Graphite/polyimide laminates with near-zero thermal expansion

Composite structures can be laminated to have very low coefficients of thermal expansion. Such structures are light and strong and have many uses where expansion or contraction with temperature change is undesirable. One application is with instruments that measure thermal expansion

Large-eddy simulation of a turbulent mixing layer

The three dimensional, time dependent (incompressible) vorticity equations were used to simulate numerically the decay of isotropic box turbulence and time developing mixing layers. The vorticity equations were spatially filtered to define the large scale turbulence field, and the subgrid scale turbulence was modeled. A general method was developed to show numerical conservation of momentum, vorticity, and energy. The terms that arise from filtering the equations were treated (for both periodic boundary conditions and no stress boundary conditions) in a fast and accurate way by using fast Fourier transforms. Use of vorticity as the principal variable is shown to produce results equivalent to those obtained by use of the primitive variable equations

Stabilized lanthanum sulphur compounds

Lanthanum sulfide is maintained in the stable cubic phase form over a temperature range of from 500 C to 1500 C by adding to it small amounts of calcium, barium, or strontium. This compound is an excellent thermoelectric material

Advection-Dominated Accretion with Infall and Outflows

We present self-similar solutions for advection-dominated accretion flows with radial viscous force in the presence of outflows from the accretion flow or infall. The axisymmetric flow is treated in variables integrated over polar sections and the effects of infall and outflows on the accretion flow are parametrised for possible configurations compatible with the self-similar solution. We investigate the resulting accretion flows for three different viscosity laws and derive upper limits on the viscosity parameter alpha. In addition, we find a natural connection to non-rotating and spherical accretion with turbulent viscosity, which is assumed to persist even without differential rotation. Positive Bernoulli numbers for advection-dominated accretion allow a fraction of the gas to be expelled in an outflow and the upper limit on the viscosity predicts that outflows are inevitable for equations of state close to an ideal gas.Comment: 17 pages, 9 figures, accepted for publication in the Astrophysical Journa

Detection of an X-ray periodicity in the Seyfert galaxy IRAS18325-5926

We report the detection of a 58 ks (16 hr) periodicity in the 0.5-10 keV X-ray light curve of the Seyfert galaxy IRAS18325-5926 (Fairall49), obtained from a 5-day ASCA observation. Nearly 9 cycles of the periodic variation are seen; it shows no strong energy dependence and has an amplitude of about 15 per cent. Unlike most other well-studied Seyfert galaxies, there is no evidence for strong power-law red noise in the X-ray power spectrum of IRAS18325-5926. Scaling from the QPOs found in Galactic black hole candidates suggests that the mass of the black hole in IRAS18325-5926 is (6-40) million solar masses.Comment: 5 pages, 4 Postscript figures, to be published in MNRA

On broad iron K-alpha lines in Seyfert 1 galaxies

The X-ray spectrum obtained by Tanaka et al from a long observation of the active galaxy MCG$-6-30-15$ shows a broad iron K$\alpha$ line skewed to low energies. The simplest interpretation of the shape of the line is that it is due to doppler and gravitational redshifts from the inner parts of a disk about a massive black hole. Similarly broad lines are evident in shorter observations of several other active galaxies. In this paper we investigate other line broadening and skewing mechanisms such as Comptonization in cold gas and doppler shifts from outflows. We have also fitted complex spectral models to the data of MCG$-6-30-15$ to see whether the broad skewed line can be mimicked well by other absorption or emission features. No satisfactory mechanism or spectral model is found, thus strengthening the relativistic disk line model.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

Improved gene delivery to human saphenous vein cells and tissue using a peptide-modified adenoviral vector

