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Several letters to the editor are presented in response to articles in previous issues including "Be Your Own-- How to start a business at any age," "The great escape," and the Auckland Writers Festivals.

Electroabsorption from GeSi on silicon-on-insulator (SOI) is expected to have promising potential for optical modulation due to its low power consumption, small footprint, and more importantly, wide spectral bandwidth for wavelength division multiplexing (WDM) applications. Germanium, as a bulk crystal, has a sharp absorption edge with a strong coefficient at the direct band gap close to the C-band wavelength. Unfortunately, when integrated onto Silicon, or when alloyed with dilute Si for blueshifting to the C-band operation, this strong Franz-Keldysh (FK) effect in bulk Ge is expected to degrade. Here, we report experimental results for GeSi epi when grown under a variety of conditions such as different Si alloy content, under selective versus non selective growth modes for both Silicon and SOI substrates. We compare the measured FK effect to the bulk Ge material. Reduced pressure CVD growth of GeSi heteroepitaxy with various Si content was studied by different characterization tools: X-ray diffraction (XRD), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), Hall measurement and optical transmission/absorption to analyze performance for 1550 nm operation. State-of-the-art GeSi epi with low defect density and low root-mean-square (RMS) roughness were fabricated into pindiodes and tested in a surface-normal geometry. They exhibit low dark current density of 5 mA/cm2at 1V reverse bias with breakdown voltages of 45 Volts. Strong electroabsorption was observed in our GeSi alloy with 0.6% Si content having maximum absorption contrast of / ~5 at 1580 nm at 75 kV/cm.

The influence of an acetamido group in directing the preferred choice of hydration sites in glucosamine and a consequent extension of the working rules governing regioselective hydration and conformational choice, have been revealed through comparisons between the conformations and structures of “free” and multiply hydrated phenyl N‐acetyl‐β‐D‐glucosamine (βpGlcNAc) and phenyl β‐D‐glucopyranoside (βpGlc), isolated in the gas phase at low temperatures. The structures have been assigned through infrared ion depletion spectroscopy conducted in a supersonic jet expansion, coupled with computational methods. The acetamido motif provides a hydration focus that overwhelms the directing role of the hydroxymethyl group; in multiply hydrated βpGlcNAc the water molecules are all located around the acetamido motif, on the “axial” faces of the pyranose ring rather than around its edge, despite the equatorial disposition of all the hydrophilic groups in the ring. The striking and unprecedented role of the C‐2 acetamido group in controlling hydration structures may, in part, explain the differing and widespread roles of GlcNAc, and perhaps GalNAc, in nature.

The effect of carbon is subtle but sweet: The flexible C‐linkage in the newly synthesised C‐glycosyl mimetic, Manα(1,6)‐C‐ManαOPh allows OHπ bonding, both in the gas phase and in aqueous solution. This interaction is absent in the O‐linked disaccharide (see figure).

Factors governing hydration, regioselectivity and conformational choice in hydrated carbohydrates have been examined by determining and reviewing the structures of a systematically varied set of singly and multiply hydrated monosaccharide complexes in the gas phase. This has been achieved through a combination of experiments, including infrared ion‐depletion spectroscopy conducted in a supersonic jet expansion, and computation through molecular mechanics, density functional theory (DFT) and ab initio calculations. New spectroscopic and/or computational results obtained for the singly hydrated complexes of phenyl β‐D‐mannopyranoside (β‐D‐PhMan), methyl α‐D‐gluco‐ and α‐D‐galactopyranoside (α‐D‐MeGlc and α‐D‐MeGal), when coupled with those reported earlier for the singly hydrated complexes of α‐D‐PhMan, β‐D‐PhGlc and β‐D‐PhGal, have created a comprehensive data set, which reveals a systematic pattern of conformational preference and binding site selectivity, driven by the provision of optimal, co‐operative hydrogen‐bonded networks in the hydrated sugars. Their control of conformational choice and structure has been further revealed through spectroscopic and/or computational investigations of a series of multiply hydrated complexes; they include β‐D‐PhMan⋅(H2O)2,3, which has an exocyclic hydroxymethyl group, and the doubly hydrated complex of phenyl α‐L‐fucopyranoside, α‐L‐PhFuc⋅(H2O)2, which does not. Despite the very large number of potential structures and binding sites, the choice is highly selective with binding invariably “focussed” around the hydroxymethyl group (when present). In β‐D‐PhMan⋅(H2O)2,3, the bound water molecules are located exclusively on its polar face and their orientation is dictated by the (perturbed) conformation of the carbohydrate to which they are attached. The possible operation of similar rules governing the structures of hydrogen‐bonded protein–carbohydrate complexes is proposed.

