Nonalloyed ohmic contacts in AlGaN/GaN HEMTs by ion implantation with reduced activation annealing temperature

This letter reports AlGaN/GaN high-electron mobility transistors with capless activation annealing of implanted Si for nonalloyed ohmic contacts. Source and drain areas were implanted with an Si dose of 1/spl times/10/sup 16/ cm/sup -2/ and were activated at /spl sim/1260/spl deg/C in a metal-organic chemical vapor deposition system in ammonia and nitrogen at atmospheric pressure. Nonalloyed ohmic contacts to ion-implanted devices showed a contact resistance of 0.96 /spl Omega//spl middot/mm to the channel. An output power density of 5 W/mm was measured at 4 GHz, with 58% power-added efficiency and a gain of 11.7 dB at a drain bias of 30 V.     

Empirical validation of different internal superficial heat transfer models on a full-scale passive house

Being highly insulated, low-energy buildings are very sensitive to variable solar and internal gains. In this context, some modelling assumptions frequently used in simplified building energy simulation tools might be called into question. While higher insulation levels reduce the influence of heat transmission through opaque walls, absorption of solar and internal gains at inner wall surfaces, and indoor superficial heat transfers, become concerning. The convective and long-wave radiative heat transfer models are investigated in COMFIE, a dynamic energy simulation platform. More detailed internal heat transfer models are developed by decoupling convective and long-wave radiative heat transfers and using time-dependent coefficients. Furthermore, an empirical validation process on both simplified and detailed models is carried out using measurements from a full-scale experimental concrete passive house, addressing the model uncertainty vs. complexity issue.     

A superconducting electron spectrometer

The set-up and tests of an electron spectrometer for in-beam conversion electron measurements are described. A superconducting solenoid is used to transport the electrons from the target to cooled Si(Li) detectors. The solenoid is designed to produce either a homogeneous axially symmetric field of up to 2 T or a variety of field profiles by powering the inner and outer set of coils of the solenoid separately. The electron trajectories resulting for various field profiles are discussed. In-beam electron spectra taken in coincidence with electrons, gammas and alpha-particles are shown.     

Time resolved plastic deformations in rods subjected to transverse impact

This paper describes experiments to record deformation profiles versus time in metallic rods subjected to transverse ballistic impacts. Rod materials included a tungsten alloy, four alloys of steel, titanium, and copper. The deformation profiles were analyzed to determine time resolved transverse plastic deformation wave speeds in all the rod materials and to estimate effective fracture shear strains in some of the materials. These material parameters are key elements in an analytical model to estimate deformations and failure in long rod penetrators subjected to transverse loads arising from non-ideal plate penetration geometries (yaw and obliquity). The rod materials were also subjected to tensile tests and Taylor anvil impact tests to measure static tensile and dynamic compressive strengths and longitudinal plastic wave speeds. The Taylor anvil and transverse rod impact tests together furnish the required dynamic material properties for comparing the penetration effectiveness of candidate rod materials and geometries.     

Inducing the Residential Land Market to Grow Timber in an Antiquated Rural Subdivision

Land Use Planning: The Ballot Box Revolution Roger W. Caves. Sage Library of Social Research, Newbury Park, CA. 1992. 247 pp. $22.95 (paperback).

Geographic Information Systems: A Guide to the Technology John C. Antenucci, Kay Brown, Peter L. Croswell, Michael J. Kevany, and Hugh Archer. Van Nostrand Reinhold, New York, 1991.301pp. $59.95.

Sources of Metropolitan Growth Edwin S. Mills and John F. McDonald, editors. Center for Urban Policy Research, Rutgers University, New Brunswick, NJ, 1992. 307 pp. $29.95.

Inventing Times Square: Commerce and Culture at the Crossroads of the World William R. Taylor, editor. Russell Sage Foundation, New York, 1991. 467 pp. $39.95.

Cities and Development in the Third World Robert B. Potter and Ademola T. Salau, editors. Mansell, London and New York, 1990. 200 pp.

Industrialization, Economic Development and the Regional Question in the Third World: From Import Substitution to Flexible Production Michael Storper. Pion, London, 1991. 149 pp. £25.00.

The Good Society Robert N. Bellah, Richard Madsen, William M. Sullivan, Ann Swidler, and Steven M. Tipton. Alfred A. Knopf, New York, 1991.347 pp. $25.00.

Over the Edge: The Growth of Homelessness in the 1980's Martha R. Burt. Russell Sage Foundation, The Urban Institute Press, Washington, DC, 1992. 267 pp. $29.95.

The Maze of Urban Housing Markets—Theory, Evidence, and Policy Jerome Rothenberg, George C. Galster, Richard V. Butler, and John Pitkin. The University of Chicago Press, Chicago, 1991. 549 pp. $62.95.

Housing Markets and Housing Institutions: An International Comparison Björn Hårsman and John M. Quigley, editors. Kluwer Academic Publishers, Boston, 1991.338 pp. $79.95.

Tourism Planning: An Integrated and Sustainable Development Approach Edward Inskeep. Van Nostrand Reinhold, New York, 1991. 508 pp. $49.95.

State of the World 1992 Worldwatch Institute, Lester R. Brown, editor. Norton, New York, 1992. 256 pp. $10.95 (paperback).

Rural Policies for the 1990s Cornelia B. Flora and James A. Christenson, editors. Westview Press, Boulder, CO, 1991. 361 pp. $58.00 (paperback) $24.95.

