14,194 research outputs found
Vertical Load Tests of Footings on Silt
Vertical load tests were performed on two shallow spread footings founded on nonplastic silt. Maximum vertical loads of 500 kips were applied to the test footings which were about 24 x 12 x 4 ft in size. Instrumentation was installed to measure footing displacements, footing contact stresses, and soil displacements below the footings. Results of the load tests have been presented in graphic form. Comparisons have been made between measured settlements of the footings and predicted settlements based on standard penetration test results in the silt deposit
Ultrafast Molecular Imaging by Laser Induced Electron Diffraction
We address the feasibility of imaging geometric and orbital structure of a
polyatomic molecule on an attosecond time-scale using the laser induced
electron diffraction (LIED) technique. We present numerical results for the
highest molecular orbitals of the CO2 molecule excited by a near infrared
few-cycle laser pulse. The molecular geometry (bond-lengths) is determined
within 3% of accuracy from a diffraction pattern which also reflects the nodal
properties of the initial molecular orbital. Robustness of the structure
determination is discussed with respect to vibrational and rotational motions
with a complete interpretation of the laser-induced mechanisms
Reciprocal space mapping of magnetic order in thick epitaxial MnSi films
We report grazing incidence small angle neutron scattering (GISANS) and
complementary off-specular neutron reflectometry (OSR) of the magnetic order in
a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit.
Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a
magnetic modulation perpendicular to the films under magnetic fields parallel
and perpendicular to the film, where additional polarized neutron reflectometry
(PNR) and magnetization measurements are in excellent agreement with the
literature. Regardless of field orientation, our data does not suggest the
presence of more complex spin textures, notably the formation of skyrmions.
This observation establishes a distinct difference with bulk samples of MnSi of
similar thickness under perpendicular field, in which a skyrmion lattice
dominates the phase diagram. Extended x-ray absorption fine structure
measurements suggest that small shifts of the Si positions within the
unstrained unit cell control the magnetic state, representing the main
difference between the films and thin bulk samples
All-Optical Production of Chromium Bose-Einstein Condensates
We report on the production of ^52Cr Bose Einstein Condensates (BEC) with an
all-optical method. We first load 5.10^6 metastable chromium atoms in a 1D
far-off-resonance optical trap (FORT) from a Magneto Optical Trap (MOT), by
combining the use of Radio Frequency (RF) frequency sweeps and depumping
towards the ^5S_2 state. The atoms are then pumped to the absolute ground
state, and transferred into a crossed FORT in which they are evaporated. The
fast loading of the 1D FORT (35 ms 1/e time), and the use of relatively fast
evaporative ramps allow us to obtain in 20 s about 15000 atoms in an almost
pure condensate.Comment: 4 pages, 4 figure
Continuity of the four-point function of massive -theory above threshold
In this paper we prove that the four-point function of massive
\vp_4^4-theory is continuous as a function of its independent external
momenta when posing the renormalization condition for the (physical) mass
on-shell. The proof is based on integral representations derived inductively
from the perturbative flow equations of the renormalization group. It closes a
longstanding loophole in rigorous renormalization theory in so far as it shows
the feasibility of a physical definition of the renormalized coupling.Comment: 23 pages; to appear in Rev. Math. Physics few corrections, two
explanatory paragraphs adde
Laser induced electron diffraction: a tool for molecular orbital imaging
We explore the laser-induced ionization dynamics of N2 and CO2 molecules
subjected to a few-cycle, linearly polarized, 800\,nm laser pulse using
effective two-dimensional single active electron time-dependent quantum
simulations. We show that the electron recollision process taking place after
an initial tunnel ionization stage results in quantum interference patterns in
the energy resolved photo-electron signals. If the molecule is initially
aligned perpendicular to the field polarization, the position and relative
heights of the associated fringes can be related to the molecular geometrical
and orbital structure, using a simple inversion algorithm which takes into
account the symmetry of the initial molecular orbital from which the ionized
electron is produced. We show that it is possible to extract inter-atomic
distances in the molecule from an averaged photon-electron signal with an
accuracy of a few percents
Time-dependent unitary perturbation theory for intense laser driven molecular orientation
We apply a time-dependent perturbation theory based on unitary
transformations combined with averaging techniques, on molecular orientation
dynamics by ultrashort pulses. We test the validity and the accuracy of this
approach on LiCl described within a rigid-rotor model and find that it is more
accurate than other approximations. Furthermore, it is shown that a noticeable
orientation can be achieved for experimentally standard short laser pulses of
zero time average. In this case, we determine the dynamically relevant
parameters by using the perturbative propagator, that is derived from this
scheme, and we investigate the temperature effects on the molecular orientation
dynamics.Comment: 16 pages, 6 figure
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