4,759 research outputs found
Solitary Waves in Discrete Media with Four Wave Mixing
In this paper, we examine in detail the principal branches of solutions that
arise in vector discrete models with nonlinear inter-component coupling and
four wave mixing. The relevant four branches of solutions consist of two single
mode branches (transverse electric and transverse magnetic) and two mixed mode
branches, involving both components (linearly polarized and elliptically
polarized). These solutions are obtained explicitly and their stability is
analyzed completely in the anti-continuum limit (where the nodes of the lattice
are uncoupled), illustrating the supercritical pitchfork nature of the
bifurcations that give rise to the latter two, respectively, from the former
two. Then the branches are continued for finite coupling constructing a full
two-parameter numerical bifurcation diagram of their existence. Relevant
stability ranges and instability regimes are highlighted and, whenever
unstable, the solutions are dynamically evolved through direct computations to
monitor the development of the corresponding instabilities. Direct connections
to the earlier experimental work of Meier et al. [Phys. Rev. Lett. {\bf 91},
143907 (2003)] that motivated the present work are given.Comment: 13 pages, 10 figure
Testing Bekenstein's Relativistic MOND gravity with Lensing Data
We propose to use multiple-imaged gravitational lenses to set limits on
gravity theories without dark matter, specificly TeVeS (Bekenstein 2004), a
theory which is consistent with fundamental relativistic principles and the
phenomenology of MOdified Newtonian Dynamics (MOND) theory. After setting the
framework for lensing and cosmology, we derive analytically the deflection
angle for the point lens and the Hernquist galaxy profile, and fit
galaxy-quasar lenses in the CASTLES sample. We do this with three methods,
fitting the observed Einstein ring sizes, the image positions, or the flux
ratios. In all cases we consistently find that stars in galaxies in MOND/TeVeS
provide adequate lensing. Bekenstein's toy function provides more
efficient lensing than the standard MOND function. But for a handful of
lenses [indicated in Table 2,3, fig 16] a good fit would require a lens mass
orders of magnitude larger/smaller than the stellar mass derived from
luminosity unless the modification function and modification scale
for the universal gravity were allowed to be very different from what spiral
galaxy rotation curves normally imply. We discuss the limitation of present
data and summarize constraints on the MOND function. We also show that
the simplest TeVeS "minimal-matter" cosmology, a baryonic universe with a
cosmological constant, can fit the distance-redshift relation from the
supernova data, but underpredicts the sound horizon size at the last
scattering. We conclude that lensing is a promising approach to differentiate
laws of gravity (see also astro-ph/0512425).Comment: reduced to 17p, 16 figs, discussed cosmology and constraints on
mu-function, MNRAS accepte
PHP1 COST EFFECTIVENESS OF INTERVENTIONS TO IMPROVE ADHERENCE: WHAT IS THE QUALITY OF THE EVIDENCE?
Proteomimetics as protein-inspired scaffolds with defined tertiary folding patterns
Proteins have evolved as a variable platform that provides access to molecules with diverse shapes, sizes and functions. These features have inspired chemists for decades to seek artificial mimetics of proteins with improved or novel properties. Such work has focused primarily on small protein fragments, often isolated secondary structures; however, there has lately been a growing interest in the design of artificial molecules that mimic larger, more complex tertiary folds. In this Perspective, we define these agents as ‘proteomimetics’ and discuss the recent advances in the field. Proteomimetics can be divided into three categories: protein domains with side-chain functionality that alters the native linear-chain topology; protein domains in which the chemical composition of the polypeptide backbone has been partially altered; and protein-like folded architectures that are composed entirely of non-natural monomer units. We give an overview of these proteomimetic approaches and outline remaining challenges facing the field
Radar UAV and Bird Signature comparisons with Micro-Doppler
This chapter reviews the similarities and differences between micro Unmanned Aerial Vehicles (UAVs), also referred to as drones, and bird targets from the signals they present to radar sensors. With the increasing usage of UAV platforms in both military and civilian applications, the demand for the ability to sense drone locations and discriminate them from background clutter and non-drone targets is becoming a vital requirement. A comparable target in size, speed and Radar Cross Section (RCS) is a bird. These are present almost everywhere that radar systems have to operate and have been detected by radar since the early origin of radar engineering. Due to the similarity in radar signature birds can cause common misclassification between them and the priority drone targets which has been identified as a current key challenge in radar sensing. In this chapter radar bird and drone signature research is initially summarised, then a fundamental model that represents the key contributions from drone rotor blades is introduced and compared to real measurements. Laboratory measurements of quadcopter rotor blade signatures with across 4 linear polarisations are then investigated in order to evaluate the trend of Signal-to-Noise-Ratio (SNR) vs. aspect angle. Next bird signatures from two separate radar systems are shown and compared to drone targets also present in the captures which are of comparable size and RCS. The outputs of all research presented are then summarised in the concluding remarks
Joint Active Passive Sensing using a Radio Frequency System-on-a-Chip based sensor
In this paper we present a dual active and passive radar experimental setup that uses the UCL ARESTOR platform. This is a multi-role RF sensor based on a Xilinx Radio Frequency System on a Chip (RFSoC) device. The system is capable of operating as an active radar, passive radar and wideband electronic surveillance receiver. Experimental results are shown that leverage 2.4 GHz passive radar experiments along with a 5.8 GHz active radar mode that are operating simultaneously observing a target of interest. Details of a bespoke designed RF front-end to access higher frequency bands are included within the paper as well as information on processing pipelines developed within the Field Programmable Gate Array (FPGA). Comparison of the target signature and how both modes could be best utilised are analysed and discussed. The target of interest within this paper is a person walking while being sensing by both modes simultaneously
Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm
Abstract The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17-19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 - 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1-0.5fce (theelectron equatorial gyrofrequency), with a peak spectral density ∼10-4 nT 2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102-103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 h, fitting well with the observation. Key Points Initial RBSP correlated data of chorus waves and relativistic electron fluxes A realistic simulation to examine effect of chorus on relativistic electron flux Chorus yields huge increases inelectron flux rapidly, consistent with data
Kostprijs eieren het hoogst in Nederland
Uit onderzoek naar de kostprijs van consumptie-eieren in het jaar 2000 is gebleken dat de productiekosten van eieren in Nederland 71 eurocent per kilogram bedragen
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