Disk System Research Articles

Untangling stellar components of galaxies: Evaluation of dynamical decomposition methods in simulated galaxies with GalaxyChop

Galaxy formation is intrinsically connected to the distinct evolutionary processes of disk and spheroidal systems, which are the fundamental stellar components of galaxies. Understanding the mutual, dynamical interplay and co-evolution of these components requires a detailed dynamical analysis to allow for disentanglement of these systems. We introduce JEHistogram, a new method for the dynamical decomposition of simulated galaxies into disk and spheroidal stellar components that utilizes the angular momentum and energy of star particles. We evaluate its performance against five previously established methods using a sample of equilibrium galaxies with stellar masses in the range $10^ M_ gal /M_ $. Our assessment involves several metrics, including the completeness and purity of stellar particle classification, scale lengths, mass density profiles, velocity dispersion, and rotational velocity profiles. While all methods approximate the properties of the original components, such as mass fractions and density or velocity profiles, JEHistogram demonstrates a better accuracy, particularly in the inner regions of galaxies where component overlap complicates separation. Additionally, we apply JEHistogram to a Milky Way-like galaxy from the IllustrisTNG cosmological simulations, showcasing its capability to derive properties such as the size, mass, velocity, color, and age of dynamically defined disk and spheroidal components. All the dynamical decomposition methods we analyzed are publicly accessible through the Python package GalaxyChop

A Control Strategy of Multiple Microrobots Using a Hybrid Electromagnetic System

AbstractMagnetic microrobots are controlled to exhibit a wide range of motions, allowing them to navigate complex environments and perform multifunctional tasks with high precision. This work presents a novel hybrid electromagnetic actuation system by integrating two distinct conventional configurations, such as a paired‐coils electromagnetic disc (EMD) system and a distributed electromagnetic array coil (EAC) system. In order to ensure the effective functioning of the microrobot, its motion dynamics are thoroughly analyzed to identify the critical kinetic parameters. For demonstration purposes, first, a mixing task is performed by employing a single microrobot actuated with simultaneous motions. The mixing efficiency is observed to reach 83% within 30 s, in contrast to the efficiency of control of 45%. Second, a structural reconfiguration function is demonstrated by employing an independent control of two U‐shaped microrobots to form a new I‐shaped microrobot. Last, differentiated motion control of multiple magnetic pads is demonstrated, resulting in various 2D static formations in the shapes of numbers and alphabets. The presented results hold great promise for advancing the field of microrobotics by offering a novel solution for versatile microrobot motion controls.

Microscopic mechanisms of diffusion dynamics: A comparative efficiency study of event-chain Monte Carlo variants in dense hard disk systems.

In molecular simulations, efficient methods for investigating equilibration and slow relaxation in dense systems are crucial yet challenging. This study focuses on the diffusional characteristics of monodisperse hard disk systems at equilibrium, comparing novel methodologies of event-chain Monte Carlo variants, specifically the Newtonian event-chain and straight event-chain algorithms. We systematically analyze both event-based and CPU time-based efficiency in liquid and solid phases, aiming to elucidate the microscopic mechanisms underlying structural relaxation. Our results demonstrate how chain length or duration, system size, and phase state influence the efficiency of diffusion dynamics, including hopping motion. This work provides insights into optimizing simulation techniques for highly packed systems and has the potential to improve our understanding of diffusion dynamics even in complex many-body systems.

Influence of non-linear thermal radiation on the dynamics of homogeneous and heterogeneous chemical reactions between the cone and the disk

