Simulation of a collisionless planar electrostatic shock in a proton-electron plasma with a strong initial thermal pressure change

The localized deposition of the energy of a laser pulse, as it ablates a solid target, introduces high thermal pressure gradients in the plasma. The thermal expansion of this laser-heated plasma into the ambient medium (ionized residual gas) triggers the formation of non-linear structures in the collisionless plasma. Here an electron-proton plasma is modelled with a particle-in-cell simulation to reproduce aspects of this plasma expansion. A jump is introduced in the thermal pressure of the plasma, across which the otherwise spatially uniform temperature and density change by a factor of 100. The electrons from the hot plasma expand into the cold one and the charge imbalance drags a beam of cold electrons into the hot plasma. This double layer reduces the electron temperature gradient. The presence of the low-pressure plasma modifies the proton dynamics compared with the plasma expansion into a vacuum. The jump in the thermal pressure develops into a primary shock. The fast protons, which move from the hot into the cold plasma in the form of a beam, give rise to the formation of phase space holes in the electron and proton distributions. The proton phase space holes develop into a secondary shock that thermalizes the beam.

Quantitative analysis of proton imaging measurements of laser-induced plasmas

A method for obtaining quantitative information about electric field and charge distributions from proton imaging measurements of laser-induced plasmas is presented. A parameterised charge distribution is used as target plasma. The deflection of a proton beam by the electric field of such a plasma is simulated numerically as well as the resulting proton density, which will be obtained on a screen behind the plasma according to the proton imaging technique. The parameters of the specific charge distributions are delivered by a combination of linear regression and nonlinear fitting of the calculated proton density distribution to the measured optical density of a radiochromic film screen changed by proton exposure. It is shown that superpositions of spherical Gaussian charge distributions as target plasma are sufficient to simulate various structures in proton imaging measurements, which makes this method very flexible.

A new algorithm for spectral and spatial reconstruction of proton beams from dosimetric measurements

We report on a new algorithm developed for the dosimetric analysis of broad-spectrum, multi-MeV laser-accelerated proton beams. The algorithm allows the reconstruction of the proton beam spectrum from radiochromic film data. This processing technique makes dosimetry measurements a viable alternative to the use of track detectors for spatially and spectrally resolved proton beam analysis. (C) 2003 Elsevier B.V. All rights reserved.

Proton moire fringes for diagnosing electromagnetic fields in opaque materials and plasmas

High contrast proton moire fringes have been obtained in a laser-produced proton beam. Moire u fringes with modulation of 20%-30% were observed in protons with energies in the range of 4 - 7 MeV. Monte Carlo simulations with simple test fields showed that shifts in the moire u fringes can be used to give quantitative information on the strength of transient electromagnetic fields inside plasmas and materials that are opaque to conventional probing methods. (C) 2003 American Institute of Physics.

Ultrafast Melting of Carbon Induced by Intense Proton Beams

Laser-produced proton beams have been used to achieve ultrafast volumetric heating of carbon samples at solid density. The isochoric melting of carbon was probed by a scattering of x rays from a secondary laser-produced plasma. From the scattering signal, we have deduced the fraction of the material that was melted by the inhomogeneous heating. The results are compared to different theoretical approaches for the equation of state which suggests modifications from standard models.

Peptide IC-20, encoded by skin kininogen-1 of the European yellow-bellied toad, Bombina variegata, antagonizes bradykinin-induced arterial smooth muscle relaxation

