a r X i v :n l i n /0204044v 1 [n l i n .C D ] 18 A p r 2002Anomalous scaling of a passive scalar advected by the turbulent velocity ?eld with
?nite correlation time:Two-loop approximation
L.Ts.Adzhemyan 1,N.V.Antonov 1,and J.Honkonen 21Department of Theoretical Physics,St.Petersburg University,Ulyanovskaya 1,St.Petersburg—Petrodvorez,198504,Russia 2Theory Division,Department of Physical Sciences,P.O.Box 64,FIN-00014University of Helsinki,Finland
(24December 2001)
The renormalization group and operator product expansion are applied to the model of a passive
scalar quantity advected by the Gaussian self-similar velocity ?eld with ?nite,and not small,corre-
lation time.The inertial-range energy spectrum of the velocity is chosen in the form E (k )∝k 1?2ε,
and the correlation time at the wavenumber k scales as k ?2+η.Inertial-range anomalous scaling for
the structure functions and other correlation functions emerges as a consequence of the existence
in the model of composite operators with negative scaling dimensions,identi?ed with anomalous
exponents.For η>ε,these exponents are the same as in the rapid-change limit of the model;for
η<ε,they are the same as in the limit of a time-independent (quenched)velocity ?eld.For ε=η
(local turnover exponent),the anomalous exponents are nonuniversal through the dependence on a
dimensionless parameter,the ratio of the velocity correlation time and the scalar turnover time.The
universality reveals itself,however,only in the second order of the εexpansion,and the exponents
are derived to order O (ε2),including anisotropic contributions.It is shown that,for moderate n ,
the order of the structure function,and d ,the space dimensionality,?nite correlation time enhances
the intermittency in comparison with the both limits:the rapid-change and quenched ones.The
situation changes when n and/or d become large enough:the correction to the rapid-change limit
due to the ?nite correlation time is positive (that is,the anomalous scaling is suppressed),it is
maximal for the quenched limit and monotonically decreases as the correlation time tends to zero.
PACS number(s):47.27.?i,47.10.+g,https://www.doczj.com/doc/e212309648.html,
I.INTRODUCTION In recent years,considerable progress has been achieved in the understanding of intermittency and anomalous scaling of ?uid turbulence.The crucial role in these studies was played by a simple model of a passive scalar quantity advected by a random Gaussian ?eld,white in time and self-similar in space,the so-called Kraichnan’s rapid-change model [1].There,for the ?rst time the existence of anomalous scaling was established on the basis of a microscopic model [2]and the corresponding anomalous exponents were calculated within controlled approximations [3–6]and a systematic perturbation expansion in a formal small parameter [7].Detailed review of the recent theoretical research on the passive scalar problem and the bibliography can be found in Ref.[8].Within the approach developed in Refs.[3–6],nontrivial anomalous exponents are related to “zero modes,”that is,homogeneous solutions of the closed exact di?erential equations satis?ed by the equal-time correlation functions.In this sense,the rapid-change model appears “exactly solvable.”In a wider context,zero modes can be interpreted as statistical conservation laws of the particle dynamics [9].The concept of statistical conservation laws appears rather general,being also con?rmed in numerical simulations by Refs.[10,11],where the passive advection in the two-dimensional Navier–Stokes velocity ?eld [10]and a shell model of a
passive scalar [11]were studied.This observation is rather intriguing because in those models no closed equations for equal-time quantities can be derived due to the fact that the advecting velocity has a ?nite correlation time (for a passive ?eld advected by a velocity with given statistics,closed equations can be derived only for di?erent-time correlation functions,and they involve in?nite diagrammatic series).
One may thus conclude that breaking the arti?cial assumption of the time decorrelation of the velocity ?eld is the crucial point [10,11].
An important issue related to the e?ects of the ?nite correlation time is the universality of the anomalous exponents.It was argued that the exponents may depend on more details of the velocity statistics than only the exponents ηand ε[12].This idea was supported in Refs.[13,14],where the case of short but ?nite correlation time was considered for the special case of a local turnover exponent.In those studies,the anomalous exponents were derived to ?rst order in small correlation time,with Kraichnan’s rapid-change model [13]or analogous shell model for a scalar ?eld [14]taken as zeroth order approximations.The exponents obtained appear nonuniversal through the dependence on the correlation time.
In Ref.[7]and subsequent papers[15–19],the?eld theoretic renormalization group(RG)and operator product expansion(OPE)were applied to the rapid-change model and its descendants.In that approach,anomalous scaling emerges as a consequence of the existence in the model of composite operators with negative scaling dimensions, identi?ed with the anomalous exponents.This allows one to construct a systematic perturbation expansion for the anomalous exponents,analogous to the famousεexpansion in the RG theory of critical behavior,and to calculate the exponents to the second[7,15]and third[16]orders.For passively advected vector?elds,any calculation of the exponents for higher-order correlations calls for the RG techniques already in the lowest-order approximation[17]. Besides the calculational e?ciency,an important advantage of the RG approach is its relative universality:it is not related to the aforementioned solvability of the rapid-change model and can also be applied to the case of?nite correlation time or non-Gaussian advecting?eld.In Ref.[18](see also[19]for the case of compressible?ow)the RG and OPE were applied to the problem of a passive scalar advected by a Gaussian self-similar velocity with?nite(and not small)correlation time.The energy spectrum of the velocity in the inertial range has the form E(k)∝k1?2ε, while the correlation time at the wavenumber k scales as k?2+η.It was shown that,depending on the values of the exponentsεandη,the model reveals various types of inertial-range scaling regimes with nontrivial anomalous exponents.Forη>ε,they coincide with the exponents of the rapid-change model and depend on the only parameter 2ε?η,while forε>ηthey coincide with the exponents of the opposite(“quenched”or“frozen”)case and depend only onε.
The most interesting case isη=ε,when the exponents can be nonuniversal through the dependence on the correlation time(more precisely,on the ratio u of the velocity correlation time and the turnover time of the passive scalar).In the?eld theoretic language,the nonuniversality of the exponents in this regime is a consequence of the degeneracy of the corresponding?xed point of the RG equations.It agrees with the?ndings of Refs.[13,14]since the borderlineη=ε,including the“Kolmogorov”pointη=ε=4/3,corresponds to the case of a local turnover exponent.It is also interesting to note that the same relationη=εfor the boundary between the time-decorrelated and quenched cases is encountered in a model of passive advection by a strongly anisotropic?ow,studied in Refs.
[20].It was argued in[21]that the same boundary will be observed with very general assumptions on the velocity statistics.Although the possibility of the nonuniversality of anomalous exponents forη=εwas demonstrated by the rigorous RG analysis,the practical calculation by Ref.[18]has shown that they appear universal(independent of u)to the?rst order inεandη:in the one-loop approximation,the anomalous dimensions of the relevant composite operators depend on a combination of the model parameters(couplings)that remains constant along the line of the ?xed points.This fact is rather disappointing,because it means that in the one-loop approximation it is impossible to judge how the?nite correlation time a?ects intermittency,in particular,whether the anomalous scaling is enhanced or suppressed in comparison with the rapid-change or quenched limits.
In this paper,we present the anomalous exponents to order O(ε2)(two-loop approximation)for the most interesting caseη=ε,including the exponents of the anisotropic contributions,and study their dependence on u.[It is not necessary to separately consider the casesη>ε(η<ε),because the corresponding exponents are the same as for the rapid-change(quenched)velocity?eld and can be obtained from the caseη=εin the limits u→∞(u→0)].
In Sec.II,we describe our model and its interesting special cases.In Sec.III,we brie?y recall the?eld theoretic formulation,the RG and OPE approach to the model,and the O(ε)result for the anomalous exponents[18].The results of the two-loop calculation are presented and discussed in Sec.IV:in Sec.IV A,we give the anomalous exponents to order O(ε2)and then discuss them separately for the isotropic(Sec.IV B)and anisotropic(Sec.IV C) contributions.
