2,781 research outputs found
Analog of Astrophysical Magnetorotational Instability in a Couette-Taylor Flow of Polymer Fluids
We report experimental observation of an instability in a Couette-Taylor flow
of a polymer fluid in a thin gap between two coaxially rotating cylinders in a
regime where their angular velocity decreases with the radius while the
specific angular momentum increases with the radius. In the considered regime,
neither the inertial Rayleigh instability nor the purely elastic instability
are possible. We propose that the observed "elasto-rotational" instability is
an analog of the magnetorotational instability which plays a fundamental role
in astrophysical Keplerian accretion disks.Comment: 4 pages, 1 figur
Vibrational spectroscopy of GdCr3(BO3)4: Quantitative separation of crystalline phases
This work is devoted to the investigation of GdCr3(BO3)4 crystals by the method of infrared spectroscopy. Incongruently melting borate GdCr3(BO3)4 was obtained as a result of spontaneous crystallization. Crystal structures were identified by the method of infrared spectroscopy. Ab initio calculations in the frame of density functional theory enabled us to separate modes belonging to the R32 and C2/c phases and to estimate the ratio of these phases in GdCr3(BO3)4 crystals. We have found that the content of the rhombohedral R32 (non- centrosymmetric) modification is about 85%. Β© Published under licence by IOP Publishing Ltd
Dust Dynamics in Compressible MHD Turbulence
We calculate the relative grain-grain motions arising from interstellar
magnetohydrodynamic (MHD) turbulence. The MHD turbulence includes both fluid
motions and magnetic fluctuations. While the fluid motions accelerate grains
through hydro-drag, the electromagnetic fluctuations accelerate grains through
resonant interactions. We consider both incompressive (Alfv\'{e}n) and
compressive (fast and slow) MHD modes and use descriptions of MHD turbulence
obtained in Cho & Lazarian (2002). Calculations of grain relative motion are
made for realistic grain charging and interstellar turbulence that is
consistent with the velocity dispersions observed in diffuse gas, including
cutoff of the turbulence from various damping processes. We show that fast
modes dominate grain acceleration, and can drive grains to supersonic
velocities. Grains are also scattered by gyroresonance interactions, but the
scattering is less important than acceleration for grains moving with
sub-Alfv\'{e}nic velocities. Since the grains are preferentially accelerated
with large pitch angles, the supersonic grains will be aligned with long axes
perpendicular to the magnetic field. We compare grain velocities arising from
MHD turbulence with those arising from photoelectric emission, radiation
pressure and H thrust. We show that for typical interstellar conditions
turbulence should prevent these mechanisms from segregating small and large
grains. Finally, gyroresonant acceleration is bound to preaccelerate grains
that are further accelerated in shocks. Grain-grain collisions in the shock may
then contribute to the overabundance of refractory elements in the composition
of galactic cosmic rays.Comment: 15 pages, 17 figure
Dirac cones in two-dimensional borane
We introduce two-dimensional borane, a single-layered material of BH
stoichiometry, with promising electronic properties. We show that, according to
Density Functional Theory calculations, two-dimensional borane is semimetallic,
with two symmetry-related Dirac cones meeting right at the Fermi energy .
The curvature of the cones is lower than in graphene, thus closer to the ideal
linear dispersion. Its structure, formed by a puckered trigonal boron network
with hydrogen atoms connected to each boron atom, can be understood as
distorted, hydrogenated borophene (Science \textbf{350}, 1513 (2015)). Chemical
bonding analysis reveals the boron layer in the network being bound by
delocalized four-center two-electron bonds. Finally, we suggest
high-pressure could be a feasible route to synthesise two-dimensional borane.Comment: 5 pages, 3 figures, 1 tabl
Amplification of magnetic fields by dynamo action in Gaussian-correlated helical turbulence
We investigate the growth and structure of magnetic fields amplified by
kinematic dynamo action in turbulence with non-zero kinetic helicity. We assume
a simple Gaussian velocity correlation tensor, which allows us to consider very
large magnetic Reynolds numbers, up to one trillion. We use the kinematic
Kazantsev-Kraichnan model of dynamo and find a complete numerical solution for
the correlation functions of growing magnetic fields.Comment: 7 pages, 3 figure
A Turbulent Origin for Flocculent Spiral Structure in Galaxies
The flocculent structure of star formation in 7 galaxies has a Fourier
transform power spectrum for azimuthal intensity scans with a power law slope
that increases systematically from -1 at large scales to -1.7 at small scales.
