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When two bodies collide with each other, they change their motion. Many physics textbooks explain that the change in motion is caused by the force or impulse exerted on the body during the collision. This is not the whole story, I argue, in case the bodies are rigid. In this case, the change in motion cannot be causally explained solely by how the bodies are configured before and during the collision but instead should be explained partly by what happens after the collision. That is, the collision between rigid bodies should better be interpreted as a case of retrocausation where the future causally affects the past or present. This retrocausal interpretation of the collision does not suffer a general problem raised against retrocausation, known as the bilking argument. And how the influence of the cause propagates backward in time to the effect in the collision is no more mysterious than how a body moves continuously in classical mechanics or how the future affects the past in proposed retrocausal models for the EPR thought experiment in quantum mechanics., Author(s): Chunghyoung Lee [sup.1] Author Affiliations: (1) grid.49100.3c, 0000 0001 0742 4007, Division of Humanities and Social Sciences, Pohang University of Science and Technology, , 37673, Pohang, Gyeongbuk, Republic of [...]

We have carried out a calculation of 241 levels for Ne-like Ge (Z = 36) to calculate electron impact collision strengths and effective collision strengths belonging to 1[s.sup.2]2[s.sup.2]2[p.sup.5]nl, 1[s.sup.2]2[s.sup.1]2[p.sup.6]nl (n = 3,4, 5, 6; l = s, p, d, f, g, and h) configurations, which have been calculated by the fully relativistic flexible atomic code (FAC). Our calculations, based on the distorted-wave method with large configuration interactions, are included. Collision strengths have been generated over an electron energy range of (10-20 000 eV) and they have been listed at seven representative energies of 65.33, 1714.98, 2944.1, 4868.3, 7564.6, 11040, and 15 221 eV in this work, and effective collision strengths data have been calculated from these at electron plasma temperatures 650, 850, 1050, 1250, 1450, 1650, and 1850 eV. Our results are compared with those available in the literature. It is found that the resonance effects are important in calculating the effective collision strengths. Key words: effective collision strength, laser, atomic, collision strengths, Ne -like Ge. Nous utilisons le Flexible Atomic Code completement relativiste pour calculer les 241 niveaux de Ge de type Ne (Z = 36), de facon a evaluer les forces de collision sous impact electronique et les forces de collision effectives qui appartiennent aux configurations 1[s.sup.2]2[s.sup.2]2[p.sup.5]nl, 1[s.sup.2]2[s.sup.1]2[p.sup.6]nl (n = 3, 4, 5, 6 ; l = s, p, d, g, h). Nos calculs sont bases sur une methode d'onde distordue, incluant des interactions de configurations etendues. Nous avons calcule les forces de collisions sur un large domaine d'energie electronique (10-20 000 eV) et nous les presentons ici a sept energies representatives de 65.33, 1714.98, 2944.1, 7564.6, 11 040 et 15 221 eV et les forces de collision effectives obtenues de ces resultats a des temperatures electroniques dans le plasma de 650, 850, 1050, 1250, 1450, 1650 et 1850 eV. Nous comparons nos resultats avec des resultats dans la litterature. Nous trouvons que les effets de resonance sont importants dans le calcul des forces de collision effectives. [Traduit par la Redaction] Mots-cles: forces de collision effectives, laser, atomique, forces de collision, Ge de type Cl., 1. Introduction Electron impact collision strengths and effective collision strengths are of fundamental importance in analyzing the physical state and chemical composition of gaseous nebulae and laboratory plasmas. At present [...]

Collision strengths for all 1326 transitions among lowest 52 fine-structure levels of Br XXVII have been computed using Dirac atomic R-matrix code (DARC). Resonances in the threshold region have been completely resolved and the contributions of these resonances to allowed and forbidden transitions have been presented. The partial collision strength for each angular momentum has been studied graphically. Effective collision strengths have also been determined within the temperature range for all 1326 transitions among the lowest 52 levels. Target state energies of the lowest 52 fine-structure levels have been computed from the multi-configuration Dirac-Fock method (MCDF). Additionally, similar calculations with the relativistic distorted wave method and flexible atomic code (FAC) have also been performed to check the accuracy of our results. The present work represents a new and significant work with improvement in the field. We believe that our presented data of collision and effective collision strengths may be useful in the future for benchmark calculations and for plasma diagnostics. Key words: energy levels, collision strength, effective collision strength. Nous calculons les forces de collision pour toutes les 1326 transitions entre les 52 niveaux de structure fine du Br XXVII, en utilisant le logiciel de la matrice R atomique de Dirac. Nous identifions completement les resonances dans la region du seuil et presentons la contribution de ces resonances aux transitions permises et interdites. Nous etudions graphiquement les forces de collision partielles pour chaque valeur du moment angulaire. Les forces de collision effectives sont egalement determinees dans un domaine de temperature pour les 1326 transitions entre les 52 niveaux. Les energies des etats cibles pour les 52 plus bas niveaux de structure fine sont calculees par la methode de Dirac-Fock multi -configurationnelle (MDFC/MCDF). De plus, nous recalculons ces quantites a l'aide d'une methode d'ondes partielles relativiste, l'approche du Flexible atomic code, afin de verifier l'exactitude de nos resultats. Notre travail represente une avancee nouvelle et significative du domaine. Nous croyons que nos donnees de collision et de force de collision effective seront utiles dans l'avenir pour des calculs etalons et dans les diagnostiques du plasmas. [Traduit par la Redaction] Mots-cles: force de collision, force de collision effective, resonances, diagnostique du plasm, niveaux d'energie., 1. Introduction During the last few years, the study of the spectroscopic parameters and atomic processes for highly charged ions has become a topic of interest because of its applications [...]

Avian mortality from collisions with windows and buildings is one of the top sources of anthropogenic mortality of birds. Each year in the United States, an estimated 100 million to one billion birds die from window collisions. Many studies of bird-window collision mortality have aimed to identify architectural, landscape, and species-specific factors that may influence collision rates, but little research has assessed the potential for spatiotemporal variation in collision mortality. We studied window collision mortality at 42 residential houses located within an urban landscape, along the shores of Lake Superior in Duluth MN, USA from 2006-2009 to quantify window-related fatalities during migration. The rate of window collision mortality was modeled as a function of house location and season using Poisson regression. We also conducted carcass distribution trials to estimate scavenging and detection rates, and analyzed the resulting data using a multistate Markov model. We used hierarchical models of scavenging probability to compare the relationship between scavenging rates and six measured covariates. Models for collision mortality and scavenging were evaluated using Akaike's Information Criterion (AIC). The adjusted number of birds killed (Ay over the full course of monitoring was estimated using the Horvitz-Thompson estimator. A total of 40 species and 108 individual birds were recorded as window kills. Fatalities increased with distance from the city center, were higher at houses on the lake side of the study site, and on windows facing Lake Superior. Scavenging rates also increased with distance from the city center, with small carcasses being removed more quickly than large carcasses, and removal rates decreasing over time for all carcass sizes. Because of the low detection probability of homeowners, combined detection by both homeowners and researchers was Key words: avian mortality, detectability, Great Lakes, migration, multistate Markov model, scavenging, window kills., Experimental and observational studies have shown that birds are unable to recognize glass as a barrier (e.g., Klem 1989, Ogden 1996), and approximately half of all window collisions result in [...]

