Ion conductors derived from cholic acid and spermine: importance of facial hydrophilicity on NA(+) transport and membrane selectivity

A series of ion conductors have been synthesized in which the degree of facial hydrophilicity has been systematically varied. Specifically, conjugates have been prepared from cholic acid and spermine in which the hydrophilic face of each sterol bears methoxy (1), hydroxy (2), carbamate (3), or sulfate groups (4). The ability of these conjugates to promote the transport of Na(+) across phosphatidylcholine membranes of varying thickness has been investigated by (23)Na NMR spectroscopy. Examination of observed activities in three different phosphatidylcholine membranes has provided evidence for membrane-spanning dimers as the transport-active species. In the thinnest membranes investigated, made from 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (C14), Na(+)-transport activity was found to increase, substantially, with increasing facial hydrophilicity. In thicker membranes, made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (C18), observed activities were found to decrease with increasing facial hydrophilicity; with a membrane of intermediate thickness, prepared from 1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine (C16), ion-conducting activity increased and then decreased, with continuous increases in facial hydrophilicity. The possible origins for these variations in activity are briefly discussed.     

Diode laser spectroscopic measurements and theoretical calculations of line parameters of nitrogen-broadened water vapor overtone transitions in the 818-834 nm wavelength region

Nitrogen-broadened water vapor line parameters of the (2 1 1) ← (0 0 0) overtone band transitions in the 818-834 nm wavelength region are measured by using a tunable diode laser spectrometer. Water vapor is kept at its saturated vapor pressure at room temperature within a sample cell. Use of a balanced detector and a lock-in amplifier helps to increase the detection efficiency and the signal-to-noise ratio. The collisional broadening coefficients are extracted from the fitting of the experimental data by using a standard Voigt line profile. Collisional half-widths of water vapor lines perturbed by nitrogen are evaluated using the complex-valued implementation of the Robert-Bonamy (CRB) formalism. The rotational wave functions and the energy eigenvalues in the (2 1 1) vibrational state of water molecule are assumed on the basis of symmetry properties. Hence the outcome of this work also tests the validity of the theoretical approximations. The experimental data are compared with the corresponding theoretical values and the possible causes of deviation between the two have also been discussed.     

Self-assembled Monolayers of Two Aromatic Disulfides and a Diselenide on Polycrystalline Silver Films: An Investigation by SERS and XPS

Self-assembled monolayers of diphenyldisufide (DDS), naphthalenedisulfide (NDS), and diphenyldiselenide (DDSe) on polycrystalline silver films have been investigated by surface enhanced Raman spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS). DDS adsorbs on Ag through a homolytic cleavage of the S-S bond and resultant thiolate at the surface decomposes upon prolonged exposure to air. The geometry of the molecule is such that the benzene ring is almost horizontal to the surface. The Raman spectrum has been assigned in the light of ab-initio molecular orbital calculations. In DDSe, the Se-Se bond is retained upon adsorption and the molecule sticks up. In contrast, NDS is highly reactive on the microscopically rough surface so that a stable monolayer could not be prepared. A temperature dependent Raman study of the DDS monolayer shows the absence of any reorientation at the surface as one would expect from the adsorption geometry. XPS study complements the SERS data and shows the presence of Ag2S on an NDS exposed surface. Copyright 1999 Academic Press.     

Construction of Improved Stress-Energy Tensor in d ≥ 2

The weakest set of necessary and sufficientconditions for the existence of a conserved tracelesssymmetric stress-energy tensor for a scale-invariantPoincare field theory over a d-dimensional flatspace-time manifold has been proved. This improved tensoris explicitly constructed for arbitrary space-timedimensions including d = 2. The example of a vectorfield in d 3, d 4 demonstrates that fullconformal symmetry over a flat space-time is sufficientbut not necessary for the existence of an improvedtensor.     

Sol-gel synthesis of cubic titanium dioxide nanoparticle using poly(ethylene glycol) as a capping agent: voltammetric simultaneous determination of uric acid and guanine

Titanium dioxide nanoparticles (NPs) were synthesized by a sol-gel method from hexafluorotitanic acid using poly(ethylene glycol) as a capping agent. The crystal structure and morphology of the NPs were characterized by X-ray diffraction, FESEM, and TEM. The NPs were used to modify a graphite paste electrode for simultaneous determination of uric acid (UA) and guanine (GU). The effect of calcination temperature on crystal structure and electrocatalytic activity was investigated. The electrochemical responses to UA and GU at bare GP, TiO₂–350/GP, and TiO₂–600/GP electrodes were compared. The DPV oxidation peaks of UA and GU were found to be strongest at around 304 and 673 mV, respectively, against Ag/AgCl reference electrode, and this are well separated for effective simultaneous determination. UA and GU can be simultaneously determined by this method. Response is linear within the range 0.1–500 μM and 0.1–40 μM for UA and GU, respectively. The detection limits are 70 nM for UA and 50 nM for GU (at an S/N? ratio of?3). The TiO₂–600/GP electrode showed excellent analytical performance when analyzing spiked urine and serum samples.

