2,699 research outputs found
The influence of rifle carriage on the kinetics of human gait
The influence that rifle carriage has on human gait has received little attention in the published literature. Rifle carriage has two main effects, to add load to the anterior of the body and to restrict natural arm swing patterns. Kinetic data were collected from 15 male participants, with 10 trials in each of four experimental conditions. The conditions were: walking without a load (used as a control condition); carrying a lightweight rifle
simulator, which restricted arm movements but applied no additional load; wearing a 4.4 kg diving belt, which allowed arms to move freely; carrying a weighted (4.4 kg)
replica SA80 rifle. Walking speed was fixed at 1.5 m/s (+5%) and data were sampled at 400 Hz. Results showed that rifle carriage significantly alters the ground reaction forces produced during walking, the most important effects being an increase in the impact peak and mediolateral forces. This study suggests that these effects are due to the increased range of motion of the body’s centre of mass caused by the impeding of natural arm swing patterns. The subsequent effect on the potential development of injuries in rifle carriers is unknown
Digital simulation of a communication link for Pioneer Saturn Uranus atmospheric entry probe, part 1
A digital simulation study is presented for a candidate modulator/demodulator design in an atmospheric scintillation environment with Doppler, Doppler rate, and signal attenuation typical of the conditions of an outer planet atmospheric probe. The simulation results indicate that the mean channel error rate with and without scintillation are similar to theoretical characterizations of the link. The simulation gives information for calculating other channel statistics and generates a quantized symbol stream on magnetic tape from which error correction decoding is analyzed. Results from the magnetic tape data analyses are also included. The receiver and bit synchronizer are modeled in the simulation at the level of hardware component parameters rather than at the loop equation level and individual hardware parameters are identified. The atmospheric scintillation amplitude and phase are modeled independently. Normal and log normal amplitude processes are studied. In each case the scintillations are low pass filtered. The receiver performance is given for a range of signal to noise ratios with and without the effects of scintillation. The performance is reviewed for critical reciever parameter variations
Digital simulation of a communication link for Pioneer Saturn Uranus atmospheric entry probe, part 2
For abstract, see N75-26198
Preentry communications study. Outer planets atmospheric entry probe
A pre-entry communications study is presented for a relay link between a Jupiter entry probe and a spacecraft in hyperbolic orbit. Two generic communications links of interest are described: a pre-entry link to a spun spacecraft antenna, and a pre-entry link to a despun spacecraft antenna. The propagation environment of Jupiter is defined. Although this is one of the least well known features of Jupiter, enough information exists to reasonably establish bounds on the performance of a communications link. Within these bounds, optimal carrier frequencies are defined. The next step is to identify optimal relative geometries between the probe and the spacecraft. Optimal trajectories are established for both spun and despun spacecraft antennas. Given the optimal carrier frequencies, and the optimal trajectories, the data carrying capacities of the pre-entry links are defined. The impact of incorporating pre-entry communications into a basic post entry probe is then assessed. This assessment covers the disciplines of thermal control, power source, mass properties and design layout. A conceptual design is developed of an electronically despun antenna for use on a Pioneer class of spacecraft
On the uniqueness of the equation for state-vector collapse
The linearity of quantum mechanics leads, under the assumption that the wave
function offers a complete description of reality, to grotesque situations
famously known as Schroedinger's cat. Ways out are either adding elements of
reality or replacing the linear evolution by a nonlinear one. Models of
spontaneous wave function collapses took the latter path. The way such models
are constructed leaves the question, whether such models are in some sense
unique, i.e. whether the nonlinear equations replacing Schroedinger's equation,
are uniquely determined as collapse equations. Various people worked on
identifying the class of nonlinear modifications of the Schroedinger equation,
compatible with general physical requirements. Here we identify the most
general class of continuous wavefunction evolutions under the assumption of
no-faster-than-light signalling.Comment: 7 pages, LaTeX. Major changes performe
Tractability of multivariate problems for standard and linear information in the worst case setting: part II
We study QPT (quasi-polynomial tractability) in the worst case setting for
linear tensor product problems defined over Hilbert spaces. We assume that the
domain space is a reproducing kernel Hilbert space so that function values are
well defined. We prove QPT for algorithms that use only function values under
the three assumptions:
1) the minimal errors for the univariate case decay polynomially fast to
zero,
2) the largest singular value for the univariate case is simple and
3) the eigenfunction corresponding to the largest singular value is a
multiple of the function value at some point.
The first two assumptions are necessary for QPT. The third assumption is
necessary for QPT for some Hilbert spaces
- …