Weighted-density approximation for general nonuniform fluid mixtures

In order to construct a general density-functional theory for nonuniform fluid mixtures, we propose an extension to multicomponent systems of the weighted-density approximation (WDA) of Curtin and Ashcroft [Phys. Rev. A 32, 2909 (1985)]. This extension corrects a deficiency in a similar extension proposed earlier by Denton and Ashcroft [Phys. Rev. A 42, 7312 (1990)], in that that functional cannot be applied to the multi-component nonuniform fluid systems with spatially varying composition, such as solid-fluid interfaces. As a test of the accuracy of our new functional, we apply it to the calculation of the freezing phase diagram of a binary hard-sphere fluid, and compare the results to simulation and the Denton-Ashcroft extension.Comment: 4 pages, 4 figures, to appear in Phys. Rev. E as Brief Repor

Upper and lower bounds for the eigenvalues of vibrating beams with linearly varying axial load

Upper and lower bounds for eigenvalues of vibrating beams and flat plates with varying axial loa

The X-ray luminosity function of AGN at z~3

We combine Lyman-break colour selection with ultradeep (> 200 ks) Chandra X-ray imaging over a survey area of ~0.35 deg^2 to select high redshift AGN. Applying careful corrections for both the optical and X-ray selection functions, the data allow us to make the most accurate determination to date of the faint end of the X-ray luminosity function (XLF) at z~3. Our methodology recovers a number density of X-ray sources at this redshift which is at least as high as previous surveys, demonstrating that it is an effective way of selecting high z AGN. Comparing to results at z=1, we find no evidence that the faint slope of the XLF flattens at high z, but we do find significant (factor ~3.6) negative evolution of the space density of low luminosity AGN. Combining with bright end data from very wide surveys we also see marginal evidence for continued positive evolution of the characteristic break luminosity L*. Our data therefore support models of luminosity-dependent density evolution between z=1 and z=3. A sharp upturn in the the XLF is seen at the very lowest luminosities (Lx < 10^42.5 erg s^-1), most likely due to the contribution of pure X-ray starburst galaxies at very faint fluxes.Comment: 16 pages, 9 figures, accepted for publication in MNRA

Direct calculation of the hard-sphere crystal/melt interfacial free energy

We present a direct calculation by molecular-dynamics computer simulation of the crystal/melt interfacial free energy, $\gamma$, for a system of hard spheres of diameter $\sigma$. The calculation is performed by thermodynamic integration along a reversible path defined by cleaving, using specially constructed movable hard-sphere walls, separate bulk crystal and fluid systems, which are then merged to form an interface. We find the interfacial free energy to be slightly anisotropic with $\gamma$ = 0.62$\pm 0.01$, 0.64$\pm 0.01$ and 0.58$\pm 0.01 k_BT/\sigma^2$ for the (100), (110) and (111) fcc crystal/fluid interfaces, respectively. These values are consistent with earlier density functional calculations and recent experiments measuring the crystal nucleation rates from colloidal fluids of polystyrene spheres that have been interpreted [Marr and Gast, Langmuir {\bf 10}, 1348 (1994)] to give an estimate of $\gamma$ for the hard-sphere system of $0.55 \pm 0.02 k_BT/\sigma^2$, slightly lower than the directly determined value reported here.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

A Modified Field Infiltrometer Test for Clay Liners

Regulatory agencies are looking more frequently to in situ field hydraulic conductivity tests for the assessment of a liner\u27s compliance to a specified hydraulic conductivity. Most field tests have evaluated hydraulic conductivity by measuring the infiltration rate of the liner. The infiltration rate can be used to arrive at a hydraulic conductivity value if the hydraulic boundary conditions of the test can be identified or if the head loss at different depths can be measured. A test fill of a clay liner was evaluated for its saturated vertical hydraulic conductivity. This paper discusses the use of eight tensiometers to measure soil suction at four depths beneath a double ring infiltrometer. The hydraulic conductivity results using the tensiometer data displayed good consistency and agreed well with laboratory test results

The Effects of PVP(Fe(III)) Catalyst on Polymer Molecular Weight and Gene Delivery via Biodegradable Cross-Linked Polyethylenimine