Abstract Purpose The current work presents a theoretical framework to boost heat transmission in a ternary hybrid nanofluid with homogeneous and heterogeneous reactions in the conical gap between the cone and disk apparatus. Furthermore, the impacts of non-linear thermal radiation on the ternary hybrid nanofluid composed of white graphene, diamond, and titanium dioxide dispersed in water are analyzed. Originality/value The combination of cone and disk systems is crucial for designing efficient heat exchange devices in the field of biomedical science for various purposes. For instance, in medical devices, the cone–disk apparatus is used to study the flow and heat transfer characteristics for better design and functionality. Hence, a sincere attempt has been made to study the impact of homogeneous and heterogeneous reactions on the nanofluid flow between the cone and disk in the presence of non-linear thermal radiation. Design/methodology/approach The mathematical model’s governing equations are partial differential equations (PDEs) which are then transformed into non-linear ordinary differential equations through appropriate similarity transformations. These transformed resultant equations are approximated by the Runge–Kutta–Fehlberg fourth/fifth order (RKF45) technique. The influence of essential aspects on the flow field, heat, and mass transfer rates was analyzed using a graphical representation. Findings The interesting part of this research is to discuss the power of parameters in three cases, namely, (1) rotating cone/disk, (2) rotating cone/stationary disk, and (3) stationary cone/rotating disk. Furthermore, the thermal variation of the fluid is analyzed by an artificial neural network with the help of the Levenberg–Marquardt backpropagation algorithm. The regression analysis, mean square error, and error histogram of the neural network are analyzed using this algorithm. From the graph, it is perceived that the flow field climbed up significantly with an increase in the values of radiation parameters in all cases. Also, it is noticed that temperature upsurges significantly by upward values of solid volume fraction of the nanoparticles ( ϕ \phi ).

General relativistic self-gravitating equilibrium discs around rotating neutron stars

ABSTRACT In modelling a relativistic disc around a compact object, the self-gravity of the disc is often neglected while it needs to be incorporated for more accurate descriptions in several circumstances. Extending the Komatsu–Eriguchi–Hachisu self-consistent field method, we present numerical models of a rapidly rotating neutron star with a self-gravitating disc in stationary equilibrium. In particular, our approach allows us to obtain numerical solutions involving a massive disc with the rest mass $\mathcal {O}(10^{-1})-\mathcal {O}(10^0)\, \mathrm{ M}_\odot$ closely attached to a rotating neutron star, given that the disc is mainly supported by the relativistic electron degeneracy pressure. We also assess the impact of self-gravity on the internal structure of the disc and the neutron star. These axisymmetric, stationary solutions can be employed for simulations involving the neutron star–disc system in the context of high-energy transients and gravitational-wave emissions.

Comparison of physical characteristics of mass and luminosity function of disk systems in barred and unbarred spiral galaxies

إحدى أهم الطرق لتقصي توزيع المجرات عبر الزمن الكوني هي دالة اللمعان LF بدلالة كتلة القرص الباريوني ψS(Mb)، القدر . لقد درسنا تقديرًا لكثافة كتلة الباريون في عينة من المجرات الحلزونية القضيبية وغير القضيبية من الادبيات السابقة، والتي تتضمن فعليًا، لكل صنف من الاجرام السماوية ذات المحتوى الباريون المرئي، جزءًا لا يتجزأ من ناتج دالة الضيائية (LF) ونسبة الكتلة إلى الضوء. استخدمت تقنية الانحدار المتعدد لحزمة البرامج الإحصائية في دراستنا ونتائجنا، مثل برنامج تحليل قواعد البيانات والرسوم البيانية)برامج Statistics Win و(Origin Pro . وفقًا للتحليل الإحصائي، هناك علاقة إيجابية قوية وارتباط وثيق للغاية (α MB~1), ، وغالبًا ما تظهر المجرات الحلزونية القرصية القضيبية وغير القضيبية قدراً مطلقاً بحدود MB < -18 mag . "الركبة" لدالة الضيائية للمجرات الحلزونية تبين قطعًا كبيرًا عند كتلة باريونية تبلغ Mb > 1010 Mʘ للمجرات الحلزونية القضيبية وغير القضيبية. يوفر هذا دليلاً يدعم الفرضية القائلة بأن اللوالب الحلزونية لنظام القرص بدأت تتشكل داخل عتبة كتلة متزايدة. نظرًا لأن زيادة دالة الكتلة الأولية للنجم مع الانزياح نحو الأحمر تكون أسرع بكثير، فقد أشارت النتائج التي توصلنا إليها إلى أن دالة الكتلة الأولية المنتقلة ψS(Mb) للمجرات القضيبية وغير القضيبيةعند انزياح أحمر مرتفع z > 0.027 للمجرات االقضيبية وz > 0.02للمجرات غير القضيبية والذي يبدو أنه يتناقص مقارنة بالكون الحرج.

