Significant Curvature Research Articles

Acoustic Ducting, Reflection, Refraction, and Dispersion by Curved Nonlinear Internal Waves in Shallow Water

Nonlinear internal waves in shallow water have been shown to be effective ducts of acoustic energy, through theory, numerical modeling, and experiment. To date, most work on such ducting has concentrated on rectilinear internal wave ducts or those with very slight curvature. In this paper, we examine the acoustic effects of significant curvature of these internal waves. (By significant curvature, we mean lateral deviation of the internal wave duct by more than half the spacing between internal waves over an acoustic path, giving a transition from ducting to antiducting.) We develop basic analytical models of these effects, employ fully 3-D numerical models of sound propagation and scattering, and examine simultaneous acoustical and oceanographic data from the 2006 Shallow Water Experiment (SW06). It will be seen that the effects of curvature should be evident in the mode amplitudes and arrival angles, and that observations are consistent with curvature, though with some possible ambiguity with other scattering mechanisms.

A case of concha bullosa mucopyocele in a medieval human skull

The term ‘concha bullosa’ refers to the pneumatisation of the intranasal turbinates. The pneumatisation can occur at any level (superior, middle, inferior), but the term is typically used to describe the aeration of the middle turbinate. This case report concerns a medieval skull from Tomb Chamber Number One in St. Nicholas's Church in Głogów, Poland. The burial dates from the 13th or 14th century. Direct measurements of the skull according to Martin's technique and computed tomography (CT) were made. The skull is from a male whose age was estimated as 40–55 years. In the nasal cavity, a large bony formation with the appearances of a tumor, a lesion of the maxillary sinus wall, and a significant curvature of the nasal septum were found. The CT scan demonstrated changes that could be described as a type IV concha bullosa, according to Krzeski's classification. This anatomical variation was first described by Zuckerkandl in 1893. The symptoms that were often associated with concha bullosa include nasal obstruction or congestion, facial pain, and headache. Concha bullosa can result in recurrent sinusitis, mucocele, or mucopyocele. In the case of the Głogów skull, an extensive lesion and inflammatory changes in the maxillary sinus and destruction of the orbital floor suggests the presence of a mucopyocele that arose from a concha bullosa. Copyright © 2009 John Wiley & Sons, Ltd.

A MULTI-WAVELENGTH SPECTRAL AND POLARIMETRIC STUDY OF THE JET OF 3C 264

We present a comprehensive multiband spectral and polarimetric study of the jet of 3C 264 (NGC 3862). Included in this study are three HST optical and ultraviolet polarimetry data sets, along with new and archival VLA radio imaging and polarimetry, a re-analysis of numerous HST broadband data sets from the near infrared to the far ultraviolet, and a Chandra ACIS-S observation. We investigate similarities and differences between optical and radio polarimetry, in both degree of polarization and projected magnetic field direction. We also examine the broadband spectral energy distribution of both the nucleus and jet of 3C 264, from the radio through the X-rays. From this we place constraints on the physics of the 3C 264 system, the jet and its dynamics. We find significant curvature of the spectrum from the near-IR to ultraviolet, and synchrotron breaks steeper than 0.5, a situation also encountered in the jet of M87. This likely indicates velocity and/or magnetic field gradients and more efficient particle acceleration localized in the faster/higher magnetic field parts of the flow. The magnetic field structure of the 3C 264 jet is remarkably smooth; however, we do find complex magnetic field structure that is correlated with changes in the optical spectrum. We find that the X-ray emission is due to the synchrotron process; we model the jet spectrum and discuss mechanisms for accelerating particles to the needed energies, together with implications for the orientation of the jet under a possible spine-sheath model.

