Ring Model Research Articles

Terrestrial planet formation from a ring

It has been long proposed that, if all the terrestrial planets form within a tiny ring of solid material at around 1 AU, the concentrated mass-distance distribution of the current system can be reproduced. Recent planetesimal formation models also support this idea. In this study, we revisit the ring model by performing a number of high-resolution N-body simulations for 10 Myr of a ring of self-interacting planetesimals, with various radial distributions of the gas disc. We found that even if all the planetesimals form at ∼1 AU in a minimum mass solar nebula-like disc, the system tends to spread radially as accretion proceeds, resulting in a system of planetary embryos lacking mass-concentration at ∼1 AU. Modifying the surface density of the gas disc into a concave shape with a peak at ∼1 AU helps to maintain mass concentrated at ∼1 AU and solve the radial dispersion problem. We further propose that such a disc should be short lived (≤ 1 Myr) and with a shallower radial gradient in the innermost region (< 1 AU) than previously proposed to prevent a too-rapid growth of Earth. Future studies should extend to ∼100 Myr the most promising simulations and address in a self-consistent manner the evolution of the asteroid belt and its role in the formation of the terrestrial planets.

Disconnect between COX-2 selective inhibition and cardiovascular risk in preclinical models

IntroductionSecondary pharmacology profiling is routinely applied in pharmaceutical drug discovery to investigate the pharmaceutical effects of a drug at molecular targets distinct from (off-target) the intended therapeutic molecular target (on-target). Data from a randomized, placebo-controlled clinical trial, the APPROVe (Adenomatous Polyp Prevention on VIOXX, rofecoxib) trial, raised significant concerns about COX-2 inhibition as a primary or secondary target, shaping the screening and decision-making processes of some pharmaceutical companies. COX-2 is often included in off-target screens due to cardiovascular (CV) safety concerns about secondary interactions with this target. Several potential mechanisms of COX-2-mediated myocardial infarctions have been considered including, effects on platelet stickiness/aggregation, vasal tone and blood pressure, and endothelial cell activation. In the present study, we focused on each of these mechanisms as potential effects of COX-2 inhibitors, to find evidence of mechanism using various in vitro and in vivo preclinical models. MethodsCompounds tested in the study, with a range of COX-2 selectivity, included rofecoxib, celecoxib, etodolac, and meloxicam. Compounds were screened for inhibition of COX-2 vs COX-1 enzymatic activity, ex vivo platelet aggregation (using whole blood from multiple species), ex vivo canine femoral vascular ring model, in vitro human endothelial cell activation (with and without COX-2 induction), and in vivo cardiovascular assessment (anesthetized dog). ResultsThe COX-2 binding assessment generally confirmed the COX-2 selectivity previously reported. COX-2 inhibitors did not have effects on platelet function (spontaneous aggregation or inhibition of aggregation), cardiovascular parameters (mean arterial pressure, heart rate, and left ventricular contractility), or endothelial cell activation. However, rofecoxib uniquely produced an endothelial mediated constriction response in canine femoral arteries. ConclusionOur data suggest that rofecoxib-related cardiovascular events in humans are not predicted by COX-2 potency or selectivity. In addition, the vascular ring model suggested possible adverse cardiovascular effects by COX-2 inhibitors, although these effects were not seen in vivo studies. These results may also suggest that COX-2 inhibition alone is not responsible for rofecoxib-mediated adverse cardiovascular outcomes.

An in-plane flexible ring model for the analysis of the free and forced response of a rolling tyre

The increased demand for vibroacoustic comfort as well as regulations on noise and vibration levels have made the NVH (Noise, Vibration, Harshness) performances of a vehicle to become one of the fundamental design criteria. Therefore, predictive models for the analysis of noise and vibration transmission mechanisms represent interesting tools to support the R&amp;D department of the automotive companies. Focusing the attention on passenger's comfort, the vibrations induced by the tyre/road interaction propagate from the contact area to the hub and finally inside the cockpit through structure-borne transmission paths. This can be regarded as one of the major contributors to the car cabin interior noise at low frequencies (between 20 and 500 Hz). Simplified models able to interpret the waves propagating inside the tyre structure and influenced by the angular speed may support the studies in this research field. To this end, an analytical model based on the theory of the flexible ring on elastic foundation has been developed. It allows analysing the tyre dynamics in both static and rolling conditions. Model parameters have been calibrated based on an Experimental Modal Analysis of the static tyre. The free response of the tyre shows the bifurcation effect at different rolling speeds, while a cleat test simulation has been carried out to investigate the forced response of the tyre.

