All-Optical Wavelength Conversion with Amplitude Equalization and Pulse Shaping

A dual-wavelength-injection-locked (DWIL) Fabry-Perot (FP) laser is used as an all-optical wavelength converter and regenerator.Regenerated pulses have narrower pulse-width of 37ps.Power penalty and extinction-ratio improvement of 1.5dB and 4dB respectively were achieved.     

Interaction of anomalous muonium with electronic excitations in Si studied by longitudinal field μSR

We report longitudinal muon spin relaxation measurements in Si doped with phosphorus below room temperature. The data can be described qualitatively in a model where bond-centered muonium is undergoing spin exchange interactions below 150 K. Above this temperature, charge state cycling becomes important.This work is partially supported by the National Sciences and Engineering Research Council of Canada.     

Spin dynamics in conducting polymers studied by μSR

We report studies of spin dynamics in the conducting polymers polyaniline and polypyrrole using both μ⁺SR and μ^-SR techniques. These measurements reveal characteristic field dependences and cutoff frequencies for the muon spin relaxation which can be related to the spin diffusion process. Clear evidence is seen for increased spin localisation at low temperatures where a crossover occurs from two or three dimensional spin diffusion to a one dimensional diffusion regime. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fracture toughness determination for compact tension specimens

An analysis of determining the plane stress fracture toughness based on a beam-on-elastic foundation model for compact tension specimens (CTS) covering a wide range of a/2H and d/W ratios is presented. The solution is achieved by using the Timoshenko beam theory and Pasternak foundation with alternative formulations of the foundation modulus and the shear parameter to reflect more accurately the stress-strain distributions at the crack tip.The solution applicable to a wider range of a/2H and d/W ratios becomes desirable for practical reasons. For instance, the determination of plane-strain fracture toughness from the CTS specimens at higher a/W ratios enables the reduction of loading capacity from a testing machine which may become prohibitively high for medium strength engineering materials. Maximum fatigue crack growth data to be measured from a CTS specimen also becomes possible when the validity of fracture toughness can be ensured at the extended a/W ratios.The computed fracture toughness from the present analysis are compared with those measured experimentally and found to be satisfactory not only for high a/W ratios but also for a wide range of a/2H ratios commonly used in double-cantilever beam specimens.     

The effect of inflation pressure and vehicle loading on the sidewall of a radial tire

The sidewall is one of the regions where service failures occur in a pneumatic tire. Knowledge of the stresses or strains developed in the sidewall under varying service conditions is required if such pneumatic-tire failures are to be avoided. This paper describes an experimental investigation into the effect of inflation pressure, vehicle load and camber angle on the sidewall-surface strains in a radial tire. Photoelastic coating and a specially designed strain-gaging technique were used. For pure-inflation pressure, the magnitude of the measured shear strains in the sidewall is directly related to the inflation pressure. The maximum sidewall shear strains in pure inflation are located in the lower sidewall (18 mm from bead), irrespective of the magnitude of the inflation pressure. The mendional sidewall strain is predominant in the inflated but otherwise unloaded tire. The meridional strain is proportional to the square root of the inflation pressure. The maximum mendional strain is located in the mid-sidewall region. For a constant vehicle loading, there is a transition inflation pressure below or above which the circumterential shoulder strain increases sharply. This observation highlights the importance of maintaining satistactory inflation pressure in passenger-car tires as an under-inflated tire will induce severe strain development at the shoulder. In addition to the vehicle load, the introduction of camber angle produces localized change in the meridional and circumterential strains within the contact zone. The increase of camber angle up to 10 deg causes continuous increase in the meridional strain in the lower sidewall but decrease in the upper sidewall. The mid-sidewall meridional strains remain practically unchanged. The circumferential strains along the load line are, in general, lower due to the increase in camber angle.     

NMR flow imaging of Newtonian liquids and a concentrated suspension through an axisymmetric sudden contraction

Using nuclear magnetic resonance (NMR) flow imaging to examine fluid motions at constant velocities or flows that change relatively slowly has been well-documented in the literature. Application of this technique to accelerative flows, on the other hand, has been limited. This study reports the use of an NMR flow imaging method, for which acceleration is not explicitly compensated in the NMR pulse sequence, to measure axial and radial fluid motions during flow through an axisymmetric sudden contraction. In this flow geometry, both velocity and acceleration are spatially dependent. The flow contraction ratio was 2:1. The method was first applied to examine Newtonian liquids at low and high Reynolds numbers under laminar flow conditions. The measured axial and radial velocity profiles, without accounting for acceleration effects in the data analysis, across the contraction are in excellent qualitative agreement with previous experimental data and theoretical calculations reported in the literature. Quantitative comparison of the axial and radial velocities with numerical results indicates that the maximum error from acceleration effects is about 10%. The method has also been used to examine the flow of a concentrated suspension (50% by volume of solid particles) through the contraction. The flow kinematics of the suspension at creeping flow conditions appear to mimic those of the Newtonian fluid with some slight differences. NMR images taken immediately following the cessation of flow suggest a slight degree of particle migration toward the center of the pipe downstream of the contraction.     

