Post Geometry Research Articles

Black hole spin estimation of XTE J2012+381 using simultaneous observations of Swift/XRT and NuSTAR

ABSTRACT A sufficiently precise measurement of black hole spin is required to carry out quantitative tests of the Kerr metric and to understand several phenomena related to astrophysical black holes. After 24 yr, XTE J2012+381 again underwent an outburst in 2022 December. In this work, we focused on the measurement of the spin and mass of the black hole candidate XTE J2012+381 using broad-band spectral analysis of X-ray data from Swift/XRT and NuSTAR. Using the relxillCp model, the spin and inclination of the source were found to be $0.883_{-0.061}^{+0.033}$ and $46.2_{-2.0}^{+3.7}$ deg, respectively, for high disc density ($i.e.\,\,10^{20}\,\,\mathrm{cm}^{-3}$). We further test our results for lamp-post geometry using the relxilllpCp model. The spin and inclination of the source were found to be $0.892_{-0.044}^{+0.020}$ and $43.1_{-1.2}^{+1.4}$ deg, respectively. Then ‘continuum-fitting’ method was used for the soft state to estimate the mass of BH and found to be $7.95_{-3.25}^{+7.65}\,\,\mathrm{M}_{\odot }$ and $7.48_{-2.75}^{+5.80}\,\,\mathrm{M}_{\odot }$ for the spin and inclination estimated from the relxillCp and relxilllpCp model, respectively. We used a distance of 5.4 kpc as measured by Gaia using the parallax method. This study also addresses the issue of supersolar iron abundance in XTE J2012+381 using reflionx-based reflection model and found high disc density for the source.

Time resolved spectroscopy of a GRS 1915 + 105 flare during its unusual low state using AstroSat

ABSTRACT Since its discovery in 1992, GRS 1915 + 105 has been among the brightest sources in the X-ray sky. However, in early 2018, it dimmed significantly and has stayed in this faint state ever since. We report on AstroSat and NuSTAR observation of GRS 1915 + 105 in its unusual low/hard state during 2019 May. We performed time-resolved spectroscopy of the X-ray flares observed in this state and found that the spectra can be fitted well using highly ionized absorption models. We further show that the spectra can also be fitted using a highly relativistic reflection dominated model, where for the lamp post geometry, the X-ray emitting source is always very close to the central black hole. For both interpretations, the flare can be attributed to a change in the intrinsic flux, rather than dramatic variation in the absorption or geometry. These reflection dominated spectra are very similar to the reflection dominated spectra reported for active galactic nuclei in their low flux states.

Understanding droplet breakup in a post-array device with sheath-flow configuration.

Microfluidic post-array devices have the potential to generate quasi-monodisperse emulsion droplets with high throughput and dispersed phase fractions by splitting droplets with regularly arranged posts. However, the lack of understanding of post-array devices makes it challenging to predict droplet size and quantitatively evaluate the influence of post geometry, hindering their widespread application. Therefore, we investigated the characteristics of droplet breakup through a post array using a series of devices with sheath-flow configurations, in which the dispersed and continuous flow rates could be flexibly tuned. Using a poly(dimethylsiloxane)-glass device fabricated via soft lithography, we found that the volume ratio of the dispersed phase to the continuous phase significantly affects the droplet size, even when the viscosity ratio is close to one. For the first time, we demonstrated that the effective capillary number calculated from the emulsion viscosity and effect of the dispersed phase fraction consistently describes various experimental results. Furthermore, our flow observations and droplet diameter measurement showed two breakup modes: the size-constant obstruction and shear-induced modes with a power-law correlation similar to droplet splitting in a T-junction. Thus, the power-law correlation in microfluidic droplet splitting successfully expresses the droplet generation characteristics in post-array devices. A combination of effective viscosity correction and curve fitting allowed us to evaluate the influence of the material and post-geometry on droplet generation characteristics. This study contributes to the understanding of droplet breakup in post-array devices and extends their unique droplet generation properties to include high-throughput, high-fraction, robust, and continuous emulsification processes.

Experimental Investigation of Material and Geometry Effects on Microwave Breakdown of Evanescent-Mode Cavity Resonators

This article presents an experimental investigation of microwave breakdown in evanescent-mode cavity resonators with different surface materials and post geometries, aiming at unveiling the role of secondary electron emission (SEE), attachment, and diffusion on microwave breakdown in inhomogeneous electric fields. The breakdown power of six cavities resonating at 2.6 GHz was measured at pressures ranging from 1 to 100 mbar in ambient air. The cavity with lower secondary emission yield surface material has a higher breakdown power on the left side of the breakdown curves, indicating the importance of SEE in microwave breakdown, especially at low pressures. Meanwhile, except for the cavity with hemisphere post, it was found that the quality factor has little effect on the breakdown power since electric field distributions inside these cavities are not significantly linked to post geometry. Two distinct regimes are observed in the breakdown curves with a transition pressure of 10 mbar. Namely, the breakdown curves present an emission-free branch above the transition, where microwave breakdown occurs in the gap, and a diffusion branch below the transition, where the microwave plasma expands out of the gap. We performed a theoretical calculation and found that the transition occurs when the attachment length equals the post radius.

