Force and power characteristics of a resistive exercise device for use in space

We have developed a non-gravity dependent mechanical device, which provides resistance during coupled concentric and eccentric muscle actions, through the inertia of a spinning fly-wheel (Fly-Wheel Ergometry; FWE). Our research shows that lower-limb FWE exercise can produce forces and thus muscular stress comparable to what is typical of advanced resistance training using free weights. FWE also offers greater training stimuli during eccentric relative to concentric muscle actions, as evidenced by force and electromyographic (EMG) measurements. Muscle use of specific muscle groups, as assessed by the exercise-induced contrast shift of magnetic resonance images, is similar during lower-limb FWE and the barbell squat. Unlike free-weight exercise, FWE allows for maximal voluntary effort in each repetition of an exercise bout. Likewise, FWE exercise, not unassisted free-weight exercise, produces eccentric "overload". Collectively, the inherent features of this resistive exercise device and the results of the physiological evaluations we have performed, suggest that resistance exercise using FWE could be used as an effective exercise counter-measure in space. The flywheel principle can be employed to any exercise configuration and designed into a compact device allowing for exercises stressing those muscles and bone structures, which are thought to be most affected by long-duration spaceflight.     

The MESSENGER Gamma-Ray and Neutron Spectrometer

A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation. The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum for ⁶⁰Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft, but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort, and a look at some early in-flight data.     

THE ELECTRIC FIELD AND WAVE EXPERIMENT FOR THE CLUSTER MISSION

The electric-field and wave experiment (EFW) on Cluster is designed to measure the electric-field and density fluctuations with sampling rates up to 36000 samples s^-1. Langmuir probe sweeps can also be made to determine the electron density and temperature. The instrument has several important capabilities. These include (1) measurements of quasi-static electric fields of amplitudes up to 700 mV m^-1 with high amplitude and time resolution, (2) measurements over short periods of time of up to five simualtaneous waveforms (two electric signals and three magnetic signals from the seach coil magnetometer sensors) of a bandwidth of 4 kHz with high time resolution, (3) measurements of density fluctuations in four points with high time resolution. Among the more interesting scientific objectives of the experiment are studies of nonlinear wave phenomena that result in acceleration of plasma as well as large- and small-scale interferometric measurements. By using four spacecraft for large-scale differential measurements and several Langmuir probes on one spacecraft for small-scale interferometry, it will be possible to study motion and shape of plasma structures on a wide range of spatial and temporal scales. This paper describes the primary scientific objectives of the EFW experiment and the technical capabilities of the instrument.     

旋转方截面U型通道分离流二阶相关分量测量

为了深入了解旋转涡轮叶片内冷通道中的紊流特性，并为CFD研究提供实验数据，用激光多普勒测速仪（LDA）测量了旋转U型通道中分离流的雷诺应力分量。通道的转轴与弯道的曲率轴平行，测量是在与转轴垂直的对称平面中进行的，流动状态为Re=100,000,Ro=0,0.2和－0．2。直接测量的分量为ux^2^-,Ux^2^-和uxux^-，结果表明旋转对紊流分布的形式有很强的影响。在测量的三种旋转状态中Ro=0.2的正转和Ro=0.2的负转分别具有最低和最高的紊流强度。根据测量到的信息估算了雷诺应力uiuj^-的产生率，结果显示负转的产生率比正转时高。     

Numerical integration of stochastic differential equations: A parallel cosmic ray modulation implementation on Africa’s fastest computer

Three-dimensional studies of the transport and modulation of cosmic ray particles in turbulent astrospheres require large-scale simulations using specialized scientific codes. Essentially, a multi-dimensional Fokker-Planck type equation (a parabolic diffusion equation) must be integrated numerically. One such approach is to convert the relevant transport equation into a set of stochastic differential equations (SDEs), with the latter much easier to handle numerically. Due to the growing demand for high performance computing resources, research into the application of effective and suitable numerical algorithms to solve such equations is needed. We present a case study of the performance of a custom-written FORTRAN SDE numerical solver on the CHPC (Centre for High Performance Computing) Lengau cluster in South Africa for a realistic test problem with different set-ups. It is shown that SDE codes can scale very well on large parallel computing platforms. Finally, we consider an extremely computationally expensive application of the SDE approach to cosmic ray modulation, studying the behaviour of galactic cosmic ray proton latitude gradients and relative amplitudes in a physics-first manner. This is done using a modulation code that employs diffusion coefficients derived from first principles, which in turn are functions of turbulence quantities in reasonable agreement with spacecraft observations and modelled using a two-component turbulence transport model (TTM). We show that this approach leads to reduced latitude gradients qualitatively in line with spacecraft observations of the same, without making ad hoc assumptions as to anisotropic perpendicular diffusion coefficients as are often made in many cosmic ray modulation studies.     

Transient measurements of HV interaction with the ambient and perturbed space environment

Transient measurements of current collected by a rocket payload charged to several kilovolts negative with respect to the ambient plasma were made during the SPEAR-3 sounding rocket mission. The measurements were taken in short bursts at 1MHz, coincident with the application of the high voltage. The measured current is seen to rise approximately parabolically for approximately 15μs before rolling over into an exponential decay towards steady state current collection. The exponential time constant of 40 to 50μs is interpreted as the characteristic ion-collection sheath formation time for the SPEAR-3 payload.