Study of an attitude control system for the astronaut maneuvering unit final report, dec. 1963 - jul. 1964

Attitude control system for astronaut maneuvering unit

External and internal noise surveys of London primary schools

Internal and external noise surveys have been carried out around schools in London, UK, to provide information on typical levels and sources to which children are exposed while at school. Noise levels were measured outside 142 schools, in areas away from flightpaths into major airports. 86% of the schools surveyed were exposed to noise from road traffic, the average external noise level outside a school being 57 dB LAeq. Detailed internal noise surveys have been carried out in 140 classrooms in 16 schools, together with classroom observations. It was found that noise levels inside classrooms depend upon the activities in which the children are engaged, with a difference of 20 dB LAeq between the 'quietest' and 'noisiest' activities. The average background noise level in classrooms exceeds the level recommended in current standards. The number of children in the classroom was found to affect noise levels. External noise influenced internal noise levels only when children were engaged in the quietest classroom activities. The effects of the age of the school buildings and types of window upon internal noise were examined but results were inconclusive

Gravitational intraction on quantum level and consequences thereof

The notion of gravitational emission as an emission of the same level with electromagnetic emission is based on the proven fact of existence of electrons stationary states in its own gravitational field, characterized by gravitational constantComment: 22 pages, 9 figure

Burst dynamics during drainage displacements in porous media: Simulations and experiments

We investigate the burst dynamics during drainage going from low to high injection rate at various fluid viscosities. The bursts are identified as pressure drops in the pressure signal across the system. We find that the statistical distribution of pressure drops scales according to other systems exhibiting self-organized criticality. The pressure signal was calculated by a network model that properly simulates drainage displacements. We compare our results with corresponding experiments.Comment: 7 pages, 4 figures. Submitted to Europhys. Let

Magnetoelastic properties and behaviour of 4C pyrrhotite, Fe7S8, through the Besnus transition

Pyrrhotite, Fe7S8, is a commonly occurring carrier of magnetic remanence and has a low temperature transition, the Besnus transition, involving a change in spin state. Variations of the thermodynamic, magnetic and elastic properties through this transition at ~33 K in a natural sample of 4C pyrrhotite have been tested against a group theoretical model for coupling between order parameters relating to Fe/vacancy ordering (irrep U 1(1/2,0,1/4)) and magnetic ordering (irreps m${{\Gamma}}_{4}^{+}$ and m${{\Gamma}}_{5}^{+}$). Magnetoelastic coupling is weak but the pre-existing microstructure of ferroelastic and magnetic domains, that develop as a consequence of Fe/vacancy and ferrimagnetic ordering during slow cooling in nature (P63/mmc → C2'/c'), causes subtle changes in the low temperature transition (C2'/c' → P $\overline{1}$). The Besnus transition involves a rotation of magnetic moments out of the a–c plane of the monoclinic structure, but it appears that the transition temperature might vary locally according to whether it is taking place within the pre-existing domain walls or in the domains that they separate. Evidence of metamagnetic transitions suggests that the magnetic field–temperature phase diagram will display some interesting diversity. Low temperature magnetic transitions in minerals of importance to the palaeomagnetism community have been used to identify the presence of magnetite and haematite in rocks and the Besnus transition is diagnostic of the existence of pyrrhotite, Fe7S8

X-point collapse and saturation in the nonlinear tearing mode reconnection

We study the nonlinear evolution of the resistive tearing mode in slab geometry in two dimensions. We show that, in the strongly driven regime (large Delta'), a collapse of the X-point occurs once the island width exceeds a certain critical value ~1/Delta'. A current sheet is formed and the reconnection is exponential in time with a growth rate ~eta^1/2, where eta is the resistivity. If the aspect ratio of the current sheet is sufficiently large, the sheet can itself become tearing-mode unstable, giving rise to secondary islands, which then coalesce with the original island. The saturated state depends on the value of Delta'. For small Delta', the saturation amplitude is ~Delta' and quantitatively agrees with the theoretical prediction. If Delta' is large enough for the X-point collapse to have occured, the saturation amplitude increases noticeably and becomes independent of Delta'.Comment: revtex4, 4 pages, 18 figure

Viscous stabilization of 2D drainage displacements with trapping

We investigate the stabilization mechanisms due to viscous forces in the invasion front during drainage displacement in two-dimensional porous media using a network simulator. We find that in horizontal displacement the capillary pressure difference between two different points along the front varies almost linearly as function of height separation in the direction of the displacement. The numerical result supports arguments taking into account the loopless displacement pattern where nonwetting fluid flow in separate strands (paths). As a consequence, we show that existing theories developed for viscous stabilization, are not compatible with drainage when loopless strands dominate the displacement process.Comment: The manuscript has been substantially revised. Accepted in Phys. Rev. Let

Indirect effects on fitness between individuals that have never met via an extended phenotype

Interactions between organisms are ubiquitous and have important consequences for phenotypes and fitness. Individuals can even influence those they never meet, if they have extended phenotypes that alter the environments others experience. North American red squirrels (Tamiasciurus hudsonicus) guard food hoards, an extended phenotype that typically outlives the individual and is usually subsequently acquired by non‐relatives. Hoarding by previous owners can, therefore, influence subsequent owners. We found that red squirrels breed earlier and had higher lifetime fitness if the previous hoard owner was a male. This was driven by hoarding behaviour, as males and mid‐aged squirrels had the largest hoards, and these effects persisted across owners, such that if the previous owner was male or died in mid‐age, subsequent occupants had larger hoards. Individuals can, therefore, influence each other’s resource‐dependent traits and fitness without ever meeting, such that the past can influence contemporary population dynamics through extended phenotypes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148423/1/ele13230.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148423/2/ele13230_am.pd

Search for very high energy gamma-rays from WIMP annihilations near the Sun with the Milagro Detector

The neutralino, the lightest stable supersymmetric particle, is a strong theoretical candidate for the missing astronomical ``dark matter''. A profusion of such neutralinos can accumulate near the Sun when they lose energy upon scattering and are gravitationally captured. Pair-annihilations of those neutralinos may produce very high energy (VHE, above $100 GeV$) gamma-rays. Milagro is an air shower array which uses the water Cherenkov technique to detect extensive air showers and is capable of observing VHE gamma-rays from the direction of the Sun with an angular resolution of $0.75^{\circ}$. Analysis of Milagro data with an exposure to the Sun of 1165 hours presents the first attempt to detect TeV gamma-rays produced by annihilating neutralinos captured by the Solar system and shows no statistically significant signal. Resulting limits that can be set on gamma-ray flux due to near-Solar neutralino annihilations and on neutralino cross-section are presented

Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique

The recent advances in TeV gamma-ray astronomy are largely the result of the ability to differentiate between extensive air showers generated by gamma rays and hadronic cosmic rays. Air Cherenkov telescopes have developed and perfected the "imaging" technique over the past several decades. However until now no background rejection method has been successfully used in an air shower array to detect a source of TeV gamma rays. We report on a method to differentiate hadronic air showers from electromagnetic air showers in the Milagro gamma ray observatory, based on the ability to detect the energetic particles in an extensive air shower. The technique is used to detect TeV emission from the Crab nebula. The flux from the Crab is estimated to be 2.68(+-0.42stat +- 1.4sys) x10^{-7} (E/1TeV)^{-2.59} m^{-2} s^{-1} TeV^{-1}, where the spectral index is assumed to be as given by the HEGRA collaboration.Comment: 22 pages, 11 figures, submitted to Astrophysical Journa