Small Central Hole Research Articles

Elastic-Plastic Finite Element New Method for Lower Bound Shakedown Analysis

Shakedown analysis methods have been well developed to determine the shakedown limit load of structures under various repeated loading situations. However, to take the limited kinematic hardening, geometric effect, and deformation into account, further research is required. A new numerical method is proposed for the lower bound shakedown analysis that applies the extended static shakedown theorem for limited kinematic hardening. The new method determines the shakedown limit load with two kinds of elastic-plastic finite element (FE) analyses: (1) the elastic-plastic loading and unloading analysis is carried out using the hardening model with the actual material parameters and (2) the elastic-perfectly plastic model with ultimate stress as the yield stress is used for the limit analysis. An incremental FE technique for finite strain plasticity is utilized to take the geometric effect into account. Furthermore, the deformation of the structure is monitored by checking the calculated deformation parameters. The method is applied to a square plate with a small central hole subjected to cyclic tensile load. The corresponding physical shakedown experiment of the above square plate was conducted for verification. The numerical result shows a good agreement with the experimental result. The new method provides a valid method for the structural lower bound shakedown analysis taking into account limited kinematic hardening, geometric effect, and deformation.

Pinhole amniotic membrane for peripheral corneal defects in patients with a single eye or low vision.

To describe the efficacy of a new pinhole amniotic membrane placement technique in cases of peripheral epithelial defects in patients with a single eye or low vision in the contrye. This technique is based on a small central hole done with a dermatological 3 to 4mm punch (according to pupillary diameter in mesoscopic conditions) and a continuous suture in the perilimbal cornea to fix the amniotic membrane. We performed this technique in 6 patients. Patients were followed clinical and photographically. No changes in the visual acuity before and after the surgery were observed. During follow-up, a complete re-epithelialization was observed with no need for reinterventions. Amniotic membrane transplantation is a very useful option in patients with persistent epithelial defects; however, its use is limited by the subsequent visual acuity. The use of the pinhole amniotic membrane technique allows us to treat peripheral persistent corneal lesions without modifying patients' visual acuity. This new technique may become especially useful in patients with functional single eye of low vision in the contralateral eye.

Toroidal nuclei of columnar lyotropic chromonic liquid crystals coexisting with an isotropic phase.

Nuclei of ordered materials emerging from the isotropic state usually show a shape topologically equivalent to a sphere; the well-known examples are crystals and nematic liquid crystal droplets. In this work, we explore experimentally and theoretically the toroidal in shape nuclei of columnar lyotropic chromonic liquid crystals coexisting with the isotropic phase. The geometry of these toroids depends strongly on concentrations of the disodium cromoglycate (DSCG) and the crowding agent, polyethylene glycol (PEG). High concentrations of DSCG and PEG result in thick toroids with small central holes, while low concentrations yield thin toroids with wide holes. The multitude of the observed shapes is explained by the balance of bending elasticity and anisotropic interfacial tension.

Observations of the γ-ray-emitting narrow-line Seyfert 1, SBS 0846+513, and its host galaxy

ABSTRACT The γ-ray-emitting galaxy SBS 0846+513 has been classified as a narrow-line Seyfert 1 (NLS1) from its spectroscopy, and on that basis would be thought likely to have a small central black hole hosted in a spiral galaxy. However, very few of the γ-ray NLS1s have high-resolution imaging of their hosts, so it is unknown how the morphology expectation holds up for the γ-emitting class. We have observed this galaxy in the J band with the Large Binocular Telescope’s LUCI1 camera and the ARGOS adaptive optics system. We estimate its black hole mass to lie between $4.2\times 10^7 \le \frac{\rm{\it{ M}}}{\text{M}_\odot } \le 9.7\times 10^7$, using the correlation with bulge luminosity, or $1.9\times 10^7 \le \frac{\rm{\it{ M}}}{\text{M}_\odot } \le 2.4\times 10^7$ using the correlation with Sérsic index. Our favoured estimate is 4.2 × 107 M⊙, putting its mass at the high end of the NLS1 range in general but consistent with others that are γ-ray emitters. These estimates are independent of the broad-line region viewing geometry and avoid any underestimates due to looking down the jet axis. Its host shows evidence of a bulge + disc structure, from the isophote shape and residual structure in the nuclear-subtracted image. This supports the idea that γ-ray NLS1 may be spiral galaxies, like their non-jetted counterparts.

