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continuum–discontinuum methods

Stability analysis of the blast-induced damage zone by continuum and coupled continuum –discontinuum methods

David Saiang

Division of Mining and Geotechnical Engineering,Lule?University of Technology,SE-97187Lule?,Sweden

a b s t r a c t

a r t i c l e i n f o Article history:

Received 13November 2008

Received in revised form 23June 2009Accepted 19July 2009

Available online 24July 2009

Keywords:

Blast-induced damage zone (BIDZ)Blast-induced radial cracks

Continuum –discontinuum coupled model Failure Fallout

Volumetric strain

100%yielded elements Failed zone

The presence of a blast-induced damage zone (BIDZ)around a tunnel boundary is of signi ?cant concern mainly with regard to safety,stability,costs and the overall performance of the tunnel.The BIDZ is essentially characterized by reduction in strength and stiffness,and increase in permeability.Guidelines have been developed based on perimeter blasting experiences and overbreak characterization to regulate damage due to blasting.Although the over-break approach of assessing the degree of blast-induced damage is practical,the method does not provide a measure of the competency of the damaged rock.Very often it is important to know how the damaged rock mass will behave under any given conditions.In this paper a series of numerical analyses was performed using continuum and coupled continuum –discontinuum methods to study the behaviour of the blast-induced damage zone.In the coupled continuum –discontinuum method FLAC and PFC 2D were coupled together.The inner segment of the model was simulated using PFC 2D ,while the outer segment was simulated using FLAC.This enabled the tracking of failure and fallout from the PFC 2D model.The tunnel was excavated within the PFC 2D segment.Blast-induced radial cracks were traced and individually implemented in the models.Models were also run independently in FLAC and Phase 2and the results were compared to those of the coupled models.The results show that the failure around the tunnel was con ?ned in most parts to the damaged zone at shallow depths,but not in deep excavations.The failures and fallouts mapped with the coupled models were consistent with practical observations.Since the continuum models cannot simulate failure,results from the coupled model were used to identify indicators for failure in the continuum models.It was seen that yielding due to volumetric straining (in FLAC)and 100%yielded elements (in Phase 2)were consistent with the failures mapped in the coupled models for shallow excavations,but was less consistent for deep excavations.

1.Introduction

The most cost effective method for excavating tunnels in massive hard rock masses,where the uniaxial compressive strength very often exceeds 200MPa,is by drilling and blasting.A very important concern often arises with this method:unwanted damage induced by blasting beyond the desired perimeter of the tunnel.The signi ?cance and importance of this damage have been deliberated by among others;Oriad (1982),MacKown (1986),Ricketts (1988),Plis et al.(1991),Andersson (1992),Forsyth (1993),Persson et al.(1996)Raina et al.(2000)and Warneke et al.(2007).To minimize this damage perimeter blasting techniques,such as smooth blasting (e.g.Holmberg and Persson,1980)are commonly used,complemented by theoretical blast damage tables and charts (e.g.Anl?ggningsAMA-98,1999).In spite of these precautionary measures blast damage is still inevitable and the conceived consequences are evidenced in the form of increased support

cost and requirements,slow tunnel advance,unforeseen stability pro-blems originating from blast damage,conduit for water ?ow,reduction in tunnel life,etc.

Although the blast-induced damage guidelines,mentioned above,are useful in tunnelling and drifting works,it is still unclear how,when and to what degree the damaged zone affects the stability of an excavation.The construction of a tunnel for example can either speed up or slow down if the effects of the damaged zone are understood at a reasonable level so that the blast-induced damage can be controlled optimally without making too many sacri ?ces.Cautious blasting is costly and time consuming.If it can be eliminated in some cases then it will save cost and time for clients and contractors alike.On the other hand if no such controls are in place then the excavation can be in danger of uncontrolled blasting,which will lead to instability pro-blems and unsafe working environment,bad tunnel geometry,and additional material to remove.

In order to understand the effect of the BIDZ on the stability and performance of an excavation,an understanding of how the zone behaves under certain scenarios is essential.This was the focus of a paper by Saiang and Nordlund (2008).This paper (i.e.Saiang and

Engineering Geology 116(2010)1–11

E-mail address:david.saiang@ltu.se

10.1016/j.enggeo.2009.07.011

Contents lists available at ScienceDirect

Engineering Geology

j o u rn a l h o m e p a g e :w ww.e l s evi e r.c o m /l o c a t e /e n g g e o

Nordlund,2008)also revealed the need for detailed modelling of the blast-induced damage zone,in order to gain a proper understanding of its behaviour.Hence,in the present paper the damaged zone was studied after coupling FLAC (Itasca,2005)and PFC 2D (Itasca,2008)to create a continuum –discontinuum coupled model.In the coupled model the inner segment of the model was simulated using PFC 2D ,while the outer segment was simulated using FLAC.This enabled the tracking of failure and fallout within the PFC 2D segment where the tunnel was excavated.Blast-induced radial cracks were individually implemented in the model.Models were also run independently in continuum based codes,FLAC and Phase 2.The results of these models were compared to the coupled models.Since continuum models cannot simulate failure,results from the coupled model were used to identify indicators for failure in the continuum models,i.e.in the FLAC and Phase 2models.It must be noted that the numerical analyses presented in this paper do not concern the actual blasting process,but the effects and behaviour of the damage created by blasting.

SveBeFo (Swedish Rock Engineering Research)has performed an extensive investigation into damage caused by blasting for over a decade,starting in the early 1990's (Olsson,1992;Olsson and Bergqvist,1993,1995,1997;Ouchterlony,1997;Nyberg et al.,2000;Ouchterlony et al.,2001;Nyberg and Fjellborg,2002;Olsson and Ouchterlony,2003;Olsson et al.,2004).Results from these investigations were used as a basis to develop computer models in this paper.

2.Background

2.1.Blast-induced fracture characterization

In order to make an educated judgement on the failure processes and expected effects,the understanding of the characteristics of the BIDZ is important.The blast-induced damage can generally be de ?ned as any damage that originates from blasting.SveBeFo developed a simple methodology to differentiate between blast-induced damages (or cracks according to SveBeFo)and those that originate from other sources.This is illustrated in Fig.1.Cracks that originate from the half-pipes are considered as blast-induced and those not originating from the half-pipes are considered to be from other sources,either natural or stress-induced.The SveBeFo investigations revealed that the max-imum depth of damage (i.e.in terms of crack length)resulting from controlled blasting usually extends to about 0.7m and in less controlled conditions can reach 1.2m.The average depth of these crack lengths was about 0.3

Fig.1.Blast-induced cracks originate from the half-casts while stress-induced and natural cracks do not (modi ?ed after Olsson et al.,

2004).

Fig.2.Radial cracks observed around (?64mm blast-holes from a bench blast and 0.5m by 0.5m burden and spacing respectively.The explosive used was Kumulux with 22mm cylindrical column charge,with the holes blasted instantaneously (Olsson and Bergqvist,1995

Fig.3.Tangential cracks observed around (?64mm blast-holes from bench a blast with 1.0m by 0.8m burden and spacing respectively.The explosive used is Gurit with 22mm cylindrical column charge and blasted instantaneously (Olsson and Bergqvist,1995

Fig.5.Radial cracks generated within the PFC and Phase 2models as per observations in Figs.2and 3.The spacing between the blast-holes is 1.0m and the tunnel dimension is 7m ×7

Fig.4.Estimation of intersecting cracks from adjacent blast-holes.Cracks with orientation angles up to 25°from the blast-hole row intersect each other,while those greater than 25°do not intersect.

2 D.Saiang /Engineering Geology 116(2010)1–11

The crack patterns observed had various characteristics which depended on the many factors,including for example;explosive proper-ties,rock mass properties and blast-hole geometrical parameters.Two examples of these crack patterns are shown Figs.2and3,which are the results of different blast-hole burden and spacing.The former shows a well-developed radial crack pattern around the blast-holes with smooth half-pipes.The burden and spacing in this case is0.5m by0.5m respectively.The latter shows“bow-shaped”tangential cracks parallel to the blast-hole row.The burden and spacing in this case is0.8m×1.0m respectively.These observations were irrespective of the explosive types used(see Olsson and Bergqvist,1995).

The physical characteristics of the blast-induced damage are important if the mechanical behaviour of the damage zone is to be assessed.The blast damaged zone is composed of macroscopic to microscopic fractures of varying sizes,shapes and lengths.Micro-scopic fractures can signi?cantly destroy the rock fabric and thus contribute to the overall reduction in the strength of the damaged rock.Within the damaged zone there are numerous rock bridges. These rock bridges must be broken before rock mass failure could occur.Diederichs and Kaiser(1999)have shown that1%of the rock bridges within1m2can produce cohesive strength equal to the strength of one cable bolt.Under low con?nement conditions the role of these rock bridges for stability and the behaviour of the damaged zone can be signi?cant.ISRM(1981)recognized the importance of rock bridges for strength and stability at low con?nement conditions, such as open pit slopes,and therefore a relationship was proposed for estimating the cohesive strength of the rock bridges as a function of the compressive and tensile strengths of the intact rock.

