bluuebunny/crossref_metadata_2025 huggingface dataset:
Transversality of the resummed thermal gluon self-energy
Authors: Kunstatter G.
Published: April 2011

The perturbative Ward identities obeyed by the effective vertices and propagators for thermal quantum chromodynamics (QCD) have recently been used to prove to order g2T the on-shell transversality of the imaginary part of the (resummed) gluon self-energy in all linear gauges. Here the same result is derived for both the real and imaginary parts of the self-energy using the nonperturbative gauge-fixing identities obeyed by the generating functional for QCD.
Gauge (in)dependence of the fermion damping rate in hot gauge theories
Authors: Nakkagawa Hisao , Niégawa Akira , Pire Bernard
Published: April 2011

The gauge-(in)dependence problem of the fermion damping rate in hot gauge theories is carefully examined to the effective one-loop order using a recently proposed resummation method in terms of the so-called "hard thermal loops." Explicit analysis is given in the case of a heavy fermion [Formula: see text], which enables us to investigate the essential point of the controversy in detail. Calculation in general covariant gauges shows in which calculation procedure we can get a gauge-parameter independent result. We also show, with explicit calculations, that the difference in the damping rate in the Landau and the Coulomb gauges is nonleading. Thus the leading-order damping rate is gauge independent within the Coulomb and general covariant gauges if an appropriate calculation procedure is employed.
Influence of phase conjugate optical feedback on the emission properties of visible low-power diode lasers
Authors: Mailhot Sylvain , McCarthy Nathalie
Published: April 2011

A significant narrowing of the longitudinal-mode spectrum of continuous-wave visible gain-guided diode lasers was achieved by using an external cavity bounded by a phase conjugate mirror. Longitudinal-mode discrimination was further improved by inserting a thin étalon in the external cavity. With this technique, the coherence length of the laser beam has been increased by a factor of 4 and the emission wavelength was tunable over a range of 1.4 nm, at constant temperature.
Effects of the thickness of the substrate on the performance and the design of planar kinoform lenses for axial stigmatism in finite conjugate-imaging
Authors: Hazra L. N. , Han Y. , Delisle C. A.
Published: April 2011

The imaging performance of zero-thickness substrate planar kinoform lenses designed for infinite conjugate-imaging is not affected when a plane parallel plate, placed in the object space, is used as a substrate. This invariance property does not hold good in the case of kinoform lenses designed for finite conjugate-imaging purposes. It is shown that the imaging performance of a planar kinoform lens, designed with the assumption of zero substrate thickness for stigmatic imaging between two axial points, is drastically changed when the lens is used in combination with a plane parallel substrate of finite thickness. For ensuring axial stigmatism as well as 100% diffraction efficiency at the desired image, the thickness of the substrate has to be taken into account ab initio in the design of the kinoform lens. A seminumerical procedure for implementing the same is presented and the convenient amenability of our method in the design of planar kinoform lenses on substrate of prespecified thicknesses is demonstrated with some illustrative examples.
A BOXCARS investigation of vibrational relaxation in highly excited 1, 2-trans-dichloroethene
Authors: Wang L. , Xu J. R. , Jones W. E.
Published: April 2011

The BOXCARS technique has been used to study the collisional vibrational energy transfer from 1, 2-trans-dichloroethene excited into a quasicontinuum by a pulsed CO2 laser. The temporal evolution behaviour for vibrational energies in different modes was obtained. It has been shown that both the rate and maximum energy transferral to the ν4 mode are slightly larger than rates and energy transferral to the ν1 and ν2 modes and that this specificity declines with increase in excitation energy. The mechanism for this specificity is discussed.
Optical propagation in a nonhomogeneous medium and squeezed states
Authors: Xu Jing-Bo , Gao Xiao-Chun
Published: April 2011

In this paper, using the concept of the basic invariant, we study optical propagation in a nonhomogeneous medium and obtain the squeezed states for the system. These should be of importance for the discussion of the propagation of waves with finite width.
Three-particle forces in the lattice dynamics of some hexagonal close-packed metals
Authors: Upadhyaya J. C. , Sharma D. K. , Prakash D. , Upadhyaya S. C.
Published: April 2011

A lattice dynamical model is developed by applying the Clark–Gazis–Wallis-type three-particle forces in the hexagonal close-packed (hcp) system. The model is then applied in the study of the phonon dispersion in four hep metals, namely, Be, Tb, Ho, and Lu. The present scheme gives the dynamical matrix element Im D12 (q, 11) to be nonzero and explains the peculiar behaviour of dispersion branches along ΓKM direction in these hep metals. Further more, a single expression for C44 is found and the Cauchy discrepancy (C13-C44) is entirely ascribed to the three-particle forces.
Casimir operators of the exceptional group G2 in a B3 basis
Authors: Bincer Adam M.
Published: April 2011

Expressions are given for the Casimir operators of the exceptional group G2 in a concise form similar to that used for the classical groups. This is achieved by expressing the generators of G2 in a B3 basis.
Colourings of quasicrystals
Authors: Moody R. V. , Patera J.
Published: April 2011

