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The motion of a particle in a potential well is studied when the particle is attached to an infinite elastic string. This is generic with the problem of dissipative quantum mechanics investigated by Caldeira and Leggett (Ann. Phys. 149, 374 (1983). doi:10.1016/0003-4916(83)90202-6). Besides the dissipative motion there is another scenario of interaction of the string with the particle attached. Stationary particle-string states exist with string deformations accompanying the particle. This is like polaronic states in solids. Our polaronic states in the well are non-decaying and have a continuous energy spectrum. These states may have a link to quantum electrodynamics. Key words: particle, string, interaction, spectrum, polaron. Nous etudions le mouvement d'une particule dans un puits de potentiel ou la particule est attachee a une bande elastique infinie. Ceci est en ligne avec le probleme de la mecanique quantique dissipative investiguee par Caldeira et Leggett (Ann. Phys. 149, 374 (1983). doi:10.1016/0003-4916(83)90202-6). A part la dissipation, il y a un autre scenario d'interaction entre la particule et l'elastique. Il existe des etats stationnaires particule-elastique avec des deformations de l'elastique accompagnant le mouvement de la particule. Ceci ressemble aux etats du polaron dans les solides. Nos etats de type polaron dans le puits ne se desintegrent pas et ont un spectre continu en energie. Ces etats peuvent avoir un lien avec l'EDQ/QED. [Traduit par la Redaction] Mots-cles: particule, bande, interaction, spectre, polaron., 1. Introduction Discrete energy levels of the electron in a potential well become of a finite width under the interaction with photons. This provides finite lifetimes of levels with respect [...]

Reactive rotational molding (RAM) is a process to manufacture hollow plastic articles. Comparing to rotational molding of thermoplastics, it decreases the process cycle time due to the reactivity of the system. However, the number of influent parameters is relatively high and optimization of the process is complex. During RRM, the viscosity is one of the key parameters and varies according to the polymer molecular weight due to chemical reactions. Simulation is a way to optimize this process. Prediction of the reactive flow is of great interest to optimize process conditions and wall thickness distribution of the molded part. We developed a solver based on smoothed particle hydrodynamics method. This Lagrangian meshfree method is well adapted to simulate free surface flows like those occurring in ARM. First, we validated the code comparing the simulation results to analytical Couette flow solution and experimental measurements of dam break problem. Then, we performed two-dimensional (2D) and 3D simulations to observe the influence of the change of viscosity on the flow, due to the chemical reactions. Adhesion of the polymer on the mold surface is modeled by new boundary conditions. POLYM. ENG. SCI., 53:2509-2518, 2013. 0 2013 Society of Plastics Engineers, INTRODUCTION Rotational molding is a process for manufacturing the hollow plastic parts from few centimeter to several meters (1), (2). The main advantages of this method are no residual stresses [...]

We study the interparticle potentials for few-particle systems in a scalar theory with a nonlinear mediating field of the Higgs type. We use the variational method, in a reformulated Hamiltonian formalism of quantum field theory, to derive relativistic three- and four-particle wave equations for stationary states of these systems. We show that the cubic and quartic nonlinear terms modify the attractive Yukawa potentials but do not change the attractive nature of the interaction if the mediating fields are massive. PACS Nos.: 03.70.+k, 11.10.Ef, 11.10.Lm, 14.80.Bn. Nous etudions les potentiels inter-particules pour les systemes a petit nombre de corps dans une theorie scalaire, avec un champ mediateur non lineaire de type Higgs. Nous utilisons la methode variationnelle dans une reformulation hamiltonienne de la theorie quantique des champs (QFT), afin d'obtenir les equations pour les etats stationnaires de systemes relativistes a trois et quatre corps. Nous montrons que les termes non lineaires cubique et quartique modifient le potentiel attractif de Yukawa, mais ne changent pas le caractere attractif de l'interaction si le champ mediateur est massif. [Traduit par la Redaction], Introduction Interparticle interactions in systems described by quantum field theories (QFT), such as QED or the Yukawa model and its variants (like the boson exchange model in nuclear theory), are [...]

1. Introduction In a previous paper [1] referred to as paper #1, it was demonstrated that the Lorenz-Mie (L-M) cross section for light scattering from monodisperse microspheres suspended in water [...]

