7,116 research outputs found
Electrically conductive, optically transparent polymer/carbon nanotube composites
The present invention is directed to the effective dispersion of carbon nanotubes (CNTs) into polymer matrices. The nanocomposites are prepared using polymer matrices and exhibit a unique combination of properties, most notably, high retention of optical transparency in the visible range (i.e., 400-800 nm), electrical conductivity, and high thermal stability. By appropriate selection of the matrix resin, additional properties such as vacuum ultraviolet radiation resistance, atomic oxygen resistance, high glass transition (T.sub.g) temperatures, and excellent toughness can be attained. The resulting nanocomposites can be used to fabricate or formulate a variety of articles such as coatings on a variety of substrates, films, foams, fibers, threads, adhesives and fiber coated prepreg. The properties of the nanocomposites can be adjusted by selection of the polymer matrix and CNT to fabricate articles that possess high optical transparency and antistatic behavior
Abstract: Analysis of acute skin rejection in non-human primate models of face and hand allotransplantation
Introduction: The incidence of acute rejection (AR) of the skin within the first year after hand or face transplantation is approximately 85% and up to 56% of patients experience multiple episodes1. Significant immunosuppression is required to prevent allograft loss, and recent studies suggest that repeated AR episodes can lead to VCA dysfunction and loss2. The mechanisms underlying variability in AR presentation remain poorly defined however.
Materials and Methods: 8 cynomolgus monkeys received either an orthotopic hand (n=2) or heterotopic face VCA (n=6) from MHC-mismatched donors following induction with anti-thymocyte globulin. Post-operatively, triple immunosuppression – tacrolimus, mycophenolate mofetil, methylprednisolone – was maintained for up to 120 days before bone marrow transplantation (BMT) was performed. Protocol biopsies of VCA skin were performed at 30-day intervals for histopathology and flow cytometric analysis of resident skin leukocyte populations; VCA-resident cells were differentiated by H38 status (mouse antihuman HLA class I monoclonal antibody that cross reacts with cynomolgus monkeys) for donor or recipient derivation. Clinical AR was treated with steroids and further biopsies were taken for histologic confirmation; corresponding anti-donor responses were evaluated by mixed lymphocyte reaction (MLR) and allo-antibody formation.
Results: Up to three episodes of AR (from POD 14, Banff I to II) developed while recipient animals were maintained on triple immunosuppression. Corresponding flow cytometric analyses demonstrate > 80% of skin-resident T lymphocytes (CD4+, CD8+) within VCA dermis were of recipient origin, suggesting rapid immigration of various lineages into the VCA. These observations coincided with the first episode of AR in fully mismatched recipients but haplomatched animals remained rejection-free. All but one episode of AR were successfully treated. No allo-antibodies were detected and anti-donor responses by MLR were comparable to that against third-party. Following BMT, mixed chimerism was detected and enabled immunosuppression withdrawal. However, this was transient and once lost, clinical AR developed and nearly 100% of both dermal and epidermal lymphocytes were recipient-derived.
