3,470 research outputs found
Equation of motion approach to the Hubbard model in infinite dimensions
We consider the Hubbard model on the infinite-dimensional Bethe lattice and
construct a systematic series of self-consistent approximations to the
one-particle Green's function, . The first
equations of motion are exactly fullfilled by and the
'th equation of motion is decoupled following a simple set of decoupling
rules. corresponds to the Hubbard-III approximation. We
present analytic and numerical results for the Mott-Hubbard transition at half
filling for .Comment: 10pager, REVTEX, 8-figures not available in postscript, manuscript
may be understood without figure
Cluster persistence in one-dimensional diffusion--limited cluster--cluster aggregation
The persistence probability, , of a cluster to remain unaggregated is
studied in cluster-cluster aggregation, when the diffusion coefficient of a
cluster depends on its size as . In the mean-field the
problem maps to the survival of three annihilating random walkers with
time-dependent noise correlations. For the motion of persistent
clusters becomes asymptotically irrelevant and the mean-field theory provides a
correct description. For the spatial fluctuations remain relevant
and the persistence probability is overestimated by the random walk theory. The
decay of persistence determines the small size tail of the cluster size
distribution. For the distribution is flat and, surprisingly,
independent of .Comment: 11 pages, 6 figures, RevTeX4, submitted to Phys. Rev.
Goodbye Radicalism! Conceptions of conservatism among Chinese intellectuals during the early 1990s
This research has analyzed the topic of “conservatism” (baoshou zhuyi) in early 1990s China from a twofold perspective. Firstly, in the tradition of conceptual history (Begriffsgeschichte), the concrete use of the concept of “conservatism” in Chinese intellectual discourse has been studied in relation to the “counterconcept” of “radicalism” (jijin zhuyi). This approach has enabled the study of a variety of references to “conservatism,” such as the “neo-conservatism” of Xiao Gongqin and the “princelings,” the 1992 debate on the nature of modern Chinese history that was triggered by the overseas Chinese historian Yü Ying-shih, the New Confucianism of Chen Lai, and Zheng Min’s criticism of the Literary Revolution. On a second level, it has been investigated whether these criticisms of “radicalism” were expressions of a conservative “style of thought” that went beyond the critique of historical events such as the May Fourth Movement, the Cultural Revolution, or the quest for science and democracy of the 1980s.LEI Universiteit LeidenNWO, Fulbright Center AmsterdamAsian Studie
Charge-density-wave order parameter of the Falicov-Kimball model in infinite dimensions
In the large-U limit, the Falicov-Kimball model maps onto an effective Ising
model, with an order parameter described by a BCS-like mean-field theory in
infinite dimensions. In the small-U limit, van Dongen and Vollhardt showed that
the order parameter assumes a strange non-BCS-like shape with a sharp reduction
near T approx T_c/2. Here we numerically investigate the crossover between
these two regimes and qualitatively determine the order parameter for a variety
of different values of U. We find the overall behavior of the order parameter
as a function of temperature to be quite anomalous.Comment: (5 pages, 3 figures, typeset with ReVTeX4
Many Body Correlation Corrections to Superconducting Pairing in Two Dimensions.
We demonstrate that in the strong coupling limit (the superconducting gap
is as large as the chemical potential ), which is relevant to the
high- superconductivity, the correlation corrections to the gap and
critical temperature are about 10\% of the corresponding mean field
approximation values. For the weak coupling () the correlation
corrections are very large: of the order of 100\% of the corresponding mean
field values.Comment: LaTeX 12 page
Nontrivial Polydispersity Exponents in Aggregation Models
We consider the scaling solutions of Smoluchowski's equation of irreversible
aggregation, for a non gelling collision kernel. The scaling mass distribution
f(s) diverges as s^{-tau} when s->0. tau is non trivial and could, until now,
only be computed by numerical simulations. We develop here new general methods
to obtain exact bounds and good approximations of . For the specific
kernel KdD(x,y)=(x^{1/D}+y^{1/D})^d, describing a mean-field model of particles
moving in d dimensions and aggregating with conservation of ``mass'' s=R^D (R
is the particle radius), perturbative and nonperturbative expansions are
derived.
For a general kernel, we find exact inequalities for tau and develop a
variational approximation which is used to carry out the first systematic study
of tau(d,D) for KdD. The agreement is excellent both with the expansions we
derived and with existing numerical values. Finally, we discuss a possible
application to 2d decaying turbulence.Comment: 16 pages (multicol.sty), 6 eps figures (uses epsfig), Minor
corrections. Notations improved, as published in Phys. Rev. E 55, 546
- …