Disk Array Research Articles

The Cyber Attack on Saudi Aramco in 2012

In recent years, information security has become a corporate priority due tothe large number of cyber-attacks that happen every day. These attacks could cause a regression in economic growth, which makes corporations another reason to defend their system. This paper provides an introduction to Saudi Aramco as well as an overview of its products. Then, the paper examines the Aramco cyber-attack in 2012. Aramco is a massive company with huge facilities that require powerful policies on security. Aramco should implement a Redundant Array of Independent Disks and Intrusion Detection System and review the log files on the server to protect its servers against attacks.

A numerical study on the closed packed array of gold discs as an efficient dual mode plasmonic tweezers

In this report, we propose the closed pack array of gold discs on glass, as a dual mode plasmonic tweezers that benefits from two trapping modes. The first trapping mode is based on leaky surface plasmon mode (LSPM) on the gold discs with a longer penetration depth in the water and a longer spatial trapping range, so that target nanoparticles with a radius of 100 nm can be attracted toward the gold surface from a vertical distance of about 2 µm. This trapping mode can help to overcome the inherent short range trapping challenge in the plasmonic tweezers. The second trapping mode is based on the dimer surface plasmonic mode (DSPM) in the nano-slits between the neighboring gold discs, leading to isolated and strong trapping sites for nanoparticles smaller than 34 nm. The proposed plasmonic tweezers can be excited in both LSPM and DSPM modes by switching the incident wavelength, resulting in promising and complementary functionalities. In the proposed plasmonic tweezers, we can attract the target particles towards the gold surface by LSPM gradient force, and trap them within a wide half widthhalfmaximum (HWHM) that allows studying the interactions between the trapped particles, due to their spatial proximity. Then, by switching to the DSPM trapping mode, we can rearrange the particles in a periodic pattern of isolated and stiff traps. The proposed plasmonic structure and the presented study opens a new insight for realizing efficient, dual-mode tweezers with complementary characteristics, suitable for manipulation of nanoparticles. Our thermal simulations demonstrate that the thermal-induced forces does not interefe with the proposed plasmonic tweezing.

Ultra-narrowband and highly-directional THz thermal emitters based on the bound state in the continuum

AbstractThe development of novel and cost-effective THz emitters, with properties superior to current THz sources, is an active and important field of research. In this work, we propose and numerically demonstrate a simple yet effective approach of realizing terahertz sources working in continuous-wave form, by incorporating the new physics of bound state in the continuum (BIC) into thermal emitters. By deliberately designing the structure of slotted disk array made of high-resistivity silicon on top of a low index dielectric buffer layer supported by a conducting substrate, a quasi-BIC mode with ultra-high quality factor (∼104) can be supported. Our results reveal that the structure can operate as an efficient terahertz thermal emitter with near-unity emissivity and ultranarrow bandwidth. For example, an emitter working at 1.3914 THz with an ultranarrow linewidth less than 130 MHz, which is roughly 4 orders of magnitude smaller than that obtained from a metallic metamaterial-based thermal emitter, is shown. In addition to its high monochromaticity, this novel emitter has additional important advantages including high directionality and linear polarization, which makes it a promising candidate as the new generation of THz sources. It holds a great potential for practical applications where high spectral resolving capability is required.

Ultra-confined low-loss surface phonon polaritonic resonances in periodically patterned monolayer hexagonal boron nitride

Surface plasmon polaritons in two-dimensional (2D) materials such as graphene have drawn much attention in the past decades, nevertheless, suffer from ohmic losses. Recently, monolayer hexagonal boron nitride (hBN) has been found the capability to support low-loss surface phonon polaritons (SPhPs). In this work, we theoretically propose the atom-thin metasurface with monolayer-hBN. We reveal that monolayer-hBN disk array can support SPhP resonances with ultra-small effective mode volumes (~10−9 λ03) as well as high quality factors (102-103) in mid-infrared (mid-IR). The corresponding frequency dispersions with geometrical parameters and ambient environment are also discussed in detail. Furthermore, the phenomenon of phonon hybridization is demonstrated based on monolayer-hBN ring array. Finally, the local field enhancement with an enhancement factor ~103 is realized by breaking the symmetry of the ring. This work reveals that monolayer-hBN can play an important role in 2D material polaritonics and atom-thin metasurfaces, and has great potential in mid-IR quantum emission, sensing and spectroscopic applications.

