bluuebunny/crossref_metadata_2025 huggingface dataset:
Genome size variation inHordeum spontaneumpopulations
Authors: Turpeinen Timo , Kulmala Johanna , Nevo Eviatar
Published: April 2011

Populations of wild barley, Hordeum spontaneum (C. Koch), originating from 10 ecologically and geographically different sites in Israel, were assessed for genome size. Measurements were obtained by flow cytometry using propidium iodide staining. Genome sizes ranged from 9.35 to 9.81 pg. Variance analysis indicated a significant difference between populations. Genome sizes were positively correlated with mean January temperature. Our results corroborate previous findings of intraspecific variation in genome size from different plant species. The positive correlations between climate and genome size suggest that the latter is adaptive and determined by natural selection.Key words: Hordeum spontaneum, genome size, flow cytometry, intraspecific variation, natural selection.
Quantitative karyotyping and dual-color FISH mapping of 5S and 18S-25S rDNA probes in the cultivatedPhaseolusspecies (Leguminosae)
Authors: Moscone Eduardo A , Klein Franz , Lambrou Maria , Fuchs Jörg , Schweizer Dieter
Published: April 2011

Double-color fluorescence in situ hybridization (FISH) followed by DAPI counterstaining allowed the chromosomal assignment of 5S and 18S-25S rRNA genes in the four cultivated Phaseolus species; P. vulgaris, P. coccineus, P. acutifolius, and P. lunatus (all: 2n = 2x = 22). The rRNA gene loci display variation between species as reflected in differences of signal size and (or) number. From one to three pairs of 5S sites and one to seven pairs of 18S-25S sites were found in the diploid complements of the four taxa studied. Intraspecific variation was studied in P. vulgaris, and it is shown that the number of 18S-25S rDNA sites differs between cultivars. Cytogenetic mapping was complemented by karyotype analyses. Each of the four cultivated Phaseolus species exhibits a characteristic heterochromatin endowment, with P. acutifolius var. latifolius having the highest amount of C-band material. Quantitative karyotyping in combination with cytogenetic mapping allowed the identification of homeologous chromosomes in the different species.Key words: Phaseolus cultivars, 5S rRNA genes, 18S-25S rRNA genes, molecular cytogenetic mapping.
A CAPS marker to assist selection of tomato spotted wilt virus (TSWV) resistance in pepper
Authors: Moury B , Pflieger S , Blattes A , Lefebvre V , Palloix A
Published: April 2011

The hypersensitive resistance to tomato spotted wilt virus (TSWV) in pepper is determined by a single dominant gene (resistant allele: Tsw) in several Capsicum chinense genotypes. In order to facilitate the selection for this resistance, four RAPD (among 250 10-mer primers tested) were found linked to the Tsw locus using the bulked segregant analysis and 153 F2individuals. A close RAPD marker was converted into a codominant cleaved amplified polymorphic sequence (CAPS) using specific PCR primers and restriction enzymes. This CAPS marker is tightly linked to Tsw (0.9 ± 0.6 cM) and is helpful for marker-assisted selection in a wide range of genetic intercrosses. Key words: Capsicum sp., PCR marker, bulked segregant analysis, Tospovirus, resistance gene.
Construction of a bacterial artificial chromosome (BAC) library for potato molecular cytogenetics research
Authors: Song Junqi , Dong Fenggao , Jiang Jiming
Published: April 2011

Lack of reliable techniques for chromosome identification is the major obstacle for cytogenetics research in plant species with large numbers of small chromosomes. To promote molecular cytogenetics research of potato (Solanum tuberosum, 2n = 4x = 48) we developed a bacterial artificial chromosome (BAC) library of a diploid potato species S. bulbocastanum. The library consists of 23 808 clones with an average insert size of 155 kb, and represents approximately 3.7 equivalents to the potato genome. The majority of the clones in the BAC library generated distinct signals on specific potato chromosomes using fluorescence in situ hybridization (FISH). The hybridization signals provide excellent cytological markers to tag individual potato chromosomes. We also demonstrated that the BAC clones can be mapped to specific positions on meiotic pachytene chromosomes. The excellent resolution of pachytene FISH can be used to construct a physical map of potato by mapping molecular marker-targeted BAC clones on pachytene chromosomes. Key words: potato, BAC library, chromosome identification, physical mapping, molecular cytogenetics.
Expressed retrotransposed 5S rRNA genes in the mouse and rat genomes
Authors: Drouin Guy
Published: April 2011

The analyses of previously described 5S rRNA gene sequences show that some of the expressed 5S rRNA genes present in the mouse and rat genomes were derived from the retrotransposition of 5S rRNA transcripts. These analyses demonstrate that new 5S rRNA gene copies can originate by retrotransposition and that some of these retrotranscribed genes are expressed. Key words: 5S ribosomal RNA genes, retrotransposition, retroposons.
Identification ofrpaP1-5andrpaP2-6genes encoding two additional variants of the 60S acidic ribosomal proteins ofSchizosaccharomyces pombe
Authors: Bonnet Christine , Perret Eric , Bonnin Odile , Picard André , Caput Daniel , Lenaers Guy
Published: April 2011

