85 research outputs found
Magnetic induction ¯elds and potentials from electrical currents on elliptical cylinders
Indução magnética de campos e potenciais produzidos por correntes elétricas ao longo de um cilindro elíptico infinito e ao longo de um solenóide cilíndrico infinitamente longo, respectivamente, são calculados explicitamente. As similaridades e as diferenças das distribuições de correntes, campos de indução magnética e potenciais desses sistemas eletromagnéticos são comparados com os dos cilindros correspondentes com secções circulares
Free-particle and harmonic-oscillator propagators in two and three dimensions
This contribution illustrates how to construct free-particle and harmonic-oscillator quantum-mechanical propagators in two and three dimensions in cartesian, and in circular and spherical coordinates, respectively, starting from the corresponding one-dimensional propagators in cartesian coordinates
Connection Between Type A and E Factorizations and Construction of Satellite Algebras
Recently, we introduced a new class of symmetry algebras, called satellite
algebras, which connect with one another wavefunctions belonging to different
potentials of a given family, and corresponding to different energy
eigenvalues. Here the role of the factorization method in the construction of
such algebras is investigated. A general procedure for determining an so(2,2)
or so(2,1) satellite algebra for all the Hamiltonians that admit a type E
factorization is proposed. Such a procedure is based on the known relationship
between type A and E factorizations, combined with an algebraization similar to
that used in the construction of potential algebras. It is illustrated with the
examples of the generalized Morse potential, the Rosen-Morse potential, the
Kepler problem in a space of constant negative curvature, and, in each case,
the conserved quantity is identified. It should be stressed that the method
proposed is fairly general since the other factorization types may be
considered as limiting cases of type A or E factorizations.Comment: 20 pages, LaTeX, no figure, to be published in J. Phys.
Singular Coexistence-curve Diameters: Experiments and Simulations
Precise calculations of the coexistence-curve diameters of a hard-core
square-we ll (HCSW) fluid and the restricted primitive model (RPM) electrolyte
exhibit mar ked deviations from rectilinear behavior. The HCSW diameter
displays a singularity that sets in sharply for ; this compares favorably with extensive data for
, also reflec ted in CH, N, etc. By contrast, the curvature
of the RPM diameter va ries slowly over a wide range ; this
behavior mirrors observati ons for liquid alkali metals, specifically Rb and
Cs. Amplitudes for the leading singular terms can be estimated numerically but
their values cannot be taken li terally.Comment: 9 pages and 4 figure
Generalized Morse Potential: Symmetry and Satellite Potentials
We study in detail the bound state spectrum of the generalized Morse
potential~(GMP), which was proposed by Deng and Fan as a potential function for
diatomic molecules. By connecting the corresponding Schr\"odinger equation with
the Laplace equation on the hyperboloid and the Schr\"odinger equation for the
P\"oschl-Teller potential, we explain the exact solvability of the problem by
an symmetry algebra, and obtain an explicit realization of the latter
as . We prove that some of the generators
connect among themselves wave functions belonging to different GMP's (called
satellite potentials). The conserved quantity is some combination of the
potential parameters instead of the level energy, as for potential algebras.
Hence, belongs to a new class of symmetry algebras. We also stress
the usefulness of our algebraic results for simplifying the calculation of
Frank-Condon factors for electromagnetic transitions between rovibrational
levels based on different electronic states.Comment: 23 pages, LaTeX, 2 figures (on request). one LaTeX problem settle
Exact solutions for vibrational levels of the Morse potential via the asymptotic iteration method
Exact solutions for vibrational levels of diatomic molecules via the Morse
potential are obtained by means of the asymptotic iteration method. It is shown
that, the numerical results for the energy eigenvalues of are all
in excellent agreement with the ones obtained before. Without any loss of
generality, other states and molecules could be treated in a similar way
Asymmetric Fluid Criticality I: Scaling with Pressure Mixing
The thermodynamic behavior of a fluid near a vapor-liquid and, hence,
asymmetric critical point is discussed within a general ``complete'' scaling
theory incorporating pressure mixing in the nonlinear scaling fields as well as
corrections to scaling. This theory allows for a Yang-Yang anomaly in which
\mu_{\sigma}^{\prime\prime}(T), the second temperature derivative of the
chemical potential along the phase boundary, diverges like the specific heat
when T\to T_{\scriptsize c}; it also generates a leading singular term,
|t|^{2\beta}, in the coexistence curve diameter, where t\equiv
(T-T_{\scriptsize c}) /T_{\scriptsize c}. The behavior of various special loci,
such as the critical isochore, the critical isotherm, the k-inflection loci, on
which \chi^{(k)}\equiv \chi(\rho,T)/\rho^{k} (with \chi = \rho^{2}
k_{\scriptsize B}TK_{T}) and C_{V}^{(k)}\equiv C_{V}(\rho,T)/\rho^{k} are
maximal at fixed T, is carefully elucidated. These results are useful for
analyzing simulations and experiments, since particular, nonuniversal values of
k specify loci that approach the critical density most rapidly and reflect the
pressure-mixing coefficient. Concrete illustrations are presented for the
hard-core square-well fluid and for the restricted primitive model electrolyte.
