6,642 research outputs found
High power diode laser surface glazing of concrete
This present work describes the utilisation of the relatively novel high power diode laser
(HPDL) to generate a surface glaze on the ordinary Portland cement (OPC) surface of
concrete. The value of such an investigation would be to facilitate the hitherto impossible
task of generating a durable and long-lasting surface seal on the concrete, thereby extending
the life and applications base of the concrete. The basic process phenomena are investigated
and the laser effects in terms of glaze morphology, composition and microstructure
are presented. Also, the resultant heat affects are analysed and described, as well as
the effects of the shield gases, O2 and Ar, during laser processing. HPDL glazing of OPC
was successfully demonstrated with power densities as low as 750 W cm-2 and at scanning
rates up to 480 mm min-1. The work showed that the generation of the surface glaze resulted
in improved mechanical and chemical properties over the untreated OPC surface of concrete.
Both untreated and HPDL glazed OPC were tested for pull-off strength, rupture strength,
water absorption, wear resistance and corrosion resistance. The OPC laser glaze exhibited
clear improvements in wear, water sorptivity, and resistance (up to 80% concentration) to
nitric acid, sodium hydroxide and detergent. Life assessment testing revealed that the OPC
laser glaze had an increase in actual wear life of 1.3 to 14.8 times over the untreated OPC
surface of concrete, depending upon the corrosive environment
Agrin isoforms and their role in synaptogenesis
Agrin is thought to mediate the motor neuron-induced aggregation of synaptic proteins on the surface of muscle fibers at neuromuscular junctions. Recent experiments provide direct evidence in support of this hypothesis, reveal the nature of agrin immunoreactivity at sites other than neuromuscular junctions, and have resulted in findings that are consistent with the possibility that agrin plays a role in synaptogenesis throughout the nervous system
Nonequilibrium steady states of driven magnetic flux lines in disordered type-II superconductors
We investigate driven magnetic flux lines in layered type-II superconductors
subject to various configurations of strong point or columnar pinning centers
by means of a three-dimensional elastic line model and Metropolis Monte Carlo
simulations. We characterize the resulting nonequilibrium steady states by
means of the force-velocity / current-voltage curve, static structure factor,
mean vortex radius of gyration, number of double-kink and half-loop
excitations, and velocity / voltage noise spectrum. We compare the results for
the above observables for randomly distributed point and columnar defects, and
demonstrate that the three-dimensional flux line structures and their
fluctuations lead to a remarkable variety of complex phenomena in the
steady-state transport properties of bulk superconductors.Comment: 23 pages, IOP style, 18 figures include
Circularly polarized resonant soft x-ray diffraction study of helical magnetism in hexaferrite
Magnetic spiral structures can exhibit ferroelectric moments as recently
demonstrated in various multiferroic materials. In such cases the helicity of
the magnetic spiral is directly correlated with the direction of the
ferroelectric moment and measurement of the helicity of magnetic structures is
of current interest. Soft x-ray resonant diffraction is particularly
advantageous because it combines element selectivity with a large magnetic
cross-section. We calculate the polarization dependence of the resonant
magnetic x-ray cross-section (electric dipole transition) for the basal plane
magnetic spiral in hexaferrite Ba0.8Sr1.2Zn2Fe12O22 and deduce its domain
population using circular polarized incident radiation. We demonstrate there is
a direct correlation between the diffracted radiation and the helicity of the
magnetic spiral.Comment: 4 pages, 4 figure
Improved prediction of clay soil expansion using machine learning algorithms and meta-heuristic dichotomous ensemble classifiers
Soil swelling-related disaster is considered as one of the most devastating geo-hazards in modern history. Hence, proper determination of a soil's ability to expand is very vital for achieving a secure and safe ground for infrastructures. Accordingly, this study has provided a novel and intelligent approach that enables an improved estimation of swelling by using kernelised machines (Bayesian linear regression (BLR) & bayes point machine (BPM) support vector machine (SVM) and deep-support vector machine (D-SVM)); (multiple linear regressor (REG), logistic regressor (LR) and artificial neural network (ANN)), tree-based algorithms such as decision forest (RDF) & boosted trees (BDT). Also, and for the first time, meta-heuristic classifiers incorporating the techniques of voting (VE) and stacking (SE) were utilised. Different independent scenarios of explanatory featuresâ combination that influence soil behaviour in swelling were investigated. Preliminary results indicated BLR as possessing the highest amount of deviation from the predictor variable (the actual swell-strain). REG and BLR performed slightly better than ANN while the meta-heuristic learners (VE and SE) produced the best overall performance (greatest R2 value of 0.94 and RMSE of 0.06% exhibited by VE). CEC, plasticity index and moisture content were the features considered to have the highest level of importance. Kernelized binary classifiers (SVM, D-SVM and BPM) gave better accuracy (average accuracy and recall rate of 0.93 and 0.60) compared to ANN, LR and RDF. Sensitivity-driven diagnostic test indicated that the meta-heuristic modelsâ best performance occurred when ML training was conducted using k-fold validation technique. Finally, it is recommended that the concepts developed herein be deployed during the preliminary phases of a geotechnical or geological site characterisation by using the best performing meta-heuristic models via their background coding resource
