Detonation front curvatures and detonation rates
NASA Astrophysics Data System (ADS)
Lauderbach, Lisa M.; Lorenz, K. Thomas; Lee, Edward L.; Souers, P. Clark
2017-01-01
Many detonation front curvatures are reviewed. Most are of the Shock Dynamics type, which are described as a combination of quadratic and 8th power-of-the-radius curves. The integrated fraction of the 8th power curve is taken as a measure of curvature, which we are able to relate to the logarithm of the detonation rate. This provides a means of estimating the rates of some unknown explosives from the curvature. Using the edge lag divided by the radius is an even better way. A second group of curvatures are almost or purely quadratic. This is probably not associated with density gradients but may be caused by low sound speeds. A final group of "sombreros" show curvy fronts for ideal explosives, which appear to be caused by density gradients.
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.
Instant curvature measurement for microcantilever sensors
Jeon, Sangmin; Thundat, Thomas
2004-08-09
A multiple-point deflection technique has been developed for the instant measurement of microcantilever curvature. Eight light-emitting diodes are focused on various positions of a gold-coated silicon cantilever through optical fibers, and temperature change or chemical adsorption induces cantilever bending. The deflection at each point on the cantilever is measured with subnanometer precision by a position-sensitive detector, and thus the curvature of the cantilever is obtained.
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.
Laser triangulation measurements of scoliotic spine curvatures.
Čelan, Dušan; Jesenšek Papež, Breda; Poredoš, Primož; Možina, Janez
2015-01-01
The main purpose of this research was to develop a new method for differentiating between scoliotic and healthy subjects by analysing the curvatures of their spines in the cranio-caudal view. The study included 247 subjects with physiological curvatures of the spine and 28 subjects with clinically confirmed scoliosis. The curvature of the spine was determined by a computer analysis of the surface of the back, measured with a non-invasive, 3D, laser-triangulation system. The determined spinal curve was represented in the transversal plane, which is perpendicular to the line segment that was defined by the initial point and the end point of the spinal curve. This was achieved using a rotation matrix. The distances between the extreme points in the antero-posterior (AP) and left-right (LR) views were calculated in relation to the length of the spine as well as the quotient of these two values LR/AP. All the measured parameters were compared between the scoliotic and control groups using the Student's t-Test in case of normal data and Kruskal-Wallis test in case of non-normal data. Besides, a comprehensive diagram representing the distances between the extreme points in the AP and LR views was introduced, which clearly demonstrated the direction and the size of the thoracic and lumbar spinal curvatures for each individual subject. While the distances between the extreme points of the spine in the AP view were found to differ only slightly between the groups (p = 0.1), the distances between the LR extreme points were found to be significantly greater in the scoliosis group, compared to the control group (p < 0.001). The quotient LR/AP was statistically significantly different in both groups (p < 0.001). The main innovation of the presented method is the ability to differentiate a scoliotic subject from a healthy subject by assessing the curvature of the spine in the cranio-caudal view. Therefore, the proposed method could be useful for human posture
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.
Sonic-boom wave-front shapes and curvatures associated with maneuvering flight
NASA Technical Reports Server (NTRS)
Barger, R. L.
1979-01-01
Sonic-boom wave shapes and caustic lines generated by an airplane performing a general maneuver are studied. The equations are programmed for graphical output as a perspective view of the wave shape. This quasi three-dimensional presentation provides a qualitative insight into the effects of the maneuver on the wave shape and the caustic locations. For the special case of planar maneuvers, the principal curvatures of the wave front are derived. These curvatures are needed to calculate the sound field in the vicinity of a caustic. The results of the analysis are applicable not only to sonic-boom studies but also to the calculation of noise generated by a supersonic rotor or propeller blade tip.
A Novel Quantitative Measure of Breast Curvature Based on Catenary
Lee, Juhun; Chen, Si; Reece, Gregory P.; Crosby, Melissa A.; Beahm, Elisabeth K.
2012-01-01
Quantitative, objective measurements of breast curvature computed from clinical photographs could be used to investigate factors that impact reconstruction and facilitate surgical planning. This paper introduces a novel quantitative measure of breast curvature based on catenary. A catenary curve is used to approximate the overall curvature of the breast contour, and the curvature measure is extracted from the catenary curve. The catenary curve was verified by comparing its length, the area enclosed by the curve, and the curvature measure from the catenary curve to those from manual tracings of the breast contour. The evaluation of the proposed analysis employed untreated and postoperative clinical photographs of women who were undergoing tissue expander/implant (TE/Implant) reconstruction. Logistic regression models were developed to distinguish between the curvature of breasts undergoing TE/Implant reconstruction and that of untreated breasts based on the curvature measure and patient variables (age and body mass index). The relationships between the curvature measures of untreated breasts and patient variables were also investigated. The catenary curve approximates breast curvature reliably. The curvature measure contains useful information for quantifying the curvature differences between breasts undergoing TE/Implant reconstruction and untreated breasts, and identifying the effect of patient variables on the breast shape. PMID:22271826
A novel quantitative measure of breast curvature based on catenary.
Lee, Juhun; Chen, Si; Reece, Gregory P; Crosby, Melissa A; Beahm, Elisabeth K; Markey, Mia K
2012-04-01
Quantitative, objective measurements of breast curvature computed from clinical photographs could be used to investigate factors that impact reconstruction and facilitate surgical planning. This paper introduces a novel quantitative measure of breast curvature based on catenary. A catenary curve is used to approximate the overall curvature of the breast contour, and the curvature measure is extracted from the catenary curve. The catenary curve was verified by comparing its length, the area enclosed by the curve, and the curvature measure from the catenary curve to those from manual tracings of the breast contour. The evaluation of the proposed analysis employed untreated and postoperative clinical photographs of women who were undergoing tissue expander/implant (TE/Implant) reconstruction. Logistic regression models were developed to distinguish between the curvature of breasts undergoing TE/Implant reconstruction and that of untreated breasts based on the curvature measure and patient variables (age and body mass index). The relationships between the curvature measures of untreated breasts and patient variables were also investigated. The catenary curve approximates breast curvature reliably. The curvature measure contains useful information for quantifying the curvature differences between breasts undergoing TE/Implant reconstruction and untreated breasts, and identifying the effect of patient variables on the breast shape.
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.
The curvature measurement of Sagnac loop based on PMF
NASA Astrophysics Data System (ADS)
Zhao, Yu; Jin, Yongxing; Gong, Huaping; Wang, Jianfeng
2010-12-01
An optical fiber curvature sensor is fabricated by using a short section of polarization maintaining fiber (PMF) as the sensing component spliced in an optical fiber Sagnac loop. The length of the sensing element for the curvature sensing is about 142 mm. The sensitivity of the curvature measurement of 0.0344 m-1/pm is achieved experimentally. The propose sensor is more convenient and simply than that of photonic crystal fiber (PCF).
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
Measuring Intrinsic Curvature of Space with Electromagnetism
NASA Astrophysics Data System (ADS)
Mabin, Mason; Becker, Maria; Batelaan, Herman
2016-10-01
The concept of curved space is not readily observable in everyday life. The educational movie "Sphereland" attempts to illuminate the idea. The main character, a hexagon, has to go to great lengths to prove that her world is in fact curved. We present an experiment that demonstrates a new way to determine if a two-dimensional surface, the 2-sphere, is curved. The behavior of an electric field, placed on a spherical surface, is shown to be related to the intrinsic Gaussian curvature. This approach allows students to gain some understanding of Einstein's theory of general relativity, which relates the curvature of spacetime to the presence of mass and energy. Additionally, an opportunity is provided to investigate the dimensionality of Gauss's law.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-09
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.
Performance analysis of curvature sensors: optimum positioning of the measurement planes.
Soto, M; Acosta, E; Ríos, S
2003-10-06
Curvature sensors are used to measure wave-front aberrations in a number of different applications ranging from adaptive optics to optical testing. In practice, their performance is limited not only by the quality of the detector used for irradiance measurements but also by the separation between measurement planes used for the calculation of the axial derivative of intensity. This work resolves the problem of determining the separation between intensity measurement planes thus optimizing the variance in experimental measurements. To do this, the variance of the local curvature of the phase will be analyzed as a function of the noise level in the measurements and the separation between planes. Moreover, error bounds will be established for experimental measurements.
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.
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.
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.
Characterizing Suspension Plasma Spray Coating Formation Dynamics through Curvature Measurements
NASA Astrophysics Data System (ADS)
Chidambaram Seshadri, Ramachandran; Dwivedi, Gopal; Viswanathan, Vaishak; Sampath, Sanjay
2016-12-01
Suspension plasma spraying (SPS) enables the production of variety of microstructures with unique mechanical and thermal properties. In SPS, a liquid carrier (ethanol/water) is used to transport the sub-micrometric feedstock into the plasma jet. Considering complex deposition dynamics of SPS technique, there is a need to better understand the relationships among spray conditions, ensuing particle behavior, deposition stress evolution and resultant properties. In this study, submicron yttria-stabilized zirconia particles suspended in ethanol were sprayed using a cascaded arc plasma torch. The stresses generated during the deposition of the layers (termed evolving stress) were monitored via the change in curvature of the substrate measured using an in situ measurement apparatus. Depending on the deposition conditions, coating microstructures ranged from feathery porous to dense/cracked deposits. The evolving stresses and modulus were correlated with the observed microstructures and visualized via process maps. Post-deposition bi-layer curvature measurement via low temperature thermal cycling was carried out to quantify the thermo-elastic response of different coatings. Lastly, preliminary data on furnace cycle durability of different coating microstructures were evaluated. This integrated study involving in situ diagnostics and ex situ characterization along with process maps provides a framework to describe coating formation mechanisms, process parametrics and microstructure description.
A novel setup for wafer curvature measurement at very high heating rates.
Islam, T; Zechner, J; Bernardoni, M; Nelhiebel, M; Pippan, R
2017-02-01
The curvature evolution of a thin film layer stack containing a top Al layer is measured during temperature cycles with very high heating rates. The temperature cycles are generated by means of programmable electrical power pulses applied to miniaturized polysilicon heater systems embedded inside a semiconductor chip and the curvature is measured by a fast wafer curvature measurement setup. Fast temperature cycles with heating duration of 100 ms are created to heat the specimen up to 270 °C providing an average heating rate of 2500 K/s. As a second approach, curvature measurement utilizing laser scanning Doppler vibrometry is also demonstrated which verifies the results obtained from the fast wafer curvature measurement setup. Film stresses calculated from the measured curvature values compare well to literature results, indicating that the new method can be used to measure curvature during fast temperature cycling.
A novel setup for wafer curvature measurement at very high heating rates
NASA Astrophysics Data System (ADS)
Islam, T.; Zechner, J.; Bernardoni, M.; Nelhiebel, M.; Pippan, R.
2017-02-01
The curvature evolution of a thin film layer stack containing a top Al layer is measured during temperature cycles with very high heating rates. The temperature cycles are generated by means of programmable electrical power pulses applied to miniaturized polysilicon heater systems embedded inside a semiconductor chip and the curvature is measured by a fast wafer curvature measurement setup. Fast temperature cycles with heating duration of 100 ms are created to heat the specimen up to 270 °C providing an average heating rate of 2500 K/s. As a second approach, curvature measurement utilizing laser scanning Doppler vibrometry is also demonstrated which verifies the results obtained from the fast wafer curvature measurement setup. Film stresses calculated from the measured curvature values compare well to literature results, indicating that the new method can be used to measure curvature during fast temperature cycling.
An Improved Method to Measure the Cosmic Curvature
NASA Astrophysics Data System (ADS)
Wei, Jun-Jie; Wu, Xue-Feng
2017-04-01
In this paper, we propose an improved model-independent method to constrain the cosmic curvature by combining the most recent Hubble parameter H(z) and supernovae Ia (SNe Ia) data. Based on the H(z) data, we first use the model-independent smoothing technique, Gaussian processes, to construct a distance modulus μ H (z), which is susceptible to the cosmic curvature parameter Ω k . In contrary to previous studies, the light-curve-fitting parameters, which account for the distance estimation of SN (μ SN(z)), are set free to investigate whether Ω k has a dependence on them. By comparing μ H (z) to μ SN(z), we put limits on Ω k . Our results confirm that Ω k is independent of the SN light-curve parameters. Moreover, we show that the measured Ω k is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat universe at the current observational data level. We also test the influence of different H(z) samples and different Hubble constant H 0 values, finding that different H(z) samples do not have a significant impact on the constraints. However, different H 0 priors can affect the constraints of Ω k to some degree. The prior of H 0 = 73.24 ± 1.74 km s‑1 Mpc‑1 gives a value of Ω k , a little bit above the 1σ confidence level away from 0, but H 0 = 69.6 ± 0.7 km s‑1 Mpc‑1 gives it below 1σ.
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.
Turbulence spectra measured during fire front passage
Daisuke Seto; Craig B. Clements; Warren E. Heilman
2013-01-01
Four field experiments were conducted over various fuel and terrain to investigate turbulence generation during the passage of wildland fire fronts. Our results indicate an increase in horizontal mean winds and friction velocity, horizontal and vertical velocity variances as well as a decreased degree of anisotropy in TKE during fire front passage (FFP) due to fire-...
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.
Measurement of spinal sagittal curvatures using the laser triangulation method.
Celan, Dusan; Palfy, Miroslav; Bracun, Drago; Turk, Zmago; Mozina, Janez; Komadina, Radko
2012-03-01
The purpose of the first part of the study was to establish the variability of repeated measurements in different measuring conditions. In the second part, we performed in a large number of patients, a measurement of thoracic kyphosis and lumbar lordosis and compared them to age, gender, and level of nourishment. In the first part, measurements were performed on a plastic model of the back of a patient with a rigid and a normal spine. In the second part, 250 patients participated in the study (126 men and 124 women). For measuring spinal curvatures we used an apparatus for laser triangulation constructed at the Faculty of Mechanical Engineering, University of Ljubljana. A comparison of 30 repeated measurements was shown as the average value +/- 2 SD which included 95% of the results. Thirty repeated readings of one 3D measurement: thoracic kyphosis 41.2 degrees +/- 0.6 degrees, lumbar lordosis 4.4 degrees +/- 1.2 degrees; 30 measurements on a plastic model: thoracic kyphosis 36.8 degrees +/- 1.2 degrees, lumbar lordosis 30.9 degrees +/- 2.0 degrees; 30 measurements on a patient with a rigid spine: thoracic kyphosis 41.5 degrees +/- 2.4 degrees, lumbar lordosis 4.0 degrees +/- 1.8 degrees; 30 measurements on a patient with a normal spine: thoracic kyphosis 48.8 degrees +/- 7.4 degrees, lumbar lordosis 21.1 degrees +/- 4.4 degrees. The average size of thoracic kyphosis in 250 patients was 46.8 degrees (SD 10.1 degrees) and lumbar lordosis 31.7 degrees (SD 12.5 degrees). The angle size was statistically significantly correlated to gender (increased thoracic kyphosis and lumbar lordosis in women) and body mass index (increased thoracic kyphosis and lumbar lordosis in more nourished patients). Age was not significantly correlated to the observed angles. During measurements of the spinal angles it was important to pay attention to relaxation and the patient's position as well as to perform more measurements providing the average value. The age and the level of
Dynamic lumbar curvature measurement in acute and chronic low back pain sufferers.
Williams, Jonathan Mark; Haq, Inam; Lee, Raymond Y
2012-11-01
(1) To determine the reliability of a novel fiber-optic method to dynamically measure lumbar curvature in low back pain (LBP) sufferers, and (2) to investigate the dynamic lumbar curvature in acute and chronic LBP sufferers. Cross-sectional study. Physiotherapy clinic. Acute (n=20) and chronic (n=20) LBP sufferers recruited from general practitioner and therapist referrals. Not applicable. A fiber-optic device was used to measure curvature through time during flexion, lifting, and extension movements. Repeated-measures reliability for curvature-time curves was tested using coefficients of multiple correlation (CMCs) and root mean square error, and for peak curvature values intraclass correlation coefficients (ICCs) and mean absolute errors were used. Acute and chronic LBP groups were compared using peak curvatures and sequencing of curvature change. The fiber-optic method was shown to be highly reliable in measuring both whole lumbar and lower lumbar curvature with CMC values >.81 and ICC values >.99. Chronic LBP sufferers displayed greater peak curvatures during flexion and lifting for the whole lumbar spine and lifting for the lower lumbar spine. The sequencing behavior demonstrated that the quartile of movement associated with the greatest curvature change was the second for flexion and lifting and first and second for extension across both groups. No significant differences in sequencing were demonstrated between the 2 groups. This method is reliable for dynamic lumbar curvature measurement in back pain sufferers and is a viable option for clinicians. Acute LBP sufferers display less kyphosis during flexion and lifting. Sequencing of curvature change is similar across the 2 groups. Copyright © 2012 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.
Ciulla, Carlo; Veljanovski, Dimitar; Rechkoska Shikoska, Ustijana; Risteski, Filip A.
2015-01-01
This research presents signal-image post-processing techniques called Intensity-Curvature Measurement Approaches with application to the diagnosis of human brain tumors detected through Magnetic Resonance Imaging (MRI). Post-processing of the MRI of the human brain encompasses the following model functions: (i) bivariate cubic polynomial, (ii) bivariate cubic Lagrange polynomial, (iii) monovariate sinc, and (iv) bivariate linear. The following Intensity-Curvature Measurement Approaches were used: (i) classic-curvature, (ii) signal resilient to interpolation, (iii) intensity-curvature measure and (iv) intensity-curvature functional. The results revealed that the classic-curvature, the signal resilient to interpolation and the intensity-curvature functional are able to add additional information useful to the diagnosis carried out with MRI. The contribution to the MRI diagnosis of our study are: (i) the enhanced gray level scale of the tumor mass and the well-behaved representation of the tumor provided through the signal resilient to interpolation, and (ii) the visually perceptible third dimension perpendicular to the image plane provided through the classic-curvature and the intensity-curvature functional. PMID:26644943
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.
Singh, Devinder K; Bailey, Martin; Lee, Raymond
2010-01-01
Singh DK, Bailey M, Lee R. Biplanar measurement of thoracolumbar curvature in older adults using an electromagnetic tracking device. To develop a new biplanar method of thoracolumbar curvature measurement by using an electromagnetic tracking device and to study the effects of aging on the thoracolumbar curvature. Cross-sectional study. Human movement laboratory. Healthy (N=52, 26 younger and 26 older) volunteers. Not applicable. An electromagnetic tracking device was used to trace the thoracolumbar curvature by recording the positions of the spinous processes of the spine. The coordinates of the curvature were fitted with polynomial equations, and the magnitudes of thoracic kyphosis, lumbar lordosis, and lateral thoracic and lumbar curves were determined. The present technique was shown to be highly reliable in measuring thoracolumbar curvature with an intraclass correlation coefficient of more than .90. The mean thoracic kyphosis (-46.95 degrees +/-11.41 degrees ) in the older adults was significantly larger than that in the younger adults (-38.82 degrees +/-9.86 degrees ) (P<.01). However, there were no significant differences in lumbar lordosis and lateral curvatures between the 2 subject groups. The present study provided evidence of an increase in thoracic kyphosis in older adults. The method of measurement presented in this study was found to provide reliable biplanar data that will be useful in a clinical setting. Copyright (c) 2010 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.
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. Here we show how the curvature can be measured experimentally via Higgs cross-sections, WLscattering, and the Sparameter. The one-loop action of HEFT is given in terms of geometric invariants of M. Moreover, the distinction between the Standard Model (SM) and HEFT is whether Mis flat or curved, and the curvature is a signal of the scale of new physics.
Gaussian weighting of ocular wave-front measurements.
Schwiegerling, Jim
2004-11-01
The measurement of ocular wave-front error gives insight into the optical performance of the eye and possibly a means for assessing visual performance. The visual system responds not only to the quality of the optical image formed on the retina but also to the processing that occurs in the retina and the brain. To develop a metric of visual performance based on wave-front error measurements, these latter processes must somehow be incorporated. In representing the wave-front error in terms of Zernike polynomials, it appears that terms with lower angular frequency have a greater deleterious effect on visual performance than higher-angular-frequency terms. A technique for weighting the pupil function of the eye with a Gaussian filter is demonstrated. It is further demonstrated that the variance of the Gaussian-weighted wave-front error is well correlated with visual performance.
Curvature adaptive optics and low light imaging
NASA Astrophysics Data System (ADS)
Ftaclas, C.; Chun, M.; Kuhn, J.; Ritter, J.
We review the basic approach of curvature adaptive optics (AO) and show how its many advantages arise. A curvature wave front sensor (WFS) measures exactly what a curvature deformable mirror (DM) generates. This leads to the computational and operational simplicity of a nearly diagonal control matrix. The DM automatically reconstructs the wave front based on WFS curvature measurements. Thus, there is no formal wave front reconstruction. This poses an interesting challenge to post-processing of AO images. Physical continuity of the DM and the reconstruction of phase from wave front curvature data assure that each actuated region of the DM corrects local phase, tip-tilt and focus. This gain in per-channel correction efficiency, combined with the need for only one pixel per channel detector reads in the WFS allows the use of photon counting detectors for wave front sensing. We note that the use of photon counting detectors implies penalty-free combination of correction channels either in the WFS or on the DM. This effectively decouples bright and faint source performance in that one no longer predicts the other. The application of curvature AO to the low light moving target detection problem, and explore the resulting challenges to components and control systems. Rapidly moving targets impose high-speed operation posing new requirements unique to curvature components. On the plus side, curvature wave front sensors, unlike their Shack-Hartmann counterparts, are tunable for optimum sensitivity to seeing and we are examining autonomous optimization of the WFS to respond to rapid changes in seeing.
Non-scanning measurement of convex and concave curvature with an annular array
NASA Astrophysics Data System (ADS)
Lenz, Michael; Kühnicke, Elfgard
2012-05-01
The paper describes a novel ultrasonic method for measuring local object curvature radii without scanning. For the measurements, an ultrasonic annular array is used, where the phase and amplitude differences on the different receivers are used to determine the object curvature radius and its distance from the transducer simultaneously. The method aims at measurements of spherical or oval inclusions in fluids and solids in general, and of the curvature radius of eye lens and retina in particular. It is intended to work as a supplement to conventional imaging applications. To verify the measurement method, theoretical and experimental results with steel spheres as reflectors are presented. After measuring and taking into account the acoustically effective size of the single transducer elements, good agreement between measurements and simulations could be achieved.
Measurement and analyses of the effects of adjacent end plate curvatures on vertebral stresses.
Langrana, Noshir A; Kale, Shreedhar P; Edwards, W Thomas; Lee, Casey K; Kopacz, Kenneth J
2006-01-01
Vertebral end plates of the lumbosacral spine have various degrees of concavity and convexity. It is believed that the shape of the end plates alters the distribution of loads transferred along the spine, between the vertebrae. Animal models have been regularly used in the design and development of vertebral disc implants and cages; to date, very little information is known about the animal vertebral end plate curvature. The purpose was to measure and analyze the end plate curvature in the cadaver human male-female, chimpanzee, and canine lumbar vertebral bones. Nondestructive and nontouching scanning method was designed to obtain curvature in anterior-posterior and medial-lateral directions in the cadaver bones. Statistical analysis was performed on the data collected, and this data was then used to create a biomechanical model to evaluate the load transmission. Measurements in anterior-posterior and medial-lateral directions were performed on human, canine, and chimpanzee cadaver lumbar bones to obtain accurate data for the end plate curvatures. Six sets of measurements (on human male-female L4 lower to S1 upper end plates) were performed. A parametric vertebral motion segment model (with and without posterior elements) that includes the experimental curvature information was developed. The characteristic kidney-shaped cross-sectional model was created using a parametric equation. This model was used to perform finite element analyses investigating the effects of the location of maximum curvature on the stress distributions. The measurements for different species showed that the canine and chimpanzees, the quadrupeds, have entirely different curvature of their upper end plates compared with those in humans, the bipeds. Also, the curvatures of the human S1 upper end plates are significantly different from the rest of the vertebrae. This is a very useful piece of information in the comparison of these species. The stress distribution varied as the location of the
The coherent gradient sensor for film curvature measurements at cryogenic temperature.
Liu, Cong; Zhang, Xingyi; Zhou, Jun; Zhou, Youhe; Feng, Xue
2013-11-04
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.
Curvature Measurement and Tracking of Nonwetting Phase Trapping and Pressure State in Porous Media
NASA Astrophysics Data System (ADS)
Wildenschild, D.; Li, T.; Schlüter, S.
2015-12-01
X-ray microtomography images are used to predict capillary pressure of trapped phase via interfacial curvature measurement and applying the Young-LaPlace equation. We have made several improvements to previous algorithms by removing interface segments that are affected by proximity to the solid surface, and by using distance-weighted curvature estimates. The algorithm shows significant improvement over previous quantification and allows for a close match to externally-measured capillary pressure values obtained using pressure transducers. The data also allows us to track the pressure state of trapped nonwetting phase and illustrates the dependence of pressure state of trapped objects (nonwetting phase blobs) on pore morphology as opposed to the bulk fluid pressure when the object is trapped. Individual objects can be followed during several drainage and imbibition cycles, and curvature changes followed as the object expands or contracts. This has important implications for how we understand trapping in multi-phase porous medium systems.
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
FY 2016 Status Report: CIRFT Testing Data Analyses and Updated Curvature Measurements
Wang, Jy-An John; Wang, Hong
2016-08-01
This report provides a detailed description of FY15 test result corrections/analysis based on the FY16 Cyclic Integrated Reversible-Bending Fatigue Tester (CIRFT) test program methodology update used to evaluate the vibration integrity of spent nuclear fuel (SNF) under normal transportation conditions. The CIRFT consists of a U-frame testing setup and a real-time curvature measurement method. The three-component U-frame setup of the CIRFT has two rigid arms and linkages to a universal testing machine. The curvature of rod bending is obtained through a three-point deflection measurement method. Three linear variable differential transformers (LVDTs) are used and clamped to the side connecting plates of the U-frame to capture the deformation of the rod. The contact-based measurement, or three-LVDT-based curvature measurement system, on SNF rods has been proven to be quite reliable in CIRFT testing. However, how the LVDT head contacts the SNF rod may have a significant effect on the curvature measurement, depending on the magnitude and direction of rod curvature. It has been demonstrated that the contact/curvature issues can be corrected by using a correction on the sensor spacing. The sensor spacing defines the separation of the three LVDT probes and is a critical quantity in calculating the rod curvature once the deflections are obtained. The sensor spacing correction can be determined by using chisel-type probes. The method has been critically examined this year and has been shown to be difficult to implement in a hot cell environment, and thus cannot be implemented effectively. A correction based on the proposed equivalent gauge-length has the required flexibility and accuracy and can be appropriately used as a correction factor. The correction method based on the equivalent gauge length has been successfully demonstrated in CIRFT data analysis for the dynamic tests conducted on Limerick (LMK) (17 tests), North Anna (NA) (6 tests), and Catawba mixed oxide (MOX
NASA Astrophysics Data System (ADS)
Kao, T. Y.; Chiang, F. P.
1982-08-01
A family of optical methods are developed for the measurement of slope and curvature of flexed plate surfaces. Slope and curvature contour fringes are generated by using gratings as filters in the light path emerging from the flexed surface. General field equations are derived for gratings placed anywhere in the field. Depending upon the pitch and the position and the number of gratings used, a variety of techniques are obtained for the contouring of slopes or curvatures. When a low density grating is used, the resulting shadowgram yields slope contour fringes if it is placed at the real focal plane of the field lens. Otherwise, the shadow gram fringes are not slope contours. However, slope contours can be obtained if a double-exposure technique or a double grating is used to generate the moire fringes. If a grating of sufficiently high frequency is used, the resulting pattern is a curvature pattern, for which a monochromatic light source is needed. A successive plotting method is also proposed for curvature contouring whereby white light and a grating of arbi-trary pitch can be used. The methods are verified by a series of experiments using cantilever beams and clamped circular plates. Applications to a variety of other problems, including flexure wave propagation, are also demonstrated.
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.
Subnanosecond measurements of detonation fronts in solid high explosives
NASA Astrophysics Data System (ADS)
Sheffield, S. A.; Bloomquist, D. D.; Tarver, C. M.
1984-04-01
Detonation fronts in solid high explosives have been examined through measurements of particle velocity histories resulting from the interaction of a detonation wave with a thin metal foil backed by a water window. Using a high time resolution velocity-interferometer system, experiments were conducted on three explosives—a TATB (1,3,5-triamino-trinitrobenzene)-based explosive called PBX-9502, TNT (2,4,6-Trinitrotoluene), and CP (2-{5-cyanotetrazolato} pentaamminecobalt {III} perchlorate). In all cases, detonation-front rise times were found to be less than the 300 ps resolution of the interferometer system. The thermodynamic state in the front of the detonation wave was estimated to be near the unreacted state determined from an extrapolation of low-pressure unreacted Hugoniot data for both TNT and PBX-9502 explosives. Computer calculations based on an ignition and growth model of a Zeldovich-von Neumann-Doering (ZND) detonation wave show good agreement with the measurements. By using the unreacted Hugoniot and a JWL equation of state for the reaction products, we estimated the initial reaction rate in the high explosive after the detonation wave front interacted with the foil to be 40 μs-1 for CP, 60 μs-1 for TNT, and 80 μs-1 for PBX-9502. The shape of the profiles indicates the reaction rate decreases as reaction proceeds.
Subnanosecond measurements of detonation fronts in solid high explosives
Sheffield, S.A.; Bloomquist, D.D.; Tarver, C.M.
1984-04-15
Detonation fronts in solid high explosives have been examined through measurements of particle velocity histories resulting from the interaction of a detonation wave with a thin metal foil backed by a water window. Using a high time resolution velocity-interferometer system, experiments were conducted on three explosives: a TATB (1,3,5-triamino-trinitrobenzene)-based explosive called PBX-9502, TNT (2,4,6-Trinitrotoluene), and CP (2-)5-cyanotetrazolato) pentaamminecobalt )III) perchlorate). In all cases, detonation-front rise times were found to be less than the 300 ps resolution of the interferometer system. The thermodynamic state in the front of the detonation wave was estimated to be near the unreacted state determined from an extrapolation of low-pressure unreacted Hugoniot data for both TNT and PBX-9502 explosives. Computer calculations based on an ignition and growth model of a Zeldovich--von Neumann--Doering (ZND) detonation wave show good agreement with the measurements. By using the unreacted Hugoniot and a JWL equation of state for the reaction products, we estimated the initial reaction rate in the high explosive after the detonation wave front interacted with the foil to be 40 ..mu..s/sup -1/ for CP, 60 ..mu..s/sup -1/ for TNT, and 80 ..mu..s/sup -1/ for PBX-9502. The shape of the profiles indicates the reaction rate decreases as reaction proceeds.
NASA Astrophysics Data System (ADS)
Albayari, Diya'J.; Gobithaasan, R. U.; Miura, Kenjiro T.
2016-10-01
Cross and Cripps [2] approximated the generalized Cornu spiral (GCS) with a G 3 quintic Bezier curves based on a curvature error measure, the curvatures by means of parameterized arc length. However, this measure computationally expensive. In order to overcome this problem, Lu [6] suggested another error measure which reduces both time and computation time. However, Cross and Cripps's error measure was still needed in order assess its approximation quality. In this paper we propose a new approach to compute the error measure by making a correspondence between the general parameter t and arc length parameter s. Numerical examples show that this error measure reduce both time and computations to certain extend, and preserves the approximation quality as obtained by Cross and Cripps.
AFM nanoindentation: tip shape and tip radius of curvature effect on the hardness measurement
NASA Astrophysics Data System (ADS)
Calabri, L.; Pugno, N.; Menozzi, C.; Valeri, S.
2008-11-01
AFM nanoindentation is nowadays not so widespread for the study of mechanical properties of materials at the nanoscale. 'Nanoindenter' machines are presently more accurate and more standardized. However, AFM could provide interesting features such as imaging the indentation impression right after the load application. In this work a new method for nanoindentation via AFM is proposed. The use of AFM allows hardness measurement with standard sharp AFM probes and a simultaneous high-resolution imaging (which is not achievable with standard indenters—cube corner and Berkovich). How the shape of the indenter and the tip radius of curvature affect the hardness measurement is here analysed with three different approaches: experiments, numerical simulations and theoretical models. In particular the effect of the tip radius of curvature, which is not negligible for the real indenters, has been considered both in the nature of the indentation process, than in the practice of imaging with AFM. A final theoretical model has been developed, that includes the effect of the tip radius of curvature as well as variable corner angle. Through this model we have been able to define a correction factor which permits us to evaluate the actual hardness of the material, once the radius of curvature of the tip is measured.
In-fiber directional coupler for high-sensitivity curvature measurement.
Guzman-Sepulveda, J R; May-Arrioja, D A
2013-05-20
A curvature fiber optic sensor using a two-core fiber (TCF) is proposed and demonstrated. The TCF is designed to operate as a directional coupler with one core located exactly at the center of the fiber and the other off-axis, but close to the center of the fiber. This design allows straightforward splicing of the TCF to single mode fibers (SMF), and alignment of the off-axis core is not strictly required for optimum operation. The sensor is fabricated by simply splicing a 5 cm long section of TCF between two SMF sections, which provides a sinusoidal spectral response. When the fiber is bent, the coupling parameters are modified due to stress-optic and effective length effects, effectively blue-shifting the sinusoidal spectral response of the sensor and allowing for the measurement of curvature. The sensor exhibits linear response and a sensitivity of -137.87 nm/m(-1) for curvature ranging from 0 to 0.27 m(-1), making it suitable to measure small curvatures with high sensitivity.
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.
Effect of Grain Curvature on Nano-Indentation Measurements of Thin Films
NASA Astrophysics Data System (ADS)
Tsai, Kuang-Yue; Chin, Tsung-Shune; Shieh, Han-Ping D.
2004-09-01
Grain curvature effect on the measurement of nano-indentation has been observed for the first time, taking VO2 thin film as an example. As the grain size of thin film is comparable to the diameter of indenter tip, the maximum penetration depths under the same maximum load (Pmax) vary and lead to deviations in estimated hardness and Young’s modulus. Under the same Pmax, larger penetration depth leads to a larger projected area, and a decrease in hardness. The large deviation of stiffness, affected by surface roughness under low Pmax, produces fluctuation of Young’s modulus. Increase in penetration depth diminishes the roughness effect so that deviations in penetration depths dominate the variations in Young’s modulus. The hardness and Young’s modulus curves measured at lowest penetration depth, being thought to be free from effect of grain curvature, coincide very well to the curves measured by continuous stiffness measurements mode.