Influence of Different Fibreglass Post Geometries on the Stress Distribution and Pull-Out Bond Strength Before and After Mechanical Cycling.

Objective:There are no reports in the literature on whether FGP geometry influences the bond strength of the endodontically restored tooth. This study aimed to determine the stress distribution and the pull-out bond strength of different FGP geometries, before and after chewing loads simulation.Methods:One hundred and twenty root analogues were prepared and randomly distributed in six groups according to the post geometry. Half of the specimens were aged in water at 37 °C using a mechanical fatigue machine (84 N, 2 bar, 45°, 106 cycles, 4 Hz); while the remaining specimens were immediately submitted to the pull-out bond strength test. The specimens were tested in a universal testing machine and the bond strength in MPa was calculated. To assess the stress concentration, the finite element method was used simulating the same post geometries that were used in the in vitro test.Results:Two-way ANOVA (95%) showed no influence of post geometry on the bond strength (P=0.055) while fatigue cycling was statistical significant to reduce the bond strength values (P=0.000). The factors interaction was significant (P=0.019); however, TUKEY test (5%) showed no significant difference between post geometries after mechanical cycling. The tensile stress result showed critical areas in the post’s cervical region regardless of the design.Conclusion:The FGP geometry does not affect the root stress distribution and the long-term bond strength. However, FGP that allow a reduced cement layer thickness can improve the immediate pull-out bond strength value.

Joule heating effects in optimized insulator-based dielectrophoretic devices: An interplay between post geometry and temperature rise.

Insulator-based dielectrophoresis (iDEP) is the electrokinetic migration of polarized particles when subjected to a non-uniform electric field generated by the inclusion of insulating structures between two remote electrodes. Electrode spacing is considerable in iDEP systems when compared to electrode-based DEP systems, therefore, iDEP systems require high voltages to achieve efficient particle manipulation. A consequence of this is the temperature increase within the channel due to Joule heating effects, which, in some cases, can be detrimental when manipulating biological samples. This work presents an experimental and modeling study on the increase in temperature inside iDEP devices. For this, we studied seven distinct channel designs that mainly differ from each other in their post array characteristics: post shape, post size and spacing between posts. Experimental results obtained using a custom-built copper Resistance Temperature Detector, based on resistance changes, show that the influence of the insulators produces a difference in temperature rise of approximately 4°C between the designs studied. Furthermore, a 3D COMSOL model is also introduced to evaluate heat generation and dissipation, which is in good agreement with the experiments. The model allowed relating the difference in average temperature for the geometries under study to the electric resistance posed by the post array in each design.

Effects of electrothermal vortices on insulator-based dielectrophoresis for circulating tumor cell separation.

Insulator-based dielectrophoresis (iDEP) is a powerful technique for separation and manipulation of bioparticles. In recent years, iDEP designs using arrays of insulating posts have shown promising results toward reaching high-efficiency bioparticle manipulation. Joule heating (JH) and electrothermal (ET) flows have been observed in iDEP microdevices and significantly affecting their performances. In this research, we utilize mathematical modeling to study, iDEP technique and the effects of JH and ET flow on device performance and propose a separation scenario for selective trapping of circulating tumor cells (CTCs). A robust numerical model is developed to calculate the distribution of electric and fluid flow fields in the presence of JH and ET flow, and predict the cells' trajectory inside the system. Our results indicate that JH not only induces temperature rise in the system, but also may alter the design iDEP separation scenario by inducing ET vortices that affect the cell's trajectory. To investigate the impact of JH-induced ET flow characteristics and vortex generation on separation efficiency, we introduce a dimensionless force ratio encompassing the effects of electrical field, drag forces, JH, and ET flow. Interestingly, it was found that ET flows can be used to significantly enhance the separation efficiency, even in higher inlet flow rates. Lastly, the effect of post geometry has been discussed.

