9,505 research outputs found
Antimicrobial and modulation effects of selected Ghanaian medicinal plants
The alarming rise in the incidences of multidrug-resistant microorganisms and the decline innew antibiotic discovery make the search for new antimicrobial agents or efforts at restoring the activity of older antibiotics to which the microbes have developed resistance very necessary. The aim of the present study is to investigate the antimicrobial and modulation effects of the 70% ethanol extracts of Lannea schimperi, Commelina nudiflora and Piliostigma reticulatum against usceptible strains of microorganisms. Using the broth microdilution method, the minimum inhibitory concentrations (MICs) of the extracts were determined. The checkerboard assay was used to determine the modulation effects when sub-inhibitory concentrations of plant extracts were combined with the standard antibiotics. All three plants extracts possessed weak antimicrobial effects. For the modulation experiments, fifteen of the twenty-seven combinatorial casesyielded biologically significant effects. The ethanol extracts of the three plants studied here are good modulators as they reduced the MIC of ciprofloxacin and ketoconazole by factors that are comparable to that of reserpine. However the exact compounds and their exact mechanism of modulation require further investigation.Keywords: Anti-infective, modulation, Lannea schimperi, Commelina nudiflora, Piliostigmareticulatum, ethnomedicin
Performance requirements analysis for payload delivery from a space station
Operations conducted from a space station in low Earth orbit which have different constraints and opportunities than those conducted from direct Earth launch were examined. While a space station relieves many size and performance constraints on the space shuttle, the space station's inertial orbit has different launch window constraints from those associated with customary Earth launches which reflect upon upper stage capability. A performance requirements analysis was developed to provide a reference source of parametric data, and specific case solutions and upper stage sizing trade to assist potential space station users and space station and upper stage developers assess the impacts of a space station on missions of interest
β3-integrin is required for differentiation in OC-2 cells derived from mammalian embryonic inner ear
<p>Abstract</p> <p>Background</p> <p>The mammalian inner ear contains the organ of Corti which is responsible for the conversion of sound into neuronal signals. This specialised epithelial tissue is the product of a complex developmental process where a common precursor cell type differentiates into the sound transducing hair cells and the non-innervated supporting cells. We hypothesised that integrin proteins, which are involved in cell attachment to extracellular matrix proteins and cellular signalling, play a role in the differentiation process of the precursor inner ear epithelial cells. To test our hypothesis we have utilised a cell line (OC-2) derived from E13 embryonic immortomouse inner ears. In vitro, by switching the incubation temperature from 33°C to 39°C, the OC-2 cells can be induced to differentiate and express hair cells markers, such as Myosin VIIa. The OC-2 cells are thus a useful model system for testing mechanism of hair cells differentiation.</p> <p>Results</p> <p>We have identified 4 integrin subunits which are expressed in OC-2 cells: ι6, ιv, β1 and β3. Among these, the relative level of expression of the ιv, β1 and β3 subunits increased in a time dependent manner when the cells were exposed to the differentiating temperature of 39°C, most notably so for β3 which was not detectable at 33°C. Treatment of fully differentiated OC-2 cells with siRNA against the four integrin subunits reduced the expression of not only the respective integrin proteins but also of the hair cell marker Myosin VIIa. Conversely over-expression of β3 was sufficient to induce the expression of Myosin VIIa at 33°C.</p> <p>Conclusions</p> <p>Our data demonstrate that modulation of integrin expression is associated with the differentiation process of the OC-2 cells. This suggests that the maturation of the organ of Corti, from where OC-2 cells are derived, may also depend on changes of gene expression associated with integrin expression.</p
Testing Comptonizing coronae on a long BeppoSAX observation of the Seyfert 1 galaxy NGC 5548
We test accurate models of Comptonization spectra over the high quality data
of the BeppoSAX long look at NGC 5548, allowing for different geometries of the
scattering region, different temperatures of the input soft photon field and
different viewing angles. We find that the BeppoSAX data are well represented
by a plane parallel or hemispherical corona viewed at an inclination angle of
30. For both geometries the best fit temperature of the soft photons
is close to 15 eV. The corresponding best fit values of the hot
plasma temperature and optical depth are 250--260 keV and
0.16--0.37 for the slab and hemisphere respectively. These values
are substantially different from those derived fitting the data with a
power-law + cut off approximation to the Comptonization component (kT_{\rm
e}\lta 60 keV, 2.4). This is due to the fact that accurate
Comptonization spectra in anisotropic geometries show "intrinsic" curvature
which reduces the necessity of a high energy cut-off. The Comptonization
parameter derived for the slab model {is} larger than predicted for a two phase
plane parallel corona in energy balance, suggesting that a more
``photon-starved'' geometry is necessary. The spectral softening detected
during a flare which occurred in the central part of the observation
corresponds to a decrease of the Comptonization parameter, probably associated
with an increase of the soft photon luminosity, the {hard} photon luminosity
remaining constant.Comment: 36 pages, 9 figures, accepted by Ap
A Medium Survey of the Hard X-Ray Sky with ASCA. II.: The Source's Broad Band X-Ray Spectral Properties
A complete sample of 60 serendipitous hard X-ray sources with flux in the
range \ecs to \ecs (2 - 10
keV), detected in 87 ASCA GIS2 images, was recently presented in literature.
