Total positive curvature of circular DNA.
Bohr, Jakob; Olsen, Kasper W
2013-11-01
The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature are presented.
Total positive curvature of circular DNA
NASA Astrophysics Data System (ADS)
Bohr, Jakob; Olsen, Kasper W.
2013-11-01
The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature are presented.
Curvature constraints from large scale structure
NASA Astrophysics Data System (ADS)
Di Dio, Enea; Montanari, Francesco; Raccanelli, Alvise; Durrer, Ruth; Kamionkowski, Marc; Lesgourgues, Julien
2016-06-01
We modified the CLASS code in order to include relativistic galaxy number counts in spatially curved geometries; we present the formalism and study the effect of relativistic corrections on spatial curvature. The new version of the code is now publicly available. Using a Fisher matrix analysis, we investigate how measurements of the spatial curvature parameter ΩK with future galaxy surveys are affected by relativistic effects, which influence observations of the large scale galaxy distribution. These effects include contributions from cosmic magnification, Doppler terms and terms involving the gravitational potential. As an application, we consider angle and redshift dependent power spectra, which are especially well suited for model independent cosmological constraints. We compute our results for a representative deep, wide and spectroscopic survey, and our results show the impact of relativistic corrections on spatial curvature parameter estimation. We show that constraints on the curvature parameter may be strongly biased if, in particular, cosmic magnification is not included in the analysis. Other relativistic effects turn out to be subdominant in the studied configuration. We analyze how the shift in the estimated best-fit value for the curvature and other cosmological parameters depends on the magnification bias parameter, and find that significant biases are to be expected if this term is not properly considered in the analysis.
Reading Materials in Large Type. Reference Circular.
ERIC Educational Resources Information Center
Ovenshire, Ruthann, Comp.
Listed in the circular are approximately 32 commercial and volunteer producers of large type materials, approximately 50 large type books for reference and special needs, and five further sources of large type materials. Usually given for each alphabetically listed producer are the address, specialty (whether producer of specific categories or of…
Curvature wavefront sensing for the large synoptic survey telescope.
Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian
2015-10-20
The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing. PMID:26560396
Curvature wavefront sensing for the large synoptic survey telescope.
Xin, Bo; Claver, Chuck; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian
2015-10-20
The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from four curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1 mm on either side of focus. In this paper, we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intrafocal and extrafocal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LSST optical system. The algorithm extensions reported here are generic and can easily be adapted to other wide-field optical systems including similar telescopes with large central obscuration and off-axis curvature sensing.
Large Circular Basin - 1300-km diameter
NASA Technical Reports Server (NTRS)
1974-01-01
Close-up view of one-half of a 1300-km diameter circular basin the largest observed on Mercury. The other half is hidden beyond the terminator to the left. Hills and valleys extend in a radial fashion outward from the main ring. Interior of the large basin is completely flooded by plains materials; adjacent lowlands are also partially flooded and superimposed on the plains are bowl shaped craters. Wrinkle ridges are abundant on the plains materials. The area shown is 1008 miles (1600 km) from the top to the bottom of the picture. Sun's illumination is from the right. Blurred linear lines extending across the picture near bottom are missing data lines that have been filled in by the computer. Mariner 10 encountered Mercury on Friday, March 29th, 1974, passing the planet on the darkside 431 miles (690-km) from the surface.
The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.
NOTE: This image was scanned from physical media.
Accelerator considerations of large circular colliders
NASA Astrophysics Data System (ADS)
Chao, Alex
2016-07-01
As we consider the tremendous physics reaches of the big future circular electron-positron and proton-proton colliders, it might be advisable to keep a close track of what accelerator challenges they face. Good progresses are being made, and yet it is reported here that substantial investments in funding, manpower, as well as a long sustained time to the R&D efforts will be required in preparation to realize these dream colliders.
Turbulent boundary layers with large streamline curvature effects
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mellor, G. L.
1978-01-01
It has been shown that turbulent flows are greatly affected by streamline curvature. In spite of this and the fact that curved shear flows are frequently encountered in engineering applications, the predictions of such flows are relatively less developed than the predictions of two-dimensional plane flows. Recently, various attempts were made by different investigators; however, their methods are only successful when the product of the boundary layer thickness to the local surface curvature is approximately 0.05. The present paper investigates the more general case where this product is in the range from 0.1 to 0.5. Results show that the calculated boundary-layer characteristics for arbitrary free stream conditions are in good agreement with measurements.
Effect of Circular p- n Junction Curvature on the Diode Current Density
NASA Astrophysics Data System (ADS)
Borblik, Vitalii
2016-08-01
The influence of the circular geometry of a p- n junction built into a nanowire or a nanorod, on the radial diode current density is investigated. While the current density from the core to the shell proves to be larger than that in a planar diode at the same values of the parameters, the density of the diode current from the shell to the core, on the contrary, proves to be smaller. A dependence of the effect on the core and the shell radii has been demonstrated. The nature of the effect is explained on the basis of radial distributions of the nonequilibrium current carriers.
No large scale curvature perturbations during the waterfall phase transition of hybrid inflation
Abolhasani, Ali Akbar; Firouzjahi, Hassan
2011-03-15
In this paper the possibility of generating large scale curvature perturbations induced from the entropic perturbations during the waterfall phase transition of the standard hybrid inflation model is studied. We show that whether or not appreciable amounts of large scale curvature perturbations are produced during the waterfall phase transition depends crucially on the competition between the classical and the quantum mechanical backreactions to terminate inflation. If one considers only the classical evolution of the system, we show that the highly blue-tilted entropy perturbations induce highly blue-tilted large scale curvature perturbations during the waterfall phase transition which dominate over the original adiabatic curvature perturbations. However, we show that the quantum backreactions of the waterfall field inhomogeneities produced during the phase transition dominate completely over the classical backreactions. The cumulative quantum backreactions of very small scale tachyonic modes terminate inflation very efficiently and shut off the curvature perturbation evolution during the waterfall phase transition. This indicates that the standard hybrid inflation model is safe under large scale curvature perturbations during the waterfall phase transition.
Design and experimental demonstration of variable curvature mirror having a large saggitus variation
NASA Astrophysics Data System (ADS)
Xie, Xiaopeng; Zhao, Hui; Ren, Guorui; Wei, Jingxuan; Menke, Neimule
2014-11-01
Variable curvature mirror (VCM) is a simplified active optical component being capable of changing its curvature radius. Curvature radius variation within a wide range requires that the VCM should be able to generate a large saggitus variation. Besides that, the surface form accuracy should be maintained above a reasonable level. In this paper, a piezoelectric actuation based prototype VCM is designed, constructed and experimentally tested. The thickness of the K9 plane mirror is only 3mm over the full aperture of 100mm. Six piezoelectric actuators are fixed into a base plate and the head of each actuator is connected to an annular ring through the screw thread. With such a structure, the force provided by each actuator can be transformed to the mirror backside through this annular ring. With each actuator generating the same force, the curvature radius can be changed in a uniform way. At the mean time, the surface form accuracy could be adjusted one point by point to compensation asymmetric modes as well. Mathematical analysis and FEA (finite element analysis) are used together to demonstrate the theoretical correctness. Besides that, the prototype VCM is successfully constructed and experiments have been carried out to give a quantitative assessment on the saggitus variation.
Signatures of the very early Universe: Inflation, spatial curvature, and large scale anomalies
NASA Astrophysics Data System (ADS)
Aslanyan, Grigor; Easther, Richard
2015-06-01
A short inflationary phase may not erase all traces of the primordial Universe. Associated observables include both spatial curvature and "anomalies" in the microwave background or large-scale structure. The present curvature ΩK ,0 reflects the initial curvature, ΩK ,start , and the angular size of anomalies depends on kstart, the comoving horizon size at the onset of inflation. We estimate posteriors for ΩK ,start and kstart using current data and simulations, and show that if either quantity is measured to have a nonzero value, both are likely to be observable. Mappings from ΩK ,start and kstart to present-day observables depend strongly on the primordial equation of state; ΩK ,0 spans 10 orders of magnitude for a given ΩK ,start, while a simple and general relationship connects ΩK ,0 and kstart. We show that current bounds on ΩK ,0 imply that if kstart is measurable, the curvature was already small when inflation began. Finally, since the energy density changes slowly during inflation, primordial gravitational wave constraints require that a short inflationary phase be preceded by a nontrivial preinflationary phase with critical implications for the expected value of ΩK ,start.
Large-amplitude circularly polarized electromagnetic waves in magnetized plasma
Vasko, I. Y. Artemyev, A. V.; Zelenyi, L. M.
2014-05-15
We consider large-amplitude circularly polarized (LACP) waves propagating in a magnetized plasma. It is well-known that the dispersion relation for such waves coincides with the dispersion relation given by the linear theory. We develop the model of LACP wave containing a finite population of Cerenkov resonant particles. We find that the current of resonant particles modifies the linear dispersion relation. Dispersion curves of low-frequency (i.e., whistler and magnetosonic) waves are shifted toward larger values of the wave vector, i.e., waves with arbitrarily large wavelengths do not exist in this case. Dispersion curves of high-frequency waves are modified so that the wave phase velocity becomes smaller than the speed of light.
Large quasi-circular features beneath frost on Triton
NASA Astrophysics Data System (ADS)
Helfenstein, Paul; Veverka, Joseph; McCarthy, Derek; Lee, Pascal; Hillier, John
1992-02-01
Specially processed Voyager 2 images of Neptune's largest moon, Triton, reveal three large quasi-circular features ranging in diameter from 280 to 935 km within Triton's equatorial region. The largest of these features contains a central irregularly shaped area of comparatively low albedo about 380 km in diameter, surrounded by crudely concentric annuli of higher albedo materials. None of the features exhibit significant topographic expression, and all appear to be primarily albedo markings. The features are located within a broad equatorial band of anomalously transparent frost that renders them nearly invisible at the large phase angles (alpha greater than 90 deg) at which Voyager obtained its highest resolution coverage of Triton. The features can be discerned at smaller phase angles (alpha = 66 deg) at which the frost only partially masks underlying albedo contrasts. The origin of the features is uncertain but may have involved regional cryovolcanic activity.
Large quasi-circular features beneath frost on Triton
NASA Technical Reports Server (NTRS)
Helfenstein, Paul; Veverka, Joseph; Mccarthy, Derek; Lee, Pascal; Hillier, John
1992-01-01
Specially processed Voyager 2 images of Neptune's largest moon, Triton, reveal three large quasi-circular features ranging in diameter from 280 to 935 km within Triton's equatorial region. The largest of these features contains a central irregularly shaped area of comparatively low albedo about 380 km in diameter, surrounded by crudely concentric annuli of higher albedo materials. None of the features exhibit significant topographic expression, and all appear to be primarily albedo markings. The features are located within a broad equatorial band of anomalously transparent frost that renders them nearly invisible at the large phase angles (alpha greater than 90 deg) at which Voyager obtained its highest resolution coverage of Triton. The features can be discerned at smaller phase angles (alpha = 66 deg) at which the frost only partially masks underlying albedo contrasts. The origin of the features is uncertain but may have involved regional cryovolcanic activity.
Evolution of large scale curvature fluctuations during the perturbative decay of the inflaton
Di Marco, Fabrizio; Finelli, Fabio; Gruppuso, Alessandro
2007-08-15
We study the evolution of cosmological fluctuations during and after inflation driven by a scalar field coupled to a perfect fluid through a friction term. During the slow-roll regime for the scalar field, the perfect fluid is also frozen and isocurvature perturbations are generated. After the end of inflation, during the decay of the inflaton, we find that a change in the observationally relevant large scale curvature fluctuations is possible.
Compensation for large tensor modes with iso-curvature perturbations in CMB anisotropies
Kawasaki, Masahiro; Yokoyama, Shuichiro E-mail: shu@icrr.u-tokyo.ac.jp
2014-05-01
Recently, BICEP2 has reported the large tensor-to-scalar ratio r = 0.2{sup +0.07}{sub −0.05} from the observation of the cosmic microwave background (CMB) B-mode at degree-scales. Since tensor modes induce not only CMB B-mode but also the temperature fluctuations on large scales, to realize the consistent temperature fluctuations with the Planck result we should consider suppression of scalar perturbations on corresponding large scales. To realize such a suppression, we consider anti-correlated iso-curvature perturbations which could be realized in the simple curvaton model.
Radius of Curvature Measurement of Large Optics Using Interferometry and Laser Tracker
NASA Technical Reports Server (NTRS)
Hagopian, John; Connelly, Joseph
2011-01-01
The determination of radius of curvature (ROC) of optics typically uses either a phase measuring interferometer on an adjustable stage to determine the position of the ROC and the optics surface under test. Alternatively, a spherometer or a profilometer are used for this measurement. The difficulty of this approach is that for large optics, translation of the interferometer or optic under test is problematic because of the distance of translation required and the mass of the optic. Profilometry and spherometry are alternative techniques that can work, but require a profilometer or a measurement of subapertures of the optic. The proposed approach allows a measurement of the optic figure simultaneous with the full aperture radius of curvature.
Plastic set of smooth large radii of curvature thermal conductance specimens at light loads.
NASA Technical Reports Server (NTRS)
Mckinzie, D. J., Jr.
1972-01-01
Thermal contact conductance test data at high vacuum were obtained from two Armco iron specimens having smooth, large radii of curvature, convex, one-half wave length surfaces. The data are compared with calculations based on two macroscopic elastic deformation theories and an empirical expression. Major disagreement with the theories and fair agreement with the empirical expression resulted. Plastic deformation of all the contacting surfaces was verified from surface analyzer statistics. These results indicate that the theoretical assumption of macroscopic elastic deformation is inadequate for accurate prediction of heat transfer with light loads for Armco iron specimens similar to those used in this investigation.
Plastic set of smooth large radii of curvature thermal conductance specimens at light loads
NASA Technical Reports Server (NTRS)
Mckinzie, D. J., Jr.
1972-01-01
Thermal contact conductance test data at high vacuum were obtained from two Armco iron specimens having smooth, large radii of curvature, convex, one-half wave length surfaces. The data are compared with calculations based on two macroscopic elastic deformation theories and an empirical expression. Major disagreement with the theories and fair agreement with the empirical expression resulted. Plastic deformation of all the contacting surfaces was verified from surface analyzer statistics. These results indicate that the theoretical assumption of macroscopic elastic deformation is inadequate for accurate prediction of heat transfer with light loads for Armco iron specimens similar to those used in this investigation.
A Novel Low-Cost, Large Curvature Bend Sensor Based on a Bowden-Cable.
Jeong, Useok; Cho, Kyu-Jin
2016-06-24
Bend sensors have been developed based on conductive ink, optical fiber, and electronic textiles. Each type has advantages and disadvantages in terms of performance, ease of use, and cost. This study proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. This bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable's inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The proposed sensor is not affected by a bend curvature of up to 80.0 m(-1), unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor.
A Novel Low-Cost, Large Curvature Bend Sensor Based on a Bowden-Cable
Jeong, Useok; Cho, Kyu-Jin
2016-01-01
Bend sensors have been developed based on conductive ink, optical fiber, and electronic textiles. Each type has advantages and disadvantages in terms of performance, ease of use, and cost. This study proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. This bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable’s inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The proposed sensor is not affected by a bend curvature of up to 80.0 m−1, unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor. PMID:27347959
A Novel Low-Cost, Large Curvature Bend Sensor Based on a Bowden-Cable.
Jeong, Useok; Cho, Kyu-Jin
2016-01-01
Bend sensors have been developed based on conductive ink, optical fiber, and electronic textiles. Each type has advantages and disadvantages in terms of performance, ease of use, and cost. This study proposes a new and low-cost bend sensor that can measure a wide range of accumulated bend angles with large curvatures. This bend sensor utilizes a Bowden-cable, which consists of a coil sheath and an inner wire. Displacement changes of the Bowden-cable's inner wire, when the shape of the sheath changes, have been considered to be a position error in previous studies. However, this study takes advantage of this position error to detect the bend angle of the sheath. The bend angle of the sensor can be calculated from the displacement measurement of the sensing wire using a Hall-effect sensor or a potentiometer. Simulations and experiments have shown that the accumulated bend angle of the sensor is linearly related to the sensor signal, with an R-square value up to 0.9969 and a root mean square error of 2% of the full sensing range. The proposed sensor is not affected by a bend curvature of up to 80.0 m(-1), unlike previous bend sensors. The proposed sensor is expected to be useful for various applications, including motion capture devices, wearable robots, surgical devices, or generally any device that requires an affordable and low-cost bend sensor. PMID:27347959
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.
GUVs melt like LUVs: the large heat capacity of MLVs is not due to large size or small curvature.
Kreutzberger, Mark A; Tejada, Emmanuel; Wang, Ying; Almeida, Paulo F
2015-06-01
The excess heat capacity functions (ΔCp) associated with the main phase transition of large unilamellar vesicles (LUVs) and multilamellar vesicles (MLVs) are very different. Two explanations are possible. First, the difference in vesicle size (curvature) results in different gel-fluid interactions in the membrane; those interactions have a large effect on the cooperativity of the phase transition. Second, there is communication between the bilayers in an MLV when they undergo the gel-fluid transition; this communication results in thermodynamic coupling of the phase transitions of the bilayers in the MLV and, consequently, in an apparent increase in the cooperativity of the transition. To test these hypotheses, differential scanning calorimetry was performed on giant unilamellar vesicles (GUVs) of pure dipalmitoylphosphatidylcholine. The ΔCp curve of GUVs was found to resemble that of the much smaller LUVs. The transition in GUVs and LUVs is much broader (half-width ∼1.5°C) than in MLVs (∼0.1°C). This similarity in GUVs and LUVs indicates that their size has little effect on gel-fluid interactions in the phase transition. The result suggests that coupling between the transitions in the bilayers of an MLV is responsible for their apparent higher cooperativity in melting.
NASA Astrophysics Data System (ADS)
Zhao, Hui; Fan, Xuewu; Pang, Zhihai; Ren, Guorui; Wang, Wei; Xie, Yongjie; Ma, Zhen; Du, Yunfei; Su, Yu; Wei, Jingxuan; Xie, Xiaopeng
2014-11-01
The key to realize non-moving-element optical zooming lies in VCM (variable curvature mirror). In order to obtain a large optical magnification, VCM should be capable of providing a large center deflection and this requires that the mirror material should be robust enough, require less force to deform and have a high ultimate strength. In this paper, CFRP (carbon-fiber-reinforced-polymer) is selected as the mirror material and a prototype VCM has been fabricated. With diameter of 100mm, thickness of 2mm and initial curvature radius of 1740mm, this VCM can provide a center deflection approaching nearly 23um, which proves the feasibility of CFRP in constructing VCM. Compared with the work reported in [Proc. of SPIE, 8725, 87250W, 2013], the center deflection obtained here becomes even larger.
Large-eddy simulation of turbulent circular jet flows
Jones, S. C.; Sotiropoulos, F.; Sale, M. J.
2002-07-01
This report presents a numerical method for carrying out large-eddy simulations (LES) of turbulent free shear flows and an application of a method to simulate the flow generated by a nozzle discharging into a stagnant reservoir. The objective of the study was to elucidate the complex features of the instantaneous flow field to help interpret the results of recent biological experiments in which live fish were exposed to the jet shear zone. The fish-jet experiments were conducted at the Pacific Northwest National Laboratory (PNNL) under the auspices of the U.S. Department of Energy’s Advanced Hydropower Turbine Systems program. The experiments were designed to establish critical thresholds of shear and turbulence-induced loads to guide the development of innovative, fish-friendly hydropower turbine designs.
Circularity measuring system: A shape gauge designed especially for use on large objects
NASA Technical Reports Server (NTRS)
Rohrkaste, G. R.
1990-01-01
The Circularity Measuring System (CMS) was developed to make an in-situ determination of shape similarity for selected fit large cylinders (RSRM segments). It does this to a repeatable accuracy of 0.10 mm (0.004 inch). This is less that the goal of 0.07 mm (0.003 inch), but was determined adequate because of the addition of an assembly aid that increased the entry chamfer of the clevis side of the joint. The usefulness of the CMS is demonstrated by the application to measurements other than its specified design purpose, such as submarine hull circularity, SRM mid-case circularity, as well as circularity of interfacing SRM tooling, specifically the rounding devices and horizontal disassembly devices. Commercialization of the tool is being pursued, since it is an enhancement of metrology technology for circularity determination. The most accurate in-situ technology it replaces is determined from a template. The CMS is an improvement in accuracy and operation.
Experimental study of noise emitted by circular cylinders with large roughness
NASA Astrophysics Data System (ADS)
Alomar, Antoni; Angland, David; Zhang, Xin; Molin, Nicolas
2014-12-01
The aerodynamic noise generated by high Reynolds number flow around a bluff body with large surface roughness was investigated. This is a relevant problem in many applications, in particular aircraft landing gear noise. A circular cylinder in cross-flow and a zero-pressure-gradient turbulent boundary layer with various types of roughness was tested in a series of wind tunnel experiments. It has been shown that distributed roughness covering a circular cylinder affects the spectra over the entire frequency range. Roughness noise is dominant at high frequencies, and the peak frequency is well described by Howe's roughness noise model when scaled with the maximum outer velocity. There are differences between hemispherical and cylindrical roughness elements for both the circular cylinder and the zero-pressure-gradient turbulent boundary layer cases, indicating a dependence on roughness shape, not described by the considered roughness noise models. Cylindrical roughness generates higher noise levels at the highest frequencies, especially for the zero-pressure-gradient turbulent boundary layer case. Cable-type roughness aligned with the mean flow does not generate roughness noise, and its spectrum has been found to collapse with the smooth cylinder at medium and high frequencies. At low and medium frequencies the noise spectra have the same features as the smooth cylinder, but with higher shedding peak levels and fall-off levels, despite the decrease in spanwise correlation length. Roughness induces early separation, and thus a shift of the spectra to lower frequencies.
NASA Astrophysics Data System (ADS)
Serra, E.; Bawaj, M.; Borrielli, A.; Di Giuseppe, G.; Forte, S.; Kralj, N.; Malossi, N.; Marconi, L.; Marin, F.; Marino, F.; Morana, B.; Natali, R.; Pandraud, G.; Pontin, A.; Prodi, G. A.; Rossi, M.; Sarro, P. M.; Vitali, D.; Bonaldi, M.
2016-06-01
In view of the integration of membrane resonators with more complex MEMS structures, we developed a general fabrication procedure for circular shape SiNx membranes using Deep Reactive Ion Etching (DRIE). Large area and high-stress SiNx membranes were fabricated and used as optomechanical resonators in a Michelson interferometer, where Q values up to 1.3 × 106 were measured at cryogenic temperatures, and in a Fabry-Pérot cavity, where an optical finesse up to 50000 has been observed.
Nayak, Ajaya K.; Fischer, Julia Erika; Sun, Yan; Yan, Binghai; Karel, Julie; Komarek, Alexander C.; Shekhar, Chandra; Kumar, Nitesh; Schnelle, Walter; Kübler, Jürgen; Felser, Claudia; Parkin, Stuart S. P.
2016-01-01
It is well established that the anomalous Hall effect displayed by a ferromagnet scales with its magnetization. Therefore, an antiferromagnet that has no net magnetization should exhibit no anomalous Hall effect. We show that the noncolinear triangular antiferromagnet Mn3Ge exhibits a large anomalous Hall effect comparable to that of ferromagnetic metals; the magnitude of the anomalous conductivity is ~500 (ohm·cm)−1 at 2 K and ~50 (ohm·cm)−1 at room temperature. The angular dependence of the anomalous Hall effect measurements confirms that the small residual in-plane magnetic moment has no role in the observed effect except to control the chirality of the spin triangular structure. Our theoretical calculations demonstrate that the large anomalous Hall effect in Mn3Ge originates from a nonvanishing Berry curvature that arises from the chiral spin structure, and that also results in a large spin Hall effect of 1100 (ħ/e) (ohm·cm)−1, comparable to that of platinum. The present results pave the way toward the realization of room temperature antiferromagnetic spintronics and spin Hall effect–based data storage devices. PMID:27152355
Nayak, Ajaya K; Fischer, Julia Erika; Sun, Yan; Yan, Binghai; Karel, Julie; Komarek, Alexander C; Shekhar, Chandra; Kumar, Nitesh; Schnelle, Walter; Kübler, Jürgen; Felser, Claudia; Parkin, Stuart S P
2016-04-01
It is well established that the anomalous Hall effect displayed by a ferromagnet scales with its magnetization. Therefore, an antiferromagnet that has no net magnetization should exhibit no anomalous Hall effect. We show that the noncolinear triangular antiferromagnet Mn3Ge exhibits a large anomalous Hall effect comparable to that of ferromagnetic metals; the magnitude of the anomalous conductivity is ~500 (ohm·cm)(-1) at 2 K and ~50 (ohm·cm)(-1) at room temperature. The angular dependence of the anomalous Hall effect measurements confirms that the small residual in-plane magnetic moment has no role in the observed effect except to control the chirality of the spin triangular structure. Our theoretical calculations demonstrate that the large anomalous Hall effect in Mn3Ge originates from a nonvanishing Berry curvature that arises from the chiral spin structure, and that also results in a large spin Hall effect of 1100 (ħ/e) (ohm·cm)(-1), comparable to that of platinum. The present results pave the way toward the realization of room temperature antiferromagnetic spintronics and spin Hall effect-based data storage devices.
Nayak, Ajaya K; Fischer, Julia Erika; Sun, Yan; Yan, Binghai; Karel, Julie; Komarek, Alexander C; Shekhar, Chandra; Kumar, Nitesh; Schnelle, Walter; Kübler, Jürgen; Felser, Claudia; Parkin, Stuart S P
2016-04-01
It is well established that the anomalous Hall effect displayed by a ferromagnet scales with its magnetization. Therefore, an antiferromagnet that has no net magnetization should exhibit no anomalous Hall effect. We show that the noncolinear triangular antiferromagnet Mn3Ge exhibits a large anomalous Hall effect comparable to that of ferromagnetic metals; the magnitude of the anomalous conductivity is ~500 (ohm·cm)(-1) at 2 K and ~50 (ohm·cm)(-1) at room temperature. The angular dependence of the anomalous Hall effect measurements confirms that the small residual in-plane magnetic moment has no role in the observed effect except to control the chirality of the spin triangular structure. Our theoretical calculations demonstrate that the large anomalous Hall effect in Mn3Ge originates from a nonvanishing Berry curvature that arises from the chiral spin structure, and that also results in a large spin Hall effect of 1100 (ħ/e) (ohm·cm)(-1), comparable to that of platinum. The present results pave the way toward the realization of room temperature antiferromagnetic spintronics and spin Hall effect-based data storage devices. PMID:27152355
Jose, K V Jovan; Beckett, Daniel; Raghavachari, Krishnan
2015-09-01
We present the first implementation of the vibrational circular dichroism (VCD) spectrum of large molecules through the Molecules-in-Molecules (MIM) fragment-based method. An efficient projection of the relevant higher energy derivatives from smaller fragments to the parent molecule enables the extension of the MIM method for the evaluation of VCD spectra (MIM-VCD). The overlapping primary subsystems in this work are constructed from interacting fragments using a number-based scheme and the dangling bonds are saturated with link hydrogen atoms. Independent fragment calculations are performed to evaluate the energies, Hessian matrix, atomic polar tensor (APT), and the atomic axial tensor (AAT). Subsequently, the link atom tensor components are projected back onto the corresponding host and supporting atoms through the Jacobian projection method, as in the ONIOM approach. In the two-layer model, the long-range interactions between fragments are accounted for using a less computationally intensive lower level of theory. The performance of the MIM model is calibrated on the d- and l-enantiomers of 10 carbohydrate benchmark molecules, with strong intramolecular interactions. The vibrational frequencies and VCD intensities are accurately reproduced relative to the full, unfragmented, results for these systems. In addition, the MIM-VCD method is employed to predict the VCD spectra of perhydrotriphenylene and cryptophane-A, yielding spectra in agreement with experiment. The accuracy and performance of the benchmark systems validate the MIM-VCD model for exploring vibrational circular dichroism spectra of large molecules.
NASA Astrophysics Data System (ADS)
Booshehri, L. G.; Mielke, C. H.; Rickel, D. G.; Crooker, S. A.; Zhang, Q.; Ren, L.; Hároz, E. H.; Rustagi, A.; Stanton, C. J.; Jin, Z.; Sun, Z.; Yan, Z.; Tour, J. M.; Kono, J.
2012-05-01
Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 μm, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong p-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still p-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples.
Yang, Zhongming; Wang, Kailiang; Cheng, Jinlong; Gao, Zhishan; Yuan, Qun
2016-06-10
We have proposed a virtual quadratic Newton rings phase-shifting moiré-fringes measurement method in a nonnull interferometer to measure the large radius of curvature for a spherical surface. In a quadratic polar coordinate system, linear carrier testing Newton rings interferogram and virtual Newton rings interferogram form the moiré fringes. It is possible to retrieve the wavefront difference data between the testing and standard spherical surface from the moiré fringes after low-pass filtering. Based on the wavefront difference data, we deduced a precise formula to calculate the radius of curvature in the quadratic polar coordinate system. We calculated the retrace error in the nonnull interferometer using the multi-configuration model of the nonnull interferometric system in ZEMAX. Our experimental results indicate that the measurement accuracy is better than 0.18% for a spherical mirror with a radius of curvature of 41,400 mm.
Post Main Sequence Orbital Circularization of Binary Stars in the Large and Small Magellanic Clouds.
Faccioli, L; Alcock, C; Cook, K
2007-11-20
We present results from a study of the orbits of eclipsing binary stars (EBs) in the Magellanic Clouds. The samples comprise 4510 EBs found in the Large Magellanic Cloud (LMC) by the MACHO project, 2474 LMC EBs found by the OGLE-II project (of which 1182 are also in the MACHO sample), 1380 in the Small Magellanic Cloud (SMC) found by the MACHO project, and 1317 SMC EBs found by the OGLE-II project (of which 677 are also in the MACHO sample); we also consider the EROS sample of 79 EBs in the bar of the LMC. Statistics of the phase differences between primary and secondary minima allow us to infer the statistics of orbital eccentricities within these samples. We confirm the well-known absence of eccentric orbit in close binary stars. We also find evidence for rapid circularization in longer period systems when one member evolves beyond the main sequence, as also found by previous studies.
Null reconstruction of orthogonal circular polarization hologram with large recording angle.
Wu, An'an; Kang, Guoguo; Zang, Jinliang; Liu, Ying; Tan, Xiaodi; Shimura, Tsutomu; Kuroda, Kazuo
2015-04-01
We report on the null reconstruction of polarization volume hologram recorded by orthogonal circularly polarized waves with a large cross angle. Based on the recently developed tensor theory for polarization holography, the disappearance of the reconstruction was analytically verified, where a nice agreement was found between the experimental and theoretical results. When the polarization and intensity hologram attain a balance, not only the null reconstruction but also the faithful reconstruction can be realized by the illumination of the orthogonal reference wave and original reference wave. As a consequence of the hologram recorded without paraxial approximation, the null reconstruction may lead to important applications, such as a potential enhancement in optical storage capacity for volume holograms.
Nonlinear evolution of a large-amplitude circularly polarized Alfven wave: High beta
NASA Technical Reports Server (NTRS)
Ghosh, S.; Vinas, A. F.; Goldstein, M. L.
1994-01-01
The nonlinear dynamics following saturation of the parametric instabilities of a monochromatic field-aligned large-amplitude circularly polarized Alfven wave is investigated via direct numerical simulation in the case of high plasma beta and no wave dispersion. The magnetohydrodynamic (MHD) code permits nonlinear couplings in the parallel direction to the ambient magnetic field and one perpendicular direction. Compressibility is included in the form of a polytropic equation of state. Turbulent cascades develop after saturation of two coupled oblique three-wave parametric instabilities; one of which is an oblique filamentationlike instability reported earlier. Remnants of the parametric processes, as well as of the original Alfven pump wave, persist during late nonlinear times. Nearly incompressible MHD features such as spectral anisotropies appear as well.
Nonlinear evolution of a large-amplitude circularly polarized Alfven wave: Low beta
NASA Technical Reports Server (NTRS)
Ghosh, S.; Goldstein, M. L.
1994-01-01
The nature of turbulent cascades arising from the parametric instabilities of a monochromatic field-aligned large-amplitude circularly polarized Alfven wave is investigated via direct numerical simulation for the case of low plasma Beta and no wave dispersion. The magnetohydrodynamic code permits nonlinear couplings in the parallel direction to the ambient magnetic field and one perpendicular direction. Compressibility is included in the form of a polytropic equation of state. Anisotropic turbulent cascades, similar to those found in early incompressible two-dimensional simulations, occur after nonlinear saturation of the parallel propagating decay instability. The turbulent spectrum can be divided into three regimes: the lowest wave numbers are dominated by lower sideband remnants of the parametric process, intermediate wave numbers display nearly incompressible dynamics, and the highest wave numbers are dominated by acoustic turbulence.
Qin, H.; Reiman, A.
1996-09-25
An analytic solution is obtained for free-boundary, high-beta equilibria in large aspect ratio tokamaks with a nearly circular plasma boundary. In the absence of surface currents at the plasma-vacuum interface, the free-boundary equilibrium solution introduces constraints arising from the need to couple to an external vacuum field which is physically realizable with a reasonable set of external field coils. This places a strong constraint on the pressure profiles that are consistent with a given boundary shape at high {epsilon}{beta}{sub p}. The equilibrium solution also provides information on the flux surface topology. The plasma is bounded by a separatrix. Increasing the plasma pressure at fixed total current causes the plasma aperture to decrease in a manner that is described.
Technology Transfer Automated Retrieval System (TEKTRAN)
A survey was conducted to determine the geometry, operating parameters, and other key features of large circular or octagonal culture tanks used to produce Atlantic salmon smolt and post-smolt at six major Norwegian Atlantic salmon production companies. A total of 55 large tanks were reported at sev...
Fabrication of a microarray using a combination of the large circular sense and antisense DNA.
Doh, Kyung-Oh; Lee, Yun-Han; Han, Kil-Hwan; Uhm, Seok-Yong; Kim, Jong-Pil; Bae, Yun-Ui; Park, Jeong-Hoh; Moon, Ik-Jae; Park, Jong-Gu
2010-01-01
In the present study, single-stranded large circular (LC)-sense molecules were utilized as probes for DNA microarrays and showed stronger binding signals than those of PCR-amplified cDNA probes. A microarray experiment using 284 LC-sense DNA probes found 6 upregulated and 7 downregulated genes in A549 cells as compared to WI38VA13 cells. Repeated experiments showed largely consistent results, and microarray data strongly correlated with data acquired from quantitative real-time RT-PCR. A large array comprising 5,079 LC-sense DNA was prepared, and analysis of the mean differential expression from dye-swap experiments revealed 332 upregulated and 509 downregulated genes in A549 cells compared to WI38VA13 cells. Subsequent functional analysis using an LC-antisense library of overexpressed genes identified 28 genes involved in A549 cell growth. These experiments demonstrated the proper features of LC-sense molecules as probe DNA for microarray and the potential utility of the combination of LC-sense and -antisense libraries for an effective functional validation of genes.
An experimental approach to measure particle deposition in large circular ventilation ducts.
Da, Guillaume; Géhin, Evelyne; Ben-Othmane, Mourad; Havet, Michel; Solliec, Camille; Motzkus, Charles
2015-04-01
The topic of this study is related to airborne particle dynamics in indoor environments. Lab-scale experiments have been performed to investigate particle deposition velocity to six different surfaces orientations (with respect to gravity) for fully developed turbulent flow in horizontal large circular ventilation ducts. Monodispersed aerosol particles (1-6 μm) were used in the deposition experiments. A very low particle mass (40 ng) was measured reliably above background level on duct surfaces by a means of a nondestructive stencil technique associated with fluorescence analysis. For 2-6 μm particles (diffusion and impaction regime), deposition rates to floors were much greater than rates to the ceiling and greater than rates to the wall. For 1-μm particles, the effect of surface orientation to particle deposition was not significant. Results were compared to the very few similar and published studies. This work was conducted in the frame of the CleanAirNet project which aimed at producing new knowledge, models, and techniques to help controlling the safety food stuffs, through a better control of aerosol particle (bioaerosols) transport and deposition in the ventilation networks of the food industry. PMID:24756675
Psi-type circular dichroism of large molecular aggregates. III. Calculations
Kim, M.; Ulibarri, L.; Keller, D.; Maestre, M.F.; Bustamante, C.
1986-03-15
Computations have been carried out to determine how the magnitude and shape of the polymer and salt induced (psi)-type CD spectra depend on the structural properties of a collection of randomly oriented large chiral aggregates. Uniaxial polarizable groups located at the cubic lattice points have been used to model the aggregates. The structure of the model is similar to that of a cholesteric liquid crystal. All computations have been carried out for the case of polarizable groups possessing only one electronic transition between 200 and 320 nm. It is found that the radiation and intermediate couplings between the chromophores in the aggregate which are neglected in previous theories play an important role in determining the shape and magnitude of the psi-type CD spectrum. It is shown that when these couplings are included, only three-dimensional large chiral aggregates show huge and nonconservative psi-type CD spectra. It is shown that the magnitude of the psi-type CD spectrum is controlled by the volume, the chromophore density, and the pitch of the aggregate, while the shape of the psi-type CD spectrum is determined mostly by the pitch and the handedness of an aggregate. When the pitch is close to the center of the absorption band of the chromophore in the aggregate the most distorted (least conservative) psi-type CD spectrum is obtained. The CD spectra of aggregates with opposite handedness are mirror images of each other. It is shown that a rotationally disordered collection of chiral aggregates cannot give rise to a selective reflection of one circular polarization over the other as shown by liquid crystals. The results obtained confirm the theoretical predictions of the two previous papers in this series.
Photo-induced large-scale circular surface-relief diffraction gratings on azo-glass
NASA Astrophysics Data System (ADS)
Leibold, James; Sabat, Ribal Georges
2015-03-01
Novel metallic light-interfering fixtures were designed and fabricated in order to achieve a laser interference pattern of constant-pitch, concentric and sinusoidal light variations. These fixtures consisted of annular rings with the inner diameter shaped conically. Azobenzene-containing solid thin-films were subsequently placed behind the fixture and circular surface-relief diffraction gratings were inscribed due to the azo molecules photochemical isomerization process. Gratings pitches were dependent on the fixture dimensions and ranged from 600 to 1400 nm with depths up to 250 nm.
Analysis of microtubule curvature.
Bicek, Andrew D; Tüzel, Erkan; Kroll, Daniel M; Odde, David J
2007-01-01
The microtubule cytoskeleton in living cells generate and resist mechanical forces to mediate fundamental cell processes, including cell division and migration. Recent advances in digital fluorescence microscopy have enabled the direct observation of bending of individual microtubules in living cells, which has enabled quantitative estimation of the mechanical state of the microtubule array. Although a variety of mechanisms have been proposed, the precise origins of microtubule deformation in living cells remain largely obscure. To investigate these mechanisms and their relative importance in cellular processes, a method is needed to accurately quantify microtubule bending within living cells. Here we describe a method for quantification of bending, using digital fluorescence microscope images to estimate the distribution of curvature in the microtubule. Digital images of individual microtubules can be used to obtain a set of discrete x-y coordinates along the microtubule contour, which is then used to estimate the curvature distribution. Due to system noise and digitization error, the estimate will be inaccurate to some degree. To quantify the inaccuracy, a computational model is used to simulate both the bending of thermally driven microtubules and their observation by digital fluorescence microscopy. This allows for direct comparison between experimental and simulated images, a method which we call model convolution microscopy. We assess the accuracy of various methods and present a suitable method for estimating the curvature distribution for thermally driven semiflexible polymers. Finally, we discuss extensions of the method to quantify microtubule curvature in living cells. PMID:17613311
Distribution of circular proteins in plants: large-scale mapping of cyclotides in the Violaceae
Burman, Robert; Yeshak, Mariamawit Y.; Larsson, Sonny; Craik, David J.; Rosengren, K. Johan; Göransson, Ulf
2015-01-01
During the last decade there has been increasing interest in small circular proteins found in plants of the violet family (Violaceae). These so-called cyclotides consist of a circular chain of approximately 30 amino acids, including six cysteines forming three disulfide bonds, arranged in a cyclic cystine knot (CCK) motif. In this study we map the occurrence and distribution of cyclotides throughout the Violaceae. Plant material was obtained from herbarium sheets containing samples up to 200 years of age. Even the oldest specimens contained cyclotides in the preserved leaves, with no degradation products observable, confirming their place as one of the most stable proteins in nature. Over 200 samples covering 17 of the 23–31 genera in Violaceae were analyzed, and cyclotides were positively identified in 150 species. Each species contained a unique set of between one and 25 cyclotides, with many exclusive to individual plant species. We estimate the number of different cyclotides in the Violaceae to be 5000–25,000, and propose that cyclotides are ubiquitous among all Violaceae species. Twelve new cyclotides from six phylogenetically dispersed genera were sequenced. Furthermore, the first glycosylated derivatives of cyclotides were identified and characterized, further increasing the diversity and complexity of this unique protein family. PMID:26579135
Ståhl, F; Wettergren, Y; Levan, G
1992-01-01
Multidrug resistance (MDR) in tumor cell lines is frequently correlated with amplification of one or more mdr genes. Usually the amplified domain also includes several neighboring genes. Using pulsed-field gel electrophoresis, we have established a restriction map covering approximately 2,200 kb in the drug-sensitive mouse tumor cell line TC13K. The mapped region is located on mouse chromosome 5 and includes the three mdr genes, the gene for the calcium-binding sorcin protein, and a gene with unknown function designated class 5. Long-range maps of the amplified DNA sequences in five of six MDR sublines that had been independently derived from TC13K generally displayed the same pattern as did the parental cell line. All six MDR sublines exhibited numerous double minutes, and one of them displayed a homogeneously staining region in a subpopulation. Large circular molecules, most likely identical to one chromatid of the double minutes, were detected in four of the sublines by linearization with gamma irradiation. The size of the circles was about 2,500 kb, which correlated to a single unit of the amplified domain. We therefore propose that in four independent instances of MDR development, a single unit of about 2,500 kb has been amplified in the form of circular DNA molecules. The restriction enzyme map of the amplified unit is unchanged compared with that of the parental cell line, whereas the joining sites of the circular DNA molecules are not identical but are in the same region. Images PMID:1545798
Crowder/grader units improve harvest efficiency in large circular tanks
Technology Transfer Automated Retrieval System (TEKTRAN)
The use of larger and deeper tanks can reduce building, labor and other aquaculture production costs. However, the ability to grade and transfer large numbers of fish is more challenging when using large tanks. At The Conservation Fund Freshwater Institute, the authors have developed and evaluated i...
Launch window analysis of satellites in high eccentricity or large circular orbits
NASA Technical Reports Server (NTRS)
Renard, M. L.; Bhate, S. K.; Sridharan, R.
1973-01-01
Numerical methods and computer programs for studying the stability and evolution of orbits of large eccentricity are presented. Methods for determining launch windows and target dates are developed. Mathematical models are prepared to analyze the characteristics of specific missions.
NASA Astrophysics Data System (ADS)
Guo, Li; Zhang, Xing; He, Guowei
2016-02-01
The flows past a circular cylinder at Reynolds number 3900 are simulated using large-eddy simulation (LES) and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volume scheme is used to discretize the incompressible Navier-Stokes equations. The dynamic global coefficient version of the Vreman's subgrid scale (SGS) model is used to compute the sub-grid stresses. Curle's integral of Lighthill's acoustic analogy is used to extract the sound radiated from the cylinder. The profiles of mean velocity and turbulent fluctuations obtained are consistent with the previous experimental and computational results. The sound radiation at far field exhibits the characteristic of a dipole and directivity. The sound spectra display the -5/3 power law. It is shown that Vreman's SGS model in company with dynamic procedure is suitable for LES of turbulence generated noise.
Relativistic mergers of black hole binaries have large, similar masses, low spins and are circular
NASA Astrophysics Data System (ADS)
Amaro-Seoane, Pau; Chen, Xian
2016-05-01
Gravitational waves are a prediction of general relativity, and with ground-based detectors now running in their advanced configuration, we will soon be able to measure them directly for the first time. Binaries of stellar-mass black holes are among the most interesting sources for these detectors. Unfortunately, the many different parameters associated with the problem make it difficult to promptly produce a large set of waveforms for the search in the data stream. To reduce the number of templates to develop, one must restrict some of the physical parameters to a certain range of values predicted by either (electromagnetic) observations or theoretical modelling. In this work, we show that `hyperstellar' black holes (HSBs) with masses 30 ≲ MBH/M⊙ ≲ 100, i.e black holes significantly larger than the nominal 10 M⊙, will have an associated low value for the spin, i.e. a < 0.5. We prove that this is true regardless of the formation channel, and that when two HSBs build a binary, each of the spin magnitudes is also low, and the binary members have similar masses. We also address the distribution of the eccentricities of HSB binaries in dense stellar systems using a large suite of three-body scattering experiments that include binary-single interactions and long-lived hierarchical systems with a highly accurate integrator, including relativistic corrections up to O(1/c^5). We find that most sources in the detector band will have nearly zero eccentricities. This correlation between large, similar masses, low spin and low eccentricity will help to accelerate the searches for gravitational-wave signals.
NASA Astrophysics Data System (ADS)
Léonard, J.; Perrier, E.; de Marsily, G.
2001-12-01
This paper reports the development and test, at the scale of 1 m2, of an event- based model that aims at simulating the influence of a spatial distribution of large circular macropores on surface runoff. The main originality of this model is that it focuses on the way macropores are supplied with water at the soil surface, by coupling an original model for water interception by individual macropores to a high-resolution spatialized overland flow model. A three-step evaluation of the model was carried out, involving (1) an experimental test of the model for water interception by macropores; (2) a sensitivity analysis of the model to time and space discretization; and (3) a comparison between numerical and field results in the case of runoff on a crusted soil surface with a population of large macropores made by termites in the Sahel. The model was found to accurately simulate the effect of a spatial distribution of large macropores on runoff, and it showed that small heterogeneities, like macropores or areas where a crust has been destroyed, which cover a very limited proportion of the soil surface, can have a high impact on runoff.
