National Case-Control Study of Kaposi\u27s Sarcoma and Pneumocystis Carinii Pneumonia in Homosexual Men: Part 1. Epidemiologic Results

To identify risk factors for the occurrence of Kaposi\u27s sarcoma and Pneumocystis carinii pneumonia in homosexual men, we conducted a case-control study in New York City, San Francisco, Los Angeles, and Atlanta. Fifty patients (cases) (39 with Kaposi\u27s sarcoma, 8 with pneumocystis pneumonia, and 3 with both) and 120 matched homosexual male controls (from sexually transmitted disease clinics and private medical practices) participated in the study. The variable most strongly associated with illness was a larger number of male sex partners per year (median, 61 for patients; 27 and 25 for clinic and private practice controls, respectively). Compared with controls, cases were also more likely to have been exposed to feces during sex, have had syphilis and non-B hepatitis, have been treated for enteric parasites, and have used various illicit substances. Certain aspects of a lifestyle shared by a subgroup of the male homosexual population are associated with an increased risk of Kaposi\u27s sarcoma and pneumocystis pneumonia

A toolbox to demystify probabilistic and statistical paradoxes

Finanziert aus dem DFG-geförderten Open-Access-Publikationsfonds der Universität Siegen für ZeitschriftenartikelThere is a variety of empirical evidence that the coverage of paradoxes in mathematics education helps to support thorough understanding of probabilistic and statistical concepts. However, existing literature often focuses on extensive analysis of a specific paradox, provides new perspectives or an analysis from a different angle. Often neglected aspects in this context are common features between different paradoxes and the fact, that the same situation might look paradoxical to different people for entirely different reasons. We develop a toolbox to demystify paradoxes in probability and statistics. Therefore, we first analyze in which steps of stochastic modeling one might be faced with a paradoxical situation. Secondly, we build on a representative selection of well-known paradoxes and isolate the techniques and methods which help to explain why people find the paradox surprising, identify the class of scenarios where the paradox may occur and make a choice between the seemingly contradictory conclusions. Thirdly, we present the toolbox, which helps to demystify various paradoxical situations. This helps teachers to chose appropriate problems and students to find the right method to resolve these problems. While the developed toolbox is not exhaustive, it helps to dissect the anatomy of probabilistic and statistical paradoxes

Field evaluation of broadband spectral electrical imaging for soil and aquifer characterization

Spectral electrical impedance tomography (EIT) involves the imaging of the complex electrical distribution in the mHz to kHz range. Until now, field EIT measurements were limited to frequencies below 100 Hz because strong electromagnetic coupling effects associated with longer cables and high electrode contact impedances prohibit accurate field measurements at higher frequencies. In this paper, we aim to evaluate the capability of recent improvements in the pre-processing and inversion of wideband EIT measurements to improve the accuracy and spectral consistency of field EIT measurements of the complex electrical conductivity distributions in the mHz to kHz frequency range. In a first case study, time-lapse surface EIT measurements were performed during an infiltration experiment to investigate the spectral complex electrical conductivity as a function of water content. State-of-the-art data processing and inversion approaches were used to obtain images of the complex electrical conductivity in a frequency range from 100mHz to 1 kHz, and integral parameters were obtained using Debye decomposition. Results showed consistent spectral and spatial variation of the phase of the complex electrical conductivity in a broad frequency range, and a complex dependence on water saturation. In a second case study, borehole EIT measurements were made in a well-characterized gravel aquifer. These measurements were inverted to obtain broadband images of the complex conductivity after correction of inductive coupling effects using a recently developed correction procedure that relies on a combination of calibration measurements and model-based corrections. The inversion results were spatially and spectrally consistent in a broad frequency range up to 1 kHz only after removal of inductive coupling effects. Overall, it was concluded that recent improvements in spectral EIT measurement technology combined with advances in inversion and data processing now allow accurate broadband EIT measurements up to 1 kHz

Imaging patterns in soil hydraulic conductivity using electrical impedance tomography

Flow and transport processes in soils are governed by their hydraulic properties. Conventional methods for measuring soil hydraulic properties in the field are invasive and typically have a poor spatial resolution. Recent results of low-frequency electrical impedance spectroscopy measurements on a range of saturated and unsaturated soil samples suggest that spectral electrical properties can be related to hydraulic conductivity. Therefore, electrical impedance tomography (EIT) is a promising non-invasive measurement technique to determine hydraulic conductivity patterns in soils and aquifers. In this project, we aim to establish EIT as a method to determine spatial patterns in hydraulic conductivity and to validate the hydraulic property patterns derived from EIT measurements, in the laboratory and the field. In the laboratory, a series of stationary flow, infiltration and drainage experiments will be performed on soil columns with different degrees of heterogeneity. To validate the hydraulic property distributions derived by EIT, self-potential and electrical resistivity tomography (ERT) data will be collected in addition to the EIT data. For the validation of our method on the field scale, a field infiltration experiment is planned, where water movement will be monitored using nuclear magnetic resonance, time-lapse surface EIT and ERT, time-domain reflectometry and ground-penetrating radar measurements. The validation procedure will include comparison of the EIT-derived hydraulic conductivity distributions with the pattern, independently obtained from the available time-lapse geophysical measurements, using a coupled hydrogeophysical inversion scheme