Time-step coupling for hybrid simulations of multiscale flows

A new method is presented for the exploitation of time-scale separation in hybrid continuum-molecular models of multiscale flows. Our method is a generalisation of existing approaches, and is evaluated in terms of computational efficiency and physical/numerical error. Comparison with existing schemes demonstrates comparable, or much improved, physical accuracy, at comparable, or far greater, efficiency (in terms of the number of time-step operations required to cover the same physical time). A leapfrog coupling is proposed between the ‘macro’ and ‘micro’ components of the hybrid model and demonstrates potential for improved numerical accuracy over a standard simultaneous approach. A general algorithm for a coupled time step is presented. Three test cases are considered where the degree of time-scale separation naturally varies during the course of the simulation. First, the step response of a second-order system composed of two linearly-coupled ODEs. Second, a micro-jet actuator combining a kinetic treatment in a small flow region where rarefaction is important with a simple ODE enforcing mass conservation in a much larger spatial region. Finally, the transient start-up flow of a journal bearing with a cylindrical rarefied gas layer. Our new time-stepping method consistently demonstrates as good as or better performance than existing schemes. This superior overall performance is due to an adaptability inherent in the method, which allows the most-desirable aspects of existing schemes to be applied only in the appropriate conditions

環境発電を用いた通信システムのための高効率MACプロトコルの実環境特性に関する研究

近年、高範囲の環境情報を効率的に長期間観測する技術として，無線センサネットワーク（WSNs: Wireless Sensor Networks）への注目が高まっている．さらに各センサ端末にエナジーハーベスティング（EH: Energy Harvesting）電源を具備することで，半永久的に情報を取得可能なWSNsの実現が期待されている．しかし，EH電源のみを用いたWSNsでは，各端末は一次電池ではなく，自然界から回収される電力のみによって動作するため，各端末の動作電源は微弱かつ確率的に変動する性質をもつ．そのため各端末の消費電力がEH電源からの回収電力を上回った場合は，各端末が電池切れを引き起こし，ネットワークが動作不能となることが懸念される．よって，各端末の電池切れに対してロバスト性をもち，通信の必要が生じた時のみ通信を行うことで，省電力性を達成する方式が必要となる．　媒体アクセス制御（MAC: Medium Access Control）層における研究では，端末間の時間同期を行うことなく，日和見的に通信を行う受信機駆動型MACが検討されている．特に，Intermittent-receiver driven data transmission（IRDT）は，高い省電力性と通信品質を達成する通信方式として知られている．IRDTは，各端末の供給電力が確率的に変動することを考慮していない．そのため，EH電源を用いたWSNsにおいては，回収電力が小さい端末が動作不能に陥る可能性があり，通信品質の劣化を引き起こす．そこでIRDTに対して，EH電源からの回収電力の多寡と通信可能端末数の情報を用いて，適応的に各端末が間欠間隔を制御することで消費電力制御を可能にしたEnergy-Neutral Receiver-Initiated MAC（ENRI-MAC）が提案されており，IRDTに比べ，高い通信品質を達成可能であることが示されている．しかし，ENRI-MACの特性評価は，各端末の回収電力を3つのクラスタに分類することで回収電力の多寡を考慮した疑似的なモデルで性能評価を行ったものであり，実環境に則して空間的・時間的に回収電力が変化するモデルにおいて，同様に高い通信品質を達成するかについては議論の余地がある．　そこで本研究では，ENRI-MACの間欠間隔の動的制御機能が通信品質を改善し得るかを評価するため，実環境の回収電力モデルに即した特性評価を行う．回収電力は環境的要因により変動し，同一の実験環境で評価することが困難であるため，今回は実環境に多数の照度センサを配置することで，日中の照度を実測し，この値を回収電力の実測値として用いた計算機シミュレーションを行う．数値評価を通じて，実環境では，間欠間隔の伸延を行うことで自端末の消費電力を低減する機能が，他端末の消費電力を著しく増加させてしまい，ネットワーク内に電池切れを連鎖的に引き起こし，通信品質を劣化させる可能性があることを明らかにする．　この問題を解決するために，本稿ではENRI-MACにおいて提案される間欠間隔設計を見直すことで，回収電力をENRI-MACよりも効率的に利用可能な間欠間隔を制御可能改良された改良ENRI-MACを提案する．さらに，先に述べた実環境に即した回収電力モデルにおいて，提案する改良ENRI-MACの間欠間隔設計が高い通信品質を達成可能であることを示す．電気通信大学201

