Potential energy landscape equation of state

Depth, number, and shape of the basins of the potential energy landscape are the key ingredients of the inherent structure thermodynamic formalism introduced by Stillinger and Weber [F. H. Stillinger and T. A. Weber, Phys. Rev. A 25, 978 (1982)]. Within this formalism, an equation of state based only on the volume dependence of these landscape properties is derived. Vibrational and configurational contributions to pressure are sorted out in a transparent way. Predictions are successfully compared with data from extensive molecular dynamics simulations of a simple model for the fragile liquid orthoterphenyl.     

Testing the hypothesis of absence of unobserved confounding in semiparametric bivariate probit models

Lagrange multiplier and Wald tests for the hypothesis of absence of unobserved confounding are extended to the context of semiparametric recursive and sample selection bivariate probit models. The finite sample size properties of the tests are examined through a Monte Carlo study using several scenarios: correct model specification, distributional and functional misspecification, with and without an exclusion restriction. The simulation results provide some guidelines which may be important for empirical analysis. The tests are illustrated using two datasets in which the issue of unobserved confounding arises.     

Functional analysis of integral transport equations in linear rarefied gas dynamics

Summary A study is proposed on the functional properties of the solutions of an interesting class of linear integral equations governing linear problems in rarefied gas dynamics. The analysis is carried out through a systematic study of the integral operator generated by the kernel of the equations themselves.

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Sommario In questa nota vengono studiate le proprietà funzionali di alcune equazioni integrali lineari che regolano problemi basilari della dinamica dei gas rarefatti. Gli operatori integrali, relativi alle operazioni stesse, sono analizzati in dettaglio.

     

Shock Wave Structure of Multi-Temperature Euler Equations from Kinetic Theory for a Binary Mixture

A multi-temperature hydrodynamic limit of kinetic equations is employed for the analysis of the steady shock problem in a binary mixture. Numerical results for varying parameters indicate possible occurrence of either smooth profiles or of weak solutions with one or two discontinuities.     

The vibrational density of states of a disordered gel model

We investigate the vibrational density of states (vDOS) in harmonic approximation of a binary mixture of colloidal patchy particles with two and three patches for different relative compositions x(2). At low temperature, this system forms a thermo-reversible gel, i.e., a fully bonded network of chains of two-patches particles, in which the branching points are provided by three-patches particles. For all the compositions, we find in the vDOS a pronounced peak at low frequency whose height grows on increasing the fraction of two-functional particles or equivalently with the average length of the chains. To identify the various spectral features, we compare the vDOS of the whole system with the one of small representative structures of the network and with the vDOS of a long linear chain of two-patches particles and we find that these structures are indeed able to rationalize the various peaks in the vDOS of the full system. At large x(2) the vDOSs of the gel and of the long chain show remarkable similarities. Analyzing the dispersion relations and the spectrum of the linear chain we show that the excess of low frequency modes, the analog of the boson peak in glassy disordered systems, arises from the strong coupling between rotations and translations.     

Characterization of silver sulfadiazine-loaded solid lipid nanoparticles by thermal analysis

The aim of this study is the solid-state characterization of solid lipid nanoparticles (SLN) based on Compritol^® 888 (C888) and Lutrol^® F68 (F68), loaded with silver sulfadiazine (AgSD), used to develop sponge-like dressings to treat chronic skin ulcers such as decubitis and leg ulcers. Silver compounds like AgSD, in fact, are used to prevent and/or to treat wound colonization that could impair healing, also in the case of antibiotic-resistant bacteria. Thermal analysis, with support from powder X-ray diffractometry and Fourier transform infrared spectroscopy, is used to characterize lipid and drug bulk, unloaded and drug-loaded SLN. In particular, differential scanning calorimetry is used to investigate the degree of crystallinity and the solid-state modification of lipid, two parameters correlated to drug incorporation and drug release rates. The solid-state characterization demonstrates AgSD entrapment in C888 as a core enclosed into F68 shell. AgSD SLN are also stored at different temperatures 25 and 37 °C, respectively, to study the effect of storage conditions, that induce an increase of the lipid crystallinity index correlated to drug release from the lipid matrix.     

Multiwell cartridge with integrated array of amorphous silicon photosensors for chemiluminescence detection: development,characterization and comparison with cooled-CCD luminograph

We propose a disposable multiwell microcartridge with integrated amorphous silicon photosensors array for bio- and chemiluminescence-based bioassays, where the enzymatic reactions and the detection unit are coupled on the same glass substrate. Each well, made in a polydimethylsiloxane (PDMS) unit, hosts an enzymatic reaction that is monitored by one photosensor of the array. Photosensors were characterized in terms of their dark current background noise and response to different wavelengths of visible light in order to determine their suitability as detection devices for chemical luminescent phenomena. Calibration curves of the photosensors’ response to different luminescent systems were then evaluated by using the chemiluminescent reactions catalyzed by alkaline phosphatase and horseradish peroxidase and the bioluminescent reaction catalyzed by firefly luciferase. Limits of detection in the order of attomoles for chemiluminescence enzymes and femtomoles for luciferase and sensitivities in the range between 0.007 and 0.1 pA pmol^?1 L were reached. We found that, without the need of cooling systems, the analytical performances of the proposed cartridge are comparable with those achievable with state-of-the-art thermoelectrically cooled charge-coupled device-based laboratory instrumentation. In addition, thanks to the small amount of generated output data, the proposed device allows the monitoring of long-lasting reactions with significant advantages in terms of data-storage needs, transmission bandwidth, ease of real-time signal processing and limited power consumption. Based on these results, the operation in model bioanalytical assays exploiting luminescent reactions was tested demonstrating that a-Si:H photosensors arrays, when integrated with PDMS microfluidic units, provide compact, sensitive and potentially low-cost microdevices for chemiluminescence and bioluminescence-based bioassays with a wide range of possible applications for in-field and point-of-care bio-analyses.     

DNA closed nanostructures: a structural and Monte Carlo simulation study

DNA nanoconstructs are obtained in solution by using six unique 42-mer DNA oligonucleotides, whose sequences have been designed to form a pseudohexagonal structure. The required flexibility is provided by the insertion of two non-base-paired thymines in the middle of each sequence that work as flexible hinges and constitute the corners of the nanostructure when formed. We show that hexagonally shaped nanostructures of about 7 nm diameter and their corresponding linear open constructs are formed by self-assembly of the specifically designed linear oligonucleotides. The structural and dynamical characterization of the nanostructure is obtained in situ for the first time by using dynamic light scattering (DLS), a noninvasive method that provides a fast dynamic and structural analysis and allows the characterization of the different synthetic DNA nanoconstructs in solution. A validation of the LS results is obtained through Monte Carlo (MC) simulations and atomic force microscopy (AFM). In particular, a mesoscale molecular model for DNA, developed by Knotts et al., is exploited to perform MC simulations and to obtain information about the conformations as well as the conformational flexibilities of these nanostructures, while AFM provides a very detailed particle analysis that yields an estimation of the particle size and size distribution. The structural features obtained by MC and AFM are in good agreement with DLS, showing that DLS is a fast and reliable tool for characterization of DNA nanostructures in solution.