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Graphical abstract A graphical representation of cubic TiO₂ nanoparticle formation during hydrolysis through sol-gel process.

     

Flexible electrospun PET/TiO2 nanofibrous structures: Morphology,thermal and mechanical properties

In this study, a solvothermal method was used to synthesize anatase titanium dioxide (TiO₂) nanoparticles in the presence of oleic acid (OA) and oleylamine (OM) as morphology‐directing agents. Functional nanocomposite fibers of poly(ethylene terephtalate) (PET) containing surfactants‐capped TiO₂ nanoparticles were developed by electrospinning technique. The morphology, thermal stability and mechanical properties of PET/TiO₂ nanocomposite mats were investigated as a function of TiO₂ concentration. Morphology investigation showed interesting results in terms of the level of TiO₂ dispersion inside the fibers and the improvement of the quality (smoothness) of the fibers' surface when the synthesized nanorhombic TiO₂ nanoparticles were used compared to a commercial P25 TiO₂ (AEROXIDE P25)_. The presence of OA and OM on the surface of the nanorhombic synthesized TiO₂ led to a significant improvement of TiO₂ dispersion inside the PET matrix. Furthermore, the physical interaction between the PET matrix and TiO₂ nanoparticles resulted in an enhanced thermal stability, and an increase of the Young's modulus and tensile strength for TiO₂ concentration up to 10 wt%.     

Stereospecific cross-coupling of alpha-(thiocarbamoyl)organostannanes with alkenyl, aryl, and heteroaryl iodides

Racemic and scalemic PTC-protected alpha-hydroxystannanes cross-couple with alkenyl/aryl/heteroaryl iodides in moderate to good yields using copper(I) thiophene-2-carboxylate (CuTC) in THF at or below room temperature. Simple aryl iodides and 1-iodocyclohexene, two classes of electrophiles that typically react sluggishly, are also good substrates. Cross-couplings proceed with retention of configuration at the alkenyl- and stannyl-substituted stereocenters.     

Sensitivity analysis of the newsvendor model

Quality of decisions in inventory management models depends on the accuracy of parameter estimates used for decision making. In many situations, error in decision making is unavoidable. In such cases, sensitivity analysis is necessary for better implementation of the model. Though the newsvendor model is one of the most researched inventory models, little is known about its robustness. In this paper, we perform sensitivity analysis of the classical newsvendor model. Conditions for symmetry/skewness of cost deviation (i.e., deviation of expected demand–supply mismatch cost from its minimum) have been identified. These conditions are closely linked with symmetry/skewness of the demand density function. A lower bound of cost deviation is established for symmetric unimodal demand distributions. Based on demonstrations of the lower bound, we found the newsvendor model to be sensitive to sub-optimal ordering decisions, more sensitive than the economic order quantity model. Order quantity deviation (i.e., deviation of order quantity from its optimum) is explored briefly. We found the magnitude of order quantity deviation to be comparable with that of parameter estimation error. Mean demand is identified as the most influential parameter in deciding order quantity deviation.     

Wigner distribution of elliptical quantum optical vortex

We calculate the Wigner quasiprobability distribution function of the quantum elliptical vortex in elliptical beam (EEV), produced by coupling squeezed coherent states of two modes. The coupling between the two modes is performed by using beam splitter (BS) or a dual channel directional coupler (DCDC). The quantum interference due to the coupling between the two modes promises the generation of controlled entanglement for quantum computation and quantum tomography.     

High-precision half-life measurement for the superallowed β+ emitter ²⁶Al(m)

A high-precision half-life measurement for the superallowed β+ emitter 26Al(m) was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1/2 6346.54 ± 0.46(stat) ± 0.60 (syst) ms, consistent with, but 2.5 times more precise than, the previous world average. The 26Al(m) half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed β decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for (26)Al(m), 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi β-decay studies used to test the conserved vector current hypothesis and determine the V(ud) element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.