2,873 research outputs found

    Probing equilibrium glass flow up to exapoise viscosities

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    Glasses are out-of-equilibrium systems aging under the crystallization threat. During ordinary glass formation, the atomic diffusion slows down rendering its experimental investigation impractically long, to the extent that a timescale divergence is taken for granted by many. We circumvent here these limitations, taking advantage of a wide family of glasses rapidly obtained by physical vapor deposition directly into the solid state, endowed with different "ages" rivaling those reached by standard cooling and waiting for millennia. Isothermally probing the mechanical response of each of these glasses, we infer a correspondence with viscosity along the equilibrium line, up to exapoise values. We find a dependence of the elastic modulus on the glass age, which, traced back to temperature steepness index of the viscosity, tears down one of the cornerstones of several glass transition theories: the dynamical divergence. Critically, our results suggest that the conventional wisdom picture of a glass ceasing to flow at finite temperature could be wrong.Comment: 4 figures and 1 supplementary figur

    Engineering a static verification tool for GPU kernels

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    We report on practical experiences over the last 2.5 years related to the engineering of GPUVerify, a static verification tool for OpenCL and CUDA GPU kernels, plotting the progress of GPUVerify from a prototype to a fully functional and relatively efficient analysis tool. Our hope is that this experience report will serve the verification community by helping to inform future tooling efforts. © 2014 Springer International Publishing

    Wong-Zakai approximation of solutions to reflecting stochastic differential equations on domains in Euclidean spaces II

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    The strong convergence of Wong-Zakai approximations of the solution to the reflecting stochastic differential equations was studied in [2]. We continue the study and prove the strong convergence under weaker assumptions on the domain.Comment: To appear in "Stochastic Analysis and Applications 2014-In Honour of Terry Lyons", Springer Proceedings in Mathematics and Statistic

    Stiction, Adhesion Energy and the Casimir Effect in Micromechanical Systems

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    We measure the adhesion energy of gold using a micromachined doubly-clamped beam. The stress and stiffness of the beam are characterized by measuring the spectrum of mechanical vibrations and the deflection due to an external force. To determine the adhesion energy we induce stiction between the beam and a nearby surface by capillary forces. Subsequent analysis yields a value γ=0.06\gamma =0.06 J/m2^{2} that is a factor of approximately six smaller than predicted by idealized theory. This discrepancy may be resolved with revised models that include surface roughness and the effect of adsorbed monolayers intervening between the contacting surfaces in these mesoscopic structures.Comment: RevTex, 4 pages, 4 eps figure

    Biotic and Abiotic Drivers of Topsoil Organic Carbon Concentration in Drylands Have Similar Effects at Regional and Global Scales

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    Drylands contain 25% of the world’s soil organic carbon (SOC), which is controlled by many factors, both abiotic and biotic. Thus, understanding how these factors control SOC concentration can help to design more sustainable land-use practices in drylands aiming to foster and preserve SOC storage, something particularly important to fight ongoing global warming. We use two independent, largescale databases with contrasting geographic coverage (236 sites in global drylands and 185 sites in Patagonia, Argentina) to evaluate the relative importance of abiotic (precipitation, temperature and soil texture) and biotic (primary productivity) factors as drivers of SOC concentration in drylands at global and regional scales. We found that biotic and abiotic factors had similar effects on SOC concentration across regional and global scales: Maximum temperature and sand content had negative effects, while precipitation and plant productivity exerted positive effects. Our findings provide empirical evidence that increases in temperature and reductions in rainfall, as forecasted by climatic models in many drylands worldwide, promote declines in SOC both directly and indirectly via the reduction in plant productivity. This has important implications for the conservation of drylands under climate change; land management should seek to enhance plant productivity as a tool to offset the negative impact of climate change on SOC storage and on associated ecosystem services.Estación Experimental Agropecuaria BarilocheFil: Gaitan, Juan Jose. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Suelos; Argentina. Universidad Nacional de Luján. Departamento de Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Maestre, Fernando T. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; EspañaFil: Bran, Donaldo Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Buono, Gustavo Gabriel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Chubut; ArgentinaFil: Dougill, Andrew J. University of Leeds. School of Earth and Environment; Reino UnidoFil: Garcia Martinez, Guillermo Carlos. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Esquel; ArgentinaFil: Ferrante, Daniela. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; ArgentinaFil: Guuroh, Reginald Tang. CSIR-Forestry Research Institute of Ghana; GhanaFil: Linstadter, Anja. University of Cologne. Botanical Institute; AlemaniaFil: Massara Paletto, Virginia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Chubut; ArgentinaFil: Thomas, Andrew David. Aberystwyth University. Department of Geography and Earth Sciences; Reino UnidoFil: Oliva, Gabriel Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentin

    Ambiguous figures and the content of experience

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    Representationalism is the position that the phenomenal character of an experience is either identical with, or supervenes on, the content of that experience. Many representationalists hold that the relevant content of experience is nonconceptual. I propose a counterexample to this form of representationalism that arises from the phenomenon of Gestalt switching, which occurs when viewing ambiguous figures. First, I argue that one does not need to appeal to the conceptual content of experience or to judgements to account for Gestalt switching. I then argue that experiences of certain ambiguous figures are problematic because they have different phenomenal characters but that no difference in the nonconceptual content of these experiences can be identified. I consider three solutions to this problem that have been proposed by both philosophers and psychologists and conclude that none can account for all the ambiguous figures that pose the problem. I conclude that the onus is on representationalists to specify the relevant difference in content or to abandon their position

