66,399 research outputs found
A new measure of volatility using induced heavy moving averages
The volatility is a dispersion technique widely used in statistics and economics. This paper presents a new way to calculate volatility by using different extensions of the ordered weighted average (OWA) operator. This approach is called the induced heavy ordered weighted moving average (IHOWMA) volatility. The main advantage of this operator is that the classical volatility formula only takes into account the standard deviation and the average, while with this formulation it is possible to aggregate information according to the decision maker knowledge, expectations and attitude about the future. Some particular cases are also presented when the aggregation information process is applied only on the standard deviation or on the average. An example in three different exchange rates for 2016 are presented, these are for: USD/MXN, EUR/MXN and EUR/USD
Introductory lectures on jet quenching in heavy ion collisions
Jet quenching has become an essential signal for the characterization of the
medium formed in experiments of heavy-ion collisions. After a brief
introduction to the field, we present the full derivation of the medium-induced
gluon radiation spectrum, starting from the diagrammatical origin of the Wilson
lines and the medium averages and including all intermediate steps. The
application of this spectrum to actual phenomenological calculations is then
presented, making comparisons with experimental data and indicating some
improvements of the formalism to the future LHC program. The last part of the
lectures reviews calculations based on the AdS/CFT correspondence on the medium
parameters controlling the jet quenching phenomenon.Comment: 63 pages, 17 figures, Presented at the XLVII Cracow School of
Theoretical Physics, Zakopane, Poland, June 14-22, 200
Climatological Assessment of Urban Effects on Precipitation: Final Report Part I
published or submitted for publicationis peer reviewedOpe
Non-spherical core collapse supernovae III. Evolution towards homology and dependence on the numerical resolution
(abridged) We study the hydrodynamic evolution of a non-spherical
core-collapse supernova in two spatial dimensions. We find that our model
displays a strong tendency to expand toward the pole. We demonstrate that this
expansion is a physical property of the low-mode, SASI instability. The SASI
leaves behind a large lateral velocity gradient in the post shock layer which
affects the evolution for minutes and hours later. This results in a prolate
deformation of the ejecta and a fast advection of Ni-rich material from
moderate latitudes to the polar regions. This effect might actually be
responsible for the global asymmetry of the nickel lines in SN 1987A. The
simulations demonstrate that significant radial and lateral motions in the
post-shock region, produced by convective overturn and the SASI during the
early explosion phase, contribute to the evolution for minutes and hours after
shock revival. They lead to both later clump formation, and a significant
prolate deformation of the ejecta which are observed even as late as one week
after the explosion. As pointed out recently by Kjaer et al., such an ejecta
morphology is in good agreement with the observational data of SN 1987A.
Systematic future studies are needed to investigate how the SASI-induced
late-time lateral expansion depends on the dominant mode of the SASI, and to
which extent it is affected by the dimensionality of the simulations. The
impact on and importance of the SASI for the distribution of iron group nuclei
and the morphology of the young SNR argues for future three-dimensional
explosion and post-explosion studies on singularity-free grids that cover the
entire sphere. Given the results of our 2D resolution study, present 3D
simulations must be regarded as underresolved, and their conclusions must be
verified by a proper numerical convergence analysis in three dimensions.Comment: 16 pages, 20 figures, accepted for publication in Astronomy &
Astrophysic
Dynamics of bidisperse suspensions under stokes flows: linear shear flow and eedimentation
Sedimenting and sheared bidisperse homogeneous suspensions of non-Brownian particles are investigated by numerical simulations in the limit of vanishing small Reynolds number and negligible inertia of the particles. The numerical approach is based on the solution of the three-dimensional Stokes equations forced by the presence of the dispersed phase. Multi-body hydrodynamic interactions are achieved by a low order multipole expansion of the velocity perturbation. The accuracy of the model is validated on analytic solutions of generic flow configurations involving a pair of particles.
The first part of the paper aims at investigating the dynamics of monodisperse and bidisperse suspensions embedded in a linear shear flow. The macroscopic transport properties due to hydrodynamic and non hydrodynamic interactions (short range repulsion force) show good agreement with previous theoretical and experimental works on homogeneous monodisperse particles. Increasing the volumetric concentration of the suspension leads to an enhancement of particle fluctuations and self-diffusion. The velocity fluctuation tensor scales linearly up to 15% concentration. Multi-body interactions weaken the correlation of velocity fluctuations and lead to a diffusion like motion of the particles. Probability density functions show a clear transition from Gaussian to exponential tails while the concentration decreases. The behavior of bidisperse suspensions is more complicated, since the respective amount of small and large particles modifies the overall response of the flow. Our simulations show that, for a given concentration of both species, when the size ratio varies from 1 to 2.5, the fluctuation level of the small particles is strongly enhanced. A similar trend is observed on the evolution of the shear induced self-diffusion coefficient. Thus for a fixed and total concentration, increasing the respective volume fraction of large particles can double the velocity fluctuation of small particles.