A multidisciplinary approach incorporating otolith chemistry, age data, and numerical Lagrangian particle simulations indicated a single, self-recruiting population of Antarctic toothfish (Dissostichus mawsoni) in the Southeast Pacific Basin (SPB) and Ross Sea, with a life history structured by the large-scale circulation. Chemistry deposited prior to capture along otolith edges demonstrated strong environmental heterogeneity, yet the chemistry in otolith nuclei, deposited during early life, showed no differences. Age data showed only adult fish in catches on the Pacific-Antarctic Ridge in the SPB and structuring of life stages consistent with transport pathways from the northern Ross Sea. Lagrangian particle simulations predicted that early life stages following the flow in the SPB would be transported to areas in the Ross Sea where juveniles are caught, whereas the circulation would facilitate adult movement along the shelf slope and back into the SPB where spawning adults are caught. These results suggest that successfully spawning fish spend only a part of their adult life history in the Ross Sea, areas in the eastern Ross Sea contribute disproportionately to the spawning population, and areas in the southwestern Ross Sea may supply fisheries in the southern Indian Ocean. Une approche multidisciplinaire combinant la chimie des otolites, des donnees sur l'age et des simulations lagrangiennes du transport de particules indique qu'il n'y aurait qu'une seule population auto-recrutante de legine antarctique (Dissostichus mawsoni) dans le bassin du sud-est du Pacifique (SPB) et la mer de Ross, dont le cycle biologique serait structure par la circulation a grande echelle. Si la chimie des pourtours d'otolites deposes avant la capture temoigne d'une grande heterogeneite du milieu ambiant, celle des noyaux d'otolites, deposes dans les premiers stades de la vie des poissons, ne presente aucune variation. Les donnees sur l'age n'indiquent que la presence de poissons adultes dans les prises au-dessus de la dorsale Pacifique-Antarctique dans le SPB et une structuration des stades du cycle de vie qui concorde avec des voies de transport issues de la mer de Ross. Les simulations lagrangiennes de particules predisent que les legines a des stades de vie precoces qui suivent le courant dans le SPB seraient transportees vers des zones de la mer de Ross caracterisees par la prise de juveniles, alors que la circulation faciliterait le mouvement des adultes le long du talus du plateau pour ensuite retourner dans le SPB ou sont captures des adultes en frai. Ces resultats suggerent que les poissons qui reussissent a se reproduire passent seulement une partie de leur vie adulte dans la mer de Ross, qu'une part disproportionnee de la population reproductrice provient de regions de l'est de la mer de Ross et que des regions du sud-ouest de la mer de Ross pourraient contribuer aux ressources halieutiques dans le sud de l'ocean Indien. [Traduit par la Redaction], Introduction A life cycle hypothesis for Antarctic toothfish The well-documented success of spatial refuges in restoring overexploited fish stocks (e.g., Roberts et al. 2001) has focused attention on protecting marine [...]

Synchronization occurs widely in the natural and technological worlds, from the rhythm of applause and neuron firing (1) to the quantum mechanics of coupled Josephson junctions (2), but has not [...]

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology (1) to climate science (2), yet these properties are surprisingly difficult to measure in the particles' native environment. Electron microscopy requires collection of particles on a substrate (3); visible light scattering provides insufficient resolution (4); and X-ray synchrotron studies have been limited to ensembles of particles (5). Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source (6) free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins (7), vibrational energy transfer by the hydrodynamic interaction of amino acids (8), and large-scale production of nanoscale structures by flame synthesis (9)., Complex airborne particulate matter, with particle mobility diameters less than 2.5 µm, efficiently enters the human lungs, and also constitutes the second most important contribution to current global warming (10). [...]

An experimental study was carried out to investigate the effects of particles in coating suspensions on the curtain coating window. Different concentrations of poly (methyl methacrylate) (PMMA) particles were dispersed in aqueous glycerol solutions. The maximum coating speed could be extended with the addition of PMMA particles provided the dynamic wetting line was beneath the falling curtain, the so-called 'hydrodynamic assist.' The extension of the maximum coating speed was found to be strongly dependent on the particle number density. The onset of air entrainment was strongly dependent on the ability of direct contact of particles in the suspension with the air film on the moving substrate. POLYM. ENG. SCI., 52:1-11, 2012. © 2011 Society of Plastics Engineers, INTRODUCTION Curtain coating has been considered an effective means for applying a thin liquid layer on a moving substrate for decades. Brown (1) first examined the stability of a falling [...]

Trapped atomic ions have been used successfully to demonstrate (1) basic elements of universal quantum information processing. Nevertheless, scaling up such methods to achieve large-scale, universal quantum information processing (or more specialized quantum simulations (2-5)) remains challenging. The use of easily controllable and stable microwave sources, rather than complex laser systems (6,7), could remove obstacles to scalability. However, the microwave approach has drawbacks: it involves the use of magnetic-field-sensitive states, which shorten coherence times considerably, and requires large, stable magnetic field gradients. Here we show how to overcome both problems by using stationary atomic quantum states as qubits that are induced by microwave fields (that is, by dressing magnetic-field-sensitive states with microwave fields). This permits fast quantum logic, even in the presence of a small (effective) Lamb-Dicke parameter (and, therefore, moderate magnetic field gradients). We experimentally demonstrate the basic building blocks of this scheme, showing that the dressed states are long lived and that coherence times are increased by more than two orders of magnitude relative to those of bare magnetic-field-sensitive states. This improves the prospects of microwave-driven ion trap quantum information processing, and offers a route to extending coherence times in all systems that suffer from magnetic noise, such as neutral atoms, nitrogen-vacancy centres, quantum dots or circuit quantum electrodynamic systems., Using laser light for coherent manipulation of quantum bits (qubits) gives rise to fundamental issues, notably unavoidable spontaneous emission that destroys quantum coherence (8,9). The difficulty of cooling a collection [...]

Control over physical systems at the quantum level is important in fields as diverse as metrology, information processing, simulation and chemistry. For trapped atomic ions, the quantized motional and internal degrees of freedom can be coherently manipulated with laser light (1,2). Similar control is difficult to achieve with radio-frequency or microwave radiation: the essential coupling between internal degrees of freedom and motion requires significant field changes over the extent of the atoms' motion (2,3), but such changes are negligible at these frequencies for freely propagating fields. An exception is in the near field of microwave currents in structures smaller than the free-space wavelength (4,5), where stronger gradients can be generated. Here we first manipulate coherently (on timescales of 20 nanoseconds) the internal quantum states of ions held in a microfabricated trap. The controlling magnetic fields are generated by microwave currents in electrodes that are integrated into the trap structure. We also generate entanglement between the internal degrees of freedom of two atoms with a gate operation (4,6-8) suitable for general quantum computation9; the entangled state has a fidelity of 0.76(3), where the uncertainty denotes standard error of the mean. Our approach, which involves integrating the quantum control mechanism into the trapping device in a scalable manner, could be applied to quantum information processing (4), simulation (5,10) and spectroscopy (3,11)., The quantized mechanical motion and internal states of trapped atoms can be coherently controlled by laser radiation. This optical control has led to the creation of non-classical motional states (1-3), [...]