2.2.Rock mass properties

Most of the blast-induced damage investigations by SveBeFo's were conducted at a granite quarry.The average compressive and tensile strengths of the granite were200MPa and12MPa,re-spectively.For the majority of the rock masses in Sweden,which comprise mostly of hard crystalline rock,the intact strengths given above are generally considered typical.In terms of engineering classi?cation,the rock mass in Sweden is generally classed as good quality or above average.The generally reported Geological Strength Index or GSI(Hoek et al.,1995)values for these rock masses generally averages60.

3.Method

3.1.Tracing of blast-induced cracks

For the sake of simplicity the crack patterns shown in Figs.2and3 were used as the basis for developing the blast-induced radial crack patterns,although SveBeFo's work revealed complicated crack patterns.The cracks were?rst individually traced as shown in Fig.4. Cracks with orientation angles of up to25°from blast-hole row were made to intersect those with similar orientation from neighbouring blast-holes as shown in Fig.4.Those with orientation angles greater than25°do not intersect.To make it easier to implement in the computer models the traced cracks were generated at15°intervals. Fig.5shows the?nal but simpli?ed implementation of these cracks around the periphery of a7.0m×7.0m tunnel.The maximum lengths of the cracks were taken as0.5m.This length was also found to numerically suit Phase2(Rocscience,2007:Version6.0)when?nite element grids were generated.The spacing between the centre of a set of radial cracks to another is0.8m,which also conforms to the average spacing of the contour holes when?64mm drill-holes are used in smooth tunnel blasting(see for example Zare and Bruland,2006).

3.2.Coupling of FLAC and PFC2D

The coupling of FLAC(Itasca,2005)and PFC2D(Itasca,2008)is done by the use of the socket I/O(Input/Output)functions to transfer data between the two codes.Initially,a series of walls is created in PFC2D,where each wall corresponds to a single surface segment of

a Fig.7.FLAC–PFC2D coupled model,with the embedded?gure showing radial cracks in the PFC2D

component.

Fig.6.Coupling of FLAC and PFC2D with illustration of the important features.

D.Saiang/Engineering Geology116(2010)1–11

FLAC zone.In other words FLAC and PFC2D must share the same geometrical coordinates at their interfaces.As the FLAC zones deform in large-strains,grid point velocities are transferred to PFC2D,so that the walls move in exactly the same way as the boundary segment of the FLAC grid.The resulting wall forces,due to particle interacting with the walls,are transferred to FLAC as applied grid point forces.In this way,a fully coupled simulation is performed(see Itasca,2004). One of the codes,in this case FLAC,acts as a server while PFC2D as a client,to establish the contact.Cycling is synchronized in both codes so that the same displacements are calculated in each code at the

same time step.

In the present paper the coupling was done by invoking a series of FISH?les found in FLAC and PFC2D FISHTanks that deal with coupling of the two codes.The FISH?les were custom edited and then systematically executed.It was important that FLAC and PFC2D share the same geometrical boundaries where they were to be interfaced. Furthermore,the FLAC zone sizes near or at the interface were suf-?ciently small to within a tolerable range for the small PFC2D ball sizes. Stresses were initialized with stress gradients.As with geometrical boundaries,the two components shared the same stresses;however, the stress initialization was done in PFC2D,which served as the source code for the coupling.In order for the model to work properly the stresses were initialized to a tolerance factor of0.001,in order to eliminate stress imbalance in the two components.Note that the stress initialization with the option to apply stress gradients is not available in versions earlier than PFC2D 4.0(Itasca,2008).Fig.6 illustrates the important features of coupling FLAC and PFC2D.FLAC was set to run in large strain mode to conform to PFC2D.

3.3.Smooth-joint model

The smooth-joint model was used in simulating the blast-induced damage fractured zone in PFC2D.A smooth-joint model simulates the behaviour of an interface regardless of the local particle contact orientations along the interface(Potyondi,2008).Particles on opposite of an interface(a joint or a crack)can overlap thus ensuring slip to occur along the interface without moving around one another as in the ordinary contact models(see Potyondi,2008).The response when slip occurs at interface(i.e.the post-peak response)is smooth when the smooth-joint model is used,while it is“pumpy”with ordinary contact models.The signi?cance of this behaviour is that the dilation and the frictional resistance of the interface can be affected. Since the post-peak behaviour was important for this study the smooth joint model was selected.3.4.Implementation of blast-induced damage in coupled FLAC-PFC2D model

The implementation of the radial cracks in PFC2D is not straight forward.Several steps were followed in the implementation.Without going into too many details the following eight sequential steps were used:(i)the inner horse-shoe shell for the damaged zone and the tunnel were created in PFC2D,(ii)cracks with desired origins were introduced,but at this time the cracks have the same properties as the intact rock,(iii)an outer rectangular shell of the PFC2D model was created,(iv)the completed PFC2D model is coupled with FLAC, (v)stresses were initialised in PFC2D and the coupled model brought to equilibrium,(vi)the tunnel was excavated inside PFC2D(vii)properties of the cracks were changed to those of the blast-damaged cracks,and

Table2

Micro-mechanical and sample properties for the synthetic rock mass(Saiang,2008). Micro-mechanical properties Sample properties

Normal stiffness58GN/m Porosity:0.17

Shear stiffness23GN/m Contact number: 3.87

Normal bond strength2MN Ball radius0.5to1.0cm Shear bond strength10MN

Friction coef?cient

1.0

Fig.8.Blast-induced radial cracks implemented in Phase2

Fig.9.(a)Implementation of the damaged zone in the FLAC model.Both damaged and undamaged zones were treated as equivalent continuum,however,the damaged zone has reduced mechanical properties(see Saiang and Nordlund,2008).(b)Linear variation of the rock mass modulus from the tunnel boundary and into the virgin rock in FLAC.E m is the virgin rock mass modulus and E D is the damaged rock mass modulus at the tunnel boundary.

Table1

Properties of the blast-induced cracks(stiffness and strength data is assumed from

Saiang et al.,2005).

Parameter Value

Normal stiffness 1.3GN/m

Shear stiffness 1.3GN/m

Shear strength 1.4MPa

Normal strength0

Friction coef?cient 1.0

4 D.Saiang/Engineering Geology116(2010)1–11

(viii)cycling began.The above steps were necessary to avoid blast-induced radial cracks extending into the undamaged rock mass region.

Blast-induced radial cracks were individually implemented in the PFC 2D component of the coupled model at 15°intervals (see the embedment in Fig.7).This was done explicitly by de ?ning the coordinates and the orientation of each crack.The spacing between the blast holes is 1.0m.The smooth joint model was applied to the cracks and the properties of the cracks are those shown in Table 1.Because of limited information about the mechanical properties of a blast-induced crack,the values shown in Table 1are assumed from Saiang et al.(2005).A friction angle of 45°was assumed for the blast-induced cracks.

For the ordinary rock mass the micromechanical properties were derived using a procedure described in Saiang (2008).This involved a series of repeated uniaxial compression tests on a synthetic rock mass specimen.The rock mass in this case was idealized as an equivalent continuum (intact)with reduced mechanical properties,whose com-pressive strength and deformation modulus can be derived using empirical methods such as the Hoek –Brown –GSI.Hence,the target deformation modulus and compressive strength for the rock mass were ?rst calculated on the basis of Hoek –Brown –GSI empirical method (Hoek et al.,2002).Then using charts and empirical relations found in for example Diederichs (1999)and Huang et al.(1999)the initial micromechanical parameters were estimated.The ?ne-tuning of the micromechanical parameters were achieved through repeated uniaxial compression tests until the target values of for the modulus and the compressive strength were achieved.The ?nal synthetic rock

mass micromechanical and sample properties are show in Table 2.Note that the PFC 2D ball radii were chosen considering that,the FLAC zones and PFC 2D balls must share approximately the same dimensions at the interface or the segment boundary.In these models the FLAC zones at the segment boundary averaged 1.0cm×1.0cm,which connected reasonably well with the PFC 2D particles of the chosen sizes.Radial grids were generated for FLAC zones to assist in proper contact at the boundary segments (see Fig.7).

The overall size of coupled model was 160m×100m,with the PFC 2D component being 20m×20m.This model size was suf ?cient enough to eliminate boundary effects for shallow depth models without signi ?cantly affecting computational time.Roller boundaries were applied on the FLAC component in both x -and y -directions.However,for shallow tunnel depths of 10to 50m the top boundary was free in the y -direction.

3.5.Implementation of blast-induced damage in Phase 2

The primary reason for using Phase 2in this study was that,it was easy to implement the radial cracks in the model.Fig.8shows the blast-induced cracks implemented in Phase 2.The cracks can be treated either as open-ended or closed-ended.In the models of this paper the cracks with orientation angles up to 25°are open at both ends since the cracks intersect each other.Those with orientation angles greater than 25°are open at one end and closed at the other.The Mohr –Coulomb friction model was applied to the cracks.The deformation of the cracks is via the shear and normal displacements,which are dependent on the normal and shear stiffness.Slip along the crack surfaces will occur when the shear strength of the slip surface is exceeded.The mechanical properties of the cracks are the same as those used in the coupled model,see Table 1.The undamaged rock mass is treated as an equivalent continuum,whose properties can be estimated by empirical methods such as Hoek –Brown (e.g.Hoek et al.,2002).

