Kinetic information from detonation front curvature
Souers, P. C., LLNL
1998-06-15
The time constants for time-dependent modeling may be estimated from reaction zone lengths, which are obtained from two sources One is detonation front curvature, where the edge lag is close to being a direct measure The other is the Size Effect, where the detonation velocity decreases with decreasing radius as energy is lost to the cylinder edge A simple theory that interlocks the two effects is given A differential equation for energy flow in the front is used, the front is described by quadratic and sixth-power radius terms The quadratic curvature comes from a constant power source of energy moving sideways to the walls Near the walls, the this energy rises to the total energy of detonation and produces the sixth-power term The presence of defects acting on a short reaction zone can eliminate the quadratic part while leaving the wall portion of the cuvature A collection of TNT data shows that the reaction zone increases with both the radius and the void fraction
Hill, L.G.; Bdzil, J.B.; Aslam, T.D.
1998-12-31
Detonation velocity and wave shape are measured for PBX 9502 (95 wt.% TATB, 5 wt.% Kel-F 800) rate sticks at the temperatures {minus}55, 25, and 75 C. At each temperature three different diameters were fired: 50 mm, 18 mm, and 8, 10, and 12 mm respectively for the hot, ambient, and cold sticks. The measured wave shapes are fit with an analytic form and the fitting parameters are tabulated along with thermal expansion and diameter effect data. The simplest detonation shock dynamics (DSD) model assumes a unique calibration function relating the local normal wave speed D{sub n} to the local total curvature {kappa}. The data confirm this notion for sufficiently small curvature, but at large curvature the curves for different charge diameters diverge. Global optimization is used to determine a best single D{sub n}-{kappa} function at each initial temperature T{sub 0}. From these curves a D{sub n}({kappa},T{sub 0}) calibration surface is generated that allows computation of problems with temperature gradients.
Detonation Front Curvatures and Detonation Rates
NASA Astrophysics Data System (ADS)
Lauderbach, Lisa M.; Lorenz, K. Thomas; Lee, Edward L.; Souers, P. Clark
2015-06-01
We have normalized the LLNL library of detonation front curvatures by dividing lags by the edge lag and radii by the edge radius. We then fit the normalized data to the equation L = AR2 + BR8, where L is the normalized lag and R is the normalized radius. We attribute the quadratic term to thermal processes and the 8th-power term to shock processes. We compare the % of the quadratic term J at the edge with detonation rates obtained from the size effect. One class of results is made up of fine-grained, uniform explosives with large lags, where a low detonation rate leads to a high J and vice versa. This provides a rough way of estimating unknown rates if the unknown explosive is of high quality. The other, equally-large class contains rough-grained materials, often with small lags and small radii. These have curves that do not fit the equation but superfically often look quadratic. Some HMX and PETN curvatures even show a ``sombrero'' effect. Code models show that density differences of 0.03 g/cc in ram-pressed parts can cause pseudo-quadratic curves and even sombreros. Modeling is used to illustrate J at the lowest and highest possible detonation rates. This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Toward assessing the effects of crack front curvature /CFC/.
NASA Technical Reports Server (NTRS)
Swedlow, J. L.; Ritter, M. A.
1972-01-01
Consideration of the effect of crack front curvature (CFC) on the K calibration of five special geometries in which CFC occurs. The five cases considered include an elliptical crack in an infinite medium, an internal annular crack in a thick-walled cylinder, a through crack in a flat plate, a part-through crack in a plate, and an irregularly shaped crack in a solid. It is shown that K depends on CFC differently in each case.
Theory for the curvature dependence of delta front progradation
NASA Astrophysics Data System (ADS)
Ke, Wun-Tao; Capart, Hervé
2015-12-01
When Gilbert-type deltas respond to uneven sediment supply or advance over irregular basin bathymetry, they develop curved, creased fronts prograding at speeds that vary with location along the shoreline. Relations governing the progradation rate, however, have so far been proposed only for simple special cases. In this paper, we exploit the special properties of solutions to the eikonal equation to derive a general progradation relation, applicable to delta fronts of finite angle of repose and arbitrary shoreline planform. In these circumstances, the theory explicitly relates the progradation rate to the local shoreline curvature. We illustrate the resulting morphodynamics with numerical and analytical solutions for a sinuous delta front. The proposed relation can be used to model deltaic evolution or deduce spanwise distributions of sediment supply rates from observations of foreset evolution.
Effects of curvature and compressibility on the stability of thermal fronts
Ibanez S, Miguel H.; Bessega L, Maria C.; Shchekinov, Yuri
2006-06-15
The stability of subsonic thermal fronts against corrugation is analyzed and an exact dispersion relation is obtained taking into account the effects of the curvature of the distorted front as well as the compressibility of the gas. At a certain value of the Mach number ahead of the thermal front, unstable rates show a maximum; these rates drop to zero when a Chapman-Jouguet regime is established behind heat fronts. It is shown that curvature effects tend to stabilize conductive heat fronts propagating in a compressible gas.
NASA Astrophysics Data System (ADS)
Vallmitjana, S.; Ricart, I.; Bosch, S.; Gargallo, A.; Acosta, E.
2015-02-01
The study of caustics is important because they contain information about the image formation properties of optical systems. In this work we use the concept of caustic as a set of focal points, and we have developed a second order approach theory to determine local slopes and curvatures of a wavefront emerging from an optical system. The method is based on the use of a point diffraction interferometer, and the analysis of the interferograms allows us to compute the focal region. Experimental results obtained with a plano-convex lens demonstrate the accuracy of the combined theoretical-experimental method here developed. Application to noisy wavefronts such as those produced by biological samples, specifically in crystalline lenses of fish eyes, are also exposed.
Influence of the bonding front propagation on the wafer stack curvature
Navarro, E.; Bréchet, Y.; Barthelemy, A.; Radu, I.; Pardoen, T.; Raskin, J.-P.
2014-08-11
The influence of the dynamics of the direct wafer bonding process on the curvature of the final wafer stack is investigated. An analytical model for the final curvature of the bonded wafers is developed, as a function of the different load components acting during the bonding front propagation, using thin plate theory and considering a strain discontinuity locked at the bonding interface. Experimental profiles are measured for different bonding conditions and wafer thicknesses. A very good agreement with the model prediction is obtained and the influence of the thin air layer trapped in-between the two wafers is demonstrated. The proposed model contributes to further improvement of the bonding process, in particular, for the stacking of layers of electronic devices, which requires a high accuracy of wafer-to-wafer alignment and a very low distortion level.
Geometry-specific scaling of detonation parameters from front curvature
Jackson, Scott I; Short, Mark
2011-01-20
It has previously been asserted that classical detonation curvature theory predicts that the critical diameter and the diameter-effect curve of a cylindrical high-explosive charge should scale with twice the thickness of an analogous two-dimensional explosive slab. The varied agreement of experimental results with this expectation have led some to question the ability of curvature-based concepts to predict detonation propagation in non-ideal explosives. This study addresses such claims by showing that the expected scaling relationship (hereafter referred to d = 2w) is not consistent with curvature-based Detonation Shock Dynamics (DSD) theory.
Controllable soliton propagation based on phase-front curvature in asymmetrical nonlocal media
NASA Astrophysics Data System (ADS)
Zhang, Huafeng; Lü, Hua; Luo, Jianghua; Sun, Lihui
2016-08-01
The influence of phase-front curvature on the dynamical behavior of the fundamental mode soliton during its transmission in asymmetrical nonlocal media is studied in detail and the phase-front curvature can be imposed on the fundamental mode soliton by reshaping or phase imprinting technologies. By changing the phase-front curvature or its imposed position, controllable soliton propagation in asymmetrical nonlocal media can be achieved. Project supported by the National Natural Science Foundation of China (Grants Nos. 11547007 and 11304024), the Innovation Personnel Training Plan for Excellent Youth of Guangdong University Project (Grant No. 2013LYM_0023), and the Yangtze Fund for Youth Teams of Science and Technology Innovation (Grant No. 2015cqt03).
Fronts propagating with curvature dependent speed: Algorithms based on Hamilton-Jacobi formulations
NASA Technical Reports Server (NTRS)
Osher, Stanley; Sethian, James A.
1987-01-01
New numerical algorithms are devised (PSC algorithms) for following fronts propagating with curvature-dependent speed. The speed may be an arbitrary function of curvature, and the front can also be passively advected by an underlying flow. These algorithms approximate the equations of motion, which resemble Hamilton-Jacobi equations with parabolic right-hand-sides, by using techniques from the hyperbolic conservation laws. Non-oscillatory schemes of various orders of accuracy are used to solve the equations, providing methods that accurately capture the formation of sharp gradients and cusps in the moving fronts. The algorithms handle topological merging and breaking naturally, work in any number of space dimensions, and do not require that the moving surface be written as a function. The methods can be used also for more general Hamilton-Jacobi-type problems. The algorithms are demonstrated by computing the solution to a variety of surface motion problems.
Tube curvature measuring probe and method
Sokol, George J.
1990-01-01
The present invention is directed to a probe and method for measuring the radius of curvature of a bend in a section of tubing. The probe includes a member with a pair of guide means, one located at each end of the member. A strain gauge is operatively connected to the member for detecting bending stress exrted on the member as the probe is drawn through and in engagement with the inner surface of a section of tubing having a bend. The method of the present invention includes steps utilizing a probe, like the aforementioned probe, which can be made to detect bends only in a single plane when having a fixed orientation relative the section of tubing to determine the maximum radius of curvature of the bend.
Curvature sensor for ocular wavefront measurement.
Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O
2006-08-01
We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes. PMID:16832447
Applications of variable focus liquid lenses for curvature wave-front sensors in astronomy
NASA Astrophysics Data System (ADS)
Fuentes-Fernández, J.; Cuevas, S.; Alvarez-Nuñez, L. C.; Watson, A. M.
2014-08-01
Curvature wavefront sensors obtain the wave-front aberrations from two defocused intensity images at each side of the pupil plane. Typically, when high modulation speeds are required, as it is the case with Adaptive Optics, that defocusing is done with a fast vibrating membrane mirror. We propose an alternative defocusing mechanism based on an electrowetting variable focus liquid lens. The use of such lenses may perform the required focus modulation without the need of extra moving parts, reducing the overall size of the system.
Pulsar Polar Cap Heating and Surface Thermal X-ray Emission. 1; Curvature Radiation Pair Fronts
NASA Technical Reports Server (NTRS)
Harding, Alice K.; Muslimov, Alexander G.; White, Nicholas E. (Technical Monitor)
2002-01-01
We investigate the effect of pulsar polar cap (PC) heating produced by positrons returning from the upper pair formation front. Our calculations are based on a self-consistent treatment of the pair dynamics and the effect of electric field screening by the returning positrons. We calculate the resultant X-ray luminosities and discuss the dependence of the PC heating efficiencies on pulsar parameters, such as characteristic spin-down age, spin period, and surface magnetic field strength. In this study we concentrate on the regime where the pairs are produced in a magnetic field by curvature photons emitted by accelerating electrons. Our theoretical results are not in conflict with the available observational x-ray data and suggest that the effect of PC heating should significantly contribute to the thermal x-ray fluxes from middle-aged and old pulsars. The implications for current and future x-ray observations of pulsars are briefly outlined.
Novel imaging system for measuring microscale curvatures at high temperatures
NASA Astrophysics Data System (ADS)
Tada, Haruna; Kumpel, Amy E.; Lathrop, Richard E.; Slanina, John B.; Nieva, Patricia; Zavracky, Paul; Miaoulis, Ioannis N.; Wong, Peter Y.
2000-01-01
An innovative system was designed to optically measure the curvature of microelectromechanical system at high temperatures. The system takes advantage of the limited numerical aperture of the imaging system to detect the curvature of cantilever beams. Images of the beam are used to determine beam curvature at high temperatures of up to 850 °C by analyzing the apparent change in beam length as seen by the camera during an experimental trial. The system is designed to operate at very high temperatures, which is difficult in conventional microscale curvature measurement techniques such as scanning electron microscopy or stylus profilometry due to excess heating of peripheral equipment. The system can measure curvatures as small as 300 m-1, which corresponds to tip deflections of 1.5 μm for a 100 μm beam. The resolution of the system is limited by the image resolution of the charge-coupled device camera, and increases at large curvatures. The maximum curvature that can be measured by the system is limited by the increase in system resolution, and is estimated to be 4500 m-1, corresponding to 22 μm deflection for a 100 μm beam. The apparatus was demonstrated to measure the thermally induced curvature of multilayered thin-film cantilever beams. The beams bend at high temperatures due to mismatch in thermal expansion coefficients between the layers. One innovative application of such curvature measurement is the determination of thermophysical properties of thin films at elevated temperatures. This article presents the experimental setup and operational theory of apparatus, as well as curvature measurements obtained by the system. The thermal expansion coefficient of polycrystalline silicon, determined from the curvature measurements, are also discussed.
Eddy-Current Measurement Of Turning Or Curvature
NASA Technical Reports Server (NTRS)
Chern, Engmin J.
1993-01-01
Rotatable conductive plate covers sensing coil to varying degree. Curvature of pipe at remote or otherwise inaccessible location inside pipe measured using relatively simple angular-displacement eddy-current probe. Crawler and sensor assemblies move along inside of pipe on wheels. Conductive plate pivots to follow curvature of pipe, partly covering one of eddy-current coils to degree depending on local curvature on pipe.
Local curvature measurements of a lean, partially premixed swirl-stabilised flame
NASA Astrophysics Data System (ADS)
Bayley, Alan E.; Hardalupas, Yannis; Taylor, Alex M. K. P.
2012-04-01
A swirl-stabilised, lean, partially premixed combustor operating at atmospheric conditions has been used to investigate the local curvature distributions in lifted, stable and thermoacoustically oscillating CH4-air partially premixed flames for bulk cold-flow Reynolds numbers of 15,000 and 23,000. Single-shot OH planar laser-induced fluorescence has been used to capture instantaneous images of these three different flame types. Use of binary thresholding to identify the reactant and product regions in the OH planar laser-induced fluorescence images, in order to extract accurate flame-front locations, is shown to be unsatisfactory for the examined flames. The Canny-Deriche edge detection filter has also been examined and is seen to still leave an unacceptable quantity of artificial flame-fronts. A novel approach has been developed for image analysis where a combination of a non-linear diffusion filter, Sobel gradient and threshold-based curve elimination routines have been used to extract traces of the flame-front to obtain local curvature distributions. A visual comparison of the effectiveness of flame-front identification is made between the novel approach, the threshold binarisation filter and the Canny-Deriche filter. The novel approach appears to most accurately identify the flame-fronts. Example histograms of the curvature for six flame conditions and of the total image area are presented and are found to have a broader range of local flame curvatures for increasing bulk Reynolds numbers. Significantly positive values of mean curvature and marginally positive values of skewness of the histogram have been measured for one lifted flame case, but this is generally accounted for by the effect of flame brush curvature. The mean local flame-front curvature reduces with increasing axial distance from the burner exit plane for all flame types. These changes are more pronounced in the lifted flames but are marginal for the thermoacoustically oscillating flames. It is
Electric current measurement using fiber-optic curvature sensor
NASA Astrophysics Data System (ADS)
Di, Haiting; Xin, Ying; Sun, Suping
2016-02-01
A novel fiber-optic curvature sensor, which can measure curvature directly, has been developed in recent years. The electric current measurements system based on fiber-optic curvature sensor and electromagnetic principle is developed. A fiber-optic curvature sensor is bonded to a thin-walled cantilever and two circular magnet targets with the same parameters are configured at the tip of the cantilever symmetrically. In this case, the throughput of the sensor will be changed due to the bending deformation of cantilever, which is proportional to the electromagnetic force caused by measured electric current. Direct and alternate characteristics of the proposed measurement system are studied experimentally. The results show that the measurement errors are within the range of ±5.5 mA and the corresponding accuracy is within 1% at the current measurement range from -300 mA to 300 mA, which indicate the feasibility of the proposed measurement system.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed. PMID:25615464
Clinical workflow for spinal curvature measurement with portable ultrasound
NASA Astrophysics Data System (ADS)
Tabanfar, Reza; Yan, Christina; Kempston, Michael; Borschneck, Daniel; Ungi, Tamas; Fichtinger, Gabor
2016-03-01
PURPOSE: Spinal curvature monitoring is essential in making treatment decisions in scoliosis. Monitoring entails radiographic examinations, however repeated ionizing radiation exposure has been shown to increase cancer risk. Ultrasound does not emit ionizing radiation and is safer for spinal curvature monitoring. We investigated a clinical sonography protocol and challenges associated with position-tracked ultrasound in spinal curvature measurement in scoliosis. METHODS: Transverse processes were landmarked along each vertebra using tracked ultrasound snapshots. The transverse process angle was used to determine the orientation of each vertebra. We tested our methodology on five patients in a local pediatric scoliosis clinic, comparing ultrasound to radiographic curvature measurements. RESULTS: Despite strong correlation between radiographic and ultrasound curvature angles in phantom studies, we encountered new challenges in the clinical setting. Our main challenge was differentiating transverse processes from ribs and other structures during landmarking. We observed up to 13° angle variability for a single vertebra and a 9.85° +/- 10.81° difference between ultrasound and radiographic Cobb angles for thoracic curvatures. Additionally, we were unable to visualize anatomical landmarks in the lumbar region where soft tissue depth was 25-35mm. In volunteers with large Cobb angles (greater than 40° thoracic and 60° lumbar), we observed spinal protrusions resulting in incomplete probe-skin contact and partial ultrasound images not suitable for landmarking. CONCLUSION: Spinal curvature measurement using tracked ultrasound is viable on phantom spine models. In the clinic, new challenges were encountered which must be resolved before a universal sonography protocol can be developed.
An analytical investigation of delamination front curvature in double cantilever beam specimens
NASA Technical Reports Server (NTRS)
Davidson, B. D.
1990-01-01
An analytical investigation is conducted to determine the shape of a growing delamination and the distribution of the energy release rate along the delamination front in a laminated composite double cantilever beam specimen. Distributions of the energy release rate for specimens with straight delamination fronts and delamination front contours for delaminations whose growth is governed by the fracture criterion that G = Gc at all points are predicted as a function of material properties and delamination length. The predicted delamination front contours are utilized to ascertain the effect of the changing shape of the delamination front on the value of the critical strain energy release rate as computed from double cantilever beam fracture toughness test data.
NASA Astrophysics Data System (ADS)
Ma, Shuang; Yi, Shengzhen; Chen, Shenghao; Wang, Zhanshan
2014-11-01
Monochromatic energy multilayer Kirkpatrick-Baez microscope is one of key diagnostic tools for researches on inertial confinement fusion. It is composed by two orthogonal concave spherical mirrors with small curvature and aperture, and produce the image of an object by collecting X-rays in each orthogonal direction, independently. Accurate measurement of radius of curvature of concave spherical mirrors is very important to achieve its design optical properties including imaging quality, optical throughput and energy resolution. However, it is difficult to measure the radius of curvature of spherical optical surfaces with small curvature and aperture by conventional methods, for the produced reflective intensity of glass is too low to correctly test. In this paper, we propose an improved measuring method of optical profiler to accomplish accurate measurement of radius of curvature of spherical optical surfaces with small curvature and aperture used in the monochromatic energy multilayer Kirkpatrick-Baez microscope. Firstly, we use a standard super-smooth optical flat to calibrate reference mirror before each experiment. Following, deviation of central position between measurement area and interference pattern is corrected by the theory of Newton's rings, and the zero-order fringe position is derived from the principle of interference in which surface roughness has minimum values in the position of zero light path difference. Measured results by optical profiler show the low relative errors and high repeatability. Eventually, an imaging experiment of monochromatic energy multilayer Kirkpatrick-Baez microscope determines the measurement accuracy of radius of curvature.
Direct and alignment-insensitive measurement of cantilever curvature
Hermans, Rodolfo I.; Aeppli, Gabriel; Bailey, Joe M.
2013-07-15
We analytically derive and experimentally demonstrate a method for the simultaneous measurement of deflection for large arrays of cantilevers. The Fresnel diffraction patterns of a cantilever independently reveal tilt, curvature, cubic, and higher order bending of the cantilever. It provides a calibrated absolute measurement of the polynomial coefficients describing the cantilever shape, without careful alignment and could be applied to several cantilevers simultaneously with no added complexity. We show that the method is easily implemented, works in both liquid media and in air, for a broad range of displacements and is especially suited to the requirements for multi-marker biosensors.
Determination of Thermal Spray Coating Property with Curvature Measurements
NASA Astrophysics Data System (ADS)
Dwivedi, Gopal; Nakamura, Toshio; Sampath, Sanjay
2013-12-01
Real-time curvature measurement of a coating-substrate system during deposition has facilitated the monitoring of coating stresses and provided additional insights into thermal spray deposition mechanisms. However, the non-equilibrium state of coating formation along with harsh spray booth environment introduces complexity not only in data interpretation but also in the coating properties estimation. In this paper, a new procedure is proposed to estimate the elastic modulus of thermal sprayed ceramic coatings using in situ curvature and temperature measurements. In order to correlate the measurable parameters to coating elastic modulus, a systematic study is conducted to develop a suitable methodology. First, various finite element model analyses are carried out to formulate suitable relations between the measurements and elastic modulus. Subsequently, experiments are conducted to validate the procedure to estimate coating moduli. The results are compared with more accurate measurements obtained from post-deposition characterization technique under low temperature thermal cycles. The comparison suggests that the moduli estimated using the proposed procedure are in good agreements with those obtained from the post-deposition technique. Further, the nonlinear response of coatings are evaluated from the estimated moduli during deposition and cool down, which offer additional information on the characteristics of thermal spray coatings.
Residual stress determination from a laser-based curvature measurement
W. D. Swank; R. A. Gavalya; J. K. Wright; R. N. Wright
2000-05-08
Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.
Residual Stress Determination from a Laser-Based Curvature Measurement
Swank, William David; Gavalya, Rick Allen; Wright, Julie Knibloe; Wright, Richard Neil
2000-05-01
Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.
Camera-based curvature measurement of a large incandescent object
NASA Astrophysics Data System (ADS)
Ollikkala, Arttu V. H.; Kananen, Timo P.; Mäkynen, Anssi J.; Holappa, Markus
2013-04-01
The goal of this work was to implement a low-cost machine vision system to help the roller operator to estimate the amount of strip camber during the rolling process. The machine vision system composing of a single camera, a standard PC-computer and a LabVIEW written program using straightforward image analysis determines the magnitude and direction of camber and presents the results both in numerical and graphical form on the computer screen. The system was calibrated with LED set-up which was also used to validate the accuracy of the system by mimicking the strip curvatures. The validation showed that the maximum difference between the true and measured values was less than +/-4 mm (k=0.95) within the 22 meter long test pattern.
Coherent gradient sensing method and system for measuring surface curvature
NASA Technical Reports Server (NTRS)
Rosakis, Ares J. (Inventor); Singh, Ramen P. (Inventor); Kolawa, Elizabeth (Inventor); Moore, Jr., Nicholas R. (Inventor)
2000-01-01
A system and method for determining a curvature of a specularly reflective surface based on optical interference. Two optical gratings are used to produce a spatial displacement in an interference field of two different diffraction components produced by one grating from different diffraction components produced by another grating. Thus, the curvature of the surface can be determined.
Radius of Curvature Measurements: An Independent Look at Accuracy Using Novel Optical Metrology
NASA Technical Reports Server (NTRS)
Taylor, Bryon; Kahan, Mark; Russell, Kevin (Technical Monitor)
2002-01-01
The AMSD (Advanced Mirror System Demonstrator) program mirror specifications include the ability to manufacture the mirror to a radius of curvature of 10 m +/- 1 mm and to control its radius at 30K to the same specification. Therefore, it is necessary for the Government Team to be able to measure mirror radius of curvature to an accuracy of better than 0.5 mm. This presentation discusses a novel optical metrology system for measuring radius of curvature.
Wave-front measurement errors from restricted concentric subdomains.
Goldberg, K A; Geary, K
2001-09-01
In interferometry and optical testing, system wave-front measurements that are analyzed on a restricted subdomain of the full pupil can include predictable systematic errors. In nearly all cases, the measured rms wave-front error and the magnitudes of the individual aberration polynomial coefficients underestimate the wave-front error magnitudes present in the full-pupil domain. We present an analytic method to determine the relationships between the coefficients of aberration polynomials defined on the full-pupil domain and those defined on a restricted concentric subdomain. In this way, systematic wave-front measurement errors introduced by subregion selection are investigated. Using vector and matrix representations for the wave-front aberration coefficients, we generalize the method to the study of arbitrary input wave fronts and subdomain sizes. While wave-front measurements on a restricted subdomain are insufficient for predicting the wave front of the full-pupil domain, studying the relationship between known full-pupil wave fronts and subdomain wave fronts allows us to set subdomain size limits for arbitrary measurement fidelity. PMID:11551047
Measurement of curvature and twist of a deformed object using digital holography
Chen Wen; Quan Chenggen; Cho Jui Tay
2008-05-20
Measurement of curvature and twist is an important aspect in the study of object deformation. In recent years, several methods have been proposed to determine curvature and twist of a deformed object using digital shearography. Here we propose a novel method to determine the curvature and twist of a deformed object using digital holography and a complex phasor. A sine/cosine transformation method and two-dimensional short time Fourier transform are proposed subsequently to process the wrapped phase maps. It is shown that high-quality phase maps corresponding to curvature and twist can be obtained. An experiment is conducted to demonstrate the validity of the proposed method.
Mazeh, Nachaat; Haines, David E; Kay, Matthew W; Roth, Bradley J
2013-12-01
The velocity and curvature of a wave front are important factors governing the propagation of electrical activity through cardiac tissue, particularly during heart arrhythmias of clinical importance such as fibrillation. Presently, no simple computational model exists to determine these values simultaneously. The proposed model uses the arrival times at four or five sites to determine the wave front speed (v), direction (θ), and radius of curvature (ROC) (r 0). If the arrival times are measured, then v, θ, and r 0 can be found from differences in arrival times and the distance between these sites. During isotropic conduction, we found good correlation between measured values of the ROC r 0 and the distance from the unipolar stimulus (r = 0.9043 and p < 0.0001). The conduction velocity (m/s) was correlated (r = 0.998, p < 0.0001) using our method (mean = 0.2403, SD = 0.0533) and an empirical method (mean = 0.2352, SD = 0.0560). The model was applied to a condition of anisotropy and a complex case of reentry with a high voltage extra stimulus. Again, results show good correlation between our simplified approach and established methods for multiple wavefront morphologies. In conclusion, insignificant measurement errors were observed between this simplified approach and an approach that was more computationally demanding. Accuracy was maintained when the requirement that ε (ε = b/r 0, ratio of recording site spacing over wave fronts ROC) was between 0.001 and 0.5. The present simplified model can be applied to a variety of clinical conditions to predict behavior of planar, elliptical, and reentrant wave fronts. It may be used to study the genesis and propagation of rotors in human arrhythmias and could lead to rotor mapping using low density endocardial recording electrodes. PMID:24772193
Focal length and radius of curvature measurement using wavefront difference method
NASA Astrophysics Data System (ADS)
Yang, Zhongming; Gao, Zhishan; Wang, Shuai; Cheng, Jinlong; Yuan, Qun
2015-10-01
A method for measuring the focal length of the lens and the radius of curvature of the spherical surface using wavefront difference method is proposed. Based on Fizeau interferometer, an experimental system for focal length measurements is set up to verify the principle. Based on the point diffraction interferometer, an experimental system for radius of curvature measurements is proposed to verify the proposed method. With the focal length testing system, both the positive and negative lens experimental results indicate that the measurement accuracy is less than 0.16%under normal experimental environment. With the radius of curvature testing system, the radius of curvature of spherical mirrors and the surface figure can be measured in a higher precision simultaneously. The experimental results indicate that the measurement accuracy is in the order of 10-4 .
NASA Astrophysics Data System (ADS)
Yang, Zhongming; Gao, Zhishan; Yuan, Qun; Ye, Jingfei; Li, Minjue
2014-05-01
A method for measuring the radius of curvature with a pinhole point diffraction interferometer (PDI) is proposed. Using the wavefront difference method and the Gaussian imaging equation, the longitudinal displacement of the converging rays passing through a standard plane-parallel-plate sample in PDI interference cavity is determined. Based on this longitudinal displacement, a precise formula for radius of curvature calculation is deduced. An experimental system for radius of curvature measurements is set up to verify the principle. With this testing system, the radius of curvature of spherical mirrors and the surface figure can be measured in a higher precision simultaneously. Some sources of uncertainty in measurement are discussed based on detailed error analysis. The experimental results indicate that the measurement accuracy ΔR/R0 is in the order of 10-4.
NASA Astrophysics Data System (ADS)
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-03-01
A geometric formulation of Higgs Effective Field Theory (HEFT) is presented. Experimental observables are given in terms of geometric invariants of the scalar sigma model sector such as the curvature of the scalar field manifold M. We show how the curvature can be measured experimentally via Higgs cross-sections, WL scattering, and the S parameter. The one-loop action of HEFT is given in terms of geometric invariants of M. The distinction between the Standard Model (SM) and HEFT is whether M is flat or curved, and the curvature is a signal of the scale of new physics.
The coherent gradient sensor for film curvature measurements at cryogenic temperature.
Liu, Cong; Zhang, Xingyi; Zhou, Jun; Zhou, Youhe; Feng, Xue
2013-11-01
Coherent Gradient Sensor (CGS) system is presented for measurement of curvatures and nonuniform curvatures changes in film-substrate systems at cryogenic temperature. The influences of the interface of refrigerator and itself on the interferograms which are accounting for the temperature effect are successfully eliminated. Based on the measurement technique, the thermal stresses (including the radial stress, circumferential stress and shear stress) of superconducting YBCO thin-film are obtained by the extended Stoney's formula during the heating process from 30K to 150K. Take the superconducting YBCO thin film as an example, the thermal stresses of which are gained successfully. PMID:24216858
Pulse front tilt measurement of femtosecond laser pulses
NASA Astrophysics Data System (ADS)
Dimitrov, Nikolay; Stoyanov, Lyubomir; Stefanov, Ivan; Dreischuh, Alexander; Hansinger, Peter; Paulus, Gerhard G.
2016-07-01
In this work we report experimental investigations of an intentionally introduced pulse front tilt on femtosecond laser pulses by using an inverted field correlator/interferometer. A reliable criterion for the precision in aligning (in principle) dispersionless systems for manipulating ultrashort pulses is developed, specifically including cases when the pulse front tilt is a result of a desired spatio-temporal coupling. The results obtained using two low-dispersion diffraction gratings are in good qualitative agreement with the data from a previously developed analytical model and from an independent interferometric measurement.
4. Photocopy of measured drawing dated January, 1948 FRONT ELEVATION ...
4. Photocopy of measured drawing dated January, 1948 FRONT ELEVATION An addendum to Hanson-Cramer House, Sea Street, south end, Rockport, Knox County, Maine - Hanson-Cramer House, End of Sea Street (moved from Pascal's Avenue), Rockport, Knox County, ME
Precise curvature measurement of Yb:YAG thin disk
NASA Astrophysics Data System (ADS)
Muzik, Jiri; Chyla, Michal; Nagisetty, Siva S.; Miura, Taisuke; Mann, Klaus; Endo, Akira; Mocek, Tomas
2015-01-01
We are developing an Yb:YAG thin disk regenerative amplifier operating at 1 kHz repetition rate which should deliver output of 100 W of average power which corresponds to the pulse energy of 100 mJ. In order to achieve such high output energy, large size mode matching on a thin-disk is required to avoid optical damage but on the other hand, larger mode area is more susceptible to the influence of optical phase distortions (OPD's) thus limits achievable pulse energy and beam quality. We developed a compact setup allowing precise measurement of the thin-disk deformations by implementation of a Hartmann-Shack wavefront sensor and a single mode probe laser diode. In comparison to the interferometric measurement methods, our approach brings a number of advantages like simplicity of alignment, compactness and robustness, at the same time keeping the high precision of measurement in a range of few nanometers.
Aligning and measuring the curvature and thickness of high-precision lens
NASA Astrophysics Data System (ADS)
Wu, Kun-Huan; Chang, Shenq-Tsong; Hsu, Ming-Ying; Huang, Ting-Ming; Hsu, Wei-Yao; Tseng, Shih-Feng
2015-09-01
The radius of curvature is one of the most important specifications for spherical optics [1]. There are several methods and devices currently on the market that can be used to measure it, including optical level, non-contact laser interferometer (Interferometer), a probe-contact profiler (Profilometer), the centering machine and three-point contact ball diameter meter (Spherometer). The amount that can be measured with a radius of curvature of the lens aperture range depends on the interferometer standard lens f / number and lens of R / number (radius of curvature divided by the clear aperture of the spherical surface ratio between them). Unfortunately, for lens with diameter greater than 300 mm, the device is limited by the size of the holding fixture lenses or space. This paper aims to provide a novel surface contour detection method and machine, named "CMM spherometry by probe compensation," to measure the radius and thickness of the curvature of the optical surface by a coordinate measurement machine (CMM). In order to obtain more accurate optimization results, we used probe and temperature compensation to discuss the effect. The trace samples and the measurement results of CMM and the centering machine, which has top and bottom autocollimators, are compared.
NASA Astrophysics Data System (ADS)
Chen, Yixuan; Mills, Shaun; Liu, Ying
In monolayer graphene, the local deviation of carbon positions from the perfect lattice has been predicted to lead to a pseudo magnetic field with measurable effects. A striking confirmation of this effect is the observation of Landau levels that are attributed to a pseudo magnetic field in excess of 300 T in graphene nanobubbles. However, typical experimental methods of generating such local deviations in graphene rely on strain accompanied by a surface curvature. Whether a surface curvature alone can produce measurable effects in graphene has not been explored experimentally. It is therefore of interest to study graphene in a system that decouples strain from surface curvature. Of particular interest is its response to an external magnetic field. We developed a grayscale electron beam lithography technique for preparing PMMA substructures with a continuously variable radius of curvature from ~100 nm to ~1 μm. Magnetoelectrical transport measurements on exfoliated graphene supported by these substructures are being carried out. The flexibility of this process may be further exploited in the study of the bilayer and trilayer graphene systems. We will also study hybrid structures of 2D superconductors and graphene.
Front surface thermal property measurements of air plasma spray coatings
Bennett, Ted; Kakuda, Tyler; Kulkarni, Anand
2009-04-15
A front-surface measurement for determining the thermal properties of thermal barrier coatings has been applied to air plasma spray coatings. The measurement is used to determine all independent thermal properties of the coating simultaneously. Furthermore, with minimal requirements placed on the sample and zero sample preparation, measurements can be made under previously impossible conditions, such as on serviceable engine parts. Previous application of this technique was limited to relatively thin coatings, where a one-dimensional heat transfer model is applied. In this paper, the influence of heat spreading on the measurement of thicker coatings is investigated with the development of a two-dimensional heat transfer model.
Radius of Curvature Measurement of Large Optics Using Interferometry and Laser Tracker
NASA Technical Reports Server (NTRS)
Hagopian, John; Connelly, Joseph
2011-01-01
The determination of radius of curvature (ROC) of optics typically uses either a phase measuring interferometer on an adjustable stage to determine the position of the ROC and the optics surface under test. Alternatively, a spherometer or a profilometer are used for this measurement. The difficulty of this approach is that for large optics, translation of the interferometer or optic under test is problematic because of the distance of translation required and the mass of the optic. Profilometry and spherometry are alternative techniques that can work, but require a profilometer or a measurement of subapertures of the optic. The proposed approach allows a measurement of the optic figure simultaneous with the full aperture radius of curvature.
Bortolotti, Carolina T; Barrozo, Marcos A S
2013-01-01
In the present work, we performed a discrimination analysis of the nonlinear equations used to describe sorption isotherms of the lettuce seeds. The equilibrium data were obtained by the static method using saturated salt solutions. The best model to describe the equilibrium moisture of lettuce seeds was selected using measures of curvature and bias. The obtained results showed that the Copace equation was the best model in terms of nonsignificance for bias and nonlinearity measures. PMID:24804051
Assessment of scoliosis by direct measurement of the curvature of the spine
NASA Astrophysics Data System (ADS)
Dougherty, Geoff; Johnson, Michael J.
2009-02-01
We present two novel metrics for assessing scoliosis, in which the geometric centers of all the affected vertebrae in an antero-posterior (A-P) radiographic image are used. This is in contradistinction to the existing methods of using selected vertebrae, and determining either their endplates or the intersections of their diagonals, to define a scoliotic angle. Our first metric delivers a scoliotic angle, comparable to the Cobb and Ferguson angles. It measures the sum of the angles between the centers of the affected vertebrae, and avoids the need for an observer to decide on the extent of component curvatures. Our second metric calculates the normalized root-mean-square curvature of the smoothest path comprising piece-wise polynomial splines fitted to the geometric centers of the vertebrae. The smoothest path is useful in modeling the spinal curvature. Our metrics were compared to existing methods using radiographs from a group of twenty subjects with spinal curvatures of varying severity. Their values were strongly correlated with those of the scoliotic angles (r = 0.850 - 0.886), indicating that they are valid surrogates for measuring the severity of scoliosis. Our direct use of positional data removes the vagaries of determining variably shaped endplates, and circumvented the significant interand intra-observer errors of the Cobb and Ferguson methods. Although we applied our metrics to two-dimensional (2- D) data in this paper, they are equally applicable to three-dimensional (3-D) data. We anticipate that they will prove to be the basis for a reliable 3-D measurement and classification system.
Simple yet accurate noncontact device for measuring the radius of curvature of a spherical mirror
Spiridonov, Maxim; Toebaert, David
2006-09-10
An easily reproducible device is demonstrated to be capable of measuring the radii of curvature of spherical mirrors, both convex and concave, without resorting to high-end interferometric or tactile devices. The former are too elaborate for our purposes,and the latter cannot be used due to the delicate nature of the coatings applied to mirrors used in high-power CO2 laser applications. The proposed apparatus is accurate enough to be useful to anyone using curved optics and needing a quick way to assess the values of the radii of curvature, be it for entrance quality control or trouble shooting an apparently malfunctioning optical system. Specifically, the apparatus was designed for checking 50 mm diameter resonator(typically flat or tens of meters concave) and telescope (typically some meters convex and concave) mirrors for a high-power CO2 laser, but it can easily be adapted to any other type of spherical mirror by a straightforward resizing.
Measurement of the curvature of a surface using parallel light beams
Chason, Eric H.; Floro, Jerrold A.; Seager, Carleton H.; Sinclair, Michael B.
1999-01-01
Apparatus for measuring curvature of a surface wherein a beam of collimated light is passed through means for producing a plurality of parallel light beams each separated by a common distance which then reflect off the surface to fall upon a detector that measures the separation of the reflected beams of light. This means can be an etalon and the combination of a diffractive element and a converging lens. The curvature of the surface along the line onto which the multiple beams fall can be calculated from this information. A two-dimensional map of the curvature can be obtained by adding a second etalon (or a second combination of a diffractive element and a converging lens) which is rotated 90.degree. about the optical axis relative to the first etalon and inclined at the same angle. The second etalon creates an individual set of parallel light beams from each of the individual beams created by the first etalon with the sets of parallel light beams from the second etalon rotated 90.degree. relative to the line onto which the single set of parallel beams from the first etalon would have fallen.
Measurement of the curvature of a surface using parallel light beams
Chason, E.H.; Floro, J.A.; Seager, C.H.; Sinclair, M.B.
1999-06-15
Apparatus is disclosed for measuring curvature of a surface wherein a beam of collimated light is passed through a means for producing a plurality of parallel light beams each separated by a common distance which then reflect off the surface to fall upon a detector that measures the separation of the reflected beams of light. This means can be an etalon and the combination of a diffractive element and a converging lens. The curvature of the surface along the line onto which the multiple beams fall can be calculated from this information. A two-dimensional map of the curvature can be obtained by adding a second etalon (or a second combination of a diffractive element and a converging lens) which is rotated 90[degree] about the optical axis relative to the first etalon and inclined at the same angle. The second etalon creates an individual set of parallel light beams from each of the individual beams created by the first etalon with the sets of parallel light beams from the second etalon rotated 90[degree] relative to the line onto which the single set of parallel beams from the first etalon would have fallen. 5 figs.
Shock front velocity measurements in a T-tube plasma
NASA Astrophysics Data System (ADS)
Vujičić, B.; Ciršan, M.; Djurović, S.; Mijatović, Z.
2002-12-01
In the sense of investigation of T-tube shock front influence to the material surfaces, we analysed dependence of shock front velocity on deposited electric energy in capacitor bank i.e. applied voltage to discharge electrodes. A simple, cheap and reliable method for the shock front velocity determination by using a photomultiplier and oscilloscope is described in this paper.
NASA Astrophysics Data System (ADS)
Oberti, Sylvain; Bonnet, Henri; Fedrigo, Enrico; Ivanescu, Liviu; Kasper, Markus E.; Paufique, Jerome
2004-10-01
The accurate calibration of an AO system is fundamental in order to reach the top performance expected from design. To improve this aspect, we propose procedures for calibrating a curvature AO system in view of optimizing performances and robustness, based on the experience accumulated by the ESO AO team through the development of MACAO systems for VLTI and SINFONI. The approach maximizes the quality of the Interaction Matrix (IM) while maintaining the system in its linear regime and minimizing noise and bias on the measurement.
González-Sánchez, Manuel; Cuesta-Vargas, Antonio I.
2014-01-01
To analyse and compare standing thoracolumbar curves in normal weight participants and participants with obesity, using an electromagnetic device, and to analyse the measurement reliability. Material and Methods. Cross-sectional study was carried out. 36 individuals were divided into two groups (normal-weight and participants with obesity) according to their waist circumference. The reference points (T1–T8–L1–L5 and both posterior superior iliac spines) were used to perform a description of thoracolumbar curvature in the sagittal and coronal planes. A transformation from the global coordinate system was performed and thoracolumbar curves were adjusted by fifth-order polynomial equations. The tangents of the first and fifth lumbar vertebrae and the first thoracic vertebra were determined from their derivatives. The reliability of the measurement was assessed according to the internal consistency of the measure and the thoracolumbar curvature angles were compared between groups. Results. Cronbach's alpha values ranged between 0.824 (95% CI: 0.776–0.847) and 0.918 (95% CI: 0.903–0.949). In the coronal plane, no significant differences were found between groups; however, in sagittal plane, significant differences were observed for thoracic kyphosis. Conclusion. There were significant differences in thoracic kyphosis in the sagittal plane between two groups of young adults grouped according to their waist circumference. PMID:25276833
177-207 GHz Radiometer Front End: Single Sideband Measurements
NASA Technical Reports Server (NTRS)
Galin, I.; Schnitzer, C. A.; Dengler, R. J.; Quintero, O.
1999-01-01
Twenty years of progress in 200 GHz receivers for spaceborne remote sensing has yielded a 180-220 GHz technology with maturing characteristics, as evident by increasing availability of relevant hardware, paralleled by further refinement in receiver performance requirements at this spectrum band. The 177-207 GHz superheterodyne receiver, for the Earth observing system (EOS) microwave limb sounder (MLS), effectively illustrates such technology developments. This MLS receiver simultaneously detects six different signals, located at sidebands below and above its 191.95 GHZ local-oscillator (LO). The paper describes the MLS 177-207 GHz receiver front-end (RFE), and provides measured data for its lower and upper sidebands. Sideband ratio data is provided as a function of IF frequency, at different LO power drive, and for variation in the ambient temperature.
Realization of sub-micron radius of curvature measurement in vertical interferometer workstation
NASA Astrophysics Data System (ADS)
Miao, Erlong; Wang, Rudong; Zhang, Wei; Peng, Shijun
2014-09-01
Radius of curvature (ROC) is one of the key parameters for optical elements and it is especially important for high quality optical system, in which the computer-aided integration is wildly used. ROC is one of the main input parameters and its measurement accuracy is a premise for high quality integration. In this paper, sub-micron ROC measurements are realized in a vertical interference workstation based on Fizeau interferometer. The error sources and uncertainty of the system are analyzed. Experiment results based on samples with difference ROC are presented and in accordance with the analysis. At last, a ROC comparing tests between the system and a three-coordinates measuring machine (CMM) are performed on a SiC ball to certify the workstation's measurement uncertainty.
Measurement of the absolute wavefront curvature radius in a heterodyne interferometer.
Hechenblaikner, Gerald
2010-09-01
We present an analytical derivation of the coupling parameter relating the angle between two interfering beams in a heterodyne interferometer to the differential phase signals detected by a quadrant photodiode. This technique, also referred to as differential wavefront sensing, is commonly used in space-based gravitational wave detectors to determine the attitude of a test mass in one of the interferometer arms from the quadrant diode signals. Successive approximations to the analytical expression are made to simplify the investigation of parameter dependencies. Motivated by our findings, we propose what we believe to be a new measurement method to accurately determine the absolute wavefront curvature of a single measurement beam. We also investigate the change in the coupling parameter when the interferometer "test mirror" is moved from its nominal position, an effect which mediates the coupling of mirror displacement noise into differential phase measurements. PMID:20808419
Comparison of portable and conventional ultrasound imaging in spinal curvature measurement
NASA Astrophysics Data System (ADS)
Yan, Christina; Tabanfar, Reza; Kempston, Michael; Borschneck, Daniel; Ungi, Tamas; Fichtinger, Gabor
2016-03-01
PURPOSE: In scoliosis monitoring, tracked ultrasound has been explored as a safer imaging alternative to traditional radiography. The use of ultrasound in spinal curvature measurement requires identification of vertebral landmarks, but bones have reduced visibility in ultrasound imaging and high quality ultrasound machines are often expensive and not portable. In this work, we investigate the image quality and measurement accuracy of a low cost and portable ultrasound machine in comparison to a standard ultrasound machine in scoliosis monitoring. METHODS: Two different kinds of ultrasound machines were tested on three human subjects, using the same position tracker and software. Spinal curves were measured in the same reference coordinate system using both ultrasound machines. Lines were defined by connecting two symmetric landmarks identified on the left and right transverse process of the same vertebrae, and spinal curvature was defined as the transverse process angle between two such lines, projected on the coronal plane. RESULTS: Three healthy volunteers were scanned by both ultrasound configurations. Three experienced observers localized transverse processes as skeletal landmarks and obtained transverse process angles in images obtained from both ultrasounds. The mean difference per transverse process angle measured was 3.00 +/-2.1°. 94% of transverse processes visualized in the Sonix Touch were also visible in the Telemed. Inter-observer error in the Telemed was 4.5° and 4.3° in the Sonix Touch. CONCLUSION: Price, convenience and accessibility suggest the Telemed to be a viable alternative in scoliosis monitoring, however further improvements in measurement protocol and image noise reduction must be completed before implementing the Telemed in the clinical setting.
Curvature Radius Measurements From the Ulnar Trochlear Notch in Large Dogs.
Alves-Pimenta, Sofia; Ginja, Mário Manuel; Colaço, Jorge; Fernandes, Armando Manuel; Melo-Pinto, Pedro; Colaço, Bruno
2015-10-01
Assessing the ulnar trochlear notch (UTN) radiographic anatomy has been considered important, but difficult, in the diagnosis of elbow dysplasia. The purpose of this study was to evaluate UTN curvature of natural elbows in radiographs, using a methodology applied to disarticulated joints. The methodology was implemented and validated using dedicated software created by the authors. Mediolateral extended (MLE) and mediolateral flexed (MLF) elbow views were used from 20 joints from canine cadavers that were over 20 kg. After arranging the bones to avoid radiographic overlapping of the bones, an additional mediolateral radioulnar (MLRU) view was made. Curvature radius measurements from the central ridge of the UTN of each elbow were acquired in the MLRU view, using the software. The measurements were repeated in a second session, to determine repeatability. Then similar UTN measurements were taken from the MLE and MLF views, to determine reproducibility. Intraclass correlation coefficient (ICC) for repeatability and reproducibility of measurements were above 0.98 (95% confidence interval limits >0.75). The 95% limits of agreement (LA) for repeatability were -2.98 to 3.19 mm. The 95% LA for reproducibility between MLRU and MLE views were -4.32 to 3.75 mm. The 95% LA for reproducibility between MLRU and MLF views were -5.02 to 4.07 mm. The methodology and software are determined to be both precise and suitable to evaluate the UTN in MLE and MLF elbow views of large breed dogs, for anatomical and clinical purposes. In the future it would be useful to characterize normal and dysplastic UTN of different dog breeds. PMID:26138926
Measurement of the shock front velocity produced in a T-tube
Djurović, S.; Mijatović, Z.; Vujičić, B.; Kobilarov, R.; Savić, I.; Gavanski, L.
2015-01-15
A set of shock front velocity measurements is described in this paper. The shock waves were produced in a small electromagnetically driven shock T-tube. Most of the measurements were performed in hydrogen. The shock front velocity measurements in other gases and the velocity of the gas behind the shock front were also analyzed, as well as the velocity dependence on applied input energy. Some measurements with an applied external magnetic field were also performed. The used method of shock front velocity is simple and was shown to be very reliable. Measured values were compared with the calculated ones for the incident and reflected shock waves.
Measurements of Fluorescent Bioaerosol Particles in the Colorado Front Range
NASA Astrophysics Data System (ADS)
Perring, A. E.; Emerson, J. B.; Fierer, N.; Schwarz, J. P.; Fahey, D. W.
2013-12-01
Bioaerosols are of atmospheric interest due to their potential importance as cloud condensation and heterogeneous ice nuclei and because they represent a sizeable fraction of coarse mode aerosol in some locations. Relatively little data exists, however, regarding diurnal, seasonal and annual cycles of bioaerosols and the meteorological processes that control them. Newly developed real-time instrumentation allows for sensitive, high time resolution detection of fluorescent bioaerosols and is uniquely suited to address key uncertainties in the sources, distributions and behavior of these particles in the atmosphere. Here we present observations of ambient fluorescent biological aerosol made on the Front Range of Colorado using a custom-modified Wideband Integrated Bioaerosol Sensor (WIBS) during the summer and fall of 2013. The summertime measurements were made from the roof of the NOAA ESRL David Skaggs Research Center in Boulder and the fall measurements were made both at the surface and aloft at the Boulder Atmospheric Observatory Tall Tower. We examine diurnal variations in loading and size distribution of fluorescent bioaerosol at the two locations. We also investigate the relationship between meteorological events and fluorescent bioaerosol. For example, we observe higher concentrations and markedly different number distributions associated with precipitation events. Simultaneous filter samples were collected for DNA sequencing and flow cytometry. To our knowledge this represents the first such comparison for the WIBS under ambient conditions and the microbial identification accomplished with the filters adds significantly to the analysis. This data set will provide useful insight into the sources, loadings and properties of fluorescent bioaerosol and the local and regional processes that drive them.
NASA Astrophysics Data System (ADS)
Mutter, Markus; Mauer, Georg; Mücke, Robert; Vaßen, Robert; Back, Hyoung Chul; Gibmeier, Jens
2016-04-01
The residual stresses within plasma-sprayed coatings are an important factor that can influence the lifetime as well as the performance in operation. The investigation of stresses evolving during deposition and post-deposition cooling for atmospheric plasma spraying of yttria-stabilized zirconia coatings using in situ measurement of the samples curvature is a powerful tool for identifying the factors that contribute to stress generation. Under various spray conditions, the first deposition pass leads to a significantly larger increase in samples curvature than the subsequent passes. It is shown in this work that the amount of curvature change at the onset of spraying is significantly influenced by the spray conditions, as well as by the substrate material. More information on the origin of this steep curvature increase at the onset of spraying was obtained by single splat experiments, which yielded information on the splat bonding behavior under various conditions. A comparison of the compressive yield strength for different substrate materials indicated the influence of substrate residual stress relaxation. Residual stress measurements using the incremental hole-drilling method and x-ray diffraction confirmed that the coating deposition affects the substrate residual stress level. The yield strength data were combined with the substrate near-surface temperature during deposition, obtained by finite element simulations, and with the measured residual stress-profile. This revealed that residual stress relaxation is the key factor for the initial curvature increase.
Asaoka, Ryo; Nakakura, Shunsuke; Tabuchi, Hitoshi; Murata, Hiroshi; Nakao, Yoshitaka; Ihara, Noriko; Rimayanti, Ulfah; Aihara, Makoto; Kiuchi, Yoshiaki
2015-01-01
The purpose of the study was to investigate the correlation between Corneal Visualization Scheimpflug Technology (Corvis ST tonometry: CST) parameters and various other ocular parameters, including intraocular pressure (IOP) with Goldmann applanation tonometry. IOP with Goldmann applanation tonometry (IOP-G), central corneal thickness (CCT), axial length (AL), corneal curvature, and CST parameters were measured in 94 eyes of 94 normal subjects. The relationship between ten CST parameters against age, gender, IOP-G, AL, CST-determined CCT and average corneal curvature was investigated using linear modeling. In addition, the relationship between IOP-G versus CST-determined CCT, AL, and other CST parameters was also investigated using linear modeling. Linear modeling showed that the CST measurement ‘A time-1’ is dependent on IOP-G, age, AL, and average corneal curvature; ‘A length-1’ depends on age and average corneal curvature; ‘A velocity-1’ depends on IOP-G and AL; ‘A time-2’ depends on IOP-G, age, and AL; ‘A length-2’ depends on CCT; ‘A velocity-2’ depends on IOP-G, age, AL, CCT, and average corneal curvature; ‘peak distance’ depends on gender; ‘maximum deformation amplitude’ depends on IOP-G, age, and AL. In the optimal model for IOP-G, A time-1, A velocity-1, and highest concavity curvature, but not CCT, were selected as the most important explanatory variables. In conclusion, many CST parameters were not significantly related to CCT, but IOP usually was a significant predictor, suggesting that an adjustment should be made to improve their usefulness for clinical investigations. It was also suggested CST parameters were more influential for IOP-G than CCT and average corneal curvature. PMID:26485129
NASA Astrophysics Data System (ADS)
Ding, Xiang; Sun, Ruoduan; Li, Fei; Zhao, Weiqian; Liu, Wenli
2011-11-01
A new approach based on laser differential confocal technique is potential to achieve high accuracy in radius of curvature (ROC) measurement. It utilizes two digital microscopes with virtual pinholes on the CCD detectors to precisely locate the cat's-eye and the confocal positions, which can enhance the focus-identification resolution. An instrumental system was established and experimental research was carried out to determine how error sources contribute to the uncertainty of ROC measurement, such as optical axis misalignment, dead path of the interferometer, surface figure error of tested lenses and temperature fluctuation, etc. Suggestions were also proposed on how these factors could be avoided or suppressed. The system performance was tested by employing four pairs of template lenses with a serial of ROC values. The relative expanded uncertainty was analyzed and calculated based on theoretical analysis and experimental determination, which was smaller than 2x10-5 (k=2). The results were supported by comparison measurement between the differential confocal radius measurement (DCRM) system and an ultra-high accuracy three-dimensional profilometer, showing good consistency. It demonstrated that the DCRM system was capable of high-accuracy ROC measurement.
Brown, M.A.; Park, T.-S.; Rosakis, A.; Ustundag, E.; Huang, Y.; Tamura, N.; Valek, B.C.
2006-01-01
Background. The Coherent Gradient Sensor (CGS) is a shearing interferometer which has been proposed for the rapid, full-field measurement of deformation states (slopes and curvatures) in thin film-wafer substrate systems, and for the subsequent inference of stresses in the thin films. This approach needs to be verified using a more well-established but time-consuming grain orientation and stress measurement tool, X-ray microdiffraction. Method of Approach. Both CGS and XRD are used to measure the deformation state of the same W film/Si wafer at room temperature. CGS provides a global, wafer-level measurement of slopes while XRD provides a local micromeasurement of lattice rotations. An extreme case of a circular Si wafer with a circular W film island in its center is used because of the presence of discontinuous system curvatures across the wafer. The results are also compared with a theoretical model based on elastic plate analysis of the axisymmetric biomaterial film-substrate system. Results and Conclusions. Slope and curvature measurements by XRD and by CGS compare very well with each other and with theory. The favorable comparison demonstrates that wafer-level CGS metrology provides a quick and accurate alternative to other measurements. It also demonstrates the accuracy of plate theory in modeling thin film-substrate systems, even in the presence of curvature discontinuities.
