Theory of the effects of destruction of localization by inelastic scattering in the resistivity of pure thin potassium wires

Measurements of the electrical resistivity of thin potassium wires at temperatures near 1 K have revealed a minimum in the resistivity as a function of temperature. By proposing that the electrons in these wires have undergone localization, albeit with large localization length, and that inelastic-scattering events destroy the coherence of that state, we can explain both the magnitude and shape of the temperature-dependent resistivity data. Localization of electrons in these wires is to be expected because, due to the high purity of the potassium, the elastic mean free path is comparable to the diameters of the thinnest samples, making the Thouless length lT (or inelastic diffusion length) much larger than the diameter, so that the wire is effectively one dimensional. The inelastic events effectively break the wire into a series of localized segments, whose resistances can be added to obtain the total resistance of the wire. The ensemble-averaged resistance for all possible segmented wires, weighted with a Poisson distribution of inelastic-scattering lengths along the wire, yields a length dependence for the resistance that is proportional to [L3/lin(T)], provided that lin(T)?L, where L is the sample length and lin(T) is some effective temperature-dependent one-dimensional inelastic-scattering length. A more sophisticated approach using a Poisson distribution in inelastic-scattering times, which takes into account the diffusive motion of the electrons along the wire through the Thouless length, yields a length- and temperature-dependent resistivity proportional to (L/lT)4 under appropriate conditions. Inelastic-scattering lifetimes are inferred from the temperature-dependent bulk resistivities (i.e., those of thicker, effectively three-dimensional samples), assuming that a minimum amount of energy must be exchanged for a collision to be effective in destroying the phase coherence of the localized state. If the dominant inelastic mechanism is electron-electron scattering, then our result, given the appropriate choice of the channel number parameter, is consistent with the data. If electron-phason scattering were of comparable importance, then our results would remain consistent. However, the inelastic-scattering lifetime inferred from bulk resistivity data is too short. This is because the electron-phason mechanism dominates in the inelastic-scattering rate, although the two mechanisms may be of comparable importance for the bulk resistivity. Possible reasons why the electron-phason mechanism might be less effective in thin wires than in bulk are discussed.

Common epitopes of serum retinol-binding proteins: a study with monoclonal antibodies

Monoclonal antibodies were raised against purified chicken retinol-binding protein. These were characterised extensively with respect to their ability to recognize retinol-binding proteins from different species. The monoclonal antibodies exhibited differential recognition characteristics. Though the majority presented restricted reactivities, one out of the four monoclonal antibodies studied cross-reacted with retinol-binding proteins from all species tested so far.

Antigenic determinants of human serum retinol binding protein as probed with monoclonal antibodies

Monoclonal antibodies raised against human serum retinol-binding protein (hRBP) were used as probes for the study of the antigenic determinants of hRBP and those shared with the same protein from other species. The antibodies could be classified into four distinct groups and react with the homologous proteins from the rat as well as the rabbit sera. Three of these antibodies recognize sequential or continuous epitopes while the remaining antibody is directed against a discontinuous or conformational epitope. By chemical cleavage with cyanogen bromide, the domains recognized by the monoclonal antibodies could be delineated. By solid-phase synthetic approach, the core sequences recognized by two of these monoclonal antibodies were identified to amino acid sequences 45–51 and 128–131 of the primary amino acid sequence of hRBP.

Coupled substitution of niobium and silicon in potassium titanyl phosphate and arsenate (KTiOPO4 and KTiOAsO4. Synthesis and nonlinear optical properties of KTi1-xNbxOX1-xSixO4 (X = P, As)

Coupled substitution of Nb(V) and Si(IV) for Ti(IV) and P(V)/As(V) in KTiOP04 (KTP) and KTiOAsO4 (KTA) giving new series of nonlinear optical materials, KTi1-xNbxOX1-xSixO4 (X=P,As), has been investigated. Substitution up to x = 0.40 readily occurs, the members retaining the orthorhombic (Pna2(1)) structure of KTP. The second harmonic generation (SHG) property of the parent KTP and KTA is not adversely affected by the coupled substitution. SHG intensity of the powder samples of the X = P series shows a slight increase with x up to x = 0.15; for 0.15 < x less-than-or-equal-to 0.40, there is a decrease in SHG intensity as compared to that for KTP. A similar trend in SHG intensity is seen for the arsenic analogs.

Development of an LH receptor assay capable of measuring serum LH/CG in a wide variety of species

The development of a radioreceptor assay (RRA) that can measure serum LH in a variety of species and CG in sera and urine of pregnant women and monkeys is reported. Using sheep luteal membrane as the receptor source and I-125-labelled hLH/hCG as the tracer, dose-response (displacement) curves were obtained using hLH or hCG as standard. The addition of LH-free serum (200 mul per tube) had no affect on the standard displacement curve. The assay is simple, requires less than 90 min to complete and provides reproducible results. The sensitivity of the assay was 0.6 ng hLH per tube and the intra- and interassay variations were 9.6 and 9.8, respectively. Sera obtained from male and female bonnet monkeys (Macaca radiata) and monkey pituitary extract showed parallelism to the standard curve. The concentrations of LH measured correlated with the physiological status of the animals. Sera of rats, rabbits, hamsters, guinea-pigs, sheep and humans showed parallelism to the hLH standard curve indicating the viability of the RRA to measure serum LH of different species. Since the receptors recognize LH and CG, detection of pregnancy in monkeys and women was possible using this assay. The sensitivity of the assay for hCG was 8.7 miu per tube. This RRA could be a convenient alternative to the Leydig cell bioassay for obtaining the LH bioactivity profile of sera and biological fluids.