NASA Astrophysics Data System (ADS)
Isaev, S. A.; Kalinin, E. I.; Tereshkin, A. A.; Usachov, A. E.
2015-03-01
The Reynolds equations for incompressible viscous fluid, closed using the Menter shear-stress-transfer model modified with allowance for the curvature of flow lines, have been numerically solved using multiblock computational technologies. The obtained solution has been used to calculate the turbulent flow in a U-bend channel containing a circular cavern with a variable opening angle. Predictions based on the results of numerical simulations agree well with the experimental data of Savelsberg and Castro at moderate cavern opening angles. It is established that hydraulic losses in a U-bend channel with completely open cavern are significantly (by ˜25%) decreased as compared to those in a smooth channel at Re = 105.
NASA Technical Reports Server (NTRS)
Lee, M. A.; Lerche, I.
1978-01-01
It is demonstrated that a self-consistent circularly polarized wave in an otherwise field-free homogeneous cold plasma is unstable to small amplitude perturbations. For either an electron-positron plasma or an electron-proton plasma the instability rate is at least about the order of the effective plasma frequency when the bulk flow speed is zero. For finite bulk flow speeds of the plasma, it is shown that the electron-positron plasma is unstable, again with a growth rate of the order of the effective plasma frequency; it is also shown that the electron-proton plasma is unstable (at least at small wave numbers, k) with a growth rate proportional to k. The calculated instability rates are conservative, for other modes not investigated here may be more unstable. The results of these calculations bear directly on the understanding of plasma systems thought to be driven by large amplitude waves.
Robust, angstrom level circularity profilometry
NASA Technical Reports Server (NTRS)
Glenn, Paul
1990-01-01
A noncontacting approach is presented which involves measuring the local circumferential curvature of the test piece by simultaneously measuring its circumferential slope at two slightly displaced locations. A pair of sensing beams is scanned along the circumference, and a profile of curvature is built, from which the circularity profile is deduced. The sensing of curvature makes the approach insensitive to all types of vibration and drift and runout errors in the relative rotation. The special qualities of the approach are summarized which make it well suited to measuring cylindrical optics and enable it to accommodate radii as small as twenty millimeters.
Characterization of Circular RNAs.
Zhang, Yang; Yang, Li; Chen, Ling-Ling
2016-01-01
Accumulated lines of evidence reveal that a large number of circular RNAs are produced in transcriptomes from fruit fly to mouse and human. Unlike linear RNAs shaped with 5' cap and 3' tail, circular RNAs are characterized by covalently closed loop structures without open terminals, thus requiring specific treatments for their identification and validation. Here, we describe a detailed pipeline for the characterization of circular RNAs. It has been successfully applied to the study of circular intronic RNAs derived from intron lariats (ciRNAs) and circular RNAs produced from back spliced exons (circRNAs) in human. PMID:26721494
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.
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.
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.
NASA Technical Reports Server (NTRS)
Rosu, Grigore; Goguen, Joseph; Norvig, Peter (Technical Monitor)
2001-01-01
Circular coinduction is a technique for behavioral reasoning that extends cobasis coinduction to specifications with circularities. Because behavioral satisfaction is not recursively enumerable, no algorithm can work for every behavioral statement. However. algorithms using circular coinduction can prove every practical behavioral result that we know. This paper proves the correctness of circular coinduction and some consequences.
Spatial curvature, spacetime curvature, and gravity
NASA Astrophysics Data System (ADS)
Price, Richard H.
2016-08-01
The belief that curved spacetime gravity cannot be simply and correctly presented results in such misleading presentations as elastic two-dimensional sheets deformed as they support heavy objects. This article attempts to show that the conceptual basis of curved spacetime gravity can be simply and correctly presented, and that the spatial curvature of a deformed elastic sheet is very different from the spacetime curvature underlying gravity. This article introduces the idea of a "splittable" spacetime that has spatial curvature, but is missing most of the manifestations of gravity. A section in which no mathematics is used is directed at students who have studied no more than introductory physics. A separate section, for students who have taken only an introductory course in general relativity, gives mathematical arguments centering on splittable spacetimes.
NASA Astrophysics Data System (ADS)
Raybould, T. A.; Fedotov, V. A.; Papasimakis, N.; Kuprov, I.; Youngs, I. J.; Chen, W. T.; Tsai, D. P.; Zheludev, N. I.
2016-07-01
We demonstrate that the induced toroidal dipole, represented by currents flowing on the surface of a torus, makes a distinct and indispensable contribution to circular dichroism. We show that toroidal circular dichroism supplements the well-known mechanism involving electric dipole and magnetic dipole transitions. We illustrate this with rigorous analysis of the experimentally measured polarization-sensitive transmission spectra of an artificial metamaterial, constructed from elements of toroidal symmetry. We argue that toroidal circular dichroism will be found in large biomolecules with elements of toroidal symmetry and should be taken into account in the interpretation of circular dichroism spectra of organics.
Intrinsic versus imposed curvature in cyclical oligomers: the portal protein of bacteriophage SPP1.
van Heel, M; Orlova, E V; Dube, P; Tavares, P
1996-01-01
Large cyclical oligomers may be formed by (curvi-) linear polymerization of monomers until the n(th) monomer locks in with the first member of the chain. The subunits in incomplete structures exhibit a natural curvature with respect to each other which can be perturbed when the oligomer closes cyclically. Using cryo-electron microscopy and multivariate statistical image processing we report herein a direct structural observation of this effect. A sub-population (approximately 15%) of incomplete oligomers was found within a sample of SPP1 bacteriophage portal proteins embedded in vitreous ice. Whereas the curvature between adjacent subunits of the closed circular 13-fold symmetric oligomer is 27.7 degrees, in these incomplete oligomers the angle is only 25.8 degrees, a value which almost allows for a 14-subunit cyclical arrangement. A simple model for the association of large cyclical oligomers is suggested by our data. Images PMID:8890151
Remya, B.; Reddy, R. V.; Lakhina, G. S.; Tsurutani, B. T.; Falkowski, B. J.; Echer, E.; Glassmeier, K.-H.
2014-09-20
During 1999 August 18, both Cassini and WIND were in the Earth's magnetosheath and detected transverse electromagnetic waves instead of the more typical mirror-mode emissions. The Cassini wave amplitudes were as large as ∼14 nT (peak to peak) in a ∼55 nT ambient magnetic field B {sub 0}. A new method of analysis is applied to study these waves. The general wave characteristics found were as follows. They were left-hand polarized and had frequencies in the spacecraft frame (f {sub scf}) below the proton cyclotron frequency (f{sub p} ). Waves that were either right-hand polarized or had f {sub scf} > f{sub p} are shown to be consistent with Doppler-shifted left-hand waves with frequencies in the plasma frame f{sub pf} < f{sub p} . Thus, almost all waves studied are consistent with their being electromagnetic proton cyclotron waves. Most of the waves (∼55%) were found to be propagating along B {sub 0} (θ{sub kB{sub 0}}<30{sup ∘}), as expected from theory. However, a significant fraction of the waves were found to be propagating oblique to B {sub 0}. These waves were also circularly polarized. This feature and the compressive ([B {sub max} – B {sub min}]/B {sub max}, where B {sub max} and B {sub min} are the maximum and minimum field magnitudes) nature (ranging from 0.27 to 1.0) of the waves are noted but not well understood at this time. The proton cyclotron waves were shown to be quasi-coherent, theoretically allowing for rapid pitch-angle transport of resonant protons. Because Cassini traversed the entire subsolar magnetosheath and WIND was in the dusk-side flank of the magnetosheath, it is surmised that the entire region was filled with these waves. In agreement with past theory, it was the exceptionally low plasma β (0.35) that led to the dominance of the proton cyclotron wave generation during this interval. A high-speed solar wind stream ((V{sub sw} ) = 598 km s{sup –1}) was the source of this low-β plasma.
Magnetic curvature effects on plasma interchange turbulence
NASA Astrophysics Data System (ADS)
Li, B.; Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-01
The magnetic curvature effects on plasma interchange turbulence and transport in the Z-pinch and dipole-like systems are explored with two-fluid global simulations. By comparing the transport levels in the systems with a different magnetic curvature, we show that the interchange-mode driven transport strongly depends on the magnetic geometry. For the system with large magnetic curvature, the pressure and density profiles are strongly peaked in a marginally stable state and the nonlinear evolution of interchange modes produces the global convective cells in the azimuthal direction, which lead to the low level of turbulent convective transport.
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).
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.}
Diffraction with wavefront curvature
NASA Astrophysics Data System (ADS)
Nugent, K. A.; Peele, A. G.; Quiney, H. M.; Chapman, H. N.
2005-05-01
Modern X-ray optics can produce a focused synchrotron beam with curvature on a scale comparable to that of an isolated biomolecule or to the lattice spacing of a biomolecular crystal. It is demonstrated that diffraction of phase-curved beams from such systems allows unique and robust phase recovery.
Curvature calculations with GEOCALC
Moussiaux, A.; Tombal, P.
1987-04-01
A new method for calculating the curvature tensor has been recently proposed by D. Hestenes. This method is a particular application of geometric calculus, which has been implemented in an algebraic programming language on the form of a package called GEOCALC. They show how to apply this package to the Schwarzchild case and they discuss the different results.
Kuller, L H
1999-11-01
Circular epidemiology can be defined as the continuation of specific types of epidemiologic studies beyond the point of reasonable doubt of the true existence of an important association or the absence of such an association. Circular epidemiology is an extreme example of studies of the consistency of associations. A basic problem for epidemiology is the lack of a systematic approach to acquiring new knowledge to reach a goal of improving public health and preventive medicine. For epidemiologists, research support unfortunately is biased toward the continued study of already proven hypotheses. Circular epidemiology, however, freezes at one point in the evolution of epidemiologic studies, failing to move from descriptive to analytical case-control and longitudinal studies, for example, to experimental, clinical trials. Good epidemiology journals are filled with very well-conducted epidemiologic studies that primarily repeat the obvious or are variations on the theme.
NASA Astrophysics Data System (ADS)
Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji
2013-09-01
Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.
Photon Drag Effect due to Berry Curvature
NASA Astrophysics Data System (ADS)
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-01
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results.
Photon Drag Effect due to Berry Curvature.
Kurosawa, Hiroyuki; Sawada, Kei; Ohno, Seigo
2016-08-19
A theoretical investigation reveals that the photon drag effect (PDE) is induced in a grating slab with deformation by the Berry curvature in phase space. It drifts the momentum of light, and gives asymmetric PDE signals in momentum space. Large PDE signals are observed even near the Γ point. This characteristic agrees well with our theoretical results. PMID:27588858
Variable-curvature mirrors for the VLTI
NASA Astrophysics Data System (ADS)
Ferrari, Marc; Derie, Frederic
1998-07-01
A variable curvature mirror is a powerful device that can increase the field of view of optical interferometers. Such a mirror has being developed for the coherent combined focus of the European Southern Observatory Very Large Telescope Interferometer. The variable focal length permits positioning of the pupil image of an individual telescope at a precise location after the delay-line. This property is necessary to exactly remap homothetically the output pupil configuration at the image beam combiner. Given the large zoom range that is needed in the delay line, when the mirror is not stressed the optical surface is a plane while it is convex with f/2.5 at maximum stress. The mirror itself is a very small stainless steel meniscus, with a 300 micrometers thickness, because only the high elasticity of such material allows to achieve the full domain of curvature. The thickness distribution of the meniscus is calculated using elasticity theory in the case of a large deformation. The realization of this micro-optic active device requires advanced techniques in optical fabrication and in particular high precision manufacturing with numerical command lathe. This article also presents the testing of this highly variable curvature mirror and the surface quality obtained within the full curvature range.
NASA Astrophysics Data System (ADS)
Semenova, E. K.; Montoncello, F.; Tacchi, S.; Dürr, G.; Sirotkin, E.; Ahmad, E.; Madami, M.; Gubbiotti, G.; Neusser, S.; Grundler, D.; Ogrin, F. Y.; Hicken, R. J.; Kruglyak, V. V.; Berkov, D. V.; Gorn, N. L.; Giovannini, L.
2013-05-01
We report a combined experimental and theoretical study of the quasistatic hysteresis and dynamic excitations in large-area arrays of NiFe nanodisks forming a hexagonal lattice with the lattice constant of 390 nm. Arrays were fabricated by patterning a 20-nm-thick NiFe film using the etched nanosphere lithography. We have studied a close-packed (edge-to-edge separation between disks dcp = 65 nm) and an ultraclosed packed (ducp = 20 nm) array. Hysteresis loops for both arrays were qualitatively similar and nearly isotropic, i.e., independent on the in-plane external field orientation. The shape of these loops revealed that magnetization reversal is governed by the formation and expulsion of vortices inside the nanodisks. When we assumed that the nanodisks’ magnetization significantly decreases near their edges, micromagnetic simulations with material parameters deter-mined independently from continuous film measu-rements could satisfactorily reproduce the hysteresis. Despite the isotropic hysteresis, significant in-plane anisotropy of the dynamic response of the ultraclose-packed array was found experimentally by the all-electrical spin-wave spectroscopy and Brillouin light scattering. Dynamical simulations could successfully reproduce the difference between excitation spectra for fields directed along the two main symmetry axes of the hexagonal lattice. Simulations revealed that this difference is caused by the magnetodipolar interaction between nanodisks, which leads to a strong variation of the spatial distribution of the oscillation power both for bulk and edge modes as a function of the bias field orientation. Comparison of simulated and measured frequencies enabled the unambiguous identification of experimentally observed modes. Results of this systematic research are relevant both for fundamental studies of spin-wave modes in patterned magnetic structures and for the design of magnonic crystals for potential applications as, e.g., spin-wave guides and
Complete manifolds with bounded curvature and spectral gaps
NASA Astrophysics Data System (ADS)
Schoen, Richard; Tran, Hung
2016-08-01
We study the spectrum of complete noncompact manifolds with bounded curvature and positive injectivity radius. We give general conditions which imply that their essential spectrum has an arbitrarily large finite number of gaps. In particular, for any noncompact covering of a compact manifold, there is a metric on the base so that the lifted metric has an arbitrarily large finite number of gaps in its essential spectrum. Also, for any complete noncompact manifold with bounded curvature and positive injectivity radius we construct a metric uniformly equivalent to the given one (also of bounded curvature and positive injectivity radius) with an arbitrarily large finite number of gaps in its essential spectrum.
Anisotropic cubic curvature couplings
NASA Astrophysics Data System (ADS)
Bailey, Quentin G.
2016-09-01
To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass-dimension-eight coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the weak equivalence principle for self-gravitating bodies. These coefficients can be measured in Solar-System tests, while binary-pulsar systems and short-range gravity tests are particularly sensitive.
Aithal, H P; Singh, G R; Hoque, M; Maiti, S K; Kinjavdekar, P; Pawde, A M; Setia, H C
2004-08-01
The study was undertaken to evaluate the feasibility of a simple, inexpensive model of circular external fixator (CEF) for use in large ruminants. A simple model of CEF frames consisting of four full rings (13-19 cm diameter, 4 cm wide and 4 mm thick with 18-24 holes) connected by threaded rods (8 mm diameter, 10-15 cm long) and nuts was developed using mild (low carbon) steel and were nickel-plated. In the first phase of the study, three male cow calves were utilized to study the feasibility of application of the fixators in the metatarsus, tibia and radius, in reference of adaptation and tolerance by animals. In the second phase, the fixators were tested in osteotomized bones. Six bull calves of 1.5-2 years of age weighing about 200-250 kg were utilized for this purpose. After preparing the area for aseptic surgery, under xylazine (at 0.1 mg/kg, i.m.)-ketamine (i.v. till effect) general anaesthesia, the test bone (metatarsus, radius and tibia in two animals each) was approached through the medial surface and an osteotomy was created with a saw and chisel at the mid-diaphysis. The pre-constructed 4-ring CEF was mounted on the limb around the test bone in such a way that it formed a cylinder with the axis of the limb at the centre. Each ring was then fixed to the bone with a pair of beaded wires (316 SS) of 3.5 mm diameter. During the post-operative period, the animals were observed for any change in behaviour, tolerance of the fixators, the weight bearing on the test limb, the status of the fixator, and the level of reduction of the osteotomy, alignment and healing at different intervals. The fixation of CEF was easier in the metatarsus and radius than in the tibia. The inner ring diameters found adequate for metatarsus, radius and tibia were 13-15 cm, 15-17 cm and 17-19 cm, respectively. The fixators applied to different bones were well-tolerated, and the animals could lay down, stand and walk freely with the fixator without any problems. All the animals showed
NASA Astrophysics Data System (ADS)
Smellie, J. L.; Walker, A. J.; McGarvie, D. W.; Burgess, R.
2016-08-01
Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial infilling and reworking, and erosion of the outcrop to reveal the deeper geometry. The ice-melt subsidence structures at Varða are a proxy for buried ice. They are the only known evidence for a subglacial eruption and associated jökulhlaup that created the ice blocks. The recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice-proximal settings during palaeoenvironmental investigations.
Chaotic mixing in a helix-like pipe with periodic variations in curvature and torsion
NASA Astrophysics Data System (ADS)
Jang, Bongkyun; Funakoshi, Mitsuaki
2010-06-01
Chaotic motion of fluid particles due to a steady viscous flow in a helix-like circular pipe caused by an axial pressure gradient, and the mixing efficiency of this flow are numerically examined here. The pipe is wound around a circular or elliptic cylinder with a constant pitch so that the curvature κ and torsion τ of the centerline of this pipe vary continuously and periodically. If both κ and τ are small and slowly varying, the cross-sectional motion of fluid particles is expected to be approximately governed by the sum of Dean's flow and the flow of rigid rotation. From Poincaré sections and the values of an index of the extent of mixing, it is found that there is an intermediate range of Reynolds number Re of flow within which chaotic regions in Poincaré sections are large and mixing efficiency over a short time is high. Moreover, larger chaotic regions and higher mixing efficiency are observed for pipes wound around a circular cylinder of smaller radius and for pipes wound around a thinner elliptic cylinder. These results can be explained by the variation in characteristic ratio λ=12τ/(κRe) in one period.
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
Flow of an elastico-viscous liquid in a curved pipe of slowly varying curvature.
Sarin, V B
1993-03-01
Curvature forms an important feature of thoracic aorta and this paper deals with the flow of an idealized elastico-viscous liquid in a curved pipe of circular cross-section and slowly varying curvature, under a pressure gradient. The flow is assumed to be steady and at low Reynolds numbers. By using the series expansion method of Dean (Phil Mag 4 (1927) 208-223; Phil Mag 5 (1928) 673-693) in powers of a parameter L, which can be considered as the square of ratio of the centrifugal force induced by the circular motion of the fluid to the viscous force, it is shown that in a tube of increasing curvature, there will be delay in setting up of the secondary motion. The wall shear stress, an important parameter in physiological flows, is calculated. The flow of Newtonian fluid in a tube of circular cross section is discussed, as a particular case. PMID:8449591
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-08-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of coseismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth and the other with a larger radius can approximate a half-space model. Then, we calculate the coseismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum coseismic displacement. The results show that the maximum curvature effect is about 4 per cent for source depths of less than 100 km, and about 30 per cent for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100 per cent. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Thomas, R
2006-07-01
The problem of disentangling complex dynamic systems is addressed, especially with a view to identifying those variables that take part in the essential qualitative behaviour of systems. The author presents a series of reflections about the methods of formalisation together with the principles that govern the global operation of systems. In particular, a section on circuits, nuclei, and circular causality and a rather detailed description of the analytic use of the generalised asynchronous logical description, together with a brief description of its synthetic use (OreverseO logic). Some basic rules are recalled, such as the fact that a positive circuit is a necessary condition of multistationarity. Also, the interest of considering as a model, rather than a well-defined set of differential equations, a variety of systems that differ from each other only by the values of constant terms is emphasised. All these systems have a common Jacobian matrix and for all of them phase space has exactly the same structure. It means that all can be partitioned in the same way as regards the signs of the eigenvalues and thus as regards the precise nature of any steady states that might be present. Which steady states are actually present, depends on the values of terms of order zero in the ordinary differential equations (ODEs), and it is easy to find for which values of these terms a given point in phase space is steady. Models can be synthesised first at the level of the circuits involved in the Jacobian matrix (that determines which types and numbers of steady states are consistent with the model), then only at the level of terms of order zero in the ODE's (that determines which of the steady states actually exist), hence the title 'Circular casuality'.
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.
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.
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.
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.
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.
Curvature perturbation and waterfall dynamics in hybrid inflation
Abolhasani, Ali Akbar; Firouzjahi, Hassan; Sasaki, Misao E-mail: firouz@mail.ipm.ir
2011-10-01
We investigate the parameter spaces of hybrid inflation model with special attention paid to the dynamics of waterfall field and curvature perturbations induced from its quantum fluctuations. Depending on the inflaton field value at the time of phase transition and the sharpness of the phase transition inflation can have multiple extended stages. We find that for models with mild phase transition the induced curvature perturbation from the waterfall field is too large to satisfy the COBE normalization. We investigate the model parameter space where the curvature perturbations from the waterfall quantum fluctuations vary between the results of standard hybrid inflation and the results obtained here.
Solving higher curvature gravity theories
NASA Astrophysics Data System (ADS)
Chakraborty, Sumanta; SenGupta, Soumitra
2016-10-01
Solving field equations in the context of higher curvature gravity theories is a formidable task. However, in many situations, e.g., in the context of f( R) theories, the higher curvature gravity action can be written as an Einstein-Hilbert action plus a scalar field action. We show that not only the action but the field equations derived from the action are also equivalent, provided the spacetime is regular. We also demonstrate that such an equivalence continues to hold even when the gravitational field equations are projected on a lower-dimensional hypersurface. We have further addressed explicit examples in which the solutions for Einstein-Hilbert and a scalar field system lead to solutions of the equivalent higher curvature theory. The same, but on the lower-dimensional hypersurface, has been illustrated in the reverse order as well. We conclude with a brief discussion on this technique of solving higher curvature field equations.
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 capillary migration of microspheres.
Sharifi-Mood, Nima; Liu, Iris B; Stebe, Kathleen J
2015-09-14
We address the question: how does capillarity propel microspheres along curvature gradients? For a particle on a fluid interface, there are two conditions that can apply at the three phase contact line: either the contact line adopts an equilibrium contact angle, or it can be pinned by kinetic trapping, e.g. at chemical heterogeneities, asperities, or other pinning sites on the particle surface. We formulate the curvature capillary energy for both scenarios for particles smaller than the capillary length and far from any pinning boundaries. The scale and range of the distortion made by the particle are set by the particle radius; we use singular perturbation methods to find the distortions and to rigorously evaluate the associated capillary energies. For particles with equilibrium contact angles, contrary to the literature, we find that the capillary energy is negligible, with the first contribution bounded to fourth order in the product of the particle radius and the deviatoric curvature of the host interface. For pinned contact lines, we find curvature capillary energies that are finite, with a functional form investigated previously by us for disks and microcylinders on curved interfaces. In experiments, we show microspheres migrate along deterministic trajectories toward regions of maximum deviatoric curvature with curvature capillary energies ranging from 6 × 10(3)-5 × 10(4)kBT. These data agree with the curvature capillary energy for the case of pinned contact lines. The underlying physics of this migration is a coupling of the interface deviatoric curvature with the quadrupolar mode of nanometric disturbances in the interface owing to the particle's contact line undulations. This work is an example of the major implications of nanometric roughness and contact line pinning for colloidal dynamics.
Cosmological signatures of anisotropic spatial curvature
NASA Astrophysics Data System (ADS)
Pereira, Thiago S.; Mena Marugán, Guillermo A.; Carneiro, Saulo
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Surface geometry of circular cut spiral bevel gears
NASA Technical Reports Server (NTRS)
Huston, R. L.; Coy, J. J.
1981-01-01
An analysis of the surface geometry of spiral bevel gears formed by a circular cutter is presented. The emphasis is upon determining the tooth surface principal radii of curvature of crown (flat) gears. Specific results are presented for involute, straight, and hyperbolic cutter profiles. It is shown that the geometry of circular cut spiral bevel gears is somewhat simpler than a theoretical logarithmic spiral bevel gear.
Influence of Coanda surface curvature on performance of bladeless fan
NASA Astrophysics Data System (ADS)
Li, Guoqi; Hu, Yongjun; Jin, Yingzi; Setoguchi, Toshiaki; Kim, Heuy Dong
2014-10-01
The unique Coanda surface has a great influence on the performance of bladeless fan. However, there is few studies to explain the relationship between the performance and Coanda surface curvature at present. In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan, numerical studies are performed in this paper. Firstly, three-dimensional numerical simulation is done by Fluent software. For the purpose to obtain detailed information of the flow field around the Coanda surface, two-dimensional numerical simulation is also conducted. Five types of Coanda surfaces with different curvature are designed, and the flow behaviour and the performance of them are analyzed and compared with those of the prototype. The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance, It is found that there is an optimal curvature of Coanda surfaces among the studied models. Simulation result shows that there is a special low pressure region. With increasing curvature in Y direction, several low pressure regions gradually enlarged, then begin to merge slowly, and finally form a large area of low pressure. From the analyses of streamlines and velocity angle, it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall. Thus, it leads to that the curvature of the streamlines is consistent with that of Coanda surface. Meanwhile, it also causes the fluid movement towards the most suitable direction. This study will provide useful information to performance improvements of bladeless fans.
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.
NASA Astrophysics Data System (ADS)
Beguet, Florian; Bali, Sarah; Christoff, Nicole; Jorda, Laurent; Viseur, Sophie; Bouley, Sylvain; Manolova, Agata; Mari, Jean-Luc
2016-04-01
Impact craters is a typical feature observed at the surface of most bodies in the solar system: terrestrial planets, their satellites, asteroids and even possibly cometary nuclei exhibit impact craters. Their spatial density yields the estimation of the age of the surface, a key parameter required for subsequent geological studies. With the development of interplanetary missions, a large number of solar system objects have been mapped at a high spatial resolution, emphasizing the need for new automatic methods of crater detection and counting. In this work, we present such a method using a new approach based on the analysis of reconstructed 3D meshes instead of 2D images. The robust extraction of feature areas on surface objects embedded in 3D, like circular shapes, is a challenging problem. Classical approaches generally rely on image processing and template matching on a 2D flat projection of the 3D object (for instance a high-resolution picture). In this paper, we propose a full 3D method that mainly relies on curvature analysis. Mean and Gaussian curvatures are estimated on the surface. They are used to label vertices that belong to concave parts corresponding to specific pits on the surface. Centers are located in the targeted surface regions, corresponding to potential crater features. Then "best fit circles" are extracted, based on the rims of the circular shapes. They consist in closed lines exclusively composed of edges of the initial mesh. This approach has been applied to the detection of craters on the asteroid Vesta. Keywords: geometric modeling, 3D meshes, shape recognition, mesh processing, discrete curvatures, asteroids, crater detection, geology, geomorphology.
Shape Coherence and Finite-Time Curvature Evolution
NASA Astrophysics Data System (ADS)
Ma, Tian; Bollt, Erik M.
We introduce a definition of finite-time curvature evolution along with our recent study on shape coherence in nonautonomous dynamical systems. Comparing to slow evolving curvature preserving the shape, large curvature growth points reveal the dramatic change on shape such as the folding behaviors in a system. Closed trough curves of low finite-time curvature (FTC) evolution field indicate the existence of shape coherent sets, and troughs in the field indicate the most significant shape coherence. Here, we will demonstrate these properties of the FTC, as well as contrast to the popular Finite-Time Lyapunov Exponent (FTLE) computation, often used to indicate hyperbolic material curves as Lagrangian Coherent Structures (LCS). We show that often the FTC troughs are in close proximity to the FTLE ridges, but in other scenarios, the FTC indicates entirely different regions.
Surface geometry of circular cut spiral bevel gears
NASA Technical Reports Server (NTRS)
Huston, R. L.; Coy, J. J.
1981-01-01
The tooth surface principal radii of curvature of crown (flat) gears were determined. Specific results are presented for involute, straight, and hyperbolic cutter profiles. It is shown that the geometry of circular cut spiral bevel gears is somewhat simpler than a theoretical logarithmic spiral bevel gear.
Geometrical analysis of circular-cut spiral bevel gears
NASA Technical Reports Server (NTRS)
Huston, R. L.
1983-01-01
Geometrical studies of circular cut spiral bevel gears are reported. Tooth profile changes heel to toe are studied in the transverse plane. Pressure angle changes are determined. The radiuses of curvature of the tooth surfaces generated by various cutter profiles are also determined. The consequences of cutter profile changes are explored. Crown gears are emphasized and the implications for conical gears are discussed.
NASA Astrophysics Data System (ADS)
Prezzi, Claudia B.; Orgeira, María Julia; Acevedo, Rogelio D.; Ponce, Juan Federico; Martinez, Oscar; Rabassa, Jorge O.; Corbella, Hugo; Vásquez, Carlos; González-Guillot, Mauricio; Subías, Ignacio
2012-02-01
An impact origin has been proposed for the circular structures found in Bajada del Diablo, Patagonia, Argentina. Taking into account its extension and the number of impact structures, Bajada del Diablo would be the largest meteoritic impact areas known on Earth, being an extremely interesting area for the research of impact events and processes. Moreover, the global distribution of known impact structures shows a surprising asymmetry. Particularly, South America has only seven described areas. It is evident that this situation is an artifact, highlighting the importance of intensifying the research in the least studied areas such as Argentina. Circular structures in Bajada del Diablo have been identified on two rock types: the Quiñelaf eruptive complex and Pampa Sastre Formation. In the first case, circular structures are placed in olivine basalts. On the other hand, Pampa Sastre Formation (late Pliocene/early Pleistocene) corresponds to conglomerate layers with basalt clasts boulder and block in size in a coarse sandy matrix. With the aim of further the investigation of the proposed impact origin for these circular structures, we carried out detailed topographic, magnetic and electromagnetic ground surveys in two circular structures ("8" and "A") found in Pampa Sastre conglomerates. Both circular structures are simple, bowl-shaped with rim diameters of 300 m and maximum depths of 10 m. They have been partially filled in by debris flows from the rims and wind-blown sands. Two preliminary magnetic profiles have also been carried out in circular structure "G" found in Quiñelaf basalts. The magnetic anomalies show a circular pattern with a slightly negative and relatively flat signal in the circular structures' bases. Furthermore in the circular structures' rims, high-amplitude, conspicuous and localized (short wavelength) anomalies are observed. Such large amplitude and short wavelength anomalies are not detected outside the circular structures. For all used
Cosmic strings with curvature corrections
NASA Astrophysics Data System (ADS)
Boisseau, Bruno; Letelier, Patricio S.
1992-08-01
A generic model of string described by a Lagrangian density that depends on the extrinsic curvature of the string worldsheet is studied. Using a system of coordinates adapted to the string world sheet the equation of motion and the energy-momentum tensor are derived for strings evolving in curved spacetime. We find that the curvature corrections may change the relation between the string energy density and the tension. It can also introduce heat propagation along the string. We also find for the Polyakov as well as Nambu strings with a topological term that the open string end points can travel with a speed less than the velocity of light.
Higher curvature corrections to primordial fluctuations in slow-roll inflation
Satoh, Masaki; Soda, Jiro E-mail: jiro@tap.scphys.kyoto-u.ac.jp
2008-09-15
We study higher curvature corrections to the scalar spectral index, the tensor spectral index, the tensor-to-scalar ratio, and the polarization of gravitational waves. We find that there are cases where the higher curvature corrections cannot be negligible in the dynamics of the scalar field, although they are always negligible energetically. Indeed, it turns out that the tensor-to-scalar ratio could be enhanced and the tensor spectral index could be blue due to the Gauss-Bonnet term. We estimate the degree of circular polarization of gravitational waves generated during the slow-roll inflation. We argue that the circular polarization could be observable with the help of both the Gauss-Bonnet and the parity violating terms. We also present several examples to reveal observational implications of higher curvature corrections for chaotic inflationary models.
Negative Gaussian curvature from induced metric changes
NASA Astrophysics Data System (ADS)
Modes, Carl D.; Warner, Mark
2015-07-01
We revisit the light or heat-induced changes in topography of initially flat sheets of a solid that elongate or contract along patterned in-plane director fields. For radial or azimuthal directors, negative Gaussian curvature is generated—so-called "anticones." We show that azimuthal material displacements are required for the distorted state to be stretch free and bend minimizing. The resultant shapes are smooth and asterlike and can become reentrant in the azimuthal coordinate for large deformations. We show that care is needed when considering elastomers rather than glasses, although the former offer huge deformations.
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.
Thermodynamic Curvature and Black Holes
NASA Astrophysics Data System (ADS)
Ruppeiner, George
In my talk, I will discuss black hole thermodynamics, particularly what happens when you add thermodynamic curvature to the mix. Although black hole thermodynamics is a little off the main theme of this workshop, I hope nevertheless that my message will be of some interest to researchers in supersymmetry and supergravity.
Robust disparity estimation based on color monogenic curvature phase.
Zang, Di; Li, Jie; Zhang, Dongdong; Zhang, Junqi
2012-07-01
Disparity estimation for binocular images is an important problem for many visual tasks such as 3D environment reconstruction, digital hologram, virtual reality, robot navigation, etc. Conventional approaches are based on brightness constancy assumption to establish spatial correspondences between a pair of images. However, in the presence of large illumination variation and serious noisy contamination, conventional approaches fail to generate accurate disparity maps. To have robust disparity estimation in these situations, we first propose a model - color monogenic curvature phase to describe local features of color images by embedding the monogenic curvature signal into the quaternion representation. Then a multiscale framework to estimate disparities is proposed by coupling the advantages of the color monogenic curvature phase and mutual information. Both indoor and outdoor images with large brightness variation are used in the experiments, and the results demonstrate that our approach can achieve a good performance even in the conditions of large illumination change and serious noisy contamination. PMID:22772192
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)
17 CFR 230.253 - Offering circular.
Code of Federal Regulations, 2013 CFR
2013-04-01
... presented in a clear, concise and understandable manner and in a type size that is easily readable... permitted. (2) Where an offering circular is distributed through an electronic medium, issuers may satisfy... in boldfaced type at least as large as that used generally in the body of such offering circular:...
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.
Waterfall field in hybrid inflation and curvature perturbation
Gong, Jinn-Ouk; Sasaki, Misao E-mail: misao@yukawa.kyoto-u.ac.jp
2011-03-01
We study carefully the contribution of the waterfall field to the curvature perturbation at the end of hybrid inflation. In particular we clarify the parameter dependence analytically under reasonable assumptions on the model parameters. After calculating the mode function of the waterfall field, we use the δN formalism and confirm the previously obtained result that the power spectrum is very blue with the index 4 and is absolutely negligible on large scales. However, we also find that the resulting curvature perturbation is highly non-Gaussian and hence we calculate the bispectrum. We find that the bispectrum is at leading order independent of momentum and exhibits its peak at the equilateral limit, though it is unobservably small on large scales. We also present the one-point probability distribution function of the curvature perturbation.
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.
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
Curvature operator for loop quantum gravity
NASA Astrophysics Data System (ADS)
Alesci, E.; Assanioussi, M.; Lewandowski, J.
2014-06-01
We introduce a new operator in loop quantum gravity—the 3D curvature operator—related to the three-dimensional scalar curvature. The construction is based on Regge calculus. We define this operator starting from the classical expression of the Regge curvature, we derive its properties and discuss some explicit checks of the semiclassical limit.
Circular codes, symmetries and transformations.
Fimmel, Elena; Giannerini, Simone; Gonzalez, Diego Luis; Strüngmann, Lutz
2015-06-01
Circular codes, putative remnants of primeval comma-free codes, have gained considerable attention in the last years. In fact they represent a second kind of genetic code potentially involved in detecting and maintaining the normal reading frame in protein coding sequences. The discovering of an universal code across species suggested many theoretical and experimental questions. However, there is a key aspect that relates circular codes to symmetries and transformations that remains to a large extent unexplored. In this article we aim at addressing the issue by studying the symmetries and transformations that connect different circular codes. The main result is that the class of 216 C3 maximal self-complementary codes can be partitioned into 27 equivalence classes defined by a particular set of transformations. We show that such transformations can be put in a group theoretic framework with an intuitive geometric interpretation. More general mathematical results about symmetry transformations which are valid for any kind of circular codes are also presented. Our results pave the way to the study of the biological consequences of the mathematical structure behind circular codes and contribute to shed light on the evolutionary steps that led to the observed symmetries of present codes. PMID:25008961
Disformal invariance of curvature perturbation
NASA Astrophysics Data System (ADS)
Motohashi, Hayato; White, Jonathan
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.
On the collective curvature radiation
NASA Astrophysics Data System (ADS)
Istomin, Ya. N.; Philippov, A. A.; Beskin, V. S.
2012-05-01
In this paper, we study one possible mechanism of pulsar radio emission (i.e. with the collective curvature radiation of the relativistic particle stream moving along the curved magnetospheric magnetic field lines). We show that an electromagnetic wave that contains one cylindrical harmonic exp {isφ} cannot be radiated by the curvature radiation mechanism, which corresponds to the radiation of a charged particle moving along curved magnetic field lines. The point is that a particle in a vacuum radiates the triplex of harmonics (s, s± 1) in which the polarization of the emitted wave changes from one point to another on a circle of constant radius, while for one s-harmonic the polarization remains constant. So, for the collective curvature radiation, the wave polarization is very important and cannot be fixed a priori. For this reason, the polarization of real unstable waves must be determined directly from the solution of wave equations for the media. Its electromagnetic properties should be described by the dielectric permittivity tensor ?, which contains information on the reaction on all possible types of radiation.
Thermodynamic curvature and ensemble nonequivalence
NASA Astrophysics Data System (ADS)
Bravetti, Alessandro; Nettel, Francisco
2014-08-01
In this work we consider thermodynamic geometries defined as Hessians of different potentials and derive some useful formulas that show their complementary role in the description of thermodynamic systems with 2 degrees of freedom that show ensemble nonequivalence. From the expressions derived for the metrics, we can obtain the curvature scalars in a very simple and compact form. We explain here the reason why each curvature scalar diverges over the line of divergence of one of the specific heats. This application is of special interest in the study of changes of stability in black holes as defined by Davies. From these results we are able to prove on a general footing a conjecture first formulated by Liu, Lü, Luo, and Shao stating that different Hessian metrics can correspond to different behaviors in the various ensembles. We study the case of two thermodynamic dimensions. Moreover, comparing our result with the more standard turning point method developed by Poincaré, we obtain that the divergence of the scalar curvature of the Hessian metric of one potential exactly matches the change of stability in the corresponding ensemble.
NASA Astrophysics Data System (ADS)
Zhou, Changhe; Jia, Jia; Liu, Liren
2003-11-01
A circular Dammann grating that can produce circular equal intensities at various orders in the far field is described. A set of parameters such as order, circular number, uniformity, and diffraction efficiency has been defined to describe the novel diffractive phase elements. Numerical solutions of binary-phase (0, π) circular Dammann gratings are given. The results of experiments with a four-order circular Dammann grating made by a lithographic technique are presented. This novel diffractive optical element should be highly interesting in a wide variety of practical applications.
Flow in a rotating curved circular pipe.
Zhang, Jinsuo; Li, Ning; Zhang, Benzhao
2003-05-01
The flow in a rotating curved pipe with circular cross section is investigated theoretically and numerically. A perturbation solution up to the second order is obtained. A numerical procedure is used to solve the full governing equations and the simplified governing equations in the small curvature limit. Comparisons are made between the numerical and perturbation results, elucidating the lost information due to simplification and the valid range of the perturbation solution. The flow characteristics, including the secondary flow, the axial flow, and the friction factor ratio, are examined in detail.
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.
Wright, Anthony R; McKenzie, Ross H
2014-02-26
We show that in a layered metal, the angle dependent, finite frequency, interlayer magnetoresistance is altered due to the presence of a non-zero Berry curvature at the Fermi surface. At zero frequency, we find a conservation law which demands that the 'magic angle' condition for interlayer magnetoresistance extrema as a function of magnetic field tilt angle is essentially both field and Berry curvature independent. In the finite frequency case, however, we find that surprisingly large signatures of a finite Berry curvature occur in the periodic orbit resonances. We outline a method whereby the presence and magnitude of the Berry curvature at the Fermi surface can be extracted.
ODE/PDE analysis of corneal curvature.
Płociniczak, Lukasz; Griffiths, Graham W; Schiesser, William E
2014-10-01
The starting point for this paper is a nonlinear, two-point boundary value ordinary differential equation (BVODE) that defines corneal curvature according to a static force balance. A numerical solution to the BVODE is computed by first converting the BVODE to a parabolic partial differential equation (PDE) by adding an initial value (t, pseudo-time) derivative to the BVODE. A numerical solution to the PDE is then computed by the method of lines (MOL) with the calculation proceeding to a sufficiently large value of t such that the derivative in t reduces to essentially zero. The PDE solution at this point is also the solution for the BVODE. This procedure is implemented in R (an open source scientific programming system) and the programming is discussed in some detail. A series approximation to the solution is derived from which an estimate for the rate of convergence is obtained. This is compared to a fitted exponential model. Also, two linear approximations are derived, one of which leads to a closed form solution. Both provide solutions very close to that obtained from the full nonlinear model. An estimate for the cornea radius of curvature is also derived. The paper concludes with a discussion of the features of the solution to the ODE/PDE system.
Magneto-reheating constraints from curvature perturbations
Ringeval, Christophe; Suyama, Teruaki; Yokoyama, Jun'ichi E-mail: suyama@resceu.s.u-tokyo.ac.jp
2013-09-01
As additional perturbative degrees of freedom, it is known that magnetic fields of inflationary origin can source curvature perturbations on super-Hubble scales. By requiring the magnetic generated curvature to remain smaller than its inflationary adiabatic counterpart during inflation and reheating, we derive new constraints on the maximal field value today, the reheating energy scale and its equation of state parameter. These bounds end up being stronger by a few order of magnitude than those associated with a possible backreaction of the magnetic field onto the background. Our results are readily applicable to any slow-roll single field inflationary models and any magnetic field having its energy density scaling as a{sup γ} during inflation. As an illustrative example, massive inflation is found to remain compatible with a magnetic field today B{sub 0} = 5 × 10{sup −15} G for some values of γ only if a matter dominated reheating takes place at energies larger than 10{sup 5} GeV. Conversely, assuming γ = −1, massive inflation followed by a matter dominated reheating cannot explain large scale magnetic fields larger than 10{sup −20} G today.
Probing Persistence in DNA Curvature Properties with Atomic Force Microscopy
NASA Astrophysics Data System (ADS)
Moukhtar, J.; Fontaine, E.; Faivre-Moskalenko, C.; Arneodo, A.
2007-04-01
We elaborate on a mean-field extension of the wormlike chain model that accounts for the presence of long-range correlations (LRC) in the intrinsic curvature disorder of genomic DNA, the stronger the LRC, the smaller the persistence length. The comparison of atomic force microscopy imaging of straight, uncorrelated virus and correlated human DNA fragments with DNA simulations confirms that the observed decrease in persistence length for human DNA more likely results from a sequence-induced large-scale intrinsic curvature than from some increased flexibility.
The formation of mountain range curvature by gravitational spreading
NASA Astrophysics Data System (ADS)
Copley, Alex
2012-10-01
This paper presents a mechanism by which mountain ranges can form curved range-fronts. Gravitational spreading of mountain ranges that have been thrust onto rigid lowlands will result in the formation of curvature, provided that enough gravity-driven flow occurs to dominate the shape of the topography. Whether this mechanism can operate during the lifetime of a given mountain range depends upon the viscosity of the range, the square of the along-strike length of the range, and the cube of the elevation of the range. The curvature of the southern edge of the Tibetan Plateau is consistent with formation by gravitational spreading provided that the viscosity is similar to that previously estimated using other, independent, methods. The low elevation and young age of the Zagros mountains mean that large-scale curvature has not had time to develop. The short along-strike extent and possibly low viscosity of the Sulaiman Ranges in Pakistan may have allowed the ranges to form their distinctive arcuate shape. The formation of range-front curvature plays an important role in controlling the tectonic evolution of the interiors of the ranges, with arc-parallel extension becoming progressively more important as range-front curvature develops.
Representation of tactile curvature in macaque somatosensory area 2
Connor, Charles E.; Hsiao, Steven S.
2013-01-01
Tactile shape information is elaborated in a cortical hierarchy spanning primary (SI) and secondary somatosensory cortex (SII). Indeed, SI neurons in areas 3b and 1 encode simple contour features such as small oriented bars and edges, whereas higher order SII neurons represent large curved contour features such as angles and arcs. However, neural coding of these contour features has not been systematically characterized in area 2, the most caudal SI subdivision in the postcentral gyrus. In the present study, we analyzed area 2 neural responses to embossed oriented bars and curved contour fragments to establish whether curvature representations are generated in the postcentral gyrus. We found that many area 2 neurons (26 of 112) exhibit clear curvature tuning, preferring contours pointing in a particular direction. Fewer area 2 neurons (15 of 112) show preferences for oriented bars. Because area 2 response patterns closely resembled SII patterns, we also compared area 2 and SII response time courses to characterize the temporal dynamics of curvature synthesis in the somatosensory system. We found that curvature representations develop and peak concurrently in area 2 and SII. These results reveal that transitions from orientation tuning to curvature selectivity in the somatosensory cortical hierarchy occur within SI rather than between SI and SII. PMID:23536717
Representation of tactile curvature in macaque somatosensory area 2.
