Sensitivity of a wide-band F.I.R. receiver using a Josephson self oscillator mixer

The system temperature of a receiver using a Josephson junction as a self oscillator mixer has been measured in the range 0.6 to 2 THz. The experimental value T_S=53000K (DSB) at 900 GHz is in good agreement with the calculated value. A T_S～12 000 K is predicted with a 30 K i.f. amplifier Possible applications are related to fast frequency tunable receivers (over one octave) with limited spectral resolution.     

Optical properties of F.I.R. metallic grids: Reflection phase shift measurements

Utilization of metallic grids stacks for F.I.R filters needs a good knowledge of optical properties of each grid. We study here an experimental method in order to determine the wave's change of phase by reflection on a wire grid. We use a Perot-Fabry interferometer constituted by these grids.     

Absolute measurement at 1 THz of the optical coupling of a F.I.R. conical antenna with a Josephson detector

We present the first absolute measurement of the optical coupling of a FIR antenna with a Josephson detector. We have studied a wide band FIR coupling system made of a conical antenna (discone) and a focussing paraboloid mirror. The calculated efficiency is (6.8±0.3)10^?2 for the optimum choice of parameters at 1 THz. The best measurements using a HCN laser at 891 GHz are in agreement while the average achieved coupling is (2.3±0.4)10^?2 reflecting the experimental difficulties.     

V.H.F.-turnstile-antenna performance as a function of antenna geometry on large cylindrical satellites

Until recently, development of v.h.f.-turnstile-antenna systems for satellites was carried out mainly empirically by using r.f. models, but computer programs are now available to assist in this. One of these programs has been used to model turnstile systems on large cylindrical satellites (of the size of current European scientific satellites) and some general conclusions have been reached concerning the choice of monopole base radius and inclination.     

A feasibility study of stripline-fed slots arranged as a planararray with circular grid and circular boundary

An experimental study of the self-impedance of stripline-fed slots has been undertaken, with slot length and slot offset relative to the strip as parameters. The slot is cut in one wall of a parallel plate waveguide, and locally a cylindrical cavity is created around the slot by two ρ=constant walls and two φ=constant walls. Such cavities can be used as modules to build a circular-grid planar array. Anticipating a corporate feed, it is demonstrated that sufficient dynamic range in the self-impedance to overcome the effects of mutual coupling is achievable, thereby opening up the prospect of an efficient circular-grid array for seeker antenna applications that require good sum and difference patterns     

Media Impact: Games in the Classroom: Using Games as a Motivator for the Study of Computing: Part 2

It's no secret that undergraduate computer science enrollment, which has suffered through one of its periodic downturns, seems to have bottomed out but is now on an upswing. This cyclic behavior has been occurring for many years now, producing many exciting ideas concerning how to revamp introductory computer science courses to make them more exciting and relevant, and to show beginning students that computer science entails more than just programming. Georgia Tech, one of the active participants in this revamp, has developed the concept of threads (a means to connect chunks of related knowledge across different courses) and is devising techniques to enrich beginning courses using minirobots and multimedia. The present article, the second of two parts, written by Andrew Phelps and his group at the Rochester Institute of Technology, describes a parallel effort to use gaming as a way to improve learning and to demonstrate to students that computer science is indeed exciting and cool.     

A useful modification of the technique for measuring capacitance as a function of voltage

Measurements of small signal capacitance as a function of applied bias voltage are widely used for the determination of information about metal-insulator-semiconductor (MIS) capacitors. The information that can be derived from the measurements includes interface-state density and flat-band charge density at the insulator-semiconductor (IS) interface, semiconductor doping, and charge stability under bias-temperature stress. A limitation on the use of this measurement method which has until now prevented its even more general application is the requirement that in order to determine Cs, the semiconductor space-charge capacitance, with reasonable accuracy the ratio of Csto CI, the insulating layer capacitance, must be ∼ 10. In the present work it is shown that a modification of the usual method can significantly relax this restriction and allow the accurate determination of Cswhen the ratio Cs/Cris as large as 100 or more, In fact, the inherent limit is no longer directly dependent on this ratio but on the noise level in the capacitance measurement. In some cases Cs/CI≥ 1 due to a thick insulating layer, A very large bias voltage is then required to span the capacitance range of interest; commercially available capacitance meters which typically have applied bias capabilities of ±600 V or less may be inadequate. A simple circuit modification has been employed to allow much larger bias voltages (up to ± 7 kV in the present Work) to be applied to the sample without alteration of or damage to the capacitance meter.     

