Mechanism of thermally activated c-axis dissipation in layered High-Tc_c superconductors at high fields

We propose a simple model which explains experimental behavior of $c$-axis resistivity in layered High-T$_c$ superconductors at high fields in a limited temperature range. It is generally accepted that the in-plane dissipation at low temperatures is caused by small concentration of mobile pancake vortices whose diffusive motion is thermally activated. We demonstrate that in such situation a finite conductivity appears also in $c$-direction due to the phase slips between the planes caused by the mobile pancakes. The model gives universal relation between the components of conductivity which is in good agreement with experimental data.Comment: RevTeX, 4 pages, 2 Postscript figure

The European Network for Translational Research in Atrial Fibrillation (EUTRAF): objectives and initial results.

Atrial fibrillation (AF) is the most common sustained arrhythmia in the general population. As an age-related arrhythmia AF is becoming a huge socio-economic burden for European healthcare systems. Despite significant progress in our understanding of the pathophysiology of AF, therapeutic strategies for AF have not changed substantially and the major challenges in the management of AF are still unmet. This lack of progress may be related to the multifactorial pathogenesis of atrial remodelling and AF that hampers the identification of causative pathophysiological alterations in individual patients. Also, again new mechanisms have been identified and the relative contribution of these mechanisms still has to be established. In November 2010, the European Union launched the large collaborative project EUTRAF (European Network of Translational Research in Atrial Fibrillation) to address these challenges. The main aims of EUTRAF are to study the main mechanisms of initiation and perpetuation of AF, to identify the molecular alterations underlying atrial remodelling, to develop markers allowing to monitor this processes, and suggest strategies to treat AF based on insights in newly defined disease mechanisms. This article reports on the objectives, the structure, and initial results of this network

Increased Ventricular Premature Contraction Frequency During REM Sleep in Patients with Coronary Artery Disease and Obstructive Sleep Apnea

Background Patients with obstructive sleep apnea are reported to have a peak of sudden cardiac death at night, in contrast to patients without apnea whose peak is in the morning. We hypothesized that ventricular premature contraction (VPC) frequency would correlate with measures of apnea and sympathetic activity.Methods Electrocardiograms from a sleep study of 125 patients with coronary artery disease were evaluated. Patients were categorized by apnea-hypopnea index (AHI) into Moderate (AHI <15) or Severe (AHI>15) apnea groups. Sleep stages studied were Wake, S1, S2, S34, and rapid eye movement (REM). Parameters of a potent autonomically-based risk predictor for sudden cardiac death called heart rate turbulence were calculated.Results There were 74 Moderate and 51 Severe obstructive sleep apnea patients. VPC frequency was affected significantly by sleep stage (Wake, S2 and REM, F=5.8, p<.005) and by AHI (F=8.7, p<.005). In Severe apnea patients, VPC frequency was higher in REM than in Wake (p=.011). In contrast, patients with Moderate apnea had fewer VPCs and exhibited no sleep stage dependence (p=.19). Oxygen desaturation duration per apnea episode correlated positively with AHI (r2=.71, p<.0001), and was longer in REM than in non-REM (p<.0001). The heart rate turbulence parameter TS correlated negatively with oxygen desaturation duration in REM (r2=.06, p=.014).Conclusions Higher VPC frequency coupled with higher sympathetic activity caused by longer apnea episodes in REM sleep may be one reason for increased nocturnal death in apneic patients

Non-instantaneous polarization dynamics in dielectric media

Third-order optical nonlinearities play a vital role for generation1,2 and characterization 3-5 of some of the shortest optical pulses to date, for optical switching applications6,7, and for spectroscopy8,9. In many cases, nonlinear optical effects are used far off resonance, and then an instantaneous temporal response is expected. Here, we show for the first time resonant frequency-resolved optical gating measurements1012 that indicate substantial nonlinear polarization relaxation times up to 6.5 fs in dielectric media, i.e., significantly beyond the shortest pulses directly available from commercial lasers. These effects are among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrödinger equation13,14 are in excellent agreement with experimental observations. The simulations indicate that pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect. Moreover, our approach opens an avenue for application of frequency-resolved optical gating as a highly selective spectroscopic probe in high-field physics