Villa, Chiara; Gaudio, Daniel; Cattaneo, Cristina; Buckberry, Jo; Wilson, Andrew S; Lynnerup, Niels
2015-03-01
Recent studies have reported that quantifying symphyseal and auricular surface curvature changes on 3D models acquired by laser scanners has a potential for age estimation. However, no tests have been carried out to evaluate the repeatability of the results between different laser scanners. 3D models of the two pelvic joints were generated using three laser scanners (Custom, Faro, and Minolta). The surface curvature, the surface area, and the distance between co-registered meshes were investigated. Close results were found for surface areas (differences between 0.3% and 2.4%) and for distance deviations (average <20 μm, SD <200 μm). The curvature values were found to be systematically biased between different laser scanners, but still showing similar trends with increasing phases/scores. Applying a smoothing factor to the 3D models, it was possible to separate anatomy from the measurement error of each instrument, so that similar curvature values could be obtained (p < 0.05) independent of the specific laser scanner.
Assessment of the effect of vessel curvature on Doppler measurements in steady flow.
Balbis, S; Guiot, C; Roatta, S; Arina, R; Todros, T
2004-05-01
Blood vessel curvature is responsible for the appearance of nonaxial velocity components and for minor changes in the pattern of the axial flow. All the velocity components are expected to contribute to the Doppler signal produced by the ultrasound (US) backscattered by the insonated blood cells, the axial velocity, contributing to the actual volumetric blood flow, and the transverse velocity, causing the recirculating vortices. A detailed, separate analysis of the velocity components is, therefore, mandatory to quantify how vessel curvature can affect results and clinical diagnosis. Both experimental in vitro measures and numerical simulations were performed on a curved tube and the Doppler power spectra so obtained were compared. The satisfactorily agreement of the above spectra shows that the nonaxial velocity components are easily detectable with clinical equipment and that their amplitude, as expected, is not negligible and can bias Doppler measurements and resulting clinical diagnosis.
Real time measurement of epilayer strain using a simplified wafer curvature technique
Floro, J.A.; Chason, E.; Lee, S.R.
1995-12-31
We describe a technique for measuring thin film stress using wafer curvature that is robust, compact, easy to setup, and sufficiently sensitive to serve as a routine diagnostic of semiconductor epilayer strain in real time during MBE or CVD growth. We demonstrate, using growth of SiGe alloys on Si, that the critical thickness for misfit dislocation can clearly be resolved, and that the subsequent strain relaxation kinetics during growth or post-growth annealing are readily obtained.
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.
Reflective meniscometry: a non-invasive method to measure tear meniscus curvature
Yokoi, N.; Bron, A.; Tiffany, J.; Brown, N.; Hsuan, J.; Fowler, C.
1999-01-01
AIMS—To devise a method to measure tear meniscus curvature by a non-invasive specular technique. METHODS—A photographic system was devised. The system consisted of a camera and an illuminated target with a series of black and white stripes oriented parallel to the axis of the lower tear meniscus. The target was mounted on a flash gun close to the objective of a Brown macrocamera and calibrated using a graduated series of glass capillaries of known diameter, ground down to expose the inner wall. It was then applied to normal human eyes (n=45) to measure the tear meniscus curvature. A video system was also assessed which provided qualitative online information about the tear meniscus. RESULTS—Using the photographic system, measured values for capillary radii were in excellent agreement with theoretical calculations (r2=0.996, p<0.0001). The radii of curvature of lower tear menisci in normal human subjects (mean 0.365 (SD 0.153) mm, range 0.128-0.736; n=45) were similar to those reported in the literature. Both systems demonstrated variations in meniscus shape. The video system provided stable images of human menisci over prolonged periods of time and promises to be useful for the analysis of dynamic changes in meniscus volume. CONCLUSIONS—Reflective meniscometry is a non-invasive technique providing quantitative information about tear meniscus shape and volume and of potential value in the study of ocular surface disease. Keywords: tear meniscus; reflective meniscometry; radius of curvature; tear kinetics PMID:10209444
Wave-front aberration measurements on GRIN-rod lenses.
Cline, T W; Jander, R B
1982-03-15
A survey of the optical quality of commercial and experimental Selfoc GRIN-rod lenses was made using a digital Twyman-Green wave-front interferometer. The technique provides an accurate and reproducible method for predicting lens performance in microoptic devices. Wave-front aberrations are reported for (1/4) pitch lenses measured in a double-pass configuration. It was found that spherical aberration is dominant in commercial lenses. SLW (1/4) pitch lenses have lower aberrations than SLS lenses and are quite suitable for microoptic devices based on fiber-to-fiber coupling. Measured multimode coupling efficiency under steady-state modal propagation is compared to measured spherical aberration for a number of lenses. The slope of the coupling dependence on spherical aberration was found to be -0.1 dB/wave. Effects due to mechanical alignment and the modal distribution in the fibers had a greater influence on the measured coupling efficiency than the contribution due the intrinsic lens aberrations, especially for the SLW lenses. Comparison of this empirical dependence with theoretical predictions for a uniform distribution, which suggests a stronger dependence, is discussed. This work suggests that commercially available GRIN-rod lenses are suitable for use in microoptic components.
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.
Laser confocal measurement system for curvature radius of lenses based on grating ruler
NASA Astrophysics Data System (ADS)
Tian, Jiwei; Wang, Yun; Zhou, Nan; Zhao, Weirui; Zhao, Weiqian
2015-02-01
In the modern optical measurement field, the radius of curvature (ROC) is one of the fundamental parameters of optical lens. Its measurement accuracy directly affects the other optical parameters, such as focal length, aberration and so on, which significantly affect the overall performance of the optical system. To meet the demand of measurement instruments for radius of curvature (ROC) with high accuracy in the market, we develop a laser confocal radius measurement system with grating ruler. The system uses the peak point of the confocal intensity curve to precisely identify the cat-eye and confocal positions and then measure the distance between these two positions by using the grating ruler, thereby achieving the high-precision measurement for the ROC. The system has advantages of high focusing sensitivity and anti-environment disturbance ability. And the preliminary theoretical analysis and experiments show that the measuring repeatability can be up to 0.8 um, which can provide an effective way for the accurate measurement of ROC.
Measurement of the Time Required for a Termite to Pass Through Tunnels with Different Curvatures
Sim, Seungwoo; Lee, Sang-Hee
2012-01-01
The subterranean termite, Reticulitermes speratus kyushuensis (Isoptera: Rhinotermitidae), excavate complex tunnel networks below the ground for foraging. The tunnels are either curved or meandering. In our previous study, results showed that termites passed smooth—rounded corners faster than they did around sharp corners. Smooth—rounded corners can be mathematically quantified by the curvature, representing the amount by which a geometric object deviates from a straight line. The present study explored how the time spent inside a tunnel changes in accordance with the degree of tunnel curvature. To do so, artificial tunnels with different curvatures were constructed in acryl substrates. Tunnels were 5 cm in length with widths of W — 2, 3, or 4 mm, and the distance between the two ends of the tunnel was D = 2, 3, 4, or 5 cm. A higher value of D signified a lower curvature. The time (τ) taken by a termite to pass through the tunnel was measured. In the case of W = 2 mm, the values of τ were statistically equal for D = 2, 3, or 4 cm, while τ for D = 5 cm was significantly lesser. In the case of W = 3, τ was statistically more for D = 2 and 3 cm than it was for D = 4 and 5 cm. For W = 4, τ was statistically equal for D = 2 and 3 cm, while τ for D = 4 cm was relatively shorter. Interestingly, the value of τ when D = 5 cm was statistically the same as D = 3 or 4 cm. These resulted from two types of termite behavior: biased walking and zigzag walking. PMID:22938393
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.
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
Localization of the transverse processes in ultrasound for spinal curvature measurement
NASA Astrophysics Data System (ADS)
Kamali, Shahrokh; Ungi, Tamas; Lasso, Andras; Yan, Christina; Lougheed, Matthew; Fichtinger, Gabor
2017-03-01
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 such as transverse processes, but as bones have reduced visibility in ultrasound imaging, skeletal landmarks are typically segmented manually, which is an exceedingly laborious and long process. We propose an automatic algorithm to segment and localize the surface of bony areas in the transverse process for scoliosis in ultrasound. METHODS: The algorithm uses cascade of filters to remove low intensity pixels, smooth the image and detect bony edges. By applying first differentiation, candidate bony areas are classified. The average intensity under each area has a correlation with the possibility of a shadow, and areas with strong shadow are kept for bone segmentation. The segmented images are used to reconstruct a 3-D volume to represent the whole spinal structure around the transverse processes. RESULTS: A comparison between the manual ground truth segmentation and the automatic algorithm in 50 images showed 0.17 mm average difference. The time to process all 1,938 images was about 37 Sec. (0.0191 Sec. / Image), including reading the original sequence file. CONCLUSION: Initial experiments showed the algorithm to be sufficiently accurate and fast for segmentation transverse processes in ultrasound for spinal curvature measurement. An extensive evaluation of the method is currently underway on images from a larger patient cohort and using multiple observers in producing ground truth segmentation.
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.
NASA Astrophysics Data System (ADS)
Zhao, Yong; Cai, Lu; Li, Xue-gang
2017-07-01
An in-fiber modal interferometer is presented and experimentally demonstrated for simultaneous measurement of curvature and temperature. The sensing part is fabricated by splicing single mode fiber (SMF) and hollow core fiber (HCF) via two abrupt tapered joints. Light couples to the wall of HCF due to the collapse in abrupt taper region and then modal interference occurs among multiple modes. Not only intensity but also wavelength of the dip around 1556 nm linearly responses to the curvature and temperature change thus a sensitivity matrix could be built to demodulate both curvature and temperature simultaneously. In addition, the interference dip around 1540 nm performs a decrease trend and the highest curvature sensitivity of 5.05 dB/m-1 is achieved in a wide range from 0.765 m-1 to 3.423 m-1.
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.
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.
AC-coupled front-end for biopotential measurements.
Spinelli, Enrique Mario; Pallàs-Areny, Ramon; Mayosky, Miguel Angel
2003-03-01
AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz.
Curvature and Temperature Measurement Based on a Few-Mode PCF Formed M-Z-I and an Embedded FBG
Liu, Hui; Yang, Hangzhou; Qiao, Xueguang; Wang, Yongqiang; Liu, Xiaochong; Lee, Yen-Sian; Lim, Kok-Sing; Ahmad, Harith
2017-01-01
We have experimentally demonstrated an optical fiber Mach-Zehnder interferometer (MZI) structure formed by a few-mode photonic crystal fiber (PCF) for curvature measurement and inscribed a fiber Bragg grating (FBG) in the PCF for the purpose of simultaneously measuring temperature. The structure consists of a PCF sandwiched between two multi-mode fibers (MMFs). Bending experimental results show that the proposed sensor has a sensitivity of −1.03 nm/m−1 at a curvature range from 10 m−1 to 22.4 m−1, and the curvature sensitivity of the embedded FBG was −0.003 nm/m−1. Temperature response experimental results showed that the MZI’s wavelength, λa, has a sensitivity of 60.3 pm/°C, and the FBG’s Bragg wavelength, λb, has sensitivity of 9.2 pm/°C in the temperature range of 8 to 100 °C. As such, it can be used for simultaneous measurement of curvature and temperature over ranges of 10 m−1 to 22.4 m−1 and 8 °C to 100 °C, respectively. The results show that the embedded FBG can be a good indicator to compensate the varying ambient temperature during a curvature measurement. PMID:28749437
Curvature and Temperature Measurement Based on a Few-Mode PCF Formed M-Z-I and an Embedded FBG.
Liu, Hui; Yang, Hangzhou; Qiao, Xueguang; Wang, Yongqiang; Liu, Xiaochong; Lee, Yen-Sian; Lim, Kok-Sing; Ahmad, Harith
2017-07-27
We have experimentally demonstrated an optical fiber Mach-Zehnder interferometer (MZI) structure formed by a few-mode photonic crystal fiber (PCF) for curvature measurement and inscribed a fiber Bragg grating (FBG) in the PCF for the purpose of simultaneously measuring temperature. The structure consists of a PCF sandwiched between two multi-mode fibers (MMFs). Bending experimental results show that the proposed sensor has a sensitivity of -1.03 nm/m(-1) at a curvature range from 10 m(-1) to 22.4 m(-1), and the curvature sensitivity of the embedded FBG was -0.003 nm/m(-1). Temperature response experimental results showed that the MZI's wavelength, λa, has a sensitivity of 60.3 pm/°C, and the FBG's Bragg wavelength, λb, has sensitivity of 9.2 pm/°C in the temperature range of 8 to 100 °C. As such, it can be used for simultaneous measurement of curvature and temperature over ranges of 10 m(-1) to 22.4 m(-1) and 8 °C to 100 °C, respectively. The results show that the embedded FBG can be a good indicator to compensate the varying ambient temperature during a curvature measurement.
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.
New approach to accuracy enhancement and traceability realization of radius of curvature measurement
NASA Astrophysics Data System (ADS)
Ding, Xiang; Li, Fei; Liu, Wenli
2012-10-01
High accuracy radius of curvature (ROC) measurement of optical surfaces is usually realized by techniques such as autocollimation, interferometry and profilometry, with theoretical accuracy as high as 10-6. In practical application, significant discrepancy may exist in results obtained by different methods owing to figure error of measured surfaces. In this paper, mathematical models are built up to characterize the relationship between the ROC and the figure error as well as the aperture angle. Based on the models, equations for calculating the ROC accuracy are derived and tested on several ROC measuring methods. Experiments are carried out on a set of high quality spheres whose diameters are from 11mm to 93mm and roundness is from 0.03μm to 0.07μm, measured by instruments with top level accuracy, which are a length measuring machine, a profilometer and a homemade differential confocal system. Uncertainties are calculated and analyzed against several factors. The reason for the discrepancy between different methods is explained. An approach is also proposed which could reduce the uncertainty of ROC by 1~2 scales, making it possible to trace the results of ROC measuring instruments to the primary standard of length via diameter and roundness measurement method.
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.
NASA Astrophysics Data System (ADS)
Mielimąka, Ryszard; Orwat, Justyna
2017-07-01
The mean square approximation of average course of mining area subsidence with the use of a flat spline as a approximating function was conducted to determine an approximate course of curvatures observed on a measuring line set over exploitation run by "Chwałowice" coalmine. The assumed minimising criterion of loss function was referred to the forecast values of vertical ground displacements calculated via Knothe's formulas. The average courses of inclinations and curvatures of mining area were obtained via the calculation of their values by means of empirical formulas taking into consideration the obtained approximate values of measured subsidence.
Observation of atmospheric fronts using Raman lidar moisture measurements
NASA Technical Reports Server (NTRS)
Melfi, S. H.; Whiteman, D.; Ferrare, R.
1989-01-01
This paper presents the results of a field program using a ground-based Raman lidar system to observe changes in moisture profiles as a cold and a warm front passed over the NASA/Goddard Space Flight Center in Greenbelt, Maryland. The lidar operating only during darkness is capable of providing continuous high vertical resolution profiles of water vapor mixing ratio and aerosol scattering ratio from near the surface to about 7 km altitude. The lidar data acquired on three consecutive nights from shortly after sunset to shortly before sunrise, along with upper air data from specially launched rawinsondes, have provided a unique visualization of the detailed structure of the two fronts.
Laser Phase Front Measurements Using a Phase Conjugate Twyman-Green Interferometer
1992-12-01
34 AD-A258 821 AFIT/GEP/ENP/92-D-08 LASER PHASE FRONT MEASUREMENTS USING A PHASE CONJUGATE TWYMAN -GREEN INTERFEROMETER THESIS William J. Mandeville...LASER PHASE FRONT MEASUREMENTS USING A PHASE CONJUGATE TWYMAN -GREEN INTERFEROMETER THESIS Presented to the Faculty of the School of Engineering of the... Interferometer .............................................. 19 8. Phase conjugate Twyman -Green Interferometer .................................. 21
NASA Astrophysics Data System (ADS)
Zhang, Yunshan; Zhang, Weigang; Zhang, Yanxin; Wang, Song; Yu, Lin; Yan, Yieyi
2017-05-01
A robust and compact fiber sensor for simultaneous measurement of curvature and temperature based on LP 11 mode Bragg grating is proposed and demonstrated in this paper. The sensor is formed by splicing a short piece of seven-core fiber (SCF) with Bragg grating to single mode fiber (SMF). The Bragg grating is inscribed by UV light exposure, and mainly LP 01 resonance peak and LP 11 resonance peak are observed in the reflection spectrum. The experimental results show that the wavelength of the LP 11 Bragg resonance is insensitive to curvature but the power is very sensitive to curvature. The curvature sensitivity is -7.27 dB/m-1 with a linearity of 0.997 in the curvature range of 0-1 m-1. The temperature characteristic shows that the Bragg resonance has almost the same sensitivity as the common fiber Bragg grating (FBG). The sensor is also available to be independent of the ambient refractive index(RI).
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.
Measuring the composition-curvature coupling in binary lipid membranes by computer simulations.
Barragán Vidal, I A; Rosetti, C M; Pastorino, C; Müller, M
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 Cut Front Properties in Laser Cutting
NASA Astrophysics Data System (ADS)
Thombansen, Ulrich; Hermanns, Torsten; Molitor, Thomas; Pereira, Milton; Schulz, Wolfgang
Cut-front properties are a key variable in laser-cutting and thus of major importance for self-optimization. Within the Cluster of Excellence at RWTH Aachen University, several achievements were made in setting up sensor-systems that provide information on the operating-point of this melt-based manufacturing process. These achievements contribute to a gradual increase in system-transparency which is seen as an enabler for self-optimization. Instead of searching for a single measurand to characterize the course of the process, an approach is being presented which establishesa surrogate criterion to allow determination of the current operating-point. In the depicted area, this is done by joining sources of information from process observation, determining boundary-conditions such as actual feed-rate and modeling of process-variables. Although process-variables like properties of the cutting-front are influenced through more than one process parameter, a concept for a sensor-system is reported showing the correlation between properties of the melt-front and the current feed-rate. The results are compared to a solution derived from process-simulation.
NASA Astrophysics Data System (ADS)
Orwat, Justyna; Mielimąka, Ryszard
2017-07-01
The article presents the original results of the study concerning the way of approximation of average course of measured curvatures of mining area. The mean square approximation of average course of mining area subsidence with the use of a flat spline as a approximating function was conducted to determine an approximate course of curvatures observed on a measuring line set over exploitation run by "Chwałowice" coalmine. The assumed minimising criterion of loss function was referred to the forecast values of vertical ground displacements calculated via Bialek's formulas. The average courses of inclinations and curvatures of mining area were obtained via the calculation of their values by means of empirical formulas taking into consideration the obtained approximate values of measured subsidence. Subsequently, they were compared with the forecast values by Bialek's formulas and theoretical values obtained on the basis of empirical formulas including subsidence values forecast by Bialek's formulas. Due to that the determination of errors of the forecast and theoretical distributions of curvatures and estimation of usefulness of the conducted analyses was possible.
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.
NASA Astrophysics Data System (ADS)
Gruppetta, Steve; Koechlin, Laurent; Lacombe, François; Puget, Pascal
2005-10-01
A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses.
The effects of thermal field in interferometric measurements of radius of curvature
NASA Astrophysics Data System (ADS)
Mao, Jie; Hou, Xi; Wu, Fan
2014-09-01
The radius of curvature is one of the most important parameters to determine the properties of spherical surfaces. Based on the interferometric method, the importance of thermal analysis of spherical optical elements is stated in the paper. And then using different material, such as K9 and fused silica, the change of the curvature radius of spherical elements in different static temperature field is calculated and analyzed theoretically in the change of sag and surface. Finally, the theoretic results and simulated results by ANSYS have been compared. It is found that the radius of curvature of spherical optical elements is not only connected with the magnitude and direction of the temperature gradient, but also directly connected with material and structural parameters.
NASA Astrophysics Data System (ADS)
Dai, Lei; Zhang, Jian; Gu, Yongqiang; Miao, Erlong
2016-10-01
The radius of curvature (ROC) is one of the most important parameters of sphere optic components. In optic fine grinding process, radius of curvature accuracy requires up to 0.1%. We propose a method based on high precision CNC grinding machine, develop ROC online measurement method for fine grinding optics. This rapid method only takes few measurement points based on spiral route path, attaining enough accuracy and reduce the time cost, furthermore, can greatly reduce the repeated installation error. Analyzing the uncertainty sources that affect to the ROC measurement results, calculates the combined standard uncertainty 32.8 micron. Completed comparison experiments with CMM, the standard deviation of the experiment result are about 18 micron that approaches to CMM results.
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…
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…
NASA Astrophysics Data System (ADS)
Coghlan, Leslie; Singleton, H. R.; Dell'Italia, L. J.; Linderholm, C. E.; Pohost, G. M.
1995-05-01
We have developed a method for measuring the detailed in vivo three dimensional geometry of the left and right ventricles using cine-magnetic resonance imaging. From data in the form of digitized short axis outlines, the normal vectors, principal curvatures and directions, and wall thickness were computed. The method was evaluated on simulated ellipsoids and on human MRI data. Measurements of normal vectors and of wall thickness were very accurate in simulated data and appeared appropriate in patient data. On simulated data, measurements of the principal curvature k1 (corresponding approximately to the short axis direction of the left ventricle) and of principal directions were quite accurate, but measurements of the other principal curvature (k2) were less accurate. The reasons behind this are considered. We expect improvements in the accuracy with thinner slices and improved representation of the surface data. Gradient echo images were acquired from 8 dogs with a 1.5T system (Philips Gyroscan) at baseline and four months after closed chest experimentally produced mitral regurgitation (MR). The product (k1 + k2) X wall thickness averaged over all slices at end-diastole was significantly lower after surgery (n equals 8, p < 0.005). These geometry changes were consistent with the expected increase in wall stress after MR.
NASA Astrophysics Data System (ADS)
Lee, Stephen; Breiland, William; Koleske, Dan
2003-03-01
Wafer-curvature measurements of thin-film stress during chemical-vapor deposition of epitaxial GaN films on sapphire substrates are made using a multi-beam optical stress sensor (MOSS). The stress measurements are impacted by thickness nonuniformities in the growing film; lateral variations in film thickness produce optical diffraction effects that steer the reflected laser beams of the MOSS sensor away from the normally specular direction. These unintended beam-steering effects oscillate with film thickness and superimpose on the desired time-dependent beam deflections due to the wafer-curvature produced by true stress variations in the growing film. The oscillations can substantially impact stress-measurement accuracy, but allow the film nonuniformity to be assessed in real time. We develop a Fresnel-Kirchhoff diffraction model of laser-beam steering by nonuniform films that we compare to MOSS wafer-curvature measurements. Steering effects vary with the degree of film nonuniformity, the film thickness, the wavelength dispersion of the light source, the illuminated spot size, and the refractive indices of the film and substrate. Lockheed-Martin operates Sandia National Laboratories for the U. S. Dept. of Energy (Contract No. DE-AC04-94AL85000).
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.
Hao, Qun; Li, Tengfei; Hu, Yao; Wang, Shaopu; Ning, Yan; Tan, Yifeng; Zhang, Xinmu
2017-07-24
Vertex radius of curvature (VROC) is an important shape parameter used to determine the properties of an optical aspheric surface. Precise measurement of VROC error is critical for manufacturing and aligning optical aspheric surfaces. This paper introduces VROC error measurement of aspheric surface by using slope asphericity with partial compensation interferometry. VROC error and the decoupled surface figure error (SFE) can be simultaneously measured. Experimental results indicate that the method exhibits relative measurement accuracy of 0.01% when the nominal VROC is 889 mm, and the decoupled SFE error is λ/10 of the peak-to-valley value.
Wilcox, Rand R
2010-05-01
This paper considers the problem of estimating the overall strength of an association, including situations where there is curvature. The general strategy is to fit a robust regression line, or some type of smoother that allows curvature, and then use a robust analogue of explanatory power, say eta(2). When the regression surface is a plane, an estimate of eta(2) via the Theil-Sen estimator is found to perform well, relative to some other robust regression estimators, in terms of mean squared error and bias. When there is curvature, a generalization of a kernel estimator derived by Fan performs relatively well, but two alternative smoothers have certain practical advantages. When eta(2) is approximately equal to zero, estimation using smoothers has relatively high bias. A variation of eta(2) is suggested for dealing with this problem. Methods for testing H(0): eta(2)=0 are examined that are based in part on smoothers. Two methods are found that control Type I error probabilities reasonably well in simulations. Software for applying the more successful methods is provided.
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.
Direct measurement of the wetting front capillary pressure in a clay brick ceramic
NASA Astrophysics Data System (ADS)
Ioannou, Ioannis; Hall, Christopher; Wilson, Moira A.; Hoff, William D.; Carter, Margaret A.
2003-12-01
The absorption of a liquid into a rectangular bar of an initially dry porous material that is sealed on all surfaces except the inflow face is analysed in terms of Sharp Front theory. Sharp Front models are developed for both complete and incomplete displacement of air ahead of the advancing wetting front. Experiments are described from which a characteristic capillary potential of the material is obtained by measuring the equilibrium pressure of the air displaced and compressed ahead of the advancing wetting front. Results for the absorption of water and n-heptane by a fired clay brick ceramic suggest that this wetting front capillary pressure (or capillary potential) scales approximately with the surface tension and also that the permeability scales inversely with the liquid viscosity. The pressure of the air trapped in the wetted region is found to be the same as the pressure of the displaced air. For this material the wetting front capillary pressure for water at 20°C is 0.113 MPa, equivalent to a hydraulic tension head of 11.5 m and to a Young-Laplace pore diameter of 2.6 µm. The capillary pressure so measured is apparently a fundamental percolation property of the material that can be interpreted as the air pressure at which liquid phase continuity and unsaturated conductivity both vanish. The method described can be applied generally to porous materials.
NASA Astrophysics Data System (ADS)
Tung, Y. T.; Hsu, C. Y.; Yeh, J. A.; Wang, P. J.
2012-10-01
Liquid lenses based on the principle of driving two dielectric fluids via controlled electric field were investigated with an experimental apparatus designed for analysis of wave front read from a Shack-Hartmann sensor. Due to small available aperture and requirements in dynamic responses, wave front measurement was selected for study of optical characteristics in dielectric lenses. With the advent of commercial electro-optics sensors in wave front measurement, the experimental apparatus was first designed and simulated with the help of ASAP program. The simulated results proved the conceptual design with handful of engineering insights so that less trial and error efforts could be relieved from building the optics system on the bench. In-house built liquid lens modules with driving circuits were then set on the apparatus for initial calibration and functional tests. Since the electric field generated for the control of liquid profile must be alternating current, various frequency and modulation schemes were put through the liquid lens module to further study the influences on dynamic responses in terms of optical characteristics. Furthermore, effects due to material impurity and ambient effects were also carefully studied for established the fundamental phenomena of liquid lenses made of dielectric fluids. More detailed observations were possible with the measured wave-front data. In conclusion, the wave-front measurement proved to be more reliable and less expensive compared to measurement based on interferometer.
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.
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.
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.
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.
Measurement and prediction of post-fire erosion at the hillslope scale, Colorado Front Range
Juan de Dios Benavides-Solorio; Lee H. MacDonald
2005-01-01
Post-fire soil erosion is of considerable concern because of the potential decline in site productivity and adverse effects on downstream resources. For the Colorado Front Range there is a paucity of post-fire erosion data and a corresponding lack of predictive models. This study measured hillslope-scale sediment production rates and site characteristics for three wild...
Measurements of shock-front structure in multi-species plasmas on OMEGA
NASA Astrophysics Data System (ADS)
Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Wilks, S. C.; Amendt, P. A.; Heeter, R. F.; Katz, J.; Hoffman, N. M.; Vold, E.; Taitano, W.; Simakov, A.; Chacon, L.
2016-10-01
The structure of a shock front in a plasma with multiple ion species is measured for the first time in experiments on the OMEGA laser. Thomson scattering of a 263.25 nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks (M 5) propagating through low-density (ρ 0.1 mg/cc) plasmas composed of H(98%)+Ne(2%) and H(98%)+C(2%). Separation of the ion species within the shock front is inferred. Although shocks play an important role in ICF and astrophysical plasmas, the intrinsically kinetic nature of the shock front indicates the need for experiments to benchmark hydrodynamic models. Comparison with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. This work performed under auspices of U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
NASA Astrophysics Data System (ADS)
Jiazhen, Wang; Jun, Xu; Lirong, Zheng; Junyan, Ren
2010-10-01
A continuously tunable gain and bandwidth analog front-end for ambulatory biopotential measurement systems is presented. The front-end circuit is capable of amplifying and conditioning different biosignals. To optimize the power consumption and simplify the system architecture, the front-end only adopts two-stage amplifiers. In addition, careful design eliminates the need for chopping circuits. The input-referred noise of the system is only 1.19 μVrms (0.48-2000 Hz). The chip is fabricated via a SMIC 0.18 μm CMOS process. Although the power consumption is only 32.1 μW under a 3 V voltage supply, test results show that the chip can successfully extract biopotential signals.
Subbarayalu, Arun Vijay
2016-01-01
The Modified Head Posture Spinal Curvature Instrument (MHPSCI) is an extension of the Head Posture Spinal Curvature Instrument. Two specific modifications were made in the original design by adding a third arm projecting horizontally from the protractor to objectively fix the pivot exactly over the C7 vertebra and the addition of a spirit-level to properly align the instrument. In order to demonstrate reliability and validity, this study was conducted using patients with postural neck pain (N = 65) and healthy subjects (N = 20). All the subjects were working at a selected Information Technology Industry in India and had been recruited using a criterion-based sampling approach. The craniovertebral (CV) angle of each subject was evaluated by two raters consecutively. The measurements were taken by using both MHPSCI and the standard photographic method in a standardized sitting posture for the purpose of establishing criterion-validity of the instrument. The results of this study indicate a good inter-rater reliability (ICC = 0.76; CI = 0.65-0.84) as well as intra-rater reliability (ICC = 0.87; CI = 0.82-0.91) between three successive CV angle measurements (with 2 minutes interval between each measurement) through MHPSCI. While keeping the digital photographic measurement as a standard, this study established that the MHPSCI is a valid tool for measuring the CV angle as shown by non-significant difference (p > 0.01) and high correlation between the two methods (r = 0.79-0.84). This study demonstrates that the MHPSCI is a reliable and valid instrument for measuring CV angle in subjects with or without postural neck pain.
NASA Astrophysics Data System (ADS)
Chen, S. H.; Lee, D. D.; Kimishima, K.; Jinnai, H.; Hashimoto, T.
1996-12-01
Small-angle x-ray and neutron-scattering (SAXS and SANS) measurements are made of a three-component isometric microemulsion, C10E4-D2O-octane, in the one-phase channel around the hydrophile-lipophile balance temperature of the system. A previous SANS contrast variation experiment indicated that the microstructure of this isometric microemulsion is bicontinuous in water and oil, with the surfactant film having a zero mean curvature. We analyze the SAXS and SANS data taken with a bulk contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters a, b, and c, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function for the microemulsion. The analysis gives an excellent agreement with the intensity data in an absolute scale. We then use the three parameters so obtained to calculate the mean Gaussian curvature of the surfactant film. We also show a three-dimensional-reconstructed morphology of the microemulsion.
Zheng, Rui; Young, Michelle; Hill, Douglas; Le, L H; Hedden, Douglas; Moreau, Marc; Mahood, James; Southon, Sarah; Lou, Edmond
2016-03-01
Retrospective study of the coronal curvature measurement on ultrasound (US) images with the aid of previous radiographs. To compare the reliability and accuracy of the coronal curvature measurements from US images on children who have adolescent idiopathic scoliosis (AIS) with and without the knowledge of previous radiographs. Using US imaging technique to measure coronal curvature on children with AIS has demonstrated high intra- and interrater reliabilities. However, the selection of end-vertebrae and the measurement difference between radiography and the US method were only moderately reliable. Two raters measured the coronal curvatures from 65 AIS standing US spine images, without (measured one time) and with the aid of previous standing radiographs (measured two times). The intra- and interrater reliability, the correlation and the difference between the radiographic and US measurements, and the error index of the end-vertebrae selection were assessed. Overall, 109 curves were investigated. The intraclass correlation coefficients (ICC) of intra- and interrater reliability of the US coronal curvature measurement with the aid of previous radiographs (AOR) were 0.95 and 0.91, respectively. In comparison with the radiographic measurements, the correlation of AOR method (R) was 0.90 and the MAD was 2.8°; the corresponding results of the US measurement without the AOR (blinded US method) were 0.73° and 4.8°, respectively. The average error index on end-vertebral selection improved 43% with the AOR. The AOR method significantly improved reliability and accuracy of the spinal curvature measurement on US images compared with the blinded US method (P<0.001). It indicates that US standing images with the AOR can be used as a reliable and accurate nonionizing imaging method to monitor children with AIS. 3.
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.
NASA Astrophysics Data System (ADS)
Crawford, David F.
Curvature Cosmology proposes a new cosmological model very different from, and more elegant than, the Big-Bang Theory. Curvature Cosmology is based on two major hypotheses that Hubble redshift is due to an interaction of photons with curved spacetime and that there is a pressure that acts to stabilise expansion and provides a static, stable universe. The main focus of this book is to describe these two hypotheses in detail and to examine all relevant cosmological data in the context of this new model of the universe. This model proposes that, though evolution of stars and galaxies is evident, the statistical properties of the universe are the same at all places and at all times. In short, the universe is ageless, has no defined beginning (unlike the Big-Bang model), and carries no evidence of expansion, despite the changeability of its components. Curvature Cosmology calls for a paradigm shift in current cosmology and requires at least basic (if not more complex) knowledge of past and current cosmological models and equations.
Sparse aperture differential piston measurements using the pyramid wave-front sensor
NASA Astrophysics Data System (ADS)
Arcidiacono, Carmelo; Chen, Xinyang; Yan, Zhaojun; Zheng, Lixin; Agapito, Guido; Wang, Chaoyan; Zhu, Nenghong; Zhu, Liyun; Cai, Jianqing; Tang, Zhenghong
2016-07-01
In this paper we report on the laboratory experiment we settled in the Shanghai Astronomical Observatory (SHAO) to investigate the pyramid wave-front sensor (WFS) ability to measure the differential piston on a sparse aperture. The ultimate goal is to verify the ability of the pyramid WFS work in close loop to perform the phasing of the primary mirrors of a sparse Fizeau imaging telescope. In the experiment we installed on the optical bench we performed various test checking the ability to flat the wave-front using a deformable mirror and to measure the signal of the differential piston on a two pupils setup. These steps represent the background from which we start to perform full close loop operation on multiple apertures. These steps were also useful to characterize the achromatic double pyramids (double prisms) manufactured in the SHAO optical workshop.
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,
Measurement of the temperature profile of an exothermic autocatalytic reaction front.
Martin, J; Rakotomalala, N; Talon, L; Salin, D
2009-11-01
Autocatalytic reactions may propagate as solitary waves, namely, at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. When the reaction is exothermic, a thermal wave is linked to the chemical front. As the thermal diffusivity is nearly two orders of magnitude larger than the molecular one, the temperature profile spreads over length scales (mm) two orders of magnitude larger than the concentration one. Using an infrared camera, we measure the temperature profiles for a chlorite-tetrathionate autocatalytic reaction. The profiles are compared quantitatively to lattice Bhatnagar-Gross-Krook (BGK) numerical simulations. Our analysis also accounts for the lack of observation of the thermal wave for the iodate arsenous acid reaction.
