Continuum description of finite-size particles advected by external flows. The effect of collisions

The equation of the density field of an assembly of macroscopic particles advected by a hydrodynamic flow is derived from the microscopic description of the system. This equation allows to recognize the role and the relative importance of the different microscopic processes implicit in the model: the driving of the external flow, the inertia of the particles, and the collisions among them. The validity of the density description is confirmed by comparisons of numerical studies of the continuum equation with Direct Simulation Monte Carlo (DSMC) simulations of hard disks advected by a chaotic flow. We show that the collisions have two competing roles: a dispersing-like effect and a clustering effect (even for elastic collisions). An unexpected feature is also observed in the system: the presence of collisions can reverse the effect of inertia, so that grains with lower inertia are more clusterized.Comment: Final (strongly modified) version accepted in PRE; 6 pages, 3 figure

Trehalose counteracts the dissociation of tetrameric rabbit lactate dehydrogenase induced by acidic pH conditions

The lactate dehydrogenase from rabbit skeletal muscle (rbLDH) is a tetrameric enzyme, known to undergo dissociation when exposed to acidic pH conditions. Moreover, it should be mentioned that this dissociation translates into a pronounced loss of enzyme activity. Notably, among the compounds able to stabilize proteins and enzymes, the disaccharide trehalose represents an outperformer. In particular, trehalose was shown to efficiently counteract quite a number of physical and chemical agents inducing protein denaturation. However, no information is available on the effect, if any, exerted by trehalose against the dissociation of protein oligomers. Accordingly, we thought it of interest to investigate whether this disaccharide is competent in preventing the dissociation of rbLDH induced by acidic pH conditions. Further, we compared the action of trehalose with the effects triggered by maltose and cellobiose. Surprisingly, both these disaccharides enhanced the dissociation of rbLDH, with maltose being responsible for a major effect when compared to cellobiose. On the contrary, trehalose was effective in preventing enzyme dissociation, as revealed by activity assays and by Dynamic Light Scattering (DLS) experiments. Moreover, we detected a significant decrease of both K0.5 and Vmax when the rbLDH activity was tested (at pH 7.5 and 6.5) as a function of pyruvate concentration in the presence of trehalose. Further, we found that trehalose induces a remarkable increase of Vmax when the enzyme is exposed to pH 5. Overall, our observations suggest that trehalose triggers conformational rearrangements of tetrameric rbLDH mirrored by resistance to dissociation and peculiar catalytic features

Application of differential SAR interferometry for studying eruptive event of 22July 1998 at Mt.Etna

One of the main objectives of the project “Development and application of remote sensing methods for the monitoring of active Italian volcanoes” is directed to an operational use of differential interferometry as a tool for volcano monitoring. A first step to achieve this goal is to test commercial software in order to evaluate the most suitable for the project purposes. For testing software, SAR images collected by ERS2 from May 98 to August 98, before and after the strong eruptive event occurred on 22 July 98 at Voragine crater of Etna, have been selected. The explosive event was classified sub-plinian producing a 12 km high eruptive column and lapilli fell on land as far as 70 km south-eastward along the dispersal axis. Pre, post and across event image pairs have been processed. In particular the pair 13 May 98-22 July 98, 22 July 98-26 August 98, 13 May 98-26 August 98 are used for testing respectively pre, post and across event. In first analysis, the fringes in the differential products show a positive elevation trend in the summit area of the volcano. In particular, an increased of about 1,5 fringes in the period pre-event, and a decrement of 1 fringe in the period post-event is observed. This result is agreement whit field of deformation expected in such kind of event, confirming that the interferometric processing tool used id suitable for the purpose of the project

Effects of mole fraction variations and scaling on total variability in InGaAs MOSFETs