In the fission yeast, four genes (rpaP1-1, rpaP1-3,rpaP2-2, and rpaP2-4) encoding two variants of the RpaP1 and RpaP2 ribosomal proteins (rp) have been characterized. We have identified cDNA for additional variants called RpaP1.5 and RpaP2.6. Sequence comparison suggests that RpaP1.5 diverged before RpaP1.1 and RpaP1.3 and that RpaP2.6 is closer to RpaP2.2 than to RpaP2.4. The corresponding genes, rpaP1-5 and rpaP2-6, are transcribed coordinately with other rp genes. Key words: acidic ribosomal protein, RpaP1.5, RpaP2.6, rpaP1-5, rpaP2-6, variants.
Meiotic mutants of Medicago sativa show altered levels of α- and β-tubulin
Authors: Mariani Anna , Campanoni Prisca , Gianì Silvia , Breviario Diego
Published: April 2011

We have analysed the level of accumulation of α- and β-tubulin polypeptides in flowers collected from different meiotic mutants of alfalfa (Medicago sativa L.). The H33 mutant previously identified as a producer of male and female gametes with the somatic chromosome number (2n gametes) as a result of defective spindle orientation or, more rarely, abnormal cytokinesis, showed a higher level of α- and β-tubulin compared to control diploid plants and approximately the same level as control tetraploid plants. A higher level of tubulin was likewise observed in diploid plants displaying abnormalities in spindle orientation and cytokinesis, which had gone through 3-4 cycles of phenotypic recurrent selection to increase 2n gamete production. A similar analysis was performed on another class of Medicago meiotic mutants characterized by production of 4n pollen (jumbo pollen, due to the absence of cytokinesis at the end of meiosis) and 2n eggs. Again, the level of α- and β-tubulin was found to be higher in the mutants than in diploid controls. We conclude that meiotic defects, such as abnormal spindle orientation or cytokinesis leading to the formation of 2n gametes, determine an increased level of tubulin, the main constituent of plant microtubules (MTs). Key words: meiotic mutants, 2n gametes, cytoskeleton, α- and β-tubulin.
Identification of a 5S rDNA spacer type specific toTriticum urartuand wheats containing theT. urartugenome
Authors: Allaby Robin G , Brown Terence A
Published: April 2011

A PCR system was designed to amplify 5S spacer rDNA specifically from homeologous chromosome 1 in a variety of species representative of the Aegilops and Triticum genera. Two polymerase chain reaction (PCR) primer combinations were used, one of which appears to be apomorphic in nature and specific to chromosome 1A in Triticum urartu and tetraploid and hexaploid wheats containing the AA genome donated by T. urartu. The value of studying single repeat types to investigate the molecular evolution of 5S-rDNA arrays is considered.

Key words: 5S rDNA, polymerase chain reaction, Triticum, wheat.
Changes in host cell membrane activities in response to adhesion of Neisseria gonorrhoeae
Authors: Wiseman G. M. , Martin C. F.
Published: April 2011

Physiological changes in host cell model membranes (intact human erythrocytes and ghosts) as a consequence of bacterial adhesion were studied with special reference to Neisseria gonorrhoeae. Membrane activities examined were transport of K+, Cl− ions, pyruvate kinase, Na–K-dependent ATPase, and cAMP. We found that K+ and Cl− transport were affected, more so in membranes with attached pilated (P+) organisms than in those with apilated (P−) isogenic strains. In N. gonorrhoeae and in several other species of gram-negative bacteria studied, hemagglutination titres were directly correlated with effects on anion transport, suggesting that perturbations in anion transport are an immediate result of adhesion. Of three P+ gonococcus strains tested, two depressed Na–K–ATPase activity in the membrane, indicating a possible effect on the Na–K pump. Pyruvate kinase activity associated with the membrane appeared to be stimulated by attached gonococci, again by P+ strains to higher levels than P− organisms. Clearly, some enzyme properties of host membranes are intrinsically affected by bacterial adhesion. Human polymorphonuclear neutrophils were also investigated, and with some exceptions, changes observed in leukocyte enzyme activities tended to parallel those in erythrocytes. Since hypochlorous acid production is considered to be an important microbicidal mechanism in neutrophils, interference with Cl− transport could jeopardize their role in host defense.
Methanococcus frisius sp.nov., a new methylotrophic marine methanogen
Authors: Blotevogel Karl Heinz , Fischer Ulrich , Lüpkes Karl Heinz
Published: April 2011

A Gram-negative, nonmotile, coccoid methanogenic bacterium of 0.9–1.6 μm in diameter was isolated from shoal mud of the southern North Sea (West Germany). The isolate grew on H2 + CO2, methanol, and methylamines. Best growth occurred between 35 and 42 °C in a pH range of 6.5–7.2. The organism was highly sensitive to detergents and the cell wall probably consisted only of proteins. Growth of the organism was inhibited in the presence of ionophores like monensin or lasalocid. The DNA base composition was 38.2 ± 1.0 mol% G+C. The isolate is considered to be anew species and the name Methanococcus frisius is proposed.
The relation of population densities of the antagonist, Laetisaria arvalis, to seedling diseases of table beet incited by Pythium ultimum
Authors: Martin S. Bruce , Abawi G. S. , Hoch H. C.
Published: April 2011

