Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.Comment: 4 pages, 5 figure

Preliminary validation of the European Portuguese version of the Robotic Social Attributes Scale (RoSAS)

Background: People’s perception of social robots is essential in determining their responses and acceptance of this type of agent. Currently, there are few instruments validated for the European Portuguese population that measures the perception of social robots. Method: Our goal was to translate, validate, and evaluate the psychometric properties of the Robotic Social Attributes Scale (RoSAS) to European Portuguese. To achieve this goal, we conducted a validation study using a sample of 185 participants. We measured the temporal validity of the scale (over a two-week interval) and its divergent and convergent validity using the Portuguese Negative Attitudes towards Robots Scale (PNARS) and the Godspeed scales. Results: Our data analysis resulted in a shortened version of the Portuguese RoSAS with 11 items while retaining the original three-factor structure. The scale presented poor to acceptable levels of temporal reliability. We found a positive correlation between the warmth and competence dimensions. Further validation studies are needed to investigate the psychometric properties of this scale.info:eu-repo/semantics/publishedVersio

Fear or humour in anti-smoking campaigns? Impact on perceived effectiveness and support for tobacco control policies

Several anti-smoking campaigns have been used for decades to reduce smoking consumption. However, so far, there is no consensus regarding the effectiveness of inducing distinct emotions in reducing smoke consumption. This study tested the effects of two types of anti-smoking ads, inducing fear or humor, on emotions, perceived effectiveness, support for tobacco control policies, urges to smoke, and susceptibility to smoke. Participants (N = 108; 54 smokers) of both genders were randomly assigned to one of the two following emotion ads condition: fear (N = 52) or humor (N = 56). During exposure, the continuous flow of their emotions by self-report and physiologically was collected. Measures of ads impact on emotions, perceived effectiveness, urges and susceptibility to smoking, and support for tobacco policies were applied after exposure. The results have shown that fear ads were perceived as more effective and reduced the urges to smoke in smokers. Non-smokers were more supportive of tobacco control policies. In conclusion, this study showed that fear campaigns can reduce the urge to smoke among smokers and are perceived to be more effective. This perceived effectiveness can be partially explained by feelings of fear, regardless the other emotions it also triggers, and of the smoking status.info:eu-repo/semantics/publishedVersio

Agent Based Model of the Cytosine Radiation Induced Reaction

The stability of cytosine in aqueous solution was studied in the laboratory, simulating prebiotic conditions and using gamma radiation as an energy source, to describe cytosine behavior under radiation. For a better understanding of the radiation-induced processes, we proposed a mathematical model that considers chemical reactions as nonlinear ordinary differential equations. The radiolysis can be computationally simulated by an agent-based model, wherein each chemical species involved is considered to be an agent that can interact with other species with known reaction rates. The radiation is contemplated as a factor that promotes product formation/destruction, and the temperature determines the diffusion speed of the agents. With this model, we reproduce the changes in cytosine concentration obtained in the laboratory under different irradiation conditions

Tape-tether design for de-orbiting from given altitude and inclination

The product of the tether-to-satellite mass ratio and the probability of tether cuts by small debris must be small to make electrodynamic bare tethers a competitive and useful de-orbiting technology. In the case of a circular orbit and assuming a model for the debris population, the product can be written as a function that just depends on the initial orbit parameters (altitude and inclination) and the tether geometry. This formula, which does not contain the time explicitly and ignores the details of the tether dynamics during the de-orbiting, is used to find design rules for the tape dimensions and the orbit parameter ranges where tethers dominate other de-orbiting technologies like rockets, electrical propulsion, and sails

Optimum sizing of bare-tape tethers for de-orbiting satellites at end of mission

De-orbiting satellites at end of mission would prevent generation of new space debris. A proposed de-orbit technology involves a bare conductive tape-tether, which uses neither propellant nor power supply while generating power for on-board use during de-orbiting. The present work shows how to select tape dimensions for a generic mission so as to satisfy requirements of very small tether-to-satellite mass ratio m(t)/M-s and probability N-f of tether cut by small debris, while keeping de-orbit time t(f) short and product t(f) x tether length low to reduce maneuvers in avoiding collisions with large debris. Design is here discussed for particular missions (initial orbit of 720 km altitude and 63 and 92 inclinations, and 3 disparate M-s values, 37.5, 375, and 3750 kg), proving it scalable. At mid-inclination and a mass-ratio of a few percent, de-orbit time takes about 2 weeks and N-f is a small fraction of 1%, with tape dimensions ranging from 1 to 6 cm, 10 to 54 mu m, and 2.8 to 8.6 km. Performance drop from middle to high inclination proved moderate: if allowing for twice as large m(t)/M-s, increases are reduced to a factor of 4 in tf and a slight one in N-f; except for multi-ton satellites, somewhat more requiring because efficient orbital-motion-limited electron collection restricts tape-width values, resulting in tape length (slightly) increasing too.This work was supported by the European Commission FP7/Space Project 262972 (BETs), the Ministry of Science and Innovation of Spain (BES-2009-013319 FPI Grant), and Universidad Politécnica de Madrid (Research Grant RR01 2009)

Ion acceleration in underdense plasmas by ultra-short laser pulses

We report on the ion acceleration mechanisms that occur during the interaction of an intense and ultrashort laser pulse ( λ > μ I 2 1018 W cm−2 m2) with an underdense helium plasma produced from an ionized gas jet target. In this unexplored regime, where the laser pulse duration is comparable to the inverse of the electron plasma frequency ωpe, reproducible non-thermal ion bunches have been measured in the radial direction. The two He ion charge states present energy distributions with cutoff energies between 150 and 200 keV, and a striking energy gap around 50 keV appearing consistently for all the shots in a given density range. Fully electromagnetic particle-in-cell simulations explain the experimental behaviors. The acceleration results from a combination of target normal sheath acceleration and Coulomb explosion of a filament formed around the laser pulse propagation axi

Study of L-Glutamic Acid in Solid State for its Possible Use as a Gamma Dosimeter at Different Temperatures (77, 195 and 295 K)

The experimental response of the dosimeter as a function of the irradiation temperature plays an important role, and this effect has consequences in the practical applications of dosimetry. In this work, L-glutamic acid (2-aminopentanedioic acid) is proposed to be a good response, easy to handle, and a cheap gamma dosimeter. For this purpose, polycrystalline samples were irradiated with gamma rays at 77, 195, and 295 K and doses in the kiloGray range (43–230 kGy). The potential use of the glutamic acid system as a chemical dosimeter is based on the formation of stable free radicals when the amino acid is exposed to ionizing radiation. The observed species in these experiments were attributed to deamination and decarboxylation reactions that were studied using electron spin resonance (ESR). The results indicate that the analysis generates a linear response as the irradiation dose increases in a reliable range for industrial and research purposes at three different temperatures