We probe the attosecond electron motion in [H.sup.+.sub.2], at short internuclear distances, by exact numerical solution of the 3D time-dependent Schrodinger equation in the Born-Oppenheimer approximation. We simulate a pump-probe experiment to calculate the energy distributions of ionized electrons. We start the experiment with a pump pulse that creates a coherent electronic wavepacket combination of the 1s[σ.sub.g] and 2p[σ.sub.u] states. We let the electronic wavepacket oscillate during a time delay Δt. In the second step of the experiment, we submit the wavepacket to an intense attosecond X-ray laser pulse. We observe an asymmetry in the energy distributions of ionized electrons that allows the mapping of the attosecond electron motion in [H.sup.+.sub.2]. PACS Nos: 33., 33.80.-b Nous sondons le mouvement electronique attoseconde dans [H.sup.+.sub.2], fixe a de courtes distances internucleaires, avec une methode non perturbative basee sur la resolution exacte de l'equation de Schrodinger dependante du temps en trois dimensions dans l'approximation de Born-Oppenheimer. Nous simulons une experience de type pompe-sonde pour calculer les distributions energetiques des electrons ionises. L'experience est declenchee a l'aide d'une premiere impulsion laser creant un paquet d'ondes electroniques coherent qui est une combinaison des etats 1s[σ.sub.g] and 2p[σ.sub.u]. Dans la deuxieme etape de l' experience, apres avoir laisser le paquet d'ondes osciller durant un certain temps delai Δt, nous le soumettons a une impulsion laser attoseconde intense dans le domaine des rayons-X. Nous observons alors une asymetrie dans les distributions des electrons ionises qui permet d'imager le mouvement electronique attoseconde dans [H.sup.+.sub.2]. [Traduit par la Redaction], 1. Introduction Irradiation of molecules by intense short laser pulses is a tool to investigate the ultrafast electron motion. The control of electron dynamics will open the way to the [...]

ABSTRACT A major source of particle number emissions is road traffic. However, scientific knowledge concerning secondary particle formation and growth of ultrafine particles within vehicle exhaust plumes is still very [...]

Nanoscale semiconductor heterostructures such as tetrapods can be used to mimic light-harvesting processes. We used single-particle light-harvesting action spectroscopy to probe the impact of particle morphology on energy transfer and carrier relaxation across a heterojunction. The generic form of an action spectrum [in our experiments, photoluminescence excitation (PLE) under absorption in CdS and emission from CdSe in nanocrystal tetrapods, rods, and spheres] was controlled by the physical shape and resulting morphological variation in the quantum confinement parameters of the nanoparticle. A correlation between single-particle PLE and physical shape as determined by scanning electron microscopy was demonstrated. Such an analysis links local structural non-uniformities such as CdS bulbs forming around the CdSe core in CdSe/CdS nanorods to a tower probability of manifesting excitation energy-dependent emission spectra, which in turn is probably related to band alignment and electron delocatization at the heterojunction interface. 10.1126/science.1198070

The classic image problem in electromagnetism involves a grounded infinite conducting plane and a point charge. The force of attraction between the point charge and the plane is identified using an equivalent-field picture of an image charge with an opposite sign equidistant behind the plane, resulting in a 1 / [r.sup.2] attractive force between the original charge and the plane. If the point charge is released from rest, it will reach the plane in a time T, which has not been calculated correctly. The inconsistency is clarified along with an improved solution to the classic image problem. Similar electromagnetism problems are also discussed. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3467049]

The impact and penetration of high speed particles with the human skin is of interest for targeted drug delivery by transdermal powder injection. However, it is often difficult to perform penetration experiments on dermal tissue using micron scale particles. To address this, a finite element model of the impact and penetration of a 2 [micro]m gold particle into the human dermis was developed and calibrated using experiments found in the literature. Using dimensional analysis, the model was linked to a larger scale steel ball-gelatin system in order to extract key material parameters for both systems and perform impact studies. In this manner, an elastic modulus of 2.25 MPa was found for skin, in good agreement with reported values from the literature. Further gelatin experiments were performed with steel, polymethyl methacrylate, titanium, and tungsten carbide balls in order to determine the effects of particle size and density on penetration depth. Both the finite element model and the steel-gelatin experiments were able to predict the penetration behavior that was found by other investigators in the study of the impact of typical particles used for vaccine delivery into the human dermis. It can therefore be concluded that scaled up systems utilizing ballistic gelatins can be used to investigate the performance of transdermal powder injection technology. [DOI: 10.1115/1.4002428] Keywords: drug delivery, mechanical properties, finite element analysis, gelatin, powder injection, skin stimulant

Single vacuum bubble collapse in subcooled water has been simulated using the moving particle semi-implicit (MPS) method in the present study. The liquid is described using moving particles, and the bubble-liquid interface was set to be the vacuum pressure boundary without interfacial heat mass transfer. The topological shape of the vacuum bubble is determined according to the location of interfacial particles. The time dependent bubble diameter, interfacial velocity, and bubble collapse time were obtained within a wide parametric range. Comparison with Rayleigh's prediction indicates a good consistency, which validates the applicability and accuracy of the MPS method. The potential void-induced water hammer pressure pulse was also evaluated, which is instructive for the cavitation erosion study. The present paper discovers fundamental characteristics of vacuum bubble hydrodynamics, and it is also instructive f or further applications of the MPS method to complicated bubble dynamics. [DOI: 10.1115/1.4001058] Keywords: vacuum bubble collapse, particle method, interfacial velocity, bubble collapse time

