A rate equation method for the sequential double ionisation, including autoionising state excitation, of a noble gas

A set of rate equations have been tested against a more robust set of Time-Dependent Density Matrix (TDDM) equations [D. P. W. Middleton, L. A. A. Nikolopoulos, J. Mod. Opti. 59, 1650 (2012)] by using them to determine the populations of ion species and autoionising states (AIS) in noble gas atoms when interacting with a strong external field. Two field shapes were tested here — sinusoidal and square — and a variety of pulse characteristics were examined, i.e. intensity, duration and photon energy, for the neon atomic system. It was found that the rate equations were sufficiently accurate only when the external field is way off-resonant with the AIS. Moreover, analytical solutions of the rate equations in the square pulse case agree with the numerical solutions for a time-dependent pulse containing many cycles. An attempt to model a stochastic field was also made and it was found that the use of such a field diminished and broadened the ion yield ratio due to the presence of an added bandwidth.     

Synthesis and reactivity of the methoxozirconium pentatungstate (nBu4N)6[{(mu-MeO)ZrW5O18}2]: insights into proton-transfer reactions, solution dynamics, and assembly of {ZrW5O18}2- building blocks

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(mu-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(mu-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4-8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(mu-MeO)(mu-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surface are important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6-8. Given the inert nature of the methoxo bridges in 1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinate ligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate [(mu3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. This work demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis by tungstated zirconia surfaces.     

Zero- and low-temperature behavior of the two-dimensional ±J Ising spin glass

Scaling arguments and precise simulations are used to study the square lattice ±J Ising spin glass, a prototypical model for glassy systems. Droplet theory explains, and our numerical results show, entropically stabilized long-range spin-glass order at zero temperature, which resembles the energetic stabilization of long-range order in higher-dimensional models at finite temperature. At low temperature, a temperature-dependent crossover length scale is used to predict the power-law dependence on temperature of the heat capacity and clarify the importance of disorder distributions.     

Qualitative Analyse

Ohne Zusammenfassung     

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Ohne Zusammenfassung     

Romano-British wall-paintings II: Raman spectroscopic analysis of two villa sites at Nether Heyford, Northants

We report the analysis of 31 fragments of Roman wall-paintings from two adjacent villa sites near Northampton, which date from about 1800 years b.p. The specimens comprise pigments which are still attached to their substrate, affording an opportunity for the examination of interaction. The palette is rather restricted to a predominance of red (with shades varying from pink through to deep red), white and grey colours, with yellow, blue, brown and green being only rarely observed. This contrasts with Romano-British villa specimens from other sites where a more extensive palette has been recognised.     

Gamma-spectroscopy of the 199At nucleus with the Recoil Filter Detector

The neutron deficient ¹⁹⁹At nucleus has been studied in the ¹⁷⁵Lu+²⁸Si reaction at E_b= 141 MeV. In order to select events of interest in the presence of the very strong background caused by fission, γ-rays have been detected in coincidence with recoiling evaporation residues. The excited states of ¹⁹⁹At observed for the first time may indicate that this nucleus is deformed. Received: 17 September 1998 / Revised version: 14 October 1998     

Sensitive Morphological Characterization of Oriented High-Density Lipoprotein Nanoparticles Using 31P NMR Spectroscopy

The biological function of high-density lipoprotein (HDL) nanoparticles, the so-called good cholesterol that is associated with a low risk of heart disease, depends on their composition, morphology, and size. The morphology of HDL particles composed of apolipoproteins, lipids and cholesterol is routinely visualised by transmission electron microscopy (TEM), but higher-resolution tools are needed to observe more subtle structural differences between particles of different composition. Here, reconstituted HDL formulations are oriented on glass substrates and solid-state ³¹P NMR spectroscopy is shown to be highly sensitive to the surface curvature of the lipid headgroups. The spectra report potentially functionally important differences in the morphology of different HDL preparations that are not detected by TEM. This method provides new morphological insights into HDL comprising a naturally occurring apolipoprotein A-I mutant, which may be linked to its atheroprotective properties, and holds promise as a future research tool in the clinical analysis of plasma HDL.     

The dynamics and orientation of a lipophilic drug within model membranes determined by 13C solid-state NMR

Methods for determining how a drug interacts with cellular membranes at the molecular level can give valuable insight into the mode of action of the drug and its absorption, distribution and metabolism profile. A procedure is described here to determine the orientation and location of the lipophilic drug trifluoperazine (TFP) intercalated into dimyristoylphosphatidylcholine (DMPC) bilayers, by using a novel combination of high-resolution solid-state nuclear magnetic resonance (SSNMR) methods to observe signals from (13)C within the drug at natural abundance. SSNMR measurements of (1)H-(13)C dipolar couplings for TFP and selective broadening of (13)C NMR peaks by paramagnetic Mn(2+) together suggest a model for the location, orientation and dynamics of the drug within lipid bilayers that offers an explanation for the lysoprotective effect of the drug at low concentrations. The experiments described are straightforward to implement and can be used for the routine analysis of drug-membrane interactions to provide useful information for drug design and structure refinement.