Molecular weight averages and distributions of unsaturated polyesters: Their effect on the properties of styrene-crosslinked networks

Unsaturated polyesters have been synthesised and modified to determine the effect of number-average molecular weight (M̄_n) and molecular weight distribution (MWD) on the following properties of the polyesters after crosslinking with styrene: (i) water absorption, (ii) initial mechanical properties and (iii) property retention after immersion The most important factor was found to be the very low molecular weight ‘tail’ which adversely affected behaviour in several respects. Above a certain M̄_n, initial mechanical properties were insensitive to the variables mentioned, but mechanical property retention after immersion closely reflected the water absorption behaviour by its dependence on the average chain length and the low molecular weight constituents. The importance of removing such constituents is apparent.     

BWR control rod drive system aging

This Phase I Nuclear Plant Aging Research (NPAR) study examines the aging phenomena associated with BWR control rod drive mechanisms (CRDMs) and assesses the merits of various methods of “managing” this aging. Information for this study was acquired from (1) the results of a special CRDM aging questionnaire distributed to each U.S. BWR utility, (2) a first-of-its-kind workshop held to discuss CRDM aging and maintenance concerns, (3) an analysis of the Nuclear Plant Reliability Data System (NPRDS) failure cases attributed to the control rod drive (CRD) system, and (4) personal information exchange with nuclear industry CRDM maintenance experts. The report documenting the findings of this research, NUREG-5699, will be published this year.Nearly 23% of the NPRDS CRD system component failure reports were attributed to the CRDM. The CRDM components most often requiring replacement due to aging are the Graphitar seals. The predominant causes of aging for these seals are mechanical wear and thermal embrittlement. More than 59% of the NPRDS CRD system failure reports were attributed to components that comprise the hydraulic control unit (HCU). The predominant HCU components affected by the effects of service wear and aging are valve seals, discs, seats, stems, packing, and diaphragms.     

Technology and the social regulation of fertility

Fertility patterns are rooted in a society's culture and social structure, and in the economics of childbearing that is thereby set up. Technological change affects the demand for children, and hence for fertility regulation, both by directly altering the expected benefits and costs of children to parents and by influencing the cultural and social structural underpinnings of that economic calculus. Routes of that influence include the demand for education generated by competition for modern sector employment, the consumerist values and lifestyles conveyed by communications media, and the erosion of community and kin pressures on individual behavior in a more mobile and more commercialized society. Such forces for behavioral change, it is argued, are more powerful factors in fertility decline than either the “social technology” of contraceptive service delivery (family planning programs) or improvements in the technology of contraception itself.     

Rapid quenching of molten lithium-aluminum jets in water

The behavior of melted lithium-aluminum control rod material from the Savannah River K reactor, when contacted with water, was observed experimentally at a scale corresponding to hypothesized accident conditions. Although pressure pulses of up to 124 kPa were observed, and water and steam were vigorously expelled from the experimental apparatus, no steam explosion occurred. A number of experiments were performed, in which accident phenomena that might initiate a steam explosion were simulated, without effect. Some chemical reaction was observed, indicating that hydrogen was produced. These experiments were used to establish the safety of reactor operation in a recent campaign.     

The isolated choroid plexus cyst

A 48-year-old asymptomatic male hepatitis B virus carrier presented with a 2-day history of fever, chills, right upper quadrant abdominal pain, and jaundice. Shock was detected on admission. Emergency abdominal computed tomography (CT) scanning without contrast enhancement showed the features of acute pancreatitis. Hemobilia, edematous pancreatitis, cholestasis and cholecystitis were found on exploratory laparotomy. Neither stone nor active bleeding were detected on intraoperative choledochoscopic examination. Postoperative T-tube cholangiography one month later revealed non-opacification of the left intrahepatic duct. The patient's abdominal pain and hemobilia recurred. Celiac angiography and CT scanning with contrast showed two hepatocellular carcinomas (HCC) in the left lobe of the liver. This is the first case report in the English literature of HCC presenting as jaundice, hemobilia, and acute pancreatitis.     

Effects of maintenance rehearsal on human memory.

There has been a conflict among several theories of memory as to whether the duration of the rehearsal of an item is necessarily related to its long-term retention. This conflict has centered on the question of whether rote rehearsal intended solely to maintain an item in awareness will lead to an increase in long-term-memory performance for that item. This question has been addressed with a variety of paradigms and has been answered in several ways. A review of the literature suggests that the duration of maintenance rehearsal affects the memory trace chiefly by increasing self-coding (item information) and that, consequently, its effects tend to be more evident on recognition than on recall tests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scattering of protons by hydrogen atoms at low energies: Phase shifts and differential cross sections

Phase shifts and differential cross sections for spin exchange (charge transfer) and total elastic scattering of protons by hydrogen atoms are presented for 36 and 38 values, respectively, of the collisional kinetic energy in the range 0.0001 to 10 eV (center of mass). The phase shifts are tabulated with a precision of six decimal digits. Each cross section is presented as a graph covering the complete angular range from 0 to π radians (in center-of-mass coordinates). The phase shifts were obtained via partial wave analysis within a modified Perturbed-Stationary-States theory by calculations based upon very accurate (nonrelativistic) internuclear potential energies for the 1Sσ_g and 2Pσ_u electronic states of H₂⁺. The cross sections demonstrate a transition from purely quantum behavior at very low energies (<0.1 eV) to semicllssical behavior at higher energies (>1 eV) in which protons scattered by spin exchange are angularly separated from those scattered without exchange. Thus the in-principle unobservable charge-transfer cross section becomes physically measurable at energies greater than about 1 eV.