35,671 research outputs found
Spatial Compressive Sensing for MIMO Radar
We study compressive sensing in the spatial domain to achieve target
localization, specifically direction of arrival (DOA), using multiple-input
multiple-output (MIMO) radar. A sparse localization framework is proposed for a
MIMO array in which transmit and receive elements are placed at random. This
allows for a dramatic reduction in the number of elements needed, while still
attaining performance comparable to that of a filled (Nyquist) array. By
leveraging properties of structured random matrices, we develop a bound on the
coherence of the resulting measurement matrix, and obtain conditions under
which the measurement matrix satisfies the so-called isotropy property. The
coherence and isotropy concepts are used to establish uniform and non-uniform
recovery guarantees within the proposed spatial compressive sensing framework.
In particular, we show that non-uniform recovery is guaranteed if the product
of the number of transmit and receive elements, MN (which is also the number of
degrees of freedom), scales with K(log(G))^2, where K is the number of targets
and G is proportional to the array aperture and determines the angle
resolution. In contrast with a filled virtual MIMO array where the product MN
scales linearly with G, the logarithmic dependence on G in the proposed
framework supports the high-resolution provided by the virtual array aperture
while using a small number of MIMO radar elements. In the numerical results we
show that, in the proposed framework, compressive sensing recovery algorithms
are capable of better performance than classical methods, such as beamforming
and MUSIC.Comment: To appear in IEEE Transactions on Signal Processin
Multiple influences on participating in physical activity in older age: Developing a social ecological approach
Background: Evidence of the benefits of engaging in physical activity (PA) is strong, yet the number of older adults meeting the recommended 150 min/wk is low. Policy to increase uptake and adherence has focussed on the health benefits of PA, but may not be the most successful approach.
Objective: This qualitative study sought to ask older adults what the components of a successful intervention to promote PA would be, by asking active older adults what motivated them to be active and asking inactive older adults what might encourage them to change.
Design, setting and participants: Focus groups and semi‐structured interviews were held with 60 community‐dwelling older adults, aged 50‐87 years. Framework analysis was used to analyse the data, and themes congruent with a social ecological model of behaviour change were developed.
Findings: Five themes emerged that influenced PA engagement at multiple levels: individual; interpersonal; perceived environment; community or organizational; and policy. PA engagement was determined by attitude or health status for some participants, but for the majority, PA being enjoyable, sociable, affordable, accessible, flexible and seasonal were more important than the health benefits.
Discussion and conclusions: A social ecological model is presented, highlighting the fact that both motivated and unmotivated older adults need to have a range of appropriately labelled, appealing and accessible activities to choose from when thinking about engaging in PA. Policymakers and practitioners need to ensure that their offers of activity sessions are easy to access and easy to remain involved in
Spinodal Instabilities in Nuclear Matter in a Stochastic Relativistic Mean-Field Approach
Spinodal instabilities and early growth of baryon density fluctuations in
symmetric nuclear matter are investigated in the basis of stochastic extension
of relativistic mean-field approach in the semi-classical approximation.
Calculations are compared with the results of non-relativistic calculations
based on Skyrme-type effective interactions under similar conditions. A
qualitative difference appears in the unstable response of the system: the
system exhibits most unstable behavior at higher baryon densities around
in the relativistic approach while most unstable
behavior occurs at lower baryon densities around in
the non-relativistic calculationsComment: 18 pages, 7 figure
Analytic Review of Modeling Studies of ARV Based PrEP Interventions Reveals Strong Influence of Drug-Resistance Assumptions on the Population-Level Effectiveness
Background Four clinical trials have shown that oral and topical pre-exposure prophylaxis (PrEP) based on tenofovir may be effective in preventing HIV transmission. The expected reduction in HIV transmission and the projected prevalence of drug resistance due to PrEP use vary significantly across modeling studies as a result of the broad spectrum of assumptions employed. Our goal is to quantify the influence of drug resistance assumptions on the predicted population-level impact of PrEP. Methods All modeling studies which evaluate the impact of oral or topical PrEP are reviewed and key assumptions regarding mechanisms of generation and spread of drug-resistant HIV are identified. A dynamic model of the HIV epidemic is developed to assess and compare the impact of oral PrEP using resistance assumptions extracted from published studies. The benefits and risks associated with ten years of PrEP use are evaluated under identical epidemic, behavioral and intervention conditions in terms of cumulative fractions of new HIV infections prevented, resistance prevalence among those infected with HIV, and fractions of infections in which resistance is transmitted. Results Published models demonstrate enormous variability in resistance-generating assumptions and uncertainty in parameter values. Depending on which resistance parameterization is used, a resistance prevalence between 2% and 44% may be expected if 50% efficacious oral PrEP is used consistently by 50% of the population over ten years. We estimated that resistance may be responsible for up to a 10% reduction or up to a 30% contribution to the fraction of prevented infections predicted in different studies. Conclusions Resistance assumptions used in published studies have a strong influence on the projected impact of PrEP. Modelers and virologists should collaborate toward clarifying the set of resistance assumptions biologically relevant to the PrEP products which are already in use or soon to be added to the arsenal against HIV
