Large Number Of Disks Research Articles

Architecture of Planetary Systems Predicted from Protoplanetary Disks Observed with ALMA. II. Evolution Outcomes and Dynamical Stability

Recent ALMA observations on disk substructures suggest the presence of embedded protoplanets in a large number of disks. The primordial configurations of these planetary systems can be deduced from the morphology of the disk substructure and serve as initial conditions for numerical investigation of their future evolution. Starting from the initial configurations of 12 multiplanetary systems deduced from ALMA disks, we carried out two-stage N-body simulation to investigate the evolution of the planetary systems at the disk stage, as well as the long-term orbital stability after the disk dispersal. At the disk stage, our simulation includes both the orbital migration and pebble/gas accretion effects. We found that a variety of planetary systems are produced and can be categorized into distant giant planets, Jupiter-like planets, Neptune-like planets, and distant small planets. We found that the disk-stage evolution and the final configurations are sensitive to both the initial mass assignments and viscosity. After the disk stage, we implement only mutual gravity between star and planets and introduce stochastic perturbative forces. All systems are integrated for up to 10 Gyr to test their orbital stability. Most planetary systems are found to be stable for at least 10 Gyr, with perturbative force in a reasonable range. Our result implies that a strong perturbation source such as stellar flybys is required to drive the planetary system unstable. We discuss the implications of our results on both the disk and planet observation, which may be confirmed by the next-generation telescopes such as JWST and ngVLA.

Seeking an alternative to tape-based custodial storage

In November 2018, the KISTI Tier-1 centre started a project to design, develop and deploy a disk-based custodial storage with error rate and reliability compatible with a tape-based storage. This project has been conducted in collaboration with KISTI and CERN; especially the initial design was laid out from the intensive discussion with CERN IT and ALICE. The system design of the disk-based custodial storage consisted of high density JBOD enclosures and erasure coding data protection, implemented in EOS, the open-source storage management developed at CERN. In order to balance the system reliability, data security and I/O performance, we investigated the possible SAS connections of JBOD enclosures to the front-end node managed by EOS and the technology constraints of interconnections in terms of throughput to accommodate large number of disks foreseen in the storage. This project will be completed and enter production before the start of LHC Run3 in 2021. In this paper we present the detailed description on the initial system design, the brief results of test equipment for the procurement, the deployment of the system, and the further plans for the project.

Carbonaceous nano-dust emission in proto-planetary discs: the aliphatic-aromatic components

Context. In the interstellar medium, carbon (nano-)grains are a major component of interstellar dust. This solid phase is more vulnerable to processing and destruction than its silicate counterpart. It exhibits a complex, size-dependent evolution that is due to interactions within different radiative and dynamical environments. Infrared signatures of these carbon nano-grains are seen in a large number of discs around Herbig HAeBe stars. Aims. We probe the composition and evolution of carbon nano-grains at the surface of (pre-)transitional proto-planetary discs around Herbig stars. Methods. We present spatially resolved infrared emission spectra obtained with the Nasmyth Adaptive Optics System (NAOS) Near-Infrared Imager and Spectrograph (CONICA) at the Very Large Telescope (VLT) in the 3–4 μm range with a spatial resolution of 0.1′′, which allowed us to trace aromatic, olefinic, and aliphatic bands that are attributed to sub-nanometer hydrocarbon grains. We applied a Gaussian fitting to analyse the observed spectral signatures. Finally, we propose an interpretation in the framework of the The Heterogeneous dust Evolution Model of Interstellar Solids (THEMIS). Results. We show the presence of several spatially extended spectral features that are related to aromatic and aliphatic hydrocarbon material in discs around Herbig stars, from ~10 to 50–100 au, and even in inner gaps that are devoid of large grains. The correlation and constant intensity ratios between aliphatic and aromatic CH stretching bands suggests a common nature of the carriers. Given their expected high destruction rates through UV photons, our observations suggest that they are continuously replenished at the disc surfaces.