The main conclusion of the paper can be formulated as follows:the qualitative e?ect of the?nite correlation time on the anomalous scaling depends essentially on the correlation function considered,the value of u,and the space dimensionality d.For the low-order structure functions and in low dimensions(d=2or3),the inclusion of?nite correlation time enhances the intermittency in comparison with the both limits:the time-decorrelated(u=∞)and time-independent(u=0)ones.Although the anomalous exponents have a well-de?ned limits for u→0,they show interesting irregularities in the vicinity of the quenched limit:a rapid fallo?when u=0increases from zero,with in?nite slope for d=2,with a pronounced minimum for u～1.On the contrary,the behavior in the region of large u is smooth,like for the shell model studied in[14].For higher-order structure functions and large d,the anomalous scaling is always weaker in comparison with the rapid-change limit and the corresponding(positive)correction is maximal for u=0and monotonically decreases to zero as u tends to in?nity.
II.THE MODEL
The advection of a passive scalar?eldθ(x)≡θ(t,x)is described by the stochastic equation
?tθ=ν0?2θ+f,?t≡?t+v i?i,(2.1)
where?t≡?/?t,?i≡?/?x i,ν0is the molecular di?usivity coe?cient,?2is the Laplace operator,v(x)≡{v i(x)}is the divergence-free(owing to the incompressibility)velocity?eld,and f≡f(x)is an arti?cial Gaussian random noise with zero mean and correlation function
f(x)f(x′) =C(t?t′,r),r=x?x′.(2.2) The form of the correlator is unessential;it is only important that the function C in Eq.(2.2)decreases rapidly for r?L,where L is some integral scale.The noise maintains the steady state of the system and,if C depends on the vector r and not only its modulus r≡r,is a source of large-scale anisotropy.In a more realistic formulation,the noise is replaced by an imposed constant gradient of the scalar?eld;see e.g.Refs.[5,6,18,19,22].
In the real problem,the velocity?eld satis?es the Navier–Stokes equation.Following Refs.[14,18,19,22],we assume for v(x)in Eq.(2.1)a Gaussian distribution with zero mean and correlator
v i(x)v j(x′) = d k
1
2u0
βg≡ Dμg=g[?2ε?η+3γν],βu≡ Dμu=u[?η+γν],γν≡ Dμln Zν(3.4)
vanish.Here Dμis the operationμ?μfor?xed bare parameters and the relations betweenβfunctions and the anomalous dimensionγνresult from the de?nitions and the relation(3.3).
From Eq.(3.4)the exact relationβg/g?3βu/u=2(η?ε)follows which shows that theβfunctions cannot vanish simultaneously for?nite values of their arguments,except for the caseη=ε.Therefore,to?nd the?xed points we must set either u=∞or u=0and simultaneously rescale g so that the anomalous dimensionγνremain?nite. These two options correspond to the two limits(2.5)and(2.6),so that the rapid-change and quenched cases are?xed points of the general model.The analysis shows that the former is IR stable(and thus describes the inertial-range asymptotic behavior)forη>εwhile the latter is stable forη<ε.
Most interesting is the caseη=ε,when theβfunctions become proportional,and the setβg=βu=0reduces to a single equation.As a result,the corresponding?xed point is degenerate:rather than a point,one obtains a line of ?xed points in the g–u plane.They can be labelled by the value of the parameter u,which has the meaning of the ratio of the velocity correlation time and the scalar turnover time.
Existence of the IR stable?xed points implies certain scaling properties of various correlation functions at scales
larger than the dissipative length～g?1/3ε
.In particular,for the equal-time structure functions
S n(r)= [θ(t,x)?θ(t,x′)]n ,r=x?x′(3.5) one obtains
S n(r)=D?n/2
r n(1?ε/2)F n(m r)(3.6) (odd structure functions are nontrivial if the correlation function vf is nonzero or if a constant gradient of the scalar?eld is imposed).In the presence of anisotropy the scaling functions F n(m r)can be decomposed in irreducible representations of the SO(d)group.In the simplest case of uniaxial anisotropy(which is su?cient to reveal all anomalous exponents)one can write
F n(m r)=P l(z)F nl(mr),z=(n·r)/r,(3.7) where P l(z)is the l th order Gegenbauer polynomial(Legendre polynomial for d=3)and n is a unit vector that determines the distinguished direction.
The leading behavior of the functions F nl for mr?0(inertial range)is found from the corresponding operator product expansion and has the form
F nl∝(mr)?nl,(3.8) where the“anomalous exponent”?nl is nothing other than the critical dimension of the irreducible traceless l th rank tensor composite operator built of n?eldsθand minimal possible number of derivatives[18].For l≤n such an operator has the form
?i
1θ···?i
l
θ(?iθ?iθ)p+···,n=l+2p.(3.9)
Here the dots stand for the appropriate subtractions involving the Kroneckerδsymbols,which ensure that the resulting expressions are traceless with respect to any given pair of indices,for example,?iθ?jθ?δij?kθ?kθ/d.We also note that the numbers n and l necessarily have the same parity,that is,they can only be simultaneously even or odd. For the most interesting case of the degenerate?xed point,the dimensions?nl are calculated in the form of series in the only independent exponentε=η,that is,
?nl=
∞
k=1εk?(k)nl.(3.10)
In the lowest order one obtains[18]:
?(1)
nl
=?n(n?2)(d?1)+λl(d+1)
The reader not interested in the details of practical calculation can skip the end of this section and pass to the
result for?(2)
nl .Calculation of the higher-order coe?cients in theεexpansions for the rapid-change model is presented
in Refs.[15,16]in detail.Analogous calculations for the?nite correlated case are more di?cult in two respects.First, there are more relevant Feynman diagrams in the same order of perturbation theory(for zero correlation time,many diagrams contain closed circuits of retarded propagators and vanish).Second,and more important distinction,is that the diagrams for the?nite correlated case involve two di?erent dispersion laws:ω∝k2for the scalar andω∝k2?ηfor the velocity?elds.As a result,the calculation,as well as expressions for the renormalization constants,become rather cumbersome already in the lowest(one-loop)approximation;see Refs.[18,19].
The latter di?culty can be circumvented as follows.Careful analysis shows that in the MS scheme all the needed anomalous dimensions,γνfrom(3.4)andγnl≡ Dμln Z nl,in contrast with the respective renormalization constants Zνand Z nl,are independent of the exponentsεandηin the two-loop approximation(for the one-loop approximation this is obvious from the explicit expressions;see[18,19]).It is thus su?cient to calculate them for any speci?c choice of the exponentsεandηthat guarantees UV?niteness of the diagrams.The most convenient choice isη=0and arbitraryε:all the diagrams remain?nite,the exponents in the aforementioned dispersion laws become identical,and the practical calculations drastically simplify and become feasible.
To avoid possible misunderstandings,it should be emphasized that such an independence is not guaranteed by the renormalizability of the model.The renormalizability in the analytic regularization only guarantees that the renormalization scheme can be chosen such that the correlation functions,along with the coe?cientsβandγin the RG equations,will be analytic at the origin in the space of two complex variablesεandη[25].We used another scheme in which the functionsβandγare independent ofεandηin the?rst two orders,which does not exclude nonanalytic dependence on these parameters in higher orders.We expect that in the three-loop approximation nonanalytic constructions like(ε+η)/(ε+2η)will indeed appear in the anomalous dimensions,in particular,due to the necessity to take into account UV?nite parts of the two-loop diagrams(with our choice of the sharp IR cuto?in Eq.(2.4),the one-loop diagrams have no UV?nite parts;cf.[16]for the rapid-change case).
Thus,we conclude that the knowledge of the renormalization constants forη=0is su?cient to obtain the anomalous dimensions,βfunctions,coordinates of the?xed points,and the critical dimensions of composite operators for arbitrary values ofηandε,including the most interesting caseη=ε,which we always discuss from now on.
IV.ANOMALOUS EXPONENTS IN THE TWO-LOOP APPROXIMATION
A.General expressions
We have performed the complete two-loop calculation of the RG functions(3.4)and the critical dimensions(3.10) of the composite operators(3.9)for arbitrary values of n,l,d,and u and obtained the following expression for the second coe?cient in expansion(3.10):
?(2)
nl =
1
2(d+2)(1?u)+
(d+1)
(u+1)2 +2ud(d+2)
3(1?u)2(d+4) u2(u+1) ?1(u+1)2 ?u24 ,(4.2b)
C=14F2 1(u+1)F2 1(u+1)2F2 1 (d+4)
F3 1(u+1)(d+4)F3 1(u+1)2(d+4)F3 1
c z+
a(a+1)b(b+1)
2!
