A comparison of two approaches to feedback circuit analysis

Two approaches for analyzing single-loop feedback circuits are compared and contrasted. One approach is based on the return-radio concept, and the other is based on two-port analysis. A frequent error in many popular texts-interchanging the computation of return ratio for a dependent source and loop gain of the idealized feedback network-is discussed. Assumptions commonly made in many texts when presenting two-port feedback analysis are examined for validity. Examples are given to highlight the differences between the two approaches     

Presentation of colonic carcinoma via genetic testing in the offspring

We describe the case of a 33-year-old man who injected 4 ml of India ink into one of the median cubital veins with suicidal intent. He was hospitalized in good general condition 10 h after the injection. Abnormal laboratory test results were a leukocytosis, an oximetrically determined methemoglobin level of 36.9% (normal range: 1.5%) and a free hemoglobin level of 74 mumol/L (normal range: < 25 mumol/L). Toxicological examination showed the presence of nitrobenzene in blood and urine. Intravenous administration of vitamin C and tolonium chloride plus forced diuresis led to an improvement in cyanosis and a fall in the methemoglobin concentration. Repeated increase in the concentration of aminobenzene were successfully treated by hemodialysis with a high-flux dialyzer.     

Reduced expression of retinoblastoma gene product (pRB) and high expression of p53 are associated with poor prognosis in ovarian cancer

Paraffin sections (n = 168, 27 benign, 16 low malignant potential [LMP] and 125 malignant tumours) from epithelial ovarian tumours were evaluated immunohistochemically for expression of retinoblastoma gene product (pRB) and p53 protein, and the relationship among pRB, p53 and cyclin-dependent kinase inhibitor 2 (CDKN2) gene product p16INK4A (p16) was analysed, following our previous study of p16. Forty-one percent of the benign, 50% of the LMP and most (71%) of the malignant tumours showed high pRB expression. High expression of pRB (>50% pRB-positive cells) significantly correlated with non-mucinous histological subtypes. Reduced pRB expression, substage and residual disease were significant predictors for poor prognosis in stage I patients. All the benign and most of the LMP (81%) tumours were in either the p53-negative or low p53-positive category, but nearly half of the malignant tumours had high p53 expression. High p53 accumulation was found in non-mucinous, high grade and late stage tumours. For well-differentiated carcinomas, high p53 expression was a predictor of poor prognosis. However, even though high p53 expression was not associated with histological subtype, stage or the presence of residual disease, high p53 expression was not an independent predictor when all clinical parameters were combined. For all ovarian cancers, a close correlation was found between high p53 and high p16 expression. The relationship between the expression of pRB and p16 depended on tumour stage. In stage I tumours, high pRB was associated with low p16 reactivity. On the other hand, most advanced tumours showed both high pRB and high p16 reactivity.     

The influence of silicon and yttrium on the scaling behaviour of an Austenitic Fe-Cr-Ni alloy under athermal conditions

Data obtained using thermogravimetric and resonant frequency techniques and the results of structural analysis are used to evaluate the effects on oxidation of silicon and/or yttrium additions to an Fe-24% Cr-24% Ni alloy tested under thermal cycling conditions. Silicon promotes the formation of a protective chromia scale, but the accumulation of a mechanically weak, silicon-rich oxide at the scale-metal interface eventually leads to scale spalling. Yttrium alone is found to have little influence on the rate of alloy degradation, but in alloys containing silicon its presence prevents the accumulation of the interfacial silicon-rich oxide layer. The temperature change required to cause scale failure and loss of protection to the substrate material is used as a measure of the mechanical integrity of the scales formed. The ability of alloys to form scales rapidly under conditions of frequent thermal cycling and to repair damage caused to a scale grown over a prolonged period of isothermal exposure are separately examined.     

