Flight craft Patent

Designing spacecraft for flight into space, atmospheric reentry, and landing at selected site

Local Statistics of Realizable Vertex Models

We study planar "vertex" models, which are probability measures on edge subsets of a planar graph, satisfying certain constraints at each vertex, examples including dimer model, and 1-2 model, which we will define. We express the local statistics of a large class of vertex models on a finite hexagonal lattice as a linear combination of the local statistics of dimers on the corresponding Fisher graph, with the help of a generalized holographic algorithm. Using an $n\times n$ torus to approximate the periodic infinite graph, we give an explicit integral formula for the free energy and local statistics for configurations of the vertex model on an infinite bi-periodic graph. As an example, we simulate the 1-2 model by the technique of Glauber dynamics

Terrestrial Planet Formation I. The Transition from Oligarchic Growth to Chaotic Growth

We use a hybrid, multiannulus, n-body-coagulation code to investigate the growth of km-sized planetesimals at 0.4-2 AU around a solar-type star. After a short runaway growth phase, protoplanets with masses of roughly 10^26 g and larger form throughout the grid. When (i) the mass in these `oligarchs' is roughly comparable to the mass in planetesimals and (ii) the surface density in oligarchs exceeds 2-3 g/sq cm at 1 AU, strong dynamical interactions among oligarchs produce a high merger rate which leads to the formation of several terrestrial planets. In disks with lower surface density, milder interactions produce several lower mass planets. In all disks, the planet formation timescale is roughly 10-100 Myr, similar to estimates derived from the cratering record and radiometric data.Comment: Astronomical Journal, accepted; 22 pages + 15 figures in ps format; eps figures at http://cfa-www.harvard.edu/~kenyon/dl/ revised version clarifies evolution and justifies choice of promotion masse

Quadri-tilings of the plane

We introduce {\em quadri-tilings} and show that they are in bijection with dimer models on a {\em family} of graphs $\{R^*\}$ arising from rhombus tilings. Using two height functions, we interpret a sub-family of all quadri-tilings, called {\em triangular quadri-tilings}, as an interface model in dimension 2+2. Assigning "critical" weights to edges of $R^*$, we prove an explicit expression, only depending on the local geometry of the graph $R^*$, for the minimal free energy per fundamental domain Gibbs measure; this solves a conjecture of \cite{Kenyon1}. We also show that when edges of $R^*$ are asymptotically far apart, the probability of their occurrence only depends on this set of edges. Finally, we give an expression for a Gibbs measure on the set of {\em all} triangular quadri-tilings whose marginals are the above Gibbs measures, and conjecture it to be that of minimal free energy per fundamental domain.Comment: Revised version, minor changes. 30 pages, 13 figure

The risks of concurrent treatment with tenofovir and aminoglycosides in patients with HIV-associated tuberculosis

The South African public sector antiretroviral treatment (ART) guidelines have recently been changed to include tenofovir in the first-line regimen.1 Injectable drugs from the aminoglycoside class are part of the intensive phase of regimen 2 tuberculosis (TB) treatment and the multidrug-resistant (MDR) TB treatment regimen in the South African TB programme. We wish to draw the attention of clinicians managing patients with HIVassociated TB to the potential dangers of concurrent administration of these drugs. We present two illustrative cases

Summary of the recent short-haul systems studies

The results of several NASA sponsored high density short haul air transportation systems studies are reported as well as analyzed. Included are the total STOL systems analysis approach, a companion STOL composites study conducted in conjunction with STOL systems studies, a STOL economic assessment study, an evaluation of STOL aircraft with and without externally blown flaps, an alternative STOL systems for the San Francisco Bay Area, and the quiet, clean experimental engine studies. Assumptions and results of these studies are summarized, their differences, analyzed, and the results compared with those in-house analyses performed by the Systems Studies Division of the NASA-Ames Research Center. Pertinent conclusions are developed and the more significant technology needs for the evaluation of a viable short haul transportation system are identified

