2,069 research outputs found
Power injected in a granular gas
A granular gas may be modeled as a set of hard-spheres undergoing inelastic
collisions; its microscopic dynamics is thus strongly irreversible. As pointed
out in several experimental works bearing on turbulent flows or granular
materials, the power injected in a dissipative system to sustain a steady-state
over an asymptotically large time window is a central observable. We describe
an analytic approach allowing us to determine the full distribution of the
power injected in a granular gas within a steady-state resulting from
subjecting each particle independently either to a random force (stochastic
thermostat) or to a deterministic force proportional to its velocity (Gaussian
thermostat). We provide an analysis of our results in the light of the
relevance, for other types of systems, of the injected power to fluctuation
relations.Comment: 9 pages, 4 figures. Contribution to Proceedings of "Work,
Dissipation, and Fluctuations in Nonequilibrium Physics", Brussels, 200
Injected power and entropy flow in a heated granular gas
Our interest goes to the power injected in a heated granular gas and to the
possibility to interpret it in terms of entropy flow. We numerically determine
the distribution of the injected power by means of Monte-Carlo simulations.
Then, we provide a kinetic theory approach to the computation of such a
distribution function. Finally, after showing why the injected power does not
satisfy a Fluctuation Relation a la Gallavotti-Cohen, we put forward a new
quantity which does fulfill such a relation, and is not only applicable in a
variety of frameworks outside the granular world, but also experimentally
accessible.Comment: accepted in Europhys. Let
Fluctuations of power injection in randomly driven granular gases
We investigate the large deviation function pi(w) for the fluctuations of the
power W(t)=w t, integrated over a time t, injected by a homogeneous random
driving into a granular gas, in the infinite time limit. Starting from a
generalized Liouville equation we obtain an equation for the generating
function of the cumulants mu(lambda) which appears as a generalization of the
inelastic Boltzmann equation and has a clear physical interpretation.
Reasonable assumptions are used to obtain mu(lambda) in a closed analytical
form. A Legendre transform is sufficient to get the large deviation function
pi(w). Our main result, apart from an estimate of all the cumulants of W(t) at
large times t, is that pi(w) has no negative branch. This immediately results
in the failure of the Gallavotti-Cohen Fluctuation Relation (GCFR), that in
previous studies had been suggested to be valid for injected power in driven
granular gases. We also present numerical results, in order to discuss the
finite time behavior of the fluctuations of W(t). We discover that their
probability density function converges extremely slowly to its asymptotic
scaling form: the third cumulant saturates after a characteristic time larger
than 50 mean free times and the higher order cumulants evolve even slower. The
asymptotic value is in good agreement with our theory. Remarkably, a numerical
check of the GCFR is feasible only at small times, since negative events
disappear at larger times. At such small times this check leads to the
misleading conclusion that GCFR is satisfied for pi(w). We offer an explanation
for this remarkable apparent verification. In the inelastic Maxwell model,
where a better statistics can be achieved, we are able to numerically observe
the failure of GCFR.Comment: 23 pages, 15 figure
Real-time assembly of ribonucleoprotein complexes on nascent RNA transcripts.
Cellular protein-RNA complexes assemble on nascent transcripts, but methods to observe transcription and protein binding in real time and at physiological concentrations are not available. Here, we report a single-molecule approach based on zero-mode waveguides that simultaneously tracks transcription progress and the binding of ribosomal protein S15 to nascent RNA transcripts during early ribosome biogenesis. We observe stable binding of S15 to single RNAs immediately after transcription for the majority of the transcripts at 35 °C but for less than half at 20 °C. The remaining transcripts exhibit either rapid and transient binding or are unable to bind S15, likely due to RNA misfolding. Our work establishes the foundation for studying transcription and its coupled co-transcriptional processes, including RNA folding, ligand binding, and enzymatic activity such as in coupling of transcription to splicing, ribosome assembly or translation
The Effects of Violations of Bar Chart Standards on Managerial Decision Making
This thesis investigated whether a difference in data display, modes or a difference in data trends affected mid-level Air Force managers trend impressions, risk assessments. and loan decisions. By presenting data in four different modes, and by three data trends, a 4 x 3 factorial design experiment was prepared 180 subjects were tested, 15 in each of the twelve treatment cells. Each subject viewed three graphs or tables and made a decision based on the trend observed, their assessment of the trend, and a decision table. At the end of the experiment. they were asked for their impression of the trend and their assessment of the risk involved in each of the three data sets. The subjects also completed a demographic questionnaire. Using an automated statistical analysis package, a multifactor analysis of variance was conducted. It was shown that mode of presentation did have an effect on the subjects loan decisions, trend impressions, and risk assessments. Trend type was also a significant factor in each response category. A one-way analysis of variance was conducted on the demographic data for each area. It was found that age, gender. area of expertise, and graphics training were significant factors in some response areas