Promoting a culture of reciprocity to build social capital in advanced practice nursing students.

A virtual activity integrating the evidence-based Reciprocity Ring model was designed to enhance confidence and skills for building social capital for advanced practice registered nursing (APRN) students. The central objective of the activity was to reduce the stigma of asking for help by providing a framework for the balanced exchange of favors, thus supporting new connections and feelings of trust among APRN students. Students from two APRN practice tracks (N = 44) participated in a virtual Reciprocity Ring activity where they could post and respond to requests for help. On average, students posted 2.5 requests and received three offers for assistance; 220 connections were made overall with the major theme requests related to stress management. A retrospective survey was administered at the conclusion of the activity. Questions inquired about student confidence before, and then after, the activity for identifying resources, providing help to others, finding personal support when needed, accessing resources related to academic success, and finding solutions to problems. Student mean confidence scores were significantly higher after the activity compared with mean confidence scores before the activity (p = .01). Additionally, the effect size was large (Cohen d = 0.89). Therefore, we suggest that integrating Reciprocity Ring exercises into nursing curricula and practice can be a useful tool for promoting skills related to productive help-seeking that will support APRN students' academic and professional success.

Physcion prevents high-fat diet-induced endothelial dysfunction by inhibiting oxidative stress and endoplasmic reticulum stress pathways

High-fat diet (HFD)-induced obesity leads endothelial dysfunction and contributes to cardiovascular diseases. Palmitic acid (PA), a free fatty acid, is the main component of dietary saturated fat. Physcion, a chemical ingredient from Rhubarb, has been shown anti-hypertensive, anti-bacteria, and anti-tumor properties. However, the effects of physcion on endothelial dysfunction under HFD-induced obesity have not been reported. The purpose of the present study was to define the protective effect of physcion on HFD-induced endothelial dysfunction and its mechanisms involved. Obesity rat model was induced by HFD for 12 weeks. A rat thoracic aortic ring model was used to investigate the effects of physcion on HFD-induced impairment of vasorelaxation. Endothelial cell injury model was constructed in human umbilical vein endothelial cells (HUVECs) by treating with PA (0.25 mM) for 24 h. The results revealed that physcion reduced body weight and the levels of plasma TG, prevented impairment of endothelium-dependent relaxation in HFD-fed rats. In PA-injured HUVECs, physcion inhibited impaired viability, apoptosis and inflammation. Physcion also suppressed PA-induced both oxidative stress and ER stress in HUVECs. Furthermore, physcion increased PA-induced decrease in the activation of eNOS/Nrf2 signaling in HUVECs. These findings suggest that physcion has a significant beneficial effect on regulating HFD-induced endothelial dysfunction, which may be related to the inhibition of oxidative stress and ER stress through activation of eNOS/Nrf2 signaling pathway.

Peridynamics for mechanism analysis of soil desiccation cracking: Coupled hygro-mechanical model, staggered and monolithic solution

Soil shrinkage cracking is a hygro-mechanical coupled phenomenon and it can significantly weaken the mechanical properties of soil and cause various potential natural disasters. This study proposes an improved bond-based peridynamics (PD) formulation, based on a comprehensive review of the hygro-mechanical peridynamic models. The proposed model with a certain influence function can be recast as an existing bond-based PD diffusion model. Also, an attenuation kernel function and discretized micro-modulus are adopted to revise the bond force density in the prototype micro-elastic brittle (PMB) model. For the numerical implementation, both monolithic and staggered schemes are adopted for the coupled hygro-mechanical problem. Specifically, the coupled stiffness matrix in the discretized equilibrium equation is constructed by using the Lagrange multiplier method for the monolithic scheme. While the direct integration method of explicit dynamics with an artificial damping term is adopted for the staggered scheme. For modeling of soil drying and cracking, two-dimensional soil rings, and two- and three-dimensional soil strips are simulated and demonstrated. The soil ring model verifies the accuracy of the coupled moisture-soil bond-based PD model through an explicit staggered scheme, and explores the effect of the relative thickness of rings on the number of cracks. The implicit monolithic solution is adopted to analyze the mechanisms of soil strip cracking. A detailed discussion on the scheme for controlling the maximum number of bond breakage is provided to guarantee convergency and accuracy with optimal efficiency. The soil strip cracking pattern and upward curling deformation agree well with experimental observations. The results show that the hygro-mechanical coupled peridynamic model has great advantages in solving soil drying and cracking. The present work shows a potential way in soil desiccation cracking investigation for real-scale simulation and fine mechanism exploration.