Stochasticity in the Switching of Nanodisks for Probabilistic Computing

Author(s): Han, HS; Lee, S; Je, SG; Kang, M; Ok, HJ; Kim, N; Chao, W; Im, MY; Lee, KS | Abstract: Stochasticity in magnetic nanodevices is an essential characteristic for harnessing these devices to computing based on population coding or the building blocks of probabilistic computing, p-bits. A magnetic tunneling junction (MTJ) consisting of a patterned magnetic element is considered a promising computing unit in the concept of artificial neurons and p-bits. A comprehensive understanding of the stochasticity in the switching of patterned magnetic elements is crucial for realizing MTJ-based probabilistic computing technology. In the present work, the stochastic behavior in the switching process of a perpendicularly magnetized Co/Pt disk within an array was directly observed utilizing full-field soft X-ray microscopy. Within 50 repeated hysteretic cycles, the stochastic magnetization switching of individual Co/Pt disks within disk arrays is identified. We found that the stochasticity in the magnetization switching of disks considerably depends on the disk size. The stochasticity initially decreases as the disk radius gets bigger from 125 to 375 nm (region I), then increases with further enlarging the disk size to 625 nm (region II). The variance of thermal fluctuation relevant to the disk size and the multilevel switching within a disk are severely involved in the observed size-dependent stochasticity. This work provides the way for controlling the stochasticity in the switching of nanopatterned elements, which is a key aspect of MTJ-based probabilistic computing.

Reconfigurable acoustic multiplexer/demultiplexer using time division

Implementing guided-wave technologies in mechanical systems has always been a significant challenge due to losses associated with defects and sharp angles. Inspired by quantum Hall effects in condensed matter physics, mechanical topological insulators (TIs) have recently addressed these issues using efficient and robust signal transport supported by backscattering-immune topological protection. In this Letter, we demonstrate the first mechanical TI-based multiplexer/demultiplexer using acoustic waves. Triangular arrays of circular piezoelectric disks bonded to an aluminum host medium, shunted through external circuits with equivalent negative capacitance, break inversion symmetry and create topologically protected interface states. Combined with programmable switches, the device enables acoustic waves to travel efficiently from an input source to multiple output receivers, or vice versa, via dynamic topological interfaces. The proposed acoustic multiplexer/demultiplexer is envisioned to find application in wave-based devices, as an accompaniment to ubiquitous surface acoustic wave filtering used in communication devices, such as cell phones, radios, and computer peripherals.

Determination of Forced Convective Heat Transfer Coefficients on an Array of Discs

Forced convection heat transfer due to airflow across an array of thin discs is encountered in various engineering applications. In this work, a three-dimensional steady Reynolds-Averaged Navier-Stokes computational fluid dynamics (CFD) simulation is performed to investigate the phenomenon at the surfaces of an array of discs. A computational grid comprising of a solid domain representing the array of discs and a fluid domain denoting the airflow is set up. A two-step solution procedure is employed whereby first the airflow across the discs is simulated till convergence and then the heat transfer is calculated. The temperature of the air before the array of discs, that of each surface of the discs, and the wall heat flux are monitored to calculate average convective heat transfer coefficients (CHTCs). The CFD model is validated using a wind tunnel experiment and it is shown that both are in close agreement with each other based on the surface temperatures and average CHTC predictions. The CHTCs are found to be significantly higher on the upwind face of the discs compared to the downwind side. Finally, based on the simulations, a correlation based on the non-dimensional average Nusselt number versus Reynolds and Prandtl numbers is derived.

Short- and Long-Range Microparticle Transport on Permalloy Disk Arrays in Time-Varying Magnetic Fields

We investigate maneuvering superparamagnetic microparticles, or beads, in a remotely-controlled, automated way across arrays of few-micron-diameter permalloy disks. This technique is potentially useful for applying tunable forces to or for sorting biological structures that can be attached to magnetic beads, for example nucleic acids, proteins, or cells. The particle manipulation method being investigated relies on a combination of stray fields emanating from permalloy disks as well as time-varying externally applied magnetic fields. Unlike previous work, we closely examine particle motion during a capture, rotate, and controlled repulsion mechanism for particle transport. We measure particle velocities during short-range motion—the controlled repulsion of a bead from one disk toward another—and compare this motion to a simulation based on stray fields from disk edges. We also observe the phase-slipping and phase-locked motion of particles engaging in long-range transport in this manipulation scheme.