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.
Approach to nonphotoperturbed differential capacitance measurements: A front-wing cantilever
NASA Astrophysics Data System (ADS)
Chang, M. N.; Chen, C. Y.; Huang, W. J.; Cheng, T. C.
2005-07-01
We have developed a front-wing (FW) cantilever structure that can significantly suppress photoperturbation effects during scanning capacitance microscopy (SCM) and scanning capacitance spectroscopy (SCS) measurements. The FW cantilever provides an effective shadow area that fully covers the scan region, allowing us to synchronously obtain SCM images and the corresponding topographic images without photoperturbation problems. Nonphotoperturbed differential capacitance characteristics versus tip biases were also obtained for SCS by the use of these FW cantilevers. This means that nonphotoperturbed SCM and SCS measurements can be carried out during the typical SCM operations.
Measurement of corneal topography through Hartmann-Shack wave-front sensor
NASA Astrophysics Data System (ADS)
Yang, Jinsheng; Rao, Xuejun; Rao, Changhui
2008-12-01
A corneal topography based on Hartmann-Shack Sensor is presented in this paper. In the system, the focus of an objective lens is precisely positioned on cornea's curve center. Wave-front of the reflecting beam can be measured by the Hartmann-Shack sensor which is conjugate to the cornea plane. If the corneal surface is a perfect sphere, wave-front detected by the Hartmann-Shack sensor is a plane. As a result, data measured by Hartmann-Shacks sensor is the deviation between the sphere and the real cornea surface. This paper describes a methodology for designing instrument based on Hartmann-Shack sensor. Then, applying this method, an instrument is developed for accurate measurement of corneal topography. In addition, measuring principle of Hartmann-Shack sensor which determined system parameters is also introduced. Repeatability is demonstrated by a series of data. The instrument was able to accurately measure simulative cornea's reflective aberrations, from which corneal topography and corneal refractive aberrations were derived.
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.
de Oliveira, Tatiana Scheeren; Candotti, Cláudia Tarragô; La Torre, Marcelo; Pelinson, Patricia Paula Tonin; Furlanetto, Tássia Silveira; Kutchak, Fernanda Machado; Loss, Jefferson Fagundes
2012-01-01
Objective. to verify the validity and reproducibility of using the flexicurve to measure the angles of the thoracic and lumbar curvatures. Method. 47 subjects were evaluated by: (1) palpation and marking of the spinous processes using lead markers, (2) using X-rays in the sagittal plane to measure the Cobb angles, (3) molding the flexicurve to the spine, and (4) drawing the contour of the flexicurve onto graph paper. The angle of curvature was determined with the flexicurve based on a 3rd order polynomial. Results. No differences were found between the Cobb angles and the angles obtained using the flexicurve in thoracic and lumbar curvatures (P > 0.05). Correlations were strong and significant for the thoracic (r = 0.72, P < 0.01) and lumbar (r = 0.60, P < 0.01) curvatures. Excellent and significant correlations were found for both the intraevaluator and interevaluator measurements. Conclusion. The results show that there is no significant difference between the values obtained using the flexicurve and those obtained using the X-ray procedure and that there is a strong correlation between the two methods. This, together with the excellent level of inter- and intraevaluator reproducibility justifies its recommendation for use in clinical practice. PMID:22619723
Front-crawl instantaneous velocity estimation using a wearable inertial measurement unit.
Dadashi, Farzin; Crettenand, Florent; Millet, Grégoire P; Aminian, Kamiar
2012-09-25
Monitoring the performance is a crucial task for elite sports during both training and competition. Velocity is the key parameter of performance in swimming, but swimming performance evaluation remains immature due to the complexities of measurements in water. The purpose of this study is to use a single inertial measurement unit (IMU) to estimate front crawl velocity. Thirty swimmers, equipped with an IMU on the sacrum, each performed four different velocity trials of 25 m in ascending order. A tethered speedometer was used as the velocity measurement reference. Deployment of biomechanical constraints of front crawl locomotion and change detection framework on acceleration signal paved the way for a drift-free integration of forward acceleration using IMU to estimate the swimmers velocity. A difference of 0.6 ± 5.4 cm · s(-1) on mean cycle velocity and an RMS difference of 11.3 cm · s(-1) in instantaneous velocity estimation were observed between IMU and the reference. The most important contribution of the study is a new practical tool for objective evaluation of swimming performance. A single body-worn IMU provides timely feedback for coaches and sport scientists without any complicated setup or restraining the swimmer's natural technique.
Front-Crawl Instantaneous Velocity Estimation Using a Wearable Inertial Measurement Unit
Dadashi, Farzin; Crettenand, Florent; Millet, Grégoire P.; Aminian, Kamiar
2012-01-01
Monitoring the performance is a crucial task for elite sports during both training and competition. Velocity is the key parameter of performance in swimming, but swimming performance evaluation remains immature due to the complexities of measurements in water. The purpose of this study is to use a single inertial measurement unit (IMU) to estimate front crawl velocity. Thirty swimmers, equipped with an IMU on the sacrum, each performed four different velocity trials of 25 m in ascending order. A tethered speedometer was used as the velocity measurement reference. Deployment of biomechanical constraints of front crawl locomotion and change detection framework on acceleration signal paved the way for a drift-free integration of forward acceleration using IMU to estimate the swimmers velocity. A difference of 0.6 ± 5.4 cm·s−1 on mean cycle velocity and an RMS difference of 11.3 cm·s−1 in instantaneous velocity estimation were observed between IMU and the reference. The most important contribution of the study is a new practical tool for objective evaluation of swimming performance. A single body-worn IMU provides timely feedback for coaches and sport scientists without any complicated setup or restraining the swimmer's natural technique. PMID:23201978
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.
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.
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
Classification and quantification of leaf curvature.
Liu, Zhongyuan; Jia, Liguo; Mao, Yanfei; He, Yuke
2010-06-01
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.
Test of a slow off-axis parabola at its center of curvature.
Parks, R E; Evans, C J; Shao, L
1995-11-01
We describe the interferometric testing of a slow (ƒ/16 at the center of curvature) off-axis parabola, intended for use in an x-ray spectrometer, that uses a spherical wave front matched to the mean radius of the asphere. We find the figure error in the off-axis mirror by removing the theoretical difference between the off-axis segment and the spherical reference from the measured wave-front error. This center of curvature test is easy to perform because the spherical reference wave front has no axis and thus alignment is trivial. We confirm that the test results are the same as the double-pass null test for a parabola that uses a plane autocollimating mirror. We also determine that the off-axis section apparently warped as the result of being cut from the symmetric parent part.
Aerial and in situ Measurements of Submesoscale Eddies, Fronts, and Filaments
NASA Astrophysics Data System (ADS)
Baschek, Burkard; Maarten Molemaker, Jeroen
2010-05-01
Submesoscale eddies, fronts, and filaments on scales of 10 m to 20 km are common features of many coastal regions of the world. Modeling results suggest that these submesoscale phenomena play an important role in local energy cascades, transferring energy from the large-scale ocean circulation to turbulence. It is also likely that submesoscale features are important for mixing, vertical transport, or biogeochemical processes. While submesoscale features have been observed using SAR satellite imagery, only very limited in situ measurements exist that reveal the dynamically relevant internal structure. Submesoscale features have a life time of several hours to a few days and advective speeds of up to 0.5 ms-1, which makes it very hard to measure them with traditional in situ sampling. Also satellite sea surface temperature (SST) data cannot sufficiently resolve the small scales of these features. We present aerial and in situ measurements of submesoscale eddies, fronts, and filaments, and believe to have carried out the first time in situ measurements of a spiral eddy (~2.5 km diameter) during a 5-day experiment in September 2009 off Catalina Island, CA. The observations are taken with a cost efficient and pragmatic observational approach for repeat quasi-synoptic measurements of submesoscale features in real-time and on the required small spatial and temporal scales of ~30min and ~20m. An IR camera mounted on a small plane is used to derive fine-resolution SST maps of this area and to guide a fast response vessel to distinct submesoscale features. A temperature/pressure array is towed in the upper 45m at speeds of 5 ms-1 through the features. The properties of the submesoscale features are examined within the context of the larger-scale circulation patterns of this highly variable coastal region combined with the analysis of satellite SST, coastal radar, and mooring data.
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.
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.
Sigma models with negative curvature
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-03-16
Here, 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.
NASA Astrophysics Data System (ADS)
Leusink, G. J.; Oosterlaken, T. G. M.; Janssen, G. C. A. M.; Radelaar, S.
1993-09-01
An in situ study of the evolution of the biaxial state of intrinsic stress during nucleation and growth of polycrystalline tungsten chemical vapor deposition films deposited by the hydrogen reduction of tungsten hexafluoride is presented. The evolution of biaxial stress was determined from in situ wafer curvature measurements. It is shown that the intrinsic stress is a growth stress, i.e., a stress developing in close vicinity to the advancing surface of the film due to metastable film growth processes. The stress developing depends strongly on the thickness of the film. High tensile stress (≊4 GPa) is observed during the initial stage of growth, compressive stress (up to -1 GPa) is observed in an intermediate thickness regime after film closure and tensile stress (0.1-1 GPa) is observed in the thick film regime. The associated stress gradients in the film are preserved during and after growth. The development of growth stress is determined by deposition temperature and growth rate. The tensile stress in the thick film regime is larger at a higher growth rate or a lower deposition temperature, while the compressive stress in the intermediate thickness regime showed the opposite dependency. Film properties as the evolution of grain size, impurity content, and resistivity are found not to vary significantly with the growth conditions. Therefore, the development of growth stress is ascribed to kinetical processes. The development of tensile stress in the thick film regime is described with a (kinetic) grain boundary formation and relaxation model. The compressive stress in the intermediate thickness regime is tentatively ascribed to compressive coherency strains induced by interfacial tensions of the grains in the stage of island growth.
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.
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
NASA Astrophysics Data System (ADS)
Aliverti, Matteo; Pariani, Giorgio; Moschetti, Manuele; Riva, Marco
2016-08-01
Traditional techniques usually rely on optical feedback to align optical elements over all the degrees of freedom needed. This strongly iterative process implies the use of bulky and/or flexible adjustable mountings. Another solution under study consists in the characterization of every optomechanical elements and the integration of the parts without any optical feedback. The characterization can be performed using different 3D Coordinate Measuring Machines (like Laser Tracker, Articulated Arms and Cartesian ones) and referencing different parts like the optomechanical mounts or the optical surfaces. The alignment of the system is done adjusting the six degrees of freedom of every element with metallic shims. Those calibrated elements are used to correct the interfaces position of the semikinematic system composed by 3 screws and 3 pins. In this paper, the integration and alignment of the ESPRESSO Front End Units (FEUs) will be used as pathfinder to test different alignment methods and evaluate their performances.
Theoretical and measured power density in front of VHF/UHF broadcasting antennas.
Jokela, K
1988-05-01
A simple and easy-to-use model based on more rigorous computations was formulated for the prediction of power density levels in front of dipole array-type VHF (very high frequency) and UHF (ultra high frequency) broadcasting antennas. Measurements on site verified the usefulness of the model. The distance at which the power density begins to exceed 10 W.m-2--the value established by standards as a limit--is roughly 40 m for UHF-TV antennas, 30 m for FM (frequency modulated) radio antennas and 15 m for VHF-TV antennas. Typical average input powers of antennas are 20 kW, 4 kW and 10 kW for FM radio, VHF-TV and UHF transmissions, respectively.
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
Convective chemical fronts in a Poiseuille flow.
Vasquez, Desiderio A
2007-11-01
Autocatalytic reaction fronts propagating in a Poiseuille flow present a change of speed and curvature depending on the strength of the flow and on the direction of front propagation. These chemical fronts separate reacted and unreacted fluids of different densities, consequently convection will always be present due to the horizontal density gradient of the curved front. In this paper, we find the change of speed caused by gravity for fronts propagating in vertical tubes under a Poiseuille flow. For small density differences, we find axisymmetric fronts. Our theory predicts a transition to nonaxisymmetric fronts as the distance between the walls is increased. The transition depends on the average speed of the Poiseuille flow.
NASA Astrophysics Data System (ADS)
Ouyang, Xiaowei; Guo, Huiyong; Zheng, Zhou; Ding, Liyun; Zhou, Ai
2017-04-01
An in-fiber Mach-Zehnder interferometer (MZI) based on dual side-hole fiber (DSHF) was demonstrated for highly sensitive measurement of curvature. The MZI-based bending sensor is fabricated by fusion splicing a piece of DSHF in between two standard single mode fibers (SMF) with cladding alignment. Due to the existence of the two air holes and the asymmetrical cross-section of the DSHF, the DSHF-based MZI is a core-cladding interferometer which is sensitive to directional bending. The bending characteristics are investigated experimentally within the curvature range of 0-8.172m-1. The bending sensitivities of the sensor are respectively 1.464 nm/m-1 and -1.394 nm/m-1 at their two opposite bending directions.
Nedzelnitsky, Victor; Wagner, Randall P.
2008-01-01
To achieve an acceptable degree of accuracy at high frequencies in some standardized methods for primary calibration of laboratory standard (LS) microphones, the front cavity depth lfc of each microphone must be known. This dimension must be measured using non-contact methods to prevent damage to the microphone diaphragm. The basic capabilities of an optical depth-measuring microscope were demonstrated by the agreement of its measurements within 0.7 μm of the known values of reference gage blocks. Using this microscope, two basic methods were applied to measure lfc. One (D) uses direct measurements at the microphone front surface annulus and conventional data reduction techniques. The other (GB) uses measurements at the surface of a gage block placed on the annulus, and plane-fitting data reduction techniques intended to reduce the effects of the slightly imperfect geometries of the microphones. The GB method was developed to provide a smoother surface of measurement than the relatively rough surface of the annulus, and to simulate the contact that occurs between the annulus and the smooth, plane surface of an acoustic coupler during microphone calibration. Using these methods, full data sets were obtained at 33 measurement positions (D), or 25 positions (GB). In addition, D and GB subsampling methods were applied by using subsamples of either the D or the GB full data sets. All these methods were applied to six LS microphones, three each of two different types. The GB subsampling methods are preferred for several reasons. The measurement results for lfc obtained by these methods agree well with those obtained by the GB method using the full data set. The expanded uncertainties of results from the GB subsampling methods are not very different from the expanded uncertainty of results from the GB method using the full data set, and are smaller than the expanded uncertainties of results from the D subsampling methods. Measurements of lfc using the GB subsampling
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 falsifies eternal inflation
Kleban, Matthew; Schillo, Marjorie E-mail: mls604@nyu.edu
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 O(10{sup −5}). Consequently, the low-l multipole moments in the CMB temperature map predict the value of the measured spatial curvature Ω{sub k}. On this basis we argue that a measurement of |Ω{sub k}| > 10{sup −4} would rule out slow-roll eternal inflation in our past with high confidence, while a measurement of Ω{sub k} < −10{sup −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 Ω{sub k} measurements and constitute a sharp test of these predictions.
Improvement of Shack-Hartmann wave-front sensor measurement for extreme adaptive optics.
Nicolle, M; Fusco, T; Rousset, G; Michau, V
2004-12-01
The development of high-performance adaptive optics systems requires the optimization of wave-front sensors (WFSs) working in the high-order correction regime. We propose a new method to improve the wave-front slope estimation of a Shack-Hartmann WFS in such a regime. Based on a detailed analysis of the different errors in the slope estimation with a classical centroid and with the new method, the gain in terms of wave-front-sensing accuracy in both the detector and the photon noise regimes is stressed. This improvement is proposed without major system disruption.
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.
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.
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
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.
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.
Higher measured than modeled ozone production at increased NOx levels in the Colorado Front Range
NASA Astrophysics Data System (ADS)
Baier, Bianca C.; Brune, William H.; Miller, David O.; Blake, Donald; Long, Russell; Wisthaler, Armin; Cantrell, Christopher; Fried, Alan; Heikes, Brian; Brown, Steven; McDuffie, Erin; Flocke, Frank; Apel, Eric; Kaser, Lisa; Weinheimer, Andrew
2017-09-01
Chemical models must correctly calculate the ozone formation rate, P(O3), to accurately predict ozone levels and to test mitigation strategies. However, air quality models can have large uncertainties in P(O3) calculations, which can create uncertainties in ozone forecasts, especially during the summertime when P(O3) is high. One way to test mechanisms is to compare modeled P(O3) to direct measurements. During summer 2014, the Measurement of Ozone Production Sensor (MOPS) directly measured net P(O3) in Golden, CO, approximately 25 km west of Denver along the Colorado Front Range. Net P(O3) was compared to rates calculated by a photochemical box model that was constrained by measurements of other chemical species and that used a lumped chemical mechanism and a more explicit one. Median observed P(O3) was up to a factor of 2 higher than that modeled during early morning hours when nitric oxide (NO) levels were high and was similar to modeled P(O3) for the rest of the day. While all interferences and offsets in this new method are not fully understood, simulations of these possible uncertainties cannot explain the observed P(O3) behavior. Modeled and measured P(O3) and peroxy radical (HO2 and RO2) discrepancies observed here are similar to those presented in prior studies. While a missing atmospheric organic peroxy radical source from volatile organic compounds co-emitted with NO could be one plausible solution to the P(O3) discrepancy, such a source has not been identified and does not fully explain the peroxy radical model-data mismatch. If the MOPS accurately depicts atmospheric P(O3), then these results would imply that P(O3) in Golden, CO, would be NOx-sensitive for more of the day than what is calculated by models, extending the NOx-sensitive P(O3) regime from the afternoon further into the morning. These results could affect ozone reduction strategies for the region surrounding Golden and possibly other areas that do not comply with national ozone regulations
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.
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.
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…
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)
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.
NASA Astrophysics Data System (ADS)
Meyer, Eileen T.
The effects of modeling the intrinsic curvature of the spectral energy distributions of BL Lacertae objects in the soft x-ray on the V/V M evolutionary statistic were studied. It was found that the power law approximations in the soft x-ray could cause a significant bias in V/V M towards values supporting either negative or positive evolution for BL Lacs. The effects of such a bias on the Sedentary Survey, a large sample of 150 BL Lacertae objects, were found to be negligible on average though individual effects were appreciable. The luminosity function and parametric values of evolution for pure luminosity and pure density evolution were computed for the Sedentary Sample.
NASA Astrophysics Data System (ADS)
Karabetsos, Sotiris; Koulouras, Grigorios; Charamis, Panagiotis; Adamidis, George; Vardiambasis, Ioannis O.; Nassiopoulos, Athanasios
2015-09-01
Microwave Thermograph (MT) is based on measuring the electromagnetic field spontaneously emitted by a body in micro-wave frequency range. In microwave radiometers, temperature measurement is made by measuring the thermal noise power. The primary module that is used for detecting this thermal noise power is the RF Front-end, which must meet very challenging requirements in terms of accuracy for measuring the noise power at the input of the receiver. The work that will be presented here will exhibit the design approaches and specifications as well as the trade-offs and performance criteria towards the development and prototyping of the RF Front-end for a Multi-Channel Microwave Radiometer for internal body temperature measurements in the l-4GHz frequency bands. The RF Front-end is intended to be integrated and be a part of a full Microwave Radiometer device that targets early detection of malignant tumours. The latter relate with the increase of temperature in cancerous cells and the precise detection of the temperature difference, which is the goal of the radiometer.
Difference displacement measurement by digital holography by use of simulated wave fronts.
Gombköto, Balázs; Kornis, János; Füzessy, Zoltán; Kiss, Márta; Kovács, Péter
2004-03-10
A concept called fringe compensation was first presented in phase-shifting electronic speckle-pattern interferometry. We apply a similar principle to digital holographic interferometry; here the phase of a wave front is known and can be manipulated. The basic mathematical formulation of fringe compensation and some experimental results are shown with relatively large, simple rigid-body rotation and circular membrane deformation.
Passive Microwave Measurments of Water Vapor Fields and Rain for Locating Fronts in Cyclonic Storms
1988-03-01
during 1979, which was the first year of Nimbus 7 operation, and which also coincided with the First GARP Global Experiment (FGGE). Good...60 km consistently marked the fronts in all seasons and in all areas of the global oceans without a need for scaling the parameter. 3.3 The...deepening cyclones or occurred during the First GARP Global Experiment (FGGE), where GARP stands for Global Atmospheric Research Program. Since
a Study of the Dynamics of Maritime Fronts Using Remotely Sensed Wind and Stress Measurements.
NASA Astrophysics Data System (ADS)
Levy, Gad
The satellite scatterometer data open unprecedented opportunities to look at maritime storms and fronts. They are combined with observations, modeling efforts, and theory to study five cases. These provide the data to investigate frontal behavior in terms of its vorticity and divergence. The appropriate momentum, divergence and vorticity equations are derived and investigated including the inertial and the frictional terms. The analysis is used to study frontal dynamics. The results indicate that the large scale horizontal and vertical thermodynamic structure of the boundary layer significantly influence baroclinic waves and frontal structure. These effects promote more efficient mixing and transport of heat, moisture, and westerly momentum in midlatitude storms. The conclusions are: (1) The analyzed satellite scatterometer winds are suited for input to a planetary boundary layer model which yields synoptic scale surface pressure analyses commensurate with current analyses based on buoy and ship observations. (2) Surface analysis may be improved when model pressure fields, scatterometer convergence patterns, and microwave radiometer vapor fields are used together. (3) The convergence usually coincides with cyclonic vorticity at frontal zones. However, the maxima in vorticity and convergence normally do not completely coincide. A significant out-of-phase relationship which was observed for one storm in its explosive stage is suggested to be a result of gravity wave activity. (4) Surface friction is important in frontal processes. This is shown in the divergence and the vorticity equations through the role of friction in determining the dissipation and the ageostrophic terms. (5) In frontal situations the dissipation term normally acts to weaken the front and thus could be regarded as a mechanism that can help in bringing a front towards a steady state. (6) The ageostrophic term normally acts to strengthen a front, and except for some special conditions, could be
Curvatures Estimation in Orientation Selection
1991-01-31
than is-obtained in length-tuning measurements . Hence, over a limited range, increasing the size or gain of the small RF has a similar effect . The...the remaining larger, lower curvature units to represent the curve. An indirect test involves measuring the time for the effect to set in, with and...31Jan 91 By, Steen .Zcke * ax . Cnadr tDistribution/ Steen .Zcke *MaxS. ynaer ~ Availability Codes Dist Special Computer Vision and Robotics Laboratory
Chou, James J; Kaufman, Joshua D; Stahl, Stephen J; Wingfield, Paul T; Bax, Ad
2002-03-20
The structure of a water-insoluble fragment encompassing residues 282-304 of the HIV envelope protein gp41 is studied when solubilized by dihexanoyl phosphatidylcholine (DHPC) and by small bicelles, consisting of a 4:1 molar ratio of DHPC and dimyristoyl phosphatidylcholine (DMPC). Weak alignment with the magnetic field was accomplished in a stretched polyacrylamide gel, permitting measurement of one-bond (1)H-(15)N, (13)Ca-(13)C', and (13)C'-(15)N dipolar couplings, which formed the basis for determining the peptide structure. In both detergent systems, the peptide adopts an alpha-helical conformation from residue 4 through 18. In the presence of the DHPC micelles the helix is strongly curved towards the hydrophobic surface, whereas in the presence of bicelles a much weaker curvature in the opposite direction is observed.
NASA Astrophysics Data System (ADS)
Zolotukhin, D. S.; Nechaev, D. V.; Ivanov, S. V.; Zhmerik, V. N.
2017-03-01
An original optical system for measuring substrate curvature (OSMSC) is described. The system enables a high-precision analysis of the processes of generation and relaxation of elastic stresses in growth of heterostructures (HSs) based on nitride compounds III-N by plasma-assisted molecular-beam epitaxy (PA-MBE). The application of OSMSC to analyze the growth of GaN/AlN/Si(111) HSs made it possible not only to observe in detail the variation dynamics of elastic stresses in this structure in its metal-enriched growth by low-temperature PA-MBE, but also to develop an HS design eliminating the effect of layer cracking by controlling the compressive stresses.
NASA Astrophysics Data System (ADS)
Shishkovskiy, I.; Sherbakov, V.; Morozov, Yu.
2007-06-01
Rapid prototyping (RP) and manufacturing (M) is a novel layer-by-layer fabrication technique which has become increasingly popular due to its inherent flexibility for the manufacture of simple and complex 3D parts. Early we had been shown opportunity of selective laser sintering (SLS) of different type powder systems (intermetallics, ceramics, ferrites, high-temperature superconductors), traditional use for self-propagated high-temperature synthesis (SHS). The non-thermal heating affect of an external electromagnetic field during SHS is related to the specific system under study due to differences in movement of defects and ions at the 'plasma-like' molten combustion wave front. We have developed and refined the testing scheme for electro-thermal phenomena studies which can directly influence on the SHS combustion wave front. This work studies electromotive force (EMF) measurements across the front of combustion wave during layer by layer surface laser sintering of exothermal powder compositions (Ni-Ti, Ni-Al). Analysis using an analog-digital-analog computer converter allowed some control of the laser movement and hence some control of the exothermal reaction - in so doing it provided near optimum conditions for forming layered 3D articles. Comparative results of structural-phase transformation during laser control SHS in reaction-capable compositions are presented.
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.
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
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.
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.
Ruppel, F.R.
1991-01-01
An evaluation of the novel self-calibrating thermocouple was performed to determine whether the sensor would be acceptable as a front end to a smart temperature measurement system. The evaluation consisted of a fast-ramp test, long-term drift tests, and physical examinations including X rays, microphotography, and energy-dispersive spectrometry. The results of the tests show that the sensor is a viable industrial-grade device worthy for use in this application. However, recommendations for improving fabrication of the assembly are made and caveats are given for conditions that may constrain the use of the sensor in certain situations. 4 refs., 17 figs., 1 tab.
Importance of plan curvature in watershed modeling
NASA Astrophysics Data System (ADS)
Boll, J.; Ribail, J.; Zhao, M.
2016-12-01
A hillslope's hydrologic response to precipitation events is largely controlled by the topographic features of a given hillslope, specifically the profile and plan curvature. Many models simplify hillslope topography and ignore the curvature properties, and some use alternate measures such as a topographic index or the hillslope width function. Models that ignore curvature properties may be calibrated to produce the statistically acceptable integrated response of runoff at a watershed outlet, but incorporating these properties is necessary to model accurately hydrologic processes such as surface flow, erosion, subsurface lateral flow, location of runoff generation and drainage response. In this study, we evaluated the sensitivity of rainfall-runoff modelling to profile and plan curvature in two models. In the first model, the Water Erosion Prediction Project (WEPP) model, hillslope uses a representative width to the hillslope by dividing the drainage area by the average surface channel length. Profile curvature is preserved with a limited spatial resolution due to the number of overland flow elements. In the second model, the distributed Soil Moisture Routing (SMR) model, the geographic information system uses the D8 algorithm to capture profile and plan curvature. Sensitivity to topographic features was tested for three profile curvatures (convex, concave, straight) combined with three plan curvatures (diverging, converging, uniform) resulting in a total of nine hillslopes. Each hillslope was subjected to different rainfall events to detect threshold behavior for when topographic features cannot be ignored. Our findings indicate that concave and convex plan curvature need to be included when subsurface flow processes are the dominant flow process for surface flow runoff generation. We present thresholds for acceptable cases when profile and plan curvature can be simplified in larger spatial hydrologic units.
NASA Astrophysics Data System (ADS)
Wu, Fenxiang; Xu, Yi; Yu, Linpeng; Yang, Xiaojun; Li, Wenkai; Lu, Jun; Leng, Yuxin
2016-11-01
Pulse front distortion (PFD) is mainly induced by the chromatic aberration in femtosecond high-peak power laser systems, and it can temporally distort the pulse in the focus and therefore decrease the peak intensity. A novel measurement scheme is proposed to directly measure the PFD of ultra-intensity ultra-short laser pulses, which can work not only without any extra struggle for the desired reference pulse, but also largely reduce the size of the required optical elements in measurement. The measured PFD in an experimental 200TW/27fs laser system is in good agreement with the calculated result, which demonstrates the validity and feasibility of this method effectively. In addition, a simple compensation scheme based on the combination of concave lens and parabolic lens is also designed and proposed to correct the PFD. Based on the theoretical calculation, the PFD of above experimental laser system can almost be completely corrected by using this compensator with proper parameters.
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.
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.
Fleas on operations in Afghanistan--environmental health measures on the front line.
Naumann, D N; Baird-Clarke, C D; Ross, D A
2011-09-01
Flea bites can cause irritating symptoms, secondary infections, and may potentiate the spread of vector-borne disease. Flea infestation and bites may also cause significant psychological distress, and can reduce the morale and fighting fitness of deployed military personnel. The problem of flea infestation was highlighted during Op HERRICK 12 in two 'front line' Check Points (CPs) where the entire population of soldiers suffered from multiple symptoms due to flea infestation and bites. Several attempts at infestation control initially succeeded but later lead to recurrence. Such failure was due to the incomplete killing of all stages of the flea life cycle, and due to constraints on education, training, communication, and resupply in the isolated and austere environment of the CPs. A dedicated operation (designated Op Insecticide) was put into action in order to eradicate the problem and return the affected troops back to full fighting fitness. Op Insecticide was thorough, systematic and sustainable, and lead to an eradication of the flea infestation problem at the affected CPs.
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.
NASA Astrophysics Data System (ADS)
Monga, Olivier; Ayache, Nicholas; Sander, Peter T.
1991-09-01
Modern medical image techniques, such as magnetic resonance image (MRI) or x-ray computed tomography provide three dimensional images of internal structures of the body, usually by means of a stack of tomographic images. The first stage in the automatic analysis of such data is 3-D edge detection1,2 which provides points corresponding to the boundaries of the surfaces forming the 3-D structure. The next stage is to characterize the local geometry of these surfaces in order to extract points or lines on which registration and/or tracking procedures can rely.3,4,5,6 This paper presents a pipeline of processes which define a hierarchical description of the second order differential characteristics of the surfaces. The focus is on the theoretical coherence of these levels of representation. Using uncertainty, a link is established between the edge detection and the local surface approximation by addressing the uncertainties inherent to edge detection in 2-D or 3-D images; and how to incorporate these uncertainties into the computation of local geometric models. In particular, calculate the uncertainty of edge location, direction, and magnitude for the 3-D Deriche operator is calculated.1,2 Statistical results are then used as a solid theoretical foundation on which to base subsequent computations, such as the determination of local surface curvature using local geometric models for surface segmentation. From the local fitting, for each edge point the mean and Gaussian curvature, principal curvatures and directions, curvature singularities, lines of curvature singularities, and covariance matrices defining the uncertainties are calculated. Experimental results for real data using two 3-D scanner images of the same organ taken at different positions demonstrate the stability of the mean and Gaussian curvatures. Experimental results for real data showing the determination of local curvature extremes of surfaces extracted from MR images are presented.
NASA Astrophysics Data System (ADS)
Farooq, Omer; Ranjeet Madiyar, Foram; Crandall, Sara; Ratra, Bharat
2017-01-01
We compile an updated list of 38 measurements of the Hubble parameter H(z) between redshifts 0.07 ≤ z ≤ 2.36 and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration–acceleration transition, zda, from these H(z) data. Within the error bars, the measured zda are insensitive to the model used, depending only on the value assumed for the Hubble constant H0. The weighted mean of our measurements is zda = 0.72 ± 0.05 (0.84 ± 0.03) for H0 = 68 ± 2.8 (73.24 ± 1.74) km s‑1 Mpc‑1 and should provide a reasonably model-independent estimate of this cosmological parameter. The H(z) data are consistent with the standard spatially flat ΛCDM cosmological model but do not rule out nonflat models or dynamical dark energy models.
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.
Zeh, W G; Koch, D D
1999-07-01
To assess the accuracy of corneal power measurement by contact lens overrefraction in patients with normal corneas and to determine the suitability of this method for use in intraocular lens (IOL) calculations. General ophthalmology clinic at a public hospital (Ben Taub General Hospital, Houston, Texas, USA). Using contact lens overrefraction (CLO), and standard keratometry, the corneal power in 33 eyes of 20 normal patients and patients scheduled for cataract extraction was prospectively measured. The eyes were divided into 3 groups based on their best spectacle-corrected visual acuity: (1) 20/20 to 20/40, (2) 20/50 to 20/70, and (3) 20/80 to 20/400. For each group, the means (absolute and arithmetic), standard deviations, and ranges of differences in corneal power as measured by CLO and keratometry were calculated. These values were used to estimate the induced variance in refractive outcome for IOL calculations. The mean absolute differences in corneal power by group were 0.35 diopter (D) +/- 0.18 (SD), 0.54 +/- 0.33 D, and 0.77 +/- 0.28 D, respectively. The mean arithmetic differences in corneal power were -0.05 +/- 0.39 D, +0.37 +/- 0.51 D, and +0.17 +/- 0.80 D, respectively. In eyes of patients with good visual acuity (20/20 to 20/40), corneal power measurements by CLO and keratometry were similar. The accuracy of the CLO-derived value decreased with increasing media opacity but was still acceptable with acuity of 20/70. Contact lens overrefraction may be a viable alternative to refractive history and videokeratography for estimating true corneal power in patients with surgically altered or irregular corneas.
The front end electronics of the NA62 Gigatracker: challenges, design and experimental measurements
NASA Astrophysics Data System (ADS)
Noy, M.; Aglieri Rinella, G.; Ceccucci, A.; Dellacasa, G.; Fiorini, M.; Garbolino, S.; Jarron, P.; Kaplon, J.; Kluge, A.; Marchetto, F.; Martin, E.; Mazza, G.; Martoiu, S.; Morel, M.; Perktold, L.; Rivetti, A.; Tiuraniemi, S.
2011-06-01
The beam spectrometer of the NA62 experiment consists of 3 Gigatracker (GTK) stations. Each station comprises a pixel detector of 16 cm active area made of an assembly of 10 readout ASICs bump bonded to a 200 μm thick pixel silicon sensor, comprising 18000 pixels of 300 μm×300 μm. The main challenge of the NA62 pixel GTK station is the combination of an extremely high kaon/pion beam rate, where the intensity in the center of the beam reaches up to 1.5 Mhit s mm together with an extreme time resolution of 100 ps. To date, it is the first silicon tracking system with this time resolution. To face this challenge, the pixel analogue front end has been designed with a peaking time of 4 ns, with a planar silicon sensor operating up to 300 V over depletion. Moreover, the radiation level is severe, 2×10 1 MeV n cm per year of operation. Easy replacement of the GTK stations is foreseen as a design requirement. The amount of material of a single station should also be less than 0.5% X to minimize the background, which imposes strong constraints on the mechanics and the cooling system. We report upon the design and architecture of the 2 prototype demonstrator chips both designed in 130 nm CMOS technology, one with a constant fraction discriminator and the time stamp digitisation in each pixel (In-Pixel), and the other with a time-over-threshold discriminator and the processing of the time stamp located in the End of Column (EoC) region at the chip periphery. Some preliminary results are presented.
