6,697 research outputs found
Pattern densities in fluid dimer models
In this paper, we introduce a family of observables for the dimer model on a
bi-periodic bipartite planar graph, called pattern density fields. We study the
scaling limit of these objects for liquid and gaseous Gibbs measures of the
dimer model, and prove that they converge to a linear combination of a
derivative of the Gaussian massless free field and an independent white noise.Comment: 38 pages, 3 figure
Forming the Dusty Ring in HR 4796A
We describe planetesimal accretion calculations for the dusty ring observed
in the nearby A0 star HR 4796A. Models with initial masses of 10-20 times the
minimum mass solar nebula produce a ring of width 7-15 AU and height 0.3-0.6 AU
at 70 AU in roughly 10 Myr. The ring has a radial optical depth of 1. These
results agree with limits derived from infrared images and from the excess
infrared luminosity.Comment: 6 pages, including 2 figures and 1 table; ApJ Letters, in pres
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
Detecting the Dusty Debris of Terrestrial Planet Formation
We use a multiannulus accretion code to investigate debris disks in the
terrestrial zone, at 0.7-1.3 AU around a 1 solar mass star. Terrestrial planet
formation produces a bright dusty ring of debris with a lifetime of at least 1
Myr. The early phases of terrestrial planet formation are observable with
current facilities; the late stages require more advanced instruments with
adaptive optics.Comment: 11 pages of text, 3 figures, accepted for ApJ Letters, additional
info at http://cfa-www.harvard.edu/~kenyon/pf/terra/td
Flight craft Patent
Designing spacecraft for flight into space, atmospheric reentry, and landing at selected site
Recommended from our members
Electrospray synthesis of PLGA TIPS microspheres
We successfully demonstrate the synthesis of polymer microspheres using a single electrospray source, and show their physical characterisation. Electrospray has proven to be a versatile method to manufacture particles, giving tight control over size with quasi-monodisperse size distributions. It is a liquid atomisation technique that generates a monodisperse population of highly charged liquid droplets over a broad size range (nanometres to tens of microns). The droplets contain liquid precursors for the in-flight synthesis of particles, and control over the trajectory of these droplets can be precisely manipulated with the use of electric fields to drive them to a grounded substrate. This study reports a method to synthesize poly(lactic-co-glycolic) acid (PLGA) microspheres using the electrospray and thermally induced phase separation (TIPS) techniques, followed by subsequent freeze-drying, for particle production. These microspheres are of interest as vehicles for controlled drug release systems
Studies on disease transmission in spacecraft environments
The effects of the Skylab gas mixtures on general health and immunocompetence of mice and ferrets subjected to the Skylab space cabin environment (SCE) were initially studied in a stainless steel low pressure facility which was maintained at gas ratios of 30% nitrogen and 70% oxygen under 5 psia, and which consisted of two subchambers, that permitted mutual isolation of experimental groups and/or selective removal of animals without return of the entire cabin to ambient pressure was developed. The studies demonstrated that ferrets immunized with Brucella Strain 19 prior to being housed in SCE had decreased synthesis of IgG compared to their respective controls. The possibility of latent infections being responsible for stress-induced upper respiratory diseases of astronauts required that the role of neutralizing antibody as a function of antibody affinity/avidity be investigated. The model consisted of Aleutian disease virus (ADV) which infects ferrets and mink resulting in nonneutralized immune complexes. These studies demonstrated that early antibody to ADV had lower affinity/avidity than late antibody with respect to chronicity. These studies culminated in a description of antibody affinity, first isolation of ADV and its cultivation in vitro
Biological activity of lunar soil Final report, 7 Jan. - 31 Oct. 1970
Development of clinical pathology procedures for detection of diseases in germfree mice and detection of titanium in lymphoid structures of hamsters, mice, and rat
Studies of effects of closed microbial ecology. Report of 180-day test period
Experiments were performed to determine the influence closed microbial ecologies have on modification or simplification of natural intestinal flora of ferrets in a closed environmental system. On the basis of previous tests in which certain species (Salmonella and Bacteroides) were decreased at 90 days of enclosure, a second trial was constructed for 180-day tests. In this trial there was little difference in the 8 major classes of intestinal flora between animals in the Open and Closed environmental groups except for the level of Lactobacillus. It is of extreme importance to note that when both Open and Closed groups contracted hemorrhagic gastritis, the interrelationship of this agent with other intestinal flora produced a more profound effect on animals from the Closed Group, particularly with reference to Lactobacillus levels
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