1,514 research outputs found
Dark Matter Prediction from Canonical Quantum Gravity with Frame Fixing
We show how, in canonical quantum cosmology, the frame fixing induces a new
energy density contribution having features compatible with the (actual) cold
dark matter component of the Universe. First we quantize the closed
Friedmann-Robertson-Walker (FRW) model in a sinchronous reference and determine
the spectrum of the super-Hamiltonian in the presence of ultra-relativistic
matter and a perfect gas contribution. Then we include in this model small
inhomogeneous (spherical) perturbations in the spirit of the Lemaitre-Tolman
cosmology. The main issue of our analysis consists in outlining that, in the
classical limit, the non-zero eigenvalue of the super-Hamiltonian can make
account for the present value of the dark matter critical parameter.
Furthermore we obtain a direct correlation between the inhomogeneities in our
dark matter candidate and those one appearing in the ultra-relativistic matter.Comment: 5 pages, to appear on Modern Physics Letters
Shape-memory Sponge Hydrogel Biomaterial
A hydrogel biomaterial that can be utilized as a nucleus pulposus replacement material is described. The hydrogel biomaterial can is an elastin-glycosaminoglycan-collagen composite hydrogel biomaterial that can mimic the biochemical and functional characteristics of the human nucleus pulposus. Methods for forming the hydrogel biomaterial are also described as are methods for use of the hydrogel biomaterial, one of which is as an in vivo nucleus pulposus replacement material, another of which is a scaffolding material for use in nucleus pulposus tissue engineering applications
ECONOMY AND ENVIRONMENT OF THE GREEK COLONIAL SYSTEM IN SOUTHERN ITALY: POLLEN AND NPPS EVIDENCE OF GRAZING FROM THE RURAL SITE OF FATTORIA FABRIZIO (VI-IV CENT. BC; METAPONTO, BASILICATA)
this paper reports a study case showing integrated analyses of microscopic records from an archaeological site of southern italy. pollen and non pollen palynomorphs-Npps were found in archaeological layers and were basic in reconstructing both the past environment and the economic activities of the site. the site, Fattoria Fabrizio, is a modest 4th-cenury bc farmhouse of the chora (rural territory) of the Greek city (polis) of Metaponto (basilicata). pollen analyses in addition to the study of Npps have been particularly worthwhile for palaeoenvironmental and palaeoeconomical reconstructions of this site and others in the chora. the pollen spectra delineate an open plant landscape, with scanty woodlands and presence of local wet environments. Olea pollen is fairly well represented in all samples, suggesting that this tree was an important element of the agricultural economy of the chora. shrubby grasslands and a well-developed macchia characterized the territory, probably as result of grazing activities by sheep and goats. accordingly, the high percentages of poaceae and cichorieae pollen, together with coprophilous fungal spores (such as Sordaria type and Sporormiella type), suggest that pastoral activities were widely practiced. the low number of cerealia pollen grains suggests that the inhabitants’ fields covered small areas or were quite far from the farmhouse
Chirality of tensor perturbations for complex values of the Immirzi parameter
In this paper we generalise previous work on tensor perturbations in a de
Sitter background in terms of Ashtekar variables to cover all complex values of
the Immirzi parameter gamma (previous work was restricted to imaginary gamma).
Particular attention is paid to the case of real gamma. Following the same
approach as in the imaginary case, we can obtain physical graviton states by
invoking reality and torsion free conditions. The Hamiltonian in terms of
graviton states has the same form whether gamma has a real part or not; however
changes occur for the vacuum energy and fluctuations. Specifically, we observe
a gamma dependent chiral asymmetry in the vacuum fluctuations only if gamma has
an imaginary part. Ordering prescriptions also change this asymmetry. We thus
present a measurable result for CMB polarisation experiments that could shed
light on the workings of quantum gravity.Comment: 6 pages, 1 figur
Generating functional for the gravitational field: implementation of an evolutionary quantum dynamics
We provide a generating functional for the gravitational field, associated to
the relaxation of the primary constraints as extended to the quantum sector.
