8,967 research outputs found
Novel sol–gel preparation of (PO)–(CaO)–(NaO)–(TiO) bioresorbable glasses (X = 0.05, 0.1, and 0.15)
Quaternary phosphate-based glasses in the PO–CaO–NaO–TiO system with a fixed PO and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), P nuclear magnetic resonance (P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The P NMR and FTIR results revealed that the glass structure consist of mainly Q and Q phosphate units and the Ti cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing NaO content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed
The Formaldehyde Masers in Sgr B2: Very Long Baseline Array and Very Large Array Observations
Observations of two of the formaldehyde (H2CO) masers (A and D) in Sgr B2
using the VLBA+Y27 (resolution ~0.01") and the VLA (resolution ~9") are
presented. The VLBA observations show compact sources (<10 milliarcseconds, <80
AU) with brightness temperatures >10^8 K. The maser sources are partially
resolved in the VLBA observations. The flux densities in the VLBA observations
are about 1/2 those of the VLA; and, the linewidths are about 2/3 of the VLA
values. The applicability of a core-halo model for the emission distribution is
demonstrated. Comparison with earlier H2CO absorption observations and with
ammonia (NH3) observations suggests that H2CO masers form in shocked gas.
Comparison of the integrated flux densities in current VLA observations with
those in previous observations indicates that (1) most of the masers have
varied in the past 20 years, and (2) intensity variations are typically less
than a factor of two compared to the 20-year mean. No significant linear or
circular polarization is detected with either instrument.Comment: 20 pages, 3 figures, 5 tables, accepted to Ap
Characterization of effector and memory T cell subsets in the immune response to bovine tuberculosis in cattle
Cultured IFN-γ ELISPOT assays are primarily a measure of central memory T cell (Tcm) responses with humans; however, this important subset of lymphocytes is poorly characterized in cattle. Vaccine-elicited cultured IFN-γ ELISPOT responses correlate with protection against bovine tuberculosis in cattle. However, whether this assay measures cattle Tcm responses or not is uncertain. The objective of the present study was to characterize the relative contribution of Tcm (CCR7+, CD62Lhi, CD45RO+), T effector memory (Tem, defined as: CCR7-, CD62Llow/int, CD45RO+), and T effector cells (CCR7-, CD62L-/low, CD45RO-), in the immune response to Mycobacterium bovis. Peripheral blood mononuclear cells (PBMC) from infected cattle were stimulated with a cocktail of M. bovis purified protein derivative, rTb10.4 and rAg85A for 13 days with periodic addition of fresh media and rIL-2. On day 13, cultured PBMC were re-stimulated with medium alone, rESAT-6:CFP10 or PPDb with fresh autologous adherent cells for antigen presentation. Cultured cells (13 days) or fresh PBMCs (ex vivo response) from the same calves were analyzed for IFN-γ production, proliferation, and CD4, CD45RO, CD62L, CD44, and CCR7 expression via flow cytometry after overnight stimulation. In response to mycobacterial antigens, ~75% of CD4+ IFN-γ+ cells in long-term cultures expressed a Tcm phenotype while less than 10% of the ex vivo response consisted of Tcm cells. Upon re-exposure to antigen, long-term cultured cells were highly proliferative, a distinctive characteristic of Tcm, and the predominant phenotype within the long-term cultures switched from Tcm to Tem. These findings suggest that proliferative responses of Tcm cells to some extent occurs simultaneously with reversion to effector phenotypes (mostly Tem). The present study characterizes Tcm cells of cattle and their participation in the response to M. bovis infection
The Formaldehyde Masers in NGC 7538 and G29.96-0.02: VLBA, MERLIN, and VLA Observations
The 6 cm formaldehyde (H2CO) maser sources in the compact HII regions NGC
7538-IRS1 and G29.96-0.02 have been imaged at high resolution (beams < 50 mas).
Using the VLBA and MERLIN, we find the angular sizes of the NGC 7538 masers to
be ~10 mas (30 AU) corresponding to brightness temperatures ~10^8 K. The
angular sizes of the G29.96-0.02 masers are ~20 mas (130 AU) corresponding to
brightness temperatures ~10^7 K. Using the VLA, we detect 2 cm formaldehyde
absorption from the maser regions. We detect no emission in the 2 cm line,
indicating the lack of a 2 cm maser and placing limits on the 6 cm excitation
process. We find that both NGC 7538 maser components show an increase in
intensity on 5-10 year timescales while the G29.96-0.02 masers show no
variability over 2 years. A search for polarization provides 3-sigma upper
limits of 1% circularly polarized and 10% linearly polarized emission in NGC
7538 and of 15% circularly polarized emission in G29.96-0.02. A pronounced
velocity gradient of 28 km/s/arcsecond (1900 km/s/pc) is detected in the NGC
7538 maser gas.Comment: accepted to ApJ, 15 figures, 11 table
Inclusive J/psi and psi(2S) Production from B Decay in p p-bar Collisions
Using information on B-meson fragmentation functions from CERN LEP 1 and
adopting the nonrelativistic QCD factorization formalism proposed by Bodwin,
Braaten, and Lepage, we predict the transverse-momentum distribution of J/psi
mesons originating from the inclusive decays of b hadrons produced in p p-bar
collisions at the Fermilab Tevatron. We determine the relevant colour-octet
charmonium matrix elements from fits to CDF data on prompt charmonium
hadroproduction and to CLEO data on charmonium production from B-meson decay.
