Some methods to regulate low-bias negative differential resistance in σ barrier separating nanoscale molecular transport systems

NASA Astrophysics Data System (ADS)

Shen, Ji-Mei; Liu, Jing; Min, Yi; Zhou, Li-Ping

2016-12-01

Using the first-principles method which combines the nonequilibrium Green’s function (NEGF) with density functional theory (DFT), the role of defect, dopant, barrier length and geometric deformation for low-bias negative differential resistance (NDR) in two capped armchair carbon nanotubes (CNTs) sandwiching σ barrier are systematically analyzed. We found that this method can regulate the negative differential resistance (NDR) effects such as current peak and peak position. The adjusting mechanism may originate from orbital interaction and orbital reconstruction. Our calculations try to manipulate the transport characteristics in energy space by simply manipulating the structure in real space, which may promise the potential applications in nanomolecular-electronics in the future.

Helium isotope enrichment by resonant tunneling through nanoporous graphene bilayers.

PubMed

Mandrà, Salvatore; Schrier, Joshua; Ceotto, Michele

2014-08-21

Graphene is impermeable to gases, but introducing subnanometer pores can allow for selective gas separation. Because graphene is only one atom thick, tunneling can play an important role, especially for low-mass gases such as helium, and this has been proposed as a means of separating (3)He from (4)He. In this paper, we consider the possibility of utilizing resonant tunneling of helium isotopes through nanoporous graphene bilayers. Using a model potential fit to previously reported DFT potential energy surfaces, we calculate the thermal rate constant as a function of interlayer separation using a recently described time-independent method for arbitrary multibarrier potentials. Resonant transmission allows for the total flux rate of (3)He to remain the same as the best-known single-barrier pores but doubles the selectivity with respect to (4)He when the optimal interlayer spacing of 4.6 Å is used. The high flux rate and selectivity are robust against variations of the interlayer spacing and asymmetries in the potential that may occur in experiment.

Assessing Controls on the Geometry and Dimensions of Modern Barrier Islands

NASA Astrophysics Data System (ADS)

Mulhern, J.; Johnson, C. L.; Martin, J. M.

2015-12-01

Barrier islands are highly ephemeral features, shaped by wave, tide, and storm energy. The processes that govern the size, shape, and motion of barrier islands are not well constrained, yet central to coastal dynamics. While the global distribution of barrier islands has been mapped and assessed, there is little consensus on the forces controlling barrier island formation, motion, or preservation. This study presents a new semi-global database of modern barrier islands to better understand their morphology and spatial distribution. We have mapped, in Google Earth, the subaerial extent of >350 barrier islands and spits, measuring spatial characteristic such as exposed area, perimeter, length, and width. These objects are cross-referenced with parameters that potentially control morphology, including tidal range, wave height, climate, distance from the continental shelf, proximity to fluvial output, and tectonic setting. This approach provides a more optimal framework to assess controls on coastal features, including barrier island morphology, and to investigate potential geometric scaling relationships. Preliminary analysis shows trends in the spatial characteristics of barrier islands. There is a strong linear relationship between the perimeter and length (y= -0.59 + 0.42x, R2=0.95). Linear trends also relate length to area when the data are separated by tidal range to wave height ratio. Assessment of barrier island shape supports the hypothesis of Hayes (1979) that barrier islands in wave-dominated settings are long and linear while those in mixed energy setting are more rounded. The barrier islands of the Texas Gulf of Mexico are larger than the global average for the database, with distinctly longer length values (41.16 km vs. 15.77 km respectively) and larger areas (103.81 km2 vs. 42.14 km2 respectively). Initial assessment shows that tidal range and wave height are primary controls barrier island dimensions. Future work will consider climate, latitude, fluvial input, and tectonic regime as additional factors. Assessing modern barrier islands will lend insight into potential paleomorphodynamic relationships and help determine how islands are transferred into the rock record, with implications for sequence stratigraphy, subsurface reservoirs, etc.

Landau level splitting due to graphene superlattices

NASA Astrophysics Data System (ADS)

Pal, G.; Apel, W.; Schweitzer, L.

2012-06-01

The Landau level spectrum of graphene superlattices is studied using a tight-binding approach. We consider noninteracting particles moving on a hexagonal lattice with an additional one-dimensional superlattice made up of periodic square potential barriers, which are oriented along the zigzag or along the armchair directions of graphene. In the presence of a perpendicular magnetic field, such systems can be described by a set of one-dimensional tight-binding equations, the Harper equations. The qualitative behavior of the energy spectrum with respect to the strength of the superlattice potential depends on the relation between the superlattice period and the magnetic length. When the potential barriers are oriented along the armchair direction of graphene, we find for strong magnetic fields that the zeroth Landau level of graphene splits into two well-separated sublevels, if the width of the barriers is smaller than the magnetic length. In this situation, which persists even in the presence of disorder, a plateau with zero Hall conductivity can be observed around the Dirac point. This Landau level splitting is a true lattice effect that cannot be obtained from the generally used continuum Dirac-fermion model.

Early Stages of Interface Formation at Compound Semiconductor Surfaces Studied by Scanning Tunneling Microscopy

DTIC Science & Technology

1991-10-01

classical image potential in an ideal creasing gap separation, that is specific to the form of the metal- insulator -semiconductor (MIS) junction...with which one can precisely adjust s, and hence continuously vary the vacvuum barrier, is a potentially valuable tool for investigating this effect- By... insulator -semiconductor (MIS) junction similar to that shown in Fig. I diverge at the semiconductor-vacuum and vacuum-metal interfaces [7,81. These

Quantum coherence in the reflection of above barrier wavepackets

NASA Astrophysics Data System (ADS)

Petersen, Jakob; Pollak, Eli

2018-02-01

The quantum phenomenon of above barrier reflection is investigated from a time-dependent perspective using Gaussian wavepackets. The transition path time distribution, which in principle is experimentally measurable, is used to study the mean flight times ⟨t⟩R and ⟨t⟩T associated with the reflection and the transmission over the barrier paying special attention to their dependence on the width of the barrier. Both flight times, and their difference Δt, exhibit two distinct regimes depending on the ratio of the spatial width of the incident wavepacket and the length of the barrier. When the ratio is larger than unity, the reflection and transmission dynamics are coherent and dominated by the resonances above the barrier. The flight times ⟨t⟩R/T and the flight time difference Δt oscillate as a function of the barrier width (almost in phase with the transmission probability). These oscillations reflect a momentum filtering effect related to the coherent superposition of the reflected and transmitted waves. For a ratio less than unity, the barrier reflection and transmission dynamics are incoherent and the oscillations are absent. The barrier width which separates the coherent and incoherent regimes is identified analytically. The oscillatory structure of the time difference Δt as a function of the barrier width in the coherent regime is absent when considered in terms of the Wigner phase time delays for reflection and transmission. We conclude that the Wigner phase time does not correctly describe the temporal properties of above barrier reflection. We also find that the structure of the reflected and transmitted wavepackets depends on the coherence of the process. In the coherent regime, the wavepackets can have an overlapping peak structure, but the peaks are not fully resolved. In the incoherent regime, the wavepackets split in time into distinct separated Gaussian like waves, each one reflecting the number of times the wavepacket crosses the barrier region before exiting. A classical Wigner approximation, using classical trajectories which upon reaching an edge of the barrier are reflected or transmitted as if the edge was a step potential, is quantitative in the incoherent regime. The implications of the coherence observed on resonance reactive scattering are discussed.

Hindered rotation and nuclear spin isomers separation of molecularly chemisorbed H2 on Pd(210)

NASA Astrophysics Data System (ADS)

Arguelles, Elvis F.; Kasai, Hideaki

2018-03-01

We investigated the hindered rotation and nuclear spin isomer separation of H2 on Pd(210) for various pre-adsorbed atomic hydrogen coverages (Θ), by total energy calculations based on density functional theory. Our results revealed that H2 is in the molecularly chemisorbed state and the adsorption is characterized by a highly anisotropic potential energy surface. Further, we found that J = 1 degenerate level splitting is insensitive to the increase in Θ from 1 to 2 ML. This is due to the comparable potential strengths hindering/restricting the polar rotations in both coverages. On a fully H passivated (3 ML) Pd(210), H2 is in a weakly physisorbed state with a negligible potential anisotropy. Our findings suggest that the activation barrier for polar rotational motion does not strongly depend on the adsorption energy but rather on the surface-molecule bond. The estimated rotational state desorption energies show a separation of ortho and para isomers by around 7.0 meV.

Metal-semiconductor barrier modulation for high photoresponse in transition metal dichalcogenide field effect transistors.

PubMed

Li, Hua-Min; Lee, Dae-Yeong; Choi, Min Sup; Qu, Deshun; Liu, Xiaochi; Ra, Chang-Ho; Yoo, Won Jong

2014-02-10

A gate-controlled metal-semiconductor barrier modulation and its effect on carrier transport were investigated in two-dimensional (2D) transition metal dichalcogenide (TMDC) field effect transistors (FETs). A strong photoresponse was observed in both unipolar MoS2 and ambipolar WSe2 FETs (i) at the high drain voltage due to a high electric field along the channel for separating photo-excited charge carriers and (ii) at the certain gate voltage due to the optimized barriers for the collection of photo-excited charge carriers at metal contacts. The effective barrier height between Ti/Au and TMDCs was estimated by a low temperature measurement. An ohmic contact behavior and drain-induced barrier lowering (DIBL) were clearly observed in MoS2 FET. In contrast, a Schottky-to-ohmic contact transition was observed in WSe2 FET as the gate voltage increases, due to the change of majority carrier transport from holes to electrons. The gate-dependent barrier modulation effectively controls the carrier transport, demonstrating its great potential in 2D TMDCs for electronic and optoelectronic applications.

Dynamical ion transfer between coupled Coulomb crystals in a double-well potential.

PubMed

Klumpp, Andrea; Zampetaki, Alexandra; Schmelcher, Peter

2017-09-01

We investigate the nonequilibrium dynamics of coupled Coulomb crystals of different sizes trapped in a double well potential. The dynamics is induced by an instantaneous quench of the potential barrier separating the two crystals. Due to the intra- and intercrystal Coulomb interactions and the asymmetric population of the potential wells, we observe a complex reordering of ions within the two crystals as well as ion transfer processes from one well to the other. The study and analysis of the latter processes constitutes the main focus of this work. In particular, we examine the dependence of the observed ion transfers on the quench amplitude performing an analysis for different crystalline configurations ranging from one-dimensional ion chains via two-dimensional zigzag chains and ring structures to three-dimensional spherical structures. Such an analysis provides us with the means to extract the general principles governing the ion transfer dynamics and we gain some insight on the structural disorder caused by the quench of the barrier height.

Separating effective high density polyethylene segments from olefin block copolymers using high temperature liquid chromatography with a preloaded discrete adsorption promoting solvent barrier.

PubMed

Chatterjee, Tirtha; Rickard, Mark A; Pearce, Eric; Pangburn, Todd O; Li, Yongfu; Lyons, John W; Cong, Rongjuan; deGroot, A Willem; Meunier, David M

2016-09-23

Recent advances in catalyst technology have enabled the synthesis of olefin block copolymers (OBC). One type is a "hard-soft" OBC with a high density polyethylene (HDPE) block and a relatively low density polyethylene (VLDPE) block targeted as thermoplastic elastomers. Presently, one of the major challenges is to fractionate HDPE segments from the other components in an experimental OBC sample (block copolymers and VLDPE segments). Interactive high temperature liquid chromatography (HTLC) is ineffective for OBC separation as the HDPE segments and block copolymer chains experience nearly identical enthalpic interactions with the stationary phase and co-elute. In this work we have overcome this challenge by using liquid chromatography under the limiting conditions of desorption (LC LCD). A solvent plug (discrete barrier) is introduced in front of the sample which specifically promotes the adsorption of HDPE segments on the stationary phase (porous graphitic carbon). Under selected thermodynamic conditions, VLDPE segments and block copolymer chains crossed the barrier while HDPE segments followed the pore-included barrier solvent and thus enabled separation. The barrier solvent composition was optimized and the chemical composition of fractionated polymer chains was investigated as a function of barrier solvent strength using an online Fourier-transform infrared (FTIR) detector. Our study revealed that both the HDPE segments as well as asymmetric block copolymer chains (HDPE block length≫VLDPE block length) are retained in the separation and the barrier strength can be tailored to retain a particular composition. At the optimum barrier solvent composition, this method can be applied to separate effective HDPE segments from the other components, which has been demonstrated using an experimental OBC sample. Copyright © 2016 Elsevier B.V. All rights reserved.

Distillation of bose-einstein condensates in a double-well potential.

PubMed

Shin, Y; Saba, M; Schirotzek, A; Pasquini, T A; Leanhardt, A E; Pritchard, D E; Ketterle, W

2004-04-16

Bose-Einstein condensates of sodium atoms, prepared in an optical dipole trap, were distilled into a second empty dipole trap adjacent to the first one. The distillation was driven by thermal atoms spilling over the potential barrier separating the two wells and then forming a new condensate. This process serves as a model system for metastability in condensates, provides a test for quantum kinetic theories of condensate formation, and also represents a novel technique for creating or replenishing condensates in new locations.

First-Principles Study of the Band Diagrams and Schottky-Type Barrier Heights of Aqueous Ta3N5 Interfaces.

PubMed

Watanabe, Eriko; Ushiyama, Hiroshi; Yamashita, Koichi

2017-03-22

The photo(electro)chemical production of hydrogen by water splitting is an efficient and sustainable method for the utilization of solar energy. To improve photo(electro)catalytic activity, a Schottky-type barrier is typically useful to separate excited charge carriers in semiconductor electrodes. Here, we focused on studying the band diagrams and the Schottky-type barrier heights of Ta 3 N 5 , which is one of the most promising materials as a photoanode for water splitting. The band alignments of the undoped and n-type Ta 3 N 5 with adsorbents in a vacuum were examined to determine how impurities and adsorbents affect the band positions and Fermi energies. The band edge positions as well as the density of surface states clearly depended on the density of O N impurities in the bulk and surface regions. Finally, the band diagrams of the n-type Ta 3 N 5 /water interfaces were calculated with an improved interfacial model to include the effect of electrode potential with explicit water molecules. We observed partial Fermi level pinning in our calculations at the Ta 3 N 5 /water interface, which affects the driving force for charge separation.

Ring Shake in Eastern Hemlock: Frequency and Relationship to Tree Attributes

Treesearch

John E. Baumgras; Paul E. Sendak; David L. Sonderman; David L. Sonderman

2000-01-01

Ring shake is a barrier to improved utilization of eastern hemlock, an important component of the total softwood timber resource in the Eastern United States and Canada. Ring shake is the lengthwise separation of wood that occurs between and parallel to growth rings, diminishing lumber yields and values. Evaluating the potential for ring shake is essential to improving...

Ring shake in eastern hemlock: frequency and relationship to tree attributes

Treesearch

John E. Baumgras; Paul E. Sendak; David L. Sonderman

2000-01-01

Ring shake is a barrier to improved utilization of eastern hemlock, an important component of the total softwood timber resource in the Eastern United States and Canada. Ring shake is the lengthwise separation of wood that occurs between and parallel to growth rings, diminishing lumber yields and values. Evaluating the potential for ring shake is essential to improving...

Signs on concrete median barriers.

DOT National Transportation Integrated Search

2013-04-01

Concrete median barriers have been used throughout the state as permanent and temporary barriers for providing separation of traffic. Typically, these barriers are tested and considered crashworthy through crash testing according to National Cooperat...

Habitat fragmentation caused by contaminants: Atrazine as a chemical barrier isolating fish populations.

PubMed

Araújo, Cristiano V M; Silva, Daniel C V R; Gomes, Luiz E T; Acayaba, Raphael D; Montagner, Cassiana C; Moreira-Santos, Matilde; Ribeiro, Rui; Pompêo, Marcelo L M

2018-02-01

Information on how atrazine can affect the spatial distribution of organisms is non-existent. As this effect has been observed for some other contaminants, we hypothesized that atrazine-containing leachates/discharges could trigger spatial avoidance by the fish Poecilia reticulata and form a chemical barrier isolating upstream and downstream populations. Firstly, guppies were exposed to an atrazine gradient in a non-forced exposure system, in which organisms moved freely among the concentrations, to assess their ability to avoid atrazine. Secondly, a chemical barrier formed by atrazine, separating two clean habitats (extremities of the non-forced system), was simulated to assess whether the presence of the contaminant could prevent guppies from migrating to the other side of the system. Fish were able to avoid atrazine contamination at environmentally relevant concentrations (0.02 μg L -1 ), below those described to cause sub-lethal effects. The AC 50 (atrazine concentration causing avoidance to 50% of the population) was 0.065 μg L -1 . The chemical barrier formed by atrazine at 150 μg L -1 (concentration that should produce an avoidance around 82%) caused a reduction in the migratory potential of the fish by 47%; while the chemical barrier at 1058 μg L -1 (concentration that produces torpidity) caused a reduction in the migratory potential of the fish by 91%. Contamination by atrazine, besides driving the spatial distribution of fish populations, has potential to act as a chemical barrier by isolating fish populations. This study includes a novel approach to be integrated in environmental risk assessment schemes to assess high-tier contamination effects such as habitat fragmentation and population displacement and isolation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Extended optical model analyses of elastic scattering and fusion cross sections for heavy-ion collisions with loosely bound projectiles at near-Coulomb-barrier energies

NASA Astrophysics Data System (ADS)

So, W. Y.; Hong, S. W.; Kim, B. T.; Udagawa, T.

2004-06-01

Within the framework of an extended optical model, simultaneous χ2 analyses are performed for elastic scattering and fusion cross-section data for 9Be + 209 Bi and 6Li + 208 Pb systems, both involving loosely bound projectiles, at near-Coulomb-barrier energies to determine the polarization potential as decomposed into direct reaction (DR) and fusion parts. We show that both DR and fusion potentials extracted from χ2 analyses separately satisfy the dispersion relation, and that the expected threshold anomaly appears in the fusion part. The DR potential turns out to be a rather smooth function of the incident energy, and has a magnitude at the strong absorption radius much larger than the fusion potential, explaining why a threshold anomaly has not been seen in optical potentials deduced from fits to the elastic-scattering data without such a decomposition. Using the extracted DR potential, we examine the effects of projectile breakup on fusion cross sections σF . The observed suppression of σF in the above-barrier region can be explained in terms of the flux loss due to breakup. However, the observed enhancement of σF in the subbarrier region cannot be understood in terms of the breakup effect. Rather, the enhancement can be related to the Q value of the neutron transfer within the systems, supporting the ideas of

You Can Teach an Old Dog New Tricks: A Qualitative Analysis of How Residents of Senior Living Communities May Use the Web to Overcome Spatial and Social Barriers*

PubMed Central

Winstead, Vicki; Anderson, William A.; Yost, Elizabeth A.; Cotten, Shelia R.; Warr, Amanda; Berkowsky, Ronald W.

2017-01-01

For adults in senior living communities, information and communication technologies, (ICTs) can be used to increase and expand communication for a population that is often spatially and socially separated from the general public. Using qualitative observational data from a longitudinal study of the impact of ICT usage on the quality of life among residents in assisted and independent living communities, we examine whether ICTs can mitigate the effects of social and spatial barriers. We find that ICTs have the potential to allow individuals to transcend social and spatial barriers, providing residents with the ability to maintain and enhance social networks as well as provide a greater sense of connection to the world at large. PMID:25474761

Hydrodynamic optical soliton tunneling

NASA Astrophysics Data System (ADS)

Sprenger, P.; Hoefer, M. A.; El, G. A.

2018-03-01

A notion of hydrodynamic optical soliton tunneling is introduced in which a dark soliton is incident upon an evolving, broad potential barrier that arises from an appropriate variation of the input signal. The barriers considered include smooth rarefaction waves and highly oscillatory dispersive shock waves. Both the soliton and the barrier satisfy the same one-dimensional defocusing nonlinear Schrödinger (NLS) equation, which admits a convenient dispersive hydrodynamic interpretation. Under the scale separation assumption of nonlinear wave (Whitham) modulation theory, the highly nontrivial nonlinear interaction between the soliton and the evolving hydrodynamic barrier is described in terms of self-similar, simple wave solutions to an asymptotic reduction of the Whitham-NLS partial differential equations. One of the Riemann invariants of the reduced modulation system determines the characteristics of a soliton interacting with a mean flow that results in soliton tunneling or trapping. Another Riemann invariant yields the tunneled soliton's phase shift due to hydrodynamic interaction. Soliton interaction with hydrodynamic barriers gives rise to effects that include reversal of the soliton propagation direction and spontaneous soliton cavitation, which further suggest possible methods of dark soliton control in optical fibers.

Hydrodynamic optical soliton tunneling.

PubMed

Sprenger, P; Hoefer, M A; El, G A

2018-03-01

A notion of hydrodynamic optical soliton tunneling is introduced in which a dark soliton is incident upon an evolving, broad potential barrier that arises from an appropriate variation of the input signal. The barriers considered include smooth rarefaction waves and highly oscillatory dispersive shock waves. Both the soliton and the barrier satisfy the same one-dimensional defocusing nonlinear Schrödinger (NLS) equation, which admits a convenient dispersive hydrodynamic interpretation. Under the scale separation assumption of nonlinear wave (Whitham) modulation theory, the highly nontrivial nonlinear interaction between the soliton and the evolving hydrodynamic barrier is described in terms of self-similar, simple wave solutions to an asymptotic reduction of the Whitham-NLS partial differential equations. One of the Riemann invariants of the reduced modulation system determines the characteristics of a soliton interacting with a mean flow that results in soliton tunneling or trapping. Another Riemann invariant yields the tunneled soliton's phase shift due to hydrodynamic interaction. Soliton interaction with hydrodynamic barriers gives rise to effects that include reversal of the soliton propagation direction and spontaneous soliton cavitation, which further suggest possible methods of dark soliton control in optical fibers.

Scattering of charged particles on two spatially separated time-periodic optical fields

NASA Astrophysics Data System (ADS)

Szabó, Lóránt Zs.; Benedict, Mihály G.; Földi, Péter

2017-12-01

We consider a monoenergetic beam of moving charged particles interacting with two separated oscillating electric fields. Time-periodic linear potential is assumed to model the light-particle interaction using a nonrelativistic, quantum mechanical description based on Gordon-Volkov states. Applying Floquet theory, we calculate transmission probabilities as a function of the laser field parameters. The transmission resonances in this Ramsey-like setup are interpreted as if they originated from a corresponding static double-potential barrier with heights equal to the ponderomotive potential resulting from the oscillating field. Due to the opening of new "Floquet channels," the resonances are repeated at input energies when the corresponding frequency is shifted by an integer multiple of the exciting frequency. These narrow resonances can be used as precise energy filters. The fine structure of the transmission spectra is determined by the phase difference between the two oscillating light fields, allowing for the optical control of the transmission.

Double barrier system for an in situ conversion process

DOEpatents

McKinzie, Billy John [Houston, TX; Vinegar, Harold J [Bellaire, TX; Cowan, Kenneth Michael [Sugar land, TX; Deeg, Wolfgang Friedrich Johann [Houston, TX; Wong, Sau-Wai [Rijswijk, NL

2009-05-05

A barrier system for a subsurface treatment area is described. The barrier system includes a first barrier formed around at least a portion of the subsurface treatment area. The first barrier is configured to inhibit fluid from exiting or entering the subsurface treatment area. A second barrier is formed around at least a portion of the first barrier. A separation space exists between the first barrier and the second barrier.

Integration of air separation membrane and coalescing filter for use on an inlet air system of an engine

DOEpatents

Moncelle, Michael E.

2003-01-01

An intake air separation system suitable for combustion air of an internal combustion engine. An air separation device of the system includes a plurality of fibers, each fiber having a tube with a permeation barrier layer on the outer surface thereof and a coalescing layer on the inner surface thereof, to restrict fluid droplets from contacting the permeation barrier layer.

A potential vorticity-based determination of the transport barrier in the Asian summer monsoon anticyclone

NASA Astrophysics Data System (ADS)

Ploeger, F.; Gottschling, C.; Griessbach, S.; Grooß, J.-U.; Guenther, G.; Konopka, P.; Müller, R.; Riese, M.; Stroh, F.; Tao, M.; Ungermann, J.; Vogel, B.; von Hobe, M.

2015-11-01

The Asian summer monsoon provides an important pathway of tropospheric source gases and pollution into the lower stratosphere. This transport is characterized by deep convection and steady upwelling, combined with confinement inside a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS). In this paper, we show that a barrier to horizontal transport along the 380 K isentrope in the monsoon anticyclone can be determined from a local maximum in the gradient of potential vorticity (PV), following methods developed for the polar vortex (e.g., Nash et al., 1996). The monsoon anticyclone is dynamically highly variable and the maximum in the PV gradient is weak, such that additional constraints are needed (e.g., time averaging). Nevertheless, PV contours in the monsoon anticyclone agree well with contours of trace gas mixing ratios (CO, O3) and mean age from model simulations with a Lagrangian chemistry transport model (CLaMS) and satellite observations from the Microwave Limb Sounder (MLS) instrument. Hence, the PV-based transport barrier reflects the separation between air inside the core of the anticyclone and the background atmosphere well. For the summer season 2011 we find an average PV value of 3.6 PVU for the transport barrier in the anticyclone on the 380 K isentrope.

Influence of single-neutron stripping on near-barrier 6He+208Pb and 8He+208Pb elastic scattering

NASA Astrophysics Data System (ADS)

Marquínez-Durán, G.; Keeley, N.; Kemper, K. W.; Mackintosh, R. S.; Martel, I.; Rusek, K.; Sánchez-Benítez, A. M.

2017-02-01

The influence of single-neutron stripping on the near-barrier elastic scattering angular distributions for the He,86+208Pb systems is investigated through coupled reaction channels (CRC) calculations fitting recently published data to explore the differences in the absorptive potential found in the scattering of these two neutron-rich nuclei. The inclusion of the coupling reduces the elastic cross section in the Coulomb-nuclear interference region for 8He scattering, whereas for 6He its major impact is on the large-angle elastic scattering. The real and imaginary dynamic polarization potentials are obtained by inverting the CRC elastic scattering S -matrix elements. These show that the main absorptive features occur between 11 and 12 fm for both projectiles, while the attractive features are separated by about 1 fm, with their main structures occurring at 10.5 fm for 6He and 11.5 fm for 8He.

Recreating blood-brain barrier physiology and structure on chip: A novel neurovascular microfluidic bioreactor.

PubMed

Brown, Jacquelyn A; Pensabene, Virginia; Markov, Dmitry A; Allwardt, Vanessa; Neely, M Diana; Shi, Mingjian; Britt, Clayton M; Hoilett, Orlando S; Yang, Qing; Brewer, Bryson M; Samson, Philip C; McCawley, Lisa J; May, James M; Webb, Donna J; Li, Deyu; Bowman, Aaron B; Reiserer, Ronald S; Wikswo, John P

2015-09-01

The blood-brain barrier (BBB) is a critical structure that serves as the gatekeeper between the central nervous system and the rest of the body. It is the responsibility of the BBB to facilitate the entry of required nutrients into the brain and to exclude potentially harmful compounds; however, this complex structure has remained difficult to model faithfully in vitro. Accurate in vitro models are necessary for understanding how the BBB forms and functions, as well as for evaluating drug and toxin penetration across the barrier. Many previous models have failed to support all the cell types involved in the BBB formation and/or lacked the flow-created shear forces needed for mature tight junction formation. To address these issues and to help establish a more faithful in vitro model of the BBB, we have designed and fabricated a microfluidic device that is comprised of both a vascular chamber and a brain chamber separated by a porous membrane. This design allows for cell-to-cell communication between endothelial cells, astrocytes, and pericytes and independent perfusion of both compartments separated by the membrane. This NeuroVascular Unit (NVU) represents approximately one-millionth of the human brain, and hence, has sufficient cell mass to support a breadth of analytical measurements. The NVU has been validated with both fluorescein isothiocyanate (FITC)-dextran diffusion and transendothelial electrical resistance. The NVU has enabled in vitro modeling of the BBB using all human cell types and sampling effluent from both sides of the barrier.

Finite barrier corrections to the PGH solution of Kramers' turnover theory

NASA Astrophysics Data System (ADS)

Pollak, Eli; Ianconescu, Reuven

2014-04-01

Kramers [Physica 7, 284 (1940)], in his seminal paper, derived expressions for the rate of crossing a barrier in the underdamped limit of weak friction and the moderate to strong friction limit. The challenge of obtaining a uniform expression for the rate, valid for all damping strengths is known as Kramers turnover theory. Two different solutions have been presented. Mel'nikov and Meshkov [J. Chem. Phys. 85, 1018 (1986)] (MM) considered the motion of the particle, treating the friction as a perturbation parameter. Pollak, Grabert, and Hänggi [J. Chem. Phys. 91, 4073 (1989)] (PGH), considered the motion along the unstable mode which is separable from the bath in the barrier region. In practice, the two theories differ in the way an energy loss parameter is estimated. In this paper, we show that previous numerical attempts to resolve the quality of the two approaches were incomplete and that at least for a cubic potential with Ohmic friction, the quality of agreement of both expressions with numerical simulation is similar over a large range of friction strengths and temperatures. Mel'nikov [Phys. Rev. E 48, 3271 (1993)], in a later paper, improved his theory by introducing finite barrier corrections. In this paper we note that previous numerical tests of the finite barrier corrections were also incomplete. They did not employ the exact rate expression, but a harmonic approximation to it. The central part of this paper, is to include finite barrier corrections also within the PGH formalism. Tests on a cubic potential demonstrate that finite barrier corrections significantly improve the agreement of both MM and PGH theories when compared with numerical simulations.

A strain-controlled C2N monolayer membrane for gas separation in PEMFC application

NASA Astrophysics Data System (ADS)

Deng, Shengwei; Hu, Hui; Zhuang, Guilin; Zhong, Xing; Wang, Jianguo

2018-05-01

Ultrathin membranes with controllable pore sizes have great potential to realize high-selectivity gas separation at low energy cost, especially for those mixtures with narrow size distributions. Using a combination of van der Waals-corrected density functional theory (DFT) calculations and molecular dynamics (MD) simulation, we examine the separation ability of biaxial stretched monolayer C2N nanosheets which is applied to the O2 separation from CO/CO2/O2 mixtures in the cathode of proton exchange membrane fuel cells (PEMFC). The DFT calculations show that the diffusion energy barrier for molecules passing through the membrane followed by CO, CO2 and O2 in descending order, and an overall decrease of energy barriers due to the widen the pore size is observed with the increase of applied strains. Furthermore, MD results show that the nanosheet can effectively purify O2 from CO2 and CO with a strain from 8% to 10%. It confirms that the selectivity is determined by the electronic structure related interaction in addition to the kinetic diameter of individual molecules. The O2 permeability is improved progressively with further increase of strain, and small amount of CO2 begins to permeate through the nanosheet at relatively large strain, while the excellent CO isolation is not compromised until the theoretical maximum strain.

A molecular dynamics study of chloride binding by the cryptand SC24

NASA Technical Reports Server (NTRS)

Owenson, B.; MacElroy, R. D.; Pohorille, A.

1988-01-01

The capture of chloride from water by the tetraprotonated form of the spherical macrotricyclic molecule SC24 was studied using molecular dynamics simulation methods. This model ionophore represents a broad class of molecules which remove ions from water. Two binding sites for the chloride were found, one inside and one outside the ligand. These sites are separated by a potential energy barrier of approximately 20 kcal mol-1. The major contribution to this barrier comes from dehydration of the chloride. The large, unfavorable dehydration effect is compensated for by an increase in electrostatic attraction between the oppositely charged chloride and cryptand, and by energetically favorable rearrangements of water structure. Additional assistance in crossing the barrier and completing the dehydration of the ion is provided by the shift of three positively charged hydrogen atoms of the cryptand towards the chloride. This structural rigidity is partially responsible for its selectivity.

Dynamical approach to fusion-fission process in superheavy mass region

NASA Astrophysics Data System (ADS)

Aritomo, Y.; Hinde, D. J.; Wakhle, A.; du Rietz, R.; Dasgupta, M.; Hagino, K.; Chiba, S.; Nishio, K.

2012-10-01

In order to describe heavy-ion fusion reactions around the Coulomb barrier with an actinide target nucleus, we propose a model which combines the coupled-channels approach and a fluctuation-dissipation model for dynamical calculations. This model takes into account couplings to the collective states of the interacting nuclei in the penetration of the Coulomb barrier and the subsequent dynamical evolution of a nuclear shape from the contact configuration. In the fluctuation-dissipation model with a Langevin equation, the effect of nuclear orientation at the initial impact on the prolately deformed target nucleus is considered. Fusion-fission, quasifission and deep quasifission are separated as different Langevin trajectories on the potential energy surface. Using this model, we analyze the experimental data for the mass distribution of fission fragments (MDFF) in the reaction of 36S+238U at several incident energies around the Coulomb barrier.

Improving Service Coordination and Reducing Mental Health Disparities Through Adoption of Electronic Health Records.

PubMed

McGregor, Brian; Mack, Dominic; Wrenn, Glenda; Shim, Ruth S; Holden, Kisha; Satcher, David

2015-09-01

Despite widespread support for removing barriers to the use of electronic health records (EHRs) in behavioral health care, adoption of EHRs in behavioral health settings lags behind adoption in other areas of health care. The authors discuss barriers to use of EHRs among behavioral health care practitioners, suggest solutions to overcome these barriers, and describe the potential benefits of EHRs to reduce behavioral health care disparities. Thoughtful and comprehensive strategies will be needed to design EHR systems that address concerns about policy, practice, costs, and stigma and that protect patients' privacy and confidentiality. However, these goals must not detract from continuing to challenge the notion that behavioral health and general medical health should be treated as separate and distinct. Ultimately, utilization of EHRs among behavioral health care providers will improve the coordination of services and overall patient care, which is essential to reducing mental health disparities.

Industrial waste exchange: a mechanism for saving energy and money

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaines, L.L.

1983-01-01

Although considerable savings of both energy and money are possible through waste exchange, several major impediments limit the number of actual exchanges that take place. These impediments include the lack of economical separation technology, the small quantities of material available at each site, restrictive or uncertain regulation, and lack of knowledge on the part of potential waste users. None of these barriers is insurmountable if appropriate action is taken.

The nature of cation-pi binding: interactions between tetramethylammonium ion and benzene in aqueous solution.

PubMed Central

Gao, J; Chou, L W; Auerbach, A

1993-01-01

A combined quantum mechanical and molecular mechanical Monte Carlo simulation method was used to determine the free energy of binding between tetramethylammonium ion (TMA+) and benzene in water. The computed free energy as a function of distance (the potential of mean force) has two minima that represent contact and solvent-separated complexes. These species are separated by a broad barrier of about 3 kJ/mol. The results are in good accord with experimental data and suggest that TMA+ binds to benzene more favorably than to chloride ion, with an association constant of about 0.8 M-1. Images FIGURE 2 PMID:8369448

Enhanced Ligand Sampling for Relative Protein–Ligand Binding Free Energy Calculations

PubMed Central

2016-01-01

Free energy calculations are used to study how strongly potential drug molecules interact with their target receptors. The accuracy of these calculations depends on the accuracy of the molecular dynamics (MD) force field as well as proper sampling of the major conformations of each molecule. However, proper sampling of ligand conformations can be difficult when there are large barriers separating the major ligand conformations. An example of this is for ligands with an asymmetrically substituted phenyl ring, where the presence of protein loops hinders the proper sampling of the different ring conformations. These ring conformations become more difficult to sample when the size of the functional groups attached to the ring increases. The Adaptive Integration Method (AIM) has been developed, which adaptively changes the alchemical coupling parameter λ during the MD simulation so that conformations sampled at one λ can aid sampling at the other λ values. The Accelerated Adaptive Integration Method (AcclAIM) builds on AIM by lowering potential barriers for specific degrees of freedom at intermediate λ values. However, these methods may not work when there are very large barriers separating the major ligand conformations. In this work, we describe a modification to AIM that improves sampling of the different ring conformations, even when there is a very large barrier between them. This method combines AIM with conformational Monte Carlo sampling, giving improved convergence of ring populations and the resulting free energy. This method, called AIM/MC, is applied to study the relative binding free energy for a pair of ligands that bind to thrombin and a different pair of ligands that bind to aspartyl protease β-APP cleaving enzyme 1 (BACE1). These protein–ligand binding free energy calculations illustrate the improvements in conformational sampling and the convergence of the free energy compared to both AIM and AcclAIM. PMID:25906170

Barriers to and Facilitators of Health for Latina Undergraduate Students

ERIC Educational Resources Information Center

Mount, Jill

2015-01-01

Latina undergraduate students' barriers and facilitators of health are examined: Barriers to psychological health--separating from family, pressure to succeed, and racism; Barriers to physical health--lacking health insurance, and discomfort using campus sports facilities; and Facilitators of psychological health--membership in Latina student…

Vacuum barrier for excimer lasers

DOEpatents

Shurter, Roger P.

1992-01-01

A barrier for separating the vacuum area of a diode from the pressurized gas area of an excimer laser. The barrier is a composite material comprising layers of a metal such as copper, along with layers of polyimide, and a matrix of graphite fiber yarns impregnated with epoxy. The barrier is stronger than conventional foil barriers, and allows greater electron throughput.

Interfacial ionic 'liquids': connecting static and dynamic structures

DOE PAGES

Uysal, Ahmet; Zhou, Hua; Feng, Guang; ...

2014-12-05

It is well known that room temperature ionic liquids (RTILs) often adopt a charge-separated layered structure, i.e. with alternating cation- and anion-rich layers, at electrified interfaces. However, the dynamic response of the layered structure to temporal variations in applied potential is not well understood. For this research, we used in situ, real-time x-ray reflectivity to study the potential-dependent electric double layer (EDL) structure of an imidazolium-based RTIL on charged epitaxial graphene during potential cycling as a function of temperature. The results suggest that the graphene–RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can bemore » described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by fully atomistic molecular dynamics simulations at various static potentials. Lastly, the potential-driven transition between the two structures is characterized by an increasing width but with an approximately fixed hysteresis magnitude as a function of temperature. The results are consistent with the coexistence of distinct anion- and cation-adsorbed structures separated by an energy barrier (~0.15 eV).« less

Interfacial ionic 'liquids': connecting static and dynamic structures.

PubMed

Uysal, Ahmet; Zhou, Hua; Feng, Guang; Lee, Sang Soo; Li, Song; Cummings, Peter T; Fulvio, Pasquale F; Dai, Sheng; McDonough, John K; Gogotsi, Yury; Fenter, Paul

2015-01-28

It is well known that room temperature ionic liquids (RTILs) often adopt a charge-separated layered structure, i.e. with alternating cation- and anion-rich layers, at electrified interfaces. However, the dynamic response of the layered structure to temporal variations in applied potential is not well understood. We used in situ, real-time x-ray reflectivity to study the potential-dependent electric double layer (EDL) structure of an imidazolium-based RTIL on charged epitaxial graphene during potential cycling as a function of temperature. The results suggest that the graphene-RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by fully atomistic molecular dynamics simulations at various static potentials. The potential-driven transition between the two structures is characterized by an increasing width but with an approximately fixed hysteresis magnitude as a function of temperature. The results are consistent with the coexistence of distinct anion- and cation-adsorbed structures separated by an energy barrier (∼0.15 eV).

Wholegrain Food Acceptance in Young Singaporean Adults

PubMed Central

Neo, Jia En; Brownlee, Iain A.

2017-01-01

Previous epidemiological evidence suggests that habitual consumption of whole grains is associated with reduction of disease risk. While wholegrain food consumption appears to be increasing in Singapore, it is still low, with more infrequent consumption noted in younger Singaporeans. Therefore, the primary objective of this study is to determine the knowledge of whole grains and barriers to consumption of wholegrain foods. Thirty participants (age range 21–26 year, 19 females) took part in two focus groups separated by a 2-week period in which participants trialled a range of wholegrain foods. Barriers towards whole grain consumption and experiences of products during this familiarization period were discussed during the focus groups and knowledge of whole grains was assessed by questionnaire. Potential barriers such as personal factors, product-specific factors and external factors were identified with sensory and habitual being stronger barriers. The whole grain familiarization period did not alter the taste expectations of the consumers but it did manage to increase acceptance for four of the wholegrain products tested (muesli, cookies, granola bars and wholewheat pasta). These findings suggest existing barriers to wholegrain food consumption should be considered by public health agencies and manufacturing companies. PMID:28397752

Introduction to Session 5

NASA Astrophysics Data System (ADS)

Zullo, Luca; Snyder, Seth W.

Production of bio-based products that are cost competitive in the market place requires well-developed operations that include innovative processes and separation solutions. Separations costs can make the difference between an interesting laboratory project and a successful commercial process. Bioprocessing and separations research and development addresses some of the most significant cost barriers in production of bioffuels and bio-based chemicals. Models of integrated biorefineries indicate that success will require production of higher volume fuels in conjunction with high margin chemical products. Addressing the bioprocessing and separations cost barriers will be critical to the overall success of the integrated biorefinery.

Vacuum barrier for excimer lasers

DOEpatents

Shurter, R.P.

1992-09-15

A barrier for separating the vacuum area of a diode from the pressurized gas area of an excimer laser. The barrier is a composite material comprising layers of a metal such as copper, along with layers of polyimide, and a matrix of graphite fiber yarns impregnated with epoxy. The barrier is stronger than conventional foil barriers, and allows greater electron throughput. 3 figs.

Barriers and facilitators to implementing the Baby-Friendly hospital initiative in neonatal intensive care units.

PubMed

Benoit, Britney; Semenic, Sonia

2014-01-01

To explore manager, educator, and clinical leader perceptions of barriers and facilitators to implementing Baby-Friendly practice in the neonatal intensive care unit (NICU). Qualitative, descriptive design. Two university-affiliated level-III NICUs in Canada. A purposive sample of 10 medical and nursing managers, nurse educators, lactation consultants, and neonatal nurse practitioners. In-depth, semistructured interviews transcribed and analyzed using qualitative content analysis. Participants valued breastfeeding and family-centered care yet identified numerous contextual barriers to Baby-Friendly care including infant health status, parent/infant separation, staff workloads and work patterns, gaps in staff knowledge and skills, and lack of continuity of breastfeeding support. Facilitators included breastfeeding education, breastfeeding champions, and interprofessional collaboration. Despite identifying numerous barriers, participants recognized the potential value of expanding the Baby-Friendly Hospital Initiative (BFHI) to the NICU setting. Recommendations include promoting BFHI as a facilitator of family-centered care, interdisciplinary staff education, increasing access to lactation consultants, and establishing a group of NICU champions dedicated to BFHI implementation. © 2014 AWHONN, the Association of Women's Health, Obstetric and Neonatal Nurses.

Pandemic Influenza and Farmworkers: The Effects of Employment, Social, and Economic Factors

PubMed Central

Baron, Sherry; Davis, Shelley; Torres-Kilgore, Judith; Sweeney, Marie Haring

2009-01-01

Employment, social, and economic factors have the potential to affect the magnitude of an influenza pandemic among farmworkers. Prevention efforts targeted toward livestock farmworkers, including increased access to seasonal influenza vaccine, risk reduction training, various forms of personal protection, and workplace sanitation, are needed. Crop and livestock farmworkers are at increased risk of exposure to influenza A viruses because of limited resources, substandard housing, immigration status, communication and cultural barriers, and discrimination. Recommendations were gathered from migrant clinicians, farmworker advocates, state and federal government agencies, industry stakeholders, and researchers to overcome these barriers, including surveillance of livestock farmworkers, inclusion of farmworker service organizations in planning efforts, and separation of immigration enforcement from emergency assistance. PMID:19797742

Evaluation of the performance of portable precast concrete traffic barriers.

DOT National Transportation Integrated Search

1978-01-01

The portable precast concrete traffic barrier is used to separate high speed vehicular traffic and construction activities. However, since there was a lack of information on the barrier's performance in a construction zone environment, officials of t...

Advanced Separators for Lithium-Ion and Lithium-Sulfur Batteries: A Review of Recent Progress.

PubMed

Xiang, Yinyu; Li, Junsheng; Lei, Jiaheng; Liu, Dan; Xie, Zhizhong; Qu, Deyu; Li, Ke; Deng, Tengfei; Tang, Haolin

2016-11-09

Li-ion and Li-S batteries find enormous applications in different fields, such as electric vehicles and portable electronics. A separator is an indispensable part of the battery design, which functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of the separators directly influence the performance of the batteries. Traditional polyolefin separators showed low thermal stability, poor wettability toward the electrolyte, and inadequate barrier properties to polysulfides. To improve the performance and durability of Li-ion and Li-S batteries, development of advanced separators is required. In this review, we summarize recent progress on the fabrication and application of novel separators, including the functionalized polyolefin separator, polymeric separator, and ceramic separator, for Li-ion and Li-S batteries. The characteristics, advantages, and limitations of these separators are discussed. A brief outlook for the future directions of the research in the separators is also provided. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multidimensionally constrained relativistic mean-field study of triple-humped barriers in actinides

NASA Astrophysics Data System (ADS)

Zhao, Jie; Lu, Bing-Nan; Vretenar, Dario; Zhao, En-Guang; Zhou, Shan-Gui

2015-01-01

Background: Potential energy surfaces (PES's) of actinide nuclei are characterized by a two-humped barrier structure. At large deformations beyond the second barrier, the occurrence of a third barrier was predicted by macroscopic-microscopic model calculations in the 1970s, but contradictory results were later reported by a number of studies that used different methods. Purpose: Triple-humped barriers in actinide nuclei are investigated in the framework of covariant density functional theory (CDFT). Methods: Calculations are performed using the multidimensionally constrained relativistic mean field (MDC-RMF) model, with the nonlinear point-coupling functional PC-PK1 and the density-dependent meson exchange functional DD-ME2 in the particle-hole channel. Pairing correlations are treated in the BCS approximation with a separable pairing force of finite range. Results: Two-dimensional PES's of 226,228,230,232Th and 232,235,236,238U are mapped and the third minima on these surfaces are located. Then one-dimensional potential energy curves along the fission path are analyzed in detail and the energies of the second barrier, the third minimum, and the third barrier are determined. The functional DD-ME2 predicts the occurrence of a third barrier in all Th nuclei and 238U . The third minima in 230 ,232Th are very shallow, whereas those in 226 ,228Th and 238U are quite prominent. With the functional PC-PK1 a third barrier is found only in 226 ,228 ,230Th . Single-nucleon levels around the Fermi surface are analyzed in 226Th, and it is found that the formation of the third minimum is mainly due to the Z =90 proton energy gap at β20≈1.5 and β30≈0.7 . Conclusions: The possible occurrence of a third barrier on the PES's of actinide nuclei depends on the effective interaction used in multidimensional CDFT calculations. More pronounced minima are predicted by the DD-ME2 functional, as compared to the functional PC-PK1. The depth of the third well in Th isotopes decreases with increasing neutron number. The origin of the third minimum is due to the proton Z =90 shell gap at relevant deformations.

Functionalized low defect graphene nanoribbons and polyurethane composite film for improved gas barrier and mechanical performances.

PubMed

Xiang, Changsheng; Cox, Paris J; Kukovecz, Akos; Genorio, Bostjan; Hashim, Daniel P; Yan, Zheng; Peng, Zhiwei; Hwang, Chih-Chau; Ruan, Gedeng; Samuel, Errol L G; Sudeep, Parambath M; Konya, Zoltan; Vajtai, Robert; Ajayan, Pulickel M; Tour, James M

2013-11-26

A thermoplastic polyurethane (TPU) composite film containing hexadecyl-functionalized low-defect graphene nanoribbons (HD-GNRs) was produced by solution casting. The HD-GNRs were well distributed within the polyurethane matrix, leading to phase separation of the TPU. Nitrogen gas effective diffusivity of TPU was decreased by 3 orders of magnitude with only 0.5 wt % HD-GNRs. The incorporation of HD-GNRs also improved the mechanical properties of the composite films, as predicted by the phase separation and indicated by tensile tests and dynamic mechanical analyses. The improved properties of the composite film could lead to potential applications in food packaging and lightweight mobile gas storage containers.

Analysis of the barriers to renewable energy development on tribal lands

NASA Astrophysics Data System (ADS)

Jones, Thomas Elisha

Native American lands have significant renewable energy resource potential that could serve to ensure energy security and a low carbon energy future for the benefit of tribes as well as the United States. Economic and energy development needs in Native American communities match the energy potential. A disproportionate amount of Native American households have no access to electricity, which is correlated with high poverty and unemployment rates. Despite the vast resources and need for energy, the potential for renewable energy development has not fully materialized. This research explores this subject through three separate articles: 1) a case study of the Navajo Nation that suggests economic viability is not the only significant factor for low adoption of renewable energy on Navajo lands; 2) an expert elicitation of tribal renewable energy experts of what they view as barriers to renewable energy development on tribal lands; and 3) a reevaluation of Native Nation Building Theory to include external forces and the role that inter-tribal collaboration plays with renewable energy development by Native nations. Major findings from this research suggests that 1) many Native nations lack the technical and legal capacity to develop renewable energy; 2) inter-tribal collaboration can provide opportunities for sharing resources and building technical, legal, and political capacity; and 3) financing and funding remains a considerable barrier to renewable energy development on tribal lands.

Microscopic dynamics of charge separation at the aqueous electrochemical interface.

PubMed

Kattirtzi, John A; Limmer, David T; Willard, Adam P

2017-12-19

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na + I - , or classical ions, and the products of water autoionization, H 3 O + OH - , or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface.

Microscopic dynamics of charge separation at the aqueous electrochemical interface

PubMed Central

Kattirtzi, John A.; Limmer, David T.; Willard, Adam P.

2017-01-01

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water–metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali–halide pair, Na+I−, or classical ions, and the products of water autoionization, H3O+OH−, or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water’s collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface. PMID:28698368

Safety and effectiveness of a polyvinyl alcohol barrier in reducing risks of vascular tissue damage during anterior spinal revision surgery.

PubMed

Jeffords, Paul; Li, Jinsheng; Panchal, Deepal; Denoziere, Guilhem; Fetterolf, Donald

2012-05-01

This study was conducted as a controlled, prospective investigation to show the safety and efficacy of a polyvinyl alcohol (PVA) device in a sheep model. To evaluate the ability of a permanent PVA hydrogel barrier to reduce the risk of potential vessel damage during anterior vertebral revision surgery, to provide a nonadhesive barrier at the surgical site, and to create a surgical revision plane of dissection. The development of scar tissue and adhesions presents a significant postoperative problem in spine surgery, where adhesion involvement of overlying structures can cause pain, neurovascular complications, and present a difficult surgical environment during revisions. The devices were implanted onto the ventral surface of exposed lumbar intervertebral discs using an anterolateral approach. One disc separated from the study site was also exposed to serve as a control. Three sheep each were then evaluated with an explant procedure at 30 and 90 days. Extensive sampling was undertaken to evaluate gross anatomic, micropathologic, and biochemical environments and properties of the device. The structural properties and appearance of the device remained intact at both 30 and 90 days. The material remained flexible, hydrophilic, and soft, without visible resorption or decomposition. The material was well tolerated by the animal, with minimal histologic signs of inflammation or rejection. Tissue planes were easily able to be localized by the surgeon attempting to locate the prior surgical site at the time of resection. The PVA vessel shield effectively protected the structures overlying the sheep spine during revision, providing a clear dissection plane for resection at repeat surgery. The overlying structures separated from the previous surgical site with no adhesion, and allowed safe separation of adjacent tissues without the use of sharp dissection.

Free energy surface of two- and three-dimensional transitions of Au 12 nanoclusters obtained by ab initio metadynamics

NASA Astrophysics Data System (ADS)

Santarossa, Gianluca; Vargas, Angelo; Iannuzzi, Marcella; Baiker, Alfons

2010-05-01

The description of the conformational space generated by metal nanoparticles is a fundamental issue for the study of their physicochemical properties. In this investigation, an exhaustive exploration and a unified view of the conformational space of a gold nanocluster is provided using a Au 12 cluster as an example. Such system is characterized by coexisting planar/quasiplanar and tridimensional conformations separated by high-energy barriers. The conformational space of Au 12 has been explored by means of Born-Oppenheimer ab initio metadynamics, i.e., a molecular dynamics simulation coupled with a history dependent potential to accelerate events that might occur on a long time scale compared to the time step used in the simulations (rare events). The sampled conformations have complex, in general not intuitive topologies that we have classified as planar/quasiplanar or tridimensional, belonging to different regions of the free energy surface. Three conformational free energy basins were identified, one for the planar/quasiplanar and two for the tridimensional structures. At thermodynamic equilibrium, the planar/quasi-planar and tridimensional conformations were found to coexist, to be fluxional and to be separated by high-free-energy barriers. The comparison between the free energy and the potential energy revealed the relevance of the entropic contribution in the equilibrium distribution of the conformations of the cluster.

Energy Levels in Quantum Wells.

NASA Astrophysics Data System (ADS)

Zang, Jan Xin

Normalized analytical equations for eigenstates of an arbitrary one-dimensional configuration of square potentials in a well have been derived. The general formulation is used to evaluate the energy levels of a particle in a very deep potential well containing seven internal barriers. The configuration can be considered as a finite superlattice sample or as a simplified model for a sample with only several atom layers. The results are shown in graphical forms as functions of the height and width of the potential barriers and as functions of the ratio of the effective mass in barrier to the mass in well. The formation of energy bands and surface eigenstates from eigenstates of a deep single well, the coming close of two energy bands and a surface state which are separate ordinarily, and mixing of the wave function of a surface state with the bulk energy bands are seen. Then the normalized derivation is extended to study the effect of a uniform electric field applied across a one-dimensional well containing an internal configuration of square potentials The general formulation is used to calculate the electric field dependence of the energy levels of a deep well with five internal barriers. Typical results are shown in graphical forms as functions of the barrier height, barrier width, barrier effective mass and the field strength. The formation of Stark ladders and surface states from the eigenstates of a single deep well in an electric field, the localization process of wave functions with changing barrier height, width, and field strength and their anticrossing behaviors are seen. The energy levels of a hydrogenic impurity in a uniform medium and in a uniform magnetic field are calculated with variational methods. The energy eigenvalues for the eigenstates with major quantum number less than or equal to 3 are obtained. The results are consistent with previous results. Furthermore, the energy levels of a hydrogenic impurity at the bottom of a one-dimensional parabolic quantum well with a magnetic field normal to the plane of the well are calculated with the finite-basis-set variational method. The limit of small radial distance and the limit of great radial distance are considered to choose a set of proper basis functions. It is found that the energy levels increase with increasing parabolic parameter alpha and increase with increasing normalized magnetic field strength gamma except those levels with magnetic quantum number m < 0 at small gamma.

Implementation of a Non-Metallic Barrier in an Electric Motor

NASA Technical Reports Server (NTRS)

M'Sadoques, George A. (Inventor); Carra, Michael R. (Inventor); Beringer, Durwood M. (Inventor)

2013-01-01

A motor for use in a volatile environment includes a rotor exposed to the volatile environment, electronics for rotating the rotor, an impervious ceramic barrier separating the electronics and the rotor, and a flexible seal for preventing the volatile environment from contacting the electronics and for minimizing vibratory and twisting loads upon the barrier to minimize damage to the barrier.

30 CFR 75.819 - Motor-starter enclosures; barriers and interlocks.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Motor-starter enclosures; barriers and...-Voltage Distribution High-Voltage Longwalls § 75.819 Motor-starter enclosures; barriers and interlocks. Compartment separation and cover interlock switches for motor-starter enclosures must be maintained in...

Artificial barriers prevent genetic recovery of small isolated populations of a low-mobility freshwater fish.

PubMed

Coleman, R A; Gauffre, B; Pavlova, A; Beheregaray, L B; Kearns, J; Lyon, J; Sasaki, M; Leblois, R; Sgro, C; Sunnucks, P

2018-06-01

Habitat loss and fragmentation often result in small, isolated populations vulnerable to environmental disturbance and loss of genetic diversity. Low genetic diversity can increase extinction risk of small populations by elevating inbreeding and inbreeding depression, and reducing adaptive potential. Due to their linear nature and extensive use by humans, freshwater ecosystems are especially vulnerable to habitat loss and fragmentation. Although the effects of fragmentation on genetic structure have been extensively studied in migratory fishes, they are less understood in low-mobility species. We estimated impacts of instream barriers on genetic structure and diversity of the low-mobility river blackfish (Gadopsis marmoratus) within five streams separated by weirs or dams constructed 45-120 years ago. We found evidence of small-scale (<13 km) genetic structure within reaches unimpeded by barriers, as expected for a fish with low mobility. Genetic diversity was lower above barriers in small streams only, regardless of barrier age. In particular, one isolated population showed evidence of a recent bottleneck and inbreeding. Differentiation above and below the barrier (F ST  = 0.13) was greatest in this stream, but in other streams did not differ from background levels. Spatially explicit simulations suggest that short-term barrier effects would not be detected with our data set unless effective population sizes were very small (<100). Our study highlights that, in structured populations, the ability to detect short-term genetic effects from barriers is reduced and requires more genetic markers compared to panmictic populations. We also demonstrate the importance of accounting for natural population genetic structure in fragmentation studies.

Method and apparatus for increasing resistance of bipolar buried layer integrated circuit devices to single-event upsets

NASA Technical Reports Server (NTRS)

Zoutendyk, John A. (Inventor)

1991-01-01

Bipolar transistors fabricated in separate buried layers of an integrated circuit chip are electrically isolated with a built-in potential barrier established by doping the buried layer with a polarity opposite doping in the chip substrate. To increase the resistance of the bipolar transistors to single-event upsets due to ionized particle radiation, the substrate is biased relative to the buried layer with an external bias voltage selected to offset the built-in potential just enough (typically between about +0.1 to +0.2 volt) to prevent an accumulation of charge in the buried-layer-substrate junction.

Ferroelectric-field-effect-enhanced electroresistance in metal/ferroelectric/semiconductor tunnel junctions

NASA Astrophysics Data System (ADS)

Wen, Zheng; Li, Chen; Wu, Di; Li, Aidong; Ming, Naiben

2013-07-01

Ferroelectric tunnel junctions (FTJs), composed of two metal electrodes separated by an ultrathin ferroelectric barrier, have attracted much attention as promising candidates for non-volatile resistive memories. Theoretical and experimental works have revealed that the tunnelling resistance switching in FTJs originates mainly from a ferroelectric modulation on the barrier height. However, in these devices, modulation on the barrier width is very limited, although the tunnelling transmittance depends on it exponentially as well. Here we propose a novel tunnelling heterostructure by replacing one of the metal electrodes in a normal FTJ with a heavily doped semiconductor. In these metal/ferroelectric/semiconductor FTJs, not only the height but also the width of the barrier can be electrically modulated as a result of a ferroelectric field effect, leading to a greatly enhanced tunnelling electroresistance. This idea is implemented in Pt/BaTiO3/Nb:SrTiO3 heterostructures, in which an ON/OFF conductance ratio above 104, about one to two orders greater than those reported in normal FTJs, can be achieved at room temperature. The giant tunnelling electroresistance, reliable switching reproducibility and long data retention observed in these metal/ferroelectric/semiconductor FTJs suggest their great potential in non-destructive readout non-volatile memories.

Decontamination systems information and research program. Quarterly report, April--June 1996

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

This report contains separate reports on the following subtasks: analysis of the Vortec cyclone melting system for remediation of PCB contaminated soils using CFD; drain enhanced soil flushing using prefabricated vertical drains; performance and characteristics evaluation of acrylates as grout barriers; development of standard test protocol barrier design models for desiccation barriers, and for in-situ formed barriers; in-situ bioremediation of chlorinated solvents at Portsmouth Gaseous Diffusion Plant; development of a decision support system and a prototype database for management of the EM50 technology development program; GIS-based infrastructure for site characterization and remediation; treatment of mixed wastes via fluidized bed steammore » reforming; use of centrifugal membrane technology to treat hazardous/radioactive waste; environmental pollution control devices based on novel forms of carbon; development of instrumental methods for analysis of nuclear wastes and environmental materials; production and testing of biosorbents and cleaning solutions for D and D; use of SpinTek centrifugal membrane and sorbents/cleaning solutions for D and D; West Virginia High Tech Consortium Foundation--Environmental support program; small business interaction opportunities; and approach for assessing potential voluntary environmental protection.« less

Electrode Reactions in Slowly Relaxing Media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matyushov, Dmitry V.; Newton, Marshall D.

Here, standard models of reaction kinetics in condensed materials rely on the Boltzmann-Gibbs distribution for the population of reactants at the top of the free energy barrier separating them from the products. While energy dissipation and quantum effects at the barrier top can potentially affect the transmission coefficient entering the rate preexponential factor, much stronger dynamical effects on the reaction barrier are caused by the breakdown of ergodicity for populating the reaction barrier (violation of the Boltzmann-Gibbs statistics). When the spectrum of medium modes coupled to the reaction coordinate includes fluctuations slower than the reaction rate, such nuclear motions dynamicallymore » freeze on the reaction time-scale and do not contribute to the activation barrier. In this paper, we consider the consequences of this scenario for electrode reactions in slowly relaxing media. Changing electrode overpotential speeds electrode electron transfer up, potentially cutting through the spectrum of nuclear modes coupled to the reaction coordinate. The reorganization energy of electrochemical electron transfer becomes a function of the electrode overpotential, switching between the thermodynamic value at low rates to the nonergodic limit at higher rates. The sharpness of this transition depends of the relaxation spectrum of the medium. The reorganization energy experiences a sudden drop with increasing overpotential for a medium with a Debye relaxation, but becomes a much shallower function of the overpotential for media with stretched exponential dynamics. The latter scenario characterizes electron transfer in ionic liquids. The analysis of electrode reactions in room-temperature ionic liquids shows that the magnitude of the free energy of nuclear solvation is significantly below its thermodynamic limit. Finally, this result applies to reaction times faster than microseconds and is currently limited by the available dielectric relaxation data.« less

Electrode Reactions in Slowly Relaxing Media

DOE PAGES

Matyushov, Dmitry V.; Newton, Marshall D.

2017-11-17

Here, standard models of reaction kinetics in condensed materials rely on the Boltzmann-Gibbs distribution for the population of reactants at the top of the free energy barrier separating them from the products. While energy dissipation and quantum effects at the barrier top can potentially affect the transmission coefficient entering the rate preexponential factor, much stronger dynamical effects on the reaction barrier are caused by the breakdown of ergodicity for populating the reaction barrier (violation of the Boltzmann-Gibbs statistics). When the spectrum of medium modes coupled to the reaction coordinate includes fluctuations slower than the reaction rate, such nuclear motions dynamicallymore » freeze on the reaction time-scale and do not contribute to the activation barrier. In this paper, we consider the consequences of this scenario for electrode reactions in slowly relaxing media. Changing electrode overpotential speeds electrode electron transfer up, potentially cutting through the spectrum of nuclear modes coupled to the reaction coordinate. The reorganization energy of electrochemical electron transfer becomes a function of the electrode overpotential, switching between the thermodynamic value at low rates to the nonergodic limit at higher rates. The sharpness of this transition depends of the relaxation spectrum of the medium. The reorganization energy experiences a sudden drop with increasing overpotential for a medium with a Debye relaxation, but becomes a much shallower function of the overpotential for media with stretched exponential dynamics. The latter scenario characterizes electron transfer in ionic liquids. The analysis of electrode reactions in room-temperature ionic liquids shows that the magnitude of the free energy of nuclear solvation is significantly below its thermodynamic limit. Finally, this result applies to reaction times faster than microseconds and is currently limited by the available dielectric relaxation data.« less

Accelerated molecular dynamics and protein conformational change: a theoretical and practical guide using a membrane embedded model neurotransmitter transporter.

PubMed

Gedeon, Patrick C; Thomas, James R; Madura, Jeffry D

2015-01-01

Molecular dynamics simulation provides a powerful and accurate method to model protein conformational change, yet timescale limitations often prevent direct assessment of the kinetic properties of interest. A large number of molecular dynamic steps are necessary for rare events to occur, which allow a system to overcome energy barriers and conformationally transition from one potential energy minimum to another. For many proteins, the energy landscape is further complicated by a multitude of potential energy wells, each separated by high free-energy barriers and each potentially representative of a functionally important protein conformation. To overcome these obstacles, accelerated molecular dynamics utilizes a robust bias potential function to simulate the transition between different potential energy minima. This straightforward approach more efficiently samples conformational space in comparison to classical molecular dynamics simulation, does not require advanced knowledge of the potential energy landscape and converges to the proper canonical distribution. Here, we review the theory behind accelerated molecular dynamics and discuss the approach in the context of modeling protein conformational change. As a practical example, we provide a detailed, step-by-step explanation of how to perform an accelerated molecular dynamics simulation using a model neurotransmitter transporter embedded in a lipid cell membrane. Changes in protein conformation of relevance to the substrate transport cycle are then examined using principle component analysis.

Method of manufacturing lightweight thermo-barrier material

NASA Technical Reports Server (NTRS)

Blair, Winford (Inventor)

1987-01-01

A method of manufacturing thermal barrier structures comprising at least three dimpled cores separated by flat plate material with the outer surface of the flat plate material joined together by diffusion bonding.

Are All Latinas the Same?: Perceived Breast Cancer Screening Barriers and Facilitative Conditions

ERIC Educational Resources Information Center

Buki, Lydia P.; Borrayo, Evelinn A.; Feigal, Benjamin M.; Carrillo, Iris Y.

2004-01-01

In this article, we examine perceived breast cancer screening barriers and facilitative conditions for immigrant women from Mexico, Puerto Rico, Cuba, El Salvador, and South America (N=58). Focus groups conducted separately with women of each ancestry were analyzed using grounded theory methods. Identified barriers comprise secrecy, lack of…

Arctic warming will promote Atlantic-Pacific fish interchange

NASA Astrophysics Data System (ADS)

Wisz, M. S.; Broennimann, O.; Grønkjær, P.; Møller, P. R.; Olsen, S. M.; Swingedouw, D.; Hedeholm, R. B.; Nielsen, E. E.; Guisan, A.; Pellissier, L.

2015-03-01

Throughout much of the Quaternary Period, inhospitable environmental conditions above the Arctic Circle have been a formidable barrier separating most marine organisms in the North Atlantic from those in the North Pacific. Rapid warming has begun to lift this barrier, potentially facilitating the interchange of marine biota between the two seas. Here, we forecast the potential northward progression of 515 fish species following climate change, and report the rate of potential species interchange between the Atlantic and the Pacific via the Northwest Passage and the Northeast Passage. For this, we projected niche-based models under climate change scenarios and simulated the spread of species through the passages when climatic conditions became suitable. Results reveal a complex range of responses during this century, and accelerated interchange after 2050. By 2100 up to 41 species could enter the Pacific and 44 species could enter the Atlantic, via one or both passages. Consistent with historical and recent biodiversity interchanges, this exchange of fish species may trigger changes for biodiversity and food webs in the North Atlantic and North Pacific, with ecological and economic consequences to ecosystems that at present contribute 39% to global marine fish landings.

