Shear Peaks Research Articles

FE analysis of single-lap adhesive joints with tapered adherends

Adhesive joints are becoming increasingly popular in various industrial sectors. However, in spite of numerous recent studies in literature, the design phase of the adhesive joint is still challenging. The main issue in the design phase is the determination of the stress distribution in the adhesive layer under external mechanical loads. In the present study, a classical adhesive joint is analysed in comparison to its modified geometric configuration (i.e. tapered) aimed at reducing the magnitude of stress peaks. In particular, a single-lap joint with steel adherends bonded with a commercial epoxy adhesive is analysed. A 3D FE analysis is conducted to determine the distribution of normal and shear stresses in the mid-plane of the adhesive layer. The results obtained from the present study show that the inclusion of a small taper angle (i.e. 5°) leads to a remarkable reduction of normal stresses (up to 30%) compared to the classical configuration. It is observed that the further increase of the taper angle (up to 15°) does not lead to significant reductions of the stress peaks. The trend in shear stresses, on the other hand, is in contrast: an increase in the taper angle leads to an increase in the shear peaks. The method of tapering the adherends is effective in reducing the normal stresses, which are responsible for triggering the failure in the adhesive joint.

KiDS-450: cosmological constraints from weak-lensing peak statistics – II: Inference from shear peaks using N-body simulations

We study the statistics of peaks in a weak lensing reconstructed mass map of the first 450 square degrees of the Kilo Degree Survey. The map is computed with aperture masses directly applied to the shear field with an NFW-like compensated filter. We compare the peak statistics in the observations with that of simulations for various cosmologies to constrain the cosmological parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$, which probes the ($\Omega_{\rm m}, \sigma_8$) plane perpendicularly to its main degeneracy. We estimate $S_8=0.750\pm0.059$, using peaks in the signal-to-noise range $0 \leq {\rm S/N} \leq 4$, and accounting for various systematics, such as multiplicative shear bias, mean redshift bias, baryon feedback, intrinsic alignment, and shear-position coupling. These constraints are $\sim25\%$ tighter than the constraints from the high significance peaks alone ($3 \leq {\rm S/N} \leq 4$) which typically trace single-massive halos. This demonstrates the gain of information from low-S/N peaks. However we find that including ${\rm S/N} < 0$ peaks does not add further information. Our results are in good agreement with the tomographic shear two-point correlation function measurement in KiDS-450. Combining shear peaks with non-tomographic measurements of the shear two-point correlation functions yields a $\sim20\%$ improvement in the uncertainty on $S_8$ compared to the shear two-point correlation functions alone, highlighting the great potential of peaks as a cosmological probe.

X-Ray Temperatures, Luminosities, and Masses from XMM-Newton Follow-upof the First Shear-selected Galaxy Cluster Sample∗

Abstract We continue the study of the first sample of shear-selected clusters from the initial 8.6 square degrees of the Deep Lens Survey (DLS); a sample with well-defined selection criteria corresponding to the highest ranked shear peaks in the survey area. We aim to characterize the weak lensing selection by examining the sample’s X-ray properties. There are multiple X-ray clusters associated with nearly all the shear peaks: 14 X-ray clusters corresponding to seven DLS shear peaks. An additional three X-ray clusters cannot be definitively associated with shear peaks, mainly due to large positional offsets between the X-ray centroid and the shear peak. Here we report on the XMM-Newton properties of the 17 X-ray clusters. The X-ray clusters display a wide range of luminosities and temperatures; the L X −T X relation we determine for the shear-associated X-ray clusters is consistent with X-ray cluster samples selected without regard to dynamical state, while it is inconsistent with self-similarity. For a subset of the sample, we measure X-ray masses using temperature as a proxy, and compare to weak lensing masses determined by the DLS team. The resulting mass comparison is consistent with equality. The X-ray and weak lensing masses show considerable intrinsic scatter (∼48%), which is consistent with X-ray selected samples when their X-ray and weak lensing masses are independently determined.