We solve the problem of a sphere rolling on a curved surface by mapping it to the precession of a spin 1/2 in a magnetic field of variable magnitude and direction. The mapping can be instructive for discussing both rolling and spin precession. As an example, we show that the Landau--Zener problem corresponds to the rolling of a sphere on a Cornu spiral and derive the probability of a nonadiabatic transition using this correspondence. We also discuss the adiabatic limit and the vanishing of geometric phases for rolling on curved surfaces. [c] 2o10 American Association of Physics Teachers. [DOI: 10.1119/1.3456565]

The similar forms of Coulomb's law of electrostatics and Newton's law of gravitation suggest that two oppositely charged spheres can orbit each other by means of the electrostatic force. We demonstrate electrostatic binary orbits using two oppositely charged graphite coated Styrofoam[R] spheres. The experiment was conducted on the NASA aircraft Weightless Wonder which simulates weightless conditions. Videos of 23 orbital attempts were analyzed to investigate the dynamics and orbital stability of the two sphere system. The results support predictions of a recently developed theory that establishes criteria for stable orbits between two conducting, electrically charged spheres. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3456117]

Secondary organic aerosols (SOA) formed in the atmosphere from the condensation of semivolatile oxidation products are a significant component of airborne particles which have deleterious effects on health, visibility, and climate. In this study, atmospheric solids analysis probe mass spectrometry (ASAP-MS) is applied for the first time to the identification of organics in particles from laboratory systems as well as from ambient air. SOA were generated in the laboratory from the ozonolysis of [alpha]-pinene and isoprene, as well as from N[O.sub.3] oxidation of [alpha]-pinene, and ambient air was sampled at forested and suburban sites. Particles were collected by impaction on ZnSe disks, analyzed by Fourier transform-infrared spectroscopy (FT-IR) and then transferred to an ASAP-MS probe for further analysis. ASAP-MS data for the 'laboratory-generated samples show peaks from well-known products of these reactions, and higher molecular weight oligomers are present in both laboratory and ambient samples. Oligomeric products are shown to be present in the NO3 reaction products for the first time. A major advantage of this technique is that minimal sample preparation is required, and complementary information from nondestructive techniques such as FT-IR can be obtained on the same samples. In addition, a dedicated instrument is not required for particle analysis. This work establishes that ASAP-MS will be useful for identification of organic components of SOA in a variety of field and laboratory studies. 10.1021/ac101028j

We study the electron propagator in quantum electrodynamics in one and two spatial dimensions in the presence of external electromagnetic fields. In this case, the propagator is not diagonal in momentum space. We obtain the propagator on the basis of the eigenfunctions of the operator [([gamma]-[PI]).sup.2] in terms of which the propagator acquires a free form. [[PI].sub.[mu]] is the canonical momentum operator and [[gamma].sup.[mu]] are the Dirac matrices. In two dimensions, we work with an irreducible representation of the Clifford algebra and consider to all orders the effects of an arbitrary magnetic field perpendicular to the plane of motion of the electrons. We then discuss the special cases of a uniform magnetic field and an exponentially damped static magnetic field. These cases are relevant to graphene in the massless limit. We further consider the electron propagator for the massive Schwinger model and incorporate the effects of a constant electric field to all orders. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3311656]

In the Baltic Sea ice, the spectral absorption coefficients for particulate matter (PM) were about two times higher at ultraviolet wavelengths than at photosynthetically available radiation (PAR) wavelengths. PM absorption spectra included significant absorption by mycosporine-like amino acids (MAAs) between 320 and 345 nm. In the surface ice layer, the concentration of MAAs (1.37 [micro]g [L.sup.-1]) was similar to that of chlorophyll a, resulting in a MAAs-to-chlorophyll a ratio as high as 0.65. Ultraviolet radiation (UVR) intensity and the ratio of UVR to PAR had a strong relationship with MAAs concentration ([R.sup.2] = 0.97, n = 3) in the ice. In the surface ice layer, PM and especially MAAs dominated the absorption (absorption coefficient at 325 nm: 0.73 [m.sup.-1]). In the columnar ice layers, colored dissolved organic matter was the most significant absorber in the UVR (< 380 nm) (absorption coefficient at 325 nm: 1.5 [m.sup.-1]). Our measurements and modeling of UVR and PAR in Baltic Sea ice show that organic matter, both particulate and dissolved, influences the optical properties of sea ice and strongly modifies the UVR exposure of biological communities in and under snow-free sea ice.

The extent to which sinking particles disaggregate and exchange with surrounding material affects the efficiency of particulate organic carbon export to the deep sea. In 2003 and 2005, we compared the pigment and amino acid compositions of sediment trap and in situ pump samples collected in the northwest Mediterranean Sea to assess exchange between sinking and suspended particles. While sediment traps collected only sinking particles, in situ pumps collected both larger (> 70-[micro]m) particles, believed to represent the sinking fraction, as well as smaller (1-70-[micro]m) particles, believed to represent the suspended fraction. The organic compound compositions of sinking and suspended particles were very different and remained consistently so with depth, suggesting that exchange between them was limited. This difference was particularly pronounced during the high flux periods in spring. Sinking particles appeared to be composed of many fecal pellets and a few phytoplankton aggregates, and were enriched in diatom indicators. Suspended particles appeared to be more enriched in fresh phytoplankton and contained indicators of calcium carbonate bearing organisms. During the low-flux summer period, the contribution of fecal pellet indicators to sinking particles was lower, whereas the contribution of microbial degradation products in both particle types was higher, possibly indicating greater exchange during periods of low flux when fecal pellets were not as abundant. Results from this study suggest that fecal pellets, although already degraded upon formation, are more robust than phytoplankton aggregates and, therefore, more likely to resist disaggregation and further decomposition during transit through the water column.

