Endocrine and fluid metabolism in males and females of different ages after bedrest, acceleration and lower body negative pressure

Space shuttle flight simulations were conducted to determine the effects of weightlessness, lower body negative pressure (LBNP), and acceleration of fluid and electrolyte excretion and the hormones that control it. Measurements were made on male and female subjects of different ages before and after bedrest. After admission to a controlled environment, groups of 6 to 14 subjects in the age ranges 25 to 35, 35 to 45, 45 to 55 to 65 years were exposed to +3 G sub z for 15 minutes (G1) and to LBNP (LBNP1) on different days. On 3 days during this prebedrest period, no tests were conducted. Six days of bedrest followed, and the G sub z (G2) and LBNP (LBNP2) tests were run again. Hormones, electrolytes, and other parameters were measured in 24-hour urine pools throughout the experiment. During bedrest, cortisol and aldosterone excretion increased. Urine volume decreased, and specific gravity and osmolality increased. Urinary electrolytes were statistically unchanged from levels during the non-stress control period. During G2, cortisol increased significantly over its control and bedrest levels. Urine volume, sodium, and chloride were significantly lower; specific gravity and osmolality were higher during the control period or bedrest. The retention of fluids and electrolytes after +G sub z may at least partially explain decreased urine volume and increased osmolality observed during bedrest in this study. There were some who indicated that space flight would not affect the fluid and electrolyte metabolism of females or older males any more severely than it has affected that of male astronauts

Analytic Behaviour of Competition among Three Species

We analyse the classical model of competition between three species studied by May and Leonard ({\it SIAM J Appl Math} \textbf{29} (1975) 243-256) with the approaches of singularity analysis and symmetry analysis to identify values of the parameters for which the system is integrable. We observe some striking relations between critical values arising from the approach of dynamical systems and the singularity and symmetry analyses.Comment: 14 pages, to appear in Journal of Nonlinear Mathematical Physic

Maps, charts, and graphs study of elements of difficulty and their effect on programming for instruction

Thesis (Ed.M.)--Boston UniversityThe purpose of this thesis is to conduct a study of the elements which cause difficulty in the reading of maps, charts, and graphs and the effect which the elements have on programming the reading of maps, charts, and graphs for instruction. The experiment was made to determine (1) if work of this kind is profitable for students and (2) which elements cause the greatest difficulty for students: (a) types of graphic aids used; (b) the numbers of aids used: (c) the depth of thought required to answer the questions

Quantum Charge Transport and Conformational Dynamics of Macromolecules

We study the dynamics of quantum excitations inside macromolecules which can undergo conformational transitions. In the first part of the paper, we use the path integral formalism to rigorously derive a set of coupled equations of motion which simultaneously describe the molecular and quantum transport dynamics, and obey the fluctuation/dissipation relationship. We also introduce an algorithm which yields the most probable molecular and quantum transport pathways in rare, thermally-activated reactions. In the second part of the paper, we apply this formalism to simulate the propagation of a charge during the collapse of a polymer from an initial stretched conformation to a final globular state. We find that the charge dynamics is quenched when the chain reaches a molten globule state. Using random matrix theory we show that this transition is due to an increase of quantum localization driven by dynamical disorder.Comment: 11 pages, 2 figure

Two-subband conduction in a gated high density InAlN/AlN/GaN heterostructure

Magnetotransport measurements on an In0.16Al0.84N/AlN/GaN gated Hall bar sample have been performed at 0.28 K. By the application of a gate voltage we were able to vary the total two-dimensional electron gas density from 1.83×1013 to 2.32×1013 cm−2. Two frequency Shubnikov–de Haas oscillations indicate occupation of two subbands by electrons. The density of electrons in the first and second sublevels are found to increase linearly with gate voltage with a slope of 2.01×1012 cm−2/V and 0.47×1012 cm−2/V, respectively. And the quantum lifetimes for the first and second subbands ranged from 0.55 to 0.95×10−13 s and from 1.2 to 2.1×10−13 s

Unitary relations in time-dependent harmonic oscillators

For a harmonic oscillator with time-dependent (positive) mass and frequency, an unitary operator is shown to transform the quantum states of the system to those of a harmonic oscillator system of unit mass and time-dependent frequency, as well as operators. For a driven harmonic oscillator, it is also shown that, there are unitary transformations which give the driven system from the system of same mass and frequency without driving force. The transformation for a driven oscillator depends on the solution of classical equation of motion of the driven system. These transformations, thus, give a simple way of finding exact wave functions of a driven harmonic oscillator system, provided the quantum states of the corresponding system of unit mass are given.Comment: Submitted to J. Phys.

Ultrafast decay of hot phonons in an AlGaN/AlN/AlGaN/GaN camelback channel

A bottleneck for heat dissipation from the channel of a GaN-based heterostructure field-effect transistor is treated in terms of the lifetime of nonequilibrium (hot) longitudinal optical phonons, which are responsible for additional scattering of electrons in the voltage-biased quasi-two-dimensional channel. The hot-phonon lifetime is measured for an Al0.33Ga0.67N/AlN/Al0.1Ga0.9N/GaN heterostructure where the mobile electrons are spread in a composite Al0.1Ga0.9N/GaN channel and form a camelback electron density profile at high electric fields. In accordance with plasmon-assisted hot-phonon decay, the parameter of importance for the lifetime is not the total charge in the channel (the electron sheet density) but rather the electron density profile. This is demonstrated by comparing two structures with equal sheet densities (1 × 1013 cm−2), but with different density profiles. The camelback channel profile exhibits a shorter hot-phonon lifetime of ∼270 fs as compared with ∼500 fs reported for a standard Al0.33Ga0.67N/AlN/GaN channel at low supplied power levels. When supplied power is sufficient to heat the electrons \u3e 600 K, ultrafast decay of hot phonons is observed in the case of the composite channel structure. In this case, the electron density profile spreads to form a camelback profile, and hot-phonon lifetime reduces to ∼50 fs

Fourier transforming a trapped Bose-Einstein condensate by waiting a quarter of the trap period: simulation and applications

We investigate the property of isotropic harmonic traps to Fourier transform a weakly interacting Bose–Einstein condensate (BEC) every quarter of a trap period. We solve the Gross–Pitaevskii equation numerically to investigate the time evolution of interacting BECs in the context of the Fourier transform, and we suggest potential applications

Lie symmetries for two-dimensional charged particle motion

We find the Lie point symmetries for non-relativistic two-dimensional charged particle motion. These symmetries comprise a quasi-invariance transformation, a time-dependent rotation, a time-dependent spatial translation and a dilation. The associated electromagnetic fields satisfy a system of first-order linear partial differential equations. This system is solved exactly, yielding four classes of electromagnetic fields compatible with Lie point symmetries

Spherically Symmetric Solutions to Fourth-Order Theories of Gravity

Gravitational theories generated from Lagrangians of the form f(R) are considered. The spherically symmetric solutions to these equations are discussed, paying particular attention to features that differ from the standard Schwarzschild solution. The asymptotic form of solutions is described, as is the lack of validity of Birkhoff's theorem. Exact solutions are presented which illustrate these points and their stability and geodesics are investigated.Comment: 10 pages, published versio