MASKED AREAS IN SHEAR PEAK STATISTICS: A FORWARD MODELING APPROACH

ABSTRACT The statistics of shear peaks have been shown to provide valuable cosmological information beyond the power spectrum, and will be an important constraint of models of cosmology in forthcoming astronomical surveys. Surveys include masked areas due to bright stars, bad pixels etc., which must be accounted for in producing constraints on cosmology from shear maps. We advocate a forward-modeling approach, where the impacts of masking and other survey artifacts are accounted for in the theoretical prediction of cosmological parameters, rather than correcting survey data to remove them. We use masks based on the Deep Lens Survey, and explore the impact of up to 37% of the survey area being masked on LSST and DES-scale surveys. By reconstructing maps of aperture mass the masking effect is smoothed out, resulting in up to 14% smaller statistical uncertainties compared to simply reducing the survey area by the masked area. We show that, even in the presence of large survey masks, the bias in cosmological parameter estimation produced in the forward-modeling process is ≈1%, dominated by bias caused by limited simulation volume. We also explore how this potential bias scales with survey area and evaluate how much small survey areas are impacted by the differences in cosmological structure in the data and simulated volumes, due to cosmic variance.

Imprints of primordial non-Gaussianity on the number counts of cosmic shear peaks

We studied the effect of primordial non-Gaussianity with varied bispectrum shapes on the number counts of signal-to-noise ratio peaks in wide-field cosmic shear maps. The two cosmological contributions to this particular weak lensing statistic, namely the chance projection of Large Scale Structure (LSS) and the occurrence of real, cluster-sized dark matter haloes, have been modelled semianalytically, thus allowing to easily introduce the effect of non-Gaussian initial conditions. We performed a Fisher matrix analysis by taking into account the full covariance of the peak counts in order to forecast the joint constraints on the level of primordial non-Gaussianity and the amplitude of the matter power spectrum that are expected from future wide-field imaging surveys. We find that positive-skewed non-Gaussianity increases the number counts of cosmic shear peaks, more so at high signal-to-noise ratio values, where the signal is mostly dominated by massive clusters as expected. The increment is at the level of ∼1 per cent for fNL= 10 and ∼10 per cent for fNL= 100 for a local shape of the primordial bispectrum, while different bispectrum shapes give generically a smaller effect. For a future survey on the model of the proposed ESA space mission Euclid and by avoiding the strong assumption of being capable of distinguishing the weak-lensing signal of galaxy clusters from the chance projection of LSSs, we forecast a 1σ error on the level of non-Gaussianity of ∼30–40 for the local and equilateral models, and of ∼100–200 for the less explored enfolded and orthogonal bispectrum shapes.

WEAK-LENSING PEAK FINDING: ESTIMATORS, FILTERS, AND BIASES

Large catalogs of shear-selected peaks have recently become a reality. In order to properly interpret the abundance and properties of these peaks, it is necessary to take into account the effects of the clustering of source galaxies, among themselves and with the lens. In addition, the preferred selection of lensed galaxies in a flux- and size-limited sample leads to fluctuations in the apparent source density which correlate with the lensing field (lensing bias). In this paper, we investigate these issues for two different choices of shear estimators which are commonly in use today: globally-normalized and locally-normalized estimators. While in principle equivalent, in practice these estimators respond differently to systematic effects such as lensing bias and cluster member dilution. Furthermore, we find that which estimator is statistically superior depends on the specific shape of the filter employed for peak finding; suboptimal choices of the estimator+filter combination can result in a suppression of the number of high peaks by orders of magnitude. Lensing bias generally acts to increase the signal-to-noise \nu of shear peaks; for high peaks the boost can be as large as \Delta \nu ~ 1-2. Due to the steepness of the peak abundance function, these boosts can result in a significant increase in the abundance of shear peaks. A companion paper (Rozo et al., 2010) investigates these same issues within the context of stacked weak lensing mass estimates.

