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Effects of front surface plasma expansion on proton acceleration in ultraintense laser irradiation of foil targets

Effects of front surface plasma expansion on proton acceleration in ultraintense laser irradiation of foil targets

The properties of beams of high energy protons accelerated during ultraintense, picosecond laser-irradiation of thin foil targets are investigated as a function of preplasma expansion at the target front surface. Significant enhancement in the maximum proton energy and laser-to-proton energy conversion efficiency is observed at optimum preplasma density gradients, due to self-focusing of the incident laser pulse. For very long preplasma expansion, the propagating laser pulse is observed to filament, resulting in highly uniform proton beams, but with reduced flux and maximum energy.
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High energy conversion efficiency in laser-proton acceleration by controlling laser-energy deposition onto thin foil targets

High energy conversion efficiency in laser-proton acceleration by controlling laser-energy deposition onto thin foil targets

An all-optical approach to laser-proton acceleration enhancement is investigated using the simplest of target designs to demonstrate application-relevant levels of energy conversion efficiency between laser and protons. Controlled deposition of laser energy, in the form of a double-pulse temporal envelope, is investigated in combination with thin foil targets, in which recirculation of laser-accelerated electrons can lead to optimal conditions for coupling laser drive energy into the proton beam. This approach is shown to deliver a substantial enhancement in the coupling of laser energy to 5-30 MeV protons, compared to single pulse irradiation, reaching a record high 15 % conversion efficiency with a temporal separation of 1 ps between the two pulses and a 5 µm-thick Au foil. A 1D simulation code is used to support and explain the origin of the observation of an optimum pulse separation of ∼ 1 ps.
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Hot surface ionic line emission and cold K-inner shell emission from petawatt-laser-irradiated Cu foil targets

Hot surface ionic line emission and cold K-inner shell emission from petawatt-laser-irradiated Cu foil targets

these experiments. Hydrodynamic effects are probably not negligible at 20 ps pulse duration. 共2兲 A coupling efficiency that increases with laser intensity might be compensated for thin foil targets 共NOVA used several 100 ␮ m thick layers兲 by a growing number of hot electrons leaving the target and making refluxing less efficient. The simple model that was used here and the relative large uncertainty of the experimen- tal points allow only an estimate of the coupling efficiency, while more precise measurements require a careful CCD calibration and elaborate modeling, as it was done in Refs. 6 and 8.
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Carbon ion acceleration from thin foil targets irradiated by ultrahigh-contrast, ultraintense laser pulses

Carbon ion acceleration from thin foil targets irradiated by ultrahigh-contrast, ultraintense laser pulses

energy spectral shape obtained for targets with thickness greater than or equal to 100 nm and is consistent with previous measurements of ions accelerated by the TNSA mechanism [3, 36]. The energy distribution shifts to higher energy with increasing charge state, and higher charge state ions exhibit more plateau-like distributions. By contrast, when targets thinner than 50 nm are irradiated, changes to the shape of the spectra at high energy, including the onset of peaks and the detection of ion species with the same maximum velocity, are measured. These spectral changes indicate that TNSA is not the sole mechanism responsible for the ion acceleration in ultrathin ( < 50 nm) targets and that RPA may start becoming important under these conditions. These observations, which primarily occur with circularly polarized laser pulses and for θ L = 0 ◦ ,
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Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions

Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions

In this paper, we will present our observation of proton beams emitted from micron-thickness foils irradiated by 30-TW Ti: sapphire laser pulses by using an angle-resolved magnetic spectrometer. We find that modulated spectral peaks are presented at 2.5° off the target normal direction for 4 m thick aluminum foil targets. Our PIC simulations show that a strong toroidal magnetic field is also generated at the rear target surface. This field will deflect (rather than focus) the low energy protons away and make the protons with certain energies outstanding.
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Characterization of proton and heavier ion acceleration in ultrahigh-intensity laser interactions with heated target foils

Characterization of proton and heavier ion acceleration in ultrahigh-intensity laser interactions with heated target foils

The recently developed petawatt arm of the VULCAN Nd:glass laser at the Rutherford Appleton Laboratory, UK, was used in this experiment. p-polarized laser pulses with energy up to 400 J, wavelength ⬃ 1 ␮ m and average dura- tion 0.7 ps, were focused onto foil targets at an angle of 45° and to a peak intensity of the order of 2 ⫻ 10 20 Wcm −2 . No direct measurement of the temporal profile of the rising edge of the laser pulse is available. However, a 20 GHz photodi- ode coupled to a 6 GHz LeCroy digital storage oscilloscope was used, with appropriate filtering and on full energy laser shots, to measure the level of any amplified spontaneous emission ( ASE ) or prepulse activity. An intensity contrast measurement of over 7 orders of magnitude was achieved and at this level no prepulses were observed within a 10 ns period prior to the main pulse. The upper limit of the ASE or prepulse intensity for this experiment was therefore ⬃ 10 13 Wcm −2 .
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Enhanced He-alpha emission from "smoked" Ti targets irradiated with 400nm, 45 fs laser pulses