Relativistic reflection: Review and recent developments in modeling

AbstractMeasuring relativistic reflection is an important tool to study the innermost regions of the an accreting black hole system. In the following we present a brief review on the different aspects contributing to the relativistic reflection. The combined approach is for the first time incorporated in the new “relxill” model. The advantages of this more self‐consistent approach are briefly summarized. A special focus is put on the new definition of the intrinsic reflection fraction in the lamp post geometry, which allows to draw conclusions about the primary source of radiation in these system. Additionally the influence of the high energy cutoff of the primary source on the reflection spectrum is motivated, revealing the remarkable capabilities of constraining Ecut by measuring relativistic reflection spectra from NuSTAR, preferably with lower energy coverage. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Revealing the broad iron Kαline in Cygnus X-1 through simultaneousXMM-Newton, RXTE, and INTEGRAL observations

We report on the analysis of the broad Fe Kalpha line feature of Cygnus X-1 in the spectra of four simultaneous hard intermediate state observations made with the X-ray Multiple Mirror mission (XMM-Newton), the Rossi X-ray Timing Explorer (RXTE), and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). The high quality of the XMM-Newton data taken in the Modified Timing Mode of the EPIC-pn camera provides a great opportunity to investigate the broadened Fe Kalpha reflection line at 6.4keV with a very high signal to noise ratio. The 4-500keV energy range is used to constrain the underlying continuum and the reflection at higher energies. We first investigate the data by applying a phenomenological model that consists of the sum of an exponentially cutoff power law and relativistically smeared reflection. Additionally, we apply a more physical approach and model the irradiation of the accretion disk directly from the lamp post geometry. All four observations show consistent values for the black hole parameters with a spin of $a\sim 0.9$, in agreement with recent measurements from reflection and disk continuum fitting. The inclination is found to be $i\sim30^\circ$, consistent with the orbital inclination and different from inclination measurements made during the soft state, which show a higher inclination. We speculate that the difference between the inclination measurements is due to changes in the inner region of the accretion disk.

NUSTARANDSUZAKUX-RAY SPECTROSCOPY OF NGC 4151: EVIDENCE FOR REFLECTION FROM THE INNER ACCRETION DISK

We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spin a>0.9 accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection flux variation drives the spectral variability during the observations. We discuss various physical scenarios for the inner disk reflection model, and we find that a compact corona is consistent with the observed features.

Removal of excess interfacial material from surface-modified emulsions using a microfluidic device with triangular post geometry

We report on a microfluidic device used to create water-in-oil and oil-in-water emulsions with controlled interfacial properties in pure solvent. Functional particles, specifically lipids, surfactants, and magnetic particulates, are delivered to the emulsion surface where they assemble to form a monolayer. This is achieved by immersing the emulsions in a high concentration of the functional particles and then separating excess material from the surrounding continuous phase. Separation is achieved using only passive hydrodynamic forces. It is desirable to remove the excess material so it is neither wasted nor available to interfere with applications where the surface-modified emulsions alone are needed. The separation of the surface-modified emulsions from the excess material is achieved by a variation of pinched flow fractionation. The emulsions are forced across streamlines into a pure solvent stream, while the smaller functional particles track a single streamline into a waste port. Numerical modeling confirms the validity of this streamline rationale for separation. The emulsions built using the microfluidic device support applications in drug delivery and membrane biology studies.

The role of the reflection fraction in constraining black hole spin

Abstract In many active galaxies, the X-ray reflection features from the innermost regions of the accretion disc are relativistically distorted. This distortion allows us to measure parameters of the black hole such as its spin. The ratio in flux between the direct and the reflected radiation, the so-called reflection fraction, is determined directly from the geometry and location of primary source of radiation. We calculate the reflection fraction in the lamp post geometry in order to determine its maximal possible value for a given value of black hole spin. We show that high reflection fractions in excess of two are only possible for rapidly rotating black holes, suggesting that the high spin sources produce the strongest relativistic reflection features. Using simulations we show that taking this constraint into account does significantly improve the determination of the spin values. We make software routines for the most popular X-ray data analysis packages available that incorporate these additional constraints.

Retraction: A three-dimensional finite element analysis of the effects of restorative materials and post geometry on stress distribution in mandibular molar tooth restored with post-core crown

Retraction: A three-dimensional finite element analysis of the effects of restorative materials and post geometry on stress distribution in mandibular molar tooth restored with post-core crown

Semi-experimental characterisation of the 3-port waveguide junction circulator containing a gyromagnetic post resonator

The original 3-port waveguide circulator relies for its operation on a simple gyromagnetic post resonator with top and bottom electric walls and an open magnetic side wall with no variation of the fields along its axis. Its description is a seminal paper in the literature. The purpose of this study is to characterise its first circulation condition (frequency) using a finite-element package and to characterise its second (complex gyrator circuit) experimentally. This is done for one-third-height, half-height and full-height resonator posts. The shortest of these three resonators is compatible with the synthesis of a circulator with an equal ripple degree-2 frequency response with a return loss of 23 dB over a 20 bandwidth. This sort of junction is met in the design of the externally latched junction circulator. This study includes a characterisation of a composite post resonator geometry consisting of an undersized ferrite cylinder surrounded by a dielectric sleeve.

