Facile Synthesis and Proposed Mechanism of α,ω‐Oxetanyl-Telechelic Poly(3-nitratomethyl-3-methyl oxetane) by an SN2(i) Nitrato Displacement Method in Basic Media

The synthesis of a novel heterocyclic–telechelic polymer, α,ω-oxetanyl-telechelic poly(3-nitratomethyl-3-methyl oxetane), is described. Infrared spectroscopy (IR), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy have been used to confirm the successful synthesis, demonstrating the presence of the telechelic-oxetanyl moieties. Synthesis of the terminal functionalities has been achieved via displacement of nitrato groups, in a manner similar to that employed with other leaving groups such as azido, bromo, and nitro, initiated by nucleophiles. In the present case, displacement occurs on the ends of a nitrato-functionalized polymer driven by the formation of sodium nitrate, which is supported by the polar aprotic solvent N,N-dimethyl formamide. The formation of an alkoxide at the polymer chain ends is favored and allows internal back-biting to the nearest carbon bearing the nitrato group, intrinsically in an S_N2(i) reaction, leading to α,ω-oxetanyl functionalization. The telechelic-oxetanyl moieties have the potential to be cross-linked by chemical (e.g., acidic) or radiative (e.g., ultraviolet) curing methods without the use of high temperatures, usually below 100°C. This type of material was designed for future use as a contraband simulant, whereby it would form the predominant constituent of elastomeric composites comprising rubbery polymer with small quantities of solids, typically crystals of contraband substances, such as explosives or narcotics. This method also provides an alternative approach to ring closure and synthesis of heterocycles.     

Hydrogeochemistry and groundwater circulation in the Xi’an geothermal field, China

Geothermal waters from the Tertiary aquifers located at 1000–3000 m beneath Xi’an city, Shaanxi Province, China, show unique isotopic composition as compared to local groundwaters from shallower Quaternary aquifers. Positive oxygen shifts of as much as 8‰ VSMOW are observed, while the corresponding δ²H values remain essentially constant at about −80‰ VSMOW, which is significantly different from those of waters in the Quaternary aquifers with a mean δ²H value of −60‰ VSMOW. The strong ¹⁸O shift is a result of isotope exchange between geothermal water and carbonate minerals such as calcite over a residence time of several thousand years up to 30,000 years, based on ¹⁴C dating. A comparison of the isotopic composition of geothermal waters with neighbouring groundwater units on both sides of the Guanzhong Basin indicates that the geothermal reservoirs are recharged by rain that falls on the northern slope of the Qinling Mountains, south of the Xi’an geothermal field, but not from the North Mountains to the north of the field. Based on chemical geothermometers the highest temperature estimated for the Tertiary aquifers of the Xi’an area is around 130 °C.     

Degradation of cell wall material of apple and wheat bran by human faecal bacteria in vitro

The effect of the structures of plant cell walls and their component polymers on the degradability of dietary fibre by bacteria of the human colon was investigated by inoculating culture media containing cell wall materials of apple and wheat bran with slurries of human faeces which were then incubated for periods of up to 72 h. In the apple substrates the amounts of pectic polysaccharides were extensively depleted after 12 h, and after 24 h over 90% of the initial carbohydrate had been degraded. Material which remained after incubation was probably comprised of highly branched fragments of rhamnogalacturonans, cross-linked by phenolics and proteins, highly branched fragments of cross-linked xyloglucans, and degraded cellulose. In wheat bran the aleurone layer was preferentially degraded, but the glucuronoarabinoxylans, which were cross-linked by phenolic groups, and the lignified outer layers of the bran were very resistant to attack. Bacteria adhered mainly to the broken or damaged surfaces of the plant cell walls, and in the more resistant tissues only penetrated the intercellular regions.     