The establishment of efficient gene delivery to target human tissue is a major obstacle for transition of gene therapy from the pre-clinical phases to the clinic. The poor long-term patency rates for coronary artery bypass grafting (CABG) is a major clinical problem that lacks an effective and proven pharmacological intervention. Late vein graft failure occurs due to neointima formation and accelerated atherosclerosis. Since CABG allows a clinical window of opportunity to genetically modify vein ex vivo prior to grafting it represents an ideal opportunity to develop gene-based therapies. Adenoviral vectors have been frequently used for gene delivery to vein ex vivo and pre-clinical studies have shown effective blockade in neointima development by overexpression of candidate therapeutic genes. However, high titers of adenovirus are required to achieve sufficient gene delivery to provide therapeutic benefit. Improvement in the uptake of adenovirus into the vessel wall would therefore be of benefit. Here we determined the ability of an adenovirus serotype 5 vector genetically-engineered with the RGD-4C integrin targeting peptide inserted into the HI loop (Ad-RGD) to improve the transduction of human saphenous vein smooth muscle cells (HSVSMC), endothelial cells (HSVEC) and intact saphenous vein compared to a non-modified virus (Ad-CTL). We exposed each cell type to virus for 10, 30 or 60 mins and measured transgene at 24 h post infection. For both HSVSMC and HSVEC Ad-RGD mediated increased transduction, with the largest increases observed in HSVSMC. When the experiments were repeated with intact human saphenous vein (the ultimate clinical target for gene therapy), again Ad-RGD mediated higher levels of transduction, at all clinically relevant exposures times (10, 30 and 60 mins tissue:virus exposure). Our study demonstrates the ability of peptide-modified Ad vectors to improve transduction to human vein graft cells and tissue and has important implications for gene therapy for CABG

Jet power extracted from ADAF and the applications to X-ray binaries and radio galaxy FR dichotomy

We calculate the jet power of the classical Blandford-Znajek(BZ) model and hybrid model developed by Meier based on the global solutions of advection dominated accretion flows (ADAFs) surrounding Kerr black holes. We find that the jet power of the hybrid model is larger than that of the pure BZ model. The jet power will dominate over the accretion power, and the objects will enter into "jet-power-dominated advective systems", when the accretion rate is less than a critical value mdot_c=Mdot_c/Mdot_Edd, where 3*10^-4 < mdot_c < 5*10^-3 is a function of black hole spin parameter. The accretion power will be dominant when mdot<mdot_c and the objects will enter into "accretion-power-dominated advective systems." This is roughly consistent with that constrained from the low/hard-state black hole X-ray binaries (e.g., Fender et al.). We calculate the maximal jet power as a function of black hole mass with the hybrid jet formation model, and find it can roughly reproduce the dividing line of the Ledlow-Owen relation for FR I/FR II dichotomy in the jet power-black hole(BH) mass plane (Q_jet-M_BH) if the dimensionless accretion rate mdot~0.01 and BH spin parameter j~0.9-0.99 are adopted. This accretion rate mdot~0.01 is consistent with that of the critical accretion rate for the accretion mode transition of a standard disk to an ADAF constrained from the state transition of X-ray binaries. Our results imply that most FR I galaxies may be in the ADAF accretion mode similar to the low/hard-state XRBs.Comment: 6 pages, 3 color figures, ApJ in press, edited with ApJ style and English is improved as suggested by Edito

On The Reddening in X-ray Absorbed Seyfert 1 Galaxies

There are several Seyfert galaxies for which there is a discrepancy between the small column of neutral hydrogen deduced from X-ray observations and the much greater column derived from the reddening of the optical/UV emission lines and continuum. The standard paradigm has the dust within the highly ionized gas which produces O~VII and O~VIII absorption edges (i.e., a ``dusty warm absorber''). We present an alternative model in which the dust exists in a component of gas in which hydrogen has been stripped, but which is at too low an ionization state to possess significant columns of O~VII and O~VIII (i.e, a ``lukewarm absorber''). The lukewarm absorber is at sufficient radial distance to encompass much of the narrow emission-line region, and thus accounts for the narrow-line reddening, unlike the dusty warm absorber. We test the model by using a combination of photoionization models and absorption edge fits to analyze the combined ROSAT/ASCA dataset for the Seyfert 1.5 galaxy, NGC 3227. We show that the data are well fit by a combination of the lukewarm absorber and a more highly ionized component similar to that suggested in earlier studies. We predict that the lukewarm absorber will produce strong UV absorption lines of N V, C IV, Si IV and Mg II. Finally, these results illustrate that singly ionized helium is an important, and often overlooked, source of opacity in the soft X-ray band (100 - 500 eV).Comment: 17 pages, Latex, includes 1 figure (encapsulated postscript), one additional table in Latex (landscape format), to appear in the Astrophysical Journa