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A solution of electromagnetic four-potential for polarized photon is obtained by solving its wave equations in elliptic cylindrical coordinates. An explicit energy wave function for the photon is presented in the form of a linear combination of the electric field and magnetic field from the solution. This wave function is used to calculate the angular momentum value of the photon. The elliptic coordinate parameter, a, for the photon is considered to be equal to a quarter of its wavelength., 1 Introduction Photon as a quantum of light has attracted many researchers to develop explanations on its behaviors and to experiment to determine its properties. The photon as a fundamental [...]

The utility of electrically-driven peristaltic flow to enhance the mechanical efficiency of a biological system is diverse. This motivates us to discuss the mathematical modelling of magnetic fluid flow via complex wavy walls. Additionally, an electric field is also applied in the axial direction. The non-Newtonian couple stress fluid model is used here. The analysis is performed under the Debye-Huckel linearization. The governing equations are modelled under long wavelength and low Reynolds number assumptions. A closed form solution is obtained for the stream function, which is further used to calculate other physical quantities. To observe the remarkable effects of eminent parameters on the velocity distribution and volumetric flow rate, we have plotted graphs in both the two- and three-dimensional axes. A comparison between the simple and complex peristaltic waves is also provided. This study is very useful for designing a non-uniform microperistaltic pump in which flow can be controlled by electromagnetic forces. Key words: peristaltic waves, transient magnetic field, axial electric field, creeping flow, Debye-Huckel linearization, microchannel, electro-osmosis, complex wavy boundary. La stimulation electrostatique des flots/ecoulements peristaltique, afin d'ameliorer l'efficience d'un systeme biologique, a plusieurs utilisations biologiques. Ceci nous motive a analyser la modelisation mathematique du flot d'un fluide magnetique contre des parois ondulees complexes. De plus, nous appliquons un champ electrique dans la direction axiale. Nous utilisons ici le modele du fluide non newtonien sous contrainte. L'analyse se fait a l'aide de la linearisation de Debye-Huckel. Les equations directrices sont restreintes aux approximations de grandes longueurs d'onde et de faible nombre de Reynolds. Une solution analytique est obtenue pour la fonction de courant, qui est alors utilisee pour calculer d'autres quantites physiques. Afin d'observer les effets remarquables des parametres principaux sur la distribution de vitesse et le taux de flot volumetrique, nous utilisons des presentations graphiques a deux et trois axes. Nous faisons aussi une comparaison entre ondes peristaltiques simples et complexes. Cette etude se veut tres utile pour le design de pompes micro-peristaltiques non uniformes, dans lesquelles le flot peut etre controle par des forces electromagnetiques. [Traduit par la Redaction] Mots-cles : ondes peristaltiques, champ magnetique transitoire, champ electrique axial, ecoulement par fluage, linearisation de Debye-Huckel, micro-canal, electro-osmose, frontiere a ondulation complexe., 1. Introduction There have been many developments in the field of fluid mechanics [1, 2] in last few decades. The combination of this field with electric and magnetic forces give [...]

Quantum mechanics ascribes to the ground state of the electromagnetic radiation.sup.1 zero-point electric field fluctuations that permeate empty space at all frequencies. No energy can be extracted from the ground state of a system, and therefore these fluctuations cannot be measured directly with an intensity detector. The experimental proof of their existence therefore came from more indirect evidence, such as the Lamb shift.sup.2,3,4, the Casimir force between close conductors.sup.5,6,7 or spontaneous emission.sup.1,8. A direct method of determining the spectral characteristics of vacuum field fluctuations has so far been missing. Here we perform a direct measurement of the field correlation on these fluctuations in the terahertz frequency range by using electro-optic detection.sup.9 in a nonlinear crystal placed in a cryogenic environment. We investigate their temporal and spatial coherence, which, at zero time delay and spatial distance, has a peak value of 6.2 × 10.sup.-2 volts squared per square metre, corresponding to a fluctuating vacuum field.sup.10,11 of 0.25 volts per metre. With this measurement, we determine the spectral components of the ground state of electromagnetic radiation within the bandwidth of our electro-optic detection. Electro-optic detection in a nonlinear crystal is used to measure coherence properties of vacuum fluctuations of the electromagnetic field and deduce the spectrum of the ground state of electromagnetic radiation., Author(s): Ileana-Cristina Benea-Chelmus [sup.1] , Francesca Fabiana Settembrini [sup.1] , Giacomo Scalari [sup.1] , Jérôme Faist [sup.1] Author Affiliations: (1) ETH Zurich, Institute of Quantum Electronics, Zurich, Switzerland Main The [...]

