Ultrafast structural dynamics of the Fe-pnictide parent compound BaFe(2)As(2)

Using femtosecond time-resolved x-ray diffraction we investigate the structural dynamics of the coherently excited A(1g) phonon mode in the Fe-pnictide parent compound BaFe(2)As(2). The fluence dependent intensity oscillations of two specific Bragg reflections with distinctly different sensitivity to the pnictogen height in the compound allow us to quantify the coherent modifications of the Fe-As tetrahedra, indicating a transient increase of the Fe magnetic moments. By a comparison with time-resolved photoemission data, we derive the electron-phonon deformation potential for this particular mode. The value of Δμ/Δz=-(1.0-1.5)  eV/Å is comparable with theoretical predictions and demonstrates the importance of this degree of freedom for the electron-phonon coupling in the Fe pnictides.

Origin of the tetragonal-to-orthorhombic phase transition in FeSe: a combined thermodynamic and NMR study of nematicity

The nature of the tetragonal-to-orthorhombic structural transition at T_{s}≈90  K in single crystalline FeSe is studied using shear-modulus, heat-capacity, magnetization, and nuclear magnetic resonance measurements. The transition is shown to be accompanied by a large shear-modulus softening, which is practically identical to that of underdoped Ba(Fe,Co)_{2}As_{2}, suggesting a very similar strength of the electron-lattice coupling. On the other hand, a spin-fluctuation contribution to the spin-lattice relaxation rate is only observed below T_{s}. This indicates that the structural, or "nematic," phase transition in FeSe is not driven by magnetic fluctuations.

Improved virological and immunological efficacy of resistance-guided switch in antiretroviral therapy: a Frankfurt HIV cohort analysis

To evaluate the treatment outcome of antiretroviral therapy, depending on the use and utility of a concept of resistance-guided switch, patients from the Frankfurt HIV cohort have been followed for 24 weeks. If available, prior resistance data have been evaluated and patients were grouped into their expected viral response. The data of 354 patients were thus analysed, taking into account the genotypic sensitivity score of the administered medication (> or ≤2). When looking at the proportion of patients who achieved a viral load of <50/ml, the response rates differed significantly better for patients with a favourable resistance scoring as compared to an unfavourable one (71.9 % as compared to 56.0 %, p = 0.008). Interestingly, patients with a favourable resistance score also showed a better immunological response, as measured by median CD4 cell count of 391/µl [interquartal range (IQR) 250-530/µl] against 287/µl (IQR 174-449/µl) and a larger total increase of 141/µl against 38/µl. A significant virological and immunological benefit could be demonstrated for patients of a cohort with resistance-guided antiretroviral therapy adjustments.

[Nostalgia and the functions of autobiographical memory]

BACKGROUND

Current research on autobiographical memory distinguishes between a self function, a directive function, and a social function of autobiographical memory. From a lifespan perspective, the use of autobiographical memory for these functions is expected to decrease with age. The present study extended these functions by the function of nostalgia: Often triggered by negative emotions, remembering personal and positive experiences might, among others, enhance positive effects. This emotion-regulating function is expected to become more important in old age.

MATERIAL AND METHODS

In the present study 273 adults (aged between 19 and 90 years) completed the Thinking About Life Experiences Questionnaire (TALE) as well as 11 newly developed items to assess the nostalgia function.

RESULTS

Exploratory and confirmatory factor analyses supported a four-factor model reflecting the presumed self, directive, social, and nostalgia functions of autobiographical memory. The results showed a decrease in the use of autobiographical memory for self, directive and social functions with increasing age, whereas the nostalgia function followed a U-shaped pattern.

Superconducting properties of (Ba-K)Fe2As2 single crystals disordered with fast neutron irradiation

Resistivity ρ(T), Hall coefficient RH(T), superconducting transition temperature Tc and slopes of the upper critical field dHc2/dT were studied in (Ba1-xKx)Fe2As2 (x = 0.218, 0.356, 0.531) single crystals irradiated with fast neutrons. It is found that dTc/dρSC-the rate of decreasing Tc as a function of the ρSC (ρSC is the resistivity at T = Tc)-linearly increases with concentration x. Slow changes in the Hall coefficient RH, as well as the quadratic electronic contribution to the resistivity, show that there are no substantial changes in the topology of the Fermi surface caused by irradiation. The slopes of the upper critical field dHc2/dT in ab and c directions as a function of ρSC determined by Hall measurements show a reasonable agreement with a model that suggests constancy of the band parameters.

