45915 research outputs found
Sort by
Theoretical and numerical analysis of radiation belt electron precipitation by coherent whistler mode waves
No full textThe interaction between coherent whistler mode waves and energetic radiation belt electrons can result in pitch angle scattering of electrons into the bounce loss cone and subsequent precipitation. In studying the effects of VLF transmitter signals on particle precipitation, past modeling efforts have focused on the computation of diffusion coefficients for a Fokker-Planck model. In contrast, to capture the nonlinear effects of large-amplitude coherent waves, we evaluate particle precipitation using a Vlasov-Liouville (VL) model which computes the phase space particle distribution function directly using a characteristic-based solution of the Vlasov equation. Previous work has shown that in the case of large-amplitude coherent waves, phase trapping can significantly perturb resonant particles from their adiabatic paths. We evaluate the importance of phase trapping over a range of wave amplitudes (up to 200 pT); the percentage of particles that precipitate after being phase trapped is computed over a phase space grid in the loss cone. The results demonstrate that phase trapping contributes significantly to precipitation when a large-amplitude wave (> 100 pT) is present. Additionally, linear theory can be valid over a broad range of amplitudes and the relative accuracy of linear theory in calculating the precipitated flux depends strongly on the initial particle distribution. Additionally, we demonstrate the ability of the VL model to calculate the time evolution of the precipitated flux due to short-duration whistler mode pulses. The physical parameters used in this study are typical of those associated with the Siple Station wave injection experiment
The relationship between geophysical conditions and ELF amplitude in modulated heating experiments at HAARP: Modeling and experimental results
No full textExperiments for generating extremely low frequency (ELF) radio waves using modulated HF heating of the auroral ionosphere have been conducted and refined at the High Frequency Active Auroral Research Program (HAARP) facility at Gakona, Alaska. Because this technique is dependent on strength of the naturally generated electrojet current system, the amplitude of the generated ELF changes with geophysical conditions. Past work has shown that electrojet current strength as measured by magnetometers often correlates with generated ELF amplitude, but there are periods of poor or negative correlation. We attempt to use additional diagnostics from a radar, riometer, ionosonde, and magnetometer chain to understand how ionospheric conditions affect ELF generation. We then present the results of a statistical model that shows that ELF amplitude is roughly proportional to magnetometer measurements for a fixed value of riometer absorption and that the proportionality constant decreases as riometer absorption increases. Theoretical simulations of modulated heating are conducted for a variety of ionospheric density profiles to verify that denser profiles result in smaller gains for ELF generation as a function of electrojet current at a given electric field
A retrospective study of 39 patients treated with anterior approach of thoracic and lumbar spondylodiscitis clinical manifestations, anterior surgical treatment, and outcome
No full textThe aim of this study is to report our 39 patients treated with anterior debridement and autologous iliac bone grafting with or without anterior instrumentation, which is the presumed treatment of choice for thoracic or lumbar spondylodiscitis.Our patients underwent surgical treatment of spondylodiscitis using anterior debridement and autologous iliac bone grafting with or without anterior instrumentation and were analyzed with a mean follow-up of 8 years (range, 2-11 years). Kaneda 2-rod system instrumentation was used in 12 patients, in total. Clinical outcomes were assessed by the Frankel grade. Radiographic fusion was characterized based on 3-dimensional computed tomography.Of the whole group, 20 patients suffered from tuberculous spondylodiscitis and 19 suffered from hematogenous spondylodiscitis. Pathogens responsible for pyogenic infection included Staphylococcus aureus (4 patients), Pseudomonas aeruginosa (3 patients), and Brucella melitensis (1 patient). Fifteen patients had thoracic involvement, 20 had lumbar involvement, and 4 had thoracolumbar junction involvement. Preoperative neurological deficits were noted in 13 of the 39 patients. In terms of Frankel grade, 8 patients have improved, 4 have remained the same, and 1 patient has worsened during the follow-up period. Imaging-documented fusion was achieved in 23 of 27 patients in the graft group (85% fusion rate) and 11 of 12 patients in the graft+Kaneda instrumentation group (91% fusion rate).There was no instrumentation failure, loosening, or graft-related complication such as slippage or fracture of the graft. This approach demonstrated a good recovery rate of neurological functions and a high fusion rate
Microsphere based resonant cavity silicon photodetector
