Search

The interaction of intense particle bunches with plasma can give rise to plasma wakes1,2 capable of sustaining gigavolt-per-metre electric fields3,4, which are orders of magnitude higher than provided by state-of-the-art radio-frequency technology5. Plasma wakefields can, therefore, strongly accelerate charged particles and offer the opportunity to reach higher particle energies with smaller and hence more widely available accelerator facilities. However, the luminosity and brilliance demands of high-energy physics and photon science require particle bunches to be accelerated at repetition rates of thousands or even millions per second, which are orders of magnitude higher than demonstrated with plasma-wakefield technology6,7. Here we investigate the upper limit on repetition rates of beam-driven plasma accelerators by measuring the time it takes for the plasma to recover to its initial state after perturbation by a wakefield. The many-nanosecond-level recovery time measured establishes the in-principle attainability of megahertz rates of acceleration in plasmas. The experimental signatures of the perturbation are well described by simulations of a temporally evolving parabolic ion channel, transferring energy from the collapsing wake to the surrounding media. This result establishes that plasma-wakefield modules could be developed as feasible high-repetition-rate energy boosters at current and future particle-physics and photon-science facilities.Relaxation of a perturbed plasma back to its initial state over nanosecond timescales establishes that megahertz repetition rates are supported, and high luminosities and brilliances are in principle attainable with plasma-wakefield accelerator facilities. [ABSTRACT FROM AUTHOR]

The FLASHForward experimental facility is a highperformance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'. [ABSTRACT FROM AUTHOR]

Two new polyoxovanadoborates based crystalline lattices are being reported: K(HO)(1,3-diapH)[VBOH]·10.80HO ( 1), and K(HO)(enH)[VBOH]·9HO ( 2). These structures are characterized by presenting multiple hydrogen bonds between the diprotonated diamines (enH and 1,3-diapH) and hydronium ions, and the oxygen atoms of the [VBOH] cluster. The crystalline packing and stability of these new polyoxovanadoborates is dominated by the different types of hydrogen interactions present in the lattices ranging from unidirectional to trifurcated ones. The crystallographic data, together with the BVS method, permit to assign a mixed valence ratios for the [VBOH] anionic cluster for ( 1) and ( 2) being 11/1 (V/V) ratio. [ABSTRACT FROM AUTHOR]

Two new polyoxovanadoborates based crystalline lattices are being reported: K(HO)(1,3-diapH)[VBOH]·10.80HO ( 1), and K(HO)(enH)[VBOH]·9HO ( 2). These structures are characterized by presenting multiple hydrogen bonds between the diprotonated diamines (enH and 1,3-diapH) and hydronium ions, and the oxygen atoms of the [VBOH] cluster. The crystalline packing and stability of these new polyoxovanadoborates is dominated by the different types of hydrogen interactions present in the lattices ranging from unidirectional to trifurcated ones. The crystallographic data, together with the BVS method, permit to assign a mixed valence ratios for the [VBOH] anionic cluster for ( 1) and ( 2) being 11/1 (V/V) ratio. [ABSTRACT FROM AUTHOR]

A new tetranuclear complex Cu4, [Cu2L(OH)]2·2CH3OH·H2O (1), with the functionalized Schiff base ligand 2,6-bis((2-(acetylamino)phenylimino)methyl)-4-tert-butylphenol (H3L) has been obtained and characterized in the solid state by X-ray diffraction. The formation of the tetranuclear species is solvent dependent, the presence of water being a determinant in its isolation. Based on the mass-spectrometric evidence, the behaviour of the H3L–CuII system in the presence of water was investigated. Namely, water can switch the nuclearity of the CuII cluster from dinuclear to tetranuclear. The redox behaviour of this species in DMSO solution, showing two cathodic metal-centred peaks at EP = −0.80 and −1.35 V and an irreversible ligand-centred anodic peak at EP = 1.03 V, was found to be similar to that of a pristine dinuclear complex. The tetranuclear species was also characterized in the solid state by magnetic measurements, showing a dominating bulk antiferromagnetic behaviour, with a singlet ground state at approximately 2 K. DFT calculations permitted us to estimate the strong intradimer antiferromagnetic exchange interaction (J1 = −440 cm−1), together with two weak interdimer ferromagnetic exchange interactions (J2 = +0.5 and J3 = +1.7 cm−1). [ABSTRACT FROM AUTHOR]

