251 research outputs found
Is current disruption associated with an inverse cascade?
Current disruption (CD) and the related kinetic instabilities in the
near-Earth magnetosphere represent physical mechanisms which can trigger
multi-scale substorm activity including global reorganizations of the
magnetosphere. Lui et al. (2008) proposed a CD scenario in which the kinetic
scale linear modes grow and reach the typical dipolarization scales through an
inverse cascade. The experimental verification of the inverse nonlinear cascade
is based on wavelet analysis. In this paper the Hilbert-Huang transform is used
which is suitable for nonlinear systems and allows to reconstruct the
time-frequency representation of empirical decomposed modes in an adaptive
manner. It was found that, in the Lui et al. (2008) event, the modes evolve
globally from high-frequencies to low-frequencies. However, there are also
local frequency evolution trends oriented towards high-frequencies, indicating
that the underlying processes involve multi-scale physics and non-stationary
fluctuations for which the simple inverse cascade scenario is not correct.Comment: 6 pages, 4 figure
High resolution measurements of kinetic energy release distributions of neon, argon, and krypton cluster ions using a three sector field mass spectrometer
Using a newly constructed three sector field mass spectrometer (resulting in a BE1E2 field configuration) we have measured the kinetic energy release distributions of neon, argon, and krypton cluster ions. In the present study we used the first two sectors, B and E1, constituting a high resolution mass spectrometer, to select the parent ions in terms of mass, charge, and energy, and studied the decay of those ions in the third field free region. Due to the improved mass resolution we were able to extend earlier studies carried out with a two sector field machine, where an upper size limit arose from the fact that several isotopomers contribute to a decaying parent ion beam when the cluster size exceeds a certain value. Furthermore we developed a new data analysis. It allows us to model also fragment ion peaks that are a superposition of different decay reactions and thus we can determine the average kinetic energy release for all decay reactions of a given cluster ion. In a further step we used these results to determine the binding energies of cluster ions Rg(n) (ngreater than or equal to10) by applying finite heat bath theory. The smaller sizes have not been included in this analysis, because the validity of finite heat bath theory becomes questionable below napproximate to10. The present average kinetic energy releases and binding energies are compared with other experiments and various calculations. (C) 2004 American Institute of Physics
Kinetic-energy release in Coulomb explosion of metastable C3H52+
C3H52+, formed by electron impact ionization of propane, undergoes metastable decay into C2H2++CH3+. We have monitored this reaction in a magnetic mass spectrometer of reversed geometry that is equipped with two electric sectors (BEE geometry). Three different techniques were applied to identify the fragment ions and determine the kinetic-energy release (KER) of spontaneous Coulomb explosion of C3H52+ in the second and third field free regions of the mass spectrometer. The KER distribution is very narrow, with a width of about 3% [root-mean square standard deviation]. An average KER of 4.58+/-0.15 eV is derived from the distribution. High level ab initio quantum-chemical calculations of the structure and energetics of C3H52+ are reported. The activation barrier of the reverse reaction, CH3++C2H2+ (vinylidene), is computed. The value closely agrees with the experimental average KER, thus indicating that essentially all energy available in the reaction is partitioned into kinetic energy. (C) 2003 American Institute of Physics
Entropic Upper Bound on Gravitational Binding Energy
We prove that the gravitational binding energy {\Omega} of a self gravitating
system described by a mass density distribution {\rho}(x) admits an upper bound
B[{\rho}(x)] given by a simple function of an appropriate, non-additive
Tsallis' power-law entropic functional Sq evaluated on the density {\rho}. The
density distributions that saturate the entropic bound have the form of
isotropic q-Gaussian distributions. These maximizer distributions correspond to
the Plummer density profile, well known in astrophysics. A heuristic scaling
argument is advanced suggesting that the entropic bound B[{\rho}(x)] is unique,
in the sense that it is unlikely that exhaustive entropic upper bounds not
based on the alluded Sq entropic measure exit. The present findings provide a
new link between the physics of self gravitating systems, on the one hand, and
the statistical formalism associated with non-additive, power-law entropic
measures, on the other hand
Evolution of kinklike fluctuations associated with ion pickup within reconnection outflows in the Earth's magnetotail
Magnetic reconnection (MR) in Earth's magnetotail is usually followed by a
systemwide redistribution of explosively released kinetic and thermal energy.
