Two closely related ABC transporters in streptococcus mutans are involved in disaccharide and/or oligosaccharide uptake.

Streptococcus mutans has a large number of transporters apparently involved in the uptake of carbohydrates. At least two of these, the multiple sugar metabolism transporter, MsmEFGK, and the previously uncharacterized MalXFGK, are members of the ATP-binding cassette (ABC) superfamily. Mutation analysis revealed that the MsmEFGK and MalXFGK transporters are principally involved in the uptake of distinct disaccharides and/or oligosaccharides. Furthermore, the data also indicated an unusual protein interaction between the components of these two related transporters. Strains lacking msmE (which encodes a solute binding protein) can no longer utilize raffinose or stachyose but grow normally on maltodextrins in the absence of MalT, a previously characterized EII(mal) phosphotransferase system component. In contrast, a mutant of malX (which encodes a solute binding protein) cannot utilize maltodextrins but grows normally on raffinose or stachyose. Radioactive uptake assays confirmed that MalX, but not MsmE, is required for uptake of [U-14C]maltotriose and that MalXFGK is principally involved in the uptake of maltodextrins with as many as 7 glucose units. Surprisingly, inactivation of the corresponding ATPase components did not result in an equivalent abolition of growth: the malK mutant can grow on maltotetraose as a sole carbon source, and the msmK mutant can utilize raffinose. We propose that the ATPase domains of these ABC transporters can interact with either their own or the alternative transporter complex. Such unexpected interaction of ATPase subunits with distinct membrane components to form complete multiple ABC transporters may be widespread in bacteria

Computational Methods and Results for Structured Multiscale Models of Tumor Invasion

We present multiscale models of cancer tumor invasion with components at the molecular, cellular, and tissue levels. We provide biological justifications for the model components, present computational results from the model, and discuss the scientific-computing methodology used to solve the model equations. The models and methodology presented in this paper form the basis for developing and treating increasingly complex, mechanistic models of tumor invasion that will be more predictive and less phenomenological. Because many of the features of the cancer models, such as taxis, aging and growth, are seen in other biological systems, the models and methods discussed here also provide a template for handling a broader range of biological problems

Nanoscale Morphology and Electrical Behaviour of a Pressure Sensitive Ink

Pressure Sensitive Ink is an electrically conductive composite material made by Peratech Ltd. The conductivity of the inks is sensitive to touch pressure, which have a range of applications in areas including telecommunications and robotics and are printable as functional electronic devices. The inks are complex and composed of electrically conductive acicular (needle-like) refractory filler particles dispersed in an insulating organic base ink. Inks mixed, prepared and stored in a variety of conditions have been studied using high resolution scanning and transmission electron microscopy, focused ion beam and EDX elemental analysis in conjunction with DC electrical characterization. The research has aimed to investigate possible links between the structure and electrical behaviour of the inks. The results have shown that inks stored for greater amounts of time, prior to printing, lose touch sensitivity. Causes for this are uncertain, but may be linked with the growth of nanoscale features on the filler particles and partial settling of constituents. EDX analysis revealed candidate elements for the nanoscale features found on filler particles. Modeling current-voltage plots with non-linear fits has shown there might be a switching of conduction mechanism with increasing compression of the inks. Additionally, the unclear process by which inks lose touch sensitivity was shown to be temperature dependent. Inks more vigorously blended were found to have shorter filler particles through a statistical survey of filler particle lengths, measured through scanning electron microscopy imaging. Inks produced with a lower filler particle to base ink ratio were found to be less sensitive to touch pressure than those made with comparatively more filler particles. A survey of filler particle clumps (groups of 3 or more particles) revealed that the addition of hyper-dispersant, an anti – clumping chemical agent, aided better dispersion of filler particles and increased the touch sensitivity of low filler particle fraction inks

Temperature Dependence and Touch Sensitivity of Electrical Transport in Novel Nanocomposite Printable Inks

Printed electronics is an established industry allowing the production of electronic components such as resistors, and more complex structures such as solar cells, from functional inks. Composites, a mixture of two or more materials with different physical and/or chemical properties that combine to create a new material with properties differing from its constituent parts, have been important in areas such as the textile and automotive industries, and are significant in printed electronics as inks for printed circuit components, touch and vapour sensors. Here, the functional performance and physical behaviour of two screen printable multi-component nanocomposite inks, formulated for touch-pressure sensing applications, are investigated. They each comprise a proprietary mixture of electrically conducting and insulating nanoparticles dispersed in an insulating polymer binder, where one is opaque and the other transparent. The opaque ink has a complex surface structure consisting of a homogeneous dispersion of nanoparticles. The transparent inks structure is characterised by large aggregates of nanoparticles distributed through the printed layer. Temperature dependent electrical transport measurements under a range of compressive loadings reveal similar non-linear behaviour in both inks, with some hysteresis observed, and this behaviour is linked to the inks structures. A physical model comprising a combination of linear and non-linear conduction contributions, with the linear term attributed to direct connections between conductive particles and the non-linear term attributed to field-assisted quantum tunnelling, has been developed and used successfully to describe the underpinning physical processes behind the unique electrical functionality of the opaque ink and, to a lesser extent, the transparent ink

