Epitaxial ferromagnetic metal - semiconductor heterostructures are investigated using polarization-dependent electroabsorption measurements on GaAs p-type and n-type Schottky diodes with embedded In1-xGaxAs quantum wells. We have conducted studies as a function of photon energy, bias voltage, magnetic field, and excitation geometry. For optical pumping with circularly polarized light at energies above the band edge of GaAs, photocurrents with spin polarizations on the order of 1 % flow from the semiconductor to the ferromagnet under reverse bias. For optical pumping at normal incidence, this polarization may be enhanced significantly by resonant excitation at the quantum well ground-state. Measurements in a side-pumping geometry, in which the ferromagnet can be saturated in very low magnetic fields, show hysteresis that is also consistent with spin-dependent transport. Magneto-optical effects that influence these measurements are discussed.
Much of aerospace academia is anticipating a boom in Unmanned Aircraft (UA) funding and research opportunities. The expectation is built on the premise that UAs will revolutionize aerospace, which is likely based on current trends. There is also an anticipation of an increasing number of new platforms and research investment, which is likely but must be analysed carefully to determine where the opportunities might lie. This paper draws on the state of industry and a systems engineering approach. We explore what aspects of UAs really are the results of aerospace science advances and what aspects will be rather more mundane works of engineering.
Abstract This chapter discusses the traumatic crystallization of Hebrew scriptures. It reviews the motive of the Hasmoneans on supporting scriptural standardization and addresses the effect of communal trauma on scripture. It illustrates that the Jewish kings' preliminary development of standardized Hebrew scriptures was a precursor to the Christian Bible, Muslim Koran, and the Jewish Tanach.
Pyrite ${\mathrm{FeS}}_{2}$ is an outstanding candidate for a low-cost, nontoxic, sustainable photovoltaic material, but efficient pyrite-based solar cells are yet to materialize. Recent studies of single crystals have shed much light on this by uncovering a $p$-type surface inversion layer on $n$-type (S-vacancy doped) crystals, and the resulting internal p-n junction. This leaky internal junction likely plays a key role in limiting efficiency in pyrite-based photovoltaic devices, also obscuring the true bulk semiconducting transport properties of pyrite crystals. Here, we demonstrate complete mitigation of the internal p-n junction in ${\mathrm{FeS}}_{2}$ crystals by fabricating metallic ${\mathrm{CoS}}_{2}$ contacts via a process that simultaneously diffuses Co (a shallow donor) into the crystal, the resulting heavy $n$ doping yielding direct Ohmic contact to the interior. Low-temperature bulk transport studies of controllably Co- and S-vacancy doped semiconducting crystals then enable a host of previously inaccessible observations and measurements, including determination of donor activation energies (which are as low as 5 meV for Co), observation of an unexpected second activated transport regime, realization of electron mobility up to $2100\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\text{--}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\text{--}1}$, elucidation of very different mobilities in Co- and S-vacancy-doped cases, and observation of an abrupt temperature-dependent crossover to bulk Efros-Shklovskii variable-range hopping, accompanied by an unusual form of nonlinear Hall effect. Aspects of the results are interpreted with the aid of first-principles electronic structure calculations on both Co- and S-vacancy-doped ${\mathrm{FeS}}_{2}$. This work thus demonstrates unequivocal mitigation of the internal p-n junction in pyrite single crystals, with important implications for both future fundamental studies and photovoltaic devices.
Much of aerospace academia is anticipating a boom in Unmanned Aircraft (UA) funding and research opportunities. The expectation is built on the premise that UAs will revolutionize aerospace, which is likely based on current trends. There is also an anticipation of an increasing number of new platforms and research investment, which is likely but must be analysed carefully to determine where the opportunities might lie. This paper draws on the state of industry and a systems engineering approach. We explore what aspects of UAs really are the results of aerospace science advances and what aspects will be rather more mundane works of engineering.
Radial velocities derived from 40 medium-dispersion spectrograms acquired between 1970 and 1981, and light curves based on 440 UBV photometric observations, are presented for the truly Algol-type system DM Persei. The spectroscopic data yield a mass ratio of 0.32±0.02 for the binary, and show that it is part of a triple system with an orbital period of ∼100 day and semi-major axis ∼0.9 AU. The third component has a mass (for co-planar orbits) of ∼3.6 M⊙, and since it is not readily detected in the observed spectrum, could possibly be a binary system itself. An analysis of the three light curves by means of the synthesis code LIGHT confirms that the binary system is semi-detached and consists of a B5V primary and an A5III secondary. The parameters of the primary component concur with the empirical mass–luminosity relationship for detached systems. DM Per joins the small group of short-period early-type semi-detached massive systems, which include V Pup and u Her, whose characteristics differ significantly from the classical Algols.
The ability to remotely detect and map chemical vapour clouds in open air environments is a topic of significant interest to both defence and civilian communities. In this study, we integrate a prototype miniature colorimetric chemical sensor developed for methyl salicylate (MeS), as a model chemical vapour, into a micro unmanned aerial vehicle (UAV), and perform flights through a raised MeS vapour cloud. Our results show that that the system is capable of detecting MeS vapours at low ppm concentration in real-time flight and rapidly sending this information to users by on-board telemetry. Further, the results also indicate that the sensor is capable of distinguishing “clean” air from “dirty”, multiple times per flight, allowing us to look towards autonomous cloud mapping and source localization applications. Further development will focus on a broader range of integrated sensors, increased autonomy of detection and improved engineering of the system.
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