Pore-Confined Carriers and Biomolecules in Mesoporous Silica for Biomimetic Separation and Targeting

NASA Astrophysics Data System (ADS)

Zhou, Shanshan

Selectively permeable biological membranes composed of lipophilic barriers inspire the design of biomimetic carrier-mediated membranes for aqueous solute separation. This work imparts selective permeability to lipid-filled pores of silica thin film composite membranes using carrier molecules that reside in the lipophilic self-assemblies. The lipids confined inside the pores of silica are proven to be a more effective barrier than bilayers formed on the porous surface through vesicle fusion, which is critical for quantifying the function of an immobilized carrier. The ability of a lipophilic carrier embedded in the lipid bilayer to reversibly bind the target solute and transport it through the membrane is demonstrated. Through the functionalization of the silica surface with enzymes, enzymatic catalysis and biomimetic separations can be combined on this nanostructured composite platform. The successful development of biomimetic nanocomposite membrane can provide for efficient dilute aqueous solute upgrading or separations using engineered carrier/catalyst/support systems. While the carrier-mediated biomimetic membranes hold great potential, fully understanding of the transport processes in composite synthetic membranes is essential for improve the membrane performance. Electrochemical impedance spectroscopy (EIS) technique is demonstrated to be a useful tool for characterizing the thin film pore accessibility. Furthermore, the effect of lipid bilayer preparation methods on the silica thin film (in the form of pore enveloping, pore filling) on ion transport is explored, as a lipid bilayer with high electrically insulation is essential for detecting activity of proteins or biomimetic carriers in the bilayer. This study provides insights for making better barriers on mesoporous support for carrier-mediated membrane separation process. Porous silica nanoparticles (pSNPs) with pore sizes appropriate for biomolecule loading are potential for encapsulating dsRNA within the pores to achieve effective delivery of dsRNA to insects for RNA interference (RNAi). The mobility of dsRNA in the nanopores of the pSNPs is expected to have a functional effect on delivery of dsRNA to insects. The importance of pores to a mobile dsRNA network is demonstrated by the lack of measurable mobility for both lengths of RNA on nonporous materials. In addition, when the dsRNA could not penetrate the pores, dsRNA mobility is also not measurable at the surface of the particle. Thus, the pores seem to serve as a "sink" in providing a mobile network of dsRNA on the surface of the particle. This work successfully demonstrates the loading of RNA on functionalized pSNPs and identified factors that affects RNA loading and releasing, which provides basis for the delivery of RNA-loaded silica particles in vivo.

Landscape effects on extremely fragmented populations of a rare solitary bee, Colletes floralis.

PubMed

Davis, Emily S; Murray, Tomás E; Fitzpatrick, Una; Brown, Mark J F; Paxton, Robert J

2010-11-01

Globally, there is concern over the decline of bees, an ecologically important group of pollinating insects. Genetic studies provide insights into population structure that are crucial for conservation management but that would be impossible to obtain by conventional ecological methods. Yet conservation genetic studies of bees have primarily focussed on social species rather than the more species-rich solitary bees. Here, we investigate the population structure of Colletes floralis, a rare and threatened solitary mining bee, in Ireland and Scotland using nine microsatellite loci. Genetic diversity was surprisingly as high in Scottish (Hebridean island) populations at the extreme northwestern edge of the species range as in mainland Irish populations further south. Extremely high genetic differentiation among populations was detected; multilocus F(ST) was up to 0.53, and and D(est) were even higher (maximum: 0.85 and 1.00, respectively). A pattern of isolation by distance was evident for sites separated by land. Water appears to act as a substantial barrier to gene flow yet sites separated by sea did not exhibit isolation by distance. C. floralis populations are extremely isolated and probably not in regional migration-drift equilibrium. GIS-based landscape genetic analysis reveals urban areas as a potential and substantial barrier to gene flow. Our results highlight the need for urgent site-specific management action to halt the decline of this and potentially other rare solitary bees. © 2010 Blackwell Publishing Ltd.

Self-assembly of vertically aligned quantum ring-dot structure by Multiple Droplet Epitaxy

NASA Astrophysics Data System (ADS)

Elborg, Martin; Noda, Takeshi; Mano, Takaaki; Kuroda, Takashi; Yao, Yuanzhao; Sakuma, Yoshiki; Sakoda, Kazuaki

2017-11-01

We successfully grow vertically aligned quantum ring-dot structures by Multiple Droplet Epitaxy technique. The growth is achieved by depositing GaAs quantum rings in a first droplet epitaxy process which are subsequently covered by a thin AlGaAs barrier. In a second droplet epitaxy process, Ga droplets preferentially position in the center indentation of the ring as well as attached to the edge of the ring in [ 1 1 bar 0 ] direction. By designing the ring geometry, full selectivity for the center position of the ring is achieved where we crystallize the droplets into quantum dots. The geometry of the ring and dot as well as barrier layer can be controlled in separate growth steps. This technique offers great potential for creating complex quantum molecules for novel quantum information technologies.

Conformational analysis investigation into the influence of nano-porosity of ultra-permeable ultra-selective polyimides on its diffusivity as potential membranes for use in the "green" separation of natural gases

NASA Astrophysics Data System (ADS)

Madkour, Tarek M.

2013-08-01

Nano-porous polymers of intrinsic microporosity, PIM, have exhibited excellent permeability and selectivity characteristics that could be utilized in an environmentally friendly gas separation process. A full understanding of the mechanism through which these membranes effectively and selectively allow for the permeation of specific gases will lead to further development of these membranes. Three factors obviously influenced the conformational behavior of these polymers, which are the presence of electronegative atoms, the presence of non-linearity in the polymeric backbones (backbone kinks) and the presence of bulky side groups on the polymeric chains. The dipole moment increased sharply with the presence of backbone kinks more than any other factor. Replacing the fluorine atoms with bulky alkyl groups didn't influence the dipole moment greatly indicating that the size of the side chains had much less dramatic influence on the dipole moment than having a bent backbone. Similarly, the presence of the backbone kinks in the polymeric chains influenced the polymeric chains to assume less extended configuration causing the torsional angles around the interconnecting bonds unable to cross the high potential energy barriers. The presence of the bulky side groups also caused the energy barriers of the cis-configurations to increase dramatically, which prevented the polymeric segments from experiencing full rotation about the connecting bonds. For these polymers, it was clear that the fully extended configurations are the preferred configurations in the absence of strong electronegative atoms, backbones kinks or bulky side groups. The addition of any of these factors to the polymeric structures resulted in the polymeric chains being forced to assume less extended configurations. Rather interestingly, the length or bulkiness of the side groups didn't affect the end-to-end distance distribution to a great deal since the presence of quite large bulky side chain such as the pentyl group has caused the polymeric chains to revert back to the fully extended configurations possibly due to the quite high potential energy barriers that the chains have to cross to reach the less extended configurational states.

Potential barrier classification by short-time measurement

NASA Astrophysics Data System (ADS)

Granot, Er'El; Marchewka, Avi

2006-03-01

We investigate the short-time dynamics of a delta-function potential barrier on an initially confined wave packet. There are mainly two conclusions: (A) At short times the probability density of the first particles that passed through the barrier is unaffected by it. (B) When the barrier is absorptive (i.e., its potential is imaginary) it affects the transmitted wave function at shorter times than a real potential barrier. Therefore, it is possible to distinguish between an imaginary and a real potential barrier by measuring its effect at short times only on the transmitting wave function.

Breaking Barriers, Building Bridges: Critical Discussion of Social Issues.

ERIC Educational Resources Information Center

Moss, Joy

Noting that picture books can invite students to engage in critical discussion of complex issues of race, class, and gender, this lesson plan helps students to confront the injustice of barriers that separate human beings from one another and to examine the role of prejudice and stereotypes in sustaining these barriers. During the five 45-minute…

Program To Address Sociocultural Barriers to Health Care in Hispanic Communities. National Program Report.

ERIC Educational Resources Information Center

Jackson, Mike; Heroux, Janet

Many members of the Hispanic community are separated from the larger community by language barriers and different cultures and belief systems. These factors can affect Hispanic Americans' ability to seek and gain access to the health care system. The Program To Address Sociocultural Barriers to Health Care in the Hispanic Community, known as…

Heat dissipation in controlled environment enclosures through the application of water screens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warrington, I.J.; Halligan, E.A.; Ruby, L.C.

1994-12-31

The use of plate glass-water thermal barriers in controlled environment facilities effectively reduces the thermal load within the plant growth chamber. This allows high PPFs to be provided for plant growth and development studies, adequate simulation of daily light integrals, and simulation of peak PPFs. Further, substantial amounts of incandescent lamp supplementation can be used to achieve simulation of daylight R:FR ratios which are needed to ensure adequate stem development in some species. While the focus in this paper has been on the use of entire thermal barriers which separate the lighting enclosure from the plant growth chamber, the samemore » principles apply to the use of water jackets for cooling individual lamps (such as can occur with xenon-arc lamps). In this instance, the barrier separating the lamps from the plant chamber can be much simpler (e.g., plexiglas) as the main function of the barrier is to separate the air ventilation of the lamp enclosure from the air system within the plant growth chamber. The main advantage of water as a thermal barrier is the negligible absorption of radiation in the photosynthetically-active and near infra-red wavebands. Consequently, plate glass-water barriers typically allow transmission of approximately 90% of radiation in these regions. While ventilated double and triple glazing systems appear to be attractive alternative to water barriers from an operating standpoint, their significant absorption in the biologically-important wavebands (7 - 12 %) with each glass layer and longer-wave cut-offs (typically 2500 - 4000 nm) makes them a much less attractive alternative. The data presented demonstrate clearly that measurement of PPF alone is not an adequate representation of the radiation environment being used in a controlled environment study.« less

Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells.

PubMed

Yan, Yaming; Song, Linze; Shi, Qiang

2018-02-28

By employing several lattice model systems, we investigate the free energy barrier and real-time dynamics of charge separation in organic photovoltaic (OPV) cells. It is found that the combined effects of the external electric field, entropy, and charge delocalization reduce the free energy barrier significantly. The dynamic disorder reduces charge carrier delocalization and results in the increased charge separation barrier, while the effect of static disorder is more complicated. Simulation of the real-time dynamics indicates that the free charge generation process involves multiple time scales, including an ultrafast component within hundreds of femtoseconds, an intermediate component related to the relaxation of the hot charge transfer (CT) state, and a slow component on the time scale of tens of picoseconds from the thermally equilibrated CT state. Effects of hot exciton dissociation as well as its dependence on the energy offset between the Frenkel exciton and the CT state are also analyzed. The current results indicate that only a small energy offset between the band gap and the lowest energy CT state is needed to achieve efficient free charge generation in OPV devices, which agrees with recent experimental findings.

Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Yan, Yaming; Song, Linze; Shi, Qiang

2018-02-01

By employing several lattice model systems, we investigate the free energy barrier and real-time dynamics of charge separation in organic photovoltaic (OPV) cells. It is found that the combined effects of the external electric field, entropy, and charge delocalization reduce the free energy barrier significantly. The dynamic disorder reduces charge carrier delocalization and results in the increased charge separation barrier, while the effect of static disorder is more complicated. Simulation of the real-time dynamics indicates that the free charge generation process involves multiple time scales, including an ultrafast component within hundreds of femtoseconds, an intermediate component related to the relaxation of the hot charge transfer (CT) state, and a slow component on the time scale of tens of picoseconds from the thermally equilibrated CT state. Effects of hot exciton dissociation as well as its dependence on the energy offset between the Frenkel exciton and the CT state are also analyzed. The current results indicate that only a small energy offset between the band gap and the lowest energy CT state is needed to achieve efficient free charge generation in OPV devices, which agrees with recent experimental findings.

The QTP family of consistent functionals and potentials in Kohn-Sham density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Yifan; Bartlett, Rodney J., E-mail: bartlett@qtp.ufl.edu

This manuscript presents the second, consistent density functional in the QTP (Quantum Theory Project) family, that is, the CAM-QTP(01). It is a new range-separated exchange-correlation functional in which the non-local exchange contribution is 100% at large separation. It follows the same basic principles of this family that the Kohn-Sham eigenvalues of the occupied orbitals approximately equal the vertical ionization energies, which is not fulfilled by most of the traditional density functional methods. This new CAM-QTP(01) functional significantly improves the accuracy of the vertical excitation energies especially for the Rydberg states in the test set. It also reproduces many other propertiesmore » such as geometries, reaction barrier heights, and atomization energies.« less

Ab initio and empirical energy landscapes of (MgF2)n clusters (n = 3, 4).

PubMed

Neelamraju, S; Schön, J C; Doll, K; Jansen, M

2012-01-21

We explore the energy landscape of (MgF(2))(3) on both the empirical and ab initio level using the threshold algorithm. In order to determine the energy landscape and the dynamics of the trimer we investigate not only the stable isomers but also the barriers separating these isomers. Furthermore, we study the probability flows in order to estimate the stability of all the isomers found. We find that there is reasonable qualitative agreement between the ab initio and empirical potential, and important features such as sub-basins and energetic barriers follow similar trends. However, we observe that the energies are systematically different for the less compact clusters, when comparing empirical and ab initio energies. Since the underlying motivation of this work is to identify the possible clusters present in the gas phase during a low-temperature atom beam deposition synthesis of MgF(2), we employ the same procedure to additionally investigate the energy landscape of the tetramer. For this case, however, we use only the empirical potential.

Spatial characterization of the edge barrier in wide superconducting films

NASA Astrophysics Data System (ADS)

Sivakov, A. G.; Turutanov, O. G.; Kolinko, A. E.; Pokhila, A. S.

2018-03-01

The current-induced destruction of superconductivity is discussed in wide superconducting thin films, whose width is greater than the magnetic field penetration depth, in weak magnetic fields. Particular attention is paid to the role of the boundary potential barrier (the Bin-Livingston barrier) in critical state formation and detection of the edge responsible for this critical state with different mutual orientations of external perpendicular magnetic field and transport current. Critical and resistive states of the film were visualized using the space-resolving low-temperature laser scanning microscopy (LTLSM) method, which enables detection of critical current-determining areas on the film edges. Based on these observations, a simple technique was developed for investigation of the critical state separately at each film edge, and for the estimation of residual magnetic fields in cryostats. The proposed method only requires recording of the current-voltage characteristics of the film in a weak magnetic field, thus circumventing the need for complex LTLSM techniques. Information thus obtained is particularly important for interpretation of studies of superconducting film single-photon light emission detectors.

Possible origin and roles of nano-porosity in ZrO2 scales for hydrogen pick-up in Zr alloys

NASA Astrophysics Data System (ADS)

Lindgren, Mikaela; Geers, Christine; Panas, Itai

2017-08-01

A mechanistic understanding of Wagnerian build-up and subsequent non-Wagnerian break-down of barrier oxide upon oxidation of zirconium alloys by water is reiterated. Hydrogen assisted build-up of nano-porosity is addressed. Growth of sub-nanometer wide stalactitic pores owing to increasing aggregation of neutral oxygen vacancies offering a means to permeate hydrogen into the alloy is explored by density functional theory. The Wagnerian channel utilizes charge separation allowing charged oxygen vacancies and electrons to move separately from nominal anode to nominal cathode. This process becomes increasingly controlled by the charging of the barrier oxide resulting in sub-parabolic rate law for oxide growth. The break-down of the barrier oxide is understood to be preceded by avalanching hydrogen pick-up in the alloy. Pore mediated diffusion allows water to effectively short circuit the barrier oxide.

Neural Network and Nearest Neighbor Algorithms for Enhancing Sampling of Molecular Dynamics.

PubMed

Galvelis, Raimondas; Sugita, Yuji

2017-06-13

The free energy calculations of complex chemical and biological systems with molecular dynamics (MD) are inefficient due to multiple local minima separated by high-energy barriers. The minima can be escaped using an enhanced sampling method such as metadynamics, which apply bias (i.e., importance sampling) along a set of collective variables (CV), but the maximum number of CVs (or dimensions) is severely limited. We propose a high-dimensional bias potential method (NN2B) based on two machine learning algorithms: the nearest neighbor density estimator (NNDE) and the artificial neural network (ANN) for the bias potential approximation. The bias potential is constructed iteratively from short biased MD simulations accounting for correlation among CVs. Our method is capable of achieving ergodic sampling and calculating free energy of polypeptides with up to 8-dimensional bias potential.

Wilson-loop instantons

NASA Technical Reports Server (NTRS)

Lee, Kimyeong; Holman, Richard; Kolb, Edward W.

1987-01-01

Wilson-loop symmetry breaking is considered on a space-time of the form M4 x K, where M4 is a four-dimensional space-time and K is an internal space with nontrivial and finite fundamental group. It is shown in a simple model that the different vacua obtained by breaking a non-Abelian gauge group by Wilson loops are separated in the space of gauge potentials by a finite energy barrier. An interpolating gauge configuration is then constructed between these vacua and shown to have minimum energy. Finally some implications of this construction are discussed.

Mass-Related Dynamical Barriers in Triatomic Reactions

NASA Astrophysics Data System (ADS)

Yanao, T.; Koon, W. S.; Marsden, J. E.

2006-06-01

A methodology is given to determine the effect of different mass distributions for triatomic reactions using the geometry of shape space. Atomic masses are incorporated into the non-Euclidean shape space metric after the separation of rotations. Using the equations of motion in this non-Euclidean shape space, an averaged field of velocity-dependent fictitious forces is determined. This force field, as opposed to the force arising from the potential, dominates branching ratios of isomerization dynamics of a triatomic molecule. This methodology may be useful for qualitative prediction of branching ratios in general triatomic reactions.

Observational learning without a model is influenced by the observer's possibility to act: evidence from the Simon task.

PubMed

Iani, Cristina; Rubichi, Sandro; Ferraro, Luca; Nicoletti, Roberto; Gallese, Vittorio

2013-07-01

We assessed whether observational learning in perceptual-motor tasks is affected by the visibility of an action producing perceived environmental effects and by the observer's possibility to act during observation. To this end, we conducted three experiments in which participants were required to observe a spatial compatibility task in which only the effects of computer-generated responses were visible before executing a Simon task. In Experiment 1, we compared the effects of a passively observed practice with either a spatially compatible or incompatible stimulus-response (S-R) association. In Experiment 2, during the observed spatially incompatible practice participants were prevented from potentially acting, either because a plexiglas barrier separated the participant from the response device rendering it out of reach; or because the participant's hands were tied; or the device affording a response was absent. In Experiment 3, the plexiglas presented an opening that could allow the participant to potentially reach and interact with it. As when the practice is physically performed, we found an elimination of the Simon effect following a spatially incompatible observed practice, suggesting that participants learned an incompatible S-R association by observing and transferred this knowledge to the subsequent Simon task. No evidence of transfer of learning was found when, during passive observation, the participant's hands were tied, or a barrier prevented him/her from potentially interacting with the device, or no response device was present. Differently, a transfer-of-learning effect was observed when the barrier presented an opening. These results suggest that learning can derive from the mere observation of action effects, even when an action is not visible, as long as the observer has the potential to act. Copyright © 2013 Elsevier B.V. All rights reserved.

Universal time-dependent dispersion properties for diffusion in a one-dimensional critically tilted potential

NASA Astrophysics Data System (ADS)

Guérin, T.; Dean, D. S.

2017-01-01

We consider the time-dependent dispersion properties of overdamped tracer particles diffusing in a one-dimensional periodic potential under the influence of an additional constant tilting force F . The system is studied in the region where the force is close to the critical value Fc at which the barriers separating neighboring potential wells disappear. We show that, when F crosses the critical value, the shape of the mean-square displacement (MSD) curves is strongly modified. We identify a diffusive regime at intermediate-time scales with an effective diffusion coefficient which is much larger than the late-time diffusion coefficient for F >Fc , whereas for F

The B 1Πu potential energy curve and dissociation energy of 39K2

NASA Astrophysics Data System (ADS)

Heinze, Johannes; Engelke, Friedrich

1988-07-01

The 39K2 B 1Πu potential energy curve has been determined using laser spectroscopic techniques and quantum mechanical calculations. The dissociation energy is 2407.6±0.5 cm-1 (0.2985±0.0001 eV) including a potential barrier of 298±10 cm-1 (0.037±0.0013 eV) found with its maximum at 8.08±0.05 Å (15.3±0.1 bohr). The long-range behavior matches smoothly onto the form predicted from dispersion forces. The dissociation energy of the ground state X 1Σ+g, obtained by a long-range extrapolation of the vibrational separations, is De =4444±10 cm-1 (0.5506±0.0013 eV), in agreement with recent theoretical prediction.

Diffusion chamber system for testing of collagen-based cell migration barriers for separation of ligament enthesis zones in tissue-engineered ACL constructs.

PubMed

Hahner, J; Hoyer, M; Hillig, S; Schulze-Tanzil, G; Meyer, M; Schröpfer, M; Lohan, A; Garbe, L-A; Heinrich, G; Breier, A

2015-01-01

A temporary barrier separating scaffold zones seeded with different cell types prevents faster growing cells from overgrowing co-cultured cells within the same construct. This barrier should allow sufficient nutrient diffusion through the scaffold. The aim of this study was to test the effect of two variants of collagen-based barriers on macromolecule diffusion, viability, and the spreading efficiency of primary ligament cells on embroidered scaffolds. Two collagen barriers, a thread consisting of a twisted film tape and a sponge, were integrated into embroidered poly(lactic-co-caprolactone) and polypropylene scaffolds, which had the dimension of lapine anterior cruciate ligaments (ACL). A diffusion chamber system was designed and established to monitor nutrient diffusion using fluorescein isothiocyanate-labeled dextran of different molecular weights (20, 40, 150, 500 kDa). Vitality of primary lapine ACL cells was tested at days 7 and 14 after seeding using fluorescein diacetate and ethidium bromide staining. Cell spreading on the scaffold surface was measured using histomorphometry. Nuclei staining of the cross-sectioned scaffolds revealed the penetration of ligament cells through both barrier types. The diffusion chamber was suitable to characterize the diffusivity of dextran molecules through embroidered scaffolds with or without integrated collagen barriers. The diffusion coefficients were generally significantly lower in scaffolds with barriers compared to those without barriers. No significant differences between diffusion coefficients of both barrier types were detected. Both barriers were cyto-compatible and prevented most of the ACL cells from crossing the barrier, whereby the collagen thread was easier to handle and allowed a higher rate of cell spreading.

Polymer depletion-driven cluster aggregation and initial phase separation in charged nanosized colloids

NASA Astrophysics Data System (ADS)

Gögelein, Christoph; Nägele, Gerhard; Buitenhuis, Johan; Tuinier, Remco; Dhont, Jan K. G.

2009-05-01

We study polymer depletion-driven cluster aggregation and initial phase separation in aqueous dispersions of charge-stabilized silica spheres, where the ionic strength and polymer (dextran) concentration are systematically varied, using dynamic light scattering and visual observation. Without polymers and for increasing salt and colloid content, the dispersions become increasingly unstable against irreversible cluster formation. By adding nonadsorbing polymers, a depletion-driven attraction is induced, which lowers the stabilizing Coulomb barrier and enhances the cluster growth rate. The initial growth rate increases with increasing polymer concentration and decreases with increasing polymer molar mass. These observations can be quantitatively understood by an irreversible dimer formation theory based on the classical Derjaguin, Landau, Verwey, and Overbeek pair potential, with the depletion attraction modeled by the Asakura-Oosawa-Vrij potential. At low colloid concentration, we observe an exponential cluster growth rate for all polymer concentrations considered, indicating a reaction-limited aggregation mechanism. At sufficiently high polymer and colloid concentrations, and lower salt content, a gas-liquidlike demixing is observed initially. Later on, the system separates into a gel and fluidlike phase. The experimental time-dependent state diagram is compared to the theoretical equilibrium phase diagram obtained from a generalized free-volume theory and is discussed in terms of an initial reversible phase separation process in combination with irreversible aggregation at later times.

Polymer depletion-driven cluster aggregation and initial phase separation in charged nanosized colloids.

PubMed

Gögelein, Christoph; Nägele, Gerhard; Buitenhuis, Johan; Tuinier, Remco; Dhont, Jan K G

2009-05-28

We study polymer depletion-driven cluster aggregation and initial phase separation in aqueous dispersions of charge-stabilized silica spheres, where the ionic strength and polymer (dextran) concentration are systematically varied, using dynamic light scattering and visual observation. Without polymers and for increasing salt and colloid content, the dispersions become increasingly unstable against irreversible cluster formation. By adding nonadsorbing polymers, a depletion-driven attraction is induced, which lowers the stabilizing Coulomb barrier and enhances the cluster growth rate. The initial growth rate increases with increasing polymer concentration and decreases with increasing polymer molar mass. These observations can be quantitatively understood by an irreversible dimer formation theory based on the classical Derjaguin, Landau, Verwey, and Overbeek pair potential, with the depletion attraction modeled by the Asakura-Oosawa-Vrij potential. At low colloid concentration, we observe an exponential cluster growth rate for all polymer concentrations considered, indicating a reaction-limited aggregation mechanism. At sufficiently high polymer and colloid concentrations, and lower salt content, a gas-liquidlike demixing is observed initially. Later on, the system separates into a gel and fluidlike phase. The experimental time-dependent state diagram is compared to the theoretical equilibrium phase diagram obtained from a generalized free-volume theory and is discussed in terms of an initial reversible phase separation process in combination with irreversible aggregation at later times.

Highway planning and operations for the Dallas district: Implementation and evaluation of concurrent flow HOV lanes in Texas. Project summary report 1994-14S, September 1996--August 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skowronek, D.A.; Stoddard, A.M.; Ranft, S.E.

1997-11-01

Limited capital investment for major transportation improvements and growth in metropolitan areas require the most efficient use of the existing transportation system. One means to achieve this is high-occupancy vehicle (HOV) lanes. While an extensive system of permanent HOV lanes is planned for the Dallas-Fort Worth urbanized area, the Texas Department of Transportation (TxDOT) and Dallas Area Rapid Transit (DART) have pursued and continue to pursue short-term or interim HOV lane projects that would enhance public transportation and overall mobility. There are currently 57 km (35.4 mi) of interim HOV lanes operational in the Dallas area, including a barrier-separated contraflowmore » lane on I-30 (East R.L. Thornton Freeway) and buffer-separated concurrent flow HOV lanes on I-35E North (Stemmons Freeway) and I-635 (Lyndon B. Johnson Freeway). The objective of this research is to investigate the operational effectiveness of concurrent flow (buffer-separated) versus contraflow (barrier-separated) HOV lanes. Issues such as person movement, carpool formation, travel time savings, violation rates, and project cost effectiveness are addressed. By understanding the operational performance and issues of both concurrent flow (buffer-separated) HOV lanes and contraflow (barrier-separated) HOV lanes, recommendations can be made on suggested HOV lane policies, including the type of permanent HOV lanes to be implemented in the Dallas area.« less

Floral scent and species divergence in a pair of sexually deceptive orchids.

PubMed

Gervasi, Daniel D L; Selosse, Marc-Andre; Sauve, Mathieu; Francke, Wittko; Vereecken, Nicolas J; Cozzolino, Salvatore; Schiestl, Florian P

2017-08-01

Speciation is typically accompanied by the formation of isolation barriers between lineages. Commonly, reproductive barriers are separated into pre- and post-zygotic mechanisms that can evolve with different speed. In this study, we measured the strength of different reproductive barriers in two closely related, sympatric orchids of the Ophrys insectifera group, namely Ophrys insectifera and Ophrys aymoninii to infer possible mechanisms of speciation. We quantified pre- and post-pollination barriers through observation of pollen flow, by performing artificial inter- and intraspecific crosses and analyzing scent bouquets. Additionally, we investigated differences in mycorrhizal fungi as a potential extrinsic factor of post-zygotic isolation. Our results show that floral isolation mediated by the attraction of different pollinators acts apparently as the sole reproductive barrier between the two orchid species, with later-acting intrinsic barriers seemingly absent. Also, the two orchids share most of their fungal mycorrhizal partners in sympatry, suggesting little or no importance of mycorrhizal symbiosis in reproductive isolation. Key traits underlying floral isolation were two alkenes and wax ester, present predominantly in the floral scent of O. aymoninii . These compounds, when applied to flowers of O. insectifera , triggered attraction and a copulation attempt of the bee pollinator of O. aymoninii and thus led to the (partial) breakdown of floral isolation. Based on our results, we suggest that adaptation to different pollinators, mediated by floral scent, underlies species isolation in this plant group. Pollinator switches may be promoted by low pollination success of individuals in dense patches of plants, an assumption that we also confirmed in our study.

Hydrogen-permeable composite metal membrane and uses thereof

DOEpatents

Edlund, D.J.; Friesen, D.T.

1993-06-08

Various hydrogen production and hydrogen sulfide decomposition processes are disclosed that utilize composite metal membranes that contain an intermetallic diffusion barrier separating a hydrogen-permeable base metal and a hydrogen-permeable coating metal. The barrier is a thermally stable inorganic proton conductor.

Shot Noise in Superconducting Wires Applied with a Periodic Electric Field.

PubMed

Chen, Qiao; Xu, Ning

2018-05-01

We have investigated the differential conductance and shot noise for the system of superconducting nanowires irradiated with a periodic electric field by nonequilibrium Green's functions. The numerical results show that the coupling between the Majorana bound states (MBSs) can be tuned by the periodic electric field. The width of barriers has huge influence on the coupling of MBSs, however, the separation between barriers affect the coupling faintly. The coupling increases with the width of barriers, the number of barriers and the strength of barriers. In addition, super-Poissonian shot noise emerges as the coupling increases.

System and method for producing metallic iron

DOEpatents

Bleifuss, Rodney L; Englund, David J; Iwasaki, Iwao; Fosnacht, Donald R; Brandon, Mark M; True, Bradford G

2013-09-17

A hearth furnace for producing metallic iron material has a furnace housing having a drying/preheat zone, a conversion zone, a fusion zone, and optionally a cooling zone, the conversion zone is between the drying/preheat zone and the fusion zone. A moving hearth is positioned within the furnace housing. A hood or separation barrier within at least a portion of the conversion zone, fusion zone or both separates the fusion zone into an upper region and a lower region with the lower region adjacent the hearth and the upper region adjacent the lower region and spaced from the hearth. An injector introduces a gaseous reductant into the lower region adjacent the hearth. A combustion region may be formed above the hood or separation barrier.

Intraperitoneal adhesions--an ongoing challenge between biomedical engineering and the life sciences.

PubMed

Brochhausen, Christoph; Schmitt, Volker H; Rajab, Taufiek K; Planck, Constanze N E; Krämer, Bernhard; Wallwiener, Markus; Hierlemann, Helmut; Kirkpatrick, C James

2011-07-01

Peritoneal adhesions remain a relevant clinical problem despite the currently available prophylactic barrier materials. So far, the physical separation of traumatized serosa areas using barriers represents the most important clinical strategy for adhesion prevention. However, the optimal material has not yet been found. Further optimization or pharmacological functionalization of these barriers could give an innovative input for peritoneal adhesion prevention. Therefore, a more complete understanding of pathogenesis is required. On the basis of the pathophysiology of adhesion formation the main barriers currently in clinical practice as well as new innovations are discussed in the present review. Physiologically, mesothelial cells play a decisive role in providing a frictionless gliding surface on the serosa. Adhesion formation results from a cascade of events and is regulated by a variety of cellular and humoral factors. The main clinically applied strategy for adhesion prevention is based on the use of liquid or solid adhesion barriers to separate physically any denuded tissue. Both animal and human trials have not yet been able to identify the optimal barrier to prevent adhesion formation in a sustainable way. Therefore, further developments are required for effective prevention of postoperative adhesion formation. To reach this goal the combination of structural modification and pharmacological functionalization of barrier materials should be addressed. Achieving this aim requires the interaction between basic research, materials science and clinical expertise. Copyright © 2011 Wiley Periodicals, Inc.

FAST TRACK COMMUNICATION: Graphene based quantum dots

NASA Astrophysics Data System (ADS)

Zhang, H. G.; Hu, H.; Pan, Y.; Mao, J. H.; Gao, M.; Guo, H. M.; Du, S. X.; Greber, T.; Gao, H.-J.

2010-08-01

Laterally localized electronic states are identified on a single layer of graphene on ruthenium by low temperature scanning tunneling spectroscopy (STS). The individual states are separated by 3 nm and comprise regions of about 90 carbon atoms. This constitutes a highly regular quantum dot-array with molecular precision. It is evidenced by quantum well resonances (QWRs) with energies that relate to the corrugation of the graphene layer. The dI/dV conductance spectra are modeled by a layer height dependent potential-well with a delta-function potential that describes the barrier for electron penetration into graphene. The resulting QWRs are strongest and lowest in energy on the isolated 'hill' regions with a diameter of 2 nm, where the graphene is decoupled from the surface.

Determination of phthalate ester plasticizers in the aquatic environment using hollow fibre supported liquid membranes

NASA Astrophysics Data System (ADS)

Mtibe, A.; Msagati, Titus A. M.; Mishra, Ajay K.; Mamba, Bhekie B.

Phthalates are known to be carcinogenic, teratogenic as well as endocrine disruptors. The potential risk to human and animals health generated from them has drawn great attention all over the world. Hollow fibre supported liquid membrane (HFSLM) online with high pressure liquid chromatography (HPLC) was used to determine benzyl butyl phthalate (BBP), dibutyl phthalate (DBP) and Diethylhexyl phthalate (DEHP) in wastewater. Toluene, di-n-hexyl ether and undecane were used as liquid barriers separating both donor (sample) and acceptor phase. Toluene performed much better than undecane and was used in sample preparation. The presence of toluene showed the potential for the enrichment and removal of phthalates to the concentrations ranges from 0 to 1.7 mg L-1.

Graphene based quantum dots.

PubMed

Zhang, H G; Hu, H; Pan, Y; Mao, J H; Gao, M; Guo, H M; Du, S X; Greber, T; Gao, H-J

2010-08-04

Laterally localized electronic states are identified on a single layer of graphene on ruthenium by low temperature scanning tunneling spectroscopy (STS). The individual states are separated by 3 nm and comprise regions of about 90 carbon atoms. This constitutes a highly regular quantum dot-array with molecular precision. It is evidenced by quantum well resonances (QWRs) with energies that relate to the corrugation of the graphene layer. The dI/dV conductance spectra are modeled by a layer height dependent potential-well with a delta-function potential that describes the barrier for electron penetration into graphene. The resulting QWRs are strongest and lowest in energy on the isolated 'hill' regions with a diameter of 2 nm, where the graphene is decoupled from the surface.

MASH test 3-11 of the TxDOT portable type 2 PCTB with sign support assembly

DOT National Transportation Integrated Search

2010-01-01

Portable concrete traffic barriers (PCTBs) are commonly used in work zones or in temporary median : barrier applications. PCTBs are needed for separation and channelization of vehicle movement and for : worker protection. Signage is often necessary w...

Effect of confinement potential on exciton diamagnetism in the perspective of constituent carriers in a Quantum Well

NASA Astrophysics Data System (ADS)

Vignesh, G.; Nithiananthi, P.

2018-03-01

Diamagnetic susceptibility of excitons is investigated in the perspective of the electron and hole separation along the lateral (ρ) and normal direction (z) of a GaAs/AlxGa1-xAs quantum well. Using a variational technique, the spatial extensions of these carriers has been observed. The coulomb interaction of the carriers is investigated by subjecting the carriers to three confinement potentials, Square (SQW), Parabolic (PQW) and Triangular Quantum Wells (TQW). The stability of the exciton has been estimated by observing the diamagnetic susceptibility. The hole is very sensitive to confinement potential and has tremendous variations in spatial extension. Among the three confinements, TQW offers more localization and high stability to excitons. The anisotropy of band parameters and the dielectric constants of the well and barrier materials are taken into consideration.

Universal time-dependent dispersion properties for diffusion in a one-dimensional critically tilted potential.

PubMed

Guérin, T; Dean, D S

2017-01-01

We consider the time-dependent dispersion properties of overdamped tracer particles diffusing in a one-dimensional periodic potential under the influence of an additional constant tilting force F. The system is studied in the region where the force is close to the critical value F_{c} at which the barriers separating neighboring potential wells disappear. We show that, when F crosses the critical value, the shape of the mean-square displacement (MSD) curves is strongly modified. We identify a diffusive regime at intermediate-time scales with an effective diffusion coefficient which is much larger than the late-time diffusion coefficient for F>F_{c}, whereas for F

Multinucleon transfer in O,1816,19F+208Pb reactions at energies near the fusion barrier

NASA Astrophysics Data System (ADS)

Rafferty, D. C.; Dasgupta, M.; Hinde, D. J.; Simenel, C.; Simpson, E. C.; Williams, E.; Carter, I. P.; Cook, K. J.; Luong, D. H.; McNeil, S. D.; Ramachandran, K.; Vo-Phuoc, K.; Wakhle, A.

2016-08-01

Background: Nuclear reactions are complex, involving collisions between composite systems where many-body dynamics determines outcomes. Successful models have been developed to explain particular reaction outcomes in distinct energy and mass regimes, but a unifying picture remains elusive. The irreversible transfer of kinetic energy from the relative motion of the collision partners to their internal states, as is known to occur in deep inelastic collisions, has yet to be successfully incorporated explicitly into fully quantal reaction models. The influence of these processes on fusion is not yet quantitatively understood. Purpose: To investigate the population of high excitation energies in transfer reactions at sub-barrier energies, which are precursors to deep inelastic processes, and their dependence on the internuclear separation. Methods: Transfer probabilities and excitation energy spectra have been measured in collisions of O,1816,19F+208Pb , at various energies below and around the fusion barrier, by detecting the backscattered projectile-like fragments in a Δ E -E telescope. Results: The relative yields of different transfer outcomes are strongly driven by Q values, but change with the internuclear separation. In 16O+208Pb , single nucleon transfer dominates, with a strong contribution from -2 p transfer close to the Coulomb barrier, though this channel becomes less significant in relation to the -2 p 2 n transfer channel at larger separations. For 18O+208Pb , the -2 p 2 n channel is the dominant charge transfer mode at all separations. In the reactions with 19F,-3 p 2 n transfer is significant close to the barrier, but falls off rapidly with energy. Multinucleon transfer processes are shown to lead to high excitation energies (up to ˜15 MeV), which is distinct from single nucleon transfer modes which predominantly populate states at low excitation energy. Conclusions: Kinetic energy is transferred into internal excitations following transfer, with this energy being distributed over a larger number of states and to higher excitations with increasing numbers of transferred nucleons. Multinucleon transfer is thus a mechanism by which energy can be dissipated from the relative motion before reaching the fusion barrier radius.

Highway planning and operations for the Dallas district: Implementation and evaluation of concurrent flow HOV lanes in Texas. Research report, September 1996--August 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skowronek, D.A.; Stoddard, A.M.; Ranft, S.E.

1997-11-01

Limited capital investment for major transportation improvements and growth in metropolitan areas require the most efficient use of the existing transportation system. One means to achieve this is high-occupancy vehicle (HOV) lanes. While an extensive system of permanent HOV lanes is planned for the Dallas-Fort Worth urbanized area, the Texas Department of Transportation (TxDOT) and Dallas Area Rapid Transit (DART) have pursued and continue short-term or interim HOV lane projects that would enhance public transportation and overall mobility. There are currently 57 km (35.4 mi) of interim HOV lanes operational in the Dallas area, including a barrier-separated contraflow lane onmore » I-30 (East R.L. Thornton Freeway) and buffer-separated concurrent flow HOV lanes on I-35E North (Stemmons Freeway) and I-635 (Lyndon B. Johnson Freeway). The objective of this research is to investigate the operational effectiveness of the new concurrent flow HOV lanes in the Dallas area, as well as to assess the effectiveness of concurrent flow (buffer-separated) versus contraflow (barrier-separated) HOV lanes. Issues such as person movement, carpool formation, travel time savings, violation rates, and project cost effectiveness are addressed. By understanding the operational performance and issues of both concurrent flow (buffer-separated) HOV lanes and contraflow (barrier-separated) HOV lanes, recommendations can be made on suggested HOV lane polices, including the type of permanent HOV lanes to be implemented in the Dallas area.« less

Homophobic and Transphobic Bullying: Barriers and Supports to School Intervention

ERIC Educational Resources Information Center

O'Donoghue, Kate; Guerin, Suzanne

2017-01-01

This study explores the perceived barriers and supports identified by school staff in tackling homophobic and transphobic bullying, using Bronfenbrenner's ecological model as a framework. Semi-structured interviews were conducted with participants from five separate second-level/high schools (two designated disadvantaged schools, and three…

Asian American Educational Goals: Racial Barriers and Cultural Factors

ERIC Educational Resources Information Center

Chen, Yung-Lung; Fouad, Nadya A.

2013-01-01

Educational success among Asian American students has often been misunderstood as an occupational development separate from any experience of racism. However, several theorists have suggested that racial barriers in occupational mobility correlate with educational pursuits. Therefore, this research aims to examine the direct effect of perceived…

Quiescent double barrier regime in the DIII-D tokamak.

PubMed

Greenfield, C M; Burrell, K H; DeBoo, J C; Doyle, E J; Stallard, B W; Synakowski, E J; Fenzi, C; Gohil, P; Groebner, R J; Lao, L L; Makowski, M A; McKee, G R; Moyer, R A; Rettig, C L; Rhodes, T L; Pinsker, R I; Staebler, G M; West, W P

2001-05-14

A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate.

Horizontal insulating barriers as a way to protect groundwater

NASA Astrophysics Data System (ADS)

Cicha-Szot, Renata; Labus, Krzysztof; Falkowicz, Sławomir; Madetko, Norbert

2018-06-01

Trenchless Technology of Forming Horizontal Insulating Barriers (TFHB) can be considered a method of groundwater protection against inflow of pollutants. In TFHB technology, the working fluid (sodium silicate solution) and the gelling agent (CO2) are injected separately, using one tool, to different zones of the aquifer profile. Carbon dioxide injected into the saturation zone rises due to buoyancy forces and reaches the silicate which was injected at the water table level. This initiates the process of silicate gelation, resulting in the formation of an insulating barrier. For technological purposes, the gelation time must be controlled, and the resulting gel must have certain mechanical properties. In order to apply THFB in real conditions it was necessary to identify important technological and technical parameters, as well as to define interactions between the injected fluid and the aquifer rocks. Geochemical modelling (equilibrium, reaction path and reactive transport) was used to identify potential geochemical effects of the application of TFHB in sandy aquifers. Certain petrophysical parameters and mineralogical assemblages of aquifers were addressed, taking into account both low and strongly mineralized groundwater. The simulations revealed that TFHB does not have a negative impact on the chemistry of rock-water systems described in this work.

Directional mass transport in an atmospheric pressure surface barrier discharge.

PubMed

Dickenson, A; Morabit, Y; Hasan, M I; Walsh, J L

2017-10-25

In an atmospheric pressure surface barrier discharge the inherent physical separation between the plasma generation region and downstream point of application reduces the flux of reactive chemical species reaching the sample, potentially limiting application efficacy. This contribution explores the impact of manipulating the phase angle of the applied voltage to exert a level of control over the electrohydrodynamic forces generated by the plasma. As these forces produce a convective flow which is the primary mechanism of species transport, the technique facilitates the targeted delivery of reactive species to a downstream point without compromising the underpinning species generation mechanisms. Particle Imaging Velocimetry measurements are used to demonstrate that a phase shift between sinusoidal voltages applied to adjacent electrodes in a surface barrier discharge results in a significant deviation in the direction of the plasma induced gas flow. Using a two-dimensional numerical air plasma model, it is shown that the phase shift impacts the spatial distribution of the deposited charge on the dielectric surface between the adjacent electrodes. The modified surface charge distribution reduces the propagation length of the discharge ignited on the lagging electrode, causing an imbalance in the generated forces and consequently a variation in the direction of the resulting gas flow.

Social isolation and perceived barriers to establishing social networks among Latina immigrants.

PubMed

Hurtado-de-Mendoza, Alejandra; Gonzales, Felisa A; Serrano, Adriana; Kaltman, Stacey

2014-03-01

Research has identified numerous mechanisms through which perceived social isolation and lack of social support negatively impact health. Little research attention has been dedicated to factors that influence the development of social networks, which have the potential to decrease perceptions of social isolation and provide social support. There is mixed evidence concerning the availability of supportive social networks for Latinos in the US. This study explores trauma-exposed Latina immigrants' experiences of social isolation in the US and its perceived causes. Twenty-eight Latina immigrant women participated in an interview about traumatic experiences. Informal help seeking and the availability of friendships in the US were also queried. Frequent comparisons between experiences in their home countries and in the US shaped the emerging themes of social isolation and lack of social support. Women reported feeling lonely, isolated, closed-in, and less free in the US due to family separation and various obstacles to developing and maintaining relationships. Socioeconomic, environmental, and psychosocial barriers were offered as explanations for their limited social networks in the US. Understanding experiences of social isolation as well as barriers to forging social networks can help inform the development of social support interventions that can contribute to improved health among Latinos.

The impact of aging on epithelial barriers.

PubMed

Parrish, Alan R

2017-10-02

The epithelium has many critical roles in homeostasis, including an essential responsibility in establishing tissue barriers. In addition to the fundamental role in separating internal from external environment, epithelial barriers maintain nutrient, fluid, electrolyte and metabolic waste balance in multiple organs. While, by definition, barrier function is conserved, the structure of the epithelium varies across organs. For example, the skin barrier is a squamous layer of cells with distinct structural features, while the lung barrier is composed of a very thin single cell to minimize diffusion space. With the increased focus on age-dependent alterations in organ structure and function, there is an emerging interest in the impact of age on epithelial barriers. This review will focus on the impact of aging on the epithelial barrier of several organs, including the skin, lung, gastrointestinal tract and the kidney, at a structural and functional level.

Numerical investigation of dielectric barrier discharges

NASA Astrophysics Data System (ADS)

Li, Jing

1997-12-01

A dielectric barrier discharge (DBD) is a transient discharge occurring between two electrodes in coaxial or planar arrangements separated by one or two layers of dielectric material. The charge accumulated on the dielectric barrier generates a field in a direction opposite to the applied field. The discharge is quenched before an arc is formed. It is one of the few non-thermal discharges that operates at atmospheric pressure and has the potential for use in pollution control. In this work, a numerical model of the dielectric barrier discharge is developed, along with the numerical approach. Adaptive grids based on the charge distribution is used. A self-consistent method is used to solve for the electric field and charge densities. The Successive Overrelaxation (SOR) method in a non-uniform grid spacing is used to solve the Poisson's equation in the cylindrically-symmetric coordinate. The Flux Corrected Transport (FCT) method is modified to solve the continuity equations in the non-uniform grid spacing. Parametric studies of dielectric barrier discharges are conducted. General characteristics of dielectric barrier discharges in both anode-directed and cathode-directed streamer are studied. Effects of the dielectric capacitance, the applied field, the resistance in external circuit and the type of gases (O2, air, N2) are investigated. We conclude that the SOR method in an adaptive grid spacing for the solution of the Poisson's equation in the cylindrically-symmetric coordinate is convergent and effective. The dielectric capacitance has little effect on the g-factor of radical production, but it determines the strength of the dielectric barrier discharge. The applied field and the type of gases used have a significant role on the current peak, current pulse duration and radical generation efficiency, discharge strength, and microstreamer radius, whereas the external series resistance has very little effect on the streamer properties. The results are helpful in further understanding the ozone generation and pollution control process in a dielectric barrier discharge.

Problems in characterizing barrier performance

NASA Technical Reports Server (NTRS)

Jordan, Harry F.

1988-01-01

The barrier is a synchronization construct which is useful in separating a parallel program into parallel sections which are executed in sequence. The completion of a barrier requires cooperation among all executing processes. This requirement not only introduces the wait for the slowest process delay which is inherent in the definition of the synchronization, but also has implications for the efficient implementation and measurement of barrier performance in different systems. Types of barrier implementation and their relationship to different multiprocessor environments are described. Then the problem of measuring the performance of barrier implementations on specific machine architecture is discussed. The fact that the barrier synchronization requires the cooperation of all processes makes the problem of performance measurement similarly global. Making non-intrusive measurements of sufficient accuracy can be tricky on systems offering only rudimentary measurement tools.

A tunable acoustic barrier based on periodic arrays of subwavelength slits

NASA Astrophysics Data System (ADS)

Rubio, Constanza; Uris, Antonio; Candelas, Pilar; Belmar, Francisco; Gomez-Lozano, Vicente

2015-05-01

The most usual method to reduce undesirable enviromental noise levels during its transmission is the use of acoustic barriers. A novel type of acoustic barrier based on sound transmission through subwavelength slits is presented. This system consists of two rows of periodic repetition of vertical rigid pickets separated by a slit of subwavelength width and with a misalignment between them. Here, both the experimental and the numerical analyses are presented. The acoustic barrier proposed can be easily built and is frequency tunable. The results demonstrated that the proposed barrier can be tuned to mitigate a band noise without excesive barrier thickness. The use of this system as an environmental acoustic barrier has certain advantages with regard to the ones currently used both from the constructive and the acoustical point of view.

Method of recognizing the high-speed railway noise barriers based on the distance image

NASA Astrophysics Data System (ADS)

Ma, Le; Shao, Shuangyun; Feng, Qibo; Liu, Bingqian; Kim, Chol Ryong

2016-10-01

The damage or lack of the noise barriers is one of the important hidden troubles endangering the safety of high-speed railway. In order to obtain the vibration information of the noise barriers, the online detection systems based on laser vision were proposed. The systems capture images of the laser stripe on the noise barriers and export data files containing distance information between the detection systems on the train and the noise barriers. The vibration status or damage of the noise barriers can be estimated depending on the distance information. In this paper, we focused on the method of separating the area of noise barrier from the background automatically. The test results showed that the proposed method is in good efficiency and accuracy.

One-Dimensional Nature of InAs/InP Quantum Dashes Revealed by Scanning Tunneling Spectroscopy.

PubMed

Papatryfonos, Konstantinos; Rodary, Guillemin; David, Christophe; Lelarge, François; Ramdane, Abderrahim; Girard, Jean-Christophe

2015-07-08

We report on low-temperature cross-sectional scanning tunneling microscopy and spectroscopy on InAs(P)/InGaAsP/InP(001) quantum dashes, embedded in a diode-laser structure. The laser active region consists of nine InAs(P) quantum dash layers separated by the InGaAsP quaternary alloy barriers. The effect of the p-i-n junction built-in potential on the band structure has been evidenced and quantified on large-scale tunneling spectroscopic measurements across the whole active region. By comparing the tunneling current onset channels, a consistent energy shift has been measured in successive quantum dash or barrier layers, either for the ground state energy of similar-sized quantum dashes or for the conduction band edge of the barriers, corresponding to the band-bending slope. The extracted values are in good quantitative agreement with the theoretical band structure calculations, demonstrating the high sensitivity of this spectroscopic measurement to probe the electronic structure of individual nanostructures, relative to local potential variations. Furthermore, by taking advantage of the potential gradient, we compared the local density of states over successive quantum dash layers. We observed that it does not vanish while increasing energy, for any of the investigated quantum dashes, in contrast to what would be expected for discrete level zero-dimensional (0D) structures. In order to acquire further proof and fully address the open question concerning the quantum dash dimensionality nature, we focused on individual quantum dashes obtaining high-energy-resolution measurements. The study of the local density of states clearly indicates a 1D quantum-wirelike nature for these nanostructures whose electronic squared wave functions were subsequently imaged by differential conductivity mapping.

"Body property": challenging the ethical barriers in organ transplantation to protect individual autonomy.

PubMed

Dunham, Charles C

2008-01-01

One of two articles related to the current organ shortage, this article advocates the need for legislation to recognize organs and tissues separated from the body as a distinct category of personal property. After addressing the legislative history of organ procurement and psychological barriers to donor consent, the article examines the importance of separating the lifetime rights of ownership in our own bodies from postmortem rights. Ultimately, the author proposes a futures market approach to this problem in which individuals before death, or surviving family members after death, are permitted sell the decedent's organs in a private contract.

Sustainable Applications of Magnetic Nano-catalysts and Graphitic Carbon Nitrides (presentation)

EPA Science Inventory

Homogeneous catalysts, known for chemo-, regio- and enantioselectivity, have better contact with the reactants but the catalyst separation creates barriers. Heterogeneous systems enable better separation although at the cost of reduction in the availability of active sites. Becau...

Heat dissipation in controlled environment enclosures through the application of water screens

NASA Technical Reports Server (NTRS)

Warrington, I. J.; Halligan, E. A.; Ruby, L. C.; Mcnaughton, K. G.

1994-01-01

The use of plate glass-water thermal barriers in controlled environment facilities effectively reduces the thermal load within the plant growth chamber. This allows high PPFs to be provided for plant growth and development studies, adequate simulation of daily light integrals, and simulation of peak PPF's. Further, substantial amounts of incandescent lamp supplementation can be used to achieve simulation of daylight R:FR ratios which are needed to ensure adequate stem development in some species. While the focus in this paper is on the use of entire thermal barriers which separate the lighting enclosure from the plant growth chamber, the same principles apply to the use of water jackets for cooling individual lamps (such as can occur with xenon-arc lamps). In this instance, the barrier separating the lamps from the plant chamber can be much simpler (e.g., plexiglass) as the main function of the barrier is to separate the air ventilation of the lamp enclosure from the air system within the plant growth chamber. The main advantage of water as a thermal barrier is the negligible absorption of radiation in the photosynthetically-active and near infrared wavebands. Consequently, plate glass-water barriers typically allow transmission of approximately 90% of radiation in these regions. While ventilated double and triple glazing systems appear to be attractive alternative to water barriers from an operating standpoint, their significant absorption in the biologically-important wavebands (7 - 12%) with each glass layer and longer-wave cut-offs (typically 2500 - 4000 nm) makes them a much less attractive alternative. The data presented here demonstrate clearly that measurement of PPF alone is not an adequate representation of the radiation environment being used in a controlled environment study. The amounts and proportions of long-wave and short-wave radiation in a plant growth chamber are dependent on lamp type, lamp combination, presence of a thermal barrier, the type of thermal barrier between the lamps and the plant growing area and the overall construction and design of the chamber. It is important, therefore, in reporting results of controlled environment studies, to adequately describe both the details of the lighting system used and the characteristics of the radiation produced by that system, so results of different studies can be adequately evaluated and compared.

Skyrme forces and the fusion-fission dynamics of the 132Sn+64Ni→196Pt* reaction

NASA Astrophysics Data System (ADS)

Jain, Deepika; Kumar, Raj; Sharma, Manoj K.; Gupta, Raj K.

2012-02-01

The dependence of the fusion-fission process on Skyrme forces is studied by using the dynamical cluster-decay model (DCM) and the ℓ-summed extended-Wong model in the 132Sn+64Ni→196Pt* reaction, where the nuclear proximity potential is obtained by using the semiclassical extended Thomas-Fermi (ETF) approach in the Skyrme energy density formalism (SEDF) under the frozen density approximation. The DCM gives an excellent fit to the measured fusion evaporation residue (ER) and the fission cross sections below and above barrier energies, with ER data needing “barrier lowering” at below-barrier energies for each Skyrme force (an in-built property of the DCM). The fission cross sections show a contribution of quasifission (qf) at the above-barrier two or three highest energies, depending on the Skyrme force. Calculations are illustrated for three Skyrme forces, GSkI, SSk, and SIII. Another interesting result is that there is a change of fission mass distribution from a predominantly asymmetric one to a symmetric one with a decrease in the N/Z ratio of the compound nucleus, independent of the choice of nuclear interaction potential, which gives an opportunity to address the isospin effects in the Pt* nucleus. Within the ℓ-summed extended-Wong model we find that the GSkI and SSk forces fit the total fusion cross-section data exactly, whereas the SIII force needs “barrier modification” in order to fit the data at below-barrier energies. This happens because the isospin and neutron-proton asymmetry nature of GSkI and SSk forces is different from that of the SIII force, and because the center-of-mass energy Ec.m. dependence of the barrier height for the SIII force and that of Blocki [Ann. Phys. (NY)10.1016/0003-4916(77)90249-4 105, 427 (1977)] differs strongly (by a constant amount of ˜7 MeV) from those for GSKI and SSk forces. Note that, because of the associated preformation factor with each fragment, the DCM has the advantage of treating various decay processes separately, whereas the Wong model describes only the total fusion cross section, a sum of cross sections due to all contributing processes.

Lateral tunneling through voltage-controlled barriers

NASA Technical Reports Server (NTRS)

Manion, S. J.; Bell, L. D.; Kaiser, W. J.; Maker, P. D.; Muller, R. E.

1991-01-01

The paper reports on a detailed experimental investigation of lateral tunneling between electrodes of a two-dimensional electron gas separated by the voltage-controlled barrier of a nanometer Schottky gate. The experimental data are modeled using the WKB method to calculate the tunneling probability of electrons through a barrier whose shape is determined from a solution of the two-dimensional Poisson equation. This model is in excellent agreement with the experimental data over a two order of magnitude range of current.

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants.

PubMed

Simal-Gándara, J; Sarria-Vidal, M; Koorevaar, A; Rijk, R

2000-08-01

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick oriented PP) into the food stimulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.

Intercalation and de-intercalation pathway of proflavine through the minor and major grooves of DNA: roles of water and entropy.

PubMed

Sasikala, Wilbee D; Mukherjee, Arnab

2013-05-07

DNA intercalation is a clinically relevant biophysical process due to its potential to inhibit the growth and survival of tumor cells and microbes through the arrest of the transcription and replication processes. Extensive kinetic and thermodynamic studies have followed since the discovery of the intercalative binding mode. However, the molecular mechanism and the origin of the thermodynamic and kinetic profile of the process are still not clear. Here we have constructed the free energy landscape of intercalation, de-intercalation and dissociation from both the major and minor grooves of DNA using extensive all-atom metadynamics simulations, capturing both the free energy barriers and stability in close agreement with fluorescence kinetic experiments. In the intercalated state, an alternate orientation of proflavine is found with an almost equal stability compared to the crystal orientation, however, separated by a 5.0 kcal mol(-1) barrier that decreases as the drug approaches the groove edges. This study provides a comprehensive picture in comparison with experiments, which indicates that the intercalation and de-intercalation of proflavine happen through the major groove side, although the effective intercalation barrier increases because the path of intercalation goes through the stable (abortive) minor groove bound state, making the process a millisecond long one in excellent agreement with the experiments. The molecular origin of the higher barrier for the intercalation from the minor groove side is attributed to the desolvation energy of DNA and the loss of entropy, while the barrier from the major groove, in the absence of desolvation energy, is primarily entropic.

Structure, internal mobility, and spectrum of the ammonia dimer: Calculation of the vibration-rotation-tunneling states

NASA Astrophysics Data System (ADS)

Olthof, E. H. T.; van der Avoird, A.; Wormer, P. E. S.

1994-11-01

We have obtained a potential for (NH3)2 by calculating the six-dimensional vibra- tion-rotation-tunneling (VRT) states from a model potential with some variable parameters, and adjusting some calculated transition frequencies to the observed far-infrared spectrum. The equilibrium geometry is strongly bent away from a linear hydrogen bonded structure. Equivalent minima with the proton donor and acceptor interchanged are separated by a barrier of only 7 cm-1. The barriers to rotation of the monomers about their C3 axes are much higher. The VRT levels from this potential agree to about 0.25 cm-1 with all far-infrared frequencies of (NH3)2 observed for K=0, ‖K‖=1, and ‖K‖=2 and for all the symmetry species: Ai=ortho-ortho, Ei=para-para, and G=ortho-para. Moreover, the dipole moments and the nuclear quadrupole splittings agree well with the values that are observed for the G states. The potential has been explicitly transformed to the center-of-mass coordinates of (ND3)2 and used to study the effects of the deuteration on the VRT states. The observed decrease of the dipole moment and the (small) changes in the nuclear quadrupole splittings are well reproduced. It follows from our calculations that the ammonia dimer is highly nonrigid and that vibrational averaging effects are essential. Seemingly contradictory effects of this averaging on its properties are the consequence of the different hindered rotor behavior of ortho and para monomers.

Understanding the physics and chemistry of reaction mechanisms from atomic contributions: a reaction force perspective.

PubMed

Vöhringer-Martinez, Esteban; Toro-Labbé, Alejandro

2012-07-12

Studying chemical reactions involves the knowledge of the reaction mechanism. Despite activation barriers describing the kinetics or reaction energies reflecting thermodynamic aspects, identifying the underlying physics and chemistry along the reaction path contributes essentially to the overall understanding of reaction mechanisms, especially for catalysis. In the past years the reaction force has evolved as a valuable tool to discern between structural changes and electrons' rearrangement in chemical reactions. It provides a framework to analyze chemical reactions and additionally a rational partition of activation and reaction energies. Here, we propose to separate these energies further in atomic contributions, which will shed new insights in the underlying reaction mechanism. As first case studies we analyze two intramolecular proton transfer reactions. Despite the atom based separation of activation barriers and reaction energies, we also assign the participation of each atom in structural changes or electrons' rearrangement along the intrinsic reaction coordinate. These participations allow us to identify the role of each atom in the two reactions and therfore the underlying chemistry. The knowledge of the reaction chemistry immediately leads us to suggest replacements with other atom types that would facilitate certain processes in the reaction. The characterization of the contribution of each atom to the reaction energetics, additionally, identifies the reactive center of a molecular system that unites the main atoms contributing to the potential energy change along the reaction path.

Resonant tunneling across a ferroelectric domain wall

NASA Astrophysics Data System (ADS)

Li, M.; Tao, L. L.; Velev, J. P.; Tsymbal, E. Y.

2018-04-01

Motivated by recent experimental observations, we explore electron transport properties of a ferroelectric tunnel junction (FTJ) with an embedded head-to-head ferroelectric domain wall, using first-principles density-functional theory calculations. We consider a FTJ with L a0.5S r0.5Mn O3 electrodes separated by a BaTi O3 barrier layer and show that an in-plane charged domain wall in the ferroelectric BaTi O3 can be induced by polar interfaces. The resulting V -shaped electrostatic potential profile across the BaTi O3 layer creates a quantum well and leads to the formation of a two-dimensional electron gas, which stabilizes the domain wall. The confined electronic states in the barrier are responsible for resonant tunneling as is evident from our quantum-transport calculations. We find that the resonant tunneling is an orbital selective process, which leads to sharp spikes in the momentum- and energy-resolved transmission spectra. Our results indicate that domain walls embedded in FTJs can be used to control the electron transport.

Compound earthquakes on a bimaterial interface and implications for rupture mechanics

NASA Astrophysics Data System (ADS)

Wang, E.; Rubin, A. M.

2012-12-01

Earthquake ruptures on the San Andreas are affected by the material contrast across the fault. Previous observations of microearthquakes in the northern creeping section have found strong signals of asymmetry in both rupture directivity (preferential propagation to the SE; Wang & Rubin, 2011), and aftershock asymmetry (many more to the NW, on timescales from 10 to 1000 s; Rubin & Gillard, 2000; Rubin, 2002). To understand the aftershock asymmetry, Rubin & Ampuero [2007] simulated slip-weakening ruptures on a bimaterial interface and observed differences in the timescales for the two edges to experience their peak stress after being slowed by barriers. While the barrier on the "positive" side (SE in the case of the San Andreas fault) reached the peak stress almost instantaneously, the "negative" side (NW) has to wait for the arrival of the P-wave stopping phase from the opposite end. For a 100 m main event the delay between the two potential ruptures is 20 ms, which may be long enough for the secondary rupture to be observed as a distinct subevent. A second possible source of subevent asymmetry is that when slowed by barriers, a significant tensile stress pulse propagates in the positive but not the negative direction. The events in the region where previous asymmetries were found have high spatial density and similar focal mechanisms, which makes it possible to use an Empirical Green's Function's method to do a comprehensive search. About 200 candidate compound events were identified in an 8300-event catalog from 1984 to 2009. Most delays between the two subevents cluster around the shear-wave transit time over the subevent separation, although with considerable scatter. For subevents separated by 0.7 to 2 estimated mainshock radii (the same spatial separation found by Rubin [2002] to maximize the longer-term aftershock asymmetry), about twice as many second events occurred on the SE (positive) side of the first, and the origin time delays also tend to be shorter for SE aftershocks. One interpretation is that these subevents represent the events "missing" from the aftershock population because they became part of the mainshock.

Increasing the applicability of density functional theory. IV. Consequences of ionization-potential improved exchange-correlation potentials.

PubMed

Verma, Prakash; Bartlett, Rodney J

2014-05-14

This paper's objective is to create a "consistent" mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchange-correlation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dft does. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a "consistent" KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach.

System and method for producing metallic iron

DOEpatents

Bleifuss, Rodney L [Grand Rapids, MN; Englund, David J [Bovey, MN; Iwasaki, Iwao [Grand Rapids, MN; Fosnacht, Donald R [Hermantown, MN; Brandon, Mark M [Charlotte, NC; True, Bradford G [Charlotte, NC

2012-01-17

A hearth furnace 10 for producing metallic iron material has a furnace housing 11 having a drying/preheat zone 12, a conversion zone 13, a fusion zone 14, and optionally a cooling zone 15, the conversion zone 13 is between the drying/preheat zone 12 and the fusion zone 14. A moving hearth 20 is positioned within the furnace housing 11. A hood or separation barrier 30 within at least a portion of the conversion zone 13, fusion zone 14 or both separates the fusion zone 14 into an upper region and a lower region with the lower region adjacent the hearth 20 and the upper region adjacent the lower region and spaced from the hearth 20. An injector introduces a gaseous reductant into the lower region adjacent the hearth 20. A combustion region may be formed above the hood or separation barrier.