Ultra-broadband, near-perfect and thin-film scale solar absorber based on semiconductor-metal nanocone

In this paper, a solar energy absorber consisting of a periodic array of GaAs-Ti disks placed on the surface of a metal substrate tungsten (W) is proposed to realize the ultra-wideband, near-perfect absorption. The absorption characteristics of the absorber are investigated theoretically by using of the finite-difference time-domain method (FDTD). The researched results indicate that the absorption bandwidth with the absorption rate of over 90% exceeds 3400 nm, which is wider than that of the advanced solar energy absorption reported previously. The average absorption rate of this absorber at this bandwidth is up to 96.2%. The solar spectral weighted absorption efficiency η reaches 96.1%, and the ratio of the missed energy γ drops to 0.039. What’s more, the absorption performance of the absorber with different parameters, structures and materials is investigated systematically to determine the best absorption performance. The researched results discovery that propagating surface plasmons (PSPs), cavity modes, guided mode resonances (GMRs), localized surface plasmons (LSPs), plasmonic coupling and their synergy are excited to achieve the ultra-broadband and near-perfect absorption in visible and infrared wavelengths. It also has the characteristics of independent incident and polarization angles. These excellent properties and attractive findings demonstrate that the proposed solar absorber has more extensive applications in the field of energy collection and energy conversion.

Realization of a sensitivity multi-band tunable sensor through modulating the phase change of Ge2Sb2Te5

Metamaterials with active modulation properties have broad application prospects. Here, we demonstrate a metamaterial with a structured phase-change alloy Ge2Sb2Te5 (GST) disk array, which supports the active tunability by changing crystallinity. At room temperature, two transmission peaks (0.642 at 6.21 THz, 0.659 at 10.96 THz) are achieved based on bright-dark mode coupling. In experiments, the P1 peak is enhanced by reducing the vertical distance of GST disks, while the P2 peak is enhanced by reducing the horizontal distance. In further experiments, as the crystallinity increases, the resonance position of the P1 peak is replaced by the valley V1, thereby realizing the “OPEN” and “CLOSE” of the transmission window of the metamaterial. This metamaterial shows a new direction to achieve active optics devices or sensors.

Effect of Metasurface Quality Factor on the Thermal Time Constant in Microbolometers

This paper investigates the effects of the metasurface quality on the thermal mass of metasurface integrated microbolometers. In this configuration, a temperature sensitive layer forms the insulator in a metal/insulator/metal metasurface. The geometric parameters of a hexagonal close packed disk array are optimized for perfect absorption at $A=10.6 \mu \mathrm{m}$ for different thicknesses. Increasing the thickness of the insulator increases the quality factor but increases the thermal mass of the microbolometer.

Analytical design of tunable disk, patch and ribbon-patterned graphene absorbers in the terahertz spectrum

Three topologies of periodic arrays of graphene consisting of disk, ribbon, and patch for realizing terahertz absorbers are proposed and analyzed in this work. The circuit model was utilized in the design of the absorbers. The main goal was to implement tunable bandwidth in terahertz absorbers by changing the chemical potential in graphene. In this respect, a novel method for calculating the relaxation time which is related to chemical potential of graphene is presented, of importance in the absorber design process. Absorbers have been designed and simulated in central frequencies of 8, 10, and 12 terahertz with bandwidths of 0.5, 0.8, and 1 THz at 95% absorption. The absorbers' key advantages are their simple structure (consisting of graphene arrays, dielectric spacer, and a bottom metal layer), bandwidth tuning via a backed-gate voltage of graphene, their independence of input wave polarization – in the case of disk and patch shape graphene arrays - and their extremely low sensitivity to angle of incidence.