3.6.Implementation of blast-induced damage in FLAC

Unlike Phase 2the implementation of radial cracks in FLAC was dif ?cult.Hence,the radial cracks were not implemented in FLAC.However,the approach used in FLAC is the assumption of equivalent continuum.The mechanical properties of the BIDZ are rationally reduced from those of the undamaged rock mass.This approach is presented in Saiang and Nordlund (2008),which is illustrated in Fig.9.Both the damaged and undamaged zones were treated as equivalent continuum (see Fig.9(a)).However,for the damaged zone the rock mass modulus was varied shown in Fig.9(b).

Table 4

Strength parameters determined from the PFC 2D models (Saiang,2008).Parameter Values

Undamaged rock mass Damaged rock mass Cohesion,c 5.8 3.1Friction,?(°)3231Tension,σt (MPa) 2.5 1.3Dilation,ψ(°)

Fig.10.(a)Sample of cracking and fallout in the PFC 2D component of the coupled model in the 100m depth model and (b)failed zone mapped from (a).

Table 3

Rock parameters used in deriving inputs for the numerical analyses.Parameter

Value Intact rock compressive strength,σci 200MPa Geological strength index,GSI 60Hoek –Brown rock constant,m i

D.Saiang /Engineering Geology 116(2010)1–11

Table5

Failed zones mapped from the FLAC–PFC2D coupled models for excavation depths of10,100,500and1000m—with the blast-induced damaged zone. Overburden10m100m500m1000m

Failed zones mapped from coupled

model

Maximum depth of failure and failure mechanisms ?Roof?Roof?Roof?Roof

–b1cm–17cm–80cm–102cm

–Compressive shear–Compressive shear–Compressive shear–Compressive shear ?Wall?Wall?Wall?Wall

–5cm–24cm–45cm–63cm

–Tension–Tension–Tension–Tension ?Floor?Floor?Floor?Floor

–b1cm–4cm–11cm–25cm

–Compressive shear–Compressive shear–Compressive shear–Compressive shear

Table6

Failed zones mapped from the FLAC–PFC2D coupled models for excavation depths of10,100,500and1000m—without the blast-induced damaged zone. Overburden10m100m500m1000m

Failed zones mapped from coupled

model

Maximum depth of failure and failure mechanisms

?Roof?Roof?Roof?Roof

–b1cm–15cm–48cm–80cm

–Compressive shear–Compressive shear–Compressive shear–Compressive shear ?Wall?Wall?Wall?Wall

–3cm–20cm–34cm–52cm

–Tension–Tension–Tension–Tension

?Floor?Floor?Floor?Floor

–b1cm–2cm–8cm–24cm

–Compressive shear–Compressive shear–Compressive shear–Compressive

shear Fig.11.(a)Contour of the yielded elements in the100m depth model(b)mapped region of the100%yielded elements.

6 D.Saiang/Engineering Geology116(2010)1–11

3.7.In-situ parameters

The in-situ rock mass parameters shown in Table 3were used in deriving the inputs for the continuum models (i.e.Phase 2and FLAC).The properties in Table 3re ?ect a typical Swedish hard rock mass system,which is generally (for engineering purposes)described as good or above average quality.These rock masses generally comprise hard massive crystalline rocks.

The in-situ stresses used in the models were those reported by Stephansson (1993),which are based on over-coring measurements.These are:σV =ρgz

e1TσH =6:7+0:044z e2Tσh =0:8+0:034z

e3T

where σV is the vertical stress,σH and σh are the maximum and minimum horizontal stresses respectively,ρis the density,g is the gravity and z is the depth.In the models σH is perpendicular to tunnel axis and σh is in the direction of the tunnel.3.8.Inputs for Phase 2and FLAC models

3.8.1.Rock mass modulus

The rock mass modulus was estimated using the simpli ?ed Hoek –Diederichs equation given below (Hoek and Diederichs,2006).E rm

=100000

1?D =2

1+e 75+25D ?GSI eT=11eT

e4T

where E rm is the rock mass modulus,D is the disturbance factor and GSI is the geological strength index.A disturbance factor of 0.15is assumed so that the resulting modulus of the damaged zone is about 70%of the undamaged rock modulus,which can be considered typical for drill and blast excavations (e.g.Priest,2005).Hence the modulus of the BIDZ is 14GPa with a D value of 0.15.The modulus of the undamaged rock mass is 20GPa according to Eq.(4)when D is 0.

For the FLAC models the modulus of the damaged zone was linearly varied as illustrated earlier in Fig.9(b).The calculated modulus of the damaged zone,E D ,was assumed to be the value at the tunnel boundary.The linear variation of modulus was implemented using a FISH program.This approach of linearly varying the modulus of the damaged zone was needed in the Phase 2models since blast-induced cracks were directly implement in the models.The only required modulus is that of the undamaged rock,which is 20GPa.3.8.2.Rock mass strength parameters

The rock mass strength parameters were determined via PFC modelling.This involved performing a series of numerical laboratory tests using PFC to obtain a failure envelope and subsequently the strength parameters from it.Saiang (2008)describes the procedure and the determination of the strength parameters through PFC modelling.The reason for determining the strength parameter values using PFC 2D is the dif ?culty of determining the correct input values for

Table 7

Failed zones mapped from the Phase 2models for excavation depths of 10,100,500and 1000m.Overburden

10m 100m 500m 1000m

Failed zones mapped from Phase 2

model

Maximum depth of failure and failure mechanisms

?Roof

–b 1cm

–34cm

–100cm

–170cm

–Compressive shear –Compressive shear –Compressive shear –Compressive shear ?Wall ?Wall ?Wall ?Wall

–4cm –43cm –45cm –110cm –Tension –Tension –Tension –Tension ?Floor

?Floor ?Floor

?Floor

–b 1cm

–30cm

–120cm

–180cm

–Compressive shear –Compressive shear –Compressive shear –Compressive shear

All models with the damaged

zone.

Fig.12.Pockets of high tensile and compressive stresses develop around the radial cracks,thus inducing tensile and compressive shear failures.

D.Saiang /Engineering Geology 116(2010)1–11

the hard rock mass using the Hoek –Brown empirical equations (see for example Carter et al.,2007;Diederichs et al.,2007;Saiang,2008).Table 4shows the strength parameters for the damaged and undamaged rock masses.These parameters were used as inputs for the Phase 2and FLAC models.In the Phase 2models however,the strength properties of the damaged zone were not used since cracks were implemented to represent the damaged zone.3.9.Simulation method

In the coupled FLAC –PFC 2D model,the parallel bond model was applied to the synthetic rock mass,while the smooth joint model was applied to the cracks (that is within the PFC 2D segment).In the FLAC segment the Mohr –Coulomb constitutive model was used.In the Phase 2and FLAC models the Mohr –Coulomb model was used for simulating rock mass.Although Saiang (2008)concluded that the Mohr –Coulomb Strain-Softening model captured the behaviour of the brittle rock reasonably well,the Mohr –Coulomb is nevertheless used in the present analysis for the sake of consistency.This is because the Mohr –Coulomb Strain-Softening model is not found in Phase 2.The consistency in the constitutive model will also enable a fair com-parison of the results from the models.

The goal of this modelling work was to capture the behaviour of the BIDZ and not the actual excavation process.Hence,the method of simulation is important.Cai (2008)has for example,shown that the effects of sudden loading,which happens when the elements re-presenting the excavation are suddenly removed,can signi ?cantly affect the excavation response and thus the numerical results.For the work presented in this paper the simulation was systematically executed to eliminate the effects of sudden loading and unloading.This was done by gradually relaxing the excavation.Since three codes were used the relaxation procedure was handled accordingly.In the FLAC models the relaxation was done using a FISH program to apply internal pressure and gradually releasing it.In the Phase models the relaxation was done in 5stages by reducing the modulus gradually from a higher value down to actual calculated value.In the PFC 2D models (i.e.the FLAC –PFC 2D coupled models)the stiffness properties were reduced gradually after every 5,000cycles by 10%,a combination which was observed to be ef ?cient in terms of computation time and model stability.This was further assisted by the fact that the

stress

Fig.13.(a)Region where the incremental volumetric strain exceeded 0.05%and (b)contour of the region where the volumetric strain was exceeded.

Table 8

Failed zones mapped from the FLAC coupled models for excavation depths of 10,100,500and 1000m.Overburden

10m

100m

500m

1000m

Failed zones mapped from FLAC

model

Maximum depth of failure and failure mechanisms

?Roof

–b 1cm

–36cm

–96cm

–180cm

–Compressive shear –Compressive shear –Compressive shear –Compressive shear ?Wall ?Wall ?Wall ?Wall –8cm –38cm –40cm –86cm –Tension –Tension –Tension –Tension ?Floor ?Floor ?Floor

?Floor

–0cm

–32cm

–122cm

–200cm

–Compressive shear –Compressive shear –Compressive shear –Compressive shear

The models have blast-induced damaged zone.