Sclerotia of Laetisaria arvalis were added to raw or steamed table beet field soils infested with Pythium ultimum and other low-temperature Pythium spp. to determine the relationship between soil population densities of the antagonist to disease incidence. Decrease in disease incidence of table beet seedlings and final Pythium spp. inoculum densities were linearly related to increasing population density of the antagonist in raw field soils. In P. ultimum infested steamed soils, decreasing disease incidence was also related to increasing population densities of L. arvalis, but the relationship was curvilinear and was described by a quadratic model. The latter models also described the decrease in P. ultimum inoculum densities with increasing levels of the antagonist. Percentages of healthy plants (those surviving the pre- and post-emergence damping-off disease phases) were increased approximately 20% in raw soils containing 100 sclerotia of L. arvalis per gram soil in comparison with those of unamended soils. However, in Pythium infested steamed soils, percentages of healthy plants in soil amended with 100 sclerotia of L. arvalis per gram soil were increased by 40–60%.
Cell wall associations of some antigenic proteins of slime-forming, encapsulated Streptococcus cremoris from the fermented milk product "viili"
Authors: Forsén Raili , Hentunen Teuvo , Valkonen Kaua , Kontusaari Sirpa
Published: April 2011

Cell walls were isolated from mechanically disrupted cells of the slime-forming, encapsulated Streptococcus cremoris strains T5 and MLS96 by using sucrose gradient centrifugation as the last purification step. This cell wall isolation procedure was developed to obtain cell wall associated protein components. Sodium dodecyl sulfate – polyacrylamide gel electrophoresis revealed several polypeptide bands; the 50 kiloDalton band was major in strain T5 cell walls and the 26 and 30 kiloDalton bands were major in strain MLS96 cell walls. Both strains contained five antigenic polypeptides with molecular radius (Mr) values of 40, 47, 50, 54, and 70 kiloDaltons as analysed by immunoblotting and autoradiography. The polypeptides of strain MLS96 with molecular mass of 40 and 70 kiloDaltons reacted most strongly with homologous anti-whole cell serum. In addition, antigenic polypeptides with molecular mass of 100 and 160 kiloDaltons were also detected in strain T5.
Shifted 1/N expansion for confined quantum systems
Authors: Sinha Anjana , Roychoudhury Rajkumar , Varshni Y P
Published: April 2011

In this paper we formulate the shifted 1/N expansion method for constrained quantum mechanical systems with spherically symmetric potentials. As an example, we apply our technique to the confined Hulthén potential V(r) = Zδ[e -δr/(1 e-δr)] for different values of the confinement parameter b and the screening parameter δ. It is found that the agreement between our results and the exact numerical values is reasonably good.PACS No.: 03.65Ge
Hamiltonian and BRST formulations of the two-dimensional Abelian Higgs model
Authors: Kulshreshtha Usha
Published: April 2011

The Hamiltonian and BRST formulations of the Abelian Higgs model in one-space one-time dimensions are investigated.

PACS Nos.: 03.65+, 03.70tk, 11.10lm, 11.10Ef, 11.30Rd
Nonequilibrium effects in α-particle-induced reactions in Cs and I
Authors: Bhardwaj M K , Rizvi I A , Chaubey A K
Published: April 2011

The excitation functions for the reactions 127I(α,n)130Cs, 127I(α,2n)129Cs, 127I(α,4n)127Cs, 133Cs(α,2n)135La, and 133Cs(α,4n)133La have been measured up to 50 MeV alpha-particle energy using the stacked-foil activation technique and Ge(Li) gamma-ray spectroscopy. The measured cross sections were compared with theoretical calculations considering equilibrium as well as the pre-equilibrium geometry-dependent hybrid models of Blann. The high-energy tails of the excitation functions show a substantial contribution from pre-equilibrium emission. A general agreement is observed between the experimental results and theoretical predictions with an initial exciton configuration n0 = 4(2n + 2p + 0h).PACS No. 25.40-h
An introduction to physics education research
Authors: Aalst Jan van
Published: April 2011

At a number of U.S. universities, some physicists are focusing their research effort on physics education research (PER). This paper examines this development in terms of the knowledge of teaching and learning, curriculum projects and practices it has produced. First, a selective review of research and curriculum development projects provides an introduction to PER for readers unfamiliar with it. Studies based on surveys and interviews are emphasized, as well as curriculum projects that make use of microcomputer-based laboratory tools (MBL). Other efforts are mentioned more briefly, but illustrate the breath of research and development activity. Following the review, I examine the evidence for the effectiveness of some of the curricula discussed, and identify three areas in which greater interaction between the PER and educational researchers working in other fields should be fostered: (a) statistical data analysis, (b) micro-analysis of learning situations, and (c) ways in which subject matter knowledge in physics can contribute to school-based projects and educational research. The concluding section of the paper argues for multi-disciplinary graduate programs in physics education, which are intended to provide a solid base in physics as well as research and innovation in education.

PACS Nos.: 01.40.Fk, 01.50.Ht
Preprofessional students' beliefs about learning physics
Authors: Aalst Jan van , Key Tony
Published: April 2011

We report results obtained with the Maryland Physics Expectations (MPEX) survey in: (a) a course for students who have not previously taken a second course in physics in high school; (b) physics for the life sciences; (c) honors physics; and (d) physics for engineers. Comparing the responses with a group of experienced teachers Redish et al. call the ``expert group'', we find that (i) overall, agreement with experts decreased after the two semesters of instruction, and (ii) there were significant differences between the response patterns for students in the first two courses, compared with the last two. The data suggest that the context of learning, i.e., a program in physical science versus one in the life sciences must be taken into account in research on students' beliefs about learning physics.