New interpretation of matter-antimatter asymmetry based on branes and possible observational consequences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai Ronggen; Li Tong; Li Xueqian

2007-11-15

Motivated by the alpha-magnetic-spectrometer (AMS) project, we assume that after the big bang or inflation epoch, antimatter was repelled onto one brane which is separated from our brane where all the observational matter resides. It is suggested that CP may be spontaneously broken, the two branes would correspond to ground states for matter and antimatter, respectively. Generally a complex scalar field which is responsible for the spontaneous CP violation, exists in the space between the branes. The matter and antimatter on the two branes attract each other via gravitational force, meanwhile the scalar field causes a Casimir effect to resultmore » in a repulsive force against the gravitation. We find that the Casimir force is much stronger than the gravitational force, as long as the separation of the two branes is small. Thus at early epoch after the big bang, the two branes were closer and then have been separated by the Casimir repulsive force from each other. The trend will continue until the separation is sufficiently large and then the gravitational force observed in our four-space would obviously deviate from the Newton's universal gravitational law. We suppose that there is a potential barrier at the brane boundary, which is similar to the surface tension for a water membrane. The barrier prevents the matter (antimatter) particles from entering the space between two branes and jump from one brane to another. However, by the quantum tunneling, a sizable antimatter flux may come to our brane and be observed by the AMS. In this work by considering two possible models, i.e. the naive flat space-time and Randall-Sundrum models, and using the observational data on the visible matter in our universe as inputs, we derive the antimatter flux which comes to our detector in the nonrelativistic approximation and make a rough numerical estimate of possible numbers of antihelium at AMS.« less

Predicting the continuum between corridors and barriers to animal movements using Step Selection Functions and Randomized Shortest Paths.

PubMed

Panzacchi, Manuela; Van Moorter, Bram; Strand, Olav; Saerens, Marco; Kivimäki, Ilkka; St Clair, Colleen C; Herfindal, Ivar; Boitani, Luigi

2016-01-01

The loss, fragmentation and degradation of habitat everywhere on Earth prompts increasing attention to identifying landscape features that support animal movement (corridors) or impedes it (barriers). Most algorithms used to predict corridors assume that animals move through preferred habitat either optimally (e.g. least cost path) or as random walkers (e.g. current models), but neither extreme is realistic. We propose that corridors and barriers are two sides of the same coin and that animals experience landscapes as spatiotemporally dynamic corridor-barrier continua connecting (separating) functional areas where individuals fulfil specific ecological processes. Based on this conceptual framework, we propose a novel methodological approach that uses high-resolution individual-based movement data to predict corridor-barrier continua with increased realism. Our approach consists of two innovations. First, we use step selection functions (SSF) to predict friction maps quantifying corridor-barrier continua for tactical steps between consecutive locations. Secondly, we introduce to movement ecology the randomized shortest path algorithm (RSP) which operates on friction maps to predict the corridor-barrier continuum for strategic movements between functional areas. By modulating the parameter Ѳ, which controls the trade-off between exploration and optimal exploitation of the environment, RSP bridges the gap between algorithms assuming optimal movements (when Ѳ approaches infinity, RSP is equivalent to LCP) or random walk (when Ѳ → 0, RSP → current models). Using this approach, we identify migration corridors for GPS-monitored wild reindeer (Rangifer t. tarandus) in Norway. We demonstrate that reindeer movement is best predicted by an intermediate value of Ѳ, indicative of a movement trade-off between optimization and exploration. Model calibration allows identification of a corridor-barrier continuum that closely fits empirical data and demonstrates that RSP outperforms models that assume either optimality or random walk. The proposed approach models the multiscale cognitive maps by which animals likely navigate real landscapes and generalizes the most common algorithms for identifying corridors. Because suboptimal, but non-random, movement strategies are likely widespread, our approach has the potential to predict more realistic corridor-barrier continua for a wide range of species. © 2015 The Authors. Journal of Animal Ecology © 2015 British Ecological Society.

Turkish and Moroccan Young Adults in the Netherlands: The Relationship Between Acculturation and Psychological Problems.

PubMed

Özbek, Emel; Bongers, Ilja L; Lobbestael, Jill; van Nieuwenhuizen, Chijs

2015-12-01

This study investigated the relationship between acculturation and psychological problems in Turkish and Moroccan young adults living in the Netherlands. A sample of 131 healthy young adults aged between 18 and 24 years old, with a Turkish or Moroccan background was recruited using snowball sampling. Data on acculturation, internalizing and externalizing problems, beliefs about psychological problems, attributions of psychological problems and barriers to care were collected and analyzed using Latent Class Analysis and multinomial logistic regression. Three acculturation classes were identified in moderately to highly educated, healthy Turkish or Moroccan young adults: integration, separation and diffusion. None of the participants in the sample were marginalized or assimilated. Young adults reporting diffuse acculturation reported more internalizing and externalizing problems than those who were integrated or separated. Separated young adults reported experiencing more practical barriers to care than integrated young adults. Further research with a larger sample, including young adult migrants using mental health services, is required to improve our understanding of acculturation, psychological problems and barriers to care in this population. Including experiences of discrimination in the model might improve our understanding of the relationship between different forms of acculturation and psychological problems.

Alkaline battery containing a separator of a cross-linked copolymer of vinyl alcohol and unsaturated carboxylic acid

NASA Technical Reports Server (NTRS)

Hsu, L. C.; Philipp, W. H.; Sheibley, D. W.; Gonzalez-Sanabria, O. D. (Inventor)

1985-01-01

A battery separator for an alkaline battery is described. The separator comprises a cross linked copolymer of vinyl alcohol units and unsaturated carboxylic acid units. The cross linked copolymer is insoluble in water, has excellent zincate diffusion and oxygen gas barrier properties and a low electrical resistivity. Cross linking with a polyaldehyde cross linking agent is preferred.

Construction of Large-Volume Tissue Mimics with 3D Functional Vascular Networks

PubMed Central

Kang, Tae-Yun; Hong, Jung Min; Jung, Jin Woo; Kang, Hyun-Wook; Cho, Dong-Woo

2016-01-01

We used indirect stereolithography (SL) to form inner-layered fluidic networks in a porous scaffold by introducing a hydrogel barrier on the luminal surface, then seeded the networks separately with human umbilical vein endothelial cells and human lung fibroblasts to form a tissue mimic containing vascular networks. The artificial vascular networks provided channels for oxygen transport, thus reducing the hypoxic volume and preventing cell death. The endothelium of the vascular networks significantly retarded the occlusion of channels during whole-blood circulation. The tissue mimics have the potential to be used as an in vitro platform to examine the physiologic and pathologic phenomena through vascular architecture. PMID:27228079

Evaluating the DLVO Model for Non-Aqueous Colloidal Suspensions

NASA Astrophysics Data System (ADS)

DeCarlo, Keith Joseph

Application of DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory for suspensions utilizing non-aqueous suspension mediums has been tested. Prediction of suspension stability using DLVO theory requires the calculation of the attractive and repulsive forces between the suspended colloids and that the only significant stabilization mechanism present is electrostatic stabilization which was tested. The van der Waals attractive potential was calculated for 12 different colloids in 11 suspending mediums in accord with Lifshitz's treatment and a new approximation proposing that the material bandgap energy can be used to approximate the Hamaker constant was developed. This treatment requires the complete knowledge of the permittivity as a function of frequency for all the components in the respective suspension. The permittivity data was simplified using a damped oscillator model described by Ninham and Parsegian. All permittivity data was compiled from the literature. Microwave data was tabulated by NIST, infrared parameters were determined from FTIR data, and the ultraviolet/visual parameters were determined via Cauchy plots or estimated by the bandgap. Using the bandgap to approximate the ultraviolet/visual parameters proved to be more accurate than other approximations when compared to the accepted values. It was found that the non-oxide and non-stoichiometric colloids tested had the largest associated van der Waals attractive force. The van der Waals potential calculated for oxide particles was found to follow a direct relationship with the ionic character of the bonding. Repulsive forces were calculated for 12 different colloids in 11 suspending mediums. The calculated repulsive potential generated is a function of both the magnitude of charge generated on each colloid (zeta-potential) and the size of the interacting double-layers. zeta-potential was measured for each suspension using a microelectrophoretic technique and the double-layer thickness was calculated. It was demonstrated that as the polarity of the suspending medium increased, the thickness of the double-layer also increased. A large double-layer thickness was found to directly correlate to the suspension stability. A large double-layer thickness results in a decreased slope of the charge degradation from the colloidal surface to the bulk suspension. This coupled with a large magnitude of surface charge increases the probability of dispersion. Through viscosity measurements, the stability mechanism of each suspension was determined by comparison of the viscosity at a shear rate of 1.0s -1 with the shear thinning exponent. It was determined that, of the suspension mediums tested, heptane, octanoic acid, and poly(ethylene glycol) introduce non-electrostatic stabilization mechanisms significant enough to invalidate the DLVO predictions for suspensions made using those mediums. Consistent with DLVO theory, the total interaction potential was calculated by summation of the repulsive and attractive potentials of each suspension (84 suspensions total) as a function of separation distance. Based upon the results of the summation, the suspension stability can be predicted. 64 of the 84 suspensions were determined to be unstable as the colloids agglomerated in the primary minimum, 11 suspensions were determined to be weakly flocculated, and nine suspensions were found to be stable. Viscosity was used to determine the critical value for the thermal energy barrier and to test the DLVO predictions. The critical value of the thermal energy barrier was found to be 2.0 x 10 -6J/m2. Therefore, for suspensions calculated to have a thermal energy barrier less than the critical value, the Brownian motion of the colloids in suspension at 298K were enough to overcome it, resulting in agglomeration at the primary minimum. For suspensions with a thermal barrier larger than 2.0 x 10-6J/m2, the interacting colloids moved into the secondary energy minimum. All suspensions tested in which the thermal energy barrier was less than 2.0 x 10-6J/m 2 had a specific viscosity at a shear rate of 1.0s-1 greater than the cut-off viscosity for stability. If the colloids moved into the secondary minimum, the resulting suspension was characterized as either being weakly flocculated or stable. Weakly flocculated suspensions had an equilibrium separation distance of colloids less than 40nm resulting in a viscosity at a shear rate of 1.0s-1 larger than the determined specific viscosity cut-off (1.1x 104), but a shear thinning exponent greater than 1.0. Stable suspensions were defined by the colloids as having an equilibrium separation distance greater than 40nm, resulting in viscosity values at a shear rate of 1.0s-1 smaller than that of the determined cut-off viscosity value.

Unexpected ancestry of Populus seedlings from a hybrid zone implies a large role for postzygotic selection in the maintenance of species.

PubMed

Lindtke, Dorothea; Gompert, Zachariah; Lexer, Christian; Buerkle, C Alex

2014-09-01

In the context of potential interspecific gene flow, the integrity of species will be maintained by reproductive barriers that reduce genetic exchange, including traits associated with prezygotic isolation or poor performance of hybrids. Hybrid zones can be used to study the importance of different reproductive barriers, particularly when both parental species and hybrids occur in close spatial proximity. We investigated the importance of barriers to gene flow that act early vs. late in the life cycle of European Populus by quantifying the prevalence of homospecific and hybrid matings within a mosaic hybrid zone. We obtained genotypic data for 11 976 loci from progeny and their maternal parents and constructed a Bayesian model to estimate individual admixture proportions and hybrid classes for sampled trees and for the unsampled pollen parent. Matings that included one or two hybrid parents were common, resulting in admixture proportions of progeny that spanned the whole range of potential ancestries between the two parental species. This result contrasts strongly with the distribution of admixture proportions in adult trees, where intermediate hybrids and each of the parental species are separated into three discrete ancestry clusters. The existence of the full range of hybrids in seedlings is consistent with weak reproductive isolation early in the life cycle of Populus. Instead, a considerable amount of selection must take place between the seedling stage and maturity to remove many hybrid seedlings. Our results highlight that high hybridization rates and appreciable hybrid fitness do not necessarily conflict with the maintenance of species integrity. © 2014 John Wiley & Sons Ltd.

Measurement and potential barrier evolution analysis of cold field emission in fracture fabricated Si nanogap

NASA Astrophysics Data System (ADS)

Banerjee, Amit; Hirai, Yoshikazu; Tsuchiya, Toshiyuki; Tabata, Osamu

2017-06-01

Cold field emission characteristics of a fracture fabricated Si nanogap (˜100 nm) were investigated with an ascending electric field (voltage) sweep. The nanogap was formed by controlled fracture of a free-standing silicon micro-beam along <111> direction by a microelectromechanical device, which results in flat, smooth, and conformal electrode pairs. This facilitates simultaneous large area emission, which gives rise to a significant current at low bias voltage, which usually remains indiscernible in nanogaps of this size. The measured emission current-voltage (I-V) characteristics clearly depict two distinct regimes: a linear (I ∝ V) regime at low bias voltage and a nonlinear [ln(I/V 2) ∝ V -1] regime at high bias voltage, separated by a transition point. We propose that the linear regime is owed to direct tunneling of electrons, whereas the nonlinear regime is due to Fowler-Nordheim type emission. This proposition essentially implies that the tunneling potential barrier gradually evolved from a rectangular shape to a triangular shape with increasing field (V). This type of evolution is usually observed in molecular size gaps. We have attempted to correlate the I-V curves acquired through the experiments with the electric field induced barrier shape evolution by numerical calculations involving standard quantum mechanics. The observed linear regime at low bias voltage (<5 V) in a relatively large size gap (˜100 nm) is attributed to the fabrication method adopted in this study. The reported study and the fabricated device are significant for developing a futuristic thermotunneling refrigerator that will find a wide range of application in nanoelectronic devices.

Planar varactor frequency multiplier devices with blocking barrier

NASA Technical Reports Server (NTRS)

Lieneweg, Udo (Inventor); Frerking, Margaret A. (Inventor); Maserjian, Joseph (Inventor)

1994-01-01

The invention relates to planar varactor frequency multiplier devices with a heterojunction blocking barrier for near millimeter wave radiation of moderate power from a fundamental input wave. The space charge limitation of the submillimeter frequency multiplier devices of the BIN(sup +) type is overcome by a diode structure comprising an n(sup +) doped layer of semiconductor material functioning as a low resistance back contact, a layer of semiconductor material with n-type doping functioning as a drift region grown on the back contact layer, a delta doping sheet forming a positive charge at the interface of the drift region layer with a barrier layer, and a surface metal contact. The layers thus formed on an n(sup +) doped layer may be divided into two isolated back-to-back BNN(sup +) diodes by separately depositing two surface metal contacts. By repeating the sequence of the drift region layer and the barrier layer with the delta doping sheet at the interfaces between the drift and barrier layers, a plurality of stacked diodes is formed. The novelty of the invention resides in providing n-type semiconductor material for the drift region in a GaAs/AlGaAs structure, and in stacking a plurality of such BNN(sup +) diodes stacked for greater output power with and connected back-to-back with the n(sup +) GaAs layer as an internal back contact and separate metal contact over an AlGaAs barrier layer on top of each stack.

Dense, layered membranes for hydrogen separation

DOEpatents

Roark, Shane E.; MacKay, Richard; Mundschau, Michael V.

2006-02-21

This invention provides hydrogen-permeable membranes for separation of hydrogen from hydrogen-containing gases. The membranes are multi-layer having a central hydrogen-permeable layer with one or more catalyst layers, barrier layers, and/or protective layers. The invention also relates to membrane reactors employing the hydrogen-permeable membranes of the invention and to methods for separation of hydrogen from a hydrogen-containing gas using the membranes and reactors. The reactors of this invention can be combined with additional reactor systems for direct use of the separated hydrogen.

Revival of cloaking effect in a driven bilayer graphene vector barrier

NASA Astrophysics Data System (ADS)

Maiti, S.; Panigrahi, A.; Biswas, R.; Sinha, C.

2018-05-01

Transmission profiles in bilayer graphene are studied theoretically through a rectangular vector potential (magnetic) barrier with and without the presence of an oscillatory potential. Unlike the electrostatic barrier, the Fano resonances (FR) are noted in the transmission spectra both for normal and glancing incidences due to non-conservation of chirality for a static vector barrier. The results for normal incidence indicate that the cloaking effect is a manifestation of the chirality conservation in charge transport through bilayer graphene scalar barriers. It is also noted that the aforesaid FR for a static vector barrier might disappear (photon induced electronic cloaking effect) due to the predominant photon exchange processes in presence of an external oscillating potential. The study of Fano resonances in transmission spectrum is in high demand in respect of localization of charge carriers in graphene nano structures for its potential applications in digital device fabrications.

Design of all-optical, hot-electron current-direction-switching device based on geometrical asymmetry

PubMed Central

Kumarasinghe, Chathurangi S.; Premaratne, Malin; Gunapala, Sarath D.; Agrawal, Govind P.

2016-01-01

We propose a nano-scale current-direction-switching device(CDSD) that operates based on the novel phenomenon of geometrical asymmetry between two hot-electron generating plasmonic nanostructures. The proposed device is easy to fabricate and economical to develop compared to most other existing designs. It also has the ability to function without external wiring in nano or molecular circuitry since it is powered and controlled optically. We consider a such CDSD made of two dissimilar nanorods separated by a thin but finite potential barrier and theoretically derive the frequency-dependent electron/current flow rate. Our analysis takes in to account the quantum dynamics of electrons inside the nanorods under a periodic optical perturbation that are confined by nanorod boundaries, modelled as finite cylindrical potential wells. The influence of design parameters, such as geometric difference between the two nanorods, their volumes and the barrier width on quality parameters such as frequency-sensitivity of the current flow direction, magnitude of the current flow, positive to negative current ratio, and the energy conversion efficiency is discussed by considering a device made of Ag/TiO2/Ag. Theoretical insight and design guidelines presented here are useful for customizing our proposed CDSD for applications such as self-powered logic gates, power supplies, and sensors. PMID:26887286

Design of all-optical, hot-electron current-direction-switching device based on geometrical asymmetry.

PubMed

Kumarasinghe, Chathurangi S; Premaratne, Malin; Gunapala, Sarath D; Agrawal, Govind P

2016-02-18

We propose a nano-scale current-direction-switching device(CDSD) that operates based on the novel phenomenon of geometrical asymmetry between two hot-electron generating plasmonic nanostructures. The proposed device is easy to fabricate and economical to develop compared to most other existing designs. It also has the ability to function without external wiring in nano or molecular circuitry since it is powered and controlled optically. We consider a such CDSD made of two dissimilar nanorods separated by a thin but finite potential barrier and theoretically derive the frequency-dependent electron/current flow rate. Our analysis takes in to account the quantum dynamics of electrons inside the nanorods under a periodic optical perturbation that are confined by nanorod boundaries, modelled as finite cylindrical potential wells. The influence of design parameters, such as geometric difference between the two nanorods, their volumes and the barrier width on quality parameters such as frequency-sensitivity of the current flow direction, magnitude of the current flow, positive to negative current ratio, and the energy conversion efficiency is discussed by considering a device made of Ag/TiO2/Ag. Theoretical insight and design guidelines presented here are useful for customizing our proposed CDSD for applications such as self-powered logic gates, power supplies, and sensors.

Waste information management system: a web-based system for DOE waste forecasting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geisler, T.J.; Shoffner, P.A.; Upadhyay, U.

2007-07-01

The implementation of the Department of Energy (DOE) mandated accelerated cleanup program has created significant potential technical impediments that must be overcome. The schedule compression will require close coordination and a comprehensive review and prioritization of the barriers that may impede treatment and disposition of the waste streams at each site. Many issues related to site waste treatment and disposal have now become potential critical path issues under the accelerated schedules. In order to facilitate accelerated cleanup initiatives, waste managers at DOE field sites and at DOE headquarters in Washington, D.C., need timely waste forecast information regarding the volumes andmore » types of waste that will be generated by DOE sites over the next 25 years. Each local DOE site has historically collected, organized, and displayed site waste forecast information in separate and unique systems. However, waste information from all sites needs a common application to allow interested parties to understand and view the complete complex-wide picture. A common application would allow identification of total waste volumes, material classes, disposition sites, choke points, and technological or regulatory barriers to treatment and disposal. The Applied Research Center (ARC) at Florida International University (FIU) in Miami, Florida, has completed the development of this web-based forecast system. (authors)« less

Micromachined peristaltic pump

NASA Technical Reports Server (NTRS)

Hartley, Frank T. (Inventor)

1998-01-01

A micromachined pump including a channel formed in a semiconductor substrate by conventional processes such as chemical etching. A number of insulating barriers are established in the substrate parallel to one another and transverse to the channel. The barriers separate a series of electrically conductive strips. An overlying flexible conductive membrane is applied over the channel and conductive strips with an insulating layer separating the conductive strips from the conductive membrane. Application of a sequential voltage to the series of strips pulls the membrane into the channel portion of each successive strip to achieve a pumping action. A particularly desirable arrangement employs a micromachined push-pull dual channel cavity employing two substrates with a single membrane sandwiched between them.

An Evaluation of Stereoscopic Digital Mammography for Earlier Detection of Breast Cancer and Reduced Rate of Recall

DTIC Science & Technology

2007-08-01

is accomplished using either an AMLCD with a lenticular lens20 or a parallax barrier21 or two separate optical paths with a pair of image sources.22...24 The primary advantage of this approach is no eyewear is required. The designs using the parallax barrier or lenticular lens place these optical

Energy barriers between metastable states in first-order quantum phase transitions

NASA Astrophysics Data System (ADS)

Wald, Sascha; Timpanaro, André M.; Cormick, Cecilia; Landi, Gabriel T.

2018-02-01

A system of neutral atoms trapped in an optical lattice and dispersively coupled to the field of an optical cavity can realize a variation of the Bose-Hubbard model with infinite-range interactions. This model exhibits a first-order quantum phase transition between a Mott insulator and a charge density wave, with spontaneous symmetry breaking between even and odd sites, as was recently observed experimentally [Landig et al., Nature (London) 532, 476 (2016), 10.1038/nature17409]. In the present paper, we approach the analysis of this transition using a variational model which allows us to establish the notion of an energy barrier separating the two phases. Using a discrete WKB method, we then show that the local tunneling of atoms between adjacent sites lowers this energy barrier and hence facilitates the transition. Within our simplified description, we are thus able to augment the phase diagram of the model with information concerning the height of the barrier separating the metastable minima from the global minimum in each phase, which is an essential aspect for the understanding of the reconfiguration dynamics induced by a quench across a quantum critical point.

Influence of rotational energy barriers to the conformational search of protein loops in molecular dynamics and ranking the conformations.

PubMed

Tappura, K

2001-08-15

An adjustable-barrier dihedral angle potential was added as an extension to a novel, previously presented soft-core potential to study its contribution to the efficacy of the search of the conformational space in molecular dynamics. As opposed to the conventional soft-core potential functions, the leading principle in the design of the new soft-core potential, as well as of its extension, the soft-core and adjustable-barrier dihedral angle (SCADA) potential (referred as the SCADA potential), was to maintain the main equilibrium properties of the original force field. This qualifies the methods for a variety of a priori modeling problems without need for additional restraints typically required with the conventional soft-core potentials. In the present study, the different potential energy functions are applied to the problem of predicting loop conformations in proteins. Comparison of the performance of the soft-core and SCADA potential showed that the main hurdles for the efficient sampling of the conformational space of (loops in) proteins are related to the high-energy barriers caused by the Lennard-Jones and Coulombic energy terms, and not to the rotational barriers, although the conformational search can be further enhanced by lowering the rotational barriers of the dihedral angles. Finally, different evaluation methods were studied and a few promising criteria found to distinguish the near-native loop conformations from the wrong ones.

Determination of Fusion Barrier Distributions from Quasielastic Scattering Cross Sections towards Superheavy Nuclei Synthesis

NASA Astrophysics Data System (ADS)

Tanaka, Taiki; Narikiyo, Yoshihiro; Morita, Kosuke; Fujita, Kunihiro; Kaji, Daiya; Morimoto, Kouji; Yamaki, Sayaka; Wakabayashi, Yasuo; Tanaka, Kengo; Takeyama, Mirei; Yoneda, Akira; Haba, Hiromitsu; Komori, Yukiko; Yanou, Shinya; Jean-Paul Gall, Benoît; Asfari, Zouhair; Faure, Hugo; Hasebe, Hiroo; Huang, Minghui; Kanaya, Jumpei; Murakami, Masashi; Yoshida, Atsushi; Yamaguchi, Takayuki; Tokanai, Fuyuki; Yoshida, Tomomi; Yamamoto, Shoya; Yamano, Yuki; Watanabe, Kenyu; Ishizawa, Satoshi; Asai, Masato; Aono, Ryuji; Goto, Shin-ichi; Katori, Kenji; Hagino, Kouichi

2018-01-01

In order to study the nucleus-nucleus interactions for syntheses of superheavy nuclei, we measured excitation functions for the quasielastic scattering of 48Ca+208Pb, 50Ti+208Pb, and 48Ca+248Cm using the gas-filled-type recoil ion separator GARIS. The quasielastic scattering events were clearly separated from deep-inelastic events by using GARIS and its focal plan detectors, except for high-incident-energy points. The quasielastic barrier distributions were successfully extracted for these systems, and compared with coupled-channels calculations. The results of the calculations indicate that vibrational and rotational excitations of the colliding nuclei, as well as neutron transfers before contact, strongly affect the structure of the barrier distribution. For the reactions of 48Ca+208Pb and 50Ti+208Pb, a local maximum of the barrier distribution occurred at the same energy as the peak of the 2n evaporation cross section of the system. On the other hand, for the hot fusion reaction of 48Ca+248Cm, the 4n evaporation cross section of the system peaks at energies well above the maximum of the barrier distribution. This may be attributed to the deformation of the target nucleus. We argue that these findings can be utilized to locate the optimal energy for future searches for undiscovered superheavy nuclei.

Neurotoxicology of the Brain Barrier System: New Implications

PubMed Central

Zheng, Wei

2014-01-01

The concept of a barrier system in the brain has existed for nearly a century. The barrier that separates the blood from the cerebral interstitial fluid is defined as the blood-brain barrier, while the one that discontinues the circulation between the blood and cerebrospinal fluid is named the blood-cerebrospinal fluid barrier. Evidence in the past decades suggests that brain barriers are subject to toxic insults from neurotoxic chemicals circulating in blood. The aging process and some disease states render barriers more vulnerable to insults arising inside and outside the barriers. The implication of brain barriers in certain neurodegenerative diseases is compelling, although the contribution of chemical-induced barrier dysfunction in the etiology of any of these disorders remains poorly understood. This review examines what is currently understood about brain barrier systems in central nervous system disorders by focusing on chemical-induced neurotoxicities including those associated with nitrobenzenes, N-methyl-D-aspartate, cyclosporin A, pyridostigmine bromide, aluminum, lead, manganese, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and 3-nitropropionic acid. Contemporary research questions arising from this growing understanding show enormous promises for brain researchers, toxicologists, and clinicians. PMID:11778669

[Effects of mulberry/soybean intercropping on the plant growth and rhizosphere soil microbial number and enzyme activities].

PubMed

Hu, Ju-Wei; Zhu, Wen-Xu; Zhang, Hui-Hui; Xu, Nan; Li, Xin; Yue, Bing-Bing; Sun, Guang-yu

2013-05-01

A root separation experiment was conducted to investigate the plant growth and rhizosphere soil microbes and enzyme activities in a mulberry/soybean intercropping system. As compared with those in plastic barrier and nylon mesh barrier treatments, the plant height, leaf number, root length, root nodule number, and root/shoot ratio of mulberry and soybean in non-barrier treatment were significantly higher, and the soybean's effective nodule number was larger. The available phosphorous content in the rhizosphere soils of mulberry and soybean in no barrier and nylon mesh barrier treatments was increased by 10.3% and 11.1%, and 5.1% and 4.6%, respectively, as compared with that in plastic barrier treatment. The microbial number, microbial diversity, and enzyme activities in the rhizosphere soils of mulberry and soybean were higher in the treatments of no barrier and nylon mesh barrier than in the treatment of plastic barrier. All the results indicated that there was an obvious interspecific synergistic effect between mulberry and soybean in the mulberry/soybean intercropping system.

Communication: Relationship between local structure and the stability of water in hydrophobic confinement

NASA Astrophysics Data System (ADS)

Altabet, Y. Elia; Debenedetti, Pablo G.

2017-12-01

Liquid water confined between nanoscale hydrophobic objects can become metastable with respect to its vapor at nanoscale separations. While the separations are only several molecular diameters, macroscopic theories are often invoked to interpret the thermodynamics and kinetics of water under confinement. We perform detailed rate and free energy calculations via molecular simulations in order to assess the dependence of the rate of evaporation, free energy barriers, and free energy differences between confined liquid and vapor upon object separation and compare them to the relevant macroscopic theories. At small enough separations, the rate of evaporation appears to deviate significantly from the predictions of classical nucleation theory, and we attribute such deviations to changes in the structure of the confined liquid film. However, the free energy difference between the confined liquid and vapor phases agrees quantitatively with macroscopic theory, and the free energy barrier to condensation displays qualitative agreement. Overall, the present work suggests that theories attempting to capture the kinetic behavior of nanoscale systems should incorporate structural details rather than treating it as a continuum.

Conductance and refraction across a Barrier in Phosphorene

NASA Astrophysics Data System (ADS)

Dahal, Dipendra; Gumbs, Godfrey

The transmission coefficient and ballistic conductance for monolayer black phosphorene is calculated when a potential step or square barrier is present. The Landauer-B¨uttiker formalism is employed in our calculations of the conductance. We obtain the refractive index for the step potential barrier when an incident beam of electron travel along different paths so as to observe what role the anisotropy of the energy bands plays. Numerical results are presented for various potential heights and barrier widths and these are compared with those for gapless and gapped graphene.

Revealing the Sub-Barrier Phase using a Spatiotemporal Interferometer with Orthogonal Two-Color Laser Fields of Comparable Intensity

NASA Astrophysics Data System (ADS)

Han, Meng; Ge, Peipei; Shao, Yun; Liu, Ming-Ming; Deng, Yongkai; Wu, Chengyin; Gong, Qihuang; Liu, Yunquan

2017-08-01

We measure photoelectron momentum distributions of Ar atoms in orthogonally polarized two-color laser fields with comparable intensities. The synthesized laser field is used to manipulate the oscillating tunneling barrier and the subsequent motion of electrons onto two spatial dimensions. The subcycle structures associated with the temporal double-slit interference are spatially separated and enhanced. We use such a spatiotemporal interferometer to reveal sub-barrier phase of strong-field tunneling ionization. This study shows that the tunneling process transfers the initial phase onto momentum distribution. Our work has the implication that the sub-barrier phase plays an indispensable role in photoelectron interference processes.

The ultrastructure of cerebral blood capillaries in the ratfish, Chimaera monstrosa.

PubMed

Bundgaard, M

1982-01-01

Sharks and skates (Chondrichthyes: Elasmobranchii) have a glial blood-brain barrier, while all other vertebrates examined so far have an endothelial barrier. For comparative reasons it is desirable to examine the blood-brain barrier in species from the other subclass of cartilaginous fish, the holocephalans. The ultrastructure of cerebral capillaries in the chimaera (Chondrichthyes: Holocephali) is described in the present study. The endothelial cells are remarkably thick. Fenestrae and transendothelial channels were not observed. The endothelial cells are joined by elaborate tight junctions. The perivascular glial processes are separated by wide spaces (15-60 nm) without obliterating junctional complexes. These findings indicate that the chimaera has an endothelial blood-brain barrier.

Older Adults Perceptions of Technology and Barriers to Interacting with Tablet Computers: A Focus Group Study.

PubMed

Vaportzis, Eleftheria; Clausen, Maria Giatsi; Gow, Alan J

2017-10-04

New technologies provide opportunities for the delivery of broad, flexible interventions with older adults. Focus groups were conducted to: (1) understand older adults' familiarity with, and barriers to, interacting with new technologies and tablets; and (2) utilize user-engagement in refining an intervention protocol. Eighteen older adults (65-76 years old; 83.3% female) who were novice tablet users participated in discussions about their perceptions of and barriers to interacting with tablets. We conducted three separate focus groups and used a generic qualitative design applying thematic analysis to analyse the data. The focus groups explored attitudes toward tablets and technology in general. We also explored the perceived advantages and disadvantages of using tablets, familiarity with, and barriers to interacting with tablets. In two of the focus groups, participants had previous computing experience (e.g., desktop), while in the other, participants had no previous computing experience. None of the participants had any previous experience with tablet computers. The themes that emerged were related to barriers (i.e., lack of instructions and guidance, lack of knowledge and confidence, health-related barriers, cost); disadvantages and concerns (i.e., too much and too complex technology, feelings of inadequacy, and comparison with younger generations, lack of social interaction and communication, negative features of tablets); advantages (i.e., positive features of tablets, accessing information, willingness to adopt technology); and skepticism about using tablets and technology in general. After brief exposure to tablets, participants emphasized the likelihood of using a tablet in the future. Our findings suggest that most of our participants were eager to adopt new technology and willing to learn using a tablet. However, they voiced apprehension about lack of, or lack of clarity in, instructions and support. Understanding older adults' perceptions of technology is important to assist with introducing it to this population and maximize the potential of technology to facilitate independent living.

Older Adults Perceptions of Technology and Barriers to Interacting with Tablet Computers: A Focus Group Study

PubMed Central

Vaportzis, Eleftheria; Giatsi Clausen, Maria; Gow, Alan J.

2017-01-01

Background: New technologies provide opportunities for the delivery of broad, flexible interventions with older adults. Focus groups were conducted to: (1) understand older adults' familiarity with, and barriers to, interacting with new technologies and tablets; and (2) utilize user-engagement in refining an intervention protocol. Methods: Eighteen older adults (65–76 years old; 83.3% female) who were novice tablet users participated in discussions about their perceptions of and barriers to interacting with tablets. We conducted three separate focus groups and used a generic qualitative design applying thematic analysis to analyse the data. The focus groups explored attitudes toward tablets and technology in general. We also explored the perceived advantages and disadvantages of using tablets, familiarity with, and barriers to interacting with tablets. In two of the focus groups, participants had previous computing experience (e.g., desktop), while in the other, participants had no previous computing experience. None of the participants had any previous experience with tablet computers. Results: The themes that emerged were related to barriers (i.e., lack of instructions and guidance, lack of knowledge and confidence, health-related barriers, cost); disadvantages and concerns (i.e., too much and too complex technology, feelings of inadequacy, and comparison with younger generations, lack of social interaction and communication, negative features of tablets); advantages (i.e., positive features of tablets, accessing information, willingness to adopt technology); and skepticism about using tablets and technology in general. After brief exposure to tablets, participants emphasized the likelihood of using a tablet in the future. Conclusions: Our findings suggest that most of our participants were eager to adopt new technology and willing to learn using a tablet. However, they voiced apprehension about lack of, or lack of clarity in, instructions and support. Understanding older adults' perceptions of technology is important to assist with introducing it to this population and maximize the potential of technology to facilitate independent living. PMID:29071004

Structural details of Al/Al 2O3 junctions and their role in the formation of electron tunnel barriers

NASA Astrophysics Data System (ADS)

Koberidze, M.; Puska, M. J.; Nieminen, R. M.

2018-05-01

We present a computational study of the adhesive and structural properties of the Al/Al 2O3 interfaces as building blocks of the metal-insulator-metal (MIM) tunnel devices, where electron transport is accomplished via tunneling mechanism through the sandwiched insulating barrier. The main goal of this paper is to understand, on the atomic scale, the role of the geometrical details in the formation of the tunnel barrier profiles. Initially, we concentrate on the adhesive properties of the interfaces. To provide reliable results, we carefully assess the accuracy of the traditional methods used to examine Al/Al 2O3 systems. These are the most widely employed exchange-correlation functionals—local-density approximation and two different generalized gradient approximations; the universal binding-energy relation for predicting equilibrium interfacial distances and adhesion energies; and the ideal work of separation as a measure of junction stability. In addition, we show that the established interpretation of the computed ideal work of separation might be misleading in predicting the optimal interface structures. Finally, we perform a detailed analysis of the atomic and interplanar relaxations in each junction, and identify their contributions to the tunnel barrier parameters. Our results imply that the structural irregularities on the surface of the Al film have a significant contribution to lowering the tunnel barrier height, while atomic relaxations at the interface and interplanar relaxations in Al2O3 may considerably change the width of the barrier and, thus, distort its uniformity. Both the effects may critically influence the performance of the MIM tunnel devices.

Solvent recovery opportunities in the pharmaceutical industry.

PubMed

Barton, P I

2000-11-01

Opportunities for recovering and recycling waste solvent streams in the pharmaceutical industry are reviewed. A major obstacle to solvent recovery and recycling is the existence of azeotropic compositions, and thus separation barriers, in the mixtures in question. Advances in the understanding of these complex separation problems are discussed. Recent progress on novel designs for small-scale, flexible azeotropic separation processes is reviewed. Also considered is the alternative and complementary approach of integrating solvent use within a batch process so that the formation of hard-to-separate azeotropic compositions is prevented.

Trapping gases in metal-organic frameworks with a selective surface molecular barrier layer

DOE PAGES

Tan, Kui; Zuluaga, Sebastian; Fuentes, Erika; ...

2016-12-13

The main challenge for gas storage and separation in nanoporous materials is that many molecules of interest adsorb too weakly to be effectively retained. Instead of synthetically modifying the internal surface structure of the entire bulk—as is typically done to enhance adsorption—here we show that post exposure of a prototypical porous metal-organic framework to ethylenediamine can effectively retain a variety of weakly adsorbing molecules (for example, CO, CO 2, SO 2, C 2H 4, NO) inside the materials by forming a monolayer-thick cap at the external surface of microcrystals. Furthermore, this capping mechanism, based on hydrogen bonding as explained bymore » ab initio modelling, opens the door for potential selectivity. For example, water molecules are shown to disrupt the hydrogen-bonded amine network and diffuse through the cap without hindrance and fully displace/release the retained small molecules out of the metal-organic framework at room temperature. Lastly, these findings may provide alternative strategies for gas storage, delivery and separation.« less

Using structured expert judgment to assess invasive species prevention: Asian carp and the Mississippi-Great Lakes hydrologic connection.

PubMed

Wittmann, Marion E; Cooke, Roger M; Rothlisberger, John D; Lodge, David M

2014-02-18

Recently, authors have theorized that invasive species prevention is more cost-effective than control in protecting ecosystem services. However, quantification of the effectiveness of prevention is rare because experiments at field scales are expensive or infeasible. We therefore used structured expert judgment to quantify the efficacy of 17 proposed strategies to prevent Asian carp invasion of the Laurentian Great Lakes via the hydrologic connection between the Mississippi and Great Lakes watersheds. Performance-weighted expert estimates indicated that hydrologic separation would prevent 99% (95,100; median, 5th and 95th percentiles) of Asian carp access, while electric and acoustic-bubble-strobe barriers would prevent 92% (85,95) and 92% (75,95), respectively. For all other strategies, estimated effectiveness was lower, with greater uncertainty. When potential invasions by other taxa are considered, the effectiveness of hydrologic separation increases relative to strategies that are effective primarily for fishes. These results could help guide invasive species management in many waterways globally.

Sorting and measurement of single gold nanoparticles in an optofluidic chip

NASA Astrophysics Data System (ADS)

Shi, Y. Z.; Xiong, S.; Zhang, Y.; Chin, L. K.; Wu, J. H.; Chen, T. N.; Liu, A. Q.

2017-08-01

Gold nanoparticles have sparked strong interest owing to their unique optical and chemical properties. Their sizedependent refractive index and plasmon resonance are widely used for optical sorting, biomedicine and chemical sensing. However, there are only few examples of optical separation of different gold nanoparticles. Only separating 100-200 nm gold nanoparticles using wavelength selected resonance of the extinction spectrum has been demonstrated. This paper reports an optofluidic chip for sorting single gold nanoparticles using loosely overdamped optical potential wells, which are created by building optical and fluidic barriers. It is the first demonstration of sorting single nanoparticles with diameters ranging from 60 to 100 nm in a quasi-Bessel beam with an optical trapping stiffness from 10-10 to 10-9 N/m. The nanoparticles oscillate in the loosely overdamped potential wells with a displacement amplitude of 3-7 μm in the microchannel. The sizes and refractive indices of the nanoparticles can be determined from their trapping positions using Drude and Mie theory, with a resolution of 0.35 nm/μm for the diameter, 0.0034/μm and 0.0017/μm for the real and imaginary parts of the refractive index, respectively. Here we experimentally demonstrate the sorting of bacteria and protozoa on the optofluidic chip. The chip has high potential for the sorting and characterization of nanoparticles in biomedical applications such as tumour targeting, drug delivery and intracellular imaging.

A theory of X and Z multiquark resonances

NASA Astrophysics Data System (ADS)

Maiani, Luciano; Polosa, Antonio D.; Riquer, Veronica

2018-03-01

We introduce the hypothesis that diquarks and antidiquarks in tetraquarks are separated by a potential barrier. We show that this notion can answer satisfactorily long standing questions challenging the diquark-antidiquark model of exotic resonances. The tetraquark description of X and Z resonances is shown to be compatible with present limits on the non-observation of charged partners X±, of the X (3872) and the absence of a hyperfine splitting between two different neutral states. In the same picture, Zc and Zb particles are expected to form complete isospin triplets plus singlets. It is also explained why the decay rate into final states including quarkonia are suppressed with respect to those having open charm/beauty states.

Finite-size polyelectrolyte bundles at thermodynamic equilibrium

NASA Astrophysics Data System (ADS)

Sayar, M.; Holm, C.

2007-01-01

We present the results of extensive computer simulations performed on solutions of monodisperse charged rod-like polyelectrolytes in the presence of trivalent counterions. To overcome energy barriers we used a combination of parallel tempering and hybrid Monte Carlo techniques. Our results show that for small values of the electrostatic interaction the solution mostly consists of dispersed single rods. The potential of mean force between the polyelectrolyte monomers yields an attractive interaction at short distances. For a range of larger values of the Bjerrum length, we find finite-size polyelectrolyte bundles at thermodynamic equilibrium. Further increase of the Bjerrum length eventually leads to phase separation and precipitation. We discuss the origin of the observed thermodynamic stability of the finite-size aggregates.

Proteome profile and biological activity of caprine, bovine and human milk fat globules.

PubMed

Spertino, Stefano; Cipriani, Valentina; De Angelis, Chiara; Giuffrida, Maria Gabriella; Marsano, Francesco; Cavaletto, Maria

2012-04-01

Upon combining bidimensional electrophoresis with monodimensional separation, a more comprehensive analysis of the milk fat globule membrane has been obtained. The proteomic profile of caprine milk fat globules revealed the presence of butyrophilin, lactadherin and perilipin as the major proteins, they were also associated to bovine and human milk fat globule membranes. Xanthine dehydrogenase/oxidase has been detected only in monodimensional gels. Biological activity of milk fat globules has been evaluated in Caco2-cells, as a representative model of the intestinal barrier. The increase of cell viability was indicative of a potential nutraceutical role for the whole milk fat globule, suggesting a possible employment in milk formula preparation.

Investigating the complementary value of discrete choice experiments for the evaluation of barriers and facilitators in implementation research: a questionnaire survey

PubMed Central

van Helvoort-Postulart, Debby; van der Weijden, Trudy; Dellaert, Benedict GC; de Kok, Mascha; von Meyenfeldt, Maarten F; Dirksen, Carmen D

2009-01-01

Background The potential barriers and facilitators to change should guide the choice of implementation strategy. Implementation researchers believe that existing methods for the evaluation of potential barriers and facilitators are not satisfactory. Discrete choice experiments (DCE) are relatively new in the health care sector to investigate preferences, and may be of value in the field of implementation research. The objective of our study was to investigate the complementary value of DCE for the evaluation of barriers and facilitators in implementation research. Methods Clinical subject was the implementation of the guideline for breast cancer surgery in day care. We identified 17 potential barriers and facilitators to the implementation of this guideline. We used a traditional questionnaire that was made up of statements about the potential barriers and facilitators. Respondents answered 17 statements on a five-point scale ranging from one (fully disagree) to five (fully agree). The potential barriers and facilitators were included in the DCE as decision attributes. Data were gathered among anaesthesiologists, surgical oncologists, and breast care nurses by means of a paper-and-pencil questionnaire. Results The overall response was 10%. The most striking finding was that the responses to the traditional questionnaire hardly differentiated between barriers. Forty-seven percent of the respondents thought that DCE is an inappropriate method. These respondents considered DCE too difficult and too time-consuming. Unlike the traditional questionnaire, the results of a DCE provide implementation researchers and clinicians with a relative attribute importance ranking that can be used to prioritize potential barriers and facilitators to change, and hence to better fine-tune the implementation strategies to the specific problems and challenges of a particular implementation process. Conclusion The results of our DCE and traditional questionnaire would probably lead to different implementation strategies. Although there is no 'gold standard' for prioritising potential barriers and facilitators to the implementation of change, theoretically, DCE would be the method of choice. However, the feasibility of using DCE was less favourable. Further empirical applications should investigate whether DCE can really make a valuable contribution to the implementation science. PMID:19250555

Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

NASA Astrophysics Data System (ADS)

Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

2015-09-01

We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

Method of filtering a target compound from a first solvent that is above its critical density

DOEpatents

Phelps, Max R [Richland, WA; Yonker, Clement R [Kennewick, WA; Fulton, John L [Richland, WA; Bowman, Lawrence E [Richland, WA

2001-07-24

The present invention is a method of separating a first compound having a macromolecular structure from a mixture. The first solvent is a fluid that is a gas at standard temperature and pressure and is at a density greater than a critical density of the fluid. A macromolecular structure containing a first compound is dissolved therein as a mixture. The mixture is contacted onto a selective barrier and the first solvent passed through the selective barrier thereby retaining the first compound, followed by recovering the first compound. By using a fluid that is a gas at standard temperature and pressure at a density greater than its critical density, separation without depressurization is fast and efficient.

Natural and man-made radioactivity in soils and plants around the research reactor of Inshass.

PubMed

Higgy, R H; Pimpl, M

1998-12-01

The specific radioactivities of the U-series, 232Th, 137Cs and 40K were measured in soil samples around the Inshass reactor in Cairo, using a gamma-ray spectrometer with a HpGe detector. The alpha activity of 238U, 234U and 235U was measured in the same soil samples by surface barrier detectors after radiochemical separation and the obtained results were compared with the specific activities determined by gamma-measurements. The alpha-activity of 238Pu, 239+240Pu, 241Am, 242Cm and 244Cm was measured after radiochemical separation by surface barrier detectors for both soil and plant samples. Then beta-activity of 241Pu was measured using liquid scintillation spectrometry.

Crossability and relationships of Washoe pine

Treesearch

William B. Critchfield

1984-01-01

Washoe pine, related to ponderosa pine but occurring at higher elevations along the western edge of the Great Basin, crosses freely with the Rocky Mountain race of ponderosa despite evidence of long-term separation. Washoe is morphologically distinct from the parapatric Pacific race of ponderosa pine, and the two taxa are kept separate partly by genetic barriers that...

Controlled thermoelectric response of a tunable Rashba coupled metal-insulator-superconductor junction

NASA Astrophysics Data System (ADS)

Kapri, Priyadarshini; Adhikary, Priyanka; Sinha, Shubham; Basu, Saurabh

2018-05-01

Thermoelectric effect for metal, insulator and the superconductor junctions has been studied with Rashba spin-orbit coupling (RSOC) being present at the interfaces via modified Blonder-Tinkham-Klapwijk (BTK) theory. We find that the thermopower, as a function of an effective barrier potential that characterizes the intermediate insulating layer, displays an oscillatory behavior. Interesting interplay between the strength of RSOC and the effective barrier potential has been carried out in details in this regard. For specific ranges of the effective barrier potential, RSOC enhances the thermopower, while the reverse happens for other values. Moreover it is found that the effective barrier potential plays a crucial role in determining the thermopower spectrum. For a tunable Rashba coupling, the thermopower of the junction can be controlled with precision, which may useful for the thermoelectric applications, at low temperatures. Further the efficiency of the system is obtained for different pairing correlations of the superconducting lead where we find that the system with a d-wave symmetry is more efficient as compared to a s-wave correlation, in some selective regions of effective barrier potential. It is found that for some selective regions of effective barrier potential, the efficiency of the system increases with RSOC and the opposite happens for other values.

Uropathogenic E. coli Promote a Paracellular Urothelial Barrier Defect Characterized by Altered Tight Junction Integrity, Epithelial Cell Sloughing and Cytokine Release

PubMed Central

Wood, M. W.; Breitschwerdt, E. B.; Nordone, S. K.; Linder, K. E.; Gookin, J. L.

2013-01-01

Summary The urinary bladder is a common site of bacterial infection with a majority of cases attributed to uropathogenic Escherichia coli. Sequels of urinary tract infections (UTIs) include the loss of urothelial barrier function and subsequent clinical morbidity secondary to the permeation of urine potassium, urea and ammonia into the subepithelium. To date there has been limited research describing the mechanism by which this urothelial permeability defect develops. The present study models acute uropathogenic E. coli infection in vitro using intact canine bladder mucosa mounted in Ussing chambers to determine whether infection induces primarily a transcellular or paracellular permeability defect. The Ussing chamber sustains tissue viability while physically separating submucosal and lumen influences, so this model is ideal for quantitative measurement of transepithelial electrical resistance (TER) to assess alterations of urothelial barrier function. Using this model, changes in both tissue ultrastructure and TER indicated that uropathogenic E. coli infection promotes a paracellular permeability defect associated with the failure of umbrella cell tight junction formation and umbrella cell sloughing. In addition, bacterial interaction with the urothelium promoted secretion of cytokines from the urinary bladder with bioactivity capable of modulating epithelial barrier function including tumour necrosis factor-α, interleukin (IL)-6 and IL-15. IL-15 secretion by the infected bladder mucosa is a novel finding and, because IL-15 plays key roles in reconstitution of tight junction function in damaged intestine, this study points to a potential role for IL-15 in UTI-induced urothelial injury. PMID:22014415

Fish community dynamics following dam removal in a fragmented agricultural stream

USGS Publications Warehouse

Kornis, Matthew; Weidel, Brian C.; Powers, Stephens; Diebel, Matthew W.; Cline, Timpthy; Fox, Justin; Kitchell, James F.

2014-01-01

Habitat fragmentation impedes dispersal of aquatic fauna, and barrier removal is increasingly used to increase stream network connectivity and facilitate fish dispersal. Improved understanding of fish community response to barrier removal is needed, especially in fragmented agricultural streams where numerous antiquated dams are likely destined for removal. We examined post-removal responses in two distinct fish communities formerly separated by a small aging mill dam. The dam was removed midway through the 6 year study, enabling passage for downstream fishes affiliated with a connected reservoir into previously inaccessible habitat, thus creating the potential for taxonomic homogenization between upstream and downstream communities. Both communities changed substantially post-removal. Two previously excluded species (white sucker, yellow perch) established substantial populations upstream of the former dam, contributing to a doubling of total fish biomass. Meanwhile, numerical density of pre-existing upstream fishes declined. Downstream, largemouth bass density was inversely correlated with prey fish density throughout the study, while post-removal declines in bluegill density coincided with cooler water temperature and increased suspended and benthic fine sediment. Upstream and downstream fish communities became more similar post-removal, represented by a shift in Bray-Curtis index from 14 to 41 % similarity. Our findings emphasize that barrier removal in highly fragmented stream networks can facilitate the unintended and possibly undesirable spread of species into headwater streams, including dispersal of species from remaining reservoirs. We suggest that knowledge of dispersal patterns for key piscivore and competitor species in both the target system and neighboring systems may help predict community outcomes following barrier removal.

Yangtze River, an insignificant genetic boundary in tufted deer (Elaphodus cephalophus): the evidence from a first population genetics study.

PubMed

Sun, Zhonglou; Pan, Tao; Wang, Hui; Pang, Mujia; Zhang, Baowei

2016-01-01

Great rivers were generally looked at as the geographical barrier to gene flow for many taxonomic groups. The Yangtze River is the third largest river in the world, and flows across South China and into the East China Sea. Up until now, few studies have been carried out to evaluate its effect as a geographical barrier. In this study, we attempted to determine the barrier effect of the Yangtze River on the tufted deer ( Elaphodus cephalophus ) using the molecular ecology approach. Using mitochondrial DNA control region (CR) sequences and 13 nuclear microsatellite loci, we explored the genetic structure and gene flow in two adjacent tufted deer populations (Dabashan and Wulingshan populations), which are separated by the Yangtze River. Results indicated that there are high genetic diversity levels in the two populations, but no distinguishable haplotype group or potential genetic cluster was detected which corresponded to specific geographical population. At the same time, high gene flow was observed between Wulingshan and Dabashan populations. The tufted deer populations experienced population decrease from 0.3 to 0.09 Ma BP, then followed by a distinct population increase. A strong signal of recent population decline ( T = 4,396 years) was detected in the Wulingshan population by a Markov-Switching Vector Autoregressions(MSVAR) process population demography analysis. The results indicated that the Yangtze River may not act as an effective barrier to gene flow in the tufted deer. Finally, we surmised that the population demography of the tufted deer was likely affected by Pleistocene climate fluctuations and ancient human activities.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matvejeff, M., E-mail: mikko.matvejeff@picosun.com; Department of Chemistry, Aalto University, Kemistintie 1, 02150 Espoo; Ahvenniemi, E.

We study magnetic coupling between hole-doped manganite layers separated by either a perovskite or a rock-salt barrier of variable thickness. Both the type and the quality of the interface have a strong impact on the minimum critical barrier thickness where the manganite layers become magnetically decoupled. A rock-salt barrier layer only 1 unit cell (0.5 nm) thick remains insulating and is able to magnetically de-couple the electrode layers. The technique can therefore be used for developing high-performance planar oxide electronic devices such as magnetic tunnel junctions and quantum well structures that depend on magnetically and electronically sharp heterointerfaces.

Observation of the isotope effect in sub-kelvin reactions

NASA Astrophysics Data System (ADS)

Lavert-Ofir, Etay; Shagam, Yuval; Henson, Alon B.; Gersten, Sasha; Kłos, Jacek; Żuchowski, Piotr S.; Narevicius, Julia; Narevicius, Edvardas

2014-04-01

Quantum phenomena in the translational motion of reactants, which are usually negligible at room temperature, can dominate reaction dynamics at low temperatures. In such cold conditions, even the weak centrifugal force is enough to create a potential barrier that keeps reactants separated. However, reactions may still proceed through tunnelling because, at low temperatures, wave-like properties become important. At certain de Broglie wavelengths, the colliding particles can become trapped in long-lived metastable scattering states, leading to sharp increases in the total reaction rate. Here, we show that these metastable states are responsible for a dramatic, order-of-magnitude-strong, quantum kinetic isotope effect by measuring the absolute Penning ionization reaction rates between hydrogen isotopologues and metastable helium down to 0.01 K. We demonstrate that measurements of a single isotope are insufficient to constrain ab initio calculations, making the kinetic isotope effect in the cold regime necessary to remove ambiguity among possible potential energy surfaces.

Great Barrier Reef, Queensland, Australia

NASA Technical Reports Server (NTRS)

1991-01-01

Along the coast of Queensland, Australia (18.0S, 147.5E), timbered foothills of the Great Dividing Range separate the semi-arid interior of Queensland from the farmlands of the coastal plains. Prominent cleared areas in the forest indicate deforestation for farm and pasture lands. Offshore, islands and the Great Barrier Reef display sand banks along the southern sides of the structures indicating a dominant southerly wind and current direction.

A Novel Multilayered Multidisk Oral Tablet for Chronotherapeutic Drug Delivery

PubMed Central

Khan, Zaheeda; Choonara, Yahya E.; du Toit, Lisa C.; Ndesendo, Valence M. K.; Pillay, Viness

2013-01-01

A Multilayered Multidisk Tablet (MLMDT) comprising two drug-loaded disks enveloped by three drug-free barrier layers was developed for use in chronotherapeutic disorders, employing two model drugs, theophylline and diltiazem HCl. The MLMDT was designed to achieve two pulses of drug release separated by a lag phase. The polymer disk comprised hydroxyethylcellulose (HEC) and ethylcellulose (EC) granulated using an aqueous dispersion of EC. The polymeric barrier layers constituted a combination of pectin/Avicel (PBL) (1st barrier layer) and hydroxypropylmethylcellulose (HPMC) (HBL1 and HBL2) as the 2nd and 3rd barrier layers, respectively. Sodium bicarbonate was incorporated into the diltiazem-containing formulation for delayed drug release. Erosion and swelling studies confirmed the manner in which the drug was released with theophylline formulations exhibiting a maximum swelling of 97% and diltiazem containing formulations with a maximum swelling of 119%. FTIR spectra displayed no interactions between drugs and polymers. Molecular mechanics simulations were undertaken to predict the possible orientation of the polymer morphologies most likely affecting the MLMDT performance. The MLMDT provided two pulses of drug release, separated by a lag phase, and additionally it displayed desirable friability, hardness, and uniformity of mass indicating a stable formulation that may be a desirable candidate for chronotherapeutic drug delivery. PMID:24024200

Current transient spectroscopy for trapping analysis on Au-free AlGaN/GaN Schottky barrier diode

NASA Astrophysics Data System (ADS)

Hu, J.; Stoffels, S.; Lenci, S.; Bakeroot, B.; Venegas, R.; Groeseneken, G.; Decoutere, S.

2015-02-01

This paper presents a combined technique of high voltage off-state stress and current transient measurements to investigate the trapping/de-trapping characteristics of Au-free AlGaN/GaN Schottky barrier diodes. The device features a symmetric three-terminal structure with a central anode contact surrounded by two separate cathodes. Under the diode off-state stress conditions, the two separate cathodes were electrically shorted. The de-trapping dynamics was studied by monitoring the recovery of the two-dimensional electron gas (2DEG) current at different temperatures by applying 0.5 V at cathode 2 while grounding cathode 1. During the recovery, the anode contact acts as a sensor of changes in diode leakage current. This leakage variation was found to be mainly due to the barrier height variation. With this method, the energy level and capture cross section of different traps in the AlGaN/GaN Schottky barrier diode can be extracted. Furthermore, the physical location of different trapping phenomena is indicated by studying the variation of the diode leakage current during the recovery. We have identified two distinct trapping mechanisms: (i) electron trapping at the AlGaN surface in the vicinity of the Schottky contact which results in the leakage reduction (barrier height ϕB increase) together with RON degradation; (ii) the electron trapping in the GaN channel layer which partially depletes the 2DEG. The physical origin of the two different traps is discussed in the text.

Multiple biogeographical barriers identified across the monsoon tropics of northern Australia: phylogeographic analysis of the brachyotis group of rock-wallabies.

PubMed

Potter, Sally; Eldridge, Mark D B; Taggart, David A; Cooper, Steven J B

2012-05-01

The monsoon tropics of northern Australia are a globally significant biodiversity hotspot, but its phylogeography is poorly known. A major challenge for this region is to understand the biogeographical processes that have shaped the distribution and diversity of taxa, without detailed knowledge of past climatic and environmental fluctuations. Although molecular data have great potential to address these questions, only a few species have been examined phylogeographically. Here, we use the widely distributed and abundant short-eared rock-wallaby (Petrogale brachyotis; n = 101), together with the sympatric monjon (P. burbidgei; n = 11) and nabarlek (P. concinna; n = 1), to assess historical evolutionary and biogeographical processes in northern Australia. We sequenced ∼1000 bp of mitochondrial DNA (control region, ND2) and ∼3000 bp of nDNA (BRCA1, ω-globin and two anonymous loci) to investigate phylogeographic structuring and delineate the time-scale of diversification within the region. Our results indicate multiple barriers between the Top End (Northern Territory) and Kimberley (Western Australia), which have caused divergence throughout the Plio-Pleistocene. Eight geographically discrete and genetically distinct lineages within the brachyotis group were identified, five of which are separated by major river valleys (Ord, Victoria, Daly), arid lowlands and discontinuous sandstone ranges. It is likely that these barriers have similarly influenced genetic structure in other monsoonal biota. © 2012 Blackwell Publishing Ltd.

Band-selective filter in a zigzag graphene nanoribbon.

PubMed

Nakabayashi, Jun; Yamamoto, Daisuke; Kurihara, Susumu

2009-02-13

Electric transport of a zigzag graphene nanoribbon through a steplike potential and a barrier potential is investigated by using the recursive Green's function method. In the case of the steplike potential, we demonstrate numerically that scattering processes obey a selection rule for the band indices when the number of zigzag chains is even; the electrons belonging to the "even" ("odd") bands are scattered only into the even (odd) bands so that the parity of the wave functions is preserved. In the case of the barrier potential, by tuning the barrier height to be an appropriate value, we show that it can work as the "band-selective filter", which transmits electrons selectively with respect to the indices of the bands to which the incident electrons belong. Finally, we suggest that this selection rule can be observed in the conductance by applying two barrier potentials.

Apparatus and method for stripping tritium from molten salt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holcomb, David E.; Wilson, Dane F.

A method of stripping tritium from flowing stream of molten salt includes providing a tritium-separating membrane structure having a porous support, a nanoporous structural metal-ion diffusion barrier layer, and a gas-tight, nonporous palladium-bearing separative layer, directing the flowing stream of molten salt into contact with the palladium-bearing layer so that tritium contained within the molten salt is transported through the tritium-separating membrane structure, and contacting a sweep gas with the porous support for collecting the tritium.

Plastics disassembly versus bulk recycling: engineering design for end-of-life electronics resource recovery.

PubMed

Rios, Pedro; Stuart, Julie Ann; Grant, Ed

2003-12-01

Annual plastic flows through the business and consumer electronics manufacturing supply chain include nearly 3 billion lb of high-value engineering plastics derived from petroleum. The recovery of resource value from this stream presents critical challenges in areas of materials identification and recycling process design that demand new green engineering technologies applied together with life cycle assessment and ecological supply chain analysis to create viable plastics-to-plastics supply cycles. The sustainable recovery of potentially high-value engineering plastics streams requires that recyclers either avoid mixing plastic parts or purify later by separating smaller plastic pieces created in volume reduction (shredding) steps. Identification and separation constitute significant barriers in the plastics-to-plastics recycling value proposition. In the present work, we develop a model that accepts randomly arriving electronic products to study scenarios by which a recycler might identify and separate high-value engineering plastics as well as metals. Using discrete eventsimulation,we compare current mixed plastics recovery with spectrochemical plastic resin identification and subsequent sorting. Our results show that limited disassembly with whole-part identification can produce substantial yields in separated streams of recovered engineering thermoplastics. We find that disassembly with identification does not constitute a bottleneck, but rather, with relatively few workers, can be configured to pull the process and thus decrease maximum staging space requirements.

Resonant tunneling of spin-wave packets via quantized states in potential wells.

PubMed

Hansen, Ulf-Hendrik; Gatzen, Marius; Demidov, Vladislav E; Demokritov, Sergej O

2007-09-21

We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.

Selectivity trend of gas separation through nanoporous graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Hongjun; Chen, Zhongfang; Dai, Sheng

2015-04-15

By means of molecular dynamics (MD) simulations, we demonstrate that porous graphene can efficiently separate gases according to their molecular sizes. The flux sequence from the classical MD simulation is H{sub 2}>CO{sub 2}≫N{sub 2}>Ar>CH{sub 4}, which generally follows the trend in the kinetic diameters. This trend is also confirmed from the fluxes based on the computed free energy barriers for gas permeation using the umbrella sampling method and kinetic theory of gases. Both brute-force MD simulations and free-energy calcualtions lead to the flux trend consistent with experiments. Case studies of two compositions of CO{sub 2}/N{sub 2} mixtures further demonstrate themore » separation capability of nanoporous graphene. - Graphical abstract: Classical molecular dynamics simulations show the flux trend of H{sub 2}>CO{sub 2}≫N{sub 2}>Ar>CH{sub 4} for their permeation through a porous graphene, in excellent agreement with a recent experiment. - Highlights: • Classical MD simulations show the flux trend of H{sub 2}>CO{sub 2}≫N{sub 2}>Ar>CH{sub 4} for their permeation through a porous graphene. • Free energy calculations yield permeation barriers for those gases. • Selectivities for several gas pairs are estimated from the free-energy barriers and the kinetic theory of gases. • The selectivity trend is in excellent agreement with a recent experiment.« less

Quantum scattering in one-dimensional systems satisfying the minimal length uncertainty relation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernardo, Reginald Christian S., E-mail: rcbernardo@nip.upd.edu.ph; Esguerra, Jose Perico H., E-mail: jesguerra@nip.upd.edu.ph

In quantum gravity theories, when the scattering energy is comparable to the Planck energy the Heisenberg uncertainty principle breaks down and is replaced by the minimal length uncertainty relation. In this paper, the consequences of the minimal length uncertainty relation on one-dimensional quantum scattering are studied using an approach involving a recently proposed second-order differential equation. An exact analytical expression for the tunneling probability through a locally-periodic rectangular potential barrier system is obtained. Results show that the existence of a non-zero minimal length uncertainty tends to shift the resonant tunneling energies to the positive direction. Scattering through a locally-periodic potentialmore » composed of double-rectangular potential barriers shows that the first band of resonant tunneling energies widens for minimal length cases when the double-rectangular potential barrier is symmetric but narrows down when the double-rectangular potential barrier is asymmetric. A numerical solution which exploits the use of Wronskians is used to calculate the transmission probabilities through the Pöschl–Teller well, Gaussian barrier, and double-Gaussian barrier. Results show that the probability of passage through the Pöschl–Teller well and Gaussian barrier is smaller in the minimal length cases compared to the non-minimal length case. For the double-Gaussian barrier, the probability of passage for energies that are more positive than the resonant tunneling energy is larger in the minimal length cases compared to the non-minimal length case. The approach is exact and applicable to many types of scattering potential.« less

Investigation on the formation of lonsdaleite from graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greshnyakov, V. A.; Belenkov, E. A., E-mail: belenkov@csu.ru

2017-02-15

Structural stability and the possible pathways to experimental formation of lonsdaleite—a hexagonal 2H polytype of diamond—have been studied in the framework of the density functional theory (DFT). It is established that the structural transformation of orthorhombic Cmmm graphite to 2H polytype of diamond must take place at a pressure of 61 GPa, while the formation of lonsdaleite from hexagonal P6/mmm graphite must take place at 56 GPa. The minimum potential barrier height separating the 2H polytype state from graphite is only 0.003 eV/atom smaller than that for the cubic diamond. The high potential barrier is indicative of the possibility ofmore » stable existence of the hexagonal diamond under normal conditions. In this work, we have also analyzed the X-ray diffraction and electron-microscopic data available for nanodiamonds found in meteorite impact craters in search for the presence of hexagonal diamond. Results of this analysis showed that pure 3C and 2H polytypes are not contained in the carbon materials of impact origin, the structure of nanocrystals found representing diamonds with randomly packed layers. The term “lonsdaleite,” used to denote carbon materials found in meteorite impact craters and diamond crystals with 2H polytype structure, is rather ambiguous, since no pure hexagonal diamond has been identified in carbon phases found at meteorite fall sites.« less

'A good fit?' Bringing the sociology of footwear to the clinical encounter in podiatry services: a narrative review.