8 D.Saiang /Engineering Geology 116(2010)1–11

tolerance factor was set to 0.001,which was deemed suf ?cient to both stabilize the model as well as eliminate any effects due to stress imbalances such as premature bond breakage.4.Results

4.1.Coupled FLAC –PFC 2D results

The yielded or the failed zones in the coupled model were mapped as illustrated in Fig.10.Regions where the contacts between the particles have been broken but no actual fallouts occurred are also considered as failed and therefore mapped.Forces were tracked in order to observe the mechanisms that cause the failure.These mechanisms were either tension or compression.

Table 5shows the fallouts mapped from the coupled model at depths of 10,100,500and 1000m.The results are for the models with the BIDZ.For the purpose of comparing the behaviour,simulations were also performed at the same depths for the models without the damage zone.The results for these models are shown Table 6.4.2.Phase 2results

Fig.11shows an example of failure mapping done in Phase 2.The contours of 100%yielded elements were seen to be consistent with the FLAC –PFC 2D coupled model failure mapping results in the walls.However,the yielding grows larger with depth in the roof and ?oor where high compressive stresses concentrate.This can be expected since the Phase 2(and also FLAC)models are perfectly plastic.Table 7

shows the results from the mapping of the 100%yielded elements (symmetric models were constructed in Phase 2to save simulation time).In the walls (where tensile stresses were dominant)the failure is consistent with those of the coupled models.Note that,the term failure is used here since the elements have yielded both in tension and shear,that is 100%yield.

Fig.12shows the failure mechanisms within the BIDZ.It was seen that,pockets of high tensile and compressive stresses developed around the blast-induced https://www.wendangku.net/doc/db8116167.html,pressive shear failure was dominant along the cracks that were open ended,while tensile failure was occurring at the tips of closed ended cracks (for the descriptions of open and closed ended cracks see Section 3.4).4.3.FLAC results

In the FLAC analysis the regions where yielding occurred through volume straining were consistent with the failed regions mapped in the coupled models.It was observed earlier in Saiang (2008)that for the rock mass type simulated in this paper yielding begins at strain values of 0.05%to 0.06%.By contouring the volumetric strains at 0.05%intervals in FLAC models revealed that strain concentrations occurred when the 0.05%value was exceeded.Contouring of the regions where this value was exceeded showed similar behaviour and consistency with the coupled FLAC –PFC 2D models.This is illustrated by Fig.13for example,which shows the volumetric strain concentration around the tunnel for the 100m depth model and mapping of concentration in the areas where the volumetric strain exceeded 0.05%.Table

Fig.14.Maximum thickness of failure mapped for the wall,roof and ?oor from the coupled FLAC –PFC 2D model —with the damaged

zone.

Fig.15.Maximum thickness of failure mapped for the wall,roof and ?oor from the coupled FLAC –PFC 2D model —without the damaged

zone.

Fig.16.Maximum thickness of failure in the wall mapped from the coupled FLAC –PFC 2D models.The presence of the damaged zone increases the depth of

failure.

Fig.17.Maximum thickness of failure in the roof mapped from the coupled FLAC –PFC 2D models.The presence of the damaged zone increases the depth of failure.

D.Saiang /Engineering Geology 116(2010)1–11

shows the mapped regions where the volumetric strain has exceeded 0.05%for various overburdens simulated.

FLAC models also show similar results to those of Phase 2models.That is,the yielding in walls (in this case due to volumetric straining)is consistent with those seen in coupled models.However,in the roof and the ?oor the yielding grows larger with increasing depth due high concentration of compressive stresses in these areas.As with Phase 2this can be expected since the perfectly plastic model is used in FLAC.5.Discussions

The maximum depths of the failed regions mapped from the coupled model are shown in Figs.14and 15,for the models with and without the BIDZ respectively.In both cases the thickness of the failed zone increases with depth.The thicknesses of the failed region in the models with damaged zone are slightly higher than those without damaged zone.The depths of the failed zones mapped in the coupled models are within the region generally observed fail in practice,where failed areas have been reported to be in the order of 10to 70cm.Figs.14and 15also show the shift in the instability from the walls at shallow depths to the roof at greater depths.Failures were observed to increase with the presence of the damaged zone,which are shown by Figs.16and 17for the wall and the roof.

With increasing depth the failure behaviour also changes.At shallow depth,failure and fallout occurred mainly in the walls,as tensile failures.As the depth increased the failure shifted to the roof and to compression induced failures.The depth of the failed zone also increased in the roof.Figs.16and 17show the cumulative depths of failure with increasing depth plotted on a lognormal scale.These ?gures indicate the shift in the instability from the walls at shallow depths to the roof at greater depths.

The coupled models showed failures in the ?oor as being less signi ?cant than in the roof and the walls (see Tables 5and 6).An examination of the state of stresses revealed the presence of a stress arch in the tunnel ?oor,which was formed as a result of the high stresses being obstructed by the “sharp-cornered ”toe of the tunnel.Hence the compressive stresses in the ?oor were lesser in magnitudes (often between 5and 10MPa less)than in the roof for the same distance from the tunnel boundary.

Failure occurred in the following sequence:(i)First the tensile stresses develop at the blast-induced crack tips,

which occurred as “tensile stress pockets ”at the crack tips.When the tensile stresses were suf ?ciently high the rock bridges between the radial cracks fail in tension,leading to the saw-tooth failure phenomenon as observed in the coupled models.This behaviour is discrete at shallow depth.That is,failure is restricted to individual cracks and dependent on the state of the local stresses.

(ii)In the deep excavation models,where the compressive stresses

were high,total failure did not occur immediately.That is

although the rock bridges failed in tension (due to localized tensile stresses at the crack tips),which were observed as loss of bond contacts of the PFC 2D particles,translation or the displacement of particles did not occur until the individual shear strengths of the blast-induced cracks and the rock bridges were overcome.In the process the overall strength of damaged zone was enhanced by the accumulated strengths of the individual rock bridges and blast-induced cracks.Even-tually the failure occurred as a single unit or continuum.This explains the reason for the disappearance of the saw-tooth failure phenomenon observed in the shallow depth models.

There is a similarity in the behaviour observed in the tunnel wall for the numerical approaches used (i.e.FLAC –PFC 2D coupled model,FLAC and Phase 2).Comparing Tables 6–8,it can be noticed that the thickness of failed zones and the general behaviour are similar for the three numerical approaches.This indicates that the brittle failure occurring in the wall is captured reasonably by all three approaches.The compres-sion induced (shear)failures are predicted by greater amounts by FLAC and Phase 2compared to the FLAC –PFC 2D coupled model,particularly in the roof and the ?oor.This can be expected as noted earlier that FLAC and Phase 2are based on a perfectly plastic model.

At depths up to 500m failure and fallout was noticed to be in ?uenced by the blast-induced cracks.Saw-tooth type of failure surfaces observed was noticed at these depths (see Fig.10(a)for example).This characteristic was not obvious in the models without the blast-induced cracks.In the 1000m this characteristic vanished,thus indicating that in deep excavations the blast-induced cracks will have less in ?uence on how the failure should occur.

The failure in the roof at 500and 1000m depths in the coupled FLAC –PFC 2D model is ‘church ’dome shaped (see Tables 4and 5).This phenomenon has been reported in some deep underground excava-tions in Sweden.See for example Fig.18,which is a stress-induced church dome type failure observed in a deep underground mine in Sweden.Hence,the failure characteristic observed in the coupled model is not unusual in this respect.6.Conclusions

The behaviour of the BIDZ was analysed using the continuum and the coupled continuum –discontinuum methods,with blast-induced cracks individually traced and implemented in these computer models.The following conclusions can be made from these analyses.?Blast-induced cracks were observed to in ?uence the failure behaviour at shallow depths up to 500m in the coupled FLAC –PFC 2D models.This was evidenced by the saw-tooth failure surfaces where failure propagated along the radial cracks and breaking off.However,at 1000m depth this behaviour vanished.This indicates that failure is less controlled by blast-induced cracks in deep excavations,where high stresses cause regional failure.The BIDZ acts like a single continuum.At shallow depths the behaviour of the damaged zone appeared to be discrete.

?Since the continuum methods do not model failure,the results from the FLAC –PFC 2D coupled model were used to identify the indicators for failure in the continuum models.The 100%yield elements in Phase 2and yield in volume in FLAC showed consistency to coupled model results at shallow depth,but not for deep excavations.In the walls where failure was occurring largely in tension all three numerical approaches (coupled FLAC –PFC 2D ,Phase 2and FLAC)showed similar behaviour for yielding and failure.

?Tensile failure was dominant at depths less than 100m,which mainly occurred in the tunnel walls.However,the dominant failure shifted to the roof and to a compressive shear mode (according to the results coupled FLAC –PFC 2D model results)for depths greater than 100m.The maximum depth of failure also followed the same

trend.

Fig.18.The “church dome ”roof pro ?le from stress-induced failure in destressing experimental excavation in a deep underground mine in Sweden (from Borg,1989).