PACS No.: 01.40Fk
The physical meaning of the contour wave in diffraction theory
Authors: Shoucri R M
Published: April 2011

Two possible approaches for the study of diffraction of light by a screen are the methods attributed, respectively, to Young and Fresnel. The connection between those two approaches is discussed in a way to clarify possible confusion or misunderstanding of the physical meaning of the contour wave that is used to make the link between them.PACS Nos.: 31.15.Pf, 31.30.Jv, and 32.10.Hq
Vacuum ultraviolet laser/time-of-flight mass spectra of Xe2 near Xe* (5d, 6p, 6') atomic lines
Authors: Mao D M , Hu X K , Shi Y J , Ma J , Lipson R H
Published: April 2011

Four Rydberg state < ground-state transitions of supersonically cooled Xe2, in the vicinity of the Xe* (5d, 6p, 6s') manifolds, have been excited with a tunable vacuum ultraviolet (VUV) "laser" generated by four-wave mixing in Kr or Hg nonlinear media. Molecular ions produced by (1 + 1') resonance-enhanced multiphoton ionization (REMPI), and (or) atomic fragment ions resulting from excited-state predissociation followed by ionization, were mass selected in a linear time-of-flight (TOF) mass spectrometer. Vibrational analyses of two of the resultant spectra have led to excited-state molecular constants, while equilibrium bond lengths were estimated by Franck-Condon intensity simulations. Constants could be derived for a third transition but the REMPI/TOF spectra exhibit interesting intensity anomalies that prevented a bond length from being determined. The fourth system was found to be strongly perturbed. In the absence of rotational resolution, possible excited-state electronic symmetries were deduced from angular-momentum arguments. Possible reasons are presented for the observed distortions in the shapes of the Rydberg-state potential-energy curves from their expected nonbonding forms. PACS Nos.: 31.00 and 33.00
Stimulated Raman scattering with slow light
Authors: Kien Fam Le , Hakuta K
Published: April 2011

We study the propagation dynamics of weak Raman sideband fields in a far-off-resonance Raman medium driven by a strong coupling field. We show that the interaction of the system with the strong field, under the conditions of high density, narrow Raman-transition width, and small two-photon detuning, results ina slow group velocity and a substantial enhancement of the injected anti-Stokes sideband field as well as an efficient generation of a Stokes sideband field. We find that the effective group velocity is the same for the two weak fields and is proportional to the field frequency difference instead of the frequency of the corresponding field. We also discuss the condition for exponential growth of the two sideband fields in the medium. We perform numerical calculations for solid hydrogen, a realistic system where the requirements for high density and small Raman width can be met. We demonstrate that the group velocity can be slowed down by several orders, and that the slow light plays a key role for the stimulated Raman scattering process in solid hydrogen.PACS Nos.: 42.50Gy, 42.50Hz, 42.65Ky, 42.79Nv
Nonlinear optics in space
Authors: Sorokin P P , Glownia J H
Published: April 2011

A detailed model for nonlinear photoexcitation of H2 in space is proposed and considered at length. It is shown that, on the basis of this model, one is able to provide at least partial explanations for three famous astrophysical spectral mysteries pertaining to our galaxy. These concern the carrier identities of the Diffuse Interstellar (Absorption) Bands (DIBs), the Unidentified Infrared (Emission) Bands (UIBs), and the visible bands emitted by the Red Rectangle nebula.PACS Nos.: 95.30Gv, 33.70-w
Magnetic nanostructures. From physical principles to spintronics
Authors: Heinrich B
Published: April 2011

A brief summary of underlying principles governing ultrathin film magnetic nanostructures and magnetoelectronics will be presented. The presentation will be based more on physical intuition than on rather complex physical and mathematical models in order to bring this new and rapidly expanding field to a broad audience. The success of this field has been based on the ability to create new structures in which interfaces play a crucial role. Three major phenomena have strongly affected progress in the development of new magnetic materials based on ultrathin films: (a) interface anisotropies; (b) interlayer exchange coupling; and (c) magneto-electron transport. The great progress in the study of ultrathin film multilayers and films patterned with submicrometre lateral geometries has led to a new class of electronic devices whose operation is based upon the spin-polarized character of the electronic carriers. "Magnetoelectronics and spintronics" are terms used to mark the development of very small spin-polarized electronic devices . Some latest developments in magnetic sensors and magnetic RAM will be presented to emphasize the importance of spintronics in the emerging technologies of the 21st century.
Étude magnétique des matériaux de type Ln2M12P7 (Ln = Ce, Sm, Gd et Er; M = Co et Fe)
Authors: Dhahri J , Fourati N , Dhahri E
Published: April 2011

A magnetic study has been undertaken on the substances of formula Ln2M12X7. The magnetic susceptibility and the magnetization have been measured as a function of temperature for a constant field. The magnetic susceptibility measurements have been performed from ambient temperature up to 1000 K. The effective paramagnetic moments were deduced from 1 / χ = f(T) curves, assuming a zero moment on the transition metal atoms. It is shown that these values are in good agreement with the theoretical values calculated for the free ions Ln3+. The saturation moment and the paramagnetic Curie temperature values show an antiferromagnetic behavior for Ce2Co12P7 at low temperature. The magnetic moment of Sm2Co12P7 measured at 4.2 and 78 K under a 2.66 T magnetic field shows a complex magnetic structure at low temperature. Our work on these materials show that the magnetic properties of Ln2M12X7 could be interpreted from previous studies on the phases rare earth  transition metal LnM.
The pseudogap in La2xSrxCuO4: A Raman viewpoint
Authors: Naeini J G , Irwin J C , Sasagawa T , Togawa Y , Kishio K
Published: April 2011

