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Role of the plasmapause in dictating the ground accessibility of ELF/VLF chorus
No full textThis study explores the manner in which the plasmapause is responsible for dictating which magnetospheric source regions of ELF/VLF chorus are able to propagate to and be received by midlatitude stations on the ground. First, we explore the effects of plasmapause extent on ground-based observations of chorus via a 3 month study of ground-based measurements of chorus at Palmer Station, Antarctica (L = 2.4, 50 degrees S geomagnetic latitude), and data on the plasmapause extent from the IMAGE EUV instrument. It is found that chorus normalized occurrence peaks when the plasmapause is at L similar to 2.6, somewhat higher than Palmer's L shell, and that this occurrence peak persists across a range of observed chorus frequencies. Next, reverse ray tracing is employed to evaluate the portion of the equatorial chorus source region, distributed in radial distance and wave normal, from which chorus is able to reach Palmer Station via propagation in a nonducted mode. The results of ray tracing are similar to those of observations, with a peak of expected occurrence when the plasmapause is at L similar to 3. The exact location of the peak is frequency dependent. This supports the conclusion that the ability of chorus to propagate to low altitudes and the ground is a strong function of instantaneous plasmapause extent and that peak occurrence of chorus at a given ground station may occur when the L shell of the plasmapause is somewhat beyond that of the observing station. These results also suggest that chorus observed on the ground at midlatitude stations propagates predominantly in the nonducted mode
Analysis and optimization of diode end-pumped solid-state lasers: applicationto Nd3+ : YVO4 lasers at 1064 and 1342 nm
No full textWe describe a systematic procedure that uses experimental and numerical methods to analyze the continuous-wave power performance of diode end-pumped solid-state lasers. For the general case, saturation, excited-state absorption, and thermal lensing effects are considered and integral equations are derived to study the evolution of the pump and laser beams in the gain medium. As an application of the method, we consider two different diode end-pumped Nd3+:YVO4 lasers operating at 1064 and 1342 nm. Experimental efficiency data were first analyzed to determine the stimulated emission cross sections and the resonator losses. The best-fit laser parameters were then used to calculate the optimum crystal length that maximizes the output power of the laser. The described method should prove useful in the design of a wide range of efficient diode-pumped solid-state lasers. (c) 2005 Society of Photo-Optical Instrumentation Engineers
Torsional MEMS scanner design for high-resolution display systems
No full textIn scanning display systems, high horizontal and vertical resolution, and high refresh rate requirements translate into large mirror-size scan-angle product and high scanner-frequency requirements. A comparison between published scan-angle mirror-size product values for MEMS scanners and a Steel mechanical scanner is presented. Current performance levels of Steel mechanical scanners are better; however, Silicon MEMS scanners have good material properties and should be able to reach and exceed the performance levels of conventional mechanical scanners. The resolution limitations of mechanical and MEMS scanners are established using dynamic mirror deformation, flexure stress, and other oscillation mode frequencies. Analytical formulas for torsional, vertical deflection mode, lateral deflection mode, and rocking mode natural frequencies are derived using mechanical beam deflection theory
Tunable optofluidic microlasers based on optically stretched emulsion droplets
No full textWe introduce tunable optofluidic microlasers based on optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. Optically trapped microdroplets of oil emulsified in water and stained with fluorescent dye act as active ultrahigh-Q optical resonant cavities hosting whispering gallery modes (WGMs) which enable dye lasing with low threshold pump powers. In order to achieve tunable dye lasing, the droplets are pumped with a pulsed green laser beam and simultaneously stretched by light in the dual-beam trap. For a given stretching power, the magnitude of the droplet deformation is dictated by the interfacial tension between the droplet and the host liquid which is adjustable by adding surfactants. Increase of power of the dual-beam trap causes a directly proportional change of the droplet stretching deformation. Subsequently, resonant path lengths of different WGMs propagating in the droplet are modified, leading to shifts in the corresponding microlaser emission wavelenghts. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of wavelength tuning depends on the position of the pump beam focus on the droplet, consistent with the deformation of originally spherical droplet towards a prolate spheroid. In addition, we study the effects of changes of the droplet and immersion medium temperature on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength
Angular-momentum-driven chaos in small clusters
No full textThe effects of the rotational motion on the chaotic behavior of triatomic Lennard-Jones clusters are studied. A set of initial momentum distributions with tunable parameters is chosen to correspond to various rigid-body rotations around symmetry axes of the cluster. By smoothly varying the direction of the initial kicks given to the cluster, periodic transitions between regular and chaotic regimes are obtained. A study of initial conditions leading up to such transitions shows that the major factor that determines the extent of the chaotic behavior is the initial partitioning of the kinetic energy between the rotational and vibrational motion. From the analysis of the time evolution of various properties it is concluded that the basic role of this initial partitioning is to control the energy transfer between the kinetic and the potential energy
Tunneling of condensate magnetization in a double-well potential
No full textWe study quantum dynamical properties of a spin-1 atomic Bose-Einstein condensate in a double-well potential. Adopting a mean field theory and single spatial mode approximation, we characterize our model system as two coupled spins. For certain initial states, we find full magnetization oscillations between wells not accompanied by mass (or atom numbers) exchange. We identify dynamic regimes of collective spin variables arising from nonlinear self-interactions that are different from the usual Josephson oscillations. We also discuss magnetization beats and incomplete oscillations of collective spin variables other than the magnetization. Our study points to an alternative approach to observe coherent tunnelling of a condensate through a (spatial) potential barrier
Vortex lattices in dipolar two-component Bose-Einstein condensates
No full textWe consider a rapidly rotating two-component Bose-Einstein condensate with short-range s-wave interactions as well as dipolar coupling. We calculate the phase diagram of vortex lattice structures as a function of the intercomponent s-wave interaction and the strength of the dipolar interaction. We find that the long-range interactions cause new vortex lattice structures to be stable and lead to a richer phase diagram. Our results reduce to the previously found lattice structures for short-range interactions and single-component dipolar gases in the corresponding limits
Conformal black hole solutions of axidilaton gravity in D dimensions
No full textStatic, spherically symmetric solutions of axidilaton gravity in D dimensions are given in the Brans-Dicke frame for arbitrary values of the Brans-Dicke constant ω and an axion-dilaton coupling parameter k. The mass and the dilaton and axion charges are determined and a BPS bound is derived. There exists a one-parameter family of black hole solutions in the scale-invariant limit. © 2002 The American Physical Society
Possible effects of space-time nonmetricity on neutrino oscillations
No full textThe contribution of gravitational neutrino oscillations to the solar neutrino problem is studied by constructing a Dirac Hamiltonian and calculating the corresponding dynamical phase in the vicinity of the Sun in a non-Riemann background Kerr space-time with torsion and nonmetricity. We show that certain components of nonmetricity and the axial as well as nonaxial components of torsion may contribute to neutrino oscillations. We also note that the rotation of the Sun may cause a suppression of transitions among neutrinos. However, the observed solar neutrino deficit could not be explained by any of these effects because they are of the order of Planck scale
Kerr-Taub-NUT spacetime with Maxwell and dilaton fields
No full textWe present an exact solution describing a stationary and axisymmetric object with electromagnetic and dilaton fields. The solution generalizes the usual Kerr-Taub-NUT (Newman-Unti-Tamburino) spacetime in general relativity and is obtained by boosting this spacetime in the fifth dimension and performing a Kaluza-Klein reduction to four dimensions. We also discuss the physical parameters of this solution and calculate its gyromagnetic ratio