28,543 research outputs found
Evolution of a localized thermal explosion in a reactive gas
Experimental observations of ignition in premixed gaseous reactants indicate that perfectly homogeneous initiation is practically unrealizable. Instead, combustion first sets in, as a rule, at small, discrete sites where inherent inhomogeneities cause chemical activity to proceed preferentially and lead to localized explosions. Combustion waves propagating away from these hot spots or reaction centers eventually envelop the remaining bulk. This study examines the spatial structure and temporal evolution of a hot spot for a model involving Arrhenius kinetics. The hot spot, characterized by peaks in pressure and temperature with little diminution in local density, is shown to have one of two possible self-similar structures. The analysis employs a combination of asymptotics and numerics, and terminates when pressure and temperature in the explosion have peaked
Complex consultations in primary care: a tool for assessing the range of health problems and issues addressed in general practice consultations
Background: There is an increasing recognition that many consultations in general practice involve several problems covering multiple disease domains. However there is a paucity of reliable tools and techniques to understand and quantify this phenomenon. The objective was to develop a tool that can be used to measure the number and type of problems discussed in primary care consultations. Methods: Thirteen consultations between general practitioners and patients were initially videoed and reviewed to identify the problems and issues discussed. An iterative process involving a panel of clinicians and researchers and repeated cycles of testing and development was used to develop a measurement proforma and coding manual for assessment of video recorded consultations. The inter-rater reliability of this tool was assessed in 60 consultations. Results: The problems requiring action were usually readily identified. However the different dimensions of the problem and how they were addressed required the identification and definition of ‘issues’. A coding proforma was developed that allowed quantification of the numbers and types of health problems and issues discussed. Ten categories of issues were identified and defined. At the consultation level, inter-rater agreements for the number of problems discussed (within ±1), types of problems and issues were 98.3%, 96.5% and 90% respectively. The tool has subsequently been used to analyse 229 consultations. Conclusion: The iterative approach to development of the tool reflected the complexity of doctor-patient interactions. A reliable tool has been developed that can be used to analyse the number and range of problems managed in primary care consultations
Electronic and Magnetic Properties of Electron-doped Superconductor, Sm_{1.85}Ce_{0.15}CuO_{4-delta}
Temperature-dependent magnetization (M(T)) and specific heat (C_p(T))
measurements were carried out on single crystal Sm_{1.85}Ce_{0.15}CuO_{4-delta}
(T_c = 16.5 K). The magnetic anisotropy in the static susceptibility, chi
{equiv} M/H, is apparent not only in its magnitude but also in its temperature
dependence, with chi_{perp} for H{perp}c larger than chi_{parallel} for
H{parallel}c. For both field orientations, chi does not follow the Curie-Weiss
behavior due to the small energy gap of the J = 7/2 multiplet above the J = 5/2
ground-state multiplet. However, with increasing temperature, chi_{parallel}(T)
exhibits a broad minimum near 100 K and then a slow increase while
chi_{perp}(T) shows a monotonic decrease. A sharp peak in C_p(T) at 4.7 K
manifests an antiferromagnetic ordering. The electronic contribution, gamma, to
C_p(T) is estimated to be gamma = 103.2 (7) mJ/moleSmK^2. The entropy
associated with the magnetic ordering is much smaller than Rln2, where R is the
gas constant, which is usually expected for the doublet ground state of
Sm^{+3}. The unusual magnetic and electronic properties evident in M(T) and
C_p(T) are probably due to a strong anisotropic interaction between conduction
electrons and localized electrons at Sm^{+3} sites.Comment: 5 pages, 5 encapsulated postscript figures, late
Spectral characteristics for a spherically confined -1/r + br^2 potential
We consider the analytical properties of the eigenspectrum generated by a
class of central potentials given by V(r) = -a/r + br^2, b>0. In particular,
scaling, monotonicity, and energy bounds are discussed. The potential is
considered both in all space, and under the condition of spherical confinement
inside an impenetrable spherical boundary of radius R. With the aid of the
asymptotic iteration method, several exact analytic results are obtained which
exhibit the parametric dependence of energy on a, b, and R, under certain
constraints. More general spectral characteristics are identified by use of a
combination of analytical properties and accurate numerical calculations of the
energies, obtained by both the generalized pseudo-spectral method, and the
asymptotic iteration method. The experimental significance of the results for
both the free and confined potential V(r) cases are discussed.Comment: 16 pages, 4 figure
The FIR-absorption of short period quantum wires and the transition from one to two dimensions
We investigate the FIR-absorption of short period parallel quantum wires in a
perpendicular quantizing magnetic field. The external time-dependent electric
field is linearly polarized along the wire modulation. The mutual Coulomb
interaction of the electrons is treated self-consistently in the ground state
and in the absorption calculation within the Hartree approximation. We consider
the effects of a metal gate grating coupler, with the same or with a different
period as the wire modulation, on the absorption. The evolution of the
magnetoplasmon in the nonlocal region where it is split into several Bernstein
modes is discussed in the transition from: narrow to broad wires, and isolated
to overlapping wires. We show that in the case of narrow and not strongly
modulated wires the absorption can be directly correlated with the underlying
electronic bandstructure.Comment: 15 pages, 9 figures, Revtex, to appear in Phys. Rev.
Inelastic electron tunneling via molecular vibrations in single-molecule transistors
In single-molecule transistors, we observe inelastic cotunneling features
that correspond energetically to vibrational excitations of the molecule, as
determined by Raman and infrared spectroscopy. This is a form of inelastic
electron tunneling spectroscopy of single molecules, with the transistor
geometry allowing in-situ tuning of the electronic states via a gate electrode.
