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Ab initio investigation has been performed for the strontium hydride cation Sr[H.sup.+] using a standard quantum chemistry approach. It is based on the pseudopotentials for atomic core representations, Gaussian basis sets, as well as with full configuration interaction calculations. A diabatisation procedure based on the effective hamiltonian theory and an effective metric is used to produce the quasi-diabatic potential energy. Adiabatic and quasi-diabatic potential energy curves and their spectroscopic parameters for the ground and many excited electronic states of [sup.1,3][Σ.sup.+], [sup.1,3]Π, and [sup.1,3]Δ symmetries have been determined. Their predicted accuracy is discussed by comparing our well depths and equilibrium positions with the available experimental and theoretical results. Moreover, we localized and analyzed numerous avoided crossings between the electronic states of 1³[Σ.sup.+] and 1-3n symmetries. The correction of the electron affinity of the H atom is also considered, for the 1-10¹[Σ.sup.+] electronic states, to improve the accuracy of the adiabatic potential energies of these states. In addition, we calculated the dipole moments, for a wide range of internuclear distances in both diabatic and quasi-diabatic representations. The adiabatic permanent dipole moments for the 10¹[Σ.sup.+] electronic states revealed ionic characters related to electron transfer and yields both Sr[H.sup.(+)] and [Sr.sup.(+)]H arrangements. The transition dipole moments between neighbor electronic states revealed many peaks around the avoided crossing positions. Key words: pseudopotentials, configuration interaction, potential energy curves, spectroscopic parameters, dipole moments. Nous avons complete une etude ab initio du cation hydride du strontium Sr[H.sup.+] en utilisant une approche de chimie quantique standard. Elle est basee sur les pseudo-potentiels pour representer le creur atomique, sur des ensembles de base gaussiens et des calculs avec interaction a pleine configuration. Nous utilisons une procedure de diabatisation basee sur la theorie du Hamiltonien effectif et une metrique effective est utilisee pour produire l'energie potentielle quasi-diabatique. Nous determinons les courbes d'energie potentielle adiabatique et quasi-diabatique pour le fondamental et plusieurs etats excites des symetries [sup.1,3][Σ.sup.+], [sup.1,3]Π et [sup.1,3]Δ. La precision de nos predictions est analysee en comparant nos profondeurs de puits et nos positions d'equilibre avec les valeurs theoriques et experimentales disponibles. De plus, nous localisons et analysons les nombreux croisements evites entre les etats electroniques des symetries 1³[Σ.sup.+] et [sup.1,3]Π. Nous considerons aussi la correction de l'affinite electronique de l'atome H pour les etats 1-10¹[Σ.sup.+], de facon a ameliorer la precision des energies potentielles adiabatiques de ces etats. Les moments dipolaires sont calcules pour un large domaine des distances internucleaires, dans les deux representations, diabatique et quasi-diabatique. Les moments dipolaires adiabatiques permanents pour les etats electroniques 10¹[Σ.sup.+] revelent des caracteres ioniques relies au transfert d'electron et donnent les deux arrangements Sr[H.sup.(+)] et [Sr.sup.(+)]H. Les moments dipolaires de transition entre etats electroniques voisins revelent plusieurs pics autour des positions des croisements evites. [Traduit par la Redaction] Mots-cles: pseudo-potentiel, interaction de configuration, courbes d'energie potentielle, parametres spectroscopiques, moments dipolaires., 1. Introduction In the recent past, there has been considerable interest in the creation of ultracold molecules at temperatures below 1 µK by magneto-association [1, 2] or photo-association [3, 4], [...]

Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein [...]