Demonstration of Postoperative Effectiveness in Ventral Lengthening Using a Tunica Vaginalis Flap for Severe Penile Curvature With Hypospadias

To evaluate the postoperative effectiveness of ventral lengthening with a tunica vaginalis flap. Correcting penile curvature is an essential step in proximal hypospadias surgery. It is logical to lengthen the ventral radius using a graft; however, penile curvature would recur owing to a graft contracture with inadequate vascularization. Although a tunica vaginalis is considered a suitable material to be used as a flap instead of a graft, clinical application of this technique is uncommon. Information regarding the usefulness and effectiveness of this procedure is required. Between 2003 and 2008, we repaired 146 patients with hypospadias and the urethral plate was transected in 39 patients because of severe curvature. Significant severe curvature persisting even after transection of the plate was corrected with ventral corporeal lengthening procedures using a tunica vaginalis flap in 15 patients and postoperative results were evaluated. Straight penile erection was identified in all 15 boys at home by their parents. In 7 of the 15 boys, artificial erection was performed at the time of additional surgery; 5 degrees of curvature was found in 2 patients and 0 degree in 5. At the second session of surgery, we observed that penile straightening was maintained without recurrence of curvature. Additionally, the area in which the tunica vaginalis flap was placed on the ventrum did not contract. Therefore, lengthening the ventral aspect using a tunica vaginalis flap might be an important alternative for correction of severe penile curvature in hypospadias surgery.

Peyronie’s surgery: Graft choices and outcomes

Peyronie's disease (PD), a localized fibrosis of the tunica albuginea surrounding the penile corpora, results in penile curvature and sexual dysfunction. Men with significant penile curvature and satisfactory erectile function are often treated with plaque incision or excision and grafting. The advantages and disadvantages of various grafting materials have long been debated. Graft materials can be divided into three categories: autologous tissue harvested from the patient's body, allograft or xenograft from another person or species, and synthetic grafts. Despite groundbreaking advances in physiology, synthetic materials, and tissue engineering, the ideal graft material has yet to be established. This review presents and discusses the variety of graft materials available for the surgical correction of PD. For this purpose, a MEDLINE search was conducted on PD until May 2009.

A new perspective on supersymmetric inflation

We consider supersymmetric inflation with the hybrid-type potential. In the absence of the symmetry that forbids Hubble-induced mass terms, the inflaton mass will be as large as the Hubble scale during inflation. We consider gravitational decay of the trigger field as the least decay mode and find that the damping caused by the dissipation can dominate the friction of the inflaton when the heavy trigger field is coupled to the inflaton. The dissipative damping provides a solution to the traditional η problem without introducing additional symmetry and interactions. Considering the spatial inhomogeneities of the dissipative coefficient, we find that modulated inflation (modulation of the inflaton velocity) can create significant curvature perturbations.

Classifying bowhead whale call types using linear discrimination function analysis and neural networks.

Bowhead whale calls are typically divided into five categories: upsweeps, downsweeps, U and N shaped undulated calls, and complex. The frequency range, duration, and details of the frequency modulation of these calls vary considerably, even within the same call type, creating difficulties when using matched-filtering or spectrogram correlation methods. A manually reviewed test dataset has been assembled that contains examples organized by call category and signal-to-noise ratio. Using a combination of contour tracing techniques, various features were extracted, including slope, curvature, number of inflection points, and the time of the first inflection point normalized by duration. Both linear discriminant functions and a feed-forward neural network were applied to discern appropriate decision boundaries for optimum statistical classifiers. The use of linear discriminant functions resulted in a 70% good classification for all classes except for the n-shaped calls. The neural networks improved the performance to 81% for upsweeps and downsweeps but had trouble classifying calls with significant curvature. A partial explanation for the classification difficulties stems from subjective definitions of what constitutes an inflection. Results of applying the trained classifiers to bulk data collected in 2008 will be presented. [Work supported by Shell Exploration and Production Company.]

