The trade-off characteristics of acoustic and pressure sensors for the NASP

Results of a trade study for the development of pressure and acoustic sensors for use on the National Aerospace Plane (NASP) are summarized. Pressure sensors are needed to operate to 100 psia; acoustic sensors are needed that can give meaningful information about a 200 dB sound pressure level (SPL) environment. Both sensors will have to operate from a high temperature of 2000 F down to absolute zero. The main conclusions of the study are the following: (1) Diaphragm materials limit minimum size and maximum frequency response attainable. (2) No transduction is available to meet all the NASP requirements with existing technology. (3) Capacitive sensors are large relative to the requirement, have limited resolution and frequency response due to noise, and cable length is limited to approximately 20 feet. (4) Eddy current sensors are large relative to the requirement and have limited cable lengths. (5) Fiber optic sensors provide the possibility for a small sensor, even though present developments do not exhibit that characteristic. The need to use sapphire at high temperature complicates the design. Present high temperature research sensors suffer from poor resolution. A significant development effort will be required to realize the potential of fiber optics. (6) Short-term development seems to favor eddy current techniques with the penalty of larger size and reduced dynamic range for acoustic sensors. (7) Long-term development may favor fiber optics with the penalties of cost, schedule, and uncertainty

Semiparametric inference in mixture models with predictive recursion marginal likelihood

Predictive recursion is an accurate and computationally efficient algorithm for nonparametric estimation of mixing densities in mixture models. In semiparametric mixture models, however, the algorithm fails to account for any uncertainty in the additional unknown structural parameter. As an alternative to existing profile likelihood methods, we treat predictive recursion as a filter approximation to fitting a fully Bayes model, whereby an approximate marginal likelihood of the structural parameter emerges and can be used for inference. We call this the predictive recursion marginal likelihood. Convergence properties of predictive recursion under model mis-specification also lead to an attractive construction of this new procedure. We show pointwise convergence of a normalized version of this marginal likelihood function. Simulations compare the performance of this new marginal likelihood approach that of existing profile likelihood methods as well as Dirichlet process mixtures in density estimation. Mixed-effects models and an empirical Bayes multiple testing application in time series analysis are also considered

Design, construction, and utilization of a space station assembled from 5-meter erectable struts

The primary characteristics of the 5-meter erectable truss is presented, which was baselined for the Space Station. The relatively large 5-meter truss dimension was chosen to provide a deep beam for high bending stiffness yet provide convenient mounting locations for space shuttle cargo bay size payloads which are approx. 14.5 ft (4.4 m) in diameter. Truss nodes and quick attachment erectable joints are described which provide for evolutionary three dimensional growth and for simple maintenance and repair. A mobile remote manipulator system is described which is provided to assist in station construction and maintenance. A discussion is also presented of the construction of the Space Station and the associated extravehicular active (EVA) time

Mechanical end joint system for connecting structural column elements

A mechanical end joint system is presented that eliminates the possibility of free movements between the joint halves during loading or vibration. Both node joint body (NJB) and column end joint body (CEJB) have cylindrical engaging ends. Each of these ends has an integral semicircular tongue and groove. The two joint halves are engaged transversely - the tongue of the NJB mating with the groove of the CEJB and vice versa. The joint system employs a spring loaded internal latch mechanism housed in the CEJB. During mating, this mechanism is pushed away from the NJB and enters the NJB when mating is completed. In order to lock the joint and add a preload across the tongue and groove faces, an operating ring collar is rotated through 45 deg causing an internal mechanism to compress a Belleville washer preload mechanism. This causes an equal and opposite force to be exerted on the latch bolt and the latch plunger. This force presses the two joint halves tightly together. In order to prevent inadvertent disassembly, a secondary lock is also engaged when the joint is closed. Plungers are carried in the operating ring collar. When the joint is closed, the plungers fall into tracks on the CEJB, which allows the joint to be opened only when the operating ring collar and plungers are pushed directly away from the joining end. One application of this invention is the rapid assembly and disassembly of diverse skeletal framework structures which is extremely important in many projects involving the exploration of space

A Comparison of Conventional and Liberal (Free-Choice) Multiple-Choice Tests

We compare conventional multiple-choice tests with so-called “liberal” multiple-choice tests, also known as “free-choice” tests, from a theoretical standpoint. The style of the questions is identical in these two alternative test formats, but in a liberal/free-choice test candidates may select as many options per question as they wish; the marking scheme penalises incorrect selections via negative marking, to the extent that candidates have nothing to gain through blind guesswork. We show that in the absence of blind guesswork candidates really do get the marks they deserve in a liberal/freechoice test, since the format of the test does not introduce any statistical distribution whatsoever. This is the case even when the candidates have partial knowledge and can therefore engage in educated guesswork. By contrast, in conventional multiple-choice tests candidates will engage in guesswork whenever they are unsure of the correct answer. We also show that liberal/free-choice tests reward partial knowledge more generously than conventional tests do, while on the other hand they punish misinformed students more severely than conventional tests do