This paper addresses the photodetachment dynamics of a negative ion in a time-dependent electric field based on the semiclassical open-orbit theory. The photodetached electron probability density in a real time domain is studied in a gradient electric field for the first time. It is found that because of the influence of the gradient electric field, two or more electron trajectories can arrive at a given point on the detector, and the interference effect between these electron trajectories causes oscillatory structures in the electron probability density. Our calculation results suggest that when the external electric field changes very slowly with time, only two electron trajectories can arrive at a given point on the detector and the electron probability density exhibits a regular two-term oscillatory pattern. However, when the electric field changes quickly with time, four electron trajectories can reach the detector, which makes the oscillatory structures in the electron probability density become much more complicated. In addition, the electric field strength, photon energy, and the position of the detector can affect the electron probability density of this system sensitively. Our study provides a clear and intuitive picture for the photodetachment dynamics of the negative ion in the external electric field from a time-dependent viewpoint and may guide the future experimental researches on the photodetachment microscopy of negative ions in the time-dependent electric field. Key words: photodetachment dynamics, time-dependent electric field, semiclassical open-orbit theory. Nous utilisons ici la theorie de l'orbite ouverte semi-classique dans une application a la dynamique du photodetachement de l'ion negatif dans un champ electrique variant dans le temps. C'est la premiere fois qu'est etudiee la densite de probabilite du photodetachement de l'electron dans un gradient de champ electrique. Nous trouvons qu'a cause du gradient de champ electrique, deux ou plus de deux trajectoires electroniques peuvent arriver en un point donne du detecteur et l'effet d'interference entre ces trajectoires electroniques cause des oscillations dans la densite de probabilite de l'electron. Les resultats de nos calculs suggerent que si le champ exterieur varie tres lentement dans le temps (statique et quasi-statique), alors seulement deux trajectoires electroniques peuvent arriver au meme point du detecteur et la densite de probabilite de l'electron a un patron regulier d'interference a deux ondes. Cependant, lorsque le champ electrique varie rapidement, quatre trajectoires peuvent joindre le meme point du detecteur et la densite de probabilite de l'electron devient beaucoup plus compliquee. De plus, la force du champ electrique, l'energie du photon et la position du detecteur affectent sensiblement la densite de probabilite. Notre etude donne une vue claire et intuitive de la dynamique du photodetachement d'un ion negatif dans un champ electrique variant dans le temps et peut servir de guide pour des recherches experimentales ?i venir sur la microscopie du photodetachement d'ions negatifs en presence d'un champ electrique variant dans le temps. [Traduit par la Redaction] Mots-cles : champ electrique variant dans le temps, theorie de l'orbite ouverte semi-classique, dynamique du photodetachement, ion negatif, densite de probabilite., 1. Introduction A significant achievement of the photodetachment microscopy technique is that it allows people to observe macroscopic images of the electron probability density on the detector clearly. These direct [...]

Switching of static friction and adhesion of a liquid drop on a corrugated solid boron nitride surface is linked to the intercalation of hydrogen, which changes the electric field of in-plane dipole rings and thus reduces the adsorption energy. Stiction versus adhesion in a single liquid drop Stiction, or static friction, is the force required to persuade an object to start sliding across a surface. It is technologically important in devices with moving parts in contact, but is not well understood. Stijn Mertens et al. describe an inorganic model system for the study of the relationships between surface wetting, stiction, adhesion and lubrication. The system is a hexagonal boron nitride monolayer that can be electrochemically switched by intercalation of hydrogen between a corrugated and a flat morphology. The change in the surface structure of the boron nitride alters the adhesion and its balance with stiction of an aqueous drop sliding across the monolayer. The work of adhesion increases in going from the flat to the corrugated surface, whereas the stiction threshold does not change significantly. Thus the authors make a quantitative connection between the macroscopic properties of stiction and adhesion as a result of structural control at the atomic scale. When a gecko moves on a ceiling it makes use of adhesion and stiction. Stiction--static friction--is experienced on microscopic and macroscopic scales and is related to adhesion and sliding friction.sup.1. Although important for most locomotive processes, the concepts of adhesion, stiction and sliding friction are often only empirically correlated. A more detailed understanding of these concepts will, for example, help to improve the design of increasingly smaller devices such as micro- and nanoelectromechanical switches.sup.2. Here we show how stiction and adhesion are related for a liquid drop on a hexagonal boron nitride monolayer on rhodium.sup.3, by measuring dynamic contact angles in two distinct states of the solid-liquid interface: a corrugated state in the absence of hydrogen intercalation and an intercalation-induced flat state. Stiction and adhesion can be reversibly switched by applying different electrochemical potentials to the sample, causing atomic hydrogen to be intercalated or not. We ascribe the change in adhesion to a change in lateral electric field of in-plane two-nanometre dipole rings.sup.4, because it cannot be explained by the change in surface roughness known from the Wenzel model.sup.5. Although the change in adhesion can be calculated for the system we study.sup.6, it is not yet possible to determine the stiction at such a solid-liquid interface using ab initio methods. The inorganic hybrid of hexagonal boron nitride and rhodium is very stable and represents a new class of switchable surfaces with the potential for application in the study of adhesion, friction and lubrication., Author(s): Stijn F. L. Mertens [sup.1] [sup.2] , Adrian Hemmi [sup.3] , Stefan Muff [sup.3] , Oliver Gröning [sup.4] , Steven De Feyter [sup.1] , Jürg Osterwalder [sup.3] , Thomas [...]