Probabilistic Analysis of Orbital Characteristics of Rotary Systems with Centrally and Off-Center Mounted Unbalanced Disks

Rotor dynamics plays a crucial role in the performance and safety of rotating machinery, with disk position and unbalance significantly impacting system behavior. This study investigates the dynamic characteristics of two rotor configurations: a centrally mounted unbalanced disk (Rotor05un) and an off-center unbalanced disk (Rotor025un). Using numerical simulations and Monte Carlo analysis, we examined critical speeds and orbital patterns for both configurations. Probability distributions of shaft orbital positions revealed distinct patterns for each configuration. Quantile analysis revealed approximate linear trends for Rotor025un, suggesting higher system stiffness and more predictable behavior near critical speeds. Cross-sectional analyses of the orbits provided insights into the complex interactions between disk position, gyroscopic effects, and system natural frequencies. These findings provide valuable insights for rotor system design, particularly for applications with non-ideal mass distributions. The study goes beyond traditional critical speed analysis to examine orbital patterns and point on orbit occurrence from a probabilistic perspective. Based on the simulation of the orbits, an orbital is determined that allows the probability of the shaft occurring at the analyzed distance from the origin to be determined. The paper also offers insights into the complex interaction behavior of chosen rotor configurations and highlights the importance of considering disk position in predicting and optimizing rotor dynamic behavior, contributing to the development of more robust and efficient rotating machinery.

Unlocking the Potential of the CICERO Spinning Disk System: Exploring Diverse Applications

Abstract CrestOptics aims to make their products accessible to researchers, enabling a variety of applications, and to create products that are both efficient and user-friendly. The CICERO confocal spinning disk system embodies these principles, designed for easy integration into any imaging setup. Its compactness and flexibility make advanced fluorescence microscopy accessible to laboratories worldwide. This article will focus on the great versatility and strengths of the CICERO system, which is a complete widefield (WF) and spinning disk confocal (CF) solution. It will demonstrate its key features, namely its use on both inverted and upright microscopy configurations, its wide spectral range, the high resolution and sectioning power, and its large field of view (FOV). Microscopy Today has awarded CICERO a 2024 Innovation Award for these features.

Deepest Limits on Scattered Light Emission from the Epsilon Eridani Inner Debris Disk with HST/STIS

Epsilon Eridani is one of the first debris disk systems detected by the Infrared Astronomical Satellite. However, the system has thus far eluded detection in scattered light with no components having been directly imaged. Its similarity to a relatively young solar system combined with its proximity makes it an excellent candidate to further our understanding of planetary system evolution. We present a set of coronagraphic images taken using the Space Telescope Imaging Spectrograph coronagraph on the Hubble Space Telescope at a small inner working angle to detect a predicted warm inner debris disk inside 1″. We used three different postprocessing approaches—nonnegative matrix factorization (NMF), Karhunen–Loève Image Processing (KLIP), and classical reference differential imaging, to best optimize reference star subtraction—and find that NMF performed the best overall while KLIP produced the absolute best contrast inside 1″. We present limits on scattered light from warm dust, with constraints on surface brightness at 6 mJy as−2 at our inner working angle of 0.″6. We also place a constraint of 0.5 mJy as−2 outside 1″, which gives us an upper limit on the brightness for outer disks and substellar companions. Finally, we calculated an upper limit on the dust albedo at ω < 0.487.

Exploring integrated heat and mass transfer in von-Kármán dynamics involving Reiner-Rivlin fluid with regression models

The rotating disk system is widely used in several important applications, including turbomachinery design, mixing and stirring processes, centrifugal blood pumps development, optimizing electronic component, cooling efficiency, and various others. Moreover, regression models offer comprehensive and reliable prediction for important parameters in flows developed by revolving disks. This article presents similarity solutions for coupled heat and mass transfer with viscous dissipation in an inelastic non-Newtonian fluid flow across a permeable revolving disk. The inclusion of diffusion terms due to Dufour and Soret effects establishes coupling between energy and concentration equations. Temperature and concentrations at disk surface are supposed to vary quadratically along the radial direction. The impacts of MHD, heat source/sink dynamics and Joule heating effects on thermal boundary layer are also scrutinized. MATLAB's bvp5c tool, based on collocation scheme, generates numerical results. Homotopy analysis method, a widely accepted analytical solution procedure, is then applied to produce the series solution. Selection of the optimal auxiliary parameter values featured in the series solution is also included. The impact of Reiner-Rivlin fluid assumption on the torque required by the disk is assessed. Furthermore, linear and quadratic regression models are developed for the skin friction factors, Nusselt number and Sherwood number.