A study of the reaction of divalent transition metal chlorides with pyridinium poly(hydrogen fluoride), ppht, and the effect of potassium hydrogen fluoride on fluorination and complexation

Studies of the reaction of metal chlorides, MCl2 (M = Mn, Co, Ni, Cu, Zn) with PPHF at room temperature have shown that Mn, Co and Zn form the corresponding metal fluorides, MF2, while Ni and Cu form their dipyridine metal(II) dichloride complexes. Nickel and copper complexes further undergo fluorination and complexation by potassium hydrogen fluoride in PPHF to form KNiF3 and KCuF3.

Effect of blocking oestrogen synthesis with a new generation aromatase inhibitor CGS 16949A on follicular maturation induced by pregnant mare serum gonadotrophin in the immature rat

While the endocrine role of oestrogen is well established, its function in follicular maturation as an autocrine or paracrine regulator is less well understood. This study was designed to delineate the requirement of oestrogen for follicular development in immature rats. Exogenous gonadotrophin (25 IU pregnant mare serum gonadotrophin (PMSG) per rat) was administered to 21- to 23-day old female rats to induce follicular growth and development. In the experimental animals, synthesis of oestrogen was blocked by implanting an Alzet pump containing the aromatase inhibitor (AI) CGS 16949A (fadrozole hydrochloride; 50 mu g/rat per day). The treatment resulted in blockade of the PMSG induced increase in both serum and intrafollicular oestrogen (>95%), thus leading to an inhibition in uterine weight increment. Compared with the controls, ovarian weight increased markedly in both the PMSG (295%)- and PMSG+AI (216%)-primed animals. There was no significant difference in either the proliferative capabilities of the ovarian granulosa cells or their responsiveness to human chorionic gonadotrophin (hCG; 200 pg/ml) and ovine FSH (20 ng/ml) between the PMSG- and PMSG+AI-treated groups. Histological examination of the ovary, however, indicated a decrease in the number of healthy antral follicles in the Al-treated group compared with the PMSG-primed animals but both the groups showed a percentage increase over the controls (PMSG, 225; PMSG+AI, 158). The responsiveness of the animals to an ovulatory dose of hCG was drastically reduced (>80% inhibition of ovulation) in the oestrogen-deprived animals; this could be overriden by exogenous administration of oestrogen. In conclusion, although blocking oestrogen synthesis in the PMSG-primed rat does not seem to alter the functional properties of the isolated granulosa cells in vitro there appears to be an effect on the number of follicles which complete maturation and are able to ovulate in vivo.

Effect of beta-lactamase-catalyzed hydrolysis of cephalosporins on peroxynitrite-mediated nitration of serum albumin and cytochrome c

The hydrolysis of beta-lactam antibiotics by beta-lactamases is one of the major bacterial defense systems. These enzymes generally hydrolyze a variety of antibiotics including the latest generation of cephalosporins, cephamycins and imipenem. In this paper, the effect of cephalosporins-based antibiotics on the peroxynitrite-mediated nitration of protein tyrosine is described. Although some of the antibiotics have weak inhibitory effect on the nitration reactions in the absence of beta-lactamase, they exhibit very strong inhibition in the presence of beta-lactamase. This is due to the elimination of heterocyclic thiol/thione moieties from cephalosporins by beta-lactamase-mediated hydrolysis. After the elimination, the thiols/thiones effectively scavenge peroxynitrite, leading to the inhibition of the nitration reactions.

Intranasally delivered microdoses of bromocriptine (BCR) effectively reduced serum prolactin levels in hyperprolactinemic patients

It is well known that hyperprolactinaemia in the human leads to infertility. The therapy of choice in India has been the administration of bromocriptine (BCR) as tablets, This mode of administration is generally accompanied by undesirable side-effects such as giddiness, nausea, vomiting and postural hypotension, We demonstrate here the efficacy of microdoses of BCR administered intranasally (IN) to hyperprolactinaemic patients (n = 6) in reducing significantly the elevated serum prolactin levels and maintain them within the normal range, The IN mode of BCR administration, in addition to reducing the effective dose of the drug by 4-20-fold, results in little or no side-effects otherwise associated with oral therapy.

A molecular dynamics study and molecular level explanation of pressure dependence of ionic conductivity of potassium chloride in water

Experimental ionic conductivity of different alkali ions in water shows markedly different dependences on pressure. Existing theories such as that of Hubbard-Onsager are unable to explain these dependences on pressure of the ionic conductivity for all ions. We report molecular dynamics investigation of potassium chloride solution at low dilution in water at several pressures between 1 bar and 2 kbar. Two different potential models have been employed. One of the models successfully reproduces the experimentally observed trend in ionic conductivity of K+ ions in water over the 0.001-2 kbar range. We also propose a theoretical explanation, albeit at a qualitative level, to account for the dependence of ionic conductivity on pressure in terms of the previously studied Levitation Effect. It also provides a microscopic picture in terms of the pore network in liquid water.