Variability is one of the major roadblocks for III-V semiconductors in nanoscale devices, according to the recent International Roadmap for Devices and Systems (IRDS). A particular concern is the detrimental effect of variability of threshold voltage due to channel compositional variations. In this paper, we investigate the impact of this variability source and the effects of scaling on the performance of Dual-Gate-Ultra-Thin-Body (DG-UTB) In0.53Ga0.47As MOSFETs. We model mole fraction variations in terms of the Indium content by taking into account the spatial inhomogeneity of the channel and the corresponding bandgap variations, analyzing the effects on threshold voltage variability. We thus define a variability source, i.e., Band Gap Fluctuation (BGF), and we compare the associated variability with the ones from other important sources, namely, Random Dopant Fluctuation (RDF), Work Function Fluctuation (WFF), Body- and Gate-Line Edge Roughness (B-LER and G-LER). We then define three corner cases for mole fraction variations to determine worst-case variability. Finally, the impact of scaling on variability is assessed by comparing results for two technology nodes on the linear and saturation threshold voltage, V-T,V-lin,V- V-T,V-sat, on-current, I-ON, leakage current, I-OFF, and linear and saturation sub-threshold slope, SS. We find that although scaling has no impact on BGF-induced V-T variability, it increases the total V-T, lin variability as well as that for I-ON and I-OFF

Modelling ground deformations in volcanic areas by using SAR interferograms

The inversion problem dealt with is the identification of the parameters of a magma-filled dike which causes observable changes in ground deformation data. It is supposed that ground deformation data are measured by using the SAR (Synthetic Aperture Radar) Interferometry technique. The inversion approach, which is carried out by a systematic search technique based on the Simulated Annealing (SA) optimization algorithm, guarantees a high degree of accuracy. The results given in the paper are supported by experiments carried out using an interactive software tool developed ad hoc, which allows both direct and inverse modeling of SAR interferometric data related to the opening of a crack at the beginning and throughout a volcanic activity episode

Irreversible effects of memory

The steady state of a Langevin equation with short ranged memory and coloured noise is analyzed. When the fluctuation-dissipation theorem of second kind is not satisfied, the dynamics is irreversible, i.e. detailed balance is violated. We show that the entropy production rate for this system should include the power injected by ``memory forces''. With this additional contribution, the Fluctuation Relation is fairly verified in simulations. Both dynamics with inertia and overdamped dynamics yield the same expression for this additional power. The role of ``memory forces'' within the fluctuation-dissipation relation of first kind is also discussed.Comment: 6 pages, 1 figure, publishe

Ground deformation modeling of flank dynamics prior to the 2002 eruption of Mt. Etna

On 22 September 2002, 1 month before the beginning of the flank eruption on the NE Rift, an M-3.7 earthquake struck the northeastern part of Mt. Etna, on the westernmost part of the Pernicana fault. In order to investigate the ground deformation pattern associated with this event, a multi-disciplinary approach is presented here. Just after the earthquake, specific GPS surveys were carried out on two small sub-networks, aimed at monitoring the eastern part of the Pernicana fault, and some baselines belonging to the northeastern EDM monitoring network of Mt. Etna were measured. The leveling route on the northeastern flank of the volcano was also surveyed. Furthermore, an investigation using SAR interferometry was performed and also the continuous tilt data recorded at a high precision sensor close to the epicenter were analyzed to constrain the coseismic deformation. The results of the geodetic surveys show a ground deformation pattern that affects the entire northeastern flank of the volcano, clearly shaped by the Pernicana fault, but too strong and wide to be related only to an M-3.7 earthquake. Leveling and DInSAR data highlight a local strong subsidence, up to 7 cm, close to the Pernicana fault. Significant displacements, up to 2 cm, were also detected on the upper part of the NE Rift and in the summit craters area, while the displacements decrease at lower altitude, suggesting that the dislocation did not continue further eastward. Three-dimensional GPS data inversions have been attempted in order to model the ground deformation source and its relationship with the volcano plumbing system. The model has also been constrained by vertical displacements measured by the leveling survey and by the deformation map obtained by SAR interferometry