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The functional importance of carbohydrates in biological processes, particularly those involving specific molecular recognition, is immense. Characterizing the three-dimensional structures of carbohydrates and glycoconjugates and their interactions with other molecules, particularly the ubiquitous solvent, water, are key starting points on the road towards the understanding of these processes. The review introduces a new strategy, combining electronic and vibrational spectroscopy of mass-selected carbohydrate molecules and their hydrated (and also protonated) complexes, conducted under molecular beam conditions, with ab initio computation. Its early successes have revealed a uniquely powerful means of characterizing carbohydrate conformations and hydrated structures, the hydrogen-bonded networks they support (or which support them) and the specificity of their interactions with other molecules. The new information, obtained in the gas phase, complements that provided by more 'traditional' condensed phase methods such as NMR, X-ray diffraction, molecular mechanics and molecular dynamics calculations. The review concludes with a vision of the challenges and opportunities offered by applications of molecular beam spectroscopy and their relevance in a biological context.Contents PAGE1.  Preamble 4902. Sweetness and light: Sugars in the gas phase 4923. Experimental and computational strategies 4954. The conformational landscapes of some key monosaccharides: glucose, galactose, mannose, fucose and xylose 4984.1. Notation 4984.2. Glucose, galactose and mannose 4994.3. Fucose and xylose 5035. Probing the glycosidic linkage: lactose and glycan 'building blocks' 5045.1. Notation 5065.2. Lactose 5065.3. Mannose disaccharides 5086. Adding water to sugar: hydrogen-bonding, co-operativity and selectivity 5126.1. Notation 5126.2. Mono-hydrated complexes: glucose, galactose and mannose 5126.3. Co-operativity and conformational selectivity 5166.4. Mono-hydrated complexes: xylose and fucose 5196.5. Some concluding remarks 5217. Using sugars: imino sugars and peptide mimics 5227.1. Sugar mimics: imino sugars 5227.2. Mimicking peptide secondary structure: carbopeptoids 5248. Challenges and opportunities 527Acknowledgements 529References 530

A computational ab initioand molecular dynamics and experimental exploration of the relative importance of molecular conformation and explicit solvent effects on the electronic circular dichroism ECD of chiral molecules, is presented. The exploration includes an assessment of the validity of angular correlation sector rules linking ECD to molecular conformation. It is based upon studies of 1-R phenylethanol including its Raman optical activity spectrum, the corresponding ‘benchmark’ base, 1-R-phenylethylamine and its protonated cation; their hydrated clusters in the gas phase; and their non-polar and aqueous solutions. Emphasis is placed on the influence of specific, hydrogen bonded interactions with the aqueous solvent. The theoretical validity of the otherwise empirical sector rule in the neutral molecules and in their specifically hydrated clusters has been established—but with a reversal of the ‘historical’ sign convention. Protonation of the amine leads to a breakdown of the conventional sector rule but the change in its ECD intensity can still be related to the side chain dihedral angular dependence of its rotatory strength, computed ab initiofor its explicitly hydrated clusters. Comparisons between ECD spectra measured in aqueous and in hydrocarbon solutions and the results of molecular dynamics calculations for aqueous solutions at 300 K, identify solvent induced structural change as the principal determinant of their relative ECD spectral intensities. Further links connecting the structures and conformations of chiral molecules and their explicitly solvated clusters in the gas phase, to their structures and conformational populations in solution can be expected through measurement, ab initiocomputation and analysis of their vibrational, ROA spectra.