Phase modification of ammonium nitrate by potassium salts

Modification of the room temperature phase (IV-III) of ammonium nitrate (AN) has been attempted using a variety of potassium salts namely, KF, KCl, KI, KNO3, K2CO3, K2SO4, KSCN and K2Cr2O7. No phase transition was observed when AN containing 1-2% by mass of these potassium salts is heated from room temperature (25 degrees C) onwards in DTA and DSC scans, but the linear expansion due to phase transition was still observable in TMA measurements. Complete arrest of the linear expansion occurs only when a higher concentration of the additive is used. Similarly, in thermal cycling experiments, complete phase modification in the temperature range -80 to 100 degrees C occurs only with a higher percentage of the potassium salt. The extent of modification, however, is found to be dependent both on the concentration, and the type of the anion. Potassium dichromate when used as an additive modifies the phase as well as the decomposition pattern of AN.

Potassium titanyl phosphate and its isomorphs: Growth, properties, and applications

Potassium titanyl phosphate (KTP) and its isomorphs have received enormous attention in the last 2 decades. In particular, KTP assumes importance due to its large nonlinear optic and electrooptic coefficients together with the broad thermal and angular acceptance for second harmonic generation. This article provides an overview of the material aspects, structural, physical, and chemical properties and device feasibility of the KTP family of crystals. Some of the current areas of research and development along with their significance in understanding the physical properties as well as device applications are addressed. Optical waveguide fabrication processes and characteristics with their relevance to the present-day technology are highlighted. Studies performed so far have enabled us to understand the fundamental aspects of these materials and what needs to be pursued vigorously is the exploitation of their device applications to the maximum extent.

CNT loading into cationic cholesterol suspensions show improved DNA binding and serum stability and ability to internalize into cancer cells

Methods which disperse single-walled carbon nanotubes (SWNTs) in water as `debundled', while maintaining their unique physical properties are highly useful. We present here a family of cationic cholesterol compounds (Chol(+)) {Cholest-5en-3 beta-oxyethyl pyridinium bromide (Chol-PB+), Cholest-5en-3 beta-oxyethyl N-methyl pyrrolidinium bromide (Chol-MPB+), Cholest-5en-3 beta-oxyethyl N-methyl morpholinium bromide (Chol-MMB+) and Cholest-5en-3 beta-oxyethyl diazabicyclo octanium bromide (Chol-DOB+)}. Each of these could be easily dispersed in water. The resulting cationic cholesterol (Chol(+)) suspensions solubilized single-walled carbon nanotubes (SWCNTs) by the non-specific physical adsorption of Chol(+) to form stable, transparent, dark aqueous suspensions at room temperature. Electron microscopy reveals the existence of highly segregated CNTs in these samples. Zeta potential measurements showed an increase in potential of cationic cholesterol aggregates on addition of CNTs. The CNT-Chol(+) suspensions were capable of forming stable complexes with genes (DNA) efficiently. The release of double-helical DNA from such CNT-Chol(+) complexes could be induced upon the addition of anionic micellar solution of SDS. Furthermore, the CNT-based DNA complexes containing cationic cholesterol aggregates showed higher stability in fetal bovine serum media at physiological conditions. Confocal studies confirm that CNT-Chol(+) formulations adhere to HeLa cell surfaces and get internalized more efficiently than the cationic cholesterol suspensions alone (devoid of any CNTs). These cationic cholesterol-CNT suspensions therefore appear to be a promising system for further use in biological applications.

Loading of single-walled carbon nanotubes in cationic cholesterol suspensions significantly improves gene transfection efficiency in serum

We present here a series of cholesterol based cationic lipid suspensions that solubilize single-walled carbon nanotubes (SWCNT) efficiently in water. Each cationic lipid formulation was characterized in terms of their energy minimized molecular structures, bilayer widths of the aggregates based on X-ray diffraction. Then these aggregates were investigated pertaining to their DNA binding and release efficiency, effect of CNT inclusion on the stability of cationic cholesterol lipid-DNA complexes, Zeta potential values and changes in the chiro-optical property of DNA, effect on Raman spectral shift and changes in morphology by SEM and AFM. Each cationic lipid formulation was optimized for the amount of SWCNT solubilized in water, lipid-DNA ratio, amount of the plasmid DNA that can be transfected and the effect on the cellular toxicity. The resulting SWCNT-lipid formulations were then used for in vitro transfection of pEGFP-C3 in A549 (human alveolar basal epithelial) cells and HeLa (human cervical cancer) cells. Advantageously, the CNT-loaded formulations confer an excellent transfection efficiency even in high percentages of blood serum and showed significantly better gene transfer efficiency compared to one of the potent, well-known commercial transfection reagent, Lipofectamine2000.