External Disk Research Articles

Improved Approximation Algorithms for Data Migration

Our work is motivated by the need to manage data items on a collection of storage devices to handle dynamically changing demand. As demand for data items changes, for performance reasons, the system needs to automatically respond to changes in demand for different data items. The problem of computing a migration plan among the storage devices is called the data migration problem. This problem was shown to be NP-hard, and an approximation algorithm achieving an approximation factor of 9.5 was presented for the half-duplex communication model in Khuller, Kim and Wan (Algorithms for data migration with cloning. SIAM J. Comput. 33(2):448–461, 2004). In this paper we develop an improved approximation algorithm that gives a bound of 6.5+o(1) using new ideas. In addition, we develop better algorithms using external disks and get an approximation factor of 4.5 using external disks. We also consider the full duplex communication model and develop an improved bound of 4+o(1) for this model, with no external disks.

NUCLEAR STAR-FORMING RING OF THE MILKY WAY: SIMULATIONS

We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A ring of dense gas clouds forms as a result of X1-X2 orbit transfer, and our potential model results in a ring radius of ~200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star formation rate (SFR) in the CMZ, ~2x10^7 Msun and ~0.1 Msun/yr. Star formation in our simulations takes place mostly in the outermost X2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.

FALL-BACK DISKS IN LONG AND SHORT GAMMA-RAY BURSTS

We present numerical time-dependent calculations for fall-back disks relevant to GRBs in which the disk of material surrounding the black hole (BH) powering the GRB jet modulates the mass flow, and hence the strength of the jet. Given the initial existence of a small mass <10^{-4} msun near the progenitor with a circularization radius ~10^{10}-10^{11} cm, an unavoidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. For long GRBs, if the mass distribution in the initial fall-back disk traces the progenitor envelope, then a radius ~10^{11} cm gives a time scale ~10^4 s for the X-ray plateau. For late times t>10^7 s a steepening due to a cooling front in the disk may have observational support in GRB 060729. For short GRBs, one expects most of the mass initially to lie at small radii <10^8 cm; however the presence of even a trace amount ~10^{-9} msun of high angular momentum material can give a brief plateau in the light curve. By studying the plateaus in the X-ray decay of GRBs, which can last up to ~10^4 s after the prompt emission, Dainotti et al. find an apparent inverse relation between the X-ray luminosity at the end of the plateau and the duration of the plateau. We show that this relation may simply represent the fact that one is biased against detecting faint plateaus, and therefore preferentially sampling the more energetic GRBs. If, however, there were a standard reservoir in fall-back mass, our model can reproduce the inverse X-ray luminosity-duration relation. We emphasize that we do not address the very steep, initial decays immediately following the prompt emission, which have been modeled by Lindner et al. as fall-back of the progenitor core, and may entail the accretion of > 1 msun.

Thoracic scent efferent system of the Tessaratomidae sensu lato (Hemiptera: Heteroptera: Pentatomoidea) with implication to the phylogeny of the family

We studied the cuticular structures associated with the opening of the adult metathoracic scent glands in the family Tessaratomidae. The terminology previously used for these structures in the Tessaratomidae and Pentatomoidea is briefly reviewed and most suitable terms are selected (i.e., metathoracic scent apparatus, internal and external scent efferent system, internal orifice, vestibule, ostiole, ostiolar groove, peritreme, auricle, spout, groove, ruga, disc, peritremal lobes, evaporatorium, mycoid surface, mushroom body, bridge, alveole, trabeculae, and peritremal surface). We examined and illustrated external scent efferent system of 40 species from 33 genera belonging to all three subfamilies of Tessaratomidae sensu lato, i.e. Tessaratominae, Natalicolinae, and Oncomerinae. Three basic types were recognized: i) Oncomerinae – ostiole slightly removed laterally from the position between coxal acetabula, oval, ostiolar groove not developed or very short, peritreme in form of spout attached anterolaterally to the ostiole; ii) Tessaratomidae sensu stricto (= Tessaratominae + Natalicolinae) – ostiole situated between acetabula, strongly incised mesad, thus vestibule distally opened in two planes (ventrally and laterally) as ostiolar groove, peritreme in form of anterior and posterior peritremal lobes surrounding the ostiolar groove; and iii) Platytatina (Platytatus ambiguus Bergroth, 1892) – ostiole shifted near to lateral metapleural margin, ostiolar groove reduced, situated between two flat, reniform processes (median and lateral lobe). A polarity of these structures is suggested: the type i) of Oncomerinae is regarded as plesiomorphic(shared with Urostylididae, Dinidoridae, etc.); the type iii) of Platytatina is homologized with type ii) of Tessaratominae sensu stricto; the type ii) is unique within Pentatomoidea and considered as an autapomorphy. The information content of the characters of the external scent efferent system and metathoracic spiracle for a phylogenetic hypothesis of relationships within Pentatomoidea is tested by cladistic analyses. We found some apomorphies helping to define Tessaratomidae and Plataspidae, most of the characters, however, seem to be homoplasious at family level. The results of the cladistic analyses further support the monophyly of Dinidoridae + Tessaratomidae sensu lato and that of Tessaratomidae sensu stricto, while the relationships of Oncomerinae and Tessaratomidae sensu stricto as well as the relationships among the family-group taxa within Tessaratomidae sensu stricto need further studies.