The development of the optical frequency comb (a spectrum consisting of a series of evenly spaced lines) has revolutionized metrology and precision spectroscopy owing to its ability to provide a precise and direct link between microwave and optical frequencies (1,2).A further advance in frequency comb technology is the generation of frequency combs in the extreme-ultraviolet spectral range by means of high-harmonic generation in a femtosecond enhancement cavity (3,4). Until now, combs produced by this method have lacked sufficient power for applications, a drawback that has also hampered efforts to observe phase coherence of the high-repetition-rate pulse train produced by high-harmonic generation, which is an extremely nonlinear process. Here we report the generation of extremeultraviolet frequency combs, reaching wavelengths of 40 nanometres, by coupling a high-power near-infrared frequency comb (5) to a robust femtosecond enhancement cavity. These combs are powerful enough for us to observe single-photon spectroscopy signals for both an argon transition at 82 nanometres and a neon transition at 63 nanometres, thus confirming the combs' coherence in the extreme ultraviolet. The absolute frequency of the argon transition has been determined by direct frequency comb spectroscopy. The resolved ten-megahertz linewidth of the transition, which is limited by the temperature of the argon atoms, is unprecedented in this spectral region and places a stringent upper limit on the linewidth of individual comb teeth. Owing to the lack of continuous-wave lasers, extreme-ultraviolet frequency combs are at present the only promising route to extending ultrahigh-precision spectroscopy to the spectral region below 100 nanometres. At such wavelengths there is a wide range of applications, including the spectroscopy of electronic transitions in molecules (6), experimental tests of bound-state and many-body quantum electrodynamics in singly ionized helium and neutral helium (7-9), the development of next-generation 'nuclear' clocks (10-12) and searches for variation of fundamental constants (13) using the enhanced sensitivity of highly charged ions (14)., Techniques developed to control a train of ultrashort pulses in the frequency domain have led to rapid advancements not only in ultrahigh-precision metrology (1) but also in the generation of [...]

Using measured radial velocity data from six double-lined spectroscopic binary systems PV Pup, BV Dra, AI Phe, V1130 Tau, NSV 223 (or DZ Psc), and V502 Oph, we find corresponding orbital and spectroscopic elements via the method introduced by Karami et al. (New Astron. 14, 478 (2009)). Our numerical results are in good agreement with those obtained by others using more traditional methods. Using a statistical analysis, we also conclude that for BV Dra, V1130 Tau, NSV 223 (or DZ Psc), and V502 Oph, a circular orbit is quite consistent. PACS Nos: 97.80.Hn, 97.80.Fk En utilisant les donnees sur les vitesses radiales de six systemes binaires avec spectroscopie a double raie, PV Pup, BV Dra, AI Phe, V1130 Tau, NSV 223 (ou DZ Psc) et V502 Oph, nous trouvons les elements correspondants de l'orbite et de la spectroscopie via la methode introduite par Karami et al. (New Astron. 14, 478 (2009)). Nos resultats numeriques sont en bon accord avec ceux obtenus par methode plus traditionnelle. A l'aide d'une etude statistique, nous concluons que les orbites de BV Dra, V1130 Tau, NSV 223 et V502 Oph sont [V.sub.R]aisemblablement circulaires. [Traduit par la Redaction], 1. Introduction Analysis of both light and radial velocity (hereinafter [V.sub.R]) curves of binary systems helps us to determine the masses and radii of individual stars. One historically well-known method [...]

The development of nonlinear characteristics of a dynamical system could cause cascading transfer of the dynamic energy of the system. It is proposed to utilize this fact as a tool for the structural health monitoring. The traditional idea of knowledge-based structural health monitoring is primarily by identifying the change of frequencies, mode shapes, and damping, which is often less sensitive than desired for all practical health monitoring purposes. Observation of energy shift by spectral analysis of ambient survey results could be a helpful method for indicating the existence of damage at an earlier stage. An example is attached. Key words: structural health monitoring, ambient vibration survey, spectral analysis, nonlinearity. Le developpement de caracteristiques non lineaires d'un systeme dynamique pourrait engendrer le transfert graduel de l'energie dynamique du systeme. Il est propose d'utiliser ce fait comme outil de suivi de la sante structurale. L'idee traditionnelle de suivi structural base sur les connaissances s'appuie principalement sur l'identification du changement de frequences, de la forme et de l' amortissement des modes, ce qui est souvent moins sensible que voulu a des fins de suivi pratique de la sante. L'observation du deplacement de l'energie par analyse spectrale des resultats de releves de l'ambiance vibratoire pourrait etre utile pour indiquer l' existence des dommages des les premiers stages. Un exemple est presente. Mots-cles : suivi de la sante structurale, releve de l'ambiance vibratoire, analyse spectrale, non-linearite. [Traduit par la Redaction], 1. Introduction Damage detection of civil engineering structures has long been concentrated on the change of stiffness with increasing damage. This indicator, particularly when it is considered with associated changes [...]

