5,649 research outputs found
Bulk Fermi surface and electronic properties of CuBiSe
The electronic properties of CuBiSe have been
investigated using Shubnikov-de Haas and optical reflectance measurements.
Quantum oscillations reveal a bulk, three-dimensional Fermi surface with
anisotropy 2 and a modest increase in
free-carrier concentration and in scattering rate with respect to the undoped
BiSe, also confirmed by reflectivity data. The effective mass is
almost identical to that of BiSe. Optical conductivity reveals a
strong enhancement of the bound impurity bands with Cu addition, suggesting
that a significant number of Cu atoms enter the interstitial sites between Bi
and Se layers or may even substitute for Bi. This conclusion is also supported
by X-ray diffraction measurements, where a significant increase of microstrain
was found in CuBiSe, compared to BiSe.Comment: Accepted to Phys. Rev B (R
Prediction of risk of fracture in the tibia due to altered bone mineral density distribution resulting from disuse : a finite element study
The disuse-related bone loss that results from immobilisation following injury shares characteristics with osteoporosis in postmenopausal women and the aged, with decreases in bone mineral density (BMD) leading to weakening of the bone and increased risk of fracture. The aim of the study was to use the finite element method to: (i) calculate the mechanical response of the tibia under mechanical load and (ii) estimate the risk of fracture; comparing between two groups, an able bodied (AB) group and spinal cord injury (SCI) patients group suffering from varying degree of bone loss. The tibiae of eight male subjects with chronic SCI and those of four able-bodied (AB) age-matched controls were scanned using multi-slice peripheral Quantitative Computed Tomography. Images were used to develop full three-dimensional models of the tibiae in Mimics (Materialise) and exported into Abaqus (Simulia) for calculation of stress distribution and fracture risk in response to specified loading conditions – compression, bending and torsion. The percentage of elements that exceeded a calculated value of the ultimate stress provided an estimate of the risk of fracture for each subject, which differed between SCI subjects and their controls. The differences in BMD distribution along the tibia in different subjects resulted in different regions of the bone being at high risk of fracture under set loading conditions, illustrating the benefit of creating individual material distribution models. A predictive tool can be developed based on these models, to enable clinicians to estimate the amount of loading that can be safely allowed onto the skeletal frame of individual patients who suffer from extensive musculoskeletal degeneration (including SCI, multiple sclerosis and the ageing population). The ultimate aim would be to reduce fracture occurrence in these vulnerable groups
Ordered low-temperature structure in K4C60 detected by infrared spectroscopy
Infrared spectra of a K4C60 single-phase thin film have been measured between
room temperature and 20 K. At low temperatures, the two high-frequency T1u
modes appear as triplets, indicating a static D2h crystal-field stabilized
Jahn-Teller distortion of the (C60)4- anions. The T1u(4) mode changes into the
known doublet above 250 K, a pattern which could have three origins: a dynamic
Jahn-Teller effect, static disorder between "staggered" anions, or a phase
transition from an orientationally-ordered phase to one where molecular motion
is significant.Comment: 4 pages, 2 figures submitted to Phys. Rev.
Readout of solid-state charge qubits using a single-electron pump
A major difficulty in realizing a solid-state quantum computer is the
reliable measurement of the states of the quantum registers. In this paper, we
propose an efficient readout scheme making use of the resonant tunneling of a
ballistic electron produced by a single electron pump. We treat the measurement
interaction in detail by modeling the full spatial configuration, and show that
for pumped electrons with suitably chosen energy the transmission coefficient
is very sensitive to the qubit state. We further show that by using a short
sequence of pumping events, coupled with a simple feedback control procedure,
the qubit can be measured with high accuracy.Comment: 5 pages, revtex4, 4 eps figures. v2: published versio
Supermetallic conductivity in bromine-intercalated graphite
Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to
in-plane charge conductivities which increase monotonically with intercalation
time toward values (for ~6 at% Br) that are significantly higher than Cu at
temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic
susceptibility measurements confirm that the Br dopes the graphene sheets with
holes while simultaneously increasing the interplanar separation. The increase
of mobility (~ 5E4 cm^2/Vs at T=300 K) and resistance anisotropy together with
the reduced diamagnetic susceptibility of the intercalated samples suggests
that the observed supermetallic conductivity derives from a parallel
combination of weakly-coupled hole-doped graphene sheets.Comment: 5 pages, 4 figure
Study of charge dynamics in transparent single-walled carbon nanotube films
We report the transmission over a wide frequency range (far infrared -
visible) of pristine and hole-doped, free-standing carbon nanotube films at
temperatures between 50 K and 300 K. Optical constants are estimated by
Kramers-Kronig analysis of transmittance. We see evidence in the far infrared
for a gap below 10 meV. Hole doping causes a shift of spectral weight from the
first interband transition into the far infrared. Temperature dependence in
both the doped and undoped samples is restricted to the far-infrared region.Comment: 6 pages, 4 figures, submitted to Phys. Rev. B v3: Fig. 2 replaced,
changes in caption of Table II, minor changes in tex
A method to find unstable periodic orbits for the diamagnetic Kepler Problem
A method to determine the admissibility of symbolic sequences and to find the
unstable periodic orbits corresponding to allowed symbolic sequences for the
diamagnetic Kepler problem is proposed by using the ordering of stable and
unstable manifolds. By investigating the unstable periodic orbits up to length
6, a one to one correspondence between the unstable periodic orbits and their
corresponding symbolic sequences is shown under the system symmetry
decomposition
Infrared Evidence for Collagen Structures
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71134/2/JCPSA6-22-9-1621-1.pd
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