The objectives were to determine if the skin secretion of the European yellow-bellied toad (Bombina variegata), in common with other related species, contains a bradykinin inhibitor peptide and to isolate and structurally characterize this peptide. Materials and Methods: Lyophilized skin secretion obtained from this toad was subjected to reverse phase HPLC fractionation with subsequent bioassay of fractions for antagonism of the bradykinin activity using an isolated rat tail artery smooth muscle preparation. Subsequently, the primary structure of the peptide was established by a combination of microsequencing, mass spectroscopy, and molecular cloning, following which a synthetic replicate was chemically synthesised for bioassay. Results: A single peptide of molecular mass 2300.92 Da was resolved in HPLC fractions of skin secretion and its primary structure determined as IYNAIWP-KH-NK-KPGLL-. Database interrogation with this sequence indicated that this peptide was encoded by skin kininogen-1 previously cloned from B. variegata. The blank cycles were occupied by cysteinyl (C) residues and the peptide was located toward the C-terminus of the skin kininogen, and flanked N-terminally by a classical -KR- propeptide convertase processing site. The peptide was named IC-20 in accordance (I = N-terminal isoleucine, C = C-terminal cysteine, 20 = number of residues). Like the natural peptide, its synthetic replicate displayed an antagonism of bradykinin-induced arterial smooth muscle relaxation. Conclusion: IC-20 represents a novel bradykinin antagonizing peptide from amphibian skin secretions and is the third such peptide found to be co-encoded with bradykinins within skin kininogens.

Diphosphine analogues of proton sponge: X-ray crystal structure of [Pd(eta(3)-allyl)(dppn)]BF4 center dot CH2Cl2 (dppn equals 1,8-bis(diphenylphosphino)naphthalene)

The X-ray crystal structure of [Pd(eta(3)-allyl)(dppn)]BF4 . CH2Cl2 (1) where dppn = 1,8-bis(diphenylphosphino)naphthalene is reported. Comparison of the conformation of the ligand in 1 with that in the free state shows that there is a relief of strain on complexation analogous to the relief of strain observed upon protonation of proton sponge.

The Gastrointestinal Peptide Obestatin Induces Vascular Relaxation Via Specific Activation of Endothelium-Dependent Nitric Oxide Signalling.

Background and purpose: Obestatin is a recently-discovered gastrointestinal peptide with established metabolic actions, which is linked to diabetes and may exert cardiovascular benefits. Here we aimed to investigate the specific effects of obestatin on vascular relaxation. Experimental approach: Cumulative relaxation responses to obestatin peptides were assessed in isolated rat aorta and mesenteric artery (n=8) in the presence/absence of selective inhibitors. Complementary studies were performed in cultured bovine aortic endothelial cells (BAEC). Key results: Obestatin peptides elicited concentration-dependent relaxation in both aorta and mesenteric artery. Responses to full-length obestatin(1-23) were greater than those to obestatin(1-10) and obestatin(11-23). Obestatin(1-23)-induced relaxation was attenuated by endothelial denudation, L-NAME (NO synthase inhibitor), high extracellular K(+) , GDP-ß-S (G protein inhibitor), MDL-12,330A (adenylate cyclase inhibitor), wortmannin (PI3K inhibitor), KN-93 (CaMKII inhibitor), ODQ (guanylate cyclase inhibitor) and iberiotoxin (BK(Ca) blocker), suggesting that it is mediated by an endothelium-dependent NO signalling cascade involving an adenylate cyclase-linked G protein-coupled receptor, PI3K/Akt, Ca(2+) -dependent eNOS activation, soluble guanylate cyclase and modulation of vascular smooth muscle K(+) . Supporting data from BAEC indicated that nitrite production, intracellular Ca(2+) and Akt phosphorylation were increased after exposure to obestatin(1-23). Relaxations to obestatin(1-23) were unaltered by inhibitors of candidate endothelium-derived hyperpolarising factors (EDHFs) and combined SK(Ca) /IK(Ca) blockade, suggesting that EDHF-mediated pathways were not involved. Conclusions and Implications: Obestatin produces significant vascular relaxation via specific activation of endothelium-dependent NO signalling. These actions may be important in normal regulation of vascular function and are clearly relevant to diabetes, a condition characterised by endothelial dysfunction and cardiovascular complications.