This is the same pattern as in the power spectra for azimuthal scans of HI
emission in the Large Magellanic Clouds and for flocculent dust clouds in
galactic nuclei. The steep part also corresponds to the slope of -3 for
two-dimensional power spectra that have been observed in atomic and molecular
gas surveys of the Milky Way and the Large and Small Magellanic Clouds. The
same power law structure for star formation arises in both flocculent and grand
design galaxies, which implies that the star formation process is the same in
each. Fractal Brownian motion models that include discrete stars and an
underlying continuum of starlight match the observations if all of the emission
is organized into a global fractal pattern with an intrinsic 1D power spectrum
having a slope between 1.3 and 1.8. We suggest that the power spectrum of
optical light in galaxies is the result of turbulence, and that large-scale
turbulent motions are generated by sheared gravitational instabilities which
make flocculent spiral arms first and then cascade to form clouds and clusters
on smaller scales.Comment: accepted for ApJ, 31 pg, 9 figure
Aromaticity in a Surface Deposited Cluster: Pd on TiO (110)
We report the presence of \sigma-aromaticity in a surface deposited cluster,
Pd on TiO (110). In the gas phase, Pd adopts a tetrahedral
structure. However, surface binding promotes a flat, \sigma-aromatic cluster.
This is the first time aromaticity is found in surface deposited clusters.
Systems of this type emerge as a promising class of catalyst, and so
realization of aromaticity in them may help to rationalize their reactivity and
catalytic properties, as a function of cluster size and composition.Comment: 4 pages, 3 figure
ΠΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎΡΡΠΈ ΠΎΠ±Π΅Π·Π±ΠΎΠ»ΠΈΠ²Π°Π½ΠΈΡ ΠΏΡΠΈ ΡΠΎΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠ΅ΡΠ°ΠΏΠΈΠΈ
The authors consider the possibilities of pain management during photodynamic therapy (PDT) of visible tumors based on the observation of 102 patients. Of the total number of patients, 62 had verified basal cell skin cancer, 10 people - squamous cell skin cancer, another 10 - oral and oropharynx mucosa cancer, 8 - oral leukoplakia and dysplasia, in 6 - lower lip cancer, in 4 - breast cancer, in 2 - other localizations of neoplasms. In 15 patients, nonsteroidal anti-inflammatory drugs (NSAID) were used as pain management, in 69 - a combination of NSAID with tramadol, in 