Search Results

You are looking at 1 - 10 of 836 items for :

  • All content x
Clear All

Abstract  

Heat content of silicon has been measured in a temperature range of 700-1820 K using a drop calorimeter. Boron nitride was used as a sample crucible. The enthalpy of fusion and the melting point of silicon determined from the heat content-temperature plots are 48.310.18 kJ mol-1 and 16875 K, respectively. The heat content and heat capacity equations were derived using the Shomate function for the solid region and the least square method for the liquid region, respectively, and compared with the literature values.

Restricted access

Abstract

A novel method using ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6] as extracting solvent in head-space single drop microextraction followed by HPLC with fluorimetric detection has been developed for analysis of tributyltin (TBT) and triphenyltin (TPhT) in water. Experimental conditions related to SDME performance, for example micro-drop volume, extraction time, stirring rate, salt content, and sample volume were investigated. Under the optimized conditions (micro-drop volume, 10 μL; extraction time, 30 min; stirring rate, 900 rpm; salt concentration, 6% sample volume, 6 mL), the linear range, detection limit (S/N = 3), and reproducibility (RSD, n = 4) were 1−100 μL−1, 0.62 μL−1, and 7.8%, respectively, for TBT, and 2−100 μL−1, 0.95 μL−1, and 8.3% for TPhT. All micro-extraction experiments were performed at room temperature (25 ± 1°C). The optimized procedure was successfully used for analysis of TBT and TPhT in deionized water and waste water. Recovery of a 25 μL−1 spike was in the range 86.9–92.1%. The method has also been used for analysis of TBT and TPhT in natural water.

Restricted access

Abstract  

Technetium(VII) was separated from interfering substances by extraction with 0.01M tetraphenylarsonium chloride in chloroform. To avoid back-extraction, enrichment at the hanging mercury drop electrode (HMDE) has been carried out directly in the organic phase after addition of 0.01M NaOH as an electrolyte and ethanol as a homogenized agent. By application of a deposition voltage of –1.6 V, as well as DPCSV, a distinct current signal at –0.26 V (vs. Ag/AgCl) was obtained. The detection limit was found to be 3·10–8 M Tc.

Restricted access

Based on previous work studying complex microreactors, it was desired to further improve the mixing efficiency by varying the mixing unit design for fast liquid—liquid reactions. Different flow regimes were studied, including slug flow, parallel flow, and drop flow. The two-phase hydrolysis of 4-nitrophenyl acetate in sodium hydroxide solution was used to evaluate the overall volumetric mass transfer coefficients (K org a) as a function of the average rate of energy dissipation (ε) for each microreactor design and all flow regimes. The liquid—liquid systems investigated used n-butanol or toluene as the organic phase solvent and a 0.5-M NaOH aqueous solution. The use of surfactant was also investigated with the toluene—water system. All microreactor geometry designs were based on contraction—expansion repeating units with asymmetric obstacles to aid the breakup of slugs and desynchronize the recombination of split streams. The investigated designs were chosen to avoid the formation of the parallel flow regime, contrary to curvature-based mixing-unit designs. The microreactor design can then be optimized to reduce the ε required to reach drop flow, since K org a has been found to be constant at equal ε for a given solvent system in this flow regime, regardless of the reactor selection. Additionally, the “3/7th” scaleup rule was applied and confirmed with the LL-Triangle mixer. It was found that, for low interfacial-tension systems (i.e., n-butanol—water), the onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers.

Open access

Bevezetés : Minden betegség kezelése során előnyös, ha az alkalmazott gyógyszer koncentrációja a célszervben a legmagasabb. Ebből következik, hogy a kötőhártya betegségeit, ha lehet, szemcseppekkel kezeljük. Célok: Szerző célja az emedastine hatóanyagú szemcsepp hatékonyságának felmérése szezonális allergiás kötőhártya-gyulladásban szenvedő gyermekeken. Módszer: 2 vizsgálat történt. Az első vizsgálat során 20 heveny szezonális allergiás kötőhártya-gyulladásban szenvedő gyermekbeteg kapott emedastine difumarat (H 1 antihisztamin) tartalmú Emadine szemcseppet. Kötőhártyájuk vérbőségét és viszkető érzését 0-tól 4-ig terjedő skálán regisztrálták, ahol 4 jelentette a legsúlyosabb tüneteket. A 2. vizsgálatban 232 másik gyermek kapta e szemcseppet 2 pollen szezonon keresztül és vizsgálták az esetleges hatáscsökkenést és mellékhatásokat. Eredmények: A kötőhártya viszkető érzete átlagosan 3, vérbősége átlagosan 8 perc alatt csökkent szignifikáns mértékben. A 2. vizsgálat során a 232 gyermek közül egy sem kényszerült a kezelés módosítására hatástalanság, vagy valamilyen kellemetlen mellékhatás miatt. Következtetések: Az Emadine szemcsepp igen gyorsan és hatékonyan csökkenti a kötőhártya-viszketést és -vérbőséget. Már 3 éves kisgyermek is jól tűrte, és tartós használat esetén sem csökkent a hatékonysága.

Restricted access

The values of thermodynamic functions of the following eight organic compounds under non-reacting conditions within the temperature range 298.15 – 550 K are given: N,N dimethylformamide, CHO · N(CH3)2; 4-nitro-1-chlorobenzene, Cl · C6H4 · NO2; sodiump-nitrophenoxide, NO2 · C6H4 · ONa; 1-methyl-2-pyrrolidone, 4,4′-dinitrodiphenyl ether, (NO2 · C6H4)2O; 4,4′-diaminodiphenyl ether, (NH2 · C6H4)2O; bis-(4-aminophenyl)methane, (NH2 · C6H4)2CH2; bis(4-maleic acidimidphenyl)methane,

Restricted access

83 Steiner, M. Y., Spohr, L. J. and Goodwin, S. (2010): Relative humidity controls pupation success and dropping behaviour of western flower thrips, Frankliniella occidentalis (Pergande

Restricted access

[ 2 ] reported measurement of the enthalpy increments of (U 0.8 Pu 0.2 )C from 1039 to 2421 K with an induction heated drop calorimeter. Preusser [ 3 ] has given an empirical equation for the heat capacity of (U 0.8 Pu 0.2 )C, based on the hypothetical

Restricted access

.S. Geol. Survey, A modified version of OFR 00-509, 1–56. Duni Ll, Kuka N 2007: Estimates of stress-drop and high frequency diminution parameter from strong motion data recorded in Albania. In the series “NATO special series

Restricted access