1,084 research outputs found
Electronic structure and chemical bonding of nc-TiC/a-C nanocomposites
The electronic structure of nanocrystalline (nc-) TiC/amorphous C
nanocomposites has been investigated by soft x-ray absorption and emission
spectroscopy. The measured spectra at the Ti 2p and C 1s thresholds of the
nanocomposites are compared to those of Ti metal and amorphous C. The
corresponding intensities of the electronic states for the valence and
conduction bands in the nanocomposites are shown to strongly depend on the TiC
carbide grain size. An increased charge-transfer between the Ti 3d-eg states
and the C 2p states has been identified as the grain size decreases, causing an
increased ionicity of the TiC nanocrystallites. It is suggested that the
charge-transfer occurs at the interface between the nanocrystalline TiC and the
amorphous C matrix and represents an interface bonding which may be essential
for the understanding of the properties of nc-TiC/amorphous C and similar
nanocomposites.Comment: 13 pages, 6 figures, 1 table;
http://link.aps.org/doi/10.1103/PhysRevB.80.23510
A 10B-based neutron detector with stacked Multiwire Proportional Counters and macrostructured cathodes
We present the results of the measurements of the detection efficiency for a
4.7 \r{A} neutron beam incident upon a detector incorporating a stack of up to
five MultiWire Proportional Counters (MWPC) with Boron-coated cathodes. The
cathodes were made of Aluminum and had a surface exhibiting millimeter-deep
V-shaped grooves of 45{\deg}, upon which the thin Boron film was deposited by
DC magnetron sputtering. The incident neutrons interacting with the converter
layer deposited on the sidewalls of the grooves have a higher capture
probability, owing to the larger effective absorption film thickness. This
leads to a higher overall detection efficiency for the grooved cathode when
compared to a cathode with a flat surface. Both the experimental results and
the predictions of the GEANT4 model suggests that a 5-counter detector stack
with coated grooved cathodes has the same efficiency as a 7-counter stack with
flat cathodes. The reduction in the number of counters in the stack without
altering the detection efficiency will prove highly beneficial for large-area
position-sensitive detectors for neutron scattering applications, for which the
cost-effective manufacturing of the detector and associated readout electronics
is an important objective. The proposed detector concept could be a
technological option for one of the new chopper spectrometers and other
instruments planned to be built at the future European Spallation Source in
Sweden. These results with macrostructured cathodes generally apply not just to
MWPCs but to other gaseous detectors as well.Comment: 14 pages, 9 figure
Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings
Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by
pulsed DC reactive sputter deposition on Si(100) at a temperature of 550
{\deg}C. XRD showed three different crystal structures depending on V-metal
fraction in the coating: {\alpha}-V2O3 rhombohedral structure for 100 at.% V, a
defect spinel structure for the intermediate region, 63 - 42 at.% V. At lower
V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed,
shifted to larger d-spacing compared to pure {\gamma}-Al2O3. The microstructure
changes from large columnar faceted grains for {\alpha}-V2O3 to smaller
equiaxed grains when lowering the vanadium content toward pure {\gamma}-Al2O3.