The conformation and structure of phenyl-α-l-fucopyranoside (α-PhFuc), phenyl-β-l-fucopyranoside (β-PhFuc) and their singly hydrated complexes (α,β-PhFuc·H2O) isolated in a molecular beam, have been investigated by means of resonant two photon ionization (R2PI) spectroscopy and ultraviolet and infrared ion-dip spectroscopy. Conformational and structural assignments have been based on comparisons between their experimental and computed near IR spectra, calculated using density functional theory (DFT) and their relative energies, determined from ab initio(MP2) calculations. The near IR spectra of ‘free’ and hydrated α- and β-PhFuc, and many other mono- and di-saccharides, provide extremely sensitive probes of hydrogen-bonded interactions which can be finely tuned by small (or large) changes in the molecular conformation. They provide characteristic ‘signatures’ which reflect anomeric, or axial vs. equatorial differences, both revealed through comparisons between α/β-PhFuc and α/β-PhXyl; or similarities, revealed through comparisons between fucose (6-deoxy galactose) and galactose; or binding motifs, for example, ‘insertion’ vs. ‘addition’ structures in hydrated complexes. At the monosaccharide level (the first step in the carbohydrate hierarchy), these trends appear to be general. In contrast to the monohydrates of galactose (β-PhGal) and glucose (β-PhGlc), the conformations of α- and β-PhFuc are unaffected by the binding of a single water molecule though changes in the R2PI spectra of multiply hydrated α-PhFucW(n) however, may reflect a conformational transformation when n≥ 3.

The gas phase structures of phenyl α- and β-d-xylopyranoside α- and β-pXyl and their mono-hydrates have been investigated using a combination of resonant two-photon ionization R2PI, ultra-violet hole-burning and resonant infrared ion dip spectroscopy, coupled with density functional theory DFT and ab initiocomputation. The hole-burning experiments indicate the population of a single conformer only, in each of the two anomers. Their experimental and calculated infrared spectra are both consistent with a conformational assignment corresponding to the computed global minimum configuration. All three OH groups are oriented towards the oxygen atom O1 on the anomeric carbon atom to form an all transttt counter-clockwise chain of hydrogen bonds. The mono-hydrates, α- and β-pXylH2O each populate two distinct structures in the molecular beam environment, with the water molecule inserted between OH4 and OH3 or between OH3 and OH2 in α-pXylH2O, and between OH2 and O1 in either of two alternative orientations, in β-pXylH2O. In all of the mono-hydrated xyloside complexes, the water molecule inserts into the weakest link of the sugar molecules’ hydrogen-bonded chain of hydroxy groups, creating a single extended chain, strengthened by co-operativity. The all-transconfiguration of the xylose moiety is retained and the mono-hydrate structures correspond to those calculated to lie at the lowest relative energies.

The infrared spectra of hydrated complexes of tryptophan have been recorded in the gas phase over the range 160–800 cm−1using double resonance IR-UV ion dip spectroscopy. Despite the problems arising from severe UV spectral overlap of unresolved resonances, the IR measurements, combined with new DFT and ab initiocalculations have allowed a re-assessment of the spectral assignments proposed in an earlier combined near-infraredquantum computational investigation L. C. Snoek, R. T. Kroemer and J. P. Simons, Phys. Chem. Chem. Phys.2002, 4, 2130. It has reinforced the conclusion that hydration leads to conformational restructuring and also served to focus attention on the information that can be provided by spectroscopic measurements obtained in the mid and far IR.

