Eigenstate entanglement entropy in the integrable spin-1/2 XYZ model

We study the average and the standard deviation of the entanglement entropy of highly excited eigenstates of the integrable interacting spin-1/2 XYZ chain away from and at special lines with U(1) symmetry and supersymmetry. We universally find that the average eigenstate entanglement entropy exhibits a volume-law coefficient that is smaller than that of quantum-chaotic interacting models. At the supersymmetric point, we resolve the effect that degeneracies have on the computed averages. We further find that the normalized standard deviation of the eigenstate entanglement entropy decays polynomially with increasing system size, which we contrast with the exponential decay in quantum-chaotic interacting models. Our results provide state-of-the art numerical evidence that integrability in spin-1/2 chains reduces the average and increases the standard deviation of the entanglement entropy of highly excited energy eigenstates when compared with those in quantum-chaotic interacting models.

Average entanglement entropy of midspectrum eigenstates of quantum-chaotic interacting Hamiltonians

To which degree the average entanglement entropy of midspectrum eigenstates of quantum-chaotic interacting Hamiltonians agrees with that of random pure states is a question that has attracted considerable attention in the recent years. While there is substantial evidence that the leading (volume-law) terms are identical, which and how subleading terms differ between them is less clear. Here we carry out state-of-the-art full exact diagonalization calculations of clean spin-1/2 XYZ and XXZ chains with integrability breaking terms to address this question in the absence and presence of U(1) symmetry, respectively. We first introduce the notion of maximally chaotic regime, for the chain sizes amenable to full exact diagonalization calculations, as the regime in Hamiltonian parameters in which the level spacing ratio, the distribution of eigenstate coefficients, and the entanglement entropy are closest to the random matrix theory predictions. In this regime, we carry out a finite-size scaling analysis of the subleading terms of the average entanglement entropy of midspectrum eigenstates when different fractions ν of the spectrum are included in the average. We find indications that, for ν→0, the magnitude of the negative O(1) correction is only slightly greater than the one predicted for random pure states. For finite ν, following a phenomenological approach, we derive a simple expression that describes the numerically observed ν dependence of the O(1) deviation from the prediction for random pure states.

Restoring Ergodicity in a Strongly Disordered Interacting Chain

We consider a chain of interacting fermions with random disorder that was intensively studied in the context of many-body localization. We show that only a small fraction of the two-body interaction represents a true local perturbation to the Anderson insulator. While this true perturbation is nonzero at any finite disorder strength W, it decreases with increasing W. This establishes a view that the strongly disordered system should be viewed as a weakly perturbed integrable model, i.e., a weakly perturbed Anderson insulator. As a consequence, the latter can hardly be distinguished from a strictly integrable system in finite-size calculations at large W. We then introduce a rescaled model in which the true perturbation is of the same order of magnitude as the other terms of the Hamiltonian, and show that the system remains ergodic at arbitrary large disorder.

Transmission of HIV Drug Resistance and the Predicted Effect on Current First-line Regimens in Europe

Transmitted human immunodeficiency virus drug resistance in Europe is stable at around 8%. The impact of baseline mutation patterns on susceptibility to antiretroviral drugs should be addressed using clinical guidelines. The impact on baseline susceptibility is largest for nonnucleoside reverse transcriptase inhibitors.

Background. Numerous studies have shown that baseline drug resistance patterns may influence the outcome of antiretroviral therapy. Therefore, guidelines recommend drug resistance testing to guide the choice of initial regimen. In addition to optimizing individual patient management, these baseline resistance data enable transmitted drug resistance (TDR) to be surveyed for public health purposes. The SPREAD program systematically collects data to gain insight into TDR occurring in Europe since 2001.

Methods. Demographic, clinical, and virological data from 4140 antiretroviral-naive human immunodeficiency virus (HIV)–infected individuals from 26 countries who were newly diagnosed between 2008 and 2010 were analyzed. Evidence of TDR was defined using the WHO list for surveillance of drug resistance mutations. Prevalence of TDR was assessed over time by comparing the results to SPREAD data from 2002 to 2007. Baseline susceptibility to antiretroviral drugs was predicted using the Stanford HIVdb program version 7.0.

