum side length.Let every edge to a left child in T (U )be labeled with 0and every edge to a right child in T (U )be labeled with 1.Then the label of a node v ,is the sequence of all edge labels encountered when moving along the unique path from the root of T (U )downwards to v .For d =2,the result of this decomposition is shown in Figure 1.11100000100
10
0. . . . . . .
. . . . . . .0
10
1010
101011
Figure 1:The decomposition tree for d =2.
Our goal for the supervised peer-to-peer system will be to map the peers to nodes of T (U )so that
1.the subcubes of the (nodes assigned to the)peers are disjoint,
2.the union of the subcubes of the peers gives the entire set U ,and
3.the peers are only distributed among nodes of two consecutive levels in T (U ).
The above goals are important for the following reason.Recall the CAN based approach of [18].The basic idea is to combine an in?nite complete binary tree T with a family of graphs G ={G | ∈IN 0}with
|V(G )|=2 for every ≥0.The?rst two goals are required so that every path down the tree starting with the root contains exactly one peer which is the basic invariant for the CAN-based approach[18].In order to keep the degree low,a basic goal of the CAN approach is to keep the nodes in as few levels of the tree T as possible.This can be quantized by level imbalance being de?ned as the maximum difference between the levels of the nodes in T.This parameter is called the global gap in[1].The third goal thus asks for an assignment of nodes to levels so that the level imbalance is close to optimal.
Whereas CAN-based peer-to-peer systems usually satisfy the?rst two properties,they have problems with the third property.For example,using randomized strategies[1,18]involve advanced techniques such as multiple-choice hashing[15]and result in a level imbalance of O((log log n)/log d)for d≥2.But as we will see,it will be easy for our supervised peer-to-peer approach to also maintain the third property using deterministic strategies.
2.2The continuous-discrete technique
The basic idea underlying the continuous-discrete approach[16]is to de?ne a continuous model of graphs and to apply this continuous model to the discrete setting of a?nite set of peers.
Consider any d-dimensional space U=[0,1)d,and suppose that we have a set F of functions f i:U→U,i≥1.Then we de?ne E F as the set of all pairs(x,y)∈U2with y=f i(x)for some i.Given any subset S?U,letΓ(S)={y∈U\S|?x∈S:(x,y)∈E F}.We say that(U,E F)is connected if for any subset S?U it holds thatΓ(S)=φ.
Consider now any set of peers V,and let R(v)be the region in U that has been assigned to peer v.Let G F(V)be the graph with node set V and edge set
E(G F)={(v,w)∈V×V|?x∈R(v),?y∈R(w),(x,y)∈E F} That is,E(G F)contains an edge(v,w)for every pair of nodes v and w for which there is an edge (x,y)∈E F with x∈R(v)and y∈R(w).Using the above setting,the following theorem holds: Theorem2.1Suppose that∪v∈V R(v)=U and(U,E F)is connected,then also G F(V)is connected.
The proof of the above theorem follows from the de?nitions.Thus,to arrive at a situation where G F(V) is connected we have to ensure that∪v∈V R(v)=U.But the goals of the heiararchical decomposition technique ensure such an assignment.
Letρ=max u,v∈V|R(v)|/|R(u)|be the smoothness[16]of the above assignment scheme.Then,using the properties of the hierarchical decomposition technique it holds thatρis independent of n andρ≤2. Havingρa constant has nice implications as described in[16]even when considering arbitrary set F of functions.
2.3The recursive labeling technique
In the recursive labeling approach,the supervisor assigns a label to every peer that wants to join the system. The labels are represented as binary strings and are generated in the following order:
0,1,01,11,001,011,101,111,0001,0011,0101,0111,...
Basically,ignoring label0,when stripping off the least signi?cant bit,the supervisor is?rst creating all binary numbers of length0,then length1,then length2,and so on.More formally,consider the mapping :IN0→{0,1}?with the property that for every x∈IN0with binary representation(x d...x0)2(where d is minimum possible),
(x)=(x d?1...x0x d)
Then generates the sequence of labels displayed above.In the following,it will also be helpful to view labels as real numbers in[0,1).Let the function r:{0,1}?→[0,1)be de?ned so that for every label =( 1 2... d)∈{0,1}?,r( )= d i=1 i
With this strategy,it follows from Lemma2.4that all three demands formulated in the hierarchical decom-position approach are satis?ed.
Consider now any family F of functions acting on some space U=[0,1)d and let C(p)be the subcube
of the node in T(U)that p has been assigned to.Then the goal of the supervisor is to maintain the following invariant at any time.
Invariant2.5For the current set V of peers in the system it holds that
1.the set of labels used by the peers is{ (0), (1),..., (n?1)},where n=|V|,
2.every peer v in the system is connected to pred(v)and succ(v),and
3.there are bidirectional connections{v,w}for every pair of peers v and w for which there is an edge
(x,y)∈E F with x∈C(v)and y∈C(w).
2.5Maintaining Invariant2.5
Next we describe the actions that the supervisor has to perform in order to maintain Invariant2.5during
an isolated join or leave operation.For simplicity,we assume that all nodes are reliable and trustworthy and also that peers depart gracefully i.e.,they announce their departure to the supervisor.(Non-graceful departures and untrustworthy nodes are treated in Section4).We also assume that the supervisor can in each round send a message that can contain up to a constant amount of information.We start with the following important fact which can be easily shown.
Fact2.6Whenever a new peer v enters the system,then pred(v)has all the connectivity information v needs to satisfy Invariant2.5(3),and whenever an old peer w leaves the system,then it suf?ces that it transfers all of its connectivity information to pred(w)in order to maintain Invariant2.5(3).
The?rst part of the fact follows from the observation that when v enters the system,then the subcube
of pred(v)splits into two subcubes where one resides at pred(v)and the other is taken over by v.Hence,
if pred(v)passes all of its connectivity information to v,then v can establish all edges relevant for it according to the continuous-discrete approach.The second part of the fact follows from the observation that
the departure of a peer is the reverse of the insertion of a peer.
Thus,if the peers take care of the connections in Invariant2.5(3),the only part that the supervisor has to take care of is maintaining the cycle.For this we require the following invariant.
Invariant2.7At any time,the supervisor stores the contact information of pred(v),v,succ(v),and succ(succ(v)) where v is the peer with label (n?1).
We now describe how to maintain Invariant2.5during any join or leave operation.
Join:If a new peer w joins,in order to satisfy Invariant2.7,the following actions are performed.In the following,S denotes the supervisor.
?S informs w that (n)is its label,succ(v)is its predecessor,and succ(succ(v))is its successor.
?S informs succ(v)that w is its new successor.
?S informs succ(succ(v))that w is its new predecessor.
?S asks succ(succ(v))to send its successor information to the supervisor,and
?S asks v which is now pred(w)to send the connectivity information according to F to node w.?S sets n=n+1.
Leave:If an old node w leaves and reports w,pred(w),and succ(w)in order to maintain Invariant2.5(3), the following actions are performed.In the following,S denotes the supervisor.Recall that we are assuming graceful departures.
?S informs v(the node with label (n?1))that w is its new label,pred(w)is its new predecessor, and succ(w)is its new successor.
?S informs pred(w)that its new successor is v and succ(w)that its new predecessor is v.
?S informs pred(v)that succ(v)is its new successor and succ(v)that pred(v)is its new predecessor.
?S asks pred(v)to send its predecessor information to the supervisor and to ask pred(pred(v))to send its predecessor information to the supervisor.
?S asks node v to transfer all of its connectivity information according to F to pred(v),and
?S sets n=n?1.
Thus,the supervisor only needs to handle a constant number of messages for each arrival or departure of a peer.In fact,at most8messages suf?ce for each operation,and each message is very small.If we assume,for example,that the supervisor has a100Mbit/s connection,each message has a size of64bytes, we have1,000,000peers in the system,and each peer stays in the system for a minute(on average),then the bandwidth of the supervisor is in principle high enough to handle all of the arrivals and departures(though this would need a high parallelization of the handling of join and leave requests,as discussed in Section3). Moreover,a peer can join and leave the supervised system with a constant number of communication rounds. Hence,our join method is much faster than in pure peer-to-peer systems where the join request of a peer ?rst has to be forwarded to the right location,which usually takes?(log n)time.
2.6Examples
For a supervised hypercubic network,simply select F as the family of functions on[0,1)with f i(x)=
x+1/2i(mod1)for every i≥https://www.wendangku.net/doc/9d3805582.html,ing our framework,this gives an overlay network with degree
√
O(log n),diameter O(log n),and expansion O(1/
3.1Concurrent Join/Leave Operations
In order to be able to handle d join or leave requests in parallel,Invariant 2.5just needs to be extended by one more rule given below.In the following,pred i (v )(resp.succ i (v ))denotes the i th predecessor,(resp.successor),of v on the cycle of nodes.That is,pred 0(v )=pred(v )and pred i (v )=pred(pred i ?1(v )).
4.Every peer v in the system is connected to its d th predecessor and its d th successor
In addition to this,given that v is the node with label (n ?1),Invariant 2.7needs to be extended to:
Invariant 3.1At any time,the supervisor stores the contact information of v ,the 2d successors of v ,and the 3d predecessors of v .
These invariants can be preserved as follows:
Concurrent Join Operation In the following,let v be the node with label (n ?1).Let the d new peers be w 1,w 2,...w d .Then the supervisor integrates w i between succ i (v )and succ i +1(v )for every i ∈{1,...,d }.As is easy to check,this will violate rule (4)for the 2d closest successors of v and the d ?2closest predecessors of v .But since the supervisor knows all of these nodes,it can directly inform them about the change.In order to repair Invariant 3.1,the supervisor will request information about the d th successor from the d furthest successors from v and will set v to w d .Thus,we obtain the following result:Claim 3.2The supervisor needs at most O (d )work and O (1)time (given that the work can be done in parallel)to process d join operations.
