Produção de partículas secundárias em reações de “spallation” induzidas por prótons

Cosmic radiation has been identi ed as one of the main hazard to crew, aircraft and sensitive equipments involved in long-term missions and even high-altitude commercial ights. Generally, shields are used in spatial units to avoid excessive exposure, by holding the incident radiation. Unfortunatelly, shielding in space is problematic, especially when high-energy cosmic particles are considered, due to the production of large number of secondary particles, mainly neutrons, protons and alpha particles, caused by spallation reactions and quasi-elastic processes of the corpuscular radiation with the shield. Good parameters for checking the secondary particle production at target material are diferential cross section and energy deposited in the shield. Addition experiments, some computer codes based on Monte Carlo method show themselves a suitable tool to calculate shield parameters, due to have evaluated nuclear data libraries implemented on the algorithm. In view of this, the aim of this work is determining the parameters evaluated in shielding materials, by using MCNPX code, who shows good agreement with experimental data from literature. Among the materials, Aluminium had lower emission and production of secondary particles

Cálculo estrutural de barreiras: Desenvolvimento de um programa computacional de interface online

This study aimed to develop a computer program which systematizes the structural shielding design calculation in diagnostic radiology facilities. For this purpose methodology of the National Council of Radiation Protection and Measurements (NCRP 147[5]) was used. By comparative statistics studies, it was verified if reference parameters values suggested by the US publication correspond to the average national values. The World Wide Web was chosen because of its characteristics as a powerful mean of communication, especially in terms of the wide variety of useful resources and easy access. To compare the reference values of some parameters proposed by NCRP 147 to Brazilian average, studies about the normalized workload per patient, performance of X-ray tube and primary air kerma, unshielded, at one meter from the focal point of the X-ray tube were made. Through this research, relative differences were found. In workload values this differences reached up to 50% in mammography compared to those presented by the NCRP 147; in X-ray tube performance the percentage differences reached 69% in dental radiology, and air kerma results amounted 31% in fluoroscopy. This demonstrates the importance of validation of international protocols to local realities

Novel wireless-communicating textiles made from multi-material and minimally-invasive fibers

The ability to integrate multiple materials into miniaturized fiber structures enables the realization of novel biomedical textile devices with higher-level functionalities and minimally-invasive attributes. In this work, we present novel textile fabrics integrating unobtrusive multi-material fibers that communicate through 2.4 GHz wireless networks with excellent signal quality. The conductor elements of the textiles are embedded within the fibers themselves, providing electrical and chemical shielding against the environment, while preserving the mechanical and cosmetic properties of the garments. These multi-material fibers combine insulating and conducting materials into a well-defined geometry, and represent a cost-effective and minimally-invasive approach to sensor fabrics and bio-sensing textiles connected in real time to mobile communications infrastructures, suitable for a variety of health and life science applications.

Human dental enamel and dentin structural effects after Er:yag laser irradiation

Ideally projected to be applied on soft tissues, infrared lasers were improved by restorative dentistry to be used in hard dental tissues cavity preparations-namely enamel and dentin. This paper evidentiates the relevant aspects of infrared Erbium laser's action mechanism and its effects, and characterizes the different effects deriving from the laser's beams emission. The criteria for use and selection of optimal parameters for the correct application of laser systems and infuence of supporting factors on the process, such as water amount and its presence in the ablation process, protection exerted by the plasma shielding and structural factors, which are indispensable in dental tissues cavity preparation related to restorative technique, are subordinated to optical modifcations caused by the interaction of the energy dissipated by these laser light emission systems in the targeted tissue substrate. Clinical relevance: Differences in the action of infrared Erbium laser system in regard to the nature of the ablation process and variations on the morphological aspects observed in the super-fcial structure of the target tissue irradiated, may be correlated to the structural optical modifcations of the substrate produced by an interaction of the energy propagated by laser systems.

Inverted critical adsorption of polyelectrolytes in confinement

What are the fundamental laws for the adsorption of charged polymers onto oppositely charged surfaces, for convex, planar, and concave geometries? This question is at the heart of surface coating applications, various complex formation phenomena, as well as in the context of cellular and viral biophysics. It has been a long-standing challenge in theoretical polymer physics; for realistic systems the quantitative understanding is however often achievable only by computer simulations. In this study, we present the findings of such extensive Monte-Carlo in silico experiments for polymer-surface adsorption in confined domains. We study the inverted critical adsorption of finite-length polyelectrolytes in three fundamental geometries: planar slit, cylindrical pore, and spherical cavity. The scaling relations extracted from simulations for the critical surface charge density sigma(c)-defining the adsorption-desorption transition-are in excellent agreement with our analytical calculations based on the ground-state analysis of the Edwards equation. In particular, we confirm the magnitude and scaling of sigma(c) for the concave interfaces versus the Debye screening length 1/kappa and the extent of confinement a for these three interfaces for small kappa a values. For large kappa a the critical adsorption condition approaches the known planar limit. The transition between the two regimes takes place when the radius of surface curvature or half of the slit thickness a is of the order of 1/kappa. We also rationalize how sigma(c)(kappa) dependence gets modified for semi-flexible versus flexible chains under external confinement. We examine the implications of the chain length for critical adsorption-the effect often hard to tackle theoretically-putting an emphasis on polymers inside attractive spherical cavities. The applications of our findings to some biological systems are discussed, for instance the adsorption of nucleic acids onto the inner surfaces of cylindrical and spherical viral capsids.

