6,611 research outputs found
Hydrodynamic Equation for the Breakdown of the Quantum Hall Effect in a Uniform Current
The hydrodynamic equation for the spatial and temporal evolution of the
electron temperature T_e in the breakdown of the quantum Hall effect at
even-integer filling factors in a uniform current density j is derived from the
Boltzmann-type equation, which takes into account electron-electron and
electron-phonon scatterings. The derived equation has a drift term, which is
proportional to j and to the first spatial derivative of T_e. Applied to the
spatial evolution of T_e in a sample with an abrupt change of the width along
the current direction, the equation gives a distinct dependence on the current
direction as well as a critical relaxation, in agreement with the recent
experiments.Comment: 4 pages, 1 Postscript figure, corrected equations, to be published in
J. Phys. Soc. Jpn. 70 (2001) No.
Hydrodynamic Equations in Quantum Hall Systems at Large Currents
Hydrodynamic equations (HDEQs) are derived which describe spatio-temporal
evolutions of the electron temperature and the chemical potential of
two-dimensional systems in strong magnetic fields in states with large diagonal
resistivity appearing at the breakdown of the quantum Hall effect. The
derivation is based on microscopic electronic processes consisting of drift
motions in a slowly-fluctuating potential and scattering processes due to
electron-electron and electron-phonon interactions. In contrast with the usual
HDEQs, one of the derived HDEQs has a term with an energy flux perpendicular to
the electric field due to the drift motions in the magnetic field. As an
illustration, the current distribution is calculated using the derived HDEQs.Comment: 10 pages, 2 Postscript figures, to be published in J. Phys. Soc. Jpn.
71 (2002) No.
Photonuclear reactions with Zinc: A case for clinical linacs
The use of bremsstrahlung photons produced by a linac to induce photonuclear
reactions is wide spread. However, using a clinical linac to produce the
photons is a new concept. We aimed to induce photonuclear reactions on zinc
isotopes and measure the subsequent transition energies and half-lives. For
this purpose, a bremsstrahlung photon beam of 18 MeV endpoint energy produced
by the Philips SLI-25 linac has been used. The subsequent decay has been
measured with a well-shielded single HPGe detector. The results obtained for
transition energies are in good agreement with the literature data and in many
cases surpass these in accuracy. For the half-lives, we are in agreement with
the literature data, but do not achieve their precision. The obtained accuracy
for the transition energies show what is achievable in an experiment such as
ours. We demonstrate the usefulness and benefits of employing clinical linacs
for nuclear physics experiments
Thermohydrodynamics in Quantum Hall Systems
A theory of thermohydrodynamics in two-dimensional electron systems in
quantizing magnetic fields is developed including a nonlinear transport regime.
Spatio-temporal variations of the electron temperature and the chemical
potential in the local equilibrium are described by the equations of
conservation with the number and thermal-energy flux densities. A model of
these flux densities due to hopping and drift processes is introduced for a
random potential varying slowly compared to both the magnetic length and the
phase coherence length. The flux measured in the standard transport experiment
is derived and is used to define a transport component of the flux density. The
equations of conservation can be written in terms of the transport component
only. As an illustration, the theory is applied to the Ettingshausen effect, in
which a one-dimensional spatial variation of the electron temperature is
produced perpendicular to the current.Comment: 10 pages, 1 figur
Critical exponents of a three dimensional O(4) spin model
By Monte Carlo simulation we study the critical exponents governing the
transition of the three-dimensional classical O(4) Heisenberg model, which is
considered to be in the same universality class as the finite-temperature QCD
with massless two flavors. We use the single cluster algorithm and the
histogram reweighting technique to obtain observables at the critical
temperature. After estimating an accurate value of the inverse critical
temperature \Kc=0.9360(1), we make non-perturbative estimates for various
critical exponents by finite-size scaling analysis. They are in excellent
agreement with those obtained with the expansion method with
errors reduced to about halves of them.Comment: 25 pages with 8 PS figures, LaTeX, UTHEP-28
Vibration and buckling of thin-walled composite I-beams with arbitrary lay-ups under axial loads and end moments
A finite element model with seven degrees of freedom per node is developed to study vibration and buckling of thin-walled composite I-beams with arbitrary lay-ups under constant axial loads and equal end moments. This model is based on the classical lamination theory, and accounts for all the structural coupling coming from material anisotropy. The governing differential equations are derived from the Hamilton’s principle. Numerical results are obtained for thin-walled composite I-beams to investigate the effects of axial force, bending moment and fiber orientation on the buckling moments, natural frequencies, and corresponding vibration mode shapes as well as axial-moment-frequency interaction curves
Pre-operative management of Pleomorphic and florid lobular carcinoma in situ of the breast: Report of a large multi-institutional series and review of the literature
Background: Pleomorphic and Florid Lobular carcinoma in situ (P/F LCIS) are rare variants of LCIS, the exact nature of which is still debated. Aim: To collect a large series of P/F LCIS diagnosed on preoperative biopsies and evaluate their association with invasive carcinoma and high grade duct carcinoma in situ (DCIS). Data obtained were compared with those reported in the literature. Methods: A multi-institutional series of P/F LCIS was retrieved. All cases were diagnosed on pre-operative biopsies, which was followed by an open surgical excision. Data on post-operative histopathology were available. A literature review was performed. Results: A total of 117 cases were collected; invasive carcinoma and/or DCIS was present in 78/117 cases (66.7%). Seventy cases of P/F LCIS were pure on biopsy and 31 of these showed pathological upgrade in post-surgical specimens. Pre-operative biopsy accuracy was 47/78 (60.3%); pre-operative biopsy underestimation of cancer was 31/78 (39,7.%). In the literature review papers, invasive carcinoma or DCIS was associated with 274 of 418 (65.5%) cases of P/F LCIS. Pre-operative biopsy accuracy was 66% (181/274) whereas pre-operative biopsy underestimation of cancer was 33.9% (93/274). Conclusions: The data presented here indicate that P/F LCIS is frequently associated with invasive carcinoma or high grade DCIS and that pre-operative biopsy is associated with an underestimation of malignancy. Open surgery is indicated when P/F LCIS is diagnosed pre-operatively
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