15,906 research outputs found
Quantifying flow and stress in ice mĂ©lange, the worldâs largest granular material.
Tidewater glacier fjords are often filled with a collection of calved icebergs, brash ice, and sea ice. For glaciers with high calving rates, this âm Ìelangeâ of ice can be jam-packed, so that the flow of ice fragments is mostly determined by granular interactions. In the jammed state, ice m Ìelange has been hypothesized to influence iceberg calving and capsize, dispersion and attenuation of ocean waves, injection of freshwater into fjords, and fjord circulation. However, detailed measurements of ice m Ìelange are lacking due to difficulties in instrumenting remote, ice-choked fjords. Here we characterize the flow and associated stress in icem Ìelange, using a combination of terrestrial radar data, laboratory experiments, and numerical simulations. We find that, during periods of terminus quiescence, ice m Ìelange experiences laminar flow over timescales of hours to days. The uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate. In addition, the average force per unit width that is transmitted to the glacier terminus, which can exceed 107N/m, increases exponentially with them Ìelange length-to-width ratio. These âbuttressingâ forces are sufficiently high to inhibit the initiation of large-scale calving events, supporting the notion that ice m Ìelange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini.Ye
Parasitic Effects Reduction for Wafer-Level Packaging of RF-Mems
In RF-MEMS packaging, next to the protection of movable structures,
optimization of package electrical performance plays a very important role. In
this work, a wafer-level packaging process has been investigated and optimized
in order to minimize electrical parasitic effects. The RF-MEMS package concept
used is based on a wafer-level bonding of a capping silicon substrate to an
RF-MEMS wafer. The capping silicon substrate resistivity, substrate thickness
and the geometry of through-substrate electrical interconnect vias have been
optimized using finite-element electromagnetic simulations (Ansoft HFSS). Test
structures for electrical characterization have been designed and after their
fabrication, measurement results will be compared with simulations.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Can real-time visual feedback during gait retraining reduce metabolic demand for individuals with transtibial amputation?
The metabolic demand of walking generally increases following lower extremity amputation. This study used real-time visual feedback to modify biomechanical factors linked to an elevated metabolic demand of walking in individuals with transtibial amputation. Eight persons with unilateral, traumatic transtibial amputation and 8 uninjured controls participated. Two separate bouts of real-time visual feedback were provided during a single session of gait retraining to reduce 1) center of mass sway and 2) thigh muscle activation magnitudes and duration. Baseline and post-intervention data were collected. Metabolic rate, heart rate, frontal plane center of mass sway, quadriceps and hamstrings muscle activity, and co-contraction indices were evaluated during steady state walking at a standardized speed. Visual feedback successfully decreased center of mass sway 12% (p = 0.006) and quadriceps activity 12% (p = 0.041); however, thigh muscle co-contraction indices were unchanged. Neither condition significantly affected metabolic rate during walking and heart rate increased with center-of-mass feedback. Metabolic rate, center of mass sway, and integrated quadriceps muscle activity were all not significantly different from controls. Attempts to modify gait to decrease metabolic demand may actually adversely increase the physiological effort of walking in individuals with lower extremity amputation who are young, active and approximate metabolic rates of able-bodied adults
Two Bipolar Outflows and Magnetic Fields in a Multiple Protostar System, L1448 IRS 3
We performed spectral line observations of CO J=2-1, 13CO J=1-0, and C18O
J=1-0 and polarimetric observations in the 1.3 mm continuum and CO J=2-1 toward
a multiple protostar system, L1448 IRS 3, in the Perseus molecular complex at a
distance of ~250 pc, using the BIMA array. In the 1.3 mm continuum, two sources
(IRS 3A and 3B) were clearly detected with estimated envelope masses of 0.21
and 1.15 solar masses, and one source (IRS 3C) was marginally detected with an
upper mass limit of 0.03 solar masses. In CO J=2-1, we revealed two outflows
originating from IRS 3A and 3B. The masses, mean number densities, momentums,
and kinetic energies of outflow lobes were estimated. Based on those estimates
and outflow features, we concluded that the two outflows are interacting and
that the IRS 3A outflow is nearly perpendicular to the line of sight. In
addition, we estimated the velocity, inclination, and opening of the IRS 3B
outflow using Bayesian statistics. When the opening angle is ~20 arcdeg, we
constrain the velocity to ~45 km/s and the inclination angle to ~57 arcdeg.
