755 research outputs found
Response of an artificially blown clarinet to different blowing pressure profiles
Using an artificial mouth with an accurate pressure control, the onset of the
pressure oscillations inside the mouthpiece of a simplified clarinet is studied
experimentally. Two time profiles are used for the blowing pressure: in a first
set of experiments the pressure is increased at constant rates, then decreased
at the same rate. In a second set of experiments the pressure rises at a
constant rate and is then kept constant for an arbitrary period of time. In
both cases the experiments are repeated for different increase rates. Numerical
simulations using a simplified clarinet model blown with a constantly
increasing mouth pressure are compared to the oscillating pressure obtained
inside the mouthpiece. Both show that the beginning of the oscillations appears
at a higher pressure values than the theoretical static threshold pressure, a
manifestation of bifurcation delay. Experiments performed using an interrupted
increase in mouth pressure show that the beginning of the oscillation occurs
close to the stop in the increase of the pressure. Experimental results also
highlight that the speed of the onset transient of the sound is roughly the
same, independently of the duration of the increase phase of the blowing
pressure.Comment: 14 page
Association between self-reported adherence and HIV viral load suppression among older children and adolescents.
Enzyme activity below the dynamical transition at 220 K
Enzyme activity requires the activation of anharmonic motions, such as jumps between potential energy wells. However, in general, the forms and time scales of the functionally important anharmonic dynamics coupled to motion along the reaction coordinate remain to be determined. In particular, the question arises whether the temperature-dependent dynamical transition from harmonic to anharmonic motion in proteins, which has been observed experimentally and using molecular dynamics simulation, involves the activation of motions required for enzyme function. Here we present parallel measurements of the activity and dynamics of a cryosolution of glutamate dehydrogenase as a function of temperature. The dynamical atomic fluctuations faster than ~100 ps were determined using neutron scattering. The results show that the enzyme remains active below the dynamical transition observed at ~220 K, i.e., at temperatures where no anharmonic motion is detected. Furthermore, the activity shows no significant deviation from Arrhenius behavior down to 190 K. The results indicate that the observed transition in the enzyme's dynamics is decoupled from the rate-limiting step along the reaction coordinate
Inverse problem and Bertrand's theorem
The Bertrand's theorem can be formulated as the solution of an inverse
problem for a classical unidimensional motion. We show that the solutions of
these problems, if restricted to a given class, can be obtained by solving a
numerical equation. This permit a particulary compact and elegant proof of
Bertrand's theorem.Comment: 11 pages, 3 figure
Disaster Operations Management: an Empirical Study from Thailand
Disasters have unpredictable and deleterious impacts on modern societies. While recent operations management research has increasingly focused on disaster operations, only a few studies have examined the recovery phase of post-disaster operations. This research presents an overview of Disaster Operations Management as well as an empirical study using econometrics analysis to examine the recovery phase of post-disaster operations. The results suggest that when resources are scarce, at a strategic level we need to understand where to begin when planning the recovery process. This study is an exploratory analysis of the question of how flooding affects per capita income in areas with different levels of industrialization. We developed multiple regression models using panel data from Thailand to examine this effect, finding that flooding in a previous year has a positive effect on areas with a low level of industrialization, but a negative one on highly industrialized areas, meaning the residents of the latter are affected differently. Our results suggest the level of industrialization impacts the effectiveness of the recovery process. Finally, we discuss the implications of the study as well as suggestions for future research
Les valeurs mobilières détenues par les Français en mars 2005.
placements financiers, détenteurs de titres, actionnaires, titres, actions, obligations, titres d’OPCVM, épargne salariale.
On the role of semantic approximations in validation and diagnosis of constraint logic programs
Abstract is not available
Multispectral Imaging from Mars PATHFINDER
The Imager for Mars Pathfinder (IMP) was a mast-mounted instrument on the Mars Pathfinder lander which landed on Mars Ares Vallis floodplain on July 4, 1997. During the 83 sols of Mars Pathfinders landed operations, the IMP collected over 16,600 images. Multispectral images were collected using twelve narrowband filters at wavelengths between 400 and 1000 nm in the visible and near infrared (VNIR) range. The IMP provided VNIR spectra of the materials surrounding the lander including rocks, bright soils, dark soils, and atmospheric observations. During the primary mission, only a single primary rock spectral class, Gray Rock, was recognized; since then, Black Rock, has been identified. The Black Rock spectra have a stronger absorption at longer wavelengths than do Gray Rock spectra. A number of coated rocks have also been described, the Red and Maroon Rock classes, and perhaps indurated soils in the form of the Pink Rock class. A number of different soil types were also recognized with the primary ones being Bright Red Drift, Dark Soil, Brown Soil, and Disturbed Soil. Examination of spectral parameter plots indicated two trends which were interpreted as representing alteration products formed in at least two different environmental epochs of the Ares Vallis area. Subsequent analysis of the data and comparison with terrestrial analogs have supported the interpretation that the rock coatings provide evidence of earlier martian environments. However, the presence of relatively uncoated examples of the Gray and Black rock classes indicate that relatively unweathered materials can persist on the martian surface
Suppression of carrier induced ferromagnetism by composition and spin fluctuations in diluted magnetic semiconductors
We suggest an approach to account for spatial (composition) and thermal
fluctuations in "disordered" magnetic models (e.g. Heisenberg, Ising) with
given spatial dependence of magnetic spin-spin interaction. Our approach is
based on introduction of fluctuating molecular field (rather than mean field)
acting between the spins. The distribution function of the above field is
derived self-consistently. In general case this function is not Gaussian,
latter asymptotics occurs only at sufficiently large spins (magnetic ions)
concentrations . Our approach permits to derive the equation for a
critical temperature of ferromagnetic phase transition with respect to
the above fluctuations. We apply our theory to the analysis of influence of
composition fluctuations on in diluted magnetic semiconductors (DMS) with
RKKY indirect spin-spin interaction.Comment: 6 pages, 2 figure
Epitaxy and Magneto-transport properties of the diluted magnetic semiconductor p- Be(1-x)MnxTe
We report on the MBE-growth and magnetotransport properties of p-type BeMnTe,
a new ferromagnetic diluted magnetic semiconductor. BeMnTe thin film structures
can be grown almost lattice matched to GaAs for Mn concentrations up to 10%
using solid source MBE. A high p-type doping with nitrogen can be achieved by
using an RF-plasma source. BeMnTe and BeTe layers have been characterized by
magneto-transport measurements. At low temperatures, the BeMnTe samples exhibit
a large anomalous Hall effect. A hysteresis in the anomalous Hall effect
appears below 2.5K in the most heavily doped sample, which indicates the
occurrence of a ferromagnetic phase.Comment: pdf onl
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