3,750 research outputs found
Approaches to optimization of SS/TDMA time slot assignment
Reduction techniques for traffic matrices are explored in some detail. These matrices arise in satellite switched time-division multiple access (SS/TDMA) techniques whereby switching of uplink and downlink beams is required to facilitate interconnectivity of beam zones. A traffic matrix is given to represent that traffic to be transmitted from n uplink beams to n downlink beams within a TDMA frame typically of 1 ms duration. The frame is divided into segments of time and during each segment a portion of the traffic is represented by a switching mode. This time slot assignment is characterized by a mode matrix in which there is not more than a single non-zero entry on each line (row or column) of the matrix. Investigation is confined to decomposition of an n x n traffic matrix by mode matrices with a requirement that the decomposition be 100 percent efficient or, equivalently, that the line(s) in the original traffic matrix whose sum is maximal (called critical line(s)) remain maximal as mode matrices are subtracted throughout the decomposition process. A method of decomposition of an n x n traffic matrix by mode matrices results in a number of steps that is bounded by n(2) - 2n + 2. It is shown that this upper bound exists for an n x n matrix wherein all the lines are maximal (called a quasi doubly stochastic (QDS) matrix) or for an n x n matrix that is completely arbitrary. That is, the fact that no method can exist with a lower upper bound is shown for both QDS and arbitrary matrices, in an elementary and straightforward manner
Optical fiber interferometer for the study of ultrasonic waves in composite materials
The possibility of acoustic emission detection in composites using embedded optical fibers as sensing elements was investigated. Optical fiber interferometry, fiber acoustic sensitivity, fiber interferometer calibration, and acoustic emission detection are reported. Adhesive bond layer dynamical properties using ultrasonic interface waves, the design and construction of an ultrasonic transducer with a two dimensional Gaussian pressure profile, and the development of an optical differential technique for the measurement of surface acoustic wave particle displacements and propagation direction are also examined
Water-condition effects on rhizobia competition for cowpea nodule occupancy
Two indigenous bradyrhizobia strains displaying different natural behaviours towards water regime (strain ORS 3257, nodulating more frequently in favourable-water conditions and strain ORS 3260, in limited-water conditions) were studied for their competitivity for nodulation of cowpea (Mouridecultivar) under favourable and limited water conditions in non-sterile soil. The nodule occupancy was studied by PCR-RFLP analysis. Both strains showed good competition with other indigenous rhizobia populations under favourable- and limited-water conditions. Competition between the inoculatedstrains in the mixture varied between water regimes. In non-limited-water conditions, strain ORS 3257 was the best competitor, whereas in limited-water conditions, strain ORS 3260 was the best competitor. Results indicated that screening of strains according to their environmental origin could ensuresuccessful rhizobia inoculatio
Opportunities for Process Control and Quality Assurance Using Online NIR Analysis to a Continuous Wet Granulation Tableting Line
This paper investigates the application of online near-infrared measurements as a means to measure blend uniformity in a continuous tableting line. Underlying all the monitoring and control methods is the ability to measure key tablet properties online at a rate suitable for control purposes. The use of NIR to determine any deviations in blend uniformity is demonstrated by interpreting the relevant spectral signature allowing quantitative information to be acquired for process monitoring and quality assurance. In addition to demonstrating the functionality of the NIR probe, the practical issues arising in the application are discussed. The composition of the blend was measured using an NIR probe over a range of concentrations and the results were calculated comparing sub unit dose scale of scrutiny of small populations. This was compared with predicted product quality for whole tablets over the whole production period. This technique has demonstrated how data collected online can be used to successfully predict the quality of the whole production run for the purposes of real-time product quality assurance
Magnetic fields and chemical peculiarities of the very young intermediate-mass binary system HD 72106
The recently discovered magnetic Herbig Ae and Be stars may provide
qualitatively new information about the formation and evolution of magnetic Ap
and Bp stars. We have performed a detailed investigation of one particularly
interesting binary system with a Herbig Ae secondary and a late B-type primary
possessing a strong, globally ordered magnetic field. Twenty high-resolution
Stokes V spectra of the system were obtained with the ESPaDOnS instrument
mounted on the CFHT. In these observations we see clear evidence for a magnetic
field in the primary, but no evidence for a magnetic field in the secondary. A
detailed abundance analysis was performed for both stars, revealing strong
chemical peculiarities in the primary and normal chemical abundances in the
secondary. The primary is strongly overabundant in Si, Cr, and other iron-peak
elements, as well as Nd, and underabundant in He. The primary therefore appears
to be a very young Bp star. In this context, line profile variations of the
primary suggest non-uniform lateral distributions of surface abundances.
Interpreting the 0.63995 +/- 0.00009 day variation period of the Stokes I and V
profiles as the rotational period of the star, we have modeled the magnetic
field geometry and the surface abundance distributions of Si, Ti, Cr and Fe
using Magnetic Doppler Imaging. We derive a dipolar geometry of the surface
magnetic field, with a polar strength of 1230 G and an obliquity of 57 degrees.