Curvature Generation and Pressure Profile Modulation in Membrane by Lysolipids: Insights from Coarse-Grained Simulations

Although many membrane additives are known to modulate the activities of membrane proteins via perturbing the properties of lipid membrane, the underlying mechanism is often not precisely understood. In this study, we investigate the impact of asymmetrically incorporating single-tailed lysophosphatidylcholine (LPC) into a membrane bilayer using coarse-grained molecular dynamics simulations. Using a simple computational protocol designed to approximately mimic a micropipette setting, we show that asymmetric incorporation of LPC can lead to significant curvature in a bilayer. Detailed analysis of geometrical and mechanical properties (pressure profile) of the resulting mound structure indicates that the degree of pressure profile perturbation is determined not by the local curvature per se but by the packing of lipid headgroups (i.e., area-per-lipid). The findings help provide a concrete basis for understanding the activation mechanism of mechanosensitive channels by asymmetric incorporation of LPC into membrane patches in patch-clamp experiments. The calculated local pressure profiles are valuable to the construction of realistic membrane models for the analysis of mechanosensation in a continuum mechanics framework.

Effective reflection coefficients for curved interfaces in transversely isotropic media

Plane-wave reflection coefficients (PWRCs) are routinely used in amplitude-variation-with-offset analysis and for generating boundary data in Kirchhoff modeling. However, the geometrical-seismics approximation based on PWRCs becomes inadequate in describing reflected wavefields at near- and postcritical incidence angles. Also, PWRCs are derived for plane interfaces and break down in the presence of significant reflector curvature. Here, we discuss effective reflection coefficients (ERCs) designed to overcome the limitations of PWRCs for multicomponent data from heterogeneous anisotropic media. We represent the reflected wavefield in the immediate vicinity of a curved interface by a generalized plane-wave decomposition, which approximately reduces to the conventional Weyl-type integral computed for an apparent source location. The ERC then is obtainedas the ratio of the reflected and incident wavefields at each point of the interface. To conduct diffraction modeling, we combine ERCs with the tip-wave superposition method (TWSM), extended to elastic media. This methodology is implemented for curved interfaces that separate an isotropic incidence half-space and a transversely isotropic (TI) medium with the symmetry axis orthogonal to the reflector. If the interface is plane, ERCs generally are close to the exact solution, sensitive to the anisotropy parameters and source-receiver geometry. Numerical tests demonstrate that the difference between ERCs and PWRCs for typical TI models can be significant, especially at low frequencies and in the postcritical domain. For curved interfaces, ERCs provide a practical approximate tool to compute the reflected wavefield. We analyze the dependence of ERCs on reflector shape and demonstrate their advantages over PWRCs in 3D diffraction modeling of PP and PS reflection data.

Further development of a multimodal pushover analysis procedure for seismic assessment of bridges

AbstractAn improvement is first suggested to the modal pushover analysis (MPA) procedure for bridges initially proposed by the writers (Earthquake Engng Struct. Dyn. 2006; 35(11):1269–1293), the key idea being that the deformed shape of the structure responding inelastically to the considered earthquake level is used in lieu of the elastic mode shape. The proposed MPA procedure is then verified by applying it to two actual bridges. The first structure is the Krystallopigi bridge, a 638 m‐long multi‐span bridge, with significant curvature in plan, unequal pier heights, and different types of pier‐to‐deck connections. The second structure is a 100 m‐long three‐span overpass bridge, typical in modern motorway construction in Europe, which, although ostensibly a regular structure, is found to exhibit a rather unsymmetric response in the transverse direction, mainly due to torsional irregularity. The bridges are assessed using response spectrum, ‘standard’ pushover (SPA), and MPA, and finally using non‐linear response history analysis (NL‐RHA) for a number of spectrum‐compatible motions. The MPA provided a good estimate of the maximum inelastic deck displacement for several earthquake intensities. The SPA on the other hand could not predict well the inelastic deck displacements of bridges wherever the contribution of the first mode to the response of the bridge was relatively low. Copyright © 2009 John Wiley & Sons, Ltd.

