Effects of confinement on the electron-phonon interaction in Al(0.18)Ga(0.82)As/GaAs quantum wells

Photoluminescence measurements at different temperatures have been performed to investigate the effects of confinement on the electron-phonon interaction in GaAs/AlGaAs quantum wells (QWs). A series of samples with different well widths in the range from 150 up to 750 A was analyzed. Using a fitting procedure based on the Passler-p model to describe the temperature dependence of the exciton recombination energy, we determined a fit parameter which is related to the strength of the electron-phonon interaction. On the basis of the behavior of this fit parameter as a function of the well width thickness of the samples investigated, we verified that effects of confinement on the exciton recombination energy are still present in QWs with well widths as large as 450 angstrom. Our findings also show that the electron-phonon interaction is three times stronger in GaAs bulk material than in Al(0.18)Ga(0.82)As/GaAs QWs.

Government policy and private investment in Brazil (1955/82)

The questlon of the crowding-out of private !nvestment by public expenditure, public investment in particular , ln the Brazilian economy has been discussed more in ideological terrns than on empirical grounds. The present paper tries to avoid the limitation of previous studies by estlmatlng an equation for private investment whlch makes it possible to evaluate the effect of economic policies on prlvate investment. The private lnvestment equation was deduced modifylng the optimal flexible accelerator medel (OFAM) incorporating some channels through which public expendlture influences privateinvestment. The OFAM consists in adding adjustment costs to the neoclassical theory of investrnent. The investment fuction deduced is quite general and has the following explanatory variables: relative prices (user cost of capitaljimput prices ratios), real interest rates, real product, public expenditures and lagged private stock of capital. The model was estimated for private manufacturing industry data. The procedure adopted in estimating the model was to begin with a model as general as possible and apply restrictions to the model ' s parameters and test their statistical significance. A complete diagnostic testing was also made in order to test the stability of estirnated equations. This procedure avoids ' the shortcomings of estimating a model with a apriori restrictions on its parameters , which may lead to model misspecification. The main findings of the present study were: the increase in public expenditure, at least in the long run, has in general a positive expectation effect on private investment greater than its crowding-out effect on priva te investment owing to the simultaneous rise in interst rates; a change in economlc policy, such as that one of Geisel administration, may have an important effect on private lnvestment; and reI ative prices are relevant in determining the leveI of desired stock of capital and private investrnent.

Clinical and pathological assessment of 82 patients with cardiovascular diseases undergoing autopsy at the Hospital das Clínicas of the Faculdade de Medicina de Botucatu from 1988 to 1993

OBJECTIVE: To evaluated the clinical diagnostic, efficiency for basic death causes in patients dying of circulatory disease and de relative frequency of those diseases. METHODS: Analysis of medical record data of 82 patients, ages from 16 to 84 years old (68 over 40 years old), whose died of circulatory disease and had undergone necropsy in the period from 1988 to 1993 years in the University Hospital of Medicine Faculty of Botucatu-UNESP, Br. RESULTS: The functional class of patients were III or IV, in 78%, and 81.7% needed urgent hospitalization. By the clinical judgment the death were by ischemic heart disease in 32 (21 acute myocardial infarction), Chagas'disease in 12, valvopathy in 11, cardiomyopathy in 7, heart failure with no specification of cardiopathy in 11 and other causes in 9. At the necropsy the death cause was ischemic heart disease in 34 patients, valvopathy in 10, Chagas'disease in 10, cardiomyopathy in 5, and heart failure with no specification of cardiopathy in 2.The concordance taxes were in thhe same order: 94,6%, 90,0%, 83.3%, 71.4% and 28.5%. CONCLUSION: There was a great efficiency of clinical diagnosis for death cause in a general university hospital. The ischemic heart disease were the main causes of death.