The collision time is an important quantity of an elementary chemical reaction and describes the speed of the collision process in a collision reaction. In this study, we present a generalized method to calculate the collision time of a triatomic reaction in which the collision time is defined by the sum of the incoming time, the intermediate complex time, and the outgoing time. Two variables including the total distance [R.sub.total] and [R.sub.avg], the average value of [R.sub.total] over time, are used to compute the three components of the collision time. We compute three triatomic reactions including Ca + HCl [right arrow] CaCl + H, O + HCl [right arrow] OH + Cl/OCl + H, and O + HF [right arrow] OH + F at different collision energies and initial diatomic vibrational levels using the quasi-classical trajectory method to confirm that the method could be reliable and reasonable. The time evolutions of [R.sub.total] could efficiently classify the direct and indirect reactive mechanisms and reveal a distinct discrepancy of the two mechanisms. As the collision energy and initial diatomic vibrational level increase, the percentage of direct reaction trajectories increases. At the same time, the average and maximal values of collision time decrease. Comparing the maximal collision time and the reactive probability distributions of the products, it could be found that most reactive trajectories' collision time is less than 2 ps. Moreover, the present calculations indicate that the method could be applicable to estimate the lifetime of the intermediate complex for the reaction systems with deep potential wells and the collision time of the reactions with a direct abstraction mechanism. Key words: collision time, total distance, reactive probability distribution, direct and indirect reaction. Le temps de collision est une mesure quantitative importante d'une reaction chimique elementaire et temoigne de la vitesse du processus de collision lors de collisions reactionnelles. Dans la presente etude, nous presentons une methode generalisee pour le calcul du temps de collision d'une reaction triatomique dans laquelle le temps de collision correspond a la somme du temps d'approche, de la duree de vie du complexe intermediaire et du temps de retrait. Nous avons utilise deux variables: la distance totale [R.sub.total]e et la valeur moyenne [R.sub.moy] de la distance totale dans le temps pour calculer les trios composantes du temps de collision. Au moyen de la methode des trajectoires quasi classiques, nous avons effectue les calculs pour trois reactions triatomiques (Ca + HCl [right arrow] CaCl + H, O + HCl [right arrow] OH + Cl/OCl + H et O + HF [right arrow] OH + F) a differentes energies de collision et differents niveaux vibrationnels diatomiques afin de confirmer que la methode pouvait etre fiable et convenable. L'evolution de la [R.sub.total] dans le temps permettait de classifier efficacement les mecanismes de reaction directe et indirecte et revelait un ecart distinct entre les deux mecanismes. Le pourcentage des trajectoires de reaction directe augmente en fonction de l'energie de collision et du niveau vibrationnel diatomique initial, tandis que les valeurs moyennes et maximales de temps de collision diminuent. En comparant le temps de collision maximal avec les distributions de probabilite reactionnelle des produits, nous pouvions observer que pour les trajectoires les plus reactives, le temps de collision etait inferieur a 2 ps. En outre, les presents calculs indiquent que la methode pourrait etre appliquee a l'estimation de la duree de vie du complexe intermediaire dans des systemes reactionnels presentant des puits de potentiel profonds et du temps de collision de reactions dont le mecanisme d'arrachement est direct. [Traduit par la Redaction] Mots-cles: temps de collision, distance totale, distribution de probabilite reactionnelle, reaction directe et indirecte., Introduction In elementary chemical reaction research, the model A + BC is widely used. (1) Generally, three reaction channels are mostly concerned by researchers, which are (1) [MATHEMATICAL EXPRESSION NOT [...]

Atomic and molecular samples reduced to temperatures below one microkelvin, yet still in the gas phase, afford unprecedented energy resolution in probing and manipulating the interactions between their constituent particles. As a result of this resolution, atoms can be made to scatter resonantly on demand, through the precise control of a magnetic field (1). For simple atoms, such as alkalis, scattering resonances are extremely well characterized (2). However, ultracold physics is now poised to enter a new regime, where much more complex species can be cooled and studied, including magnetic lanthanide atoms and even molecules. For molecules, it has been speculated (3,4) that a dense set of resonances in ultracold collision cross-sections will probably exhibit essentially random fluctuations, much as the observed energy spectra of nuclear scattering do (5). According to the Bohigas-Giannoni-Schmit conjecture, such fluctuations would imply chaotic dynamics of the underlying classical motion driving the collision (6-8). This would necessitate new ways of looking at the fundamental interactions in ultracold atomic and molecular systems, as well as perhaps new chaos-driven states of ultracold matter. Here we describe the experimental demonstration that random spectra are indeed found at ultralow temperatures. In the experiment, an ultracold gas of erbium atoms is shown to exhibit many Fano-Feshbach resonances, of the order of three per gauss for bosons. Analysis of their statistics verifies that their distribution of nearest-neighbour spacings is what one would expect from random matrix theory (9). The density and statistics of these resonances are explained by fully quantum mechanical scattering calculations that locate their origin in the anisotropy of the atoms' potential energy surface. Our results therefore reveal chaotic behaviour in the native interaction between ultracold atoms., In the common perception, atoms are regarded as 'simple' systems in sharp contrast to 'complex' molecules, whose behaviour is dictated by many (rotational and vibrational) degrees of freedom. The recent [...]

The stereodynamics calculation of F + HO → HF + O(¹D) was carried out using the quasi-classical trajectory method on the 1¹A' potential energy surface provided by Gomez-Carrasco et al. (Chem. Phys. Lett. 2007, 435,188). The effect of the collision energy, isotopic substitution, and different initial ro-vibrational states on the reaction is discussed. It is found that for the initial ground state of HO (v = 0, j = 0), the degree of the forward scattering and the product polarizations remarkably change as the collision energy varies. Isotopic effect leads to the increase of alignment and decrease of orientation of product rotational angular momentum. Moreover, the P([θ.sub.r]) distribution and P([φ.sub.r]) distribution change noticeably by varying the initial vibrational number. The initial vibrational excitation plays a more important role in the enhancement of alignment and orientation distribution of j= for the title reaction. Although the influence of the initial rotational excitation effect on the aligned and oriented distribution of product is not stronger than that of the initial vibrational excitation effect, the initial rotational excitation makes the alignment of the product rotational angular momentum decrease to some extent. The probabilities show that the reactivity of the title reaction strongly depends on the initial vibrational state. Key words: stereodynamics, quasi-classical trajectory, collision energy, isotopic effect, initial ro-vibrational excitation. Les calculs de la stereodynamique de la reaction F + HO [right arrow] HF + O(¹D) ont ete effectues a l'aide de la methode de la trajectoire quasi-classique sur la surface d'energie potentielle 1¹A' fournie par Gomez-Carrasco et al. (Chem. Phys. Lett. 2007, 435, 188). Nous avons etudie l'effet de l'energie de collision, la substitution isotopique et differents etats ro- vibrationnels initiaux lies a la reaction ci-dessus. Il a ete decouvert que, dans l'etat fondamental initial du compose HO (v = 0, j = 0), le degre de diffusion vers l'avant et les polarisations du produit changent considerablement lorsque l'energie de collision varie. L'effet isotopique conduit a l'augmentation de l'alignement du moment angulaire de rotation du produit et a la diminution de son orientation. En outre, les distributions P([θ.sub.r]) et P([φ.sub.r]) changent significativement lorsque l'on fait varier le nombre vibrationnel initial. L'excitation vibrationnelle initiale jour un role plus important dans l'amelioration de la distribution d'alignement et d'orientation de j' dans le cas de la reaction ci-dessus. Bien que l'influence de l'effet de l'excitation rotationnelle initiale sur la distribution alignee et orientee du produit ne soit pas plus forte que celle de l'effet de l'excitation vibrationnelle initiale, on constate que l'excitation rotationnelle initiale fait diminuer, dans une certaine mesure, le moment angulaire de rotation. Les probabilites montrent que la reactivite de la reaction ci-dessus depend fortement de l'etat vibrationnel initial. [Traduit par la Redaction] Mots-cles: stereodynamique, trajectoire quasi-classique, energie de collision, effet isotopique, excitation ro- vibrationnelle initiale., Introduction The HOX (X refers to halogen) system involving atmospheric science and environment protection is attracting more and more attention. Fluorine has the lowest electron number and the smallest atomic [...]