Results. The overall prevalence of TDR did not change significantly over time and was 8.3% (95% confidence interval, 7.2%–9.5%) in 2008–2010. The most frequent indicators of TDR were nucleoside reverse transcriptase inhibitor (NRTI) mutations (4.5%), followed by nonnucleoside reverse transcriptase inhibitor (NNRTI) mutations (2.9%) and protease inhibitor mutations (2.0%). Baseline mutations were most predictive of reduced susceptibility to initial NNRTI-based regimens: 4.5% and 6.5% of patient isolates were predicted to have resistance to regimens containing efavirenz or rilpivirine, respectively, independent of current NRTI backbones.

Conclusions. Although TDR was highest for NRTIs, the impact of baseline drug resistance patterns on susceptibility was largest for NNRTIs. The prevalence of TDR assessed by epidemiological surveys does not clearly indicate to what degree susceptibility to different drug classes is affected.

Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta

Long-range order in quantum many-body systems is usually associated with equilibrium situations. Here, we experimentally investigate the quasicondensation of strongly interacting bosons at finite momenta in a far-from-equilibrium case. We prepare an inhomogeneous initial state consisting of one-dimensional Mott insulators in the center of otherwise empty one-dimensional chains in an optical lattice with a lattice constant d. After suddenly quenching the trapping potential to zero, we observe the onset of coherence in spontaneously forming quasicondensates in the lattice. Remarkably, the emerging phase order differs from the ground-state order and is characterized by peaks at finite momenta ±(π/2)(ℏ/d) in the momentum distribution function.

Nonequilibrium propagation and decay of a bound pair in driven t-J models

We perform an accurate time-dependent numerical study of an out-of-equilibrium response of a bound state within t-J systems on a two-leg ladder and a square lattice. We show that the bound hole pair decays with the onset of finite steady current if both mechanisms for binding and the dissipation share matching degrees of freedom. Moreover, by investigating the mechanism of decay on the square lattice we find that the dynamics is governed by the decay in the direction perpendicular to the electric field, leading to much shorter decay times in comparison to the ladder where such dynamics is topologically restricted.

Quantum dynamics of a driven correlated system coupled to phonons

Nonequilibrium interplay between charge, spin, and lattice degrees of freedom on a square lattice is studied for a single charge carrier doped in the t-J-Holstein model. In the presence of a static electric field we calculate the quasistationary state. With increasing electron-phonon (e-ph) coupling the carrier mobility decreases; however, we find increased steady state current due to e-ph coupling in the regime of negative differential resistance. We explore the distribution of absorbed energy between the spin and the phonon subsystem. For model parameters as relevant for cuprates, the majority of the gained energy flows into the spin subsystem.

Clinical characteristics of adult patients with influenza-like illness hospitalized in general ward during Influenza A H1N1 pandemic 2009/2010

OBJECTIVE

To investigate clinical and laboratory features of patients with Influenza A H1N1 virus infection hospitalized during 2009/2010 pandemic.

METHODS

Prospective observational study comparing clinical and laboratory characteristics of Influenza A H1N1 positive and negative patients with influenza-like illness (ILI).

RESULTS

From October 21, 2009 to February 14, 2010 196 ILI patients were admitted, of which 66 tested positive for Influenza A H1N1. The patients with H1N1 infection were younger (43 years vs. 65 years; P < 0.01), more patients were pregnant (P < 0.01), had allergies (P < 0.05) or, asthma (P < 0.01). H1N1 positive patients were more often febrile (91% vs. 72.9%; P < 0.01) and had a higher prevalence of headache (31.8% vs. 18.5%; P < 0.05). Lower values of C-reactive protein (88 pg/dl vs. 126 pg/dl; P < 0.01), procalcitonine (0.42 µg/l vs. 3.98 µg/l; P < 0.05), leukocyte count (7.4*10(9)/l vs. 11.7*10(9)/l; P < 0.01) and higher values of troponin (0.162 µ/l vs. 0.146 µg/l; P < 0.01) were found in H1N1 positive patients. More bacterial infections were found in H1N1 negative group (68.8% vs. 89.2%; P < 0.05).

CONCLUSIONS

In this study patients infected with Influenza A H1N1 differed from H1N1 negative ILI patients in several clinical and laboratory characteristics. The same was observed also by other investigators. The results of the study suggest some other specific features, such as a higher incidence of headache and higher values of troponin in Influenza A H1N1 infected patients.