14 - nerve block anesthesia, in 4 - PDT was performed under general anesthesia. The intensity of pain syndrome during laser irradiation of the tumor was assessed on the verbal rating scale (VRS). The absence of pain was recorded in 9% of cases. Mild pain was noted by 58% of patients, moderate pain - 20%, severe pain - 10%, very severe pain was noted by 3% of patients.The degree of expression of pain syndrome during PDT depends on the incidence of a lesion, histological form of tumor, and method of anesthesia. NSAID alone, or in combination with an opioid analgesic, allows effective control of pain syndrome in PDT of basal cell skin cancer in 89%, in PDT of squamous cell skin cancer in 66% of observations. Nerve block anesthesia allows stoping pain syndrome during PDT of oropharyngeal tumors.ΠΠ²ΡΠΎΡΡ ΡΠ°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°ΡΡ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎΡΡΠΈ ΠΎΠ±Π΅Π·Π±ΠΎΠ»ΠΈΠ²Π°Π½ΠΈΡ ΠΏΡΠΈ ΡΠΎΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠ΅ΡΠ°ΠΏΠΈΠΈ (Π€ΠΠ’) ΠΎΠΏΡΡ
ΠΎΠ»Π΅ΠΉ Π²ΠΈΠ·ΡΠ°Π»ΡΠ½ΡΡ
Π»ΠΎΠΊΠ°Π»ΠΈΠ·Π°ΡΠΈΠΉ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ Π°Π½Π°Π»ΠΈΠ·Π° Π΄Π°Π½Π½ΡΡ
102 ΠΏΠ°ΡΠΈΠ΅Π½ΡΠΎΠ². Π‘ΡΠ΅Π΄ΠΈ ΠΏΠ°ΡΠΈΠ΅Π½ΡΠΎΠ², Π²ΠΊΠ»ΡΡΠ΅Π½Π½ΡΡ
Π² Π²ΡΠ±ΠΎΡΠΊΡ, Ρ 62 Π²Π΅ΡΠΈΡΠΈΡΠΈΡΠΎΠ²Π°Π½ Π±Π°Π·Π°Π»ΡΠ½ΠΎΠΊΠ»Π΅ΡΠΎΡΠ½ΡΠΉ ΡΠ°ΠΊ ΠΊΠΎΠΆΠΈ, Ρ 10 - ΠΏΠ»ΠΎΡΠΊΠΎΠΊΠ»Π΅ΡΠΎΡΠ½ΡΠΉ ΡΠ°ΠΊ ΠΊΠΎΠΆΠΈ, Ρ 10 - ΡΠ°ΠΊ ΡΠ»ΠΈΠ·ΠΈΡΡΠΎΠΉ ΠΎΠ±ΠΎΠ»ΠΎΡΠΊΠΈ ΠΏΠΎΠ»ΠΎΡΡΠΈ ΡΡΠ° ΠΈ ΡΠΎΡΠΎΠ³Π»ΠΎΡΠΊΠΈ, Ρ 8 - Π»Π΅ΠΉΠΊΠΎΠΏΠ»Π°ΠΊΠΈΡ ΠΈ Π΄ΠΈΡΠΏΠ»Π°Π·ΠΈΡ ΡΠ»ΠΈΠ·ΠΈΡΡΠΎΠΉ ΠΎΠ±ΠΎΠ»ΠΎΡΠΊΠΈ ΠΏΠΎΠ»ΠΎΡΡΠΈ ΡΡΠ°, Ρ 6 - ΡΠ°ΠΊ Π½ΠΈΠΆΠ½Π΅ΠΉ Π³ΡΠ±Ρ, Ρ 4 - ΡΠ°ΠΊ ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ, Ρ 2 - Π½ΠΎΠ²ΠΎΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ ΠΈΠ½ΡΡ
Π»ΠΎΠΊΠ°Π»ΠΈΠ·Π°ΡΠΈΠΉ.Π£ 15 ΠΏΠ°ΡΠΈΠ΅Π½ΡΠΎΠ² Π΄Π»Ρ ΠΎΠ±Π΅Π·Π±ΠΎΠ»ΠΈΠ²Π°Π½ΠΈΡ ΠΏΡΠΈΠΌΠ΅Π½ΡΠ»ΠΈ Π½Π΅ΡΡΠ΅ΡΠΎΠΈΠ΄Π½ΡΠ΅ ΠΏΡΠΎΡΠΈΠ²ΠΎΠ²ΠΎΡΠΏΠ°Π»ΠΈΡΠ΅Π»ΡΠ½ΡΠ΅ ΠΏΡΠ΅ΠΏΠ°ΡΠ°ΡΡ (ΠΠΠΠ‘), Ρ 69 - ΡΠΎΡΠ΅ΡΠ°Π½ΠΈΠ΅ ΠΠΠΠ‘ ΡΠΎ ΡΠ»Π°Π±ΡΠΌΠΈ ΠΎΠΏΠΈΠΎΠΈΠ΄Π°ΠΌΠΈ (ΡΡΠ°ΠΌΠ°Π΄ΠΎΠ»ΠΎΠΌ), Ρ 14 - ΠΏΡΠΎΠ²ΠΎΠ΄Π½ΠΈΠΊΠΎΠ²ΡΡ Π°Π½Π΅ΡΡΠ΅Π·ΠΈΡ, Ρ 4 Π€ΠΠ’ ΠΏΡΠΎΠ²ΠΎΠ΄ΠΈΠ»ΠΈ ΠΏΠΎΠ΄ ΠΎΠ±ΡΠΈΠΌ ΠΎΠ±Π΅Π·Π±ΠΎΠ»ΠΈΠ²Π°Π½ΠΈΠ΅ΠΌ. ΠΠ½ΡΠ΅Π½ΡΠΈΠ²Π½ΠΎΡΡΡ Π±ΠΎΠ»Π΅Π²ΠΎΠ³ΠΎ ΡΠΈΠ½Π΄ΡΠΎΠΌΠ° ΠΎΡΠ΅Π½ΠΈΠ²Π°Π»Π°ΡΡ Π² ΠΏΡΠΎΡΠ΅ΡΡΠ΅ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ΠΈΡ Π»Π°Π·Π΅ΡΠ½ΠΎΠ³ΠΎ ΠΎΠ±Π»ΡΡΠ΅Π½ΠΈΡ ΠΎΠΏΡΡ
ΠΎΠ»ΠΈ ΠΏΠΎ ΡΠΊΠ°Π»Π΅ Π²Π΅ΡΠ±Π°Π»ΡΠ½ΡΡ
ΠΎΡΠ΅Π½ΠΎΠΊ (Π¨ΠΠ). ΠΡΡΡΡΡΡΠ²ΠΈΠ΅ Π±ΠΎΠ»Π΅Π²ΡΡ
