8,648 research outputs found
Polarization switching and nonreciprocity in symmetric and asymmetric magnetophotonic multilayers with nonlinear defect
A one-dimensional magnetophotonic crystal with a nonlinear defect placed
either symmetrically or asymmetrically inside the structure is considered.
Simultaneous effects of time-reversal nonreciprocity and nonlinear spatial
asymmetry in the structure are studied. Bistable response is demonstrated in a
such system, accompanied by abrupt polarization switching between two circular
or elliptical polarizations for transmitted and reflected waves. The effect is
explained in terms of field localization at defect-mode spectral resonances and
can be used in the design of thin-film optical isolators and polarization
transformation devices.Comment: 20 pages, 8 figure
Matrix bandwidth and profile reduction
This program, REDUCE, reduces the bandwidth and profile of sparse symmetric matrices, using row and corresponding column permutations. It is a realization of the algorithm described by the authors elsewhere. It was extensively tested and compared with several other programs and was found to be considerably faster than the others, superior for bandwidth reduction and as satisfactory as any other for profile reduction
Low-energy Antiproton Interaction with Helium
An ab initio potential for the interaction of the neutral helium atom with
antiprotons and protons is calculated using the Born-Oppenheimer approximation.
Using this potential, the annihilation cross section for antiprotons in the
energy range 0.01 microvolt to 1 eV is calculated.Comment: 13 pages, 7 figures, LaTe
Small Orbits
We study both the "large" and "small" U-duality charge orbits of extremal
black holes appearing in D = 5 and D = 4 Maxwell-Einstein supergravity theories
with symmetric scalar manifolds. We exploit a formalism based on cubic Jordan
algebras and their associated Freudenthal triple systems, in order to derive
the minimal charge representatives, their stabilizers and the associated
"moduli spaces". After recalling N = 8 maximal supergravity, we consider N = 2
and N = 4 theories coupled to an arbitrary number of vector multiplets, as well
as N = 2 magic, STU, ST^2 and T^3 models. While the STU model may be considered
as part of the general N = 2 sequence, albeit with an additional triality
symmetry, the ST^2 and T^3 models demand a separate treatment, since their
representative Jordan algebras are Euclidean or only admit non-zero elements of
rank 3, respectively. Finally, we also consider minimally coupled N = 2, matter
coupled N = 3, and "pure" N = 5 theories.Comment: 40 pages, 9 tables. References added. Expanded comments added to
sections III. C. 1. and III. F.
Test of classical nucleation theory on deeply supercooled high-pressure simulated silica
We test classical nucleation theory (CNT) in the case of simulations of
deeply supercooled, high density liquid silica, as modelled by the BKS
potential. We find that at density ~g/cm, spontaneous nucleation
of crystalline stishovite occurs in conventional molecular dynamics simulations
at temperature T=3000 K, and we evaluate the nucleation rate J directly at this
T via "brute force" sampling of nucleation events. We then use parallel,
constrained Monte Carlo simulations to evaluate , the free energy
to form a crystalline embryo containing n silicon atoms, at T=3000, 3100, 3200
and 3300 K. We find that the prediction of CNT for the n-dependence of fits reasonably well to the data at all T studied, and at 3300 K yields a
chemical potential difference between liquid and stishovite that matches
independent calculation. We find that , the size of the critical nucleus,
is approximately 10 silicon atoms at T=3300 K. At 3000 K, decreases to
approximately 3, and at such small sizes methodological challenges arise in the
evaluation of when using standard techniques; indeed even the
thermodynamic stability of the supercooled liquid comes into question under
these conditions. We therefore present a modified approach that permits an
estimation of at 3000 K. Finally, we directly evaluate at T=3000
K the kinetic prefactors in the CNT expression for J, and find physically
reasonable values; e.g. the diffusion length that Si atoms must travel in order
to move from the liquid to the crystal embryo is approximately 0.2 nm. We are
thereby able to compare the results for J at 3000 K obtained both directly and
based on CNT, and find that they agree within an order of magnitude.Comment: corrected calculation, new figure, accepted in JC
Characterization of 1D photonic crystal nanobeam cavities using curved microfiber
We investigate high-Q, small mode volume photonic crystal nanobeam cavities using a curved, tapered optical microfiber loop. The strength of the coupling between the cavity and the microfiber loop is shown to depend on the contact position on the nanobeam, angle between the nanobeam and the microfiber, and polarization of the light in the fiber. The results are compared to a resonant scattering measurement
Existence of a critical point in the phase diagram of the ideal relativistic neutral Bose gas
We explore the phase transitions of the ideal relativistic neutral Bose gas
confined in a cubic box, without assuming the thermodynamic limit nor
continuous approximation. While the corresponding non-relativistic canonical
partition function is essentially a one-variable function depending on a
particular combination of temperature and volume, the relativistic canonical
partition function is genuinely a two-variable function of them. Based on an
exact expression of the canonical partition function, we performed numerical
computations for up to hundred thousand particles. We report that if the number
of particles is equal to or greater than a critical value, which amounts to
7616, the ideal relativistic neutral Bose gas features a spinodal curve with a
critical point. This enables us to depict the phase diagram of the ideal Bose
gas. The consequent phase transition is first-order below the critical pressure
or second-order at the critical pressure. The exponents corresponding to the
singularities are 1/2 and 2/3 respectively. We also verify the recently
observed `Widom line' in the supercritical region.Comment: 1+25 pages, 6 B/W figures: Comment on the Widom line added. Minor
improvement. Version to appear in `New Journal of Physics
Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism
Dehydration hastens the decline in cerebral blood flow (CBF) during incremental exercise, while the cerebral metabolic rate for oxygen (CMRO2) is preserved. It remains unknown whether CMRO2 is also maintained during prolonged exercise in the heat and whether an eventual decline in CBF is coupled to fatigue. Two studies were undertaken. In study 1, ten male cyclists cycled in the heat for ~2 h with (control) and without fluid replacement (dehydration) while internal (ICA) and external (ECA) carotid artery blood flow and core and blood temperature were obtained. Arterial and internal jugular venous blood samples were assessed with dehydration to evaluate the CMRO2. In study 2 (8 males), middle cerebral artery blood velocity (MCA Vmean) was measured during prolonged exercise to exhaustion in both dehydrated and euhydrated states. After a rise at the onset of exercise, ICA flow declined to baseline with progressive dehydration (P < 0.05). However, cerebral metabolism remained stable through enhanced oxygen and glucose extraction (P < 0.05). ECA flow increased for one hour but declined prior to exhaustion. Fluid ingestion maintained cerebral and extra-cranial perfusion throughout non-fatiguing exercise. During exhaustive exercise, however, euhydration delayed but did not prevent the decline in cerebral perfusion. In conclusion, during prolonged exercise in the heat dehydration accelerates the decline in CBF without affecting CMRO2 and also restricts extra-cranial perfusion. Thus fatigue is related to reduction in CBF and extra-cranial perfusion rather than in CMRO2.The study was supported by a grant from the Gatorade Sports Science Institute, PepsiCo Inc, USA
The Reaction 7Li(pi+,pi-)7B and its Implications for 7B
The reaction 7Li(pi+,pi-)7B has been measured at incident pion energies of
30-90 MeV. 7Li constitutes the lightest target nucleus, where the pionic charge
exchange may proceed as a binary reaction to a discrete final state. Like in
the Delta-resonance region the observed cross sections are much smaller than
expected from the systematics found for heavier nuclei. In analogy to the
neutron halo case of 11Li this cross section suppression is interpreted as
evidence for a proton halo in the particle-unstable nucleus 7B.Comment: 4 pages, 4 figure
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