Preparations for a European R&D roadmap for an inertial fusion demo reactor

A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition, etc.; and (c) developing technologies that will be required in the future for a fusion reactor. A brief overview of these activities, presented here, along with new calculations relates the concept of auxiliary heating of inertial fusion targets, and provides possible future directions of research and development for the updated European Roadmap that is due at the end of 2020. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Whole-beam self-focusing in fusion-relevant plasma

Fast ignition inertial confinement fusion requires the production of a low-density channel in plasma with density scale-lengths of several hundred microns. The channel assists in the propagation of an ultra-intense laser pulse used to generate fast electrons which form a hot spot on the side of pre-compressed fusion fuel. We present a systematic characterization of an expanding laser-produced plasma using optical interferometry, benchmarked against three-dimensional hydrodynamic simulations. Magnetic fields associated with channel formation are probed using proton radiography, and compared to magnetic field structures generated in full-scale particle-in-cell simulations. We present observations of long-lived, straight channels produced by the Habara-Kodama-Tanaka whole-beam self-focusing mechanism, overcoming a critical barrier on the path to realizing fast ignition. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Collapse dynamics of spherical cavities in a solid under shock loading

Extraordinary states of highly localised pressure and temperature can be generated upon the collapse of impulsively driven cavities. Direct observation of this phenomenon in solids has proved challenging, but recent advances in high-speed synchrotron radiography now permit the study of highly transient, subsurface events in real time. We present a study on the shock-induced collapse of spherical cavities in a solid polymethyl methacrylate medium, driven to shock states between 0.49 and 16.60 GPa. Utilising multi-MHz phase contrast radiography, extended sequences of the collapse process have been captured, revealing new details of interface motion, material failure and jet instability formation. Results reveal a rich array of collapse characteristics dominated by strength effects at low shock pressures and leading to a hydrodynamic response at the highest loading conditions.

Counterpropagating Radiative Shock Experiments on the Orion Laser

We present new experiments to study the formation of radiative shocks and the interaction between two counterpropagating radiative shocks. The experiments are performed at the Orion laser facility, which is used to drive shocks in xenon inside large aspect ratio gas cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently three-dimensional shocks, provides a novel platform particularly suited for the benchmarking of numerical codes. The dynamics of the shocks before and after the collision are investigated using point-projection x-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modeling of the experiments using the 2D radiation hydrodynamic codes nym and petra shows very good agreement with the experimental results.

Monochromatic radiography of high energy density physics experiments on the MAGPIE generator

A monochromatic X-ray backlighter based on Bragg reflection from a spherically bent quartz crystal has been developed for the MAGPIE pulsed power generator at Imperial College (1.4 MA, 240 ns) [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (2005)]. This instrument has been used to diagnose high energy density physics experiments with 1.865 keV radiation (Silicon He-α) from a laser plasma source driven by a ∼7 J, 1 ns pulse from the Cerberus laser. The design of the diagnostic, its characterisation and performance, and initial results in which the instrument was used to radiograph a shock physics experiment on MAGPIE are discussed.

Diagnosing collisions of magnetized, high energy density plasma flows using a combination of collective Thomson scattering, Faraday rotation, and interferometry (invited)

A suite of laser based diagnostics is used to study interactions of magnetised, supersonic, radiatively cooled plasma flows produced using the Magpie pulse power generator (1.4 MA, 240 ns rise time). Collective optical Thomson scattering measures the time-resolved local flow velocity and temperature across 7-14 spatial positions. The scattering spectrum is recorded from multiple directions, allowing more accurate reconstruction of the flow velocity vectors. The areal electron density is measured using 2D interferometry; optimisation and analysis are discussed. The Faraday rotation diagnostic, operating at 1053 nm, measures the magnetic field distribution in the plasma. Measurements obtained simultaneously by these diagnostics are used to constrain analysis, increasing the accuracy of interpretation.

Distribution of MLH1 foci in horse male synaptonemal complex

Advances in molecular cytogenetics have provided the opportunity to study events during prophase I of meiosis. Immunofluorescent localization of different meiotic protein components were used to characterize the early stages of the first meiotic division in horse spermatocytes. The frequency and distribution of recombination events during prophase I were investigated using the mutL homolog 1 (MLH1) protein that is known to be associated with these events. The frequency and distribution of MLH1 foci were investigated in pachytene nuclei of 6 fertile stallions, and the average relative synaptonemal complex length was found to be highly correlated with the average number of MLH1 foci. The frequency and distribution of MLH1 foci were found to closely correspond to the frequency and distribution of chiasmata on metaphase I chromosomes, and genetic length, calculated from MLH1 foci data, for the whole genome was 2,505.5 cM.