We report the results of Raman scattering experiments on single crystals of La2xSrxCuO4 (La214) as a function of temperature and doping. In underdoped compounds low-energy B1g spectral weight is depleted in association with the opening of a pseudogap on regions of the Fermi surface located near (±π, 0) and (0, ±π).The magnitude of the depletion increases with decreasing doping, and in the most underdoped samples, with decreasing temperature.The spectral weight that is lost at low energies (ω [Formula: see text] 800 cm1) is transferred to the higher energy region normally occupied by multimagnon scattering. From the normal-state B2g spectra we have determined the scattering rate Γ(ω,T) of qausiparticles located near the diagonal directions in k-space. In underdoped compounds, Γ(ω,T) is suppressed at low temperatures for energies less than Eg(x) [Formula: see text] 800 cm1. The doping dependence of both the two-magnon scattering and the scattering rate suppression suggest that the pseudogap is characterized by an energy scale Eg ~ J, where J is the antiferromagnetic super-exchange energy. Comparison with the results from other techniques provides a consistent picture of the pseudogap in La214.PACS Nos.: 74.25.Gz, 74.72.Dn, 78.30.Er
Determination of the temperature exponent for the case of the temperature-dependent frequency factor in thermoluminescence
Authors: Bhattacharya Manabesh , Singh W Shambhunath , Mazumdar P S
Published: April 2011

We suggest a method for the determination of the temperature exponent in the case of the temperature-dependent frequency factor in thermoluminescence (TL).The applicability of the method has been tested by applying it both to numerically computed and experimental TL peaks.PACS No.: 78.60Kn
III. Geometrical optics of variable-frequency light rays in the general relativistic regime: Combined gravitational and refractive lensing
Authors: Chyla W T
Published: April 2011

The frequency-sensitive extremum principle for propagation of light rays in the geometrical optics regime is used to develop a nonperturbative method for tracing light rays in a transparent refractive medium in the general relativistic environment. The general formulation of the theory is given first; it allows for the numerical analysis of a nonlinear superposition of gravitational and refractive lensing, when neither of the two effects can be treated as a small perturbation. The scope of the general theory is gradually narrowed to the Schwarzschild field, the spherical symmetry of the refractive properties of the medium, and the small deflection regime approximation. A simple, analytically solvable example of deflection of light rays by a mass embedded in a refractive medium is considered in detail; in a vacuum, deflection of light rays by the Sun is reproduced.PACS Nos.: 42.15-i, 04.20-q, 98.90+s
II. Geometrical optics of variable-frequency light rays in special relativistic and nonrelativistic situations:The general law of reflection
Authors: Chyla W T
Published: April 2011

The general law of reflection concerns situations when the light ray undergoes a shift of frequency at the reflection point. For example, it governs reflection of light rays from a moving mirror (either in a vacuum or in a transparent medium), reflection from a motionless mirror coated with a layer of Raman-active molecules in the coherent-scattering regime, or external reflection of X-rays from the surface of a condensed matter sample, with partial dissipation of energy within the skin depth. The general law of reflection is derived from the extremum principle for propagation of variable-frequency light rays. It states that the angle of reflection depends not only on the angle of incidence but also on the frequency shift in the reflection point and dispersion of the refractive index of the medium in contact with the mirror. The compatibility of the general law of reflection and the special relativistic treatment of reflection is examined in detail. Applications of the new law of reflection are discussed in the special relativistic and the nonrelativistic regime. PACS Nos.: 42.15-i, 03.30+p
Evidence of volume bubble creation during laser ablation of PMMA organic polymer
Authors: Efthimiopoulos T , Kiagias Ch. , Heliotis G , Helidonis E
Published: April 2011

We present results related to the PMMA organic polymer laser ablation for several values of the energy flux of the XeCl laser. These results seem to support the model of volume superheating, which is associated with bubble creation, bubble association, and subsequent burst. It is shown that the laser ablation mode correlates well with the generated acoustic wave and the noise imposed on it that is detected by a sensitive pressure transducer located in the back of the sample.PACS Nos.: 72.20; 72.60; 42.62 cf; 81:05
Some singular motions of non-Abelian Toda lattices
Authors: Couch W E , Surovy M , Torrence R J
Published: April 2011

Motions of finite Toda lattices are known to be associated with linear wave equations whose general solutions can be expressed in terms of progressing waves, and this association is known to generalize to finite non-Abelian Toda lattices of n x n matrices and systems of n coupled linear wave equations. We present a nontrivial family of non-Abelian Toda lattice motions that can be specialized to ones that are not finite, but not infinitely extendible either, as they contain nonvanishing but singular matrices of rank (n  s). In these cases we give a natural continuation of the lattice dynamics by means of nonsingular matrices of dimension (n  s) x (n  s), and describe how to find s progressing wave solutions of the associated system of n coupled linear wave equations.PACS No.: 5.45-a
Gerade/ungerade symmetry-breaking in HD at the n = 2 dissociation limit
Authors: Lange A de , Reinhold E , Hogervorst W , Ubachs W
Published: April 2011