Yau, Jeffrey M; Connor, Charles E; Hsiao, Steven S
2013-06-01
Tactile shape information is elaborated in a cortical hierarchy spanning primary (SI) and secondary somatosensory cortex (SII). Indeed, SI neurons in areas 3b and 1 encode simple contour features such as small oriented bars and edges, whereas higher order SII neurons represent large curved contour features such as angles and arcs. However, neural coding of these contour features has not been systematically characterized in area 2, the most caudal SI subdivision in the postcentral gyrus. In the present study, we analyzed area 2 neural responses to embossed oriented bars and curved contour fragments to establish whether curvature representations are generated in the postcentral gyrus. We found that many area 2 neurons (26 of 112) exhibit clear curvature tuning, preferring contours pointing in a particular direction. Fewer area 2 neurons (15 of 112) show preferences for oriented bars. Because area 2 response patterns closely resembled SII patterns, we also compared area 2 and SII response time courses to characterize the temporal dynamics of curvature synthesis in the somatosensory system. We found that curvature representations develop and peak concurrently in area 2 and SII. These results reveal that transitions from orientation tuning to curvature selectivity in the somatosensory cortical hierarchy occur within SI rather than between SI and SII.
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.
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.
Symmetric curvature descriptors for label-free analysis of DNA
NASA Astrophysics Data System (ADS)
Buzio, Renato; Repetto, Luca; Giacopelli, Francesca; Ravazzolo, Roberto; Valbusa, Ugo
2014-09-01
High-resolution microscopy techniques such as electron microscopy, scanning tunnelling microscopy and atomic force microscopy represent well-established, powerful tools for the structural characterization of adsorbed DNA molecules at the nanoscale. Notably, the analysis of DNA contours allows mapping intrinsic curvature and flexibility along the molecular backbone. This is particularly suited to address the impact of the base-pairs sequence on the local conformation of the strands and plays a pivotal role for investigations relating the inherent DNA shape and flexibility to other functional properties. Here, we introduce novel chain descriptors aimed to characterize the local intrinsic curvature and flexibility of adsorbed DNA molecules with unknown orientation. They consist of stochastic functions that couple the curvatures of two nanosized segments, symmetrically placed on the DNA contour. We show that the fine mapping of the ensemble-averaged functions along the molecular backbone generates characteristic patterns of variation that highlight all pairs of tracts with large intrinsic curvature or enhanced flexibility. We demonstrate the practical applicability of the method for DNA chains imaged by atomic force microscopy. Our approach paves the way for the label-free comparative analysis of duplexes, aimed to detect nanoscale conformational changes of physical or biological relevance in large sample numbers.
Directable weathering of concave rock using curvature estimation.
Jones, Michael D; Farley, McKay; Butler, Joseph; Beardall, Matthew
2010-01-01
We address the problem of directable weathering of exposed concave rock for use in computer-generated animation or games. Previous weathering models that admit concave surfaces are computationally inefficient and difficult to control. In nature, the spheroidal and cavernous weathering rates depend on the surface curvature. Spheroidal weathering is fastest in areas with large positive mean curvature and cavernous weathering is fastest in areas with large negative mean curvature. We simulate both processes using an approximation of mean curvature on a voxel grid. Both weathering rates are also influenced by rock durability. The user controls rock durability by editing a durability graph before and during weathering simulation. Simulations of rockfall and colluvium deposition further improve realism. The profile of the final weathered rock matches the shape of the durability graph up to the effects of weathering and colluvium deposition. We demonstrate the top-down directability and visual plausibility of the resulting model through a series of screenshots and rendered images. The results include the weathering of a cube into a sphere and of a sheltered inside corner into a cavern as predicted by the underlying geomorphological models.
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.
VLTI pupil transfer: variable curvature mirrors: II. Plasticity, hysteresis, and curvature control
NASA Astrophysics Data System (ADS)
Lemaitre, Gerard R.; Ferrari, Marc; Mazzanti, Silvio P.; Lanzoni, Patrick; Joulie, Patrice; Leduc, Denis; Copede, Myriam
2000-07-01
Progress in Active Optics Methods have led to the invention of Variable Curvature Mirrors. VCMs are useful to provide optical path compensations of the imaged field of view. Preliminarily developed for Fourier transform IR spectrometers, they are now used for the coherent beam recombination of the VLT array. With the VLT Interferometer, a highly flexible VCM will be installed at the focal surface of each cat's eye delay lines. The VCM developments led to the design choice of metal substrates in a quenched state which are at least 15 times more flexible--to external loading--than gloss or vitroceram substrates and thus, have provided accurately the large zoom-range from f/(infinity) to f/2.6. Due to the very large zoom range provided by such active mirrors, it has been found necessary to take under consideration the small plastical deformation as well as the small hysterese loop deformation of the metal substrate. With the four VCMs such as now built for the 8 m telescopes, a plastical deformation model and a hysterese loop model have been determined and are presently described. Including these compensations, the VCM optical figures have been improved and the control software now performs a curvature resolution in between 10-3 and 5 10-4.
Canards and curvature: nonsmooth approximation by pinching
NASA Astrophysics Data System (ADS)
Desroches, M.; Jeffrey, M. R.
2011-05-01
In multiple time-scale (singularly perturbed) dynamical systems, canards are counterintuitive solutions that evolve along both attracting and repelling invariant manifolds. In two dimensions, canards result in periodic oscillations whose amplitude and period grow in a highly nonlinear way: they are slowly varying with respect to a control parameter, except for an exponentially small range of values where they grow extremely rapidly. This sudden growth, called a canard explosion, has been encountered in many applications ranging from chemistry to neuronal dynamics, aerospace engineering and ecology. Canards were initially studied using nonstandard analysis, and later the same results were proved by standard techniques such as matched asymptotics, invariant manifold theory and parameter blow-up. More recently, canard-like behaviour has been linked to surfaces of discontinuity in piecewise-smooth dynamical systems. This paper provides a new perspective on the canard phenomenon by showing that the nonstandard analysis of canard explosions can be recast into the framework of piecewise-smooth dynamical systems. An exponential coordinate scaling is applied to a singularly perturbed system of ordinary differential equations. The scaling acts as a lens that resolves dynamics across all time-scales. The changes of local curvature that are responsible for canard explosions are then analysed. Regions where different time-scales dominate are separated by hypersurfaces, and these are pinched together to obtain a piecewise-smooth system, in which curvature changes manifest as discontinuity-induced bifurcations. The method is used to classify canards in arbitrary dimensions, and to derive the parameter values over which canards form either small cycles (canards without head) or large cycles (canards with head).
Determining wave direction using curvature parameters.
de Queiroz, Eduardo Vitarelli; de Carvalho, João Luiz Baptista
2016-01-01
The curvature of the sea wave was tested as a parameter for estimating wave direction in the search for better results in estimates of wave direction in shallow waters, where waves of different sizes, frequencies and directions intersect and it is difficult to characterize. We used numerical simulations of the sea surface to determine wave direction calculated from the curvature of the waves. Using 1000 numerical simulations, the statistical variability of the wave direction was determined. The results showed good performance by the curvature parameter for estimating wave direction. Accuracy in the estimates was improved by including wave slope parameters in addition to curvature. The results indicate that the curvature is a promising technique to estimate wave directions.•In this study, the accuracy and precision of curvature parameters to measure wave direction are analyzed using a model simulation that generates 1000 wave records with directional resolution.•The model allows the simultaneous simulation of time-series wave properties such as sea surface elevation, slope and curvature and they were used to analyze the variability of estimated directions.•The simultaneous acquisition of slope and curvature parameters can contribute to estimates wave direction, thus increasing accuracy and precision of results. PMID:27408830
Sequence-induced curvature of Tenebrio molitor satellite DNA.
Plohl, M; Borstnik, B; Ugarković, D; Gamulin, V
1990-09-01
Single satellite DNA constitutes about 50% of the Tenebrio molitor genome. Electrophoresis of 142 base pair long satellite monomers on nondenaturating polyacrylamide gel shows retarded mobility, a characteristic of fragments with sequence-induced DNA curvature. Migrational analysis of circularly permuted satellite monomers revealed the existence of 2 bend centers in the monomer sequence. We calculated the trajectory of DNA helix axis according to the algorithm of De Santis et al. This model predicts that T molitor naked satellite DNA forms a solenoid structure with left-handed superhelix. One turn of the superhelix has approximately 310 base pairs and a 33 nm pitch. Point mutations found in the satellite DNA (1.8%) influence bending characteristics, but do not distort the general geometry of satellite superhelix.
Fiber curvature sensor based on spherical-shape structures and long-period grating
NASA Astrophysics Data System (ADS)
Xiong, Mengling; Gong, Huaping; Wang, Zhiping; Zhao, Chun-Liu; Dong, Xinyong
2016-11-01
A novel curvature sensor based on optical fiber Mach-Zehnder interferometer (MZI) is demonstrated. It consists of two spherical-shape structures and a long-period grating (LPG) in between. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivity are -22.144 nm/m-1 in the measurement range of 5.33-6.93 m-1, -28.225 nm/m-1 in the range of 6.93-8.43 m- and -15.68 nm/m-1 in the range of 8.43-9.43 m-1, respectively. And the maximum curvature error caused by temperature is only -0.003 m-1/°C. The sensor exhibits the advantages of all-fiber structure, high mechanical strength, high curvature sensitivity and large measurement scales.
Sha, Haoyan; Faller, Roland
2016-07-20
Quantum chemistry calculations were performed to investigate the effect of the surface curvature of a Boron Nitride (BN) nanotube/nanosheet on gas adsorption. Curved boron nitride layers with different curvatures interacting with a number of different gases including noble gases, oxygen, and water on both their convex and concave sides of the surface were studied using density functional theory (DFT) with a high level dispersion corrected functional. Potential energy surfaces of the gas molecules interacting with the selected BN surfaces were investigated. In addition, the charge distribution and electrostatic potential contour of the selected BN surfaces are discussed. The results reveal how the curvature of the BN surfaces affects gas adsorption. In particular, small curvatures lead to a slight difference in the physisorption energy, while large curvatures present distinct potential energy surfaces, especially for the short-range repulsion. PMID:27399852
Non-perturbative approach for curvature perturbations in stochastic δ N formalism
Fujita, Tomohiro; Kawasaki, Masahiro; Tada, Yuichiro E-mail: kawasaki@icrr.u-tokyo.ac.jp
2014-10-01
In our previous paper [1], we have proposed a new algorithm to calculate the power spectrum of the curvature perturbations generated in inflationary universe with use of the stochastic approach. Since this algorithm does not need the perturbative expansion with respect to the inflaton fields on super-horizon scale, it works even in highly stochastic cases. For example, when the curvature perturbations are very large or the non-Gaussianities of the curvature perturbations are sizable, the perturbative expansion may break down but our algorithm enables to calculate the curvature perturbations. We apply it to two well-known inflation models, chaotic and hybrid inflation, in this paper. Especially for hybrid inflation, while the potential is very flat around the critical point and the standard perturbative computation is problematic, we successfully calculate the curvature perturbations.
Out-of-plane forced vibrations of multispan circular curved beams
NASA Astrophysics Data System (ADS)
Wang, T. M.; Ahmad, M. F.; Hsiao, B. T.
1992-10-01
The dynamic stiffness matrix for circular curved members of constant section vibrating out of their initial plane of curvature is presented for the analysis of forced vibrations of multispan curved beams. A three-span circular curved beam subjected to a dynamic concentrated load is given to show the effects of the frequency of applied load and the opening angle of the arc on the joint moments of the beam.
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.
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. PMID:19161325
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.
ERIC Educational Resources Information Center
Gordon, Russell
2008-01-01
Consider a circular segment (the smaller portion of a circle cut off by one of its chords) with chord length c and height h (the greatest distance from a point on the arc of the circle to the chord). Is there a simple formula involving c and h that can be used to closely approximate the area of this circular segment? Ancient Chinese and Egyptian…
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.
Distributed curvature and stability of fullerenes.
Fowler, Patrick W; Nikolić, Sonja; De Los Reyes, Rasthy; Myrvold, Wendy
2015-09-21
Energies of non-planar conjugated π systems are typically described qualitatively in terms of the balance of π stabilisation and the steric strain associated with geometric curvature. Curvature also has a purely graph-theoretical description: combinatorial curvature at a vertex of a polyhedral graph is defined as one minus half the vertex degree plus the sum of reciprocal sizes of the faces meeting at that vertex. Prisms and antiprisms have positive combinatorial vertex curvature at every vertex. Excluding these two infinite families, we call any other polyhedron with everywhere positive combinatorial curvature a PCC polyhedron. Cubic PCC polyhedra are initially common, but must eventually die out with increasing vertex count; the largest example constructed so far has 132 vertices. The fullerenes Cn have cubic polyhedral molecular graphs with n vertices, 12 pentagonal and (n/2 - 10) hexagonal faces. We show that there are exactly 39 PCC fullerenes, all in the range 20 ≤n≤ 60. In this range, there is only partial correlation between PCC status and stability as defined by minimum pentagon adjacency. The sum of vertex curvatures is 2 for any polyhedron; for fullerenes the sum of squared vertex curvatures is linearly related to the number of pentagon adjacencies and hence is a direct measure of relative stability of the lower (n≤ 60) fullerenes. For n≥ 62, non-PCC fullerenes with a minimum number of pentagon adjacencies minimise mean-square curvature. For n≥ 70, minimum mean-square curvature implies isolation of pentagons, which is the strongest indicator of stability for a bare fullerene. PMID:26283188
Brau, Charles A.; Kurnit, Norman A.; Cooper, Richard K.
1984-01-01
A high efficiency, free electron laser utilizing a circular relativistic electron beam accelerator and a circular whispering mode optical waveguide for guiding optical energy in a circular path in the circular relativistic electron beam accelerator such that the circular relativistic electron beam and the optical energy are spatially contiguous in a resonant condition for free electron laser operation. Both a betatron and synchrotron are disclosed for use in the present invention. A free electron laser wiggler is disposed around the circular relativistic electron beam accelerator for generating a periodic magnetic field to transform energy from the circular relativistic electron beam to optical energy.
Towards future circular colliders
NASA Astrophysics Data System (ADS)
Benedikt, Michael; Zimmermann, Frank
2016-09-01
The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) presently provides proton-proton collisions at a center-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics program will extend through the second half of the 2030's. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ˜100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCCee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3 S n superconductor, for the FCC-hh hadron collider, and a highly-efficient superconducting radiofrequency system for the FCC-ee lepton collider. Following the FCC concept, the Institute of High Energy Physics (IHEP) in Beijing has initiated a parallel design study for an e + e - Higgs factory in China (CEPC), which is to be succeeded by a high-energy hadron collider (SPPC). At present a tunnel circumference of 54 km and a hadron collider c.m. energy of about 70 TeV are being considered. After a brief look at the LHC, this article reports the motivation and the present status of the FCC study, some of the primary design challenges and R&D subjects, as well as the emerging global collaboration.
Defect Motifs for Constant Mean Curvature Surfaces
NASA Astrophysics Data System (ADS)
Kusumaatmaja, Halim; Wales, David J.
2013-04-01
The energy landscapes of electrostatically charged particles embedded on constant mean curvature surfaces are analyzed for a wide range of system size, curvature, and interaction potentials. The surfaces are taken to be rigid, and the basin-hopping method is used to locate the putative global minimum structures. The defect motifs favored by potential energy agree with experimental observations for colloidal systems: extended defects (scars and pleats) for weakly positive and negative Gaussian curvatures, and isolated defects for strongly negative Gaussian curvatures. Near the phase boundary between these regimes, the two motifs are in strong competition, as evidenced from the appearance of distinct funnels in the potential energy landscape. We also report a novel defect motif consisting of pentagon pairs.
Compact waveguide circular polarizer
Tantawi, Sami G.
2016-08-16
A multi-port waveguide is provided having a rectangular waveguide that includes a Y-shape structure with first top arm having a first rectangular waveguide port, a second top arm with second rectangular waveguide port, and a base arm with a third rectangular waveguide port for supporting a TE.sub.10 mode and a TE.sub.20 mode, where the end of the third rectangular waveguide port includes rounded edges that are parallel to a z-axis of the waveguide, a circular waveguide having a circular waveguide port for supporting a left hand and a right hand circular polarization TE.sub.11 mode and is coupled to a base arm broad wall, and a matching feature disposed on the base arm broad wall opposite of the circular waveguide for terminating the third rectangular waveguide port, where the first rectangular waveguide port, the second rectangular waveguide port and the circular waveguide port are capable of supporting 4-modes of operation.
Cosmological spatial curvature probed by microwave polarization
Matzner, R.A.; Tolman, B.W.
1982-11-15
If there is a large-scale anisotropy in the expansion of the universe, the microwave background radiation is expected to be linearly polarized. This communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary ina complicated way over the celestial sphere (type VII/sub h/). These facts suggest a clear observational test of the closure of the universe. Also, an ambiguity inherent in the homogeneity of the universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called ''handedness.''
Mean curvature flow of a hyperbolic surface
Ovchinnikov, Yu. N.; Sigal, I. M.
2011-12-15
A four-parameter family of self-similar solutions is obtained to the mean curvature flow equation for a surface. This family is shown to be stable with respect to a small deformation of a hyperbolic surface. At time instant t*, a singular point is formed within a finite time interval, that is accompanied by a change in the topology of the surface. The solution is continued beyond the singular point. A relationship between the parameters describing the hyperbolic surface before and after the change in the surface topology is obtained. A particular case is analyzed when the unperturbed surface is a cylinder. A cylindrical surface is weakly unstable with respect to a perturbation in the form of a 'wide neck.' At the final stage of the development of the neck when its transverse size becomes much less than the cylinder radius at large distances from the neck, the surface flow in a wide region in the neighborhood of the neck is described by a universal two-parameter family of self-similar solutions. These solutions are stable with respect to small perturbations of the surface.
Induced gravity from curvature density preserving diffeomorphisms
NASA Astrophysics Data System (ADS)
Oda, Ichiro
2016-08-01
We construct not only an induced gravity model with restricted diffeomorphisms, that is, transverse diffeomorphisms that preserve the curvature density, but also with full diffeomorphisms. By solving the equations of motion, it turns out that these models produce Einstein's equations with a certain Newton constant in addition to the constraint for the curvature density. In the limit of the infinite Newton constant, the models give rise to induced gravity. Moreover, we discuss cosmological solutions on the basis of the gravitational models at hand.
Curvature tensors unified field equations on SEXn
NASA Astrophysics Data System (ADS)
Chung, Kyung Tae; Lee, Il Young
1988-09-01
We study the curvature tensors and field equations in the n-dimensional SE manifold SEXn. We obtain several basic properties of the vectors S λ and U λ and then of the SE curvature tensor and its contractions, such as a generalized Ricci identity, a generalized Bianchi identity, and two variations of the Bianchi identity satisfied by the SE Einstein tensor. Finally, a system of field equations is discussed in SEXn and one of its particular solutions is constructed and displayed.
The role of curvature in entanglement
NASA Astrophysics Data System (ADS)
Buck, Gregory
2015-10-01
Which tangles more readily: curly hair or straight hair? A perhaps natural thought, supported by some theoretical evidence, is to associate curvature and entanglement, and assume that they would grow together-that an increase in one fosters an increase in the other. However we have biological examples such as DNA in the chromosome, and mechanical examples such as coiled telephone cords, in which much more curvature is employed than is required for the packing, and in which tangling is presumably detrimental. We offer a resolution to this conundrum. We show, that at least for simple but generally applicable models, the relationship between curvature and entanglement is subtle: if we keep filament density constant and increase curvature, the entanglement initially increases, passes through a maximum, then decreases, so there is a regime where increasing curvature increases entanglement, and there is also a regime where increasing curvature decreases entanglement. This has implications for filament packing in many circumstances, and in particular for the compaction structure of DNA in the cell-it provides a straightforward argument for the view that one purpose of DNA coiling and supercoiling is to inhibit entanglement. It also tells us to expect that wavy hair-neither the straightest nor the curliest-tangles most readily.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-08-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
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.
Generating ekpyrotic curvature perturbations before the big bang
Lehners, Jean-Luc; Turok, Neil; McFadden, Paul; Steinhardt, Paul J.
2007-11-15
We analyze a general mechanism for producing a nearly scale-invariant spectrum of cosmological curvature perturbations during a contracting phase preceding a big bang, which can be entirely described using 4D effective field theory. The mechanism, based on first producing entropic perturbations and then converting them to curvature perturbations, can be naturally incorporated in cyclic and ekpyrotic models in which the big bang is modeled as a brane collision, as well as other types of cosmological models with a pre-big bang phase. We show that the correct perturbation amplitude can be obtained and that the spectral tilt n{sub s} tends to range from slightly blue to red, with 0.97
Imaging coexisting fluid domains in biomembrane models coupling curvature and line tension.
Baumgart, Tobias; Hess, Samuel T; Webb, Watt W
2003-10-23
Lipid bilayer membranes--ubiquitous in biological systems and closely associated with cell function--exhibit rich shape-transition behaviour, including bud formation and vesicle fission. Membranes formed from multiple lipid components can laterally separate into coexisting liquid phases, or domains, with distinct compositions. This process, which may resemble raft formation in cell membranes, has been directly observed in giant unilamellar vesicles. Detailed theoretical frameworks link the elasticity of domains and their boundary properties to the shape adopted by membranes and the formation of particular domain patterns, but it has been difficult to experimentally probe and validate these theories. Here we show that high-resolution fluorescence imaging using two dyes preferentially labelling different fluid phases directly provides a correlation between domain composition and local membrane curvature. Using freely suspended membranes of giant unilamellar vesicles, we are able to optically resolve curvature and line tension interactions of circular, stripe and ring domains. We observe long-range domain ordering in the form of locally parallel stripes and hexagonal arrays of circular domains, curvature-dependent domain sorting, and membrane fission into separate vesicles at domain boundaries. By analysing our observations using available membrane theory, we are able to provide experimental estimates of boundary tension between fluid bilayer domains. PMID:14574408
Hydrophobic surfactant proteins strongly induce negative curvature.
Chavarha, Mariya; Loney, Ryan W; Rananavare, Shankar B; Hall, Stephen B
2015-07-01
The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism. PMID:26153706
Hydrophobic Surfactant Proteins Strongly Induce Negative Curvature
Chavarha, Mariya; Loney, Ryan W.; Rananavare, Shankar B.; Hall, Stephen B.
2015-01-01
The hydrophobic surfactant proteins SP-B and SP-C greatly accelerate the adsorption of vesicles containing the surfactant lipids to form a film that lowers the surface tension of the air/water interface in the lungs. Pulmonary surfactant enters the interface by a process analogous to the fusion of two vesicles. As with fusion, several factors affect adsorption according to how they alter the curvature of lipid leaflets, suggesting that adsorption proceeds via a rate-limiting structure with negative curvature, in which the hydrophilic face of the phospholipid leaflets is concave. In the studies reported here, we tested whether the surfactant proteins might promote adsorption by inducing lipids to adopt a more negative curvature, closer to the configuration of the hypothetical intermediate. Our experiments used x-ray diffraction to determine how the proteins in their physiological ratio affect the radius of cylindrical monolayers in the negatively curved, inverse hexagonal phase. With binary mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), the proteins produced a dose-related effect on curvature that depended on the phospholipid composition. With DOPE alone, the proteins produced no change. With an increasing mol fraction of DOPC, the response to the proteins increased, reaching a maximum 50% reduction in cylindrical radius at 5% (w/w) protein. This change represented a doubling of curvature at the outer cylindrical surface. The change in spontaneous curvature, defined at approximately the level of the glycerol group, would be greater. Analysis of the results in terms of a Langmuir model for binding to a surface suggests that the effect of the lipids is consistent with a change in the maximum binding capacity. Our findings show that surfactant proteins can promote negative curvature, and support the possibility that they facilitate adsorption by that mechanism. PMID:26153706
Wiimote Experiments: Circular Motion
ERIC Educational Resources Information Center
Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary
2013-01-01
The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a…
Wiimote Experiments: Circular Motion
NASA Astrophysics Data System (ADS)
Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary
2013-03-01
The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a bicycle wheel.
ERIC Educational Resources Information Center
Library of Congress, Washington, DC. Copyright Office.
This circular answers some of the questions that are frequently asked about copyright, a form of protection provided by the laws of the United States to authors of "original works of authorship" including library, dramatic musical, artistic, and certain other intellectual works. The Copyright Act of 1976 (title 17 of the United States Code), which…
Physics at Future Circular Colliders
NASA Astrophysics Data System (ADS)
Kotwal, Ashutosh
2016-03-01
The Large Hadron Collider has been a grand success with the discovery of the Higgs boson, with bright prospects for additional discoveries since the recent increase in collider energy and the anticipated large datasets. Big open questions such as the nature of dark matter, the origin of the matter-antimatter asymmetry in the Universe, and the theoretical puzzle of the finely-tuned parameters in the Higgs sector, demand new physics principles that extend the established Standard Model paradigm. Future circular colliders in a substantially larger tunnel can house both a high luminosity electron-positron collider for precision measurements of Higgs and electroweak parameters, as well as a very high energy proton-proton collider which can directly manifest particles associated with these new physics principles. We discuss the physics goals of these future circular colliders, and the prospects for elucidating fundamental new laws of nature that will significantly extend our understanding of the Universe. Detailed studies of the discovery potential in specific benchmark models will be presented, with implications for detector design.
Voronoi-Based Curvature and Feature Estimation from Point Clouds.
Mérigot, Quentin; Ovsjanikov, Maks; Guibas, Leonidas
2011-06-01
We present an efficient and robust method for extracting curvature information, sharp features, and normal directions of a piecewise smooth surface from its point cloud sampling in a unified framework. Our method is integral in nature and uses convolved covariance matrices of Voronoi cells of the point cloud which makes it provably robust in the presence of noise. We show that these matrices contain information related to curvature in the smooth parts of the surface, and information about the directions and angles of sharp edges around the features of a piecewise-smooth surface. Our method is applicable in both two and three dimensions, and can be easily parallelized, making it possible to process arbitrarily large point clouds, which was a challenge for Voronoi-based methods. In addition, we describe a Monte-Carlo version of our method, which is applicable in any dimension. We illustrate the correctness of both principal curvature information and feature extraction in the presence of varying levels of noise and sampling density on a variety of models. As a sample application, we use our feature detection method to segment point cloud samplings of piecewise-smooth surfaces.
Curvature-undulation coupling as a basis for curvature sensing and generation in bilayer membranes.
Bradley, Ryan P; Radhakrishnan, Ravi
2016-08-30
We present coarse-grained molecular dynamics simulations of the epsin N-terminal homology domain interacting with a lipid bilayer and demonstrate a rigorous theoretical formalism and analysis method for computing the induced curvature field in varying concentrations of the protein in the dilute limit. Our theory is based on the description of the height-height undulation spectrum in the presence of a curvature field. We formulated an objective function to compare the acquired undulation spectrum from the simulations to that of the theory. We recover the curvature field parameters by minimizing the objective function even in the limit where the protein-induced membrane curvature is of the same order as the amplitude due to thermal undulations. The coupling between curvature and undulations leads to significant predictions: (i) Under dilute conditions, the proteins can sense a site of spontaneous curvature at distances much larger than their size; (ii) as the density of proteins increases the coupling focuses and stabilizes the curvature field to the site of the proteins; and (iii) the mapping of the protein localization and the induction of a stable curvature is a cooperative process that can be described through a Hill function. PMID:27531962
A new algorithm for evaluating 3D curvature and curvature gradient for improved fracture detection
NASA Astrophysics Data System (ADS)
Di, Haibin; Gao, Dengliang
2014-09-01
In 3D seismic interpretation, both curvature and curvature gradient are useful seismic attributes for structure characterization and fault detection in the subsurface. However, the existing algorithms are computationally intensive and limited by the lateral resolution for steeply-dipping formations. This study presents new and robust volume-based algorithms that evaluate both curvature and curvature gradient attributes more accurately and effectively. The algorithms first instantaneously fit a local surface to seismic data and then compute attributes using the spatial derivatives of the built surface. Specifically, the curvature algorithm constructs a quadratic surface by using a rectangle 9-node grid cell, whereas the curvature gradient algorithm builds a cubic surface by using a diamond 13-node grid cell. A dip-steering approach based on 3D complex seismic trace analysis is implemented to enhance the accuracy of surface construction and to reduce computational time. Applications to two 3D seismic surveys demonstrate the accuracy and efficiency of the new curvature and curvature gradient algorithms for characterizing faults and fractures in fractured reservoirs.
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.
A high-sensitive fiber curvature sensor using twin core fiber-based filter
NASA Astrophysics Data System (ADS)
Yin, G. L.; Lou, S. Q.; Lu, W. L.; Wang, X.
2014-04-01
A high-sensitive fiber curvature sensor is proposed and experimentally demonstrated in a large measurement range by using a twin core fiber (TCF)-based filter as sensor head. Applying the coupled-mode theory and equivalent refractive index model, we theoretically anticipate the "blue shift" of the transmission dips of the TCF-based filter when sensor head is bent. Experimentally, we fabricate an 86.9 mm TCF-based filter with a free spectral range of 49 nm and characterize its curvature performance by measuring the wavelength shift. A nonlinear "blue shift" of the wavelength is observed when we increase the curvature. The relationship between wavelength shift and curvature is a second-order polynomial function. In the range from 0 to 9.30 m-1, the maximum sensitivity is up to -14.7 nm/m-1. The measurement range can be further increased by selecting a shorter TCF.
Diameter Effect and Detonation Front Curvature of Ideal and Non-Ideal Explosives
NASA Astrophysics Data System (ADS)
Sandstrom, F. W.; Abernathy, R. L.; Leone, M. G.; Banks, M. L.
1999-06-01
Diameter effect and detonation front curvature data are presented for cast TNT, Tritonal, Urea Nitrate, ANFO, and two AN fertilizer/solid fuel explosives, designated Formula α and Formula β. Near ideal explosives, such as TNT, have relatively flat diameter effect curves and large detonation front curvatures. Although Tritonal exhibits a diameter effect curve similar to that of TNT, the presence of aluminum appears to reduce the front curvature. A low density, powdered material, Urea Nitrate, also exhibits near ideal behavior. The AN-based formulations exhibit marked non-ideal explosive characteristics: steeply falling diameter effect curves and small front curvatures. Although the AN-based explosives are similar in chemical composition and appear to have comparable infinite diameter detonation velocities, the failure diameters of Formula α and Formula β are significantly smaller than the failure diameter of ANFO.
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.
Anomalous Coupling Between Topological Defects and Curvature
NASA Astrophysics Data System (ADS)
Vitelli, Vincenzo; Turner, Ari M.
2004-11-01
We investigate a counterintuitive geometric interaction between defects and curvature in thin layers of superfluids, superconductors, and liquid crystals deposited on curved surfaces. Each defect feels a geometric potential whose functional form is determined only by the shape of the surface, but whose sign and strength depend on the transformation properties of the order parameter. For superfluids and superconductors, the strength of this interaction is proportional to the square of the charge and causes all defects to be repelled (attracted) by regions of positive (negative) Gaussian curvature. For liquid crystals in the one elastic constant approximation, charges between 0 and 4π are attracted by regions of positive curvature while all other charges are repelled.
Cosmic curvature from de Sitter equilibrium cosmology.
Albrecht, Andreas
2011-10-01
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.
Detonation wave curvature of PBXN-111
NASA Astrophysics Data System (ADS)
Forbes, J. W.; Lemar, E. R.; Baker, R. N.
1994-07-01
Spherical curvatures of detonation waves were measured by streak photography over the center 50 percent of PBXN-111 charges. These curvatures range from 54 to 143 mm for charge diameters of 41 to 68 mm and are not spherical near the edges of the charges. The wave fronts appear linear over about the last 3 mm at the charges edges. The angle between the detonation wave front and the edge of the charge was about 62 degrees over this last 3 mm for all the charges. Detonation velocity and wave front curvature data of PBXN-111 were used to calculate CJ zone lengths of 2-4 mm using the Wood-Kirkwood theory.
Extrinsic and intrinsic curvatures in thermodynamic geometry
NASA Astrophysics Data System (ADS)
Hosseini Mansoori, Seyed Ali; Mirza, Behrouz; Sharifian, Elham
2016-08-01
We investigate the intrinsic and extrinsic curvatures of a certain hypersurface in thermodynamic geometry of a physical system and show that they contain useful thermodynamic information. For an anti-Reissner-Nordström-(A)de Sitter black hole (Phantom), the extrinsic curvature of a constant Q hypersurface has the same sign as the heat capacity around the phase transition points. The intrinsic curvature of the hypersurface can also be divergent at the critical points but has no information about the sign of the heat capacity. Our study explains the consistent relationship holding between the thermodynamic geometry of the KN-AdS black holes and those of the RN (J-zero hypersurface) and Kerr black holes (Q-zero hypersurface) ones [1]. This approach can easily be generalized to an arbitrary thermodynamic system.
Substrate Curvature Gradient Drives Rapid Droplet Motion
NASA Astrophysics Data System (ADS)
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-01
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces.
Substrate curvature gradient drives rapid droplet motion.
Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui
2014-07-11
Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42 m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100 m/s on tapered surfaces. PMID:25062213
Scaling of curvature in subcritical gravitational collapse
NASA Astrophysics Data System (ADS)
Garfinkle, David; Duncan, G. Comer
1998-09-01
We perform numerical simulations of the gravitational collapse of a spherically symmetric scalar field. For those data that just barely do not form black holes we find the maximum curvature at the position of the central observer. We find a scaling relation between this maximum curvature and distance from the critical solution. The scaling relation is analogous to that found by Choptuik for the black hole mass for those data that do collapse to form black holes. We also find a periodic wiggle in the scaling exponent.
Wavefront reconstruction from tangential and sagittal curvature.
Canales, Javier; Barbero, Sergio; Portilla, Javier; López-Alonso, José Manuel
2014-12-10
In a previous contribution [Appl. Opt.51, 8599 (2012)], a coauthor of this work presented a method for reconstructing the wavefront aberration from tangential refractive power data measured using dynamic skiascopy. Here we propose a new regularized least squares method where the wavefront is reconstructed not only using tangential but also sagittal curvature data. We prove that our new method provides improved quality reconstruction for typical and also for highly aberrated wavefronts, under a wide range of experimental error levels. Our method may be applied to any type of wavefront sensor (not only dynamic skiascopy) able to measure either just tangential or tangential plus sagittal curvature data.
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.
Severe Penile Curvature following Otis Urethrotomy.
Karaguzel, Ersagun; Gur, Metin; Tok, Dogan S; Kazaz, Ilke O; Eren, Huseyin; Kutlu, Omer; Ozgur, Guner K
2013-01-01
Urethral stricture is a common urological pathology with a high recurrence rate after treatment. Urethral manipulations are among its main causes. In this paper, urethral stricture developed secondary to urethral catheterization and was treated with cold-knife internal urethrotomy and the Otis urethrotomy procedure. During the follow-up period, severe ventral penile curvature preventing sexual intercourse developed due to fibrosis of the corpus spongiosum and tunica albuginea of the penis. This ventral penile curvature was corrected with a separate operation using a tunica vaginalis flap harvested from the left scrotum.
[Guizhou planned parenthood circular].
1980-05-29
The Guizhou Provincial CCP Committee and the provinical people's government recently issued a circular on launching mass inspection of planned parenthood work throughout the province in late June. The inspection will look at whether or not the masses have been mobilized to pay serious attention to planned parenthood work, whether or not such education has been launched, what kind of concrete measures have been adopted, and what kind of concrete experiences have been learned. It will also include the implementation of birth control measures, the resolute prohibition on having a 3rd child, and the promotion of having only 1 child/couple. The circular urged the departments at all levels to strengthen their leadership over planned parenthood work, deepen investigation and study, continuously study the new situation and solve the new problems.
Circular inferences in schizophrenia.
Jardri, Renaud; Denève, Sophie
2013-11-01
A considerable number of recent experimental and computational studies suggest that subtle impairments of excitatory to inhibitory balance or regulation are involved in many neurological and psychiatric conditions. The current paper aims to relate, specifically and quantitatively, excitatory to inhibitory imbalance with psychotic symptoms in schizophrenia. Considering that the brain constructs hierarchical causal models of the external world, we show that the failure to maintain the excitatory to inhibitory balance results in hallucinations as well as in the formation and subsequent consolidation of delusional beliefs. Indeed, the consequence of excitatory to inhibitory imbalance in a hierarchical neural network is equated to a pathological form of causal inference called 'circular belief propagation'. In circular belief propagation, bottom-up sensory information and top-down predictions are reverberated, i.e. prior beliefs are misinterpreted as sensory observations and vice versa. As a result, these predictions are counted multiple times. Circular inference explains the emergence of erroneous percepts, the patient's overconfidence when facing probabilistic choices, the learning of 'unshakable' causal relationships between unrelated events and a paradoxical immunity to perceptual illusions, which are all known to be associated with schizophrenia. PMID:24065721
Circular inferences in schizophrenia.
Jardri, Renaud; Denève, Sophie
2013-11-01
A considerable number of recent experimental and computational studies suggest that subtle impairments of excitatory to inhibitory balance or regulation are involved in many neurological and psychiatric conditions. The current paper aims to relate, specifically and quantitatively, excitatory to inhibitory imbalance with psychotic symptoms in schizophrenia. Considering that the brain constructs hierarchical causal models of the external world, we show that the failure to maintain the excitatory to inhibitory balance results in hallucinations as well as in the formation and subsequent consolidation of delusional beliefs. Indeed, the consequence of excitatory to inhibitory imbalance in a hierarchical neural network is equated to a pathological form of causal inference called 'circular belief propagation'. In circular belief propagation, bottom-up sensory information and top-down predictions are reverberated, i.e. prior beliefs are misinterpreted as sensory observations and vice versa. As a result, these predictions are counted multiple times. Circular inference explains the emergence of erroneous percepts, the patient's overconfidence when facing probabilistic choices, the learning of 'unshakable' causal relationships between unrelated events and a paradoxical immunity to perceptual illusions, which are all known to be associated with schizophrenia.
Switchable circular beam deflectors
NASA Astrophysics Data System (ADS)
Shang, Xiaobing; Joshi, Pankaj; Tan, Jin-Yi; De Smet, Jelle; Cuypers, Dieter; Baghdasaryan, Tigran; Vervaeke, Michael; Thienpont, Hugo; De Smet, Herbert
2016-04-01
In this work, we report two types of electrically tunable photonic devices with circularly symmetric polarization independent beam steering performance (beam condensing resp. beam broadening). The devices consist of circular micro grating structures combined with nematic liquid crystal (LC) layers with anti-parallel alignment. A single beam deflector converts a polarized and monochromatic green laser beam (λ =543.5 nm) into a diffraction pattern, with the peak intensity appearing at the third order when 0~{{V}\\text{pp}} is applied and at the zeroth order (no deflection) for voltages above 30~{{V}\\text{pp}} . Depending on the shape of the grating structure (non-inverted or inverted), the deflection is inwards or outwards. Both grating types can be made starting from the same diamond-tooled master mold. A polarized white light beam is symmetrically condensed resp. broadened over 2° in the off state and is passed through unchanged in the on state. By stacking two such devices with mutually orthogonal LC alignment layers, polarization independent switchable circular beam deflectors are realized with a high transmittance (>80%), and with the same beam steering performance as the polarization dependent single devices.
Charged Particle Optics in Circular Higgs Factory
Cai, Yunhai
2015-02-26
Similar to a super B-factory, a circular Higgs factory will require strong focusing systems near the interaction points and a low-emittance lattice in arcs to achieve a factory luminosity. At electron beam energy of 120 GeV, beamstrahlung effects during the collision pose an additional challenge to the collider design. In particular, a large momentum acceptance at 2 percent level is necessary to retain an adequate beam lifetime. This turns out to be the most challenging aspect in the design of circular Higgs factory. In this paper, an example will be provided to illustrate the beam dynamics in circular Higgs factory, emphasizing on the chromatic optics. Basic optical modules and advanced analysis will be presented. Most important, we will show that 2% momentum aperture is achievable
Brown, M.A.; Park, T.-S.; Rosakis, A.; Ustundag, E.; Huang, Y.; Tamura, N.; Valek, B.C.
2006-01-01
Background. The Coherent Gradient Sensor (CGS) is a shearing interferometer which has been proposed for the rapid, full-field measurement of deformation states (slopes and curvatures) in thin film-wafer substrate systems, and for the subsequent inference of stresses in the thin films. This approach needs to be verified using a more well-established but time-consuming grain orientation and stress measurement tool, X-ray microdiffraction. Method of Approach. Both CGS and XRD are used to measure the deformation state of the same W film/Si wafer at room temperature. CGS provides a global, wafer-level measurement of slopes while XRD provides a local micromeasurement of lattice rotations. An extreme case of a circular Si wafer with a circular W film island in its center is used because of the presence of discontinuous system curvatures across the wafer. The results are also compared with a theoretical model based on elastic plate analysis of the axisymmetric biomaterial film-substrate system. Results and Conclusions. Slope and curvature measurements by XRD and by CGS compare very well with each other and with theory. The favorable comparison demonstrates that wafer-level CGS metrology provides a quick and accurate alternative to other measurements. It also demonstrates the accuracy of plate theory in modeling thin film-substrate systems, even in the presence of curvature discontinuities.
Circular structures in retroviral and cellular genomes.
Albert, F G; Bronson, E C; Fitzgerald, D J; Anderson, J N
1995-10-01
A computer program for predicting DNA bending from nucleotide sequence was used to identify circular structures in retroviral and cellular genomes. An 830-base pair circular structure was located in a control region near the center of the genome of the human immunodeficiency virus type I (HIV-I). This unusual structure displayed relatively smooth planar bending throughout its length. The structure is conserved in diverse isolates of HIV-I, HIV-II, and simian immunodeficiency viruses, which implies that it is under selective constraints. A search of all sequences in the GenBank data base was carried out in order to identify similar circular structures in cellular DNA. The results revealed that the structures are associated with a wide range of sequences that undergo recombination, including most known examples of DNA inversion and subtelomeric translocation systems. Circular structures were also associated with replication and transposition systems where DNA looping has been implicated in the generation of large protein-DNA complexes. Experimental evidence for the structures was provided by studies which demonstrated that two sequences detected as circular by computer preferentially formed covalently closed circles during ligation reactions in vitro when compared to nonbent fragments, bent fragments with noncircular shapes, and total genomic DNA. In addition, a single T-->C substitution in one of these sequences rendered it less planar as seen by computer analysis and significantly reduced its rate of ligase-catalyzed cyclization. These results permit us to speculate that intrinsically circular structures facilitate DNA looping during formation of the large protein-DNA complexes that are involved in site- and region-specific recombination and in other genomic processes. PMID:7559522
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.
What can the observation of nonzero curvature tell us?
NASA Astrophysics Data System (ADS)
Guth, Alan H.; Nomura, Yasunori
2012-07-01
The eternally inflating multiverse provides a consistent framework to understand coincidences and fine-tuning in the Universe. As such, it provides the possibility of finding another coincidence: if the amount of slow-roll inflation in our past was only slightly more than the anthropic threshold, then spatial curvature might be measurable. We study this issue in detail, particularly focusing on the question: “If future observations reveal nonzero curvature, what can we conclude?” We find that whether an observable signal arises or not depends crucially on three issues: the cosmic history just before the observable inflation, the measure adopted to define probabilities in the eternally inflating spacetime, and the sign and strength of the correlation between the tunneling and slow-roll parts of the potential. We find that if future measurements find positive curvature at the level Ωk≲-10-4, then the framework of the eternally inflating multiverse, as currently understood, is excluded with high significance. If the measurements instead reveal negative curvature at the level Ωk≳10-4, then we can conclude that (1) diffusive (new or chaotic type) eternal inflation did not occur in our immediate past; (2) our pocket universe was born by a bubble nucleation; (3) the probability measure does not reward volume increase; and (4) the origin of the observed slow-roll inflation is an accidental feature of the potential, presumably selected by anthropic conditions, and not due to a theoretical mechanism ensuring the flatness of the potential. Discovery of Ωk≳10-4 would also give us nontrivial information about the correlation between the tunneling and slow-roll parts of the potential; for example, a strong correlation favoring large N would be ruled out in certain measures. We also address the question of whether the current constraint on Ωk is consistent with multiverse expectations; we find the answer to be yes, except that current observations, for many choices
Size effect and detonation front curvature
Souers, P. C., LLNL
1997-07-01
Heat flow in a cylinder with internal heating is used as a basis for deriving a simple theory of detonation front curvature, leading to the prediction of quadratic curve shapes. A thermal conductivity of 50 MW/mm{sup 2} is found for TATB samples.
Curvature instability in passive diffractive resonators.
Tlidi, M; Vladimirov, A G; Mandel, Paul
2002-12-01
We study the stability of localized structures in a passive optical bistable system. We show that there is a critical value of the input field intensity above which localized structures are unstable with respect to a curvature instability. Beyond this instability boundary, a transition from the localized branch of solutions to stable hexagons is found. PMID:12485009
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.
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.
Constraining inverse curvature gravity with supernovae
Mena, Olga; Santiago, Jose; Weller, Jochen; /University Coll., London /Fermilab
2005-10-01
We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.
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.
The primordial curvature perturbation from vector fields of general non-Abelian groups
Karciauskas, Mindaugas
2012-01-01
We consider the generation of primordial curvature perturbation by general non-Abelian vector fields without committing to a particular group. Self-interactions of non-Abelian fields make the field perturbation non-Gaussian. We calculate the bispectrum of the field perturbation using the in-in formalism at tree level. The bispectrum is dominated by the classical evolution of fields outside the horizon. In view of this we show that the dominant contribution can be obtained from the homogeneous classical equation of motion. Then we calculate the power spectrum of the curvature perturbation. The anisotropy in spectrum is suppressed by the number of fields. This makes it possible for vector fields to be responsible for the total curvature perturbation in the Universe without violating observational bounds on statistical anisotropy. The bispectrum of the curvature perturbation is also anisotropic. Finally we give an example of the end-of-inflation scenario in which the curvature perturbation is generated by vector gauge fields through varying gauge coupling constant(s), which in covariant derivatives couples the Higgs field to the vector fields. We find that reasonably large gauge groups may result in the observable anisotropy in the power spectrum of the curvature perturbation.