Design and analysis of the multi-bent leaf spring considering incomplete insertion in an automatic disc storage system

An automatic disc storage system transfers discs automatically to storage or an optical disc drive using a robotic arm. For example, an optical archive system uses an automatic disc storage system to efficiently handle a large number of discs. The automatic disc storage system commonly uses a multi-bent leaf spring (MBLS) to insert and hold a disc. In the automatic disc storage system, incomplete insertion of the disc can occur if the disc is not moved properly into storage by the robotic arm. Incomplete insertion causes several problems and therefore should be analyzed carefully. This paper examines the dynamic response of the disc during insertion. Using Castigliano’s second theorem, we analyzed the relationship between deformation and the applied forces of the MBLS at the moving contact position between the MBLS and disc. The formula used to describe this relationship also provided the corresponding design parameters of the MBLS. Disc displacement was determined using a one-factor comparative design in transient analysis. An objective function was defined as a distance of the disc to ensure complete disc insertion. The number of variables was reduced based on the objective function. Interaction among variables was investigated in a 32-full-factorial design. For the MBLS design to prevent incomplete insertion, the objective function increased by 140.4%.

On designing endurance aware erasure code for SSD-based storage systems

Erasure codes are applied in both HDD and SSD storage systems to improve the reliability. The design of erasure codes for SSD-based systems should be performed with respect to a specific feature of SSDs, i.e., endurance. Endurance is defined as the number of Program/Erase (P/E)-cycles that one SSD can endure for reliable operation. The common metric for comparing the endurance of two systems is the number of P/E-cycles, which is yielded by time-consuming simulations. This paper proposes two new metrics called DPD-factor and GDP-pattern, for comparing the effect of erasure codes on the endurance of systems based on their encoding designs, without simulation. With respect to the endurance, EA-EO is designed as the modification of EVENODD with smaller DPD-factor. The endurance of EVENODD and EA-EO are compared regarding the system configurations: the size of stripe unit, the number of disks, and the sizes of request. The results of comparison show that the best configurations of system for enhanced endurance are: 1) a large number of disks are applied in systems, or 2) the size of request is equal to the stripe unit size. Furthermore, it concludes that a code with smaller DPD-factor and a sequential GDP-pattern can provide higher endurance for systems.

Reliability analysis of deduplicated and erasure-coded storage

Space efficiency and data reliability are two primary concerns for modern storage systems. Chunk-based deduplication, which breaks up data objects into single-instance chunks that can be shared across objects, is an effective method for saving storage space. However, deduplication affects data reliability because an object's constituent chunks are often spread across a large number of disks, potentially decreasing the object's reliability. Therefore, an important problem in deduplicated storage is how to achieve space efficiency yet maintain each object's original reliability. In this paper, we present initial results on the reliability analysis of HP-KVS, a deduplicated key-value store that allows each object to specify its own reliability level and that uses software erasure coding for data reliability. The combination of deduplication and erasure coding gives rise to several interesting research problems. We show how to compare the reliability of erasure codes with different parameters and how to analyze the reliability of a big data object given its constituent parts' reliabilities. We also present a method for system designers to determine under what conditions deduplication will save space for erasure-coded data.

Computational model for simultaneous Q switching and mode-locking in a solid state laser with a saturable absorber

A numerical model of rate equations for a four-level solid state laser with Cr4+:YAG saturable absorber including excited state absorption ESA is presented. The cavity is divided into a large number of disks and the model is solved for each disk and its local corresponding photon flux. The flux array is shifted for each recurrence simulating the movement of photons inside the cavity during the round trip. This simulator can describe the mode-locking phenomenon and can be used to simulate simultaneous mode locking and Q switching with a saturable absorber.

Efficient parallel processing of range queries through replicated declustering

A common technique used to minimize I/O in data intensive applications is data declustering over parallel servers. This technique involves distributing data among several disks so as to parallelize query retrieval and thus, improve performance. We focus on optimizing access to large spatial data, and the most common type of queries on such data, i.e., range queries. An optimal declustering scheme is one in which the processing for all range queries is balanced uniformly among the available disks. It has been shown that single copy based declustering schemes are non-optimal for range queries. In this paper, we integrate replication in conjunction with parallel disk declustering for efficient processing of range queries. We note that replication is largely used in database applications for several purposes like load balancing, fault tolerance and availability of data. We propose theoretical foundations for replicated declustering and propose a class of replicated declustering schemes, periodic allocations, which are shown to be strictly optimal for a number of disks. We propose a framework for replicated declustering, using a limited amount of replication and provide extensions to apply it on real data, which include arbitrary grids and a large number of disks. Our framework also provides an effective indexing scheme that enables fast identification of data of interest in parallel servers. In addition to optimal processing of single queries, we show that this framework is effective for parallel processing of multiple queries. We present experimental results comparing the proposed replication scheme to other techniques for both single queries and multiple queries, on synthetic and real data sets.

