Enthalpies of dilution of electrolyte solutions by flow microcalorimetry

The enthalpies of dilution of NaCl, Me₄NBr, andn-Bu₄NBr were measured in water at 25°C with a new flow microcalorimeter. The data were analyzed with a polynomial equation, and the derived relative apparent molal enthalpies _L are in good agreement with literature values. Provided care is taken that mixing is complete, flow calorimeters are as reliable and much less time-consuming than cell-type instruments for enthalpies of dilution measurements.     

Separation and determination of aluminium by single-column ion-chromatography

A quick, reliable method for the determination of Al(III) in the presence of other metal ions is presented. A Chromatographic system consisting of a low-capacity cation-exchange column, an eluent of diprotonated p-phenylenediamine, and a conductivity detector was used to measure the retention times for various cations. During the course of this work, it was found that Al(III) was eluted later than most bivalent metal ions but earlier than other tervalent metal ions. Therefore the concentration of eluent was adjusted so that an early sharp peak was obtained for Al(III) and the bivalent metal ions were eluted as a group. Through analysis of an NBS standard, as well as of solutions containing Al(III) and other metal ions, the method was shown to be precise, accurate and rapid for determination of Al(III) without interference from common bivalent metal ions.     

Heat capacities of binary cycloalkane mixtures at 298.15 K

Volumetric heat capacities of the six binary mixtures formed from cyclopentane, cyclohexane, cycloheptane and cyclooctane were determined at 298.15 K in a Picker flow microcalorimeter. Excess heat capacities obtained from the results are compred with the temperature variation of excess enthalpies from the literature.     

Thermodynamic properties of alkali halides. V. Temperature and pressure dependence of excess free energies in water

A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed.     

Long-term carrier-envelope phase coherence

The carrier-envelope phase of the pulse train emitted by a 10-fs mode-locked laser has been stabilized such that carrier-envelope phase coherence is maintained for at least 150 s (measurement limited). The phase coherence time was measured independently of the feedback loop.     

Spectroscopic study of the N = 27 nuclei by means of the (τ, α) reaction

The (τ, α) reaction on ⁴⁸Ca, ⁵⁰Ti, ⁵²Cr and ⁵⁴Fe target nuclei has been studied at 25 MeV incident energy. Angular distributions have been measured from 5° to 40° with a split-pole spectrometer in a large range of excitation energy. A local zero-range DWBA analysis has been carried out, using an isospin-dependent potential for the calculation of the neutron form factor, in order to get a coherent set of spectroscopic factors for both T_> and T_< levels in different nuclei. Assignments of l-values have been done for a large number of levels, most of them previously unknown, and energy centroids of hole states have been determined. Spectroscopic factors in ³⁹Ca, ⁴⁷Ti, ^{49, 52, 53}Cr have also been obtained for strongly excited states. A sum rule analysis has been carried out for the N = 27 nuclei: the $\text{1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{T}{}_{\mathrm{<}}$ hole strengths are generally fully exhausted by the observed levels, whereas only a fraction of the $\text{1}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ strength has been evidenced. The $\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{, 1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ analog states have been observed in all nuclei; in ⁵³Fe, the $\text{1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ analog states appear to be split in several components. In addition, a CRC analysis has been carried out for some levels with angular distributions not accounted for by a direct pick-up process. These levels are tentatively identified with states resulting from the coupling of one $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ neutron hole with excited states of the target nucleus. In particular, the $\text{5}\text{2}{}^{\mathrm{?}}\text{and}\text{9}\text{2}{}^{\mathrm{?}}$ members of the $\text{[2}{}^{\mathrm{+}}\text{?}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{]}$ configuration have been identified in each final nucleus. Unambiguous J^π assignments are made; and the two-step (τ, α) reaction therefo e appears as a useful spectroscopic tool, especially for investigating high spin states.     

Use of electron density critical points as chemical function-based reduced representations of pharmacological ligands

In this paper, we propose a reduced representation of molecules of pharmacological interest based on their chemical functions. The proposed representations of the molecules are obtained by a topological analysis of their electron density maps at medium resolution, leading to graphs of critical points. The distribution of the different types of critical points are compared at various levels of resolution for a training set of 22 molecules in order to define the optimal resolution level leading to the best representation of the various chemical functions. The reduced representations can in the future be used for molecular similarity research and pharmacophore proposals.     

Investigation of copper oxide impregnants prepared from various precursors for respirator carbons

Copper oxide impregnated activated carbon was prepared by three methods and studied as a respirator carbon. Using techniques such as dynamic flow testing, X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), copper oxide impregnants, derived from different sources such as basic copper carbonate (Cu₂CO₃(OH)₂), copper nitrate (Cu(NO₃)₂) and copper chloride (CuCl₂) reacted with sodium hydroxide (NaOH), have been studied. Dynamic flow tests performed using sulfur dioxide (SO₂), ammonia (NH₃) and hydrogen cyanide (HCN) challenge gases allow the determination of the stoichiometric ratio of reaction (SRR) between challenge gas and impregnant. Thermal gravimetric analysis experiments showed that an inert heating environment was required when thermally decomposing the Cu(NO₃)₂ impregnant to CuO to avoid damaging the activated carbon substrate. SEM has been used to investigate dispersal and particle size of the impregnant on the activated carbon. XRD permits the identification of crystalline and amorphous phases as well as the grain size of the impregnant. XRD analysis of samples before and after exposure to SO₂ has allowed the active impregnant in SO₂ adsorption to be identified. The relationship between SRR, impregnant loading and grain size is discussed. Methods to improve impregnant distribution are presented and their impact discussed.     

Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider

We present an optical frequency divider based on a 200 MHz repetition rate Er:fiber mode-locked laser that, when locked to a stable optical frequency reference, generates microwave signals with absolute phase noise that is equal to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz carrier, the phase noise is below -100 dBc/Hz, limited by the optical reference. For offset frequencies >10 kHz, the phase noise is shot noise limited at -145 dBc/Hz. An analysis of the contribution of the residual noise from the Er:fiber optical frequency divider is also presented.