125-TW Ti:sapphire/Nd:glass laser system

We have demonstrated a Ti:sapphire/Nd:glass laser system that produces up to 51 J of energy in 395-fs pulses (125TW). Focusing at f/3 to a 2.5-times diffraction-limited spot results in a peak irradiance greater than 10(20) W/cm(2) . Our 40-cm-diameter gold diffraction gratings have a damage threshold of 0.42 J/cm(2) for 320-fs pulses.     

Unusual rearrangement of the Ru3(μ-CO)2(CO)6{μ3-η1:η1:η4:η4-C4Ph2(CH=CHPh)2} complex containing an open triruthenium framework to the Ru3-triangular cluster Ru3(CO)8{μ3-η1:η1:η4:η2-C4Ph2(CH=CHPh)2}. Reactions of Ru3(CO)8{μ3-η1:η1:η4:η2-C4Ph2(CH=CHPh)2} with PPh3, P(OPri)3, CO, and the crystal structure of Ru3(CO)8(PPh3{μ-η1:η1:η4-C4Ph2(CH=CHPh)2}

Complex Ru₃(μ-CO)₂(CO)₆{μ₃-η¹:η¹:η⁴:η⁴-C₄Ph₂(CH=CHPh)₂} containing an open triruthenium framework undergoes rearrangement to the Ru₃-triangular Ru₃(CO)₈{μ₃-η¹:η¹:η⁴:η²-C₄Ph₂(CH=CHPh)₂) cluster when heated in refluxing hexane. Reactions of the latter complex with PPh₃, P(OPrⁱ)₃, and CO were studied. The structure of one of the reaction products, the Ru₃(CO)₈(PPh₃{μ₃-η¹:η¹:η⁴-C₄Ph₂(CH=CHPh)₂} cluster, was established by X-ray structural analysis.     

Os3(CO)9{μ3-η1-η1-η2-η2-C(SiMe3)C(Me)C(H)C(Fc)}, the second example of a cluster with the “face” coordination of the metallacyclopentadiene fragment and its conversion to the Os3(μ-H)(CO)8{μ3-η1-η1-η4-η1-C(SiMe3)C(Me)C(H)C(C5H3FeC5H5)} complex with theortho-metallated ferrocene moiety

Os₃(μ-CO)(CO)₉(μ₃-Me₃SiC₂Me) alkyne complexes react with ferrocenylacetylene in hot benzene to form Os₃(CO)₉{μ₃-η¹-η¹-η²-η²-C(SiMe₃)C(Me)C(H)C(Fe)} and a small amount of the isomeric Os₃(CO)₉(μ-η¹-η¹-η⁴-C(SiMe₃)C(Me)C(Fc)C(H)} complex. The structure of the major isomer was confirmed by X-ray structural analysis of the single crystal. Thermolysis of this complex in refluxing benzene affords the Os₃(μ-H)(CO)₈{μ₃-η¹-η¹-η⁴-η¹-C(SiMe₃)C(Me)C(H)(C₅H₃FeC₅H₅)} complex with theortho-metallated ferrocene moiety. The spectral characteristics of clusters with the μ₃-η¹-η¹-η²-η² and μ-η¹-η¹-η⁴ coordinations of the metallacyclopentadiene fragment have been established, which made it possible to choose between the alternative modes of bonding of diene with the trimetallic core.     

Nonlinear friction as a mechanism of directed motion

A simple model (ratchet model) of occurrence of directed motion under the action of a zero-mean fluctuating force is proposed. The motion arises when the symmetry in the velocity space is violated by nonlinear friction. The mechanism of the directed motion is discussed qualitatively. Existence conditions of the motion are derived. The efficiency of conversion of the fluctuating random force to the directed motion is estimated.     

Current filamentation instability in laser wakefield accelerators

Experiments using an electron beam produced by laser-wakefield acceleration have shown that varying the overall beam-plasma interaction length results in current filamentation at lengths that exceed the laser depletion length in the plasma. Three-dimensional simulations show this to be a combination of hosing, beam erosion, and filamentation of the decelerated beam. This work suggests the ability to perform scaled experiments of astrophysical instabilities. Additionally, understanding the processes involved with electron beam propagation is essential to the development of wakefield accelerator applications.     

Effect of winding edge currents

We discuss persistent currents for particles with internal degrees of freedom. The currents arise because of winding properties essential for the chaotic motion of the particles in a confined geometry. The currents do not change the particle concentrations or thermodynamics, similar to the skipping orbits in a magnetic field.     

