Ion-transport and diffusion coefficients of non-plasticised methacrylic-acrylic ion-selective membranes

The ion-transport behaviour of methacrylic-acrylic-based polymers for ion-selective electrode (ISE) membranes was investigated by a spectrophotometric method to determine the apparent diffusion coefficient. By observing the degree of deprotonation of the chromoionophore or chromogenic ionophore, the extent of penetration of cations into the polymer films was determined. The transport of the cations into the optode films depended on the stoichiometry of complexation by the ionophores. The apparent diffusion coefficients, estimated from the deprotonation data were of the order of 10⁻¹² to 10⁻¹¹ cm² s⁻¹. These values indicate that the apparent ion mobility in the methacrylic-acrylic ISE membranes is approximately a thousand times lower than that in plasticised PVC ISE membranes. For some ionophores, the value of the apparent diffusion coefficient could be modulated according to the ionophore content in the membrane and the data obtained for a calixarene containing membrane were tested against a model for facilitated diffusion with chained carriers. The data did not fit a model where intramolecular diffusion was limiting, but were consistent with a first-order rate-limiting mechanism involving an intermediate 1:2 complex between ion and ionophore. In this instance, the lowest values for D_app were thus not necessarily obtained for lowest ionophore loading and in the range examined, a trend of decreasing D_app with increasing ionophore was noted.     

Der Dreistoff: Uran-Bor-Kohlenstoff

Zusammenfassung Der Dreistoff: U-B-C wird mittels heißgepreßter Proben (etwa 60 Ansätze) röntgenographisch untersucht. Mit Ausnahme von U₂C₃ wird in diesen Legierungen das Bestehen aller übrigen bereits bekannten Zweistoffverbindungen bestätigt. Im Dreistoff-system tritt eine einzige ternäre Phase mit der ungefähren Formel UBC auf, die einen ausgedehnten homogenen Bereich besitzt. Diese Phase kristallisiert in der Raumgruppe D _2h ¹⁷ und leitet sich in ihrem Aufbau vom CrB- bzw. ZrSi₂-Typ her. Die Lage der Uranatome wird genau bestimmt (y _U=0,132 in 4c), Positionen von Bor und Kohlenstoff werden vorgeschlagen. Die ternäre Phase steht im Gleichgewicht mit: UC, UC₂, Kohlenstoff, UB₂ und UB₄.Mit 3 Abbildungen     

On the Small-Scale Mass Concentration of Modes

Let be commuting, jointly-elliptic, -pseudodifferential operators on a compact manifold, X, of dimension n≥d. Suppose γ is the ω-limit set of the bicharacteristic flow of the classical Hamiltonian, p ₁, restricted to the variety, . We discuss the corresponding concentration of mass as for a subsequence of joint eigenfunctions of the P _j 's with eigenvalues sufficiently close to . Received: 1 October 1998 / Accepted: 1 April 1999     

The HITRAN 2004 molecular spectroscopic database

This paper describes the status of the 2004 edition of the HITRAN molecular spectroscopic database. The HITRAN compilation consists of several components that serve as input for radiative transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e., spectra in which the individual lines are unresolvable; individual line parameters and absorption cross-sections for bands in the ultra-violet; refractive indices of aerosols; tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 39 molecules including many of their isotopologues.The format of the section of the database on individual line parameters of HITRAN has undergone the most extensive enhancement in almost two decades. It now lists the Einstein A-coefficients, statistical weights of the upper and lower levels of the transitions, a better system for the representation of quantum identifications, and enhanced referencing and uncertainty codes. In addition, there is a provision for making corrections to the broadening of line transitions due to line mixing.     

Evaluation of the inelastic mean free path (IMFP) of electrons in polyaniline and polyacetylene samples obtained from elastic peak electron spectroscopy (EPES)

The inelastic mean free path (IMFP) of electrons was determined experimentally for selected polyaniline and polyacetylene samples with Ag and Ni references using elastic peak electron spectroscopy (EPES). The surface composition was determined by XPS and density by helium pycnometry. The high resolution hemispherical ESA-31 and ADES-400 spectrometers were used for measurements in the energy range E = 0.5–3.0 keV and E =0.4 − 1.6 keV, respectively. The integrated elastic peak intensity ratios for sample and reference were calculated using the Monte Carlo (MC) algorithm based on the electron elastic scattering cross-sections database NIST SRD64 version 3.1 and applying TPP-2M IMFPs for polymers. Surface excitation parameters (SEP) and material parameters ( _ach ) for polymers were determined, using the model of Chen, from comparison of measured and MC calculated elastic peak intensity ratios. These corrections proved to be efficient in decreasing the percentage deviations between the obtained IMFPs and the TPP-2M formula IMFPs. The elastic peak of hydrogen was observed in the EPES spectra of polymers. The experimental contribution of the hydrogen to the total elastic peak was 0.58%, while this value obtained from the MC simulations was 1.98%.      