PubMed

Nicholls, Emily; Robinson, Victoria; Farndon, Lisa; Vernon, Wesley

2018-01-01

This narrative review explores the ways in which drawing on theories and methods used in sociological work on footwear and identity can contribute to healthcare research with podiatrists and their patients, highlighting recent research in this field, implications for practice and potential areas for future development.Traditionally, research within Podiatry Services has tended to adopt a quantitative, positivist focus, developing separately from a growing body of sociological work exploring the importance of shoes in constructing identity and self-image. Bringing qualitative research drawing on sociological theory and methods to the clinical encounter has real potential to increase our understanding of patient values, motivations and - crucially - any barriers to adopting 'healthier' footwear that they may encounter. Such work can help practitioners to understand why patients may resist making changes to their footwear practices, and help us to devise new ways for practitioners to explore and ultimately break down individual barriers to change (including their own preconceptions as practitioners). This, in turn, may lead to long-term, sustainable changes to footwear practices and improvements in foot health for those with complex health conditions and the wider population. A recognition of the complex links between shoes and identity is opening up space for discussion of patient resistance to footwear changes, and paving the way for future research in this field beyond the temporary 'moment' of the clinical encounter.

CNT-Confinement Effects on the Menshutkin SN2 Reaction: The Role of Nonbonded Interactions.

PubMed

Giacinto, Pietro; Zerbetto, Francesco; Bottoni, Andrea; Calvaresi, Matteo

2016-08-09

We investigated the effects of CNT confinement ((6,6) tube) on the model Menshutkin reaction H3N + H3CCl = H3NCH3((+)) + Cl((-)), which is representative of chemical processes involving developing of charge separation along the reaction pathway. We used either a full QM approach or a hybrid QM/MM approach. We found that the CNT significantly lowers the activation barrier with respect to the hypothetical gas-phase reaction: The activation barrier Ea varies from 34.6 to 25.7 kcal mol(-1) (a value similar to that found in a nonpolar solvent) and the endothermicity ΔE from 31.2 to 13.5 kcal mol(-1). A complex interplay between C-H···π, N-H···π, and Cl···π nonbonded interactions of the endohedral system with the CNT wall explains the lower barrier and lower endothermicity. The hybrid QM/MM approach (MM = UFF force field) does not reproduce satisfactorily the QM energy ΔE (18.1 vs 13.5 kcal mol(-1)), while optimum agreement is found in the barrier Ea (25.8 vs 25.7 kcal mol(-1)). These results suggest that the simple Qeq formalism (included in the MM potential) does not describe properly the effect of CNT polarization in the presence of the net charge separation featuring the final product. A more accurate estimate of the tube polarization was obtained with single-point QM/MM computations including PCM corrections (using the benzene dielectric constant) on the QM/MM optimized structures. After PCM corrections, Ea changes slightly (from 25.8 to 24.5 kcal mol(-1)), but a more significant variation is observed for ΔE that becomes 13.1 kcal mol(-1), in rather good agreement with the full QM. This level of theory (QM/MM with PCM correction, MM = UFF) represents a more general approach suitable for describing CNT-confined chemical processes involving significant charge separation. QM/MM computations were extended to CNTs of different radii: (4,4), (5,5), (7,7), (8,8), (9,9), (10,10), (12,12), (14,14) CNTs and, as a limit case, a graphene sheet. The lack of space available in the small tube (4,4) causes a strong structural distortion and a consequent increase in Ea and ΔE (40.8 and 44.0 kcal mol(-1), respectively). These quantities suddenly decrease with the augmented volume inside the (5,5) tube. For larger tubes, different structural arrangements of the endohedral system are possible, and Ea and ΔE remain almost constant until the limiting case of graphene.

InGaP Heterojunction Barrier Solar Cells

NASA Technical Reports Server (NTRS)

Welser, Roger E. (Inventor)

2014-01-01

A new solar cell structure called a heterojunction barrier solar cell is described. As with previously reported quantum-well and quantum-dot solar cell structures, a layer of narrow band-gap material, such as GaAs or indium-rich InGaP, is inserted into the depletion region of a wide band-gap PN junction. Rather than being thin, however, the layer of narrow band-gap material is about 400-430 nm wide and forms a single, ultrawide well in the depletion region. Thin (e.g., 20-50 nm), wide band-gap InGaP barrier layers in the depletion region reduce the diode dark current. Engineering the electric field and barrier profile of the absorber layer, barrier layer, and p-type layer of the PN junction maximizes photogenerated carrier escape. This new twist on nanostructured solar cell design allows the separate optimization of current and voltage to maximize conversion efficiency.

The Role of Structural Barriers in Risky Sexual Behavior, Victimization and Readiness to Change HIV/STI-Related Risk Behavior Among Transgender Women.

PubMed

Raiford, Jerris L; Hall, Grace J; Taylor, Raekiela D; Bimbi, David S; Parsons, Jeffrey T

2016-10-01

This study examines the role of structural barriers experienced by a community-based sample of 63 HIV-positive and negative transgender women that may elevate HIV infection and transmission risks. Separate hierarchical linear multiple regression analyses tested the association between structural barriers (e.g., unemployment, lack of food, shelter) and condomless anal sex acts, abuse, and readiness to change risk behavior, while controlling for other related factors. Among this primarily Hispanic and African-American sample, HIV-positive and negative transgender women experienced a similar number of structural barriers and experiencing structural barriers was significantly associated with an increased number of condomless anal sex acts (p = .002), victimization (p = .000) and a decreased readiness to change HIV-related risk behavior (p = .014). Structural-level interventions are needed to address this elevated risk among this underserved and hard-to-reach population.

Shoreline Evolution and Coastal Resiliency at Two Military Installations: Investigating the Potential for and Impacts of Loss of Protecting Barriers

DTIC Science & Technology

2014-05-01

control barrier morphology and migration (and potentially drowning). We have developed a numerical model of barrier evolution over the centennial ...required to maintain barrier geometries over centennial timescales. Long-term storm histories for each region show a consistent picture of...landward of the flood tidal delta is an area of over 40km2 that is over 9m deep, with some depressions as deep as 12m. During periods of rising sea-level

Universal potential-barrier penetration by initially confined wave packets

NASA Astrophysics Data System (ADS)

Granot, Er'El; Marchewka, Avi

2007-07-01

The dynamics of an initially sharp-boundary wave packet in the presence of an arbitrary potential barrier is investigated. It is shown that the penetration through the barrier is universal in the sense that it depends only on the values of the wave function and its derivatives at the boundary. The dependence on the derivatives vanishes at long distances from the barrier, where the dynamics is governed solely by the initial value of the wave function at the boundary.

Integrin-based diffusion barrier separates membrane domains enabling the formation of microbiostatic frustrated phagosomes

PubMed Central

Maxson, Michelle E; Naj, Xenia; O'Meara, Teresa R; Plumb, Jonathan D; Cowen, Leah E

2018-01-01

Candida albicans hyphae can reach enormous lengths, precluding their internalization by phagocytes. Nevertheless, macrophages engulf a portion of the hypha, generating incompletely sealed tubular phagosomes. These frustrated phagosomes are stabilized by a thick cuff of F-actin that polymerizes in response to non-canonical activation of integrins by fungal glycan. Despite their continuity, the surface and invaginating phagosomal membranes retain a strikingly distinct lipid composition. PtdIns(4,5)P2 is present at the plasmalemma but is not detectable in the phagosomal membrane, while PtdIns(3)P and PtdIns(3,4,5)P3 co-exist in the phagosomes yet are absent from the surface membrane. Moreover, endo-lysosomal proteins are present only in the phagosomal membrane. Fluorescence recovery after photobleaching revealed the presence of a diffusion barrier that maintains the identity of the open tubular phagosome separate from the plasmalemma. Formation of this barrier depends on Syk, Pyk2/Fak and formin-dependent actin assembly. Antimicrobial mechanisms can thereby be deployed, limiting the growth of the hyphae. PMID:29553370

Hypotheses to explain the origin of species in Amazonia.

PubMed

Haffer, J

2008-11-01

The main hypotheses proposed to explain barrier formation separating populations and causing the differentiation of species in Amazonia during the course of geological history are based on different factors, as follow: (1) Changes in the distribution of land and sea or in the landscape due to tectonic movements or sea level fluctuations (Paleogeography hypothesis), (2) the barrier effect of Amazonian rivers (River hypothesis), (3) a combination of the barrier effect of broad rivers and vegetational changes in northern and southern Amazonia (River-refuge hypothesis), (4) the isolation of humid rainforest blocks near areas of surface relief in the periphery of Amazonia separated by dry forests, savannas and other intermediate vegetation types during dry climatic periods of the Tertiary and Quaternary (Refuge hypothesis), (5) changes in canopy-density due to climatic reversals (Canopy-density hypothesis) (6) the isolation and speciation of animal populations in small montane habitat pockets around Amazonia due to climatic fluctuations without major vegetational changes (Museum hypothesis), (7) competitive species interactions and local species isolations in peripheral regions of Amazonia due to invasion and counterinvasion during cold/warm periods of the Pleistocene (Disturbance-vicariance hypothesis) and (8) parapatric speciation across steep environmental gradients without separation of the respective populations (Gradient hypothesis). Several of these hypotheses probably are relevant to a different degree for the speciation processes in different faunal groups or during different geological periods. The basic paleogeography model refers mainly to faunal differentiation during the Tertiary and in combination with the Refuge hypothesis. Milankovitch cycles leading to global main hypotheses proposed to explain barrier formation separating populations and causing the differentiation of species in Amazonia during the course of geological history are based on different factors, as follow: (1) Changes in the distribution of land and sea or in the landscape due to tectonic movements or sea level fluctuations (Paleogeography hypothesis), (2) the barrier effect of Amazonian rivers (River hypothesis), (3) a combination of the barrier effect of broad rivers and vegetational changes in northern and southern Amazonia (River-refuge hypothesis), (4) the isolation of humid rainforest blocks near areas of surface relief in the periphery of Amazonia separated by dry forests, savannas and other intermediate vegetation types during dry climatic periods of the Tertiary and Quaternary (Refuge hypothesis), (5) changes in canopy-density due to climatic reversals (Canopy-density hypothesis) (6) the isolation and speciation of animal populations in small montane habitat pockets around Amazonia due to climatic fluctuations without major vegetational changes (Museum hypothesis), (7) competitive species interactions and local species isolations in peripheral regions of Amazonia due to invasion and counterinvasion during cold/warm periods of the Pleistocene (Disturbance-vicariance hypothesis) and (8) parapatric speciation across steep environmental gradients without separation of the respective populations (Gradient hypothesis). Several of these hypotheses probably are relevant to a different degree for the speciation processes in different faunal groups or during different geological periods. The basic paleogeography model refers mainly to faunal differentiation during the Tertiary and in combination with the Refuge hypothesis. Milankovitch cycles leading to global climatic-vegetational changes affected the biomes of the world not only during the Pleistocene but also during the Tertiary and earlier geological periods. New geoscientific evidence for the effect of dry climatic periods in Amazonia supports the predictions of the Refuge hypothesis. The disturbance-vicariance hypothesis refers to the presumed effect of cold/warm climatic phases of the Pleistocene only and is of limited general relevance because most extant species originated earlier and probably through paleogeographic changes and the formation of ecological refuges during the Tertiary.

Flexible pile thermal barrier insulator

NASA Technical Reports Server (NTRS)

Anderson, G. E.; Fell, D. M.; Tesinsky, J. S. (Inventor)

1978-01-01

A flexible pile thermal barrier insulator included a plurality of upstanding pile yarns. A generally planar backing section supported the upstanding pile yarns. The backing section included a plurality of filler yarns forming a mesh in a first direction. A plurality of warp yarns were looped around said filler yarns and pile yarns in the backing section and formed a mesh in a second direction. A binder prevented separation of the yarns in the backing section.

Field kit and method for testing for the presence of gunshot residue

DOEpatents

Rodacy, Philip J.; Walker, Pamela K.

2003-09-02

A field test kit for gunshot residue comprises a container having at least compartments separated by a barrier. A surface is tested by wiping it with a swab and placing the swab in a first compartment. The barrier is then breached, permitting reagent in the second compartment to flow onto the swab. The first compartment is transparent, and a color change will be observed if the reagent reacts with gunshot residue.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hughes, Michael John; McConnaughhay, Johnie Franklin

A combustor includes a tube bundle that extends radially across at least a portion of the combustor. The tube bundle includes an upstream surface axially separated from a downstream surface, and a plurality of tubes extend from the upstream surface through the downstream surface to provide fluid communication through the tube bundle. A barrier extends radially inside the tube bundle between the upstream and downstream surfaces, and a baffle extends axially inside the tube bundle between the upstream surface and the barrier.

Healthcare workers' attitudes to working during pandemic influenza: a qualitative study

PubMed Central

Ives, Jonathan; Greenfield, Sheila; Parry, Jayne M; Draper, Heather; Gratus, Christine; Petts, Judith I; Sorell, Tom; Wilson, Sue

2009-01-01

Background Healthcare workers (HCWs) will play a key role in any response to pandemic influenza, and the UK healthcare system's ability to cope during an influenza pandemic will depend, to a large extent, on the number of HCWs who are able and willing to work through the crisis. UK emergency planning will be improved if planners have a better understanding of the reasons UK HCWs may have for their absenteeism, and what might motivate them to work during an influenza pandemic. This paper reports the results of a qualitative study that explored UK HCWs' views (n = 64) about working during an influenza pandemic, in order to identify factors that might influence their willingness and ability to work and to identify potential sources of any perceived duty on HCWs to work. Methods A qualitative study, using focus groups (n = 9) and interviews (n = 5). Results HCWs across a range of roles and grades tended to feel motivated by a sense of obligation to work through an influenza pandemic. A number of significant barriers that may prevent them from doing so were also identified. Perceived barriers to the ability to work included being ill oneself, transport difficulties, and childcare responsibilities. Perceived barriers to the willingness to work included: prioritising the wellbeing of family members; a lack of trust in, and goodwill towards, the NHS; a lack of information about the risks and what is expected of them during the crisis; fear of litigation; and the feeling that employers do not take the needs of staff seriously. Barriers to ability and barriers to willingness, however, are difficult to separate out. Conclusion Although our participants tended to feel a general obligation to work during an influenza pandemic, there are barriers to working, which, if generalisable, may significantly reduce the NHS workforce during a pandemic. The barriers identified are both barriers to willingness and to ability. This suggests that pandemic planning needs to take into account the possibility that staff may be absent for reasons beyond those currently anticipated in UK planning documents. In particular, staff who are physically able to attend work may nonetheless be unwilling to do so. Although there are some barriers that cannot be mitigated by employers (such as illness, transport infrastructure etc.), there are a number of remedial steps that can be taken to lesson the impact of others (providing accommodation, building reciprocity, provision of information and guidance etc). We suggest that barriers to working lie along an ability/willingness continuum, and that absenteeism may be reduced by taking steps to prevent barriers to willingness becoming perceived barriers to ability. PMID:19216738

Cellulosic Biomass-Reinforced Polyvinylidene Fluoride Separators with Enhanced Dielectric Properties and Thermal Tolerance.

PubMed

Li, Lei; Yu, Miao; Jia, Chao; Liu, Jianxin; Lv, Yanyan; Liu, Yanhua; Zhou, Yi; Liu, Chuanting; Shao, Ziqiang

2017-06-21

Safety issues are critical barriers to large-scale energy storage applications of lithium-ion batteries (LIBs). Using an ameliorated, thermally stable, shutdown separator is an effective method to overcome the safety issues. Herein, we demonstrate a novel, cellulosic biomass-material-blended polyvinylidene fluoride separator that was prepared using a simple nonsolvent-induced phase separation technique. This process formed a microporous composite separator with reduced crystallinity, uniform pore size distribution, superior thermal tolerance, and enhanced electrolyte wettability and dielectric and mechanical properties. In addition, the separator has a superior capacity retention and a better rate capability compared to the commercialized microporous polypropylene membrane. This fascinating membrane was fabricated via a relatively eco-friendly and cost-effective method and is an alternative, promising separator for high-power LIBs.

Access to Strong Opioid Analgesics in the Context of Legal and Regulatory Barriers in Eleven Central and Eastern European Countries.

PubMed

Vranken, Marjolein J M; Mantel-Teeuwisse, Aukje K; Schutjens, Marie-Hélène D B; Scholten, Willem K; Jünger, Saskia; Medic, Dr Rer; Leufkens, Hubert G M

2018-04-06

In 2011-2013, >95% of the global opioid analgesics consumption occurred in three regions, accounting for 15% of the world population. Despite abundant literature on barriers to access, little is known on the correlation between actual access to opioid analgesics and barriers to access, including legal and regulatory barriers. This study aimed to evaluate the correlation between access to strong opioid analgesics and barriers to access in national legislation and regulations in 11 central and eastern European countries that participated in the Access to Opioid Medication in Europe (ATOME) project. Two variables were contrasted to assess their correlation: the country level of access to strong opioid analgesics indicated by the Adequacy of Consumption Measure (ACM) and the number of potential legal and regulatory barriers identified by an external review of legislation and regulations. A linear correlation was evaluated using a squared linear correlation coefficient. Evaluation of the correlation between the ACM and the number of potential barriers produces an R 2 value of 0.023 and a correlation plot trend line gradient of -0.075, indicating no correlation between access to strong opioid analgesics and the number of potential barriers in national legislation and regulations in the countries studied. No correlation was found, which indicates that other factors besides potential legal and regulatory barriers play a critical role in withholding prescribers and patients essential pain medication in the studied countries. More research is needed toward better understanding of the complex interplay of factors that determine access to strong opioid analgesics.

Radiation-tolerant imaging device

DOEpatents

Colella, N.J.; Kimbrough, J.R.

1996-11-19

A barrier at a uniform depth for an entire wafer is used to produce imaging devices less susceptible to noise pulses produced by the passage of ionizing radiation. The barrier prevents charge created in the bulk silicon of a CCD detector or a semiconductor logic or memory device from entering the collection volume of each pixel in the imaging device. The charge barrier is a physical barrier, a potential barrier, or a combination of both. The physical barrier is formed by an SiO{sub 2} insulator. The potential barrier is formed by increasing the concentration of majority carriers (holes) to combine with the electron`s generated by the ionizing radiation. A manufacturer of CCD imaging devices can produce radiation-tolerant devices by merely changing the wafer type fed into his process stream from a standard wafer to one possessing a barrier beneath its surface, thus introducing a very small added cost to his production cost. An effective barrier type is an SiO{sub 2} layer. 7 figs.

Radiation-tolerant imaging device

DOEpatents

Colella, Nicholas J.; Kimbrough, Joseph R.

1996-01-01

A barrier at a uniform depth for an entire wafer is used to produce imaging devices less susceptible to noise pulses produced by the passage of ionizing radiation. The barrier prevents charge created in the bulk silicon of a CCD detector or a semiconductor logic or memory device from entering the collection volume of each pixel in the imaging device. The charge barrier is a physical barrier, a potential barrier, or a combination of both. The physical barrier is formed by an SiO.sub.2 insulator. The potential barrier is formed by increasing the concentration of majority carriers (holes) to combine with the electron's generated by the ionizing radiation. A manufacturer of CCD imaging devices can produce radiation-tolerant devices by merely changing the wafer type fed into his process stream from a standard wafer to one possessing a barrier beneath its surface, thus introducing a very small added cost to his production cost. An effective barrier type is an SiO.sub.2 layer.

Bryozoan diversity around the Falkland and South Georgia Islands: Overcoming Antarctic barriers.

PubMed

Figuerola, Blanca; Barnes, David K A; Brickle, Paul; Brewin, Paul E

2017-05-01

There are a number of remote archipelagos distributed between 45 and 60 °S. The biota of these islands provide useful information to describe and understand patterns in biodiversity and biogeography as well as potential impacts of climate change on marine ecosystems. They are in key locations either side of the Polar Front but also have limited influence from human activities. Here we investigate one taxon, bryozoans, on South Atlantic shelf habitats of the Falkland (FI) and the sub-Antarctic island of South Georgia (SG). We present new data on spatial distribution in these islands, as well as an analysis of the bryozoological similarities between these and neighbouring regions. A total of 85 species of cheilostome bryozoans (351 samples) were found, belonging to 33 genera, including 18 potentially new genera and 23 new species. Remarkably 65% and 41% of species were reported for the first time at FI and SG, respectively. The highest and the lowest value of species richness and species/genus ratio were found at East (EFI) and West Falkland (WFI), respectively, likely showing a tendency for stronger intrageneric competition. New data from this study were jointly analysed with data from the literature and existing databases, revealing new bathymetric ranges in 32 species. The biogeographic affinities of the bryozoans found give further evidence of the hypothesis of sequential separation of Gondwana and support the changing concept that although the Polar Front acts as a circumpolar biogeographic barrier it is not as impermeable as originally thought. Potential dispersal mechanisms are also discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tunable hydrogen separation in porous graphene membrane: first-principle and molecular dynamic simulation.

PubMed

Tao, Yehan; Xue, Qingzhong; Liu, Zilong; Shan, Meixia; Ling, Cuicui; Wu, Tiantian; Li, Xiaofang

2014-06-11

First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 Å) is expected to show high selectivity of H2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H2 over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES1 membranes both exhibit high selectivity for H2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.

Crossing the Telemedicine Chasm: Have the U.S. Barriers to Widespread Adoption of Telemedicine Been Significantly Reduced? †

PubMed Central

LeRouge, Cynthia; Garfield, Monica J.

2013-01-01

Barriers have challenged widespread telemedicine adoption by health care organizations for 40 years. These barriers have been technological, financial, and legal and have also involved business strategy and human resources. The article canvasses recent trends—events and activities in each of these areas as well as US health reform activities that might help to break down these barriers. The key to telemedicine success in the future is to view it as an integral part of health care services and not as a stand-alone project. Telemedicine must move from experimental and separate to integrated and equivalent to other health services within health care organizations. Furthermore, telemedicine serves as vital connective tissue for expanding health care organization networks. PMID:24287864

Barriers to the free diffusion of proteins and lipids in the plasma membrane

PubMed Central

Trimble, William S.

2015-01-01

Biological membranes segregate into specialized functional domains of distinct composition, which can persist for the entire life of the cell. How separation of their lipid and (glyco)protein components is generated and maintained is not well understood, but the existence of diffusional barriers has been proposed. Remarkably, the physical nature of such barriers and the manner whereby they impede the free diffusion of molecules in the plane of the membrane has rarely been studied in depth. Moreover, alternative mechanisms capable of generating membrane inhomogeneity are often disregarded. Here we describe prototypical biological systems where membrane segregation has been amply documented and discuss the role of diffusional barriers and other processes in the generation and maintenance of their structural and functional compartmentalization. PMID:25646084

Barriers to the free diffusion of proteins and lipids in the plasma membrane.

PubMed

Trimble, William S; Grinstein, Sergio

2015-02-02

Biological membranes segregate into specialized functional domains of distinct composition, which can persist for the entire life of the cell. How separation of their lipid and (glyco)protein components is generated and maintained is not well understood, but the existence of diffusional barriers has been proposed. Remarkably, the physical nature of such barriers and the manner whereby they impede the free diffusion of molecules in the plane of the membrane has rarely been studied in depth. Moreover, alternative mechanisms capable of generating membrane inhomogeneity are often disregarded. Here we describe prototypical biological systems where membrane segregation has been amply documented and discuss the role of diffusional barriers and other processes in the generation and maintenance of their structural and functional compartmentalization. © 2015 Trimble and Grinstein.

Vertical transport in graphene-hexagonal boron nitride heterostructure devices

PubMed Central

Bruzzone, Samantha; Logoteta, Demetrio; Fiori, Gianluca; Iannaccone, Giuseppe

2015-01-01

Research in graphene-based electronics is recently focusing on devices based on vertical heterostructures of two-dimensional materials. Here we use density functional theory and multiscale simulations to investigate the tunneling properties of single- and double-barrier structures with graphene and few-layer hexagonal boron nitride (h-BN) or hexagonal boron carbon nitride (h-BC2N). We find that tunneling through a single barrier exhibit a weak dependence on energy. We also show that in double barriers separated by a graphene layer we do not observe resonant tunneling, but a significant increase of the tunneling probability with respect to a single barrier of thickness equal to the sum of the two barriers. This is due to the fact that the graphene layer acts as an effective phase randomizer, suppressing resonant tunneling and effectively letting a double-barrier structure behave as two single-barriers in series. Finally, we use multiscale simulations to reproduce a current-voltage characteristics resembling that of a resonant tunneling diode, that has been experimentally observed in single barrier structure. The peak current is obtained when there is perfect matching between the densities of states of the cathode and anode graphene regions. PMID:26415656

Single-step CE for miniaturized and easy-to-use system.

PubMed

Ono, Koichi; Kaneda, Shohei; Fujii, Teruo

2013-03-01

We developed a novel single-step capillary electrophoresis (SSCE) scheme for miniaturized and easy to use system by using a microchannel chip, which was made from the hydrophilic material polymethyl methacrylate (PMMA), equipped with a capillary stop valve. Taking the surface tension property of liquids into consideration, the capillary effect was used to introduce liquids and control capillary stop valves in a partial barrier structure in the wall of the microchannel. Through the combined action of stop valves and air vents, both sample plug formation for electrophoresis and sample injection into a separation channel were successfully performed in a single step. To optimize SSCE, different stop valve structures were evaluated using actual microchannel chips and the finite element method with the level set method. A partial barrier structure at the bottom of the channel functioned efficiently as a stop valve. The stability of stop valve was confirmed by a shock test, which was performed by dropping the microchannel chip to a floor. Sample plug deformation could be reduced by minimizing the size of the side partial barrier. By dissolving hydroxyl ethyl cellulose and using it as the sample solution, the EOF and adsorption of the sample into the PMMA microchannel were successfully reduced. Using this method, a 100-bp DNA ladder was concentrated; good separation was observed within 1 min. At a separation length of 5 mm, the signal was approximately 20-fold higher than a signal of original sample solution by field-amplified sample stacking effect. All operations, including liquid introduction and sample separation, can be completed within 2 min by using the SSCE scheme. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analytical investigation of thermal barrier coatings for advanced power generation combustion turbines

NASA Technical Reports Server (NTRS)

Amos, D. J.

1977-01-01

An analytical evaluation was conducted to determine quantitatively the improvement potential in cycle efficiency and cost of electricity made possible by the introduction of thermal barrier coatings to power generation combustion turbine systems. The thermal barrier system, a metallic bond coat and yttria stabilized zirconia outer layer applied by plasma spray techniques, acts as a heat insulator to provide substantial metal temperature reductions below that of the exposed thermal barrier surface. The study results show the thermal barrier to be a potentially attractive means for improving performance and reducing cost of electricity for the simple, recuperated, and combined cycles evaluated.

[Prevalence of barriers for physical activity in adolescents].

PubMed

Santos, Mariana Silva; Hino, Adriano Akira Ferreira; Reis, Rodrigo Siqueira; Rodriguez-Añez, Ciro Romélio

2010-03-01

The aim of this study was to analyze the prevalence and association of barriers to physical activity among adolescents. This cross-sectional study evaluated a representative sample of public high school students in Curitiba-PR, Brazil. A total of 1,609 school adolescents (59.7% male) between 14 and 18 years of age answered a questionnaire on physical activity status and barriers to physical activity. Logistic regressions were conducted for each barrier investigated to verify the association between the prevalence of barriers and physical activity, adjusting for confounding variables (age and socioeconomic status). Analyses were done separately for boys and girls. Only 22% of boys and 9% of girls achieved the current physical activity recommendation. Among the 12 barriers investigated, only "there is nobody to take" did not differ between boys and girls. The perception of barriers was higher for girls than boys (p < 0.05) for all other barriers. "Lack of friends company" and "feel lazy" were the barriers most often reported by boys (30.4%) and girls (51.8%) respectively; however, the barrier most strongly associated with prevalence of physical inactivity was "prefer to do other things" for both boys (OR = 5.02 (2.69 - 9.37); p < 0.05) and girls (OR = 7.10 (3.71 - 13.60); p < 0.05). Perceived barriers for the practice of physical activity were more prevalent in girls and differed as to the extent of importance between genders.

Separation of Dynamics in the Free Energy Landscape

NASA Astrophysics Data System (ADS)

Ekimoto, Toru; Odagaki, Takashi; Yoshimori, Akira

2008-02-01

The dynamics of a representative point in a model free energy landscape (FEL) is analyzed by the Langevin equation with the FEL as the driving potential. From the detailed analysis of the generalized susceptibility, fast, slow and Johari-Goldstein (JG) processes are shown to be well described by the FEL. Namely, the fast process is determined by the stochastic motion confined in a basin of the FEL and the relaxation time is related to the curvature of the FEL at the bottom of the basin. The jump motion among basins gives rise to the slow relaxation whose relaxation time is determined by the distribution of the barriers in the FEL and the JG process is produced by weak modulation of the FEL.

Anomalous Coulomb oscillation in crossed carbon nanotubes

NASA Astrophysics Data System (ADS)

Baek, Seung Jae; Lee, Dongsu; Park, Seung Joo; Park, Yung Woo; Svensson, Johannes; Jonson, Mats; Campbell, Eleanor E. B.

2008-03-01

Single-walled carbon nanotube (SWCNT) crossed junctions separated by an insulating layer were fabricated to investigate the double quantum dot modulated by a single gate (DQD-sG). Anomalous Coulomb oscillations were observed on the lower CNT at low temperature, where the behavior was interpreted by the concept of a double quantum dot (DQD) system http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id =APPLAB000089000023233107000001&idtype=cvips&gifs=yes [1]. To understand it more clearly, we have intentionally fabricated crossed CNTs without oxide layer in between. The observed anomalous Coulomb oscillations indicate that the contact resistance between the two tubes becomes a potential barrier splitting the initial single QD into the DQD, and the back-gate modulates the energy levels of the DQD.

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes.

PubMed

Li, Yiyang; El Gabaly, Farid; Ferguson, Todd R; Smith, Raymond B; Bartelt, Norman C; Sugar, Joshua D; Fenton, Kyle R; Cogswell, Daniel A; Kilcoyne, A L David; Tyliszczak, Tolek; Bazant, Martin Z; Chueh, William C

2014-12-01

Many battery electrodes contain ensembles of nanoparticles that phase-separate on (de)intercalation. In such electrodes, the fraction of actively intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports of the active particle population in the phase-separating electrode lithium iron phosphate (LiFePO4; LFP) vary widely, ranging from near 0% (particle-by-particle) to 100% (concurrent intercalation). Using synchrotron-based X-ray microscopy, we probed the individual state-of-charge for over 3,000 LFP particles. We observed that the active population depends strongly on the cycling current, exhibiting particle-by-particle-like behaviour at low rates and increasingly concurrent behaviour at high rates, consistent with our phase-field porous electrode simulations. Contrary to intuition, the current density, or current per active internal surface area, is nearly invariant with the global electrode cycling rate. Rather, the electrode accommodates higher current by increasing the active particle population. This behaviour results from thermodynamic transformation barriers in LFP, and such a phenomenon probably extends to other phase-separating battery materials. We propose that modifying the transformation barrier and exchange current density can increase the active population and thus the current homogeneity. This could introduce new paradigms to enhance the cycle life of phase-separating battery electrodes.

Implementation of a Non-Metallic Barrier in an Electric Motor

NASA Technical Reports Server (NTRS)

M?Sadoques, George; Carra, Michael; Beringer, Woody

2012-01-01

Electric motors that run in pure oxygen must be sealed, or "canned," for safety reasons to prevent the oxygen from entering into the electrical portion of the motor. The current canning process involves designing a metallic barrier around the rotor to provide the separation. This metallic barrier reduces the motor efficiency as speed is increased. In higher-speed electric motors, efficiency is greatly improved if a very thin, nonmetallic barrier can be utilized. The barrier thickness needs to be approximately 0.025-in. (.0.6-mm) thick and can be made of a brittle material such as glass. The motors, however, designed for space applications are typically subject to high-vibration environments. A fragile, non-metallic barrier can be utilized in a motor assembly if held in place by a set of standard rubber O-ring seals. The O-rings provide the necessary sealing to keep oxygen away from the electrical portion of the motor and also isolate the fragile barrier from the harsh motor vibration environment. The compliance of the rubber O-rings gently constrains the fragile barrier and isolates it from the harsh external motor environment. The use of a non-metallic barrier greatly improves motor performance, especially at higher speeds, while isolating the electronics from the working fluid with an inert liner.

Free energy barriers for escape of water molecules from protein hydration layer.

PubMed

Roy, Susmita; Bagchi, Biman

2012-03-08

Free energy barriers separating interfacial water molecules from the hydration layer at the surface of a protein to the bulk are obtained by using the umbrella sampling method of free energy calculation. We consider hydration layer of chicken villin head piece (HP-36) which has been studied extensively by molecular dynamics simulations. The free energy calculations reveal a strong sensitivity to the secondary structure. In particular, we find a region near the junction of first and second helix that contains a cluster of water molecules which are slow in motion, characterized by long residence times (of the order of 100 ps or more) and separated by a large free energy barrier from the bulk water. However, these "slow" water molecules constitute only about 5-10% of the total number of hydration layer water molecules. Nevertheless, they play an important role in stabilizing the protein conformation. Water molecules near the third helix (which is the important helix for biological function) are enthalpically least stable and exhibit the fastest dynamics. Interestingly, barrier height distributions of interfacial water are quite broad for water surrounding all the three helices (and the three coils), with the smallest barriers found for those near the helix-3. For the quasi-bound water molecules near the first and second helices, we use well-known Kramers' theory to estimate the residence time from the free energy surface, by estimating the friction along the reaction coordinate from the diffusion coefficient by using Einstein relation. The agreement found is satisfactory. We discuss the possible biological function of these slow, quasi-bound (but transient) water molecules on the surface.

High-Throughput Screening for Identification of Blood-Brain Barrier Integrity Enhancers: A Drug Repurposing Opportunity to Rectify Vascular Amyloid Toxicity.

PubMed

Qosa, Hisham; Mohamed, Loqman A; Al Rihani, Sweilem B; Batarseh, Yazan S; Duong, Quoc-Viet; Keller, Jeffrey N; Kaddoumi, Amal

2016-07-06

The blood-brain barrier (BBB) is a dynamic interface that maintains brain homeostasis and protects it from free entry of chemicals, toxins, and drugs. The barrier function of the BBB is maintained mainly by capillary endothelial cells that physically separate brain from blood. Several neurological diseases, such as Alzheimer's disease (AD), are known to disrupt BBB integrity. In this study, a high-throughput screening (HTS) was developed to identify drugs that rectify/protect BBB integrity from vascular amyloid toxicity associated with AD progression. Assessing Lucifer Yellow permeation across in-vitro BBB model composed from mouse brain endothelial cells (bEnd3) grown on 96-well plate inserts was used to screen 1280 compounds of Sigma LOPAC®1280 library for modulators of bEnd3 monolayer integrity. HTS identified 62 compounds as disruptors, and 50 compounds as enhancers of the endothelial barrier integrity. From these 50 enhancers, 7 FDA approved drugs were identified with EC50 values ranging from 0.76-4.56 μM. Of these 7 drugs, 5 were able to protect bEnd3-based BBB model integrity against amyloid toxicity. Furthermore, to test the translational potential to humans, the 7 drugs were tested for their ability to rectify the disruptive effect of Aβ in the human endothelial cell line hCMEC/D3. Only 3 (etodolac, granisetron, and beclomethasone) out of the 5 effective drugs in the bEnd3-based BBB model demonstrated a promising effect to protect the hCMEC/D3-based BBB model integrity. These drugs are compelling candidates for repurposing as therapeutic agents that could rectify dysfunctional BBB associated with AD.

High-throughput screening for identification of blood-brain barrier integrity enhancers: a drug repurposing opportunity to rectify vascular amyloid toxicity

PubMed Central

Qosa, Hisham; Mohamed, Loqman A.; Al Rihani, Sweilem B.; Batarseh, Yazan S.; Duong, Quoc-Viet; Keller, Jeffrey N.; Kaddoumi, Amal

2016-01-01

The blood-brain barrier (BBB) is a dynamic interface that maintains brain homeostasis and protects it from free entry of chemicals, toxins and drugs. The barrier function of the BBB is maintained mainly by capillary endothelial cells that physically separate brain from blood. Several neurological diseases, such as Alzheimer’s disease (AD), are known to disrupt BBB integrity. In this study, a high-throughput screening (HTS) was developed to identify drugs that rectify/protect BBB integrity from vascular amyloid toxicity associated with AD progression. Assessing Lucifer Yellow permeation across in-vitro BBB model composed from mouse brain endothelial cells (bEnd3) grown on 96-well plate inserts was used to screen 1280 compounds of Sigma LOPAC®1280 library for modulators of bEnd3 monolayer integrity. HTS identified 62 compounds as disruptors, and 50 compounds as enhancers of the endothelial barrier integrity. From these 50 enhancers, 7 FDA approved drugs were identified with EC50 values ranging from 0.76–4.56 μM. Of these 7 drugs, five were able to protect bEnd3-based BBB model integrity against amyloid toxicity. Furthermore, to test the translational potential to humans, the 7 drugs were tested for their ability to rectify the disruptive effect of Aβ in the human endothelial cell line hCMEC/D3. Only 3 (etodolac, granisetron and beclomethasone) out of the 5 effective drugs in the bEnd3-based BBB model demonstrated a promising effect to protect the hCMEC/D3-based BBB model integrity. These drugs are compelling candidates for repurposing as therapeutic agents that could rectify dysfunctional BBB associated with AD. PMID:27392852

Practical Methods for Including Torsional Anharmonicity in Thermochemical Calculations on Complex Molecules: The Internal-Coordinate Multi-Structural Approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, J.; Yu, T.; Papajak, E.

2011-01-01

Many methods for correcting harmonic partition functions for the presence of torsional motions employ some form of one-dimensional torsional treatment to replace the harmonic contribution of a specific normal mode. However, torsions are often strongly coupled to other degrees of freedom, especially other torsions and low-frequency bending motions, and this coupling can make assigning torsions to specific normal modes problematic. Here, we present a new class of methods, called multi-structural (MS) methods, that circumvents the need for such assignments by instead adjusting the harmonic results by torsional correction factors that are determined using internal coordinates. We present three versions ofmore » the MS method: (i) MS-AS based on including all structures (AS), i.e., all conformers generated by internal rotations; (ii) MS-ASCB based on all structures augmented with explicit conformational barrier (CB) information, i.e., including explicit calculations of all barrier heights for internal-rotation barriers between the conformers; and (iii) MS-RS based on including all conformers generated from a reference structure (RS) by independent torsions. In the MS-AS scheme, one has two options for obtaining the local periodicity parameters, one based on consideration of the nearly separable limit and one based on strongly coupled torsions. The latter involves assigning the local periodicities on the basis of Voronoi volumes. The methods are illustrated with calculations for ethanol, 1-butanol, and 1-pentyl radical as well as two one-dimensional torsional potentials. The MS-AS method is particularly interesting because it does not require any information about conformational barriers or about the paths that connect the various structures.« less

Practical methods for including torsional anharmonicity in thermochemical calculations on complex molecules: the internal-coordinate multi-structural approximation.

PubMed

Zheng, Jingjing; Yu, Tao; Papajak, Ewa; Alecu, I M; Mielke, Steven L; Truhlar, Donald G

2011-06-21

Many methods for correcting harmonic partition functions for the presence of torsional motions employ some form of one-dimensional torsional treatment to replace the harmonic contribution of a specific normal mode. However, torsions are often strongly coupled to other degrees of freedom, especially other torsions and low-frequency bending motions, and this coupling can make assigning torsions to specific normal modes problematic. Here, we present a new class of methods, called multi-structural (MS) methods, that circumvents the need for such assignments by instead adjusting the harmonic results by torsional correction factors that are determined using internal coordinates. We present three versions of the MS method: (i) MS-AS based on including all structures (AS), i.e., all conformers generated by internal rotations; (ii) MS-ASCB based on all structures augmented with explicit conformational barrier (CB) information, i.e., including explicit calculations of all barrier heights for internal-rotation barriers between the conformers; and (iii) MS-RS based on including all conformers generated from a reference structure (RS) by independent torsions. In the MS-AS scheme, one has two options for obtaining the local periodicity parameters, one based on consideration of the nearly separable limit and one based on strongly coupled torsions. The latter involves assigning the local periodicities on the basis of Voronoi volumes. The methods are illustrated with calculations for ethanol, 1-butanol, and 1-pentyl radical as well as two one-dimensional torsional potentials. The MS-AS method is particularly interesting because it does not require any information about conformational barriers or about the paths that connect the various structures.

Economic Evaluation of Isolation of Hemicelluloses From Process Streams From Thermomechanical Pulping of Spruce

NASA Astrophysics Data System (ADS)

Persson, Tobias; Nordin, Anna-Karin; Zacchi, Guido; Jönsson, Ann-Sofi

Hemicelluloses, which are abundant in nature and have potential use in a wide variety of applications, may make an important contribution in helping relieve society of its dependence on petrochemicals. However, cost-efficient methods for the isolation of hemicelluloses are required. This article presents an economic evaluation of a full-scale process to isolate hemicelluloses from process water from a thermomechanical pulp mill. Experimental data obtained in laboratory scale were used for the scale up of the process by computer simulation. The isolation method consisted of two process steps. The suspended matter in the process water was removed by microfiltration and thereafter the hemicelluloses were concentrated by ultrafiltration, and at the same time, separated from smaller molecules and ions in the process water. The isolated hemicelluloses were intended for the production of oxygen barriers for food packaging, an application for which they have been shown to have suitable properties. The solution produced contained 30 g hemicelluloses/L with a purity (defined as the ratio between the hemicelluloses and the total solids) of approx 80%. The evaluation was performed for a plant with a daily production of 4 metric tonnes (t) of hemicelluloses, which is the estimated future need of barrier films at Tetra Pak (Lund, Sweden). The production cost was calculated to be € 670/t of hemiceluloses. This is approx 9 times lower than the price of ethylene vinyl alcohol, which is produced by petrochemicals and is currently used as an oxygen barrier in fiber-based packaging materials. This indicates that it is possible to produce oxygen barriers made of hemicelluloses at a prices that is competitive with the materials used today.

Effects of water activity and low molecular weight humectants on skin permeability and hydration dynamics - a double-blind, randomized and controlled study.

PubMed

Albèr, C; Buraczewska-Norin, I; Kocherbitov, V; Saleem, S; Lodén, M; Engblom, J

2014-10-01

The mammalian skin is a barrier that effectively separates the water-rich interior of the body from the normally dryer exterior. Changes in the external conditions, for example ambient humidity, have been shown to affect the skin barrier properties. The prime objective of this study was to evaluate the effect of water activity of a topical formulation on skin hydration and permeability. A second objective was to gain more understanding on how two commonly used humectants, urea and glycerol, affect skin barrier function in vivo. Simple aqueous formulations were applied under occlusion to the volar forearm of healthy volunteers. Following 4-h exposure, skin water loss (by transepidermal water loss measurements), skin hydration (by Corneometry) and skin permeability (by time to vasodilation due to benzyl nicotinate exposure) were monitored. The results demonstrate that a relatively small change in the water activity of a topical formulation is sufficient to induce considerable effects on stratum corneum hydration and permeability to exogenous substances. Exposing the skin to high water activity leads to increased skin hydration and also increased permeability. Furthermore, urea and glycerol promote skin hydration and permeability even at reduced water activity of the applied formulation. These results highlight the importance of considering the water activity in topically applied formulations and the potential benefit of using humectants. The results may impact formulation optimization in how to facilitate skin hydration and to modify skin permeability by temporarily open and close the skin barrier. © 2014 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Improvement of hydration and epidermal barrier function in human skin by a novel compound isosorbide dicaprylate.

PubMed

Chaudhuri, R K; Bojanowski, K

2017-10-01

The study involved the synthesis of a novel derivative of caprylic acid - isosorbide dicaprylate (IDC) - and the evaluation of its potential in improving water homoeostasis and epidermal barrier function in human skin. The effect of IDC on gene expression was assayed in skin organotypic cultures by DNA microarrays. The results were then confirmed for a few key genes by quantitative PCR, immuno- and cytochemistry. Final validation of skin hydration properties was obtained by four separate clinical studies. Level of hydration was measured by corneometer either by using 2% IDC lotion alone vs placebo or in combination with 2% glycerol lotion vs 2% glycerol only. A direct comparison in skin hydration between 2% IDC and 2% glycerol lotions was also carried out. The epidermal barrier function improvement was assessed by determining changes in transepidermal water loss (TEWL) on the arms before and after treatment with 2% IDC lotion versus placebo. IDC was found to upregulate the expression of AQP3, CD44 and proteins involved in keratinocyte differentiation as well as the formation and function of stratum corneum. A direct comparison between 2% IDC versus 2% glycerol lotions revealed a three-fold advantage of IDC in providing skin hydration. Severely dry skin treated with 2% IDC in combination with 2% glycerol showed 133% improvement, whereas 35% improvement was observed with moderately dry human skin. Topical isosorbide dicaprylate favourably modulates genes involved in the maintenance of skin structure and function, resulting in superior clinical outcomes. By improving skin hydration and epidermal permeability barrier, it offers therapeutic applications in skin ageing. © 2017 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Stage-dependency of apoptosis and the blood-testis barrier in the dogfish shark (Squalus acanthias): cadmium-induced changes as assessed by vital fluorescence techniques.

PubMed

McClusky, Leon M

2006-09-01

Naturally occurring heavy metals and synthetic compounds are potentially harmful for testicular function but evidence linking heavy metal exposure to reduced semen parameters is inconclusive. Elucidation of the exact stage at which the toxicant interferes with spermatogenesis is difficult because the various germ cell stages may have different sensitivities to any given toxicant, germ cell development is influenced by supporting testicular somatic cells and the presence of inter-Sertoli cell tight junctions create a blood-testis barrier, sequestering meiotic and postmeiotic germ cells in a special microenvironment. Sharks such as Squalus acanthias provide a suitable model for studying aspects of vertebrate spermatogenosis because of their unique features: spermatogenesis takes place within spermatocysts and relies mainly on Sertoli cells for somatic cell support; spermatocysts are linearly arranged in a maturational order across the diameter of the elongated testis; spermatocysts containing germ cells at different stages of development are topographically separated, resulting in visible zonation in testicular cross sections. We have used the vital dye acridine orange and a novel fluorescence staining technique to study this model to determine (1) the efficacy of these methods in assays of apoptosis and blood-testis barrier function, (2) the sensitivity of the various spermatogonial generations in Squalus to cadmium (as an illustrative spermatotoxicant) and (3) the way that cadmium might affect more mature spermatogenic stages and other physiological processes in the testis. Our results show that cadmium targets early spermatogenic stages, where it specifically activates a cell death program in susceptible (mature) spermatogonial clones, and negatively affects blood-testis barrier function. Since other parameters are relatively unaffected by cadmium, the effects of this toxicant on apoptosis are presumably process-specific and not attributable to general toxicity.

Making molehills out of mountains: landscape genetics of the Mojave desert tortoise

USGS Publications Warehouse

Hagerty, Bridgette E.; Nussear, Kenneth E.; Esque, Todd C.; Tracy, C. Richard

2010-01-01

Heterogeneity in habitat often influences how organisms traverse the landscape matrix that connects populations. Understanding landscape connectivity is important to determine the ecological processes that influence those movements, which lead to evolutionary change due to gene flow. Here, we used landscape genetics and statistical models to evaluate hypotheses that could explain isolation among locations of the threatened Mojave desert tortoise (Gopherus agassizii). Within a causal modeling framework, we investigated three factors that can influence landscape connectivity: geographic distance, barriers to dispersal, and landscape friction. A statistical model of habitat suitability for the Mojave desert tortoise, based on topography, vegetation, and climate variables, was used as a proxy for landscape friction and barriers to dispersal. We quantified landscape friction with least-cost distances and with resistance distances among sampling locations. A set of diagnostic partial Mantel tests statistically separated the hypotheses of potential causes of genetic isolation. The best-supported model varied depending upon how landscape friction was quantified. Patterns of genetic structure were related to a combination of geographic distance and barriers as defined by least-cost distances, suggesting that mountain ranges and extremely low-elevation valleys influence connectivity at the regional scale beyond the tortoises' ability to disperse. However, geographic distance was the only influence detected using resistance distances, which we attributed to fundamental differences between the two ways of quantifying friction. Landscape friction, as we measured it, did not influence the observed patterns of genetic distances using either quantification. Barriers and distance may be more valuable predictors of observed population structure for species like the desert tortoise, which has high dispersal capability and a long generation time.

Healthcare Access for Iraqi Refugee Children in Texas: Persistent Barriers, Potential Solutions, and Policy Implications.

PubMed

Vermette, David; Shetgiri, Rashmi; Al Zuheiri, Haidar; Flores, Glenn

2015-10-01

To identify access barriers to healthcare and potential interventions to improve access for Iraqi refugee children. Four focus groups were conducted using consecutive sampling of Iraqi refugee parents residing in the US for 8 months to 5 years. Eight key-informant interviews also were conducted with employees of organizations serving Iraqi refugee families, recruited using snowball sampling. Focus groups and interviews were audiotaped, transcribed, and analyzed using margin coding and grounded theory. Iraqi refugees identified provider availability, Medicaid maintenance and renewal, language issues, and inadequate recognition of post-traumatic stress disorder as barriers to care for their children. Interviewees cited loss of case-management services and difficulties in understanding the Medicaid renewal process as barriers. Potential interventions to improve access include community-oriented efforts to educate parents on Medicaid renewal, obtaining services, and accessing specialists. Given the enduring nature of language and Medicaid renewal barriers, policies addressing eligibility alone are insufficient.

Use of fluorescent ANTS to examine the BBB-permeability of polysaccharide

PubMed Central

Christopher, Kevin; Makani, Vishruti; Judy, Wesley; Lee, Erica; Chiaia, Nicolas; Kim, Dong Shik; Park, Joshua

2015-01-01

Recently, some polysaccharides showed therapeutic potentials for the treatment of neurodegenerative diseases while the most important property, their permeability to the blood brain barrier (BBB) that sheathes the brain and spinal cord, is not yet determined. The determination has been delayed by the difficulty in tracking a target polysaccharide among endogenous polysaccharides in animal. We developed an easy way to examine the BBB-permeability and, possibly, tissue distribution of a target polysaccharide in animal. We tagged a polysaccharide with fluorescent 8-aminonaphthalene-1,3,6-trisulfonic acid disodium salt (ANTS) for tracking. We also developed a simple method to separate ANTS-tagged polysaccharide from unconjugated free ANTS using 75% ethanol. After ANTS-polysaccharide was intra-nasally administered into animals, we could quantify the amounts of ANTS-polysaccharide in the brain and the serum by fluorocytometry. We could also separate free ANTS-polysaccharide from serum proteins using trichloroacetic acid (TCA) and 75% ethanol. Our method will help to track a polysaccharide in animal easily. • ANTS-labeling is less tedious than but as powerful as radiolabeling for tracking a target polysaccharide in animal. • Our simple method can separate structurally intact ANTS-polysaccharide from animal serum and tissues. • This method is good for the fluorometry-based measurement of ANTS-conjugated macromolecules in tissues. PMID:25914873

Agent based modeling of the effects of potential treatments over the blood-brain barrier in multiple sclerosis.

PubMed

Pennisi, Marzio; Russo, Giulia; Motta, Santo; Pappalardo, Francesco

2015-12-01

Multiple sclerosis is a disease of the central nervous system that involves the destruction of the insulating sheath of axons, causing severe disabilities. Since the etiology of the disease is not yet fully understood, the use of novel techniques that may help to understand the disease, to suggest potential therapies and to test the effects of candidate treatments is highly advisable. To this end we developed an agent based model that demonstrated its ability to reproduce the typical oscillatory behavior observed in the most common form of multiple sclerosis, relapsing-remitting multiple sclerosis. The model has then been used to test the potential beneficial effects of vitamin D over the disease. Many scientific studies underlined the importance of the blood-brain barrier and of the mechanisms that influence its permeability on the development of the disease. In the present paper we further extend our previously developed model with a mechanism that mimics the blood-brain barrier behavior. The goal of our work is to suggest the best strategies to follow for developing new potential treatments that intervene in the blood-brain barrier. Results suggest that the best treatments should potentially prevent the opening of the blood-brain barrier, as treatments that help in recovering the blood-brain barrier functionality could be less effective. Copyright © 2015 Elsevier B.V. All rights reserved.

Evidence for the Existence of a Bone Marrow Blood Barrier for the Passage of Specific Committed Stem Cells in Human and Canine and Their Physical Separation from Lymphocytes and Pluripotent Stem Cells

DTIC Science & Technology

1982-11-12

COMWITTED STEM CELLS IN HUMANS AND CANINES AND THEIR PHYSICAL SEPARATION FROM LYMPHOCYTES AND PLURIPOTENT STEM CELLS Name of Candidate: Thomas J...Passage of Specific Committed Stem CeUs in Human and Canine and Their Physical Separation From Lymphocytes and Pluripotent Stem Cells Thomas Jose...principle of counterflow centrifugation elutriation (CCE) for the broader enunciation of this theory in the canine and to postulate a similar theory

Resonances for Symmetric Two-Barrier Potentials

ERIC Educational Resources Information Center

Fernandez, Francisco M.

2011-01-01

We describe a method for the accurate calculation of bound-state and resonance energies for one-dimensional potentials. We calculate the shape resonances for symmetric two-barrier potentials and compare them with those coming from the Siegert approximation, the complex scaling method and the box-stabilization method. A comparison of the…

Effect of deformation and orientation on spin orbit density dependent nuclear potential

NASA Astrophysics Data System (ADS)

Mittal, Rajni; Kumar, Raj; Sharma, Manoj K.

2017-11-01

Role of deformation and orientation is investigated on spin-orbit density dependent part VJ of nuclear potential (VN=VP+VJ) obtained within semi-classical Thomas Fermi approach of Skyrme energy density formalism. Calculations are performed for 24-54Si+30Si reactions, with spherical target 30Si and projectiles 24-54Si having prolate and oblate shapes. The quadrupole deformation β2 is varying within range of 0.023 ≤ β2 ≤0.531 for prolate and -0.242 ≤ β2 ≤ -0.592 for oblate projectiles. The spin-orbit dependent potential gets influenced significantly with inclusion of deformation and orientation effect. The spin-orbit barrier and position gets significantly influenced by both the sign and magnitude of β2-deformation. Si-nuclei with β22<0 have higher spin-orbit barrier (compact spin-orbit configuration) in comparison to systems with β2>0. The possible role of spin-orbit potential on barrier characteristics such as barrier height, barrier curvature and on the fusion pocket is also probed. In reference to prolate and oblate systems, the angular dependence of spin-orbit potential is further studied on fusion cross-sections.

Perceived barriers to care and provider gender preferences among veteran men who have experienced military sexual trauma: a qualitative analysis.

PubMed

Turchik, Jessica A; McLean, Caitlin; Rafie, Samantha; Hoyt, Tim; Rosen, Craig S; Kimerling, Rachel

2013-05-01

Research suggests that there may be unique barriers to accessing care among men who have experienced sexual trauma. The primary goal of the current research was to elucidate potential barriers to accessing military sexual trauma (MST)-related care for male veterans. A secondary goal was to explore whether veterans have preferences regarding the gender of clinicians providing MST-related care. Qualitative analyses were used to examine data collected from semistructured interviews conducted with 20 male veterans enrolled in Veterans Health Administration care who reported MST but who had not received any MST-related mental health care. Veterans identified a number of potential barriers, with the majority of reported barriers relating to issues of stigma and gender. Regarding provider gender preferences, veterans were mixed, with 50% preferring a female provider, 25% a male provider, and 25% reporting no gender preference. These preliminary data suggest that stigma, gender, and knowledge-related barriers may exist for men regarding seeking MST-related care. Interventions to address potential barriers, such as outreach interventions and providing gender-specific psychoeducation, may increase access to care for male veterans who report MST. PsycINFO Database Record (c) 2013 APA, all rights reserved.

Comparative Analysis: Potential Barriers to Career Participation by North American Physicians in Global Health

PubMed Central

Rhee, Daniel S.; Heckman, Jennifer E.

2014-01-01

Physician interest in global health, particularly among family physicians, is reflected by an increasing proliferation of field training and service experiences. However, translating initial training involvement into a defined and sustainable global health career remains difficult and beset by numerous barriers. Existing global health literature has largely examined training experiences and related ethical considerations while neglecting the role of career development in global health. To explore this, this paper extrapolates potential barriers to global health career involvement from existing literature and compares these to salary and skills requirements for archetypal physician positions in global health, presenting a framework of possible barriers to sustained physician participation in global health work. Notable barriers identified include financial limitations, scheduling conflicts, security/family concerns, skills limitations, limited awareness of opportunities, and specialty choice, with family practice often closely aligned with global health experience. Proposed solutions include financial support, protected time, family relocation support, and additional training. This framework delineates barriers to career involvement in global health by physicians. Further research regarding these barriers as well as potential solutions may help direct policy and initiatives to better utilize physicians, particularly family physicians, as a valuable global health human resource. PMID:25405030

Neuroscience: viable applications in education?

PubMed

Devonshire, Ian M; Dommett, Eleanor J

2010-08-01

As a relatively young science, neuroscience is still finding its feet in potential collaborations with other disciplines. One such discipline is education, with the field of neuroeducation being on the horizon since the 1960s. However, although its achievements are now growing, the partnership has not been as successful as first hopes suggested it should be. Here the authors discuss the theoretical barriers and potential solutions to this, which have been suggested previously, with particular focus on levels of research in neuroscience and their applicability to education. Moreover, they propose that these theoretical barriers are driven and maintained by practical barriers surrounding common language and research literacy. They propose that by overcoming these practical barriers through appropriate training and shared experience, neuroeducation can reach its full potential.

49 CFR 229.119 - Cabs, floors, and passageways.

Code of Federal Regulations, 2010 CFR

2010-10-01

... continuous barrier between locomotives. (f) Containers shall be provided for carrying fusees and torpedoes. A single container may be used if it has a partition to separate fusees from torpedoes. Torpedoes shall be...

49 CFR 229.119 - Cabs, floors, and passageways.

Code of Federal Regulations, 2011 CFR

2011-10-01

... continuous barrier between locomotives. (f) Containers shall be provided for carrying fusees and torpedoes. A single container may be used if it has a partition to separate fusees from torpedoes. Torpedoes shall be...

Gamma rays as probe of fission and quasi-fission dynamics in the reaction 32S + 197Au near the Coulomb barrier

NASA Astrophysics Data System (ADS)

Pulcini, A.; Vardaci, E.; Kozulin, E.; Ashaduzzaman, M.; Borcea, C.; Bracco, A.; Brambilla, S.; Calinescu, S.; Camera, F.; Ciemala, M.; de Canditiis, B.; Dorvaux, O.; Harca, I. M.; Itkis, I.; Kirakosyan, V. V.; Knyazheva, G.; Kozulina, N.; Kolesov, I. V.; La Rana, G.; Maj, A.; Matea, I.; Novikov, K.; Petrone, C.; Quero, D.; Rath, P.; Saveleva, E.; Schmitt, C.; Sposito, G.; Stezowski, O.; Trzaska, W. H.; Wilson, J.

2018-05-01

Compound nucleus fission and quasi-fission are both binary decay channels whose common properties make the experimental separation between them difficult. A way to achieve this separation could be to probe the angular momentum of the binary fragments. This can be done detecting gamma rays in coincidence with the two fragments. As a case study, the reaction 32S + 197Au near the Coulomb barrier has been performed at the Tandem ALTO facility at IPN ORSAY. ORGAM and PARIS, two different gamma detectors arrays, are coupled with the CORSET detector, a two-arm time-of-flight spectrometer. TOF-TOF data were analyzed to reconstruct the mass-energy distribution of the primary fragments coupled with gamma multiplicity and spectroscopic analysis. Preliminary results of will be shown.

Safety analysis, 200 Area, Savannah River Plant: Separations area operations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perkins, W.C.; Lee, R.; Allen, P.M.

1991-07-01

The nev HB-Line, located on the fifth and sixth levels of Building 221-H, is designed to replace the aging existing HB-Line production facility. The nev HB-Line consists of three separate facilities: the Scrap Recovery Facility, the Neptunium Oxide Facility, and the Plutonium Oxide Facility. There are three separate safety analyses for the nev HB-Line, one for each of the three facilities. These are issued as supplements to the 200-Area Safety Analysis (DPSTSA-200-10). These supplements are numbered as Sup 2A, Scrap Recovery Facility, Sup 2B, Neptunium Oxide Facility, Sup 2C, Plutonium Oxide Facility. The subject of this safety analysis, the, Plutoniummore » Oxide Facility, will convert nitrate solutions of {sup 238}Pu to plutonium oxide (PuO{sub 2}) powder. All these new facilities incorporate improvements in: (1) engineered barriers to contain contamination, (2) barriers to minimize personnel exposure to airborne contamination, (3) shielding and remote operations to decrease radiation exposure, and (4) equipment and ventilation design to provide flexibility and improved process performance.« less

Review of potential subsurface permeable barrier emplacement and monitoring technologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riggsbee, W.H.; Treat, R.L.; Stansfield, H.J.

1994-02-01

This report focuses on subsurface permeable barrier technologies potentially applicable to existing waste disposal sites. This report describes candidate subsurface permeable barriers, methods for emplacing these barriers, and methods used to monitor the barrier performance. Two types of subsurface barrier systems are described: those that apply to contamination.in the unsaturated zone, and those that apply to groundwater and to mobile contamination near the groundwater table. These barriers may be emplaced either horizontally or vertically depending on waste and site characteristics. Materials for creating permeable subsurface barriers are emplaced using one of three basic methods: injection, in situ mechanical mixing, ormore » excavation-insertion. Injection is the emplacement of dissolved reagents or colloidal suspensions into the soil at elevated pressures. In situ mechanical mixing is the physical blending of the soil and the barrier material underground. Excavation-insertion is the removal of a soil volume and adding barrier materials to the space created. Major vertical barrier emplacement technologies include trenching-backfilling; slurry trenching; and vertical drilling and injection, including boring (earth augering), cable tool drilling, rotary drilling, sonic drilling, jetting methods, injection-mixing in drilled holes, and deep soil mixing. Major horizontal barrier emplacement technologies include horizontal drilling, microtunneling, compaction boring, horizontal emplacement, longwall mining, hydraulic fracturing, and jetting methods.« less

Matrix isolation infrared spectra and photochemistry of hydantoin.

PubMed

Ildiz, Gulce Ogruc; Nunes, Cláudio M; Fausto, Rui

2013-01-31

Hydantoin (C(3)H(4)N(2)O(2), 2,4-imidazolidinedione) was isolated in argon matrix at 10 K and its infrared spectrum and unimolecular photochemistry were investigated. The molecular structure of the compound was studied both at the DFT(B3LYP) and MP2 levels of approximation with valence triple- and quadruple-ζ basis sets (6-311++G(d,p); cc-pVQZ). It was concluded that the minima in the potential energy surfaces of the molecule correspond to C(1) symmetry structures. However, the energy barrier separating the two-equivalent-by-symmetry minima stays below their zero-point energy, which makes the C(s) symmetry structure, which separates the two minima, the experimentally relevant one. The electronic structure of the molecule was studied in detail by performing the Natural Bond Orbital analysis of its electronic configuration within the DFT(B3LYP)/cc-pVQZ space. The infrared spectrum of the matrix isolated compound was fully assigned also with help of the theoretically predicted spectrum. Upon irradiation at λ = 230 nm, matrix-isolated hydantoin was found to photofragment into isocyanic acid, CO, and methylenimine.

Long-range electron tunneling.

PubMed

Winkler, Jay R; Gray, Harry B

2014-02-26

Electrons have so little mass that in less than a second they can tunnel through potential energy barriers that are several electron-volts high and several nanometers wide. Electron tunneling is a critical functional element in a broad spectrum of applications, ranging from semiconductor diodes to the photosynthetic and respiratory charge transport chains. Prior to the 1970s, chemists generally believed that reactants had to collide in order to effect a transformation. Experimental demonstrations that electrons can transfer between reactants separated by several nanometers led to a revision of the chemical reaction paradigm. Experimental investigations of electron exchange between redox partners separated by molecular bridges have elucidated many fundamental properties of these reactions, particularly the variation of rate constants with distance. Theoretical work has provided critical insights into the superexchange mechanism of electronic coupling between distant redox centers. Kinetics measurements have shown that electrons can tunnel about 2.5 nm through proteins on biologically relevant time scales. Longer-distance biological charge flow requires multiple electron tunneling steps through chains of redox cofactors. The range of phenomena that depends on long-range electron tunneling continues to expand, providing new challenges for both theory and experiment.

Barriers to access to opioid medicines for patients with opioid dependence: a review of legislation and regulations in eleven central and eastern European countries.

PubMed

Vranken, Marjolein J M; Mantel-Teeuwisse, Aukje K; Jünger, Saskia; Radbruch, Lukas; Scholten, Willem; Lisman, John A; Subataite, Marija; Schutjens, Marie-Hélène D B

2017-06-01

Barriers linked to drug control systems are considered to contribute to inequitable access to controlled medicines, leaving millions of people in pain and suffering. Most studies focus on access to opioids for the treatment of severe (cancer) pain. This study aims to identify specific access barriers for patients with opioid dependence in legislation and regulations of 11 central and eastern European countries. This study builds on a previous analysis of legislation and regulations as part of the EU 7th Framework Access To Opioid Medication in Europe (ATOME) project. An in-depth analysis was undertaken to determine specific barriers for patients with opioid dependence in need of opioid analgesics or opioid agonist therapy (OAT). For each country, the number and nature of specific potential barriers for these patients were assessed according to eight categories: prescribing; dispensing; manufacturing; usage; trade and distribution; affordability; penalties; and other. An additional keyword search was conducted to minimize the omission of barriers. Barriers in an additional category, language, were recorded qualitatively. Countries included Bulgaria, Cyprus, Estonia, Greece, Hungary, Latvia, Lithuania, Serbia, Slovakia, Slovenia and Turkey. Ten of the 11 countries (all except Estonia) showed specific potential barriers in their legislation and regulations. The total number of barriers varied from two (Slovenia) to 46 (Lithuania); the number of categories varied from one (Slovenia) to five (Lithuania). Most specific potential barriers were shown in the categories 'prescribing', 'usage' and 'other'. The total number in a single category varied from one to 18 (Lithuania, prescribing). Individual differences between countries in the same specific potential barrier were shown; for example, variation in minimum age criteria for admission to OAT ranging from 15 (Lithuania, in special cases) to 20 years (Greece). All countries had stigmatizing language in their legislation. Patients with opioid dependence are likely to experience specific barriers to accessing opioids in addition to those experienced by other non-dependent patients. © 2017 Society for the Study of Addiction.

