7,188 research outputs found
Shockwaves in converging geometries
Plate impact experiments are a powerful tool in equation of state (EOS) development, but are inherently limited by the range of impact velocities accessible to the gun. In an effort to dramatically increase the range of pressures which can be studied with available impact velocities, a new experimental technique is being developed. The possibility of using a confined converging target to focus Shockwaves and produce a large amplitude pressure pulse is examined. When the planar shock resulting from impact enters the converging target the impedance mismatch at the boundary of the confinement produces reflected Mach waves and the subsequent wave interactions produce a diffraction cycle resulting in increases in the shock strength with each cycle. Since this configuration is limited to relatively low impedance targets, a second technique is proposed in which the target is two concentric cylinders designed such that the inner cylinder will have a lower shock velocity than the much larger shock velocity in the outer cylinder. The resulting dispersion in the wave front creates converging shocks, which will interact and eventually result in a steady Mach configuration with an increase in pressure in the Mach disk. Numerical simulations indicate a significant increase in pressure for both methods and show promise for the proposed concepts
MUSCLE COORDINATION IN CROSS-COUNTRY SKIING: THE EFFECT OF INCLINE ON THE V2-SKATE TECHNIQUE
This study examined differences In upper (UB) and lower-body (LB) muscle activation of twelve elite Nordic skiers using the V2-skate at two inclines via electromyography (EMG). Subjects roller-skied on a treadmill for two 2-minute bouts, one at moderate grade - high speed and one at steep grade - low speed to keep heart rate equal between bouts. EMG was recorded (1 O-second interval), normalized to maximal isometric voluntary contraction, and analyzed for cycle time, peak and average activation, and within-cycle times for activation onset, offset, and peak activation of each muscle. UB tended to remain active for a longer proportion of the cycle at steeper grades while the opposite was true of LB. UB may play an increased role in the V2-skate at steeper grades independent of intensity, although no significant difference in LB or UB response to grade was found (p < 0.05)
Layer by layer generation of cluster states
Cluster states can be used to perform measurement-based quantum computation.
The cluster state is a useful resource, because once it has been generated only
local operations and measurements are needed to perform universal quantum
computation. In this paper, we explore techniques for quickly and
deterministically building a cluster state. In particular we consider
generating cluster states on a qubus quantum computer, a computational
architecture which uses a continuous variable ancilla to generate interactions
between qubits. We explore several techniques for building the cluster, with
the number of operations required depending on whether we allow the ability to
destroy previously created controlled-phase links between qubits. In the case
where we can not destroy these links, we show how to create an n x m cluster
using just 3nm -2n -3m/2 + 3 operations. This gives more than a factor of 2
saving over a naive method. Further savings can be obtained if we include the
ability to destroy links, in which case we only need (8nm-4n-4m-8)/3
operations. Unfortunately the latter scheme is more complicated so choosing the
correct order to interact the qubits is considerably more difficult. A half way
scheme, that keeps a modular generation but saves additional operations over
never destroying links requires only 3nm-2n-2m+4 operations. The first scheme
and the last scheme are the most practical for building a cluster state because
they split up the generation into the repetition of simple sections.Comment: 16 pages, 11 figure
Using Quantum Computers for Quantum Simulation
Numerical simulation of quantum systems is crucial to further our
understanding of natural phenomena. Many systems of key interest and
importance, in areas such as superconducting materials and quantum chemistry,
are thought to be described by models which we cannot solve with sufficient
accuracy, neither analytically nor numerically with classical computers. Using
a quantum computer to simulate such quantum systems has been viewed as a key
application of quantum computation from the very beginning of the field in the
1980s. Moreover, useful results beyond the reach of classical computation are
expected to be accessible with fewer than a hundred qubits, making quantum
simulation potentially one of the earliest practical applications of quantum
computers. In this paper we survey the theoretical and experimental development
of quantum simulation using quantum computers, from the first ideas to the
intense research efforts currently underway.Comment: 43 pages, 136 references, review article, v2 major revisions in
response to referee comments, v3 significant revisions, identical to
published version apart from format, ArXiv version has table of contents and
references in alphabetical orde
Temporal and geochemical signatures in granitoids of northwestern Nevada: Evidence for the continuity of the Mesozoic magmatic arc through the western Great Basin