Conceptual design of demultiplexer using coupled-gyration-mode signals in vortex-state disk arrays

We explored, by micromagnetic simulations, a novel conceptual time- and frequency-division demultiplexer using coupled-vortex-gyration-mode propagations in specially designed vortex-state arrays composed of circular- and chopped-shape disk dots. Coupled-vortex-gyration modes are characteristic of resonant excitations in given vortex-state arrays, which are controllable with bias static fields applied to given array structures as well as with different configurations of circular- and chopped-shape disks. As examples, we designed two array structures composed of five-vortex-state disk arrays of different combinations of circular and chopped shapes. By changing the direction of the in-plane bias fields, either leftward or rightward propagation of specific coupled-gyration-mode signals can be manipulated by exciting one of the coupled gyration modes of specific resonance frequency from an input disk, which allows for time- and frequency-division demultiplexing functions. This device concept offers an energy-efficient means of information processing without joule heating in cases where a low-damping magnetic material is used in micro-to-nanometer-scale magnonic circuits.

Research on access efficiency and optimization of massive seismic data

With the continuous development of exploration technology, the magnitude of seismic data is getting larger and larger, and the access efficiency of seismic data has become the main bottleneck in the process of seismic data processing. The cluster structure realizes the separation of computing and storage. The data is stored in the disk array, and the data is calculated in the computing node. The maximum network speed between each computing node and the management node is 1GB/s, and the total maximum network speed of all computing nodes is 5GB/S (peak value). In addition, for disk array, the maximum read speed can be ignored (more than 1GB/s) without considering the network bandwidth, while the maximum write speed is 350MB/s. In the process of data processing, it needs to flow between the disk array and the computing node, and its speed must be affected by the network bandwidth. Therefore, the theoretical maximum I/O speed of the system is 1GB/s for reading and 350MB/s for writing. To build a multi format seismic data model, the loading of the system before optimization can not support the original seismic data format, so the original seismic data (such as SEGY and SEGD) needs to be converted into the internal ATT format of the system. In this process, the whole original data needs to be read circularly, and the new file is written circularly, and then the new file is decompiled, Save the header part into the table in the database. Export is the opposite process, which needs to convert ATT format to SEGY or SEGD format.

Performance Evaluations of Distributed File Systems for Scientific Big Data in FUSE Environment

Data are important and ever growing in data-intensive scientific environments. Such research data growth requires data storage systems that play pivotal roles in data management and analysis for scientific discoveries. Redundant Array of Independent Disks (RAID), a well-known storage technology combining multiple disks into a single large logical volume, has been widely used for the purpose of data redundancy and performance improvement. However, this requires RAID-capable hardware or software to build up a RAID-enabled disk array. In addition, it is difficult to scale up the RAID-based storage. In order to mitigate such a problem, many distributed file systems have been developed and are being actively used in various environments, especially in data-intensive computing facilities, where a tremendous amount of data have to be handled. In this study, we investigated and benchmarked various distributed file systems, such as Ceph, GlusterFS, Lustre and EOS for data-intensive environments. In our experiment, we configured the distributed file systems under a Reliable Array of Independent Nodes (RAIN) structure and a Filesystem in Userspace (FUSE) environment. Our results identify the characteristics of each file system that affect the read and write performance depending on the features of data, which have to be considered in data-intensive computing environments.

An Empirical Performance Evaluation of Multiple Intel Optane Solid-State Drives

Cloud computing as a service-on-demand architecture has grown in importance over the last few years. The storage subsystem in cloud computing has undergone enormous innovation to provide high-quality cloud services. Emerging Non-Volatile Memory Express (NVMe) technology has attracted considerable attention in cloud computing by delivering high I/O performance in latency and bandwidth. Specifically, multiple NVMe solid-state drives (SSDs) can provide higher performance, fault tolerance, and storage capacity in the cloud computing environment. In this paper, we performed an empirical evaluation study of performance on recent NVMe SSDs (i.e., Intel Optane SSDs) with different redundant array of independent disks (RAID) environments. We analyzed multiple NVMe SSDs with RAID in terms of different performance metrics via synthesis and database benchmarks. We anticipate that our experimental results and performance analysis will have implications for various storage systems. Experimental results showed that the software stack overhead reduced the performance by up to 75%, 52%, 76%, 91%, and 92% in RAID 0, 1, 10, 5, and 6, respectively, compared with theoretical and expected performance.

