34,486 research outputs found
Electromechanical Imaging of Biological Systems with Sub-10 nm Resolution
Electromechanical imaging of tooth dentin and enamel has been performed with
sub-10 nm resolution using piezoresponse force microscopy. Characteristic
piezoelectric domain size and local protein fiber ordering in dentin have been
determined. The shape of a single collagen fibril in enamel is visualized in
real space and local hysteresis loops are measured. Because of the ubiquitous
presence of piezoelectricity in biological systems, this approach is expected
to find broad application in high-resolution studies of a wide range of
biomaterials.Comment: 12 pages, 4 figures, submitted for publication in Appl. Phys. Let
Global Disk Oscillation Modes in Cataclysmic Variables and Other Newtonian Accretors
Diskoseismology, the theoretical study of small adiabatic hydrodynamical
global perturbations of geometrically thin, optically thick accretion disks
around black holes (and other compact objects), is a potentially powerful probe
of the gravitational field. For instance, the frequencies of the normal mode
oscillations can be used to determine the elusive angular momentum parameter of
the black hole. The general formalism developed by diskoseismologists for
relativistic systems can be readily applied to the Newtonian case of
cataclysmic variables (CVs). Some of these systems (e.g., the dwarf nova SS
Cygni) show rapid oscillations in the UV with periods of tens of seconds and
high coherence. In this paper, we assess the possibility that these dwarf nova
oscillations (DNOs) are diskoseismic modes. Besides its importance in
investigating the physical origin of DNOs, the present work could help us to
answer the following question. To what extent are the similarities in the
oscillation phenomenology of CVs and X-ray binaries (XRBs) indicative of a
common physical mechanism?Comment: 1 figur
Double Beta Decay, Nuclear Structure and Physics beyond the Standard Model
Neutrinoless Double Beta Decay () is presently the only known
experiment to distinguisch between Dirac neutrinos, different from their
antiparticles, and Majorana neutrinos, identical with their antiparticles. In
addition allows to determine the absolute scale of the
neutrino masses. This is not possible with neutrino oscillations. To determine
the neutrino masses one must assume, that the light Majorana neutrino exchange
is the leading mechanism for and that the matrix element of
this transition can ba calculated reliably. The experimental
transition amplitude in this mechanism is a product of the light left handed
effective Majorana neutrino mass and of this transition matrix element. The
different methods, Quasi-particle Random Phase Approximation (QRPA), Shell
Model (SM), Projected Hartree-Fock-Bogoliubov (PHFB) and Interacting Boson
Model (IBM2) used in the literature and the reliability of the matrix elements
in these approaches are reviewed. In the second part it is investigated how one
can determine the leading mechanism or mechanisms from the data of the
decay in different nuclei. Explicite expressions are given for
the transition matrix elements. is shown, that possible interference terms
allow to test CP (Charge and Parity conjugation) violation.Comment: Contribution to the EPS conference in Eilath: "Nuclear Physics in
Astrophysics 5." April 3rd to 8th. 201
On the Perturbations of Viscous Rotating Newtonian Fluids
The perturbations of weakly-viscous, barotropic, non-self-gravitating,
Newtonian rotating fluids are analyzed via a single partial differential
equation. The results are then used to find an expression for the
viscosity-induced normal-mode complex eigenfrequency shift, with respect to the
case of adiabatic perturbations. However, the effects of viscosity are assumed
to have been incorporated in the unperturbed (equilibrium) model. This paper is
an extension of the normal-mode formalism developed by Ipser & Lindblom for
adiabatic pulsations of purely-rotating perfect fluids. The formulas derived
are readily applicable to the perturbations of thin and thick accretion disks.