Nematic susceptibility of hole-doped and electron-doped BaFe2As2 iron-based superconductors from shear modulus measurements

The nematic susceptibility, χφ, of hole-doped Ba(1-x)K(x)Fe2As2 and electron-doped Ba(Fe(1-x)Co(x))2As2 iron-based superconductors is obtained from measurements of the elastic shear modulus using a three-point bending setup in a capacitance dilatometer. Nematic fluctuations, although weakened by doping, extend over the whole superconducting dome in both systems, suggesting their close tie to superconductivity. Evidence for quantum critical behavior of χφ is, surprisingly, only found for Ba(Fe(1-x)Co(x))2As2 and not for Ba(1-x)K(x)Fe2As2--the system with the higher maximal Tc value.

Dielectric versus magnetic pairing mechanisms in high-temperature cuprate superconductors investigated using Raman scattering

We suggest, and demonstrate, a systematic approach to the study of cuprate superconductors, namely, progressive change of ion size in order to systematically alter the interaction strength and other key parameters. R(Ba,Sr)2Cu3Oy (R={La,…,Lu,Y}) is such a system where potentially obscuring structural changes are minimal. We thereby systematically alter both dielectric and magnetic properties. Dielectric fluctuation is characterized by ionic polarizability while magnetic fluctuation is characterized by exchange interactions measurable by Raman scattering. The range of transition temperatures is 70-107 K, and we find that these correlate only with the dielectric properties, a behavior which persists with external pressure. The ultimate significance may remain to be proven, but it highlights the role of dielectric screening in the cuprates and adds support to a previously proposed novel pairing mechanism involving exchange of quantized waves of electronic polarization.

Pauli-limited multiband superconductivity in KFe2As2

The upper critical field H(c2)(T) of the multiband superconductor KFe2As2 has been studied via low-temperature thermal expansion and magnetostriction measurements. We present compelling evidence for Pauli-limiting effects dominating H(c2)(T) for H || a, as revealed by a crossover from second- to first-order phase transitions to the superconducting state in the magnetostriction measurements down to 50 mK. Corresponding features were absent for H || c. To our knowledge, this crossover constitutes the first confirmation of Pauli limiting of the H(c2)(T) of a multiband superconductor. The results are supported by modeling Pauli limits for single-band and multiband cases.

Evidence of strong correlations and coherence-incoherence crossover in the iron pnictide superconductor KFe2As2

Using resistivity, heat-capacity, thermal-expansion, and susceptibility measurements we study the normal-state behavior of KFe2As2. Both the Sommerfeld coefficient (γ≈103 mJ mol(-1) K(-2)) and the Pauli susceptibility (χ≈4×10(-4)) are strongly enhanced, which confirm the existence of heavy quasiparticles inferred from previous de Haas-van Alphen and angle-resolved photoemission spectroscopy experiments. We discuss this large enhancement using a Gutzwiller slave-boson mean-field calculation, which shows the proximity of KFe2As2 to an orbital-selective Mott transition. The temperature dependence of the magnetic susceptibility and the thermal expansion provide strong experimental evidence for the existence of a coherence-incoherence crossover, similar to what is found in heavy fermion and ruthenate compounds, due to Hund's coupling between orbitals.

High-precision nanoscale temperature sensing using single defects in diamond

Measuring local temperature with a spatial resolution on the order of a few nanometers has a wide range of applications in the semiconductor industry and in material and life sciences. For example, probing temperature on the nanoscale with high precision can potentially be used to detect small, local temperature changes like those caused by chemical reactions or biochemical processes. However, precise nanoscale temperature measurements have not been realized so far owing to the lack of adequate probes. Here we experimentally demonstrate a novel nanoscale temperature sensing technique based on optically detected electron spin resonance in single atomic defects in diamonds. These diamond sensor sizes range from a micrometer down to a few tens of nanometers. We achieve a temperature noise floor of 5 mK/Hz(1/2) for single defects in bulk sensors. Using doped nanodiamonds as sensors the temperature noise floor is 130 mK/Hz(1/2) and accuracies down to 1 mK for nanocrystal sizes and therefore length scales of a few tens of nanometers. This combination of precision and position resolution, combined with the outstanding sensor photostability, should allow the measurement of the heat produced by chemical interactions involving a few or single molecules even in heterogeneous environments like cells.

