4,332 research outputs found
Demography and public health
The health and health care needs of a population cannot be measured or met without knowledge of its size and characteristics. Demography is concerned with this and with understanding population dynamics - how populations change in response to the interplay between fertility, mortality and migration. This understanding is a pre-requisite for making the forecasts about future population size and structure which should underpin health care planning. Such analyses necessitate a review of the past. The number of very old people in a population, for example, depends on the number of births eight or nine decades earlier and risks of death at successive ages throughout the intervening period. The proportion of very old people depends partly on this numerator but more importantly on the denominator, the size of the population as a whole. The number of births in a population depends on current patterns of family building, and also on the number of women 'at risk' of reproduction - itself a function of past trends in fertility and mortality. Similarly, the number and causes of deaths are strongly influenced by age structure. Demography is largely concerned with answering questions about how populations change and their measurement. The broader field of population studies embraces questions of why these changes occur, and with what consequences. This chapter presents information on demographic methods and data sources and their application to health and population issues, together with information on demographic trends and their implications and the major theories about demographic change in order to elucidate the complex inter-relationship between population change and human health
Magnetic field generation in finite beam plasma system
For finite systems boundaries can introduce remarkable novel features. A well
known example is the Casimir effect [1, 2] that is observed in quantum
electrodynamic systems. In classical systems too novel effects associated with
finite boundaries have been observed, for example the surface plasmon mode [3]
that appears when the plasma has a finite extension. In this work a novel
instability associated with the finite transverse size of a beam owing through
a plasma system has been shown to exist. This instability leads to distinct
characteristic features of the associated magnetic field that gets generated.
For example, in contrast to the well known unstable Weibel mode of a beam
plasma system which generates magnetic field at the skin depth scale, this
instability generates magnetic field at the scales length of the transverse
beam dimension [4]. The existence of this new instability is demonstrated by
analytical arguments and by simulations conducted with the help of a variety of
Particle - In - Cell (PIC) codes (e.g. OSIRIS, EPOCH, PICPSI). Two fluid
simulations have also been conducted which confirm the observations.
Furthermore, laboratory experiments on laser plasma system also provides
evidence of such an instability mechanism at work
Performance Limits of Stochastic Sub-Gradient Learning, Part II: Multi-Agent Case
The analysis in Part I revealed interesting properties for subgradient
learning algorithms in the context of stochastic optimization when gradient
noise is present. These algorithms are used when the risk functions are
non-smooth and involve non-differentiable components. They have been long
recognized as being slow converging methods. However, it was revealed in Part I
that the rate of convergence becomes linear for stochastic optimization
problems, with the error iterate converging at an exponential rate
to within an neighborhood of the optimizer, for some and small step-size . The conclusion was established under weaker
assumptions than the prior literature and, moreover, several important problems
(such as LASSO, SVM, and Total Variation) were shown to satisfy these weaker
assumptions automatically (but not the previously used conditions from the
literature). These results revealed that sub-gradient learning methods have
more favorable behavior than originally thought when used to enable continuous
adaptation and learning. The results of Part I were exclusive to single-agent
adaptation. The purpose of the current Part II is to examine the implications
of these discoveries when a collection of networked agents employs subgradient
learning as their cooperative mechanism. The analysis will show that, despite
the coupled dynamics that arises in a networked scenario, the agents are still
able to attain linear convergence in the stochastic case; they are also able to
reach agreement within of the optimizer
Solar wind collisional heating
To properly describe heating in weakly collisional turbulent plasmas such as
the solar wind, inter-particle collisions should be taken into account.
Collisions can convert ordered energy into heat by means of irreversible
relaxation towards the thermal equilibrium. Recently, Pezzi et al. (Phys. Rev.
