1,844 research outputs found
Two dimensional symmetric and antisymmetric generalizations of sine functions
Properties of 2-dimensional generalizations of sine functions that are
symmetric or antisymmetric with respect to permutation of their two variables
are described. It is shown that the functions are orthogonal when integrated
over a finite region of the real Euclidean space, and that they are
discretely orthogonal when summed up over a lattice of any density in .
Decomposability of the products of functions into their sums is shown by
explicitly decomposing products of all types. The formalism is set up for
Fourier-like expansions of digital data over 2-dimensional lattices in .
Continuous interpolation of digital data is studied.Comment: 12 pages, 5 figure
Characterizing Granular Networks Using Topological Metrics
We carry out a direct comparison of experimental and numerical realizations
of the exact same granular system as it undergoes shear jamming. We adjust the
numerical methods used to optimally represent the experimental settings and
outcomes up to microscopic contact force dynamics. Measures presented here
range form microscopic, through mesoscopic to system-wide characteristics of
the system. Topological properties of the mesoscopic force networks provide a
key link between micro and macro scales. We report two main findings: the
number of particles in the packing that have at least two contacts is a good
predictor for the mechanical state of the system, regardless of strain history
and packing density. All measures explored in both experiments and numerics,
including stress tensor derived measures and contact numbers depend in a
universal manner on the fraction of non-rattler particles, . The force
network topology also tends to show this universality, yet the shape of the
master curve depends much more on the details of the numerical simulations. In
particular we show that adding force noise to the numerical data set can
significantly alter the topological features in the data. We conclude that both
and topological metrics are useful measures to consider when
quantifying the state of a granular system.Comment: 8 pages, 8 figure
Verification of ZVS boost converter with resonant circuit & modelling of an accurate two-diode PV array system simulator using MATLAB simulink
This thesis proposes a MATLAB Simulink simulator for Photo Voltaic (PV) Array system. The main contribution is the utilisation of a Two-Diode model to represent a PV cell. This model is preferred because of its better accuracy at low irradiance levels. A PV of Kyocera (KC200GT) 50*10 Array is taken & the characteristics curves are plotted. The same simulator can be interfaced with MPPT algorithms & Power Electronics converters for better efficiency. The P-V & I-V Curves of this simulator is found in exact with that given by the manufacturers. It is expected that the proposed work can be very useful for PV professionals who require a simple, fast & accurate PV simulator in order to design their systems. A detailed analysis of a resonant circuit based soft-switching boost-converter for PV applications is also performed. The converter operates at Zero Voltage Switching (ZVS) turn-on and turn-off of the main switch, & Zero Current Switching (ZCS) turn-on and ZVS turn-off of the auxiliary switch due to resonant circuit incorporated into the circuit. Detailed operation of the converters, analysis of various modes, simulation as well as experimental results for the design has also been aptly presented. The systems are modelled & simulated in MATLAB 2013a 64-bit version and the output waveforms are shown
The Kepler view of magnetic chemically peculiar stars
Magnetic chemically peculiar (mCP) stars exhibit complex atmospheres that
allow the investigation of such diverse phenomena as atomic diffusion, magnetic
fields, and stellar rotation. The advent of space-based photometry provides the
opportunity for the first precise characterizations of the photometric
variability properties of these stars. We carried out a search for new mCP
stars in the Kepler field with the ultimate aim of investigating their
photometric variability properties using Kepler data. As an aside, we describe
criteria for selecting mCP star candidates based on light curve properties, and
assess the accuracy of the spectral classifications provided by the MKCLASS
code. As only very few known mCP stars are situated in the Kepler field, we had
to depend largely on alternative (nonspectroscopic) means of identifying
suitable candidates that rely mostly on light curve properties; in particular
we relied on monoperiodic variability and light curve stability. Newly acquired
and archival spectra were used to confirm most of our mCP star candidates.
Linear ephemeris parameters and effective amplitudes were derived from
detrended Kepler data. Our final sample consists of 41 spectroscopically
confirmed mCP stars of which 39 are new discoveries, 5 candidate mCP stars, and
7 stars in which no chemical peculiarities could be established. Our targets
populate the whole age range from zero-age main sequence to terminal-age main
sequence and are distributed in the mass interval from 1.5 M_sun to 4 M_sun.