Penetration of Josephson vortices and measurement of the c-axis penetration depth in Bi2Sr2CaCu2O8+δBi_{2}Sr_{2}CaCu_{2}O_{8+\delta}: Interplay of Josephson coupling, surface barrier and defects

The first penetration field H_{J}(T) of Josephson vortices is measured through the onset of microwave absorption in the locked state, in slightly overdoped $\rm{Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}}$ single crystals (T_{c} ~ 84 K). The magnitude of H_{J}(T) is too large to be accounted for by the first thermodynamic critical field H_{c1}(T). We discuss the possibility of a Bean-Livingston barrier, also supported by irreversible behavior upon flux exit, and the role of defects, which relates H_{J}(T) to the c-axis penetration depth $\lambda_{c}(T)$. The temperature dependence of the latter, determined by a cavity perturbation technique and a theoretical estimate of the defect-limited penetration field are used to deduce from H_{J}(T) the absolute value of $\lambda_{c}(0)=(35 \pm 15) \mu m$.Comment: 9 pages, 6 figure

Efficacy of Chondroprotective Food Supplements Based on Collagen Hydrolysate and Compounds Isolated from Marine Organisms †

Osteoarthritis belongs to the most common joint diseases in humans and animals and shows increased incidence in older patients. The bioactivities of collagen hydrolysates, sulfated glucosamine and a special fatty acid enriched dog-food were tested in a dog patient study of 52 dogs as potential therapeutic treatment options in early osteoarthritis. Biophysical, biochemical, cell biological and molecular modeling methods support that these well-defined substances may act as effective nutraceuticals. Importantly, the applied collagen hydrolysates as well as sulfated glucosamine residues from marine organisms were strongly supported by both an animal model and molecular modeling of intermolecular interactions. Molecular modeling of predicted interaction dynamics was evaluated for the receptor proteins MMP-3 and ADAMTS-5. These proteins play a prominent role in the maintenance of cartilage health as well as innate and adapted immunity. Nutraceutical data were generated in a veterinary clinical study focusing on mobility and agility. Specifically, key clinical parameter (MMP-3 and TIMP-1) were obtained from blood probes of German shepherd dogs with early osteoarthritis symptoms fed with collagen hydrolysates. Collagen hydrolysate, a chondroprotective food supplement was examined by high resolution NMR experiments. Molecular modeling simulations were used to further characterize the interaction potency of collagen fragments and glucosamines with protein receptor structures. Potential beneficial effects of collagen hydrolysates, sulfated glycans (i.e., sulfated glucosamine from crabs and mussels) and lipids, especially, eicosapentaenoic acid (extracted from fish oil) on biochemical and physiological processes are discussed here in the context of human and veterinary medicine

220 fs Er-Yb:glass laser mode-locked by a broadband low-loss Si/Ge saturable absorber

We demonstrate femtosecond performance of an ultra-broadband high-index-contrast saturable Bragg reflector consisting of a silicon/silicon-dioxide/germanium structure that is fully compatible with CMOS processing. This device offers a reflectivity bandwidth of over 700 nm and sub-picosecond recovery time of the saturable loss. It is used to achieve mode-locking of an Er-Yb:glass laser centered at 1540 nm, generating 220 fs pulses, with the broadest output spectrum to date

Synchronous Symmetry Breaking in Neurons with Different Neurite Counts

As neurons develop, several immature processes (i.e., neurites) grow out of the cell body. Over time, each neuron breaks symmetry when only one of its neurites grows much longer than the rest, becoming an axon. This symmetry breaking is an important step in neurodevelopment, and aberrant symmetry breaking is associated with several neuropsychiatric diseases, including schizophrenia and autism. However, the effects of neurite count in neuronal symmetry breaking have never been studied. Existing models for neuronal polarization disagree: some predict that neurons with more neurites polarize up to several days later than neurons with fewer neurites, while others predict that neurons with different neurite counts polarize synchronously. We experimentally find that neurons with different neurite counts polarize synchronously. We also show that despite the significant differences among the previously proposed models, they all agree with our experimental findings when the expression levels of the proteins responsible for symmetry breaking increase with neurite count. Consistent with these results, we observe that the expression levels of two of these proteins, HRas and shootin1, significantly correlate with neurite count. This coordinated symmetry breaking we observed among neurons with different neurite counts may be important for synchronized polarization of neurons in developing organisms