Matching Items (177)

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Hydrogen mobility in the lightest reversible metal hydride, LiBeH3

Description

Lithium-beryllium metal hydrides, which are structurally related to their parent compound, BeH[subscript 2], offer the highest hydrogen storage capacity by weight among the metal hydrides (15.93 wt. % of hydrogen for

Lithium-beryllium metal hydrides, which are structurally related to their parent compound, BeH[subscript 2], offer the highest hydrogen storage capacity by weight among the metal hydrides (15.93 wt. % of hydrogen for LiBeH[subscript 3]). Challenging synthesis protocols have precluded conclusive determination of their crystallographic structure to date, but here we analyze directly the hydrogen hopping mechanisms in BeH[subscript 2] and LiBeH[subscript 3] using quasielastic neutron scattering, which is especially sensitive to single-particle dynamics of hydrogen. We find that, unlike its parent compound BeH[subscript 2], lithium-beryllium hydride LiBeH[subscript 3] exhibits a sharp increase in hydrogen mobility above 265 K, so dramatic that it can be viewed as melting of hydrogen sublattice. We perform comparative analysis of hydrogen jump mechanisms observed in BeH[subscript 2] and LiBeH[subscript 3] over a broad temperature range. As microscopic diffusivity of hydrogen is directly related to its macroscopic kinetics, a transition in LiBeH[subscript 3] so close to ambient temperature may offer a straightforward and effective mechanism to influence hydrogen uptake and release in this very lightweight hydrogen storage compound.

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Created

Date Created
  • 2017-11-24

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Room temperature structures beyond 1.5 Å by serial femtosecond crystallography

Description

About 2.5 × 10[superscript 6] snapshots on microcrystals of photoactive yellow protein (PYP) from a recent serial femtosecond crystallographic (SFX) experiment were reanalyzed to maximum resolution. The resolution is pushed

About 2.5 × 10[superscript 6] snapshots on microcrystals of photoactive yellow protein (PYP) from a recent serial femtosecond crystallographic (SFX) experiment were reanalyzed to maximum resolution. The resolution is pushed to 1.46 Å, and a PYP structural model is refined at that resolution. The result is compared to other PYP models determined at atomic resolution around 1 Å and better at the synchrotron. By comparing subtleties such as individual isotropic temperature factors and hydrogen bond lengths, we were able to assess the quality of the SFX data at that resolution. We also show that the determination of anisotropic temperature factor ellipsoids starts to become feasible with the SFX data at resolutions better than 1.5 Å.

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Created

Date Created
  • 2015-05-15

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Physical–chemical characterisation of the particulate matter inside two road tunnels in the São Paulo Metropolitan Area

Description

The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in

The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in particulate matter vehicular emission profiles. In an effort to better characterise the emitted particulate matter, measurements of aerosol physical and chemical properties were undertaken inside two tunnels located in the São Paulo Metropolitan Area (SPMA). The tunnels show very distinct fleet profiles: in the Jânio Quadros (JQ) tunnel, the vast majority of the circulating fleet are light duty vehicles (LDVs), fuelled on average with the same amount of ethanol as gasoline. In the Rodoanel (RA) tunnel, the particulate emission is dominated by heavy duty vehicles (HDVs) fuelled with diesel (5% biodiesel). In the JQ tunnel, PM[subscript 2.5] concentration was on average 52 μg m[superscript −3], with the largest contribution of organic mass (OM, 42%), followed by elemental carbon (EC, 17%) and crustal elements (13%). Sulphate accounted for 7% of PM[subscript 2.5] and the sum of other trace elements was 10%. In the RA tunnel, PM[subscript 2.5] was on average 233 μg m[superscript −3], mostly composed of EC (52%) and OM (39%). Sulphate, crustal and the trace elements showed a minor contribution with 5%, 1%, and 1%, respectively. The average OC : EC ratio in the JQ tunnel was 1.59 ± 0.09, indicating an important contribution of EC despite the high ethanol fraction in the fuel composition. In the RA tunnel, the OC : EC ratio was 0.49 ± 0.12, consistent with previous measurements of diesel-fuelled HDVs. Besides bulk carbonaceous aerosol measurement, polycyclic aromatic hydrocarbons (PAHs) were quantified. The sum of the PAHs concentration was 56 ± 5 ng m[superscript −3] and 45 ± 9 ng m[superscript −3] in the RA and JQ tunnel, respectively. In the JQ tunnel, benzo(a)pyrene (BaP) ranged from 0.9 to 6.7 ng m[superscript −3] (0.02–0.1‰ of PM[subscript 2.5)] whereas in the RA tunnel BaP ranged from 0.9 to 4.9 ng m[superscript −3] (0.004–0. 02‰ of PM[subscript 2.5]), indicating an important relative contribution of LDVs emission to atmospheric BaP.