Acantharian cysts were discovered in sediment trap samples from spring 2007 at 2000 m in the Iceland Basin. Although these single-celled organisms contribute to particulate organic matter flux in the upper mesopelagic, their contribution to bathypelagic particle flux has previously been found negligible. Four time-series sediment traps were deployed and all collected acantharian cysts, which are reproductive structures. Across all traps, cysts contributed on average 3-22%, and 4-24% of particulate organic carbon and nitrogen (POC and PON) flux, respectively, during three separate collection intervals (the maximum contribution in any one trap was 48% for POC and 59% for PON). Strontium (Sr) flux during these 6 weeks reached 3 mg [m.sup.-2] [d.sup.-1]. The acantharian celestite (SrS[O.sup.4]) skeleton clearly does not always dissolve in the mesopelagic as often thought, and their cysts can contribute significantly to particle flux at bathypelagic depths during specific flux events. Their large size (~ 1 mm) and mineral ballast result in a sinking rate of ~ 500 m [d.sup.-1]; hence, they reach the bathypelagic before dissolving. Our findings are consistent with a vertical profile of salinity-normalized Sr concentration in the Iceland Basin, which shows a maximum at 1700 m. Profiles of salinity-normalized Sr concentration in the subarctic Pacific reach maxima at [less than or equal to] 1500 m, suggesting that Acantharia might contribute to the bathypelagic particle flux there as well. We hypothesize that Acantharia at high latitudes use rapid, deep sedimentation of reproductive cysts during phytoplankton blooms so that juveniles can exploit the large quantity of organic matter that sinks rapidly to the deep sea following a bloom.

Horizontal dispersion mechanisms must be well defined in order to determine the origin and fate of heterogeneous distributions of biogeochemical material. Here data from an intensive field campaign in Valle de Bravo Reservoir, Mexico, was used to run a three-dimensional hydrodynamic model, and the simulated flow field was used to characterize the horizontal motions and investigate the dispersal of waterborne particles driven by the dominant circulation patterns. The surface layer horizontal motions included an oscillatory component associated with two basin-scale internal wave modes and a spatially and temporally complex flow field associated mostly with topographic circulation. Modeling of particle advection by the horizontal motions led to areal dispersal rates of O(1) to O(10) [m.sup.2] [s.sup.-l], comparable with bulk dispersion rates observed in other surface layer studies. The aperiodic topographic component of the horizontal flow field, not the oscillatory motion or a combination of both, sustained most of the particle dispersal. In particular, local flow features, such as stagnation points, were shown to be a significant driver for horizontal dispersion and should be taken into consideration when analyzing horizontal distributions of waterborne material.

Analysis of several million particulate volume scattering functions (VSFs) from different field sites around the world's oceans and coastlines revealed that the shape of the VSF in the backward direction was remarkably consistent (5% or less variability at angles between 90[degrees] and 170[degrees]). In agreement with theoretical models and past field measurements, the variability of the VSF shape (the VSF normalized to the backscattering coefficient) was found to be lowest between 110[degrees] and 120[degrees]. This study concludes that under most oceanic conditions, estimates of the particulate backscattering coefficient, using single angle scattering measurements near 110[degrees] to 120[degrees] and suitable conversion factors, are justified and should have a maximum uncertainty of less than a few percent once instrument noise is accounted for. OCIS codes: 010.4450, 000.2170, 120.5820, 290.1350, 350.4990.

ABSTRACT Source apportionment analyses were carried out by means of receptor modeling techniques to determine the contribution of major fine particulate matter ([PM.sub.2.5]) sources found at six sites in Mexico [...]

ABSTRACT Concurrent 24-hr samples of particulate matter of median aerodynamic diameter less than 10 µm ([PM.sub.10]) were collected over a 10-day period in August 2000 at four sites along a [...]

When small particles (e.g., flour, pollen, etc.) come in contact with a liquid surface, they immediately disperse. The dispersion can occur so quickly that it appears explosive, especially for small particles on the surface of mobile liquids like water. This explosive dispersion is the consequence of capillary force pulling particles into the interface causing them to accelerate to a relatively large velocity. The maximum velocity increases with decreasing particle size; for nanometer-sized particles (e.g., viruses and proteins), the velocity on an air-water interface can be as large as [approximately equal to] 47 m/s. We also show that particles oscillate at a relatively high frequency about their floating equilibrium before coming to stop under viscous drag. The observed dispersion is a result of strong repulsive hydrodynamic forces that arise because of these oscillations. adsorption | capillarity | fluid-fluid interfaces | monolayers doi/10.1073/pnas.0910343106

Robust control over the positions, orientations, and assembly of nonspherical colloids may aid in the creation of new types of structured composite materials that are important from both technological and fundamental standpoints. With the use of lithographically fabricated equilateral polygonal platelets, we demonstrate that colloidal interactions and self-assembly in anisotropic nematic fluids can be effectively tailored via control over the particles' shapes. The particles disturb the uniform alignment of the surrounding nematic host, resulting in both a distinct equilibrium alignment and highly directional pair interactions. Interparticte forces between polygonal platelets exhibit either dipolar or quadrupolar symmetries, depending on whether their number of sides is odd or even, and drive the assembly of a number of ensuing self-assembled colloidal structures. 20 May 2009; accepted 15 September 2009 10.1126/science.1176587