Image based overlay measurement improvements of 28nm FD-SOI CMOS front-end critical steps
NASA Astrophysics Data System (ADS)
Dettoni, F.; Shapoval, T.; Bouyssou, R.; Itzkovich, T.; Haupt, R.; Dezauzier, C.
2017-03-01
Technology shrinkage leads to tight specifications in advanced semiconductor industries. For several years', metrology for lithography has been a key technology to address this challenge and to improve yield. More specifically overlay metrology is the object of special attention for tool suppliers and semiconductor manufacturers. This work focuses on Image Based Overlay (IBO) metrology for 28 nm FD-SOI CMOS front-end critical steps (gate and contact). With Overlay specifications below 10 nm, accuracy of the measurement is critical. In this study we show specific cases where target designs need to be optimized in order to minimize process effects (CMP, etch, deposition, etc.) that could lead to overlay measurement errors. Another important aspect of the metrology target is that its design must be device-like in order to better control and correct overlay errors leading to yield loss. Methodologies to optimize overlay metrology recipes are also presented. If the process effects cannot be removed entirely by target design optimization, recipe parameters have to be carefully chosen and controlled to minimize the influence of the target imperfection on measured overlay. With target asymmetry being one of the main contributors to those residual overlay measurement errors the Qmerit accuracy flag can be used to quantify the measurement error and recipe parameters can be set accordingly in order to minimize the target asymmetry impact. Reference technique measurements (CD-SEM) were used to check accuracy of the optimized overlay measurements.
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
Measuring seeing with a Shack-Hartmann wave-front sensor during an active-optics experiment
NASA Astrophysics Data System (ADS)
Zhang, Yong; Yang, Dehua; Cui, Xiangqun
2004-02-01
We describe the measurement of atmospheric enclosure seeing along a 120-m light path by use of a Shack-Hartmann wave-front sensor (S-H WFS) for the first time to our knowledge in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) outdoor active-optics experiment system, based on the differential image motion method and a S-H WFS. Seeing estimates that were gained with the S-H WFS were analyzed and found to be in close agreement with the actual seeing conditions, the estimates of refractive-index structure constant, and the thin-mirror active optics results, which usually include the shape sensing precision and the active correction precision of the experimental system. Finally, some countermeasures against poor seeing conditions were considered and adopted.
NASA Astrophysics Data System (ADS)
Cara, A.; Lavraud, B.; Tap, H.; Ballot, Y.; Aoustin, C.; Chassela, O.; Cadu, A.; Devoto, P.; Fedorov, A.; Rouzaud, J.; Rubiella, J.; Sauvaud, J. A.; Seran, H. C.; Bernal, O.; Payan, D.; Rouzies, C.
2015-12-01
The Active Monitor Box of Electrostatic Risks (AMBER) is a double-head thermal electron and ion electrostatic analyzer (~0 - 30 keV) that will be launched onboard the Jason-3 spacecraft in 2015. The new generation AMBRE instrument (AMBER_NG) constitutes a significant new evolution that will be based on a single head with newly developed sub-systems to reduce all instrument resources. We will describe the main front-end and high-voltage electronics developments which are being made to perform such dual ion-electron measurements. The first purpose of AMBER_NG is the monitoring of spacecraft charging and of the plasma populations at the origin of this charging. The design is also appropriate for the study of space plasma processes in the Earth's magnetosphere, as well as at other planets where time resolution may not prevail over mass constraints.
Fiber Fabry-Perot interferometer for curvature sensing
NASA Astrophysics Data System (ADS)
Monteiro, Catarina S.; Ferreira, Marta S.; Silva, Susana O.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
2016-12-01
A curvature sensor based on an Fabry-Perot (FP) interferometer was proposed. A capillary silica tube was fusion spliced between two single mode fibers, producing an FP cavity. Two FP sensors with different cavity lengths were developed and subjected to curvature and temperature. The FP sensor with longer cavity showed three distinct operating regions for the curvature measurement. Namely, a linear response was shown for an intermediate curvature radius range, presenting a maximum sensitivity of 68.52 pm/m-1. When subjected to temperature, the sensing head produced a similar response for different curvature radii, with a sensitivity varying from 0.84 pm/°C to 0.89 pm/°C, which resulted in a small cross-sensitivity to temperature when the FP sensor was subjected to curvature. The FP cavity with shorter length presented low sensitivity to curvature.
In-use measurement of the activity, fuel use, and emissions of front-loader refuse trucks
NASA Astrophysics Data System (ADS)
Sandhu, Gurdas S.; Frey, H. Christopher; Bartelt-Hunt, Shannon; Jones, Elizabeth
2014-08-01
Field measurements were made for six front-loader refuse trucks for over 560 miles (901 km) and 47 h of operation using a portable emissions measurement system, electronic control unit data logger, and global positioning system receivers. Daily activity, fuel use rates, and emission rates are quantified in terms of operating mode bins defined by the U.S. Environmental Protection Agency for the MOVES emission factor model. On average, 44 (±4) percent of time was spent at idle, 5 (±1) percent braking or decelerating, 11 (±2) percent coasting, 23 (±3) percent cruising or accelerating at low speed (up to 25 mph, 40.2 kmph), 10 (±2) percent cruising or accelerating at moderate speed (25-50 mph, 40.2 to 80.4 kmph), and 7 (±3) percent cruising or accelerating at high speed (50 mph, 80.4 kmph or higher). Fuel use and emission rates varied among operating modes by factors of 6-24. The estimated daily activity cycle average fuel economy ranges from 2.3 to 3.2 mpg (0.98-1.4 kmpl). The PM emission rates for trucks with diesel particulate filters are 98 percent lower compared to those without. Variation in truck weight lead to differences in average fuel use and emission rates of 20 percent or less, except for hydrocarbons. The variation in the empirically-based daily activity cycle average rates were highly correlated with MOVES estimates, except for hydrocarbons. The data collected here are useful for quantifying daily activity specific to front-loaders, and for developing fuel use and emission estimates and models for this type of vehicle.
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.
Radius of Curvature of Off-Axis Paraboloids
NASA Technical Reports Server (NTRS)
Robinson, Brian; Reardon, Patrick; Hadaway, James; Geary, Joseph; Russell, Kevin (Technical Monitor)
2002-01-01
We present several methods for measuring the vertex radius of curvature of off-axis paraboloidal mirrors. One is based on least-squares fitting of interferometer output, one on comparison of sagittal and tangential radii of curvature, and another on measurement of displacement of the nulled test article from the ideal reference wave. Each method defines radius of curvature differently and, as a consequence, produces its own sort of errors.
Veberg, A; Olsen, E; Nilsen, A N; Wold, J P
2007-05-01
This paper shows that fluorescence spectroscopy can measure both degradation of photosensitizers and formation of lipid oxidation products in light-exposed butter. The photosensitizers were already notably degraded after 4 h of light exposure, whereas fluorescent lipid oxidation products were detected after 5 d. The fluorescence measurements were highly correlated with sensory assessments of acidic and rancid flavor. Photosensitizer degradation is therefore a promising indirect indicator of the onset of lipid oxidation in butter. Sensory analysis and measurement of peroxide value showed that the level of lipid oxidation was significantly higher for butter stored in air compared with butter stored in nitrogen (N2). This might be explained by the formation of singlet oxygen from direct photooxidation and type II photosensitized oxidation. Addition of the singlet oxygen quencher beta-carotene reduced the rancid flavor intensity in the air and N2 packages from 9.0 to 4.9 and from 6.5 to 4.7, respectively. Results indicate that lipid oxidation in the butter stored in N2 was mainly caused by type I photosensitized reactions, because addition of beta-carotene had little effect on the rancid flavor intensity.
NASA Technical Reports Server (NTRS)
Kim, J.; Simon, T. W.
1987-01-01
The effects of streamwise convex curvature, recovery, and freestream turbulence intensity on the turbulent transport of heat and momentum in a mature boundary layer are studied using a specially designed three-wire hot-wire probe. Increased freestream turbulence is found to increase the profiles throughout the boundary layer on the flat developing wall. Curvature effects were found to dominate turbulence intensity effects for the present cases considered. For the higher TI (turbulence intensity) case, negative values of the turbulent Prandtl number are found in the outer half of the boundary layer, indicating a breakdown in Reynolds analogy.
Fengjie, Xi; Zongfu, Jiang; Xiaojun, Xu; Jing, Hou; Zejin, Liu
2009-03-02
In this paper we determine the optimum propagation distance between measurement planes and the plane of the lens in a wavefront curvature sensor with the diffraction optics approach. From the diffraction viewpoint, the measured wavefront aberration can be decomposed into Fourier harmonics at various frequencies. The curvature signal produced by a single harmonic is analyzed with the wave propagation transfer function approach, which is the frequency analysis of wavefront curvature sensing. The intensity of the curvature signal is a sine function of the product of the propagation distance and the squared frequency. To maximize the curvature signal, the optimum propagation distance is proposed as one quarter of the Talbot length at the critical frequency (average power point at which the power spectrum density is the average power spectrum density). Following the determination of the propagation distance, the intensity of the curvature signal varies sinusoidally with the squared frequencies, vanishing at some higher frequency bands just like a comb filter. To cover these insensitive bands, wavefront curvature sensing with dual propagation distances or with multi-propagation distances is proposed.
Modeling and measurements of nocturnal drainage flows along the Front Range of the Rocky Mountains
Leone, J.M. Jr.; Gudiksen, P.H.
1993-05-01
In support of the DOE ASCOT program Lawrence Livermore National Laboratory has analyzed the wind, temperature, and net radiation measurements acquired by the network of sensors situated within and outside the Coal Creek Canyon drainage area during 1991. It is shown that strong cooling rates, between 50--80 W/m{sup 2}, generate will defined drainage flows with a maximum speed of approximately 6 m/s. A cooling rate of 15--30 W/m{sup 2}, produces a significantly weaker drainage flow and further reduction of the cooling rate results in the failure of any significant drainage flows to form. In an attempt to further understand these flows researchers conducted numerical simulations of two representative flows.
NASA Astrophysics Data System (ADS)
Chambolle, Antonin; Morini, Massimiliano; Ponsiglione, Marcello
2015-12-01
This paper aims at building a unified framework to deal with a wide class of local and nonlocal translation-invariant geometric flows. We introduce a class of nonlocal generalized mean curvatures and prove the existence and uniqueness for the level set formulation of the corresponding geometric flows. We then introduce a class of generalized perimeters, whose first variation is an admissible generalized curvature. Within this class, we implement a minimizing movements scheme and we prove that it approximates the viscosity solution of the corresponding level set PDE. We also describe several examples and applications. Besides recovering and presenting in a unified way existence, uniqueness, and approximation results for several geometric motions already studied and scattered in the literature, the theory developed in this paper also allows us to establish new results.
Liu, Zhihong; Muldrew, Ken; Wan, Richard G; Elliott, Janet A W
2003-06-01
Variations of the Kelvin equation [W. Thomson, Philos. Mag. 42, 448 (1871)] to describe the freezing point depression of water in capillaries exist in the literature. The differing equations, coupled with the uncertainty in input parameters, lead to various predictions. The difference between the predictions may become substantial when the capillary size decreases much below micron dimensions. An experiment was designed to investigate the predicted values using a customized directional solidification stage. The capillary freezing point depression for glass tubes with radii of 87 microm-3 microm was successfully measured. The image of the ice-water interface at equilibrium was also digitally captured and analyzed to examine the contact angle and the interface shape as well. Both are important for examining the hemispherical interface assumption that was exclusively used in the theoretical derivations. Finally, an equilibrium analysis of the thermodynamic system leads to a theoretical discussion of the problem. The effect of the temperature gradient on the interface shape is addressed, and an engineering criterion for the critical temperature gradient above which the effect must be considered for the interface shape calculation is derived.
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.
NASA Astrophysics Data System (ADS)
Zhang, Wei; ASDEX Upgrade Team; Eurofusion MST1 Team
2016-10-01
Plasma heating with waves in the Ion Cyclotron Range of Frequency (ICRF) is one of the standard heating methods in tokamaks. The parallel (to the magnetic field) component of the electric field of the waves enhances the edge plasma potential nonlinearly through radio-frequency-sheath (rf-sheath) rectification. The gradient of this potential across magnetic field drives plasma convection in the Scrape-Off Layer. To reduce the rf-sheath driven close to ICRF antennas, the parallel electric near-field has to be decreased. This can be achieved by minimization of undesired parasitic currents induced in the antenna box by the antenna currents. New antennas with a novel approach to reduce those undesired currents through the proper phase and amplitude of the current in 3-straps have been installed and validated on ASDEX Upgrade. With reflectometers embedded in one 3-strap antenna at different poloidal locations, the density profiles in front of the antenna can be measured in when the antenna is either active or passive. The ICRF induced edge plasma convection in different antenna feeding configurations (different phasing, different power ratio between the central and the side straps) has thus been studied. Also we have carried out comprehensive simulations by running the EMC3EIRENE, RAPLICASOL and SSWICH codes in an iterative and quasi self-consistent way. The steadystate ICRF induced plasma density convection can clearly be reproduced in the models and compared with the ones measured in experiments.
NASA Astrophysics Data System (ADS)
Eselevich, V. G.; Borodkova, N. L.; Eselevich, M. V.; Zastenker, G. N.; Šafránkova, Y.; Němeček, Z.; Přech, L.
2017-01-01
According to the data of the BMSW/ SPEKTR-R instrument, which measured the density and velocity of solar wind plasma with a record time resolution, up to 3 ×10-2 s, the structure of the front of interplanetary shocks has been investigated. The results of these first investigations were compared with the results of studying the structure of the bow shocks obtained in previous years. A comparison has shown that the quasi-stationary (averaged over the rapid oscillations) distribution of plasma behind the interplanetary shock front was significantly more inhomogeneous than that behind the bow-shock front, i.e., in the magnetosheath. It has also been shown that, to determine the size of internal structures of the fronts of quasi-perpendicular (θBN > 45°) shocks, one could use the magnetic field magnitude, the proton density, and the proton flux of the solar wind on almost equal terms. A comparison of low Mach ( M A < 2), low beta (β1 < 1) fronts of interplanetary and bow shocks has shown that the dispersion of oblique magnetosonic waves plays an essential role in their formation.
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.
Fringes of equal tangential inclination by curvature-induced birefringence
NASA Astrophysics Data System (ADS)
Medhat, M.; Hendawy, N. I.; Zaki, A. A.
2003-02-01
A new kind of interference fringes, fringes of equal tangential inclination by curvature-induced birefringence, is presented. These are two-beam interference fringes produced by bending a thin sheet of birefringent material into a part of an exact cylinder such that the curvature is constant. Due to this curvature there is a uniform birefringence being induced. The change in birefringence induced by applying different radii of curvatures to a Fortepan sheet is measured. The stored (fixed) or natural birefringence of this sheet is deduced.
The curvature index and synchronization of dynamical systems.
Chen, Yen-Sheng; Chang, Chien-Cheng
2012-06-01
We develop a quantity, named the curvature index, for dynamical systems. This index is defined as the limit of the average curvature of the trajectory during evolution, which measures the bending of the curve on an attractor. The curvature index has the ability to differentiate the topological change of an attractor, as its alterations exhibit the structural changes of a dynamical system. Thus, the curvature index may indicate thresholds of some synchronization regimes. The Rössler system and a time-delay system are simulated to demonstrate the effectiveness of the index, respectively.
NASA Astrophysics Data System (ADS)
Caine, N.; Liu, F.; Williams, M. W.
2003-12-01
Isotopic and geochemical tracing, including end-member mixing analysis (EMMA), has greatly improved the understanding of streamflow sources and pathways during the last two decades. A continuing problem with hydrograph separations, however, is the inability to adequately measure all end-members over time. It would be advantageous if end-members identified from expensive sampling campaigns can be used in different years or in different sites. Here we evaluate the use of data rank analysis as a diagnostic tool to determine if end-members and their ionic concentrations identified using EMMA in 1996 can be used for 1997 at the 8-ha Martinelli and the 220-ha Green Lake 4 (GL4), alpine catchments in the Green Lakes Valley, Colorado Front Range. Using principal component analysis (PCA), eigenvectors and eigenvalues were extracted for the streamflow chemistry of 1996 and 1997 from the correlation matrices of 6 conservative tracers (ANC, Ca2+, Mg2+, Na+, SO42-, and Si). The results from the diagnostic tool indicated that rank (mixing subspace) of the streamflow chemistry data was 2 (rank + 1 = number of end-member) based on random patterns of the residuals between observation and prediction using their own eigenvectors for both 1996 and 1997 at both catchments. Also, the eigenvectors derived from 1996 worked as well as those from 1997 in the data rank analysis for the 1997 data at both catchments, indicating that ionic ratios in the end-members of 1997 were consistent with those of 1996. Using the EMMA end-members from 1996, three flowpaths were determined for 1997. Measured values in streamflow were reproduced reasonably well, with R2 values close to 1 for all conservative tracers. Thus, it is believed that the processes controlling the streamflow chemistry were similar for 1996 and 1997 and all end-members from 1996 could be simply used in EMMA for 1997 at the Martinelli and GL4 catchments.
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.
Mannion, Anne F; Knecht, Katrin; Balaban, Gordana; Dvorak, Jiri; Grob, Dieter
2004-03-01
There is an increasing awareness of the risks and dangers of exposure to radiation associated with repeated radiographic assessment of spinal curvature and spinal movements. As such, attempts are continuously being made to develop skin-surface devices for use in examining the progression and response to treatment of various spinal disorders. However, the reliability and validity of measurements recorded with such devices must be established before they can be recommended for use in the research or clinical environment. The aim of this study was to examine the reliability of measurements using a newly developed skin-surface device, the Spinal Mouse. Twenty healthy volunteers (mean age 41 +/- 12 years, nine males, 11 females) took part. On 2 separate days, spinal curvature was measured with the Spinal Mouse during standing, full flexion, and full extension (each three times by each of two examiners). Paired t-tests, intraclass correlation coefficients (ICC), and standard errors of measurement (SEM) with 95% confidence intervals were used to characterise between-day and interexaminer reliability for: standing sacral angle, lumbar lordosis, thoracic kyphosis, and ranges of motion (flexion, extension) of the thoracic spine, lumbar spine, hips, and trunk. The between-day reliability for segmental ranges of flexion was also determined for each motion segment from T1-2 to L5-S1. The majority of parameters measured for the 'global regions' (thoracic, lumbar, or hips) showed good between-day reliability. Depending on the parameter of interest, between-day ICCs ranged from 0.67 to 0.92 for examiner 1 (average 0.82) and 0.57 to 0.95 for examiner 2 (average 0.83); for 70% of the parameters measured, the ICCs were greater than 0.8 and generally highest for the lumbar spine and whole trunk measures. For lumbar spine range of flexion, the SEM was approximately 3 degrees. The ICCs were also good for the interexaminer comparisons, ranging from 0.62 to 0.93 on day 1 (average 0
Hysteresis compensation technique for POF curvature sensors
NASA Astrophysics Data System (ADS)
Leal, Arnaldo G.; Frizera, Anselmo; Pontes, Maria José
2017-04-01
Polymer optical fibers (POF) have higher strain limits, fracture toughness and flexibility in bend if compared to glass optical fibers. These characteristics enable the application of POFs as curvature sensors. However, the polymer is a viscoelastic material, which does not have a constant response with stress or strain. For this reason, a curvature sensor based on POF may present high hysteresis. This paper proposes a dynamic compensation technique based on the angular velocity of the sensor. Results show a hysteresis up to 10 times lower. Furthermore, it results on a simple calibration equation, which can be applied in real-time measurements.
Cosmic curvature from de Sitter equilibrium cosmology.
Albrecht, Andreas
2011-10-07
I show that the de Sitter equilibrium cosmology generically predicts observable levels of curvature in the Universe today. The predicted value of the curvature, Ω(k), depends only on the ratio of the density of nonrelativistic matter to cosmological constant density ρ(m)(0)/ρ(Λ) and the value of the curvature from the initial bubble that starts the inflation, Ω(k)(B). The result is independent of the scale of inflation, the shape of the potential during inflation, and many other details of the cosmology. Future cosmological measurements of ρ(m)(0)/ρ(Λ) and Ω(k) will open up a window on the very beginning of our Universe and offer an opportunity to support or falsify the de Sitter equilibrium cosmology.
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
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.
Advanced Curvature Deformable Mirrors
2010-09-01
designs using just a glass wafer and a wafer of Carbon Fiber Reinforced Polymer ( CFRP ). In both cases minimum bend radius decreases and the resonant... matrix is consequently nearly diagonal. The long actuators at the outer edge of the deformable mirror are largely outside the working pupil so their...formal reconstruction of the wave front either explicitly or implicitly in the control matrix . The WFS-DM combination is acting like an analog computer
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.
Multi-scale curvature tensor analysis of machined surfaces
NASA Astrophysics Data System (ADS)
Bartkowiak, Tomasz; Brown, Christopher
2016-12-01
This paper demonstrates the use of multi-scale curvature analysis, an areal new surface characterization technique for better understanding topographies, for analyzing surfaces created by conventional machining and grinding. Curvature, like slope and area, changes with scale of observation, or calculation, on irregular surfaces, therefore it can be used for multi-scale geometric analysis. Curvatures on a surface should be indicative of topographically dependent behavior of a surface and curvatures are, in turn, influenced by the processing and use of the surface. Curvatures have not been well characterized previously. Curvature has been used for calculations in contact mechanics and for the evaluation of cutting edges. In the current work two parts were machined and then one of them was ground. The surface topographies were measured with a scanning laser confocal microscope. Plots of curvatures as a function of position and scale are presented, and the means and standard deviations of principal curvatures are plotted as a function of scale. Statistical analyses show the relations between curvature and these two manufacturing processes at multiple scales.
NASA Astrophysics Data System (ADS)
Hasegawa, Hiroki; Kowatari, Takaya; Shiroki, Yasuhiro; Shibata, Hiroyuki; Ohta, Hiromichi; Waseda, Yoshio
2012-12-01
Thermal conductivity values have been systematically obtained for molten silicates containing Al2O3, CaO, Na2O, and SiO2 by means of a front heating-front detection laser flash method. The measurements were made for 13 samples in the temperature range between 1073 K and 1823 K (800 °C and 1550 °C), depending on the composition. Thermal conductivities of the silicate melts are found to be relatively insensitive to the variation of temperature, but they depend on the composition ratio, particularly the ratio of Non-Bridging Oxygen ions per Tetrahedrally coordinated cation—NBO/T. The thermal conductivity values decrease from 2.8 W/mK to 1.5 W/mK with the NBO/T value until it reaches about 1. Thermal conductivity values become constant for silicate melts with a higher value of NBO/T. It is known that the length of the silicate chain decreases with disconnection by the addition of alkaline earth cation or alkaline cation. The strong correlation between thermal conductivity and NBO/T is quite likely to suggest that silicate chain is a preferential path for heat transport in silicate melts.
NASA Astrophysics Data System (ADS)
Berry, M. V.
2013-10-01
Wave streamlines are integral curves of the local wavevector (phase gradient). An exact formula is derived, giving the curvature of streamlines as the component transverse to the local wavevector of the gradient of the logarithm of the local wavenumber. The formula is applied to quantum particles moving in a potential and classical light in the presence of a refractive-index gradient. Three limiting regimes are encompassed. The first is geometrical, in which the bending of streamlines arises solely from the classical force or optical index gradient. The second and third limits concern singularities in the pattern of wave streamlines, of two types: optical vortices, near which the streamlines are asymptotically circular, and phase saddles, near which the streamlines are asymptotically hyperbolic.
On nonlinear higher spin curvature
NASA Astrophysics Data System (ADS)
Manvelyan, Ruben; Mkrtchyan, Karapet; Rühl, Werner; Tovmasyan, Murad
2011-05-01
We present the first nonlinear term of the higher spin curvature which is covariant with respect to deformed gauge transformations that are linear in the field. We consider the case of spin 3 after presenting spin 2 as an example, and then construct the general spin s quadratic term of the de Wit-Freedman curvature.
Michel, D. T.; Davis, A. K.; Armstrong, W.; ...
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
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.
Nagi, Sana Ehsen; Khan, Farhan Raza
2017-01-01
With root canal treatment, the organic debris and micro-organisms from pulp space is removed and an ideal canal preparation is achieved that is conducive of hermetic obturation. The purpose of this study was to correlate the pre-operative canal curvature with the postoperative curvature in human extracted teeth prepared with K-3 rotary systems. The root canal preparation was carried out on extracted human molars and premolars using K-3 endodontic rotary files. A pre and post-operative image of the teeth using digital radiograph were taken in order to compare pre and post-operative canal curvature. The images were saved in an images retrieval system (Gendex software, USA). Change in the canal curvature was measured using the software measuring tool (Vixwin software, USA). Student paired t-test and Pearson correlation test was applied at 0.05 level of significance. There is a statistically significant difference between pre-operative and post-operative canal curvature (p-value <0.001) and a strong positive correlation (91% correlation) between pre-operative and post-operative canal curvature in teeth prepared with the K-3 rotary files. A significant difference between pre and post instrumentation curvature was found. Degree of canal curvature was not correlated with time taken for canal preparation.
Modeling normal shock velocity curvature relations for heterogeneous explosives
NASA Astrophysics Data System (ADS)
Yoo, Sunhee; Crochet, Michael; Pemberton, Steven
2017-01-01
The theory of Detonation Shock Dynamics (DSD) is, in part, an asymptotic method to model a functional form of the relation between the shock normal, its time rate and shock curvature κ. In addition, the shock polar analysis provides a relation between shock angle θ and the detonation velocity Dn that is dependent on the equations of state (EOS) of two adjacent materials. For the axial detonation of an explosive material confined by a cylinder, the shock angle is defined as the angle between the shock normal and the normal to the cylinder liner, located at the intersection of the shock front and cylinder inner wall. Therefore, given an ideal explosive such as PBX-9501 with two functional models determined, a unique, smooth detonation front shape ψ can be determined that approximates the steady state detonation shock front of the explosive. However, experimental measurements of the Dn(κ) relation for heterogeneous explosives such as PBXN-111 [D. K. Kennedy, 2000] are challenging due to the non-smoothness and asymmetry usually observed in the experimental streak records of explosion fronts. Out of many possibilities the asymmetric character may be attributed to the heterogeneity of the explosives; here, material heterogeneity refers to compositions with multiple components and having a grain morphology that can be modeled statistically. Therefore in extending the formulation of DSD to modern novel explosives, we pose two questions: (1) is there any simple hydrodynamic model that can simulate 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 [1] studied constitutive models for derivation of the Dn(κ) relation for 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
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.
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
Curvature sensor based on a Fabry-Perot interferometer
NASA Astrophysics Data System (ADS)
Monteiro, Catarina; Ferreira, Marta S.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
2016-05-01
A curvature sensor based on a Fabry-Perot interferometer is proposed. A capillary tube of silica is fusion spliced between two single mode fibers, producing a Fabry-Perot cavity. The light propagates in air, when passing through the capillary tube. Two different cavities are subjected to curvature and temperature. The cavity with shorter length shows insensitivity to both measurands. The larger cavity shows two operating regions for curvature measurement, where a linear response is shown, with a maximum sensitivity of 18.77pm/m-1 for the high curvature radius range. When subjected to temperature, the sensing head produces a similar response for different curvature radius, with a sensitivity of 0.87pm/°C.
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)
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.
Propagation of curved activation fronts in anisotropic excitable media.
Morozov, V G; Davydov, N V; Davydov, V A
1999-06-01
We study theoretical and numerical propagation of autowave fronts in excitable two-variable (activator-inhibitor) systems with anisotropic diffusion. A general curvature-velocity relation is derived for the case that the inhibitor diffusion is neglected. This relation predicts the break of an activation front when the front curvature exceeds a critical value, which is corroborated by computer simulations of a particular reaction-diffusion model. Some qualitative effects associated with the inhibitor diffusion are studied numerically. It is found that the critical value of curvature decreases with an increase in the inhibitor diffusion coefficient. The core of a spiral wave increases in size and turns through an angle which depends on the inhibitor diffusion coefficient. PACS Numbers: 05.50. +q, 05.70. Ln., 82.40. -g, 87.10. +e.
EAU guidelines on penile curvature.
Hatzimouratidis, Konstantinos; Eardley, Ian; Giuliano, François; Hatzichristou, Dimitrios; Moncada, Ignacio; Salonia, Andrea; Vardi, Yoram; Wespes, Eric
2012-09-01
Penile curvature can be congenital or acquired. Acquired curvature is secondary due to La Peyronie (Peyronie's) disease. To provide clinical guidelines on the diagnosis and treatment of penile curvature. A systematic literature search on the epidemiology, diagnosis, and treatment of penile curvature was performed. Articles with the highest evidence available were selected and formed the basis for assigning levels of evidence and grades of recommendations. The pathogenesis of congenital penile curvature is unknown. Peyronie's disease is a poorly understood connective tissue disorder most commonly attributed to repetitive microvascular injury or trauma during intercourse. Diagnosis is based on medical and sexual histories, which are sufficient to establish the diagnosis. Physical examination includes assessment of palpable nodules and penile length. Curvature is best documented by a self-photograph or pharmacologically induced erection. The only treatment option for congenital penile curvature is surgery based on plication techniques. Conservative treatment for Peyronie's disease is associated with poor outcomes. Pharmacotherapy includes oral potassium para-aminobenzoate, intralesional treatment with verapamil, clostridial collagenase or interferon, topical verapamil gel, and iontophoresis with verapamil and dexamethasone. They can be efficacious in some patients, but none of these options carry a grade A recommendation. Steroids, vitamin E, and tamoxifen cannot be recommended. Extracorporeal shock wave treatment and penile traction devices may only be used to treat penile pain and reduce penile deformity, respectively. Surgery is indicated when Peyronie's disease is stable for at least 3 mo. Tunical shortening procedures, especially plication techniques, are the first treatment options. Tunical lengthening procedures are preferred in more severe curvatures or in complex deformities. Penile prosthesis implantation is recommended in patients with erectile dysfunction
Compound curvature laser window development
NASA Technical Reports Server (NTRS)
Verhoff, Vincent G.
1993-01-01
The NASA Lewis Research Center has developed and implemented a unique process for forming flawless compound curvature laser windows. These windows represent a major part of specialized, nonintrusive laser data acquisition systems used in a variety of compressor and turbine research test facilities. This report summarizes the main aspects of compound curvature laser window development. It is an overview of the methodology and the peculiarities associated with the formulation of these windows. Included in this discussion is new information regarding procedures for compound curvature laser window development.
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.
Surface tension driven flow on a thin reaction front
NASA Astrophysics Data System (ADS)
Guzman, Roberto; Vasquez, Desiderio A.
2016-11-01
Surface tension driven convection affects the propagation of chemical reaction fronts in liquids. The changes in surface tension across the front generate this type of convection. The resulting fluid motion increases the speed and changes the shape of fronts as observed in the iodate-arsenous acid reaction. We calculate these effects using a thin front approximation, where the reaction front is modeled by an abrupt discontinuity between reacted and unreacted substances. We analyze the propagation of reaction fronts of small curvature. In this case the front propagation equation becomes the deterministic Kardar-Parisi-Zhang (KPZ) equation with the addition of fluid flow. These results are compared to calculations based on a set of reaction-diffusion-convection equations.
Grosfils, P; Dubois, F; Yourassowsky, C; De Wit, A
2009-01-01
A noninvasive optical technique combining digital interferometry in transmission and transparency measurement of concentration is developed to analyze spatiotemporal dynamics of physicochemical systems. This technique allows one to measure simultaneously the two-dimensional (2D) dynamics of concentration and temperature fields in both reactive and nonreactive systems contained inside a transparent cell. When used to experimentally analyze buoyancy-driven fingering of an exothermic autocatalytic chemical front, this method reveals in the 2D temperature field the presence of hot spots where the temperature locally exceeds the adiabatic one.
Shishkovskiy, Igor V; Morozov, Yury G; Kuznetsov, Maxim V; Parkin, Ivan P
2009-05-14
Electric potentials arise between the combustion wave front and final products during layer-by-layer surface laser sintering of exothermic powder compositions (Ni-Ti, Ni-Al, Ti-Al). By using an analog-digital-analog converter to control the laser movement and hence the exothermic reaction itself, we show that near optimal conditions can be obtained for the formation of layered 3D articles. Comparative results of the structural-phase transformations that occur during laser-controlled SHS in related reaction-capable compositions are also presented.
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.
Curvature Interaction in Collective Space
NASA Astrophysics Data System (ADS)
Herrmann, Richard
2012-12-01
For the Riemannian space, built from the collective coordinates used within nuclear models, an additional interaction with the metric is investigated, using the collective equivalent to Einstein's curvature scalar. The coupling strength is determined using a fit with the AME2003 ground state masses. An extended finite-range droplet model including curvature is introduced, which generates significant improvements for light nuclei and nuclei in the trans-fermium region.
Curvature of spacetime: A simple student activity
NASA Astrophysics Data System (ADS)
Wood, Monika; Smith, Warren; Jackson, Matthew
2016-12-01
The following is a description of an inexpensive and simple student experiment for measuring the differences between the three types of spacetime topology—Euclidean (flat), Riemann (spherical), and Lobachevskian (saddle) curvatures. It makes use of commonly available tools and materials, and requires only a small amount of construction. The experiment applies to astronomical topics such as gravity, spacetime, general relativity, as well as geometry and mathematics.
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.
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.
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 (
3D curvature of muscle fascicles in triceps surae.
Rana, Manku; Hamarneh, Ghassan; Wakeling, James M
2014-12-01
Muscle fascicles curve along their length, with the curvatures occurring around regions of high intramuscular pressure, and are necessary for mechanical stability. Fascicles are typically considered to lie in fascicle planes that are the planes visualized during dissection or two-dimensional (2D) ultrasound scans. However, it has previously been predicted that fascicles must curve in three-dimensional (3D) and thus the fascicle planes may actually exist as 3D sheets. 3D fascicle curvatures have not been explored in human musculature. Furthermore, if the fascicles do not lie in 2D planes, then this has implications for architectural measures that are derived from 2D ultrasound scans. The purpose of this study was to quantify the 3D curvatures of the muscle fascicles and fascicle sheets within the triceps surae muscles and to test whether these curvatures varied among different contraction levels, muscle length, and regions within the muscle. Six male subjects were tested for three torque levels (0, 30, and 60% maximal voluntary contraction) and four ankle angles (-15, 0, 15, and 30° plantar flexion), and fascicles were imaged using 3D ultrasound techniques. The fascicle curvatures significantly increased at higher ankle torques and shorter muscle lengths. The fascicle sheet curvatures were of similar magnitude to the fascicle curvatures but did not vary between contractions. Fascicle curvatures were regionalized within each muscle with the curvature facing the deeper aponeuroses, and this indicates a greater intramuscular pressure in the deeper layers of muscles. Muscle architectural measures may be in error when using 2D images for complex geometries such as the soleus.