To be able to control the properties of a system that has strong electron-electron interactions using only an external electric field would be ideal, but the material must be thin enough to avoid shielding of the electric field in the bulk material; here pure electric-field control of the charge-density wave and superconductivity transition temperatures is achieved by electrolyte gating through an electric-field double layer transistor in the two-dimensional material 1T-TiSe.sub.2. Electronic behavior in 1T-TiSe.sub.2 The properties of a system with strong electron-electron interactions are ideally studied using only an external electric field, but this is only effective if the material is thin enough to avoid the shielding effect of the bulk material. Various fabrication techniques have been developed in recent years to produce ultrathin, two-dimensional forms of electronic materials. Antonoi Castro-Neto and colleagues use one such method to study the layered transition-metal dichalcogenide 1T-TiSe.sub.2 in the form of a flake less than 10 nanometres thick and encapsulated between hexagonal boron nitride. By varying the electric field, magnetic field and temperature, they reveal details about the transition between different electronic phases, such as a correlation between the existence of superconductivity and appearance of spatially modulated electronic states. To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices.sup.1,2,3. However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe.sub.2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram.sup.4, presenting several similarities with other layered systems such as copper oxides.sup.5, iron pnictides.sup.6, and crystals of rare-earth elements and actinide atoms.sup.7. By studying 1T-TiSe.sub.2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe.sub.2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity., Author(s): L. J. Li [sup.1] [sup.2] [sup.3] , E. C. T. O'Farrell [sup.1] [sup.2] , K. P. Loh [sup.1] [sup.3] , G. Eda [sup.1] [sup.2] [sup.3] , B. Ã-zyilmaz [sup.1] [...]

Complex topological configurations are fertile ground for exploring emergent phenomena and exotic phases in condensed-matter physics. For example, the recent discovery of polarization vortices and their associated complex-phase coexistence and response under applied electric fields in superlattices of (PbTiO.sub.3).sub.n/(SrTiO.sub.3).sub.n suggests the presence of a complex, multi-dimensional system capable of interesting physical responses, such as chirality, negative capacitance and large piezo-electric responses.sup.1-3. Here, by varying epitaxial constraints, we discover room-temperature polar-skyrmion bubbles in a lead titanate layer confined by strontium titanate layers, which are imaged by atomic-resolution scanning transmission electron microscopy. Phase-field modelling and second-principles calculations reveal that the polar-skyrmion bubbles have a skyrmion number of +1, and resonant soft-X-ray diffraction experiments show circular dichroism, confirming chirality. Such nanometre-scale polar-skyrmion bubbles are the electric analogues of magnetic skyrmions, and could contribute to the advancement of ferroelectrics towards functionalities incorporating emergent chirality and electrically controllable negative capacitance. Chiral polar-skyrmion bubbles are observed in superlattices of titanium-based perovskite oxides at room temperature., Author(s): S. Das [sup.1] , Y. L. Tang [sup.1] [sup.2] , Z. Hong [sup.3] , M. A. P. Gonçalves [sup.4] , M. R. McCarter [sup.5] , C. Klewe [sup.6] , [...]