Addressing the Shortcomings of Traditional Multiple-Choice Tests: Subset Selection Without Mark Deductions

This article presents the results of an empirical study of subset selection tests, which are a generalisation of traditional multiple-choice tests in which test takers are able to express partial knowledge. Similar previous studies have mostly been supportive of subset selection, but the deduction of marks for incorrect responses has been a cause for concern. For the present study, a novel marking scheme based on Akeroyd\u27s “dual response system†was used instead. In Akeroyd\u27s system, which assumes that every question has four answer options, test takers are able to split their single 100% bet on one answer option into two 50% bets by selecting two options, or into four 25% bets by selecting no options. To achieve full subset selection, this idea was extended so that test takers could also split their 100% bet equally between three options. The results indicate increased test reliability (in the sense of measurement consistency), and also increased satisfaction on the part of the test takers. Furthermore, since the novel marking scheme does not in principle lead to either inflated or deflated marks, this makes it easy for educators who currently use traditional multiple-choice tests to switch to using subset selection tests.. Accessed 1,149 times on https://pareonline.net from December 07, 2018 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right

Mobile remote manipulator vehicle system

A mobile remote manipulator system is disclosed for assembly, repair and logistics transport on, around and about a space station square bay truss structure. The vehicle is supported by a square track arrangement supported by guide pins integral with the space station truss structure and located at each truss node. Propulsion is provided by a central push-pull drive mechanism that extends out from the vehicle one full structural bay over the truss and locks drive rods into the guide pins. The draw bar is now retracted and the mobile remote manipulator system is pulled onto the next adjacent structural bay. Thus, translation of the vehicle is inchworm style. The drive bar can be locked onto two guide pins while the extendable draw bar is within the vehicle and then push the vehicle away one bay providing bidirectional push-pull drive. The track switches allow the vehicle to travel in two orthogonal directions over the truss structure which coupled with the bidirectional drive, allow movement in four directions on one plane. The top layer of this trilayered vehicle is a logistics platform. This platform is capable of 369 degees of rotation and will have two astronaut foot restraint platforms and a space crane integral

The FCC\u27s Minority Ownership Policies from Broadcasting to PCS

The Federal Communication Commission\u27s (FCC\u27s) proposed minority preference scheme for broadcast spectrum allocation has been called into question in the wake of the Supreme Court(s recent decision in Adarand Constructors, Inc. v. Pena. The Authors begin by discussing the development of minority preference schemes in the 1970s and 1980s and the changes in the methods through which the FCC has awarded broadcast licenses. In 1993, the FCC was granted the authority to auction spectrum allocation, provided that the FCC ensured the economic opportunity of minority-owned business under such a competitive bidding regulatory regime. However, this grant of authority presented the FCC with a legal concern: ensuring that the a minority preference scheme was not violative of the Equal Protection Clauses of the Fifth and Fourteenth Amendments. To this end, the FCC established entrepreneurs\u27 blocks in which two spectrum blocks were set-aside for applicants meeting certain financial qualifications. These financial-based eligibility restrictions appeared to create a solid legal foundation. However, the Adarand decision has resulted in the FCC postponing the proposed entrepreneurs\u27 block auction indefinitely. The remainder of the Article is a discussion of the Adarand decision and its effect on the proposed blocks. In particular, the Authors discuss whether the FCC-proposed scheme will survive the strict scrutiny standard imposed by Adarand

The FCC\u27s Minority Ownership Policies from Broadcasting to PCS

The Federal Communication Commission\u27s (FCC\u27s) proposed minority preference scheme for broadcast spectrum allocation has been called into question in the wake of the Supreme Court(s recent decision in Adarand Constructors, Inc. v. Pena. The Authors begin by discussing the development of minority preference schemes in the 1970s and 1980s and the changes in the methods through which the FCC has awarded broadcast licenses. In 1993, the FCC was granted the authority to auction spectrum allocation, provided that the FCC ensured the economic opportunity of minority-owned business under such a competitive bidding regulatory regime. However, this grant of authority presented the FCC with a legal concern: ensuring that the a minority preference scheme was not violative of the Equal Protection Clauses of the Fifth and Fourteenth Amendments. To this end, the FCC established entrepreneurs\u27 blocks in which two spectrum blocks were set-aside for applicants meeting certain financial qualifications. These financial-based eligibility restrictions appeared to create a solid legal foundation. However, the Adarand decision has resulted in the FCC postponing the proposed entrepreneurs\u27 block auction indefinitely. The remainder of the Article is a discussion of the Adarand decision and its effect on the proposed blocks. In particular, the Authors discuss whether the FCC-proposed scheme will survive the strict scrutiny standard imposed by Adarand