14,833 research outputs found
An analytic solution of the Boltzmann equation in the presence of self-generated magnetic fields in astrophysical plasmas
Through relating a self-generated magnetic field to the regular motion of
free electrons that is responsible for the magnetic field generation in
astrophysical plasmas, we solve the Boltzmann kinetic equation in the presence
of the self-generated magnetic fields to obtain a steady-state, collisional
invariant analytic solution of the equation.Comment: 4 pages, no figure, in REVTeX, accepted for publication in Phys.
lett.
Fractional chaotic inflation in the lights of PLANCK and BICEP2
In the lights of current BICEP2 observations accompanied with the PLANCK
satellite results, it has been observed that the simple single field chaotic
inflationary models provide a good agreement with their spectral index n_s and
large tensor-to-scalar ratio r (0.15 <r <0.26). To explore the other simple
models, we consider the fractional-chaotic inflationary potentials of the form
V_0 phi^(a/b) where a and b are relatively prime. We show that such kind of
inflaton potentials can be realized elegantly in the supergravity framework
with generalized shift symmetry and a nature bound a/b < 4 for consistency.
Especially, for the number of e-folding from 50 to 60 and some a/b from 2 to 3,
our predictions are nicely within at least 1 region in the r-n_s
plane. We also present a systematic investigation of such chaotic inflationary
models with fractional exponents to explore the possibilities for the
enhancement in the magnitude of running of spectral index (\alpha_{n_s}) beyond
the simplistic models.Comment: 16 pages, 5 figures, references added, published in PL
Supraspinal characterization of the thermal grill illusion with fMRI.
BackgroundSimultaneous presentation of non-noxious warm (40°C) and cold (20°C) stimuli in an interlacing fashion results in a transient hot burning noxious sensation (matched at 46°C) known as the thermal grill (TG) illusion. Functional magnetic resonance imaging and psychophysical assessments were utilized to compare the supraspinal events related to the spatial summation effect of three TG presentations: 20°C/20°C (G2020), 20°C/40°C (G2040) and 40°C/40°C (G4040) with corresponding matched thermode stimuli: 20°C (P20), 46°C (P46) and 40°C (P40) and hot pain (HP) stimuli.ResultsFor G2040, the hot burning sensation was only noted during the initial off-line assessment. In comparison to P40, G4040 resulted in an equally enhanced response from all supraspinal regions associated with both pain sensory/discriminatory and noxious modulatory response. In comparison to P20, G2020 presentation resulted in a much earlier diminished/sedative response leading to a statistically significantly (Pâ<â0.01) higher degree of deactivation in modulatory supraspinal areas activated by G4040. Granger Causality Analysis showed that while thalamic activation in HP may cast activation inference in all hot pain related somatosensory, affective and modulatory areas, similar activation in G2040 and G2020 resulted in deactivation inference in the corresponding areas.ConclusionsIn short, the transient TG sensation is caused by a dissociated state derived from non-noxious warm and cold spatial summation interaction. The observed central dissociated state may share some parallels in certain chronic neuropathic pain states
Equality of higher numerical ranges of matrices and a conjecture of Kippenhahn on Hermitian pencils
AbstractLet Mn be the algebra of all n Ă n complex matrices. For 1 ⊽ k ⊽ n, the kth numerical range of A Mn is defined by Wk(A) = (1/k)âjk=1xj*Axj : x1, âŚ, xk is an orthonormal set in ân]. It is known that tr A/n = Wn(A)â Wnâ1(A) â ⯠â W1(A). We study the condition on A under which Wm(A) = Wk(A) for some given 1 ⊽ m < k ⊽ n. It turns out that this study is closely related to a conjecture of Kippenhahn on Hermitian pencils. A new class of counterexamples to the conjecture is constructed, based on the theory of the numerical range
The Rayleigh-Taylor instability and internal waves in quantum plasmas
Influence of quantum effects on the internal waves and the Rayleigh-Taylor
instability in plasma is investigated. It is shown that quantum pressure always
stabilizes the RT instability. The problem is solved both in the limit of
short-wavelength perturbations and exactly for density profiles with layers of
exponential stratification. In the case of stable stratification, quantum
pressure modifies the dispersion relation of the inertial waves. Because of the
quantum effects, the internal waves may propagate in the transverse direction,
which was impossible in the classical case. A specific form of pure quantum
internal waves is obtained, which do not require any external gravitational
field.Comment: 9 pages, 2 figure
A Hartree-Fock ab initio band-structure calculation employing Wannier-type orbitals
An ab initio Wannier-function-based approach to electronic ground-state
calculations for crystalline solids is outlined. In the framework of the linear
combination of atomic orbitals method the infinite character of the solid is
rigorously taken into account. The Hartree-Fock ground-state energy, cohesive
energy, lattice constant and bulk modulus are calculated in a fully ab initio
manner as it is demonstrated for sodium chloride, NaCl, using basis sets close
to the Hartree-Fock limit. It is demonstrated that the Hartree-Fock
band-structure can easily be recovered with the current approach and agrees
with the one obtained from a more conventional Bloch-orbital-based calculation.
It is argued that the advantage of the present approach lies in its capability
to include electron correlation effects for crystalline insulators by means of
well-established quantum chemical procedures.Comment: 15 Pages, LaTex, 1 postscript figure (included), to appear in Chem.
Phys. Letters (1998
Comorbidities and Concomitant Medication Use in Men with Prostate Cancer or High Levels of PSA Compared to Matched Controls: A GPRD Analysis
Comorbidity influences screening practice, treatment choice, quality of life, and survival. The presence of comorbidities and medication use could place patients at greater risks of adverse effects from certain interventions. We conducted a longitudinal cohort study in the General Practice Research Database to better understand comorbidities and medication use in men with or at risk of prostate cancer (CaP). Compared with men with similar age but no CaP, CaP patients had higher incidence of urinary tract infection, impotence and breast disorder, and 2.6-fold higher all-cause mortality. Among men with elevated prostate-specific antigen (PSA) but no CaP, the mortality rates were slightly lower, and fewer differences in comorbidities and medication use were noted compared to men without elevated PSA. Many prevalent comorbidities and medications were consistent across groups and are typical of an older male population. These real-world data are broadly applicable throughout the drug development cycle and subsequent patient management
Magnetic rogue wave in a perpendicular anisotropic ferromagnetic nanowire with spin-transfer torque
We present the current controlled motion of dynamic soliton embedded in spin
wave background in ferromagnetic nanowire. With the stronger breather character
we get the novel magnetic rogue wave and clarify its formation mechanism. The
generation of magnetic rogue wave is mainly arose from the accumulation of
energy and magnons toward to its central part. We also observe that the
spin-polarized current can control the exchange rate of magnons between
envelope soliton and background, and the critical current condition is obtained
analytically. Even more interesting is that the spin-transfer torque plays the
completely opposite role for the cases of below and above the critical value.Comment: 5 figure
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