Delta Advanced Reusable Transport (DART): An alternative manned spacecraft

Although the current U.S. Space Transportation System (STS) has proven successful in many applications, the truth remains that the space shuttle is not as reliable or economical as was once hoped. In fact, the Augustine Commission on the future of the U.S. Space Program has recommended that the space shuttle only be used on missions directly requiring human capabilities on-orbit and that the shuttle program should eventually be phased out. This poses a great dilemma since the shuttle provides the only current or planned U.S. means for human access to space at the same time that NASA is building toward a permanent manned presence. As a possible solution to this dilemma, it is proposed that the U.S. begin development of an Alternative Manned Spacecraft (AMS). This spacecraft would not only provide follow-on capability for maintaining human space flight, but would also provide redundancy and enhanced capability in the near future. Design requirements for the AMS studied include: (1) capability of launching on one of the current or planned U.S. expendable launch vehicles (baseline McDonnell Douglas Delta II model 7920 expendable booster); (2) application to a wide variety of missions including autonomous operations, space station support, and access to orbits and inclinations beyond those of the space shuttle; (3) low enough costing to fly regularly in augmentation of space shuttle capabilities; (4) production surge capabilities to replace the shuttle if events require it; (5) intact abort capability in all flight regimes since the planned launch vehicles are not man-rated; (6) technology cut-off date of 1990; and (7) initial operational capability in 1995. In addition, the design of the AMS would take advantage of scientific advances made in the 20 years since the space shuttle was first conceived. These advances are in such technologies as composite materials, propulsion systems, avionics, and hypersonics

Amusement Park

Letter from a middle school student with an idea for an amusement park on Alcatraz Islandhttps://scholarlycommons.pacific.edu/moscone-alcatraz/1000/thumbnail.jp

The Hittites

Evidence, however, has pointed to Asia Minor as their home, and when therefore in the nineteenth century monuments were found at Aleppo and Carchemish on the Euphrates, Hamath on the Crontes, and other sites in Asia Minor, Syria, Cappadocia, and elsewhere, - monuments of unusual style and with inscriptions written in unknown hieroglyphics, - it was natural to attribute them to this nation whose existence was known, but whose civilization had not as yet been uncovered

On the Structure of the Helmholtz Layer and its Implications on Electrode Kinetics

Concepts and selected experiments on the structure of the Helmholtz double layer at the metal- and semiconductor - electrolyte phase boundary are reviewed. The widely used microcapacitor approach of the double layer and its limitations are assessed. Observations on the influence of the electrode potential on the energetic position of surface states at the Ag-electrolyte contact are compared to the predictions of classical charge transfer models that are based on transition state theory where adiabatic tunneling is assumed. Distance tunneling spectroscopy on Au(111) surfaces shows pronounced variations in tunneling barrier heights that are connected to the inner structure of the Helmholtz layer and implications on electrode kinetics are presented. At the semiconductor-electrolyte contact, the influence of the electrode potential on a charge injecting species that results in photocurrent doubling is reviewed for low- and higher doped Si(111) electrodes, showing that the complex that injects electrons into the conduction band is located outside the semiconductor surface. The observations are correlated with the search for low overpotential earth abundant electrocatalysts for solar fuel generation of solar fuels

Quantum phases of a chain of strongly interacting anyons

We study a strongly interacting chain of anyons with fusion rules determined by SO(5)2. The phase portrait is identified with a combination of numerical and analytical techniques. Several critical phases with different central charges and their corresponding transitions identified.Comment: 5 pages, 4 figure

Comparison of Spectroscopic Strategies to Determine Molecular Geometries and the Impact of Nuclear versus Atomic Masses: The Example of HCO + and HOC +

International audienceWe compare a recently proposed mixed experimental/theoretical procedure for the derivation of molecular equilibrium structures with several commonly used spectroscopic approaches using experimental data for several isotopologues. We also examine the sensitivity of the results from these approaches to the replacement of the commonly employed atomic masses with nuclear masses. This point is of particular importance for ionic species like HCO + and HOC + which serve as numerical reference cases. The scatter of molecular equilibrium geometries derived by different approaches is found to exceed stated statistical uncertainties by about an order of magnitude

Illegal fishing and maritime security: towards a land- and sea-based response to threats in West Africa

West African coastal states lose up to $1.5 billion a year as a result of illegal fishing. The effects of overfishing also hit these countries hard. In its Strategy on the Gulf of Guinea, the European Union highlights the threats and risks posed to these coastal states, as well as the connections to Europe as an export market for fishery products and home region of many fishing vessels. Until now, maritime security strategies for West Africa have prioritized the issues of human trafficking, smuggling of migrants, and piracy. In future, however, there should be a stronger focus on the threats posed by illegal fishing, especially when providing advice, training and equipment assistance to improve surveillance and monitoring of West African waters. An integrated approach is required, which should also address the onshore problems associated with the fisheries sector. (Autorenreferat

Genesis and Propagation of Fractal Structures During Photoelectrochemical Etching of n-Silicon

The genesis, propagation, and dimensions of fractal-etch patterns that form anodically on front- or back-illuminated n-Si(100) photoelectrodes in contact with 11.9 M NH₄F(aq) has been investigated during either linear-sweep voltammetry or when the electrode was held at a constant potential (E = +6.0 V versus Ag/AgCl). Optical images collected in situ during electrochemical experiments revealed the location and underlying mechanism of initiation and propagation of the structures on the surface. X-ray photoelectron spectroscopic (XPS) data collected for samples emersed from the electrolyte at varied times provided detailed information about the chemistry of the surface during fractal etching. The fractal structure was strongly influenced by the orientation of the crystalline Si sample. The etch patterns were initially generated at points along the circumference of bubbles that formed upon immersion of n-Si(100) samples in the electrolyte, most likely due to the electrochemical and electronic isolation of areas beneath bubbles. XPS data showed the presence of a tensile-stressed silicon surface throughout the etching process as well as the presence of SiO_xF_y on the surface. The two-dimensional fractal dimension D_(f,2D) of the patterns increased with etching time to a maximum observed value of D_(f,2D)=1.82. Promotion of fractal etching near etch masks that electrochemically and electronically isolated areas of the photoelectrode surface enabled the selective placement of highly branched structures at desired locations on an electrode surface

Oscillations at the Si/electrolyte contact: Relation to Quantum Mechanics

The basic process at the surface of the Si electrode is characterized by a cyclic oxidation of a thin silicon layer and the subsequent removal of the oxide by etching. Here, the oxide thickness evolves not uniformly due to cracks and nanopores. The mathematical model used to describe the phenomenon is based on a sequence of time dependent (oxide thickness) oscillator density functions that describes the passing of the (infinitesimal) oscillators through their minimum at each cycle. Two consecutive oscillator density functions are connected by a second order linear integral equation representing a Markov process. The kernel of the integral equation is a normalized Greens Function and represents the probability distribution for the periods of the oscillators during a cycle. Both, the oscillator density function and the two-dimensional probability density for the periods of the oscillators, define a random walk. A relation between the oscillator density functions and solutions of the Fokker-Planck equation can be constructed. This allows a connection of the oscillations, originally considered only for the description of a photo-electrochemical observation, to the Schrodinger equation. In addition, if the trajectory of a virtual particle, located at the silicon oxide electrode surface, is considered during one oscillatory cycle, then it can be shown that the displacement of the particle measured at the electrode surface performs a Brownian motion