Optical Thomson scattering measurements of plasma parameters in the ablation stage of wire array Z pinches

A Thomson scattering diagnostic has been used to measure the parameters of cylindrical wire array Z pinch plasmas during the ablation phase. The scattering operates in the collective regime (α>1) allowing spatially localized measurements of the ion or electron plasma temperatures and of the plasma bulk velocity. The ablation flow is found to accelerate towards the axis reaching peak velocities of 1.2-1.3×10(7) cm/s in aluminium and ∼1×10(7) cm/s in tungsten arrays. Precursor ion temperature measurements made shortly after formation are found to correspond to the kinetic energy of the converging ablation flow.

Suppression of the ablation phase in wire array Z pinches using a tailored current prepulse

A new wire array configuration has been used to create thin shell-like implosions in a cylindrical array. The setup introduces a ~5 kA, ~25 ns current prepulse followed by a ~140 ns current-free interval before the application of the main (~1 MA) current pulse. The prepulse volumetrically heats the wires which expand to ~1 mm diameter leaving no dense wire core and without development of instabilities. The main current pulse then ionizes all the array mass resulting in suppression of the ablation phase, an accelerating implosion, and no trailing mass. Rayleigh-Taylor instability growth in the imploding plasma is inferred to be seeded by μm-scale perturbations on the surface of the wires. The absence of wire cores is found to be the critical factor in altering the implosion dynamics.

GABAergic and glutamatergic identities of developing midbrain Pitx2 neurons

Pitx2, a paired-like homeodomain transcription factor, is expressed in post-mitotic neurons within highly restricted domains of the embryonic mouse brain. Previous reports identified critical roles for PITX2 in histogenesis of the hypothalamus and midbrain, but the cellular identities of PITX2-positive neurons in these regions were not fully explored. This study characterizes Pitx2 expression with respect to midbrain transcription factor and neurotransmitter phenotypes in mid-to-late mouse gestation. In the dorsal midbrain, we identified Pitx2-positive neurons in the stratum griseum intermedium (SGI) as GABAergic and observed a requirement for PITX2 in GABAergic differentiation. We also identified two Pitx2-positive neuronal populations in the ventral midbrain, the red nucleus, and a ventromedial population, both of which contain glutamatergic precursors. Our data suggest that PITX2 is present in regionally restricted subpopulations of midbrain neurons and may have unique functions that promote GABAergic and glutamatergic differentiation.

beta-peptides as catalysts: poly-beta-leucine as a catalyst for the Juliá-Colonna asymmetric epoxidation of enones

Poly-beta-leucines have been evaluated as catalysts for the Juliá-Colonna asymmetric epoxidation of enones; the beta 3-isomer was found to be an effective catalyst for the epoxidation of chalcone (70% ee) and some analogues.

Molecular basis for defective glycosylation and Pseudomonas pathogenesis in cystic fibrosis lung

The CFTR gene encodes a transmembrane conductance regulator, which is dysfunctional in patients with cystic fibrosis (CF). The mechanism by which defective CFTR (CF transmembrane conductance regulator) leads to undersialylation of plasma membrane glycoconjugates, which in turn promote lung pathology and colonization with Pseudomonas aeruginosa causing lethal bacterial infections in CF, is not known. Here we show by ratiometric imaging with lumenally exposed pH-sensitive green fluorescent protein that dysfunctional CFTR leads to hyperacidification of the trans-Golgi network (TGN) in CF lung epithelial cells. The hyperacidification of TGN, glycosylation defect of plasma membrane glycoconjugates, and increased P. aeruginosa adherence were corrected by incubating CF respiratory epithelial cells with weak bases. Studies with pharmacological agents indicated a role for sodium conductance, modulated by CFTR regulatory function, in determining the pH of TGN. These studies demonstrate the molecular basis for defective glycosylation of lung epithelial cells and bacterial pathogenesis in CF, and suggest a cure by normalizing the pH of intracellular compartments.

The effect of the primary structure of the polypeptide catalyst on the enantioselectivity of the Juliá-Colonna asymmetric epoxidation of enones

Epoxidation of chalcone (1), using basic hydrogen peroxide, catalysed by polypeptides with defined primary structures demonstrates that the residues in the chain near to the N-terminus determine the stereochemical outcome of the reaction.