Reaction dynamics near the barrier

NASA Astrophysics Data System (ADS)

Loveland, W.

2011-10-01

The availability of modest intensity (103-107 p/s) radioactive nuclear beams has had a significant impact on the study of nuclear reactions near the interaction barrier. The role of isospin in capture reactions is a case in point. Using heavy elements as a laboratory to explore these effects, we note that the cross section for producing an evaporation residue is σEVR(Ec . m .) = ∑ J = 0 JmaxσCN(Ec . m . , J) Wsur(Ec . m . , J) where σCN is the complete fusion cross section and Wsur is the survival probability of the completely fused system. The complete fusion cross section can be written as, σCN(Ec . m .) = ∑ J = 0 Jmaxσcapture(Ec . m .) PCN(Ec . m . , J) where σcapture(Ec.m.,J) is the ``capture'' cross section at center-of mass energy Ec.m. and spin J and PCN is the probability that the projectile-target system will evolve inside the fission saddle point to form a completely fused system rather than re-separating (quasi-fission). The systematics of the isospin dependence of the capture cross sections has been developed and the deduced interaction barriers for all known studies of capture cross sections with radioactive beams are in good agreement with recent predictions of an improved QMD model and semi-empirical models. The deduced barriers for these n-rich systems are lower than one would expect from the Bass or proximity potentials. In addition to the barrier lowering, there is an enhanced sub-barrier cross section in these n-rich systems that is of advantage in the synthesis of new heavy nuclei. Recent studies of the ``inverse fission'' of uranium (124,132Sn + 100Mo) have yielded unexpectedly low upper limits for this process due apparently to low values of the fusion probability, PCN. The fusion of halo nuclei, like 11Li with heavy nuclei, like 208Pb, promises to give new information about these and related nuclei and has led/may lead to unusual reaction mechanisms. This work was sponsored, in part, by the USDOE Office of Nuclear Physics.

Delay time in a single barrier for a movable quantum shutter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez, Alberto

2010-05-15

The transient solution and delay time for a {delta} potential scatterer with a movable quantum shutter is calculated by solving analytically the time-dependent Schroedinger equation. The delay time is analyzed as a function of the distance between the shutter and the potential barrier and also as a function of the distance between the potential barrier and the detector. In both cases, it is found that the delay time exhibits a dynamical behavior and that it tends to a saturation value {Delta}t{sub sat} in the limit of very short distances, which represents the maximum delay produced by the potential barrier nearmore » the interaction region. The phase time {tau}{sub {theta},} on the other hand, is not an appropriate time scale for measuring the time delay near the interaction region, except if the shutter is moved far away from the potential. The role played by the antibound state of the system on the behavior of the delay time is also discussed.« less

Tunneling of heat: Beyond linear response regime

NASA Astrophysics Data System (ADS)

Walczak, Kamil; Saroka, David

2018-02-01

We examine nanoscale processes of heat (energy) transfer as carried by electrons tunneling via potential barriers and molecular interconnects between two heat reservoirs (thermal baths). For that purpose, we use Landauer-type formulas to calculate thermal conductance and quadratic correction to heat flux flowing via quantum systems. As an input, we implement analytical expressions for transmission functions related to simple potential barriers and atomic bridges. Our results are discussed with respect to energy of tunneling electrons, temperature, the presence of resonant states, and specific parameters characterizing potential barriers as well as heat carriers. The simplicity of semi-analytical models developed by us allows to fit experimental data and extract crucial information about the values of model parameters. Further investigations are expected for more realistic transmission functions, while time-dependent aspects of nanoscale heat transfer may be addressed by using the concept of wave packets scattered on potential barriers and point-like defects within regular (periodic) nanostructures.

Electrochemical cell having an alkali-metal-nitrate electrode

DOEpatents

Roche, M.F.; Preto, S.K.

1982-06-04

A power-producing secondary electrochemical cell includes a molten alkali metal as the negative-electrode material and a molten-nitrate salt as the positive-electrode material. The molten material in the respective electrodes are separated by a solid barrier of alkali-metal-ion conducting material. A typical cell includes active materials of molten sodium separated from molten sodium nitrate and other nitrates in mixture by a layer of sodium ..beta..'' alumina.

Planet Formation in Small Separation Binaries: Not so Secularly Excited by the Companion

NASA Astrophysics Data System (ADS)

Rafikov, Roman R.

2013-03-01

The existence of planets in binaries with relatively small separations (around 20 AU), such as α Centauri or γ Cephei, poses severe challenges to standard planet formation theories. The problem lies in the vigorous secular excitation of planetesimal eccentricities at separations of several AU, where some of the planets are found, by the massive, eccentric stellar companions. High relative velocities of planetesimals preclude their growth in mutual collisions for a wide range of sizes, from below 1 km up to several hundred km, resulting in a fragmentation barrier to planet formation. Here we show that, for the case of an axisymmetric circumstellar protoplanetary disk, the rapid apsidal precession of planetesimal orbits caused by the disk gravity acts to strongly reduce the direct secular eccentricity excitation by the companion, lowering planetesimal velocities by an order of magnitude or even more at 1 AU. By examining the details of planetesimal dynamics, we demonstrate that this effect eliminates the fragmentation barrier for in situ growth of planetesimals as small as <~ 10 km even at separations as wide as 2.6 AU (the semimajor axis of the giant planet in HD 196885), provided that the circumstellar protoplanetary disk has a small eccentricity and is relatively massive, ~0.1 M ⊙.

Induced vibrations facilitate traversal of cluttered obstacles

NASA Astrophysics Data System (ADS)

Thoms, George; Yu, Siyuan; Kang, Yucheng; Li, Chen

When negotiating cluttered terrains such as grass-like beams, cockroaches and legged robots with rounded body shapes most often rolled their bodies to traverse narrow gaps between beams. Recent locomotion energy landscape modeling suggests that this locomotor pathway overcomes the lowest potential energy barriers. Here, we tested the hypothesis that body vibrations induced by intermittent leg-ground contact facilitate obstacle traversal by allowing exploration of locomotion energy landscape to find this lowest barrier pathway. To mimic a cockroach / legged robot pushing against two adjacent blades of grass, we developed an automated robotic system to move an ellipsoidal body into two adjacent beams, and varied body vibrations by controlling an oscillation actuator. A novel gyroscope mechanism allowed the body to freely rotate in response to interaction with the beams, and an IMU and cameras recorded the motion of the body and beams. We discovered that body vibrations facilitated body rolling, significantly increasing traversal probability and reducing traversal time (P <0.0001, ANOVA). Traversal probability increased with and traversal time decreased with beam separation. These results confirmed our hypothesis and support the plausibility of locomotion energy landscapes for understanding the formation of locomotor pathways in complex 3-D terrains.

Model of biological quantum logic in DNA.

PubMed

Mihelic, F Matthew

2013-08-02

The DNA molecule has properties that allow it to act as a quantum logic processor. It has been demonstrated that there is coherent conduction of electrons longitudinally along the DNA molecule through pi stacking interactions of the aromatic nucleotide bases, and it has also been demonstrated that electrons moving longitudinally along the DNA molecule are subject to a very efficient electron spin filtering effect as the helicity of the DNA molecule interacts with the spin of the electron. This means that, in DNA, electrons are coherently conducted along a very efficient spin filter. Coherent electron spin is held in a logically and thermodynamically reversible chiral symmetry between the C2-endo and C3-endo enantiomers of the deoxyribose moiety in each nucleotide, which enables each nucleotide to function as a quantum gate. The symmetry break that provides for quantum decision in the system is determined by the spin direction of an electron that has an orbital angular momentum that is sufficient to overcome the energy barrier of the double well potential separating the C2-endo and C3-endo enantiomers, and that enantiomeric energy barrier is appropriate to the Landauer limit of the energy necessary to randomize one bit of information.

Challenges and opportunities associated with waste management in India

PubMed Central

Kumar, Sunil; Smith, Stephen R.; Fowler, Geoff; Velis, Costas; Kumar, S. Jyoti; Arya, Shashi; Rena; Kumar, Rakesh

2017-01-01

India faces major environmental challenges associated with waste generation and inadequate waste collection, transport, treatment and disposal. Current systems in India cannot cope with the volumes of waste generated by an increasing urban population, and this impacts on the environment and public health. The challenges and barriers are significant, but so are the opportunities. This paper reports on an international seminar on ‘Sustainable solid waste management for cities: opportunities in South Asian Association for Regional Cooperation (SAARC) countries’ organized by the Council of Scientific and Industrial Research-National Environmental Engineering Research Institute and the Royal Society. A priority is to move from reliance on waste dumps that offer no environmental protection, to waste management systems that retain useful resources within the economy. Waste segregation at source and use of specialized waste processing facilities to separate recyclable materials has a key role. Disposal of residual waste after extraction of material resources needs engineered landfill sites and/or investment in waste-to-energy facilities. The potential for energy generation from landfill via methane extraction or thermal treatment is a major opportunity, but a key barrier is the shortage of qualified engineers and environmental professionals with the experience to deliver improved waste management systems in India. PMID:28405362

Ballistic Majorana nanowire devices

NASA Astrophysics Data System (ADS)

Gül, Ã.-nder; Zhang, Hao; Bommer, Jouri D. S.; de Moor, Michiel W. A.; Car, Diana; Plissard, Sébastien R.; Bakkers, Erik P. A. M.; Geresdi, Attila; Watanabe, Kenji; Taniguchi, Takashi; Kouwenhoven, Leo P.

2018-01-01

Majorana modes are zero-energy excitations of a topological superconductor that exhibit non-Abelian statistics1-3. Following proposals for their detection in a semiconductor nanowire coupled to an s-wave superconductor4,5, several tunnelling experiments reported characteristic Majorana signatures6-11. Reducing disorder has been a prime challenge for these experiments because disorder can mimic the zero-energy signatures of Majoranas12-16, and renders the topological properties inaccessible17-20. Here, we show characteristic Majorana signatures in InSb nanowire devices exhibiting clear ballistic transport properties. Application of a magnetic field and spatial control of carrier density using local gates generates a zero bias peak that is rigid over a large region in the parameter space of chemical potential, Zeeman energy and tunnel barrier potential. The reduction of disorder allows us to resolve separate regions in the parameter space with and without a zero bias peak, indicating topologically distinct phases. These observations are consistent with the Majorana theory in a ballistic system21, and exclude the known alternative explanations that invoke disorder12-16 or a nonuniform chemical potential22,23.

Sun, Sand and Water: A History of the Jacksonville District U.S. Army Corps of Engineers 1821-1975

DTIC Science & Technology

1981-01-01

plan envisioned a dredged cut through the barrier beach to Banana River. On the river there would be a turning basin with terminal facilities, and...intracoastal canal to the west This canal would cut through Merritt Island, which separated Indian River from Banana River.6 District Engineer, Colonel...canal, guarded by two jetties, through the barrier land from the 27 -foot contour line in the Atlantic to a 27 -foot turning basin in the Banana

Resonant optical device with a microheater

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lentine, Anthony L.; DeRose, Christopher

2017-04-04

A resonant photonic device is provided. The device comprises an optical waveguiding element, such as an optical resonator, that includes a diode junction region, two signal terminals configured to apply a bias voltage across the junction region, and a heater laterally separated from the optical waveguiding element. A semiconductor electrical barrier element is juxtaposed to the heater. A metallic strip is electrically and thermally connected at one end to a signal terminal of the optical waveguiding element and thermally connected at another end to the barrier element.

Potential barriers to electric vehicle commercialization : A. insurance B. vehicle recharging

DOT National Transportation Integrated Search

1981-03-01

An assessment of the potential barriers to the commercialization of electric and hybrid vehicles due to insurance considerations and the absence of a range extension infrastructure was performed. Availability of operator and manufacturers liability i...

33 CFR 328.3 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 CFR 423.11(m) which also meet the criteria of this definition) are not waters of the United States... neighboring. Wetlands separated from other waters of the United States by man-made dikes or barriers, natural...

Apoplastic domains and sub-domains in the shoots of etiolated corn seedlings

NASA Technical Reports Server (NTRS)

Epel, B. L.; Bandurski, R. S.

1990-01-01

Light Green, an apoplastic probe, was applied to the cut mesocotyl base or to the cut coleoptile apex of etiolated seedlings of Zea mays L. cv. Silver Queen. Probe transport was measured and its tissue distribution determined. In the mesocotyl, there is an apoplastic barrier between cortex and stele. This barrier creates two apoplastic domains which are non-communicating. A kinetic barrier exists between the apoplast of the mesocotyl stele and that of the coleoptile. This kinetic barrier is not absolute and there is limited communication between the apoplasts of the two regions. This kinetic barrier effectively creates two sub-domains. In the coleoptile, there is communication between the apoplast of the vascular strands and that of the surrounding cortical tissue. No apoplastic communication was observed between the coleoptile cortex and the mesocotyl cortex. Thus, the apoplastic space of the coleoptile cortex is a sub-domain of the integrated coleoptile domain and is separate from that of the apoplastic domain of the mesocotyl cortex.

The periodic table and the intrinsic barrier in s(n)2 reactions.

PubMed

Yi, Ren; Basch, Harold; Hoz, Shmaryahu

2002-08-23

The identity S(N)2 reactions on nitrogen (see eq 3) with nucleophiles having the general structure H(n)()X(-) where X belongs to the group of nonmetallic elements which do not border the line separating them from the metallic elements (X = F, Cl, Br, I, O, S, Se, N, P, and C) were studied at the G2+ level. The results show that, similarly to the previously observed phenomenon for S(N)2 reaction on carbon (J. Am. Chem. Soc. 1999, 121, 7724), the Periodic Table, through the valence of the element X, controls the intrinsic barrier for the reaction. The average intrinsic barriers obtained for nitrogen substrates were 20, 27, 39, and 57 kcal/mol for the mono-, di-, tri-, and tetravalent X's, respectively. It is also concluded that the intrinsic barriers are similar for N- and C-based substrates and dimethyl substitution on both raises the intrinsic barrier by ca. 10 kcal/mol.

A stepped pressure profile model for internal transport barriers

NASA Astrophysics Data System (ADS)

Hole, Matthew; Hudson, Stuart; Dewar, Robert

2007-11-01

B ∇x et al We develop a multiple interface variational model, comprising multiple Taylor-relaxed plasma regions separated by ideal MHD barriers. The magnetic field in each region is Beltrami, = μ, and the pressure constant. Between these regions the pressure, field strength, and rotational transform may have step changes at the ideal barrier. A principle motivation is the development of a mathematically rigorous ideal MHD model to describe intrinsically 3D equilibria, with nonzero internal pressure, using robust KAM surfaces as the barriers. As each region is locally relaxed however, such a model may also yield reasons for existence of internal transport barriers (ITBs). Focusing on the latter, we build on Hole Nuc. Fus. 47, pp746-753, 2007, which recently studied the stability of a two-interface periodic-cylinder configuration. In this work, we perform a stability scan over pressure and for a two-interface configuration with no jump in , and compare the characteristics of stable equilibria to those of ITB's.

Understanding the fusion cross section among light nuclei around the Coulomb barrier

NASA Astrophysics Data System (ADS)

Del Zoppo, Antonio; La Cognata, Marco

2017-11-01

In this work we investigate fusion induced by a radioactive 8Li projectile on a 4He gas target, at center-of-mass energies between 0.6 and 5 MeV. The main result is the tendency of the dimensionless fusion cross section to form well visible plateaus alternated to steep rises. This is likely to be the most genuine consequence of the discrete nature of the intervening angular momenta observed so far in fusion reactions right above the Coulomb barrier. A partial-wave analysis, exclusively based on a pure quantal penetration fusion model, identifies a remarkably low-height barrier. Indeed, these plateaus allow enhanced experimental sensitivity to the fusion barrier given that the most barrier-sensitive lowest partial waves are well separated. We expect that the present results for 8Li+4He will promote further investigations of the fusion reaction mechanism between very light ions at energies much below the interaction barrier. For the moment, we believe that understanding the plateau origin in the cross section above the barrier will almost certainly be useful to corroborate the extrapolation to the important astrophysical region below the Coulomb barrier, not only in the case of the 8Li+4He fusion but also for other systems, such as the 12C+12C.

[Perceived barriers to active commuting to school: reliability and validity of a scale].

PubMed

Molina-García, Javier; Queralt, Ana; Estevan, Isaac; Álvarez, Octavio; Castillo, Isabel

To examine the reliability and validity of a scale to measure perceived barriers to active commuting to school among Spanish young people. The validity of the scale was assessed in a sample of 465 adolescents (14-18 years) using a confirmatory factor analysis and studying its association with self-reported active commuting to school. The reliability of the instrument was evaluated in a sub-sample that completed the scale twice separated by a one-week interval. The results showed that the barriers scale had satisfactory fit indices, and two factors were determined. The first included environment- and safety-related items (α=0.72), while the other concerned planning and psychosocial items (α=0.64). Active commuting to school showed significant correlations with the total score of the barriers scale (rho=-0.27; p <0.001), with the environmental/safety barriers (rho=-0.22; p <0.001), as well as with the planning/psychosocial barriers (rho=-0.29; p <0.001). Test-retest ICCs for the barriers ranged from 0.68 to 0.77. The developed scale has acceptable validity and good reliability to assess barriers to active commuting to school among Spanish young people. Copyright © 2016 SESPAS. Publicado por Elsevier España, S.L.U. All rights reserved.

Self-reported barriers to medication adherence among chronically ill adolescents: a systematic review.

PubMed

Hanghøj, Signe; Boisen, Kirsten A

2014-02-01

To investigate self-reported barriers to medication adherence among chronically ill adolescents, and to investigate whether barriers are unique to specific chronic diseases or more generic across conditions. A systematic search of Web of Science, PubMed, Embase, PsycINFO, and CINAHL from January 2000 to May 2012 was conducted. Articles were included if they examined barriers to medication intake among chronically ill adolescents aged 13-19 years. Articles were excluded if adolescent's views on barriers to adherence were not separated from younger children's or caregiver's views. Data was analyzed using a thematic synthesis approach. Of 3,655 records 28 articles with both quantitative, qualitative, and q-methodology study designs were included in the review. The synthesis led to the following key themes: Relations, adolescent development, health and illness, forgetfulness, organization, medicine complexity, and financial costs. Most reported barriers to adherence were not unique to specific diseases. Some barriers seem to be specific to adolescence; for example, relations to parents and peers and adolescent development. Knowledge and assessment of barriers to medication adherence is important for both policy-makers and clinicians in planning interventions and communicating with adolescents about their treatment. Copyright © 2014 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.

Barriers, motivators and enablers for dispensing multifocal contact lenses in Mumbai, India

PubMed Central

Thite, Nilesh; Shah, Ukti; Mehta, Jasmin; Jurkus, Janice

2015-01-01

Purpose To understand the potential barriers, motivators and enablers in dispensing multifocal contact lenses (MFCL). Method Two focus group discussions were conducted to design questionnaires regarding the prescribing habits for multifocal contact lenses (MFCL). Questions on potential barriers and motivators were included. The questionnaires were distributed among 133 eye care practitioners across Mumbai, India. Practitioners fitting one or less patient per month with MFCL completed the survey describing potential barriers, while those who prescribed more MFCL's per month completed the survey describing enablers and motivators. Results Responses from 102 practitioners were received. Most common potential barriers in prescribing MFCL were increased chair time (75%), lack of readily available trials (69%) and limitation in power range (63%). Lack of awareness among patients (90%) was the most common barrier from patients’ outlook. Professional satisfaction (88%) and better business proposition (82%) were observed as main motivators while availability of the trials (84%) and correct patient selection (82%) were the major enablers. Graduate Optometrists felt dispensing MFCL did not offer a good business proposition (p = 0.02). Experienced practitioners were observed to be least motivated (p = 0.01) and believed that their patients found these lenses expensive (p = 0.02). Conclusion To enhance the MFCL practice, barriers like lack of awareness and limitations in power range must be addressed. Trial lens availability may motivate practitioners to prescribe MFCL. Further probing is required to understand lack of motivation among experienced practitioners. PMID:25563404

Barriers, motivators and enablers for dispensing multifocal contact lenses in Mumbai, India.

PubMed

Thite, Nilesh; Shah, Ukti; Mehta, Jasmin; Jurkus, Janice

2015-01-01

To understand the potential barriers, motivators and enablers in dispensing multifocal contact lenses (MFCL). Two focus group discussions were conducted to design questionnaires regarding the prescribing habits for multifocal contact lenses (MFCL). Questions on potential barriers and motivators were included. The questionnaires were distributed among 133 eye care practitioners across Mumbai, India. Practitioners fitting one or less patient per month with MFCL completed the survey describing potential barriers, while those who prescribed more MFCL's per month completed the survey describing enablers and motivators. Responses from 102 practitioners were received. Most common potential barriers in prescribing MFCL were increased chair time (75%), lack of readily available trials (69%) and limitation in power range (63%). Lack of awareness among patients (90%) was the most common barrier from patients' outlook. Professional satisfaction (88%) and better business proposition (82%) were observed as main motivators while availability of the trials (84%) and correct patient selection (82%) were the major enablers. Graduate Optometrists felt dispensing MFCL did not offer a good business proposition (p=0.02). Experienced practitioners were observed to be least motivated (p=0.01) and believed that their patients found these lenses expensive (p=0.02). To enhance the MFCL practice, barriers like lack of awareness and limitations in power range must be addressed. Trial lens availability may motivate practitioners to prescribe MFCL. Further probing is required to understand lack of motivation among experienced practitioners. Copyright © 2014 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

Lightweight Reduced Graphene Oxide@MoS2 Interlayer as Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries.

PubMed

Tan, Lei; Li, Xinhai; Wang, Zhixing; Guo, Huajun; Wang, Jiexi

2018-01-31

The further development of lithium-sulfur (Li-S) batteries is limited by the fact that the soluble polysulfide leads to the shuttle effect, thereby reducing the cycle stability and cycle life of the batteries. To address this issue, here a thin and lightweight (8 μm and 0.24 mg cm -2 ) reduced graphene oxide@MoS 2 (rGO@MoS 2 ) interlayer between the cathode and the commercial separator is developed as a polysulfide barrier. The rGO plays the roles of both a polysulfide physical barrier and an additional current collector, while MoS 2 has a high chemical adsorption for polysulfides. The experiments demonstrate that the Li-S cell constructed with an rGO@MoS 2 -coated separator shows a high reversible capacity of 1122 mAh g -1 at 0.2 C, a low capacity fading rate of 0.116% for 500 cycles at 1 C, and an outstanding rate performance (615 mAh g -1 at 2 C). Such an interlayer is expected to be ideal for lithium-sulfur battery applications because of its excellent electrochemical performance and simple synthesis process.

Absorption enhancement in type-II coupled quantum rings due to existence of quasi-bound states

NASA Astrophysics Data System (ADS)

Hsieh, Chi-Ti; Lin, Shih-Yen; Chang, Shu-Wei

2018-02-01

The absorption of type-II nanostructures is often weaker than type-I counterpart due to spatially separated electrons and holes. We model the bound-to-continuum absorption of type-II quantum rings (QRs) using a multiband source-radiation approach using the retarded Green function in the cylindrical coordinate system. The selection rules due to the circular symmetry for allowed transitions of absorption are utilized. The bound-tocontinuum absorptions of type-II GaSb coupled and uncoupled QRs embedded in GaAs matrix are compared here. The GaSb QRs act as energy barriers for electrons but potential wells for holes. For the coupled QR structure, the region sandwiched between two QRs forms a potential reservoir of quasi-bound electrons. Electrons in these states, though look like bound ones, would ultimately tunnel out of the reservoir through barriers. Multiband perfectly-matched layers are introduced to model the tunneling of quasi-bound states into open space. Resonance peaks are observed on the absorption spectra of type-II coupled QRs due to the formation of quasi-bound states in conduction bands, but no resonance exist in the uncoupled QR. The tunneling time of these metastable states can be extracted from the resonance and is in the order of ten femtoseconds. Absorption of coupled QRs is significantly enhanced as compared to that of uncoupled ones in certain spectral windows of interest. These features may improve the performance of photon detectors and photovoltaic devices based on type-II semiconductor nanostructures.

Bridges or Barriers? Conceptualization of the Role of Multiple Identity Gateway Groups in Intergroup Relations.

PubMed

Levy, Aharon; Saguy, Tamar; Halperin, Eran; van Zomeren, Martijn

2017-01-01

The modern era of globalization has been accompanied by a massive growth in interconnections between groups, and has led to the sharing of multiple identities by individuals and groups. Following these developments, research has focused on the issue of multiple identities, and has shed important light on how individuals who hold these complex forms of identity feel and behave, and on the reactions they elicit from members of other groups. However, the potential of groups with such multiple identities (e.g., biracials, immigrants, etc.) to affect the intergroup relations between the groups that represent the respective sources of the different identities (e.g., Blacks and Whites, country of origin and country of residence, etc.) has not been examined to date. Accordingly, in this paper, we first systematically explore the potential of groups in which people identify with multiple social categories, or groups that are perceived as such by others, to play a role in intergroup dynamics. Next, we offer a theoretical framework outlining what functions groups of people with shared multiple identities may serve (as bridges or barriers ) by proposing how their presence may facilitate or deteriorate intergroup relations. Finally, we present recent empirical research examining how groups of people with shared multiple identities can act as gateways and bridge the cleft between two separate groups that represent the respective sources of their different identities, and discuss the theoretical and practical implications for the field of intergroup relations.

Bridges or Barriers? Conceptualization of the Role of Multiple Identity Gateway Groups in Intergroup Relations

PubMed Central

Levy, Aharon; Saguy, Tamar; Halperin, Eran; van Zomeren, Martijn

2017-01-01

The modern era of globalization has been accompanied by a massive growth in interconnections between groups, and has led to the sharing of multiple identities by individuals and groups. Following these developments, research has focused on the issue of multiple identities, and has shed important light on how individuals who hold these complex forms of identity feel and behave, and on the reactions they elicit from members of other groups. However, the potential of groups with such multiple identities (e.g., biracials, immigrants, etc.) to affect the intergroup relations between the groups that represent the respective sources of the different identities (e.g., Blacks and Whites, country of origin and country of residence, etc.) has not been examined to date. Accordingly, in this paper, we first systematically explore the potential of groups in which people identify with multiple social categories, or groups that are perceived as such by others, to play a role in intergroup dynamics. Next, we offer a theoretical framework outlining what functions groups of people with shared multiple identities may serve (as bridges or barriers) by proposing how their presence may facilitate or deteriorate intergroup relations. Finally, we present recent empirical research examining how groups of people with shared multiple identities can act as gateways and bridge the cleft between two separate groups that represent the respective sources of their different identities, and discuss the theoretical and practical implications for the field of intergroup relations. PMID:28706501

Thermoelectric properties of nano-granular indium-tin-oxide within modified electron filtering model with chemisorption-type potential barriers

NASA Astrophysics Data System (ADS)

Brinzari, V.; Nika, D. L.; Damaskin, I.; Cho, B. K.; Korotcenkov, G.

2016-07-01

In this work, an approach to the numerical study of the thermoelectric parameters of nanoscale indium tin oxide (ITO, Sn content<10 at%) based on an electron filtering model (EFM) was developed. Potential barriers at grain boundaries were assumed to be responsible for a filtering effect. In the case of the dominant inelastic scattering of electrons, the maximal distance between potential barriers was limited in this modified model. The algorithm for such characteristic length calculation was proposed, and its value was evaluated for ITO. In addition, the contributions of different scattering mechanisms (SMs) in electron transport were examined. It was confirmed that in bulk ITO, the scattering on polar optical phonons (POPs) and ionized impurities dominates, limiting electron transport. In the framework of the filtering model, the basic thermoelectric parameters (i.e., electrical conductivity, mobility, Seebeck coefficient, and power factor (PF)) were calculated for ITO in the temperature range of 100-500 °C as a function of potential barrier height. The results demonstrated a sufficient rise of the Seebeck coefficient with an increase in barrier height and specific behavior of PF. It was found that PF is very sensitive to barrier height, and at its optimal value for granular ITO, it may exceed the PF for bulk ITO by 3-5 times. The PF maximum was achieved by band bending, slightly exceeding Fermi energy. The nature of surface potential barriers in nano-granular ITO with specific grains is due to the oxygen chemisorption effect, and this can be observed despite of the degeneracy of the conduction band (CB). This hypothesis and the corresponding calculations are in good agreement with recent experimental studies [Brinzari et al. Thin Solid Films 552 (2014) 225].

Fusion of 48Ti+58Fe and 58Ni+54Fe below the Coulomb barrier

NASA Astrophysics Data System (ADS)

Stefanini, A. M.; Montagnoli, G.; Corradi, L.; Courtin, S.; Bourgin, D.; Fioretto, E.; Goasduff, A.; Grebosz, J.; Haas, F.; Mazzocco, M.; Mijatović, T.; Montanari, D.; Pagliaroli, M.; Parascandolo, C.; Scarlassara, F.; Strano, E.; Szilner, S.; Toniolo, N.; Torresi, D.

2015-12-01

Background: No data on the fusion excitation function of 48Ti+58Fe in the energy region near the Coulomb barrier existed prior to the present work, while fusion of 58Ni+54Fe was investigated in detail some years ago, down to very low energies, and clear evidence of fusion hindrance was noticed at relatively high cross sections. 48Ti and 58Fe are soft and have a low-lying quadrupole excitation lying at ≈800 -900 keV only. Instead, 58Ni and 54Fe have a closed shell (protons and neutrons, respectively) and are rather rigid. Purpose: We aim to investigate (1) the possible influence of the different structures of the involved nuclei on the fusion excitation functions far below the barrier and, in particular, (2) whether hindrance is observed in 48Ti+58Fe , and to compare the results with current coupled-channels models. Methods: 48Ti beams from the XTU Tandem accelerator of INFN-Laboratori Nazionali di Legnaro were used. The experimental setup was based on an electrostatic beam separator, and fusion-evaporation residues (ERs) were detected at very forward angles. Angular distributions of ERs were measured. Results: Fusion cross sections of 48Ti+58Fe have been obtained in a range of nearly six orders of magnitude around the Coulomb barrier, down to σ ≃2 μ b . The sub-barrier cross sections of 48Ti+58Fe are much larger than those of 58Ni+54Fe . Significant differences are also observed in the logarithmic derivatives and astrophysical S factors. No evidence of hindrance is observed, because coupled-channels calculations using a standard Woods-Saxon potential are able to reproduce the data in the whole measured energy range. Analogous calculations for 58Ni+54Fe predict clearly too large cross sections at low energies. The two fusion barrier distributions are wide and display a complex structure that is only qualitatively fit by calculations. Conclusions: It is pointed out that all these different trends originate from the dissimilar low-energy nuclear structures of the involved nuclei. In particular, the strong quadrupole excitations in 48Ti and 58Fe produce the relative cross section enhancement and make the barrier distribution ≈2 MeV wider, thus probably pushing the threshold for hindrance below the measured limit.

Equatorward dispersion of the Sarychev volcanic plume and the relation to the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Wu, Xue; Griessbach, Sabine; Hoffmann, Lars

2017-04-01

Sulfur dioxide emissions and subsequent sulfate aerosols from strong volcanic eruptions have large impact on global climate. Although most of previous studies attribute the global influence to volcanic eruptions in the tropics, high-latitude volcanic eruptions are also an important cause for global climate variations. In fact, the potential climate impact of volcanic also largely depends on the season when eruptions occur, the erupted plume height and the surrounding meteorological conditions. This work focuses on the eruption of a high-latitude volcano Sarychev, and the role of Asian summer monsoon (ASM) during the transport and dispersion of the erupted plumes. First, the sulfur dioxide emission rate and height of emission of the Sarychev eruption in June 2009 are modelled using a Lagrangian particle dispersion model named Massive-Parallel Trajectory Calculations (MPTRAC), together with sulfur dioxide observations of the Atmospheric Infrared Sounder (AIRS/Aqua) and a backward trajectory approach. Then, the transport and dispersion of the plumes are modelled with MPTRAC and validated with sulfur dioxide observations from AIRS and aerosol observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The modelled trajectories and the MIPAS data both show the plumes are transported towards the tropics from the southeast edge of the ASM (in the vertical range of 340-400K) controlled by the clockwise winds of ASM, and from above the ASM (above 400K) in form of in-mixing process. Especially, in the vertical range around 340-400K, a transport barrier based on potential vorticity (PV) gradients separates the 'aerosol hole' inside of the ASM circulation and the aerosol-rich surrounding area, which shows the PV gradients based barrier may be more practical than the barrier based on the geopotential height. With help of ASM circulation, the aerosol transported to the tropics and stayed in the tropical lower stratosphere for about eight months, which were the main aerosol sources during that time. This enables the Sarychev eruption to have potential impact on global radiative budget similar to a tropical volcanic eruption.

Viscoelastic subdiffusion: from anomalous to normal.

PubMed

Goychuk, Igor

2009-10-01

We study viscoelastic subdiffusion in bistable and periodic potentials within the generalized Langevin equation approach. Our results justify the (ultra)slow fluctuating rate view of the corresponding bistable non-Markovian dynamics which displays bursting and anticorrelation of the residence times in two potential wells. The transition kinetics is asymptotically stretched exponential when the potential barrier V0 several times exceeds thermal energy k(B)T [V(0) approximately (2-10)k(B)T] and it cannot be described by the non-Markovian rate theory (NMRT). The well-known NMRT result approximates, however, ever better with the increasing barrier height, the most probable logarithm of the residence times. Moreover, the rate description is gradually restored when the barrier height exceeds a fuzzy borderline which depends on the power-law exponent of free subdiffusion alpha . Such a potential-free subdiffusion is ergodic. Surprisingly, in periodic potentials it is not sensitive to the barrier height in the long time asymptotic limit. However, the transient to this asymptotic regime is extremally slow and it does profoundly depend on the barrier height. The time scale of such subdiffusion can exceed the mean residence time in a potential well or in a finite spatial domain by many orders of magnitude. All these features are in sharp contrast with an alternative subdiffusion mechanism involving jumps among traps with the divergent mean residence time in these traps.

Measuring Perceived Barriers to Physical Activity in Adolescents.

PubMed

Gunnell, Katie E; Brunet, Jennifer; Wing, Erin K; Bélanger, Mathieu

2015-05-01

Perceived barriers to moderate-to-vigorous physical activity (PA) may contribute to the low rates of moderate-to-vigorous PA in adolescents. We examined the psychometric properties of scores from the perceived barriers to moderate-to-vigorous PA scale (PB-MVPA) by examining composite reliability and validity evidence based on the internal structure of the PB-MVPA and relations with other variables. This study was a cross-sectional analysis of data collected in 2013 from adolescents (N = 507; Mage = 12.40, SD = .62) via self-report scales. Using exploratory and confirmatory factor analyses, we found that perceived barriers were best represented as two factors representing internal (e.g., "I am not interested in physical activity") and external (e.g., "I need equipment I don't have") dimensions. Composite reliability was over .80. Using multiple regression to examine the relationship between perceived barriers and moderate-to-vigorous PA, we found that perceived internal barriers were inversely related to moderate-to-vigorous PA (β = -.32, p < .05). Based on results of the analysis of variances, there were no known-group sex differences for perceived internal and external barriers (p > .26). The PB-MVPA scale demonstrated evidence of score reliability and validity. To improve the understanding of the impact of perceived barriers on moderate-to- vigorous PA in adolescents, researchers should examine internal and external barriers separately.

Effect of disposable infection control barriers on light output from dental curing lights.

PubMed

Scott, Barbara A; Felix, Corey A; Price, Richard B T

2004-02-01

To prevent contamination of the light guide on a dental curing light, barriers such as disposable plastic wrap or covers may be used. This study compared the effect of 3 disposable barriers on the spectral output and power density from a curing light. The hypothesis was that none of the barriers would have a significant clinical effect on the spectral output or the power density from the curing light. Three disposable barriers were tested against a control (no barrier). The spectra and power from the curing light were measured with a spectrometer attached to an integrating sphere. The measurements were repeated on 10 separate occasions in a random sequence for each barrier. Analysis of variance (ANOVA) followed by Fisher's protected least significant difference test showed that the power density was significantly less than control (by 2.4% to 6.1%) when 2 commercially available disposable barriers were used (p < 0.05). There was no significant difference in the power density when general-purpose plastic wrap was used (p > 0.05). The effect of each of the barriers on the power output was small and probably clinically insignificant. ANOVA comparisons of mean peak wavelength values indicated that none of the barriers produced a significant shift in the spectral output relative to the control ( p > 0.05). Two of the 3 disposable barriers produced a significant reduction in power density from the curing light. This drop in power was small and would probably not adversely affect the curing of composite resin. None of the barriers acted as light filters.

Physiological Evaluation of Personal Protective Ensembles Recommended for Use in West Africa.

PubMed

Coca, Aitor; Quinn, Tyler; Kim, Jung-Hyun; Wu, Tianzhou; Powell, Jeff; Roberge, Raymond; Shaffer, Ronald

2017-10-01

Personal protective equipment (PPE) provides health care workers with a barrier to prevent human contact with viruses like Ebola and potential transmission of the disease. However, PPE can also introduce an additional physiological burden from potentially increased heat stress. This study evaluated the human physiological and subjective responses to continuous light exercise within environmental conditions similar to those in West Africa while wearing 3 different, commonly used PPE ensembles (E1, E2, and E3). Six healthy individuals were tested in an environmental chamber (32°C, 92% relative humidity) while walking (3 METs, 2.5 mph, 0% incline) on a treadmill for 60 minutes. All subjects wore medical scrubs and PPE items. E1 also had a face shield and fluid-resistant surgical gown; E2 additionally included goggles, coverall, and separate hood; and E3 also contained a highly impermeable coverall, separate hood, and surgical mask cover over the N95 respirator. Heart rate and core temperature at the end of the exercise were significantly higher for E2 and E3 than for E1. Subjective perceptions of heat and exertion were significantly higher for E2 and E3 than for E1. Heat stress and PPE training, as well as the implementation of a work-to-rest ratio that avoids dehydration and possible heat stress issues, are recommended. (Disaster Med Public Health Preparedness. 2017;11:580-586).

From coherent quasi-irreversible quantum dynamics towards the second law of thermodynamics: The model boron rotor B13+

NASA Astrophysics Data System (ADS)

Jia, Dongming; Manz, Jörn; Yang, Yonggang

2018-04-01

The planar boron cluster B13+ provides a model to investigate the microscopic origin of the second law of thermodynamics in a small system. It is a molecular rotor with an inner wheel that rotates in an outer bearing. The cyclic reaction path of B13+ passes along thirty equivalent global minimum structures (GMi, i = 1, 2, ..., 30). The GMs are embedded in a cyclic thirty-well potential. They are separated by thirty equivalent transition states with potential barrier Vb. If the boron rotor B13+ is prepared initially in one of the thirty GMs, with energy below Vb, then it tunnels sequentially to its nearest, next-nearest etc. neighbors (520 fs per step) such that all the other GMs get populated. As a consequence, the entropy of occupying the GMs takes about 6 ps to increases from zero to a value close to the maximum value for equi-distribution. Perfect recurrences are practically not observable.

Sliding states of a soft-colloid cluster crystal: Cluster versus single-particle hopping

NASA Astrophysics Data System (ADS)

Rossini, Mirko; Consonni, Lorenzo; Stenco, Andrea; Reatto, Luciano; Manini, Nicola

2018-05-01

We study a two-dimensional model for interacting colloidal particles which displays spontaneous clustering. Within this model we investigate the competition between the pinning to a periodic corrugation potential and a sideways constant pulling force which would promote a sliding state. For a few sample particle densities and amplitudes of the periodic corrugation potential we investigate the depinning from the statically pinned to the dynamically sliding regime. This sliding state exhibits the competition between a dynamics where entire clusters are pulled from a minimum to the next and a dynamics where single colloids or smaller groups leave a cluster and move across the corrugation energy barrier to join the next cluster downstream in the force direction. Both kinds of sliding states can occur either coherently across the entire sample or asynchronously: the two regimes result in different average mobilities. Finite temperature tends to destroy separate sliding regimes, generating a smoother dependence of the mobility on the driving force.

Identification of potential barriers to nurse-sensitive outcome demonstration.

PubMed

Beckel, Jean; Wolf, Gail; Wilson, Roxanne; Hoolahan, Susan

2013-12-01

The objective of this study was to determine differences in chief nursing officer, Magnet(®) program director, nurse leader, and direct care RN perspectives of potential barriers to demonstration of nurse-sensitive outcomes. The Magnet Recognition Program(®) and other designations are focusing on patient outcomes. No evidence is available addressing barriers to demonstration of nursing outcomes at multiple levels of practice. A Likert scale tool was developed and administered to 526 attendees at the 2012 national Magnet conference. Questions related to available resources, benchmarks, outcome demonstration process understanding, perception of value, and competing priorities. Significant perception differences by role were demonstrated related to available resources, competing priorities, and process understanding supporting demonstration of nurse-sensitive outcomes. No significant differences were identified related to benchmarks or perception of process value to the organization. This study provides new information demonstrating potential barriers to demonstration of nurse-sensitive outcomes differing by role. Opportunity exists to develop systems and processes to reduce perceived barriers among the nursing workforce.

Calculation of multidimensional potential energy surfaces for even-even transuranium nuclei: systematic investigation of the triaxiality effect on the fission barrier

NASA Astrophysics Data System (ADS)

Chai, Qing-Zhen; Zhao, Wei-Juan; Liu, Min-Liang; Wang, Hua-Lei

2018-05-01

Static fission barriers for 95 even-even transuranium nuclei with charge number Z = 94–118 have been systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the potential energy surface approach in multidimensional (β 2, γ, β 4) deformation space. Taking the heavier 252Cf nucleus (with the available fission barrier from experiment) as an example, the formation of the fission barrier and the influence of macroscopic, shell and pairing correction energies on it are analyzed. The results of the present calculated β 2 values and barrier heights are compared with previous calculations and available experiments. The role of triaxiality in the region of the first saddle is discussed. It is found that the second fission barrier is also considerably affected by the triaxial deformation degree of freedom in some nuclei (e.g., the Z=112–118 isotopes). Based on the potential energy curves, general trends of the evolution of the fission barrier heights and widths as a function of the nucleon numbers are investigated. In addition, the effects of Woods-Saxon potential parameter modifications (e.g., the strength of the spin-orbit coupling and the nuclear surface diffuseness) on the fission barrier are briefly discussed. Supported by National Natural Science Foundation of China (11675148, 11505157), the Project of Youth Backbone Teachers of Colleges and Universities of Henan Province (2017GGJS008), the Foundation and Advanced Technology Research Program of Henan Province (162300410222), the Outstanding Young Talent Research Fund of Zhengzhou University (1521317002) and the Physics Research and Development Program of Zhengzhou University (32410017)

Electron transport through triangular potential barriers with doping-induced disorder

NASA Astrophysics Data System (ADS)

Elpelt, R.; Wolst, O.; Willenberg, H.; Malzer, S.; Döhler, G. H.

2004-05-01

Electron transport through single-, double-, and triple-barrier structures created by the insertion of suitably δ-doped layers in GaAs is investigated. The results are compared with experiments on barriers of similar shape, but obtained by linear grading of the Al fraction x in AlxGa1-xAs structures. In the case of the doping-induced space-charge potential it is found that the effective barrier height for transport is much lower than expected from a simple model, in which uniform distribution of the doping charge within the doped layers is assumed. This reduction is quantitatively explained by taking into account the random distribution of the acceptor atoms within the δp-doped layers, which results in large spatial fluctuations of the barrier potential. The transport turns out to be dominated by small regions around the energetically lowest saddle points of the random space-charge potential. Additionally, independent on the dimensionality of the transport [three-dimensional (3D) to 3D in the single barrier, from 3D through 2D to 3D in the double barrier, and from 3D through 2D through 2D to 3D in the triple-barrier structure], fingerprints of 2D subband resonances are neither experimentally observed nor theoretically expected in the doping-induced structures. This is attributed to the disorder-induced random spatial fluctuations of the subband energies in the n layers which are uncorrelated for neighboring layers. Our interpretations of the temperature-dependent current-voltage characteristics are corroborated by comparison with the experimental and theoretical results obtained from the corresponding fluctuation-free AlxGa1-xAs structures. Quantitative agreement between theory and experiment is observed in both cases.

Effects of group status and victim sex on female bystanders' responses to a potential party rape.

PubMed

Katz, Jennifer; Colbert, Samuel; Colangelo, Liane

2015-01-01

This research examined bystander responses to 1 of 4 potential party rape scenarios. Undergraduate women (N = 249) imagined attending a party either alone or with three friends where a sober man led an intoxicated potential victim (either male or female) into a bedroom. After random assignment to conditions, participants reported on intent to help and barriers to helping the potential victim. In contrast to the classic bystander effect, bystanders in groups intended to offer more help than lone bystanders. Bystanders also intended to offer more help to potential female than male victims and experienced more barriers to helping male victims. Two of these barriers (lack of personal responsibility to help and identifying risk) explained the lower intentions to help potential male victims. Potential male victims were more likely than female victims to be perceived as gay, and bystanders reported the least intentions to help presumably gay men at risk.

Dynamical approach to heavy-ion induced fusion using actinide target

NASA Astrophysics Data System (ADS)

Aritomo, Y.; Hagino, K.; Chiba, S.; Nishio, K.

2012-10-01

To treat heavy-ion reactions using actinide target nucleus, we propose a model which takes into account the coupling to the collective states of interacting nuclei in the penetration of the Coulomb barrier and the dynamical evolution of nuclear shape from the contact configuration. A fluctuation-dissipation model (Langevin equation) was applied in the dynamical calculation, where effect of nuclear orientation at the initial impact on the prolately deformed target nucleus was considered. Using this model, we analyzed the experimental data for the mass distribution of fission fragments (MDFF) in the reaction of 36S+238U at several incident energies. Fusion-fission, quasifission and deep-quasi-fission are separated as different trajectories on the potential energy surface. We estimated the fusion cross section of the reaction.

Trojan horse measurement of the 10B(p ,α0)7Be cross section in the energy range from 3 keV to 2.2 MeV

NASA Astrophysics Data System (ADS)

Cvetinović, A.; Spitaleri, C.; Spartá, R.; Rapisarda, G. G.; Puglia, S. M. R.; La Cognata, M.; Cherubini, S.; Guardo, G. L.; Gulino, M.; Lamia, L.; Pizzone, R. G.; Romano, S.; Sergi, M. L.; Tumino, A.

2018-06-01

The 10B(p ,α0)7Be excitation function has been studied in a wide energy range, from 2.2 MeV down to astrophysical energies, reproducing the cross section above and below the Coulomb barrier in a single experiment. An optimized experimental setup ensured good energy resolution and for the first time a clear separation of α0 and α1 channels of the 10B+2H interaction has been achieved by applying the Trojan Horse method. An improved normalization of the Trojan Horse bare-nucleus astrophysical S (E )-factor to direct data was performed and a value of Ue=391 ±74 eV was obtained for the electron screening potential.

Plasma Surface Modification of Polymer Backsheets: Origins of Future Interfacial Barrier/Backsheet Failure (Poster)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pankow, J. W.; Glick, S. H.

2006-05-01

Flexible polymer substrates coated with inorganic oxide moisture barriers are a potential replacement for glass backsheets in thin-film PV (photovoltaic) modules. Silicon oxynitride (SiO{sub x}N{sub y}) deposited by plasma enhanced chemical vapor deposition (PECVD) on polyethylene terephthalate (PET) represents one potential new backsheet candidate. Barrier deposition runs at NREL have included a nitrogen-rich plasma pretreatment prior to barrier deposition with the intention of cleaning the PET surface and enhancing adhesion of the SiO{sub x}N{sub y} barrier film to PET; however, test coupons of PET/barrier/EVA/TPE failed after damp-heat exposure. (EVA is ethylene vinyl acetate and TPE is Tedlar{reg_sign}-PET-EVA). PET substrates exposedmore » to plasma conditions similar to those used in pretreatment were examined by X-ray photoelectron spectroscopy (XPS) to reveal that new low molecular weight PET fragments were created at the PET surface. These fragments are responsible for barrier/PET interfacial failure and barrier transfer to the EVA encapsulant side following damp heat exposure.« less

A novel in vivo method for isolating antibodies from a phage display library by neuronal retrograde transport selectively yields antibodies against p75(NTR.).

PubMed

Tani, Hiroaki; Osbourn, Jane K; Walker, Edward H; Rush, Robert A; Ferguson, Ian A

2013-01-01

The neurotrophin receptor p75(NTR) is utilized by a variety of pathogens to gain entry into the central nervous system (CNS). We tested if this entry portal might be exploited using a phage display library to isolate internalizing antibodies that target the CNS in vivo. By applying a phage library that expressed human single chain variable fragment (scFv) antibodies on their surface to a transected sciatic nerve, we showed that (1) phage conjugated to anti-p75(NTR) antibody or phage scFv library pre-panned against p75(NTR) are internalized by neurons expressing p75(NTR); (2) subsequent retrograde axonal transport separates internalized phage from the applied phage; and, (3) internalized phage can be recovered from a proximal ligature made on a nerve. This approach resulted in 13-fold increase in the number of phage isolated from the injured nerve compared with the starting population, and isolation of 18 unique internalizing p75(NTR) antibodies that were transported from the peripheral nerve into the spinal cord, through the blood-brain barrier. In addition, antibodies recognizing other potentially internalized antigens were identified through in vivo selection using a fully diverse library. Because p75(NTR) expression is upregulated in motor neurons in response to injury and in disease, the p75(NTR) antibodies may have substantial potential for cell-targeted drug/gene delivery. In addition, this novel selection method provides the potential to generate panels of antibodies that could be used to identify further internalization targets, which could aid drug delivery across the blood-brain barrier.

The blood-brain barrier and nasal drug delivery to the central nervous system.

PubMed

Miyake, Marcel Menon; Bleier, Benjamin S

2015-01-01

The blood-brain barrier (BBB) is a highly efficient system that separates the central nervous system (CNS) from general circulation and promotes selective transport of molecules that are essential for brain function. However, it also limits the distribution of systemically administered therapeutics to the brain; therefore, there is a restricted number of drugs available for the treatment of brain disorders. Several drug-targeting strategies have been developed to attempt to bypass the BBB, but none has proved sufficiently effective in reaching the brain. The objective of this study is to generally review these strategies of drug administration to the CNS. Noninvasive methods of drug delivery, such as chemical and biologic transport systems, do not represent a feasible platform, whereas for most drugs, it is still not possible to achieve therapeutic levels within the brain tissue after intravenous or oral administration, and the use of higher potency or more concentrated doses may cause serious toxic side effects. Direct intrathecal drug delivery through a catheter into the CNS also presents several problems. Intranasal drug delivery is a potential alternative method due to the direct transport into the cerebrospinal fluid (CSF) compartment along the olfactory pathway, but the study's conclusions are controversial. An endoscopic intranasal surgical procedure using established skull base surgery reconstruction techniques based on the use of a nasal mucosa surgical flap as the only obstacle between the nose and the subarachnoid space has appeared as a potential solution to increase the absorption of intranasal drugs to the CNS. Despite extensive efforts to develop new techniques to cross the BBB, none has proved sufficiently effective in reaching the brain, whereas minimizing adverse effects and the endoscopic mucosal grafting technique offers new potential promise.

A novel in vivo method for isolating antibodies from a phage display library by neuronal retrograde transport selectively yields antibodies against p75NTR

PubMed Central

Tani, Hiroaki; Osbourn, Jane K.; Walker, Edward H.; Rush, Robert A.; Ferguson, Ian A.

2013-01-01

The neurotrophin receptor p75NTR is utilized by a variety of pathogens to gain entry into the central nervous system (CNS). We tested if this entry portal might be exploited using a phage display library to isolate internalizing antibodies that target the CNS in vivo. By applying a phage library that expressed human single chain variable fragment (scFv) antibodies on their surface to a transected sciatic nerve, we showed that (1) phage conjugated to anti-p75NTR antibody or phage scFv library pre-panned against p75NTR are internalized by neurons expressing p75NTR; (2) subsequent retrograde axonal transport separates internalized phage from the applied phage; and, (3) internalized phage can be recovered from a proximal ligature made on a nerve. This approach resulted in 13-fold increase in the number of phage isolated from the injured nerve compared with the starting population, and isolation of 18 unique internalizing p75NTR antibodies that were transported from the peripheral nerve into the spinal cord, through the blood-brain barrier. In addition, antibodies recognizing other potentially internalized antigens were identified through in vivo selection using a fully diverse library. Because p75NTR expression is upregulated in motor neurons in response to injury and in disease, the p75NTR antibodies may have substantial potential for cell-targeted drug/gene delivery. In addition, this novel selection method provides the potential to generate panels of antibodies that could be used to identify further internalization targets, which could aid drug delivery across the blood-brain barrier. PMID:23549155

Three-cable barrier makes I-5 safer.

DOT National Transportation Integrated Search

1998-08-01

The cable median barrier system has been effective in preventing crossover accidents at the selected location, from December 1996 through March 1998. Of the 53 barrier impacts, 21 potential crossovers were restrained from entering the opposing traffi...

New twinning route in face-centered cubic nanocrystalline metals.

PubMed

Wang, Lihua; Guan, Pengfei; Teng, Jiao; Liu, Pan; Chen, Dengke; Xie, Weiyu; Kong, Deli; Zhang, Shengbai; Zhu, Ting; Zhang, Ze; Ma, Evan; Chen, Mingwei; Han, Xiaodong

2017-12-15

Twin nucleation in a face-centered cubic crystal is believed to be accomplished through the formation of twinning partial dislocations on consecutive atomic planes. Twinning should thus be highly unfavorable in face-centered cubic metals with high twin-fault energy barriers, such as Al, Ni, and Pt, but instead is often observed. Here, we report an in situ atomic-scale observation of twin nucleation in nanocrystalline Pt. Unlike the classical twinning route, deformation twinning initiated through the formation of two stacking faults separated by a single atomic layer, and proceeded with the emission of a partial dislocation in between these two stacking faults. Through this route, a three-layer twin was nucleated without a mandatory layer-by-layer twinning process. This route is facilitated by grain boundaries, abundant in nanocrystalline metals, that promote the nucleation of separated but closely spaced partial dislocations, thus enabling an effective bypassing of the high twin-fault energy barrier.

Sign of coupling in barrier-separated Bose-Einstein condensates and stability of double-ring systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brand, J.; Haigh, T. J.; Zuelicke, U.

We revisit recent claims about the instability of nonrotating tunnel coupled annular Bose-Einstein condensates leading to the emergence of angular momentum Josephson oscillation [Phys. Rev. Lett. 98, 050401 (2007)]. It was predicted that all stationary states with uniform density become unstable in certain parameter regimes. By careful analysis, we arrive at a different conclusion. We show that there is a stable nonrotating and uniform ground state for any value of the tunnel coupling and repulsive interactions. The instability of an excited state with {pi} phase difference between the condensates can be interpreted in terms of the familiar snake instability. Wemore » further discuss the sign of the tunnel coupling through a separating barrier, which carries significance for the nature of the stationary states. It is found to always be negative for physical reasons.« less

A C-terminal cyclic 8-13 neurotensin fragment analog appears less exposed to neprilysin when it crosses the blood-brain barrier than the cerebrospinal fluid-brain barrier in mice.

PubMed

Van Kemmel, F M; Dubuc, I; Bourdel, E; Fehrentz, J A; Martinez, J; Costentin, J

1996-10-11

A C-terminal cyclic 8-13 neurotensin fragment analog. JMV 1193, a direct agonist of central neurotensin receptors, is able to cross both the cerebrospinal fluid-brain barrier and the blood-brain barrier. When administered intracerebroventricularly (i.c.v.), its hypothermic effect was potentiated by the enkephalinase inhibition induced either by thiorphan (simultaneous intracerebroventricular administration of 10 micrograms) or by the thiorphan prodrug. acetorphan (intravenous (i.v.) administration of 10 mg/kg). Such a potentiation was not observed when both JMV 1193 and acetorphan were administered intravenously. Therefore it appears that the sensitivity of JMV 1193 to enkephalinase depends on its route of administration. It is exposed to this peptidase after i.c.v. injection (when crossing the cerebrospinal fluid-brain barrier), while it is not after i.v. administration (when crossing the blood-brain barrier).

Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barettin, Daniele, E-mail: Daniele.Barettin@uniroma2.it; Auf der Maur, Matthias; De Angelis, Roberta

2015-03-07

We report on numerical simulations of InP surface lateral quantum-dot molecules on In{sub 0.48}Ga{sub 0.52 }P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateralmore » quantum-dot molecules. Continuum electromechanical, k{sup →}·p{sup →} bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.« less

Inter-dot strain field effect on the optoelectronic properties of realistic InP lateral quantum-dot molecules

NASA Astrophysics Data System (ADS)

Barettin, Daniele; Auf der Maur, Matthias; De Angelis, Roberta; Prosposito, Paolo; Casalboni, Mauro; Pecchia, Alessandro

2015-03-01

We report on numerical simulations of InP surface lateral quantum-dot molecules on In0.48Ga0.52P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k →.p → bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.

Barriers to treatment adherence among African American and white women with systemic lupus erythematosus.

PubMed

Mosley-Williams, Angelia; Lumley, Mark A; Gillis, Mazy; Leisen, James; Guice, Deena

2002-12-15

To determine whether African Americans with systemic lupus erythematosus (SLE) have poorer treatment adherence than whites, and to determine ethnic group differences in barriers to adherence, and how barriers affect adherence. We compared 68 African American and 54 white women with SLE on 19 potential barriers, on 2 adherence behaviors during the past year, and on how the potential barriers relate to each nonadherence behavior. African Americans and whites were similar on most barriers, although African Americans were more likely to rely on religion and were more concerned about long-term medication effects. The 2 ethnic groups were comparable on medication nonadherence, but whites tended to have poorer clinic appointment adherence than African Americans. Finally, we found that barriers related to negative affect (depression, medication concerns, physical symptoms) as well as short-term memory problems and the need for child or elder care were associated with nonadherence among African Americans, whereas perceived treatment inefficacy and lacking trust in physicians were associated with nonadherence among whites. Relationships between adherence barriers and nonadherence may be ethnicity specific, suggesting that interventions to address barriers should be targeted to specific groups.

Method and apparatus for spatially uniform electropolishing and electrolytic etching

DOEpatents

Mayer, Steven T.; Contolini, Robert J.; Bernhardt, Anthony F.

1992-01-01

In an electropolishing or electrolytic etching apparatus the anode is separated from the cathode to prevent bubble transport to the anode and to produce a uniform current distribution at the anode by means of a solid nonconducting anode-cathode barrier. The anode extends into the top of the barrier and the cathode is outside the barrier. A virtual cathode hole formed in the bottom of the barrier below the level of the cathode permits current flow while preventing bubble transport. The anode is rotatable and oriented horizontally facing down. An extended anode is formed by mounting the workpiece in a holder which extends the electropolishing or etching area beyond the edge of the workpiece to reduce edge effects at the workpiece. A reference electrode controls cell voltage. Endpoint detection and current shut-off stop polishing. Spatially uniform polishing or etching can be rapidly performed.

Method and apparatus for spatially uniform electropolishing and electrolytic etching

DOEpatents

Mayer, S.T.; Contolini, R.J.; Bernhardt, A.F.

1992-03-17

In an electropolishing or electrolytic etching apparatus the anode is separated from the cathode to prevent bubble transport to the anode and to produce a uniform current distribution at the anode by means of a solid nonconducting anode-cathode barrier. The anode extends into the top of the barrier and the cathode is outside the barrier. A virtual cathode hole formed in the bottom of the barrier below the level of the cathode permits current flow while preventing bubble transport. The anode is rotatable and oriented horizontally facing down. An extended anode is formed by mounting the workpiece in a holder which extends the electropolishing or etching area beyond the edge of the workpiece to reduce edge effects at the workpiece. A reference electrode controls cell voltage. Endpoint detection and current shut-off stop polishing. Spatially uniform polishing or etching can be rapidly performed. 6 figs.

Doubly charged coronene clusters—Much smaller than previously observed

NASA Astrophysics Data System (ADS)

Mahmoodi-Darian, Masoomeh; Raggl, Stefan; Renzler, Michael; Goulart, Marcelo; Huber, Stefan E.; Mauracher, Andreas; Scheier, Paul; Echt, Olof

2018-05-01

The smallest doubly charged coronene cluster ions reported so far, Cor152+, were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev. A 84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene. The observation implies that Cor32+ features a non-zero fission barrier too large to overcome under the present experimental conditions. The height of the barriers for the dimer and trimer has been estimated by means of density functional theory calculations. A sizeable barrier for the trimer has been revealed in agreement with the experimental findings.

Open access for the non-English-speaking world: overcoming the language barrier

PubMed Central

Fung, Isaac CH

2008-01-01

This editorial highlights the problem of language barrier in scientific communication in spite of the recent success of Open Access Movement. Four options for English-language journals to overcome the language barrier are suggested: 1) abstracts in alternative languages provided by authors, 2) Wiki open translation, 3) international board of translator-editors, and 4) alternative language version of the journal. The Emerging Themes in Epidemiology announces that with immediate effect, it will accept translations of abstracts or full texts by authors as Additional files. Editorial note: In an effort towards overcoming the language barrier in scientific publication, ETE will accept translations of abstracts or the full text of published articles. Each translation should be submitted separately as an Additional File in PDF format. ETE will only peer review English-language versions. Therefore, translations will not be scrutinized in the review-process and the responsibility for accurate translation rests with the authors. PMID:18173854

Reaction front barriers in time aperiodic fluid flows

NASA Astrophysics Data System (ADS)

Locke, Rory; Mitchell, Kevin

2016-11-01

Many chemical and biological systems can be characterized by the propagation of a front that separates different phases or species. One approach to formalizing a general theory is to apply frameworks developed in nonlinear dynamics. It has been shown that invariant manifolds form barriers to passive transport in time-dependent or time-periodic fluid flows. More recently, analogous manifolds termed burning- invariant-manifolds (BIMs), have been shown to form one-sided barriers to reaction fronts in advection-reaction-diffusion (ARD) systems. To model more realistic time-aperiodic systems, recent theoretical work has suggested that similar one-sided barriers, termed burning Lagrangian coherent structures (bLCSs), exist for fluid velocity data prescribed over a finite time interval. In this presentation, we use a stochastic "wind" to generate time dependence in a double-vortex channel flow and demonstrate the (locally) most attracting or repelling curves are the bLCSs.

A survey of the barriers associated with academic-based cancer research commercialization.

PubMed

Vanderford, Nathan L; Weiss, L Todd; Weiss, Heidi L

2013-01-01

Commercialization within the academic setting is associated with many challenges and barriers. Previous studies investigating these challenges/barriers have, in general, broadly focused on multiple disciplines and, oftentimes, several institutions simultaneously. The goal of the study presented here was to analyze a range of barriers that may be broadly associated with commercializing academic-based cancer research. This goal was addressed via a study of the barriers associated with cancer research commercialization at the University of Kentucky (UK). To this end, a research instrument in the form of an electronic survey was developed. General demographic information was collected on study participants and two research questions were addressed: 1) What are the general barriers inhibiting cancer research commercialization at UK? and 2) Would mitigation of the barriers potentially enhance faculty engagement in commercialization activities? Descriptive and statistical analysis of the data reveal that multiple barriers likely inhibit cancer research commercialization at UK with expense, time, infrastructure, and lack of industry partnerships being among the most commonly cited factors. The potential alleviation of these factors in addition to revised University policies/procedures, risk mitigation, more emphasis on commercialization by academia research field, and increased information on how to commercialize significantly correlated with the potential for increased commercialization activity. Furthermore, multivariate logistic regression modeling demonstrated that research commercialization would incrementally increase as barriers to the process are removed and that PhD-holding respondents and respondents in commercialization-supportive research fields would be more likely to commercialize their research upon barrier removal. Overall, as with other disciplines, these data suggest that for innovations derived from academic cancer-research to move more effectively and efficiently into the marketplace, university administrators and external agents, such as policymakers, need to address what are well-documented and defined issues.

A Survey of the Barriers Associated with Academic-based Cancer Research Commercialization

PubMed Central

Vanderford, Nathan L.; Weiss, L. Todd; Weiss, Heidi L.

2013-01-01

Commercialization within the academic setting is associated with many challenges and barriers. Previous studies investigating these challenges/barriers have, in general, broadly focused on multiple disciplines and, oftentimes, several institutions simultaneously. The goal of the study presented here was to analyze a range of barriers that may be broadly associated with commercializing academic-based cancer research. This goal was addressed via a study of the barriers associated with cancer research commercialization at the University of Kentucky (UK). To this end, a research instrument in the form of an electronic survey was developed. General demographic information was collected on study participants and two research questions were addressed: 1) What are the general barriers inhibiting cancer research commercialization at UK? and 2) Would mitigation of the barriers potentially enhance faculty engagement in commercialization activities? Descriptive and statistical analysis of the data reveal that multiple barriers likely inhibit cancer research commercialization at UK with expense, time, infrastructure, and lack of industry partnerships being among the most commonly cited factors. The potential alleviation of these factors in addition to revised University policies/procedures, risk mitigation, more emphasis on commercialization by academia research field, and increased information on how to commercialize significantly correlated with the potential for increased commercialization activity. Furthermore, multivariate logistic regression modeling demonstrated that research commercialization would incrementally increase as barriers to the process are removed and that PhD-holding respondents and respondents in commercialization-supportive research fields would be more likely to commercialize their research upon barrier removal. Overall, as with other disciplines, these data suggest that for innovations derived from academic cancer-research to move more effectively and efficiently into the marketplace, university administrators and external agents, such as policymakers, need to address what are well-documented and defined issues. PMID:23991077

Effect of nanodimensional polyethylenimine layer on surface potential barriers of hybrid structures based on silicon single crystal

NASA Astrophysics Data System (ADS)

Malyar, Ivan V.; Gorin, Dmitry A.; Stetsyura, Svetlana V.