An intense laser field can remove an electron from an atom or molecule and pull the electron into a large-amplitude oscillation in which it repeatedly collides with the charged core it left behind (1-4). Such recollisions result in the emission of very energetic photons by means of high-order-harmonic generation, which has been observed in atomic and molecular gases (5-7) as well as in a bulk crystal (8). An exciton is an atom-like excitation of a solid in which an electron that is excited from the valence band is bound by the Coulomb interaction to the hole it left behind (9,10). It has been predicted that recollisions between electrons and holes in excitons will result in a new phenomenon: high-order-sideband generation (11,12). In this process, excitons are created by a weak near-infrared laser of frequency [f.sub.NIR]. An intense laser field at a much lower frequency, [f.sub.THz], then removes the electron from the exciton and causes it to recollide with the resulting hole. New emission is predicted to occur as sidebands of frequency [f.sub.NIR] + 2n[f.sub.THz], where n is an integer that can be much greater than one. Here we report the observation of high-order-sideband generation in semiconductor quantum wells. Sidebands are observed up to eighteenth order (+18[f.sub.THz],or n = 9). The intensity of the high-order sidebands decays only weakly with increasing sideband order, confirming the non-perturbative nature of the effect. Sidebands are strongest for linearly polarized terahertz radiation and vanish when the terahertz radiation is circularly polarized. Beyond their fundamental scientific significance, our results suggest a new mechanism for the ultrafast modulation of light, which has potential applications in terabit-rate optical communications., A recollision between an electron and an atomic core can be described by a three-step process (13): first the electric field associated with an intense laser (~[10.sup.13] W [cm.sup.-2] at [...]

We examined bat collision mortality, activity and species composition at an 89-turbine wind resource area in farmland of north-central Iowa from mid-Apr, to mid-Dec., 2003 and mid-Mar, to mid-Dec., 2004. We found 30 bats beneath turbines on cleared ground and gravel access areas in 2003 and 45 bats in 2004. After adjusting for search probability, search efficiency and scavenging rate, we estimated total bat mortality at 396 ± 72 (95% CI) in 2003 and 636 ± 112 (95% CI) in 2004. Although carcasses were mostly migratory tree bats, we found a considerable proportion of little brown bats (Myotis lucifugus). We recorded 1465 bat echolocation call files at turbine sites (x = 34.88 call files/detector-night) and 1536 bat call files at adjacent non-turbine sites (x = 36.57 call files/detector-night). Bat activity did not differ significantly between turbine and non-turbine sites. A large proportion of recorded call files were made by Myotis sp. but this may be because we detected activity at ground level only. There was no relationship between types of turbine lights and either collision mortality or echolocation activity. The highest levels of bat echolocation activity and collision mortality were recorded during Jul. and Aug. during the autumn dispersal and migration period. The fatality rates for bats in general and little brown bats in particular were higher at the Top of Iowa Wind Resource Area than at other, comparable studies in the region. Future efforts to study behavior of bats in flight around turbines as well as cumulative impact studies should not ignore non-tree dwelling bats, generally regarded as minimally affected., INTRODUCTION Wind power is a financially competitive source of electricity in the USA that is generally viewed as having few negative effects on the environment. Recent studies have found large [...]

Results of numerically investigated binary collisions of 32 drop pairs presented in Part I of this study are used to parameterize coalescence efficiencies and size distributions of breakup fragments of large raindrops. In contrast to the well-known results of Low and List, it is shown that coalescence efficiencies [E.sub.c] can be described best by means of the Weber number We yielding [E.sub.c] = exp(-1.15We). The fragment size distributions gained from our numerical investigations were parameterized by fitting normal, lognormal, and delta distributions and relating the parameters of the distribution functions to physical quantities relevant for the breakup event. Thus, this parameterization has formally a substantial similarity to the one of Low and List, although no reference is made to breakup modes such as filament, disk, and sheet. Additionally, mass conservation is guaranteed in the present approach. The parameterizations from Low and List, as well as the new parameterizations, are applied to compute a stationary size distribution (SSD) from solving the kinetic coagulation--breakup equation until a time-independent state is reached. Although with the parameterizations of Low and List, the SSD shows an often-reported three-peak structure, with the new parameterizations the second peak vanishes completely. DOI: 10.1175/2009JAS3175.1

Binary collisions of large raindrops moving with terminal fall velocity are numerically investigated using FS3D, a direct numerical simulation (DNS) code based on the 'volume of fluid' method. The result of this process can be a permanent coalescence or a temporal coalescence followed by a breakup of the coalesced system into smaller-sized remnants of the original raindrops and a number of fragment droplets of different sizes. In total, 32 drop pairs are studied with sizes chosen to cover nearly completely the entire size parameter range relevant to breakup. This is an important extension of investigations performed in 1982 by Low and List, who studied 10 drop pairs only. Moreover, eccentricity has been introduced as an additional parameter controlling the collision outcome. Eccentricity is defined as the horizontal distance of the initial drops' centers with values equal to approximately 0 for centric and 1 for grazing collisions. The main results include numerically calculated data of coalescence efficiencies and fragment size distributions with emphasis on eccentricity effects. It is shown that eccentricity largely determines the appearance of specific breakup modes and consequently the respective fragment size distributions. Comparisons are made with the main findings of Low and List. Coalescence efficiency values larger than those derived by Low and List show up for very small Weber numbers. Additionally, the existence of their definite limit value of collision kinetic energy necessary for coalescence could not be confirmed. The fragment size distributions are in some cases similar to those measured by Low and List but there are also major differences for other cases. The presented results are used for parameterizations of coalescence efficiencies and fragment size distributions as well as for calculations of stationary drop spectra shown in Part li of this study. DOI: 10.1175/2009JAS3174.1