Concurrent Leave Operation Let the d peers that want to leave the system be w 1,w 2,...,w d .For simplicity,we assume that they are outside of the peers known to the supervisor,but our strategy below can also be easily extended to these cases.The strategy of the supervisor is to replace w i by pred 2(i ?1)(v )for every i .As is easy to check,this will violate rule (4)for the d closest successors of v and the 3d closest predecessors of v .But since the supervisor knows all of these nodes,it can directly inform them about the change.In order to repair Invariant 3.1,the supervisor will request information about the d th predecessor from the d furthest predecessors from v and their d th predecessors and will set v to pred 2d (v ).Thus,we obtain the following result:
Claim 3.3The supervisor needs at most O (d )work and O (1)time (given that the work can be done in parallel)to process d leave operations.
3.2Multiple Supervisors
In this section,we show multiple supervisors can work together in maintaining a single supervised peer-to-peer system.We assume that the number of supervisors it not too large so that it is reasonable to connect them in a clique.In a network with k supervisors S 0,S 1,···S k ?1,the [0,1)-ring is split into the k regions R i =[(i ?
1)/k,i/k ),i ∈{1,...,k },and supervisor S i is responsible for region R i .The supervisors are assigned distinct labels s i which is equal to the binary representation of i using log 2k bits.For example,with 4supervisors,the labels of the supervisors are 00,01,10and 11.Every supervisor manages its region as described for a single supervisor above,with the exception of the borders of its region.The borders are maintained by communicating with the neighboring supervisors on the ring.Each time a new node wants to join the system via some supervisor S i ,S i forwards it to a random supervisor who will integrate it into the system.To generate labels for the nodes in the system,supervisor
S i prepends its own label to the labels generated according to section2.3with the modi?cation that label1 is the?rst label to be generated.Thus in a system with4supervisors,where supervisor2has label s1=01 supervisor S2generates0111as the label for the third node to join the system under S2.To formalize the above discussion,let n i be the number of nodes that are being managed by supervisor S i currently with n i=1n i=n being the total number of nodes in the system currently.Then,supervisor S i maintains the following invariant:
Invariant3.4The set of labels generated by supervisor i S i,i∈[k]is
{s i·1,s i·01,s i·11,s i·001,...}
where the·operator denotes binary concatenation.
The above sequence of labels is generated by stripping of the s i most signi?cant bits and the least signi?cant bit,then supervisor S i is enumerating all binary numbers of length0,followed by length1and so on.The mapping :IN0→{0,1}?from section2.3can then be easily provided.
Supervisor S i also maintains the invariant that when n i nodes are in the system managed by S i then the set of labels used is{ (0), (1),..., (n i?1)}.Using techniques from section2.1–2.3,it can be shown that supervisor S i has to only take care of maintaining the doubly linked cycle of peers and the peers have to maintain the connections according to Invariant2.5(3).
Each time a node v under some supervisor S i wants to leave the system,S i contacts a random supervisor (which may also be itself)to provide a node that can replace v.
Thus,the join rule provides a random distribution of the peers among the supervisors and it is not too dif?cult to verify that the leave rule preserves this random distribution.Hence,when using the Chernoff bounds we get:
Claim3.5Let n be the total number of nodes in the system.Then it holds for every i∈[k]that the number of nodes currently placed in R i is in the range n/k±O(
are uniformly distributed among the nodes in the[0,1)interval and the rate of ungraceful departures is low enough so that the supervisor can handle.
Towards this goal,the supervisor now maintains the following invariants for k=c log n for some large constant c.
Invariant4.1Every node v is connected to:
?pred i(v)and succ i(v)for i∈{1,2,...k},and
?all nodes w such thatΓ(R(N v))∩Γ(R(N w))=φ,where N v={v}∪{pred i(v)|i=1,2,...k}∪{succ i(v)|i=1,2,...k}and for any set V ?V,we let R(V )=∪{v∈V }R(v).
The above connectivity rules introduce a k–wise redundancy in the system as each node maintains connections to nodes in its k-neighborhood.The supervisor stores the contact information according to the following invariant.
Invariant4.2The supervisor maintains the following connections.
?Join connections:These are to the2k successors and3k predecessors of the node v with label (n?1).These connections are similar to the connections speci?ed by Invariant3.1.?Repair connections:These are to some peer w,(missing or available),the k closest predecessor of w and the k closest successors of w.
The join and leave operation are now extended as follows.To insert a new node w into the system,the supervisor assigns a label to w and proceeds according to a normal join operation in section2.5and also satisfying invariant4.1.To maintain Invariant4.2,the supervisor updates its join connections accordingly by requesting relevant information.The leave operation of a gracefully departing node w now follows similarly to that of a basic leave operation by the supervisor reversing the last join operation.
Thus the supervisor has to maintain only a logarithmic amount,c log n,of information.The cost of join and leave operation increases to O(log n)from a constant.As the size of the network increases or decreases by a factor of2,the supervisor updates the value of k accordingly by a factor of±c.The supervisor also updates its repair connections if w or any successor/predecessor of w departs by choosing the closest successor/predecessor.
The above operations along with the invariants have the following property.
