Global asymptotic stability of the Goodwin system with repression

We give a global asymptotic stability result for the classical Goodwin system. The proof follows from a combination of the Poincaré–Bendixson property enjoyed by monotone cyclic feedback systems, the theory of compound matrices and comparison techniques from the theory of monotone systems.     

Spectral control over the interaction of ultrashort pulses in fiber lasers

The interaction of light pulses in passively mode-locked fiber lasers operating has been studied. The numerical simulation has been used to demonstrate that a narrow-band selector inserted in a laser cavity allows the character of the interaction to be changed: depending on the detuning of the selector passband from the center of the gain band, ultrashort pulses can both attract and repel one another. Peculiarities of the pulse interaction have been studied at different parameters of the laser system.     

Non-Classical Traveling Solutions in a Nonlinear Klein Gordon Model

A model with interparticle inharmonic interaction under the Φ⁴ external potential is studied. Making use of the special relation of relevant parameters, in the continuous limit, it was possible to obtain various non-classical soliton solutions, specifically, compact and peak-like solutions. The solutions undergo a jump on their first derivatives at some points of the space-time manifold. These analytic solutions were obtained by considering strong restrictions on their velocities and on the jump conditions. The energy concentrated in these solutions shows in several cases a discrete spectrum.     

Morphological and thermal properties of ABS/montmorillonite nanocomposites using two different ABS polymers and four different montmorillonite clays

ABS/Clay nanocomposites were prepared using two ABS with different Acrylonitrile (AN) contents and four montmorillonite clays; a natural clay (CNa+) and three modified clays, Cloisites 10A, 20A, and 30B. The composites were prepared in a twin‐screw extruder. Results were analyzed considering the effect of clay and ABS type, on the clay dispersion, intercalation and exfoliation, as well as on the storage modulus and thermal stability of the nanocomposites. XRD and TEM confirm that when using an ABS with higher AN content (ABS2), a better dispersion and intercalation–exfoliation can be obtained. Cloisites 20A and 30B, respectively the one with greater initial intergallery spacing, but lower polarity and with smaller inter‐gallery spacing but greater polarity, produce the ABS nanocomposites with the greater intergallery spacing. Both ABS polymers have similar storage modulus and T_g and in both cases, the modulus increases with the 4 wt % clay. This increase is greater with the modified clays and slightly greater with the ABS2. T_g, from tan δ, increases very little with the 4 wt % clay, but again, this is slightly greater with ABS2. TGA and flammability tests show that the dispersed clay enhances the thermal stability and that the ABS with higher AN content produces a greater increase in fire retardancy. Tests also show that the better thermal stability and fire retardancy is obtained with the Cloisites 20A or 30B. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 190–200, 2008     

First Measurement of the Nuclear Charge Radii of Short-Lived Lithium Isotopes

A novel method for the determination of nuclear charge radii of lithium isotopes is presented. Precise laser spectroscopic measurements of the isotope shift in the lithium 2s → 3s transition are combined with highly accurate atomic physics calculation of the mass dependent isotope shift to extract the charge-distribution-sensitive information. This approach has been used to determine the charge radii of ^8,9Li for the first time.     

Magnetoresistance between oxidized Co-rich particles grown by high current electrochemical deposition

In this work, we present Co-rich particles which have been successfully grown by high current electroplating. This technique produces particles with a Co–Cu core surrounded by an oxidized shell. This shell has two consequences: on the one hand, it electrically isolates the magnetic core and acts as a tunnel barrier; on the other hand, the ferromagnetic/antiferromagnetic structure causes an exchange bias coupling when cooling the particles in the presence of magnetic field. We also present magnetoresistance measurements up to 9 T. At low field, direct tunnelling between magnetic cores through the insulating layer properly explains the experimental observations, but, at high field, a linear contribution dominates the MR. The latter behaviour can be understood by assuming second-order tunnelling.     

Photocatalytic Activity in the 2,4-Dinitroaniline Decomposition Over TiO2 Sol-Gel Derived Catalysts

Titania was prepared by the sol-gel method from titanium alkoxide. Depending on the pH of the gelling solution, specific surface areas between 88 and 10 m²/g were obtained. The band gap (E _g) of the samples was found between 3.05 and 3.32 eV. In samples gelled at pH5 and 9 and calcined at 400°C only anatase phase is observed, while for pH3 and pH7 brookite, anatase and rutile or anatase-rutile phases coexist. It was found that the photoactivity in the 2,4-dinitroanailine decomposition depends on the E _g and on the crystalline phases. The highest activity corresponds to the catalysts having the lowest E _g and more than one crystalline phases co-existing.     

A Lower Bound on the Partition Function for a Strictly Neutral Charge-Symmetric System

Journal of Statistical Physics - A lower bound on the grand partition function of a classical charge-symmetric system is adapted to the neutral grand canonical ensemble, in which the system is...     

Dissociation of C6F5SO3Li in two organic solvents with different dielectric constants: a Raman spectroscopic study

Organic solutions of lithium pentafluorobenzene sulfonate (C₆F₅SO₃Li) with varying molalities in N,N‐dimethyl formamide (DMF) and triethyleneglycol dimethylether (triglyme) were investigated by Raman spectroscopy. Spectral decomposition in the ν_s(SO₃) stretching region showed bands characteristic of free anions, ion pairs and various aggregates. The relative fraction of each species has been followed as a function of salt molality. In DMF, free anions dominate, while in triglyme ion pairs dominate, in accordance with the solvent dielectric constant. Copyright © 2007 John Wiley & Sons, Ltd.     

5,5‐Dimethyl‐3‐(5‐methyl‐1H‐pyrazol‐3‐ylamino)cyclohex‐3‐en‐1‐one

The mol­ecules of the title compound, C₁₂H₁₇N₃O, are linked by two N—H?O hydrogen bonds to form a three‐dimensional network. The N?O distances are 2.804 (3) and 2.766 (3) Å, both involving a common acceptor O atom.