6,345 research outputs found
Quantum Fluctuations Driven Orientational Disordering: A Finite-Size Scaling Study
The orientational ordering transition is investigated in the quantum
generalization of the anisotropic-planar-rotor model in the low temperature
regime. The phase diagram of the model is first analyzed within the mean-field
approximation. This predicts at a phase transition from the ordered to
the disordered state when the strength of quantum fluctuations, characterized
by the rotational constant , exceeds a critical value . As a function of temperature, mean-field theory predicts a range of
values of where the system develops long-range order upon cooling, but
enters again into a disordered state at sufficiently low temperatures
(reentrance). The model is further studied by means of path integral Monte
Carlo simulations in combination with finite-size scaling techniques,
concentrating on the region of parameter space where reentrance is predicted to
occur. The phase diagram determined from the simulations does not seem to
exhibit reentrant behavior; at intermediate temperatures a pronounced increase
of short-range order is observed rather than a genuine long-range order.Comment: 27 pages, 8 figures, RevTe
A review of High Performance Computing foundations for scientists
The increase of existing computational capabilities has made simulation
emerge as a third discipline of Science, lying midway between experimental and
purely theoretical branches [1, 2]. Simulation enables the evaluation of
quantities which otherwise would not be accessible, helps to improve
experiments and provides new insights on systems which are analysed [3-6].
Knowing the fundamentals of computation can be very useful for scientists, for
it can help them to improve the performance of their theoretical models and
simulations. This review includes some technical essentials that can be useful
to this end, and it is devised as a complement for researchers whose education
is focused on scientific issues and not on technological respects. In this
document we attempt to discuss the fundamentals of High Performance Computing
(HPC) [7] in a way which is easy to understand without much previous
background. We sketch the way standard computers and supercomputers work, as
well as discuss distributed computing and discuss essential aspects to take
into account when running scientific calculations in computers.Comment: 33 page
International consensus (ICON) on treatment of sudden sensorineural hearing loss
© 2018 Elsevier Masson SAS Sudden sensorineural hearing loss (SSNHL) is a common and alarming symptom that often prompts an urgent visit to an ENT specialist. Treatment of SSNHL remains one of the most problematic issues for contemporary otorhinolaryngology: although many meta-analyses and national guidelines have been issued, management is not standardized in terms of medical treatment, and duration and route of administration. We present several methodological suggestions for the study of treatments for SSNHL. These were developed from the existing level of evidence of the main treatments used in SSNHL by experts who convened at the IFOS 2017 ENT World Congress in Paris, France. All panelists agreed that one of the main limitations present in studies on SSNHL is related to the wide heterogeneity, which characterizes both the initial hearing deficit and the amount of hearing recovery. Although evidence of the efficacy of systemic steroids cannot be considered as strong enough to recommend their use, it is still the most widespread primary therapy and can be considered as the current standard of care. Therefore, systemic steroids stand as an adequate control for any innovative treatment. To reduce the number of subjects we suggest that the inclusion criteria should be restricted to moderate to profound levels of hearing loss. The efficacy of trans-tympanic steroids as a salvage therapy was suggested in several reports on small populations and needs to be confirmed with larger randomized controlled trials
Pattern formation driven by nematic ordering of assembling biopolymers
The biopolymers actin and microtubules are often in an ongoing
assembling/disassembling state far from thermal equilibrium. Above a critical
density this leads to spatially periodic patterns, as shown by a scaling
argument and in terms of a phenomenological continuum model, that meets also
Onsager's statistical theory of the nematic--to--isotropic transition in the
absence of reaction kinetics.
This pattern forming process depends much on nonlinear effects and a common
linear stability analysis of the isotropic distribution of the filaments is
often misleading. The wave number of the pattern decreases with the
assembling/disassembling rate and there is an uncommon discontinuous transition
between the nematic and the periodic state.Comment: 4 pages, 3 figure
770-5 Chamber Specific Regulation of the Sarcoplasmic Reticulum Calcium ATPase Pump In Human Heart Failure
Alterations in the expression of Ca2+ channels have been described in failing human left ventricle, including down regulation of the ryanodine receptor (RyR)/Ca2+ release channel and the sarcoplasmic reticulum Ca2+ ATPase pump (SERCA) which are involved in excitation-contraction coupling and relaxation (Cir Res 71: 18, 1992). We previously reported chamber specific regulation of the RyR during end-stage human heart failure (Clin Res 42(2):166A. 1994). We investigated whether SERCA is also regulated in the other cardiac chambers during human heart failure. Total RNA and protein homogenates were isolated from the left and right atria (LA, RA) and left and right ventricles (LV, RV) obtained prospectively from 32 cardiac transplant patients and 4 normal controls. Messenger RNA (mRNA) levels of SERCA were quantified using Northern and slot blot hybridizations with a 1.6kb rat cardiac SERCA cDNA probe and normalized to 28S ribosomal levels. Protein levels of SERCA were quantified using enzyme-linked immunosorbent assays with monoclonal antibodies directed against dog cardiac SERCA. Northern analyses detected a single ≈4 kb mRNA in all regions. Compared to controls. SERCA mRNA expression in failing hearts was decreased in LV by 39% (p<0.005), unchanged in RV, and increased in LA by 255% (p<0.005) and in RA by 338% (p<0.025). Consistent with the mRNA data. immunodetectable levels of SERCA were also reduced in LV by 30% (p<0.05) and unchanged in RV; however, protein levels appeared unchanged or reduced in both atria in contrast to the mRNA. This is the first study reporting simultaneous measurements of SERCA mRNA and protein levels in the human heart. We conclude that chamber specific regulation of SERCA mRNA occurs during end-stage heart failure. corroborated by protein expression in the ventricles. Down regulations of SERCA may contribute to impaired relaxation and increased diastolic tone during heart failure
