A review of particle transport theory in a binary stochastic medium

A finalidade deste trabalho ´e apresentar uma revis˜ao da teoria do transporte de part´ıculas em meios compostos por uma mistura aleat´oria bin´aria. Para atingir este objetivo n´os apresentamos brevemente alguns conceitos b´asicos de teoria do transporte, e ent˜ao discutimos em detalhes a deriva¸c˜ao de duas abordagens desenvolvidas para a solu¸c˜ao de tais problemas: os modelos de mistura atˆomica e de Levermore-Pomraning. Providenciamos ainda, com o uso da formula¸c˜ao LTSN, compara ¸c˜oes num´ericas destes modelos com resultados de benchmark gerados atrav´es de um processo de Monte Carlo.

A few-body treatment of low energy atomic collisions involving exotic particles

Faddeev-type equations are applied to three-charged particle systems. The rather satisfactory results are obtained for low energy e(+)H elastic scattering and muonic transfer reactions. The cross sections for antihydrogen formation from antiproton-positronium collisions are calculated using a six state model (Ps[1s2s2p], (H) over bar[1s2s2p]).

Deviation from the sech2 superradiant emission law in a two-level atomic system

The atomic superradiant emission is treated in the single-particle mean-field approximation. A single-particle Hamiltonian, which represents a dressed two-level atom in a radiation field, can be obtained and it is verified that it describes the transient regime of the emission process. While the line-shape emission for a bare atom follows the sech2 law, for the dressed atom the line shape deviates appreciably from this law and it is verified that the deviation depends crucially on the ratio of the dynamic frequency shift to the transition frequency. This kind of deviation is observed in experimental results. © 1990 The American Physical Society.

Single-particle momentum distributions of Efimov states in mixed-species systems

We solve the three-body bound-state problem in three dimensions for mass imbalanced systems of two identical bosons and a third particle in the universal limit where the interactions are assumed to be of zero range. The system displays the Efimov effect and we use the momentum-space wave equation to derive formulas for the scaling factor of the Efimov spectrum for any mass ratio assuming either that two or three of the two-body subsystems have a bound state at zero energy. We consider the single-particle momentum distribution analytically and numerically and analyze the tail of the momentum distribution to obtain the three-body contact parameter. Our findings demonstrate that the functional form of the three-body contact term depends on the mass ratio, and we obtain an analytic expression for this behavior. To exemplify our results, we consider mixtures of lithium with either two caesium or rubidium atoms which are systems of current experimental interest. © 2013 American Physical Society.

Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

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

Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at root s(NN)=2.76 TeV

The effect of event background fluctuations on charged particle jet reconstruction in Pb-Pb collisions at root s(NN) = 2.76 TeV has been measured with the ALICE experiment. The main sources of non-statistical fluctuations are characterized based purely on experimental data with an unbiased method, as well as by using single high p(t) particles and simulated jets embedded into real Pb-Pb events and reconstructed with the anti-k(t) jet finder. The influence of a low transverse momentum cut-off on particles used in the jet reconstruction is quantified by varying the minimum track p(t) between 0.15 GeV/c and 2 GeV/c. For embedded jets reconstructed from charged particles with p(t) > 0.15 GeV/c, the uncertainty in the reconstructed jet transverse momentum due to the heavy-ion background is measured to be 11.3 GeV/c (standard deviation) for the 10% most central Pb-Pb collisions, slightly larger than the value of 11.0 GeV/c measured using the unbiased method. For a higher particle transverse momentum threshold of 2 GeV/c, which will generate a stronger bias towards hard fragmentation in the jet finding process, the standard deviation of the fluctuations in the reconstructed jet transverse momentum is reduced to 4.8-5.0 GeV/c for the 10% most central events. A non-Gaussian tail of the momentum uncertainty is observed and its impact on the reconstructed jet spectrum is evaluated for varying particle momentum thresholds, by folding the measured fluctuations with steeply falling spectra.

J/psi production as a function of charged particle multiplicity in pp collisions at root s=7 TeV

The ALICE Collaboration reports the measurement of the relative J/psi yield as a function of charged particle pseudorapidity density dN(ch)/d eta in pp collisions at root s = 7 TeV at the LHC. J/psi particles are detected for p(t) > 0, in the rapidity interval vertical bar y vertical bar < 0.9 via decay into e(+)e(-), and in the interval 2.5 < y < 4.0 via decay into mu(+)/mu(-) pairs. An approximately linear increase of the J/psi yields normalized to their event average (dN(J/psi)/dy)/(dN(J/psi)/dy) with (dN(ch)/c eta)/(dN(ch)/d eta) is observed in both rapidity ranges, where dN(ch)/d eta is measured within vertical bar eta vertical bar < 1 and p(t) > 0. In the highest multiplicity interval with (dN(ch)/d eta)(bin)) = 24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/psi yield by a factor of about 5 at 2.5 < y <4 (8 at vertical bar y vertical bar < 0.9) is observed. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.