Theorem4.3For c≥1and suf?ciently large,the above scheme can guarantee that the overlay network speci?ed by any family of functions F such that if(x,y)∈E F then there exists at least pair of nodes v,w so that x∈R(N v)and y∈R(N w)and(v,w)is an edge in the network even if every peer fails with a constant probability p with0 Proof.Firstly,notice that the supervisor always knows the positions in the cycle that should be occupied as this is precisely the positions with a label among (0)to (n?1).Hence,using the repair connections as pivot,the supervisor can always process ungraceful departures by performing a tour around the cycle. Let us call a position valid if it has a label in between (0)and (n?1).If each peer can fail with a probability p,then it holds that in k consecutive positions the probability that all peers fail or none of them fail is polynomially small when k=max{(c log n)/log(1/p),(c log n)/log(1/1?p)}for c,c ≥2. Thus,it holds that during time the supervisor is performing a tour around the cycle,at most an =O(p) fraction of the nodes can fail with high probability.Thus the supervisor can?x all invalid positions as long as is small enough. Using the above,since in any k consecutive positions at least one of them is valid,the connectivity guarantee that for every(x,y)∈E F,there is at least one pair v,w such that x∈R(N v)and y∈R(N w) and v and w have valid positions with an edge from v to w can be shown. 4.2Robustness against adaptive adversarial attacks While the results of the previous sub-section guarantee that the system is robust to random node failures,the system is not robust against adaptive adversarial attacks.Such attacks take the form of adversarial nodes that can join and leave the system as many times as they wish.In our system,adaptive adversarial attacks can easily disconnect the supervisor from the rest of network by taking positions that the supervisor is connected to.This would then make it dif?cult for new peers to join the system.The adversary can also place nodes at critical positions so that routing in the network is disrupted by not forwarding the packets or forwarding them to the wrong location or by injecting lots of packets destined for other adversarial nodes so that the network would be heavily congested.These type of attacks are recently studied in[22]by showing how to maintain a robust ring network of nodes under the presence of such a powerful adversary.While mechanisms for other network topologies are not known,using the supervised approach we show how to extend our basic scheme to provide robustness guarantees for any overlay network under the presence of an adaptive adversary. Formally,we allow the adversary to own up to n of the n nodes in the system for some suf?ciently small constant >0.These nodes are also called adversarial nodes and the rest are called honest nodes.The supervisor and the honest nodes are oblivious to adversarial nodes,i.e.,there is no mechanism to distinguish at any time whether a particular node is honest or not.To achieve robustness in the presence of an adaptive adversary,we use the following scheme. In the following,a region is an interval of size1/2i in[0,1)starting at an integer multiple of1/2i for some i≥0,and a node v belongs to a region R if r( v)∈R.Recall that n and2c log n/8?1). 2.S2has n/8), (n/4?1). 3.S3has n/4), (n/2?1). 4.S4has n/2), (n?1). 5.S5has the remaining n?n), ( 5 Figure2:Logical organization of nodes into?ve sets.The number against node position indicates the set to which the node belongs to. Figure2shows the logical organization of the nodes and the sets S1through S5and Figure3shows the physical organization.Our organization of the nodes ensures that in a constant fraction of the network,the adversarial nodes cannot in?uence the network behavior. The set S1is also referred to as the stable set.The goal of the supervisor is to have the honest nodes in the majority in every set S1(R)of size c log n nodes,with high probability.The reason for this goal are stated shortly. The set S2is in a stage called the split-and-merge stage because S2-nodes are merged into the stable set or removed from it as nodes join or leave the system.The set S3is in a stage called mixing stage in which the supervisor performs transpositions according to a uniformly chosen permutation to ensure that the nodes are well-mixed before being integrated into the stable set. The set S4is in a reservoir stage.S4is used to?ll departed positions in the sets S1to S3by selecting random nodes in S4and?lling their positions with the last nodes in S5.Finally,the set S5is in a?lling stage where new nodes are added by assigning them the label (n). The join and leave operation have to be extended so that the supervisor can ensure the majority condition at all times.We?rst describe the modi?cations to the join/leave operations. Join: The supervisor assigns to the new node the label (n)and integrates it so that the Invariants4.4and4.5are satis?ed. Afterwards,the supervisor updates v?to be successor of v?among the nodes in M R.If there is no such node,then M R is updated to the M R where R is the region succeeding region R and v?is taken to be the ?rst node in M R .Suppose that v?belongs to the set S i in M R for a region R.Then the supervisor picks a node w with position between v?and1(exclusive)uniformly at random and exchanges the positions of w and v?.This is realized by the supervisor informing all nodes in S1(R( (n)))the positions of nodes v?and w so that this is reliably done without involving the supervisor. Each time a new node causes the supervisor to switch from a region R to succ(R),the nodes in S2(R) are merged into S1(R)as prescribed by Invariant4.5. 2 Figure3:Physical organization of nodes into?ve sets. Leave: If a node v leaves with v∈S4∪S5,the supervisor simply replaces it by the last node in S5.Otherwise,the supervisor replaces v by a random node in S4and?lls the position of that random node with the last node in S5.This is followed by performing a mixing operation similar to that done during a join operation.