This requirement of the theory, relies on the assumption that a suitable time
variable exist, when taking the T-products of the dynamical variables. More
precisely, we start from the gravitational field equations written in the
Hamiltonian formalism and expressed via Misner-like variables; hence we
construct the equation to which the T-products of the dynamical variables obey
and transform this paradigm in terms of the generating functional, as taken on
the theory phase-space. We show how the relaxation of the primary constraints
(which correspond to break down the invariance of the quantum theory under the
4-diffeomorphisms) is summarized by a free functional taken on the Lagrangian
multipliers, accounting for such constraints in the classical theory. The issue
of our analysis is equivalent to a Gupta-Bleuler approach on the quantum
implementation of all the gravitational constraints; in fact, in the limit of
small , the quantum dynamics is described by a Schr\"odinger equation,
as soon as the mean values of the momenta, associated to the lapse function and
the shift vector, are not vanishing. Finally we show how, in the classical
limit, the evolutionary quantum gravity reduces to General Relativity in the
presence of an Eckart fluid, which corresponds to the classical counterpart of
the physical clock, introduced in the quantum theory.Comment: 23 pages, no figures, to appear on International Journal of Modern
Physics
E-Voting in an ubicomp world: trust, privacy, and social implications
The advances made in technology have unchained the user from the desktop into interactions where access is anywhere, anytime. In addition, the introduction of ubiquitous computing (ubicomp) will see further changes in how we interact with technology and also socially. Ubicomp evokes a near future in which humans will be surrounded by “always-on,” unobtrusive, interconnected intelligent objects where information is exchanged seamlessly. This seamless exchange of information has vast social implications, in particular the protection and management of personal information. This research project investigates the concepts of trust and privacy issues specifically related to the exchange of e-voting information when using a ubicomp type system
Development of a Novel Biological Intervertebral Disc Scaffold
Back pain is a major public health issue in our society, and is strongly correlated with the degeneration of intervertebral discs (IVDs). Current therapies are conservative or surgical, and no attempt to regenerate the IVD. The first goal of our project is to create a fully decellularized bovine caudal IVD to be used as a scaffold on which to seed adult human stem cells in an attempt to engineer a healthy, replacement IVD for patients suffering from IVD degeneration and lower back pain. The goal of decellularization is to eliminate DNA content while retaining glycosaminoglycan (GAG) content. Eliminating DNA content will prevent a foreign body response by the host\u27s immune system once the IVD is implanted. GAG is responsible for forming interfibrillar bridges with collagen fibrils and thus assisting in resisting compressive and tensile forces. By retaining GAG content in our decellularized IVDs we will maintain structural integrity of the extracellular matrix. The IVDs closest to the base of the bovine tail were targeted, because they are similar in size and biochemistry to the human IVD. We use a mix of conventional methods including freeze thaw, sonication and agitation in a solution of sodium dodecyl sulfate (SDS) and ethylene diamine tetraacetic acid (EDTA). After decellularization, half of each IVD was placed in a tissue cassette and put formalin in preparation for histological analysis, and the other half was frozen prior to biochemical analysis (DMMB and PicoGreen assay). Our results thus far are promising in eliminating DNA content but show we have a large room for improvement in retaining GAG content
Selective laser sintering of hydroxyapatite reinforced polyethylene composites for bioactive implants and tissue scaffold development
Selective laser sintering (SLS) has been investigated for the production of bioactive implants and tissue scaffolds using composites of high-density polyethylene (HDPE) reinforced with hydroxyapatite (HA) with the aim of achieving the rapid manufacturing of customized implants. Single-layer and multilayer block specimens made of HA-HDPE composites with 30 and 40 vol % HA were sintered successfully using a CO2 laser sintering system. Laser power and scanning speed had a significant effect on the sintering behaviour. The degree of particle fusion and porosity were influenced by the laser processing parameters, hence control can be attained by varying these parameters. Moreover, the SLS processing allowed exposure of HA particles on the surface of the composites and thereby should provide bioactive products. Pores existed in the SLS-fabricated composite parts and at certain processing parameters a significant fraction of the pores were within the optimal sizes for tissue regeneration. The results indicate that the SLS technique has the potential not only to fabricate HA-HDPE composite products but also to produce appropriate features for their application as bioactive implants and tissue scaffolds
Population pharmacokinetics-based recommendations for a single delayed or missed dose of nusinersen
Nusinersen is an antisense oligonucleotide approved for the treatment of spinal muscular atrophy. The drug is given intrathecally at 12 mg, beginning with 3 loading doses at 2-week intervals, a fourth loading dose 30 days thereafter, and maintenance doses at 4-month intervals. This population pharmacokinetic model was developed to clarify how to maintain targeted nusinersen exposure after an unforeseen one-time delay or missed dose. Simulations demonstrated that the impact of a one-time delay in dosing or a missed dose on median cerebrospinal fluid exposures depended on duration of interruption and the regimen phase in which it occurred. Delays in loading doses delayed reaching the peak trough concentration by approximately the duration of the interruption. Resumption of the regimen as soon as possible resulted in achieving steady state trough concentration upon completion of the loading phase. A short delay (30-90 days) during the maintenance phase led to prolonged lower median cerebrospinal fluid concentration if all subsequent doses were shifted by the same 4-month interval. However, administration of the delayed dose, followed by the subsequent dose as originally scheduled, rapidly restored trough concentration. If a dose must be delayed, patients should return to the original dosing schedule as soon as possible
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