Investigation of Aerosol Properties Using Environmental Atomic Force Microscopy

Atmospheric aerosols affect both global and regional climate by altering the radiative balance of the atmosphere and acting as cloud condensation nuclei. Despite an increased focus on the research of atmospheric aerosols due to concerns about global climate change, current methods to observe the morphology of aerosols and to measure their hygroscopic properties are limited in various ways by experimental procedure. The primary objectives of this thesis were to use atomic force microscopy to determine the morphology of atmospherically relevant aerosols and to investigate theutility of environmental atomic force microscopy for imaging aerosols as they respond to changes in relative humidity. Traditional aerosol generation and collection techniques were used in conjunction with atomic force microscopy to image commonorganic and inorganic aerosols. In addition, environmental AFM was used to image aerosols at a variety of relative humidity values. The results of this research demonstrated the utility of atomic force microscopy for measuring the morphology of aerosols. In addition, the utility of environmental AFM for measuring the hygroscopic properties of aerosols was demonstrated. Further research in this area will lead to an increased understanding of the role oforganic and inorganic aerosols in the atmosphere, allowing for the effects of anthropogenic aerosol emissions to be quantified and for more accurate climate models to be developed.

Particle tracking at cryogenic temperatures: the Fast Annihilation Cryogenic Tracking (FACT) detector for the AEgIS antimatter gravity experiment

The AEgIS experiment is an interdisciplinary collaboration between atomic, plasma and particle physicists, with the scientific goal of performing the first precision measurement of the Earth's gravitational acceleration on antimatter. The principle of the experiment is as follows: cold antihydrogen atoms are synthesized in a Penning-Malmberg trap and are Stark accelerated towards a moiré deflectometer, the classical counterpart of an atom interferometer, and annihilate on a position sensitive detector. Crucial to the success of the experiment is an antihydrogen detector that will be used to demonstrate the production of antihydrogen and also to measure the temperature of the anti-atoms and the creation of a beam. The operating requirements for the detector are very challenging: it must operate at close to 4 K inside a 1 T solenoid magnetic field and identify the annihilation of the antihydrogen atoms that are produced during the 1 μs period of antihydrogen production. Our solution—called the FACT detector—is based on a novel multi-layer scintillating fiber tracker with SiPM readout and off the shelf FPGA based readout system. This talk will present the design of the FACT detector and detail the operation of the detector in the context of the AEgIS experiment.

Imaging ROMK1 inwardly rectifying ATP-sensitive K+ channel protein using atomic force microscopy.

The inwardly rectifying K+ channel ROMK1 has been implicated as being significant in K+ secretion in the distal nephron. ROMK1 has been shown by immunocytochemistry to be expressed in relevant nephron segments. The development of the atomic force microscope has made possible the production of high resolution images of small particles, including a variety of biological macromolecules. Recently, a fusion protein of glutathione S-transferase (GST) and ROMK1 (ROMK1-GST) has been used to produce a polyclonal antibody for immunolocalization of ROMK1. We have used atomic force microscopy to examine ROMK1-GST and the native ROMK1 polypeptide cleaved from GST. Imaging was conducted with the proteins in physiological solutions attached to mica. ROMK1-GST appears in images as a particle composed of two units of similar size. Analyses of images indicate that the two units have volumes of approximately 118 nm3, which is close to the theoretical volume of a globular protein of approximately 65 kDa (the molecular mass of ROMK1-GST). Native GST exists as a dimer, and the images obtained here are consistent with the ROMK1-GST fusion protein's existence as a heterodimer. In experiments on ROMK1 in aqueous solution, single molecules appear to aggregate, but contact to the mica was maintained. Addition of ATP to the solution produced a change in height of the aggregates. This change (which was reversible) suggests that ATP induces a structural change in the ROMK1 protein. The data show that atomic force microscopy is a useful tool for examination of purified protein molecules under near-physiological conditions, and furthermore, that structural alterations in the proteins may be continuously investigated.