GPUs are very powerful computing accelerators that are often employed in single-device configuration. However, there is a steadily growing interest in using multiple GPUs in a concurrent way both to overcome the memory limitations of the single device and to further reduce execution times. Until recently, communication among GPUs had been carried out mainly by using networking technologies originally devised for standard CPUs with the CPU playing an active role in the communication. However, new alternatives start to be available in which a moderate number of GPUs are directly connected each other by means of proprietary technologies. We present the results of a set of experiments aimed at assessing the performance of some of these hardware/software platforms using a particularly challenging application as a benchmark. We release its source code to facilitate people interested in reproducing or extending our results.

Due to the limited field of view of the microscopes, acquisitions of macroscopic specimens require many parallel image stacks to cover the whole volume of interest. Overlapping regions are introduced among stacks in order to make it possible automatic alignment by means of a 3D stitching tool. Since state-of-the-art microscopes coupled with chemical clearing procedures can generate 3D images whose size exceeds the Terabyte, parallelization is required to keep stitching time within acceptable limits. In the present paper we discuss how multi-level parallelization reduces the execution times of TeraStitcher, a tool designed to deal with very large images. Two algorithms performing dataset partition for efficient parallelization in a transparent way are presented together with experimental results proving the effectiveness of the approach that achieves a speedup close to 300×, when both coarse- and fine-grained parallelism are exploited. Multi-level parallelization of TeraStitcher led to a significant reduction of processing times with no changes in the user interface, and with no additional effort required for the maintenance of code.

We present three case studies to illustrate a methodology for conducting forensics investigation on Microsoft Skype for Business. The proposed methodology helps to retrieve information on chat and audio communications made by any account who accessed the PC, to retrieve IP addresses and communication routes for all the participants of a call, and to retrieve forensics evidence to identify the end-user devices of a VoIP call by analyzing the CODECs exchanged by the clients during the SIP (Session Initiation Protocol) handshaking phase. This information may help the investigator either to corroborate or to contradict an investigative hypothesis.

This paper introduces a dominance test that allows to determine whether or not a financial institution can be classified as being more systemically important than another in a multivariate framework. The dominance test relies on a new risk measure, the NetCoVaR that is specifically tailored to capture the joint extreme co-movements between institutions belonging to a network. The asymptotic theory for the statistical test is provided under mild regularity conditions concerning the joint distribution of asset returns which is assumed to be elliptically contoured. The proposed risk measure and risk measurement framework is used to analyse the US financial system during the recent Global Financial Crises. In the empirical analysis, the returns are assumed to be Elliptically Stable distributed and the estimation is carried out through the Sparse Multivariate Method of Simulated Quantiles, handling both the lack of an analytic expression for the probability density function and the potential high-dimensionality of the problem.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 onboard the ENVISAT satellite. The analysis of MIPAS measurements allows to study the temporal evolution of numerous species of interest for the study of the ozone in the stratosphere, pollutants and many green-house gases. The objective of the MIPAS Quality Working Group is to improve the quality of the MIPAS products through a fruitful collaboration among spectroscopists, Level 1, Level 2, and validation teams. A large effort has recently led to implement significant improvements in both ESA Level 1 and Level 2 processors, as well as in spectroscopic database and in some absorption cross-sections in order to improve the quality of the products. In addition to the products already present in the V7 dataset (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset. In order to evaluate the impact of the changes in the products before full mission reprocessing, the analysis of the performances of the products of the modified L1 and L2 processors, as well as the auxiliary data, has been performed on a Diagnostic DataSet (DDS). The orbits of the DDS have been chosen in coincidence with correlative measurements for performing also a preliminary assessment of the accuracy of the products and to evaluate possible changes in the drift. With respect to V7 products, main improvements consist in a reduction of the temperature bias in the first part of the mission, a reduction of the discontinuities in CH4 and N2O time series due to daily gain upgrade, a better filtering of clouds and a better handling of horizontal inhomogeneities.The results of the assessment of the quality of MIPAS measurements will be shown, as well as the study of the temporal evolution and variability of all species. We will also investigate the spatial, seasonal, and interannual variations in the distribution of these species.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 on board the ENVISAT satellite. The fruitful collaboration among spectroscopists, Level 1, Level 2, and validation teams in the frame of the MIPAS Quality Working Group has recently led to the implementation of significant changes in both ESA Level 1 and Level 2 processors, as well as in the spectroscopic database and in some absorption cross-sections. In addition to the products already present in V7 dataset (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset.Among the new species, methyl chloride (CH3Cl) is of great interest in stratospheric ozone chemistry since it is the most abundant chlorine-containing gas in the troposphere and, in contrast to other relatively long-lived ozone-depleting gases, it has both natural and anthropogenic sources, with the known emission being mainly natural (tropical plants, biomass burning, the ocean, salt marshes and fungi). Since it is not controlled under the Montreal Protocol, its importance is expected to increase in the coming decades as emission controls alter the relative contributions from natural and anthropogenic halogen sources.In this paper we present a preliminary assessment of the quality of the MIPAS CH3Cl data, in terms of precision, accuracy and vertical resolution, and we investigate the spatial and seasonal variations in the distribution of CH3Cl in the upper troposphere/lower stratosphere (UTLS).