Collaborative research as a function of proximity, industry, andcompany: a case study of an R&D consortium

Collaborative work among researchers at US Universities, industry, and federal laboratories is increasingly advocated in the globally competitive marketplace. Reliable and meaningful measures of such collaboration have been sparse. This study uses a bibliographic search of published, co-authored research papers to analyze collaboration patterns among researchers at one of the nation's oldest, largest, and most complex R&D consortia, the Microelectronics and Computer Technology Corporation (MCC) and its shareholders, other industry participants, universities, and federal laboratories. The data indicate that, in terms of a defined population of published research articles, MCC researchers have collaborated more frequently with academic than with corporate researchers and more often with nonshareholder than shareholder organizations. MCC is located in Austin, Texas. Geographic proximity has played a role in the consortium's collaboration with universities only for the local research university, The University of Texas at Austin. Proximity has not been an important factor in corporate collaboration, with the consortium. Among MCC shareholders, collaboration has varied by type of industry, while universities have played an important linking role between MCC and industry. R&D expenditures per employee for member companies are inversely related to the frequency of co-authorship of articles with MCC researchers. Collaboration of MCC shareholders with international researchers has been fairly frequent, given that MCC is closed to foreign membership     

Electron transport through polycyclic hydrocarbon molecules: A study of shot noise contribution to the power spectrum

We study electron transport characteristics through some polycyclic hydrocarbon molecules attached with two metallic electrodes by the use of Green’s function technique. Here we do parametric calculations based on the tight-binding model to investigate the transport properties through such molecular bridges. In this context we also discuss noise power of the current fluctuations and focus our attention on the shot noise contribution to the power spectrum. The electron transport characteristics are significantly influenced by (a) the length of the molecules, (b) the interference effects and (c) the molecule-to-electrodes coupling strength.     

A novel measurement method of a single dust particle permittivity at a microwave frequency band as I/P to accurate scattering computations. Part I

In electromagnetic scattering computation the scattering properties of a single particle can be evaluated if the solid permittivity of its constituent material is known. If the material is not homogeneous (e.g. water layer on the particle surface) both the structure and the permittivity of the different parts must be known. However, it is possible (at least at microwave frequencies) to define an equivalent homogeneous permittivity $\left( {\bar \varepsilon } \right)$ which would produce the same scattering properties for a homogeneous particle of the same outer shape as the real one. In this work a novel measurement method of a single particle scattering for evaluating the dielectric properties of dust is derived. Results are compared with another work on bulk/scaled measurement (Part II) of dust permittivity at the same frequency band (X-band) gave matched results.     

A theoretical explanation of the carrier lifetime as a function of the injection level in gold-doped silicon

An expression for the recombination rate in gold-doped silicon is derived taking into account both gold energy levels. This formula shows that the dominant energy level under high-injection conditions is not the midgap gold acceptor, but the gold donor level. The high-low injection lifetime ratio calculated with the derived expression is in good agreement with measured values. This indicates that lifetime and capture cross section measurements are consistent with each other. The relation between gold concentration and high-injection lifetime is calculated. The relative density of the neutral and the negatively and positively charged traps is shown as a function of the carrier injection level.     

A comparison of the bulk resistivity as a function of composition for some group lVA-boron and -silicon systems

The bulk resistivity as a function of composition has been measured for TiB_x, ZrB_x, HfB_x and TiSi _x and ZrSi _x (0 ≤x ≃ 2) samples. The results are discussed in conjunction with the metallurgical characteristics of the five systems. The diboride phases generally have low resistivities which are relatively insensitive to changes in boron composition. In the case of the Ti-B system the minimum resistivity occurs at a boron composition below that required for the diboride phase. In contrast to the boron systems, pronounced variations in electrical resistivities occur in the Ti-Si and Zr-Si systems with sharp peaks at about the compositions Ti₅Si₃ and Zr₅Si₄.     

Effect of detector weighting functions on the point spread function of high-resolution PET tomographs: a simulation study

The point spread function (PSF) of a ring PET tomograph is known to be spatially variant and difficult to obtain because it must be reconstructed from projections. A mathematical model was developed to simulate the data acquisition from a point source and to reconstruct the PSF, taking into account weighting functions to describe the detector response functions. In order to investigate the effect of the detector weighting function on the PSF, the reconstruction, based on the filtered backprojection algorithm, was implemented with three classes of weighting functions of decreasing complexity: exact, locally invariant, and constant. Significant differences are observed to result from the three hypotheses, and this is shown to lead to distorted PSFs and to erroneous estimates of the intrinsic resolution off the center of the tomograph.