A basic protocol for the acoustic characterization of small and medium-sized classrooms
To promote a fast and effective characterization of the sound environment in small and medium-sized classrooms, a basic measurement protocol, based on a minimum number of parameters and positions, is provided. Measurements were taken in 29 occupied classrooms belonging to 13 primary schools in Turin, Italy, that differ in location and typology. The background noise level was acquired during silent and group activities, and the reverberation time, speech clarity, useful-to-detrimental ratio and speech level, were acquired along the main axis of each classroom and in one or two offset positions. To reduce the number of measured parameters that can be used to fully characterize classroom acoustics, data were divided into two groups on the basis of a cutoff value of maximum occupied reverberation time in the case of moderate and severe requirements. Given the strong correlation among the quantities, thresholds were identified for the other acoustical parameters, and their accuracy and precision were tested to assess their ability to classify the acoustic quality as compliant or non-compliant. Results suggest that more convenient parameters, like clarity in the central position of the classroom, can be used instead of reverberation time to classify classroom acoustics
Metal-free α-trifluoromethylthiolation and α-trifluoromethylselenolation of carbonyl derivatives
The incorporation of a SCF3 or a SeCF3 group into organic molecules is a topic of great interest, especially for the pharmaceutical and agrochemical industries. Due to their high lipophilicity and high electron-withdrawing character (Hansch lipophilicity parameter piR =1.44 (SCF3) vs piR =1.29 (SeCF3)), these moieties represent a powerful opportunity to influence the pharmacokinetics properties of a drug molecule.
In the last years, new structural units, rising from the association between chalcogens and fluorinated moieties, have been introduced into carbonyl compounds, as emerging class with potential applications on several fields. New reagents have been developed as sources of electrophilic SCF3 and SeCF3 groups; however, a widespread use of such fluorinated compounds is hampered by the very limited number of strategies available for their preparation. In this contest, we have developed two methodologies for the preparation of alpha-SCF3 and alpha-SeCF3 substituted carbonyl derivatives starting from non activated ketones or their derivatives
Energy fluctuations in vibrated and driven granular gases
We investigate the behavior of energy fluctuations in several models of
granular gases maintained in a non-equilibrium steady state. In the case of a
gas heated from a boundary, the inhomogeneities of the system play a
predominant role. Interpreting the total kinetic energy as a sum of independent
but not identically distributed random variables, it is possible to compute the
probability density function (pdf) of the total energy. Neglecting correlations
and using the analytical expression for the inhomogeneous temperature profile
obtained from the granular hydrodynamic equations, we recover results which
have been previously observed numerically and which had been attributed to the
presence of correlations. In order to separate the effects of spatial
inhomogeneities from those ascribable to velocity correlations, we have also
considered two models of homogeneously thermostated gases: in this framework it
is possible to reveal the presence of non-trivial effects due to velocity
correlations between particles. Such correlations stem from the inelasticity of
collisions. Moreover, the observation that the pdf of the total energy tends to
a Gaussian in the large system limit, suggests that they are also due to the
finite size of the system.Comment: 13 pages, 10 figure
Organocatalytic Michael addition to (D)-mannitol-derived enantiopure nitroalkenes: A valuable strategy for the synthesis of densely functionalized chiral molecules
Carbohydrates are abundant renewable resources and are a feedstock for green chemistry and sustainable synthesis of the future. Among the hexoses and the pentoses present in biomass, mannitol was selected in the present project as a valuable platform, directly available from the chiral pool, to build highly functionalized molecules. Starting from (R)-2,3-O-cyclohexylidene glyceraldehyde, which is easily prepared in a large scale from D-mannitol, an enantiopure chiral nitro alkene was prepared by reaction with nitromethane, and its reactivity studied. Organocatalytic Michael addition of dimethyl malonate, \u3b2-keto esters, and other nucleophiles on the nitro alkene afforded high stereoselectivity and densely functionalized chiral molecules, which were further synthetically developed, leading to five-membered lactones and bicyclic lactams. Preliminary studies showed that the metal-free catalytic reaction on the chiral nitro alkene can be performed under continuous flow conditions, thus enabling the use of (micro)mesofluidic systems for the preparation of enantiomerically pure organic molecules from the chiral pool
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