The electron swarm coefficients (i.e., drift velocity, longitudinal diffusion coefficient, and effective ionization coefficient) have been measured using a time-resolved pulsed Townsend technique in [O.sub.2], [N.sub.2], and C[O.sub.2] and their mixtures C[O.sub.2]-[N.sub.2] and C[O.sub.2]-[O.sub.2], with C[O.sub.2] shares of 20%, 50%, and 80%. Simultaneously, these swarm data have been calculated from an adequate multiterm solution of the Boltzmann equation, using previously validated sets of electron-molecule collision cross sections. We have found good agreement between measurements and calculations, both for the pure gases and mixtures, particularly for the case of the calculated mean electron drift velocity [W.sub.m], which takes into account the effects of longitudinal diffusion and effective ionization. An effort has been placed in covering as high an E/N range as possible (0.01 Td up to 1000 Td) on specific electron swarm data such as transverse and longitudinal characteristic energies, which are also needed for a better understanding of the electrohydrodynamic and kinetic behavior of nonthermal atmospheric pressure electrical discharges. Index Terms--Atmospheric gas mixtures, attachment, basic swarm data, Boltzmann equation solution, collision cross sections, diffusion, electron swarm coefficients, electron transport, ionization, nonthermal plasma applications, time-resolved measurements.

Nonselective collision-induced dissociation (CID) is a technique for producing fragmentation products for all ions generated in an ion source. It is typical of liquid chromatography/mass spectrometry (LC/MS) analysis of complex samples that matrix-related components may contribute to the resulting product ion spectra and confound the usefulness of this technique for structure interpretation. In this proof-of-principle study, a high-resolution LC/MS-based background subtraction algorithm was used to process the nonselective CID data to obtain clean product ion spectra for metabolites in human plasma samples. With buspirone and clozapine metabolites in human plasma as examples, this approach allowed for not only facile detection of metabolites of interest but also generation of their respective product ion spectra that were clean and free of matrix-related interferences. This was demonstrated with both an [MS.sup.E] technique (where E represents collision energy) with a quadrupole time-of-flight (QTOF) instrument and an in-source fragmentation technique with an LTQ Orbitrap instrument. The combined nonselective CID and background subtraction approach should allow for detection and structural interpretation of other types of sample analyses where control samples are obtained.

The complex natural organic matter standard Suwannee river fulvic acid (SRFA) was analyzed by negative ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICR MS) using on-resonance collision induced dissociation (CID) of single ultrahigh resolved mass peaks in the ICR cell. Molecular formula assignment of precursor masses resulted in exactly one molecular formula for each of the peaks. Analyses of the corresponding fragment spectra and comparison to different standard substances revealed specific neutral losses and fragmentation patterns which result in structures consisting of a high degree of carboxyl- and fewer hydroxyl groups. The comparison of fragmented mass peaks within different pseudohomologous series (C[H.sub.2]-series, and C[H.sub.4] vs O exchange) suggested structurally based differences between these series. CID FTICR MS allowed isolating single mass peaks in a very complex natural organic matter spectrum. Subsequently, fragmentation gave structural insights into this material. Our results suggest that the structural diversity in complex humic substances is not as high as expected.

The use of mass spectra generated at 70 eV in electron ionization (EI) as a universal standard for EI has helped in the generation of searchable library databases and had a profound influence on the analytical applications of gas chromatography/mass spectrometry (GC/MS), similarly for liquid chromatography tandem mass spectrometry (LC-MS/MS), suggesting a novel method to normalize the collisional energy for the universalization of fragmentation energy for the analysis of Chemical Weapon Convention (CWC)-related chemicals by atmospheric pressure ionization-tandem mass spectrometry (API-[MS.sup.n]) using three-dimensional (3D) ion trap instruments. For normalizing fragmentation energy a 'fragmentation energy index' (FEI) is proposed which is an arbitrary scale based on the fact of specific MS/MS fragmentation obtained at different collisional energies for the reference chemicals which are not CWC scheduled compounds. FEI 6 for the generation of an [MS.sup.n] library-searchable mass spectral database is recommended.

Simultaneous transmission mode collision-induced dissociation (CID) and ion/ion proton transfer reactions have been implemented on a quadrupole/time-of-flight (TOF) tandem mass spectrometer. Reagent anions were trapped in a pressurized quadrupole collision cell by applying appropriate dc voltages while multiply protonated protein precursor ions were injected into the collision cell at energies sufficient to give rise to CID. Intact precursor ions as well as fragment ions underwent ion/ion proton transfer reactions during their passage through the collision cell and on to an orthogonal acceleration TOF mass analyzer. The resulting product ion spectrum was then submitted to deconvolution to yield a 'zero-charge' spectrum, which was then matched against in silico produced spectra derived from a protein database. Dramatic improvements in the scores associated with correct matches were obtained relative to CID data without the benefit of ion/ion reactions for proteins as large as carbonic anhydrase (29 kDa). The parameters that most affect the extent of ion/ion proton transfer during transmission through the instrument include the number of anions stored in the collision cell, the amplitude of the radio frequency trapping voltage, the voltage of the LINAC potential associated with the collision cell, and the collision gas pressure. This work demonstrates that it is possible to effect whole protein tandem mass spectrometry with simultaneous CID, ion/ion reactions, and mass analysis for high duty cycle top-down protein characterization.

The physics of ballistic penetration mechanics is of great interest in penetrator and countermeasure design. The phenomenology associated with these events can be quite complex, and a significant number of studies have been conducted ranging from purely experimental to 'engineering' models based on empirical and/or analytical descriptions to fully coupled penetrator/target, thermomechanical numerical simulations. Until recently, however, there appears to be a paucity of numerical studies considering 'non-ideal' impacts (Goldsmith, 1999, 'Non-Ideal Projectile Impact on Targets,' Int. J. Impact Eng., 22, pp. 95-395). The goal of this work is to demonstrate the SHlSM algorithm implemented in the ALEGRA multimaterial arbitrary Lagrangian Eulerian code (Boucheron, et al., 2002, ALEGRA: User Input and Physics Descriptions, Version 4.2, SAND2002-2775, Sandia National Laboratories, Albuquerque, NM). The SHISM algorithm models the three-dimensional continuum solid mechanics response of the target and penetrator in a fully coupled manner. This capability allows for the study of nonideal impacts (e.g., pitch, yaw, and/or obliquity of the target/penetrator pair). In this work predictions using the SHISM algorithm are compared with previously published experimental results for selected ideal and nonideal impacts of metal penetrator-target pairs. These results show good agreement between predicted and measured maximum depths-of-penetration (DOPs), for ogive-nose penetrators with striking velocities in the 0.5-1.5 km/s range. Ideal impact simulations demonstrate convergence in predicted DOP for the velocity range considered. A theory is advanced to explain disagreement between predicted and measured DOPs at higher striking velocities. This theory postulates uncertainties in angle-of-attack for the observed discrepancies. It is noted that material models and associated parameters used here were unmodified from those in literature. Hence, no tuning of models was performed to match experimental data. [DOI: 10.1115/1.3013859] Keywords: oblique impact, angle-of-attack, penetration, ALE, SHISM, ALEGRA

