9,294 research outputs found
Unsteady flow in a supercritical supersonic diffuser
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77051/1/AIAA-10045-786.pd
Radiative corrections to the lightest KK states in the T^2/(Z_2\times Z_2') orbifold
We study radiative corrections localized in the fixed points of the orbifold
for the field theory in six dimensions with two dimensions compactified on the
orbifold in a specific realistic model for low energy
physics that solves the proton decay and neutrino mass problem. We calculate
corrections to the masses of the lightest stable KK modes, which could be the
candidates for the dark matter.Comment: 14 pages, 2 figure
Soft x-ray magnetic circular dichroism study on Gd-doped EuO thin films
We report on the growth and characterization of ferromagnetic Gd-doped EuO
thin films. We prepared samples with Gd concentrations up to 11% by means of
molecular beam epitaxy under distillation conditions, which allows a very
precise control of the doping concentration and oxygen stoichiometry. Using
soft x-ray magnetic circular dichroism at the Eu and Gd M4,5 edges, we found
that the Curie temperature ranged from 69 K for pure stoichiometric EuO to
about 170 K for the film with the optimal Gd doping of around 4%. We also show
that the Gd magnetic moment couples ferromagnetically to that of Eu.Comment: 4 pages, 4 figure
Volume Fractions of the Kinematic "Near-Critical" Sets of the Quantum Ensemble Control Landscape
An estimate is derived for the volume fraction of a subset in the neighborhood
of the critical set
of the kinematic quantum ensemble control landscape J(U) = Tr(U\rho U' O),
where represents the unitary time evolution operator, {\rho} is the initial
density matrix of the ensemble, and O is an observable operator. This estimate
is based on the Hilbert-Schmidt geometry for the unitary group and a
first-order approximation of . An upper bound on these
near-critical volumes is conjectured and supported by numerical simulation,
leading to an asymptotic analysis as the dimension of the quantum system
rises in which the volume fractions of these "near-critical" sets decrease to
zero as increases. This result helps explain the apparent lack of influence
exerted by the many saddles of over the gradient flow.Comment: 27 pages, 1 figur
Spin blockade, orbital occupation and charge ordering in La_(1.5)Sr_(0.5)CoO4
Using Co-L_(2,3) and O-K x-ray absorption spectroscopy, we reveal that the
charge ordering in La_(1.5)Sr_(0.5)CoO4 involves high spin (S=3/2) Co^2+ and
low spin (S=0) Co^3+ ions. This provides evidence for the spin blockade
phenomenon as a source for the extremely insulating nature of the
La_(2-x)Sr_(x)CoO4 series. The associated e_g^2 and e_g^0 orbital occupation
accounts for the large contrast in the Co-O bond lengths, and in turn, the high
charge ordering temperature. Yet, the low magnetic ordering temperature is
naturally explained by the presence of the non-magnetic (S=0) Co^3+ ions. From
the identification of the bands we infer that La_(1.5)Sr_(0.5)CoO4 is a narrow
band material.Comment: 5 pages, 3 figure
Quantum properties of the Dirac field on BTZ black hole backgrounds
We consider a Dirac field on a -dimensional uncharged BTZ black hole
background. We first find out the Dirac Hamiltonian, and study its
self-adjointness properties. We find that, in analogy to the Kerr-Newman-AdS
Dirac Hamiltonian in dimensions, essential self-adjointness on
of the reduced (radial) Hamiltonian is implemented
only if a suitable relation between the mass of the Dirac field and the
cosmological radius holds true. The very presence of a boundary-like
behaviour of is at the root of this problem. Also, we determine in a
complete way qualitative spectral properties for the non-extremal case, for
which we can infer the absence of quantum bound states for the Dirac field.
Next, we investigate the possibility of a quantum loss of angular momentum for
the -dimensional uncharged BTZ black hole. Unlike the corresponding
stationary four-dimensional solutions, the formal treatment of the level
crossing mechanism is much simpler. We find that, even in the extremal case, no
level crossing takes place. Therefore, no quantum loss of angular momentum via
particle pair production is allowed.Comment: 19 pages; IOP styl
Imaging stress and magnetism at high pressures using a nanoscale quantum sensor
Pressure alters the physical, chemical and electronic properties of matter.
The development of the diamond anvil cell (DAC) enables tabletop experiments to
investigate a diverse landscape of high-pressure phenomena ranging from the
properties of planetary interiors to transitions between quantum mechanical
phases. In this work, we introduce and utilize a novel nanoscale sensing
platform, which integrates nitrogen-vacancy (NV) color centers directly into
the culet (tip) of diamond anvils. We demonstrate the versatility of this
platform by performing diffraction-limited imaging (~600 nm) of both stress
fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from
25-340 K. For the former, we quantify all six (normal and shear) stress
components with accuracy GPa, offering unique new capabilities for
characterizing the strength and effective viscosity of solids and fluids under
pressure. For the latter, we demonstrate vector magnetic field imaging with
dipole accuracy emu, enabling us to measure the pressure-driven
phase transition in iron as well as the complex
pressure-temperature phase diagram of gadolinium. In addition to DC vector
magnetometry, we highlight a complementary NV-sensing modality using T1 noise
spectroscopy; crucially, this demonstrates our ability to characterize phase
transitions even in the absence of static magnetic signatures. By integrating
an atomic-scale sensor directly into DACs, our platform enables the in situ
imaging of elastic, electric and magnetic phenomena at high pressures.Comment: 18 + 50 pages, 4 + 19 figure
Rice Straw Cellulose Nanofibrils via Aqueous Counter Collision and Differential Centrifugation and Their Self-Assembled Structures
Rice straw cellulose was completely defibrillated via aqueous counter collision (ACC) at a low energy input of 15 kWh/kg, then fractionated by differential centrifugation into four increasing weight fractions of progressively thinner cellulose nanofibrils (CNFs): 6.9% in 80-200 nm, 14.4% in 20-80 nm, 20.3% in 5-20 nm, and 58.4% in less than 5 nm thickness. The 93.1% less than 80 nm or 78.7% less than 20 nm thick CNFs yields were more than double those from wood pulp by other mechanical means but at a lower energy input. The smallest (3.7 nm thick and 5.5 nm wide) CNFs were only a third or less in lateral dimensions than those obatined through ACC processed from wood pulp, bamboo, and microbial cellulose pellicle. The less than 20 nm thick CNFs could self-assemble into continuous submicron (136 nm) wide fibers by freezing and freeze-drying or semitransparent (13-42% optical transmittance) film by ultrafiltration and air-drying with excellent mechanical properties (164 MPa tensile strength, 4 GPa Young's modulus, and 16% strain at break). ACC defibrillated CNFs retained essentially the same chemical and crystalline structures and thermal stability as the original rice straw cellulose and therefore were much more thermally stable than TEMPO oxidized CNFs and sulfuric acid hydrolyzed cellulose nanocrystals from the same rice straw cellulose
Generalization of the Scheme and the Structure of the Valence Space
The scheme, which has been extensively applied to even-even nuclei,
is found to be a very good benchmark for odd-even, even-odd, and doubly-odd
nuclei as well. There are no apparent shifts in the correlations for these four
classes of nuclei. The compact correlations highlight the deviant behavior of
the Z=78 nuclei, are used to deduce effective valence proton numbers near Z=64,
and to study the evolution of the Z=64 subshell gap.Comment: 10 pages, 4 figure
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