This contribution reviews experimental and theoretical work on spectroscopy of tungsten published since the last critical compilation of the energy levels and spectral lines of highly ionized tungsten (Kramida and Shirai. At. Data Nucl. Data Tables, 95, 305 (2009)). Since then, 18 new experimental studies were published, which resulted in new identifications and (or) significantly improved wavelengths of spectral lines and energy levels of Li-like through As-like and Pm-like tungsten. A few tens of theoretical studies of tungsten spectra were published since 2008. A number of them report on high-precision calculations of energy levels, transition wavelengths, and radiative rates for tungsten spectra, such as neutral tungsten, Yb-like, Rh-like through Rb-like, Ag-like, Ga-like, Zn-like, Ni-like, Ca-like, Al-like, Mg-like, Na-like, Ne-like, B-like, Be-like, and Li-like. These developments are reviewed. Based on new experimental data, systematic errors are removed from some of the earlier measurements. Some new data are obtained by analyzing publications of other authors. Based on new published theoretical data, some old experimental results were confirmed and assessed. Revised and extended tables of energy levels and spectral lines of highly ionized tungsten are presented. PACS Nos: 32.10.Fn, 32.30.-r, 32.30.Jc, 32.30.Rj Nous passons ici en revue les travaux experimentaux et theoriques sur la spectroscopie du tungstene, qui ont ete publies depuis la derniere compilation systematique des niveaux d'energie et des raies spectrales du tungstene hautement ionise (Kamida et Shirai. At. Data Nucl. Data Tables, 95, 305 (2009)). Depuis, 18 nouvelles etudes experimentales ont ete publiees, qui ont resulte en de nouvelles identifications et une amelioration significative des longueurs d'onde des raies et de l'energie des niveaux des ions de tungstene allant du type Li jusqu'aux types As et Pm. Quelques dizaines etudes theoriques sur le tungstene ont ete publiees depuis 2008. Certaines d'entre elles rapportent des calculs de haute precision de niveaux d' energie, de longueurs d'onde de transitions et de taux radiatifs pour des spectres de tungstene, neutre et ionise de types Yb, de Rh a Rb, Ag, Ga, Zn, Ni, Ca, Al, Mg, Na, Ne, B, Be et Li. Nous les passons en revue. Les mesures recentes ont permis d'eliminer certaines erreurs systematiques des mesures anterieures. Certains nouveaux resultats viennent de l'analyse de publications d' autres auteurs. Les nouveaux resultats theoriques ont permis de confirmer des resultats experimentaux anterieurs dont l'identification restait incertaine. Nous presentons des tables nouvelles et etendues des niveaux d'energie et des raies spectrales du tungstene hautement ionise. [Traduit par la Redaction], 1. Introduction An extensive review and critical compilation of experimental data on highly-ionized tungsten was recently made by Kramida and Shirai [1]. This compilation included data published until the beginning [...]

In many theories of unified interactions, there are additional degrees of freedom that may allow for the variation of the fundamental constants of nature. I will review the motivation for and theoretical relations between such variations. I will then review the various astrophysical and experimental constraints on the variations of constants and their dependence on spectroscopic data. PACS Nos: 32.30.Rj, 30.30.+w, 31.50.+w Dans plusieurs theories de grande unification des interactions, il y a des degres de liberte additionnels qui permettent la variation des constantes fondamentales de la nature. Je passe en revue les motifs en leur faveur et les relations theoriques entre de telles variations. Je vais aussi passer en revue les diverses contraintes astrophysiques et experimentales sur la variation des constantes et leur dependance sur les donnees spectroscopiques. [Traduit par la Redaction], 1. Introduction It is important to distinguish which constants may have physically meaningful variations. While there would appear to be a long list of potentially nonconstant constants beyond the fine-structure [...]