+...
The values of F k entering into(4.2)can be related by the
recurrent
relation(
x
?
1)F2(x)=x(d+2)F3(x)/(d+4)?1, but the resulting expressions look more cumbersome and we shall keep both F2and F3in the formulas.
The quantity J(u,d)in Eq.(4.2a)can only be expressed in the form of a single convergent integral,suitable for numerical calculation:
J(u,d)=Γ(d/2)
πΓ((d?1)/2) 10dz(1?z2)d/22
?z(u?1+2z2)arcsin z??z(1?z2)1/2(1?u?z2)(1+u?z2) ,(4.3)
whereΓ(···)is the Euler Gamma function.
The quantities(4.2),and hence the dimensions(4.1),have?nite limits for u→∞and u→0.In the?rst limit,
?(2)
nl
coincides with the known result for the Kraichnan’s rapid-change model(see[7]for l=0and2and[15]for general l).The O(1/u)correction to the rapid-change limit can be found from the following asymptotic expressions for the coe?cients(4.2):
A=(d+1)
12(d+4)
F3 1
12
F2 19(d+4)F3 1u ?(d?1)4 +2(d+1)4 +(d?2)
2d(d+2)
+u(d+1) (3d+2)d(d+2)+ln2(d+4)(d+6)F4 1(d+4)2 ,(4.5a) B=?(d+1)3 12 +4
9d(d+2)
+
u
2 +4(d+1)2
?4(d+1)(d+2)(d+2) ,(4.5c)
up to corrections of order O(u2).
It is worth noting that the O(u)terms in Eqs.(4.5a)and(4.5c)contain poles in(d?2)and thus diverge for d=2. Analysis shows that,for d=2,the leading correction to the u=0result is not analytical in u and has the form u ln u.Formally,the singularity at d=2is explained as follows.Some of the two-loop diagrams contain“energy denominators”of the form(k+q)2+O(u),where k and q are two independent integration momenta.The numerators contain factors∝(P ij(k)q i q j)2stemming from transverse projectors in the propagators.These factors suppress the singularity at k=?q,occurring in the denominators for u=0,and ensure the existence of the integrals over k and q,but the“collinear”divergence at k=?q occurs if the O(u)to the denominators is taken into account.Physically, this divergence can be related to a strong resonant interaction between the excitations of the passive scalar?eld with the opposite momenta k=?q of equal moduli in two dimensions.We shall see below that this singularity remarkably a?ects the behavior of the dimensions(4.1)for the values of d much larger than d=2.
Many studies have been devoted to the analysis of the inertial-range turbulence in the limit d→∞[4,26–28].Our model has no?nite“upper critical dimension,”above which anomalous scaling would vanish.Like in the rapid-change case[26]and,probably,in the Navier-Stokes turbulence[27,28],the anomalous scaling disappears at d=∞,but it reveals itself already in the O(1/d)approximation.Along with the results[4]for the scalar rapid-change model,where the O(1/d)expression for the anomalous exponents were derived for anyε,this con?rms the importance of the large-d expansion for the issue of anomalous scaling in fully developed turbulence.
Straightforward analysis of the expressions(4.2)shows that,for d→∞,one has A=O(d0)[it is important here that J(u,d)=O(1/d)],B=O(d0)and C=O(d),namely,
C=(u+2)(3u+2)
+O(1/d3).(4.7)
4(u+1)2d2
The general expressions(4.1),(4.2)are rather cumbersome,and in the subsequent sections we shall separately discuss isotropic contribution(even n,l=0)and anisotropic ones(general n,l=0).
B.Isotropic sectors
Expression(4.1)simpli?es for the most important case of the isotropic sector(even n and l=0):
n(n?2)
?(2)n0=
?(2)n0??(2)n0|u=∞=n(n?2)(2u+1)
,K n(d,u)≡ 2(d+4)A+9(n?2) 2B?(d+1)C .(4.13) (d?1)2(d+2)2(d+4)
(we recall that for a?xed n,all possible values of l are either even or odd,so that the subsequent values of l di?er by 2).It is clear from Eq.(4.13)that the sign and the dependence on u of the whole expression is determined by the behavior of the function K n(d,u).
In Fig.2,we plot the quantity K n(d,u)as a function of u for n=2,4,6and20(from above to below)for d=2 (a)and d=3(b).The function is always negative for all the cases studied and increases monotonically with u.This behavior persists in the limit of large d,as follows from the asymptotical expression(4.7).
We thus conclude that the O(ε2)contribution in the exact dimension(3.10)“tries to cope”with the hierarchy,set by the O(ε)term,for all values of n,l,d and u;this e?ect is at its strongest for u=0and weakens monotonically as u increases from0to∞.
Now let us turn to the dimensionless ratios R k in(4.12).From the discussion below Eq.(4.12)and asymptotic representation(3.6)one obtains the power-like inertial-range asymptotic expression R k∝(mr)?2k+1,1with?2k+1,1 from Eq.(3.10)[we recall that in our model?2,0=0;see Sec.IV B].Due to the u-independence of the?rst-order answer(3.11),the O(ε)contribution in the exponent?2k+1,1=ε(d+2?4k2)/2(d+2)+O(ε2)coincides with its analog for the Kraichnan model;see Refs.[5]for k=1and[19]for general k.It completely determines the qualitative behavior of the quantities R k:for k=1one has?3,1>0and the skewness factor R1decreases with mr,while for k≥1one has?2k+1,1<0and the higher-order ratios R k increase for mr→0.
In Fig.3,we show the behavior of the second-order correction?(2)
2k+1,1
,obtained from the general formula Eq.(4.1) and divided by(2k+1)3like for the even dimensions,as a function of u for k=1,2,3and4(from below to above) for d=2(a)and d=3(b).
One can see that the e?ect of the O(ε2)correction on the inertial-range behavior of the ratios R k is di?erent for di?erent d,k and u.In two dimensions,the corrections are negative for all u and moderate k:the decay of the skewness factor R1for mr→0appears even slower than indicated by the O(ε)approximation,while the growth of the ratios with k≥2becomes faster.
In three dimensions,the correction is negative for k=1so that the decay R1for mr→0is also slower than in the O(ε)approximation.For k=2,the correction is negative for small u(so that the growth of the hyperskewness factor R2for mr→0is faster than in the?rst-order approximation),but it changes its sign for some?nite value of u and the growth of R2slows down.For k≥3,the corrections are negative for all u and the growth of the corresponding higher-order ratios R k appears slower than predicted by the O(ε)expression.One thus may conclude that for d=3, with the exception of the k=2case,the e?ect of the second-order term is opposite to the tendency set by the ?rst-order approximation.
For k large enough and any d,the behavior of the quantities?(2)
2k+1,1
becomes similar to that of the even dimensions
?(2)
2k,0discussed in Sec.IV B:they decrease monotonically as u increases,comparatively fast for small u(due to the
singularity in the slope for d=2;see Sec.IV A)and rather slow when u becomes large enough.This follows from
the fact that the l-independent contribution in the general expression?(2)
nl behaves as O(n3)for n→∞,while its
l-dependent contribution behaves only as O(n);see Eq.(4.1).
We also note that for moderate k,the quantities?(2)
2k+1,1show a nonmonotonous dependence on u in the region of
small u and in this respect they also resemble the even dimensions;see Fig.1and the discussion in Sec.IV B.
V.CONCLUSION
We have applied the RG and OPE methods to a simple model of a passive scalar quantity advected by the synthetic Gaussian velocity?eld with a given self-similar covariance with?nite correlation time.The structure functions of the scalar?eld exhibit inertial-range anomalous scaling behavior,as a consequence of the existence in the model of composite operators with negative scaling dimensions,identi?ed with anomalous exponents.