Xu, Meng; Tian, Ye; Coates, M L; Beaulieu, L Y
2009-09-01
Measuring cantilever sensor deflections using an optical beam deflection system is more complicated than often assumed. The direction of the reflected beam is dependent on the surface normal of the cantilever, which in turn is dependent on the state of the cantilever. It is often assumed that the cantilever is both straight and perfectly level before the onset of sensing experiments although this assumption, especially the former, is rarely true. Failure to characterize the initial state of the cantilever can lead to irreproducibility in cantilever sensor measurements. We have developed three new methods for characterizing the initial state of the cantilever. In the first case we show how to define the initial angle of inclination beta of the chip on which the cantilever is attached. This method was tested using an aluminum block with a known angle of inclination. A new method for determining the initial distance L(o) between the cantilever and the position-sensitive detector (PSD) is also presented. This parameter which behaves as an amplification factor of the PSD signal is critical for obtaining precise cantilever sensor data. Lastly, we present a method for determining the initial curvature of the cantilever which often results from depositing the sensing platform on the lever. Experiments conducted using deflected cantilevers showed the model to be accurate. The characterization methods presented in this work are simple to use, easy to implement, and can be incorporated into most cantilever sensor setups. PMID:19791971
Interval estimates for nonlinear parameters using the linear approximation are sensitive to parameter curvature effects. he adequacy of the linear approximation (Wald) interval is determined using the nonlinearity measures of Bates and Watts (1980), and Clarke (1987b), and the pr...
Measuring the composition-curvature coupling in binary lipid membranes by computer simulations
Barragán Vidal, I. A. Müller, M.; Rosetti, C. M.; Pastorino, C.
2014-11-21
The coupling between local composition fluctuations in binary lipid membranes and curvature affects the lateral membrane structure. We propose an efficient method to compute the composition-curvature coupling in molecular simulations and apply it to two coarse-grained membrane models—a minimal, implicit-solvent model and the MARTINI model. Both the weak-curvature behavior that is typical for thermal fluctuations of planar bilayer membranes as well as the strong-curvature regime corresponding to narrow cylindrical membrane tubes are studied by molecular dynamics simulation. The simulation results are analyzed by using a phenomenological model of the thermodynamics of curved, mixed bilayer membranes that accounts for the change of the monolayer area upon bending. Additionally the role of thermodynamic characteristics such as the incompatibility between the two lipid species and asymmetry of composition are investigated.
Measurement of interfacial curvatures in microemulsions using small-angle neutron scattering
NASA Astrophysics Data System (ADS)
Choi, S. M.; Chen, S. H.; Sottmann, T.; Strey, R.
A new method for SANS data analysis which enables one to directly compute the average Gaussian and square mean curvatures of the interface in a bicontinuous porous structure is proposed. We present the analysis of an extensive SANS data set of one-phase bicontinuous microemulsions (18 different C iE j/D 2O/n-alkane systems) taken at the minimal specific surface point. Depending on the values of i and j, and the type of oil k, the point of minimal specific surface changes. We interpret the corresponding structural changes in terms of the interfacial curvatures and found that the dependence of the curvatures on i, j, and k cold be summarized by a single scaling law, which has a quadratic dependence of the curvatures on the surfactant volume fraction at the minimal specific surface point.
Measuring the Melt Flow on the Laser Cut Front
NASA Astrophysics Data System (ADS)
Pocorni, Jetro; Petring, Dirk; Powell, John; Deichsel, Eckard; Kaplan, Alexander F. H.
The flow characteristics on the laser cut front for 10 mm stainless steel AISI 304 (EN 1.4301) are studied in this paper using High Speed Imaging (HSI). The laser cut samples were produced with a 6 kW fiber laser with nitrogen gas assist. Previous work in this field has used unusual cutting parameters to make the experimentation easier. This work presents, for the first time, HSI results from standard commercially viable cutting parameters. This was made possible by the development of a new experimental technique. The results presented here suggest that the cut front produced when cutting stainless steel with a fiber laser and a nitrogen assist gas is covered in bumps which themselves are covered in a thin layer of liquid. Under the conditions shown here the bumps move down the cut front at an average speed of approximately 0.4m/s. The liquid flows at an average speed of approximately 1.1m/s. The average melt depth at the bottom of the cut zone under these conditions is approximately 0.17 mm.
Rajshekhar, G.; Gorthi, Sai Siva; Rastogi, Pramod
2009-09-15
Measurement of strain, curvature, and twist of a deformed object play an important role in deformation analysis. Strain depends on the first order displacement derivative, whereas curvature and twist are determined by second order displacement derivatives. This paper proposes a pseudo-Wigner-Ville distribution based method for measurement of strain, curvature, and twist in digital holographic interferometry where the object deformation or displacement is encoded as interference phase. In the proposed method, the phase derivative is estimated by peak detection of pseudo-Wigner-Ville distribution evaluated along each row/column of the reconstructed interference field. A complex exponential signal with unit amplitude and the phase derivative estimate as the argument is then generated and the pseudo-Wigner-Ville distribution along each row/column of this signal is evaluated. The curvature is estimated by using peak tracking strategy for the new distribution. For estimation of twist, the pseudo-Wigner-Ville distribution is evaluated along each column/row (i.e., in alternate direction with respect to the previous one) for the generated complex exponential signal and the corresponding peak detection gives the twist estimate.
Asymmetrical in-fiber Mach-Zehnder interferometer for curvature measurement.
Sun, Bing; Huang, Yijian; Liu, Shen; Wang, Chao; He, Jun; Liao, Changrui; Yin, Guolu; Zhao, Jing; Liu, Yinjie; Tang, Jian; Zhou, Jiangtao; Wang, Yiping
2015-06-01
We demonstrated a compact and highly-sensitive curvature sensor based on a Mach-Zehnder interferometer created in a photonic crystal fiber. Such a Mach-Zehnder interferometer consisted of a peanut-like section and an abrupt taper achieved by use of an optimized electrical arc discharge technique, where only one dominating cladding mode was excited and interfered with the fundamental mode. The unique structure exhibited a high curvature sensitivity of 50.5 nm/m^{-1} within a range from 0 to 2.8 m^{-1}, which made it suitable for high-sensitivity curvature sensing in harsh environments. Moreover, it also exhibited a temperature sensitivity of 11.7 pm/°C. PMID:26072819
Measurement of the Earth's Radius Based on Historical Evidence of Its Curvature
ERIC Educational Resources Information Center
Roura, Pere; Josep, Calbo
2005-01-01
Probably the most direct observation of the Earth's curvature is how objects appear from over the horizon when we approach them and disappear as we get further away from them. Similarly, the portion of a high object (a building or a mountain) that is visible depends on the height of the site where the observation is made. Based upon these very…
Yang, Zhongming; Wang, Kailiang; Cheng, Jinlong; Gao, Zhishan; Yuan, Qun
2016-06-10
We have proposed a virtual quadratic Newton rings phase-shifting moiré-fringes measurement method in a nonnull interferometer to measure the large radius of curvature for a spherical surface. In a quadratic polar coordinate system, linear carrier testing Newton rings interferogram and virtual Newton rings interferogram form the moiré fringes. It is possible to retrieve the wavefront difference data between the testing and standard spherical surface from the moiré fringes after low-pass filtering. Based on the wavefront difference data, we deduced a precise formula to calculate the radius of curvature in the quadratic polar coordinate system. We calculated the retrace error in the nonnull interferometer using the multi-configuration model of the nonnull interferometric system in ZEMAX. Our experimental results indicate that the measurement accuracy is better than 0.18% for a spherical mirror with a radius of curvature of 41,400 mm. PMID:27409038
Mirror with thermally controlled radius of curvature
Neil, George R.; Shinn, Michelle D.
2010-06-22
A radius of curvature controlled mirror for controlling precisely the focal point of a laser beam or other light beam. The radius of curvature controlled mirror provides nearly spherical distortion of the mirror in response to differential expansion between the front and rear surfaces of the mirror. The radius of curvature controlled mirror compensates for changes in other optical components due to heating or other physical changes. The radius of curvature controlled mirror includes an arrangement for adjusting the temperature of the front surface and separately adjusting the temperature of the rear surface to control the radius of curvature. The temperature adjustment arrangements can include cooling channels within the mirror body or convection of a gas upon the surface of the mirror. A control system controls the differential expansion between the front and rear surfaces to achieve the desired radius of curvature.
Goosman, D.R.
1988-09-20
An analytical formula is derived for the magnification error in optical size measurements of objects inside conically shaped shock fronts. End detonation of a cylindrically shaped explosive immersed in a fluid necessitates a correction due to refraction at the interface between the shocked and unshocked fluids. It is shown that for detonations immersed in a liquid such as water, the correction factor derived for a conical shock front is significantly larger than the simple correction factor derived if the shock front is assumed to be cylindrical. 2 refs., 5 figs.
HIGH RESOLUTION EMITTANCE MEASUREMENTS AT SNS FRONT END
Aleksandrov, Alexander V; Zhukov, Alexander P
2013-01-01
The Spallation Neutron Source (SNS) linac accelerates an H- beam from 2.5MeV up to 1GeV. Recently the emittance scanner in the MEBT (2.5 MeV) was upgraded. In addition to the slit - harp measurement, we now can use a slit installed on the same actuator as the harp. In combination with a faraday cup located downstream in DTL part of the linac, it represents a classical slit-slit emittance measurement device. While a slit slit scan takes much longer, it is immune to harp related problems such as wire cross talk, and thus looks promising for accurate halo measurements. Time resolution of the new device seems to be sufficient to estimate the amount of beam in the chopper gap (the scanner is downstream of the chopper), and probably to measure its emittance. This paper describes the initial measurements with the new device and some model validation data.
Forman curvature for complex networks
NASA Astrophysics Data System (ADS)
Sreejith, R. P.; Mohanraj, Karthikeyan; Jost, Jürgen; Saucan, Emil; Samal, Areejit
2016-06-01
We adapt Forman’s discretization of Ricci curvature to the case of undirected networks, both weighted and unweighted, and investigate the measure in a variety of model and real-world networks. We find that most nodes and edges in model and real networks have a negative curvature. Furthermore, the distribution of Forman curvature of nodes and edges is narrow in random and small-world networks, while the distribution is broad in scale-free and real-world networks. In most networks, Forman curvature is found to display significant negative correlation with degree and centrality measures. However, Forman curvature is uncorrelated with clustering coefficient in most networks. Importantly, we find that both model and real networks are vulnerable to targeted deletion of nodes with highly negative Forman curvature. Our results suggest that Forman curvature can be employed to gain novel insights on the organization of complex networks.
NASA Astrophysics Data System (ADS)
Rodriguez-Carranza, Claudia E.; Mukherjee, P.; Vigneron, Daniel; Barkovich, James; Studholme, Colin
2007-03-01
In this work we compare 3D Gyrification Index and our recently proposed area-independent curvature-based surface measures [26] for the in-vivo quantification of brain surface folding in clinically acquired neonatal MR image data. A meaningful comparison of gyrification across brains of different sizes and their subregions will only be possible through the quantification of folding with measures that are independent of the area of the region of analysis. This work uses a 3D implementation of the classical Gyrification Index, a 2D measure that quantifies folding based on the ratio of the inner and outer contours of the brain and which has been used to study gyral patterns in adults with schizophrenia, among other conditions. The new surface curvature-based measures and the 3D Gyrification Index were calculated on twelve premature infants (age 28-37 weeks) from which surfaces of cerebrospinal fluid/gray matter (CSF/GM) interface and gray matter/white matter (GM/WM) interface were extracted. Experimental results show that our measures better quantify folding on the CSF/GM interface than Gyrification Index, and perform similarly on the GM/WM interface.
Measurement of the Earth's radius based on historical evidence of its curvature
NASA Astrophysics Data System (ADS)
Roura, Pere; Calbó, Josep
2005-09-01
Probably the most direct observation of the Earth’s curvature is how objects appear from over the horizon when we approach them and disappear as we get further away from them. Similarly, the portion of a high object (a building or a mountain) that is visible depends on the height of the site where the observation is made. Based upon these very obvious facts, a simple method to estimate the Earth's radius R has been applied. The method does not need either sophisticated instrumentation or complex mathematics. In our application of the method presented here, the result is R = 6600 +/- 600 km in the best case. A discussion is presented about the possible use of this method in ancient times. Surprisingly enough, we have not found any reference to the use of this method despite its being simpler than, for example, the classical approach of Eratosthenes.
Observing Coastal Upwelling Front Dynamics by AUV Tracking, Remote Sensing, and Mooring Measurements
NASA Astrophysics Data System (ADS)
Zhang, Y.; Ryan, J. P.; Godin, M. A.; Bellingham, J. G.
2012-12-01
Coastal upwelling is a wind-driven ocean process that brings cooler, saltier, and usually nutrient-rich deep water upward to replace surface water displaced offshore due to Ekman transport. The nutrients carried up by upwelling are important for primary production and fisheries. The boundary between the stratified water column and the upwelling water column is called the "upwelling front". Upwelling fronts support enriched phytoplankton and zooplankton populations, thus having great influences on ocean ecosystems. Variations of wind and ocean circulation cause an upwelling front to move. In particular, as the upwelling favorable wind weakens, upwelling enters the relaxation phase. Frontal dynamics in this phase is not well understood. Satellite sea surface temperature (SST) images can show evolutions of upwelling fronts, but only their surface expressions. To enable in situ high-resolution tracking of upwelling frontal dynamics, we have developed a method for an autonomous underwater vehicle (AUV) to autonomously detect and track an upwelling front over a long duration. During the June 2012 CANON (Controlled, Agile, and Novel Observing Network) field program, the Tethys long-range AUV ran our algorithm to closely track an upwelling front in northern Monterey Bay over four days. The AUV tracking captured the front's westward movement. A series of satellite SST images show that the stratified water in the upwelling shadow (residing in the northeastern corner of the Bay) was transported westward, thus pushing the upwelling front westward. The westward movement of the upwelling filament followed weakening of the northwesterly wind (i.e., upwelling favorable wind). The AUV observations offered a window into frontal dynamics in the relaxation phase of the upwelling process. Temperature, salinity, and current velocity profiles measured at the MBARI M1 mooring (to the south of the AUV tracking line) showed that the westward frontal movement coincided with intrusion of
Front-end Electronics for Unattended Measurement (FEUM). Prototype Test Plan
Conrad, Ryan C.; Morris, Scott J.; Smith, Leon E.; Keller, Daniel T.
2015-09-16
The IAEA has requested that PNNL perform an initial set of tests on front-end electronics for unattended measurement (FEUM) prototypes. The FEUM prototype test plan details the tests to be performed, the criteria for evaluation, and the procedures used to execute the tests.
Li, Yun-Long; Li, Ti-Pei; Li, Shi-Yu; Zhang, Tong-Jie
2014-07-01
We present a model-independent determination of the curvature parameter Ω {sub k} using the Hubble parameter H(z) and the angular diameter distance D{sub A} (z) from recent baryon acoustic oscillation (BAO) measurements. Each H(z) and D{sub A} (z) pair from a BAO measurement can constrain a curvature parameter. The accuracy of the curvature measurement improves with increased redshift of H(z) and D{sub A} (z) data. By using the H(z) and D{sub A} (z) pair derived from a BAO Lyman α forest measurement at z = 2.36, the Ω {sub k} is confined to be –0.05 ± 0.06, which is consistent with the curvature of −0.037{sub −0.042}{sup +0.044} constrained by the nine year Wilkinson Microwave Anisotropy Probe data only. Considering future BAO measurements, at least one order of magnitude improvement of this curvature measurement can be expected.
NASA Astrophysics Data System (ADS)
Candoré, Jean Charles; Bodnar, J. L.; Detalle, Vincent; Remy, B.; Grossel, Philippe
2010-03-01
In this paper we present, in an experimental way, the possibilities of front face photothermal radiometry to measure, in situ, the longitudinal thermal diffusivity of mural paintings. First, we present the principle of the method of measurement. Then, we present the experimental device implemented for the study. Finally, we show, using the experimental study of a plaster sample, the photothermal method allows in a particular case, a good approximation of the parameter longitudinal thermal diffusivity.
Conversion noise measurement for front and back x-ray intensifying screens
NASA Astrophysics Data System (ADS)
Trauernicht, David P.; Van Metter, Richard L.
1990-07-01
Two years ago in these proceedings1 we reported on a new method for measuring the noise associated with the variation in light output of x-ray intensifying screens caused by absorption of x-ray quanta of equal energy, together with data for the Kodak Lanex intensifying screens. We have extended our measurements to screens in the back-screen configuration, in addition to the front-screen configuration previously reported. By back-screen configuration we mean that the x-rays are incident from the same side as that from which the emission will be measured. This has been realized by means of an integrating sphere, which allows screens to be mounted as back or front screens; or even as a pair. The light emission statistics (including the mean light output and the Swank I factor) for some Kodak Lanex intensifying screens in the front and back-screen configurations are given and compared. These data can provide a basis for understanding the depth dependent emission probability which in turn provides a useful test of theories of light propagation within the screen.
Liquid-Crystal Point-Diffraction Interferometer for Wave-Front Measurements
NASA Technical Reports Server (NTRS)
Mercer, Carolyn R.; Creath, Katherine
1996-01-01
A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a phase-stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. A focus shift was measured with the LCPDI, and the results are compared with theoretical results,
Automated measurement of human body shape and curvature using computer vision
NASA Astrophysics Data System (ADS)
Pearson, Jeremy D.; Hobson, Clifford A.; Dangerfield, Peter H.
1993-06-01
A system to measure the surface shape of the human body has been constructed. The system uses a fringe pattern generated by projection of multi-stripe structured light. The optical methodology used is fully described and the algorithms used to process acquired digital images are outlined. The system has been applied to the measurement of the shape of the human back in scoliosis.
NASA Astrophysics Data System (ADS)
Sharma, Haripriya; Golla, Ramsri G.; Zhang, Yu; Kendall, Christopher B.; Hurst, R. Todd; Tajbakhsh, Nima; Liang, Jianming
2014-03-01
Carotid intima-media thickness (CIMT) has proven to be sensitive for predicting individual risk of cardiovascular diseases (CVD). The CIMT is measured based on region of interest (ROIs) in end-diastolic ultrasound frames (EUFs). To interpret CIMT videos, in the current practice, the EUFs and ROIs must be manually selected, a process that is tedious and time consuming. To reduce CIMT interpretation time, this paper presents a novel method for automatically selecting EUFs and determining ROIs in ultrasound videos. The EUFs are selected based on the QRS complex of the electrocardiogram (ECG) signal associated with the ultrasound video, and the ROI is detected based on image intensity and curvature of the carotid artery bulb. Once a EUF is selected and its corresponding ROI is determined, our system measures CIMT using the snake algorithm extended with hard constraints [1,6-7] by computing the average thickness and maximum thickness, calculating the vascular age, and generating a patient's report. In this study, we utilize 23 subjects. Each subject has 4 videos, and 3 EUFs are selected in each video, resulting in a total of 272 ROIs. By comparing with the reference provided by an expert for both frame selection and ROI detection, we achieve 92.96% sensitivity and 97.62% specificity for EUF selection, and 81.25% accuracy in ROI detection.
NASA Astrophysics Data System (ADS)
Congedo, Giuseppe
2015-04-01
The measurement of frequency shifts for light beams exchanged between two test masses nearly in free fall is at the heart of gravitational-wave detection. It is envisaged that the derivative of the frequency shift is in fact limited by differential forces acting on those test masses. We calculate the derivative of the frequency shift with a fully covariant, gauge-independent and coordinate-free method. This method is general and does not require a congruence of nearby beams' null geodesics as done in previous work. We show that the derivative of the parallel transport is the only means by which gravitational effects shows up in the frequency shift. This contribution is given as an integral of the Riemann tensor—the only physical observable of curvature—along the beam's geodesic. The remaining contributions are the difference of velocities, the difference of nongravitational forces, and finally fictitious forces, either locally at the test masses or nonlocally integrated along the beam's geodesic. As an application relevant to gravitational-wave detection, we work out the frequency shift in the local Lorentz frame of nearby geodesics.
Ground based mobile isotopic methane measurements in the Front Range, Colorado
NASA Astrophysics Data System (ADS)
Vaughn, B. H.; Rella, C.; Petron, G.; Sherwood, O.; Mielke-Maday, I.; Schwietzke, S.
2014-12-01
Increased development of unconventional oil and gas resources in North America has given rise to attempts to monitor and quantify fugitive emissions of methane from the industry. Emission estimates of methane from oil and gas basins can vary significantly from one study to another as well as from EPA or State estimates. New efforts are aimed at reconciling bottom-up, or inventory-based, emission estimates of methane with top-down estimates based on atmospheric measurements from aircraft, towers, mobile ground-based vehicles, and atmospheric models. Attributing airborne measurements of regional methane fluxes to specific sources is informed by ground-based measurements of methane. Stable isotopic measurements (δ13C) of methane help distinguish between emissions from the O&G industry, Confined Animal Feed Operations (CAFO), and landfills, but analytical challenges typically limit meaningful isotopic measurements to individual point sampling. We are developing a toolbox to use δ13CH4 measurements to assess the partitioning of methane emissions for regions with multiple methane sources. The method was applied to the Denver-Julesberg Basin. Here we present data from continuous isotopic measurements obtained over a wide geographic area by using MegaCore, a 1500 ft. tube that is constantly filled with sample air while driving, then subsequently analyzed at slower rates using cavity ring down spectroscopy (CRDS). Pressure, flow and calibration are tightly controlled allowing precise attribution of methane enhancements to their point of collection. Comparisons with point measurements are needed to confirm regional values and further constrain flux estimates and models. This effort was made in conjunction with several major field campaigns in the Colorado Front Range in July-August 2014, including FRAPPÉ (Front Range Air Pollution and Photochemistry Experiment), DISCOVER-AQ, and the Air Water Gas NSF Sustainability Research Network at the University of Colorado.
MacIntyre, Norma J.; Bennett, Lisa; Bonnyman, Alison M.; Stratford, Paul W.
2011-01-01
The study illustrates the application of generalizability theory (G-theory) to identify measurement protocols that optimize reliability of two clinical methods for assessing spine curvatures in women with osteoporosis. Triplicate measures of spine curvatures were acquired for 9 postmenopausal women with spine osteoporosis by two raters during a single visit using a digital inclinometer and a flexicurve ruler. G-coefficients were estimated using a G-study, and a measurement protocol that optimized inter-rater and inter-trial reliability was identified using follow-up decision studies. The G-theory provides reliability estimates for measurement devices which can be generalized to different clinical contexts and/or measurement designs. PMID:22482067
Measurement of the wave-front aberration of the eye by a fast psychophysical procedure
He, J.C.; Marcos, S.; Webb, R.H.; Burns, S.A.
1998-09-01
We used a fast psychophysical procedure to determine the wave-front aberrations of the human eye {ital in vivo}. We measured the angular deviation of light rays entering the eye at different pupillary locations by aligning an image of a point source entering the pupil at different locations to the image of a fixation cross entering the pupil at a fixed location. We fitted the data to a Zernike series to reconstruct the wave-front aberrations of the pupil. With this technique the repeatability of the measurement of the individual coefficients was 0.019 {mu}m. The standard deviation of the overall wave-height estimation across the pupil is less than 0.3 {mu}m. Since this technique does not require the administration of pharmacological agents to dilate the pupil, we were able to measure the changes in the aberrations of the eye during accommodation. We found that administration of even a mild dilating agent causes a change in the aberration structure of the eye. {copyright} 1998 Optical Society of America
Canted undulator front-end exit-mask flow-induced vibration measurements.
Collins, J.; Doose, C. L.; Attig, J. N.; Baehl, M. M.
2004-11-10
All of the high-heat-load critical components in the new canted-undulator front-end (CU FE) design use wire-coil inserts inside of the cooling channels to significantly enhance heat transfer. Wire-coil inserts have replaced the copper-mesh inserts used in previous front-end high-heat-load critical-component designs. The exit mask, the most downstream component in the CU FE line relative to the x-ray beam path, has an exit aperture of 2 mm vertical x 3 mm horizontal and is the most sensitive component, in terms of final beam stability, of all of the CU FE components. In general, final beam stability is determined by the storage-ring output-beam stability and not by the CU FE components. Although front-end components are not very sensitive to vibration, several measurements have been performed to assess the flow-induced vibration associated with the CU FE exit mask. Results yield only 0.16 {micro}mrms vertical displacement and 1.0 {micro}mrms horizontal displacement under worst-case conditions. The maximum displacement values are very small compared to the aperture size, and therefore flow-induced vibration has a negligible effect on the CU FE output beam stability. More general measurements have also been performed to directly compare flow-induced vibration in an open, unrestricted tube relative to the same tube containing either a wire-coil insert or a copper-mesh insert. Operational performance data are presented for these heat-transfer-enhancing inserts, and the advantages and disadvantages, in terms of selection criteria, are discussed.
Classification and quantification of leaf curvature
Liu, Zhongyuan; Jia, Liguo; Mao, Yanfei; He, Yuke
2010-01-01
Various mutants of Arabidopsis thaliana deficient in polarity, cell division, and auxin response are characterized by certain types of leaf curvature. However, comparison of curvature for clarification of gene function can be difficult without a quantitative measurement of curvature. Here, a novel method for classification and quantification of leaf curvature is reported. Twenty-two mutant alleles from Arabidopsis mutants and transgenic lines deficient in leaf flatness were selected. The mutants were classified according to the direction, axis, position, and extent of leaf curvature. Based on a global measure of whole leaves and a local measure of four regions in the leaves, the curvature index (CI) was proposed to quantify the leaf curvature. The CI values accounted for the direction, axis, position, and extent of leaf curvature in all of the Arabidopsis mutants grown in growth chambers. Comparison of CI values between mutants reveals the spatial and temporal variations of leaf curvature, indicating the strength of the mutant alleles and the activities of the corresponding genes. Using the curvature indices, the extent of curvature in a complicated genetic background becomes quantitative and comparable, thus providing a useful tool for defining the genetic components of leaf development and to breed new varieties with leaf curvature desirable for the efficient capture of sunlight for photosynthesis and high yields. PMID:20400533
ANALOG FRONT-END ELECTRONICS FOR BEAM POSITION MEASUREMENT ON THE BEAM HALO MEASUREMENT
R.B. SHURTER; T.J. COTE; J.D. GILPATRICK
2001-06-01
Enhancements have been made to the log-ratio analog front-end electronics based on the Analog Devices 8307 logarithmic amplifier as used on the LEDA accelerator. The dynamic range of greater than 85 dB, has been extended to nearly the full capability of the AD8307 from the previous design of approximately 65 dB through the addition of a 350 MHz band-pass filter, careful use of ground and power plane placement, signal routing, and power supply bypassing. Additionally, selection of high-isolation RF switches (55dB) has been an integral part of a new calibration technique, which is fully described in another paper submitted to this conference. Provision has also been made for insertion of a first-stage low-noise amplifier for using the circuit under low-signal conditions.
Sigma models with negative curvature
NASA Astrophysics Data System (ADS)
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-05-01
We construct Higgs Effective Field Theory (HEFT) based on the scalar manifold Hn, which is a hyperbolic space of constant negative curvature. The Lagrangian has a non-compact O (n , 1) global symmetry group, but it gives a unitary theory as long as only a compact subgroup of the global symmetry is gauged. Whether the HEFT manifold has positive or negative curvature can be tested by measuring the S-parameter, and the cross sections for longitudinal gauge boson and Higgs boson scattering, since the curvature (including its sign) determines deviations from Standard Model values.
Front-end Electronics for Unattended Measurement (FEUM). Results of Prototype Evaluation
Conrad, Ryan C.; Keller, Daniel T.; Morris, Scott J.; Smith, Leon E.
2015-07-01
The International Atomic Energy Agency (IAEA) deploys unattended monitoring systems to provide continuous monitoring of nuclear material within safeguarded facilities around the world. As the number of unattended monitoring instruments increases, the IAEA is challenged to become more efficient in the implementation of those systems. In 2010, the IAEA initiated the Front-End Electronics for Unattended Measurement (FEUM) project with the goals of greater flexibility in the interfaces to various sensors and data acquisition systems, and improved capabilities for remotely located sensors (e.g., where sensor and front-end electronics might be separated by tens of meters). In consultation with the IAEA, a technical evaluation of a candidate FEUM device produced by a commercial vendor has been performed. This evaluation assessed the device against the IAEA’s original technical specifications and a broad range of important parameters that include sensor types, cable lengths and types, industrial electromagnetic noise that can degrade signals from remotely located detectors, and high radiation fields. Testing data, interpretation, findings and recommendations are provided.
NASA Astrophysics Data System (ADS)
Gunn, J. P.; Fuchs, V.; Petržílka, V.; Ekedahl, A.; Fedorczak, N.; Goniche, M.; Hillairet, J.
2016-03-01
Measurements in the tokamak scrape-off layer show the existence of fast electrons as far as a few centimeters radially in front of a lower hybrid antenna grill, which is one order of magnitude further than earlier predictions of interaction zones not exceeding 5 mm in width (Rantamäki et al 2000 Nucl. Fusion 40 1477). The present contribution aims at understanding these experimental results on the basis of electron Landau damping in a turbulent scrape-off layer. A crucial guiding element from the experiments is the observation of temporal intermittency of the fast electron signal at positions radially away from the grill mouth at a rate comparable with the detachment rate of relatively hot and dense field-aligned plasma filaments, or ‘blobs,’ from the last closed flux surface. When the dynamic character of the scrape-off layer is taken into account, transient low density and low temperature states occur during which the Landau damping can be weak enough to allow the radiated spectrum to penetrate radially deep inward. When the lower hybrid wave intercepts a dense and hot ‘blob’ a few cm in front of the antenna, then strong damping of the high wave number components can occur. This is the scenario we propose for explaining the generation of fast electrons far away from the grill mouth.
Poyneer, Lisa A; Bauman, Brian J
2015-03-31
Reference-free compensated imaging makes an estimation of the Fourier phase of a series of images of a target. The Fourier magnitude of the series of images is obtained by dividing the power spectral density of the series of images by an estimate of the power spectral density of atmospheric turbulence from a series of scene based wave front sensor (SBWFS) measurements of the target. A high-resolution image of the target is recovered from the Fourier phase and the Fourier magnitude.
Nitrogen oxides measurements in an Amazon site and enhancements associated with a cold front
NASA Astrophysics Data System (ADS)
Cordova, A. M.; Longo, K.; Freitas, S.; Gatti, L. V.; Artaxo, P.; Procópio, A.; Silva Dias, M. A. F.; Freitas, E. D.
2004-05-01
An intensive atmospheric chemistry study was carried out in a pristine Amazonian forest site (Balbina), Amazonas state, Brazil during the 2001 wet season, as part of the LBA/CLAIRE 2001 (The Large Scale Biosphere Atmosphere Experiment in Amazonia/Cooperative LBA Airborne Regional Experiment) field campaign. Measurements of nitrogen oxide (NO), nitrogen dioxide (NO2) and ozone (O3) were performed simultaneously with aerosol particles and black carbon concentrations and meteorological parameters observations. Very low trace gases and aerosol concentrations are typically observed at this pristine tropical site. During the measurement period, there was a three-day episode of enhancement of NO2 and black carbon concentration. NO2 concentration reached a maximum value of 4 ppbv, which corresponds to three times the background concentration observed for this site. Black carbon concentration increased from the approximated 100 ng/m3 average value to a 200 ng/m3 maximum during the same period. Biomass burning spots were detected southward, between latitudes 15 to 10° S, 5-6 days before this episode from GOES-8 WF_ABBA (Wildfire Automated Biomass Burning Algorithm). An atmospheric numerical simulation of the whole measurement period was carried out using the RAMS model coupled to a biomass burning emission and transport model. The simulation results pictured a smoke transport event from Central Brazil associated to an approach of a mid-latitude cold front, reinforcing the hypothesis of biomass burning products being long-range transported from the South by the cold front and crossing the Equator. This transport event shows how the pristine atmosphere pattern in Amazonia is impacted by biomass burning emissions from sites very far away.
Ferreira, João C. P.; Fujihara, Caroline J.; Fruhvald, Erika; Trevisol, Eduardo; Destro, Flavia C.; Teixeira, Carlos R.; Pantoja, José C. F.; Schmidt, Elizabeth M. S.; Palme, Rupert
2015-01-01
Parrots kept in zoos and private households often develop psychological and behavioural disorders. Despite knowing that such disorders have a multifactorial aetiology and that chronic stress is involved, little is known about their development mainly due to a poor understanding of the parrots’ physiology and the lack of validated methods to measure stress in these species. In birds, blood corticosterone concentrations provide information about adrenocortical activity. However, blood sampling techniques are difficult, highly invasive and inappropriate to investigate stressful situations and welfare conditions. Thus, a non-invasive method to measure steroid hormones is critically needed. Aiming to perform a physiological validation of a cortisone enzyme immunoassay (EIA) to measure glucocorticoid metabolites (GCM) in droppings of 24 Blue-fronted parrots (Amazona aestiva), two experiments were designed. During the experiments all droppings were collected at 3-h intervals. Initially, birds were sampled for 24 h (experiment 1) and one week later assigned to four different treatments (experiment 2): Control (undisturbed), Saline (0.2 mL of 0.9% NaCl IM), Dexamethasone (1 mg/kg IM) and Adrenocorticotropic hormone (ACTH; 25 IU IM). Treatments (always one week apart) were applied to all animals in a cross-over study design. A daily rhythm pattern in GCM excretion was detected but there were no sex differences (first experiment). Saline and dexamethasone treatments had no effect on GCM (not different from control concentrations). Following ACTH injection, GCM concentration increased about 13.1-fold (median) at the peak (after 3–9 h), and then dropped to pre-treatment concentrations. By a successful physiological validation, we demonstrated the suitability of the cortisone EIA to non-invasively monitor increased adrenocortical activity, and thus, stress in the Blue-fronted parrot. This method opens up new perspectives for investigating the connection between behavioural
Ferreira, João C P; Fujihara, Caroline J; Fruhvald, Erika; Trevisol, Eduardo; Destro, Flavia C; Teixeira, Carlos R; Pantoja, José C F; Schmidt, Elizabeth M S; Palme, Rupert
2015-01-01
Parrots kept in zoos and private households often develop psychological and behavioural disorders. Despite knowing that such disorders have a multifactorial aetiology and that chronic stress is involved, little is known about their development mainly due to a poor understanding of the parrots' physiology and the lack of validated methods to measure stress in these species. In birds, blood corticosterone concentrations provide information about adrenocortical activity. However, blood sampling techniques are difficult, highly invasive and inappropriate to investigate stressful situations and welfare conditions. Thus, a non-invasive method to measure steroid hormones is critically needed. Aiming to perform a physiological validation of a cortisone enzyme immunoassay (EIA) to measure glucocorticoid metabolites (GCM) in droppings of 24 Blue-fronted parrots (Amazona aestiva), two experiments were designed. During the experiments all droppings were collected at 3-h intervals. Initially, birds were sampled for 24 h (experiment 1) and one week later assigned to four different treatments (experiment 2): Control (undisturbed), Saline (0.2 mL of 0.9% NaCl IM), Dexamethasone (1 mg/kg IM) and Adrenocorticotropic hormone (ACTH; 25 IU IM). Treatments (always one week apart) were applied to all animals in a cross-over study design. A daily rhythm pattern in GCM excretion was detected but there were no sex differences (first experiment). Saline and dexamethasone treatments had no effect on GCM (not different from control concentrations). Following ACTH injection, GCM concentration increased about 13.1-fold (median) at the peak (after 3-9 h), and then dropped to pre-treatment concentrations. By a successful physiological validation, we demonstrated the suitability of the cortisone EIA to non-invasively monitor increased adrenocortical activity, and thus, stress in the Blue-fronted parrot. This method opens up new perspectives for investigating the connection between behavioural
Zemp, Roland; List, Renate; Gülay, Turgut; Elsig, Jean Pierre; Naxera, Jaroslav; Taylor, William R.; Lorenzetti, Silvio
2014-01-01
Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R2, of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes. PMID:24748013
Zemp, Roland; List, Renate; Gülay, Turgut; Elsig, Jean Pierre; Naxera, Jaroslav; Taylor, William R; Lorenzetti, Silvio
2014-01-01
Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R2, of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes. PMID:24748013
Novel front-surface thermal-diffusivity measurement method based on phase analysis
NASA Astrophysics Data System (ADS)
Braggiotti, Alberto; Marinetti, Sergio
2000-05-01
The technique described in this paper is for one-side thermal diffusivity measurement. A single stripe-shaped pulse provided by a flash lamp is used to heat the front surface of a specimen slab. Classical methods for estimating a parameter out of a distribution involve fitting the temperature distribution with its theoretical model. With the technique described in this paper the evolution of the temperature distribution along a line perpendicular to the heated stripe is analyzed in the frequency domain. An estimate of the thermal diffusivity is then obtained from comparison of the phase component behavior with an abacus similarly built from the theoretical model. This technique is valid for any shape of flash lamp pulse (i.e. laser spot), and can be used also for estimating the thermal diffusivity of anisotropic materials. The choice of the stripe shape is due to the limitations of the simulation environment used.
Measures of the environmental footprint of the front end of the nuclear fuel cycle
E. Schneider; B. Carlsen; E. Tavrides; C. van der Hoeven; U. Phathanapirom
2013-11-01
Previous estimates of environmental impacts associated with the front end of the nuclear fuel cycle (FEFC) have focused primarily on energy consumption and CO2 emissions. Results have varied widely. This work builds upon reports from operating facilities and other primary data sources to build a database of front end environmental impacts. This work also addresses land transformation and water withdrawals associated with the processes of the FEFC. These processes include uranium extraction, conversion, enrichment, fuel fabrication, depleted uranium disposition, and transportation. To allow summing the impacts across processes, all impacts were normalized per tonne of natural uranium mined as well as per MWh(e) of electricity produced, a more conventional unit for measuring environmental impacts that facilitates comparison with other studies. This conversion was based on mass balances and process efficiencies associated with the current once-through LWR fuel cycle. Total energy input is calculated at 8.7 x 10- 3 GJ(e)/MWh(e) of electricity and 5.9 x 10- 3 GJ(t)/MWh(e) of thermal energy. It is dominated by the energy required for uranium extraction, conversion to fluoride compound for subsequent enrichment, and enrichment. An estimate of the carbon footprint is made from the direct energy consumption at 1.7 kg CO2/MWh(e). Water use is likewise dominated by requirements of uranium extraction, totaling 154 L/MWh(e). Land use is calculated at 8 x 10- 3 m2/MWh(e), over 90% of which is due to uranium extraction. Quantified impacts are limited to those resulting from activities performed within the FEFC process facilities (i.e. within the plant gates). Energy embodied in material inputs such as process chemicals and fuel cladding is identified but not explicitly quantified in this study. Inclusion of indirect energy associated with embodied energy as well as construction and decommissioning of facilities could increase the FEFC energy intensity estimate by a factor of up
Spatial curvature falsifies eternal inflation
NASA Astrophysics Data System (ADS)
Kleban, Matthew; Schillo, Marjorie
2012-06-01
Inflation creates large-scale cosmological density perturbations that are characterized by an isotropic, homogeneous, and Gaussian random distribution about a locally flat background. Even in a flat universe, the spatial curvature measured within one Hubble volume receives contributions from long wavelength perturbations, and will not in general be zero. These same perturbations determine the Cosmic Microwave Background (CMB) temperature fluctuations, which are Script O(10-5). Consequently, the low-l multipole moments in the CMB temperature map predict the value of the measured spatial curvature Ωk. On this basis we argue that a measurement of |Ωk| > 10-4 would rule out slow-roll eternal inflation in our past with high confidence, while a measurement of Ωk < -10-4 (which is positive curvature, a locally closed universe) rules out false-vacuum eternal inflation as well, at the same confidence level. In other words, negative curvature (a locally open universe) is consistent with false-vacuum eternal inflation but not with slow-roll eternal inflation, and positive curvature falsifies both. Near-future experiments will dramatically extend the sensitivity of Ωk measurements and constitute a sharp test of these predictions.
Excitation ahead of shock fronts in krypton measured by single line laser absorption
NASA Astrophysics Data System (ADS)
Boetticher, W.; Kilpin, D.
1984-12-01
The absorption of single-mode radiation (from a dye laser tuned to 587.25 and 557.18 nm) by Kr in front of shock waves with Mach numbers 12-21 in a 50-mm-diameter 4.4-m-long free-position driver shock tube at preshock pressures 0.7-2.7 kPa is measured to determine the number densities of the metastable 5s(1 1/2)2 and 5s(1 1/2)1 precursor states (1s5 and 1s4 in Paschen notation, respectively). The measurement technique and calculations follow those of Ernst (1982). The results are presented in tables and graphs and characterized in comparison with previous findings. The time constant of the exponential rise of the precursor is found to be about 8 microsec, and the concentration of 1s5 + 1s4 for Mach 20 is calculated as about 10 ppm, in agreement (to within a factor of 5) with model predictions for Ar and Xe.
NASA Astrophysics Data System (ADS)
Jing, Zhiyou; Qi, Yiquan; Fox-Kemper, Baylor; Du, Yan; Lian, Shumin
2016-03-01
Seasonal thermal fronts associated with wind-driven coastal downwelling/upwelling in the northern South China Sea are investigated using satellite measurements and three repeated fine-resolution mapping surveys in winter, spring, and summer. The results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons, which tend to be approximately aligned with the 20-100 m isobaths. Driven by the prevailing winter/summer monsoon, the band-shaped fronts were observed with a magnitude exceeding 0.1°C/km in the subsurface, and accompanied by energetic coastal downwelling/upwelling due to shoreward/offshore Ekman transport. The downward/upward tilting of seasonal thermoclines across the shelf exceeds 20 m, significantly contributing to the development of thermal fronts over the shelf. In addition, the diagnostic analysis of Potential Vorticity (PV) suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling-favorable monsoon forcing. This is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing. At the same time, the coastal currents are substantially regulated by the seasonal winds. An expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region. These results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf.
Spatial curvature endgame: Reaching the limit of curvature determination
NASA Astrophysics Data System (ADS)
Leonard, C. Danielle; Bull, Philip; Allison, Rupert
2016-07-01
Current constraints on spatial curvature show that it is dynamically negligible: |ΩK|≲5 ×10-3 (95% C.L.). Neglecting it as a cosmological parameter would be premature however, as more stringent constraints on ΩK at around the 10-4 level would offer valuable tests of eternal inflation models and probe novel large-scale structure phenomena. This precision also represents the "curvature floor," beyond which constraints cannot be meaningfully improved due to the cosmic variance of horizon-scale perturbations. In this paper, we discuss what future experiments will need to do in order to measure spatial curvature to this maximum accuracy. Our conservative forecasts show that the curvature floor is unreachable—by an order of magnitude—even with Stage IV experiments, unless strong assumptions are made about dark energy evolution and the Λ CDM parameter values. We also discuss some of the novel problems that arise when attempting to constrain a global cosmological parameter like ΩK with such high precision. Measuring curvature down to this level would be an important validation of systematics characterization in high-precision cosmological analyses.
Measuring Kinematic Variables in Front Crawl Swimming Using Accelerometers: A Validation Study
Callaway, Andrew J.
2015-01-01
Objective data on swimming performance is needed to meet the demands of the swimming coach and athlete. The purpose of this study is to use a multiple inertial measurement units to calculate Lap Time, Velocity, Stroke Count, Stroke Duration, Stroke Rate and Phases of the Stroke (Entry, Pull, Push, Recovery) in front crawl swimming. Using multiple units on the body, an algorithm was developed to calculate the phases of the stroke based on the relative position of the body roll. Twelve swimmers, equipped with these devices on the body, performed fatiguing trials. The calculated factors were compared to the same data derived to video data showing strong positive results for all factors. Four swimmers required individual adaptation to the stroke phase calculation method. The developed algorithm was developed using a search window relative to the body roll (peak/trough). This customization requirement demonstrates that single based devices will not be able to determine these phases of the stroke with sufficient accuracy. PMID:26007718
Wide Dynamic Range Front-end Electronics for Beam Current and Position Measurement
Rawnsley, W. R.; Potter, R. J.; Verzilov, V. A.; Root, L.
2006-11-20
An Analog Devices log detector, AD8306, and a Digital Signal Processor (DSP), ADSP-21992, have been found useful for building wide dynamic range, accurate and inexpensive front-end electronics to measure and process the RF signals from TRIUMF's beam monitors. The high-precision log detector has a useful dynamic range of over 100 dB. The 160 MHz mixed-signal DSP is used to digitize the log detector output, linearize it via a lookup table, perform temperature compensation, and remove the variable duty cycle 1 kHz pulse structure of the beam. This approach has been applied to two types of devices in a 500 MeV proton beamline. The 0.1% DC to CW total current monitor is based on a capacitive pickup resonant at 46.11 MHz, the second harmonic of the bunch frequency. The DSP software provides low pass filtering, calculates the antilog of the data and passes the output to a CAMAC input register. The BPM electronics process data from inductive pickup loops. The DSP controls a GaAs switch which multiplexes signals from four adjacent pickups to a single log detector. The DSP performs difference-over-sum or log-ratio data analysis along with averaging over an arbitrary number of samples.
NASA Astrophysics Data System (ADS)
Rossi, L.; Molinier, T.; Pieri, A.; Akhloufi, M.; Tison, Y.; Bosseur, F.
2011-12-01
This paper presents stereovision techniques for measurement of the geometrical properties (position, rate of spread, fire height, fire inclination angle, fire base width, view factor) of fires obtained by experimental burnings at field scale. The system consists of two synchronized and pre-calibrated multi-baseline stereo cameras operating in the visible spectrum. The cameras are positioned in the back and the lateral positions relatively to the direction of fire propagation. Algorithms have been developed in order to (i) register these cameras, (ii) model in three dimensions the fire front from the back stereoscopic images and (iii) estimate some geometrical properties of fire such as the inclination angle and the fire base width from the lateral stereoscopic images. A user graphical interface was developed as a practical tool to estimate fire propagation features and to display the obtained results. Fire spread experiments were conducted at field scale (about 20 m wide and 3 m high). The fuel consists of Mediterranean shrub vegetation. The obtained results are promising and show interesting performance achieved by the proposed system in operational and complex fire scenarios.
NASA Astrophysics Data System (ADS)
Pech-May, Nelson Wilbur; Mendioroz, Arantza; Salazar, Agustín
2014-10-01
In this work, we have extended the front-face flash method to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of semitransparent plates. A complete theoretical model that allows calculating the front surface temperature rise of the sample has been developed. It takes into consideration additional effects, such as multiple reflections of the heating light beam inside the sample, heat losses by convection and radiation, transparency of the sample to infrared wavelengths, and heating pulse duration. Measurements performed on calibrated solids, covering a wide range of absorption coefficients (from transparent to opaque) and thermal diffusivities, validate the proposed method.
Pech-May, Nelson Wilbur; Mendioroz, Arantza; Salazar, Agustín
2014-10-15
In this work, we have extended the front-face flash method to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of semitransparent plates. A complete theoretical model that allows calculating the front surface temperature rise of the sample has been developed. It takes into consideration additional effects, such as multiple reflections of the heating light beam inside the sample, heat losses by convection and radiation, transparency of the sample to infrared wavelengths, and heating pulse duration. Measurements performed on calibrated solids, covering a wide range of absorption coefficients (from transparent to opaque) and thermal diffusivities, validate the proposed method.
NASA Technical Reports Server (NTRS)
Demoz, Belay; Miller, David; Schwemmer, Geary; Starr, David OC (Technical Monitor)
2001-01-01
Lidar atmospheric systems have required large telescope for receiving atmospheric backscatter signals. Thus, the relative complexity in size and ease of operation has limited their wider use in the atmospheric science and meteorology community. The Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE) uses a scanning holographic receiver and demonstrates that these issues can be overcome. HARLIE participated at the DOE-ARM Southern Great Plains site (CART) during the Water Vapor Intensive Operation Period (WVIOP2000) held September-October 2000. It provided exceptional high temporal and spatial resolution measurements of aerosol and cloud backscatter in three dimensions. HARLIE recorded over 110 hours of data were recorded on 16 days between 17 September and 6 October 2000. Placed in a ground-based trailer for upward looking scanning measurements of clouds and aerosols, HARLIE provided a unique record of time-resolved atmospheric backscatter at 1-micron wavelength. The conical scanning lidar measures atmospheric backscatter on the surface of an inverted 90 degree (full angle) cone up to an altitude of 20 km, 360-degree scans having spatial resolutions of 20 meters in the vertical and 1 degree in azimuth were obtained every 36 seconds during the daily, operating period. In this study we present highlights of HARLIE-based measurements of the boundary layer and cloud parameters as well as atmospheric wind vectors where there is sufficiently resolved structure in the backscatter. In particular we present data and discussions from a bore-front case observed on 23 September 2000.
Refractive index change and curvature in shock waves by angled beam refraction
NASA Astrophysics Data System (ADS)
Kiefer, J. H.; Manson, A. C.
1981-09-01
Observations of front geometry and refractive index jump across shock waves in rare gases have been made with a new particularly simple technique. The technique involves determination of the angular deflection of a narrow laser beam intersecting the shock front at a shallow angle. Measured refractive index jumps in rare gases are in excellent agreement with those calculated using Snell's law and ideal shock theory. The apparent shock curvature is in close accord with deBoer's theory for loading pressures below 20 Torr, but above this pressure there is evidence of an indentation near tube center.
NASA Astrophysics Data System (ADS)
Zisman, Alexander
2016-04-01
Starting from Nye's tensor, alternative characteristics of crystal curvature indicative of dislocation content are considered subject to very low thickness of investigated matter under the free surface and discreteness of orientation sampling. Analysis within the framework of continuum mechanics, undertaken to allow for such conditions peculiar to the electron backscatter diffraction (EBSD) technique, has shown the variable part of orientations expressed in a vector form to be most sensitive to lattice defects when projected to the free surface plane. Hence, as verified with EBSD data on a grain junction in a low deformed IF steel, magnitude of the projected field allows one to map plastic strains inhomogeneous within grains whereas divergence of this field distinctly images and quantifies low-angle dislocation boundaries formed at low strains.
ERIC Educational Resources Information Center
Ngo, Duc Minh
2009-01-01
Current methodologies used for the inference of thin film stresses through curvatures are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. In this dissertation, we extend these methodologies to non-uniform stress and curvature states for the single layer of thin film or…
NASA Astrophysics Data System (ADS)
Verlinden, Pierre; Van de Wiele, Fernand
1985-03-01
A method is proposed for measuring the diffusion length and surface recombination velocity of Interdigitated Back Contact (IBC) solar cells by means of a simple linear regression on experimental quantum efficiency values versus the inverse of the absorption coefficient. This method is extended to the case of Front Surface Field (FSF) solar cells. Under certain conditions, the real or the effective surface recombination velocity may be measured.
A three-dimensional validation of crack curvature in muscovite mica
J. C. Hill; J. W. Foulk III; P. A. Klein; E. P. Chen
2001-01-07
Experimental and computational efforts focused on characterizing crack tip curvature in muscovite mica. Wedge-driven cracks were propagated under monochromatic light. Micrographs verified the subtle curvature of the crack front near the free surface. A cohesive approach was employed to model mixed-mode fracture in a three-dimensional framework. Finite element calculations captured the crack curvature observed in experiment.
Measures of the Environmental Footprint of the Front End of the Nuclear Fuel Cycle
Brett Carlsen; Emily Tavrides; Erich Schneider
2010-08-01
Previous estimates of environmental impacts associated with the front end of the nuclear fuel cycle have focused primarily on energy consumption and CO2 emissions. Results have varied widely. Section 2 of this report provides a summary of historical estimates. This study revises existing empirical correlations and their underlying assumptions to fit to a more complete set of existing data. This study also addresses land transformation, water withdrawals, and occupational and public health impacts associated with the processes of the front end of the once-through nuclear fuel cycle. These processes include uranium mining, milling, refining, conversion, enrichment, and fuel fabrication. Metrics are developed to allow environmental impacts to be summed across the full set of front end processes, including transportation and disposition of the resulting depleted uranium.
Spatial curvature, spacetime curvature, and gravity
NASA Astrophysics Data System (ADS)
Price, Richard H.
2016-08-01
The belief that curved spacetime gravity cannot be simply and correctly presented results in such misleading presentations as elastic two-dimensional sheets deformed as they support heavy objects. This article attempts to show that the conceptual basis of curved spacetime gravity can be simply and correctly presented, and that the spatial curvature of a deformed elastic sheet is very different from the spacetime curvature underlying gravity. This article introduces the idea of a "splittable" spacetime that has spatial curvature, but is missing most of the manifestations of gravity. A section in which no mathematics is used is directed at students who have studied no more than introductory physics. A separate section, for students who have taken only an introductory course in general relativity, gives mathematical arguments centering on splittable spacetimes.
NASA Astrophysics Data System (ADS)
Garber, J. L.; Wohl, E. E.; Riebe, C. S.
2012-12-01
Multiple authors have delineated the CO Front Range landscape into distinct elevational zones with respect to contemporary geomorphologic processes, landscape development, and sediment dynamics in bedrock canyons. Several studies have estimated denudation rates using rates of post-fire erosion, alpine soil erosion, beaver dam sedimentation, and cosmogenic tor erosion, but comparison is limited due to differences in the time scale captured by different measurements. We address this gap by using cosmogenic 10Be to measure denudation rates in three process domains: flat Front Range summits, five unglaciated watersheds above the terminal moraine, and five watersheds below the moraine. These data are coupled with soil and rock geochemistry data from the flats, and a basin of homogenous bedrock type, to constrain long-term chemical erosion rates and eolian dust influx into the headwaters of the Front Range. Two paired bedrock outcrop and soil samples were taken on flat summits in Rocky Mountain National Park. Bedrock samples were taken from a low-lying bedrock outcrop and large boulder with accompanying colluvial soil samples from the surrounding surface. Fluvial sediment was collected for 10Be analysis from the outlets of 10 watersheds. We also conducted soil surveys in each basin to examine relationships between physical characteristics and depths of soil, and hillslope position. To constrain long-term chemical weathering rates and estimate eolian inputs, we analyzed 30 soil and 5 bedrock samples using X Ray Fluorescence (XRF) in each basin. We estimated eolian input by assuming the silt fraction of peak soils were derived from dust, as well as using dust chemistry reported in the literature. Basin-averaged denudation rates will be compared to basin morphometric parameters. These data will provide insight into long term landscape evolution of the Front Range, as well as sequestration of atmospheric carbon via chemical weathering, and eolian deposition.
Determining wave direction using curvature parameters.
de Queiroz, Eduardo Vitarelli; de Carvalho, João Luiz Baptista
2016-01-01
The curvature of the sea wave was tested as a parameter for estimating wave direction in the search for better results in estimates of wave direction in shallow waters, where waves of different sizes, frequencies and directions intersect and it is difficult to characterize. We used numerical simulations of the sea surface to determine wave direction calculated from the curvature of the waves. Using 1000 numerical simulations, the statistical variability of the wave direction was determined. The results showed good performance by the curvature parameter for estimating wave direction. Accuracy in the estimates was improved by including wave slope parameters in addition to curvature. The results indicate that the curvature is a promising technique to estimate wave directions.•In this study, the accuracy and precision of curvature parameters to measure wave direction are analyzed using a model simulation that generates 1000 wave records with directional resolution.•The model allows the simultaneous simulation of time-series wave properties such as sea surface elevation, slope and curvature and they were used to analyze the variability of estimated directions.•The simultaneous acquisition of slope and curvature parameters can contribute to estimates wave direction, thus increasing accuracy and precision of results. PMID:27408830
Curvature of the penis is an abnormal bend in the penis that occurs during erection. It is also called Peyronie's disease. ... tissue develops in the deep tissues of the penis. The cause of this fibrous tissue is often ...
