9,457 research outputs found
Emission Optics of the Steigerwald Type Electron Gun
The emission optics of a Steigerwald type electron gun is re-examined. The
virtual and real points of divergence, divergence angles and beam-widths of the
electron beams at different telefocusing strength are measured in detail for
first time . Two different Wehnelt cylinders are used to establish a
contrasting viewpoint. The original `focusing' curves measured by Braucks are
reconstructed and will be explained only through a `new' interpretation which
is different from the conventional views. While the image of the emitting
surface in front of the filament is indeed telefocused beyond the anode, the
envelope of the beam does not `focus' as expected. A new model for the emission
mechanism is established based on our results.Comment: 14 pages, 10 figure
Anisotropic superconducting properties of aligned SmLaFeAsOF microcrystalline powder
The SmLaFeAsOF compound is a quasi-2D
layered superconductor with a superconducting transition temperature T = 52
K. Due to the Fe spin-orbital related anisotropic exchange coupling
(antiferromagnetic or ferromagnetic fluctuation), the tetragonal
microcrystalline powder can be aligned at room temperature using the
field-rotation method where the tetragonal -plane is parallel to the
aligned magnetic field B and -axis along the rotation axis.
Anisotropic superconducting properties with anisotropic diamagnetic ratio
2.4 + 0.6 was observed from low field susceptibility
(T) and magnetization M(B). The anisotropic low-field phase diagram
with the variation of lower critical field gives a zero-temperature penetration
depth (0) = 280 nm and (0) = 120 nm. The magnetic
fluctuation used for powder alignment at 300 K may be related with the pairing
mechanism of superconductivity at lower temperature.Comment: 4 pages, 6 figure
Evolution of population with sexual and asexual reproduction in changing environment
Using a lattice model based on Monte Carlo simulations, we study the role of
the reproduction pattern on the fate of an evolving population. Each individual
is under the selection pressure from the environment and random mutations. The
habitat ("climate") is changing periodically. Evolutions of populations
following two reproduction patterns are compared, asexual and sexual. We show,
via Monte Carlo simulations, that sexual reproduction by keeping more
diversified populations gives them better chances to adapt themselves to the
changing environment. However, in order to obtain a greater chance to mate, the
birth rate should be high. In the case of low birth rate and high mutation
probability there is a preference for the asexual reproduction.Comment: 11 pages including figs., for Int. J. Mod. Phys. C 15, issue 2 (2004
Prospects of cold dark matter searches with an ultra-low-energy germanium detector
The report describes the research program on the development of
ultra-low-energy germanium detectors, with emphasis on WIMP dark matter
searches. A threshold of 100 eV is achieved with a 20 g detector array,
providing a unique probe to the low-mas WIMP. Present data at a surface
laboratory is expected to give rise to comparable sensitivities with the
existing limits at the WIMP-mass range. The projected
parameter space to be probed with a full-scale, kilogram mass-range experiment
is presented. Such a detector would also allow the studies of neutrino-nucleus
coherent scattering and neutrino magnetic moments.Comment: 3 pages, 4 figures, Proceedings of TAUP-2007 Conferenc
Wigner Crystalline Edges in nu < 1 Quantum Dots
We investigate the edge reconstruction phenomenon believed to occur in
quantum dots in the quantum Hall regime when the filling fraction is nu < 1.
Our approach involves the examination of large dots (< 40 electrons) using a
partial diagonalization technique in which the occupancies of the deep interior
orbitals are frozen. To interpret the results of this calculation, we evaluate
the overlap between the diagonalized ground state and a set of trial
wavefunctions which we call projected necklace (PN) states. A PN state is
simply the angular momentum projection of a maximum density droplet surrounded
by a ring of localized electrons. Our calculations reveal that PN states have
up to 99% overlap with the diagonalized ground states, and are lower in energy
than the states identified in Chamon and Wen's study of the edge
reconstruction.Comment: 8 pages, 8 figures, to be published in Phys. Rev.
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Upgrade of the A0 photo injector laser system for NML accelerator test facility at Fermilab
The current Fermilab A0 Photoinjector laser system includes a seed laser, a flashlamp pumped multipass amplifier cavity, a flashlamp pumped 2-pass amplifier system followed by an Infra-Red (IR) to Ultra-Violet (UV) conversion stage. However the current system can only deliver up to 800 pulses due to the low efficiency of Nd:Glass used inside multi-pass cavity. In this paper we will report the effort to develop a new multi pass cavity based on Nd:YLF crystal end-pumped by diode laser. We will also discuss the foreseen design of the laser system for the NML accelerator test facility at Fermilab
Association Between Stigma Towards HIV and MSM and Intimate Partner Violence Among Newly HIV-Diagnosed Chinese Men Who Have Sex With Men
Background: HIV- and MSM-related stigma are well documented as common for Chinese men who have sex with men (MSM) living with HIV, yet there is sparse literature on intimate partner violence (IPV) and its relationship with stigma in this vulnerable population. To evaluate the association between HIV-stigma and stigma related to homosexuality and IPV among newly HIV-diagnosed MSM in China. Methods: Data were collected in the baseline survey among newly HIV-diagnosed Chinese MSM in a randomized clinical trial via face-to-face interviews. Univariate logistic and multivariate logistic regression analyses were performed to assess the associations between IPV and HIV- and MSM-related stigma. Results: Of 367 newly HIV-diagnosed Chinese MSM, 23.7% experienced any IPV, including 16.6% physical, 7.4% psychological and 5.2% sexual IPV. Positive associations were found between HIV- and MSM-related stigma and IPV. Men with high HIV-related stigma (score ≥ 27) were 1.67 times as likely to experience any IPV as those with low stigma (adjusted odds ratio [AOR]: 1.67, 95% confidence interval [CI]: 1.02-2.76). Men with high MSM-related stigma (score ≥ 6) were 1.99 times as likely to experience any IPV as those with low stigma (AOR: 1.99, 95% CI: 1.18-3.36). Conclusions: HIV- and MSM-related stigmas was positively associated with IPV experiences among newly diagnosed MSM in China. The manner in which stigma may exacerbate IPV, and/or the influence of IPV on worsening stigma should be further evaluated. The high prevalence of IPV and stigma in this population suggests that interventions should be taken to reduce stigma and prevent this risky behavior among MSM
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