Analysis of the influence of baffles and shields on the cooling of a digital transmission equipment

In this work design criteria for cooling of electronic systems used in a digital transmission equipment are considered. An experimental study using a simulated electronic equipment in which vertically oriented circuit boards are aligned to form vertical channels is carried out. Resistors are used to simulate actual components. The temperature of several components in the printed circuit boards are measured and the influence of the baffles and shields on the cooling effect are discussed. It was observed that the use of the baffles reduce the temperature levels and, the use of shields, although protecting the components from magnetic effects, cause an increase in the temperature levels.

Computer simulation of configurational properties of partially ionized polyelectrolytes

Monte Carlo simulation methods were used in order to study the conformational properties of partially ionized polyelectrolyte chains with Debye-Hückel screening in 1:1 electrolyte solution at room temperature. Configurational properties such as the distributions of probability for the square end to end distances, for the square radii of gyration and for the angles between polyion bonds were investigated as a function of the chain ionization and the salt concentration. © 1993.

Corrosion behaviour of aluminium syntactic functionally graded composites

Syntactic Functionally Graded Metal Matrix Composites (SFGMMC) are a type of composites reinforced by microballoons exhibiting a graded reinforcement distribution. These materials constitute a promising new generation of lightweight structural materials for aerospace, marine and shielding/insulation applications. In this work, A356 alloy reinforced with silica-alumina microballoons (SiO2-Al2O3) was processed by casting techniques. The influence of the microballoon distribution gradient on the corrosion behaviour of the composite was investigated by potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS). Composite surfaces were analysed before and after testing by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) to determine the influence of microstructural changes.

Determinação da estrutura de diferentes alcoóis terpênicos: um estudo teórico e experimental

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Cordas cósmicas e gravitação planar de ordem superior

The possibility of generalizing gravity in 2+1 dimensions to include higher-derivative terms, thereby allowing for a dynamical theory, opens up a variety of new interesting questions. This is in great contrast with pure Einstein gravity which is a generally covariant theory that has no degrees of freedom - a peculiarity that, in a sense, renders it a little insipid and odorless. The research on gravity of particles moving in a plane, that is, living in flatland, within the context of higher-derivative gravity, leads to novel and interesting effects. For instance, the generation of gravity, antigravity, and gravitational shielding by the interaction of massive scalar bosons via a graviton exchange. In addition, the gravitational deffection angle of a photon, unlike that of Einstein gravity, is dependent of the impact parameter. On the other hand, the great drawback to using linearized general relativity for describing a gravitating string is that this description leads to some unphysical results such as: (i) lack of a gravity force in the nonrelativistic limit; (ii) gravitational deffection independent of the impact parameter. Interesting enough, the effective cure for these pathologies is the replacement of linearized gravity by linearized higher-derivative gravity. We address these issues here

Theoretical and Experimental Studies in Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) is a tool used to probe the physical and chemical environments of specific atoms in molecules. This research explored small molecule analogues to biological materials to determine NMR parameters using ab initio computations, comparing the results with solid-state NMR measurements. Models, such as dimethyl phosphate (DMP) for oligonucleotides or CuCl for the active site of the protein azurin, represented computationally unwieldy macromolecules. 31P chemical shielding tensors were calculated for DMP as a function of torsion angles, as well as for the phosphate salts, ammonium dihydrogen phosphate (ADHP), diammonium hydrogen phosphate, and magnesium dihydrogen phosphate. The computational DMP work indicated a problem with the current standard 31P reference of 85% H3PO4(aq.). Comparison of the calculations and experimental spectra for the phosphate salts indicated ADHP might be a preferable alternative as a solid state NMR reference for 31P. Experimental work included magic angle spinning experiments on powder samples using the UNL chemistry department’s Bruker Avance 600 MHz NMR to collect data to determine chemical shielding anisotropies. For the quadrupolar nuclei of copper and scandium, the electric field gradient was calculated in diatomic univalent metal halides, allowing determination of the minimal level of theory necessary to compute NMR parameters for these nuclei.