A NEW PARADIGM FOR GAMMA-RAY BURSTS: LONG-TERM ACCRETION RATE MODULATION BY AN EXTERNAL ACCRETION DISK

We present a new way of looking at the very long-term evolution of gamma-ray bursts (GRBs) in which the disk of material surrounding the putative black hole powering the GRB jet modulates the mass flow, and hence the efficacy of the process that extracts rotational energy from the black hole and inner accretion disk. The pre-Swift paradigm of achromatic, shallow-to-steep "breaks" in the long-term GRB light curves has not been borne out by detailed Swift data amassed in the past several years. We argue that, given the initial existence of a fall-back disk near the progenitor, an unavoidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. The mass reservoir at large radii moves outward with time and gives a natural power-law decay to the GRB light curves. In this model, the different canonical power-law decay segments in the GRB identified by Zhang et al. and Nousek et al. represent different physical states of the accretion disk. We identify a physical disk state with each power-law segment.

On the metallicity gradient of the Galactic disk

Aims: The iron abundance gradient in the Galactic stellar disk provides fundamental constraints on the chemical evolution of this important Galaxy component. However the spread around the mean slope is, at fixed Galactocentric distance, larger than estimated uncertainties. Methods: To provide quantitative constraints on these trends we adopted iron abundances for 265 classical Cepheids (more than 50% of the currently known sample) based either on high-resolution spectra or on photometric metallicity indices. Homogeneous distances were estimated using near-infrared Period-Luminosity relations. The sample covers the four disk quadrants and their Galactocentric distances range from ~5 to ~17 kpc. Results: A linear regression over the entire sample provides an iron gradient of -0.051+/-0.004 dex/kpc. The above slope agrees quite well, within the errors, with previous estimates based either on Cepheids or on open clusters covering similar Galactocentric distances. However, once we split the sample in inner (Rg < 8 kpc) and outer disk Cepheids we found that the slope (-0.130+/-0.015 dex/kpc) in the former region is ~3 times steeper than the slope in the latter one (-0.042+/-0.004 dex/kpc). We found that in the outer disk the radial distribution of metal-poor (MP, [Fe/H]<-0.02 dex) and metal-rich (MR) Cepheids across the four disk quadrants does not show a clear trend when moving from the innermost to the external disk regions. We also found that the relative fractions of MP and MR Cepheids in the 1st and in the 3rd quadrant differ at 8 sigma (MP) and 15 sigma (MR) level.

The Milky Way's external disc constrained by 2MASS star counts

Context. Thanks to recent large-scale surveys in the near infrared, such as 2MASS, the galactic plane that most suffers from extinction is revealed so its overall structure can be studied. Aims. This work aims at constraining the structure of the Milky Way external disc as seen in 2MASS data, and in particular the warp. Methods. We use the Two Micron All Sky Survey (hereafter 2MASS) along with the Stellar Population Synthesis Model of the Galaxy, developed in Besancon, to constrain the external disc parameters, such as its scale length, its cutoff radius, and the slope of the warp. To properly interpret the observations, the simulated stars are reddened using a 3D extinction map. The shape of the stellar warp is then compared with previous results and with similar structures in gas and dust. Results. We find new constraints on the stellar disc, which is shown to be asymmetrical, similar to observations of HI. The positive longitude side is found to be easily modelled with S-shaped warp but with a significantly smaller slope than the one seen in the HI warp. At negative longitudes, the disc presents peculiarities that are not reproduced well by any simple model. Finally, comparing with the warp seen in the dust, it seems to follow an intermediate slope between the gas and the stars.