The original publication is available at www.springerlink.comPurpose Crosslinked, degradable derivatives of low-molecular-weight polyethylenimine (PEI) are relatively efficient and non-cytotoxic gene delivery agents. To further investigate these promising materials, a new synthetic approach was developed using a poly(4-vinylpyridine)-supported Fe(III) catalyst (PVP(Fe(III))) that provides more facile synthesis and enhanced control of polymer molecular weight. Methods Biodegradable polymers (D.PEI) comprising 800-Da PEI crosslinked with 1,6-hexanediol diacrylate and exhibiting molecular weights of 1.2, 6.2, and 48 kDa were synthesized utilizing the PVP(Fe(III)) catalyst. D.PEI/DNA polyplexes were characterized using gel retardation, ethidium bromide exclusion, heparan sulfate displacement, and dynamic light scattering. In vitro transfection, cellular uptake, and cytotoxicity of the polyplexes were tested in human cervical cancer cells (HeLa) and human breast cancer cells (MDA-MB-231). Results D.PEIs tightly complexed plasmid DNA and formed 320- to 440-nm diameter polyplexes, similar to those comprising non-degradable, 25-kDa, branched PEI. D.PEI polyplexes mediated 2- to 5-fold increased gene delivery efficacy compared to 25-kDa PEI and exhibited 20% lower cytotoxicity in HeLa and no toxicity in MDA-MB-231. In addition, 2- to 7-fold improved cellular uptake of DNA was achieved with D.PEI polyplexes. Conclusions PVP(Fe(III)) catalyst provided a more controlled synthesis of D.PEIs, and these materials demonstrated improved in vitro transfection efficacy and reduced cytotoxicity

Observing Strategies for the NICI Campaign to Directly Image Extrasolar Planets

We discuss observing strategy for the Near Infrared Coronagraphic Imager (NICI) on the 8-m Gemini South telescope. NICI combines a number of techniques to attenuate starlight and suppress superspeckles: 1) coronagraphic imaging, 2) dual channel imaging for Spectral Differential Imaging (SDI) and 3) operation in a fixed Cassegrain rotator mode for Angular Differential Imaging (ADI). NICI will be used both in service mode and for a dedicated 50 night planet search campaign. While all of these techniques have been used individually in large planet-finding surveys, this is the first time ADI and SDI will be used with a coronagraph in a large survey. Thus, novel observing strategies are necessary to conduct a viable planet search campaign.Comment: 12 pages, 10 figures, submitted to Proceedings of the SPI

An experimental investigation of the mechanical properties of a selected group of plastic materials

Dynamic and static testing of selected plastics for determination of mechanical propertie

External field control of donor electron exchange at the Si/SiO2 interface

We analyze several important issues for the single- and two-qubit operations in Si quantum computer architectures involving P donors close to a SiO2 interface. For a single donor, we investigate the donor-bound electron manipulation (i.e. 1-qubit operation) between the donor and the interface by electric and magnetic fields. We establish conditions to keep a donor-bound state at the interface in the absence of local surface gates, and estimate the maximum planar density of donors allowed to avoid the formation of a 2-dimensional electron gas at the interface. We also calculate the times involved in single electron shuttling between the donor and the interface. For a donor pair, we find that under certain conditions the exchange coupling (i.e. 2-qubit operation) between the respective electron pair at the interface may be of the same order of magnitude as the coupling in GaAs-based two-electron double quantum dots where coherent spin manipulation and control has been recently demonstrated (for example for donors ~10 nm below the interface and \~40 nm apart, J~10^{-4} meV), opening the perspective for similar experiments to be performed in Si.Comment: 11 pages, 15 figures. Changes in Eq. 24 plus minor typo

Interplay between distribution of live cells and growth dynamics of solid tumours

Experiments show that simple diffusion of nutrients and waste molecules is not sufficient to explain the typical multilayered structure of solid tumours, where an outer rim of proliferating cells surrounds a layer of quiescent but viable cells and a central necrotic region. These experiments challenge models of tumour growth based exclusively on diffusion. Here we propose a model of tumour growth that incorporates the volume dynamics and the distribution of cells within the viable cell rim. The model is suggested by in silico experiments and is validated using in vitro data. The results correlate with in vivo data as well, and the model can be used to support experimental and clinical oncology