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Created

Date Created
  • 2013-12-17

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Black carbon concentrations and sources in the marine boundary layer of the tropical Atlantic Ocean using four methodologies

Description

Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a

Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a high concentration of aerosols, such as black carbon, due to the African emission plume of biomass and agricultural burning products. Atmospheric particulate matter samples across the tropical Atlantic boundary layer were collected in the summer of 2010 during the southern hemispheric dry season when open fire events were frequent in Africa and South America. The highest black carbon concentrations were detected in the Caribbean Sea and within the African plume, with a regional average of 0.6 μg m[superscript −3] for both. The lowest average concentrations were measured off the coast of South America at 0.2 to 0.3 μg m[superscript −3]. Samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols (i.e., thermally unstable organic carbon, soot like, and charcoal like). Soot-like aerosols composed up to 45% of the carbonaceous aerosols in the Caribbean Sea to as little as 4% within the African plume. Charcoal-like aerosols composed up to 29% of the carbonaceous aerosols over the oligotrophic Sargasso Sea, suggesting that non-soot-like particles could be present in significant concentrations in remote environments. To better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions.

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Created

Date Created
  • 2014-07-18

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Strain induced fragility transition in metallic glass

Description

Relaxation dynamics are the central topic in glassy physics. Recently, there is an emerging view that mechanical strain plays a similar role as temperature in altering the relaxation dynamics. Here,

Relaxation dynamics are the central topic in glassy physics. Recently, there is an emerging view that mechanical strain plays a similar role as temperature in altering the relaxation dynamics. Here, we report that mechanical strain in a model metallic glass modulates the relaxation dynamics in unexpected ways. We find that a large strain amplitude makes a fragile liquid become stronger, reduces dynamical heterogeneity at the glass transition and broadens the loss spectra asymmetrically, in addition to speeding up the relaxation dynamics. These findings demonstrate the distinctive roles of strain compared with temperature on the relaxation dynamics and indicate that dynamical heterogeneity inherently relates to the fragility of glass-forming materials.

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Created

Date Created
  • 2015-05-18

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Elastic, magnetic and electronic properties of iridium phosphide Ir2P

Description

Cubic (space group: Fmm) iridium phosphide, Ir[subscript 2]P, has been synthesized at high pressure and high temperature. Angle-dispersive synchrotron X-ray diffraction measurements on Ir[subscript 2]P powder using a diamond-anvil cell

Cubic (space group: Fmm) iridium phosphide, Ir[subscript 2]P, has been synthesized at high pressure and high temperature. Angle-dispersive synchrotron X-ray diffraction measurements on Ir[subscript 2]P powder using a diamond-anvil cell at room temperature and high pressures (up to 40.6 GPa) yielded a bulk modulus of B[subscript 0] = 306(6) GPa and its pressure derivative B[subscript 0]′ = 6.4(5). Such a high bulk modulus attributed to the short and strongly covalent Ir-P bonds as revealed by first – principles calculations and three-dimensionally distributed [IrP[subscript 4]] tetrahedron network. Indentation testing on a well–sintered polycrystalline sample yielded the hardness of 11.8(4) GPa. Relatively low shear modulus of ~64 GPa from theoretical calculations suggests a complicated overall bonding in Ir[subscript 2]P with metallic, ionic, and covalent characteristics. In addition, a spin glass behavior is indicated by magnetic susceptibility measurements.

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Created

Date Created
  • 2016-02-24

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High quality transparent TiO2/Ag/TiO2 composite electrode films deposited on flexible substrate at room temperature by sputtering

Description

Multilayer structures of TiO[subscript 2]/Ag/TiO[subscript 2] have been deposited onto flexible substrates by room temperature sputtering to develop indium-free transparent composite electrodes. The effect of Ag thicknesses on optical and

Multilayer structures of TiO[subscript 2]/Ag/TiO[subscript 2] have been deposited onto flexible substrates by room temperature sputtering to develop indium-free transparent composite electrodes. The effect of Ag thicknesses on optical and electrical properties and the mechanism of conduction have been discussed. The critical thickness (t[subscript c]) of Ag mid-layer to form a continuous conducting layer is 9.5 nm and the multilayer has been optimized to obtain a sheet resistance of 5.7 Ω/sq and an average optical transmittance of 90% at 590 nm. The Haacke figure of merit (FOM) for t[subscript c] has one of the highest FOMs with 61.4 × 10[superscript −3] Ω[superscript −1]/sq.