Development of a variable curvature mirror for the delay lines of the VLT interferometer
NASA Astrophysics Data System (ADS)
Ferrari, M.
1998-02-01
This paper presents the variable curvature mirror (vcm) serving for beam management purposes in the interferometric mode of the Very Large Telescope (VLT). This special device located in the delay line system provides for a precise positioning of the pupil image of an individual telescope in the recombination laboratory. The particularity of this active mirror is its continuous variable curvature from (2800 mm)(-1) to (84 mm)(-1) which has to be achieved with a reasonable optical quality. This large curvature variation needed in the system, lead us to extend the classical theory of elasticity to the range of large deformations (i.e. the achieved flexions are larger than the mirror's thickness). This new approach, in the domain of active optics, gave us a theoretical support to determine the physical parameters of the mirror (thickness distribution, loading configuration). Today the vcm system has been thoroughly tested and its performances evaluated. The experimental results have shown good agreements with the theory.
Tests on Stiffened Circular Cylinders
NASA Technical Reports Server (NTRS)
Holt, Marshall
1941-01-01
Compressive tests were made of two series of stiffened circular cylindrical shells under axial load. All the shells were 16 inches in diameter by 24 inches in length and were made of aluminum-alloy sheet curved to the proper radius and welded with one longitudinal weld. The ratios of diameter to thickness of shell wall in the two series of specimens were 258 and 572. Strains were measured with Huggenberger tensometers at a number of gage lines on the stiffeners and shell. The results of these tests indicate that a spacing of circumferential stiffeners equal to 0.67 times the radius is too great to strengthen the shell wall appreciably. The results are not inclusive enough to show the optimum in stiffeners. Plain cylinders without stiffeners developed ultimate strengths approximately half as great as the buckling strengths computed by the equation resulting from the classical theory and slightly greater than those computed by Donnell's large deflection theory.
NASA Astrophysics Data System (ADS)
Zhao, Hui; Fan, Xuewu; Pang, Zhihai; Ren, Guorui; Wang, Wei; Xie, Yongjie; Ma, Zhen; Du, Yunfei; Su, Yu; Wei, Jingxuan
2015-02-01
In recent years, optical zoom imaging without moving elements has received much attention. The key to realizing this technique lies in the design of the variable-curvature mirror (VCM). To obtain enough optical magnification, the VCM should be able to change its radius of curvature over a wide range. In other words, the VCM must be able to provide a large sagittal variation, which requires the mirror material to be robust during curvature variation, require little force to deform, and have high ultimate strength. Carbon-fiber-reinforced polymer (CFRP) satisfies all these requirements and is suitable for fabricating such a VCM. Therefore, in this research, a CFRP prototype VCM has been designed, fabricated, and tested. With a diameter of 100 mm, a thickness of 2 mm, and an initial radius of curvature of 1740 mm, this VCM can provide a maximum 23-μm sagittal variation and a minimum and maximum radius of curvature of 1705 and 1760 mm.
Velocity-curvature relationship of colliding spherical calcium waves in rat cardiac myocytes.
Wussling, M H; Scheufler, K; Schmerling, S; Drygalla, V
1997-01-01
Colliding spherical calcium waves in enzymatically isolated rat cardiac myocytes develop new wavefronts propagating perpendicular to the original direction. When investigated by confocal laser scanning microscopy (CLSM), using the fluorescent Ca2+ indicator fluo-3 AM, "cusp"-like structures become visible that are favorably approximated by double parabolae. The time-dependent position of the vertices is used to determine propagation velocity and negative curvature of the wavefront in the region of collision. It is evident that negatively curved waves propagate faster than positively curved, single waves. Considering two perfectly equal expanding circular waves, we demonstrated that the collision of calcium waves is due to an autocatalytic process (calcium-induced calcium release), and not to a simple phenomenon of interference. Following the spatiotemporal organization in simpler chemical systems maintained under conditions far from the thermodynamic equilibrium (Belousov-Zhabotinskii reaction), the dependence of the normal velocity on the curvature of the spreading wavefront is given by a linear relation. The so-called velocity-curvature relationship makes clear that the velocity is enhanced by curvature toward the direction of forward propagation and decreased by curvature away from the direction of forward propagation (with an influence of the diffusion coefficient). Experimentally obtained velocity data of both negatively and positively curved calcium waves were approximated by orthogonal weighted regression. The negative slope of the straight line resulted in an effective diffusion coefficient of 1.2 x 10(-4) mm2/s. From the so-called critical radius, which must be exceeded to initiate a traveling calcium wave, a critical volume (with enhanced [Ca2+]i) of approximately 12 microm3 was calculated. This is almost identical to the volume that is occupied by a single calcium spark. Images FIGURE 2 FIGURE 4 FIGURE 5 FIGURE 6 PMID:9284291
CFRP variable curvature mirror used for realizing non-moving-element optical zoom imaging
NASA Astrophysics Data System (ADS)
Zhao, Hui; Fan, Xuewu; Pang, Zhihai; Ren, Guorui; Wang, Wei; Xie, Yongjie; Ma, Zhen; Du, Yunfei; Su, Yu; Wei, Jingxuan
2014-12-01
In recent years, how to eliminate moving elements while realizing optical zoom imaging has been paid much attention. Compared with the conventional optical zooming techniques, removing moving elements would bring in many benefits such as reduction in weight, volume and power cost and so on. The key to implement non-moving-element optical zooming lies in the design of variable curvature mirror (VCM). In order to obtain big enough optical magnification, the VCM should be capable of generating a large variation of saggitus. Hence, the mirror material should not be brittle, in other words the corresponding ultimate strength should be high enough to ensure that mirror surface would not be broken during large curvature variation. Besides that, the material should have a not too big Young's modulus because in this case less force is required to generate a deformation. Among all available materials, for instance SiC, Zerodur and et.al, CFRP (carbon fiber reinforced polymer) satisfies all these requirements and many related research have proven this. In this paper, a CFRP VCM is designed, fabricated and tested. With a diameter of 100mm, a thickness of 2mm and an initial curvature radius of 1740mm, this component could change its curvature radius from 1705mm to 1760mm, which correspond to a saggitus variation of nearly 23μm. The work reported further proves the suitability of CFRP in constructing variable curvature mirror which could generate a large variation of saggitus.
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.
Cold Rydberg atoms in circular states
NASA Astrophysics Data System (ADS)
Anderson, David; Schwarzkopf, Andrew; Raithel, Georg
2012-06-01
Circular-state Rydberg atoms are interesting in that they exhibit a unique combination of extraordinary properties; long lifetimes (˜n^5), large magnetic moments (l=|m|=n-1) and no first order Stark shift. Circular states have found applications in cavity quantum electrodynamics and precision measurements [1,2], among other studies. In this work we present the production of circular states in an atom trapping apparatus using an adiabatic state-switching method (the crossed-field method [3]). To date, we have observed lifetimes of adiabatically prepared states of several milliseconds. Their relatively large ionization electric fields have been verified by time-of-flight signatures of ion trajectories. We intend to explore the magnetic trapping of circular state Rydberg atoms, as well as their production and interaction properties in ultra-cold and degenerate samples.[4pt] [1] P. Bertet et al., Phys. Rev. Lett., 88, 14 (2002)[0pt] [2] M. Brune et al., Phys. Rev. Lett., 72, 21 (1994)[0pt] [3] D. Delande and J.C. Gay, Europhys. Lett., 5, 303-308 (1988).
NASA Astrophysics Data System (ADS)
Landis, Emily K.; Karnick, Pushpak
2006-02-01
This study uses new three-dimensional imaging techniques to compare the articular curvature of the proximal tibial articular surface of hominoids. It has been hypothesized that the curvature of the anteroposterior contour of the lateral condyle in particular can be used to differentiate humans and apes and reflect locomotor function. This study draws from a large comparative sample of extant hominoids to obtain quantitative curvature data. Three-dimensional models of the proximal tibiae of 26 human, 15 chimpanzee, 15 gorilla, 17 orangutan, 16 gibbon and four Australopithecus fossil casts (AL 129-1b, AL 288-1aq, AL 333x-26, KNM-KP 29285A) were acquired with a Cyberware Model 15 laser digitizer. Curvature analysis was accomplished using a software program developed at Arizona State University's Partnership for Research In Stereo Modeling (PRISM) lab, which enables the user to extract curvature profiles and compute the difference between analogous curves from different specimens. Results indicate that the curvature of chimpanzee, gorilla and orangutan tibiae is significantly different from the curvature of human tibiae, thus supporting the hypothesized dichotomy between humans and great apes. The non-significant difference between gibbons and all other taxa indicates that gibbons have an intermediate pattern of articular curvature. All four Australopithecus tibia were aligned with the great apes.
Curvature Elasticities of the Micellar Nematics.
NASA Astrophysics Data System (ADS)
Zhou, E.
This dissertation is concerned with the curvature elastic and viscous properties of two micellar nematic systems. The mixtures of the first system had a nematic phase (N_{rm L}) with a second order transition to a lamellar smectic phase. The second system has three different nematic phases, two uniaxial phases (N_{rm L} and N_{rm C}) and an intermediate biaxial nematic phase (N_ {rm bx}). The experimental procedures used in this research are modifications of the conventional method which is based on magnetic field induced deformations of surface aligned films. Modifications were required for measurements close to the nematic-lamellar smectic transition, where the elastic constants assume very large values, and for the biaxial nematic phase and the adjacent higher temperature uniaxial phase, where the surface by itself does not impose a homogeneous alignment. A theoretical study of limiting cases, of small deformations in general and of small deformations at high magnetic fields, proved useful to select the proper experimental conditions and to evaluate the data. The nematic-lamellar smectic transition was studied on mixtures of decylammoniumchloride (DACl), ammoniumchloride, and water. The bend elastic coefficient and the rotational viscosity were found to vary over more than three orders of magnitude due to an exponential divergence at the transition. We obtained an exponent of 1.07 +/- 0.05 for a weight ratio of DACl/NHL_4Cl = 20, and an exponent of 0.87 +/- 0.02 for a weight ratio of 10, but an unexpected thermal hysteresis interferes with a reliable determination of the critical properties. The three different nematic phases were studied on potassium laurate in mixtures with 1-decanol and D _2O. The elastic constants for bend and splay in the N_{rm L} phase are nearly equal. They are about one order of magnitude smaller than the lowest values measured in the nematic phase of the DACl system. Because of surface alignment problems, only one elastic constant could
Planetary Rings: Circular and Non-circular
NASA Astrophysics Data System (ADS)
French, R. G.; Nicholson, P. D.; Colwell, J.; Marouf, E. A.; Rappaport, N. J.; Hedman, M. M.; McGhee, C.; Lonergan, K.; Sepersky, T.
2011-12-01
Although Saturn's rings appear at first glance to be axisymmetric, more precise measurements reveal that many of the gap edges and narrow ringlets within the rings are noncircular, a characteristic they share with the narrow uranian rings. A careful study of these features is of interest for several reasons: (i) resonantly-forced perturbations are believed to prevent the rings from spreading under the influence of collisions, (ii) unforced distortions, mostly eccentricities, can lead to estimates of the surface mass density and viscosity of the rings, and (iii) accurately-measured apsidal precession rates provide information on Saturn's zonal gravity harmonics. We present preliminary results from a comprehensive study of noncircular features in the Cassini Division and in the C ring. The data used in this study come from three Cassini experiments, and cover the period from May 2005 to September 2010. Over 120 stellar occultations have been observed by the Ultraviolet Imaging Spectrometer (UVIS) and by the Visual and Infrared Imaging Spectrometer (VIMS). In addition, we include 12 occultations of the spacecraft's radio Radio Science Subsystem (RSS) by the rings observed on Earth in May-September 2005. The simplest noncircular features can be modeled as inclined Keplerian ellipses, freely precessing under the influence of Saturn's oblate gravity field. In agreement with similar fits to the VIMS occultation data alone, we find that the inner edges of 7 of the 8 gaps within the Cassini Division are eccentric, with amplitudes ranging from 0.9 km to 28.3 km. In contrast, most of the outer gap edges are near-circular. We also find a rich assortment of normal modes on the edges of both ringlets and gaps. We have searched for modes with wavenumber m as high as 8, and find convincing evidence for modes with m = 0, 2, 3, 4 and 5, all with amplitudes of 1 km or greater. In some cases, as many as 3 or 4 normal modes coexist at a single edge with comparable amplitudes. Our fits
Diameter Effect Curve and Detonation Front Curvature Measurements for ANFO
NASA Astrophysics Data System (ADS)
Catanach, R. A.; Hill, L. G.
2002-07-01
Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium-nitrate/fuel-oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm (approximately failure diameter) to 205 mm, with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity Dn, and local total curvature kappa, were generated as a function of radius R, then plotted parametrically to generate a Dn(kappa) function. The observed behavior deviates substantially from that of previous explosives, for which curves for different diameters overlay well for small kappa but diverge for large kappa, and for which kappa increases monotonically with R. For ANFO, we find that Dn(kappa) curves for individual sticks 1) show little or no overlap--with smaller sticks lying to the right of larger ones, 2) exhibit a large velocity deficit with little kappa variation, and 3) reach a peak kappa at an intermediate R.
Diameter effect curve and detonation front curvature measurements for ANFO
Catanach, R. A.; Hill, L. G.
2001-01-01
Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium-nitrate/fuel-oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm ({approx} failure diameter) to 205 mm, with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity Dn, and local total curvature {kappa}, were generated as a function of radius R, then plotted parametrically to generate a Dn({kappa}) function. The observed behavior deviates substantially from that of previous explosives, for which curves for different diameters overlay well for small {kappa} but diverge for large {kappa}, and for which {kappa} increases monotonically with R. For ANFO, we find that Dn({kappa}) curves for individual sticks (1) show little or no overlap--with smaller sticks lying to the right of larger ones, (2) exhibit a large velocity deficit with little {kappa} variation, and (3) reach a peak {kappa} at an intermediate R.
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.
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.
Coarse-grained modeling of DNA curvature
NASA Astrophysics Data System (ADS)
Freeman, Gordon S.; Hinckley, Daniel M.; Lequieu, Joshua P.; Whitmer, Jonathan K.; de Pablo, Juan J.
2014-10-01
The interaction of DNA with proteins occurs over a wide range of length scales, and depends critically on its local structure. In particular, recent experimental work suggests that the intrinsic curvature of DNA plays a significant role on its protein-binding properties. In this work, we present a coarse grained model of DNA that is capable of describing base-pairing, hybridization, major and minor groove widths, and local curvature. The model represents an extension of the recently proposed 3SPN.2 description of DNA [D. M. Hinckley, G. S. Freeman, J. K. Whitmer, and J. J. de Pablo, J. Chem. Phys. 139, 144903 (2013)], into which sequence-dependent shape and mechanical properties are incorporated. The proposed model is validated against experimental data including melting temperatures, local flexibilities, dsDNA persistence lengths, and minor groove width profiles.
Space-time curvature and cosmology
NASA Astrophysics Data System (ADS)
Nurgaliev, I. S.; Ponomarev, V. N.
1982-10-01
The possibility is considered of obtaining a steady-state cosmological solution in the framework of the Einstein-Cartan theory. It is found that the Einstein-Cartan equations without the cosmological constant admit a solution in the form of the static de Sitter metric for a specific value of the spin-spin gravitational interaction constant, whose introduction is required by gauge theory. It is shown that the steady-state solution might serve as a model for the pre-Friedmann stage of the expansion of the universe, when the spin-curvature interaction was comparable to the interaction between space-time curvature and energy-momentum. A value of about 10 to the -20th is obtained for the spin-spin interaction constant in the case where the de Sitter stage occurs at quantum densities (10 to the 94th g/cu cm).
Trench curvature and deformation of the subducting lithosphere
NASA Astrophysics Data System (ADS)
Schettino, Antonio; Tassi, Luca
2012-01-01
The subduction of oceanic lithosphere is generally accompanied by downdip and lateral deformation. The downdip component of strain is associated with external forces that are applied to the slab during its sinking, namely the gravitational force and the mantle resistance to penetration. Here, we present theoretical arguments showing that a tectonic plate is also subject to a predictable amount of lateral deformation as a consequence of its bending along an arcuate trench zone, independently from the long-term physical processes that have determined the actual curvature of the subduction zone. In particular, we show that the state of lateral strain and the lateral strain rate of a subducting slab depend from geometric and kinematic parameters, such as trench curvature, dip function and subduction velocity. We also demonstrate that the relationship between the state of lateral strain in a subducting slab and the geometry of bending at the corresponding active margin implies a small component of lateral shortening at shallow depths, and may include large extensional lateral deformation at intermediate depths, whereas a state of lateral mechanical equilibrium can only represent a localized exception. Our formulation overcomes the flaws of the classic 'ping-pong ball' model for the bending of the lithosphere at subduction zones, which lead to severe discrepancies with the observed geometry and style of deformation of the modern subducting slabs. A study of the geometry and seismicity of eight modern subduction zones is performed, to assess the validity of the theoretical relationship between trench curvature, slab dip function, and lateral strain rate. The strain pattern within the eight present-day slabs, which is reconstructed through an analysis of Harvard CMT solutions, shows that tectonic plates cannot be considered as flexible-inextensible spherical caps, whereas the lateral intraslab deformation which is accommodated through seismic slip can be explained in terms
Transformation optics, curvature and beyond (Conference Presentation)
NASA Astrophysics Data System (ADS)
McCall, Martin W.
2016-04-01
Although the transformation algorithm is very well established and implemented, some intriguing questions remain unanswered. 1) In what precise mathematical sense is the transformation optics algorithm `exact'? The invariance of Maxwell's equations is well understood, but in what sense does the same principle not apply to acoustics (say)? 2) Even if the fields are transformed in a way that apparently mimic vacuum perfectly, it is easy to construct very simple examples where the impedance of the transformed medium is no longer isotropic and homogeneous. This would seem to imply a fundamental shortcoming in any claim that electromagnetic cloaking has been reduced to technology. 3) Transformations are known to exist that introduce a discrepancy between the Poynting vector and the wave-vector. Does this distinction carry any physical significance? We have worked extensively on understanding a commonality between transformation theories that operates at the level of rays - being interpreted as geodesics of an appropriate manifold. At this level we now understand that the *key* problem underlying all attempts to unify the transformational approach to disparate areas of physics is how to relate the transformation of the base metric (be it Euclidean for spatial transformation optics, or Minkowskian for spacetime transformation optics) to the medium parameters of a given physical domain (e.g. constitutive parameters for electromagnetism, bulk modulus and mass density for acoustics, diffusion constant and number density for diffusion physics). Another misconception we will seek to address is the notion of the relationship between transformation optics and curvature. Many have indicated that transformation optics evinces similarities with Einstein's curvature of spacetime. Here we will show emphatically that transformation optics cannot induce curvature. Inducing curvature in an electromagnetic medium requires the equivalent of a gravitational source. We will propose a scheme
Curvature continuity in arbitrary bicubic Bezier patches
NASA Technical Reports Server (NTRS)
Roach, Robert L.
1990-01-01
Two methods are outlined for imposing interpatch curvature continuity in existing Bezier bicubic patch surfaces. Each method assumes that coordinates of the corners of the patches can not be altered but the interior Bezier control point can. Each method also preserves outer edge slope and outer corner twist derivatives. Neither method requires intersection or C0 continuity nor slope or C1 continuity at the start. A computer program for each method is given in the appendices.
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.
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
Circularly polarized conical patterns from circular microstrip antennas
NASA Technical Reports Server (NTRS)
Huang, J.
1984-01-01
A method is presented for generating circularly polarized conical patterns from circular microstrip antennas. These antennas are excited at higher order modes and require different feed arrangements for different mode excitations. It is determined that the peak direction of the conical pattern can be varied over a wide angular range. Modal expansion technique is employed to calculate the radiation patterns of these antennas.
The nature of circular maria based on gravity studies.
NASA Technical Reports Server (NTRS)
Phillips, R. J.; Conel, J. E.; Sjogren, W. L.
1973-01-01
Current thinking on the evolution of major lunar morphological features, i.e., large lunar circular basins, and on the nature and origin of surface structures observed in the fill deposits is summarized. The great lunar circular basins must result from high-velocity impact of large bodies with the moon. A hydrostatic mechanism is outlined, and a working hypothesis is presented for the evolution of lunar circular basins subsequent to their origin by impact. In the main appeal is made to Doppler gravity data to support the hypothesis, although photographic and altimetric information is also used. It is considered that all large ringed circular basins follow a common evolutionary path of superisostatic volcanic flooding followed by partial and variable isostatic adjustment. The difference between basins is the amount of flooding, which in turn may be related to the center of figure-center of mass offset of the moon.
Circularly polarized microstrip antennas
NASA Technical Reports Server (NTRS)
Lo, Y. T.; Engst, B.; Lee, R. Q. H.
1985-01-01
A simple microstrip antenna can be made to radiate EM waves of any polarization, in particular, the circular polarization (CP) without any phasing network and power divider. A simple and accurate theory for this family of antennas was developed. However, the CP bandwidth, (CPBW) the bandwidth in which the axial ratio (AR) is less than a certain specified value, is very small. Most of the experimental designs were made for a feed placed along the diagonal of the patch. It is shown that there are practically infinitely many possible designs with different feed location. The speculation that other designs might give a wider bandwidth is clarified and an effective method for broadening the bandwidth is shown.
Kerley, P.L.
1959-01-01
A small-size antenna having a doughnut-shaped field pattern and which can act both as an antenna and a resonant circuit is described. The antenna is of the slotted type and comprises a resonant cavity with a center hole. A circular slot is provided in one wall of the cavity concentric with the hole and a radio frequency source is connected across the slot. The pattern and loading of the antenna are adjusted by varying the position and shape of a center element slidably disposed within the hole and projecting from the slotted side of the resonant cavity. The disclosed structure may also be used to propagate the oscillator signal down a transniission line by replacing the center element with one leg of the transmission line in a spaced relation from the walls of the cavity.
Circularly Polarized MHOHG with Bichromatic Circularly Polarized Laser Pulses
NASA Astrophysics Data System (ADS)
Bandrauk, Andre D.; Mauger, Francois; Uzer, Turgay
2016-05-01
Circularly polarized MHOHG-Molecular High Order Harmonic Generation is shown to occur efficiently with intense ultrashort bichromatic circularly polarized pulses due to frequent electron-parent -ion recollision with co-or counter-rotating incident circular pulses as predicted in 1995. We show in this context that molecules offer a very robust and efficient frameworkfor the production of circularly polarized harmonics for the generation of single circularly polarized ``attosecond'' pulses. The efficiency of such new MHOHG is shown to depend on the compatibility of the symmetry of the molecular medium with the net electric field generated by the combination of the laser pulses.Using a time-dependent symmetry analysis with concrete examples such as H 2 + vs H 3 + we show how all the features(harmonic order and ∧ polarization) of MHOHG can be explained and predicted.
Circularization pathway of a bacterial group II intron.
Monat, Caroline; Cousineau, Benoit
2016-02-29
Group II introns are large RNA enzymes that can excise as lariats, circles or in a linear form through branching, circularization or hydrolysis, respectively. Branching is by far the main and most studied splicing pathway while circularization was mostly overlooked. We previously showed that removal of the branch point A residue from Ll.LtrB, the group II intron from Lactococcus lactis, exclusively leads to circularization. However, the majority of the released intron circles harbored an additional C residue of unknown origin at the splice junction. Here, we exploited the Ll.LtrB-ΔA mutant to study the circularization pathway of bacterial group II introns in vivo. We demonstrated that the non-encoded C residue, present at the intron circle splice junction, corresponds to the first nt of exon 2. Intron circularization intermediates, harboring the first 2 or 3 nts of exon 2, were found to accumulate showing that branch point removal leads to 3' splice site misrecognition. Traces of properly ligated exons were also detected functionally confirming that a small proportion of Ll.LtrB-ΔA circularizes accurately. Overall, our data provide the first detailed molecular analysis of the group II intron circularization pathway and suggests that circularization is a conserved splicing pathway in bacteria.
Circularization pathway of a bacterial group II intron
Monat, Caroline; Cousineau, Benoit
2016-01-01
Group II introns are large RNA enzymes that can excise as lariats, circles or in a linear form through branching, circularization or hydrolysis, respectively. Branching is by far the main and most studied splicing pathway while circularization was mostly overlooked. We previously showed that removal of the branch point A residue from Ll.LtrB, the group II intron from Lactococcus lactis, exclusively leads to circularization. However, the majority of the released intron circles harbored an additional C residue of unknown origin at the splice junction. Here, we exploited the Ll.LtrB-ΔA mutant to study the circularization pathway of bacterial group II introns in vivo. We demonstrated that the non-encoded C residue, present at the intron circle splice junction, corresponds to the first nt of exon 2. Intron circularization intermediates, harboring the first 2 or 3 nts of exon 2, were found to accumulate showing that branch point removal leads to 3′ splice site misrecognition. Traces of properly ligated exons were also detected functionally confirming that a small proportion of Ll.LtrB-ΔA circularizes accurately. Overall, our data provide the first detailed molecular analysis of the group II intron circularization pathway and suggests that circularization is a conserved splicing pathway in bacteria. PMID:26673697
Stable hypersurfaces with zero scalar curvature in Euclidean space
NASA Astrophysics Data System (ADS)
Alencar, Hilário; do Carmo, Manfredo; Neto, Gregório Silva
2016-10-01
In this paper we prove some results concerning stability of hypersurfaces in the four dimensional Euclidean space with zero scalar curvature. First we prove there is no complete stable hypersurface with zero scalar curvature, polynomial growth of integral of the mean curvature, and with the Gauss-Kronecker curvature bounded away from zero. We conclude this paper giving a sufficient condition for a regular domain to be stable in terms of the mean and the Gauss-Kronecker curvatures of the hypersurface and the radius of the smallest extrinsic ball which contains the domain.
Distributed mean curvature on a discrete manifold for Regge calculus
NASA Astrophysics Data System (ADS)
Conboye, Rory; Miller, Warner A.; Ray, Shannon
2015-09-01
The integrated mean curvature of a simplicial manifold is well understood in both Regge Calculus and Discrete Differential Geometry. However, a well motivated pointwise definition of curvature requires a careful choice of the volume over which to uniformly distribute the local integrated curvature. We show that hybrid cells formed using both the simplicial lattice and its circumcentric dual emerge as a remarkably natural structure for the distribution of this local integrated curvature. These hybrid cells form a complete tessellation of the simplicial manifold, contain a geometric orthonormal basis, and are also shown to give a pointwise mean curvature with a natural interpretation as the fractional rate of change of the normal vector.
Annular force based variable curvature mirror aiming to realize non-moving element optical zooming
NASA Astrophysics Data System (ADS)
Zhao, Hui; Xie, Xiaopeng; Wei, Jingxuan; Ren, Guorui; Pang, Zhihai; Xu, Liang
2015-10-01
Recently, a new kind of optical zooming technique in which no moving elements are involved has been paid much attention. The elimination of moving elements makes optical zooming suitable for applications which has exacting requirements in space, power cost and system stability. The mobile phone and the space-borne camera are two typical examples. The key to realize non-moving elements optical zooming lies in the introduction of variable curvature mirror (VCM) whose radius of curvature could be changed dynamically. When VCM is about to be used to implement optical zoom imaging, two characteristics should be ensured. First, VCM has to provide large enough saggitus variation in order to obtain a big magnification ratio. Second, after the radius of curvature has been changed, the corresponding surface figure accuracy should still be maintained superior to a threshold level to make the high quality imaging possible. In this manuscript, based on the elasticity theory, the physical model of the annular force based variable curvature mirror is established and numerically analyzed. The results demonstrate that when the annular force is applied at the half-the-aperture position, the actuation force is reduced and a smaller actuation force is required to generate the saggitus variation and thus the maintenance of surface figure accuracy becomes easier during the variation of radius of curvature. Besides that, a prototype VCM, whose diameter and thickness are 100mm and 3mm respectively, have been fabricated and the maximum saggitus variation that could be obtained approaches more than 30 wavelengths. At the same time, the degradation of surface figure accuracy is weakly correlated to the curvature radius variation. Keywords: optical zooming; variable curvature mirror; surface figure accuracy; saggitus;
Diameter Effect Curve and Detonation Front Curvature Measurements for ANFO
NASA Astrophysics Data System (ADS)
Catanach, R. A.; Hill, L. G.
2001-06-01
Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium nitrate-fuel oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm. (≈ failure diameter) to 200 mm., with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity Dn and total curvature κ were generated as a function of radius R, then plotted parametrically to generate a D_n(κ) function. The resulting behavior deviates substantially from that of previous explosives,(Hill,L.G., Bdzil,J.B., and Aslam,T.D., 11^th) Detonation Symposium, 1998^,(Hill,L.G., Bdzil,J.B., Davis,W.C., and Engelke,R., Shock Compression of Condensed Matter, 1999) in which curves for different stick sizes overlay well for small κ but diverge for large κ, and for which κ increases monotonically with R to achieve a maximum value at the charge edge. For ANFO, we find that κ achieves a maximum at an intermediate R and that D_n(κ) curves for different stick sizes are widely separated with no overlap whatsoever.
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.
Dynamic cutaneous information is sufficient for precise curvature discrimination
Cheeseman, Jacob R.; Norman, J. Farley; Kappers, Astrid M. L.
2016-01-01
Our tactual perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration often enhances the tactual perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 28 younger (mean age was 23.1 years) and older adults (mean age was 71.4 years) to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. While dynamic cutaneous stimulation was therefore present in both conditions, active exploratory movements only occurred in one. The results indicated that there was a significant and large effect of age, such that the older participants’ thresholds were 43.8 percent higher than those of the younger participants. Despite the overall adverse effect of age, the pattern of results across the active and passive touch conditions was identical. For both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch. Curvature discrimination performance was therefore best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement. PMID:27137417
Dynamic cutaneous information is sufficient for precise curvature discrimination.
Cheeseman, Jacob R; Norman, J Farley; Kappers, Astrid M L
2016-01-01
Our tactual perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration often enhances the tactual perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 28 younger (mean age was 23.1 years) and older adults (mean age was 71.4 years) to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. While dynamic cutaneous stimulation was therefore present in both conditions, active exploratory movements only occurred in one. The results indicated that there was a significant and large effect of age, such that the older participants' thresholds were 43.8 percent higher than those of the younger participants. Despite the overall adverse effect of age, the pattern of results across the active and passive touch conditions was identical. For both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch. Curvature discrimination performance was therefore best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement. PMID:27137417
NASA Astrophysics Data System (ADS)
Kondo, Norio
2014-07-01
It is well known from a lot of experimental data that fluid forces acting on two tandem circular cylinders are quite different from those acting on a single circular cylinder. Therefore, we first present numerical results for fluid forces acting on two tandem circular cylinders, which are mounted at various spacings in a smooth flow, and second we present numerical results for flow-induced vibrations of the upstream circular cylinder in the tandem arrangement. The two circular cylinders are arranged at close spacing in a flow field. The upstream circular cylinder is elastically placed by damper-spring systems and moves in both the in-line and cross-flow directions. In such models, each circular cylinder is assumed as a rigid body. On the other hand, we do not introduce a turbulent model such as the Large Eddy Simulation (LES) or Reynolds Averaged Navier-Stokes (RANS) models into the numerical scheme to compute the fluid flow. Our numerical procedure to capture the flow-induced vibration phenomena of the upstream circular cylinder is treated as a fluid-structure interaction problem in which the ideas of weak coupling is taken into consideration.
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.
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
2016-07-01
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.
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. PMID:26590553
Curvature inducing macroion condensation driven shape changes of fluid vesicles
NASA Astrophysics Data System (ADS)
Sreeja, K. K.; Ipsen, John H.; Sunil Kumar, P. B.
2015-11-01
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.
Ho, Ruoya; Stroupe, Christopher
2016-10-01
Membrane tethering is a physical association of two membranes before their fusion. Many membrane tethering factors have been identified, but the interactions that mediate inter-membrane associations remain largely a matter of conjecture. Previously, we reported that the homotypic fusion and protein sorting/Class C vacuolar protein sorting (HOPS/Class C Vps) complex, which has two binding sites for the yeast vacuolar Rab GTPase Ypt7p, can tether two low-curvature liposomes when both membranes bear Ypt7p. Here, we show that HOPS tethers highly curved liposomes to Ypt7p-bearing low-curvature liposomes even when the high-curvature liposomes are protein-free. Phosphorylation of the curvature-sensing amphipathic lipid-packing sensor (ALPS) motif from the Vps41p HOPS subunit abrogates tethering of high-curvature liposomes. A HOPS complex without its Vps39p subunit, which contains one of the Ypt7p binding sites in HOPS, lacks tethering activity, though it binds high-curvature liposomes and Ypt7p-bearing low-curvature liposomes. Thus, HOPS tethers highly curved membranes via a direct protein-membrane interaction. Such high-curvature membranes are found at the sites of vacuole tethering and fusion. There, vacuole membranes bend sharply, generating large areas of vacuole-vacuole contact. We propose that HOPS localizes via the Vps41p ALPS motif to these high-curvature regions. There, HOPS binds via Vps39p to Ypt7p in an apposed vacuole membrane. PMID:27307091
Circular chemiresistors for microchemical sensors
Ho, Clifford K.
2007-03-13
A circular chemiresistor for use in microchemical sensors. A pair of electrodes is fabricated on an electrically insulating substrate. The pattern of electrodes is arranged in a circle-filling geometry, such as a concentric, dual-track spiral design, or a circular interdigitated design. A drop of a chemically sensitive polymer (i.e., chemiresistive ink) is deposited on the insulating substrate on the electrodes, which spreads out into a thin, circular disk contacting the pair of electrodes. This circularly-shaped electrode geometry maximizes the contact area between the pair of electrodes and the polymer deposit, which provides a lower and more stable baseline resistance than with linear-trace designs. The circularly-shaped electrode pattern also serves to minimize batch-to-batch variations in the baseline resistance due to non-uniform distributions of conductive particles in the chemiresistive polymer film.
Non-constant mean curvature trumpet solutions for the Einstein constraint equations
NASA Astrophysics Data System (ADS)
Leach, Jeremy
2016-07-01
We prove the existence of a large class of initial data for the vacuum Einstein equations which possess a finite number of asymptotically Euclidean and asymptotically conformally cylindrical or periodic ends. Aside from being asymptotically constant, only mild conditions on the mean curvature of these initial data sets are imposed.
76 FR 62148 - Title VI; Proposed Circular, Environmental Justice; Proposed Circular
Federal Register 2010, 2011, 2012, 2013, 2014
2011-10-06
... Circular'' (76 FR 60593) and ``Environmental Justice; Proposed Circular'' (76 FR 60590). Corrections The... Federal Transit Administration Title VI; Proposed Circular, Environmental Justice; Proposed Circular... information sessions, as published in the September 29, 2011, Federal Register Notices titled ``Title...
Curvature-induced activation of a passive tracer in an active bath
NASA Astrophysics Data System (ADS)
Mallory, S. A.; Valeriani, C.; Cacciuto, A.
2014-09-01
We use numerical simulations to study the motion of a large asymmetric tracer immersed in a low-density suspension of self-propelled particles in two dimensions. Specifically, we analyze how the curvature of the tracer affects its translational and rotational motion in an active environment. We find that even very small amounts of curvature are sufficient for the active bath to impart directed motion to the tracer, which results in its effective activation. We propose simple scaling arguments to characterize this induced activity in terms of the curvature of the tracer and the strength of the self-propelling force. Our results suggest new ways of controlling the transport properties of passive tracers in an active medium by carefully tailoring their geometry.
Curvature-induced activation of a passive tracer in an active bath.
Mallory, S A; Valeriani, C; Cacciuto, A
2014-09-01
We use numerical simulations to study the motion of a large asymmetric tracer immersed in a low-density suspension of self-propelled particles in two dimensions. Specifically, we analyze how the curvature of the tracer affects its translational and rotational motion in an active environment. We find that even very small amounts of curvature are sufficient for the active bath to impart directed motion to the tracer, which results in its effective activation. We propose simple scaling arguments to characterize this induced activity in terms of the curvature of the tracer and the strength of the self-propelling force. Our results suggest new ways of controlling the transport properties of passive tracers in an active medium by carefully tailoring their geometry. PMID:25314448
Vector and tensor contributions to the curvature perturbation at second order
NASA Astrophysics Data System (ADS)
Carrilho, Pedro; Malik, Karim A.
2016-02-01
We derive the evolution equation for the second order curvature perturbation using standard techniques of cosmological perturbation theory. We do this for different definitions of the gauge invariant curvature perturbation, arising from different splits of the spatial metric, and compare the expressions. The results are valid at all scales and include all contributions from scalar, vector and tensor perturbations, as well as anisotropic stress, with all our results written purely in terms of gauge invariant quantities. Taking the large-scale approximation, we find that a conserved quantity exists only if, in addition to the non-adiabatic pressure, the transverse traceless part of the anisotropic stress tensor is also negligible. We also find that the version of the gauge invariant curvature perturbation which is exactly conserved is the one defined with the determinant of the spatial part of the inverse metric.
The curvature elastic-energy function of the lipid-water cubic mesophase
NASA Astrophysics Data System (ADS)
Chung, Hesson; Caffrey, Martin
1994-03-01
CELL and lipid membranes are able to bend, as manifested during membrane fusion and the formation of non-lamellar lyotropic mesopbases in water. But there is an energy cost to bending of lipid layers, called the curvature elastic energy. Although the functional form of this energy is known1, a complete quantitative knowledge of the curvature elastic energy, which is central to predicting the relative stability of the large number of phases that lipid membranes can adopt, has been lacking. Here we use X-ray synchrotron diffraction measurements of the variation of lattice parameter with pressure and temperature for the periodic Ia3d (Q230) cubic phase of hydrated monoolein to calculate the complete curvature elastic-energy function for the lipid cubic mesophase. This allows us to predict the stabilities of different cubic and lamellar phases for this system as a function of composition.
Superintegrable potentials on 3D Riemannian and Lorentzian spaces with nonconstant curvature
Ballesteros, A.; Enciso, A.; Herranz, F. J.; Ragnisco, O.
2010-02-15
A quantum sl(2,R) coalgebra (with deformation parameter z) is shown to underly the construction of a large class of superintegrable potentials on 3D curved spaces, that include the nonconstant curvature analog of the spherical, hyperbolic, and (anti-)de Sitter spaces. The connection and curvature tensors for these 'deformed' spaces are fully studied by working on two different phase spaces. The former directly comes from a 3D symplectic realization of the deformed coalgebra, while the latter is obtained through a map leading to a spherical-type phase space. In this framework, the nondeformed limit z {yields} 0 is identified with the flat contraction leading to the Euclidean and Minkowskian spaces/potentials. The resulting Hamiltonians always admit, at least, three functionally independent constants of motion coming from the coalgebra structure. Furthermore, the intrinsic oscillator and Kepler potentials on such Riemannian and Lorentzian spaces of nonconstant curvature are identified, and several examples of them are explicitly presented.
Curvature and shape determination of growing bacteria
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Ranjan; Wingreen, Ned S.
2009-12-01
Bacterial cells come in a variety of shapes, determined by the stress-bearing cell wall. Though many molecular details about the cell wall are known, our understanding of how a particular shape is produced during cell growth is at its infancy. Experiments on curved Escherichia coli grown in microtraps, and on naturally curved Caulobacter crescentus, reveal different modes of growth: one preserving arc length and the other preserving radius of curvature. We present a simple model for curved cell growth that relates these two growth modes to distinct but related growth rules—“hooplike growth” and “self-similar growth”—and discuss the implications for microscopic growth mechanisms.
Curvature sensor for ocular wavefront measurement.
Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O
2006-08-01
We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes. PMID:16832447
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.
Spacetime Curvature and Higgs Stability after Inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2015-12-11
We investigate the dynamics of the Higgs field at the end of inflation in the minimal scenario consisting of an inflaton field coupled to the standard model only through the nonminimal gravitational coupling ξ of the Higgs field. Such a coupling is required by renormalization of the standard model in curved space, and in the current scenario also by vacuum stability during high-scale inflation. We find that for ξ≳1, rapidly changing spacetime curvature at the end of inflation leads to significant production of Higgs particles, potentially triggering a transition to a negative-energy Planck scale vacuum state and causing an immediate collapse of the Universe. PMID:26705621
Holographic entropy increases in quadratic curvature gravity
NASA Astrophysics Data System (ADS)
Bhattacharjee, Srijit; Sarkar, Sudipta; Wall, Aron C.
2015-09-01
Standard methods for calculating the black hole entropy beyond general relativity are ambiguous when the horizon is nonstationary. We fix these ambiguities in all quadratic curvature gravity theories, by demanding that the entropy be increasing at every time, for linear perturbations to a stationary black hole. Our result matches with the entropy formula found previously in holographic entanglement entropy calculations. We explicitly calculate the entropy increase for Vaidya-like solutions in Ricci-tensor gravity to show that (unlike the Wald entropy) the holographic entropy obeys a second law.
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.
Nuclear spin circular dichroism
Vaara, Juha; Rizzo, Antonio; Kauczor, Joanna; Norman, Patrick; Coriani, Sonia
2014-04-07
Recent years have witnessed a growing interest in magneto-optic spectroscopy techniques that use nuclear magnetization as the source of the magnetic field. Here we present a formulation of magnetic circular dichroism (CD) due to magnetically polarized nuclei, nuclear spin-induced CD (NSCD), in molecules. The NSCD ellipticity and nuclear spin-induced optical rotation (NSOR) angle correspond to the real and imaginary parts, respectively, of (complex) quadratic response functions involving the dynamic second-order interaction of the electron system with the linearly polarized light beam, as well as the static magnetic hyperfine interaction. Using the complex polarization propagator framework, NSCD and NSOR signals are obtained at frequencies in the vicinity of optical excitations. Hartree-Fock and density-functional theory calculations on relatively small model systems, ethene, benzene, and 1,4-benzoquinone, demonstrate the feasibility of the method for obtaining relatively strong nuclear spin-induced ellipticity and optical rotation signals. Comparison of the proton and carbon-13 signals of ethanol reveals that these resonant phenomena facilitate chemical resolution between non-equivalent nuclei in magneto-optic spectra.
Entropic derivation of F=ma for circular motion
NASA Astrophysics Data System (ADS)
Duncan, Michael; Singleton, Douglas; Myrzakulov, Ratbay
2011-11-01
We examine the entropic picture of Newton's second law for the case of circular motion. It is shown that one must make modifications to the derivation of F = ma due to a change in the effective Unruh temperature for circular motion. These modifications present a challenge to the entropic derivation of Newton's second law, but also open up the possibility to experimentally test and constrain this model for large centripetal accelerations. (Phys. Lett. B 703 (2011) 516-518)
Entropic derivation of F = m a for circular motion
NASA Astrophysics Data System (ADS)
Duncan, Michael; Myrzakulov, Ratbay; Singleton, Douglas
2011-09-01
We examine the entropic picture of Newton's second law for the case of circular motion. It is shown that one must make modifications to the derivation of F = ma due to a change in the effective Unruh temperature for circular motion. These modifications present a challenge to the entropic derivation of Newton's second law, but also open up the possibility to experimentally test and constrain this model for large centripetal accelerations.
The lemon illusion: seeing curvature where there is none
Strother, Lars; Killebrew, Kyle W.; Caplovitz, Gideon P.
2015-01-01
Curvature is a highly informative visual cue for shape perception and object recognition. We introduce a novel illusion—the Lemon Illusion—in which subtle illusory curvature is perceived along contour regions that are devoid of physical curvature. We offer several perceptual demonstrations and observations that lead us to conclude that the Lemon Illusion is an instance of a more general illusory curvature phenomenon, one in which the presence of contour curvature discontinuities lead to the erroneous extension of perceived curvature. We propose that this erroneous extension of perceived curvature results from the interaction of neural mechanisms that operate on spatially local contour curvature signals with higher-tier mechanisms that serve to establish more global representations of object shape. Our observations suggest that the Lemon Illusion stems from discontinuous curvature transitions between rectilinear and curved contour segments. However, the presence of curvature discontinuities is not sufficient to produce the Lemon Illusion, and the minimal conditions necessary to elicit this subtle and insidious illusion are difficult to pin down. PMID:25755640
Circular RNAs in Eukaryotic Cells.
Chen, Liang; Huang, Chuan; Wang, Xiaolin; Shan, Ge
2015-10-01
Circular RNAs (circRNAs) are now recognized as large species of transcripts in eukaryotic cells. From model organisms such as C. elegans, Drosophila, mice to human beings, thousands of circRNAs formed from back-splicing of exons have been identified. The known complexity of transcriptome has been greatly expanded upon the discovery of these RNAs. Studies about the biogenesis and physiological functions have yielded substantial knowledge for the circRNAs, and they are now more likely to be viewed as regulatory elements coded by the genome rather than unavoidable noise of gene expression. Certain human diseases may also relate to circRNAs. These circRNAs show diversifications in features such as sequence composition and cellular localization, and thus we propose that they may be divided into subtypes such as cytoplasmic circRNAs, nuclear circRNAs, and exon-intron circRNAs (EIciRNAs). Here we summarize and discuss knowns and unknowns for these RNAs, and we need to keep in mind that the whole field is still at the beginning of exciting explorations.
