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AbstractA TRACE/PARCS model has been developed to analyze anticipated transient without scram (ATWS) events for a boiling water reactor (BWR) operating in the maximum extended load line limit analysis-plus (MELLLA+) expanded operating domain. The MELLLA+ domain expands the allowable operation in the power/flow map of a BWR to low flow rates at high-power conditions. Such operation exacerbates the likelihood of large-amplitude power/flow oscillations during certain ATWS scenarios. The analysis shows that large-amplitude power/flow oscillations, both core-wide and out-of-phase, arise following the establishment of natural-circulation flow in the reactor pressure vessel after the trip of the recirculation pumps and an increase in core inlet subcooling. The analysis also indicates a mechanism by which the fuel may experience heatup that could result in localized fuel damage. TRACE predicts that heatup will occur when the cladding surface temperature exceeds the minimum stable film boiling temperature after periodic cycles of dryout and rewet, and the fuel becomes locked into a boiling-film regime. Further, the analysis demonstrates the effectiveness of the simulated manual operator actions to suppress the instability.

AbstractA program is underway to convert the current high-enriched uranium (HEU) fuel to low-enriched uranium (LEU) fuel in the 20-MW D2O-moderated research reactor (NBSR) at the National Institute of Standards and Technology. A RELAP5 model has been developed to analyze postulated accidents in the NBSR with the present HEU fuel and a proposed LEU fuel. The model includes the reactor vessel, primary pumps, shutdown pumps, various valves, heat exchangers, and average and hottest fuel elements and flow channels in the region where flow enters through an inner plenum (6 fuel elements) and a region where flow enters through an outer plenum (24 elements). The equilibrium cycle power distributions in the fuel elements were determined based on three-dimensional Monte Carlo neutron transport calculations performed with the MCNPX code. In this paper we discuss safety analyses conducted for the loss-of-flow accidents resulting from either loss of electrical power or inadvertent throttling of flow control valves at the inlets to the inner and outer plena. The analysis shows that the fuel conversion will not lead to significant changes in the safety analysis and that the calculated maximum clad temperatures, minimum critical heat flux ratios, and minimum onset of flow instability ratios assure that there is adequate margin to fuel failure.

Reactivity insertion accidents have been analyzed for the 20-MW D2O-moderated research reactor (NBSR) at the National Institute of Standards and Technology (NIST). The analysis has been carried out for the present core, which contains highly enriched uranium fuel, and for a proposed equilibrium core with low-enriched uranium fuel. The time-dependent analysis of the primary system is performed with a RELAP5 model that includes the reactor vessel, primary coolant pump, heat exchanger, fuel element geometry, and flow channels for both the 6 inner and 24 outer fuel elements. Postprocessing of the simulation results has been conducted to evaluate minimum critical heat flux (CHF) ratio and minimum onset of flow instability (OFI) ratio using the Sudo-Kaminaga correlations and Saha-Zuber criteria, respectively.Evaluations are carried out for the control rod withdrawal start-up accident and the maximum reactivity insertion accident. In both cases the RELAP5 results indicate that no damage to the fuel will occur and there is adequate margin to CHF and OFI because of sufficient coolant flow through the fuel channels and the negative reactivity insertion due to scram.

Farmland is an important habitat for many amphibians. However, the widespread and prolonged use of agro‐chemicals creates predictable difficulties and limitations for the conservation of agrobiodiversity. Farmland is an ecosystem in which human forces are greatly involved; therefore, conservation of natural resources in agricultural ecosystems must also relate to the existence of humans in order to achieve its goal. The Taipei frog Rana taipehensishas become a seriously threatened species in Taiwan because of wetland destruction and extensive use of agro‐chemicals on farmland. Nowadays, the species can only be found in Taipei, Taoyuan, Tainan and Pingtung Counties. Since 1999, Taipei Zoo has been surveying the distribution of Taipei frogs in Sanzhi, a small town in northern Taiwan. Taipei Zoo has adopted a two‐pronged approach to its conservation project. Aside from collecting ecological data on Taipei frog populations, we also cooperated with a local school and the Tse‐Xing Organic Agriculture Foundation (TXOAF) to carry out habitat‐improvement work and community‐education programmes about wetland conservation. We persuaded and assisted a farmer to halt his use of pesticides and eventually adopt organic‐farming practices because his farm was located right in the centre of the Taipei frog's breeding habitat and our sampling area. We also helped the farmer to sell his organically grown water lilies to TXOAF in order to provide a long‐term and stable income. From October 2002, the farmer stopped using agro‐chemicals on his fields. Beginning in 2003, when the population of Taipei frogs was apparently increasing, the farmer also became a follower of an organic lifestyle and is proud of the Taipei frogs on his land.