Annealing in air resulted in formation of V2O5 crystals on the surface of the
coating after annealing to 500 {\deg}C for 42 at.% V and 700 {\deg}C for 18
at.% V metal fraction respectively. The highest thermal stability was shown for
pure {\gamma}-Al2O3-coating, which transformed to {\alpha}-Al2O3 after
annealing to 1100{\deg} C. Highest hardness was observed for the Al-rich
oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7
at.% V metal fraction. The measured hardness after annealing in air decreased
in conjunction with the onset of further oxidation of the coatings
Optimal Pacing for Running 400 m and 800 m Track Races
Physicists seeking to understand complex biological systems often find it
rewarding to create simple "toy models" that reproduce system behavior. Here a
toy model is used to understand a puzzling phenomenon from the sport of track
and field. Races are almost always won, and records set, in 400 m and 800 m
running events by people who run the first half of the race faster than the
second half, which is not true of shorter races, nor of longer. There is
general agreement that performance in the 400 m and 800 m is limited somehow by
the amount of anaerobic metabolism that can be tolerated in the working muscles
in the legs. A toy model of anaerobic metabolism is presented, from which an
optimal pacing strategy is analytically calculated via the Euler-Lagrange
equation. This optimal strategy is then modified to account for the fact that
the runner starts the race from rest; this modification is shown to result in
the best possible outcome by use of an elementary variational technique that
supplements what is found in undergraduate textbooks. The toy model reproduces
the pacing strategies of elite 400 m and 800 m runners better than existing
models do. The toy model also gives some insight into training strategies that
improve performance.Comment: 14 pages, 4 figures, submitted to the American Journal of Physic
Bonding mechanism in the nitrides Ti2AlN and TiN: an experimental and theoretical investigation
The electronic structure of nanolaminate Ti2AlN and TiN thin films has been
investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured
Ti L, N K, Al L1 and Al L2,3 emission spectra are compared with calculated
spectra using ab initio density-functional theory including dipole transition
matrix elements. Three different types of bond regions are identified; a
relatively weak Ti 3d - Al 3p bonding between -1 and -2 eV below the Fermi
level, and Ti 3d - N 2p and Ti 3d - N 2s bonding which are deeper in energy
observed at -4.8 eV and -15 eV below the Fermi level, respectively. A strongly
modified spectral shape of 3s states of Al L2,3 emission from Ti2AlN in
comparison to pure Al metal is found, which reflects the Ti 3d - Al 3p
hybridization observed in the Al L1 emission. The differences between the
electronic and crystal structures of Ti2AlN and TiN are discussed in relation
to the intercalated Al layers of the former compound and the change of the
materials properties in comparison to the isostructural carbides.Comment: 18 pages, 7 figures;
http://link.aps.org/doi/10.1103/PhysRevB.76.19512
Managerial mindset effects on international marketing strategy adaptation decisions
This research investigates how managerial implicit theories—people's implicit beliefs about the malleability of human characteristics—affect international marketing strategy adaptation decisions among B2B exporting managers. Building on mindset theory and the international marketing literature, we hypothesize that managers with a growth mindset will opt for higher levels of marketing strategy adaptation while fixed-mindset managers, who believe in the immutability of human traits, will likely standardize across markets. Across two experimental studies that manipulate mindset, we test these hypotheses and their underlying mechanism and boundary conditions. The results of Study 1 show that mindset affects lifestyle adaptation intentions for individuals in general, thus establishing the baseline relationship. Study 2 finds that business-to-business international marketing managers exposed to a growth (fixed) mindset are indeed more likely to adapt (standardize) their international marketing strategy toward foreign markets. We further show that mindset affects ambiguity tolerance, which in turn affects adaptation decisions, and that the effect of mindset is dampened (strengthened) under low (high) psychic distance conditions. This research enriches the international marketing literature by showing a managerially relevant antecedent of international marketing strategy adaptation decisions and extends implicit theory by showing a behavioral outcome of mindset
Some Restrictions Abroad Affecting Corporations
