Large wind turbine generators

The development associated with large wind turbine systems is briefly described. The scope of this activity includes the development of several large wind turbines ranging in size from 100 kW to several megawatt levels. A description of the wind turbine systems, their programmatic status and a summary of their potential costs is included

An experimental 100 kilowatt wind turbine generator

Experimental generator consists of two blades mounted on 100 foot tower, driving transmission train and electric generator mounted on top of tower. Machine generates 100 kW of electricity at wind speeds from 18 to 60 miles per hour. Yaw control mechanism automatically orients machine into wind

Status of wind-energy conversion

The utilization of wind energy is technically feasible as evidenced by the many past demonstrations of wind generators. The cost of energy from the wind has been high compared to fossil fuel systems; a sustained development effort is needed to obtain economical systems. The variability of the wind makes it an unreliable source on a short term basis. However, the effects of this variability can be reduced by storage systems or connecting wind generators to: (1) fossil fuel systems; (2) hydroelectric systems; or (3) dispersing them throughout a large grid network. Wind energy appears to have the potential to meet a significant amount of our energy needs

Quasar-galaxy associations

There is controversy about the measurement of statistical associations between bright quasars and faint, presumably foreground galaxies. We look at the distribution of galaxies around an unbiased sample of 63 bright, moderate redshift quasars using a new statistic based on the separation of the quasar and its nearest neighbour galaxy. We find a significant excess of close neighbours at separations less than about 10 arcsec which we attribute to the magnification by gravitational lensing of quasars which would otherwise be too faint to be included in our sample. About one quarter to one third of the quasars are so affected although the allowed error in this fraction is large.Comment: uuencoded Postscript file (including figures and tables), SUSSEX-AST 94/8-

Twist-controlled Resonant Tunnelling between Monolayer and Bilayer Graphene

We investigate the current-voltage characteristics of a field-effect tunnelling transistor comprised of both monolayer and bilayer graphene with well-aligned crystallographic axes, separated by three layers of hexagonal boron nitride. Using a self-consistent description of the device's electrostatic configuration we relate the current to three distinct tunable voltages across the system and hence produce a two-dimensional map of the I-V characteristics in the low energy regime. We show that the use of gates either side of the heterostructure offers a fine degree of control over the device's rich array of characteristics, as does varying the twist between the graphene electrodes.Comment: 5 pages including references and 3 figure

Suppression of complete fusion due to breakup in the reactions 10,11^{10,11}B + 209^{209}Bi

Above-barrier cross sections of $\alpha$-active heavy reaction products, as well as fission, were measured for the reactions of $^{10,11}$B with $^{209}$Bi. Detailed analysis showed that the heavy products include components from incomplete fusion as well as complete fusion (CF), but fission originates almost exclusively from CF. Compared with fusion calculations without breakup, the CF cross sections are suppressed by 15% for $^{10}$B and 7% for $^{11}$B. A consistent and systematic variation of the suppression of CF for reactions of the weakly bound nuclei $^{6,7}$Li, $^{9}$Be, $^{10,11}$B on targets of $^{208}$Pb and $^{209}$Bi is found as a function of the breakup threshold energy

Effect of dose rate on ion beam mixing in Nb-Si

The influence of dose rate, i.e., ion flux, on ion beam mixing in Nb‐Si bilayer samples was measured at room temperature and 325 °C. At the higher temperature, an increase in dose rate of a factor of 20 caused a decrease in the thickness of the mixed layer by a factor of 1.6 for equal total doses. At room temperature, the same change in flux had no effect on mixing. These results are consistent with radiation‐enhanced diffusion theory in the recombination‐limited regime

Is there a "most perfect fluid" consistent with quantum field theory?

It was recently conjectured that the ratio of the shear viscosity to entropy density, $\eta/ s$, for any fluid always exceeds $\hbar/(4 \pi k_B)$. This conjecture was motivated by quantum field theoretic results obtained via the AdS/CFT correspondence and from empirical data with real fluids. A theoretical counterexample to this bound can be constructed from a nonrelativistic gas by increasing the number of species in the fluid while keeping the dynamics essentially independent of the species type. The question of whether the underlying structure of relativistic quantum field theory generically inhibits the realization of such a system and thereby preserves the possibility of a universal bound is considered here. Using rather conservative assumptions, it is shown here that a metastable gas of heavy mesons in a particular controlled regime of QCD provides a realization of the counterexample and is consistent with a well-defined underlying relativistic quantum field theory. Thus, quantum field theory appears to impose no lower bound on $\eta/s$, at least for metastable fluids.Comment: 4 pages; typos corrected and references added in new versio

Black Hole - Neutron Star Mergers as Central Engines of Gamma-Ray Bursts

Hydrodynamic simulations of the merger of stellar mass black hole - neutron star binaries (BH/NS) are compared with mergers of binary neutron stars (NS/NS). The simulations are Newtonian, but take into account the emission and backreaction of gravitational waves. The use of a physical nuclear equation of state allows us to include the effects of neutrino emission. For low neutron star to black hole mass ratios the neutron star transfers mass to the black hole during a few cycles of orbital decay and subsequent widening before finally being disrupted, whereas for ratios near unity the neutron star is already distroyed during its first approach. A gas mass between about 0.3 and about 0.7 solar masses is left in an accretion torus around the black hole and radiates neutrinos at a luminosity of several 10^{53} erg/s during an estimated accretion time scale of about 0.1 s. The emitted neutrinos and antineutrinos annihilate into electron-positron pairs with efficiencies of 1-3% percent and rates of up to 2*10^{52} erg/s, thus depositing an energy of up to 10^{51} erg above the poles of the black hole in a region which contains less than 10^{-5} solar masses of baryonic matter. This could allow for relativistic expansion with Lorentz factors around 100 and is sufficient to explain apparent burst luminosities of up to several 10^{53} erg/s for burst durations of approximately 0.1-1 s, if the gamma emission is collimated in two moderately focussed jets in a fraction of about 1/100-1/10 of the sky.Comment: 8 pages, LaTex, 4 postscript figures, 2 tables. ApJ Letters, accepted; revised and shortened version, Fig. 2 change