Structural and electronic properties of 1,2-bis(5-methyl-[2,2'-bithiophen]-4-yl)cyclopent-1-ene in closed form and open form under various external electric field with strengths, 0,10 x [10.sup.-4], 20 x [10.sup.-4], 30 x [10.sup.-4], 40 x [10.sup.-4], and 50 x [10.sup.-4] a.u., were studied using the DFT-B3LYP/6-31G* method. As a positive index, structural parameters, length of the photoisomers, and the electronic spatial extents are almost stable at different external electric fields. The UV-Vis electronic spectrum based on time-dependent density functional theory indicated that the HOMO → LUMO transition in the closed form under different electric field strengths is strongly allowed, whereas is very weak in the open form. Electronic response parameters such as the HOMO-LUMO gap, electric dipole moment, and polarizability showed that electric conductivity of the closed form at different field strengths is greater than in the open form. Results of electronic density of states show that at high external electric field, the conductivity of the open form and closed form will be probably equal and switching behavior cannot be observed. Isomerization of the closed form to the open form at different external electric fields can be considered as exothermic and spontaneous. Key words: TD-DFT, photoisomerization, DOS, external field effect. Les proprietes electroniques et structurales du 1,2-bis(5-methyl-[2,2'-bithiophen]-4-yl)cyclopent-1-ene, sous ses formes ouverte et fermee, lorsque celui-ci est soumis a un champ electrique externe variable de force egale a 0,10 x [10.sup.-4], 20 x [10.sup.-4], 30 x [10.sup.-4], 40 x [10.sup.-4] et 50 x [10.sup.-4] u.a., ont ete etudiees a l'aide de la methode DFT-B3LYP/6-31G*. Un signe positif est que les parametres structuraux, la longueur des photoisomeres et les extensions spatiales des electrons sont quasiment stables lorsque le compose est soumis a des champs electriques de forces differentes. Le spectre electronique UV-Vis, combine a la theorie de la fonctionnelle de la densite dependante du temps, a indique que la transition HOMO → LUMO est fortement permise lorsque le compose, soumis a des champs electriques de forces differentes, est sous sa forme fermee tandis qu'elle est tres faiblement permise lorsque ce meme compose est sous sa forme ouverte. Les parametres lies au comportement des electrons, tels que l'ecart HOMO-LUMO (HLG), le moment dipolaire electrique et la polarisabilite ont montre que la conductivite electrique de la forme fermee du compose soumis a des champs electriques de forces differentes est plus grande que celle de sa forme ouverte. Les resultats du calcul de la densite des etats electroniques montrent que, lorsque le champ electrique externe est eleve, les conductivites des formes ouverte et fermee soumises sont susceptibles d'etre egales et le phenomene de permutation ne peut pas etre observe. La reaction d'isomerisation transformant la forme fermee en forme ouverte, lorsque le compose est soumis a differents champs electrique externes, peut etre consideree comme exothermique et spontanee. [Traduit par la Redaction] Mots-cles: TD-DFT, photoisomerisation, DOS, effet de champ externe., Introduction Molecular-scale electronics is a field of nanotechnology that uses single molecules, or nanoscale collections of single molecules, as electronic devices. This is conceptually different from conventional solid-state semiconductor electronics [...]

Structured features on top of nominally smooth distributions of radiation-belt particles at Earth have been previously associated with particle acceleration and transport mechanisms powered exclusively by enhanced solar-wind activity (1-4). Although planetary rotation is considered to be important for particle acceleration at Jupiter and Saturn (5-9), the electric field produced in the inner magnetosphere by Earth's rotation can change the velocity of trapped particles by only about 1-2 kilometres per second, so rotation has been thought inconsequential for radiation-belt electrons with velocities of about 100,000 kilometres per second. Here we report that the distributions ofenergetic electrons across the entire spatial extent of Earth's inner radiation belt are organized in regular, highly structured and unexpected 'zebra stripes', even when the solar-wind activity is low. Modelling reveals that the patterns are produced by Earth's rotation. Radiation-belt electrons are trapped in Earth's dipole-like magnetic field, where they undergo slow longitudinal drift motion around the planet because of the gradient and curvature of the magnetic field. Earth's rotation induces global diurnal variations of magnetic and electric fields that resonantly interact with electrons whose drift period is close to 24 hours, modifying electron fluxes over a broad energy range into regular patterns composed of multiple stripes extending over the entire span of the inner radiation belt., Radiation belts comprise electrons and ions trapped in the near-Earth region (distance from the Earth's centre [??] 6 Earth radii, RE) where the planetary magnetic field is approximately dipolar. The [...]

. It is well established that elasmobranchs can detect dipole electric fields. However, it is unclear whether they can discriminate between the anode and cathode. To investigate this subject, we employed a behavioral assay to determine the discriminatory ability of the yellow stingray, Urobatis jamaicensis. We conditioned stingrays with food rewards to bite either the anode (n = 5) or the cathode (n 6) of a direct-current dipole located on the floor of an experimental tank. All individuals successfully performed the task after 18 to 22 days. Stingrays were then tested in experimental sessions when they were rewarded only after they identified the correct pole. Stingrays successfully discriminated between the poles at a rate greater than chance, ranging among individuals from a mean of 66% to 93% correct. During experimental sessions, stingrays conditioned to distinguish the anode performed similarly to those conditioned to distinguish the cathode. We hypothesize that the ability to discriminate anode from cathode is physiologically encoded, but its utility in providing spatial information under natural conditions remains to be demonstrated. The ability to discriminate polarity may eliminate ambiguity in induction-based magnetoreception and facilitate navigation with respect to the geomagnetic field., Introduction Elasmobranch fishes (sharks, skates, and rays) were first demonstrated to be electrosensitive half a century ago (Dijk-graaf and Kalmijn, 1962; Murray, 1962). In subsequent field and laboratory trials, numerous [...]