A technique to estimate the relative gains, tuning phases, and RE phase shifts of the elements of a phased-array radar

An in-situ technique to estimate the following parameters of a phased-array antenna is described: 1) the relative array-element excitation voltages, 2) the array-element tuning phases, and 3) the RF phase shifts at the array elements. This technique has several significant features. First, it involves the use of two auxiliary antennas. One is a remote continuous wave (CW) source directed at the phased-array antenna. The other is a passive antenna mounted close to the phased-array antenna. Its output is used to produce a reference phase for phase measurements. Second, it contains a technique to reduce the errors in phase estimates. Third, it takes note that beam steering uses phase sums of the form (phi_{k} + beta_{kl}), wherephi_{k}is the tuning phase for thekth array elemenet andbeta_{kl}, is an RF phase shift of the array element, and pays special attention to reduce the errors associated with the estimates of these sums. Fourth, it assumes the use of a reasonably stable and strong CW source of commerically available quality. No other assumptions are made. Experimental results obtained with a 295-elementS-band space-fed phased-array antenna are given.     

Hot-rolling and forging of mica-filled polyolefins

As in the case of fibers, the mechanical properties of plastic composites containing mica flakes are extremely sensitive to flake orientation in the direction of an applied stress, so that even a small angular displacement can cause major reductions in the strength, modulus, and fracture toughness. In order to encourage parallel alignment of mica flakes in a thermoplastic composite, two methods of flow orientation were examined. In the first series, rectangular billets of mica-filled, high-density polyethylene were hot-pressed in order to cause longitudinal melt flow in a narrow channel. A parallel series of experiments was also carried out with mica-filled polypropylene in which the composite was extruded and calendered into a thin, continuous strip. In both processing techniques, the resulting extensional flow produced large increases in the tensile and flexural properties. The performance of the mica-filled poly-propylene was limited by its tendency to fibrillate during rolling. Drop-impact measurements recorded a four-fold increase in fracture toughness. The increased tensile and flexural properties were attributed to both the greater degree of parallel alignment of the mica flakes and the increased molecular orientation in the direction of flow. Such flow orientation methods appear necessary if the full benefit of mica-flake reinforcement is to be achieved.     

Herpes simplex virus type 1 alkaline nuclease is required for efficient processing of viral DNA replication intermediates

Mutations in the alkaline nuclease gene of herpes simplex type 1 (HSV-1) (nuc mutations) induce almost wild-type levels of viral DNA; however, mutant viral yields are 0.1 to 1% of wild-type yields (L. Shao, L. Rapp, and S. Weller, Virology 195:146-162, 1993; R. Martinez, L. Shao, J.C. Bronstein, P.C. Weber, and S. Weller, Virology 215:152-164, 1996). nuc mutants are defective in one or more stages of genome maturation and appear to package DNA into aberrant or defective capsids which fail to egress from the nucleus of infected cells. In this study, we used pulsed-field gel electrophoresis to test the hypothesis that the defects in nuc mutants are due to the failure of the newly replicated viral DNA to be processed properly during DNA replication and/or recombination. Replicative intermediates of HSV-1 DNA from both wild-type- and mutant-infected cells remain in the wells of pulsed-field gels, while free linear monomers are readily resolved. Digestion of this well DNA with restriction enzymes that cleave once in the viral genome releases discrete monomer DNA from wild-type virus-infected cells but not from nuc mutant-infected cells. We conclude that both wild-type and mutant DNAs exist in a complex, nonlinear form (possibly branched) during replication. The fact that discrete monomer-length DNA cannot be released from nuc DNA by a single-cutting enzyme suggests that this DNA is more branched than DNA which accumulates in cells infected with wild-type virus. The well DNA from cells infected with wild-type and nuc mutants contains XbaI fragments which result from genomic inversions, indicating that alkaline nuclease is not required for mediating recombination events within HSV DNA. Furthermore, nuc mutants are able to carry out DNA replication-mediated homologous recombination events between inverted repeats on plasmids as evaluated by using a quantitative transient recombination assay. Well DNA from both wild-type- and mutant-infected cells contains free U(L) termini but not free U(S) termini. Various models to explain the structure of replicating DNA are considered.     