About 25% of the mCP stars show a hitherto unobserved wealth of detail in their
light curves indicative of complex surface structures. We identified light
curve stability as a primary criterion for identifying mCP star candidates
among early-type stars in large photometric surveys, and prove the reliability
of the spectral classifications provided by the MKCLASS code.Comment: Accepted for publication in Astronomy and Astrophysics. 20 pages, 12
figures, 5 tables. Given above is a slightly shortened version of the
abstract; for the full abstract, please refer to the pape
Hazard and risk assessment of human exposure to toxic metals using in vitro digestion assay
Acknowledgements The authors, acknowledge with thanks DSR technical and financial support. Funding This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under grant no. 1434-142-514. The authors, therefore, acknowledge with thanks DSR technical and financial support.Peer reviewedPublisher PD
The influence of structural changes on electrical and magnetic characteristics of amorphous powder of the nixmoy alloy
Nickel and molybdenum alloy powder was electrodeposited on a titanium cathode from a NiSO4⋅7H2O and (NH4)6 Mo7O24⋅4H2O ammonium solution. The desired chemical composition, structure, size and shape of particles in the powder samples were achieved by an appropriate choice of electrolysis parameters (current density, composition and temperature of the solution, cathode material and electrolysis duration). Metal coatings form in the current density range 15 mA cm-2<j<30 mA cm-2. If the current density is greater than 40mA cm-2 then powders form. The chemical composition of powder samples depends on the current density of electrodeposition. The molybdenum content in the powder increases with the increase of current density (in the low current density range), while in the higher current density range the molybdenum content in the alloy decreases with the increase of the current density of deposition. Smaller sized particles form at higher current density. X-ray analysis, differential scanning calorimetric and measurements of the temperature dependence of electric resistance and magnetic permeability of the powder samples were all used to establish a predominantly amorphous structure of the powder samples formed at the current density of j≥70mA cm-2. The crystalline particle content in the powder samples increases with the decrease of the current density of deposition. Powder heating causes structural changes. The process of thermal stabilization of nickel and molybdenum amorphous powders takes place in the temperature interval from 463K to 573K and causes a decrease in electrical resistance and increase in magnetic permeability. The crystallization temperature depends on the value of current density of powder electrodeposition. Powder formed at j=180 mA cm-2 begins to crystallize at 573K, while the powder deposited at j=50 mA cm-2 begins to crystallize at 673K. Crystallization of the powder causes a decrease in electric resistivity and magnetic permeability. The Curie temperature of the crystallized powders is about 10 K higher than the Curie temperature of amorphous powders
Physical properties of seven binary and higher-order multiple OB systems
Analyses of multi-epoch, high-resolution (~ 50000) optical spectra of seven
early-type systems provided various important new insights with respect to
their multiplicity. First determinations of orbital periods were made for HD
92206C (2.022 d), HD 112244 (27.665 d), HD 164438 (10.25 d), HD 123056A (~ 1314
d) and HD 123056B (< 2 d); the orbital period of HD 318015 could be improved
(23.445975 d). Concerning multiplicity, a third component was discovered for HD
92206C by means of He I line profiles. For HD 93146A, which was hitherto
assumed to be SB1, lines of a secondary component could be discerned. HD 123056
turns out to be a multiple system consisting of a high-mass component A (~
O8.5) displaying a broad He II 5411 A feature with variable radial velocity,
and of an inner pair B (~ B0) with double He I lines. The binary HD 164816 was
revisited and some of its system parameters were improved. In particular, we
determined its systemic velocity to be -7 km/s, which coincides with the radial
velocity of the cluster NGC 6530. This fact, together with its distance,
suggests the cluster membership of HD 164816. The OB system HD 318015 (V1082
Sco) belongs to the rare class of eclipsing binaries with a supergiant primary
(B0.5/0.7). Our combined orbital and light-curve analysis suggests that the
secondary resembles an O9.5III star. Our results for a limited sample
corroborate the findings that many O stars are actually massive multiple
systems.Comment: 16 pages, 16 figures, to appear in Astronomy and Astrophysic
Health effects of dietary phospholipids
Beneficial effects of dietary phospholipids (PLs) have been mentioned since the early 1900's in relation to different illnesses and symptoms, e.g. coronary heart disease, inflammation or cancer. This article gives a summary of the most common therapeutic uses of dietary PLs to provide an overview of their approved and proposed benefits; and to identify further investigational needs
Melvin universe as a limit of the C-metric
It is demonstrated that the Melvin universe representing the spacetime with a
strong 'homogeneous' electric field can by obtained from the spacetime of two
accelerated charged black holes by a suitable limiting procedure. The behavior
of various invariantly defined geometrical quantities in this limit is also
studied.Comment: 5 pages, no figures [v2: two references added
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