Using this sample it was possible to extend the description of the 2-10 keV
LogN(>S)-LogS down to a flux limit of \ecs (the
faintest detectable flux), resolving about a quarter of the Cosmic X-ray
Background. In this paper we have combined the ASCA GIS2 and GIS3 data of these
sources to investigate their X-ray spectral properties using the "hardness"
ratios and the "stacked" spectra method. Because of the sample statistical
representativeness, the results presented here, that refer to the faintest hard
X-ray sources that can be studied with the current instrumentation, are
relevant to the understanding of the CXB and of the AGN unification scheme.Comment: 28 pages plus 6 figures, LaTex manuscript, Accepted for publication
in the Astrophysical Journal, Figure 5 can retrieved via anonymous ftp at
ftp://ftp.brera.mi.astro.it/pub/ASCA/paper2/fig5.ps.g
INTEGRAL observations of the black hole candidate H 1743-322 in outburst
INTEGRAL made 3 observations in 2003 April of the black hole candidate H
1743-322 during the rising part, and close to the maximum, of an outburst. H
1743-322 was previously observed in outburst in 1977-1978. The source is
located in a crowded region of the sky (l = 357 deg, b = -2 deg) and at least
18 sources are clearly detected in the field of view of the gamma-ray imager
during a 277 ksec exposure. These are well known persistent X-ray binaries and
3 transient sources in outburst. The combined 5-200 keV JEM-X and SPI spectrum
of H 1743-322 is well fit with an absorbed ((2.5 10E22 atom/cm2) soft (photon
index 2.70 +/- 0.09) power-law model consistent with J 1743-322 being in a
high/soft state.Comment: 5 pages. Figs. 2 and 3 are best viewed in color. To appear in
INTEGRAL special edition of A&A
Popular music, psychogeography, place identity and tourism: The case of Sheffield
Tourism and cultural agencies in some English provincial cities are promoting their popular music âheritageâ and, in some cases, contemporary musicians through the packaging of trails, sites, âiconicâ venues and festivals. This article focuses on Sheffield, a âpost-industrialâ northern English city which is drawing on its associations with musicians past and present in seeking to attract tourists. This article is based on interviews with, among others, recording artists, promoters, producers and venue managers, along with reflective observational and documentary data. Theoretical remarks are made on the representations of popular musicians through cultural tourism strategies, programmes and products and also on the ways in which musicians convey a âpsychogeographicalâ sense of place in the âsoundscapeâ of the city
Cavitation inception of a van der Waals fluid at a sack-wall obstacle
Cavitation in a liquid moving past a constraint is numerically investigated
by means of a free-energy lattice Boltzmann simulation based on the van der
Waals equation of state. The fluid is streamed past an obstacle and, depending
on the pressure drop between inlet and outlet, vapor formation underneath the
corner of the sack-wall is observed. The circumstances of cavitation formation
are investigated and it is found that the local bulk pressure and mean stress
are insufficient to explain the phenomenon. Results obtained in this study
strongly suggest that the viscous stress, interfacial contributions to the
local pressure, and the Laplace pressure are relevant to the opening of a vapor
cavity. This can be described by a generalization of Joseph's criterion that
includes these contributions. A macroscopic investigation measuring mass flow
rate behavior and discharge coefficient was also performed. As theoretically
predicted, mass flow rate increases linearly with the square root of the
pressure drop. However, when cavitation occurs, the mass flow growth rate is
reduced and eventually it collapses into a choked flow state. In the cavitating
regime, as theoretically predicted and experimentally verified, the discharge
coefficient grows with the Nurick cavitation number
Control-volume representation of molecular dynamics
A Molecular Dynamics (MD) parallel to the Control Volume (CV) formulation of
fluid mechanics is developed by integrating the formulas of Irving and
Kirkwood, J. Chem. Phys. 18, 817 (1950) over a finite cubic volume of molecular
dimensions. The Lagrangian molecular system is expressed in terms of an
Eulerian CV, which yields an equivalent to Reynolds' Transport Theorem for the
discrete system. This approach casts the dynamics of the molecular system into
a form that can be readily compared to the continuum equations. The MD
equations of motion are reinterpreted in terms of a
Lagrangian-to-Control-Volume (\CV) conversion function , for
each molecule . The \CV function and its spatial derivatives are used to
express fluxes and relevant forces across the control surfaces. The
relationship between the local pressures computed using the Volume Average (VA,
Lutsko, J. Appl. Phys 64, 1152 (1988)) techniques and the Method of Planes
(MOP, Todd et al, Phys. Rev. E 52, 1627 (1995)) emerges naturally from the
treatment. Numerical experiments using the MD CV method are reported for
equilibrium and non-equilibrium (start-up Couette flow) model liquids, which
demonstrate the advantages of the formulation. The CV formulation of the MD is
shown to be exactly conservative, and is therefore ideally suited to obtain
macroscopic properties from a discrete system.Comment: 19 pages, 15 figure
- âŚ