(The supervisor initiates the leave operation for v only if a majority of S1-nodes in v’s region notify it about that. In this case,the supervisor has the necessary information to correctly initiate the replacement.)Each time a departure causes the supervisor to switch from a region R to pred(R),the nodes in S2(pred(R))are split away from S1(R)as prescribed by Invariant4.5. Majority Condition The goal of the above scheme of the supervisor is to ensure that in any region of R of logarithmic size,the honest nodes are in a majority with high probability.This condition is referred as the majority condition and is useful in the following way.Suppose the majority condition holds.Then quorum strategies can be used to wash out adversarial behavior as follows.Consider any set T of c log n nodes in S1.According to Invariant4.5,all the honest nodes in T are connected to all nodes in T.To perform any network operation such as?nding the node with a given label,all the nodes in T perform majority voting.The outcome of the operation is determined uniquely if a majority of the nodes in T agree on the outcome.This means that for adversarial nodes to have any in?uence on the outcome of a network operation,they should be in a majority in the set T of c log n nodes since we assume that honest nodes act honestly. Join/leave model Before we proceed further,we outline the way in which the nodes join/leave the system.We start by con-sidering a model similar to that[22]where honest nodes do not leave the system and only adversarial nodes may join/leave the system in an adaptive manner.Certainly this is a simple model but is very illustrative. We then extend the model to allow also honest nodes to leave the system but so that the leave operations of the honest nodes are spread uniformly around the[0,1)interval.This means that the honest nodes are not adaptive in their join/leave reqeusts. Observe that during the join operation,nodes in M R undergo transpositions that has the effect of per-muting the nodes according to a permutation chosen uniformly at random from the set of all permutations of size|M R|.This is crucial to guarantee robustness as shown in the following result.Thus,once a pass has been made through all positions of S1∪S2∪S3,the positions in S i,i∈{1,2,3}form a random permutation. Theorem4.6For a suf?ciently small constant >0it holds that as long as the adversary owns at most n nodes,the above scheme guarantees that in every region R of size c log n for c≥1,the honest nodes are in the majority in S1(R),with high probability. Proof.Consider the following random experiment.Consider m positions and the random experiment of switching the?rst position with a position in{1,2,...,m}uniformly at random,followed by switching the second position with a position in{2,3,...,m}uniformly at random and independently,and so on.This random experiment creates a random permutation of m positions as it holds that: ?Every permutation is an outcome of the random experiment,i.e.,any permutation can be produced by the above experiment,and ?Any permutation,or outcome of the random experiment,is equally likely with a probability of1/m!. Consider the basic model where only adversarial nodes may join/leave the system.After n join/leave operations the effect of the mixing operations is the same as that of choosing a random permutation of size |S1∪S2∪S3|.It then follows that as nodes in S1,S2and S3are permuted during the mixing operations R, the effect is that of arriving at a situation where given any position in S i,for i∈{1,2,3},the probability that the node at that position is an adversarial node is at most n constantδ>0.Assume that a majority of the honest nodes in R leave successively.During each such leave operation,the probability that an adversarial node enters R isΘ( ).So afterΘ(log n)leave operations of honest nodes from R,the expected number of adversarial nodes in R is(1/2)?δ+Θ( )which can be made to be greater than1/2for aδsmall enough.Thus,the majority condition for R can be violated. What led to the failure of the existing scheme is that the supervisor does not have a chance to make any transpositions in region R untilΘ(n)join/leave operations have occurred.This presented a window for the adversarial nodes to gain a majority in region R as the honest nodes leave en-masse. It is worth noting that such a strong guarantee can be provided with a simple scheme.The amount of information the supervisor has to maintain is only logarithmic.The analysis is also not as complicated as that of[22]and the presence of a supervisor limits the ability of the adversary even with adaptive join/leave attacks.The simpli?cation results from the fact that nodes in S1,S2and S3are isolated from the node join/leave operations allowing the supervisor to permute the nodes before integrating them into the existing network. 5Applications We now discuss some applications of the supervised overlay networks that arise in the area of distributed computing. 5.1Grid Computing Recently,many systems such as SETI@home[23],https://www.wendangku.net/doc/9d3805582.html,[9]have been proposed for distributed computing.A main drawback of such systems is that the topology of the system is a star graph with the central server maintaining a direct connection to each client.Such a topology imposes heavy demands on the central server.Instead,we can use the basic approach of Section2to design a overlay network for distributed computing.Peer-to-peer connections allow subtasks to be spawned without the involvement of the supervisor so that the demands on the server can be signi?cantly reduced.This is particularly interesting for distributed branch-and-bound computations as was discussed in[20]. 5.2WebTv Our approach can also be used in Internet applications such as WebTv.In such an application,there are typically various channels that users can browse or watch while being connected to the Internet.The number of channels ranges in the scale of hundreds while the number of users can range in the scale of millions. Such a system should allow users to quickly zap through channels.Hence,such a system should allow for rapid integration and be scalable to large number of users.Our supervised overlay networks can easily achieve such a smooth operation.Suppose that every channel has a supervisor,each supervisor maintains its own broadcast network,and the supervisors form a clique.Then it follows from our supervised approach, which can handle join and leave operations in constant time,that users browsing through channels can be moved between the networks in a very fast way,comparable to server-based networks,so that users only experience an insigni?cant delay. 