Broadband Geodesic Pulses for Three Spin Systems: Time-Optimal Realization of Effective Trilinear Coupling Terms and Indirect SWAP Gates
Broadband implementations of time-optimal geodesic pulse elements are
introduced for the efficient creation of effective trilinear coupling terms for
spin systems consisting of three weakly coupled spins 1/2. Based on these pulse
elements, the time-optimal implementation of indirect SWAP operations is
demonstrated experimentally. The duration of indirect SWAP gates based on
broadband geodesic sequence is reduced by 42.3% compared to conventional
approaches.Comment: 22 pages, incl. 8 figure
Late left ventricular dysfunction after anatomic repair of congenitally corrected transposition of the great arteries
ObjectiveEarly results for anatomic repair of congenitally corrected transposition of the great arteries (ccTGA) are excellent. However, the development of left ventricular dysfunction late after repair remains a concern. In this study we sought to determine factors leading to late left ventricular dysfunction and the impact of cardiac resynchronization as a primary and secondary (upgrade) mode of pacing.MethodsFrom 1992 to 2012, 106 patients (median age at surgery, 1.2 years; range, 2 months to 43 years) with ccTGA had anatomic repair. A retrospective review of preoperative variables, surgical procedures, and postoperative outcomes was performed.ResultsIn-hospital deaths occurred in 5.7% (n = 6), and there were 3 postdischarge deaths during a mean follow-up period of 5.2 years (range, 7 days to 18.2 years). Twelve patients (12%) developed moderate or severe left ventricular dysfunction. Thirty-eight patients (38%) were being paced at latest follow-up evaluation. Seventeen patients had resynchronization therapy, 9 as an upgrade from a prior dual-chamber system (8.5%) and 8 as a primary pacemaker (7.5%). Factors associated with left ventricular dysfunction were age at repair older than 10 years, weight greater than 20 kg, pacemaker implantation, and severe neo-aortic regurgitation. Eight of 9 patients undergoing secondary cardiac resynchronization therapy (upgrade) improved left ventricular function. None of the 8 patients undergoing primary resynchronization developed left ventricular dysfunction.ConclusionsLate left ventricular dysfunction after anatomic repair of ccTGA is not uncommon, occurring most often in older patients and in those requiring pacing. Early anatomic repair and cardiac resynchronization therapy in patients requiring a pacemaker could preclude the development of left ventricular dysfunction
Valve-sparing aortic root replacement and remodeling with complex aortic valve reconstruction in children and young adults with moderate or severe aortic regurgitation
ObjectivesThe durability of valve-sparing aortic root procedures with aortic regurgitation due to leaflet disease is questioned. Here, we review our experience in combined aortic root and valve reconstruction in children and young adults.MethodsAll valve-sparing aortic root procedures from 2000 to 2012 were reviewed, and patients with aortic valve repair beyond resuspension were included. Root procedures were classified as replacement with reimplantation, root remodeling, or aortic annular and sinotubular junction stabilization. The primary end point was structural valve deterioration, a composite of aortic valve reoperation and/or moderate or greater regurgitation at follow-up.ResultsThirty-four patients were included during the study period. The surgery consisted of reimplantation in 13 patients, remodeling in 16 patients, and annular and sinotubular junction stabilization in 5 patients. Valve repair consisted of leaflet procedures in 26 patients and subannular reduction in 15 patients. During a median follow-up of 4.2 months (range, 2 weeks-8 years), there were 5 reoperations for aortic valve replacement due to aortic regurgitation, and 2 patients presented with moderate or greater regurgitation. Freedom from structural valve deterioration was 70.1% ± 10.3% at 1 year and remained stable thereafter, although it was significantly worse in the reimplantation group (P = .039). A more severe degree of preoperative aortic regurgitation (P = .001) and smaller graft to aortic annulus ratio (P = .003) were predictors of structural valve deterioration.ConclusionsValve-sparing root and valve reconstruction can be done with low operative risk and allows valve preservation in most patients. These data should question the assumption that reimplantation is superior when associated with complex valve reconstruction
Observation of Bound Surface States in Grain Boundary Junctions of High Temperature Superconductors
We have performed a detailed study of the tunneling spectra of bicrystal
grain boundary junctions (GBJs) fabricated from the HTS YBCO, BSCCO, LSCO, and
NCCO. In all experiments the tunneling direction was along the CuO planes. With
the exception of NCCO, for all materials a pronounced zero bias conductance
peak was observed which decreases with increasing temperature and disappears at
the critical temperature. These results can be explained by the presence of a
dominating d-wave symmetry of the order parameter resulting in the formation of
zero energy Andreev bound states at surfaces and interfaces of HTS. The absence
of a ZBCP for NCCO is consistent with a dominating s-wave symmetry of the pair
potential in this material. The observed nonlinear shift of spectral weight to
finite energies by applying a magnetic field is in qualitative agreement with
recent theoretical predictions.Comment: 4 pages, 4 figures, to be published in Phys. Rev.
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