No full textMicro Electro Mechanical Systems (MEMS) are among the new and emerging technologies of the future and have many applications in different disciplines. This study presents the dynamic characterization methods that we use to identify the modal parameters of a MEMS device and also the techniques that can be implemented to change the modal parameters. A micro scanner mirror was chosen as the case study to demonstrate the developed methodologies. Initially, the micro mirror was dynamically characterized using experimental modal analysis techniques to identify the modal parameters such as resonance frequencies and mode shapes. Then, it was introduced in a velocity feedback control loop to alter the effective damping of the structure. This method proves to be a very efficient method to alter the modal damping of a micro structure, especially when high quality factors are required for MEMS applications
Solitons in a trapped spin-1 atomic condensate
No full textWe numerically investigate a particular type of spin soliton inside a trapped atomic spin-1 Bose-Einstein condensate with ferromagnetic interactions. Within the mean-field theory approximation, our study of the solitonic dynamics shows that the solitonic wave function, its center-of-mass motion, and the local spin evolutions are stable and are intimately related to the domain structures studied recently in spin-1 Rb-87 condensates. We discuss a rotating reference frame wherein the dynamics of the solitonic local spatial spin distribution becomes time independent
Path-integral formulation of pseudo-Hermitian quantum mechanics and the role of the metric operator
No full textWe provide a careful analysis of the generating functional in the path-integral formulation of pseudo-Hermitian and in particular PT-symmetric quantum mechanics and show how the metric operator enters the expression for the generating functional
Blume-Emery-Griffiths spin glass and inverted tricritical points
No full textThe Blume-Emery-Griffiths spin glass is studied by renormalization-group theory in d=3. The boundary between the ferromagnetic and paramagnetic phases has first-order and two types of second-order segments. This topology includes an inverted tricritical point, first-order transitions replacing second-order transitions as temperature is lowered. The phase diagrams show disconnected spin-glass regions, spin-glass and paramagnetic reentrances, and complete reentrance, where the spin-glass phase replaces the ferromagnet as temperature is lowered for all chemical potentials
Multicritical points for spin-glass models on hierarchical lattices
No full textThe locations of multicritical points on many hierarchical lattices are numerically investigated by the renormalization group analysis. The results are compared with an analytical conjecture derived by using the duality, the gauge symmetry, and the replica method. We find that the conjecture does not give the exact answer but leads to locations slightly away from the numerically reliable data. We propose an improved conjecture to give more precise predictions of the multicritical points than the conventional one. This improvement is inspired by a different point of view coming from the renormalization group and succeeds in deriving very consistent answers with many numerical data
Rapid stress system drives chemical transfer of fear from sender to receiver
No full textHumans can register another person's fear not only with their eyes and ears, but also with their nose. Previous research has demonstrated that exposure to body odors from fearful individuals elicited implicit fear in others. The odor of fearful individuals appears to have a distinctive signature that can be produced relatively rapidly, driven by a physiological mechanism that has remained unexplored in earlier research. The apocrine sweat glands in the armpit that are responsible for chemosignal production contain receptors for adrenalin. We therefore expected that the release of adrenalin through activation of the rapid stress response system (i.e., the sympathetic-adrenal medullary system) is what drives the release of fear sweat, as opposed to activation of the slower stress response system (i.e., hypothalamus-pituitary-adrenal axis). To test this assumption, sweat was sampled while eight participants prepared for a speech. Participants had higher heart rates and produced more armpit sweat in the fast stress condition, compared to baseline and the slow stress condition. Importantly, exposure to sweat from participants in the fast stress condition induced in receivers (N = 31) a simulacrum of the state of the sender, evidenced by the emergence of a fearful facial expression (facial electromyography) and vigilant behavior (i.e., faster classification of emotional facial expressions)
MEMS stage integrated with microlens arrays for high-resolution beam steering
No full textA novel micromechanical stage with a uniaxial set of combfingers capable of 2D actuation is designed and developed. Driven at resonance the stage deflects up to 108 mu m out-of-plane and 102 mu m in-plane, with 140V and 94V peak-to-peak actuation voltage, respectively