A Sparse Stress Model
Force-directed layout methods constitute the most common approach to draw
general graphs. Among them, stress minimization produces layouts of
comparatively high quality but also imposes comparatively high computational
demands. We propose a speed-up method based on the aggregation of terms in the
objective function. It is akin to aggregate repulsion from far-away nodes
during spring embedding but transfers the idea from the layout space into a
preprocessing phase. An initial experimental study informs a method to select
representatives, and subsequent more extensive experiments indicate that our
method yields better approximations of minimum-stress layouts in less time than
related methods.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Oil palm smallholders and its sustainability practices in Malaysia
The demand for Palm oil has increasing over the several decades and it has led to criticisms and question about sustainability on biodiversity loss, water pollution and deforestation.This study aims to explore the sustainability of oil palm smallholders in Malaysia based on environmental, social and economic perspectives.The aim of the study is to examine the sustainability of smallholding scheme in Malaysia.A questionnaire survey was conducted with 50 smallholders in Terengganu state under the Federal Land Development Authority of Malaysia (FELDA).It’s revealed that most of the smallholders have sufficient knowledge of sustainability consistent with Roundtable on Sustainable Palm Oil (RSPO) and other local agricultural laws practices. The study also indicates that on social aspect, the smallholders have better quality of life through the provision of basic facilities.The study concludes that there is a high degree of sustainability amongst oil palm smallholders under the management of FELDA
The response of a neutral atom to a strong laser field probed by transient absorption near the ionisation threshold
We present transient absorption spectra of an extreme ultraviolet attosecond pulse train in helium dressed by an 800 nm laser field with intensity ranging from W/cm to W/cm. The energy range probed spans 16-42 eV, straddling the first ionisation energy of helium (24.59 eV). By changing the relative polarisation of the dressing field with respect to the attosecond pulse train polarisation we observe a large change in the modulation of the absorption reflecting the vectorial response to the dressing field. With parallel polarized dressing and probing fields, we observe significant modulations with periods of one half and one quarter of the dressing field period. With perpendicularly polarized dressing and probing fields, the modulations of the harmonics above the ionisation threshold are significantly suppressed. A full-dimensionality solution of the single-atom time-dependent Schr odinger equation obtained using the recently developed ab-initio time-dependent B-spline ADC method reproduce some of our observations
From z>6 to z~2: Unearthing Galaxies at the Edge of the Dark Ages
Galaxies undergoing formation and evolution can now be observed over a time
baseline of some 12 Gyr. An inherent difficulty with high-redshift observations
is that the objects are very faint and the best resolution (HST) is only ~0.5
kpc. Such studies thereby combine in a highly synergistic way with the great
detail that can be obtained for nearby galaxies. 3 new developments are
highlighted. First is the derivation of stellar masses for galaxies from SEDs
using HST and now Spitzer data, and dynamical masses from both sub-mm
observations of CO lines and near-IR observations of optical lines like Halpha.
A major step has been taken with evidence that points to the z~2-3 LBGs having
masses that are a few x 10^10 Msolar. Second is the discovery of a population
of evolved red galaxies at z~2-3 which appear to be the progenitors of the more
massive early-type galaxies of today, with dynamical masses around a few x
10^11 Msolar. Third are the remarkable advances that have occurred in
characterizing dropout galaxies to z~6 and beyond, < 1 Gyr from recombination.
The HST ACS has played a key role here, with the dropout technique being
applied to i & z images in several deep ACS fields, yielding large samples of
these objects. This has allowed a detailed determination of their properties
and meaningful comparisons against lower-z samples. The use of cloning
techniques has overcome many of the strong selection biases affecting the study
of these objects. A clear trend of size with redshift has been identified, and
its impact on the luminosity density and SFR estimated. There is a significant
though modest decrease in the SFR from z~2.5 to z~6. The latest data also allow
for the first robust determination of the LF at z~6. Finally, the latest UDF
ACS and NICMOS data has resulted in the detection of some galaxies at z~7-8.Comment: 18 pages, 8 figures. To appear in Penetrating Bars through Masks of
Cosmic Dust: The Hubble Tuning Fork Strikes a New Note, eds. D. Block, K.
Freeman, R. Groess, I. Puerari, & E.K. Block (Dordrecht: Kluwer), in pres
Feynman Rules in the Type III Natural Flavour-Conserving Two-Higgs Doublet Model
We consider a two Higgs-doublet model with symmetry, which implies a
rather than 0 relative phase between the vacuum expectation
values . The corresponding Feynman rules are derived
accordingly and the transformation of the Higgs fields from the weak to the
mass eigenstates includes not only an angle rotation but also a phase
transformation. In this model, both doublets couple to the same type of
fermions and the flavour-changing neutral currents are naturally suppressed. We
also demonstrate that the Type III natural flavour-conserving model is valid at
tree-level even when an explicit symmetry breaking perturbation is
introduced to get a reasonable CKM matrix. In the special case , as the ratio runs from 0 to ,
the dominant Yukawa coupling will change from the first two generations to the
third generation. In the Feynman rules, we also find that the charged Higgs
currents are explicitly left-right asymmetric. The ratios between the left- and
right-handed currents for the quarks in the same generations are estimated.Comment: 16 pages (figures not included), NCKU-HEP/93-1
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