Optimization of transmitter and receiver filters for digitalcommunication systems using mean field annealing

A technique for finding transmitter and receiver filters for a wide class of digital communication systems which minimize the bit-error rate (BER) is presented. The technique uses Monte Carlo simulation to estimate the BER and mean field annealing (MFA) to optimize the pulse shapes. Modeling of the link can be as complex as simulation will allow, while MFA is resistant to the statistical variation in the BER estimate from the simulation. Initially, the MFA technique was applied to a binary symmetric channel in a nonsimulation environment, and an approximate analysis of the behavior of MFA for this problem was performed. In a more complex example, MFA was coupled with Monte Carlo simulation techniques to find near-optimal transmit and receive filters for a satellite communications link, taking 6 CPU hours on a DECstation 3100. The BER of the link was found to be as much as three orders of magnitude lower when using the MFA-constructed optimal filters than when using filters from other comparison results. For this example, the pulse shapes obtained using MFA exhibit a low BER even as the parameter controlling the nonlinearity of the satellite-link model is varied over a wide range, thus showing the solution is robust     

Evolution of cavity size distributions in dual-ion irradiated austenitic stainless steel and Fe-Cr-Ni ternary alloys

The first four moments of experimentally measured cavity size distributions in dual-ion irradiated 304SS, Fe-12Ni-15Cr and Fe-30Ni-15Cr alloys have been calculated for a range of fluences, helium injection rates, and irradiation temperatures. The moments are shown to correctly describe the effects of alloy composition, fluence, helium and temperature on the evolution of the cavity size distributions. Experimentally determined moments are compared with those calculated from cavity nucleation and growth theories. The moments reflect the competition between nucleation and growth processes and provide insight into the details of the transient low swelling regime.     

Evaluation of a modified TCLP methodology for RCRA toxicity characterization of computer CPUs

A leaching method similar to the toxicity characteristic leaching procedure (TCLP) was designed and evaluated for testing of bulky wastes, such as discarded electronic devices. The objective was to meet the intent of the TCLP (same leaching solution, liquid-to-solid ratio and same leaching time) but to allow more representative and rapid testing. The procedure was evaluated by examining lead leaching from computer CPUs as a test case; disassembled CPUs were leached in their entirety (or close to entirety) in a large vessel using a drum rotator. The difference in rotation speed between the large-scale test and the TCLP was found to have no statistical impact on lead leaching. The lack of size reduction resulted in less reducing conditions than the standard TCLP (because of increased iron and zinc leaching), and this resulted in greater lead leaching. For electronic wastes with large amounts of steel, the large-scale procedure provides a more conservative estimate of TCLP lead leaching. The large-scale procedure greatly reduces sample processing effort but does increase the cost of analysis. Evaluation of this approach by the regulatory community is important as the CPUs tested here tended to leach lead at greater than the toxicity characteristic (TC) limit (5 mg/L) using the large-scale test, but less than the TC limit using the standard TCLP.     

An algorithm for three-dimensional reconstruction incorporating cross-plane rays

Conventional multislice positron cameras reconstruct a three-dimensional distribution of a positron-emitting radioscope as a set of two-dimensional transverse sections. Consequently, annihilation photons which cross two or more planes are eliminated from the data. Such an approach makes efficient use of the emitted photon flux. A method is proposed which makes more efficient use of the available photons by including both oblique and transverse section in the reconstruction. The implementation of the method consists of centering a scaled convolution filter on each detected coincidence event line and backprojecting the filter values through the three-dimensional reconstruction volume. The final image is normalized to allow for the different number of oblique and transverse sections that contribute to each point in the imaging volume. The method has been evaluated using both simulated data and measured data obtained with a routing area detector positron camera.     

Exposure to environmental and mainstream tobacco smoke and risk of spontaneous abortion

The present nationwide, multicenter clinical study was carried out in 26 departments of surgery to define the incidence and attendant mortality of intestinal infarction following abdominal aortic surgery, and to identify patients at risk of it. The data consist of 1752 patients who underwent abdominal aortic reconstruction during 1991-1993 as recorded in the Finnish national vascular registry (FINNVASC). Among the 1752 operations, 27 patients treated at 14 different hospitals had intestinal ischemia, and the complete patient records of all 27 cases were reanalyzed. The incidence of bowel infarction was 1.2%. Among patients operated on for a ruptured aneurysm it was 3.1%, whereas 1.0% of patients with nonruptured aneurysm and 0.6% of those operated on for aortoiliac occlusive disease developed intestinal infarction. In 14 patients (67%) the lesion affected the left colon. The overall 30-day mortality rate was 13% but reached 67% among those with intestinal infarction. We conclude that acute intestinal ischemia with bowel infarction is an infrequent but serious complication of abdominal aortic surgery. It is mainly related to surgery due to aneurysmal disease, and patients with occlusive aortoiliac disease present ischemic complications in the intestines less often. Hypotensive patients being treated for ruptured aneurysm are at greatest risk of intestinal ischemia.