Spectral Induced Polarization (SIP) signatures of clayey soils containing toluene

We performed laboratory experiments to investigate the sensitivity of the Spectral Induced Polarization (SIP) method to toluene contamination in clayey soils. We used mixtures of quartzitic sand and montmorillonite as soil samples, artificially contaminated with varying amounts of toluene. Care was taken to quantify the experimental uncertainty resulting from packing since such effects must be quantified if variations in SIP signatures between samples are to be reliably interpreted in terms of the effects of hydrocarbon concentration. The SIP response of all samples following addition of toluene was monitored for a period of 40 days following sample preparation. Stepwise regression was used to examine the statistical significance of correlations between (i) clay content and (ii) toluene concentration and SIP parameters. Both single-frequency real and imaginary conductivity measurements, along with the integral chargeability, normalized chargeability, DC conductivity and time constant obtained from a Debye decomposition fitting, were examined in this regression analysis. The SIP measurements show a clear time dependence following sample preparation, indicating that samples containing toluene may take significant time to reach an equilibrium electrical response. SIP measurements are significantly related to toluene content shortly after sample preparation, when the expected dependence of SIP on clay concentration is apparently suppressed. However, for the state of electrical equilibrium after 40 days (interpreted to indicate surface chemistry at equilibrium) there is no significant relation between SIP measurements and toluene content; instead SIP measurements are then significantly correlated with clay concentration. The total chargeability, normalized chargeability and relaxation time obtained from the Debye decomposition show no correlation with toluene content, indicating that this procedure, which likely integrates over multiple mechanisms, may not be suitable for understanding relationships between SIP and hydrocarbon contamination. We find only small low-frequency polarization signals observed in relation to toluene concentration (2 mrad at 0.01 Hz), which initially decreases the interfacial polarization. Unlike earlier works, our results do not support the use of the SIP method as a tool for monitoring toluene contamination in clay soils.

Prediction of the Temperature Distribution of Partially Submersed Umbilical Cables

The objective of this work is to predict the temperature distribution of partially submersed umbilical cables under different operating and environmental conditions. The commercial code Fluent (R) was used to simulate the heat transfer and the air fluid flow of part of a vertical umbilical cable near the air-water interface. A free-convective three-dimensional turbulent flow in open-ended vertical annuli was solved. The influence of parameters such as the heat dissipating rate, wind velocity, air temperature and solar radiation was analyzed. The influence of the presence of a radiation shield consisting of a partially submersed cylindrical steel tube was also considered. The air flow and the buoyancy-driven convective heat transfer in the annular region between the steel tube and the umbilical cable were calculated using the standard k-epsilon turbulence model. The radiative heat transfer between the umbilical external surface and the radiation shield was calculated using the Discrete Ordinates model. The results indicate that the influence of a hot environment and intense solar radiation may affect the umbilical cable performance in its dry portion.

Interstitial doping induced superconductivity at 15.3 K in Nb5Ge3 compound

It is reported superconductivity in Nb5Ge3C0.3, an interstitial carbide compound. The temperature dependence of the electrical resistivity, ac-susceptibility, and heat capacity (HC) indicate that a bulk type-II superconductivity appears at T-C - 15.3 K. Magneto-resistance measurements suggest an upper critical field of B-C2 similar to 10.6 T and a coherence length of xi similar to 55 angstrom at zero temperature. Neutron diffraction analyzes locate the carbon atoms at the interstitial 2b site of the Mn5Si3 type-structure. Heat capacity data below T-C are well described by BCS theory. The size of the jump at T-C is in good agreement with the superconducting volume fraction observed in susceptibility measurements. A Debye temperature and Sommerfeld constant were also extracted from heat capacity data as 343 K and 34 mJ/mol K-2, respectively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730611]

Electronic Properties of Water in Liquid Environment. A Sequential QM/MM Study Using the Free Energy Gradient Method

There is a continuous search for theoretical methods that are able to describe the effects of the liquid environment on molecular systems. Different methods emphasize different aspects, and the treatment of both the local and bulk properties is still a great challenge. In this work, the electronic properties of a water molecule in liquid environment is studied by performing a relaxation of the geometry and electronic distribution using the free energy gradient method. This is made using a series of steps in each of which we run a purely molecular mechanical (MM) Monte Carlo Metropolis simulation of liquid water and subsequently perform a quantum mechanical/molecular mechanical (QM/MM) calculation of the ensemble averages of the charge distribution, atomic forces, and second derivatives. The MP2/aug-cc-pV5Z level is used to describe the electronic properties of the QM water. B3LYP with specially designed basis functions are used for the magnetic properties. Very good agreement is found for the local properties of water, such as geometry, vibrational frequencies, dipole moment, dipole polarizability, chemical shift, and spin-spin coupling constants. The very good performance of the free energy method combined with a QM/MM approach along with the possible limitations are briefly discussed.