A two-dimensional (2-D) AlGaInP light-emitting diode (LED) array with monolithic integration of one-to-four GaAs MESFET decode circuits has been developed as an image source for portable virtual displays. The epitaxial layers of AlGaInP LEDs with light emission at a wavelength of 605 nm were grown on a semi-insulating GaAs substrate by organometallic vapor phase epitaxy. LED arrays consisting of 240 columns and 144 rows for a total of 34560 pixels were then fabricated on such epitaxial wafers. One-to-four GaAs MESFET decode circuits consisting of eight MESFET's for each decode circuit and a total of 768 MESFET's for a 34 K decode array were fabricated on the semi-insulating GaAs substrate with removal of LED epitaxial layers around the periphery of the LED array. LED arrays with the integrated decode circuits provide a great reduction in I/O terminals. The I/O count of the demonstrated 34 K decode LED array is 104, which is much less than 384 for a comparable array without the integrated decode circuits. The pixel pitch of the LED array is 20 /spl mu/m and each LED pixel has 10/spl times/10 /spl mu/m/sup 2/ emitting area. The output power of LED pixel is 50 nW at an operation current of 50 /spl mu/A. The address voltages used to activate the column decode circuits are 3 V for high and -3 V for low, while the address voltages used to activate the row decode circuits are 0 V for high and -3 V for low. The operating voltage of the decode LED array ranges from 3 to 5 V, and the total power dissipation of the decode LED array is less than 16 mW.

OBJECTIVE:To compare the three month outcome of open and laparoscopic cholecystectomy.DESIGN:Prospective assessment of outcome for a series of patients encompassing the introduction of the laparoscopic technique.SETTING:One teaching hospital.PATIENTS:269 patients admitted for open cholecystectomy between January 1989 and March 1992 and 122 admitted for laparoscopic cholecystectomy between January 1991 and March 1992.MAIN MEASURES:Patients' reported symptoms and self assessed scores with the Nottingham health profile before operation and at three month follow up. Incidence of complications and adverse events after discharge.RESULTS:Similar improvements in symptom rates and health scores were seen regardless of surgical technique. A lower rate of postoperative complications was seen in the patients given laparoscopic surgery (6/95(6%) v 45/235(19%)), and their mean length of stay was lower (4.5 v 9.8 days). Similar results were obtained when the analysis was restricted to a subset of fairly uncomplicated cases (patients aged 60 or less without other illnesses on admission who were not undergoing emergency or urgent surgery), which constituted a larger proportion of the group given laparoscopy (35/95(37%) v 40/235(17%)). Between these two groups no significant difference was seen in the frequency of relevant readmissions to hospital or visits to general practitioners or accident and emergency departments.CONCLUSION:Ideally, a new surgical technique would be evaluated in a randomised trial. In the absence of such a trial, this observational study provides some evidence that the switch from open to laparoscopic cholecystectomy has brought benefits, particularly in terms of reduced length of stay in hospital. A range of clinical and patient derived indicators suggests that these gains have not been associated with a reduction in the quality of the outcome at three months.

The political economic structure of the South African Dairy Industry is analyzed using public choice theory. The Industry is comprised of various interest groups which are found to be interdependent. Some groups have the ability to inflict internal and external effects on other groups as a result of political power they possess. Manufacturers are the most politically effective group, having the ability to inflict external effects on other interest groups. They can spread the costs of the ‘milk is milk’ system among interest groups in the Industry. Their political power is mainly due to the dominant position they attained under protection of the Board before deregulation. Extensions of the public choice theory were found to be beneficial in explaining certain actions within the Industry. A gradual phasing out of regulation is recommended. Policymakers can still play an important role in providing traditional public goods and services such as information, restricting monopoly control and marketing promotions. Freedom of entry of new dairies is essential to protect the interests of consumers and producers.

The effects of government intervention in the South African Maize Industry are evaluated using a partial equilibrium framework. Large monetary transfers have resulted from government policy with a bias towards more powerful producer interest groups. Transfers significantly exceed the welfare gains to producers. However, the per capita gain for producers is greater than the per capita loss for consumers creating an incentive for producers to continue lobbying for the current South African maize policy. Intervention results from market failure followed by political failure where interest groups manipulate government for their own benefit. As long as vested interests remain, policy reform seems remote. A new political dispensation may shift vested interests towards consumers away from producers. Policy reform is discussed along with conditions to facilitate this process of reform.

