851 research outputs found
Method of preparing radially homogeneous mercury cadmium telluride crystals
Hg(1-x)Cd(x)Te is prepared in an improved directional solidification method in which a precast alloy sample containing predetermined amounts of Hg, Cd, and Te is disposed in a sealed ampule and a furnace providing two controlled temperature zones is translated upward past the ampule to provide melting and resolidification. The present improvement is directed to maintaining the zones at temperatures determined in accordance with a prescribed formula providing a thermal barrier between the zones with a maximum thickness and translating the furnace past the zones at a rate less the 0.31 micron/sec
Accuracy of state space collapse for earliest-deadline-first Queues
This paper presents a second-order heavy traffic analysis of a single server
queue that processes customers having deadlines using the
earliest-deadline-first scheduling policy. For such systems, referred to as
real-time queueing systems, performance is measured by the fraction of
customers who meet their deadline, rather than more traditional performance
measures, such as customer delay, queue length or server utilization. To model
such systems, one must keep track of customer lead times (the time remaining
until a customer deadline elapses) or equivalent information. This paper
reviews the earlier heavy traffic analysis of such systems that provided
approximations to the system's behavior. The main result of this paper is the
development of a second-order analysis that gives the accuracy of the
approximations and the rate of convergence of the sequence of real-time
queueing systems to its heavy traffic limit.Comment: Published at http://dx.doi.org/10.1214/105051605000000809 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Non-contact temperature measurement requirements for electronic materials processing
The requirements for non-contact temperature measurement capabilities for electronic materials processing in space are assessed. Non-contact methods are probably incapable of sufficient accuracy for the actual absolute measurement of temperatures in most such applications but would be useful for imaging in some applications
Growth of solid solution single crystals
Based on the thermophysical properties of Hg sub 1-x Cd sub x Te alloys, the reasons are discussed for the failure of conventional Bridgman-Stockbarger growth methods to produce high quality homogeneous crystals in the presence of Earth's gravity. The deleterious effects are considered which arise from the dependence of the thermophysical properties on temperature and composition and from the large amount of heat carried by the fused silica ampules. An improved growth method, developed to optimize heat flow conditions, is described and experimental results are presented. The problems associated with growth in a gravitational environment are discussed. The anticipated advantages of growth in microgravity are given and the implications of the requirements for spaceflight experiments are summarized
Advanced methods for preparation and characterization of infrared detector materials
Differential thermal analysis data were obtained on mercury cadmium telluride alloys in order to establish the liquidus temperatures for the various alloy compositions. Preliminary theoretical analyses was performed to establish the ternary phase equilibrium parameters for the metal rich region of the phase diagram. Liquid-solid equilibrium parameters were determined for the pseudobinary alloy system. Phase equilibrium was calculated and Hg(l-x) Cd(x) Te alloys were directionally solidified from pseudobinary melts. Electrical resistivity and Hall coefficient measurements were obtained
Further evidences concerning the systemic spreading of Agrobacterium tumefaciens in the vascular system of grapevines
The isolation of pathogen, A. tumefaciens, was successful first from the buds, callus tissue and fresh root-tips of forced short cuttings made from symptom-free canes, and furthermore from fresh root-tips and callus tissue of forced, symptomfree root pieces.Both the canes and roots were collected from natural infected, self-rooted vines (cuttings). The results give further evidence regarding systemic spreading of the pathogen in the vascular system of grapevine and to its transmissibility by vegetative propagating material. The tumor-formation on green-wood grafted vines, of which the shoots were collected in a vineyard which was more than 25 percent infected with crown gall, gives further convincing evidence
Growth of solid solution single crystals
Based on the thermophysical properties of Hg sub 1-x Cd sub x Te alloys, the reasons are discussed for the failure of conventional Bridgman-Stockbarger growth methods to produce high quality homogeneous crystals in the prescence of Earth's gravity. The deleterious effects are considered which arise from the dependence of the thermophysical properties on temperature and composition and from the large amount of heat carried by the fused silica ampules. An improved growth method, developed to optimize heat flow conditions, is described and experimental results are presented. The problems associated with growth in a gravitational environment are discussed. The anticipated advantages of growth in microgravity are given and the implications of the requirements for spaceflight experiments are summarized
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