The infrared spectra of hydrated complexes of tryptophan have been recorded in the gas phase over the range 160–800 cm−1 using double resonance IR-UV ion dip spectroscopy. Despite the problems arising from severe UV spectral overlap of unresolved resonances, the IR measurements, combined with new DFT and ab initio calculations have allowed a re-assessment of the spectral assignments proposed in an earlier combined near-infrared/quantum computational investigation [L. C. Snoek, R. T. Kroemer and J. P. Simons, Phys. Chem. Chem. Phys. 2002, 4, 2130]. It has reinforced the conclusion that hydration leads to conformational restructuring and also served to focus attention on the information that can be provided by spectroscopic measurements obtained in the mid and far IR.

A potentially general approach to the infrared spectroscopic detection and structural assignment of protonated molecules in general, and neurotransmitters in particular, generated in high concentration in the gas phase has been implemented, and applied to ethanolamine. Proton transfer in the cationic phenol–ethanolaminecomplex, generated by resonant two photon ionisation, creates a phenoxy–protonated ethanolamine complex. Its infrared photodissociation spectrum is almost identical to vibrational spectrum of freeprotonated ethanolamine; the perturbation introduced by the phenoxy ligand is highly localised and it has very little effect on the structure of its protonated partner. In this respect, the strategy should be able to provide a direct view of the vibrational spectroscopy and structure of a wide range of protonated molecules, including many of biological importance. It is a close relative of the ‘messenger’ technique, involving the infrared photo-dissociation of molecular clusters, that has been exploited by Lee and co-workers (J. C. Jiang, C. Chaudhuri, Y. T. Lee and H.-C. Chang, J. Phys. Chem. A, 2002, 106, 10 937), Solcá and Dopfer (N. Solcá and O. Dopfer, Angew. Chem., Int. Ed. Engl., 2002, 41, 3628) and Mikami and co-workers (A. Fujii, E. Fujimaki, T. Ebata and N. Mikami, J. Chem. Phys., 2000, 112, 6275) in infrared photodissociation studies of protonated clusters of methanol and benzene and of alkyl benzene cations.

The molecular conformation and structure of 2-phenoxy ethylamine and its hydrated complexes and of the generic β-blocker molecule, 3-phenoxy propanolamine have been investigated and assigned using a combination of mass-selected, resonant two-photon ionisation R2PI, coupled with infrared ion-dip spectroscopy and ab initiocalculations. The results are compared with recent investigations of 2-phenoxy ethanol, 2-phenyl ethanolamine, the ephedra and noradrenaline. Attention is focused particularly on the degree of hydrogen bonding and rigidity or flexibility in the side chain and on the organisation and structural influence of bound water molecules.

The gas-phase conformation of the model glycoside, phenyl β-D-galactopyranoside (phe-β-D-gal) was examined using a combination of resonant two-photon ionization (R2PI) and resonant ion-dip infrared spectroscopy (RIDIRS) in tandem with electronic structure theory calculations. A single conformer, in which the hydroxy methyl is in a gauche+ orientation, is predominant in the free-jet expansion. This conformer is the analogue of the lowest-energy conformer found in a previous study of phenyl β-D-glucopyranoside. A minor second conformer has also been identified. Other weak bands in the R2PI spectrum have been attributed to hot bands though it is possible that other conformers are also present at low abundance. The dominant conformer identified in this work has the same (gauche+) orientation of the hydroxy methyl group as the major rotamer identified in solution by NMR spectroscopy.

Clusters of phenol and ethanolamine (2-aminoethanol) have been studied using a combination of spectroscopic techniques (mass-selected resonant two-photon ionisation (R2PI), two-colour ultraviolet hole-burning, and infrared ion-dip spectroscopy) and ab initio computation. Three distinct 1∶1 clusters have been identified and assigned to two alternative types of hydrogen-bonded structure. The phenol molecule either binds (as a proton donor) to the alcoholic oxygen of ethanolamine, leaving the intramolecular hydrogen bond of ethanolamine intact, or it inserts across the intramolecular OH → N bond. Insertion provokes a change in the configuration of the ethanolamine molecule; the gGg' conformation, which is energetically unfavourable and not populated in the bare molecule, presents an ideal geometry to accommodate phenol in a 1∶1 cluster. The time-of-flight mass spectra of all three 1∶1 clusters indicate the formation of protonated ethanolamine following ultraviolet excitation. While this may occur within the neutral excited state or within the cation, the distinct asymmetry in the time-of-flight profiles coupled with ab initio computation of the preferred cationic cluster structures, provides evidence for proton transfer in the ionic state, a conclusion in agreement with the relative proton affinities of ethanolamine and the phenoxy radical.