Vasquez, Dionicio; Scharcanski, Jacob; Wong, Alexander
2015-01-01
This paper presents a new automatic framework for extracting and characterizing the dynamic shape of the 3D wetting front and its propagation, based in a sequence of tomographic images acquired as water (moisture) infiltrates in unsaturated soils. To the best of the authors’ knowledge, the shape of the 3D wetting front and its propagation and progress over time has not been previously produced as a whole by methods in existing literature. The proposed automatic framework is composed two important and integrated modules: i) extraction of the 3D wetting front, and ii) characterization and description of the 3D wetting front to obtain important information about infiltration process. The 3D wetting front surface is segmented from 3D CT imagery provided as input via a 3D stochastic region merging strategy using quadric-regressed bilateral space-scale representations. Based on the 3D segmentation results, the normal directions at local curvature maxima of the wetting front surface are computed for 3D images of soil moisture, and its propagation is analyzed at the local directions in sites of maximal water adsorption, and described using histograms of curvature changes over time in response to sample saturation. These curvature change descriptors provide indirect measurements of moisture infiltration in soils, and soil saturation. Results using a field tomograph equipment specific for soil studies are encouraging, and suggest that the proposed automatic framework can be applied to estimate the infiltration of water in soils in 3D and in time. PMID:25602498
Front lighted optical tooling method and apparatus
Stone, William J.
1985-06-18
An optical tooling method and apparatus uses a front lighted shadowgraphic technique to enhance visual contrast of reflected light. The apparatus includes an optical assembly including a fiducial mark, such as cross hairs, reflecting polarized light with a first polarization, a polarizing element backing the fiducial mark and a reflective surface backing the polarizing element for reflecting polarized light bypassing the fiducial mark and traveling through the polarizing element. The light reflected by the reflecting surface is directed through a second pass of the polarizing element toward the frontal direction with a polarization differing from the polarization of the light reflected by the fiducial mark. When used as a tooling target, the optical assembly may be mounted directly to a reference surface or may be secured in a mounting, such as a magnetic mounting. The optical assembly may also be mounted in a plane defining structure and used as a spherometer in conjunction with an optical depth measuring instrument. A method of measuring a radius of curvature of an unknown surface includes positioning the spherometer on a surface between the surface and a depth measuring optical instrument. As the spherometer is frontally illuminated, the distance from the depth measuring instrument to the fiducial mark and the underlying surface are alternately measured and the difference in these measurements is used as the sagittal height to calculate a radius of curvature.
NASA Astrophysics Data System (ADS)
Semmelroth, K.; Berwian, P.; Schröter, C.; Leibiger, G.; Schönleber, M.; Friedrich, J.
2015-10-01
For improved real-time process control we integrated a novel optical in-situ monitoring system in a vertical reactor for hydride vapor phase epitaxy (HVPE) growth of gallium nitride (GaN) bulk crystals. The in-situ monitoring system consists of a fiber-optical interferometric sensor in combination with an optimized differential measuring head. The system only needs one small optical path perpendicular to the center of the layer stack typically consisting of sapphire as substrate and GaN. It can handle sample distances up to 1 m without difficulty. The in-situ monitoring system is simultaneously measuring the optical layer thicknesses of the GaN/sapphire layer stack and the absolute change of the distance between the measuring head and the backside of the layer stack. From this data it is possible to calculate the thickness of the growing GaN up to a thickness of about 1000 μm and the absolute change in curvature of the layer stack. The performance of the in-situ monitoring system is shown and discussed based on the measured interference signals recorded during a short-time and a long-time HVPE growth run.
Analog front-end measuring biopotential signal with effective offset rejection loop.
Lim, Seunghyun; Kim, Hyunho; Song, Haryong; Cho, Dong-il Dan; Ko, Hyoungho
2015-01-01
This paper presents an analog front-end (AFE) IC design for recording biopotential signals. The AFE employs a capacitively coupled instrumentation amplifier to achieve a low-noise and high-common mode rejection ratio (CMRR) system. A ripple reduction loop is proposed to reduce the ripple generated by the up-modulating chopper. The low frequency noise is attenuated by an input AC coupling capacitor, and is attenuated again by a DC servo loop. The proposed AFE features a differential gain of 71 dB, and a CMRR of 89 dB, at 50 Hz. Furthermore, the proposed AFE can robustly acquire biopotential signals even in the presence of an input offset and ripples. PMID:26406095
NASA Astrophysics Data System (ADS)
Monteil, E.; Demaria, N.; Pacher, L.; Rivetti, A.; Da Rocha Rolo, M.; Rotondo, F.; Leng, C.
2016-03-01
The upgrade of the silicon pixel sensors for the HL-LHC experiments requires the development of new readout integrated circuits due to unprecedented radiation levels, very high hit rates and increased pixel granularity. The design of a very compact, low power, low threshold analog very front-end in CMOS 65 nm technology is described. It contains a synchronous comparator which uses an offset compensation technique based on storing the offset in output. The latch can be turned into a local oscillator using an asynchronous logic feedback loop to implement a fast time-over-threshold counting. This design has been submitted and the measurement results are presented.
Dayton, D; Gonglewski, J; Rogers, S
1997-06-10
Deconvolution from wave-front sensing (DWFS) has been proposed as a method for achieving high-resolution images of astronomical objects from ground-based telescopes. The technique consists of the simultaneous measurement of a short-exposure focal-plane speckled image, as well as the wave front, by use of a Shack-Hartmann sensor placed at the pupil plane. In early studies it was suspected that some problems would occur in poor seeing conditions; however, it was usually assumed that the technique would work well as long as the wave-front sensor subaperture spacing was less than r(0) (L/r(0) < 1). Atmosphere-induced phase errors in the pupil of a telescope imaging system produce both phase errors and magnitude errors in the effective short-exposure optical transfer function (OTF) of the system. Recently it has been shown that the commonly used estimator for this technique produces biased estimates of the magnitude errors. The significance of this bias problem is that one cannot properly estimate or correct for the frame-to-frame fluctuations in the magnitude of the OTF but can do so only for fluctuations in the phase. An auxiliary estimate must also be used to correct for the mean value of the magnitude error. The inability to compensate for the magnitude fluctuations results in a signal-to-noise ratio (SNR) that is less favorable for the technique than was previously thought. In some situations simpler techniques, such as the Knox-Thompson and bispectrum methods, which require only speckle gram data from the focal plane of the imaging system, can produce better results. We present experimental measurements based on observations of bright stars and the Jovian moon Ganymede that confirm previous theoretical predictions. PMID:18253416
Barenboim, Gabriela; Martínez, Enrique Fernández; Mena, Olga; Verde, Licia E-mail: enfmarti@mppmu.mpg.de E-mail: liciaverde@icc.ub.edu
2010-03-01
Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d{sub A}(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Ω{sub k} in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d{sub A}(z) up to sufficiently high redshifts z ∼ 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z)−Ω{sub k} degeneracy.
NASA Astrophysics Data System (ADS)
Block, Martin M.; Durand, Loyal; Ha, Phuoc; Halzen, Francis
2016-06-01
We study the effects of curvature in the expansion of the logarithm of the differential elastic scattering cross section near t =0 as d σ (s ,t )/d t =d σ (s ,0 )/d t ×exp (B t +C t2+D t3⋯) in an eikonal model for p p and p ¯p scattering, and use the results to discuss the extrapolation of measured differential cross sections and the slope parameters B to t =-q2=0 . We find that the curvature effects represented by the parameters C and D , while small, lead to significant changes in the forward slope parameter relative to that determined in a purely exponential fit, and to smaller but still significant changes in the forward elastic scattering and total cross sections. Curvature effects should therefore be considered in future analyses or reanalyses of the elastic scattering data.
Zhao, Chunyu; Burge, James H
2013-12-16
Zernike polynomials are an orthonormal set of scalar functions over a circular domain, and are commonly used to represent wavefront phase or surface irregularity. In optical testing, slope or curvature of a surface or wavefront is sometimes measured instead, from which the surface or wavefront map is obtained. Previously we derived an orthonormal set of vector polynomials that fit to slope measurement data and yield the surface or wavefront map represented by Zernike polynomials. Here we define a 3-element curvature vector used to represent the second derivatives of a continuous surface, and derive a set of orthonormal curvature basis functions that are written in terms of Zernike polynomials. We call the new curvature functions the C polynomials. Closed form relations for the complete basis set are provided, and we show how to determine Zernike surface coefficients from the curvature data as represented by the C polynomials. PMID:24514717
A new front-end ASIC for GEM detectors with time and charge measurement capabilities
NASA Astrophysics Data System (ADS)
Ciciriello, F.; Corsi, F.; De Robertis, G.; Felici, G.; Loddo, F.; Marzocca, C.; Matarrese, G.; Ranieri, A.
2016-07-01
A 32 channel CMOS front-end ASIC has been designed to read out the GEM detectors intended to be used for beam monitoring in a new proton-therapy facility currently under construction. In order to improve the spatial resolution by exploiting charge centroid algorithms, the analog channels, based on the classic CSA+shaper architecture, are equipped with a peak detector (PD) which works as an analog memory during the read-out phase. The outputs of the PDs are multiplexed towards an integrated 8-bit subranging ADC. An accurate trigger signal marks the arrival of a valid event and is generated by fast-ORing the outputs of 32 voltage discriminators which compare the shaper outputs with a programmable threshold. The digital part of the ASIC manages the read-out of the channels, the A/D conversion and the configuration of the ASIC. A 100 Mbit/s LVDS serial link is used for data communication. The sensitivity of the analog channel is 15 mV/fC and the dynamic range is 80 fC. The simulated ENC is about 650 e- for a detector capacitance of 10 pF. © 2001 Elsevier Science. All rights reserved
Distributed curvature and stability of fullerenes.
Fowler, Patrick W; Nikolić, Sonja; De Los Reyes, Rasthy; Myrvold, Wendy
2015-09-21
Energies of non-planar conjugated π systems are typically described qualitatively in terms of the balance of π stabilisation and the steric strain associated with geometric curvature. Curvature also has a purely graph-theoretical description: combinatorial curvature at a vertex of a polyhedral graph is defined as one minus half the vertex degree plus the sum of reciprocal sizes of the faces meeting at that vertex. Prisms and antiprisms have positive combinatorial vertex curvature at every vertex. Excluding these two infinite families, we call any other polyhedron with everywhere positive combinatorial curvature a PCC polyhedron. Cubic PCC polyhedra are initially common, but must eventually die out with increasing vertex count; the largest example constructed so far has 132 vertices. The fullerenes Cn have cubic polyhedral molecular graphs with n vertices, 12 pentagonal and (n/2 - 10) hexagonal faces. We show that there are exactly 39 PCC fullerenes, all in the range 20 ≤n≤ 60. In this range, there is only partial correlation between PCC status and stability as defined by minimum pentagon adjacency. The sum of vertex curvatures is 2 for any polyhedron; for fullerenes the sum of squared vertex curvatures is linearly related to the number of pentagon adjacencies and hence is a direct measure of relative stability of the lower (n≤ 60) fullerenes. For n≥ 62, non-PCC fullerenes with a minimum number of pentagon adjacencies minimise mean-square curvature. For n≥ 70, minimum mean-square curvature implies isolation of pentagons, which is the strongest indicator of stability for a bare fullerene. PMID:26283188
NASA Astrophysics Data System (ADS)
Andrew, Matthew; Bijeljic, Branko; Blunt, Martin J.
2014-11-01
X-ray microtomography was used to image the shape and size of residual ganglia of supercritical CO2 at resolutions of 3.5 and 2 μm and at representative subsurface conditions of temperature and pressure. The capillary pressure for each ganglion was found by measuring the curvature of the CO2-brine interface, while the pore structure was parameterized using distance maps of the pore space. The formation of the residual clusters by snap-off was examined by comparing the ganglion capillary pressure to local pore topography. The capillary pressure was found to be inversely proportional to the radius of the largest restriction (throat) surrounding the ganglion, which validates the imbibition mechanisms used in pore-network modeling. The potential mobilization of residual ganglia was assessed using a reformulation of both the capillary (Ncmacro) and Bond numbers (Nbmacro), rigorously based on a balance of pore-scale forces, with the majority of ganglia remobilized at Ncmacro around 1. Buoyancy forces were found to be small in this system (Nbmacro << 1), meaning the gravitational remobilization of CO2 after residual trapping would be extremely difficult.
Spline-Based Smoothing of Airfoil Curvatures
NASA Technical Reports Server (NTRS)
Li, W.; Krist, S.
2008-01-01
Constrained fitting for airfoil curvature smoothing (CFACS) is a splinebased method of interpolating airfoil surface coordinates (and, concomitantly, airfoil thicknesses) between specified discrete design points so as to obtain smoothing of surface-curvature profiles in addition to basic smoothing of surfaces. CFACS was developed in recognition of the fact that the performance of a transonic airfoil is directly related to both the curvature profile and the smoothness of the airfoil surface. Older methods of interpolation of airfoil surfaces involve various compromises between smoothing of surfaces and exact fitting of surfaces to specified discrete design points. While some of the older methods take curvature profiles into account, they nevertheless sometimes yield unfavorable results, including curvature oscillations near end points and substantial deviations from desired leading-edge shapes. In CFACS as in most of the older methods, one seeks a compromise between smoothing and exact fitting. Unlike in the older methods, the airfoil surface is modified as little as possible from its original specified form and, instead, is smoothed in such a way that the curvature profile becomes a smooth fit of the curvature profile of the original airfoil specification. CFACS involves a combination of rigorous mathematical modeling and knowledge-based heuristics. Rigorous mathematical formulation provides assurance of removal of undesirable curvature oscillations with minimum modification of the airfoil geometry. Knowledge-based heuristics bridge the gap between theory and designers best practices. In CFACS, one of the measures of the deviation of an airfoil surface from smoothness is the sum of squares of the jumps in the third derivatives of a cubicspline interpolation of the airfoil data. This measure is incorporated into a formulation for minimizing an overall deviation- from-smoothness measure of the airfoil data within a specified fitting error tolerance. CFACS has been
Curvature calculations with GEOCALC
NASA Astrophysics Data System (ADS)
Moussiaux, A.; Tombal, Ph.
1987-04-01
A new method for calculating the curvature tensor has been recently proposed by D. Hestenes. This method is a particular application of geometric calculus, which has been implemented in an algebraic programming language on the form of a package called GEOCALC. We show how to apply this package to the Schwarzchild case and we discuss the different results.
Curvature calculations with GEOCALC
Moussiaux, A.; Tombal, P.
1987-04-01
A new method for calculating the curvature tensor has been recently proposed by D. Hestenes. This method is a particular application of geometric calculus, which has been implemented in an algebraic programming language on the form of a package called GEOCALC. They show how to apply this package to the Schwarzchild case and they discuss the different results.
Curvature-induced radiation of surface plasmon polaritons propagating around bends
Hasegawa, Keisuke; Noeckel, Jens U.; Deutsch, Miriam
2007-06-15
We present a theoretical study of the curvature-induced radiation of surface plasmon polaritons propagating around bends at metal-dielectric interfaces. We explain qualitatively how the curvature leads to distortion of the phase front, causing the fields to radiate energy away from the metal-dielectric interface. We then quantify, both analytically and numerically, radiation losses and energy transmission efficiencies of surface plasmon polaritons propagating around bends with varying radii as well as sign of curvature.
2014-01-01
The second KES International Conference on Innovation in Medicine and Healthcare (InMed-14) was held over 9-11 July 2014 in San Sebastian, Spain, organised by KES International in partnership with the University of the Basque Country, UPV/EHU and the Institute of Knowledge Transfer. InMed-14 gathered researchers and engineers, managers, students and practitioners from a broad medically-related arena. This multi-disciplinary group met to discuss the ways that technological and methodological innovation, knowledge exchange and enterprise can be applied to issues relating to medicine, surgery, healthcare and the issues of an ageing population. A central theme of the conference was Smart Medical and Healthcare Systems which covered the ways in which modern intelligent systems contribute to the solution of problems faced by healthcare and medical practitioners today, addressing the application of these systems. The conference featured five excellent keynote talks from internationally renowned experts, namely: • Edward J. Ciaccio, Columbia University, NY (talk entitled 'Model of Reentrant Ventricular Tachycardia based on Wavefront Curvature'); • Jesus Cortes, Biocruces, Ikerbasque, Spain (talk entitled 'Computational Neuroimaging for Health and Disease'); • Juan Manuel Gorriz, University of Granada, Spain (talk entitled 'DiagnoSIS: Diagnosis by means of Statistical and Intelligent Systems'); • Ricardo Sanchez Peña, ITBA & CONICET, Argentina (talk entitled 'Automatic Control of Diabetes type 1'); and • Sebastiano Stramaglia, Ikerbasque Visiting Professor, Spain (talk entitled 'Causality measures for Brain Computation'). In addition to the General Track, chaired by Prof Manuel Grana, University of the Basque Country UPV/EHU and the Workshop on Smart Medical and Healthcare, chaired by Dr Carlos Toro, Vicomtech-IK4, Systems, there were special sessions on Medical Decision-Support Systems chaired by Dr Elena Hernández-Pereira, University of La Coruña, Spain
Shearlet-based detection of flame fronts
NASA Astrophysics Data System (ADS)
Reisenhofer, Rafael; Kiefer, Johannes; King, Emily J.
2016-03-01
Identifying and characterizing flame fronts is the most common task in the computer-assisted analysis of data obtained from imaging techniques such as planar laser-induced fluorescence (PLIF), laser Rayleigh scattering (LRS), or particle imaging velocimetry (PIV). We present Complex Shearlet-Based Ridge and Edge Measure (CoShREM), a novel edge and ridge (line) detection algorithm based on complex-valued wavelet-like analyzing functions—so-called complex shearlets—displaying several traits useful for the extraction of flame fronts. In addition to providing a unified approach to the detection of edges and ridges, our method inherently yields estimates of local tangent orientations and local curvatures. To examine the applicability for high-frequency recordings of combustion processes, the algorithm is applied to mock images distorted with varying degrees of noise and real-world PLIF images of both OH and CH radicals. Furthermore, we compare the performance of the newly proposed complex shearlet-based measure to well-established edge and ridge detection techniques such as the Canny edge detector, another shearlet-based edge detector, and the phase congruency measure.
Measured and computed induced body currents in front of an experimental RF dielectric heater.
Kännälä, Sami; Puranen, Lauri; Sihvonen, Ari-Pekka; Jokela, Kari
2008-02-01
Operators of industrial high-frequency dielectric heaters are exposed to electromagnetic fields that are high enough to significantly increase body temperature. The assessment of exposure based on the measurement of external field strengths is, however, inaccurate due to the non-uniformity of the fields. This paper presents an exposure assessment method based on the measurement of the current induced by the external electric field in the body of the operator. Body current distributions were measured at 27.12 MHz using various current meters under a condition simulating the exposure to stray fields emitted by a dielectric heater. The specific absorption rates and induced body currents were computed with the finite-difference time-domain method using heterogeneous and homogeneous human models. The numerical analysis indicated that the basic restrictions for occupational exposure are not exceeded when the current induced in the limbs is lower than the action level (100 mA), even though the maximum electric field significantly exceeds the action value (61 V m(-1)). For the heterogeneous human model the exposure limit for local specific absorption rate was exceeded when the current induced in the ankle was 166 mA at a distance of 0.3 m from the electrode of the device. The vertical component of current density proved to be much more significant than the horizontal components. The importance of the horizontal components was highest near the electrode. The computations showed no concentration of the induced current to the superficial tissues due to the skin effect. PMID:18188050
Wavefront reconstruction from tangential and sagittal curvature.
Canales, Javier; Barbero, Sergio; Portilla, Javier; López-Alonso, José Manuel
2014-12-10
In a previous contribution [Appl. Opt.51, 8599 (2012)], a coauthor of this work presented a method for reconstructing the wavefront aberration from tangential refractive power data measured using dynamic skiascopy. Here we propose a new regularized least squares method where the wavefront is reconstructed not only using tangential but also sagittal curvature data. We prove that our new method provides improved quality reconstruction for typical and also for highly aberrated wavefronts, under a wide range of experimental error levels. Our method may be applied to any type of wavefront sensor (not only dynamic skiascopy) able to measure either just tangential or tangential plus sagittal curvature data. PMID:25608069
Hybrid curvature and modal wavefront sensor
NASA Astrophysics Data System (ADS)
Dong, Shihao; Haist, Tobias; Dietrich, Tom; Osten, Wolfgang
2014-09-01
The crosstalk effect considerably limits the capability of holography-based modal wavefront sensing (HMWS) when measuring wavefronts with large aberrations. In this contribution, we introduce a curvature-based measurement technique into HMWS to extend the dynamic range and the sensitivity of HMWS via a compact holographic design. If the input aberrations are large, the dominating aberration modes are first detected via curvature sensing and compensated using a wavefront correcting device, e.g. a membrane mirror. The system then switches to HMWS to obtain better sensitivity and accuracy with reduced aberrations. Different approaches for the reconstruction of the wavefront have been tested and extensive simulations for different aberrations have been analyzed.
NASA Astrophysics Data System (ADS)
Wilbur Pech-May, Nelson; Cifuentes, Ángel; Mendioroz, Arantza; Oleaga, Alberto; Salazar, Agustín
2015-08-01
Both thermal diffusivity and effusivity (or conductivity) are necessary to characterize the thermal transport properties of a material. The flash method is the most recognized procedure to measure the thermal diffusivity of free-standing opaque plates. However, it fails to simultaneously obtain the thermal effusivity (or conductivity). This is due to the difficulty of knowing the total energy absorbed by the sample surface after the light pulse. In this work, we propose using the flash method in the front-face configuration on a two-layer system made of the unknown plate and a fluid of known thermal properties. We demonstrate that the surface temperature is sensitive to the thermal mismatch between the plate and the fluid, which is governed by their thermal effusivity ratio. In order to verify the validity of the method and to establish its application limits we have performed flash measurements, using a pulsed laser and an infrared camera, on a set of calibrated materials (metals, alloys, ceramics and polymers) covering a wide range of thermal transport properties. These results confirm the ability of the flash method to simultaneously retrieve thermal diffusivity and effusivity in a fast manner in samples whose effusivities are lower than three times the effusivity of the liquid used as backing fluid.
Turbulent boundary layers subjected to multiple curvatures and pressure gradients
NASA Technical Reports Server (NTRS)
Bandyopadhyay, Promode R.; Ahmed, Anwar
1993-01-01
The effects of abruptly applied cycles of curvatures and pressure gradients on turbulent boundary layers are examined experimentally. Two two-dimensional curved test surfaces are considered: one has a sequence of concave and convex longitudinal surface curvatures and the other has a sequence of convex and concave curvatures. The choice of the curvature sequences were motivated by a desire to study the asymmetric response of turbulent boundary layers to convex and concave curvatures. The relaxation of a boundary layer from the effects of these two opposite sequences has been compared. The effect of the accompaying sequences of pressure gradient has also been examined but the effect of curvature dominates. The growth of internal layers at the curvature junctions have been studied. Measurements of the Gortler and corner vortex systems have been made. The boundary layer recovering from the sequence of concave to convex curvature has a sustained lower skin friction level than in that recovering from the sequence of convex to concave curvature. The amplification and suppression of turbulence due to the curvature sequences have also been studied.
NASA Technical Reports Server (NTRS)
Bever, R. S.
1976-01-01
Internal embedment stress measurements were performed, using tiny ferrite core transformers, whose voltage output was calibrated versus pressure by the manufacturer. Comparative internal strain measurements were made by attaching conventional strain gages to the same type of resistors and encapsulating these in various potting compounds. Both types of determinations were carried out while temperature cycling from 77 C to -50 C.
A methodology for quantifying seated lumbar curvatures.
Leitkam, Samuel T; Bush, Tamara Reid; Li, Mingfei
2011-11-01
To understand the role seating plays in the support of posture and spinal articulation, it is necessary to study the interface between a human and the seat. However, a method to quantify lumbar curvature in commercially available unmodified seats does not currently exist. This work sought to determine if the lumbar curvature for normal ranges of seated posture could be documented by using body landmarks located on the anterior portion of the body. The development of such a methodology will allow researchers to evaluate spinal articulation of a seated subject while in standard, commercially available seats and chairs. Anterior measurements of boney landmarks were used to quantify the relative positions of the ribcage and pelvis while simultaneous posterior measurements were made of lumbar curvature. The relationship between the anterior and the posterior measures was compared. The predictive capacity of this approach was evaluated by determining linear and second-order regressions for each of the four postures across all subjects and conducting a leave-one-out cross validation. The relationships between the anterior and posterior measures were approximated by linear and second-order polynomial regressions (r(2 ) = 0.829, 0.935 respectively) across all postures. The quantitative analysis showed that openness had a significant relationship with lumbar curvature, and a first-order regression was superior to a second-order regression. Average standard errors in the prediction were 5.9° for the maximum kyphotic posture, 9.9° for the comfortable posture, 12.8° for the straight and tall, and 22.2° for the maximum lordotic posture. These results show predictions of lumbar curvature are possible in seated postures by using a motion capture system and anterior measures. This method of lumbar curvature prediction shows potential for use in the assessment of seated spinal curvatures and the corresponding design of seating to accommodate those curvatures; however
Curvature constraints from large scale structure
NASA Astrophysics Data System (ADS)
Di Dio, Enea; Montanari, Francesco; Raccanelli, Alvise; Durrer, Ruth; Kamionkowski, Marc; Lesgourgues, Julien
2016-06-01
We modified the CLASS code in order to include relativistic galaxy number counts in spatially curved geometries; we present the formalism and study the effect of relativistic corrections on spatial curvature. The new version of the code is now publicly available. Using a Fisher matrix analysis, we investigate how measurements of the spatial curvature parameter ΩK with future galaxy surveys are affected by relativistic effects, which influence observations of the large scale galaxy distribution. These effects include contributions from cosmic magnification, Doppler terms and terms involving the gravitational potential. As an application, we consider angle and redshift dependent power spectra, which are especially well suited for model independent cosmological constraints. We compute our results for a representative deep, wide and spectroscopic survey, and our results show the impact of relativistic corrections on spatial curvature parameter estimation. We show that constraints on the curvature parameter may be strongly biased if, in particular, cosmic magnification is not included in the analysis. Other relativistic effects turn out to be subdominant in the studied configuration. We analyze how the shift in the estimated best-fit value for the curvature and other cosmological parameters depends on the magnification bias parameter, and find that significant biases are to be expected if this term is not properly considered in the analysis.
Curvature-dependent excitation propagation in cultured cardiac tissue
NASA Astrophysics Data System (ADS)
Kadota, S.; Kay, M. W.; Magome, N.; Agladze, K.
2012-02-01
The geometry of excitation wave front may play an important role on the propagation block and spiral wave formation. The wave front which is bent over the critical value due to interaction with the obstacles may partially cease to propagate and appearing wave breaks evolve into rotating waves or reentry. This scenario may explain how reentry spontaneously originates in a heart. We studied highly curved excitation wave fronts in the cardiac tissue culture and found that in the conditions of normal, non-inhibited excitability the curvature effects do not play essential role in the propagation. Neither narrow isthmuses nor sharp corners of the obstacles, being classical objects for production of extremely curved wave front, affect non-inhibited wave propagation. The curvature-related phenomena of the propagation block and wave detachment from the obstacle boundary were observed only after partial suppression of the sodium channels with Lidocaine. Computer simulations confirmed the experimental observations. The explanation of the observed phenomena refers to the fact that the heart tissue is made of finite size cells so that curvature radii smaller than the cardiomyocyte size loses sense, and in non-inhibited tissue the single cell is capable to transmit excitation to its neighbors.
Suyu, S. H.; Hilbert, S.; Marshall, P. J.; Blandford, R. D.; Auger, M. W.; Treu, T.; Koopmans, L. V. E.; Fassnacht, C. D.
2010-03-01
Strong gravitational lens systems with measured time delays between the multiple images provide a method for measuring the 'time-delay distance' to the lens, and thus the Hubble constant. We present a Bayesian analysis of the strong gravitational lens system B1608+656, incorporating (1) new, deep Hubble Space Telescope (HST) observations, (2) a new velocity-dispersion measurement of 260 +- 15 km s{sup -1} for the primary lens galaxy, and (3) an updated study of the lens' environment. Our analysis of the HST images takes into account the extended source surface brightness, and the dust extinction and optical emission by the interacting lens galaxies. When modeling the stellar dynamics of the primary lens galaxy, the lensing effect, and the environment of the lens, we explicitly include the total mass distribution profile logarithmic slope gamma' and the external convergence kappa{sub ext}; we marginalize over these parameters, assigning well-motivated priors for them, and so turn the major systematic errors into statistical ones. The HST images provide one such prior, constraining the lens mass density profile logarithmic slope to be gamma' = 2.08 +- 0.03; a combination of numerical simulations and photometric observations of the B1608+656 field provides an estimate of the prior for kappa{sub ext}: 0.10{sup +0.08}{sub -0.05}. This latter distribution dominates the final uncertainty on H{sub 0}. Fixing the cosmological parameters at OMEGA{sub m} = 0.3, OMEGA{sub L}AMBDA = 0.7, and w = -1 in order to compare with previous work on this system, we find H{sub 0} = 70.6{sup +3.1}{sub -3.1} km s{sup -1} Mpc{sup -1}. The new data provide an increase in precision of more than a factor of 2, even including the marginalization over kappa{sub ext}. Relaxing the prior probability density function for the cosmological parameters to that derived from the Wilkinson Microwave Anisotropy Probe (WMAP) five-year data set, we find that the B1608+656 data set breaks the degeneracy
Suyu, S.H.; Marshall, P.J.; Auger, M.W.; Hilbert, S.; Blandford, R.D.; Koopmans, L.V.E.; Fassnacht, C.D.; Treu, T.; /UC, Santa Barbara
2009-12-11
Strong gravitational lens systems with measured time delays between the multiple images provide a method for measuring the 'time-delay distance' to the lens, and thus the Hubble constant. We present a Bayesian analysis of the strong gravitational lens system B1608+656, incorporating (1) new, deep Hubble Space Telescope (HST) observations, (2) a new velocity dispersion measurement of 260 {+-} 15 km s{sup -1} for the primary lens galaxy, and (3) an updated study of the lens environment. Our analysis of the HST images takes into account the extended source surface brightness, and the dust extinction and optical emission by the interacting lens galaxies. When modeling the stellar dynamics of the primary lens galaxy, the lensing effect, and the environment of the lens, we explicitly include the total mass distribution profile logarithmic slope {gamma}{prime} and the external convergence {kappa}{sub ext}; we marginalize over these parameters, assigning well-motivated priors for them, and so turn the major systematic errors into statistical ones. The HST images provide one such prior, constraining the lens mass density profile logarithmic slope to be {gamma}{prime} = 2.08 {+-} 0.03; a combination of numerical simulations and photometric observations of the B1608+656 field provides an estimate of the prior for {kappa}{sub ext}: 0.10{sub -0.05}{sup +0.08}. This latter distribution dominates the final uncertainty on H{sub 0}. Fixing the cosmological parameters at {Omega}{sub m} = 0.3, {Omega}{sub {Lambda}} = 0.7, and w = -1 in order to compare with previous work on this system, we find H{sub 0} = 70.6{sub -3.1}{sup +3.1} km s{sup -1} Mpc{sup -1}. The new data provide an increase in precision of more than a factor of two, even including the marginalization over {kappa}{sub ext}. Relaxing the prior probability density function for the cosmological parameters to that derived from the WMAP 5-year data set, we find that the B1608+656 data set breaks the degeneracy between {Omega
Improving the Sensitivity of Astronomical Curvature Wavefront Sensor Using Dual-Stroke Curvature
NASA Astrophysics Data System (ADS)
Guyon, Olivier; Blain, Celia; Takami, Hideki; Hayano, Yutaka; Hattori, Masayuki; Watanabe, Makoto
2008-06-01
Curvature wavefront sensors measure wavefront phase aberration by acquiring two intensity images on either side of the pupil plane. Low-order adaptive optics (AO) systems using curvature wavefront sensing (CWFS) have proved to be highly efficient for astronomical applications: they are more sensitive, use fewer detector elements, and achieve, for the same number of actuators, higher Strehl ratios than AO systems using more traditional Shack-Hartmann wavefront sensors. In higher-order systems, however, curvature wavefront sensors lose sensitivity to low spatial frequencies wavefront aberrations. This effect, often described as "noise propagation," limits the usefulness of curvature wavefront sensing for high-order AO systems and/or large telescopes. In this paper, we first explain how this noise propagation effect occurs and then show that this limitation can be overcome by acquiring four defocused images of the pupil instead of two. This solution can be implemented without significant technology development and can run with a simple linear wavefront reconstruction algorithm at >kHz speed. We have successfully demonstrated in the laboratory that the four conjugation planes can be sequentially obtained at >kHz speed using a speaker-vibrating membrane assembly commonly used in current curvature AO systems. Closed loop simulations show that implementing this scheme is equivalent to making the guide star 1 to 1.5 magnitude brighter for the configuration tested (188 actuator elements on 8-m telescope). Higher sensitivity gains are expected on curvature systems with higher number of actuators.
NASA Astrophysics Data System (ADS)
Anderlini, L.; Anelli, M.; Archilli, F.; Auriemma, G.; Baldini, W.; Bencivenni, G.; Bizzeti, A.; Bocci, V.; Bondar, N.; Bonivento, W.; Bochin, B.; Bozzi, C.; Brundu, D.; Cadeddu, S.; Campana, P.; Carboni, G.; Cardini, A.; Carletti, M.; Casu, L.; Chubykin, A.; Ciambrone, P.; Dané, E.; De Simone, P.; Falabella, A.; Felici, G.; Fiore, M.; Fontana, M.; Fresch, P.; Furfaro, E.; Graziani, G.; Kashchuk, A.; Kotriakhova, S.; Lai, A.; Lanfranchi, G.; Loi, A.; Maev, O.; Manca, G.; Martellotti, G.; Neustroev, P.; Oldeman, R. G. C.; Palutan, M.; Passaleva, G.; Penso, G.; Pinci, D.; Polycarpo, E.; Saitta, B.; Santacesaria, R.; Santimaria, M.; Santovetti, E.; Saputi, A.; Sarti, A.; Satriano, C.; Satta, A.; Schmidt, B.; Schneider, T.; Sciascia, B.; Sciubba, A.; Siddi, B. G.; Tellarini, G.; Vacca, C.; Vazquez-Gomez, R.; Vecchi, S.; Veltri, M.; Vorobyev, A.
2016-04-01
A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing rate of 20 MHz. The measured values of the dead-time range from ~ 70 ns to ~ 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity.
Cideciyan, Artur V.; Swider, Malgorzata; Schwartz, Sharon B.; Stone, Edwin M.; Jacobson, Samuel G.
2015-01-01
Purpose To evaluate the progression of the earliest stage of disease in ABCA4-associated retinal degenerations (RDs). Methods Near-infrared excited reduced-illuminance autofluorescence imaging was acquired across the retina up to 80 degrees eccentricity in 44 patients with two ABCA4 alleles. The eccentricity of the leading disease front (LDF) corresponding to the earliest stage of disease was measured along the four meridians. A mathematical model describing the expansion of the LDF was developed based on 6 years of longitudinal follow-up. Results The extent of LDF along the superior, inferior, and temporal meridians showed a wide spectrum from 3.5 to 70 degrees. In patients with longitudinal data, the average centrifugal expansion rate was 2 degrees per year. The nasal extent of LDF between the fovea and ONH ranged from 4.3 to 16.5 degrees and expanded at 0.35 degrees per year. The extent of LDF beyond ONH ranged from 19 to 75 degrees and expanded on average at 2 degrees per year. A mathematical model fit well to the longitudinal data describing the expansion of the LDF. Conclusions The eccentricity of the LDF in ABCA4-RD shows a continuum from parafovea to far periphery along all four meridians consistent with a wide spectrum of severity observed clinically. The model of progression may provide a quantitative prediction of the LDF expansion based on the age and eccentricity of the LDF at a baseline visit, and thus contribute significantly to the enrollment of candidates appropriate for clinical trials planning specific interventions, efficacy outcomes, and durations. PMID:26377081
Wallace, John Paul; Myneni, Ganapati Rao; Pike, Robert
2011-03-31
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Cosmic curvature and condensation
NASA Technical Reports Server (NTRS)
Harwit, Martin
1992-01-01
It is shown that the universe may consist of a patchwork of domains with different Riemann curvature constants k = 0, +/-1. Features of a phase transition in which flat space breaks up in a transition 2k0 - k(-) + k(+) with initial scale factors R(-) = R(+) are postulated and explored. It is shown that such a transition is energetically permitted, has the equivalent of a Curie temperature, and can lead in a natural way to the formation of voids and galaxies. It is predicted that, if the ambient universe on average is well fitted by a purely k(-) space, with only occasional domains of k(+) containing galaxies, a density parameter of (A(z sub c + 1)) super -1 should be expected, where z sub c represents the redshift of the earliest objects to have condensed, and A takes on values ranging from about 5 to 3. Present observations of quasars would suggest a density of about 0.03 or 0.05, respectively, but it could be lower if earlier condensation took place.
John Paul Wallace, Ganapati Rao Myneni, and Robert Pike
2011-03-01
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Geometrical constraint on curvature with BAO experiments
NASA Astrophysics Data System (ADS)
Takada, Masahiro; Doré, Olivier
2015-12-01
The spatial curvature (K or ΩK) is one of the most fundamental parameters of an isotropic and homogeneous universe and has a close link to the physics of the early Universe. Combining the radial and angular diameter distances measured via the baryon acoustic oscillation (BAO) experiments allows us to unambiguously constrain the curvature. The method is primarily based on the metric theory, and is less sensitive to the theory of structure formation (other than the existence of the BAO scale) and is free of any model of dark energy. In this paper, we estimate a best achievable accuracy of constraining the curvature with the BAO experiments. We show that an all-sky, cosmic-variance-limited galaxy survey covering the Universe up to z ≳4 enables a precise determination of the curvature to an accuracy of σ (ΩK)≃1 0-3. When we assume a model of dark energy—either the cosmological constraint or the (w0,wa) model—it can achieve a precision of σ (ΩK)≃a few×10-4. These forecasts require a high sampling density of galaxies, and are degraded by up to a factor of a few for a survey with a finite number density of ˜10-3 (h /Mpc )3 .
Membrane Curvature Sensing by Amphipathic Helices
Jensen, Martin Borch; Bhatia, Vikram Kjøller; Jao, Christine C.; Rasmussen, Jakob Ewald; Pedersen, Søren L.; Jensen, Knud J.; Langen, Ralf; Stamou, Dimitrios
2011-01-01
Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues. PMID:21953452
Graph Curvature for Differentiating Cancer Networks
Sandhu, Romeil; Georgiou, Tryphon; Reznik, Ed; Zhu, Liangjia; Kolesov, Ivan; Senbabaoglu, Yasin; Tannenbaum, Allen
2015-01-01
Cellular interactions can be modeled as complex dynamical systems represented by weighted graphs. The functionality of such networks, including measures of robustness, reliability, performance, and efficiency, are intrinsically tied to the topology and geometry of the underlying graph. Utilizing recently proposed geometric notions of curvature on weighted graphs, we investigate the features of gene co-expression networks derived from large-scale genomic studies of cancer. We find that the curvature of these networks reliably distinguishes between cancer and normal samples, with cancer networks exhibiting higher curvature than their normal counterparts. We establish a quantitative relationship between our findings and prior investigations of network entropy. Furthermore, we demonstrate how our approach yields additional, non-trivial pair-wise (i.e. gene-gene) interactions which may be disrupted in cancer samples. The mathematical formulation of our approach yields an exact solution to calculating pair-wise changes in curvature which was computationally infeasible using prior methods. As such, our findings lay the foundation for an analytical approach to studying complex biological networks. PMID:26169480
Graph Curvature for Differentiating Cancer Networks
NASA Astrophysics Data System (ADS)
Sandhu, Romeil; Georgiou, Tryphon; Reznik, Ed; Zhu, Liangjia; Kolesov, Ivan; Senbabaoglu, Yasin; Tannenbaum, Allen
2015-07-01
Cellular interactions can be modeled as complex dynamical systems represented by weighted graphs. The functionality of such networks, including measures of robustness, reliability, performance, and efficiency, are intrinsically tied to the topology and geometry of the underlying graph. Utilizing recently proposed geometric notions of curvature on weighted graphs, we investigate the features of gene co-expression networks derived from large-scale genomic studies of cancer. We find that the curvature of these networks reliably distinguishes between cancer and normal samples, with cancer networks exhibiting higher curvature than their normal counterparts. We establish a quantitative relationship between our findings and prior investigations of network entropy. Furthermore, we demonstrate how our approach yields additional, non-trivial pair-wise (i.e. gene-gene) interactions which may be disrupted in cancer samples. The mathematical formulation of our approach yields an exact solution to calculating pair-wise changes in curvature which was computationally infeasible using prior methods. As such, our findings lay the foundation for an analytical approach to studying complex biological networks.
The curvature adaptive optics system modeling
NASA Astrophysics Data System (ADS)
Yang, Qiang
A curvature adaptive optics (AO) simulation system has been built. The simulation is based on the Hokupa'a-36 AO system for the NASA IRTF 3m telescope and the Hokupa'a-85 AO system for the Gemini Near Infrared Coronagraphic Imager. Several sub-models are built separately for the AO simulation system, and they are: (1) generation and propagation of atmospheric phase screens, (2) the bimorph deformable mirror (DM), (3) the curvature wave-front sensor (CWFS), (4) generation of response functions, interaction matrices and calculation of command matrices, (5) Fresnel propagation from the DM pupil to the lenslet pupil, (6) AO servo loop, and (7) post processing. The AO simulation system is then applied to the effects of DM hysteresis, and to the optimization of DM actuator patterns for the Hokupa'a-85 and Hokupa'a-36 AO systems. In the first application, an enhancing Coleman-Hodgdon model is introduced to approximate the hysteresis curves, and then the Lambert W function is introduced to calculate the inverse of the Coleman-Hodgdon equation. Step response, transfer functions and Strehl Ratios from the AO system have been compared under the cases with/without DM hysteresis. The servo-loop results show that the bandwidth of an AO system is improved greatly after the DM hysteresis is corrected. In the second application, many issues of the bimorph mirror will be considered to optimize the DM patterns, and they include the type and length of the edge benders, gap size of electrodes, DM size, and DM curvature limit.
Michel, D. T.; Davis, A. K.; Armstrong, W.; Bahr, R.; Epstein, R.; Goncharov, V. N.; Hohenberger, M.; Igumenshchev, I. V.; Jungquist, R.; Meyerhofer, D. D.; et al
2015-07-08
Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays (> 1 keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (more » $${\\it\\delta}R=\\pm 1.15~{\\rm\\mu}\\text{m}$$), image-to-image timing ($${\\it\\delta}({\\rm\\Delta}t)=\\pm 2.5$$ ps) and absolute timing ($${\\it\\delta}t=\\pm 10$$ ps) are presented. Angular averaging of the images provides an average radius measurement of$${\\it\\delta}(R_{\\text{av}})=\\pm 0.15~{\\rm\\mu}\\text{m}$$and an error in velocity of$${\\it\\delta}V/V=\\pm 3\\%$$. This technique was applied on the Omega Laser Facility and the National Ignition Facility.« less
Effects of Iris Surface Curvature on Iris Recognition
Thompson, Joseph T; Flynn, Patrick J; Bowyer, Kevin W; Santos-Villalobos, Hector J
2013-01-01
To focus on objects at various distances, the lens of the eye must change shape to adjust its refractive power. This change in lens shape causes a change in the shape of the iris surface which can be measured by examining the curvature of the iris. This work isolates the variable of iris curvature in the recognition process and shows that differences in iris curvature degrade matching ability. To our knowledge, no other work has examined the effects of varying iris curvature on matching ability. To examine this degradation, we conduct a matching experiment across pairs of images with varying degrees of iris curvature differences. The results show a statistically signi cant degradation in matching ability. Finally, the real world impact of these ndings is discussed
Modeling Normal Shock Velocity Curvature Relation for Heterogeneous Explosives
NASA Astrophysics Data System (ADS)
Yoo, Sunhee; Crochet, Michael; Pemberton, Steve
2015-06-01
The normal shock velocity and curvature, Dn(κ) , relation on a detonation shock surface has been an important functional quantity to measure to understand the shock strength exerted against the material interface between a main explosive charge and the case of an explosive munition. The Dn(κ) relation is considered an intrinsic property of an explosive, and can be experimentally deduced by rate stick tests at various charge diameters. However, experimental measurements of the Dn(κ) relation for heterogeneous explosives such as PBXN-111 are challenging due to the non-smoothness and asymmetry usually observed in the experimental streak records of explosion fronts. Out of the many possibilities, the asymmetric character may be attributed to the heterogeneity of the explosives, a hypothesis which begs two questions: (1) is there any simple hydrodynamic model that can explain such an asymmetric shock evolution, and (2) what statistics can be derived for the asymmetry using simulations with defined structural heterogeneity in the unreacted explosive? Saenz, Taylor and Stewart studied constitutive models for derivation of the Dn(κ) relation on porous `homogeneous' explosives and carried out simulations in a spherical coordinate frame. In this paper, we extend their model to account for `heterogeneity' and present shock evolutions in heterogeneous explosives using 2-D hydrodynamic simulations with some statistical examination. (96TW-2015-0004)
NASA Astrophysics Data System (ADS)
Herrero, Vicente; Colom, Ricardo; Gadea, Rafael; Lerche, Christoph W.; Cerdá, Joaquín; Sebastiá, Ángel; Benlloch, José M.
2007-06-01
Silicon Photomultipliers, though still under development for mass production, may be an alternative to traditional Vacuum Photomultipliers Tubes (VPMT). As a consequence, electronic front-ends initially designed for VPMT will need to be modified. In this simulation, an improved architecture is presented which is able to obtain impact position and depth of interaction of a gamma ray within a continuous scintillation crystal, using either kind of PM. A current sensitive preamplifier stage with individual gain adjustment interfaces the multi-anode PM outputs with a current division resistor network. The preamplifier stage allows to improve front-end processing delay and temporal resolution behavior as well as to increase impact position calculation resolution. Depth of interaction (DOI) is calculated from the width of the scintillation light distribution, which is related to the sum of voltages in resistor network input nodes. This operation is done by means of a high-speed current mode scheme.
NASA Technical Reports Server (NTRS)
2006-01-01
[figure removed for brevity, see original site] Context image for PIA02171 Cloud Front
These clouds formed in the south polar region. The faintness of the cloud system likely indicates that these are mainly ice clouds, with relatively little dust content.
Image information: VIS instrument. Latitude -86.7N, Longitude 212.3E. 17 meter/pixel resolution.
Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.
NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.
Shearlet-based edge detection: flame fronts and tidal flats
NASA Astrophysics Data System (ADS)
King, Emily J.; Reisenhofer, Rafael; Kiefer, Johannes; Lim, Wang-Q.; Li, Zhen; Heygster, Georg
2015-09-01
Shearlets are wavelet-like systems which are better suited for handling geometric features in multi-dimensional data than traditional wavelets. A novel method for edge and line detection which is in the spirit of phase congruency but is based on a complex shearlet transform will be presented. This approach to detection yields an approximate tangent direction of detected discontinuities as a byproduct of the computation, which then yields local curvature estimates. Two applications of the edge detection method will be discussed. First, the tracking and classification of flame fronts is a critical component of research in technical thermodynamics. Quite often, the flame fronts are transient or weak and the images are noisy. The standard methods used in the field for the detection of flame fronts do not handle such data well. Fortunately, using the shearlet-based edge measure yields good results as well as an accurate approximation of local curvature. Furthermore, a modification of the method will yield line detection, which is important for certain imaging modalities. Second, the Wadden tidal flats are a biodiverse region along the North Sea coast. One approach to surveying the delicate region and tracking the topographical changes is to use pre-existing Synthetic Aperture Radar (SAR) images. Unfortunately, SAR data suffers from multiplicative noise as well as sensitivity to environmental factors. The first large-scale mapping project of that type showed good results but only with a tremendous amount of manual interaction because there are many edges in the data which are not boundaries of the tidal flats but are edges of features like fields or islands. Preliminary results will be presented.
An Optical Method For Surface Curvature Testing
NASA Astrophysics Data System (ADS)
Jarisch, W.
1985-01-01
Inspection and measurement of surface quality play increasingly an important role in most machining and polishing processes. A typical example is the manufacturing of magnetic disks. The quality of a disk file essentially depends on the surface flatness of the substrate material. For many measurement aspects largearea topography variations are of less interest than high local changes of slope and curvature of the surface to be tested. Mathematically, the surface curvature is expressed as the second derivative of the profile function of the substrate, while the first derivative is known as the slope. Rapid local variations of the slope, that means high curvature values, cause high vertical accelerations of the magnetic head flying over the disk surface in fractions of a micrometer flight-height. Such irregularities of the substrate in the azimuthal disk direction would lead to uncontrolled fluctuations of the air gap between disk and head causing an attenuation of the write/read signal, to head vibrations, or even to a direct contact of the head with the disk (head crash). In the radial direction, the high-speed radial positioning of the head by voice coil driven motors also may cause a head crash at high local changes of the disk slope. Limits of the tolerable head accelerations, found by experience and theoretically by calculations, are listed in manufacturing specifications. For a fast, large area disk quality inspection and evaluation, a compact and highly sensitive measuring method has been developed. A testing tool based on this method displays the test area superimposed with a clear fringe pattern on a TV screen. The fringe pattern represents the surface curvature. From this, both components of the disk curvature, the azimuthal as well as the radial component, can be measured. Coherent optical interference and Moire techniques are the basic principles of the method providing the fringe pattern of the surface area under test. Each fringe interconnects
On the Weyl curvature hypothesis
NASA Astrophysics Data System (ADS)
Stoica, Ovidiu Cristinel
2013-11-01
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity.
Curvature calculations with spacetime algebra
Hestenes, D.
1986-06-01
A new method for calculating the curvature tensor is developed and applied to the Scharzschild case. The method employs Clifford algebra and has definite advantages over conventional methods using differential forms or tensor analysis.
NASA Astrophysics Data System (ADS)
Maaßdorf, A.; Zeimer, U.; Grenzer, J.; Weyers, M.
2013-07-01
AlxGa1-xAs grown on GaAs is known to be almost perfectly lattice matched with a maximum lattice mismatch of 0.14% at room temperature and even less at temperatures of 700 °C-800 °C. However, as layer structures for edge-emitting diode lasers exhibit an increasing overall thickness of several microns of AlxGa1-xAs, e.g., diode lasers comprising a super-large optical cavity, the accumulated elastic strain energy increases as well. Depending on the growth temperature the formation energy of dislocations can be reached, which is limiting the pseudomorphic growth. In this regard, the thermal expansion coefficient difference between layer and substrate is an important parameter. We utilize in situ curvature measurements during growth of AlxGa1-xAs by metal-organic vapour phase epitaxy to determine the thermal expansion coefficient α. The curvature change with increasing layer thickness, as well as with wafer temperature at constant layer thickness is used to assess α. This is compared to ex situ temperature dependent X-ray diffraction measurements to obtain α. All determined values for α are in good agreement, yielding αAlAs=4.1×10-6 K-1 for a given GaAs linear thermal expansion coefficient of αGaAs=5.73×10-6 K-1.
NASA Astrophysics Data System (ADS)
Chueca, Sergio; Marín-Franch, Antonio; Cenarro, Andrés. Javier; Varela, Jesús; Ederoclite, Alessandro; Cristóbal-Hornillos, David; Hernández-Monteagudo, Carlos; Gruel, Nicolás.; Moles, Mariano; Yanes, Axel; Rueda, Fernando; Rueda, Sergio; Luis-Simoes, Roberto; Hernández-Fuertes, Javier; López-Sainz, Angel; Maícas-Sacristán, Natalio; Lamadrid, José Luis; Díaz-Martín, Miguel Chioare; Taylor, Keith
2012-09-01
In order to maintain image quality during Javalambre wide field telescope operations, deformations and rigid body motions must be actively controlled to minimize optical disturbances. For JST/T250 the aberrations of the telescope will be measured with four curvature sensors at the focal plane. To correct the measured distortions, the secondary mirror position (with a hexapod support) and the camera position can be modified in a control closed loop. Multiple software tools have been developed to accomplish this goal, constituting the "Observatorio Astrofísico de Javalambre" (OAJ) Active Optics Pipeline. We present a comprehensive analysis of the wave-front sensing system, including the availability of reference stars, pupil registration, wavefront estimators and the iteration matrix evaluation techniques. Some preliminary simulations have been made using a telescope model with a Optical Ray Tracing Software.
Caumes, Jean Pascal; Videau, Laurent; Rouyer, Claude; Freysz, Eric
2004-04-15
The wave-front distortion of femtosecond laser pulses recorded with a Shack-Hartmann analyzer makes it possible to retrieve the nonlinear index of refraction of different glasses and the nonlinear phase shift induced during second-harmonic generation in beta-barium borate (BBO) crystal versus the phase mismatch. It is shown that the nonlinear phase shift induced in a 2-mm-thick BBO crystal allows compensation for up to a 2pi breakup-integral induced in a 4-cm fused-silica glass. The stability of the compensation is reported to be from 10 to 100 GW cm(-2). PMID:15119415
Ionic liquid tunes microemulsion curvature.
Liu, Liping; Bauduin, Pierre; Zemb, Thomas; Eastoe, Julian; Hao, Jingcheng
2009-02-17
Middle-phase microemulsions formed from cationic dioctadecyldimethylammonium chloride (DODMAC), anionic sodium dodecylsulfate (SDS), n-butanol, and n-heptane were studied. An ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), was employed as the electrolyte in the aqueous media instead of inorganic salts usually used in microemulsion formulation. Studies have been carried out as a function of the concentrations of [bmim][BF4], n-butanol, total surfactant (cDODMAC+SDS), and temperature on the phase behavior and the ultralow interfacial tensions in which the anionic component is present in excess in the catanionic film. Ultralow interfacial tension measurements confirmed the formation of middle-phase microemulsions and the necessary conditions for stabilizing middle-phase microemulsions. Electrical conductivity, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments were also performed, indicating that the typical heptane domain size has an average radius of 360 A and the ionic liquid induces softening of the charged catanionic film. Most interestingly, the IL concentration (cIL) is shown to act as an effective interfacial curvature-control parameter, representing a new approach to tuning the formulation of microemulsions and emulsions. The results expand the potential uses of ILs but also point to the design of new ILs that may achieve superefficient control over interfacial and self-assembly systems. PMID:19161325
Magnetophoretic Induction of Root Curvature
NASA Technical Reports Server (NTRS)
Hasenstein, Karl H.
1997-01-01
The last year of the grant period concerned the consolidation of previous experiments to ascertain that the theoretical premise apply not just to root but also to shoots. In addition, we verified that high gradient magnetic fields do not interfere with regular cellular activities. Previous results have established that: (1) intracellular magnetophoresis is possible; and (2) HGMF lead to root curvature. In order to investigate whether HGMF affect the assembly and/or organization of structural proteins, we examined the arrangement of microtubules in roots exposed to HGMF. The cytoskeletal investigations were performed with fomaldehyde-fixed, nonembedded tissue segments that were cut with a vibratome. Microtubules (MTs) were stained with rat anti-yeast tubulin (YOL 1/34) and DTAF-labeled antibody against rat IgG. Microfilaments (MFs) were visualized by incubation in rhodamine-labeled phalloidin. The distribution and arrangement of both components of the cytoskeleton were examined with a confocal microscope. Measurements of growth rates and graviresponse were done using a video-digitizer. Since HGMF repel diamagnetic substances including starch-filled amyloplasts and most The second aspect of the work includes studies of the effect of cytoskeletal inhibitors on MTs and MFs. The analysis of the effect of micotubular inhibitors on the auxin transport in roots showed that there is very little effect of MT-depolymerizing or stabilizing drugs on auxin transport. This is in line with observations that application of such drugs is not immediately affecting the graviresponsiveness of roots.