Effects found in a one-year oral toxicity study in Sprague-Dawley rats of a novel 5-HT1A receptor partial agonist for the treatment of anxiety in humans

Regeneration of motor axons is enhanced if they have sprouted prior to nerve injury. We examined whether sensory axon regeneration and recovery of pain response was affected by previous collateral sprouting. In the experimental group of rats, the right saphenous, tibial, and sural nerves were transected and ligated. The peroneal nerve was left to sprout into the adjacent denervated skin. Two months later, the axons of the peroneal nerve were crushed in the sciatic nerve. In the control group, the right sciatic nerve was crushed at the same time that the saphenous, tibial, and sural nerves were transected. Recovery of pain response in the foot was determined by the skin pinch test. Sensory axon elongation rate was measured by the nerve pinch test. The number of myelinated axons was determined in nerve cross sections stained by Azur blue. Recovery of pain sensitivity in the animals of the experimental group was delayed for 2-3 weeks in comparison to the control group. Moreover, the spatial pattern of pain response in the experimental group was irregular, displaying residual regions of insensitive skin which were not present in controls. The elongation rate of regenerating sensory axons in the experimental group was not decreased, and the number of myelinated axons in the peroneal nerves was even about 10% higher than in the control group. Therefore, we assume that the terminal arborization of the neurilemmal tubes pertaining to the former axon sprouts delayed regrowth of sensory axon terminals in the skin.     

Enrichment of rare gas isotopes using a quadrupole mass spectrometer

A small quadrupole mass spectrometer was operated in the static mode to enrich selected rare gas isotopes. Memory effects in the apparatus were observed and attributed to the re-emission of atoms implanted by the electron-impact ion source. Studies of the pumping mechanism led us to a practical means for reducing the rate of noble gas pumping     

External barium block of Shaker potassium channels: evidence for two binding sites

External barium ions inhibit K+ currents of Xenopus oocytes expressing ShH4 delta 6-46, the non-inactivating deletion of the Shaker K+ channel. At the macroscopic level, Ba2+ block comprises both a fast and a slow component. The fast component is less sensitive to Ba2+ (apparent dissociation constant at 0 mV, K(0), approximately 19.1 mM) than the slow component and is also less voltage dependent (apparent electrical distance, delta, approximately 0.14). The slow component (K(0), approximately 9.4 mM, delta approximately 0.25) is relieved by outward K+ current, which suggests that the corresponding binding site resides within the channel conduction pathway. At the single channel level, the fast component of block is evidenced as an apparent reduction in amplitude, suggesting an extremely rapid blocking and unblocking reaction. In contrast, the slow component appears to be associated with long blocked times that are present from the beginning of a depolarizing command. Installation of the slow component is much slower than a diffusion limited process; for example, the blocking time constant (tau) produced by 2 mM Ba2+ is approximately 159 s (holding potential, HP = -90 mV). However, the blocking rate of this slow component is not a linear function of external Ba2+ and tends to saturate at higher concentrations. This is inconsistent with a simple bi-molecular blocking reaction. These features of external Ba2+ block can be accounted for by a simple model of two sequential Ba2+ binding sites, where the deeper of the two sites produces the slow component of block.     

Recovery of uranium from lignites

There is a renewed interest in lignites as a source of fuel and for the possible by-product recovery of uranium. This paper summarizes the experimental work carried out at Oak Ridge National Laboratory during 1952 to 1954 that deals with the sulfuric acid leaching of lignite ash for uranium recovery. A discussion of the possible utilization of sulfur dioxides in flue gases should be of value to those companies planning to process lignites.     

Preoperative sonographic measurement of endometrial pattern predicts outcome of surgical repair in patients with severe Asherman's syndrome

OBJECTIVE: To assess the predictive value of preoperative endometrial sonography in the diagnosis and surgical treatment of women with amenorrhea due to severe Asherman's syndrome. DESIGN: Patient series. SETTING: Academic clinical practice. PATIENTS: Seven women with severe Asherman's syndrome characterized by amenorrhea despite normal ovulatory function and complete obstruction of the uterine cavity at the level of the cervix or lower uterine segment at hysterosalpingogram. MAIN OUTCOME: Ability of vaginal sonography to predict successful hysteroscopic treatment as assessed by resumption of menstrual cyclicity and normalization of the uterine cavity. RESULTS: Transvaginal sonography demonstrated a well-developed endometrial stripe in three of seven women, while three others had virtually no endometrium seen. All women with well-developed endometrium were found to have adhesions occluding the lower uterine segment and had resumption of normal menses and normalization of the cavity after hysteroscopy. The women with minimal endometrium had no cavity identified and derived no benefit from surgery. A seventh woman with endometrium seen only on one side of the cavity had patency successfully established only on that side. CONCLUSION: The endometrial pattern seen with transvaginal sonography is highly predictive of surgical and clinical outcome in women with severe Asherman's syndrome characterized by complete obstruction of the cavity at hysterosalpingogram.