Laser-Driven Proton Beams: Acceleration Mechanism, Beam Optimization, and Radiographic Applications

This paper reviews recent experimental activity in the area of optimization, control, and application of laser accelerated proton beams, carried out at the Rutherford Appleton Laboratory and the Laboratoire pour l’Utilisation des Lasers Intenses 100 TW facility in France. In particular, experiments have investigated the role of the scale length at the rear of the plasma in reducing target-normal-sheath-acceleration acceleration efficiency. Results match with recent theoretical predictions and provide information in view of the feasibility of proton fast-ignition applications. Experiments aiming to control the divergence of the proton beams have investigated the use of a laser-triggered microlens, which employs laser-driven transient electric fields in cylindrical geometry, enabling to focus the emitted
protons and select monochromatic beam lets out of the broad spectrum beam. This approach could be advantageous in view
of a variety of applications. The use of laser-driven protons as a particle probe for transient field detection has been developed and
applied to a number of experimental conditions. Recent work in this area has focused on the detection of large-scale self-generated magnetic fields in laser-produced plasmas and the investigation of fields associated to the propagation of relativistic electron both on the surface and in the bulk of targets irradiated by high-power laser pulses.

Uptake of carbon, nitrogen and phosphorus by phytoplankton along the 20 degrees W meridian in the NE Atlantic between 57.5 degrees N and 37 degrees N

Phytoplankton biomass and rate of production were measured along a transect from 57.54 degreesN to 37.01 degreesN in the northeast Atlantic during July 1996 and at a series of stations over a 7-day period at 37 degreesN 20 degreesW. Surface nutrient concentrations ranged from 4 mu mol l(-1) NO3-, and 0.35 mu mol l(-1) PO43- at 57.54 degreesN to <10 nmol l(-1) NO3- and similar to 10 nmol l(-1) PO43- at 37.01 degreesN. The greatest phytoplankton biomass and production were measured in the vicinity of a frontal system at 50 degreesN, and there was a general decline in total phytoplankton biomass and production to the south of the transect. Production was measured in three size fractions. At the station with the highest chlorophyll concentrations (50.34 degreesN), phytoplankton cells larger than 5 mum dominated the assemblage, accounting for 72% of the chlorophyll concentration (22.9 mg m(-2)) and 51% of primary production (54.1 mmol Cm-2 d(-1)), but picophytoplankton production was also high (43%). At 57 degreesN, carbon fixation by the > 5 mum fraction accounted for 75% of the daily production of 60.75 mmol Cm-2 d(-1). At 37 degreesN, picophytoplankton was the dominant group, accounting for similar to 58% (10 mg m(-2)) of chlorophyll and similar to 64% (46 mmol Cm-2 d(-1)), of primary production. Nitrate, ammonium and phosphate uptake rates also were determined. Although high nitrate uptake rates were measured in the surface water at similar to 50 degreesN, the greatest uptake rates of both depth-integrated nitrate and ammonium were at the south of the transect. At 37 degreesN, a deep euphotic zone was present and light penetrated through the nitracline; total nitrate uptake was enhanced because of assimilation at the base of the euphotic zone. As a consequence, high values of depth-integrated f-ratio were measured in the oligotrophic waters at the south of the transect. Phosphate was predominantly incorporated into the picoplankton fraction, which included heterotrophic and autotrophic components, at all stations and a significant proportion of phosphate uptake occurred in the dark. The C:N:P assimilation ratios were variable throughout the region; phosphate uptake was generally greater than would be expected if nutrient assimilation were in proportion to the Redfield ratio. (C) 2001 Elsevier Science Ltd. All rights reserved.

Resolution of an ancient surface science anomaly: Work function change induced by N adsorption on W{100}

For many decades it has been assumed that an adsorbate centered above a metal surface and with a net negative charge should increase the work function of the surface. However, despite their electronegativity, N adatoms on W{100} cause a significant work function decrease. Here we present a resolution of this anomaly. Using density functional theory, we demonstrate that while the N atom carries a negative charge, of overriding importance is a reduction in the surface overspill electron density into the vacuum, when that charge is engaged in bonding to the adatom. This novel interpretation is fundamentally important in the general understanding of work function changes induced by atomic adsorbates.

The persistence of the HgCl2 molecule in five new compounds in the system (NH4)(w)HgxCly(H2O)(z) with w : x : y : z=1 : 5 : 11 : 0, 2 : 3 : 8 : 1, 4 : 3 : 10 : 2, 2 : 1 : 4 : 1, and 10 : 3 : 16 : 0

Five new compounds in the system (NH4)Cl/HgCl2/H2O have been obtained as colourless single crystals, (NH4)Hg5Cl11, (NH4)(2)Hg3Cl8(H2O), (NH4)(4)Hg3Cl10(H2O)(2), (NH4)(2)HgCl4(H2O), and (NH4)(10)Hg3Cl16. In all of these, as in HgCl2 itself, (almost) linear HgCl2 molecules persist with Hg-Cl distances varying from 229 to 236 pm. In (NH4)(10)Hg3Cl16 there are also tetrahedra [HgCl4] with d(Hg-Cl) = 247 pm present. If larger Hg-Cl distances (of up to 340 pm) are considered as belonging to the coordination sphere of Hg-II, the structures may be described as consisting of isolated octahedra and tetrahedra as in (NH4)(10)Hg3Cl16, edge-connected chains as in (NH4)(2)HgCl4(H2O), edge-connected chains and layers of octahedra as in (NH4)(4)Hg3Cl10(H2O)(2), corrugated layers of edge-connected octahedra as in (NH4)(2)Hg3Cl8(H2O), and, finally, a three-dimensional network of connected six- and seven-coordinate Hg-Cl polyhedra as in (NH4)Hg5Cl11. The water molecules are never attached to Hg-II. The (NH4)(+) cations, and sometimes Cl- anions, play a role for electroneutrality only.

