A novel, highly sensitive probe consisting of a uniform region sandwiched between two linear tapers for an evanescent wave fibre-optic absorption sensor is proposed. The diameter of the uniform region is chosen to be equal to the minimum allowed diameter of the taper's output end. The first taper is used to bring the angles of the rays in the input fibre close to the critical angle of the sensing region while the second taper reconverts the angles into their initial values so that they can propagate in the output fibre. It has been shown that the sensitivity of the sensor depends on the length of the uniform region of the probe, the refractive index of the fluid and the numerical aperture of the fibre. The sensitivity increases with increase in the length of the uniform region and also with decrease in the numerical aperture of the fibre. In addition, the sensitivity of the proposed probe can be further increased by launching the selected rays into the input fibre. 相似文献
The aggregation behavior of cationic gemini surfactants with respect to variation in head group polarity and spacer length is studied through conductance, surface tension, viscosity, and small-angle neutron-scattering (SANS) measurements. The critical micellar concentration (cmc), average degree of micelle ionization (beta(ave)), minimum area per molecule of surfactant at the air-water interface (A(min)), surface excess concentration (gamma(max)), and Gibb's free energy of micellization (delta G(mic)) of the surfactants were determined from conductance and surface tension data. The aggregation numbers (N), dimensions of micelles (b/a), effective fractional charge per monomer (alpha), and hydration of micelles (h(E)) were determined from SANS and viscosity data, respectively. The increasing head group polarity of gemini surfactant with spacer chain length of 4 methylene units promotes micellar growth, leading to a decrease in cmc, beta(ave), and delta G(mic) and an increase in N and b/a. This is well supported by the observed increase in hydration (h(E)) of micelles with increase in aggregation number (N) and dimension (b/a) of micelle. 相似文献
In high-field NMR microscopy rapid single-shot imaging methods, for example, echo planar imaging, cannot be used for determination of the apparent diffusion tensor (ADT) due to large magnetic susceptibility effects. We propose a pulse sequence in which a diffusion-weighted spin-echo is followed by multiple gradient-echoes with additional diffusion weighting. These additional echoes can be used to calculate the ADT and maps. We show here that this results in modest but consistent improvements in the accuracy of ADT determination within a given total data acquisition time. The method is tested on excised, chemically fixed rat spinal cords. 相似文献
We explore the coupling between the helix-coil and coil-globule transitions of a helical polymer using Monte Carlo simulations. A very rich state diagram is found. Each state is characterized by a specific configuration of the chain which could be a helix, a random coil, an amorphous globule, or one of various other globular states which carry residual helical strands. We study the boundaries between states and provide further insight into the physics of the system with a detailed analysis of the order parameter and other properties. 相似文献
GaN phase is synthesized using systemic implantation of nitrogen ions of multiple energies (290, 130 and 50 keV) into Zn-doped GaAs (1 0 0) at room temperature and subsequent annealing at 850 °C for 30 min in Ar + H2 atmosphere. The implanted doses of nitrogen ions are 5 × 1016 and 1 × 1017 ions-cm−2. Glancing angle X-ray diffraction studies show that hexagonal phase of GaN were formed. The photoluminescence studies show the emission from the band edge as well as from point defects. 相似文献
Research on Chemical Intermediates - A series of 2-aryl-4-((4-aryl-1H-1,2,3-triazol-1-yl)methyl)thiazole derivatives (8a–p) have been synthesized. The structure of the newly synthesized... 相似文献
The similarity solutions to the problem of cylindrically symmetric strong shock waves in an ideal gas with a constant azimuthal magnetic field are presented. The flow behind the shock wave is assumed to spatially isothermal rather than adiabatic. We use the method of Lie group invariance to determine the possible class of self-similar solutions. Infinitesimal generators of Lie group transformations are determined by using the invariance surface conditions to the system and on the basis of arbitrary constants occurring in the expressions for the generators, four different possible cases of the solutions are reckoned and we observed that only two out of all possibilities hold self-similar solutions, one of which follows the power law and another follows the exponential law. To obtain the similarity exponents numerical calculations have been performed and comparison is made with the existing results in the literature. The flow patterns behind the shock are analyzed graphically.
Gold nanorods and nanospheres capped with positively charged CTAB are deposited on the surface of gram-positive bacterium having negatively charged teichoic acid brushes. The deposition rate is more than an order of magnitude faster than that for peptide and nucleic acid capped nanoparticles. For the nanorods, never been reported before, the strong electrostatic attraction causes the rods to bend conformally over the curved bacterium surface in random orientations. This leads to formation of an efficient percolating cluster (i.e., low contact resistance and high radius of gyration) with 104-fold higher current at 3-fold lower coverage compared to a monolayer from nanospheres. The high monolayer conductivity at only approximately 10% coverage for nanorods has potential for fabricating a novel class of bioelectronic devices by coupling electronic "nanocircuitry" at the surface to the biological function of microorganisms. 相似文献
The sorption of 241Am, 233U and 137Cs from nitric acid solutions on a synthesized sodium potassium fluoro-phlogopite (SPFP) gel, structurally close to the fluorine mica mineral, has been studied. The synthesized gel was characterized by energy dispersive spectrometry, X-ray powder diffraction pattern, FTIR and thermogravimetric analysis and has a composition of Na0.5K0.5Mg3(Si3AlO10)F2.6H2O. Different parameters like contact time, acid concentration, amount of SPFP, metal ion concentrations, effect of competing cations, desorption of the nuclides from the loaded SPFP gel etc., were studied using batch technique. Also, the SPFP gel was loaded with Eu(III), U(VI) and Cs(I) and the amounts sorbed on the gel has been estimated by difference from the concentrations in the original solution and those remaining in the solution after loading. Na, K, Mg, Eu and U were estimated by ICP-AES and Cs by electrothermal atomization atomic absorption spectrometry. The exchange of Na, K and Mg with the loaded cations has been evaluated and discussed in the light of ion exchange and surface precipitate sorption mechanisms. 相似文献
Osmotic vapor pressure and density measurements have been carried out for binary aqueous and ternary aqueous solutions containing
a fixed concentration of 18-crown-6 (0.2 mol⋅kg−1) and ammonium chloride or ammonium bromide at 298.15 K. The concentration of the ammonium salts was varied between 0.02 to
0.5 mol⋅kg−1. The measured water activities were used to obtain the activity coefficient of water and the mean molal activity coefficient
of the ions in binary as well as ternary solutions. Using the method developed by Patil and Dagade reported earlier in this
journal and the McMillan-Meyer pair and triplet Gibbs energy interaction parameters, the thermodynamic equilibrium constant
(K) for the 18-crown-6:NH4+ complexes were determined. It is observed that the nature and polarizability of anions play important roles in imparting
stability to the complexed species. The log10K values for the 18-crown-6:NH4+ complexed species are lower than for the complexes involving alkali metal ions such as K+. The volume of complexation for the studied systems obtained from the apparent molar volumes of ammonium halides in ternary
solutions are positive and of smaller magnitude than those reported for complexation with alkali ions. The results are further
discussed in terms of water structural effects, complex formation, the role of counter anions and hydrophobic interactions. 相似文献