First-Order Phase Transition in Potts Models with finite-range interactions

We consider the $Q$-state Potts model on $\mathbb Z^d$, $Q\ge 3$, $d\ge 2$, with Kac ferromagnetic interactions and scaling parameter \ga. We prove the existence of a first order phase transition for large but finite potential ranges. More precisely we prove that for \ga small enough there is a value of the temperature at which coexist $Q+1$ Gibbs states. The proof is obtained by a perturbation around mean-field using Pirogov-Sinai theory. The result is valid in particular for $d=2$, Q=3, in contrast with the case of nearest-neighbor interactions for which available results indicate a second order phase transition. Putting both results together provides an example of a system which undergoes a transition from second to first order phase transition by changing only the finite range of the interaction.Comment: Soumis pour publication a Journal of statistical physics - version r\'{e}vis\'{e}

Physical nature of critical wave functions in Fibonacci systems

We report on a new class of critical states in the energy spectrum of general Fibonacci systems. By introducing a transfer matrix renormalization technique, we prove that the charge distribution of these states spreads over the whole system, showing transport properties characteristic of electronic extended states. Our analytical method is a first step to find out the link between the spatial structure of these critical wave functions and the quasiperiodic order of the underlying lattice.Comment: REVTEX 3.0, 11 pages, 2 figures available upon request. To appear in Phys. Rev. Let

Phonon distributions of a single bath mode coupled to a quantum dot

The properties of an unconventional, single mode phonon bath coupled to a quantum dot, are investigated within the rotating wave approximation. The electron current through the dot induces an out of equilibrium bath, with a phonon distribution qualitatively different from the thermal one. In selected transport regimes, such a distribution is characterized by a peculiar selective population of few phonon modes and can exhibit a sub-Poissonian behavior. It is shown that such a sub-Poissonian behavior is favored by a double occupancy of the dot. The crossover from a unequilibrated to a conventional thermal bath is explored, and the limitations of the rotating wave approximation are discussed.Comment: 21 Pages, 7 figures, to appear in New Journal of Physics - Focus on Quantum Dissipation in Unconventional Environment

Localization and Mobility Edge in One-Dimensional Potentials with Correlated Disorder

We show that a mobility edge exists in 1D random potentials provided specific long-range correlations. Our approach is based on the relation between binary correlator of a site potential and the localization length. We give the algorithm to construct numerically potentials with mobility edge at any given energy inside allowed zone. Another natural way to generate such potentials is to use chaotic trajectories of non-linear maps. Our numerical calculations for few particular potentials demonstrate the presence of mobility edges in 1D geometry.Comment: 4 pages in RevTex and 2 Postscript figures; revised version published in Phys. Rev. Lett. 82 (1999) 406

Mean-field driven first-order phase transitions in systems with long-range interactions

We consider a class of spin systems on $\Z^d$ with vector valued spins (\bS_x) that interact via the pair-potentials J_{x,y} \bS_x\cdot\bS_y. The interactions are generally spread-out in the sense that the $J_{x,y}$'s exhibit either exponential or power-law fall-off. Under the technical condition of reflection positivity and for sufficiently spread out interactions, we prove that the model exhibits a first-order phase transition whenever the associated mean-field theory signals such a transition. As a consequence, e.g., in dimensions $d\ge3$, we can finally provide examples of the 3-state Potts model with spread-out, exponentially decaying interactions, which undergoes a first-order phase transition as the temperature varies. Similar transitions are established in dimensions $d=1,2$ for power-law decaying interactions and in high dimensions for next-nearest neighbor couplings. In addition, we also investigate the limit of infinitely spread-out interactions. Specifically, we show that once the mean-field theory is in a unique ``state,'' then in any sequence of translation-invariant Gibbs states various observables converge to their mean-field values and the states themselves converge to a product measure.Comment: 57 pages; uses a (modified) jstatphys class fil

Hijacking the Fusion Complex of Human Parainfluenza Virus as an Antiviral Strategy