AEgIS (Antimatter experiment: gravity, interferometry, spectroscopy) is an experiment approved by CERN with the goal of studying antihydrogen physics. In AEgIS, antihydrogen will be produced by charge exchange reactions of cold antiprotons with positronium atoms excited in a Rydberg state (n > 20). In the first phase of the experiment, controlled acceleration by an electric field gradient (Stark effect) and subsequent measurement of free fall in a Moire deflectometer will allow a test of the weak equivalence principle. In a second phase, the antihydrogen will be slowed, confined, and laser-cooled to perform CPT studies and detailed spectroscopy. In the present work, after a general description of the experiment, the present status of advancement will be reviewed, with special attention to the production and excitation of positronium atoms. PACS Nos: 03.75.Dg, 06.30.Gv, 25.43.+t, 34.80.Lx AEgIS (Experience sur l'Antimatiere: Gravite;, Interfeerometrie, Spectromeetrie) est une experience approuvee par le CERN qui vise une etude globale de la physique de l'anti-hydrogene. Dans AEgIS, l'anti-hydrogene sera produit par des reactions d'echange de charges d'anti-protons froids avec des atomes de positronium excitees dans un etat de Rydberg (n > 20). Dans la premiere phase de l'experience, l'acceileration est controlee par un gradient de champ electrique (effet Stark); une mesure subsequente en chute libre dans un deflectometre de Moire nous fournira un test du principe d'equivalence faible. Dans une deuxieme phase, l'anti-hydrogene sera ralenti, confine et refroidi par laser pour des etudes de CPT et de spectroscopie de precision. Apres une description geenerale de l'experience, nous passons ici en revue l'etat d'avancement des travaux en accordant une attention particuliere a la production et l'excitation des atomes de positronium. [Traduit par la Redaction], 1. Introduction A new generation of antimatter experiments has been opened after the first experiments of antihydrogen production in laboratory conditions at the CERN laboratory [1] and at Fermilab [2]. [...]

We describe the implementation of precision laser transmission spectroscopy for sizing and counting nanoparticles in suspension. Our apparatus incorporates a tunable laser and balanced optical system that measures light transmission over a wide (210-2300 nm) wavelength range with high precision and sensitivity. Spectral inversion is employed to determine both the particle size distribution and absolute particle density. In this paper we discuss results for particles with sizes (diameters) in the range from 5 to 3000 nm. For polystyrene particles 404 to 1025 nm in size, uncertainties of [+ or -]0.5% in size and [+ or -]4% in density were obtained. For polystyrene particles from 46 to 3000 nm in size, the dynamic range of the system spans densities from ~[10.sup.3]/ml to ~[10.sup.10]/ml (5 x [10.sup.-8] to 0.5 vol. %), implying a sensitivity 5 orders of magnitude higher than dynamic light scattering. [c] 2010 Optical Society of America OCIS codes: 120.7000, 300.6360, 290.5850, 290.2200, 290.4020.

A trace gas sensor for the detection of nitrogen dioxide based on cavity ringdown spectroscopy (CRDS) and a continuous wave external cavity tunable quantum cascade laser operating at room temperature has been designed, and its features and performance characteristics are reported. By measuring the ringdown times of the cavity at different concentrations of N[O.sub.2], we report a sensitivity of 1.2 ppb for the detection of N[O.sub.2] in Zero Air. OCIS codes: 000.2170, 010.1120, 010.0280, 120.6200, 300.6360.