We introduce a notion of colouring the points of a quasicrystal analogous to the idea of colouring or grading of the points of a lattice. Our results apply to quasicrystals that can be coordinatized by the ring R of integers of the quadratic number field [Formula: see text] and provide a useful and wide ranging tool for determining of sub-quasicrystals of quasicrystals. Using the arithmetic properties of R we determine all possible finite colourings. As examples we discuss the 4-colours of vertices of a Penrose tiling arising as a subset of 5-colouring of an R lattice, and the 4-colouring of quasicrystals arising from the D6 weight lattice.
New classes of summable Skyrmions
Authors: Marleau Luc
Published: April 2011

We introduce two new classes of summable Skyrmions. The Lagrangians they originate from are explicitely constructed. We also analyse how some models could be solve. Exact solutions are found for Skyrme-like toy models.
Product trial function for confined quantum systems
Authors: Brownstein K. R.
Published: April 2011

To obtain the energy of a confined quantum system (e.g., a quantum-well wire) using the variational method, one usually uses a product ψ(r) = F(r)G(r) form for a trial wave function. The envelope function F takes care of the boundary condition (ψ = 0) by vanishing on the boundary of the confining region R while the function G can contain variational parameters for flexibility. We show that by judicious choice for F and G, the kinetic energy decouples into the sum of two terms: one associated with F and the other with G. For the particular case of a Coulomb potential (e.g., a hydrogenic impurity) we obtain (i) an expression for [Formula: see text] and (ii) a differential equation for the associated binding energy as a function of the size of the containing region R; both of these being valid for regions of arbitrary shape and size. A prediction of the differential equation is shown to agree with a published calculation for a quantum-well wire.
On the electromagnetic form factors of the nucleon
Authors: Bhattacharya A. , Remadevi T. L. , Banerjee S. N.
Published: April 2011

In the context of the modified version of the statistical model, a new wave function for a baryon is suggested. Properties such as formfactors, polarizabilities, etc. of the proton were studied using the aforesaid wave function and the properties of neutron were also probed through the properties of the proton. The estimated results are in good agreement with existing experimental data.
On the algebraic treatment of the spin–orbit interaction
Authors: Humi Mayer
Published: April 2011

The spin–orbit interaction term in the Hamiltonian H of the heavier atoms or nuclei is a quadratic operator. It does not commute with the central field Hamiltonian H0 and in many cases represents a strong interaction term. In this paper we show how to accommodate this operator within an extended Lie algebra structure that contains the symmetry algebra of H0. The representations of this extended algebra can be used then to classify the states of the Hamiltonian H.
La relation d'Einstein pour le mouvement brownien des membranes
Authors: Golo V. L. , Kats E. I.
Published: April 2011

We study form fluctuations of topologically nontrivial membranes, sponges for instance, assuming that there is a principal mode described by Langevin's equation, which has a character of chaotic relaxation to the equilibrium position. The influence of the ambient liquid being taken into account by the relaxation coefficients and the source of noise. The chaotic change of the surface is characterized by the quantity Δ2 (similar to the activity of rotational Brownian motion), which satisfies Einstein's equation Δ2/t = γIT, where t is the time, I a factor depending on the form of the membrane, and γ the dissipative constant. Fluctuations are studied by using the chiral field that is obtained from the Gauss–Weingarten local frame, usual in the classical theory of surfaces. Thus, we determine the effective action for a chiral field having a supersymmetric structure, we derive the correlation functions, and develop the theory of perturbations by the curvature of the surface.[Journal translation]
Theory of interacting parallel quantum wires
Authors: Sun Yinlong , Kirczenow George
Published: April 2011

We present self-consistent numerical calculations of the electronic structure of parallel Coulomb-confined quantum wires, based on the Hohenberg–Kohn–Sham density functional theory of inhomogeneous electron systems. We find that the corresponding transverse energy levels of two parallel wires lock together when the wires' widths are similar and their separation is not too small. This energy-level locking is an effect of Coulomb interactions and of the density of states singularities that are characteristic of quasi-one-dimensional fermionic systems. In dissimilar parallel wires, level lockings are much less likely to occur. Energy-level locking in similar wires persists to quite large wire separations, but is gradually suppressed by inter-wire tunneling when the separation becomes small. The experimental implications of these theoretical results are discussed.
Electrodynamics in a rotating frame of reference with application to global ocean circulation
Authors: Tyler Robert H. , Mysak Lawrence A.
Published: April 2011

The electrodynamic equations in a rotating reference frame (with velocities of rotation much less than the speed of light) are derived for the cases of a medium stationary in the rotating frame, and a medium with a general velocity relative to the rotating frame. The second case is considered as a necessary formalism for use in the modelling of large-scale electromagnetic fields induced by a prescribed ocean circulation. The terms that include rotational effects depend not only on the relative velocities but also on the electric properties of the material media. Hence, the assumption that rotational terms can be neglected simply because the velocities involved are much less than that of light in a vacuum is not supported. For typical values of the parameters describing the electric properties of the ocean, three of the four Maxwell equations (in Minkowskian form) are similar in form to those in an inertial frame. A governing induction equation in one vector variable (the magnetic field, b) is derived and written out explicitly in various coordinate systems.
The effect of renormalization in a finite massive theory
Authors: McKeon D. G. C.
Published: April 2011

