545 research outputs found
Design and Observation of Steep Reinforced Embankments
Using the design method proposed by R. A. Jewell et al. numerous steep reinforced embankments have been constructed in the authors’ home country since the year 1984. In fact these soil structures are built with the reinforcement of polymer grids (the so-called geogrids invented by F. B. Mercer of U.K.) which have a unique structural composition with high-tensile and low-ductility characteristics. This paper deals with first the development of steep reinforced soil structures and their design method, and then introduces a well-documented case history of steep reinforced embankment. The authors propose a current design method developed on the basis of the findings obtained from the observations at several steep reinforced embankments including the present one of the case history. And finally an ultimate seismic-design method for steep reinforced embankment adopted recently in Japan is presented
Magnetoresistance Anomalies in (Ga,Mn)As Epilayers with Perpendicular Magnetic Anisotropy
We report the observation of anomalies in the longitudinal magnetoresistance
of tensile-strained (Ga,Mn)As epilayers with perpendicular magnetic anisotropy.
Magnetoresistance measurements carried out in the planar geometry (magnetic
field parallel to the current density) reveal "spikes" that are antisymmetric
with respect to the direction of the magnetic field. These anomalies always
occur during magnetization reversal, as indicated by a simultaneous change in
sign of the anomalous Hall effect. The data suggest that the antisymmetric
anomalies originate in anomalous Hall effect contributions to the longitudinal
resistance when domain walls are located between the voltage probes. This
interpretation is reinforced by carrying out angular sweeps of ,
revealing an antisymmetric dependence on the helicity of the field sweep.Comment: Submitted to Phys. Rev.
Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy
The ferromagnetism of a thin GaMnAs layer with a perpendicular easy
anisotropy axis is investigated by means of several techniques, that yield a
consistent set of data on the magnetic properties and the domain structure of
this diluted ferromagnetic semiconductor. The magnetic layer was grown under
tensile strain on a relaxed GaInAs buffer layer using a procedure that limits
the density of threading dislocations. Magnetometry, magneto-transport and
polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality
of this layer, in particular through its high Curie temperature (130 K) and
well-defined magnetic anisotropy. We show that magnetization reversal is
initiated from a limited number of nucleation centers and develops by easy
domain wall propagation. Furthermore, MOKE microscopy allowed us to
characterize in detail the magnetic domain structure. In particular we show
that domain shape and wall motion are very sensitive to some defects, which
prevents a periodic arrangement of the domains. We ascribed these defects to
threading dislocations emerging in the magnetic layer, inherent to the growth
mode on a relaxed buffer
Quantum dynamics of proton migration in H2O dications: formation of H2+ on ultrafast timescales
Irradiation of isolated water molecules by few-cycle pulses of intense
infrared laser light can give rise to ultrafast rearrangement resulting in
formation of the H2+ ion. Such unimolecular reactions occur on the potential
energy surface of the H2O2+ dication that is accessed when peak laser
intensities in the 1015 W cm-2 range and pulse durations as short as 9-10 fs
are used; ion yields of ~1.5% are measured. We also study such reactions by
means of time-dependent wavepacket dynamics on an ab initio potential energy
surface of the dication and show that a proton, generated from O-H bond
rupture, migrates towards the H-atom, and forms vibrationally-excited H2+ in a
well-defined spatial zone.Comment: To appear in J. Chem. Phys. (tentatively the 22 January 2012 issue
Current-induced interactions of multiple domain walls in magnetic quantum wires
We show that an applied charge current in a magnetic nanowire containing
domain walls (DWs) results in an interaction between DWs mediated by
spin-dependent interferences of the scattered carriers. The energy and torque
associated with this interaction show an oscillatory behaviour as a function of
the mutual DWs orientations and separations, thus affecting the DWs'
arrangements and shapes. Based on the derived DWs interaction energy and torque
we calculate DW dynamics and uncover potential applications of interacting DWs
as a tunable nano-mechanical oscillator. We also discuss the effect of
impurities on the DW interaction.Comment: Published as Phys. Rev. B 79, 174422 (2009
Time-Domain Studies of Very-Large-Angle Magnetization Dynamics Excited by Spin Transfer Torques
We describe time-domain measurements which provide new information about the
large-angle nonlinear dynamics of nanomagnets excited by spin-transfer torque
from a spin-polarized current. Sampling-oscilloscope measurements, which
average over thousands of experimental time traces, show that the mean reversal
time for spin-transfer-driven magnetic switching has a step-like dependence on
magnetic field, because an integer number of precession cycles is required for
reversal. Storage-oscilloscope measurements of individual experimental traces
reveal non-periodic large-amplitude resistance variations at values of magnetic
field and current in a crossover region between the regimes of
spin-transfer-driven switching and steady-state precession. We also observe
directly the existence of time-dependent switching, on the nanosecond scale,
between different precessional modes and between a precessional mode and a
static state, at particular values of magnetic field and current bias.Comment: 20 pages, 6 figures, submitted to Phys. Rev.