A neutron detector concept based on solid layers of boron carbide enriched in 1 B has been in development for the last few years as an alternative for He-3 by collaboration between the ILL, ESS and Linkoping University. This Multi-Grid detector uses layers of aluminum substrates coated with (B4C)-B-10 on both sides that are traversed by the incoming neutrons. Detection is achieved using a gas counter readout principle. By segmenting the substrate and using multiple anode wires, the detector is made inherently position sensitive. This development is aimed primarily at neutron scattering instruments with large detector areas, such as time-of-flight chopper spectrometers. The most recent prototype has been built to be interchangeable with the He-3 detectors of IN6 at ILL. The 1 B detector has an active area of 32 x 48 cm(2). It was installed at the IN6 instrument and operated for several weeks, collecting data in parallel with the regularly scheduled experiments, thus providing the first side-by-side comparison with the conventional He-3 detectors. Results include an efficiency comparison, assessment of the in-detector scattering contribution, sensitivity to gamma-rays and the signal-to-noise ratio in time-of-flight spectra. The good expected performance has been confirmed with the exception of an unexpected background count rate. This has been identified as natural alpha activity in aluminum. New convertor substrates are under study to eliminate this source of background
Reflection thermal diffuse x-ray scattering for quantitative determination of phonon dispersion relations
Synchrotron reflection x-ray thermal diffuse scattering (TDS) measurements, rather than previously reported transmission TDS, are carried out at room temperature and analyzed using a formalism based upon second-order interatomic force constants and long-range Coulomb interactions to obtain quantitative determinations of MgO phonon dispersion relations ℏω_j(q), phonon densities of states g(ℏω), and isochoric temperature-dependent vibrational heat capacities c_v(T). We use MgO as a model system for investigating reflection TDS due to its harmonic behavior as well as its mechanical and dynamic stability. Resulting phonon dispersion relations and densities of states are found to be in good agreement with independent reports from inelastic neutron and x-ray scattering experiments. Temperature-dependent isochoric heat capacities c_v(T), computed within the harmonic approximation from ℏω_j(q) values, increase with temperature from 0.4 × 10^(−4) eV/atom K at 100 K to 1.4 × 10^(−4) eV/atom K at 200 K and 1.9 × 10^(−4) eV/atom K at 300 K, in excellent agreement with isobaric heat capacity values c_p(T) between 4 and 300 K. We anticipate that the experimental approach developed here will be valuable for determining vibrational properties of heteroepitaxial thin films since the use of grazing-incidence (θ≲θ_c, where θ_c is the density-dependent critical angle) allows selective tuning of x-ray penetration depths to ≲10nm
Spectroscopic ellipsometry study on the dielectric function of bulk Ti2AlN, Ti2AlC, Nb2AlC, (Ti0.5,Nb0.5)2AlC, and Ti3GeC2 MAX-phases
Effect of 28 days of creatine ingestion on muscle metabolism and performance of a simulated cycling road race
<p>Abstract</p> <p>Purpose</p> <p>The effects of creatine supplementation on muscle metabolism and exercise performance during a simulated endurance road race was investigated.</p> <p>Methods</p> <p>Twelve adult male (27.3 ± 1.0 yr, 178.6 ± 1.4 cm, 78.0 ± 2.5 kg, 8.9 ± 1.1 %fat) endurance-trained (53.3 ± 2.0 ml* kg<sup>-1</sup>* min<sup>-1</sup>, cycling ~160 km/wk) cyclists completed a simulated road race on a cycle ergometer (Lode), consisting of a two-hour cycling bout at 60% of peak aerobic capacity (VO<sub>2peak</sub>) with three 10-second sprints performed at 110% VO<sub>2 peak </sub>every 15 minutes. Cyclists completed the 2-hr cycling bout before and after dietary creatine monohydrate or placebo supplementation (3 g/day for 28 days). Muscle biopsies were taken at rest and five minutes before the end of the two-hour ride.</p> <p>Results</p> <p>There was a 24.5 ± 10.0% increase in resting muscle total creatine and 38.4 ± 23.9% increase in muscle creatine phosphate in the creatine group (<it>P </it>< 0.05). Plasma glucose, blood lactate, and respiratory exchange ratio during the 2-hour ride, as well as VO<sub>2 peak</sub>, were not affected by creatine supplementation. Submaximal oxygen consumption near the end of the two-hour ride was decreased by approximately 10% by creatine supplementation (P < 0.05). Changes in plasma volume from pre- to post-supplementation were significantly greater in the creatine group (<sup>+</sup>14.0 ± 6.3%) than the placebo group (<sup>-</sup>10.4 ± 4.4%; <it>P </it>< 0.05) at 90 minutes of exercise. The time of the final sprint to exhaustion at the end of the 2-hour cycling bout was not affected by creatine supplementation (creatine pre, 64.4 ± 13.5s; creatine post, 88.8 ± 24.6s; placebo pre, 69.0 ± 24.8s; placebo post 92.8 ± 31.2s: creatine vs. placebo not significant). Power output for the final sprint was increased by ~33% in both groups (creatine vs. placebo not significant).</p> <p>Conclusions</p> <p>It can be concluded that although creatine supplementation may increase resting muscle total creatine, muscle creatine phosphate, and plasma volume, and may lead to a reduction in oxygen consumption during submaximal exercise, creatine supplementation does not improve sprint performance at the end of endurance cycling exercise.</p
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