The fact that a theory is finite does not preclude the possibility of making finite renormalizations. With this in mind, we consider massive N = 4 super Yang–Mills theory, a model known to have a vanishing β function and to be finite at one-loop order when one uses the formulation using N = 1 superfields. The mass that appears in the Lagrangian is not a pole of the propagator when radiative effects are included; we fix the position of this pole and then discuss how the effective coupling constant in the theory depends on this pole mass. This procedure is akin to the original Gell-Mann–Low approach to the renormalization group. A one-loop calculation indicates that the effective coupling vanishes as the pole mass goes to zero and diverges for large values of the pole mass.
Influence of substitutional impurities on the static and dynamical behaviour of K2OsCl6 in the vicinity of the structural phase transition: A neutron diffraction study
Authors: Prado Pablo J. , Armstrong Robin L. , Powell Brian
Published: April 2011

The effect of IrCl62− and ReCl62− impurity ions substituted for OsCl62− ion in K2OsCl6 is studied using neutron powder diffraction. The introduction of the impurity ions causes measurable changes in the lattice parameters but not in the Os—Cl bond length. The dynamical parameters of the model structure used to fit the data are well described by a Debye model of the lattice vibrations. The structural phase-transition temperature is affected by the addition of the impurity ions. Evidence is provided for suppression, in the presence of the impurities, of the development of precursor dynamical clusters above the phase-transition temperature.
Properties of perylene reacted with AsF5
Authors: Datars W. R. , Chien T. R. , Ummat P. K.
Published: April 2011

Perylene (Per) was reacted with AsF5 dissolved in liquid SO2 to produce Per(AsF6)2. Far infrared absorption showed absorption by AsF6−. Nuclear magnetic resonance of 19F consisted of a quartet formed by indirect nuclear–nuclear coupling. The change of mass through the reaction indicated the formula Per(AsF6)2. Mass spectroscopy showed bonding between perylene and F and indicated no SO2 solvent in the sample. This solvent-free material does not conduct electrically. X-ray diffraction showed that the structure has an orthorhombic cell. Exposure to air changes the sample weight and colour, and results in conduction with semiconducting properties and reduced bonding between AsF6− and perylene.
Anion-anion repulsion, coordination number, and the asymmetry of hydrogen bonds
Authors: Brown I. D.
Published: April 2011

By examining which coordination numbers are not known for a large variety of cations, it is found that the closest approach of two O atoms, Rmin, is given by, Rmin = 220 – 34.1n(s′) pm, where s′ is the projection onto the O–O vector of the valence of the bonds formed to a common cation. This equation is then used to show that the asymmetry of O—H … O hydrogen bonds is a consequence of the repulsion between the donor and acceptor O atoms. The model leads to a natural division of hydrogen bonds into three classes: strong, normal, and weak, and it gives good predictions for the geometries of each.
Ab initio simulation of the structure and dynamics of white phosphorus (P4) at low temperatures
Authors: Ungar P. Jeffrey , Laasonen Kari , Klein Michael L.
Published: April 2011

Ab initio simulations of low-temperature white phosphorus (β-P4) were performed using Car–Parrinello density-functional-theory molecular dynamics and a plane-wave basis set. Gradient corrections to the local density approximation were used to obtain a better description of the weak intermolecular forces. Starting with unit-cell parameters and atomic coordinates recently verified using neutron scattering, molecular dynamics trajectories over 9–10 ps were obtained for temperatures of 50 and 145 K. The computations show that the distortions from ideal tetrahedral P4 molecules found in the reduction of the neutron data may be a finite-temperature effect and not an artifact of the data analysis. Examination of the molecular reorientational dynamics shows that orientational order persists throughout the simulations, which suggests that β-P4 is an orientational crystal.
Experimental behaviour and modelling of an unsaturated compacted soil
Authors: Rampino Celestino , Mancuso Claudio , Vinale Filippo
Published: April 2011

This paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the Metramo dam, Italy. Specimens were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-controlled conditions by a stress path triaxial cell and an oedometer. The experimental program consists of 23 tests carried out in the suction range of 0-400 kPa. The findings indicate the strong influence of suction on compressibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gradient. Furthermore, the soil exhibited collapsible behaviour upon wetting even at low stress levels. Interesting results were also achieved in elastoplastic modelling as well. The results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils, providing noteworthy suggestions about their applicability for granular materials with a non-negligible fine component. Finally, some remarks are made for the extension under unsaturated conditions of the "Nor sand" model for saturated granular soils. The proposed approach yields improved predictions of deviator soil response of the tested soil when Cambridge-type frameworks prove invalid.Key words: unsaturated soils, stress state variables, triaxial tests, oedometer tests, constitutive model.
Alternative method of determining resilient modulus of subgrade soils using a static triaxial test
Authors: Kim Dong-Soo , Kweon Gi-Chul , Lee Kwang-Ho
Published: April 2011

The resilient moduli (MR) of subgrade and subbase soils are very important properties in the analysis and design of a flexible pavement system. However, difficulties and complexities in performing cyclic MRtesting and the high cost of the testing system have prevented the cyclic MRtest from becoming a routine test. Therefore, the development of an alternative simple and reliable MRtesting technique is essential to the application of the mechanistic design of a flexible pavement system. In this study, an alternative MRtesting technique for subgrade soils was developed using a static triaxial compression (TX) test. For the development of the alternative testing method, the effects of strain amplitude, loading frequency, mean effective stress, and number of loading cycles on the resilient modulus of subgrade soils were fully investigated. Cyclic MR, static TX, and resonant column  torsional shear tests were performed to evaluate the deformational characteristics. Synthetic specimens of known stiffnesses ranging from those of soft subgrade soils to those of subbase materials were developed, and all of the testing systems used in this study were calibrated. The alternative MRtesting procedures were proposed considering deformational characteristics of subgrade soils. The reliability of the proposed test method was verified by comparing the moduli determined by the proposed alternative MRtesting method with those determined by the standard MRtests.Key words: resilient modulus (MR), alternative MRtest, subgrade soils, static triaxial test, deformational characteristics.
The River Aire slope failure at the St. Aidans Extension Opencast Coal Site, West Yorkshire, United Kingdom
Authors: Hughes D B , Clarke B G
Published: April 2011

