55,764 research outputs found

### The impact of NRZ data asymmetry on the performance of a space telemetry system

The telemetry data asymmetry due to rising and falling voltage transitions can cause undesired spectral components at the output of a spacecraft transmitter. The performance of a space telemetry system can potentially degrade because of these undesired components. Here, an expression is derived for the power spectral density of an asymmetric nonreturn-to-zero (NRZ) data stream. This formula is then used to investigate how the data bandwidth varies with data asymmetry. At the receiver end, the threshold levels of undesired spectral components that fall into the carrier-tracking-loop bandwidth are determined by examining the derived spectral density. Further, based on this formula, a simple technique is developed for the computation of bit signal-to-noise ratio (SNR) degradation due to data asymmetry. The telemetry bit SNR degradations derived using this technique are compared with results obtained previously and with measurements by the Electronic Systems Test Laboratory (ESTL) at the Lyndon B. Johnson Space Center

### Magnetic field dependence of the many-electron states in a magnetic quantum dot: The ferromagnetic-antiferromagnetic transition

The electron-electron correlations in a many-electron (Ne = 1, 2,..., 5)
quantum dot confined by a parabolic potential is investigated in the presence
of a single magnetic ion and a perpendicular magnetic field. We obtained the
energy spectrum and calculated the addition energy which exhibits cusps as
function of the magnetic field. The vortex properties of the many-particle wave
function of the ground state are studied and for large magnetic fields are
related to composite fermions. The position of the impurity influences strongly
the spin pair correlation function when the external field is large. In small
applied magnetic field, the spin exchange energy together with the Zeeman terms
leads to a ferromagnetic-antiferromagnetic(FM-AFM) transition. When the
magnetic ion is shifted away from the center of the quantum dot a remarkable
re-entrant AFM-FM-AFM transition is found as function of the strength of the
Coulomb interaction. Thermodynamic quantities as the heat capacity, the
magnetization, and the susceptibility are also studied. Cusps in the energy
levels show up as peaks in the heat capacity and the susceptibility.Comment: 16 pages, 24 figure

### Cyclotron resonance of a magnetic quantum dot

The energy spectrum of a one-electron quantum dot doped with a single
magnetic ion is studied in the presence of an external magnetic field. The
allowed cyclotron resonance (CR) transitions are obtained together with their
oscillator strength (OS) as function of the magnetic field, the position of the
magnetic ion, and the quantum dot confinement strength. With increasing
magnetic field a ferromagnetic - antiferromagnetic transition is found that
results in clear signatures in the CR absorption. It leads to discontinuities
in the transition energies and the oscillator strengths and an increase of the
number of allowed transitions.Comment: 11 pages, 14 figure

### Many-body effects in the cyclotron resonance of a magnetic dot

Intraband cyclotron resonance (CR) transitions of a two-electron quantum dot
containing a single magnetic ion is investigated for different Coulomb
interaction strengths and different positions of the magnetic ion. In contrast
to the usual parabolic quantum dots where CR is independent of the number of
electrons, we found here that due to the presence of the magnetic ion Kohn's
theorem no longer holds and CR is different for systems with different number
of electrons and different effective electron-electron Coulomb interaction
strength. Many-body effects result in \emph{shifts in the transition energies}
and \emph{change the number of CR lines}. The position of the magnetic ion
inside the quantum dot affects the structure of the CR spectrum by changing the
position and the number of crossings and anti-crossings in the transition
energies and oscillator strengths.Comment: 10 pages, 10 figures. Phys. Rev. B (in press

### Coarse-Graining and Renormalization of Atomistic Binding Relations and Universal Macroscopic Cohesive Behavior

We present two approaches for coarse-graining interplanar potentials and
determining the corresponding macroscopic cohesive laws based on energy
relaxation and the renormalization group. We analyze the cohesive behavior of a
large---but finite---number of interatomic planes and find that the macroscopic
cohesive law adopts a universal asymptotic form. The universal form of the
macroscopic cohesive law is an attractive fixed point of a suitably-defined
renormalization-group transformation.Comment: 15 pages, 6 figures, submitted to the Journal of the Mechanics and
Physics of Solid

### A new root-knot nematode, Meloidogyne moensi n. sp. (Nematoda : Meloidogynidae), parasitizing Robusta coffee from Western Highlands, Vietnam

A new root-knot nematode, parasitizing Robusta coffee in Dak Lak Province, Western Highlands of Vietnam, is described as Meloidogyne moensi n. sp. Morphological and molecular analyses demonstrated that this species differs clearly from other previously described root-knot nematodes. Morphologically, the new species is characterized by a swollen body of females with a small posterior protuberance that elongated from ovoid to saccate; perineal patterns with smooth striae, continuous and low dorsal arch; lateral lines marked as a faint space or linear depression at junction of the dorsal and ventral striate; distinct phasmids; perivulval region free of striae; visible and wide tail terminus surrounding by concentric circles of striae; medial lips of females in dumbbell-shaped and slightly raised above lateral lips; female stylet is normally straight with posteriorly sloping stylet knobs; lip region of second stage juvenile (J2) is not annulated; medial lips and labial disc of J2 formed dumbbell shape; lateral lips are large and triangular; tail of J2 is conoid with rounded unstriated tail tip; distinct phasmids and hyaline; dilated rectum. Meloidogyne moensi n. sp. is most similar to M. africana, M. ottersoni by prominent posterior protuberance. Results of molecular analysis of rDNA sequences including the D2-D3 expansion regions of 28S rDNA, COI, and partial COII/16S rRNA of mitochondrial DNA support for the new species status

### Complexation of DNA with positive spheres: phase diagram of charge inversion and reentrant condensation

The phase diagram of a water solution of DNA and oppositely charged spherical
macroions is studied. DNA winds around spheres to form beads-on-a-string
complexes resembling the chromatin 10 nm fiber. At small enough concentration
of spheres these "artificial chromatin" complexes are negative, while at large
enough concentrations of spheres the charge of DNA is inverted by the adsorbed
spheres. Charges of complexes stabilize their solutions. In the plane of
concentrations of DNA and spheres the phases with positive and negative
complexes are separated by another phase, which contains the condensate of
neutral DNA-spheres complexes. Thus when the concentration of spheres grows,
DNA-spheres complexes experience condensation and resolubilization (or
reentrant condensation). Phenomenological theory of the phase diagram of
reentrant condensation and charge inversion is suggested. Parameters of this
theory are calculated by microscopic theory. It is shown that an important part
of the effect of a monovalent salt on the phase diagram can be described by the
nontrivial renormalization of the effective linear charge density of DNA wound
around a sphere, due to the Onsager-Manning condensation. We argue that our
phenomenological phase diagram or reentrant condensation is generic to a large
class of strongly asymmetric electrolytes. Possible implication of these
results for the natural chromatin are discussed.Comment: Many corrections to text. SUbmitted to J. Chem. Phy

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