This study aimed to determine whether there was a difference in skin permeability to methylene blue dye or skin morphology between dairy cows that differed in their susceptibility to digital dermatitis (DD) and to assess the effect of contact with slurry on skin permeability. Twenty nine dairy cows were monitored for DD during the winter housing period and classed as DD+ (previous DD infection, n = 17), or DD− (no recorded infection, n = 12). The animals were culled and a skin sample was taken from above the heel of each hind foot and frozen. Samples were later defrosted and one sample from each cow was tested for permeability, whereas the other was treated with slurry for 24 h before permeability testing. To test permeability, methylene blue dye was applied to the skin surface in a Franz diffusion cell. After 48 h, the amount of dye that had passed through the skin was estimated. The stratum corneum thickness and the density of hair follicles were determined from additional heel skin samples. Skin permeability to methylene blue dye was significantly greater for samples that had been treated with slurry but did not differ between DD+ and DD− animals. No difference was found in the stratum corneum thickness or density of hair follicles between DD+ and DD− animals. These findings imply that individual differences in general skin permeability are not a major factor in determining DD susceptibility and suggest that contact with slurry could contribute to DD infection by increasing the permeability of the skin, which may facilitate pathogen entry. Further work is required to clarify the role played by slurry in the pathogenesis of DD. [ABSTRACT FROM PUBLISHER]

The inter-conversions of platinum carbonyl dianionic clusters, ([Pt3(CO)6]n2−, n= 2–5), have been studied in THF and acetonitrile using in situFTIR spectroscopy. These inter-conversions were facilitated by the addition (or removal) of molecular hydrogen. The individual reactions, namely reductions and oxidations of [Pt3(CO)6]n2−were fast and reversible. BTEM analysis of the data provided the pure component spectra of the individual species without the need for physical separation. It is shown, for the first time, that the species [Pt3(CO)6]n2−(n= 2) can be formed from the reduction of [Pt3(CO)6]n2−(n= 3–5) by hydrogen alone in acetonitrile. Also, detection of dissolved CO2in solution suggests that a room-temperature water gas shift reaction occurs. This has been shown to arise from nucleophilic attack of water on a coordinated CO of [Pt3(CO)6]n2−which leads to the formation of [HPt15(CO)19]3−and [H2Pt15(CO)19]2−. The parent tetraanion, [Pt15(CO)19]4−, has been isolated in high yields by reaction of [Pt3(CO)6]n2−(n= 2, 3) with NaOH at 60 °C and has been structurally characterized by X-ray analysis. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of 1- and 2-phenyl substituted polyaromatic hydrocarbons have been measured and estimated under conditions relevant to heat transport applications almost to the critical point. Densities, vapor pressures, and heat capacity measurements were used to derive critical temperature, pressure, and density for the phenylnaphthalenes. The thermal and radiolytic stability of 1-phenylnaphthalene was examined using thermogravimetric analysis, differential scanning calorimetery, and gamma irradiation. Low melting point, low vapor pressure, high critical temperature, and resistance to thermal decomposition may make phenylnaphthalenes suitable for heat transfer applications up to 800 K, including power generation and separations processes. [ABSTRACT FROM AUTHOR]

The phosphonium ylidic diesters, methyl and ethyl isopropyl and, methyl and ethyl t-butyl triphenylphosphoranylidene malonates, 1a,b and 2a,b, respectively, have the syn-anti conformation in solution, as in the crystal, and the bulkier alkoxy group is oriented towards phosphorus. The 1H NMR spectra show that in 1a,b, the isopropyl group is oriented towards the face of a phenyl group, consistent with π shielding in the 1H signals, and examination of the 1H coupled 13C NMR spectra allows assignment of the acyl carbon signals. Computed bond lengths and angles for isolated molecules are similar to those in the crystal, and the geometry and the NMR spectra indicate extensive ylidic resonance. Estimated partial atomic charges on the ester oxygens are more negative when they are oriented towards, rather than away from, phosphorus. [ABSTRACT FROM AUTHOR]