We examine the constraints on the Yukawa regime from the nonminimally coupled curvature-matter gravity theory arising from deep underwater ocean experiments. We consider the geophysical experiment of Zumberge et al. [Phys. Rev. Lett. 67, 3051 (1991)] for searching deviations of Newton's inverse square law in ocean. In the context of nonminimally coupled curvature-matter theory of gravity the results of Zumberge et al. can be used to obtain an upper bound both on the strength a and range lambda of the Yukawa potential arising from the nonrelativistic limit of the nonminimally coupled theory. The existence of an upper bound on lambda is related to the presence of an extra force, specific of the nonminimally coupled theory, which depends on lambda and on the gradient of mass density, and has an effect in the ocean because of compressibility of seawater. These results can be achieved after a suitable treatment of the conversion of pressure to depth in the ocean by resorting to the equation of state of seawater and taking into account the effect of the extra force on hydrostatic equilibrium. If the sole Yukawa interaction were present, the experiment would yield only a bound on alpha, while, in the presence of the extra force we find an upper bound on the range: lambda(max )= 57.4 km. In the interval 1 m < lambda < lambda(max) the upper bound on alpha is consistent with the constraint alpha < 0.002 found in [Phys. Rev. Lett. 67, 3051 (1991)].

This paper proposes improving the solve time of a bootstrap algebraic multigrid (AMG) designed previously by the authors. This is achieved by incorporating the information, a set of algebraically smooth vectors, generated by the bootstrap algorithm, in a single hierarchy by using sufficiently large aggregates, and these aggregates are compositions of aggregates already built throughout the bootstrap algorithm. The modified AMG method has good convergence properties and shows significant reduction in both memory and solve time. These savings with respect to the original bootstrap AMG are illustrated on some difficult (for standard AMG) linear systems arising from discretization of scalar and vector function elliptic partial differential equations in both 2D and 3D.

Molecular dynamics (MD) has become one of the most powerful tools of investigation in soft matter. Despite such success, simulations of large molecular environments are mostly run using the approximation of closed systems without the possibility of exchange of matter. Due to the molecular complexity of soft matter systems, an optimal simulation strategy would require the application of concurrent multiscale resolution approaches such that each part of a large system can be considered as an open subsystem at a high resolution embedded in a large coarser reservoir of energy and particles. This paper discusses the current capability and the future perspectives of multiscale adaptive resolution MD methods to satisfy the conceptual principles of open systems and to perform simulations of complex molecular environments in soft matter.

We explore the impact of geometrical corrugations on the near-wall flow properties of a soft material driven in a confined rough microchannel. By means of numerical simulations, we perform a quantitative analysis of the relation between the flow rate ? and the wall stress ?w for a number of setups, by changing both the roughness values as well as the roughness shape. Roughness suppresses the flow, with the existence of a characteristic value of ?w at which flow sets in. Just above the onset of flow, we quantitatively analyze the relation between ? and ?w. While for smooth walls a linear dependence is observed, steeper behaviours are found to set in by increasing wall roughness. The variation of the steepness, in turn, depends on the shape of the wall roughness, wherein gentle steepness changes are promoted by a variable space localization of the roughness.