On the Weyl curvature hypothesis
Stoica, Ovidiu Cristinel
2013-11-15
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity. In previous papers it has been proposed an equivalent form of Einstein’s equation, which extends it and remains valid at an important class of singularities (including in particular the Schwarzschild, FLRW, and isotropic singularities). Here it is shown that if the Big-Bang singularity is from this class, it also satisfies the Weyl curvature hypothesis. As an application, we study a very general example of cosmological models, which generalizes the FLRW model by dropping the isotropy and homogeneity constraints. This model also generalizes isotropic singularities, and a class of singularities occurring in Bianchi cosmologies. We show that the Big-Bang singularity of this model is of the type under consideration, and satisfies therefore the Weyl curvature hypothesis. -- Highlights: •The singularities we introduce are described by finite geometric/physical objects. •Our singularities have smooth Riemann and Weyl curvatures. •We show they satisfy Penrose’s Weyl curvature hypothesis (Weyl=0 at singularities). •Examples: FLRW, isotropic singularities, an extension of Schwarzschild’s metric. •Example: a large class of singularities which may be anisotropic and inhomogeneous.
Spontaneous Curvature of Polymer Brushes
NASA Astrophysics Data System (ADS)
Sheiko, Sergei; da Silva, Marcelo; Shirvaniants, David; Rodrigues, Carlos; Beers, Kathryn; Matyjaszewski, Krzysztof; Potemkin, Igor; Moeller, Martin
2003-03-01
Experimental studies of cylindrical brushes on surfaces revealed peculiar shape of brush molecules with a curved backbone. According to scaling analysis, spontaneous bending of the backbone can be driven by entropic elasticity of the side chains: smaller extension of the chains is attained due to their asymmetric distribution with respect to the backbone. An equilibrium, i.e. spontaneous curvature results from the balance of the elasticity of the side chains and the elasticity of the interface. The curvature is predicted to increase with the side chain length. The system is of general interest because cylindrical brushes confined to a flat surface represent a two-dimensional cross-section of a planar brush grafted on both sides. Here we present systematic studies of cylindrical brushes with different length of the side chains. The curvature of cylindrical brushes confined to a flat substrate was investigated by atomic force microscopy. The method allowed visualization of individual molecules and quantitative analysis of their conformation. In agreement with theory, adsorbed brushes demonstrated spontaneous curvature, however the curvature was shown to decrease with the side chain length.
Membrane curvature at a glance.
McMahon, Harvey T; Boucrot, Emmanuel
2015-03-15
Membrane curvature is an important parameter in defining the morphology of cells, organelles and local membrane subdomains. Transport intermediates have simpler shapes, being either spheres or tubules. The generation and maintenance of curvature is of central importance for maintaining trafficking and cellular functions. It is possible that local shapes in complex membranes could help to define local subregions. In this Cell Science at a Glance article and accompanying poster, we summarize how generating, sensing and maintaining high local membrane curvature is an active process that is mediated and controlled by specialized proteins using general mechanisms: (i) changes in lipid composition and asymmetry, (ii) partitioning of shaped transmembrane domains of integral membrane proteins or protein or domain crowding, (iii) reversible insertion of hydrophobic protein motifs, (iv) nanoscopic scaffolding by oligomerized hydrophilic protein domains and, finally, (v) macroscopic scaffolding by the cytoskeleton with forces generated by polymerization and by molecular motors. We also summarize some of the discoveries about the functions of membrane curvature, where in addition to providing cell or organelle shape, local curvature can affect processes like membrane scission and fusion as well as protein concentration and enzyme activation on membranes. PMID:25774051
Spontaneous curvature of phosphatidic acid and lysophosphatidic acid.
Kooijman, Edgar E; Chupin, Vladimir; Fuller, Nola L; Kozlov, Michael M; de Kruijff, Ben; Burger, Koert N J; Rand, Peter R
2005-02-15
The formation of phosphatidic acid (PA) from lysophosphatidic acid (LPA), diacylglycerol, or phosphatidylcholine plays a key role in the regulation of intracellular membrane fission events, but the underlying molecular mechanism has not been resolved. A likely possibility is that PA affects local membrane curvature facilitating membrane bending and fission. To examine this possibility, we determined the spontaneous radius of curvature (R(0p)) of PA and LPA, carrying oleoyl fatty acids, using well-established X-ray diffraction methods. We found that, under physiological conditions of pH and salt concentration (pH 7.0, 150 mM NaCl), the R(0p) values of PA and LPA were -46 A and +20 A, respectively. Thus PA has considerable negative spontaneous curvature while LPA has the most positive spontaneous curvature of any membrane lipid measured to date. The further addition of Ca(2+) did not significantly affect lipid spontaneous curvature; however, omitting NaCl from the hydration buffer greatly reduced the spontaneous curvature of PA, turning it into a cylindrically shaped lipid molecule (R(0p) of -1.3 x 10(2) A). Our quantitative data on the spontaneous radius of curvature of PA and LPA at a physiological pH and salt concentration will be instrumental in developing future models of biomembrane fission. PMID:15697235
Michel, D. T.; Davis, A. K.; Armstrong, W.; Bahr, R.; Epstein, R.; Goncharov, V. N.; Hohenberger, M.; Igumenshchev, I. V.; Jungquist, R.; Meyerhofer, D. D.; Radha, P. B.; Sangster, T. C.; Sorce, C.; Froula, D. H.
2015-07-08
Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays (> 1 keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (
Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens
NASA Technical Reports Server (NTRS)
Alam, J.; Mendelson, A.
1983-01-01
The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge.
Curvature generation in nematic surfaces
NASA Astrophysics Data System (ADS)
Mostajeran, Cyrus
2015-06-01
In recent years there has been a growing interest in the study of shape formation using modern responsive materials that can be preprogrammed to undergo spatially inhomogeneous local deformations. In particular, nematic liquid crystalline solids offer exciting possibilities in this context. Considerable recent progress has been made in achieving a variety of shape transitions in thin sheets of nematic solids by engineering isolated points of concentrated Gaussian curvature using topological defects in the nematic director field across textured surfaces. In this paper, we consider ways of achieving shape transitions in thin sheets of nematic glass by generation of nonlocalized Gaussian curvature in the absence of topological defects in the director field. We show how one can blueprint any desired Gaussian curvature in a thin nematic sheet by controlling the nematic alignment angle across the surface and highlight specific patterns which present feasible initial targets for experimental verification of the theory.
Cosmic strings with curvature corrections
NASA Astrophysics Data System (ADS)
Boisseau, Bruno; Letelier, Patricio S.
1992-08-01
A generic model of string described by a Lagrangian density that depends on the extrinsic curvature of the string worldsheet is studied. Using a system of coordinates adapted to the string world sheet the equation of motion and the energy-momentum tensor are derived for strings evolving in curved spacetime. We find that the curvature corrections may change the relation between the string energy density and the tension. It can also introduce heat propagation along the string. We also find for the Polyakov as well as Nambu strings with a topological term that the open string end points can travel with a speed less than the velocity of light.
Intrinsically disordered proteins drive membrane curvature
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-01-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures. PMID:26204806
Intrinsically disordered proteins drive membrane curvature
NASA Astrophysics Data System (ADS)
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-07-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures.
Curvature sensors: noise and its propagation.
Kellerer, Aglae
2010-11-01
The signal measured with a curvature sensor is analyzed. At the outset, we derive the required minimum number of sensing elements at the pupil edges, depending on the total number of sensing elements. The distribution of the sensor signal is further characterized in terms of its mean, variance, kurtosis, and skewness. It is established that while the approximation in terms of a Gaussian distribution is correct down to fairly low photon numbers, much higher numbers are required to obtain meaningful sensor measurements for small wavefront distortions. Finally, we indicate a closed expression for the error propagation factor and for the photon-noise-induced Strehl loss. PMID:21045888
Kohmura, Yoshiki; Sawada, Kei; Taguchi, Munetaka; Ishikawa, Tetsuya; Ohigashi, Takuji; Suzuki, Yoshio
2009-03-09
We have devised a method for generating x-ray vortices by using a diffraction pattern from a simple aperture with illumination wave fronts with spherical curvatures. The interferometry visualized the x-ray vortex dipoles by the direct phase measurement. Our interference technique enabled us to sensitively detect and quantitatively measure various phase dislocations on the x-ray wave fronts, providing useful methodologies for beam diagnostics and materials science.
PEAPOD regulates lamina size and curvature in Arabidopsis
White, Derek W. R.
2006-01-01
Although a complex pattern of interspersed cell proliferation and cell differentiation is known to occur during leaf blade development in eudicot plants, the genetic mechanisms coordinating this growth are unclear. In Arabidopsis, deletion of the PEAPOD (PPD) locus increases leaf lamina size and results in dome-shaped rather than flat leaves. Siliques are also altered in shape because of extra lamina growth. The curvature of a Δppd leaf reflects the difference between excess growth of the lamina and a limitation to the extension capacity of its perimeter. Excess lamina growth in Δppd plants is due to a prolonged phase of dispersed meristematic cell (DMC) proliferation (for example, the meristemoid and procambium cells that form stomatal stem cells and vascular cells, respectively) during blade development. The PPD locus is composed of two homologous genes, PPD1 and PPD2, which encode plant-specific putative DNA-binding proteins. Overexpression of PPD reduces lamina size by promoting the early arrest of DMC proliferation during leaf and silique development. Therefore, by regulating the arrest of DMC proliferation, the PPD genes coordinate tissue growth, modulate lamina size, and limit curvature of the leaf blade. I propose a revised model of leaf development with two cell-cycle arrest fronts progressing from the tip to the base: the known primary front, which determines arrest of general cell proliferation, followed by a secondary front that involves PPD and arrests DMC division. PMID:16916932
Monomeric Synucleins Generate Membrane Curvature*
Westphal, Christopher H.; Chandra, Sreeganga S.
2013-01-01
Synucleins are a family of presynaptic membrane binding proteins. α-Synuclein, the principal member of this family, is mutated in familial Parkinson disease. To gain insight into the molecular functions of synucleins, we performed an unbiased proteomic screen and identified synaptic protein changes in αβγ-synuclein knock-out brains. We observed increases in the levels of select membrane curvature sensing/generating proteins. One of the most prominent changes was for the N-BAR protein endophilin A1. Here we demonstrate that the levels of synucleins and endophilin A1 are reciprocally regulated and that they are functionally related. We show that all synucleins can robustly generate membrane curvature similar to endophilins. However, only monomeric but not tetrameric α-synuclein can bend membranes. Further, A30P α-synuclein, a Parkinson disease mutant that disrupts protein folding, is also deficient in this activity. This suggests that synucleins generate membrane curvature through the asymmetric insertion of their N-terminal amphipathic helix. Based on our findings, we propose to include synucleins in the class of amphipathic helix-containing proteins that sense and generate membrane curvature. These results advance our understanding of the physiological function of synucleins. PMID:23184946
NASA Astrophysics Data System (ADS)
Han, Yue; Cai, Guo-Biao; Xu, Xu; Renou, Bruno; Boukhalfa, Abdelkrim
2014-05-01
A novel approach to extract flame fronts, which is called the conditioned level-set method with block division (CLSB), has been developed. Based on a two-phase level-set formulation, the conditioned initialization and region-lock optimization appear to be beneficial to improve the efficiency and accuracy of the flame contour identification. The original block-division strategy enables the approach to be unsupervised by calculating local self-adaptive threshold values autonomously before binarization. The CLSB approach has been applied to deal with a large set of experimental data involving swirl-stabilized premixed combustion in diluted regimes operating at atmospheric pressures. The OH-PLIF measurements have been carried out in this framework. The resulting images are, thus, featured by lower signal-to-noise ratios (SNRs) than the ideal image; relatively complex flame structures lead to significant non-uniformity in the OH signal intensity; and, the magnitude of the maximum OH gradient observed along the flame front can also vary depending on flow or local stoichiometry. Compared with other conventional edge detection operators, the CLSB method demonstrates a good ability to deal with the OH-PLIF images at low SNR and with the presence of a multiple scales of both OH intensity and OH gradient. The robustness to noise sensitivity and intensity inhomogeneity has been evaluated throughout a range of experimental images of diluted flames, as well as against a circle test as Ground Truth (GT).
2016-01-01
This volume contains the proceedings of the Special Topic Conference (STC) of the European Federation for Medical Informatics (EFMI). The organisation of the STC is part of a long tradition of EFMI working groups to organise scientific events focused on important trends in medical informatics and eHealth. In 2016, the special topic is "Transforming Healthcare with the Internet of Things" in relation to the EFMI working group Personal Portable Devices (PPD). STC 2016 takes place in Paris, France, organised by the Laboratoire d'Informatique Médicale et d'Ingénierie des Connaissances en e-Santé (LIMICS) under the auspices of EFMI and the French Association for Medical Informatics (AIM). Only a few years ago, devices were limited to health cards and personal portable devices. Since then, devices have dramatically evolved to include wearables, sensors, and actuators for measuring health values. The application of such technologies in the field of health, social care and wellness has attracted the attention of both patients and members of the general public interested in supporting or improving their health and wellbeing. One of the characteristics of these 'devices' (sometimes too small to observe thanks to nanotechnology) is to be 'connected' and to communicate with other connected devices and systems. This has been the game changer, as it replaces the cumbersome and often error-prone intervention of the human being who was previously necessary to enter data. The Internet of Things (IoT) is thus turning out to have a major impact on the information paradigm in healthcare. The patient can now become their own Chief Operational Officer, as described by Eric Topol in his recent book The Patient will see you now
A novel curvature-controllable steerable needle for percutaneous intervention.
Bui, Van Khuyen; Park, Sukho; Park, Jong-Oh; Ko, Seong Young
2016-08-01
Over the last few decades, flexible steerable robotic needles for percutaneous intervention have been the subject of significant interest. However, there still remain issues related to (a) steering the needle's direction with less damage to surrounding tissues and (b) increasing the needle's maximum curvature for better controllability. One widely used approach is to control the fixed-angled bevel-tip needle using a "duty-cycle" algorithm. While this algorithm has shown its applicability, it can potentially damage surrounding tissue, which has prevented the widespread adoption of this technology. This situation has motivated the development of a new steerable flexible needle that can change its curvature without axial rotation, while at the same time producing a larger curvature. In this article, we propose a novel curvature-controllable steerable needle. The proposed robotic needle consists of two parts: a cannula and a stylet with a bevel-tip. The curvature of the needle's path is controlled by a control offset, defined by the offset between the bevel-tip and the cannula. As a result, the necessity of rotating the whole needle's body is decreased. The duty-cycle algorithm is utilized to a limited degree to obtain a larger radius of curvature, which is similar to a straight path. The first prototype of 0.46 mm (outer diameter) was fabricated and tested with both in vitro gelatin phantom and ex vivo cow liver tissue. The maximum curvatures measured 0.008 mm(-1) in 6 wt% gelatin phantom, 0.0139 mm(-1) in 10 wt% gelatin phantom, and 0.0038 mm(-1) in cow liver. The experimental results show a linear relationship between the curvature and the control offset, which can be utilized for future implementation of this control algorithm. PMID:27206444
Space Curvature and the "Heavy Banana 'Paradox.'"
ERIC Educational Resources Information Center
Gruber, Ronald P.; And Others
1991-01-01
Two ways to visually enhance the concept of space curvature are described. Viewing space curvature as a meterstick contraction and the heavy banana "paradox" are discussed. The meterstick contraction is mathematically explained. (KR)
Dynamics of curved fronts in systems with power-law memory
NASA Astrophysics Data System (ADS)
Abu Hamed, M.; Nepomnyashchy, A. A.
2016-08-01
The dynamics of a curved front in a plane between two stable phases with equal potentials is modeled via two-dimensional fractional in time partial differential equation. A closed equation governing a slow motion of a small-curvature front is derived and applied for two typical examples of the potential function. Approximate axisymmetric and non-axisymmetric solutions are obtained.
Nonlinear Sorting, Curvature Generation, and Crowding of Endophilin N-BAR on Tubular Membranes
Zhu, Chen; Das, Sovan L.; Baumgart, Tobias
2012-01-01
The curvature of biological membranes is controlled by membrane-bound proteins. For example, during endocytosis, the sorting of membrane components, vesicle budding, and fission from the plasma membrane are mediated by adaptor and accessory proteins. Endophilin is a peripherally binding membrane protein that functions as an endocytic accessory protein. Endophilin's membrane tubulation capacity is well known. However, to understand the thermodynamic and mechanical aspects of endophilin function, experimental measurements need to be compared to quantitative theoretical models. We present measurements of curvature sorting and curvature generation of the endophilin A1 N-BAR domain on tubular membranes pulled from giant unilamellar vesicles. At low concentration, endophilin functions primarily as a membrane curvature sensor; at high concentrations, it also generates curvature. We determine the spontaneous curvature induced by endophilin and observe sigmoidal curvature/composition coupling isotherms that saturate at high membrane tensions and protein solution concentrations. The observation of saturation is supported by a strong dependence of lateral diffusion coefficients on protein density on the tether membrane. We develop a nonlinear curvature/composition coupling model that captures our experimental observations. Our model predicts a curvature-induced phase transition among two states with varying protein density and membrane curvature. This transition could act as a switch during endocytosis. PMID:22768939
NASA Astrophysics Data System (ADS)
Estep, J. D.; Shaw, J.; Edmonds, D. A.
2015-12-01
Quantifying the progradation of the Wax Lake Delta (WLD), a sub-delta of the Mississippi River Delta, can lend valuable insight into coastal land-building patterns. Previous studies of WLD progradation have relied on subaerially-exposed land for indicating delta extent, but an inherent problem with this method lies in the high variability of exposed land due to vegetative, hydrologic, and atmospheric fluctuations. By mapping water surface films observed in remote imagery which form streaklines along flow paths in the delta, we show that the shallow delta front flow patterns are relatively unaffected by short term water level changes and can be used to evaluate WLD progradation over time. Remotely sensed imagery from multiple sources (infrared aerial photography, SPOT, UAVSAR) spanning from 1988 to 2015 was used to map streaklines from which we calculate a flow direction divergence field across the delta. Measuring the translation of this field through time, such as areas containing extreme divergence values along the delta front, quantifies the progradation over the time elapsed. Preliminary measurements of WLD progradation were subdivided into the eastern, southern, and western thirds of the delta. The eastern third prograded at 110 ±20m/yr from 1988 - 1997, 100 ±40m/yr from 1997 - 2002, and then remained relatively constant to 2015. The southern third prograded at 130 ±20m/yr from 1988 - 1997, 200 ±40m/yr from 1997 - 2002, and remained relatively constant to 2015. The western third prograded at 130 ±30m/yr from 1988 - 1997, 220 ±60 m from 1997 - 2002, and then remained relatively constant from 2002 - 2015. Also of note is the retrogradation on the average of 700 ±400m observed from January to August, 1992 which we interpret as being caused by the impact of Hurricane Andrew. The streakline methodology of evaluating WLD progradation could provide new methods for analysis of land change in other deltas around the world.
NASA Technical Reports Server (NTRS)
Ecker, A.; Alexander, J. Iwan D.; Frazier, D. O.
1987-01-01
A holographic technique for the simultaneous measurement of temperature and concentration in solidifying transparent model alloy systems was developed. Its application to the study of the interactions between the temperature, concentration, and fluid flow fields in such systems at 1 g and micro-g conditions is discussed.
NASA Astrophysics Data System (ADS)
Ecker, A.; Alexander, J. Iwan D.; Frazier, D. O.
1987-02-01
A holographic technique for the simultaneous measurement of temperature and concentration in solidifying transparent model alloy systems was developed. Its application to the study of the interactions between the temperature, concentration, and fluid flow fields in such systems at 1 g and micro-g conditions is discussed.
A novel approach in assessment of root canal curvature
Sadeghi, Shiva; Poryousef, Vahideh
2009-01-01
Introduction: The purpose of this in vitro study was to introduce a new method to describe root canal curvatures and to assess the degree of curvature of human permanent mandibular teeth with curved root canals. Materials and Methods: One hundred and thirty five mesial root canals of mandibular first and second molar teeth were selected. Access cavities were prepared. After inserting a K-file size #10 into each canal, radiographs were taken. Canal curvature was determined by measuring the Schneider angle, canal access angle, as well as the canal radius, length, height and curvature starting distance on scanned radiographs using a computerized image processing system. Data was evaluated statistically using Pearson correlation. Results: The mean canal access angle (CAA) and Schneider angle (S) were 8.04◦ (3.46) and 19◦ (6.99), respectively. The Pearson correlation analysis found significant positive correlation between S and CAA (r=0.826, P<0.0001). Negative correlations were found between radius and length (r= –0.4, P<0.0001), radius and Schneider angle (r= –0.4, P<0.0001), radius and CAA (r= –0.24, P=0.004) and CAA and curvature starting distance (r= 0.4, P<0.0001). There was no correlation between height and distance (r=0.013, P=0.789), as well as CAA and height (r=0.654, P=0.001). Conclusion: Under the limitations of this study, the results indicated that the shape of root canal curvature can be more accurately described using two angles, Schneider in combination with Canal access angle. The related parameters included radius, length, distance and height of curvature. [Iranian Endodontic Journal 2009;4(4):131-4] PMID:24019833
SLED phenomenology: curvature vs. volume
NASA Astrophysics Data System (ADS)
Niedermann, Florian; Schneider, Robert
2016-03-01
We assess the question whether the SLED (Supersymmetric Large Extra Dimensions) model admits phenomenologically viable solutions with 4D maximal symmetry. We take into account a finite brane width and a scale invariance (SI) breaking dilaton-brane coupling, both of which should be included in a realistic setup. Provided that the brane tension and the microscopic size of the brane take generic values set by the fundamental bulk Planck scale, we find that either the 4D curvature or the size of the extra dimensions is unacceptably large. Since this result is independent of the dilaton-brane couplings, it provides the biggest challenge to the SLED program.
Almond, P. M.; Kaplan, D. I.; Langton, C. A.; Stefanko, D. B.; Spencer, W. A.; Hatfield, A.; Arai, Y.
2012-08-23
The objective of this work was to develop and evaluate a series of methods and validate their capability to measure differences in oxidized versus reduced saltstone. Validated methods were then applied to samples cured under field conditions to simulate Performance Assessment (PA) needs for the Saltstone Disposal Facility (SDF). Four analytical approaches were evaluated using laboratory-cured saltstone samples. These methods were X-ray absorption spectroscopy (XAS), diffuse reflectance spectroscopy (DRS), chemical redox indicators, and thin-section leaching methods. XAS and thin-section leaching methods were validated as viable methods for studying oxidation movement in saltstone. Each method used samples that were spiked with chromium (Cr) as a tracer for oxidation of the saltstone. The two methods were subsequently applied to field-cured samples containing chromium to characterize the oxidation state of chromium as a function of distance from the exposed air/cementitious material surface.
NASA Astrophysics Data System (ADS)
Abeleira, A.; Farmer, D.; Fischer, E. V.; Pollack, I. B.; Zaragoza, J.
2015-12-01
Authors: Ilana Pollock1,2, Jake Zaragoza2, Emily V. Fischer2, Delphine K. Farmer11. Department of Chemistry, Colorado State University, Fort Collins, CO 2. Department of Atmospheric Science, Colorado State University, Fort Collins, CO During summer months, the Northern Front Range Metropolitan Area (NFRMA) of Colorado consistently violates the 75 ppbv 8-hour EPA National Ambient Air Quality Standard (NAAQS) for ambient ozone (O3), despite continued reduction in anthropogenic emissions. The region has been deemed an O3 non-attainment zone since 2008. Ground-level O3 is produced from photochemical catalytic cycles involving OH radicals, volatile organic compounds (VOCs), and NOx (NO + NO2). VOC emissions in the NFRMA are dominated by anthropogenic sources and influenced by biogenic and agricultural sources, while NOx emissions are mainly from automobile exhaust. A growing concern in the region is the role of oil and natural gas (ONG) on VOC concentrations and the potential for O3 production. Increases in local VOC emissions will likely cause subsequent increase in local O3 concentrations as PO3 increases in a region that is already affected by high O3episodes. As a part of the SONGNEX 2015 (Shale Oil and Natural Gas Nexus) campaign, we measured a broad suite of speciated VOCs during two 8-week deployments (March-May 2015, July-September 2015) at the Boulder Atmospheric Observatory in Erie, CO. VOC measurements were made with a custom-online multichannel gas chromatography system (50+ compounds hourly), along with measurements of O3, SO2, NOx, NOy, PAN, CO, CO2, and CH4. We use these data to investigate the role of different VOC sources, and ONG in particular, in contributing to VOC reactivity and thus instantaneous O3 production. Preliminary analysis of the Spring VOC data indicates that VOC reactivity is dominated by light alkanes typical of ONG emissions - specifically propane, consistent with previous winter-time studies. We will use the observed temperature
Femoral condyle curvature is correlated with knee walking kinematics in ungulates.
Sylvester, Adam D
2015-12-01
The knee has been the focus of many studies linking mammalian postcranial form with locomotor behaviors and animal ecology. A more difficult task has been linking joint morphology with joint kinematics during locomotor tasks. Joint curvature represents one opportunity to link postcranial morphology with walking kinematics because joint curvature develops in response to mechanical loading. As an initial examination of mammalian knee joint curvature, the curvature of the medial femoral condyle was measured on femora representing 11 ungulate species. The position of a region of low curvature was measured using a metric termed the "angle to low curvature". This low-curvature region is important because it provides the greatest contact area between femoral and tibial condyles. Kinematic knee angles during walking were derived from the literature and kinematic knee angles across the gait cycle were correlated with angle to low curvature values. The highest correlation between kinematic knee angle and the angle to low curvature metric occurred at 20% of the walking gait cycle. This early portion of the walking gait cycle is associated with a peak in the vertical ground reaction force for some mammals. The chondral modeling theory predicts that frequent and heavy loading of particular regions of a joint surface during ontogeny will result in these regions being flatter than the surrounding joint surface. The locations of flatter regions of the femoral condyles of ungulates, and their association with knee angles used during the early stance phase of walking provides support for the chondral modeling theory. PMID:26414648
Effect of curvature on the backscattering from leaves
NASA Technical Reports Server (NTRS)
Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.
1988-01-01
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.
Effect of curvature on the backscattering from a leaf
NASA Technical Reports Server (NTRS)
Sarabandi, K.; Senior, T. B. A.; Ulaby, F. T.
1988-01-01
Using a model previously developed for the backscattering cross section of a planar leaf at X-band frequencies and above, the effect of leaf curvature is examined. For normal incidence on a rectangular section of a leaf curved in one and two dimensions, an integral expression for the backscattered field is evaluated numerically and by a stationary phase approximation, leading to a simple analytical expression for the cross-section reduction produced by the curvature. Numerical results based on the two methods are virtually identical, and in excellent agreement with measured data for rectangular sections of coleus leaves applied to the surfaces of styrofoam cylinders and spheres of different radii.
Focal Length Controllable Ultrasonic Array Transducer with Adjustable Curvature
NASA Astrophysics Data System (ADS)
Kim, Jungsoon; Kim, Moojoon; Ha, Kanglyel
2012-07-01
In the underwater imaging field, the control of the focal length of a transducer is very useful. As one of the control methods, we suggested an ultrasonic array transducer with adjustable curvature by using air pressure. The curvature of the transducer was investigated according to the air pressure level in the back space of the transducer. Concave-, planar-, and convex-type transducers were obtained with different air pressure levels. The acoustic fields of the transducer were measured for different shapes of the radiation surface.
Kinetics for phototropic curvature by etiolated seedlings of Arabidopsis thaliana
NASA Technical Reports Server (NTRS)
Orbovic, V.; Poff, K. L.
1991-01-01
An infrared-imaging system has been used to study the influence of gravity on the kinetics of first positive phototropism. The development of phototropic curvature of etiolated seedlings of Arabidopsis thaliana was measured in the absence of visible radiation. Following a pulse of blue light, stationary seedlings curved to a maximum of approximately 16 degrees about 80 minutes after stimulation. The seedlings then curved upward again or straightened by about 6 degrees during the subsequent 100 minutes. Seedlings rotated on a clinostat reached a similar maximum curvature following photostimulation. These seedlings maintained that curvature for 30 to 40 minutes before subsequently straightening to the same extent as the stationary seedlings. It is concluded that straightening is not a consequence of gravitropism, although gravity has some effect on the phototropism kinetics.
Exploiting cantilever curvature for noise reduction in atomic force microscopy.
Labuda, Aleksander; Grütter, Peter H
2011-01-01
Optical beam deflection is a widely used method for detecting the deflection of atomic force microscope (AFM) cantilevers. This paper presents a first order derivation for the angular detection noise density which determines the lower limit for deflection sensing. Surprisingly, the cantilever radius of curvature, commonly not considered, plays a crucial role and can be exploited to decrease angular detection noise. We demonstrate a reduction in angular detection shot noise of more than an order of magnitude on a home-built AFM with a commercial 450 μm long cantilever by exploiting the optical properties of the cantilever curvature caused by the reflective gold coating. Lastly, we demonstrate how cantilever curvature can be responsible for up to 45% of the variability in the measured sensitivity of cantilevers on commercially available AFMs. PMID:21280834
x-y curvature wavefront sensor.
Cagigal, Manuel P; Valle, Pedro J
2015-04-15
In this Letter, we propose a new curvature wavefront sensor based on the principles of optical differentiation. The theoretically modeled setup consists of a diffractive optical mask placed at the intermediate plane of a classical two-lens coherent optical processor. The resulting image is composed of a number of local derivatives of the entrance pupil function whose proper combination provides the wavefront curvature. In contrast to the common radial curvature sensors, this one is able to provide the x and y wavefront curvature maps simultaneously. The sensor offers other additional advantages like having high spatial resolution, adjustable dynamic range, and not being sensitive to misalignment. PMID:25872040
NASA Technical Reports Server (NTRS)
Bagshaw, S. L.; Cleland, R. E.
1990-01-01
Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates could be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower (Helianthus annuus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.
Flame front geometry in premixed turbulent flames
Shepherd, I.G.; Ashurst, W.T.
1991-12-01
Experimental and numerical determinations of flame front curvature and orientation in premixed turbulent flames are presented. The experimental data is obtained from planar, cross sectional images of stagnation point flames at high Damkoehler number. A direct numerical simulation of a constant energy flow is combined with a zero-thickness, constant density flame model to provide the numerical results. The computational domain is a 32{sup 3} cube with periodic boundary conditions. The two-dimensional curvature distributions of the experiments and numerical simulations compare well at similar q{prime}/S{sub L} values with means close to zero and marked negative skewness. At higher turbulence levels the simulations show that the distributions become symmetric about zero. These features are also found in the three dimensional distributions of curvature. The simulations support assumptions which make it possible to determine the mean direction cosines from the experimental data. This leads to a reduction of 12% in the estimated flame surface area density in the middle of the flame brush. 18 refs.
Radius of curvature controlled mirror
Neil, George R.; Rathke, John Wickham; Schultheiss, Thomas John; Shinn, Michelle D.; Dillon-Townes, Lawrence A.
2006-01-17
A controlled radius of curvature mirror assembly comprising: a distortable mirror having a reflective surface and a rear surface; and in descending order from the rear surface; a counter-distortion plate; a flow diverter having a flow diverter aperture at the center thereof; a flow return plate having a flow return aperture at the center thereof; a thermal isolation plate having a thermal isolation plate aperture at the center thereof and a flexible heater having a rear surface and a flexible heater aperture at the center thereof; a double walled tube defining a coolant feed chamber and a coolant return chamber; said coolant feed chamber extending to and through the flow diverter aperture and terminating at the counter-distortion plate and the coolant return chamber extending to and through the thermal isolation backplate and terminating at the flow diverter; and a coolant feed and a coolant return exit at the rear of said flexible heater.
The role of curvature in Diels-Alder functionalization of carbon-based materials.
Willocq, B; Lemaur, V; El Garah, M; Ciesielski, A; Samorì, P; Raquez, J-M; Dubois, Ph; Cornil, J
2016-06-18
We have estimated theoretically the impact of curvature on the free energies of activation and reaction associated with Diels-Alder reactions on carbon-based materials. Significant reduction is observed for both energy values with increasing curvature for core-functionalization, while the opposite trend prevails for edge-functionalization, as further supported by SEM/fluorescence measurements. PMID:27226252
Rapid acceleration of protons upstream of earthward propagating dipolarization fronts
Ukhorskiy, AY; Sitnov, MI; Merkin, VG; Artemyev, AV
2013-01-01
[1] Transport and acceleration of ions in the magnetotail largely occurs in the form of discrete impulsive events associated with a steep increase of the tail magnetic field normal to the neutral plane (Bz), which are referred to as dipolarization fronts. The goal of this paper is to investigate how protons initially located upstream of earthward moving fronts are accelerated at their encounter. According to our analytical analysis and simplified two-dimensional test-particle simulations of equatorially mirroring particles, there are two regimes of proton acceleration: trapping and quasi-trapping, which are realized depending on whether the front is preceded by a negative depletion in Bz. We then use three-dimensional test-particle simulations to investigate how these acceleration processes operate in a realistic magnetotail geometry. For this purpose we construct an analytical model of the front which is superimposed onto the ambient field of the magnetotail. According to our numerical simulations, both trapping and quasi-trapping can produce rapid acceleration of protons by more than an order of magnitude. In the case of trapping, the acceleration levels depend on the amount of time particles stay in phase with the front which is controlled by the magnetic field curvature ahead of the front and the front width. Quasi-trapping does not cause particle scattering out of the equatorial plane. Energization levels in this case are limited by the number of encounters particles have with the front before they get magnetized behind it. PMID:26167430
NASA Astrophysics Data System (ADS)
Belkin, Igor M.; Hunt, George L.; Hazen, Elliott L.; Zamon, Jeannette E.; Schick, Robert S.; Prieto, Rui; Brodziak, Jon; Teo, Steven L. H.; Thorne, Lesley; Bailey, Helen; Itoh, Sachihiko; Munk, Peter; Musyl, Michael K.; Willis, Jay K.; Zhang, Wuchang
2014-09-01
Ocean fronts play a key role in marine ecosystems. Fronts shape oceanic landscapes and affect every trophic level across a wide range of spatio-temporal scales, from meters to thousands of kilometers, and from days to millions of years. At some fronts, there is an elevated rate of primary production, whereas at others, plankton is aggregated by advection and by the behavior of organisms moving against gradients in temperature, salinity, light irradiance, hydrostatic pressure and other physico-chemical and biological factors. Lower trophic level organisms - phytoplankton and zooplankton - that are aggregated in sufficient densities, attract organisms from higher trophic levels, from planktivorous schooling fish to squid, large piscivorous fish, seabirds and marine mammals. Many species have critical portions of their life stages or behaviors closely associated with fronts, including spawning, feeding, ontogenetic development, migrations, and other activities cued to frontal dynamics. At different life stages, an individual species or population might be linked to different fronts. The nature and strength of associations between fronts and biota depend on numerous factors such as the physical nature and spatio-temporal scales of the front and the species and their life stages in question. In other words, fronts support many different niches and micro/macro-habitats over a wide range of spatial and temporal scales.
NASA Astrophysics Data System (ADS)
Blanc, Christophe; Fedorenko, Denys; Gross, Michel; In, Martin; Abkarian, Manouk; Gharbi, Mohamed Amine; Fournier, Jean-Baptiste; Galatola, Paolo; Nobili, Maurizio
2013-08-01
We report theoretical predictions and measurements of the capillary force acting on a spherical colloid smaller than the capillary length that is placed on a curved fluid interface of arbitrary shape. By coupling direct imaging and interferometry, we are able to measure the in situ colloid contact angle and to correlate its position with respect to the interface curvature. Extremely tiny capillary forces down to femtonewtons can be measured with this method. Measurements agree well with a theory relating the capillary force to the gradient of Gaussian curvature and to the mean curvature of the interface prior to colloidal deposition. Numerical calculations corroborate these results.
A METHODOLOGY FOR ANALYZING CURVATURE IN THE DEVELOPING BRAIN FROM PRETERM TO ADULT
PIENAAR, R.; FISCHL, B.; CAVINESS, V.; MAKRIS, N.; GRANT, P. E.
2009-01-01
The character and timing of gyral development is one manifestation of the complex orchestration of human brain development. The ability to quantify these changes would not only allow for deeper understanding of cortical development, but also conceivably allow for improved detection of pathologies. This paper describes a FreeSurfer based image-processing analysis “pipeline” or methodology that inputs an MRI volume, corrects possible contrast defects, creates surface reconstructions, and outputs various curvature-based function analyses. A technique of performing neonate reconstructions using FreeSurfer, which has not been possible previously due to inverted image contrast in pre-myelinated brains, is described. Once surfaces are reconstructed, the analysis component of the pipeline incorporates several surface-based curvature functions found in literature (principle curvatures, Gaussian, mean curvature, “curvedness”, and Willmore Bending Energy). We consider the problem of analyzing curvatures from different sized brains by introducing a Gaussian-curvature based variable-radius filter. Segmented volume data is also analyzed for folding measures: a gyral folding index (gyrification-white index GWI), and a gray-white matter junction folding index (WMF). A very simple curvature-based classifier is proposed that has the potential to discriminate between certain classes of subjects. We also present preliminary results of this curvature analysis pipeline on nine neonate subjects (30.4 weeks through 40.3 weeks Corrected Gestational Age), 3 children (2, 3, and 7 years) and 3 adults (33, 37, and 39 years). Initial results demonstrate that curvature measures and functions across our subjects peaked at term, with a gradual decline through early childhood and further decline continuing through to adults. We can also discriminate older neonates, children, and adults based on curvature analysis. Using a variable radius Gaussian-curvature filter, we also observed that the
Igor Kaganovich
2000-12-18
Negative ions tend to stratify in electronegative plasmas with hot electrons (electron temperature Te much larger than ion temperature Ti, Te > Ti ). The boundary separating a plasma containing negative ions, and a plasma, without negative ions, is usually thin, so that the negative ion density falls rapidly to zero-forming a negative ion density front. We review theoretical, experimental and numerical results giving the spatio-temporal evolution of negative ion density fronts during plasma ignition, the steady state, and extinction (afterglow). During plasma ignition, negative ion fronts are the result of the break of smooth plasma density profiles during nonlinear convection. In a steady-state plasma, the fronts are boundary layers with steepening of ion density profiles due to nonlinear convection also. But during plasma extinction, the ion fronts are of a completely different nature. Negative ions diffuse freely in the plasma core (no convection), whereas the negative ion front propagates towards the chamber walls with a nearly constant velocity. The concept of fronts turns out to be very effective in analysis of plasma density profile evolution in strongly non-isothermal plasmas.
Variation and Heritability in Hair Diameter and Curvature in an Australian Twin Sample.
Ho, Yvonne Y W; Brims, Mark; McNevin, Dennis; Spector, Timothy D; Martin, Nicholas G; Medland, Sarah E
2016-08-01
Hair diameter and curvature are two characteristics of human scalp hair used in forensic contexts. While previous data show that subjective categorization of hair curvature is highly heritable, the heritability of objectively measured curvature and diameter, and variability of hair characteristics within each individual have not yet been studied. The present study measured hair diameter and curvature using an optical fiber diameter analyzer in a sample of 2,332 twins and siblings. Heritability was estimated using maximum likelihood structural equation modeling. Results show sex differences in the magnitude of genetic influence for mean diameter and curvature, with the vast majority of the variance accounted for by genetic effects in males (diameter = 86%, curvature = 53%) and females (diameter = 77%, curvature = 61%). The consistency of diameter (variance within an individual) was also highly heritable, but did not show sex limitation, with 68% of the variance accounted for by genetic factors. Moderate phenotypic correlations were seen between diameter and consistency (r = 0.3) but there was little correlation between diameter and curvature (r = -0.13). A bivariate Cholesky analysis was used to estimate the genetic and environmental correlations between hair diameter and consistency, yielding genetic correlations of r gF = 0.27 for females and r gM = 0.25 for males. PMID:27291867
Gao, Dengliang
2013-03-01
In 3D seismic interpretation, curvature is a popular attribute that depicts the geometry of seismic reflectors and has been widely used to detect faults in the subsurface; however, it provides only part of the solutions to subsurface structure analysis. This study extends the curvature algorithm to a new curvature gradient algorithm, and integrates both algorithms for fracture detection using a 3D seismic test data set over Teapot Dome (Wyoming). In fractured reservoirs at Teapot Dome known to be formed by tectonic folding and faulting, curvature helps define the crestal portion of the reservoirs that is associated with strong seismic amplitude and high oil productivity. In contrast, curvature gradient helps better define the regional northwest-trending and the cross-regional northeast-trending lineaments that are associated with weak seismic amplitude and low oil productivity. In concert with previous reports from image logs, cores, and outcrops, the current study based on an integrated seismic curvature and curvature gradient analysis suggests that curvature might help define areas of enhanced potential to form tensile fractures, whereas curvature gradient might help define zones of enhanced potential to develop shear fractures. In certain fractured reservoirs such as at Teapot Dome where faulting and fault-related folding contribute dominantly to the formation and evolution of fractures, curvature and curvature gradient attributes can be potentially applied to differentiate fracture mode, to predict fracture intensity and orientation, to detect fracture volume and connectivity, and to model fracture networks.
Sebestíková, L
2013-09-01
Buoyantly unstable 3D chemical fronts were seen traveling through an iodate-arsenous acid reaction solution. The experiments were performed in channel reactors with rectangular cross sections, where the top of the reaction solution was in contact with air. A concave or convex meniscus was pinned to reactor lateral walls. Influence of the meniscus shape on front development was investigated. For the concave meniscus, an asymptotic shape of fronts holding negative curvature was observed. On the other hand, fronts propagating in the solution with the convex meniscus kept only positive curvature. Those fronts were also a bit faster than fronts propagating in the solution with the concave meniscus. A relation between the meniscus shape, flow distribution, velocity, and shape is discussed. PMID:24125360
Programming curvature using origami tessellations
NASA Astrophysics Data System (ADS)
Dudte, Levi H.; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L.
2016-05-01
Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures--we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.
Effect of shockwave curvature on run distance observed with a modified wedge test
NASA Astrophysics Data System (ADS)
Lee, Richard; Dorgan, Robert J.; Sutherland, Gerrit; Benedetta, Ashley; Milby, Christopher
2012-03-01
The effect of wave curvature on shock initiation in PBXN-110 was investigated using a modified wedge test configuration. Various widths of PBXN-110 donor slabs were used to define the shockwave curvature introduced to wedge samples of the same explosive. The donor slabs were initiated with line-wave generators so that the shock from the donor would be the same shape, magnitude and duration across the entire input surface of the wedge. The shock parameters were varied for a given donor with PMMA spacers placed between the donor and the wedge sample. A high-speed electronic framing camera was used to observe where initiation occurred along the face of the wedge. Initiation always occurred at the center of the shock front instead of along the sides like that reported by others using a much smaller test format. Results were compared to CTH calculations to indicate if there were effects associated with highly curved shock fronts that could not be adequately predicted. The run distance predicted in CTH for a 50.8 mm wide donor slab (low curvature) compared favorably with experimental results. However, results from thinner donor slabs (higher curvature) indicate a more sensitive behavior than the simulations predicted.
Effect of Shockwave Curvature on Run Distance Observed with a Modified Wedge Test
NASA Astrophysics Data System (ADS)
Lee, Richard; Dorgan, Robert; Sutherland, Gerrit; Benedetta, Ashley; Milby, Christopher
2011-06-01
The effect of wave curvature on shock initiation in PBXN-110 was investigated using a modified wedge test configuration. Various thicknesses of PBXN-110 donor slabs were used to define the shockwave curvature introduced to wedge samples of the same explosive. The donor slabs were initiated with line-wave generators so that the introduced shock would be the same shape, magnitude and duration across the entire input surface of the wedge. The shock parameters were varied for a given donor thickness via different widths of PMMA spacers placed between the donor and the wedge. A framing camera was used to observe where initiation occurred along the face of the wedge. Initiation always occurred at the center of the shock front instead of the sides like that reported by others using a much smaller test format. Results were compared to CTH calculations to indicate if there were effects associated with highly curved shock fronts that could not be adequately predicted. The run distance predicted in CTH for a 50.8 mm thick donor slab (low curvature) compared favorably with experimental results. However, results from thinner donor slabs (higher curvature) indicate a more sensitive behavior than the simulations predicted.
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni; Goldman, Martin; Newman, David; olshevskyi, Vyacheslav; Markidis, Stefano
2016-04-01
Dipolarization fronts (DF) are formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy exchanges [1], particle acceleration [2] and a complex structure and evolution [3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability devel- ops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability with the formation of "fingers" of plasma and embedded magnetic fields. These fingers interact and produce secondary reconnection sites. We present several different diagnostics that prove the existence of these secondary reconnection sites. Each site is surrounded by its own electron diffusion region. At the fronts the ions are generally not magnetized and considerable ion slippage is present. The discovery we present is that electrons are also slipping, forming localized diffusion regions near secondary reconnection sites [1]. The consequence of this discovery is twofold. First, the instability in the fronts has strong energetic implications. We observe that the energy transfer locally is very strong, an order of magnitude stronger than in the "X" line. However, this energy transfer is of both signs as it is natural for a wavy rippling with regions of magnetic to kinetic and regions of kinetic to magnetic energy conversion. Second, and most important for this session, is that MMS should not limit the search for electron diffusion regions to the location marked with X in all reconnection cartoons. Our simulations predict more numerous and perhaps more easily measurable electron diffusion
NASA Technical Reports Server (NTRS)
Morrison, John R.; Sosik, Heidi M.
2003-01-01
Fronts in the coastal ocean describe areas of strong horizontal gradients in both physical and biological properties associated with tidal mixing and freshwater estuarine output (e.g. Simpson, 1981 and O Donnell, 1993). Related gradients in optically important constituents mean that fronts can be observed from space as changes in ocean color as well as sea surface temperature (e.g., Dupouy et al., 1986). This research program is designed to determine which processes and optically important constituents must be considered to explain ocean color variations associated with coastal fronts on the New England continental shelf, in particular the National Ocean Partnership Program (NOPP) Front Resolving Observational Network with Telemetry (FRONT) site. This site is located at the mouth of Long Island sound and was selected after the analysis of 12 years of AVHRR data showed the region to be an area of strong frontal activity (Ullman and Cornillon, 1999). FRONT consists of a network of modem nodes that link bottom mounted Acoustic Doppler Current Profilers (ADCPs) and profiling arrays. At the center of the network is the Autonomous Vertically Profiling Plankton Observatory (AVPPO) (Thwaites et al. 1998). The AVPPO consists of buoyant sampling vehicle and a trawl-resistant bottom-mounted enclosure, which holds a winch, the vehicle (when not sampling), batteries, and controller. Three sampling systems are present on the vehicle, a video plankton recorder, a CTD with accessory sensors, and a suite of bio-optical sensors including Satlantic OCI-200 and OCR-200 spectral radiometers and a WetLabs ac-9 dual path absorption and attenuation meter. At preprogrammed times the vehicle is released, floats to the surface, and is then winched back into the enclosure with power and data connection maintained through the winch cable. Communication to shore is possible through a bottom cable and nearby surface telemetry buoy, equipped with a mobile modem, giving the capability for near
Soliton curvatures of surfaces and spaces
Konopelchenko, B.G.
1997-01-01
An intrinsic geometry of surfaces and three-dimensional Riemann spaces is discussed. In the geodesic coordinates the Gauss equation for two-dimensional Riemann spaces (surfaces) is reduced to the one-dimensional Schr{umlt o}dinger equation, where the Gaussian curvature plays a role of potential. The use of this fact provides an infinite set of explicit expressions for curvature and metric of surface. A special case is governed by the KdV equation for the Gaussian curvature. Integrable dynamics of curvature via the KdV equation, higher KdV equations, and 2+1-dimensional integrable equations with breaking solitons is considered. For a special class of three-dimensional Riemann spaces the relation between metric and scalar curvature is given by the two-dimensional stationary Schr{umlt o}dinger or perturbed string equations. This provides us an infinite family of Riemann spaces with explicit scalar curvature and metric. Particular class of spaces and their integrable evolutions are described by the Nizhnik{endash}Veselov{endash}Novikov equation and its higher analogs. Surfaces and three-dimensional Riemann spaces with large curvature and slow dependence on the variable are considered. They are associated with the Burgers and Kadomtsev{endash}Petviashvili equations, respectively. {copyright} {ital 1997 American Institute of Physics.}
Curvature and torsion in growing actin networks
NASA Astrophysics Data System (ADS)
Shaevitz, Joshua W.; Fletcher, Daniel A.
2008-06-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque.
Magnetic curvature effects on plasma interchange turbulence
NASA Astrophysics Data System (ADS)
Li, B.; Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-01
The magnetic curvature effects on plasma interchange turbulence and transport in the Z-pinch and dipole-like systems are explored with two-fluid global simulations. By comparing the transport levels in the systems with a different magnetic curvature, we show that the interchange-mode driven transport strongly depends on the magnetic geometry. For the system with large magnetic curvature, the pressure and density profiles are strongly peaked in a marginally stable state and the nonlinear evolution of interchange modes produces the global convective cells in the azimuthal direction, which lead to the low level of turbulent convective transport.
Sequence-dependent DNA curvature and flexibility from scanning force microscopy images.
Scipioni, Anita; Anselmi, Claudio; Zuccheri, Giampaolo; Samori, Bruno; De Santis, Pasquale
2002-01-01
This paper reports a study of the sequence-dependent DNA curvature and flexibility based on scanning force microscopy (SFM) images. We used a palindromic dimer of a 1878-bp pBR322 fragment and collected a large pool of SFM images. The curvature of each imaged chain was measured in modulus and direction. It was found that the ensemble curvature modulus does not allow the separation of static and dynamic contributions to the curvature, whereas the curvature, when its direction in the two dimensions is taken into account, permits the direct separation of the intrinsic curvature contributions static and dynamic contributions. The palindromic symmetry also acted as an internal gauge of the validity of the SFM images statistical analysis. DNA static curvature resulted in good agreement with the predicted sequence-dependent intrinsic curvature. Furthermore, DNA sequence-dependent flexibility was found to correlate with the occurrence of A.T-rich dinucleotide steps along the chain and, in general, with the normalized basepair stacking energy distribution. PMID:12414677
The role of the epidermis and cortex in gravitropic curvature of maize roots
NASA Technical Reports Server (NTRS)
Bjorkman, T.; Cleland, R. E.
1988-01-01
In order to determine the role of the epidermis and cortex in gravitropic curvature of seedling roots of maize (Zea mays L. cv. Merit), the cortex on the two opposite flanks was removed from the meristem through the growing zone; gravitropic curvature was measured with the roots oriented horizontally with the cut flanks either on the upper and lower side, or on the lateral sides as a wound control. Curvature was slower in both these treatments (53 degrees in 5 h) than in intact roots (82 degrees), but there was no difference between the two orientations in extent and rate of curvature, nor in the latent time, showing that epidermis and cortex were not the site of action of the growth-regulating signal. The amount of cortex removed made no difference in the extent of curvature. Curvature was eliminated when the endodermis was damaged, raising the possibility that the endodermis or the stele-cortex interface controls gravitropic curvature in roots. The elongation rate of roots from which just the epidermis had been peeled was reduced by 0.01 mM auxin (indole-3-acetic acid) from 0.42 to 0.27 mm h-1, contradicting the hypothesis that only the epidermis responds to changes in auxin activity during gravistimulation. These observations indicate that gravitropic curvature in maize roots is not driven by differential cortical cell enlargement, and that movement of growth regulator(s) from the tip to the elongating zone is unlikely to occur in the cortex.
Anisotropic Membrane Curvature Sensing by Amphipathic Peptides.
Gómez-Llobregat, Jordi; Elías-Wolff, Federico; Lindén, Martin
2016-01-01
Many proteins and peptides have an intrinsic capacity to sense and induce membrane curvature, and play crucial roles for organizing and remodeling cell membranes. However, the molecular driving forces behind these processes are not well understood. Here, we describe an approach to study curvature sensing by simulating the interactions of single molecules with a buckled lipid bilayer. We analyze three amphipathic antimicrobial peptides, a class of membrane-associated molecules that specifically target and destabilize bacterial membranes, and find qualitatively different sensing characteristics that would be difficult to resolve with other methods. Our findings provide evidence for direction-dependent curvature sensing mechanisms in amphipathic peptides and challenge existing theories of hydrophobic insertion. The buckling approach is generally applicable to a wide range of curvature-sensing molecules, and our results provide strong motivation to develop new experimental methods to track position and orientation of membrane proteins. PMID:26745422
Gravitropic basis of leaf blade nastic curvatures
NASA Technical Reports Server (NTRS)
Hayes, A. B.
1982-01-01
The curvatures produced in leaf blades by auxin treatment have been described as nastic curvatures because the initial differential growth is always enhanced on the lower side, regardless of the side of application. It is now known, however, that blades can show differential growth of either the upper or the lower side depending on the conditions of treatment. The dorsiventrality of the blade therefore influences but does not limit the direction of curvature. The dorsiventral directionality of response to growth regulators and the response to changes in the orientation to gravity are seen as indicating that blade curvatures are analogous to negative or positive gravitropism. It is noted that neither blade hyponasty or epinasty can be accounted for by ethylene alone. Petiole responses, however, are not directional, and the leaf angle changes induced by rotation or auxin treatment can be accounted for by ethylene production.
Visually discerning the curvature of the Earth.
Lynch, David K
2008-12-01
Reports and photographs claiming that visual observers can detect the curvature of the Earth from high mountains or high-flying commercial aircraft are investigated. Visual daytime observations show that the minimum altitude at which curvature of the horizon can be detected is at or slightly below 35,000 ft, providing that the field of view is wide (60 degrees ) and nearly cloud free. The high-elevation horizon is almost as sharp as the sea-level horizon, but its contrast is less than 10% that of the sea-level horizon. Photographs purporting to show the curvature of the Earth are always suspect because virtually all camera lenses project an image that suffers from barrel distortion. To accurately assess curvature from a photograph, the horizon must be placed precisely in the center of the image, i.e., on the optical axis. PMID:19037349
Radius of Curvature of the Cornea--An Experiment for the Life-Science Physics Lab
ERIC Educational Resources Information Center
MacLatchy, C. S.
1978-01-01
Presents a quantitative laboratory experiment in geometrical optics. It involves the student in the measurement of the radius of curvature of the cornea and is based on an old method devised by Kohlrausch in 1839. (Author/GA)
Induced gravity from curvature density preserving diffeomorphisms
NASA Astrophysics Data System (ADS)
Oda, Ichiro
2016-08-01
We construct not only an induced gravity model with restricted diffeomorphisms, that is, transverse diffeomorphisms that preserve the curvature density, but also with full diffeomorphisms. By solving the equations of motion, it turns out that these models produce Einstein's equations with a certain Newton constant in addition to the constraint for the curvature density. In the limit of the infinite Newton constant, the models give rise to induced gravity. Moreover, we discuss cosmological solutions on the basis of the gravitational models at hand.
Curvature tensors unified field equations on SEXn
NASA Astrophysics Data System (ADS)
Chung, Kyung Tae; Lee, Il Young
1988-09-01
We study the curvature tensors and field equations in the n-dimensional SE manifold SEXn. We obtain several basic properties of the vectors S λ and U λ and then of the SE curvature tensor and its contractions, such as a generalized Ricci identity, a generalized Bianchi identity, and two variations of the Bianchi identity satisfied by the SE Einstein tensor. Finally, a system of field equations is discussed in SEXn and one of its particular solutions is constructed and displayed.