Granitoid magmatism in the Basin and Range Province of northwestern Nevada remains an important gap in our understanding of the along-strike variability of Mesozoic Cordilleran arc systems. We present a comprehensive investigation on a suite of intrusions within the Santa Rosa Range (SRR) and Bloody Run Hills (BRH) of northwestern Nevada. Petrography, whole-rock geochemistry, and zircon U-Pb geochronology indicate two distinct magmatic systems in the SRR: an older, mafic, and metaluminous pulse (Santa Rosa/Andorno [SRA] group—ca. 102–100 Ma) and a younger, felsic, and peraluminous pulse (Granite Peak/Sawtooth [GPS] group—ca. 94–92 Ma). Within the BRH to the south, the Flynn (ca. 105 Ma) and Bloody Run stocks (ca. 96 Ma) are compositionally similar to the SRA group. New Al-in-hornblende thermobarometry reveals emplacement paleodepths of ~5–10 km for the SRA group. Slightly deeper emplacement levels (~10.5–12 km) are inferred for the GPS group from structural relationships and metamorphic contact aureole assemblages. Elemental characteristics are correlated with whole-rock Sr and Nd isotope ratios, revealing higher εNd(t) (+0.8 to +2.5) and lower initial 87Sr/86Sr (0.7040–0.7054) in the older SRA group than the younger GPS group (εNd(t) = −3.2 to −1.5; 87Sr/86Sr(i) 0.7056–0.7061). New zircon εHf isotope analyses reveal that with the exception of the Bloody Run stock (−0.4 ± 2.1), the SRA group has more primitive zircon εHf(t) values (+2.9 to +5.3) than the GPS group (+0.4 to −3.7). The systematic shift in whole-rock Sr and Nd isotope and zircon εHf(t) values with time suggests fundamental changes in the relative contributions of mantle and crustal sources. A comparison of published geochronology and geochemistry from regional intrusive suites confirms that SRR-BRH magmatism was coeval and geochemically similar to the larger Cordilleran batholiths, providing evidence for the continuity of the Mesozoic magmatic arc through northwestern Nevada
Neutron knockout of 12Be populating neutron-unbound states in 11Be
Neutron-unbound resonant states of 11Be were populated in neutron knock-out
reactions from 12Be and identified by 10Be-n coincidence measurements. A
resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly
excited unbound state in 11Be at 3.949(2) MeV decaying to the 2+ excited state
in 10Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2)
MeV state suggesting a spectroscopic factor near unity for this 0p3/2- level,
consistent with the detailed shell model calculations.Comment: 5 pages, 2 figures \pacs{29.38.Db, 29.30.Hs, 24.50.+g, 21.10.Pc,
21.10.Hw, 27.20.+n} \keywords{neutron decay spectroscopy, neutron-unbound
states in 11Be
Ancilla-based quantum simulation
We consider simulating the BCS Hamiltonian, a model of low temperature
superconductivity, on a quantum computer. In particular we consider conducting
the simulation on the qubus quantum computer, which uses a continuous variable
ancilla to generate interactions between qubits. We demonstrate an O(N^3)
improvement over previous work conducted on an NMR computer [PRL 89 057904
(2002) & PRL 97 050504 (2006)] for the nearest neighbour and completely general
cases. We then go on to show methods to minimise the number of operations
needed per time step using the qubus in three cases; a completely general case,
a case of exponentially decaying interactions and the case of fixed range
interactions. We make these results controlled on an ancilla qubit so that we
can apply the phase estimation algorithm, and hence show that when N \geq 5,
our qubus simulation requires significantly less operations that a similar
simulation conducted on an NMR computer.Comment: 20 pages, 10 figures: V2 added section on phase estimation and
performing controlled unitaries, V3 corrected minor typo
Exploring the limits of the self consistent Born approximation for inelastic electronic transport
The non equilibrium Green function formalism is today the standard
computational method for describing elastic transport in molecular devices.
This can be extended to include inelastic scattering by the so called
self-consistent Born approximation (SCBA), where the interaction of the
electrons with the vibrations of the molecule is assumed to be weak and it is
treated perturbatively. The validity of such an assumption and therefore of the
SCBA is difficult to establish with certainty. In this work we explore the
limitations of the SCBA by using a simple tight-binding model with the
electron-phonon coupling strength chosen as a free parameter. As
model devices we consider Au mono-atomic chains and a molecule
sandwiched between Pt electrodes. In both cases our self-consistent
calculations demonstrate a breakdown of the SCBA for large and we
identify a weak and strong coupling regime. For weak coupling our SCBA results
compare closely with those obtained with exact scattering theory. However in
the strong coupling regime large deviations are found. In particular we
demonstrate that there is a critical coupling strength, characteristic of the
materials system, beyond which multiple self-consistent solutions can be found
depending on the initial conditions in the simulation. We attribute these
features to the breakdown of the perturbative expansion leading to the SCBA.Comment: 12 pages, 16 figures, 1 Tabl
Size segregation and convection
The size segregation of granular materials in a vibrating container is
investigated using Molecular Dynamics. We find that the rising of larger
particles is accompanied by the existence of convection cells even in the case
of the lowest possible frequencies. The convection can, however, also be
triggered by the larger particle itself. The possibility of rising through this
mechanism strongly depends on the depth of the larger particle.Comment: 7 pages, 4 figure
Semiclassical charged black holes with a quantized massive scalar field
Semiclassical perturbations to the Reissner-Nordstrom metric caused by the
presence of a quantized massive scalar field with arbitrary curvature coupling
are found to first order in \epsilon = \hbar/M^2. The DeWitt-Schwinger
approximation is used to determine the vacuum stress-energy tensor of the
massive scalar field. When the semiclassical perturbation are taken into
account, we find extreme black holes will have a charge-to-mass ratio that
exceeds unity, as measured at infinity. The effects of the perturbations on the
black hole temperature (surface gravity) are studied in detail, with particular
emphasis on near extreme ``bare'' states that might become precisely zero
temperature ``dressed'' semiclassical black hole states. We find that for
minimally or conformally coupled scalar fields there are no zero temperature
solutions among the perturbed black holes.Comment: 19 pages; 1 figure; ReVTe
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