MULTIYEAR STUDY OF MULTIVARIATE LINEAR AND NONLINEAR PHENOTYPIC SELECTION ON FLORAL TRAITS OF HUMMINGBIRD-POLLINATEDSILENE VIRGINICA

Pollination syndromes suggest that convergent evolution of floral traits and trait combinations reflects similar selection pressures. Accordingly, a pattern of selection on floral traits is expected to be consistent with increasing the attraction and pollen transfer of the important pollinator. We measured individual variation in six floral traits and yearly and lifetime total plant seed and fruit production of 758 plants across nine years of study in natural populations of Ruby-Throated Hummingbird-pollinated Silene virginica. The type, strength, and direction of selection gradients were observed by year, and for two cohorts selection was estimated through lifetime maternal fitness. Positive directional selection was detected on floral display height in all years of study and stigma exsertion in all years but one. Significant quadratic and correlational selection gradients were rare. However, a canonical analysis of the gamma matrix indicated nonlinear selection was common; if significant curvature was detected it was convex with one exception. Our analyses demonstrated selection favored trait combinations and the integration of floral features of attraction and pollen transfer efficiency that were consistent with the hummingbird pollination syndrome.

Variability in aerosol optical and physical characteristics over the Bay of Bengal and the Arabian Sea deduced from Ångström exponents

Spectral distribution of aerosol optical depths (AODs) measured in the 0.4–0.875 μm wavelength region using a Sun photometer over Bay of Bengal and Arabian Sea during the 2006 premonsoon season are analyzed to obtain more interesting information on the physical and optical characteristics of aerosols. Examination of spectral AODs measured over the Bay of Bengal and the Arabian Sea by deriving the Ångström exponent (α) for the entire spectral range (0.4–0.875 μm), α for different spectral ranges, and second derivative (α′) showed that the aerosol size distribution is of mixed type or bimodal with contributions from fine and coarse modes. The α‐AOD relationships in short (0.4–0.5 μm), long (0.65–0.9 μm), and full (0.4–0.9 μm) spectral ranges determined for various aerosol models (urban, maritime clean, maritime polluted, and desert) suggest that the α‐AOD relationship can vary depending on whether the size distribution is unimodal, mixed type, or bimodal, similar to the results obtained for measured AOD spectra. Significant curvature in the ln AOD versus ln λ is observed which causes spectral variation in α derived in different spectral ranges. Over the Bay of Bengal for 76% of AOD spectra, α2 − α1 is >1, suggesting the presence of fine‐mode aerosols from a wide variety of fine‐mode fractions or a mixture of modes, while over the Arabian Sea, α2 − α1 is <1 for 84% of AOD spectra, clearly indicating the dominance of coarse‐mode aerosols. These characteristics can be used in modeling the regional and seasonal aerosol radiative effects and in remote sensing.

Water entry of spinning spheres

The complex hydrodynamics of water entry by a spinning sphere are investigated experimentally for low Froude numbers. Standard billiard balls are shot down at the free surface with controlled spin around one horizontal axis. High-speed digital video sequences reveal unique hydrodynamic phenomena which vary with spin rate and impact velocity. As anticipated, the spinning motion induces a lift force on the sphere and thus causes significant curvature in the trajectory of the object along its descent, similar to a curveball pitch in baseball. However, the splash and cavity dynamics are highly altered for the spinning case compared to impact of a sphere without spin. As spin rate increases, the splash curtain and cavity form and collapse asymmetrically with a persistent wedge of fluid emerging across the centre of the cavity. The wedge is formed as the sphere drags fluid along the surface, due to the no-slip condition; the wedge crosses the cavity in the same time it takes the sphere to rotate one-half a revolution. The spin rate relaxation time plateaus to a constant for tangential velocities above half the translational velocity of the sphere. Non-dimensional time to pinch off scales with Froude number as does the depth of pinch-off; however, a clear mass ratio dependence is noted in the depth to pinch off data. A force model is used to evaluate the lift and drag forces on the sphere after impact; resulting forces follow similar trends to those found for spinning spheres in oncoming flow, but are altered as a result of the subsurface air cavity. Images of the cavity and splash evolution, as well as force data, are presented for a range of spin rates and impact speeds; the influence of sphere density and diameter are also considered.