The effects of collisional quenching on photofragment emission (PFE) detection of vapor-phase Hg[Cl.sub.2] in combustion flue gas constituents are investigated. Exciting Hg[Cl.sub.2] via the 1 [sup.1][[PI].sub.u] [left arrow] 1 [sup.1][[summation].sup.+.sub.g] transition, time-resolved measurements of emission from the Hg([6.sup.3][P.sub.1]) daughter in buffer-gas mixtures of [N.sub.2], [O.sub.2], and C[O.sub.2] indicate that the fragmentation pathway passes through a long-lived intermediate species, which we assign to Hg([6.sup.3][P.sub.2]). Total quenching rate coefficients of Hg([6.sup.3][P.sub.1]) by [N.sub.2], [O.sub.2], and C[O.sub.2] are consistent with values reported in the literature. In addition, total quenching rate coefficients for the intermediate Hg([6.sup.3][P.sub.2]) state are determined to be 1.72([+ or -] 0.08) x [10.sup.-10] [cm.sup.3] [molecule.sup.-1] [s.sup.-1] and 2.90([+ or -] 0.37) x [10.sup.-10] [cm.sup.3] [molecule.sup.-1] [s.sup.-1] for [N.sub.2] and [O.sub.2], respectively. An analysis of the impact of the collisionally dependent energy-transfer process that precedes the formation of Hg([6.sup.3][P.sub.1]) on the use of PFE to measure Hg[Cl.sub.2] concentration is presented. OCIS codes: 280.1120, 300.2530, 120.0280.

The Theory of Relativity requires that there should be a gravitational analogue to electromagnetic radiation. It is impossible to generate measurable quantities in the laboratory but recent observations indicate that there may be a tremendous flux coming from the centre of our galaxy. Collisions between gravitationally collapsed objects (black holes) seem to be the only mechanism which could produce this amount of radiation.

We have measured differential cross sections (DCSs) for the vibrationally inelastic scattering process H + o-[D.sub.2](v = 0, j = 0,2) [right arrow] H + o-[D.sub.2](v' = 1-4, j' even). Several different collision energies and nearly the entire range of populated product quantum states are studied. The products are dominantly forward-scattered in all cases. This behavior is the opposite of what is predicted by the conventional textbook mechanism, in which collisions at small impact parameters compress the bond and cause the products to recoil in the backward direction. Recent quasiclassical trajectory (QCT) calculations examining only the o-[D.sub.2](v' = 3, j') products suggest that vibrationally inelastic scattering is the result of a frustrated reaction in which the D--D bond is stretched, but not broken, during the collision. These QCT calculations provide a qualitative explanation for the observed forward-scattering, but they do not agree with experiments at the lowest values of j'. The present work shows that quantum mechanical calculations agree closely with experiments and expands upon previous results to show that forward-scattering is universally observed in vibrationally inelastic H + [D.sub.2] collisions over a broad range of conditions. fully quantum calculations | ion imaging | reaction dynamics | vibrationally inelastic scattering

A tandem mass spectrometry approach is demonstrated for complete sequencing of a model small interfering RNA (siRNA) based on ion trap collisional activation of intact single-stranded anions. Various charge states of the siRNA duplex and the individual strands were generated by nanoelectrospray (nano-ESI). The siRNA duplex anions were predominantly dissociated into the sense and anti-sense strands by collisional activation. The characteristic fragment ions (c/y- and a-B/w-ion series) from both strands were observed when higher activation amplitude was applied and when beam-type collisional activation was examined; however, the coexistence of fragment ions from both strands complicated spectral interpretation. The effect of precursor ion charge state on the dissociation of the individual sense and antisense strand siRNA anions was studied using ion hap collision-induced dissociation under various activation amplitudes. Through the activation of relatively low charge state precursor ions at relatively low excitation energy, selective backbone dissociation predominantly via the c/y channels was achieved. By applying relatively high excitation energy, the a-B/w channels also became prominent; however, the increase in spectral complexity made complete peak assignment difficult. In order to simplify the product ion spectra, proton-transfer reactions were applied, and complete sequencing of each strand was achieved. The application of tandem mass spectrometry to intact single-stranded anions demonstrated in this study can be adapted for the rapid identification of other noncoding RNAs in RNomics studies.

When one hard steel ball collides with another, kinetic energy is conserved, even if the balls have different diameters. Why is kinetic energy conserved in such a collision, given that kinetic energy is not conserved when two unequal length steel springs or rods collide? Experimental results with bouncing balls, springs, and rods are presented, which reveal the answer. For colliding springs and rods a significant fraction of the initial kinetic energy is retained after the collision as vibrational energy in the longer spring and rod. When two hard balls collide, a negligible fraction of the initial energy is converted to vibrational energy because the collision time is much longer than the transit time of an acoustic wave across each ball due to the fact that the contact region of a hard spherical ball is much softer than the rest of the ball. [DOI: 10.1119/1.2948778]

Electron transfer dissociation (ETD) is a recently introduced mass spectrometric technique which has proven to be an excellent tool for the elucidation of labile posttranslational modifications such as phosphorylation and O-GlcNAcylation of serine and threonine residues. However, unlike collision induced dissociation (CID), which has been studied for decades, the intricacies of ETD-based fragmentation have not yet been firmly established or systematically addressed. In this analysis, we have systematically compared the CID and ETD fragmentation patterns for the large majority of the peptides that do not contain such labile modifications. Using a standard 48 protein mix, we were able to measure false-positive rates for the experiments and also assess a large number of peptides for a detailed comparison of CID and ETD fragmentation pattern. Analysis of ~19 000 peptides derived from both standard proteins and complex protein samples revealed that (i) CID identified 50% more peptides than ETD; (ii) ETD resulted in ~20% increase in amino acid sequence coverage over CID; and (iii) combining CID and ETD fragmentation increased the sequence coverage for an average tryptic peptide to 92%. Interestingly, our analysis revealed that nearly 60% of all ETD-identified peptides carried two positive charges, which is in sharp contrast to what has been generally accepted. We also present a novel strategy for automatic validation of peptide assignments based on identification of a peptide by consecutive CID and ETD fragmentation in an alternating mode.

The present study is a continuation of the series of studies dedicated to the investigation of cloud droplet collisions in turbulent flow with characteristics that are typical of real clouds. Detailed tables of collision kernels and collision efficiencies calculated in the presence of hydrodynamic interaction of droplets are presented. These tables were calculated for a wide range of turbulent parameters. To illustrate the sensitivity of droplet size distribution (DSD) evolution to the turbulence-induced increase in the collision rate, simulations of DSD evolution are preformed by solving the stochastic kinetic equation for collisions. The results can be applied to cloud modeling. The tables of collision efficiencies and collision kernels are available upon request. Some unsolved problems related to collisions of droplets and ice hydrometeors in turbulent clouds are discussed in the conclusion.

In mountainous areas, accidental rock falls are common hazards, which can cause a lot of damage. The passive protection systems of roads are usually rock-shed galleries composed of reinforced concrete elements. In this paper, a new type of structure is presented. The main innovation, compared to conventional solutions, is to dissipate the impact energy directly into the reinforced concrete slab or into fuse supports, and no longer into a cushion layer. The dynamic phenomena, taking place during the impact of a block onto the slab, are analyzed by means of experiments on a one-third-scale model (slab of 12 m x 4.80 m x 0.28 m) of a real structure. The results made it possible to validate the operating and repair principles of the structurally dissipation rock-shed and revealed that the slab is damaged by three main mechanisms: punching, bending, and surface level breaking below of the impacted zone. These three damage modes are analyzed by means of data resulting from the various experimental tests. DOI: 10.1061/(ASCE)0733-9445(2007)133:10(1426) CE Database subject headings: Protective structures; Concrete slabs; Concrete, reinforced; Experimentation; Bending; Hazards; Damage.