2013-01-01

In this report we present the analysis of I-V curves for MIS-structures like silicon substrate / nanodimensional polyelectrolyte layer / metal probe (contact) which is promising for biosensors, microfluidic chips, different devices of molecular electronics, such as OLEDs, solar cells, where polyelectrolyte layers can be used to modify semiconductor surface. The research is directed to investigate the contact phenomena which influence the resulting signal of devices mentioned above. The comparison of I-V characteristics of such structures measured by scanning tunnel microscopy (contactless technique) and using contact areas deposited by thermal evaporation onto the organic layer (the contact one) was carried out. The photoassisted I-V measurements and complex analysis based on Simmons and Schottky models allow one to extract the potential barriers and to observe the changes of charge transport in MIS-structures under illumination and after polyelectrolyte adsorption. The direct correlation between the thickness of the deposited polyelectrolyte layer and both equilibrium tunnel barrier and Schottky barrier height was observed for hybrid structures with polyethylenimine. The possibility of control over the I-V curves of hybrid structure and the height of the potential barriers (for different charge transports) by illumination was confirmed. Based on experimental data and complex analysis the band diagrams were plotted which illustrate the changes of potential barriers for MIS-structures due to the polyelectrolyte adsorption and under the illumination.

Crossing the Barriers: An Analysis of Market Barriers to Geothermal Development and Potential Improvement Scenarios

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, Katherine R; Levine, Aaron L; Cook, Jeffrey J

Developers have identified many non-technical barriers to geothermal power development, including market barriers. Understanding the challenges to market deployment of geothermal power is important since obtaining power purchase agreements is often cited as one of the largest barriers to geothermal development. This paper discusses the impacts to deployment caused by market challenges, including market demand, price of electricity, policies and incentives.

Large silver-cadmium technology program

NASA Technical Reports Server (NTRS)

Charlip, S.; Lerner, S.

1971-01-01

The effects of varying cell design on operation factors on the electrochemical performance of sealed, silver-cadmium cells were determined. A factorial experiment was conducted for all test cells constructed with organic separators. Three operating factors were evaluated: temperature, depth of discharge, and charge rate. The six construction factors considered were separator, absorber, electrolyte quantity, cadmium electrode type, cadmium-to-silver ratio, and auxiliary electrode. Test cells of 4 ampere-hour capacity were fabricated and cycled. The best performing cells, on a 94 minute orbit, at 40% depth of discharge, were those containing silver-treated fibrous sausage casings as the separator, and Teflon-ated, pressed cadmium electrodes. Cycling data of cells with inorganic separators (Astroset) are given. Best performance was shown by cells with nonwoven nylon absorbers. Rigid inorganic separators provided the best barrier to silver migration.

Transmittance and Tunneling Current through a Trapezoidal Barrier under Spin Polarization Consideration

NASA Astrophysics Data System (ADS)

Noor, F. A.; Nabila, E.; Mardianti, H.; Ariani, T. I.; Khairurrijal

2018-04-01

The transmittance and tunneling current in heterostructures under spin polarization consideration were studied by employing a zinc-blended structure for the heterostructures. An electron tunnels through a potential barrier by applying a bias voltage to the barrier, which is called the trapezoidal potential barrier. In order to study the transmittance, an Airy wave function approach was employed to find the transmittance. The obtained transmittance was then utilized to compute the tunneling current by using a Gauss quadrature method. It was shown that the transmittances were asymmetric with the incident angle of the electron. It was also shown that the tunneling currents increased as the bias voltage increased.

Super-giant magnetoresistance at room-temperature in copper nanowires due to magnetic field modulation of potential barrier heights at nanowire-contact interfaces

NASA Astrophysics Data System (ADS)

Hossain, Md I.; Maksud, M.; Palapati, N. K. R.; Subramanian, A.; Atulasimha, J.; Bandyopadhyay, S.

2016-07-01

We have observed a super-giant (∼10 000 000%) negative magnetoresistance at 39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over, these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This lowers the potential barrier at the accumulated edge and raises it at the depleted edge, causing a super-giant magnetoresistance at room temperature.

Super-giant magnetoresistance at room-temperature in copper nanowires due to magnetic field modulation of potential barrier heights at nanowire-contact interfaces.

PubMed

Hossain, Md I; Maksud, M; Palapati, N K R; Subramanian, A; Atulasimha, J; Bandyopadhyay, S

2016-07-29

We have observed a super-giant (∼10 000 000%) negative magnetoresistance at 39 mT field in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over, these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This lowers the potential barrier at the accumulated edge and raises it at the depleted edge, causing a super-giant magnetoresistance at room temperature.

Influence of solid noise barriers on near-road and on-road air quality

NASA Astrophysics Data System (ADS)

Baldauf, Richard W.; Isakov, Vlad; Deshmukh, Parikshit; Venkatram, Akula; Yang, Bo; Zhang, K. Max

2016-03-01

Public health concerns regarding adverse health effects for populations spending significant amounts of time near high traffic roadways has increased substantially in recent years. Roadside features, including solid noise barriers, have been investigated as potential methods that can be implemented in a relatively short time period to reduce air pollution exposures from nearby traffic. A field study was conducted to determine the influence of noise barriers on both on-road and downwind pollutant concentrations near a large highway in Phoenix, Arizona, USA. Concentrations of nitrogen dioxide, carbon monoxide, ultrafine particles, and black carbon were measured using a mobile platform and fixed sites along two limited-access stretches of highway that contained a section of noise barrier and a section with no noise barrier at-grade with the surrounding terrain. Results of the study showed that pollutant concentrations behind the roadside barriers were significantly lower relative to those measured in the absence of barriers. The reductions ranged from 50% within 50 m from the barrier to about 30% as far as 300 m from the barrier. Reductions in pollutant concentrations generally began within the first 50 m of the barrier edge; however, concentrations were highly variable due to vehicle activity behind the barrier and along nearby urban arterial roadways. The concentrations on the highway, upwind of the barrier, varied depending on wind direction. Overall, the on-road concentrations in front of the noise barrier were similar to those measured in the absence of the barrier, contradicting previous modeling results that suggested roadside barriers increase pollutant levels on the road. Thus, this study suggests that noise barriers do reduce potential pollutant exposures for populations downwind of the road, and do not likely increase exposures to traffic-related pollutants for vehicle passengers on the highway.

Exercise barriers self-efficacy: development and validation of a subcale for individuals with cancer-related lymphedema.

PubMed

Buchan, Jena; Janda, Monika; Box, Robyn; Rogers, Laura; Hayes, Sandi

2015-03-18

No tool exists to measure self-efficacy for overcoming lymphedema-related exercise barriers in individuals with cancer-related lymphedema. However, an existing scale measures confidence to overcome general exercise barriers in cancer survivors. Therefore, the purpose of this study was to develop, validate and assess the reliability of a subscale, to be used in conjunction with the general barriers scale, for determining exercise barriers self-efficacy in individuals facing lymphedema-related exercise barriers. A lymphedema-specific exercise barriers self-efficacy subscale was developed and validated using a cohort of 106 cancer survivors with cancer-related lymphedema, from Brisbane, Australia. An initial ten-item lymphedema-specific barrier subscale was developed and tested, with participant feedback and principal components analysis results used to guide development of the final version. Validity and test-retest reliability analyses were conducted on the final subscale. The final lymphedema-specific subscale contained five items. Principal components analysis revealed these items loaded highly (>0.75) on a separate factor when tested with a well-established nine-item general barriers scale. The final five-item subscale demonstrated good construct and criterion validity, high internal consistency (Cronbach's alpha = 0.93) and test-retest reliability (ICC = 0.67, p < 0.01). A valid and reliable lymphedema-specific subscale has been developed to assess exercise barriers self-efficacy in individuals with cancer-related lymphedema. This scale can be used in conjunction with an existing general exercise barriers scale to enhance exercise adherence in this understudied patient group.

Combined acoustical and visual performance of noise barriers in mitigating the environmental impact of motorways.

PubMed

Jiang, Like; Kang, Jian

2016-02-01

This study investigated the overall performance of noise barriers in mitigating environmental impact of motorways, taking into consideration their effects on reducing noise and visual intrusions of moving traffic, but also potentially inducing visual impact themselves. A laboratory experiment was carried out, using computer-visualised video scenes and motorway traffic noise recordings to present experimental scenarios covering two traffic levels, two distances of receiver to road, two types of background landscape, and five barrier conditions including motorway only, motorway with tree belt, motorways with 3 m timber barrier, 5m timber barrier, and 5m transparent barrier. Responses from 30 participants of university students were gathered and perceived barrier performance analysed. The results show that noise barriers were always beneficial in mitigating environmental impact of motorways, or made no significant changes in environmental quality when the impact of motorways was low. Overall, barriers only offered similar mitigation effect as compared to tree belt, but showed some potential to be more advantageous when traffic level went high. 5m timber barrier tended to perform better than the 3m one at the distance of 300 m but not at 100 m possibly due to its negative visual effect when getting closer. The transparent barrier did not perform much differently from the timber barriers but tended to be the least effective in most scenarios. Some low positive correlations were found between aesthetic preference for barriers and environmental impact reduction by the barriers. Copyright © 2015 Elsevier B.V. All rights reserved.

Diffusion barriers in modified air brazes

DOEpatents

Weil, Kenneth Scott; Hardy, John S; Kim, Jin Yong; Choi, Jung-Pyung

2013-04-23

A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

Diffusion barriers in modified air brazes

DOEpatents

Weil, Kenneth Scott [Richland, WA; Hardy, John S [Richland, WA; Kim, Jin Yong [Richland, WA; Choi, Jung-Pyung [Richland, WA

2010-04-06

A method for joining two ceramic parts, or a ceramic part and a metal part, and the joint formed thereby. The method provides two or more parts, a braze consisting of a mixture of copper oxide and silver, a diffusion barrier, and then heats the braze for a time and at a temperature sufficient to form the braze into a bond holding the two or more parts together. The diffusion barrier is an oxidizable metal that forms either a homogeneous component of the braze, a heterogeneous component of the braze, a separate layer bordering the braze, or combinations thereof. The oxidizable metal is selected from the group Al, Mg, Cr, Si, Ni, Co, Mn, Ti, Zr, Hf, Pt, Pd, Au, lanthanides, and combinations thereof.

Identification of a barrier height threshold where brook trout population genetic diversity, differentiation, and relatedness are affected

Treesearch

Anne Timm; Eric Hallerman; Andy Dolloff; Mark Hudy; Randall Kolka

2016-01-01

The overall goal of the study was to evaluate effects of landscape features, barriers, on Brook Trout Salvelinus fontinalis population genetics and to identify a potential barrier height threshold where genetic diversity was reduced upstream of the barrier and differentiation and relatedness increase. We screened variation at eight...

Perceived barriers to the regionalization of adult critical care in the United States: a qualitative preliminary study

PubMed Central

Kahn, Jeremy M; Asch, Rebecca J; Iwashyna, Theodore J; Rubenfeld, Gordon D; Angus, Derek C; Asch, David A

2008-01-01

Background Regionalization of adult critical care services may improve outcomes for critically ill patients. We sought to develop a framework for understanding clinician attitudes toward regionalization and potential barriers to developing a tiered, regionalized system of care in the United States. Methods We performed a qualitative study using semi-structured interviews of critical care stakeholders in the United States, including physicians, nurses and hospital administrators. Stakeholders were identified from a stratified-random sample of United States general medical and surgical hospitals. Key barriers and potential solutions were identified by performing content analysis of the interview transcriptions. Results We interviewed 30 stakeholders from 24 different hospitals, representing a broad range of hospital locations and sizes. Key barriers to regionalization included personal and economic strain on families, loss of autonomy on the part of referring physicians and hospitals, loss of revenue on the part of referring physicians and hospitals, the potential to worsen outcomes at small hospitals by limiting services, and the potential to overwhelm large hospitals. Improving communication between destination and source hospitals, provider education, instituting voluntary objective criteria to become a designated referral center, and mechanisms to feed back patients and revenue to source hospitals were identified as potential solutions to some of these barriers. Conclusion Regionalization efforts will be met with significant conceptual and structural barriers. These data provide a foundation for future research and can be used to inform policy decisions regarding the design and implementation of a regionalized system of critical care. PMID:19014704

Rigid open-cell polyurethane foam for cryogenic insulation

NASA Technical Reports Server (NTRS)

Faddoul, J. R.; Lindquist, C. R.; Niendorf, L. R.; Nies, G. E.; Perkins, P. J., Jr.

1971-01-01

Lightweight polyurethane foam assembled in panels is effective spacer material for construction of self-evacuating multilayer insulation panels for cryogenic liquid tanks. Spacer material separates radiation shields with barrier that minimizes conductive and convective heat transfer between shields.

Anomalously high potentials observed on ISEE

NASA Technical Reports Server (NTRS)

Whipple, E. C.; Krinsky, I. S.; Torbert, R. B.; Olsen, R. C.

1985-01-01

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 are used to show that the spacecraft charged to close to -70 V in sunlight at 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Interferometry of Klein tunnelling electrons in graphene quantum rings

NASA Astrophysics Data System (ADS)

de Sousa, D. J. P.; Chaves, Andrey; Pereira, J. M.; Farias, G. A.

2017-01-01

We theoretically study a current switch that exploits the phase acquired by a charge carrier as it tunnels through a potential barrier in graphene. The system acts as an interferometer based on an armchair graphene quantum ring, where the phase difference between interfering electronic wave functions for each path can be controlled by tuning either the height or the width of a potential barrier in the ring arms. By varying the parameters of the potential barriers, the interference can become completely destructive. We demonstrate how this interference effect can be used for developing a simple graphene-based logic gate with a high on/off ratio.

Role of the supersymmetric semiclassical approach in barrier penetration and heavy-ion fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sil, T.; Dutt, R.; Varshni, Y.P.

1994-11-01

The problem of heavy-ion fusion reactions in the one-dimensional barrier penetration model (BPM) has been reexamined in light of supersymmetry-inspired WKB (SWKB) method. Motivated by our recent work [Phys. Lett. A 184, 209 (1994)] describing the SWKB method for the computation of the transmission coefficient [ital T]([ital E]), we have performed similar calculations for a potential barrier that mimics the proximity potential obtained by fitting experimentally measured fusion cross section [sigma][sub [ital F

Controlling the hydration of the skin though the application of occluding barrier creams

PubMed Central

Sparr, Emma; Millecamps, Danielle; Isoir, Muriel; Burnier, Véronique; Larsson, Åsa; Cabane, Bernard

2013-01-01

The skin is a barrier membrane that separates environments with profoundly different water contents. The barrier properties are assured by the outer layer of the skin, the stratum corneum (SC), which controls the transepidermal water loss. The SC acts as a responding membrane, since its hydration and permeability vary with the boundary condition, which is the activity of water at the outer surface of the skin. We show how this boundary condition can be changed by the application of a barrier cream that makes a film with a high resistance to the transport of water. We present a quantitative model that predicts hydration and water transport in SC that is covered by such a film. We also develop an experimental method for measuring the specific resistance to water transport of films made of occluding barrier creams. Finally, we combine the theoretical model with the measured properties of the barrier creams to predict how a film of cream changes the activity of water at the outer surface of the SC. Using the known variations of SC permeability and hydration with the water activity in its environment (i.e. the relative humidity), we can thus predict how a film of barrier cream changes SC hydration. PMID:23269846

Controlling the hydration of the skin though the application of occluding barrier creams.

PubMed

Sparr, Emma; Millecamps, Danielle; Isoir, Muriel; Burnier, Véronique; Larsson, Åsa; Cabane, Bernard

2013-03-06

The skin is a barrier membrane that separates environments with profoundly different water contents. The barrier properties are assured by the outer layer of the skin, the stratum corneum (SC), which controls the transepidermal water loss. The SC acts as a responding membrane, since its hydration and permeability vary with the boundary condition, which is the activity of water at the outer surface of the skin. We show how this boundary condition can be changed by the application of a barrier cream that makes a film with a high resistance to the transport of water. We present a quantitative model that predicts hydration and water transport in SC that is covered by such a film. We also develop an experimental method for measuring the specific resistance to water transport of films made of occluding barrier creams. Finally, we combine the theoretical model with the measured properties of the barrier creams to predict how a film of cream changes the activity of water at the outer surface of the SC. Using the known variations of SC permeability and hydration with the water activity in its environment (i.e. the relative humidity), we can thus predict how a film of barrier cream changes SC hydration.

Barriers, Obstacles, and Mine Warfare for Joint Operations

DTIC Science & Technology

2007-04-26

separated from the anchor. Mines that separate from their anchors and rise to the surface are known as floaters . These may continue to float until...the 1907 Hague Treaty, these mines have been used on occasion. A drifting mine is classified differently from a moored mine that has become a floater ...as a floater was designed to be anchored, while a drifter was designed to float freely with the tides and currents. (c) The principal advantage of

Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

NASA Astrophysics Data System (ADS)

Gao, Qingxue; Liu, Rong; Xiao, Hongdi; Cao, Dezhong; Liu, Jianqiang; Ma, Jin

2016-11-01

A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

Outer brain barriers in rat and human development

PubMed Central

Brøchner, Christian B.; Holst, Camilla B.; Møllgård, Kjeld

2015-01-01

Complex barriers at the brain's surface, particularly in development, are poorly defined. In the adult, arachnoid blood-cerebrospinal fluid (CSF) barrier separates the fenestrated dural vessels from the CSF by means of a cell layer joined by tight junctions. Outer CSF-brain barrier provides diffusion restriction between brain and subarachnoid CSF through an initial radial glial end feet layer covered with a pial surface layer. To further characterize these interfaces we examined embryonic rat brains from E10 to P0 and forebrains from human embryos and fetuses (6–21st weeks post-conception) and adults using immunohistochemistry and confocal microscopy. Antibodies against claudin-11, BLBP, collagen 1, SSEA-4, MAP2, YKL-40, and its receptor IL-13Rα2 and EAAT1 were used to describe morphological characteristics and functional aspects of the outer brain barriers. Claudin-11 was a reliable marker of the arachnoid blood-CSF barrier. Collagen 1 delineated the subarachnoid space and stained pial surface layer. BLBP defined radial glial end feet layer and SSEA-4 and YKL-40 were present in both leptomeningeal cells and end feet layer, which transformed into glial limitans. IL-13Rα2 and EAAT1 were present in the end feet layer illustrating transporter/receptor presence in the outer CSF-brain barrier. MAP2 immunostaining in adult brain outlined the lower border of glia limitans; remnants of end feet were YKL-40 positive in some areas. We propose that outer brain barriers are composed of at least 3 interfaces: blood-CSF barrier across arachnoid barrier cell layer, blood-CSF barrier across pial microvessels, and outer CSF-brain barrier comprising glial end feet layer/pial surface layer. PMID:25852456

Outer brain barriers in rat and human development.

PubMed

Brøchner, Christian B; Holst, Camilla B; Møllgård, Kjeld

2015-01-01

Complex barriers at the brain's surface, particularly in development, are poorly defined. In the adult, arachnoid blood-cerebrospinal fluid (CSF) barrier separates the fenestrated dural vessels from the CSF by means of a cell layer joined by tight junctions. Outer CSF-brain barrier provides diffusion restriction between brain and subarachnoid CSF through an initial radial glial end feet layer covered with a pial surface layer. To further characterize these interfaces we examined embryonic rat brains from E10 to P0 and forebrains from human embryos and fetuses (6-21st weeks post-conception) and adults using immunohistochemistry and confocal microscopy. Antibodies against claudin-11, BLBP, collagen 1, SSEA-4, MAP2, YKL-40, and its receptor IL-13Rα2 and EAAT1 were used to describe morphological characteristics and functional aspects of the outer brain barriers. Claudin-11 was a reliable marker of the arachnoid blood-CSF barrier. Collagen 1 delineated the subarachnoid space and stained pial surface layer. BLBP defined radial glial end feet layer and SSEA-4 and YKL-40 were present in both leptomeningeal cells and end feet layer, which transformed into glial limitans. IL-13Rα2 and EAAT1 were present in the end feet layer illustrating transporter/receptor presence in the outer CSF-brain barrier. MAP2 immunostaining in adult brain outlined the lower border of glia limitans; remnants of end feet were YKL-40 positive in some areas. We propose that outer brain barriers are composed of at least 3 interfaces: blood-CSF barrier across arachnoid barrier cell layer, blood-CSF barrier across pial microvessels, and outer CSF-brain barrier comprising glial end feet layer/pial surface layer.

Visual selective attention with virtual barriers.

PubMed

Schneider, Darryl W

2017-07-01

Previous studies have shown that interference effects in the flanker task are reduced when physical barriers (e.g., hands) are placed around rather than below a target flanked by distractors. One explanation of this finding is the referential coding hypothesis, whereby the barriers serve as reference objects for allocating attention. In five experiments, the generality of the referential coding hypothesis was tested by investigating whether interference effects are modulated by the placement of virtual barriers (e.g., parentheses). Modulation of flanker interference was found only when target and distractors differed in size and the virtual barriers were beveled wood-grain objects. Under these conditions and those of previous studies, the author conjectures that an impression of depth was produced when the barriers were around the target, such that the target was perceived to be on a different depth plane than the distractors. Perception of depth in the stimulus display might have led to referential coding of the stimuli in three-dimensional (3-D) space, influencing the allocation of attention beyond the horizontal and vertical dimensions. This 3-D referential coding hypothesis is consistent with research on selective attention in 3-D space that shows flanker interference is reduced when target and distractors are separated in depth.

[Neurological disorders and the blood-brain barrier. Strategies and limitations for drug delivery to the brain].

PubMed

Domínguez, Alazne; Álvarez, Antonia; Suárez-Merino, Blanca; Goñi-de-Cerio, Felipe

2014-03-01

The incidence in the central nervous system diseases has increased with a growing elderly population. Unfortunately, conventional treatments used to treat the mentioned diseases are frequently ineffective due to the presence of the blood brain barrier. To illustrate the blood-brain barrier properties that limit drug transport into the brain and the main strategies employed to treat neurologic disorders. The blood-brain barrier is mainly composed of a specialized microvascular endothelium and of glial cells. It constitutes a valuable tool to separate the central nervous system from the rest of the body. Nevertheless, it also represents an obstacle to the delivery of therapeutic drugs to the brain. To be effective, drugs must reach their target in the brain. On one hand, therapeutic agents could be designed to be able to cross the blood brain barrier. On the other hand, drug delivery systems could be employed to facilitate the therapeutic agents' entry into the central nervous system. In vivo models of neurological diseases, in addition to in vitro models of the blood brain barrier, have been widely employed for the evaluation of drugs utilized to treat central nervous system diseases.

External electric field effects on Schottky barrier at Gd3N@C80/Au interface

NASA Astrophysics Data System (ADS)

Onishi, Koichi; Nakashima, Fumihiro; Jin, Ge; Eto, Daichi; Hattori, Hayami; Miyoshi, Noriko; Kirimoto, Kenta; Sun, Yong

2017-08-01

The effects of the external electric field on the height of the Schottky barrier at the Gd3N@C80/Au interface were studied by measuring current-voltage characteristics at various temperatures from 200 K to 450 K. The Gd3N@C80 sample with the conduction/forbidden/valence energy band structure had a face-centered cubic crystal structure with the average grain size of several nanometers. The height of the Gd3N@C80/Au Schottky barrier was confirmed to be 400 meV at a low electric field at room temperature. Moreover, the height decreases with the increasing external electric field through a change of permittivity in the Gd3N@C80 sample due to a polarization of the [Gd3] 9 +-[N3 -+("separators="|C80 ) 6 -] dipoles in the Gd3N@C80 molecule. The field-dependence of the barrier height can be described using a power math function of the electric field strength. The results of the field-dependent barrier height indicate that the reduction in the Schottky barrier is due to an image force effect of the transport charge carrier at the Gd3N@C80/Au interface.

Method and apparatus for producing durationally short ultraviolet or x-ray laser pulses

DOEpatents

MacGowan, B.J.; Matthews, D.L.; Trebes, J.E.

1987-05-05

A method and apparatus is disclosed for producing ultraviolet or x- ray laser pulses of short duration. An ultraviolet or x-ray laser pulse of long duration is progressively refracted, across the surface of an opaque barrier, by a streaming plasma that is produced by illuminating a solid target with a pulse of conventional line focused high power laser radiation. The short pulse of ultraviolet or x-ray laser radiation, which may be amplified to high power, is separated out by passage through a slit aperture in the opaque barrier.

Drop-wise and film-wise water condensation processes occurring on metallic micro-scaled surfaces

NASA Astrophysics Data System (ADS)

Starostin, Anton; Valtsifer, Viktor; Barkay, Zahava; Legchenkova, Irina; Danchuk, Viktor; Bormashenko, Edward

2018-06-01

Water condensation was studied on silanized (superhydrophobic) and fluorinated (superoleophobic) micro-rough aluminum surfaces of the same topography. Condensation on superhydrophobic surfaces occurred via film-wise mechanism, whereas on superoleophobic surfaces it was drop-wise. The difference in the pathways of condensation was attributed to the various energy barriers separating the Cassie and Wenzel wetting states on the investigated surfaces. The higher barriers inherent for superoleophobic surfaces promoted the drop-wise condensation. Triple-stage kinetics of growth of droplets condensed on superoleophobic surfaces is reported and discussed.

76 FR 38655 - Agency Information Collection Activities: Proposed Collection; Comment Request

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-01

... Request: New collection; Title of Information Collection: Analysis of Transportation Barriers to... of the proposed study is to identify and analyze transportation barriers associated with the... analyze the health outcomes resulting from those barriers, and ultimately to identify potential solutions...

Financial Strain and Regional Unemployment as Barriers to Job Search Self-Efficacy: A Test of Social Cognitive Career Theory

ERIC Educational Resources Information Center

Dahling, Jason J.; Melloy, Robert; Thompson, Mindi N.

2013-01-01

Social cognitive career theory (SCCT) emphasizes the potential impact of contextual barriers on vocational self-efficacy, interests, and goals. However, most tests of SCCT to date have focused exclusively on person-level, perceptual barriers rather than objective, macroeconomic barriers that may influence large groups of people. In this study, we…

Using models to interpret the impact of roadside barriers on near-road air quality

NASA Astrophysics Data System (ADS)

Amini, Seyedmorteza; Ahangar, Faraz Enayati; Schulte, Nico; Venkatram, Akula

2016-08-01

The question this paper addresses is whether semi-empirical dispersion models based on data from controlled wind tunnel and tracer experiments can describe data collected downwind of a sound barrier next to a real-world urban highway. Both models are based on the mixed wake model described in Schulte et al. (2014). The first neglects the effects of stability on dispersion, and the second accounts for reduced entrainment into the wake of the barrier under unstable conditions. The models were evaluated with data collected downwind of a kilometer-long barrier next to the I-215 freeway running next to the University of California campus in Riverside. The data included measurements of 1) ultrafine particle (UFP) concentrations at several distances from the barrier, 2) micrometeorological variables upwind and downwind of the barrier, and 3) traffic flow separated by automobiles and trucks. Because the emission factor for UFP is highly uncertain, we treated it as a model parameter whose value is obtained by fitting model estimates to observations of UFP concentrations measured at distances where the barrier impact is not dominant. Both models provide adequate descriptions of both the magnitude and the spatial variation of observed concentrations. The good performance of the models reinforces the conclusion from Schulte et al. (2014) that the presence of the barrier is equivalent to shifting the line sources on the road upwind by a distance of about HU/u∗ where H is the barrier height, U is the wind velocity at half of the barrier height, and u∗ is the friction velocity. The models predict that a 4 m barrier results in a 35% reduction in average concentration within 40 m (10 times the barrier height) of the barrier, relative to the no-barrier site. This concentration reduction is 55% if the barrier height is doubled.

Electronic tunneling through a potential barrier on the surface of a topological insulator

NASA Astrophysics Data System (ADS)

Zhou, Benliang; Zhou, Benhu; Zhou, Guanghui

2016-12-01

We investigate the tunneling transport for electrons on the surface of a topological insulator (TI) through an electrostatic potential barrier. By using the Dirac equation with the continuity conditions for all segments of wave functions at the interfaces between regions inside and outside the barrier, we calculate analytically the transmission probability and conductance for the system. It is demonstrated that, the Klein paradox can also been observed in the system same as in graphene system. Interestingly, the conductance reaches the minimum value when the incident electron energy is equal to the barrier strength. Moreover, with increasing barrier width, the conductance turns up some tunneling oscillation peaks, and larger barrier strength can cause lower conductance, shorter period but larger oscillation amplitude. The oscillation amplitude decreases as the barrier width increases, which is similar as that of the system consisting of the compressive uniaxial strain applied on a TI, but somewhat different from that of graphene system where the oscillation amplitude is a constant. The findings here imply that an electrostatic barrier can greatly influence the electron tunneling transport of the system, and may provide a new way to realize directional filtering of electrons.

Conducting Research with LGB People of Color: Methodological Challenges and Strategies

ERIC Educational Resources Information Center

DeBlaere, Cirleen; Brewster, Melanie E.; Sarkees, Anthony; Moradi, Bonnie

2010-01-01

Methodological barriers have been highlighted as a primary reason for the limited research with lesbian, gay, and bisexual (LGB) people of color. Thus, strategies for anticipating and addressing potential methodological barriers are needed. To address this need, this article discusses potential challenges associated with conducting research with…

The potential oral health impact of cost barriers to dental care: findings from a Canadian population-based study

PubMed Central

2014-01-01

Background Prior to the 2007/09 Canadian Health Measures Survey, there was no nationally representative clinical data on the oral health of Canadians experiencing cost barriers to dental care. The aim of this study was to determine the oral health status and dental treatment needs of Canadians reporting cost barriers to dental care. Methods A secondary data analysis of the 2007/09 Canadian Health Measures Survey was undertaken using a sample of 5,586 Canadians aged 6 to 79. Chi square tests were conducted to test the association between reporting cost barriers to care and oral health outcomes. Logistic regressions were conducted to identify predictors of reporting cost barriers. Results Individuals who reported cost barriers to dental care had poorer oral health and more treatment needs compared to their counterparts. Conclusions Avoiding dental care and/or foregoing recommended treatment because of cost may contribute to poor oral health. This study substantiates the potential likelihood of progressive dental problems caused by an inability to treat existing conditions due to financial barriers. PMID:24962622

Novel delivery methods bypassing the blood-brain and blood-tumor barriers.

PubMed

Hendricks, Benjamin K; Cohen-Gadol, Aaron A; Miller, James C

2015-03-01

Glioblastoma (GBM) is the most common primary brain tumor and carries a grave prognosis. Despite years of research investigating potentially new therapies for GBM, the median survival rate of individuals with this disease has remained fairly stagnant. Delivery of drugs to the tumor site is hampered by various barriers posed by the GBM pathological process and by the complex physiology of the blood-brain and blood-cerebrospinal fluid barriers. These anatomical and physiological barriers serve as a natural protection for the brain and preserve brain homeostasis, but they also have significantly limited the reach of intraparenchymal treatments in patients with GBM. In this article, the authors review the functional capabilities of the physical and physiological barriers that impede chemotherapy for GBM, with a specific focus on the pathological alterations of the blood-brain barrier (BBB) in this disease. They also provide an overview of current and future methods for circumventing these barriers in therapeutic interventions. Although ongoing research has yielded some potential options for future GBM therapies, delivery of chemotherapy medications across the BBB remains elusive and has limited the efficacy of these medications.

Numerical simulation of tunneling through arbitrary potential barriers applied on MIM and MIIM rectenna diodes

NASA Astrophysics Data System (ADS)

Abdolkader, Tarek M.; Shaker, Ahmed; Alahmadi, A. N. M.

2018-07-01

With the continuous miniaturization of electronic devices, quantum-mechanical effects such as tunneling become more effective in many device applications. In this paper, a numerical simulation tool is developed under a MATLAB environment to calculate the tunneling probability and current through an arbitrary potential barrier comparing three different numerical techniques: the finite difference method, transfer matrix method, and transmission line method. For benchmarking, the tool is applied to many case studies such as the rectangular single barrier, rectangular double barrier, and continuous bell-shaped potential barrier, each compared to analytical solutions and giving the dependence of the error on the number of mesh points. In addition, a thorough study of the J ‑ V characteristics of MIM and MIIM diodes, used as rectifiers for rectenna solar cells, is presented and simulations are compared to experimental results showing satisfactory agreement. On the undergraduate level, the tool provides a deeper insight for students to compare numerical techniques used to solve various tunneling problems and helps students to choose a suitable technique for a certain application.

Potential of mean force and molecular dynamics study on the transient interactions between α and β synuclein that drive inhibition of α-synuclein aggregation.

PubMed

Sanjeev, Airy; Sahu, Ravi Kumar; Mattaparthi, Venkata Satish Kumar

2017-11-01

Self-association of α-synuclein (αS) into pathogenic oligomeric species and subsequent formation of highly ordered amyloid fibrils is linked to the Parkinson's disease. So most of the recent studies are now focused on the development of potential therapeutic strategies against this debilitating disease. β-synuclein (βS), a presynaptic protein that co-localizes with αS has been recently reported to act as an inhibitor of αS self-assembly. But the specificity of molecular interaction, nature and location between αS/βS is not known despite the potential importance of βS as an inhibitor of αS. We used molecular dynamics and potential of mean force (PMF) to study association of αS/βS and αS/αS. The calculated PMF indicates that contact wells are significantly deeper and presence of a minimum at αS/βS separation of 13.5 Å with a free energy barrier of 40 kcal/mol. We observed the dissociation energy barrier to be two times higher for the hetero-dimer (αS/βS) than the homo-dimer (αS/αS). We also carried out umbrella samplings involving two degrees of freedom (one being the distance between the monomeric units and the other angle between the long axes of the two monomeric chains) and observed similar PMF profile. We noticed relatively stronger range of transient interactions between the monomeric units in hetero-dimer (αS/βS) than homo-dimer (αS/αS). So our findings suggest that αS readily combines with βS to form hetero-dimer than combining with itself in forming homo-dimer. Hence we see predominant transient interactions between αS and βS can be used to drive inhibition of αS aggregation.

In vitro models of the blood–brain barrier: An overview of commonly used brain endothelial cell culture models and guidelines for their use

PubMed Central

Helms, Hans C; Abbott, N Joan; Burek, Malgorzata; Cecchelli, Romeo; Couraud, Pierre-Olivier; Deli, Maria A; Förster, Carola; Galla, Hans J; Romero, Ignacio A; Shusta, Eric V; Stebbins, Matthew J; Vandenhaute, Elodie; Weksler, Babette

2016-01-01

The endothelial cells lining the brain capillaries separate the blood from the brain parenchyma. The endothelial monolayer of the brain capillaries serves both as a crucial interface for exchange of nutrients, gases, and metabolites between blood and brain, and as a barrier for neurotoxic components of plasma and xenobiotics. This “blood-brain barrier” function is a major hindrance for drug uptake into the brain parenchyma. Cell culture models, based on either primary cells or immortalized brain endothelial cell lines, have been developed, in order to facilitate in vitro studies of drug transport to the brain and studies of endothelial cell biology and pathophysiology. In this review, we aim to give an overview of established in vitro blood–brain barrier models with a focus on their validation regarding a set of well-established blood–brain barrier characteristics. As an ideal cell culture model of the blood–brain barrier is yet to be developed, we also aim to give an overview of the advantages and drawbacks of the different models described. PMID:26868179

Fast Self-Healing of Polyelectrolyte Multilayer Nanocoating and Restoration of Super Oxygen Barrier.

PubMed

Song, Yixuan; Meyers, Kevin P; Gerringer, Joseph; Ramakrishnan, Ramesh K; Humood, Mohammad; Qin, Shuang; Polycarpou, Andreas A; Nazarenko, Sergei; Grunlan, Jaime C

2017-05-01

A self-healable gas barrier nanocoating, which is fabricated by alternate deposition of polyethyleneimine (PEI) and polyacrylic acid (PAA) polyelectrolytes, is demonstrated in this study. This multilayer film, with high elastic modulus, high glass transition temperature, and small free volume, has been shown to be a super oxygen gas barrier. An 8-bilayer PEI/PAA multilayer assembly (≈700 nm thick) exhibits an oxygen transmission rate (OTR) undetectable to commercial instrumentation (<0.005 cc (m -2 d -1 atm -1 )). The barrier property of PEI/PAA nanocoating is lost after a moderate amount of stretching due to its rigidity, which is then completely restored after high humidity exposure, therefore achieving a healing efficiency of 100%. The OTR of the multilayer nanocoating remains below the detection limit after ten stretching-healing cycles, which proves this healing process to be highly robust. The high oxygen barrier and self-healing behavior of this polymer multilayer nanocoating makes it ideal for packaging (food, electronics, and pharmaceutical) and gas separation applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Disruption of the epithelial barrier during intestinal inflammation: Quest for new molecules and mechanisms.

PubMed

Lechuga, Susana; Ivanov, Andrei I

2017-07-01

The intestinal epithelium forms a key protective barrier that separates internal organs from the harmful environment of the gut lumen. Increased permeability of the gut barrier is a common manifestation of different inflammatory disorders contributing to the severity of disease. Barrier permeability is controlled by epithelial adherens junctions and tight junctions. Junctional assembly and integrity depend on fundamental homeostatic processes such as cell differentiation, rearrangements of the cytoskeleton, and vesicle trafficking. Alterations of intestinal epithelial homeostasis during mucosal inflammation may impair structure and remodeling of apical junctions, resulting in increased permeability of the gut barrier. In this review, we summarize recent advances in our understanding of how altered epithelial homeostasis affects the structure and function of adherens junctions and tight junctions in the inflamed gut. Specifically, we focus on the transcription reprogramming of the cell, alterations in the actin cytoskeleton, and junctional endocytosis and exocytosis. We pay special attention to knockout mouse model studies and discuss the relevance of these mechanisms to human gastrointestinal disorders. Copyright © 2017 Elsevier B.V. All rights reserved.

Insertion loss of noise barriers on an aboveground, full-scale model longwall coal mining shearer.

PubMed

Sweeney, Daniel D; Slagley, Jeremy M; Smith, David A

2010-05-01

The U.S. mining industry struggles with hazardous noise and dust exposures in underground mining. Specifically, longwall coal mine shearer operators are routinely exposed to noise levels at 151% of the allowable daily dose, and approximately 20% exceed regulatory dust levels. In the current study, a partial barrier was mounted on the full-scale mock shearer at the National Institute for Occupational Safety and Health Pittsburgh Research Laboratory. A simulated, full-scale, coal mine longwall shearer operation was employed to test the feasibility of utilizing a barrier to separate the shearer operator from the direct path of the noise and dust source during mining operations. In this model, noise levels at the operators' positions were reduced by 2.6 to 8.2 A-weighted decibels (dBA) from the application of the test barriers. Estimated insertion loss underground was 1.7 to 7.3 dBA. The barrier should be tested in an underground mining operation to determine if it can reduce shearer operators' noise exposure to below regulatory limits.

The Human “Cochlear Battery” – Claudin-11 Barrier and Ion Transport Proteins in the Lateral Wall of the Cochlea

PubMed Central

Liu, Wei; Schrott-Fischer, Annelies; Glueckert, Rudolf; Benav, Heval; Rask-Andersen, Helge

2017-01-01

Background: The cochlea produces an electric field potential essential for hair cell transduction and hearing. This biological “battery” is situated in the lateral wall of the cochlea and contains molecular machinery that secretes and recycles K+ ions. Its functioning depends on junctional proteins that restrict the para-cellular escape of ions. The tight junction protein Claudin-11 has been found to be one of the major constituents of this barrier that maintains ion gradients (Gow et al., 2004; Kitajiri et al., 2004a). We are the first to elucidate the human Claudin-11 framework and the associated ion transport machinery using super-resolution fluorescence illumination microscopy (SR-SIM). Methods: Archival cochleae obtained during meningioma surgery were used for SR-SIM together with transmission electron microscopy after ethical consent. Results: Claudin-11-expressing cells formed parallel tight junction lamellae that insulated the epithelial syncytium of the stria vascularis and extended to the suprastrial region. Intercellular gap junctions were found between the barrier cells and fibrocytes. Conclusion: Transmission electron microscopy, confocal microscopy and SR-SIM revealed exclusive cell specialization in the various subdomains of the lateral wall of the human cochlea. The Claudin-11-expressing cells exhibited both conductor and isolator characteristics, and these micro-porous separators may selectively mediate the movement of charged units to the intrastrial space in a manner that is analogous to a conventional electrochemical “battery.” The function and relevance of this battery for the development of inner ear disease are discussed. PMID:28848383

Pleistocene and ecological effects on continental-scale genetic differentiation in the bobcat (Lynx rufus).

PubMed

Reding, Dawn M; Bronikowski, Anne M; Johnson, Warren E; Clark, William R

2012-06-01

The potential for widespread, mobile species to exhibit genetic structure without clear geographic barriers is a topic of growing interest. Yet the patterns and mechanisms of structure--particularly over broad spatial scales--remain largely unexplored for these species. Bobcats occur across North America and possess many characteristics expected to promote gene flow. To test whether historical, topographic or ecological factors have influenced genetic differentiation in this species, we analysed 1 kb mtDNA sequence and 15 microsatellite loci from over 1700 samples collected across its range. The primary signature in both marker types involved a longitudinal cline with a sharp transition, or suture zone, occurring along the Great Plains. Thus, the data distinguished bobcats in the eastern USA from those in the western half, with no obvious physical barrier to gene flow. Demographic analyses supported a scenario of expansion from separate Pleistocene refugia, with the Great Plains representing a zone of secondary contact. Substructure within the two main lineages likely reflected founder effects, ecological factors, anthropogenic/topographic effects or a combination of these forces. Two prominent topographic features, the Mississippi River and Rocky Mountains, were not supported as significant genetic barriers. Ecological regions and environmental correlates explained a small but significant proportion of genetic variation. Overall, results implicate historical processes as the primary cause of broad-scale genetic differentiation, but contemporary forces seem to also play a role in promoting and maintaining structure. Despite the bobcat's mobility and broad niche, large-scale landscape changes have contributed to significant and complex patterns of genetic structure. © 2012 Blackwell Publishing Ltd.

Conformational transition free energy profiles of an adsorbed, lattice model protein by multicanonical Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Castells, Victoria; Van Tassel, Paul R.

2005-02-01

Proteins often undergo changes in internal conformation upon interacting with a surface. We investigate the thermodynamics of surface induced conformational change in a lattice model protein using a multicanonical Monte Carlo method. The protein is a linear heteropolymer of 27 segments (of types A and B) confined to a cubic lattice. The segmental order and nearest neighbor contact energies are chosen to yield, in the absence of an adsorbing surface, a unique 3×3×3 folded structure. The surface is a plane of sites interacting either equally with A and B segments (equal affinity surface) or more strongly with the A segments (A affinity surface). We use a multicanonical Monte Carlo algorithm, with configuration bias and jump walking moves, featuring an iteratively updated sampling function that converges to the reciprocal of the density of states 1/Ω(E), E being the potential energy. We find inflection points in the configurational entropy, S(E)=klnΩ(E), for all but a strongly adsorbing equal affinity surface, indicating the presence of free energy barriers to transition. When protein-surface interactions are weak, the free energy profiles F(E)=E-TS(E) qualitatively resemble those of a protein in the absence of a surface: a free energy barrier separates a folded, lowest energy state from globular, higher energy states. The surface acts in this case to stabilize the globular states relative to the folded state. When the protein surface interactions are stronger, the situation differs markedly: the folded state no longer occurs at the lowest energy and free energy barriers may be absent altogether.

Soliton tunneling in the nonlinear Schrödinger equation with variable coefficients and an external harmonic potential.

PubMed

Zhong, Wei-Ping; Belić, Milivoj R

2010-05-01

We report on the nonlinear tunneling effects of spatial solitons of the generalized nonlinear Schrödinger equation with distributed coefficients in an external harmonic potential. By using the homogeneous balance principle and the F-expansion technique we find the spatial bright and dark soliton solutions. We then display tunneling effects of such solutions occurring under special conditions; specifically when the spatial solitons pass unchanged through the potential barriers and wells affected by special choices of the diffraction and/or the nonlinearity coefficients. Our results show that the solitons display tunneling effects not only when passing through the nonlinear potential barriers or wells but also when passing through the diffractive barriers or wells. During tunneling the solitons may also undergo a controllable compression.

Electronic health records: what are the most important barriers?

PubMed

Ayatollahi, Haleh; Mirani, Nader; Haghani, Hamid

2014-01-01

The process of design and adoption of electronic health records may face a number of barriers. This study aimed to compare the importance of the main barriers from the experts' point of views in Iran. This survey study was completed in 2011. The potential participants (62 experts) included faculty members who worked in departments of health information technology and individuals who worked in the Ministry of Health in Iran and were in charge of the development and adoption of electronic health records. No sampling method was used in this study. Data were collected using a Likert-scale questionnaire ranging from 1 to 5. The validity of the questionnaire was established using content and face validity methods, and the reliability was calculated using Cronbach's alpha coefficient. The response rate was 51.6 percent. The participants' perspectives showed that the most important barriers in the process of design and adoption of electronic health records were technical barriers (mean = 3.84). Financial and ethical-legal barriers, with the mean value of 3.80 were other important barriers, and individual and organizational barriers, with the mean values of 3.59 and 3.50 were found to be less important than other barriers from the experts' perspectives. Strategic planning for the creation and adoption of electronic health records in the country, creating a team of experts to assess the potential barriers and develop strategies to eliminate them, and allocating financial resources can help to overcome most important barriers to the adoption of electronic health records.

Along the speciation continuum: Quantifying intrinsic and extrinsic isolating barriers across five million years of evolutionary divergence in California jewelflowers.

PubMed

Christie, Kyle; Strauss, Sharon Y

2018-05-01

Understanding the relative roles of intrinsic and extrinsic reproductive barriers, and their interplay within the geographic context of diverging taxa, remains an outstanding challenge in the study of speciation. We conducted a comparative analysis of reproductive isolation in California Jewelflowers (Streptanthus, s.l., Brassicaceae) by quantifying potential barriers to gene flow at multiple life history stages in 39 species pairs spanning five million years of evolutionary divergence. We quantified nine potential pre- and postzygotic barriers and explored patterns of reproductive isolation in relation to genetic distance. Intrinsic postzygotic isolation was initially weak, increased at intermediate genetic distances, and reached a threshold characterized by complete genetic incompatibility. Climatic niche differences were strong at shallow genetic distances, and species pairs with overlapping ranges showed slight but appreciable phenological isolation, highlighting the potential for ecological barriers to contribute to speciation. Geographic analyses suggest that speciation is not regionally allopatric in the California Jewelflowers, as recently diverged taxa occur in relatively close proximity and display substantial range overlap. Young pairs are characterized by incomplete intrinsic postzygotic isolation, suggesting that extrinsic barriers or fine-scale spatial segregation are more important early in the divergence process than genetic incompatibilities. © 2018 The Author(s). Evolution © 2018 The Society for the Study of Evolution.

Tunneling effect on double potential barriers GaAs and PbS

NASA Astrophysics Data System (ADS)

Prastowo, S. H. B.; Supriadi, B.; Ridlo, Z. R.; Prihandono, T.

2018-04-01

A simple model of transport phenomenon tunnelling effect through double barrier structure was developed. In this research we concentrate on the variation of electron energy which entering double potential barriers to transmission coefficient. The barriers using semiconductor materials GaAs (Galium Arsenide) with band-gap energy 1.424 eV, distance of lattice 0.565 nm, and PbS (Lead Sulphide) with band gap energy 0.41 eV distance of lattice is 18 nm. The Analysisof tunnelling effect on double potentials GaAs and PbS using Schrodinger’s equation, continuity, and matrix propagation to get transmission coefficient. The maximum energy of electron that we use is 1.0 eV, and observable from 0.0025 eV- 1.0 eV. The shows the highest transmission coefficient is0.9982 from electron energy 0.5123eV means electron can pass the barriers with probability 99.82%. Semiconductor from materials GaAs and PbS is one of selected material to design semiconductor device because of transmission coefficient directly proportional to bias the voltage of semiconductor device. Application of the theoretical analysis of resonant tunnelling effect on double barriers was used to design and develop new structure and combination of materials for semiconductor device (diode, transistor, and integrated circuit).

The biological significance of brain barrier mechanisms: help or hindrance in drug delivery to the central nervous system?

PubMed Central

Saunders, Norman R.; Habgood, Mark D.; Møllgård, Kjeld; Dziegielewska, Katarzyna M.

2016-01-01

Barrier mechanisms in the brain are important for its normal functioning and development. Stability of the brain’s internal environment, particularly with respect to its ionic composition, is a prerequisite for the fundamental basis of its function, namely transmission of nerve impulses. In addition, the appropriate and controlled supply of a wide range of nutrients such as glucose, amino acids, monocarboxylates, and vitamins is also essential for normal development and function. These are all cellular functions across the interfaces that separate the brain from the rest of the internal environment of the body. An essential morphological component of all but one of the barriers is the presence of specialized intercellular tight junctions between the cells comprising the interface: endothelial cells in the blood-brain barrier itself, cells of the arachnoid membrane, choroid plexus epithelial cells, and tanycytes (specialized glial cells) in the circumventricular organs. In the ependyma lining the cerebral ventricles in the adult brain, the cells are joined by gap junctions, which are not restrictive for intercellular movement of molecules. But in the developing brain, the forerunners of these cells form the neuroepithelium, which restricts exchange of all but the smallest molecules between cerebrospinal fluid and brain interstitial fluid because of the presence of strap junctions between the cells. The intercellular junctions in all these interfaces are the physical basis for their barrier properties. In the blood-brain barrier proper, this is combined with a paucity of vesicular transport that is a characteristic of other vascular beds. Without such a diffusional restrain, the cellular transport mechanisms in the barrier interfaces would be ineffective. Superimposed on these physical structures are physiological mechanisms as the cells of the interfaces contain various metabolic transporters and efflux pumps, often ATP-binding cassette (ABC) transporters, that provide an important component of the barrier functions by either preventing entry of or expelling numerous molecules including toxins, drugs, and other xenobiotics. In this review, we summarize these influx and efflux mechanisms in normal developing and adult brain, as well as indicating their likely involvement in a wide range of neuropathologies. There have been extensive attempts to overcome the barrier mechanisms that prevent the entry of many drugs of therapeutic potential into the brain. We outline those that have been tried and discuss why they may so far have been largely unsuccessful. Currently, a promising approach appears to be focal, reversible disruption of the blood-brain barrier using focused ultrasound, but more work is required to evaluate the method before it can be tried in patients. Overall, our view is that much more fundamental knowledge of barrier mechanisms and development of new experimental methods will be required before drug targeting to the brain is likely to be a successful endeavor. In addition, such studies, if applied to brain pathologies such as stroke, trauma, or multiple sclerosis, will aid in defining the contribution of brain barrier pathology to these conditions, either causative or secondary. PMID:26998242

Genetic structure in the European endemic seabird, Phalacrocorax aristotelis, shaped by a complex interaction of historical and contemporary, physical and nonphysical drivers.

PubMed

Thanou, Evanthia; Sponza, Stefano; Nelson, Emily J; Perry, Annika; Wanless, Sarah; Daunt, Francis; Cavers, Stephen

2017-05-01

Geographically separated populations tend to be less connected by gene flow, as a result of physical or nonphysical barriers preventing dispersal, and this can lead to genetic structure. In this context, highly mobile organisms such as seabirds are interesting because the small effect of physical barriers means nonphysical ones may be relatively more important. Here, we use microsatellite and mitochondrial data to explore the genetic structure and phylogeography of Atlantic and Mediterranean populations of a European endemic seabird, the European shag, Phalacrocorax aristotelis, and identify the primary drivers of their diversification. Analyses of mitochondrial markers revealed three phylogenetic lineages grouping the North Atlantic, Spanish/Corsican and eastern Mediterranean populations, apparently arising from fragmentation during the Pleistocene followed by range expansion. These traces of historical fragmentation were also evident in the genetic structure estimated by microsatellite markers, despite significant contemporary gene flow among adjacent populations. Stronger genetic structure, probably promoted by landscape, philopatry and local adaptation, was found among distant populations and those separated by physical and ecological barriers. This study highlights the enduring effect of Pleistocene climatic changes on shag populations, especially within the Mediterranean Basin, and suggests a role for cryptic northern refugia, as well as known southern refugia, on the genetic structure of European seabirds. Finally, it outlines how contemporary ecological barriers and behavioural traits may maintain population divergence, despite long-distance dispersal triggered by extreme environmental conditions (e.g. population crashes). © 2017 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd.

Very highly excited vibrational states of LiCN using a discrete variable representation

NASA Astrophysics Data System (ADS)

Henderson, James R.; Tennyson, Jonathan

Calculations are presented for the lowest 900 vibrational (J = 0) states of the LiCN floppy system for a two dimensional potential energy surface (rCN frozen). Most of these states lie well above the barrier separating the two linear isomers of the molecule and the point where the classical dynamics of the system becomes chaotic. Analysis of the wavefunctions of individual states in the high energy region shows that while most have an irregular nodal structure, a significant number of states appear regular - corresponding to solutions of standard, 'mode localized' hamiltonians. Motions corresponding in zero-order to Li-CN and Li-NC normal modes as well as free rotor states are identified. The distribution of level spacings is also studied and yields results in good agreement with those obtained by analysing nodal structures.

Experiments on water detritiation and cryogenic distillation at TLK; Impact on ITER fuel cycle subsystems interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cristescu, I.; Cristescu, I. R.; Doerr, L.

2008-07-15

The ITER Isotope Separation System (ISS) and Water Detritiation System (WDS) should be integrated in order to reduce potential chronic tritium emissions from the ISS. This is achieved by routing the top (protium) product from the ISS to a feed point near the bottom end of the WDS Liquid Phase Catalytic Exchange (LPCE) column. This provides an additional barrier against ISS emissions and should mitigate the memory effects due to process parameter fluctuations in the ISS. To support the research activities needed to characterize the performances of various components for WDS and ISS processes under various working conditions and configurationsmore » as needed for ITER design, an experimental facility called TRENTA representative of the ITER WDS and ISS protium separation column, has been commissioned and is in operation at TLK The experimental program on TRENTA facility is conducted to provide the necessary design data related to the relevant ITER operating modes. The operation availability and performances of ISS-WDS have impact on ITER fuel cycle subsystems with consequences on the design integration. The preliminary experimental data on TRENTA facility are presented. (authors)« less

The influence of distance on movement of tabanids (Diptera: Tabanidae) between horses.

PubMed

Barros, A T M; Foil, L D

2007-03-31

Two studies evaluated the potential use of spatial barriers to reduce the mechanical transmission of disease agents by tabanids in the Pantanal region of Brazil. Tabanids at stations separated by four different distances (5, 10, 25, and 50m) were marked. In the first study, tabanids were marked and allowed to feed until engorgement or natural interruption occurred and captured if they transferred to the other horse. A total of 2847 tabanids belonging to nine different species were marked. The percentage of tabanids that moved between horses was 10.5 at 5m, 6.8 at 10m, and 4.6 at 25m. In the second study, flies were marked, feeding was then interrupted, and the flies were released approximately 50cm from the host. A total of 1274 tabanids belonging to five different species were marked. The percentage of flies that moved between horses was 9.7 at 5m, 9.7 at 10m, and 4.6 at 25m. No tabanids transferred between animals separated by 50m in either experiment. The results of this study strongly support the recommendation that segregation of animals effectively prevents the mechanical transmission of pathogens by tabanids.

Long-Distance Connection

ERIC Educational Resources Information Center

Clift, Kate

2010-01-01

Transient populations, cultural diversity, language barriers, competing loyalties, and geographic separation are just some of the challenges international schools face in communicating and connecting with their alumni. And these issues are not going to get any easier as the sector grows. Communicating effectively with large, diverse groups of…

The Relevance of Canadian Business History: Some Nineteenth-Century Examples.

ERIC Educational Resources Information Center

McCalla, Douglas

1982-01-01

Nineteenth century Canadian business history reveals intricate connections and barriers among government and business institutions. The nineteenth century spheres of government, politics, and business were not separate; it was natural that businesspersons and politicians should have many connections. (Author/KC)

Guidance for effective use of pylons for lane separation on preferential lanes and freeway ramps.

DOT National Transportation Integrated Search

2013-05-01

Flexible pylons are gaining popularity as traffic channelizing devices in a variety of applications. The : flexible pylons are less rigid (as compared to concrete barriers) enabling easier access for emergency : vehicles and provide more positive con...

Meteorite Dichotomy Implies that Jupiter Formed Early

NASA Astrophysics Data System (ADS)

Kruijer, T. S.; Burkhardt, C.; Budde, G.; Kleine, T.

2018-05-01

Meteorites derive from two distinct nebular reservoirs that co-existed and remained spatially separated between 1 and 3–4 Ma after CAIs. This can most easily be explained if Jupiter acted as a barrier and formed early, within less than 1 Ma.

MOSFET Replacement Devices for Energy-Efficient Digital Integrated Circuits

DTIC Science & Technology

2009-12-17

MOSFET is limited by the thermal voltage kBT/q; it is greater than or equal to 60mV/dec at room temperature. Fig. 1.4 The potential barrier for...60mV/dec can be explained by the electron energy band profile of a MOSFET, which is shown in Fig. 1.4. As Vgs increases, the channel potential is...channel potential (φs) reduces the potential barrier for electron injection, and hence the electron energy (E) increases. According to the Boltzmann

Depression in African American Men: A Review of What We Know and Where We Need to Go From Here

PubMed Central

Ward, Earlise; Mengesha, Maigenete

2014-01-01

Depression is one of the most common mental disorders in the United States and affects an estimated 17 million people each year. Projections about depression have generated concern on both the domestic and global levels because of its impact on health outcomes and quality of life. We examined and summarized published research focusing on depression among African American men with the goal of identifying prevalence of depression, risk factors, treatment-seeking behaviors, and treatment-seeking barriers. In the use of a systematic review, inclusion criteria were studies focused on depression among African American or Black men, separated analysis by race and gender, and conducted in the United States. Each study was critically reviewed to identify depression prevalence, risk factors, treatment-seeking behaviors, and barriers. Only 19 empirical studies focusing on depression among African American men were identified in a 25-year time span. Findings suggest the prevalence of depression among African American men ranges from 5% to 10%, they face a number of risk factors, yet evidence low use of mental health services. Consequently, depression among African American men needs to be at the forefront of our research, practice, and outreach agendas. A focus on this group has the potential to reduce mental health disparities experienced by African American men. PMID:23889029

Lateral Cricoarytenoid Release: Development of a Novel Surgical Treatment Option for Adductor Spasmodic Dysphonia in a Canine Laryngeal Model.

PubMed

Park, Andrea M; Paniello, Randal C

2016-09-01

To investigate the efficacy of a novel adductor muscle-releasing technique designed to decrease the force of vocal fold adduction, as a potential surgical therapy for patients with adductor spasmodic dysphonia (ADSD). Experimental animal study. A canine laryngeal model was used to assess the acute and sustained efficacy of a lateral cricoarytenoid (LCA) muscle release. A total of 34 canine hemilaryngeal preparations were divided among 7 experimental groups. The LCA muscle was separated from its cricoid cartilage origin via an open, anterior, submucosal approach. The laryngeal adductory pressures (LAP) were assessed pre- and post-muscle release via direct recurrent laryngeal nerve stimulation. Measurements were repeated at 1.5, 3, or 6 months postoperatively. Another study evaluated release of the thyroarytenoid (TA) muscle from its thyroid cartilage origin. Releasing the LCA muscle demonstrated a significant decrease in LAP acutely and was maintained at all 3 time points with the aid of a barrier (P < .05). Without the barrier, the LCA muscle reattached to the cricoid. Acute release of the TA muscle did not significantly decrease the LAP. The proposed LCA release procedure may provide patients with a permanent treatment option for ADSD. However, longer-term studies and human trials are needed. © The Author(s) 2016.

A proposed clinical decision support architecture capable of supporting whole genome sequence information.

PubMed

Welch, Brandon M; Loya, Salvador Rodriguez; Eilbeck, Karen; Kawamoto, Kensaku

2014-04-04

Whole genome sequence (WGS) information may soon be widely available to help clinicians personalize the care and treatment of patients. However, considerable barriers exist, which may hinder the effective utilization of WGS information in a routine clinical care setting. Clinical decision support (CDS) offers a potential solution to overcome such barriers and to facilitate the effective use of WGS information in the clinic. However, genomic information is complex and will require significant considerations when developing CDS capabilities. As such, this manuscript lays out a conceptual framework for a CDS architecture designed to deliver WGS-guided CDS within the clinical workflow. To handle the complexity and breadth of WGS information, the proposed CDS framework leverages service-oriented capabilities and orchestrates the interaction of several independently-managed components. These independently-managed components include the genome variant knowledge base, the genome database, the CDS knowledge base, a CDS controller and the electronic health record (EHR). A key design feature is that genome data can be stored separately from the EHR. This paper describes in detail: (1) each component of the architecture; (2) the interaction of the components; and (3) how the architecture attempts to overcome the challenges associated with WGS information. We believe that service-oriented CDS capabilities will be essential to using WGS information for personalized medicine.

A Proposed Clinical Decision Support Architecture Capable of Supporting Whole Genome Sequence Information

PubMed Central

Welch, Brandon M.; Rodriguez Loya, Salvador; Eilbeck, Karen; Kawamoto, Kensaku

2014-01-01

Whole genome sequence (WGS) information may soon be widely available to help clinicians personalize the care and treatment of patients. However, considerable barriers exist, which may hinder the effective utilization of WGS information in a routine clinical care setting. Clinical decision support (CDS) offers a potential solution to overcome such barriers and to facilitate the effective use of WGS information in the clinic. However, genomic information is complex and will require significant considerations when developing CDS capabilities. As such, this manuscript lays out a conceptual framework for a CDS architecture designed to deliver WGS-guided CDS within the clinical workflow. To handle the complexity and breadth of WGS information, the proposed CDS framework leverages service-oriented capabilities and orchestrates the interaction of several independently-managed components. These independently-managed components include the genome variant knowledge base, the genome database, the CDS knowledge base, a CDS controller and the electronic health record (EHR). A key design feature is that genome data can be stored separately from the EHR. This paper describes in detail: (1) each component of the architecture; (2) the interaction of the components; and (3) how the architecture attempts to overcome the challenges associated with WGS information. We believe that service-oriented CDS capabilities will be essential to using WGS information for personalized medicine. PMID:25411644

Endothelial NOS activation induces the blood-brain barrier disruption via ER stress following status epilepticus.

PubMed

Ko, Ah-Reum; Kim, Ji Yang; Hyun, Hye-Won; Kim, Ji-Eun

2015-10-05

The blood-brain barrier (BBB) maintains the unique brain microenvironment, which is separated from the systemic circulating system. Since the endoplasmic reticulum (ER) is an important cell organelle that is responsible for protein synthesis, the correct folding and sorting of proteins contributing to cell survivals, ER stress is a potential cause of cell damage in various diseases. Therefore, it would be worthy to explore the the relationship between the ER stress and BBB disruption during vasogenic edema formation induced by epileptogenic insults. In the present study, we investigated the roles of ER stress in vasogenic edema and its related events in rat epilepsy models provoked by pilocarpine-induced status epilepticus (SE). SE-induced eNOS activation induces BBB breakdown via up-regulation of GRP78 expression and dysfunction of SMI-71 (an endothelial BBB marker) in the piriform cortex (PC). In addition, caveolin-1 peptide (an eNOS inhibitor) effectively attenuated GRP78 expression and down-regulation of SMI-71. Taken together, our findings suggest that eNOS-mediated ER stress may participate in SE-induced vasogenic edema formation. Therefore, the modulation of ER stress may be a considerable strategy for therapy in impairments of endothelial cell function. Copyright © 2015 Elsevier B.V. All rights reserved.

'Acupuncture for antenatal depression: It's worth giving it a go' - A qualitative study.

PubMed

Ormsby, Simone M; Dahlen, Hannah G; Ee, Carolyn C; Keedle, Hazel; Smith, Caroline A

2018-06-01

Treatment strategies for the management of antenatal depression are limited by varied and often modest response rates, unpleasant medication side effects and uncertainty regarding foetal safety. Consequently, many pregnant women experiencing depression seek alternative non-pharmaceutical options. Acupuncture may provide a safe and potentially effective additional treatment, however further investigation is required. In this qualitative study, we explored the views of health professionals regarding the possible incorporation of acupuncture into mainstream care. Two separate focus groups were run with 16 midwives. In-depth interviews were conducted with two maternity service managers and nine doctors (3 obstetricians, 2 psychiatrists and 4 general practitioners). Data was analysed using thematic analysis. Participants were generally positive about acupuncture and open to its possible inclusion in conventional care, on the proviso that it was safe and could be shown to be effective. The overarching theme to emerge was 'acupuncture for antenatal depression: it's worth giving it a go', which participants concluded after considering 'the dilemma of mental health' treatment during the antenatal period and the additional limitations this presented, along with the belief that 'if it doesn't do any harm, I'm not against it'. Practical considerations regarding potential 'barriers' and facilitators' to implementation were additionally explored in 'making it mainstream', whereby the different 'philosophical beliefs' held by participants were seen to influence perspectives. Participants expressed an overall positive attitude towards the possible inclusion of acupuncture into mainstream care for antenatal depression, suggesting various hospital barriers could be overcome with further safety and effectiveness evidence. Copyright © 2017 Australian College of Midwives. Published by Elsevier Ltd. All rights reserved.

Herbicide effects on the growth and photosynthetic efficiency of Cassiopea maremetens.

PubMed

Rowen, David J; Templeman, Michelle A; Kingsford, Michael J

2017-09-01

Herbicides from agricultural run-off have been measured in coastal systems of the Great Barrier Reef over many years. Non-target herbicide exposure, especially photosystem II herbicides has the potential to affect seagrasses and other marine species. The symbiotic benthic jellyfish Cassiopea maremetens is present in tropical/sub-tropical estuarine and marine environments. Jellyfish (n = 8 per treatment) were exposed to four separate concentrations of agricultural formulations of diuron or hexazinone to determine their sensitivity and potential for recovery to pulsed herbicide exposure. Jellyfish growth, symbiont photosynthetic activity and zooxanthellae density were analysed for herbicide-induced changes for 7 days followed by a 7 day recovery period. Both the jellyfish and endosymbiont were more sensitive to diuron than hexazinone. The 7-day EC 50 for jellyfish growth was 0.35 μg L -1 for Diuron and 17.5 μg L -1 for Hexazinone respectively. Diuron exposure caused a significant decrease (p < 0.05) in jellyfish growth at 0.1 μg L -1 , a level that is below the regional Great Barrier Reef guideline value. Jellyfish recovery was rapid with growth rates similar to control animals following removal from herbicide exposure. Both diuron and hexazinone caused significant decreases in photosynthetic efficiency (effective quantum yield) in all treatment concentrations (0.1 μg L -1 and above) and this effect continued in the post-exposure period. As this species is frequently found in near-shore environments, they may be particularly vulnerable to herbicide run-off. Copyright © 2017 Elsevier Ltd. All rights reserved.