Enhanced He-alpha emission from "smoked" Ti targets irradiated with 400nm, 45 fs laser pulses

drops very quickly in a FWHM of 50 µmas we go away fromthe focus, whereas the emission from smoked targets remains high and relatively predictable despite the break-up of the beam, out to more than 200 µmfrombest focus. Fromthe standard error bars, it seems that the break-up of the beaminto hot spots at high defocus does not adversely affect reproducibility significantly. The increased efficiency of p-polarisation over s-polarisation is easily understood for the foil targets. As can be seen from the comparison of figs. 3(a) and (b), the temperature of the surface plasma in case of p-polarised light is about two orders of magnitude higher than in the case of s-polarised pulses. Furthermore, a substantially increased absorption from a few percent for s-polarisation [27] to over 50% for p-polarisation is expected due to the vacuum heating mechanism [26]. In addition super-thermal generated electrons will enhance ionisation and excitation rates in the plasma for p-polarisation.
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The solution of the two-dimensional inverse heat transfer problem with the use of the FEM in combination with Trefftz functions

The solution of the two-dimensional inverse heat transfer problem with the use of the FEM in combination with Trefftz functions

In a two-dimensional approximation of heat flow through major elements of the test section (Fig. 4), there occurs a simple problem in the glass barrier and an inverse problem in the heating foil [9,10]. To solve them, temperature measurements in the foil on the glass-side boundary, obtained thanks to the application of liquid crystal thermography, are used. When solving the inverse problem (no boundary condition on the boundary y = G G +G F ), the temperature field and heat flux density in the foil on the boundary y = G G +G F are determined. Local values of heat transfer coefficient are calculated with the assumption of linear temperature distribution of the liquid flowing along the minichannel (measurement of the liquid temperature at minichannel inlet and outlet). It is assumed that in the foil operates a heat source of constant efficiency q V , distributed evenly in the entire volume of the foil. The heating foil is single-sided enhanced on the selected area on side of the fluid flowing in the minichannel. On the basis of the 3D enhanced surface topography for a single microrecess (see Fig. 3b) a mathematical model was developed, featured in Fig. 5.
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Graphene Oxide Based Nanocomposites Decorated with Silver Nanoparticles as an Antibacterial Agent

Graphene Oxide Based Nanocomposites Decorated with Silver Nanoparticles as an Antibacterial Agent

Many studies have sought to establish a mechanism of action of antibacterial activity exhibited by silver in both its colloidal and ionic form. A disruption of membrane functionality from an interaction between released Ag + ions and the cell membrane and extensive cell membrane damage caused by the formation of ROS ultimately causes damage to the cell due to oxidative stress. Additionally, Ag + ions could cause dysfunction of the respiratory electron transport chain by uncoupling it from oxidative phosphorylation by inhibiting respiratory chain enzymes [54]. Foils coated with Ag-NPs and GO- Ag increased the ROS production of all tested microor- ganisms compared to the control group. The biological targets are DNA, RNA, proteins, and lipids. Lipids are one major target during oxidative stress. Free radicals can directly attack polyunsaturated fatty acids in bacter- ial and yeast membranes and activate peroxidation of lipids. A fundamental effect of lipid peroxidation is a de- crease in membrane fluidity, which can significantly dis- rupt membrane-bound proteins. DNA is also a main target. Mechanisms of DNA damage involve abstractions and addition reactions by free radicals leading to carbon-centered sugar radicals and OH- or H-adduct
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EMP control and characterisation on high-power laser systems

EMP control and characterisation on high-power laser systems

Control and characterisation of EMP emission at the VULCAN TAW facility has been achieved through the alteration of laser, target foil and stalk/mount charac- teristics. EMP energy was found to scale linearly with applied laser energy, but it is also sensitive to laser pre- pulse delay, pulse duration, defocus, stalk material and target transverse area. A dielectric spiral mount was shown to be an effective and unobtrusive means of reduc- ing EMP emission from solid targets. 3D particle-in-cell simulations suggest that this reduction may be due to a shadowing effect that limits photoionisation and charge implantation along the length of the stalk. A full theo- retical description of the current discharge mechanism in these modified stalks is left to future work.
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Progress status in fabrication of HBC stripper foil for 3-GeV RCS at J-PARC in Tokai site

Progress status in fabrication of HBC stripper foil for 3-GeV RCS at J-PARC in Tokai site