We report on a study of the I'1Πg outer well state of HD. Via a resonance-enhanced XUV + IR (extreme ultraviolet + infrared) excitation scheme, rovibronic levels (v = 0-2, J = 1-4) are populated and probed by pulsed lasers. Level energies are measured with an accuracy of [Formula: see text] 0.03 cm-1. Due to gerade-ungerade symmetry breaking, the long-range behavior of the I' potential in HD deviates from that of H2 and D2. When this deviation is taken into account a semi-empirical potential for the I'1Πg state may be constructed, resulting in better agreement with the observed level energies than derived from an adiabatic ab initio potential. With this new potential it is predicted that the I' well can sustain only 4 vibrational levels, with the v = 3 level having a binding energy of [Formula: see text]1.38(3) cm-1. PACS Nos.: 33.80.Rv, 34.20.Cf, 33.20.Ni, 31.50.+w
Optical Ramsey spectroscopy and coherence measurements of the clock transition in a single trapped Sr ion
Authors: Marmet L , Madej A A
Published: April 2011

We report on the observation of coherent excitation and spectroscopy performed using Ramsey's method of separated excitation fields on a single trapped and laser cooled ion of strontium. Single pulse Rabi excitation studies of the ion have shown linewidths approaching the transform limited value. Studies of transition rate versus pulse duration have shown a quadratic initial increase in transition rate with a duration consistent with coherent excitation and a rapid loss of Rabi oscillations, consistent with the concept of a dephasing of the thermally populated trap oscillator states as the excitation evolves. When two-pulse Ramsey excitation is applied to the single ion, fringe widths down to a linewidth of 840 Hz (FWHM) were observed with measured fringe contrasts consistent with a probe laser linewidth of 500 Hz.PACS Nos.: 32.80Qk, 32.30Jc, 06.30Ft
Semiclassical calculation of quantum energy levels using variational principles:application to He@C70
Authors: Lee-Dadswell G R , Gray C G
Published: April 2011

The reformulated Maupertuis variational principle is used in a semiclassical calculation to obtain the quantum energy levels of a nonseparable oscillator potential approximating the endohedral fullerene complex He@C70. The results are compared with levels obtained from a purely quantum mechanical, numerical calculation and are found to agree to better than 1% over at least the lowest 600 levels. The semiclassical calculation is found not to produce some level splittings seen in the purely quantum mechanical results. A simple modification of the calculation is described whereby the splittings may be predicted.PACS No.: 5.45Mt
The linear baryon
Authors: Bukta D , Karl G , Nickel B G
Published: April 2011

We describe classical orbits and quantum states of a three-particle system, which is weakly chaotic. The quantum energies of the lowest 48 states, which are invariant under permutations, are given both for various approximations and to high accuracy. The quantum mechanical probability distributions are given in a two-dimensional version of the system, the hexagonal pit. The quantum probabilities show strong resemblance to classical orbits of various types, including chaotic ones.PACS Nos.: 3.65-w, 5.45Mt, 45.50Jf
Anisotropie induite en électro-dynamique des milieux diélectriques mobiles
Authors: Kallas N C , Hobeika R
Published: April 2011

We emphasize the existence of a non-colinearity between the momentum and the velocity of a photon propagating in a moving medium, in disagreement with previous expectations, entailing some anisotropy induced by the motion.
Formation and decay of the HgZn(B0+) exciplex
Authors: Czajkowski A , Atkinson J B , Krause L
Published: April 2011

The HgZn exciplex was produced in the B0+ state by irradiatinga HgZn vapour mixture at temperatures in the range 600900°C with 2572 Å cw or 2660 Å pulsed laser light. The B0+ [Formula: see text] X0+ fluorescence band was recorded, as well as the time evolutions of various components present in the fluorescence spectrum, providing some additional insight into the possible mechanism of the exciplex formation.PACS Nos.: 33.50, 33.70.H, 33.90
Dissociative excitation of SO2 by electron impact
Authors: Kedzierski W , Malone C , McConkey J W
Published: April 2011

Dissociative excitation of SO2 by electron impact to produce excited oxygen fragments, in particular O (1S), has been studied in the energy range from threshold to 400 eV. Three processes leading to O (1S) production have been identified and the positions of the relevant repulsive states of SO2 in the FranckCondon region have been determined. The multiplicities and symmetry characteristics of two of these states have also been established. The absolute cross section for production of O (1S) by all channels is measured to be 2.2 x 10-18 cm2 at 150 eV. The relative cross section for production of O (3p 3P and 3p 5P) from threshold to 400 eV has also been measured. The existence of a hitherto unidentified triplet state of SO2 that emits in the near infra red has been established. PACS No.: 34.80Gs
Enhancement of diffraction efficiency for optical gratings
Authors: Zhang G Z
Published: April 2011

A method to increase the diffraction efficiency for optical gratings is proposed. Using a simple glass plate sitting parallel to the top of a grating surface, one can form an air gap between the surfaces of the grating and the glass plate to reflect a grazing-incident light beam and make diffraction through multiple reflection of the beam between the grating and glass plate surfaces. As a result, this device can efficiently enhance the grating efficiency by diffracting the input beam energy into various diffraction orders. PACS Nos.: 07.60-j, 42.25Fx, 42.40Lx, 42.79Dj, 42.40Fg
Embryonic tissues are viscoelastic materials
Authors: Beysens D A , Forgacs G , Glazier J A
Published: April 2011