CFTR and pseudomonas infections in cystic fibrosis

Pseudomonas aeruginosa is a significant threat to human health as it is frequently recalcitrant to conventional antibacterial therapy. This ubiquitous gram-negative bacterium is notorious for its nutritional and ecological flexibility and its resistance to both antibiotic treatments and sanitary measures. These properties contribute to its prominence as a leading source of opportunistic nosocomial (hospital acquired) and a less appreciated, but significant cause of community acquired infections. P. aeruginosa remains a considerable problem for patients with burns, neutropenic individuals, and cystic fibrosis patients (CF). In this review, we will address the current issues in P. aeruginosa infections in CF. A major emphasis will be placed on the factors predisposing CF patients to colonization with P. aeruginosa.

Efficient asymmetric epoxidation of alpha,beta-unsaturated ketones using a soluble triblock polyethylene glycol-polyamino acid catalyst

[reaction: see text]. Polyethylene glycol (PEG)-bound poly-L-leucine acts as a THF-soluble catalyst for the Juliá-Colonna asymmetric epoxidation of enones. Excellent enantioselectivities may be obtained even with short chain length polyleucine. FT-IR investigations have determined that the catalytically active polyleucine components of these copolymers have an alpha-helical structure.

Alanine scan mutagenesis of the switch I domain of the Caulobacter crescentus CgtA protein reveals critical amino acids required for in vivo function

The Caulobacter crescentus CgtA protein is a member of the Obg/GTP1 subfamily of monomeric GTP-binding proteins. In vitro, CgtA displays moderate affinity for both GDP and GTP and displays rapid exchange rate constants for either nucleotide, indicating that the guanine nucleotide-binding and exchange properties of CgtA are different from those of the well-characterized Ras-like GTP-binding proteins. The Obg/GTP1 proteins share sequence similarity along the putative effector-binding domain. In this study, we examined the functional consequences of altering amino acid residues within this conserved domain, and identified that T193 was critical for CgtA function. The in vitro binding, exchange and GTP hydrolysis of the T192A, T193A and T192AT193A mutant proteins was examined using fluorescent guanine nucleotide analogues (mant-GDP and mant-GTP). Substitution of either T192 and/or T193 for alanine modestly reduced binding to GDP and significantly reduced the binding affinity for GTP. Furthermore, the T193A mutant protein was more severely impaired for binding GTP than the T192A mutant. The T193A mutation appeared to account solely for the impaired GTP binding of the T192AT193A double mutation. This is the first report that demonstrates that a confirmed defect in guanine nucleotide binding and GTP hydrolysis of an Obg-like protein results in the lack of function in vivo.

Regulators of membrane trafficking and Mycobacterium tuberculosis phagosome maturation block

The biogenesis and maturation of phagosomes is an area of study which has been employing aspects of proteomic analyses and variations on that theme by identifying components on isolated organelles and following their dynamic changes and interactions with the endocytic pathway. In the case of Mycobacterium tuberculosis phagosome, the arrest of its maturation in infected macrophages, referred to in classical texts as the inhibition of phagosome-lysosome fusion, represents a phenomenon that is used to functionally dissect the phagosomal maturation pathway. In this review, we summarize the recent studies on regulators of membrane trafficking and other organelle components in the context of phagosomal biogenesis and mycobacterial phagosome maturation arrest.

Polar clustering of the chemoreceptor complex in Escherichia coli occurs in the absence of complete CheA function

Bacterial chemotaxis requires a phosphorelay system initiated by the interaction of a ligand with its chemoreceptor and culminating in a change in the directional bias of flagellar rotation. Chemoreceptor-CheA-CheW ternary complexes mediate transduction of the chemotactic signal. In vivo, these complexes cluster predominantly in large groups at the cell poles. The function of chemoreceptor clustering is currently unknown. To gain insight into the relationship between signaling and chemoreceptor clustering, we examined these properties in several Escherichia coli mutant strains that produce CheA variants altered in their ability to mediate chemotaxis, autophosphorylate, or bind ATP. We show here that polar clustering of chemoreceptor complexes does not require functional CheA protein, although maximal clustering occurred only in chemotactically competent cells. Surprisingly, in cells containing a minimum of 13 gold particles at the cell pole, a significant level of clustering was observed in the absence of CheA, demonstrating that CheA is not absolutely essential for chemoreceptor clustering. Nonchemotactic cells expressing only CheA(S), a C-terminal CheA deletion, or CheA bearing a mutation in the ATP-binding site mediated slightly less than maximal chemoreceptor clustering. Cells expressing only full-length CheA (CheA(L)) from either a chromosomal or a plasmid-encoded allele displayed a methyl-accepting chemotaxis protein localization pattern indistinguishable from that of strains carrying both CheA(L) and CheA(S), demonstrating that CheA(L) alone can mediate polar clustering.