APPLYING AND COMPARING FOUR DIFFERENT PSO APPROACHES IN INTEGRATED PROBLEM OF PRODUCT CHANGE PLANNING, PART SUPPLIER SELECTION, AND QUANTITY ALLOCATION

ABSTRACT Previous studies on strategy selection of product configuration changes often ignored part supplies, resulting in disruptions to the execution of modification strategies during the manufacturing process. Therefore, this study focuses on an optimization assessment of simultaneous product changes in order to establish a mathematical model, which included supplier selection, coupled with quantity discounts from each part supplier. For instance, this study used external Hard Disk Drive (HDD) enclosures; we designed models using Particle Swarm Optimization-Original (PSO-O), Particle Swarm Optimization-Inertia Weight (PSO-IW), Particle Swarm Optimization-Constriction Factor (PSO-CF), Particle Swarm Optimization-Dynamically Changing Inertia weight (PSO-DW), and then compared the efficiency of the strategies obtained by the four methods. Results showed that PSO-CF was more efficient than the other three methods for this problem.

AGILE detection of intense gamma-ray emission from the blazar PKS 1510-089

We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini LEggero) satellite of an intense gamma-ray flare from the source AGL J1511-0909, associated with the powerful quasar PKS 1510-089, during ten days of observations from 23 August to 1 September 2007. During the observation period, the source was in optical decrease following a flaring event monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to study the spectral energy distribution and the theoretical models based on the synchrotron and inverse Compton (IC) emission mechanisms. AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV - 50 GeV and 18 - 60 keV bands, respectively. Between 23 and 27 August 2007, AGILE detected gamma-ray emission from PKS 1510-089 when this source was located about 50 degrees off-axis, with an average flux of (270 +/- 65) x 10^{-8} photons cm^{-2} s^{-1} for photon energy above 100 MeV. In the following period, 28 August - 1 September, after a satellite re-pointing, AGILE detected the source at about 35 degrees off-axis, with an average flux (E > 100 MeV) of (195 +/- 30) x 10^{-8} photons cm^{-2} s^{-1}. No emission was detected by Super-AGILE, with a 3-sigma upper limit of 45 mCrab in 200 ksec. The spectral energy distribution is modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions by external photons: the SSC emission contributes primarily to the X-ray band, whereas the contribution of the IC from the external disc and the broad line region match the hard gamma-ray spectrum observed.

FPGA Electronics for OPET: A Dual-Modality Optical and Positron Emission Tomograph.

The development of a prototype dual-modality optical and PET (OPET) small animal imaging tomograph is underway in the Crump Institute for Molecular Imaging at the University of California Los Angeles. OPET consists of a single ring of six detector modules with a diameter of 3.5 cm. Each detector has an 8 × 8 array of optically isolated BGO scintillators which are coupled to multichannel photomultiplier tubes and open on the front end. The system operates in either PET or optical mode and reconstructs the data sets as 3D tomograms. The detectors are capable of detecting both annihilation events (511 keV) from PET tracers as well as Single Photon Events (SPEs) (2-3 eV) from bioluminescence. Detector channels are readout using a custom multiplex readout scheme and then filtered in analog circuitry using either a γ-ray or SPE specific filter. Shaped pulses are sent to a Digital Signal Processing (DSP) unit for event processing. The DSP unit has 100 MHz Analog-to-Digital Converters on the front-end which send digitized samples to Field Programmable Gate Arrays which are programmed via user configurable algorithms to process PET coincidence events or bioluminescence SPEs. Information determined using DSP includes: event timing, energy determination-discrimination, position determination-lookup, and coincidence processing. Coincidence or SPE events are recorded to an external disk and minimal post processing is required prior to image reconstruction. Initial imaging results from a phantom filled with 18FDG solution and an optical pattern placed on the front end of a detector module in the vicinity of a SPE source are shown.

