Symmetry Relations for Trajectories of a Brownian Motor

A Brownian Motor is a nanoscale or molecular device that combines the effects of thermal noise, spatial or temporal asymmetry, and directionless input energy to drive directed motion. Because of the input energy, Brownian motors function away from thermodynamic equilibrium and concepts such as linear response theory, fluctuation dissipation relations, and detailed balance do not apply. The {\em generalized} fluctuation-dissipation relation, however, states that even under strongly thermodynamically non-equilibrium conditions the ratio of the probability of a transition to the probability of the time-reverse of that transition is the exponent of the change in the internal energy of the system due to the transition. Here, we derive an extension of the generalized fluctuation dissipation theorem for a Brownian motor for the ratio between the probability for the motor to take a forward step and the probability to take a backward step

A unique facility for V/STOL aircraft hover testing

The Langley Impact Dynamics Research Facility (IDRF) was modified to obtain static force and moment data and to allow assessment of aircraft handling qualities during dynamic tethered hover flight. Test probe procedures were also established. Static lift and control measurements obtained are presented along with results of limited dynamic tethered hover flight

Molecular Clock on a Neutral Network

The number of fixed mutations accumulated in an evolving population often displays a variance that is significantly larger than the mean (the overdispersed molecular clock). By examining a generic evolutionary process on a neutral network of high-fitness genotypes, we establish a formalism for computing all cumulants of the full probability distribution of accumulated mutations in terms of graph properties of the neutral network, and use the formalism to prove overdispersion of the molecular clock. We further show that significant overdispersion arises naturally in evolution when the neutral network is highly sparse, exhibits large global fluctuations in neutrality, and small local fluctuations in neutrality. The results are also relevant for elucidating the topological structure of a neutral network from empirical measurements of the substitution process.Comment: 10 page

Analysis of multiple incidence angle SIR-B data for determining forest stand characteristics

For the first time in the U.S. space program, digital synthetic aperture radar (SR) data were obtained from different incidence angles during Space Shuttle Mission 41-G. Shuttle Imaging Radar-B (SIR-B) data were obtained at incidence angles of 58 deg., 45 deg., and 28 deg., on October 9, 10, and 11, 1984, respectively, for a predominantly forested study area in northern Florida. Cloud-free LANDSAT Thematic Mapper (T.M.) data were obtained over the same area on October 12. The SIR-B data were processed and then digitally registered to the LANDSAT T.M. data by scientists at the Jet Propulsion Laboratory. This is the only known digitally registered SIR-B and T.M. data set for which the data were obtained nearly simultaneously. The data analysis of this information is discussed

Sunflower Competition in Wheat

Wheat yield losses from various sunflower densities and durations of competition had not been determined previously. The objectives of the research in this article were to determine the influence of sunflower density, duration of competition and rate of control on wheat yield

Murex medic field evaluation.

Trials: 90GE113, 90MO62, 90WH87, 90ME72, 90NO115, 90A24, 90AB17, 90AL35 Locations: Geraldton, New Norcia, Wongan Hills, Merredin, Southern Brook, Avondale, Katanning, Tenderden. The selection SEP29.1 was outstanding for both dry matter production and seed yield over a wide range of sites varying in both rainfall and soil type. On the basis of these trials, six lines have been selected for further evaluation in 1991. They are: SEP29.1 SEP26.2.7 GRC69 GRC87.1 87F01.28 87FB2.36 Trials 90A25 and 90NO116 Redlegged earthmite field experiments. Very low levels of redlegged earthmite and only minor damage to test varieties was recorded in this trial. Damage ratings were recorded at 3, 4 and 5 weeks after sowing and plant yields at 3, 5 and 7 weeks, but the trial was then abandoned due to minimal responses. 90NO116 - This trial was abandoned soon after sowing due to massive germination of contaminant clover present in the paddock and negligible levels of redlegged earthmite

Enhancement of the stability of genetic switches by overlapping upstream regulatory domains

We study genetic switches formed from pairs of mutually repressing operons. The switch stability is characterised by a well defined lifetime which grows sub-exponentially with the number of copies of the most-expressed transcription factor, in the regime accessible by our numerical simulations. The stability can be markedly enhanced by a suitable choice of overlap between the upstream regulatory domains. Our results suggest that robustness against biochemical noise can provide a selection pressure that drives operons, that regulate each other, together in the course of evolution.Comment: 4 pages, 5 figures, RevTeX

Megawatt solar power systems for lunar surface operations

The work presented here shows that a solar power system can provide power on the order of one megawatt to a lunar base with a fairly high specific power. The main drawback to using solar power is still the high mass, and therefore, cost of supplying energy storage through the solar night. The use of cryogenic reactant storage in a fuel cell system, however, greatly reduces the total system mass over conventional energy storage schemes

Numerical simulation of unconstrained cyclotron resonant maser emission

When a mainly rectilinear electron beam is subject to significant magnetic compression, conservation of magnetic moment results in the formation of a horseshoe shaped velocity distribution. It has been shown that such a distribution is unstable to cyclotron emission and may be responsible for the generation of Auroral Kilometric Radiation (AKR) an intense rf emission sourced at high altitudes in the terrestrial auroral magnetosphere. PiC code simulations have been undertaken to investigate the dynamics of the cyclotron emission process in the absence of cavity boundaries with particular consideration of the spatial growth rate, spectral output and rf conversion efficiency. Computations reveal that a well-defined cyclotron emission process occurs albeit with a low spatial growth rate compared to waveguide bounded simulations. The rf output is near perpendicular to the electron beam with a slight backward-wave character reflected in the spectral output with a well defined peak at 2.68GHz, just below the relativistic electron cyclotron frequency. The corresponding rf conversion efficiency of 1.1% is comparable to waveguide bounded simulations and consistent with the predictions of kinetic theory that suggest efficient, spectrally well defined radiation emission can be obtained from an electron horseshoe distribution in the absence of radiation boundaries.Publisher PD