The Lewis Research Center geomagnetic substorm simulation facility

A simulation facility was established to determine the response of typical spacecraft materials to the geomagnetic substorm environment and to evaluate instrumentation that will be used to monitor spacecraft system response to this environment. Space environment conditions simulated include the thermal-vacuum conditions of space, solar simulation, geomagnetic substorm electron fluxes and energies, and the low energy plasma environment. Measurements for spacecraft material tests include sample currents, sample surface potentials, and the cumulative number of discharges. Discharge transients are measured by means of current probes and oscilloscopes and are verified by a photomultiplier. Details of this facility and typical operating procedures are presented

Data acquisition from high-speed rotating shafts

Data system, when used with a rotary transformer, results in increased life, negligible noise, and capability for a large number of data channels in testing rotating equipment. It is used to multiplex many channels of analog transducer output data and convert this signal to binary digital output

Investigation of nonlinear absorption processes with femtosecond light pulses in lithium niobate crystals

The propagation of high-power femtosecond light pulses in lithium niobate crystals (LiNbO3) is investigated experimentally and theoretically in collinear pump-probe transmission experiments. It is found within a wide intensity range that a strong decrease of the pump transmission coefficient at wavelength 388 nm fully complies with the model of two-photon absorption; the corresponding nonlinear absorption coefficient is betap~=3.5 cm/GW. Furthermore, strong pump pulses induce a considerable absorption for the probe at 776 nm. The dependence of the probe transmission coefficient on the time delay Deltat between probe and pump pulses is characterized by a narrow dip (at Deltat~=0) and a long (on the picosecond time scale) lasting plateau. The dip is due to direct two-photon transitions involving pump and probe photons; the corresponding nonlinear absorption coefficient is betar~=0.9 cm/GW. The plateau absorption is caused by the presence of pump-excited charge carriers; the effective absorption cross section at 776 nm is sigmar~=8×10^–18 cm^2. The above nonlinear absorption parameters are not strongly polarization sensitive. No specific manifestations of the relaxation of hot carriers are found for a pulse duration of ~=0.24 ps

Femtosecond time-resolved absorption processes in lithium niobate crystals

emtosecond pump pulses are strongly attenuated in lithium niobate owing to two-photon absorption; the relevant nonlinear coefficient beta_p ranges from ~3.5 cm/GW for lambda_p = 388 nm to ~0.1 cm/GW for 514 nm. In collinear pump-probe experiments the probe transmission at the double pump wavelength 2lambda_p=776 nm is controlled by two different processes: A direct absorption process involving pump and probe photons (beta_r ~ or = 0.9 cm/GW) leads to a pronounced short-duration transmission dip, whereas the probe absorption by pump-excited charge carriers results in a long-duration plateau. Coherent pump-probe interactions are of no importance. Hot-carrier relaxation occurs on the time scale of < or ~0.1 ps

Maxwell-Drude-Bloch dissipative few-cycle optical solitons

We study the propagation of few-cycle pulses in two-component medium consisting of nonlinear amplifying and absorbing two-level centers embedded into a linear and conductive host material. First we present a linear theory of propagation of short pulses in a purely conductive material, and demonstrate the diffusive behavior for the evolution of the low-frequency components of the magnetic field in the case of relatively strong conductivity. Then, numerical simulations carried out in the frame of the full nonlinear theory involving the Maxwell-Drude-Bloch model reveal the stable creation and propagation of few-cycle dissipative solitons under excitation by incident femtosecond optical pulses of relatively high energies. The broadband losses that are introduced by the medium conductivity represent the main stabilization mechanism for the dissipative few-cycle solitons.Comment: 38 pages, 10 figures. submitted to Physical Review

Development of environmental charging effect monitors for operational satellites

Design details and design goals are given of an instrumentation package to monitor the effects of the environmental charging of spacecraft surfaces on the systems of operational spacecraft

The Effect of Cost of Living on Employee Wages in the Hospitality Industry

This study examines the effect of cost of living (COL) on employee wages in the hotel industry. Although prior research clearly indicates that COL and wages are positively related, there is a lack of research explicitly considering the specific nature of the relationship between COL and wages, and potential moderators to the relationship. Using a dataset containing information on 97 jobs over 67 cities, our study shows that while there is a positive effect of COL on wages, the adjustment is not equal in magnitude to the difference that the COL levels would indicate. Furthermore, the effect of COL decreases as the average wage for the given job increases. We also show differences in COL’s effects for full-service versus limited-service hotels. We illustrate the implications of our findings by showing predicted wage rates for four jobs in five different cities, at both full-service and limit-service hotels. The study has implications for research, particularly for future work on COL and compensation. The findings also have important implications for practice, and may be particularly useful when managers need to set pay levels when local market data are unavailable

Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators

Whispering gallery resonators (WGR's), based on total internal reflection, possess high quality factors in a broad spectral range. Thus, nonlinear optical processes in such cavities are ideally suited for the generation of broadband or tunable electromagnetic radiation. Experimentally and theoretically, we investigate the tunability of optical parametric oscillation in a radially structured WGR made of lithium niobate. With a 1.04 /mum pump wave, the signal and idler waves are tuned from 1.78 to 2.5 \mum - including the point of degeneracy - by varying the temperature between 20 and 62 {\deg}C. A weak off-centering of the radial domain structure extends considerably the tuning capabilities. The oscillation threshold lies in the mW-power range.Comment: 4 pages, 5 figure

Electrometer system measures nanoamps at high voltage

Floating electrometer eliminates major source of error since any leakage from electrometer case, which is at high voltage, appears only as load on high voltage supply and not as part of current being measured. Commands to and data from floating electrometer are transferred across high voltage interface by means of optical channels

Asymmetry of Nonlinear Transport and Electron Interactions in Quantum Dots

The symmetry properties of transport beyond the linear regime in chaotic quantum dots are investigated experimentally. A component of differential conductance that is antisymmetric in both applied source-drain bias V and magnetic field B, absent in linear transport, is found to exhibit mesoscopic fluctuations around a zero average. Typical values of this component allow a measurement of the electron interaction strength.Comment: related papers at http://marcuslab.harvard.ed