Thin polystyrene (PS) films embedded with multiwalled carbon nanotubes (MWNTs) grafted with PS chains were prepared via solution casting, and the nanomechanical behavior of the thin films was probed by using AFM, TEM, and SEM. Percolated network of entangled nanotubes was observed to be well-dispersed in the PS thin films, and the films demonstrated strikingly different mechanical properties as compared to the pristine PS film. The MWNT/PS films were very tough showing no microfracture at large strains beyond 20%. Although crazes of similar microstructure to those in pristine PS were developed upon stretching, they were short and narrow with a width no more than approximately 2 μm. AFM analyses revealed that crazes grew by following a micronecking mechanism, similar to that commonly observed in neat polymers, but craze widening was substantially restricted. As a result, nucleation of new crazes became the dominant process over widening of the existing crazes as the applied strain increased. No nanotubes were observed inside crazes; they appeared to be excluded from craze fibrillation and were observed to accumulate at the craze boundaries. The growth of crazes in the MWNT/PS films was constrained by the nanotubes too rigid to be drawn into the crazes during the deformation.

Numerical computations of the strain energy release rate for cracks propagating around the interface between a spherical particle and a matrix have been used to determine the strain energy release rate function for the case where stresses arise due to differential thermal contraction. The strain-energy release rate function was found to exhibit a maximum as a function of crack length consistent with the theoretical conditions for crack extension and arrest proposed by Lange. The calculations show that a critical particle size exists below which crack extention does not occur for a given thermalmechanical stress. The predicted critical particle size correlates well with experimental results.

Based on the notion that regions of structural genes which encode critical domains of the corresponding proteins are highly conserved among closely related species, oligonucleotide primers were designed and used to amplify the α-globin sequence(s) of the Sprague-Dawley (SD) rat. Data of these amplified sequence constructs showed that two new rat a-globin specific sequences have been identified. Southern hybridization confirmed the presence of these sequences in the rat genome.

Plasma membrane proteins were extracted either from epididymal spermatozoa after incubation with ventral prostrate gland secretion or from spermatozoa recovered from uteri of females mated with surgically treated males belonging to the following groups: TX (excision of all accessory sex glands, ASG), VPX (bilateral excision of ventral prostate), VP (bilateral excision of all ASG except the ventral prostate), and SH (sham-operated). Incubation of spermatozoa with ventral prostatic secretion resulted in an 11-fold increase in glycoprotein content of the plasma membrane, but total protein concentration remained unchanged. The in vivo study indicated that interactions of ASG secretions and spermatozoa were complicated by the presence of uterine secretions. Glycoprotein content was reduced in the presence of ventral prostatic secretions. SDS-PAGE profiles showed that both uterine and ASG secretions could modify proteins on the sperm surface. Enrichment of a 25-kD subunit was apparently effected by uterine secretions and further promoted by combined secretions of the ampullary gland, coagulating gland, dorsolateral prostate, and seminal vesicle, but was reduced by the ventral prostate. A number of other protein subunits appeared to be specifically modified by the ventral prostate, while other ASG secretions were also shown to alter the effects of the ventral prostate on the sperm surface.