The role of curvature in entanglement
NASA Astrophysics Data System (ADS)
Buck, Gregory
2015-10-01
Which tangles more readily: curly hair or straight hair? A perhaps natural thought, supported by some theoretical evidence, is to associate curvature and entanglement, and assume that they would grow together-that an increase in one fosters an increase in the other. However we have biological examples such as DNA in the chromosome, and mechanical examples such as coiled telephone cords, in which much more curvature is employed than is required for the packing, and in which tangling is presumably detrimental. We offer a resolution to this conundrum. We show, that at least for simple but generally applicable models, the relationship between curvature and entanglement is subtle: if we keep filament density constant and increase curvature, the entanglement initially increases, passes through a maximum, then decreases, so there is a regime where increasing curvature increases entanglement, and there is also a regime where increasing curvature decreases entanglement. This has implications for filament packing in many circumstances, and in particular for the compaction structure of DNA in the cell-it provides a straightforward argument for the view that one purpose of DNA coiling and supercoiling is to inhibit entanglement. It also tells us to expect that wavy hair-neither the straightest nor the curliest-tangles most readily.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-08-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
Cosmological attractor models and higher curvature supergravity
NASA Astrophysics Data System (ADS)
Cecotti, Sergio; Kallosh, Renata
2014-05-01
We study cosmological α-attractors in superconformal/supergravity models, where α is related to the geometry of the moduli space. For α = 1 attractors [1] we present a generalization of the previously known manifestly superconformal higher curvature supergravity model [2]. The relevant standard 2-derivative supergravity with a minimum of two chiral multiplets is shown to be dual to a 4-derivative higher curvature supergravity, where in general one of the chiral superfields is traded for a curvature superfield. There is a degenerate case when both matter superfields become non-dynamical and there is only a chiral curvature superfield, pure higher derivative supergravity. Generic α-models [3] interpolate between the attractor point at α = 0 and generic chaotic inflation models at large α, in the limit when the inflaton moduli space becomes flat. They have higher derivative duals with the same number of matter fields as the original theory or less, but at least one matter multiplet remains. In the context of these models, the detection of primordial gravity waves will provide information on the curvature of the inflaton submanifold of the Kähler manifold, and we will learn if the inflaton is a fundamental matter multiplet, or can be replaced by a higher derivative curvature excitation.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-05-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
Flame front configuration of turbulent premixed flames
Furukawa, Junichi; Maruta, Kaoru; Hirano, Toshisuke
1998-02-01
The present study is performed to explore dependence of the wrinkle scale of propane-air turbulent premixed flames on the characteristics of turbulence in the nonreacting flow, burner size, and mixture ratio. The wrinkle scales are examined and expressed in the frequency distribution of the radii of flame front curvatures. The average wrinkle scale depends not only on the characteristics of turbulence in the nonreacting flow but also on burner diameter and mixture ratio. The average wrinkle scale of a lean propane-air flame is larger than those of the near stoichiometric and rich flames. The smallest wrinkle scale of turbulent premixed flame is in the range of 0.75--1.0 mm, which is much larger than the Kolmogorov scale of turbulence in the nonreacting flow.
Nonlinear diffusion filtering influenced by mean curvature
NASA Astrophysics Data System (ADS)
Kollár, Michal; Mikula, Karol; Čunderlík, Róbert
2016-04-01
The presentation introduces a new nonlinear diffusion filtering method on closed surfaces such as a sphere, ellipsoid or the Earth's surface. Our new model extends the regularized surface Perona-Malik model by including a local extrema detector based on a mean curvature of processed data. The model is thus represented by a nonlinear diffusion equation which filters noise while preserves main edges, local extrema and details important for a correct interpretation of data. We define a surface finite-volume method to approximate numerically the nonlinear parabolic partial differential equation on a closed surface. The closed surface is approximated by a polyhedral surface created by planar triangles representing subdivision of an initial icosahedron grid and we use a piece-wise linear approximation of a solution in space and the backward Euler time discretization. Numerical experiments present nonlinear diffusion filtering of artificial data and real measurements, namely the GOCE satellite observations. They aim to point out a main advantage of the new nonlinear model which, on the contrary of Perona-Malik model, preserves local extremal values of filtered data.
Curvature-tuned preparation of nanoliposomes.
Genç, Rükan; Ortiz, Mayreli; O'Sullivan, Ciara K
2009-11-01
Numerous methods have been reported for the preparation of liposomes, many of which, in addition to requiring time-consuming preparative steps and the use of organic solvents, result in heterogeneous liposome populations of incontrollable size. Taking into consideration the phenomenon of spontaneous vesiculation and the theory of curvature, here we present an extremely rapid and simple, solvent-free method for the preparation of monodisperse solutions of highly stable small unilamellar vesicles using both charged and zwitterionic lipids mixed with lyso-palmitoylphosphatidylcholine, exploiting a combination of a rapid pH change followed by a defined period of equilibration. Various experimental parameters and their interactions were evaluated in terms of their effect on resulting liposome size and shape, as well as on liposome stability and size distribution, with transmission electron microscope imaging being used to visualize the formed liposomes, and photon correlation spectroscopy to obtain statistical data on mean diameter and monodispersity of the liposome population. zeta potential measurements also provided information about the interpretation of vesiculation kinetics and liposome stability. The time interval of pH jump, operation temperature, equilibration time, and lipid type were shown to be the determining factors controlling the size, shape, and monodispersity of the liposomes. Buffer type was also found to be important for the long-term storage of the liposomes. Ongoing work is looking at the application of the developed method for encapsulation of bioactive molecules, such as drugs, genetic materials, and enzymes. PMID:19856992
A kind of wavefront curvature sensor with diffraction grating and application
NASA Astrophysics Data System (ADS)
Shen, Hongbin; Li, Gang; Huang, Fuyu; Liu, Jie; Wang, Yuanbo
2009-11-01
The basic principle of wavefront curvature sensor (WFS) is described, and the strongpoints and shortcomings of traditional schemes are analyzed. As a novel WFS, the wavefront curvature sensor comprising a diffraction grating (DGWFS), which consist a defocus grating and lens, and can measure the light intensity distribution at the two defocused spots simultaneity, has the advantage of realization easily, adjustment expediently, low cost, and so on. The DGWFS has a wide application in astronomy, measurement, laser, optical component testing etc. Its principle is analyzed. Two kinds of phase retrieval arithmetics of wavefront curvature sensor are analyzed by comparison. Besides, the latest applications of wavefront curvature sensor are generally presented. Finally a novel method for measurement on solid-state laser thermal lens utilizing DGWFS is presented.
A high-sensitive fiber curvature sensor using twin core fiber-based filter
NASA Astrophysics Data System (ADS)
Yin, G. L.; Lou, S. Q.; Lu, W. L.; Wang, X.
2014-04-01
A high-sensitive fiber curvature sensor is proposed and experimentally demonstrated in a large measurement range by using a twin core fiber (TCF)-based filter as sensor head. Applying the coupled-mode theory and equivalent refractive index model, we theoretically anticipate the "blue shift" of the transmission dips of the TCF-based filter when sensor head is bent. Experimentally, we fabricate an 86.9 mm TCF-based filter with a free spectral range of 49 nm and characterize its curvature performance by measuring the wavelength shift. A nonlinear "blue shift" of the wavelength is observed when we increase the curvature. The relationship between wavelength shift and curvature is a second-order polynomial function. In the range from 0 to 9.30 m-1, the maximum sensitivity is up to -14.7 nm/m-1. The measurement range can be further increased by selecting a shorter TCF.
NASA Technical Reports Server (NTRS)
Lee, J. S.; Evans, M. L.
1990-01-01
We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.
Lee, June S.; Chang, Wha-Kyung; Evans, Michael L.
1990-01-01
We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus. PMID:11537475
Lee, J S; Chang W-K; Evans, M L
1990-01-01
We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus. PMID:11537475
Experimental reconstruction of the Berry curvature in a Floquet Bloch band.
Fläschner, N; Rem, B S; Tarnowski, M; Vogel, D; Lühmann, D-S; Sengstock, K; Weitenberg, C
2016-05-27
Topological properties lie at the heart of many fascinating phenomena in solid-state systems such as quantum Hall systems or Chern insulators. The topology of the bands can be captured by the distribution of Berry curvature, which describes the geometry of the eigenstates across the Brillouin zone. Using fermionic ultracold atoms in a hexagonal optical lattice, we engineered the Berry curvature of the Bloch bands using resonant driving and show a full momentum-resolved measurement of the ensuing Berry curvature. Our results pave the way to explore intriguing phases of matter with interactions in topological band structures. PMID:27230375
Experimental reconstruction of the Berry curvature in a Floquet Bloch band
NASA Astrophysics Data System (ADS)
Fläschner, N.; Rem, B. S.; Tarnowski, M.; Vogel, D.; Lühmann, D.-S.; Sengstock, K.; Weitenberg, C.
2016-05-01
Topological properties lie at the heart of many fascinating phenomena in solid-state systems such as quantum Hall systems or Chern insulators. The topology of the bands can be captured by the distribution of Berry curvature, which describes the geometry of the eigenstates across the Brillouin zone. Using fermionic ultracold atoms in a hexagonal optical lattice, we engineered the Berry curvature of the Bloch bands using resonant driving and show a full momentum-resolved measurement of the ensuing Berry curvature. Our results pave the way to explore intriguing phases of matter with interactions in topological band structures.
Strong curvature effects in Neumann wave problems
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-15
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schroedinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
Hydrophobic surfactant proteins strongly induce negative curvature.
Chavarha, Mariya; Loney, Ryan W; Rananavare, Shankar B; Hall, Stephen B
2015-07-01
The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism. PMID:26153706
Strong curvature effects in Neumann wave problems
NASA Astrophysics Data System (ADS)
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-01
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schrödinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
Confinement for Thin Film on Substrates with Different Geometric Curvatures
NASA Astrophysics Data System (ADS)
Xu, Jie; Chen, Jiao; Xue, Gi
2014-03-01
Molecular chain conformation in thin polymer film on substrates with different geometric curvature was examined using fluorescence non-radiative energy transfer (NRET) spectroscopy. We find that thin film on concave substrate exihibits significant differences in vitrification behavior, in both magnitude and thickness dependence, from the planar film. NRET measured a more compact morphology, while dynamical scanning calorimetry detected an increased glass transition temperature (Tg) for the concave thin film, with respect to bulk film. In contrast to planar film where properties are thickness dependent, polymer concave film shows that its conformation and Tg are solely dependent on curvature radius. Surprisingly, these properties converted back to the bulk values when the substrate was removed, indicating the crucial importance of interaction imposed by the concave hard wall. These spectroscopic data matched perfectly the calorimetric results and provided a new implication to understanding geometric confinement on dynamics.
Stress-induced curvature engineering in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Aksyuk, Vladimir A.; Pardo, Flavio; Bishop, David J.
1999-03-01
Residual stress and stress gradients play an important role in determining equilibrium shape and behavior of various Si surface-micromachined devices under applied loads. This is particularly true for system having large-area plates and long beams where curvature resulting from stress can lead to significant deviations from stress-free shape. To gain better understanding of these properties, we have measured the equilibrium shapes of various structures built on the MCNC MUMPs using an interferometric profiler. The structures were square plates and long beams composed of various combinations of polysilicon an oxide layers. Some of the structures had additional MUMPs metal layer on top, while on others in-house chromium-gold stacks of varying thickness have been deposited. Temperature dependence of the curvature was measured for some plates. We have used these data in conjunction with simple models to significantly improve the performance of our micromachined devices. While for some structures such as large area reflectors the curvature had to be minimized, it could be advantageously exploited by others, for example vertical actuators for self-assembly.
ERIC Educational Resources Information Center
Melnick, Blake
2002-01-01
Shares some of the author's personal experiences from the "front line" to illustrate the potential of computer-supported learning environments. Concludes that technology, if used in conjunction with sound pedagogy, allows students to tep outside the confines of the traditional classroom and school structure and take responsibility for both their…
Nanoparticle Oscillations and Fronts
Lagzi, Istvan; Kowalczyk, Bartlomiej; Wang, Dawei; Grzybowski, Bartosz A.
2010-09-30
Chemical oscillations can be coupled to the dynamic self-assembly of nanoparticles. Periodic pH changes translate into protonation and deprotonation of the ligands that stabilize the nanoparticles, thus altering repulsive and attractive interparticle forces. In a continuous stirred-tank reactor, rhythmic aggregation and dispersion is observed; in spatially distributed media, propagation of particle aggregation fronts is seen.
NASA Astrophysics Data System (ADS)
The Front Range Branch of AGU has installed officers for 1990: Ray Noble, National Center for Atmospheric Research, chair; Sherry Oaks, U.S. Geological Survey, chair-elect; Howard Garcia, NOAA, treasurer; Catharine Skokan, Colorado School of Mines, secretary. JoAnn Joselyn of NOAA is past chair. Members at large are Wallace Campbell, NOAA; William Neff, USGS; and Stephen Schneider, NCAR.
Curvature-undulation coupling as a basis for curvature sensing and generation in bilayer membranes.
Bradley, Ryan P; Radhakrishnan, Ravi
2016-08-30
We present coarse-grained molecular dynamics simulations of the epsin N-terminal homology domain interacting with a lipid bilayer and demonstrate a rigorous theoretical formalism and analysis method for computing the induced curvature field in varying concentrations of the protein in the dilute limit. Our theory is based on the description of the height-height undulation spectrum in the presence of a curvature field. We formulated an objective function to compare the acquired undulation spectrum from the simulations to that of the theory. We recover the curvature field parameters by minimizing the objective function even in the limit where the protein-induced membrane curvature is of the same order as the amplitude due to thermal undulations. The coupling between curvature and undulations leads to significant predictions: (i) Under dilute conditions, the proteins can sense a site of spontaneous curvature at distances much larger than their size; (ii) as the density of proteins increases the coupling focuses and stabilizes the curvature field to the site of the proteins; and (iii) the mapping of the protein localization and the induction of a stable curvature is a cooperative process that can be described through a Hill function. PMID:27531962
A new algorithm for evaluating 3D curvature and curvature gradient for improved fracture detection
NASA Astrophysics Data System (ADS)
Di, Haibin; Gao, Dengliang
2014-09-01
In 3D seismic interpretation, both curvature and curvature gradient are useful seismic attributes for structure characterization and fault detection in the subsurface. However, the existing algorithms are computationally intensive and limited by the lateral resolution for steeply-dipping formations. This study presents new and robust volume-based algorithms that evaluate both curvature and curvature gradient attributes more accurately and effectively. The algorithms first instantaneously fit a local surface to seismic data and then compute attributes using the spatial derivatives of the built surface. Specifically, the curvature algorithm constructs a quadratic surface by using a rectangle 9-node grid cell, whereas the curvature gradient algorithm builds a cubic surface by using a diamond 13-node grid cell. A dip-steering approach based on 3D complex seismic trace analysis is implemented to enhance the accuracy of surface construction and to reduce computational time. Applications to two 3D seismic surveys demonstrate the accuracy and efficiency of the new curvature and curvature gradient algorithms for characterizing faults and fractures in fractured reservoirs.
Unfolding the Berry curvature of supercell calculations
NASA Astrophysics Data System (ADS)
Bianco, Raffaello; Resta, Raffaele; Souza, Ivo
2014-03-01
Unfolding band structures of supercell calculations has become a valuable tool for visualizing the influence of point impurities on the electronic states in crystals. In the same spirit, we introduce a procedure which maps the k-space Berry curvature of the occupied states from the small BZ of a supercell onto the normal BZ of the perfect (or virtual) crystal. As an application, we analyze the k-space distribution of the unfolded curvature of bcc Fe1-xCox ordered alloys, to better understand the influence of alloying on the anomalous Hall conductivity. Comparing with the ordinary curvature calculated in the virtual-crystal approximation, we find that the lowering of translational symmetry by the Co ``impurities'' introduces ``extrinsic'' contributions, which correlate with changes in the spectral function near the Fermi surface. In particular, the unfolded curvature displays additional sharp peaks associated with low-energy pseudovertical transitions. These occur in regions of k-space where two unfolded bands, which in the virtual crystal would be separated in k-space (and therefore would not jointly contribute to its Berry curvature), lie on either side of the Fermi level and are coupled by the impurity potential.
Curvature constraints from the causal entropic principle
Bozek, Brandon; Albrecht, Andreas; Phillips, Daniel
2009-07-15
Current cosmological observations indicate a preference for a cosmological constant that is drastically smaller than what can be explained by conventional particle physics. The causal entropic principle (Bousso et al.) provides an alternative approach to anthropic attempts to predict our observed value of the cosmological constant by calculating the entropy created within a causal diamond. We have extended this work to use the causal entropic principle to predict the preferred curvature within the 'multiverse'. We have found that values larger than {rho}{sub k}=40{rho}{sub m} are disfavored by more than 99.99% peak value at {rho}{sub {lambda}}=7.9x10{sup -123} and {rho}{sub k}=4.3{rho}{sub m} for open universes. For universes that allow only positive curvature or both positive and negative curvature, we find a correlation between curvature and dark energy that leads to an extended region of preferred values. Our universe is found to be disfavored to an extent depending on the priors on curvature. We also provide a comparison to previous anthropic constraints on open universes and discuss future directions for this work.
Curvature Sensing by a Viral Scission Protein.
Martyna, Agnieszka; Gómez-Llobregat, Jordi; Lindén, Martin; Rossman, Jeremy S
2016-06-28
Membrane scission is the final step in all budding processes wherein a membrane neck is sufficiently constricted so as to allow for fission and the release of the budded particle. For influenza viruses, membrane scission is mediated by an amphipathic helix (AH) domain in the viral M2 protein. While it is known that the M2AH alters membrane curvature, it is not known how the protein is localized to the center neck of budding virions where it would be able to cause membrane scission. Here, we use molecular dynamics simulations on buckled lipid bilayers to show that the M2AH senses membrane curvature and preferentially localizes to regions of high membrane curvature, comparable to that seen at the center neck of budding influenza viruses. These results were then validated using in vitro binding assays to show that the M2AH senses membrane curvature by detecting lipid packing defects in the membrane. Our results show that the M2AH senses membrane curvature and suggest that the AH domain may localize the protein at the viral neck where it can then mediate membrane scission and the release of budding viruses. PMID:27299375
Lipids, curvature, and nano-medicine*
Mouritsen, Ole G
2011-01-01
The physical properties of the lamellar lipid-bilayer component of biological membranes are controlled by a host of thermodynamic forces leading to overall tensionless bilayers with a conspicuous lateral pressure profile and build-in curvature-stress instabilities that may be released locally or globally in terms of morphological changes. In particular, the average molecular shape and the propensity of the different lipid and protein species for forming non-lamellar and curved structures are a source of structural transitions and control of biological function. The effects of different lipids, sterols, and proteins on membrane structure are discussed and it is shown how one can take advantage of the curvature-stress modulations brought about by specific molecular agents, such as fatty acids, lysolipids, and other amphiphilic solutes, to construct intelligent drug-delivery systems that function by enzymatic triggering via curvature. Practical applications: The simple concept of lipid molecular shape and how it impacts on the structure of lipid aggregates, in particular the curvature and curvature stress in lipid bilayers and liposomes, can be exploited to construct liposome-based drug-delivery systems, e.g., for use as nano-medicine in cancer therapy. Non-lamellar-forming lysolipids and fatty acids, some of which may be designed to be prodrugs, can be created by phospholipase action in diseased tissues thereby providing for targeted drug release and proliferation of molecular entities with conical shape that break down the permeability barrier of the target cells and may hence enhance efficacy. PMID:22164124
Using hilltop curvature to derive the spatial distribution of erosion rates
NASA Astrophysics Data System (ADS)
Hurst, Martin D.; Mudd, Simon M.; Walcott, Rachel; Attal, Mikael; Yoo, Kyungsoo
2012-06-01
Erosion rates dictate the morphology of landscapes, and therefore quantifying them is a critical part of many geomorphic studies. Methods to directly measure erosion rates are expensive and time consuming, whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents. If hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates. In this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high-resolution (1 m) digital elevation data. Published and new cosmogenic radionuclide analyses in the Feather River basin, California, suggest that erosion rates vary by over an order of magnitude (10 to 250 mm kyr-1). Hilltop curvature increases with erosion rates, allowing calibration of the hillslope sediment transport coefficient, which controls the relationship between gradient and sediment flux. Having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature. Additionally, we show that hilltop curvature continues to increase with rising erosion rates after gradient-limited hillslopes have emerged. Hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient, providing soil production on hilltops can keep pace with erosion. Finally, hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels.
Renormalization of curvature elastic constants for elastic and fluid membranes
NASA Astrophysics Data System (ADS)
Ami, S.; Kleinert, H.
1987-02-01
We study the fluctuations of membranes with area and curvature elasticity and calculate the renormalization of the curvature elastic constants due to thermal fluctuations. For the mean curvature elastic constant the result is the same as obtained previously for “ideal membranes” which resist only to curvature deformations. The renormalization of the gaussian curvature, on the other hand, depends on the elastic contants. In an incompressible membrane, it is five times weaker than in an ideal membrane.
Curvature corrections and Kac Moody compatibility conditions
NASA Astrophysics Data System (ADS)
Damour, Thibault; Hanany, Amihay; Henneaux, Marc; Kleinschmidt, Axel; Nicolai, Hermann
2006-10-01
We study possible restrictions on the structure of curvature corrections to gravitational theories in the context of their corresponding Kac Moody algebras, following the initial work on E 10 in Damour and Nicolai [Class Quant Grav 22:2849 (2005)]. We first emphasize that the leading quantum corrections of M-theory can be naturally interpreted in terms of (non-gravity) fundamental weights of E 10. We then heuristically explore the extent to which this remark can be generalized to all over-extended algebras by determining which curvature corrections are compatible with their weight structure, and by comparing these curvature terms with known results on the quantum corrections for the corresponding gravitational theories.
Substrate Curvature Gradient Drives Rapid Droplet Motion
NASA Astrophysics Data System (ADS)
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-01
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces.
Substrate curvature gradient drives rapid droplet motion.
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-11
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces. PMID:25062213
Superintegrable systems on spaces of constant curvature
NASA Astrophysics Data System (ADS)
Gonera, Cezary; Kaszubska, Magdalena
2014-07-01
Construction and classification of two-dimensional (2D) superintegrable systems (i.e. systems admitting, in addition to two global integrals of motion guaranteeing the Liouville integrability, the third global and independent one) defined on 2D spaces of constant curvature and separable in the so-called geodesic polar coordinates are presented. The method proposed is applicable to any value of curvature including the case of Euclidean plane, sphere and hyperbolic plane. The main result is a generalization of Bertrand's theorem on 2D spaces of constant curvature and covers most of the known separable and superintegrable models on such spaces (in particular, the so-called Tremblay-Turbine-Winternitz (TTW) and Post-Winternitz (PW) models which have recently attracted some interest).
Extrinsic and intrinsic curvatures in thermodynamic geometry
NASA Astrophysics Data System (ADS)
Hosseini Mansoori, Seyed Ali; Mirza, Behrouz; Sharifian, Elham
2016-08-01
We investigate the intrinsic and extrinsic curvatures of a certain hypersurface in thermodynamic geometry of a physical system and show that they contain useful thermodynamic information. For an anti-Reissner-Nordström-(A)de Sitter black hole (Phantom), the extrinsic curvature of a constant Q hypersurface has the same sign as the heat capacity around the phase transition points. The intrinsic curvature of the hypersurface can also be divergent at the critical points but has no information about the sign of the heat capacity. Our study explains the consistent relationship holding between the thermodynamic geometry of the KN-AdS black holes and those of the RN (J-zero hypersurface) and Kerr black holes (Q-zero hypersurface) ones [1]. This approach can easily be generalized to an arbitrary thermodynamic system.
On the curvature effect of thin membranes
NASA Astrophysics Data System (ADS)
Wang, Duo; Jiao, Xiangmin; Conley, Rebecca; Glimm, James
2013-01-01
We investigate the curvature effect of a thin, curved elastic interface that separates two subdomains and exerts a pressure due to a curvature effect. This pressure, which we refer to as interface pressure, is similar to the surface tension in fluid mechanics. It is important in some applications, such as the canopy of parachutes, biological membranes of cells, balloons, airbags, etc., as it partially balances a pressure jump between the two sides of an interface. In this paper, we show that the interface pressure is equal to the trace of the matrix product of the curvature tensor and the Cauchy stress tensor in the tangent plane. We derive the theory for interfaces in both 2-D and 3-D, and present numerical discretizations for computing the quality over triangulated surfaces.
35. EAST FRONT OF POWERHOUSE AND CAR BARN: East front ...
35. EAST FRONT OF POWERHOUSE AND CAR BARN: East front of powerhouse and car barn. 'Annex' is right end of building. - San Francisco Cable Railway, Washington & Mason Streets, San Francisco, San Francisco County, CA
9. DETAIL OF INTERIOR OF FRONT PORCH SHOWING FRONT ENTRY ...
9. DETAIL OF INTERIOR OF FRONT PORCH SHOWING FRONT ENTRY (LEFT) AND BLANK WALL (CENTER) CORRESPONDING TO LOCATION OF INTERIOR VAULTS. VIEW TO SOUTHEAST. - Boise Project, Boise Project Office, 214 Broadway, Boise, Ada County, ID
View of portion of the front entry on the front ...
View of portion of the front entry on the front (west) side of the Mueller house, looking northeast. Sheds are in the background. - Ernst Mueller House, 6563 East Avenue, Rancho Cucamonga, San Bernardino County, CA
3. VIEW NORTH, SOUTHWEST FRONT, SOUTHEAST SIDE Front and side ...
3. VIEW NORTH, SOUTHWEST FRONT, SOUTHEAST SIDE Front and side elevation. Note gasoline sign post added. Flush store window not altered, 1900 clapboard siding and panelling remaining. - 510 Central Avenue (Commercial Building), Ridgely, Caroline County, MD
Damage detection for beam-like structures using the normalized curvature of a uniform load surface
NASA Astrophysics Data System (ADS)
Sung, S. H.; Jung, H. J.; Jung, H. Y.
2013-03-01
This paper presents a new vibration-based damage detection method for beam-like structures that uses the normalized uniform load surface (NULS) curvature obtained by modal flexibility. Analytical studies on the NULS curvature method for beam-like structures, which follow Bernoulli-Euler beam theory, have shown that changes in NULS curvature only occur at damaged elements and not at intact ones because the internal forces induced by damage only act on the damaged elements and not on the undamaged elements. Therefore, computing the changes in NULS curvature set indicating only damaged elements at a normalized level is central to the approach. Also, a damage index is proposed based on outlier analysis to account for measurement noise. In order to confirm the feasibility of the proposed method, a cantilever beam and a simply supported beam were numerically investigated for two damage scenarios by using modal parameters obtained by eigenvalue analysis and simulations of an impact test using MATLAB/Simulink. The results showed that the proposed method could accurately localize multiple damage locations as well as single damage locations without any false-positive or false-negative detections. For comparison, damage detection was also conducted using the uniform load surface (ULS) curvature method and the mode shape curvature method. The ULS curvature method clearly identified single damage locations but some missed multiple damage locations. For the mode shape curvature method, it was shown that the false-positive and false-negative detections were performed at several damaged or undamaged locations. The comparison showed that the proposed detection method can more effectively identify single and multiple damage locations than the other two methods. In conclusion, the proposed method performed better in detecting damages than the other two methods in terms of sensitivity to damage regardless of location and robustness against noisy signals generated from calculating the
Scaling of curvature in subcritical gravitational collapse
NASA Astrophysics Data System (ADS)
Garfinkle, David; Duncan, G. Comer
1998-09-01
We perform numerical simulations of the gravitational collapse of a spherically symmetric scalar field. For those data that just barely do not form black holes we find the maximum curvature at the position of the central observer. We find a scaling relation between this maximum curvature and distance from the critical solution. The scaling relation is analogous to that found by Choptuik for the black hole mass for those data that do collapse to form black holes. We also find a periodic wiggle in the scaling exponent.
NASTRAN modifications for recovering strains and curvatures
NASA Technical Reports Server (NTRS)
Hennrich, C. W.
1975-01-01
Modifications to the NASTRAN structural analysis computer program are described. The modifications allow the recovery of strain and curvature data for the general two-dimensional elements, in addition to the usual stress data. Option features allow the transformation of the strain/curvature (or stress) data to a common coordinate system and representation at the grid points of the structural model rather than at the conventional element center locations. Usage information is provided which will allow present users of NASTRAN to easily utilize the new capability.
Modulus stabilization in higher curvature dilaton gravity
NASA Astrophysics Data System (ADS)
Choudhury, Sayantan; Mitra, Joydip; SenGupta, Soumitra
2014-08-01
We propose a framework of modulus stabilization in two brane warped geometry scenario in presence of higher curvature gravity and dilaton in bulk space-time. In the prescribed setup we study various features of the stabilized potential for the modulus field, generated by a bulk scalar degrees of freedom with quartic interactions localized on the two 3-branes placed at the orbifold fixed points. We determine the parameter space for the gravidilaton and Gauss-Bonnet couplings required to stabilize the modulus in such higher curvature dilaton gravity setup.
Instability in bacterial populations and the curvature tensor
NASA Astrophysics Data System (ADS)
Melgarejo, Augusto; Langoni, Laura; Ruscitti, Claudia
2016-09-01
In the geometry associated with equilibrium thermodynamics the scalar curvature Rs is a measure of the volume of correlation, and therefore the singularities of Rs indicates the system instabilities. We explore the use of a similar approach to study instabilities in non-equilibrium systems and we choose as a test example, a colony of bacteria. In this regard we follow the proposal made by Obata et al. of using the curvature tensor for studying system instabilities. Bacterial colonies are often found in nature in concentrated biofilms, or other colony types, which can grow into spectacular patterns visible under the microscope. For instance, it is known that a decrease of bacterial motility with density can promote separation into bulk phases of two coexisting densities; this is opposed to the logistic law for birth and death that allows only a single uniform density to be stable. Although this homogeneous configuration is stable in the absence of bacterial interactions, without logistic growth, a density-dependent swim speed v(ρ) leads to phase separation via a spinodal instability. Thus we relate the singularities in the curvature tensor R to the spinodal instability, that is the appearance of regions of different densities of bacteria.
NASA Astrophysics Data System (ADS)
Marchetto, M.; Baartman, R. A.; Laxdal, R. E.
2014-01-01
The ARIEL project at TRIUMF will greatly expand the variety and availability of radioactive ion beams (RIBs) (Laxdal, Nucl Inst Methods Phys Res B 204:400-409, 2003). The ARIEL front end connects the two ARIEL target stations to the existing ISAC facility to expand delivery to two and eventually three simultaneous RIB beams with up to two simultaneous accelerated beams (Laxdal et al. 2008). The low-energy beam transport lines and mass separators are designed for maximum flexibility to allow a variety of operational modes in order to optimize the radioactive ion beam delivery. A new accelerator path is conceived for high mass delivery from an EBIS charge state breeder. The front-end design utilizes the experience gained in 15 years of ISAC beam delivery.
Soil Moisture, Coastline Curvature, and Sea Breeze Initiated Precipitation Over Florida
NASA Technical Reports Server (NTRS)
Baker, R. David; Lynn, Barry H.; Boone, Aaron; Tao, Wei-Kuo
1999-01-01
Land surface-atmosphere interaction plays a key role in the development of summertime convection and precipitation over the Florida peninsula. Land-ocean temperature contrasts induce sea-breeze circulations along both coasts. Clouds develop along sea-breeze fronts, and significant precipitation can occur during the summer months. However, other factors such as soil moisture distribution and coastline curvature may modulate the timing, location, and intensity of sea breeze initiated precipitation. Here, we investigate the role of soil moisture and coastline curvature on Florida precipitation using the 3-D Goddard Cumulus Ensemble (GCE) cloud model coupled with the Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) land surface model. This study utilizes data from the Convection and Precipitation Electrification Experiment (CaPE) collected on 27 July 1991. Our numerical simulations suggest that a realistic distribution of soil moisture influences the location and intensity of precipitation but not the timing of precipitation. In contrast, coastline curvature affects the timing and location of precipitation but has little influence on peak rainfall rates. However, both factors (soil moisture and coastline curvature) are required to fully account for observed rainfall amounts.
NASA Astrophysics Data System (ADS)
Spence, William
The second regional conference of the Front Range Branch, AGU, was attended by more than 80 professionals and some 20 outstanding high school students. The conference included 2 days of interdisciplinary talks, and lots of discussion, that primarily were keyed to geophysical studies of Colorado, Wyoming, and New Mexico. Other talks reported on nonregional, and sometimes global, studies being done by geophypsicists of the Front Range region.Topics included tectonics of the Front Range and the Colorado Plateau, pollution of the Arkansas and Mississippi rivers, and a supreme polluting event that caused the late-Cretaceous extinctions. Other notable talks were on toxic cleanup, microburst (wind shear) detection at U.S. airports, and other meteorological studies. Several talks treated the audience to the excitement of new work and surprise discoveries. The meeting was multimedia, including the playing of two videos through a projection TV and the playing of a fascinating tape between an airport control tower and incoming pilots during a severe microburst event.
Radiative thermal conduction fronts
NASA Technical Reports Server (NTRS)
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-01-01
The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence.
NASA Astrophysics Data System (ADS)
Weissmann, Haim; Shnerb, Nadav M.; Kessler, David A.
2016-01-01
The properties of a front between two different phases in the presence of a smoothly inhomogeneous external field that takes its critical value at the crossing point is analyzed. Two generic scenarios are studied. In the first, the system admits a bistable solution and the external field governs the rate in which one phase invades the other. The second mechanism corresponds to a continuous transition that, in the case of reactive systems, takes the form of a transcritical bifurcation at the crossing point. We solve for the front shape and for the response of competitive fronts to external noise, showing that static properties and also some of the dynamical features cannot discriminate between the two scenarios. A reliable indicator turns out to be the fluctuation statistics. These take a Gaussian form in the bifurcation case and a double-peaked shape in a bistable system. Our results are discussed in the context of biological processes, such as species and communities dynamics in the presence of a resource gradient.
Radiative thermal conduction fronts
NASA Astrophysics Data System (ADS)
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-07-01
The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence.
Thermodynamics and Mechanics of Membrane Curvature Generation and Sensing by Proteins and Lipids
Baumgart, Tobias; Capraro, Benjamin R.; Zhu, Chen; Das, Sovan L.
2014-01-01
Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations. PMID:21219150
Thermodynamics and Mechanics of Membrane Curvature Generation and Sensing by Proteins and Lipids
NASA Astrophysics Data System (ADS)
Baumgart, Tobias; Capraro, Benjamin R.; Zhu, Chen; Das, Sovan L.
2011-05-01
Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations.
New Model-independent Method to Test the Curvature of the Universe
NASA Astrophysics Data System (ADS)
Yu, H.; Wang, F. Y.
2016-09-01
We propose a new model-independent method to test the cosmic curvature by comparing the proper distance and transverse comoving distance. Using the measurements of the Hubble parameter H(z) and the angular diameter distance d A , the cosmic curvature parameter {{{Ω }}}K is constrained to be ‑0.09 ± 0.19, which is consistent with a flat universe. We also use a Monte Carlo simulation to test the validity and efficiency, and find that our method can give a reliable and efficient constraint on cosmic curvature. Compared with other model-independent methods testing the cosmic curvature, our method can avoid some drawbacks and give a better constraint.
Photon Drag Effect due to Berry Curvature
NASA Astrophysics Data System (ADS)
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-01
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results.
Constraining inverse curvature gravity with supernovae
Mena, Olga; Santiago, Jose; Weller, Jochen; /University Coll., London /Fermilab
2005-10-01
We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.
Photon Drag Effect due to Berry Curvature.
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-19
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results. PMID:27588858
Thermal Fronts in Solar Flares
NASA Astrophysics Data System (ADS)
Karlický, Marian
2015-12-01
We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front.
CURVATURE EFFECT QUANTIFICATION FOR IN-VIVO IR THERMOGRAPHY.
Cheng, Tze-Yuan; Deng, Daxiang; Herman, Cila
2012-01-01
Medical Infrared (IR) Imaging has become an important diagnostic tool over recent years. However, one underlying problem in medical diagnostics is associated with accurate quantification of body surface temperatures. This problem is caused by the artifacts induced by the curvature of objects, which leads to inaccurate temperature mapping and biased diagnostic results. Therefore, in our study, an experiment-based analysis is conducted to address the curvature effects toward the 3D temperature reconstruction of the IR thermography image. For quantification purposes, an isothermal copper plate with flat surface, and a cylindrical metal container filled with water are imaged. For the flat surface, the tilting angle measured from camera axis was varied incrementally from 0° to 60 °, such that the effects of surface viewing angle and travel distance on the measured temperature can be explored. On the cylindrical curved surface, the points viewed from 0° to 90° with respect to the camera axis are simultaneously imaged at different temperature levels. The experimental data obtained for the flat surface indicate that both viewing angle and distance effects become noticeable for angles over 40 °. The travel distance contributes a minor change when compared with viewing angle. The experimental results from the curved surface indicate that the curvature effect becomes pronounced when the viewing angle is larger than 60 °. The measurement error on the curved surface is compared with the simulation using the non-dielectric model, and the normalized temperature difference relative to 0° viewing angle was analyzed at six temperature levels. These results indicate that the linear formula associated with directional emissivity is a reasonable approximation for the measurement error, and the normalized error curves change consistently with viewing angle at various temperatures. Therefore, the analysis in this study implies that the directional emissivity based on the non
Whole field curvature and residual stress determination of silicon wafers by reflectometry
NASA Astrophysics Data System (ADS)
Ng, Chi Seng; Asundi, Anand K.
2011-10-01
Reflectometry, a simple whole-field curvature measurement system using a novel computer aided phase shift reflection grating method has been improved to certain extend. The similar system was developed from our earlier works on Computer Aided Moiré Methods and Novel Techniques in Reflection Moiré, Experimental Mechanics (1994) in which novel structured light approach was shown for surface slope and curvature measurement. This method uses similar technology but coupled with a novel phase shift system to accurately measure surface profile, slope and curvature. In our previous paper, "Stress Measurement of thin wafer using Reflection Grating Method", the surface curvature and residual stresses were evaluated using the versatility of the proposed system.. The curvature of wafers due to the deposition of backside metallization was evaluated and compared with a commercially stress measurement system from KLA-Tencor. In this paper, some aspects of the work are extended. Our proposed system is calibrated using a reference flat mirror and spherical mirror certified by Zygo Corporation. The mirrors together with the camera calibration toolbox allow the system to acquire measurement accuracy that is demanded by semiconductor industry. Finally, the results obtained from Reflectometry are compared and contrast with results from KLA Tencor System.
Conversion of radius of curvature to power (and vice versa)
NASA Astrophysics Data System (ADS)
Wickenhagen, Sven; Endo, Kazumasa; Fuchs, Ulrike; Youngworth, Richard N.; Kiontke, Sven R.
2015-09-01
Manufacturing optical components relies on good measurements and specifications. One of the most precise measurements routinely required is the form accuracy. In practice, form deviation from the ideal surface is effectively low frequency errors, where the form error most often accounts for no more than a few undulations across a surface. These types of errors are measured in a variety of ways including interferometry and tactile methods like profilometry, with the latter often being employed for aspheres and general surface shapes such as freeforms. This paper provides a basis for a correct description of power and radius of curvature tolerances, including best practices and calculating the power value with respect to the radius deviation (and vice versa) of the surface form. A consistent definition of the sagitta is presented, along with different cases in manufacturing that are of interest to fabricators and designers. The results make clear how the definitions and results should be documented, for all measurement setups. Relationships between power and radius of curvature are shown that allow specifying the preferred metric based on final accuracy and measurement method. Results shown include all necessary equations for conversion to give optical designers and manufacturers a consistent and robust basis for decision-making. The paper also gives guidance on preferred methods for different scenarios for surface types, accuracy required, and metrology methods employed.
NASA Astrophysics Data System (ADS)
Keller, Brad M.; Reeves, Anthony P.; Barr, R. Graham; Yankelevitz, David F.; Henschke, Claudia I.
2010-03-01
CT scans allow for the quantitative evaluation of the anatomical bases of emphysema. Recently, a non-density based geometric measurement of lung diagphragm curvature has been proposed as a method for the quantification of emphysema from CT. This work analyzes variability of diaphragm curvature and evaluates the effectiveness of a compensation methodology for the reduction of this variability as compared to emphysema index. Using a dataset of 43 scan-pairs with less than a 100 day time-interval between scans, we find that the diaphragm curvature had a trend towards lower overall variability over emphysema index (95% CI:-9.7 to + 14.7 vs. -15.8 to +12.0), and that the variation of both measures was reduced after compensation. We conclude that the variation of the new measure can be considered comparable to the established measure and the compensation can reduce the apparent variation of quantitative measures successfully.
Variable Curvature Mirrors for ELT Laser Guide Star refocusing systems
NASA Astrophysics Data System (ADS)
Challita, Zalpha; Hugot, Emmanuel; Ferrari, Marc; Madec, Fabrice; Le Mignant, David; Cuby, Jean-Gabriel
2011-09-01
The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, LGS defocusing is one of the system issues that can be tackled using active refocusing mirrors such as Variable Curvature Mirrors (VCM). Indeed, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope, and induces a large defocusing at the LGS wave-front sensor focal plane. To compensate for that, we propose an original concept including a VCM specifically designed to keep a focused spot on the wave-front sensor: the mirror is made of a thin meniscus bend using a pressure applied on its back face. Due to the large defocusing, the LGS-VCM must be able to change its shape from F/12.5 to F/5, leading to more than 1 mm sag. The VCM benefits of a specific shape with a variable radial thickness distribution, allowing keeping an optical quality better than λ/5 over this very large range of deformation. The work presented here details the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Two prototypes have been manufactured to compare the real behaviour of the mirror and the simulations data. Results obtained on the prototypes show that the deformation of the VCM is very close to the simulation, and leads to a realistic concept.
How to calculate normal curvatures of sampled geological surfaces
NASA Astrophysics Data System (ADS)
Bergbauer, Stephan; Pollard, David D.
2003-02-01
Curvature has been used both to describe geological surfaces and to predict the distribution of deformation in folded or domed strata. Several methods have been proposed in the geoscience literature to approximate the curvature of surfaces; however we advocate a technique for the exact calculation of normal curvature for single-valued gridded surfaces. This technique, based on the First and Second Fundamental Forms of differential geometry, allows for the analytical calculation of the magnitudes and directions of principal curvatures, as well as Gaussian and mean curvature. This approach is an improvement over previous methods to calculate surface curvatures because it avoids common mathematical approximations, which introduce significant errors when calculated over sloped horizons. Moreover, the technique is easily implemented numerically as it calculates curvatures directly from gridded surface data (e.g. seismic or GPS data) without prior surface triangulation. In geological curvature analyses, problems arise because of the sampled nature of geological horizons, which introduces a dependence of calculated curvatures on the sample grid. This dependence makes curvature analysis without prior data manipulation problematic. To ensure a meaningful curvature analysis, surface data should be filtered to extract only those surface wavelengths that scale with the feature under investigation. A curvature analysis of the top-Pennsylvanian horizon at Goose Egg dome, Wyoming shows that sampled surfaces can be smoothed using a moving average low-pass filter to extract curvature information associated with the true morphology of the structure.
The influence of pipe organ reed curvature on tone quality.
Plitnik, George R; Angster, Judit
2012-11-01
Although organ flue pipes have been widely studied, the same claim cannot be made for pipe organ reed stops. Given certain design constraints, such as the type of reed stop being voiced and the desired tone quality, the reed voicer must use consummate skill to curve the reed tongue so as to produce the best and most stable tone as well as to guarantee that each pipe blends with its neighbors. The amount and type of curve given to a reed tongue influences not only the harmonic structure of the steady-state sound but also the attack. There are two fundamentally different types of curvature that can be given to a reed tongue, the trompette (chorus reed) curve (which gives a bright sound) and the smooth-toned curve employed for clarinet pipes. This study investigated the effect of reed curvature on the vibration and tone (as assessed by professionals) on reed tongues of both types. Two F2 (8'F, 87.3 Hz) pipes (a trompette and a clarinet) were constructed and voiced with differently curved tongues to produce a variety of tones. The vibration of the reed tongue was measured under typical conditions by laser vibrometer; the pressure waves in the boot and in the shallot were measured by means of one-quarter inch microphones, and the pipe's sound was recorded at the egress. By performing various measurements simultaneously, phase differences were also determined, the extreme sensitivity of tone to reed curvature was demonstrated, and a recently proposed theory of reed vibration was shown to be more accurate than the standard model. PMID:23145630
Crustal thickening drives arc front migration
NASA Astrophysics Data System (ADS)
Karlstrom, L.; Lee, C.; Manga, M.
2012-12-01
The position of active volcanism relative to the trench in arcs depends on melt focusing processes within the mantle wedge and the geometric parameters of subduction. Arc front migration has been observed in relic (Sierra Nevada, Andes) as well as active (Cascades) arcs, sometimes with cycles of retreat and return of the front towards the trench over millions of years. Other arcs, particularly where backarc extension dominates, exhibit a more stationary front in time relative to the trench. In addition, crustal indices of magmatism as measured by the ratio of trace elements La/Yb or isotopes 87}Sr/{86Sr covary with arc front migration (e.g., Haschke et al., 2002). Arc front migration is commonly attributed to variation in dip angle of the downgoing slab, delamination of overthickened crust, or to subduction erosion. Here we present an alternative hypothesis. Assuming mantle wedge melting is a largely temperature-dependant process, the maximum isotherm in the wedge sets arc front location. Isotherm location depends on slab angle, subduction velocity and wedge thermal diffusivity (England and Katz, 2010). It also depends on crustal thickness, which evolves as melt is transferred from the wedge to the crust. Arc front migration can thus occur purely through magmatic thickening of crust. Thickening proceeds through intrusive as well as extrusive volcanism, modulated by tectonics and surface erosion. Migration rate is set by the mantle melt flux into the crust, which decreases as thickening occurs. Thus slab angle need not change, and in the absence of other contribution processes front location and crustal thickness have long-time steady state values. We develop an analytic model of this process that produces migration rates consistent with published data and explains arc fronts that do not move (dominated by extension, such as in the case of intra-oceanic arcs). We present new geochemical and age data from the Peninsular Ranges Batholith that are also consistent with
Myopic aberrations: Simulation based comparison of curvature and Hartmann Shack wavefront sensors
NASA Astrophysics Data System (ADS)
Basavaraju, Roopashree M.; Akondi, Vyas; Weddell, Stephen J.; Budihal, Raghavendra Prasad
2014-02-01
In comparison with a Hartmann Shack wavefront sensor, the curvature wavefront sensor is known for its higher sensitivity and greater dynamic range. The aim of this study is to numerically investigate the merits of using a curvature wavefront sensor, in comparison with a Hartmann Shack (HS) wavefront sensor, to analyze aberrations of the myopic eye. Aberrations were statistically generated using Zernike coefficient data of 41 myopic subjects obtained from the literature. The curvature sensor is relatively simple to implement, and the processing of extra- and intra-focal images was linearly resolved using the Radon transform to provide Zernike modes corresponding to statistically generated aberrations. Simulations of the HS wavefront sensor involve the evaluation of the focal spot pattern from simulated aberrations. Optical wavefronts were reconstructed using the slope geometry of Southwell. Monte Carlo simulation was used to find critical parameters for accurate wavefront sensing and to investigate the performance of HS and curvature sensors. The performance of the HS sensor is highly dependent on the number of subapertures and the curvature sensor is largely dependent on the number of Zernike modes used to represent the aberration and the effective propagation distance. It is shown that in order to achieve high wavefront sensing accuracy while measuring aberrations of the myopic eye, a simpler and cost effective curvature wavefront sensor is a reliable alternative to a high resolution HS wavefront sensor with a large number of subapertures.
Stress compensation for arbitrary curvature control in vanadium dioxide phase transition actuators
NASA Astrophysics Data System (ADS)
Dong, Kaichen; Lou, Shuai; Choe, Hwan Sung; Liu, Kai; You, Zheng; Yao, Jie; Wu, Junqiao
2016-07-01
Due to its thermally driven structural phase transition, vanadium dioxide (VO2) has emerged as a promising material for micro/nano-actuators with superior volumetric work density, actuation amplitude, and repetition frequency. However, the high initial curvature of VO2 actuators severely obstructs the actuation performance and application. Here, we introduce a "seesaw" method of fabricating tri-layer cantilevers to compensate for the residual stress and realize nearly arbitrary curvature control of VO2 actuators. By simply adjusting the thicknesses of the individual layers, cantilevers with positive, zero, or negative curvatures can be engineered. The actuation amplitude can be decoupled from the curvature and controlled independently as well. Based on the experimentally measured residual stresses, we demonstrate sub-micron thick VO2 actuators with nearly zero final curvature and a high actuation amplitude simultaneously. This "seesaw" method can be further extended to the curvature engineering of other microelectromechanical system multi-layer structures where large stress-mismatch between layers are inevitable.
Micron-scale plasma membrane curvature is recognized by the septin cytoskeleton.
Bridges, Andrew A; Jentzsch, Maximilian S; Oakes, Patrick W; Occhipinti, Patricia; Gladfelter, Amy S
2016-04-11
Cells change shape in response to diverse environmental and developmental conditions, creating topologies with micron-scale features. Although individual proteins can sense nanometer-scale membrane curvature, it is unclear if a cell could also use nanometer-scale components to sense micron-scale contours, such as the cytokinetic furrow and base of neuronal branches. Septins are filament-forming proteins that serve as signaling platforms and are frequently associated with areas of the plasma membrane where there is micron-scale curvature, including the cytokinetic furrow and the base of cell protrusions. We report here that fungal and human septins are able to distinguish between different degrees of micron-scale curvature in cells. By preparing supported lipid bilayers on beads of different curvature, we reconstitute and measure the intrinsic septin curvature preference. We conclude that micron-scale curvature recognition is a fundamental property of the septin cytoskeleton that provides the cell with a mechanism to know its local shape. PMID:27044896
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel; Pitoňák, Martin
2016-05-01
In this study we assume that a gravitational curvature tensor, i.e. a tensor of third-order directional derivatives of the Earth's gravitational potential, is observable at satellite altitudes. Such a tensor is composed of ten different components, i.e. gravitational curvatures, which may be combined into vertical-vertical-vertical, vertical-vertical-horizontal, vertical-horizontal-horizontal and horizontal-horizontal-horizontal gravitational curvatures. Firstly, we study spectral properties of the gravitational curvatures. Secondly, we derive new quadrature formulas for the spherical harmonic analysis of the four gravitational curvatures and provide their corresponding analytical error models. Thirdly, requirements for an instrument that would eventually observe gravitational curvatures by differential accelerometry are investigated. The results reveal that measuring third-order directional derivatives of the gravitational potential imposes very high requirements on the accuracy of deployed accelerometers which are beyond the limits of currently available sensors. For example, for orbital parameters and performance similar to those of the GOCE mission, observing third-order directional derivatives requires accelerometers with the noise level of {˜}10^{-17} {m} {s}^{-2} Hz^{-1/2}.
3D Hole Inspection Using Lens with High Field Curvature
NASA Astrophysics Data System (ADS)
Zavyalov, Petr
2015-02-01
One of the actual 3D measurement problems is the optical inspection of various holes. In this respect, the task of plane image formation of holes as extended 3D objects using optical methods turns out to be of primary importance. We have developed specialized lenses that perform such transformations due to specially increased aberrations (field curvature, astigmatism) for the formation of extended objects plane images. The calculations of the lens parameters are presented. The detail analysis of the imaging properties was carried out. The presented hole inspection lens has been designed, constructed and used for inspection of the fuel assembly spacer grids.
Information content in F (R ) brane models with nonconstant curvature
NASA Astrophysics Data System (ADS)
Correa, R. A. C.; Moraes, P. H. R. S.; Dutra, A. de Souza; da Rocha, Roldão
2015-12-01
In this work we investigate the entropic information measure in the context of braneworlds with nonconstant curvature. The braneworld entropic information is studied for gravity modified by the square of the Ricci scalar, besides the usual Einstein-Hilbert term. We showed that the minimum value of the brane configurational entropy provides a stricter bound on the parameter that is responsible for the F (R ) model differing from the Einstein-Hilbert standard one. Our results are moreover consistent to a negative bulk cosmological constant.
2008 ULTRASONIC BENCHMARK STUDIES OF INTERFACE CURVATURE--A SUMMARY
Schmerr, L. W.; Huang, R.; Raillon, R.; Mahaut, S.; Leymarie, N.; Lonne, S.; Spies, M.; Lupien, V.
2009-03-03
In the 2008 QNDE ultrasonic benchmark session researchers from five different institutions around the world examined the influence that the curvature of a cylindrical fluid-solid interface has on the measured NDE immersion pulse-echo response of a flat-bottom hole (FBH) reflector. This was a repeat of a study conducted in the 2007 benchmark to try to determine the sources of differences seen in 2007 between model-based predictions and experiments. Here, we will summarize the results obtained in 2008 and analyze the model-based results and the experiments.
Vectorial detection of sub-microscale capillary curvature by laser beam profile
NASA Astrophysics Data System (ADS)
Verma, Gopal; Singh, Kamal P.
2015-10-01
We demonstrate a simple and non-invasive optical technique to detect direction and magnitude of long-range, sub-microscale capillary curvature of fluid interfaces in various situations. By analyzing magnitude and direction of the distorted spatial profile of the laser beam, following its weak Fresnel's reflection from the air-water interface, ultra-low curvature of 0.1 μm-1 caused by dipped slides, glass tubes, and microscopic twisted silk fibers was measured up to six capillary lengths away from the object. The flexibility of this technique allows us to measure curvature of remotely placed fluid-fluid interfaces and interaction between capillary curves of multiple objects. The high sensitivity of our technique is demonstrated in measuring magnetic susceptibility of water and the full spatial profile of deformation under weak magnetic field. This technique might find applications in precision measurements in optofluidics and interface physics.
Brodsky, Stanley J.; de Teramond, Guy F.; /SLAC /Southern Denmark U., CP3-Origins /Costa Rica U.
2011-01-10
AdS/QCD, the correspondence between theories in a dilaton-modified five-dimensional anti-de Sitter space and confining field theories in physical space-time, provides a remarkable semiclassical model for hadron physics. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The result is a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound state wavefunctions as a function of the invariant mass of the constituents. The hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. Higher Fock states with extra quark-anti quark pairs also arise. The soft-wall model also predicts the form of the nonperturbative effective coupling and its {beta}-function. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method to systematically include QCD interaction terms. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. A method for computing the hadronization of quark and gluon jets at the amplitude level is outlined.
Price, Stephen
2009-01-01
The causes of recent dynamic thinning of Greenland's outlet glaciers have been debated. Realistic simulations suggest that changes at the marine fronts of these glaciers are to blame, implying that dynamic thinning will cease once the glaciers retreat to higher ground. For the last decade, many outlet glaciers in Greenland that terminate in the ocean have accelerated, thinned, and retreated. To explain these dynamic changes, two hypotheses have been discussed. Atmospheric warming has increased surface melting and may also have increased the amount of meltwater reaching the glacier bed, increasing lubrication at the base and hence the rate of glacier sliding. Alternatively, a change in the delicate balance of forces where the glacier fronts meet the ocean could trigger the changes. Faezeh Nick and colleagues5 present ice-sheet modeling experiments that mimic the observations on Helheim glacier, East Greenland, and suggest that the dynamic behaviour of outlet glaciers follows from perturbations at their marine fronts. Greenland's ice sheet loses mass partly through surface melting and partly through fast flowing outlet glaciers that connect the vast plateau of inland ice with the ocean. Earlier ice sheet models have failed to reproduce the dynamic variability exhibited by ice sheets over time. It has therefore not been possible to distinguish with confidence between basal lubrication from surface meltwater and changes at the glaciers' marine fronts as causes for the observed changes on Greenland's outlet glaciers. But this distinction bears directly on future sea-level rise, the raison d'etre of much of modern-day glaciology: If the recent dynamic mass loss Greenland's outlet glaciers is linked to changing atmospheric temperatures, it may continue for as long as temperatures continue to increase. On the other hand, if the source of the dynamic mass loss is a perturbation at the ice-ocean boundary, these glaciers will lose contact with that perturbation after a finite
Curvature Dependence of Hydrophobic Hydration Dynamics
NASA Astrophysics Data System (ADS)
Weiß, R. Gregor; Heyden, Matthias; Dzubiella, Joachim
2015-05-01
We investigate the solute curvature dependence of water dynamics in the vicinity of hydrophobic spherical solutes using molecular dynamics simulations. For both the lateral and perpendicular diffusivity, as well as for H-bond kinetics of water in the first hydration shell, we find a nonmonotonic solute-size dependence, exhibiting extrema close to the well-known structural crossover length scale for hydrophobic hydration. Additionally, we find an apparent anomalous diffusion for water moving parallel to the surface of small solutes, which, however, can be explained by topology effects. Our findings regarding the intimate connection between solute curvature and water dynamics has implications for our understanding of hydration dynamics at heterogeneous biomolecular surfaces.