Shen, Chong; Meng, Qin; Zhang, Guoliang
2013-08-01
Tissue engineering devices as in vitro cell culture systems in scaffolds has encountered the bottleneck due to their much lower cell functions than real tissues/organs in vivo. Such situation has been improved in some extent by mimicking the cell microenvironments in vivo from either chemical or physical ways. However, microenvironmental curvature, commonly seen in real tissues/organs, has never been manipulated to regulate the cell performance in vitro. In this regard, this paper fabricated polysulfone membranes with or without polyethylene glycol modification to investigate the impact of curvature on two renal tubular cells. Regardless the varying membrane curvatures among hollow fiber membranes of different diameters and flat membrane of zero curvature, both renal cells could well attach at 4 h of seeding and form similar confluent layers at 6 days on each membrane. Nevertheless, the renal cells on hollow fibers, though showing confluent morphology as those on flat membranes, expressed higher renal functions and, moreover, the renal functions significantly increased with the membrane curvature among hollow fibers. Such upregulation on functions was unassociated with mass transport barrier of hollow fibers, because the cultures on lengthwise cut hollow fibers without mass transfer barrier showed same curvature effect on renal functions as whole hollow fibers. It could be proposed that the curvature of hollow fiber membrane approaching to the large curvature in kidney tubules increased the mechanical stress in the renal cells and thus might up-regulate the renal cell functions. In conclusion, the increase of substrate curvature could up-regulate the cell functions without altering the confluent cell morphology and this finding will facilitate the design of functional tissue engineering devices.
Armbruster, Ute; Labs, Mathias; Pribil, Mathias; Viola, Stefania; Xu, Wenteng; Scharfenberg, Michael; Hertle, Alexander P.; Rojahn, Ulrike; Jensen, Poul Erik; Rappaport, Fabrice; Joliot, Pierre; Dörmann, Peter; Wanner, Gerhard; Leister, Dario
2013-01-01
Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. A granum consists of a core of appressed membranes, two stroma-exposed end membranes, and margins, which connect pairs of grana membranes at their lumenal sides. Multiple forces contribute to grana stacking, but it is not known how the extreme curvature at margins is generated and maintained. We report the identification of the CURVATURE THYLAKOID1 (CURT1) protein family, conserved in plants and cyanobacteria. The four Arabidopsis thaliana CURT1 proteins (CURT1A, B, C, and D) oligomerize and are highly enriched at grana margins. Grana architecture is correlated with the CURT1 protein level, ranging from flat lobe-like thylakoids with considerably fewer grana margins in plants without CURT1 proteins to an increased number of membrane layers (and margins) in grana at the expense of grana diameter in overexpressors of CURT1A. The endogenous CURT1 protein in the cyanobacterium Synechocystis sp PCC6803 can be partially replaced by its Arabidopsis counterpart, indicating that the function of CURT1 proteins is evolutionary conserved. In vitro, Arabidopsis CURT1A proteins oligomerize and induce tubulation of liposomes, implying that CURT1 proteins suffice to induce membrane curvature. We therefore propose that CURT1 proteins modify thylakoid architecture by inducing membrane curvature at grana margins. PMID:23839788
Particles and curvatures in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Serra, Francesca; Luo, Yimin; Yang, Shu; Kamien, Randall D.; Stebe, Kathleen J.
Elastic interactions in anisotropic fluids can be harnessed to direct particle interactions. A strategy to smoothly manipulate the director field in nematic liquid crystals is to vary the topography of the bounding surfaces. A rugged landscape with peaks and valleys create local deformations of the director field which can interact with particles in solution. We study this complex interaction in two different settings. The first consists of an array of shallow pores in a poly-dimethyl-siloxane (PDMS) membrane, whose curvature can be tuned either by swelling the PDMS membrane or by mechanical stretching. The second is a set of grooves with wavy walls, fabricated by photolithography, with various parameters of curvature and shapes. In this contexts we study how the motion of colloidal particles in nematic liquid crystals can be influenced by their interaction with the peaks and valleys of the bottom substrate or of the side walls. Particles with different associated topological defects (hedgehogs or Saturn rings) behave differently as they interact with the topographical features, favoring the docking on peaks or valleys. These experimental systems are also ideal to study the ``lock and key'' mechanism of particles in holes and to investigate a possible route for particle sorting.
Effects of streamline curvature on separation prediction
NASA Astrophysics Data System (ADS)
Arolla, Sunil K.; Durbin, Paul A.
2009-11-01
In this study, the effects of streamline curvature on prediction of flow separation are investigated. The geometry is a circulation control airfoil, a high-lift configuration that has been under extensive research for more than two decades. A tangential jet is blown over a thick, rounded trailing edge, using the Coanda effect to delay separation. An attempt is made to understand, through numerical simulations, the dynamics of turbulent separation and reattachment on the Coanda surface. Highly curved, attached recirculation regions are seen to form. A physics based curvature correction proposed by Pettersson-Reif et al. (1999) is used in conjunction with ζ-f turbulence model. The chord-based Reynolds number is Re = 10^6. Two jet momentum coefficients of Cμ=0.03 and 0.1 are computed. In this paper, comparisons between the computed and experimental pressure distributions, velocity profiles and the position of flow detachment are presented. Comparisons with other closures such as Menter's SST model are also discussed.
Multidimensional integrable vacuum cosmology with two curvatures
NASA Astrophysics Data System (ADS)
Gavrilov, V. R.; Ivashchuk, V. D.; Melnikov, V. N.
1996-11-01
The vacuum cosmological model on the manifold 0264-9381/13/11/018/img1 describing the evolution of n Einstein spaces of non-zero curvatures is considered. For n = 2 the Einstein equations are reduced to the Abel (ordinary differential) equation and solved, when 0264-9381/13/11/018/img2. The Kasner-like behaviour of the solutions near the singularity 0264-9381/13/11/018/img3 is considered (0264-9381/13/11/018/img4 is synchronous time). The exceptional (`Milne-type') solutions are obtained for arbitrary n. For n = 2 these solutions are attractors for other ones, when 0264-9381/13/11/018/img5. For 0264-9381/13/11/018/img6 and 0264-9381/13/11/018/img7 certain two-parametric families of solutions are obtained from n = 2 ones using the `curvature-splitting' trick. In the case n = 2, 0264-9381/13/11/018/img8 a family of non-singular solutions with the topology 0264-9381/13/11/018/img9 is found.
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
Vortex motion on surfaces of small curvature
Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.
2013-12-15
We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.
Curvature dependent modulation of fish fin stiffness
NASA Astrophysics Data System (ADS)
Nguyen, Khoi; Yu, Ning; Bandi, Mahesh; Venkadesan, Madhusudhan; Mandre, Shreyas
Propulsion and maneuvering ability of fishes depends on the stiffness of their fins. However, increasing stiffness by simply adding material to thicken the fin would incur a substantial energetic cost associated with flapping the fin. We propose that fishes increase stiffness of the fin not by building thicker fins, but by geometrically coupling out-of-plane bending of the fin's rays with in-plane stretching of a stiff membrane that connects the rays. We present a model of fin elasticity for ray-finned fish, where we decompose the fin into a series of elastic beams (rays) with springy interconnections (membrane). In one limit, where the membranes are infinitely extensible, the fin's stiffness is no more than the sum of the stiffness of individual rays. At the other limit of an inextensible membrane, fin stiffness reaches an asymptotic maximum. The asymptote value increases monotonically with curvature. We propose that musculature at the base of the fin controls fin curvature, and thereby modulates stiffness.
Polarized curvature radiation in pulsar magnetosphere
NASA Astrophysics Data System (ADS)
Wang, P. F.; Wang, C.; Han, J. L.
2014-07-01
The propagation of polarized emission in pulsar magnetosphere is investigated in this paper. The polarized waves are generated through curvature radiation from the relativistic particles streaming along curved magnetic field lines and corotating with the pulsar magnetosphere. Within the 1/γ emission cone, the waves can be divided into two natural wave-mode components, the ordinary (O) mode and the extraordinary (X) mode, with comparable intensities. Both components propagate separately in magnetosphere, and are aligned within the cone by adiabatic walking. The refraction of O mode makes the two components separated and incoherent. The detectable emission at a given height and a given rotation phase consists of incoherent X-mode and O-mode components coming from discrete emission regions. For four particle-density models in the form of uniformity, cone, core and patches, we calculate the intensities for each mode numerically within the entire pulsar beam. If the corotation of relativistic particles with magnetosphere is not considered, the intensity distributions for the X-mode and O-mode components are quite similar within the pulsar beam, which causes serious depolarization. However, if the corotation of relativistic particles is considered, the intensity distributions of the two modes are very different, and the net polarization of outcoming emission should be significant. Our numerical results are compared with observations, and can naturally explain the orthogonal polarization modes of some pulsars. Strong linear polarizations of some parts of pulsar profile can be reproduced by curvature radiation and subsequent propagation effect.
Converting entropy to curvature perturbations after a cosmic bounce
NASA Astrophysics Data System (ADS)
Fertig, Angelika; Lehners, Jean-Luc; Mallwitz, Enno; Wilson-Ewing, Edward
2016-10-01
We study two-field bouncing cosmologies in which primordial perturbations are created in either an ekpyrotic or a matter-dominated contraction phase. We use a non-singular ghost condensate bounce model to follow the perturbations through the bounce into the expanding phase of the universe. In contrast to the adiabatic perturbations, which on large scales are conserved across the bounce, entropy perturbations can grow significantly during the bounce phase. If they are converted into adiabatic/curvature perturbations after the bounce, they typically form the dominant contribution to the observed temperature fluctuations in the microwave background, which can have several beneficial implications. For ekpyrotic models, this mechanism loosens the constraints on the amplitude of the ekpyrotic potential while naturally suppressing the intrinsic amount of non-Gaussianity. For matter bounce models, the mechanism amplifies the scalar perturbations compared to the associated primordial gravitational waves.
Topological implications of negative curvature for biological and social networks
NASA Astrophysics Data System (ADS)
Albert, Réka; DasGupta, Bhaskar; Mobasheri, Nasim
2014-03-01
Network measures that reflect the most salient properties of complex large-scale networks are in high demand in the network research community. In this paper we adapt a combinatorial measure of negative curvature (also called hyperbolicity) to parametrized finite networks, and show that a variety of biological and social networks are hyperbolic. This hyperbolicity property has strong implications on the higher-order connectivity and other topological properties of these networks. Specifically, we derive and prove bounds on the distance among shortest or approximately shortest paths in hyperbolic networks. We describe two implications of these bounds to crosstalk in biological networks, and to the existence of central, influential neighborhoods in both biological and social networks.
Circular RNA is expressed across the eukaryotic tree of life.
Wang, Peter L; Bao, Yun; Yee, Muh-Ching; Barrett, Steven P; Hogan, Gregory J; Olsen, Mari N; Dinneny, José R; Brown, Patrick O; Salzman, Julia
2014-01-01
An unexpectedly large fraction of genes in metazoans (human, mouse, zebrafish, worm, fruit fly) express high levels of circularized RNAs containing canonical exons. Here we report that circular RNA isoforms are found in diverse species whose most recent common ancestor existed more than one billion years ago: fungi (Schizosaccharomyces pombe and Saccharomyces cerevisiae), a plant (Arabidopsis thaliana), and protists (Plasmodium falciparum and Dictyostelium discoideum). For all species studied to date, including those in this report, only a small fraction of the theoretically possible circular RNA isoforms from a given gene are actually observed. Unlike metazoans, Arabidopsis, D. discoideum, P. falciparum, S. cerevisiae, and S. pombe have very short introns (∼ 100 nucleotides or shorter), yet they still produce circular RNAs. A minority of genes in S. pombe and P. falciparum have documented examples of canonical alternative splicing, making it unlikely that all circular RNAs are by-products of alternative splicing or 'piggyback' on signals used in alternative RNA processing. In S. pombe, the relative abundance of circular to linear transcript isoforms changed in a gene-specific pattern during nitrogen starvation. Circular RNA may be an ancient, conserved feature of eukaryotic gene expression programs.
Beam Rounders for Circular Colliders
A. Burov; S. Nagaitsev; Ya. Derbenev
2001-07-01
By means of linear optics, an arbitrary uncoupled beam can be locally transformed into a round (rotation-invariant) state and then back. This provides an efficient way to round beams in the interaction region of circular colliders.
Biological Synthesis of Circular Polypeptides*
Aboye, Teshome L.; Camarero, Julio A.
2012-01-01
Here, we review the use of different biochemical approaches for biological synthesis of circular or backbone-cyclized proteins and peptides. These methods allow the production of circular polypeptides either in vitro or in vivo using standard recombinant DNA expression techniques. Protein circularization can significantly impact protein engineering and research in protein folding. Basic polymer theory predicts that circularization should lead to a net thermodynamic stabilization of a folded protein by reducing the entropy associated with the unfolded state. Protein cyclization also provides a valuable tool for exploring the effects of topology on protein folding kinetics. Furthermore, the biological production of cyclic polypeptides makes possible the production of cyclic polypeptide libraries. The generation of such libraries, which was previously restricted to the domain of synthetic chemists, now offers biologists access to highly diverse and stable molecular libraries for probing protein structure and function. PMID:22707722
Circularly-Polarized Microstrip Antenna
NASA Technical Reports Server (NTRS)
Stanton, P. H.
1985-01-01
Microstrip construction compact for mobile applications. Circularly polarized microstrip antenna made of concentric cylindrical layers of conductive and dielectric materials. Coaxial cable feedlines connected to horizontal and vertical subelements from inside. Vertical subelement acts as ground for horizontal subelement.
Beam rounders for circular colliders
A. Burov and S. Nagaitsev
2002-12-10
By means of linear optics, an arbitrary uncoupled beam can be locally transformed into a round (rotation-invariant) state and then back. This provides an efficient way to round beams in the interaction region of circular colliders.
Compact surfaces of constant Gaussian curvature in Randers manifolds
NASA Astrophysics Data System (ADS)
Cui, Ningwei
2016-08-01
The flag curvature of a Finsler surface is called the Gaussian curvature in Finsler geometry. In this paper, we characterize the surfaces of constant Gaussian curvature (CGC) in the Randers 3-manifold. Then we give a classification of the orientable closed CGC surfaces in two Randers space forms, which are the non-Euclidean Minkowski-Randers 3-space (K = 0) and the Bao-Shen sphere (K = 1).
Wrinkles and splay conspire to give positive disclinations negative curvature
Matsumoto, Elisabetta A.; Vega, Daniel A.; Pezzutti, Aldo D.; García, Nicolás A.; Chaikin, Paul M.; Register, Richard A.
2015-01-01
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
Eddy-Current Measurement Of Turning Or Curvature
NASA Technical Reports Server (NTRS)
Chern, Engmin J.
1993-01-01
Rotatable conductive plate covers sensing coil to varying degree. Curvature of pipe at remote or otherwise inaccessible location inside pipe measured using relatively simple angular-displacement eddy-current probe. Crawler and sensor assemblies move along inside of pipe on wheels. Conductive plate pivots to follow curvature of pipe, partly covering one of eddy-current coils to degree depending on local curvature on pipe.
Curvature and geodesic instabilities in a geometrical approach to the planar three-body problem
NASA Astrophysics Data System (ADS)
Krishnaswami, Govind S.; Senapati, Himalaya
2016-10-01
The Maupertuis principle allows us to regard classical trajectories as reparametrized geodesics of the Jacobi-Maupertuis (JM) metric on configuration space. We study this geodesic reformulation of the planar three-body problem with both Newtonian and attractive inverse-square potentials. The associated JM metrics possess translation and rotation isometries in addition to scaling isometries for the inverse-square potential with zero energy E. The geodesic flow on the full configuration space ℂ3 (with collision points excluded) leads to corresponding flows on its Riemannian quotients: the center of mass configuration space ℂ2 and shape space ℝ3 (as well as 𝕊3 and the shape sphere 𝕊2 for the inverse-square potential when E = 0). The corresponding Riemannian submersions are described explicitly in "Hopf" coordinates which are particularly adapted to the isometries. For equal masses subject to inverse-square potentials, Montgomery shows that the zero-energy "pair of pants" JM metric on the shape sphere is geodesically complete and has negative gaussian curvature except at Lagrange points. We extend this to a proof of boundedness and strict negativity of scalar curvatures everywhere on ℂ2, ℝ3, and 𝕊3 with collision points removed. Sectional curvatures are also found to be largely negative, indicating widespread geodesic instabilities. We obtain asymptotic metrics near collisions, show that scalar curvatures have finite limits, and observe that the geodesic reformulation "regularizes" pairwise and triple collisions on ℂ2 and its quotients for arbitrary masses and allowed energies. For the Newtonian potential with equal masses and zero energy, we find that the scalar curvature on ℂ2 is strictly negative though it could have either sign on ℝ3. However, unlike for the inverse-square potential, geodesics can encounter curvature singularities at collisions in finite geodesic time.
Topologically non-linked circular duplex DNA.
Biegeleisen, Ken
2002-05-01
The discovery of circular DNA, over 30 years ago, introduced an element of uneasiness in what had been, up to that point, the almost picture-perfect story of the elucidation of the molecular biology of heredity. If DNA indeed has the Watson-Crick right-handed helical secondary structure, then in circular DNA, thousands, or perhaps even millions of twists must be removed in each generation, and re-wound in the next generation. Although enzyme systems adequate for this task have long since been found and characterized, there have nevertheless arisen a number of proposals for alternative DNA structures in which the strands are topologically non-linked, so that they might separate during replication without having to be unwound. These structures have generally been put forth as theory only, and have been largely unaccompanied by experimental evidence to support their applicability to native DNA from living systems. Recently, however, a report has emerged suggesting that it might be possible to separate, intact, the individual single-stranded circular half-chromosomes which constitute the double-stranded circular chromosomes of certain plasmids. This would not be possible unless the chromosomes had one of the alternative, topologically non-linked structures. It is widely believed that after a half-century of worldwide DNA research, any significant change to the Watson-Crick structure is unlikely to stand up to scrutiny. Nevertheless, the present author has found that in many instances in which the behavior of circular duplex DNA is considered to be explicable only in terms of the topologically linked helical model, it is also possible to explain that same behavior in terms of a topologically non-linked model. It is necessary, in these instances, to make certain logical assumptions which cannot be conclusively proven at the present time. The author herein offers an example of one such instance, namely an examination of the behavior of circular duplex DNA in an alkaline
The curvature index and synchronization of dynamical systems
NASA Astrophysics Data System (ADS)
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.
Evolving extrinsic curvature and the cosmological constant problem
NASA Astrophysics Data System (ADS)
Capistrano, Abraão J. S.; Cabral, Luis A.
2016-10-01
The concept of smooth deformation of Riemannian manifolds associated with the extrinsic curvature is explained and applied to the Friedmann-Lemaître-Robertson-Walker cosmology. We show that such deformation can be derived from the Einstein-Hilbert-like dynamical principle may produce an observable effect in the sense of Noether. As a result, we show how the extrinsic curvature compensates both quantitative and qualitative differences between the cosmological constant Λ and the vacuum energy {ρ }{vac} obtaining the observed upper bound for the cosmological constant problem at electroweak scale. The topological characteristics of the extrinsic curvature are discussed showing that the produced extrinsic scalar curvature is an evolving dynamical quantity.
Plane wave gravitons, curvature singularities and string physics
Brooks, R. . Center for Theoretical Physics)
1991-03-21
This paper discusses bounded (compactifying) potentials arising from a conspiracy between plane wave graviton and dilaton condensates. So are string propagation and supersymmetry in spacetimes with curvature singularities.
Circular code motifs in genomes of eukaryotes.
El Soufi, Karim; Michel, Christian J
2016-11-01
A set X of 20 trinucleotides was identified in genes of bacteria, eukaryotes, plasmids and viruses, which has in average the highest occurrence in reading frame compared to its two shifted frames (Michel, 2015; Arquès and Michel, 1996). This set X has an interesting mathematical property as X is a circular code (Arquès and Michel, 1996). Thus, the motifs from this circular code X, called X motifs, have the property to always retrieve, synchronize and maintain the reading frame in genes. In this paper, we develop several statistical analyzes of X motifs in 138 available complete genomes of eukaryotes in which genes as well as non-gene regions are examined. Large X motifs (with lengths of at least 15 consecutive trinucleotides of X and compositions of at least 10 different trinucleotides of X among 20) have the highest occurrence in genomes of eukaryotes compared to its 23 large bijective motifs, its two large permuted motifs and large random motifs. The largest X motifs identified in eukaryotic genomes are presented, e.g. an X motif in a non-gene region of the genome Solanum pennellii with a length of 155 trinucleotides (465 nucleotides) and an expectation E=10(-71). In the human genome, the largest X motif occurs in a non-gene region of the chromosome 13 with a length of 36 trinucleotides and an expectation E=10(-11). X motifs in non-gene regions of genomes could be evolutionary relics of primitive genes using the circular code for translation. However, the proportion of X motifs (with lengths of at least 10 consecutive trinucleotides of X and compositions of at least 5 different trinucleotides of X among 20) in genes/non-genes of the 138 complete eukaryotic genomes is about 8. Thus, the X motifs occur preferentially in genes, as expected from the previous works of 20 years.
Circular block matching based video stabilization
NASA Astrophysics Data System (ADS)
Xu, Lidong; Fu, Fangwen; Lin, Xinggang
2005-07-01
Video sequences captured by handheld digital camera need to be stabilized to eliminate the tiresome effects caused by camera"s undesirable shake or jiggle. The key issue of video stabilization is to estimate the global motion parameters between two successive frames. In this paper, a novel circular block matching algorithm is proposed to estimate the global motion parameters. This algorithm can deal with not only translational motion but even large rotational motion. For an appointed circular block in current frame, a four-dimensional rotation invariant feature vector is firstly extracted from it and used to judge if it is an effective block. Then the rotation invariant features based circular block matching process is performed to find the best matching blocks in reference frame for those effective blocks. With the matching results of any two effective blocks, a two-dimensional motion model is constructed to produce one group of frame motion parameters. A statistical method is proposed to calculate the estimated global motion parameters with all groups of global motion parameters. Finally, using the estimated motion parameters as the initial values, an iteration algorithm is introduced to obtain the refined global motion parameters. The experimental results show that the proposed algorithm is excellent in stabilizing frames with even burst global translational and rotational motions.
Curvature effects in thin magnetic shells.
Gaididei, Yuri; Kravchuk, Volodymyr P; Sheka, Denis D
2014-06-27
A magnetic energy functional is derived for an arbitrary curved thin shell on the assumption that the magnetostatic effects can be reduced to an effective easy-surface anisotropy; it can be used for solving both static and dynamic problems. General static solutions are obtained in the limit of a strong anisotropy of both signs (easy-surface and easy-normal cases). It is shown that the effect of the curvature can be treated as the appearance of an effective magnetic field, which is aligned along the surface normal for the case of easy-surface anisotropy and is tangential to the surface for the case of easy-normal anisotropy. In general, the existence of such a field excludes the solutions that are strictly tangential or strictly normal to the surface. As an example, we consider static equilibrium solutions for a cone surface magnetization.
Hawking temperature of constant curvature black holes
Cai Ronggen; Myung, Yun Soo
2011-05-15
The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of M{sub D-1}xS{sup 1}, where D is the spacetime dimension and M{sub D-1} stands for a conformal Minkowski spacetime in D-1 dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both the static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.
Natural curvature for manifest T-duality
NASA Astrophysics Data System (ADS)
Poláček, Martin; Siegel, Warren
2014-01-01
We reformulate the manifestly T-dual description of the massless sector of the closed bosonic string, directly from the geometry associated with the (left and right) affine Lie algebra of the coset space Poincaré/Lorentz. This construction initially doubles not only the (spacetime) coordinates for translations but also those for Lorentz transformations (and their "dual"). As a result, the Lorentz connection couples directly to the string (as does the vielbein), rather than being introduced ad hoc to the covariant derivative as previously. This not only reproduces the old definition of T-dual torsion, but automatically gives a general, covariant definition of T-dual curvature (but still with some undetermined connections).
Circularly polarized light detection with hot electrons in chiral plasmonic metamaterials
Li, Wei; Coppens, Zachary J.; Besteiro, Lucas V.; Wang, Wenyi; Govorov, Alexander O.; Valentine, Jason
2015-01-01
Circularly polarized light is utilized in various optical techniques and devices. However, using conventional optical systems to generate, analyse and detect circularly polarized light involves multiple optical elements, making it challenging to realize miniature and integrated devices. While a number of ultracompact optical elements for manipulating circularly polarized light have recently been demonstrated, the development of an efficient and highly selective circularly polarized light photodetector remains challenging. Here we report on an ultracompact circularly polarized light detector that combines large engineered chirality, realized using chiral plasmonic metamaterials, with hot electron injection. We demonstrate the detector's ability to distinguish between left and right hand circularly polarized light without the use of additional optical elements. Implementation of this photodetector could lead to enhanced security in fibre and free-space communication, as well as emission, imaging and sensing applications for circularly polarized light using a highly integrated photonic platform. PMID:26391292
Circularly polarized light detection with hot electrons in chiral plasmonic metamaterials
NASA Astrophysics Data System (ADS)
Li, Wei; Coppens, Zachary J.; Besteiro, Lucas V.; Wang, Wenyi; Govorov, Alexander O.; Valentine, Jason
2015-09-01
Circularly polarized light is utilized in various optical techniques and devices. However, using conventional optical systems to generate, analyse and detect circularly polarized light involves multiple optical elements, making it challenging to realize miniature and integrated devices. While a number of ultracompact optical elements for manipulating circularly polarized light have recently been demonstrated, the development of an efficient and highly selective circularly polarized light photodetector remains challenging. Here we report on an ultracompact circularly polarized light detector that combines large engineered chirality, realized using chiral plasmonic metamaterials, with hot electron injection. We demonstrate the detector's ability to distinguish between left and right hand circularly polarized light without the use of additional optical elements. Implementation of this photodetector could lead to enhanced security in fibre and free-space communication, as well as emission, imaging and sensing applications for circularly polarized light using a highly integrated photonic platform.
Circular polarization interferometry: circularly polarized modes of cholesteric liquid crystals.
Sanchez-Castillo, A; Eslami, S; Giesselmann, F; Fischer, P
2014-12-15
We describe a novel polarization interferometer which permits the determination of the refractive indices for circularly-polarized light. It is based on a Jamin-Lebedeff interferometer, modified with waveplates, and permits us to experimentally determine the refractive indices nL and nR of the respectively left- and right-circularly polarized modes in a cholesteric liquid crystal. Whereas optical rotation measurements only determine the circular birefringence, i.e. the difference (nL - nR), the interferometer also permits the determination of their absolute values. We report refractive indices of a cholesteric liquid crystal in the region of selective (Bragg) reflection as a function of temperature. PMID:25607071
Individual muscle contributions to circular turning mechanics.
Ventura, Jessica D; Klute, Glenn K; Neptune, Richard R
2015-04-13
Turning is an activity of daily living that involves both the acceleration of the body center-of-mass (COM) towards the center of curvature and rotation of the pelvis towards the new heading. The purpose of this study was to understand which muscles contribute to turning using experimentation, musculoskeletal modeling and simulation. Ten healthy adults consented to walk around a 1-m radius circular path at their self-selected walking speed and then along a straight line at the same speed. Forward dynamics simulations of the individual subjects during the turning and straight-line walking tasks were generated to identify the contributions of individual muscle groups to the body mediolateral and anterior-posterior COM acceleration impulse and to the pelvis angular acceleration impulse. The stance leg gluteus medius and ankle plantarflexor muscles and the swing leg adductor muscles were the primary contributors to redirect the body's COM relative to straight-line walking. In some cases, contributions to mediolateral COM acceleration were modulated through changes in leg orientation rather than through changes in muscle force. While modulation of the muscle contributions generally occurred in both the inner and outer legs, greater changes were observed during inner single-leg support than during outer single-leg support. Total pelvis angular acceleration was minimal during the single-support phase, but the swing leg muscles contributed significantly to balancing the internal and external rotation of the pelvis. The understanding of which muscles contribute to turning the body during walking may help guide the development of more effective locomotor therapies for those with movement impairments.
Structural origin of circularly polarized iridescence in jeweled beetles
NASA Astrophysics Data System (ADS)
Crne, Matija; Sharma, Vivek; Park, Jung O.; Srinivasarao, Mohan
2010-03-01
The iridescent metallic green beetle, Chrysina gloriosa, selectively reflects left circularly polarized light. The exoskeleton is decorated by hexagonal cells (˜10 micron) that coexist with pentagons and heptagons. We find that the fraction of hexagons decreases with an increase in curvature. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the core disappears in the dark field. Using confocal microscopy, we observe that these cells consist of nearly concentric, nested arcs that lie on surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. The microstructure provides the bases for the morphogenesis as well as key insights for emulating the intricate optical response the exoskeleton of scarab beetles.
Structural Origin of Circularly Polarized Iridescence in Jeweled Beetles
NASA Astrophysics Data System (ADS)
Sharma, Vivek; Crne, Matija; Park, Jung Ok; Srinivasarao, Mohan
2009-07-01
The iridescent metallic green beetle, Chrysina gloriosa, which selectively reflects left circularly polarized light, possesses an exoskeleton decorated by hexagonal cells (~10 μm) that coexist with pentagons and heptagons. The fraction of hexagons decreases with an increase in curvature. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the core disappears in dark field. With use of confocal microscopy, we observe that these cells consist of nearly concentric nested arcs that lie on the surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. These textures provide the basis for the morphogenesis as well as key insights for emulating the intricate optical response of the exoskeleton of scarab beetles.
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.
Robust pupil center detection using a curvature algorithm
NASA Technical Reports Server (NTRS)
Zhu, D.; Moore, S. T.; Raphan, T.; Wall, C. C. (Principal Investigator)
1999-01-01
Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.
Curvature 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.
Elliptic inflation: generating the curvature perturbation without slow-roll
NASA Astrophysics Data System (ADS)
Matsuda, Tomohiro
2006-09-01
There are many inflationary models in which the inflaton field does not satisfy the slow-roll condition. However, in such models, it is always difficult to generate the curvature perturbation during inflation. Thus, to generate the curvature perturbation, one must introduce another component into the theory. To cite a case, curvatons may generate the dominant part of the curvature perturbation after inflation. However, we question whether it is realistic to consider the generation of the curvature perturbation during inflation without slow-roll. Assuming multifield inflation, we encounter the generation of curvature perturbation during inflation without slow-roll. The potential along the equipotential surface is flat by definition and thus we do not have to worry about symmetry. We also discuss KKLT (Kachru Kallosh Linde Trivedi) models, in which corrections lifting the inflationary direction may not become a serious problem if there is a symmetry enhancement at the tip (not at the moving brane) of the inflationary throat.
Nastic curvatures of wheat coleoptiles that develop in true microgravity
NASA Technical Reports Server (NTRS)
Heathcote, D. G.; Chapman, D. K.; Brown, A. H.
1995-01-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Curvature-processing network in macaque visual cortex
Yue, Xiaomin; Pourladian, Irene S.; Tootell, Roger B. H.; Ungerleider, Leslie G.
2014-01-01
Our visual environment abounds with curved features. Thus, the goal of understanding visual processing should include the processing of curved features. Using functional magnetic resonance imaging in behaving monkeys, we demonstrated a network of cortical areas selective for the processing of curved features. This network includes three distinct hierarchically organized regions within the ventral visual pathway: a posterior curvature-biased patch (PCP) located in the near-foveal representation of dorsal V4, a middle curvature-biased patch (MCP) located on the ventral lip of the posterior superior temporal sulcus (STS) in area TEO, and an anterior curvature-biased patch (ACP) located just below the STS in anterior area TE. Our results further indicate that the processing of curvature becomes increasingly complex from PCP to ACP. The proximity of the curvature-processing network to the well-known face-processing network suggests a possible functional link between them. PMID:25092328
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
Holographic curvature perturbations in a cosmology with a space-like singularity
NASA Astrophysics Data System (ADS)
Ferreira, Elisa G. M.; Brandenberger, Robert
2016-07-01
We study the evolution of cosmological perturbations in an anti-de-Sitter (AdS) bulk through a cosmological singularity by mapping the dynamics onto the boundary conformal fields theory by means of the AdS/CFT correspondence. We consider a deformed AdS space-time obtained by considering a time-dependent dilaton which induces a curvature singularity in the bulk at a time which we call t = 0, and which asymptotically approaches AdS both for large positive and negative times. The boundary field theory becomes free when the bulk curvature goes to infinity. Hence, the evolution of the fluctuations is under better controle on the boundary than in the bulk. To avoid unbounded particle production across the bounce it is necessary to smooth out the curvature singularity at very high curvatures. We show how the bulk cosmological perturbations can be mapped onto boundary gauge field fluctuations. We evolve the latter and compare the spectrum of fluctuations on the infrared scales relevant for cosmological observations before and after the bounce point. We find that the index of the power spectrum of fluctuations is the same before and after the bounce.
NASA Astrophysics Data System (ADS)
Wang, Qian-cheng; Wang, Zhen-guo; Zhao, Yu-xin
2016-09-01
By employing particle image velocimetry, the response of a Mach 2.95 turbulent boundary layer to the concave curvature is experimentally investigated. The radius of the concave wall is 350 mm, and the turning angle is 20∘. Logarithmic law is well preserved in the profile of streamwise velocity at all streamwise positions despite the impact of curvature. The varying trend of principal strain rate is found to be different at different heights within the boundary layer, which cannot be explained by the suggestion given by former researchers. Based on the three-layer model proposed in this paper, distribution of the principal strain rate is carefully analyzed. The streamwise increase of wall friction is suggested to be brought by the increase of velocity gradient in the thin subsonic layer. Increases of the static temperature and the related sound speed are responsible for that. Larger correlated turbulent motions could be introduced by the concave curvature. The probability density histograms of streamwise velocity reveal that the large scale hairpin packets are statistically well organized. The concave curvature is found to have the potential of reinforcing the organization, which explains the increase of turbulent level in the supersonic concave boundary layer.
Circular birefringence of banded spherulites.
Cui, Xiaoyan; Shtukenberg, Alexander G; Freudenthal, John; Nichols, Shane; Kahr, Bart
2014-04-01
Crystal optical properties of banded spherulites of 21 different compounds--molecular crystals, polymers, and minerals--with helically twisted fibers were analyzed with Mueller matrix polarimetry. The well-established radial oscillations in linear birefringence of many polycrystalline ensembles is accompanied by oscillations in circular birefringence that cannot be explained by the natural optical activity of corresponding compounds, some of which are centrosymmetric in the crystalline state. The circular birefringence is shown to be a consequence of misoriented, overlapping anisotropic lamellae, a kind of optical activity associated with the mesoscale stereochemistry of the refracting components. Lamellae splay as a consequence of space constraints related to simultaneous twisting of anisometric lamellae. This mechanism is supported by quantitative simulations of circular birefringence arising from crystallite twisting and splaying under confinement. PMID:24625095
Rand, R.P.; Fuller, N.L. ); Gruner, S.M. ); Parsegian, V.A. )
1990-01-09
Amphiphiles respond both to polar and to nonpolar solvents. In this paper X-ray diffraction and osmotic stress have been used to examine the phase behavior, the structural dimensions, and the work of deforming the monolayer-lined aqueous cavities formed by mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC) as a function of the concentration of two solvents, water and tetradecane (td). In the absence of td, most PE/PC mixtures show only lamellar phases in excess water; all of these become single reverse hexagonal (H{sub II}) phases with addition of excess td. The spontaneous radius of curvature R{sub 0} of lipid monolayers, as expressed in these H{sub II} phases, is allowed by the relief of hydrocarbon chain stress by td; R{sub 0} increases with the ratio DOPC/DOPE. Single H{sub II} phases stressed by limited water or td show several responses. (a) the molecular area is compressed at the polar end of the molecule and expanded at the hydrocarbon ends. (b) For circularly symmetrical water cylinders, the degrees of hydrocarbon chain splaying and polar group compression are different for molecules aligned in different directions around the water cylinder. (c) A pivotal position exists along the length of the phospholipid molecule where little area change occurs as the monolayer is bent to increasing curvatures. (d) By defining R{sub 0} at the pivotal position, the authors find that measured energies are well fit by a quadratic bending energy. (e) For lipid mixtures, enforced deviation of the H{sub II} monolayer from R{sub 0} is sufficiently powerful to cause demixing of the phospholipids in a way suggesting that the DOPE/DOPC ratio self-adjusts so that its R{sub 0} matches the amount of td or water available, i.e., that curvature energy is minimized.
NASA Astrophysics Data System (ADS)
Jordan, Stephen A.
2016-05-01
Long thin circular cylinders commonly serve as towed sonar tracking devices, where the radius-of-curvature along the longitudinal axis is quite low [ρr = O(10-4)]. Because no understanding presently exists about the direct impact of longitudinal curvature on the turbulent statistics, the long cylinder is simply viewed as a chain of straight segments at various (increasing then decreasing) small inclinations to the freestream direction. Realistically, even our statistical evidence along straight thin cylinders at low incidence angles is inadequate to build solid evidence towards forming reliable empirical models. In the present study, we address these shortcomings by executing Large-Eddy Simulations (LESs) of straight and longitudinally curved thin cylinders at low to moderate turbulent radius-based Reynolds numbers (500 ≤ Rea ≤ 3500) and small angles-of-incidence (α = 0° → 9°). Coupled with the previous experimental measurements and numerical results, the new expanded database (311 ≤ Rea ≤ 56 500) delivered sufficient means to propose power-law expressions for the longitudinal evolution of the skin friction, normal drag, and turbulent boundary layer (TBL) length scales. Surprisingly, the LES computations of the curved cylinders at analogous geometric and kinematic conditions as the straight cylinder showed similar character in terms of the longitudinal skin friction. Beyond incidence 1°-3° (upper end corresponds to the highest simulated Rea), the skin friction was directly proportional to the yaw angle and monotonically shifted downward with higher Rea. Conversely, the flow structure, normal drag, TBL length scales, Reynolds stresses, and the separation state of the transverse shear layers towards regular vortex shedding for the curved cylinder were highly dissimilar than the straight one at equivalent incidence angles.
Accelerated Transonic Flow past a curvature discontinuity
NASA Astrophysics Data System (ADS)
de Cointet, Thomas; Ruban, Anatoly
2014-11-01
The aim of this talk is to investigate High Reynolds number Transonic flow past a discontinuity in body curvature. Starting with the inviscid flow outside the boundary layer, our analysis will focus on the flow in a vicinity of the point of discontinuity, where a solution of the Euler equations will be sought in self-similar form. This reduces the Euler equations to an ordinary differential equation. The analysis of this equation shows that the pressure gradient on the airfoil surface develops a strong singularity, which is proportional to (x0 - x) - 1 / 3 as the discontinuity point x0 is approached. We then study the response of the boundary layer to this extremely favourable pressure gradient. We show that the boundary layer splits into two parts, the main body of the boundary layer that becomes inviscid on approach to the singularity, and a thin viscous sublayer situated near the wall. The analysis of the behaviour of the solution in the viscous sublayer shows that Prandtl's hierarchical concept breaks down in a small region surrounding the singular point, where the viscous-inviscid interaction model should be used. In the final part of this talk we present a full formulation of the viscous-inviscid interaction problem and discuss numerical results.
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.
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.
Dark energy, matter creation and curvature
NASA Astrophysics Data System (ADS)
Cárdenas, Víctor H.
2012-09-01
The most studied way to explain the current accelerated expansion of the universe is to assume the existence of dark energy; a new component that fills the universe, does not form clumps, currently dominates the evolution, and has a negative pressure. In this work I study an alternative model proposed by Lima et al. (Abramo and Lima in Class. Quantum Gravity 13:2953, 1996; Zimdahl in Phys. Rev. D 53:5483, 1996; Zimdahl and Pavón in Mon. Not. R. Astron. Soc. 266:872, 1994), which does not need an exotic equation of state, but assumes instead the existence of gravitational particle creation. Because this model fits the supernova observations as well as the ΛCDM model, I perform in this work a thorough study of this model, considering an explicit spatial curvature. I found that in this scenario we can alleviate the cosmic coincidence problem, basically showing that these two components, dark matter and dark energy, are of the same nature, but they act at different scales. I also shown the inadequacy of some particle creation models, and I study a previously proposed new model that overcomes these difficulties.
Geodesic Curvature Effects in the WCMs
NASA Astrophysics Data System (ADS)
Zhou, Tianchun
2015-11-01
The favorable features of the steady state I-Regime discovered on Alcator C-Mod recently make this regime a hopeful working regime for future burning plasma experiments. Accompanying the I-regime are the weakly coherent modes (WCMs) with frequency around 200 kHz that propagate poloidally in the electron diamagnetic drift direction in the lab frame. The WCMs were interpreted as certain type of heavy impurity modes in the 3-fluid framework in a 1-D plane magnetic field geometry. Once considering in a simplified toroidal magnetic field geometry, the geodesic curvature will play important roles in that the contribution of the geodesic compression may catch up with or outweighs that of the parallel compression in the plasma edge region where the fluctuations are highly localized. This geodesic coupling to the neighboring bands modifies the marginal stability condition and mode profiles in Refs.. In the same framework, attempts will be made to interpret the concomitant low frequency (~ 20kHz) fluctuations as a type of impurity drift wave-like modes propagating in the ion diamagnetic drift direction. Supported by China National MCFE Research Program under Grant No. 2015GB11000.
BICEP2, the curvature perturbation and supersymmetry
Lyth, David H.
2014-11-01
The tensor fraction r ≅ 0.16 found by BICEP2 corresponds to a Hubble parameter H ≅ 1.0 × 10{sup 14} GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index n{sub s}. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Interaction effect of number of circular holes in a circular plate
Ukadgaonker, V.G.; Agnahotri, N.A.
1996-12-01
The problem of circular tubesheet with uniform tension at its circular boundary and nine holes in the circular pitch pattern at its center is solved using complex stress functions. The Schwarz Alternating Technique is used to find the interaction effect of the holes on each other and then the superposition method is used to obtain desired geometry of the nine holes. This superposition gives the stress free boundary at the central hole exactly satisfied. When these results are compared with those obtained by Ukadgaonker and Kale by Finite Element Method it is found that the theoretical solutions give higher stress concentration than FEM by about 20% for a large outer radius. When the outer radius is reduced the stress concentration factor increases considerably and the difference in the analytical and the FEM solution also increases to a large extent. The analytical solution found in the present paper is verified with the FEM and Photoelasticity solution obtained by Ukadgaonker and Kale (1996) earlier. This problem is further generalized for a rhombic pitch pattern, which can be reduced to particular cases such as square pitch pattern, triangular pitch pattern, diagonal pitch pattern by changing the angle of the rhombus. The stress concentration factor around the central hole varies very little for various ligament efficiencies which is given in percentage.
NASA Astrophysics Data System (ADS)
Phillips, G.; Robinson, J.; Glen, R.; Roberts, J.
2016-05-01
The middle to late Permian Hunter Bowen Event is credited with the development of orogenic curvature in the southern New England Orogen, yet contention surrounds the structural dynamics responsible for the development of this curvature. Debate is largely centred on the roles of orogen parallel strike-slip and orogen normal extension and contraction to explain the development of curvature. To evaluate the dynamic history of the Hunter Bowen Event, we present new kinematic reconstructions of the Tamworth Belt. The Tamworth Belt formed as a Carboniferous forearc basin and was subsequently inverted during the Hunter Bowen Event. Kinematic reconstructions of the Tamworth Belt are based on new maps and cross-sections built from a synthesis of best-available mapping, chronostratigraphic data and new interpretations of depth-converted seismic data. The following conclusions are made from our study: (i) the Hunter Bowen Event was dominantly driven by margin normal contraction (east-west shortening; present-day coordinates), and; (ii) variations in structural style along the strike of the Tamworth Belt can be explained by orthogonal vs. oblique inversion, which reflects the angular relationship between the principal shortening vector and continental-arc margin. Given these conclusions, we suggest that curvature around the controversial Manning Bend was influenced by the presence of primary curvature in the continental margin, and that the Hastings Block was translated along a sinistral strike-slip fault system that formed along this oblique (with respect to the regional east-west extension and convergence direction) part of the margin. Given the available temporal data, the translation of the Hastings Block took place in the Early Permian (Asselian) and therefore preceded the Hunter Bowen Event. Accordingly, we suggest that the Hunter Bowen Event was dominantly associated with enhancing curvature that was either primary in origin, or associated with fault block translation
Spontaneous curvature of phosphatidic acid and lysophosphatidic acid.
Kooijman, Edgar E; Chupin, Vladimir; Fuller, Nola L; Kozlov, Michael M; de Kruijff, Ben; Burger, Koert N J; Rand, Peter R
2005-02-15
The formation of phosphatidic acid (PA) from lysophosphatidic acid (LPA), diacylglycerol, or phosphatidylcholine plays a key role in the regulation of intracellular membrane fission events, but the underlying molecular mechanism has not been resolved. A likely possibility is that PA affects local membrane curvature facilitating membrane bending and fission. To examine this possibility, we determined the spontaneous radius of curvature (R(0p)) of PA and LPA, carrying oleoyl fatty acids, using well-established X-ray diffraction methods. We found that, under physiological conditions of pH and salt concentration (pH 7.0, 150 mM NaCl), the R(0p) values of PA and LPA were -46 A and +20 A, respectively. Thus PA has considerable negative spontaneous curvature while LPA has the most positive spontaneous curvature of any membrane lipid measured to date. The further addition of Ca(2+) did not significantly affect lipid spontaneous curvature; however, omitting NaCl from the hydration buffer greatly reduced the spontaneous curvature of PA, turning it into a cylindrically shaped lipid molecule (R(0p) of -1.3 x 10(2) A). Our quantitative data on the spontaneous radius of curvature of PA and LPA at a physiological pH and salt concentration will be instrumental in developing future models of biomembrane fission.
An intuitive approach to measuring protein surface curvature.