10 D.Saiang /Engineering Geology 116(2010)1–11

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D.Saiang/Engineering Geology116(2010)1–11

表观遗传学

表观遗传学大家晚上好！很高兴有机会和大家交流，我最近看了一些这方面的材料，借这个机会和大家交流一下，讲的不一定对，就是自己的理解，有问题的地方大家可以讨论。我想从以下几个方面进行介绍： 1、表观遗传学概念 2、表观遗传学的研究内容一、表观遗传学概念经典遗传学认为遗传的分子基础是核酸, 生命的遗传信息储存在核酸的碱基序列上，碱基序列的改变会引起生物体表现型的改变，而这种改变可以从上一代传递到下一代。然而，随着遗传学的发展，人们发现,，DNA、组蛋白、染色质水平的修饰也会造成基因表达模式的变化，并且这种改变是可以遗传的。这种基因结构没有变化，只是其表达发生改变的遗传变化叫表观遗传改变。表观遗传学是一门研究生命有机体发育与分化过程中，导致基因发生表观遗传改变的新兴学科。 1939年，生物学家Waddington CH 首先在《现代遗传学导论》中提出了epihenetics这一术语，并于1942年定义表观遗传学为他把表观遗传学描述为一个控制从基因型到表现型的机制。 1975年，Hollidy R 对表观遗传学进行了较为准确的描述。他认为表观遗传学不仅在发育过程，而且应在成体阶段研究可遗传的基因表达改变，这些信息能经过有丝分裂和减数分裂在细胞和个体世代间传递，而不借助于DNA序列的改变，也就是说表观遗传是非DNA序列差异的核遗传。 Allis等的一本书中可以找到两种定义，一种定义是表观遗传是与DNA突变无关的可遗传的表型变化；另一种定义是染色质调节的基因转录水平的变化，这种变化不涉及DNA序列的改变。二、表观遗传学研究内容从现在的研究情况来看，表观遗传学变化主要集中在三大方面：DNA甲基化修饰、组蛋白修饰、非编码RNA的调控作用。这三个方面各自影响特有的表观遗传学现象，而且它们还相互作用，共同决定复杂的生物学过程。因此，表观遗传学也可理解为环境和遗传相互作用的一门学科。 DNA甲基化组蛋白共价修饰染色质重塑基因组中非编码RNA 微小RNA（miRNA）反义RNA 内含子、核糖开关等基因印记 1、DNA甲基化(DNA methylation)是研究得最清楚、也是最重要的表观遗传修饰形式，主要是基因组DNA上的胞嘧啶第5位碳原子和甲基间的共价结合，胞嘧啶由此被修饰为5甲基胞嘧啶(5-methylcytosine，5mC)。

表观遗传学

表观遗传学：营养之间的新桥梁与健康摘要：营养成分能逆转或改变表观遗传现象，如DNA甲基化和组蛋白修饰，从而改变表达与生理和病理过程，包括胚胎发育，衰老，和致癌作用有关的关键基因。它出现营养成分和生物活性食物成分能影响表观遗传现象，无论是催化DNA直接抑制酶甲基化或组蛋白修饰，或通过改变所必需的那些酶反应底物的可用性。在这方面，营养表观遗传学一直被看作是一个有吸引力的工具，以预防儿科发育疾病和癌症以及延迟衰老相关的过程。在最近几年，表观遗传学已成为广泛的疾病，例如2型糖尿病的新出现的问题糖尿病，肥胖，炎症，和神经认知障碍等。虽然开发治疗或预防发现的可能性这些疾病的措施是令人兴奋的，在营养表观遗传学当前的知识是有限的，还需要进一步的研究来扩大可利用的资源，更好地了解使用营养素或生物活性食品成分对保持我们的健康和预防疾病经过修改的表观遗传机制。介绍：表观遗传学可以被定义为基因的体细胞遗传状态，从不改变染色质结构产生的表达改变的DNA序列中，包括DNA甲基化，组蛋白修饰和染色质重塑。在过去的几十年里，表观遗传学的研究主要都集中在胚胎发育，衰老和癌症。目前，表观遗传学在许多其它领域，如炎症，肥胖，胰岛素突出抵抗，2型糖尿病，心血管疾病，神经变性疾病和免疫疾病。由于后生修饰可以通过外部或内部环境的改变因素和必须改变基因表达的能力，表观遗传学是现在被认为是在不明病因的重要机制的许多疾病。这种诱导表观遗传变化可以继承在细胞分裂，造成永久的保养所获得的表型。因此，表观遗传学可以提供一个新的框架为寻求病因在环境相关疾病，以及胚胎发育和衰老，这也是已知受许多环境因素的影响。在营养领域，表观遗传学是格外重要的，因为营养物质和生物活性食物成分可以修改后生现象和改变的基因的表达在转录水平。叶酸，维生素B-12，甲硫氨酸，胆碱，和甜菜碱可以影响通过改变DNA甲基化和组蛋白甲基化1 - 碳代谢。两个代谢物的1-碳代谢可以影响DNA 和组蛋白的甲基化：S-腺苷甲硫氨酸（的AdoMet）5，这是一个甲基供体为甲基化反应，并S-腺苷高半胱氨酸（的AdoHcy），这是一种产物抑制剂的甲基化。因此，理论上，任何营养素，生物活性组件或条件可影响的AdoMet或的AdoHcy水平在组织中可以改变DNA和组蛋白的甲基化。其他水溶性维生素B像生物素，烟酸和泛酸也发挥组蛋白修饰重要的作用。生物素是组蛋白生物素化的底物。烟酸参与组蛋白ADPribosylation如聚（ADP-核糖）的基板聚合酶作为以及组蛋白乙酰为底物Sirt1的，其功能作为组蛋白乙酰化酶（HDAC）（1）。泛酸是的一部分辅酶A以形成乙酰CoA，这是乙酰基的中组蛋白乙酰化的源。生物活性食物成分直接影响酶参与表观遗传机制。例如，染料木黄酮和茶儿茶素会影响DNA甲基（转移酶）。白藜芦醇，丁酸盐，萝卜硫素，和二烯丙基硫化物抑制HDAC和姜黄素抑制组蛋白乙酰转移酶（HAT）。改变酶activit这些化合物可能我们的有生之年通过改变基因表达过程中影响到生理和病理过程。在这次审查中，我们更新了关于最新知识营养表观遗传学，这将是一个有助于理解如何营养素有助于我们的健康。知识的现状 DNA甲基化 DNA甲基化，它修改在CpG二残基与甲基的胞嘧啶碱基，通过转移酶催化和通过改变染色质结构调节基因表达模式。目前，5个不同的转移酶被称为：DNMT1，DNMT2转移酶3A，DNMT3B和DnmtL。DNMT1是一个维护转移酶和转移酶图3a，3b和L分别从头转移酶。DNMT2的功能尚不明确。通过在我们的一生，营养成分影响这些转移酶和生物活性食物成分可以改变全球DNA甲基化，这是与染色体完整性以及genespecific启动子DNA甲基化，

表观遗传学

表观遗传学比较通俗的讲表观遗传学是研究在没有细胞核DNA序列改变的情况时，基因功能的可逆的、可遗传的改变。也指生物发育过程中包含的程序的研究。在这两种情况下，研究的对象都包括在DNA序列中未包含的基因调控信息如何传递到（细胞或生物体的）下一代这个问题。表观遗传学是与遗传学(genetic)相对应的概念。遗传学是指基于基因序列改变所致基因表达水平变化，如基因突变、基因杂合丢失和微卫星不稳定等；而表观遗传学则是指基于非基因序列改变所致基因表达水平变化，如DNA甲基化和染色质构象变化等；表观基因组学(epigenomics)则是在基因组水平上对表观遗传学改变的研究。所谓DNA甲基化是指在DNA 甲基化转移酶的作用下，在基因组CpG二核苷酸的胞嘧啶5'碳位共价键结合一个甲基基团。正常情况下，人类基因组“垃圾”序列的CpG二核苷酸相对稀少，并且总是处于甲基化状态，与之相反，人类基因组中大小为100—1000 bp左右且富含CpG二核苷酸的CpG岛则总是处于未甲基化状态，并且与56%的人类基因组编码基因相关。人类基因组序列草图分析结果表明，人类基因组CpG岛约为28890个，大部分染色体每1 Mb就有5—15个CpG岛，平均值为每Mb含10．5个CpG岛，CpG岛的数目与基因密度有良好的对应关系[9]。由于DNA甲基化与人类发育和肿瘤疾病的密切关系，特别是CpG岛甲基化所致抑癌基因转录失活问题，DNA甲基化已经成为表观遗传学和表观基因组学的重要研究内容。几十年来，ＤＮＡ一直被认为是决定生命遗传信息的核心物质，但是近些年新的研究表明，生命遗传信息从来就不是基因所能完全决定的，比如科学家们发现，可以在不影响ＤＮＡ序列的情况下改变基因组的修饰，这种改变不仅可以影响个体的发育，而且还可以遗传下去。这种在基因组的水平上研究表观遗传修饰的领域被称为“表观基因组学(epigenomics）”。表观基因组学使人们对基因组的认识又增加了一个新视点：对基因组而言，不仅仅是序列包含遗传信息，而且其修饰也可以记载遗传信息。摘要表观遗传学是研究没有DNA 序列变化的可遗传的基因表达的改变。遗传学和表观遗传学系统既相区别、彼此影响，又相辅相成，共同确保细胞的正常功能。表观遗传学信息的改变，可导致基因转录抑制、基因组印记、细胞凋亡、染色体灭活以及肿瘤发生等。关键词表观遗传学；甲基化；组蛋白修饰；染色质重塑；非编码RNA 调控；副突变表观遗传学( epigenetics) 是研究没有DNA序列变化的可遗传的基因表达的改变。它最早是在1939 年由Waddington在《现代遗传学导论》一书中提出，当时认为表观遗传学是研究基因型产生表型的过程。1996 年，国内学术界开始介绍epigenetics 研究，其中译名有表遗传学、表观遗传学、表型遗传修饰等10 余种，其中，表观遗传学、表遗传学在科技文献中出现的频率较高。 1 表观遗传学调控的分子机制基因表达正确与否，既受控于DNA 序列，又受制于表观遗传学信息。表观遗传学主要通过DNA 的甲基化、组蛋白修饰、染色质重塑和非编码RNA 调控等方式控制基因表达。近年发现，副突变也包含有表观遗传性质的变化。 1.1 DNA 甲基化DNA 甲基化是由酶介导的一种化学修饰，即将甲基选择性地添加到蛋白质、DNA 或RNA上，虽未改变核苷酸顺序及组成，但基因表达却受影响。其修饰有多种方式，即被修饰位点的碱基可以是腺嘌呤N!6 位、胞嘧啶的N!4 位、鸟嘌呤的N!7 位和胞嘧啶的C!5 位，分别由不同的DNA 甲基化酶催化。在真核生物DNA 中，5- 甲基胞嘧啶是唯一存在的化学性修饰碱基，CG 二核苷酸是最主要的甲基化位点。DNA 甲基化时，胞嘧啶从DNA 双螺旋突出，进入能与酶结合的裂隙中，在胞嘧啶甲基转移酶催化下，有活性的甲基从S- 腺苷甲硫氨酸转移至胞嘧啶5' 位上，形成5- 甲基胞嘧啶( 5mC)。DNA 甲基化不仅可影响细胞基因的表达，