Abstract: In the context of collision-induced dissociation in chemistry and kinematics in physics, we have determined that a beam of hyperthermal protons can be used as tiny hammers to preferentially [...]

A typical assumption for rigid body collisions with multiple impact points is that all collisions occur simultaneously and are synchronized in their compression/expansion behavior, a useful assumption given the microscopic time scale at which collisions occur. In the case in which collisions are dependent upon one another, however, there is interaction between and within compression and expansion phases. Instead of treating the collisions as separate consecutive impacts or by activating all constraints at the same time, a rule is presented that orders the collisions as a sequence of interacting events at a point in time to handle the normal component of the collisions. [DOI: 10.1115/1.2712237] Keywords: hybrid modeling, systematic model abstractions, parameter abstraction, time scale abstraction, collision behavior

To identify the transition from continuous to discontinuous modes in the failure evolution of quasibrittle materials under impact, a coupled rate-dependent damage and plasticity model is developed within the thermodynamics framework. Due to the simplicity in model formulation, a continuum tangent stiffness tensor could be obtained for discontinuous bifurcation analysis, and the model parameters could be calibrated from split Hopkins pressure bar experimental data available. The coupled rate-dependent model could describe not only the pressure-dependent hardening/softening response but also the degradation of material stiffness under impact. A geometric criterion with a corresponding solution scheme is presented to explore the rate-dependent transition from continuous to discontinuous failure modes in the Mohr coordinates. The uniaxial compressive loading path is considered to illustrate the loading rate effect on the critical localization orientation and hardening parameters. It appears from the preliminary results that the coupled rate-dependent local continuum model might be combined with a decohesion model via discontinuous bifurcation analysis so that large-scale simulation of failure evolution could be performed without invoking higher-order spatial terms in the stress-strain space. CE Database subject headings: Bifurcations: Coupling; Discontinuities; Impact forces; Plasticity.

On-site collision tests of full-scale concrete barriers are an important method to understand what happens to concrete barriers when vehicles collide with them. However, such tests require both time and money, so modeling and simulation of collisions by computer have been developed as an alternative in this research. First, spring subgrade models were developed to formulate the ground boundary of concrete barriers based on previous experiments. Then, the finite element method models were developed for both heavy trucks and concrete barriers to simulate their dynamic collision performances. Comparison of the results generated from computer simulations and on-site experiments demonstrates that the developed models can be applied to simulate the collision of heavy trucks with concrete barriers, to replicate the movement of the truck at the collision, and to investigate the performance of the concrete barriers. The developed research methodology can be widely used to support the design of new concrete barriers and the safety analysis of existing ones. CE Database subject headings: Barriers; Collisions; Concrete; Trucks; Finite element method; Numerical analysis; Simulation.

Author(s): John Ellis [1] The unparalleled high energy of the Large Hadron Collider (LHC), with its 7 TeV per beam and its enormously high collision rate that should reach a [...]

A study report of a classical-trajectory of the dynamics of high-energy collisions between Ar atoms and the [C.sub.2][H.sub.6] and [C.sub.2][F.sub.6] molecules is presented. The results suggest that high-energy collisions between closed-shell species of the natural low-earth-orbit environment and spacecraft could contribute to the observed degradation of polymers that coat spacecraft surfaces.

Four ambiguities are inherent in time-independent quantum-mechanical scattering theory: two in the normalization of continuum functions, and two in the relation between various scattering matrices. These ambiguities allow the use of different conventions in scattering theory. This freedom has led to inconsistencies among textbooks, monographs, review articles, and research papers. We identify these ambiguities, indicate their context and origin in scattering theory, give the key equations of scattering theory in a form that can by adapted to any convention, and show interrelations between these equations that can lead to confusion and error. We also give several diagnostic approaches for determining the conventions used in a particular source, and reference conventions adopted in widely used books on scattering theory. [DOI: 10.1119/1.2358156]

We analyze the problem of one-dimensional collisions between a target mass m and the incident mass M and a third object, the mediator. The concept of an optimal mediator that yields the most efficient energy transfer between the incident and target objects is introduced. A mediator consisting of a chain of colliding particles with masses that follow a geometric progression is considered. A paradox that arises when the number of particles in the chain goes to infinity is discussed. In this case a complete energy transfer from the incident to the target mass can be achieved for any mass ratio M/m. The analogs of this problem in multilayer optics and quantum mechanics are also discussed. [DOI: 10.1119/1.2345654]

The dynamic vibration absorber is a device for reducing the vibration of many structures and mechanical equipment. It consists of a small mass which is attached to the primary vibrating system or main mass. The impact damper is one of such dynamic vibration absorbers in which motion of auxiliary mass is limited by motion-limiting stop or placed inside a container In this paper, in order to consider energy loss for an impact represented by the coefficient of restitution and duration of collision, an analytical model with hysteresis damping is introduced. Using this model, dynamic response of the system under harmonic and that under random excitations are analyzed. Some numerical results are shown. [DOI: 10.1115/1.2349557] Keywords: nonlinear vibration, dynamic damper, collision, hysteresis loop, resonance curve

The computational and experimental results of impact loading a thin wall liquid filled cylindrical target within a vacuum chamber are presented. The impact velocity ranges from 2.2 to 4.2 km/s. Both experimental and computational results are presented. It will be shown that impact dynamics and the early time fluid expansion are well modeled and understood. This includes the mass distribution and resulting expansion velocity. However, the late time dynamics, which includes the liquid breakup and droplet formation process of impacted liquid filled cylinders, is not well understood. [DOI: 10.1115/1.2353270] Keywords: impact, fluid impact, fluid dispersion, fluid-structure interaction