Coleman, Ryan G; Burr, Michael A; Souvaine, Diane L; Cheng, Alan C
2005-12-01
A natural way to measure protein surface curvature is to generate the least squares fitted (LSF) sphere to a surface patch and use the radius as the curvature measure. While the concept is simple, the sphere-fitting problem is not trivial and known means of protein surface curvature measurement use alternative schemes that are arguably less straightforward to interpret. We have developed an approach to solve the LSF sphere problem by turning the sphere-fitting problem into a solvable plane-fitting problem using a transformation known as geometric inversion. The approach works on any arbitrary surface patch, and returns a radius of curvature that has direct physical interpretation. Additionally, it is flexible in its ability to find the curvature of an arbitrary surface patch, and the "resolution" can be adjusted to highlight atomic features or larger features such as peptide binding sites. We include examples of applying the method to visualization of peptide recognition pockets and protein conformational change, as well as a comparison with a commonly used solid-angle curvature method showing that the LSF method produces more pronounced curvature results.
Circular RNA expands its territory.
Bao, Chunyang; Lyu, Dongbin; Huang, Shenglin
2016-03-01
Circular RNAs (circRNAs) represent a novel class of widespread non-coding RNAs in eukaryotes. They are unusually stable RNA molecules with cell type-specific expression patterns, and are predominantly present in the cytoplasm. We recently demonstrated the existence of abundant circRNAs in exosomes and suggest a potential application of exosomal circRNAs for cancer detection. PMID:27308606
Class IIc or Circular Bacteriocins
NASA Astrophysics Data System (ADS)
Martin-Visscher, Leah A.; van Belkum, Marco J.; Vederas, John C.
The circular bacteriocins produced by Gram-positive bacteria represent a diverse class of antimicrobial peptides. These bacteriocins display enhanced stability compared to linear bacteriocins, which arises from their characteristic circular backbone. Currently, eight unique circular bacteriocins have been identified, and analysis of their gene clusters indicates that they likely utilize complex mechanisms for maturation and secretion, as well as for immunity. These bacteriocins target the cytoplasmic membrane of sensitive cells, leading to pore formation that results in loss of ions, dissipation of membrane potential, and ultimately, cell death. Structural studies suggest that despite variation in their sequences, most of these bacteriocins likely adopt a common three-dimensional architecture, consisting of four or five tightly packed helices encompassing a hydrophobic core. There are many mysteries surrounding the biosynthesis of these peptides, particularly in regard to the mechanism by which they are cyclized. Elucidation of such a mechanism may provide exciting new approaches to the bioengineering of new, stable, and antimicrobially active circular peptides.
NASA Astrophysics Data System (ADS)
RóŻycki, Bartosz; Lipowsky, Reinhard
2015-02-01
Biomimetic and biological membranes consist of molecular bilayers with two leaflets which are typically exposed to different aqueous environments and may differ in their molecular density or composition. Because of these asymmetries, the membranes prefer to curve in a certain manner as quantitatively described by their spontaneous curvature. Here, we study such asymmetric membranes via coarse-grained molecular dynamics simulations. We consider two mechanisms for the generation of spontaneous curvature: (i) different lipid densities within the two leaflets and (ii) leaflets exposed to different concentrations of adsorbing particles. We focus on membranes that experience no mechanical tension and describe two methods to compute the spontaneous curvature. The first method is based on the detailed structure of the bilayer's stress profile which can hardly be measured experimentally. The other method starts from the intuitive view that the bilayer represents a thin fluid film bounded by two interfaces and reduces the complexity of the stress profile to a few membrane parameters that can be measured experimentally. For the case of asymmetric adsorption, we introduce a simulation protocol based on two bilayers separated by two aqueous compartments with different adsorbate concentrations. The adsorption of small particles with a size below 1 nm is shown to generate large spontaneous curvatures up to about 1/(24 nm). Our computational approach is quite general: it can be applied to any molecular model of bilayer membranes and can be extended to other mechanisms for the generation of spontaneous curvatures as provided, e.g., by asymmetric lipid composition or depletion layers of solute molecules.
3D curvature of muscle fascicles in triceps surae
Hamarneh, Ghassan; Wakeling, James M.
2014-01-01
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. PMID:25324510
Lunar Maria and circular basins-a review
Stuart-Alexander, D. E.; Howard, K.A.
1970-01-01
Lunar Orbiter data make it possible to examine the distribution and relations of maria and large circular basins over the entire Moon. The restricted distribution and age of the maria are in marked contrast to the apparently random distribution in time and place of the circular basins, some of which contain mare fillings. The circular basins are believed to be impact scars, and the maria to be volcanic fills which in each case are younger than the structures they fill. Twenty-nine circular basins 300 km wide or wider are recognized. They are placed in an age sequence because successive stages of degradation can be recognized from the fresh Orientale basin to the almost obliterated basin containing Mare Australe. The maria were emplaced during a short span of lunar history, although some light plains of the highlands may be older maria lightened through age. The present maria are topographically low, tend to be associated with large circular basins, and lie in a crude global belt of regional concentrations; 94% are on the hemisphere facing the Earth. Possible explanations offered for these patterns of mare distribution include impact-induced volcanism, volcanic extrusion to a hydrostatic level, isostatic compensation, lateral heterogeneity in the lunar interior, subcrustal convection, and volcanism due to disruption by Earth's gravity. ?? 1970.
Variable Curvature Mirrors for ELT Laser Guide Star refocusing systems
NASA Astrophysics Data System (ADS)
Challita, Zalpha; Hugot, Emmanuel; Ferrari, Marc; Madec, Fabrice; Le Mignant, David; Cuby, Jean-Gabriel
2011-09-01
The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, LGS defocusing is one of the system issues that can be tackled using active refocusing mirrors such as Variable Curvature Mirrors (VCM). Indeed, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope, and induces a large defocusing at the LGS wave-front sensor focal plane. To compensate for that, we propose an original concept including a VCM specifically designed to keep a focused spot on the wave-front sensor: the mirror is made of a thin meniscus bend using a pressure applied on its back face. Due to the large defocusing, the LGS-VCM must be able to change its shape from F/12.5 to F/5, leading to more than 1 mm sag. The VCM benefits of a specific shape with a variable radial thickness distribution, allowing keeping an optical quality better than λ/5 over this very large range of deformation. The work presented here details the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Two prototypes have been manufactured to compare the real behaviour of the mirror and the simulations data. Results obtained on the prototypes show that the deformation of the VCM is very close to the simulation, and leads to a realistic concept.
Curvature and isocurvature perturbations in two-field inflation
NASA Astrophysics Data System (ADS)
Lalak, Z.; Langlois, D.; Pokorski, S.; Turzyński, K.
2007-07-01
We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, up to first order in the slow-roll parameters. We also compute numerically the evolution of the curvature and isocurvature modes from well within the Hubble radius until the end of inflation. We show explicitly for a few examples, including the recently proposed model of 'roulette' inflation, how isocurvature perturbations affect significantly the curvature perturbation between Hubble crossing and the end of inflation.
Dynamic Curvature Steering Control for Autonomous Vehicle: Performance Analysis
NASA Astrophysics Data System (ADS)
Aizzat Zakaria, Muhammad; Zamzuri, Hairi; Amri Mazlan, Saiful
2016-02-01
This paper discusses the design of dynamic curvature steering control for autonomous vehicle. The lateral control and longitudinal control are discussed in this paper. The controller is designed based on the dynamic curvature calculation to estimate the path condition and modify the vehicle speed and steering wheel angle accordingly. In this paper, the simulation results are presented to show the capability of the controller to track the reference path. The controller is able to predict the path and modify the vehicle speed to suit the path condition. The effectiveness of the controller is shown in this paper whereby identical performance is achieved with the benchmark but with extra curvature adaptation capabilites.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed. PMID:25615464
Geometry-specific scaling of detonation parameters from front curvature
Jackson, Scott I; Short, Mark
2011-01-20
It has previously been asserted that classical detonation curvature theory predicts that the critical diameter and the diameter-effect curve of a cylindrical high-explosive charge should scale with twice the thickness of an analogous two-dimensional explosive slab. The varied agreement of experimental results with this expectation have led some to question the ability of curvature-based concepts to predict detonation propagation in non-ideal explosives. This study addresses such claims by showing that the expected scaling relationship (hereafter referred to d = 2w) is not consistent with curvature-based Detonation Shock Dynamics (DSD) theory.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-01
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
Tidal invariants for compact binaries on quasi-circular orbits
NASA Astrophysics Data System (ADS)
Warburton, Niels; Dolan, Sam; Nolan, Patrick; Ottewill, Adrian; Wardell, Barry
2015-04-01
We extend the gravitational self-force approach to encompass `self-interaction' tidal effects for a compact body of mass μ on a quasi-circular orbit around a black hole of mass M >> μ . Specifically, we define and calculate at O(μ) (conservative) shifts in the eigenvalues of the electric- and magnetic-type tidal tensors, and a (dissipative) shift in a scalar product between their eigenbases. This approach yields four gauge-invariant functions, from which one may construct other tidal quantities such as the curvature scalars and the speciality index. First, we analyze the general case of a geodesic in a regular perturbed vacuum spacetime admitting a helical Killing vector and a reflection symmetry. Next, we specialize to focus on circular orbits in the equatorial plane of Kerr spacetime at O(μ) . We present accurate numerical results for the Schwarzschild case for orbital radii up to the light-ring, calculated via independent implementations in Lorenz and Regge-Wheeler gauges. We show that our results are consistent with leading-order post-Newtonian expansions, and demonstrate the existence of additional structure in the strong-field regime. We anticipate that our strong-field results will inform (e.g.) effective one-body models for the gravitational two-body probl
Curvature-driven assembly in soft matter.
Liu, Iris B; Sharifi-Mood, Nima; Stebe, Kathleen J
2016-07-28
Control over the spatial arrangement of colloids in soft matter hosts implies control over a wide variety of properties, ranging from the system's rheology, optics, and catalytic activity. In directed assembly, colloids are typically manipulated using external fields to form well-defined structures at given locations. We have been developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. Such potential fields allow particles to interact with each other. If the soft matter host is deformed in some way, the potential allows the particles to interact with the global system distortion. One important example is capillary assembly of colloids on curved fluid interfaces. Upon attaching, the particle distorts that interface, with an associated energy field, given by the product of its interfacial area and the surface tension. The particle's capillary energy depends on the local interface curvature. We explore this coupling in experiment and theory. There are important analogies in liquid crystals. Colloids in liquid crystals elicit an elastic energy response. When director fields are moulded by confinement, the imposed elastic energy field can couple to that of the colloid to define particle paths and sites for assembly. By improving our understanding of these and related systems, we seek to develop new, parallelizable routes for particle assembly to form reconfigurable systems in soft matter that go far beyond the usual close-packed colloidal structures.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298434
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.
Magazines in Special Media. Reference Circular No. 81-3.
ERIC Educational Resources Information Center
Gibson, Merrillyn, Comp.
This circular lists 384 magazines produced in media suitable for use by persons who are unable to read conventional print materials. The media included are braille, cassette, disc, large type, Moon type, and open-reel tape. The entry for each title gives frequency of publication, medium or media in which it is available, method or methods by which…
The inviscid axisymmetric stability of the supersonic flow along a circular cylinder
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1990-01-01
The supersonic flow past a thin straight circular cylinder is investigated. The associated boundary-layer flow (i.e. the velocity and temperature field) is computed; the asymptotic, far downstream solution is obtained, and compared with the full numerical results. The inviscid, linear, axisymmetric (temporal) stability of this boundary layer is also studied. A so-called 'doubly generalized' inflexion condition is derived, which is a condition for the existence of so-called 'subsonic' neutral modes. The eigenvalue problem (for the complex wavespeed) is computed for two free-stream Mach numbers (2.8 and 3.8), and this reveals that curvature has a profound effect on the stability of the flow. The first unstable inviscid mode is seen to disappear rapidly as curvature is introduced, while the second (and generally the most important) mode suffers a substantially reduced amplification rate.
The inviscid axisymmetric stability of the supersonic flow along a circular cylinder
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1989-01-01
The supersonic flow past a thin straight circular cylinder is investigated. The associated boundary layer flow (i.e., the velocity and temperature field) is computed; the asymptotic, far downstream solution is obtained, and compared with the full numerical results. The inviscid, linear, axisymmetric (temporal) stability of this boundary layer is also studied. A so called doubly generalized inflexion condition is derived, which is a condition for the existence of so called subsonic neutral modes. The eigenvalue problem (for the complex wavespeed) is computed for two freestream Mach numbers (2.8 and 3.8), and this reveals that curvature has a profound effect on the stability of the flow. The first unstable inviscid mode is seen to rapidly disappear as curvature is introduced, while the second (and generally the most important) mode suffers a substantially reduced amplification rate.
16. Detail of curvature of northern parapet, with 1932 concrete ...
16. Detail of curvature of northern parapet, with 1932 concrete extension of parapet in foreground, facing east. - Dubbs Bridge, Spinnerstown Road (State Route 2031) spanning Hosensack Creek, Dillingerville, Lehigh County, PA
Curvature and bow of bulk GaN substrates
NASA Astrophysics Data System (ADS)
Foronda, Humberto M.; Romanov, Alexey E.; Young, Erin C.; Roberston, Christian A.; Beltz, Glenn E.; Speck, James S.
2016-07-01
We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.
Curvature-Squared Cosmology In The First-Order Formalism
NASA Technical Reports Server (NTRS)
Shahid-Saless, Bahman
1993-01-01
Paper presents theoretical study of some of general-relativistic ramifications of gravitational-field energy density proportional to R - alpha R(exp 2) (where R is local scalar curvature of space-time and alpha is a constant).
Curvature Control of Silicon Microlens for THz Dielectric Antenna
NASA Technical Reports Server (NTRS)
Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran
2012-01-01
We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.
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.
Raft Formation in Lipid Bilayers Coupled to Curvature
Sadeghi, Sina; Müller, Marcus; Vink, Richard L.C.
2014-01-01
We present computer simulations of a membrane in which the local composition is coupled to the local membrane curvature. At high temperatures (i.e., above the temperature of macroscopic phase separation), finite-sized transient domains are observed, reminiscent of lipid rafts. The domain size is in the range of hundred nanometers, and set by the membrane elastic properties. These findings are in line with the notion of the membrane as a curvature-induced microemulsion. At low temperature, the membrane phase separates. The transition to the phase-separated regime is continuous and belongs to the two-dimensional Ising universality class when the coupling to curvature is weak, but becomes first-order for strong curvature-composition coupling. PMID:25296311
Raft formation in lipid bilayers coupled to curvature.
Sadeghi, Sina; Müller, Marcus; Vink, Richard L C
2014-10-01
We present computer simulations of a membrane in which the local composition is coupled to the local membrane curvature. At high temperatures (i.e., above the temperature of macroscopic phase separation), finite-sized transient domains are observed, reminiscent of lipid rafts. The domain size is in the range of hundred nanometers, and set by the membrane elastic properties. These findings are in line with the notion of the membrane as a curvature-induced microemulsion. At low temperature, the membrane phase separates. The transition to the phase-separated regime is continuous and belongs to the two-dimensional Ising universality class when the coupling to curvature is weak, but becomes first-order for strong curvature-composition coupling.
The probability equation for the cosmological comoving curvature perturbation
Riotto, Antonio; Sloth, Martin S. E-mail: sloth@cern.ch
2011-10-01
Fluctuations of the comoving curvature perturbation with wavelengths larger than the horizon length are governed by a Langevin equation whose stochastic noise arise from the quantum fluctuations that are assumed to become classical at horizon crossing. The infrared part of the curvature perturbation performs a random walk under the action of the stochastic noise and, at the same time, it suffers a classical force caused by its self-interaction. By a path-interal approach and, alternatively, by the standard procedure in random walk analysis of adiabatic elimination of fast variables, we derive the corresponding Kramers-Moyal equation which describes how the probability distribution of the comoving curvature perturbation at a given spatial point evolves in time and is a generalization of the Fokker-Planck equation. This approach offers an alternative way to study the late time behaviour of the correlators of the curvature perturbation from infrared effects.
Constructing empirical resolution diagnostics for kriging and minimum curvature gridding
NASA Astrophysics Data System (ADS)
Chiao, Ling-Yun; Chen, Ying-Nien; Gung, Yuancheng
2014-05-01
Resolution analysis is a crucial appraisal procedure in solving general estimation problems, especially for correctly interpreting the results of spatial analysis schemes. Resolution analyses based on the resolving kernels are typically applied to small inverse problems only when the inverse operators are explicitly accessible. Stochastic simulation schemes have been proposed to extract empirical resolution information for solving large inverse problem. In this study, we generalize the formulation of the empirical resolution length and derive the characteristic length of the point spread function for general estimation methods such as minimum curvature gridding and kriging interpolation schemes that are not equipped with explicitly accessible resolving kernels. The implementation of these resolution diagnostics has not been possible in the past and is demonstrated in this study to facilitate clarifying the advantages and limitations of these widely used methods. In addition, we compare these schemes, based on the resolution appraisal, with a multiscale gridding algorithm in the spatial analysis of the Pacific seafloor heat flow observations. By depicting the pattern of the resolution length variations of both the empirical averaging function and the point spread function for each of the estimated models, we demonstrate that schemes equipped with multiscale capability are more favorable for accommodating sparse, nonuniform data distribution than stationary schemes, such as the kriging method. Furthermore, the empirical resolution pattern constructed in this study facilitates the selection of an appropriate reference function and radii of influence for fitting the variogram, which is difficult but critical when using the kriging method.
Influence of curvature on the losses of doubly clad fibers.
Marcuse, D
1982-12-01
The loss increase of the HE(11) mode of a doubly clad (depressed-index) fiber due to constant curvature is considered. The calculations presented in this paper are based on a simplified theory. We find that for typical fibers the leakage loss of the HE(11) mode begins to increase significantly when the radius of curvature of the fiber axis reaches the 1-10-cm range.
Layered devices having surface curvature and method of constructing same
Woodbury, Richard C.; Perkins, Raymond T.; Thorne, James M.
1989-01-01
A method of treating a substrate having first and second sides with corresponding oppositely facing first and second surfaces, to produce curvature in the first surface. The method includes the steps of removing material, according to a predetermined pattern, from the second side of the substrate, and applying a stress-producing film of material to at least one surface of the substrate to thereby cause the substrate to bend to produce the desired curvature in the first surface.
Topology of codimension-one foliations of nonnegative curvature
Bolotov, Dmitry V
2013-05-31
We show that a transversely oriented C{sup 2}-foliation of codimension one with nonnegative Ricci curvature on a closed orientable manifold is a foliation with almost no holonomy. This allows us to decompose the manifold into blocks on which this foliation has a simple structure. We also show that a manifold homeomorphic to a 5-dimensional sphere does not admit a codimension-one C{sup 2}-foliation with nonnegative sectional curvature. Bibliography: 29 titles.
Fresnel diffractive imaging: Experimental study of coherence and curvature
NASA Astrophysics Data System (ADS)
Whitehead, L. W.; Williams, G. J.; Quiney, H. M.; Nugent, K. A.; Peele, A. G.; Paterson, D.; de Jonge, M. D.; McNulty, I.
2008-03-01
A Fresnel coherent diffractive imaging experiment is performed using a pinhole as a test object. The experimental parameters of the beam curvature and coherence length of the illuminating radiation are varied to investigate their effects on the reconstruction process. It is found that a sufficient amount of curvature across the sample strongly ameliorates the effects of low coherence, even when the sample size exceeds the coherence length.
FAST TRACK COMMUNICATION: Lorentzian manifolds and scalar curvature invariants
NASA Astrophysics Data System (ADS)
Coley, Alan; Hervik, Sigbjørn; Pelavas, Nicos
2010-05-01
We discuss (arbitrary-dimensional) Lorentzian manifolds and the scalar polynomial curvature invariants constructed from the Riemann tensor and its covariant derivatives. Recently, we have shown that in four dimensions a Lorentzian spacetime metric is either \\mathcal {I}-non-degenerate, and hence locally characterized by its scalar polynomial curvature invariants, or is a degenerate Kundt spacetime. We present a number of results that generalize these results to higher dimensions and discuss their consequences and potential physical applications.
Adhesive Nanoparticles as Local Probes of Membrane Curvature.
Agudo-Canalejo, Jaime; Lipowsky, Reinhard
2015-10-14
Biological and biomimetic membranes display complex shapes with nonuniform curvature. Because the interaction of adhesive nanoparticles with such membranes depends on the local membrane curvature, different segments of the same membrane can differ in their engulfment behavior. For a single vesicle in contact with many nanoparticles, we predict ten distinct engulfment patterns as well as morphological transitions between these patterns, which are directly accessible to experiment.
Negative circular polarization as a universal property of quantum dots
Taylor, Matthew W.; Spencer, Peter; Murray, Ray
2015-03-23
This paper shows that negative circular polarization, a spin flip of polarized carriers resulting in emission of opposite helicity, can be observed in undoped, n-doped, and p-doped InAs/GaAs quantum dots. These results contradict the usual interpretation of the effect. We show using power dependent and time resolved spectroscopy that the generation of negative circular polarization correlates with excited state emission. Furthermore, a longer spin lifetime of negatively polarized excitons is observed where emission is largely ground state in character.
Design of a curvature sensor using a flexoelectric material
NASA Astrophysics Data System (ADS)
Yan, X.; Huang, W. B.; Kwon, S. R.; Yang, S. R.; Jiang, X. N.; Yuan, F. G.
2013-04-01
A curvature sensor based on flexoelectricity using Ba0.64Sr0.36TiO3 (BST) material is proposed and developed in this paper. The working principle of the sensor is based on the flexoelectricity, exhibiting coupling between mechanical strain gradient and electric polarization. A BST curvature sensor is lab prepared using a conventional solid state processing method. The curvature sensing is demonstrated in four point bending tests of the beam under harmonic loads. BST sensors are attached on both side surfaces of an aluminum beam, located symmetrically with respect to its neutral axis. Analyses have shown that the epoxy bonding layer plays a critical role for curvature transfer. Consequently a shear lag effect is taken into account for extracting actual curvature from the sensor measurement. Experimental results demonstrated good linearity from the charge outputs under the frequencies tests and showed a sensor sensitivity of 30.78pC•m in comparison with 32.48pC•m from theoretical prediction. The BST sensor provides a direct curvature measure instead of using traditional strain gage through interpolation and may offer an optional avenue for on-line and in-situ structural health monitoring.
Nanoscale Membrane Curvature detected by Polarized Localization Microscopy
NASA Astrophysics Data System (ADS)
Kelly, Christopher; Maarouf, Abir; Woodward, Xinxin
Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology.
Control of microelectromechanical systems membrane curvature by silicon ion implantation
NASA Astrophysics Data System (ADS)
Jin, S.; Mavoori, H.; Kim, J.; Aksyuk, V. A.
2003-09-01
Thin silicon membranes in microelectromechanical systems (MEMS) optical devices such as beam-steering, movable mirrors may exhibit undesirable curvature when their surface is metallized with light-reflecting metals to enhance optical performance. We have applied Si+ ion implantations at dose levels of 0.4-5×1016/cm2 into the gold metallization layer to successfully reduce the mirror curvature as well as the degree of its temperature-dependent changes. The curvature change as well as the temperature dependence is found to be dependent on the implantation dose. The mechanism of the observed curvature flattening effect is attributed mostly to the induced compressive stress in gold metallization caused by the insertion of foreign implanted atoms of silicon. Such a Si implantation approach can be useful as a means for post-fabrication correction of unwanted curvature in MEMS membranes, as well as a technique to intentionally introduce a desired degree of curvature if needed. A convenient blanket implantation process can be utilized with minimal contamination problems as Si is a common element already present in the MEMS.
Monolayer spontaneous curvature of raft-forming membrane lipids
NASA Astrophysics Data System (ADS)
Kollmitzer, Benjamin; Heftberger, Peter; Rappolt, Michael; Pabst, Georg
Monolayer spontaneous curvatures for cholesterol, DOPE, POPE, DOPC, DPPC, DSPC, POPC, SOPC, and egg sphingomyelin were obtained using small-angle X-ray scattering (SAXS) on inverted hexagonal phases (HII). Spontaneous curvatures of bilayer forming lipids were estimated by adding controlled amounts to a HII forming template following previously established protocols. Spontanous curvatures of both phosphatidylethanolamines and cholesterol were found to be at least a factor of two more negative than those of phosphatidylcholines, whose J0 are closer to zero. Interestingly, a significant positive J0 value (+0.1 1/nm) was retrieved for DPPC at 25 {\\deg}C. We further determined the temperature dependence of the spontaneous curvatures J0(T) in the range from 15 to 55 \\degC, resulting in a quite narrow distribution of -1 to -3 * 10^-3 1/nm{\\deg}C for most investigated lipids. The data allowed us to estimate the monolayer spontaneous curvatures of ternary lipid mixtures showing liquid ordered / liquid disordered phase coexistence. We report spontaneous curvature phase diagrams for DSPC/DOPC/Chol, DPPC/DOPC/Chol and SM/POPC/Chol and discuss effects on protein insertion and line tension.
Nonlinear dynamics of the tearing mode with two-fluid and curvature effects in tokamaks
Meshcheriakov, Dmytro; Maget, Patrick; Garbet, Xavier; Lütjens, Hinrich; Beyer, Peter
2014-01-15
Curvature and diamagnetic effects are both known to have an influence on tearing mode dynamics. In this paper, we investigate the impact of these effects on the nonlinear stability and saturation of a (2, 1) island using non-linear two-fluid MHD simulations and we apply our results to Tore Supra experiments, where its behavior is not well understood from the single fluid MHD model. Simulations show that a metastable state induced by diamagnetic effect exists for this mode and that it also produces a reduction of the saturated island size, in presence of toroidal curvature. The mode is found to be nonlinearly destabilized by a seed island and it saturates at a macroscopic level causing a significant confinement degradation. The interpretation of dual states, with either no island on q = 2 or a large one, observed on discharges with high non inductive current source on Tore Supra, is revisited.
Effects of anisotropy and spatial curvature on the pre-big-bang scenario
NASA Astrophysics Data System (ADS)
Clancy, Dominic; Lidsey, James E.; Tavakol, Reza
1998-08-01
A class of exact, anisotropic cosmological solutions to the vacuum Brans-Dicke theory of gravity is considered within the context of the pre-big-bang scenario. Included in this class are the Bianchi type III, V and VIh models and the spatially isotropic, negatively curved Friedmann-Robertson-Walker universe. The effects of large anisotropy and spatial curvature are determined. In contrast with a negatively curved Friedmann-Robertson-Walker model, there exist regions of the parameter space in which the combined effects of curvature and anisotropy prevent the occurrence of inflation. When inflation is possible, the necessary and sufficient conditions for successful pre-big-bang inflation are more stringent than in the isotropic models. The initial state for these models is established and corresponds in general to a gravitational plane wave.
Optics design for J-TEXT ECE imaging with field curvature adjustment lens
Zhu, Y.; Zhao, Z.; Liu, W. D.; Xie, J.; Hu, X.; Muscatello, C. M.; Domier, C. W.; Luhmann, N. C.; Chen, M.; Ren, X.; Tobias, B. J.; Zhuang, G.; Yang, Z.
2014-11-15
Significant progress has been made in the imaging and visualization of magnetohydrodynamic and microturbulence phenomena in magnetic fusion plasmas. Of particular importance has been microwave electron cyclotron emission imaging (ECEI) for imaging T{sub e} fluctuations. Key to the success of ECEI is a large Gaussian optics system constituting a major portion of the focusing of the microwave radiation from the plasma to the detector array. Both the spatial resolution and observation range are dependent upon the imaging optics system performance. In particular, it is critical that the field curvature on the image plane is reduced to decrease crosstalk between vertical channels. The receiver optics systems for two ECEI on the J-TEXT device have been designed to ameliorate these problems and provide good performance with additional field curvature adjustment lenses with a meniscus shape to correct the aberrations from several spherical surfaces.
Curvature effects in the band structure of carbon nanotubes including spin-orbit coupling
NASA Astrophysics Data System (ADS)
Liu, Hong; Heinze, Dirk; Thanh Duc, Huynh; Schumacher, Stefan; Meier, Torsten
2015-11-01
The Kane-Mele model was previously used to describe effective spin-orbit couplings (SOCs) in graphene. Here we extend this model and also incorporate curvature effects to analyze the combined influence of SOC and curvature on the band structure of carbon nanotubes (CNTs). The extended model then reproduces the chirality-dependent asymmetric electron-hole splitting for semiconducting CNTs and in the band structure for metallic CNTs shows an opening of the band gap and a change of the Fermi wave vector with spin. For chiral semiconducting CNTs with large chiral angle we show that the spin-splitting configuration of bands near the Fermi energy depends on the value of \\text{mod}(2n+m,3) .
Non-universality in dynamically triangulated random surfaces with extrinsic curvature
Baillie, C.F.; Williams, R.D. ); Johnston, D.A. . Dept. of Physics)
1990-08-30
Earlier simulations of dynamically triangulated random surfaces with a pure Gaussian (Polyakov) action have suggested that the incorporation of a term which is equivalent to the square of the scalar curvature, R{sup 2}, in the continuum can affect the properties of the surfaces, despite the fact that such a term appears to be irrelevant on dimensional grounds. However, simulations by the current authors and Catterall of dynamically triangulated random surfaces with extrinsic curvature produced essentially identical results despite differing coefficients for the R{sup 2} term. In this paper, the authors show that small (positive or negative) values of this coefficient have little effect but that large values do produce measurable effects. This explains the concordance of our previous results with Catterall's and also provides evidence for nonuniversal behavior in the random surface model.
Circular on planned parenthood, 1987.
1987-01-01
In 1987 fourteen units of the Government of Henan issued a Circular stating that: "Planned parenthood must be publicized deep into the grass roots and among the people, and importance must be attached to results." The Circular stresses: "In the propaganda drive, it is necessary to successfully grasp three key links: 1. It is necessary to disseminate intensively the important directive on population problems that is contained in the report of the 13th CPC National Congress and the seriousness of the population situation of our country and province so that the cadres and the masses can understand the relationship between population control and the achievement of the strategic target of the three big steps, understand the reason for carrying out planned parenthood, understand that the one-child policy is still advocated, and conscientiously carry out planned parenthood. 2. It is essential to succeed in propagating knowledge of contraception, sterilization, childbirth, and child care and in conducting ideological education for those who undergo operations and for their family members. 3. It is imperative to visit those who have undergone operations and to help them solve practically their difficulties in making a living." The Circular concludes by demanding that under the unified leadership of party committees and governments at all levels, the propaganda drive be carried out by relying on the efforts of all of society. In conjunction with their own work, departments, including the propaganda, education, public health, and cultural departments, must carry out propaganda and education for planned parenthood.
Synthetic-Aperture Coherent Imaging From A Circular Path
NASA Technical Reports Server (NTRS)
Jin, Michael Y.
1995-01-01
Imaging algorithms based on exact point-target responses. Developed for use in reconstructing image of target from data gathered by radar, sonar, or other transmitting/receiving coherent-signal sensory apparatus following circular observation path around target. Potential applications include: Wide-beam synthetic-aperture radar (SAR) from aboard spacecraft in circular orbit around target planet; SAR from aboard airplane flying circular course at constant elevation around central ground point, toward which spotlight radar beam pointed; Ultrasonic reflection tomography in medical setting, using one transducer moving in circle around patient or else multiple transducers at fixed positions on circle around patient; and Sonar imaging of sea floor to high resolution, without need for large sensory apparatus.
On electrostatically actuated NEMS/MEMS circular plates
NASA Astrophysics Data System (ADS)
Caruntu, Dumitru I.; Alvarado, Iris
2011-04-01
This paper deals with electrostatically actuated micro and nano-electromechanical (MEMS/NEMS) circular plates. The system under investigation consists of two bodies, a deformable and conductive circular plate placed above a fixed, rigid and conductive ground plate. The deformable circular plate is electrostatically actuated by applying an AC voltage between the two plates. Nonlinear parametric resonance and pull-in occur at certain frequencies and relatively large AC voltage, respectively. Such phenomena are useful for applications such as sensors, actuators, switches, micro-pumps, micro-tweezers, chemical and mass sensing, and micro-mirrors. A mathematical model of clamped circular MEMS/NEMS electrostatically actuated plates has been developed. Since the model is in the micro- and nano-scale, surface forces, van der Waals and/or Casimir, acting on the plate are included. A perturbation method, the Method of Multiple Scales (MMS), is used for investigating the case of weakly nonlinear MEMS/NEMS circular plates. Two time scales, fast and slow, are considered in this work. The amplitude-frequency and phase-frequency response of the plate in the case of primary resonance are obtained and discussed.
Chirped microlens arrays for diode laser circularization and beam expansion
NASA Astrophysics Data System (ADS)
Schreiber, Peter; Dannberg, Peter; Hoefer, Bernd; Beckert, Erik
2005-08-01
Single-mode diode lasers are well-established light sources for a huge number of applications but suffer from astigmatism, beam ellipticity and large manufacturing tolerances of beam parameters. To compensate for these shortcomings, various approaches like anamorphic prism pairs and cylindrical telescopes for circularization as well as variable beam expanders based on zoomed telescopes for precise adjustment of output beam parameters have been employed in the past. The presented new approach for both beam circularization and expansion is based on the use of microlens arrays with chirped focal length: Selection of lenslets of crossed cylindrical microlens arrays as part of an anamorphic telescope enables circularization, astigmatism correction and divergence tolerance compensation of diode lasers simultaneously. Another promising application of chirped spherical lens array telescopes is stepwise variable beam expansion for circular laser beams of fiber or solid-state lasers. In this article we describe design and manufacturing of beam shaping systems with chirped microlens arrays fabricated by polymer-on-glass replication of reflow lenses. A miniaturized diode laser module with beam circularization and astigmatism correction assembled on a structured ceramics motherboard and a modulated RGB laser-source for photofinishing applications equipped with both cylindrical and spherical chirped lens arrays demonstrate the feasibility of the proposed system design approach.
Frazão, Orlando; Baptista, José M; Santos, José L; Roy, Philippe
2008-05-01
A curvature sensor based on a highly birefringent (Hi-Bi) photonic crystal fiber inserted into a Sagnac interferometer is demonstrated. For this purpose, a novel Hi-Bi photonic crystal fiber was designed and fabricated. Half of the microstructured region of the photonic crystal fiber was composed by large diameter holes, while the other half contained small diameter holes. Because of this geometry, the fiber core was shifted from the center and high birefringence appears in the optical fiber. Curvature was applied for three different fiber directions for a range of 0.6-5 m(-1). Temperature and longitudinal strain was also characterized for constant curvature. The configuration showed insensitivity to these two physical parameters. PMID:18449321
Overriding plate thickness control on subducting slab curvature
NASA Astrophysics Data System (ADS)
Holt, A.; Buffett, B. A.; Becker, T. W.
2014-12-01
The curvature of subducting lithosphere controls deformation due to bending at the trench, which results in a force that dissipates gravitational potential energy and may affect seismic coupling. We use 2-D, thermo-mechanical subduction models to explore the dependence of the radius of curvature on the thickness of the subducting and overriding plates for models with both viscous and effectively plastic lithospheric rheologies. Such a plastic rheology has been shown to reproduce the bending stresses/moment computed using a kinematic strain rate description and a laboratory derived composite rheology. Laboratory and numerical models show that the bending geometry of subducting slabs with a viscous rheology is strongly dependent on slab thickness; thicker plates have a larger radius of curvature. However, the curvature of subducting plates on Earth, illuminated by the distribution of earthquake hypocenters, shows little to no dependence on the plate thickness or age. Such an observation is instead compatible with plates that have a plastic rheology. Indeed, our numerical models show that the radius of curvature of viscous plates has a stronger dependence on subducting plate thickness than in equivalent plastic models. In viscous plates, the bending moment produces a torque, which balances the torque exerted by buoyancy. However, for the plastic plate case the bending moment saturates at a maximum value and so cannot balance the gravitational torque. The saturation of bending moment means that, (a) the radius of curvature of the bending region is not constrained by this torque balance, and, (b) other forces are required to balance the gravitational torque. We explore the role that the overriding plate could play in controlling the subducting plate curvature in plastic plate models where the bending stresses have saturated. For such plates, we find that increasing the thickness of the overriding plate causes the radius of curvature to increase. The same correlation is
Curvature facilitates prey fixation in predatory insect claws.
Petie, Ronald; Muller, Mees
2007-02-21
Insects show a large variety in prey capture strategies, with a correspondingly large diversity in predatory adaptations. We studied a specific type of predatory claws, these can for example be found in praying mantis species. The claw is closeable over its entire length and the prey is fixed between the femur (upper arm) and the tibia (lower arm) of the insect leg. The morphology of these predatory claws is diverse. Some species have straight claws covered with spines, while other species have smooth, curved claws. We have studied the mechanics of this femur-tibia type of predatory insect claws, by making a physical model, eventually trying to explain why in some insect species the claws are curved instead of straight. The main results are (1) when comparing curved claws to straight claws, curvature leads to a strong reduction of forces driving the prey away from the pivoting point, thereby reducing the need for friction generating structures. (2) In the curved claw model a position exists where the resulting force on the prey is exactly zero. This is because the normal forces on the femur and tibia are opposed, and in line. At this position the prey is perfectly clamped and not driven out of the claw. This feature does not exist in straight claws. (3) In the curved claw, the prey cannot be placed at a position further than a certain maximum distance from the pivoting point. Near this maximum position, the resulting force on the prey reaches high values because moment arms are near zero. (4) Between the zero position and the maximum position the resulting force is directed toward the pivoting point, which stabilizes prey fixation. PMID:17056069
QT/RR curvatures in healthy subjects: sex differences and covariates.
Malik, Marek; Hnatkova, Katerina; Kowalski, Donna; Keirns, James J; van Gelderen, E Marcel
2013-12-01
Data of a large clinical study were used to investigate how much are the QT/RR patterns in healthy subjects curved and whether these curvatures differ between women and men. Daytime drug-free 12-lead Holter recordings were repeated 4 times in each of 176 female healthy subjects and 176 male healthy subjects aged 32.7 ± 9.1 yr. In each of the subjects, up to 1,440 carefully verified QT interval measurements were obtained with QT/RR hysteresis-corrected RR intervals. Individual subject data were used to fit the following regression equation: QT = χ + (δ/γ)(1 - RR(γ)) + ε, where QT and RR are QT and RR measurements (in s), χ is regression intercept, δ is the QT/RR slope, γ is the QT/RR curvature and provides the lowest regression residual, and ε represents normally distributed zero-centered errors. The bootstrap technique showed the intrasubject reproducibility of QT/RR slopes and curvatures. In women and men, QT/RR curvatures were 0.544 ± 0.661 and 0.797 ± 0.706, respectively (P = 0.0006). The corresponding QT/RR slopes were 0.158 ± 0.030 and 0.139 ± 0.023, respectively (P < 0.0001). QT/RR curvatures were related to QT/RR slopes but not to individually corrected mean QTc intervals or individual QT/RR hysteresis profiles. The individual heart rate correction formula derived from the curvilinear regression provided a significantly lower intrasubject variability of QTc interval than individual optimisation of linear or log-linear QT/RR heart rate corrections. The QT/RR curvature can be reliable measured and expressed numerically. The corresponding heart rate correction formula provides more compact data than the previously proposed approaches. There are substantial sex differences in QT/RR patterns. Women have a QT/RR pattern that is not only steeper than men but also more curved. PMID:24163079
Circular dichroism spectroscopy of membrane proteins.
Miles, A J; Wallace, B A
2016-09-21
Circular dichroism (CD) spectroscopy is a well-established technique for studying the secondary structures, dynamics, folding pathways, and interactions of soluble proteins, and is complementary to the high resolution but generally static structures produced by X-ray crystallography, NMR spectroscopy, and cryo electron microscopy. CD spectroscopy has special relevance for the study of membrane proteins, which are difficult to crystallise and largely ignored in structural genomics projects. However, the requirement for membrane proteins to be embedded in amphipathic environments such as membranes, lipid vesicles, detergent micelles, bicelles, oriented bilayers, or nanodiscs, in order for them to be soluble or dispersed in solution whilst maintaining their structure and function, necessitates the use of different experimental and analytical approaches than those employed for soluble proteins. This review discusses specialised methods for collecting and analysing membrane protein CD data, highlighting where protocols for soluble and membrane proteins diverge.
Rectenna composed of a circular microstrip antenna
Itoh, K.; Ohgane, T.; Ogawa, Y.
1986-01-01
One of the big problems in the SPS system is reradiation of the harmonic waves generated by the rectifying diode. The authors proposed the use of a circular microstrip antenna (CMSA), since the CMSA has no higher resonance-harmonic of integer multiple of the dominant resonance frequency. However, characteristics of a large rectenna array of CMSA's have not been clarified. This paper is concerned with the absorption efficiency of the rectenna composed of the CMSA. The efficiency is estimated explicitly using an infinite array model. The results show that the absorption efficiency of the infinite rectenna array composed of the CMSA is 100%. Also, this paper considers the effect of the losses of the composed of the CMSA is 100%. Also, this paper considers the effect of the losses of the CMSA. 4 references, 4 figures.
Circular dichroism spectroscopy of membrane proteins.
Miles, A J; Wallace, B A
2016-09-21
Circular dichroism (CD) spectroscopy is a well-established technique for studying the secondary structures, dynamics, folding pathways, and interactions of soluble proteins, and is complementary to the high resolution but generally static structures produced by X-ray crystallography, NMR spectroscopy, and cryo electron microscopy. CD spectroscopy has special relevance for the study of membrane proteins, which are difficult to crystallise and largely ignored in structural genomics projects. However, the requirement for membrane proteins to be embedded in amphipathic environments such as membranes, lipid vesicles, detergent micelles, bicelles, oriented bilayers, or nanodiscs, in order for them to be soluble or dispersed in solution whilst maintaining their structure and function, necessitates the use of different experimental and analytical approaches than those employed for soluble proteins. This review discusses specialised methods for collecting and analysing membrane protein CD data, highlighting where protocols for soluble and membrane proteins diverge. PMID:27347568
NASA Astrophysics Data System (ADS)
Buczkowski, Debra L.; Seelos, Kim D.; Cooke, Michele L.
2012-08-01
Large-scale fracture systems surrounding the Utopia basin include giant polygons and circular graben. Data covering the northern Utopia basin now allow high-resolution mapping of these features in all regions of the basin. Giant polygons to the north and south of the basin are different in both size and morphology, leading to the polygon classifications (1) S-style, (2) subdued S-style, (3) northern S-style and (4) N-style. Also, ten circular graben have been identified to the north of the Utopia basin. These have generally larger diameters than southern circular graben, and their fracture morphology is similar to N-style giant polygons. As with southern circular graben, the surface relief of the depression inside the northern circular graben scales directly with diameter. However, northern circular graben have less steep trend slopes, larger average diameters and greater ring spacing compared to southern circular graben of the same diameter and similar distance to the center of the Utopia basin. Both the giant polygons and circular graben of Utopia Planitia are consistent with formation by volumetric compaction of a fine-grained sedimentary material covering an uneven buried surface. Giant polygon size variations can be explained by the material being wet to the south but frozen or partially frozen to the north, while differences between northern and southern circular graben may be attributed to changes in cover thickness. Differences in fracture morphology can be explained by subsequent alteration of the northern troughs due to polar processes.
Research on compensation of motion, Earth curvature and tropospheric delay in GEOSAR
NASA Astrophysics Data System (ADS)
Sheng, Wei; Hobbs, Stephen E.
2011-06-01
GEOSAR (synthetic aperture radar on geosynchronous satellite) becomes a potential method of space-borne geoscience remote sensing. Though it has attractive characters such as extra long observing time and very large observing area the unique geometry and relative motion are quite different from straight line required by SAR, and long integration time also causes delay by troposphere and ionosphere. Curvature of the Earth is no long negligible in GEOSAR. Especially, principle of azimuth compression in GEOSAR should be different from that of traditional SAR. In order to fulfill practical GEOSAR such problems should be solved. A new solution of azimuth compression together with motion compensation is presented here by taking the advantages of GEOSAR movement. A new method to overcome the Earth curvature in range compression of EACH footprint is testified. After compensating the Earth curvature traditional methods for range cell migration correction can be used in GEOSAR. Multi-sub-aperture method is applied to eliminate the phase delay caused by troposphere. This modified imaging algorithm makes it possible for GEOSAR to have long integration time and high resolution.
High-Temperature Characterization of Silicon Dioxide Films with Wafer Curvature
NASA Astrophysics Data System (ADS)
Bigl, S.; Heinz, W.; Kahn, M.; Schoenherr, H.; Cordill, M. J.
2015-12-01
Amorphous silicon dioxide films used as dielectric layers in microelectronic devices are deposited using plasma-enhanced chemical vapor deposition. Because of the presence of hydrogen and nitrogen species in the precursor gases, incorporation of such species in the films can lead to crack formation during subsequent annealing processes up to 1000°C. In this study, the role of film chemistry on the thermo-mechanical behavior of silicon dioxide films is studied with in situ film stress measurements using wafer curvature to maximum temperatures of 1000°C. This is a significant advance because normal wafer curvature can only reach maximum temperatures of around 500°C. The increased temperature range allows for the stress evolution and film chemistry to be examined for the relevant processing conditions. It was found that at temperatures higher than 550°C, hydrogen bond cleavage led to a large stress increase and film chemistry change due to new bonding arrangements between nitrogen and silicon as well as subsequent film densification causing cracking of films. These changes could only be identified with wafer curvature measurements up to 1000°C.
