High sensitivity refractive index sensor based on simple diffraction from phase grating

We present a technique for refractive index sensing using a phase grating structure. A grating under normal incidence can be designed such that the 1st order diffracted light travels at a diffraction angle of 90o with respect to the 0th order. The diffracted light which is along the direction of periodicity can further get diffracted from the grating and interfere with the 0th order light. Under this condition, the π phase difference that arises between the two interfering beams results in a transmission dip. We can tune this dip wavelength for senor applications, based on the grating equation. Both simulation and experimental data are presented in the paper which shows good agreement with each other

The Acceleration Mechanism of Resistive MHD Jets Launched from Accretion Disks

We analyzed the results of non-linear resistive magnetohydrodynamical (MHD) simulations of jet formation to study the acceleration mechanism of axisymmetric, resistive MHD jets. The initial state is a constant angular momentum, polytropic torus threaded by weak uniform vertical magnetic fields. The time evolution of the torus is simulated by applying the CIP-MOCCT scheme extended for resistive MHD equations. We carried out simulations up to 50 rotation period at the innermost radius of the disk created by accretion from the torus. The acceleration forces and the characteristics of resistive jets were studied by computing forces acting on Lagrangian test particles. Since the angle between the rotation axis of the disk and magnetic field lines is smaller in resistive models than in ideal MHD models, magnetocentrifugal acceleration is smaller. The effective potential along a magnetic field line has maximum around $z \sim 0.5r_0$ in resistive models, where $r_0$ is the radius where the density of the initial torus is maximum. Jets are launched after the disk material is lifted to this height by pressure gradient force. Even in this case, the main acceleration force around the slow magnetosonic point is the magnetocentrifugal force. The power of the resistive MHD jet is comparable to the mechanical energy liberated in the disk by mass accretion. Joule heating is not essential for the formation of jets.Comment: 15 pages, 15 figures, 1 table, accepted for publication in Ap

Wide wavelength range tunable one-dimensional silicon nitride nano-grating guided mode resonance filter based on azimuthal rotation

We describe wavelength tuning in a one dimensional (1D) silicon nitride nano-grating guided mode resonance (GMR) structure under conical mounting configuration of the device. When the GMR structure is rotated about the axis perpendicular to the surface of the device (azimuthal rotation) for light incident at oblique angles, the conditions for resonance are different than for conventional GMR structures under classical mounting. These resonance conditions enable tuning of the GMR peak position over a wide range of wavelengths. We experimental demonstrate tuning over a range of 375 nm between 500 nm˜875 nm. We present a theoretical model to explain the resonance conditions observed in our experiments and predict the peak positions with show excellent agreement with experiments. Our method for tuning wavelengths is simpler and more efficient than conventional procedures that employ variations in the design parameters of structures or conical mounting of two-dimensional (2D) GMR structures and enables a single 1D GMR device to function as a high efficiency wavelength filter over a wide range of wavelengths. We expect tunable filters based on this technique to be applicable in a wide range of fields including astronomy and biomedical imaging

Cervical myeloradiculopathy due to ossification of the posterior longitudinal ligament with versus without diffuse idiopathic spinal hyperostosis

Study Design Retrospective study. Objectives Assess demographics, ossification characteristics, surgical outcomes, and complications in patients with both diffuse idiopathic spinal hyperostosis (DISH) and ossification of the posterior longitudinal ligament (OPLL) compared with patients who only have OPLL. Methods Clinical charts and radiographs of all patients treated surgically from February 2004 to July 2012 for cervical myeloradiculopathy due to DISH with OPLL or OPLL alone were reviewed retrospectively. All patients were observed for a minimum of 1 year. Pre- and postoperative Nurick grades were assessed for all patients. Results Forty-nine patients underwent surgical treatment for cervical myeloradiculopathy due to OPLL, and 8 also had DISH (average 58.9 years, range 37 to 70). The DISH with OPLL group had a significantly higher proportion of subjects with diabetes mellitus (50 versus 9.8% in the OPLL-only group). Everyone in the DISH with OPLL group had continuous or mixed-type OPLL, whereas 78% of patients in the OPLL-only group had primarily segmental type. Operative treatments for patients in the DISH with OPLL group included laminoplasty, anterior decompression and fusion, and posterior laminectomy with fusion. By Nurick grade, 5 patients improved and 3 showed no change. Conclusion Patients with both DISH and OPLL had a higher prevalence of diabetes mellitus and either continuous or mixed-type OPLL classifications. Surgical outcomes were mostly satisfactory; there was no aggravation of symptoms after surgery during the follow up period