Static deformation of heavy spring due to gravity and centrifugal force

The static equilibrium deformation of a heavy spring due to its own weight is calculated for two cases. First for a spring hanging in a constant gravitational field, then for a spring which is at rest in a rotating system where it is stretched by the centrifugal force. Two different models are considered. First a discrete model assuming a finite number of point masses connected by springs of negligible weight. Then the continuum limit of this model. In the second case the differential equation for the deformation is obtained by demanding that the potential energy is minimized. In this way a simple application of the variational calculus is obtained.Comment: 11 pages, 2 figure

A Hybrid N-body--Coagulation Code for Planet Formation

We describe a hybrid algorithm to calculate the formation of planets from an initial ensemble of planetesimals. The algorithm uses a coagulation code to treat the growth of planetesimals into oligarchs and explicit N-body calculations to follow the evolution of oligarchs into planets. To validate the N-body portion of the algorithm, we use a battery of tests in planetary dynamics. Several complete calculations of terrestrial planet formation with the hybrid code yield good agreement with previously published calculations. These results demonstrate that the hybrid code provides an accurate treatment of the evolution of planetesimals into planets.Comment: Astronomical Journal, accepted; 33 pages + 11 figure

The Century Survey Galactic Halo Project II: Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars

We discuss a 175 deg^2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and find that the 2MASS and SDSS color-selection is 38% and 50% efficient, respectively, for BHB stars. Our samples include one likely run-away B7 star 6 kpc below the Galactic plane. The global properties of the BHB samples are consistent with membership in the halo population: the median metallicity is [Fe/H]=-1.7, the velocity dispersion is 108 km/s, and the mean Galactic rotation of the BHB stars 3<|z|<15 kpc is -4 +- 30 km/s. We discuss the theoretical basis of the Preston, Shectman & Beers M_V-color relation for BHB stars, and conclude that intrinsic shape of the BHB M_V-color relation results from the physics of stars on the horizontal branch. We calculate the luminosity function for the field BHB star samples using the Efstathiou, Ellis, & Peterson maximum-likelihood method which is unbiased by density variations. The field BHB luminosity function exhibits a steep rise at bright luminosities, a peak between 0.8 < M_V < 1.0, and a tail at faint luminosities. We compare the field BHB luminosity functions with the luminosity functions derived from sixteen different globular cluster BHBs. Kolmogorov-Smirnov tests suggest that field BHB stars and BHB stars in globular clusters share a common distribution of luminosities, with the exception of globular clusters with extended BHBs.Comment: 14 pages, including 16 figures, accepted for publication in A

Hypervelocity Stars III. The Space Density and Ejection History of Main Sequence Stars from the Galactic Center

We report the discovery of 3 new unbound hypervelocity stars (HVSs), stars traveling with such extreme velocities that dynamical ejection from a massive black hole (MBH) is their only suggested origin. We also detect a population of possibly bound HVSs. The significant asymmetry we observe in the velocity distribution -- we find 26 stars with v_rf > 275 km/s and 1 star with v_rf < -275 km/s -- shows that the HVSs must be short-lived, probably 3 - 4 Msun main sequence stars. Any population of hypervelocity post-main sequence stars should contain stars falling back onto the Galaxy, contrary to the observations. The spatial distribution of HVSs also supports the main sequence interpretation: longer-lived 3 Msun HVSs fill our survey volume; shorter-lived 4 Msun HVSs are missing at faint magnitudes. We infer that there are 96 +- 10 HVSs of mass 3 - 4 Msun within R < 100 kpc, possibly enough HVSs to constrain ejection mechanisms and potential models. Depending on the mass function of HVSs, we predict that SEGUE may find up to 5 - 15 new HVSs. The travel times of our HVSs favor a continuous ejection process, although a ~120 Myr-old burst of HVSs is also allowed.Comment: 10 pages, 8 figures, accepted to ApJ, minor revision