577 research outputs found
Influence of temperature gradients on tunnel junction thermometry below 1 K: cooling and electron-phonon coupling
We have studied thermal gradients in thin Cu and AlMn wires, both
experimentally and theoretically. In the experiments, the wires were Joule
heated non-uniformly at sub-Kelvin temperatures, and the resulting temperature
gradients were measured using normal metal-insulator-superconducting tunnel
junctions. The data clearly shows that even in reasonably well conducting thin
wires with a short (m) non-heated portion, significant temperature
differences can form. In most cases, the measurements agree well with a model
which includes electron-phonon interaction and electronic thermal conductivity
by the Wiedemann-Franz law.Comment: J. Low Temp. Phys. in pres
Random Exchange Disorder in the Spin-1/2 XXZ Chain
The one-dimensional XXZ model is studied in the presence of disorder in the
Heisenberg Exchange Integral. Recent predictions obtained from renormalization
group calculations are investigated numerically using a Lanczos algorithm on
chains of up to 18 sites. It is found that in the presence of strong
X-Y-symmetric random exchange couplings, a ``random singlet'' phase with
quasi-long-range order in the spin-spin correlations persists. As the planar
anisotropy is varied, the full zero-temperature phase diagram is obtained and
compared with predictions of Doty and Fisher [Phys. Rev. B {\bf 45 }, 2167
(1992)].Comment: 9 pages + 8 plots appended, RevTex, FSU-SCRI-93-98 and
ORNL/CCIP/93/1
Educational and health outcomes of children treated for type 1 diabetes: Scotland-wide record linkage study of 766,047 children
Objective: This study was conducted to determine the association between childhood type 1 diabetes and educational and health outcomes.
Research Design and Methods: Record linkage of nine Scotland-wide databases (diabetes register, dispensed prescriptions, maternity records, hospital admissions, death certificates, annual pupil census, school absences/exclusions, school examinations, and unemployment) produced a cohort of 766,047 singleton children born in Scotland who attended Scottish schools between 2009 and 2013. We compared the health and education outcomes of schoolchildren receiving insulin with their peers, adjusting for potential confounders.
Results: The 3,330 children (0.47%) treated for type 1 diabetes were more likely to be admitted to the hospital (adjusted hazard ratio [HR] 3.97, 95% CI 3.79–4.16), die (adjusted HR 3.84, 95% CI 1.98–7.43), be absent from school (adjusted incidence rate ratio [IRR] 1.34, 95% CI 1.30–1.39), and have learning difficulties (adjusted odds ratio [OR] 1.19, 95% CI 1.03–1.38). Among children with type 1 diabetes, higher mean HbA1c (particularly HbA1c in the highest quintile) was associated with greater absenteeism (adjusted IRR 1.75, 95% CI 1.56–1.96, P < 0.001), increased school exclusion (adjusted IRR 2.82, 95% CI 1.14–6.98), poorer attainment (adjusted OR 3.52, 95% CI 1.72–7.18), and higher risk of unemployment (adjusted OR 2.01, 95% CI 1.05–3.85).
Conclusions: Children with type 1 diabetes fare worse than their peers in respect of education and health outcomes, especially if they have higher mean HbA1c. Interventions are required to minimize school absence and ensure that it does not affect educational attainment
Hund's Rule for Composite Fermions
We consider the ``fractional quantum Hall atom" in the vanishing Zeeman
energy limit, and investigate the validity of Hund's maximum-spin rule for
interacting electrons in various Landau levels. While it is not valid for {\em
electrons} in the lowest Landau level, there are regions of filling factors
where it predicts the ground state spin correctly {\em provided it is applied
to composite fermions}. The composite fermion theory also reveals a
``self-similar" structure in the filling factor range .Comment: 10 pages, revte
Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass
Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T
pulsed magnetic fields. The CF effective mass is found to increase
approximately linearly with the effective field , in agreement with our
earlier work at lower fields. For a of 14 T it reaches , over 20
times the band edge electron mass. Data from all fractions are unified by the
single parameter for all the samples studied over a wide range of
electron densities. The energy gap is found to increase like at
high fields.Comment: Has final table, will LaTeX without error
Fractional Quantum Hall States in Low-Zeeman-Energy Limit
We investigate the spectrum of interacting electrons at arbitrary filling
factors in the limit of vanishing Zeeman splitting. The composite fermion
theory successfully explains the low-energy spectrum {\em provided the
composite fermions are treated as hard-core}.Comment: 12 pages, revte
Systematic study of the effect of short range correlations on the form factors and densities of s-p and s-d shell nuclei
Analytical expressions of the one- and two-body terms in the cluster
expansion of the charge form factors and densities of the s-p and s-d shell
nuclei with N=Z are derived. They depend on the harmonic oscillator parameter b
and the parameter which originates from the Jastrow correlation
function. These expressions are used for the systematic study of the effect of
short range correlations on the form factors and densities and of the mass
dependence of the parameters b and . These parameters have been
determined by fit to the experimental charge form factors. The inclusion of the
correlations reproduces the experimental charge form factors at the high
momentum transfers (). It is found that while the parameter
is almost constant for the closed shell nuclei, He, O and
Ca, its values are larger (less correlated systems) for the open shell
nuclei, indicating a shell effect in the closed shell nuclei.Comment: Latex, 21 pages, 6 figures, 1 tabl
Asymptotic normalization coefficients for 8B->7Be+p from a study of 8Li->7Li+n
Asymptotic normalization coefficients (ANCs) for 8Li->7Li+n have been
extracted from the neutron transfer reaction 13C(7Li,8Li)12C at 63 MeV. These
are related to the ANCs in 8B->7Be+p using charge symmetry. We extract ANCs for
8B that are in very good agreement with those inferred from proton transfer and
breakup experiments. We have also separated the contributions from the p_1/2
and p_3/2 components in the transfer. We find the astrophysical factor for the
7Be(p,gamma)8B reaction to be S_17(0)=17.6+/-1.7 eVb. This is the first time
that the rate of a direct capture reaction of astrophysical interest has been
determined through a measurement of the ANCs in the mirror system.Comment: 5 pages, 3 figures, 2 table
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
Energy, interaction, and photoluminescence of spin-reversed quasielectrons in fractional quantum Hall systems
The energy and photoluminescence spectra of a two-dimensional electron gas in
the fractional quantum Hall regime are studied. The single-particle properties
of reversed-spin quasielectrons (QE's) as well as the
pseudopotentials of their interaction with one another and with Laughlin
quasielectrons (QE's) and quasiholes (QH's) are calculated. Based on the
short-range character of the QE--QE and QE--QE
repulsion, the partially unpolarized incompressible states at the filling
factors and are postulated within Haldane's
hierarchy scheme. To describe photoluminescence, the family of bound
QE states of a valence hole and QE's are
predicted in analogy to the found earlier fractionally charged excitons
QE. The binding energy and optical selection rules for both families are
compared. The QE is found radiative in contrast to the dark QE,
and the QE is found non-radiative in contrast to the bright
QE.Comment: 9 pages, 6 figure
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