Use of cribriform amplatzer septal occluder in the pediatric population: Feasibility, safety, and technical considerations.

Purpose :Fenestrated atrial septal defects (F-ASDs) in the pediatric population pose a challenge for transcatheter device closure since multiple devices are not preferred in small hearts. Oversizing the Amplatzer Septal Occluder (ASO) to cover the surrounding fenestrations usually distorts the central waist as well as the disc profile and often defeats the purpose. This is a retrospective observational study with an aim to assess the feasibility and safety of cribriform ASO in closing F-ASDs in small children.Methods:Sixteen children with F-ASD who underwent device closure with cribriform ASO were included in the study. The fenestrated septal length (FSL) and the total septal length (TSL) were measured on transesophageal echocardiogram. A device size which was 1.5–2 times the FSL but smaller than the TSL was selected. The defect was closed with a device passed through a relatively centrally placed smaller fenestration.Results:The median age of the cohort was 5 years (2.5–10.5). Majority (14/16) required 25 or 30 mm cribriform ASO. Aneurysmal interatrial septum was seen in most of our patients (11/15). All the patients had successful device implantation. Complete closure of the defect was seen in 11 patients while 5 patients had insignificant residual shunt at a median follow-up of 40 months (1–60 months). There were no other complications.Conclusions:Cribriform ASO can be used safely and effectively in closing F-ASDs in children. Deployment of the device through a small central hole allows covering maximum fenestrations and gives more stability to the device. Residual shunts, although not infrequent, are insignificant.

Intra-day variability of three Seyfert galaxies measured with XMM-Newton

We present and analyze the variability of three Seyfert galaxies on intra-day timescales. We have analyzed in a uniform manner the 38 longest (>30 ks) observations made for NGC 4051, MCG-06–30–15 and NGC 4151 by XMM-Newton between 2000 and 2015. The nuclei were quite active during essentially all of these observations and the overall X-ray fluxes (0.3–10 keV) varied by an order of magnitude. Most of the observations do appear to show characteristic timescales, estimated through their auto-correlation functions, ranging between ∼2.9 ks and ∼45.3 ks. The hard (2–10 keV) and soft (0.3–2.0 keV) bands are very well correlated but consideration of their hardness ratios shows that the sources typically soften during flares. We also provide new estimates of the central black hole masses for these three AGNs that support the hypothesis that Narrow Line Seyfert 1 galaxies have relatively small central black holes.

Multi-functional photonic crystal fiber splitter for the two communication bands

Abstract A compact multi-functional dual core photonic crystal fiber (DC-PCF) is presented and analyzed. The proposed PCF has a small central hole filled with chalcogenide glass ( As 2 S 3 ). Further, the cladding region has six large holes infiltrated by nematic liquid crystal (NLC) in order to enhance the birefringence between the two orthogonal polarized modes. The proposed splitter is analyzed using a full-vectorial finite element method based on COMSOL Multiphysics software with perfectly matched layer boundary condition. The suggested design with a compact device length of 83.0 μm can separate the two polarized beams with bandwidths of 30 nm and 64 nm for x- and y-polarized modes, respectively at a wavelength of 1.55 μm. At the same device length, x-polarized modes with wavelengths of 1.55 and 1.30 μm can be separated with bandwidths of 23 nm and 12 nm, respectively. If the device length is doubled to 166.0 μm, the reported PCF can split the × and y-polarized modes at wavelength of 1.30 μm with bandwidths of 23 nm and 38 nm, respectively. Additionally, the y-polarized modes at λ = 1.55 and 1.30 μm can be separated with bandwidths of 34 nm and 38 nm, respectively at a device length of 166.0 μm. Therefore, the reported PCF can be used as a multi-functional device for polarization or wavelength splitting with good bandwidths and low crosstalks.

