Instabilities in free-surface electroosmotic flows

Instability of a thin electrolyte film undergoing a direct current electroosmotic flow has been investigated. The film with a compliant electrolyte–air interface is flowing over a rigid charged substrate. Unlike previous studies, inclusion of the Maxwell stresses in the formulation shows the presence of a new finite wavenumber shear-flow mode of instability, alongside the more frequently observed long-wave interfacial mode. The shear mode is found to be the dominant mode of instability when the electrolyte–solid and electrolyte–air interfaces are of opposite charge or of same charge but have very large zeta-potential at the electrolyte–air interface. The conditions for mode-switch (interfacial to shear) and the direction of the travelling waves are discussed through stability diagrams. Interestingly, the analysis shows that when the interfaces are of nearly same zeta potential, the ‘free’ electrolyte–air interface behaves more like a ‘stationary’ wall because of the ion transport in the reverse direction of the flow.     

High pressure phase transitions in organic solids II: X-ray diffraction study ofp-dichlorobenzene at high pressures

X-ray diffraction experiments onp-dichlorobenzene at high pressures show a transition at ～ 0.3 GPa, to a new phase, the diffraction pattern of which cannot be indexed on the anticipated low temperature monoclinic crystal structure. We have instead found an orthorhombic cell, very closely related to the low temperature monoclinic cell, for this new phase. This structure, which also occurs inp-diiodobenzene at ambient conditions, has cell constantsa =14.02,b = 6.06,c = 7.41Å andZ = 4. The space group is Pbca. This new phase has a non-β herring-bone structure, in contrast with the initialα phase which has aβ-structure with ribbon-like arrangement of molecules, with Cl-Cl contacts of ～ 4A between adjacent molecules. This implies that with pressure the halogen-halogen interaction in this compound plays a less dominant role in crystal engineering.     

Calorimetric study of laser-irradiated thin foil targets

Hydrodynmaic efficiency of laser-irradiated thin aluminum and gold-coated aluminum targets was experimentally determined using a specially designed cone calorimeter. Velocity of the accelerated target and ablation pressure were also estimated from the experimental data. The laser irradiance range used in the experiments was between 10¹² and 10¹³ watts/cm². Experiments indicate that the fall in the hydrodynamic efficiency due to gold coating on aluminum target is about 12% at an irradiance of 8 × 10¹² W/cm².     

The proposed Penning trap mass spectrometer facility at TASCC

The proposed Penning trap mass spectrometer, to be located at the TASCC facility of the Chalk River Laboratories, is described. The facility will be used for precise atomic mass determinations among both stable and unstable nuclides. The unstable nuclides would be produced in heavy ion reactions using the TASCC facility. The products from these reactions would be collected using an He-jet transport system loaded with NaCl aerosols. After transport to a background free area, the nuclides of interest would be laser desorbed and resonantly ionized. Subsequently, these ions would be accumulated in a Paul trap, cooled and injected into a precision Penning trap mass spectrometer for mass analysis.     

Study of effects of dopants on structure of vitreous semiconductors (GeSe3.5)100-xMx (M = Bi,Sb) using high pressure techniques

An investigation of the problem of controlled doping of amorphous chalcogenide semiconductors utilizing a Bridgman anvil high pressure technique, has been undertaken. Bulk amorphous semiconducting materials (GeSe_3.5)_100-x doped with M = Bi (x = 2, 4, 10) and M = Sb (x = 10) respectively are studied up to a pressure of 100 kbar down to liquid nitrogen temperature, with a view to observe the impurity induced modifications. Measurement of the electrical conductivity of the doped samples under quasi-hydrostatic pressure reveals that the pressure induced effects in lightly doped (2 at % Bi) and heavily doped (x = 4, 10) semiconductors are markedly different. The pressure effects in Sb-doped semiconductors are quite different from those in Bi-doped material.     

Theoretical Study of Screening Dependence of Aluminium Doped MgB_2

The screening dependence of superconducting state parameters(λ, μ*, T_c, and N_0V(1) of six alloys of aluminium doped Mg B2 systems are studied in the BCS–Eliashberg–Mc Millan framework by employing five forms of dielectric screening function, viz. random phase approximation(RPA), Harrison, Geldart and Vosko(GV), Hubbard and Overhauser in conjunction with Ashcroft's potential. It is observed that electron-phonon coupling strength λ and Coulomb pseudopotential μ*are quite sensitive to the form of dielectric screening, whereas transition temperature T_c, isotope effect exponent α and effective interaction strength N_0V(1 show weak dependence on the form of dielectric screening function. It is found that the RPA form of dielectric screening function yields the best results for transition temperature T_c for all alloys of the Mg-Al-B system. The results obtained using GV screening are much higher than the experimental results. This shows that all the four dielectric screenings used here almost describe superconductivity in all the alloys of the Mg-Al-B system, but the GV screening is not suitable for such an alloy system.     

Modify SRS-induced crosstalk with variety of fiber in SCM–WDM transmission links

In this paper, the SRS-induced crosstalk has been evaluated in a SCM–WDM communication links at different modulation frequencies and transmission lengths for variety of fiber. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fiber, standard single mode fiber (SMF) has minimum crosstalk (−78 to −38) dB, (−55 to −33) dB and (−46 to −34) dB at modulation frequencies, transmission lengths and optical powers. Dispersion compensation fiber (DCF) has maximum crosstalk (−60 to −12) dB, (−37 to −12) dB and (−27 to −12) dB at modulation frequencies and transmission lengths.     

Thermosolutal convection in a Maxwellian viscoelastic fluid in porous medium

The thermosolutal convection in a layer of Maxwellian viscoelastic fluid heated and soluted from below in porous medium is considered. The effects of uniform magnetic field and uniform rotation on the thermosolutal convection are also considered. For stationary convection, the Maxwellian viscoelastic fluid behaves like a Newtonian fluid. The sufficient conditions for the nonexistence of overstability are obtained. The critical Rayleigh number is found to increase with the increase in magnetic field, rotation and stable solute gradient.     

Raman spectroscopy of the BC3 phase obtained under high pressure and high temperature

A direct transformation of the g‐BC₃ phase to a new diamond‐like d‐BC₃ phase was observed in a diamond‐anvil cell (DAC) at high temperature, 2033 ± 241 K, and high pressure, 50 GPa. Analysis of the peak positions of the d‐BC₃, B₄C, α‐boron, and the boron‐doped diamond leads to the conclusion that the positions of the peaks of the d‐BC₃ are more similar to the peak pattern of the boron‐doped diamond rather than that of boron carbide, α‐boron. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimization of facet coating for highly strained InGaAs quantum well lasers operating at 1200 nm

The optical output power of a laser diode can be enhanced by anti-reflection (AR) and high-reflection (HR) facet coatings, respectively, at the front and back facet. AR and HR coatings also serve the purpose of protection and passivation of laser diode facets. In this work, we have designed and optimized a single layer λ/4 thick Al₂O₃ film for the AR coating and a stack of λ/4 thick Al₂O₃/λ/4 thick Si bi-layers for the HR coating for highly strained InGaAs quantum-well edge emitting broad area (BA) laser diodes. Effect of the front and back facet reflectivities on output power of the laser diodes has been studied. The light output versus injected current (L–I characteristics) measurements were carried out on selected devices before and after the facet coatings. We have also carried out the numerical simulation and analysis of L–I characteristics for this particular diode structure. The experimental results have been compared and verified with the numerical simulation.