Instabilities of an electron cloud in a Penning trap

We have measured the storage instabilities of electrons in a Penning trap at low magnetic fields. These measurements are carried out as a function of the trapping voltage, for different magnetic fields. It is seen that these instabilities occur at the same positions when the trapping voltage is expressed as a percentage of the maximum voltage, given by the stability limit. The characteristic frequencies at which these instabilities occur, obey a relation that is given by n _zω _z + n ₊ω ₊ + n _-ω _- = 0, where ω _z, ω ₊ and ω _- are the axial, perturbed cyclotron and the magnetron frequencies of the trapped electrons respectively, and the n's are integers. The reason for these instabilities are attributed to higher order static perturbations in the trapping potential. Received 5 August 2002 / Received in final form 14 October 2002 Published online 17 December 2002 RID="a" ID="a"Present address: Dept. of Physics, Rampurhat College, Rampurhat, Birbhum, West Bengal, India. RID="b" ID="b"e-mail: werth@mail.uni-mainz.de     

Study of gain flatness for multi-channel amplification in single stage EDFA for WDM applications

In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ± 0.5 dB gain-variation which is an important parameter in optical network system.     

Renormalization in few-body nuclear physics

Renormalized fixed-point Hamiltonians are formulated for systems described by interactions that originally contain point-like singularities (as the Dirac-delta and/or its derivatives). They express the renormalization group invariance of quantum mechanics. The present approach for the renormalization scheme relies on a subtracted T-matrix equation.     

Emergent universe scenario in the Einstein–Gauss–Bonnet gravity with dilaton

We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss–Bonnet (GB) gravity coupled with a dilaton field in 4-dimensions. The coupling parameter of the GB terms and the dilaton in the theory are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined. It is found that the GB terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates once again. We note that the Einstein’s static universe solution permitted here is unstable which the asymptotic EU might follow. We also compare our EU model with supernova data.     

Solutions to the Zakharov-Kuznetsov equation with higher order nonlinearity by mapping and ansatz methods

Solutions to the Zakharov-Kuznetsov equation with higher order nonlinearity are obtained using the mapping method. Several solutions are determined inclusing the cnoidal waves, shock waves, solitary waves, periodic singular waves and others. Finally, the ansatz method is applied to solve the equation with power law nonlinearity. It has been proved that the shock waves or topological solitons exist only for specific values of the power law parameter.     

Size distributions of aerosols in an indoor environment with engineered nanoparticle synthesis reactors operating under different scenarios

Size distributions of nanoparticles in the vicinity of synthesis reactors will provide guidelines for safe operation and protection of workers. Nanoparticle concentrations and size distributions were measured in a research academic laboratory environment with two different types of gas-phase synthesis reactors under a variety of operating conditions. The variation of total particle number concentration and size distribution at different distances from the reactor, off-design state of the fume hood, powder handling during recovery, and maintenance of reactors are established. Significant increases in number concentration were observed at all the locations during off-design conditions (i.e., failure of the exhaust system). Clearance of nanoparticles from the work environment was longer under off-design conditions (20 min) compared to that under normal hood operating conditions (4–6 min). While lower particle number concentrations are observed during operation of furnace aerosol reactors in comparison to flame aerosol reactors, the handling, processing, and maintenance operations result in elevated concentrations in the work area.     

Thermodynamics of Black Holes in Einstein-Maxwell-Gauss-Bonnet Theory

We study the black hole solution in Einstein-Maxwell-Gauss-Bonnet (EMGB) gravity theory with a cosmological constant in five dimension. It is a generalization of the Reissner-Nordström-de Sitter (RNdS) or RNAdS (Reissner-Nordström-Anti-de Sitter) black hole solutions (according as the cosmological constant is positive or negative) in the Einstein-Gauss-Bonnet (EGB) theory. We analyze the thermodynamic quantities of EMGB black hole and find a restriction involving the charge and the cosmological constant for the existence of an extremal black hole. Finally, Hawking-Page phase transition has been discussed for the present black hole.     

Electronic and magnetic properties of quasifreestanding graphene on Ni

For the purpose of recovering the intriguing electronic properties of freestanding graphene at a solid surface, graphene self-organized on a Au monolayer on Ni(111) is prepared and characterized by scanning tunneling microscopy. Angle-resolved photoemission reveals a gapless linear pi-band dispersion near K[over] as a fingerprint of strictly monolayer graphene and a Dirac crossing energy equal to the Fermi energy (EF) within 25 meV meaning charge neutrality. Spin resolution shows a Rashba effect on the pi states with a large (approximately 13 meV) spin-orbit splitting up to EF which is independent of k.