15,739 research outputs found
Hyperbolic outer billiards : a first example
We present the first example of a hyperbolic outer billiard. More precisely
we construct a one parameter family of examples which in some sense correspond
to the Bunimovich billiards.Comment: 11 pages, 8 figures, to appear in Nonlinearit
Ionization signals from electrons and alpha-particles in mixtures of liquid Argon and Nitrogen - perspectives on protons for Gamma Resonant Nuclear Absorption applications
In this paper we report on a detailed study of ionization signals produced by
Compton electrons and alpha-particles in a Time Projection Chamber (TPC) flled
with different mixtures of liquid Argon and Nitrogen. The measurements were
carried out with Nitrogen concentrations up to 15% and a drift electric feld in
the range 0-50 kV/cm. A prediction for proton ionization signals is made by
means of interpolation. This study has been conducted in view of the possible
use of liquid Ar-N2 TPCs for the detection of gamma-rays in the resonant band
of the Nitrogen absorption spectrum, a promising technology for security and
medical applications
30 kV coaxial vacuum-tight feedthrough for operation at cryogenic temperatures
In this paper we describe the technology of building a vacuum-tight high
voltage feedthrough which is able to operate at voltages up to 30 kV. The
feedthrough has a coaxial structure with a grounded sheath which makes it
capable to lead high voltage potentials into cryogenic liquids, without risk of
surface discharges in the gas phase above the liquid level. The feedthrough is
designed to be used in ionization detectors, based on liquefied noble gases,
such as Argon or Xenon
Spin chain from membrane and the Neumann-Rosochatius integrable system
We find membrane configurations in AdS_4 x S^7, which correspond to the
continuous limit of the SU(2) integrable spin chain, considered as a limit of
the SU(3) spin chain, arising in N=4 SYM in four dimensions, dual to strings in
AdS_5 x S^5. We also discuss the relationship with the Neumann-Rosochatius
integrable system at the level of Lagrangians, comparing the string and
membrane cases.Comment: LaTeX, 16 pages, no figures; v2: 17 pages, title changed,
explanations and references added; v3: more explanations added; v4: typos
fixed, to appear in Phys. Rev.
Donor binding energy and thermally activated persistent photoconductivity in high mobility (001) AlAs quantum wells
A doping series of AlAs (001) quantum wells with Si delta-modulation doping
on both sides reveals different dark and post-illumination saturation
densities, as well as temperature dependent photoconductivity. The lower dark
two-dimensional electron density saturation is explained assuming deep binding
energy of Delta_DK = 65.2 meV for Si-donors in the dark. Persistent
photoconductivity (PPC) is observed upon illumination, with higher saturation
density indicating shallow post-illumination donor binding energy. The
photoconductivity is thermally activated, with 4 K illumination requiring
post-illumination annealing to T = 30 K to saturate the PPC. Dark and
post-illumination doping efficiencies are reported.Comment: The values of binding energy changed from previous versions because
of a better understanding for the dielectric permittivity. Also, the Gamma -
X donor states are better explaine
Laboratory simulations of astrophysical jets and solar coronal loops: new results
An experimental program underway at Caltech has produced plasmas where the shape is neither fixed by the vacuum chamber nor fixed by an external coil set, but instead is determined by self-organization. The plasma dynamics is highly reproducible and so can be studied in considerable detail even though the morphology of the plasma is both complex and time-dependent. A surprising result has been the observation that self-collimating MHD-driven plasma jets are ubiquitous and play a fundamental role in the self-organization. The jets can be considered lab-scale simulations of astrophysical jets and in addition are intimately related to solar coronal loops. The jets are driven by the combination of the axial component of the J×B force and the axial pressure gradient resulting from the non-uniform pinch force associated with the flared axial current density. Behavior is consistent with a model showing that collimation results from axial non-uniformity of the jet velocity. In particular, flow stagnation in the jet frame compresses frozen-in azimuthal magnetic flux, squeezes together toroidal magnetic field lines, thereby amplifying the embedded toroidal magnetic field, enhancing the pinch force, and hence causing collimation of the jet
Ovarian hormones: a long overlooked but critical contributor to cognitive brain structures and function
Cognitive neuroscience research has traditionally overlooked half of the population. Arguing that variability in ovarian hormones confounds empirical findings, girls and women have been excluded from research for decades. But times are changing. This review summarizes historical trends that have led to a knowledge gap in the role of ovarian hormones in neuroscience, synthesizes recent findings on ovarian hormone contributions to cognitive brain structures and function, and highlights areas ripe for future work. This is accomplished by reviewing research that has leveraged natural experiments in humans across the life span that focus on puberty, the menstrual cycle, hormonal contraceptive use, menopause, and menopausal hormone therapy. Although findings must be considered in light of study designs (e.g., sample characteristics and group comparisons versus randomized crossover trials), across natural experiments there is consistent evidence for associations of estradiol with cortical thickness, especially in frontal regions, and hippocampal volumes, as well as with frontal regions during cognitive processing. There are also emerging investigations of resting state connectivity and progesterone along with exciting opportunities for future work, particularly concerning biopsychosocial moderators of and individual differences in effects in novel natural experiments. Thus, delineating complex ovarian hormone contributions to cognitive brain structures and function will advance neuroscience.This review summarizes historical trends that have led to a knowledge gap in the role of ovarian hormones in neuroscience, synthesizes recent findings on ovarian hormone contributions to cognitive brain structures and function, and highlights areas ripe for future work.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154624/1/nyas14255_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154624/2/nyas14255.pd
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