Early embryonic development is characterized by spectacular morphogenetic processes such as sorting or spreading of tissues. Analogy between viscoelastic fluids and certain properties of embryonic tissues turned out to be useful in interpreting some aspects of these morphogenetic phenomena. In accordance with the differential adhesion hypothesis, the values of tissue-specific surface tensions have been shown to be consistent with the equilibrium configurations such tissues reach in the course of sorting and spreading. A method to measure tissue surface tension and viscoelastic properties is described. Notions like the Laplace's equation relating surface tension to radii of curvature, or the Kelvin model of viscoelasticity are used to analyze the results of these measurements. The fluid analogy is extended to time-dependent phenomena, in particular, to the analysis of cellular pattern evolution in the course of spreading. On the basis of recent experimental findings, we demonstrate that the kinetics of spreading and nucleation in binary fluids can be analyzed using the same formalism. We illustrate how our results can be used to obtain biologically relevant information on the strength of binding between specific cell adhesion molecules under near physiological conditions. We also suggest a diagnostic application of our method to monitor the metastatic potential of tumors. PACS No.: 03.65Ge
High-power 1.48 µm phosphoro-silicate-fiber-based laser pumped by laser diodes
Authors: Karpov V I , Clements W RL , Dianov E M , Papernyi S B
Published: April 2011

An all-fiber 1.48 µm generator based on a LD-pumped Yb-doped double-clad laser and cascaded Raman wavelength converter has been developed. Second-order Raman Stokes radiation was generated in a phosphosilicate-fiber resonator formed by two pairs of Bragg gratings. The Yb-doped double-clad fiber laser was pumped by seven laser diodes combined via a low-loss fused fiber coupler and provided 4.4 W at 1.06 µm at the input of the Raman converter. A slope efficiency of the Raman converter of 40% with respect to the power emitted by the double-clad Yb laser has been achieved. We obtained an output power of 1.5 W with a total optical-to-optical efficiency of 21%. It was found that four-wave mixing, initiated in the fiber by the high-intensity light, results in spectral broadening of the 1.48 µm radiation and leaking of the first-Stokes radiation from the resonator formed by the 1.24 µm Bragg gratings, thus reducing the efficiency of the first-to-second-Stokes conversion.PACS No.: 42.55Wd
Anomalies and regularities in the broadening, shifting, and diffusion of D2 in D2 and D2-He mixtures
Authors: Fakhr-Eslam S H , Sheldon G D , Sinclair P M , May A D , Drummond J R
Published: April 2011

Precise and accurate measurements of the Q branch lines of D2 in D2 and D2He mixtures at several temperatures and low densities reveal a regular broadening at very low densities but only if allowance is made for departures from the soft-collision model. Above about 2 amagat the broadening becomes anomalous and is consistent with earlier observations. Because of the anomalies, a meaningful comparison between broadening and shifting coefficientsand ab initio calculations was not possible. Diffusion constants, as extracted from the data for mixtures, allow us to establish an empirical relation between this diffusion constant and those for pure D2 and for D2 infinitely diluted in He.PACS Nos. 33.70Jg and 33.70-W
Tunable coherent vacuum ultraviolet radiation and its application to molecular spectroscopy: The seminal contributions of Professor B.P. Stoicheff
Authors: Eden J G
Published: April 2011

Few have had the impact of Professor Boris P. Stoicheff on atomic, molecular, and optical physics and in the fields of nonlinear optics and molecular spectroscopy, in particular. This paper recounts a few of his accomplishments in the generation of coherent radiation tunable in the VUV and the application of this short wavelength source to the spectroscopy of diatomic molecules, with emphasis on the rare gas dimers Ar2, Kr2, and Xe2. PACS No.: 33.20Ni
The influence of transient solar-wind events on the cosmic-ray intensity modulation
Authors: Sabbah I
Published: April 2011

We have studied the behavior of cosmic rays observed by three stations during a time of high-speed solar-wind (HSSW) events. These stations cover the median rigidity range 16-164 GV. The influence of the IMF (interplanetary magnetic field) associated with HSSW has also been studied. Our analysis covers the period 1967-1986. Both the cosmic-ray intensity and geomagnetic activity are enhanced by coronal-mass-ejection events. The IMF magnitude and fluctuation are responsible for the depression of cosmic-ray intensity during HSSW events. This depression is rigidity dependent. Low-energy cosmic rays suffer more intensity depression. The rigidity spectrum of the cosmic-ray intensity decreases is dependent upon the phase of the solar cycle. It was steeper during the period 1979-1980. The power exponent is dependent upon the magnetic state of the solar cycle in support of the prediction of the drift model. PACS Nos.: 96.50Ci, 96.40-z
Some possibilities for laboratory searches for variations of fundamental constants
Authors: Karshenboim S G
Published: April 2011

We consider different options for the search for possible variations of the fundamental constants. We give a brief overview of the results obtained with several methods. We discuss their advantages and disadvantages with respect to simultaneous variations of all constants in both time and space in the range 1081010 years. We also suggest a few possibilities for the laboratory search. Particularly, we propose some experiments with the hyperfine structure of hydrogen, deuterium, and ytterbium171 and of some atoms with a small magnetic moment. Other suggestions are for some measurements of the fine structure associated with the ground state. Special attention is paid to the interpretation of the hfs measurements in terms of variations of the fundamental constants. PACS No.: 31.30G
Dirac spinors and tachyon quantization
Authors: Pant M C , Bisht P S , Negi O PS , Rajput B S
Published: April 2011