J-PARC RCS has been using the HBC stripper foils since the start of its operation, and the good performance of the stripper foil has been verified. Beam power for user beam operation has been increasing smoothly, and the HBC foil can be used for long-term user operation. The deposition apparatus for the HBC foil was relocated from the KEK Tsukuba site to the JAEA Tokai site in 2017 and we started fabrication of a new HBC foil at the JAEA Tokai site (J-HBC). Before using the J-HBC foil for user beam operation, offline beam test for the performance evaluation in the TIARA took place. The obtained test results are as follows: The cluster structure of the J-HBC foil is the same as that of the original HBC foil. The boron-to-carbon ratio of the J-HBC foil is slightly lower than that of the original HBC foil. The concentrations of trace impurities in the J-HBC foil are very low compared to those in the original HBC. Moreover, the endurance of the J-HBC foil against beam irradiation is the same as that of the original HBC foil. After the performance verification of the J-HBC foil, it was employed successfully in RCS user operation for 1 week. This great result is a major milestone for HBC foil manufacture at J-PARC. In the future, we will attempt to use the J-HBC foil for long-term operation to evaluate its performance. As a consequence, we have not only been carrying out stable supply for the J-PARC user operation but also done research and development on HBC foil to improve the performance and quality.
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Preliminary Experiments on Human Sensitivity to Rhythmic Structure in a Grammar with Recursive Self-Similarity

Preliminary Experiments on Human Sensitivity to Rhythmic Structure in a Grammar with Recursive Self-Similarity

account and balanced in the future is age of participants; although not significant in the statistical analysis, older participants may perform better on this type of rhythm detection task (Figure 2B). Taking into account the important difference in foil grammars between our experiments and those reported in Shirley (2014), we hypothesize that when given a complex grammar as foil that is not part of the Fibonacci grammatical space, participants would be able to draw upon rhythmic detection abilities to accurately accept grammatical and reject ungrammatical sequences. Success of some individuals on our potentially more difficult task (as compared to Shirley’s) already points in this direction. Success in learning Fibonacci grammars using percussion sounds would add support to the claim that rhythm detection is being used to solve this type of Artificial Grammar Learning task, as well as the type of task using speech sounds in Shirley (2014). Future work will address these outstanding issues.
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Apology and Medical Mistake: Opportunity or Foil?

Apology and Medical Mistake: Opportunity or Foil?

debriefed the mock jurors, they learned that the failure to disclose the error "exacerbated the belief that the organization should be punished for more than compe[r]

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Design and CFD Analysis of Air Foil

Design and CFD Analysis of Air Foil

Based on the CFD analysis of the flow over NACA 0012 air foil we can conclude that at the two degree of AOA there is no lift force generated and if we want to increase amount of lift force and value of lift co efficient then we have to increase the value of AOA. By doing

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Würl, Matthias
  

(2018):


	On the spectrometry of laser-accelerated particle bunches and laser-driven proton radiography.


Dissertation, LMU München: Fakultät für Physik

Würl, Matthias (2018): On the spectrometry of laser-accelerated particle bunches and laser-driven proton radiography. Dissertation, LMU München: Fakultät für Physik

One attempt to build a compact online scintillator stack, based on a CMOS pixel detector is shown in Englbrecht et al. [2018]. The prototype device consists of a stack of nine layers of radiation hard polysiloxane scintillators [Dalla Palma et al., 2015] on teflon support structures. The thickness of polysiloxane and teflon layers was ∼ 150 µm each. The polysiloxane layers are mounted perpendicularly to and are optically coupled to a large- area pixelated CMOS sensor (RadEye1, see section 4.2.3 for details on the detector). The light-sensitive CMOS sensor then detects the radiation-induced scintillation light. To avoid optical cross-talk of adjacent layers, the polysiloxane layers were covered with a thin foil of aluminized Mylar foil. The number of scintillating layers is then a direct measure for the range, and hence for the kinetic energy of the particles. Given that the light yield scales (almost) linearly with the energy deposition, the entire spectrum could then be reconstructed, similarly as for the offline RCF stacks. However, several shortcomings due to problems in the manufacturing have been encountered for this prototype spectrometer, namely a non-uniform coupling of the layers to the CMOS sensor and a non-homogeneous thickness of the layers. Accurate and precise spectrometry is hence not possible with this first prototype, whereas further developments and improvements in the design could potentially result in a reliable spectral diagnostic device for laser-accelerated ion bunches. The limited spatial resolution can be enhanced by the use of a second CMOS sensor coupled to the other edge of the polysiloxane layers.
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Learning to merge - language and vision: A deep evaluation of the encoder, the role of the two modalities, the role of the training task.

Learning to merge - language and vision: A deep evaluation of the encoder, the role of the two modalities, the role of the training task.