Proton pump inhibitors and histamine-2-receptor antagonists and pancreatic cancer risk: a nested case-control study

Background: The relationship between use of proton pump inhibitors (PPIs) and histamine-2-receptor antagonists (H₂RAs) and pancreatic cancer risk has yet to be examined. Data from a range of studies suggest biologically plausible mechanisms, whereby these drugs (or the conditions for which they are prescribed) may affect pancreatic cancer risk. The objective of this study was to investigate the relationship between use of PPIs/H₂RAs and pancreatic cancer risk.

Methods: A nested case – control study was conducted within the UK general practice research database (GPRD). Cases had a diagnosis of exocrine pancreatic cancer and controls were matched to cases on general practice site, sex and year of birth. Exposure to PPIs and to H₂RAs since entry into GPRD until 2 years before the diagnosis date (corresponding date in controls) and in the 5 years before the diagnosis date were separately assessed. Conditional logistic regression analyses were used to generate odds ratios (ORs) and 95% confidence intervals (CIs) associated with PPI or H₂RA use compared with nonuse.

Results: Ever use of PPIs since entry into the GPRD (excluding the 2 years prior to diagnosis) was not associated with risk of pancreatic cancer; OR (95% CI) 1.02 (0.85 – 1.22). Neither the dose nor the duration of PPI or H₂RA use was associated with pancreatic cancer risk. No consistent patterns of association were seen when cumulative exposure (dose and duration) to these drugs was examined separately or together.

Conclusion: PPI/H₂RA use, in a UK population, was not associated with pancreatic cancer risk.

On the investigation of fast electron beam filamentation in laser-irradiated solid targets using multi-MeV proton emission

The transverse filamentation of beams of fast electrons transported in solid targets irradiated by ultraintense (5 x 10(20) W cm(-2)), picosecond laser pulses is investigated experimentally. Filamentation is diagnosed by measuring the uniformity of a beam of multi-MeV protons accelerated by the sheath field formed by the arrival of the fast electrons at the rear of the target, and is investigated for metallic and insulator targets ranging in thickness from 50 to 1200 mu m. By developing an analytical model, the effects of lateral expansion of electron beam filaments in the sheath during the proton acceleration process is shown to account for measured increases in proton beam nonuniformity with target thickness for the insulating targets.

Dosimetry and spectral analysis of a radiobiological experiment using laser-driven proton beams

Laser-driven proton and ion acceleration is an area of increasing research interest given the recent development of short pulse-high intensity lasers. Several groups have reported experiments to understand whether a laser-driven beam can be applied for radiobiological purposes and in each of these, the method to obtain dose and spectral analysis was slightly different. The difficulty with these studies is that the very large instantaneous dose rate is a challenge for commonly used dosimetry techniques, so that other more sophisticated procedures need to be explored. This paper aims to explain a method for obtaining the energetic spectrum and the dose of a laser-driven proton beam irradiating a cell dish used for radiobiology studies. The procedure includes the use of a magnet to have charge and energy separation of the laser-driven beam, Gafchromic films to have information on dose and partially on energy, and a Monte Carlo code to expand the measured data in order to obtain specific details of the proton spectrum on the cells. Two specific correction factors have to be calculated: one to take into account the variation of the dose response of the films as a function of the proton energy and the other to obtain the dose to the cell layer starting from the dose measured on the films. This method, particularly suited to irradiation delivered in a single laser shot, can be applied in any other radiobiological experiment performed with laser-driven proton beams, with the only condition that the initial proton spectrum has to be at least roughly known. The method was tested in an experiment conducted at Queen's University of Belfast using the TARANIS laser, where the mean energy of the protons crossing the cells was between 0.9 and 5 MeV, the instantaneous dose rate was estimated to be close to 10(9) Gy s(-1) and doses between 0.8 and 5 Gy were delivered to the cells in a single laser shot. The combination of the applied corrections modified the initial estimate of dose by up to 40%.