26 research outputs found
A mechanical model of normal and anomalous diffusion
The overdamped dynamics of a charged particle driven by an uniform electric
field through a random sequence of scatterers in one dimension is investigated.
Analytic expressions of the mean velocity and of the velocity power spectrum
are presented. These show that above a threshold value of the field normal
diffusion is superimposed to ballistic motion. The diffusion constant can be
given explicitly. At the threshold field the transition between conduction and
localization is accompanied by an anomalous diffusion. Our results exemplify
that, even in the absence of time-dependent stochastic forces, a purely
mechanical model equipped with a quenched disorder can exhibit normal as well
as anomalous diffusion, the latter emerging as a critical property.Comment: 16 pages, no figure
Symmetry Properties on Magnetization in the Hubbard Model at Finite Temperatures
By making use of some symmetry properties of the relevant Hamiltonian, two
fundamental relations between the ferromagnetic magnetization and a spin
correlation function are derived for the -dimensional Hubbard model
at finite temperatures. These can be viewed as a kind of Ward-Takahashi
identities. The properties of the magnetization as a function of the applied
field are discussed. The results thus obtained hold true for both repulsive and
attractive on-site Coulomb interactions, and for arbitrary electron fillings.Comment: Latex file, no figur
Ferromagnetic phase transition and Bose-Einstein condensation in spinor Bose gases
Phase transitions in spinor Bose gases with ferromagnetic (FM) couplings are
studied via mean-field theory. We show that an infinitesimal value of the
coupling can induce a FM phase transition at a finite temperature always above
the critical temperature of Bose-Einstein condensation. This contrasts sharply
with the case of Fermi gases, in which the Stoner coupling can not lead
to a FM phase transition unless it is larger than a threshold value . The
FM coupling also increases the critical temperatures of both the ferromagnetic
transition and the Bose-Einstein condensation.Comment: 4 pages, 4 figure
Commensurate and incommensurate correlations in Haldane gap antiferromagnets
We analyze the onset of incommensurabilities around the VBS point of the S=1
bilinear-biquadratic model. We propose a simple effective field theory which is
capable of reproducing all known properties of the commensurate-incommensurate
transition at the disorder point . Moreover, the theory
predicts another special point , distinct from the VBS
point, where the Haldane gap behaves singularly. The ground state energy
density is an analytic function of the model parameters everywhere, thus we do
not have phase transitions in the conventional sense.Comment: 8 pages, 2 figures, to appear in PR
Generalized Inverse Participation Numbers in Metallic-Mean Quasiperiodic Systems
From the quantum mechanical point of view, the electronic characteristics of
quasicrystals are determined by the nature of their eigenstates. A practicable
way to obtain information about the properties of these wave functions is
studying the scaling behavior of the generalized inverse participation numbers
with the system size . In particular, we
investigate -dimensional quasiperiodic models based on different
metallic-mean quasiperiodic sequences. We obtain the eigenstates of the
one-dimensional metallic-mean chains by numerical calculations for a
tight-binding model. Higher dimensional solutions of the associated generalized
labyrinth tiling are then constructed by a product approach from the
one-dimensional solutions. Numerical results suggest that the relation
holds for these models. Using the
product structure of the labyrinth tiling we prove that this relation is always
satisfied for the silver-mean model and that the scaling exponents approach
this relation for large system sizes also for the other metallic-mean systems.Comment: 7 pages, 3 figure
Trastuzumab after Adjuvant Chemotherapy in HER2-Positive Breast Cancer
BACKGROUND: Trastuzumab, a recombinant monoclonal antibody against HER2, has clinical activity in advanced breast cancer that overexpresses HER2. We investigated its efficacy and safety after excision of early-stage breast cancer and completion of chemotherapy. METHODS: This international, multicenter, randomized trial compared one or two years of trastuzumab given every three weeks with observation in patients with HER2-positive and either node-negative or node-positive breast cancer who had completed locoregional therapy and at least four cycles of neoadjuvant or adjuvant chemotherapy. RESULTS: Data were available for 1694 women randomly assigned to two years of treatment with trastuzumab, 1694 women assigned to one year of trastuzumab, and 1693 women assigned to observation. We report here the results only of treatment with trastuzumab for one year or observation. At the first planned interim analysis (median follow-up of one year), 347 events (recurrence of breast cancer, contralateral breast cancer, second nonbreast malignant disease, or death) were observed: 127 events in the trastuzumab group and 220 in the observation group. The unadjusted hazard ratio for an event in the trastuzumab group, as compared with the observation group, was 0.54 (95 percent confidence interval, 0.43 to 0.67; P<0.0001 by the log-rank test, crossing the interim analysis boundary), representing an absolute benefit in terms of disease-free survival at two years of 8.4 percentage points. Overall survival in the two groups was not significantly different (29 deaths with trastuzumab vs. 37 with observation). Severe cardiotoxicity developed in 0.5 percent of the women who were treated with trastuzumab. CONCLUSIONS: One year of treatment with trastuzumab after adjuvant chemotherapy significantly improves disease-free survival among women with HER2-positive breast cancer. (ClinicalTrials.gov number, NCT00045032.)published_or_final_versio