Parametric instability in warped astrophysical discs: growth, saturation, and feedback

ABSTRACT Attempts to understand the dynamics of warped astrophysical discs have garnered significant attention, largely motivated by the growing catalogue of observed distorted systems. Previous studies have shown that the evolution of the warp is crucially regulated by the internal flow fields established by the undulating geometry. These are typically modelled as laminar horizontal, shearing flows which oscillate back and forth at approximately the orbital frequency. However this shearing motion is known to be susceptible to a hydrodynamic, parametric instability of inertial waves which might modify the warped dynamics. Whilst the linear growth phase is well understood, the subsequent non-linear saturation combined with the self-consistent feedback onto the warp has not been studied. In this work, we implement a novel numerical setup using the recent ring model framework of Fairbairn and Ogilvie, within the Lagrangian code gizmo. We formally identify several locally growing modes in the simulation, as predicted by a three-mode coupling analysis of the instability, and find decent agreement with the theoretical growth rates. We understand the saturation mechanism as a wave breaking process which suppresses the growth of shorter wavelength parametric couplings first, whilst allowing the longest mode to dominate the final quasi-steady, wave-like turbulence. The Reynolds stresses, transporting energy from the warp to the small scales, can be effectively modelled using a time-dependent, anisotropic viscous alpha model which closely captures the amplitude and phase evolution of the warp. Consequently, this model might help inform future global studies which are commonplace but typically do not resolve the parametric instability.

A spiking network model for clustering report in a visual working memory task.

Working memory (WM) plays a key role in many cognitive processes, and great interest has been attracted by WM for many decades. Recently, it has been observed that the reports of the memorized color sampled from a uniform distribution are clustered, and the report error for the stimulus follows a Gaussian distribution. Based on the well-established ring model for visuospatial WM, we constructed a spiking network model with heterogeneous connectivity and embedded short-term plasticity (STP) to investigate the neurodynamic mechanisms behind this interesting phenomenon. As a result, our model reproduced the clustering report given stimuli sampled from a uniform distribution and the error of the report following a Gaussian distribution. Perturbation studies showed that the heterogeneity of connectivity and STP are necessary to explain experimental observations. Our model provides a new perspective on the phenomenon of visual WM in experiments.

Thermal hysteresis and front propagation in dense planetary rings

ABSTRACT Saturn’s rings are composed of icy grains, most in the mm to m size ranges, undergoing several collisions per orbit. Their collective behaviour generates a remarkable array of structures over many orders of magnitude, much of it not well understood. On the other hand, the collisional properties and parameters of individual ring particles are poorly constrained; usually, N-body simulations and kinetic theory employ hard-sphere models with a coefficient of restitution ϵ that is constant or a decreasing function of impact speed. Due to the plastic deformation of surface regolith, however, it is likely that ϵ will be more complicated, at the very least a non-monotonic function. We undertake N-body simulations with the REBOUND code with non-monotonic ϵ laws to approximate surfaces that are friable but not sticking. Our simulations reveal that such ring models can support two thermally stable steady states for the same (dynamical) optical depth: a cold and a warm state. If the ring breaks up into radial bands of one or the other, we find that warmer states tend to migrate into the colder states via a coherent travelling front. We also find stationary ‘viscous’ fronts, which connect states of different optical depths, but the same angular momentum flux. We discuss these preliminary results and speculate on their implications for structure formation in Saturn’s B and C-rings, especially with respect to structures that appear in Cassini images but not in occultations.

Structural predictions of three medium-sized thiolate-protected gold nanoclusters Au44(SR)30, Au56(SR)32, and Au60(SR)34.