Numerical and experimental analysis of hot dry rock fracturing stimulation with high-pressure abrasive liquid nitrogen jet

Abrasive liquid nitrogen (L-nitrogen) jet fracturing is a novel technology, which is expected to be suitable for hot dry rock (HDR) fracturing. In this paper, numerical simulation has been presented to analyze the fluid flow, heat transfer and thermal stresses distribution in HRD fracturing with abrasive L-nitrogen jet. The simulation is carried out with a three-dimensional model in transient state. The low Reynolds number κ-ε model is employed to accurately predict the near wall flow. The heat transfer between L-nitrogen and hot rock on solid-liquid interface is computed by an inverse method of conjugate heat transfer. The thermo-elastic model is used to calculate the thermal stresses distribution in rock. Numerical results indicate that abrasive L-nitrogen jet has a better performance in perforation than abrasive water and supercritical CO2 jet. Great tensile stress distributes in the region near interface, however, its affected depth is limited. This tensile is expected to be favor for fractures generation and growth along perforation direction. Short perforation length can promote the heat transfer on interface. The initial rock temperature has an important influence on values of thermal stresses. Experiments, in which the hot granite specimens with a small hole in center were impacted by L-nitrogen jet, have been conducted to validate the effect of thermal stresses on fracturing. The fractal method is adopt to quantitatively describe the flow and transport capability in rock masses. Experimental results show that numerous thermal cracks were generated on the interface. Rising rock temperature can significantly increase the number and size of thermal cracks and improve the connectivity of fractured rock, which are benefit to fracture initiation during L-nitrogen jet fracturing. The results in this paper would shed light on L-nitrogen jet fracturing for HDR as well as some high-temperature oil reservoirs.

General analytical shakedown solution for structures with kinematic hardening materials

The effect of kinematic hardening behavior on the shakedown behaviors of structure has been investigated by performing shakedown analysis for some specific problems. The results obtained only show that the shakedown limit loads of structures with kinematic hardening model are larger than or equal to those with perfectly plastic model of the same initial yield stress. To further investigate the rules governing the different shakedown behaviors of kinematic hardening structures, the extended shakedown theorem for limited kinematic hardening is applied, the shakedown condition is then proposed, and a general analytical solution for the structural shakedown limit load is thus derived. The analytical shakedown limit loads for fully reversed cyclic loading and non-fully reversed cyclic loading are then given based on the general solution. The resulting analytical solution is applied to some specific problems: a hollow specimen subjected to tension and torsion, a flanged pipe subjected to pressure and axial force and a square plate with small central hole subjected to biaxial tension. The results obtained are compared with those in literatures, they are consistent with each other. Based on the resulting general analytical solution, rules governing the general effects of kinematic hardening behavior on the shakedown behavior of structure are clearly.

Morphological and molecular characterization of the small armoured dinoflagellate Heterocapsa minima (Peridiniales, Dinophyceae)

The dinophycean genus Heterocapsa is of considerable interest as it contains a number of bloom-forming and/or harmful species. Fine structure of organic body scales is regarded as the most important morphological feature for species determination but currently is unknown for the species H. minima described by Pomroy 25 years ago. Availability of a culture of H. minima collected in the south-west of Ireland allowed us to provide important information for this species, including cell size, cell organelle location, thecal plate pattern, body scale fine structure and molecular phylogeny. Light microscopy revealed the presence of one reticulate chloroplast, an elongated centrally located nucleus, and the presence of one pyrenoid surrounded by a starch sheath. Scanning electron microscopy (SEM) of the thecal plate pattern indicated that Pomroy erroneously designated the narrow first cingular plate as a sulcal plate. In addition, SEM revealed as yet unreported details of the apical pore complex and uncommon ornamentations of hypothecal plates. Organic body scales of H. minima were about 400 nm in size, roundish, with a small central hole and one central, six peripheral and three radiating spines. They differ from other body scales described within this genus allowing for positive identification of H. minima. Heterocapsa minima shares gross cell morphological features (hyposome smaller than episome, elongated nucleus in the middle of the cell, one pyrenoid located in the episome on its left side) with H. arctica (both subspecies H. arctica subsp. arctica and H. arctica subsp. frigida), H. lanceolata and H. rotundata. These relationships are reflected in the phylogenetic trees based on LSU and ITS rDNA sequence data, which identified H. arctica (both subspecies), H. rotundata and H. lanceolata as close relatives of H. minima.