An Optimization Method for Stiffness and Damping Mistuning Identification From Blade Tip Timing Data

Abstract System identification of dynamic properties is of large interest in the turbomachinery industry to create more accurate computational models and more effective designs. Previous identification techniques were able to accurately capture the blade variability, known as mistuning, in the stiffness as well as the average damping of all the blades. Mistuning is vital to accurately identify and study because the symmetry of the system is broken and can lead to vibration localization and high amplitudes. In this work, a new method is proposed to not only capture the stiffness mistuning values, but also the blade-to-blade variability in damping. These damping mistuning values have been shown to have a significant effect on the dynamics of bladed disk systems. Incorporation of the damping mistuning into the computational model can be done utilizing an augmented component mode mistuning method with either structural or proportional damping. The mistuning values for this new identification method were compared to a well-established direct method and a previously studied optimization method. Blade responses were then found using a harmonic analysis and the newly identified mistuning values. These blade responses were then compared to experimental tip timing data from full scale rotating experiments. These comparisons show that the new model is able to better reproduce experimental data using computational models that incorporate both stiffness and damping mistuning values.

A repeated strike loading organ culture model for studying compression-associated chronic disc degeneration.

Mechanical stress has been viewed as one of the key risk factors in accelerating the intervertebral disc degeneration process. The goal of the present study was to employ a repeated strike loading bovine caudal disc system to elucidate the pathophysiological impacts of cumulative mechanical stress on the disc. The discs in the model groups were subjected to two different mechanical stresses: one strike loading or repeated strike loading. The following indices were analyzed: histological morphology, glycosaminoglycan release, disc height, cell viability, apoptosis-related protein expression, and catabolism-related gene expression. Both mechanical stress modes induced degenerative changes in the discs by day 11, such as clefts and delamination of the annulus fibrosus; they increased glycosaminoglycan release. Cell viability was significantly decreased and catabolic gene expression was significantly up-regulated in the degenerative loading group and repeated strike loading group by day 9. These alterations remained evident in the annulus fibrosus tissue of the repeated strike loading group on day 11.Our data suggests that the repeated strike loading model adopted in this study could lead to degenerative changes in the disc organ model. Annulus fibrosus cells displayed a more noticeable response to mechanical stress damage and a slower recovery process, suggesting that the annulus fibrosus serves as a pivotal factor in disc degeneration due to mechanical stress injuries. The study also indicates that due to the gradual self-repair of intervertebral disc cells after injury, it is necessary to apply repeated strike loading on the disc at specific intervals when researching the repair of chronic disc injuries.

Identifying and Characterizing Infrared Excesses in the Spitzer Kepler Survey (SpiKeS)

We report our search for infrared excesses in the Spitzer/Infrared Array Camera survey of the Kepler field at 3.6 and 4.5 μm. The Spitzer Kepler Survey contains ∼190,000 targets, which we reduce to ∼117,000 targets after applying multiple filters to arrive at a high-quality sample for spectral energy distribution fitting. Of the ∼117,000, we find 11 Sun-like stars (T eff ∼ 6000 K) with infrared excesses of high significance (>4σ) ranging from 10% to 40% above the photosphere at 4.5 μm, which is characteristic of debris disk systems. Blackbody fits of the infrared excesses for the 11 debris disk candidates suggest dust temperatures of 400–1400 K. None of the candidates have reported exoplanet detections. High-quality 1–5 μm or longer spectra or photometry would be necessary to confirm the candidates as debris disk systems.

An Expanding Accretion Disk and a Warm Disk Wind as Seen in the Spectral Evolution of HBC 722

We present a comprehensive analysis of the post-outburst evolution of the FU Ori object HBC 722 in optical/near-infrared (NIR) photometry and spectroscopy. Using a modified viscous accretion disk model, we fit the outburst epoch spectral energy distribution to determine the physical parameters of the disk, including Ṁacc=10−4.0M⊙ yr−1, R inner = 3.65 R ⊙, i = 79°, and a maximum disk temperature of Tmax=5700 K. We then use a decade of optical/NIR spectra to demonstrate a changing accretion rate drives the visible-range photometric variation, while the NIR shows the outer radius of the active accretion disk expands outward as the outburst progresses. We also identify the major components of the disk system: a plane-parallel disk atmosphere in Keplerian rotation and a two-part warm disk wind that is collimated near the star and wide-angle at larger radii. The wind is traced by classic wind lines, and appears as a narrow, low-velocity, deep absorption component in several atomic lines spanning the visible spectrum and in the CO 2.29 μm band. We compare the wind lines to those computed from wind models for other FU Ori systems and rapidly accreting young stellar disks and find a 4000–6000 K wind can explain the observed line profiles. Fitting the progenitor spectrum, we find M * = 0.2 M ⊙ and Ṁprogenitor=7.8×10−8M⊙yr−1 . Finally, we discuss HBC 722 relative to V960 Mon, another FU Ori object we have previously studied in detail.