NASA Astrophysics Data System (ADS)
Li, Chunyan; Chen, Changsheng
2014-11-01
Shelf circulation impacted by a shift in wind regime during the passage of an atmospheric cold front system is studied with a field survey over the mid-shelf of the South Atlantic Bight between Oct 4 and 9, 2004. Weak southerly winds preceded the cold front for a few days, followed by a rapid shift in wind direction and strengthening of northeasterly winds over a few more days. More than 93 h of acoustic Doppler current profiler (ADCP) data were obtained along an equilateral triangle of 105 km in perimeter, which was continuously occupied for 11 times. A harmonic analysis was applied to extract tidal and subtidal wind-driven flow components by collapsing the 93 hour data into one M2 tidal period. It was found that the cross-shelf flow was barely affected by the wind while the along-shelf flow responded with a spatially uniform and almost steadily increasing mean flow velocity, superimposed on an oscillatory tidal current. The wind induced along-shelf transport was estimated to be ~ 0.3 Sv over the inner and middle shelf. The net cross-shelf transport was negligible. Apparently, the northeasterly wind causes an along-shelf current which was subject to Coriolis force that sets up an increasing coastal sea level pressure gradient as the water kept piling up against the coast, which was confirmed by tide gauge data. The observations found that the flow field prior to the strong winds had more complicated structures including eddy-like features, while after the strong northeasterly winds, the flow became eddy free and uniform in space. A theoretical model solved by a Laplace Transform was used to examine the wind-driven flow mechanism and the results were compared with the observations of net along-shelf flow velocity.
Static optical designs for Wavefront Curvature Sensing
NASA Astrophysics Data System (ADS)
Bharmal, Nazim A.
2006-06-01
A bulk optic is presented, the Parallel Output Beamsplitter, which allows simultaneous imaging of two planes either side of the focus using static imaging optics. The POB is used to create novel optical configurations for Wavefront Curvature Sensing and two designs are presented. The first is suited to small-amplitude aberration measurements in situations where compactness, a large field of view, and high optical throughput are desirable. A laboratory experiment using a POB to make such a wavefront sensor was undertaken, and results are presented. The second design is a conceptual idea which offers image-scale invariant imaging of two planes whose conjugation satisfies the requirements of a conventional Wavefront Curvature Sensor concept.
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.
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.
Membrane curvature at a glance
McMahon, Harvey T.; Boucrot, Emmanuel
2015-01-01
ABSTRACT 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
Curvature of the localized surface plasmon resonance peak.
Chen, Peng; Liedberg, Bo
2014-08-05
Localized surface plasmon resonance (LSPR) occurring in noble metal nanoparticles (e.g., Au) is a widely used phenomenon to report molecular interactions. Traditional LSPR sensors typically monitor shifts in the peak position or extinction in response to local refractive index changes in the close vicinity of the nanoparticle surface. The ability to resolve minute shifts/extinction changes is to a large extent limited by instrumental noise. A new strategy to evaluate LSPR responses utilizing changes in the shape of the extinction spectrum (the curvature) is proposed. The response of curvature to refractive index changes is investigated theoretically using Mie theory and an analytical expression relating the curvature to the refractive index is presented. The experimentally derived curvatures for 13 nm spherical gold nanoparticles (AuNPs) exposed to solvents with different bulk refractive indices confirm the theoretical predictions. Moreover, both the calculated and experimental findings suggest that the curvature is approximately a linear function of refractive index in regimes relevant to bio and chemical sensing. We demonstrate that curvature is superior over peak shift and extinction both in terms of signal-to-noise (S/N) ratio and reliability of LSPR sensors. With a curvature, one could readily monitor submonolayer adsorption of a low molecular weight thiol molecule (M(w) = 458.6) onto 13 nm AuNPs. It is also worthwhile mentioning that curvature is virtually insensitive to instrumental instabilities and artifacts occurring during measurement. Instabilities such as baseline tilt and shift, shift in peak position as well as sharp spikes/steps in the extinction spectra do not induce artifacts in the sensorgrams of curvature.
DSD front models : nonideal explosive detonation
Bdzil, J. B.; Short, M.; Aslam, T. D.; Catanach, R. A.; Hill, L. G.
2001-01-01
The Detonation Shock Dynamics (DSD) method for propagating detonation in numerical simulation of detonation in high explosive (HE) is based on three elements: (1) a subscale theory of multi-dimensional detonation that treats the evolving detonation as a front with dynamics that depends only on metrics of the front (such as curvature, etc.), (2) high-resolution direct numerical sirnuliltion of detonation serving both to test existing subscale theories and suggest modifications, and (3) physical experiments to characterize multi-dimensional detonation propagation on real explosives and to calibrate the front models for use in engineering simulations. In this paper we describe our work on all three of these elements of the DSD method as it applies to detonation in nonideal explosives.
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.
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.
Intrinsically disordered proteins drive membrane curvature.
Busch, David J; Houser, Justin R; Hayden, Carl C; Sherman, Michael B; Lafer, Eileen M; Stachowiak, Jeanne C
2015-07-24
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.
Changes on the corneal thickness and curvature after orthokeratology
NASA Astrophysics Data System (ADS)
Mitsui, Iwane; Yamada, Yoshiya
2004-07-01
To evaluate the corneal thickness and curvature changes after Orthokeratology contact lens wear, using the ORBSCAN II corneal topography system, corneal thickness and corneal curvature were measured on one hundred and twenty eyes of sixty patients before and after wearing the custom rigid gas permeable contact lenses for Orthokeratology. The contact lenses were specially designed for each eye. The subjects wore the orthokeratology lenses for approximately Four hours with their eyes closed. The corneal thickness of the subjects was increased on fifty-five eyes at not only the peripheral zone but also the center of the cornea. The average increase of central and peripheral corneal thickness was 18 micrometer and 22micrometer, respectively. The mean anterior curvature of corneal surface changed 1.25D. The mean posterior curvature of corneal endothelium side changed 0.75D.
Correlation between thoracolumbar curvatures and respiratory function in older adults
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were −46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=−0.23, P<0.05; forced vital capacity: r=−0.32, P<0.05), quiet expiration intercostal thickness (r=−0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=−0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=−0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=−0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar
Correlation between thoracolumbar curvatures and respiratory function in older adults.
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were -46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=-0.23, P<0.05; forced vital capacity: r=-0.32, P<0.05), quiet expiration intercostal thickness (r=-0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=-0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=-0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=-0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar curvatures
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.
The effect of illuminant position on perceived curvature.
Curran, W; Johnston, A
1996-05-01
In shaded scenes surface features can appear either concave or convex, depending upon the viewer's judgement about the direction of the prevailing illumination. If other curvature cues are added to the image this ambiguity can be removed. However, it is not clear to what extent, if any, illuminant position exerts an influence on the perceived magnitude of surface curvature. Subjects were presented with pairs of spherical surface patches in a curvature matching task. The patches were defined by shading and texture cues. The perceived curvature of a standard patch was measured as a function of light source position. We found a clear effect of light source position on apparent curvature. Perceived curvature decreased as light source tilt increased and as light source slant decreased. We also found that the strength of this effect is determined partly by a surface's reflectance function and partly by the relative weight of the texture cue. When a specular component was added to the stimuli, the effect of light source orientation was weakened. The weight of the texture cue was manipulated by disrupting the regular distribution of texture elements. We found an inverse relationship between the strength of the effect and the weight of the texture cue: lowering the texture cue weight resulted in an enhancement of the illuminant position effect.
Stability of convective patterns in reaction fronts: a comparison of three models.
Vasquez, Desiderio A; Coroian, Dan I
2010-09-01
Autocatalytic reaction fronts generate density gradients that may lead to convection. Fronts propagating in vertical tubes can be flat, axisymmetric, or nonaxisymmetric, depending on the diameter of the tube. In this paper, we study the transitions to convection as well as the stability of different types of fronts. We analyze the stability of the convective reaction fronts using three different models for front propagation. We use a model based on a reaction-diffusion-advection equation coupled to the Navier-Stokes equations to account for fluid flow. A second model replaces the reaction-diffusion equation with a thin front approximation where the front speed depends on the front curvature. We also introduce a new low-dimensional model based on a finite mode truncation. This model allows a complete analysis of all stable and unstable fronts.
Stability of convective patterns in reaction fronts: A comparison of three models
NASA Astrophysics Data System (ADS)
Vasquez, Desiderio A.; Coroian, Dan I.
2010-09-01
Autocatalytic reaction fronts generate density gradients that may lead to convection. Fronts propagating in vertical tubes can be flat, axisymmetric, or nonaxisymmetric, depending on the diameter of the tube. In this paper, we study the transitions to convection as well as the stability of different types of fronts. We analyze the stability of the convective reaction fronts using three different models for front propagation. We use a model based on a reaction-diffusion-advection equation coupled to the Navier-Stokes equations to account for fluid flow. A second model replaces the reaction-diffusion equation with a thin front approximation where the front speed depends on the front curvature. We also introduce a new low-dimensional model based on a finite mode truncation. This model allows a complete analysis of all stable and unstable fronts.
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)
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)
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.
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
Curvature-induced lipid segregation
NASA Astrophysics Data System (ADS)
Zheng, Bin; Meng, Qing-Tian; B. Selinger Robin, L.; V. Selinger, Jonathan; Ye, Fang-Fu
2015-06-01
We investigate how an externally imposed curvature influences lipid segregation on two-phase-coexistent membranes. We show that the bending-modulus contrast of the two phases and the curvature act together to yield a reduced effective line tension. On largely curved membranes, a state of multiple domains (or rafts) forms due to a mechanism analogous to that causing magnetic-vortex formation in type-II superconductors. We determine the criterion for such a multi-domain state to occur; we then calculate respectively the size of the domains formed on cylindrically and spherically curved membranes. Project supported by the Hundred-Talent Program of the Chinese Academy of Sciences (FY) and the National Science Foundation of USA via Grant DMR-1106014 (RLBS, JVS).
Quantum complexity and negative curvature
NASA Astrophysics Data System (ADS)
Brown, Adam R.; Susskind, Leonard; Zhao, Ying
2017-02-01
As time passes, once simple quantum states tend to become more complex. For strongly coupled k -local Hamiltonians, this growth of computational complexity has been conjectured to follow a distinctive and universal pattern. In this paper we show that the same pattern is exhibited by a much simpler system—classical geodesics on a compact two-dimensional geometry of uniform negative curvature. This striking parallel persists whether the system is allowed to evolve naturally or is perturbed from the outside.
Design and Measurement of a Low-Noise 64-Channels Front-End Readout ASIC for CdZnTe Detectors
Gan, Bo; Wei, Tingcun; Gao, Wu; Liu, Hui; Hu, Yann
2015-07-01
Cadmium zinc telluride (CdZnTe) detectors, as one of the principal detectors for the next-generation X-ray and γ-ray imagers, have high energy resolution and supporting electrode patterning in the radiation environment at room-temperature. In the present, a number of internationally renowned research institutions and universities are actively using these detector systems to carry out researches of energy spectrum analysis, medical imaging, materials characterization, high-energy physics, nuclear plant monitoring, and astrophysics. As the most important part of the readout system for the CdZnTe detector, the front-end readout application specific integrated circuit (ASIC) would have an important impact on the performances of the whole detector system. In order to ensure the small signal to noise ratio (SNR) and sufficient range of the output signal, it is necessary to design a front-end readout ASIC with very low noise and very high dynamic range. In addition, radiation hardness should be considered when the detectors are utilized in the space applications and high energy physics experiments. In this paper, we present measurements and performances of a novel multi-channel radiation-hardness low-noise front-end readout ASIC for CdZnTe detectors. The readout circuits in each channel consist of charge sensitive amplifier, leakage current compensation circuit (LCC), CR-RC shaper, S-K filter, inverse proportional amplifier, peak detect and hold circuit (PDH), discriminator and trigger logic, time sequence control circuit and driving buffer. All of 64 readout channels' outputs enter corresponding inputs of a 64 channel multiplexer. The output of the mux goes directly out of the chip via the output buffer. The 64-channel readout ASIC is implemented using the TSMC 0.35 μm mixed-signal CMOS technology. The die size of the prototype chip is 2.7 mm x 8 mm. At room temperature, the equivalent noise level of a typical channel reaches 66 e{sup -} (rms) at zero farad for a power
Disformal invariance of curvature perturbation
Motohashi, Hayato; White, Jonathan E-mail: jwhite@post.kek.jp
2016-02-01
We show that under a general disformal transformation the linear comoving curvature perturbation is not identically invariant, but is invariant on superhorizon scales for any theory that is disformally related to Horndeski's theory. The difference between disformally related curvature perturbations is found to be given in terms of the comoving density perturbation associated with a single canonical scalar field. In General Relativity it is well-known that this quantity vanishes on superhorizon scales through the Poisson equation that is obtained on combining the Hamiltonian and momentum constraints, and we confirm that a similar result holds for any theory that is disformally related to Horndeski's scalar-tensor theory so long as the invertibility condition for the disformal transformation is satisfied. We also consider the curvature perturbation at full nonlinear order in the unitary gauge, and find that it is invariant under a general disformal transformation if we assume that an attractor regime has been reached. Finally, we also discuss the counting of degrees of freedom in theories disformally related to Horndeski's.
Substrate curvature regulates cell migration
NASA Astrophysics Data System (ADS)
He, Xiuxiu; Jiang, Yi
2017-06-01
Cell migration is essential in many aspects of biology. Many basic migration processes, including adhesion, membrane protrusion and tension, cytoskeletal polymerization, and contraction, have to act in concert to regulate cell migration. At the same time, substrate topography modulates these processes. In this work, we study how substrate curvature at micrometer scale regulates cell motility. We have developed a 3D mechanical model of single cell migration and simulated migration on curved substrates with different curvatures. The simulation results show that cell migration is more persistent on concave surfaces than on convex surfaces. We have further calculated analytically the cell shape and protrusion force for cells on curved substrates. We have shown that while cells spread out more on convex surfaces than on concave ones, the protrusion force magnitude in the direction of migration is larger on concave surfaces than on convex ones. These results offer a novel biomechanical explanation to substrate curvature regulation of cell migration: geometric constrains bias the direction of the protrusion force and facilitates persistent migration on concave surfaces.
Substrate curvature regulates cell migration.
He, Xiuxiu; Jiang, Yi
2017-05-23
Cell migration is essential in many aspects of biology. Many basic migration processes, including adhesion, membrane protrusion and tension, cytoskeletal polymerization, and contraction, have to act in concert to regulate cell migration. At the same time, substrate topography modulates these processes. In this work, we study how substrate curvature at micrometer scale regulates cell motility. We have developed a 3D mechanical model of single cell migration and simulated migration on curved substrates with different curvatures. The simulation results show that cell migration is more persistent on concave surfaces than on convex surfaces. We have further calculated analytically the cell shape and protrusion force for cells on curved substrates. We have shown that while cells spread out more on convex surfaces than on concave ones, the protrusion force magnitude in the direction of migration is larger on concave surfaces than on convex ones. These results offer a novel biomechanical explanation to substrate curvature regulation of cell migration: geometric constrains bias the direction of the protrusion force and facilitates persistent migration on concave surfaces.
Wu, Hao; Wang, Ruoxu; Liu, Deming; Fu, Songnian; Zhao, Can; Wei, Huifeng; Tong, Weijun; Shum, Perry Ping; Tang, Ming
2016-04-01
We proposed and demonstrated a few-mode fiber (FMF) based optical-fiber sensor for distributed curvature measurement through quasi-single-mode Brillouin frequency shift (BFS). By central-alignment splicing FMF and single-mode fiber (SMF) with a fusion taper, a SMF-components-compatible distributed curvature sensor based on FMF is realized using the conventional Brillouin optical time-domain analysis system. The distributed BFS change induced by bending in FMF has been theoretically and experimentally investigated. The precise BFS response to the curvature along the fiber link has been calibrated. A proof-of-concept experiment is implemented to validate its effectiveness in distributed curvature measurement.
Turning maneuvers in sharks: Predicting body curvature from axial morphology.
Porter, Marianne E; Roque, Cassandra M; Long, John H
2009-08-01
Given the diversity of vertebral morphologies among fishes, it is tempting to propose causal links between axial morphology and body curvature. We propose that shape and size of the vertebrae, intervertebral joints, and the body will more accurately predict differences in body curvature during swimming rather than a single meristic such as total vertebral number alone. We examined the correlation between morphological features and maximum body curvature seen during routine turns in five species of shark: Triakis semifasciata, Heterodontus francisci, Chiloscyllium plagiosum, Chiloscyllium punctatum, and Hemiscyllium ocellatum. We quantified overall body curvature using three different metrics. From a separate group of size-matched individuals, we measured 16 morphological features from precaudal vertebrae and the body. As predicted, a larger pool of morphological features yielded a more robust prediction of maximal body curvature than vertebral number alone. Stepwise linear regression showed that up to 11 features were significant predictors of the three measures of body curvature, yielding highly significant multiple regressions with r(2) values of 0.523, 0.537, and 0.584. The second moment of area of the centrum was always the best predictor, followed by either centrum length or transverse height. Ranking as the fifth most important variable in three different models, the body's total length, fineness ratio, and width were the most important non-vertebral morphologies. Without considering the effects of muscle activity, these correlations suggest a dominant role for the vertebral column in providing the passive mechanical properties of the body that control, in part, body curvature during swimming. (c) 2009 Wiley-Liss, Inc.
Spinal curvature and characteristics of postural change in pregnant women.
Okanishi, Natsuko; Kito, Nobuhiro; Akiyama, Mitoshi; Yamamoto, Masako
2012-07-01
Pregnant women often report complaints due to physiological and postural changes. Postural changes during pregnancy may cause low back pain and pelvic girdle pain. This study aimed to compare the characteristics of postural changes in pregnant compared with non-pregnant women. Prospective case-control study. Pregnancy care center. Fifteen women at 17-34 weeks pregnancy comprised the study group, while 10 non-pregnant female volunteers comprised the control group. Standing posture was evaluated in the sagittal plane with static digital pictures. Two angles were measured by image analysis software: (1) between the trunk and pelvis; and (2) between the trunk and lower extremity. Spinal curvature was measured with Spinal Mouse® to calculate the means of sacral inclination, thoracic and lumbar curvature and inclination. The principal components were calculated until eigenvalues surpassed 1. Three distinct factors with eigenvalues of 1.00-2.49 were identified, consistent with lumbosacral spinal curvature and inclination, thoracic spine curvature, and inclination of the body. These factors accounted for 77.2% of the total variance in posture variables. Eleven pregnant women showed postural characteristics of lumbar kyphosis and sacral posterior inclination. Body inclination showed a variety of patterns compared with those in healthy women. Spinal curvature demonstrated a tendency for lumbar kyphosis in pregnant women. Pregnancy may cause changes in spinal curvature and posture, which may in turn lead to relevant symptoms. Our data provide a basis for investigating the effects of spinal curvature and postural changes on symptoms during pregnancy. © 2012 The Authors Acta Obstetricia et Gynecologica Scandinavica© 2012 Nordic Federation of Societies of Obstetrics and Gynecology.
Novel magnetic method for the detection of residual curvature in electrical steel
NASA Astrophysics Data System (ADS)
Hall, J. P.; Moses, A. J.; Irons, T.; Snell, D.
2003-01-01
A method to detect residual curvature in electrical steel strip is described. A single C-core yoke, carrying primary and secondary windings, placed on strip containing a stress gradient to measure the vector product of current and voltage (loss in stress-free material), yields differences in measurements on opposite surfaces which are dependent on the degree of residual curvature.
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.
Status of the front-end-electronics for the time-of-flight measurements at the MPD experiment
NASA Astrophysics Data System (ADS)
Buryakov, M. G.; Babkin, V. A.; Golovatyuk, V. M.; Volgin, S. V.; Rumyantsev, M. M.
2016-09-01
The preamplifier based on the ASIC NINO for the Time of Flight system (TOF) of MPD/NICA was developed and tested. The signal is read from both sides of the strip of the multi gap Resistive Plate Chamber (MRPC). In total there are around 14000 channels of electronics. To measure time of flight of secondary particles from collision of heavy ions on the collider NICA the Time over Threshold (ToT) method is used. According to the bench tests the preamplifier board showed stable work and good time resolution <10 ps for one channel. It was also tested at the test beam facility of the Nuclotron. The time resolution of the TOF detector which used the described preamplifier was reached ˜42 ps.
Novel tilt-curvature coupling in lipid membranes
NASA Astrophysics Data System (ADS)
Terzi, M. Mert; Deserno, Markus
2017-08-01
On mesoscopic scales, lipid membranes are well described by continuum theories whose main ingredients are the curvature of a membrane's reference surface and the tilt of its lipid constituents. In particular, Hamm and Kozlov [Eur. Phys. J. E 3, 323 (2000)] have shown how to systematically derive such a tilt-curvature Hamiltonian based on the elementary assumption of a thin fluid elastic sheet experiencing internal lateral pre-stress. Performing a dimensional reduction, they not only derive the basic form of the effective surface Hamiltonian but also express its emergent elastic couplings as trans-membrane moments of lower-level material parameters. In the present paper, we argue, though, that their derivation unfortunately missed a coupling term between curvature and tilt. This term arises because, as one moves along the membrane, the curvature-induced change of transverse distances contributes to the area strain—an effect that was believed to be small but nevertheless ends up contributing at the same (quadratic) order as all other terms in their Hamiltonian. We illustrate the consequences of this amendment by deriving the monolayer and bilayer Euler-Lagrange equations for the tilt, as well as the power spectra of shape, tilt, and director fluctuations. A particularly curious aspect of our new term is that its associated coupling constant is the second moment of the lipid monolayer's lateral stress profile—which within this framework is equal to the monolayer Gaussian curvature modulus, κ¯ m. On the one hand, this implies that many theoretical predictions now contain a parameter that is poorly known (because the Gauss-Bonnet theorem limits access to the integrated Gaussian curvature); on the other hand, the appearance of κ¯ m outside of its Gaussian curvature provenance opens opportunities for measuring it by more conventional means, for instance by monitoring a membrane's undulation spectrum at short scales.
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
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
NASA Astrophysics Data System (ADS)
Asakura, N.; Tsuji-Iio, S.; Ikeda, Y.; Neyatani, Y.; Seki, M.
1995-12-01
A fast reciprocating probe system with a long drive shaft was incorporated into a multi-junction lower hybrid (LH) wave launcher on JT-60U in order to investigate an improved coupling mechanism of the radio frequency wave to the core plasma. The system has been operated reliably over a horizontal scan of 25 cm in 1.5 s using a compact pneumatic cylinder drive and springs. A double probe measurement provided the scrape-off layer plasma profile between the last closed flux surface and the first wall with the spatial resolution of 1-2 mm measured with a laser displacement gauge. The profiles of the electron density ne and temperature Te were in good agreement with those obtained with a triple probe method. During the LH wave injection with good coupling to the core plasma, an increase in the local Te was observed in front of the LH launcher mouth. The local ne was (7-10)×1016 m-3, consistent values needed for the good coupling.
Asakura, N.; Tsuji-Iio, S.; Ikeda, Y.; Neyatani, Y.; Seki, M.
1995-12-01
A fast reciprocating probe system with a long drive shaft was incorporated into a multi-junction lower hybrid (LH) wave launcher on JT-60U in order to investigate an improved coupling mechanism of the radio frequency wave to the core plasma. The system has been operated reliably over a horizontal scan of 25 cm in 1.5 s using a compact pneumatic cylinder drive and springs. A double probe measurement provided the scrape-off layer plasma profile between the last closed flux surface and the first wall with the spatial resolution of 1{minus}2 mm measured with a laser displacement gauge. The profiles of the electron density {ital n}{sub {ital e}} and temperature {ital T}{sub {ital e}} were in good agreement with those obtained with a triple probe method. During the LH wave injection with good coupling to the core plasma, an increase in the local {ital T}{sub {ital e}} was observed in front of the LH launcher mouth. The local {ital n}{sub {ital e}} was (7{minus}10){times}10{sup 16} m{sup {minus}3}, consistent values needed for the good coupling. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Salvage penile curvature correction surgery.
Hsieh, Cheng-Hsing; Chen, Heng-Shuen; Lee, Wen-Yuan; Chen, Kuo-Liang; Chang, Chao-Hsiang; Hsu, Geng-Long
2010-01-01
It is commonly believed that coarser suture materials should be used to provide sufficient tenacity in surgery for penile curvature correction. We report our 15-year experience of fine sutures in a second operation in 31 patients who underwent prior curvature correction elsewhere with coarser sutures, resulting in recurrent penile curvature. Suture materials used in prior surgeries in these patients were either 2-0 or 3-0 nylon sutures. In this series, all 31 patients underwent a modified Nesbit procedure at the level of the collagen bundles using finer sutures. Prior to July 1998, 10 men underwent salvage surgery using 4-0 polyglactin sutures. Thereafter, we adapted 6-0 nylon sutures for another 21 patients. We categorized the patients into the polyglactin (n = 10) and nylon (n = 21) groups respectively. Overall, 29 patients were available for follow-up while using the abridged 5-item version of the International Index of Erectile Function (IIEF-5) scoring system, with 21 patients in the nylon group. We have found cavernosography a practical and reliable method to objectively assess penile morphology in these patients. The penile morphology both subjectively and objectively was excellent in all patients, except for 1 in each group. Erectile function restoration showed a trend of satisfaction in the polyglactin group and based on IIEF-5 was significantly improved in the nylon group (14.2 ± 3.6 vs 21.9 ± 2.1, n = 20, P < .001). These results suggest that in penile tunical surgery, fine sutures such as 6-0 nylon may result in better penile morphology and functional outcomes.
Actin filament curvature biases branching direction
Risca, Viviana I.; Wang, Evan B.; Chaudhuri, Ovijit; Chia, Jia Jun; Geissler, Phillip L.; Fletcher, Daniel A.
2012-01-01
Mechanical cues affect many important biological processes in metazoan cells, such as migration, proliferation, and differentiation. Such cues are thought to be detected by specialized mechanosensing molecules linked to the cytoskeleton, an intracellular network of protein filaments that provide mechanical rigidity to the cell and drive cellular shape change. The most abundant such filament, actin, forms branched networks nucleated by the actin-related protein (Arp) 2/3 complex that support or induce membrane protrusions and display adaptive behavior in response to compressive forces. Here we show that filamentous actin serves in a mechanosensitive capacity itself, by biasing the location of actin branch nucleation in response to filament bending. Using an in vitro assay to measure branching from curved sections of immobilized actin filaments, we observed preferential branch formation by the Arp2/3 complex on the convex face of the curved filament. To explain this behavior, we propose a fluctuation gating model in which filament binding or branch nucleation by Arp2/3 occur only when a sufficiently large, transient, local curvature fluctuation causes a favorable conformational change in the filament, and we show with Monte Carlo simulations that this model can quantitatively account for our experimental data. We also show how the branching bias can reinforce actin networks in response to compressive forces. These results demonstrate how filament curvature can alter the interaction of cytoskeletal filaments with regulatory proteins, suggesting that direct mechanotransduction by actin may serve as a general mechanism for organizing the cytoskeleton in response to force. PMID:22308368
Model-independent Constraints on Cosmic Curvature and Opacity
NASA Astrophysics Data System (ADS)
Wang, Guo-Jian; Wei, Jun-Jie; Li, Zheng-Xiang; Xia, Jun-Qing; Zhu, Zong-Hong
2017-09-01
In this paper, we propose to estimate the spatial curvature of the universe and the cosmic opacity in a model-independent way with expansion rate measurements, H(z), and type Ia supernova (SNe Ia). On the one hand, using a nonparametric smoothing method Gaussian process, we reconstruct a function H(z) from opacity-free expansion rate measurements. Then, we integrate the H(z) to obtain distance modulus μ H, which is dependent on the cosmic curvature. On the other hand, distances of SNe Ia can be determined by their photometric observations and thus are opacity-dependent. In our analysis, by confronting distance moduli μ H with those obtained from SNe Ia, we achieve estimations for both the spatial curvature and the cosmic opacity without any assumptions for the cosmological model. Here, it should be noted that light curve fitting parameters, accounting for the distance estimation of SNe Ia, are determined in a global fit together with the cosmic opacity and spatial curvature to get rid of the dependence of these parameters on cosmology. In addition, we also investigate whether the inclusion of different priors for the present expansion rate (H 0: global estimation, 67.74 ± 0.46 km s‑1 Mpc‑1, and local measurement, 73.24 ± 1.74 km s‑1 Mpc‑1) exert influence on the reconstructed H(z) and the following estimations of the spatial curvature and cosmic opacity. Results show that, in general, a spatially flat and transparent universe is preferred by the observations. Moreover, it is suggested that priors for H 0 matter a lot. Finally, we find that there is a strong degeneracy between the curvature and the opacity.
Measuring Intrinsic Curvature of Space with Electromagnetism
ERIC Educational Resources Information Center
Mabin, Mason; Becker, Maria; Batelaan, Herman
2016-01-01
The concept of curved space is not readily observable in everyday life. The educational movie "Sphereland" attempts to illuminate the idea. The main character, a hexagon, has to go to great lengths to prove that her world is in fact curved. We present an experiment that demonstrates a new way to determine if a two-dimensional surface,…
Measuring Intrinsic Curvature of Space with Electromagnetism
ERIC Educational Resources Information Center
Mabin, Mason; Becker, Maria; Batelaan, Herman
2016-01-01
The concept of curved space is not readily observable in everyday life. The educational movie "Sphereland" attempts to illuminate the idea. The main character, a hexagon, has to go to great lengths to prove that her world is in fact curved. We present an experiment that demonstrates a new way to determine if a two-dimensional surface,…
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.
Geometric curvature and phase of the Rabi model
Mao, Lijun; Huai, Sainan; Guo, Liping; Zhang, Yunbo
2015-11-15
We study the geometric curvature and phase of the Rabi model. Under the rotating-wave approximation (RWA), we apply the gauge independent Berry curvature over a surface integral to calculate the Berry phase of the eigenstates for both single and two-qubit systems, which is found to be identical with the system of spin-1/2 particle in a magnetic field. We extend the idea to define a vacuum-induced geometric curvature when the system starts from an initial state with pure vacuum bosonic field. The induced geometric phase is related to the average photon number in a period which is possible to measure in the qubit–cavity system. We also calculate the geometric phase beyond the RWA and find an anomalous sudden change, which implies the breakdown of the adiabatic theorem and the Berry phases in an adiabatic cyclic evolution are ill-defined near the anti-crossing point in the spectrum.
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.
Smoldering wave-front velocity in fiberboard
John J. Brenden; Erwin L. Schaffer
1980-01-01
In fiberboard, the phenomena of smoldering can be visualized as decomposition resulting from the motion of a thermal wave-front through the material. The tendency to smolder is then directly proportional to the velocity of the front. Velocity measurements were made on four fiberboards and were compared to values given in the literature for several substances....
Interaction of a cold front with a sea-breeze front Observations
NASA Astrophysics Data System (ADS)
Brümmer, B.; Hennemuth, B.; Rhodin, A.; Thiemann, S.
1995-08-01
On 9 May 1989, during the field experiment FRONTEX, a synoptic-scale cold front was observed which moved from the North Sea to Northern Germany and interacted with a sea-breeze front. The modification of the cold front is documented by satellite images and measurements over the sea, at the coast and further inland. The synoptic-scale front was characterized by weak frontal gradients over the sea. It was aligned approximately parallel to the coast as was approximately the wind ahead of it. While the synoptic-scale front approached the coast during the forenoon hours, a strong temperature contrast developed between sea and land due to solar heating of the land surface. This led to the formation of a sea-breeze front associated with a stronger temperature gradient than the synoptic-scale front. At about noon, when the synoptic-scale front almost reached the coast, the sea-breeze front began to move inland. The onshore wind behind the sea-breeze front and ahead of the synoptic-scale front was so large that the wind field at the synoptic-scale front changed from confluence to difluence. This process was supported by a shallow inversion ahead of the synoptic-scale front which confined the vertical depth of the sea-breeze. The former sea-breeze front overtook the main frontal characteristics, continued its inland propagation and was the only frontal event observed over the land. As a result of the interaction, the synoptic-scale front was significantly intensified in the boundary layer.
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.
NASA Astrophysics Data System (ADS)
Kuang, Shi; Newchurch, Michael J.; Johnson, Matthew S.; Wang, Lihua; Burris, John; Pierce, Robert B.; Eloranta, Edwin W.; Pollack, Ilana B.; Graus, Martin; Gouw, Joost; Warneke, Carsten; Ryerson, Thomas B.; Markovic, Milos Z.; Holloway, John S.; Pour-Biazar, Arastoo; Huang, Guanyu; Liu, Xiong; Feng, Nan
2017-01-01
Stratosphere-to-troposphere transport (STT) and biomass burning (BB) are two important natural sources for tropospheric ozone that can result in elevated ozone and air-quality episode events. High-resolution observations of multiple related species are critical for complex ozone source attribution. In this article, we present an analysis of coinciding ground-based and airborne observations, including ozone lidar, ozonesonde, high spectral resolution lidar (HSRL), and multiple airborne in situ measurements, made on 28 and 29 June 2013 during the Southeast Nexus field campaign. The ozone lidar and HSRL reveal detailed ozone and aerosol structures as well as the temporal evolution associated with a cold front passage. The observations also captured two enhanced (+30 ppbv) ozone layers in the free troposphere (FT), which were determined from this study to be caused by a mixture of BB and stratospheric sources. The mechanism for this STT is tropopause folding associated with a cutoff upper level low-pressure system according to the analysis of its potential vorticity structure. The depth of the tropopause fold appears to be shallow for this case compared to events observed in other seasons; however, the impact on lower tropospheric ozone was clearly observed. This event suggests that strong STT may occur in the southeast United States during the summer and can potentially impact lower troposphere during these times. Statistical analysis of the airborne observations of trace gases suggests a coincident influence of BB transport in the FT impacting the vertical structure of ozone during this case study.
Biostereometric Analysis Of Spine Curvatures On Living Human Body
NASA Astrophysics Data System (ADS)
Pineau, J.-C.; Ignazi, G.; Prudent, J.
1986-07-01
An analysis of the external and internal curvatures of spine was carried out on a sample of nine males from biostereometric measurements for different imposed postures. The results concerning the modifications of the external shape of the curves are used for the 3-D human body modeling in C.A.D. applications.
Discrimination of curvature from motion during smooth pursuit eye movements and fixation.