Properties of aerosols and their wet deposition in the arctic spring during ASTAR2004 at Ny-Alesund, Svalbard
During the period of scientific campaign "Arctic Study of Tropospheric Aerosols, Clouds and Radiation 2004" (ASTAR2004), precipitation samples were collected in late spring at Ny-Alesund, Svalbard and their ionic components were analyzed in parallel with the measurement of properties of atmospheric aerosol particles at the same place. Backward trajectory analyses indicated that the air mass above the observatory initially dominated by air masses from the Arctic Ocean, then those from western Siberia and later those from Greenland and the Arctic Ocean. In the measurement period, six precipitation samples were obtained and five of them were analyzed their ionic components by ionchromatography. The concentrations of nss-sulphate in precipitations were between 1.8 and 24.6 ppm from which the scavenging ratio and scavenging coefficients were calculated using the data such as the concentrations of nss-sulphate in aerosol particles, amounts of precipitations, and the heights of precipitations obtained from radar echo data. The scavenging ratio ranged from 1.0&times;10<sup>6</sup> to 17&times;10<sup>6</sup> which are comparable values reported in other areas. A detailed comparison between precipitation events and the number concentration of aerosol particles obtained from optical particle counters suggests that the type of precipitations, i.e. rain or snow, significantly affects the number concentrations of aerosol particles
A NEW COMPRESSION-MOLDING APPROACH USING UNIDIRECTIONALLY ARRAYED CHOPPED STRANDS
SUMMARY In this study, we propose a new compression-molding approach using a sheet-like molding material made by regularly and unidirectionally arrayed chopped strands (UACS). UACS achieves both excellent flowablity during molding and distinguished mechanical properties comparable to continuous fiber composites
Normal-state conductivity in underdoped La_{2-x}Sr_xCuO_4 thin films: Search for nonlinear effects related to collective stripe motion
We report a detailed study of the electric-field dependence of the
normal-state conductivity in La_{2-x}Sr_xCuO_4 thin films for two
concentrations of doped holes, x=0.01 and 0.06, where formation of diagonal and
vertical charged stripes was recently suggested. In order to elucidate whether
high electric fields are capable of depinning the charged stripes and inducing
their collective motion, we have measured current-voltage characteristics for
various orientations of the electric field with respect to the crystallographic
axes. However, even for the highest possible fields (~1000 V/cm for x=0.01 and
\~300 V/cm for x=0.06) we observed no non-linear-conductivity features except
for those related to the conventional Joule heating of the films. Our analysis
indicates that Joule heating, rather than collective electron motion, may also
be responsible for the non-linear conductivity observed in some other 2D
transition-metal oxides as well. We discuss that a possible reason why moderate
electric fields fail to induce a collective stripe motion in layered oxides is
that fairly flexible and compressible charged stripes can adjust themselves to
the crystal lattice and individual impurities, which makes their pinning much
stronger than in the case of conventional rigid charge-density waves.Comment: 10 pages, 10 figures, accepted for publication in Phys. Rev.
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