Content-based image retrieval using visually significant point features

This paper presents a new image retrieval scheme using visually significant point features. The clusters of points around significant curvature regions (high, medium, and weak type) are extracted using a fuzzy set theoretic approach. Some invariant color features are computed from these points to evaluate the similarity between images. A set of relevant and non-redundant features is selected using the mutual information based minimum redundancy-maximum relevance framework. The relative importance of each feature is evaluated using a fuzzy entropy based measure, which is computed from the sets of retrieved images marked relevant and irrelevant by the users. The performance of the system is evaluated using different sets of examples from a general purpose image database. The robustness of the system is also shown when the images undergo different transformations.

The perception of 3-D shape from shadows cast onto curved surfaces

In a natural environment, cast shadows abound. Objects cast shadows both upon themselves and upon background surfaces. Previous research on the perception of 3-D shape from cast shadows has only examined the informativeness of shadows cast upon flat background surfaces. In outdoor environments, however, background surfaces often possess significant curvature (large rocks, trees, hills, etc.), and this background curvature distorts the shape of cast shadows. The purpose of this study was to determine the extent to which observers can “discount” the distorting effects of curved background surfaces. In our experiments, observers viewed deforming or static shadows of naturally shaped objects, which were cast upon flat and curved background surfaces. The results showed that the discrimination of 3-D object shape from cast shadows was generally invariant over the distortions produced by hemispherical background surfaces. The observers often had difficulty, however, in identifying the shadows cast onto saddle-shaped background surfaces. The variations in curvature which occur in different directions on saddle-shaped background surfaces cause shadow distortions that lead to difficulties in object recognition and discrimination.

Turbulent Stresses and Secondary Currents in a Tidal-Forced Channel with Significant Curvature and Asymmetric Bed Forms

Acoustic Doppler current profilers are deployed to measure both the mean flow and turbulent properties in a channel with significant curvature. Direct measurements of the Reynolds stress show a significant asymmetry over the tidal cycle where stresses are enhanced during the flood tide and less prominent over the ebb tide. This asymmetry is corroborated by logarithmic fits using 10 min averaged velocity data. A smaller yet similar tendency asymmetry in drag coefficient is inferred by fitting the velocity and estimated large-scale pressure gradient to a one-dimensional along-channel momentum balance. This smaller asymmetry is consistent with recent modeling work simulating regional flows in the vicinity of the study site. The asymmetry in drag suggests the importance of previously reported bed forms for this channel and demonstrates spatial and temporarily variations in bed stress. Secondary circulation patterns observed in a relatively straight section of channel appear driven by local curvature rather th...

Particle trajectory calculations with a two‐step three‐time level semi‐Lagrangian scheme well suited for curved flows

AbstractThis study proposes a new two‐step three‐time level semi‐Lagrangian scheme for calculation of particle trajectories. The scheme is intended to yield accurate determination of the particle departure position, particularly in the presence of significant flow curvature. Experiments were performed both for linear and non‐linear idealized advection problems, with different flow curvatures. Results for simulations with the proposed scheme, and with three other semi‐Lagrangian schemes, and with an Eulerian method are presented. In the linear advection problem the two‐step three‐time level scheme produced smaller root mean square errors and more accurate replication of the angular displacement of a Gaussian hill than the other schemes. In the non‐linear advection experiments the proposed scheme produced, in general, equal or better conservation of domain‐averaged quantities than the other semi‐Lagrangian schemes, especially at large Courant numbers. In idealized frontogenesis simulations the scheme performed equally or better than the other schemes in the representation of sharp gradients in a scalar field. The two‐step three‐time level scheme has some computational overhead as compared with the other three semi‐Lagrangian schemes. Nevertheless, the additional computational effort was shown to be worthwhile, due to the accuracy obtained by the scheme in the experiments with large time steps. The most remarkable feature of the scheme is its robustness, since it performs well both for small and large Courant numbers, in the presence of weak as well strong flow curvatures. Copyright © 2009 John Wiley & Sons, Ltd.