Cosmological signatures of anisotropic spatial curvature
NASA Astrophysics Data System (ADS)
Pereira, Thiago S.; Mena Marugán, Guillermo A.; Carneiro, Saulo
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Coarse-grained modeling of DNA curvature
NASA Astrophysics Data System (ADS)
Freeman, Gordon S.; Hinckley, Daniel M.; Lequieu, Joshua P.; Whitmer, Jonathan K.; de Pablo, Juan J.
2014-10-01
The interaction of DNA with proteins occurs over a wide range of length scales, and depends critically on its local structure. In particular, recent experimental work suggests that the intrinsic curvature of DNA plays a significant role on its protein-binding properties. In this work, we present a coarse grained model of DNA that is capable of describing base-pairing, hybridization, major and minor groove widths, and local curvature. The model represents an extension of the recently proposed 3SPN.2 description of DNA [D. M. Hinckley, G. S. Freeman, J. K. Whitmer, and J. J. de Pablo, J. Chem. Phys. 139, 144903 (2013)], into which sequence-dependent shape and mechanical properties are incorporated. The proposed model is validated against experimental data including melting temperatures, local flexibilities, dsDNA persistence lengths, and minor groove width profiles.
NASA Astrophysics Data System (ADS)
Libu, M.; Susanth, S.; Vasanthakumari, K. G.; Dileep Kumar, C. J.; Raghu, N.
2012-01-01
Piezoelectric based bimorph mirrors (PBM) find extensive use in focusing of x-ray beams. Many optical instruments require use of PBM whose radii of curvature can be tuned precisely. The 100 mm and 300 mm PBMs were fabricated with varying piezoelectric to fused silica plate thicknesses. The radii of curvature of free standing mirrors were measured as a function of voltage and it was found to decrease with increasing voltage. For a given piezoelectric plate thickness, as the fused silica thickness increases, the radii of curvature was found to increase owing to increase in stiffness of the mirror. On the other hand, for a given fused silica plate thickness, when the piezoelectric plate thickness is increased, the radii of curvature are decreased for a given electric field, due to increase in generated force. This study brings out the influence of piezoceramic to fused silica plate thickness on the radii of curvature of PBM.
Pulse front adaptive optics in multiphoton microscopy
NASA Astrophysics Data System (ADS)
Sun, B.; Salter, P. S.; Booth, M. J.
2016-03-01
The accurate focusing of ultrashort laser pulses is extremely important in multiphoton microscopy. Using adaptive optics to manipulate the incident ultrafast beam in either the spectral or spatial domain can introduce significant benefits when imaging. Here we introduce pulse front adaptive optics: manipulating an ultrashort pulse in both the spatial and temporal domains. A deformable mirror and a spatial light modulator are operated in concert to modify contours of constant intensity in space and time within an ultrashort pulse. Through adaptive control of the pulse front, we demonstrate an enhancement in the measured fluorescence from a two photon microscope.
Transformation optics, curvature and beyond (Conference Presentation)
NASA Astrophysics Data System (ADS)
McCall, Martin W.
2016-04-01
Although the transformation algorithm is very well established and implemented, some intriguing questions remain unanswered. 1) In what precise mathematical sense is the transformation optics algorithm `exact'? The invariance of Maxwell's equations is well understood, but in what sense does the same principle not apply to acoustics (say)? 2) Even if the fields are transformed in a way that apparently mimic vacuum perfectly, it is easy to construct very simple examples where the impedance of the transformed medium is no longer isotropic and homogeneous. This would seem to imply a fundamental shortcoming in any claim that electromagnetic cloaking has been reduced to technology. 3) Transformations are known to exist that introduce a discrepancy between the Poynting vector and the wave-vector. Does this distinction carry any physical significance? We have worked extensively on understanding a commonality between transformation theories that operates at the level of rays - being interpreted as geodesics of an appropriate manifold. At this level we now understand that the *key* problem underlying all attempts to unify the transformational approach to disparate areas of physics is how to relate the transformation of the base metric (be it Euclidean for spatial transformation optics, or Minkowskian for spacetime transformation optics) to the medium parameters of a given physical domain (e.g. constitutive parameters for electromagnetism, bulk modulus and mass density for acoustics, diffusion constant and number density for diffusion physics). Another misconception we will seek to address is the notion of the relationship between transformation optics and curvature. Many have indicated that transformation optics evinces similarities with Einstein's curvature of spacetime. Here we will show emphatically that transformation optics cannot induce curvature. Inducing curvature in an electromagnetic medium requires the equivalent of a gravitational source. We will propose a scheme
Multiple Manifold Clustering Using Curvature Constrained Path
Babaeian, Amir; Bayestehtashk, Alireza; Bandarabadi, Mojtaba
2015-01-01
The problem of multiple surface clustering is a challenging task, particularly when the surfaces intersect. Available methods such as Isomap fail to capture the true shape of the surface near by the intersection and result in incorrect clustering. The Isomap algorithm uses shortest path between points. The main draw back of the shortest path algorithm is due to the lack of curvature constrained where causes to have a path between points on different surfaces. In this paper we tackle this problem by imposing a curvature constraint to the shortest path algorithm used in Isomap. The algorithm chooses several landmark nodes at random and then checks whether there is a curvature constrained path between each landmark node and every other node in the neighborhood graph. We build a binary feature vector for each point where each entry represents the connectivity of that point to a particular landmark. Then the binary feature vectors could be used as a input of conventional clustering algorithm such as hierarchical clustering. We apply our method to simulated and some real datasets and show, it performs comparably to the best methods such as K-manifold and spectral multi-manifold clustering. PMID:26375819
Effects of wall curvature on turbulence statistics
NASA Technical Reports Server (NTRS)
Moser, R. D.; Moin, P.
1985-01-01
A three-dimensional, time-dependent, direct numerical simulation of low-Reynolds number turbulent flow in a mildly curved channel was performed, and the results examined to determine the mechanism by which curvature affects wall-bounded turbulent shear flows. A spectral numerical method with about one-million modes was employed, and no explicit subgrid scale model was used. The effects of curvature on this flow were determined by comparing the concave and convex sides of the channel. The observed effects are consistent with experimental observations for mild curvature. The most significant difference in the turbulence statistics between the concave and convex sides is in the Reynolds shear stress. This is accompanied by significant differences in the terms of the Reynolds shear stress balance equations. In addition, it was found that stationary Taylor-Goertler vortices were present and that they had a significant effect on the flow by contributing to the mean Reynolds shear stress, and by enhancing the difference between the wall shear stresses.
Superintegrable systems on spaces of constant curvature
Gonera, Cezary Kaszubska, Magdalena
2014-07-15
Construction and classification of two-dimensional (2D) superintegrable systems (i.e. systems admitting, in addition to two global integrals of motion guaranteeing the Liouville integrability, the third global and independent one) defined on 2D spaces of constant curvature and separable in the so-called geodesic polar coordinates are presented. The method proposed is applicable to any value of curvature including the case of Euclidean plane, sphere and hyperbolic plane. The main result is a generalization of Bertrand’s theorem on 2D spaces of constant curvature and covers most of the known separable and superintegrable models on such spaces (in particular, the so-called Tremblay–Turbiner–Winternitz (TTW) and Post–Winternitz (PW) models which have recently attracted some interest). -- Highlights: •Classifying 2D superintegrable, separable (polar coordinates) systems on S{sup 2}, R{sup 2}, H{sup 2}. •Construction of radial, angular potentials leading to superintegrability. •Generalization of Bertrand’s theorem covering known models, e.g. Higgs, TTW, PW, and Coulomb.
About Shape of an Interplanetary Shock Front.
NASA Astrophysics Data System (ADS)
Petukhov, Ivan; Petukhov, Stanislav
The form of an interplanetary shock front has been investigated by the statistical method. Results of determination the components of normals to the interplanetary shock fronts obtained from data of ACE experiment during from 1998 to 2003 years (about 200 measurements) are used. North-south asymmetry of shock amount about 15% is revealed. Possibly, it is caused by more activity of the north semi-sphere of the Sun. East-west asymmetry of shock area are obtained. At probability 95% values of asymmetry more 0.53 and less 0.65 at most probability 0.59. Here asymmetry is ratio west part of area to whole area of shock front. Possibly, it is formed at propagation of a shock in interplanetary space. The reason of asymmetry may be self-generation turbulence by the accelerated particles which influences on velocity of shock propagation.
Speed of fast and slow rupture fronts along frictional interfaces
NASA Astrophysics Data System (ADS)
Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Thøgersen, Kjetil; Scheibert, Julien; Malthe-Sørenssen, Anders
2015-07-01
The transition from stick to slip at a dry frictional interface occurs through the breaking of microjunctions between the two contacting surfaces. Typically, interactions between junctions through the bulk lead to rupture fronts propagating from weak and/or highly stressed regions, whose junctions break first. Experiments find rupture fronts ranging from quasistatic fronts, via fronts much slower than elastic wave speeds, to fronts faster than the shear wave speed. The mechanisms behind and selection between these fronts are still imperfectly understood. Here we perform simulations in an elastic two-dimensional spring-block model where the frictional interaction between each interfacial block and the substrate arises from a set of junctions modeled explicitly. We find that material slip speed and rupture front speed are proportional across the full range of front speeds we observe. We revisit a mechanism for slow slip in the model and demonstrate that fast slip and fast fronts have a different, inertial origin. We highlight the long transients in front speed even along homogeneous interfaces, and we study how both the local shear to normal stress ratio and the local strength are involved in the selection of front type and front speed. Last, we introduce an experimentally accessible integrated measure of block slip history, the Gini coefficient, and demonstrate that in the model it is a good predictor of the history-dependent local static friction coefficient of the interface. These results will contribute both to building a physically based classification of the various types of fronts and to identifying the important mechanisms involved in the selection of their propagation speed.
Shocks and cold fronts in galaxy clusters
NASA Astrophysics Data System (ADS)
Markevitch, Maxim; Vikhlinin, Alexey
2007-05-01
The currently operating X-ray imaging observatories provide us with an exquisitely detailed view of the Megaparsec-scale plasma atmospheres in nearby galaxy clusters. At z<0.05, the Chandra's 1 angular resolution corresponds to linear resolution of less than a kiloparsec, which is smaller than some interesting linear scales in the intracluster plasma. This enables us to study the previously unseen hydrodynamic phenomena in clusters: classic bow shocks driven by the infalling subclusters, and the unanticipated “cold fronts,” or sharp contact discontinuities between regions of gas with different entropies. The ubiquitous cold fronts are found in mergers as well as around the central density peaks in “relaxed” clusters. They are caused by motion of cool, dense gas clouds in the ambient higher-entropy gas. These clouds are either remnants of the infalling subclusters, or the displaced gas from the cluster's own cool cores. Both shock fronts and cold fronts provide novel tools to study the intracluster plasma on microscopic and cluster-wide scales, where the dark matter gravity, thermal pressure, magnetic fields, and ultrarelativistic particles are at play. In particular, these discontinuities provide the only way to measure the gas bulk velocities in the plane of the sky. The observed temperature jumps at cold fronts require that thermal conduction across the fronts is strongly suppressed. Furthermore, the width of the density jump in the best-studied cold front is smaller than the Coulomb mean free path for the plasma particles. These findings show that transport processes in the intracluster plasma can easily be suppressed. Cold fronts also appear less prone to hydrodynamic instabilities than expected, hinting at the formation of a parallel magnetic field layer via magnetic draping. This may make it difficult to mix different gas phases during a merger. A sharp electron temperature jump across the best-studied shock front has shown that the electron proton
NASA Astrophysics Data System (ADS)
Corbett, S.; Sklar, L. S.; Davis, J.
2009-12-01
Linkages between form and process are much better understood in soil-mantled landscapes than in bedrock landscapes, despite the wide occurrence of bedrock landscapes in arid and mountainous terrain. Soil-mantled hillslope topography can be characterized by hillslope gradient and its spatial derivative, which is commonly referred to as curvature and defined as the Laplacian of elevation. Surface curvature can also be quantified using techniques that are invariant to the orientation of the surface. These approaches are useful in many geoscience applications, including structural analysis of folded surfaces within deforming crustal blocks. Here we explore the use of surface curvature of bedrock topography as a metric to identify and map distinct geomorphic process regimes in a landscape devoid of soil cover. Our study site is Simpson Creek, a 2.5 km2 watershed on the east flank of Mt. Hillers in the Henry Mountains, Utah, which drains to the Colorado River in Glen Canyon. The land surface is entirely exposed Navajo Sandstone bedrock, with isolated patches of wind-blown sand deposits. The channel network is discontinuous, with alternating reaches of steep, deeply-incised, frequently-potholed slots, and lower-gradient, sand-bedded channels. Hillslope topography is characterized by dome-shaped and sub-linear ridges, and is influenced by prominent structural joints. We calculate two measures of the surface-normal curvature using an ALSM-derived digital elevation model. The mean and Gaussian surface curvatures are the average and product respectively of the magnitudes of the maximum and minimum curvature vectors, obtained by differentiating a polynomial fit at each point in a grid with 1 m spacing. Plots of mean versus Gaussian curvature reveal distinct clusters of landscape elements, which we associate with specific process regimes. In this parameter space, there are four quadrants, classified as dome, basin, synformal saddle and antiformal saddle. The channel and valley
Stable hypersurfaces with zero scalar curvature in Euclidean space
NASA Astrophysics Data System (ADS)
Alencar, Hilário; do Carmo, Manfredo; Neto, Gregório Silva
2016-04-01
In this paper we prove some results concerning stability of hypersurfaces in the four dimensional Euclidean space with zero scalar curvature. First we prove there is no complete stable hypersurface with zero scalar curvature, polynomial growth of integral of the mean curvature, and with the Gauss-Kronecker curvature bounded away from zero. We conclude this paper giving a sufficient condition for a regular domain to be stable in terms of the mean and the Gauss-Kronecker curvatures of the hypersurface and the radius of the smallest extrinsic ball which contains the domain.
Distributed mean curvature on a discrete manifold for Regge calculus
NASA Astrophysics Data System (ADS)
Conboye, Rory; Miller, Warner A.; Ray, Shannon
2015-09-01
The integrated mean curvature of a simplicial manifold is well understood in both Regge Calculus and Discrete Differential Geometry. However, a well motivated pointwise definition of curvature requires a careful choice of the volume over which to uniformly distribute the local integrated curvature. We show that hybrid cells formed using both the simplicial lattice and its circumcentric dual emerge as a remarkably natural structure for the distribution of this local integrated curvature. These hybrid cells form a complete tessellation of the simplicial manifold, contain a geometric orthonormal basis, and are also shown to give a pointwise mean curvature with a natural interpretation as the fractional rate of change of the normal vector.
FACILITY 209, SINGLESTORY DUPLEX, FRONT OBLIQUE VIEW OF FRONT FROM ...
FACILITY 209, SINGLE-STORY DUPLEX, FRONT OBLIQUE VIEW OF FRONT FROM CENTER DRIVE, FACING SW. - U.S. Naval Base, Pearl Harbor, Housing Area 1, Single Story Duplex Type, Bounded by Kamehameha Highway, Plantation Drive, South Avenue, Pearl City, Honolulu County, HI
FACILITY 1042. FRONT OBLIQUE SHOWING ROYAL PALMS LINING FRONT WALK. ...
FACILITY 1042. FRONT OBLIQUE SHOWING ROYAL PALMS LINING FRONT WALK. VIEW FACING SOUTHEAST - U.S. Naval Base, Pearl Harbor, Naval Housing Area Hale Alii, Junior Officers' Quarters Type, 9-10 Hale Alii Avenue, 1-2 Eighth Street, Pearl City, Honolulu County, HI
Determination of curvature and twist of deformed object by digital holographic interferometry
NASA Astrophysics Data System (ADS)
Quan, C.; Chen, W.; Tay, C. J.
2008-11-01
This paper describes a feasibility study of digital holographic interferometry for the measurement of curvature and twist of a deformed object. Measurement of curvature and twist is an important aspect in experimental mechanics. Numerous methods have been proposed to determine the curvature and twist by using digital shearography. We proposed a novel method to determine curvature and twist based on digital holography (DH) and complex phasor (CP). In the conventional methods, phase difference between the first and second states is obtained directly by digital phase subtraction (DPS) and Fourier transform is then employed to extract phase maps. In this study, CP method is proposed to improve the quality of phase maps corresponding to second-order derivatives. Subsequently, sine/cosine transformation and short time Fourier transform (STFT) are employed to process the wrapped phase maps. An experiment is conducted on a clamped circular plate under a point load at centre. The experimental results show that the proposed method is valid and able to obtain high quality phase maps corresponding to curvature and twist of a deformed object.
Numerical analysis of corneal curvature dynamics based on Corvis tonometer images.
Kasprzak, Henryk; Boszczyk, Agnieszka
2016-05-01
The paper presents numerical analysis of corneal curvature distribution, based on Corvis ST images. It was shown that a new approach to analysis of corneal curvature from tonometer images enables a better description and understanding of processes during fast corneal deformation. Ten healthy volunteers participated in nine repeated measurements on one eye. 90 sequences of images were processed with software written in Matlab, with the use of the Image Processing Toolbox. Time-spatial distribution of the local curvature distribution of the corneal profile was obtained for each and every measurement. Some new curvature parameters were proposed and analyzed. A high repeatability for individual subjects was obtained for the proposed parameters. For four of these new parameters, the ICC coefficients were higher than 0.85. The ICC value for the calculated curvature of the cornea before deformation reaches 0.989. Such high repeatability of the proposed new parameters can be useful in examination and differentiation of corneas due to their geometrical and biomechanical properties. PMID:26997615
PIV tracer behavior on propagating shock fronts
NASA Astrophysics Data System (ADS)
Glazyrin, Fyodor N.; Mursenkova, Irina V.; Znamenskaya, Irina A.
2016-01-01
The present work was aimed at the quantitative particle image velocimetry (PIV) measurement of a velocity field near the front of a propagating shock wave and the study of the dynamics of liquid tracers crossing the shock front. For this goal, a shock tube with a rectangular cross-section (48 × 24 mm) was used. The flat shock wave with Mach numbers M = 1.4-2.0 propagating inside the tube channel was studied as well as an expanding shock wave propagating outside the channel with M = 1.2-1.8 at its main axis. The PIV imaging of the shock fronts was carried out with an aerosol of dioctyl sebacate (DEHS) as tracer particles. The pressures of the gas in front of the shock waves studied ranged from 0.013 Mpa to 0.1 MPa in the series of experiments. The processed PIV data, compared to the 1D normal shock theory, yielded consistent values of wake velocity immediately behind the plain shock wave. Special attention was paid to the blurring of the velocity jump on the shock front due to the inertial particle lag and peculiarities of the PIV technique. A numerical algorithm was developed for analysis and correction of the PIV data on the shock fronts, based on equations of particle-flow interaction. By application of this algorithm, the effective particle diameter of the DEHS aerosol tracers was estimated as 1.03 ± 0.12 μm. A number of different formulations for particle drag were tested with this algorithm, with varying success. The results show consistency with previously reported experimental data obtained for cases of stationary shock waves.
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2012-02-16
QCD Hamiltonian 'Light-Front Holography'. Light-Front Holography is in fact one of the most remarkable features of the AdS/CFT correspondence. The Hamiltonian equation of motion in the light-front (LF) is frame independent and has a structure similar to eigenmode equations in AdS space. This makes a direct connection of QCD with AdS/CFT methods possible. Remarkably, the AdS equations correspond to the kinetic energy terms of the partons inside a hadron, whereas the interaction terms build confinement and correspond to the truncation of AdS space in an effective dual gravity approximation. One can also study the gauge/gravity duality starting from the bound-state structure of hadrons in QCD quantized in the light-front. The LF Lorentz-invariant Hamiltonian equation for the relativistic bound-state system is P{sub {mu}}P{sup {mu}}|{psi}(P)> = (P{sup +}P{sup -} - P{sub {perpendicular}}{sup 2})|{psi}(P)> = M{sup 2}|{psi}(P)>, P{sup {+-}} = P{sup 0} {+-} P{sup 3}, where the LF time evolution operator P{sup -} is determined canonically from the QCD Lagrangian. To a first semiclassical approximation, where quantum loops and quark masses are not included, this leads to a LF Hamiltonian equation which describes the bound-state dynamics of light hadrons in terms of an invariant impact variable {zeta} which measures the separation of the partons within the hadron at equal light-front time {tau} = x{sup 0} + x{sup 3}. This allows us to identify the holographic variable z in AdS space with an impact variable {zeta}. The resulting Lorentz-invariant Schroedinger equation for general spin incorporates color confinement and is systematically improvable. Light-front holographic methods were originally introduced by matching the electromagnetic current matrix elements in AdS space with the corresponding expression using LF theory in physical space time. It was also shown that one obtains identical holographic mapping using the matrix elements of the energy-momentum tensor by perturbing
Experimental study of curvature-driven flute instability in the gas-dynamic trap
Ivanov, A.A.; Anikeev, A.V.; Bagryansky, P.A.; Bocharov, V.N.; Deichuli, P.P.; Karpushov, A.N.; Maximov, V.V.; Pod'minogin, A.A.; Rogozin, A.I.; Salikova, T.V.; Tsidulko, Y.A. )
1994-05-01
A curvature-driven flute instability will be excited in the magnetized plasmas if the magnetic field lines curve toward the entire plasma boundary. Conditions under which it can be effectively stabilized in axisymmetric geometry have been experimentally studied in a gas-dynamic trap (GDT) at Novosibirsk. Flexible design of the experimental device and the availability of neutral beams and ion cyclotron heating enabled the pressure-weighted curvature to be varied over a wide range. The stability limits were thus measured and compared with those predicted by the modified Rosenbluth--Longmire criterion. Characteristics of unstable curvature-driven flute modes were also measured and found to conform to a theory including finite ion Larmor radius (FLR) effects. Stable operation during neutral beam injection was achieved with a cusp end cell, resulting in an increase in [ital T][sub [ital e
Influence of wave-front aberrations on bit error rate in inter-satellite laser communications
NASA Astrophysics Data System (ADS)
Yang, Yuqiang; Han, Qiqi; Tan, Liying; Ma, Jing; Yu, Siyuan; Yan, Zhibin; Yu, Jianjie; Zhao, Sheng
2011-06-01
We derive the bit error rate (BER) of inter-satellite laser communication (lasercom) links with on-off-keying systems in the presence of both wave-front aberrations and pointing error, but without considering the noise of the detector. Wave-front aberrations induced by receiver terminal have no influence on the BER, while wave-front aberrations induced by transmitter terminal will increase the BER. The BER depends on the area S which is truncated out by the threshold intensity of the detector (such as APD) on the intensity function in the receiver plane, and changes with root mean square (RMS) of wave-front aberrations. Numerical results show that the BER rises with the increasing of RMS value. The influences of Astigmatism, Coma, Curvature and Spherical aberration on the BER are compared. This work can benefit the design of lasercom system.
Surface properties of ocean fronts
NASA Technical Reports Server (NTRS)
Wolff, P. M.; Hubert, W. E.
1976-01-01
Background information on oceanic fronts is presented and the results of several models which were developed to study the dynamics of oceanic fronts and their effects on various surface properties are described. The details of the four numerical models used in these studies are given in separate appendices which contain all of the physical equations, program documentation and running instructions for the models.
MMS Observations of Dipolarization Fronts
NASA Astrophysics Data System (ADS)
Hwang, K. J.; Goldstein, M. L.; Sibeck, D. G.; Ashour-Abdalla, M.; Nakamura, R.; Burch, J. L.; Torbert, R. B.; Moore, T. E.; Ergun, R. E.; Pollock, C. J.; Mauk, B.; Fuselier, S. A.
2015-12-01
We present MMS observations of dipolarization fronts. Dipolarization fronts commonly observed in Earth's plasma sheet are characterized by intense gradients in the current sheet-normal component of the magnetic field and plasma/magnetic pressure across the front. These fronts are often embedded within fast earthward flows, i.e., bursty bulk flows. Analysis using data from all four spacecraft shows the presence of both typical and atypical dipolarization fronts. Typically dipolarization fronts propagate earthward and their normals point radially inward, however, we have identified dipolarization fronts propagating tailward with normals pointing significantly away from the radial direction. Atypical dipolarization fronts observed on 7 May 2015 and 21 July 2015 are preceded or accompanied by a rapid decrease in the Bx or By components of the magnetic field. These decreases indicate that the magnetotail is first thinning and then thickening. The resulting magnetic pile-up can cause the local Bz to increase rapidly, indicating propagation tailward, as observed. These new high time resolution field and plasma observations from MMS provide exciting new insights about the dynamical changes of magnetotail topology.
Snowplow Injection Front Effects
NASA Technical Reports Server (NTRS)
Moore, T. E.; Chandler, M. O.; Buzulukova, N.; Collinson, G. A.; Kepko, E. L.; Garcia-Sage, K. S.; Henderson, M. G.; Sitnov, M. I.
2013-01-01
As the Polar spacecraft apogee precessed through the magnetic equator in 2001, Polar encountered numerous substorm events in the region between geosynchronous orbit and 10 RE geocentric distance; most of them in the plasma sheet boundary layers. Of these, a small number was recorded near the neutral sheet in the evening sector. Polar/Thermal Ion Dynamics Experiment provides a unique perspective on the lowest-energy ion plasma, showing that these events exhibited a damped wavelike character, initiated by a burst of radially outward flow transverse to the local magnetic field at approximately 80 km/s. They then exhibit strongly damped cycles of inward/outward flow with a period of several minutes. After one or two cycles, they culminated in a hot plasma electron and ion injection, quite similar to those observed at geosynchronous orbit. Cold plasmaspheric plasmas comprise the outward flow cycles, while the inward flow cycles contain counterstreaming field-parallel polar wind-like flows. The observed wavelike structure, preceding the arrival of an earthward moving substorm injection front, suggests an outward displacement driven by the inward motion at local times closer to midnight, that is, a "snowplow" effect. The damped in/out flows are consistent with interchange oscillations driven by the arrival at the observed local time by an injection originating at greater radius and local time.
Constant mean curvature foliations in cosmological spacetimes.
NASA Astrophysics Data System (ADS)
Rendall, A. D.
1996-11-01
Foliations by constant mean curvature hypersurfaces provide a possibility of defining a preferred time coordinate in general relativity. In the following various conjectures are made about the existence of foliations of this kind in spacetimes satisfying the strong energy condition and possessing compact Cauchy hypersurfaces. Recent progress on proving these conjectures under supplementary assumptions is reviewed. The method of proof used is explained and the prospects for generalizing it discussed. The relations of these questions to cosmic censorship and the closed universe recollapse conjecture are pointed out.
Negative Gaussian curvature from induced metric changes.
Modes, Carl D; Warner, Mark
2015-07-01
We revisit the light or heat-induced changes in topography of initially flat sheets of a solid that elongate or contract along patterned in-plane director fields. For radial or azimuthal directors, negative Gaussian curvature is generated-so-called "anticones." We show that azimuthal material displacements are required for the distorted state to be stretch free and bend minimizing. The resultant shapes are smooth and asterlike and can become reentrant in the azimuthal coordinate for large deformations. We show that care is needed when considering elastomers rather than glasses, although the former offer huge deformations. PMID:26274106
Curvature and temperature of complex networks
NASA Astrophysics Data System (ADS)
Krioukov, Dmitri; Papadopoulos, Fragkiskos; Vahdat, Amin; Boguñá, Marián
2009-09-01
We show that heterogeneous degree distributions in observed scale-free topologies of complex networks can emerge as a consequence of the exponential expansion of hidden hyperbolic space. Fermi-Dirac statistics provides a physical interpretation of hyperbolic distances as energies of links. The hidden space curvature affects the heterogeneity of the degree distribution, while clustering is a function of temperature. We embed the internet into the hyperbolic plane and find a remarkable congruency between the embedding and our hyperbolic model. Besides proving our model realistic, this embedding may be used for routing with only local information, which holds significant promise for improving the performance of internet routing.
Amplification of curvature perturbations in cyclic cosmology
Zhang Jun; Liu Zhiguo; Piao Yunsong
2010-12-15
We analytically and numerically show that through the cycles with nonsingular bounce, the amplitude of curvature perturbation on a large scale will be amplified and the power spectrum will redden. In some sense, this amplification will eventually destroy the homogeneity of the background, which will lead to the ultimate end of cycles of the global universe. We argue that for the model with increasing cycles, it might be possible that a fissiparous multiverse will emerge after one or several cycles, in which the cycles will continue only at corresponding local regions.
Double curvature mirrors for linear concentrators
NASA Astrophysics Data System (ADS)
Lance, Tamir; Ackler, Harold; Finot, Marc
2012-10-01
Skyline Solar's medium concentration photovoltaic system uses quasi-parabolic mirrors and one axis tracking. Improvements in levelized cost of energy can be achieved by effective management of non-uniformity of the flux line on the panels. To reduce non uniformity of the flux line due to mirror to mirror gaps, Skyline developed a dual curvature mirror that stretches the flux line along the panel. Extensive modeling and experiments have been conducted to analyze the impact of this new design and to optimize the design.
Holographic entropy increases in quadratic curvature gravity
NASA Astrophysics Data System (ADS)
Bhattacharjee, Srijit; Sarkar, Sudipta; Wall, Aron C.
2015-09-01
Standard methods for calculating the black hole entropy beyond general relativity are ambiguous when the horizon is nonstationary. We fix these ambiguities in all quadratic curvature gravity theories, by demanding that the entropy be increasing at every time, for linear perturbations to a stationary black hole. Our result matches with the entropy formula found previously in holographic entanglement entropy calculations. We explicitly calculate the entropy increase for Vaidya-like solutions in Ricci-tensor gravity to show that (unlike the Wald entropy) the holographic entropy obeys a second law.
Spacetime Curvature and Higgs Stability after Inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2015-12-11
We investigate the dynamics of the Higgs field at the end of inflation in the minimal scenario consisting of an inflaton field coupled to the standard model only through the nonminimal gravitational coupling ξ of the Higgs field. Such a coupling is required by renormalization of the standard model in curved space, and in the current scenario also by vacuum stability during high-scale inflation. We find that for ξ≳1, rapidly changing spacetime curvature at the end of inflation leads to significant production of Higgs particles, potentially triggering a transition to a negative-energy Planck scale vacuum state and causing an immediate collapse of the Universe. PMID:26705621
Steering electromagnetic beams with conical curvature singularities.
Zhang, Yong-Liang; Dong, Xian-Zi; Zheng, Mei-Ling; Zhao, Zhen-Sheng; Duan, Xuan-Ming
2015-10-15
We describe how the transformation-optics technique can be used to design an effective medium mimicking the conical curvature singularity. Anholonomic coordinate transformation gives rise to linear topological defects that break the rotational symmetry. The bending and splitting of the optical beams are found analytically and numerically, depending on the incident direction and the topological charge. Beyond their practical applications to omnidirectional beam steering for photonics, our findings set forth an attractive realm to simulate the relevant physical phenomena in the optical laboratory. PMID:26469619
Grain boundary curvature and grain growth kinetics with particle pinning
NASA Astrophysics Data System (ADS)
Shahandeh, Sina; Militzer, Matthias
2013-08-01
Second-phase particles are used extensively in design of polycrystalline materials to control the grain size. According to Zener's theory, a distribution of particles creates a pinning pressure on a moving grain boundary. As a result, a limiting grain size is observed, but the effect of pinning on the detail of grain growth kinetics is less known. The influence of the particles on the microstructure occurs in multiple length scales, established by particle radius and the grain size. In this article, we use a meso-scale phase-field model that simulates grain growth in the presence of a uniform pinning pressure. The curvature of the grain boundary network is measured to determine the driving pressure of grain growth in 2D and 3D systems. It was observed that the grain growth continues, even under conditions where the average driving pressure is smaller than the pinning pressure. The limiting grain size is reached when the maximum of driving pressure distribution in the structure is equal to the pinning pressure. This results in a limiting grain size, larger than the one predicted by conventional models, and further analysis shows consistency with experimental observations. A physical model is proposed for the kinetics of grain growth using parameters based on the curvature analysis of the grain boundaries. This model can describe the simulated grain growth kinetics.
Controls on thrust belt curvature, Wyoming-Idaho thrust belt
Montgomery, J.M. Jr. . Dept. of Geological Sciences)
1993-04-01
Structural curvature in the northern part of the Wyoming-Idaho thrust belt (WITB) may be the result of either along-strike variations in pre-thrust stratigraphy or a buttress which physically concentrated shortening, or possibly both. Most thrust sheets of the WITB strike northward and were translated eastward, but in the Snake River Range (SRR) (the northernmost range in the WITB), structural strike curves from northward to nearly westward. Structural cross sections of the SRR are generally drawn in a radial pattern creating a volumetric imbalance in regional palinspastic restorations. Stratigraphic separation diagrams of major, through-going thrust faults in the SRR show extensive cut off in upper Paleozoic strata. New measured sections of upper Paleozoic stratigraphy at locations in several major thrust sheets of the WITB and in the foreland, new structural cross sections and mapping, and existing paleomagnetic data are used in a new interpretation of the origin of structural curvature in the WITB. Published paleomagnetic data require counterclockwise rotation of frontal thrust sheets along the northern boundary of the WITB, but no rotation of eastward-translated thrust sheets farther south along most of the WITB. Evidence for both a pre-existing west-trending depositional margin and rotation of frontal thrust sheets suggests that buttressing and modification of structural strike occurred along an oblique ramp where differences in stratigraphic thickness and possible pre-existing fault partitioning of the Paleozoic strata are localized.
Lipid membrane-mediated attraction between curvature inducing objects.
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J
2016-01-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (-3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles. PMID:27618764
Fronts in Large Marine Ecosystems
NASA Astrophysics Data System (ADS)
Belkin, Igor M.; Cornillon, Peter C.; Sherman, Kenneth
2009-04-01
Oceanic fronts shape marine ecosystems; therefore front mapping and characterization are among the most important aspects of physical oceanography. Here we report on the first global remote sensing survey of fronts in the Large Marine Ecosystems (LME). This survey is based on a unique frontal data archive assembled at the University of Rhode Island. Thermal fronts were automatically derived with the edge detection algorithm of Cayula and Cornillon (1992, 1995, 1996) from 12 years of twice-daily, global, 9-km resolution satellite sea surface temperature (SST) fields to produce synoptic (nearly instantaneous) frontal maps, and to compute the long-term mean frequency of occurrence of SST fronts and their gradients. These synoptic and long-term maps were used to identify major quasi-stationary fronts and to derive provisional frontal distribution maps for all LMEs. Since SST fronts are typically collocated with fronts in other water properties such as salinity, density and chlorophyll, digital frontal paths from SST frontal maps can be used in studies of physical-biological correlations at fronts. Frontal patterns in several exemplary LMEs are described and compared, including those for: the East and West Bering Sea LMEs, Sea of Okhotsk LME, East China Sea LME, Yellow Sea LME, North Sea LME, East and West Greenland Shelf LMEs, Newfoundland-Labrador Shelf LME, Northeast and Southeast US Continental Shelf LMEs, Gulf of Mexico LME, and Patagonian Shelf LME. Seasonal evolution of frontal patterns in major upwelling zones reveals an order-of-magnitude growth of frontal scales from summer to winter. A classification of LMEs with regard to the origin and physics of their respective dominant fronts is presented. The proposed classification lends itself to comparative studies of frontal ecosystems.
Topological implications of negative curvature for biological and social networks
NASA Astrophysics Data System (ADS)
Albert, Réka; DasGupta, Bhaskar; Mobasheri, Nasim
2014-03-01
Network measures that reflect the most salient properties of complex large-scale networks are in high demand in the network research community. In this paper we adapt a combinatorial measure of negative curvature (also called hyperbolicity) to parametrized finite networks, and show that a variety of biological and social networks are hyperbolic. This hyperbolicity property has strong implications on the higher-order connectivity and other topological properties of these networks. Specifically, we derive and prove bounds on the distance among shortest or approximately shortest paths in hyperbolic networks. We describe two implications of these bounds to crosstalk in biological networks, and to the existence of central, influential neighborhoods in both biological and social networks.
Particles and curvatures in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Serra, Francesca; Luo, Yimin; Yang, Shu; Kamien, Randall D.; Stebe, Kathleen J.
Elastic interactions in anisotropic fluids can be harnessed to direct particle interactions. A strategy to smoothly manipulate the director field in nematic liquid crystals is to vary the topography of the bounding surfaces. A rugged landscape with peaks and valleys create local deformations of the director field which can interact with particles in solution. We study this complex interaction in two different settings. The first consists of an array of shallow pores in a poly-dimethyl-siloxane (PDMS) membrane, whose curvature can be tuned either by swelling the PDMS membrane or by mechanical stretching. The second is a set of grooves with wavy walls, fabricated by photolithography, with various parameters of curvature and shapes. In this contexts we study how the motion of colloidal particles in nematic liquid crystals can be influenced by their interaction with the peaks and valleys of the bottom substrate or of the side walls. Particles with different associated topological defects (hedgehogs or Saturn rings) behave differently as they interact with the topographical features, favoring the docking on peaks or valleys. These experimental systems are also ideal to study the ``lock and key'' mechanism of particles in holes and to investigate a possible route for particle sorting.
Effects of streamline curvature on separation prediction
NASA Astrophysics Data System (ADS)
Arolla, Sunil K.; Durbin, Paul A.
2009-11-01
In this study, the effects of streamline curvature on prediction of flow separation are investigated. The geometry is a circulation control airfoil, a high-lift configuration that has been under extensive research for more than two decades. A tangential jet is blown over a thick, rounded trailing edge, using the Coanda effect to delay separation. An attempt is made to understand, through numerical simulations, the dynamics of turbulent separation and reattachment on the Coanda surface. Highly curved, attached recirculation regions are seen to form. A physics based curvature correction proposed by Pettersson-Reif et al. (1999) is used in conjunction with ζ-f turbulence model. The chord-based Reynolds number is Re = 10^6. Two jet momentum coefficients of Cμ=0.03 and 0.1 are computed. In this paper, comparisons between the computed and experimental pressure distributions, velocity profiles and the position of flow detachment are presented. Comparisons with other closures such as Menter's SST model are also discussed.
Vortex motion on surfaces of small curvature
Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.
2013-12-15
We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.
Analysis of dynamic smile and upper lip curvature in young Chinese
Liang, Ling-Zhi; Hu, Wen-Jie; Zhang, Yan-Ling; Chung, Kwok-Hung
2013-01-01
During smile evaluation and anterior esthetic construction, the anatomic and racial variations should be considered in order to achieve better matching results. The aims of this study were to validate an objective method for recording spontaneous smile process and to categorize the smile and upper lip curvature of Chinese Han-nationality youth. One hundred and eighty-eight Chinese Han-nationality youths (88 males and 100 females) ranged from 20 to 35 years of age were selected. Spontaneous smiles were elicited by watching comical movies and the dynamics of the spontaneous smile were captured continuously with a digital video camera. All subjects' smiles were categorized into three types: commissure, cuspid and gummy smile based on video editing software and final images. Subjects' upper lip curvatures were also measured and divided into three groups: upward, straight and downward. Reliability analysis was conducted to obtain intra-rater reliabilities on twice measurements. The Pearson Chi-square test was used to compare differences for each parameters (α=0.05). In smile classification, 60.6% commissure smile, 33.5% cuspid smile and 5.9% gummy smile were obtained. In upper lip measurement, 26.1% upward, 39.9% straight and 34.0% downward upper lip curvature were determined. The commissure smile group showed statistically significant higher percentage of straight (46.5%) and upward (40.4%) in upper lip curvatures (P<0.05), while cuspid smile group (65.1%) and gummy smile group (72.7%) showed statistically significant higher frequency in downward upper lip curvature (P<0.05). It is evident that differences in upper lip curvature and smile classification exist based on race, when comparing Chinese subjects with those of Caucasian descent, and gender. PMID:23558343
A SANS study of the interfacial curvatures and the phase behavior in bicontinuous microemulsions
NASA Astrophysics Data System (ADS)
Choi, Sung-Min
A microemulsion is a three-component system in which oil and water are solubilized via an interfacial surfactant monolayer. Depending on the composition and various external conditions, it exhibits a wide variety of phases with corresponding mesoscopic scale interfacial structures. For scientific as well as industrial purposes, knowledge of the relation between the interfacial structure and the phase behavior is crucial but its quantitative measure is lacking. To identify the relation in a quantitative way, the natural parameters to be measured are the interfacial curvatures: Gaussian, mean, and square mean curvatures. A new small-angle neutron scattering (SANS) data analysis method to extract the interfacial curvatures was developed and applied to various microemulsions. The method involves the use of a clipped random wave model with an inverse 8th order polynomial spectral function. The spectral density function contains three basic length scales: the inter- domain distance, the coherence length, and the surface roughness parameter. These three length scales are essential to describe mesoscopic scale interfaces. A series of SANS experiments were performed at various phase points of isometric and non-isometric microemulsions. Using the developed model, the three interfacial curvatures at each phase point were determined for the first time in a practical way. In isometric bicontinuous microemulsions, the Gaussian curvature is negative and has a parabolic dependence on the surfactant volume fraction. In non-isometric systems, based on the measured interfacial curvatures, a characteristic structural transformation was identified. As the water and oil volume ratio moves away from unity, the bicontinuous structure transforms to a spherical structure through an intermediate cylindrical structure. (Copies available exclusively from MIT Libraries, Rm. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
Quantifying Membrane Curvature Generation of Drosophila Amphiphysin N-BAR Domains
Heinrich, Michael C.; Capraro, Benjamin R.; Tian, Aiwei; Isas, Jose M.; Langen, Ralf; Baumgart, Tobias
2012-01-01
Biological membrane functions are coupled to membrane curvature, the regulation of which often involves membrane-associated proteins. The membrane-binding N-terminal amphipathic helix-containing BIN/Amphiphysin/Rvs (N-BAR) domain of amphiphysin is implicated in curvature generation and maintenance. Improving the mechanistic understanding of membrane curvature regulation by N-BAR domains requires quantitative experimental characterization. We have measured tube pulling force modulation by the N-BAR domain of Drosophila amphiphysin (DA-N-BAR) bound to tubular membranes pulled from micropipette-aspirated giant vesicles. We observed that fluorescently-labeled DA-N-BAR showed significantly higher protein density on tubules compared to the connected low-curvature vesicle membrane. Furthermore, we found the equilibrium tube pulling force to be systematically dependent on the aqueous solution concentration of DA-N-BAR, thereby providing the first quantitative assessment of spontaneous curvature generation. At sufficiently high protein concentrations, pulled tubes required no external force to maintain mechanical equilibrium, in agreement with the qualitative spontaneous tubulation previously reported for amphiphysin. PMID:23772271
Using Single-Scattering Albedo Spectral Curvature to Characterize East Asian Aerosol Mixtures
NASA Technical Reports Server (NTRS)
Li, Jing; Carlson, Barbara E.; Lacis, Andrew A.
2015-01-01
Spectral dependence of aerosol single-scattering albedo (SSA) has been used to infer aerosol composition. In particular, aerosol mixtures dominated by dust absorption will have monotonically increasing SSA with wavelength while that dominated by black carbon absorption has monotonically decreasing SSA spectra. However, by analyzing SSA measured at four wavelengths, 440, 675, 870, and 1020 nm from the Aerosol Robotic Network data set, we find that the SSA spectra over East Asia are frequently peaked at 675 nm. In these cases, we suggest that SSA spectral curvature, defined as the negative of the second derivative of SSA as a function of wavelength, can provide additional information on the composition of these aerosol mixtures. Aerosol SSA spectral curvatures for East Asia during fall and winter are considerably larger than those found in places primarily dominated by biomass burning or dust aerosols. SSA curvature is found to increase as the SSA magnitude decreases. The curvature increases with coarse mode fraction (CMF) to a CMF value of about 0.4, then slightly decreases or remains constant at larger CMF. Mie calculations further verify that the strongest SSA curvature occurs at approx. 40% dust fraction, with 10% scattering aerosol fraction. The nonmonotonic SSA spectral dependence is likely associated with enhanced absorption in the shortwave by dust, absorption by black carbon at longer wavelengths, and also the flattened absorption optical depth spectral dependence due to the increased particle size.
Direct curvature correction for noncontact imaging modalities applied to multispectral imaging
Kainerstorfer, Jana M.; Amyot, Franck; Ehler, Martin; Hassan, Moinuddin; Demos, Stavros G.; Chernomordik, Victor; Hitzenberger, Christoph K.; Gandjbakhche, Amir H.; Riley, Jason D.
2010-01-01
Noncontact optical imaging of curved objects can result in strong artifacts due to the object’s shape, leading to curvature biased intensity distributions. This artifact can mask variations due to the object’s optical properties, and makes reconstruction of optical∕physiological properties difficult. In this work we demonstrate a curvature correction method that removes this artifact and recovers the underlying data, without the necessity of measuring the object’s shape. This method is applicable to many optical imaging modalities that suffer from shape-based intensity biases. By separating the spatially varying data (e.g., physiological changes) from the background signal (dc component), we show that the curvature can be extracted by either averaging or fitting the rows and columns of the images. Numerical simulations show that our method is equivalent to directly removing the curvature, when the object’s shape is known, and accurately recovers the underlying data. Experiments on phantoms validate the numerical results and show that for a given image with 16.5% error due to curvature, the method reduces that error to 1.2%. Finally, diffuse multispectral images are acquired on forearms in vivo. We demonstrate the enhancement in image quality on intensity images, and consequently on reconstruction results of blood volume and oxygenation distributions. PMID:20799815
A curvature based approach using long-gage fiber optic sensors
NASA Astrophysics Data System (ADS)
Kliewer, Kaitlyn; Glisic, Branko
2016-04-01
Fiber Bragg grating (FBG) sensors offer a significant advantage for structural health monitoring due to their ability to simultaneously monitor both static and dynamic strain while being durable, lightweight, capable of multiplexing, and immune to electro-magnetic interference. Drawing upon the benefits of FBG sensors, this research explores the use of a series of long-gage fiber optic sensors for damage detection of a structure through dynamic strain measurements and curvature analysis. Typically structural monitoring relies upon detecting structural changes through frequency and acceleration based analysis. However, curvature and strain based analysis may be a more reliable means for structural monitoring as they show more sensitivity to damage compared to modal parameters such as displacement mode shapes and natural frequency. Additionally, long gage FBG strain sensors offer a promising alternative to traditional dynamic measurement methods as the curvature can be computed directly from the FBG strain measurements without the need for numerical differentiation. Small scale experimental testing was performed using an aluminum beam instrumented with a series of FBG optical fiber sensors. Dynamic strain measurements were obtained as the aluminum beam was subjected to various loading and support conditions. From this, a novel normalized parameter based on the curvature from the dynamic strain measurements has been identified as a potential damage sensitive feature. Theoretical predictions and experimental data were compared and conclusions carried out. The results demonstrated the potential of the novel normalized parameter to facilitate dynamic monitoring at both the local and global scale, thus allowing assessment of the structures health.
You, Jae Eung; Lee, Hye Young; Kim, Kyoung
2015-01-01
[Purpose] Degree of curvature on the spine is known to affect respiratory function and back muscle activation. We compared pulmonary function and back muscle strength according to the degree of curvature of the spine of healthy adults. [Subjects and Methods] Twenty-three healthy volunteers were enrolled. They were divided into two groups according to the degree of curvature of the spine: the below 2° group, and the above 2° group. The degree of curvature was assessed using the Adams forward bending test and a scoliometer. A pulmonary function test (PFT) was conducted, and back muscle strength was measured. [Results] No significant differences in PFT were found between the below 2° group and the above 2° group, in terms of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC), or peak expiratory flow (PEF). However, back muscle strength in the below 2 group was significantly higher than that of the above 2 group. [Conclusion] Our findings indicate that the degree of curvature of the spine is associated with back muscle strength in subjects who have spinal curvature within the normal range. Therefore, evaluation and treatment of back muscle strength might be helpful for preventing the progress of curvature of the spine in adolescents with potential scoliosis. PMID:26180321
You, Jae Eung; Lee, Hye Young; Kim, Kyoung
2015-06-01
[Purpose] Degree of curvature on the spine is known to affect respiratory function and back muscle activation. We compared pulmonary function and back muscle strength according to the degree of curvature of the spine of healthy adults. [Subjects and Methods] Twenty-three healthy volunteers were enrolled. They were divided into two groups according to the degree of curvature of the spine: the below 2° group, and the above 2° group. The degree of curvature was assessed using the Adams forward bending test and a scoliometer. A pulmonary function test (PFT) was conducted, and back muscle strength was measured. [Results] No significant differences in PFT were found between the below 2° group and the above 2° group, in terms of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC), or peak expiratory flow (PEF). However, back muscle strength in the below 2 group was significantly higher than that of the above 2 group. [Conclusion] Our findings indicate that the degree of curvature of the spine is associated with back muscle strength in subjects who have spinal curvature within the normal range. Therefore, evaluation and treatment of back muscle strength might be helpful for preventing the progress of curvature of the spine in adolescents with potential scoliosis. PMID:26180321
Wu, Jin-Yuan; Shi, Z.; /Fermilab
2004-12-01
Strong magnetic field in today's colliding detectors causes track recognition more difficult due to large track curvatures. In this document, we present a global track recognition scheme based on track angle measurements for circular tracks passing the collision point. It uses no approximations in the track equation and therefore is suitable for both large and small curvature tracks. The scheme can be implemented both in hardware for lower-level trigger or in software for higher-level trigger or offline analysis codes. We will discuss an example of FPGA implementations using ''hash sorter''.
Experimental reconstruction of the Berry curvature in a topological Bloch band
NASA Astrophysics Data System (ADS)
Weitenberg, Christof; Flaeschner, Nick; Rem, Benno; Tarnowski, Matthias; Vogel, Dominik; Luehmann, Dirk-Soeren; Sengstock, Klaus
2016-05-01
Topological properties lie at the heart of many fascinating phenomena in solid state systems such as quantum Hall systems or Chern insulators. The topology can be captured by the distribution of Berry curvature, which describes the geometry of the eigenstates across the Brillouin zone. Employing fermionic ultracold atoms in a hexagonal optical lattice, we engineer the Berry curvature of the Bloch bands using resonant driving and measure it with full momentum resolution. Our results pave the way to explore intriguing phases of matter with interactions in topological band structures.
Error propagation: a comparison of Shack-Hartmann and curvature sensors.
Kellerer, Aglaé N; Kellerer, Albrecht M
2011-05-01
Phase estimates in adaptive-optics systems are computed by use of wavefront sensors, such as Shack-Hartmann or curvature sensors. In either case, the standard error of the phase estimates is proportional to the standard error of the measurements; but the error-propagation factors are different. We calculate the ratio of these factors for curvature and Shack-Hartmann sensors in dependence on the number of sensors, n, on a circular aperture. If the sensor spacing is kept constant and the pupil is enlarged, the ratio increases as n(0.4). When more sensing elements are accommodated on the same aperture, it increases even faster, namely, proportional to n(0.8). With large numbers of sensing elements, this increase can limit the applicability of curvature sensors. PMID:21532691
Kinetics for Phototropic Curvature by Etiolated Seedlings of Arabidopsis thaliana 1
Orbović, Vladimir; Poff, Kenneth L.
1991-01-01
An infrared-imaging system has been used to study the influence of gravity on the kinetics of first positive phototropism. The development of phototropic curvature of etiolated seedlings of Arabidopsis thaliana was measured in the absence of visible radiation. Following a pulse of blue light, stationary seedlings curved to a maximum of approximately 16° about 80 minutes after stimulation. The seedlings then curved upward again or straightened by about 6° during the subsequent 100 minutes. Seedlings rotated on a clinostat reached a similar maximum curvature following photostimulation. These seedlings maintained that curvature for 30 to 40 minutes before subsequently straightening to the same extent as the stationary seedlings. It is concluded that straightening is not a consequence of gravitropism, although gravity has some effect on the phototropism kinetics. PMID:11538373
The curvature elastic-energy function of the lipid-water cubic mesophase
NASA Astrophysics Data System (ADS)
Chung, Hesson; Caffrey, Martin
1994-03-01
CELL and lipid membranes are able to bend, as manifested during membrane fusion and the formation of non-lamellar lyotropic mesopbases in water. But there is an energy cost to bending of lipid layers, called the curvature elastic energy. Although the functional form of this energy is known1, a complete quantitative knowledge of the curvature elastic energy, which is central to predicting the relative stability of the large number of phases that lipid membranes can adopt, has been lacking. Here we use X-ray synchrotron diffraction measurements of the variation of lattice parameter with pressure and temperature for the periodic Ia3d (Q230) cubic phase of hydrated monoolein to calculate the complete curvature elastic-energy function for the lipid cubic mesophase. This allows us to predict the stabilities of different cubic and lamellar phases for this system as a function of composition.
Asymptotic behavior of curvature of surface elements in isotropic turbulence
NASA Technical Reports Server (NTRS)
Girimaji, S. S.
1991-01-01
The asymptotic behavior of the curvature of material elements in turbulence is investigated using Lagrangian velocity-gradient time series obtained from direct numerical simulations of isotropic turbulence. Several material-element ensembles of different initial curvatures and shapes are studied. It is found that, at long times, the (first five) moments of the logarithm of characteristic curvature and shape factor asymptote to values that are independent of the initial curvature or shape. This evidence strongly suggests that the asymptotic pdf's of the curvature and shape of material elements are stationary and independent of initial conditions. Irrespective of initial curvature or shape, the asymptotic shape of a material surface is cylindrical with a high probability.
Flame front as hydrodynamic discontinuity
NASA Astrophysics Data System (ADS)
Fukumoto, Yasuhide; Abarzhi, Snezhana
2012-11-01
We applied generalized Rankine-Hugoniot conditions to study the dynamics of unsteady and curved fronts as a hydrodynamic discontinuity. It is shown that the front is unstable and Landau-Darrieus instability develops only if three conditions are satisfied (1) large-scale vorticity is generated in the fluid bulk; (2) energy flux across the front is imbalanced; (3) the energy imbalance is large. The structure of the solution is studied in details. Flows with and without gravity and thermal diffusion are analyzed. Stabilization mechanisms are identified. NSF 1004330.
Asymmetric counterpropagating fronts without flow.
Andrade-Silva, I; Clerc, M G; Odent, V
2015-06-01
Out-of-equilibrium systems exhibit domain walls between different states. These walls, depending on the type of connected states, can display rich spatiotemporal dynamics. In this Rapid Communication, we investigate the asymmetrical counterpropagation of fronts in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the different front shapes and propagation speeds. These fronts present dissimilar elastic deformations that are responsible for their asymmetric speeds. Theoretically, using a phenomenological model, we describe the observed dynamics with fair agreement. PMID:26172647
NASA Astrophysics Data System (ADS)
Gerilowski, K.; Krautwurst, S.; Kolyer, R.; Jonsson, H.; Krings, T.; Horstjann, M.; Leifer, I.; Schuettemeyer, D.; Fladeland, M. M.; Burrows, J. P.; Bovensmann, H.
