Splitting of the phonon spectrum in3He-4He solutions

The dynamic structure function for ⁴ He- ⁴ He density correlationsS ⁴⁴(k, ) is calculated as a function of the wave vectork and frequency for a simple model of a ³ He- ⁴ He solution at various temperatures and small ³ He molar concentrationx. The inputs to the model include the measured ⁴ He phonon spectrum and the zero-concentration ³ He quasiparticle energy (above thek=0 value), which is taken to be quadratic ink and to intersect the phonon spectrum atk _c near the roton minimum. Taking into account the decay of a phonon into a quasiparticle-hole pair, which is effected in the model by a quantum hydrodynamic interaction, we find that the phonon spectrum is split into two distinct branches. Atk _c the splitting of the phonon branches depends on a coupling constant and the crossover parameter (k _c )/k _c . If in ³ He- ⁴ He solutions is large enough and (k _c )/k _c is small enough, then the phonon spectrum is split into two branches.Work performed in part under the auspices of the U.S. Atomic Energy Commission.Resident Student Associate, Summer 1972, at Argonne National Laboratory, Argonne, Illinois.Supported in part by a Faculty Research Grant and Fellowship from the Horace H. Rackham School of Graduate Studies at the University of Michigan.     

EvaluatingWater Vapor Permeance Measurement Techniques for Highly Permeable Membranes

The cup method and dynamic moisture permeation cell (DMPC) method are two common techniques used to determine the water vapor permeation properties of a membrane. Often, ignoring the resistance of boundary air layers to the transport of water vapor results in the water vapor permeance of the membrane being underestimated in practical tests. The measurement errors are higher with highly permeable membranes. In this study, the two methods were simulated using COMSOL Multiphysics platform and the extent of the error was evaluated. Initial results showed that the error is equally high in both methods. With the correction for the still air gap, the cup method produces a relatively reduced error. In the DMPC method, reducing the error caused by the boundary air layer by increasing the sweep speed can produce higher instrument error. Highly accurate and precise instrument is needed for DMPC method; however, its error is still higher than that in the cup method. Simulations also show that lowering the test pressure is favorable to both methods.     

Phenanthrene and pyrene uptake by arbuscular mycorrhizal maize and their dissipation in soil

Polycyclic aromatic hydrocarbons (PAHs) commonly found in soils can be degraded in rhizosphere, but may also be taken up by plants. The effects of arbuscular mycorrhizal (AM) fungi on uptake of phenanthrene (PHE) and pyrene (PYR) in maize and on their dissipation in soil were investigated using the three-compartmentalized rhizoboxes. Inoculation of Glomus mosseae significantly (p<0.01) increased PHE and PYR concentrations in maize roots and significantly (p<0.05) enhanced PYR translocation from roots to stems in the soil treatments of the PHE+PYR spiked-soils added into the central compartment of the rhizoboxes. There was a significant (p<0.05) dissipation gradient of PHE and PYR observed away from the maize roots, with the highest dissipation rates recorded in rhizosphere zone in the central compartments of the rhizoboxes, followed by near rhizosphere zone and bulk soil zone in the outer compartments. However, G. mosseae only exerted minimal impacts on dissipation of PHE and PYR in the rhizosphere. The present study suggested that the hyphae and extraradical mycelium of AM fungi could play important roles in the uptake and translocation of PHE and PYR in plants. The present results indicated that there is a potential for the use of AM fungi and plant for remediating PAHs contaminated soils.     

Thermophilic anaerobic digestion of palm oil mill effluent

A laboratory study was carried out using the thermophilic anaerobic process to treat palm oil mill effluent containing 67,000 mg 1⁻¹, COD, 31,800 mg 1⁻¹ suspended solids and a pH of 4.5. Completely mixed reactors were operated to evaluate the effects of feed strength and solids retention times on the system's performance. A range of 5–35 days solids retention time was studied. COD reduction was 72% for the 5-day unit and greater than 90% for units having detention time 15 days or more. pH of all units was self adjusted to 7.4. Gas production was, in general, greater than 0.3 m³ kg⁻¹ volatile solids feed.     

商场室内温度分布不均的解决

１现状近几年来,为满足广大顾客对购物环境的要求,大部分商场都设置了集中空调系统,这些商场在夏季一般都取得了较好的降温效果。但在北方地区,冬季供暖时,部分商场首层温度偏低,而顶层温度又偏高。特别是有共享空间、层数多、外门多的商场,温度不均现象更为严重。...     

Encryption and Authentication in On-Board Processing Satellite Communication Systems

Encryption is an efficient method for information protection in communication links which are subject to wiretapping. In this paper we discuss the application of encryption to satellite communication systems in which the satellite has on-board processing capability. The on-board processor can be used in the key distribution process. Two examples of such processes are described. The first requires the storage in the satellite of one key for each user of the communication system. These are used together with a conventional encryption algorithm (DES, for example) to distribute communication keys to the users. The communication keys are then used to encrypt and decrypt information. The other key distribution process utilizes a trap-door one-way function, whose inverse is implemented in the satellite. The need for storage space in the satellite is smaller than that with the first method.     

Optical appearance of alpha particle tracks in CR-39 SSNTD

A ray tracing method based on geometrical optics was used to study the tracks from alpha particles with different energies and with an incident angle of 50°. The transmission operation mode of the microscope is simulated. Considering the distribution of light intensities from the tracks, the mean and the 80% percentile gray levels from real experiments are proposed as quantitative variables to differentiate among tracks. The gray level properties for the same track for different exposures can vary to large extents. We introduce three variables, κ, λ and ε, to make empirical corrections. It is interesting to see that these coefficients are very consistent for the same alpha particle track despite the very different gray level properties. Gray level results have been obtained for tracks from alpha particles with 50° incident angle and different incident energies. However, the track depths cannot be predicted by any one of the coefficients κ, λ and ε. Multivariate analyses can help separate the tracks corresponding to different alpha energies. By using discriminant analysis with κ, λ and ε as independents, effectively all alpha energies can be determined with an accuracy of ±0.5 MeV.     

Sequential Destruction Method for Monte Carlo Evaluation of System Reliability

Circumstances favoring the use of Monte Carlo methods for evaluating the reliability of large systems are discussed. A new method, that of Sequential Destruction (SD) is introduced. The SD method requires no preparatory topological analysis of the system, and remains viable when element failure probabilities are small. It applies to a variety of reliability measures and does not require element failures to be s-independent. The method can be used to improve the performance of selective sampling techniques. Substantial variance reductions, as well as computational savings, are demonstrated using a sample system with more than 100 elements.     

Admissible, Minimax and Equivariant Estimators of Life Distributions from Type II Censored Samples

In life testing, the unique minimum variance unbiased estimator (MVUE) ? is often used when it exists. However it has been shown for certain distributions that an estimator of the form k? with uniformly smaller mean square error exists. Such extimators are derived here for a class of life distributions and are shown to be admissible, minimax, and (in most cases) equivariant. The underlying distribution from which the samples are drawn follows a generalized life model (GLM) which includes a model proposed by Epstein & Sobel, Weibull, exponential, and Rayleigh distributions as special cases. Results are also given for the Type II asymptotic distribution of largest values, Pareto, and limited distributions. In addition, admissible linear estimators of the form a? + b are obtained and it is shown that they are a form of locally best estimators for some portion of the parameter space. Both k? and a? + b could be used in nonrepetitive estimation problems where bias causes no difficulty.