1,888 research outputs found
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
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