Are the Red Halos of Galaxies Made of Low‐Mass Stars? Constraints from Subdwarf Star Counts in the Milky Way Halo

Surface photometry detections of red and exceedingly faint halos around galaxies have resurrected the old question of whether some nonnegligible fraction of the missing baryons of the universe could be hiding in the form of faint, hydrogen-burning stars. The optical/near-infrared colors of these red halos have proved very difficult to reconcile with any normal type of stellar population, but can, in principle, be explained by advocating a bottom-heavy stellar initial mass function. This implies a high stellar mass-to-light ratio and hence a substantial baryonic mass locked up in such halos. Here we explore the constraints imposed by current observations of ordinary stellar halo subdwarfs on a putative red halo of low-mass stars around the Milky Way. Assuming structural parameters similar to those of the red halo recently detected in stacked images of external disk galaxies, we find that a smooth halo component with a bottom-heavy initial mass function is completely ruled out by current star count data for the Milky Way. All viable smooth red halo models with a density slope even remotely similar to that of the stacked halo moreover contain far too little mass to have any bearing on the missing-baryon problem. However, we note that these constraints can be sidestepped if the red halo stars are locked up in star clusters, and we discuss potential observations of other nearby galaxies that may be able to put such scenarios to the test.

The Milky Way, an Exceptionally Quiet Galaxy: Implications for the Formation of Spiral Galaxies

[Abridged]We compare both the Milky Way and M31 galaxies to local external disk galaxies within the same mass range, using their relative locations in the planes formed by V_flat versus M_K, j_disk, and the average Fe abundance of stars in the galaxy outskirts. We find, for all relationships, that the MW is systematically offset by ~ 1 sigma, showing a significant deficiency in stellar mass, in angular momentum, in disk radius and [Fe/H] in the stars in its outskirts at a given V_flat. On the basis of their location in the M_K, V_flat, and R_d volume, the fraction of spirals like the MW is 7+/-1%, while M31 appears to be a "typical'' spiral. Our Galaxy appears to have escaped any significant merger over the last ~10 Gyrs which may explain why it is deficient by a factor 2 to 3 in stellar mass, angular momentum and outskirts metallicity and then, unrepresentative of the typical spiral. As with M31, most local spirals show evidence for a history shaped mainly by relatively recent merging. We conclude that the standard scenario of secular evolution is generally unable to reproduce the properties of most (if not all) spiral galaxies. However, the so-called "spiral rebuilding'' scenario proposed by Hammer et al. 2005 is consistent with the properties of both distant galaxies and of their descendants - the local spirals.

The broad band spectral index of blazars in a low state

Using the broad band spectral index of 164 blazars in a low state, we studied the possible correlation between different broad band spectral index (α r.ir , α r.o , α r.x , α r.γ , α ir.o , α ir.x , α ir.γ , α o.x , α o.γ , α x.γ ). We also studied the possible correlation between different broad band spectral index of high-frequency peaked Bl Lac object (HBL), low-frequency peaked BL Lac object (LBL) and flat spectral radio quasars (FSRQs), respectively. The strong anti-correlations were found between α r.o and α o.γ , between α r.o and α x.γ in a low state for our blazar sample. For LBL and FSRQs, the strong anti-correlations were found between α r.ir and α ir.x , between α r.o and α o.x , and between α r.o and α o.γ in a low state. Based on these results, we suggested that the seed photons of the γ-ray drive from both the jet and the external accretion disk or the broad-line region, and that the subclasses of blazars seem to the different emission mechanism.

Continuous acquisition and storage of uncompressed image data based on a personal computer equipped with a CCD camera and an external hard disk drive

An image acquisition and storage system without data compression was constructed by combining a personal computer, an external hard disk drive and a charge-coupled device camera (1024 × 768 pixels, monochrome 8 bit/pixel) operating at 30 frame s−1. Test runs indicated the system performance: the storage time, size and speed of 37 min, 55 GB and 25 MB s−1 respectively. The design of the system program was shown and discussed on the basis of the test run results. The constructed system can be applied to various scientific and engineering applications including digital microscopy. The technical information shown in this study is helpful to researchers and engineers in constructing their own system by themselves.

Torque quality and comparison of internal and external rotor axial flux surface-magnet disc machines

In this paper, pulsating torque components of permanent magnet machines and pulsating torque minimization techniques are discussed for axial flux surface-magnet disc-type PM machines. The pulsating torque analysis describing general instantaneous electromagnetic torque equation and torque ripple factor is briefly provided in order to analyze torque ripple component. Detailed finite-element analyses focusing on the minimization of cogging and torque ripple components using several techniques are also given. A detailed comparison of the two techniques is also illustrated in this paper.