Atmospheric Ecology for Designers and Planners William P. Lowry, Van Nostrand Reinhold, New York, 1991. 435 pp. $51.95.

Planning Settlements Naturally Stephen Owen. Packard Publishing Ltd, Chichester, UK, 1991. 141 pp. £19.95.

Privatization and Its Alternatives William T. Gormley, Jr, editor. Madison, University of Wisconsin Press, 1991. 342 pp. $40.00, $19.75 (paperback).     

Family history and treatment outcome in young women after breast-conserving surgery and radiation therapy for early-stage breast cancer

PURPOSE: To evaluate the safety and efficacy of breast-conserving therapy for young women with a family history (FH) suggestive of inherited breast cancer susceptibility. MATERIALS AND METHODS: A total of 201 patients aged 36 or younger at diagnosis treated with breast-conserving surgery and radiation therapy (> or = 60 Gy) for early-stage breast cancer were categorized by FH. FH was considered positive in 29 patients who, at the time of diagnosis, had a mother or sister previously diagnosed with breast cancer before age 50 or ovarian cancer at any age. Clinical, pathologic, and demographic variables; sites of first failure; disease-free survival; and overall survival (OS) were compared between FH-positive and -negative groups. Median follow-up time was 11 years. RESULTS: Patient and tumor features were similar between those with and without an FH. Regression analysis of sites of first failure at 5 years demonstrated a risk ratio (RR) of 5.7 for opposite breast cancer for FH-positive patients. Rates of local, regional, and distant failure and disease-free survival or OS did not differ between FH-positive and -negative patients. Age at diagnosis and Ashkenazi heritage were not significantly predictors of patterns of failure. CONCLUSION: Breast-conserving surgery combined with radiation therapy is not associated with a higher rate of local recurrence, distant failure, or second (non-breast) cancers in young women with an FH suggestive of inherited breast cancer susceptibility compared with young women without an FH. However, their increased risk of opposite breast cancer should be taken into account when considering breast conservation as a treatment option.     

MR imaging of the knee ligaments and the postoperative knee

MR imaging is an accurate, noninvasive, and cost-effective method for the evaluation of acute knee ligament injuries and in the examination of the postoperative knee. Understanding the normal anatomy and the pertinent clinical aspects of knee injuries is a prerequisite for accurate interpretation of MR imaging studies. The increasing popularity of ACL reconstruction following disruption of this ligament requires knowledge of the various surgical techniques and their MR imaging appearance as well as the appearance of possible complications.     

Cerebrospinal fluid cytology in patients with cancer: minimizing false-negative results

To investigate the contribution of dietary carbohydrate to glutamate and acetyl CoA synthesis, two groups of adult mice were fed a high- (HCD) or a low-carbohydrate diet (LCD) in which 5% of the carbohydrate was [U-13C]-glucose. Four animals from each dietary group were killed after 1, 2 and 5 d. The tracer:tracee ratios of [13C3] and [13C6]blood glucose and of the [13C2] and [13C3] isotopomers of blood, mucosal, hepatic and muscle alanine and glutamate were used to calculate the fractional contribution of glucose to the 3-carbon, acetyl CoA and oxaloacetate pools of each tissue. In the HCD mice, glucose contributed 66, 33 and 31% of the acetyl CoA pool of muscle, liver and mucosa, respectively. The contribution of glucose to acetyl CoA was lowered by 33% (P < 0.05) and 55% (P < 0.01) in the liver and muscle of the LCD group, respectively, but was unaltered in the mucosa. Glucose made a minor contribution to glutamate synthesis via oxaloacetate in the liver (23%) and muscle (10%) of the HCD group. The fraction of hepatic and muscle glutamate synthesis derived from glucose was not affected by the diet. We conclude that glucose oxidation in liver and muscle parallels the contribution of carbohydrate to dietary energy and that glucose is not a major carbon precursor for muscle glutamate synthesis. Net glutamate synthesis in extraintestinal tissues is preserved when dietary carbohydrate is restricted.     

High resolution morphologic imaging and T2 mapping of cartilage at 7 Tesla: comparison of cartilage repair patients and healthy controls

Object

Our objective was to use 7 T MRI to compare cartilage morphology (thickness) and collagen composition (T2 values) in cartilage repair patients and healthy controls.

Materials and methods

We scanned the knees of 11 cartilage repair patients and 11 controls on a 7 T MRI scanner using a high-resolution, gradient-echo sequence to measure cartilage thickness and a multi-echo spin-echo sequence to measure cartilage T2 values. We used two-tailed t tests to compare cartilage thickness and T2 values in: repair tissue (RT) versus adjacent cartilage (AC); RT versus healthy control cartilage (HC); AC versus HC.

Results

Mean thickness in RT, AC, HC were: 2.2 ± 1.4, 3.6 ± 1.1, 3.3 ± 0.7 mm. Differences in thickness between RT–AC (p = 0.01) and RT–HC (p = 0.02) were significant, but not AC–HC (p = 0.45). Mean T2 values in RT, AC, HC were: 51.6 ± 7.6, 40.0 ± 4.7, 45.9 ± 3.7 ms. Differences in T2 values between RT–AC (p = 0.0005), RT-HC (p = 0.04), and AC–HC (p = 0.004) were significant.

Conclusion

7 T MRI allows detection of differences in morphology and collagen architecture in: (1) cartilage repair tissue compared to adjacent cartilage and (2) cartilage repair tissue compared to cartilage from healthy controls. Although cartilage adjacent to repair tissue may be normal in thickness, it can demonstrate altered collagen composition.