The conformational and molecular structures of singly hydrated noradrenaline complexes have been explored through a combination of electronic structure computation (at the B3LYP/6-31+G*, MP2/6-31+G* and MP2/aug-cc-pVDZ levels of theory) and mass-selected ultraviolet and infrared ion-dip spectroscopy following laser ablation of the neurotransmitter into a freely expanding moist argon jet. Under these conditions, almost all the hydrated complexes are located in the global minimum energy configuration, associated with an extended, AG1a, ethanolamine side-chain conformation; the water molecule, which is located slightly above the plane of the catechol ring, is bound primarily as a proton acceptor to the m-OH substituent, and only weakly, as a proton donor, to the hydroxyl group on the side chain.

The conformational and molecular structures of singly hydrated noradrenaline complexes have been explored through a combination of electronic structure computation at the B3LYP6-31G, MP26-31G and MP2aug-cc-pVDZ levels of theory and mass-selected ultraviolet and infrared ion-dip spectroscopy following laser ablation of the neurotransmitter into a freely expanding moist argon jet. Under these conditions, almost all the hydrated complexes are located in the global minimum energy configuration, associated with an extended, AG1a, ethanolamine side-chain conformation; the water molecule, which is located slightly above the plane of the catechol ring, is bound primarily as a proton acceptor to the m-OH substituent, and only weakly, as a proton donor, to the hydroxyl group on the side chain.

Singly and multiply hydrated clusters of the two diastereoisomers, (1R,2S) ephedrine and (1S,2S) pseudoephedrine have been generated in a free-jet expansion and structurally assigned by comparing their mass-selected resonant two photon ionisation spectra, their partially resolved ultra-violet rotational band contours and/or their infra-red ion-dip spectra with the results of quantum chemical calculations. The singly hydrated clusters display two distinct types of structure; addition to the alcohol group, with water acting as the proton donor, or insertion of water into the intramolecular OH → N hydrogen bond of the monomer. In the doubly hydrated clusters, water dimer insertion structures are preferred. Hydration of ephedrine promotes relatively little change in its conformational landscape but dramatic changes are observed in the case of pseudoephedrine: the conformational landscapes of the two molecules are sensitive to the absolute configuration of their chiral centres. The sensitivity is attributed to a balance between a number of competing interactions including hydrogen bonding (both intra- and inter-molecular) and steric/non-bonded interactions (involving both the methyl groups of the side chain and the aromatic ring). The dramatic differences between ephedrine and pseudoephedrine mirror their differing biological activities.

Mass-selected R2PI spectra of hydrated tryptophan clusters, generated through thermal evaporation into an expanding moist argon jet, have been recorded and analysed using ultra-violet hole-burn and infra-red ion dip spectroscopy, and interpreted in the light of a series of ab initio calculations for singly, doubly and triply hydrated structures. Despite the wide range of conformers populated in the monomer, the majority of the hydrated tryptophan clusters populate two, very similar structures only. Analysis of their infrared ion-dip spectra does not favour their assignment to either single or double hydrates, but does support their assignment to a pair of near degenerate, triply hydrated clusters. In contrast to other, related molecules, the most stable monomer tryptophan conformation is altered by the hydration. Time of flight mass spectra, reflecting the population of hydrated tryptophan clusters prepared through thermal evaporation into an expanding moist argon jet, differ strikingly from the equivalent spectra generated under laser desorption conditions, where a propensity for generating signal in the Trp·W(3)+ mass channel is observed.