A three-dimensional finite element analysis of the effects of restorative materials and post geometry on stress distribution in mandibular molar tooth restored with post-core crown

This study investigated the effects of crown material, post material, and post geometry on stress distribution in molar tooth restored with post-core crown. A three-dimensional solid model consisting of the mandibular second molar tooth, periodontal ligament, cortical bone, and spongy bone was generated. Finite element analysis results showed that prefabricated posts with a composite resin core increased stress concentration at the cementoenamel junction (CEJ), while cast posts induced high stress at post-dentin interface. Increase in the elastic modulus of crown material also increased the stress concentration, especially at CEJ.

Design of High-Ionic Conductivity Electrodes for Direct Methanol Fuel Cells

Axiomatic Design Theory is used to analyze the design of conventional DMFC anodes. The difficulty conventional electrode design have satisfying the requirements for ionic conductivity in the anode are shown to lead to functional coupling, and therefore, an inability to meet performance requirements. A new anode design is proposed using embossed ionically conductive channels through the thickness of the electrode. Numerical simulation of the proposed design indicates that ionic resistance is greatly reduced and, crucially, no longer a function of catalyst loading. Electrodes are fabricated with 75 μm diameter posts spaced 175 μm apart. These electrodes are tested with impedance spectroscopy and show a 46% reduction in ionic resistance and a 6% increase in catalyst area available. Cell power is estimated to increase by 4% with the current post geometry, while ideal geometry may be able to deliver 9% power improvement.

A unified scaling model for flow through a lattice of microfabricated posts

A scaling model is presented for low Reynolds number viscous flow within an array of microfabricated posts. Such posts are widely used in several lab-on-a-chip applications such as heat pipes, antibody arrays and biomolecule separation columns. Finite element simulations are used to develop a predictive model for pressure driven viscous flow through posts. The results indicate that the flow rate per unit width scales as approximately h1.17g1.33/d0.5 where h is the post height, d post diameter and g is the spacing between the posts. These results compare favorably to theoretical limits. The scaling is extended to capillary pressure driven viscous flows. This unified model is the first report of a scaling that incorporates both viscous and capillary forces in the microfabricated post geometry. The model is consistent with Washburn dynamics and was experimentally validated to within 8% using wetting on microfabricated silicon posts.

Multivariable Parameter Optimization Of Microfluidic Post Arrays For DNA Fractionation

Length-based fractionation of long DNA is a fundamental process in genomic analysis. Traditional methods, such as pulsed-field gel electrophoresis or capillary electrophoresis, are slow and not easily coupled to downstream analytical processes. Microfluidic devices containing arrays of micron-scale posts have previously been described for length-based fractionation of kilobase length DNA. [1] Here, we present experimental and computational studies defining and optimizing a broad array of parameters in order to maximize mass throughput and isolation of DNA > 150 kb. Parameters explored include post field geometry, electric field intensity, and field oscillation timing. Experimental studies were performed by analyzing of the mobility of single YOYO-1 intercalated DNA molecules in PDMS post arrays. Computational studies simulated kilobase length DNA as a worm-like chain model and investigated the interaction of such molecules with post arrays of various geometries. Optimization of our system results in the ability to isolate 165 kb DNA from 125 kb DNA and process 5 ng of DNA within 30 minutes of operation. This research was supported by the Department of Homeland Security, Science and Technology Directorate.[1] Huang et al.., Nature Biotechnology, 2002, 20, 1048.

Optimisation of the posterior stabilised tibial post for greater femoral rollback after total knee arthroplasty—a finite element analysis

Femoral rollback after total knee arthroplasty (TKA) is necessary for flexion beyond 90-100 degrees. Femoral rollback in posterior cruciate substituting TKA occurs as a result of the interaction between the femoral cam and tibial post. The geometric design of the cam post mechanism determines the kinematics of rollback. The purpose of this study is to optimise the design of the femoral cam-tibial post articulation through finite element analysis and suggest various design parameters that would optimise femoral rollback. Modifications to the tibial post geometry without changing the relative post position or slope are made. Results are characterised in terms femoral rollback and pressure distribution at the tibial post. Small design modifications to the tibial post are seen to produce large changes in femoral rollback with relatively small accompanying increases in contact pressures at the tibial post.

Dynamics of DNA Polymers in Post Arrays: Comparison of Single Molecule Experiments and Simulations

Understanding the dynamics of biopolymers in complex flows is critical for the successful design of lab-on-a-chip devices. In this paper, we demonstrate the first direct comparison of experiments and simulations of DNA transport in a pressure-driven post array flow. High aspect ratio ordered silicon posts arrays were microfabricated, and single molecule experiments were employed to examine the dynamics of DNA traversing through arrays of ordered obstacles. Three different geometries with varying post spacing were tested, and probability distributions of DNA hooking location and fractional DNA lengths were generated. It is demonstrated that the appropriate design of post array geometry can be used to control DNA conformation and guide the location of hooking events. Finally, agreement between experimental and Brownian dynamics simulation results is good, validating the simulations that can be used to guide future array designs.