The photodetachment of [H.sup.-] ions in a nonuniform electric field has been investigated on the basis of closed orbit theory. Firstly, we give a clear physical description of the detached electron's movement in a nonuniform electric field. Then we put forward an analytical formula for calculating the photodetachment cross section of this system. Our study suggests besides the closed orbit previously reported for the photodetachment of [H.sup.-] in a uniform electric field, some additional closed orbits are produced owing to the effect of the nonuniform electric field. Compared with the photodetachment cross section of [H.sup.-] in a uniform electric field, the oscillation in the cross section of our system becomes much more complicated and the cross section exhibits a multiperiodic oscillatory structure. To show the relation between the oscillation in the photodetachment cross section and the detached electron's classical closed orbits clearly, we make a Fourier transformation for the scaled photodetachment cross section of this system. Each peak in the Fourier transformed cross section corresponds to the contribution of one closed orbit. This study provides a new understanding of the photodetachment of negative ions in the presence of a nonuniform electric field. PACS Nos.: 34.35.+a, 32.80.Gc, 32.80.Qk, 42.50.Hz. Nous etudions le photo-detachement de l'ion [H.sup.-] dans un champ electrique non uniforme, sur la base de la theorie de l'orbite fermee. Nous donnons d'abord une description detaillee du mouvement de l'electron detache dans un champ electrique non uniforme. Ensuite, nous proposons une formule analytique pour la section efficace de photo-detachement de ce systeme. En plus de l'orbite fermee prealablement rapportee pour le photo-detachement de [H.sup.-], notre etude suggere des orbites fermees additionnelles dues a la non uniformite du champ electrique. La comparaison avec la section efficace de photo-detachement de [H.sup.-] en champ electrique uniforme montre que l'oscillation de la section eficace de notre systeme devient beaucoup plus compliquee et cette section eficace presente une structure oscillante multiperiodique. Nous operons la transformation de Fourier de la section eficace de ce systeme ain de montrer clairement la relation entre l'oscillation de la section eficace de photo-detachement et les orbites classiques fermees de l'electron detache. Chaque pic de la transformation correspond a la contribution d'une orbite fermee. Ces resultats jettent une lumiere nouvelle sur le photo-detachement d'ions negatifs en presence d'un champ electrique non uniforme. [Traduit par la Redaction], 1. Introduction The photodetachment of [H.sup.-] in various external fields has been studied by many authors over the past 20 years. Pioneering measurements of the photodetachment cross section of [H.sup.-] [...]

The control of the electric and optical properties of semiconductors with microwave fields forms the basis of modern electronics, information processing and optical communications. The extension of such control to [...]

The density functional theory calculations are applied for [C.sub.20] cage fullerenes. Furan, pyrole, and phenylvinyle monomers are made to interact with a [C.sub.20] cage at the same C position. An electric field was applied with varying strength. Computations were carried out for all cases at the [B3LYP/6-31G.sup.*] level. The structure, energetic, and relative stabilities of the compounds were compared with each other and analyzed. In addition, the electric field dependent and independent electronic transition spectra of the proposed stable neutral [C.sub.20] cage are investigated. PACS No.: 36.20.Kd. Des calculs de fonctionnelle de densite sont appliques a des cages fullerenes [C.sub.20]. Nous produisons differents composes en laissant interagir du furane, du pyrrole et du phenyle-vinyle avec le fullerene a la meme position C. Un champ electrique variable est applique. Les calculs sont du type [B3LYP/6-31G.sup.*]. Nous comparons et analysons les stabilites structurelles, energetiques et relatives des differents composes. De plus, nous etudions les spectres de transition electronique, dependants et independants du champ electrique, de la cage fullerene stable neutre [C.sub.20] proposee. [Traduit par la Redaction], 1. Introduction In the fullerene family, [C.sub.20] is the smallest possible fullerene without hexagonal rings. It contains just 12 pentagons, in a highly strained structure. The stable isomers of [C.sub.20] [...]