The St. Aidans Extension Opencast Coal Site is located in the flood plain of the River Aire 10 km southeast of Leeds, United Kingdom. In March 1988, a massive (600 000 m3) slope failure caused a breach of the riverbanks and flood-protection levee, and so connected the river to the opencast void, resulting in flooding of the site. A lake of about 100 ha and up to 70 m depth was created, and coal winning operations had to be suspended for 10 years. The causes of this slope failure included the effects of previous underground coal mining beneath those seams which were being surface mined, resulting in large tensile strains (up to 10 mm/m) in a heavily faulted zone that lay beneath the river bed and an adjacent navigation canal. The fracturing and opening of existing faults and joints greatly increased the permeability beneath the river, which then acted as a source of continuous recharge as the failed mass moved towards the opencast void. Subsequent remedial and recovery works (costing £20 million) have included the rerouting of the River Aire together with the canal, and pumping the flood water from the void and restarting opencast mining operations (tender sum £36 million) with a new box cut. This paper details the ground conditions and the history of events and discusses the probable mode of failure.Key words: opencast mining, slope failure, flooding, mining subsidence, ground strains, faulting.
Interpretation of the limits in shear strength in binary granular mixtures
Authors: Vallejo Luis E
Published: April 2011

Many natural slopes and rockfill structures are made of a mixture of rock fragments and sand-size particles. To analyze the stability of such natural slopes and rockfills, a knowledge of how rocksand mixtures develop their shear strength is needed. Laboratory tests conducted on mixtures of glass beads of two different sizes (5 and 0.4 mm) have indicated that their shear strength depends upon the relative concentration by weight of the large and small beads in the mixtures. If the concentration by weight of the large beads is greater than 70%, the shear strength of the mixtures is controlled by the frictional resistance of the large beads. If the concentration of the large beads is less than 40%, the shear strength of the mixtures is controlled by the frictional resistance of the small beads. If the concentration of the large beads is between 40 and 70%, the shear strength of the mixture is partially controlled by the frictional resistance provided by the large beads in the mixtures. These limits are very similar to those reported for rocksand mixtures. To date, no explanation has been put forward to account for why these limits exist. This study presents an explanation for their existence. The explanation is based on the porosity developed by the mixtures and the type of structural support provided by the coarse and fine grains.Key words: shear strength, granular mixtures, porosity, fabric, compaction.
Interpretation of sieve analysis data using the box-counting method for gravelly cobbles
Authors: Yang Zon-Yee , Juo Jian-Liang
Published: April 2011

In fractal theory, the fractal dimension (D) is a measure of the complexity of particle distribution in nature. It can provide a description of how much space a particle set fills. The box-counting method uses squared grids of various sizes to cover the particles to obtain a box dimension. This sequential counting concept is analogous to the sieve analysis test using stacked sieves. In this paper the box-counting method is applied to describe the particle-size distribution of gravelly cobbles. Three approaches to obtain the fractal dimension are presented. In the first approach the data obtained from a classic laboratory sieve analysis are rearranged into a double-logarithmic plot, according to a fractal model, to obtain the fractal dimension of the particle collection. In addition, an equivalent number of covered grids on each sieve during the sieve analysis are counted to produce the box dimension. According to the box-counting method concept, a photo-sieving technique used in scanning electron microscope microstructure analysis is adopted for use on gravelly cobbles in the field. The box-counting method concept is capable of explaining the sieve analysis data to clarify the information on the particle-size distribution. Using photo-sieving to produce the fractal dimension from field photographs can provide another approach for understanding the particle-size distribution. However, the representative cross-profile should be chosen carefully. The composition of the particle-size distribution for gravelly cobbles with higher D values is more complicated than those at sites with smaller D values.Key words: sieve analysis, box-counting method, fractal dimension, particle-size distribution, gravelly cobbles.
Landslides And Pleistocene Deposits in the Meikle River Valley of Northern Alberta
Authors: Nasmith Hugh
Published: April 2011

The paper describes Pleistocene deposits and landslides in the Meikle River valley in northwestern Alberta. A 300 ft. section of post-glacial lacustrine silts, clayey glacial till, and heavily overconsolidated sediments was explored by test drilling in connection with a railway route survey. The valley walls are cut by a continuous series of landslides. A “mature” and a “youthful” landslide profile were recognized as representing different stages in the development of the valley. Lateral erosion by the river is keeping many of the landslides in an unstable condition and this situation will continue in the future.
INFLUENCE OF SOIL-STRUCTURE INTERACTION ON THE EARTHQUAKE RESPONSE OF BUILDINGS
Authors: Singhal A , Tahiani C
Published: April 2011

