Gyro spring augmentation system

Spring-loaded piston with provision for hydraulic control of spring action varies the stiffness of hydraulic control systems

Investigation of Group V doping and passivating oxides to reduce the voltage deficit in CdTe solar cells

Includes bibliographical references.2022 Fall.Thin film cadmium telluride is one of the most successful photovoltaic technologies on the market today. Second only to silicon in yearly output and accounting for 40% of U.S. utility-scale photovoltaic installation, CdTe is known for its ease of manufacture, ideal bandgap, and low levelized cost of energy. Despite its commercial success, CdTe underperforms compared to its theoretical potential. The current world record CdTe device is only 21.0% compared to a theoretical maximum of 33.1%. This significant discrepancy in efficiencies can mostly be attributed to the poor open-circuit voltage of CdTe devices. Compared to silicon technologies, CdTe has a large voltage deficiency, exceeding 250 mV. While copper doping has traditionally been used for CdTe devices, it has proven to be incapable of sufficiently doping CdTe. Copper typically dopes CdTe in the 1014 to 1015 holes/cm3 range where most models predict that 1016–1017 is needed. Additionally, interstitial copper is a fast diffuser in CdTe, and can lead to numerous stability issues. As an alternative to copper, this work explores arsenic as a dopant for CdTe. Using a novel arsenic doping technique, hole concentrations greater than 1015 cm-3, microsecond lifetimes, and increased radiative efficiency are achieved. These are important prerequisites to achieving higher voltages. Achieving high doping levels alone is not sufficient to achieve higher device performance. A well-passivated and carrier selective contact is needed to ensure that electron-hole pairs do not recombine and are extracted as useable energy. Aluminum oxide has been shown to passivate CdTe surfaces. This work illustrates the explorations of using Al2O¬3 as a passivation layer, pairing it with highly doped amorphous silicon as a hole contact, resulting in excess-carrier lifetimes up to 8 µs, the highest reported to date for polycrystalline Cd(Se)Te. Although the inclusion of arsenic doping and an aluminum oxide back contact are each explored separately, the combination of both methods result in massive improvements to the carrier lifetime, interface passivation and radiative efficiency. Through this combination, microsecond lifetime and External Radiative Efficiency of over 4% are achieved. The excellent ERE values measured here are indicative of large quasi-Fermi level splitting, leading to an implied voltage with multiple device structures of nearly 1 V and an implied voltage of 25%. Finally, while CdSeTe serves as a more promising photovoltaic absorber candidate compared to CdTe, certain difficulties remain which must be addressed. Careful selection of processing conditions is shown to create a dense and large-grained film while eliminating wurtzite-phase crystal growth, which has been shown to degrade device performance. Surprisingly, as-deposited CdSeTe is shown to be n-type or nearly intrinsic rather than the previously supposed p-type. This necessitates additional steps to account for very poor hole conductivity, which can produce zero-current devices if not addressed. Challenges notwithstanding, CdSeTe absorbers are shown to be a key component in devices capable of a photovoltaic conversion efficiency of greater than 25%

Thinking Hard About \u27Race-Neutral\u27 Admissions

Our exploration is organized as follows. In Part I, we sympathetically consider the very difficult dilemmas facing higher education leaders. Understanding the often irreconcilable pressures that constrain university administrators is essential if we are to envision the plausible policies they might undertake. In Part II, we draw on a range of data to illustrate some of the “properties” of admissions systems and, in particular, the ways in which race, SES, and academic preparation interact dynamically both within individual schools and across the educational spectrum. Partly because the questions we examine here have been so little studied, ideal data does not exist, but there are enough government and university sources of data to grasp many key dynamics. In Part III, we turn to the “compliance” question—how have major schools conformed with or evaded the requirement of race-neutral policies? We examine in some depth admissions data from the University of California and the University of Michigan and find strong evidence of non-compliance in both cases. What does their conduct tell us about the operation of these policies? In Part IV, we detail a tentative policy agenda that follows from our findings