Fluorescence excitation, resonant two-photon ionisation (R2PI) and IR-UV ion-depletion spectroscopy were used to study the structures of 2-phenylacetamide (2PA) and its dimer and water clusters in their S₀, S₁ and ionic states. The n=1–3 hydrates have ‘daisy chain’ structures in which the water molecules link the amide NH and CO sites. The dimer is symmetric, connected via two strong NH···OC hydrogen bonds. Hydrogen-bonded NH and OH modes of the 1:1 hydrates are strongly coupled, to the extent that the symmetric combination is almost IR forbidden. Examination and reinterpretation of previously published IR data on the 1:1 hydrates of formamide and 2-pyridone revealed similar coupling. Solvation affects the photophysics of 2PA as it does N-benzylformamide; the isolated 2PA molecule does not appear to fluoresce but its clusters do. Hydrogen bonding to the amide carbonyl group could account for this behaviour by raising the energy of the lowest amide (n,π*) states above that of the fluorescent S₁ (π,π*) level.

The last few years have seen a very rapid growth in understanding the influence of non-bonded, particularly hydrogen-bonded interactions, on the shapes and conformations of flexible molecules, including those of pharmacological or biological importance, and of the supramolecular structures of their hydrated clusters. This has come about through the combination of a wide range of newly developed spectroscopic strategies, many of which are laser-based, coupled with powerful and widely available ab initio codes for structural computation. The consequent rapid growth of a new link between the worlds of chemistry and biophysics is surveyed in a review which introduces the range of present strategies, their origins, and their application to studies of neutrotransmitters, amides and peptides, amino acids and nucleic acid bases. It concludes with a prospectus for the future.

The stereodynamics of the title reaction on two ab initio versions of the ground (A') state potential energy surface, and one version of the excited (A") state potential surface, have been studied in detail using quasi-classical trajectory methods. The calculations were carried out at a collision energy of 0.1 eV (≡9.6 kJ mol^-1). The polarizations of the reagent and product orbital angular momenta (l and l'), and of the product rotational angular momenta (j') in the (k,k') scattering frame were found to be very sensitive to the OH(v',j') rovibrational product state, and to the choice of potential energy surface employed. Differences in the angular momentum polarization with potential energy surface are traced to differences in microscopic reaction mechanism. State resolved orientation and alignment of the OH product rotational angular momentum are shown to be potential keys to understanding the dynamics on the attractive ground state surface, and to elucidating the degree of involvement of excited electronic state surfaces.

The conformational structures of 4-hydroxy phenyl ethanol (p-tyrosol) and its 1:1 hydrated cluster, have been characterised in the low temperature environment of a free jet expansion through a combination of mass-selected, resonantly enhanced two-photon ionisation spectroscopy (MS-R2PI), fluorescence excitation and ultra-violet ‘hole-burning’ spectroscopy. These strategies, coupled with rotational band contour analysis (using a cross-correlation fitting procedure) and abinitio computation at the HF/6-31G*, MP2/6-31G* and CIS levels of theory, indicate a strong preference for a folded, gauche conformation of the flexible side chain, stabilised by hydrogen-bonded interaction between the terminal OH group and the aromatic ring. Folded conformations that do not allow this are not detected experimentally. It has also been possible to assign the structures of both the gauchecis and gauchetrans OH rotamers, as well as the extended anti conformer and their 1:1 hydrated clusters. The ‘tagging’ of the phenolic OH group by the hydrogen-bonded water molecule also allows the unambiguous assignment of the cis and transgauche conformers through rotational band contour analysis. Although the OH substituent strongly attenuates the degree of rotation, promoted by side-chain folding, of the electronic transition moment in the molecular frame, the residual angle continues to be modulated by the cis–trans rotation of the phenolic OH group.