In this paper, the influence of the soil properties on the dynamic response of a building subjected to different earthquakes is quantitatively analyzed. The proposed mathematical model for foundation and surrounding soil consists of (1) an equivalent soil-foundation mass M0, (2) a translational spring of stiffness K0, (3) a rotational spring of stiffness Kθ, and (4) dashpots for damping in translational and rocking modes. By using existing theory, values for K0and Kθhave been selected for a rigid foundation supported by semi-infinite soil mass. A numerical incremental-iterative type of scheme is devised and a linear acceleration method is utilized to obtain the elastic and inelastic structural response. Digitized earthquake records from El Centro 1934 and 1940 have been utilized to study the influence of foundation conditions on the structural response of a multi-storey building. A range of soil properties and soil damping characteristics are chosen and various response curves are presented; this leaves complete freedom to a soil and foundation engineer to choose any desired value of the soil properties.Numerical analyses of a three-storey building show that for the foundation, the largest relative displacement occurs in the translational mode and the largest foundation rotation can be obtained by combining translational and rotational modes. It is shown that the natural frequency for a building in which the foundation effects are considered is always lower than that obtained for a building in which foundation effects are neglected. It is found that the soil damping characteristics have a major influence on the structural response, but Poisson's ratio of the soil has a minor influence. Various other recommendations regarding earthquake foundation designs are also suggested.
Field Tests of Deep Power-installed Screw Anchors in Permafrost
Authors: Johnston G. H. , Ladanyi B.
Published: April 2011

A test program was conducted in northern Manitoba to evaluate the creep behavior and load capacity of 8-, 10-, and 15-in. (20.3-, 25.4-, and 38.1-cm) diameter power-installed screw anchors embedded in permafrost (frozen, stratified silts and clays containing ice at about 31.5 °F (−0.3 °C)). The test results show that the anchors behaved under uplift loads, in a manner that was essentially very similar to that exhibited by deep footings of the same size. No failure planes (slip surfaces) were observed around the plates but a deformed zone above the plates was clearly visible in the varved soil when the anchors were excavated after testing. A method of analysis which allows the test data to be used directly for design, based on secondary creep rates and allowable displacements, is described.
A predictive model for the water retention curve: application to tailings from hard-rock mines
Authors: Aubertin Michel , Ricard Jean-François , Chapuis Robert P
Published: April 2011

It is now commonly recognized that many geotechnical problems are related to the unsaturated behavior of soils. Such is the case for phenomena occurring at shallow depths in the so-called vadose zone. Unsaturated flow is also very important for the management of milling wastes, especially for seepage in and around tailings ponds. Suction properties constitute a key element for the functional representation of unsaturated flow conditions. These are usually shown by the water retention curve, which gives the relationship between volumetric water content ( theta ) and matric suction ( psi ). Laboratory measurements have been performed on three different tailings from hard-rock mines in the Abitibi region to study the effect of various factors, including grain size and porosity, on the theta - psi relationship. The main results are presented in this paper. The data are first analyzed using a well-known descriptive model. The experimental results are also used to estimate the air-entry value according to various procedures including a simple method proposed by the authors. Then, it is shown how an existing predictive model can be modified to obtain, from basic material properties, the complete water retention curve.Key words: unsaturated flow, tailings, water retention curve, moisture content, saturation ratio, porosity.
Interprétation des mesures inclinométriques durant la construction des remblais zonés des ouvrages de retenue du Complexe La Grande, phase I
Authors: Massiéra Michel , Boncompain Bernard , Merheb-Harb Joseph
Published: April 2011

Une simulation du comportement de sept sections instrumentées au droit de cinq grands ouvrages de retenue du Complexe La Grande à la Baie James a été effectuée par la méthode des éléments finis. Ces sections ont été instrumentées à l'aide d'inclinomètres placés en général dans le noyau de moraine (vertical ou légèrement incliné). Ce noyau est protégé par des filtres en sable et gravier de plus faible compressibilité et par des épaulements réalisés en sable et gravier ou en enrochement. Les simulations ont été effectuées en utilisant le programme FEADAM 84. Elles présentent un intérêt, car les matériaux utilisés dans les cinq ouvrages de retenue sont très similaires, mais leur géométrie et leur zonage varient d'un ouvrage à l'autre. Cette étude permet de valider les paramètres utilisés pour les matériaux à granulométrie grossière et justifie les méthodes de choix de paramètres. De plus, elle permet de calculer les contraintes qui existent dans le noyau à la fin de la construction. Ces résultats indiquent que la comparaison de la charge hydraulique avec la contrainte principale mineure calculée, à la fin de la construction, dans l'axe du noyau ne permet pas de faire une estimation correcte du potentiel de claquage hydraulique. Mots clés : barrage en remblai, contraintes, déformations, effet de voûte, sols à granulométrie grossière, modèle hyperbolique, modules, noyau, paramètres, oedomètre.
Interslice force functions for computing active and passive earth force
Authors: Zakerzadeh Noshin , Fredlund D G , Pufahl D E
Published: April 2011