5.3Massive Multi-player Online Gaming Distributed architectures for massive multi-player online gaming(MMOG)are being studied recently(see e.g.,[12]).The basic requirements of such a system includes authentication,scalability,and rapid integra-tion.Traditionally,such systems have been managed by a central server that takes care of the overall system with limited communication between the users.As can be seen,such a system will not be scalable and also might experience heavy congestion at the central server.Hence,distributed architectures are required at a certain scale.A supervised overlay network naturally satis?es the requirements.Authentication of entities can be done by the supervisor(or multiple supervisors)and the system stays highly scalable because of the relatively low load on the supervisor.Rapid integration is also possible since the supervisor can handle integration of new peers(players in this setting)with a constant number of communication rounds. Typically in a MMOG,it is possible to partition the virtual world into what are called locales.In an architecture based on supervised overlay networks then it would be possible to have one(or more)super-visor to be responsible for each such locale.Whenever a player moves between locales,the supervisor can coordinate the join/leave of the player quickly.Also,based on number of players based at various locales, the supervisors can be distributed so that the load at the supervisors stays balanced. References [1]I.Abraham,B.Awerbuch,Y.Azar,Y.Bartal,D.Malkhi,and E.Pavlov.A generic scheme for building overlay networks in adversarial scenarios.In Proc.of the IEEE International Parallel and Distributed Processing Symposium(IPDPS),2003. [2]S.Banerjee,B.Bhattacharjee,and C.Kommareddy.Scalable application layer multicast.Technical Report UMIACS-TR2002-53and CS-TR4373,University of Maryland,2002. [3]S.Banerjee,S.Lee,B.Bhattacharjee,and A.Srinivasan.Resilient multicast using overlays.ACM SIGMETRICS Performance Evaluation Review,31(1):102–113,2003. [4]A.Bhargava,K.Kothapalli,C.Riley,M.Thober,and C.Scheideler.Pagoda:An overlay network for data management,routing and multicasting.In Proc.of the ACM Symposium on Parallelism in Algorithms and Architectures(SPAA),pages170–179,2004. [5]M.Castro,P.Druschel,A.Kermarrec,and A.Rowstron.Scribe:A large-scale and decentral- ized application-level multicast infrastructure.IEEE Journal on Selected Areas in communications, 20:1489–1499,2002. [6]M.Castro,P.Druschel,A.-M.Kermarrec,A.Nandi,A.Rowstron,and A.Singh.Splitstream:High- bandwidth multicast in cooperative environments.In Proc.of ACM SIGMETRICS2003,2003. [7]M.Castro,M.B.Jones,A.-M.Kermarrec,A.Rowstron,M.Theimer,H.Wang,and A.Wolman.An evaluation of scalable application-level multicast built using peer-to-peer overlay network.In Proc.of the IEEE Infocom,2003. [8]H.Deshpande,M.Bawa,and H.Garcia-Molina.Streaming live media over a peer-to-peer network. Technical Report Technical Report2001-31,Stanford University,2001. [9]https://www.wendangku.net/doc/9d3805582.html,.Available at https://www.wendangku.net/doc/9d3805582.html,/. [10]D.Jefferson et al.Distributed simulation and the time warp operating system.In Proc.of the11th ACM Symposium on Operating Systems Principles(SOSP),1987. [11]Folding@home.Available at https://www.wendangku.net/doc/9d3805582.html,/. [12]C.GauthierDickey,D.Zappala,and V.Lo.A fully distributed architecture for massively multiplayer online games.In ACM SIGCOMM Workshop on Network and System Support for Games,2004. [13]J.Jannotti,D.Gifford,K.Johnson,F.Kaashoek,and J.O’Toole.Overcast:Reliable multicasting with an overlay network.In USENIX Symposium on Operating Systems Design and Implementation (OSDI),pages197–212,2000. [14]M.Frans Kaashoek and David R.Karger.Koorde:A simple degree-optimal distributed hash table.In Proc.of the International Workshop on Peer-to-Peer Systems(IPTPS),2003. [15]M.Mitzenmacher,A.Richa,and R.Sitaraman.The power of two choices:A survery of techniques and results.pages255–312.Kluwer Academic Publishers,2001. [16]M.Naor and U.Wieder.Novel architectures for P2P applications:the continuous-discrete approach. In Proc.of the ACM Symposium on Parallelism in Algorithms and Architectures(SPAA),pages50–59, 2003. [17]G.Pandurangan,P.Raghavan,and E.Upfal.Building low-diameter P2P networks.In Proc.of the 42nd IEEE Symposium on Foundations of Computer Science(FOCS),pages492–499,2001. [18]S.Ratnasamy,P.Francis,M.Handley,R.Karp,and S.Shenker.A scalable content-addressable net- work.In ACM SIGCOMM,pages161–172,2001. [19]S.Ratnasamy,M.Handley,R.M.Karp,,and S.Shenker.Application-level multicast using content- addressable networks.In Networked Group Communication,2001. [20]C.Riley and C.Scheideler.A distributed hash table for computational grids.In Proc.of the IEEE International Parallel and Distributed Processing Symposium(IPDPS),2004. [21]C.Riley and C.Scheideler.Guaranteed broadcasting using spon:Supervised p2p overlay network.In International Z¨u rich Seminar on Communications,2004. [22]C.Scheideler.How to spread adversarial nodes?rotate!In Proc.of the ACM Symposium on Theory of Computing(STOC),2005. [23]SETI@home.Available at https://www.wendangku.net/doc/9d3805582.html,/. [24]I.Stoica,D.Adkins,S.Zhuang,S.Shenker,and S.Surana.Internet indirection infrastructure.In Proc. of the International Peer-to-Peer Systems(IPTPS),pages191–202,2002. [25]I.Stoica,R.Morris,D.Karger,M.F.Kaashoek,and H.Balakrishnan.Chord:A scalable peer-to-peer lookup service for internet applications.In ACM SIGCOMM,2001. [26]R.Zhang and Y.C.Hu.Borg:A hybrid protocol for scalable application level multicast in peer-to-peer networks.In Proc.of the,2003. [27]S.Q.Zhuang,B.Y.Zhao,A.D.Joseph,R.H.Katz,and J.D.Kubiatowicz.Bayeux:An architecture for scalable and fault tolerant wide-area data dissemination.In Proc.of NOSSDAV,2001. 