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.05.015 Byline: Henrik N. Latter, Gordon I. Ogilvie Keywords: Planetary rings; Collisional physics Abstract: Irregular structure in planetary rings is often attributed to the intrinsic instabilities of a homogeneous state undergoing Keplerian shear. Previously these have been analysed with simple hydrodynamic models. We instead employ a kinetic theory, in which we solve the linearised moment equations derived in Shu and Stewart 1985 for a dilute ring. This facilitates an examination of velocity anisotropy and non-Newtonian stress, and their effects on the viscous and viscous/gravitational instabilities thought to occur in Saturn's rings. Because we adopt a dilute gas model, the applicability of our results to the actual dense rings of Saturn are significantly curtailled. Nevertheless this study is a necessary preliminary before an attack on the difficult problem of dense ring dynamics. We find the Shu and Stewart formalism admits analytic stability criteria for the viscous overstability, viscous instability, and thermal instability. These criteria are compared with those of a hydrodynamic model incorporating the effective viscosity and cooling function computed from the kinetic steady state. We find the two agree in the 'hydrodynamic limit' (i.e., many collisions per orbit) but disagree when collisions are less frequent, when we expect the viscous stress to be increasingly non-Newtonian and the velocity distribution increasingly anisotropic. In particular, hydrodynamics predicts viscous overstability for a larger portion of parameter space. We also numerically solve the linearised equations of the more accurate Goldreich and Tremaine 1978 kinetic model and discover its linear stability to be qualitatively the same as that of Shu and Stewart's. Thus the simple collision operator adopted in the latter would appear to be an adequate approximation for dilute rings, at least in the linear regime. Author Affiliation: DAMTP, University of Cambridge, CMS, Wilberforce Road, Cambridge CB3 0WA, UK Article History: Received 12 December 2005; Revised 16 May 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.05.002 Byline: J.L. Ortiz (a), F.J. Aceituno (a), J.A. Quesada (b), J. Aceituno (c), M. Fernandez (a), P. Santos-Sanz (a), J.M. Trigo-Rodriguez (d)(e), J. Llorca (e)(f), F.J. Martin-Torres (g), P. MontaA[+ or -]es-Rodriguez (h), E. Palle (h) Keywords: Impact processes; Moon; Collisional physics; Cratering Abstract: We present the first redundant detection of sporadic impact flashes on the Moon from a systematic survey performed between 2001 and 2004. Our wide-field lunar monitoring allows us to estimate the impact rate of large meteoroids on the Moon as a function of the luminous energy received on Earth. It also shows that some historical well-documented mysterious lunar events fit in a clear impact context. Using these data and traditional values of the luminous efficiency for this kind of event we obtain that the impact rate on Earth of large meteoroids (0.1-10 m) would be at least one order of magnitude larger than currently thought. This discrepancy indicates that the luminous efficiency of the hypervelocity impacts is higher than 10.sup.-2, much larger than the common belief, or the latest impact fluxes are somewhat too low, or, most likely, a combination of both. Our nominal analysis implies that on Earth, collisions of bodies with masses larger than 1 kg can be as frequent as 80,000 per year and blasts larger than 15-kton could be as frequent as one per year, but this is highly dependent on the exact choice of the luminous efficiency value. As a direct application of our results, we expect that the impact flash of the SMART-1 spacecraft should be detectable from Earth with medium-sized telescopes. Author Affiliation: (a) Instituto de Astrofisica de Andalucia, CSIC, Apt. 3004, Camino Bajo de Huetor 50, 18080 Granada, Spain (b) Huetor Santillan Observatory, Avda Puente Nuevo 27, 18183 Huetor-Santillan, Granada, Spain (c) Centro Astronomico Hispano-Aleman de Calar Alto, Almeria, Apt. 04004, Almeria, Spain (d) Institut de Ciencies de l'Espai (CSIC) Campus UAB, Facultat de Ciencies, 08193 Bellaterra (Barcelona), Spain (e) Institut d'Estudis Espacials de Catalunya (IEEC), Campus UAB, Facultat de Ciencies, 08193 Bellaterra (Barcelona), Spain (f) Institut de Tecniques Energetiques, Univ. Politecnica de Catalunya, 08028 Barcelona, Spain (g) Analytical Services and Materials, Inc., 107 Research Drive, Hampton, VA 23666, USA (h) Big Bear Solar Observatory, New Jersey Institute of Technology, Big Bear City, CA 92314-9672, USA Article History: Received 24 February 2006; Revised 27 April 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.03.008 Byline: David NesvornA1/2 (a), Brian L. Enke (a), William F. Bottke (a), Daniel D. Durda (a), Erik Asphaug (b), Derek C. Richardson (c) Keywords: Asteroids; Collisional physics Abstract: Insights into collisional physics may be obtained by studying the asteroid belt, where large-scale collisions produced groups of asteroid fragments with similar orbits and spectra known as the asteroid families. Here we describe our initial study of the Karin cluster, a small asteroid family that formed 5.8[+ or -]0.2 Myr ago in the outer main belt. The Karin cluster is an ideal 'natural laboratory' for testing the codes used to simulate large-scale collisions because the observed fragments produced by the 5.8-Ma collision suffered apparently only limited dynamical and collisional erosion. To date, we have performed more than 100 hydrocode simulations of impacts with non-rotating monolithic parent bodies. We found good fits to the size-frequency distribution of the observed fragments in the Karin cluster and to the ejection speeds inferred from their orbits. These results suggest that the Karin cluster was formed by a disruption of an [approximately equal to]33-km-diameter asteroid, which represents a much larger parent body mass than previously estimated. The mass ratio between the parent body and the largest surviving fragment, (832) Karin, is [approximately equal to]0.15-0.2, corresponding to a highly catastrophic event. Most of the parent body material was ejected as fragments ranging in size from yet-to-be-discovered sub-km members of the Karin cluster to dust grains. The impactor was [approximately equal to]5.8km across. We found that the ejections speeds of smaller fragments produced by the collision were larger than those of the larger fragments. The mean ejection speeds of >3-km-diameter fragments were [approximately equal to]10ms.sup.-1. The model and observed ejection velocity fields have different morphologies perhaps pointing to a problem with our modeling and/or assumptions. We estimate that [approximately equal to]5% of the large asteroid fragments created by the collision should have satellites detectable by direct imaging (separations larger than 0.1 arcsec). We also predict a large number of ejecta binary systems with tight orbits. These binaries, located in the outer main belt, could potentially be detected by lightcurve observations. Hydrocode modeling provides important constraints on the interior structure of asteroids. Our current work suggests that the parent asteroid of the Karin cluster may have been an unfractured (or perhaps only lightly fractured) monolithic object. Simulations of impacts into fractured/rubble pile targets were so far unable to produce the observed large gap between the first and second largest fragment in the Karin cluster, and the steep slope at small sizes ([approximately equal to]6.3 differential index). On the other hand, the parent asteroid of the Karin cluster was produced by an earlier disruptive collision that created the much larger, Koronis family some 2-3 Gyr ago. Standard interpretation of hydrocode modeling then suggests that the parent asteroid of the Karin cluster should have been formed as a rubble pile from Koronis family debris. We discuss several solutions to this apparent paradox. Author Affiliation: (a) Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 400, Boulder, CO 80302, USA (b) Earth Sciences Department, University of California, 1156 High St., Santa Cruz, CA 95064, USA (c) Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA Article History: Received 19 August 2005; Revised 14 March 2006