Charge exchange is one of the most important atomic processes in plasmas. Charge exchange and crossings of corresponding energy levels that enhance charge exchange are strongly connected with problems of energy losses and of diagnostics in high temperature plasmas. Charge exchange was also proposed as an effective mechanism for population inversion in the soft X-ray and vacuum ultraviolet ranges. One of the most fundamental theoretical domains for studying charge exchange is the problem of electron terms in the field of two stationary Coulomb centers (TCC) of charges Z and Z' separated by a distance R. It presents an intriguing atomic physics: the terms can have crossings and quasi crossings. These intrinsic features of the TCC problem also manifest in different areas of physics, such as plasma spectroscopy: a quasi crossing of the TCC terms, by enhancing charge exchange, can result in an unusual structure (a dip) in the spectral line profile emitted by a Z-ion from a plasma consisting of both Z- and Z'-ions, as was shown theoretically and experimentally. Before the year 2000, the paradigm was that the preceding sophisticated features of the TCC problem and its flourishing applications were inherently quantum phenomena. In 2000, a purely classical description of the crossings of energy terms was presented. In the present paper we study the effect of an electric field (along the internuclear axis) on circular Rydberg states of the TCC system. We provide analytical results for strong fields, as well as numerical results for moderate fields. We show that the electric field has several effects. First, it leads to the appearance of an extra energy term: the fourth classical energy term--in addition to the three classical energy terms at zero field. Second, but more importantly, the electric field creates additional crossings of these energy terms. We show that some of these crossings significantly enhance charge exchange, while other crossings enhance the ionization of the Rydberg quasi molecule. PACS Nos: 32.60.+i, 32.80.Ee, 34.70.+e, 33.80.Be, 31.15.-p L'echange de charge est le plus important mecanisme atomique dans les plasmas. L'echange de charge et le croisement des niveaux d'energie correspondants qui augmente l'echange de charge sont fortement connectes aux problemes de perte d' energie et de diagnostique dans les plasmas de haute temperature. L' echange de charge a aussi ete propose comme un mecanisme efficace pour l'inversion de population dans les domaines VUV et rayon-X mou. Le probleme des termes de l' electron dans le champ de deux centres coulombiens stationnaires (TCC) de charges Z'et Z' separes par une distance R, est central dans l' etude de l' echange de charge. C' est un probleme intriguant en physique atomique : les termes peuvent avoir des croisements et des quasi croisements. Ces caracteristiques intrinseques se manifestent egalement dans d'autres domaines de la physique, comme la spectroscopie du plasma : un quasi croisement des termes TCC, par augmentation de l'echange de charge, peut donner une structure inhabituelle (un creux) dans le profile de raies spectrales emis par un ion Z'dans un plasma contenant des ions Z'et Z', comme il a ete demontre experimentalement et theoriquement. Avant l'an 2000, le paradigme etait que les caracteristiques sophistiquees du probleme TCC et ses applications croissantes etaient des phenomenes essentiellement quantiques. En 2000, est apparue une description purement classique des termes de croisement. Ici, nous etudions l'effet du champ electrique (le long de l'axe internucleaire) sur les etats circulaires de Rydberg du systeme TCC. Nous presentons des resultats analytiques en champ fort, ainsi que des resultats numeriques pour champs intermediaires. Nous montrons que le champ electrique a differents effets. En premier, il mene a l'apparition d'un terme d'energie additionnel : le quatrieme terme d'energie--en addition aux trois termes classiques d'energie en champ nul. Deuxiemement, mais plus important, le champ electrique genere des croisements additionnels de ces termes d' energie. Nous montrons que certains de ces croisements augmente de facon significative l'echange de charge, alors que d'autres croisements augmentent l' ionisation de la quasi molecule de Rydberg. [Traduit par la Redaction], 1. Introduction Charge exchange is one of the most important atomic processes in plasmas. Charge exchange and crossings of corresponding energy levels that enhance charge exchange are strongly connected with [...]

Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) was electrospun into ultrafine fibrous nonwoven mats. Different from the conventional electrospinning process, which involves a positively charged conductive needle and a grounded fiber collector (i.e., positive voltage (PV) electrospinning), pseudo-negative voltage (NV) electrospinning, which adopted a setup such that the needle was grounded and the fiber collector was positively charged, was investigated for making ultrafine PHBV fibers. For pseudo-NV electrospinning, the effects of various electrospinning parameters on fiber morphology and diameter were assessed systematically. The average diameters of PHBV fibers electro-spun via pseudo-NVs were compared with those of PHBV fibers electrospun via PVs. With either PV electrospinning or pseudo-NV electrospinning, the average diameters of electrospun fibers ranged between 500 nm and 4 pm, and they could be controlled by varying the electrospinning parameters. The scientific significance and technological implication of fiber formation by PV electrospinning and pseudo-NV electrospinning in the field of tissue engineering were discussed. POLYM. ENG. SCI., 51:1325-1338, 2011- © 2011 Society of Plastics Engineers, INTRODUCTION Electrospinning is a versatile technique that is capable of producing micro-and nanofibrous materials. Over the past decades, this technique has been receiving considerable attention from researchers of different fields. [...]