We present two novel parallel algorithms for rapidly constructing bounding volume hierarchies on manycore GPUs. The first uses a linear ordering derived from spatial Morton codes to build hierarchies extremely quickly and with high parallel scalability. The second is a top-down approach that uses the surface area heuristic (SAH) to build hierarchies optimized for fast ray tracing. Both algorithms are combined into a hybrid algorithm that removes existing bottlenecks in the algorithm for GPU construction performance and scalability leading to significantly decreased build time. The resulting hierarchies are close in to optimized SAH hierarchies, but the construction process is substantially faster, leading to a significant net benefit when both construction and traversal cost are accounted for. Our preliminary results show that current GPU architectures can compete with CPU implementations of hierarchy construction running on multicore systems. In practice, we can construct hierarchies of models with up to several million triangles and use them for fast ray tracing or other applications. [ABSTRACT FROM AUTHOR]

Computed bond lengths and angles of methyl ethyl and dimethyl triphenyl phosphonium ylidic diesters, 1b, c, respectively, are similar to those in the crystal, as for the diethyl ester, 1a, where both acyl oxygens are anti to phosphorus. The 1H and 13C NMR spectra of the methyl ethyl diester, 1b, where one acyl oxygen is syn and the other anti to phosphorus, are as expected in terms of the conformation in the crystal, but the dimethyl ester, 1c, in the crystal is an equimolar mixture of conformers. For a given ylidic diester the different conformers have similar energies from B3LYP//6-31G(d) computations, interconversions of conformers should not be slow at ambient temperatures and 1H and 13C NMR signals in solution are sharp. Estimation of Natural Atomic Charges indicates significant cationoid character on phosphorus and the acyl carbons, and anionoid character on the ylidic carbon and the ester oxygens depending on orientations towards phosphorus. [ABSTRACT FROM AUTHOR]

An upright, partly rooted tree stump preserved within a late Early Jurassic basalt flow of the Ferrar Group, Coombs hills, is described from southern Victoria land, Antarctica. The wood structure allows the tree to be identified as a conifer (possibly Podocarpaceae) that from the stump diameter of 35-40 cm was c. 24 m tall. The possibly transported tree may have survived the lava flow because the stump was waterlogged or already mineralised. Conifers of similar age (early Middle Jurassic) are known from fossil forests at Curio Bay and Kawhia harbour in New Zealand, and this discovery extends the known distribution of forests living in moderately warm, humid climates at very high southern latitudes during the late early Jurassic. [ABSTRACT FROM AUTHOR]

The diacyl ylid, 3-triphenylphosphoranylidene-2,4-pentanedione 2 can adopt conformations with one oxygen syn- and the other anti- to phosphorus 2a as in the crystal, or with both oxygens syn- to phosphorus 2b. In solution, 1H and 13C NMR signals are sharp, but 13C signals in the solid confirm that the two acyl groups are in different positions, and a comparison of the 13C signals in solution and a solid shows that conformations differ. Ab initio geometrical optimizations give, for 2a, a geometry similar to that in a crystal, and structures of both conformers permit extended ylidic resonance through near planar ylidic and acyl moieties. In crystalline diethyl 2-triphenyl phosphoranylidene malonate 3, the torsional angles of the ester moieties to the plane of the near trigonal ylidic moiety are -149.2° and 170.4°, due to packing forces and interactions with adjacent molecules, which limit ylidic resonance. The 13C NMR spectrum in the solid differs from that in solution, with the two ester groups in different positions, but in solution, 13C and 1H NMR signals are sharp. Ab initio geometrical optimizations indicate that for an isolated molecule, the conformer with torsional angles as in the crystal is energetically unfavored but energetic barriers to interconversion are small, and rapidly equilibrating conformers probably exist in solution. [ABSTRACT FROM AUTHOR]

