Search

New neutron transmission data at resonance energies using a $$^{197}$$ 197 Au sample were measured using an early version of the Device for Indirect Capture Experiments on Radionuclides (DICER), which is under development at the Los Alamos Neutron Science Center (LANSCE). These data were combined with previous neutron transmission and capture data in a simultaneous R-matrix analysis to extract improved neutron resonance parameters for this nuclide. As a result, total radiation widths, $$\varGamma _{\gamma }$$ Γ γ , were obtained for 33 $$J=1$$ J = 1 and 44 $$J=2$$ J = 2 $$^{197}$$ 197 Au+n resonances. $$\varGamma _{\gamma }$$ Γ γ distributions for these two spins states were compared to distributions calculated according to the nuclear statistical model using published nuclear level density (NLD) and photon strength functions (PSF) measured using the Oslo technique. The calculated distributions were found to be narrower and the average values for the two spins states closer together than the data. The calculation can be brought into agreement with the data by substantial modifications to the spin distribution in $$^{198}$$ 198 Au as a function of excitation energy. As far as we know, the spin distribution currently is otherwise poorly constrained. The modified spin distribution changes the shapes of the NLD and PSF extracted using the Oslo technique and so could have broad implications.

The ion exchange of α-zirconium phosphate (ZrP) nanoparticles, highly crystalline zirconium phosphates prepared by the hydrothermal method, and epoxide functionalized zirconium phosphates were investigated. A series of exchange reactions involving both the surface and interlayer were used to determine exchange capacities for each environment and investigate the relationship between the interlayer and surface phosphates of ZrP. The resulting relationship was used to develop a new methodology to determine the average particle thickness within a sample of ZrP. Upon functionalization, the exchange capacities of derivatives prepared by surface functionalization (SF) and full functionalization (FF) were compared to the pristine ZrP, and an additional method was developed to determine the degree of functionalization in each sample.

A two-step intercalation and surface modification procedure was used to synthesize heterofunctional zirconium phosphates (ZrP) with different groups in the interlayer and on the surface. The relationship of the interlayer and surface was then investigated through evaluation of the stability and reactivity of heterofunctional ZrP materials by thermal analysis. Intercalated samples were prepared by the ion-exchange mechanism with variation in the loading, charge, and size of ions. An identical epoxide was used to modify the surface in all investigations. It was found that the two-step procedure could be performed in either order to prepare heterofunctional ZrP materials. In both cases, the contents of the interlayer were found to impact the reactivity of the surface and stability of covalently attached surface groups, with higher interlayer loadings leading to decreased stability and reactivity of surface phosphates.

Electrodeposited crystalline Cu 2 Sb thin films are studied to evaluate the use of these electrodes as model systems for studying Cu 2 Sb as a lithium ion battery anode material. The films have been characterized with an emphasis on determining the film quality and relating the structure, composition, and morphology to the resulting electrochemical and morphological transformations that occur during electrochemical lithiation and delithiation. It is shown that electrodeposition can produce high quality films that are devoid of major defects and can be used to provide mechanistic insight on the electrochemistry of reversible lithium alloying. The Cu x Sb films show that the fundamental reaction mechanism remains largely unchanged for copper concentrations of 1 > x > 3. For the first time we show that the copper concentration greatly affects critical criteria for anode materials such as the initial coulombic efficiency and reversible capacity of the electrode material. Voltage limit experiments show that an overpotential is required to remove trapped lithium states. Additional ex-situ experiments reveal that internal strain created during the lithiation process is relieved by buckling, greatly altering the film surface area and geometry, and resulting in the formation of cracks upon delithiation. This process is only semi-reversible, and strained areas remain visible even when discharged outside the voltage window of Cu 2 Sb determined by differential capacity plots. The results presented here indicate that these electroplated thin films are useful as analytical tools for showing pathways to improving the performance and fundamental understanding of alloy based lithium-ion battery anodes.

The physical properties of neutrons emitted from neutron-induced fission are fundamental to our understanding of nuclear fission. However, while state-of-the-art fission models still incorporate isotropic fission neutron spectra, it is believed that the preequilibrium prefission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic neutron spectra in fission models, though any significant anisotropy would impact descriptions of a fissioning system. In the present work, an excess of counts at high energies in the fission neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium prefission distribution above the postfission neutron spectrum. This excess is separated from the underlying postfission neutron spectrum, and its angular distribution is determined as a function in incident neutron energy and outgoing neutron detection angle. Comparison with neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the fission axis. The results presented here also impact the interpretation of several influential prompt fission neutron spectrum measurements.