We provide explicit expressions for thin disks, employing results from previous
relativistic analyses of adiabatic normal modes of oscillation. In this case,
we find that viscosity causes the fundamental p- and g- modes to grow while the
fundamental c-mode could have either sign of the damping rate.Comment: Accepted for publication by The Astrophysical Journal. 11 pages, no
figure
GOES observations of solar protons during ground level enhancements
Since 1974, the U.S. National Oceanic and Atmospheric Administration (NOAA) has observed solar proton fluxes from the Geostationary Operational Environmental Satellites (GOES). These observations frequently have served as measurements of the primary component of ground level enhancements (GLEs). Until March 2020, when GOES-14 and -15 were turned off, solar proton measurements were made by the Energetic Particle Sensor (EPS) and the High-Energy Proton and Alpha Detector (HEPAD). EPS had poor energy resolution above 100 MeV, and NOAA derived a >100 MeV integral flux from the EPS channels to support alerts issued by the Space Weather Forecast Office. HEPAD provided some energy resolution in the 330-700 MeV range and a >700 MeV integral channel. Starting with GOES-16, a new instrument called the Solar and Galactic Proton Sensor (SGPS) has replaced EPS and HEPAD. SGPS uses three solid-state telescopes to observe solar proton fluxes between 1 and 500 MeV with a >500 MeV integral channel. The >100 MeV integral flux is now derived from SGPS observations and includes the >500 MeV flux in its derivation. In this paper, we describe the older EPS and HEPAD observations and the new SGPS solar proton observations. We also compare methods for detecting solar proton event onsets currently used with GOES and neutron monitor observations and recommend some innovations
Superconductivuty versus Tunneling in a Doped Antiferromagnetic Ladder
The low-energy charge excitations of a doped antiferromagnetic ladder are
modeled by a system of interacting spinless fermions that live on the same
ladder. A relatively large spin gap is assumed to ``freeze out'' all spin
fluctuations. We find that the formation of rung hole pairs coincides with the
opening of a single-particle gap for charge excitations along chains and with
the absence of coherent tunneling in between chains. We also find that such
hole pairs condense into either a crystalline or superconducting state as a
function of the binding energy.Comment: 15 pgs. in PLAIN TeX, 2 figs. in postscript, to appear in Phys. Rev.
Berezinskii-Kosterlitz-Thouless Transition in Spin-Charge Separated Superconductor
A model for spin-charge separated superconductivity in two dimensions is
introduced where the phases of the spinon and holon order parameters couple
gauge-invariantly to a statistical gauge-field representing chiral
spin-fluctuations. The model is analyzed in the continuum limit and in the
low-temperature limit. In both cases we find that physical electronic phase
correlations show a superconducting-normal phase transition of the
Berezinskii-Kosterlitz-Thouless type, while statistical gauge-field excitations
are found to be strictly gapless. The normal-to-superconductor phase boundary
for this model is also obtained as a function of carrier density, where we find
that its shape compares favorably with that of the experimentally observed
phase diagram for the oxide superconductors.Comment: 35 pages, TeX, CSLA-P-93-
Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin-1/2
Quantum magnetic properties in a geometrically frustrated lattice of spin-1/2
magnet, such as quantum spin liquid or solid and the associated spin
fractionalization, are considered key in developing a new phase of matter. The
feasibility of observing the quantum magnetic properties, usually found in
geometrically frustrated lattice of spin-1/2 magnet, in a perovskite material
with controlled disorder is demonstrated. It is found that the controlled
chemical disorder, due to the chemical substitution of Ru ions by Co-ions, in a
simple perovskite CaRuO3 creates a random prototype configuration of artificial
spin-1/2 that forms dimer pairs between the nearest and further away ions. The
localization of the Co impurity in the Ru matrix is analyzed using the Anderson
localization formulation. The dimers of artificial spin-1/2, due to the
localization of Co impurities, exhibit singlet-to-triplet excitation at low
temperature without any ordered spin correlation. The localized gapped
excitation evolves into a gapless quasi-continuum as dimer pairs break and
create freely fluctuating fractionalized spins at high temperature. Together,
these properties hint at a new quantum magnetic state with strong resemblance
to the resonance valence bond system.Comment: 8 pages, 6 figure
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