The vibrational features shift and change shape as the electronic levels are
tuned near resonance, indicating significant modification of the vibrational
states. When the molecule contains an unpaired electron, we also observe
vibrational satellite features around the Kondo resonance.Comment: 5 pages, 4 figures. Supplementary information available upon reques
Lipid accumulation in isolated perfused rat hearts has no apparent effect on mechanical function or energy metabolism as measured by 31P NMR.
Male Sprague-Dawley rats were fed diets that contained 20% by weight soybean oil or rapeseed oil (21% and 43% erucic acid) for 7 days. The rapeseed oil diets increased the cardiac triacylglycerol content 5-fold and 25-fold, respectively, above control values. Hearts were removed from the animals and perfused with modified Krebs-Henseleit buffer at 37 degrees C. The calculated rate-pressure product was used as a measure of contractile function. 31P NMR spectra were acquired throughout a protocol that consisted of 12 min control perfusion, followed by 12 min perfusion with 20 microM isoproterenol, 12 min washout, 12 min total global ischemia, and 28 min reperfusion. The steady state levels of creatine phosphate, ATP, intracellular pH, contractile function, and the free energy of ATP hydrolysis (delta GATP) were determined for all three groups of hearts. Isoproterenol more than doubled the rate-pressure product of the hearts on all diets and decreased the concentrations of creatine phosphate and ATP with a concomitant rise in Pi. After global ischemia, creatine phosphate levels recovered fully, ATP levels remained low, and most hearts developed ventricular fibrillation. Changes in intracellular pH were the same for all groups: pH was 7.1 throughout the equilibration and isoproterenol perfusion period, decreased to pH approximately 6.4 during ischemia, and returned to 7.0 during reperfusion. The results indicate that the fat accumulation that occurs in the hearts of rats fed diets rich in high erucic acid rapeseed oil does not interfere with the cardiac high energy phosphate metabolism or contractile function.(ABSTRACT TRUNCATED AT 250 WORDS
Magnetic Flux Periodic Response of Nano-perforated Ultrathin Superconducting Films
We have patterned a hexagonal array of nano-scale holes into a series of
ultrathin, superconducting Bi/Sb films with transition temperatures 2.65 K
5 K. These regular perforations give the films a phase-sensitive
periodic response to an applied magnetic field. By measuring this response in
their resistive transitions, , we are able to distinguish regimes in
which fluctuations of the amplitude, both the amplitude and phase, and the
phase of the superconducting order parameter dominate the transport. The
portion of dominated by amplitude fluctuations is larger in lower
films and thus, grows with proximity to the superconductor to
insulator transition.Comment: Revised title, abstract, text, figure
Decitabine impact on the endocytosis regulator RhoA, the folate carriers RFC1 and FOLR1, and the glucose transporter GLUT4 in human tumors.
BackgroundIn 31 solid tumor patients treated with the demethylating agent decitabine, we performed tumor biopsies before and after the first cycle of decitabine and used immunohistochemistry (IHC) to assess whether decitabine increased expression of various membrane transporters. Resistance to chemotherapy may arise due to promoter methylation/downregulation of expression of transporters required for drug uptake, and decitabine can reverse resistance in vitro. The endocytosis regulator RhoA, the folate carriers FOLR1 and RFC1, and the glucose transporter GLUT4 were assessed.ResultsPre-decitabine RhoA was higher in patients who had received their last therapy >3 months previously than in patients with more recent prior therapy (P = 0.02), and varied inversely with global DNA methylation as assessed by LINE1 methylation (r = -0.58, P = 0.006). Tumor RhoA scores increased with decitabine (P = 0.03), and RFC1 also increased in patients with pre-decitabine scores ≤150 (P = 0.004). Change in LINE1 methylation with decitabine did not correlate significantly with change in IHC scores for any transporter assessed. We also assessed methylation of the RFC1 gene (alias SLC19A1). SLC19A1 methylation correlated with tumor LINE1 methylation (r = 0.45, P = 0.02). There was a small (statistically insignificant) decrease in SLC19A1 methylation with decitabine, and there was a trend towards change in SLC19A1 methylation with decitabine correlating with change in LINE1 methylation (r = 0.47, P <0.15). While SLC19A1 methylation did not correlate with RFC1 scores, there was a trend towards an inverse correlation between change in SLC19A1 methylation and change in RFC1 expression (r = -0.45, P = 0.19).ConclusionsIn conclusion, after decitabine administration, there was increased expression of some (but not other) transporters that may play a role in chemotherapy uptake. Larger patient numbers will be needed to define the extent to which this increased expression is associated with changes in DNA methylation
Perturbations of spacetime: gauge transformations and gauge invariance at second order and beyond
We consider in detail the problem of gauge dependence that exists in
relativistic perturbation theory, going beyond the linear approximation and
treating second and higher order perturbations. We first derive some
mathematical results concerning the Taylor expansion of tensor fields under the
action of one-parameter families (not necessarily groups) of diffeomorphisms.
Second, we define gauge invariance to an arbitrary order . Finally, we give
a generating formula for the gauge transformation to an arbitrary order and
explicit rules to second and third order. This formalism can be used in any
field of applied general relativity, such as cosmological and black hole
perturbations, as well as in other spacetime theories. As a specific example,
we consider here second order perturbations in cosmology, assuming a flat
Robertson-Walker background, giving explicit second order transformations
between the synchronous and the Poisson (generalized longitudinal) gauges.Comment: slightly revised version, accepted for publication in Classical and
Quantum Gravity. 27 pages including 4 figures, latex using 2 CQG style files:
ioplppt.sty, iopl10.st
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