Doping and temperature dependence of Mn 3d states in A-site ordered manganites
We present a systematic study of the electronic structure in A-site ordered
manganites as function of doping and temperature. The energy dependencies
observed with soft x-ray resonant diffraction (SXRD) at the Mn L_{2,3} edges
are compared with structural investigations using neutron powder diffraction as
well as with cluster calculations. The crystal structures obtained with neutron
powder diffraction reflect the various orbital and charge ordered phases and
show an increase of the Mn-O-Mn bond angle as function of doping and
temperature. Cluster calculations show that the observed spectral changes in
SXRD as a function of doping are more pronounced than expected from an increase
in bandwitdh due to the increase in Mn-O-Mn bond angle, and are best described
by holes that are distributed at the neighbouring oxygen ions. These holes are
not directly added to the Mn 3d shell, but centered at the Mn site. In
contrast, the spectral changes in SXRD as function of temperature are best
described by an increase of magnetic correlations. This demonstrates the strong
correlations between orbitals and magnetic moments of the 3d states
Indirect detection of light neutralino dark matter in the NMSSM
We explore the prospects for indirect detection of neutralino dark matter in
supersymmetric models with an extended Higgs sector (NMSSM). We compute, for
the first time, one-loop amplitudes for NMSSM neutralino pair annihilation into
two photons and two gluons, and point out that extra diagrams (with respect to
the MSSM), featuring a potentially light CP-odd Higgs boson exchange, can
strongly enhance these radiative modes. Expected signals in neutrino telescopes
due to the annihilation of relic neutralinos in the Sun and in the Earth are
evaluated, as well as the prospects of detection of a neutralino annihilation
signal in space-based gamma-ray, antiproton and positron search experiments,
and at low-energy antideuteron searches. We find that in the low mass regime
the signals from capture in the Earth are enhanced compared to the MSSM, and
that NMSSM neutralinos have a remote possibility of affecting solar dynamics.
Also, antimatter experiments are an excellent probe of galactic NMSSM dark
matter. We also find enhanced two photon decay modes that make the possibility
of the detection of a monochromatic gamma-ray line within the NMSSM more
promising than in the MSSM.Comment: 26 pages, 12 figures. Updated references and corrected discussion of
Upsilon decay
Space-Time Distribution of G-Band and Ca II H-Line Intensity Oscillations in Hinode/SOT-FG Observations
We study the space-time distributions of intensity fluctuations in 2 - 3 hour
sequences of multi-spectral, high-resolution, high-cadence broad-band
filtergram images (BFI) made by the SOT-FG system aboard the Hinode spacecraft.
In the frequency range 5.5 < f < 8.0 mHz both G-band and Ca II H-line
oscillations are suppressed in the presence of magnetic fields, but the
suppression disappears for f > 10 mHz. By looking at G-band frequencies above
10 mHz we find that the oscillatory power, both at these frequencies and at
lower frequencies too, lies in a mesh pattern with cell scale 2 - 3 Mm, clearly
larger than normal granulation, and with correlation times on the order of
hours. The mesh pattern lies in the dark lanes between stable cells found in
time-integrated G-band intensity images. It also underlies part of the bright
pattern in time-integrated H-line emission. This discovery may reflect
dynamical constraints on the sizes of rising granular convection cells together
with the turbulence created in strong intercellular downflows.Comment: 24 pages, 15 figure
The Cosmological Constant is Back
A diverse set of observations now compellingly suggest that Universe
possesses a nonzero cosmological constant. In the context of quantum-field
theory a cosmological constant corresponds to the energy density of the vacuum,
and the wanted value for the cosmological constant corresponds to a very tiny
vacuum energy density. We discuss future observational tests for a cosmological
constant as well as the fundamental theoretical challenges---and
opportunities---that this poses for particle physics and for extending our
understanding of the evolution of the Universe back to the earliest moments.Comment: latex, 8 pages plus one ps figure available as separate compressed
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High field x-ray diffraction study on a magnetic-field-induced valence transition in YbInCu4
We report the first high-field x-ray diffraction experiment using synchrotron
x-rays and pulsed magnetic fields exceeding 30 T. Lattice deformation due to a
magnetic-field-induced valence transition in YbInCu4 is studied. It has been
found that the Bragg reflection profile at 32 K changes significantly at around
27 T due to the structural transition. In the vicinity of the transition field
the low-field and the high-field phases are observed simultaneously as the two
distinct Bragg reflection peaks: This is a direct evidence of the fact that the
field-induced valence state transition is the first order phase transition. The
field-dependence of the low-field-phase Bragg peak intensity is found to be
scaled with the magnetization.Comment: 5 pages, 6 figures, submitted to J. Phys. Soc. Jp
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