Drug releasing capsules and droplets are largely used in biomedical applications. Such vehicles consist of a drug-loaded core surrounded by a thin semi-permeable layer. Diffusion is by far the dominant mechanism in drug delivery, beside other physico-chemical factors, such as osmosis, drug dissolution, polymer swelling and degradation. We upgrade existing mechanistic models by extending their applications to the composite structures, and characterize the kinetics of the drug eluted from the vehicle into the external targeted medium. We develop a theoretical and computational study aimed at modelling the drug release from a composite spherical core-shell capsule or a double emulsion having either a protective coating or a surfactant, under the assumption of radial symmetry. The problem of release from such a layer-by-layer composite systems is described by a system of coupled partial differential equations, which we solve analytically in terms of Fourier series or using numerical solutions. In addition to the conventional partitioning and interlayer conditions, we consider a finite mass transfer coefficient, to model the resistance at the surface. Expressions for the concentration and the cumulative mass in all layers are given to show the dependence and sensitivity to parameters, such as diffusivity, permeability and partition coefficients. The release curve characterizes the drug transport mechanism and suggests how to guarantee a controlled release. The proposed model constitutes a simple tool to predict the release from composite materials that, measuring their performance or comparing different configurations, can help in designing novel drug delivery systems.

The migration of endothelial cells (ECs) is critical for various processes including vascular wound healing, tumor angiogenesis, and the development of viable endovascular implants. EC migration is regulated by intracellular ATP and recent observations in our laboratory on ECs cultured on line patterns - surfaces where cellular adhesion is limited to 15 m-wide lines that physically confine the cells - have demonstrated very different migration behavior from cells on control unpatterned surfaces. Specifically, while ECs on unpatterned surfaces exhibit random motion in the absence of flow and persistent directed motion under flow, cells on line patterns both in the presence and absence of flow exhibit three distinct migration phenotypes: a) running- cells are polarized and migrate continuously and persistently on the adhesive lines with possible directional changes, b) undecided- cells are elongated and exhibit periodic changes in the direction of their polarization and minimal net migration, and c) tumbling-like - cells migrate persistently for a certain amount of time but then stop and round up for a few hours before spreading again and resuming migration. We hypothesize that the three migration phenotypes on patterns reflect differences in intracellular ATP profiles. Specifically, we propose that running ECs have sufficiently high ATP concentrations at all time in order to elongate, polarize, and migrate. In contrast, we suggest that undecided ECs have an intermediate level of ATP concentration that is sufficiently high for cell spreading but not for sustained polarization and migration. Finally, tumbling-like cells are thought to have low levels of intracellular ATP during the rounding-up phase but manage to "recharge their batteries" so that ATP levels recover sufficiently for the cells to eventually elongate, polarize, and migrate. To test this hypothesis, we have developed a mathematical model that describes the time evolution of intracellular ATP concentration. The computations provide the time dynamics of both EC length and intracellular ATP concentration. The results demonstrate that depending on the parameter values adopted for the simulations, the different hypothesized intracellular ATP profiles can indeed be obtained. Thus, for certain parameter values, we observe a rapid and sustained increase in ATP concentration, corresponding to the hypothesized behavior for running cells. For other parameter values, the ATP concentration remains within an intermediate range throughout, presumably reflecting undecided cells. Finally, for part of the parameter space, we obtain an initial drop in the concentration followed by recovery, as suggested for tumbling-like cells. The results are consistent with the notion that changes in intracellular ATP modulate the phenotype of EC migration on line patterns.

The migration of endothelial cells (ECs) is critical for various processes including vascular wound healing, tumor angiogenesis, and the development of viable endovascular implants. EC migration is regulated by intracellular ATP; thus, elucidating the dynamics of intracellular ATP concentration is important. Recent observations (time-lapse imaging over 12-hr periods) in our laboratory on ECs cultured on line patterns - surfaces where cellular adhesion is limited to 15 ?m-wide lines that physically confine the cells - have demonstrated very different migration behavior from cells on control unpatterned surfaces. Specifically, while ECs on unpatterned surfaces exhibit random motion in the absence of flow and persistent directed motion under flow, cells on line patterns both in the presence and absence of flow exhibit three distinct migration phenotypes (Fig. 1): a) running - cells are polarized and migrate continuously and persistently on the adhesive lines with possible directional changes, b) undecided - cells are elongated and exhibit periodic changes in the direction of their polarization and minimal net migration, and c) tumbling-like - cells migrate persistently for a certain amount of time but then stop and round up for a few hours before spreading again and resuming migration. We hypothesize that the three migration phenotypes on line patterns reflect differences in intracellular ATP profiles. Specifically, we propose that running ECs have sufficiently high ATP concentrations at all time in order to elongate, polarize, and migrate. In contrast, we suggest that undecided ECs have an intermediate level of ATP concentration that is sufficiently high for cell spreading but not for sustained polarization and migration. Finally, tumbling-like cells are thought to have low levels of intracellular ATP during the rounding-up phase but manage to "recharge their batteries" so that ATP levels recover sufficiently for the cells to eventually elongate, polarize, and migrate. To test this hypothesis, we have developed a mathematical model that describes the time evolution of intracellular ATP concentration.