A method has been developed for the design of reinforced concrete (RC) members when subjected to blast loadings based on the nondimensional energy spectrum. Numerical analyzes showed good agreement between the approximate responses of RC members designed to their respective levels of target response. This paper further verifies this method through the actual response of a RC column and beam subjected an actual denotation of explosives at a short standoff. When subjected to blast loading from a short standoff distance, the cantilever column behaved predominantly in direct shear. Thus, ways to mitigate the damage of a cantilever column should draw focus on the robustness. The developed design procedure provides a feasible method for the blast resistant design of members, subjected to blast loads at a short standoff distance. DOI: 10.1061/(ASCE)ST.1943-541 X.0000149 CE Database subject headings: Blast loads; Reinforced concrete; Numerical analysis. Author keywords: Blast load; Blast-resistant design; Reinforced concrete; Nondimensional energy spectrum.

Cavity ring-down spectroscopy is a spectroscopic method that uses a high quality optical cavity to amplify the optical loss due to the light absorption by a sample. In this presentation we highlight two applications of phase-shift cavity ring-down spectroscopy that are suited for absorption measurements in the condensed phase and make use of waveguide cavities. In the first application, a fiber loop is used as an optical cavity and the sample is introduced in a gap in the loop to allow absorption measurements of nanoliters of solution at the micromolar level. A second application involves silica microspheres as high finesse cavities. Information on the refractive index and absorption of a thin film of ethylene diamine on the surface of the microresonator is obtained simultaneously by the measurements of the wavelength shift of the cavity mode spectrum and the change in optical decay time, respectively. Key words: cavity ring-down spectroscopy, microresonator, microsphere, fiber loop. La spectroscopie a cavite ring-down est une meethode spectroscopique qui utilise une cavite optique de haute qualite pour amplifier la perte optique due a l'absorption de lumiere par l'echantillon. Durant cette presentation, nous mettons en evidence deux applications de la spectroscopie a cavite; ring-down avec deeplacement de phase qui convient aux mesures d'absorption en phase condenseee et fait usage de caviteesa guide d'onde. Dans la premiere application, une boucle de fibre est utiliseie comme cavite optique et l'eechantillon est introduit dans un intervalle de la boucle pour permettre des mesures d'absorption sur des nanolitres de solution au niveau micromolaire. Une seconde application est basee sur des microspheres de silice comme caviteesa haute finesse. Des informations sur l'index de refraction et l'absorption d'un film mince d'ethylene diamine sur la surface d'un micro-resonateur sont obtenues simultaneement par des mesures de deplacement de longueur d'onde du spectre modal de la cavite et de changement de temps de decroissance optique, respectivement. Mots-cles: spectroscopie a cavite; ring-down, micro-resonateur, microsphere, boucle de fibre., In the past years, absorption spectroscopy has undergone a rapid change and the absorption spectrometers that are developed in many research labs have little in common with the teaching instruments [...]

COMPARATIVE STUDY OF BITTER GOURD (Mormodica charantia) AND TURMERIC (Curcuma longa) USING HIGH PERFORMANCE LIQUID CHROMATOGRAPHY (HPLC). Sunde M. Jones, Nagarajan Vasumathi, Nixon Mwebi, Mijitaba Hamissou.Department of Chemistry and Biology, [...]

The peridinin-chlorophyll a-protein (PCP) of dinoflagellates is unique among the large variety of natural photosynthetic light-harvesting systems. In contrast to other chlorophyll protein complexes, the soluble PCP is located in the thylakoid lumen, and the carotenoid pigments outnumber the chlorophylls. The structure of the PCP complex consists of two symmetric domains, each with a central chlorophyll a (Chl-a) surrounded by four peridinin molecules. The protein provides distinctive surroundings for the pigment molecules, and in PCP, the specific environment around each peridinin results in overlapping spectral line shapes, suggestive of different functions within the protein. One particular Per, Per-614, is hypothesized to show the strongest electronic interaction with the central Chl-a. We have performed an in vitro reconstitution of pigments into recombinant PCP apo-protein (RFPCP) and into a mutated protein with an altered environment near Per-614. Steady-state and transient optical spectroscopic experiments comparing the RFPCP complex with the reconstituted mutant protein identify specific amino acid-induced spectral shifts. The spectroscopic assignments are reinforced by a determination of the structures of both RFPCP and the mutant by x-ray crystallography to a resolution better than 1.5 [Angstrom]. RFPCP and mutated RFPCP are unique in representing crystal structures of in vitro reconstituted light-harvesting pigment-protein complexes. light harvesting | peridinin | protein crystallography | refolding | transient absorption spectroscopy doi/10.1073/pnas.0908938106

