Repeated sorption of water in SBA-15 investigated by means of in?situ small-angle x-ray scattering

The effect of repeated cycles of water adsorption/desorption on the structural stability of ordered mesoporous silica SBA-15 is studied by small-angle x-ray scattering (SAXS). In?situ sorption measurements are conducted using a custom-built sorption apparatus in connection with a laboratory SAXS setup. Two striking irreversible changes are observed in the sorption isotherms as derived from the integrated SAXS intensity. First, the capillary condensation pressure shifts progressively to lower relative pressure values with increasing number of sorption cycles. This effect is attributed to chemisorption of water at the silica walls, resulting in a change of the fluid-wall interaction. Second, the sorption cycles do not close completely at vanishing vapour pressure, suggesting that progressively more water remains trapped within the porous material after each cycle. This effect is interpreted to be the result of an irreversible collapse of parts of mesopores, originating from pore wall deformation due to the large Laplace pressure of water acting on the pore walls at capillary condensation and capillary evaporation.     

Quantitative analysis of a quaternary ammonium drug: ipratropium bromide by LC/ESI-MS(n) in horse plasma and urine

A quantitative method, using LC/ESI-MS(n) with a quadrupole linear ion trap mass analyzer, has been developed for the analysis of ipratropium cation in horse plasma and urine. The method applies solid-phase extraction with WCX cartridges for plasma and MM2 cartridges for urine, prior to analysis by LC/ESI-MS(n). The efficiency of extraction combined with the sensitivity and the selectivity of MS(n) allows for the quantification of ipratropium cation at picogram per milliliter levels. The analytical capabilities of the method have been successfully checked by the quantitative analysis of ipratropium cation in post-administration samples collected from horses treated by nebulization.     

Closed-form BER analysis of variable weight MPPM coding under gamma-gamma scintillation for atmospheric optical communications

In this paper, the performance of the variable weight multiple pulse-position modulation (MPPM) coding technique in an atmospheric optical communication environment under gamma-gamma optical scintillation is analyzed, proposing a closed-form expression for the average bit error rate (BER). This study is based on a hyperexponential fitting of the conditional BER in absence of turbulence fluctuations, leading to closed-form expressions that characterize the behavior of this nonlinear coding scheme. Finally, conditional and average BER expressions proposed here are corroborated with Monte Carlo simulations results.     

ChemInform Abstract: Crystal Chemistry and Electronic Structure of the Photovoltaic Buffer Layer, (In1-xAlx)2S3.

The effects of aluminium substitution in In₂S₃ are investigated by single crystal XRD, ²⁷Al NMR spectroscopy, and DFT calculations.     

New properties and representations for members of the power-variance family. I

We derive new Wright-function representations for the densities of the generating measures of most representatives of the power-variance family of distributions. For all members of this family, we construct new saddlepoint-type approximations having an arbitrary fixed number of refining terms. To this end, we derive new, ??exponentially small,?? Poincaré series for a subclass of the Wright functions whose coefficients are expressed in terms of the Zolotarev polynomials.     

The 130Nd↦130Pr↦130Ce decay chain revisited

An investigation of low-lying energy levels of ¹³⁰Pr and ¹³⁰Ce has been made via β-decay. The radioactive parent nuclei were produced via ^94,96Mo + ⁴⁰Ca reactions at 6.8 MeV/nucleon and transported by a He-jet system. Gamma-γ-t, γ-X-t, γ-e^--t coincidence measurements were performed. Internal conversion coefficients have been measured with a magnetic spectrometer. The new β-decay half-life of ¹³⁰Nd has been determined to be 21(3) s. A partial level scheme of ¹³⁰Pr at low-spin has been constructed. The β-decay of ¹³⁰Pr to ¹³⁰Ce suggests the existence of three β-instable isomeric states in ¹³⁰Pr, while only one half-life T _1/2 = 40(4) s has been measured. Based on the present work and low-lying excited states in neighbouring odd-mass nuclei, the spins and parities of isomeric states in ¹³⁰Pr are proposed to be 2⁺, (4,5)⁺ and (7,8^±). The ground state in ¹³⁰Pr is still undetermined. Received: 20 August 2001 / Accepted: 6 November 2001     

On-line separation of163Ta and162Ta

A new 12s activity has been produced via the³⁵C1+¹¹²Sn reaction at 191 MeV and ascribed to the¹⁴³Tb EC/β⁺ decay. A decay scheme is derived from γ-γ and γ-X-ray coincidence measurements.     

The components of the venom of a spider Scodra griseipes. 1. Analysis of low molecular weight products using gas chromatography/mass spectrometry.

Low molecular weight venom constituents of the spider Scodra griseipes have been derivatized using bis(trimethylsilyl)-trifluoroacetamide and pentafluoropropionic anhydride. Examination of these derivatives by coupled gas chromatography/mass spectrometry using electron ionization or ammonia- or isobutane-chemical ionization allows their structural identification. Comparisons have also been made with retention time and mass spectra of the pure compounds. Four acids: phosphoric, lactic, citric, gamma-aminobutyric (neurotransmitter) and four basic biogenic amines: putrescine, cadaverine, spermidine and spermine have been found.