Recent methods to calculate the lateral earth force on a retaining wall have involved the method of slices and limit equilibrium concepts. An important issue in formulating the solution is the selection of an appropriate interslice force function (i.e., the ratio of the shear force to the normal force of vertical slices along the slip surface). This paper proposes interslice force functions that can be used to compute the active and passive earth forces in conjunction with the limit equilibrium method. An example problem involving a vertical wall with a horizontal backslope is analyzed using the general limit equilibrium (GLE) method and the proposed interslice force functions. The procedure recommended to compute the lateral earth force and the point of application of the force is outlined. The computed lateral earth forces, and the point of application, are compared with those from the classical solutions. For the active case, reasonable results were obtained when using an interslice force function that varies linearly from the starting point of the slip surface (at some distance from the wall) to the end point of the slip surface (adjacent to the wall). For the passive case, reasonable results were obtained when using an interslice force function that remains at zero from the starting point of the slip surface (at some distance from the wall) to the midpoint of the slip surface and then varies linearly from the midpoint of the slip surface to the end point of the slip surface (adjacent to the wall).
Influence of the temperature on the viscosity measurements of solutions of a soil fulvic acid
Authors: Rey Francisco , Machado Adelio ASC
Published: April 2011

The influence of the concentration (ca. 45 to 300 mg L-1), the pH (3.0 to 8.0), the ionic strength (0.005 to 0.10 M), and the temperature (283 to 303 K) on the viscosimetric behaviour of solutions of a soil fulvic acid has been analysed, and their molecular parameters (length, thickness, and molecular volume) calculated. The results indicate that the polyelectrolytic behaviour of the fulvic acid is similar at all the temperatures, i.e., increasing the viscosity when reducing the ionic strength and to increase the temperature. With respect to the pH an initial decrease in the viscosity is obtained followed by a rise to the highest pH values. These variations have been interpreted by their molecular parameters as due to modifications of the structure of the molecules of the fulvic acid.Key words: fulvic acid, viscosity, temperature.
Cyclic five-membered phosphinate esters as transition state analogues for obtaining phosphohydrolase antibodies
Authors: Hum Gabriel , Wooler Krista , Lee Jeremy , Taylor Scott D
Published: April 2011

Two novel cyclic five-membered phosphinate esters (6 and 7) were synthesized and used as transition state analogues (TSAs) for raising phosphohydrolase antibodies. The key step in the syntheses was a McCormack reaction between (2-chloroethyl)dichlorophosphite and 1,4-diphenyl-1,3-butadiene to form isomeric cyclic phosphinyl chlorides which upon further elaboration yielded the TSAs. X-ray crystal structures of two cyclic phosphinate TSA precursors (14a and 14b) show highly compressed CPC bond angles of 94°-97° indicating that the CPC bond angles in 6 and 7 are significantly distorted towards the ideal trigonal bipyramidal equatorial-apical transition state angle of 90° formed during phosphate ester hydrolysis. Antibodies were raised to 6 and 7 using standard hybridoma technology. One antibody, Jel 541, an IgM class antibody, was obtained that was capable of catalyzing the hydrolysis of phosphonate substrate 9 and, to a much lesser extent, phosphate substrate 8. This antibody bound TSA 6 approximately 100 times more tightly than TSA 7 as determined by solid phase radio immune assays. The activity of the antibody-catalyzed reaction was completely inhibited by the presence of TSA6. Although the relative instability and poor solubility of Jel 541 made it impossible to perform a detailed kinetic analysis of the antibody-catalyzed reactions, these results demonstrate that phosphohydrolase antibodies can indeed be obtained using cyclic five membered phosphinates as haptens.Key words: transition state analogues, phosphate ester hydrolysis, catalytic antibodies.
On diastereomeric perturbations
Authors: Girard Christian , Kagan Henri B
Published: April 2011

For more than a century, organic chemists have been playing in Nature's laboratory. Their first goal was to understand the organization of atoms in the living matter and then to reproduce it by synthesis. This quest gave rise to several efficient techniques to synthesise molecules; many of them still in use nowadays, as such or with little modifications. Even at the beginning of this journey, the chemists discovered that their methods were far from being as efficient as the ones used by Nature to produce substances. The natural molecules were chiral and there was even an enantiomer that was produced over the other;a lesson of perfection. This was another challenge for the chemists and they succeeded by first developing techniques to separate enantiomers and more recently reagents and reactions to produce only the desired stereoisomer. Asymmetric synthesis uses chiral auxiliaries, reagents or catalysts to create chirality into the desired compound. The common perception, as a minimum condition, was that the chiral substance used to perform such a transformation has to be of the highest enantiomeric purity to obtain a very high selectivity. The relation between the enantiomeric excesses of the chiral substance and the product was suggested to be linear. But there were a lot of surprises left in the laboratory. Who would have thought that an impure substance could give an enantiomeric excess in the product higher than its own purity? The molecules are acting in different ways in solution. Self-organization and aggregation can arise depending on the structure of the substance or its environment. Such phenomenon can generate deviations to the awaited behaviour of the molecules that can be observed in many cases. This article tries to present some examples of the historical reports of such peculiar behaviours, their influence on physico-chemical properties and the final discovery of the now well-known nonlinear effects in asymmetric synthesis.Key words: asymmetric synthesis, diastereomeric interactions, nonlinear effects.
Synthesis of dimeric and tetrameric macrolactams with cytotoxic activity1
Authors: Gentile Gabriella , Fattori Daniela , Botta Maurizio , Corelli Federico , Fusar-Bassini Domenico , Lamba Doriano
Published: April 2011