OBJECTIVE--To assess the validity of the Nottingham health profile (NHP) as an indicator of short term outcome of cholecystectomy. DESIGN--Prospective assessment of outcome. SETTING--One teaching hospital. Patients--161 consecutive patients admitted for cholecystectomy between January 1989 and September 1990. MAIN MEASURES--Patients' reported symptoms and self assessed NHP scores before cholecystectomy and at follow up at three and 12 months (76 patients); assessment before admission (19). RESULTS--Complete data were obtained preoperatively and at three months' follow up from 154 patients; seven did not respond to the follow up questionnaire. 76/84(90%) patients in the study 12 months or more answered the 12 month follow up questionnaire; eight did not respond. Significant changes in score before and at three months after the operation were observed for four of the six dimensions: energy (35.34 v 19.53, p < 0.0001), pain (27.38 v 9.8, p < 0.0001), sleep (26.99 v 17.51, p = 0.0002), and emotional reactions (16.12 v 7.56, p = 0.001). The mean scores for 76 patients followed up at three and 12 months showed little subsequent change. Scores in readmitted patients were all significantly higher, suggesting poor health. Patients with five reported symptoms had significantly worse scores for all dimensions. Scores were similar before cholecystectomy whether the questionnaire was completed before or after admission. CONCLUSION--The NHP is an appropriate tool for monitoring changes in health after cholecystectomy.

Forty patients with widely disseminated or locally advanced malignant obstruction of the middle or lower third of the oesophagus underwent endoscopic treatment by either NdYAG laser recanalization or intubation. Groups were matched on the basis of tumour location and swallowing was graded clinically before and after treatment. Technical success was achieved in 17 of 20 laser treated and 18 of 20 intubated patients. Pretreatment swallowing ability, histology, tumour location and overall length were unrelated to functional outcome in both groups. However, circumferential tumour length identified endoscopically strongly influenced the quality of swallowing after laser recanalization. Patients with excellent swallowing quality (n = 7) had significantly shorter circumferential tumour lengths, 3.1(1.0) cm, than those with poorer quality swallowing (n = 10), 6.3(1.6)cm, (P less than 0.001). Both methods of treatment had low complication rates and there was one death in the series in the laser-treated group. Laser recanalization provides a better functional result than intubation for short (less than 4 cm) circumferential tumour. Intubation at a single session seems more appropriate than repeated laser therapy when tumour length exceeds 4 cm.

We report measured T0values as high as 127 K for 1.3 μm InGaAsP buried heterostructure lasers. An analysis of the electrical characteristics of high T0lasers indicates the presence of shunt leakage currents. The actual T0of the current flowing through the active layer junction is shown to be 70 ± 10 K. The observed reduction in threshold temperature sensitivity may be useful in some applications.

Discrete InGaAsP double heterostructure lasers (λ=1.3 μm) have been fabricated by a novel batch process which incorporates chemically etched end reflectors. The etched-mirror lasers have threshold current densities as low as 3.5 kA/cm2. The average threshold current density for the etched-mirror lasers is approxiamtely 40% higher than for standard cleaved-mirror devices fabricated from the same wafer. The laser fabrication process permits batch fabrication of a much wider variety of discrete laser geometries than conventional laser-cleaving techniques.

Stripe-geometry InGaAsP double heterojunction lasers with chemically-etched mirrors have been fabricated. External differential quantum efficiencies as high as ∼ 30% have been obtained for devices with two chemically-etched mirrors. Etched-mirror lasers with 25 µm wide stripes have threshold currents as low as 210mA (room-temperature, pulsed). The etched-mirror lasers are compared to cleaved-mirror devices prepared from the same wafer.

An InGaAsP (λ=1.3 μm) strip-buried heterostructure laser with active layer strip widths of 5 μm is described. These devices show stable fundamental-transverse-mode operation with linear light-current characteristics to pulsed output powers over 100 mW. Output powers as high as 500 mW are observed without catastrophic damage, which corresponds to twice the power output at which catastrophic mirror damage occurs for similar GaAlAs SBH lasers. Far-field beam divergence is approximately 10° and 30° in the directions parallel and perpendicular to the junction, respectively. cw operation with a threshold current of 170 mA has been achieved at room temperature.