电动机分类及介绍 电动机是一种旋转式电动机器，它将电能改动为机械能，它首要包含一个用以发作磁场的电磁铁绕组或散布的定子绕组和一个旋转电枢或转子。在定子绕组旋转磁场的效果下，其在电枢鼠笼式铝框中有电流转过并受磁场的效果而使其翻滚。这些机器中有些类型可作电动机用，也可作发电机用。它是将电能改动为机械能的一种机器。通常电动机的作功有些作旋转运动，这种电动机称为转子电动机;也有作直线运动的，称为直线电动机。以下为电动机的各种分类。 几种多见电动机介绍直流电动机将直流电能改换为机械能的电动机。因其超卓的调速功用而在电力拖动中得到广泛运用。直流电动机按励磁办法分为永磁、他励和自励3类,其间自励又分为并励、串励和复励3种。沟通电动机将沟通电的电能改动为机械能的一种机器。沟通电动机首要由一个用以发作磁场的电磁铁绕组或散布的定子绕组和一个旋转电枢或转子构成。电动机运用通电线圈在磁场中受力翻滚的景象而制成的。沟通电动机由定子和转子构成，并且定子和转子是选用同一电源，所以定子和转子中电流的方向改动老是同步的。沟通电动机即是运用这个原理而作业的。三相电动机三相电机是指当电机的三相定子绕组(各相差120度电视点)，通入三相 沟通电后，将发作一个旋转磁场，该旋转磁场切开转子绕组，然后在转子绕组中发作感应电流(转子绕组是闭合通路)，载流的转子导体在定子旋转磁场效果下将发作电磁力，然后在电机转轴上构成电磁转矩，驱动电动机旋转，并且电机旋转方向与旋转磁场方向相同。三相异步电动机的三相定子绕组每相绕组都有两个引出线头，总共六个引出线头，别离以U1、U2;V1、V2;W1、W2标明。这六个引出线头引进电机接线盒的接线柱上。单相电动机单相电机通常是指用单相沟通电源(AC220V)供电的小功率单相异步电动机。单相异步电动机通常在定子上有两相绕组，转子是通常鼠笼型的。两相绕组在定子上的散布以及供电状况的纷歧样，能够发作纷歧样的起动特性和作业特性。下图是带正回转开关的接线图，通常这种电机的起动绕组与作业绕组的电阻值是相同的，即是说电机的起动绕组与作业绕组是线径与线圈数完全一同的。通常洗衣机用得到这种电机。这种正回转操控办法简略，不必杂乱的改换开关。步进电动机步进电动机又称脉冲电机，是数字操控体系中的一种首要的施行元件，它是将电脉冲信号改换成转角或转速的施行电动机，其角位移量与输入电脉冲数成正比;其转速与电脉冲的频率成正比。在负载才调方案内，这些联络将不受电源电压、负载、环境、温度等要素的影响，还可在很宽的方案内完毕调速，活络主张、制动和回转。伺服电动 电机及电机学概念 （electric machine and electric machine theory concept） 电机定义：是指依据电磁感应定律实现电能的转换或传递的一种电磁装置。 电动机也称电机（俗称马达），在电路中用字母"M"（旧标准用"D"）表示。它的主要作用是产生驱动转矩，作为用电器或各种机械的动力源。 电动机的种类 1．按工作电源分类根据电动机工作电源的不同，可分为直流电动机和交流电动机。其中交流电动机还分为单相电动机和三相电动机。 2．按结构及工作原理分类电动机按结构及工作原理可分为直流电动机，异步电动机和同步电动机。 同步电动机还可分为永磁同步电动机、磁阻同步电动机和磁滞同布电动机。 异步电动机可分为感应电动机和交流换向器电动机。感应电动机又分为三相异步电动机、单相异步电动机和罩极异步电动机等。交流换向器电动机又分为单相串励电动机、交直流两用电动机和推斥电动机。 直流电动机按结构及工作原理可分为无刷直流电动机和有刷直流电动机。有刷直流电动机可分为永磁直流电动机和电磁直流电动机。电磁直流电动机又分为串励直流电动机、并励直流电动机、他励直流电动机和复励直流电动机。永磁直流电动机又分为稀土永磁直流电动机、铁氧体永磁直流电动机和铝镍钴永磁直流电动机。 3．按起动与运行方式分类电动机按起动与运行方式可分为电容起动式单相异步电动机、电容运转式单相异步电动机、电容起动运转式单相异步电动机和分相式单相异步电动机。 4．按用途分类电动机按用途可分为驱动用电动机和控制用电动机。 驱动用电动机又分为电动工具（包括钻孔、抛光、磨光、开槽、切割、扩孔等工具）用电动机、家电（包括洗衣机、电风扇、电冰箱、空调器、录音机、录像机、影碟机、吸尘器、照相机、电吹风、电动剃须刀等）用电动机及其它通用小型机械设备（包括各种小型机床、小型机械、医疗器械、电子仪器等）用电动机。 控制用电动机又分为步进电动机和伺服电动机等。 5．按转子的结构分类电动机按转子的结构可分为笼型感应电动机（旧标准称为鼠笼型异步电动机）和绕线转子感应电动机（旧标准称为绕线型异步电动机）。 6．按运转速度分类电动机按运转速度可分为高速电动机、低速电动机、恒速电动机、调速电动机。 舌尖上的中国分集简介 第一集自然的馈赠 本集导入作为一个美食家，食物的美妙味感固然值得玩味，但是食物是从哪里来的？毫无疑问，我们从大自然中获得所有的食物，在我们走进厨房，走向餐桌之前，先让我们回归自然，看看她给我们的最初的馈赠。本集将选取生活在中国境内截然不同的地理环境（如海洋，草原，山林，盆地，湖泊）中的具有代表性的个人、家庭和群落为故事主角，以及由于自然环境的巨大差异（如干旱，潮湿，酷热，严寒）所带来的截然不同的饮食习惯和生活方式为故事背景，展现大自然是以怎样不同的方式赋予中国人食物，我们又是如何与自然和谐相处，从而了解在世代相传的传统生活方式中，通过各种不同的途径获取食物的故事。 美食介绍 烤松茸油焖春笋雪菜冬笋豆腐汤 腊味飘香腌笃鲜排骨莲藕汤椒盐藕夹酸辣藕丁煎焖鱼头泡饼煎焗马鲛鱼酸菜鱼松鼠桂鱼侉炖鱼本集部分旁白中国拥有世界上最富戏剧性的自然景观，高原， 第一集: 自然的馈赠 山林，湖泊，海岸线。这种地理跨度有助于物种的形成和保存，任何一个国家都没有这样多潜在的食物原材料。为了得到这份自然的馈赠，人们采集，捡拾，挖掘，捕捞。穿越四季，本集将展现美味背后人和自然的故事。香格里拉，松树和栎树自然杂交林中，卓玛寻找着一种精灵般的食物——松茸。松茸保鲜期只有短短的两天，商人们以最快的速度对松茸进行精致的加工，这样一只松茸24小时之后就会出现在东京的市场中。松茸产地的凌晨3点，单珍卓玛和妈妈坐着爸爸开的摩托车出发。穿过村庄，母女俩要步行走进30公里之外的原始森林。雨让各种野生菌疯长，但每一个藏民都有识别松茸的慧眼。松茸出土后， 卓玛立刻用地上的松针把菌坑掩盖好，只有这样，菌丝才可以不被破坏，为了延续自然的馈赠，藏民们小心翼翼地遵守着山林的规矩。为期两个月的松茸季节，卓玛和妈妈挣到了5000元，这个收入是对她们辛苦付出的回报。 舌尖上的中国DVD 老包是浙江人，他的毛竹林里，长出过遂昌最大的一个冬笋。冬笋藏在土层的下面，从竹林的表面上看，什么也没有，老包只需要看一下竹梢的叶子颜色，就能知道笋的准确位置，这完全有赖于他丰富的经验。笋的保鲜从来都是个很大的麻烦，笋只是一个芽，是整个植物机体活动最旺盛的部分。聪明的老包保护冬笋的方法很简单，扒开松松的泥土，把笋重新埋起来，保湿，这样的埋藏方式就地利用自然，可以保鲜两周以上。在中国的四大菜系里，都能见到冬笋。厨师偏爱它，也是因为笋的材质单纯，极易吸收配搭食物的滋味。老包正用冬笋制作一道家常笋汤，腌笃鲜主角本来应该是春笋，但是老包却使用价格高出20倍的遂昌冬笋。因为在老包眼里，这些不过是自家毛竹林里的一个小菜而已。在云南大理北部山区，醒目的红色砂岩中间，散布着不少天然的盐井，这些盐成就了云南山里人特殊的美味。老黄和他的儿子在树江小溪边搭建一个炉灶，土灶每年冬天的工作就是熬盐。云龙县的冬季市场，老黄和儿子赶到集市上挑选制作火腿的猪肉，火腿的腌制在老屋的院子里开始。诺邓火腿的腌制过程很简单，老黄把多余的皮肉去除，加工成一个圆润的火腿，洒上白酒除菌，再把自制的诺盐均匀的抹上，不施锥针，只用揉、压，以免破坏纤维。即使用现代的标准来判断，诺邓井盐仍然是食盐中的极品，虽然在这个古老的产盐地，盐业生产已经停止，但我们仍然相信诺邓盐是自然赐给山里人的一个珍贵礼物。圣武和茂荣是兄弟俩，每年9月，他们都会来到湖北的嘉鱼县，来采挖一种自然的美味。这种植物生长在湖水下面的深深的淤泥之中，茂荣挖到的植物的根茎叫做莲藕，是一种湖泊中高产的蔬菜——藕。作为职业挖藕人，每年茂荣和圣武要只身出门7个月，采藕的季节，他们就从老家安徽赶到有藕的地方。较高的人工报酬使得圣武和茂荣愿意从事这个艰苦的工作。挖藕的人喜欢天气寒冷，这不是因为天冷好挖藕，而是天气冷买藕吃藕汤的人就多一些，藕的价格就会涨。整整一湖的莲藕还要采摘5个月的时间，在嘉鱼县的珍湖上，300个职业挖藕人，每天从日出延续到日落，在中国遍布淡水湖的大省，这样场面年年上演。今天当我们有权远离自然，享受美食的时候，最应该感谢的是这些通过劳动和智慧成就餐桌美味的人们。 第二集主食的故事 本集导入主食是餐桌上的主要食物，是人们所需能量的主要来源。从远古时代赖以充饥的自然谷物到如今人们餐桌上丰盛的、让人垂涎欲滴的美食，一个异彩纷呈、变化多端的主食世界呈现在你面前。本集着重描绘不同地域、不同民族、不同风貌的有关主食的故事，展现人们对主食的样貌、口感的追求，处理和加工主食的智慧，以及中国人对主食的深 电机 电机泛指能使机械能转化为电能、电能转化为机械能的一切机器。特指发电机、电能机、电动机。是指依据电磁感应定律实现电能的转换或传递的一种电磁装置。电动机也称（俗称马达），在电路中用字母“M”（旧标准用“D”）表示。它的主要作用是产生驱动转矩，作为用电器或各种机械的动力源。 基本介绍 电机是指依据电磁感应定律实现电能的转换或传递的一种电磁装置。电机也称电机（俗称马达），在电路中用字母“M”（旧标准用“D”）表示。它的主要作用是产生驱动转矩，作为用电器或各种机械的动力源。 主要分类 分类概述 1、按工作电源种类划分：可分为直流电机和交流电机。 1）直流电动机按结构及工作原理可划分：无刷直流电动机和有刷直流电动机。 有刷直流电动机可划分：永磁直流电动机和电磁直流电动机。 电磁直流电动机划分：串励直流电动机、并励直流电动机、他励直流电动机和复励直流电动机。 永磁直流电动机划分：稀土永磁直流电动机、铁氧体永磁直流电动机和铝镍钴永磁直流电动机。 2）其中交流电机还可划分：单相电机和三相电机。 2、按结构和工作原理可划分：可分为直流电动机、异步电动机、同步电动机。 1）同步电机可划分：永磁同步电动机、磁阻同步电动机和磁滞同步电动机。 2）异步电机可划分：感应电动机和交流换向器电动机。 感应电动机可划分：三相异步电动机、单相异步电动机和罩极异步电动机等。 交流换向器电动机可划分：单相串励电动机、交直流两用电动机和推斥电动机。 3、按起动与运行方式可划分：电容起动式单相异步电动机、电容运转式单相异步电动机、电容起动运转式单相异步电动机和分相式单相异步电动机。 4、按用途可划分：驱动用电动机和控制用电动机。 1）驱动用电动机可划分：电动工具（包括钻孔、抛光、磨光、开槽、切割、扩孔等工具）用电动机、家电（包括洗衣机、电风扇、电冰箱、空调器、录音机、录像机、影碟机、吸尘器、照相机、电吹风、电动剃须刀等）用电动机及其它通用小型机械设备（包括各种小型机床、小型机械、医疗器械、电子仪器等）用电动机。 2）控制用电动机又划分：步进电动机和伺服电动机等。 《舌尖上的中国》解说词 第一集《自然的馈赠》 中国拥有世界上最富戏剧性的自然景观，高原，山林，湖泊，海岸线。这种地理跨度有助于物种的形成和保存，任何一个国家都没有这样多潜在的食物原材料。为了得到这份自然的馈赠，人们采集，捡拾，挖掘，捕捞。穿越四季，本集将展现美味背后人和自然的故事。 香格里拉，松树和栎树自然杂交林中，卓玛寻找着一种精灵般的食物——松茸。松茸保鲜期只有短短的两天，商人们以最快的速度对松茸的进行精致的加工，这样一只松茸24小时之后就会出现在东京的市场中。 松茸产地的凌晨3点，单珍卓玛和妈妈坐着爸爸开的摩托车出发。穿过村庄，母女俩要步行走进30公里之外的原始森林。雨让各种野生菌疯长，但每一个藏民都有识别松茸的慧眼。松茸出土后，卓玛立刻用地上的松针把菌坑掩盖好，只有这样，菌丝才可以不被破坏，为了延续自然的馈赠，藏民们小心翼翼地遵守着山林的规矩。 为期两个月的松茸季节，卓玛和妈妈挣到了5000元，这个收入是对她们辛苦付出的回报。 老包是浙江人，他的毛竹林里，长出过遂昌最大的一个冬笋。冬笋藏在土层的下面，从竹林的表面上看，什么也没有，老包只需要看一下竹梢的叶子颜色，就能知道笋的准确位置，这完全有赖于他丰富的经验。 笋的保鲜从来都是个很大的麻烦，笋只是一个芽，是整个植物机体活动最旺盛的部分。聪明的老包保护冬笋的方法很简单，扒开松松的泥土，把笋重新埋起来，保湿，这样的埋藏方式就地利用自然，可以保鲜两周以上。 在中国的四大菜系里，都能见到冬笋。厨师偏爱它，也是因为笋的材质单纯，极易吸收配搭食物的滋味。老包正用冬笋制作一道家常笋汤，腌笃鲜主角本来应该是春笋，但是老包却使用价格高出20倍的遂昌冬笋。因为在老包眼里，这些不过是自家毛竹林里的一个小菜而已。 在云南大理北部山区，醒目的红色砂岩中间，散布着不少天然的盐井，这些盐成就了云南山里人特殊的美味。老黄和他的儿子树江小溪边搭建一个炉灶，土灶每年冬天的工作就是熬盐。 云龙县的冬季市场，老黄和儿子赶到集市上挑选制作火腿的猪肉，火腿的腌制在老屋的院子里开始。诺邓火腿的腌制过程很简单，老黄把多余的皮肉去除，加工成一个圆润的火腿，洒上白酒除菌，再把自制的诺盐均匀的抹上，不施锥针，只用揉、压，以免破坏纤维。 即使用现代的标准来判断，诺邓井盐仍然是食盐中的极品，虽然在这个古老的产盐地，盐业生产已经停止，但我们仍然相信诺邓盐是自然赐给山里人的一个珍贵礼物。 圣武和茂荣是兄弟俩，每年9月，他们都会来到湖北的嘉鱼县，来采挖一种自然的美味。这种植物生长在湖水下面的深深的淤泥之中，茂荣挖到的植物的根茎叫做莲藕，是一种湖泊中高产的蔬菜——藕。 《舌尖上的中国》电视节目策划书 一、背景浅析 改革开放以来，国人物质生活更加富足，在吃方面也变得更加讲究。食客、美食家、吃货等的出现，则从另一方面体现国人口味的变化。衣食住行为人之根本，古人读万卷书、行万里路已是满足，今人在此之外加上品万种美食，才称得上是真正的享受生活。而中国幅员辽阔，有八大菜系，淮扬菜、粤菜、鲁菜、湘菜，每种菜系都有其特色美食，而且烹调方法各有不同，可以说，国人够有口福的了。在《舌尖上的中国》这部纪录片中，导演和摄制组带着观众探访祖国各地美食，了解各式各样与美食有关的人和事，总共七集、每集50分钟的容量，节奏紧凑、制作精良，尝遍美食的同时又能遍览祖国风物，纪录片煞是好。而随着中国经济的飞速发展，人们的物质生活水平也得到了极大地提高，已经不再局限于吃饱穿暖这样基本的要求。