Modified frequency domain kurtosis for signal processing

An operator sensitive to signal probability distribution is obtained, by integrating ideas from higher-order statistics and a frequency approach to signal processing. This function, based on a modified frequency domain kurtosis, assigns a level of stationarity to each signal spectrum component and enhances unsteady components over stationary sinusoids embedded in noise     

Effect of internal heating during hot compression on the stress-strain behavior of alloy 304L

The temperature change due to the conversion of mechanical deformation to internal heat and its effect on the as-measured stress-strain behavior of alloy 304L was investigated by means of initially isothermal (compression specimen, dies, and environment at same temperature at initiation of test), constant strain rate, uniaxial compression of laboratory-sized cylindrical specimens. Strain rate was varied in the range 0.01 to 1 s⁻¹, where the thermal state of the test specimen varied from nearly isothermal to nearly adiabatic, respectively. Specimens were deformed in the temperature range of 750 °C to 1150 °C to a strain of 1. The change in specimen temperature with applied strain was calculatedvia finite-element analysis (FEA) from the asmeasured stress-strain data. Selected predictions were confirmed with embedded thermocouples to verify the model employed. Temperature was found to increase monotonically with strain at a strain rate of 1 s^-1, consistent with what is theoretically expected for the adiabatic case. At the 0.1 and 0.01 s^-1 rates, the sample temperature initially increased, peaked, and then decreased as the sample thinned and the contact area between the sample and the cooler dies increased. As-measured stress was corrected for softening associated with deformational heating by interpolation between the various instantaneous stress-temperature behaviors. The resulting isothermal flow data are compared to those predicted by a conventional method that employs an empirical estimate of the heat retention efficiency of the test specimen, assumed dependent on strain rate but independent of strain, to reduce the increase in temperature calculated for the adiabatic case. Differences between the calculated isothermal stress-strain data from the two methods are discussed. Values for the apparent activation energy of deformation and the strain to the peak in the flow curve, which is associated with the onset of dynamic recrystallization, determined from isothermal stress-strain data differed significantly from those obtained from the as-measured compression test data. Formerly Senior Systems Engineer with EG&G Rocky Flats, Inc., is retired.     

A comprehensive introduction to the geometric theory of linearmultivariable systems

A simple tutorial introduction to the geometric theory of linear multivariable control is presented. This corresponds to approximately three two-hour lectures in a graduate-level course. The authors emphasise the intuitive control interpretation of the main geometric concepts. To this end, the authors focus interest on trajectory formulation for subspace invariance and discrete-time interpretation of the basic subspaces and their construction algorithms. Application of geometric theory for solving the disturbance decoupling problem is illustrated via two pedagogical examples     

Opiate users and the first years after treatment: outcome analysis of the proportion of follow up time spent in abstinence

This second report on a follow-up study of drug users focuses on changes that occurred on a number of variables between intake and follow-up and during the follow-up period. The length of abstinence from opiates was considered as a proportion of the total follow-up period. Overall there was a reduction in opiate use, in injecting and sharing equipment at follow-up. There had been, however, a high level of these risky activities during the follow-up period. Sustained abstinence from opiates was associated with increased employment, enhanced social stability and mental health. Intake drug use was strongly related to follow-up drug status. In particular, those who were injectors of multiple drugs at intake were far less likely to be long term opiate abstainers at follow-up than those who were not injectors at intake or injectors of opiates only.     

Chemotherapy and immunotherapy in adult malignant gliomas

This review summarizes papers published during 1991 and 1992. The poor results obtained in the postneurosurgical treatment of gliomas led researchers to pursue attempts to try to overcome glioma cell resistance. The intra-arterial route was explored in several phase II studies with new drugs and even immunoconjugates; rates of response between 30% to 60% were obtained. New drugs (fotemustine, eflornithine, and estramustine) or combined protocols planned to circumvent chemoresistance were tested and showed some efficiency with moderate toxicity, enlarging the number of drugs available against malignant gliomas. On the contrary, two retrospective analyses warned about the risk of reduction of median time to survival due to adjuvant chemotherapy in anaplastic astrocytomas; this finding, if confirmed, would suggest to defer chemotherapy at the time of recurrence in this type of glial tumor. Immunobiologic therapies as immunomodifiers, immunoconjugates, or cytotoxic lymphocyte-activated killer cells and tumor-infiltrating lymphocytes were tested and allowed some responses to be obtained. In young children, chemotherapy regimens were found to be efficient in malignant plexus choroid carcinomas and low-grade gliomas, allowing radiation therapy to be deferred. Many studies were methodologically unsatisfactory because of uncertain pathology grouping, noncompliance to initial protocols, or too small populations of patients.     

Hepatitis C virus RNA in serum of blood donors with or without elevated transaminase levels

The pattern of hepatitis C virus (HCV) viremia in blood donors who are positive for antibody to HCV (anti-HCV) according to the level of transaminase activity is unclear. A polymerase chain reaction-based HCV RNA detection method was used to study two clearly defined groups of anti-HCV-positive blood donors with repeatedly normal (n = 27) and elevated (n = 17) alanine aminotransferase (ALT) levels. HCV RNA was detected in only 4 of 27 blood donors with normal ALT values and 15 of 17 with elevated ALT values. These results indicate that anti-HCV-positive blood donors with normal ALT levels constitute a heterogeneous group, as HCV viremia is detectable in only a small proportion of cases. Polymerase chain reaction should be useful in the surveillance of anti-HCV-positive blood donors with normal ALT levels, by identifying those who might benefit from further investigation and treatment.     

Liver glutathione content and glutathione-dependent enzymes of two species of freshwater fish as bioindicators of chemical pollution

Glutathione content and glutathione-dependent enzymes were measured in the liver of two fish species, gudgeon (Gobio gobio) and roach (Rutilus arcasii), from the river Bernesga (Spain) caught downstream and upstream of the waste site of several chemical industries. Animals from contaminated sites display a reduced glutathione concentration and a tendency to the decrease of glutathione S-transferase activity. Glutathione peroxidase activity was significantly elevated only in the liver of Gobio gobio and glutathione reductase activity in that of Rutilus arcasii. Our data indicate that the glutathione system constitutes a sensitive biochemical indicator of chemical pollution. Relative changes of glutathione and glutathione-dependent enzymes in both fish species suggest a different susceptibility to toxins.