Coherent excitations and electron-phonon coupling in Ba/EuFe2As2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy

We employed femtosecond time- and angle-resolved photoelectron spectroscopy to analyze the response of the electronic structure of the 122 Fe-pnictide parent compounds Ba/EuFe(2)As(2) and optimally doped BaFe(1.85)Co(0.15)As(2) near the Γ point to optical excitation by an infrared femtosecond laser pulse. We identify pronounced changes of the electron population within several 100 meV above and below the Fermi level, which we explain as a combination of (i) coherent lattice vibrations, (ii) a hot electron and hole distribution, and (iii) transient modifications of the chemical potential. The responses of the three different materials are very similar. In the coherent response we identify three modes at 5.6, 3.3, and 2.6 THz. While the highest frequency mode is safely assigned to the A(1g) mode, the other two modes require a discussion in comparison to the literature. Employing a transient three temperature model we deduce from the transient evolution of the electron distribution a rather weak, momentum-averaged electron-phonon coupling quantified by values for λ<ω(2)> between 30 and 70 meV(2). The chemical potential is found to present pronounced transient changes reaching a maximum of 15 meV about 0.6 ps after optical excitation and is modulated by the coherent phonons. This change in the chemical potential is particularly strong in a multiband system like the 122 Fe-pnictide compounds investigated here due to the pronounced variation of the electron density of states close to the equilibrium chemical potential.

Tuberculosis skin test, but not interferon-γ-releasing assays is affected by BCG vaccination in HIV patients

OBJECTIVE

Of this study was to compare the results of tuberculin skin test (TST) with two interferon-γ releasing-assays (IGRA) in a cohort of HIV positive patients, to analyze impact of prior Bacille-Calmette-Guérin (BCG)-vaccination.

METHODS

Prospective cross sectional study, enrolling only asymptomatic adult HIV infected outpatients from a large German University hospital clinic. All participants were simultaneously tested for latent tuberculosis infection (LTBI) by QuantiFERON-TB Gold, T-SPOT.TB and TST. Only individuals with available definite results (positive/negative, indeterminates excluded) from all three test systems and recalling BCG-vaccination status by interview questionnaire were evaluated.

RESULTS

From 286 study participants, 133 were evaluable; BCG-vaccination history was positive for 18 individuals, and negative for 115. The proportion of individuals with a positive TST was significantly higher for vaccinated (n = 6, 33.3%) than for unvaccinated individuals (n = 13, 11.3%, p = 0.013). There were no significant differences in the proportion of patients with CDC stage C, origin from a TB endemic country or in the CD4 count between the two groups.

CONCLUSION

TST but not IGRAs interfered significantly with prior BCG vaccination in a cohort of HIV infected individuals from a low prevalence TB country. Therefore IGRA should preferentially be used for LTBI-testing in BCG-vaccinated adult HIV-patients.

Metagenomic sequencing of the human gut microbiome before and after bariatric surgery in obese patients with type 2 diabetes: correlation with inflammatory and metabolic parameters

Roux-en-Y gastric bypass (RYGB) has become a prominent therapeutic option for long-term treatment of morbid obesity and type 2 diabetes mellitus (T2D). Cross talk and pathogenetic consequences of RYGB-induced profound effects on metabolism and gut microbiome are poorly understood. The aim of the present study therefore was to characterize intra-individual changes of gut microbial composition before and 3 months after RYGB by metagenomic sequencing in morbidly obese patients (body mass index (BMI)>40 kg m(-)(2)) with T2D. Subsequently, metagenomic data were correlated with clinical indices. Based on gene relative abundance profile, 1061 species, 729 genera, 44 phyla and 5127 KO (KEGG Orthology) were identified. Despite high diversity, bacteria could mostly be assigned to seven bacterial divisions. The overall metagenomic RYGB-induced shift was characterized by a reduction of Firmicutes and Bacteroidetes and an increase of Proteobacteria. Twenty-two microbial species and 11 genera were significantly altered by RYGB. Using principal component analysis, highly correlated species were assembled into two common components. Component 1 consisted of species that were mainly associated with BMI and C-reactive protein. This component was characterized by increased numbers of Proteobacterium Enterobacter cancerogenus and decreased Firmicutes Faecalibacterium prausnitzii and Coprococcus comes. Functional analysis of carbohydrate metabolism by KO revealed significant effects in 13 KOs assigned to phosphotransferase system. Spearmen's Rank correlation indicated an association of 10 species with plasma total- or low-density lipoprotein cholesterol, and 5 species with triglycerides. F. prausnitzii was directly correlated to fasting blood glucose. This is the first clinical demonstration of a profound and specific intra-individual modification of gut microbial composition by full metagenomic sequencing. A clear correlation exists of microbiome composition and gene function with an improvement in metabolic and inflammatory parameters. This will allow to develop new diagnostic and therapeutic strategies based on metagenomic sequencing of the human gut microbiome.