Plasma membrane proteins were extracted either from epididymal sperm after incubation with ampullary gland secretion or from uterine sperm derived from surgically treated males belonging to the following groups: TX, excision of all accessory sex glands (ASG); AGX, bilateral excision of ampullary glands; AG, excision of all ASG except ampullary glands; and SH, sham-operated. Total membrane protein, glycoprotein, and SDS-PAGE of individual polypeptide subunits were quantified. After incubation with ampullary gland secretion, both protein and glycoprotein concentrations of epididymal sperm membrane were increased. The protein profile was also significantly altered, with the removal of the 43- and 71-kD subunits and the addition of the 36- and 50-kD subunits. The in vitro results confirmed this proteolytic effect of ampullary gland and other ASG on the 43- and 71-kD subunits, despite a reduction in membrane protein concentration. Modification of the 17-, 20-, 25-, 28-, 56-, and 66-kD proteins were also observed. This report is the first demonstration that the ampullary gland is capable of modifying proteins on the sperm surface.

The results of dc conductivity experiments at intermediate temperatures on a material of initial composition Li5AlO4invarious environments are reported. These results indicate that, unde: certain conditions, dc charge conduction in this system is due to the transport of hydroxide ions derived from the formation of LiOH. The possible application of this system for the electrolytic decomposition of water vapor is discussed.

Wave propagation in bubbly two-phase, two-component flow was analyzed to assess the validity of some interfacial transfer laws for two-fluid models of two-phase flow. A dispersion relation was derived from the linearized conservation equations and the Rayleigh equation. The phase velocity and wave attenuation calculated from the dispersion relation, compared well with existing high- and low-frequency data. The virtual mass term was found to have a significant effect on wave dispersion in the bubbly flow regime. Thermal effects were found to be important in determining the resonance phenomenon and wave scattering was a major source of damping at frequencies higher than the resonance frequency.

This study employs the finite element approach developed in Part I to analyze mechanical experiments on cells. It views cells as axisymmetric membrane structures containing a body of incompressible material, and models the mechanical contact between a cell and the loading apparatus by a contact algorithm. Since the method is valid for analyzing axisymmetric shell-like bodies with arbitrary shapes, it treates various mechanical experiments on cells in a unified manner. For demonstration purposes, three commonly used mechanical experiments on cells are considered; (1) the compression experiment; (2) the suction (micropipette aspiration) experiment; and (3) the magnetic particle experiment. Based on an estimate of the mechanical property data for unfertilized sea urchin eggs, this analysis method predicts the responses for all three experiments using the same assumptions and approximations. This parallel treatment gives a broad basis for data correlation with experiments. The method also provides insights into mechanical experiments not offered by other approximate methods. For example, it gives the distributions of tensions and stretches on the cell cortex, and suggests the role of friction in the suction experiment.

This study presents a computational approach for the deformation analyses of problems in cell and developmental biology. Cells and embryos are viewed mechanically as axisymmetric shell-like bodies containing a body of incompressible material. The analysis approach is based on the finite element method. It is comprised of three finite element ingredients: (1) an axisymmetric shell/membrane element valid for modeling finite bending, shearing and stretching; (2) a volume constraint algorithm for modeling the membrane-bound incompressible material; and (3) a contact algorithm for modeling the mechanical interactions between deformable bodies. Part II of this study will demonstrate how these three ingredients can be applied to analyze mechanical experiments on cells. This same method is also useful for simulating embryonic shape changes during development.

1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly triiodothyronine and reverse triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and triiodothyronine entry into brain were probably similar, whereas those for reverse triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and triiodothyronine were mainly transported across the BBB. They shared with reverse triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected reverse triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out reverse triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)

A detailed three-dimensional finite element model for radial keratotomy has been developed. The model includes the full load-bearing tunic of the eye and employs realistic geometry. Incisions are modeled explicitly, and material parameters are obtained from in vivo data. Calculated results obtained with the model are compared with data from two independent medical studies on radial keratotomy.

A detailed three-dimensional finite element model for radial keratotomy has been developed. The model includes the full load-bearing tunic of the eye and employs realistic geometry. Incisions are modeled explicitly, and material parameters are obtained from in vivo data. Calculated results obtained with the model are compared with data from two independent medical studies on radial keratotomy.