Experimental investigation of damping flexural vibrations in plates containing tapered indentations of power-law profile

In the present paper, experimental results are reported on damping flexural vibrations in rectangular plates containing tapered indentations (pits) of power-law profile, with the centres of the indentations covered by a small amount of absorbing material. In the case of quadratic or higher-order profiles, such indentations materialise two-dimensional acoustic ‘black holes’ for flexural waves that can absorb almost 100% of the incident elastic energy. In the present investigation, pits have been made in different locations of rectangular plates, and the corresponding frequency response functions have been measured. It has been found that basic power-law indentations, with no or very small central hole, result in rather low reduction in resonant peak amplitudes, which may be due to the relatively small effective absorption area in this case. To increase the damping efficiency of power-law profiled indentations, this absorption area has been enlarged by increasing the size of the central hole in the pit, while keeping the edges sharp. As expected, such pits, being in fact curved power-law wedges, result in substantially increased damping. When multiple indentations are used, the resultant damping increases substantially, as expected, and may become comparable if not greater than that achieved by one-dimensional wedges of power-law profile.

A simplified technique for shakedown limit load determination of a large square plate with a small central hole under cyclic biaxial loading

A simplified technique for determining the shakedown limit load of a structure was previously developed and successfully applied to benchmark shakedown problems involving uniaxial states of stress (Abdalla et al., 2007a,b,c). In this paper, the simplified technique is further developed to handle cyclic biaxial loading resulting in multi-axial states of stress within the large square plate with a small central hole problem. Two material models are adopted namely: an elastic-linear strain hardening material model obeying Ziegler's linear kinematic hardening (KH) rule and an elastic-perfectly-plastic (EPP) material model. The simplified technique utilizes the finite element (FE) method and employs small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full elastic–plastic cyclic loading FE simulations or conventional iterative elastic techniques. The simplified technique is utilized to generate the shakedown domain for the plate problem subjected to cyclic biaxial tension along its edges. The outcomes of the simplified technique showed very good correlation with the results of analytical solutions as well as full elastic–plastic cyclic loading FE simulations. Material hardening showed no effect on the shakedown domain of the plate in comparison to employing EPP-material.

Backreaction of frame dragging

The backreaction on black holes due to dragging heavy, rather than test, objects is discussed. As a case study, a five-dimensional regular black Saturn system where the central black hole has vanishing intrinsic angular momentum, ${J}^{\mathrm{BH}}=0$, is considered. It is shown that there is a correlation between the sign of two response functions. One is interpreted as a moment of inertia of the black ring in the black Saturn system. The other measures the variation of the black ring horizon angular velocity with the central black hole mass, for fixed ring mass and angular momentum. The two different phases defined by these response functions collapse, for small central black hole mass, to the thin and fat ring phases. In the fat phase, the zero area limit of the black Saturn ring has reduced spin ${j}^{2}>1$, which is related to the behavior of the ring angular velocity. Using the ``gravitomagnetic clock effect,'' for which a universality property is exhibited, it is shown that frame dragging measured by an asymptotic observer decreases, in both phases, when the central black hole mass increases, for fixed ring mass and angular momentum. A close parallelism between the results for the fat phase and those obtained recently for the double Kerr solution is drawn, considering also a regular black Saturn system with ${J}^{\mathrm{BH}}\ensuremath{\ne}0$.