Two dimensional (2D) nanostructured α-zirconium phosphate (ZrP) was studied for its effects on lubrication. Tribological characterization revealed that these nanoplatelets were effective as lubricant additives in both non-aqueous and aqueous media. Friction was reduced as much as by 65% and 91%, respectively in mineral oil and water when they were added. Two mechanisms of friction were proposed: viscosity modification and intermolecular interaction. This research has uncovered a novel approach for minimizing energy loss by friction reduction and should benefit many sectors such as manufacturing and consumer automobiles. Additionally, a clear understanding of properties-performance relationship of 2D nanoparticles would enable innovative design of novel materials for a variety of end uses.

Surface-functionalized zirconium phosphate (ZrP) nanoparticles were synthesized using a combination of ion exchange and self-assembly techniques. The surface of ZrP was used as a platform to deposit tetravalent metal ions by direct ion exchange with the protons of the surface phosphate groups. Subsequently, phosphonic acids were attached to the metal ion layer, effectively functionalizing the ZrP nanoparticles. Use of axially oriented bisphosphonic acids led to the ability to build layer-by-layer assemblies from the nanoparticle surface. Varying the metal ion and ligand used allowed designable architectures to be synthesized on the nanoparticle surface. X-ray powder diffraction, XPS, electron microprobe, solid-state NMR, FTIR, and TGA were used to characterize the synthesized materials.

The intercalation of inorganic layered materials has resulted in a wide range of applicability. In such cases the applicability of the material is largely dependent upon the species intercalated within the layer, and the layered material acts largely as a host. Recently, the surface modification of inorganic layered materials has been investigated and it has been shown that the exterior layers can be exclusively functionalized. The advent of surface chemistry allows for the synthesis of particles with both a controlled interlayer and surface. This approach can be used to tailor nanoparticles for specific applications. Herein we review the surface chemistry of α-zirconium bis(monohydrogen orthophosphate) monohydrate (Zr(HPO4)2·H2O, α-ZrP) along with some applications of recent interest. Not only can these reactions be applied to α-ZrP, but similar chemistry can also be expanded to other layered materials and systems.

A search for the neutron-unbound nucleus $^{21}$C was performed via the single proton removal reaction from a beam of 22 N at 68 MeV/u. Neutrons were detected with the Modular Neutron Array (MoNA) in coincidence with $^{20}$C fragments. No evidence for a low-lying state was found, and the reconstructed $^{20}$C+n decay energy spectrum could be described with an s-wave line shape with a scattering length limit of |as| < 2.8 fm, consistent with shell model predictions. A comparison with a renormalized zero-range three-body model suggests that $^{22}$C is bound by less than 70 keV., Accepted for publication in Nuclear Physics A

Organically surface-modified α-zirconium phosphate was obtained by reacting the surface P–O–H groups of α-zirconium phosphate nanoparticles (α-ZrP) with octadecyltrichlorosilane (OTS). Surface functionalization of α-ZrP with OTS was accomplished using a one-step synthesis producing highly hydrophobic nanoparticles. The formation of P–O–Si bonds arising from nucleophilic attack of POH to the silane was confirmed by solid-state NMR experiments. The surface coverage of the organic modifier was characterized by TGA, AFM, and FTIR. In addition, we show the applicability of this system with a photoinduced electron-transfer reaction in a nonpolar solvent. Using an organically surface-modified α-ZrP previously loaded with tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+), the quenching of the luminescence of Ru(bpy)32+ in the presence of p-benzoquinone was monitored; a static quenching constant (Ks) value of 8.82 × 102 M–1 and a dynamic quenching constant (KD) value of 6.99 × 102 M–1 were obtained.

Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other small autonomous devices. Although there are few examples to date of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. This overview highlights the various architectures proposed for 3D batteries, the advances made in the fabrication of components designed for these devices, and the remaining technical challenges. Efforts directed at establishing design rules for 3D architectures and modeling are providing insight concerning the energy density and current uniformity achievable with these architectures. The significant progress made on the fabrication of electrodes and electrolytes designed for 3D batteries is an indication that a number of these battery architectures will be successfully demonstrated within the next few years.

We describe the direct single potential electrodeposition of crystalline Cu2Sb, a promising anode material for lithium-ion batteries, from aqueous solutions at room temperature. The use of citric acid as a complexing agent increases the solubility of antimony salts and shifts the reduction potentials of copper and antimony toward each other, enabling the direct deposition of the intermetallic compound at pH 6. Electrodeposition of Cu2Sb directly onto conducting substrates represents a facile synthetic method for the synthesis of high quality samples with excellent electrical contact to a substrate, which is critical for further battery testing.