A scalar-tensor cosmological model with dynamical light velocity

The dynamical consequences of a bimetric scalar-tensor theory of gravity with a dynamical light speed are investigated in a cosmological setting. The model consists of a minimally-coupled self-gravitating scalar field coupled to ordinary matter fields in the standard way through the metric: \metric_{\mu\nu}+B\partial_\mu\phi\partial_\nu\phi. We show that in a universe with matter that has a radiation-dominated equation of state, the model allows solutions with a de Sitter phase that provides sufficient inflation to solve the horizon and flatness problems. This behaviour is achieved without the addition of a potential for the scalar field, and is shown to be largely independent of its introduction. We therefore have a model that is fundamentally different than the potential-dominated, slowly-rolling scalar field of the standard models inflationary cosmology. The speed of gravitational wave propagation is predicted to be significantly different from the speed of matter waves and photon propagation in the early universe.Comment: 12 pages, uses amsart and amssymb. Minor corrections, to appear in Phys. Lett.

Roadside Environments and the Effects of Roadside Management Practices on Milkweeds and Monarchs

The potential of roadsides as habitat for wildlife has gained interest in recent years, with research suggesting positive effects for several taxa. Roadsides cover a vast area in the United States, and are actively managed by state and federal agencies. However, not much is known about the potential of roadsides to provide habitat for the monarch butterfly (Danaus plexippus). Therefore, I assessed milkweed densities on roadsides and in adjacent lands, the effects of different mowing times in roadsides on milkweed density, number of stems per plant, plant height (cm), and latex production, and mortality rates for monarch butterflies on roadsides oriented in a north/south and east/west direction during fall migration. My results show Asclepias viridis and A. asperula milkweed densities are higher on roadsides than adjacent lands in Oklahoma; mowing roadsides lowers counts of A. viridis milkweed but those lower counts are limited to the actual times of mowing; monarch mortality during fall migration did not differ with highway orientation. Although additional research is needed, roadsides have the potential to provide monarch butterfly habitat and should be considered when assessing conservation strategies.Zoolog

The HDF-North SCUBA Super-map II: Multi-wavelength properties

We present radio, optical and X-ray detected counterparts to the sub-mm sources found using SCUBA in the Hubble Deep Field North region (GOODS-N). A new counterpart identification statistic is developed to identify properties of galaxies detected at other wavelengths that can be used to aid counterpart identification. We discriminate between criteria that can be used to pre-select sub-mm bright objects, and those that identify the counterpart to a known sub-mm object. Optically faint galaxies detected in the deepest 1.4 GHz radio continuum maps are the only effective way of pre-selecting SCUBA galaxies, and radio sources are the best way to identify counterparts to known sub-mm detections. Looking at radio spectral indices, only the steeper sources (indicative of star formation) are detected in the sub-mm. Although we find several X-ray identifications, we show that deep Chandra images do not contribute to counterpart identifications, since in all cases they are already detected in the more easily obtained VLA radio maps. We also find find no evidence for clustering between Chandra and SCUBA sources in this field. For a known SCUBA position, the reddest source tends to be the correct association, although we can find no cut on colour, magnitude, or clustering property that efficiently pre-selects for SCUBA sources. 15 micron ISO sources are statistically detected by SCUBA, but the limiting mid-IR flux is not low enough to provide useful constraints. We present postage stamp strips for each SCUBA detection in separate bands from X-ray to radio, providing direct visual evidence that approximately half of the sub-mm sources in this field remain unidentified, despite an abundance of deep multi-wavelength data.Comment: Accepted for publication in MNRAS. High resolution version available at http://www.submm.caltech.edu/~borys/paper

Is it e or is it c? Experimental Tests of Varying Alpha

Is the recent evidence for a time-varying fine structure 'constant' $\alpha$ to be interpreted as a varying $e$, $c$, $\hbar$, or a combination thereof? We consider the simplest varying electric charge and varying speed of light theories (VSL) and prove that for the same type of dark matter they predict opposite senses of variation in $\alpha$ over cosmological times. We also show that unlike varying $e$ theories, VSL theories do not predict violations of the weak equivalence principle (WEP). Varying $e$ theories which explain astronomical inferences of varying $\alpha$ predict WEP violations only an order of magnitude smaller than existing E\"otv\"os experiment limits but could be decisively tested by STEP. We finally exhibit a set of atomic-clock and related experiments for which {\it all} (hyperbolic) varying $\alpha$ theories predict non-null results. They provide independent tests of the recent astronomical evidence