Curvature properties of some class of warped product manifolds
NASA Astrophysics Data System (ADS)
Deszcz, Ryszard; Głogowska, Małgorzata; Jełowicki, Jan; Zafindratafa, Georges
2016-10-01
We prove that warped product manifolds with p-dimensional base, p = 1, 2, satisfy some pseudosymmetry type curvature conditions. These conditions are formed from the metric tensor g, the Riemann-Christoffel curvature tensor R, the Ricci tensor S and the Weyl conformal curvature C of the considered manifolds. The main result of the paper states that if p = 2 and the fiber is a semi-Riemannian space of constant curvature (when n is greater or equal to 5) then the (0, 6)-tensors R ṡ R - Q(S,R) and C ṡ C of such warped products are proportional to the (0, 6)-tensor Q(g,C) and the tensor C is a linear combination of some Kulkarni-Nomizu products formed from the tensors g and S. We also obtain curvature properties of this kind of quasi-Einstein and 2-quasi-Einstein manifolds, and in particular, of the Goedel metric, generalized spherically symmetric metrics and generalized Vaidya metrics.
Intermembrane Docking Reactions Are Regulated by Membrane Curvature
Kunding, Andreas H.; Mortensen, Michael W.; Christensen, Sune M.; Bhatia, Vikram K.; Makarov, Ivan; Metzler, Ralf; Stamou, Dimitrios
2011-01-01
The polymorphism of eukaryotic cellular membranes is a tightly regulated and well-conserved phenotype. Recent data have revealed important regulatory roles of membrane curvature on the spatio-temporal localization of proteins and in membrane fusion. Here we quantified the influence of membrane curvature on the efficiency of intermembrane docking reactions. Using fluorescence microscopy, we monitored the docking of single vesicle–vesicle pairs of different diameter (30–200 nm) and therefore curvature, as mediated by neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and streptavidin-biotin. Surprisingly, the intermembrane docking efficiency exhibited an ∼30–60 fold enhancement as a function of curvature. In comparison, synaptotagmin and calcium accelerate SNARE-mediated fusion in vitro by a factor of 2–10. To explain this finding, we formulated a biophysical model. On the basis of our findings, we propose that membrane curvature can regulate intermembrane tethering reactions and consequently any downstream process, including the fusion of vesicles and possibly viruses with their target membranes. PMID:22261058
Variable curvature mirrors: implementation in the VLTI delay-lines for field compensation
NASA Astrophysics Data System (ADS)
Ferrari, Marc; Lemaitre, Gerard R.; Mazzanti, Silvio P.; Derie, Frederic; Huxley, Alexis; Lemerrer, J.; Lanzoni, Patrick; Dargent, Pascal; Wallander, Anders
2003-02-01
As the result of an analysis pursued from the very beginning, today the VLT Interferometer is the only interferometer allowing to have a 2 arcsec interferometric field of view (f.o.v) available at the instruments entrance. This accessible interferometric field is the direct result of a careful pupil transfer from the individual telescopes to the central laboratory, unique feature of the VLTI. For this goal it has been necessary to develop a new optical device, the Variable Curvature Mirror (VCM.), using large deformation theory of elasticity, and advanced techniques in optical fabrication. The possibility with the VLTI to use various baselines, from 8 to 200 m with UTs or ATs, leads to severe conditions on the VCM curvature range. A given delay-line, and its associated VCM, should be able to transfer a pupil to the interferometric laboratory from a very far or relatively close position of an ATs. Considering the f.o.v required in the VLTI (2 arcsec), the delay-lines strokes or the OPD to compensate for, and the various locations of the UTs and ATs stations, the curvature of the VCM has to be continuously variable within a range from 84 mm-1 to 2800 mm-1. The location of the VCM in the delay-line system, on the piezo-translator used for small OPD compensation, led to minimize its dimensions and to realize a small active mirror with a 16mm diameter. With this small optical aperture, the VCM range of curvature corresponds to a f ratio from f/∞ to f/2.625. The two first VCM complete systems (mirror, mechanics and control command software) have been achieved in 2001/2002 and will be installed in the VLTI delay-lines during fall 2002. Their final performances (optical quality, pupil transfer accuracy, etc.) are reviewed.
Circular Dichroism Spectra of Granal and Agranal Chloroplasts of Maize
Faludi-Dániel, Ágnes; Demeter, S.; Garay, A. S.
1973-01-01
Granum-containing chloroplasts from mesophyll cells of maize (Zea mays L. var. MV 861) leaves exhibited circular dichroism spectra with a large double signal; peaks at 696 nm (+) and 680 nm (−). In the circular dichroism spectra obtained with agranal chloroplasts of bundle sheath cells, this large double signal is absent. Separation of grana lamellae, in a medium of low salt concentration and in KSCN solution, resulted only in a slight decrease of the amplitude, while upon treatment with digitonin the large double signal disappeared. A negative signal of the chlorophyll b peak at 654 nm was observed in the case of both granal and agranal chloroplasts, and it was not affected either by low salt or by digitonin treatment. A positive peak at about 515 nm was higher in granal than in agranal chloroplasts. PMID:16658498
Studies of the effects of curvature on dilution jet mixing
NASA Astrophysics Data System (ADS)
Holdeman, James D.; Srinivasan, Ram; Reynolds, Robert S.; White, Craig D.
1992-02-01
An analytical program was conducted using both three-dimensional numerical and empirical models to investigate the effects of transition liner curvature on the mixing of jets injected into a confined crossflow. The numerical code is of the TEACH type with hybrid numerics; it uses the power-law and SIMPLER algorithms, an orthogonal curvilinear coordinate system, and an algebraic Reynolds stress turbulence model. From the results of the numerical calculations, an existing empirical model for the temperature field downstream of single and multiple rows of jets injected into a straight rectangular duct was extended to model the effects of curvature. Temperature distributions, calculated with both the numerical and empirical models, are presented to show the effects of radius of curvature and inner and outer wall injection for single and opposed rows of cool dilution jets injected into a hot mainstream flow.
Numerical Estimation of the Curvature of Biological Surfaces
NASA Technical Reports Server (NTRS)
Todd, P. H.
1985-01-01
Many biological systems may profitably be studied as surface phenomena. A model consisting of isotropic growth of a curved surface from a flat sheet is assumed. With such a model, the Gaussian curvature of the final surface determines whether growth rate of the surface is subharmonic or superharmonic. These properties correspond to notions of convexity and concavity, and thus to local excess growth and local deficiency of growth. In biological models where the major factors controlling surface growth are intrinsic to the surface, researchers thus gained from geometrical study information on the differential growth undergone by the surface. These ideas were applied to an analysis of the folding of the cerebral cortex, a geometrically rather complex surface growth. A numerical surface curvature technique based on an approximation to the Dupin indicatrix of the surface was developed. A metric for comparing curvature estimates is introduced, and considerable numerical testing indicated the reliability of this technique.
The role of membrane curvature for the wrapping of nanoparticles.
Bahrami, Amir Houshang; Lipowsky, Reinhard; Weikl, Thomas R
2016-01-14
Cellular internalization of nanoparticles requires the full wrapping of the nanoparticles by the cell membrane. This wrapping process can occur spontaneously if the adhesive interactions between the nanoparticles and the membranes are sufficiently strong to compensate for the cost of membrane bending. In this article, we show that the membrane curvature prior to wrapping plays a key role for the wrapping process, besides the size and shape of the nanoparticles that have been investigated in recent years. For membrane segments that initially bulge away from nanoparticles by having a mean curvature of the same sign as the mean curvature of the particle surface, we find strongly stable partially wrapped states that can prevent full wrapping. For membrane segments that initially bulge towards the nanoparticles, in contrast, partially wrapped states can constitute a significant energetic barrier for the wrapping process.
An Experimental Study of Laminarization Induced by Acceleration and Curvature
NASA Astrophysics Data System (ADS)
Jackson, R. Brian
The Generation IV Very High Temperature Reactor (VHTR) design is being actively studied in various countries for application due to its inherent passive safe design, higher thermal efficiencies, and proposed capability of providing high temperature process heat. The pebble bed core is one of two core designs used in gas reactors. In the pebble bed core there are mechanisms present which can cause the flow to laminarize, thus reducing its heat transfer effectiveness. Wind tunnel experiments were conducted using Particle Image Velocimetry (PIV) to investigate boundary layer laminarization due to flow acceleration and convex curvature effects. The flow was subject to acceleration and curvature both separately and together and the flow behavior characterized with velocity flow profiles, mean boundary layer parameters, and turbulence quantities. Laminarization was identified and the influence of acceleration and curvature was characterized.
Characterization of inherent curvature in DNA lacking polyadenine runs.
McNamara, P T; Harrington, R E
1991-07-01
Sequence-directed DNA curvature is most commonly associated with AA dinucleotides in the form of polyadenine runs. We demonstrate inherent curvature in DNA which lacks AA/TT dinucleotides using the criteria of polyacrylamide gel mobility and efficiency of DNA cyclization. These studies are based upon two 21-base pair synthetic DNA fragments designed to exhibit fixed curvature according to deflections made to the helical axis by non-AA dinucleotide stacks. Repeats of these sequences display anomalously slow migration in polyacrylamide gels. Moreover, both sequences describe helical conformations that are closed into circles by DNA ligase at much smaller sizes than is typical of nondeformed DNA. Chemical cleavage of these DNA molecules with hydroxyl radical is also consistent with local variation in helical conformation at specific dinucleotide steps. PMID:1648100
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.
Flow control by means of a traveling curvature wave in fishlike escape responses.
Liu, Geng; Yu, Yong-Liang; Tong, Bing-Gang
2011-11-01
Fish usually bend their bodies into a ''C'' shape and then beat their tails one or more times to escape from predators (in nature) or stimuli (in experiments). The maneuvering behavior, i.e., the C-shape bending and the return flapping, is called C-start. In this paper, the escaping performance of fishlike C-start motions has been numerically investigated for a flow physics study by the use of a two-dimensional deformable foil bending and stretching quickly. The C-start motions, performed in the quiescent water and based on prescribed deforming modes, are predicted by a numerical method coupling the two-dimensional incompressible Navier-Stokes equations and the deforming body dynamic equations. It has been found earlier that a typical C-start motion consists of (1) a main C-shape bending and (2) a rearward travelling curvature wave which was seldom mentioned in previous studies. In order to reveal the flow control mechanism of the traveling curvature wave in a fish's C-start motion, two kinds of C-start flows with different deforming modes, namely the integrated mode (IM, a C-shape bending plus a travelling curvature wave) and the basic mode (BM, a C-shape bending only) are analyzed and compared in detail. According to the numerical results, it shows that if proper values of the travelling curvature wave parameters are chosen, the foil's escaping maneuverability presented in the IM is much better than that in the BM, i.e. the turn angle and the speed of the center of mass at the end of a C-start in the IM is almost twice as large as those in the BM. Further study shows that the travelling curvature wave not only can enhance the thrust and the centripetal force but also increase the propulsive efficiency. These results suggest that an efficient travelling curvature wave is of great significance in the flow control of a C-start motion. Finally, a parametric study finds that the phase difference between the C-shape bending and the travelling curvature wave (i.e., the
Flow control by means of a traveling curvature wave in fishlike escape responses
NASA Astrophysics Data System (ADS)
Liu, Geng; Yu, Yong-Liang; Tong, Bing-Gang
2011-11-01
Fish usually bend their bodies into a ‘‘C’’ shape and then beat their tails one or more times to escape from predators (in nature) or stimuli (in experiments). The maneuvering behavior, i.e., the C-shape bending and the return flapping, is called C-start. In this paper, the escaping performance of fishlike C-start motions has been numerically investigated for a flow physics study by the use of a two-dimensional deformable foil bending and stretching quickly. The C-start motions, performed in the quiescent water and based on prescribed deforming modes, are predicted by a numerical method coupling the two-dimensional incompressible Navier-Stokes equations and the deforming body dynamic equations. It has been found earlier that a typical C-start motion consists of (1) a main C-shape bending and (2) a rearward travelling curvature wave which was seldom mentioned in previous studies. In order to reveal the flow control mechanism of the traveling curvature wave in a fish's C-start motion, two kinds of C-start flows with different deforming modes, namely the integrated mode (IM, a C-shape bending plus a travelling curvature wave) and the basic mode (BM, a C-shape bending only) are analyzed and compared in detail. According to the numerical results, it shows that if proper values of the travelling curvature wave parameters are chosen, the foil's escaping maneuverability presented in the IM is much better than that in the BM, i.e. the turn angle and the speed of the center of mass at the end of a C-start in the IM is almost twice as large as those in the BM. Further study shows that the travelling curvature wave not only can enhance the thrust and the centripetal force but also increase the propulsive efficiency. These results suggest that an efficient travelling curvature wave is of great significance in the flow control of a C-start motion. Finally, a parametric study finds that the phase difference between the C-shape bending and the travelling curvature wave (i
Detonation wave velocity and curvature of brass encased PBXN-111
NASA Astrophysics Data System (ADS)
Forbes, J. W.; Lemar, E. R.
1996-05-01
Detonation velocities and wave front curvatures were measured for PBXN-111 charges encased in 5 mm thick brass tubes. In all the experiments (charge diameters from 19 to 47 mm) the brass case affected the detonation properties of PBXN-111. Steady detonation waves propagated in brass encased charges with diameters as small as 19 mm, which is about half of the unconfined failure diameter. The radii of curvature of the detonation waves at the center of the wave fronts ranged from 52 to 141 mm for charge diameters of 25 to 47 mm. The angles between the detonation wave fronts and the brass/charge interfaces were between 72 and 74 degrees.
Subaperture method for aspheric surface metrology using curvature data
NASA Astrophysics Data System (ADS)
Lee, SeongWon; Jeon, WooKyung; Park, TaeJin; Kim, ByoungChang; Kim, GeonHee; Hyun, SangWon; Kim, IJong; Kim, Seunghyun; Kim, ChangKyu; Lee, HyungSuk
2016-04-01
We present a profilometry for measuring aspheric surface, which determines the curvature from the sub-aperture topography along two orthogonal directions and then reconstructs the entire surface profile from the measured curvature data. The entire surface was divided into a number of sub-apertures with overlapping zones. Each sub-aperture was measured using white-light scanning interferometry to avoid any optical alignment error along an optical axis. Simulation studies are also presented based on the mathematical model. The proposed mathematical model was also experimentally tested on freeform surfaces using white-light scanning interferometry under deveolpment.
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.
Electron energy transport and magnetic curvature driven modes
Coppi, B.; Tang, W.M.
1984-10-01
A transport coefficient for anomalous electron thermal conduction is constructed on the basis of the so-called Principle of Profile Consistency. It is assumed that the relevant modes in plasma where a substantial fraction of the electron population is magnetically trapped produce magnetic reconnection at a microscopic level and are driven by the combined effects of the plasma pressure gradient and the magnetic field curvature. Consequently, the scaling for the electron energy confinement time exhibits a strongly favorable dependence on the radius of magnetic curvature.
Circular permutant GFP insertion folding reporters
Waldo, Geoffrey S.; Cabantous, Stephanie
2008-06-24
Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.
Circular permutant GFP insertion folding reporters
Waldo, Geoffrey S.; Cabantous, Stephanie
2013-04-16
Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.
Circular permutant GFP insertion folding reporters
Waldo, Geoffrey S; Cabantous, Stephanie
2013-02-12
Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.
Circular permutant GFP insertion folding reporters
Waldo, Geoffrey S.; Cabantous, Stephanie
2011-06-14
Provided are methods of assaying and improving protein folding using circular permutants of fluorescent proteins, including circular permutants of GFP variants and combinations thereof. The invention further provides various nucleic acid molecules and vectors incorporating such nucleic acid molecules, comprising polynucleotides encoding fluorescent protein circular permutants derived from superfolder GFP, which polynucleotides include an internal cloning site into which a heterologous polynucleotide may be inserted in-frame with the circular permutant coding sequence, and which when expressed are capable of reporting on the degree to which a polypeptide encoded by such an inserted heterologous polynucleotide is correctly folded by correlation with the degree of fluorescence exhibited.
The circular velocity function of group galaxies
Abramson, Louis E.; Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S.
2014-09-20
A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v {sub c} ≲ 200 km s{sup –1}. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v {sub c} estimators, we find no transition from field to ΛCDM-shaped CVF above v {sub c} = 50 km s{sup –1} as a function of group halo mass. All groups with 12.4 ≲ log M {sub halo}/M {sub ☉} ≲ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v {sub c} compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v {sub c} slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.
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.
The benefits of planar circular mouths on suction feeding performance
Skorczewski, Tyler; Cheer, Angela; Wainwright, Peter C.
2012-01-01
Suction feeding is the most common form of prey capture across aquatic feeding vertebrates and many adaptations that enhance efficiency and performance are expected. Many suction feeders have mechanisms that allow the mouth to form a planar and near-circular opening that is believed to have beneficial hydrodynamic effects. We explore the effects of the flattened and circular mouth opening through computational fluid dynamics simulations that allow comparisons with other mouth profiles. Compared to mouths with lateral notches, we find that the planar mouth opening results in higher flow rates into the mouth and a region of highest flow that is positioned at the centre of the mouth aperture. Planar mouths provide not only for better total fluid flow rates through the mouth but also through the centre of the mouth near where suction feeders position their prey. Circular mouths are shown to provide the quickest capture times for spherical and elliptical prey because they expose the prey item to a large region of high flow. Planar and circular mouths result in higher flow velocities with peak flow located at the centre of the mouth opening and they maximize the capacity of the suction feeders to exert hydrodynamic forces on the prey. PMID:22319101
Spectra of circularly polarized radiation from astrophysical OH masers
NASA Technical Reports Server (NTRS)
Nedoluha, Gerald E.; Watson, William D.
1990-01-01
A striking feature of astrophysical masers is the tendency for either one or the other of the circular polarizations to dominate in the radiation from the strong, widely observed masing transitions of OH at 18 cm. Spectral line profiles are calculated for polarized maser radiation due to the combined effects of a velocity gradient and, as is indicated for these transitions, a Zeeman splitting that is at least comparable with the thermal contributions to the breadths of the spectral lines. The resulting spectral features are similar in appearance, including the presence of large net circular polarization and narrow line breadths, to the commonly observed spectra of OH masers in molecular clouds. The calculations presented here are performed as a function of frequency without making the approximations of a large velocity gradient. Rapid cross relaxation, which has been advocated by others for the OH masers, is assumed.
Cloud, Beth A; Zhao, Kristin D; Breighner, Ryan; Giambini, Hugo; An, Kai-Nan
2014-07-01
Spinal posture affects how individuals function from a manual wheelchair. There is a need to directly quantify spinal posture in this population to ultimately improve function. A fiber optic system, comprised of an attached series of sensors, is promising for measuring large regions of the spine in individuals sitting in a wheelchair. The purpose of this study was to determine the agreement between fiber optic and optoelectronic systems for measuring spinal curvature, and describe the range of sagittal plane spinal curvatures in natural sitting. Able-bodied adults (n = 26, 13 male) participated. Each participant assumed three sitting postures: natural, slouched (accentuated kyphosis), and extension (accentuated lordosis) sitting. Fiber optic (ShapeTape) and optoelectronic (Optotrak) systems were applied to the skin over spinous processes from S1 to C7 and used to measure sagittal plane spinal curvature. Regions of kyphosis and lordosis were identified. A Cobb angle-like method was used to quantify lordosis and kyphosis. Generalized linear model and Bland-Altman analyses were used to assess agreement. A strong correlation exists between curvature values obtained with Optotrak and ShapeTape (R(2) = 0.98). The mean difference between Optotrak and ShapeTape for kyphosis in natural, extension, and slouched postures was 4.30° (95% LOA: -3.43 to 12.04°), 3.64° (95% LOA: -1.07 to 8.36°), and 4.02° (95% LOA: -2.80 to 10.84°), respectively. The mean difference for lordosis, when present, in natural and extension postures was 2.86° (95% LOA: -1.18 to 6.90°) and 2.55° (95% LOA: -3.38 to 8.48°), respectively. In natural sitting, the mean ± SD of kyphosis values was 35.07 ± 6.75°. Lordosis was detected in 8/26 participants: 11.72 ± 7.32°. The fiber optic and optoelectronic systems demonstrate acceptable agreement for measuring sagittal plane thoracolumbar spinal curvature.
The effect of nanoscale surface curvature on the oligomerization of surface-bound proteins
Kurylowicz, M.; Paulin, H.; Mogyoros, J.; Giuliani, M.; Dutcher, J. R.
2014-01-01
The influence of surface topography on protein conformation and association is used routinely in biological cells to orchestrate and coordinate biomolecular events. In the laboratory, controlling the surface curvature at the nanoscale offers new possibilities for manipulating protein–protein interactions and protein function at surfaces. We have studied the effect of surface curvature on the association of two proteins, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), which perform their function at the oil–water interface in milk emulsions. To control the surface curvature at the nanoscale, we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that are highly curved and are stable in aqueous buffer. We have used single-molecule force spectroscopy to measure the contour lengths Lc for α-LA and β-LG adsorbed on highly curved PS surfaces (NP diameters of 27 and 50 nm, capped with a 10 nm thick PS film), and we have compared these values in situ with those measured for the same proteins adsorbed onto flat PS surfaces in the same samples. The Lc distributions for β-LG adsorbed onto a flat PS surface contain monomer and dimer peaks at 60 and 120 nm, respectively, while α-LA contains a large monomer peak near 50 nm and a dimer peak at 100 nm, with a tail extending out to 200 nm, corresponding to higher order oligomers, e.g. trimers and tetramers. When β-LG or α-LA is adsorbed onto the most highly curved surfaces, both monomer peaks are shifted to much smaller values of Lc. Furthermore, for β-LG, the dimer peak is strongly suppressed on the highly curved surface, whereas for α-LA the trimer and tetramer tail is suppressed with no significant change in the dimer peak. For both proteins, the number of higher order oligomers is significantly reduced as the curvature of the underlying surface is increased. These results suggest that the surface curvature provides a new
Equilibrium models of coronal loops that involve curvature and buoyancy
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Determination of light beam curvature in a rotating Luneburg lens
NASA Astrophysics Data System (ADS)
Gladyshev, V. O.; Bazleva, D. D.; Tereshin, A. A.; Gladysheva, T. M.
2016-09-01
We have determined the curvature of a beam of coherent electromagnetic radiation and its angular and linear deviation in a rotating microsatellite representing a Luneburg lens in the optical segment of accuracy augmentation for new-generation global navigation satellite systems.
The influence of curvature on film cooling performance
NASA Astrophysics Data System (ADS)
Schwarz, S. G.; Goldstein, R. J.; Eckert, E. R. G.
1990-06-01
The effects of injection rate and strength of curvature on film cooling performance of gas injected through a row of holes on a convex surface is studied. Comparisons are made to film cooling of concave and flat surfaces. Three different relative strengths of curvature (ratio of radius of curvature to radius of injection hole), two density ratios (0.95 and 2.0), and a wide range of blowing rates (0.3 to 2.7) are considered. A foreign gas injection technique (mass transfer analogy) is used. The strength of curvature was controlled by varying the injection hole diameter. At low blowing rates, film cooling is more effective on the convex surface than on a flat or a concave surface. The cross stream pressure gradient present in curved flows tends to push the jet into the convex wall. As the injection rate is increased, normal and tangential jet momentum promote lift-off from the convex surface, thereby lowering performance. In contrast, previous studies show that a concave surface, tangential jet momentum, flow instabilities, and blockage improve performance on a concave surface as blowing rate is increased.
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.
Effect of Asymmetric Auxin Application on Helianthus Hypocotyl Curvature 1
Migliaccio, Fernando; Rayle, David L.
1989-01-01
Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution. PMID:11537460
Frustration and curvature - Glasses and the cholesteric blue phase
NASA Technical Reports Server (NTRS)
Sethna, J. P.
1983-01-01
An analogy is drawn between continuum elastic theories of the blue phase of cholesteric liquid crystals and recent theories of frustration in configurational glasses. Both involve the introduction of a lattice of disclination lines to relieve frustration; the frustration is due to an intrinsic curvature in the natural form of parallel transport. A continuum theory of configurational glasses is proposed.
Wormhole geometries supported by a nonminimal curvature-matter coupling
Garcia, Nadiezhda Montelongo; Lobo, Francisco S. N.
2010-11-15
Wormhole geometries in curvature-matter coupled modified gravity are explored, by considering an explicit nonminimal coupling between an arbitrary function of the scalar curvature, R, and the Lagrangian density of matter. It is the effective stress-energy tensor containing the coupling between matter and the higher order curvature derivatives that is responsible for the null energy condition violation, and consequently for supporting the respective wormhole geometries. The general restrictions imposed by the null energy condition violation are presented in the presence of a nonminimal R-matter coupling. Furthermore, obtaining exact solutions to the gravitational field equations is extremely difficult due to the nonlinearity of the equations, although the problem is mathematically well defined. Thus, we outline several approaches for finding wormhole solutions, and deduce an exact solution by considering a linear R nonmiminal curvature-matter coupling and by considering an explicit monotonically decreasing function for the energy density. Although it is difficult to find exact solutions of matter threading the wormhole satisfying the energy conditions at the throat, an exact solution is found where the nonminimal coupling does indeed minimize the violation of the null energy condition of normal matter at the throat.
Compound Schmidt telescope designs with nonzero Petzval curvatures.
Sigler, R D
1975-09-01
A variety of aplanatic and anastigmatic Schmidt Cassegrain and Schmidt Gregorian telescope designs with nonzero Petzval curvatures are investigated. Relaxing the Petzval constraint permits the development of high performance photo/visual instruments which are capable of diffraction limited imaging over fields of view of 1-2 degrees . PMID:20155004
Simple partitions of a hyperbolic plane of positive curvature
Romakina, Lyudmila N
2012-09-30
We construct special monohedral isotropic partitions with symmetries of the hyperbolic plane H of positive curvature with a simple 4-contour as a cell. An analogue of mosaic in these partitions called a tiling is introduced. Also we consider some fractal tilings. The existence of band tilings in each homological series with code (m, n) is proved. Bibliography: 14 titles.
Negative voltage bandgap reference with multilevel curvature compensation technique
NASA Astrophysics Data System (ADS)
Xi, Liu; Qian, Liu; Xiaoshi, Jin; Yongrui, Zhao; Lee, Jong-Ho
2016-05-01
A novel high-order curvature compensation negative voltage bandgap reference (NBGR) based on a novel multilevel compensation technique is introduced. Employing an exponential curvature compensation (ECC) term with many high order terms in itself, in a lower temperature range (TR) and a multilevel curvature compensation (MLCC) term in a higher TR, a flattened and better effect of curvature compensation over the TR of 165 °C (‑40 to 125 °C) is realised. The MLCC circuit adds two convex curves by using two sub-threshold operated NMOS. The proposed NBGR implemented in the Central Semiconductor Manufacturing Corporation (CSMC) 0.5 μm BCD technology demonstrates an accurate voltage of ‑1.183 V with a temperature coefficient (TC) as low as 2.45 ppm/°C over the TR of 165 °C at a ‑5.0 V power supply; the line regulation is 3 mV/V from a ‑5 to ‑2 V supply voltage. The active area of the presented NBGR is 370 × 180 μm2. Project supported by the Fund of Liaoning Province Education Department (No. L2013045).
Effect of asymmetric auxin application on Helianthus hypocotyl curvature
NASA Technical Reports Server (NTRS)
Migliaccio, F.; Rayle, D. L.
1989-01-01
Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution.
Curvature and torsion estimation for coronary-artery motion analysis
NASA Astrophysics Data System (ADS)
Medina, Ruben; Wahle, Andreas; Olszewski, Mark E.; Sonka, Milan
2004-04-01
The dynamics of curvature and torsion are important for the geometric description of arteries and for the distribution of accumulating plaque. In this research, two methods for estimating curvature and torsion are analyzed with respect to their accuracy. The first method is based on estimating the curvature and torsion of the artery centerline using the Fourier transform. Since the centerline always represents an open curve, extensions ensuring a minimal spectral energy are added on both ends to obtain a closed curve suitable for Fourier analysis. The second method has been previously used for analyzing the motion of coronary arteries and is based on the least squares fitting of a cubic polynomial to the centerline of the artery. Validation is performed using two mathematical, time-varying phantoms as well as 4-D (3-D plus time) in-vivo data of coronary arteries reconstructed by fusion of biplane angiograms and intravascular ultrasound images. Results show that both methods are accurate for estimating curvature and torsion, and that both methods have average errors below 2.15%.
Protein-Induced Membrane Curvature Alters Local Membrane Tension
Rangamani, Padmini; Mandadap, Kranthi K.; Oster, George
2014-01-01
Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface properties of the membrane, such as membrane tension, change in response to protein adsorption. In this article, we show that the partial differential equations arising from classical elastic model of lipid membranes, which account for simultaneous changes in shape and membrane tension due to protein adsorption in a local region, cannot be solved for nonaxisymmetric geometries using straightforward numerical techniques; instead, a viscous-elastic formulation is necessary to fully describe the system. Therefore, we develop a viscous-elastic model for inhomogeneous membranes of the Helfrich type. Using the newly available viscous-elastic model, we find that the lipids flow to accommodate changes in membrane curvature during protein adsorption. We show that, at the end of protein adsorption process, the system sustains a residual local tension to balance the difference between the actual mean curvature and the imposed spontaneous curvature. We also show that this change in membrane tension can have a functional impact such as altered response to pulling forces in the presence of proteins. PMID:25099814
Geometric optics radome analysis wall incorporating effects of wall curvature
NASA Astrophysics Data System (ADS)
Kozakoff, Dennis J.
1993-07-01
In this research, a principal unmodeled error contributor in radome analysis is identified as the local plane approximation at the ray intercept point. An improved approach to modeling and computing the effects of the radome wall was developed which improves the radome wall transmission wall analysis in three respects: use of surface integration, utilization of a divergence factor (DF) to account for wall curvature, and incorporation of the effects of multiple refraction (MR). Modeling an incident plane wave on an external reference plane as an ensemble of Huygen's sources, geometric optics is used to trace the fields from the reference plane through the radome wall to a receiving monopulse antenna, where the wall transmissions on each ray are collected. The fact that the integration of a bundle of rays through the radome wall, as opposed to a single ray, more densely samples the curvature variation results in a more robust model. A DF derived from Snell's law for spherical shells accounts for the local wall curvature at the ray intercept point. To validate the approach, a microwave measurement setup was assembled around a network analyzer. Swept frequency data were obtained for similar monolithic wall dielectric panels but with different wall curvatures. Comparisons were then with measured data and the predictions of the model herein.
Relaxation and curvature-induced molecular flows within multicomponent membranes.
Morris, Richard G
2014-06-01
The quantitative understanding of membranes is still rooted in work performed in the 1970s by Helfrich and others, concerning amphiphilic bilayers. However, most biological membranes contain a wide variety of nonamphiphilic molecules too. Drawing analogy with the physics of nematic-non-nematic mixtures, we present a dynamical (out-of-equilibrium) description of such multicomponent membranes. The approach combines nematohydrodynamics in the linear regime and a proper use of (differential-) geometry. The main result is to demonstrate that one can obtain equations describing a cross-diffusion effect (similar to the Soret and Dufour effects) between curvature and the (in-membrane) flow of amphiphilic molecules relative to nonamphiphilic ones. Surprisingly, the shape of a membrane relaxes according to a simple heat equation in the mean curvature, a process that is accompanied by a simultaneous boost to the diffusion of amphiphiles away from regions of high curvature. The model also predicts the inverse process, by which the forced bending of a membrane induces a flow of amphiphilic molecules towards areas of high curvature. In principle, numerical values for the relevant diffusion coefficients should be verifiable by experiment. PMID:25019811
Analysis of models for curvature driven motion of interfaces
NASA Astrophysics Data System (ADS)
Swartz, Drew E.
Interfacial energies frequently appear in models arising in materials science and engineering. To dissipate energy in these systems, the interfaces will often move by a curvature dependent velocity. The present work details the mathematical analysis of some models for curvature dependent motion of interfaces. In particular we focus on two types, thresholding schemes and phase field models. With regard to thresholding schemes, we give a new proof of the convergence of the Merriman-Bence-Osher thresholding algorithm to motion by mean curvature. This new proof does not rely on the scheme satisfying a comparison principle. The technique shows promise in proving the convergence of thresholding schemes for more general motions, such as fourth-order motions and motions of higher codimension interfaces. The application of the proof technique to these more general schemes is discussed, along with rigorous consistency estimates. With regard to phase-field models, we examine the L 2-gradient flow of a second order gradient model for phase transitions, introduced by Fonseca and Mantegazza. In the case of radial symmetry we demonstrate that the diffuse interfacial dynamics converge to motion by mean curvature as the width of the interface decreases to zero. This is in accordance with the first-order Allen-Cahn model for phase transitions. But unlike the Allen-Cahn model, the gradient flow for the Fonseca-Mantegazza model is a fourth-order parabolic PDE. This creates new and novel difficulties in its analysis.
On the Surprising Salience of Curvature in Grouping by Proximity
ERIC Educational Resources Information Center
Strother, Lars; Kubovy, Michael
2006-01-01
The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the…
Focus retrocollimated interferometry for long-radius-of-curvature measurement
NASA Astrophysics Data System (ADS)
Xiang, Yang
2001-12-01
Focus retrocollimated interferometry is described for measuring long radius of curvature (>1 m), and achievable accuracy is discussed. It is shown that this method can be applied to both concave and convex spherical surfaces and can provide measurement to accuracy of 0.01-0.1%.
Compound Schmidt telescope designs with nonzero Petzval curvatures.
Sigler, R D
1975-09-01
A variety of aplanatic and anastigmatic Schmidt Cassegrain and Schmidt Gregorian telescope designs with nonzero Petzval curvatures are investigated. Relaxing the Petzval constraint permits the development of high performance photo/visual instruments which are capable of diffraction limited imaging over fields of view of 1-2 degrees .
Effect of track asymmetry and curvature on shingle writing scheme
NASA Astrophysics Data System (ADS)
Liu, Feng; Li, Shaoping; Bai, Daniel; Mendez, Hector; Pan, Tao; Han, Dehua; Mao, Sining
2011-04-01
Written transition curvature in perpendicular magnetic recording is generally understood to result in increased transition jitter noise and degraded signal to noise ratio or byte error rate (BER) performance. For the shingle writing scheme, asymmetry or curvature in written tracks is considered inherent due to the erasure and track edge writing characteristics. It is proposed that such a track asymmetry is more prominent at high track density/smaller track pitch recording conditions. In this report we present spin stand experimental results to study the effect of the possible track asymmetry or curvature by shingle writing and reading back in different skews. By comparing shingle writing BER bathtub profiles in different writing skew conditions 0°, +/-2°, +/-4°, +/-6°, the effect of varying shingle track asymmetry and curvature is analyzed via subsequent skewed reading process. The shingle writing BER bathtub profiles as well as the read back amplitude cross track profile are generally symmetric upon one sided erasure at different track pitches. We found that the 0° skew writing and reading process provides both the maximum BER and amplitude.
The flow curvature method applied to canard explosion
NASA Astrophysics Data System (ADS)
Ginoux, Jean-Marc; Llibre, Jaume
2011-11-01
The aim of this work is to establish that the bifurcation parameter value leading to a canard explosion in dimension 2 obtained by the so-called geometric singular perturbation method can be found according to the flow curvature method. This result will be then exemplified with the classical Van der Pol oscillator.
Intracellular magnetophoresis of amyloplasts and induction of root curvature
NASA Technical Reports Server (NTRS)
Kuznetsov, O. A.; Hasenstein, K. H.
1996-01-01
High-gradient magnetic fields (HGMFs) were used to induce intracellular magnetophoresis of amyloplasts. The HGMFs were generated by placing a small ferromagnetic wedge into a uniform magnetic field or at the gap edge between two permanent magnets. In the vicinity of the tip of the wedge the dynamic factor of the magnetic field, delta(H2/2), was about 10(9) Oe2.cm-1, which subjected the amyloplasts to a force comparable to that of gravity. When roots of 2-d-old seedlings of flax (Linum usitatissimum L.) were positioned vertically and exposed to an HGMF, curvature away from the wedge was transient and lasted approximately 1 h. Average curvature obtained after placing magnets, wedge and seedlings on a 1-rpm clinostat for 2 h was 33 +/- 5 degrees. Roots of horizontally placed control seedlings without rotation curved about 47 +/- 4 degrees. The time course of curvature and changes in growth rate were similar for gravicurvature and for root curvature induced by HGMFs. Microscopy showed displacement of amyloplasts in vitro and in vivo. Studies with Arabidopsis thaliana (L.) Heynh. showed that the wild type responded to HGMFs but the starchless mutant TC7 did not. The data indicate that a magnetic force can be used to study the gravisensing and response system of roots.
Quasi-Maxwell interpretation of the spin-curvature coupling
NASA Astrophysics Data System (ADS)
Natário, José
2007-09-01
We write the Mathisson-Papapetrou equations of motion for a spinning particle in a stationary spacetime using the quasi-Maxwell formalism and give an interpretation of the coupling between spin and curvature. The formalism is then used to compute equilibrium positions for spinning particles in the NUT spacetime.
Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy
NASA Astrophysics Data System (ADS)
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Unstable strip resonators with misaligned circular mirrors.
Santana, C; Felsen, L B
1978-08-01
The waveguide approach developed previously by the authors is here applied to unstable strip resonators with unequal sharp-edged circular mirrors that have been tilted with respect to the resonator axis. An equivalent resonator with nontilted mirrors is defined wherein the mirror edges form asymmetrically placed terminations of the open-ended transverse waveguide. The eigenmode losses are found by calculating the waveguide mode reflection coefficients for each pair of edges and inserting these into the previously derived resonance equation. Numerical calculations for the low-loss detached mode are presented for the special case of symmetrical resonators with equally tilted mirrors since results for this configuration, for moderately large Fresnel numbers, have previously been given by Sanderson and Streifer. Our solutions agree with those of Sanderson and Streifer but accommodate also the range of large Fresnel numbers. It is found that misalignment introduces additional ripples into the power loss vs Fresnel number curves. A ray-optical interpretation in terms of edge diffraction is shown to account for this behavior. PMID:20203787
Stimulation of root elongation and curvature by calcium.
Takahashi, H; Scott, T K; Suge, H
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms. PMID:11537880
Stimulation of root elongation and curvature by calcium
NASA Technical Reports Server (NTRS)
Takahashi, H.; Scott, T. K.; Suge, H.
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms.
77 FR 42077 - Environmental Justice: Final Circular
Federal Register 2010, 2011, 2012, 2013, 2014
2012-07-17
... relevant definitions. FTA's EJ Circular builds on the DOT Order, and provides further guidance for... Register notice (76 FR 60590). II. Chapter-by-Chapter Analysis A. General Comments This section addresses... illustrations have been added. FTA reviewed all of the definitions and terms used in the Circular to ensure...
Exon circularization in mammalian nuclear extracts.
Pasman, Z; Been, M D; Garcia-Blanco, M A
1996-06-01
Correct ligation of exons in pre-mRNA splicing requires splice site juxtaposition (splice site pairing), usually involving a 5' splice site and a downstream 3' splice site. Splicing of a 5' splice site to an upstream 3' splice site, however, is predicted to result in a circular RNA. This mode of splice site pairing across the axon has been hypothesized to account for rare RNAs containing scrambled exons (Nigro JM et al., 1991, Celt 64:607-613; Cocquerelle C et al., 1992, EMBO J 11:1 095-1098). Additionally, this mode of splice site pairing has been postulated to explain the formation of SRY circular transcripts in mouse testis (Capel B et al., 1993, Celt 73:1019- 1030). Here we show that splice site pairing across the exon can result in exon circularization in vitro. These results indicate that spliceosome-mediated axon circularization indeed can account for the formation of scrambled exons and circular RNAs. Exon circularization efficiency decreased dramatically as the length of the exon was increased from 95 nt to 274 nt. Circularization of this longer exon was restored, however, when intronic complementary sequences were included in the RNA substrate. These complementary sequences could form a stem that served to bring the splice sites into proximity and thereby promote splice site pairing. Therefore, the splicing of this structured RNA recapitulated SRY-like exon circularization in vitro.
Microstrip Antenna Generates Circularly Polarized Beam
NASA Technical Reports Server (NTRS)
Huang, J.
1986-01-01
Circular microstrip antenna excited with higher order transverse magnetic (TM) modes generates circularly polarized, conical radiation patterns. Found both theoretically and experimentally that peak direction of radiation pattern is varied within wide angular range by combination of mode selection and loading substrate with materials of different dielectric constants.
A Random Walk on a Circular Path
ERIC Educational Resources Information Center
Ching, W.-K.; Lee, M. S.
2005-01-01
This short note introduces an interesting random walk on a circular path with cards of numbers. By using high school probability theory, it is proved that under some assumptions on the number of cards, the probability that a walker will return to a fixed position will tend to one as the length of the circular path tends to infinity.
Jakowatz, C.V. Jr.; Wahl, D.E.; Thompson, P.A.; Doren, N.E.
1996-12-31
Wavefront curvature defocus effects can occur in spotlight-mode SAR imagery when reconstructed via the well-known polar formatting algorithm (PFA) under certain scenarios that include imaging at close range, use of very low center frequency, and/or imaging of very large scenes. The range migration algorithm (RMA), also known as seismic migration, was developed to accommodate these wavefront curvature effects. However, the along-track upsampling of the phase history data required of the original version of range migration can in certain instances represent a major computational burden. A more recent version of migration processing, the Frequency Domain Replication and Downsampling (FReD) algorithm, obviates the need to upsample, and is accordingly more efficient. In this paper the authors demonstrate that the combination of traditional polar formatting with appropriate space-variant post-filtering for refocus can be as efficient or even more efficient than FReD under some imaging conditions, as demonstrated by the computer-simulated results in this paper. The post-filter can be pre-calculated from a theoretical derivation of the curvature effect. The conclusion is that the new polar formatting with post filtering algorithm (PF2) should be considered as a viable candidate for a spotlight-mode image formation processor when curvature effects are present.
Gauge-Invariant Formulation of Circular Dichroism.
Raimbault, Nathaniel; de Boeij, Paul L; Romaniello, Pina; Berger, J A
2016-07-12
Standard formulations of magnetic response properties, such as circular dichroism spectra, are plagued by gauge dependencies, which can lead to unphysical results. In this work, we present a general gauge-invariant and numerically efficient approach for the calculation of circular dichroism spectra from the current density. First we show that in this formulation the optical rotation tensor, the response function from which circular dichroism spectra can be obtained, is independent of the origin of the coordinate system. We then demonstrate that its trace is independent of the gauge origin of the vector potential. We also show how gauge invariance can be retained in practical calculations with finite basis sets. As an example, we explain how our method can be applied to time-dependent current-density-functional theory. Finally, we report gauge-invariant circular dichroism spectra obtained using the adiabatic local-density approximation. The circular dichroism spectra we thus obtain are in good agreement with experiment. PMID:27295541
Treytl, William J.; Slemmons, Arthur J.; Andeen, Gerry B.
1979-01-01
A heliostat apparatus includes a frame which is rotatable about an axis which is parallel to the aperture plane of an elongate receiver. A plurality of flat flexible mirror elements are mounted to the frame between several parallel, uniformly spaced resilient beams which are pivotally connected at their ends to the frame. Channels are mounted to the sides of the beams for supporting the edges of the mirror elements. Each of the beams has a longitudinally varying configuration designed to bow into predetermined, generally circular curvatures of varying radii when the center of the beam is deflected relative to the pivotally connected ends of the beams. All of the parallel resilient beams are simultaneously deflected by a cam shaft assembly extending through openings in the centers of the beams, whereby the mirror elements together form an upwardly concave, cylindrical reflecting surface. The heliostat is rotated about its axis to track the apparent diurnal movement of the sun, while the reflecting surface is substantially simultaneously bowed into a cylindrical trough having a radius adapted to focus incident light at the plane of the receiver aperture.
Tulip-form variable-curvature mirrors: interferometry and field compensation
NASA Astrophysics Data System (ADS)
Lemaitre, Gerard R.; Mazzanti, Silvio; Ferrari, Marc
1998-07-01
Active Optics methods are now capable to provide variable curvature mirrors (VCMs) having controlled sags in the focal range from f/(infinity) to f/2.5. Those development have been carried out by the authors for the optical path equalizer dedicated to each Mersenne focus of the VLTI. The basic principle is to use VCMs as cat's eye mirrors in each delay line in order to achieve field compensations at the recombined Mersenne focii. During the VLTI development phase, cycloid form VCMs controlled by air pressure have been performed with a 10(superscript -4) mirror sag resolution. The cycloid form has been selected for the VLTi delay lines. However, other analytical solutions from circular plates elasticity theory have been found. Two thickness distributions lead to tulip form VCMs controlled by a central force. One of them, using a lineic reaction at the edge is the object of this paper. Active optics design, construction features, test and experimental He-Ne interferograms obtained with 16mm boundary aperture and 10mm clear aperture are presented. The mean aspect-ratio of the tulip from VCM is d/t(subscript 0.5) approximately equals 60, providing a focal zoom range from f/(infinity) to f/2.5. The experiment is carried out form f/(infinity) to f/5.
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-01-01
description, the protein is expressed in the form of a spontaneous curvature field. The approaches include field theoretical methods limited to the small deformation regime, triangulated surfaces and particle-based computational models to investigate the large-deformation regimes observed in the natural state of many biological membranes. Applications of these methods to understand the properties of biological membranes in homogeneous and inhomogeneous environments of proteins, whose underlying curvature fields are either isotropic or anisotropic, are discussed. The diversity in the curvature fields elicits a rich variety of morphological states, including tubes, discs, branched tubes, and caveola. Mapping the thermodynamic stability of these states as a function of tuning parameters such as concentration and strength of curvature induction of the proteins is discussed. The relative stabilities of these self-organized shapes are examined through free-energy calculations. The suite of methods discussed here can be tailored to applications in specific cellular settings such as endocytosis during cargo trafficking and tubulation of filopodial structures in migrating cells, which makes these methods a powerful complement to experimental studies. PMID:25484487
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
NASA Astrophysics Data System (ADS)
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-10-01
protein is expressed in the form of a spontaneous curvature field. The approaches include field theoretical methods limited to the small deformation regime, triangulated surfaces and particle-based computational models to investigate the large-deformation regimes observed in the natural state of many biological membranes. Applications of these methods to understand the properties of biological membranes in homogeneous and inhomogeneous environments of proteins, whose underlying curvature fields are either isotropic or anisotropic, are discussed. The diversity in the curvature fields elicits a rich variety of morphological states, including tubes, discs, branched tubes, and caveola. Mapping the thermodynamic stability of these states as a function of tuning parameters such as concentration and strength of curvature induction of the proteins is discussed. The relative stabilities of these self-organized shapes are examined through free-energy calculations. The suite of methods discussed here can be tailored to applications in specific cellular settings such as endocytosis during cargo trafficking and tubulation of filopodial structures in migrating cells, which makes these methods a powerful complement to experimental studies.