The knowledge of structural evolution among thiolate-protected gold nanoclusters is not only helpful for understanding their structure-property relationship but also provides scientific evidence to rule-guided structure predictions of gold nanoclusters. In this paper, three new atomic structures of medium-sized thiolate-protected gold nanoclusters, i.e. Au44(SR)30, Au56(SR)32, and Au60(SR)34, are predicted based on the grand unified model and ring model. Two structural evolution rules, i.e., Au44(SR)28 + [Au12(SR)4] → Au56(SR)32 + [Au12(SR)4] → Au68(SR)36 and Au44(SR)30 + [Au8(SR)2] → Au52(SR)32 + [Au8(SR)2] → Au60(SR)34 + [Au8(SR)2] → Au68(SR)36, are explored. The generic growth patterns underlying both sequences of nanoclusters can be viewed as sequential addition of four and three highly stable tetrahedral Au4 units on the cores, respectively. In addition, density functional theory calculations show that these three newly predicted gold nanoclusters have very close formation energies with their adjacent structures, large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, and all-positive harmonic vibration frequencies, indicating their high stabilities.

Design and Development of Mathematical Equivalent Circuit Model of Broadband Circularly Polarized Semi-annular Ring Shaped Monopole Antenna

Design and Development of Mathematical Equivalent Circuit Model of Broadband Circularly Polarized Semi-annular Ring Shaped Monopole Antenna

RIGID PROPERTIES OF ELASTIC BUSHINGS OF ENGINES HIGH SPEED ELEMENTS

In the work, theoretical foundations of behavior analysis of elastic bushings of modern engines high-speed elements under load were created. Several variation settings are offered. The first one of them is based on the model of a thin ring. The second model is formed on a flat setting. The third model is a three-dimensional formulation of the contact problem. It was established that during radial force loading, uneven deformation of the elastic intermediate ring occurs. At the same time, the contact zones gradually change their location in the direction of the radial force. The dependence of the radial displacement on the loading force is significantly nonlinear. It was established that the static characteristic of an elastic ring has a complex form. Unlike the traditional linear characteristic, it consists of three sections. The first one corresponds to a zero reaction to the action of the load. The second is a linear part. The third is a tough section. Thus, new formulations of the problem of determining the stress-strain state of an elastic intermediate ring, taking into account the contact interaction, have been developed. This forms, in contrast to traditional linear, significantly nonlinear models of the stress-strain state. They are more adequate and take into account factors that were not taken into account before. In particular, the clearances, tension and contact in the coupling of the elastic intermediate ring with other parts of the structure of the support of the rotor system are taken into account. Keywords: high-speed element, elastic bushing, support, critical rotational speeds, air blower, internal combustion engine

Research on Root Strain Response Characteristics of Inner Ring of Planetary Gear Transmission System with Crack Fault

This paper established the system dynamics model for two kinds of tooth cracks of different depths of the sun gear and inner gear ring to study the influence mechanism of crack failure on the tooth root strain of the planetary gear transmission system. Combined with the finite element model of the inner gear ring, the tooth root strain of the ring was solved. Experiments verified the correctness of the solution method. The root strain under the crack fault of the sun gear and the tooth crack fault of the inner gear ring is analyzed, and the following conclusions are drawn: Periodic fault impact occurs in the strain signal of the tooth root of the inner gear ring during the crack fault of the sun gear root. The fault can be extracted by the fast spectral kurtosis method (FSK), and the fault components are used to determine whether the sun gear cracks. The Lempel-Ziv index showed a tendency to increase gradually during the process of solar wheel crack deepening, which could be used as the damage index of crack depth. The results can provide a basis and reference for fault diagnosis.

Contractile ring composition dictates kinetics of in silico contractility

Constriction kinetics of the cytokinetic ring are expected to depend on dynamic adjustment of contractile ring composition, but the impact of ring component abundance dynamics on ring constriction is understudied. Computational models generally assume that contractile networks maintain constant total amounts of components, which is not always true. To test how compositional dynamics affect constriction kinetics, we first measured F-actin, non-muscle myosin II, septin, and anillin during Caenorhabditis elegans zygotic mitosis. A custom microfluidic device that positioned the cell with the division plane parallel to a light sheet allowed even illumination of the cytokinetic ring. Measured component abundances were implemented in a three-dimensional agent-based model of a membrane-associated contractile ring. With constant network component amounts, constriction completed with biologically unrealistic kinetics. However, imposing the measured changes in component quantities allowed this model to elicit realistic constriction kinetics. Simulated networks were more sensitive to changes in motor and filament amounts than those of crosslinkers and tethers. Our findings highlight the importance of network composition for actomyosin contraction kinetics.