Spectral tungsten data taken on an electron beam ion trap (EBIT) at Lawrence Livermore National Laboratory are analyzed between 3 and 8 Å for electron beam energies between 2.5 and 4.1 keV. The advantage of using charge state balancing with the experimental EBIT spectra for the identification of lines is employed and discussed. Theoretical Hebrew University Lawrence Livermore Atomic Code (HULLAC) modeling is then benchmarked against the experimental EBIT results. In particular, Co-, Ni-, Zn-, Cu-, Ga-, and Ge-like transitions were modeled independently using HULLAC to aid in charge state balancing. This model is then compared with Z-pinch plasma data collected on Zebra, the 1.6 MA pulse power generator located in the Nevada Terawatt Facility at the University of Nevada, Reno. The model is used to calculate charge balance and average ionization levels of these experimental plasma results, with particular focus on planar tungsten arrays. PACS Nos: 32.30.Rj, 52.59.Qy Nous avons utilise le piege ionique avec faisceau d'electrons, EBIT du Lawrence Livermore National Laboratory pour obtenir des donnees spectrales sur le tungstene entre 0,3 et 0,8 nm, avec un faisceau d'electrons entre 2,5 et 4,1 keV. Nous utilisons et analysons l'avantage de la repartition des etats de charge dans le montage experimental EBIT pour identifier les lignes spectrales. Le code de theorie atomique de l'universite Hebrai'que et du Livermore Laboratory (HULLAC) est ensuite utilise comme point de reference pour les donnees experimentales. En particulier, les transitions dans les ions de type Co-, Ni-, Zn-, Cu-, Ga- et Ge- sont modelisees separement avec HULLAC pour aider dans la repartition de l'etat de charge. Ce modele est alors compare aux donnees collectees au montage experimental de striction axiale (Z-pinch) Zeta, le generateur d'impulsion de 1,6 MA localise au laboratoire Nevada Terawatt de l'universite du Nevada a Reno. Nous utilisons ce modele pour calculer la repartition de charge et les niveaux moyens d' ionisation dans ces resultats experimentaux sur les plasmas, en focalisant sur les reseaux plans de tungstene. [Traduit par la Redaction], 1. Introduction Recent interest at the Sandia National Laboratory in the application of tungsten (W) for inertial confinement fusion using Z-pinch wire arrays has inspired the generation of a large [...]

A reduced density matrix approach is employed to provide a general theoretical description of polarized radiative emission during single-photon transitions from bound and auto-ionizing states of many-electron atomic systems in the presence of a general arrangement of static (or quasi-static) electric and magnetic fields. Polarized radiative emission from partially ionized atomic systems can occur as a result of the excitation of the radiating atomic states by electrons or ions with an anisotropic velocity distribution, which can be produced in an electron or ion beam experiment, and in a non-equilibrium plasma environment. Polarized radiative emission can also be produced or modified during the excitation of the atomic system in the presence of electric and magnetic fields, and electromagnetic fields. In electric and magnetic fields, the normally overlapping angular momentum projection components of atomic spectral lines can be substantially shifted from their fieldfree positions and split into spectroscopically resolvable (and inherently polarized) features. Because of the breakdown of the field-free angular momentum and parity selection rules, otherwise forbidden components of atomic spectral lines can be generated. Using a representation based on the field-free many-electron atomic states, the Stark-Zeeman patterns can be determined by a diagonalization of the atomic Hamiltonian in the presence of electric and magnetic fields. In the density operator approach, account can be taken of the coherent excitation of a particular subspace of the initial atomic bound or auto-ionizing states. A general expression for the matrix elements of the detected-photon density operator is obtained and provides a unified framework for the analysis of the spectral intensity, angular distribution, and polarization of the Stark- Zeeman patterns. From a unified development of time-domain (equation-of-motion) and frequency-domain (resolvent- operator) formulations of the more comprehensive reduced density matrix approach, the non-equilibrium atomic state kinetics and the homogeneous spectral line shapes can be systematically and self-consistently described. PACS Nos: 32.60.+i, 32.70.-n, 03.65.Ca, 34.10.+x Nous utilisons une approche par matrice densite reduite pour donner une description theorique generale de l'emission de radiation polarisee lors de transitions a un photon entre le fondamental et les etats autoionisants d'atomes a plusieurs electrons, en presence de champs electriques et magnetiques statiques ou quasi statiques, repartis de facon generale. L'emission de radiation polarisee a partir d'un systeme atomique partiellement ionise peut resulter de l'excitation des etats atomiques rayonnants par un faisceau d'electrons ou d'ions avec une distribution de vitesse anisotrope ou dans un plasma hors d'equilibre. Cette emission peut aussi etre produite ou modifiee pendant l'excitation d'un systeme atomique en presence de champs electriques, magnetiques et electromagnetiques. En presence de champs electriques et magnetiques, les composantes des projections de moment angulaire des lignes spectrales atomiques, qui se recouvrent en champ nul, peuvent etre deplacees significativement de leur position champ nul et se separer en elements spectroscopiquement separables (et polarises). A cause des modifications des regles de selection et de parite, par rapport a la situation en champ nul, des lignes spectrales autrement interdites peuvent maintenant apparaitre. Utilisant une representation basee sur les etats electroniques en champ nul, on peut obtenir le schema de raies Stark-Zeeman en y diagonalisant le Hamiltonien atomique avec champs electriques et magnetiques. Dans l'approche de la matrice densite, on peut tenir compte de l'excitation coherente d'un sous-espace particulier de l'espace initial d'etats lies ou autoionisants. Nous obtenons une expression generale pour les elements de matrice de l'operateur de densite des photons detectes, qui nous fournit un cadre unifie pour l' analyse de l' intensite spectrale, de la distribution angulaire et de la polarisation des schemas de raies Stark-Zeeman. En unifiant le developpement des formulations dans le domaine temps (equation de mouvement) et le domaine frequence (operateur resolvant) de l' approche de la matrice densite reduite, nous pouvons decrire systematiquement et de facon auto coherente la cinetique des etats atomiques hors d' equilibre et les profils des raies spectrales. [Traduit par la Redaction], 1. Introduction Polarized atomic radiative emission can be produced by a non-uniform (or non-statistical) distribution of the population densities among the degenerate (or nearly degenerate) angular momentum projection or magnetic [...]