Computing the Viscosity of Supercooled Liquids: Markov Network Model

PubMed Central

Li, Ju; Kushima, Akihiro; Eapen, Jacob; Lin, Xi; Qian, Xiaofeng; Mauro, John C.; Diep, Phong; Yip, Sidney

2011-01-01

The microscopic origin of glass transition, when liquid viscosity changes continuously by more than ten orders of magnitude, is challenging to explain from first principles. Here we describe the detailed derivation and implementation of a Markovian Network model to calculate the shear viscosity of deeply supercooled liquids based on numerical sampling of an atomistic energy landscape, which sheds some light on this transition. Shear stress relaxation is calculated from a master-equation description in which the system follows a transition-state pathway trajectory of hopping among local energy minima separated by activation barriers, which is in turn sampled by a metadynamics-based algorithm. Quantitative connection is established between the temperature variation of the calculated viscosity and the underlying potential energy and inherent stress landscape, showing a different landscape topography or “terrain” is needed for low-temperature viscosity (of order 107 Pa·s) from that associated with high-temperature viscosity (10−5 Pa·s). Within this range our results clearly indicate the crossover from an essentially Arrhenius scaling behavior at high temperatures to a low-temperature behavior that is clearly super-Arrhenius (fragile) for a Kob-Andersen model of binary liquid. Experimentally the manifestation of this crossover in atomic dynamics continues to raise questions concerning its fundamental origin. In this context this work explicitly demonstrates that a temperature-dependent “terrain” characterizing different parts of the same potential energy surface is sufficient to explain the signature behavior of vitrification, at the same time the notion of a temperature-dependent effective activation barrier is quantified. PMID:21464988

Charter School Barriers: Do Enrollment Requirements Limit Student Access to Charter Schools?

ERIC Educational Resources Information Center

Weiler, Spencer C.; Vogel, Linda R.

2015-01-01

The potential of the charter school movement to positively influence traditional public education lies in the ability of charter school officials to provide all students access to the curriculum. The aim of this study was to document potential registration and enrollment barriers incorporated into the practices of Colorado charter schools. The…

Internal structure of a barrier beach as revealed by ground penetrating radar (GPR): Chesil beach, UK

NASA Astrophysics Data System (ADS)

Bennett, Matthew R.; Cassidy, Nigel J.; Pile, Jeremy

2009-03-01

Chesil Beach (Dorset) is one of the most famous coastal landforms on the British coast. The gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as The Fleet. The beach links the Isle of Portland in the east to the mainland in the west. Despite its iconic status there is little available information on its internal geometry and evolutionary history. Here we present a three-fold model for the evolution of Chesil Beach based on a series of nine ground penetrating radar (GPR) traverses located at three sites along its length at Abbotsbury, Langton Herring and at Ferry Bridge. The GPR traverses reveal a remarkably consistent picture of the internal structure of this barrier beach. The first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr BP. The second evolutionary phase involves the 'bulking-out' of the beach during continued sea level rise, but in the presence of abundant gravel supplied by down-drift erosion of periglacial slope deposits. This episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole. The final phase in the evolution of Chesil Beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance, but during a still-stand or slight fall in relative sea level. This phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the South Coast of Britain and dated to between 1.2 and 2.4 k yr BP. Subsequently the barrier appears to have become largely inactive, except for the reworking of sediment on the beach face during storm events. The case study not only refines the evolutionary picture of Chesil Beach, but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system. In addition, it also illustrates the potential of GPR in resolving the evolutionary history of gravel-rich coastal landforms such as Chesil Beach.

Simulation study of light transport in laser-processed LYSO:Ce detectors with single-side readout

NASA Astrophysics Data System (ADS)

Bläckberg, L.; El Fakhri, G.; Sabet, H.

2017-11-01

A tightly focused pulsed laser beam can locally modify the crystal structure inside the bulk of a scintillator. The result is incorporation of so-called optical barriers with a refractive index different from that of the crystal bulk, that can be used to redirect the scintillation light and control the light spread in the detector. We here systematically study the scintillation light transport in detectors fabricated using the laser induced optical barrier technique, and objectively compare their potential performance characteristics with those of the two mainstream detector types: monolithic and mechanically pixelated arrays. Among countless optical barrier patterns, we explore barriers arranged in a pixel-like pattern extending all-the-way or half-way through a 20 mm thick LYSO:Ce crystal. We analyze the performance of the detectors coupled to MPPC arrays, in terms of light response functions, flood maps, line profiles, and light collection efficiency. Our results show that laser-processed detectors with both barrier patterns constitute a new detector category with a behavior between that of the two standard detector types. Results show that when the barrier-crystal interface is smooth, no DOI information can be obtained regardless of barrier refractive index (RI). However, with a rough barrier-crystal interface we can extract multiple levels of DOI. Lower barrier RI results in larger light confinement, leading to better transverse resolution. Furthermore we see that the laser-processed crystals have the potential to increase the light collection efficiency, which could lead to improved energy resolution and potentially better timing resolution due to higher signals. For a laser-processed detector with smooth barrier-crystal interfaces the light collection efficiency is simulated to  >42%, and for rough interfaces  >73%. The corresponding numbers for a monolithic crystal is 39% with polished surfaces, and 71% with rough surfaces, and for a mechanically pixelated array 35% with polished pixel surfaces and 59% with rough surfaces.

Simulation study of light transport in laser-processed LYSO:Ce detectors with single-side readout.

PubMed

Bläckberg, L; El Fakhri, G; Sabet, H

2017-10-19

A tightly focused pulsed laser beam can locally modify the crystal structure inside the bulk of a scintillator. The result is incorporation of so-called optical barriers with a refractive index different from that of the crystal bulk, that can be used to redirect the scintillation light and control the light spread in the detector. We here systematically study the scintillation light transport in detectors fabricated using the laser induced optical barrier technique, and objectively compare their potential performance characteristics with those of the two mainstream detector types: monolithic and mechanically pixelated arrays. Among countless optical barrier patterns, we explore barriers arranged in a pixel-like pattern extending all-the-way or half-way through a 20 mm thick LYSO:Ce crystal. We analyze the performance of the detectors coupled to MPPC arrays, in terms of light response functions, flood maps, line profiles, and light collection efficiency. Our results show that laser-processed detectors with both barrier patterns constitute a new detector category with a behavior between that of the two standard detector types. Results show that when the barrier-crystal interface is smooth, no DOI information can be obtained regardless of barrier refractive index (RI). However, with a rough barrier-crystal interface we can extract multiple levels of DOI. Lower barrier RI results in larger light confinement, leading to better transverse resolution. Furthermore we see that the laser-processed crystals have the potential to increase the light collection efficiency, which could lead to improved energy resolution and potentially better timing resolution due to higher signals. For a laser-processed detector with smooth barrier-crystal interfaces the light collection efficiency is simulated to  >42%, and for rough interfaces  >73%. The corresponding numbers for a monolithic crystal is 39% with polished surfaces, and 71% with rough surfaces, and for a mechanically pixelated array 35% with polished pixel surfaces and 59% with rough surfaces.

Reverse transendothelial cell migration in inflammation: to help or to hinder?

PubMed

Burn, Thomas; Alvarez, Jorge Ivan

2017-05-01

The endothelium provides a strong barrier separating circulating blood from tissue. It also provides a significant challenge for immune cells in the bloodstream to access potential sites of infection. To mount an effective immune response, leukocytes traverse the endothelial layer in a process known as transendothelial migration. Decades of work have allowed dissection of the mechanisms through which immune cells gain access into peripheral tissues, and subsequently to inflammatory foci. However, an often under-appreciated or potentially ignored question is whether transmigrated leukocytes can leave these inflammatory sites, and perhaps even return across the endothelium and re-enter circulation. Although evidence has existed to support "reverse" transendothelial migration for a number of years, it is only recently that mechanisms associated with this process have been described. Here we review the evidence that supports both reverse transendothelial migration and reverse interstitial migration within tissues, with particular emphasis on some of the more recent studies that finally hint at potential mechanisms. Additionally, we postulate the biological significance of retrograde migration, and whether it serves as an additional mechanism to limit pathology, or provides a basis for the dissemination of systemic inflammation.

Multistate metadynamics for automatic exploration of conical intersections

NASA Astrophysics Data System (ADS)

Lindner, Joachim O.; Röhr, Merle I. S.; Mitrić, Roland

2018-05-01

We introduce multistate metadynamics for automatic exploration of conical intersection seams between adiabatic Born-Oppenheimer potential energy surfaces in molecular systems. By choosing the energy gap between the electronic states as a collective variable the metadynamics drives the system from an arbitrary ground-state configuration toward the intersection seam. Upon reaching the seam, the multistate electronic Hamiltonian is extended by introducing biasing potentials into the off-diagonal elements, and the molecular dynamics is continued on a modified potential energy surface obtained by diagonalization of the latter. The off-diagonal bias serves to locally open the energy gap and push the system to the next intersection point. In this way, the conical intersection energy landscape can be explored, identifying minimum energy crossing points and the barriers separating them. We illustrate the method on the example of furan, a prototype organic molecule exhibiting rich photophysics. The multistate metadynamics reveals plateaus on the conical intersection energy landscape from which the minimum energy crossing points with characteristic geometries can be extracted. The method can be combined with the broad spectrum of electronic structure methods and represents a generally applicable tool for the exploration of photophysics and photochemistry in complex molecules and materials.

Barriers to cancer screening in Hmong Americans: the influence of health care accessibility, culture, and cancer literacy.

PubMed

Lee, Hee Yun; Vang, Suzanne

2010-06-01

Hmong Americans face high cancer mortality rates even in comparison to their Asian American counterparts, and report low utilization of cancer screenings. To date, no study has been conducted on the cultural barriers this population faces in undergoing cancer screenings. A systematic review of the literature was conducted to examine the existing knowledge regarding the barriers to cancer screening for Hmong Americans. Potential barriers were identified from this examination to include: health access factors (type of health insurance, ethnicity of provider, low English proficiency, and years spent in the U.S.); cultural factors (belief in the spiritual etiology of diseases, patriarchal values, modesty, and mistrust of the western medical system); and cancer literacy factors (cancer and prevention illiteracy). Based on this review, potential cultural and ethnic group-specific prevention strategies and cancer health policies are discussed to address these barriers and enhance screening behavior among the Hmong.

A comparative study of wood highway sound barriers

Treesearch

Stefan Grgurevich; Thomas Boothby; Harvey Manbeck; Courtney Burroughs; Stephen Cegelka; Craig Bernecker; Michael A. Ritter

2002-01-01

Prototype designs for wood highway sound barriers meeting the multiple criteria of structural integrity, acoustic effectiveness, durability, and potential for public acceptance have been developed. Existing installations of wood sound barriers were reviewed and measurements conducted in the field to estimate acoustic insertion losses. A complete matrix of design...

"My Award Is for My Students"

ERIC Educational Resources Information Center

Adults Learning, 2009

2009-01-01

This article features ESOL (English for Speakers of Other Languages) co-ordinator Lynn Evans, recipient of the Learning and Skills Improvement Service STAR Award. Lynn's teaching is all about breaking down barriers, whether that means the personal barriers that prevent learners from achieving their potential or the barriers that exist among…

Barriers to Education for the Marginalized Adult Learner

ERIC Educational Resources Information Center

Flynn, Sarah; Brown, Jason; Johnson, Andrew; Rodger, Susan

2011-01-01

This qualitative study examines barriers to adult education by the marginalized adult learner. We adopted an inclusive approach by interviewing potential adult learners who had not participated in adult education programs due to illiteracy. Five overlapping themes related to barriers emerged and were categorized as: family values and…

Vaccination Perceptions and Barriers of School Employees: A Pilot Study

ERIC Educational Resources Information Center

Luthy, Karlen E.; Houle, Kim; Beckstrand, Renea L.; Macintosh, Janelle; Lakin, Richard G.

2013-01-01

Schools are where vaccine-preventable diseases can spread. Vaccination of school children has been studied; however, data are lacking on the vaccination status, perceptions, and barriers to vaccination for school employees. We surveyed school employees' vaccination perceptions, awareness of current vaccination status, and potential barriers to…

Perfect Spin Filter by Periodic Drive of a Ferromagnetic Quantum Barrier

NASA Astrophysics Data System (ADS)

Thuberg, Daniel; Muñoz, Enrique; Eggert, Sebastian; Reyes, Sebastián A.

2017-12-01

We consider the problem of particle tunneling through a periodically driven ferromagnetic quantum barrier connected to two leads. The barrier is modeled by an impurity site representing a ferromagnetic layer or a quantum dot in a tight-binding Hamiltonian with a local magnetic field and an ac-driven potential, which is solved using the Floquet formalism. The repulsive interactions in the quantum barrier are also taken into account. Our results show that the time-periodic potential causes sharp resonances of perfect transmission and reflection, which can be tuned by the frequency, the driving strength, and the magnetic field. We demonstrate that a device based on this configuration could act as a highly tunable spin valve for spintronic applications.

Creation and validation of the barriers to alcohol reduction (BAR) scale using classical test theory and item response theory.

PubMed

Kunicki, Zachary J; Schick, Melissa R; Spillane, Nichea S; Harlow, Lisa L

2018-06-01

Those who binge drink are at increased risk for alcohol-related consequences when compared to non-binge drinkers. Research shows individuals may face barriers to reducing their drinking behavior, but few measures exist to assess these barriers. This study created and validated the Barriers to Alcohol Reduction (BAR) scale. Participants were college students ( n  = 230) who endorsed at least one instance of past-month binge drinking (4+ drinks for women or 5+ drinks for men). Using classical test theory, exploratory structural equation modeling found a two-factor structure of personal/psychosocial barriers and perceived program barriers. The sub-factors, and full scale had reasonable internal consistency (i.e., coefficient omega = 0.78 (personal/psychosocial), 0.82 (program barriers), and 0.83 (full measure)). The BAR also showed evidence for convergent validity with the Brief Young Adult Alcohol Consequences Questionnaire ( r  = 0.39, p  < .001) and discriminant validity with Barriers to Physical Activity ( r  = -0.02, p  = .81). Item Response Theory (IRT) analysis showed the two factors separately met the unidimensionality assumption, and provided further evidence for severity of the items on the two factors. Results suggest that the BAR measure appears reliable and valid for use in an undergraduate student population of binge drinkers. Future studies may want to re-examine this measure in a more diverse sample.

Metal diffusion barriers for GaAs solar cells.

PubMed

van Leest, R H; Mulder, P; Bauhuis, G J; Cheun, H; Lee, H; Yoon, W; van der Heijden, R; Bongers, E; Vlieg, E; Schermer, J J

2017-03-15

In this study accelerated ageing testing (AAT), J-V characterization and TEM imaging in combination with phase diagram data from literature are used to assess the potential of Ti, Ni, Pd and Pt as diffusion barriers for Au/Cu-based metallization of III-V solar cells. Ni barriers show the largest potential as at an AAT temperature of 250 °C both cells with 10 and 100 nm thick Ni barriers show significantly better performance compared to Au/Cu cells, with the cells with 10 nm Ni barriers even showing virtually no degradation after 7.5 days at 250 °C (equivalent to 10 years at 100 °C at an E a of 0.70 eV). Detailed investigation shows that Ni does not act as a barrier in the classical sense, i.e. preventing diffusion of Cu and Au across the barrier. Instead Ni modifies or slows down the interactions taking place during device degradation and thus effectively acts as an 'interaction' barrier. Different interactions occur at temperatures below and above 250 °C and for thin (10 nm) and thick (100 nm) barriers. The results of this study indicate that 10-100 nm thick Ni intermediate layers in the Cu/Au based metallization of III-V solar cells may be beneficial to improve the device stability upon exposure to elevated temperatures.

Superluminal tunneling of a relativistic half-integer spin particle through a potential barrier

NASA Astrophysics Data System (ADS)

Nanni, Luca

2017-11-01

This paper investigates the problem of a relativistic Dirac half-integer spin free particle tunneling through a rectangular quantum-mechanical barrier. If the energy difference between the barrier and the particle is positive, and the barrier width is large enough, there is proof that the tunneling may be superluminal. For first spinor components of particle and antiparticle states, the tunneling is always superluminal regardless the barrier width. Conversely, the second spinor components of particle and antiparticle states may be either subluminal or superluminal depending on the barrier width. These results derive from studying the tunneling time in terms of phase time. For the first spinor components of particle and antiparticle states, it is always negative while for the second spinor components of particle and antiparticle states, it is always positive, whatever the height and width of the barrier. In total, the tunneling time always remains positive for particle states while it becomes negative for antiparticle ones. Furthermore, the phase time tends to zero, increasing the potential barrier both for particle and antiparticle states. This agrees with the interpretation of quantum tunneling that the Heisenberg uncertainty principle provides. This study's results are innovative with respect to those available in the literature. Moreover, they show that the superluminal behaviour of particles occurs in those processes with high-energy confinement.

Use of electric and bubble barriers to limit the movement of Eurasian ruffe (Gymnocephalus cernuus)

USGS Publications Warehouse

Dawson, Heather A.; Reinhardt, Ulrich G.; Savino, Jacqueline F.

2006-01-01

Eurasian ruffe (Gymnocephalus cernuus) is an aquatic invasive species accidentally introduced via ballast water to the Great Lakes in the mid-1980s. Fish barrier technology is being studied to stop the spread of invasive fish species such as ruffe. Electrical barriers have been constructed, most notably in the Chicago Sanitary and Ship Canal, to prevent non-indigenous species such as ruffe from spreading into areas where they are currently absent. Information on the response of an invasive fish to barriers can help managers determine strategies to prevent the spread of these species via artificial waterways. In this laboratory study electrical barriers were set up to determine effectiveness of four electrical settings for repelling Eurasian ruffe measuring 10 cm or more in length. In separate tests, airbubble curtains with two bubble sizes and densities were created to test this type of barrier in blocking movement of ruffe less than 10 cm in length. The most effective electrical settings found (5 ms, 6 Hz) repelled only about half of the attempted passes. When ruffe were offered food or shelter on the opposite side of the electrical barrier, neither food-starved nor shelter-deprived ruffe made significantly more attempts to cross the barrier. Ruffe were significantly repelled by all air-bubble curtains, but a large proportion of passes (4.5 passes per fish on average in the treatments) were still observed. Electrical barrier settings and air-bubble curtains used in this study were found ineffective at completely blocking the movement, but somewhat effective at inhibiting the passage of ruffe.

Horizontal hydraulic conductivity estimates for intact coal barriers between closed underground mines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mccoy, K.J.; Donovan, J.J.; Leavitt, B.R.

2006-08-15

Unmined blocks of coal, called barriers, separate and restrict horizontal leakage between adjacent bituminous coal mines. Understanding the leakage rate across such barriers is important in planning mine closure and strongly affects recharge calculations for postmining flooding. This study presents upper-limit estimates for hydraulic conductivity (K) of intact barriers in two closed mines at moderate depth (75-300 m) in the Pittsburgh coal basin. The estimates are based on pumping rates from these mines for the years ranging from 1992 to 2000. The two mines do not approach the outcrop and are sufficiently deep that vertical infiltration is thought to bemore » negligible. Similarly, there are no saturated zones on the pumped mines' side of shared barriers with other mines, and therefore pumping is the only outflow. Virtually all of the pumping is attributed to leakage across or over the top of barriers shared with upgradient flooded mines. The length of shared barriers totals 24 km for the two mines, and the barriers range in thickness from 15 to 50 m. K values calculated independently for each of the 9 years of the pumping record ranged from 0.037 m/d to 0.18 m/d using an isotropic model of barrier flow. Using an anisotropic model for differential K in the face cleat (K{sub f}) and butt cleat (K{sub b}) directions, results range from 0.074 to 0.34 m/d for K{sub f} and from 0.022 to 0.099 m/d for K{sub b}.« less

Comparison of the effects of artificial and natural barriers on large African carnivores: implications for interspecific relationships and connectivity.

PubMed

Cozzi, Gabriele; Broekhuis, Femke; McNutt, J Weldon; Schmid, Bernhard

2013-05-01

1. Physical barriers contribute to habitat fragmentation, influence species distribution and ranging behaviour, and impact long-term population viability. Barrier permeability varies among species and can potentially impact the competitive balance within animal communities by differentially affecting co-occurring species. The influence of barriers on the spatial distribution of species within whole communities has nonetheless received little attention. 2. During a 4-year period, we studied the influence of a fence and rivers, two landscape features that potentially act as barriers on space use and ranging behaviour of lions Panthera leo, spotted hyenas Crocuta crocuta, African wild dogs Lycaon pictus and cheetahs Acinonyx jubatus in Northern Botswana. We compared the tendencies of these species to cross the barriers using data generated from GPS-radio collars fitted to a total of 35 individuals. Barrier permeability was inferred by calculating the number of times animals crossed a barrier vs. the number of times they did not cross. Finally, based on our results, we produced a map of connectivity for the broader landscape system. 3. Permeability varied significantly between fence and rivers and among species. The fence represented an obstacle for lions (permeability = 7.2%), while it was considerably more permeable for hyenas (35.6%) and wild dogs and cheetahs (≥ 50%). In contrast, the rivers and associated floodplains were relatively permeable to lions (14.4%) while they represented a nearly impassable obstacle for the other species (<2%). 4. The aversion of lions to cross the fence resulted in a relatively lion-free habitat patch on one side of the fence, which might provide a potential refuge for other species. For instance, the competitively inferior wild dogs used this refuge significantly more intensively than the side of the fence with a high presence of lions. 5. We showed that the influence of a barrier on the distribution of animals could potentially result in a broad-scale modification of community structure and ecology within a guild of co-occurring species. As habitat fragmentation increases, understanding the impact of barriers on species distributions is thus essential for the implementation of landscape-scale management strategies, the development and maintenance of corridors and the enhancement of connectivity. © 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.

Why the Equal Rights Amendment?

ERIC Educational Resources Information Center

Denmark, Florence L.

The Equal Rights Amendment proposes to ensure constitutional protection against all legislative sex discrimination. "Separate but Equal" standards, be they legal, social or psychological, are inevitably incompatable with equal protection under the law and act as a barrier to each individual's freedom for self determination. Equal rights,…

PRB CHEMISTRY CASE STUDY: DENVER FEDERAL CENTER

EPA Science Inventory

The Denver Federal Center permeable reactive barrier is a funnel-and-gate system with four reactive gates, each separated by up to about 120 m of metal sheet pile. In this study, ground water sampling, core collection, and solid phase characterization studies were carried out in...

The Dynamic Difference: Montessori's Legacy for the New Century.

ERIC Educational Resources Information Center

Loeffler, Margaret Howard

2000-01-01

Maintains that Montessori education must regain its dynamism by recognizing barriers that separate Montessori from mainstream educational thinking and entering into meaningful dialog with other educators. Suggests ways to improve understanding of Montessori's basic principles and practices and their current relevance, including defining core…

40 CFR 98.238 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... unit that separates hydrogen sulfide and/or carbon dioxide from sour natural gas using liquid or solid... sealing compound), metal to metal compression, or fluid barrier through which natural gas or liquid can... gas or CO2. Condensate means hydrocarbon and other liquid, including both water and hydrocarbon...

Soliton stability in some knot soliton models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adam, C.; Sanchez-Guillen, J.; Wereszczynski, A.

2007-02-15

We study the issue of stability of static solitonlike solutions in some nonlinear field theories which allow for knotted field configurations. Concretely, we investigate the Aratyn-Ferreira-Zimerman model [Phys. Lett. B 456, 162 (1999); Phys. Rev. Lett. 83, 1723 (1999)], based on a Lagrangian quartic in first derivatives with infinitely many conserved currents, for which infinitely many soliton solutions are known analytically. For this model we find that sectors with different (integer) topological charges (Hopf index) are not separated by an infinite energy barrier. Further, if variations which change the topological charge are allowed, then the static solutions are not evenmore » critical points of the energy functional. We also explain why soliton solutions can exist at all, in spite of these facts. In addition, we briefly discuss the Nicole model [J. Phys. G 4, 1363 (1978)], which is based on a sigma-model-type Lagrangian. For the Nicole model we find that different topological sectors are separated by an infinite energy barrier.« less

A Comprehensive Biophysical Model of Ion and Water Transport in Plant Roots. I. Clarifying the Roles of Endodermal Barriers in the Salt Stress Response

PubMed Central

Foster, Kylie J.; Miklavcic, Stanley J.

2017-01-01

In this paper, we present a detailed and comprehensive mathematical model of active and passive ion and water transport in plant roots. Two key features are the explicit consideration of the separate, but interconnected, apoplastic, and symplastic transport pathways for ions and water, and the inclusion of both active and passive ion transport mechanisms. The model is used to investigate the respective roles of the endodermal Casparian strip and suberin lamellae in the salt stress response of plant roots. While it is thought that these barriers influence different transport pathways, it has proven difficult to distinguish their separate functions experimentally. In particular, the specific role of the suberin lamellae has been unclear. A key finding based on our simulations was that the Casparian strip is essential in preventing excessive uptake of Na+ into the plant via apoplastic bypass, with a barrier efficiency that is reflected by a sharp gradient in the steady-state radial distribution of apoplastic Na+ across the barrier. Even more significantly, this function cannot be replaced by the action of membrane transporters. The simulations also demonstrated that the positive effect of the Casparian strip of controlling Na+ uptake, was somewhat offset by its contribution to the osmotic stress component: a more effective barrier increased the detrimental osmotic stress effect. In contrast, the suberin lamellae were found to play a relatively minor, even non-essential, role in the overall response to salt stress, with the presence of the suberin lamellae resulting in only a slight reduction in Na+ uptake. However, perhaps more significantly, the simulations identified a possible role of suberin lamellae in reducing plant energy requirements by acting as a physical barrier to preventing the passive leakage of Na+ into endodermal cells. The model results suggest that more and particular experimental attention should be paid to the properties of the Casparian strip when assessing the salt tolerance of different plant varieties and species. Indeed, the Casparian strip appears to be a more promising target for plant breeding and plant genetic engineering efforts than the suberin lamellae for the goal of improving salt tolerance. PMID:28804493

Incentives and Barriers That Influence Clinical Computerization in Hong Kong: A Population-based Physician Survey

PubMed Central

Leung, Gabriel M.; Yu, Philip L. H.; Wong, Irene O. L.; Johnston, Janice M.; Tin, Keith Y. K.

2003-01-01

Objective: Given the slow adoption of medical informatics in Hong Kong and Asia, we sought to understand the contributory barriers and potential incentives associated with information technology implementation. Design and Measurements: A representative sample of 949 doctors (response rate = 77.0%) was asked through a postal survey to rank a list of nine barriers associated with clinical computerization according to self-perceived importance. They ranked seven incentives or catalysts that may influence computerization. We generated mean rank scores and used multidimensional preference analysis to explore key explanatory dimensions of these variables. A hierarchical cluster analysis was performed to identify homogenous subgroups of respondents. We further determined the relationships between the sets of barriers and incentives/catalysts collectively using canonical correlation. Results: Time costs, lack of technical support and large capital investments were the biggest barriers to computerization, whereas improved office efficiency and better-quality care were ranked highest as potential incentives to computerize. Cost vs. noncost, physician-related vs. patient-related, and monetary vs. nonmonetary factors were the key dimensions explaining the barrier variables. Similarly, within-practice vs external and “push” vs “pull” factors accounted for the incentive variables. Four clusters were identified for barriers and three for incentives/catalysts. Canonical correlation revealed that respondents who were concerned with the costs of computerization also perceived financial incentives and government regulation to be important incentives/catalysts toward computerization. Those who found the potential interference with communication important also believed that the promise of improved care from computerization to be a significant incentive. Conclusion: This study provided evidence regarding common barriers associated with clinical computerization. Our findings also identified possible incentive strategies that may be employed to accelerate uptake of computer systems. PMID:12595409

Recovery of cesium

DOEpatents

Izatt, Reed M.; Christensen, James J.; Hawkins, Richard T.

1984-01-01

A process of recovering cesium ions from mixtures of ions containing them and other ions, e.g., a solution of nuclear waste materials, which comprises establishing a separate source phase containing such a mixture of ions, establishing a separate recipient phase, establishing a liquid membrane phase in interfacial contact with said source and recipient phases, said membrane phase containing a ligand, preferably a selected calixarene as depicted in the drawing, maintaining said interfacial contact for a period of time long enough to transport by said ligand a substantial portion of the cesium ion from the source phase to the recipient phase, and recovering the cesium ion from the recipient phase. The separation of the source and recipient phases may be by the membrane phase only, e.g., where these aqueous phases are emulsified as dispersed phases in a continuous membrane phase, or may include a physical barrier as well, e.g., an open-top outer container with an inner open-ended container of smaller cross-section mounted in the outer container with its open bottom end spaced from and above the closed bottom of the outer container so that the membrane phase may fill the outer container to a level above the bottom of the inner container and have floating on its upper surface a source phase and a recipient phase separated by the wall of the inner container as a physical barrier. A preferred solvent for the ligand is a mixture of methylene chloride and carbon tetrachloride.

Stacking fault induced tunnel barrier in platelet graphite nanofiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lan, Yann-Wen, E-mail: chiidong@phys.sinica.edu.tw, E-mail: ywlan@phys.sinica.edu.tw; Chang, Yuan-Chih; Chang, Chia-Seng

A correlation study using image inspection and electrical characterization of platelet graphite nanofiber devices is conducted. Close transmission electron microscopy and diffraction pattern inspection reveal layers with inflection angles appearing in otherwise perfectly stacked graphene platelets, separating nanofibers into two domains. Electrical measurement gives a stability diagram consisting of alternating small-large Coulomb blockade diamonds, suggesting that there are two charging islands coupled together through a tunnel junction. Based on these two findings, we propose that a stacking fault can behave as a tunnel barrier for conducting electrons and is responsible for the observed double-island single electron transistor characteristics.

Electrically tunable g factors in quantum dot molecular spin states.

PubMed

Doty, M F; Scheibner, M; Ponomarev, I V; Stinaff, E A; Bracker, A S; Korenev, V L; Reinecke, T L; Gammon, D

2006-11-10

We present a magnetophotoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g factors of different spin states that have molecular wave functions distributed over both quantum dots. We propose a phenomenological model for the change in g factor based on resonant changes in the amplitude of the wave function in the barrier due to the formation of bonding and antibonding orbitals.

Electrically Tunable g Factors in Quantum Dot Molecular Spin States

NASA Astrophysics Data System (ADS)

Doty, M. F.; Scheibner, M.; Ponomarev, I. V.; Stinaff, E. A.; Bracker, A. S.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.

2006-11-01

We present a magnetophotoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g factors of different spin states that have molecular wave functions distributed over both quantum dots. We propose a phenomenological model for the change in g factor based on resonant changes in the amplitude of the wave function in the barrier due to the formation of bonding and antibonding orbitals.

SODIUM DEUTERIUM REACTOR

DOEpatents

Oppenheimer, E.D.; Weisberg, R.A.

1963-02-26

This patent relates to a barrier system for a sodium heavy water reactor capable of insuring absolute separation of the metal and water. Relatively cold D/sub 2/O moderator and reflector is contained in a calandria into which is immersed the fuel containing tubes. The fuel elements are cooled by the sodium which flows within the tubes and surrounds the fuel elements. The fuel containing tubes are surrounded by concentric barrier tubes forming annular spaces through which pass inert gases at substantially atmospheric pressure. Header rooms above and below the calandria are provided for supplying and withdrawing the sodium and inert gases in the calandria region. (AEC)

Applications and Properties of Ionic Liquid- Based Gels and Soft Solid Composites

NASA Astrophysics Data System (ADS)

Voss, Bret Alan McGinness

2011-12-01

Solid-liquid composites (gels) have a combination of properties that afford new material applications in which high solute diffusion is desirable. These composites have a soft-solid mechanical integrity and will not flow under gravity, but entrain a liquid matrix (i.e. 60-98 mass %) which allows for high diffusion and high reactivity. Room temperature ionic liquid (RTILs) are molten organic salts with a melting point below room temperature and negligible vapor pressure. If the RTILs are used as the liquid component of a gel, then the gel matrix will not evaporate (unlike other organic solvents) and may be used for long term applications. This thesis research applies RTIL gels for two new applications; carbon dioxide/nitrogen separation and chemical warfare agent (CWA) barrier and decontamination. Separating CO2 from the flue gas of coal and gas fired power-plants is an increasingly economically and environmentally important gas separation. In this first study, RTIL gels are cast in a supported membrane and gas permeability and ideal selectivity are measured. The RTIL matrix has an inherent affinity for CO2 and provides a high diffusion, hence high permeability (i.e. 500-700 barrer). The solidifying component is a low molecular-weight organic gelator (LMOG) which through physical bonding interactions (i.e. hydrogen bonding, pi-pi stacking and van der Walls forces) forms an entangled network which provides mechanical stability (i.e. increase trans-membrane pressure required to expel selective material from the support). In these studies two LMOGs and five RTILs are used to make supported gel membranes and determine gas permeability and temperature dependent trends. The second application for RTIL gels is a decontaminating barrier for CWAs and toxic industrial compounds (TICs). In these studies a layer of RTIL gel is applied on top of a substrate contaminated with a CWA simulant (i.e. chloroethylethylsulfide, CEES). The gel performs well as a barrier, preventing CEES vapor from penetrating the gel. Simultaneously, the RTIL gel actively decontaminated the substrate by reacting CEES with a sacrificial amine. The RTIL gel barrier was able to decontaminate up to 98% of the CEES applied to a painted steel substrate. Two gel barriers are tested: (1) RTIL gel with a LMOG solidifying agent, and (2) RTIL gel with a polymeric cross-linked network solidifying agent. The polymer gel provided a more mechanically robust barrier, however, the LMOG gel decontaminated at a faster rate. These new applications are but two of many possible applications for RTIL gels. Their negligible vapor pressure affords long term application in ambient conditions and their unique chemistry allows them to be tailored for specific applications.

Proton Transfer Dynamics at the Membrane/Water Interface: Dependence on the Fixed and Mobile pH Buffers, on the Size and Form of Membrane Particles, and on the Interfacial Potential Barrier

PubMed Central

Cherepanov, Dmitry A.; Junge, Wolfgang; Mulkidjanian, Armen Y.

2004-01-01

Crossing the membrane/water interface is an indispensable step in the transmembrane proton transfer. Elsewhere we have shown that the low dielectric permittivity of the surface water gives rise to a potential barrier for ions, so that the surface pH can deviate from that in the bulk water at steady operation of proton pumps. Here we addressed the retardation in the pulsed proton transfer across the interface as observed when light-triggered membrane proton pumps ejected or captured protons. By solving the system of diffusion equations we analyzed how the proton relaxation depends on the concentration of mobile pH buffers, on the surface buffer capacity, on the form and size of membrane particles, and on the height of the potential barrier. The fit of experimental data on proton relaxation in chromatophore vesicles from phototropic bacteria and in bacteriorhodopsin-containing membranes yielded estimates for the interfacial potential barrier for H+/OH− ions of ∼120 meV. We analyzed published data on the acceleration of proton equilibration by anionic pH buffers and found that the height of the interfacial barrier correlated with their electric charge ranging from 90 to 120 meV for the singly charged species to >360 meV for the tetra-charged pyranine. PMID:14747306

Theoretical studies of the potential surface for the F - H2 greater than HF + H reaction

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Walch, Stephen, P.; Langhoff, Stephen R.; Taylor, Peter R.; Jaffe, Richard L.

1987-01-01

The F + H2 yields HF + H potential energy hypersurface was studied in the saddle point and entrance channel regions. Using a large (5s 5p 3d 2f 1g/4s 3p 2d) atomic natural orbital basis set, a classical barrier height of 1.86 kcal/mole was obtained at the CASSCF/multireference CI level (MRCI) after correcting for basis set superposition error and including a Davidson correction (+Q) for higher excitations. Based upon an analysis of the computed results, the true classical barrier is estimated to be about 1.4 kcal/mole. The location of the bottleneck on the lowest vibrationally adiabatic potential curve was also computed and the translational energy threshold determined from a one-dimensional tunneling calculation. Using the difference between the calculated and experimental threshold to adjust the classical barrier height on the computed surface yields a classical barrier in the range of 1.0 to 1.5 kcal/mole. Combining the results of the direct estimates of the classical barrier height with the empirical values obtained from the approximation calculations of the dynamical threshold, it is predicted that the true classical barrier height is 1.4 + or - 0.4 kcal/mole. Arguments are presented in favor of including the relatively large +Q correction obtained when nine electrons are correlated at the CASSCF/MRCI level.

Kinetic barriers for Cd and Te adatoms on Cd and Te terminated CdTe (111) surface using ab initio simulations

NASA Astrophysics Data System (ADS)

Naderi, Ebadollah; Nanavati, Sachin P.; Majumder, Chiranjib; Ghaisas, S. V.

2014-03-01

In the present work we have calculated using density functional theory (DFT), diffusion barrier potentials on both the CdTe (111) surfaces, Cd terminated (A-type) & Te terminated (B-type). We employ nudge elastic band method (NEB) for obtaining the barrier potentials. The barrier is computed for Cd and for Te adatoms on both A-type and B-type surfaces. We report two energetically favourable positions along the normal to the surface, one above and other below the surface. The one above the surface has binding energy slightly more the one below. According to the results of this work, binding energy (in all cases) for adatoms are reasonable and close to experimental data. The barrier potential for hopping adatoms (Cd and Te) on both the surfaces is less than 0.35 eV. Apart from these most probable sites, there are other at least two sites on both the types of surfaces which are meta stable. We have also computed barriers for hopping to and from these meta stable positions. The present results can shade light on the defect formation mechanism in CdTe thin films during growth. The authors would like to thank C-DAC for the computing time on its PARAM series of supercomputers and DST Govt. of India, for partial funding.

Splaying of aliphatic tails plays a central role in barrier crossing during liposome fusion.

PubMed

Mirjanian, Dina; Dickey, Allison N; Hoh, Jan H; Woolf, Thomas B; Stevens, Mark J

2010-09-02

The fusion between two lipid bilayers involves crossing a complicated energy landscape. The limiting barrier in the process appears to be between two closely opposed bilayers and the intermediate state where the outer leaflets are fused. We have performed molecular dynamics simulations to characterize the free energy barrier for the fusion of two liposomes and to examine the molecular details of barrier crossing. To capture the slow dynamics of fusion, a model using coarse-grained representations of lipids was used. The fusion between pairs of liposomes was simulated for four systems: DPPC, DOPC, a 3:1 mixture of DPPC/DPPE, and an asymmetric lipid tail system in which one tail of DPPC was reduced to half the length (ASTail). The weighted histogram method was used to compute the free energy as a function of separation distance. The relative barrier heights for these systems was found to be ASTail > DPPC > DPPC/DPPE > DOPC, in agreement with experimental observations. Further, the free energy curves for all four can be overlaid on a single curve by plotting the free energy versus the surface separation (differing only in the point of fusion). These simulations also confirm that the two main contributions to the free energy barrier are the removal of water between the vesicles and the deformation of the vesicle. The most prominent molecular detail of barrier crossing in all cases examined was the splaying of lipid tails, where initially a single splayed lipid formed a bridge between the two outer leaflets that promotes additional lipid mixing between the vesicles and eventually leads to fusion. The tail splay appears to be closely connected to the energetics of the process. For example, the high barrier for the ASTail is the result of a smaller distance between terminal methyl groups in the splayed molecule. The shortening of this distance requires the liposomes to be closer together, which significantly increases the cost of water removal and bilayer deformation. Before tail splay can initiate fusion, contact must occur between a tail end and the external water. In isolated vesicles, the contact fraction is correlated to the fusogenicity difference between DPPC and DOPC. Moreover, for planar bilayers, the contact fraction is much lower for DPPC, which is consistent with its lack of fusion in giant vesicles. The simulation results show the key roles of lipid tail dynamics in governing the fusion energy landscape.

Classical vs. non-classical pathways of mineral formation (Invited)

NASA Astrophysics Data System (ADS)

De Yoreo, J. J.

2013-12-01

Recent chemical analyses, microscopy studies and computer simulations suggest many minerals nucleate through aggregation of pre-nucleation clusters and grow by particle-mediated processes that involve amorphous or disordered precursors. Still other analyses, both experimental and computational, conclude that even simple mineral systems like calcium carbonate form via a barrier-free process of liquid-liquid separation, which is followed by dehydration of the ion-rich phase to form the solid products. However, careful measurements of calcite nucleation rates on a variety of ionized surfaces give results that are in complete agreement with the expectations of classical nucleation theory, in which clusters growing through ion-by-ion addition overcome a free energy barrier through the natural microscopic density fluctuations of the system. Here the challenge of integrating these seemingly disparate observations and analyses into a coherent picture of mineral formation is addressed by considering the energy barriers to calcite formation predicted by the classical theory and the changes in those barriers brought about by the introduction of interfaces and clusters, both stable and metastable. Results from a suite of in situ TEM, AFM, and optical experiments combined with simulations are used to illustrate the conclusions. The analyses show that the expected barrier to homogeneous calcite nucleation is prohibitive even at concentrations exceeding the solubility limit of amorphous calcium carbonate. However, as demonstrated by experiments on self-assembled monolayers, the introduction of surfaces that moderately decrease the interfacial energy associated with the forming nucleus can reduce the magnitude of the barrier to a level that is easily surmounted under typical laboratory conditions. In the absence of such surfaces, experiments that proceed by continually increasing supersaturation with time can easily by-pass direct nucleation of calcite and open up pathways through all other solid phases, as well as dense liquid phases associated with a spinodal. Simulations predict that this phase boundary lies within the region of the calcium carbonate - water phase diagram accessible at room temperature. AFM and TEM analyses of other mineral systems, particularly calcium phosphate, suggest cluster aggregation can play important roles both in modifying barriers and in biasing pathways towards or away from amorphous phases. Most importantly, analysis of the energetic changes shows that barriers are only reduced if the clusters are metastable relative to the free ions and that the reduction is naturally accompanied by a bias towards formation of amorphous precursors. Finally, results from in situ TEM observations of nanoparticle interactions are used to understand the mechanisms controlling particle-mediated growth following formation of primary nuclei of either crystalline phases or disordered precursors. Measurements of the particle speeds and accelerations are used to estimate the magnitude of the attractive potential that drives particle-particle aggregation.

Thermal decay of a metastable state: Influence of rescattering on the quasistationary dynamical rate

NASA Astrophysics Data System (ADS)

Chushnyakova, M. V.; Gontchar, I. I.

2018-03-01

We study the effect of backscattering of the Brownian particles as they escape out of a metastable state overcoming the potential barrier. For this aim, we model this process numerically using the Langevin equations. This modeling is performed for the wide range of the friction constant covering both the energy and spatial diffusion regimes. It is shown how the influence of the descent stage on the quasistationary decay rate gradually disappears as the friction constant decreases. It is found that, in the energy diffusion regime, the rescattering absents and the descent stage does not influence the decay rate. As the value of friction increases, the descent alters the value of the rate by more than 50% for different values of thermal energy and different shapes of the potential. To study the influence of the backscattering on the decay rate, four potentials have been considered which coincide near the potential well and the barrier but differ beyond the barrier. It is shown that the potential for which the well and the barrier are described by two smoothly joined parabolas ("the parabolic potential") plays a role of a dividing range for the mutual layout of the quasistationary dynamical rate and the widely used in the literature Kramers rate. Namely, for the potentials with steeper tails, the Kramers rate RKM underestimates the true quasistationary dynamical rate RD, whereas for the less steep tails the opposite holds (inversion of RD/RKM ). It is demonstrated that the mutual layout of the values of RD for different potentials is explained by the rescattering of the particles from the potential tail.

Stimulated emission of surface plasmons by electron tunneling in metal-barrier-metal structures

NASA Technical Reports Server (NTRS)

Siu, D. P.; Gustafson, T. K.

1978-01-01

It is shown that correlation currents arising from the superposition of pairs of states on distinct sides of a potential barrier in metal-barrier-metal structures can result in inelastic tunneling through the emission of surface plasmons. Net gain of an externally excited plasmon field is possible.

INVESTIGATION OF RECYCLED TIRE CHIPS FOR USE IN GDOT CONCRETE USED TO CONSTRUCT BARRIER WALLS AND OTHER APPLIATIONS–PHASE I

DOT National Transportation Integrated Search

2017-09-01

In 2013, GDOT constructed more than 42,000 LF of concrete barrier utilizing a Class A concrete mixture design (3000 psi). There may be potential for the beneficial utilization of recycled tire chips in concrete barrier applications which can possibly...

The Status of and key barriers in lignocellulosic ethanol production : a technological perspective

Treesearch

J.Y. Zhu; G.S. Wang; X.J. Pan; R. Gleisner

2008-01-01

The development of biorefineries to produce fuel ethanol and commodity chemicals from lignocellulosic biomass is a potential alternative to current reliance on non-renewable resources. However, many technological barriers remain despite research progress in the past several decades. This article examines the major process barriers in biochemical conversion of biomass...

Barriers to Successful Treatment Completion in Child Sexual Abuse Survivors

ERIC Educational Resources Information Center

McPherson, Paul; Scribano, Philip; Stevens, Jack

2012-01-01

Child sexual abuse (CSA) often requires psychological treatment to address the symptoms of victim trauma. Barriers to entry and completion of counseling services can compromise long-term well-being. An integrated medical and mental health evaluation and treatment model of a child advocacy center (CAC) has the potential to reduce barriers to mental…

Incentives and Barriers for Potential Music Teacher Education Doctoral Students

ERIC Educational Resources Information Center

Teachout, David J.

2004-01-01

The purpose of this study was to examine positive influences and barriers associated with entering a music teacher education doctoral program. Practicing music educators (N = 63), were asked to rate 48 positive-influence items and 54 barrier items. The highest-ranked positive influence was "Training young teachers to provide worthwhile…

[On Atomic Nuclear Fusion Processes at Low-Temperatures. An Enhancement of the Probability of Transition through a Potential Barrier Due to the So-Called Barrier Anti-Zeno Effect].

PubMed

Namiot, V A

2016-01-01

It is known that in quantum mechanics the act of observing the experiment can affect the experimental findings in some cases. In particular, it happens under the so-called Zeno effect. In this work it is shown that in contrast to the "standard" Zeno-effect where the act of observing a process reduces the probability of its reality, an inverse situation when a particle transmits through a potential barrier (a so-called barrier anti-Zeno effect) can be observed, the observation of the particle essentially increases the probability of its transmission through the barrier. The possibility of using the barrier anti-Zeno effect is discussed to explain paradoxical results of experiments on "cold nuclear fusion" observed in various systems including biological ones. (According to the observers who performed the observations, the energy generation, which could not be explained by any chemical processes, as well as the change in the isotope and even element composition of the studied object may occur in these systems.

Barriers to Clinical Trial Enrollment in Racial and Ethnic Minority Patients With Cancer

PubMed Central

Hamel, Lauren M.; Penner, Louis A.; Albrecht, Terrance L.; Heath, Elisabeth; Gwede, Clement K.; Eggly, Susan

2016-01-01

Background Clinical trials that study cancer are essential for testing the safety and effectiveness of promising treatments, but most people with cancer never enroll in a clinical trial — a challenge exemplified in racial and ethnic minorities. Underenrollment of racial and ethnic minorities reduces the generalizability of research findings and represents a disparity in access to high-quality health care. Methods Using a multilevel model as a framework, potential barriers to trial enrollment of racial and ethnic minorities were identified at system, individual, and interpersonal levels. Exactly how each level directly or indirectly contributes to doctor–patient communication was also reviewed. Selected examples of implemented interventions are included to help address these barriers. We then propose our own evidence-based intervention addressing barriers at the individual and interpersonal levels. Results Barriers to enrolling a diverse population of patients in clinical trials are complex and multilevel. Interventions focused at each level have been relatively successful, but multilevel interventions have the greatest potential for success. Conclusion To increase the enrollment of racial and ethnic minorities in clinical trials, future interventions should address barriers at multiple levels. PMID:27842322

Waste deposit influences on groundwater quality as a tool for waste type and site selection for final storage quality

NASA Astrophysics Data System (ADS)

Arneth, Jan-Dirk; Milde, Gerald; Kerndorff, Helmut; Schleyer, Ruprecht

Leachates from deposits of wastes may, in the long run, adversely influence groundwater quality. Since tipping still constitutes the most important form of waste disposal, strategies must be developed which are capable of protecting groundwater against contamination from leachates. In the first instance such protective measures must provide for a minimization of contamination by setting up optimal barriers. Since it would seem difficult to reach this goal in a forseeable future, the avoidance of substances with a high potential for groundwater hazards has to be attributed much importance. In former times, little attention was given to impermeability or avoidance of substances with a high potential for groundwater hazards contained in wastes. Therefore, results of the investigation of groundwater near abandoned sites can be used to optimize groundwater protection on future tipping sites. In the present study, the results of chemical investigation of groundwater from the vicinity of 92 waste disposal sites in the Federal Republic of Germany are presented and the changes in groundwater quality owing to the penetration of leachates are discussed separately for inorganic and organic contaminants.

Sensing charges of the Ciona intestinalis voltage-sensing phosphatase.

PubMed

Villalba-Galea, Carlos A; Frezza, Ludivine; Sandtner, Walter; Bezanilla, Francisco

2013-11-01

Voltage control over enzymatic activity in voltage-sensitive phosphatases (VSPs) is conferred by a voltage-sensing domain (VSD) located in the N terminus. These VSDs are constituted by four putative transmembrane segments (S1 to S4) resembling those found in voltage-gated ion channels. The putative fourth segment (S4) of the VSD contains positive residues that likely function as voltage-sensing elements. To study in detail how these residues sense the plasma membrane potential, we have focused on five arginines in the S4 segment of the Ciona intestinalis VSP (Ci-VSP). After implementing a histidine scan, here we show that four arginine-to-histidine mutants, namely R223H to R232H, mediate voltage-dependent proton translocation across the membrane, indicating that these residues transit through the hydrophobic core of Ci-VSP as a function of the membrane potential. These observations indicate that the charges carried by these residues are sensing charges. Furthermore, our results also show that the electrical field in VSPs is focused in a narrow hydrophobic region that separates the extracellular and intracellular space and constitutes the energy barrier for charge crossing.

Conductance of graphene based normal-superconductor junction with double magnetic barriers

NASA Astrophysics Data System (ADS)

Abdollahipour, B.; Mohebalipour, A.; Maleki, M. A.

2018-05-01

We study conductance of a graphene based normal metal-superconductor junction with two magnetic barriers. The magnetic barriers are induced via two applied magnetic fields with the same magnitudes and opposite directions accompanied by an applied electrostatic potential. We solve Dirac-Bogoliubov-De-Gennes (DBdG) equation to calculate conductance of the junction. We find that applying the magnetic field leads to suppression of the Andreev reflection and conductance for all energies. On the other hand, we observe a crossover from oscillatory to tunneling behavior of the conductance as a function of the applied potential by increasing the magnetic field.

Investigation of a New Concept in Semiconductor Microwave Oscillators: The Contiguous Domain Oscillator

DTIC Science & Technology

1993-02-28

on a potential microwave source with many novel properties. It combines the transferred electron effect in n-type GaAs material together with 2 the...the channel direction. This barrier could be a physical barrier provided by a high band-gap material in a MOSFET structure or a potential barrier...rralivtic vcloocltv flc’ld curve of GmAs\\. chargc- oscillation ii po, ~ible once the dectnic fiC Xi di ’!I;ihU1]0n ClC(I OceCd OheMO) Osld fticl, ’Idh in 3

Enzymatic studies using quantum mechanical and molecular mechanical techniques

NASA Astrophysics Data System (ADS)

Faulder, Paul F.

Enzymes have evolved to increase the rate of biological reactions using fundamental physical processes. Until recently, the nature of catalysis has been based upon a classical model but it has since been considered that certain aspects of catalysis, particularly those concerning the transfer of a hydrogen species, may be accounted for using the theory of quantum mechanics. This thesis reports the use of reaction paths obtained using QMMM (combined quantum mechanics-molecular mechanics), combined with canonical variational transition state theory and multidimensional tunnelling corrections, to study two dehydrogenase enzymes, Liver Alcohol Dehydrogenase (LADH) and Methylamine Dehydrogenase (MADH). These methods are used to investigate the nature of these models in explaining reported experimental data indicative of quantum mechanical tunnelling within these enzymes. The results obtained are in good agreement with experimental data indicating the presence of tunnelling in LADH and, to a greater degree, in MADH, reflected in the magnitude of the calculated kinetic isotope effects (KIEs). For LADH, a primary tritium KIE of 5.6 is reported, calculated using transition state theory (TST) with a Wigner tunnelling correction, and compares favourably with an experimental value of 7.1. For MADH, a KIE of 11.1 was determined using canonical variational theory (CVT) with a small curvature tunnelling (SCT) correction, and compared favourably with an experimental value of 16.8. In addition, a relationship is observed between the contribution due to tunnelling in each system and the geometric positioning of the donating and accepting atoms of the transferring species, and is in qualitative agreement with current opinion concerning tunnelling and the dynamic nature of catalysis. Potential energy barriers have been obtained for both systems using QMMM. For LADH, barriers of 8.2 kcal mol-1 and 22.0 kcal mol-1, and reaction energies of -25.7 kcal mol-1 and +3.4 kcal mol-1, are reported for PM3 semiempirical and HF/3-21G respectively compared with an experimental barrier of 15.6 kcal mol-1 and reaction energy of +1.0 kcal mol-1. In MADH, a potential energy barrier of 9.1 kcal mol-1 is reported for PM3, compared with 10.7 kcal mol-1 experimentally. A reaction energy of -3.5 kcal mol-1 is also reported although no experimental data is available for comparison. All ah initio calculations produced significantly higher barriers and endothermic reaction energies. Chapter 1 presents a review of protein structure and classical enzyme catalysis, providing the foundations for a discussion of recent work concerning the application of quantum tunnelling in rationalising catalysis in certain enzymatic systems. Chapter 2 utilises the background information provided in Chapter 1 in a discussion specifically applied to previous experimental data concerning the structure, function and catalytic behaviour reported for the enzymes LADH and MADH. Chapter 3 presents a background to the methodology behind the theoretical methods used in the investigation of LADH and MADH reported in this thesis, in addition to reporting the development of extra code which has allowed the integration of our QMMM software with the rate determining program, POLYRATE, allowing the calculation of KIEs for these enzymes. Chapter 4 presents the preparation of the enzyme model of LADH with two separate substrates and the results obtained from subsequent QMMM calculations carried out on these models. These results are presented alongside results obtained by other workers, for comparative analysis. Chapter 5 details the preparation of a model of MADH with the substrate methylamine, and the QMMM investigation of the mode of catalysis for this enzyme using a variety of separate QMMM models. The calculation of KIEs on this enzyme, using the modified POLYRATE, are then presented in addition to KIEs determined for LADH based on results obtained from Chapter 4, and are discussed. The results of QMMM calculations carried out on MADH from a separate species are then presented in the context of validating the first set of results. Finally, QMMM calculations are presented for MADH bound to the substrate ethanolamine, attempting to elucidate the catalytically similar mechanism to methylamine.

Non-Saccharomyces yeasts protect against epithelial cell barrier disruption induced by Salmonella enterica subsp. enterica serovar Typhimurium.

PubMed

Smith, I M; Baker, A; Arneborg, N; Jespersen, L

2015-11-01

The human gastrointestinal epithelium makes up the largest barrier separating the body from the external environment. Whereas invasive pathogens cause epithelial barrier disruption, probiotic micro-organisms modulate tight junction regulation and improve epithelial barrier function. In addition, probiotic strains may be able to reduce epithelial barrier disruption caused by pathogenic species. The aim of this study was to explore non-Saccharomyces yeast modulation of epithelial cell barrier function in vitro. Benchmarking against established probiotic strains, we evaluated the ability of four nonpathogenic yeast species to modulate transepithelial electrical resistance (TER) across a monolayer of differentiated human colonocytes (Caco-2 cells). Further, we assessed yeast modulation of a Salmonella Typhimurium-induced epithelial cell barrier function insult. Our findings demonstrate distinct patterns of non-Saccharomyces yeast modulation of epithelial cell barrier function. While the established probiotic yeast Saccharomyces boulardii increased TER across a Caco-2 monolayer by 30%, Kluyveromyces marxianus exhibited significantly stronger properties of TER enhancement (50% TER increase). In addition, our data demonstrate significant yeast-mediated modulation of Salmonella-induced epithelial cell barrier disruption and identify K. marxianus and Metschnikowia gruessii as two non-Saccharomyces yeasts capable of protecting human epithelial cells from pathogen invasion. This study demonstrates distinct patterns of non-Saccharomyces yeast modulation of epithelial cell barrier function in vitro. Further, our data demonstrate significant yeast-mediated modulation of Salmonella Typhimurium-induced epithelial cell barrier disruption and identify Kluyveromyces marxianus and Metschnikowia gruessii as two non-Saccharomyces yeasts capable of protecting human epithelial cells from pathogen invasion. This study is the first to demonstrate significant non-Saccharomyces yeast-mediated epithelial cell barrier protection from Salmonella invasion, thus encouraging future efforts aimed at confirming the observed effects in vivo and driving further strain development towards novel yeast probiotics. © 2015 The Society for Applied Microbiology.

Gut barrier in health and disease: focus on childhood.

PubMed

Viggiano, D; Ianiro, G; Vanella, G; Bibbò, S; Bruno, G; Simeone, G; Mele, G

2015-01-01

The gut barrier is a functional unit, organized as a multi-layer system, made up of two main components: a physical barrier surface, which prevents bacterial adhesion and regulates paracellular diffusion to the host tissues, and a deep functional barrier, that is able to discriminate between pathogens and commensal microorganisms, organizing the immune tolerance and the immune response to pathogens. Other mechanisms, such as gastric juice and pancreatic enzymes (which both have antibacterial properties) participate in the luminal integrity of the gut barrier. From the outer layer to the inner layer, the physical barrier is composed of gut microbiota (that competes with pathogens to gain space and energy resources, processes the molecules necessary to mucosal integrity and modulates the immunological activity of deep barrier), mucus (which separates the intraluminal content from more internal layers and contains antimicrobial products and secretory IgA), epithelial cells (which form a physical and immunological barrier) and the innate and adaptive immune cells forming the gut-associated lymphoid tissue (which is responsible for antigen sampling and immune responses). Disruption of the gut barrier has been associated with many gastrointestinal diseases, but also with extra-intestinal pathological condition, such as type 1 diabetes mellitus, allergic diseases or autism spectrum disorders. The maintenance of a healthy intestinal barrier is therefore of paramount importance in children, for both health and economic reasons. Many drugs or compounds used in the treatment of gastrointestinal disorders act through the restoration of a normal intestinal permeability. Several studies have highlighted the role of probiotics in the modulation and reduction of intestinal permeability, considering the strong influence of gut microbiota in the modulation of the function and structure of gut barrier, but also on the immune response of the host. To date, available weapons for the maintenance and repair of gut barrier are however few, even if promising. Considerable efforts, including both a better understanding of the gut barrier features and mechanisms in health and disease, and the development of new pharmacological approaches for the modulation of gut barrier components, are needed for the prevention and treatment of gastrointestinal and extraintestinal diseases associated with gut barrier impairment.

Enhancing the diversity of the pediatrician workforce.

PubMed

Friedman, Aaron L

2007-04-01

This policy statement describes the key issues related to diversity within the pediatrician and health care workforce to identify barriers to enhancing diversity and offer policy recommendations to overcome these barriers in the future. The statement addresses topics such as health disparities, affirmative action, recent policy developments and reports on workforce diversity, and research on patient and provider diversity. It also broadens the discussion of diversity beyond the traditional realms of race and ethnicity to include cultural attributes that may have an effect on the quality of health care. Although workforce diversity is related to the provision of culturally effective pediatric care, it is a discrete issue that merits separate discussion and policy formulation. At the heart of this policy-driven action are multiorganizational and multispecialty collaborations designed to address substantive educational, financial, organizational, and other barriers to improved workforce diversity.

Barriers and facilitators to implementing a patient-centered model of contraceptive provision in community health centers.

PubMed

Politi, Mary C; Estlund, Amy; Milne, Anne; Buckel, Christina M; Peipert, Jeffrey F; Madden, Tessa

2016-01-01

The Contraceptive CHOICE Project developed a patient-centered model for contraceptive provision including: (1) structured, evidence-based counseling; (2) staff and health care provider education; and (3) removal of barriers such as cost and multiple appointments to initiate contraception. In preparation for conducting a research study of the CHOICE model in three community health settings, we sought to identify potential barriers and facilitators to implementation. Using a semi-structured interview guide guided by a framework of implementation research, we conducted 31 qualitative interviews with female patients, staff, and health care providers assessing attitudes, beliefs, and barriers to receiving contraception. We also asked about current contraceptive provision and explored organizational practices relevant to implementing the CHOICE model. We used a grounded theory approach to identify major themes. Many participants felt that current contraceptive provision could be improved by the CHOICE model. Potential facilitators included agreement about the necessity for improved contraceptive knowledge among patients and staff; importance of patient-centered contraceptive counseling; and benefits to same-day insertion of long-acting reversible contraception (LARC). Potential barriers included misconceptions about contraception held by staff and providers; resistance to new practices; costs associated with LARC; and scheduling challenges required for same-day insertion of LARC. In addition to staff and provider training, implementing a patient-centered model of contraceptive provision needs to be supplemented by strategies to manage patient and system-level barriers. Community health center staff, providers, and patients support patient-centered contraceptive counseling to improve contraception provision if organizations can address these barriers.

Only Above Barrier Energy Components Contribute to Barrier Traversal Time

NASA Astrophysics Data System (ADS)

Galapon, Eric A.

2012-04-01

A time of arrival operator across a square potential barrier is constructed. The expectation value of the barrier time of arrival operator for a sufficiently localized incident wave packet is compared with the expectation value of the free particle time of arrival operator for the same wave packet. The comparison yields an expression for the expected traversal time across the barrier. It is shown that only the above barrier components of the momentum distribution of the incident wave packet contribute to the barrier traversal time, implying that below the barrier components are transmitted without delay. This is consistent with the recent experiment in attosecond ionization in helium indicating that there is no real tunneling delay time [P. Eckle , Science 322, 1525 (2008)SCIEAS0036-807510.1126/science.1163439].

Origins and implications of the ordering of oxygen vacancies and localized electrons on partially reduced CeO 2(111)

DOE PAGES

Sutton, Jonathan E.; Beste, Ariana; Steven H. Overbury

2015-10-12

In this study, we use density functional theory to explain the preferred structure of partially reduced CeO 2(111). Low-energy ordered structures are formed when the vacancies are isolated (maximized intervacancy separation) and the size of the Ce 3+ ions is minimized. Both conditions help minimize disruptions to the lattice around the vacancy. The stability of the ordered structures suggests that isolated vacancies are adequate for modeling more complex (e.g., catalytic) systems. Oxygen diffusion barriers are predicted to be low enough that O diffusion between vacancies is thermodynamically controlled at room temperature. The O-diffusion-reaction energies and barriers are decreased when onemore » Ce f electron hops from a nearest-neighbor Ce cation to a next-nearest-neighbor Ce cation, with a barrier that has been estimated to be slightly less than the barrier to O diffusion in the absence of polaron hopping. In conculsion, this indicates that polaron hopping plays a key role in facilitating the overall O diffusion process, and depending on the relative magnitudes of the polaron hopping and O diffusion barriers, polaron hopping may be the kinetically limiting process.« less

Chromium-induced skin damage among Taiwanese cement workers.

PubMed

Chou, Tzu-Chieh; Wang, Po-Chih; Wu, Jyun-De; Sheu, Shiann-Cherng

2016-10-01

Little research has been done on the relationships between chromium exposure, skin barrier function, and other hygienic habits in cement workers. Our purpose was to investigate chromium-induced skin barrier disruption due to cement exposure among cement workers. One hundred and eight cement workers were recruited in this study. Urinary chromium concentration was used to characterize exposure levels. The biological exposure index was used to separate high and low chromium exposure. Transepidermal water loss (TEWL) was used to assess the skin barrier function. TEWL was significantly increased in workers with high chromium exposure levels than those with low chromium exposure levels (p = 0.048). A positive correlation was also found between urinary chromium concentration and TEWL (R = 0.28, p = 0.004). After adjusting for smoking status and glove use, a significant correlation between urinary chromium concentrations and TEWL remained. Moreover, workers who smoked and had a high chromium exposure had significantly increased TEWL compared to nonsmokers with low chromium exposure (p = 0.01). Skin barrier function of cement workers may have been disrupted by chromium in cement, and smoking might significantly enhance such skin barrier perturbation with chromium exposure. Decreased chromium skin exposure and smoking cessation should be encouraged at work. © The Author(s) 2015.

Magnetic coherent tunnel junctions with periodic grating barrier

PubMed Central

Fang, Henan; Xiao, Mingwen; Rui, Wenbin; Du, Jun; Tao, Zhikuo

2016-01-01

A new spintronic theory has been developed for the magnetic tunnel junction (MTJ) with single-crystal barrier. The barrier will be treated as a diffraction grating with intralayer periodicity, the diffracted waves of tunneling electrons thus contain strong coherence, both in charge and especially in spin. The theory can answer the two basic problems present in MgO-based MTJs: (1) Why does the tunneling magnetoresistance (TMR) oscillate with the barrier thickness? (2) Why is the TMR still far away from infinity when the two electrodes are both half-metallic? Other principal features of TMR can also be explained and reproduced by the present work. It also provides possible ways to modulate the oscillation of TMR, and to enhance TMR so that it can tend to infinity. Within the theory, the barrier, as a periodic diffraction grating, can get rid of the confinement in width, it can vary from nanoscale to microscale. Based on those results, a future-generation MTJ is proposed where the three pieces can be fabricated separately and then assembled together, it is especially appropriate for the layered materials, e.g., MoS2 and graphite, and most feasible for industries. PMID:27063998

Role of Desolvation in Thermodynamics and Kinetics of Ligand Binding to a Kinase

PubMed Central

2015-01-01

Computer simulations are used to determine the free energy landscape for the binding of the anticancer drug Dasatinib to its src kinase receptor and show that before settling into a free energy basin the ligand must surmount a free energy barrier. An analysis based on using both the ligand-pocket separation and the pocket-water occupancy as reaction coordinates shows that the free energy barrier is a result of the free energy cost for almost complete desolvation of the binding pocket. The simulations further show that the barrier is not a result of the reorganization free energy of the binding pocket. Although a continuum solvent model gives the location of free energy minima, it is not able to reproduce the intermediate free energy barrier. Finally, it is shown that a kinetic model for the on rate constant in which the ligand diffuses up to a doorway state and then surmounts the desolvation free energy barrier is consistent with published microsecond time-scale simulations of the ligand binding kinetics for this system [Shaw, D. E. et al. J. Am. Chem. Soc.2011, 133, 9181−918321545110]. PMID:25516727

Fission barriers from multidimensionally-constrained covariant density functional theories

NASA Astrophysics Data System (ADS)

Lu, Bing-Nan; Zhao, Jie; Zhao, En-Guang; Zhou, Shan-Gui

2017-11-01

In recent years, we have developed the multidimensionally-constrained covariant density functional theories (MDC-CDFTs) in which both axial and spatial reflection symmetries are broken and all shape degrees of freedom described by βλμ with even μ, such as β20, β22, β30, β32, β40, etc., are included self-consistently. The MDC-CDFTs have been applied to the investigation of potential energy surfaces and fission barriers of actinide nuclei, third minima in potential energy surfaces of light actinides, shapes and potential energy surfaces of superheavy nuclei, octupole correlations between multiple chiral doublet bands in 78Br, octupole correlations in Ba isotopes, the Y32 correlations in N = 150 isotones and Zr isotopes, the spontaneous fission of Fm isotopes, and shapes of hypernuclei. In this contribution we present the formalism of MDC-CDFTs and the application of these theories to the study of fission barriers and potential energy surfaces of actinide nuclei.