For the special case of a local turnover exponent,the anomalous exponents are nonuniversal through the dependence on a dimensionless parameter u that has the meaning of the ratio of the velocity correlation time and the scalar turnover time.The universality reveals itself only in the second order of theεexpansion,and we have derived the exponents to order O(ε2),including anisotropic contributions.
It is shown that,for isotropic contributions,the qualitative e?ect of?nite correlation time depends essentially on n,the order of the structure function,and the space dimensionality d.For moderate n and d,?nite correlation time enhances the intermittency in comparison with the both limits:the rapid-change(u=∞)and quenched(u=0) ones.The O(ε2)term shows a highly nontrivial behavior in the vicinity of the quenched limit:a rapid fallo?when u=0increases from zero,with in?nite derivative at u=0for d=2,with a pronounced minimum for u～1.This irregularity shows that the time-independent advecting?eld can hardly be a reasonable approximation in studying
more realistic models of passive advection by the velocity?eld with?nite correlation time.The behavior near the opposite limit,u=∞,is smooth in agreement with the existing simulation for a shell model[14].
The behavior changes remarkably when n and/or d become large enough:the correction to the limit u=∞due to?nite correlation time is positive for all u(that is,the anomalous scaling is suppressed in comparison with the rapid-change case),it is maximal for u=0and monotonically decreases to zero as u tends to in?nity.
In the anisotropic sectors,the O(ε2)terms diminish the hierarchy revealed by the?rst-order terms for all values of the parameters n,l and d;this e?ect is maximal at u=0and decreases monotonically with1/u.
The e?ect of the O(ε2)corrections on the inertial-range behavior of the dimensionless ratios involving odd-order structure functions depends on d.For d=2and moderate k these corrections are negative;the decay of the skewness factor R1for mr→0is slower while the growth of the higher-order ratios R k with k≥2is faster than indicated by the O(ε)approximation by Refs.[5,18].For d=3,the e?ect is,for most cases,opposite to the tendency set by the?rst-order approximation:the decay of the skewness factor slows down as well as the growth of the higher-order ratios.
Our analysis has been con?ned with the region of smallε,where the results obtained within theεexpansion are internally consistent and undoubtedly reliable[we recall again that,although the leading terms of the anomalous exponents are of order O(ε),the leading terms in which the e?ects of?nite correlation time occur are of order O(ε2)]. We do not discuss here the serious issue of validity of theεexpansions for?niteε=O(1).One can think that,in our model,the natural region of validity of theεexpansion is restricted by the valueε=1/2,where the velocity?eld acquires negative critical dimension(along with all its powers)and new IR singularities,related to the well-known sweeping e?ects,occur in the diagrams;see the discussion in Ref.[18].(It should be noted,however,that such singularities do not necessarily lead to a changeover in the inertial-range behavior,as shown in[18]for the special case of the structure function S2for u=0).On the other hand,ε=1/2can be regarded as the upper bound of the range of validity of the model itself:the lack of Galilean covariance becomes a serious drawback of the synthetic Gaussian velocity ensemble when the sweeping e?ects become important.The next important step should be the analytical derivation of anomalous exponents of a passive scalar advected by the Galilean covariant velocity?eld;this work is now in progress.
ACKNOWLEDGMENTS
The authors are thankful M.Hnatich,A.Kupiainen,P.Muratore Ginanneschi,M.Yu.Nalimov,A.N.Vasil’ev, and A.Vulpiani for discussions.The work was supported by the Nordic Grant for Network Cooperation with the Baltic Countries and Northwest Russia No.FIN-18/2001.N.V.A.and L.Ts.A.were also supported by the program “Universities of Russia”and the GRACENAS Grant No.E00-3-24.N.V.A.and L.Ts.A.acknowledge the Department of Physical Sciences of the University of Helsinki for kind hospitality.
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–4–2
2
4
6
8
10
12345u –0.8–0.6–0.4–0.200.20.40.60.811.21.41.61.822.212345u 0.10.20.30.4u 0.040.060.080.10.12u FIG.1.Behavior of the quantity ζn from Eq.(4.10)for n =4,6,8and 20(from below to above)as a function of u for d =2,3,5,and 10(from the left to the right)in the units of 10?3.
–70
–60
–50
–40
–30
–20
–10
u –100–80
–60–40–20u FIG.2.Behavior of the quantity K n (d,u )from Eq.(4.13)as a function of u for n =2,3,4,5,and 6(from above to below)for d =2(left)and d =3(right).
–20
–18
–16
–14
–12
–10
–8
–6
–4
u –5
–4–3–2–101u FIG.3.Behavior of the quantity ξk ≡?(2)
2k +1,1/(2k +1)3from Eq.(4.1)as a function of u for k =1,2,3and 4,(from below to above)for d =2(left)and d =3(right),in the units of 10?3.
从实践的角度探讨在日语教学中多媒体课件的应用 在今天中国的许多大学，为适应现代化，信息化的要求，建立了设备完善的适应多媒体教学的教室。许多学科的研究者及现场教员也积极致力于多媒体软件的开发和利用。在大学日语专业的教学工作中，教科书、磁带、粉笔为主流的传统教学方式差不多悄然向先进的教学手段而进展。 一、多媒体课件和精品课程的进展现状 然而，目前在专业日语教学中能够利用的教学软件并不多见。比如在中国大学日语的专业、第二外語用教科书常见的有《新编日语》（上海外语教育出版社）、《中日交流标准日本語》（初级、中级）（人民教育出版社）、《新编基础日语（初級、高級）》（上海译文出版社）、《大学日本语》（四川大学出版社）、《初级日语》《中级日语》（北京大学出版社）、《新世纪大学日语》（外语教学与研究出版社）、《综合日语》（北京大学出版社）、《新编日语教程》（华东理工大学出版社）《新编初级（中级）日本语》（吉林教育出版社）、《新大学日本语》（大连理工大学出版社）、《新大学日语》（高等教育出版社）、《现代日本语》（上海外语教育出版社）、《基础日语》（复旦大学出版社）等等。配套教材以录音磁带、教学参考、习题集为主。只有《中日交流標準日本語（初級上）》、《初級日语》、《新编日语教程》等少数教科书配备了多媒体DVD视听教材。 然而这些试听教材，有的内容为日语普及读物，并不适合专业外语课堂教学。比如《新版中日交流标准日本语（初级上）》，有的尽管DVD视听教材中有丰富的动画画面和语音练习。然而，课堂操作则花费时刻长，不利于教师重点指导，更加适合学生的课余练习。比如北京大学的《初级日语》等。在这种情形下，许多大学的日语专业致力于教材的自主开发。 其中，有些大学的还推出精品课程，取得了专门大成绩。比如天津外国语学院的《新编日语》多媒体精品课程为2007年被评为“国家级精品课”。目前已被南开大学外国语学院、成都理工大学日语系等全国40余所大学推广使用。
Unit1 Americans believe no one stands still. If you are not moving ahead, you are falling behind. This attitude results in a nation of people committed to researching, experimenting and exploring. Time is one of the two elements that Americans save carefully, the other being labor. "We are slaves to nothing but the clock,” it has been said. Time is treated as if it were something almost real. We budget it, save it, waste it, steal it, kill it, cut it, account for it; we also charge for it. It is a precious resource. Many people have a rather acute sense of the shortness of each lifetime. Once the sands have run out of a person’s hourglass, they cannot be replaced. We want every minute to count. A foreigner’s first impression of the U.S. is li kely to be that everyone is in a rush -- often under pressure. City people always appear to be hurrying to get where they are going, restlessly seeking attention in a store, or elbowing others as they try to complete their shopping. Racing through daytime meals is part of the pace
