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Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains. To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional (1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However, double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.
The objective was to determine the effects of immunization against gonadotropin-releasing hormone on reproductive characteristics in boars. A total of 72 boars were used in a randomized design with three treatments: single immunization (SI) (10 weeks of age) or double immunization (DI) (10 and 15 weeks of age) with Improvest® and intact controls (no Improvest®; CNT) (n=24/group). At 10, 15, 20, 25 and 40 weeks of age, blood was collected and serum harvested to evaluate testosterone concentrations. Testosterone concentrations were less for DI boars compared with CNT boars and SI boars at 20 and 25 weeks (P<0.001), but not at 40 weeks of age. At week 25, 18 pigs (n=6/group) were sacrificed and testes were removed, weighed and measured, and seminiferous tubules were examined and scored using histological slides of testes parenchyma. A sample of neck fat was assessed for boar taint aroma. All testicular measurements and weights and seminiferous tubule scores were less for DI boars compared with SI and CNT boars (P<0.001). More (P<0.05) SI and CNT boars had detectable boar taint aroma than DI boars. Libido was assessed at 32, 36, 47, 60 and 63 weeks of age and semen collected at 60 weeks of age was analyzed for indicators of quality. There were no effects of treatment (P=0.41) or treatment by week (P=0.71) on libido. Semen volume, gel weight and total number of sperm cells, determined in a subset of boars (n=3/treatment), were not different among treatments. Sperm concentration was greater for DI than SI (P=0.01), and tended to be greater for DI compared with CNT (P=0.10). Sperm motility tended to be greater for DI boars compared with CNT boars (P=0.066). In conclusion, our results show that there are no long-term effects of immunocastration on reproductive characteristics in boars.
Zinc Oxide crystals have historically been grown in hydrothermal autoclaves with a basic mineralizer; however, doubts have been raised about the quality of such crystals because they have often exhibited large x-ray rocking curve widths and low photoluminescence (PL) yield with large linewidths. Several ZnO crystals were grown hydrothermally and sliced parallel to the c-plane. This resulted in opposite surfaces (the C+ and C−) exhibiting pronounced chemical and mechanical differences. Different surface treatments were investigated and compared by PL both at room temperature and liquid helium temperatures, and by double axis X-ray rocking curve measurements. The high quality of hydrothermally-grown ZnO is substantiated by the narrow rocking curve widths and sharp PL peaks obtained. A critical factor in obtaining these results was found to be surface preparation.
A new process for synthesis and bulk crystal growth of GaN is described. GaN single crystal c-plane platelets up to 9mm by 2mm by 100μm thick have been grown by the Chemical Vapor Reaction Process (CVRP). The reaction between gallium and a nitrogen precursor is produced by sublimation of solid ammonium chloride in a carrier gas, which passes over gallium at a temperature of approximately 900°C at near atmospheric pressures. Growth rates for the platelets were 25-100 μm/hr in the hexagonal plane. Seeded growth in the c-direction was also accomplished by re-growth on previously grown c-plane platelets. The crystals were characterized by X-ray diffractometry, atomic force microscopy, secondary ion mass spectrometry, inert gas fusion, and room temperature Hall effect and resistivity measurements.
There is little information on the association of the APOEe4 allele and AD risk in African populations. In previous analyses from the Indianapolis-Ibadan dementia project, we have reported that APOE ε4 increased the risk for Alzheimer's disease (AD) in African Americans but not in Yoruba. This study represents a replication of this earlier work using enriched cohorts and extending the analysis to include cognitive decline.
In this longitudinal study of two community dwelling cohorts of elderly Yoruba and African Americans, APOE genotyping was conducted from blood samples taken on or before 2001 (1,871 African Americans & 2,200 Yoruba). Mean follow up time was 8.5 years for African Americans and 8.8 years for Yoruba. The effects of heterozygosity or homozygosity of ε4 and of the possession of e4 on time to incident AD and on cognitive decline were determined using Cox's proportional hazards regression and mixed effects models.
After adjusting for covariates, one or two copies of the APOE ε4 allele were significant risk factors for incident AD (p < 0.0001) and cognitive decline in the African-American population (p < 0001). In the Yoruba, only homozygosity for APOE ε4 was a significant risk factor for AD (p = 0.0002) but not for cognitive decline (p = 0.2346), however, possession of an e4 allele was significant for both incident AD (p = 0.0489) and cognitive decline (p = 0.0425).