The distributions Ti, Cr and Fe are all qualitatively similar, with an
elongated patch of enhanced abundance situated near the positive magnetic pole.
The Si distribution is somewhat different, and its relationship to the magnetic
field geometry less clear.Comment: Accepted by Monthly Notices of the Royal Astronomical Society,
September 2008. 15 pages, 10 figure
Confirmation of ξ1 CMa's ultra-slow rotation:magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines
The magnetic beta Cep pulsator xi^1 CMa has the longest rotational period of
any known magnetic B-type star. It is also the only magnetic B-type star with
magnetospheric emission that is known to be modulated by both rotation and
pulsation. We report here the first unambiguous detection of a negative
longitudinal magnetic field in xi^1 CMa (=-87 +/- 2 G in 2019 and =-207
+/- 3 G in 2020), as well as the results of ongoing monitoring of the star's
Halpha variability. We examine evidence for deviation from a purely dipolar
topology. We also report a new HST UV spectrum of xi^1 CMa obtained near
magnetic null that is consistent with an equatorial view of the magnetosphere,
as evidenced by its similarity to the UV spectrum of beta Cep obtained near
maximum emission. The new UV spectrum of xi^1 CMa provides additional evidence
for the extremely long rotation period of this star via comparison to archival
data.Comment: 13 pages, Accepted 2021 May 14 to Monthly Notices of the Royal
Astronomical Society 202
Why Global Inequality Matters: Derivative Global Egalitarianism
This article integrates empirical and normative discussions about why global economic inequalities matter in critically examining an approach known as derivative global egalitarianism (DGE). DGE is a burgeoning perspective that opposes excessive global economic inequality not based on the intrinsic value of equality but inequality\u27s negative repercussions on other values. The article aims to advance the research agenda by identifying and critically evaluating four primary varieties of DGE arguments from related but distinct literatures, which span a number of disciplines, including economics, international relations, and political philosophy. Overall, DGE offers a number of persuasive arguments as to why current levels of global inequality are of concern, but aspects of DGE beg further philosophical and empirical examination. By situating DGE within the wider theoretical and empirical contexts, this article provides resources for its critical assessment and theoretical development
Quenching across quantum critical points in periodic systems: dependence of scaling laws on periodicity
We study the quenching dynamics of a many-body system in one dimension
described by a Hamiltonian that has spatial periodicity. Specifically, we
consider a spin-1/2 chain with equal xx and yy couplings and subject to a
periodically varying magnetic field in the z direction or, equivalently, a
tight-binding model of spinless fermions with a periodic local chemical
potential, having period 2q, where q is a natural number. For a linear quench
of the magnetic field strength (or potential strength) at rate 1/\tau across a
quantum critical point, we find that the density of defects thereby produced
scales as 1/\tau^{q/(q+1)}, deviating from the 1/\sqrt{\tau} scaling that is
ubiquitous to a range of systems. We analyze this behavior by mapping the
low-energy physics of the system to a set of fermionic two-level systems
labeled by the lattice momentum k undergoing a non-linear quench as well as by
performing numerical simulations. We also find that if the magnetic field is a
superposition of different periods, the power law depends only on the smallest
period for very large values of \tau although it may exhibit a cross-over at
intermediate values of \tau. Finally, for the case where a zz coupling is also
present in the spin chain, or equivalently, where interactions are present in
the fermionic system, we argue that the power associated with the scaling law
depends on a combination of q and interaction strength.Comment: 13 pages including 11 figure
Inverting the handedness of circularly polarized luminescence from light-emitting polymers using film thickness
The emission of circularly polarized light is central to many applications, including data storage, optical quantum computation, biosensing, environmental monitoring, and display technologies. An emerging method to induce (chiral) circularly polarized (CP) electroluminescence from the active layer of polymer light-emitting diodes (polymer OLEDs; PLEDs) involves blending achiral polymers with chiral small-molecule additives, where the handedness/sign of the CP light is controlled by the absolute stereochemistry of the small molecule. Through the in-depth study of such a system we report an interesting chiroptical property: the ability to tune the sign of CP light as a function of active layer thickness for a fixed enantiomer of the chiral additive. We demonstrate that it is possible to achieve both efficient (4.0 cd/A) and bright (8000 cd/m2) CP-PLEDs, with high dissymmetry of emission of both left-handed (LH) and right-handed (RH) light, depending on thickness (thin films, 110 nm: gEL = 0.51, thick films, 160 nm: gEL = -1.05, with the terms "thick" and "thin" representing the upper and lower limits of the thickness regime studied), for the same additive enantiomer. We propose that this arises due to an interplay between localized CP emission originating from molecular chirality and CP light amplification or inversion through a chiral medium. We link morphological, spectroscopic, and electronic characterization in thin films and devices with theoretical studies in an effort to determine the factors that underpin these observations. Through the control of active layer thickness and device architecture, this study provides insights into the mechanisms that result in CP luminescence and high performance from CP-PLEDs, as well as demonstrating new opportunities in CP photonic device design
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