Swept volumes of cloud droplets with radii below 20 [micro]m are calculated under conditions typical of atmospheric cloud turbulence characterized by enormous values of Reynolds numbers, high turbulent intermittency, and characteristic values of the dissipation rate. To perform the calculations, the motion equation for small droplets proposed by Maxey is generalized for Stokes numbers St > 0.1, which allows one to simulate relative droplet motion even for very high turbulence intensities typical of deep cumulus clouds. Analytical considerations show that droplet motion is fully determined by turbulent shears and the Lagrangian accelerations. A new statistical representation of a turbulent flow has been proposed based on the results of the scale analysis of turbulence characteristics and those related to the droplet motion. According to the method proposed, statistical properties of turbulent flow are represented by a set of noncorrelated samples of turbulent shears and Lagrangian accelerations. Each sample can be assigned to a certain point of the turbulent flow. Each such point can be surrounded by a small 'elementary' volume with linear length scales of the Kolmogorov length scale, in which the Lagrangian acceleration and turbulent shears can be considered as uniform in space and invariable in time. This present study (Part III) investigates the droplet collisions in a turbulent flow when hydrodynamic droplet interaction (HDI) is disregarded. Using a statistical model, long series of turbulent shears and accelerations were generated, reproducing probability distribution functions (PDF) at high Reynolds numbers, as they were obtained in recent laboratory and theoretical studies. Swept volumes of droplets are calculated for each sample of an acceleration-shear pair, and the PDF of swept volumes is calculated for turbulent parameters typical of cloud turbulence. The effect of turbulent flow intermittency manifests itself in two aspects: 1) an increase of swept volume variance with increasing Reynolds number, and 2) formation of the swept volume PDF that has a sharp maximum and an elongated tail. In spite of the fact that the magnitude of the mean swept volume increases significantly with Reynolds number and the dissipation rate, this increase does not exceed ~60% of pure gravity values even under turbulent conditions typical of strong cumulus clouds. A comparison with the classical results of Saffman and Turner is presented and discussed.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.02.008 Byline: David P. O'Brien (a)(b), Richard Greenberg (a), James E. Richardson (a) Keywords: Asteroids; Cratering; Collisional physics Abstract: O'Brien and Greenberg [O'Brien, D.P., Greenberg, R., 2005. Icarus 178, 179-212] developed a self-consistent numerical model of the collisional and dynamical evolution of the main-belt and NEA populations that was tested against a diverse range of observational and theoretical constraints. In this paper, we use those results to update the asteroid cratering model of Greenberg et al. [Greenberg, R., Nolan, M.C., Bottke, W.F., Kolvoord, R.A., Veverka, J., 1994. Icarus 107, 84-97; Greenberg, R., Bottke, W.F., Nolan, M., Geissler, P., Petit, J., Durda, D.D., Asphaug, E., Head, J., 1996. Icarus 120, 106-118], and show that the main-belt asteroid population from the O'Brien and Greenberg collisional/dynamical evolution modeling is consistent with the crater records on Gaspra, Ida, Mathilde, and Eros, the four asteroids that have been observed by spacecraft. Author Affiliation: (a) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA (b) Observatoire de Nice, B.P. 4229, 06304 Nice Cedex 4, France Article History: Received 13 April 2005; Revised 26 December 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.02.002 Byline: Satoru Yamamoto (a), Koji Wada (b), Norihisa Okabe (a), Takafumi Matsui (a) Keywords: Cratering; Impact processes; Collisional physics Abstract: We experimentally studied the formation and collapse processes of transient craters. Polycarbonate projectiles with mass of 0.49 g were impacted into the soda-lime glass sphere target (mean diameters of glass spheres are [approximately equal to]36, 72, and 220 [mu]m, respectively) using a single-stage light-gas gun. Impact velocity ranged from 11 to 329 mas.sup.-1. We found that the transient crater collapses even at laboratory scales. The shape (diameter and depth) of the transient crater differs from that of the final crater. The depth-rim diameter ratios of the final and transient craters are 0.11-0.14 and 0.26-0.27, respectively. The rim diameter of both the transient and final crater depends on target material properties; however, the ratio of final to transient crater diameter does not. This suggests that target material properties affect the formation process of transient craters even in the gravity regime, and must be taken into account when scaling experimental results to planetary scales. By observing impacts into glass sphere targets, we show that although the early stage of the excavation flow does not depend on the target material properties, the radial expansion of the cavity after the end of vertical expansion does. This suggests that the effect of target material properties is specifically important in the later part of the crater excavation and collapse. Author Affiliation: (a) Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8562, Japan (b) Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan Article History: Received 1 June 2005; Revised 31 January 2006

Thermally assisted collision-induced dissociation (TA-CID) provides increased dissociation in comparison with CID performed at ambient temperature in a quadrupole ion trap mass spectrometer. Heating the bath/collision gas during CID increases the initial internal energy of the ions and reduces the collisional cooling rate. Thus, using the same CID parameters, the parent ion can be activated to higher levels of internal energy, increasing the efficiency of dissociation and the number of dissociation pathways. The increase in the number of dissociation pathways can provide additional structural information. A consequence of the increase in initial internal energy is the ability to use less power to effect collisional activation. This allows lower [q.sub.z] values to be used and, thus, a greater mass range of product ions to be observed. TA-CID alleviates the problems associated with traditional CID and results in more available information than traditional CID.

We experimentally studied the formation and collapse processes of transient craters. Polycarbonate projectiles with mass of 0.49 g were impacted into the soda-lime glass sphere target (mean diameters of glass spheres are ~36,72, and 220 [micro]m, respectively) using a single-stage light-gas gun. Impact velocity ranged from 11 to 329 m [s.sup.-1]. We found that the transient crater collapses even at laboratory scales. The shape (diameter and depth) of the transient crater differs from that of the final crater. The depth-rim diameter ratios of the final and transient craters are 0.11-0.14 and 0.26-0.27, respectively. The rim diameter of both the transient and final crater depends on target material properties; however, the ratio of final to transient crater diameter does not. This suggests that target material properties affect the formation process of transient craters even in the gravity regime, and must be taken into account when scaling experimental results to planetary scales. By observing impacts into glass sphere targets, we show that although the early stage of the excavation flow does not depend on the target material properties, the radial expansion of the cavity after the end of vertical expansion does. This suggests that the effect of target material properties is specifically important in the later part of the crater excavation and collapse. Keywords: Cratering; Impact processes; Collisional physics

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.01.004 Byline: Masahisa Yanagisawa (a), Kouji Ohnishi (b), Yuzaburo Takamura (c), Hiroshi Masuda (c), Yoshihito Sakai (d), Miyoshi Ida (e), Makoto Adachi (e), Masayuki Ishida (f) Keywords: Impact processes; Meteoroids; Meteors; Moon; surface Abstract: The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18.sup.h28.sup.m27.sup.s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are 48[+ or -]1[degrees]N and 72[+ or -]2[degrees]E, and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have been 12 g based on a nominal model with conversion efficiency from kinetic to optical energy of 2x10.sup.-3. Extrapolation of a power law size-frequency distribution fitting the sub-centimeter Perseid meteoric particles to large meteoroids suggests that several flashes should have been observed at this optical efficiency. The detection of only one flash may indicate that the optical efficiency for Perseid lunar impact is much lower, or that the slope of the size distribution differs between large meteoroids and typical sub-centimeter meteoric particles. Author Affiliation: (a) University of Electro-Communications, Chofu-shi, Tokyo 182-8585, Japan (b) Nagano National College of Technology, Nagano-shi, Nagano 381-8550, Japan (c) Ichinomiya High School, Ichinomiya-shi, Aichi 491-8533, Japan (d) Ogawa Observatory, Ogawa-mura, Nagano 381-3301, Japan (e) Dynic AstroPark Observatory, Taga-cho, Shiga 522-0341, Japan (f) Moriyama-shi, Shiga 524-0104, Japan Article History: Received 29 September 2005; Revised 4 January 2006