硕037班 刘文3110038020 2011/4/20交互式多模型仿真与分析IMM算法与GBP算法的比较，算法实现和运动目标跟踪仿真，IMM算法的特性分析 多源信息融合实验报告
交互式多模型仿真与分析 一、 算法综述 由于混合系统的结构是未知的或者随机突变的，在估计系统状态参数的同时还需要对系统的运动模式进行辨识，所以不可能通过建立起一个固定的模型对系统状态进行效果较好的估计。针对这一问题，多模型的估计方法提出通过一个模型集{}(),1,2,,j M m j r == 中不同模型的切换来匹配不同目标的运动或者同一目标不同阶段的运动，达到运动模式的实时辨识的效果。 目前主要的多模型方法包括一阶广义贝叶斯方法（BGP1），二阶广义贝叶斯方法（GPB2）以及交互式多模型方法等（IMM ）。这些多模型方法的共同点是基于马尔科夫链对各自的模型集进行切换或者融合，他们的主要设计流程如下图： M={m1,m2,...mk} K 时刻输入 值的形式 图一 多模型设计方法 其中，滤波器的重初始化方式是区分不同多模型算法的主要标准。由于多模型方法都是基于一个马尔科夫链来切换与模型的，对于元素为r 的模型集{}(),1,2,,j M m j r == ，从0时刻到k 时刻，其可能的模型切换轨迹为 120,12{,,}k i i i k trace k M m m m = ，其中k i k m 表示K-1到K 时刻，模型切换到第k i 个， k i 可取1,2,,r ，即0,k trace M 总共有k r 种可能。再令1 2 1 ,,,,k k i i i i μ+ 为K+1时刻经由轨迹0,k trace M 输入到第1k i +个模型滤波器的加权系数，则输入可以表示为 0,11 2 1 12|,,,,|,,,???k k trace k k k i M k k i i i i k k i i i x x μ++=?∑ 可见轨迹0,k trace M 的复杂度直接影响到算法计算量和存储量。虽然全轨迹的
新视野三版读写B2U4Text A College sweethearts 1I smile at my two lovely daughters and they seem so much more mature than we,their parents,when we were college sweethearts.Linda,who's21,had a boyfriend in her freshman year she thought she would marry,but they're not together anymore.Melissa,who's19,hasn't had a steady boyfriend yet.My daughters wonder when they will meet"The One",their great love.They think their father and I had a classic fairy-tale romance heading for marriage from the outset.Perhaps,they're right but it didn't seem so at the time.In a way, love just happens when you least expect it.Who would have thought that Butch and I would end up getting married to each other?He became my boyfriend because of my shallow agenda:I wanted a cute boyfriend! 2We met through my college roommate at the university cafeteria.That fateful night,I was merely curious,but for him I think it was love at first sight."You have beautiful eyes",he said as he gazed at my face.He kept staring at me all night long.I really wasn't that interested for two reasons.First,he looked like he was a really wild boy,maybe even dangerous.Second,although he was very cute,he seemed a little weird. 3Riding on his bicycle,he'd ride past my dorm as if"by accident"and pretend to be surprised to see me.I liked the attention but was cautious about his wild,dynamic personality.He had a charming way with words which would charm any girl.Fear came over me when I started to fall in love.His exciting"bad boy image"was just too tempting to resist.What was it that attracted me?I always had an excellent reputation.My concentration was solely on my studies to get superior grades.But for what?College is supposed to be a time of great learning and also some fun.I had nearly achieved a great education,and graduation was just one semester away.But I hadn't had any fun;my life was stale with no component of fun!I needed a boyfriend.Not just any boyfriend.He had to be cute.My goal that semester became: Be ambitious and grab the cutest boyfriend I can find. 4I worried what he'd think of me.True,we lived in a time when a dramatic shift in sexual attitudes was taking place,but I was a traditional girl who wasn't ready for the new ways that seemed common on campus.Butch looked superb!I was not immune to his personality,but I was scared.The night when he announced to the world that I was his girlfriend,I went along
?哈弗曼编码 A method for the construction of minimum-re-dundancy codes, 耿国华1数据结构1北京:高等教育出版社,2005:182—190 严蔚敏,吴伟民.数据结构(C语言版)[M].北京:清华大学出版社,1997. 冯桂,林其伟,陈东华.信息论与编码技术[M].北京:清华大学出版社,2007. 刘大有,唐海鹰,孙舒杨,等.数据结构[M].北京:高等教育出版社,2001 ?压缩实现 速度要求 为了让它(huffman.cpp)快速运行，同时不使用任何动态库，比如STL或者MFC。它压缩1M数据少于100ms（P3处理器，主频1G）。 压缩过程 压缩代码非常简单，首先用ASCII值初始化511个哈夫曼节点： CHuffmanNode nodes[511]; for(int nCount = 0; nCount < 256; nCount++) nodes[nCount].byAscii = nCount; 其次，计算在输入缓冲区数据中，每个ASCII码出现的频率： for(nCount = 0; nCount < nSrcLen; nCount++) nodes[pSrc[nCount]].nFrequency++; 然后，根据频率进行排序： qsort(nodes, 256, sizeof(CHuffmanNode), frequencyCompare); 哈夫曼树，获取每个ASCII码对应的位序列： int nNodeCount = GetHuffmanTree(nodes); 构造哈夫曼树 构造哈夫曼树非常简单，将所有的节点放到一个队列中，用一个节点替换两个频率最低的节点，新节点的频率就是这两个节点的频率之和。这样，新节点就是两个被替换节点的父
Unit 1 1学习外语是我一生中最艰苦也是最有意义的经历之一。虽然时常遭遇挫折，但却非常有价值。 2我学外语的经历始于初中的第一堂英语课。老师很慈祥耐心，时常表扬学生。由于这种积极的教学方法，我踊跃回答各种问题，从不怕答错。两年中，我的成绩一直名列前茅。 3到了高中后，我渴望继续学习英语。然而，高中时的经历与以前大不相同。以前，老师对所有的学生都很耐心，而新老师则总是惩罚答错的学生。每当有谁回答错了，她就会用长教鞭指着我们，上下挥舞大喊：“错！错！错！”没有多久，我便不再渴望回答问题了。我不仅失去了回答问题的乐趣，而且根本就不想再用英语说半个字。 4好在这种情况没持续多久。到了大学，我了解到所有学生必须上英语课。与高中老师不。大学英语老师非常耐心和蔼，而且从来不带教鞭！不过情况却远不尽如人意。由于班大，每堂课能轮到我回答的问题寥寥无几。上了几周课后，我还发现许多同学的英语说得比我要好得多。我开始产生一种畏惧感。虽然原因与高中时不同，但我却又一次不敢开口了。看来我的英语水平要永远停步不前了。 5直到几年后我有机会参加远程英语课程，情况才有所改善。这种课程的媒介是一台电脑、一条电话线和一个调制解调器。我很快配齐了必要的设备并跟一个朋友学会了电脑操作技术，于是我每周用5到7天在网上的虚拟课堂里学习英语。 6网上学习并不比普通的课堂学习容易。它需要花许多的时间，需要学习者专心自律，以跟上课程进度。我尽力达到课程的最低要求，并按时完成作业。 7我随时随地都在学习。不管去哪里，我都随身携带一本袖珍字典和笔记本，笔记本上记着我遇到的生词。我学习中出过许多错，有时是令人尴尬的错误。有时我会因挫折而哭泣，有时甚至想放弃。但我从未因别的同学英语说得比我快而感到畏惧，因为在电脑屏幕上作出回答之前，我可以根据自己的需要花时间去琢磨自己的想法。突然有一天我发现自己什么都懂了，更重要的是，我说起英语来灵活自如。尽管我还是常常出错，还有很多东西要学，但我已尝到了刻苦学习的甜头。 8学习外语对我来说是非常艰辛的经历，但它又无比珍贵。它不仅使我懂得了艰苦努力的意义，而且让我了解了不同的文化，让我以一种全新的思维去看待事物。学习一门外语最令人兴奋的收获是我能与更多的人交流。与人交谈是我最喜欢的一项活动，新的语言使我能与陌生人交往，参与他们的谈话，并建立新的难以忘怀的友谊。由于我已能说英语，别人讲英语时我不再茫然不解了。我能够参与其中，并结交朋友。我能与人交流，并能够弥合我所说的语言和所处的文化与他们的语言和文化之间的鸿沟。 III. 1. rewarding 2. communicate 3. access 4. embarrassing 5. positive 6. commitment 7. virtual 8. benefits 9. minimum 10. opportunities IV. 1. up 2. into 3. from 4. with 5. to 6. up 7. of 8. in 9. for 10.with V. 1.G 2.B 3.E 4.I 5.H 6.K 7.M 8.O 9.F 10.C Sentence Structure VI. 1. Universities in the east are better equipped, while those in the west are relatively poor. 2. Allan Clark kept talking the price up, while Wilkinson kept knocking it down. 3. The husband spent all his money drinking, while his wife saved all hers for the family. 4. Some guests spoke pleasantly and behaved politely, while others wee insulting and impolite. 5. Outwardly Sara was friendly towards all those concerned, while inwardly she was angry. VII. 1. Not only did Mr. Smith learn the Chinese language, but he also bridged the gap between his culture and ours. 2. Not only did we learn the technology through the online course, but we also learned to communicate with friends in English. 3. Not only did we lose all our money, but we also came close to losing our lives.