2014-12-01
During three flights performed with the MAMAP (Methane Airborne MAPper) airborne remote sensing instrument in the framework of the CO2 and MEthane Experiment (COMEX) - a NASA and ESA funded campaign in support of HyspIRI and CarbonSat mission definition activities - large scale methane plumes were detected over the Kern River and Kern Front Oil fields in the period between June 3 and 13, 2014. MAMAP was installed for these flights aboard of the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft, together with a Picarro fast in-situ greenhouse gas (GHG) analyzer (operate by the Ames Research Center, ARC), a 5 hole turbulence probe as well as a atmospheric measurement package (operated by CIRPAS), measuring aerosols, temperature, dew-point and other atmospheric parameters. Data collected with the in-situ GHG analyzer will be used for validation of MAMAP remotely sensed data by acquiring vertical cross sections of the discovered plumes at a fixed downwind distance. Precise airborne wind information from the turbulence probe together with ground based wind data from the nearby airport will be used to estimate emission rates from the remote sensed and in-situ measured data. Remote sensed and in-situ data as well as initial flux estimates for the three flights will be presented.
Compact surfaces of constant Gaussian curvature in Randers manifolds
NASA Astrophysics Data System (ADS)
Cui, Ningwei
2016-08-01
The flag curvature of a Finsler surface is called the Gaussian curvature in Finsler geometry. In this paper, we characterize the surfaces of constant Gaussian curvature (CGC) in the Randers 3-manifold. Then we give a classification of the orientable closed CGC surfaces in two Randers space forms, which are the non-Euclidean Minkowski-Randers 3-space (K = 0) and the Bao-Shen sphere (K = 1).
Wrinkles and splay conspire to give positive disclinations negative curvature.
Matsumoto, Elisabetta A; Vega, Daniel A; Pezzutti, Aldo D; García, Nicolás A; Chaikin, Paul M; Register, Richard A
2015-10-13
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
Wrinkles and splay conspire to give positive disclinations negative curvature
Matsumoto, Elisabetta A.; Vega, Daniel A.; Pezzutti, Aldo D.; García, Nicolás A.; Chaikin, Paul M.; Register, Richard A.
2015-01-01
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
Assessment of Spinal Curvature: An Evaluation of the Flexicurve and Associated Means of Analysis.
ERIC Educational Resources Information Center
Caine, M. P.; And Others
1996-01-01
Several interrelated issues pertaining to the measurement of spinal curvature are discussed, including the inherent limitations of the kyphotic index, the most widely used indicator in the evaluation of kyphosis. The paper suggests use of the Flexicurve to quantify spinal posture, suggests modifications to the Flexicurve, and presents results on…
Evolution of the curvature perturbations during warm inflation
Matsuda, Tomohiro
2009-06-15
This paper considers warm inflation as an interesting application of multi-field inflation. Delta-N formalism is used for the calculation of the evolution of the curvature perturbations during warm inflation. Although the perturbations considered in this paper are decaying after the horizon exit, the corrections to the curvature perturbations sourced by these perturbations can remain and dominate the curvature perturbations at large scales. In addition to the typical evolution of the curvature perturbations, inhomogeneous diffusion rate is considered for warm inflation, which may lead to significant non-Gaussianity of the spectrum.
Mean Curvature Flow in a Ricci Flow Background
NASA Astrophysics Data System (ADS)
Lott, John
2012-07-01
Following work of Ecker (Comm Anal Geom 15:1025-1061, 2007), we consider a weighted Gibbons-Hawking-York functional on a Riemannian manifold-with-boundary. We compute its variational properties and its time derivative under Perelman's modified Ricci flow. The answer has a boundary term which involves an extension of Hamilton's differential Harnack expression for the mean curvature flow in Euclidean space. We also derive the evolution equations for the second fundamental form and the mean curvature, under a mean curvature flow in a Ricci flow background. In the case of a gradient Ricci soliton background, we discuss mean curvature solitons and Huisken monotonicity.
Plane wave gravitons, curvature singularities and string physics
Brooks, R. . Center for Theoretical Physics)
1991-03-21
This paper discusses bounded (compactifying) potentials arising from a conspiracy between plane wave graviton and dilaton condensates. So are string propagation and supersymmetry in spacetimes with curvature singularities.
QCD and Light-Front Holography
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2010-10-27
The soft-wall AdS/QCD model, modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics. The model predicts a zero-mass pion for zero-mass quarks and a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number N. Light-Front Holography maps the amplitudes which are functions of the fifth dimension variable z of anti-de Sitter space to a corresponding hadron theory quantized on the light front. The resulting Lorentz-invariant relativistic light-front wave equations are functions of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. The result is to a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryon light-quark bound states, which in turn predict the behavior of the pion and nucleon form factors. The theory implements chiral symmetry in a novel way: the effects of chiral symmetry breaking increase as one goes toward large interquark separation, consistent with spectroscopic data, and the the hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. The soft-wall model also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function which agrees with the effective coupling {alpha}{sub g1} extracted from the Bjorken sum rule. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms. A new perspective on quark and gluon condensates is also reviewed.
Nonminimal coupling of perfect fluids to curvature
Bertolami, Orfeu; Lobo, Francisco S. N.; Paramos, Jorge
2008-09-15
In this work, we consider different forms of relativistic perfect fluid Lagrangian densities that yield the same gravitational field equations in general relativity (GR). A particularly intriguing example is the case with couplings of the form [1+f{sub 2}(R)]L{sub m}, where R is the scalar curvature, which induces an extra force that depends on the form of the Lagrangian density. It has been found that, considering the Lagrangian density L{sub m}=p, where p is the pressure, the extra-force vanishes. We argue that this is not the unique choice for the matter Lagrangian density, and that more natural forms for L{sub m} do not imply the vanishing of the extra force. Particular attention is paid to the impact on the classical equivalence between different Lagrangian descriptions of a perfect fluid.
Natural curvature for manifest T-duality
NASA Astrophysics Data System (ADS)
Poláček, Martin; Siegel, Warren
2014-01-01
We reformulate the manifestly T-dual description of the massless sector of the closed bosonic string, directly from the geometry associated with the (left and right) affine Lie algebra of the coset space Poincaré/Lorentz. This construction initially doubles not only the (spacetime) coordinates for translations but also those for Lorentz transformations (and their "dual"). As a result, the Lorentz connection couples directly to the string (as does the vielbein), rather than being introduced ad hoc to the covariant derivative as previously. This not only reproduces the old definition of T-dual torsion, but automatically gives a general, covariant definition of T-dual curvature (but still with some undetermined connections).
Hawking temperature of constant curvature black holes
Cai Ronggen; Myung, Yun Soo
2011-05-15
The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of M{sub D-1}xS{sup 1}, where D is the spacetime dimension and M{sub D-1} stands for a conformal Minkowski spacetime in D-1 dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both the static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.
A miniature curvature wavefront sensor with coherent fiber image bundle
NASA Astrophysics Data System (ADS)
Zheng, Jessica; Richards, Samuel; Goodwin, Michael; Lawrence, Jon; Leon-Saval, Sergio; Argyros, Alexander
2014-08-01
A miniature curvature wavefront sensor with a coherent fiber image bundle is proposed in which a miniature lateral displacement beamsplitter is designed to obtain the intra- and extra- focus images from a telescope simultaneously at its exit. The two images are received and relayed by two coherent fiber image bundles. The relayed images are then re-imaged to one camera and processed to obtain the input wavefront at telescope pupil. The whole device is quite compact and can be driven by a "Starbug" fiber positioning device currently under development within the Australian Astronomical Observatory. In this paper, the performance of the proposed sensor is investigated in details by applying a simulated atmospheric turbulence at the telescope pupil plane. We study the offset distance of two image measurement planes, fiber core size, fiber fill factor and the magnitude of natural guide star effects to its performance. This study provides guidance to the sensor design.
DNA curvature and flexibility in vitro and in vivo
Peters, Justin P.; Maher, L. James
2014-01-01
It has been more than 50 years since the elucidation of the structure of double-helical DNA. Despite active research and progress in DNA biology and biochemistry, much remains to be learned in the field of DNA biophysics. Predicting the sequence-dependent curvature and flexibility of DNA is difficult. Applicability of the conventional worm-like chain polymer model of DNA has been challenged. The fundamental forces responsible for the remarkable resistance of DNA to bending and twisting remain controversial. The apparent “softening” of DNA measured in vivo in the presence of kinking proteins and superhelical strain is incompletely understood. New methods and insights are being applied to these problems. This review places current work on DNA biophysics in historical context and illustrates the ongoing interplay between theory and experiment in this exciting field. PMID:20478077
Canards and curvature: nonsmooth approximation by pinching
NASA Astrophysics Data System (ADS)
Desroches, M.; Jeffrey, M. R.
2011-05-01
In multiple time-scale (singularly perturbed) dynamical systems, canards are counterintuitive solutions that evolve along both attracting and repelling invariant manifolds. In two dimensions, canards result in periodic oscillations whose amplitude and period grow in a highly nonlinear way: they are slowly varying with respect to a control parameter, except for an exponentially small range of values where they grow extremely rapidly. This sudden growth, called a canard explosion, has been encountered in many applications ranging from chemistry to neuronal dynamics, aerospace engineering and ecology. Canards were initially studied using nonstandard analysis, and later the same results were proved by standard techniques such as matched asymptotics, invariant manifold theory and parameter blow-up. More recently, canard-like behaviour has been linked to surfaces of discontinuity in piecewise-smooth dynamical systems. This paper provides a new perspective on the canard phenomenon by showing that the nonstandard analysis of canard explosions can be recast into the framework of piecewise-smooth dynamical systems. An exponential coordinate scaling is applied to a singularly perturbed system of ordinary differential equations. The scaling acts as a lens that resolves dynamics across all time-scales. The changes of local curvature that are responsible for canard explosions are then analysed. Regions where different time-scales dominate are separated by hypersurfaces, and these are pinched together to obtain a piecewise-smooth system, in which curvature changes manifest as discontinuity-induced bifurcations. The method is used to classify canards in arbitrary dimensions, and to derive the parameter values over which canards form either small cycles (canards without head) or large cycles (canards with head).
Wang, Wangchen; Yang, Lin; Huang, Huey W.
2007-01-01
Recent experiments suggested that cholesterol and other lipid components of high negative spontaneous curvature facilitate membrane fusion. This is taken as evidence supporting the stalk-pore model of membrane fusion in which the lipid bilayers go through intermediate structures of high curvature. How do the high-curvature lipid components lower the free energy of the curved structure? Do the high-curvature lipid components modify the average spontaneous curvature of the relevant monolayer, thereby facilitate its bending, or do the lipid components redistribute in the curved structure so as to lower the free energy? This question is fundamental to the curvature elastic energy for lipid mixtures. Here we investigate the lipid distribution in a monolayer of a binary lipid mixture before and after bending, or more precisely in the lamellar, hexagonal, and distorted hexagonal phases. The lipid mixture is composed of 2:1 ratio of brominated di18:0PC and cholesterol. Using a newly developed procedure for the multiwavelength anomalous diffraction method, we are able to isolate the bromine distribution and reconstruct the electron density distribution of the lipid mixture in the three phases. We found that the lipid distribution is homogenous and uniform in the lamellar and hexagonal phases. But in the distorted hexagonal phase, the lipid monolayer has nonuniform curvature, and cholesterol almost entirely concentrates in the high curvature region. This finding demonstrates that the association energies between lipid molecules vary with the curvature of membrane. Thus, lipid components in a mixture may redistribute under conditions of nonuniform curvature, such as in the stalk structure. In such cases, the spontaneous curvature depends on the local lipid composition and the free energy minimum is determined by lipid distribution as well as curvature. PMID:17259270
Radiative magnetized thermal conduction fronts
NASA Technical Reports Server (NTRS)
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-01-01
The evolution of plane-parallel magnetized thermal conduction fronts in the interstellar medium (ISM) was studied. Separating the coronal ISM phase and interstellar clouds, these fronts have been thought to be the site of the intermediate-temperature regions whose presence was inferred from O VI absorption-line studies. The front evolution was followed numerically, starting from the initial discontinuous temperature distribution between the hot and cold medium, and ending in the final cooling stage of the hot medium. It was found that, for the typical ISM pressure of 4000 K/cu cm and the hot medium temperature of 10 to the 6th K, the transition from evaporation to condensation in a nonmagnetized front occurs when the front thickness is 15 pc. This thickness is a factor of 5 smaller than previously estimated. The O VI column densities in both evaporative and condensation stages agree with observations if the initial hot medium temperature Th exceeds 750,000 K. Condensing conduction fronts give better agreement with observed O VI line profiles because of lower gas temperatures.
Restless rays, steady wave fronts.
Godin, Oleg A
2007-12-01
Observations of underwater acoustic fields with vertical line arrays and numerical simulations of long-range sound propagation in an ocean perturbed by internal gravity waves indicate that acoustic wave fronts are much more stable than the rays comprising these wave fronts. This paper provides a theoretical explanation of the phenomenon of wave front stability in a medium with weak sound-speed perturbations. It is shown analytically that at propagation ranges that are large compared to the correlation length of the sound-speed perturbations but smaller than ranges at which ray chaos develops, end points of rays launched from a point source and having a given travel time are scattered primarily along the wave front corresponding to the same travel time in the unperturbed environment. The ratio of root mean square displacements of the ray end points along and across the unperturbed wave front increases with range as the ratio of ray length to correlation length of environmental perturbations. An intuitive physical explanation of the theoretical results is proposed. The relative stability of wave fronts compared to rays is shown to follow from Fermat's principle and dimensional considerations. PMID:18247745
A Novel Curvature-Based Algorithm for Automatic Grading of Retinal Blood Vessel Tortuosity.
Aghamohamadian-Sharbaf, Masoud; Pourreza, Hamid Reza; Banaee, Touka
2016-03-01
Tortuosity of retinal blood vessels is an important symptom of diabetic retinopathy or retinopathy of prematurity. In this paper, we propose an automatic image-based method for measuring single vessel and vessel network tortuosity of these vessels. Simplicity of the algorithm, low-computational burden, and an excellent matching to the clinically perceived tortuosity are the important features of the proposed algorithm. To measure tortuosity, we use curvature which is an indicator of local inflection of a curve. For curvature calculation, template disk method is a common choice and has been utilized in most of the state of the art. However, we show that this method does not possess linearity against curvature and by proposing two modifications, we improve the method. We use the basic and the modified methods to measure tortuosity on a publicly available data bank and two data banks of our own. While interpreting the results, we pursue three goals. First, to show that our algorithm is more efficient to implement than the state of the art. Second, to show that our method possesses an excellent correlation with subjective results (0.94 correlation for vessel tortuosity, 0.95 correlation for vessel network tortuosity in diabetic retinopathy, and 0.7 correlation for vessel network tortuosity in retinopathy of prematurity). Third, to show that the tortuosity perceived by an expert and curvature possess a nonlinear relation. PMID:25622332
Mean cortical curvature reflects cytoarchitecture restructuring in mild traumatic brain injury.
King, Jace B; Lopez-Larson, Melissa P; Yurgelun-Todd, Deborah A
2016-01-01
In the United States alone, the number of persons living with the enduring consequences of traumatic brain injuries is estimated to be between 3.2 and 5 million. This number does not include individuals serving in the United States military or seeking care at Veterans Affairs hospitals. The importance of understanding the neurobiological consequences of mild traumatic brain injury (mTBI) has increased with the return of veterans from conflicts overseas, many of who have suffered this type of brain injury. However, identifying the neuroanatomical regions most affected by mTBI continues to prove challenging. The aim of this study was to assess the use of mean cortical curvature as a potential indicator of progressive tissue loss in a cross-sectional sample of 54 veterans with mTBI compared to 31 controls evaluated with MRI. It was hypothesized that mean cortical curvature would be increased in veterans with mTBI, relative to controls, due in part to cortical restructuring related to tissue volume loss. Mean cortical curvature was assessed in 60 bilateral regions (31 sulcal, 29 gyral). Of the 120 regions investigated, nearly 50% demonstrated significantly increased mean cortical curvature in mTBI relative to controls with 25% remaining significant following multiple comparison correction (all, pFDR < .05). These differences were most prominent in deep gray matter regions of the cortex. Additionally, significant relationships were found between mean cortical curvature and gray and white matter volumes (all, p < .05). These findings suggest potentially unique patterns of atrophy by region and indicate that changes in brain microstructure due to mTBI are sensitive to measures of mean curvature. PMID:26909332
Mean cortical curvature reflects cytoarchitecture restructuring in mild traumatic brain injury
King, Jace B.; Lopez-Larson, Melissa P.; Yurgelun-Todd, Deborah A.
2016-01-01
In the United States alone, the number of persons living with the enduring consequences of traumatic brain injuries is estimated to be between 3.2 and 5 million. This number does not include individuals serving in the United States military or seeking care at Veterans Affairs hospitals. The importance of understanding the neurobiological consequences of mild traumatic brain injury (mTBI) has increased with the return of veterans from conflicts overseas, many of who have suffered this type of brain injury. However, identifying the neuroanatomical regions most affected by mTBI continues to prove challenging. The aim of this study was to assess the use of mean cortical curvature as a potential indicator of progressive tissue loss in a cross-sectional sample of 54 veterans with mTBI compared to 31 controls evaluated with MRI. It was hypothesized that mean cortical curvature would be increased in veterans with mTBI, relative to controls, due in part to cortical restructuring related to tissue volume loss. Mean cortical curvature was assessed in 60 bilateral regions (31 sulcal, 29 gyral). Of the 120 regions investigated, nearly 50% demonstrated significantly increased mean cortical curvature in mTBI relative to controls with 25% remaining significant following multiple comparison correction (all, pFDR < .05). These differences were most prominent in deep gray matter regions of the cortex. Additionally, significant relationships were found between mean cortical curvature and gray and white matter volumes (all, p < .05). These findings suggest potentially unique patterns of atrophy by region and indicate that changes in brain microstructure due to mTBI are sensitive to measures of mean curvature. PMID:26909332
NASA Astrophysics Data System (ADS)
Liu, Huilian; Li, Weijun; Li, Hongbo; Sun, Yunfei; Song, Junlin; Yang, Jinghai; Gao, Ming; Liu, Xiaoyan
2015-07-01
The influence of substrate curvature on structural, optical properties of Cu, Co codoped ZnO thin films were investigated in this study. XRD analysis indicated that the crystal quality of the ZnO films could been influenced by the substrate curvature. The biaxial stress of our samples was measured by side-inclination X-ray diffraction technique. The results indicated that the type of the stress was biaxial compressive stress. Optical absorption spectra showed the absorption edge of our samples displayed blueshift with decreasing substrate curvature. Gauss fit for PL emission spectra showed that the substrate curvature affected the PL properties of the Cu, Co codoped ZnO thin films deposited on polystyrene particles. The various substrates induced defect-related emission increased in visible region.
Effects of curvature on asymmetric steady states in catalyst particles
Lucier, B J
1981-02-01
The effects of curvature on steady states of chemical catalytic reactions are investigated by studying the cases of the catalytic particle being a spherical or cylindrical shell. Existence and stability of solutions are studied. It is shown that the solutions converge to the solutions for the catalytic slab when the curvature goes to 0 in each case.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-06-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of co-seismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth, the other with a larger radius can approximate a half-space model. Then, we calculate the co-seismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum co-seismic displacement. The results show that the maximum curvature effect is about 4% for source depths of less than 100 km, and about 30% for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100%. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Determination of Radius of Curvature for Teeth With Cycloid Profile
NASA Astrophysics Data System (ADS)
Shatalov, E. V.; Efremenkov, E. A.; Shibinskiy, K. G.
2016-04-01
In the article the geometric determination of curvature radius is considered for teeth with cycloid profile. The equations are obtained for the determination of a radius of curvature with point coordinates of a cycloid profile. The conditions of convexo-concavity of a teeth profile are defined for transmission with intermediate rollers.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-08-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of coseismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth and the other with a larger radius can approximate a half-space model. Then, we calculate the coseismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum coseismic displacement. The results show that the maximum curvature effect is about 4 per cent for source depths of less than 100 km, and about 30 per cent for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100 per cent. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Determination of cut front position in laser cutting
NASA Astrophysics Data System (ADS)
Pereira, M.; Thombansen, U.
2016-07-01
Laser cutting has a huge importance to manufacturing industry. Laser cutting machines operate with fixed technological parameters and this does not guarantee the best productivity. The adjustment of the cutting parameters during operation can improve the machine performance. Based on a coaxial measuring device it is possible to identify the cut front position during the cutting process. This paper describes the data analysis approach used to determine the cut front position for different feed rates. The cut front position was determined with good resolution, but improvements are needed to make the whole process more stable.
NASA Astrophysics Data System (ADS)
Araujo, F. M.; Ferreira, L. A.; Santos, J. L.
2002-05-01
We present what we believe to be a novel miniaturized sensor configuration based on fiber Bragg gratings for simultaneous measurement of curvature and temperature in smart structures and composite materials. Because of the particular geometry of the sensing head, it is possible not only to measure the radius of curvature but also to determine the plane of curvature. We arrange three Bragg gratings in the vertices of the smallest equilateral triangle that can be defined by the cross sections of the fibers. The set is then inserted into a glue-filled capillary stainless-steel tube to provide both suitable protection for the Bragg sensors and rotational symmetry to the sensing head. This tube also ensures isolation from axial strain, allowing for the additional determination of temperature. The proposed sensing head is particularly well suited for applications in smart structures because it can be embedded along any layer of a composite material (including the neutral line) without special concern for the relative orientation of the Bragg gratings and the composite layers. We can also use this sensing configuration to implement more-sophisticated sensors dedicated, for example, to the measurement of multiaxial acceleration or flow and temperature.
Nastic curvatures of wheat coleoptiles that develop in true microgravity
NASA Technical Reports Server (NTRS)
Heathcote, D. G.; Chapman, D. K.; Brown, A. H.
1995-01-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Elliptic inflation: generating the curvature perturbation without slow-roll
NASA Astrophysics Data System (ADS)
Matsuda, Tomohiro
2006-09-01
There are many inflationary models in which the inflaton field does not satisfy the slow-roll condition. However, in such models, it is always difficult to generate the curvature perturbation during inflation. Thus, to generate the curvature perturbation, one must introduce another component into the theory. To cite a case, curvatons may generate the dominant part of the curvature perturbation after inflation. However, we question whether it is realistic to consider the generation of the curvature perturbation during inflation without slow-roll. Assuming multifield inflation, we encounter the generation of curvature perturbation during inflation without slow-roll. The potential along the equipotential surface is flat by definition and thus we do not have to worry about symmetry. We also discuss KKLT (Kachru Kallosh Linde Trivedi) models, in which corrections lifting the inflationary direction may not become a serious problem if there is a symmetry enhancement at the tip (not at the moving brane) of the inflationary throat.
Robust pupil center detection using a curvature algorithm
NASA Technical Reports Server (NTRS)
Zhu, D.; Moore, S. T.; Raphan, T.; Wall, C. C. (Principal Investigator)
1999-01-01
Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.
Curvature-processing network in macaque visual cortex
Yue, Xiaomin; Pourladian, Irene S.; Tootell, Roger B. H.; Ungerleider, Leslie G.
2014-01-01
Our visual environment abounds with curved features. Thus, the goal of understanding visual processing should include the processing of curved features. Using functional magnetic resonance imaging in behaving monkeys, we demonstrated a network of cortical areas selective for the processing of curved features. This network includes three distinct hierarchically organized regions within the ventral visual pathway: a posterior curvature-biased patch (PCP) located in the near-foveal representation of dorsal V4, a middle curvature-biased patch (MCP) located on the ventral lip of the posterior superior temporal sulcus (STS) in area TEO, and an anterior curvature-biased patch (ACP) located just below the STS in anterior area TE. Our results further indicate that the processing of curvature becomes increasingly complex from PCP to ACP. The proximity of the curvature-processing network to the well-known face-processing network suggests a possible functional link between them. PMID:25092328
Wang, Q.; Li, M.; Lou, Edmond H. M.; Wong, M. S.
2015-01-01
Background Non-ionizing radiation imaging assessment has been advocated for the patients with adolescent idiopathic scoliosis (AIS). As one of the radiation-free methods, ultrasound imaging has gained growing attention in scoliosis assessment over the past decade. The center of laminae (COL) method has been proposed to measure the spinal curvature in the coronal plane of ultrasound image. However, the reliability and validity of this ultrasound method have not been validated in the clinical setting. Objectives To evaluate the reliability and validity of clinical ultrasound imaging on lateral curvature measurements of AIS with their corresponding magnetic resonance imaging (MRI) measurements. Methods Thirty curves (ranged 10.2°–68.2°) from sixteen patients with AIS were eligible for this study. The ultrasound scan was performed using a 3-D ultrasound unit within the same morning of MRI examination. Two researchers were involved in data collection of these two examinations. The COL method was used to measure the coronal curvature in ultrasound image, compared with the Cobb method in MRI. The intra- and inter-rater reliability of the COL method was evaluated by intra-class correlation coefficient (ICC). The validity of this method was analyzed by paired Student’s t-test, Bland–Altman statistics and Pearson correlation coefficient. The level of significance was set as 0.05. Results The COL method showed high intra- and inter-rater reliabilities (both with ICC (2, K) >0.9, p<0.05) to measure the coronal curvature. Compared with Cobb method, COL method showed no significant difference (p<0.05) when measuring coronal curvature. Furthermore, Bland-Altman method demonstrated an agreement between these two methods, and Pearson’s correlation coefficient (r) was high (r>0.9, p<0.05). Conclusion The ultrasound imaging could provide a reliable and valid measurement of spinal curvature in the coronal plane using the COL method. Further research is needed to validate the
RF photonic front-end integrating with local oscillator loop.
Yu, H; Chen, M; Gao, H; Yang, S; Chen, H; Xie, S
2014-02-24
Broadband Radio frequency (RF) photonic front-ends are one of the vital applications of the microwave photonics. A tunable and broadband RF photonic front-end integrating with the optoelectronic oscillator (OEO) based local oscillator has been proposed and experimentally demonstrated, in which only one phase modulator (PM) is employed thanks to the characteristic of the PM. The silicon-on-insulator based narrow-bandwidth band-pass filter is introduced for signal processing. The application condition of the proposed RF photonic front-end has been discussed and the performance of the front-end has also been measured. The SFDR at a frequency of about 7.02 GHz is measured to be 88.6 dB-Hz(2/3). PMID:24663712
NASA Technical Reports Server (NTRS)
2001-01-01
These MISR images from May 12, 2001 (Terra orbit 7447) include portions of southern Wyoming, central Colorado, and western Nebraska. The top view is from the instrument's vertical-viewing (nadir) camera. The bottom image is a stereo 'anaglyph' generated using data from the nadir and 46-degree-forward cameras. Viewing the anaglyph with red/blue glasses (red filter over your left eye) gives a 3-D effect. To facilitate stereo viewing, the images have been oriented with north at the left. Each image measures 422 kilometers x 213 kilometers.
The South Platte River enters just to the right of center at the top of the images. It wends its way westward (down), then turns southward (right) where it flows through the city of Denver. Located at the western edge of the Great Plains, Denver is nicknamed the 'Mile High City', a consequence of its 1609-meter (5280-foot) elevation above sea level. It shows up in the imagery as a grayish patch surrounded by numerous agricultural fields to the north and east. Denver is situated just east of the Front Range of the Rocky Mountains, located in the lower right of the images. The Rockies owe their present forms to tectonic uplift and sculpting by millions of years of erosion. Scattered cumulus clouds floating above the mountain peaks are visible in these images, and stand out most dramatically in the 3-D stereo view.
To the north of Denver, other urban areas included within these images are Boulder, Greeley, Longmont, and Fort Collins, Colorado; Cheyenne and Laramie, Wyoming; and Scottsbluff, Nebraska.
MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.
Detonative propagation and accelerative expansion of the Crab Nebula shock front.
Gao, Yang; Law, Chung K
2011-10-21
The accelerative expansion of the Crab Nebula's outer envelope is a mystery in dynamics, as a conventional expanding blast wave decelerates when bumping into the surrounding interstellar medium. Here we show that the strong relativistic pulsar wind bumping into its surrounding nebula induces energy-generating processes and initiates a detonation wave that propagates outward to form the current outer edge, namely, the shock front, of the nebula. The resulting detonation wave, with a reactive downstream, then provides the needed power to maintain propagation of the shock front. Furthermore, relaxation of the curvature-induced reduction of the propagation velocity from the initial state of formation to the asymptotic, planar state of Chapman-Jouguet propagation explains the observed accelerative expansion. Potential richness in incorporating reactive fronts in the description of various astronomical phenomena is expected. PMID:22107499
A generalized front marching algorithm for the solution of the eikonal equation
NASA Astrophysics Data System (ADS)
Covello, Paul; Rodrigue, Garry
2003-07-01
A new front marching algorithm for solving the eikonal equation is presented. An important property of the algorithm is that it can be used on nodes that are located on highly distorted grids or on nodes that are randomly located. When the nodes are located on an orthogonal grid, the method is first-order accurate and is shown to be a generalization of the front marching algorithm in (Proc. Natl. Acad. Sci. 93 (4) (1996) 1591). The accuracy of the method is also shown to be dependent on the principle curvature of the wave front solution. Numerical results on a variety of node configurations as well as on shadow, nonconvex and nondifferentiable solutions are presented.
NASA Astrophysics Data System (ADS)
Clavin, P.; Searby, G.
A heuristic derivation of a flame front model is presented that takes into account the effects of gravity, nonlinear effects introduced by advection of the front, and gradients in the tangential component of the flow. A local equation is defined to relate the normal flame speed to the upstream gas flow characteristics. Jump conditions are obtained from an asymptotic analysis of the local structure of the wrinkled flame in order to address the hydrodynamic problem possed by the front being treated as a free boundary between fresh and burnt gases. The expression for the jump conditions is defined in Fourier space. The model extends the equations defined in Fourier space. The model extends the equations defined by Sivashinsky (1977) to cover the effects of gas expansion.
Cosmological spatial curvature probed by microwave polarization
Matzner, R.A.; Tolman, B.W.
1982-11-15
If there is a large-scale anisotropy in the expansion of the universe, the microwave background radiation is expected to be linearly polarized. This communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary ina complicated way over the celestial sphere (type VII/sub h/). These facts suggest a clear observational test of the closure of the universe. Also, an ambiguity inherent in the homogeneity of the universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called ''handedness.''
Actin filament curvature biases branching direction
NASA Astrophysics Data System (ADS)
Wang, Evan; Risca, Viviana; Chaudhuri, Ovijit; Chia, Jia-Jun; Geissler, Phillip; Fletcher, Daniel
2012-02-01
Actin filaments are key components of the cellular machinery, vital for a wide range of processes ranging from cell motility to endocytosis. Actin filaments can branch, and essential in this process is a protein complex known as the Arp2/3 complex, which nucleate new ``daughter'' filaments from pre-existing ``mother'' filaments by attaching itself to the mother filament. Though much progress has been made in understanding the Arp2/3-actin junction, some very interesting questions remain. In particular, F-actin is a dynamic polymer that undergoes a wide range of fluctuations. Prior studies of the Arp2/3-actin junction provides a very static notion of Arp2/3 binding. The question we ask is how differently does the Arp2/3 complex interact with a straight filament compared to a bent filament? In this study, we used Monte Carlo simulations of a surface-tethered worm-like chain to explore possible mechanisms underlying the experimental observation that there exists preferential branch formation by the Arp2/3 complex on the convex face of a curved filament. We show that a fluctuation gating model in which Arp2/3 binding to the actin filament is dependent upon a rare high-local-curvature shape fluctuation of the filament is consistent with the experimental data.
Geodesic Curvature Effects in the WCMs
NASA Astrophysics Data System (ADS)
Zhou, Tianchun
2015-11-01
The favorable features of the steady state I-Regime discovered on Alcator C-Mod recently make this regime a hopeful working regime for future burning plasma experiments. Accompanying the I-regime are the weakly coherent modes (WCMs) with frequency around 200 kHz that propagate poloidally in the electron diamagnetic drift direction in the lab frame. The WCMs were interpreted as certain type of heavy impurity modes in the 3-fluid framework in a 1-D plane magnetic field geometry. Once considering in a simplified toroidal magnetic field geometry, the geodesic curvature will play important roles in that the contribution of the geodesic compression may catch up with or outweighs that of the parallel compression in the plasma edge region where the fluctuations are highly localized. This geodesic coupling to the neighboring bands modifies the marginal stability condition and mode profiles in Refs.. In the same framework, attempts will be made to interpret the concomitant low frequency (~ 20kHz) fluctuations as a type of impurity drift wave-like modes propagating in the ion diamagnetic drift direction. Supported by China National MCFE Research Program under Grant No. 2015GB11000.
BICEP2, the curvature perturbation and supersymmetry
NASA Astrophysics Data System (ADS)
Lyth, David H.
2014-11-01
The tensor fraction r simeq 0.16 found by BICEP2 corresponds to a Hubble parameter H simeq 1.0 × 1014 GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index ns. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Characterizing repulsive gravity with curvature eigenvalues
NASA Astrophysics Data System (ADS)
Luongo, Orlando; Quevedo, Hernando
2014-10-01
Repulsive gravity has been investigated in several scenarios near compact objects by using different intuitive approaches. Here, we propose an invariant method to characterize regions of repulsive gravity, associated to black holes and naked singularities. Our method is based upon the behavior of the curvature tensor eigenvalues, and leads to an invariant definition of a repulsion radius. The repulsion radius determines a physical region, which can be interpreted as a repulsion sphere, where the effects due to repulsive gravity naturally arise. Further, we show that the use of effective masses to characterize repulsion regions can lead to coordinate-dependent results whereas, in our approach, repulsion emerges as a consequence of the spacetime geometry in a completely invariant way. Our definition is tested in the spacetime of an electrically charged Kerr naked singularity and in all its limiting cases. We show that a positive mass can generate repulsive gravity if it is equipped with an electric charge or an angular momentum. We obtain reasonable results for the spacetime regions contained inside the repulsion sphere whose size and shape depend on the value of the mass, charge and angular momentum. Consequently, we define repulsive gravity as a classical relativistic effect by using the geometry of spacetime only.
Gradient expansion, curvature perturbations, and magnetized plasmas
Giovannini, Massimo; Rezaei, Zahra
2011-04-15
The properties of magnetized plasmas are always investigated under the hypothesis that the relativistic inhomogeneities stemming from the fluid sources and from the geometry itself are sufficiently small to allow for a perturbative description prior to photon decoupling. The latter assumption is hereby relaxed and predecoupling plasmas are described within a suitable expansion where the inhomogeneities are treated to a given order in the spatial gradients. It is argued that the (general relativistic) gradient expansion shares the same features of the drift approximation, customarily employed in the description of cold plasmas, so that the two schemes are physically complementary in the large-scale limit and for the low-frequency branch of the spectrum of plasma modes. The two-fluid description, as well as the magnetohydrodynamical reduction, is derived and studied in the presence of the spatial gradients of the geometry. Various solutions of the coupled system of evolution equations in the anti-Newtonian regime and in the quasi-isotropic approximation are presented. The relation of this analysis to the so-called separate universe paradigm is outlined. The evolution of the magnetized curvature perturbations in the nonlinear regime is addressed for the magnetized adiabatic mode in the plasma frame.
BICEP2, the curvature perturbation and supersymmetry
Lyth, David H.
2014-11-01
The tensor fraction r ≅ 0.16 found by BICEP2 corresponds to a Hubble parameter H ≅ 1.0 × 10{sup 14} GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index n{sub s}. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Flow structure in front of the broad-crested weir
NASA Astrophysics Data System (ADS)
Zachoval, Zbyněk; Roušar, Ladislav
2015-05-01
The paper deals with research focused on description of flow structure in front of broad-crested weir. Based on experimental measurement, the flow structure in front of the weir (the recirculation zone of flow and tornado vortices) and flow structure on the weir crest has been described. The determined flow character has been simulated using numerical model and based on comparing results the suitable model of turbulence has been recommended.
NASA Astrophysics Data System (ADS)
Cao, Mao-Sen; Xu, Wei; Ren, Wei-Xin; Ostachowicz, Wiesław; Sha, Gang-Gang; Pan, Li-Xia
2016-08-01
Detection of multiple damage using modal curvature in noisy environments has become a research focus of considerable challenge and great significance over the last few years. However, a noticeable deficiency of modal curvature is its susceptibility to noise, which usually results in a noisy modal curvature with obscured damage signature. To address this deficiency, this study formulates a new concept of complex-wavelet modal curvature. Complex-wavelet modal curvature features the ability to reveal and delineate damage under noisy conditions. The effectiveness of the concept is analytically verified using cracked beams with various types of boundary conditions. The applicability is further experimentally validated by an aluminum beam with a single crack and a carbon-fiber-reinforced polymer composite beam with three cracks in the laboratory with mode shapes measured by a scanning laser vibrometer. Both analytical and experimental results have demonstrated that the complex-wavelet modal curvature is capable of revealing slight damage by eliminating noise interference, with no need for prior knowledge of either material properties or boundary conditions of the beam under inspection.
Lagrangian fronts in the ocean
NASA Astrophysics Data System (ADS)
Prants, S. V.; Budyansky, M. V.; Uleysky, M. Yu.
2014-05-01
We introduce the concept of Lagrangian fronts (LFs) in the ocean and describe their importance for analyzing water mixing and transport and the specific features and differences from hydrological fronts. A method of calculating LFs in a given velocity field is proposed. Based on altimeter velocity fields from AVISO data in the northwestern Pacific, we calculate the Lagrangian synoptic maps and identify LFs of different spatial and temporal scales. Using statistical analysis of saury catches in different years according to the Goskomrybolovstvo (State Fisheries Committee of the Russian Federation), we show that LFs can serve as good indicators of places that are favorable for fishing.
Using Surface Curvature to Control the Dimerization of a Surface-Active Protein
NASA Astrophysics Data System (ADS)
Kurylowicz, Martin; Giuliani, Maximiliano; Dutcher, John
2012-02-01
Understanding the influence of surface geometry on adsorbed proteins promises new possibilities in biophysics, such as topographical catalysis, molecular recognition of geometric cues, and modulations of oligomerization or ligand binding. We have created nano-textured hydrophobic surfaces that are stable in buffer by spin coating polystyrene (PS) nanoparticles (NPs) to form patchy NP monolayers on a PS substrate, yielding flat and highly curved areas on the same sample. Moreover, we have separated surface chemistry from texture by floating a 10 nm thick film of monodisperse PS onto the NP-functionalized surface. Using Single Molecule Force Spectroscopy we have compared in situ the distribution of detachment lengths for proteins on curved surfaces to that measured on flat surfaces. We have shown that β-Lactoglobulin (β-LG), a surface-active protein which helps to stabilize oil droplets in milk, forms dimers on both flat PS surfaces and surfaces with a radius of curvature of 100 nm, whereas β-LG monomers exist for more highly curved surfaces with radii of curvature of 25 and 40 nm. It is surprising that rather large radii of curvature have such a strong influence on proteins whose radius is only ˜2 nm. Furthermore, the transition from dimer to monomer with changes in surface curvature offers promising applications for proteins whose function can be modified by their oligomerization state.
Effect of contact angle on capillary displacement curvatures in pore throats formed by spheres
Mason, G. . Dept. of Chemical Engineering); Morrow, N.R. )
1994-11-01
The curvature of an interface in a pore depends upon the shape of the pore and the operative contact angle that the interface makes with the solid surface. Even relatively simple pores formed by the surfaces of equal spheres have a complex shape including nonaxisymmetric cross-section and converging-diverging geometry. For such pores, a theory for meniscus behavior has been devised that uses a combination of a theory for meniscus curvature in rods together with the toroidal approximation of Purcell. The results of the theory show that converging-diverging geometry tends to compensate for the effect of contact angle. This is because the position at which the nonzero contact angle meniscus has maximum curvature in a converging-diverging pore is not the narrowest part of the pore throat. Due to this compensation, the effect of contact angle on maximum meniscus curvatures for drainage is approximately proportional to cos 2/3 [theta] (rather than the cos [theta] appropriate for cylindrical tubes). Experiments on pores formed by PTFE spheres using partially wetting liquids confirmed the theoretical prediction. Contact angle measurements on the PTFE spheres also demonstrated that, because of microscopic surface roughness, receding contact angles (these being operative with respect to drainage) on ground surfaces are significantly lower than values for smooth surfaces.
Sim, SeungWoo; Kang, Seung-Ho; Lee, Sang-Hee
2015-02-01
Subterranean termites live underground and build tunnel networks to obtain food and nesting space. After obtaining food, termites return to their nests to transfer it. The efficiency of termite movement through the tunnels is directly connected to their survival. Tunnels should therefore be optimized to ensure highly efficient returns. An optimization factor that strongly affects movement efficiency is tunnel curvature. In the present study, we investigated traveling behavior in tunnels with different curvatures. We then characterized traveling behavior at the level of the individual using hidden Markov models (HMMs) constructed from the experimental data. To observe traveling behavior, we designed 5-cm long artificial tunnels that had different curvatures. The tunnels had widths (W) of 2, 3, or 4mm, and the linear distances between the two ends of the tunnels were (D) 20, 30, 40, or 50mm. High values of D indicate low curvature. We systematically observed the traveling behavior of Coptotermes formosanus shiraki and Reticulitermes speratus kyushuensis and measured the time (τ) required for a termite to pass through the tunnel. Using HMM models, we calculated τ for different tunnels and compared the results with the τ of real termites. We characterized the traveling behavior in terms of transition probability matrices (TPM) and emission probability matrices (EPM) of HMMs. We briefly discussed the construction of a sinusoidal-like tunnels in relation to the energy required for termites to pass through tunnels and provided suggestions for the development of more sophisticated HMMs to better understand termite foraging behavior. PMID:25562190
Yoshida, Kenji; Takagi, Toshimi
1999-07-01
Experimental and numerical studies are made of transient H{sub 2}/N{sub 2}--air counterflow diffusion flames unsteadily strained by an impinging micro jet. Two-dimensional temperature measurements by laser Rayleigh scattering method and numerical computations taking into account detailed chemical kinetics are conducted paying attention to transient local extinction and reignition in relation to the unsteadiness, flame curvature and preferential diffusion effects. The results are as follows. (1) Transient local flame extinction is observed where the micro jet impinges. But, the transient flame can survive instantaneously in spite of quite high stretch rate where the steady flame cannot exist. (2) Reignition is observed after the local extinction due to the micro air jet impingement. The temperature after reignition becomes significantly higher than that of the original flame. This high temperature is induced by the concentration of H{sub 2} species due to the preferential diffusion in relation to the concave curvature. The predicted behaviors of the local transient extinction and reignition are well confirmed by the experiments. (3) The reignition is induced after the formation of combustible premixed gas mixture and the consequent flame propagation. (4) The reignition is hardly observed after the extinction by micro fuel jet impingement. This is due to the dilution of H{sub 2} species induced by the preferential diffusion in relation to the convex curvature. (5) The maximum flame temperature cannot be rationalized by the stretch rate but changes widely depending on the unsteadiness and the flame curvature in relation with preferential diffusion.
NASA Astrophysics Data System (ADS)
RóŻycki, Bartosz; Lipowsky, Reinhard
2015-02-01
Biomimetic and biological membranes consist of molecular bilayers with two leaflets which are typically exposed to different aqueous environments and may differ in their molecular density or composition. Because of these asymmetries, the membranes prefer to curve in a certain manner as quantitatively described by their spontaneous curvature. Here, we study such asymmetric membranes via coarse-grained molecular dynamics simulations. We consider two mechanisms for the generation of spontaneous curvature: (i) different lipid densities within the two leaflets and (ii) leaflets exposed to different concentrations of adsorbing particles. We focus on membranes that experience no mechanical tension and describe two methods to compute the spontaneous curvature. The first method is based on the detailed structure of the bilayer's stress profile which can hardly be measured experimentally. The other method starts from the intuitive view that the bilayer represents a thin fluid film bounded by two interfaces and reduces the complexity of the stress profile to a few membrane parameters that can be measured experimentally. For the case of asymmetric adsorption, we introduce a simulation protocol based on two bilayers separated by two aqueous compartments with different adsorbate concentrations. The adsorption of small particles with a size below 1 nm is shown to generate large spontaneous curvatures up to about 1/(24 nm). Our computational approach is quite general: it can be applied to any molecular model of bilayer membranes and can be extended to other mechanisms for the generation of spontaneous curvatures as provided, e.g., by asymmetric lipid composition or depletion layers of solute molecules.
MARCKS-ED Peptide as a Curvature and Lipid Sensor
Morton, Leslie A.; Yang, Hengwen; Saludes, Jonel P.; Fiorini, Zeno; Beninson, Lida; Chapman, Edwin R.; Fleshner, Monika; Xue, Ding; Yin, Hang
2012-01-01
Membrane curvature and lipid composition regulate important biological processes within a cell. Currently, several proteins have been reported to sense and/or induce membrane curvatures, e.g. Synaptotagmin-1 and Amphiphysin. However, the large protein scaffold of these curvature sensors limits their applications in complex biological systems. Our interest focuses on identifying and designing peptides that can sense membrane curvature based on established elements observed in natural curvature-sensing proteins. Membrane curvature remodeling also depends on their lipid composition, suggesting strategies to specifically target membrane shape and lipid components simultaneously. We have successfully identified a 25-mer peptide, MARCKS-ED, based on the effector domain sequence of the intracellular membrane protein myristoylated alanine-rich C-kinase substrate that can recognize PS with preferences for highly curved vesicles in a sequence specific manner. These studies further contribute to the understanding of how proteins and peptides sense membrane curvature, as well as provide potential probes for membrane shape and lipid composition. PMID:23075500
On 3-gauge transformations, 3-curvatures, and Gray-categories
Wang, Wei
2014-04-15
In the 3-gauge theory, a 3-connection is given by a 1-form A valued in the Lie algebra g, a 2-form B valued in the Lie algebra h, and a 3-form C valued in the Lie algebra l, where (g,h,l) constitutes a differential 2-crossed module. We give the 3-gauge transformations from one 3-connection to another, and show the transformation formulae of the 1-curvature 2-form, the 2-curvature 3-form, and the 3-curvature 4-form. The gauge configurations can be interpreted as smooth Gray-functors between two Gray 3-groupoids: the path 3-groupoid P{sub 3}(X) and the 3-gauge group G{sup L} associated to the 2-crossed module L, whose differential is (g,h,l). The derivatives of Gray-functors are 3-connections, and the derivatives of lax-natural transformations between two such Gray-functors are 3-gauge transformations. We give the 3-dimensional holonomy, the lattice version of the 3-curvature, whose derivative gives the 3-curvature 4-form. The covariance of 3-curvatures easily follows from this construction. This Gray-categorical construction explains why 3-gauge transformations and 3-curvatures have the given forms. The interchanging 3-arrows are responsible for the appearance of terms with the Peiffer commutator (, )
Active optics: variable curvature mirrors for ELT laser guide star refocusing systems
NASA Astrophysics Data System (ADS)
Challita, Zalpha; Hugot, Emmanuel; Madec, Fabrice; Ferrari, Marc; Le Mignant, David; Vivès, Sébastien; Cuby, Jean-Gabriel
2011-10-01
The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope. This variation leads to a defocusing effect on the LGS wave-front sensor which needs to be compensated. We propose an active mirror able to compensate for this variation, based on an original optical design including this active optics component. This LGS Variable Curvature Mirror (LGS-VCM) is a 120 mm spherical active mirror able to achieve 820 μm deflection sag with an optical quality better than 150 nm RMS, allowing the radius of curvature variation from F/12 to F/2. Based on elasticity theory, the deformation of the metallic mirror is provided by an air pressure applied on a thin meniscus with a variable thickness distribution. In this article, we detail the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Three prototypes have been manufactured to compare the real behavior of the mirror and the simulations data. Results obtained on the prototypes are detailed, showing that the deformation of the VCM is very close to the simulation, and leads to a realistic active concept.
NASA Astrophysics Data System (ADS)
Wells, Conrad; Olczak, Gene; Merle, Cormic; Dey, Tom; Waldman, Mark; Whitman, Tony; Wick, Eric; Peer, Aaron
2010-08-01
The James Webb Space Telescope (JWST) Optical Telescope Element (OTE) consists of a 6.6 m clear aperture, allreflective, three-mirror anastigmat. The 18-segment primary mirror (PM) presents unique and challenging assembly, integration, alignment and testing requirements. A full aperture center of curvature optical test is performed in cryogenic vacuum conditions at the integrated observatory level to verify PM performance requirements. The Center of Curvature Optical Assembly (CoCOA), designed and being built by ITT satisfies the requirements for this test. The CoCOA contains a multi wave interferometer, patented reflective null lens, actuation for alignment, full in situ calibration capability, coarse and fine alignment sensing systems, as well as a system for monitoring changes in the PM to CoCOA distance. Two wave front calibration tests are utilized to verify the low and Mid/High spatial frequencies, overcoming the limitations of the standard null/hologram configuration in its ability to resolve mid and high spatial frequencies. This paper will introduce the systems level architecture and optical test layout for the CoCOA.
Influence of Coanda surface curvature on performance of bladeless fan
NASA Astrophysics Data System (ADS)
Li, Guoqi; Hu, Yongjun; Jin, Yingzi; Setoguchi, Toshiaki; Kim, Heuy Dong
2014-10-01
The unique Coanda surface has a great influence on the performance of bladeless fan. However, there is few studies to explain the relationship between the performance and Coanda surface curvature at present. In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan, numerical studies are performed in this paper. Firstly, three-dimensional numerical simulation is done by Fluent software. For the purpose to obtain detailed information of the flow field around the Coanda surface, two-dimensional numerical simulation is also conducted. Five types of Coanda surfaces with different curvature are designed, and the flow behaviour and the performance of them are analyzed and compared with those of the prototype. The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance, It is found that there is an optimal curvature of Coanda surfaces among the studied models. Simulation result shows that there is a special low pressure region. With increasing curvature in Y direction, several low pressure regions gradually enlarged, then begin to merge slowly, and finally form a large area of low pressure. From the analyses of streamlines and velocity angle, it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall. Thus, it leads to that the curvature of the streamlines is consistent with that of Coanda surface. Meanwhile, it also causes the fluid movement towards the most suitable direction. This study will provide useful information to performance improvements of bladeless fans.
The Arctic Front in the Fram Strait in autumn 2011
NASA Astrophysics Data System (ADS)
Ullgren, Jenny; Falck, Eva; Beszczynska-Möller, Agnieszka; Sagen, Hanne
2016-04-01
The front between Atlantic water carried northward by the main branch of the West Spitsbergen Current and the cooler, fresher Arctic domain in the central Fram Strait, here called the Arctic Front, is important because of the exchange of heat and salt across it. The marked water mass boundary and the dynamics of the front also profoundly affect the living conditions for marine organisms. A northwest-to-southeast transect across the Arctic Front with concurrent shipboard and glider measurements was done in September 2011. The CTD data, nutrient and pigment samples, and underway ADCP data from the research cruise are complemented by the glider observations of temperature and salinity at higher horizontal resolution. In addition, images from the ship's scientific echo sounder are used to qualitatively describe the water column structure and distribution of marine organisms along the transect. Crossing the front from northwest to southeast, the near-surface (5 m) temperature increased by more than 4°C and salinity increased by 0.98 PSU between stations 19 km apart. The front was thus clearly marked in salinity and temperature in the upper 200 m, but below the surface layer it was largely density compensated. The highest chlorophyll-a concentrations were found in subsurface maxima on the Arctic side of the front. We investigate the hydrographic structure of the front, considering properties relevant to cross-frontal exchange and mixing. We also assess the environmental conditions on each side of the front - for example mixed layer depths, nutrient availability, and bio-optical properties - and their implications for marine life.
Dynamic Curvature Steering Control for Autonomous Vehicle: Performance Analysis
NASA Astrophysics Data System (ADS)
Aizzat Zakaria, Muhammad; Zamzuri, Hairi; Amri Mazlan, Saiful
2016-02-01
This paper discusses the design of dynamic curvature steering control for autonomous vehicle. The lateral control and longitudinal control are discussed in this paper. The controller is designed based on the dynamic curvature calculation to estimate the path condition and modify the vehicle speed and steering wheel angle accordingly. In this paper, the simulation results are presented to show the capability of the controller to track the reference path. The controller is able to predict the path and modify the vehicle speed to suit the path condition. The effectiveness of the controller is shown in this paper whereby identical performance is achieved with the benchmark but with extra curvature adaptation capabilites.
Complete manifolds with bounded curvature and spectral gaps
NASA Astrophysics Data System (ADS)
Schoen, Richard; Tran, Hung
2016-08-01
We study the spectrum of complete noncompact manifolds with bounded curvature and positive injectivity radius. We give general conditions which imply that their essential spectrum has an arbitrarily large finite number of gaps. In particular, for any noncompact covering of a compact manifold, there is a metric on the base so that the lifted metric has an arbitrarily large finite number of gaps in its essential spectrum. Also, for any complete noncompact manifold with bounded curvature and positive injectivity radius we construct a metric uniformly equivalent to the given one (also of bounded curvature and positive injectivity radius) with an arbitrarily large finite number of gaps in its essential spectrum.
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
Motion on constant curvature spaces and quantization using Noether symmetries.
Bracken, Paul
2014-12-01
A general approach is presented for quantizing a metric nonlinear system on a manifold of constant curvature. It makes use of a curvature dependent procedure which relies on determining Noether symmetries from the metric. The curvature of the space functions as a constant parameter. For a specific metric which defines the manifold, Lie differentiation of the metric gives these symmetries. A metric is used such that the resulting Schrödinger equation can be solved in terms of hypergeometric functions. This permits the investigation of both the energy spectrum and wave functions exactly for this system. PMID:25554048
Motion on constant curvature spaces and quantization using noether symmetries
NASA Astrophysics Data System (ADS)
Bracken, Paul
2014-12-01
A general approach is presented for quantizing a metric nonlinear system on a manifold of constant curvature. It makes use of a curvature dependent procedure which relies on determining Noether symmetries from the metric. The curvature of the space functions as a constant parameter. For a specific metric which defines the manifold, Lie differentiation of the metric gives these symmetries. A metric is used such that the resulting Schrödinger equation can be solved in terms of hypergeometric functions. This permits the investigation of both the energy spectrum and wave functions exactly for this system.
Curvature perturbation and waterfall dynamics in hybrid inflation
Abolhasani, Ali Akbar; Firouzjahi, Hassan; Sasaki, Misao E-mail: firouz@mail.ipm.ir
2011-10-01
We investigate the parameter spaces of hybrid inflation model with special attention paid to the dynamics of waterfall field and curvature perturbations induced from its quantum fluctuations. Depending on the inflaton field value at the time of phase transition and the sharpness of the phase transition inflation can have multiple extended stages. We find that for models with mild phase transition the induced curvature perturbation from the waterfall field is too large to satisfy the COBE normalization. We investigate the model parameter space where the curvature perturbations from the waterfall quantum fluctuations vary between the results of standard hybrid inflation and the results obtained here.
LPG-based sensor for curvature and vibration
NASA Astrophysics Data System (ADS)
Nascimento, I. M.; Chesini, G.; Baptista, J. M.; Cordeiro, Cristiano M. B.; Jorge, P. A. S.
2016-05-01
A long-period grating (LPG) written on a standard single mode fiber is investigated as a curvature and vibration sensor. It is demonstrated a high sensitivity to applied curvature and the possibility to monitor vibration in a wide range of frequencies from 30 Hz to 2000 Hz. The system was tested using an intensity based interrogation scheme with the LPG sensor operating in the curvature regime. Results have shown a reproducible frequency discrimination in the 30 Hz to 2000 Hz, with resolutions between 11 mHz and 913 mHz. Frequency retrieval could be performed independent of temperature up to 86 °C.
Advanced RF Front End Technology
NASA Technical Reports Server (NTRS)
Herman, M. I.; Valas, S.; Katehi, L. P. B.