The spectral analysis of surface waves (SASW) method is a nondestructive testing method of pavements based on the dispersive characteristic of seismic surface waves. The method can provide the thickness and stiffness of pavement layers. One of the more complex aspects of the SASW method is an iterative process to estimate the pavement parameters, called the inversion procedure. In this paper, the feasibility of completely automating the inversion process and substituting it with artificial neural network (ANN) models was explored. A number of different ANN models were developed using various ANN training strategies. To improve the performance of some ANN models, a sequential modeling technique was implemented. In the sequential modeling, some pavement parameters are estimated first from an initial set of ANN models, which is then the input to subsequent ANN models to estimate other parameters of interest. Furthermore, the performance of the ANN models was evaluated using a number of well-characterized pavement sections. The results illustrated that ANN models could estimate the upper layers' parameters so well that they could replace the inversion process. The ANN models for other layers were capable of generating robust initial estimates for a well-constrained formal inversion that can be readily automated. DOI: 10.1061/(ASCE)0899-1561(2009)21:12(722) CE Database subject headings: Neural networks; Pavements; Surface waves; Automation.

A multiple-line-of-sight tunable diode laser absorption system for measuring shock-train structure inside a model scramjet isolator at the Wright-Patterson Air Force Base Propulsion Directorate's research cell 18 supersonic combustion facility is described. Multiple rovibrational lines of water are probed using time-multiplexing of multiple diode lasers projected across a rectangular isolator duct along 16 lines of sight. Static temperatures and water concentration (path-averaged) are computed from a Boltzmann plot for the multiple lines that are measured, and static pressures are determined from the absorption line width. The experimental setup and measurement technique are presented here along with the Mach 2 flow (no shock train) results. The absorption measurements agree to within 2 % of sidewall pressure transducer measurements and calculated (path-averaged) static temperatures at 5 Hz. The motivation for the development of this sensor was to demonstrate that it is possible to obtain accurate tunable diode laser absorption spectroscopy measurements over multiple lines of sight in a supersonic flow in real-time, allowing useful data about the spatial and temporal changes of the static pressure and temperature within a supersonic shock train. The present measurements demonstrate that multiple-line-of-sight measurements can obtain temperature, pressure, and water density information with an overall accuracy better than 5% at 1000 Hz and show that sensing based on real-time tunable diode laser absorption spectroscopy of supersonic flows is possible.

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 [...]

To get mechanistic insight into the DNA strand-exchange reaction of homologous recombination, we solved a filament structure of a human Rad51 protein, combining molecular modeling with experimental data. We build our structure on reported structures for central and N-terminal parts of pure (uncomplexed) Rad51 protein by aid of linear dichroism spectroscopy, providing angular orientations of substituted tyrosine residues of Rad51-dsDNA filaments in solution. The structure, validated by comparison with an electron microscopy density map and results from mutation analysis, is proposed to represent an active solution structure of the nucleo-protein complex. An inhomogeneously stretched double-stranded DNA fitted into the filament emphasizes the strategic positioning of 2 putative DNA-binding loops in a way that allows us speculate about their possibly distinct roles in nucleo-protein filament assembly and DNA strand-exchange reaction. The model suggests that the extension of a single-stranded DNA molecule upon binding of Rad51 is ensured by intercalation of Tyr-232 of the L1 loop, which might act as a docking tool, aligning protein monomers along the DNA strand upon filament assembly. Arg-235, also sitting on L1, is in the right position to make electrostatic contact with the phosphate backbone of the other DNA strand. The L2 loop position and its more ordered compact conformation makes us propose that this loop has another role, as a binding site for an incoming double-stranded DNA. Our filament structure and spectroscopic approach open the possibility of analyzing details along the multistep path of the strand-exchange reaction. homologous recombination | HsRad51