Isomerism effects in relaxation dynamics of Au24(SR)16 thiolate-protected gold nanoclusters

Understanding the excited state behavior of isomeric structures of thiolate-protected gold nanoclusters is still a challenging task. In this paper, based on grand unified model and ring model for describing thiolate-protected gold nanoclusters, we have predicted four isomers of Au24(SR)16 nanoclusters. Density functional theory calculations show that the total energy of one of the predicted isomers is 0.1 eV lower in energy than previously crystallized isomer. The nonradiative relaxation dynamics simulations of Au24(SH)16 isomers are performed to reveal the effects of structural isomerism on relaxation process of the lowest energy states, in which that most of the low-excited states consist of core states. In addition, crystallized isomer possesses the shorter e–h recombination time, whereas the most stable isomer has the longer recombination time, which may be attributed to the synergistic effect of nonadiabatic coupling and decoherence time. Our results could provide practical guidance to predict new gold nanoclusters for future experimental synthesis, and stimulate the exploration of atomic structures of same sized gold nanoclusters for photovoltaic and optoelectronic devices.

Investigations on IC Engine Piston Ring made of Composite Materials

This paper is respecting the evaluation of stress distribution on IC engine (four-stroke) piston ring and analysis of finite element by using FEA software. The purpose of this analysis is to calculate strain for SiC reinforced ZrB2, A360, A2618 and deformation resulting through ring elastic pressure and gas pressure. The total deformation and strain on the piston ring have been obtained in this project. The characteristics of such vibrations are analyzed with the help of solid works software and analysis of finite element is performed on the Ansys workbench software. The material used is Silicon Carbide reinforced Zirconium Diboride (SiC reinforced ZrB2), Aluminium alloy (A360), Aluminium alloy (A2618). This is a ceramic matrix composite (CMC) which has good safety factor and lower cost. The experiment is conducted on three types of composites to evaluate the strain on SiC reinforced ZrB2, A360, A2618 resulting from the total deformation and strain. Compressive strength has also been analyzed for the structural model of the piston ring.

Data transmission reduction using prediction and aggregation techniques in IoT-based wireless sensor networks

Currently, broad ranges of economic sectors exploit the Internet of Things (IoT) and Wireless Sensor Networks (WSNs) technology generating problems to be managing, processing and organizing the big data streams. Given the inherent sensor constraints (battery-dependent life, lack of memory space, limited processor power), there is a need for systems capable of reducing data transmission flux of the distributed IoT-based WSNs applications to mitigate the continuously increasing network traffic. Prediction and data aggregation techniques are promising solutions to meet this requirement. These techniques are particularly powerful solutions in forecasting processes where a huge data to be collected, transmitted and recorded. This is right even if we consider the integration of IoT-based WSNs with cloud computing technology. This paper proposes the combination of the recently developed prediction scheme EADPS (Extended Adaptive Dual Prediction Scheme) and the temporal correlation based data aggregation technique as a power tool to address the problem of communication reduction in connected IoT-based WSNs. First, we studied separately the impact of each technique before considering their combination. To achieve this goal, we consider the multi-hop ring model of the IoT-based WSNs. The results show that the aggregation technique is powerful compared to the DPS prediction scheme but loses its superiority for small WSNs size (with lesser than five rings) when the EADPS schema is applied. In addition, the data correlation has a feeble impact on reduction of transmission rates. According to the imposed tolerance thresholds, we show that the proposed scheme reduced the average transmission rates in the range 85%–96% for the entire network. The obtained results are presented and discussed.

Interaction decompositions for tensor network regression

It is well known that tensor network regression models operate on an exponentially large feature space, but questions remain as to how effectively they are able to utilize this space. Using a polynomial featurization, we propose an interaction decomposition as a tool that can assess the relative importance of different regressors as a function of their polynomial degree. We apply this decomposition to tensor ring and tree tensor network models trained on the MNIST and Fashion MNIST datasets, and find that up to 75% of interaction degrees are contributing meaningfully to these models. We also introduce a new type of tensor network model that is explicitly trained on only a small subset of interaction degrees, and find that these models are able to match or even outperform the full models using only a fraction of the exponential feature space. This suggests that standard tensor network models utilize their polynomial regressors in an inefficient manner, with the lower degree terms being vastly under-utilized.

