3,133 research outputs found
Scalars, Vectors and Tensors from Metric-Affine Gravity
The metric-affine gravity provides a useful framework for analyzing
gravitational dynamics since it treats metric tensor and affine connection as
fundamentally independent variables. In this work, we show that, a
metric-affine gravity theory composed of the invariants formed from
non-metricity, torsion and curvature tensors can be decomposed into a theory of
scalar, vector and tensor fields. These fields are natural candidates for the
ones needed by various cosmological and other phenomena. Indeed, we show that
the model accommodates TeVeS gravity (relativistic modified gravity theory),
vector inflation, and aether-like models. Detailed analyses of these and other
phenomena can lead to a standard metric-affine gravity model encoding scalars,
vectors and tensors.Comment: 13 p
Optimized isolation and expansion of human airway epithelial basal cells from endobronchial biopsy samples
Autologous airway epithelial cells have been used in clinical tissue-engineered airway transplantation procedures with a view to assisting mucosal regeneration and restoring mucociliary escalator function. However, limited time is available for epithelial cell expansion due to the urgent nature of these interventions and slow epithelial regeneration has been observed in patients. Human airway epithelial cells can be expanded from small biopsies or brushings taken during bronchoscopy procedures but the optimal mode of tissue acquisition from patients has not been investigated. Here, we compare endobronchial brushing and endobronchial biopsy samples in terms of their cell number and their ability to initiate basal epithelial stem cell cultures. We found that direct co-culture of samples with 3T3-J2 feeder cells in culture medium containing a Rho-associated protein kinase (ROCK) inhibitor, Y-27632, led to the selective expansion of greater numbers of basal epithelial stem cells during the critical early stages of culture than traditional techniques. Additionally, we established the benefit of initiating cell cultures from cell suspensions, either using brushing samples or through enzymatic digestion of biopsies, over explant culture. Primary epithelial cell cultures were initiated from endobronchial biopsy samples that had been cryopreserved prior to the initiation of cell cultures, suggesting that cryopreservation could eliminate the requirement for close proximity between the clinical facility in which biopsy samples are taken and the specialist laboratory in which epithelial cells are cultured. Overall, our results suggest ways to expedite epithelial cell preparation in future airway cell therapy or bioengineered airway transplantation procedures
Cosmological Birefringence: an Astrophysical test of Fundamental Physics
We review the methods used to test for the existence of cosmological
birefringence, i.e. a rotation of the plane of linear polarization for
electromagnetic radiation traveling over cosmological distances, which might
arise in a number of important contexts involving the violation of fundamental
physical principles. The main methods use: (1) the radio polarization of radio
galaxies and quasars, (2) the ultraviolet polarization of radio galaxies, and
(3) the cosmic microwave background polarization. We discuss the main results
obtained so far, the advantages and disadvantages of each method, and future
prospects.Comment: To appear in the Proceedings of the JENAM 2010 Symposium "From
Varying Couplings to Fundamental Physics", held in Lisbon, 6-10 Sept. 201
Probing Density Fluctuations using the FIRST Radio Survey
We use results of angular clustering measurements in 3000 sq. deg's of the
FIRST radio survey to infer information on spatial clustering. Measurements are
compared with CDM-model predictions. Clustering of FIRST sources with optical
ID's in the APM catalog are also investigated. Finally, we outline a
preliminary search for a weak lensing signal in the survey.Comment: 6 pages latex, 2 figures, to appear in Cosmology with the New Radio
Surveys (Kluwer
A longitudinal evaluation of dexamethasone and cortisol plasma concentrations in the dexamethasone suppression test before and during treatment with antidepressant drugs
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66095/1/j.1600-0447.1990.tb03073.x.pd
Water Challenges for Geologic Carbon Capture and Sequestration