Cyclization of amino acid 14, in turn prepared from 4,4-dimethylcyclohex-2-en-1-one by standard chemistry, yielded the dimeric and tetrameric macrolactams 15 and 16, respectively, representing the first examples of "taxoid-like" compounds with heterocyclic B rings. Compounds 15 and 16 exhibited moderate antiproliferative activity in an in vitro cytotoxicity assay. Consequently, an orthogonally diprotected, dimeric macrolactam 19 was synthesized and, after selective deprotection of the hydroxy group, was coupled with the docetaxel side chain to give the final compound 2, showing three-dimensional shape similarity to paclitaxel. Contrary to our expectations, 2 proved to be as active as the parent compound 15. The structure of 15 has been confirmed by X-ray crystallographic analysis and is also reported.Key words: macrolactams, macrocyclic compounds, taxane analogs, cytotoxic activity.
Substrate specificity of fucosyl transferase III: An efficient synthesis of sialyl Lewisx-, sialyl Lewisa-derivatives and mimetics thereof
Authors: Ernst Beat , Wagner Bea , Baisch Gabi , Katopodis Andreas , Winkler Tammo , Öhrlein Reinhold
Published: April 2011

Fucosyl transferase III (FucT III) has previously been characterized as the most general enzyme of the FucT family, as judged from its ability to catalyze the transfer of fucose to both Galβ(1-3)GlcNAc and Galβ(1-4)GlcNAc. In order to explore the synthetic potential of FucT III for the enzymatic synthesis of sialyl Lewisxand sialyl Lewisaderivatives, its substrate specificity has been probed using a number of natural substrate mimetics. A remarkable range of acceptor substrates was found when N-acetyl glucosamine was replaced by D-glucal, (R,R)-1,2-cyclohexanediol and (R,R)-butan-2,3-diol. Although the reaction rates were low compared to the reaction with the natural substrates, they proved to be sufficient for the synthesis of preparative amounts.Key words: fucosyl transferase III, sialyl Lewisa, sialyl Lewisx, carbohydrate mimetics.
Photolysis of tris(trimethylsilyl)silane: trapping of sisyl radicals
Authors: Mohamed Mustafa , Brook Michael A
Published: April 2011

The photolysis of tris(trimethylsilyl)silane (TTMSS) was studied in the absence and in the presence of added trapping agents such as alkenes and alcohols. It was found that, unlike the case with pyrolysis, silyl radicals rather than silylenes are produced. They may be efficiently trapped with alkenes, to give the hydrosilylation products, but not with alcohols. The major product from the photolysis of TTMSS in the absence of added trapping agent (or with alcohols as trapping agents) was tetrakis(trimethylsilyl)silane. Possible mechanisms to account for the photoproducts are presented.Key words: hydrosilane, photolysis, silylenes, silyl radical, sisyl hydride.
The photoequilibration of the ortho-, meta-, and para-isomers of substituted benzenes in ace- tonitrile and the photoaddition of 2,2,2-tri- fluoroethanol (TFE) to the same isomers: a survey
Authors: Foster J , Pincock A L , Pincock J A , Rifai S , Thompson K A
Published: April 2011

The phototransposition (ortho, meta, para) in acetonitrile of a number (25) of disubstituted benzenes have been examined. For some cases (methylbenzonitriles, trifluoromethyltoluenes, and trifluoromethylbenzonitriles) photostationary states could be reached but others (methylanisoles, methoxybenzonitriles, dicyanobenzenes, and methy 4-toluyl sulfone) were unreactive. The photoaddition of 2,2,2-trifluoroethanol (TFE) to the same compounds as well as 5 monosubstituted cases was also examined. The products obtained for reactive compounds were all TFE ethers of bicyclo[3.1.0]hex-3-en-2-ol derivatives. For benzene and alkylbenzenes (toluene, ortho-xylene) these photoadducts are formed by ground state addition of TFE to benzvalene derivatives. For others (methylbenzonitriles), bicyclic diradicals or carbenes are likely intermediates. Many substituted compounds (anisole, fluorobenzene, methyl benzoate, methyl anisoles, methoxybenzonitriles, dicyanobenzenes, trifluoromethylbenzonitriles, and fluorotoluenes) did not react with TFE. The trifluoromethylbenzonitriles did however undergo phototransposition in TFE, the only compounds to do so.Key words: substituted benzenes, phototransposition, photoaddition.
Synthesis, characterization, and properties of some cyclopentadienyl molybdenum nitrosyl benzyl complexes
Authors: Legzdins Peter , Smith Kevin M , Rettig Steven J
Published: April 2011

Reaction of CpMo(NO)(CH2Ph)Cl with Me2Mg, Ph2Mg, or PhCCLi reagents in THF affords the corresponding alkyl, aryl, or alkynyl CpMo(NO)(CH2Ph)R (R = hydrocarbyl) complexes as orange powders in good yields. Unlike related 16-electron CpMo(NO)R2 complexes, these 18-electron species exhibit good thermal stability due to their η2-benzyl-Mo interactions. Treatment of CpMo(NO)(CH2Ph)Cl with Na(DME)Cp provides dark green Cp2Mo(NO)(CH2Ph), whose solid-state molecular structure has been established by a single-crystal X-ray crystallographic analysis. The two Cp rings display different binding modes to the Mo atom, while the benzyl ligand is coordinated to the metal centre in an η1 fashion. The triflate complex, CpMo(NO)(CH2Ph)(OTf), is obtained by addition of AgOTf to the benzyl chloride precursor. The covalent MoOTf bond in this compound can be disrupted by the addition of Lewis bases (L) such as PPh3 or pyridine, leading to the corresponding [CpMo(NO)(CH2Ph)(L)][OTf] salts. Attempts to generate neutral benzylidene complexes by deprotonation of [CpMo(NO)(CH2Ph)(PPh3)][OTf] have not yet been successful.Key words: nitrosyl, molybdenum, benzyl, hydrocarbyl, triflate.
Chiral metallocenes: the synthesis and X-ray crystal structures of TiCl2η5:η5-C5Me4SiMe2C5H3R*) (R* = menthyl or neomenthyl) and related compounds
Authors: Beagley Paul , Davies Philip , Adams Harry , White Colin
Published: April 2011