Background: CD40–CD154 is a receptor–ligand pair that provides key communication signals between cells of the adaptive immune system in states of inflammation and autoimmunity. The CD40 receptor is expressed constitutively on B lymphocytes, for which it provides important signals regulating clonal expansion and antibody production. CD154 is a member of the tumor necrosis factor superfamily, which is primarily expressed by activated T cells. Methods: Because many chronic liver diseases are characterized by lymphocytic infiltration of the liver and several have increased immunoglobulin (Ig) production, the role of CD40–CD154 in hepatic Ig production was investigated in patients with primary biliary cirrhosis (PBC), primary sclerosing cholangitis, autoimmune hepatitis (AIH), hepatitis C, hepatitis B, alcoholic and non-alcoholic steatohepatitis, as well as normal controls. Results: Soluble CD154 levels in the serum were found to be no different in chronic liver diseases vs normal controls. Likewise, CD154 mRNA levels in peripheral blood mononuclear cells did not differ. However, mRNA for CD154 was significantly increased in the liver of individuals with PBC and AIH as compared with the other groups. The quantity of CD154 mRNA in the liver correlated positively with the quantity of mRNA for secretory Ig. Conclusion: These findings suggest that CD40–CD154 signals may be involved in Ig production within the liver of autoimmune liver diseases.

Objectives. Body weight-supported treadmill training (BWSTT) is a task-specific rehabilitation strategy that enhances functional locomotion in patients following spinal cord injury (SCI). Supraspinal centers may play an important role in the recovery of over-ground locomotor function in patients with motor-incomplete SCI. The purpose of this study was to evaluate the potential for supraspinal reorganization associated with 12 weeks of robotic BWSTT using functional magnetic resonance imaging (fMRI). Methods. Four men with motor-incomplete SCI participated in this study. Time since onset ranged from 14 weeks to 48 months post-SCI injury. All subjects were trained with BWSTT 3 times weekly for 12 weeks. This training was preceded and followed by fMRI study of supraspinal activity during a movement task. Testing of locomotor disability included the Walking Index for Spinal Cord Injury (WISCI II) and over-ground gait speed. Results. All subjects demonstrated some degree of change in the blood-oxygen-level-dependent (BOLD) signal following BWSTT. fMRI results demonstrated greater activation in sensorimotor cortical regions (S1, S2) and cerebellar regions following BWSTT. Conclusions. Intensive task-specific rehabilitative training, such as robotic BWSTT, can promote supraspinal plasticity in the motor centers known to be involved in locomotion. Furthermore, improvement in over-ground locomotion is accompanied by an increased activation of the cerebellum.

Inorganic-organic hybrid materials were synthesized by covalent attachment of epoxides to the surface of zirconium phosphate (ZrP) nanoplatelets. X-ray powder diffraction, FTIR, and TGA were utilized to confirm the presence of the modifiers and exclusive functionalization of the ZrP surface. NMR experiments were conducted to confirm the formation of P-O-C bonds between surface phosphate groups and epoxide rings. The applicability of the organically modified products was demonstrated by their use as fillers in a polymer matrix. Subsequently, a two step intercalation and surface modification procedure was utilized to prepare polymer nanocomposites that were imparted with functionality through the encapsulation of molecules within the interlayer of surface modified ZrP.

The neutron-unbound nucleus ${}^{15}$Be was observed for the first time. It was populated using neutron transfer from a deuterated polyethylene target with a 59 MeV/u ${}^{14}$Be beam. Neutrons were measured in coincidence with outgoing ${}^{14}$Be particles and the reconstructed decay energy spectrum exhibits a resonance at 1.8(1) MeV. This corresponds to ${}^{15}$Be being unbound by 0.45 MeV more then ${}^{16}$Be thus significantly hindering the sequential two-neutron decay of ${}^{16}$Be to ${}^{14}$Be through this state.