Nonequilibrium quantum dynamics of a charge carrier doped into a Mott insulator

We study real-time dynamics of a charge carrier introduced into an undoped Mott insulator propagating under a constant electric field F on the t-J ladder and a square lattice. We calculate the quasistationary current. In both systems an adiabatic regime is observed followed by a positive differential resistivity (PDR) at moderate fields where the carrier mobility is determined. Quantitative differences between the ladder and two-dimensional (2D) systems emerge when at large fields both systems enter the negative differential resistivity (NDR) regime. In the ladder system Bloch-like oscillations prevail, while in two dimensions the current remains finite, proportional to 1/F. The crossover between the PDR and NDR in two dimensions is accompanied by a change of the spatial structure of the propagating spin polaron.

Bipolaron in the t-J model coupled to longitudinal and transverse quantum lattice vibrations

We explore the influence of two different polarizations of quantum oxygen vibrations on the spacial symmetry of the bound magnetic bipolaron in the context of the t-J model by using exact diagonalization within a limited functional space. Linear as well as quadratic electron-phonon coupling to transverse polarization stabilize d-wave symmetry. The existence of a magnetic background is essential for the formation of a d-wave bipolaron state. With increasing linear electron-phonon coupling to longitudinal polarization the symmetry of a d-wave bipolaron state changes to a p wave. Bipolaron develops a large anisotropic effective mass.

A Prediction Model for Community-Acquired Chlamydia pneumoniae Pneumonia in Hospitalized Patients

BACKGROUND

The objective of the study was to identify factors that help to predict community-acquired Chlamydia pneumoniae pneumonia in hospitalized patients.

PATIENTS AND METHODS

Clinical data of 83 patients with serologically confirmed C. pneumoniae pneumonia were compared with the data obtained from 72 patients with bacterial pneumonia. The criteria of bacterial pneumonia included positive blood and/or sputum cultures and negative serology for Mycoplasma pneumoniae, Chlamydia psittaci, Chlamydia pneumoniae and Coxiella burnetii. The data collected included demographics, chronic diseases, pre- and post-hospitalization course of pneumonia, clinical data on admission and laboratory findings. Descriptive statistical analysis, involving numerous variables, was followed by univariate and multivariate logistic regression analysis.

RESULTS

Two different situations, one including demographic data and information on the pre-hospitalization course of pneumonia, and another based on clinical information on admission and on laboratory results, were modeled using multivariate logistic regression. Several variables selected from these two models were incorporated into the third model, and the following four variables were found to have the highest predictive value of C. pneumoniae pneumonia: nursing home residence (odds ratio [OD] 3.73, 95% confidence interval [CI] 1.39-10.06), low c-reactive protein (CRP) levels (OD 5.99, 95% CI 1.82-19.67), nonproductive cough (OD 0.32, 95% CI 0.14-0.73), and a normal urinalysis (OD 0.38, 95% CI 0.17-0.83).

CONCLUSION

Our findings seem to allow for a more reliable differentiation between C. pneumoniae pneumonia and other bacterial pneumonias, but further investigations will be needed to validate the proposed model.

Low prevalence of hepatitis C virus infection among human immunodeficiency virus type 1-infected individuals from Slovenia and Croatia

The prevalence of hepatitis C virus (HCV) infection in the population of human immunodeficiency virus 1 (HIV-1)-infected individuals from Slovenia and Croatia was determined. One hundred and sixty-six out of a total of 188 Slovenian HIV-1-infected individuals and 120 subjects who were randomly chosen out of a total 342 Croatian HIV-1 antibodies-positive individuals were tested for HCV infection. Detection of HCV antibodies was carried out by a third generation enzyme-linked immunoassay (ELISA) and the positive samples were additionally tested by a third generation immuno-blot assay. Additionally, the presence of HCV RNA was determined in all serum samples by a qualitative polymerase chain reaction (PCR). Twenty-four (14.5%) out of 166 Slovenian and 18 (15.0%) out of 120 Croatian HIV-1-infected individuals were HCV antibodies-positive. Nineteen out of 24 (79.2%) Slovenian and 13 out of 18 (72.2%) Croatian anti-HCV positive individuals were also viremic. HCV RNA was not detected in any of 244 HCV antibodies-negative/HIV-1-infected individual from both countries. A significant difference in the prevalence of HCV infection between blood (77.8% in Slovenia and 66.7% in Croatia) and sexual exposure risk groups (1.6% in Slovenia and 6.6% in Croatia) was found in both countries. In a study carried out on the highest proportion of entire population of HIV-1-infected individuals from a certain country or geographic region, Slovenia and Croatia were identified as countries with the second and third lowest prevalence of HCV infection among HIV-1/HIV-2 infected individuals worldwide.

