3,003 research outputs found
Composite fermions from the algebraic point of view
Composite fermion wavefuctions have been used to describe electrons in a
strong magnetic field. We show that the polynomial part of these wavefunctions
can be obtained by applying a normal ordered product of suitably defined
annihilation and creation operators to an even power of the Vandermonde
determinant, which can been considered as a kind of a non-trivial Fermi sea. In
the case of the harmonic interaction we solve the system exactly in the lowest
Landau level. The solution makes explicit the boson-fermion correspondence
proposed recently.Comment: 11 pages 1 figur
Computer assisted Doppler waveform analysis and ultrasound derived turbulence intensity ratios can predict early hyperplasia development in newly created vascular access fistula: Pilot study, methodology and analysis.
OBJECTIVES:
Following surgical creation of arterio-venous fistulae (AVF), the desired outward remodeling is often accompanied by the development of neointimal hyperplasia (NIH), which can stymie maturation and may lead to thrombosis and access failure. The aim of this study was to investigate the feasibility of using a non-invasive test, to detect and quantify the turbulent flow patterns believed to be associated with NIH development.
DESIGN: This was a prospective, observational study. Ultrasound derived turbulence intensity ratios (USTIR) were calculated from spectral Doppler waveforms, recorded from newly formed AVF, and were compared with haemodynamic and structural changes observed during the initial maturation period.
SETTING: Measurements were obtained by accredited Clinical Vascular Scientists, at the Royal Free Hospital, London.
PARTICIPANTS: Patients with newly created AVF were invited to participate in the study. A total of 30 patients were initially recruited with 19 participants completing the 10 week study protocol.
OUTCOME MEASURES:
The primary outcome measure was the development of NIH resulting in a haemodynamically significant lesion.
The secondary outcome was successful maturation of the AVF at 10 weeks.
RESULTS: Elevated USTIR in the efferent vein 2 weeks post surgery corresponded to the development of NIH formation (P = 0.02). A cut off of 6.39% predicted NIH development with a sensitivity of 87.5% and a specificity of 80%.
CONCLUSION:
Analysis of Doppler waveforms can successfully identify deleterious flow patterns and predict inward luminal remodelling in maturing AVF. We propose a longitudinal follow up study to assess the viability of this technique as a surveillance tool
Search for a simultaneous signal from small transient events in the Pierre Auger Observatory and the Tupi muon telescopes
We present results of a search for a possible signal from small scale solar
transient events (such as flares and interplanetary shocks) as well as possible
counterparts to Gamma-Ray Burst (GRB) observed simultaneously by the Tupi muon
telescope Niteroi-Brazil, 22.90S, 43.20W, 3 m above sea level) and the Pierre
Auger Observatory surface detectors (Malargue-Argentina, 69.30S, 35.30W,
altitude 1400 m). Both cosmic ray experiments are located inside the South
Atlantic Anomaly (SAA) region. Our analysis of several examples shows
similarities in the behavior of the counting rate of low energy (above 100 MeV)
particles in association with the solar activity (solar flares and
interplanetary shocks). We also report an observation by the Tupi experiment of
the enhancement of muons at ground level with a significance higher than 8
sigma in the 1-sec binning counting rate (raw data) in close time coincidence
(T-184 sec) with the Swift-BAT GRB110928B (trigger=504307). The GRB 110928B
coordinates are in the field of view of the vertical Tupi telescope, and the
burst was close to the MAXI source J1836-194. The 5-min muon counting rate in
the vertical Tupi telescope as well as publicly available data from Auger (15
minutes averages of the scaler rates) show small peaks above the background
fluctuations at the time following the Swift-BAT GRB 110928B trigger. In
accordance with the long duration trigger, this signal can possibly suggest a
long GRB, with a precursor narrow peak at T-184 sec.Comment: 9 pages, 13 figure
Toroidal equilibria in spherical coordinates
The standard Grad-Shafranov equation for axisymmetric toroidal plasma
equilibrium is customary expressed in cylindrical coordinates with toroidal
contours, and through which benchmark equilibria are solved. An alternative
approach to cast the Grad-Shafranov equation in spherical coordinates is
presented. This equation, in spherical coordinates, is examined for toroidal
solutions to describe low Solovev and high plasma equilibria in
terms of elementary functions
Time-dependent magnetohydrodynamic self-similar extragalactic jets
Extragalactic jets are visualized as dynamic erruptive events modelled by
time-dependent magnetohydrodynamic (MHD) equations. The jet structure comes
through the temporally self-similar solutions in two-dimensional axisymmetric
spherical geometry. The two-dimensional magnetic field is solved in the finite
plasma pressure regime, or finite regime, and it is described by an
equation where plasma pressure plays the role of an eigenvalue. This allows a
structure of magnetic lobes in space, among which the polar axis lobe is
strongly peaked in intensity and collimated in angular spread comparing to the
others. For this reason, the polar lobe overwhelmes the other lobes, and a jet
structure arises in the polar direction naturally. Furthermore, within each
magnetic lobe in space, there are small secondary regions with closed
two-dimensional field lines embedded along this primary lobe. In these embedded
magnetic toroids, plasma pressure and mass density are much higher accordingly.
These are termed as secondary plasmoids. The magnetic field lines in these
secondary plasmoids circle in alternating sequence such that adjacent plasmoids
have opposite field lines. In particular, along the polar primary lobe, such
periodic plasmoid structure happens to be compatible with radio observations
where islands of high radio intensities are mapped
Magnetic-field-dependent zero-bias diffusive anomaly in Pb oxide-n-InAs structures: Coexistence of two- and three-dimensional states
The results of experimental and theoretical studies of zero-bias anomaly
(ZBA) in the Pb-oxide-n-InAs tunnel structures in magnetic field up to 6T are
presented. A specific feature of the structures is a coexistence of the 2D and
3D states at the Fermi energy near the semiconductor surface. The dependence of
the measured ZBA amplitude on the strength and orientation of the applied
magnetic field is in agreement with the proposed theoretical model. According
to this model, electrons tunnel into 2D states, and move diffusively in the 2D
layer, whereas the main contribution to the screening comes from 3D electrons.Comment: 8 double-column pages, REVTeX, 9 eps figures embedded with epsf,
published versio
Tunnelling Studies of Two-Dimensional States in Semiconductors with Inverted Band Structure: Spin-orbit Splitting, Resonant Broadening
The results of tunnelling studies of the energy spectrum of two-dimensional
(2D) states in a surface quantum well in a semiconductor with inverted band
structure are presented. The energy dependence of quasimomentum of the 2D
states over a wide energy range is obtained from the analysis of tunnelling
conductivity oscillations in a quantizing magnetic field. The spin-orbit
splitting of the energy spectrum of 2D states, due to inversion asymmetry of
the surface quantum well, and the broadening of 2D states at the energies, when
they are in resonance with the heavy hole valence band, are investigated in
structures with different strength of the surface quantum well. A quantitative
analysis is carried out within the framework of the Kane model of the energy
spectrum. The theoretical results are in good agreement with the tunnelling
spectroscopy data.Comment: 29 pages, RevTeX, submitted in Phys.Rev.B. Figures available on
request from [email protected]
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