Ross, Nicholas M; Goettker, Alexander; Schütz, Alexander C; Braun, Doris I; Gegenfurtner, Karl R
2017-09-01
Smooth pursuit and motion perception have mainly been investigated with stimuli moving along linear trajectories. Here we studied the quality of pursuit movements to curved motion trajectories in human observers and examined whether the pursuit responses would be sensitive enough to discriminate various degrees of curvature. In a two-interval forced-choice task subjects pursued a Gaussian blob moving along a curved trajectory and then indicated in which interval the curve was flatter. We also measured discrimination thresholds for the same curvatures during fixation. Motion curvature had some specific effects on smooth pursuit properties: trajectories with larger amounts of curvature elicited lower open-loop acceleration, lower pursuit gain, and larger catch-up saccades compared with less curved trajectories. Initially, target motion curvatures were underestimated; however, ∼300 ms after pursuit onset pursuit responses closely matched the actual curved trajectory. We calculated perceptual thresholds for curvature discrimination, which were on the order of 1.5 degrees of visual angle (°) for a 7.9° curvature standard. Oculometric sensitivity to curvature discrimination based on the whole pursuit trajectory was quite similar to perceptual performance. Oculometric thresholds based on smaller time windows were higher. Thus smooth pursuit can quite accurately follow moving targets with curved trajectories, but temporal integration over longer periods is necessary to reach perceptual thresholds for curvature discrimination.NEW & NOTEWORTHY Even though motion trajectories in the real world are frequently curved, most studies of smooth pursuit and motion perception have investigated linear motion. We show that pursuit initially underestimates the curvature of target motion and is able to reproduce the target curvature ∼300 ms after pursuit onset. Temporal integration of target motion over longer periods is necessary for pursuit to reach the level of precision found
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.
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.
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
Rapid acceleration of protons upstream of earthward propagating dipolarization fronts.
Ukhorskiy, A Y; Sitnov, M I; Merkin, V G; Artemyev, A V
2013-08-01
[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.
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.
Crystalline particle packings on constant mean curvature (Delaunay) surfaces
NASA Astrophysics Data System (ADS)
Bendito, Enrique; Bowick, Mark J.; Medina, Agustin; Yao, Zhenwei
2013-07-01
We investigate the structure of crystalline particle arrays on constant mean curvature (CMC) surfaces of revolution. Such curved crystals have been realized physically by creating charge-stabilized colloidal arrays on liquid capillary bridges. CMC surfaces of revolution, classified by Delaunay in 1841, include the 2-sphere, the cylinder, the vanishing mean curvature catenoid (a minimal surface), and the richer and less investigated unduloid and nodoid. We determine numerically candidate ground-state configurations for 1000 pointlike particles interacting with a pairwise-repulsive 1/r3 potential, with distance r measured in three-dimensional Euclidean space R3. We mimic stretching of capillary bridges by determining the equilibrium configurations of particles arrayed on a sequence of Delaunay surfaces obtained by increasing or decreasing the height at constant volume starting from a given initial surface, either a fat cylinder or a square cylinder. In this case, the stretching process takes one through a complicated sequence of Delaunay surfaces, each with different geometrical parameters, including the aspect ratio, mean curvature, and maximal Gaussian curvature. Unduloids, catenoids, and nodoids all appear in this process. Defect motifs in the ground state evolve from dislocations at the boundary to dislocations in the interior to pleats and scars in the interior and then isolated sevenfold disclinations in the interior as the capillary bridge narrows at the waist (equator) and the maximal (negative) Gaussian curvature grows. We also check theoretical predictions that the isolated disclinations are present in the ground state when the surface contains a geodesic disk with integrated Gaussian curvature exceeding -π/3. Finally, we explore minimal energy configurations on sets of slices of a given Delaunay surface, and we obtain configurations and defect motifs consistent with those seen in stretching.
Curvature of the spectral energy distributions of blazars
Chen, Liang
2014-06-20
In this paper, spectral energy distributions (SED) of both synchrotron and inverse Compton (IC) components of a sample of Fermi bright blazars are fitted by a log-parabolic law. The second-degree term of the log parabola measures the curvature of an SED. We find a statistically significant correlation between the synchrotron peak frequency and its curvature. This result is in agreement with the theoretical prediction and confirms previous studies that dealt with a single source with observations at various epochs or a small sample. If a broken power law is employed to fit the SED, the difference between the two spectral indices (i.e., |α{sub 2} – α{sub 1}|) can be considered a 'surrogate' of the SED curvature. We collect data from the literature and find a correlation between the synchrotron peak frequency and the spectral difference. We do not find a significant correlation between the IC peak frequency and its curvature, which may be caused by a complicated seed photon field. It is also found that the synchrotron curvatures are on average larger than those of IC curvatures, and there is no correlation between these two parameters. As suggested by previous works, both the log-parabolic law of the SED and the above correlation can be explained by statistical and/or stochastic particle accelerations. Based on a comparison of the slops of the correlation, our result seems to favor stochastic acceleration mechanisms and emission processes. Additional evidence, including SED modeling, particle acceleration simulation, and comparisons between some predictions and empirical relations/correlations, also seems to support the idea that the electron energy distribution (and/or synchrotron SED) may be log-parabolic.
Single Lipid Molecule Dynamics on Supported Lipid Bilayers with Membrane Curvature
Cheney, Philip P.; Weisgerber, Alan W.; Feuerbach, Alec M.; Knowles, Michelle K.
2017-01-01
The plasma membrane is a highly compartmentalized, dynamic material and this organization is essential for a wide variety of cellular processes. Nanoscale domains allow proteins to organize for cell signaling, endo- and exocytosis, and other essential processes. Even in the absence of proteins, lipids have the ability to organize into domains as a result of a variety of chemical and physical interactions. One feature of membranes that affects lipid domain formation is membrane curvature. To directly test the role of curvature in lipid sorting, we measured the accumulation of two similar lipids, 1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and hexadecanoic acid (HDA), using a supported lipid bilayer that was assembled over a nanopatterned surface to obtain regions of membrane curvature. Both lipids studied contain 16 carbon, saturated tails and a head group tag for fluorescence microscopy measurements. The accumulation of lipids at curvatures ranging from 28 nm to 55 nm radii was measured and fluorescein labeled DHPE accumulated more than fluorescein labeled HDA at regions of membrane curvature. We then tested whether single biotinylated DHPE molecules sense curvature using single particle tracking methods. Similar to groups of fluorescein labeled DHPE accumulating at curvature, the dynamics of single molecules of biotinylated DHPE was also affected by membrane curvature and highly confined motion was observed. PMID:28294967
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
Streamline curvature effects on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Wilcox, D. C.; Chambers, T. L.
1976-01-01
A theoretical tool has been developed for predicting, in a nonempirical manner, effects of streamline curvature and coordinate-system rotation on turbulent boundary layers. The second-order closure scheme developed by Wilcox and Traci has been generalized for curved streamline flow and for flow in a rotating coordinate system. A physically based straightforward argument shows that curvature/rotation primarily affects the turbulent mixing energy; the argument yields suitable curvature/rotation terms which are added to the mixing-energy equation. Singular-perturbation solutions valid in the wall layer of a curved-wall boundary layer and a fully developed rotating channel flow demonstrate that, with the curvature/rotation terms, the model predicts the curved-wall and the rotating coordinate system laws of the wall. Results of numerical computations of curved-wall boundary layers and of rotating channel flow show that curvature/rotation effects can be computed accurately with second-order closure.
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.
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.
Reposition sense of lumbar curvature with flexed and asymmetric lifting postures.
Wilson, Sara E; Granata, Kevin P
2003-03-01
Reposition sense of lumbar curvature was assessed as a function of trunk flexion, trunk asymmetry, and target lumbar curvature using a repeated-measures design and an active-active proprioception paradigm. The objectives of the research were to measure the ability of the subjects to sense and control the lumbar curvature in different lifting postures and to see if error in the lumbar curvature would increase in high-risk postures. The risk of low back disorders (LBDs) is related to trunk posture, with greater risk reported in flexed and asymmetric trunk positions. Spinal posture, including trunk position and lumbar lordosis, influences spinal stability. Hence, the ability to accurately sense and control spinal curvature may be an important factor in the control of LBD risk. Eleven subjects were trained to assume specified lumbar curvatures using visual feedback. The ability of the subjects to reproduce this curvature without feedback was then assessed. This procedure was repeated for different trunk postures, including flexion and asymmetry, and with different target lumbar curvatures. These measurements demonstrated reposition error was increased in flexed trunk positions but was unchanged with trunk asymmetry. This increase in reposition error with flexion was diminished when the target posture and lumbar curvature were highly flexed and kyphotic. This research suggests that it may be difficult to control spinal curvature in flexed positions, leading to an increased risk of injury. For jobs in which flexed working postures are unavoidable, therefore, it is important to minimize potentially unstable events such as slipping or shifting loads to avoid injury.
The Barents Sea Polar Front in summer
NASA Astrophysics Data System (ADS)
Parsons, A. Rost; Bourke, Robert H.; Muench, Robin D.; Chiu, Ching-Sang; Lynch, James F.; Miller, James H.; Plueddemann, Albert J.; Pawlowicz, Richard
1996-06-01
In August 1992 a combined physical oceanography and acoustic tomography experiment was conducted to describe the Barents Sea Polar Front (BSPF) and investigate its impact on the regional oceanography. The study area was an 80 × 70 km grid east of Bear Island where the front exhibits topographic trapping along the northern slope of the Bear Island Trough. Conductivity-temperature-depth, current meter, and acoustic Doppler current profiler (ADCP) data, combined with tomographic cross sections, presented a highly resolved picture of the front in August. All hydrographic measurements were dominated by tidal signals, with the strongest signatures associated with the M2 and S2 semidiurnal species. Mean currents in the warm saline water to the south of the front, derived from a current meter mooring and ADCP data, were directed to the southwest and may be associated with a barotropic recirculation of Norwegian Atlantic Water (NAW) within the Bear Island Trough. The geostrophic component of the velocity was well correlated with the measured southwestward mean surface layer flow north of the front. The frontal structure was retrograde, as the frontal isopleths sloped opposite to the bathymetry. The surface signature of the front was dominated by salinity gradients associated with the confluence of Atlantic and Arctic water masses, both warmed by insolation to a depth of about 20 m. The surface manifestation of the front varied laterally on the order of 10 km associated with tidal oscillations. Below the mixed layer, temperature and salinity variations were compensating, defining a nearly barotropic front. The horizontal scale of the front in this region was ˜3 km or less. At middepth beneath the frontal interface, tomographic cross sections indicated a high-frequency (˜16 cpd) upslope motion of filaments of NAW origin. The summertime BSPF was confirmed to have many of the general characteristics of a shelf-slope frontal system [Mooers et al., 1978] as well as a
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.
Curvature function and coarse graining
NASA Astrophysics Data System (ADS)
Díaz-Marín, Homero; Zapata, José A.
2010-12-01
A classic theorem in the theory of connections on principal fiber bundles states that the evaluation of all holonomy functions gives enough information to characterize the bundle structure (among those sharing the same structure group and base manifold) and the connection up to a bundle equivalence map. This result and other important properties of holonomy functions have encouraged their use as the primary ingredient for the construction of families of quantum gauge theories. However, in these applications often the set of holonomy functions used is a discrete proper subset of the set of holonomy functions needed for the characterization theorem to hold. We show that the evaluation of a discrete set of holonomy functions does not characterize the bundle and does not constrain the connection modulo gauge appropriately. We exhibit a discrete set of functions of the connection and prove that in the abelian case their evaluation characterizes the bundle structure (up to equivalence), and constrains the connection modulo gauge up to "local details" ignored when working at a given scale. The main ingredient is the Lie algebra valued curvature function F_S (A) defined below. It covers the holonomy function in the sense that exp {F_S (A)} = Hol(l= partial S, A).
Curvature function and coarse graining
Diaz-Marin, Homero; Zapata, Jose A.
2010-12-15
A classic theorem in the theory of connections on principal fiber bundles states that the evaluation of all holonomy functions gives enough information to characterize the bundle structure (among those sharing the same structure group and base manifold) and the connection up to a bundle equivalence map. This result and other important properties of holonomy functions have encouraged their use as the primary ingredient for the construction of families of quantum gauge theories. However, in these applications often the set of holonomy functions used is a discrete proper subset of the set of holonomy functions needed for the characterization theorem to hold. We show that the evaluation of a discrete set of holonomy functions does not characterize the bundle and does not constrain the connection modulo gauge appropriately. We exhibit a discrete set of functions of the connection and prove that in the abelian case their evaluation characterizes the bundle structure (up to equivalence), and constrains the connection modulo gauge up to ''local details'' ignored when working at a given scale. The main ingredient is the Lie algebra valued curvature function F{sub S}(A) defined below. It covers the holonomy function in the sense that expF{sub S}(A)=Hol(l={partial_derivative}S,A).
Forelimb bone curvature in terrestrial and arboreal mammals
Henderson, Keith; Pantinople, Jess; McCabe, Kyle; Milne, Nick
2017-01-01
It has recently been proposed that the caudal curvature (concave caudal side) observed in the radioulna of terrestrial quadrupeds is an adaptation to the habitual action of the triceps muscle which causes cranial bending strains (compression on cranial side). The caudal curvature is proposed to be adaptive because longitudinal loading induces caudal bending strains (increased compression on the caudal side), and these opposing bending strains counteract each other leaving the radioulna less strained. If this is true for terrestrial quadrupeds, where triceps is required for habitual elbow extension, then we might expect that in arboreal species, where brachialis is habitually required to maintain elbow flexion, the radioulna should instead be cranially curved. This study measures sagittal curvature of the ulna in a range of terrestrial and arboreal primates and marsupials, and finds that their ulnae are curved in opposite directions in these two locomotor categories. This study also examines sagittal curvature in the humerus in the same species, and finds differences that can be attributed to similar adaptations: the bone is curved to counter the habitual muscle action required by the animal’s lifestyle, the difference being mainly in the distal part of the humerus, where arboreal animals tend have a cranial concavity, thought to be in response the carpal and digital muscles that pull cranially on the distal humerus. PMID:28462036
Ultrasoft Electronics for Hyperelastic Strain, Pressure, and Direct Curvature Sensing
NASA Astrophysics Data System (ADS)
Majidi, Carmel; Kramer, Rebecca; Wood, Robert
2011-03-01
Progress in soft robotics, wearable computing, and programmable matter demands a new class of ultrasoft electronics for tactile control, contact detection, and deformation mapping. This next generation of sensors will remain electrically functional under extreme deformation without influencing the natural mechanics of the host system. Ultrasoft strain and pressure sensing has previously been demonstrated with elastomer sheets (eg. PDMS, silicone rubber) embedded with microchannels of conductive liquid (mercury, eGaIn). Building on these efforts, we introduce a novel method for direct curvature sensing that registers the location and intensity of surface curvature. An elastomer sheet is embedded with micropatterned cavities and microchannels of conductive liquid. Bending the elastomer or placing it on a curved surface leads to a change in channel cross-section and a corresponding change in its electrical resistance. In contrast to conventional methods of curvature sensing, this approach does not depend on semi-rigid components or differential strain measurement. Direct curvature sensing completes the portfolio of sensing elements required to completely map hyperelastic deformation for future soft robotics and computing. NSF MRSEC DMR-0820484.
In vitro dimensions and curvatures of human lenses.
Rosen, Alexandre M; Denham, David B; Fernandez, Viviana; Borja, David; Ho, Arthur; Manns, Fabrice; Parel, Jean-Marie; Augusteyn, Robert C
2006-03-01
The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.
Forelimb bone curvature in terrestrial and arboreal mammals.
Henderson, Keith; Pantinople, Jess; McCabe, Kyle; Richards, Hazel L; Milne, Nick
2017-01-01
It has recently been proposed that the caudal curvature (concave caudal side) observed in the radioulna of terrestrial quadrupeds is an adaptation to the habitual action of the triceps muscle which causes cranial bending strains (compression on cranial side). The caudal curvature is proposed to be adaptive because longitudinal loading induces caudal bending strains (increased compression on the caudal side), and these opposing bending strains counteract each other leaving the radioulna less strained. If this is true for terrestrial quadrupeds, where triceps is required for habitual elbow extension, then we might expect that in arboreal species, where brachialis is habitually required to maintain elbow flexion, the radioulna should instead be cranially curved. This study measures sagittal curvature of the ulna in a range of terrestrial and arboreal primates and marsupials, and finds that their ulnae are curved in opposite directions in these two locomotor categories. This study also examines sagittal curvature in the humerus in the same species, and finds differences that can be attributed to similar adaptations: the bone is curved to counter the habitual muscle action required by the animal's lifestyle, the difference being mainly in the distal part of the humerus, where arboreal animals tend have a cranial concavity, thought to be in response the carpal and digital muscles that pull cranially on the distal humerus.
High-Curvature Nanostructuring Enhances Probe Display for Biomolecular Detection.
De Luna, Phil; Mahshid, Sahar S; Das, Jagotamoy; Luan, Binquan; Sargent, Edward H; Kelley, Shana O; Zhou, Ruhong
2017-02-08
High-curvature electrodes facilitate rapid and sensitive detection of a broad class of molecular analytes. These sensors have reached detection limits not attained using bulk macroscale materials. It has been proposed that immobilized DNA probes are displayed at a high deflection angle on the sensor surface, which allows greater accessibility and more efficient hybridization. Here we report the first use of all-atom molecular dynamics simulations coupled with electrochemical experiments to explore the dynamics of single-stranded DNA immobilized on high-curvature versus flat surfaces. We find that high-curvature structures suppress DNA probe aggregation among adjacent probes. This results in conformations that are more freely accessed by target molecules. The effect observed is amplified in the presence of highly charged cations commonly used in electrochemical biosensing. The results of the simulations agree with experiments that measure the degree of hybridization in the presence of mono-, di-, and trivalent cations. On high-curvature structures, hybridization current density increases as positive charge increases, whereas on flat electrodes, the trivalent cations cause aggregation due to electrostatic overscreening, which leads to decreased current density and less sensitive detection.
The effect of detonation curvature on cylindrical wall motion
Aldis, D.F.; Quirk, W.; Breithaupt, R.D.
1991-06-04
In the large scale analysis of explosive response, discrepancies have been found between the results predicted by a computer models using various sets of equation of state parameters derived from different experiments. In this report, we will present recent progress toward determining possible reasons for the differences. The system that we have modeled in this study is the cylinder test. Numerous researchers have used this test to study the work potential of detonating explosives for the transverse expansion of metals. One of the original purposes for the development of the test was for the determination of equations of state for detonation products of explosives. The method that is used to determine the parameters for these empirical equations of state, is to iteratively simulate the detonating explosive expansion using a two dimensional hydrodynamic code, adjust the parameters, and repeat until a best fit'' to the experimental results is obtained. We will, in this present report, explore a small part of this problem. We will concentrate on the effect of the material that is used in the all of the cylinder, the effect of detonation front curvature, and how the curvature might influence the cylindrical wall expansion. 8 refs., 6 figs.
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
Folkesson, Jenny; Dam, Erik B; Olsen, Ole F; Karsdal, Morten A; Pettersen, Paola C; Christiansen, Claus
2008-06-01
The objective of this study was to quantitatively assess the surface curvature of the articular cartilage from low-field magnetic resonance imaging (MRI) data, and to investigate its role in populations with varying radiographic signs of osteoarthritis (OA), cross-sectionally and longitudinally. The curvature of the articular surface of the medial tibial compartment was estimated both on fine and coarse scales using two different automatic methods which are both developed from an automatic 3D segmentation algorithm. Cross-sectionally (n=288), the surface curvature for both the fine- and coarse-scale estimates were significantly higher in the OA population compared with the healthy population, with P<0.001 and P<0.001, respectively. For the longitudinal study (n=245), there was a significant increase in fine-scale curvature for healthy and borderline OA populations (P<0.001), and in coarse-scale curvature for severe OA populations (P<0.05). Fine-scale curvature could predict progressors using the estimates of those healthy at baseline (P<0.001). The inter-scan precision was 2.2 and 6.5 (mean CV) for the fine- and coarse scale curvature measures, respectively. The results showed that quantitative curvature estimates from low-field MRI at different scales could potentially become biomarkers targeted at different stages of OA. Copyright (c) 2008 Wiley-Liss, Inc.
The role of the epidermis and cortex in gravitropic curvature of maize roots.
Björkman, T; Cleland, R E
1988-12-01
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.
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.
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.
Curvature and torsion in growing actin networks
Shaevitz, Joshua W; Fletcher, Daniel A
2011-01-01
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. PMID:18560043
Curvature in solid oxide fuel cells
NASA Astrophysics Data System (ADS)
Li, Wenxia; Hasinska, Kathy; Seabaugh, Matt; Swartz, Scott; Lannutti, John
At this point in history, curvature is inherent to the laminated components that comprise solid oxide fuel cells (SOFCs). Surprisingly, however, this fact has never been previously quantified in the literature. In addition, potential curvature changes associated with NiO reduction and re-oxidation during operation have not been investigated. In this report, an optical profilometer was employed to non-destructively quantify the surface curvature or cracking behavior observed on a large scale in industrially manufactured cells. This provides insights into the challenges that the component materials face as well as additional appreciation for why, in spite of a concerted effort to commercialize SOFC power generation, all currently manufactured SOFC stacks fail. Our results demonstrate that cracked electrolyte areas (caused by differential sintering) are flatter than uncracked regions. The height of the electrolyte surface ranged from 86 to 289 μm above the baseline following sintering. Reduction typically results in increases in curvature of up to 214 μm. Initial crack density appears to affect curvature evolution during reduction; the higher the crack density, the smaller the curvature increase following reduction at 600 °C. In general, however, we observed that the electrolyte layer is remarkably resistant to further cracking during these typographic changes. Following oxidation at 750 °C, large changes in curvature (up to 280 μm) are noted that appear to be related to the strength of the bond between the electrolyte and the underlying anode.
Linking pore-scale interfacial curvature to column-scale capillary pressure
NASA Astrophysics Data System (ADS)
Armstrong, Ryan T.; Porter, Mark L.; Wildenschild, Dorthe
2012-09-01
Synchrotron-based tomographic datasets of oil-water drainage and imbibition cycles have been analyzed to quantify phase saturations and interfacial curvature as well as connected and disconnected fluid configurations. This allows for close observation of the drainage and imbibition processes, assessment of equilibrium states, and studying the effects of fluid phase disconnection and reconnection on the resulting capillary pressures and interfacial curvatures. Based on this analysis estimates of capillary pressure calculated from interfacial curvature can be compared to capillary pressure measured externally with a transducer. Results show good agreement between curvature-based and transducer-based measurements when connected phase interfaces are considered. Curvature measurements show a strong dependence on whether an interface is formed by connected or disconnected fluid and the time allowed for equilibration. The favorable agreement between curvature-based and transducer-based capillary pressure measurements shows promise for the use of image-based estimates of capillary pressure for interfaces that cannot be probed with external transducers as well as opportunities for a detailed assessment of interfacial curvature during drainage and imbibition.
Linking pore-scale interfacial curvature to column-scale capillary pressure
Armstrong, Ryan T.; Porter, Mark L.; Wildenschild, Dorthe
2012-10-24
Synchrotron-based tomographic datasets of oil-water drainage and imbibition cycles have been analyzed to quantify phase saturations and interfacial curvature as well as connected and disconnected fluid configurations. This allows for close observation of the drainage and imbibition processes, assessment of equilibrium states, and studying the effects of fluid phase disconnection and reconnection on the resulting capillary pressures and interfacial curvatures. Based on this analysis estimates of capillary pressure calculated from interfacial curvature can be compared to capillary pressure measured externally with a transducer. Results show good agreement between curvature-based and transducer-based measurements when connected phase interfaces are considered. Curvature measurements show a strong dependence on whether an interface is formed by connected or disconnected fluid and the time allowed for equilibration. The favorable agreement between curvature-based and transducer-based capillary pressure measurements shows promise for the use of image-based estimates of capillary pressure for interfaces that cannot be probed with external transducers as well as opportunities for a detailed assessment of interfacial curvature during drainage and imbibition.
Magnetic curvature effects on plasma interchange turbulence
Li, B. Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-15
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.
Impact of curvature on topological defects
NASA Astrophysics Data System (ADS)
Mesarec, L.; Góźdź, W.; Iglič, A.; Kralj, S.
2017-01-01
We analyze the impact of extrinsic and intrinsic curvature on positions of topological defects (TDs) in two-dimensional (2D) nematic films. We demonstrate that both these curvature contributions are commonly present and are expected to be weighted by comparable elastic constants. A simple Landau-de Gennes approach in terms of tensor nematic order parameter is used to numerically demonstrate impact of the curvatures on position of TDs on 2D ellipsoidal nematic shells. In particular, in oblate ellipsoids the extrinsic and intrinsic elastic terms enforce conflicting tendencies to positions of TDs.
The Gaussian curvature elastic energy of intermediates in membrane fusion.
Siegel, David P
2008-12-01
The Gaussian curvature elastic energy contribution to the energy of membrane fusion intermediates has usually been neglected because the Gaussian curvature elastic modulus, kappa, was unknown. It is now possible to measure kappa for phospholipids that form bicontinuous inverted cubic (Q(II)) phases. Here, it is shown that one can estimate kappa for lipids that do not form Q(II) phases by studying the phase behavior of lipid mixtures. The method is used to estimate kappa for several lipid compositions in excess water. The values of kappa are used to compute the curvature elastic energies of stalks and catenoidal fusion pores according to recent models. The Gaussian curvature elastic contribution is positive and similar in magnitude to the bending energy contribution: it increases the total curvature energy of all the fusion intermediates by 100 units of k(B)T or more. It is important to note that this contribution makes the predicted intermediate energies compatible with observed lipid phase behavior in excess water. An order-of-magnitude fusion rate equation is used to estimate whether the predicted stalk energies are consistent with the observed rates of stalk-mediated processes in pure lipid systems. The current theory predicts a stalk energy that is slightly too large, by approximately 30 k(B)T, to rationalize the observed rates of stalk-mediated processes in phosphatidylethanolamine or N-monomethylated dioleoylphosphatidylethanolamine systems. Despite this discrepancy, the results show that models of fusion intermediate energy are accurate enough to make semiquantitative predictions about how proteins mediate biomembrane fusion. The same rate model shows that for proteins to drive biomembrane fusion at observed rates, they have to perform mediating functions corresponding to a reduction in the energy of a purely lipidic stalk by several tens of k(B)T. By binding particular peptide sequences to the monolayer surface, proteins could lower fusion intermediate
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)
Influence of implant rod curvature on sagittal correction of scoliosis deformity.
Salmingo, Remel Alingalan; Tadano, Shigeru; Abe, Yuichiro; Ito, Manabu
2014-08-01
Deformation of in vivo-implanted rods could alter the scoliosis sagittal correction. To our knowledge, no previous authors have investigated the influence of implanted-rod deformation on the sagittal deformity correction during scoliosis surgery. To analyze the changes of the implant rod's angle of curvature during surgery and establish its influence on sagittal correction of scoliosis deformity. A retrospective analysis of the preoperative and postoperative implant rod geometry and angle of curvature was conducted. Twenty adolescent idiopathic scoliosis patients underwent surgery. Average age at the time of operation was 14 years. The preoperative and postoperative implant rod angle of curvature expressed in degrees was obtained for each patient. Two implant rods were attached to the concave and convex side of the spinal deformity. The preoperative implant rod geometry was measured before surgical implantation. The postoperative implant rod geometry after surgery was measured by computed tomography. The implant rod angle of curvature at the sagittal plane was obtained from the implant rod geometry. The angle of curvature between the implant rod extreme ends was measured before implantation and after surgery. The sagittal curvature between the corresponding spinal levels of healthy adolescents obtained by previous studies was compared with the implant rod angle of curvature to evaluate the sagittal curve correction. The difference between the postoperative implant rod angle of curvature and normal spine sagittal curvature of the corresponding instrumented level was used to evaluate over or under correction of the sagittal deformity. The implant rods at the concave side of deformity of all patients were significantly deformed after surgery. The average degree of rod deformation Δθ at the concave and convex sides was 15.8° and 1.6°, respectively. The average preoperative and postoperative implant rod angle of curvature at the concave side was 33.6° and 17.8
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
Helical Microfilaments with Alternating Imprinted Intrinsic Curvatures.
Silva, Pedro Emanuel Santos; Godinho, Maria Helena
2017-03-01
There has been an intense research for developing techniques that can produce filaments with helical shapes, given the widespread of potential applications. In this work, how helices with different curvatures can be precisely imprinted in microfilaments is shown. It is also shown that using this technique, it is possible to produce, in a single fiber, helices with different curvatures. This striking and innovative behavior is observed when one side of the stretched filaments is irradiated with UV light, modifying the mechanical properties at surface. Upon release, the regions with higher curvature start to curl first, while regions with lower intrinsic curvature remain stretched until start to curl later. The results presented here can be important to understand why structures adopt a helical shape in general, which can be of interest in nanotechnology, biomolecular science, or even to understand why plant filaments curl. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Role of feature curvature in contact guidance
Mathur, Anurag; Moore, Simon W.; Sheetz, Michael P.; Hone, James
2012-01-01
This study examines the role of feature curvature in cellular topography sensing. To separate the effects of feature size and curvature, we have developed a method to fabricate grooved substrates whose radius of curvature (r) is varied from under 10 nm to 400 nm, while all other dimensions are kept constant. With increasing r up to 200 nm, mouse embryonic fibroblasts increased their spread area, but reduced their polarization (aspect ratio). Interestingly, on features with an r of 200 and 400 nm - where there was very little effect on spreading area and polarization - we find that internal structures such as stress fibers are nevertheless still strongly aligned to the topography. These findings are of importance to studies of both tissue engineering and curvature sensing proteins. PMID:22426288
Gravitational energy in quadratic-curvature gravities.
Deser, S; Tekin, Bayram
2002-09-02
We define energy (E) and compute its values for gravitational systems involving terms quadratic in curvature. There are significant differences, both conceptually and concretely, from Einstein theory. For D=4, all purely quadratic models admit constant curvature vacua with arbitrary Lambda, and E is the "cosmological" Abbott-Deser (AD) expression; instead, E always vanishes in flat, Lambda=0, background. For combined Einstein-quadratic curvature systems without explicit Lambda-term vacuum must be flat space, and E has the usual Arnowitt-Deser-Misner form. A Lambda-term forces unique de Sitter vacuum, with E the sum of contributions from Einstein and quadratic parts to the AD form. We also discuss the effects on energy definition of higher curvature terms and of higher dimension.
DSD front models: nonideal explosive detonation in ANFO
Bdzil, J. B.; Aslam, T. D.; Catanach, R. A.; Hill, L. G.; Short, M.
2002-01-01
The DSD method for modeling propagating detonation is based on three elements: (1) a subscale theory of multi-dimensional detonation that treats the detonation as a front whose dynamics depends only on metrics of the front (such as curvature, etc.), (2) high-resolution, direct numerical simulation of detonation using Euler equation models, and (3) physical experiments to characterize multi-dimensional detonation propagation in real explosives and to provide data to calibrate DSD front models. In this paper, we describe our work on elements (1) and (3), develop a DSD calibration for the nonideal explosive ANFO and then demonstrate the utility of the ANFO calibration, with an example 3D detonation propagation calculation.
Curvature Analysis of Cardiac Excitation Wavefronts
2013-04-01
computational cardiac-cell network accurately reproduces a particular kind of cardiac arrhythmia , such as ventricular fibrillation. Curvature Analysis of Cardiac...network accurately reproduces a particular kind of cardiac arrhythmia , such as ventricular fibrillation. Index Terms Cardiac excitation waves...isopotentials, Bézier curves, curvature, cardiac arrhythmia and fibrillation Ç 1 INTRODUCTION AN estimated 81,000,000 American adults, more than onein three
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.
Experimental determination of the radius of curvature of an isotropic Gaussian Schell-model beam.
Zhu, Shijun; Chen, Yahong; Cai, Yangjian
2013-02-01
We propose a method to determine the radius of curvature of an isotropic Gaussian Schell-model (GSM) beam by measuring the transverse beam widths and the transverse coherence widths at two different planes. Furthermore, we carry out experimental determination of the radius of curvature of a GSM beam. Using the measured beam parameters, we carry out a comparative study of the propagation properties of a GSM beam both theoretically and experimentally. Our experimental results agree well with theoretical predictions.
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.
Nonadditive Compositional Curvature Energetics of Lipid Bilayers
NASA Astrophysics Data System (ADS)
Sodt, A. J.; Venable, R. M.; Lyman, E.; Pastor, R. W.
2016-09-01
The unique properties of the individual lipids that compose biological membranes together determine the energetics of the surface. The energetics of the surface, in turn, govern the formation of membrane structures and membrane reshaping processes, and thus they will underlie cellular-scale models of viral fusion, vesicle-dependent transport, and lateral organization relevant to signaling. The spontaneous curvature, to the best of our knowledge, is always assumed to be additive. We describe observations from simulations of unexpected nonadditive compositional curvature energetics of two lipids essential to the plasma membrane: sphingomyelin and cholesterol. A model is developed that connects molecular interactions to curvature stress, and which explains the role of local composition. Cholesterol is shown to lower the number of effective Kuhn segments of saturated acyl chains, reducing lateral pressure below the neutral surface of bending and favoring positive curvature. The effect is not observed for unsaturated (flexible) acyl chains. Likewise, hydrogen bonding between sphingomyelin lipids leads to positive curvature, but only at sufficient concentration, below which the lipid prefers negative curvature.
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.
Nonadditive Compositional Curvature Energetics of Lipid Bilayers.
Sodt, A J; Venable, R M; Lyman, E; Pastor, R W
2016-09-23
The unique properties of the individual lipids that compose biological membranes together determine the energetics of the surface. The energetics of the surface, in turn, govern the formation of membrane structures and membrane reshaping processes, and thus they will underlie cellular-scale models of viral fusion, vesicle-dependent transport, and lateral organization relevant to signaling. The spontaneous curvature, to the best of our knowledge, is always assumed to be additive. We describe observations from simulations of unexpected nonadditive compositional curvature energetics of two lipids essential to the plasma membrane: sphingomyelin and cholesterol. A model is developed that connects molecular interactions to curvature stress, and which explains the role of local composition. Cholesterol is shown to lower the number of effective Kuhn segments of saturated acyl chains, reducing lateral pressure below the neutral surface of bending and favoring positive curvature. The effect is not observed for unsaturated (flexible) acyl chains. Likewise, hydrogen bonding between sphingomyelin lipids leads to positive curvature, but only at sufficient concentration, below which the lipid prefers negative curvature.
Anisotropic Cosmology and Curvature Invariants.
NASA Astrophysics Data System (ADS)
Skea, James E. F.
greater when non-axisymmetric cosmologies are considered. In the limit where the particle production is switched on at the Planck time (t _{rm Pl}), isotropisation is found to occur at _{Omega } 10^5 t_ {rm Pl}, compatible with restrictions on anistropy at that time. Particle production is not found to isotropise Bianchi VIII and IX cosmologies. In Part 3, we study the structure of various curvature invariants and, following a suggestion by Karlhede, we investigate their relationship to horizons in particular space-times. (Abstract shortened by UMI.).
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.
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.
Automobile front body construction
Harasaki, H.
1987-06-23
This patent describes an automobile front body structure having an engine compartment and also having a pair of spaced first longitudinal frames extending beneath the engine compartment in a direction longitudinally of an automobile and connected at a rear end to a floor panel. The structure comprises: suspension arm support members secured to front ends of the first longitudinal frames, respectively, for the support of left-hand and right-hand suspension arms; and a transverse connecting member extending between the first longitudinal frames in a direction widthwise of the automobile and having its opposite ends connected to the respective support members.
