404 research outputs found
Zero-Delay Joint Source-Channel Coding in the Presence of Interference Known at the Encoder
Zero-delay transmission of a Gaussian source over an additive white Gaussian noise (AWGN) channel is considered in the presence of an additive Gaussian interference signal. The mean squared error (MSE) distortion is minimized under an average power constraint assuming that the interference signal is known at the transmitter. Optimality of simple linear transmission does not hold in this setting due to the presence of the known interference signal. While the optimal encoder-decoder pair remains an open problem, various non-linear transmission schemes are proposed in this paper. In particular, interference concentration (ICO) and one-dimensional lattice (1DL) strategies, using both uniform and non-uniform quantization of the interference signal, are studied. It is shown that, in contrast to typical scalar quantization of Gaussian sources, a non-uniform quantizer, whose quantization intervals become smaller as we go further from zero, improves the performance. Given that the optimal decoder is the minimum MSE (MMSE) estimator, a necessary condition for the optimality of the encoder is derived, and the numerically optimized encoder (NOE) satisfying this condition is obtained. Based on the numerical results, it is shown that 1DL with nonuniform quantization performs closer (compared to the other schemes) to the numerically optimized encoder while requiring significantly lower complexity
Killing-Yano Forms of a Class of Spherically Symmetric Space-Times II: A Unified Generation of Higher Forms
Killing-Yano (KY) two and three forms of a class of spherically symmetric
space-times that includes the well-known Minkowski, Schwarzschild,
Reissner-Nordstrom, Robertson-Walker and six different forms of de Sitter
space-times as special cases are derived in a unified and exhaustive manner. It
is directly proved that while the Schwarzschild and Reissner-Nordstrom
space-times do not accept any KY 3-form and they accept only one 2-form, the
Robertson-Walker space-time admits four KY 2-forms and only one KY 3-form.
Maximal number of KY-forms are obtained for Minkowski and all known forms of de
Sitter space-times. Complete lists comprising explicit expressions of KY-forms
are given.Comment: 28 page
Basic Gravitational Currents and Killing-Yano Forms
It has been shown that for each Killing-Yano (KY)-form accepted by an
-dimensional (pseudo)Riemannian manifold of arbitrary signature, two basic
gravitational currents can be defined. Conservation of the currents are
explicitly proved by showing co-exactness of the one and co-closedness of the
other. Some general geometrical facts implied by these conservation laws are
also elucidated. In particular, the conservation of the one-form currents
implies that the scalar curvature of the manifold is a flow invariant for all
of its Killing vector fields. It also directly follows that, while all KY-forms
and their Hodge duals on a constant curvature manifold are the eigenforms of
the Laplace-Beltrami operator, for an Einstein manifold this is certain only
for KY 1-forms, -forms and their Hodge duals.Comment: 11 page
Understanding parental concerns related to their child’s development and factors influencing their decisions to seek help from health care professionals: Results of a qualitative study.
Background: Early identification of children at risk of developmental delay is crucial to promote healthy development. Assessing parental concerns about development is often part of identification processes. However, we currently do not understand well how and why parents become concerned, and, how and why they access early identification and intervention services. The purpose of this study was to explore parental perceptions about their child’s development, and the factors influencing their reported professional help-seeking behaviours.
Methods: This exploratory study was part of a larger study describing child development in children aged 2-5 in a small Canadian city. We conducted semi-structured interviews with 16 parents whose children were at risk of developmental delay to examine their perceptions of their child’s development, their use of community services promoting development, and their recommendations to optimize those services.
Results: Four themes were identified: 1) Vision of child development influencing help-seeking behaviours: Natural or Supported?, 2) Internal and external sources contributing to parents’ level of developmental concern, 3) Using internal resources and struggling to access external resources, and 4) Satisfaction with services accessed and recommendations to access more support. Parents’ vision of child development along with sources of parental concern appeared to influence the level of concern, enhancing our understanding of how parents become concerned. The level of concern, and parents’ knowledge and perceived access to resources seemed to influence their decision whether or not to consult health care professionals. Parents provided many suggestions to improve services to promote child development and support families.