In the second part of the paper, the sedimentation of a single test particle embedded in a suspension of monodisperse particles allows the determination of basic hydrodynamic interactions involved in a bidisperse suspension. Good agreement is achieved when comparing the mean settling velocity and fluctuations levels of the test sphere with experiments. Two distinct behaviors are observed depending on the physical properties of the particle. The Lagrangian velocity autocorrelation function has a negative region when the test particle has a settling velocity twice as large as the reference velocity of the surrounding suspension. The test particle settles with a zig-zag vertical trajectory while a strong reduction of horizontal dispersion occurs. Then, several configurations of bidisperse settling suspensions are investigated. Mean velocity depends on concentration of both species, density ratio and size ratio. Results are compared with theoretical predictions at low concentration and empirical correlations when the assumption of a dilute regime is no longer valid. For particular configurations, a segregation instability sets in. Columnar patterns tend to collect particles of the same species and eventually a complete separation of the suspension is observed. The instability threshold is compared with experiments in the case of suspensions of buoyant and heavy spheres. The basic features are well reproduced by the simulation model
Dynein structure and power stroke
Dynein ATPases are microtubule motors that are critical to diverse processes such as vesicle transport and the beating of sperm tails; however, their mechanism of force generation is unknown. Each dynein comprises a head, from which a stalk and a stem emerge. Here we use electron microscopy and image processing to reveal new structural details of dynein c, an isoform from Chlamydomonas reinhardtii flagella, at the start and end of its power stroke. Both stem and stalk are flexible, and the stem connects to the head by means of a linker approximately 10 nm long that we propose lies across the head. With both ADP and vanadate bound, the stem and stalk emerge from the head 10 nm apart. However, without nucleotide they emerge much closer together owing to a change in linker orientation, and the coiled-coil stalk becomes stiffer. The net result is a shortening of the molecule coupled to an approximately 15-nm displacement of the tip of the stalk. These changes indicate a mechanism for the dynein power stroke
Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium
Understanding excited carrier dynamics in semiconductors is crucial for the
development of photovoltaics and efficient photonic devices. However,
overlapping spectral features in optical/NIR pump-probe spectroscopy often
render assignments of separate electron and hole carrier dynamics ambiguous.
Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin
films are directly and simultaneously observed by attosecond transient
absorption spectroscopy (ATAS) in the extreme ultraviolet at the germanium
M_{4,5}-edge (~30 eV). We decompose the ATAS spectra into contributions of
electronic state blocking and photo-induced band shifts at a carrier density of
8*10^{20}cm^{-3}. Separate electron and hole relaxation times are observed as a
function of hot carrier energies. A first order electron and hole decay of ~1
ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous
observation of electrons and holes with ATAS paves the way for investigating
few to sub-femtosecond dynamics of both holes and electrons in complex
semiconductor materials and across junctions.Comment: Includes Supplementary Informatio
Relating the description of gluon production in pA collisions and parton energy loss in AA collisions
We calculate the classical gluon field of a fast projectile passing through a
dense medium. We show that this allows us to calculate both the initial state
gluon production in proton-nucleus collisions and the final state gluon
radiation off a hard parton produced in nucleus-nucleus collisions. This
unified description of these two phenomena makes the relation between the
saturation scale and the transport coefficient more transparent.
Also, we discuss the validity of the eikonal approximation for gluon
propagation inside the nucleus in proton-nucleus collisions at RHIC energy.Comment: 18 pages, 3 figure
Magnetohydrodynamics and charged currents in heavy ion collisions
The hot QCD matter produced in any heavy ion collision with a nonzero impact
parameter is produced within a strong magnetic field. We study the imprint the
magnetic fields produced in non-central heavy ion collisions leave on the
azimuthal distributions and correlations of the produced charged hadrons. The
magnetic field is time-dependent and the medium is expanding, which leads to
the induction of charged currents due to the combination of Faraday and Hall
effects. We find that these currents result in a charge-dependent directed flow
that is odd in rapidity and odd under charge exchange. It can be detected
by measuring correlations between the directed flow of charged hadrons at
different rapidities, .Comment: Contribution to the Proceedings of the Quark Matter 2014 conference;
talk given by U. Gurso
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