The product state‐resolved stereodynamics of the reaction of O(1D2) with H2have been studied at 300 K at a mean collision energy of ca. 12 kJ mol−1, using polarized, Doppler‐resolved laser‐induced fluorescence to probe the scattered products, OH(X2Πi; v′ = 0, N′, f′), and polarized photodissociation of N2O to provide the reagent O(1D2) atoms. Product state‐resolved differential cross sections, rotational polarizations, and excitation functions are in very good qualitative agreement with the results of quasi‐classical trajectory (QCT) calculations, conducted on the Schinke‐Lester, SL1 ab initio potential energy surface (PES) for the ground electronic state of the collision complex. The experimental and computational results are compared with those obtained in a complementary study of the reaction of O(1D2) with CH4and remarkable parallels have been exposed. The linear and angular momentum vector correlations are all consistent with an “insertion” mechanism, proceeding over an attractive PES, which presents no entrance barrier.

Information theoretic analysis and subjective paired-comparison and task ranking techniques were employed in order to scale the workload of 20 communications-related tasks frequently performed by the captain and first officer of transport category aircraft. Tasks were drawn from taped conversations between aircraft and air traffic controllers (ATC). Twenty crewmembers performed subjective message comparisons and task rankings on the basis of workload. Information theoretic results indicated a broad range of task difficulty levels, and substantial differences between captain and first officer workload levels. Preliminary subjective data tended to corroborate these results. A hybrid scale reflecting the results of both the analytical and the subjective techniques is currently being developed. The findings will be used to select representative sets of communications for use in high fidelity simulation.

When a triatomic molecule ABC is photolysed by a beam of light to produce the fragments AB and C, the directional nature of the photo-dissociation process manifests itself in a number of ways; in particular, the angular distribution of each fragment is anisotropic, and the angular momentum vector J of the AB photofragment points in space with a preferential distribution with respect to the direction of the light beam. If the AB diatomic fragment is electronically excited, then the emission from AB* will, in the absence of collisions, be polarized, and a measurement of the degree of polarization, p, will provide information about the symmetry nature and dissociation dynamics of the photoexcited state (ABC)*. A number of limiting cases are presented for the sign and magnitude of p, calculated in the classical high J limit, following dissociation of both linear and bent triatomic molecules.

The molecular dynamics of the chemiluminescent reaction of Xe(3P2,0) with Br2, ICl, CH3I, CF3I and CCl4 have been studied at collision energies in the range 10-125 kJ mol-1 using a rotor accelerated cross-beam system. Individual measurements include chemiluminescence spectra of the rare gas halide products, their excitation functions and the translational energy dependence of their rotational alignment (obtained from the observed fluorescence polarization). The results correlate closely with the behaviour of the analogous alkali metal atomic reactions despite the opportunity for curve crossings associated with the multiplicity of electronically excited potential surfaces. Simple dynamical models (e.g. the DIPR model) are used to assess the relative importance of kinematic and dynamical factors, particularly in controlling the degree of alignment impressed on the rotating rare gas halide product.

This article discusses a methodology for flying advanced concepts for piloted vehicles and proposed applications for that methodology. Concept flying, in the most simplistic definition, can be pictured as scaling down a flight environment, inserting operators, and then intuitively looking at the operators response in the situation.