Our predictions are found to agree well with recent CDF and D0 data.Comment: 27 pages (Latex), 9 figures (Postscript
Ambiguous figures and the content of experience
Representationalism is the position that the phenomenal character of an experience is either identical with, or supervenes on, the content of that experience. Many representationalists hold that the relevant content of experience is nonconceptual. I propose a counterexample to this form of representationalism that arises from the phenomenon of Gestalt switching, which occurs when viewing ambiguous figures. First, I argue that one does not need to appeal to the conceptual content of experience or to judgements to account for Gestalt switching. I then argue that experiences of certain ambiguous figures are problematic because they have different phenomenal characters but that no difference in the nonconceptual content of these experiences can be identified. I consider three solutions to this problem that have been proposed by both philosophers and psychologists and conclude that none can account for all the ambiguous figures that pose the problem. I conclude that the onus is on representationalists to specify the relevant difference in content or to abandon their position
The response function of a sphere in a viscoelastic two-fluid medium
In order to address basic questions of importance to microrheology, we study
the dynamics of a rigid sphere embedded in a model viscoelastic medium
consisting of an elastic network permeated by a viscous fluid. We calculate the
complete response of a single bead in this medium to an external force and
compare the result to the commonly-accepted, generalized Stokes-Einstein
relation (GSER). We find that our response function is well approximated by the
GSER only within a particular frequency range determined by the material
parameters of both the bead and the network. We then discuss the relevance of
this result to recent experiments. Finally we discuss the approximations made
in our solution of the response function by comparing our results to the exact
solution for the response function of a bead in a viscous (Newtonian) fluid.Comment: 12 pages, 2 figure
Glassy timescale divergence and anomalous coarsening in a kinetically constrained spin chain
We analyse the out of equilibrium behavior of an Ising spin chain with an
asymmetric kinetic constraint after a quench to a low temperature T. In the
limit T\to 0, we provide an exact solution of the resulting coarsening process.
The equilibration time exhibits a `glassy' divergence \teq=\exp(const/T^2)
(popular as an alternative to the Vogel-Fulcher law), while the average domain
length grows with a temperature dependent exponent, \dbar ~ t^{T\ln 2}. We show
that the equilibration time \teq also sets the timescale for the linear
response of the system at low temperatures.Comment: 4 pages, revtex, includes two eps figures. Proof of energy barrier
hierarchy added. Version to be published in Phys Rev Let
Application of long-term cultured interferon-γ enzyme-linked immunospot assay for assessing effector and memory T cell responses in cattle
doi:10.3791/52833 (2015). Effector and memory T cells are generated through developmental programing of naïve cells following antigen recognition. If the infection is controlled up to 95 % of the T cells generated during the expansion phase are eliminated (i.e., contraction phase) and memory T cells remain, sometimes for a lifetime. In humans, two functionally distinct subsets of memory T cells have been described based on the expression of lymph node homing receptors. Central memory T cells express C-C chemokine receptor 7 and CD45RO and are mainly located in T-cell areas of secondary lymphoid organs. Effector memory T cells express CD45RO, lack CCR7 and display receptors associated with lymphocyte homing to peripheral or inflamed tissues. Effector T cells do not express either CCR7 or CD45RO but upon encounter with antigen produce effector cytokines, such as interferon-γ. Interferon-γ release assays are used for the diagnosis of bovine and human tuberculosis and detect primaril
CI and CO in the nearby spiral galaxies IC 342 and Maffei 2
We present J=2-1, J=3-2, J=4-3 12CO and 492 GHz [CI] maps as well as J=2-1
and J=3-2 13CO measurements of the central regions in the nearby Sc galaxies IC
342 and Maffei 2. In both galaxies, the distribution of CO and [CI] is strongly
concentrated towards the modest starburst centers. Both galaxies have nearly
identical 12CO transitional ratios but the relative intensities of their 13CO
and [CI] emission lines differ significantly and require modelling with a
multi-component molecular gas. Both have a dense component (n(H2) = 10**4 -
10**5 cm**-3) with kinetic temperatures T(kin) = 10 - 20 K (IC 342) or 20 - 60
K (Maffei 2), and a less dense (IC 342: a few hundred cm**-3 at most; Maffei 2:
about 3 x 10**3 cm**-3 and hotter (T(kin) = 100 - 150 K) component. In both
galaxies, neutral and ionized atomic carbon amounts are between 1.5 and 2.5
times those of CO, and in both about half to two thirds of the molecular gas
mass is associated with a hot PDR phase. Within R = 0.25 kpc, the center of IC
342 contains an (atomic and molecular) gas mass of 1 x 10**7 M(sun) and a peak
face-on gas mass density of about 70 M(sun) pc**-2. For Maffei 2 these numbers
are less clearly defined, mainly because of its uncertain distance and carbon
abundance. We find a gass mass M(gas) > 0.5 x 10**7 M(sun) and a peak face-on
gas mass density of about 35 M(sun) pc**-2.Comment: 11 pages; accepted by astronomy and Astrophysic
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