Upper-bound Using Crowdflower, we collected human answers from 738 na- tive English speakers for 984 image-caption pairs randomly selected from the test set. Subjects were given an image and a caption and had to decide whether it was correct or wrong (T1). If they thought it was wrong, they were required to mark the error in the caption (T2). We collected 2952 judgments (i.e., 3 judgments per pair and 4 judgments per rater) and computed human accuracy in T1 when considering an answer (a) the one provided by at least 2 out of 3 annotators (majority) and (b) the one provided by all 3 annotators (unanimity). The same procedure was adopted for computing accuracies in T2. Accuracies in both T1 an T2 are reported in Table 4.2 and 4.3 respectively. As can be seen, in the majority setting annotators are quasi-perfect in classifying captions (92.89%) and detecting foil words (97.00%). Though lower, accuracies in the unanimity setting are still very high, with raters providing the correct answer in 3 out of 4 cases in both tasks. Hence, although we have collected human answers only on rather a small subset of the test set, we believe their results are the representative of how easy the tasks are for humans.
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Studies on New Type Current Collectors for Polyaniline Batteries

Studies on New Type Current Collectors for Polyaniline Batteries

Five kinds of possible material as current collectors for PANI batteries were selected. Stainless steel (SS) was offered by Dongguan Mingnuo metal materials co., LTD. Aluminum foil (AF) was supplied by National medicine group chemical reagent co., LTD. Lead foil (LF) came from Qingdao Yongjiasheng industry and trade co., LTD. They were polished with abrasive paper to remove the oxidation layer on the surface before tested. Conductive plastics (CP) came from Shenzhen Xinrida technology co., LTD. Carbon fiber (CF) was supplied by Nantong Senyou carbon fiber co., LTD.
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Free surface interaction of a ‘T foil’ hydrofoil

Free surface interaction of a ‘T foil’ hydrofoil

Two sources of natural ventilation have been noted to exist in hydrofoils; strut and tip ventilation. Surface perturbations have been observed to interact with the hydrofoil low pressure field during strut ventilation, these perturbations growing away from the free surface providing the air pathway required for ventilation inception (Wright et al., 1972). The occurrence of tip ventilation and tip vortex ventilation is reported to be intermittent. At the present time the causes of the intermittent occurrence of tip ventilation are unclear, presenting a problem for designers as to where efforts should be focused to avoid or mitigate the effects of this phenomenon. Faltinsen (2005) speculated that the existence of cavitation in the vortex core may create a pathway from the hydrofoil tip to the surface. An explanation of the intermittency of tip ventilation might be that if the low pressure fields of the hydrofoil and tip vortex are not contiguous, or either pressure field is not sufficiently low to result in cavitation, foil ventilation via the tip vortex would not occur as the air pathway would be interrupted and the hydrofoil would remain unventilated. Even without the existence of cavitation, the low pressure region of a tip vortex core when in close proximity to free surface perturbations or entrained gas bubbles would appear to provide a viable mechanism for the creation of a tip ventilation pathway. Furthermore, this process is aided by the interruption of cohesion of the free surface due to the occurrence of a breaking wake as the submergence of a t-foil is reduced.
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In situ fabrication of silver nanoparticle-filled hydrogen titanate nanotube layer on metallic titanium surface for bacteriostatic and biocompatible implantation

In situ fabrication of silver nanoparticle-filled hydrogen titanate nanotube layer on metallic titanium surface for bacteriostatic and biocompatible implantation

Figure 8 shows the fluorescence images of the MC3T3- E1 cells cultured for 5 days on different samples: titanium control NT-Ti and AgNP-NT-Ti. The cell morphology for all the samples is polygonal, which is the characteristic shape of mouse preosteoblast cells. As shown in Figure 7B, 7E, and 7C, 7F, the cell density on NT-Ti and AgNP-NT-Ti is almost the same, and both are much larger than on titanium foil. This result indicates that H 2 Ti 3 O 7 can significantly enhance cell adhesion, cell migration, and final cell density on a sample surface, which is in agreement with the results from the cell proliferation experiments described above. This result also proves that AgNP-filled H 2 Ti 3 O 7 nanotubes do not give rise to cytotoxicity for MC 3T3-E1 cells, and that AgNP-NT-Ti pos- sesses good self-sterilizing properties without cytotoxicity.
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Determination of oxygen permeability of polyethylene and polypropylene nonwoven fabric foils

Determination of oxygen permeability of polyethylene and polypropylene nonwoven fabric foils

was made in the company Gabriel-Chemie, Lázně Bohdaneč, Czech Republic. Then the polyethyl- ene Polyten®MLB black&white foils were stud- ied, which were made in the company Chemosvit Fólie, a.s., Svit, Slovak Republic. The thickness of the foils was 90 m m. Black polypropylene nonwo- Table 2. Measured quantities of (A) the PE Bralen 2-63 with 9% coloured concentrate Maxithen HP 533041 – violet foil (thickness 50 m m), (B) PE Polyten®MLB black&white foil (thickness 90 m m) and (C) PP polypropylene nonwoven fabric foil (thickness 50 m m) at the air temperature 295 K
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