    Software Model Checking with Explicit Scheduler and Symbolic Threads

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    In many practical application domains, the software is organized into a set of threads, whose activation is exclusive and controlled by a cooperative scheduling policy: threads execute, without any interruption, until they either terminate or yield the control explicitly to the scheduler. The formal verification of such software poses significant challenges. On the one side, each thread may have infinite state space, and might call for abstraction. On the other side, the scheduling policy is often important for correctness, and an approach based on abstracting the scheduler may result in loss of precision and false positives. Unfortunately, the translation of the problem into a purely sequential software model checking problem turns out to be highly inefficient for the available technologies. We propose a software model checking technique that exploits the intrinsic structure of these programs. Each thread is translated into a separate sequential program and explored symbolically with lazy abstraction, while the overall verification is orchestrated by the direct execution of the scheduler. The approach is optimized by filtering the exploration of the scheduler with the integration of partial-order reduction. The technique, called ESST (Explicit Scheduler, Symbolic Threads) has been implemented and experimentally evaluated on a significant set of benchmarks. The results demonstrate that ESST technique is way more effective than software model checking applied to the sequentialized programs, and that partial-order reduction can lead to further performance improvements.Comment: 40 pages, 10 figures, accepted for publication in journal of logical methods in computer scienc

    Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej

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    We present extensive optical (UBVRIUBVRI, grizg'r'i'z', and open CCD) and near-infrared (ZYJHZYJH) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD 56496.9±0.356496.9\pm0.3. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive UBVRIJHKUBVRIJHK bolometric calibrations from UBVRIUBVRI and unfiltered measurements that potentially reach 2\% precision with a BVB-V color-dependent correction. We observe moderately strong Si II λ6355\lambda6355 as early as +8 days. The photospheric velocity (vphv_{\rm ph}) is determined by modeling the spectra in the vicinity of Fe II λ5169\lambda5169 whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives vph=4500±500v_{\rm ph} = 4500\pm500 km s1^{-1} at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be 9.00.6+0.49.0_{-0.6}^{+0.4} Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be 94±794\pm7 days long, yields an explosion energy of 0.9±0.3×10510.9\pm0.3\times10^{51} ergs, a final pre-explosion progenitor mass of 15.2±4.215.2\pm4.2~M_\odot and a radius of 250±70250\pm70~R_\odot. We observe a broken exponential profile beyond +120 days, with a break point at +183±16183\pm16 days. Measurements beyond this break time yield a 56^{56}Ni mass of 0.013±0.0010.013\pm0.001~M_\odot.Comment: 29 pages, 23 figures, 15 tables, Published in The Astrophisical Journa

    Enhanced inverse bremsstrahlung heating rates in a strong laser field

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    Test particle studies of electron scattering on ions, in an oscillatory electromagnetic field have shown that standard theoretical assumptions of small angle collisions and phase independent orbits are incorrect for electron trajectories with drift velocities smaller than quiver velocity amplitude. This leads to significant enhancement of the electron energy gain and the inverse bremsstrahlung heating rate in strong laser fields. Nonlinear processes such as Coulomb focusing and correlated collisions of electrons being brought back to the same ion by the oscillatory field are responsible for large angle, head-on scattering processes. The statistical importance of these trajectories has been examined for mono-energetic beam-like, Maxwellian and highly anisotropic electron distribution functions. A new scaling of the inverse bremsstrahlung heating rate with drift velocity and laser intensity is discussed.Comment: 12 pages, 12 figure

    Lung cancer surgery in octogenarians: a meta-analysis of predictors for postoperative complications

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    Background: Recently, several reports had focused on the feasibility of lung cancer surgery in octogenarians, describing encouraging short and long-term survival. However, the postoperative complication rate remains high. Some papers analyzed the role of potential predictors of post-operative complications, showing discordant results. We aimed at systematically assessing the evidence on risk factors for post-operative complications in octogenarians undergoing lung cancer surgery. Methods: Literature search was performed through PubMed and MEDLINE using the terms “lung cancer”, “non-small cell lung cancer” or “lung cancer surgery” combined with “octogenarian” or “80 years”. Last search was performed on 03/2021. Inclusion criteria were: clinical studies involving octogenarians undergoing lung cancer surgery between 1990 and 2020; studies explicitly appraising risk factors for postoperative complications and providing adjusted risk effect estimates. Studies that did not explicitly investigate predictors of postoperative complications and papers published in other language than English were not included. Risk of bias was assessed using the Quality in Prognostic Factor Studies (QUIPS) tool. More than 20 potential predictors were screened, finally limiting the inferential analysis to the six most frequently reported: performance status (PS), forced expiratory volume in 1 second (FEV1), type of resection, surgical approach, history of tobacco abuse and male gender. Adjusted P values from individual studies were pooled with the Fisher method. A pooled 2-tailed P value ≤0.05 was considered statistically significant. Results: A final set of 13 cohort studies, including 2,596 patients, was considered. Effect estimates were reported for PS by 6 studies (46%), for FEV1 by 10 (77%), for type of resection by 11 (85%), for surgical approach by 4 (31%), for history of tobacco abuse by 6 (46%), and for male gender by 8 (62%). After inferential analysis with the Fisher method, a significant association with post-operative complications was found for PS (P=0.004), major resections (P=0.002) and open approach (P=0.007); male gender showed only a borderline trend (P=0.053). Preoperative FEV1 (P=0.109) and history of tobacco abuse (P=0.399) were not associated with increased postoperative complications. Conclusions: Lung cancer surgery in octogenarian patients represent a viable and useful treatment. According to our analysis, patients should be carefully selected considering that a good preoperative PS is associated with a lower rate of postoperative complications. Similarly, thoracoscopic approach and sublobar resection should be preferred in octogenarian patients if technically and oncologically sound. Interestingly, impaired lung function was not significantly associated to post-operative complications
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