We describe a simple mechanical system that operates as a ponderomotive particle trap. The system consists of a circular hoop and a frictionless bead, with the hoop rotating about a horizontal axis lying in the plane of the hoop. The system is analyzed in the ideal case of small displacements from the minimum, and the motion of the particle is shown to satisfy the Mathieu equation. If the axis of rotation is tangential to the hoop, the system is an exact analog to the rf Paul ion trap. Various complicating factors such as anharmonic terms, friction, and noise are considered. A working model of the system was constructed using a ball-bearing rolling in a tube along the outside of a bicycle rim. The apparatus demonstrates the operation of an rf Paul trap by reproducing the dynamics of trapped atomic ions and illustrating the manner in which the electric potential varies with time. [DOI: 10.1119/1.3167216]

The effect of dextran nanoparticles on the conformation and compaction of single DNA molecules confined in a nanochannel was investigated with fluorescence microscopy. It was observed that the DNA molecules elongate and eventually condense into a compact form with increasing volume fraction of the crowding agent. Under crowded conditions, the channel diameter is effectively reduced, which is interpreted in terms of depletion in DNA segment density in the interfacial region next to the channel wall. Confinement in a nanochannel also facilitates compaction with a neutral crowding agent at low ionic strength. The threshold volume fraction for condensation is proportional to the size of the nanoparticle, due to depletion induced attraction between DNA segments. We found that the effect of crowding is not only related to the coliigative properties of the agent and that confinement is also important. It is the interplay between anisotropic confinement and osmotic pressure which gives the elongated conformation and the possibility for condensation at low ionic strength. depletion | dextran | fluorescence | nanofluidics | nanoparticles

Excitation functions are measured for a-particle-induced reactions on [sup.197]Au, [sup.181]Ta, [sup.nat]In, and [sup.93]Nb in the energy region 18 to 60 MeV using the activation method and γ-ray spectrometry. The experimental results are compared with semiclassical model codes, STAPRE, ALICE-91, and COMPLET. These models take into account compound nuclei as well as pre-equilibrium emissions. The angular momentum removal effects have also been included in the COMPLET code. The Monte Carlo simulation code PACE4 is also employed for the calculations of equilibrium cross sections. In the case of neutron emission channels, both the model codes give fairly good agreement. The COMPLET code on the other hand, explains the a-particle emission channels in a more convincing manner. PACS Nos: 25.55.Hp, 27.60.+j Nous avons utilise la methode d'activation et la spectroscopie gamma pour mesurer les fonctions d'excitation des reactions induites par articules alpha sur [sup.197]Au, [sup.181]Ta, [sup.nat]In et [sup.93]Nb dans la region entre 18 et 60 MeV. Nous avons compare ces fonctions d'excitation avec les resultats obtenus des logiciels semi-classiques, tel STAPRE, avec trois options differentes pour la densite de niveaux. Les fonctions d'excitation mesurees ont aussi ete comparees aux predictions des modeles semi-classiques ALICE-91 et COMPLET. Ce modele tient compte de la formation d'un noyau compose et d'emissions pre-equilibre. Les effets de transfert de moment cinetique sont egalement inclus dans le logiciel COMPLET. Nous avons utilise le logiciel de simulation Monte-Carlo PACE4 pour calculer les sections efficaces de pre-equilibre. Les deux logiciels donnent de bons resultats pour les canaux d'emission de neutrons, alors que COMPLET est meilleur dans la description des canaux d'emission alpha. [Traduit par la Redaction], 1. Introduction Nuclear level density is important in understanding the statistical nature of a large number of nuclear reactions over a wide energy range. Initially, the nuclear level density parameter [...]

The exact solutions of the Duffin-Kemmer-Petiau (DKP) oscillator for spin-0 particles have been studied in noncommutative phase space. The results show that due to the noncommutative effect, the energy spectrum of the DKP oscillator for spin-0 particles is no longer degenerate. In addition, we obtain the nonrelativistic limit of the energy spectrum. PACS Nos: 02.40.Gh, 03.65.-w, 03.65.Ge, 03.65.Pm Nous avons etudie sur un espace de phase non commutatif les solutions exactes de l'oscillateur Duffin-Kemmer-Petiau (DKP) pour des particules de spin zero. Les resultats montrent qu'a cause de la non commutativite, le spectre d'energie de particules massives de spin nul dans le potentiel d'oscillateur de Dirac n'est pas degenere. Nous obtenons aussi la limite non relativiste du spectre d'energie. [Traduit par la Redaction], 1. Introduction It is well known that the Duffin-Kemmer-Petiau (DKP) equation is a first-order relativistic wave equation for spin 0 and 1 bosons [1-3], which describes some problems in nuclear [...]

The Klein-Gordon equation in the presence of a spatially one-dimensional Hulthen potential is solved exactly and the scattering solutions are obtained in terms of hypergeometric functions. The transmission coefficient is derived by the matching conditions on the wave functions and the conditions for the existence of transmission resonances are investigated. It is shown how the zero-reflection condition depends on the shape of the potential. PACS Nos: 03.65.Nk, 03.65.Pm Nous solutionnons exactement l'equation de Klein-Gordon en 1+1 D avec un potentiel a une dimension spatiale de Hulthen et nous obtenons les solutions de diffusion sous la forme de fonctions hypergeometriques. Le coefficient de transmission est obtenu en mariant les conditions sur les fonctions d'onde et nous etudions les conditions d'existence d'une transmission resonante. Nous montrons que la condition de reflexion nulle depend de la forme du potentiel. [Traduit par la Redaction], The study of low-momentum scattering in the Schrodinger equation in one-dimensional even potentials shows that, as momentum goes to zero, the reflection coefficient goes to unity unless the potential V(x) [...]

