Revised Fowler-Dubridge model for photoelectron emission from two-dimensional materials

We revise the Fowler-Dubridge (FB) model for photoelectron emission from two-dimensional (2D) materials to include the effects of reduced dimensionality, non-parabolic and anisotropic energy dispersion of 2D materials. Two different directions of electron emission are studied, namely vertical emission from the surface and lateral emission from the edge. Our analytical model reveals a universal temperature scaling of T\b{eta} with \b{eta} = 1 and \b{eta} = 3/2, respectively, for the surface and edge emission over a wide class of 2D materials, which are distinct from the traditional scaling of \b{eta} = 2 originally derived for the traditional bulk materials. Our comparison shows good agreement to two experiments of photo-electron emitted from graphene for both surface and edge emission. Our calculations also show the photoelectron emission is more pronounced than the coexisting thermionic emission for materials with low temperature and Fermi energy. This model provides helpful guidance in choosing proper combinations of light intensity, temperature range and type of 2D materials for the design of photoemitters, photodetectors and other optoelectronicsComment: 6 pages, 4 figure

Absolute instability in a traveling wave tube model

A model is constructed to evaluate absolute instability which may lead to bandedge oscillations in a traveling wave tube. Under the assumptions (a) that all modes have forward group velocities, and (b) that the slow wave structure has a parabolic dispersion relation in the ω-kω-k plane, the threshold coupling constant (Pierce’s parameter CC) is calculated for the onset of absolute instability. The effect of distributed resistive loss in the circuit is included. The axial wave number and the characteristic frequency of the oscillation at the onset are given. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70326/2/PHPAEN-5-12-4408-1.pd

Control of atom-photon interactions with shaped quantum electron wavepackets

Photon emission from atoms and free electrons underlie a wealth of fundamental science and technological innovations. We present a regime where atom-photon and electron-photon interactions interfere with each other, resulting in substantial changes in the spontaneous emission rate compared to the sum of each interaction considered in isolation. We highlight the critical role played by quantum electron wavepackets, and how the emission can be tailored via the electron waveshape, as well as the atomic population and coherence. Our findings reveal that atom-photon and electron-photon interactions cannot be considered in isolation even when higher-order contributions involving all three bodies (atom, photon and free electron) are negligible. Our findings pave the way to more precise control over photon emission processes and related diagnostics.Comment: 9 pages, 4 figure

Monotectic and syntectic alloys: ASTP experiment MA-044

A postflight preliminary technical evaluation is presented of the returned samples of aluminum antimonide (AlSb) syntectic compound and lead-zinc (PbZn) monotectic immiscible processed during the Apollo-Soyuz Test Project (ASTP) mission. The returned cartridges, extracted ampoules, and removed samples were examined in detail. A genesis of the experiment is given along with a summary of the efforts and various scheduled tests up to the ASTP mission. A tentative characterization plan is developed from the postflight preliminary examination which makes use of the limited number of available samples and is based on the initial observations. It is indicated that a higher degree of compositional homogeneity in aluminum antimonide was achieved under flight test conditions

Resonant absorption of a short-pulse laser in a doped dielectric

A simple model is used to calculate the energy absorption efficiency when a laser of short pulse length impinges on a dielectric slab that is doped with an impurity with a resonant line at the laser frequency. It is found that the energy absorption efficiency is maximized for a certain degree of doping concentration (at a given pulse length) and also for a certain pulselength (at a given doping concentration). Dimensionless parameters are constructed, allowing calculations with one set of parameters be used to infer the results expected for other sets of parameters. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70124/2/APPLAB-74-20-2912-1.pd

Analysis of laser absorption on a rough metal surface

We have developed a simple model to estimate the cumulative absorption coefficient of an ultraviolet laser pulse impinging on a pure metal, including the effects of surface roughness whose scale is much larger than the laser wavelength λ. The multiple reflections from the rough surface may increase the absorption coefficient over a pristine, flat surface by an order of magnitude. Thus, as much as 16% (at room temperature) of the power of a 248 nm KrF excimer laser pulse may be absorbed by an aluminum target. A comparison with experimental data is given. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71289/2/APPLAB-70-6-696-1.pd

The association between overall health, psychological distress, and occupational heat stress among a large national cohort of 40,913 Thai workers

BACKGROUND Occupational heat stress is a well-known problem, particularly in tropical countries, affecting workers, health and well-being. There are very few recent studies that have reported on the effect of heat stress on mental health, or overall health in workers, although socioeconomic development and rapid urbanization in tropical developing countries like Thailand create working conditions in which heat stress is likely. OBJECTIVE This study is aimed at identifying the relationship between self-reported heat stress and psychological distress, and overall health status in Thai workers. RESULTS 18% of our large national cohort (>40,000 subjects) often works under heat stress conditions and males are exposed to heat stress more often than females. Furthermore, working under heat stress conditions is associated with both worse overall health and psychological distress (adjusted odds ratios ranging from 1.49 to 1.84). CONCLUSIONS This association between occupational heat stress and worse health needs more public health attention and further development on occupational health interventions as climate change increases Thailand's temperatures.This study was supported by the International Collaborative Research Grants Scheme with joint grants from the Wellcome Trust UK (GR0587MA) and the Australian NHMRC (268055)

Effects of an external magnetic field, and of oblique radio-frequency electric fields on multipactor discharge on a dielectric

This paper analyzes, separately, the effects of an external magnetic field, the rf magnetic field, and of an oblique rf electric field, on multipactor discharge on a dielectric. Using Monte Carlo simulation, we obtain the susceptibility diagram in terms of the magnetic field, the rf electric field, and the dc charging field for various dielectric materials. We find that a magnetic field parallel to either the rf electric field or the dc electric field does not qualitatively change the susceptibility diagram. However, an external magnetic field perpendicular to both the rf electric field and the dc electric field can significantly affect the susceptibility diagram. Thus oriented magnetic fields lower the upper susceptibility bound when the magnetic field strength is approximately equal to Bres[T] = 0.036f(GHz),Bres[T]=0.036f(GHz), where f is the rf frequency. Both the lower and upper susceptibility boundary may be raised significantly by a large external magnetic field, B≫Bres.B≫Bres. Susceptibility to single surface multipactor is greatest when the rf electric field is nearly parallel to the dielectric, but is dramatically decreased for angles of obliqueness greater than approximately 5°–10°. The rf magnetic field does not affect the lower boundary, but may extend the upper boundary greatly. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70933/2/PHPAEN-7-2-750-1.pd