民以食为天，在物质文明丰富至如斯的今天，人们开始重视对于生活品质更高层次的追求。对于吃，食不厌精、烩不厌细，不只吃味道，还要吃环境、吃服务、吃文化，吃健康。 二、企划动机 《舌尖上的中国》这部以美食为主题的纪录片，前些日子风头力压各种电视连续剧，成为连日来的微博“刷屏利器”并高居话题榜榜首，甚至让许多早已抛弃了电视的80后“吃货”们，纷纷锁定夜间的央视坐等这部“吃货指南”。人们为美食流口水，为美食的故事流眼泪，为美食的文化而感动自豪，自豪于中国饮食文化的博大精深，甚至有人高调地赞美“这才是最好的爱国主义教育片”。看要应对新的发展形势，就必须有新的态度与措施。饮食行业发展到今日，大街小巷、五花八门，各种价位、各种地域乃至跨国界的美食比比皆是。如何从 千篇一律的店面经营中脱颖而出？不仅仅是商家绞尽脑汁，着力打开销售额与知名度。美食老饕们也寻寻觅觅，力图享受到有特色、有内涵的精彩美食。《舌尖上的中国》这档美食资讯节目，是继《舌尖上的中国》这个记录片之后的后续美食资讯类节目，更实现其为商家和消费者两者搭建一个交流的平台，优秀的商家可以尽展己之所长，以此为基础展示自身特色美食功夫。而美食爱好者们则可以通过节目的推介，节省大量的时间、精力，接触到平时踏破铁鞋无觅处，只能通过口口相传难辨优劣，隐藏在街头巷尾的各种美食。大可以凭此慕名而来、亦可尽兴而去。 一、节目名称——《舌尖上的中国》 二、节目类别——继纪录片《舌尖上的中国》之后，观众参与度高的一档各地美食资讯节目 三、节目主旨——让爱美食的人走进节目让看节目的人走近美食 四、节目目标 借助最近《舌尖上的中国》的热点，重点打造一档精品的美食资讯节目，不仅仅做美食，还囊括了相关的综合资讯。力图达到“美食主动靠过来，观众自然看进去”的效果，打造口碑，铸就精品。 五、节目定位 这是一档集继纪录片《舌尖上的中国》之后的观众参与度高的一档各地美食资讯节目。将美食推介节目与菜肴烹饪节目于一身，力图更好的开发各地特色美食资源的服务资讯类美食节目，兼顾一定的娱乐性质。采用立体全面的推介方式，为现场和电视机前的观众提供优质精选的美食信息，商家现场展示、与美食爱好者们现场沟通交流。 《舌尖上的中国》解说词1-7集 第一季：1.自然的馈赠 作为一个美食家，食物的美妙味感固然值得玩味，但是食物是从哪里来的？毫无疑问，我们从大自然中获得所有的食物，在我们走进厨房，走向餐桌之前，先让我们回归自然，看看她给我们的最初的馈赠。 本集将选取生活在中国境内截然不同的地理环境(如海洋,草原,山林,盆地,湖泊)中的具有代表性的个人、家庭和群落为故事主角，以及由于自然环境的巨大差异(如干旱，潮湿，酷热，严寒)所带来的截然不同的饮食习惯和生活方式为故事背景，展现大自然是以怎样不同的方式赋予中国人食物，我们又是如何与自然和谐相处，从而了解在世代相传的传统生活方式中，通过各种不同的途径获取食物的故事。 第一季：2.主食的故事 主食是餐桌上的主要食物，是人们所需能量的主要来源。从远古时代赖以充饥的自然谷物到如今人们餐桌上丰盛的、让人垂涎欲滴的美食，一个异彩纷呈、变化多端的主食世界呈现在你面前。本集着重描绘不同地域、不同民族、不同风貌的有关主食的故事，展现人们对主食的样貌、口感的追求，处理和加工主食的智慧，以及中国人对主食的深厚情感。 第一季：3.转化的灵感 腐乳、豆豉、黄酒、泡菜，都有一个共同点，它们都具有一种芳香浓郁的特殊风味。这种味道是人与微生物携手贡献的成果。而这种手法被称作“发酵”。中国人的老祖宗，用一些坛坛罐罐，加上敏锐的直觉，打造了一个食物的新境界。要达到让食物转化成美食的境界，这其中要逾越障碍，要营造条件，要把握机缘，要经历挫败，从而由“吃”激发出最大的智慧。 第一季：4.时间的味道 腌制食品，风干晾晒的干货，以及酱泡、冷冻等是中国历史最为久远的食物保存方式。时至今日，中国人依然对此类食品喜爱有加。 本集涉及的美食主要有腊肉，火腿，烧腊，咸鱼(腌鱼)，腌菜，泡菜，渍菜，以及盐渍，糖渍，油浸，晾晒，风干，冷冻等不同食物保存方法，展现以此为基础和原材料的各种中国美食。贮藏食物从早先的保存食物 方便携带发展到人们对食物滋味的不断追求，保鲜的技术中蕴涵了中国人的智慧，呈现着中国人的生活，同时“腌制发酵保鲜”也蕴含有中国人的情感与文化意象，如对故乡的思念，内心长时间蕴含的某种情感等等。第一季：5.厨房的秘密 与西方“菜生而鲜，食分而餐”的饮食传统文化相比，中国的菜肴更讲究色、香、味、形、器。而在这一系列意境的追逐中，中国的厨师个个都像魔术大师，都能把“水火交攻”的把戏玩到如火纯青的地步，这是 8000年来的修炼。我们也在这漫长的过程中经历了煮、蒸、炒三次重要 的飞跃，他们共同的本质无非是水火关系的调控，而至今世界上懂得蒸菜和炒菜的民族也仅此一家。本集将主要透过与具有精湛美食技艺的人有关的故事，一展中国人在厨房中的绝技。 第一季：6.五味的调和 电动摩托车用小型电机的种类、特性报告电动机是电动摩托车的一个重要部件，目前在电动摩托车驱动领域，主要有直流电动机驱动系统、交流永磁电动机驱动系统和开关磁阻电动机驱动系统应用范围比交广泛。 1 直流电动机驱动系统 1.1 直流电机的工作原理 下图为直流电动机的物理模型，N、S为定子磁极，abcd是固定在可旋转导磁圆柱体上的线圈，线圈连同导磁圆柱体称为电机的转子或电枢。线圈的首末端a、d连接到两个相互绝缘并可随电枢一同旋转的换向片上。转子线圈与外电路的连接是通过放置在换向片上固定不动的电刷进行的。换向片与电刷滑动接触。把电刷A、B接到直流电源上，电刷A接正极，电刷B接负极。此时电枢线圈中将有电流流过，根据左手定则，电枢逆时针旋转。 当电枢旋转几何中性线时，F=0，电枢由于惯性继续运转。取下图所示位置，原N极性下导体ab转到S极下，受力方向从左向右，原S 极下导体cd转到N极下， 受力方向从右向左，该电磁力形成逆时针方向的电磁转矩，线圈在该电磁力形成的电磁转矩作用下继续逆时针方向旋转，直流电动机在直流电源作用下转动起来。 1.2 直流电机的数学方程 1.2.1 电枢中感应电动势 电枢中通入直流电流后，产生电磁转矩，使电机在磁场中转动。而通电线圈在磁场中转动，又会在线圈中产生感应电动势E 。 感应电动势为：n K E E φ= 式中，K E ——与电机结构相关的参数； Φ——电机每极磁通量，Wb ； n ——电机转速，r/min 。 1.2.2 电枢电压方程 如图所示，a a R I E U += M U R a + - E 式中，U ——外接电源电压，V ； I a ——电枢电流，A ； R a ——电枢电阻，Ω。 1.2.3 电磁转矩方程 式中，T ——电磁转矩，Nm ； K T ——与电机结构相关的常数。 1.3 直流电机的机械特性 直流电机按照励磁方式可分为两种，永磁式和电励磁式。电磁式是由磁性材料提供磁场；电励磁式是由磁极上绕线圈，在线圈中通入直流电，来产生电磁场。根据励磁线圈和转子绕组的连接关系，励磁式的直流电机可以分为：串励电机、他励电机、并励电机、复励电机。 1.3.1 串励直流电机的机械特性 串励直流电机数学模型： 式中，R f ——串励绕组电阻，Ω。 K Φ——励磁系数。 由此可推出： 这种励磁方式的特点是：当电压U 一定时，随负载转矩的增大，n 下降很快， n T T 0 《舌尖上的中国》7集（全）解说词 《舌尖上的中国》是纪录频道推出的第一部高端美食类系列纪录片，从2011年3月开始大规模拍摄，是国内第一次使用高清设备拍摄的大型美食类纪录片。共在国内拍摄60个地点方，涵盖了包括港澳台在内的中国各个地域，它全方位展示博大精深的中华美食文化。向观众，尤其是海外观众展示中国的日常饮食流变，千差万别的饮食习惯和独特的味觉审美，以及上升到生存智慧层面的东方生活价值观，让观众从饮食文化的侧面认识和理解传统和变化着的中国。 而台词优美而清新，听着解说看着画面，让人心醉··· 第一集《自然的馈赠》 中国拥有世界上最富戏剧性的自然景观，高原，山林，湖泊，海岸线。这种地理跨度有助于物种的形成和保存，任何一个国家都没有这样多潜在的食物原材料。为了得到这份自然的馈赠，人们采集，捡拾，挖掘，捕捞。穿越四季，本集将展现美味背后人和自然的故事。 香格里拉，松树和栎树自然杂交林中，卓玛寻找着一种精灵般的食物——松茸。松茸保鲜期只有短短的两天，商人们以最快的速度对松茸的进行精致的加工，这样一只松茸24小时之后就会出现在东京的市场中。 松茸产地的凌晨3点，单珍卓玛和妈妈坐着爸爸开的摩托车出发。穿过村庄，母女俩要步行走进30公里之外的原始森林。雨让各种野生菌疯长，但每一个藏民都有识别松茸的慧眼。松茸出土后，卓玛立刻用地上的松针把菌坑掩盖好，只有这样，菌丝才可以不被破坏，为了延续自然的馈赠，藏民们小心翼翼地遵守着山林的规矩。 为期两个月的松茸季节，卓玛和妈妈挣到了5000元，这个收入是对她们辛苦付出的回报。老包是浙江人，他的毛竹林里，长出过遂昌最大的一个冬笋。冬笋藏在土层的下面，从竹林的表面上看，什么也没有，老包只需要看一下竹梢的叶子颜色，就能知道笋的准确位置，这完全有赖于他丰富的经验。 笋的保鲜从来都是个很大的麻烦，笋只是一个芽，是整个植物机体活动最旺盛的部分。聪明的老包保护冬笋的方法很简单，扒开松松的泥土，把笋重新埋起来，保湿，这样的埋藏方式就地利用自然，可以保鲜两周以上。 在中国的四大菜系里，都能见到冬笋。厨师偏爱它，也是因为笋的材质单纯，极易吸收配搭食物的滋味。老包正用冬笋制作一道家常笋汤，腌笃鲜主角本来应该是春笋，但是老包却使用价格高出20倍的遂昌冬笋。因为在老包眼里，这些不过是自家毛竹林里的一个小菜而已。在云南大理北部山区，醒目的红色砂岩中间，散布着不少天然的盐井，这些盐成就了云南山里人特殊的美味。老黄和他的儿子树江小溪边搭建一个炉灶，土灶每年冬天的工作就是熬盐。云龙县的冬季市场，老黄和儿子赶到集市上挑选制作火腿的猪肉，火腿的腌制在老屋的院子里开始。诺邓火腿的腌制过程很简单，老黄把多余的皮肉去除，加工成一个圆润的火腿，洒上白酒除菌，再把自制的诺盐均匀的抹上，不施锥针，只用揉、压，以免破坏纤维。 即使用现代的标准来判断，诺邓井盐仍然是食盐中的极品，虽然在这个古老的产盐地，盐业生产已经停止，但我们仍然相信诺邓盐是自然赐给山里人的一个珍贵礼物。 圣武和茂荣是兄弟俩，每年9月，他们都会来到湖北的嘉鱼县，来采挖一种自然的美味。这 第一集《自然的馈赠》 中国拥有世界上最富戏剧性的自然景观，高原，山林，湖泊，海岸线。这种地理跨度有助于物种的形成和保存，任何一个国家都没有这样多潜在的食物原材料。为了得到这份自然的馈赠，人们采集，捡拾，挖掘，捕捞。穿越四季，本集将展现美味背后人和自然的故事。 香格里拉，松树和栎树自然杂交林中，卓玛寻找着一种精灵般的食物——松茸。松茸保鲜期只有短短的两天，商人们以最快的速度对松茸的进行精致的加工，这样一只松茸24小时之后就会出现在东京的市场中。 松茸产地的凌晨3点，单珍卓玛和妈妈坐着爸爸开的摩托车出发。穿过村庄，母女俩要步行走进30公里之外的原始森林。雨让各种野生菌疯长，但每一个藏民都有识别松茸的慧眼。松茸出土后，卓玛立刻用地上的松针把菌坑掩盖好，只有这样，菌丝才可以不被破坏，为了延续自然的馈赠，藏民们小心翼翼地遵守着山林的规矩。 为期两个月的松茸季节，卓玛和妈妈挣到了5000元，这个收入是对她们辛苦付出的回报。 老包是浙江人，他的毛竹林里，长出过遂昌最大的一个冬笋。冬笋藏在土层的下面，从竹林的表面上看，什么也没有，老包只需要看一下竹梢的叶子颜色，就能知道笋的准确位置，这完全有赖于他丰富的经验。 笋的保鲜从来都是个很大的麻烦，笋只是一个芽，是整个植物机体活动最旺盛的部分。聪明的老包保护冬笋的方法很简单，扒开松松的泥土，把笋重新埋起来，保湿，这样的埋藏方式就地利用自然，可以保鲜两周以上。 在中国的四大菜系里，都能见到冬笋。厨师偏爱它，也是因为笋的材质单纯，极易吸收配搭食物的滋味。老包正用冬笋制作一道家常笋汤，腌笃鲜主角本来应该是春笋，但是老包却使用价格高出20倍的遂昌冬笋。因为在老包眼里，这些不过是自家毛竹林里的一个小菜而已。 在云南大理北部山区，醒目的红色砂岩中间，散布着不少天然的盐井，这些盐成就了云南山里人特殊的美味。老黄和他的儿子树江小溪边搭建一个炉灶，土灶每年冬天的工作就是熬盐。 云龙县的冬季市场，老黄和儿子赶到集市上挑选制作火腿的猪肉，火腿的腌制在老屋的院子里开始。诺邓火腿的腌制过程很简单，老黄把多余的皮肉去除，加工成一个圆润的火腿，洒上白酒除菌，再把自制的诺盐均匀的抹上，不施锥针，只用揉、压，以免破坏纤维。 即使用现代的标准来判断，诺邓井盐仍然是食盐中的极品，虽然在这个古老的产盐地，盐业生产已经停止，但我们仍然相信诺邓盐是自然赐给山里人的一个珍贵礼物。 圣武和茂荣是兄弟俩，每年9月，他们都会来到湖北的嘉鱼县，来采挖一种自然的美味。这种植物生长在湖水下面的深深的淤泥之中，茂荣挖到的植物的根茎叫做莲藕，是一种湖泊中高产的蔬菜——藕。 作为职业挖藕人，每年茂荣和圣武要只身出门7个月，采藕的季节，他们就从老家安徽赶到有藕的地方。较高的人工报酬使得圣武和茂荣愿意从事这个艰苦的工作。挖藕的人喜欢天气寒冷，这不是因为天冷好挖藕，而是天气冷买藕吃藕汤的人就多一些，藕的价格就会涨。 《舌尖上的中国》中提到的所有美食统计 第一集自然的馈赠 1，香格里拉松茸 2，江浙地区冬笋油焖冬笋 3，广西柳州酸笋黄豆酸笋小黄鱼 4，云南大理诺邓山区诺邓盐血肠火腿莴笋炒火腿火腿炒饭 5，湖北嘉鱼藕莲藕炖排骨 6，吉林查干湖湖水大鱼鱼头泡饼（北京） 7，海南香煎马鲛鱼酸菜鱼汤水煮红螺 第二集主食的故事 1，山西襄汾县花馍花卷油卷 2，陕西绥德黄馍馍（糜子面） 3，新疆库车馕饼 4，中原地区馒头（馍馍，古时又叫炊饼，现在想通武大郎为啥喊“炊饼”了） 长期发展形成南稻北麦，2000年前五谷排行顺序：稻，黍shu，稗bai，麦，菽shu；现在以稻，麦，玉米为主。5，贵州黎平米粉汤粉 6，广州沙河河粉干炒牛河 7，陕西西安凉皮汉中米皮（这是本人自己加上的，因为说到米粉，河粉，如果不说凉皮就说不过去了，导 演组失职啊） 8，陕西肉夹馍，牛羊肉泡馍，粉蒸肉夹馍（也叫荷叶饼夹馍，这个也是按自己加的） 9，兰州拉面 10，广州竹升面云吞捞面 11，中原地区手擀面 12，陕西岐山臊子面 13，嘉兴粽肉子蛋黄棕（关于粽子南方有肉粽，蛋黄粽等，北方一般都是蜜枣棕，北方人吃不惯肉粽，咸棕） 15，北方饺子焖面（陕西河南） 第三集转化的灵感 本集介绍三大部分1豆腐，2，酒，3醋（第六集时会讲一下醋所以这集就说了一下），4酱油，5酱油，6大酱 豆腐篇 1，云南红河建木县碳烤豆腐球石屏县老豆腐 2，中原地区石膏豆腐（各种豆制品，相信大家都是很喜欢吃豆腐的吧 ，尤其是嫩的。） 