The interstellar medium distribution, gas kinematics, and system dynamics of the far-infrared luminous quasar SDSS J2310+1855 atz= 6.0

We present Atacama Large Millimeter/submillimeter Array (ALMA) sub-kiloparsec- to kiloparsec-scale resolution observations of the [C II], CO (9–8), and OH+(11–01) lines along with their dust continuum emission toward the far-infrared (FIR) luminous quasar SDSS J231038.88+185519.7 atz = 6.0031, to study the interstellar medium distribution, the gas kinematics, and the quasar-host system dynamics. We decompose the intensity maps of the [C II] and CO (9–8) lines and the dust continuum with two-dimensional elliptical Sérsic models. The [C II] brightness follows a flat distribution with a Sérsic index of 0.59. The CO (9–8) line and the dust continuum can be fit with an unresolved nuclear component and an extended Sérsic component with a Sérsic index of ∼1, which may correspond to the emission from an active galactic nucleus dusty molecular torus and a quasar host galaxy, respectively. The different [C II] spatial distribution may be due to the effect of the high dust opacity, which increases the FIR background radiation on the [C II] line, especially in the galaxy center, significantly suppressing the [C II] emission profile. The dust temperature drops with distance from the center. The effective radius of the dust continuum is smaller than that of the line emission and the dust mass surface density, but is consistent with that of the star formation rate surface density. This may indicate that the dust emission is a less robust tracer of the dust and gas distribution but is a decent tracer of the obscured star formation activity. The OH+(11–01) line shows a P-Cygni profile with an absorption at ∼–400 km s−1, which may indicate an outflow with a neutral gas mass of (6.2 ± 1.2)×108 M⊙along the line of sight. We employed a three-dimensional tilted ring model to fit the [C II] and CO (9–8) data cubes. The two lines are both rotation dominated and trace identical disk geometries and gas motions. This suggest that the [C II] and CO (9–8) gas are coplanar and corotating in this quasar host galaxy. The consistent circular velocities measured with [C II] and CO (9–8) lines indicate that these two lines trace a similar gravitational potential. We decompose the circular rotation curve measured from the kinematic model fit to the [C II] line into four matter components (black hole, stars, gas, and dark matter). The quasar-starburst system is dominated by baryonic matter inside the central few kiloparsecs. We constrain the black hole mass to be 2.97+0.51-0.77 × 109M⊙; this is the first time that the dynamical mass of a black hole has been measured atz ∼ 6. This mass is consistent with that determined using the scaling relations from quasar emission lines. A massive stellar component (on the order of 109 M⊙) may have already existed when the Universe was only ∼0.93 Gyr old. The relations between the black hole mass and the baryonic mass of this quasar indicate that the central supermassive black hole may have formed before its host galaxy.

Recent developments to the Radia magnetostatics code for improved performance and interface

Radia is a 3D magnetostatics code that is widely used to model a range of magnets for particle accelerators, with particularly broad usage within the synchrotron light source community. Recently, Radia has been released as open source and made available for collaborative development on GitHub. A US DOE SBIR grant has been obtained for its upgrade and extension. The ongoing improvements are focused on the core physics engine, performance enhancements, and the development of a graphical user interface. Additionally, a new Python API (PyRadia) has been developed to allow for wider use of Radia outside of the existing Mathematica API. We have implemented the majority of the Radia examples in Python scripts and in Jupyter notebooks, including advanced visualization features for interactively viewing 3D geometries based on the VTK toolkit. The interaction matrix and field calculations have been parallelized using MPI and show good scaling performance on a variety of cluster architectures. The parallel Radia may be accessed via Python scripts or using the Jupyter interface. A Sirepo application is under development to provide a browser based interface to the Radia code allowing modeling of synchrotron light source magnets, with a focus on undulators. Kick maps and field maps may be exported for use in electron storage ring modeling codes such as elegant or AT, and tabulated undulator files may be exported for x-ray optics computation in a physical optics code such as Synchrotron Radiation Workshop. We summarize these developments and give an outlook for future development.