In this large longitudinal comparative study, APOE ε4 had a significant, but weaker, effect on incident AD and on cognitive decline in Yoruba than in African Americans. The reasons for these differences remain unclear.
Part of the eighteenth-century Spanish crown's attempt to restore national power through the promotion of trade and manufacturing was a campaign to eradicate the aversions of the nobility toward commerce and industry. Don Juan de Goyeneche was most often held up as the model of what the state expected of its noblemen. But Professor Callahan concludes that Goyeneche's significance lies more in symbol that in accomplishment.
The best-known interrelated mechanisms through which coloration can act to reduce predator detection rates of potential prey are background matching and disruptive coloration (Thayer 1909; Cott 1940; Kingsland 1978; Ruxton et al. 2004; Wilkinson & Sherratt 2008; Stevens & Merilaita 2009). With background matching, objects are difficult to detect simply due to their similarity to their background. Conversely, the striking/high-contrast markings involved in disruptive coloration create ‘the appearance of false edges and boundaries and hinders the detection or recognition of an object's outline and shape’ (Stevens & Merilaita 2009). Coloration is but one means through which animals achieve crypsis; others include behaviour and morphology, including body size and shape. Here we focus on behaviour and its interaction with coloration in relation to crypsis.
High peak electron mobilities were observed in free-standing c-plane GaN substrates. Two layers, a low mobility degenerate layer and a high mobility bulk layer, were present in these samples. The carrier concentrations and mobilities for the layers were extracted using two methods: 1) magnetic field dependent Hall effect analysis and 2) a simple two carrier model with the assumption that one of the layers is degenerate. In addition, measurements were performed after etching away the degenerate layer. The mobility of the bulk layer is found to peak at nearly 8000 cm2/Vs at 60K using the magnetic field dependent Hall effect data. Record room temperature mobility for bulk GaN of 1190 cm2/V s was measured.
This paper reports the most recent results from the cluster chemistry program at the Naval Research Laboratory, in which our efforts in the characterization of gas-phase cluster properties have been extended to studies of condensed-phase species. First, in an attempt to investigate the fundamental interactions between mass-selected cluster ions and surfaces, two tandem mass spectrometers were constructed or modified, and the results of the initial experiments will be discussed. The emphasis will be on illustrating the general utility of ion/surface collisions to study fragmentations, reactions, and deposition. Second, clusters were deposited into a matrix in order to perform spectroscopic analyses. The initial experiments have been directed at optimization of the techniques. Finally, recent measurement of the ionization potentials of large carbon clusters will be reported. These results are especially significant because of the new developments in large-scale production, isolation, and characterization of these species.
The physical and chemical properties of large carbon clusters, Cn(n>40), have been studied extensively over the past six years. The spherical nature of these clusters has been debated and inferred from both experimental and theoretical studies until the recent isolation and subsequent spectroscopic identification of bulk C60 and C70. Although the n=60 and 70 cluster ions are anomalously abundant (“magic numbers”) in the mass spectra and are proposed to be highly symmetric species, the other “magic number” clusters have yet to be isolated.
Fullerenes with a metal atom inside of the cage, metallofulierenes, were produced by either laser vaporization or a graphite arc and characterized using a variety of mass spectrometric methods. First, yttrium-fullerene adducts were formed by direct laser vaporization of samples consisting of graphite, yttrium oxide and fullerenes. Fragmentation and oxidation ion/molecule reactions showed that the laser-generated adducts are endohedral complexes (Yx@Cn), in contrast to externally-bound Y(Cn)+ species formed by gas-phase reactions. In addition, evidence was obtained for laserinduced bulk coalescence reactions yielding the metallofullerenes. Second, negative ion/desorption chemical ionization mass spectrometry was used to characterize metallofullerenes in arc-generated soot, pyridine extracts and the extract residue. The pyridine extracts of La2O3/graphite soot contain mostlyLa@C82 and La2@C80', in addition to (empty) fullerenes. However, the raw soot and the extract residue contain a broader range of metallofullerenes with relative abundances different than those observed from the extract (e.g. abundant La@C60', Lax@Cn') and La@C74). The thermal desorption behavior of the doped and undoped fullerenes indicate an interaction between the Cn and Lax@Cn species. Analysis of aqueous solutions of dried pyridine extracts of La2O3/graphite soot show Cn and Lax;@Cn' which is consistent with the possible presence ofmetallofullerene/ fullerene ionic complexes, (Lax@Cn)+C-n.
