An Ab Initio Computation of the Potential Energy Surfaces of the DNA Bases

The potential energy surfaces of atoms in DNA can be analyzed and compared to show how their bonds break. This DNA potential energy reference data is very useful to understanding how DNA damage occurs, however, a dataset of relevant potential energy surfaces is not available for scientific use. We obtain the potential energy surfaces of various atoms in the four DNA bases adenine, thymine, guanine, and cytosine, by moving an atom in these molecules in three orthogonal directions using ORCA, an ab initio quantum chemistry software. Density functional theory isused to compute potential energies as an atom is moved, and this data is compiled into a useful three-dimensional surface for experimental application

Vibrational effects in the quantum dynamics of the H + D_2^+ charge transfer reaction

The H + D_2^+(v=0,1 and 2) charge transfer reaction is studied using an accurate wave packet method, using recently proposed coupled diabatic potential energy surfaces. The state-to-state cross section is obtained for three different channels: non-reactive charge transfer, reactive charge transfer, and exchange reaction. The three processes proceed via the electronic transition from the first excited to the ground electronic state. The cross section for the three processes increases with the initial vibrational excitation. The non-reactive charge transfer process is the dominant channel, whose branching ratio increases with collision energy, and it compares well with experimental measurements at collision energies around 0.5 eV. For lower energies the experimental cross section is considerably higher, suggesting that it corresponds to higher vibrational excitation of D_2^+(v) reactants. Further experimental studies of this reaction and isotopic variants are needed, where conditions are controlled to obtain a better analysis of the vibrational effects of the D_2^+ reagents.Comment: 15 pages, 7 figure

Active feedback scheme for minimization of helicity-dependent instrumental asymmetries

A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10−5

Active feedback scheme for minimization of helicity-dependent instrumental asymmetries

A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10−5

Assignment of resonances in dissociative recombination of HD+ ions: high-resolution measurements compared with accurate computations

The collision-energy resolved rate coefficient for dissociative recombination of HD+ ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with ro-vibrational excitation of the HD+ core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermal equilibrium level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting low-temperature ionized media.Comment: 15 pages, 10 figures. Paper to appear in Phys. Rev. A (version as accepted

“‘Wisdom is the principal thing; therefore, get wisdom’ Prov. 4:7,”

“‘Wisdom is the principal thing; therefore, get wisdom’ Prov. 4:7,” first edition, is the fruit of more than twenty years of experience in teaching introductory and college level laboratories at different colleges and universities in the United States as well as in Europe. It is a physics laboratory compendium that has enough materials to cover a two-semester course, but it is easily adjustable to the quarter system and adoptable into three sequential classes. The targeted audience includes students taking calculus-based physics courses as well as students taking non-calculus-based physics courses. Therefore, this physics laboratory compendium is especially useful in a system where both students in non-calculus-based and students in calculus-based classes are combined into the same laboratory sessions. All thirty chapters of this compendium are written in the same format that is described in the section “Laboratory Session Format” below. With its thirty chapters, it constitutes a pool of laboratories that makes a weekly synchronization with lecture topics easier. Each lab has at least one hands-on activity, which can be partly used as in class demo. The other activities use PASCO equipment, which reduces the length of the laboratory sessions with computer-assisted data-taking. However, these activities could be done with simple and standard equipment too, which might be beneficial if the time allocated to the laboratory sessions is long enough. Each single laboratory presented in this compendium is meant to last 2 to 2.5 hours in its current form

Mesure de l'énergie interne d'ions moléculaires par imagerie à trois dimensions. Application aux réactions d'ionisation associative d'atomes métastables

Doctorat en sciences (sciences physiques) (PHYS 3)--UCL, 200

Eye Accommodation, Near Vision, and Far Vision from a Geometrical Optics Point of View

The eye should have a particular focal length in order to see an object. As there are many things to see, the focal length of the eye must vary because these things are not all at the same distance from the eye. We explore the eye accommodation from a geometrical optics point of view and present our results in this paper; the study includes a description of the accommodation mechanism and a scientific definition of near vision and far vision

Isotope effect for the mutual neutralization reaction at low collision energies: He+ + H−

We measured the branching ratios of the He+ + H− and He+ + D− mutual neutralization at a collision energy below 25 meV. Those are correctly reproduced using the Landau-Zener model applied to potential energy curves computed by an anion-centered asymptotic model. The analyticity of both models allows getting a deeper insight into the reaction. It allows defining a low collision energy regime for the mutual neutralization at which the collision energy no longer affects the branching ratios. Using those models, we explain how heavier isotopes favor the production of higher excited states