For comparison, a discussion of the classical (or Landau) theory is presented
briefly and various interesting loci are determined explicitly and illustrated
quantitatively for a van der Waals fluid.Comment: 21 pages in two-column format including 8 figure
Full capacitance-matrix effects in driven Josephson-junction arrays
We study the dynamic response to external currents of periodic arrays of
Josephson junctions, in a resistively capacitively shunted junction (RCSJ)
model, including full capacitance-matrix effects}. We define and study three
different models of the capacitance matrix : Model A
includes only mutual capacitances; Model B includes mutual and self
capacitances, leading to exponential screening of the electrostatic fields;
Model C includes a dense matrix that is constructed
approximately from superposition of an exact analytic solution for the
capacitance between two disks of finite radius and thickness. In the latter
case the electrostatic fields decay algebraically. For comparison, we have also
evaluated the full capacitance matrix using the MIT fastcap algorithm, good for
small lattices, as well as a corresponding continuum effective-medium analytic
evaluation of a finite voltage disk inside a zero-potential plane. In all cases
the effective decays algebraically with distance, with
different powers. We have then calculated current voltage characteristics for
DC+AC currents for all models. We find that there are novel giant capacitive
fractional steps in the I-V's for Models B and C, strongly dependent on the
amount of screening involved. We find that these fractional steps are quantized
in units inversely proportional to the lattice sizes and depend on the
properties of . We also show that the capacitive steps
are not related to vortex oscillations but to localized screened phase-locking
of a few rows in the lattice. The possible experimental relevance of these
results is also discussed.Comment: 12 pages 18 Postscript figures, REVTEX style. Paper to appear in July
1, Vol. 58, Phys. Rev. B 1998 All PS figures include
The extraordinary evolutionary history of the reticuloendotheliosis viruses
The reticuloendotheliosis viruses (REVs) comprise several closely related amphotropic retroviruses isolated from birds. These viruses exhibit several highly unusual characteristics that have not so far been adequately explained, including their extremely close relationship to mammalian retroviruses, and their presence as endogenous sequences within the genomes of certain large DNA viruses. We present evidence for an iatrogenic origin of REVs that accounts for these phenomena. Firstly, we identify endogenous retroviral fossils in mammalian genomes that share a unique recombinant structure with REVs—unequivocally demonstrating that REVs derive directly from mammalian retroviruses. Secondly, through sequencing of archived REV isolates, we confirm that contaminated Plasmodium lophurae stocks have been the source of multiple REV outbreaks in experimentally infected birds. Finally, we show that both phylogenetic and historical evidence support a scenario wherein REVs originated as mammalian retroviruses that were accidentally introduced into avian hosts in the late 1930s, during experimental studies of P. lophurae, and subsequently integrated into the fowlpox virus (FWPV) and gallid herpesvirus type 2 (GHV-2) genomes, generating recombinant DNA viruses that now circulate in wild birds and poultry. Our findings provide a novel perspective on the origin and evolution of REV, and indicate that horizontal gene transfer between virus families can expand the impact of iatrogenic transmission events
Pan-cancer Alterations of the MYC Oncogene and Its Proximal Network across the Cancer Genome Atlas
Although theMYConcogene has been implicated incancer, a systematic assessment of alterations ofMYC, related transcription factors, and co-regulatoryproteins, forming the proximal MYC network (PMN),across human cancers is lacking. Using computa-tional approaches, we define genomic and proteo-mic features associated with MYC and the PMNacross the 33 cancers of The Cancer Genome Atlas.Pan-cancer, 28% of all samples had at least one ofthe MYC paralogs amplified. In contrast, the MYCantagonists MGA and MNT were the most frequentlymutated or deleted members, proposing a roleas tumor suppressors.MYCalterations were mutu-ally exclusive withPIK3CA,PTEN,APC,orBRAFalterations, suggesting that MYC is a distinct onco-genic driver. Expression analysis revealed MYC-associated pathways in tumor subtypes, such asimmune response and growth factor signaling; chro-matin, translation, and DNA replication/repair wereconserved pan-cancer. This analysis reveals insightsinto MYC biology and is a reference for biomarkersand therapeutics for cancers with alterations ofMYC or the PMN
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