Numerical Simulation of Modal Vibration Response of Wavy Carbon Nanotubes

The potential use of carbon nanotubes (CNTs) in applications such as reinforcing materials in nanocomposites has motivated interest in the measurement of their mechanical properties. Several researchers have used the experimentally measured resonance frequencies of CNTs, along with classical beam theory for straight beams to `back out' CNT modulus values. However, from photomicrographic images of CNTs, it is clear that they are not straight, and that they typically have significant waviness or curvature associated with them. This research involves the development of carbon nanotube models using the finite element (FE) approach and the benchmarking of the developed models against results from other models and experiments. Subsequently, the FE models were used to study the effect of waviness and aspect ratio on the modal vibration response of CNTs, so that a better understanding of the characterization of their mechanical properties can be established. It was found that significant errors in `backed out' modulus values of CNTs can occur when waviness is not accounted for in modal analysis. For example, with a change in waviness factor (amplitude of waviness divided by the projected length of the CNT) from 0 to 0.6, frequency values can change by 29% for the fundamental mode, and the corresponding change in the `backed out' modulus from the straight beam equation can be as high as 66%. The analysis of vibrating CNTs is also important in studies of the sonication process for improving dispersion of CNTs in manufacturing of nanocomposites.

The distribution of range sizes of native and alien plants in four European countries and the effects of residence time

ABSTRACTAim Do the statistical distributions of range sizes of native and alien species differ? If so, is this because of residence time effects? And can such effects indicate an average time to a maximum?Location Ireland, Britain, Germany and the Czech Republic.Methods The data are presence or absence of higher plants in mapping units of 100 km2(Ireland and Britain) orc. 130 km2(Germany and the Czech Republic) in areas varying from 79 to 357 thousand km2. Logit transforms of range sizes so defined were tested for normality, and examined by ANOVA, and by loess, ordinary least square (OLS) and reduced major axis regressions.Results Current range sizes, in logits, are near normally distributed. Those of native plants are larger than those of naturalized neophytes (plants introduced since 1500ad) and much larger than those of casual neophytes. Archaeophytes (introduced earlier) have range sizes slightly larger than natives, except in Ireland. Residence time, the time since an invasive species arrived in the wild at a certain place, affects range sizes. The relationships of the range of naturalized neophytes to residence time are effectively straight in all four places, showing no significant curvature or asymptote back to 1500, though there are few records between 1500 and 1800. The relationships have anr2of only about 10%. Both OLS regressions and reduced major axes can be used to estimate the time it takes for the range of a naturalized neophyte to reach a maximum.Main conclusions Established neophytes have smaller range size distributions than natives probably because many have not yet reached their maximum. We estimate it takes at least 150 years, possibly twice that, on average, for the maximum to be reached in areas of the order of 105km2. Policy needs to allow for the variation in rates of spread and particularly the long time needed to fill ranges. Most naturalized neophytes are still expanding their ranges in Europe.

Imprint of Inhomogeneous Hydrogen Reionization on the Temperature Distribution of the Intergalactic Medium

We study the impact of inhomogeneous hydrogen reionization on the thermal evolution of the intergalactic medium (IGM) using hydrodynamic + radiative transfer simulations where reionization is completed either early (z ~ 9) or late (z ~ 6). In general, we find that low-density gas near large-scale overdensities is ionized and heated earlier than gas in the large-scale, underdense voids. Furthermore, at a later time the IGM temperature is inversely related to the reionization redshift because gas that is heated earlier has more time to cool through adiabatic expansion and Compton scattering. Thus, at the end of reionization the median temperature-density relation is an inverted power-law with slope gamma-1 ~ -0.2, in both models. However, at fixed density, there is up to order unity scatter in the temperature due to the distribution of reionization redshifts. Because of the complex equation-of-state, the evolved IGM temperature-density relations for the redshift range 4 < z < 6 can still have significant curvature and scatter. These features must be taken into account when interpreting the Lyman alpha absorption in high redshift quasar spectra.