Resource-Based Striping: An Efficient Striping Strategy for Video Servers Using Heterogeneous Disk-Subsystems

In building a large-scale video server, it is highly desirable to use heterogeneous disk-subsystems for the following reasons. First, existing disks may fail, especially in an environment with a large number of disks, enforcing the use of new disks. Second, for a scalable server, to cope with the increasing demand of customers, new disks may be needed to increase the server's storage capacity and throughput. With rapid advances in the performance of disks, the newly added disks generally have a higher data transfer rate and a larger storage capacity than the disks originally in the system. In this paper, we propose a novel striping scheme, termed as resource-based striping (RBS), for video servers built on heterogeneous disks. RBS combines the techniques of wide striping and narrow striping so that it can obtain the optimal stripe allocation and efficiently utilize both the I/O bandwidth and storage capacity of all disks. RBS is suitable for applications whose files are not updated frequently, such as course-on-demand and movie-on-demand. We examine the performance of RBS via simulation experiments. Our results show that RBS greatly outperforms the conventional striping schemes proposed for video servers with heterogeneous or homogeneous disks, in terms of the number of simultaneous streams supported and the number of files that can be stored.

Automated tuning of parallel I/O systems: an approach to portable I/O performance for scientific applications

Parallel I/O systems typically consist of individual processors, communication networks, and a large number of disks. Managing and utilizing these resources to meet performance, portability, and usability goals of high performance scientific applications has become a significant challenge. For scientists, the problem is exacerbated by the need to retune the I/O portion of their code for each supercomputer platform where they obtain access. We believe that a parallel I/O system that automatically selects efficient I/O plans for user applications is a solution to this problem. The authors present such an approach for scientific applications performing collective I/O requests on multidimensional arrays. Under our approach, an optimization engine in a parallel I/O system selects high quality I/O plans without human intervention, based on a description of the application I/O requests and the system configuration. To validate our hypothesis, we have built an optimizer that uses rule based and randomized search based algorithms to tune parameter settings in Panda, a parallel I/O library for multidimensional arrays. Our performance results obtained from an IBM SP using an out-of-core matrix multiplication application show that the Panda optimizer is able to select high quality I/O plans and deliver high performance under a variety of system configurations with a small total optimization overhead.

Threshold-Based Dynamic Replication in Large-ScaleVideo-on-Demand Systems

Recent advances in high speed networking technologies and video compression techniques have made Video-on-Demand (VOD) services feasible. A large-scale VOD system imposes a large demand on I/O bandwidth and storage resources, and therefore, parallel disks are typically used for providing VOD service. Although striping of movie data across a large number of disks can balance the utilization among these disks, such a striping technique can exhibit additional complexity, for instance, in data management, such as synchronization among disks during data delivery, as well as in supporting fault tolerant behavior. Therefore, it is more practical to limit the extent of data striping, for example, by arranging the disks in groups (or nodes) and then allowing intra-group (or intra-node) data striping only. With multiple striping groups, however, we may need to assign a movie to multiple nodes so as to satisfy the total demand of requests for that movie. Such an approach gives rise to several design issues, including: (1) what is the right number of copies of each movie we need so as to satisfy the demand and at the same time not waste storage capacity, (2) how to assign these movies to different nodes in the system, and (3) what are efficient approaches to altering the number of copies of each movie (and their placement) when the need for that arises. In this paper, we study an approach to dynamically reconfiguring the VOD system so as to alter the number of copies of each movie maintained on the server as the access demand for these movies fluctuates. We propose various approaches to addressing the above stated issues, which result in a VOD design that is adaptive to the changes in data access patterns. Performance evaluation is carried out to quantify the costs and the performance gains of these techniques.

Data striping and reliability aspects in distributed video servers

To provide the required amount of storage and bandwidth, a video server typically comprises a large number of disks. As the total number of disks increases, the influence of the striping algorithm that determines how video data are distributed across the disks becomes decisive in terms of overall server cost and performance. Also introducing fault-tolerance against disk failures becomes a must. In this paper, we first evaluate different striping algorithms in terms of throughput, buffer requirement, and start-up latency for a non-fault-tolerant server. We then examine the impact of data striping on a fault-tolerant server and show that the striping policy and the optimal technique to assure fault-tolerance are related: Depending on the technique used to assure fault-tolerance (mirroring or parity), different striping techniques perform best.