A novel variation of conventional pulsed laser deposition, called matrix assisted pulsed laser evaporation, or MAPLE, has been utilized for growing organic thin films. The MAPLE technique is carried out in a vacuum chamber and involves directing a pulsed laser beam) onto a frozen target consisting of an organic compound dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target with both solvent and organic molecules being released into the chamber. The volatile solvent is pumped away, whereas the organic molecules coat the surface of a substrate. Very thin and uniform films (50 to 100 nm) of various organic materials, such as carbohydrates, have been deposited on Si(111) and NaCl substrates. The films prepared using this method have been examined by optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and electrospray mass spectrometry. Careful control of the processing conditions allowed carbohydrates such as sucrose and glucose, in addition to high molecular weight polymers such as dextran, to be transferred to the substrate as uniform films, without significant chemical decomposition. The use of MAPLE films for chemical and biological sensor applications is being investigated and the potential of this technique for producing high quality thin films of other organic compounds will be discussed.
Zinc Oxide crystals have historically been grown in hydrothermal autoclaves with a basic mineralizer; however, doubts have been raised about the quality of such crystals because they have often exhibited large x-ray rocking curve widths and low photoluminescence (PL) yield with large linewidths. Several ZnO crystals were grown hydrothermally and sliced parallel to the c-plane. This resulted in opposite surfaces (the C+ and C-) exhibiting pronounced chemical and mechanical differences. Different surface treatments were investigated and compared by PL both at room temperature and liquid helium temperatures, and by double axis X-ray rocking curve measurements. The high quality of hydrothermally-grown ZnO is substantiated by the narrow rocking curve widths and sharp PL peaks obtained. A critical factor in obtaining these results was found to be surface preparation.
Large hydrothermal ZnO crystals were grown using 3N NaOH, 1N KOH and 0.5N Li2CO3 mineralizer. The crystals were studied by cathodoluminescence (CL), showing a good crystalline quality. Different growth regions were identified by CL imaging. These regions were characterized by their corresponding luminescence spectra, showing that the incorporation of impurities and non radiative recombination centers depend on the growth sector. The surface is shown to introduce band tailing modifying the high energy part of the spectrum. The main spectral signatures of each sector are discussed.
A new matrix assisted pulsed laser evaporation (MAPLE) technique has been developed at the Naval Research Laboratory, to deposit superior quality ultra thin, and uniform films for a range of highly functionalized polymeric materials. The MAPLE technique is carried out in a vacuum chamber, and involves directing a pulsed laser beam onto a frozen target, consisting of a polymer dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target, where both solvent and polymer molecules are lifted into the evacuated gas phase. A solvent and polymer plume are generated incident to the substrate being coated. Si(111), and NaCl substrates coated with thin layers of polymer have been examined by a range of techniques including: optical microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy. Under optimum conditions the native polymer was transferred to the substrate without chemical modification as a highly uniform film.
The MAPLE technique offers a number of advantages over conventional polymer deposition techniques, including the ability to precisely and accurately coat a relatively large or small targeted area with an ultrathin, and uniform coating with sub monolayer thickness control. Conventional pulsed laser ablation techniques can be utilized for coating a limited number of polymers, but we have found that for highly functionalized materials the native polymer structure is almost completely lost in the process. In contrast, when the MAPLE conditions are optimized the deposition of even highly functionalized polymeric materials proceeds with little effect on the intrinsic polymer structure.
In this work we investigate the lattice damage induced in ZnO implanted with potential group V acceptors by means of Raman scattering. ZnO samples were implanted with N and P to high doses and Raman spectra were obtained prior and after rapid thermal annealing (RTA). Characteristic disorder-activated modes are observed in the spectra that can be used to assess the degree of lattice damage. ZnO samples were also implanted with native Zn+ and O+ ions under similar conditions to study specific effects of implantation with N+ and P+. As revealed by the intensity of disorder-activated bands, the implantation induced lattice damage is considerably higher for Zn+ than for the lighter O+ ion. In samples implanted with N+ additional Raman peaks emerge that are not observed either in the samples implanted with the native Zn+ and O+ ions or in the samples implanted with P+, thus pointing to a local vibrational mode of N or a N complex as the origin of these modes. Disorder-activated features are fully removed by RTA, indicating a high degree of lattice recovery by RTA even for the heavily damaged ZnO samples implanted with Zn+.