黄铜矿原地氨浸的研究

美国矿务局研究人员正在按今后原地浸出的条件，对黄铜矿的氨／氧浸出进行研究。在某篇评述性文献中指出两个主要问题：（１）提供充足的氧化剂可以推进浸出反应；（２）由于在矿物表面形成一层Ｆｅ２Ｏ３的反应产物，故会降低浸出动力学。初步性能研究在２Ｌ、充分搅拌的高压釜中进行，包括自动取样及数据采集，利用统计实验设计确定了从较纯黄铜矿样品中浸出铜的最重要参数，即温度、氧化剂浓度、氢氧化铵浓度、以及温度与氢氧化铵浓度之间的相互制约作甩。结果表明，为了评估氧化剂进人原地矿体的情况，需要作进一步的研究工作；并表明，添加某些有机化合物（例如单糖、聚乙烯醇）至少能使溶液中已反应的某些铁得以稳定，从而减少由于Ｆｅ２Ｏ３包裹作用造成的钝化作用。为了确认这种方法的实用效果，已研究了几种类型的有机添加剂、添加剂对铁较合的程度以及控制螯合铁的一些方法。     

Advanced concepts flight simulation facility

The cockpit environment is changing rapidly. New technology allows airborne computerised information, flight automation and data transfer with the ground. By 1995, not only will the pilot's task have changed, but also the tools for doing that task. To provide knowledge and direction for these changes, the National Aeronautics and Space Administration (NASA) and the Lockheed-Georgia Company have completed three identical Advanced Concepts Flight Simulation Facilities.

Many advanced features have been incorporated into the simulators — e g, cathode ray tube (CRT) displays of flight and systems information operated via touch-screen or voice, print-outs of clearances, cockpit traffic displays, current databases containing navigational charts, weather and flight plan information, and fuel-efficient autopilot control from take-off to touchdown. More importantly, this cockpit is a versatile test bed for studying displays, controls, procedures and crew management in a full-mission context. The facility also has an air traffic control simulation, with radio and data communications, and an outside visual scene with variable weather conditions. These provide a veridical flight environment to evaluate accurately advanced concepts in flight stations.     

我国拟在南极地区建立遥感卫星接收站

国家卫星海洋应用中心、国家海洋环境预报中心主任蒋兴伟透露．我国拟在南极地区建立遥感卫星接收站．以完善我国海洋卫星应用体系．从而进一步加强对全球海洋环境的实时监测．为我国应对全球气候变化提供数据支持。     

Quantitation of the human basal ganglia with positron emission tomography: a phantom study of the effect of contrast and axial positioning

The accurate measurement of the concentration of a radioisotope in small structures with positron emission tomography (PET) requires a correction for quantitation loss due to the partial volume effect and the effect of scattered radiation. To evaluate errors associated with measures in the human basal ganglia (BG), a unilateral model of the BG has been inserted in a 20-cm cylinder. The recovery coefficient (RC=measured activity/true activity) for the BG phantom has been measured on a CTI tomograph with different background concentrations (contrast) and at different axial locations in the gantry. The BG was visualized on four or five slices, depending on its position in the gantry and on the contrast used. The RC was 0.75 with no background (contrast equal to 1.0). Increasing the relative radioactivity concentration in the background increased the RC from 0.75 to 2.00 when the contrast was -0.7 (BG相似文献   

Age is more than just a number: implications for an aging workforce in the US transportation sector

The US workforce is aging. At the same time, there are a record number of open positions in the transportation sector, which has traditionally been a well-paying, but stressful and schedule-dependent, occupation. Due to increasing longevity, need, and ability to work, a possible solution to the transportation workforce shortfall may lie within the retention and recruitment of older workers. This paper uses a socio-technical framework to examine the pertinent, though scant, literature and data related to older workforce demographics and operational needs, the regulatory environment, requisite knowledge, skills and abilities, and application of support technology and training. Although there is evidence of age-related changes in physiology and cognition, the current science remains unable to resolve how an older workforce may most appropriately be applied to transportation to maximize system safety and minimize negative impact to worker well-being.     

The effect of alternative product-label design on warning compliance

Many potentially hazardous products are packaged in small containers. Because of the limited amount of space available on these containers for warnings and other information, manufacturers often reduce the size and amount of printed material on the labels. This frequently impairs the message's legibility, noticeability and comprehensibility. Recently, several alternative label designs have been investigated using preference ratings, but whether the designs facilitate safer behaviour has not been determined. In the present experiment, two alternative designs (tag and wings) were compared with a conventional (control) design for their effect on behavioural compliance with a warning on a very small container of glue. Participants performed a parts-assembly task using the glue without being informed of the study's real purpose. Whether participants wore protective gloves as directed by the warning was measured. Results showed that the tag design produced significantly greater compliance than the other two designs. Measures of noticing, reading and recall of the warning mirrored the compliance results. While participants generally preferred the control label, they most preferred the tag warning. Overall, the results suggest that alternative designs like the tag can enhance warning communication and compliance in cases where surface area is limited.     

Use of a laser beam with an oblique angle of incidence to measure the reduced scattering coefficient of a turbid medium

A simple and quick approach is used to measure the reduced scattering coefficient (μ(s)') of a semi-infinite turbid medium having a much smaller absorption coefficient than μ(s)'. A laser beam with an oblique angle of incidence to the medium causes the center of the diffuse reflectance that is several transport mean-free paths away from the incident point to shift away from the point of incidence by an amount Δx. This amount is used to compute μ(s)' by μ(s)' = sin(α(i))/(nΔx) where n is the refractive index of the turbid medium divided by that of the incident medium and α(i) is the angle of incidence measured from the surface normal. For a turbid medium having an absorption coefficient comparable with μ(s)', a revision to the above formula is made. This method is tested theoretically by Monte Carlo simulations and experimentally by a video reflectometer.     

Equivalent-optical-waveguide model for the analysis of optical waveguides by means of an asymptotic effective-index method

We present a theoretical method that makes it possible to analyze three-dimensional (3-D) integrated optical waveguides with arbitrary refractive-index profiles. With this method it is easy to obtain effective indexes, propagation constants, and coupling-switching properties of planar and channel optical waveguides. This theoretical approach involves one's modeling the original optical waveguide by means of an equivalent optical waveguide whose effective index is evaluated by the application of a technique that we call the asymptotic effective-index method. The numerical values show good convergence and accuracy for effective indexes, propagation constants, and coupling-switching characteristics. Theoretical and experimental results are given.     

Polarization-Dependent Periodic Pulse Oscillation in a Diode-Laser-Pumped and Intracavity Frequency-Doubled Nd:YVO 4 Laser

We demonstrate that two cross-polarized longitudinal modes can have 50% higher conversion efficiency than two parallel-polarized longitudinal modes in a diode-laser-pumped and intracavity frequency-doubled Nd:YVO(4) laser when operated under periodic pulse oscillation. Through simulations of the rate equations for primary frequency intensities and gains, we also verify that this effect can be attributed to gain competition and complementary conversion coefficient between second-harmonic and sum-frequency generations.