The syntheses of the chiral ansa-metallocene complexes TiCl2(η5:η5-C5Me4SiMe2C5H3R*) (R* = menthyl (4a) or neomenthyl (4b)) are reported; initially 4a was obtained as a 3:1 mixture of (R:S) diastereoisomers, which differ only in which face of the asymmetrically substituted cyclopentadienyl ring is bonded to the titanium (chiral descriptor shown). The major diastereomer 4aR was crystallized out optically pure from the initial reaction mixture, whereas the 4aS diastereoisomer was isolated after isomerizing a racemic mixture of 4a to a 1:3 mixture of (R:S) diastereoisomers using UV irradiation. The corresponding neomenthyl complex 4b was obtained as a 1.3:1 mixture of diastereoisomers that could not be separated. The optically pure 4aR was converted stereoselectively into the corresponding (R)-TiMe2(η5:η5-C5Me4SiMe2C5H3R*) (R* = menthyl). Syntheses of the related indenyl ligand system C5Me4SiMe2C9H7 (3) is reported but complexation to titanium proved to be problematic although ZrCl2(η5:η5-C5Me4SiMe2C9H6) (6) was isolated. The crystal structures of both 4aR and 4aS are reported and compared. Crystals of 4aR are orthorhombic, a = 27.857(11), b = 9.985(5), and c = 9.596(4) Å, Z = 4, space group P212121 (D24, No. 19), and those of 4aS are monoclinic, a = 8.5810(10), b = 38.679(4), and c = 8.5842(10) Å, β = 113.001(2)°, Z = 4, space group P21 (C22, No. 4). The structures were solved by the Patterson method and 4aR was refined by blocked-cascade least-squares procedures to R = 0.0628 (Rω = 0.0503) for 902 reflections with |F|/σ(|F|) [Formula: see text] 3.0, whereas 4aS was refined by full-matrix least-squares procedures to R = 0.0646 (wR2 = 0.1829) for 5734 reflections with |F|/σ(|F|) [Formula: see text] 4.0. Both diastereomers of 4a catalyze hydrosilylation of ketones, but as expected from a comparison of the two crystal structures, the 4aR isomer is the more stereoselective catalyst, i.e., hydrosilylation of acetophenone followed by hydrolysis gives 82% enantiomeric excess (ee) of (S)-PhCH(Me)OH with 4aR whereas only 16% ee of (R)-PhCH(Me)OH with 4aS.Key words: titanium, metallocene, chiral, structure, catalyst.
Sulfate as a ligand in ruthenium(II) and (III) ammines
Authors: dos Santos Silva Hildo Antonio , McGarvey Bruce R , de Almeida Santos Regina Helena , Bertotti Mauro , Mori Vânia , Franco Douglas Wagner
Published: April 2011

The trans-[RuSO4(NH3)4(L)]Cl complexes, (L = nicotinamide (nia), L-histidine (L-hist), 4-picoline (4-pic), 4-chloropyridine (4-Clpy), isonicotinamide (isn), pyrazine (pyz), 4-aminopyridine (4-NH2py), 4-cyanopyridine (4-CNpy), pyridine (py), imidazole (Him), and water (H2O)), were characterized by elemental analysis cyclic voltammetry, UV-vis, IR, and electron paramagnetic resonance spectroscopies. From the four ν (SO42) observed only ν3 and ν4 split in two bands each for the sulfate unidentate coordination. The values of Δ/ξ parameters, extracted from g values, allow us to write the following order of increasing π-donation ability: pyz < (py, 4-CNpy, 4-Clpy. 4-pic, isn, nia) < Him < L-hist < 4-NH2py. The intense absorption in the 317-347 nm (ε ~ 2.3-5.6 × 103 M-1 cm-1) region was tentatively assigned to sulfate-to-metal charge transfer (LMCT) and the absorption in the range of 230-270 nm (ε ~ 2 - 6 × 103 M-1 cm-1) assigned to an internal (IL) π-π* transition in the heterocyclic ligands. The rate for the sulfate aquation in trans-[RuSO4(NH3)4L]0 complexes was evaluated through chronopotentiometric measurements and are in the 2.6 s-1 (chloropyridine) to 20 s-1 (pyrazine) range. The SO42 is aquated in trans-[RuIIISO4(NH3)4(4-pic)]Cl at the specific rate constant of (1.4 ± 0.4) × 10-5 s-1, which is very much slower than in trans-[RuIISO4(NH3)4(4-pic)] (5.4 s-1). The X-ray crystal structure data show that the Ru-Cl (2.3444(9) Å) and Ru-NH3 (2.100(2) Å) mean distances in trans-[RuCl(NH3)4(4-pic)]Cl2·H2O are similar to the ones observed in other tetraammineruthenium(III) complexes.Key words: ruthenium, sulfate, ammines.