Numerical Techniques for Estimating the Surface Areas of Ellipsoids Representing Food Materials

Abstract Food materials (seeds, grains, fruits and vegetables) resembling the shape of a general ellipsoid were modelled for accurate determination of surface area from measurements of their three principal dimensions. The process of surface area estimation involved partitioning the ellipsoid into an appropriate number of elliptical discs, determination of the surface areas of the edges of the discs and summing them to obtain the total surface area. Two types of perimeters were used to determine the edge surface areas: (1) the average perimeter; and (2) the root mean square perimeter. For edge length, three measures were considered: (1) parallel to the axis; (2) inclined to the axis; and (3) length of the elliptical arc. Six different surface area models were developed by combining the two perimeters with the three edge lengths and these were validated against exact analytical solutions for a sphere, prolate spheroid and oblate spheroid. The models with parallel edge length always produced the greatest underestimate of surface area and they cannot, in fact, give accurate results, even if a large number of discs is used. The models with inclined and elliptic arc edge length performed well in the entire range of width/length of prolate spheroids and thickness/length of oblate spheroids. For practical computations involving the general ellipsoid, a minimum of 100 discs was found to be sufficient, as it produced a maximum deviation of less than ±0·1% from 1000 discs for all the models and geometries considered. The performances of two approximate formulae for the surface area of the general ellipsoid were also studied for comparison but they were suitable only in the near-spherical range. Predictions were made and compared with the reported surface areas for a few paddy varieties, which were experimentally determined by previous researchers, and were found to deviate within +7·0 to +30·0%.

Scalability analysis of declustering methods for multidimensional range queries

Efficient storage and retrieval of multi-attribute data sets has become one of the essential requirements for many data-intensive applications. The Cartesian product file has been known as an effective multi-attribute file structure for partial-match and best-match queries. Several heuristic methods have been developed to decluster Cartesian product files across multiple disks to obtain high performance for disk accesses. Although the scalability of the declustering methods becomes increasingly important for systems equipped with a large number of disks, no analytic studies have been done so far. The authors derive formulas describing the scalability of two popular declustering methods-Disk Module and Fieldwise Xor-for range queries, which are the most common type of queries. These formulas disclose the limited scalability of the declustering methods, and this is corroborated by extensive simulation experiments. From the practical point of view, the formulas given in the paper provide a simple measure that can be used to predict the response time of a given range query and to guide the selection of a declustering method under various conditions.

Measuring tree-ring increments on tree bole sections with a video-based robotic positioner.

We report on the design and performance of a system that speeds measurement of radial tree-ring increments on tree stem disks; this method replaces the usual binocular microscope with a video image, and automates the measuring and recording processes. The system was used to measure bole sections cut from stems at various heights to determine volume growth of representative trees in an old-growth ponderosa pine stand. The objective of the measurement system was to speed acquisition of annual growth increments from a large number of disks. A personal computer controls the location of a video camera in a 3-axis positioning system. The operator views the sample on a video monitor and positions the camera over each ring by selecting it with a computer-driven mouse. The computer measures and records the distance that the camera moves between each ring. Task selection is facilitated by menu-driven software that also formats, checks and organizes data files. Measurements have a resolution of 0.026 mm; however, finer resolution could be obtained with a different camera lens. Tests of measurement variability (repeated measurements by individual operators on a single radius) indicated standard errors of 0.006 mm or less for the first measurement sets for four operators. Correlation coefficients among four radii per bole section were as low as 0.66 for a whole tree, suggesting that measurements on single radii may provide poor estimates of radial growth for old trees. This system also offers the potential for automatic ring detection and measurement.

Issues in the design of a storage server for video-on-demand

We examine issues related to the design of a storage server for video-on-demand (VOD) applications. The storage medium considered is magnetic disks or arrays of disks. We investigate disk scheduling policies, buffer management policies and I/O bus protocol issues. We derive the number of sessions that can be supported from a single disk or an array of disks and determine the amount of buffering required to support a given number of users. Furthermore, we propose a scheduling mechanism for disk accesses that significantly lowers the buffer-size requirements in the case of disk arrays. The buffer size required under the proposed scheme is independent of the number of disks in the array. This property allows for striping video content over a large number of disks to achieve higher concurrency in access to a particular video object. This enables the server to satisfy hundreds of independent requests to the same video object or to hundreds of different objects while storing only one copy of each video object. The reliability implications of striping content over a large number of disks are addressed and two solutions are proposed. Finally, we examine various policies for dealing with disk thermal calibration and the placement of videos on disks and disk arrays.

