15,171 research outputs found
Deep shower interpretation of the cosmic ray events observed in excess of the Greisen-Zatsepin-Kuzmin energy
We consider the possibility that the ultra-high-energy cosmic ray flux has a
small component of exotic particles which create showers much deeper in the
atmosphere than ordinary hadronic primaries. It is shown that applying the
conventional AGASA/HiRes/Auger data analysis procedures to such exotic events
results in large systematic biases in the energy spectrum measurement. SubGZK
exotic showers may be mis-reconstructed with much higher energies and mimick
superGZK events. Alternatively, superGZK exotic showers may elude detection by
conventional fluorescence analysis techniques.Comment: 22 pages, 5 figure
Condensation of the atomic relaxation vibrations in lead-magnesium-niobate at
We present neutron diffraction, dielectric permittivity and photoconductivity
measurements, evidencing that lead-magnesium niobate experiences a diffuse
phase transformation between the spherical glass and quadrupole glass phases,
in the temperature interval between 400 K and 500 K, with the quadrupole phase
possessing extremely high magnitudes of dielectric permittivity. Our analysis
shows that the integral diffuse scattering intensity may serve as an order
parameter for this transformation. Our experimental dielectric permittivity
data support this choice. These data are important for the aplications desiring
giant dielectric responses, in a wide temperature intervals and not related to
electron's excitations.Comment: 6 figure
Basic studies of baroclinic flows
Computations were completed of transition curves in the conventional annulus, including hysteresis effect. The model GEOSIM was used to compute the transition between axisymmetric flow and baroclinic wave flow in the conventional annulus experiments. Thorough testing and documentation of the GEOSIM code were also completed. The Spacelab 3 results from the Geophysical Fluid Flow Cell (GFFC) were reviewed and numerical modeling was performed of many of the cases with horizontal temperature gradients as well as heating from below, with different rates of rotation. A numerical study of the lower transition to axisymmetric flow in the baroclinic annulus was performed using GEOSIM
Spectroscopic applications and frequency locking of THz photomixing with distributed-Bragg-reflector diode lasers in low-temperature-grown GaAs
A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Distributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidths of the DBR lasers. The heterodyne linewidth full-width at half-maximum of two optically locked DBR lasers is 50 kHz on the 20 ms time scale and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 and 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limits of 1 × 10^–4 Hz^1/2 (noise/total power) have been achieved, with the noise floor dominated by the detector's noise equivalent power
Generalized Rayleigh and Jacobi processes and exceptional orthogonal polynomials
We present four types of infinitely many exactly solvable Fokker-Planck
equations, which are related to the newly discovered exceptional orthogonal
polynomials. They represent the deformed versions of the Rayleigh process and
the Jacobi process.Comment: 17 pages, 4 figure
Photo-Crosslinked Alginate Hydrogels Support Enhanced Matrix Accumulation by Nucleus Pulposus Cells in Vivo
Objective Intervertebral disc (IVD) degeneration is a major health concern in the United States. Replacement of the nucleus pulposus (NP) with injectable biomaterials represents a potential treatment strategy for IVD degeneration. The objective of this study was to characterize the extracellular matrix (ECM) assembly and functional properties of NP cell-encapsulated, photo-crosslinked alginate hydrogels in comparison to ionically crosslinked alginate constructs. Methods Methacrylated alginate was synthesized by esterification of hydroxyl groups with methacrylic anhydride. Bovine NP cells were encapsulated in alginate hydrogels by ionic crosslinking using CaCl2 or through photo-crosslinking upon exposure to long-wave UV light in the presence of a photoinitiator. The hydrogels were evaluated in vitro by gross and histological analysis and in vivo using a murine subcutaneous pouch model. In vivo samples were analyzed for gene expression, ECM localization and accumulation, and equilibrium mechanical properties. Results Ionically crosslinked hydrogels exhibited inferior proteoglycan accumulation in vitro and were unable to maintain structural integrity in vivo. In further studies, photo-crosslinked alginate hydrogels were implanted for up to 8 weeks to examine NP tissue formation. Photo-crosslinked hydrogels displayed temporal increases in gene expression and assembly of type II collagen and proteoglycans. Additionally, hydrogels remained intact over the duration of the study and the equilibrium Young\u27s modulus increased from 1.24 ± 0.09 kPa to 4.31 ± 1.39 kPa, indicating the formation of functional matrix with properties comparable to those of the native NP. Conclusions These findings support the use of photo-crosslinked alginate hydrogels as biomaterial scaffolds for NP replacement
Bank competition and financial stability : evidence from the U.S. banking deregulation
This paper examines the causal relationship between banking competition and financial stability. We find that an exogenous competition shock significantly improved the stability of banks, consistent with the ‘competition-stability hypothesis’. We
show that banks improved their cost efficiency and reduced credit risks in response to U.S. banking deregulation. In addition, we show the competition shock had a larger impact on banks who were initially operating in a less competitive environment. Our findings provide the first quasi-natural experimental evidence on the non-linear relationship between bank competition and financial stability
Phase control of La2CuO4 in thin-film synthesis
The lanthanum copper oxide, La2CuO4, which is an end member of the prototype
high-Tc superconductors (La,Sr)2CuO4 and (La,Ba)2CuO4, crystallizes in the
"K2NiF4" structure in high-temperature bulk synthesis. The crystal chemistry,
however, predicts that La2CuO4 is at the borderline of the K2NiF4 stability and
that it can crystallize in the Nd2CuO4 structure at low synthesis temperatures.
In this article we demonstrate that low-temperature thin-film synthesis
actually crystallizes La2CuO4 in the Nd2CuO4 structure. We also show that the
phase control of "K2NiF4"-type La2CuO4 versus "Nd2CuO4"-type La2CuO4 can be
achieved by varying the synthesis temperature and using different substrates.Comment: 4 pages, 5 figures, submitted to PRB, revte
Experimental signatures of the quantum-classical transition in a nanomechanical oscillator modeled as a damped driven double-well problem
We demonstrate robust and reliable signatures for the transition from quantum
to classical behavior in the position probability distribution of a damped
double-well system using the Qunatum State Diffusion approach to open quantum
systems. We argue that these signatures are within experimental reach, for
example in a doubly-clamped nanomechanical beam.Comment: Proceedings of the conference FMQT 1
Singlet-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr
We have performed time-of-flight neutron scattering measurements on powder
samples of the unconventional spin-Peierls compound TiOBr using the
fine-resolution Fermi chopper spectrometer (SEQUOIA) at the SNS. These
measurements reveal two branches of magnetic excitations within the
commensurate and incommensurate spin-Peierls phases, which we associate with n
= 1 and n = 2 triplet excitations out of the singlet ground state. These
measurements represent the first direct measure of the singlet-triplet energy
gap in TiOBr, which is determined to be Eg = 21.2 +/- 1.0 meV.Comment: 5 pages, 4 figures, submitted for publicatio
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