Symmetry without Symmetry: Numerical Simulation of Axisymmetric Systems using Cartesian Grids

We present a new technique for the numerical simulation of axisymmetric systems. This technique avoids the coordinate singularities which often arise when cylindrical or polar-spherical coordinate finite difference grids are used, particularly in simulating tensor partial differential equations like those of 3+1 numerical relativity. For a system axisymmetric about the z axis, the basic idea is to use a 3-dimensional Cartesian (x,y,z) coordinate grid which covers (say) the y=0 plane, but is only one finite-difference-molecule--width thick in the y direction. The field variables in the central y=0 grid plane can be updated using normal (x,y,z)--coordinate finite differencing, while those in the y \neq 0 grid planes can be computed from those in the central plane by using the axisymmetry assumption and interpolation. We demonstrate the effectiveness of the approach on a set of fully nonlinear test computations in 3+1 numerical general relativity, involving both black holes and collapsing gravitational waves.Comment: 17 pages, 4 figure

Postoperative severe headache following cervical posterior surgical fixation from C2 distally

Study DesignRetrospective study.PurposeTo identify the prevalence of severe headache occurring after cervical posterior surgical fixation (PSF) and to evaluate the clinical and radiological findings associated with severe headache after surgery.Overview of LiteratureSeveral studies have reported on the axial pain after cervical surgery. However, to our knowledge, the incidence of severe headache after cervical PSF has not been elucidated.MethodsThe medical records and radiological assessment of patients who underwent surgical treatment from August 2002 to May 2012 were reviewed to identify the prevalence and risk factors for severe headaches occurring following PSF from C2 distally. Neck disability index scores (NDI) (the item for neck pain), the type of C2 screw, number of cervical fused levels (1–6), and smoking habit were calculated preoperatively and postoperatively. In addition, radiological parameters (T1 slope angle, C1/2 angle, C2–7 Cobb angle, C2–7 sagittal vertical axis and C1-implant distance) were assessed for all patients. Severe headache was defined as a high NDI headache score (>4 out of 5).ResultsEighty-two patients met the inclusion criteria. The mean age was 59.2 years (range, 21–78 years), and the mean number of fused levels was 5.1. The mean follow-up period was 2.9 years (range, 1–10.9 years). While only one severe headache occurred de novo postoperatively in a patient in the C3 or C4 distally group (total 30 patients, average age of 50.2 years), 11 patients in the C2 distally group (p=0.04) had severe headache occur postoperatively. The radiological parameters were not significantly different between the postoperative milder headache and severe headache (SH) groups. The SH group had a significantly higher preoperative NDI score (neck pain) (p<0.01).ConclusionsNewly occurring severe headaches can occur in 18% of patients after PSF from C2 distally. The patients with newly occurring severe headaches had significantly higher preoperative NDI score (neck pain)

Three Dimensional Distorted Black Holes

We present three-dimensional, {\it non-axisymmetric} distorted black hole initial data which generalizes the axisymmetric, distorted, non-rotating [Bernstein93a] and rotating [Brandt94a] single black hole data developed by Bernstein, Brandt, and Seidel. These initial data should be useful for studying the dynamics of fully 3D, distorted black holes, such as those created by the spiraling coalescence of two black holes. We describe the mathematical construction of several families of such data sets, and show how to construct numerical solutions. We survey quantities associated with the numerically constructed solutions, such as ADM masses, apparent horizons, measurements of the horizon distortion, and the maximum possible radiation loss ($MRL$).Comment: 23 pages, 12 figures, accepted for publication in Classical and Quantum Gravit