Thermal conductivity of metals at high temperatures

A new method of measuring thermal diffusivity and hence thermal conductivity of metals is suggested. Like previously reported dynamic methods, this method uses a heat source, whose temperature varies sinusoidally located at one end of an effectively infinite rod. Unlike these methods only one period of the heat wave is required to eliminate the unknown coefficient determining the heat lost by radiation since both velocity and amplitude decrement of the heat wave are measured. The new method is faster in taking data and simpler in computation. The thermoelectric potentials from two thermojunctions are amplified and plotted on a Brown Electronic recorder in order to obtain a permanent record of all necessary data for computing the thermal diffusivity. Results for copper over the temperature range 0-560°C and for thorium over the temperature range 0-430°C are given

Thermal excitation of Trivelpiece-Gould modes in a pure electron plasma

Thermally excited plasma modes are observed in trapped, near-thermal-equilibrium pure electron plasmas over a temperature range of 0.05<T<5 eV. The measured thermal emission spectra together with a separate measurement of the wave absorption coefficient uniquely determines the temperature. Alternately, kinetic theory including the antenna geometry and the measured mode damping (i.e. spectral width) gives the plasma impedance, obviating the reflection measurement. This non-destructive temperature diagnostic agrees well with standard diagnostics, and may be useful for expensive species such as anti-matter

The Mars observer camera

A camera designed to operate under the extreme constraints of the Mars Observer Mission was selected by NASA in April, 1986. Contingent upon final confirmation in mid-November, the Mars Observer Camera (MOC) will begin acquiring images of the surface and atmosphere of Mars in September-October 1991. The MOC incorporates both a wide angle system for low resolution global monitoring and intermediate resolution regional targeting, and a narrow angle system for high resolution selective surveys. Camera electronics provide control of image clocking and on-board, internal editing and buffering to match whatever spacecraft data system capabilities are allocated to the experiment. The objectives of the MOC experiment follow

Experimental Crystallization of Yamato 980459

Currently, only two martian meteorites QUE 94201 (QUE) and Yamato 980459 (Y98) have been experimentally shown to me true melt compositions. Most martian meteorites are instead, cumulates or partial cumulates. We have performed experiments on a Y98 composition to assess whether QUE could be related to Y98 by some fractionation process [1]. Y98 is a basaltic shergottite from the SNC (Shergotty, Nakhla, Chassigny) meteorite group. Y98 is composed of 26% olivine, 48% pyroxene, 25% mesostasis, and no plagioclase [2]. The large size of the olivine megacrysts and absence of plagioclase suggest that the parental melt which formed this meteorite had begun cooling slowly until some mechanism, such as magma ascent, caused rapid cooling [3]. Y98 s olivines have the highest Mg content of all the shergottites suggesting that it is the most primitive [4]. Y98 has been determined to be a melt composition by comparing the composition of experimental liquidus olivines with the composition of the cores of Y98 olivines [4]. The liquidus of Y98 is predicted by MELTS [5] and by experimentation [6] to be ~1450 C. Analyses of Y98 show it to be very depleted in LREEs and it has similar depleted patterns as other shergottites such as QUE [7]

Blamelessly Optimal Control For Polytopic Safety Sets

In many safety-critical optimal control problems, users may request multiple safety constraints that are jointly infeasible due to external factors such as subsystem failures, unexpected disturbances, or fuel limitations. In this manuscript, we introduce the concept of blameless optimality to characterize control actions that a) satisfy the highest prioritized and feasible safety constraints and b) remain optimal with respect to a mission objective. For a general optimal control problem with jointly infeasible safety constraints, we prove that a single optimization problem cannot find a blamelessly optimal controller. Instead, finding blamelessly optimal control actions requires sequentially solving at least two optimal control problems: one to determine the highest priority level of constraints that is feasible and another to determine the optimal control action with respect to these constraints. We apply our results to a helicopter emergency landing scenario in which violating at least one safety-induced landing constraint is unavoidable. Leveraging the concept of blameless optimality, we formulate blamelessly optimal controllers that can autonomously prioritize human safety over property integrity