2001-01-01
The ability to achieve low-mass low-cost micro/nanospacecraft for Deep Space exploration requires extensive miniaturization of all subsystems. The front end of the Telecommunication subsystem is an area in which major mass (factor of 10) and volume (factor of 100) reduction can be achieved via the development of new silicon based micromachined technology and devices. Major components that make up the front end include single-pole and double-throw switches, diplexer, and solid state power amplifier. JPL's Center For Space Microsystems - System On A Chip (SOAC) Program has addressed the challenges of front end miniaturization (switches and diplexers). Our objectives were to develop the main components that comprise a communication front end and enable integration in a single module that we refer to as a 'cube'. In this paper we will provide the latest status of our Microelectromechanical System (MEMS) switches and surface micromachined filter development. Based on the significant progress achieved we can begin to provide guidelines of the proper system insertion for these emerging technologies. Additional information is contained in the original extended abstract.
ERIC Educational Resources Information Center
Perry, Jim
1995-01-01
Discussion of management styles and front-end analysis focuses on a review of Douglas McGregor's theories. Topics include Theories X, Y, and Z; leadership skills; motivational needs of employees; intrinsic and extrinsic rewards; and faulty implementation of instructional systems design processes. (LRW)
Teaching the French Popular Front.
ERIC Educational Resources Information Center
Wall, Irwin M.
1987-01-01
Examines the French Popular Front of 1936 as a vehicle to investigate the turbulent decade of the 1930s. Reviews current historiography and discusses various facets of Leon Blum's government, examining the interrelationship of major economic and political forces. Concludes that the French Left still faces Blum's dilemma of implementing socialism…
Curvature-driven assembly in soft matter.
Liu, Iris B; Sharifi-Mood, Nima; Stebe, Kathleen J
2016-07-28
Control over the spatial arrangement of colloids in soft matter hosts implies control over a wide variety of properties, ranging from the system's rheology, optics, and catalytic activity. In directed assembly, colloids are typically manipulated using external fields to form well-defined structures at given locations. We have been developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. Such potential fields allow particles to interact with each other. If the soft matter host is deformed in some way, the potential allows the particles to interact with the global system distortion. One important example is capillary assembly of colloids on curved fluid interfaces. Upon attaching, the particle distorts that interface, with an associated energy field, given by the product of its interfacial area and the surface tension. The particle's capillary energy depends on the local interface curvature. We explore this coupling in experiment and theory. There are important analogies in liquid crystals. Colloids in liquid crystals elicit an elastic energy response. When director fields are moulded by confinement, the imposed elastic energy field can couple to that of the colloid to define particle paths and sites for assembly. By improving our understanding of these and related systems, we seek to develop new, parallelizable routes for particle assembly to form reconfigurable systems in soft matter that go far beyond the usual close-packed colloidal structures.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298434
Curvature instability of a vortex ring
NASA Astrophysics Data System (ADS)
Fukumoto, Yasuhide; Hattori, Yuji
2005-03-01
A global stability analysis of Kelvin's vortex ring to three-dimensional disturbances of infinitesimal amplitude is made. The basic state is a steady asymptotic solution of the Euler equations, in powers of the ratio ɛ of the core radius to the ring radius, for an axisymmetric vortex ring with vorticity proportional to the distance from the symmetric axis. The effect of ring curvature appears at first order, in the form of a dipole field, and a local straining field, which is a quadrupole field, follows at second order. The eigenvalue problem of the Euler equations, retaining the terms to first order, is solved in closed form, in terms of the Bessel and the modified Bessel functions. We show that the dipole field causes a parametric resonance instability between a pair of Kelvin waves whose azimuthal wavenumbers are separated by 1. The most unstable mode occurs in the short-wavelength limit, under the constraint that the radial and the azimuthal wavenumbers are of the same magnitude, and the limiting value of maximum growth rate coincides with the value 165/256 ɛ obtained by Hattori & Fukumoto (Phys. Fluids, vol. 15, 2003, p. 3151) by means of the geometric optics method. The instability mechanism is traced to stretching of disturbance vorticity in the toroidal direction. In the absence of viscosity, the dipole effect outweighs the straining field effect of O(ɛ2) known as the Moore-Saffman-Tsai-Widnall instability. The viscosity acts to damp the former preferentially and these effects compete with each other.
Fluctuation-controlled front propagation
NASA Astrophysics Data System (ADS)
Ridgway, Douglas Thacher
1997-09-01
A number of fundamental pattern-forming systems are controlled by fluctuations at the front. These problems involve the interaction of an infinite dimensional probability distribution with a strongly nonlinear, spatially extended pattern-forming system. We have examined fluctuation-controlled growth in the context of the specific problems of diffusion-limited growth and biological evolution. Mean field theory of diffusion-limited growth exhibits a finite time singularity. Near the leading edge of a diffusion-limited front, this leads to acceleration and blowup. This may be resolved, in an ad hoc manner, by introducing a cutoff below which growth is weakened or eliminated (8). This model, referred to as the BLT model, captures a number of qualitative features of global pattern formation in diffusion-limited aggregation: contours of the mean field match contours of averaged particle density in simulation, and the modified mean field theory can form dendritic features not possible in the naive mean field theory. The morphology transition between dendritic and non-dendritic global patterns requires that BLT fronts have a Mullins-Sekerka instability of the wavefront shape, in order to form concave patterns. We compute the stability of BLT fronts numerically, and compare the results to fronts without a cutoff. A significant morphological instability of the BLT fronts exists, with a dominant wavenumber on the scale of the front width. For standard mean field fronts, no instability is found. The naive and ad hoc mean field theories are continuum-deterministic models intended to capture the behavior of a discrete stochastic system. A transformation which maps discrete systems into a continuum model with a singular multiplicative noise is known, however numerical simulations of the continuum stochastic system often give mean field behavior instead of the critical behavior of the discrete system. We have found a new interpretation of the singular noise, based on maintaining
Antarctic Ice-Shelf Front Dynamics from ICESat
NASA Technical Reports Server (NTRS)
Robbins, John W.; Zwally, H. Jay; Saba, Jack L.; Yi, Donghui
2012-01-01
Time variable elevation profiles from ICESat Laser Altimetry over the period 2003-2009 provide a means to quantitatively detect and track topographic features on polar ice surfaces. The results of this study provide a measure of the horizontal motion of ice-shelf fronts. We examine the time histories of elevation profiles crossing the ice fronts of the Ross, Ronne, Filchner, Riiser-Larson and Fimbul shelves. This provides a basis for estimating dynamics in two dimensions, i.e. in elevation and horizontally in the along-track direction. Ice front velocities, corrected for ground-track intersection angle, range from nearly static to 1.1 km/yr. In many examples, a decrease in elevation up to 1 m/yr near the shelf frontis also detectable. Examples of tabular calving along shelf fronts are seen in some elevation profiles and are confirmed by corresponding MODIS imagery.
Murphy, Ryan J.; Armand, Mehran
2016-01-01
Reliably estimating the shape of variable curvature continuum dexterous manipulators (CDMs) is necessary to use these devices in biomedical applications. Embedding shape-sensing elements have been shown to effectively measure the shape of constant curvature CDMs. This paper explores several methods for estimating the configuration of variable curvature CDMs. Experiments bent the CDM in varying configurations, applied an external load, and measured the configuration. Three methods are described that use the measurements from simulated shape-sensing elements. Analyses included varying the number and placement of the shape sensors. The results showed at least three shape-sensing elements are necessary to predict manipulator configuration, with one method demonstrating average error less than 0.35 mm for a CDM under an external load. The presented techniques offer promise for successfully predicting, tracking, and controlling CDM configuration during surgery. PMID:26737480
A Linearization Time-Domain CMOS Smart Temperature Sensor Using a Curvature Compensation Oscillator
Chen, Chun-Chi; Chen, Hao-Wen
2013-01-01
This paper presents an area-efficient time-domain CMOS smart temperature sensor using a curvature compensation oscillator for linearity enhancement with a −40 to 120 °C temperature range operability. The inverter-based smart temperature sensors can substantially reduce the cost and circuit complexity of integrated temperature sensors. However, a large curvature exists on the temperature-to-time transfer curve of the inverter-based delay line and results in poor linearity of the sensor output. For cost reduction and error improvement, a temperature-to-pulse generator composed of a ring oscillator and a time amplifier was used to generate a thermal sensing pulse with a sufficient width proportional to the absolute temperature (PTAT). Then, a simple but effective on-chip curvature compensation oscillator is proposed to simultaneously count and compensate the PTAT pulse with curvature for linearization. With such a simple structure, the proposed sensor possesses an extremely small area of 0.07 mm2 in a TSMC 0.35-μm CMOS 2P4M digital process. By using an oscillator-based scheme design, the proposed sensor achieves a fine resolution of 0.045 °C without significantly increasing the circuit area. With the curvature compensation, the inaccuracy of −1.2 to 0.2 °C is achieved in an operation range of −40 to 120 °C after two-point calibration for 14 packaged chips. The power consumption is measured as 23 μW at a sample rate of 10 samples/s. PMID:23989825
The relationship between sagittal curvature and extensor muscle volume in the lumbar spine.
Meakin, Judith R; Fulford, Jonathan; Seymour, Richard; Welsman, Joanne R; Knapp, Karen M
2013-06-01
A previous modelling study predicted that the forces applied by the extensor muscles to stabilise the lumbar spine would be greater in spines that have a larger sagittal curvature (lordosis). Because the force-generating capacity of a muscle is related to its size, it was hypothesised that the size of the extensor muscles in a subject would be related to the size of their lumbar lordosis. Magnetic resonance imaging (MRI) data were obtained, together with age, height, body mass and back pain status, from 42 female subjects. The volume of the extensor muscles (multifidus and erector spinae) caudal to the mid-lumbar level was estimated from cross-sectional area measurements in axial T1-weighted MRIs spanning the lumbar spine. Lower lumbar curvature was determined from sagittal T1-weighted images. A stepwise linear regression model was used to determine the best predictors of muscle volume. The mean lower lumbar extensor muscle volume was 281 cm(3) (SD = 49 cm(3)). The mean lower lumbar curvature was 30 ° (SD = 7 °). Five subjects reported current back pain and were excluded from the regression analysis. Nearly half the variation in muscle volume was accounted for by the variables age (standardised coefficient, B = -3.2, P = 0.03) and lower lumbar curvature (B = 0.47, P = 0.002). The results support the hypothesis that extensor muscle volume in the lower lumbar spine is related to the magnitude of the sagittal curvature; this has implications for assessing muscle size as an indicator of muscle strength. PMID:23600615
Linear response to long wavelength fluctuations using curvature simulations
NASA Astrophysics Data System (ADS)
Baldauf, Tobias; Seljak, Uroš; Senatore, Leonardo; Zaldarriaga, Matias
2016-09-01
We study the local response to long wavelength fluctuations in cosmological N-body simulations, focusing on the matter and halo power spectra, halo abundance and non-linear transformations of the density field. The long wavelength mode is implemented using an effective curved cosmology and a mapping of time and distances. The method provides an alternative, more direct, way to measure the isotropic halo biases. Limiting ourselves to the linear case, we find generally good agreement between the biases obtained from the curvature method and the traditional power spectrum method at the level of a few percent. We also study the response of halo counts to changes in the variance of the field and find that the slope of the relation between the responses to density and variance differs from the naïve derivation assuming a universal mass function by approximately 8–20%. This has implications for measurements of the amplitude of local non-Gaussianity using scale dependent bias. We also analyze the halo power spectrum and halo-dark matter cross-spectrum response to long wavelength fluctuations and derive second order halo bias from it, as well as the super-sample variance contribution to the galaxy power spectrum covariance matrix.
Osteonal lamellae elementary units: lamellar microstructure, curvature and mechanical properties.
Faingold, Anna; Cohen, Sidney R; Reznikov, Natalie; Wagner, H Daniel
2013-04-01
The mechanical and structural properties of the sublayers of osteonal lamellae were studied. Young's modulus (E) of adjacent individual lamellae was measured by nanoindentation of parallel slices every 1-3 μm, in planes parallel and perpendicular to the osteon axis (OA). In planes parallel to the OA, the modulus of a lamella could vary significantly between sequential slices. Significant modulus variations were also sometimes found on opposing sides of the osteonal canal for the same lamella. These results are rationalized by considerations involving the microstructural organization of the collagen fibrils in the lamellae. Scanning electron microscope imaging of freeze fractured surfaces revealed that the substructure of a single lamella can vary significantly on the opposing sides of the osteonal axis. Using a serial surface view method, parallel planes were exposed every 8-10 nm using a dual-beam microscope. Analysis of the orientations of fibrils revealed that the structure is rotated plywood like, consisting of unidirectional sublayers of fibrils of several orientations, with occasional randomly oriented sublayers. The dependence of the measured mechanical properties of the lamellae on the indentation location may be explained by the observed structure, as well as by the curvature of the osteonal lamellae through simple geometrical-structural considerations. Mechanical advantages arising from the curved laminate structure are discussed. PMID:23220032
Local curvature analysis for classifying breast tumors: Preliminary analysis in dedicated breast CT
Lee, Juhun; Nishikawa, Robert M.; Reiser, Ingrid; Boone, John M.; Lindfors, Karen K.
2015-01-01
Purpose: The purpose of this study is to measure the effectiveness of local curvature measures as novel image features for classifying breast tumors. Methods: A total of 119 breast lesions from 104 noncontrast dedicated breast computed tomography images of women were used in this study. Volumetric segmentation was done using a seed-based segmentation algorithm and then a triangulated surface was extracted from the resulting segmentation. Total, mean, and Gaussian curvatures were then computed. Normalized curvatures were used as classification features. In addition, traditional image features were also extracted and a forward feature selection scheme was used to select the optimal feature set. Logistic regression was used as a classifier and leave-one-out cross-validation was utilized to evaluate the classification performances of the features. The area under the receiver operating characteristic curve (AUC, area under curve) was used as a figure of merit. Results: Among curvature measures, the normalized total curvature (CT) showed the best classification performance (AUC of 0.74), while the others showed no classification power individually. Five traditional image features (two shape, two margin, and one texture descriptors) were selected via the feature selection scheme and its resulting classifier achieved an AUC of 0.83. Among those five features, the radial gradient index (RGI), which is a margin descriptor, showed the best classification performance (AUC of 0.73). A classifier combining RGI and CT yielded an AUC of 0.81, which showed similar performance (i.e., no statistically significant difference) to the classifier with the above five traditional image features. Additional comparisons in AUC values between classifiers using different combinations of traditional image features and CT were conducted. The results showed that CT was able to replace the other four image features for the classification task. Conclusions: The normalized curvature measure contains
Curvature Control of Silicon Microlens for THz Dielectric Antenna
NASA Technical Reports Server (NTRS)
Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran
2012-01-01
We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.
16. Detail of curvature of northern parapet, with 1932 concrete ...
16. Detail of curvature of northern parapet, with 1932 concrete extension of parapet in foreground, facing east. - Dubbs Bridge, Spinnerstown Road (State Route 2031) spanning Hosensack Creek, Dillingerville, Lehigh County, PA
Wavefront curvature of an opticaly pumped waveguide laser
Tacke, M.
1983-05-01
The influence of inhomogeneous gain on the wavefront shape is discussed for waveguide lasers. As an example, the curvature of the EH(11) mode of an optically pumped FIR laser is computed, its influence on the output beam is discussed.
Curvature-Squared Cosmology In The First-Order Formalism
NASA Technical Reports Server (NTRS)
Shahid-Saless, Bahman
1993-01-01
Paper presents theoretical study of some of general-relativistic ramifications of gravitational-field energy density proportional to R - alpha R(exp 2) (where R is local scalar curvature of space-time and alpha is a constant).
Curvature and bow of bulk GaN substrates
NASA Astrophysics Data System (ADS)
Foronda, Humberto M.; Romanov, Alexey E.; Young, Erin C.; Roberston, Christian A.; Beltz, Glenn E.; Speck, James S.
2016-07-01
We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.
Constraints on the geometric and dynamic spatial curvature
NASA Astrophysics Data System (ADS)
Yu, Bo
2015-10-01
In this paper, the geometric and dynamic spatial curvature parameters of the Universe are constrained by type Ia supernova, baryon acoustic oscillation, and cosmic microwave background data. Compared with the previous result, a more stringent constraint is obtained, especially for the dynamic spatial curvature in the case of variable dark energy. No evidence is found that the geometric spatial curvature deviates from the dynamic spatial curvature, which is consistent with general relativity. In the case of dark energy with constant equation of state, it is found that -8.4 ×1 0-3≤ΩKgeo≤6.6 ×1 0-3 (95% C.L.). This supports the hypothesis of a flat Universe in a very general meaning.
Bacterial cell curvature through mechanical control of cell growth
Cabeen, Matthew T; Charbon, Godefroid; Vollmer, Waldemar; Born, Petra; Ausmees, Nora; Weibel, Douglas B; Jacobs-Wagner, Christine
2009-01-01
The cytoskeleton is a key regulator of cell morphogenesis. Crescentin, a bacterial intermediate filament-like protein, is required for the curved shape of Caulobacter crescentus and localizes to the inner cell curvature. Here, we show that crescentin forms a single filamentous structure that collapses into a helix when detached from the cell membrane, suggesting that it is normally maintained in a stretched configuration. Crescentin causes an elongation rate gradient around the circumference of the sidewall, creating a longitudinal cell length differential and hence curvature. Such curvature can be produced by physical force alone when cells are grown in circular microchambers. Production of crescentin in Escherichia coli is sufficient to generate cell curvature. Our data argue for a model in which physical strain borne by the crescentin structure anisotropically alters the kinetics of cell wall insertion to produce curved growth. Our study suggests that bacteria may use the cytoskeleton for mechanical control of growth to alter morphology. PMID:19279668
The longitudinal thickness of air-shower fronts
NASA Technical Reports Server (NTRS)
Clay, R. W.; Elton, S. D.; Wild, N. R.; Brissenden, R. J. V.
1985-01-01
Linsely (1983) has proposed a technique for the detection and analysis of air showers at large distances from the shower axis based on a measurement of the shower front thickness and the assumption that this thickness is closely related to the core distance. Some of the problems involved with realizing such a technique were investigated, and some related observations are reported. The practical problems of how consistent the measurements of the shower front would be, how one would use the measurement, and how the rate of triggered events would depend on the minimum pulse width required are studied.
Reaction front formation in contaminant plumes
NASA Astrophysics Data System (ADS)
Cribbin, Laura B.; Winstanley, Henry F.; Mitchell, Sarah L.; Fowler, Andrew C.; Sander, Graham C.
2014-12-01
The formation of successive fronts in contaminated groundwater plumes by subsoil bacterial action is a commonly accepted feature of their propagation, but it is not obviously clear from a mathematical standpoint quite how such fronts are formed or propagate. In this paper we show that these can be explained by combining classical reaction-diffusion theory involving just two reactants (oxidant and reductant), and a secondary reaction in which a reactant on one side of such a front is (re-)formed on the other side of the front via diffusion of its product across the front. We give approximate asymptotic solutions for the reactant profiles, and the propagation rate of the front.
Modeling of stress-induced curvature in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Cowan, William D.; Bright, Victor M.; Elvin, Alex A.; Koester, David A.
1997-09-01
This paper compares measured to modeled stress-induced curvature of simple piston micromirrors. Two similar flexure-beam micromirror designs were fabricate using the 11th DARPA-supported multi-user MEMS processes (MUMPs) run. The test devices vary only in the MUMPs layers used for fabrication. In one case the mirror plate is the 1.5 micrometers thick Poly2 layer. The other mirror design employs stacked Poly1 and Poly2 layers for a total thickness of 3.5 micrometers . Both mirror structures are covered with the standard MUMPs metallization of approximately 200 angstrom of chromium and 0.5 micrometers of gold. Curvature of these devices was measured to within +/- 5 nm with a computer controlled microscope laser interferometer system. As intended, the increased thickness of the stacked polysilicon layers reduces the mirror curvature by a factor of 4. The two micromirror designs were modeled using IntelliCAD, a commercial CAD system for MEMS. The basis of analysis was the finite element method. Simulated results using MUMPs 11 film parameters showed qualitative agreement with measured data, but obvious quantitative differences. Subsequent remeasurement of the metal stress and use of the new value significantly improved model agreement with the measured data. The paper explores the effect of several film parameters on the modeled structures. Implications for MEMS film metrology, and test structures are considered.
Layered devices having surface curvature and method of constructing same
Woodbury, Richard C.; Perkins, Raymond T.; Thorne, James M.
1989-01-01
A method of treating a substrate having first and second sides with corresponding oppositely facing first and second surfaces, to produce curvature in the first surface. The method includes the steps of removing material, according to a predetermined pattern, from the second side of the substrate, and applying a stress-producing film of material to at least one surface of the substrate to thereby cause the substrate to bend to produce the desired curvature in the first surface.
Topology of codimension-one foliations of nonnegative curvature
Bolotov, Dmitry V
2013-05-31
We show that a transversely oriented C{sup 2}-foliation of codimension one with nonnegative Ricci curvature on a closed orientable manifold is a foliation with almost no holonomy. This allows us to decompose the manifold into blocks on which this foliation has a simple structure. We also show that a manifold homeomorphic to a 5-dimensional sphere does not admit a codimension-one C{sup 2}-foliation with nonnegative sectional curvature. Bibliography: 29 titles.
Hedgehogs in higher dimensional gravity with curvature self-interactions
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2001-04-01
Static solutions of the higher dimensional Einstein-Hilbert gravity supplemented by quadratic curvature self-interactions are discussed in the presence of hedgehog configurations along the transverse dimensions. The quadratic part of the action is parametrized in terms of the (ghost-free) Euler-Gauss-Bonnet curvature invariant. Spherically symmetric profiles of the transverse metric admit exponentially decaying warp factors both for positive and negative bulk cosmological constants.
Curvature recognition and force generation in phagocytosis
2010-01-01
Background The uptake of particles by actin-powered invagination of the plasma membrane is common to protozoa and to phagocytes involved in the immune response of higher organisms. The question addressed here is how a phagocyte may use geometric cues to optimize force generation for the uptake of a particle. We survey mechanisms that enable a phagocyte to remodel actin organization in response to particles of complex shape. Results Using particles that consist of two lobes separated by a neck, we found that Dictyostelium cells transmit signals concerning the curvature of a surface to the actin system underlying the plasma membrane. Force applied to a concave region can divide a particle in two, allowing engulfment of the portion first encountered. The phagosome membrane that is bent around the concave region is marked by a protein containing an inverse Bin-Amphiphysin-Rvs (I-BAR) domain in combination with an Src homology (SH3) domain, similar to mammalian insulin receptor tyrosine kinase substrate p53. Regulatory proteins enable the phagocyte to switch activities within seconds in response to particle shape. Ras, an inducer of actin polymerization, is activated along the cup surface. Coronin, which limits the lifetime of actin structures, is reversibly recruited to the cup, reflecting a program of actin depolymerization. The various forms of myosin-I are candidate motor proteins for force generation in particle uptake, whereas myosin-II is engaged only in retracting a phagocytic cup after a switch to particle release. Thus, the constriction of a phagocytic cup differs from the contraction of a cleavage furrow in mitosis. Conclusions Phagocytes scan a particle surface for convex and concave regions. By modulating the spatiotemporal pattern of actin organization, they are capable of switching between different modes of interaction with a particle, either arresting at a concave region and applying force in an attempt to sever the particle there, or extending the cup
Nanoscale Membrane Curvature detected by Polarized Localization Microscopy
NASA Astrophysics Data System (ADS)
Kelly, Christopher; Maarouf, Abir; Woodward, Xinxin
Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology.
Weather fronts and acute myocardial infarction
NASA Astrophysics Data System (ADS)
Kveton, Vit
1991-03-01
Some methodological aspects are discussed of the investigation of acute infarct myocarditis (AIM) in relation to weather fronts. Results of a new method of analysis are given. Data were analysed from about the hour of the onset of symptoms, and led to the diagnosis of AIM either immediately or within a few hours or days (3019 cases observed over 4.5 years during 1982 1986 in Plzen, Czechoslovakia). Weather classification was based on three factors (the type of the foregoing front, the type of the subsequent front, the time section of the time interval demarcated by the passage of the surfaces of the fronts). AIM occurrence increased in particular types of weather fronts: (i) by 30% during 7 12 h after a warm front, if the time span between fronts exceeded 24 h; (ii) by 10% in time at least 36 h distant from the foregoing cold or occlusion front and from the succeeding warm or occlusion front; (iii) by 20% during 0 2 h before the passage of the front, provided the foregoing front was not warm and the interval between fronts exceeded 5 h. AIM occurrence decreased by 15% 20% for time span between fronts > 24 h at times 6 11, 6 23 and 6 35 h before a coming warm or occlusion front (for interfrontal intervals 25 48, 49 72 and possibly > 72 h), and also at 12 23 and possibly 12 35 h before a cold front (for intervals 49 72 and possibly > 72 h), if the foregoing front was cold or an occlusion front.
Schwarz, Thomas A.; /Michigan U.
2006-01-01
Quarks, along with leptons and force carrying particles, are predicted by the Standard Model to be the fundamental constituents of nature. In distinction from the leptons, the quarks interact strongly through the chromodynamic force and are bound together within the hadrons. The familiar proton and neutron are bound states of the light ''up'' and ''down'' quarks. The most massive quark by far, the ''top'' quark, was discovered by the CDF and D0 experiments in March, 1995. The new quark was observed in p{bar p} collisions at 1.8 TeV at the Fermilab Tevatron. The mass of the top quark was measured to be 176 {+-} 13 GeV/c{sup 2} and the cross section 6.8{sub -2.4}{sup +3.6} pb. It is the Q = 2/3, T{sub 3} = +1/2 member of the third generation weak-isospin doublet along with the bottom quark. The top quark is the final Standard Model quark to be discovered. Along with whatever is responsible for electroweak symmetry breaking, top quark physics is considered one of the least understood sectors of the Standard Model and represents a front line of our understanding of particle physics. Currently, the only direct measurements of top quark properties come from the CDF and D0 experiments observing p{bar p} collisions at the Tevatron. Top quark production at the Tevatron is almost exclusively by quark-antiquark annihilation, q{bar q} {yields} t{bar t} (85%), and gluon fusion, gg {yields} t{bar t} (15%), mediated by the strong force. The theoretical cross-section for this process is {sigma}{sub t{bar t}} = 6.7 {+-} 0.8 pb for m{sub t} = 175 GeV/c{sup 2}. Top quarks can also be produced at the Tevatron via q{bar b}{prime} {yields} tb and qg {yields} q{prime}tb through the weak interaction. The cross section for these processes is lower (3pb) and the signal is much more difficult to isolate as backgrounds are much higher. The top quark is predicted to decay almost exclusively into a W-boson and a bottom quark (t {yields} Wb). The total decay width t {yields} Wb is {Lambda} = 1
Różycki, Bartosz; Lipowsky, Reinhard
2016-08-21
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
Waves, instabilities and turbulence properties in Depolarisation Fronts
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni; Goldman, Martin; Newman, David L.; Olshevskyi, Vyacheslav; Eastwood, Jonathan; Divin, Andrey; Pucci, Francesco
2016-04-01
The new mission MMS is currently focusing on the magnetopause but we need to be ready for the study of the tail. An aspect of great importance there are the Dipolarization fronts (DF), formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy and wave phenomena [1-3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4-5]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability develops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability and the onset of waves and secondary instabilities, transitioning towards a turbulent state. We investigate here especially the wave signatures that are observed in fully 3D simulations, looking for signatures of interchange-type lower hybrid waves [8], of whistler waves [7]. The end result present a vast array of waves and it is best analysed relying on concepts mutated by the turbulence theory. The end result of these waves and particle flows [2,6] are energy exchanges. We evaluate the different terms of the energy exchanges (energy deposition, J.E, and energy fluxes) and evaluate their relative improtance. The results presented are contrasted against existing results [1,9] and will provided useful guidance in analysis of future MMS data. [1] Hamrin, Maria, et al. "The evolution of flux pileup regions in the plasma sheet: Cluster observations." Journal of Geophysical Research: Space Physics 118.10 (2013): 6279-6290. [2] Angelopoulos, V., et al. "Electromagnetic energy conversion at reconnection fronts." Science 341.6153 (2013): 1478-1482. [3] Zhou, Meng, et al. "THEMIS observation of multiple
Experimental studies of stationary reaction fronts in a chain of vortices with imposed wind
NASA Astrophysics Data System (ADS)
Solomon, Tom; Boyer, Carleen
2013-03-01
We present experiments that study the behavior of the excitable Belousov-Zhabotinsky (BZ) reaction in a chain of alternating vortices with an imposed uniform wind. Previous experiments[2] have shown that fronts in this system are pinned for a wide range of imposed wind speeds, propagating neither forward against the wind nor in the downwind direction. We explain this behavior with a recent theory[3] that proposes the existence of burning invariant manifolds (BIMs) that act as local barriers to front propagation. Fronts are pinned when a BIM or a combination of BIMs spans the width of the vortex chain, blocking the reaction front. We show experimental measurements of the shape of the pinned front for a range of different wind speeds, and compare these shapes to the BIMs calculated theoretically. We also consider the dependence of the front shape on the location of the initial trigger for the front. Supported by NSF Grants DMR-0703635, DMR-1004744, and and PHY-1156964.
Experimental studies of stationary reaction fronts in a chain of vortices
NASA Astrophysics Data System (ADS)
Boyer, Carleen; Solomon, Tom
2012-11-01
We present results of experiments studying the behavior of the excitable Belousov-Zhabotinsky (BZ) reaction in a chain of alternating vortices with an imposed uniform wind. Previous experiments have shown that fronts in this system are pinned for a wide range of imposed wind speeds, propagating neither forward against the wind nor in the downwind direction. We explain this behavior with a recent theory that proposes the existence of burning invariant manifolds (BIMs) that act as local barriers to front propagation. Fronts are pinned when a BIM or a combination of BIMs spans the width of the vortex chain, blocking the reaction front. We show experimental measurements of the shape of the pinned front for a range of different wind speeds, and compare these shapes to the BIMs calculated theoretically. We also consider the dependence of the front shape on the location of the initial trigger for the front. Supported by NSF Grants DMR-0703635, DMR-1004744, and and PHY-1156964.
Self-Assembly of Charged Nanoparticles by an Autocatalytic Reaction Front.
Bohner, Bíborka; Schuszter, Gábor; Nakanishi, Hideyuki; Zámbó, Dániel; Deák, András; Horváth, Dezső; Tóth, Ágota; Lagzi, István
2015-11-10
In this work we present that aggregation of charged and pH sensitive nanoparticles can be spatiotemporally controlled by an autonomous way using the chlorite-tetrathionate autocatalytic front, where the front regulates the electrostatic interaction between nanoparticles due to protonation of the capping (carboxylate-terminated) ligand. We found that the aggregation and sedimentation of nanoparticles in liquid phase with the effect of reversible binding of the autocatalyst (H(+)) play important roles in changing the front stability (mixing length) and the velocity of the front in both cases when the fronts propagate upward and downward. Calculation of interparticle interactions (electrostatic and van der Waals) with the measurement of front velocity revealed that the aggregation process occurs fast (within a few seconds) at the front position. PMID:26479840
Katzenbach, J R; Santamaria, J A
1999-01-01
For many organizations, achieving competitive advantage means eliciting superior performance from employees on the front line--the burger flippers, hotel room cleaners, and baggage handlers whose work has an enormous effect on customers. That's no easy task. Front line workers are paid low wages, have scant hope of advancement, and--not surprisingly--often care little about the company's performance. But then how do some companies succeed in engaging the emotional energy of rank-and-file workers? A team of researchers at McKinsey & Company and the Conference Board recently explored that question and discovered that one highly effective route is demonstrated by the U.S. Marine Corps. The Marines' approach to motivation follows the "mission, values, and pride" path, which researchers say is practical and relevant for the business world. More specifically, the authors say the Marines follow five practices: they over-invest in cultivating core value; prepare every person to lead, including front line supervisors; learn when to create teams and when to create single-leader work groups; attend to all employees, not just the top half; and encourage self-discipline as a way of building pride. The authors admit there are critical differences between the Marines and most businesses. But using vivid examples from companies such as KFC and Marriott International, the authors illustrate how the Marines' approach can be translated for corporate use. Sometimes, the authors maintain, minor changes in a company's standard operating procedure can have a powerful effect on front line pride and can result in substantial payoffs in company performance. PMID:10387573
Karidas, Premananda; Challa, Krishna Reddy; Nath, Utpal
2015-01-01
The leaf surface usually stays flat, maintained by coordinated growth. Growth perturbation can introduce overall surface curvature, which can be negative, giving a saddle-shaped leaf, or positive, giving a cup-like leaf. Little is known about the molecular mechanisms that underlie leaf flatness, primarily because only a few mutants with altered surface curvature have been isolated and studied. Characterization of mutants of the CINCINNATA-like TCP genes in Antirrhinum and Arabidopsis have revealed that their products help maintain flatness by balancing the pattern of cell proliferation and surface expansion between the margin and the central zone during leaf morphogenesis. On the other hand, deletion of two homologous PEAPOD genes causes cup-shaped leaves in Arabidopsis due to excess division of dispersed meristemoid cells. Here, we report the isolation and characterization of an Arabidopsis mutant, tarani (tni), with enlarged, cup-shaped leaves. Morphometric analyses showed that the positive curvature of the tni leaf is linked to excess growth at the centre compared to the margin. By monitoring the dynamic pattern of CYCLIN D3;2 expression, we show that the shape of the primary arrest front is strongly convex in growing tni leaves, leading to excess mitotic expansion synchronized with excess cell proliferation at the centre. Reduction of cell proliferation and of endogenous gibberellic acid levels rescued the tni phenotype. Genetic interactions demonstrated that TNI maintains leaf flatness independent of TCPs and PEAPODs. PMID:25711708
Light-Front Holography and AdS/QCD Correspondence
Brodsky, Stanley J.; de Teramond, Guy F.
2008-04-23
Light-Front Holography is a remarkable consequence of the correspondence between string theory in AdS space and conformal field theories in physical-space time. It allows string modes {Phi}(z) in the AdS fifth dimension to be precisely mapped to the light-front wavefunctions of hadrons in terms of a specific light-front impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron. This mapping was originally obtained by matching the exact expression for electromagnetic current matrix elements in AdS space with the corresponding exact expression for the current matrix element using light-front theory in physical space-time. More recently we have shown that one obtains the identical holographic mapping using matrix elements of the energy-momentum tensor, thus providing an important consistency test and verification of holographic mapping from AdS to physical observables defined on the light-front. The resulting light-front Schrodinger equations predicted from AdS/QCD give a good representation of the observed meson and baryon spectra and give excellent phenomenological predictions for amplitudes such as electromagnetic form factors and decay constants.
Light-Front Holography, Light-Front Wavefunctions, and Novel QCD Phenomena
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2012-02-16
Light-Front Holography is one of the most remarkable features of the AdS/CFT correspondence. In spite of its present limitations it provides important physical insights into the nonperturbative regime of QCD and its transition to the perturbative domain. This novel framework allows hadronic amplitudes in a higher dimensional anti-de Sitter (AdS) space to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The model leads to an effective confining light-front QCD Hamiltonian and a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound-state wavefunctions, and thus the fall-off as a function of the invariant mass of the constituents. The soft-wall holographic model modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics - a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryons. The model predicts a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number n. The hadron eigensolutions projected on the free Fock basis provides the complete set of valence and non-valence light-front Fock state wavefunctions {Psi}{sub n/H} (x{sub i}, k{sub {perpendicular}i}, {lambda}{sub i}) which describe the hadron's momentum and spin distributions needed to compute the direct measures of hadron structure at the quark and gluon level, such as elastic and transition form factors, distribution amplitudes, structure functions, generalized parton distributions and transverse
Radar Backscatter Across the Gulf Stream Sea Surface Temperature Front
NASA Technical Reports Server (NTRS)
Nghiem, S. V.; Li, F. K.; Walsh, E. J.; Lou, S. H.
1998-01-01
Ocean backscatter signatures were measured by the Jet Propulsion Laboratory airborne NUSCAT K(sub u)-band scatterometer across the Gulf Stream sea surface temperature front. The measurements were made during the Surface Wave Dynamics Experiment (SWADE) off the coast of Virginia and Maryland in the winter of 1991.
The influence of reed curvature on the tone quality of lingual organ pipes
NASA Astrophysics Data System (ADS)
Plitnik, G. R.; Angster, J.
2002-11-01
Given certain design constraints, such as the type of stop being voiced and the desired tone quality, reed voicers must use consummate skill to curve each tongue so as to produce the best and most stable tone, as well as maintaining a consistent tone quality across an entire rank of pipes. The curvature given to a reed tongue influences not only the harmonic structure of the steady-state sound, but also the attack. Two fundamentally different types of curvature are typically employed, the chorus reed (trompette) curve (which yields a bright sound) and the smooth-toned curve employed for solo reeds such as the clarinet. This study investigated the effect of reed curvature on the vibration and tone of reed tongues of both types. Two F2 pipes (a trompette and a clarinet) were constructed and voiced with 6 different tongues each to produce a variety of tones. The reed's vibration was measured under typical conditions by laser vibrometer; the pressure waves in the boot and in the shallot were measured by means of one-eighth inch microphones and the emitted sound was recorded at the egress. By performing various measurements simultaneously, phase differences were also determined.
Moire deflectometry with a focused beam: radius of curvature, microscopy, and thickness analysis.
Kafri, O; Keren, E; Kreske, K; Zac, Y
1990-01-01
Three uses of moire deflectometry employing a focused beam are described. A microscopic mode provides inspection of magnified images of the test object. The moire fringes are used as a noncontact tunable caliper for measuring the dimensions of small imperfections and other features of the surface. The tunable scale is independent of the zooming ratio. The spherometer mode measures the radius of curvature of concave or convex spherical objects. Deviations from spherical shape are measured with variable sensitivity. The thickness of transparent objects is measured by focusing the beam on each face in turn. PMID:20556078
Li, Yun-He; Wang, Shuang; Zhang, Xin; Li, Xiao-Dong E-mail: swang@mail.ustc.edu.cn E-mail: zhangxin@mail.neu.edu.cn
2013-02-01
In this paper, we report the results of constraining the holographic dark energy model with spatial curvature and massive neutrinos, based on a Markov Chain Monte Carlo global fit technique. The cosmic observational data include the full WMAP 7-yr temperature and polarization data, the type Ia supernova data from Union2.1 sample, the baryon acoustic oscillation data from SDSS DR7 and WiggleZ Dark Energy Survey, and the latest measurements of H{sub 0} from HST. To deal with the perturbations of dark energy, we adopt the parameterized post-Friedmann method. We find that, for the simplest holographic dark energy model without spatial curvature and massive neutrinos, the phenomenological parameter c < 1 at more than 4σ confidence level. The inclusion of spatial curvature enlarges the error bars and leads to c < 1 only in about 2.5σ range; in contrast, the inclusion of massive neutrinos does not have significant influence on c. We also find that, for the holographic dark energy model with spatial curvature but without massive neutrinos, the 3σ error bars of the current fractional curvature density Ω{sub k0} are still in order of 10{sup −2}; for the model with massive neutrinos but without spatial curvature, the 2σ upper bound of the total mass of neutrinos is Σm{sub ν} < 0.48 eV. Moreover, there exists clear degeneracy between spatial curvature and massive neutrinos in the holographic dark energy model, which enlarges the upper bound of Σm{sub ν} by more than 2 times. In addition, we demonstrate that, making use of the full WMAP data can give better constraints on the holographic dark energy model, compared with the case using the WMAP ''distance priors''.
Curvature effects in rapid alloy solidification
NASA Astrophysics Data System (ADS)
Conti, Massimo
2001-04-01
The growth of a cylindrical or spherical crystal into its undercooled melt is a process whose description is complicated by the lack of a stationary regime. A simple approach to the problem, justified for low growth rates and widely used in the past for both pure substances and alloy solidification, is based on a quasistatic approximation which assumes an instantaneous adaptation of the diffusional field to the interface configuration. For alloy solidification, assuming isothermal conditions and local interface equilibrium, this simplified model predicts a diffusion controlled growth, with the radius of the crystal increasing asymptotically as ~t1/2. However, as pointed out by recent investigations, thermal diffusion and nonequilibrium effects enter as essential ingredients in rapid alloy solidification. In the present paper we use the phase-field model to simulate the cylindrical and spherical growth of a solid germ into a supersaturated alloy melt. The problem is treated in its full time-dependent characteristics, accounting for nonequilibrium effects as well as for the rejection of both heat and solute away from the advancing front. We observe a complex behavior and a rich variety of dynamic regimes: in different regions of parameter space the growth rate is limited by diffusion (either thermal or chemical) or is kinetic controlled. Traversing the boundaries which limit these regions, the process undergoes sharp transitions which leave a trace in the solidified alloy. For realistic values of the Lewis number, thermal effects drive the process into a a diffusive regime, in which the rate limiting mechanism is the rejection of solute.
Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem.
Gancedo, Francisco; Strain, Robert M
2014-01-14
In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the "splash singularity" blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time. PMID:24347645
Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem
Gancedo, Francisco; Strain, Robert M.
2014-01-01
In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the “splash singularity” blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time. PMID:24347645
Overriding plate thickness control on subducting slab curvature
NASA Astrophysics Data System (ADS)
Holt, A.; Buffett, B. A.; Becker, T. W.
2014-12-01
The curvature of subducting lithosphere controls deformation due to bending at the trench, which results in a force that dissipates gravitational potential energy and may affect seismic coupling. We use 2-D, thermo-mechanical subduction models to explore the dependence of the radius of curvature on the thickness of the subducting and overriding plates for models with both viscous and effectively plastic lithospheric rheologies. Such a plastic rheology has been shown to reproduce the bending stresses/moment computed using a kinematic strain rate description and a laboratory derived composite rheology. Laboratory and numerical models show that the bending geometry of subducting slabs with a viscous rheology is strongly dependent on slab thickness; thicker plates have a larger radius of curvature. However, the curvature of subducting plates on Earth, illuminated by the distribution of earthquake hypocenters, shows little to no dependence on the plate thickness or age. Such an observation is instead compatible with plates that have a plastic rheology. Indeed, our numerical models show that the radius of curvature of viscous plates has a stronger dependence on subducting plate thickness than in equivalent plastic models. In viscous plates, the bending moment produces a torque, which balances the torque exerted by buoyancy. However, for the plastic plate case the bending moment saturates at a maximum value and so cannot balance the gravitational torque. The saturation of bending moment means that, (a) the radius of curvature of the bending region is not constrained by this torque balance, and, (b) other forces are required to balance the gravitational torque. We explore the role that the overriding plate could play in controlling the subducting plate curvature in plastic plate models where the bending stresses have saturated. For such plates, we find that increasing the thickness of the overriding plate causes the radius of curvature to increase. The same correlation is
System Estimates Radius of Curvature of a Segmented Mirror
NASA Technical Reports Server (NTRS)
Rakoczy, John
2008-01-01
A system that estimates the global radius of curvature (GRoC) of a segmented telescope mirror has been developed for use as one of the subsystems of a larger system that exerts precise control over the displacements of the mirror segments. This GRoC-estimating system, when integrated into the overall control system along with a mirror-segment- actuation subsystem and edge sensors (sensors that measure displacements at selected points on the edges of the segments), makes it possible to control the GROC mirror-deformation mode, to which mode contemporary edge sensors are insufficiently sensitive. This system thus makes it possible to control the GRoC of the mirror with sufficient precision to obtain the best possible image quality and/or to impose a required wavefront correction on incoming or outgoing light. In its mathematical aspect, the system utilizes all the information available from the edge-sensor subsystem in a unique manner that yields estimates of all the states of the segmented mirror. The system does this by exploiting a special set of mirror boundary conditions and mirror influence functions in such a way as to sense displacements in degrees of freedom that would otherwise be unobservable by means of an edge-sensor subsystem, all without need to augment the edge-sensor system with additional metrological hardware. Moreover, the accuracy of the estimates increases with the number of mirror segments.
Damage Detection Using the Frequency-Response Curvature Method
NASA Astrophysics Data System (ADS)
SAMPAIO, R. P. C.; MAIA, N. M. M.; SILVA, J. M. M.
1999-10-01
Structural damage detection has gained increasing attention from the scientific community since unpredicted major hazards, most with human losses, have been reported. Aircraft crashes and the catastrophic bridge failures are some examples. Security and economy aspects are the important motivations for increasing research on structural health monitoring. Since damage alters the dynamic characteristics of a structure, namely its eigenproperties (natural frequencies, modal damping and modes of vibration), several techniques based on experimental modal analysis have been developed in recent years. A method that covers the four steps of the process of damage detection—existence, localization, extent and prediction—has not yet been recognized or reported. The frequency-response-function (FRF) curvature method encompasses the first three referred steps being based on only the measured data without the need for any modal identification. In this paper, the method is described theoretically and compared with two of the most referenced methods on literature. Numerically generated data, from a lumped-mass system, and experimental data, from a real bridge, are used for better illustration.
Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts.
Piacsek, Andrew A
2002-01-01
The propagation and subsequent distortion of sonic booms with rippled wave fronts are investigated theoretically using a nonlinear time-domain finite-difference scheme. This work seeks to validate the rippled wave front approach as a method for explaining the significant effects of turbulence on sonic booms [A. S. Pierce and D. J. Maglieri, J. Acoust. Soc. Am. 51, 702-721 (1971)]. A very simple description of turbulence is employed in which velocity perturbations within a shallow layer of the atmosphere form strings of vortices characterized by their size and speed. Passage of a steady-state plane shock front through such a vortex layer produces a periodically rippled wave front which, for the purposes of the present investigation, serves as the initial condition for a finite-difference propagation scheme. Results show that shock strength and ripple curvature determine whether ensuing propagation leads to wave front folding. High resolution images of the computed full wave field provide insights into the spiked and rounded features seen in sonic booms that have propagated through turbulence. PMID:11837957
NASA Astrophysics Data System (ADS)
Yeoman, T. K.; James, M.; Mager, P. N.; Klimushkin, D. Y.
2012-06-01
The Hankasalmi SuperDARN radar in Finland, while operating in a high spatial and temporal resolution mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially induced by the Tromsø Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about 180 km along a single radar beam). Spatial information provided by the radar has enabled an m-number for the wave of about 38 to be determined. It is demonstrated here that the curved phase fronts are a generic feature of nonstationary poloidal waves in a transverse resonator, caused by the common action of the field line curvature, the plasma pressure, and the equilibrium current. Some features of the observed event agree with the resonator in the vicinity of the ring current, where it is proposed that the wave is excited by a moving source in the form of a proton cloud drifting in the magnetosphere in the azimuthal direction.
NASA Astrophysics Data System (ADS)
Yeoman, T. K.; James, M.; Klimushkin, D. Y.; Mager, P. N.
2012-12-01
The Hankasalmi SuperDARN radar in Finland, whilst operating in a high spatial and temporal resolution mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially-induced by the Tromso Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about 180 km along a single radar beam). Spatial information provided by the radar has enabled an m-number for the wave of about 38 to be determined. It is demonstrated here that the curved phase fronts are a generic feature of nonstationary poloidal waves in a transverse resonator, caused by the common action of the field line curvature, the plasma pressure, and the equilibrium current. This represents the first direct evidence for a transverse resonator, with the features of the observed event agreeing with a resonator in the vicinity of the ring current, where it is proposed that the wave is excited by a moving source in the form of a proton cloud drifting in the magnetosphere in the azimuthal direction. Future possibilities for confirmation of these ideas will be discussed.
NASA Technical Reports Server (NTRS)
Allen, R. W.; Mcruer, D. T.
1977-01-01
A simulation experiment was conducted to determine the effect of reduced visibility on driver lateral (steering) control. The simulator included a real car cab and a single lane road image projected on a screen six feet in front of the driver. Simulated equations of motion controlled apparent car lane position in response to driver steering actions, wind gusts, and road curvature. Six drivers experienced a range of visibility conditions at various speeds with assorted roadmaking configurations (mark and gap lengths). Driver describing functions were measured and detailed parametric model fits were determined. A pursuit model employing a road curvature feedforward was very effective in explaining driver behavior in following randomly curving roads. Sampled-data concepts were also effective in explaining the combined effects of reduced visibility and intermittent road markings on the driver's dynamic time delay. The results indicate the relative importance of various perceptual variables as the visual input to the driver's steering control process is changed.
Sea-surface temperature fronts in the Yellow and East China Seas from TRMM microwave imager data
NASA Astrophysics Data System (ADS)
Huang, Daji; Zhang, Tao; Zhou, Feng
2010-06-01
Swath data from the Tropical Rainfall Measuring Mission microwave imager of sea-surface temperatures (SST) from 1998 to 2005 have been used to analyze the climatology and seasonal variability of the SST fronts in the Yellow and East China Seas (YES). Seven fronts have been identified and placed into three categories, namely, (1) the shelf-break front (Kuroshio Front), (2) the coastal fronts (Zhe-Min, Jiangsu, Shangdong Peninsula, Western Korean, and Western Chejudo Fronts), and (3) the shelf front (Western Yellow Sea Shelf Front). The Kuroshio Front exists from December through May, with the maximum SST gradient and highest frontal probability in April. The five coastal fronts exist year-round, all with their maximum SST gradient and highest frontal probability in February. The shelf front in the western Yellow Sea exists only from January to March. Frontogenesis in winter is due to effects of both air-sea heat exchange and advection by currents. The coastal fronts in the stratified months are expressed as tidal fronts. The coastal frontal zones coincide with the major spawning grounds of fish in the YES. The overwintering fishery ground in the Yellow Sea overlaps with the narrow band of favorable water temperature in the frontal zone. The overwintering grounds in the East China Sea are broad and bounded by fronts.
Structure and Propagation of the Outer Front of the Columbia River Plume
NASA Astrophysics Data System (ADS)
Orton, P. M.; Jay, D. A.
2002-12-01
As part of a study of juvenile salmon survival, the structure and propagation of the outer Columbia River plume front was examined using vessel observations and Synthetic Aperture Radar (SAR) satellite data. During low-to-moderate riverflow and typical anti-cyclonic summertime winds, two vessels followed successive tidally-pulsed greater-ebb plume fronts as they propagated radially to sea. Shipboard and helicopter-derived front tracking maps showed similar front propagation patterns to those seen in SAR observations. The plume was strongly stratified, with a vertical salinity gradient typically ranging from 2-4 m-1, yet rapidly mixing, with a consistent supercritical internal Froude number. Within and immediately behind the front, ADCP current profiler measurements indicated that velocities were convergent above and within the pycnocline, but divergent in the lower water column. SAR and drifter data also confirmed convergence in surface currents. This convergence likely explains observations of elevated concentrations of certain surface-seeking salmon prey within the front. Although there was convergence in the across-front velocity, the shear in along-front velocity was strong, providing a mechanism for dispersing organisms along the front line. At 8 h past higher-high water (HHW), in 40 m deep water, the front was characterized by a strong surface across-front salinity difference, ~10. Limited ADCP observations of vertical velocities were obtained when the ship cruised within the front line, showing downwelling at up to 0.35 m s-1. Elevated acoustic backscatter and velocities were seen in the bottom boundary layer directly below the front, suggesting that internal bore velocities may have been strong enough to locally resuspend sediment. By 12 h past HHW, front propagation had slowed dramatically, the across-front salinity difference had declined to ~5, and the front location implied a mean frontal velocity of 0.8 m s-1 since frontogenesis. Maximum downwelling
Khatam, Hamed; Ravi-Chandar, K.
2013-01-01
A nonlinear optimization procedure is established to determine the elastic modulus of slender, soft materials using beams with unknown initial curvature in the presence of large rotations. Specifically, the deflection of clamped-free beams under self-weight – measured at different orientations with respect to gravity – is used to determine the modulus of elasticity and the intrinsic curvature in the unloaded state. The approach is validated with experiments on a number of different materials – steel, polyetherimide, rubber and pig skin. Since the loading is limited to self-weight, the strain levels attained in these tests are small enough to assume a linear elastic material behavior. This nondestructive methodology is also applicable to engineered tissues and extremely delicate materials in order to obtain a quick estimate of the material’s elastic modulus. PMID:24159244
Shape matters: corolla curvature improves nectar discovery in the hawkmoth Manduca sexta
Campos, E. O.; Bradshaw, H. D.; Daniel, T. L.
2014-01-01
Summary 1. We measured the effects of variation in corolla curvature and nectary aperture radius on pollinator foraging ability using the hawkmoth Manduca sexta and 3D-printed artificial flowers whose shapes were mathematically specified. 2. In dimorphic arrays containing trumpet-shaped flowers and flat-disk flowers, hawkmoths were able to empty the nectaries of significantly more trumpet-shaped flowers regardless of nectary aperture size. Interestingly, trumpet-shaped flowers needed to deviate only slightly from the flat-disk morphotype in order to significantly increase hawkmoth foraging ability. 3. Whole-flower three-dimensional shape, particularly corolla curvature, has the potential to act as a mechanical guide for Manduca sexta, further implicating direct flower-proboscis contact as an important contributor to foraging success during flower handling in hawkmoths. PMID:25987763
Effect of Tension and Curvature of Skin on Insertion Characteristics of Microneedle Array
NASA Astrophysics Data System (ADS)
Tachikawa, Hiroto; Takano, Naoki; Nishiyabu, Kazuaki; Miki, Norihisa; Ami, Yoshimichi
Recent MEMS (micro electro mechanical system) fabrication techniques have made it possible to produce painless microneedles precisely enough to be inserted into epidermis layer penetrating the stratum corneum of human skin. This paper presents a testing procedure to evaluate the insertion characteristics of microneedle array using cultured human skin considering the tension and the curvature. First, the biaxial strain applied to the cultured human skin was measured by optical technique with image processing. It was found that almost constant strain could be successfully given within a certain area and that error factors in the experiment except the thickness variation of the cultured skin were negligible. Next, using a microneedle square array for brain machine interface (BMI) application, the effects of biaxial tension and the curvature on insertion characteristics were discussed. Within the above mentioned area with high strain, the needles were successfully inserted.
Non-universality in dynamically triangulated random surfaces with extrinsic curvature
Baillie, C.F.; Williams, R.D. ); Johnston, D.A. . Dept. of Physics)
1990-08-30
Earlier simulations of dynamically triangulated random surfaces with a pure Gaussian (Polyakov) action have suggested that the incorporation of a term which is equivalent to the square of the scalar curvature, R{sup 2}, in the continuum can affect the properties of the surfaces, despite the fact that such a term appears to be irrelevant on dimensional grounds. However, simulations by the current authors and Catterall of dynamically triangulated random surfaces with extrinsic curvature produced essentially identical results despite differing coefficients for the R{sup 2} term. In this paper, the authors show that small (positive or negative) values of this coefficient have little effect but that large values do produce measurable effects. This explains the concordance of our previous results with Catterall's and also provides evidence for nonuniversal behavior in the random surface model.
High-Temperature Characterization of Silicon Dioxide Films with Wafer Curvature
NASA Astrophysics Data System (ADS)
Bigl, S.; Heinz, W.; Kahn, M.; Schoenherr, H.; Cordill, M. J.
2015-12-01
Amorphous silicon dioxide films used as dielectric layers in microelectronic devices are deposited using plasma-enhanced chemical vapor deposition. Because of the presence of hydrogen and nitrogen species in the precursor gases, incorporation of such species in the films can lead to crack formation during subsequent annealing processes up to 1000°C. In this study, the role of film chemistry on the thermo-mechanical behavior of silicon dioxide films is studied with in situ film stress measurements using wafer curvature to maximum temperatures of 1000°C. This is a significant advance because normal wafer curvature can only reach maximum temperatures of around 500°C. The increased temperature range allows for the stress evolution and film chemistry to be examined for the relevant processing conditions. It was found that at temperatures higher than 550°C, hydrogen bond cleavage led to a large stress increase and film chemistry change due to new bonding arrangements between nitrogen and silicon as well as subsequent film densification causing cracking of films. These changes could only be identified with wafer curvature measurements up to 1000°C.