Line positions and strengths of OCO, OCO and OCO between 2200 and 7000 cm

Line positions and strengths of ¹⁶O¹²C¹⁸O (628), ¹⁸O¹²C¹⁸O (828) and ¹⁷O¹²C¹⁸O (728) were measured between 2200 and 7000 cm⁻¹ using 22 near infrared (NIR) absorption spectra recorded at 0.01-0.013 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. These data were obtained at room temperature using absorption cells with optical path lengths ranging from 2.4 to 385 m; the cells were filled with natural and ¹⁸O-enriched samples of CO₂ at pressures ranging from 0.54 to 252 torr. The observed line positions were analyzed to obtain the upper state band centers and rotational constants for 17 bands of ¹⁶O¹²C¹⁸O, 19 bands of ¹⁸O¹²C¹⁸O and 8 bands of ¹⁷O¹²C¹⁸O. The majority of the ¹⁸O¹²C¹⁸O and ¹⁷O¹²C¹⁸O bands were measured for the first time. In addition, the rotational constants for the lower states 00001, 01101e and 01101f were derived for all three species using the method of combination differences in which the averaged values obtained from the line positions of two or more bands were least-squares-fitted. Rovibrational parameters were also obtained for the 02201e, 02201f, 10002 and 10001 states of ¹⁸O¹²C¹⁸O. The line position analysis revealed that transitions of the levels 38 ? J′ ? 46 of the 11111f ← 01101f band of ¹⁸O¹²C¹⁸O are perturbed. Perturbed transitions were also observed for the 12212 ← 02201 band and in the high-J transitions (J′ ? 49) of the 20012 ← 00001 band of ¹⁸O¹²C¹⁸O. Band strengths and Herman-Wallis-like F-factor coefficients were determined for 21 bands of ¹⁶O¹²C¹⁸O, 25 bands of ¹⁸O¹²C¹⁸O and 8 bands of ¹⁷O¹²C¹⁸O from least-squares fits to more than 3700 measured transition intensities; band strengths and line positions for 34 of these bands were obtained for the first time.     

Air-broadened halfwidth and pressure shift coefficients of CO2 bands: 4750-7000 cm

Previously we obtained self-broadened halfwidth and self-induced shift coefficients at room temperature for 15 near infrared CO₂ bands between 4750 and 7000 cm⁻¹ [R.A. Toth, L.R. Brown, C.E. Miller, V.M. Devi, D.C. Benner, J. Mol. Spectrosc., 239 (2006) 243-271]. The present study expands our work on the near infrared line parameters of CO₂ to include air broadening coefficients. Here we report nearly 400 air-broadened half width and air-induced pressure shift coefficients spanning 11 different CO₂ vibrational bands in the 4750-7000 cm⁻¹ region. Retrievals have been performed using Voigt line profiles over three distinct spectral intervals: (a) 4750-5200 cm⁻¹, covering the 20011 ← 00001, 20012 ← 00001, and 20013 ← 00001 Fermi Triad and three associated hot bands 21111 ← 01101, 21112 ← 01101, 21113 ← 01101; (b) 6100-7000 cm⁻¹, covering the 30011 ← 00001, 30012 ← 00001, 30013 ← 00001 and 30014 ← 00001 Fermi Tetrad; (c) near 6950 cm⁻¹ for the 00031 ← 00001 overtone band. The air-broadened halfwidth and air-induced pressure shift coefficients have been modeled with empirical expressions and compared to other measurements available in the literature.     

Mössbauer Study of Microstructure and Magnetic Properties (Co,Ni)–Zr Substituted Ba Ferrite Particles

The β-NMR of short-lived β-emitter in a rutile TiO₂ single crystal has been measured as functions of temperature and external magnetic field. Atomic motion induced spin lattice relaxation was observed for two known sites, O substitutional and interstitial sites. The data were analyzed in terms of the thermal atomic jump, which suggests that the motion of defects around the substitutional ¹²N atom for O, and of the interstitial ¹²N atom are attributed to the spin lattice relaxation. The electric field gradients have shown temperature dependence for both sites, which is probably due to the thermal expansion of rutile.     

The mandelamide keto-enol system in aqueous solution. Generation of the enol by hydration of phenylcarbamoylcarbene

Flash photolysis of diazophenylacetamide in aqueous solution produced phenylcarbamoylcarbene, whose hydration generated a transient species that was identified as the enol isomer of mandelamide. This assignment is based on product identification and the shape of the rate profile for decay of the enol transient, through ketonization to its carbonyl isomer, as well as by the form of acid-base catalysis of and solvent isotope effects on the decay reaction. Rates of enolization of mandelamide were also determined, by monitoring hydrogen exchange at its benzylic position, and these, in combination with the ketonization rate measurements, gave the keto-enol equilibrium constant pK(E) = 15.88, the acidity constant of the enol ionizing as an oxygen acid, pQ(E)(a)= 8.40, and the acidity constant of the amide ionizing as a carbon acid pQ(K)(a)= 24.29. (These acidity constants are concentration quotients applicable at ionic strength = 0.10 M.) These results show the enol content and carbon acid strength of mandelamide, like those of mandelic acid and methyl mandelate, to be orders of magnitude less than those of simple aldehydes and ketones; this difference can be attributed to resonance stabilization of the keto isomers of mandelic acid and its ester and amide derivatives, through electron delocalization into their carbonyl groups from the oxygen and nitrogen substituents adjacent to these groups. The enol of mandelamide, on the other hand, again like the enols of mandelic acid and methyl mandelate, is a substantially stronger acid than the enols of simple aldehydes and ketones. This difference can be attributed to the electronegative nature of the oxygen and nitrogen substituents geminal to the enol hydroxyl group in the enols of mandelic acid and its derivatives; in support of this, the acidity constants of these enols correlate well with field substituent constants of these geminal groups.