Detection of thermal responses of the retina by use of polyvinylidene fluoride multilayer detector.

The design and properties of thermal detectors constructed with multiple layers of polyvinylidene fluoride film are described. By use of these detectors, production of heat by the photoreceptors in the dark-adapted bullfrog retina in response to brief pulses of very weak light was examined. In response to brief light pulses delivering an average of 1 photon per retinal rod, the retina was found to produce heat more-or-less abruptly after a latent period of 0.2 to 0.4 s. At this level of pulse intensity, the thermal energy produced by the retina was approximately 1,500,000 times as large as the total radiant energy delivered to the retina for stimulation. It appears possible that a large number of disks in the rod outer segment are activated by absorption of a single photon.

Analysis of the epibiotic bacteria of lobster ( Homarus) eggs and their influence on the loss of eggs from the pleopods

Epibiotic bacteria on eggs from 66 female lobsters ( Homarus) were examined to determine if these flora were causally related to loss of eggs from the pleopods. Eggs from five categories of berried female were examined. These included (1) wild born/wild spawned H. americanus, N=11, (2) wild born/lab spawned H. gammarus, N=16, (3) wild born/lab spawned H. americanus, N=18, (4) lab born/lab spawned H. americanus, N=10, and (5) laboratory bred hybrids of H. gammarus × H. americanus crosses, N=11. Four morphological types of bacteria were observed. These are: (1) filamentous bacteria, primarily Leucothrix-like, (2) disc-shaped bacteria resembling Microcyclus, (3) colonial rods, and (4) other rods which attached to surfaces by one end only. Wild born/wild spawned H. americanus eggs had all four types of epibionts. Egg coats had a higher number of total bacteria than stalks, including numberous colonial rods, but fewer filaments and other rods. Samples from laboratory spawned H. americanus contained all four types of bacteria with no distinction noted between egg coat and stalks. H. gammarus eggs had fewer surface bacteria than all other samples; these eggs were consistently occupied by a large number of discs, but were without filaments. Hybrid egg samples resembled H. americanus in both the number (high) and diversity (all four) of epibiotic bacteria on egg coat and stalks. Observations showed that: (1) wild spawned eggs can develop a high bacterial load yet still develop normally and be retained, (2) laboratory spawned eggs may drop off for reasons independent of epibiotic growth, or may be retained even when epibiotic growth is severe, or may drop off as epibiotic bacteria establish themselves on coat/stalk surfaces, (3) H. gammarus eggs have relatively clean egg/stalk surfaces and were retained well, (4) hybrid females have eggs resembling those from lab spawned H. americanus females both in epibiotic composition and proclivity toward drop off.

Use of a filter-paper disk assay in the measurement of lipid biosynthesis

The precipitation by trichloroacetic acid (TCA) of radioactive lipids on disks of filter-paper, followed by extraction with TCA and water to remove soluble radioactive precursors, provides the means for a convenient assay for lipid biosynthesis. Large numbers of disks can be washed in the same vessel, dried, and assayed for radioactivity with liquid scintillation counting equipment. Extraction of disks with lipid solvents provides a convenient control for the possible presence of TCA- and water-insoluble, nonlipid products. The application of the method to the assay of cyclopropane fatty acid synthetase is shown.

A disposable rotating oxygenator capable of being sterilized by heat for a heart-lung machine.

This rotating oxygenator is of a design differing from other rotating oxygenators in that the large surface area necessary for filming blood at high rates of flow is obtained by using a small number of concentric drums rather than a large number of discs. This makes for simplicity of manufacture and ease of assembly. The design is such that it can be cast in plastic in three parts and mass produced at small cost. A number of plasti_s capable of being sterilized by heat are now available; preliminary tests of araldite (epoxide resin) suggest that it may be the most suitable for this purpose. A prototype has been machined out of perspex and has been us.d to test the design in regard to its oxygenating capacity and its effect on blood cells.