重要哲学术语英汉对照

a priori瞐 posteriori distinction 先验-后验的区分 abstract ideas 抽象理念 abstract objects 抽象客体 ad hominem argument 谬误论证 alienation/estrangement 异化，疏离 altruism 利他主义 analysis 分析 analytic瞫ynthetic distinction 分析-综合的区分 aporia 困惑 argument from design 来自设计的论证 artificial intelligence (AI) 人工智能 association of ideas 理念的联想 autonomy 自律 axioms 公理 Categorical Imperative 绝对命令 categories 范畴 Category mistake 范畴错误 causal theory of reference 指称的因果论 causation 因果关系 certainty 确定性 chaos theory 混沌理论

class 总纲、类 clearness and distinctness 清楚与明晰 cogito ergo sum 我思故我在 concept 概念 consciousness 意识 consent 同意 consequentialism 效果论 conservative 保守的 consistency 一致性，相容性 constructivism 建构主义 contents of consciousness 意识的内容 contingent瞡ecessary distinction 偶然-必然的区分 continuum 连续体 continuum hypothesis 连续性假说 contradiction 矛盾（律） conventionalism 约定论 counterfactual conditional 反事实的条件句 criterion 准则，标准 critique 批判，批评 Dasein 此在，定在 deconstruction 解构主义 defeasible 可以废除的

表观遗传学(总结)资料

1.表观遗传学概念表观遗传是与DNA 突变无关的可遗传的表型变化，且是染色质调节的基因转录水平的变化，这种变化不涉及DNA 序列的改变。表观遗传学是研究基因的核苷酸序列不发生改变的情况下，基因表达了可遗传的变化的一门遗传学分支学科。表观遗传学内容包括DNA 甲基化、组蛋白修饰、染色质重塑、遗传印记、随机染色体失活及非编码RNA 等调节。研究表明，这些表观遗传学因素是对环境各种刺激因素变化的反映，且均为维持机体内环境稳定所必需。它们通过相互作用以调节基因表达，调控细胞分化和表型，有助于机体正常生理功能的发挥，然而表观遗传学异常也是诸多疾病发生的诱因。因此，进一步了解表观遗传学机制及其生理病理意义，是目前生物医学研究的关键切入点。别名：实验胚胎学、拟遗传学、、外遗传学以及后遗传学表观遗传学是与遗传学(genetic)相对应的概念。遗传学是指基于基因序列改变所致基因表达水平变化，如基因突变、基因杂合丢失和微卫星不稳定等；而表观遗传学则是指基于非基因序列改变所致基因表达水平变化，如和染色质构象变化等；表观基因组学(epigenomics)则是在基因组水平上对表观遗传学改变的研究。 2.表观遗传学现象（1）DNA甲基化是指在DNA甲基化转移酶的作用下，在基因组CpG二核苷酸的胞嘧啶5'碳位共价键结合一个甲基基团。正常情况下，人类基因组“垃圾”序列的CpG二核苷酸相对稀少，并且总是处于甲基化状态，与之相反，人类基因组中大小为100—1000 bp左右且富含CpG二核苷酸的CpG岛则总是处于未甲基化状态，并且与56%的人类基因组编码基因相关。人类基因组序列草图分析结果表明，人类基因组CpG岛约为28890个，大部分每1 Mb就有5—15个CpG岛，平均值为每Mb含10．5个CpG岛，CpG岛的数目与基因密度有良好的对应关系[9]。由于DNA甲基化与人类发育和肿瘤疾病的密切关系，特别是CpG岛甲基化所致抑癌基因转录失活问题，DNA甲基化已经成为表观遗传学和表观基因组学的重要研究内容。（2）基因组印记基因组印记是指来自父方和母方的等位基因在通过精子和传递给子代时发生了修饰，使带有亲代印记的等位基因具有不同的表达特性，这种修饰常为DNA甲基化修饰，也包括组蛋白乙酰化、甲基化等修饰。在形成早期，来自父方和母方的印记将全部被消除，父方等位基因在精母细胞形成精子时产生新的甲基化模式，但在受精时这种甲基化模式还将发生改变；母方等位基因甲基化模式在卵子发生时形成，因此在受精前来自父方和母方的等位基因具有不同的甲基化模式。目前发现的大约80%成簇，这些成簇的基因被位于同一条链上的所调控，该位点被称做印记中心(imprinting center, IC)。印记基因的存在反映了性别的竞争，从目前发现的印记基因来看，父方对的贡献是加速其发育，而母方则是限制胚胎发育速度，亲代通过印记基因来影响其下一代，使它们具有性别行为特异性以保证本方基因在中的优势。印记基因的异常表达引发伴有复杂突变和表型缺陷的多种人类疾病。研究发现许多印记基因对胚胎和胎

continuum shell 与shell element 的比较

Abaqus 6.9‐EF 中continuum shell 與shell element 的比較 Abaqus 6.9‐EF 在shell element 後處理顯示上有了新增的功能，就是能夠顯示在section 定義時的厚度，如同以往在beam element 的功能，幫助在後處理圖形顯示上能有更直覺、忠實呈現原始模型的效果，厚度呈現也可透過比例因子來做縮放。在此以例子示範，100mm x 20mm x 1mm 的懸臂樑薄板在表面受1KPa 的壓力，分別以continuum shell 及shell element 做兩個model 以示區別。兩者section 的category 皆指定為shell ，但continuum shell 在create part 時的shape 為solid ，shell element 則為shell ，此為差異所在；將厚度輸入為1 mm ，積分點若使用高斯積分法預設為5點，有塑性變化時，可增加數量以求準確性。一般continuum shell 與shell element 分析的問題以bending 為主，因此在後處理輸出預設為兩外側面積分點，但也可依需求輸出其餘的截面點，可依下列步驟作改變： i 、 step 模組中，edit field output request ii 、 use default 為預設輸出，選specify ，輸入欲輸出的截面點編號(編號順序為依負法線方向編號增加)。 iii 、將其餘邊界條件等設定好，mesh 之後求解。 continuum shell shell element