Generation and characterization of the highest laser intensities (10(22) W/cm2)

We generated a record peak intensity of 0.7 x 10(22) W/cm2 by focusing a 45-TW laser beam with an f/0.6 off-axis paraboloid. The aberrations of the paraboloid and the low-energy reference laser beam were measured and corrected, and a focal spot size of 0.8 microm was achieved. It is shown that the peak intensity can be increased to 1.0 x 10(22) W/cm2 by correction of the wave front of a 45-TW beam relative to the reference beam. The phase and amplitude measurement provides for an efficient full characterization of the focal field.     

Uniaxial extension and shear in combination with cyclic straining as a promising method for studying the viscoelasticity of polymers over a wide range of stresses and strains atT > T g

Simple relations are found between the fracture strains, the long-term durability and the initial values of parameters characterizing polymer rheology at deformation rates and stresses approaching zero. Fracture regimes are determined by two groups of parameters. One includes critical values of stresses. They are invariant with repect to temperature and molecular weight of the polymers; the values of critical stresses for different polymer compositions differ by a factor of 10 to 20. The second group of critical parameters includes the rates of deformation determined by the initial viscosity. The latter may vary by many orders of magnitude. There exists a universal critical value determining polymer fracture independent of linear macromolecule composition, its molecular weight, the temperature and the way of attaining a given state. This value is the recoverable strain and is equal to 0.5 according to Hencky. There exists a relation between the maximum value of recoverable strain in the transition region from the rubbery to the leathery state and the extensibility of macromolecules for polymers with various molecular weights. Quenching of the polymer near the maximum recoverable strain makes it possible to obtain high strength samples. Overspurt regimes for polymer flow have also been studied. It has been shown that this causes polymer static electrification. Simple and unique dependences of the charge density on temperature and polymer molecular weight have been established.Presented at the 28th IUPAC International Symposium on Macromolecules, June 1982, Amherst, Mass. (USA)Dedicated to Prof. Dr. Josef Schurz on the occassion of his 60th birthday     

Synthesis and characterization of novel monocarbollide exo-closo-(pi-arene)biruthenacarboranes [(PPh3)mClRu(eta6-C6H5R)Ru'CB10H11-n(OMe)n] (where R = H, m = 2, n = 1; R = mu-PPh2, m = 1, n = 0, 1)

The monocarbon carborane [Cs][nido-7-CB(10)H(13)] reacts with the 16-electron [RuCl(2)(PPh(3))(3)] in a solution of benzene/methanol in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine as the base to give a series of 12-vertex monocarbon arene-biruthenacarborane complexes of two types: [closo-2-[7,11-exo-RuClPPh(3)(mu,eta(6)-C(6)H(5)PPh(2))]-7,11-(mu-H)(2)-2,1-RuCB(10)H(8)R] (5, R = H; 6, R = 6-MeO; 7, R = 3-MeO) and [closo-2-(eta(6)-C(6)H(6))-10,11,12-[exo-RuCl(PPh(3))(2)]-10,11,12-(mu-H)(3)-2,1-RuCB(10)H(7)R(1)] (8a, R(1) = 6-MeO; 8b, R(1) = 3-MeO, inseparable mixture of isomers) along with trace amounts of 10-vertex mononuclear hypercloso/isocloso-type complexes [2,2-(PPh(3))(2)-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(7)] (9) and [2,5-(Ph(3)P)-2-Cl-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(6)] (10). Binuclear ruthenacarborane clusters of both series were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of three selected complexes, 6-8. In solution, isomers 8a,b have been shown to undergo the isomerization process through the scrambling of the exo-[RuCl(PPh(3))(2)] fragment about two adjacent triangular cage boron faces B(7)B(11)B(12) and B(8)B(9)B(12).     

Formation and structure of diruthenium complexes Ru2(CO)6−n (PPh3) n {μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} (n=1, 2)

Ruthenium carbonyl triphenylphosphine complexes Ru₂(CO)_6−n (PPh₃) _n {μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} (n=1, 2) were obtained by the reaction of complex Ru₂(CO)₆{μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} containing the ruthenacyclopentadiene moiety with PPh₃ in refluxing toluene. The complexes were characterized by IR and by¹H,¹³C, and³¹P NMR spectroscopy, and by X-ray analysis. The monophosphine derivative is identical to the complex formed by fragmentation of the Ru₃(CO)₈(PPh₃){μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} cluster and contains the PPh₃ ligand at the ruthenium atom of the ruthenacyclopentadiene moiety. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1836–1843, September, 1998