LZ77压缩算法实验报告 一、实验内容 使用C++编程实现LZ77压缩算法的实现。 二、实验目的 用LZ77实现文件的压缩。 三、实验环境 1、软件环境：Visual C++ 6.0 2、编程语言：C++ 四、实验原理 LZ77 算法在某种意义上又可以称为“滑动窗口压缩”，这是由于该算法将一个虚拟的，可以跟随压缩进程滑动的窗口作为术语字典，要压缩的字符串如果在该窗口中出现，则输出其出现位置和长度。使用固定大小窗口进行术语匹配，而不是在所有已经编码的信息中匹配，是因为匹配算法的时间消耗往往很多，必须限制字典的大小才能保证算法的效率；随着压缩的进程滑动字典窗口，使其中总包含最近编码过的信息，是因为对大多数信息而言，要编码的字符串往往在最近的上下文中更容易找到匹配串。 五、LZ77算法的基本流程 1、从当前压缩位置开始，考察未编码的数据，并试图在滑动窗口中找出最长的匹 配字符串，如果找到，则进行步骤2，否则进行步骤3。 2、输出三元符号组( off, len, c )。其中off 为窗口中匹
配字符串相对窗口边 界的偏移，len 为可匹配的长度，c 为下一个字符。然后将窗口向后滑动len + 1 个字符，继续步骤1。 3、输出三元符号组( 0, 0, c )。其中c 为下一个字符。然后将窗口向后滑动 len + 1 个字符，继续步骤1。 六、源程序 /********************************************************************* * * Project description: * Lz77 compression/decompression algorithm. * *********************************************************************/ #include 新大学日语简明教程课文翻译 第21课 一、我的留学生活 我从去年12月开始学习日语。已经3个月了。每天大约学30个新单词。每天学15个左右的新汉字，但总记不住。假名已经基本记住了。 简单的会话还可以，但较难的还说不了。还不能用日语发表自己的意见。既不能很好地回答老师的提问，也看不懂日语的文章。短小、简单的信写得了，但长的信写不了。 来日本不久就迎来了新年。新年时，日本的少女们穿着美丽的和服，看上去就像新娘。非常冷的时候，还是有女孩子穿着裙子和袜子走在大街上。 我在日本的第一个新年过得很愉快，因此很开心。 现在学习忙，没什么时间玩，但周末常常运动，或骑车去公园玩。有时也邀朋友一起去。虽然我有国际驾照，但没钱，买不起车。没办法，需要的时候就向朋友借车。有几个朋友愿意借车给我。 二、一个房间变成三个 从前一直认为睡在褥子上的是日本人，美国人都睡床铺，可是听说近来纽约等大都市的年轻人不睡床铺，而是睡在褥子上，是不是突然讨厌起床铺了？ 日本人自古以来就睡在褥子上，那自有它的原因。人们都说日本人的房子小，从前，很少有人在自己的房间，一家人住在一个小房间里是常有的是，今天仍然有人过着这样的生活。 在仅有的一个房间哩，如果要摆下全家人的床铺，就不能在那里吃饭了。这一点，褥子很方便。早晨，不需要褥子的时候，可以收起来。在没有了褥子的房间放上桌子，当作饭厅吃早饭。来客人的话，就在那里喝茶；孩子放学回到家里，那房间就成了书房。而后，傍晚又成为饭厅。然后收起桌子，铺上褥子，又成为了全家人睡觉的地方。 如果是床铺的话，除了睡觉的房间，还需要吃饭的房间和书房等，但如果使用褥子，一个房间就可以有各种用途。 据说从前，在纽约等大都市的大学学习的学生也租得起很大的房间。但现在房租太贵，租不起了。只能住更便宜、更小的房间。因此，似乎开始使用睡觉时作床，白天折小能成为椅子的、方便的褥子。 新视野大学英语第一册Unit 1课文翻译 学习外语是我一生中最艰苦也是最有意义的经历之一。 虽然时常遭遇挫折，但却非常有价值。 我学外语的经历始于初中的第一堂英语课。 老师很慈祥耐心，时常表扬学生。 由于这种积极的教学方法，我踊跃回答各种问题，从不怕答错。 两年中，我的成绩一直名列前茅。 到了高中后，我渴望继续学习英语。然而，高中时的经历与以前大不相同。 以前，老师对所有的学生都很耐心，而新老师则总是惩罚答错的学生。 每当有谁回答错了，她就会用长教鞭指着我们，上下挥舞大喊：“错！错！错！” 没有多久，我便不再渴望回答问题了。 我不仅失去了回答问题的乐趣，而且根本就不想再用英语说半个字。 好在这种情况没持续多久。 到了大学，我了解到所有学生必须上英语课。 与高中老师不同，大学英语老师非常耐心和蔼，而且从来不带教鞭！ 不过情况却远不尽如人意。 由于班大，每堂课能轮到我回答的问题寥寥无几。 上了几周课后，我还发现许多同学的英语说得比我要好得多。 我开始产生一种畏惧感。 虽然原因与高中时不同，但我却又一次不敢开口了。 看来我的英语水平要永远停步不前了。 直到几年后我有机会参加远程英语课程，情况才有所改善。 这种课程的媒介是一台电脑、一条电话线和一个调制解调器。 我很快配齐了必要的设备并跟一个朋友学会了电脑操作技术，于是我每周用5到7天在网上的虚拟课堂里学习英语。 网上学习并不比普通的课堂学习容易。 它需要花许多的时间，需要学习者专心自律，以跟上课程进度。 我尽力达到课程的最低要求，并按时完成作业。 我随时随地都在学习。 不管去哪里，我都随身携带一本袖珍字典和笔记本，笔记本上记着我遇到的生词。 我学习中出过许多错，有时是令人尴尬的错误。 有时我会因挫折而哭泣，有时甚至想放弃。 但我从未因别的同学英语说得比我快而感到畏惧，因为在电脑屏幕上作出回答之前，我可以根据自己的需要花时间去琢磨自己的想法。 突然有一天我发现自己什么都懂了，更重要的是，我说起英语来灵活自如。 尽管我还是常常出错，还有很多东西要学，但我已尝到了刻苦学习的甜头。 学习外语对我来说是非常艰辛的经历，但它又无比珍贵。 它不仅使我懂得了艰苦努力的意义，而且让我了解了不同的文化，让我以一种全新的思维去看待事物。 学习一门外语最令人兴奋的收获是我能与更多的人交流。 与人交谈是我最喜欢的一项活动，新的语言使我能与陌生人交往，参与他们的谈话，并建立新的难以忘怀的友谊。 由于我已能说英语，别人讲英语时我不再茫然不解了。 我能够参与其中，并结交朋友。 实验名称：LZSS压缩算法实验报告 一、实验内容 使用Visual 6..0 C++编程实现LZ77压缩算法。 二、实验目的 用LZSS实现文件的压缩。 三、实验原理 LZSS压缩算法是词典编码无损压缩技术的一种。LZSS压缩算法的字典模型使用了自适应的方式，也就是说，将已经编码过的信息作为字典， 四、实验环境 1、软件环境：Visual C++ 6.0 2、编程语言：C++ 五、实验代码 #include -- need byte-swap function for big endian CPU */ #define READ_LE32(X) *(uint32_t *)(X) #define WRITE_LE32(X,Y) *(uint32_t *)(X) = (Y) /* this assumes sizeof(long)==4 */ typedef unsigned long uint32_t; /* text (input) size counter, code (output) size counter, and counter for reporting progress every 1K bytes */ static unsigned long g_text_size, g_code_size, g_print_count; /* ring buffer of size N, with extra F-1 bytes to facilitate string comparison */ static unsigned char g_ring_buffer[N + F - 1]; /* position and length of longest match; set by insert_node() */ static unsigned g_match_pos, g_match_len; /* left & right children & parent -- these constitute binary search tree */ static unsigned g_left_child[N + 1], g_right_child[N + 257], g_parent[N + 1]; /* input & output files */ static FILE *g_infile, *g_outfile; /***************************************************************************** initialize trees *****************************************************************************/ static void init_tree(void) { unsigned i; /* For i = 0 to N - 1, g_right_child[i] and g_left_child[i] will be the right and left children of node i. These nodes need not be initialized. Also, g_parent[i] is the parent of node i. These are initialized to NIL (= N), which stands for 'not used.' For i = 0 to 255, g_right_child[N + i + 1] is the root of the tree for strings that begin with character i. These are initialized to NIL. Note there are 256 trees. */ for(i = N + 1; i <= N + 256; i++) g_right_child[i] = NIL; for(i = 0; i < N; i++) g_parent[i] = NIL; } /***************************************************************************** Inserts string of length F, g_ring_buffer[r..r+F-1], into one of the trees (g_ring_buffer[r]'th tree) and returns the longest-match position and length via the global variables g_match_pos and g_match_len. If g_match_len = F, then removes the old node in favor of the new one, because the old one will be deleted sooner. 习惯与礼仪 我是个漫画家，对旁人细微的动作、不起眼的举止等抱有好奇。所以，我在国外只要做错一点什么，立刻会比旁人更为敏锐地感觉到那个国家的人们对此作出的反应。 譬如我多次看到过，欧美人和中国人见到我们日本人吸溜吸溜地出声喝汤而面露厌恶之色。过去，日本人坐在塌塌米上，在一张低矮的食案上用餐，餐具离嘴较远。所以，养成了把碗端至嘴边吸食的习惯。喝羹匙里的东西也象吸似的，声声作响。这并非哪一方文化高或低，只是各国的习惯、礼仪不同而已。 日本人坐在椅子上围桌用餐是1960年之后的事情。当时，还没有礼仪规矩，甚至有人盘着腿吃饭。外国人看见此景大概会一脸厌恶吧。 韩国女性就座时，单腿翘起。我认为这种姿势很美，但习惯于双膝跪坐的日本女性大概不以为然，而韩国女性恐怕也不认为跪坐为好。 日本等多数亚洲国家，常有人习惯在路上蹲着。欧美人会联想起狗排便的姿势而一脸厌恶。 日本人常常把手放在小孩的头上说“好可爱啊！”，而大部分外国人会不愿意。 如果向回教国家的人们劝食猪肉和酒，或用左手握手、递东西，会不受欢迎的。当然，饭菜也用右手抓着吃。只有从公用大盘往自己的小盘里分食用的公勺是用左手拿。一旦搞错，用黏糊糊的右手去拿， 会遭人厌恶。 在欧美，对不受欢迎的客人不说“请脱下外套”，所以电视剧中的侦探哥隆波总是穿着外套。访问日本家庭时，要在门厅外脱掉外套后进屋。穿到屋里会不受欢迎的。 这些习惯只要了解就不会出问题，如果因为不知道而遭厌恶、憎恨，实在心里难受。 过去，我曾用色彩图画和简短的文字画了一本《关键时刻的礼仪》（新潮文库）。如今越发希望用各国语言翻译这本书。以便能对在日本的外国人有所帮助。同时希望有朝一日以漫画的形式画一本“世界各国的习惯与礼仪”。 练习答案 ５、 （１）止める並んでいる見ているなる着色した （２）拾った入っていた行ったしまった始まっていた 新视野大学英语第三版第二册读写课文翻译 Unit 1 Text A 一堂难忘的英语课 1 如果我是唯一一个还在纠正小孩英语的家长，那么我儿子也许是对的。对他而言，我是一个乏味的怪物：一个他不得不听其教诲的父亲，一个还沉湎于语法规则的人，对此我儿子似乎颇为反感。 2 我觉得我是在最近偶遇我以前的一位学生时，才开始对这个问题认真起来的。这个学生刚从欧洲旅游回来。我满怀着诚挚期待问她：“欧洲之行如何？” 3 她点了三四下头，绞尽脑汁，苦苦寻找恰当的词语，然后惊呼：“真是，哇！” 4 没了。所有希腊文明和罗马建筑的辉煌居然囊括于一个浓缩的、不完整的语句之中！我的学生以“哇！”来表示她的惊叹，我只能以摇头表达比之更强烈的忧虑。 5 关于正确使用英语能力下降的问题，有许多不同的故事。学生的确本应该能够区分诸如their/there/they're之间的不同，或区别complimentary 跟complementary之间显而易见的差异。由于这些知识缺陷，他们承受着大部分不该承受的批评和指责，因为舆论认为他们应该学得更好。 6 学生并不笨，他们只是被周围所看到和听到的语言误导了。举例来说，杂货店的指示牌会把他们引向stationary（静止处），虽然便笺本、相册、和笔记本等真正的stationery（文具用品）并没有被钉在那儿。朋友和亲人常宣称They've just ate。实际上，他们应该说They've just eaten。因此，批评学生不合乎情理。 7 对这种缺乏语言功底而引起的负面指责应归咎于我们的学校。学校应对英语熟练程度制定出更高的标准。可相反，学校只教零星的语法，高级词汇更是少之又少。还有就是，学校的年轻教师显然缺乏这些重要的语言结构方面的知识，因为他们过去也没接触过。学校有责任教会年轻人进行有效的语言沟通，可他们并没把语言的基本框架——准确的语法和恰当的词汇——充分地传授给学生。 多媒体数据压缩实验报告 篇一：多媒体实验报告_文件压缩 课程设计报告 实验题目：文件压缩程序 姓名：指导教师：学院：计算机学院专业：计算机科学与技术学号： 提交报告时间：20年月日 四川大学 一，需求分析： 有两种形式的重复存在于计算机数据中，文件压缩程序就是对这两种重复进行了压 缩。 一种是短语形式的重复，即三个字节以上的重复，对于这种重复，压缩程序用两个数字：1.重复位置距当前压缩位置的距离；2.重复的长度，来表示这个重复，假设这两个数字各占一个字节，于是数据便得到了压缩。 第二种重复为单字节的重复，一个字节只有256种可能的取值，所以这种重复是必然的。给 256 种字节取值重新编码，使出现较多的字节使用较短的编码，出现较少的字节使用较长的编码，这样一来，变短的字节相对于变长的字节更多，文件的总长度就会减少，并且，字节使用比例越不均 匀，压缩比例就越大。 编码式压缩必须在短语式压缩之后进行，因为编码式压缩后，原先八位二进制值的字节就被破坏了，这样文件中短语式重复的倾向也会被破坏（除非先进行解码）。另外，短语式压缩后的结果：那些剩下的未被匹配的单、双字节和得到匹配的距离、长度值仍然具有取值分布不均匀性，因此，两种压缩方式的顺序不能变。 本程序设计只做了编码式压缩，采用Huffman编码进行压缩和解压缩。Huffman编码是一种可变长编码方式，是二叉树的一种特殊转化形式。编码的原理是：将使用次数多的代码转换成长度较短的代码，而使用次数少的可以使用较长的编码，并且保持编码的唯一可解性。根据 ascii 码文件中各 ascii 字符出现的频率情况创建 Huffman 树，再将各字符对应的哈夫曼编码写入文件中。同时，亦可根据对应的哈夫曼树，将哈夫曼编码文件解压成字符文件. 一、概要设计： 压缩过程的实现: 压缩过程的流程是清晰而简单的: 1. 创建 Huffman 树 2. 打开需压缩文件 3. 将需压缩文件中的每个 ascii 码对应的 huffman 编码按 bit 单位输出生成压缩文件压缩结束。 新视野大学英语1课文翻译 1下午好！作为校长，我非常自豪地欢迎你们来到这所大学。你们所取得的成就是你们自己多年努力的结果，也是你们的父母和老师们多年努力的结果。在这所大学里，我们承诺将使你们学有所成。 2在欢迎你们到来的这一刻，我想起自己高中毕业时的情景，还有妈妈为我和爸爸拍的合影。妈妈吩咐我们：“姿势自然点。”“等一等,”爸爸说，“把我递给他闹钟的情景拍下来。”在大学期间，那个闹钟每天早晨叫醒我。至今它还放在我办公室的桌子上。 3让我来告诉你们一些你们未必预料得到的事情。你们将会怀念以前的生活习惯，怀念父母曾经提醒你们要刻苦学习、取得佳绩。你们可能因为高中生活终于结束而喜极而泣，你们的父母也可能因为终于不用再给你们洗衣服而喜极而泣！但是要记住：未来是建立在过去扎实的基础上的。 4对你们而言，接下来的四年将会是无与伦比的一段时光。