Carbon capture and sequestration (CCS) has been proposed as a means to dramatically reduce greenhouse gas emissions with the continued use of fossil fuels. For geologic sequestration, the carbon dioxide is captured from large point sources (e.g., power plants or other industrial sources), transported to the injection site and injected into deep geological formations for storage. This will produce new water challenges, such as the amount of water used in energy resource development and utilization and the ācapture penaltyā for water use. At depth, brine displacement within formations, storage reservoir pressure increases resulting from injection, and leakage are potential concerns. Potential impacts range from increasing water demand for capture to contamination of groundwater through leakage or brine displacement. Understanding these potential impacts and the conditions under which they arise informs the design and implementation of appropriate monitoring and controls, important both for assurance of environmental safety and for accounting purposes. Potential benefits also exist, such as co-production and treatment of water to both offset reservoir pressure increase and to provide local water for beneficial use
Long-term survival of donor-specific pancreatic islet xenografts in fully xenogeneic chimeras (F344 rat to B10 mouse)
We recently reported that reconstitution of lethally irradiated BIO mouse recipients with 40x10s untreated WF rat bone marrow cells resulted in stable fully xenogeneic chimerism (WF rat ā B10 mouse). In these animals, the tolerance induced for skin xenografts was highly MHC specific in that donor-specific WF rat skin grafts were significantly prolonged while MHC-dispar-ate third-party xenografts were rapidly rejected (median survival time [MST] = 9 days). We have now examined whether islet cell xenografts placed under the renal capsule of chimeras rendered diabetic with strep-tozotocin would be accepted and remain functional to maintain euglycemia. Animals were prepared, typed for chimerism at 6 weeks, and diabetes induced with strep-tozotocin. Donor-specific WF (RtlA") islet cell xenografts were significantly prolonged (MST >180 days) in WF ā B10 chimeras, while MHC-disparate third-party F344 rat (RtlA1) grafts were rejected with a time course similar to unmanipulated BIO mice (MST=8 days). The transplanted donor-specific islet cells were functional to maintain euglycemia, since removal of the grafts at from 100 to 180 days in selected individual chimeras uniformly resulted in return of the diabetic state. These data suggest that donor-specific islet cell xenografts are accepted and remain functional in mice rendered tolerant to rat xenoantigens following bone marrow transplantation. Ā© 1992 by Williams and Wilkins
Scale Dependence of Dark Energy Antigravity
We investigate the effects of negative pressure induced by dark energy
(cosmological constant or quintessence) on the dynamics at various
astrophysical scales. Negative pressure induces a repulsive term (antigravity)
in Newton's law which dominates on large scales. Assuming a value of the
cosmological constant consistent with the recent SnIa data we determine the
critical scale beyond which antigravity dominates the dynamics () and discuss some of the dynamical effects implied. We show that
dynamically induced mass estimates on the scale of the Local Group and beyond
are significantly modified due to negative pressure. We also briefly discuss
possible dynamical tests (eg effects on local Hubble flow) that can be applied
on relatively small scales (a few ) to determine the density and equation
of state of dark energy.Comment: Contributed talk at the 2nd Hellenic Cosmology Workshop at NOA
(Athens) Jan. 2001.To appear in the proceedings. Based on work done in
collaboration with M. Axenides and E. Florato
Classicalization and Unitarity
We point out that the scenario for UV completion by "classicalization",
proposed recently is in fact Wilsonian in the classical Wilsonian sense. It
corresponds to the situation when a field theory has a nontrivial UV fixed
point governed by a higher dimensional operator. Provided the kinetic term is a
relevant operator around this point the theory will flow in the IR to the free
scalar theory. Physically, "classicalization", if it can be realized, would
correspond to a situation when the fluctuations of the field operator in the UV
are smaller than in the IR. As a result there exists a clear tension between
the "classicalization" scenario and constraints imposed by unitarity on a
quantum field theory, making the existence of classicalizing unitary theories
questionable.Comment: Some clarifications and refs added. Accepted as a JHEP publication;
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