Dirac spinors for spin-1/2 free tachyons are derived from the Dirac and Klein-Gordon equations in terms of the standard helicity representation of the Poincaré group and superluminal transformations (SLTs). It is shown that the proposed theory of second quantization is Lorentz invariant without inverting the spin-statistics relationship and without introducing indefinite pseudotachyonic states. Second quantized theory of spin-1/2 tachyons in the time-energy representation shows that tachyons are localized in time and that the most natural space for the description of tachyons is T4-space. It has been emphasized that on passing from R4-space (bradyons) to T4-space (tachyons) via either, i.e., complex or real SLTs, tachyons behave in T4-space exactly as bradyons do in R4-space. T4-space can be visualized as an internal space for a subluminal observer while R4-space appears as an internal space for a superluminal observer. PACS Nos.: 14.80K, 03.30t
Time-dependent angular and energy distributions of sputtered copper atoms
Authors: Vichev R G , Karpuzov D S
Published: April 2011

Time reference was introduced in the TRIM computer simulation code without changing the "event-driven" logic of the program. The code was applied to model the atomic collision cascades and sputtering of amorphous copper targets caused by bombardment of keV ions of different masses (Be, Ne, Ar, Cu, Xe, Au). Time-dependent characteristics of ion-induced processes such as mean number and energy of moving target atoms, number of collisions and vacancies (or) recoils created, sputtering yield, mean energy and angle of ejection of sputtered atoms were obtained, and their dependence on the ion/atom mass ratio is discussed.

PACS No.: 79.20-m
Mathematical methods for the characterization of ultrasound in anisotropic materials
Authors: O'Neill B , Maev R Gr.
Published: April 2011

Although the fundamental equations for the propagation of elastic and acoustic waves in anisotropic materials have not changed in more than a 100 years, the last few decades have seen a surge in interest in the topic. Much of this interest stems from the growing need for characterization of an increasing number of exotic materials. The intent of this paper is to review, for the benefit of beginning researchers in acoustics and ultrasonics, the fundamental phenomena related to elastic wave propagation in anisotropic media. We also present the most common and interesting theoretical methods developed over the past 20 years to model bulk wave propagation in such media. The methods discussed include plane wave superpositions, ray asymptotic theory, paraxial beams, and Green's functions. More peripheral issues, including anisotropic effects combined with various other exotic effects, are dealt with in the bibliography.

PACS No.: 43.90
Charged-particle pseudorapidity (rapidity) distribution in nucleusnucleus collisions at alternating-gradient synchrotron energy
Authors: Liu F -H
Published: April 2011

The charged-particle pseudorapidity (rapidity) distributions in nucleusnucleus collisions at the alternating-gradient synchrotron energy (1115A GeV) have been described by the thermalized cylinder picture. The calculated results are in agreement with the experimental data of the reactions 28Si + Au, Ag, Cu, and Al at 14.6A GeV/c bombarding energy. It is shown that the target stopping power (the leading participant target nucleon rapidity shift with respect to the projectile) increases with the target size, and the projectile penetrating power (the leading participant projectile nucleon rapidity shift with respect to the target) decreases with the increasing of target size.

PACS Nos.: 25.75-q, 25.75Dw, and 24.10pa
Effect of radiation on forced convection flow of a micropolar fluid over a horizontal plate
Authors: Elbashbeshy E MA , Bazid M AA
Published: April 2011

We determine the effect of radiation on forced convection flow of a micropolar fluid over a horizontal plate. The governing nonsimilar boundary-layer equations are solved using the cubic spline collocation method. The solutions are expressed in terms of the local shear stress and local rate of heat transfer. The effect of varying the Prandtl number, the radiation parameter, and the micropolar material parameter are determined.PACS No.: 47.27-i
Negative dimensional approach for scalar two-loop three-point and three-loop two-point integrals
Authors: Suzuki A T , Schmidt A GM
Published: April 2011

The well-known D-dimensional Feynman integrals were shown, by Halliday and Ricotta, to be capable of undergoing analytic continuation into the domain of negative values for the dimension of space-time. Furthermore, this could be identified with Grassmannian integration in positive dimensions. From this possibility follows the concept of negative-dimensional integration for loop integrals in field theories. Using this technique, we evaluate three two-loop three-point scalar integrals, with five and six massless propagators, with specific external kinematic configurations (two legs on-shell), and four three-loop two-point scalar integrals. These results are given for arbitrary exponents of propagators and dimension, in Euclidean space, and the particular cases compared to results published in the literature. PACS Nos.: 02.90+p, 11.15Bt, 12.38Bx
Finite β destabilization of long-wavelength drift mode in tokamaks
Authors: Hirose A , Elia M
Published: April 2011

Analysis based on integral equation formalism in the ballooning space indicates that in toroidal geometry, extremely long-wavelength modes with the ion finite Larmor radius parameter (k[Formula: see text]ρ)2 [Formula: see text] O(10-2) and mode frequency of the order of the ion transit frequency can be strongly destabilized by a finite β (the ratio of plasma to magnetic pressure). In high β regimes, a resultant mixing length thermal diffusivity is linearly proportional to β. PACS Nos.: 52.65Tt, 52.55Fa, 52.35Py
Higher order interelectronic-interaction correctionsto the ground-state hyperfine splitting in lithiumlike ions
Authors: Zherebtsov O M , Shabaev V M
Published: April 2011

The interelectronic-interaction corrections of the second order in 1/Z to the ground-state hyperfine splitting in lithiumlike ions are evaluated. The calculations are performed by using the relativistic configuration-interaction method and perturbation theory. In addition, the nuclear magnetization distribution effect on the interelectronic-interaction correction of the first order in 1/Z is evaluated within the single-particle nuclear model. The calculations provide an improvement in the theoretical predictions for the hyperfine splitting in lithiumlike ions. PACS Nos.: 31.30Gs, 31.30Jv