Comparison of mechanical and electrical activity and interstitial cells of Cajal in urinary bladders from wild-type and W/W-v mice

Background and purpose: W/Wv and wild-type murine bladders were studied to determine whether the W/Wv phenotype, which causes a reduction in, but not abolition of, tyrosine kinase activity, is a useful tool to study the function of bladder interstitial cells of Cajal (ICC).

Experimental approach: Immunohistochemistry, tension recordings and microelectrode recordings of membrane potential were performed on wild-type and mutant bladders.

Key results: Wild-type and W/Wv detrusors contained c-Kit- and vimentin-immunopositive cells in comparable quantities, distribution and morphology. Electrical field stimulation evoked tetrodotoxin-sensitive contractions in wild-type and W/Wv detrusor strips. Atropine reduced wild-type responses by 50% whereas a 25% reduction occurred in W/Wv strips. The atropine-insensitive component was blocked by pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid in both tissue types. Wild-type and W/Wv detrusors had similar resting membrane potentials of -48 mV. Spontaneous electrical activity in both tissue types comprised action potentials and unitary potentials. Action potentials were nifedipine-sensitive whereas unitary potentials were not. Excitatory junction potentials were evoked by single pulses in both tissues. These were reduced by atropine in wild-type tissues but not in W/Wv preparations. The atropine-insensitive component was abolished by pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid in both preparations.

Conclusions and implications: Bladders from W/Wv mice contain c-Kit- and vimentin-immunopositive ICC. There are similarities in the electrical and contractile properties of W/Wv and wild-type detrusors. However, significant differences were found in the pharmacology of the responses to neurogenic stimulation with an apparent up-regulation of the purinergic component. These findings indicate that the W/Wv strain may not be the best model to study ICC function in the bladder.

The Perils of Moviegoing in America, 1896-1950

The Perils of Moviegoing in America is a film history that examines the various physical and (perceived) moral dangers facing audiences during the first fifty years of film exhibition.

Chapter 1: “Conflagration”
As early as 1897, a major fire broke out at a film exhibition in San Francisco, with flames burning the projectionist and nearby audience members. From that point until the widespread adoption of safety stock in 1950, fires were a very common movie-going experience. Hundreds of audience members lost their lives in literally thousands of theatre fires, ranging from early nickelodeons to the movie palaces of the thirties and forties.

Chapter 2: “Thieves Among Us”
Bandits robbed movie theatres on hundreds of occasions from the early days of film exhibition through the end of the Great Depression. They held up ticket booths, and they dynamited theatre safes. They also shot theatre managers, ushers, and audience members, as a great many of the robberies occurred while movies were playing on the screens inside.

Chapter 3: “Bombs Away”
Bombings at movie theatres became common in small towns and large cities on literally hundreds of occasions from 1914 to the start of World War II. Some were incendiary bombs, and some were stench bombs; both could be fatal, whether due to explosions or to the trampling of panicked moviegoers

Chapter 4: “It’s Catching”
Widespread movie-going in the early 20th century provoked an outcry from numerous doctors and optometrists who believed that viewing films could do irreparable harm to the vision of audience members. Medical publications (including the Journal of the American Medical Association) published major studies on this perceived problem, which then filtered into popular-audience magazines and newspapers.

Chapter 5: “The Devil’s Apothecary Shops”
Sitting in the dark with complete strangers proved worrisome for many early filmgoers, who had good reason to be concerned. Darkness meant that prostitutes could easily work in the balconies of some movie theatres, as could “mashers” who molested female patrons (and sometimes children) after the lights were dimmed. That was all in addition to the various murderers who used the cover of darkness to commit their crimes at movie theatres.

Chapter 6: “Blue Sundays”
Blue laws were those regulations that prohibited businesses from operating on Sundays. Most communities across the US had such legislation on their books, which by the nickelodeon era were at odds with the thousands of filmgoers who went to the movies every Sunday. Theatre managers were often arrested, making newspaper headlines over and over again. Police sometimes even arrested entire film audiences as accomplices in the Blue Law violations.

Chapter 7: “Something for Nothing”
In an effort to bolster ticket sales, many movie theatres in the 1910s began to hold lotteries in which lucky audience members won cash prizes; by the time of the Great Depression, lotteries like “Bank Night” became a common aspect of the theatre-going enterprise. However, reception studies have generally overlooked the intense (and sometimes coordinated) efforts by police, politicians, and preachers to end this practice, which they viewed as illegal and immoral gambling.