Biological electrospray techniques are rapidly becoming a promising means for controlling living organisms in applications ranging from mass spectrometry to developmental biology. We investigated the generation characteristics of airborne MS2 bacteriophage particles 1 h. Compared with the generation characteristics observed using the previous nebulization process (51.5 [ + or -] 0.86 nm GMD), this electrospray technique produced nonagglomerated particles, resulting in a narrow size range of generated particles. The total MS2 particle number concentration and GMD increased with changes in the suspension flow rate from 5 to 25 [micro]L/h. As the applied voltage increased in cone-jet mode, the GMD and culturable bacteriophage concentration decreased slightly. Our investigation shows that the electrospray process, driven by high-intensity electric fields, can be used for nanometer-sized living organisms.

Particle crushing can adversely affect geotechnical system performance; examples include clogging in wells, pile shaft capacity degradation, and postconstruction settlements. The generation of fines results in volumetric compression and a reduction hydraulic conductivity, which is important for geotechnical systems whose performance is directly dependent on pore pressure dissipation, groundwater flow, or hydraulic pumping. Knowledge of hydraulic conductivity change is poorly understood due to limited experimental data, and an ability to predict this change is lacking. The role of single particle properties, initial specimen state conditions, and loading conditions on the evolution of hydraulic conductivity with particle crushing was examined experimentally. Specimen response exhibited an overshoot behavior and the convergence to a unique condition independent of initial relative density, gradation, and particle shape. The hydraulic conductivity decreased by 2-3 times before specimen yield, and by 2-3 orders of magnitude after specimen yield. Empirical correlations were developed to estimate the change in hydraulic conductivity given the initial permeability and select crushing parameter values at the stress level of interest. CE Database subject headings: Crushing; Hydraulic conductivity; Compression; Sand; Particles.

This work deals with thermophoresis particle deposition and thermal radiation interaction on mixed convection heat and mass transfer by steady laminar boundary-layer flow over a nonisothermal vertical flat plate embedded in a fluid-saturated porous medium. The governing partial-differential equations are transformed into nonsimilar form by using a special transformation and then solved numerically by using an implicit finite-difference method. Different results are obtained and displayed graphically to explain the effect of various physical parameters on the wall thermophoretic deposition velocity, Nusselt numbers, and temperature and concentration profiles. It was found that the increasing of radiation parameter or dimensionless temperature ratio heated the fluid and decreased the temperature gradients near the impermeable wall, which increased the local Nusselt numbers and decreased the wall thermophoresis velocities. It was also found that the effect of power indexes of either temperatures or concentration enhances both local Nusselt numbers and wall thermophoresis velocities. Comparison with previously published work in the limits of absent thermophoresis and thermal radiation effects shows excellent agreement. PACS Nos.: 44.20.+b, 44.30+v, 44.25.+f, 44.40+a Nous etudions ici le depot de particules par therrmophorese et l'interaction de radiation thermique sur un transfert mixte de chaleur et de masse par une mince couche laminaire limite en ecoulement stationnaire sur une surface plane verticale non isotherme plongee dans un milieu poreux sature de fluide. Les equations maitresses differentielles sont transforme es en une forme non similaire en utilisant une transformation speciale que nous solutionnons alors par une methode numerique aux differences finies. Les resultats obtenus sont presentes graphiquement pour mettre en evidence le role des differents parametres physiques sur la vitesse de depot par thermophorese sur la surface verticale, comme le nombre de Nusselt et les profils de temperature et de concentration. Nous trouvons qu'augmenter les parametres de radiation ou le rapport sans dimension de temperature chauffe le fluide et diminue le gradient de temperature pres du mur impermeable, ce qui augmente le nombre de Nusselt local et diminue la vitesse de depot. Nous trouvons aussi que les effets des indices de puissance soit de la temperature, soit de la concentration augmentent a la fois le nombre de Nusselt local et le vitesse de depot. La comparaison avec des resultats publies dans la limite sans radiation therrmique ni thermophorese montre un excellent accord. [Traduit par la Redaction], 1. Introduction Thermophoresis is a phenomenon, which causes small particles to be driven away from a hot surface and toward a cold one. Small particles, such as dust, when suspended [...]

We describe a new method for simultaneously collecting particles in exhaled air for subsequent chemical analysis and measuring their size distribution. After forced exhalation, particles were counted and collected in spots on silicon wafers with a cascade impactor. Several phospholipids were identified by time-of-flight secondary ion mass spectrometric analysis of the collected spots, suggesting that the particles originated from the lower airways. The amount of particles collected in ten exhalations was sufficient for characterizing the phospholipid composition. The feasibility of the technique in respiratory research is demonstrated by analysis of the phospholipid composition of exhaled particles from healthy controls, patients with asthma, and patients with cystic fibrosis. We believe this technology will be useful for monitoring patients with respiratory disease and has a high potential to detect new biomarkers in exhaled air.