A transportable prototype Faraday rotation spectroscopic system based on a tunable external cavity quantum cascade laser has been developed for ultrasensitive detection of nitric oxide (NO). A broadly tunable laser source allows targeting the optimum [Q.sub.3/2](3/2) molecular transition at 1875.81 [cm.sup.-1] of the NO fundamental band. For an active optical path of 44 cm and 1-s lock-in time constant minimum NO detection limits (1[sigma]) of 4.3 parts per billion by volume (ppbv) and 0.38 ppbv are obtained by using a thermoelectrically cooled mercury--cadmium--telluride photodetector and liquid nitrogen-cooled indium--antimonide photodetector, respectively, Laboratory performance evaluation and results of continuous, unattended monitoring of atmospheric NO concentration levels are reported. external cavity laser | nitric oxide detection | midinfrared | magnetic circular birefringence | paramagnetic species

We investigated the effects of operator-applied force on diffuse optical spectroscopy (DOS) by integrating a force transducer into the handheld probe. Over the typical range of contact forces measured in the breasts of eight patients, absorption and reduced scattering coefficients (650 to 1000nm) variance was 3.1 [+ or -] 1.0% and 1.0 [+ or -] 0.4%. For trained operators, we observed OCIS codes: 170.3880, 170.3890, 170.5280, 170.6510, 170.6935, 120.3890.

Logarithmic-conversion data processing used in wavelength modulation spectroscopy (WMS) with a current-modulated diode laser as its source is analyzed and compared with second-to-first ratio detection. Analytic Fourier coefficients of logarithmic-converted residual amplitude modulation (RAM) of a light source are given. An experimental setup for methane absorption detection at 1650 nm is described. It is shown theoretically and experimentally that logarithmic-converted WMS cannot only eliminate the fluctuation of received light power, but also improve the signal-to-noise ratio significantly. OCIS codes: 060.2370, 300.1030, 300.6260, 300.6300, 300.6320, 300.6380.

We investigate the dispersion mechanism of surface magnetoplasmons for periodic layered structures in the Voigt configuration. An analytical dispersion relation that retains a similar form with ordinary surface plasmons is obtained. The splitting of surface plasma frequency is accompanied with unequal field strengths of surface modes at the two interfaces and is characterized by a simple dynamic model that recasts the role of magnetic force on to the effective mass. The underlying mechanism is illustrated with the transverse currents induced by the cyclotron motion of electrons, which appears as the typical feature of the dynamic Hall effect. In particular, the acoustical and optical branches exhibit an anticrossing scheme for small filling fractions, due to the like symmetry of modes in the two branches. As the parallel wave number changes, the two interaction branches experience a transition of mode pattern from symmetry to antisymmetry, or vice versa. OCIS codes: 240.6680, 160.1190, 050.5745.

Dynamic force spectroscopy probes the kinetic and thermodynamic properties of single molecules and molecular assemblies. Here, we propose a simple procedure to extract kinetic information from such experiments. The cornerstone of our method is a transformation of the rupture-force histograms obtained at different force-loading rates into the force-dependent lifetimes measurable in constant-force experiments. To interpret the force-dependent lifetimes, we derive a generalization of Bell's formula that is formally exact within the framework of Kramers theory. This result complements the analytical expression for the lifetime that we derived previously for a class of model potentials. We illustrate our procedure by analyzing the nanopore unzipping of DNA hairpins and the unfolding of a protein attached by flexible linkers to an atomic force microscope. Our procedure to transform rupture-force histograms into the force-dependent lifetimes remains valid even when the molecular extension is a poor reaction coordinate and higher-dimensional free-energy surfaces must be considered. In this case the microscopic interpretation of the lifetimes becomes more challenging because the lifetimes can reveal richer, and even nonmonotonic, dependence on the force. atomic force microscope | optical tweezers | nanopore unzipping Kramers theory | rupture force distribution