3，内蒙古锡林郭勒旗奶茶奶豆腐奶制品 4，云南白族豆腐皮 5，北京蒙古餐厅烤羊背 6，浙江天台山僧人的素食中豆制品很重要 7，安徽毛豆腐 酒篇 8，绍兴黄酒 9，安徽休林糯米酒 10 ，安昌镇腊肠 11，东北大豆酱酸菜 第四集时间的味道 这一集是介绍腌制品，脱水，酱菜 1，黑龙江绥化市朝鲜族泡菜， 2，广粤地区腊肠各种腊制品煲仔饭荔芋腊鸭煲南安腊鸭 3，湖南靖州县腌鱼腊鸭 4，徽州臭鳜鱼 5，安徽黔县腊八豆腐刀板鱼 黄山火腿咸肉 6，浙江金华火腿蜜汁上方 7，上海的三阳南货店经营各种腌制品腊肉等： 杭州酱鸭 上海腌笃鲜 温州黄鱼鲞xiang 宁波笋干 绍兴梅干菜梅干菜烧肉 8，上海醉虾醉蟹 9，福建霞浦紫菜 10，台湾云朴县乌鱼子 11，香港大奥海盐产地咸鱼虾膏虾酱 12，中原地区各种酱菜（腌萝卜，鬼子姜，辣椒，黄瓜各种蔬菜） 第五集厨房的秘密 这一集最后一句“厨房的秘密就是没有秘密”很是狗血啊。 电机与拖动基础讨论课课题：各种电机应用现状调研 班级：13级工程机械1班 组员：李昊天张晨阳崔超钰 陈杰董亚飞潘帅 时间：2016年4月5日 指导老师：马云飞 目录 前言 (3) 1、电机产业现状 (4) 2、电机行业格局 (4) 3、电机行业前景预测 (4) 4、电机的分类及应用概述 (5) 5、信号电机 (6) 5.1、位置信号电机 (6) 5.2、感应同步器 (6) 5.3、自整角机 (7) 5.4、速度信号电机 (7) 6、功率电动机 (8) 6.1、直流电动机 (8) 6.2、交流电机 (8) 6.3、同步电动机 (9) 6.4、异步电动机 (10) 7、控制电机 (10) 7.1伺服电机 (10) 7.2、步进电动机 (11) 7.3、力矩电动机 (12) 7.4、开关磁阻电机 (13) 7.5、无刷直流电动机 (13) 参考文献 (15) 前言 从广义上讲，电机是电能的变换装置，包括旋转电机和静止电机。旋转电机是根据电磁感应原理实现电能与机械能之间相互转换的一种能量转换装置；静止电机是根据电磁感应定律和磁势平衡原理实现电压变化的一种电磁装置，也称其为变压器。本文我们主要讨论旋转电机，旋转电机的种类很多，在现代工业领域中应用极其广泛，可以说，有电能应用的场合都会有旋转电机的身影。与内燃机和蒸汽机相比，旋转电机的运行效率要高的多；并且电能比其它能源传输更方便、费用更廉价，此外电能还具有清洁无污、容易控制等特点，所以在实际生活中和工程实践中，旋转电机的应用日益广泛。不同的电机有不同的应用场合，随着电机制造技术的不断发展和对电机工作原理研究的不断深入，目前还出现了许多新型的电机，例如，美国EAD公司研制的无槽无刷直流电动机，日本SERVO公司研制的小功率混合式步进电机，我国自行研制适用于工业机床和电动自行车上的大力矩低转速电机等。本文下面主要讨论部分电机种类及应用情况。 舌尖上的中国中英文介绍 《舌尖上的中国》第二季于2013年1月10日在京正式启动，该片于2014年4月18日至6月6日，每周五在中央电视台综合频道（CCTV-1）21点档、中央电视台纪录频道（CCTV-9）22点档同步开播，同时在爱奇艺，乐视网等网络平台播出。 A bite of China2 was started on January 10th,2013 in Beijing. This documentary will be on from April 18th,2014 to June 6th,2014.Each Friday, audience can enjoy this documentary in CCTV1 at 21.pm, or CCTV9,22pm.In the meanwhile, it shows in IQIYI or Letv and other network platform. 《舌尖上的中国》讲述了从远古时代赖以充饥的自然谷物到如今人们餐桌上丰盛的、让人垂涎欲滴的美食，一个异彩纷呈、变化多端的主食世界呈现在你面前。这部纪录片将着重描绘不同地域、不同民族、不同风貌的有关主食的故事，展现人们对主食的样貌、口感的追求，处理和加工主食的智慧，以及中国人对主食的深厚情感。据导演透露《舌尖上的中国2》将加重川菜的部分。 A bite of China describes food’s transition from ancient to nowadays. In ancient, humans just could solve the hunger , they could not eat delicious food. But now, there are various of food on people’s dinner-table. A colorful and changeable major food world emerges your eyes. This documentary pays most attention on describing the stories about major food in different areas, different races and features. It shows the intelligence about Chinese. They went after food’s features, tastes, solution and process. Of course, it also reflects Chinese feelings. From the director, A bite of China will introduce the food of Sichuan most detail. 《舌尖上的中国2》共分为《脚步》、《心传》、《时节》、《家常》、《秘境》、《相逢》、《三餐》，第八集则为拍摄花絮。每集50分钟 A bite of China covers 8 segments, including 《Steps》，《Heart inheriting》，《Seasons》,《The daily life of a family》，《Nulls》，《Meeting》，《Three meals》. The eighth part is tidbits. Each section lasts 50 minutes. 第一集《脚步》 The first segment:《Steps》. 【汗水中的苦辣酸甜】 Four tastes in sweat, bitter, hot, acid and sweet. “路菜”是先人保存食物的智慧，进而被演化成标志性的中国美食。味觉记忆的强大，往往让人们对故乡食物的迷恋十分牢固，甚至被赋予“乡愁”这样的文学语汇。舌尖第二季分集《脚步》，将跟随那些奔波在路上的人们，品尝辛劳与汗水中的苦辣酸甜。 “Lucai” is wisdom of Chinese ancestor which comes from food’s keeping. It has became a symbol of Chinese delicious food. The strong strength of gustation 第一章概述 第一节电机的定义 电机可泛指所有实施电能生产、传输、使用和电能特性变换的机械或装置。然而，由于生产、传输、使用电能和电能特性变换的方式很多，原理各异，如机械摩擦、电磁感应、光电效应、磁光效应、热电效应、压电效应、化学效应等等，内容广泛，不可能由一门课程包括。电机学的主要研究范畴仅限于那些依据电磁感应定律和电磁力定律实现机电能量转换和信号传递与转换的装置。 一、电机的能量交换原理 根据电机学定义，电机是一种将电能转换成机械能或将机械能转换成电能的设备，其中将机械能变为电能的称发电机；将电能变为机械能的称为电动机。电机实现能量转换都基于两个基本定律： 1、法拉第-楞次定律（感应电动势定律） 导体在磁场中运动切割磁力线，在导体两端必然会产生感应电动势，感应电动势e的大小与导体运动速度v、导体的长度L以及磁场的磁感应强度B成正比，即：e=BLV 感应电动势的方向符合右手定律。 2、毕奥-萨戈尔定律（电磁力定律） 载流导体在磁场中必然会受到电磁力的作用。电磁力的大小与导体所载电流I、磁场的磁感应强度B以及导体的长度L成正比，即：F=BIL 电磁力的方向符合左手定律。 所有电机都是根据上述两个定律基本原理设计的。电机类型很多，结构类型很多，结构形式也各不相同，但其能量转换和转矩产生原理是相同的，由于励磁方式不同，各类电机磁场性能和变化不同，才有电机的不同类型和不同特性。 电机内部实现能量转换包括电系统、耦合系统和机械系统三个环节，如图1-1。电动机通常是在其接线端子上输入电能，在轴上输出机械功率。外电路电能通过耦合系统在在机械系统中产生机械能，在机械系统轴头以机械能输出。发电机则是在其轴上输入机械功率，其端子上输出电功率。驱动机械的机械能通过耦合系统，在电系统中产生电能输出。在上述能量转换过程中，三个系统都会产生部分能量损失，最终都以热量形式向周围环境散逸。 哈尔滨工业大学寒假社会调查报告 题目：电机种类及其使用情况调查 指导教师：江善林 院系：电气学院电气工程系 班级：11306108 姓名：况麒麒 学号：1130610823 日期：2013年03月01日 电机类型及其使用情况调查 1 调查背景 从1820年丹麦物理教学家奥斯特发现了电流的磁效应以来，各种发现不断地涌现出来。1821年，英国科学家法拉第总结了载流导体在磁场中受力并发生机械运动的现象他的模型可以认为是现代直流电动机的雏形。1824年，阿拉果发现了旋转磁场，为交流感应电动机的发明奠定了基础。1831年，法拉第发现了电磁感应定律，并发明了单极直流电动机。1834年俄国物理学家雅可比设计并制成了第一台实用的直流电动机。1864年，英国物理学家麦克斯韦创立了完整的经典电磁学理论体系为电机电磁场分析奠定了基础。1888年，特斯拉发明了感应电动机。随着时代的进步，各种各样功能不同的电机被不断地发明出来。 电机的发展历史大致可分为四个阶段，1. 直流电机阶段，2. 交流电机阶段，3. 控制电机阶段，4. 特种电机阶段。 本次调查主要是想通过调查能让我们加深对电机的了解，为以后的学习工作打下一定的基础。 2 调查内容 2.1 时间安排：本次调查主要安排在寒假假期。 2.2 调查对象：本次调查主要调查电机的类型和电机的使用情况。 2.3 调查内容：电机类型有很多，分类方法也各种各样。下面主要介绍按工作电源和按结构和工作原理两种分类方法中的电机。 1. 按工作电源分，包括直流电动机和交流电动机，其中交流电动机又分为单相电动机和三相电动机；直流电动机分为无刷直流电动机和有刷直流电动机，有刷直流电动机又分为永磁直流电动机和电磁直流电动机。永磁直流电动机包括稀土永磁直流电机，铁氧体永磁直流电机，铝镍钴永磁直流电机三类; 电磁直流电机包括串励直流电机，并励直流电机，和复励直流电机三类。 直流电动机 无刷直流 电动机 永磁直流电动机 稀土永磁直流电动机 铁氧体永磁直流电动机 电动机 交流电动机 有刷直流 电动机 电磁直流电动机 铝镍钴永磁直流电动机 串励直流电动机 并励直流电动机 他励直流电动机 复励直流电动机 单相电动机 三相电动机 步进电机的种类、结构及工作原理 步进式伺服驱动系统是典型的开环控制系统。在此系统中，执行元件是步进电机。它受驱动控制线路的控制，将代表进给脉冲的电平信号直接变换为具有一定方向、大小和速度的机械转角位移，并通过齿轮和丝杠带动工作台移动。由于该系统没有反馈检测环节，它的精度较差，速度也受到步进电机性能的限制。但它的结构和控制简单、容易调整，故在速度和精度要求不太高的场合具有一定的使用价值。 1.步进电机的种类 步进电机的分类方式很多，常见的分类方式有按产生力矩的原理、按输出力矩的大小以及按定子和转子的数量进行分类等。根据不同的分类方式，可将步进电机分为多种类型，如表5-1所示。 表5-1 步进电机的分类 分类方式具体类型 按力矩产生的原理（1）反应式：转子无绕组，由被激磁的定子绕组产生反应力矩实现 步进运行 （2）激磁式：定、转子均有激磁绕组（或转子用永久磁钢），由电 磁力矩实现步进运行 按输出力矩大小 （1）伺服式：输出力矩在百分之几之几至十分之几（N·m）只能驱动较小的负载，要与液压扭矩放大器配用，才能驱动机床工作台等较大 的负载 （2）功率式：输出力矩在5-50 N·m以上，可以直接驱动机床工作 台等较大的负载 按定子数（1）单定子式（2）双定子式（3）三定子式（4）多定子式按各相绕组分布 （1）径向分布式：电机各相按圆周依次排列 （2）轴向分布式：电机各相按轴向依次排列 2.步进电机的结构 目前，我国使用的步进电机多为反应式步进电机。在反应式步进电机中，有轴向分相和径向分相两种，如表5--1所述。 图5--2是一典型的单定子、径向分相、反应式伺服步进电机的结构原理图。它与普通电机一样，分为定子和转子两部分，其中定子又分为定子铁心和定子绕组。定子铁心由电工钢片叠压而成，其形状如图中所示。定子绕组是绕置在定子铁心6个均匀分布的齿上的线圈，在直径方向上相对的两个齿上的线圈串联在一起，构成一相控制绕组。图5--2所示的步进电机可构成三相控制绕组，故也称三相步进电机。若任一相绕组通电，便形成一组定子磁极，其方向即图中所示的NS极。在定子的每个磁极上，即定子铁心上的每个齿上又开了5个小齿，齿槽等宽，齿间夹角为9°，转子上没有绕组，只有均匀分布的40个小齿，齿槽也是等宽的，齿间夹角也是9°，与磁极上的小齿一致。此外，三相定子磁极上的小齿在空间位置上依次错开1/3齿距，如图5--3所示。当A相磁极上的小齿与转子上的小齿对齐时，B相磁极上的齿刚好超前(或滞后)转子齿1/3齿距角，C相磁极齿超前(或滞后)转子齿2/3齿距角。 图5-2 单定子径向分相反应式伺服步进电机结构原理图电动机分类及介绍
电机的种类及其介绍
舌尖上的中国分集简介
电机的基本常识及分类
舌尖上的中国解说词全文
舌尖上的中国栏目策划
《舌尖上的中国》简介和解说词1-7集
电动摩托车用小型电机的种类 特性介绍
舌尖上的中国(1-7)全集解说词
舌尖上的中国的解说词
《舌尖上的中国》中提到的所有美食统计资料
各种电机种类及应用
舌尖上的中国中英文介绍
电机概述及各类型电机介绍知识培训资料
电动机种类及其应用教材
步进电机的种类结构及工作原理