We present a general mechanistic model of mass diffusion for a composite sphere placed in a large ambient medium. The multi-layer problem is described by a system of diffusion equations coupled via interlayer boundary conditions such as those imposing a finite mass resistance at the external surface of the sphere. While the work is applicable to the generic problem of heat or mass transfer in a multi-layer sphere, the analysis and results are presented in the context of drug kinetics for desorbing and absorbing spherical microcapsules. We derive an analytical solution for the concentration in the sphere and in the surrounding medium that avoids any artificial truncation at a finite distance. The closed-form solution in each concentric layer is expressed in terms of a suitably-defined inverse Laplace transform that can be evaluated numerically. Concentration profiles and drug mass curves in the spherical layers and in the external environment are presented and the dependency of the solution on the mass transfer coefficient at the surface of the sphere analyzed.

In this paper, we consider a multi-layer diffusion model of drug release from a composite spherical microcapsule into an external surrounding medium. Based on this model, we present two approaches for estimating the release time, i.e. the time required for the drug-filled capsule to be depleted. Both approaches make use of temporal moments of the drug concentration at the centre of the capsule, which provide useful insight into the timescale of the process and can be computed exactly without explicit calculation of the full transient solution of the multi-layer diffusion model. The first approach, which uses the zeroth and first temporal moments only, provides a crude approximation of the release time taking the form of a simple algebraic expression involving the various parameters in the model (e.g. layer diffusivities, mass transfer coefficients, partition coefficients) while the second approach yields an asymptotic estimate of the release time that depends on consecutive higher moments. Through several test cases, we show that both approaches provide a computationally- cheap and useful tool to quantify the release time of composite microcapsule configurations.

Nel documento si fornisce una caratterizzazione costruttiva dei Path Graph alternativa a quella già nota e data mediante famiglie di sottografi proibiti.

The Wigner rotations arising from the combination of boosts along two different directions arc rederived from a relative boost point of view and applied to study gyroscope spin precession along timelike geodesics in a Kerr spacetime. First this helps to clarify the geometrical properties of Marck's recipe for reducing the equations of parallel transport along such world lines expressed in terms of the constants of the motion to a single differential equation for the essential planar rotation. Second this shows how to bypass Marck's reduction procedure by direct boosting of orthonormal frames associated with natural observer families. Wigner rotations mediate the relationship between these two descriptions for reaching the same parallel transported frame along a geodesic. The comparison is particularly straightforward in the case of equatorial plane motion of a test gyroscope, where Marck's scalar angular velocity captures the essential cumulative spin precession relative to the spherical frame locked to spatial infinity. These cumulative precession effects are computed explicitly for both bound and unbound equatorial plane geodesic orbits. The latter case is of special interest in view of recent applications to the dynamics of a two-body system with spin. Our results are consistent with the point-particle limit of such two-body results and also pave the way for similar computations in the context of gravitational self-force.

The energy content of cylindrical gravitational wave spacetimes is analyzed by considering two local descriptions of energy associated with the gravitational field, namely those based on the C-energy and the Bel-Robinson super-energy tensor. A Poynting-Robertson-like effect on the motion of massive test particles, beyond the geodesic approximation, is discussed, allowing them to interact with the background field through an external force which accounts for the exchange of energy and momentum between particles and waves. In addition, the relative strains exerted on a bunch of particles displaced orthogonally to the direction of propagation of the wave are examined, providing invariant information on spacetime curvature effects caused by the passage of the wave. The explicit examples of monochromatic waves with either a single or two polarization states as well as pulses of gravitational radiation are discussed.