An update of spectroscopic line parameters for the 3.45-3.92 [micro]m ozone bands is reported. The line list includes the parameters of 15 bands of the main isotopic species and of the [v.sub.1] + [v.sub.2] + [v.sub.3] band of [sup.16][O.sup.16][O.sup.18]O and [sup.16][O.sup.18][O.sup.16]O. The results are based on previous high resolution laboratory studies. Comparisons of experimental spectra with an absorptance simulation of ozone based on the reported line list shows that the latter one is accurate enough for strong, medium, and weak transmittance in the 2550-2900 [cm.sup.-1] spectral range. The data are available on the Web in the Spectroscopy and Molecular Properties of Ozone (S&MPO, http://smpo.iao.ru and http://ozone.univ-reims.fr) and HITRAN (http://cfa-www.harvard.edu/hitran/) databanks. OCIS codes: 010.4950, 300.1030, 300.6300, 300.6320, 300.6340.

In cavity ring-down spectroscopy (CRDS), residual or stress-induced birefringence ([10.sup.-7]-[10.sup.-6] rad) of supermirrors will lift the polarization degeneracy of [TEM.sub.00] modes and generate two new polarization eigenstates in the cavity with small resonant frequency splitting (~0.1 kHz); the new eigenstates are nearly linearly polarized. When both modes are excited simultaneously, the intracavity polarization state will evolve as the energy decays in the cavity. Without polarization analysis, such mode beating would not be observable. However, real supermirrors have a linear polarization-dependent loss (dichroism) that leads to a change in the loss rate as the polarization state evolves and thus to deviation from the expected single-exponential decay. We develop a model for the evolution of the intracavity polarization state and intensity for a cavity with both birefringence and polarization-dependent loss in the mirrors. We demonstrate, experimentally, that these parameters (both magnitudes and directions) can be extracted from a series of measurements of the cavity decay and depolarization of the transmitted light. OCIS codes: 280.3420, 260.1440.

High-pressure methods are increasingly used to produce new dense materials with unusual properties. Increasing efforts to understand the reaction mechanisms at the microscopic level, to set up and optimize synthetic approaches, are currently directed at carbon-based solids. A fundamental, but still unsolved, question concerns how the electronic excited states are involved in the high-pressure reactivity of molecular systems. Technical difficulties in such experiments include small sample dimensions and possible damage to the sample as a result of the absorption of intense laser fields. These experimental challenges make the direct characterization of the electronic properties as a function of pressure by linear and nonlinear optical spectroscopies up to several GPa a hard task. We report here the measurement of two-photon excitation spectra in a molecular crystal under pressure, up to 12 GPa in benzene, the archetypal aromatic system. Comparison between the pressure shift of the exciton line and the monomer fluorescence provides evidence for different compressibilities of the ground and first excited states. The formation of structural excimers occurs with increasing pressure involving molecules on equivalent crystal sites that are favorably arranged in a parallel configuration. These species represent the nucleation sites for the transformation of benzene into amorphous hydrogenated carbon. The present results provide a unified picture of the chemical reactivity of benzene at high pressure. benzene crystal | electronic transitions | high-pressure chemistry | two-photon spectroscopy

To our knowledge we present the first experiments with a fully reflective external-cavity quantum-cascade laser system at mid-infrared wavelengths for use as a local oscillator in a heterodyne receiver. The performance of the presented setup was investigated using absorption spectroscopy as well as heterodyne techniques. Tunability over [approximately equal to] 30 [cm.sup.-1] at 1130 [cm.sup.-1] was demonstrated using a grating spectrometer. A continuous tuning range of 0.28 [cm.sup.-1] was verified by observing the spectra of an internally coupled confocal Fabry-Perot interferometer and the absorption lines of gas phase S[O.sub.2]. In a second step the output from the system was used as a local oscillator signal for a heterodyne setup. We show that spectral stability and side mode suppression are excellent and that a compact external-cavity quantum-cascade laser system is well suited to be used as a local oscillator in infrared heterodyne spectrometers. OCIS codes: 140.3070, 140.3570, 300.6310, 280.0280.