Influenza vaccination of human immunodeficiency virus 1-infected patients receiving antiretroviral therapy

In 13 human immunodeficiency virus 1 (HIV-1) infected patients receiving a highly active antiretroviral therapy (HAART) annual influenza vaccination was conducted. It was hoped that HAART would prevent a post-vaccination increase in HIV-1 load and potential adverse effects. Only two patients had an increased viral load on day 14 post vaccination (p.v.). At 6 months p.v., the majority of the patients had a significantly increased CD4 cell count and a significantly decreased viral load. This indicates that HAART can protect patients from adverse consequences of influenza vaccination. The production of antibodies to the influenza A and B viruses in the HIV-infected patients was substantially lower than that in healthy persons. We propose that HIV-positive patients receiving HAART should be subjected to annual influenza vaccination.

Proviral HIV-1 DNA in gingival crevicular fluid of HIV-1-infected patients in various stages of HIV disease

The oral cavity is rarely reported to be a site of human immunodeficiency virus (HIV) transmission, despite detectable virus in saliva and relatively frequent prevalence of periodontal disease in HIV-infected persons yielding increased excretion of mononuclear-cell-enriched gingival fluid. To search for possible sources of HIV in saliva, and using the polymerase chain-reaction technique, we sought the presence and shedding patterns of proviral HIV-1 DNA in gingival crevicular fluid in a group of patients previously determined as HIV-1-seropositive. Periodontal status at the collection sites was monitored by several clinical parameters, including Plaque Index, Gingival Index, probing depth, and clinical attachment loss. Gingival crevicular fluid samples were collected by means of paper points. Proviral HIV-1 DNA was detected in the gingival fluid of 17 out of 35 HIV-1-infected patients. Its detection correlated significantly with higher plasma HIV-1 RNA viral load (p = 0.03) and not with peripheral blood CD4+ cell count, the presence of blood in gingival fluid, or oral lesions. There was a significant correlation between clinical attachment loss at the sites of fluid collection and plasma HIV-1 RNA viral load (p = 0.002), and borderline correlation between the latter and probing depth (p = 0.54) in the group of patients harboring proviral HIV-1 DNA in gingival crevicular fluid. The results of our study suggest that mononuclear cells present in gingival crevicular fluid and harboring proviral HIV-1 DNA could represent a potential source of HIV-1 in the presence or absence of local bleeding, especially in persons with advanced HIV infection and increased loss of clinical attachment.

Seroprevalence of HIV-1 subtypes A-E among HIV-1 infected individuals from Slovenia

To investigate the prevalence of HIV-1 subtypes A-E in Slovenia, 82 HIV-1 infected individuals were tested for the presence of HIV-1 subtype specific antibodies using a research competitive peptide enzyme immuno assay supplied by Boehringer Mannheim. In 74 individuals unambiguous results were obtained. As in other European countries, the majority of Slovenian HIV-1 infected individuals (86.5%) were infected with subtype B. Infections with subtypes C, A, D and E were detected in 8.1%, 2.7%, 1.3% and 1.3% individuals, respectively.

Prevalence of mutant CCR5 allele in Slovenian HIV-1-infected and non-infected individuals

A 32 bp deletion in the CCR5 gene designated CCR5 delta 32 has been identified recently as the cellular basis for resistance to human immunodeficiency virus type 1 (HIV-1) in some individuals which remained non-infected despite a repeated exposure to this virus. The prevalence of this deletion was examined by polymerase chain reaction (PCR) on 51 HIV-1-infected and 385 non-infected individuals from all parts of Slovenia. 84.4% of the the HIV-1-infected and 83.2% of the non-infected individuals were homozygous for wild type CCR5, and 19.6% and 16.3%, respectively, were heterozygous. No homozygous mutant genotype was observed among the HIV-1-infected patients. Of the non-infected individuals, 2 women (0.5%) were found to harbour the CCR5 delta 32/CCR5 delta 32 genotype only, which is, to the best of our knowledge, the lowest prevalence of this particular genotype found among Caucasians to date.