Proton removal reactions from a secondary 22N beam were utilized to populate unbound states in neutron-rich carbon isotopes. Neutrons were measured with the Modular Neutron Array (MoNA) in coincidence with carbon fragments. A resonance with a decay energy of 76(14) keV was observed in the system 18C+n corresponding to a state in 19C at an excitation energy of 653(95)keV. This resonance could correspond to the first 5/2+ state which was recently speculated to be unbound in order to describe 1n and 2n removal cross section measurements from 20C., Comment: accepted for publication in Nucl. Phys. A

High conversion efficiency and selectivity are the two primary attractive features of electrochemical processes, in particular those using high temperature ion selective membranes. By selectively removing specific ionic species, the radicals that are created will react to form new compounds. Oxygen ion conductors are commonly used to remove oxygen from oxidized species thus creating molecules with fuel value. Judicious selection of materials set and device operating conditions are required to achieve desired product formation. The electrocatalytic layers on the electrochemical cells perform two functions, that of a catalyst and as an electrical conductor. Appropriate choice of electrode materials is required for stable performance and to avoid unwanted product formation. Control of operating conditions, namely temperature, fraction converted, and driving potential also is critical to achieve the selectivity. Ceramatec is currently developing electrochemical technologies using zirconia membrane based electrolysis devices for multiple applications. One is the production of fuels such as hydrogen from steam and syngas from a mixture of steam and carbon dioxide. The product can be used as gaseous fuel or further converted to liquid fuels using conventional chemical processes. The process enables highly efficient conversion and storage of intermittent wind and solar energy in the form of energy dense liquid fuels. The second application involves electrolysis of carbon dioxide of Mars atmosphere to produce CO and oxygen for fuel synthesis and life support for future manned mission. A third application is to develop deoxygenation technology to remove oxygen from liquid hydrocarbon compounds produced from biomass to increase its fuel properties. The requirements of each of these applications are varied and necessitate different operating conditions and significant changes to conventional electrode materials developed for high temperature fuel cell applications. An overview of these technical challenges and approach to addressing them will be presented.

The ground state of $^{28}$F has been observed as an unbound resonance $2\underline{2}0$ keV above the ground state of $^{27}$F. Comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the $^{28}$F ground state is primarily dominated by $sd$-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of $^{28}$F was first observed. Additionally, we report the first observation of a neutron-unbound excited state in $^{27}$F at an excitation energy of $25\underline{0}0 (2\underline{2}0)$ keV., 10 pages, 11 figures, Accepted for publication in Phys. Rev. C

Background: Momentum distributions of fragmentation products as a function of fragment mass have been used to study the fragmentation mechanism. The parallel component of the momentum distribution has been well studied previously and modeled. The perpendicular component, however, is much less measured or understood.Purpose: Measure both components of the linear momentum of a wide range of fragmentation products and compare the widths of the momentum distributions to previous results and descriptions.Method: The parallel and perpendicular components of the momentum vector have been measured for projectile-like fragments produced in the reactions of ${}^{76}$Ge with ${}^{9}$Be and ${}^{197}\phantom{\rule{-0.16em}{0ex}}$Au at 130 MeV/nucleon in a magnetic spectrometer.Results: The measured parallel momentum distributions of all fragments follow established systematics. The perpendicular momentum distributions of fragments produced by fragmentation by the ${}^{197}\phantom{\rule{-0.16em}{0ex}}$Au target with masses near that of the projectile exhibit a clear peak near the momentum corresponding to the grazing angle that diminishes with decreasing fragment mass.Conclusions: The interplay between Coulomb and nuclear scattering can be used to describe results for the most peripheral collisions.

The technique of invariant mass spectroscopy has been used to measure, for the first time, the ground state energy of neutron-unbound $^{28}\textrm{F},$ determined to be a resonance in the $^{27}\textrm{F} + n$ continuum at $2\underline{2}0 (\underline{5}0)$ keV. States in $^{28}\textrm{F}$ were populated by the reactions of a 62 MeV/u $^{29}\textrm{Ne}$ beam impinging on a 288 $\textrm{mg/cm}^2$ beryllium target. The measured $^{28}\textrm{F}$ ground state energy is in good agreement with USDA/USDB shell model predictions, indicating that $pf$ shell intruder configurations play only a small role in the ground state structure of $^{28}\textrm{F}$ and establishing a low-$Z$ boundary of the island of inversion for N=19 isotones., Comment: 5 pages, 4 figures, to be published in Phys. Rev. Lett

To develop and test a clinically relevant model for predicting the recovery of over ground walking speed after 36 sessions of progressive body weight-supported treadmill training (BWSTT) in individuals with motor incomplete spinal cord injury (SCI).A retrospective review and stepwise regression analysis of a SCI clinical outcomes data set.Outpatient SCI laboratory.Thirty individuals with a motor incomplete SCI who had participated in locomotor training with BWSTT. Eight individuals with similar diagnoses were used to prospectively test the prediction model.Over ground walking speed was assessed using the 10-m walking test.The locomotor training program consisted of 36 sessions of sequential comprehensive training comprised of robotic assisted BWSTT, followed by manual assisted BWSTT, and over ground walking. The dose of locomotor training was standardized throughout the protocol.Clinical characteristics with predictive value for walking speed were time from injury onset, the presence or absence of voluntary bowel and bladder voiding, a functional spasticity assessment, and over ground walking speed before locomotor training. The model identified that these characteristics accounted for 78.3% of the variability in the actual final over ground walking speed after 36 sessions of locomotor training. The model was successful in prospectively predicting over ground walking speed in the 8 test participants within 4.15 +/- 2.22 cm/s in their recovered walking speed.This prediction model can identify individuals who are most likely to experience success using locomotor training by determining an expected magnitude of training effect, thereby allowing individualized decisions regarding the use of this intensive approach to rehabilitation.