We simulate and calculate numerically the electromagnetic field and energy flux around a surface crack of an Nd-doped phosphate laser glass by using the finite-difference time-domain method. Because of a strong interference between the incident wave and the total internal reflections from the crack and the glass surface, the electric field is redistributed and enhanced. The results show that the electric-field distribution and corresponding energy flux component depend sensitively on the light polarization and crack geometry, such as orientation and depth. The polarization of the incident laser beam relative to the crack surfaces will determine the profile of the electric field around the crack. Under TE wave incidence, the energy flux peak is always inside the glass. But under TM wave incidence, the energy flux peak will be located inside the glass or inside the air gap. For both incident modes, the light intensification factor increases with the crack depth, especially for energy flux along the surface. Because cracks on the polished surfaces are the same as the roots extending down, the probability for much larger intensification occurring is high. The results suggest that the surface laser-damage threshold of Nd-doped phosphate may decrease dramatically with subsurface damage. [c] 2010 Optical Society of America OCIS codes: 140.3330, 290.5890, 000.4430.

We show that if Maxwell's equations are expressed in a form independent of specific units, at least three Galilean limits can be extracted. The electric and magnetic limits can be regarded as nonrelativistic limits because they are obtained using the condition [absolute value of v] [much less than] c and restrictions on the magnitudes of the sources and fields. The third limit is called the instantaneous limit and is introduced by letting c [right arrow] [infinity]. The electric and instantaneous limits have the same form, but their interpretation is different because the instantaneous limit cannot be considered as a nonrelativistic limit. We emphasize the double role that the speed of light c plays in Maxwell's equations. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3442798]

Particles with different charge-to-mass ratios can be separated in a phase-sensitive process with application of a simple alternating longitudinal electric field in the absence of other electric or magnetic fields. The method suggests that a given particle can either be isolated or eliminated from a beam of several charged particles, in contrast to the conventional mass spectrometry where a particular particle is isolated. The method, based on the principles underlying phase stability in particle accelerators, could be applied to mass spectrometry or selective ion sources for plasma generation, ion traps, sputtering, or other applications. It would be especially useful in instances where the incoming ions are timed in synchrony with the proper phase of the applied voltage. PACS Nos: 45.50.-j, 45.50.Dd, 45.50.Pk, 52.20.Dq Nous pouvons separer des particules de differents rapports charge sur masse dans un dispositif sensible a la phase, en appliquant un simple champ electrique alternatif longitudinal, en l'absence de tout autre champ electrique ou magnetique. La methode suggere qu'une particule peut etre isoleeou eliminee d'un faisceau de plusieurs particules chargees, ce qui contraste avec la spectrometrie de masse conventionnelle ou une particule particuliere est isolee. La methode, basee sur les principes sous-jacents a la stabilite de phase dans les accelerateurs de particules, pourrait etre appliqueea la spectrometrie de masse ou a des sources selectives d'ions pour la generation de plasma, aux pieges ioniques, a la pulverisation cathodique ou a d'autres applications. Elle serait particulierement utile dans les cas ou les ions du faisceau sont synchronises temporellement avec la phase propre du champ applique. [Traduit par la Redaction], 1. Introduction The phase dependence of motion of a charged particle in a longitudinal alternating electric field shows the possibility of a spatially compact method of separating ions by mass [...]