Characterization of lunar surface materials for use in construction

The Workshop on the Concept of a Common Lunar Lander, which was held at the NASA Johnson Space Center on July 1 and 2, 1991, discussed potential payloads to be placed on the Moon by a common, generic, unmanned, vehicle beginning late in this decade. At this workshop, a variety of payloads were identified including a class of one-meter (and larger) optical telescopes to operate on the lunar surface. These telescopes for lunar-based astronomy are presented in an earlier section of this report. The purpose of this section is to suggest that these and other payloads for the Common Lunar Lander be used to facilitate technology development for the proposed 16-meter Aperture UV/Visible/IR Large Lunar Telescope (LLT) and a large optical aperture-synthesis instrument analogous to the Very Large Array of the National Radio Astronomy Observatory

Trapping molecules using photostop

Successful magnetic trapping of both SH at a density of 2.4 x 10^5 cm^-3 and atomic oxygen at a density of 3000 +/- 900 cm^-3 has been demonstrated with respective trapping lifetimes of 40 +/- 10 ms and 82 +/- 3 ms inside a 0.41 T deep, anti-Helmholtz configuration magnetic trap. To achieve trapping of these species, a stable precursor was cooled by supersonic expansion in a molecular beam and photodissociated in such a way as to match and oppose a photofragments recoil speed to the precursors molecular beam speed. This process is called photostop. Velocity-map images have been taken of photostop of atomic oxygen from photodissociation of NO2 in a molecular beam. They show that atomic oxygen can be photostopped from a variety of NO photodissociation co-fragments with a suitably broad molecular-beam velocity-distribution. Although photostop is simple and cheap to use, the trapping lifetimes and densities that have been achieved in this thesis are not competitive compared to other methods of trapping similar molecular species. The main problem that presents universally in photostop experiments is due to the large number of fast molecules from the supersonic expansion that pass through the trap after the photostop event. Only a small fraction of the molecules in the molecular beam are stopped and the remaining ones cause significant trap loss through high energy elastic collisions with trapped species. Work has been carried out to develop the cavity-enhanced laser-induced-fluorescence (CELIF) technique to be used more widely in the cold molecules field. The technique was employed unsuccessfully to measure photostopped SH radicals but was used elsewhere to measure cold SD radicals after Stark deceleration. In addition, the technique has been initially developed for use inside magnetic traps. Clusters of NO.Ar(n) have been studied using [1+1'] REMPI to assess the viability of a new soft-ionisation technique for molecular clusters of atmospheric interest. This work did not show conclusive evidence that [1+1'] REMPI would reduce cluster fragmentation and displayed some interesting but poorly understood data

Shrinkage Cracking in Concrete Tilt-Up Construction

The purpose of this project is to investigate a particular, undesirable cracking pattern in concrete tilt-up panels that, until now, did not have a known definite cause. The cause of this cracking pattern is hypothesized to be due to shrinkage restraint of the concrete panels. The cracking under investigation occurs at the bottom corners of the Tilt-Up panels, suggesting that the base of the panel is restrained from shrinkage. This project models various components of Tilt-Up Construction that have potential for restraining the panels from shrinking. This project consists of the following main components. The first aspect of this project was to investigate and become familiar with the means and methods of Tilt-Up Construction. To determine the potential shrinkage restraints on the panels, the connections and details associated with Tilt-Up must be thoroughly understood. This involved reviewing typical details of connections as well as contacting engineers and contractors in the field to determine the typical means and methods of Tilt-Up construction and construction sequencing. Once typical construction practices were understood, the first shrinkage restraint investigated was the friction developed by the panel setting pads. Once the panel is ready to lift, it is set on grout pads or plastic shims, typically located at the ends of the panel. To determine the amount of restraint caused by friction, an experiment was conducted to determine the coefficient of static friction. Tests were run to find the coefficient of friction for concrete against grout, and concrete against plastic shims. The third aspect of this project was to develop an effective computer model of stresses in Tilt-Up panels induced by shrinkage restraint. The goal of this model was to be able to run various scenarios, to determine the effects of panel concrete mix design, panel geometry, and construction sequencing. The last aspect of this project was to collect enough data from the computer model to determine whether or not shrinkage restraint induces enough stress in the panel to initiate cracking, determine when the cracking would occur given construction sequencing, as well as determine if the cracking pattern matches the pattern seen out in the field. Conclusions will have to be made on a case by case basis, but the panel specifications in this analysis were chosen from a Home Depot building in San Luis Obispo, CA, an as-built Tilt-Up project. After running about 70 different cases, it was discovered that the grout pads by themselves did not provide enough shrinkage restraint to initiate cracking in the panel. This led to further investigation of panel connections, specifically the panel to slab connection at the pour strip. This paper concludes that when combining the shrinkage restraint from grout pad friction and pour strip reinforcement tension, there is potential for cracking in the panel. Even further, the cracking pattern determined from the computer model provides nearly an exact match to the actual cracks under investigation and measured in the field. Although this report provides evidence for potential cracking in Tilt-Up panels due to shrinkage restraint, recommendations for limiting the potential of cracking in panels will need to be made on a case by case basis

A lunar far-side very low frequency array

Papers were presented to consider very low frequency (VLF) radio astronomical observations from the moon. In part 1, the environment in which a lunar VLF radio array would function is described. Part 2 is a review of previous and proposed low-frequency observatories. The science that could be conducted with a lunar VLF array is described in part 3. The design of a lunar VLF array and site selection criteria are considered, respectively, in parts 4 and 5. Part 6 is a proposal for precursor lunar VLF observations. Finally, part 7 is a summary and statement of conclusions, with suggestions for future science and engineering studies. The workshop concluded with a general consensus on the scientific goals and preliminary design for a lunar VLF array

Developing numerical libraries in Java

The rapid and widespread adoption of Java has created a demand for reliable and reusable mathematical software components to support the growing number of compute-intensive applications now under development, particularly in science and engineering. In this paper we address practical issues of the Java language and environment which have an effect on numerical library design and development. Benchmarks which illustrate the current levels of performance of key numerical kernels on a variety of Java platforms are presented. Finally, a strategy for the development of a fundamental numerical toolkit for Java is proposed and its current status is described.Comment: 11 pages. Revised version of paper presented to the 1998 ACM Conference on Java for High Performance Network Computing. To appear in Concurrency: Practice and Experienc

Actor-based Risk Analysis for Blockchains in Smart Mobility

Blockchain technology is a crypto-based secure ledger for data storage and transfer through decentralized, trustless peer-to-peer systems. Despite its advantages, previous studies have shown that the technology is not completely secure against cyber attacks. Thus, it is crucial to perform domain specific risk analysis to measure how viable the attacks are on the system, their impact and consequently the risk exposure. Specifically, in this paper, we carry out an analysis in terms of quantifying the risk associated to an operational multi-layered Blockchain framework for Smart Mobility Data-markets (BSMD). We conduct an actor-based analysis to determine the impact of the attacks. The analysis identified five attack goals and five types of attackers that violate the security of the blockchain system. In the case study of the public permissioned BSMD, we highlight the highest risk factors according to their impact on the victims in terms of monetary, privacy, integrity and trust. Four attack goals represent a risk in terms of economic losses and one attack goal contains many threats that represent a risk that is either unacceptable or undesirable.Comment: arXiv admin note: text overlap with arXiv:1904.11908 by other author