Aluminophosphate molecular sieves comprised of hydrated triple crankshaft chains

We report the first synthesis of pure aluminophosphate hydrate H2 (AlPO4-H2) and its structure; AlPO4-H2 is constructed exclusively from a hydrated chain building unit that also builds the 18-ring VPI-5 structure and has one-dimensional channels circumscribed by highly elliptical rings consisting often oxygen atoms, implications from the existence of this building unit for the synthesis of novel aluminophosphate molecular sieves and for the synthesis of aluminosilicate and silicate analogues of AlPO4-H2 and VPI-5 are discussed

Retinal degeneration is rescued in transgenic rd mice by expression of the cGMP phosphodiesterase ß subunit

The ß subunit of the cGMP phosphodiesterase (PDE) gene has been identified as the candidate gene for retinal degeneration in the rd mouse. To study the molecular mechanisms underlying degeneration and the potential for gene repair, we have expressed a functional bovine cGMP PDE ß subunit in transgenic rd mice. One transgenic mouse line showed complete photoreceptor rescue across the entire span of the retina. A second independently derived line showed partial rescue in which photoreceptors in the superior but not the inferior hemisphere of the retina were rescued. In the latter animals, intermediate stages of degeneration were observed in the transition zone between rescued and diseased photoreceptors. Pathologic changes in the retina ranged from vesiculation of the basalmost outer segment discs in otherwise structurally intact rod cells to photoreceptors with highly disorganized outer segments and intact inner segments. Totally or partially rescued retinas showed a corresponding restoration of cGMP PDE activity, whereas nonrescued retinas had minimal enzyme activity, characteristic of the rd phenotype. These transgenic animals provide models for studying the molecular basis of retinal degenerative disease and conclusively demonstrate that the phenotype of rd mice is produced by a defect in the ß subunit of cGMP PDE

An Optimal Control Algorithm for Ramp Metering of Urban Freeways

An urban freeway is treated as a dynamic process. A state model for the freeway is obtained with sectional traffic densities as states and entrance flow rates as controls. A linear programming problem is solved to obtain the optimal freeway densities and entrance flow rates under steady-state conditions, and a state regulator is used to minimize the deviations in traffic densities from these optimal steady-state values

On Estimation of Fully Entangled Fraction

We study the fully entangled fraction (FEF) of arbitrary mixed states. New upper bounds of FEF are derived. These upper bounds make complements on the estimation of the value of FEF. For weakly mixed quantum states, an upper bound is shown to be very tight to the exact value of FEF.Comment: 8 pages, 2 figure

Quantum Decoherence in a D-Foam Background

Within the general framework of Liouville string theory, we construct a model for quantum D-brane fluctuations in the space-time background through which light closed-string states propagate. The model is based on monopole and vortex defects on the world sheet, which have been discussed previously in a treatment of 1+1-dimensional black-hole fluctuations in the space-time background, and makes use of a T-duality transformation to relate formulations with Neumann and Dirichlet boundary conditions. In accordance with previous general arguments, we derive an open quantum-mechanical description of this D-brane foam which embodies momentum and energy conservation and small mean energy fluctuations. Quantum decoherence effects appear at a rate consistent with previous estimates.Comment: 16 pages, Latex, two eps figures include

Evaporative CO2 cooling using microchannels etched in silicon for the future LHCb vertex detector

The extreme radiation dose received by vertex detectors at the Large Hadron Collider dictates stringent requirements on their cooling systems. To be robust against radiation damage, sensors should be maintained below -20 degree C and at the same time, the considerable heat load generated in the readout chips and the sensors must be removed. Evaporative CO2 cooling using microchannels etched in a silicon plane in thermal contact with the readout chips is an attractive option. In this paper, we present the first results of microchannel prototypes with circulating, two-phase CO2 and compare them to simulations. We also discuss a practical design of upgraded VELO detector for the LHCb experiment employing this approach.Comment: 12 page

Short O-O separation in layered oxide Na0.67CoO2 enables an ultrafast oxygen evolution reaction.

The layered oxide Na0.67CoO2 with Na+ occupying trigonal prismatic sites between CoO2 layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O-O separation that favors formation of peroxide ions by O--O- interactions followed by O2 evolution in preference to the conventional route through surface O-OH- species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H+ ions from the surface oxygen to provide surface O- that may either be attacked by solution OH- or react with another O-; a short O-O separation favors the latter route. The role of a strong hybridization of the O-2p and low-spin CoIII/CoIV π-bonding d states is also important; the OER on other CoIII/CoIV oxides is compared with that on Na0.67CoO2 as well as that on IrO2

Wafer-Scale Nanopatterning and Translation into High-Performance Piezoelectric Nanowires

The development of a facile method for fabricating one-dimensional, precisely positioned nanostructures over large areas offers exciting opportunities in fundamental research and innovative applications. Large-scale nanofabrication methods have been restricted in accessibility due to their complexity and cost. Likewise, bottom-up synthesis of nanowires has been limited in methods to assemble these structures at precisely defined locations. Nanomaterials such as PbZr_xTi_(1−x)O_3 (PZT) nanowires (NWs)—which may be useful for nonvolatile memory storage (FeRAM), nanoactuation, and nanoscale power generation—are difficult to synthesize without suffering from polycrystallinity or poor stoichiometric control. Here, we report a novel fabrication method which requires only low-resolution photolithography and electrochemical etching to generate ultrasmooth NWs over wafer scales. These nanostructures are subsequently used as patterning templates to generate PZT nanowires with the highest reported piezoelectric performance (d_(eff) ~ 145 pm/V). The combined large-scale nanopatterning with hierarchical assembly of functional nanomaterials could yield breakthroughs in areas ranging from nanodevice arrays to nanodevice powering

Not so crystal clear: the structure of the human telomere G-quadruplex in solution differs from that present in a crystal

The structure of human telomere DNA is of intense interest because of its role in the biology of both cancer and aging. The sequence [5′-AGGG(TTAGGG)(3)] has been used as a model for telomere DNA in both NMR and X-ray crystallographic studies, the results of which show dramatically different structures. In Na(+) solution, NMR revealed an antiparallel G-quadruplex structure that featured both diagonal and lateral TTA loops. Crystallographic studies in the presence of K(+) revealed a flattened, propeller-shaped structure featuring a parallel-stranded G-quadruplex with symmetrical external TTA loops. We report the results of biophysical experiments in solution and computational studies that are inconsistent with the reported crystal structure, indicating that a different structure exists in K(+) solutions. Sedimentation coefficients were determined experimentally in both Na(+) and K(+) solutions and were compared with values calculated using bead models for the reported NMR and crystal structures. Although the solution NMR structure accurately predicted the observed S-value in Na(+) solution, the crystal structure predicted an S-value that differed dramatically from that experimentally observed in K(+) solution. The environments of loop adenines were probed by quantitative fluorescence studies using strategic and systematic single-substitutions of 2-aminopurine for adenine bases. Both fluorescence intensity and quenching experiments in K(+) yielded results at odds with quantitative predictions from the reported crystal structure. Circular dichroism and fluorescence quenching studies in the presence of the crowding agent polyethylene glycol showed dramatic changes in the quadruplex structure in K(+) solutions, but not in Na(+) solutions, suggesting that the crystal environment may have selected for a particular conformational form. Molecular dynamics simulations were performed to yield model structures for the K(+) quadruplex form that are consistent with our biophysical results and with previously reported chemical modification studies. These models suggest that the biologically relevant structure of the human telomere quadruplex in K(+) solution is not the one determined in the published crystalline state