Recently, two new flaviviruses, GB virus A (GBV‐A) and GB virus B (GBV‐B), were identified in the plasma of a tamarin infected with the hepatitis GB agent. A third virus, GB virus C (GBV‐C), was subsequently identified in humans. In the current study, representational difference analysis (RDA) was used to search for a new virus in the serum of a chimpanzee that developed acute resolving hepatitis following inoculation with a pool of chimpanzee plasma. The plasma pool originated from serial passages of a human sample containing virus‐like particles. Numerous cDNA clones were obtained that exhibited 62–80% identity with GBV‐C. With the exception of the extreme 5′ and 3′ ends, the complete viral genome was sequenced, revealing a single large open reading frame encoding a 2833 amino acid polyprotein that contains two envelope proteins, two proteases, a helicase, and an RNA‐dependent RNA polymerase. Phylogenetic analysis of the new virus indicates that it is closely related to GBV‐C, yet still sufficiently divergent as to be placed in a separate group, tentatively labeled GB virus Ctroglodytes(GBV‐Ctro). Numerous human samples were screened by reverse transcriptase‐polymerase chain reaction (RT‐PCR), but GBV‐Ctrosequence was not detected. However, a second chimpanzee inoculated with the same plasma pool was shown to develop a GBV‐Ctroinfection. Although isolated from an Old World primate with hepatitis, the primary host of GBV‐Ctroand any association with disease remains to be determined. J. Med. Virol. 56:44–51, 1998. © 1998 Wiley‐Liss, Inc.

We report a systematic study of the reactions of Xe(3P1, 3P2) with HCl, HBr and HI using both spectroscopic and molecular beam techniques. No reaction is observed at room temperatures for Xe(3P2) with HCl; analysis of the Xe(3P1)/HCl data yields an estimate of the endoergicity of the 3P2 reaction which agrees within experimental error with the threshold obtained from deconvolution of the excitation function measured in the molecular beam experiments, thus indicating little or no barrier in the entrance channel. Surprisal analysis of the vibrational population distributions obtained by inversion of the rare gas halide spectra yields estimates for the fraction of the available energy disposal into vibration . The results are in broad agreement with earlier estimates and are roughly independent of the spin orbit component for a given reaction. Deviations from the purely kinematic limit in the product rotational alignment () increase across the series HCl, HBr, HI while remains moderate, ∼0·5. These results taken with the backward scattering observed for the inelastic channels at low collision energies in the Xe(3P2)/HBr system and the indication of a preferred angle of attack as evidenced by the opacity functions for this system suggest that reaction proceeds via a bent transition state lying towards the product region of the potential energy surface with an important contribution from repulsive release of exoergicity in the exit channel. Similar trends have been observed in the analogous reactions of alkali metal atoms with the hydrogen halides.

Two viruses, GB virus A (GBV-A) and GB virus B (GBV-B), were recently identified in the GB hepatitis agent. Human sera containing antibodies that recognize GBV-A and/or GBV-B recombinant proteins were subjected to polymerase chain reaction studies with degenerate oligonucleotides capable of amplifying a segment of the putative helicase genes from GBV-A, GBV-B or hepatitis C virus. Novel sequences related to members of the Flaviviridaewere identified in sera from 12 individuals including 4 individuals with hepatitis. The limited nucleotide sequence identity between GBV-A, GBV-B and HCV sequences suggests that a novel virus, tentatively named GB virus C, may be responsible for some cases of non-A, non-B, non-C, non-D, non-E hepatitis.

A 336-amino-acid segment of the GB virus C second envelope protein (E2) has been produced in BHK-21 cells using the Semliki Forest virus vector system. Secretion of this protein was facilitated by deletion of a hydrophobic region at the C-terminus that may represent the membrane anchoring domain. The E2 protein recovered from the culture supernatant exhibited a molecular mass of approximately 52 kDa, with the increase in size relative to the polyprotein backbone being contributed by N-linked glycosylation. A radioimmunoprecipitation assay using GBV-C E2 was developed to test for the presence of antibodies against this protein in human sera. The prevalence of antibodies to E2 was high among injection drug users and other individuals at risk for acquiring parenterally transmitted agents. There was a much higher percentage of anti-E2 seropositivity in GBV-C RT-PCR negative compared to GBV-C RT-PCR positive samples from these populations. In addition, serial samples from patients transfused with blood containing GBV-C showed seroconversion to anti-E2 positivity and loss of GBV-C viremia as measured by RT-PCR within 11 months of transfusion in five of seven individuals. Thus, this system provided a rapid means to identify GBV-C E2 as a useful antigen for the study of GBV-C exposure.