Design Analysis of the Outwater-Murphy Single-Fiber Specimen

A design analysis of the Outwater-Murphy (OM) compression test specimen is presented. The objective is to size the dimensions of the OM specimen for interface fracture toughness testing of glass and carbon fibers in a polymer matrix. A simple fracture mechanics analysis is developed based on mechanics of materials principles assuming linear-elastic behavior of the fiber and matrix. A successful test demands fiber/matrix debonding prior to any other failure mechanisms such as net section yielding, fiber microbuckling and global buckling of the specimen. The analysis of the results indicates that the test should be viable for OM specimens with a small cross section and a small central hole. Tests on E-glass/vinylester specimens were successfully conducted providing a fiber/matrix interface toughness of 38 J/m2, in reasonable agreement with interface toughness data for similar systems determined by other test methods.

Highly birefringent and dichroic photonic crystal VCSEL design

We analyse the possibility to stabilise the polarisation of light emitted by photonic crystal vertical-cavity surface-emitting lasers (PC-VCSELs). We consider two different photonic crystal configurations in a GaAs/AlGaAs VCSEL: with elliptical holes and with selectively enlarged holes and a small central hole. Very large birefringence (∼400GHz) and dichroism (∼7%) are demonstrated for the second PC-VCSEL design.

Design criteria for microstructured-optical-fiber-based surface-plasmon-resonance sensors

Design strategies for microstructured-optical-fiber (MOF-) based surface-plasmon-resonance (SPR) sensors are presented. In such sensors, plasmons on the inner surface of the large metallized channels containing analyte can be excited by a fundamental mode of a single-mode microstructured fiber. Phase matching between a plasmon and a core mode can be enforced by introducing air-filled microstructures into the fiber core. Particularly, in its simplest implementation, the effective refractive index of a fundamental mode can be lowered to match that of a plasmon by introducing a small central hole into the fiber core. Resolution of the MOF-based sensors is demonstrated to be as low as 3×10−5 RIU, where RIU means refractive index unit. The ability to integrate large-size microfluidic channels for efficient analyte flow together with a single-mode waveguide of designable modal refractive index is attractive for the development of integrated highly sensitive MOF-SPR sensors operating at any designable wavelength.

Prediction and Measurement of Fuel Cell Flammability Safety Limits

Leakage of the fuel through a possible crack in the solid electrolyte or in the separator plate of a fuel cell, can cause uncontrolled combustion. An experimental investigation and theoretical prediction are made to simulate the above conditions. A cylindrical combustion chamber is supplied with an axial jet of methane from one side and air (or pure oxygen) jet from the other side to create a counter flow laminar diffusion flame. A disk with a small central hole is installed inside the cylinder perpendicular to its axis. It was found that the quenching distance, between oxidant nozzle and the disk, is of the order of 1.0 mm when oxygen is the oxidant while for air it is about 15 mm. These distances give an upper limit for the oxidant gap size of the fuel cell, based on safety considerations. Moreover, the measurements show that fuel cells are safer when using air as oxidant rather than pure oxygen. A new computer code is developed capable of simulating flow, heat transfer, and chemical reactions in 2D geometries, similar to the above flammability experiments. The governing laminar equations for momentum, mass, and mixture fraction are solved by a numerical iterative algorithm. The computed mixture fraction is used to calculate its dissipation rate. They are then used to access a flamelet library to obtain the local flame properties and/or its possible extinction. This flamelet library is generated separately, based on a 3-step reaction mechanism for CH4. The computed flammability distances for CH4–O2 and CH4–air flames are in reasonable agreement with, though slightly lower than, the corresponding measured quenching distances. This is a result of neglecting thermal radiation in the present combustion model.