Electric and magnetic superlattices in trilayer graphene

NASA Astrophysics Data System (ADS)

Uddin, Salah; Chan, K. S.

2016-01-01

The properties of one dimensional Kronig-Penney type of periodic electric and vector potential on ABC-trilayer graphene superlattices are investigated. The energy spectra obtained with periodic vector potentials shows the emergence of extra Dirac points in the energy spectrum with finite energies. For identical barrier and well widths, the original as well as the extra Dirac points are located in the ky = 0 plane. An asymmetry between the barrier and well widths causes a shift in the extra Dirac points away from the ky = 0 plane. Extra Dirac points having same electron hole crossing energy as that of the original Dirac point as well as finite energy Dirac points are generated in the energy spectrum when periodic electric potential is applied to the system. By applying electric and vector potential together, the symmetry of the energy spectrum about the Fermi level is broken. A tunable band gap is induced in the energy spectrum by applying both electric and vector potential simultaneously with different barrier and well widths.

Minimum free-energy paths for the self-organization of polymer brushes.

PubMed

Gleria, Ignacio; Mocskos, Esteban; Tagliazucchi, Mario

2017-03-22

A methodology to calculate minimum free-energy paths based on the combination of a molecular theory and the improved string method is introduced and applied to study the self-organization of polymer brushes under poor solvent conditions. Polymer brushes in a poor solvent cannot undergo macroscopic phase separation due to the physical constraint imposed by the grafting points; therefore, they microphase separate forming aggregates. Under some conditions, the theory predicts that the homogeneous brush and the aggregates can exist as two different minima of the free energy. The theoretical methodology introduced in this work allows us to predict the minimum free-energy path connecting these two minima as well as the morphology of the system along the path. It is shown that the transition between the homogeneous brush and the aggregates may involve a free-energy barrier or be barrierless depending on the relative stability of the two morphologies and the chain length and grafting density of the polymer. In the case where a free-energy barrier exists, one of the morphologies is a metastable structure and, therefore, the properties of the brush as the quality of the solvent is cycled are expected to display hysteresis. The theory is also applied to study the adhesion/deadhesion transition between two opposing surfaces modified by identical polymer brushes and it is shown that this process may also require surpassing a free-energy barrier.

Translating Microfluidics: Cell Separation Technologies and their Barriers to Commercialization

PubMed Central

Shields, C. Wyatt; Ohiri, Korine A.; Szott, Lizzy M.; López, Gabriel P.

2016-01-01

Advances in microfluidic cell sorting have revolutionized the ways in which cell-containing fluids are processed, now providing performances comparable to, or exceeding, traditional systems, but in a vastly miniaturized format. These technologies exploit a wide variety of physical phenomena to manipulate cells and fluid flow, such as magnetic traps, sound waves and flow-altering micropatterns, and they can evaluate single cells by immobilizing them onto surfaces for chemotherapeutic assessment, encapsulate cells into picoliter droplets for toxicity screenings and examine the interactions between pairs of cells in response to new, experimental drugs. However, despite the massive surge of innovation in these high-performance lab-on-a-chip devices, few have undergone successful commercialization, and no device has been translated to a widely distributed clinical commodity to date. Persistent challenges such as an increasingly saturated patent landscape as well as complex user interfaces are among several factors that may contribute to their slowed progress. In this article, we identify several of the leading microfluidic technologies for sorting cells that are poised for clinical translation; we examine the principal barriers preventing their routine clinical use; finally, we provide a prospectus to elucidate the key criteria that must be met to overcome those barriers. Once established, these tools may soon transform how clinical labs study various ailments and diseases by separating cells for downstream sequencing and enabling other forms of advanced cellular or sub-cellular analysis. PMID:27282966

Anomalous Seebeck coefficient observed in silicon nanowire micro thermoelectric generator

NASA Astrophysics Data System (ADS)

Hashimoto, S.; Asada, S.; Xu, T.; Oba, S.; Himeda, Y.; Yamato, R.; Matsukawa, T.; Matsuki, T.; Watanabe, T.

2017-07-01

We have found experimentally an anomalous thermoelectric characteristic of an n-type Si nanowire micro thermoelectric generator (μTEG). The μTEG is fabricated on a silicon-on-insulator wafer by electron beam lithography and dry etching, and its surface is covered with a thermally grown silicon dioxide film. The observed thermoelectric current is opposite to what is expected from the Seebeck coefficient of n-type Si. The result is understandable by considering a potential barrier in the nanowire. Upon the application of the temperature gradient across the nanowire, the potential barrier impedes the diffusion of thermally activated majority carriers into the nanowire, and it rather stimulates the injection of thermally generated minority carriers. The most plausible origin of the potential barrier is negative charges trapped at the interface between the Si nanowire and the oxide film. We practically confirmed that the normal Seebeck coefficient of the n-type Si nanowire is recovered after the hydrogen forming gas annealing. This implies that the interface traps are diminished by the hydrogen termination of bonding defects. The present results show the importance of the surface inactivation treatment of μTEGs to suppress the potential barrier and unfavorable contribution of minority carriers.

Barrier Coatings for Refractory Metals and Superalloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

SM Sabol; BT Randall; JD Edington

2006-02-23

In the closed working fluid loop of the proposed Prometheus space nuclear power plant (SNPP), there is the potential for reaction of core and plant structural materials with gas phase impurities and gas phase transport of interstitial elements between superalloy and refractory metal alloy components during service. Primary concerns are surface oxidation, interstitial embrittlement of refractory metals and decarburization of superalloys. In parallel with kinetic investigations, this letter evaluates the ability of potential coatings to prevent or impede communication between reactor and plant components. Key coating requirements are identified and current technology coating materials are reviewed relative to these requirements.more » Candidate coatings are identified for future evaluation based on current knowledge of design parameters and anticipated environment. Coatings were identified for superalloys and refractory metals to provide diffusion barriers to interstitial transport and act as reactive barriers to potential oxidation. Due to their high stability at low oxygen potential, alumina formers are most promising for oxidation protection given the anticipated coolant gas chemistry. A sublayer of iridium is recommended to provide inherent diffusion resistance to interstitials. Based on specific base metal selection, a thin film substrate--coating interdiffusion barrier layer may be necessary to meet mission life.« less

The willingness to participate in health research studies of individuals with Turkish migration backgrounds: barriers and resources.

PubMed

Dingoyan, D; Schulz, H; Mösko, M

2012-06-01

Lower participation rates of ethnic minorities in health research studies and potential participation barriers are commonly reported. Four semi-structured focus groups of individuals with Turkish migration backgrounds living in Germany were conducted to identify potential participation barriers. Documented statements and superscripted presentation cards by the participants were evaluated with a qualitative content analysis. The following eight potential reasons for the lower participation rates were identified: role of women, lack of knowledge, lack of interest, German-Turkish interactions, mistrust, anxiety, data privacy protection and benefits of the study. Additionally, the following recruitment strategies to enhance participation rates were found: public relations, especially word-of-mouth promotion and contacting Turkish key figures, (non-) tangible incentives and trust building through transparent communication of the project and its conditions. The findings provide a wide range of potential participation barriers and implications that should be considered to enhance the participation rates of minority populations. The willingness to participate in health research studies can be increased through particular efforts, which should be tailored to the recruitment of the underrepresented target population. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

Potential energy barriers to ion transport within lipid bilayers. Studies with tetraphenylborate.

PubMed Central

Andersen, P S; Fuchs, M

1975-01-01

Tetraphenylborate-induced current transients were studied in lipid bilayers formed from bacterial phosphatidylethanolamine in decane. This ion movement was essentially confined to the membrane in terior during the current transients. Charge movement through the interior of the membrane during the current transients was studied as a function of the applied potential. The transferred charge approached an upper limit with increasing potential, which is interpreted to be the amount of charge due to tetraphenylborate ions absorbed into the boundary regions of the bilayer. A further analysis of the charge transfer as a function of potential indicates that the movement of tetraphenylborate ions is only influenced by a certain farction of the applied potential. For bacterial phosphatidylethanolamine bilayers the effective potential is 77 +/- 4% of the applied potential. The initial conductance and the time constant of the current transients were studied as a function of the applied potential using a Nernst-Planck electrodiffusion regime. It was found that an image-force potential energy barrier gave a good prediction of the observed behavior, provided that the effective potential was used in the calculations. We could not get a satisfactory prediction of the observed behavior with an Eyring rate theory model or a trapezoidal potential energy barrier. PMID:1148364

Minke whale song, spacing, and acoustic communication on the Great Barrier Reef, Australia

NASA Astrophysics Data System (ADS)

Gedamke, Jason

An inquisitive population of minke whale (Balaenoptera acutorostrata ) that concentrates on the Great Barrier Reef during its suspected breeding season offered a unique opportunity to conduct a multi-faceted study of a little-known Balaenopteran species' acoustic behavior. Chapter one investigates whether the minke whale is the source of an unusual, complex, and stereotyped sound recorded, the "star-wars" vocalization. A hydrophone array was towed from a vessel to record sounds from circling whales for subsequent localization of sound sources. These acoustic locations were matched with shipboard and in-water observations of the minke whale, demonstrating the minke whale was the source of this unusual sound. Spectral and temporal features of this sound and the source levels at which it is produced are described. The repetitive "star-wars" vocalization appears similar to the songs of other whale species and has characteristics consistent with reproductive advertisement displays. Chapter two investigates whether song (i.e. the "star-wars" vocalization) has a spacing function through passive monitoring of singer spatial patterns with a moored five-sonobuoy array. Active song playback experiments to singers were also conducted to further test song function. This study demonstrated that singers naturally maintain spatial separations between them through a nearest-neighbor analysis and animated tracks of singer movements. In response to active song playbacks, singers generally moved away and repeated song more quickly suggesting that song repetition interval may help regulate spatial interaction and singer separation. These results further indicate the Great Barrier Reef may be an important reproductive habitat for this species. Chapter three investigates whether song is part of a potentially graded repertoire of acoustic signals. Utilizing both vessel-based recordings and remote recordings from the sonobuoy array, temporal and spectral features, source levels, and associated contextual data of recorded sounds were analyzed. Two categories of sound are described here: (1) patterned song, which was regularly repeated in one of three patterns: slow, fast, and rapid-clustered repetition, and (2) non-patterned "social" sounds recorded from gregarious assemblages of whales. These discrete acoustic signals may comprise a graded system of communication (Slow/fast song → Rapid-clustered song → Social sounds) that is related to the spacing between whales.

Multi-component fluid flow through porous media by interacting lattice gas computer simulation

NASA Astrophysics Data System (ADS)

Cueva-Parra, Luis Alberto

In this work we study structural and transport properties such as power-law behavior of trajectory of each constituent and their center of mass, density profile, mass flux, permeability, velocity profile, phase separation, segregation, and mixing of miscible and immiscible multicomponent fluid flow through rigid and non-consolidated porous media. The considered parameters are the mass ratio of the components, temperature, external pressure, and porosity. Due to its solid theoretical foundation and computational simplicity, the selected approaches are the Interacting Lattice Gas with Monte Carlo Method (Metropolis Algorithm) and direct sampling, combined with particular collision rules. The percolation mechanism is used for modeling initial random porous media. The introduced collision rules allow to model non-consolidated porous media, because part of the kinetic energy of the fluid particles is transfered to barrier particles, which are the components of the porous medium. Having gained kinetic energy, the barrier particles can move. A number of interesting results are observed. Some findings include, (i) phase separation in immiscible fluid flow through a medium with no barrier particles (porosity p P = 1). (ii) For the flow of miscible fluids through rigid porous medium with porosity close to percolation threshold (p C), the flux density (measure of permeability) shows a power law increase ∝ (pC - p) mu with mu = 2.0, and the density profile is found to decay with height ∝ exp(-mA/Bh), consistent with the barometric height law. (iii) Sedimentation and driving of barrier particles in fluid flow through non-consolidated porous medium. This study involves developing computer simulation models with efficient serial and parallel codes, extensive data analysis via graphical utilities, and computer visualization techniques.

Oceanographic Interpretation of Apollo Photographs. Coastal Oceanographic and Sedimentologic Interpretation of Apollo 9 Space Photographs; Carolina's Continental Shelf, USA

NASA Technical Reports Server (NTRS)

Mairs, R. L.

1971-01-01

Apollo 9 photographs, color band separations, and oceanographic and meteorological data are used in the study of the origin, movement, and dissipation of masses of discolored water near the shores of North and South Carolina. A model has been developed incorporating jet theory, climatology, currents, surface temperatures, color separations, and other oceanographic data to explain the processes involved in the life cycle of the discolored water masses. Special treatment is afforded the Gulf Stream boundary definition and the Cape Hatteras oceanographic barrier.

Industrial Membrane Filtration and Short-bed Fractal Separation Systems for Separating Monomers from Heterogeneous Plant Material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kearney, M; Kochergin, V; Hess, R

2005-03-31

Large-scale displacement of petroleum will come from low-cost cellulosic feedstocks such as straw and corn stover crop residues. This project has taken a step toward making this projection a reality by reducing capital and energy costs, the two largest cost factors associated with converting cellulosic biomass to chemicals and fuels. The technology exists for using acid or enzyme hydrolysis processes to convert biomass feedstock (i.e., waste cellulose such as straw, corn stover, and wood) into their base monomeric sugar building blocks, which can, in turn, be processed into chemicals and fuels using a number of innovative fermentation technologies. However, whilemore » these processes are technically possible, practical and economic barriers make these processes only marginally feasible or not feasible at all. These barriers are due in part to the complexity and large fixed and recurring capital costs of unit operations including filtration, chromatographic separation, and ion exchange. This project was designed to help remove these barriers by developing and implementing new purification and separation technologies that will reduce the capital costs of the purification and chromatographic separation units by 50% to 70%. The technologies fundamental to these improvements are: (a) highly efficient clarification and purification systems that use screening and membrane filtration to eliminate suspended solids and colloidal material from feed streams and (b) fractal technology based chromatographic separation and ion exchange systems that can substitute for conventional systems but at much smaller size and cost. A non-hazardous ''raw sugar beet juice'' stream (75 to 100 gal/min) was used for prototype testing of these technologies. This raw beet juice stream from the Amalgamated Sugar LLC plant in Twin Falls, Idaho contained abrasive materials and membrane foulants. Its characteristics were representative of an industrial-scale heterogeneous plant extract/hydrolysis stream, and therefore was an ideal model system for developing new separation equipment. Subsequent testing used both synthetic acid hydrolysate and corn stover derived weak acid hydrolysate (NREL produced). A two-phased approach was used for the research and development described in this project. The first level of study involved testing the new concepts at the bench level. The bench-scale evaluations provided fundamental understanding of the processes, building and testing small prototype systems, and determining the efficiency of the novel processes. The second level of study, macro-level, required building larger systems that directly simulated industrial operations and provided validation of performance to minimize financial risk during commercialization. The project goals and scope included: (1) Development of low-capital alternatives to conventional crop-based purification/separation processes; and (2) Development of each process to the point that transition to commercial operation is low risk. The project reporting period was January 2001 to December 2004. This included a one year extension of the project (without additional funding).« less

A role for long chain myosin light chain kinase (MLCK-210) in microvascular hyperpermeability during severe burns.

PubMed

Reynoso, Rashell; Perrin, Rachel M; Breslin, Jerome W; Daines, Dayle A; Watson, Katherine D; Watterson, D Martin; Wu, Mack H; Yuan, Sarah

2007-11-01

Microvascular leakage has been implicated in the pathogenesis of multiple organ dysfunction during trauma. Previous studies suggest the involvement of myosin light chain (MLC) phosphorylation-triggered endothelial contraction in the development of microvascular hyperpermeability. Myosin light chain kinase (MLCK) plays a key role in the control of MLC-phosphorylation status; thus, it is thought to modulate barrier function through its regulation of intracellular contractile machinery. The aim of this study was to further investigate the endothelial mechanism of MLC-dependent barrier injury in burns, focusing on the long isoform of MLCK (MLCK-210) that has recently been identified as the predominant isoform expressed in vascular endothelial cells. An MLCK-210 knockout mouse model was subjected to third-degree scald burn covering 25% total body surface area. The mesenteric microcirculation was observed using intravital microscopy, and the microvascular permeability was assessed by measuring the transvenular flux of fluorescein isothiocyanate-albumin. In a separate experiment, in vivo mesenteric hydraulic conductivity (Lp) was measured using the modified Landis technique. The injury caused a profound microvascular leakage, as indicated by a 2-fold increase in albumin flux and 4-fold increase in Lp at the early stages, which was associated with a high mortality within the 24-h period. Compared with wild-type control, the MLCK-210-deficient mice displayed a significantly improved survival with a greatly attenuated microvascular hyperpermeability response to albumin and fluid. These results provide direct evidence for a role of MLCK-210 in mediating burn-induced microvascular barrier injury and validate MLCK-210 as a potential therapeutic target in the treatment of burn edema.

Lost opportunities to prevent early onset type 2 diabetes mellitus after a pregnancy complicated by gestational diabetes

PubMed Central

Bernstein, Judith A; McCloskey, Lois; Gebel, Christina M; Iverson, Ronald E; Lee-Parritz, Aviva

2016-01-01

Objectives Gestational diabetes mellitus (GDM) greatly increases the risk of developing diabetes in the decade after delivery, but few women receive appropriately timed postpartum glucose testing (PPGT) or a referral to primary care (PC) for continued monitoring. This qualitative study was designed to identify barriers and facilitators to testing and referral from patient and providers' perspectives. Methods We interviewed patients and clinicians in depth about knowledge, values, priorities, challenges, and recommendations for increasing PPGT rates and PC linkage. Interviews were coded with NVIVO data analysis software, and analyzed using an implementation science framework. Results Women reported motivation to address GDM for the health of the fetus. Most women did not anticipate future diabetes for themselves, and focused on delivery outcomes rather than future health risks. Patients sought and received reassurance from clinicians, and were unlikely to discuss early onset following GDM or preventive measures. PPGT barriers described by patients included provider not mentioning the test or setting it up, transportation difficulties, work responsibilities, fatigue, concerns about fasting while breastfeeding, and timing of the test after discharge from obstetrics, and no referral to PC for follow-up. Practitioners described limited communication among multiple care providers during pregnancy and delivery, systems issues, and separation of obstetrics from PC. Conclusions Patients' barriers to PPGT included low motivation for self-care, structural obstacles, and competing priorities. Providers reported the need to balance risk with reassurance, and identified systems failures related to test timing, limitations of electronic medical record systems (EMR), lack of referrals to PC, and inadequate communication between specialties. Prevention of early onset has great potential for medical cost savings and improvements in quality of life. PMID:27347422

Temporal and Spatial Comparisons of Underwater Sound Signatures of Different Reef Habitats in Moorea Island, French Polynesia.

PubMed

Bertucci, Frédéric; Parmentier, Eric; Berten, Laëtitia; Brooker, Rohan M; Lecchini, David

2015-01-01

As environmental sounds are used by larval fish and crustaceans to locate and orientate towards habitat during settlement, variations in the acoustic signature produced by habitats could provide valuable information about habitat quality, helping larvae to differentiate between potential settlement sites. However, very little is known about how acoustic signatures differ between proximate habitats. This study described within- and between-site differences in the sound spectra of five contiguous habitats at Moorea Island, French Polynesia: the inner reef crest, the barrier reef, the fringing reef, a pass and a coastal mangrove forest. Habitats with coral (inner, barrier and fringing reefs) were characterized by a similar sound spectrum with average intensities ranging from 70 to 78 dB re 1 μPa.Hz(-1). The mangrove forest had a lower sound intensity of 70 dB re 1 μPa.Hz(-1) while the pass was characterized by a higher sound level with an average intensity of 91 dB re 1 μPa.Hz(-1). Habitats showed significantly different intensities for most frequencies, and a decreasing intensity gradient was observed from the reef to the shore. While habitats close to the shore showed no significant diel variation in sound intensities, sound levels increased at the pass during the night and barrier reef during the day. These two habitats also appeared to be louder in the North than in the West. These findings suggest that daily variations in sound intensity and across-reef sound gradients could be a valuable source of information for settling larvae. They also provide further evidence that closely related habitats, separated by less than 1 km, can differ significantly in their spectral composition and that these signatures might be typical and conserved along the coast of Moorea.

Lost opportunities to prevent early onset type 2 diabetes mellitus after a pregnancy complicated by gestational diabetes.

PubMed

Bernstein, Judith A; McCloskey, Lois; Gebel, Christina M; Iverson, Ronald E; Lee-Parritz, Aviva

2016-01-01

Gestational diabetes mellitus (GDM) greatly increases the risk of developing diabetes in the decade after delivery, but few women receive appropriately timed postpartum glucose testing (PPGT) or a referral to primary care (PC) for continued monitoring. This qualitative study was designed to identify barriers and facilitators to testing and referral from patient and providers' perspectives. We interviewed patients and clinicians in depth about knowledge, values, priorities, challenges, and recommendations for increasing PPGT rates and PC linkage. Interviews were coded with NVIVO data analysis software, and analyzed using an implementation science framework. Women reported motivation to address GDM for the health of the fetus. Most women did not anticipate future diabetes for themselves, and focused on delivery outcomes rather than future health risks. Patients sought and received reassurance from clinicians, and were unlikely to discuss early onset following GDM or preventive measures. PPGT barriers described by patients included provider not mentioning the test or setting it up, transportation difficulties, work responsibilities, fatigue, concerns about fasting while breastfeeding, and timing of the test after discharge from obstetrics, and no referral to PC for follow-up. Practitioners described limited communication among multiple care providers during pregnancy and delivery, systems issues, and separation of obstetrics from PC. Patients' barriers to PPGT included low motivation for self-care, structural obstacles, and competing priorities. Providers reported the need to balance risk with reassurance, and identified systems failures related to test timing, limitations of electronic medical record systems (EMR), lack of referrals to PC, and inadequate communication between specialties. Prevention of early onset has great potential for medical cost savings and improvements in quality of life.

Pharmacokinetic study of mangiferin in rat plasma and retina using high-performance liquid chromatography

PubMed Central

Hou, Yunlong; Fan, Shengjun; Gu, Yuanqin; Yu, Xuhui; Li, Baoxin

2010-01-01

Purpose Although the naturally occurring antioxidant mangiferin has been widely used, it is not yet known whether it can cross the blood-retina barrier (BRB) and enter the eye. The purpose of this experiment was to investigate the ability of mangiferin to pass the blood-retina barrier. Methods Sprague–Dawley rats were used for biologic fluid sampling after intravenous administration of mangiferin at doses of 10, 25, and 50 mg/kg. Blood and retina samples were collected at different time points post-dose. High-performance liquid chromatography (HPLC) separation was conducted on a COSMOSIL 5C18—MS—II column (4.6 mm×250 mm, 5 μm) with a flow rate of 1.0 ml/min using a mobile phase comprised of methanol −2% glacial acetic acid (40:60 v:v). Results The HPLC method has proven suitable to determine the presence of mangiferin in the eye. The plasma concentration of mangiferin was dose dependent. Pharmacokinetic parameters of mangiferin in plasma after intravenous administration were fitted to the two-compartment model with the first-order elimination and first-order transfer between central and peripheral compartments. The concentration of mangiferin in the retina goes with that in the blood. Mangiferin concentrations in the retina reached 5.69±1.48 μg/ml 0.5 h after intravenous administration (50 mg/kg) and then dropped gradually to 0.30±0.02 μg/ml 5.0 h later. The eye–to-plasma concentration ratio was 2.80%. Conclusions Mangiferin can pass the blood-retina barrier after a single intravenous administration and may be a potential natural antioxidant in treating eye diseases. PMID:20806037

Thermotolerance and heat acclimation may share a common mechanism in humans

PubMed Central

Gillum, Trevor; Dokladny, Karol; Bedrick, Edward; Schneider, Suzanne; Moseley, Pope

2011-01-01

Thermotolerance and heat acclimation are key adaptation processes that have been hitherto viewed as separate phenomena. Here, we provide evidence that these processes may share a common basis, as both may potentially be governed by the heat shock response. We evaluated the effects of a heat shock response-inhibitor (quercetin; 2,000 mg/day) on established markers of thermotolerance [gastrointestinal barrier permeability, plasma TNF-α, IL-6, and IL-10 concentrations, and leukocyte heat shock protein 70 (HSP70) content]. Heat acclimation reduced body temperatures, heart rate, and physiological strain during exercise/heat stress) in male subjects (n = 8) completing a 7-day heat acclimation protocol. These same subjects completed an identical protocol under placebo supplementation (placebo). Gastrointestinal barrier permeability and TNF-α were increased on the 1st day of exercise/heat stress in quercetin; no differences in these variables were reported in placebo. Exercise HSP70 responses were increased, and plasma cytokines (IL-6, IL-10) were decreased on the 7th day of heat acclimation in placebo; with concomitant reductions in exercise body temperatures, heart rate, and physiological strain. In contrast, gastrointestinal barrier permeability remained elevated, HSP70 was not increased, and IL-6, IL-10, and exercise body temperatures were not reduced on the 7th day of heat acclimation in quercetin. While exercise heart rate and physiological strain were reduced in quercetin, this occurred later in exercise than with placebo. Consistent with the concept that thermotolerance and heat acclimation are related through the heat shock response, repeated exercise/heat stress increases cytoprotective HSP70 and reduces circulating cytokines, contributing to reductions in cellular and systemic markers of heat strain. Exercising under a heat shock response-inhibitor prevents both cellular and systemic heat adaptations. PMID:21613575

Current barriers and potential strategies to increase the use of long-acting reversible contraception (LARC) to reduce the rate of unintended pregnancies in Australia: An expert roundtable discussion.

PubMed

Mazza, Danielle; Bateson, Deborah; Frearson, Meredith; Goldstone, Philip; Kovacs, Gab; Baber, Rod

2017-04-01

Australia's abortion rates are among the highest in the developed world. Efficacy of the most commonly used form of contraception (oral contraceptives and condoms) relies on regular user compliance. Long-acting reversible contraception (LARC) virtually eradicates contraceptive failure as it is not user-dependent; however, its uptake has been low. To provide an overview of barriers to LARC use in Australia and potential strategies to overcome these barriers. A roundtable of Australian experts was convened to share clinical perspectives and to explore the barriers and potential strategies to increase LARC use. Three broad barriers to LARC uptake were identified. (i) A paucity of Australian research exists that impedes closure of evidence gaps regarding contraceptive prescription and use. Systematic data collection is required. (ii) Within primary care, lack of familiarity with LARC and misperceptions about its use, lack of access to general practitioners (GPs) trained in LARC insertion/removal and affordability impede LARC uptake. Potential strategies to encourage LARC use include, GP education to promote informed choice by women, training in LARC insertions/removals, effective funding models for nurses to perform LARC insertions/removals, and rapid referral pathways. (iii) At the health system level, primary care incentives to provide LARC to women and health economic analyses to inform government policy changes are required. Although LARC decreases unintended pregnancies by eliminating user compliance issues, its uptake is low in Australia. Strategies that promote LARC uptake by targeting specific barriers may effectively reduce Australia's high unintended pregnancy rate. © 2017 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists.

Field programmable chemistry: integrated chemical and electronic processing of informational molecules towards electronic chemical cells.

PubMed

Wagler, Patrick F; Tangen, Uwe; Maeke, Thomas; McCaskill, John S

2012-07-01

The topic addressed is that of combining self-constructing chemical systems with electronic computation to form unconventional embedded computation systems performing complex nano-scale chemical tasks autonomously. The hybrid route to complex programmable chemistry, and ultimately to artificial cells based on novel chemistry, requires a solution of the two-way massively parallel coupling problem between digital electronics and chemical systems. We present a chemical microprocessor technology and show how it can provide a generic programmable platform for complex molecular processing tasks in Field Programmable Chemistry, including steps towards the grand challenge of constructing the first electronic chemical cells. Field programmable chemistry employs a massively parallel field of electrodes, under the control of latched voltages, which are used to modulate chemical activity. We implement such a field programmable chemistry which links to chemistry in rather generic, two-phase microfluidic channel networks that are separated into weakly coupled domains. Electric fields, produced by the high-density array of electrodes embedded in the channel floors, are used to control the transport of chemicals across the hydrodynamic barriers separating domains. In the absence of electric fields, separate microfluidic domains are essentially independent with only slow diffusional interchange of chemicals. Electronic chemical cells, based on chemical microprocessors, exploit a spatially resolved sandwich structure in which the electronic and chemical systems are locally coupled through homogeneous fine-grained actuation and sensor networks and play symmetric and complementary roles. We describe how these systems are fabricated, experimentally test their basic functionality, simulate their potential (e.g. for feed forward digital electrophoretic (FFDE) separation) and outline the application to building electronic chemical cells. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Formation of superheavy elements in the capture of very heavy ions at high excitation energies

NASA Astrophysics Data System (ADS)

Royer, G.

2013-05-01

The potential barriers governing the reactions 58Fe+244Pu, 238U+64Ni, and 238U+72Ge have been determined from a liquid-drop model taking into account the proximity energy, shell energies, rotational energy, and deformation of the incoming nuclei in the quasimolecular shape valley. Double-humped potential barriers appear in these entrance channels. The external saddle-point corresponds to two touching ellipsoidal nuclei when the shell and pairing effects are taken into account, while the inner barrier is due to the shell effects at the vicinity of the spherical shape of the composite system. Between them, a large potential pocket exists and persists at very high angular momenta allowing the capture of very heavy ions at high excitation energies.

Genetic structure of the four wil tomato species in the Solanum peruvianum s.l. species complex

USDA-ARS?s Scientific Manuscript database

The most diverse wild tomato species Solanum peruvianum sensu lato (s.l.) has been reclassified into four separate species. However, reproductive barriers among the species are incomplete and this can lead to discrepancies regarding genetic identity of germplasm. We used genotyping by sequencing (...

78 FR 11266 - Agency Information Collection Activities: Request for Comments for a New Information Collection

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-15

... Inspection Protocol for Reinforced Concrete Highway Barriers and Bridge Railings. Background: Highway... separations. Most bridge railings are made of reinforced concrete. Despite the important role that they play... Federal Highway Administration concerning Non- Destructive Evaluation of concrete bridge railings. One of...

Nonthermal plasma system for extending shelf life of raw broiler breast fillets

USDA-ARS?s Scientific Manuscript database

A nonthermal dielectric barrier discharge (DBD) plasma system was developed and enhanced to treat broiler breast fillets (BBF) in order to improve the microbial quality of the meat. The system consisted of a high-voltage source and two parallel, round-aluminum electrodes separated by three semi-rig...

46 CFR 28.380 - General structural fire protection.

Code of Federal Regulations, 2012 CFR

2012-10-01

... and a machinery or a fuel tank storage space must be sealed. (d) Paint and flammable liquid lockers... combustible liquids or vapors are present, e.g., machinery spaces and paint lockers, a vapor barrier which...-1. (c) Separation of machinery and fuel tank spaces from accommodation spaces. (1) Each...

46 CFR 28.380 - General structural fire protection.

Code of Federal Regulations, 2011 CFR

2011-10-01

... and a machinery or a fuel tank storage space must be sealed. (d) Paint and flammable liquid lockers... combustible liquids or vapors are present, e.g., machinery spaces and paint lockers, a vapor barrier which...-1. (c) Separation of machinery and fuel tank spaces from accommodation spaces. (1) Each...

46 CFR 28.380 - General structural fire protection.

Code of Federal Regulations, 2013 CFR

2013-10-01

... and a machinery or a fuel tank storage space must be sealed. (d) Paint and flammable liquid lockers... combustible liquids or vapors are present, e.g., machinery spaces and paint lockers, a vapor barrier which...-1. (c) Separation of machinery and fuel tank spaces from accommodation spaces. (1) Each...

46 CFR 28.380 - General structural fire protection.

Code of Federal Regulations, 2014 CFR

2014-10-01

... and a machinery or a fuel tank storage space must be sealed. (d) Paint and flammable liquid lockers... combustible liquids or vapors are present, e.g., machinery spaces and paint lockers, a vapor barrier which...-1. (c) Separation of machinery and fuel tank spaces from accommodation spaces. (1) Each...

Letting Go: Separation-Individuation in a Wife of an Alzheimer's Patient.

ERIC Educational Resources Information Center

Gwyther, Lisa P.

1990-01-01

Describes an intermittent, focused social work intervention to help overcome personal and intrapsychic barriers to using available help for wives of Alzheimer's patients. Discusses therapeutic goals, common themes, and implications for practice with caregiving wives with specific attention to supporting the wife in her wish to "responsibly…

Dynamics of House Sparrows (Passer domesticus) in Newcastle disease virus transmission within the avifaunal-poultry interface: an epidemiological modeling approach

USDA-ARS?s Scientific Manuscript database

As emerging and persistent pathogens increase in prevalence, the agriculture-wildlife interface has been identified as a field requiring further research. Acceleration of wildlife urbanization, exotic species introductions, and habitat encroachment are disrupting barriers that once separated microb...

The Impact of Immigration Enforcement Strategies on Infants and Toddlers

ERIC Educational Resources Information Center

Capps, Randy; Calderon, Miriam; Chaudry, Ajay

2008-01-01

Researchers, advocates, and community agencies are beginning to question the impact of U.S. immigration enforcement strategies on very young children. In particular, immigration raids may suddenly and sometimes violently separate children from their parents, place them in unstable living environments, and create barriers to accessing needed…

Systematic study of the fusion barriers using different proximity-type potentials for N=Z colliding nuclei: New extensions

NASA Astrophysics Data System (ADS)

Dutt, Ishwar; Puri, Rajeev K.

2010-04-01

By using 14 different versions and parametrizations of a proximity potential and two new versions of the potential proposed in this paper, we perform a comparative study of fusion barriers by studying 26 symmetric reactions. The mass asymmetry ηA=((A2-A1)/(A2+A1)), however, is very large. Our detailed investigation reveals that most of the proximity potentials reproduce experimental data within ±8% on average. A comparison of fusion cross sections indicates that Bass 80, AW 95, and Denisov DP potentials have a better edge than other potentials. We also propose new versions of the proximity potential as well as Denisov parametrized potential. These new versions improve agreement with the data.

Use of separate ZnTe interface layers to form ohmic contacts to p-CdTe films

DOEpatents

Gessert, T.A.

1999-06-01

A method of is disclosed improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurium-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact. 11 figs.

Use of separate ZnTe interface layers to form OHMIC contacts to p-CdTe films

DOEpatents

Gessert, Timothy A.

1999-01-01

A method of improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurim-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact.

Superconducting spin valves controlled by spiral re-orientation in B20-family magnets

NASA Astrophysics Data System (ADS)

Pugach, N. G.; Safonchik, M.; Champel, T.; Zhitomirsky, M. E.; Lähderanta, E.; Eschrig, M.; Lacroix, C.

2017-10-01

We propose a superconducting spin-triplet valve, which consists of a superconductor and an itinerant magnetic material, with the magnet showing an intrinsic non-collinear order characterized by a wave vector that may be aligned in a few equivalent preferred directions under the control of a weak external magnetic field. Re-orienting the spiral direction allows one to controllably modify long-range spin-triplet superconducting correlations, leading to spin-valve switching behavior. Our results indicate that the spin-valve effect may be noticeable. This bilayer may be used as a magnetic memory element for cryogenic nanoelectronics. It has the following advantages in comparison to superconducting spin valves proposed previously: (i) it contains only one magnetic layer, which may be more easily fabricated and controlled; (ii) its ground states are separated by a potential barrier, which solves the "half-select" problem of the addressed switch of memory elements.

Alternating evolutionary pressure in a genetic algorithm facilitates protein model selection

PubMed Central

Offman, Marc N; Tournier, Alexander L; Bates, Paul A

2008-01-01

Background Automatic protein modelling pipelines are becoming ever more accurate; this has come hand in hand with an increasingly complicated interplay between all components involved. Nevertheless, there are still potential improvements to be made in template selection, refinement and protein model selection. Results In the context of an automatic modelling pipeline, we analysed each step separately, revealing several non-intuitive trends and explored a new strategy for protein conformation sampling using Genetic Algorithms (GA). We apply the concept of alternating evolutionary pressure (AEP), i.e. intermediate rounds within the GA runs where unrestrained, linear growth of the model populations is allowed. Conclusion This approach improves the overall performance of the GA by allowing models to overcome local energy barriers. AEP enabled the selection of the best models in 40% of all targets; compared to 25% for a normal GA. PMID:18673557

Character displacement of Cercopithecini primate visual signals

PubMed Central

Allen, William L.; Stevens, Martin; Higham, James P.

2014-01-01

Animal visual signals have the potential to act as an isolating barrier to prevent interbreeding of populations through a role in species recognition. Within communities of competing species, species recognition signals are predicted to undergo character displacement, becoming more visually distinctive from each other, however this pattern has rarely been identified. Using computational face recognition algorithms to model primate face processing, we demonstrate that the face patterns of guenons (tribe: Cercopithecini) have evolved under selection to become more visually distinctive from those of other guenon species with whom they are sympatric. The relationship between the appearances of sympatric species suggests that distinguishing conspecifics from other guenon species has been a major driver of diversification in guenon face appearance. Visual signals that have undergone character displacement may have had an important role in the tribe’s radiation, keeping populations that became geographically separated reproductively isolated on secondary contact. PMID:24967517

Modular Chemical Process Intensification: A Review.

PubMed

Kim, Yong-Ha; Park, Lydia K; Yiacoumi, Sotira; Tsouris, Costas

2017-06-07

Modular chemical process intensification can dramatically improve energy and process efficiencies of chemical processes through enhanced mass and heat transfer, application of external force fields, enhanced driving forces, and combinations of different unit operations, such as reaction and separation, in single-process equipment. These dramatic improvements lead to several benefits such as compactness or small footprint, energy and cost savings, enhanced safety, less waste production, and higher product quality. Because of these benefits, process intensification can play a major role in industrial and manufacturing sectors, including chemical, pulp and paper, energy, critical materials, and water treatment, among others. This article provides an overview of process intensification, including definitions, principles, tools, and possible applications, with the objective to contribute to the future development and potential applications of modular chemical process intensification in industrial and manufacturing sectors. Drivers and barriers contributing to the advancement of process intensification technologies are discussed.

Modular Chemical Process Intensification: A Review

DOE PAGES

Kim, Yong-ha; Park, Lydia K.; Yiacoumi, Sotira; ...

2016-06-24

Modular chemical process intensification can dramatically improve energy and process efficiencies of chemical processes through enhanced mass and heat transfer, application of external force fields, enhanced driving forces, and combinations of different unit operations, such as reaction and separation, in single-process equipment. Dramatic improvements such as these lead to several benefits such as compactness or small footprint, energy and cost savings, enhanced safety, less waste production, and higher product quality. Because of these benefits, process intensification can play a major role in industrial and manufacturing sectors, including chemical, pulp and paper, energy, critical materials, and water treatment, among others. Thismore » article provides an overview of process intensification, including definitions, principles, tools, and possible applications, with the objective to contribute to the future development and potential applications of modular chemical process intensification in industrial and manufacturing sectors. Drivers and barriers contributing to the advancement of process intensification technologies are discussed.« less

Individual electron and hole localization in submonolayer InN quantum sheets embedded in GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feix, F., E-mail: feix@pdi-berlin.de; Flissikowski, T.; Chèze, C.

2016-07-25

We investigate sub-monolayer InN quantum sheets embedded in GaN(0001) by temperature-dependent photoluminescence spectroscopy under both continuous-wave and pulsed excitation. Both the peak energy and the linewidth of the emission band associated with the quantum sheets exhibit an anomalous dependence on temperature indicative of carrier localization. Photoluminescence transients reveal a power law decay at low temperatures reflecting that the recombining electrons and holes occupy spatially separate, individual potential minima reminiscent of conventional (In,Ga)N(0001) quantum wells exhibiting the characteristic disorder of a random alloy. At elevated temperatures, carrier delocalization sets in and is accompanied by a thermally activated quenching of the emission.more » We ascribe the strong nonradiative recombination to extended states in the GaN barriers and confirm our assumption by a simple rate-equation model.« less

Biopolymer Aerogels and Foams: Chemistry, Properties, and Applications.

PubMed

Zhao, Shanyu; Malfait, Wim J; Guerrero-Alburquerque, Natalia; Koebel, Matthias M; Nyström, Gustav

2018-06-25

Biopolymer aerogels were among the first aerogels produced, but only in the last decade has research on biopolymer and biopolymer-composite aerogels become popular, motivated by sustainability arguments, their unique and tunable properties, and ease of functionalization. Biopolymer aerogels and open-cell foams have great potential for classical aerogel applications such as thermal insulation, as well as emerging applications in filtration, oil-water separation, CO 2 capture, catalysis, and medicine. The biopolymer aerogel field today is driven forward by empirical materials discovery at the laboratory scale, but requires a firmer theoretical basis and pilot studies to close the gap to market. This Review includes a database with over 3800 biopolymer aerogel properties, evaluates the state of the biopolymer aerogel field, and critically discusses the scientific, technological, and commercial barriers to the commercialization of these exciting materials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of infection-control barriers on the light intensity of light-cure units and depth of cure of composite.

PubMed

Hodson, Nicholas A; Dunne, Stephen M; Pankhurst, Caroline L

2005-04-01

Dental curing lights are vulnerable to contamination with oral fluids during routine intra-oral use. This controlled study aimed to evaluate whether or not disposable transparent barriers placed over the light-guide tip would affect light output intensity or the subsequent depth of cure of a composite restoration. The impact on light intensity emitted from high-, medium- and low-output light-cure units in the presence of two commercially available disposable infection-control barriers was evaluated against a no-barrier control. Power density measurements from the three intensity light-cure units were recorded with a radiometer, then converted to a digital image using an intra-oral camera and values determined using a commercial computer program. For each curing unit, the measurements were repeated on ten separate occasions with each barrier and the control. Depth of cure was evaluated using a scrape test in a natural tooth model. At each level of light output, the two disposable barriers produced a significant reduction in the mean power density readings compared to the no-barrier control (P<0.005). The cure sleeve inhibited light output to a greater extent than either the cling film or the control (P<0.005). Only composite restorations light-activated by the high level unit demonstrated a small but significant decrease in the depth of cure compared to the control (P<0.05). Placing disposable barriers over the light-guide tip reduced the light intensity from all three curing lights. There was no impact on depth of cure except for the high-output light, where a small decrease in cure depth was noted but this was not considered clinically significant. Disposable barriers can be recommended for use with light-cure lights.

Effect of cross infection control barriers used on the light-curing device tips on the cure depth of a resin composite

PubMed Central

de Moraes Porto, Isabel Cristina Celerino; Ramos de Brito, Andréia Cristina; Parolia, Abhishek

2013-01-01

Background: Among the advice on prevent cross-infection was included usage of mechanical barriers on tips of photoactivation units. However, questions about the use of protective barriers placed on the light-curing unit's tips and the possibility of interference with the ability of guaranteeing an effective polymerization of composite resins need to be clarified. Aims: The aim of this study was to evaluate the effect of cross infection control barriers used on the light-curing device tips on the cure depth of composite resin. Materials and Methods: Power density measurements from the light-cure unit were recorded with a radiometer on ten separate occasions with different types and placement modes of each barrier (low-density polyethylene and polyvinyl chloride (PVC) film – smooth and folds) and no-barrier (control). Cure depth of TPH™ Spectrum™ resin, A2-A4, was evaluated by the scraping test. Statistical Analysis: The data were analyzed using Student's t-test or ANOVA one-way with Tukey's test (α =0.05). Results: Same type of barrier and different shades (A2, A4) of composite exhibited significant difference in the cure depth among all groups (P < 0.05). Both low-density polyethylene and PVC film folded barriers produced a significant reduction in the light intensity (P < 0.05). Conclusions: Regarding the resin shade, there was a significant reduction in the cure depth of A4 composite resin (dark shade) but this reduction is not enough to cause any adverse effect on the material's clinical performance. Therefore, disposable barriers can be recommended for use over the end of the light guide. PMID:23833455

Placing barrier-island transgression in a blue-carbon context

NASA Astrophysics Data System (ADS)

Theuerkauf, Ethan J.; Rodriguez, Antonio B.

2017-07-01

Backbarrier saltmarshes are considered carbon sinks; however, barrier island transgression and the associated processes of erosion and overwash are typically not included in coastal carbon budgets. Here, we present a carbon-budget model for transgressive barrier islands that includes a dynamic carbon-storage term, driven by backbarrier-marsh width, and a carbon-export term, driven by ocean and backbarrier shoreline erosion. To examine the impacts of storms, human disturbances and the backbarrier setting of a transgressive barrier island on carbon budgets and reservoirs, the model was applied to sites at Core Banks and Onslow Beach, NC, USA. Results show that shoreline erosion and burial of backbarrier marsh from washover deposition and dredge-spoil disposal temporarily transitioned each site into a net exporter (source) of carbon. The magnitude of the carbon reservoir was linked to the backbarrier setting of an island. Carbon reservoirs of study sites separated from the mainland by only backbarrier marsh (no lagoon) decreased for over a decade because carbon storage could not keep pace with erosion. With progressive narrowing of the backbarrier marsh, these barriers will begin to function more persistently as carbon sources until the reservoir is depleted at the point where the barrier welds with the mainland. Undeveloped barrier islands with wide lagoons are carbon sources briefly during erosive periods; however, at century time scales are net carbon importers (sinks) because new marsh habitat can form during barrier rollover. Human development on backbarrier saltmarsh serves to reduce the carbon storage capacity and can hasten the transition of an island from a sink to a source.

Two-terminal charge tunneling: Disentangling Majorana zero modes from partially separated Andreev bound states in semiconductor-superconductor heterostructures

NASA Astrophysics Data System (ADS)

Moore, Christopher; Stanescu, Tudor D.; Tewari, Sumanta

2018-04-01

We show that a pair of overlapping Majorana bound states (MBSs) forming a partially separated Andreev bound state (ps-ABS) represents a generic low-energy feature in spin-orbit-coupled semiconductor-superconductor (SM-SC) hybrid nanowire in the presence of a Zeeman field. The ps-ABS interpolates continuously between the "garden variety" ABS, which consists of two MBSs sitting on top of each other, and the topologically protected Majorana zero modes (MZMs), which are separated by a distance given by the length of the wire. The really problematic ps-ABSs consist of component MBSs separated by a distance of the order of the characteristic Majorana decay length ξ , and have nearly zero energy in a significant range of control parameters, such as the Zeeman field and chemical potential, within the topologically trivial phase. Despite being topologically trivial, such ps-ABSs can generate signatures identical to MZMs in local charge tunneling experiments. In particular, the height of the zero-bias conductance peak (ZBCP) generated by ps-ABSs has the quantized value 2 e2/h , and it can remain unchanged in an extended range of experimental parameters, such as Zeeman field and the tunnel barrier height. We illustrate the formation of such low-energy robust ps-ABSs in two experimentally relevant situations: a hybrid SM-SC system consisting of a proximitized nanowire coupled to a quantum dot and the SM-SC system in the presence of a spatially varying inhomogeneous potential. We then show that, unlike local measurements, a two-terminal experiment involving charge tunneling at both ends of the wire is capable of distinguishing between the generic ps-ABSs and the non-Abelian MZMs. While the MZMs localized at the opposite ends of the wire generate correlated differential conduction spectra, including correlations in energy splittings and critical Zeeman fields associated with the emergence of the ZBCPs, such correlations are absent if the ZBCPs are due to ps-ABSs emerging in the topologically trivial phase. Measuring such correlations is the clearest and most straightforward test of topological MZMs in SM-SC heterostructures that can be done in a currently accessible experimental setup.

Facilitators and Barriers to Preparedness Partnerships: A Veterans Affairs Medical Center Perspective.

PubMed

Schmitz, Susan; Wyte-Lake, Tamar; Dobalian, Aram

2017-09-13

This study sought to understand facilitators and barriers faced by local US Department of Veterans Affairs Medical Center (VAMC) emergency managers (EMs) when collaborating with non-VA entities. Twelve EMs participated in semi-structured interviews lasting 60 to 90 minutes discussing their collaboration with non-VAMC organizations. Sections of the interview transcripts concerning facilitators and barriers to collaboration were coded and analyzed. Common themes were organized into 2 categories: (1) internal (ie, factors affecting collaboration from within VAMCs or by VA policy) and (2) external (ie, interagency or interpersonal factors). Respondents reported a range of facilitators and barriers to collaboration with community-based agencies. Internal factors facilitating collaboration included items such as leadership support. An internal barrier example included lack of clarity surrounding the VAMC's role in community disaster response. External factors noted as facilitators included a shared goal across organizations while a noted barrier was a perception that potential partners viewed a VAMC partnership with skepticism. Federal institutions are important partners for the success of community disaster preparedness and response. Understanding the barriers that VAMCs confront, as well as potential facilitators to collaboration, should enhance the development of VAMC-community partnerships and improve community health resilience. (Disaster Med Public Health Preparedness. 2017; page 1 of 6).

Sociodemographic inequalities in barriers to cancer pain management: a report from the American Cancer Society's Study of Cancer Survivors-II (SCS-II).

PubMed

Stein, Kevin D; Alcaraz, Kassandra I; Kamson, Chelsey; Fallon, Elizabeth A; Smith, Tenbroeck G

2016-10-01

Research has increasingly documented sociodemographic inequalities in the assessment and management of cancer-related pain. Most studies have focused on racial/ethnic disparities, while less is known about the impact of other sociodemographic factors, including age and education. We analyzed data from a large, national, population-based study of cancer survivors to examine the influence of sociodemographic factors, and physical and mental health comorbidities on barriers to cancer pain management. The study included data from 4707 cancer survivors in the American Cancer Society's Study of Cancer Survivors-II, who reported experiencing pain from their cancer. A multilevel, socioecological, conceptual framework was used to generate a list of 15 barriers to pain management, representing patient, provider, and system levels. Separate multivariable logistic regressions for each barrier identified sociodemographic and health-related inequalities in cancer pain management, controlling for years since diagnosis, disease stage, and cancer treatment. Two-thirds of survivors reported at least 1 barrier to pain management. While patient-related barriers were most common, the greatest disparities were noted in provider- and system-level barriers. Specifically, inequalities by race/ethnicity, education, age, and physical and mental health comorbidities were observed. Findings indicate survivors who were nonwhite, less educated, older, and/or burdened by comorbidities were most adversely affected. Future efforts in research, clinical practice, and policy should identify and/or implement new strategies to address sociodemographic inequalities in cancer pain management. Copyright © 2016 John Wiley & Sons, Ltd.

Self-efficacy toward physical activity and the physical activity behavior of children with and without Developmental Coordination Disorder.

PubMed

Batey, C A; Missiuna, C A; Timmons, B W; Hay, J A; Faught, B E; Cairney, J

2014-08-01

Affecting 5-6% of children, Developmental Coordination Disorder (DCD) is a prevalent chronic condition. The nature of the disorder - impaired motor coordination - makes avoidance of physical activity (PA) common. The purpose of this study was to examine the effect of barrier and task self-efficacy on PA behavior in children with DCD and a group of typically developing (TD) children. Children were compared on their perceived ability to complete different intensities and duration of PA (task efficacy) and their confidence in completing PA when faced with everyday barriers (barrier efficacy). An accelerometer was used to record their activity over the subsequent week. Children with DCD were found to have significantly lower task efficacy and barrier efficacy. They also spent significantly less time in moderate to vigorous physical activity (MVPA). Multivariate analyses revealed that gender modified the relationship for both groups. Separate multivariate regressions, were therefore conducted by gender. A direct effect of DCD on PA was observed for boys, but not for girls. Further analyses showed that neither task efficacy nor barrier efficacy influenced the relationship between DCD and PA. Results from this study confirm that children with DCD have lower task and barrier self-efficacy than TD children and that males have lower PA levels than their TD peers; however neither task or barrier self-efficacy mediated the relationship between DCD and PA. Copyright © 2013. Published by Elsevier B.V.

Chasing boundaries and cascade effects in a coupled barrier - marshes - lagoon system

NASA Astrophysics Data System (ADS)

Lorenzo Trueba, J.; Mariotti, G.

2015-12-01

Low-lying coasts are often characterized by barriers islands, shore-parallel stretches of sand separated from the mainland by marshes and lagoons. We built an exploratory numerical model to examine the morphological feedbacks within an idealized barrier - marshes -lagoon system and predict its evolution under projected rates of sea level rise and sediment supply to the backbarrier environment. Our starting point is a recently developed morphodynamic model, which couples shoreface evolution and overwash processes in a dynamic framework. As such, the model is able to capture dynamics not reproduced by morphokinematic models, which advect geometries without specific concern to processes. These dynamics include periodic barrier retreat due to time lags in the shoreface response to barrier overwash, height drowning due to insufficient overwash fluxes as sea level rises, and width drowning, which occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash-driven landward migration. We extended the model by coupling the barrier model with a model for the evolution of the marsh platform and the boundary between the marsh and the adjacent lagoon. The coupled model explicitly describes marsh edge processes and accounts for the modification of the wave regime associated with lagoon width (fetch). Model results demonstrate that changes in factors that are not typically associated with the dynamics of coastal barriers, such as the lagoon width and the rate of export/import of sediments from and to the lagoon, can lead to previously unidentified complex responses of the coupled system. In particular, a wider lagoon in the backbarrier, and/or a reduction in the supply of muddy sediments to the backbarrier, can increase barrier retreat rates and even trigger barrier drowning. Overall, our findings highlight the importance of incorporating backbarrier dynamics in models that aim at predicting the response of barrier systems.

Review of Graphene as a Solid State Diffusion Barrier.

PubMed

Morrow, Wayne K; Pearton, Stephen J; Ren, Fan

2016-01-06

Conventional thin-film diffusion barriers consist of 3D bulk films with high chemical and thermal stability. The purpose of the barrier material is to prevent intermixing or penetration from the two materials that encase it. Adhesion to both top and bottom materials is critical to the success of the barrier. Here, the effectiveness of a single atomic layer of graphene as a solid-state diffusion barrier for common metal schemes used in microelectronics is reviewed, and specific examples are discussed. Initial studies of electrical contacts to graphene show a distinct separation in behavior between metallic groups that strongly or weakly bond to it. The two basic classes of metal reactions with graphene are either physisorbed metals, which bond weakly with graphene, or chemisorbed metals, which bond strongly to graphene. For graphene diffusion barrier testing on Si substrates, an effective barrier can be achieved through the formation of a carbide layer with metals that are chemisorbed. For physisorbed metals, the barrier failure mechanism is loss of adhesion at the metal–graphene interface. A graphene layer encased between two metal layers, in certain cases, can increase the binding energy of both films with graphene, however, certain combinations of metal films are detrimental to the bonding with graphene. While the prospects for graphene's future as a solid-state diffusion barrier are positive, there are open questions, and areas for future research are discussed. A better understanding of the mechanisms which influence graphene's ability to be an effective diffusion barrier in microelectronic applications is required, and additional experiments are needed on a broader range of metals, as well as common metal stack contact structures used in microelectronic applications. The role of defects in the graphene is also a key area, since they will probably influence the barrier properties. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of Complex Structured Anodic Oxide Dielectric Layer Grown in Pore Matrix for Aluminum Capacitor.

PubMed

Shin, Jin-Ha; Yun, Sook Young; Lee, Chang Hyoung; Park, Hwa-Sun; Suh, Su-Jeong

2015-11-01

Anodization of aluminum is generally divided up into two types of anodic aluminum oxide structures depending on electrolyte type. In this study, an anodization process was carried out in two steps to obtain high dielectric strength and break down voltage. In the first step, evaporated high purity Al on Si wafer was anodized in oxalic acidic aqueous solution at various times at a constant temperature of 5 degrees C. In the second step, citric acidic aqueous solution was used to obtain a thickly grown sub-barrier layer. During the second anodization process, the anodizing potential of various ranges was applied at room temperature. An increased thickness of the sub-barrier layer in the porous matrix was obtained according to the increment of the applied anodizing potential. The microstructures and the growth of the sub-barrier layer were then observed with an increasing anodizing potential of 40 to 300 V by using a scanning electron microscope (SEM). An impedance analyzer was used to observe the change of electrical properties, including the capacitance, dissipation factor, impedance, and equivalent series resistance (ESR) depending on the thickness increase of the sub-barrier layer. In addition, the breakdown voltage was measured. The results revealed that dielectric strength was improved with the increase of sub-barrier layer thickness.

Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

NASA Astrophysics Data System (ADS)

Good, Brian

2015-03-01

Ytterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the diffusion of oxygen and water vapor through these coatings is undesirable if high temperature corrosion is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated oxygen diffusion in Ytterbium Disilicate. Oxygen vacancy site energies and diffusion barrier energies are computed using Density Functional Theory. We find that many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small in the pure material, with the result that the material is unlikely to exhibit significant oxygen permeability.

The barriers to and benefits of conducting Q-sorts in the classroom.

PubMed

Killam, Laura; Timmermans, Katherine E; Raymond, June M

2013-11-01

To outline the barriers to and benefits of using Q methodology in a classroom. Q methodology has been established as a systematic way to measure subjectivity that is consistent with the naturalistic paradigm. While it is often confused with quantitative methods, it provides the qualitative researcher with powerful tools to investigate the diverse subjective experiences and perceptions of participants. Reflections in this paper stem from the experiences of the authors and are supported by literature. Barriers to conducting a Q-sort activity in the classroom are context dependent and may include limitations of the environment, time constraints as well as issues with comprehension. Despite these barriers, using a classroom for the activity can also enhance student learning, increase participation in research, clarify instructions, enrich study feedback and promote accessibility of the study population. With an understanding of potential pitfalls of using this methodology in the classroom setting, nurse researchers can develop strategies to reduce these barriers and enhance the quality of future research. Q-methodology is an alternate way of measuring the subjective views of individuals in a variety of settings such as clinical practice, research and educational institutions. Q-sorts may be used for research and/or classroom activities because the activity can promote discussion related to the content of a class. If using an activity like this one, educators and researchers need to be mindful of potential barriers to sorting in order to minimise them and maximise the potential of the activity.

Enhanced Conformational Sampling of N-Glycans in Solution with Replica State Exchange Metadynamics.

PubMed

Galvelis, Raimondas; Re, Suyong; Sugita, Yuji

2017-05-09

Molecular dynamics (MD) simulation of a N-glycan in solution is challenging because of high-energy barriers of the glycosidic linkages, functional group rotational barriers, and numerous intra- and intermolecular hydrogen bonds. In this study, we apply different enhanced conformational sampling approaches, namely, metadynamics (MTD), the replica-exchange MD (REMD), and the recently proposed replica state exchange MTD (RSE-MTD), to a N-glycan in solution and compare the conformational sampling efficiencies of the approaches. MTD helps to cross the high-energy barrier along the ω angle by utilizing a bias potential, but it cannot enhance sampling of the other degrees of freedom. REMD ensures moderate-energy barrier crossings by exchanging temperatures between replicas, while it hardly crosses the barriers along ω. In contrast, RSE-MTD succeeds to cross the high-energy barrier along ω as well as to enhance sampling of the other degrees of freedom. We tested two RSE-MTD schemes: in one scheme, 64 replicas were simulated with the bias potential along ω at different temperatures, while simulations of four replicas were performed with the bias potentials for different CVs at 300 K. In both schemes, one unbiased replica at 300 K was included to compute conformational properties of the glycan. The conformational sampling of the former is better than the other enhanced sampling methods, while the latter shows reasonable performance without spending large computational resources. The latter scheme is likely to be useful when a N-glycan-attached protein is simulated.

Results of an Assessment to Identify Potential Barriers to Sustainable Agriculture on American Indian Reservations in the Western United States

ERIC Educational Resources Information Center

Singletary, Loretta; Emm, Staci; Brummer, Fara Ann; Hill, George C.; Lewis, Steve; Hebb, Vicki

2016-01-01

Purpose: This paper reports the results of survey research conducted with tribal producers between 2011 and 2012 on 19 of the largest American Indian reservations in Idaho, Nevada, North Dakota, Oregon, South Dakota, and Washington. The purpose of the research was to identify potential barriers to sustainable agriculture on reservation lands. This…

Crossing the Barriers: An Analysis of Land Access Barriers to Geothermal Development and Potential Improvement Scenarios

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levine, Aaron L; Young, Katherine R

Developers have identified many non-technical barriers to geothermal power development, including access to land. Activities required for accessing land, such as environmental review and private and public leasing can take a considerable amount of time and can delay or prevent project development. This paper discusses the impacts to available geothermal resources and deployment caused by land access challenges, including tribal and cultural resources, environmentally sensitive areas, biological resources, land ownership, federal and state lease queues, and proximity to military installations. In this analysis, we identified challenges that have the potential to prevent development of identified and undiscovered hydrothermal geothermal resources.more » We found that an estimated 400 MW of identified geothermal resource potential and 4,000 MW of undiscovered geothermal resource potential were either unallowed for development or contained one or more significant barriers that could prevent development at the site. Potential improvement scenarios that could be employed to overcome these barriers include (1) providing continuous funding to the U.S. Forest Service (USFS) for processing geothermal leases and permit applications and (2) the creation of advanced environmental mitigation measures. The model results forecast that continuous funding to the USFS could result in deployment of an additional 80 MW of geothermal capacity by 2030 and 124 MW of geothermal capacity by 2050 when compared to the business-as-usual scenario. The creation of advanced environmental mitigation measures coupled with continuous funding to the USFS could result in deployment of an additional 97 MW of geothermal capacity by 2030 and 152 MW of geothermal capacity by 2050 when compared to the business-as-usual scenario. The small impact on potential deployment in these improvement scenarios suggests that these 4,400 MW have other barriers to development in addition to land access. In other words, simply making more resources available for development does not increase deployment; however, impacts to deployment could increase when coupled with other improvements (e.g., permitting, market and/or technology improvements).« less

On the persistence of reproductive barriers in Eucalyptus: the bridging of mechanical barriers to zygote formation by F1 hybrids is counteracted by intrinsic post-zygotic incompatibilities.

PubMed

Larcombe, Matthew J; Costa E Silva, João; Tilyard, Paul; Gore, Peter; Potts, Brad M

2016-09-01

Many previous studies conclude that pre-zygotic barriers such as mechanical isolation account for most reproductive isolation between pairs of taxa. However, the inheritance and persistence of barriers such as these after the first generation of hybridization is rarely quantified, even though it is a vital consideration in understanding gene flow potential. There is an asymmetrical pre-zygotic mechanical barrier to hybridization between Eucalyptus nitens and Eucalyptus globulus, which completely prevents small-flowered E. nitens pollen from mating with large E. globulus flowers, while the reverse cross is possible. We aimed to determine the relative importance of pre- and post-zygotic barriers in preventing gene flow following secondary contact between E. nitens and E. globulus, including the inheritance of barriers in advanced-generation hybrids. Experimental crossing was used to produce outcrossed E. nitens, E. globulus and their F1, F2, BCg and BCn hybrids. The strength and inheritance of a suite of pre- and post-zygotic barriers were assessed, including 20-year survival, growth and reproductive capacity. The mechanical barrier to hybridization was lost or greatly reduced in the F1 hybrid. In contrast, intrinsic post-zygotic barriers were strong and persistent. Line-cross analysis indicated that the outbreeding depression in the hybrids was best explained by epistatic loss. The removal of strong mechanical barriers between E. nitens and E. globulus allows F1 hybrids to act as a bridge for bi-directional gene flow between these species. However, strong and persistent post-zygotic barriers exist, meaning that wherever F1 hybridization does occur, intrinsic post-zygotic barriers will be responsible for most reproductive isolation in this system. This potential transient nature of mechanical barriers to zygote formation due to additive inheritance in hybrids appears under-appreciated, and highlights the often important role that intrinsic post-mating barriers play in maintaining species boundaries at zones of secondary contact. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

New capability for hazardous materials ID within sealed containers using a portable spatially offset Raman spectroscopy (SORS) device

NASA Astrophysics Data System (ADS)

Stokes, Robert J.; Bailey, Mike; Bonthron, Stuart; Stone, Thomas; Maskall, Guy; Presly, Oliver; Roy, Eric; Tombling, Craig; Loeffen, Paul W.

2016-10-01

Raman spectroscopy allows the acquisition of molecularly specific signatures of pure compounds and mixtures making it a popular method for material identification applications. In hazardous materials, security and counter terrorism applications, conventional handheld Raman systems are typically limited to operation by line-of-sight or through relatively transparent plastic bags / clear glass vials. If materials are concealed behind thicker, coloured or opaque barriers it can be necessary to open and take a sample. Spatially Offset Raman Spectroscopy (SORS)[1] is a novel variant of Raman spectroscopy whereby multiple measurements at differing positions are used to separate the spectrum arising from the sub layers of a sample from the spectrum at the surface. For the first time, a handheld system based on SORS has been developed and applied to hazardous materials identification. The system - "Resolve" - enables new capabilities in the rapid identification of materials concealed by a wide variety of non-metallic sealed containers such as; coloured and opaque plastics, paper, card, sacks, fabric and glass. The range of potential target materials includes toxic industrial chemicals, explosives, narcotics, chemical warfare agents and biological materials. Resolve has the potential to improve the safety, efficiency and critical decision making in incident management, search operations, policing and ports and border operations. The operator is able to obtain a positive identification of a potentially hazardous material without opening or disturbing the container - to gain access to take a sample - thus improving safety. The technique is fast and simple thus suit and breathing gear time is used more efficiently. SORS also allows Raman to be deployed at an earlier stage in an event before more intrusive techniques are used. Evidential information is preserved and the chain of custody protected. Examples of detection capability for a number of materials and barrier types are presented below.