The Santa Barbara Binary−disk Code Comparison

We have performed numerical calculations of a binary interacting with a gas disk, using 11 different numerical methods and a standard binary−disk setup. The goal of this study is to determine whether all codes agree on a numerically converged solution and to determine the necessary resolution for convergence and the number of binary orbits that must be computed to reach an agreed-upon relaxed state of the binary−disk system. We find that all codes can agree on a converged solution (depending on the diagnostic being measured). The zone spacing required for most codes to reach a converged measurement of the torques applied to the binary by the disk is roughly 1% of the binary separation in the vicinity of the binary components. For our disk model to reach a relaxed state, codes must be run for at least 200 binary orbits, corresponding to about a viscous time for our parameters, 0.2(a 2Ω B /ν) binary orbits, where ν is the kinematic viscosity. The largest discrepancies between codes resulted from the dimensionality of the setup (3D vs. 2D disks). We find good agreement in the total torque on the binary between codes, although the partition of this torque between the gravitational torque, orbital accretion torque, and spin accretion torque depends sensitively on the sink prescriptions employed. In agreement with previous studies, we find a modest difference in torques and accretion variability between 2D and 3D disk models. We find cavity precession rates to be appreciably faster in 3D than in 2D.

Compact SERS detection system enabling automated assay on disc combined with advanced data analysis – A case study of methotrexate

The demand for a compact, all-in-one, sample-to-answer solution for analyzing small molecules within complex matrices is persistent and challenging in analytical chemistry. This manuscript presents a breakthrough in enabling surface-enhanced Raman scattering (SERS) - based analytical assay in a compact detection system, integrating the sample preparation, detection, and data analysis enhanced by machine learning techniques. As a case study, methotrexate (MTX), an anticancer drug, was selected for detection in human serum.The compact tabletop Raman detection unit is equipped with a spectrometer and a motor for the rotation of the incorporated Lab-on-a-Disc unit, which allows simultaneous sample pretreatment of up to eight samples in less than 5 minutes and SERS mapping with a speed of 5 min/analysis. The automated program of the SERS on Disc system simplifies the workflow and enhances the efficiency of analyses.To address the complexity of serum before high sensitivity and specificity detection with SERS, we developed a sample preparation method on a microfluidic disc cartridge that involves precipitation and a nanopillar-assisted separation process, ensuring the isolation of MTX from other analytes. In addition, we implemented a machine learning technique, Partial Least Squares Regression (PLSR), to utilize the fingerprint of SERS spectra for precise and robust quantification of MTX, even in low concentrations. We calculated all figures of merit for the developed method and found that for the PLSR, the accuracy, precision, systematic error, sensitivity, analytical sensitivity, and inverse of analytical sensitivity were 9.41 μM, 9,45 μM, 0.98 μM, 211.64, 1.06 μM−1, and 0.94 μM respectively.

Perturbing the Stable Accretion Disk in Kerr and 4D Einstein–Gauss–Bonnet Gravities: Comprehensive Analysis of Instabilities and Dynamics

The study of a disturbed accretion disk holds great significance in the realm of astrophysics, as such events play a crucial role in revealing the nature of disk structure, the release of energy, and the generation of shock waves. Consequently, they can help explain the causes of X-ray emissions observed in black hole accretion disk systems. In this paper, we perturb the stable disk formed by spherical accretion around Kerr and Einstein–Gauss–Bonnet (EGB) black holes. This perturbation reveals one- and two-armed spiral shock waves around the black hole. We find a strong connection between these waves and the black hole spin parameter (a/M) and the EGB coupling constant (α). Specifically, we find that as α increases in the negative direction, the dynamics of the disk and the waves become more chaotic. Additionally, we observe that the angular momentum of the perturbing matter significantly affects mass accretion and the oscillation of the arising shock waves. This allows us to observe changes in QPO frequencies, particularly, perturbations with angular momentum matching the observed C−type low-frequency QPOs of the GRS 1915+105 source. Thus, we conclude that the possibility of the occurrence of shock waves within the vicinity of GRS 1915+105 is substantial.