Recently, multispacecraft observations from the THEMIS mission were used to
study localized explosions associated with MR in the magnetotail so as to
understand subsequent Earthward propagation of MR outbursts during substorms.
Here we investigate plasma and magnetic field fluctuations/structures
associated with MR exhaust and ion-ion kink mode instability during a well
documented MR event. Generation, evolution and fading of kinklike oscillations
are followed over a distance of 70 000 km from the reconnection site in the
midmagnetotail to the more dipolar region near the Earth. We have found that
the kink oscillations driven by different ion populations within the outflow
region can be at least 25 000 km from the reconnection site.Comment: 11 pages, 4 figure
Influence of the stabilizing ligand on the quality, signal-relevant optical properties, and stability of near-infrared emitting Cd1âââHgâTe nanocrystals
Bright and stable near-infrared (NIR) and infrared (IR) emitting chromophores are in high demand for applications in telecommunication, solar cells, security barcodes, and as fluorescent reporters in bioimaging studies. The best choice for wavelengths >750 nm are semiconductor nanocrystals, especially ternary or alloy nanocrystals like CdHgTe, which enable size and composition control of their optical properties. Here, we report on the influence of growth time and surface chemistry on the composition and optical properties of colloidal CdHgTe. Up to now, these are the only NIR and IR emissive quantum dots, which can be synthesized in high quality in water, using a simple one-pot reaction. For this study we utilized and compared three different thiol ligands, thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), and glutathione (GSH). Aiming at the rational design of bright NIR- and IR-emissive alloy materials, special emphasis was dedicated to a better understanding of the role of the surface ligand and adsorptionâdesorption equilibria on the photoluminescence quantum yield and stability. In this respect, dilution and protonation studies were performed. Our results show that with this simple synthetic procedure, strongly fluorescent CdHgTe colloids can be obtained with MPA as stabilizing ligand revealing quantum yields as high as 45% independent of particle concentration
Relativistic Landau resonances
The possible interactions between plasma waves and relativistic charged particles are considered. An electromagnetic perturbation in the plasma is formulated as an elliptically polarized wave, and the collisionless plasma is described by a distribution in phase space, which is realized in cylindrical coordinates. The linearized Vlasov equation is solved in the semi-relativistic limit, to obtain the distribution function in the rest frame of the observer. The perturbed currents supported by the ionized medium are then calculated, so that an expression can be written for the total amount of energy available for transfer through the Landau mechanism. It is found that only certain modes of the perturbed current are available for this energy transfer. The final expressions are presented in terms of Stokes parameters, and applied to the special cases of a thermal as well as a nonthermal plasma. The thermal plasma is described by a Maxwellian distribution, while two nonthermal distributions are considered: the kappa distribution and a generalized Weibull distribution
One-dimensional relativistic dissipative system with constant force and its quantization
For a relativistic particle under a constant force and a linear velocity
dissipation force, a constant of motion is found. Problems are shown for
getting the Hamiltoninan of this system. Thus, the quantization of this system
is carried out through the constant of motion and using the quantization of the
velocity variable. The dissipative relativistic quantum bouncer is outlined
within this quantization approach.Comment: 11 pages, no figure
Interplay of chiral and helical states in a Quantum Spin Hall Insulator lateral junction
We study the electronic transport across an electrostatically-gated lateral
junction in a HgTe quantum well, a canonical 2D topological insulator, with and
without applied magnetic field. We control carrier density inside and outside a
junction region independently and hence tune the number and nature of 1D edge
modes propagating in each of those regions. Outside the 2D gap, magnetic field
drives the system to the quantum Hall regime, and chiral states propagate at
the edge. In this regime, we observe fractional plateaus which reflect the
equilibration between 1D chiral modes across the junction. As carrier density
approaches zero in the central region and at moderate fields, we observe
oscillations in resistance that we attribute to Fabry-Perot interference in the
helical states, enabled by the broken time reversal symmetry. At higher fields,
those oscillations disappear, in agreement with the expected absence of helical
states when band inversion is lifted.Comment: 5 pages, 4 figures, supp. ma
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