High gain amplification of femtosecond pulses with low amplified spontaneous emission in a multipass dye cell

We present a multipass femtosecond amplifier pumped by a Nd-YAG laser where the gain medium is given by a variable length dye cell. This system allows amplification factors up to 5 · 10⁶ and output pulse energies of 150 J, while restricting the contribution of amplified spontaneous emission to 0.5% of the total output energy, without using any saturable absorber stage. A detailed study of the output pulsewidth as a function of the duration of the input chirped pulse is also presented.     

Laser-induced electron emission from an Au surface irradiated by single picosecond pulses at λ=2.94 μm. The intermediate region between multiphoton and tunneling effects

The photoinduced electron emission from the surface of a solid gold target irradiated by single picosecond pulses of an erbium laser is investigated. The applied laser intensity (5–120 GW/cm²) corresponds to the intermediate interaction region between the pure multiphoton and tunnel effects, where the decisive Keldysh-parameter, , is in the range 1<<12=n ₀. In the light intensity region which is free of surface heating (I _L<80 GW/cm²), the slope of the measured logarithmic intensity dependence of the photocurrent decreases from the n ₀=12 perturbative value down to n 5. Therefore the experiment shows that the Keldysh-type theories, which have recently been proved to describe correctly the ionization of atoms, are also valid to a certain extent in the case of the photoeffect in metals.     

Poly(styrene-b-2-vinylpyridine-1-oxide) diblock copolymers: 3. Microemulsions in water/propan-2-ol/toluene mixtures

Pseudo-ternary phase diagrams have been constructed for the three-component solvent system (toluene+water+propan-2-ol) containing diblock copolymers of poly(styrene-b-2-vinylpyridine-1-oxide). Microemulsions have been shown to form on the water-rich side of the phase diagram, in the region of the phase boundary without polymer. Dynamic light-scattering experiments have led to droplet size values in the region of 100 nm, with the size depending strongly on the propan-2-ol/water concentration, as well as the amount of solubilised toluene in the core. Viscometry experiments have been carried out to measure polymer aggregation numbers in the microemulsion droplets, and interfacial tension measurements have shown that in the absence of propan-2-ol (effectively a cosurfactant) the limiting value of the oil/water interfacial tension, even an saturation adsorption of the copolymer is 20 mNm^–1. However, addition of propan-2-ol reduces the interfacial tension to the very low values generall commensurate with microemulsion formation.     

Some properties of the riesz charge associated with a δ-subharmonic function

The first property is a refinement of earlier results of Ch. de la Vallée Poussin, M. Brelot, and A. F. Grishin. Let w=u–v with u, v superharmonic on a suitable harmonic space (for example an open subset of R ⁿ ), and let [w]=[u]–[v] denote the associated Riesz charge. If w0, and if E denotes the set of those points of at which the lim inf of w in thefine topology is 0, then the restriction of [w] to E is 0. Another property states that, if e denotes a polar subset of such that the fine lim inf of |w| at each point of e is finite, then the restriction of [w] to e is 0.     

Synthesis and Some Chemical Behaviour of Certain Substituted Thiosemicarbazides

Three new thiosemicarbazides (1 a-c ) were prepared from N-[4-phenyl-5-(2-thienyl)-1,2,4-triazol-3-yl]mercaptoacetohydrazide. Reaction of (1 a-c) with the appropriate phenacyl bromide afforded thiazoline derivatives (2 a-i) whereas their reaction with chloroacetic acid or maleic anhydride gave the corresponding thiazolidine derivatives (3 a,b) and (4 a,b) . Cyclodesulfurization of (1 a-c) with DCCD in toluene yielded 5-substituted-amino-1,3,4-oxadiazoles (5 a,b) , while their dehydration with PPA gave the corresponding 5-substituted-amino-1,3,4-thiadiazoles (6 a-c) . Six representative compounds were tested for their in-vitro antimicrobial activity against some pathogenic microorganisms, some of them were proved to be active.     

Molecular structures of β-amino-α-bromovinyl trifluoromethyl ketones

The molecular structures of β-amino-α-bromovinyl trifluoromethyl ketones was studied by UV, IR, ¹H, ¹³C, and ¹⁵N NMR spectroscopy and using the density functional (B3LYP/6-31G(d,p) and PBE/QZ3P) and ab initio riMP2/cc-pVTZm quantum-chemical calculations. Factors affecting stabilization of the EZE-conformation of the molecules, which is atypical of analogous unsubstituted amino enones, are considered.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 102–106, January, 2005.     

