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61.
In this paper, numerical simulation is conducted to investigate the generation, transmission and detection of a 110 Gbps optical Minimum Shift Keying (MSK) signal. The transmitter has been designed using a Quad Mach-Zehnder IQ Modulator. At the transmitter, a 110 Gbps optical MSK signal with constant envelope and a continuous phase is generated by combining signals of I-arm and \(90^\circ\) phase shifted of Q-arm. Error-free transmission of 110 Gbps optical MSK signal is achieved after traversing a distance of 240 km, also a comparison is made with respect to Differential Phase Shift Keying (DPSK) to show its effectiveness. At the receiver side, the original signal is recovered through a balanced detection method, with a power penalty of around 3.34 dB. Also, BER curves of different bit rates for MSK are studied ranging from 40 to 120 Gbps and found that maximum 110 Gbps can be achieved error-free. The optical spectrum of both MSK and DPSK signals are observed and found that MSK is having narrower main lobes with smaller side lobes compared with that of DPSK, which in turn results in an increase in spectral efficiency and reduction in intersymbol interference. 相似文献
62.
Parmod Kumar Yogesh Kumar Hitendra K. Malik S. Annapoorni Sanjeev Gautam Keun Hwa Chae K. Asokan 《Applied Physics A: Materials Science & Processing》2014,114(2):453-457
Room-temperature multiferroic properties in Mg-doped ZnO samples are reported wherein Mg replaces Zn in the ZnO matrix and retains hexagonal wurtzite structure. The saturation magnetisation is increased from ~2×10?4 emu/g to 3×10?4 emu/g for the dilute doping of 2 % Mg in pure ZnO and the ferroelectricity is also increased. Higher concentration of Mg does not lead to a significant enhancement in the magnetisation but improves the ferroelectric properties. An X-ray absorption spectroscopic study shows an enhancement in O vacancies with dilute doping of Mg. The origin of the multiferroic behaviour is understood based on their crystal and electronic structures. 相似文献
63.
Sanjeev Kumar Vaishali Singh Saroj Aggarwal Uttam Kumar Mandal R.K. Kotnala 《Journal of magnetism and magnetic materials》2012
CoxZnyFe3−x−yO4 ferrite (x=1 to 0; y=0 to1) nanocrystals have been synthesized by reverse microemulsion method. The nanocrystals are then comprehensively characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission transmission electron microscopy (FETEM), and magnetic properties were measured by using Vibrating sample magnetometer. X-ray analysis showed that all the crystals were cubic spinel. The lattice constant increased with the increase in Zn substitution. FETEM reveals that particle size varies in the range from 3 to 6 nm. As the concentration of Zn increases the magnetic behavior varies from ferromagnetic at y=0 and 0.2 to superparamagnetic to paramagnetic at y=1. The Curie temperature decreases with increasing concentration of Zn. 相似文献
64.
An approach for photonic generation of an arbitrary chirped microwave waveform with an increased time-bandwidth product (TBWP) is proposed and experimentally demonstrated. In the proposed model, light from the mode locked laser is splitted into two parts by using 1 × 2 power splitter: one is sent to linearly chirped fiber Bragg grating (LCFBG) through circulator and the other is time delayed by fiber delay line. The optical pulse in upper arm is time stretched by the LCFBG. Meanwhile, the optical pulse in lower arm experiences a time delay and then stretched by the dispersive single mode fiber. Temporal interference pattern is generated with an increasing or decreasing free spectral range by combination of two time-stretched optical pulses. Finally, the temporal interference pattern which is obtained at the output of optical coupler is transformed into an arbitrary chirped microwave waveform by using a photo-detector. The main advantage of this proposed model is high TBWP in the range of 750–1000 which ultimately results in an increased range resolution of radio detection and ranging. 相似文献
65.
A high-sensitive fluorescence cell has been developed with an aim to perform laser spectroscopy of exotic nuclei. This fluorescence
cell has been tested off-line for stable isotope 133Cs. Also, an investigation of the nuclear root mean square (r.m.s.) charge and neutron radii, and of the binding energies
of the cesium long isotopic chain has been carried out in the relativistic mean field (RMF) and relativistic Hartree–Bogoliubov
(RHB) formalisms. The RMF/RHB calculations are compared with the experimental data and are found to be in good agreement. 相似文献
66.
It is useful to state propagation laws for a self-focusing laser beam or a soliton in group-theoretical form to be called
Lie-optical form for being able to predict self-focusing dynamics conveniently and amongst other things, the geometrical phase.