在这里，你们拥有丰富的资源：有来自全国各地的有趣的学生，有学识渊博又充满爱心的老师，有综合性图书馆，有完备的运动设施，还有针对不同兴趣的学生社团——从文科社团到理科社团、到社区服务等等。你们将自由地探索、学习新科目。你们要学着习惯点灯熬油，学着结交充满魅力的人，学着去追求新的爱好。我想鼓励你们充分利用这一特殊的经历，并用你们的干劲和热情去收获这一机会所带来的丰硕成果。 5有这么多课程可供选择，你可能会不知所措。你不可能选修所有的课程，但是要尽可能体验更多的课程！大学里有很多事情可做可学，每件事情都会为你提供不同视角来审视世界。如果我只能给你们一条选课建议的话，那就是：挑战自己！不要认为你早就了解自己对什么样的领域最感兴趣。选择一些你从未接触过的领域的课程。这样，你不仅会变得更加博学，而且更有可能发现一个你未曾想到的、能成就你未来的爱好。一个绝佳的例子就是时装设计师王薇薇，她最初学的是艺术史。随着时间的推移，王薇薇把艺术史研究和对时装的热爱结合起来，并将其转化为对设计的热情，从而使她成为全球闻名的设计师。 6在大学里，一下子拥有这么多新鲜体验可能不会总是令人愉快的。在你的宿舍楼里，住在你隔壁寝室的同学可能会反复播放同一首歌，令你头痛欲裂！你可能喜欢早起，而你的室友却是个夜猫子！尽管如此，你和你的室友仍然可能成 价值工程 置，是一项十分有意义的工作。另外恶意代码的检测和分析是一个长期的过程，应对其新的特征和发展趋势作进一步研究，建立完善的分析库。 参考文献： [1]CNCERT/CC.https://www.doczj.com/doc/e212309648.html,/publish/main/46/index.html. [2]LO R,LEVITTK,OL SSONN R.MFC:a malicious code filter [J].Computer and Security,1995,14(6):541-566. [3]KA SP ER SKY L.The evolution of technologies used to detect malicious code [M].Moscow:Kaspersky Lap,2007. [4]LC Briand,J Feng,Y Labiche.Experimenting with Genetic Algorithms and Coupling Measures to devise optimal integration test orders.Software Engineering with Computational Intelligence,Kluwer,2003. [5]Steven A.Hofmeyr,Stephanie Forrest,Anil Somayaji.Intrusion Detection using Sequences of System calls.Journal of Computer Security Vol,Jun.1998. [6]李华,刘智,覃征,张小松.基于行为分析和特征码的恶意代码检测技术[J].计算机应用研究，2011，28（3）：1127-1129. [7]刘威，刘鑫，杜振华.2010年我国恶意代码新特点的研究.第26次全国计算机安全学术交流会论文集，2011，（09）. [8]IDIKA N,MATHUR A P.A Survey of Malware Detection Techniques [R].Tehnical Report,Department of Computer Science,Purdue University,2007. 0引言 现有的压缩算法有很多种，但是都存在一定的局限性，比如：LZw [1]。主要是针对数据量较大的图像之类的进行压缩，不适合对简单报文的压缩。比如说，传输中有长度限制的数据，而实际传输的数据大于限制传输的数据长度，总体数据长度在100字节左右，此时使用一些流行算法反而达不到压缩的目的，甚至增大数据的长度。本文假设该批数据为纯数字数据，实现压缩并解压缩算法。 1数据压缩概念 数据压缩是指在不丢失信息的前提下，缩减数据量以减少存储空间，提高其传输、存储和处理效率的一种技术方法。或按照一定的算法对数据进行重新组织，减少数据的冗余和存储的空间。常用的压缩方式[2,3]有统计编码、预测编码、变换编码和混合编码等。统计编码包含哈夫曼编码、算术编码、游程编码、字典编码等。 2常见几种压缩算法的比较2.1霍夫曼编码压缩[4]：也是一种常用的压缩方法。其基本原理是频繁使用的数据用较短的代码代替，很少使用 的数据用较长的代码代替，每个数据的代码各不相同。这些代码都是二进制码，且码的长度是可变的。 2.2LZW 压缩方法[5,6]：LZW 压缩技术比其它大多数压缩技术都复杂，压缩效率也较高。其基本原理是把每一个第一次出现的字符串用一个数值来编码，在还原程序中再将这个数值还成原来的字符串，如用数值0x100代替字符串ccddeee"这样每当出现该字符串时，都用0x100代替，起到了压缩的作用。 3简单报文数据压缩算法及实现 3.1算法的基本思想数字0-9在内存中占用的位最 大为4bit ， 而一个字节有8个bit ，显然一个字节至少可以保存两个数字，而一个字符型的数字在内存中是占用一个字节的，那么就可以实现2:1的压缩，压缩算法有几种，比如，一个自己的高四位保存一个数字，低四位保存另外一个数字，或者，一组数字字符可以转换为一个n 字节的数值。N 为C 语言某种数值类型的所占的字节长度，本文讨论后一种算法的实现。 3.2算法步骤 ①确定一种C 语言的数值类型。 —————————————————————— —作者简介：安建梅（1981-），女，山西忻州人，助理实验室，研究方 向为软件开发与软交换技术；季松华（1978-），男，江苏 南通人，高级软件工程师，研究方向为软件开发。 数据快速压缩算法的研究以及C 语言实现 The Study of Data Compression and Encryption Algorithm and Realization with C Language 安建梅①AN Jian-mei ；季松华②JI Song-hua （①重庆文理学院软件工程学院，永川402160；②中信网络科技股份有限公司，重庆400000）（①The Software Engineering Institute of Chongqing University of Arts and Sciences ，Chongqing 402160，China ； ②CITIC Application Service Provider Co.，Ltd.，Chongqing 400000，China ） 摘要：压缩算法有很多种，但是对需要压缩到一定长度的简单的报文进行处理时，现有的算法不仅达不到目的，并且变得复杂， 本文针对目前一些企业的需要，实现了对简单报文的压缩加密，此算法不仅可以快速对几十上百位的数据进行压缩，而且通过不断 的优化，解决了由于各种情况引发的解密错误，在解密的过程中不会出现任何差错。 Abstract:Although,there are many kinds of compression algorithm,the need for encryption and compression of a length of a simple message processing,the existing algorithm is not only counterproductive,but also complicated.To some enterprises need,this paper realizes the simple message of compression and encryption.This algorithm can not only fast for tens of hundreds of data compression,but also,solve the various conditions triggered by decryption errors through continuous optimization;therefore,the decryption process does not appear in any error. 关键词：压缩；解压缩；数字字符；简单报文Key words:compression ；decompression ；encryption ；message 中图分类号：TP39文献标识码：A 文章编号：1006-4311（2012）35-0192-02 ·192·新大学日语简明教程课文翻译
新视野大学英语第一册Unit 1课文翻译
LZSS压缩算法实验报告
新大学日语阅读与写作1 第3课译文
新视野大学英语(第三版)读写教程第二册课文翻译(全册)
多媒体数据压缩实验报告
新视野大学英语1课文翻译
数据快速压缩算法的C语言实现
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