Finite amplitude vibrations of a Mooney-Rivlin oscillator

The solution for the finite amplitude, uniaxial motion of a Mooney-Rivlin oscillator on suspension, compression, or horizontal supports, and for arbitrary initial data is presented. The problem is unusual. Depending upon the initial data, the type of support, the amount of static stretch, and the value of a Mooney-Rivlin parameter, the solution may have one of three distinct possible periodic forms. The three cases are solved exactly, and simple bounds on the period of the finite motion are given. Some special situations are illustrated, both analytically and graphically. The effect of the amount of static stretch on the period of superimposed small amplitude oscillations also is described. The appropriate results are compared with those obtained previously for the neo-Hookean model.Dedicated to Clifford Truesdell, in admiration and gratitude, on the occasion of the twenty-fifth anniversary of the Society for Natural Philosophy.     

On the transverse vibration of a rubber string

The nearly constant pitch of the sound radiated by a sufficiently stretched rubber cord, a phenomenon observed independently by two experimenters at the turn of the century, is explained analytically for three ideal rubberlike material models. Transverse vibrational frequency data for three kinds of rubber strings, obtained with the aid of a novel laser apparatus, are compared with the analytical results. A numerical scheme is introduced to compute from the experimental data the apparent average number of links in a molecular chain of a rubberlike material from both simple tension and transverse frequency measurements. It is shown that the nearly flat frequency response is a molecular network finite extensibility effect that is controlled by the apparent number of links in a chain of the molecular network structure.     

Assessing the exchange coupling in binuclear lanthanide(iii) complexes and the slow relaxation of the magnetization in the antiferromagnetically coupled Dy2 derivative

We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga₄Ln₂(shi^3–)₄(Hshi^2–)₂(H₂shi^–)₂(C₅H₅N)₄(CH₃OH)_x(H₂O)_x]·xC₅H₅N·xCH₃OH·xH₂O (where H₃shi = salicylhydroxamic acid and Ln = Gd^III1; Tb^III2; Dy^III3; Er^III4; Y^III5; Y^III_0.9Dy^III_0.16). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field. The dynamic susceptibility studies of 3 and of the diluted DyY 6 complexes reveal the presence of two relaxation processes for 3 that are due to the excited ferromagnetic state and to the uncoupled Dy^III ions. The antiferromagnetic coupling in 3 was shown to be mainly due to an exchange mechanism, which accounts for about 2/3 of the energy gap between the antiferro- and the ferromagnetic states. The overlap integrals between the Natural Spin Orbitals (NSOs) of the mononuclear fragments, which are related to the magnitude of the antiferromagnetic exchange, are one order of magnitude larger for the Dy₂ than for the Er₂ complex.     

Effects of Ultraviolet Radiation (UVA+UVB) and Copper on the Morphology,Ultrastructural Organization and Physiological Responses of the Red Alga Pterocladiella capillacea

The effect of ultraviolet (UV) radiation and copper (Cu) on apical segments of Pterocladiella capillacea was examined under two different conditions of radiation, PAR (control) and PAR+UVA+UVB (PAR+UVAB), and three copper concentrations, ranging from 0 (control) to 0.62, 1.25 and 2.50 μm . Algae were exposed in vitro to photosynthetically active radiation (PAR) at 70 μmol photons m^?2 s^?1, PAR + UVB at 0.35 W m^?2 and PAR +UVA at 0.70 W m^?2 during a 12‐h photocycle for 3 h each day for 7 days. The effects of radiation and copper on growth rates, content of photosynthetic pigments and photosynthetic performance were analyzed. In addition, samples were processed for light and transmission electron microscopy. The content of photosynthetic pigments decreased after exposure to radiation and Cu. Compared with PAR radiation and copper treatments modified the kinetics patterns of the photosynthesis/irradiance curve. The treatments also caused changes in the ultrastructure of cortical and subcortical cells, including increased cell wall thickness and accumulation of plastoglobuli, as well as changes in the organization of chloroplasts. The results indicate that the synergistic interaction between UV radiation and Cu in P. capillacea, led to the failure of protective mechanisms and causing more drastic changes and cellular imbalances.