Linear polarization was detected in both the 1.3 mm continuum and CO J=2-1. The
linear polarization in the continuum shows a magnetic field at the central
source (IRS 3B) perpendicular to the outflow direction, and the linear
polarization in the CO J=2-1 was detected in the outflow regions, parallel or
perpendicular to the outflow direction. Moreover, we comprehensively discuss
whether the binary system of IRS 3A and 3B is gravitationally bound, based on
the velocity differences detected in 13CO J=1-0 and C18O J=1-0 observations and
on the outflow features. The specific angular momentum of the system was
estimated as ~3e20 cm^2/s, comparable to the values obtained from previous
studies on binaries and molecular clouds in Taurus.Comment: ApJ accepted, 20 pages, 2 tables, 10 figure
Globally controlled universal quantum computation with arbitrary subsystem dimension
We introduce a scheme to perform universal quantum computation in quantum
cellular automata (QCA) fashion in arbitrary subsystem dimension (not
necessarily finite). The scheme is developed over a one spatial dimension
-element array, requiring only mirror symmetric logical encoding and global
pulses. A mechanism using ancillary degrees of freedom for subsystem specific
measurement is also presented.Comment: 7 pages, 1 figur
Effects of diabetes family history and exercise training on the expression of adiponectin and leptin and their receptors
The daughters of patients with diabetes have reduced insulin sensitivity index (ISI) scores compared with women with no family history of
diabetes, but their ISI increase more in response to exercise training(1). The present study aimed to determine whether differences between
these groups in exercise-induced changes in circulating adiponectin and leptin concentrations and expression of their genes and receptors
in subcutaneous adipose tissue (SAT), could explain differences in the exercise-induced changes in ISI between women with and without
a family history of diabetes
The Abundance of Interstellar Nitrogen
Using the HST Goddard High Resolution Spectrograph (GHRS), we have obtained
high S/N echelle observations of the weak interstellar N I 1160, 1161 A
absorption doublet toward the stars Gamma Cas, Lambda Ori, Iota Ori, Kappa Ori,
Delta Sco, and Kappa Sco. In combination with a previous GHRS measurement of N
I toward Zeta Oph, these new observations yield a mean interstellar gas phase
nitrogen abundance (per 10 H atoms) of 10 N/H = 75 +/- 4. There are no
statistically significant variations in the measured N abundances from
sightline to sightline and no evidence of density-dependent depletion from the
gas-phase. Since N is not expected to be depleted much into dust grains in
these diffuse sightlines, its gas-phase abundance should reflect the total
interstellar abundance. Consequently, the GHRS observations imply that the
abundance of interstellar nitrogen (gas plus grains) in the local Milky Way is
about 80% of the solar system value of 10 N/H = 93 +/- 16. Although this
interstellar abundance deficit is somewhat less than that recently found for
oxygen and krypton with GHRS, the solar N abundance and the N I oscillator
strengths are too uncertain to definitively rule out either a solar ISM N
abundance or a 2/3 solar ISM N abundance similar to that of O and Kr.Comment: 14 pages, LaTeX, 2 Postscript figures; ApJ Letters, in pres
Accumulation horizons and period-adding in optically injected semiconductor lasers
We study the hierarchical structuring of islands of stable periodic
oscillations inside chaotic regions in phase diagrams of single-mode
semiconductor lasers with optical injection. Phase diagrams display remarkable
{\it accumulation horizons}: boundaries formed by the accumulation of infinite
cascades of self-similar islands of periodic solutions of ever-increasing
period. Each cascade follows a specific period-adding route. The riddling of
chaotic laser phases by such networks of periodic solutions may compromise
applications operating with chaotic signals such as e.g. secure communications.Comment: 4 pages, 4 figures, laser phase diagrams, to appear in Phys. Rev. E,
vol. 7
Full stress tensor measurement using colour centres in diamond
Stress and strain are important factors in determining the mechanical,
electronic, and optical properties of materials, relating to each other by the
material's elasticity or stiffness. Both are represented by second rank field
tensors with, in general, six independent components. Measurements of these
quantities are usually achieved by measuring a property that depends on the
translational symmetry and periodicity of the crystal lattice, such as optical
phonon energies using Raman spectroscopy, the electronic band gap using
cathodoluminescence, photoelasticity via the optical birefringence, or Electron
Back Scattering Diffraction (EBSD). A reciprocal relationship therefore exists
between the maximum sensitivity of the measurements and the spatial resolution.
Furthermore, of these techniques, only EBSD and off-axis Raman spectroscopy
allow measurement of all six components of the stress tensor, but neither is
able to provide full 3D maps. Here we demonstrate a method for measuring the
full stress tensor in diamond, using the spectral and optical polarization
properties of the photoluminescence from individual nitrogen vacancy (NV)
colour centres. We demonstrate a sensitivity of order 10 MPa, limited by local
fluctuations in the stress in the sample, and corresponding to a strain of
about 10^-5, comparable with the best sensitivity provided by other techniques.
By using the colour centres as built-in local sensors, the technique overcomes
the reciprocal relationship between spatial resolution and sensitivity and
offers the potential for measuring strains as small as 10^-9 at spatial
resolution of order 10 nm. Furthermore it provides a straightforward route to
volumetric stress mapping. Aside from its value in understanding strain
distributions in diamond, this new approach to stress and strain measurement
could be adapted for use in micro or nanoscale sensors.Comment: 12 pages, 5 figures - supplementary informations included in appendi
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