Collective Dynamics in Quasi-One-Dimensional Hard Disk System

We present the results of molecular dynamic studies of collective dynamics in a system of hard disks confined to a narrow quasi-one-dimensional (quasi-1D) channel. The computer simulations have been performed for the specific channel width of 3/2 of disk diameter in which the disk arrangement at close packing resembles zigzag ordering characteristic of a vertically oriented two-dimensional (2D) triangular lattice. In such a quasi-1D system, which is intermediate between 1D and 2D arrays of hard disks, the transverse excitations obey very specific dispersion law typical of the usual optical transverse modes. This is in a sharp contrast both to the 1D case, where transverse excitations are not possible, and to the 2D case, where the regular shear waves with a propagation gap were observed. Other peculiarities of the dispersion of collective excitations as well as some results of disk structuring and thermodynamics of the quasi-1D hard disk system are presented and discussed for a range of hard disk densities typical for fluid and distorted crystal states.

Confinement discerns swarmers from planktonic bacteria.

Powered by flagella, many bacterial species exhibit collective motion on a solid surface commonly known as swarming. As a natural example of active matter, swarming is also an essential biological phenotype associated with virulence, chemotaxis, and host pathogenesis. Physical changes like cell elongation and hyper-flagellation have been shown to accompany the swarming phenotype. Less studied, however, are the contrasts of collective motion between the swarming cells and their counterpart planktonic cells of comparable cell density. Here, we show that confining bacterial movement in circular microwells allows distinguishing bacterial swarming from collective swimming. On a soft agar plate, a novel bacterial strain Enterobacter sp. SM3 in swarming and planktonic states exhibited different motion patterns when confined to circular microwells of a specific range of sizes. When the confinement diameter was between 40 μm and 90 μm, swarming SM3 formed a single-swirl motion pattern in the microwells whereas planktonic SM3 formed multiple swirls. Similar differential behavior is observed across several other species of gram-negative bacteria. We also observed 'rafting behavior' of swarming bacteria upon dilution. We hypothesize that the rafting behavior might account for the motion pattern difference. We were able to predict these experimental features via numerical simulations where swarming cells are modeled with stronger cell-cell alignment interaction. Our experimental design using PDMS microchip disk arrays enabled us to observe bacterial swarming on murine intestinal surface, suggesting a new method for characterizing bacterial swarming under complex environments, such as in polymicrobial niches, and for in vivo swarming exploration.

Toroidic and antitoroidic orders in hexagonal arrays of dielectric trimers: Magnetic group approach

Herein, we investigate the symmetry-protected toroidal dipole resonances and conditions of their excitation in a new type of electromagnetic metamaterials. These metamaterials are all-dielectric planar periodic arrays of dielectric disks disposed on a dielectric substrate. The elementary building blocks of the array are trimers which are distributed in hexagonal unit supercells. The highest geometrical symmetry of the unit supercell is C6v. The analysis is fulfilled by using the representation theory of groups with the application of the magnetic group theory, which is a new approach in solving such problems. We have shown that to get access to the toroidal supermodes of the array, the unit supercell symmetry must be broken twice: firstly, the C3v symmetry of the trimer, and secondly, the C6v symmetry of the unit supercell needs to be reduced. Selection rules for the symmetric and antisymmetric orders of the toroidal dipole moments in the arrays are defined. In particular, we have shown that with the reduction of the unit supercell symmetry to the C2v group, the array exhibits the toroidal dipole resonance with an antitoroidic order. The arrays with the lower Cs symmetry can provide the resonances with both toroidic and antitoroidic orders. It is also shown that these arrays are always polarization sensitive. Full-wave simulations and experiments confirm the theoretical predictions. The suggested metamaterials can provide an enhanced light-matter interaction due to the spatially and temporally confined light in resonant systems with very high quality factors.

Foraging Small White Butterflies, Pieris rapae, Search Flowers Using Color Vision

We demonstrate that the small white butterfly,Pieris rapae, uses color vision when searching flowers for foraging. We first trained newly emerged butterflies in a series of indoor behavioral experiments to take sucrose solution on paper disks, colored either blue, green, yellow, or red. After confirming that the butterflies were trained to visit a certain colored disk, we presented all disks simultaneously. The butterflies selected the disk of trained color, even among an array of disks with different shades of gray. We performed the training using monochromatic lights and measured the action spectrum of the feeding behavior to determine the targets’Pieris-subjective brightness. We used the subjective brightness information to evaluate the behavioral results and concluded thatPieris rapaebutterflies discriminate visual stimuli based on the chromatic content independent of the intensity: they have true color vision. We also found thatPierisbutterflies innately prefer blue and yellow disks, which appears to match with their flower preference in the field, at least in part.