Enhanced tribological performance of MoS2 and hBN-based composite friction materials: Design of tribo-pair for automotive brake pad-disc systems

This research comprehensively analyzes the friction and wear behavior of composite friction materials when dry sliding against grey cast iron and laser-clad nickel-based (LC1) and iron-based (LC2) alloy discs. The composite friction materials (P1, P2, P3, P4, P5, and P6) under investigation contain graphite, MoS2, and hBN-based solid lubricant synthesized through the powder metallurgy technique. Tribological tests were conducted using a pin-on-disc configuration to simulate the dynamic interaction between the composite materials and the laser-clad grey cast iron discs. The tests were performed at a 60 N load, 6283.19 m sliding distance, and 2.094 m/s sliding velocity under dry sliding conditions. The results provide valuable insights into the effectiveness of MoS2 and hBN-based solid lubricant composites in reducing friction and wear when in contact with iron and nickel alloy-based laser-clad grey cast iron surfaces. The study elucidates the mechanisms governing tribological behavior, including the formation of friction plateaus and the role of laser-clad counter-discs in reducing wear. The specific wear rate of the nickel-based laser-clad counter disc (LC1) and iron-based laser-clad (LC2) system improved by 63.76 % and 48.32 %, respectively, compared to the conventional grey cast iron disc system when using the hBN-based pin (P6). Additionally, the specific wear rate of the hBN-based pin was 38.49 % lower than the conventional graphite-based pin when sliding against the grey cast iron counter-disc. Artificial Neural Network (ANN) was used to validate the wear rate of the best-performing tribological pair, namely the hBN-based pin (P6) and LC2 counter discs, through supervised learning.

Anomalous flocking in nonpolar granular Brownian vibrators

Using Brownian vibrators, we investigated the structures and dynamics of quasi-2d granular materials, with packing fractions (ϕ) ranging from 0.111 to 0.832. Our observations revealed a remarkable large-scale flocking behavior in hard granular disk systems, encompassing four distinct phases: granular fluid, flocking fluid, poly-crystal, and crystal. Anomalous flocking emerges at ϕ = 0.317, coinciding with a peak in local density fluctuations, and ceased at ϕ = 0.713 as the system transitioned into a poly-crystal state. The poly-crystal and crystal phases resembled equilibrium hard disks, while the granular and flocking fluids differed significantly from equilibrium systems and previous experiments involving uniformly driven spheres. This disparity suggests that collective motion arises from a competition controlled by volume fraction, involving an active force and an effective attractive interaction resulting from inelastic particle collisions. Remarkably, these findings align with recent theoretical research on the flocking motion of spherical active particles without alignment mechanisms.

Candidate Members of the VMP/EMP Disk System of the Galaxy from the SkyMapper and SAGES Surveys

Photometric stellar surveys now cover a large fraction of the sky, probe to fainter magnitudes than large-scale spectroscopic surveys, and are relatively free from the target selection biases often associated with such studies. Photometric-metallicity estimates that include narrow/medium-band filters can achieve comparable accuracy and precision to existing low-resolution spectroscopic surveys such as Sloan Digital Sky Survey/SEGUE and LAMOST. Here we report on an effort to identify likely members of the Galactic disk system among the very metal-poor (VMP; [Fe/H] ≤ −2) and extremely metal-poor (EMP; [Fe/H] ≤ −3) stars. Our analysis is based on an initial sample of ∼11.5 million stars with full space motions selected from the SkyMapper Southern Survey (SMSS) and Stellar Abundance and Galactic Evolution Survey (SAGES). After applying a number of quality cuts to obtain the best available metallicity and dynamical estimates, we analyze a total of ∼5.86 million stars in the combined SMSS/SAGES sample. We employ two techniques that, depending on the method, identify between 876 and 1476 VMP stars (6.9%−11.7% of all VMP stars) and between 40 and 59 EMP stars (12.4%−18.3% of all EMP stars) that appear to be members of the Galactic disk system on highly prograde orbits (v ϕ > 150 km s−1). The total number of candidate VMP/EMP disklike stars is 1496, the majority of which have low orbital eccentricities, ecc ≤ 0.4; many have ecc ≤ 0.2. The large fractions of VMP/EMP stars associated with the Milky Way disk system strongly suggest the presence of an early-forming “primordial” disk.