ΠΎΡΡΡΠ΅Π½ΠΈΠΉ Π·Π°ΡΠΈΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΎ Π² 9% Π½Π°Π±Π»ΡΠ΄Π΅Π½ΠΈΠΉ. Π‘Π»Π°Π±ΡΡ Π±ΠΎΠ»Ρ ΠΎΡΠΌΠ΅ΡΠ°Π»ΠΈ Π² 58% Π½Π°Π±Π»ΡΠ΄Π΅Π½ΠΈΠΉ, ΡΠΌΠ΅ΡΠ΅Π½Π½ΡΡ Π±ΠΎΠ»Ρ β Π² 20%, ΡΠΈΠ»ΡΠ½ΡΡ Π±ΠΎΠ»Ρ - Π² 10%, ΠΎΡΠ΅Π½Ρ ΡΠΈΠ»ΡΠ½ΡΡ Π±ΠΎΠ»Ρ - Π² 3% Π½Π°Π±Π»ΡΠ΄Π΅Π½ΠΈΠΉ.Π‘ΡΠ΅ΠΏΠ΅Π½Ρ Π²ΡΡΠ°ΠΆΠ΅Π½Π½ΠΎΡΡΠΈ Π±ΠΎΠ»Π΅Π²ΠΎΠ³ΠΎ ΡΠΈΠ½Π΄ΡΠΎΠΌΠ° ΠΏΡΠΈ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ΠΈΠΈ Π€ΠΠ’ Π·Π°Π²ΠΈΡΠΈΡ ΠΎΡ ΡΠ°ΡΠΏΡΠΎΡΡΡΠ°Π½Π΅Π½Π½ΠΎΡΡΠΈ ΠΏΠΎΡΠ°ΠΆΠ΅Π½ΠΈΡ, Π³ΠΈΡΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠΎΡΠΌΡ ΠΎΠΏΡΡ
ΠΎΠ»ΠΈ ΠΈ ΡΠΏΠΎΡΠΎΠ±Π° ΠΎΠ±Π΅Π·Π±ΠΎΠ»ΠΈΠ²Π°Π½ΠΈΡ. ΠΠΠΠ‘ Π² ΡΠ°ΠΌΠΎΡΡΠΎΡΡΠ΅Π»ΡΠ½ΠΎΠΌ Π²Π°ΡΠΈΠ°Π½ΡΠ΅ ΠΈΠ»ΠΈ Π² ΡΠΎΡΠ΅ΡΠ°Π½ΠΈΠΈ Ρ ΠΎΠΏΠΈΠΎΠΈΠ΄Π½ΡΠΌ Π°Π½Π°Π»ΡΠ³Π΅ΡΠΈΠΊΠΎΠΌ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΡΡ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎ ΠΊΠΎΠ½ΡΡΠΎΠ»ΠΈΡΠΎΠ²Π°ΡΡ Π±ΠΎΠ»Π΅Π²ΠΎΠΉ ΡΠΈΠ½Π΄ΡΠΎΠΌ ΠΏΡΠΈ Π€ΠΠ’ Π±Π°Π·Π°Π»ΡΠ½ΠΎΠΊΠ»Π΅ΡΠΎΡΠ½ΠΎΠ³ΠΎ ΡΠ°ΠΊΠ° ΠΊΠΎΠΆΠΈ Π² 89%, ΠΏΠ»ΠΎΡΠΊΠΎΠΊΠ»Π΅ΡΠΎΡΠ½ΠΎΠ³ΠΎ ΡΠ°ΠΊΠ° ΠΊΠΎΠΆΠΈ β Π² 66% Π½Π°Π±Π»ΡΠ΄Π΅Π½ΠΈΠΉ. ΠΡΠΎΠ²ΠΎΠ΄Π½ΠΈΠΊΠΎΠ²Π°Ρ Π°Π½Π΅ΡΡΠ΅Π·ΠΈΡ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ ΠΊΡΠΏΠΈΡΠΎΠ²Π°ΡΡ Π±ΠΎΠ»Π΅Π²ΠΎΠΉ ΡΠΈΠ½Π΄ΡΠΎΠΌ ΠΏΡΠΈ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ΠΈΠΈ Π€ΠΠ’ ΠΎΠΏΡΡ
ΠΎΠ»Π΅ΠΉ ΠΎΡΠΎΡΠ°ΡΠΈΠ½Π³Π΅Π°Π»ΡΠ½ΠΎΠΉ ΠΎΠ±Π»Π°ΡΡΠΈ
Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection
We report on measurements of 11-18 cm wavelength radio emission from
interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield
Accelerator. The electrons were observed both in a configuration where they
produced primarily transition radiation from an aluminum foil, and in a
configuration designed for the electrons to produce Cherenkov radiation in a
silica sand target. Our aim was to emulate the large electron excess expected
to develop during an electromagnetic cascade initiated by an ultra high-energy
particle. Such charge asymmetries are predicted to produce strong coherent
radio pulses, which are the basis for several experiments to detect high-energy
neutrinos from the showers they induce in Antarctic ice and in the lunar
regolith. We detected coherent emission which we attribute both to transition
and possibly Cherenkov radiation at different levels depending on the
experimental conditions. We discuss implications for experiments relying on
radio emission for detection of electromagnetic cascades produced by ultra
high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR
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