A theoretical analysis of modulation noise and dc erased noise in magnetic recording

The modulation noise and the special case, dc erased noise in magnetic recording are discussed theoretically, taking account of two main causes at the same stage, i.e. the magnetic properties such as the inhomogeneous distribution of the particles on the tape, and the mechanical properties such as the head-to-tape space variations arising from the tape surface roughness. We derive the signal as well as the noise power spectrum of the induced voltage at the read head. This is done by generalizing the theory of the signal behaviour. The theoretical result turned out to agree quite well with the experimental one. The modulation noise power spectrum can be interpreted to consist of two parts, i.e. the steep peak due to the mechanical causes near the recorded signal wavenumber and the broad peak due to magnetic causes.Nomenclature A(k) variable defined by(Km_av L _g L _d)² - d head-to-tape spacing [m] - d _av average value ofd [m] - d variance ofd [m] - D variable defined by (8) - e(t) induced voltage at the read head [V] - g gap length [m] - H the Karlqvist head field excited by a current uniti [A/m] - i a curren unit [A] - j –1 - k=¦k¦ wavenumber [m^–1] - k _c wavenumber of recorded signal [m^–1] - K constant which includes the number of turn of head, the read head efficiency and the permeability ₀[Vs/Am] - l _d correlation length of the variationd [m] - l _m correlation length of the variationm [m] - L _d (k) spacing loss defined by exp(–kd_av) - L _g (k) gap loss defined by sin(gk/2)/(gk/2) - M magnetization of the tape [A/m] - M variable defined by (8) - m amplitude of the magnetization of the signal pattern [A/m] - m _av average value ofm [A/m] - m variance ofd [A/m] - P(k) power spectrum [V²/Hz] - P _dc(k) noise power spectrum [V²/Hz] - S signal pattern of the tape - v relative velocity between the head and the tape [m/s] - x _t =(x _t ,y_t) coordinate on the tape - (x ₀,y₀) coordinate fixed on the read head - (x ₁,y₁) coordinate defined by (10) - tape thickness [m] - _d random phase variable defined by (8) - _m random phase variable defined by (8) - _O permeability [Vs/Am] - read-head detected flux [Wb]     

Synthesis and investigation of mono- and binuclear cyano-bridged complexes of rhodium,ruthenium, and palladium

Binuclear Rh^III and Ru^II complexes of the [M¹-CN-M²]⁺BF ₄ ^– (M¹ and/or M² are (⁵-Cp)(³-C₃H₅)Rh and (⁶-C₆H₆)(³-C₃H₅)Ru) type, heteronuclear organometallic compound (⁵-Cp)(³-C₃H₅)RhCNPd(³-C₃H₅)Cl, and mononuclear Rh^III and Ru^II complexes [(³-C₃H₅)LM(MeCN)]⁺ _BF4 ^– (M = Rh, L = ⁵-Cp; M = Ru, L = ⁶-C₆H₆) were synthesized. An electrochemical study of these compounds in solutions demonstrates that the bond between the bridged CN ligand and the metal atoms is rather strong, and there is no dissociation into mononuclear fragments in solutions. The kinetics of the reaction of [(⁵-Cp)(³-C₃H₅)Rh(MeCN)]⁺ _BF4 ^– with halide ions was studied by electrochemical methods. The ligand exchange proceeds by a bimolecular dissociative-exchange mechanism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 968–973, May, 1995.     

Partial molal volumes of ions in organic solvents from ultrasonic vibration potential and density measurements. III. Dimethylsulfoxide

The partial molal volumes of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Cl^–, Br^–, I^–, and NO ₃ ^- in DMSO at 25°C have been determined from ultrasonic vibration potential data and density data for solutions of uni-univalent electrolytes. Hepler's semiemprirical equation has been used to split ionic partial molal volumes into geometric and electrostrictive contributions. The results obtained in this work confirm the conclusion of our previous studies, namely, that the contribution of electrostriction is essentially determined by the properties of that layer of atoms, 0.3 to 0.4 nm thick, in contact with the ion and by the degree of steric hindrance of the poles of the dipole of the solvent molecule. On the other hand, the geometric contribution depends on the size of the solvent molecule and also on the arrangement of the solvent molecules about the ions. It is shown that the geometric contribution to the partial molal volume of ions is largely increased when ions cannot come close enough to the poles of the solvent-molecule dipole, owing to steric hindrance.