Discussion: Results highlight the importance of supporting parents in recognizing if their child is at risk of delay, and increasing awareness of available resources. It appears particularly important to ensure health care professionals and community-based support services are accessible to provide parents with the support they need, especially when they have concerns
Generalized Chern-Simons Modified Gravity in First-Order Formalism
We propose a generalization of Chern-Simons (CS) modified gravity in
first-order formalism. CS modified gravity action has a term that comes from
the chiral anomaly which is Pontryagin invariant. First-order CS modified
gravity is a torsional theory and in a space-time with torsion the chiral
anomaly includes a torsional topological term called Nieh-Yan invariant. We
generalize the CS modified gravity by adding the Nieh-Yan term to the action
and find the effective theory. We compare the generalized theory with the
first-order CS modified gravity and comment on the similarities and
differences.Comment: 8 pages, an author added, new paragraphs, comments and references
added, published in Gen. Relativ. Gravi
Beyond Einstein-Cartan gravity: Quadratic torsion and curvature invariants with even and odd parity including all boundary terms
Recently, gravitational gauge theories with torsion have been discussed by an
increasing number of authors from a classical as well as from a quantum field
theoretical point of view. The Einstein-Cartan(-Sciama-Kibble) Lagrangian has
been enriched by the parity odd pseudoscalar curvature (Hojman, Mukku, and
Sayed) and by torsion square and curvature square pieces, likewise of even and
odd parity. (i) We show that the inverse of the so-called Barbero-Immirzi
parameter multiplying the pseudoscalar curvature, because of the topological
Nieh-Yan form, can only be appropriately discussed if torsion square pieces are
included. (ii) The quadratic gauge Lagrangian with both parities, proposed by
Obukhov et al. and Baekler et al., emerges also in the framework of Diakonov et
al.(2011). We establish the exact relations between both approaches by applying
the topological Euler and Pontryagin forms in a Riemann-Cartan space expressed
for the first time in terms of irreducible pieces of the curvature tensor.
(iii) Only in a Riemann-Cartan spacetime, that is, in a spacetime with torsion,
parity violating terms can be brought into the gravitational Lagrangian in a
straightforward and natural way. Accordingly, Riemann-Cartan spacetime is a
natural habitat for chiral fermionic matter fields.Comment: 12 page latex, as version 2 an old file was submitted by mistake,
this is now the real corrected fil
TOpic: rare and special cases, the real "Strange cases"
Introduction: The bladder hernia represents approximately 1-3% of
all inguinal hernias, where patients aged more than 50 years have a
higher incidence (10%). Many factors contribute to the development of a bladder hernia,
including the presence of a urinary outlet obstruction causing chronic
bladder distention, the loss of bladder tone, pericystitis, the perivesical
bladder fat protrusion and the obesity
The origin of life: chemical evolution of a metabolic system in a mineral honeycomb?
For the RNA-world hypothesis to be ecologically feasible, selection mechanisms acting on replicator communities need to be invoked and the corresponding scenarios of molecular evolution specified. Complementing our previous models of chemical evolution on mineral surfaces, in which selection was the consequence of the limited mobility of macromolecules attached to the surface, here we offer an alternative realization of prebiotic group-level selection: the physical encapsulation of local replicator communities into the pores of the mineral substrate. Based on cellular automaton simulations we argue that the effect of group selection in a mineral honeycomb could have been efficient enough to keep prebiotic ribozymes of different specificities and replication rates coexistent, and their metabolic cooperation protected from extensive molecular parasitism. We suggest that mutants of the mild parasites persistent in the metabolic system can acquire useful functions such as replicase activity or the production of membrane components, thus opening the way for the evolution of the first autonomous protocells on Earth
Selective Adsorption and Chiral Amplification of Amino Acids in Vermiculite Clay -Implications for the origin of biochirality
Smectite clays are hydrated layer silicates that, like micas, occur naturally
in abundance. Importantly, they have readily modifiable interlayer spaces that
provide excellent sites for nanochemistry. Vermiculite is one such smectite
clay and in the presence of small chain-length alkyl-NH3Cl ions, forms
sensitive, 1-D ordered model clay systems with expandable nano-pore inter-layer
regions. These inter-layers readily adsorb organic molecules. N-propyl NH3Cl
vermiculite clay gels were used to determine the adsorption of alanine, lysine
and histidine by chiral HPLC. The results show that during reaction with fresh
vermiculite interlayers, significant chiral enrichment of either L- and
D-enantiomers occurs depending on the amino acid. Chiral enrichment of the
supernatant solutions is up to about 1% per pass. In contrast, addition to clay
interlayers already reacted with amino acid solutions resulted in little or no
change in D/L ratio during the time of the experiment. Adsorption of small
amounts of amphiphilic organic molecules in clay inter-layers is known to
produce Layer-by-Layer or Langmuir-Blodgett films. Moreover atomistic
simulations show that self-organization of organic species in clay interlayers
is important. These non-centrosymmetric, chirally active nanofilms may cause
clays to act subsequently as chiral amplifiers, concentrating organic material
from dilute solution and having different adsorption energetics for D- and
L-enantiomers. The additional role of clays in RNA oligimerization already
postulated by Ferris and others, together with the need for the organization of
amphiphilic molecules and lipids noted by Szostak and others, suggests that
such chiral separation by clays in lagoonal environments at normal biological
temperatures might also have played a significant role in the origin of
biochirality.Comment: 17 Pages, 2 Figures, 4 Table
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