NASA Astrophysics Data System (ADS)
Rosen, David L.; Pendleton, J. David
1995-09-01
Light scattered from optically active spheres was theoretically analyzed for biodetection. The circularly polarized signal of near-forward scattering from circularly dichroic spheres was calculated. Both remote and point biodetection were considered. The analysis included the effect of a circular aperture and beam block at the detector. If the incident light is linearly polarized, a false signal would limit the sensitivity of the biodetector. If the incident light is randomly polarized, shot noise would limit the sensitivity. Suggested improvements to current techniques include a beam block, precise angular measurements, randomly polarized light, index-matching fluid, and larger apertures for large particles.
Mountain wave drag for wind profiles with shear and curvature
NASA Astrophysics Data System (ADS)
Teixeira, M.
2003-04-01
Gravity wave drag produced by stratified flow over orography is one of the physical processes that must be parameterized in large-scale atmospheric models. While in recent studies attention has been given to the way in which the reaction force of the orography on the atmosphere is distributed in height (because this is what has a direct impact on the atmospheric circulation), it is also important to know the total surface drag, and how it depends on the characteristics of the incoming atmospheric flow, because this gives the total momentum flux that is available to be deposited at critical levels. Most available formulae for the surface drag, including those that are used in operational weather forecast models, ignore the effects of wind variation with height, but the few studies that address this problem have shown that these effects are significant and therefore deserve detailed investigation. In this study, a simple analytical model is developed to calculate the surface gravity wave drag exerted by a stratified flow on a bell-shaped mountain, when the wind varies with height in a complicated way. The model is linear with respect to the orography slope, as is required for the equations of motion to be solvable analytically, but is weakly nonlinear with respect to the incoming wind velocity, (U(z),V(z)), which is assumed to vary slowly with height. The solutions to the equations of motion are expanded as power series of a small parameter ɛ, inversely proportional to the square root of the Richardson number of the flow, Ri. By retaining terms in the solutions up to second order, it is found that the drag generally depends on the curvature of the wind profile, as well as on the shear. In the hydrostatic case, for a wind profile where the x velocity component varies linearly with height while the y velocity component is constant, the drag is given by D_x=D0x (1-(3/32) Ri-1), D_y=D0y (1-(1/32) Ri-1) (where (D0y,D0y) is the corresponding drag for a constant
A fast computation method for MUSIC spectrum function based on circular arrays
NASA Astrophysics Data System (ADS)
Du, Zhengdong; Wei, Ping
2015-02-01
The large computation amount of multiple signal classification (MUSIC) spectrum function seriously affects the timeliness of direction finding system using MUSIC algorithm, especially in the two-dimensional directions of arrival (DOA) estimation of azimuth and elevation with a large antenna array. This paper proposes a fast computation method for MUSIC spectrum. It is suitable for any circular array. First, the circular array is transformed into a virtual uniform circular array, in the process of calculating MUSIC spectrum, for the cyclic characteristics of steering vector, the inner product in the calculation of spatial spectrum is realised by cyclic convolution. The computational amount of MUSIC spectrum is obviously less than that of the conventional method. It is a very practical way for MUSIC spectrum computation in circular arrays.
Dual-polarity metamaterial circular polarizer based on giant extrinsic chirality
Shi, J. H.; Shi, Q. C.; Li, Y. X.; Nie, G. Y.; Guan, C. Y.; Cui, T. J.
2015-01-01
Chirality is ubiquitous in nature. The associated optical activity has received much attention due to important applications in spectroscopy, analytical chemistry, crystallography and optics, however, artificial chiral optical materials are complex and difficult to fabricate, especially in the optical range. Here, we propose an ultrathin dual-polarity metamaterial circular polarizer by exploiting the mechanism of giant extrinsic chirality. The polarity of the circular polarizer with large suppression of linear anisotropy can be switched by changing the sign of incident angle. The microwave experiments and optical simulations demonstrate that the large angle of incidence facilitates the high-efficiency circular polarizer, which can be realized in the whole spectra from microwave to visible frequencies. The ultrathin single-layer metamaterials with extrinsic chirality will be a promising candidate for circular polarization devices. PMID:26559746
van der Laan, J. D.; Scrymgeour, D. A.; Kemme, S. A.; Dereniak, E. L.
2015-03-13
We find for infrared wavelengths there are broad ranges of particle sizes and refractive indices that represent fog and rain where the use of circular polarization can persist to longer ranges than linear polarization. Using polarization tracking Monte Carlo simulations for varying particle size, wavelength, and refractive index, we show that for specific scene parameters circular polarization outperforms linear polarization in maintaining the intended polarization state for large optical depths. This enhancement with circular polarization can be exploited to improve range and target detection in obscurant environments that are important in many critical sensing applications. Specifically, circular polarization persists better than linear for radiation fog in the short-wave infrared, for advection fog in the short-wave infrared and the long-wave infrared, and large particle sizes of Sahara dust around the 4 micron wavelength.
van der Laan, J. D.; Sandia National Lab.; Scrymgeour, D. A.; Kemme, S. A.; Dereniak, E. L.
2015-03-13
We find for infrared wavelengths there are broad ranges of particle sizes and refractive indices that represent fog and rain where the use of circular polarization can persist to longer ranges than linear polarization. Using polarization tracking Monte Carlo simulations for varying particle size, wavelength, and refractive index, we show that for specific scene parameters circular polarization outperforms linear polarization in maintaining the intended polarization state for large optical depths. This enhancement with circular polarization can be exploited to improve range and target detection in obscurant environments that are important in many critical sensing applications. Specifically, circular polarization persists bettermore » than linear for radiation fog in the short-wave infrared, for advection fog in the short-wave infrared and the long-wave infrared, and large particle sizes of Sahara dust around the 4 micron wavelength.« less
Comparison of the Single Molecule Dynamics of Linear and Circular DNAs in Planar Extensional Flows
NASA Astrophysics Data System (ADS)
Li, Yanfei; Hsiao, Kai-Wen; Brockman, Christopher; Yates, Daniel; McKenna, Gregory; Schroeder, Charles; San Francisco, Michael; Kornfield, Julie; Anderson, Rae
2015-03-01
Chain topology has a profound impact on the flow behaviors of single macromolecules. The absence of free ends separates circular polymers from other chain architectures, i.e., linear, star, and branched. In the present work, we study the single chain dynamics of large circular and linear DNA molecules by comparing the relaxation dynamics, steady state coil-stretch transition, and transient molecular individualism behaviors for the two types of macromolecules. To this end, large circular DNA molecules were biologically synthesized and studied in a microfluidic device that has a cross-slot geometry to develop a stagnation point extensional flow. Although the relaxation time of rings scales in the same way as for the linear analog, the circular polymers show quantitatively different behaviors in the steady state extension and qualitatively different behaviors during a transient stretch. The existence of some commonality between these two topologies is proposed. Texas Tech University John R. Bradford Endowment.
Różycki, Bartosz; Lipowsky, Reinhard
2016-08-21
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
NASA Astrophysics Data System (ADS)
RóŻycki, Bartosz; Lipowsky, Reinhard
2016-08-01
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
Large extinction ratio optical electrowetting shutter.
Montoya, Ryan D; Underwood, Kenneth; Terrab, Soraya; Watson, Alexander M; Bright, Victor M; Gopinath, Juliet T
2016-05-01
A large extinction ratio optical shutter has been demonstrated using electrowetting liquids. The device is based on switching between a liquid-liquid interface curvature that produces total internal reflection and one that does not. The interface radius of curvature can be tuned continuously from 9 mm at 0 V to -45 mm at 26 V. Extinction ratios from 55.8 to 66.5 dB were measured. The device shows promise for ultracold chip-scale atomic clocks.
Efficient backsplicing produces translatable circular mRNAs
Wang, Yang
2015-01-01
While the human transcriptome contains a large number of circular RNAs (circRNAs), the functions of most circRNAs remain unclear. Sequence annotation suggests that most circRNAs are generated from splicing in reversed orders across exons. However, the mechanisms of this backsplicing are largely unknown. Here we constructed a single exon minigene containing split GFP, and found that the pre-mRNA indeed produces circRNA through efficient backsplicing in human and Drosophila cells. The backsplicing is enhanced by complementary introns that form double-stranded RNA structure to bring splice sites in proximity, but such structure is not required. Moreover, backsplicing is regulated by general splicing factors and cis-elements, but with regulatory rules distinct from canonical splicing. The resulting circRNA can be translated to generate functional proteins. Unlike linear mRNA, poly-adenosine or poly-thymidine in 3′ UTR can inhibit circular mRNA translation. This study revealed that backsplicing can occur efficiently in diverse eukaryotes to generate circular mRNAs. PMID:25449546
DOREN,NEALL E.
1999-10-01
Wavefront curvature defocus effects occur in spotlight-mode SAR imagery when reconstructed via the well-known polar-formatting algorithm (PFA) under certain imaging scenarios. These include imaging at close range, using a very low radar center frequency, utilizing high resolution, and/or imaging very large scenes. Wavefront curvature effects arise from the unrealistic assumption of strictly planar wavefronts illuminating the imaged scene. This dissertation presents a method for the correction of wavefront curvature defocus effects under these scenarios, concentrating on the generalized: squint-mode imaging scenario and its computational aspects. This correction is accomplished through an efficient one-dimensional, image domain filter applied as a post-processing step to PF.4. This post-filter, referred to as SVPF, is precalculated from a theoretical derivation of the wavefront curvature effect and varies as a function of scene location. Prior to SVPF, severe restrictions were placed on the imaged scene size in order to avoid defocus effects under these scenarios when using PFA. The SVPF algorithm eliminates the need for scene size restrictions when wavefront curvature effects are present, correcting for wavefront curvature in broadside as well as squinted collection modes while imposing little additional computational penalty for squinted images. This dissertation covers the theoretical development, implementation and analysis of the generalized, squint-mode SVPF algorithm (of which broadside-mode is a special case) and provides examples of its capabilities and limitations as well as offering guidelines for maximizing its computational efficiency. Tradeoffs between the PFA/SVPF combination and other spotlight-mode SAR image formation techniques are discussed with regard to computational burden, image quality, and imaging geometry constraints. It is demonstrated that other methods fail to exhibit a clear computational advantage over polar-formatting in conjunction
The deterioration of Circular Mausoleum, Roman Necropolis of Carmona, Spain.
Cañaveras, Juan C; Fernandez-Cortes, Angel; Elez, Javier; Cuezva, Soledad; Jurado, Valme; Miller, Ana Zelia; Rogerio-Candelera, Miguel A; Benavente, David; Hernandez-Marine, Mariona; Saiz-Jimenez, Cesareo; Sanchez-Moral, Sergio
2015-06-15
The Circular Mausoleum tomb in the Roman Necropolis of Carmona was carved on a calcarenite sequence in an ancient quarry located in the town of Carmona, Southern Spain. This rock-cut tomb, representative of Roman burial practices, currently suffers from serious deterioration. A detailed survey over several years permitted the identification of the main tomb's pathologies and damaging processes, which include loss of material (scaling, flaking, granular disintegration), surface modifications (efflorescences, crusts and deposits) and extensive biological colonization. The results obtained in this study indicated that anthropogenic changes were largely responsible and enhanced the main alteration mechanisms observed in the Circular Mausoleum. Based on the deterioration diagnosis, effective corrective actions were proposed. This study shows that any conservative intervention in the interior of the tomb should be preceded by accurate in situ measurements and laboratory analyses to ascribe the source of the deterioration damages and thus designing effective treatments. PMID:25747366
Widespread noncoding circular RNAs in plants.
Ye, Chu-Yu; Chen, Li; Liu, Chen; Zhu, Qian-Hao; Fan, Longjiang
2015-10-01
A large number of noncoding circular RNAs (circRNAs) with regulatory potency have been identified in animals, but little attention has been given to plant circRNAs. We performed genome-wide identification of circRNAs in Oryza sativa and Arabidopsis thaliana using publically available RNA-Seq data, analyzed and compared features of plant and animal circRNAs. circRNAs (12037 and 6012) were identified in Oryza sativa and Arabidopsis thaliana, respectively, with 56% (10/18) of the sampled rice exonic circRNAs validated experimentally. Parent genes of over 700 exonic circRNAs were orthologues between rice and Arabidopsis, suggesting conservation of circRNAs in plants. The introns flanking plant circRNAs were much longer than introns from linear genes, and possessed less repetitive elements and reverse complementary sequences than the flanking introns of animal circRNAs. Plant circRNAs showed diverse expression patterns, and 27 rice exonic circRNAs were found to be differentially expressed under phosphate-sufficient and -starvation conditions. A significantly positive correlation was observed for the expression profiles of some circRNAs and their parent genes. Our results demonstrated that circRNAs are widespread in plants, revealed the common and distinct features of circRNAs between plants and animals, and suggested that circRNAs could be a critical class of noncoding regulators in plants.
Entanglement of quantum circular states of light
NASA Astrophysics Data System (ADS)
Horoshko, D. B.; De Bièvre, S.; Kolobov, M. I.; Patera, G.
2016-06-01
We present a general approach to calculating the entanglement of formation for superpositions of two-mode coherent states, placed equidistantly on a circle in phase space. We show that in the particular case of rotationally invariant circular states the Schmidt decomposition of two modes, and therefore the value of their entanglement, are given by analytical expressions. We analyze the dependence of the entanglement on the radius of the circle and number of components in the superposition. We also show that the set of rotationally invariant circular states creates an orthonormal basis in the state space of the harmonic oscillator, and this basis is advantageous for representation of other circular states of light.
Circular polarization memory in polydisperse scattering media
NASA Astrophysics Data System (ADS)
Macdonald, C. M.; Jacques, S. L.; Meglinski, I. V.
2015-03-01
We investigate the survival of circularly polarized light in random scattering media. The surprising persistence of this form of polarization has a known dependence on the size and refractive index of scattering particles, however a general description regarding polydisperse media is lacking. Through analysis of Mie theory, we present a means of calculating the magnitude of circular polarization memory in complex media, with total generality in the distribution of particle sizes and refractive indices. Quantification of this memory effect enables an alternate pathway toward recovering particle size distribution, based on measurements of diffusing circularly polarized light.
Detonation wave velocity and curvature of brass encased PBXN-111
Forbes, J.W.; Lemar, E.R.
1996-05-01
Detonation velocities and wave front curvatures were measured for PBXN-111 charges encased in 5 mm thick brass tubes. In all the experiments (charge diameters from 19 to 47 mm) the brass case affected the detonation properties of PBXN-111. Steady detonation waves propagated in brass encased charges with diameters as small as 19 mm, which is about half of the unconfined failure diameter. The radii of curvature of the detonation waves at the center of the wave fronts ranged from 52 to 141 mm for charge diameters of 25 to 47 mm. The angles between the detonation wave fronts and the brass/charge interfaces were between 72 and 74 degrees. {copyright} {ital 1996 American Institute of Physics.}
Membrane curvature in cell biology: An integration of molecular mechanisms.
Jarsch, Iris K; Daste, Frederic; Gallop, Jennifer L
2016-08-15
Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists.
Curvature effects on carbon nanomaterials: Exohedral versus endhohedral supercapacitors
Huang, J; Sumpter, B. G.; Meunier, V.; Yushin, G.; Portet, C.; Gogotsi, Y.
2011-01-31
Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.
Curvature effects in carbon nanomaterials: Exohedral versus endohedral supercapacitors
Huang, Jingsong; Sumpter, Bobby G; Meunier, Vincent; Gogotsi, Yury G.; Yushin, Gleb; Portet, Cristelle
2010-01-01
Capacitive energy storage mechanisms in nanoporous carbon supercapacitors hinge on endohedral interactions in carbon materials with macro-, meso-, and micropores that have negative surface curvature. In this article, we show that because of the positive curvature found in zero-dimensional carbon onions or one-dimensional carbon nanotube arrays, exohedral interactions cause the normalized capacitance to increase with decreasing particle size or tube diameter, in sharp contrast to the behavior of nanoporous carbon materials. This finding is in good agreement with the trend of recent experimental data. Our analysis suggests that electrical energy storage can be improved by exploiting the highly curved surfaces of carbon nanotube arrays with diameters on the order of 1 nm.
Adsorbate-induced curvature and stiffening of graphene.
Svatek, Simon A; Scott, Oliver R; Rivett, Jasmine P H; Wright, Katherine; Baldoni, Matteo; Bichoutskaia, Elena; Taniguchi, Takashi; Watanabe, Kenji; Marsden, Alexander J; Wilson, Neil R; Beton, Peter H
2015-01-14
The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon-carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625
Spontaneous curvature in chiral polar filaments near interfaces
NASA Astrophysics Data System (ADS)
Olmsted, Peter D.; Riley, Emily E.; Jordens, Sophia; Usov, Ivan; Isa, Lucio; Mezzenga, Raffaele
2015-03-01
Chiral filaments (actin, DNA, alpha helical strands, ...) are ubiquitous in biology, and they frequently come into contact with interfaces or inhomogeneous environments, either in biology (e.g. actin on membranes) or use and processing of biomaterials (fibrils at solvent boundaries or nanoparticle surfaces). Recent experiments have shown that amyloid fibrils can develop unusual curvatures at the air-water interface. Here we show that spontaneous curvature follows, on symmetry grounds, for chiral polar filaments placed in inhomgeneous environments such as near surfaces. We demonstrate this for simple model surface-fibril interactions, and discuss some of the implications. Financial support is acknowledged from: ETH Zurich (ETHIIRA TH 32-1), SNF (2-77002-11), and SNSF (IZK072_141955, PP00P2_144646/1, PZ00P2_142532/1).
DNA Origami with Complex Curvatures in Three-Dimensional Space
Han, Dongran; Pal, Suchetan; Nangreave, Jeanette; Deng, Zhengtao; Liu, Yan; Yan, Hao
2011-04-14
We present a strategy to design and construct self-assembling DNA nanostructures that define intricate curved surfaces in three-dimensional (3D) space using the DNA origami folding technique. Double-helical DNA is bent to follow the rounded contours of the target object, and potential strand crossovers are subsequently identified. Concentric rings of DNA are used to generate in-plane curvature, constrained to 2D by rationally designed geometries and crossover networks. Out-of-plane curvature is introduced by adjusting the particular position and pattern of crossovers between adjacent DNA double helices, whose conformation often deviates from the natural, B-form twist density. A series of DNA nanostructures with high curvature—such as 2D arrangements of concentric rings and 3D spherical shells, ellipsoidal shells, and a nanoflask—were assembled.
The role of gravity in leaf blade curvatures
NASA Technical Reports Server (NTRS)
Hayes, A. B.
1984-01-01
In the past year we have gained useful information on several aspects of leaf blade growth. The most important observations are as follows: The C(14)-1AA moves preferentially in a gravipositive dorsiventral direction through the blade. This movement is inhibited by inversion of the blade. The responding cells in leaf blade hyponasty are in the lower epidermis and bundle sheath cells. Two additional responses in the leaf were characterized. In addition to blade curvature, the leaf shows petiole curvature and changes in the liminal angle subtended by the pulvinus. Ethylene production was studied under a number of conditions. The blade, rather than the petiole or pulvinus, is the principal site of auxin-promoted ethylene synthesis. The effects of a variety of agents on the blade, including gibberellic acid, abscisic acid, vanadate, low pH buffers, and blue light were reviewed.
Constructing Graphs over with Small Prescribed Mean-Curvature
NASA Astrophysics Data System (ADS)
Carley, Holly; Kiessling, Michael K.-H.
2015-12-01
In this paper nonlinear Hodge theory and Banach algebra estimates are employed to construct a convergent series expansion which solves the prescribed mean curvature equation for n-dimensional hypersurfaces in (+ sign) and (- sign) which are graphs of a smooth function , and whose mean curvature function H is α-Hölder continuous and integrable, with small norm. The radius of convergence is estimated explicitly from below. Our approach is inspired by, and applied to, the Maxwell-Born-Infeld theory of electromagnetism in , for which our method yields the first systematic way of explicitly computing the electrostatic potential for regular charge densities and small Born parameter, with explicit error estimates at any order of truncation of the series. In particular, our results level the ground for a controlled computation of Born-Infeld effects on the Hydrogen spectrum.
NASA Astrophysics Data System (ADS)
Reeves, Matthew; Stratford, Kevin; Thijssen, Job H. J.
Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity $L$ (average interfacial separation) of the bijel is controlled by varying the radius ($r$) and volume fraction ($\\phi$) of the colloids ($L \\propto r/\\phi$). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by $L$ alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.
Membrane curvature in cell biology: An integration of molecular mechanisms.
Jarsch, Iris K; Daste, Frederic; Gallop, Jennifer L
2016-08-15
Curving biological membranes establishes the complex architecture of the cell and mediates membrane traffic to control flux through subcellular compartments. Common molecular mechanisms for bending membranes are evident in different cell biological contexts across eukaryotic phyla. These mechanisms can be intrinsic to the membrane bilayer (either the lipid or protein components) or can be brought about by extrinsic factors, including the cytoskeleton. Here, we review examples of membrane curvature generation in animals, fungi, and plants. We showcase the molecular mechanisms involved and how they collaborate and go on to highlight contexts of curvature that are exciting areas of future research. Lessons from how membranes are bent in yeast and mammals give hints as to the molecular mechanisms we expect to see used by plants and protists. PMID:27528656
On M-theory fourfold vacua with higher curvature terms
NASA Astrophysics Data System (ADS)
Grimm, Thomas W.; Pugh, Tom G.; Weißenbacher, Matthias
2015-04-01
We study solutions to the eleven-dimensional supergravity action, including terms quartic and cubic in the Riemann curvature, that admit an eight-dimensional compact space. The internal background is found to be a conformally Kähler manifold with vanishing first Chern class. The metric solution, however, is non-Ricci-flat even when allowing for a conformal rescaling including the warp factor. This deviation is due to the possible non-harmonicity of the third Chern-form in the leading order Ricci-flat metric. We present a systematic derivation of the background solution by solving the Killing spinor conditions including higher curvature terms. These are translated into first-order differential equations for a globally defined real two-form and complex four-form on the fourfold. We comment on the supersymmetry properties of the described solutions.
Control of repeat protein curvature by computational protein design
Park, Keunwan; Shen, Betty W.; Parmeggiani, Fabio; Huang, Po-Ssu; Stoddard, Barry L.; Baker, David
2014-01-01
Shape complementarity is an important component of molecular recognition, and the ability to precisely adjust the shape of a binding scaffold to match a target of interest would greatly facilitate the creation of high affinity protein reagents and therapeutics. Here we describe a general approach to control the shape of the binding surface on repeat protein scaffolds, and apply it to leucine rich repeat proteins. First, a set of self-compatible building block modules are designed that when polymerized each generate surfaces with unique but constant curvatures. Second, a set of junction modules that connect the different building blocks are designed. Finally, new proteins with custom designed shapes are generated by appropriately combining building block and junction modules. Crystal structures of the designs illustrate the power of the approach in controlling repeat protein curvature. PMID:25580576
Preference for Curvature: A Historical and Conceptual Framework
Gómez-Puerto, Gerardo; Munar, Enric; Nadal, Marcos
2016-01-01
That people find curved contours and lines more pleasurable than straight ones is a recurrent observation in the aesthetic literature. Although such observation has been tested sporadically throughout the history of scientific psychology, only during the last decade has it been the object of systematic research. Recent studies lend support to the idea that human preference for curved contours is biologically determined. However, it has also been argued that this preference is a cultural phenomenon. In this article, we review the available evidence, together with different attempts to explain the nature of preference for curvature: sensoriomotor-based and valuation-based approaches. We also argue that the lack of a unifying framework and clearly defined concepts might be undermining our efforts towards a better understanding of the nature of preference for curvature. Finally, we point to a series of unresolved matters as the starting point to further develop a consistent research program. PMID:26793092
On the breakdown of the curvature perturbation ζ during reheating
NASA Astrophysics Data System (ADS)
Tarman Algan, Merve; Kaya, Ali; Seyma Kutluk, Emine
2015-04-01
It is known that in single scalar field inflationary models the standard curvature perturbation ζ, which is supposedly conserved at superhorizon scales, diverges during reheating at times 0dot phi=, i.e. when the time derivative of the background inflaton field vanishes. This happens because the comoving gauge 0varphi=, where varphi denotes the inflaton perturbation, breaks down when 0dot phi=. The issue is usually bypassed by averaging out the inflaton oscillations but strictly speaking the evolution of ζ is ill posed mathematically. We solve this problem in the free theory by introducing a family of smooth gauges that still eliminates the inflaton fluctuation varphi in the Hamiltonian formalism and gives a well behaved curvature perturbation ζ, which is now rigorously conserved at superhorizon scales. At the linearized level, this conserved variable can be used to unambiguously propagate the inflationary perturbations from the end of inflation to subsequent epochs. We discuss the implications of our results for the inflationary predictions.
Adsorbate-Induced Curvature and Stiffening of Graphene
2014-01-01
The adsorption of the alkane tetratetracontane (TTC, C44H90) on graphene induces the formation of a curved surface stabilized by a gain in adsorption energy. This effect arises from a curvature-dependent variation of a moiré pattern due to the mismatch of the carbon–carbon separation in the adsorbed molecule and the period of graphene. The effect is observed when graphene is transferred onto a deformable substrate, which in our case is the interface between water layers adsorbed on mica and an organic solvent, but is not observed on more rigid substrates such as boron nitride. Our results show that molecular adsorption can be influenced by substrate curvature, provide an example of two-dimensional molecular self-assembly on a soft, responsive interface, and demonstrate that the mechanical properties of graphene may be modified by molecular adsorption, which is of relevance to nanomechanical systems, electronics, and membrane technology. PMID:25469625
Robust contour decomposition using a constant curvature criterion
NASA Technical Reports Server (NTRS)
Wuescher, Daniel M.; Boyer, Kim L.
1991-01-01
The problem of decomposing an extended boundary or contour into simple primitives is addressed with particular emphasis on Laplacian-of-Gaussian (LoG) zero-crossing contours. A technique is introduced for partitioning such contours into constant curvature segments. A nonlinear `blip' filter matched to the impairment signature of the curvature computation process, an overlapped voting scheme, and a sequential contiguous segment extraction mechanism are used. This technique is insensitive to reasonable changes in algorithm parameters and robust to noise and minor viewpoint-induced distortions in the contour shape, such as those encountered between stereo image pairs. The results vary smoothly with the data, and local perturbations induce only local changes in the result. Robustness and insensitivity are experimentally verified.
Effect of nano-scale curvature on the intrinsic blood coagulation system.
Kushida, Takashi; Saha, Krishnendu; Subramani, Chandramouleeswaran; Nandwana, Vikas; Rotello, Vincent M
2014-11-01
The intrinsic coagulation activity of silica nanoparticles strongly depends on their surface curvature. Nanoparticles with higher surface curvature do not denature blood coagulation factor XII on its surface, providing a coagulation 'silent' surface, while nanoparticles with lower surface curvature show denaturation and concomitant coagulation.
Impact of local vessel curvature on the circumferential plaque distribution in coronary arteries
NASA Astrophysics Data System (ADS)
Wahle, Andreas; Medina, Ruben; Braddy, Kathleen C.; Fox, James M.; Brennan, Theresa M. H.; Lopez, John J.; Rossen, James D.; Sonka, Milan
2003-05-01
Plaque in native coronary arteries is hypothesized to accumulate more likely along the inner curvature of a vessel segment as compared to its outer curvature. This behavior is likely associated with differences in local shear stress, which tends to be lower on the inner bend of a curved vessel than on the outer bend. The reported in-vivo study evaluated how the circumferential plaque distribution depends on local vessel curvature in coronaries from a limited set of 12 patients. Geometrically correct models of the vessel segments were generated utilizing fusion between biplane angiography and intravascular ultrasound. The plaque thickness was derived from the 3-D borders of the lumen/plaque and media/adventitia interfaces. Within each frame, plaque thickness was classified into "below-average" and "above-average" regions. A local curvature index was defined for each point: A positive value indicates the "inner" curvature, a negative value the "outer" curvature, with the magnitude determined from differential geometry. In the majority of the examined vessels, regions of "below-average/outer-curvature" and "above-average/inner-curvature" combined outweighed the "below-average/inner-curvature" and "above-average/outer-curvature" regions. The ratio increased with the threshold to exclude lower-curvature regions, confirming the hypothesis that plaque is more likely to accumulate on the luminal surface along the inner curvature of the coronary segment.
A three-dimensional validation of crack curvature in muscovite mica
J. C. Hill; J. W. Foulk III; P. A. Klein; E. P. Chen
2001-01-07
Experimental and computational efforts focused on characterizing crack tip curvature in muscovite mica. Wedge-driven cracks were propagated under monochromatic light. Micrographs verified the subtle curvature of the crack front near the free surface. A cohesive approach was employed to model mixed-mode fracture in a three-dimensional framework. Finite element calculations captured the crack curvature observed in experiment.
Optimizing baryon acoustic oscillation surveys - II. Curvature, redshifts and external data sets
NASA Astrophysics Data System (ADS)
Parkinson, David; Kunz, Martin; Liddle, Andrew R.; Bassett, Bruce A.; Nichol, Robert C.; Vardanyan, Mihran
2010-02-01
We extend our study of the optimization of large baryon acoustic oscillation (BAO) surveys to return the best constraints on the dark energy, building on Paper I of this series by Parkinson et al. The survey galaxies are assumed to be pre-selected active, star-forming galaxies observed by their line emission with a constant number density across the redshift bin. Star-forming galaxies have a redshift desert in the region 1.6 < z < 2, and so this redshift range was excluded from the analysis. We use the Seo & Eisenstein fitting formula for the accuracies of the BAO measurements, using only the information for the oscillatory part of the power spectrum as distance and expansion rate rulers. We go beyond our earlier analysis by examining the effect of including curvature on the optimal survey configuration and updating the expected `prior' constraints from Planck and the Sloan Digital Sky Survey. We once again find that the optimal survey strategy involves minimizing the exposure time and maximizing the survey area (within the instrumental constraints), and that all time should be spent observing in the low-redshift range (z < 1.6) rather than beyond the redshift desert, z > 2. We find that, when assuming a flat universe, the optimal survey makes measurements in the redshift range 0.1 < z < 0.7, but that including curvature as a nuisance parameter requires us to push the maximum redshift to 1.35, to remove the degeneracy between curvature and evolving dark energy. The inclusion of expected other data sets (such as WiggleZ, the Baryon Oscillation Spectroscopic Survey and a stage III Type Ia supernova survey) removes the necessity of measurements below redshift 0.9, and pushes the maximum redshift up to 1.5. We discuss considerations in determining the best survey strategy in light of uncertainty in the true underlying cosmological model.
CURVATURE-DRIFT INSTABILITY FAILS TO GENERATE PULSAR RADIO EMISSION
Kaganovich, Alexander; Lyubarsky, Yuri
2010-10-01
The curvature-drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing the propagation of short electromagnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity; therefore, this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.
Global and local curvature in density functional theory
NASA Astrophysics Data System (ADS)
Zhao, Qing; Ioannidis, Efthymios I.; Kulik, Heather J.
2016-08-01
Piecewise linearity of the energy with respect to fractional electron removal or addition is a requirement of an electronic structure method that necessitates the presence of a derivative discontinuity at integer electron occupation. Semi-local exchange-correlation (xc) approximations within density functional theory (DFT) fail to reproduce this behavior, giving rise to deviations from linearity with a convex global curvature that is evidence of many-electron, self-interaction error and electron delocalization. Popular functional tuning strategies focus on reproducing piecewise linearity, especially to improve predictions of optical properties. In a divergent approach, Hubbard U-augmented DFT (i.e., DFT+U) treats self-interaction errors by reducing the local curvature of the energy with respect to electron removal or addition from one localized subshell to the surrounding system. Although it has been suggested that DFT+U should simultaneously alleviate global and local curvature in the atomic limit, no detailed study on real systems has been carried out to probe the validity of this statement. In this work, we show when DFT+U should minimize deviations from linearity and demonstrate that a "+U" correction will never worsen the deviation from linearity of the underlying xc approximation. However, we explain varying degrees of efficiency of the approach over 27 octahedral transition metal complexes with respect to transition metal (Sc-Cu) and ligand strength (CO, NH3, and H2O) and investigate select pathological cases where the delocalization error is invisible to DFT+U within an atomic projection framework. Finally, we demonstrate that the global and local curvatures represent different quantities that show opposing behavior with increasing ligand field strength, and we identify where these two may still coincide.
Relative stability and local curvature analysis in carbon nanotori
NASA Astrophysics Data System (ADS)
Chuang, Chern; Guan, Jie; Witalka, David; Zhu, Zhen; Jin, Bih-Yaw; Tománek, David
2015-04-01
We introduce a concise formalism to characterize nanometer-sized tori based on carbon nanotubes and to determine their stability by combining ab initio density functional calculations with a continuum elasticity theory approach that requires only shape information. We find that the high strain energy in nanotori containing only hexagonal rings is significantly reduced in nanotori containing also other polygons. Our approach allows to determine local curvature and link it to local strain energy, which is correlated with local stability and chemical reactivity.
Digital elevation model visibility including Earth's curvature and atmosphere refraction
NASA Astrophysics Data System (ADS)
Santossilva, Ewerton; Vieiradias, Luiz Alberto
1990-03-01
There are some instances in which the Earth's curvature and the atmospheric refraction, optical or electronic, are important factors when digital elevation models are used for visibility calculations. This work deals with this subject, suggesting a practical approach to solve this problem. Some examples, from real terrain data, are presented. The equipment used was an IBM-PC like computer with a SITIM graphic card.
Intrinsic DNA curvature of double-crossover tiles
NASA Astrophysics Data System (ADS)
Kim, Seungjae; Kim, Junghoon; Qian, Pengfei; Shin, Jihoon; Amin, Rashid; Ahn, Sang Jung; LaBean, Thomas H.; Kim, Moon Ki; Park, Sung Ha
2011-06-01
A theoretical model which takes into account the structural distortion of double-crossover DNA tiles has been studied to investigate its effect on lattice formation sizes. It has been found that a single vector appropriately describes the curvature of the tiles, of which a higher magnitude hinders lattice growth. In conjunction with these calculations, normal mode analysis reveals that tiles with relative higher frequencies have an analogous effect. All the theoretical results are shown to be in good agreement with experimental data.
Berry Curvature and Chiral Plasmons in Massive Dirac Materials
NASA Astrophysics Data System (ADS)
Song, Justin; Rudner, Mark
2015-03-01
In the semiclassical model of carrier dynamics, quasiparticles are described as nearly free electrons with modified characteristics modified characteristics such as effective masses which may differ significantly from those of an electron in vacuum. In addition to being influenced by external electric and magnetic fields, the trajectories of electrons in topological materials are also affected by the presence of an interesting quantum mechanical field - the Berry curvature - which is responsible for a number of anomalous transport phenomena recently observed in Dirac materials including G/hBN, and MoS2. Here we discuss how Berry curvature can affect the collective behavior of electrons in these systems. In particular, we show that the collective electronic excitations in metallic massive Dirac materials can feature a chirality even in the absence of an applied magnetic field. The chirality of these plasmons arises from the Berry curvature of the massive Dirac bands. The corresponding dispersion is split between left- and right-handed modes. We also discuss experimental manifestations.
Bcl-2 apoptosis proteins, mitochondrial membrane curvature, and cancer
NASA Astrophysics Data System (ADS)
Hwee Lai, Ghee; Schmidt, Nathan; Sanders, Lori; Mishra, Abhijit; Wong, Gerard; Ivashyna, Olena; Christenson, Eric; Schlesinger, Paul; Akabori, Kiyotaka; Santangelo, Christian
2012-02-01
Critical interactions between Bcl-2 family proteins permeabilize the outer mitochondrial membrane, a common decision point early in the intrinsic apoptotic pathway that irreversibly commits the cell to death. However, a unified picture integrating the essential non-passive role of lipid membranes with the contested dynamics of Bcl-2 regulation remains unresolved. Correlating results between synchrotron x-ray diffraction and microscopy in cell-free assays, we report activation of pro-apoptotic Bax induces strong pure negative Gaussian membrane curvature topologically necessary for pore formation and membrane remodeling events. Strikingly, Bcl-xL suppresses not only Bax-induced pore formation, but also membrane remodeling by disparate systems including cell penetrating, antimicrobial or viral fusion peptides, and bacterial toxin, none of which have BH3 allosteric domains to mediate direct binding. We propose a parallel mode of Bcl-2 pore regulation in which Bax and Bcl-xL induce antagonistic and mutually interacting Gaussian membrane curvatures. The universal nature of curvature-mediated interactions allows synergy with direct binding mechanisms, and potentially accounts for the Bcl-2 family modulation of mitochondrial fission/fusion dynamics.
Formation of Curvature Subunit of Carbon in Combustion.
Wu, Xin-Zhou; Yao, Yang-Rong; Chen, Miao-Miao; Tian, Han-Rui; Xiao, Jun; Xu, Yun-Yan; Lin, Min-Song; Abella, Laura; Tian, Cheng-Bo; Gao, Cong-Li; Zhang, Qianyan; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun
2016-08-01
Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5-C18 that are online produced in the flame of acetylene-cyclopentadiene-oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process.
Encoding Gaussian curvature in glassy and elastomeric liquid crystal solids
Mostajeran, Cyrus; Ware, Taylor H.; White, Timothy J.
2016-01-01
We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains. PMID:27279777
Generic properties of curvature sensing through vision and touch.
Dresp-Langley, Birgitta
2013-01-01
Generic properties of curvature representations formed on the basis of vision and touch were examined as a function of mathematical properties of curved objects. Virtual representations of the curves were shown on a computer screen for visual scaling by sighted observers (experiment 1). Their physical counterparts were placed in the two hands of blindfolded and congenitally blind observers for tactile scaling. The psychophysical data show that curvature representations in congenitally blind individuals, who never had any visual experience, and in sighted observers, who rely on vision most of the time, are statistically linked to the same mathematical properties of the curves. The perceived magnitude of object curvature, sensed through either vision or touch, is related by a mathematical power law, with similar exponents for the two sensory modalities, to the aspect ratio of the curves, a scale invariant geometric property. This finding supports biologically motivated models of sensory integration suggesting a universal power law for the adaptive brain control and balance of motor responses to environmental stimuli from any sensory modality.
Formation of Curvature Subunit of Carbon in Combustion.
Wu, Xin-Zhou; Yao, Yang-Rong; Chen, Miao-Miao; Tian, Han-Rui; Xiao, Jun; Xu, Yun-Yan; Lin, Min-Song; Abella, Laura; Tian, Cheng-Bo; Gao, Cong-Li; Zhang, Qianyan; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun
2016-08-01
Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5-C18 that are online produced in the flame of acetylene-cyclopentadiene-oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process. PMID:27377559
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.
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.
Finger vein extraction using gradient normalization and principal curvature
NASA Astrophysics Data System (ADS)
Choi, Joon Hwan; Song, Wonseok; Kim, Taejeong; Lee, Seung-Rae; Kim, Hee Chan
2009-02-01
Finger vein authentication is a personal identification technology using finger vein images acquired by infrared imaging. It is one of the newest technologies in biometrics. Its main advantage over other biometrics is the low risk of forgery or theft, due to the fact that finger veins are not normally visible to others. Extracting finger vein patterns from infrared images is the most difficult part in finger vein authentication. Uneven illumination, varying tissues and bones, and changes in the physical conditions and the blood flow make the thickness and brightness of the same vein different in each acquisition. Accordingly, extracting finger veins at their accurate positions regardless of their thickness and brightness is necessary for accurate personal identification. For this purpose, we propose a new finger vein extraction method which is composed of gradient normalization, principal curvature calculation, and binarization. As local brightness variation has little effect on the curvature and as gradient normalization makes the curvature fairly uniform at vein pixels, our method effectively extracts finger vein patterns regardless of the vein thickness or brightness. In our experiment, the proposed method showed notable improvement as compared with the existing methods.
Encoding Gaussian curvature in glassy and elastomeric liquid crystal solids
NASA Astrophysics Data System (ADS)
Mostajeran, Cyrus; Warner, Mark; Ware, Taylor H.; White, Timothy J.
2016-05-01
We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains.
Kikuchi, Akihiro; Higuchi, Arika; Ida, Shigeru E-mail: higuchia@geo.titech.ac.jp
2014-12-10
Recently, gas giant planets in nearly circular orbits with large semimajor axes (a ∼ 30-1000 AU) have been detected by direct imaging. We have investigated orbital evolution in a formation scenario for such planets, based on a core accretion model. (1) Icy cores accrete from planetesimals at ≲ 30 AU, (2) they are scattered outward by an emerging nearby gas giant to acquire highly eccentric orbits, and (3) their orbits are circularized through the accretion of disk gas in outer regions, where they spend most of their time. We analytically derived equations to describe the orbital circularization through gas accretion. Numerical integrations of these equations show that the eccentricity decreases by a factor of more than 5 while the planetary mass increases by a factor of 10. Because runaway gas accretion increases planetary mass by ∼10-300, the orbits are sufficiently circularized. On the other hand, a is reduced at most only by a factor of two, leaving the planets in the outer regions. If the relative velocity damping by shock is considered, the circularization slows down, but is still efficient enough. Therefore, this scenario potentially accounts for the formation of observed distant jupiters in nearly circular orbits. If the apocenter distances of the scattered cores are larger than the disk sizes, their a shrink to a quarter of the disk sizes; the a-distribution of distant giants could reflect the outer edges of the disks in a similar way that those of hot jupiters may reflect inner edges.
NASA Astrophysics Data System (ADS)
Kim, Jin-Tae; Liberzon, Alex; Chamorro, Leonardo P.
2015-11-01
The distinctive differences between two jet flows that share the same hydraulic diameter dh = 0.01 m and Re ~ 6000, but different (nozzle) shape are explored via 3D Particle Tracking Velocimetry using OpenPTV (http://www.openptv.net). The two jets are formed from circular and semicircular pipes and released in a quiescent water tank of 40 dh height, 40 dh wide, and 200 dh long. The recirculating system is seeded with 100 μm particles, where flow measurements are performed in the intermediate flow field (14.5 < x /dh <18.5) at 550Hz for a total of ~ 30,000 frames. Analysis is focused on the spatial distribution of the local flow acceleration and curvature of the Lagrangian trajectories. The velocity and acceleration of particles are estimated by low-pass filtering their position with a moving cubic spline fitting, while the curvature is obtained from the Frenet-Serret equations. Probability density functions (p.d.f.) of these quantities are obtained at various sub-volumes containing a given streamwise velocity range, and compared between the two cases to evaluate the memory effects in the intermediate flow field.
NASA Astrophysics Data System (ADS)
Kong, Xiangliang; Chen, Yao; Guo, Fan; Feng, Shiwei; Du, Guohui; Li, Gang
2016-04-01
Using a test-particle simulation, we investigate the effect of large-scale coronal magnetic fields on electron acceleration at an outward-propagating coronal shock with a circular front. The coronal field is approximated by an analytical solution with a streamer-like magnetic field featuring a partially open magnetic field and a current sheet at the equator atop the closed region. We show that the large-scale shock-field configuration, especially the relative curvature of the shock and the magnetic field line across which the shock is sweeping, plays an important role in the efficiency of electron acceleration. At low shock altitudes, when the shock curvature is larger than that of the magnetic field lines, the electrons are mainly accelerated at the shock flanks; at higher altitudes, when the shock curvature is smaller, the electrons are mainly accelerated at the shock nose around the top of closed field lines. The above process reveals the shift of the efficient electron acceleration region along the shock front during its propagation. We also find that, in general, the electron acceleration at the shock flank is not as efficient as that at the top of the closed field because a collapsing magnetic trap can be formed at the top. In addition, we find that the energy spectra of electrons are power-law-like, first hardening then softening with the spectral index varying in a range of ‑3 to ‑6. Physical interpretations of the results and implications for the study of solar radio bursts are discussed.
NASA Astrophysics Data System (ADS)
Kong, Xiangliang; Chen, Yao; Guo, Fan; Feng, Shiwei; Du, Guohui; Li, Gang
2016-04-01
Using a test-particle simulation, we investigate the effect of large-scale coronal magnetic fields on electron acceleration at an outward-propagating coronal shock with a circular front. The coronal field is approximated by an analytical solution with a streamer-like magnetic field featuring a partially open magnetic field and a current sheet at the equator atop the closed region. We show that the large-scale shock-field configuration, especially the relative curvature of the shock and the magnetic field line across which the shock is sweeping, plays an important role in the efficiency of electron acceleration. At low shock altitudes, when the shock curvature is larger than that of the magnetic field lines, the electrons are mainly accelerated at the shock flanks; at higher altitudes, when the shock curvature is smaller, the electrons are mainly accelerated at the shock nose around the top of closed field lines. The above process reveals the shift of the efficient electron acceleration region along the shock front during its propagation. We also find that, in general, the electron acceleration at the shock flank is not as efficient as that at the top of the closed field because a collapsing magnetic trap can be formed at the top. In addition, we find that the energy spectra of electrons are power-law-like, first hardening then softening with the spectral index varying in a range of -3 to -6. Physical interpretations of the results and implications for the study of solar radio bursts are discussed.