Mechanical response properties of nociceptors innervating feline hairy skin

1. The responses of feline cutaneous nociceptors were examined in vivo by systematically manipulating the intensive and spatial dimensions of mechanical stimulation. A computer-controlled motor was used to apply prescribed forces (5-90 g) to a nociceptor's receptive field, with flat-tipped, cylindrical probes of various sizes (contact areas: 0.1-5.0 mm2). The stimulating device and protocols were similar to those previously used to evaluate human perception, thus allowing for comparisons of the two data sets. 2. With a ramp-and-hold stimulus of controlled force, most nociceptors showed a slowly adapting (SA) response throughout the stimulus. In this way, nociceptors resembled low-threshold SA mechanoreceptors. However, in contrast to SA mechanoreceptors, nociceptors failed to exhibit an onset burst of activity associated with the stimulus ramp. Nineteen percent (6 of 31) of the nociceptors often showed the opposite trend during the stimulus, e.g., a gradually increasing firing rate. Most of these nociceptors (5 of 6) had particularly high mechanical thresholds. 3. With 30 stimuli repeated at short intervals (6-8 s), response rates tended to decrease across trials. This phenomenon was most evident with more intense stimuli. When two series of stimuli were separated by 4-5 min, there was no apparent trend of reduced responsiveness between series. 4. Overall, nociceptors responded in an orderly way to variations in force and probe size. For a given probe size, larger forces produced greater responses; for a given force, smaller probes produced greater responses. The relationship between probe size and force was best described as an even tradeoff between force and a linear dimension of the probe (i.e., probe perimeter), rather than the area of the probe. Thus a given pressure (force/area) did not evoke the same response from nociceptors as probe size was varied. 5. There were two significant differences in the mechanical responsiveness between A fiber and C fiber nociceptors. First, for a given set of stimuli, A fiber nociceptors exhibited a greater response rate than the C fiber nociceptors. Second, the A fiber nociceptors exhibited a greater differential response related to probe size than the C fiber nociceptors. On the basis of these two features, the A fiber nociceptors' response profiles showed a closer parallel with previously reported human pain thresholds than the C fiber nociceptors did. 6. When the nociceptors were subdivided as to their mechanical threshold, those with lower thresholds [mechanically sensitive afferents (MSAs)] showed a response saturation with the more intense stimuli. On average, the stimulus levels at which saturation occurred were close to human pain threshold. Those nociceptors with higher thresholds [mechanically insensitive afferents (MIAs)] did not show such saturation. Thus only the MIAs appeared to have the capacity to unambiguously encode mechanical stimulus intensities above pain threshold. The MSAs, on the other hand, exhibited their greatest dynamic response range near the threshold for nonpainful sharpness. Thus the group of afferents commonly defined as nociceptors exhibit a heterogeneity of mechanical response properties, which may serve functionally different roles for perception.     

Elevational spatial compounding

Spatial compounding has long been explored to reduce coherent speckle noise in medical ultrasound. By laterally translating a one-dimensional array, partially correlated measurements made at different look directions can be obtained and incoherently averaged. The lateral resolution, however, is limited by the sub-array length used for each independent measurement. To reduce speckle contrast without compromising lateral resolution, a new spatial compounding technique using two-dimensional, anisotropic arrays is proposed. This technique obtains partially correlated measurements by steering the image plane elevationally with small inclinations. Incoherent averaging is then performed by adding image magnitudes. Therefore, contrast resolution is improved only at the price of a slightly wider elevational beam. Note that although anisotropic arrays have limited steering capability in elevation, grating lobes are not considered influential since only small inclinations are needed between measurements. Simulations have been performed to show both the change in spatial resolution and the improvement in contrast resolution. Results indicated minimal increase in the correlation length both laterally and axially. It was also shown that detectability can be significantly enhanced by increasing the number of measurements or increasing the differential inclination between measurements. This technique is therefore effective for reducing speckle noise while maintaining in-plane spatial resolution. Furthermore, it demonstrates a new application of two-dimensional anisotropic arrays in spite of their limited elevational steering capability.     

The relation between methods of coping during adulthood with a history of childhood sexual abuse and current psychological adjustment.

With a community sample of 192 women who had been sexually abused during childhood, the investigators determined if methods of coping in adulthood with the aftermath of child sexual abuse were associated with current symptoms of psychological distress. Multiple regression analyses indicated that disengagement methods of coping with the sexual abuse accounted for unique variance in general psychological distress even after controlling for characteristics of the abuse and methods of coping with other stressors. Disengagement methods of coping were also used more often to deal with the stressful aspects of having been sexually abused than to deal with other stressful events. In contrast, engagement methods of coping were used more often to deal with the other stressors than with sexual abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)