Numerical investigation of transient contraction flows for worm-like micellar systems using Bautista–Manero models

This study is concerned with the numerical modelling of the Modified Bautista–Manero (MBM) model, for both steady-state and transient solutions in planar 4:1 contraction flow. This model was proposed to represent the structured composition and behaviour of worm-like micellar systems which have importance in industrial oil-reservoir recovery applications. A parameter sensitivity analysis for the rheology of this model is presented in both transient and steady response, covering pure shear and uniaxial extension. In addition, some features in evolutionary flow-structure are demonstrated in contraction flows due to the influence and imposition of start-up transient boundary conditions. The different effects of various model parameter choices are described through transient field response, stress and viscosity fields in the contraction flow setting. Distinction may be drawn between fluid response in the strong/moderate extension hardening regimes by matching both steady-state and transient shear and extensional viscosity peaks, contrasting between micellar (MBM) models against network-based counterparts Phan-Thien/Tanner (PTT). Simulations are performed with a hybrid finite volume/element algorithm. The momentum and continuity equations are solved by a Taylor–Galerkin/pressure-correction finite element method, whilst the constitutive equation is dealt with by a cell-vertex finite volume algorithm.

Observations of the Transition Layer

Abstract The transition layer is the poorly understood interface between the stratified, weakly turbulent interior and the strongly turbulent surface mixed layer. The transition layer displays elevated thermohaline variance compared to the interior and maxima in current shear, vertical stratification, and potential vorticity. A database of 91 916 km or 25 426 vertical profiles of temperature and salinity from SeaSoar, a towed vehicle, is used to define the transition layer thickness. Acoustic Doppler current measurements are also used, when available. Statistics of the transition layer thickness are compared for 232 straight SeaSoar sections, which range in length from 65 to 1129 km with typical horizontal resolution of ∼4 km and vertical resolution of 8 m. Transition layer thicknesses are calculated in three groups from 1) vertical displacements of the mixed layer base and of interior isopycnals into the mixed layer; 2) the depths below the mixed layer depth of peaks in shear, stratification, and potential vorticity and their widths; and 3) the depths below or above the mixed layer depth of extrema in thermohaline variance, density ratio, and isopycnal slope. From each SeaSoar section, the authors compile either a single value or a median value for each of the above measures. Each definition yields a median transition layer thickness from 8 to 24 m below the mixed layer depth. The only exception is the median depth of the maximum isopycnal slope, which is 37 m above the mixed layer base, but its mode is 15–25 m above the mixed layer base. Although the depths of the stratification, shear, and potential vorticity peaks below the mixed layer are not correlated with the mixed layer depth, the widths of the shear and potential vorticity peaks are. Transition layer thicknesses from displacements and the full width at half maximum of the shear and potential vorticity peak give transition layer thicknesses from 0.11× to 0.22× the mean depth of the mixed layer. From individual profiles, the depth of the shear peak below the stratification peak has a median value of 6 m, which shows that momentum fluxes penetrate farther than buoyancy fluxes. A typical horizontal scale of 5–10 km for the transition layer comes from the product of the isopycnal slope and a transition layer thickness suggesting the importance of submesoscale processes in forming the transition layer. Two possible parameterizations for transition layer thickness are 1) a constant of 11–24 m below the mixed layer depth as found for the shear, stratification, potential vorticity, and thermohaline variance maxima and the density ratio extrema; and 2) a linear function of mixed layer depth as found for isopycnal displacements and the widths of the shear and potential vorticity peaks.

Simultaneous Observation of Longitudinal and Shear Phonons in Solid Glasses by Optical Beating Brillouin Spectroscopy

The propagation of shear acoustic phonons in the solid materials of fused silica and BK7 was observed by optical beating Brillouin spectroscopy in the wavenumber range of 7×104<k<9×105 m-1. Remarkably improved detection sensitivity of the optical beating Brillouin spectroscopy system enabled the simultaneous observation of longitudinal and shear phonons in solid samples. The accurate estimation of the volume and shear elasticities in the isotropic solid material is thus possible. The measured ratio between the intensities of longitudinal and shear peaks is well explained by the equipartition law of the thermal fluctuation energy to these independent phonon modes with different elastic susceptibility.