Two new experiments were carried out at the NSCL to explore the details of the linear moment and excitation energy distributions of projectile fragmentation production. In the first experiment the full linear momentum distributions of fragments from the reaction of a 76 Ge beam with beryllium and gold targets were measured in the S800 spectrometer. The results indicate a strong contribution of "far side" or attractive scattering to the near-projectile products with the gold target. In the second experiment the excitation energy of primary projectile fragments from peripheral nuclear reactions at intermediate energies was carried out at the NSCL. Sodium, neon and fluorine isotopes produced by the fragmentation of a neutron-rich 32Mg beam by a beryllium target were observed in a magnetic spectrometer in coincidence with fast neutrons detected using the Modular Neutron Array (MoNA). A new technique based on an analysis of the observed neutron multiplicity distributions was used to estimate the excitation energy and mass of the precursor intermediate products for the first time. A strong correlation between the neutron multiplicity and the total mass loss was observed indicating that large excitation energies were created in the prefragments by the initial collision. These findings are generally consistent with the internuclear cascade model of the collision dynamics but not with macroscopic abrasion-ablation models.

not Available.

not Available.

Cu2Sb was electrodeposited onto transmission electron microscopy TEM grids to investigate changes in morphology, composition, and crystal structure during the early stages of nucleation and growth. Multiple transitions were observed within the first second of the deposition, leading to the formation of crystalline Cu2Sb. These transitions were analyzed using TEM, scanning electron microscopy, selected area electron diffraction, and energy-dispersive X-ray spectroscopy. The nucleation sites are initially polycrystalline antimony with amorphous copper, which then transition through a polycrystalline copper intermediate containing some antimony before forming crystalline Cu2Sb. These analyses provide direct evidence that Cu2Sb does not deposit directly from solution but deposits by induced underpotential deposition. This is indicative of the electrodeposition of a typical alloy initially, but what is unusual is that the deposit at longer time scales is a highly crystalline intermetallic. This investigation is unique because TEM grids allow the interface between the deposited material and the substrate to be investigated. This is possible because the composite carbon film on the TEM grid behaves as a transparent substrate. This approach can be extended to other systems, allowing the development of a comprehensive understanding of the electrodeposition of intermetallic compounds.

Here we report the in situ doping of Si nanowires with Cu, which results in nanowires containing nanocrystalline inclusions of Cu3Si and significantly enhanced electrical conductivity. These nanowires are of interest for use in secondary Li batteries as well as nanowire arrays that can be directly sensitized for photovoltaic applications. This synthesis route is based on controlling the vapour-phase flux of precursor materials into the catalyst tip whereby the flux of the Cu is much less than that of Si. A compositional study utilizing SEM–EDS, XRD, and TEM–EDS techniques of vapour–liquid–solid (VLS) grown Si nanowires in the presence of Cu vapour confirms that the bulk nanowire matrix is Si doped with crystalline Cu3Si and low concentrations of Cu. The electronic transport measurements conducted on single nanowires indicate that the electronic resistivity of the doped nanowires is several orders of magnitude lower than undoped Si, thereby making them more conductive. Based on the data collected from the nanowire growth in conjunction with the in situ VLS doping mechanism, the doping density can be controlled by varying the gas-phase concentration of the dopant or the thermodynamic conditions of the nanowire growth. Both approaches will result in a change in the relative fluxes from the gas phase into the VLS catalyst as well as the kinetics for Cu3Si formation. This is advantageous because dopant density can be used to tune both the electronic and the optical properties of the nanowires.

not Available.

The fatty acid composition of the stomach contents, adipose tissue, and perinephric fat of Polynesian rats (Rattus exulans Peale), from the Tokelau Is indicated that the dietary fat consisted mainly, if not exclusively, of coconut oil. Lower ratios of lauric : myristic acids were found in the depot fats of the Polynesian rats than in the dietary coconut oil. These results were consistent with chain elongation of lauric to myristic acid after ingestion, as previously reported in rats and other mammals.