Gompertz: A Scilab Program for Estimating Gompertz Curve Using Gauss-Newton Method of Least Squares

A computer program for estimating Gompertz curve using Gauss-Newton method of least squares is described in detail. It is based on the estimation technique proposed in Reddy (1985). The program is developed using Scilab (version 3.1.1), a freely available scientific software package that can be downloaded from http://www.scilab.org/. Data is to be fed into the program from an external disk file which should be in Microsoft Excel format. The output will contain sample size, tolerance limit, a list of initial as well as the final estimate of the parameters, standard errors, value of Gauss-Normal equations namely GN₁ GN₂ and GN₃, No. of iterations, variance(σ²), Durbin-Watson statistic, goodness of fit measures such as R², D value, covariance matrix and residuals. It also displays a graphical output of the estimated curve vis a vis the observed curve. It is an improved version of the program proposed in Dastidar (2005).

Probing the Canis Major stellar over-density as due to the Galactic warp

Proper-motion, star counts and photometric catalog simulations are used to explain the detected stellar over-density in the region of Canis Major, claimed to be the core of a disrupted dwarf galaxy (CMa, Martin et al. [CITE], MNRAS, 348, 12; Bellazzini et al. [CITE], [arXiv:astro-ph/0311119]), as due to the Galactic warp and flare in the external disk. We compare the kinematics of CMa M-giant selected sample with surrounding Galactic disk stars in the UCAC2 catalog and find no peculiar proper motion signature: CMa stars mimic thick disk kinematics. Moreover, when taking into account the Galactic warp and flare of the disk, 2MASS star count profiles reproduce the CMa stellar over-density. This star count analysis is confirmed by direct comparison with synthetic color-magnitude diagrams simulated with the Besancon models (Robin et al. [CITE], AA Yanny et al. 2003, ApJ, 588, 824).

디스크 드라이브의 주기적 외란 고속 보상 제어

The control objective in hard disk drives is to move head as fast as possible to target track and position the head over the center of target track in the presence of external disturbances. The external shock or disk clamping error in manufacturing process causes the disk center to deviate from the disk rotation center. The disk shift acts on the control system as disturbance and degrades severely the performance of disk drives. In this paper, we present a new controller that compensates for the periodic disturbances very fast. The disturbance compensator is arranged in parallel with the state feedback controller. To avoid the interference with the state feedback controller, the compensator creates compensation signal without the feedback of system output until steady state. The pulse type controller is included additionally for improving the transient performance due to initial state. Finally, in order to demonstrate the superior performance of the proposed compensator. we present some experimental results using a commercially available disk drive.

Thermodynamic optimization of radial MHD flow between parallel circular disks

The radial flow between two parallel circular disks is investigated with the aim to determine the optimum convective heat transfer conditions at the external disk surfaces in order to minimize the intrinsic irreversibilities. A general situation is considered where the fluid is electrically conducting and may be under the influence of a transversal magnetic field. The velocity and electric current density fields are obtained analytically and used to solve the heat transfer equation under boundary conditions of the third kind. The analysis is in the absence of fluid inertia, under creeping flow conditions (Reynolds number ≪ 1). A perturbation approach in order to include the convective heat transfer effects in the flow is used. The Péclet number is assumed to be small. The analytic expressions for the velocity, electric current density and temperature fields are used to calculate explicitly the global entropy generation rate. When the convective heat transfer coefficients for each wall are different, this function displays a minimum for specific heat exchange conditions. The results are shown for both the hydrodynamic and the magnetohydrodynamic cases. It is also found that the mean Nusselt number at the upper wall shows a maximum value for a given value of the Hartman number, when the dimensionless heat transfer coefficients for each disk and the Péclet number are fixed. This mean Nusselt number for maximum heat transfer is near its value for minimum entropy generation conditions.

High-speed parallel external sorting of data with arbitrary distribution

Many parallel sorting algorithms of external disk data have been reported such as NOW-sort, SPsort, hill sort and so on. They all reduce the execution time compared with some known sequential sort; however, they differ in terms of the speed, throughput or cost-effectiveness. Mostly, they deal with uniformly distributed data in their value range. If we divide and redistribute data to processors by fixed and equal division of the key range, all processors will have about equal numbers of keys to sort and store. But if irregularly distributed data are given, the performance will suffer severely as the partitioning would no longer produce balanced loads among processors. Few research results have been reported for parallel external sort of data with arbitrary distribution. In this paper, we develop two distribution-insensitive scalable parallel external sorting algorithms that use sampling technique and histogram counts to achieve even distribution of keys, which eventually contribute to achieve good performance. Experimental results on a cluster of 16 Linux workstations show up to threefold enhancement of the performance compared with NOW-sort for sorting 16 GB integer keys.