The receptor binding protein of parainfluenza virus, hemagglutinin-neuraminidase (HN), is responsible for actively triggering the viral fusion protein (F) to undergo a conformational change leading to insertion into the target cell and fusion of the virus with the target cell membrane. For proper viral entry to occur, this process must occur when HN is engaged with host cell receptors at the cell surface. It is possible to interfere with this process through premature activation of the F protein, distant from the target cell receptor. Conformational changes in the F protein and adoption of the postfusion form of the protein prior to receptor engagement of HN at the host cell membrane inactivate the virus. We previously identified small molecules that interact with HN and induce it to activate F in an untimely fashion, validating a new antiviral strategy. To obtain highly active pretriggering candidate molecules we carried out a virtual modeling screen for molecules that interact with sialic acid binding site II on HN, which we propose to be the site responsible for activating F. To directly assess the mechanism of action of one such highly effective new premature activating compound, PAC-3066, we use cryo-electron tomography on authentic intact viral particles for the first time to examine the effects of PAC-3066 treatment on the conformation of the viral F protein. We present the first direct observation of the conformational rearrangement induced in the viral F protein.IMPORTANCE Paramyxoviruses, including human parainfluenza virus type 3, are internalized into host cells by fusion between viral and target cell membranes. The receptor binding protein, hemagglutinin-neuraminidase (HN), upon binding to its cell receptor, triggers conformational changes in the fusion protein (F). This action of HN activates F to reach its fusion-competent state. Using small molecules that interact with HN, we can induce the premature activation of F and inactivate the virus. To obtain highly active pretriggering compounds, we carried out a virtual modeling screen for molecules that interact with a sialic acid binding site on HN that we propose to be the site involved in activating F. We use cryo-electron tomography of authentic intact viral particles for the first time to directly assess the mechanism of action of this treatment on the conformation of the viral F protein and present the first direct observation of the induced conformational rearrangement in the viral F protein.This work was supported by National Institute of Allergy and Infectious Diseases (NIAID), NIH, grants R01AI031971 and R01AI114736 to A.M. and by USA-Israel Binational Science Foundation (BSF) grant 2017293 to N.B.-T. E.Y. was partially funded by a fellowship from the Edmond J. Safra Center for Bioinformatics at Tel Aviv University. N.B.-T.’s research is supported in part by the Abraham E. Kazan Chair in Structural Biology, Tel Aviv University.S

Spectral Measures and Generating Series for Nimrep Graphs in Subfactor Theory II: SU(3)

We complete the computation of spectral measures for SU(3) nimrep graphs arising in subfactor theory, namely the SU(3) ADE graphs associated with SU(3) modular invariants and the McKay graphs of finite subgroups of SU(3). For the SU(2) graphs the spectral measures distill onto very special subsets of the semicircle/circle, whilst for the SU(3) graphs the spectral measures distill onto very special subsets of the discoid/torus. The theory of nimreps allows us to compute these measures precisely. We have previously determined spectral measures for some nimrep graphs arising in subfactor theory, particularly those associated with all SU(2) modular invariants, all subgroups of SU(2), the torus, SU(3), and some SU(3) graphs.Comment: 38 pages, 21 figure

A new method for analyzing ground-state landscapes: ballistic search

A ``ballistic-search'' algorithm is presented which allows the identification of clusters (or funnels) of ground states in Ising spin glasses even for moderate system sizes. The clusters are defined to be sets of states, which are connected in state-space by chains of zero-energy flips of spins. The technique can also be used to estimate the sizes of such clusters. The performance of the method is tested with respect to different system sizes and choices of parameters. As an application the ground-state funnel structure of two-dimensional +or- J spin glasses of systems up to size L=20 is analyzed by calculating a huge number of ground states per realization. A T=0 entropy per spin of s_0=0.086(4)k_B is obtained.Comment: 10 pages, 11 figures, 35 references, revte

Stress from Uncertainty from Graduation to Retirement—A Population-Based Study of Swiss Physicians

BACKGROUND: Uncertainty shapes many decisions made by physicians everyday. Uncertainty and physicians’ inability to handle it may result in substandard care and unexplained variations in patterns of care. OBJECTIVE: To describe socio-demographic and professional characteristics of reactions to uncertainty among physicians from all specialties, including physicians in training. DESIGN: Cross-sectional postal survey. PARTICIPANT: All physicians practicing in Geneva, Switzerland (n = 1,994). MEASUREMENT: Reaction to medical care uncertainty was measured with the Anxiety Due to Uncertainty and Concern About Bad Outcomes scales. The questionnaire also included items about professional characteristics and work-related satisfaction scales. RESULTS: After the first mailing and two reminders, 1,184 physicians responded to the survey. In univariate analysis, women, junior physicians, surgical specialists, generalist physicians, and physicians with lower workloads had higher scores in both scales. In multivariate models, sex, medical specialty, and workload remained significantly associated with both scales, whereas clinical experience remained associated only with concern about bad outcomes. Higher levels of anxiety due to uncertainty were associated with lower scores of work-related satisfaction, while higher levels of concern about bad outcomes were associated with lower satisfaction scores for patient care, personal rewards, professional relations, and general satisfaction, but not for work-related burden or satisfaction with income-prestige. The negative effect of anxiety due to uncertainty on work-related satisfaction was more important for physicians in training. CONCLUSION: Physicians’ reactions to uncertainty in medical care were associated with several dimensions of work-related satisfaction. Physicians in training experienced the greatest impact of anxiety due to uncertainty on their work-related satisfaction. Incorporating strategies to deal with uncertainty into residency training may be useful