A Numerical Study of Hurricane Erin (2001). Part I: Model Verification and Storm Evolution

Abstract The fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) is used to simulate Hurricane Erin (2001) at high resolution (4-km spacing) from its early development as a tropical depression on 7 September 2001, through a period of rapid intensification into a strong hurricane (8–9 September), and finally into a stage during which it maintains its intensity on 10 September. These three stages of formation, intensification, and maintenance in the simulation are in good agreement with the observed evolution of Erin. The simulation shows that during the formation and early portions of the intensification stages, intensification is favored because the environmental wind shear is weak and the system moves over a warm tongue of water. As Erin intensifies, the wind shear gradually increases with the approach of an upper-level trough and strengthening of a low-level high pressure system. By 10 September, the wind shear peaks and begins to decrease, the storm moves over slightly cooler waters, and the intensification ends. Important structural changes occur at this time as the outer precipitation shifts from the northeastern and eastern sides to the western side of the eye. A secondary wind maximum and an outer eyewall begin to develop as precipitation begins to surround the entire eye. The simulation is used to investigate the role of vertical wind shear in the changes of the precipitation structure that took place between 9 and 10 September by examining the effects of changes in storm-relative flow and changes in the shear-induced tilt. Qualitative agreement is found between the divergence pattern and advection of vorticity by the relative flow with convergence (divergence) generally associated with asymmetric inflow (outflow) in the eyewall region. The shift in the outer precipitation is consistent with a shift in the low-level relative inflow from the northeastern to the northwestern side of the storm. The changes in the relative flow are associated with changes in the environmental winds as the hurricane moves relative to the upper trough and the low-level high pressure system. Examination of the shear-induced tilt of the vortex shows that the change in the tilt direction is greater than that of the shear direction as the tilt shifts from a northerly orientation to northwesterly. Consistent with theory for adiabatic vortices, the maximum low-level convergence and upper-level divergence (and the maximum upward motion) occurs in the direction of tilt. Consequently, both mechanisms may play roles in the changes in the precipitation pattern.

Schubspannungsbomben in Faserverbunden

AbstractAuch bei optimaler äußerer Bauteilgestalt mit gleichförmiger Spannungsverteilung können lokale Schubspannungsmaxima zur Entstehung von Schubrissen führen, insbesondere wenn der maximale Schub entlang des Faserverlaufes verläuft.Bäume können einmal angelegte Fasern nicht an neu auftretende Schubmaxima anpassen und sind daher eher schubspannungsgefährdet als der Knochen, der seine Innenarchitektur auch nachträglich noch an Laständerungen anpassen kann.Auch die Umlenkung des Kraftflusses um Kerben kann lokale Schubmaxima bewirken, die gleichsam als Schubkerbspannungen zu betrachten sind, der Kerbe aber nicht direkt anliegen müssen.

Effects of fluid viscosity on shear‐wave attenuation in partially saturated sandstone

Shear‐wave attenuation and velocity have been measured in the kiloHertz frequency range at temperatures varying from −80°C to 80°C in a sample of Berea sandstone partially saturated with glycerol. I investigated 7 saturation states ranging from 0 to 62 percent of the pore space. Plots of attenuation versus temperature show squirt and viscous shear peaks, even at low saturation. Their amplitudes and half‐widths increase with increasing saturation. The maxima of the peaks progressively move to higher temperatures (about 4°C for viscous shear peak and 30°C for squirt peak) with increasing saturation from 7 to 62 percent. The velocity dispersion between −80°C and 80°C progressively increases from 700 to 1200 m/s with increasing saturation from 7 to 62 percent. By introducing the crack saturation parameter, a simple viscoelastic model based on O’Connell and Budiansky and using a Cole‐Cole distribution of cracks, is proposed for calculating the shear modulus in partially saturated rocks. This model partially interprets the experimental data.