It is shown that the propagation of the gaussian laser beam is governed by a rotation group in a non-absorbing medium and
by the Lorentz group in an absorbing medium if the additional symmetry of paraxial propagation is imposed on the laser beam.
This latter symmetry, however, needs care in its implementation because the electromagnetic wave of the laser sees a different
refractive index profile than the laboratory observer in this approximation. It is explained how to estimate this non-Taylor
paraxial power series approximation. The group theoretical laws so-stated are used to predict the geometrical or Berry phase
of the laser beam by a technique developed by one of us elsewhere. The group-theoretical Lie-optic (or ABCD) laws are also
useful in predicting the laser behavior in a more complex optical arrangement like in a laser cavity etc. The nonlinear dynamical
consequences of these laws for long distance (or time) predictions are also dealt with. Ergodic dynamics of an ensemble of
laser beams on the torus during absorptionless self-focusing is discussed in this context. From the point of view of new physics
concepts, we introduce a stroboscopic invariant torus and a stroboscopic generating function in classical mechanics that is
useful for long-distance predictions of absorptionless self-focusing. 相似文献
67.
Sherif Yehia C. Mitros Sanjeev Kumar S. Jha Glenn M. Julian R. A. Dunlap 《Hyperfine Interactions》1987,34(1-4):415-418
The systematics of hyperfine magnetic fields at sp impurities on the Z-sites in Co based Heusler alloys are investigated. New TDPAC measurements of Cd hyperfine fields are reported. 相似文献
68.
Venu MankadHimadri R. Soni Sanjeev K. GuptaPrafulla K. Jha 《Physica B: Condensed Matter》2011,406(19):3599-3604
We present results of first principles total energy calculations of the structure, electronic and lattice dynamics for beryllium semiboride and its three ternary alloys using generalized gradient and local density approximations under the framework of density functional theory. The generalized gradient approximation is used for all compounds except MgBeB using the Perdew-Burke-Ernzehorf exchange correlation functional while local density approximations use the Perdew-Zunger ultrasoft exchange correlation functional. The calculated ground state structural parameters are in good agreement with those of experimental and previous theoretical studies. The electronic band structure calculations show that Be2B may transform to a semiconductor after Al substitution. A linear response approach to density functional theory is used to calculate phonon dispersion curves and vibrational density of states. The phonon dispersion curves of Be2B and AlBeB are positive indicating a dynamical stablility of the structure for these compounds. The phonon dispersion curves of NaBeB and MgBeB show the imaginary phonons throughout the Brillouin zone, which confirms dynamical instability as indicated in band structures for these alloys. We also present the partial phonon density of states for different species of Be2B and AlBeB to bring out the details of the participation of different atoms in the total phonon density of state, particularly the role played by Al atom. The first time calculated phonon properties are clearly able to bring out the significant effect of isoelectronic substitution in Be2B. 相似文献
69.
The interplay between spectator and participant matter in heavy-ion collisions is investigated within the isospin-dependent
quantum molecular dynamics (IQMD) model in terms of the rapidity distribution of light charged particles. The effect of different
types and sizes of rapidity distributions is studied in elliptical flow. The elliptical-flow patterns show the important role
of nearby spectator matter on the participant zone. This role is further explained on the basis of the passing time of the
spectator and the expansion time of the participant zone. The transition from in-plane to out-of-plane emission is observed
only when the mid-rapidity region is included into the rapidity bin. Otherwise no transition occurs. The transition energy
is found to be highly sensitive to the size of the rapidity bin, while it is only weakly dependent on the type of the rapidity
distribution. These theoretical findings are found to be in agreement with experimental results. 相似文献
70.
M. G. Kotresh K. S. Adarsh M. A. Shivkumar Sanjeev R. Inamdar 《Journal of fluorescence》2016,26(4):1249-1259
This article highlights some physical studies on the relaxation dynamics and Förster resonance energy transfer (FRET) of semiconductor quantum dots (QDs) to proximal dye molecule and the way these phenomena change with core to core-shell QD is discussed. Efforts to understand the optical and carrier relaxation dynamics of CdSe and CdSe/ZnS QDs are made by using absorption, steady-state fluorescence and time-resolved fluorescence (TCSPC) techniques. Steady-state as well as time-resolved fluorescence measurements were employed to evaluate the QD PL quenching induced by the proximal Rhodamine 101 dye molecule and to examine the influence of deep trap states on energy transfer efficiency. The FRET parameters such as spectral overlap, Förster distance, intermolecular distance for each donor-acceptor pair are determined and variation of these parameters from core to core-shell QD is discussed. 相似文献