Effects of Berry Curvature on the Collective Modes of Ultracold Gases
NASA Astrophysics Data System (ADS)
Price, Hannah M.; Cooper, Nigel R.
2013-11-01
Topological energy bands have important geometrical properties described by the Berry curvature. We show that the Berry curvature changes the hydrodynamic equations of motion for a trapped Bose-Einstein condensate, and causes significant modifications to the collective mode frequencies. We illustrate our results for the case of two-dimensional Rashba spin-orbit coupling in a Zeeman field. Using an operator approach, we derive the effects of Berry curvature on the dipole mode in very general settings. We show that the sizes of these effects can be large and readily detected in experiment. Collective modes therefore provide a sensitive way to measure geometrical properties of energy bands.
Shape and curvature error estimation in polished surfaces of ground glass molds
NASA Astrophysics Data System (ADS)
Savio, Gianpaolo; Pal, Raj Kumar; Meneghello, Roberto; D'Angelo, Luciano; Concheri, Gianmaria
2017-02-01
In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.
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.
Cosmic acceleration from matter-curvature coupling
NASA Astrophysics Data System (ADS)
Zaregonbadi, Raziyeh; Farhoudi, Mehrdad
2016-10-01
We consider f( {R,T} ) modified theory of gravity in which, in general, the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy-momentum tensor. We indicate that in this type of the theory, the coupling energy-momentum tensor is not conserved. However, we mainly focus on a particular model that matter is minimally coupled to the geometry in the metric formalism and wherein, its coupling energy-momentum tensor is also conserved. We obtain the corresponding Raychaudhuri dynamical equation that presents the evolution of the kinematic quantities. Then for the chosen model, we derive the behavior of the deceleration parameter, and show that the coupling term can lead to an acceleration phase after the matter dominated phase. On the other hand, the curvature of the universe corresponds with the deviation from parallelism in the geodesic motion. Thus, we also scrutinize the motion of the free test particles on their geodesics, and derive the geodesic deviation equation in this modified theory to study the accelerating universe within the spatially flat FLRW background. Actually, this equation gives the relative accelerations of adjacent particles as a measurable physical quantity, and provides an elegant tool to investigate the timelike and the null structures of spacetime geometries. Then, through the null deviation vector, we find the observer area-distance as a function of the redshift for the chosen model, and compare the results with the corresponding results obtained in the literature.
Influence of firing time and framework thickness on veneered Y-TZP discs curvature.
Jakubowicz-Kohen, Boris D; Sadoun, Michaël J; Douillard, Thierry; Mainjot, Amélie K
2014-02-01
The objective of the present work was to study the curvature of very thinly, veneered Y-TZP discs of different framework thicknesses submitted to different firing times. Fifteen 20-mm-wide Y-TZP discs were produced in three different thicknesses: 0.75, 1, 1.5mm. One disc from each group was left unveneered while the others were layered with a 0.1mm veneering ceramic layer. All discs underwent five firing cycles for a total cumulative firing time of 30 min, 1, 2, 5 and 10h at 900°C. The curvature profile was measured using a profilometer after the veneering process and after each firing cycle respectively. A fitted curve was then used to estimate the, curvature radius. The coefficient of thermal expansion (CTE) measurements were taken on veneering, ceramic and Y-TZP beam samples that underwent the same firing schedule. Those data were used to calculate the curvature generated by CTE variations over firing time. All bilayered samples exhibited a curvature that increased over firing time inversely to framework thickness. However non-veneered samples did not exhibit any curvature modification. The results of the present study reveal that even a very thin veneer layer (0.1mm) can induce a significant curvature of Y-TZP discs. The dilatometric results showed that Tg and CTE, variations are not sufficient to explain this curvature. A chemical-induced zirconia volume, augmentation located at the framework sub-surface near the interface could explain the sample, curvature and its increase with firing time. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
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.
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.
Perturbative High Harmonic Wave Front Control
NASA Astrophysics Data System (ADS)
Li, Zhengyan; Brown, Graham; Ko, Dong Hyuk; Kong, Fanqi; Arissian, Ladan; Corkum, P. B.
2017-01-01
We pattern the wave front of a high harmonic beam by intersecting the intense driving laser pulse that generates the high harmonic with a weak control pulse. To illustrate the potential of wave-front control, we imprint a Fresnel zone plate pattern on a harmonic beam, causing the harmonics to focus and defocus. The quality of the focus that we achieve is measured using the spectral wave-front optical reconstruction by diffraction method. We will show that it is possible to enhance the peak intensity by orders of magnitude without a physical optical element in the path of the extreme ultraviolet (XUV) beam. Through perturbative wave-front control, XUV beams can be created with a flexibility approaching what technology allows for visible and infrared light.
Curiosity Front View, Linearized
2012-08-06
This is a version of one of the first images taken by a front Hazard-Avoidance camera on NASA Curiosity rover. It was taken through a fisheye wide-angle lens but has been linearized so that the horizon looks flat rather than curved.
2011-09-05
Saturn moon Dione coasts along in its orbit appearing in front of its parent planet in this view from NASA Cassini spacecraft. The wispy terrain on the trailing hemisphere of Dione can be seen on the left of the moon here.
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…
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.
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.
NASA Astrophysics Data System (ADS)
Herring, Anna L.; Middleton, Jill; Walsh, Rick; Kingston, Andrew; Sheppard, Adrian
2017-09-01
We investigate capillary pressure-saturation (PC-S) relationships for drainage-imbibition experiments conducted with air (nonwetting phase) and brine (wetting phase) in Bentheimer sandstone cores. Three different flow rate conditions, ranging over three orders of magnitude, are investigated. X-ray micro-computed tomographic imaging is used to characterize the distribution and amount of fluids and their interfacial characteristics. Capillary pressure is measured via (1) bulk-phase pressure transducer measurements, and (2) image-based curvature measurements, calculated using a novel 3D curvature algorithm. We distinguish between connected (percolating) and disconnected air clusters: curvatures measured on the connected phase interfaces are used to validate the curvature algorithm and provide an indication of the equilibrium condition of the data; curvature and volume distributions of disconnected clusters provide insight to the snap-off processes occurring during drainage and imbibition under different flow rate conditions.
Aortic curvature as a predictor of intraoperative type Ia endoleak.
Schuurmann, Richte C L; Ouriel, Kenneth; Muhs, Bart E; Jordan, William D; Ouriel, Richard L; Boersen, Johannes T; de Vries, Jean-Paul P M
2016-03-01
Hostile infrarenal neck characteristics are associated with complications such as type Ia endoleak after endovascular aneurysm repair. Aortic neck angulation has been identified as one such characteristic, but its association with complications has not been uniform between studies. Neck angulation assumes triangular oversimplification of the aortic trajectory, which may explain conflicting findings. By contrast, aortic curvature is a measurement that includes the bending rate and tortuosity and may provide better predictive value for neck complications. Data were retrieved from the Heli-FX (Aptus Endosystems, Inc, Sunnyvale, Calif) Aortic Securement System Global Registry (ANCHOR). One cohort included patients who presented with intraoperative endoleak type Ia at the completion angiogram as the indication for EndoAnchors (Aptus Endosystems), and a second cohort comprised those without intraoperative or late type Ia endoleak (controls). The aortic trajectory was divided into six segments with potentially different influence on the stent graft performance: suprarenal, juxtarenal, and infrarenal aortic neck (-30 to -10 mm, -10 to 10 mm, and 10-30 mm from the lowest renal artery, respectively), the entire aortic neck, aneurysm sac, and terminal aorta (20 mm above the bifurcation to the bifurcation). Maximum and average curvature were automatically calculated over the six segments by proprietary custom software. Aortic curvature was compared with other standard neck characteristics, including neck length, neck diameter, maximum aneurysm sac diameter, neck thrombus and calcium thickness and circumference, suprarenal angulation, infrarenal angulation, and the neck tortuosity index. Independent risk factors for intraoperative type Ia endoleak were identified using backwards stepwise logistic regression. For the variables in the final regression model, suitable cutoff values in relation to the prediction of acute type Ia endoleak were defined with the area under the
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
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.
ORNL Interim Progress Report on Static CIRFT Testing Curvature Data Update
Wang, Jy-An John; Wang, Hong
2016-10-10
Since the CIRFT tests reported in NUREG-7198 were generated, a number of factors that influence the recorded curvature measurement data were identified. In 2016, a data reanalysis task was undertaken to implement the lessons learned. This letter report provides the revised results of previous CIRFT tests, after implementing the following data reanalysis procedures: (A) experimental data smoothing and LVDT reset, (B) LVDT probe contact and sensor spacing correction for curvature data, and (C) LVDT probe dynamic vibration adjustment procedure development.
Grain Boundary Curvature in a Model Ni-Based Superalloy (Preprint)
2006-07-01
AFRL-ML-WP-TP-2006-482 GRAIN BOUNDARY CURVATURE IN A MODEL Ni-BASED SUPERALLOY (PREPRINT) Kai Song and Mark Aindow JULY 2006... MODEL Ni-BASED SUPERALLOY (PREPRINT) 5c. PROGRAM ELEMENT NUMBER 62712E 5d. PROJECT NUMBER K720 5e. TASK NUMBER 01 6. AUTHOR(S) Kai Song...AFRL/WS 06-1882, 09 Aug 2006. 14. ABSTRACT The local grain boundary curvature in a model Ni-based superalloy was measured experimentally using
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
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
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
The effect of pain relief on dynamic changes in lumbar curvature.
Williams, Jonathan M; Haq, Inam; Lee, Raymond Y
2013-04-01
Lumbar curvature is important in the assessment of low back pain (LBP). It is often reported that changes in curvature seen in LBP sufferers are an adaptive response to pain. Studies investigating this hypothesis employing an experimental pain relief model have failed to isolate pain relief in their interventions. Therefore the purpose of this study was to investigate the immediate effects of pain relief on dynamic lumbar curvature. Twenty acute and 20 chronic LBP sufferers had their dynamic curvature measured using a novel fibre-optic device during flexion, extension and lifting before and after administration of oral analgesics. Peak curvature changes were examined using paired t-tests, numbers of responders to pain relief and changes in lumbar curvature sequencing were compared between groups using Chi-squared testing. A significant reduction in movement evoked pain was achieved. A significant reduction in kyphosis at end range flexion and lifting was identified for the acute LBP group following pain relief. No significant differences were observed for the chronic low back pain (CLBP) group. Neither the acute nor chronic LBP group were more likely to respond to pain relief by demonstrating alterations in peak curvature or in lumbar sequencing behaviour. These results demonstrate simple targeted pain relief did not result in gains in peak curvature challenging the assumption of movement alteration being possible through pain relief. Dynamic changes in curvature as displayed by sequencing showed that neither acute nor chronic LBP sufferers were more likely to respond to pain relief. Copyright © 2012 Elsevier Ltd. All rights reserved.
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.
HEREDITARY DISTAL FORELEG CURVATURE IN THE RABBIT
Pearce, Louise
1960-01-01
An inwardly directed curvature of the distal segment of both forelegs of the rabbit has been described. The condition was detected at 2 to 3 weeks of age, developed rapidly, and reached its final and permanent stage at 2 to 3 months of age. Only the distal epiphysis of the ulna was primarily affected and this in the form of a massive chondrodystrophic lesion accompanied by a progressive curvature of the shaft. The curvature of the growing radius was a secondary effect due to the firm, immovable, anatomical connection of the ulna and radius. The positional changes of the wrist and paw were likewise effects secondary to the changed form of the ulna and radius. The bowing abnormality occurred only in certain families of pure bred Beveren, Belgian, French Silver, and Dutch rabbits and was found to be inherited. The mode of inheritance was on the basis of a single recessive unit factor (5). PMID:13733755
Principal curvature for infrared small target detection
NASA Astrophysics Data System (ADS)
Zhao, Yao; Pan, Haibin; Du, Changping; Zheng, Yao
2015-03-01
Small target detection in infrared image with complex background and low signal-noise ratio is an important and difficult task in the infrared target tracking system. In this paper, a principal curvature-based method is proposed. The principal curvatures of target pixels are negative and their absolute values are larger than that of background pixels and noise pixels in a Gaussian-blurred infrared image. The proposed filter takes a composite function of the curvatures for detection. An approximate model is also built for optimizing the parameters. Experimental results show that the proposed algorithm is effective and adaptable for infrared small target detection in complex background. Compared with several popular methods, the proposed algorithm demonstrates significant improvement on detection performance in terms of the parameters of signal clutter ratio gain, background suppression factor and ROC.
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.
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.
Evaluation of Spatial Anisotropy by Curvature Analysis of Elliptical Targets
Aleci, Carlo; Piana, Giulio; Anselmino, Franco
2010-01-01
Spatial relationship perception (SRP), defined as the function able to detect the difference between the perceived extent of a shape along the x/y cardinal coordinates, has been investigated in 42 eyes of 21 emmetropic subjects by means of a psychophysical test conceived on purpose. Aiming to the highest sensibility and since curvature detection is reckoned as an hyperacuity, elliptical stimuli have been chosen to measure the spatial relationship anisotropy (SRA) in the visual system. Observers turned out to be able to detect curvature differences along the elliptical contour as low as 33.6 sec arc, which in terms of SRP means an aspect ratio (i.e. the ratio between the height and the width of the ellipse) as low as 1.0022-1.0035. By comparing these results with those obtained in previous investigations from other curvature discrimination tasks, it is argued that recognition threshold is conditioned by the amount of space anisotropy of the visual system. Indeed, in about half of the recruited subjects, vertical/horizontal anisotropy is found to a certain extent and such SRA correlates with the recognition threshold (r= 0.69, p<0.01). There is direct evidence of visual spatial distortion and in particular increased anisotropy in neuro-ophtalmological diseases such as hemianopia and around scotomatous regions in the visual field. Thence, apart from theoretical considerations in physiological field, results collected in this study may be regarded as normative data for future clinical investigations. PMID:20802805
Spectral curvature correction method based on inverse distance weighted interpolation
NASA Astrophysics Data System (ADS)
Jing, Juanjuan; Zhou, Jinsong; Li, Yacan; Feng, Lei
2016-10-01
Spectral curvature (smile effect) is universally existed in dispersive imaging spectrometer. Since most image processing systems considered all spatial pixels having the same wavelength, spectral curvature destroys the response consistence of the radiation energy in spatial dimension, it is necessary to correct the spectral curvature based on the spectral calibration data of the imaging spectrometer. Interpolation is widely used in resampling the measured spectra at the non-offset wavelength, but it is not versatile because the accuracy is different due to the spectral resolution changed. In the paper, we introduce the inverse distance weighted(IDW) method in spectrum resampling. First, calculate the Euclidean distance between the non-offset wavelength and the points near to it, the points number can be two, three, four or five, as many as you define. Then use the Euclidean distance to calculate the weight value of these points. Finally calculate the radiation of non-offset wavelength using the weight value and its corresponding radiation. The results turned out to be effective with the practical data acquired by the instrument, and it has the characteristics of versatility, simplicity, and fast.
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.
Curvature driven flow of bi-layer interfaces
NASA Astrophysics Data System (ADS)
Gavish, Nir; Hayrapetyan, Gurgen; Promislow, Keith; Yang, Li
2011-03-01
We introduce the Functionalized Cahn-Hilliard (FCH) energy, a negative multiple of the Cahn-Hilliard energy balanced against the square of its own variational derivative, as a finite width regularization of the sharp-interface Canham-Helfrich energy. Mass-preserving gradient flows associated to the FCH energy are higher-order phase field models which develop not only single-layer, or front-type interfaces, but also bi-layer, or homoclinic interfaces with associated endcap and multi-junction structures. The single-layer interfaces manifest a fingering instability which grows into endcapped bi-layers. The meandering growth of the bi-layer interfaces and the subsequent merging lead to a multi-junction dominated network that bears a striking similarity to the phase separated domains of both perfluorosulfonic membranes and amphiphilic di-block co-polymer solutions. The bi-layers generated by the gradient flows of the FCH energy have an interfacial width which scales with ε≪1, however for fixed ε, there is a class of bi-layers parameterized by width and background state. Our primary result is the asymptotic derivation of the normal velocity of a closed bi-layer hypersurface in Rd (d≥2) coupled to the evolution for the surface width, curvature, and background state. We also show the convergence of the FCH energy to a scaled Canham-Helfrich type energy for both single and bi-layer interfaces, with the surface area coefficient of the limiting Canham-Helfrich energy coupling to the bi-layer width. Thus the bi-layer networks grow to maximize surface area while minimizing the square of curvature, up to the point that the increase in surface area stretches the bi-layers too thin.
Ray Curvature and Refraction of Wave Packets.
1978-09-01
1!~~~~~ _ ‘ AD AOM 302 FLORIDA STATE UNIV TALLAHASSEE DEPT OF OCEANOGRAPHY FIG B/3 RAY CURVATURE AND REFRACTION OF WAVE PACKETS. (U) SEP 78 .J E...BREEDING N00014—77—C—0329 UNCLASSIFIED TR JE6 3 NL _ _ _ rwii__ _ ~iU ir!I I -~~ RAYOJR\\1L~[UREAND REFRACI ION OF WAVE F1~\\CKET~S ~y J. Ernest Breeding...01 29 014 -~ Technical Report No. JEB-3 Department of Oceanography • Florida State University RAY CURVATURE AND REFRACTION OF WAVE PACKETS b O G • J
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.
Cholesterol Mediates Membrane Curvature during Fusion Events
NASA Astrophysics Data System (ADS)
Ivankin, Andrey; Kuzmenko, Ivan; Gidalevitz, David
2012-06-01
Biomembranes undergo extensive shape changes as they perform vital cellular functions. The mechanisms by which lipids and proteins control membrane curvature remain unclear. We use x-ray reflectivity, grazing incidence x-ray diffraction, and epifluorescence microscopy to study binding of HIV-1 glycoprotein gp41’s membrane-bending domain to DPPC/cholesterol monolayers of various compositions at the air-liquid interface. The results offer a new insight into how membrane curvature could be regulated by cholesterol during fusion of the viral lipid envelope and the host cell membranes.
Equal-Curvature X-Ray Telescopes
NASA Technical Reports Server (NTRS)
Saha, Timo T.; Zhang, William
2002-01-01
We introduce a new type of x-ray telescope design; an Equal-Curvature telescope. We simply add a second order axial sag to the base grazing incidence cone-cone telescope. The radius of curvature of the sag terms is the same on the primary surface and on the secondary surface. The design is optimized so that the on-axis image spot at the focal plane is minimized. The on-axis RMS (root mean square) spot diameter of two studied telescopes is less than 0.2 arc-seconds. The off-axis performance is comparable to equivalent Wolter type 1 telescopes.
Curvature suppresses the Rayleigh-Taylor instability
Trinh, Philippe H.; Kim, Hyoungsoo; Hammoud, Naima; Howell, Peter D.; Chapman, S. Jonathan; Stone, Howard A.
2014-05-01
The dynamics of a thin liquid #12;lm on the underside of a curved cylindrical substrate is studied. The evolution of the liquid layer is investigated as the #12;lm thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modi#12;ed Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. Experiments and theory confirm that, below a critical value of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor instability.
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.
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.
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.
Infrared glass-based negative-curvature anti-resonant fibers fabricated through extrusion.
Gattass, Rafael R; Rhonehouse, Daniel; Gibson, Daniel; McClain, Collin C; Thapa, Rajesh; Nguyen, Vinh Q; Bayya, Shyam S; Weiblen, R Joseph; Menyuk, Curtis R; Shaw, L Brandon; Sanghera, Jasbinder S
2016-10-31
Negative curvature fibers have been gaining attention as fibers for high power infrared light. Currently, these fibers have been made of silica glass and infrared glasses solely through stack and draw. Infrared glasses' lower softening point presents the opportunity to perform low-temperature processing methods such as direct extrusion of pre-forms. We demonstrate an infrared-glass based negative curvature fiber fabricated through extrusion. The fiber shows record low losses in 9.75 - 10.5 µm range (which overlaps with the CO_{2} emission bands). We show the fiber's lowest order mode and measure the numerical aperture in the longwave infrared transmission band. The possibility to directly extrude a negative curvature fiber with no penalties in losses is a strong motivation to think beyond the limitations of stack-and-draw to novel shapes for negative curvature fibers.
Thermodynamics and mechanics of membrane curvature generation and sensing by proteins and lipids.
Baumgart, Tobias; Capraro, Benjamin R; Zhu, Chen; Das, Sovan L
2011-01-01
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.
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
Mehta, Rujul; Keawwattana, Wirunya; Guenthner, Andrew L; Kyu, Thein
2004-06-01
The present article focuses on theoretical elucidation of possible effect of mechanical deformation on spatio-temporal emergence of unusual polymer morphology subjected to quiescent isothermal crystallization conditions. The present theory developed is based on a phase field model consisted of non-conserved time dependent Ginzburg-Landau equation having an asymmetric double well potential in the crystal order parameter signifying metastability for crystallization, coupled with the chain tilt angle involving curvature elasticity and strain recovery potentials. Under quiescent crystallization conditions, the curvature elasticity term is needed to discern the emergence of sectorized single crystals. Upon coupling with the strain recovery potential, the numerical calculation captures ripple formation running across the long lamellar growth front, which may be attributed to lamellar buckling caused by the volume shrinkage. Of particular interest is that these simulated topologies of the single crystals are in good accord with the growth character of syndiotactic polypropylene single crystals observed experimentally by us during isothermal crystallization from the melt.
NASA Astrophysics Data System (ADS)
Ebert, Ute; van Saarloos, Wim
2000-11-01
Fronts that start from a local perturbation and propagate into a linearly unstable state come in two classes: pulled fronts and pushed fronts. The term “pulled front” expresses that these fronts are “pulled along” by the spreading of linear perturbations about the unstable state. Accordingly, their asymptotic speed v* equals the spreading speed of perturbations whose dynamics is governed by the equations linearized about the unstable state. The central result of this paper is the analysis of the convergence of asymptotically uniformly traveling pulled fronts towards v*. We show that when such fronts evolve from “sufficiently steep” initial conditions, which initially decay faster than e - λ*x for x→∞, they have a universal relaxation behavior as time t→∞: the velocity of a pulled front always relaxes algebraically like v(t)=v *-3/(2λ *t)+ {3}/{2}πDλ */(Dλ *2t) 3/2+ O(1/t 2) . The parameters v*, λ*, and D are determined through a saddle point analysis from the equation of motion linearized about the unstable invaded state. This front velocity is independent of the precise value of the front amplitude, which one tracks to measure the front position. The interior of the front is essentially slaved to the leading edge, and develops universally as φ(x,t)= Φv(t)(x-∫ tdt‧ v(t‧))+ O(1/t 2) , where Φ v( x- vt) is a uniformly translating front solution with velocity v< v*. Our result, which can be viewed as a general center manifold result for pulled front propagation is derived in detail for the well-known nonlinear diffusion equation of type ∂tφ= ∂x2φ+ φ- φ3, where the invaded unstable state is φ=0. Even for this simple case, the subdominant t-3/2 term extends an earlier result of Bramson. Our analysis is then generalized to more general (sets of) partial differential equations with higher spatial or temporal derivatives, to PDEs with memory kernels, and also to difference equations such as those that occur in numerical finite
THERMAL FRONTS IN SOLAR FLARES
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.
Strong curvature singularities and causal simplicity
Krolak, A. )
1992-02-01
Techniques of differential topology in Lorentzian manifolds developed by Geroch, Hawking, and Penrose are used to rule out a class of locally naked strong curvature singularities in strongly causal space-times. This result yields some support to the validity of Penrose's strong cosmic censorship hypothesis.
Geodesic curvature driven surface microdomain formation.
Adkins, Melissa R; Zhou, Y C
2017-09-15
Lipid bilayer membranes are not uniform and clusters of lipids in a more ordered state exist within the generally disorder lipid milieu of the membrane. These clusters of ordered lipids microdomains are now referred to as lipid rafts. Recent reports attribute the formation of these microdomains to the geometrical and molecular mechanical mismatch of lipids of different species on the boundary. Here we introduce the geodesic curvature to characterize the geometry of the domain boundary, and develop a geodesic curvature energy model to describe the formation of these microdomains as a result of energy minimization. Our model accepts the intrinsic geodesic curvature of any binary lipid mixture as an input, and will produce microdomains of the given geodesic curvature as demonstrated by three sets of numerical simulations. Our results are in contrast to the surface phase separation predicted by the classical surface Cahn-Hilliard equation, which tends to generate large domains as a result of the minimizing line tension. Our model provides a direct and quantified description of the structure inhomogeneity of lipid bilayer membrane, and can be coupled to the investigations of biological processes on membranes for which such inhomogeneity plays essential roles.
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.
Geodesic curvature driven surface microdomain formation
NASA Astrophysics Data System (ADS)
Adkins, Melissa R.; Zhou, Y. C.
2017-09-01
Lipid bilayer membranes are not uniform and clusters of lipids in a more ordered state exist within the generally disorder lipid milieu of the membrane. These clusters of ordered lipids microdomains are now referred to as lipid rafts. Recent reports attribute the formation of these microdomains to the geometrical and molecular mechanical mismatch of lipids of different species on the boundary. Here we introduce the geodesic curvature to characterize the geometry of the domain boundary, and develop a geodesic curvature energy model to describe the formation of these microdomains as a result of energy minimization. Our model accepts the intrinsic geodesic curvature of any binary lipid mixture as an input, and will produce microdomains of the given geodesic curvature as demonstrated by three sets of numerical simulations. Our results are in contrast to the surface phase separation predicted by the classical surface Cahn-Hilliard equation, which tends to generate large domains as a result of the minimizing line tension. Our model provides a direct and quantified description of the structure inhomogeneity of lipid bilayer membrane, and can be coupled to the investigations of biological processes on membranes for which such inhomogeneity plays essential roles.
Riemann curvature of a boosted spacetime geometry
NASA Astrophysics Data System (ADS)
Battista, Emmanuele; Esposito, Giampiero; Scudellaro, Paolo; Tramontano, Francesco
2016-10-01
The ultrarelativistic boosting procedure had been applied in the literature to map the metric of Schwarzschild-de Sitter spacetime into a metric describing de Sitter spacetime plus a shock-wave singularity located on a null hypersurface. This paper evaluates the Riemann curvature tensor of the boosted Schwarzschild-de Sitter metric by means of numerical calculations, which make it possible to reach the ultrarelativistic regime gradually by letting the boost velocity approach the speed of light. Thus, for the first time in the literature, the singular limit of curvature, through Dirac’s δ distribution and its derivatives, is numerically evaluated for this class of spacetimes. Moreover, the analysis of the Kretschmann invariant and the geodesic equation shows that the spacetime possesses a “scalar curvature singularity” within a 3-sphere and it is possible to define what we here call “boosted horizon”, a sort of elastic wall where all particles are surprisingly pushed away, as numerical analysis demonstrates. This seems to suggest that such “boosted geometries” are ruled by a sort of “antigravity effect” since all geodesics seem to refuse to enter the “boosted horizon” and are “reflected” by it, even though their initial conditions are aimed at driving the particles toward the “boosted horizon” itself. Eventually, the equivalence with the coordinate shift method is invoked in order to demonstrate that all δ2 terms appearing in the Riemann curvature tensor give vanishing contribution in distributional sense.
Fronts under arrest: Nonlocal boundary dynamics in biology.
McCalla, Scott G; von Brecht, James H
2016-12-01
We introduce a minimal geometric partial differential equation framework to understand pattern formation from interacting, counterpropagating fronts. Our approach concentrates on the interfaces between different states in a system, and relies on both nonlocal interactions and mean-curvature flow to track their evolution. As an illustration, we use this approach to describe a phenomenon in bacterial colony formation wherein sibling colonies can arrest each other's growth. This arrested motion leads to static separations between healthy, growing colonies. As our minimal model faithfully recovers the geometry of these competing colonies, it captures and elucidates the key leading-order mechanisms responsible for such patterned growth.
Fronts under arrest: Nonlocal boundary dynamics in biology
NASA Astrophysics Data System (ADS)
McCalla, Scott G.; von Brecht, James H.
2016-12-01
We introduce a minimal geometric partial differential equation framework to understand pattern formation from interacting, counterpropagating fronts. Our approach concentrates on the interfaces between different states in a system, and relies on both nonlocal interactions and mean-curvature flow to track their evolution. As an illustration, we use this approach to describe a phenomenon in bacterial colony formation wherein sibling colonies can arrest each other's growth. This arrested motion leads to static separations between healthy, growing colonies. As our minimal model faithfully recovers the geometry of these competing colonies, it captures and elucidates the key leading-order mechanisms responsible for such patterned growth.
CURVATURE EFFECT QUANTIFICATION FOR IN-VIVO IR THERMOGRAPHY
Cheng, Tze-Yuan; Deng, Daxiang; Herman, Cila
2013-01-01
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
A preliminary ultrasound study of velar fronting
NASA Astrophysics Data System (ADS)
Wodzinski, Sylvie M.; Frisch, Stefan A.
2003-10-01
The purpose of this study is to (1) evaluate the effectiveness of ultrasound imaging to measure velar consonant closure location, and (2) conduct a thorough study of velar fronting by measuring several productions of velar stops in the context of every English vowel. Word onset velar stops were measured in both words (CV or CVC) and nonwords (VCV) within a carrier phrase. Other coarticulatory influences were minimized by using words with no coda or labial coda consonants (e.g., ``Say a gap again,'' ``Say /oIkoI/ again''). Measurements were made at the point of maximal closure. Closure location was measured using the radial angle from the center of the ultrasound probe to the center of the velar closure. Pilot data for one subject has been analyzed to date. Closure location appears consistent across all central and back vowels. For front vowels, the degree of fronting of the velar appears to be correlated with the frontness of the vowel. Measures of closure location for diphthongs followed the back vowel pattern in the word targets. For nonwords, the closure location was influenced by the preceding diphthong offset quality and the following diphthong onset quality. Theoretical implications for the phonetics/phonology interface will be discussed.
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.
High bending curvature withstanding one-dimensional angle sensor with fiber Bragg gratings
NASA Astrophysics Data System (ADS)
Jang, Minsu; Kim, Ockchul; Yang, Sungwook; Kim, Jinseok
2017-04-01
We report on the development of an angle sensor which can measure at high bending curvature. Unlike the other sensors, the novel angle sensor can be durable and flexible. The sensors consist of one fiber Bragg grating (FBG) fiber which is located in the middle of each sensor, and are fabricated in varying thickness to confirm the relation between the distance of the center of the angle sensor to the core of the FBG node and the radii of curvature at which the sensor can measure. The thinnest sensor has the thickness of 200 μm and can measure at the bending radius of 5 mm. However, its angle measurement error is the largest with 1.25°, because of high sensitivity. Regulating the thickness of sensor, the angles at high curvatures can be measured reliably.
Geometrical interpretation and curvature distribution in nanocarbons
NASA Astrophysics Data System (ADS)
Gupta, Sanju; Saxena, Avadh
2011-04-01
Despite extensive research on microscopic structure and physical property characterization of advanced nanocarbon systems, they have not been viewed as topologically distinct nanoscale materials with various geometries (curvature). This work is motivated by our recent work [S. Gupta and A. Saxena, J. Raman Spectrosc. 40, 1127 (2009)] where we introduced the notion of "global" topology for novel nanocarbons and provided systematic trends by monitoring the phonon spectra via resonance Raman spectroscopy, which led to the paradigm of curvature/topology → property → functionality relationship in these materials. Here we determined the distribution of the mean (H) and Gaussian (K) curvatures as pertinent observables for geometric characterization taking into account the observed geometrical parameters, that is, radius, polar, azimuthal, or conical angle associated with tubular (single, double-, and multi-walled nanotubes; K = 0), spherical (hypo- and hyperfullerenes; K > 0) and complex (helical nanoribbons and nanotori/nanorings; K < 0) nanocarbon geometries to quantify the interplay of intrinsic surface curvature and topology, wherein global topology of the overall sp2-bonded carbon (sp2C) constrains local topology of the constituent carbon rings. We also studied various other structures such as catenoid and saddle-shaped surfaces as interesting nanocarbons. We compared these results with highly oriented pyrolytic graphite and monolayer graphene as layered and planar systems, respectively. Moreover, nanocarbons discussed herein are their derivatives. Curvature leads to nonlinearity that manifests itself in some form of symmetry breaking which can be extrapolated to topological variation due to nanoscale defects. Thus it may either close/open the bandgap leading to the introduction of new Raman spectroscopy signatures and optical absorption peaks, changes in mechanical properties, electrical behavior, and electronic density of states and possibly inducing magnetism
Seismological Constraints on Fault Plane Curvature
NASA Astrophysics Data System (ADS)
Reynolds, K.
2015-12-01
The down-dip geometry of seismically active normal faults is not well known. Many examples of normal faults with down-dip curvature exist, such as listric faults revealed in cross-section or in seismic reflection data, or the exposed domes of core complexes. However, it is not understood: (1) whether curved faults fail in earthquakes, and (2) if those faults have generated earthquakes, is the curvature a primary feature of the rupture or due to later modification of the plane? Even if an event is surface-rupturing, because of the limited depth-extent over which observations can be made, it is difficult to reliably constrain the change in dip with depth (if any) and therefore the fault curvature. Despite the uncertainty in seismogenic normal fault geometries, published slip inversions most commonly use planar fault models. We investigate the seismological constraints on normal fault geometry using a forward-modelling approach and present a seismological technique for determining down-dip geometry. We demonstrate that complexity in the shape of teleseismic body waveforms may be used to investigate the presence of down-dip fault plane curvature. We have applied this method to a catalogue of continental and oceanic normal faulting events. Synthetic models demonstrate that the shapes of SH waveforms at along-strike stations are particularly sensitive to fault plane geometry. It is therefore important to consider the azimuthal station coverage before modelling an event. We find that none of the data require significant down-dip curvature, although the modelling results for some events remain ambiguous. In some cases we can constrain that the down-dip fault geometry is within 20° of planar.
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.
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
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.
Glimm, J.; Grove, J.W.; Li, X.; Zhao, N.
1999-04-01
A new and simplified front tracking algorithm has been developed as an aspect of the extension of this algorithm to three dimensions. Here the authors emphasize two main results: (1) a simplified description of the microtopology of the interface, based on interface crossings with cell block edges, and (2) an improved algorithm for the interaction of a tracked contact discontinuity with an untracked shock wave. For the latter question, they focus on the post interaction jump at the contact, which is a purely 1D issue. Comparisons to other methods, including the level set method, are included.
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.
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
Dong, Kaichen E-mail: wuj@berkeley.edu; Lou, Shuai; Choe, Hwan Sung; Yao, Jie; Wu, Junqiao E-mail: wuj@berkeley.edu; Liu, Kai; You, Zheng
2016-07-11
Due to its thermally driven structural phase transition, vanadium dioxide (VO{sub 2}) 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 VO{sub 2} 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 VO{sub 2} 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 VO{sub 2} 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.
