Drexel University

About: Drexel University is a education organization based out in Philadelphia, Pennsylvania, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 26770 authors who have published 51438 publications receiving 1949443 citations. The organization is also known as: Drexel & Drexel Institute.

Experimental investigation of geologically produced antineutrinos with KamLAND

Abstract: The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of ^(238)U and ^(232)Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained.

Impact of irradiation technique and tumor extent in tumor control and survival of patients with unresectable non-oat cell carcinoma of the lung: report by the Radiation Therapy Oncology Group.

Abstract: An analysis of intrathoracic tumor control was carried out in 378 patients with histologically proven unresectable non-oat cell carcinoma of the lung treated with definitive radiotherapy, randomized to one of four treatment regimens: 4000 rad split course (2000 rad in five fractions in one week, two weeks rest and additional 2000 rad in five fractions in one week) or 4000, 5000 or 6000 rad continuous courses, five fractions per week. Between 85 and 101 patients are analyzed in each treatment group. The complete plus partial response was 46-51% in the 4000 rad groups in contrast to 61-66% in the 5000 to 6000 rad groups (P = 0.008). The overall two year survival rate was 10-11% for the patients treated with 4000 rad split or continuous course, and 19% in the patients treated with 5000 to 6000 rad. The complete response in patients with tumors 3 cm or less in diameter was 16% when treated with 4000 rad in contrast to 20-31% in those treated with 5000-6000 rad. In the patients with lesions from 4 to 6 cm in diameter, complete and partial tumor regression was 48% in the 4000 rad group, 67% with 5000 rad, and 71% with 6000 rad.more » Strict quality assurance criteria in radiotherapy are necessary to achieve optimal treatment results and a careful program to evaluate techniques of irradiation and protocol compliance should be maintained in cooperative group studies in order to enhance the validity of clinical trials. (JMT)« less

Consequences of Bank Distress During the Great Depression

Abstract: The consequences of bank distress for the economy during the Depression remain an area of unresolved controversy. Since John M. Keynes (1931) and Irving Fisher (1933), macroeconomists have argued that bank distress magnified the extent of the economic decline during the Depression. As the intermediaries controlling money and credit, banks were in a special position to transmit their distress to other sectors. But the mechanism through which banking distress mattered for the economy has been hotly contested. Milton Friedman and Anna J. Schwartz (1963) saw the contraction in the money multiplier—driven, in their view, by panicked depositors’ withdrawals of deposits—as the primary mechanism through which banking distress affected the real economy. They described the mechanism transmitting banking distress to the real sector as operating at the national level through changes in the aggregate supply of money and interest rates. Bank distress reduced the money supply available to the public either through the closure of banks and the consequent freezing of bank deposits, or the withdrawals of deposits by depositors that feared bank failure. Ben S. Bernanke (1983), building on Fisher (1933), emphasized the transmission of monetary shocks via their effects on the balance sheets of borrowers and on the supply of credit by banks. Borrowers’ balance sheets were worsened by debt deflation as the result of fixed dollar debt obligations—borrowers’ net worth and cash flow declined with the rising value of debt service costs relative to income. Borrowers with positive net present value projects, but weak balance sheets, had less internally generated retained earnings to invest and could not qualify for credit. Furthermore, Bernanke argued that the contraction of the money supply produced contraction of nominal income and prices relative to fixed debt service, which weakened borrowers’ balance sheets, and in turn, weakened banks. Not only did firms’ financial distress reduce the number of qualified borrowers, the contraction in banks’ net worth forced a reduction in the supply of bank loans to qualified borrowers. Many firms and individuals relied on banks for credit, and as those banks suffered losses of capital (due to asset value declines) and contractions in deposits (as depositors reacted to bank weakness by withdrawing their funds), even borrowers with viable projects and strong balance sheets experienced a decrease in the effective supply of loanable funds. Bernanke termed the combined weakening of borrowers’ balance sheets and the contraction in bank credit supply a rise in the “cost of credit intermediation.” The scarcity of perfect substitutes for the positive net present value investments of firms with weak balance sheets, and for the credit supplied by existing banks, implies that the weakening of firms’ and banks’ balance sheets, the disappearance of banks, and the contraction in surviving banks’ lending made it more difficult for the economy to channel funds to their best use. Thus, what began as a contraction in aggregate demand became a contraction in aggregate supply, which magnified adverse economic shocks and prolonged and deepened the Depression. The financial distress of firms and banks, and the decline in bank lending, were not only symptoms of the Depression, but means for magnifying the shocks that caused the Depression. Bernanke’s statistical evidence in support of this story is derived from time-series analysis at the national level, in * Calomiris: Graduate School of Business, 601 Uris Hall, Columbia University, 3022 Broadway, New York, NY 10027, and National Bureau of Economic Research (e-mail: cc374@columbia.edu); Mason: Department of Finance, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 (e-mail: joe.mason@drexel.edu). We thank Valerie Ramey, David Wheelock, Charles Himmelberg, Steve Zeldes, Gary Gorton, two referees, and seminar participants at Columbia University, Wharton, Northwestern University and the 2001 Economic History Association Meetings for helpful comments on an earlier draft. We gratefully acknowledge support from the National Science Foundation, the University of Illinois, and the Federal Reserve Bank of St. Louis.

Weight Trimming and Propensity Score Weighting

Abstract: Propensity score weighting is sensitive to model misspecification and outlying weights that can unduly influence results. The authors investigated whether trimming large weights downward can improve the performance of propensity score weighting and whether the benefits of trimming differ by propensity score estimation method. In a simulation study, the authors examined the performance of weight trimming following logistic regression, classification and regression trees (CART), boosted CART, and random forests to estimate propensity score weights. Results indicate that although misspecified logistic regression propensity score models yield increased bias and standard errors, weight trimming following logistic regression can improve the accuracy and precision of final parameter estimates. In contrast, weight trimming did not improve the performance of boosted CART and random forests. The performance of boosted CART and random forests without weight trimming was similar to the best performance obtainable by weight trimmed logistic regression estimated propensity scores. While trimming may be used to optimize propensity score weights estimated using logistic regression, the optimal level of trimming is difficult to determine. These results indicate that although trimming can improve inferences in some settings, in order to consistently improve the performance of propensity score weighting, analysts should focus on the procedures leading to the generation of weights (i.e., proper specification of the propensity score model) rather than relying on ad-hoc methods such as weight trimming.