Paper Session III-B - Development of a Microgravity-Rated Hydroponic Plant Culture Apparatus

Porous tubes provide a novel means of growing plants hydroponically under conditions of microgravity. The experimental strategy for a spaceflight experiment utilizing this technology (anticipated in the 2000-2001 timeframe) is presented. The primary question to be addressed relates to the control of optimal rates of water provision, and how it can be expected to differ between the spaceflight and earth-based environments

Determination of biomembrane bending moduli in fully atomistic simulations.

The bilayer bending modulus (Kc) is one of the most important physical constants characterizing lipid membranes, but precisely measuring it is a challenge, both experimentally and computationally. Experimental measurements on chemically identical bilayers often differ depending upon the techniques employed, and robust simulation results have previously been limited to coarse-grained models (at varying levels of resolution). This Communication demonstrates the extraction of Kc from fully atomistic molecular dynamics simulations for three different single-component lipid bilayers (DPPC, DOPC, and DOPE). The results agree quantitatively with experiments that measure thermal shape fluctuations in giant unilamellar vesicles. Lipid tilt, twist, and compression moduli are also reported

Delay-Bounded Routing for Shadow Registers

The on-chip timing behaviour of synchronous circuits can be quantified at run-time by adding shadow registers, which allow designers to sample the most critical paths of a circuit at a different point in time than the user register would normally. In order to sample these paths precisely, the path skew between the user and the shadow register must be tightly controlled and consistent across all paths that are shadowed. Unlike a custom IC, FPGAs contain prefabricated resources from which composing an arbitrary routing delay is not trivial. This paper presents a method for inserting shadow registers with a minimum skew bound, whilst also reducing the maximum skew. To preserve circuit timing, we apply this to FPGA circuits post place-and-route, using only the spare resources left behind. We find that our techniques can achieve an average STA reported delay bound of ±200ps on a Xilinx device despite incomplete timing information, and achieve <1ps accuracy against our own delay model

The NASA Spitzer Space Telescope

The National Aeronautics and Space Administration's Spitzer Space Telescope (formerly the Space Infrared Telescope Facility) is the fourth and final facility in the Great Observatories Program, joining Hubble Space Telescope (1990), the Compton Gamma-Ray Observatory (1991–2000), and the Chandra X-Ray Observatory (1999). Spitzer, with a sensitivity that is almost three orders of magnitude greater than that of any previous ground-based and space-based infrared observatory, is expected to revolutionize our understanding of the creation of the universe, the formation and evolution of primitive galaxies, the origin of stars and planets, and the chemical evolution of the universe. This review presents a brief overview of the scientific objectives and history of infrared astronomy. We discuss Spitzer's expected role in infrared astronomy for the new millennium. We describe pertinent details of the design, construction, launch, in-orbit checkout, and operations of the observatory and summarize some science highlights from the first two and a half years of Spitzer operations. More information about Spitzer can be found at http://spitzer.caltech.edu/

Power Law Distribution of Wealth in a Money-Based Model

A money-based model for the power law distribution (PLD) of wealth in an economically interacting population is introduced. The basic feature of our model is concentrating on the capital movements and avoiding the complexity of micro behaviors of individuals. It is proposed as an extension of the Equiluz and Zimmermann's (EZ) model for crowding and information transmission in financial markets. Still, we must emphasize that in EZ model the PLD without exponential correction is obtained only for a particular parameter, while our pattern will give it within a wide range. The Zipf exponent depends on the parameters in a nontrivial way and is exactly calculated in this paper.Comment: 5 pages and 4 figure

Measuring Humidity in Sealed Glass Encasements

A technique has been devised for measuring the relative humidity levels in the protective helium/water vapor atmosphere in which the Declaration of Independence, the United States Constitution, and the Bill of Rights are encased behind glass panels on display at the National Archives in Washington, DC. The technique is noninvasive: it does not involve penetrating the encasements (thereby risking contamination or damage to the priceless documents) to acquire samples of the atmosphere. The technique could also be applied to similar glass encasements used to protect and display important documents and other precious objects in museums. The basic principle of the technique is straightforward: An encasement is maintained at its normal display or operating temperature (e.g., room temperature) while a portion of its glass front panel is chilled (see Figure 1) until condensed water droplets become visible on the inside of the panel. The relative humidity of the enclosed atmosphere can then be determined as a known function of the dew point, the temperature below which the droplets condense. Notwithstanding the straightforwardness of the basic principle, careful attention to detail is necessary to enable accurate determination of the dew point. In the initial application, the affected portion of the glass panel was cooled by contact with an aluminum plate that was cooled by a thermoelectric module, the exhaust heat of which was dissipated by a heat sink cooled by a fan. A thermocouple was used to measure the interior temperature of the aluminum plate, and six other thermocouples were used to measure the temperatures at six locations on the cooled outer surface of the glass panel (see Figure 2). Thermal grease was applied to the aluminum plate and the thermocouples to ensure close thermal contact. Power was supplied to the thermoelectric module in small increments, based on previous laboratory tests. A small flashlight and a magnifying glass were used to look for water droplets condensing on the inner surface of the glass. The temperature readings of the thermocouples were taken during cool-down and upon observing condensation. In determining the dew point, it was necessary to make a correction for the differences between the temperatures measured on the chilled outer surface of the glass and the temperature of the inner surface, where the condensation took place. The correction was derived from a laboratory test on a measurement setup that was nearly identical, except that the dew location on the inner surface was also instrumented with a thermocouple. The test showed that the temperature at the dew location on the inner surface of the glass panel was 0.9 C above the temperature determined from the measurements on the chilled outer surface of the panel

Advanced Plant Habitat (APH)

The Advanced Plant Habitat (APH) hardware will be a large growth volume plant habitat, capable of hosting multigenerational studies, in which environmental variables (e.g., temperature, relative humidity, carbon dioxide level light intensity and spectral quality) can be tracked and controlled in support of whole plant physiological testing and Bio-regenerative Life Support System investigations

Self Organization and a Dynamical Transition in Traffic Flow Models

A simple model that describes traffic flow in two dimensions is studied. A sharp {\it jamming transition } is found that separates between the low density dynamical phase in which all cars move at maximal speed and the high density jammed phase in which they are all stuck. Self organization effects in both phases are studied and discussed.Comment: 6 pages, 4 figure

Second harmonic generation in SiC polytypes

LMTO calculations are presented for the frequency dependent second harmonic generation (SHG) in the polytypes 2H, 4H, 6H, 15R and 3C of SiC. All independent tensor components are calculated. The spectral features and the ratios of the 333 to 311 tensorial components are studied as a function of the degree of hexagonality. The relationship to the linear optical response and the underlying band structure are investigated. SHG is suggested to be a sensitive tool for investigating the near band edge interband excitations.Comment: 12 pages, 10 figure