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Created

Date Created
  • 2013-06-07

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ELECTRON TRANSFER PROCESS BETWEEN COFACTORS OF HELIOBACTERIA'S REACTION CENTER

Description

ABSTRACT:
The experiment was conducted to analyze the role of menaquinone (MQ) in heliobacteria’s reaction center (HbRC). Their photosynthetic apparatus is a homodimeric of type I reaction center (1). HbRC

ABSTRACT:
The experiment was conducted to analyze the role of menaquinone (MQ) in heliobacteria’s reaction center (HbRC). Their photosynthetic apparatus is a homodimeric of type I reaction center (1). HbRC contains these cofactors: P800 (special pair cholorphyll), A0 (8-hydroxy-chlorophyll [Chl] a), and FX (iron-sulfur cluster). The MQ factor is bypassed during the electron transfer process in HbRC. Electrons from the excited state of P800 (P800*) are transported to A0 and then directly to Fx. The hypothesis is that when electrons are photoaccumulated at Fx, and without the presence of any electron acceptors to the cluster, they would be transferred to MQ, and reduce it to MQH2 (quinol). Experiments conducted in the past with HbRC within the cell membranes yielded data that supported this hypothesis (Figures 4 and 5). We conducted a new experiment based on that foundation with HbRC, isolated from cell membrane. Two protein assays were prepared with cyt c553 and ascorbate in order to observe this phenomenon. The two samples were left in the glove box for several days for equilibration and then exposed to light in different intensity and periods. Their absorption was monitored at 800 nm for P800 or 554 nm for cyt c553 to observe their oxidation and reduction processes. The measurements were performed with the JTS-10 spectrophotometer. The data obtained from these experiments support the theory that P800+ reduced by the charge recombination of P800+Fx-. However, it did not confirm the reduction of P800+ done by cyt c553¬ which eventually lead to a net accumulation of oxidized cyt c553; instead it revealed another factor that could reduce P800+ faster and more efficient than cyt c553 (0.5 seconds vs several seconds), which could be MQ. More experiments need to be done in order to confirm this result. Hence, the data collected from this experiment have yet to support the theory of MQ being reduced to MQH2 outside the bacterial membranes.

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Created

Date Created
  • 2015-05

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US DRONE POLICY AND THE PROJECTION OF FORCE: AN INVESTIGATION OF DEMOCRATIC CONSTRAINTS

Description

This paper examines the development of United States drone policy outside of traditional battle zones. It poses the question of why do states use drones as a projection of force?

This paper examines the development of United States drone policy outside of traditional battle zones. It poses the question of why do states use drones as a projection of force? In particular, the paper examines the expansion of the drone program within a system of democratic checks and balances. It looks at the effect that political and legal influences have had on the expansion of the drone program and hypothesizes that the presence of these constraints should increase drone use outside of traditional battle zones. In order to investigate this hypothesis, the paper looks at data on drone strikes from Yemen and Somalia. The data partially supports the hypothesis as there has not been a clear linear increase in the number of drone strikes in each of these countries. Nevertheless, an examination of the surrounding literature regarding political and legal influences within these countries seems to favorably point to the increase of drone operations. Future research, however, needs to be cognizant of the limitations in gathering specific statistics on drone operations as these operations are covert. It's also important to understand how the covert nature of the drone operations impacts issues regarding political oversight and legality. Lastly, it's important to constantly examine the broader implications drone policy has for US policy.

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Created

Date Created
  • 2015-05

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Recombinant Expression of CapBCA Membrane Proteins from Francisella tularensis

Description

Membrane proteins located within or as attachments to the cell membrane play critical roles in many essential cellular functions and host-pathogen interactions. Knowledge of the structure and function of membrane

Membrane proteins located within or as attachments to the cell membrane play critical roles in many essential cellular functions and host-pathogen interactions. Knowledge of the structure and function of membrane proteins in pathogenic species can allow for the development of specific vaccines and therapeutic agents against the pathogen. Francisella tularensis is an intracellular pathogen that is the causative agent of the severe, life-threatening infection, tularemia, in humans and other small mammals. F. tularensis is prevalent within the environment and is a potential bioterrorism agent due to its high virulence and its ability to be spread easily as an aerosol. The CapBCA membrane protein complex has been identified as a virulence factor of F. tularensis. This project, derived from the Membrane Proteins in Infections Diseases (MPID) Project, aims to successfully express the membrane proteins CapBCA, which are crucial to the pathogenic properties of F. tularensis. To accomplish this goal, methods for in vivo recombinant expression and purification of membrane proteins are in the process of being developed. The expression of the CapA component has been successful for some time, therefore, the goal of this study is to develop an approach toward recombinant in vivo membrane protein expression of both the CapB and CapC components of the CapBCA membrane protein complex. In this study, the CapB and CapC components were expressed for the first time in vivo through the use of the novel MPID vector, pelB-MBP. The expression of the CapB and CapC components will allow for large-scale expressions to commence with the end goal of determining the crystal structures of the individual proteins or the complex. Ultimately, it is hoped that knowledge of these molecular structures can lead to the development of a vaccine or other therapeutic agents against this pathogen.

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Agent

Created

Date Created
  • 2015-05