Lett., vol. 116, 2016, p. 145001) showed that the plasma collisionality is
enhanced by the presence of fine structures in velocity space. Here, the
analysis is extended by directly comparing the effects of the fully nonlinear
Landau operator and a linearized Landau operator. By focusing on the relaxation
towards the equilibrium of an out of equilibrium distribution function in a
homogeneous force-free plasma, here it is pointed out that it is significant to
retain nonlinearities in the collisional operator to quantify the importance of
collisional effects. Although the presence of several characteristic times
associated with the dissipation of different phase space structures is
recovered in both the cases of the nonlinear and the linearized operators, the
influence of these times is different in the two cases. In the linearized
operator case, the recovered characteristic times are systematically larger
than in the fully nonlinear operator case, this suggesting that fine velocity
structures are dissipated slower if nonlinearities are neglected in the
collisional operator
Locus model for space-time fabric and quantum indeterminacies
A simple locus model for the space-time fabric is presented and is compared
with quantum foam and random walk models. The induced indeterminacies in
momentum are calculated and it is shown that these space-time fabric
indeterminacies are, in most cases, negligible compared with the quantum
mechanical indeterminacies. This result restricts the possibilities of an
experimental observation of the space-time fabric
Some Remarks about the Complexity of Epidemics Management
Recent outbreaks of Ebola, H1N1 and other infectious diseases have shown that
the assumptions underlying the established theory of epidemics management are
too idealistic. For an improvement of procedures and organizations involved in
fighting epidemics, extended models of epidemics management are required. The
necessary extensions consist in a representation of the management loop and the
potential frictions influencing the loop. The effects of the non-deterministic
frictions can be taken into account by including the measures of robustness and
risk in the assessment of management options. Thus, besides of the increased
structural complexity resulting from the model extensions, the computational
complexity of the task of epidemics management - interpreted as an optimization
problem - is increased as well. This is a serious obstacle for analyzing the
model and may require an additional pre-processing enabling a simplification of
the analysis process. The paper closes with an outlook discussing some
forthcoming problems
Ferromagnetic and insulating behavior of LaCoO3 films grown on a (001) SrTiO3 substrate. A simple ionic picture explained ab initio
This paper shows that the oxygen vacancies observed experimentally in thin
films of LaCoO3 subject to tensile strain are thermodynamically stable
according to ab initio calculations. By using DFT calculations, we show that
oxygen vacancies on the order of 6 % forming chains perpendicular to the (001)
direction are more stable than the stoichiometric solution. These lead to
magnetic Co2+ ions surrounding the vacancies that couple ferromagnetically. The
remaining Co3+ cations in an octahedral environment are non magnetic. The gap
leading to a ferromagnetic insulating phase occurs naturally and we provide a
simple ionic picture to explain the resulting electronic structure.Comment: 7 pages, 7 figure
Wave-like Decoding of Tail-biting Spatially Coupled LDPC Codes Through Iterative Demapping
For finite coupling lengths, terminated spatially coupled low-density
parity-check (SC-LDPC) codes show a non-negligible rate-loss. In this paper, we
investigate if this rate loss can be mitigated by tail-biting SC-LDPC codes in
conjunction with iterative demapping of higher order modulation formats.
Therefore, we examine the BP threshold of different coupled and uncoupled
ensembles. A comparison between the decoding thresholds approximated by EXIT
charts and the density evolution results of the coupled and uncoupled ensemble
is given. We investigate the effect and potential of different labelings for
such a set-up using per-bit EXIT curves, and exemplify the method for a 16-QAM
system, e.g., using set partitioning labelings. A hybrid mapping is proposed,
where different sub-blocks use different labelings in order to further optimize
the decoding thresholds of tail-biting codes, while the computational
complexity overhead through iterative demapping remains small.Comment: presentat at the International Symposium on Turbo Codes & Iterative
Information Processing (ISTC), Brest, Sept. 201
The Complete Calibration of the Color-Redshift Relation (C3R2) Survey: Survey Overview and Data Release 1
A key goal of the Stage IV dark energy experiments Euclid, LSST and WFIRST is
to measure the growth of structure with cosmic time from weak lensing analysis
over large regions of the sky. Weak lensing cosmology will be challenging: in
addition to highly accurate galaxy shape measurements, statistically robust and
accurate photometric redshift (photo-z) estimates for billions of faint
galaxies will be needed in order to reconstruct the three-dimensional matter
distribution. Here we present an overview of and initial results from the
Complete Calibration of the Color-Redshift Relation (C3R2) survey, designed
specifically to calibrate the empirical galaxy color-redshift relation to the
Euclid depth. These redshifts will also be important for the calibrations of
LSST and WFIRST. The C3R2 survey is obtaining multiplexed observations with
Keck (DEIMOS, LRIS, and MOSFIRE), the Gran Telescopio Canarias (GTC; OSIRIS),
and the Very Large Telescope (VLT; FORS2 and KMOS) of a targeted sample of
galaxies most important for the redshift calibration. We focus spectroscopic
efforts on under-sampled regions of galaxy color space identified in previous
work in order to minimize the number of spectroscopic redshifts needed to map
the color-redshift relation to the required accuracy. Here we present the C3R2
survey strategy and initial results, including the 1283 high confidence
redshifts obtained in the 2016A semester and released as Data Release 1.Comment: Accepted to ApJ. 11 pages, 5 figures. Redshifts can be found at
http://c3r2.ipac.caltech.edu/c3r2_DR1_mrt.tx
Joint Hybrid Precoder and Combiner Design for mmWave Spatial Multiplexing Transmission
Millimeter-wave (mmWave) communications have been considered as a key
technology for future 5G wireless networks because of the orders-of-magnitude
wider bandwidth than current cellular bands. In this paper, we consider the
problem of codebook-based joint analog-digital hybrid precoder and combiner
design for spatial multiplexing transmission in a mmWave multiple-input
multiple-output (MIMO) system. We propose to jointly select analog precoder and
combiner pair for each data stream successively aiming at maximizing the
channel gain while suppressing the interference between different data streams.
After all analog precoder/combiner pairs have been determined, we can obtain
the effective baseband channel. Then, the digital precoder and combiner are
computed based on the obtained effective baseband channel to further mitigate
the interference and maximize the sum-rate. Simulation results demonstrate that
our proposed algorithm exhibits prominent advantages in combating interference
between different data streams and offer satisfactory performance improvement
compared to the existing codebook-based hybrid beamforming schemes
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