Does water condense in carbon pores?

Using grand canonical Monte Carlo (GCMC) simulations of molecular models, we investigate the nature of water adsorption and desorption in slit pores with graphitelike surfaces. Special emphasis is placed on the question of whether water exhibits capillary condensation (i.e., condensation when the external pressure is below the bulk vapor pressure). Three models of water have been considered. These are the SPC and SPC/E models and a model where the hydrogen bonding is described by tetrahedrally coordinated square-well association sites. The water-carbon interaction was described by the Steele 10-4-3 potential. In addition to determining adsorption/desorption isotherms, we also locate the states where vapor-liquid equilibrium occurs for both the bulk and confined states of the models. We find that for wider pores (widths >1 nm), condensation does not occur in the GCMC simulations until the pressure is higher than the bulk vapor pressure, P0. This is consistent with a physical picture where a lack of hydrogen bonding with the graphite surface destabilizes dense water phases relative to the bulk. For narrow pores where the slit width is comparable to the molecular diameter, strong dispersion interactions with both carbon surfaces can stabilize dense water phases relative to the bulk so that pore condensation can occur for P < P0 in some cases. For the narrowest pores studied--a pore width of 0.6 nm--pore condensation is again shifted to P > P0. The phase-equilibrium calculations indicate vapor-liquid coexistence in the slit pores for P < P0 for all but the narrowest pores. We discuss the implications of our results for interpreting water adsorption/desorption isotherms in porous carbons.     

Photochemische Reaktionen. 97 Mitteilung [1]. Zur Photochemie konjugierter Epoxy-diene II. Versuche mit (E)-β-Jonyliden-epoxiden

Photolysis of Conjugated Epoxy-dienes Direct and sensitized excitation of the (E)-β-ionylidene-epoxides 1 and 4 leads to different types of isomerizations. Thus photocycloelimination to the cyclopropene-ketones 2 and 6 is only achieved by ¹(π, π*)-excitation (λ=254 nm), whereas ³(π, π*)-excitation (λ > 280 nm, acetone) gives selective C(1′), O-cleavage of the oxirane ( 1 → 7 – 10 and 4 → 11 – 13 ). In contrast to 1 the twofold methylsubstituted epoxy-diene 4 shows mainly (E/Z)-isomerization ( 4 → 5 ) on both ¹(π, π*)- and ³(π, π*)-excitation while the isomerizations 4 → 6 and 4 → 11 – 13 are minor processes, only.     

Detection of toluene diisocyanate with a coated quartz piezoelectric crystal: Part 4. A portable automatic detector with humidity correction

Microcomputer-controlled measurement of the frequency of two differently-coated quartz piezoelectric crystals and subsequent data processing permits the immediate correction of instrumental response for fluctuations in water vapour concentration and the display of the corrected toluene diisocyanate concentration in air. Crystal pairs with coatings of polyethylene glycol 400 or 1540 or tri-n-octylphosphine oxide and cobalt(II) chloride were used to illustrate the performance of the instrument. Toluene diisocyanate can be detected over the range 0.1—15 ppm in atmospheres with relative humidities ranging from 30 to 60% without significant interference from changes in water concentration.     

A study of the spectral emissions in laser-irradiated microdot targets at 0.53 and 0.27 μm wavelengths with micron resolution

Using a knife-edge technique, we have determined the spatial extension of H-like and He-like emissions and the time-integrated axial electron density profile in laser-irradiated aluminium microdot targets at 0.53 and 0.25 μm wavelengths with about 3 μm resolution.     

Ultralow emittance, multi-MeV proton beams from a laser virtual-cathode plasma accelerator

The laminarity of high-current multi-MeV proton beams produced by irradiating thin metallic foils with ultraintense lasers has been measured. For proton energies >10 MeV, the transverse and longitudinal emittance are, respectively, <0.004 mm mrad and <10(-4) eV s, i.e., at least 100-fold and may be as much as 10(4)-fold better than conventional accelerator beams. The fast acceleration being electrostatic from an initially cold surface, only collisions with the accelerating fast electrons appear to limit the beam laminarity. The ion beam source size is measured to be <15 microm (FWHM) for proton energies >10 MeV.     

Internal granular dynamics,shear-induced crystallization,and compaction steps

Internal imaging using index matching, and sensitive volume measurement, are used to investigate the spatial order and dynamics of a deep disordered layer of spheres sheared under a fixed load. Shearing triggers a crystallization transition accompanied by a step compaction event. The delay preceding the transition depends strongly on the layer thickness and can require a translation of about 10(5) particle diameters. The mean velocity varies with depth by more than five decades, and its profile is qualitatively altered by the transition.     

Analytical chemistry of synthetic routes to psychoactive tryptamines. Part III. Characterisation of the Speeter and Anthony route to N,N-dialkylated tryptamines using CI-IT-MS-MS

Twelve symmetrically and 13 asymmetrically N,N-disubstituted glyoxalylamide precursors and their corresponding tryptamine derivatives have been characterised by gas chromatography low-pressure chemical ionisation ion trap tandem mass spectrometry (CI-IT-MS-MS) with internal (in situ) ionisation using methanol as the chemical ionisation reagent. Mass spectral differences and similarities between the investigated compounds are discussed and put into context with previous investigations. In tryptamines the formation of [CH2=N+R2R3] iminium ions after beta-cleavage appears to be the dominating process. Dissociation of the protonated molecule into [3-vinylindole]+ for example, appears to be a minor pathway when compared with electrospray triple quadrupole tandem mass spectrometry (ESI-TQ-MS-MS) where this ion transition was found to be of distinctive importance. CI-IT-MS-MS is also found to enable the differentiation between most isomeric derivatives studied.     

On a Degenerate Zakharov System

We establish a local well-posedness result for an initial value problem associated to a Zakharov system arising in the study of laser-plasma interactions. We called this system degenerate due to the lack of dispersion presented in one of the spatial variables. One of the key tools to obtain our results is the presence of appropriate global versions of the so called local smoothing effects inherent to the dispersive character of the model.*Partially supported by CNPq-Brazil.**Partially supported by NSF grant DMS-0140023.     

n-n Effective range from the photon spectrum of the reaction π−d→γnn

Notable improvements in the treatment of the reaction π^?d→γnn, extending the validity of the calculation to lower photon energies, permit a new analysis of a high statistics photon spectrum. A precise value of the effective range parameter γ_nn = 2.83 ± 0.11 fm has been obtained. The theoretical uncertainty is 0.11 fm. The value of the scattering length previously extracted from the same spectrum is confirmed, with a_nn = ? 18.6 ± 0.5 fm.