表观遗传学

表观遗传学摘要：表观遗传学是研究基因的核苷酸序列不发生改变的情况下，基因表达了可遗传的变化的一门遗传学分支学科。表观遗传的现象很多，已知的有DNA甲基化（DNA methylation），基因组印记（genomic impriting），母体效应（maternal effects），基因沉默（gene silencing），核仁显性，休眠转座子激活和RNA编辑（RNA editing）等。表观遗传学是研究基因的核苷酸序列不发生改变的情况下，基因表达了可遗传的变化的一门遗传学分支学科。表观遗传的现象很多，已知的有DNA甲基化（DNA methylation），基因组印记（genomic impriting），母体效应（maternal effects），基因沉默（gene silencing），核仁显性，休眠转座子激活和RNA编辑（RNA editing）等。目录 [隐藏] 1 简介 2 染色质重塑 3 基因组印记 4 染色体失活 5 非编码RNA 表观遗传学简介表观遗传学表观遗传学是与遗传学(genetic) 相对应的概念。遗传学是指基于基因序列改变所致基因表达水平变化，如基因突变、基因杂合丢失和微卫星不稳定等；而表观遗传学则是指基于非基因序列改变所致基因表达水平变化，如DNA甲基化和染色质构象变化等；表观基因组学(epigenomics)则是在基因组水平上对表观遗传学改变的研究。所谓DNA甲基化是指在DNA甲基化转移酶的作用下，在基因组CpG二核苷酸的胞嘧啶5'碳位共价键结合一个甲基基团。正常情况下，人类基因组“垃圾”序列的CpG二核苷酸相对稀少，并且总是处于甲基化状态，与之相反，人类基因组中大小为100—1000 bp左右且富含CpG二核苷酸的CpG岛则总是处于未甲基化状态，并且与56％的人类基因组编码基因相关。人类基因组序列草图分析结果表明，人类基因组CpG岛约为28890个，大部分染色体每1 Mb就有5—15个CpG 岛，平均值为每Mb含10．5个CpG岛，CpG岛的数目与基因密度有良好的对应关系[9]。由于DNA甲基化与人类发育和肿瘤疾病的密切关系，特别是CpG岛甲

THE CAUSATIVE CONTINUUM_shibatani-pardeshi

THE CAUSATIVE CONTINUUM* Masayoshi Shibatani Center for Advanced Study in the Behavioral Sciences/Kobe University & Prashant Pardeshi Japan Society for the Promotion of Science/Kobe University 1. INTRODUCTION This paper has a five-fold goal of (1) cl a rifying the direct/indirect distinction in causation in relation to verbal semantics, (2) demonstrating the importance of verbal semantics in causative derivation, (3) providing more compelling evidence for a continuum along both formal and semantic dimensions in causative formation, (4) arguing for the productivity parameter as a predictor of the form-function correlation, and (5) establishing the importance of an intermediate category of ‘sociative causation’. The oft-invoked notions of direct and indirect causation as well as similar ones of manipulative/directive and contact/distant refer to a fundamental distinction in the cognition of causation. These terms have been rather vaguely and loosely used, however, and need to be either redefined or clarified in relation to the verbal semantics relevant to other issues in the grammar of causation. The verbal semantics of both root verbs and causative verbs interact in a way that calls for a finer-grained semantics going well beyond the traditional transitive/ intransitive distinction as well as the more recently recognized unaccusative/unergative distinction. In a typological study it is customary to classify causative forms into (a) the lexical (synthetic), (b) the morphological, and (c) the syntactic (analytic or periphrastic) type. We find a formal typology of this kind to be limited in a number of respects. For one thing, as noted by Givón (1980) and Comrie (1981, 1985), these three types form a continuum, and each type, furthermore, consists of a conti nuum of its own, rendering the entire formal dimension into a single continuum. More significantly, functional-typology demands articulation of the formal and the semantic dimension of a given cognitive domain, so that the relevant form-meaning correlation is captured in a systematic manner. As it turns out,

现代机械工程专业英语

Lesson 1 Engineering Drawings 1.assembly drawing 转配图 2.balloon 零件序号 3.detail drawing 零件图 4.view 视图 5.full-section view 全剖视图 6.Broken-sectional view 局部视图 7.Convention 惯例，规范 8.Cutting-plane 剖切图 9.Sketch drawing 草图 10.Interchangeable 可互换的 11.Craftsman 工匠，工人 12.Tolerance 公差 13.Procurement 采购，获得 14.Exploded drawing 分解示图 15.Pattern maker 模型工，翻铸工 16.Machinist 机械师，机工

Lesson 2 mechanics 1.mechanics 力学 2.Acceleration 加速度 3.Deformation 变形 4.Stress 应力 5.Sub discipline 分支学科 6.Static 静力学 7.Dynamics 动力学 8.Mechanics of material材料力学 9.Fluid mechanics 流体力学 10.Kinematics 运动学 11.Continuum mechanics 连续介质力学 12.static equilibrium 静力平衡 13.Newton’s first law 14.Susceptibility 敏感性 15.Newton’s second law of motion 16.Yield strength 屈服强度17.ultimate strength 极限强度 18.Failure by bucking 屈曲破坏 19.Stiffness 刚度 20.Young’s modulus 杨氏模量 21.Macroscopic 宏量 22.Microscopic 微量 https://www.wendangku.net/doc/db8116167.html,putational fluid dynamics (CFD)计算流体力学 24.trajectory 轨道 25.Astrophysics 天体物理学 26.Celestial 天空的 27.Robotics 机器人学 28.Biomechanics 生物力学 29.Rigid body 刚体

AePr视觉特效和转场BCC插件包Continuum插件中英文对照表

BCC插件中英文对照表一、BCC 3D Objects三维物体 BCC Extruded EPS 内置图形挤压成3D图形BCC Extruded Spline挤压样条曲线 BCC Extruded Spline Curves挤出的样条曲线BCC Extruded Text挤压文本 BCC Extrusion Bevel Curves挤压锥曲线BCC Extrusion Side Curves挤压边曲线BCC Extrusion T ext Paths挤压文本路径BCC Layer Deformer层变形 BCC Title Studio 文字标题效果插件BCC Type On Text类型文本二、BCC Art Looks视觉艺术 BCC Artist's Poster招贴画 BCC Bump Map凹凸贴图 BCC Cartoon Look漫画 BCC Cartooner艺术画效果 BCC Charcoal Sketch木炭画 BCC Halftone中间色 BCC Median中间的

BCC Pencil Sketch素描 BCC Posterize色调分离 BCC Spray Paint Noise喷漆噪声BCC Tile Mosaic马赛克瓷砖 BCC Water Color水彩画三、BCC Blur滤镜 BCC Directional Blur方向模糊滤镜BCC Fast Lens Blur快镜头模糊BCC Gaussian Blur高斯模糊BCC Lens Shape透镜 BCC Motion Blur动态模糊 BCC Pyramid Blur金字塔模糊BCC Radial Blur径向模糊滤镜BCC Spiral Blur旋转模糊 BCC Unsharp Mask反锐化模糊BCC Z-Blur 四、BCC Color & Tone色彩与色调BCC 3 Way Color Grade色彩分级BCC Brightness-Contrast亮度对比BCC Color Balance色彩平衡BCC Color Correction色彩校正BCC Color Match色彩搭配 BCC Colorize着色

表观遗传学涉及的几种机制

表观遗传学涉及的几种机制摘要表观遗传学是指以研究没有DNA序列变化,但是可以遗传的生命现象为主要内容的学科。它通过DNA的甲基化、组蛋白修饰、染色质重塑和非编码RNA调控4种方式来控制表观遗传的沉默。从表观遗传学所涉及的这四种机制进行描述。关键词表观遗传学;DNA的甲基化;组蛋白修饰;染色质重塑;非编码RNA调控随着生命科学的发展,几十年来,人们一直认为基因决定着生命过程中所需要的各种蛋白质,决定着生命体的表型。但随着研究的深入,越来越多无法解释的生命现象一一出现:具有完全相同的基因组的同卵双生,即使在同样的环境中长大,他们的性格、健康等方面也会有较大的差异;有些特征只是由一个亲本的基因来决定,而源自另一亲本的基因却保持“沉默”;马、驴正反交的后代差别较大等。人们无法用经典的遗传学理论解释这些现象。现在,遗传学中的一个前沿领域:表观遗传学(Epigenetics),为人们提供了解答这类问题的新思路。表观遗传学(Epigenetics)是1957年由Waddington CH提出的,是研究表观遗传变异的遗传学分支学科。表观遗传变异(Epigenetic variation)是指在基因的DNA序列没有发生改变的情况下,基因功能发生了可遗传的变化,并最终导致了表型的变化。它是不符合孟德尔遗传规律的核内遗传,由此可以认为,基因组含有2类遗传信息,一类是传统意义上的遗传信息,即DNA序列所提供的遗传信息,另一类是表观遗传学信息,它提供了何时、何地、以何种方式去应用遗传信息的指令。本文就表观遗传改变涉及DNA的甲基化、组蛋白修饰、染色质重塑、非编码RNA调控等机制进行论述。 1DNA甲基化 DNA甲基化是基因组DNA表观遗传修饰的一种主要形式,是调节基因组功能的重要手段。它是由DNA甲基转移酶催化S-腺苷甲硫氨酸作为甲基供体,将胞嘧啶转变为5-甲基胞嘧啶(mC)的反应。在真核生物DNA中,5-甲基胞嘧啶是唯一存在的化学性修饰碱基。在哺乳动物细胞的基因组DNA中,3%～5%的胞嘧啶是以5-甲基胞嘧啶形式存在的。同时70%的5-甲基胞嘧啶参与了CpG序列的形成。而非甲基化的CpG序列则与管家基因以及组织特异性表达基因有关,这提示CpG 的甲基化与否在基因的表达中起重要作用。体内甲基化状态有3种:持续的低甲基化状态,如持家基因;诱导的去甲基化状态,如发育阶段中的一些基因;高度甲基化状态,如女性的一条缢缩的X染色体。DNA甲基化影响到基因的表达,与肿瘤的发生密切相关。把癌基因组学与表观遗传学的研究结合起来,是癌症研究的发展趋势。人类的一些癌症常出现整个基因组DNA的低甲基化,但人们并不清楚这种表观遗传变化是肿瘤产生的诱因还是结果。研究者构建了携带低表达水平Dnmtl基因的小鼠,对它的研究结果显示,DNA低甲基化可能通过提高染色体的不稳定性来促进肿瘤的形成。