Polyamino acids as catalysts in asymmetric synthesis

The use of polyamino acids in asymmetric organic synthesis is reviewed. Particular emphasis is placed on the asymmetric epoxidation of alpha,beta-unsaturated ketones with hydrogen peroxide in the presence of polyalanine or polyleucine, and further transformations of the epoxide products.

Localization and environmental regulation of MCP-like proteins in Rhodobacter sphaeroides

Chemotaxis to many compounds by Rhodobacter sphaeroides requires transport and at least partial metabolism of the chemoeffector. Previous investigations using phototrophically grown cells have failed to find any homologues of the MCP chemoreceptors identified in Escherichia coli. However, using an antibody raised against the highly conserved domain of E. coli Tsr, MCP-like proteins were identified in R. sphaeroides WS8N. Analysis using Western blotting and immunogold electron microscopy showed that expression of these MCP-like proteins is environmentally regulated and that receptors are targeted to two different cellular locations: the poles of the cells and the cytoplasm. In aerobically grown cells, these proteins were shown by immunoelectron microscopy to localize predominantly to the cell poles and to an electron-dense body in the cytoplasm. Western blot analysis indicated a 17-fold reduction in protein concentration when cells were grown in the light. The number of immunogold particles was also dramatically reduced in anaerobically light-grown cells and their cellular distribution was altered. Fewer receptors localized to the cell poles and more particles randomly distributed within the cell, but the cytoplasmic cluster remained. These trends were more pronounced in cells grown anaerobically under dim light than in those grown anaerobically under bright light, suggesting that expression is controlled by redox state and either light intensity or the extent of photosynthetic membrane synthesis. Recent work on E. coli chemosensing suggests that oligomerization of receptors and chemosensory proteins is important for sensory signalling. The data presented here suggest that this oligomerization can occur with cytoplasmic receptors and also provides an explanation for the multiple copies of chemosensory proteins in R. sphaeroides.

Identification of an essential Caulobacter crescentus gene encoding a member of the Obg family of GTP-binding proteins

We have identified an essential Caulobacter crescentus gene (cgtA) that encodes a member of a recently identified subfamily of GTPases (the Obg family) conserved from Bacteria to Archaea to humans. This evolutionary conservation between distantly related species suggests that this family of GTP-binding proteins possesses a fundamental, yet unknown, cellular role. In this report, we describe the isolation and sequence of the cgtA gene. The predicted CgtA protein displays striking similarity to the Obg family of small, monomeric GTP-binding proteins, both in the conserved guanine nucleotide-binding domains and throughout the N-terminal glycine-rich domain that is found in many members of the Obg family. Disruption of the cgtA gene was lethal, demonstrating that this gene is essential for cell growth. Immunoblot analysis revealed that CgtA protein levels remained constant throughout the C. crescentus cell cycle.

Epidemiological and environmental evidence of the health effects of exposure to erionite fibres: a four-year study in the Cappadocian region of Turkey

An environmental and epidemiological study has been carried out in Central Cappadocia, Turkey, aiming at investigating the relationship between exposure to naturally occurring erionite fibres and the reported high incidence of malignant mesotheliomas. Airborne fibre levels are generally low but show a higher proportion of erionite fibres in the villages affected by malignant disease than in a control village. The same pattern is confirmed by analysis of the fibre content in lung tissues of sheep from several villages, both affected and unaffected by malignant disease. The 3 villages with the highest proportion of erionite fibres have high rates of malignant pleural mesothelioma, malignant peritoneal mesothelioma and lung cancer. No case of malignancy for the same sites has been reported during the study period from the control village. The relationships between these findings and their consistency with the results from experimental studies indicate erionite fibres as a carcinogenic agent, although some aspects of the exposure are not fully clarified.

Effect of some triphenylethylenes on oestradiol binding in vitro to macromolecules from uterus and anterior pituitary

The effects of a series of triphenylethylenes (I.C.I. 46,474, I.C.I. 47,699 and clomiphene isomers A and B) on oestradiol binding to receptors from rat, rabbit and mouse uteri and rat anterior pituitary were studied. Binding of oestradiol to receptors from uteri was inhibited competitively by I.C.I. 46,474. Receptors from uteri of the three species and from rat anterior pituitary have very similar affinities for oestradiol and the four triphenylethylenes. The order of activity of the triphenylethylenes as inhibitors of oestradiol binding is: clomiphene B > I.C.I. 46,474 > I.C.I. 47,699 > clomiphene A. Some correlations are made with the activity of the compounds in vivo.