Mesoscale hierarchical hetical structures with diverse functions are abundant in nature. Here we show how spontaneous helicity can be induced in a synthetic polymeric nanobristle assembling in an evaporating liquid. We use a simple theoretical model to characterize the geometry, stiffness, and surface properties of the pillars that favor the adhesive self-organization of bundles with pillars wound around each other. The process can be controlled to yield highly ordered helical dusters with a unique structural hierarchy that arises from the sequential assembly of self-similar coiled building brooks over multiple length scales. We demonstrate their function in the context of self-assembly into previously unseen structures with uniform, periodic patterns and controlled handedness and as an efficient particle-trapping and adhesive system.

We describe a hydrophoretic device that uses rotational flows induced by regularly patterned obstacles only on the top wall for preparing samples of biological particles, including micrometer and submicrometer particles, and DNA molecules. Many of the current continuous separation devices based on physical fields are limited to the separation of cells and micrometer-sized particles due to their dependence on a particle volume, and the purely hydrodynamic separation of macromolecules such as DNA or protein complexes remains a challenge. Hydrophoresis is entirely based on hydrodynamics using rotational flows induced by anisotropic obstacles. Different sizes of micrometer and submicrometer beads, as well as DNA molecules, were separated into distinct trajectories using two kinds of hindrance mechanisms. Continuous separation of these particles was achieved using the obstacles, demonstrating the potential of hydrophoresis for biological sample preparation on the micro- and nanoscales, with the advantages of continuous flow and sheathless passive operation.

This paper presents a study of the angle of repose of a two-dimensional particle system under the Earth and Moon gravity fields. The particles interact with electrostatic forces in addition to friction. A two-dimensional discrete element method is used in this analysis with two particle shapes, circular and noncircular. The noncircular shape is constructed with overlapping pairs of disks. For the range of parameters studied, the angle of repose shows little sensitivity to gravity. The sensitivity to friction and electrostatic charges can be either significant or negligible, depending on the range of these values. For each contact friction, there is a threshold of electric charge on the particle such that the angle of repose suddenly drops to zero when the charge exceeds this threshold. The existence of this threshold, once validated in three-dimensional systems, may provide an opportunity to measure the electrostatic charges of the lunar dust in situ. DOI: 10.1061/(ASCE)0893-1321(2009)22:1(10) CE Database subject headings: Moon: Simulation: Particles: Gravity.

Optical diffusometry is a technique used for measuring diffusion. This work explores the possibility of directly measuring diffusion coefficients of submicron particles for pathogen detection. The diffusion coefficient of these particles is a function of the drag coefficient of the particle at constant temperatures. Particles introduced into a sample containing an analyte bind with the analyte if functionalized with the appropriate antibodies. This leads to an increase in the hydrodynamic drag of the particles and hence a decrease in their diffusion coefficient. This study uses the above principle to effectively measure the diffusion coefficient of the particles using two different experimental approaches. The measured reduction in the diffusion coefficient can be correlated to the amount of analyte present and thus forms the basis of biological agent detection. Sensitivity to experimental conditions is analyzed. It is observed that alternative techniques such as optical trapping hold promise: the diffusive behavior of particles in optical traps is found to be quantitatively different from that of a free particle. Hence preconditions are identified to make optical trapping appropriate for agent detection. [DOI: 10.1115/1.2969430]

Aerosols serve as a source of cloud condensation nuclei (CCN) and influence the microphysical properties of clouds. In the case of orographic clouds, it is suspected that aerosol--cloud interactions reduce the amount of precipitation on the upslope side of the mountain and enhance the precipitation on the downslope side when the number of aerosols is increased. The net effect may lead to a shift of the precipitation distribution toward the leeward side of mountain ranges, which affects the hydrological cycle on the local scale. In this study aerosol-cloud interactions in warm-phase clouds and the possible impact on the orographic precipitation distribution are investigated. Herein, simulations of moist orographic flow over topography are conducted and the influence of anthropogenic aerosols on the orographic precipitation formation is analyzed. The degree of aerosol pollution is prescribed by different aerosol spectra that are representative for central Switzerland. The simulations are performed with the Consortium for Small-Scale Modeling's mesoscale nonhydrostatic limited-area weather prediction model (COSMO) with a horizontal grid spacing of 2 km and a fully coupled aerosol--cloud parameterization. It is found that an increase in the aerosol load leads to a downstream shift of the orographic precipitation distribution and to an increase in the spillover factor. A reduction of warm-phase orographic precipitation is observed at the upslope side of the mountain. The downslope precipitation enhancement depends critically on the width of the mountain and on the flow dynamics. In the case of orographic precipitation induced by stably stratified unblocked flow, the loss in upslope precipitation is not compensated by leeward precipitation enhancement. In contrast, flow blocking may lead to leeward precipitation enhancement and eventually to a compensation of the upslope precipitation loss. The simulations also indicate that latent heat effects induced by aerosol--cloud--precipitation interactions may considerably affect the orographic flow dynamics and consequently feed back on the orographic precipitation development.

Mixing between shallow cumulus clouds and their environment is studied using large-eddy simulations. The origin of in-cloud air is studied by two distinct methods: 1) by analyzing conserved variable mixing diagrams (Paluch diagrams) and 2) by tracing back cloud-air parcels represented by massless Lagrangian particles that follow the flow. The obtained Paluch diagrams are found to be similar to many results in the literature, but the source of entrained air found by particle tracking deviates from the source inferred from the Paluch analysis. Whereas the classical Paluch analysis seems to provide some evidence for cloud-top mixing, particle tracking shows that virtually all mixing occurs laterally. Particle trajectories averaged over the entire cloud ensemble also clearly indicate the absence of significant cloud-top mixing in shallow cumulus clouds.