Hydrogen peroxide treatment results in reduced curvature values in the Arabidopsis root apex.
Noriega, Arturo; Tocino, Angel; Cervantes, Emilio
2009-03-15
Curvature of a plane curve is a measurement related to its shape. A Mathematica code was developed [Cervantes E, Tocino A. J Plant Physiol 2005;162:1038-1045] to obtain parametric equations from microscopic images of the Arabidopsis thaliana root apex. In addition, curvature values for these curves were given. It was shown that ethylene-insensitive mutants (etr1-1 and ein2-1) have reduced curvature values in the root apex. It has also been shown that blocking ethylene action by norbornadiene, an ethylene inhibitor, results in reduced curvature values in the two outer cell layers of the root apex [Noriega A, Cervantes E, Tocino A. J Plant Physiol 2008, in press]. Because ethylene action has been related with hydrogen peroxide [Desikan R, Hancock JT, Bright J, Harrison J, Weir I, Hooley R, Neill SJ. Plant Physiol 2005;137:831-834], the effect of a treatment with hydrogen peroxide in the curvature values of three successive layers of the root apex in Arabidopsis thaliana was investigated by confocal microscopy. Treatment with 10mM hydrogen peroxide resulted in reduced curvature values in the three layers. The effect was associated with smaller cells having higher circularity indices. The results are discussed in the context of the role of ethylene in development.
Micron-scale plasma membrane curvature is recognized by the septin cytoskeleton
Bridges, Andrew A.; Jentzsch, Maximilian S.; Oakes, Patrick W.; Occhipinti, Patricia
2016-01-01
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
Bending stiffness depends on curvature of ternary lipid mixture tubular membranes.
Tian, Aiwei; Capraro, Benjamin R; Esposito, Cinzia; Baumgart, Tobias
2009-09-16
Lipid and protein sorting and trafficking in intracellular pathways maintain cellular function and contribute to organelle homeostasis. Biophysical aspects of membrane shape coupled to sorting have recently received increasing attention. Here we determine membrane tube bending stiffness through measurements of tube radii, and demonstrate that the stiffness of ternary lipid mixtures depends on membrane curvature for a large range of lipid compositions. This observation indicates amplification by curvature of cooperative lipid demixing. We show that curvature-induced demixing increases upon approaching the critical region of a ternary lipid mixture, with qualitative differences along two roughly orthogonal compositional trajectories. Adapting a thermodynamic theory earlier developed by M. Kozlov, we derive an expression that shows the renormalized bending stiffness of an amphiphile mixture membrane tube in contact with a flat reservoir to be a quadratic function of curvature. In this analytical model, the degree of sorting is determined by the ratio of two thermodynamic derivatives. These derivatives are individually interpreted as a driving force and a resistance to curvature sorting. We experimentally show this ratio to vary with composition, and compare the model to sorting by spontaneous curvature. Our results are likely to be relevant to the molecular sorting of membrane components in vivo.
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.
Pennington, D; Jovanovic, I; Comaskey, B J
2001-02-01
The next generation of Petawatt class lasers will require the development of new laser technology. Optical parametric chirped pulse amplification (OPCPA) holds a potential to increase the peak power level to >10 PW with existing grating technology through ultrashort pulses. Furthermore, by utilizing a new type of front-end system based on optical parametric amplification, pulses can be produced with substantially higher contrast than with Ti:sapphire regenerative amplifier technology. We performed extensive study of OPCPA using a single crystal-based OPA. We developed a replacement for Ti:sapphire regenerative amplifier for high peak power lasers based on OPCPA, with an output of 30 mJ, at 10 Hz repetition rate and 16.5 nm spectral bandwidth. We developed a 3D numerical model for OPCPA and we performed a theoretical study of influences of pump laser beam quality on optical parametric amplification. Our results indicate that OPCPA represents a valid replacement for Ti:sapphire in the front end of high energy short pulse lasers.
Desertification by front propagation?
Zelnik, Yuval R; Uecker, Hannes; Feudel, Ulrike; Meron, Ehud
2017-04-07
Understanding how desertification takes place in different ecosystems is an important step in attempting to forecast and prevent such transitions. Dryland ecosystems often exhibit patchy vegetation, which has been shown to be an important factor on the possible regime shifts that occur in arid regions in several model studies. In particular, both gradual shifts that occur by front propagation, and abrupt shifts where patches of vegetation vanish at once, are a possibility in dryland ecosystems due to their emergent spatial heterogeneity. However, recent theoretical work has suggested that the final step of desertification - the transition from spotted vegetation to bare soil - occurs only as an abrupt shift, but the generality of this result, and its underlying origin, remain unclear. We investigate two models that detail the dynamics of dryland vegetation using a markedly different functional structure, and find that in both models the final step of desertification can only be abrupt. Using a careful numerical analysis, we show that this behavior is associated with the disappearance of confined spot-pattern domains as stationary states, and identify the mathematical origin of this behavior. Our findings show that a gradual desertification to bare soil due to a front propagation process can not occur in these and similar models, and opens the question of whether these dynamics can take place in nature.
Inequalities for scalar curvature of pseudo-Riemannian submanifolds
NASA Astrophysics Data System (ADS)
Tripathi, Mukut Mani; Gülbahar, Mehmet; Kılıç, Erol; Keleş, Sadık
2017-02-01
Some basic inequalities, involving the scalar curvature and the mean curvature, for a pseudo-Riemannian submanifold of a pseudo-Riemannian manifold are obtained. We also find inequalities for spacelike submanifolds. Equality cases are also discussed.
Investigation of catheter curvature and genetic algorithms in conductance catheter optimization.
Thaijiam, C; Gale, T J
2007-01-01
Catheter curvature affects accuracy of intra-ventricular blood volume measurement when using conductance catheter techniques, especially with irregular geometries, such as in the right ventricle. To investigate this effect, we present results from using different curved catheter configurations and different numbers of electrodes in a simple Finite Element model. It was found that there is an apparent increase in accuracy with curvature, due to greater linearity in the field in the region of the measurement electrodes, which are located farther from the source electrodes as curvature increases. Also, optimization using Genetic Algorithms is presented as a method to find the optimal distribution of measurement electrodes. We plan to extend these results to develop improved electrode configurations for using in blood volume measurement in the right ventricle.
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
[Instabilities of autowaves in excitable media associated with critical curvature phenomena].
Pertsov, A M; Panfilov, A V; Medvedeva, F U
1983-01-01
While studying a two-dimensional excitable medium described by the Fitz--Hugh equation on a digital computer a new type of instabilities was discovered which had no analogy in one-dimensional systems. It has been shown that when the wave encounters upon an obstacle the front breaks, diverge, thus destroying the excitation waves. Initiation of such instabilities is associated with critical curvative phenomenon. The instabilities appear when the front curvature in the region of wave break is greater than the critical one for the given medium. The instabilities found are observed when medium excitability is suppressed. This phenomenon may be related to the processes which occur in the damage regions of the myocardium tissue.
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.
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.
Constraining inverse-curvature gravity with supernovae.
Mena, Olga; Santiago, José; Weller, Jochen
2006-02-03
We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07
Streamline curvature in supersonic shear layers
NASA Technical Reports Server (NTRS)
Kibens, V.
1992-01-01
Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.
Effect of intrinsic curvature on semiflexible polymers
NASA Astrophysics Data System (ADS)
Ghosh, Surya K.; Singh, Kulveer; Sain, Anirban
2009-11-01
Recently many important biopolymers have been found to possess intrinsic curvature. Tubulin protofilaments in animal cells, FtsZ filaments in bacteria and double stranded DNA are examples. We examine how intrinsic curvature influences the conformational statistics of such polymers. We give exact results for the tangent-tangent spatial correlation function C(r)=⟨t̂(s).t̂(s+r)⟩ , both in two and three dimensions. Contrary to expectation, C(r) does not show any oscillatory behavior, rather decays exponentially and the effective persistence length has strong length dependence for short polymers. We also compute the distribution function P(R) of the end to end distance R and show how curved chains can be distinguished from wormlike chains using loop formation probability.
Curvature suppresses the Rayleigh-Taylor instability
Trinh, Philippe H.; Kim, Hyoungsoo; Hammoud, Naima; ...
2014-05-20
We studied the dynamics of a thin liquid film on the underside of a curved cylindrical substrate. The evolution of the liquid layer is investigated as the film thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modified Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. We found that the experiments and theory confirm that, below a critical value of the Bondmore » number, curvature of the substrate suppresses the Rayleigh-Taylor instability.« less
Streamline curvature in supersonic shear layers
NASA Technical Reports Server (NTRS)
Kibens, V.
1992-01-01
Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.
Cosmological signatures of anisotropic spatial curvature
Pereira, Thiago S.; Marugán, Guillermo A. Mena; Carneiro, Saulo E-mail: mena@iem.cfmac.csic.es
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.
Morphological instability of failure fronts
Grinfeld, M.A.; Schoenfeld, S.E.; Wright, T.W.
2006-03-06
There are various observations and experiments showing that, in addition to standard shock-wave fronts, which propagate with high trans-sonic velocities, some other much slower wave fronts can propagate within substance undergoing intensive damage. These moving fronts propagate within intact substance leaving behind them intensively damaged substance. These fronts were coined as failure waves. The failure waves can be modeled differently--in this letter they are modeled as sharp interfaces separating two states: the intact and comminuted states. Several penetration experiments with transparent glasses and ceramics have shown that failure fronts have an extremely rough morphology. We suggest a simple thermodynamic theory which allows interpreting appearance of the roughness as a manifestation of morphological instability of failure fronts. For the case of isotropic phases the instability criterion is presented in explicit form.
Controlling Hamiltonian chaos via Gaussian curvature.
Oloumi, A; Teychenné, D
1999-12-01
We present a method allowing one to partly stabilize some chaotic Hamiltonians which have two degrees of freedom. The purpose of the method is to avoid the regions of V(q(1),q(2)) where its Gaussian curvature becomes negative. We show the stabilization of the Hénon-Heiles system, over a wide area, for the critical energy E=1/6. Total energy of the system varies only by a few percent.
Generalization of Seidel astigmatism and Petzval curvature.
Gaj, M
1966-06-01
In a paper probably to be published in Optika i Spektroskopiya the wave aberration for sagittal focus for the arbitrary surface of rotational symmetry has been carried out on the base of the astigmatic beam invariant D(s) = nu(s)d(s). The resulting expression for the wave aberration has been reformulated into three terms which, in the Seidel region, go over into astigmatism (the first) and into the Petzval curvature (the second) while the third disappears.
Breeding curvature from extended gauge covariance
NASA Astrophysics Data System (ADS)
Aldrovandi, R.
1991-05-01
Independence between spacetime and “internal” space in gauge theories is related to the adjoint-covariant behaviour of the gauge potential. The usual gauge scheme is modified to allow a coupling between both spaces. Gauging spacetime translations produce field equations similar to Einstein equations. A curvature-like quantity of mixed differential-algebraic character emerges. Enlarged conservation laws are present, pointing to the presence of an covariance.
Jones, L.
1995-01-01
Like the patients, doctors in Sarajevo depend largely on humanitarian aid; everyone in the public sector has worked without pay for almost three years. The hospital is on a front line; yet the psychiatric department continues to function, even conducting large scale studies of psychosocial aspects of war in Bosnia-Hercegovina. The type of inpatient morbidity and treatment patterns have changed. A plethora of psychosocial rehabilitation programmes has emerged, including counselling, drop in centres, and attending to special needs of elderly people, schoolchildren, and women. The most prominent psychological symptoms were exhaustion at the prospect of a third winter of war and bewilderment at the Western stereotype of Bosnians as Muslim fundamentalists. Images p1052-a p1053-a PMID:7728062
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
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.
Stiffness Modulation of Rayed Fins by Curvature
NASA Astrophysics Data System (ADS)
Nguyen, Khoi; Yu, Ning; Venkadesan, Madhusudhan; Bandi, Mahesh; Mandre, Shreyas
2016-11-01
Fishes with rayed fins comprise over 99% of all extant fish species. Multifunctional use of fins, from propulsion to station holding, requires substantial modulation of stiffness. We propose that fishes stiffen the fin by curving it transverse to its length. This effect is similar to stiffening a dollar bill by curling it because of curvature-induced coupling of out-of-plane bending with in-plane stretching. Unlike a piece of paper, rayed fins are a composite of rays and membranes. We model this as parallel elastic beams (rays) with springy interconnections (membranes). Our analysis shows that the key parameters stiffening the fin are the ray anisotropy to bending, the misalignment of principal bending directions of adjacent rays, and the membrane elasticity. The composite fin stiffens when the principal bending directions of adjacent rays are misaligned due to fin curvature, which necessarily causes the membrane to stretch. Unlike a homogenous thin sheet, composite rayed structures are able to mimic curvature-induced stiffening by using misaligned rays even if the fin appears geometrically flat. Preliminary radiographic evidence from the rays of fish fins supports such a mechanism. Funding by Human Frontier Science Program.
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.
Front tracking for characterizing and quantifying reactive mixing
NASA Astrophysics Data System (ADS)
Kelley, Douglas; Nevins, Thomas
2016-11-01
Mixing in industrial chemical reactors involves complicated interactions between advection, reaction, and diffusion that are difficult to simulate or measure in detail. However, in large-Damköhler-number systems which show sharp fronts between reacted and unreacted regions, reactor dynamics might be more simply and usefully characterized in terms of the reaction fronts themselves. In fact, prior work has already shown that the reaction rate and material diffusivity can be calculated directly if front speed and front thickness are known. We have developed methods to optically track reaction fronts, measuring their speed and thickness throughout space and time. We will present such measurements in both simulation and experiment, consider their statistics, and discuss future efforts to characterize and quantify mixing in chemical reactors.
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
Free-streaming radiation in cosmological models with spatial curvature
NASA Technical Reports Server (NTRS)
Wilson, M. L.
1982-01-01
The effects of spatial curvature on radiation anisotropy are examined for the standard Friedmann-Robertson-Walker model universes. The effect of curvature is found to be very important when considering fluctuations with wavelengths comparable to the horizon. It is concluded that the behavior of radiation fluctuations in models with spatial curvature is quite different from that in spatially flat models, and that models with negative curvature are most strikingly different. It is therefore necessary to take the curvature into account in careful studies of the anisotropy of the microwave background.
Comparison between a propane-air combustion front and a helium-air simulated combustion front
Barraclough, S.
1983-12-01
Turbulent combustion experiments were performed in a right cylindrical combustion bomb using a premixed propane-air gaseous fuel. The initial conditions inside the combustion chamber were three psig and room temperature. Prior to spark firing, the turbulence intensity inside the combustion chamber was measured and could be varied over a ten fold range. The effect of initial turbulence intensity on turbulent flame propagation was investigated. Two regimes of turbulent combustion were identified, which is in agreement with a previous investigator's results. One of them, a ''transition regime'' occurs when the turbulence intensity is approximately twice the laminar flame speed. Within the transition regime, the turbulent burning speed is linearly proportional to initial turbulence intensity and independent of laminar flame speed and turbulence length scale. A high pressure helium front was injected into the combustion chamber to simulate the combustion front. Since the helium front is isothermal, hot-wire anemometry can be used to quantify the change in turbulence intensity ahead of the propagating front. The helium front was found to have different characteristics than the combustion front.
VIEW OF FRONT, RECESSED ENTRY SHOWING FRONT WALK. VIEW FACING ...
VIEW OF FRONT, RECESSED ENTRY SHOWING FRONT WALK. VIEW FACING SOUTHWEST - Camp H.M. Smith and Navy Public Works Center Manana Title VII (Capehart) Housing, Three-Bedroom Single-Family Type 9, Birch Circle, Elm Drive, Elm Circle, and Date Drive, 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 biplane geometry and centerline curvature in vascular imaging
NASA Astrophysics Data System (ADS)
Nazareth, Daryl; Hoffmann, Kenneth R.; Walczak, Alan; Dmochowski, Jacek; Guterman, Lee R.; Rudin, Stephen; Bednarek, Daniel R.
2002-05-01
Three-dimensional (3-D) vessel trees can provide useful visual and quantitative information during interventional procedures. To calculate the 3-D vasculature from biplane images, the transformation relating the imaging systems (i.e., the rotation matrix R and the translation vector t) must be determined. We have developed a technique to calculate these parameters, which requires only the identification of approximately corresponding vessel regions in the two images. Initial estimates of R and t are generated based on the gantry angles, and then refined using an optimization technique. The objective function to be minimized is determined as follows. For each endpoint of each vessel in the first image, an epipolar line in the second image is generated. The intersection points between these two epipolar lines and the corresponding vessel centerline in the second image are determined. The vessel arclength between these intersection points is calculated as a fraction of the entire vessel region length in the image. This procedure is repeated for every vessel in each image. The value of the objective function is calculated from the sum of these fractions, and is smallest when the total fractional arclength is greatest. The 3-D vasculature is obtained from the optimal R and t using triangulation, and vessel curvature is then determined. This technique was evaluated using simulated curves and vessel centerlines obtained from clinical images, and provided rotational, magnification and relative curvature errors of 1 degree(s), 1% and 14% respectively. Accurate 3-D and curvature measures may be useful in clinical decision making, such as in assessing vessel tortuousity and access, during interventional procedures.
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.
On the Riemann Curvature Operators in Randers Spaces
NASA Astrophysics Data System (ADS)
Rafie-Rad, M.
2013-05-01
The Riemann curvature in Riemann-Finsler geometry can be regarded as a collection of linear operators on the tangent spaces. The algebraic properties of these operators may be linked to the geometry and the topology of the underlying space. The principal curvatures of a Finsler space (M, F) at a point x are the eigenvalues of the Riemann curvature operator at x. They are real functions κ on the slit tangent manifold TM0. A principal curvature κ(x, y) is said to be isotropic (respectively, quadratic) if κ(x, y)/F(x, y) is a function of x only (respectively, κ(x, y) is quadratic with respect to y). On the other hand, the Randers metrics are the most popular and prominent metrics in pure and applied disciplines. Here, it is proved that if a Randers metric admits an isotropic principal curvature, then F is of isotropic S-curvature. The same result is also established for F to admit a quadratic principal curvature. These results extend Shen's verbal results about Randers metrics of scalar flag curvature K = K(x) as well as those Randers metrics with quadratic Riemann curvature operator. The Riemann curvature Rik may be broken into two operators Rik and Jik. The isotropic and quadratic principal curvature are characterized in terms of the eigenvalues of R and J.
Bragg gratings in surface-core fibers: Refractive index and directional curvature sensing
NASA Astrophysics Data System (ADS)
Osório, Jonas H.; Oliveira, Ricardo; Aristilde, Stenio; Chesini, Giancarlo; Franco, Marcos A. R.; Nogueira, Rogério N.; Cordeiro, Cristiano M. B.
2017-03-01
In this paper, we report, to our knowledge, the first extended study of the inscription of Bragg gratings in surface-core fibers and their application in refractive index and directional curvature sensing. The research ranges from fiber fabrication and grating inscription in untapered and tapered fibers to the performance of simulations and sensing measurements. Maximum sensitivities of 40 nm/RIU and 202.7 pm/m-1 were attained in refractive index and curvature measurements respectively. The obtained results compares well to other fiber Bragg grating based devices. Ease of fabrication, robustness and versatility makes surface-core fibers an interesting platform when exploring fiber sensing devices.
Curvature inducing macroion condensation driven shape changes of fluid vesicles.
Sreeja, K K; Ipsen, John H; Sunil Kumar, P B
2015-11-21
We study the effect of curvature inducing macroion condensation on the shapes of charged deformable fluid interfaces using dynamically triangulated Monte Carlo simulations. In the weak electrostatic coupling regime, surface charges are weakly screened and the conformations of a vesicle, with fixed spherical topology, depend on the charge-charge interaction on the surface. While in the strong coupling regime, condensation driven curvature induction plays a dominant role in determining the conformations of these surfaces. Condensation itself is observed to be dependent on the induced curvature, with larger induced curvatures favoring increased condensation. We show that both curvature generation and curvature sensing, induced by the interplay of electrostatics and curvature energy, contribute to determination of the vesicle configurations.
Optimal Spatial Scale for Curvature Calculations in Multiphase Flows
NASA Astrophysics Data System (ADS)
Senecal, Jacob; Owkes, Mark
2016-11-01
In gas-liquid flows, the surface tension force often controls the dynamics of the flow and an accurate calculation of this force is necessary for predictive simulations. The surface tension force is directly proportional to the curvature of the gas-liquid interface, making accurate curvature calculations an essential consideration. Multiple methods have been developed to calculate the curvature of volume of fluid (VoF) interface capturing schemes, such as the height function method. These methods have been extensively tested. However, the impact of the scale or size of computational stencil on which the curvature is computed, has not been correlated with the rate at which interface perturbations relax under the surface tension force. In this work, the effect of varying the scale on which the curvature is computed has been tested and quantified. An optimal curvature scale is identified that leads to accurate and converging curvatures, and accurate timescales for surface tension induced, interface dynamics.
NASA Astrophysics Data System (ADS)
Karimi, Davood; Ward, Rabab K.
2016-03-01
Reducing the radiation dose in computed tomography (CT) requires reducing the number or the energy of the photons that pass through the patient's body. An image reconstructed from such noisy or undersampled measurements will contain much noise and artifacts that can significantly reduce the diagnostic value of the image. Effective sinogram denoising or interpolation can reduce these noise and artifacts. In this paper, we present a novel approach to sinogram smoothing and interpolation. The proposed method iteratively estimates the local slope and curvature of the sinogam and forces the sinogram to follow the estimated slope and curvature. This is performed by projection onto the set of constraints that define the slope and the curvature. The constraints on the slope and curvature correspond to very simple convex sets. Projection onto these sets have simple analytical solutions. Moreover, these operations are highly parallelizable because the equations defining the slope and curvature constraints for all the points in a sinogram can be summarized as five convex sets, regardless of the length of the sinogram. We apply the proposed method on simulated and real data and examine its effect on the quality of the reconstructed image. Our results show that the proposed method is highly effective and can lead to a substantial improvement in the quality of the images reconstructed from noisy sinogram measurements. A comparison with the K-SVD denoising algorithm shows that the proposed algorithm achieves better results. We suggest that the proposed method can be a useful tool for low-dose CT.
Badial, Peres R; Cisneros-Àlvarez, Luis Emiliano; Brandão, Cláudia Valéria S; Ranzani, José Joaquim T; Tomaz, Mayana A R V; Machado, Vania M; Borges, Alexandre S
2015-09-01
The aim of this study was to compare ocular dimensions, corneal curvature, and corneal thickness between horses affected with hereditary equine regional dermal asthenia (HERDA) and unaffected horses. Five HERDA-affected quarter horses and five healthy control quarter horses were used. Schirmer's tear test, tonometry, and corneal diameter measurements were performed in both eyes of all horses prior to ophthalmologic examinations. Ultrasonic pachymetry was performed to measure the central, temporal, nasal, dorsal, and ventral corneal thicknesses in all horses. B-mode ultrasound scanning was performed on both eyes of each horse to determine the dimensions of the ocular structures and to calculate the corneal curvature. Each corneal region examined in this study was thinner in the affected group compared with the healthy control group. However, significant differences in corneal thickness were only observed for the central and dorsal regions. HERDA-affected horses exhibited significant increases in corneal curvature and corneal diameter compared with unaffected animals. The ophthalmologic examinations revealed mild corneal opacity in one eye of one affected horse and in both eyes of three affected horses. No significant between-group differences were observed for Schirmer's tear test, intraocular pressure, or ocular dimensions. Hereditary equine regional dermal asthenia-affected horses exhibit decreased corneal thickness in several regions of the cornea, increased corneal curvature, increased corneal diameter, and mild corneal opacity. Additional research is required to determine whether the increased corneal curvature significantly impacts the visual accuracy of horses with HERDA. © 2014 American College of Veterinary Ophthalmologists.
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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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
Damage Identification Dependence on Number of Vibration Modes Using Mode Shape Curvature Squares
NASA Astrophysics Data System (ADS)
Janeliukstis, R.; Rucevskis, S.; Wesolowski, M.; Chate, A.
2016-09-01
In this paper a damage identification algorithm for multiple damage sites based on mode shape curvature square method of vibration mode shapes in aluminium beam is reported. The required mode shape curvature of a healthy structure was obtained via interpolation of mode shape curvature of a damaged structure with Fourier series functions of different orders. Algorithm employed calculations of standardized damage index distributions over beam coordinate. Finite element simulations of proposed methodology involving various artificial noise levels and reduction of mode shape input data points were validated on the damage identification results of experimentally measured mode shapes which were measured using scanning laser vibrometer. Results show that the algorithm is capable of capturing the areas of damage. The term called damage estimate reliability was introduced in terms of likelihood of the chosen approximation function to capture the location of damage.
Lim, Ik Soo; Leek, E Charles
2012-07-01
Previous empirical studies have shown that information along visual contours is known to be concentrated in regions of high magnitude of curvature, and, for closed contours, segments of negative curvature (i.e., concave segments) carry greater perceptual relevance than corresponding regions of positive curvature (i.e., convex segments). Lately, Feldman and Singh (2005, Psychological Review, 112, 243-252) proposed a mathematical derivation to yield information content as a function of curvature along a contour. Here, we highlight several fundamental errors in their derivation and in its associated implementation, which are problematic in both mathematical and psychological senses. Instead, we propose an alternative mathematical formulation for information measure of contour curvature that addresses these issues. Additionally, unlike in previous work, we extend this approach to 3-dimensional (3D) shape by providing a formal measure of information content for surface curvature and outline a modified version of the minima rule relating to part segmentation using curvature in 3D shape. Copyright 2012 APA, all rights reserved.
Optimization of the examination posture in spinal curvature assessment
2012-01-01
To decrease the influence of postural sway during spinal measurements, an instrumented fixation posture (called G) was proposed and tested in comparison with the free standing posture (A) using the DTP-3 system in a group of 70 healthy volunteers. The measurement was performed 5 times on each subject and each position was tested by a newly developed device for non-invasive spinal measurements called DTP-3 system. Changes in postural stability of the spinous processes for each subject/the whole group were evaluated by employing standard statistical tools. Posture G, when compared to posture A, reduced postural sway significantly in all spinous processes from C3 to L5 in both the mediolateral and anterioposterior directions. Posture G also significantly reduced postural sway in the vertical direction in 18 out of 22 spinous processes. Importantly, posture G did not significantly influence the spinal curvature. PMID:22546519
Optimization of the examination posture in spinal curvature assessment.
Krejci, Jakub; Gallo, Jiri; Stepanik, Petr; Salinger, Jiri
2012-04-30
To decrease the influence of postural sway during spinal measurements, an instrumented fixation posture (called G) was proposed and tested in comparison with the free standing posture (A) using the DTP-3 system in a group of 70 healthy volunteers. The measurement was performed 5 times on each subject and each position was tested by a newly developed device for non-invasive spinal measurements called DTP-3 system. Changes in postural stability of the spinous processes for each subject/the whole group were evaluated by employing standard statistical tools. Posture G, when compared to posture A, reduced postural sway significantly in all spinous processes from C3 to L5 in both the mediolateral and anterioposterior directions. Posture G also significantly reduced postural sway in the vertical direction in 18 out of 22 spinous processes. Importantly, posture G did not significantly influence the spinal curvature.
Hunter, D J; Lohmander, L S; Makovey, J; Tamez-Peña, J; Totterman, S; Schreyer, E; Frobell, R B
2014-07-01
Investigate the 5-year longitudinal changes in bone curvature after acute anterior cruciate ligament (ACL) injury, and identify predictors of such changes. In the KANON-trial (ISRCTN 84752559), 111/121 young active adults with an acute ACL tear to a previously un-injured knee had serial 1.5 T MR images from baseline (within 5 weeks from injury) to 5 years after injury. Of these, 86 had ACL reconstruction (ACLR) performed early or delayed, 25 were treated with rehabilitation alone. Measures of articulating bone curvature were obtained from computer-assisted segmentation of MR images. Curvature (mm(-1)) was determined for femur, tibia, medial/lateral femur, trochlea, medial/lateral tibia. Age, sex, treatment, BMI, meniscal injury, osteochondral fracture on baseline MR images were tested for association. Over 5 years, curvature decreased in each region (P < 0.001) suggesting flattening of convex shapes and increased concavity of concave shapes. A higher BMI was associated with flattening of the femur (P = 0.03), trochlea (P = 0.007) and increasing concavity of the lateral tibia (LT) (P = 0.011). ACLR, compared to rehabilitation alone, was associated with flatter curvature in the femur (P < 0.001), medial femoral condyle (P = 0.006) and trochlea (P = 0.003). Any meniscal injury at baseline was associated with a more flattened curvature in the femur (P = 0.038), trochlea (P = 0.039), lateral femoral condyle (P = 0.034) and increasing concavity of the LT (P = 0.048). ACL injury is associated with significant changes in articulating bone curvature over a 5 year period. Higher BMI, baseline meniscal injury and undergoing ACL reconstruction (as distinct from undergoing rehabilitation alone) are all associated with flattening of the articulating bone. Copyright © 2014 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.
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.
2007-09-01
TH T d TT ρ κγλ −⎟ ⎠ ⎞ ⎜ ⎝ ⎛−= 3 (5) The last term on the right accounts for the Gibbs- Thomson effect . The γsl is the solid-liquid interfacial...fusion per unit mass. The Gibbs- Thomson effect reduces the magnitude of the curvature of the solidification front (i.e. it tends to flatten the...affects the temperature at which the solidification front solidifies through the Gibbs- Thomson effect , viz.: mm sl sl mi Td T H TT 3 ⎟ ⎠ ⎞ ⎜ ⎝ ⎛−−= λ
NASA Astrophysics Data System (ADS)
Hu, Qihao; Zhang, Shuo; Yang, Wenlei; Geng, Tao; Sun, Weimin; Sun, Cuiting; Jin, Xiren; Yuan, Libo
2017-09-01
A highly sensitive curvature sensor made of a novel long period fiber grating (LPFG) is presented and experimentally demonstrated. It is constructed by splicing multiple single mode fibers (SMFs) and multi-mode fibers (MMFs) alternately (MS/MA). The measurement result shows that it has a high sensitivity of -22.4 nm/m-1 in the range from 0.223 m-1 to 4.358 m-1. It can measure curvature on all direction due to the symmetric structure. The proposed sensor was also insensitive to the temperature, whose temperature sensitivity was around -0.015 nm/°C in the range from 40 °C to 200 °C. The advantages of high curvature sensitivity and low temperature sensitivity make it has a great potential to measure curvature in practical application with high resolutions.
NASA Astrophysics Data System (ADS)
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J.; Radhakrishanan, Ravi
2012-06-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable 'neck-region' (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated.
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J.; Radhakrishanan, Ravi
2015-01-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable ‘neck-region’ (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated. PMID:26500377
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J; Radhakrishanan, Ravi
2012-06-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable 'neck-region' (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated.
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.
Lipid membrane-mediated attraction between curvature inducing objects
NASA Astrophysics Data System (ADS)
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.
2016-09-01
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.
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
Amplification of curvature perturbations in cyclic cosmology
NASA Astrophysics Data System (ADS)
Zhang, Jun; Liu, Zhi-Guo; Piao, Yun-Song
2010-12-01
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.
Solitons in curved space of constant curvature
Batz, Sascha; Peschel, Ulf
2010-05-15
We consider spatial solitons as, for example, self-confined optical beams in spaces of constant curvature, which are a natural generalization of flat space. Due to the symmetries of these spaces we are able to define respective dynamical parameters, for example, velocity and position. For positively curved space we find stable multiple-hump solitons as a continuation from the linear modes. In the case of negatively curved space we show that no localized solution exists and a bright soliton will always decay through a nonlinear tunneling process.
Zero curvature-surface driven small objects
NASA Astrophysics Data System (ADS)
Dou, Xiaoxiao; Li, Shanpeng; Liu, Jianlin
2017-08-01
In this study, we investigate the spontaneous migration of small objects driven by surface tension on a catenoid, formed by a layer of soap constrained by two rings. Although the average curvature of the catenoid is zero at each point, the small objects always migrate to the position near the ring. The force and energy analyses have been performed to uncover the mechanism, and it is found that the small objects distort the local shape of the liquid film, thus making the whole system energetically favorable. These findings provide some inspiration to design microfluidics, aquatic robotics, and miniature boats.
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.
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.
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.
Curvature-Driven Lipid Sorting in Biomembranes
Callan-Jones, Andrew; Sorre, Benoit; Bassereau, Patricia
2011-01-01
It has often been suggested that the high curvature of transport intermediates in cells may be a sufficient means to segregate different lipid populations based on the relative energy costs of forming bent membranes. In this review, we present in vitro experiments that highlight the essential physics of lipid sorting at thermal equilibrium: It is driven by a trade-off between bending energy, mixing entropy, and interactions between species. We collect evidence that lipid sorting depends strongly on lipid–lipid and protein–lipid interactions, and hence on the underlying composition of the membrane and on the presence of bound proteins. PMID:21421916
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.
Front tracking for quantifying advection-reaction-diffusion
NASA Astrophysics Data System (ADS)
Nevins, Thomas D.; Kelley, Douglas H.
2017-04-01
We present an algorithm for measuring the speed and thickness of reaction fronts, and from those quantities, the diffusivity and the reaction rate of the active chemical species. This front-tracking algorithm provides local measurements suitable for statistics and requires only a sequence of concentration fields. Though our eventual goal is front tracking in advection-reaction-diffusion, here we demonstrate the algorithm in reaction-diffusion. We test the algorithm with validation data in which front speed and thickness are prescribed, as well as simulation results in which diffusivity and reaction rate are prescribed. In all tests, measurements closely match true values. We apply the algorithm to laboratory experiments using the Belousov-Zhabotinsky reaction, producing speed, diffusivity, and reaction rate measurements that are statistically more robust than in prior studies. Finally, we use thickness measurements to quantify the concentration profile of chemical waves in the reaction.
Front tracking for quantifying advection-reaction-diffusion.
Nevins, Thomas D; Kelley, Douglas H
2017-04-01
We present an algorithm for measuring the speed and thickness of reaction fronts, and from those quantities, the diffusivity and the reaction rate of the active chemical species. This front-tracking algorithm provides local measurements suitable for statistics and requires only a sequence of concentration fields. Though our eventual goal is front tracking in advection-reaction-diffusion, here we demonstrate the algorithm in reaction-diffusion. We test the algorithm with validation data in which front speed and thickness are prescribed, as well as simulation results in which diffusivity and reaction rate are prescribed. In all tests, measurements closely match true values. We apply the algorithm to laboratory experiments using the Belousov-Zhabotinsky reaction, producing speed, diffusivity, and reaction rate measurements that are statistically more robust than in prior studies. Finally, we use thickness measurements to quantify the concentration profile of chemical waves in the reaction.
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.
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
Analysis of dynamic smile and upper lip curvature in young Chinese.
Liang, Ling-Zhi; Hu, Wen-Jie; Zhang, Yan-Ling; Chung, Kwok-Hung
2013-03-01
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.
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.)
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.