1,720,961 research outputs found
Calculation of BAS-TR imaging plate responses to carbon and titanium ion beams
No full textWe calculate BAS-TR imaging plate (IP) responses to laser-accelerated heavy ion beams such as carbon ion beam and titanium ion beam. We introduce two theoretical models widely used for the prediction of an IP response. We perform Monte Carlo simulations based on these two models, and compare the predictions with the available experimental data. Our calculations of the IP response to carbon ions show discrepancy in the location of the maximum IP response, while those to titanium ions present a different slope in the IP response curve. We find that both the linear and the exponential models are insufficient to explain the measured IP responses to carbon and titanium ion beams, and attempt to explain the reason for these differences.11Nsciescopuskc
Rapid, uniform, and efficient heat transfer into dense matter using energetic proton beams with finite energy spreads
No full text© 2022 Elsevier LtdEnergetic charged particles such as laser-driven protons or ions can transfer heat into a small solid-density sample very quickly, sometimes heating it to temperatures beyond 10,000 K. Uniform and efficient heat transfer would be desirable when measuring the physical properties of the sample after heating, but heating a thick solid-density sample both uniformly and efficiently in a short time has been very challenging. Here we show that a thick (> 1 cm) solid-density aluminum sample can be heated rapidly, uniformly, and efficiently all at the same time using an energetic proton beam with a finite energy spread. We perform Monte Carlo simulations to study the relationship between the energy spread of the incident protons and the heat transferred onto the sample for rapid, uniform, and efficient heating. We find that a 100 MeV proton beam with a Gaussian energy spread of ΔE/E ~ 70% can transfer heat into a 32 mm thick solid-density aluminum sample uniformly (temperature nonuniformity 62% heat transfer efficiency) on a sub-nanosecond time scale.11Nsciescopu
Time-resolved Rayleigh scattering measurements of methane clusters for laser-cluster fusion experiments.
No full textWe present a time-resolved analysis of Rayleigh scattering measurements to determine the average size of methane clusters and find the optimum timing for laser-cluster fusion experiments. We measure Rayleigh scattering and determine the average size of methane clusters varying the backing pressure (P0) from 11 bar to 69 bar. Regarding the onset of clustering, we estimate that the average size of methane clusters at the onset of clustering is Nc0≅20 at 11 bar. According to our measurements, the average cluster radius r follows the power law of r∝P01.86. Our ion time-of-flight measurements indicate that we have produced energetic deuterium ions with kT = 52±2 keV after laser-cluster interaction using CD4 gas at 50 bar. We find that this ion temperature agrees with the predicted temperature from CD4 clusters at 50 bar with r = 14 nm assuming the Coulomb explosion model
Neutron yield scaling law in laser-cluster fusion experiments
No full textWe present a scaling law ( Y ∼ E β ) of fusion neutron yields (Y) for laser pulse energy (E) in laser-cluster fusion experiments. We compare the available neutron yield data from previous deuterium cluster fusion experiments with those calculated using the cylindrical fusion plasma model. The calculated neutron yields are shown as functions of the incident laser pulse energy, average number density, and ion temperature. Although the deuterium-deuterium fusion reactivity is known to increase rapidly with ion temperature, the neutron yield shows a modest increase above ∼10 keV for a given laser pulse energy. We find the scaling exponent β approaching 1.0 as the ion temperature increases from 1 keV to 100 keV. We explain the observed temperature dependence of β by examining the temperature dependence of the beam-beam and beam-target fusion neutron yields separately. Our scaling law differs from previously reported scaling laws from individual experiments, but it shows an excellent agreement with the scaling law determined by the maximum neutron yields of individual experiments. © 2023 The Author(s). Published on behalf of IAEA by IOP Publishing Ltd.11Nsciescopu
Monte carlo study of imaging plate response to laser-driven aluminum ion beams
No full textWe measured the response of BAS-TR imaging plate (IP) to energetic aluminum ions up to 222 MeV, and compared it with predictions from a Monte Carlo simulation code using two different IP response models. Energetic aluminum ions were produced with an intense laser pulse, and the response was evaluated from cross-calibration between CR-39 track detector and IP energy spectrometer. For the first time, we obtained the response function of jthe BAS-TR IP for aluminum ions with a kinetic energy as high as 222 MeV. On close examination of the two IP response models, we confirm that the exponential model fits our experimental data better. Moreover, we find that the IP sensitivity in the exponential model is nearly constant in this energy range, suggesting that the response function can be determined even with little experimental data.11Nsciescopu
Electron-positron generation by irradiating various metallic materials with laser-accelerated electrons
No full textWe examined electron–positron pair production in solid iron, zinc, tungsten, and lead targets irradiated by a laser-accelerated electron beam generated with a 100 TW laser. These targets were assessed at the target thickness of 0.5, 1.25, and 2.0 radiation lengths for each material. Using a 0.75-T-magnetic spectrometer, we measured the electron and positron yields and spectra, producing 3 × 108 positrons per shot with a peak leptonic density of 4 × 1012 cm−3. These experimental results agree very well with Monte Carlo simulations conducted with the simulation code Geant4. Importantly, our findings show that normalizing the target thickness to each material's radiation length results in consistent electron and positron yields across the materials, effectively reducing discrepancies due to material differences. © 2023 The Author(s)11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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