A Ricardian Model with a Continuum of Goods under Nonhomothetic Preferences Demand Complementarities

A Ricardian Model with a Continuum of Goods under Nonhomothetic Preferences: Demand Complementarities, Income Distribution, and North-South Trade Author(s): Kiminori Matsuyama Source: The Journal of Political Economy, Vol. 108, No. 6 (Dec., 2000), pp. 1093-1120 Published by: The University of Chicago Press Stable URL: https://www.wendangku.net/doc/db8116167.html,/stable/3078494 Accessed: 09/07/2010 00:08 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at https://www.wendangku.net/doc/db8116167.html,/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at https://www.wendangku.net/doc/db8116167.html,/action/showPublisher?publisherCode=ucpress. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@https://www.wendangku.net/doc/db8116167.html,. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Political Economy. https://www.wendangku.net/doc/db8116167.html,

施耐德AS+Continuum 系统硬件搭建时的注意事项(根据SBO1.6版本整理)

AS+Continuum 系统硬件搭建时的注意事项（以下根据SBO1.6版本整理）一、AS/PS、b3851、b3608、b3920、16DI4DO不同型号的控制器在同一个DDC箱中，由于各个控制器的中性点（分为：信号公共端和电源公共端互通或者不通2种）性质类型不同，变压器应根据DDC 控制器特性进行分别配置变压器进行变压；其中b3608和16DI4DO的信号公共端和电源公共端是通的，建议各自单独使用变压器，更不建议与其他类型控制器共用一个变压器；二、对一条总线上的单个DDC控制箱内的AS/PS控制器、B3控制器、16DI4DO推荐分别使用三个独立的空气开关，以便调试时，AS/PS控制器、B3控制器、16DI4DO可以按需要分别上电上线；这样可以避免自适应控制器和硬件拨码地址控制器的地址码不被重复，一旦出现重复，只需单独重新断电、上电便可正常；三、所有DDC控制箱的接地问题，电源地是漏电保护接地（例如DDC箱体接地、弱电桥架接地、系统及控制器的电源接地等），而系统地是系统防干扰接地（如信号屏蔽接地、通讯线屏蔽接地、控制器通讯端接地等），必须分开独立接地；电源地一般来自于电源进线（火线、零线、地线）的地线接地，或者强电接地排；系统地来自于弱电系统单独接地桩，一般来自于弱电井道的接地扁铁、或者控制中心的弱电接地环，根据防雷接地系统的要求，一般接地线分支电缆要求线径在6平方，主干接地电缆16平方（主干接地电缆可用接地扁铁替代，但在固定时和安装时，必须加绝缘垫子，与大楼主体钢筋绝缘，只与大楼弱电接地桩联通）；本系统根据已有项目的调试情况，要求系统必须接地，否则干扰甚大，大家在类似项目实施时，尽可能地对系统接地进行完善，以便调试时带来的麻烦；接地电缆线径具体根据各个项目实际情况而定。四、AS+Continuum 系统中交流电源必须区分正负，即L和N极性接线不能相互交叉错位，否则会导致模块无法上线。五、AS+Continuum 系统中传感器、执行器、继电器等电源取电要从所接入的那个控制器的变压器上取电；b3920（AC220V）上传感器、执行器、继电器等电源取电,可从AS/PS、b3851控制器的变压器上取电; 六、DDC箱集中供电，取UPS为佳。七、AS下有2个RS-485端口，可建2条BACnet总线；BACnet每条总线上的16DI4DO模块数量不要超过20个，超过20个数量的，建议超过部分的16DI4DO模块挂到另外一个RS-485端口的BACnet总线上；以便解决16DI4DO模块DI信号反馈速度慢的问题；每条BACnet总线上的网络节点建议不要超过50个，如总线上增加中继器，建议网络节点不超过75个；八、在单个项目中，16DI4DO模块总数不超过127个，即1套ES下16DI4DO模块建议不超过127个。九、单个AS下，Lon总线上的XenT a控制器总数不能超过30个，网络节点数“官方资料”不超过64个，应留一定冗余；在AS下，Lon总线和BACnet有主从关系，其中1个作为主，从的那个网络节点数不能超过10个；十、在SBO系统下，不管是ModBus RTU还是ModBus TCP/IP，在AS或ES中硬件点加软件点的总点数不能超过5000个，此数量仅仅限于SBO 1.6版本，低版本软件还远远达不到该数量；十一、变频器可靠接地、DDC电源不可从动力柜取电，特别是带变频器的动力柜上取电，在无法集中供电的前提下，尽量从照明柜或者楼层配电干线箱取电。以上内容，请技术部门工作人员大家在前期现场指导及出DDC仪表盘图纸的时候尽量注意。

[遗传学的名词解释] 表观遗传学名词解释

竭诚为您提供优质的服务，优质的文档，谢谢阅读/双击去除 [遗传学的名词解释] 表观遗传学名词解释遗传学的意思是什么呢?怎么用遗传学来造句?下面是小编为你整理遗传学的意思，欣赏和精选造句，供大家阅览! 遗传学的意思遗传学(genetics)是一门学科，研究生物起源、进化与发育的基因和基因组结构、功能与演变及其规律等，是生物学的一个重要分支，经历了孟德尔经典遗传学、分子遗传学和如今系统遗传学的研究时期。在史前人们就已经利用生物体的遗传特性通过选择育种来提高谷物和牲畜的产量，虽然

遗传学在决定生物体外形和行为的过程中扮演着重要的角色，但此过程是遗传学和生物体所经历的环境共同作用的结果。遗传学中的亲子概念不限于父母子女或一个家族，还可以延伸到包括许多家族的群体，这是群体遗传学的研究对象。遗传学中的亲子概念还可以以细胞为单位，离体培养的细胞可以保持个体的一些遗传特性。1992年10月1日，伦敦发表第一张染色体图被认为是遗传学上的一个里程碑。遗传学的研究范围包括遗传物质的本质、遗传物质的传递和遗传信息的实现三个方面。遗传物质的传递包括遗传物质的复制、染色体的行为、遗传规律和基因在群体中的数量变迁等。遗传学造句欣赏 1.父母不能骂自己的孩子是小兔崽子，因为这在遗传学上是对父母不利的。 2.我们以斑马鱼为模式动物，利用发育遗传学、生物信

息学和分子化学的方法研究心脏和血管的分化形成以及环境对心血管发育的影响。 3.这是真菌进化遗传学的网页。 4.利用模式动物探索哺乳动物发育遗传学研究新方法，并研究发育和疾病机理。 5.提供固体的历史背景，序篇检查过去概念的行为遗传学流。 6.目的研究河南汉族人群的指纹纹型特点，为人类学、遗传学和医学肤纹学等研究领域提供基础皮纹学参数。 7.行为遗传学告诉我们即使在个人的范围上很多生活中的结果都似乎是路径依赖性的，或者仅仅是无法预测的，即使是同卵双生的人。

表观遗传学

Brian Dias 去年10 月晋升为父亲，和许多新父母一样，孩子出生前他就开始考虑要承担各种责任。但Dias 考虑的问题更多，他已经考虑自己的父母或祖父母是否也会对孩子产生影响。祖先生活环境，受教育程度，都可能通过遗传对后代产生影响。是否祖先的生活习惯或遭遇，例如吸烟、饥荒或战争经历也会对后代的健康产生影响？ Dias 是艾默理大学（Emory University）克里莱斯勒实验室的博士后。在儿子出生前2 年，他的研究就是和上述问题有关的。他观察暴露在恶劣气味环境动物后代大脑产生的影响。乙酰苯是一种有甜杏仁味的化合物，Dias 将雄性小鼠暴露在乙酰苯环境下，然后对他们每天5 次中度电足刺激，连续3 天。这些动物会对这些刺激恐惧，一旦有乙酰苯味道就会僵住。 10 天后，Dias 让这些动物和正常雌性小鼠动物交配。这些动物后代成年后，大部分对乙酰苯敏感，当暴露在这种气味下，有意外声音就会惊慌失措。动物的下一代（孙辈）仍会对乙酰苯敏感。研究发现，三代动物M71 肾小球结构增大，其中乙酰苯敏感神经元增加。最近这一研究发表在《自然-神经科学》杂志上，Dias 等认为，环境信息可通过表观遗传机制传递给后代。表观遗传学是在DNA碱基序列不变前提下引起基因表达或细胞表型变化的一种遗传。生物学家最早是在植物中发现表观遗传现象。开始发现西红柿存在表观遗传现象，随后证明在动物和人类也普遍存在这种现象。表观遗传学仍存在争议，尤其是会让人回想起来19世纪法国博物学家拉马克的失败理论。他提出，生物能将获得性状遗传给后代。麻省大学医学院分子生物学家Oliver Rando，研究证明了动物的表观遗传现象，对许多现代生物学家来说，