Stewart Yorke and Mike Garland describe the development of a pilot programme that set out to explore the benefits of using cognitive behavioural approaches in group work. [ABSTRACT FROM AUTHOR]

Objective: The correlates of specific childhood feeding problems are described to further examine possible predisposing factors for feeding problems. We report our experience with 349 participants evaluated by an interdisciplinary feeding team.Methods: A review of records was conducted and each participant was identified as having one or more of five functionally defined feeding problems: food refusal, food selectivity by type, food selectivity by texture, oral motor delays, or dysphagia. The prevalence of predisposing factors for these feeding problems was examined. Predisposing factors included developmental disabilities, gastrointestinal problems, cardiopulmonary problems, neurological problems, renal disease and anatomical anomalies.Results: The frequencies of predisposing factors varied by feeding problem. Differences were found in the prevalence of the five feeding problems among children with three different developmental disabilities: autism, Down syndrome and cerebral palsy. Gastro-oesophageal reflux was the most prevalent condition found among all children in the sample and was the factor most often associated with food refusal. Neurological conditions and anatomical anomalies were highly associated with skill deficits, such as oral motor delays and dysphagia.Conclusions: Specific medical conditions and developmental disabilities are often associated with certain feeding problems. Information concerning predisposing factors of feeding problems can help providers employ appropriate primary, secondary and tertiary prevention measures to decrease the frequency or severity of some feeding problems. [ABSTRACT FROM AUTHOR]

Background: Low cholesterol may act as a peripheral marker for parasuicide.Aims: To examine the relationship between total serum cholesterol and psychological parameters in parasuicide.Method: Total serum cholesterol and self-rated scores for impulsivity, depression and suicidal intent were measured in 100 consecutive patients following parasuicide, pair-matched with normal and psychiatric control groups.Results: Backward, stepwise multiple regression analysis revealed a significantly lower mean cholesterol in the parasuicide population (P < 0.01). Across all groups there was an independent significant (P < 0.01) negative correlation between cholesterol and self-reported scores of impulsivity. No correlation existed between cholesterol and scores for depression or suicidal intent.Conclusions: The data confirm previous reports of low cholesterol in parasuicide. This is the first reported investigation of the construct of impulsivity in relation to cholesterol. We hypothesise that the reported increased mortality in populations with low cholesterol may derive from increased suicide and accident rates consequent on increased tendencies to impulsivity in these populations. [ABSTRACT FROM AUTHOR]

In a 6-volunteer cross-over study the pharmacokinetics of 3 erythromycin preparations were compared. A single oral dose of 500 mg of each preparation was administered at each occasion and the levels measured in timed samples of plasma and saliva. Markedly higher blood concentrations of the estolate and propionate were obtained compared to the stearate. Comparison of serum and plasma concentration of the drugs from each split sample showed no significant differences. Plasma concentrations always exceeded those in saliva but for any one preparation a similar ratio was obtained at different times. This may be useful to ascertain compliance and to measure concentration of the compounds where direct measurement in plasma is not practicable. [ABSTRACT FROM PUBLISHER]

We compared fatty acid amounts in adipose tissue with fatty acid intake calculated from 2 separate weeks of diet recording and two food-frequency questionnaires for 140 participants in the Nurses' Health Study. Our results showed that the amounts of polyunsaturated and trans fatty acids in adipose tissue reflect dietary intake and confirm those of previous studies. The correlation between the polyunsaturated fatty acid content of adipose tissue and polyunsaturated fatty acid intake from the average of the two food-frequency questionnaires was 0.40; this correlation for trans fatty acids was also 0.40. Linolenic acid amounts in adipose tissue were also moderately correlated with intake from the average of the food-frequency questionnaires (r = 0.34). An estimate of trans fatty acid intake from vegetable sources correlated much more strongly with adipose trans fatty acids than did an estimate of trans fatty acids from animal sources. Adipose tissue aspirates can be used to indicate intake of exogenous fatty acids. Copyright (c) 1998 American Society for Clinical Nutrition [ABSTRACT FROM AUTHOR]