On X-ray variability in narrow-line and broad-line active galactic nuclei

We assembled a sample of broad-line and narrow-line active galactic nuclei (AGNs) observed by ASCA, the excess variances of which have been determined. The central black hole masses in this sample can be obtained from the reverberation mapping method and the width of the Hβ emission line. Using the black hole masses and the bolometric luminosity, the Eddington ratio (the ratio of the ionizing luminosity to the Eddington luminosity) can also be obtained. We confirmed the strong anticorrelation between X-ray variability and the central black hole mass found by Lu & Yu. In addition, we found that narrow-line Seyfert 1 galaxies (NLS1s) also follow this relation, with a larger scatter, and that there is only a weak correlation between the X-ray variability and the Eddington ratio, which suggests that rapid variability and narrow lines in NLS1s are mainly due to small central black holes in NLS1s, not the difference of circumnuclear gas around NLS1s. A strong correlation was found between the hard X-ray photon index and the Eddington ratio. If the suggestion of two distinct accretion classes [namely advection-dominated accretion flow (ADAF) and thin disc accretion] in AGNs is correct, the strong correlation between the photon index and the Eddington ratio shows that there exists a kind of two-zone accretion disc, in which the outer zone is a thin disc and the inner zone is an ADAF disc. Otherwise, the accretion process is thin disc accretion and ADAF accretion is not required.

Measurement of Indirect Tensile Strength of Anisotropic Rocks by the Ring Test

This paper presents a new approach, combined with the Boundary Element Method (BEM) analysis and the diametrical compression on a thin disc with a small central hole, referred to as the ring test, for determining the indirect tensile strength of anisotropic rocks. The stress distribution around the hole can be successfully obtained by the proposed single-domain BEM. The complex variable function method was used for conveniently computing the tractions and displacements of a two-dimensional anisotropic body. If we assume that the tensile strength is given by the maximum absolute value of stress in the direction perpendicular to the loaded diameter at the intersection of loaded diameter and the hole, then from the failure load recorded by laboratory testing of ring (disc), the indirect tensile strength of rocks could be obtained. A marble from Hualien (Taiwan) with clearly black-white foliation, which was assumed to be transversely isotropic, was selected to conduct both ring tests and Brazilian tests for evaluating the tensile strength. The variation of the marble tensile strength with the inclination angle of foliation and with the hole size was also investigated. In general, the tensile strength of anisotropic rocks determined by ring test is not a constant, but depends on the elastic properties of rocks, the angle between the planes of rock anisotropy and the loading direction, the diameter of the central hole, and the contact condition of loading.

CO Images of the Central Regions of 20 Nearby Spiral Galaxies

We report a CO(J = 1-0) aperture-synthesis survey of the central regions of 20 nearby spiral galaxies. The sample is selected on the basis of inclination, single-dish CO flux, and lack of significant dynamical perturbation. No selection is made on the basis of their nuclear activity, starburst, or infrared luminosity. The observations have been made using the Nobeyama and Owens Valley millimeter arrays, with typical resolutions of 4'' (300 pc) and 20 km s-1, and sensitivities of ~30 mJy beam-1 for a 20 km s-1 channel. In this paper, we present integrated intensity and mean velocity maps, azimuthally averaged radial distributions, and position-velocity plots. Most galaxies in the sample have scale lengths for the radial CO distribution that are much smaller in the nuclear regions than in the outer disks. Typically, the CO emission falls to 1/e of the central peak value at radii of ~500 pc. This is significantly smaller than the scale lengths for the global CO distributions in the galactic disks. CO position-velocity diagrams exhibit a steep rise in rotation velocity, dV/dr ~ 1 km s-1 pc-1, in the central regions of most galaxies. The CO line width typically reaches ~95% of the overall H I line width within a radius of 1 kpc. This steep rise in the rotation velocity mainly reflects the highly concentrated mass distributions in the galactic centers, though it may well be partly due to noncircular motions in barred galaxies. In a number of galaxies, the position-velocity diagrams show a small central hole (d ≲ 100 pc) in CO emission. In many galaxies, we detect CO clumps of subkiloparsec size which may be giant molecular associations (GMAs). In the Appendix, we demonstrate that small holes at the galactic center can be readily detected in position-velocity diagrams even when they are smaller than the spatial resolution of the data.