Conclusion: We report a clinically-relevant model for studying AR in VCA. Our results suggest that further understanding of the relative importance of MHC differences in transplant pairs may lead to differences in outcomes for VCA recipients maintained under standard immunosuppression. Immunosuppression-free tolerance of non-hematopoietic antigens in composite tissues can be achieved, but require additional strategies to achieve stable, rather than transient mixed chimerism following BMT
Minimal model for beta relaxation in viscous liquids
Contrasts between beta relaxation in equilibrium viscous liquids and glasses
are rationalized in terms of a double-well potential model with
structure-dependent asymmetry, assuming structure is described by a single
order parameter. The model is tested for tripropylene glycol where it accounts
for the hysteresis of the dielectric beta loss peak frequency and magnitude
during cooling and reheating through the glass transition.Comment: Phys. Rev. Lett. (in press
(In)finiteness of Spherically Symmetric Static Perfect Fluids
This work is concerned with the finiteness problem for static, spherically
symmetric perfect fluids in both Newtonian Gravity and General Relativity. We
derive criteria on the barotropic equation of state guaranteeing that the
corresponding perfect fluid solutions possess finite/infinite extent. In the
Newtonian case, for the large class of monotonic equations of state, and in
General Relativity we improve earlier results
Hadronic production of squark-squark pairs: The electroweak contributions
We compute the electroweak (EW) contributions to squark--squark pair
production processes at the LHC within the framework of the Minimal
Supersymmetric Standard Model (MSSM). Both tree-level EW contributions, of
O(alpha_s alpha + alpha^2), and next-to-leading order (NLO) EW corrections, of
O(alpha_s^2 alpha), are calculated. Depending on the flavor and chirality of
the produced quarks, many interferences between EW-mediated and QCD-mediated
diagrams give non-zero contributions at tree-level and NLO. We discuss the
computational techniques and present an extensive numerical analysis for
inclusive squark--squark production as well as for subsets and single
processes. While the tree-level EW contributions to the integrated cross
sections can reach the 20% level, the NLO EW corrections typically lower the LO
prediction by a few percent.Comment: 36 pages, 18 figure
Astrometry with Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae
We present an absolute parallax and relative proper motion for the
fundamental distance scale calibrator, RR Lyr. We obtain these with astrometric
data from FGS 3, a white-light interferometer on HST. We find mas. Spectral classifications and VRIJHKTM and DDO51 photometry of
the astrometric reference frame surrounding RR Lyr indicate that field
extinction is low along this line of sight. We estimate =0.07\pm0.03 for
these reference stars. The extinction suffered by RR Lyr becomes one of the
dominant contributors to the uncertainty in its absolute magnitude. Adopting
the average field absorption, =0.07 \pm 0.03, we obtain M_V^{RR} = 0.61
^{-0.11}_{+0.10}. This provides a distance modulus for the LMC, m-M = 18.38 -
18.53^{-0.11}_{+0.10} with the average extinction-corrected magnitude of RR Lyr
variables in the LMC, , remaining a significant uncertainty. We compare
this result to more than 80 other determinations of the distance modulus of the
LMC.Comment: Several typos corrected. To appear in The Astronomical Journal,
January 200
Electron correlations for ground state properties of group IV semiconductors
Valence energies for crystalline C, Si, Ge, and Sn with diamond structure
have been determined using an ab-initio approach based on information from
cluster calculations. Correlation contributions, in particular, have been
evaluated in the coupled electron pair approximation (CEPA), by means of
increments obtained for localized bond orbitals and for pairs and triples of
such bonds. Combining these results with corresponding Hartree-Fock (HF) data,
we recover about 95 % of the experimental cohesive energies. Lattice constants
are overestimated at the HF level by about 1.5 %; correlation effects reduce
these deviations to values which are within the error bounds of this method. A
similar behavior is found for the bulk modulus: the HF values which are
significantly too high are reduced by correlation effects to about 97 % of the
experimental values.Comment: 22 pages, latex, 2 figure
Superconducting p-branes and Extremal Black Holes
In Einstein-Maxwell theory, magnetic flux lines are `expelled' from a black
hole as extremality is approached, in the sense that the component of the field
strength normal to the horizon goes to zero. Thus, extremal black holes are
found to exhibit the sort of `Meissner effect' which is characteristic of
superconducting media. We review some of the evidence for this effect, and do
present new evidence for it using recently found black hole solutions in string
theory and Kaluza-Klein theory. We also present some new solutions, which arise
naturally in string theory, which are non-superconducting extremal black holes.
We present a nice geometrical interpretation of these effects derived by
looking carefully at the higher dimensional configurations from which the lower
dimensional black hole solutions are obtained. We show that other extremal
solitonic objects in string theory (such as p-branes) can also display
superconducting properties. In particular, we argue that the relativistic
London equation will hold on the worldvolume of `light' superconducting
p-branes (which are embedded in flat space), and that minimally coupled zero
modes will propagate in the adS factor of the near-horizon geometries of
`heavy', or gravitating, superconducting p-branes.Comment: 22 pages, 2 figure
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