Review of hypoxaemia in the anaesthetized horse: predisposing factors, consequences and management

Objectives: To discuss how hypoxaemia might be harmful and why the horse is particularly predisposed to developing it. To review the strategies that are used to manage hypoxaemia in anaesthetised horses, to describe how successful these strategies are and the adverse events associated with them. Databases used: Google Scholar and PubMed using the search terms – horse; pony; exercise; anaesthesia; hypoxaemia; oxygen; mortality; morbidity; ventilation perfusion mismatch. Conclusions: Although there is no evidence that hypoxaemia is associated with increased morbidity and mortality in anaesthetised horses, most anaesthetists would agree that it is important to recognise and prevent or treat it. The favourable anatomical and physiological adaptations of the horse for exercise, adversely affect gas exchange once the animal is recumbent. Hypoxaemia is recognised more frequently than in other domestic species during general anaesthesia, although its incidence in healthy horses remains unreported. The management of hypoxaemia in anaesthetised horses is challenging and often unsuccessful. Positive pressure ventilation strategies to address alveolar atelectasis in humans have been modified for implementation in the recumbent anaesthetised horse, but are often accompanied by unpredictable and unacceptable cardiopulmonary adverse effects, and some strategies are difficult or impossible to achieve in adult horses. Furthermore, the anticipated beneficial effects of these techniques are inconsistent. Increasing the inspired fraction of oxygen during anaesthesia is often unsuccessful since much of the impairment in gas exchange is a direct result of shunt. Alternative approaches to the problem involve the manipulation of pulmonary blood away from atelectatic regions of lung to better ventilated areas. However, further work is essential, with particular focus upon survival associated with general anaesthesia in the horse, before any technique can be accepted into widespread clinical use

Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View

Small satellite systems enable whole new class of missions for navigation, communications, remote sensing and scientific research for both civilian and military purposes. As individual spacecraft are limited by the size, mass and power constraints, mass-produced small satellites in large constellations or clusters could be useful in many science missions such as gravity mapping, tracking of forest fires, finding water resources, etc. Constellation of satellites provide improved spatial and temporal resolution of the target. Small satellite constellations contribute innovative applications by replacing a single asset with several very capable spacecraft which opens the door to new applications. With increasing levels of autonomy, there will be a need for remote communication networks to enable communication between spacecraft. These space based networks will need to configure and maintain dynamic routes, manage intermediate nodes, and reconfigure themselves to achieve mission objectives. Hence, inter-satellite communication is a key aspect when satellites fly in formation. In this paper, we present the various researches being conducted in the small satellite community for implementing inter-satellite communications based on the Open System Interconnection (OSI) model. This paper also reviews the various design parameters applicable to the first three layers of the OSI model, i.e., physical, data link and network layer. Based on the survey, we also present a comprehensive list of design parameters useful for achieving inter-satellite communications for multiple small satellite missions. Specific topics include proposed solutions for some of the challenges faced by small satellite systems, enabling operations using a network of small satellites, and some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications Surveys and Tutorial

A Scalable Correlator Architecture Based on Modular FPGA Hardware, Reuseable Gateware, and Data Packetization

A new generation of radio telescopes is achieving unprecedented levels of sensitivity and resolution, as well as increased agility and field-of-view, by employing high-performance digital signal processing hardware to phase and correlate large numbers of antennas. The computational demands of these imaging systems scale in proportion to BMN^2, where B is the signal bandwidth, M is the number of independent beams, and N is the number of antennas. The specifications of many new arrays lead to demands in excess of tens of PetaOps per second. To meet this challenge, we have developed a general purpose correlator architecture using standard 10-Gbit Ethernet switches to pass data between flexible hardware modules containing Field Programmable Gate Array (FPGA) chips. These chips are programmed using open-source signal processing libraries we have developed to be flexible, scalable, and chip-independent. This work reduces the time and cost of implementing a wide range of signal processing systems, with correlators foremost among them,and facilitates upgrading to new generations of processing technology. We present several correlator deployments, including a 16-antenna, 200-MHz bandwidth, 4-bit, full Stokes parameter application deployed on the Precision Array for Probing the Epoch of Reionization.Comment: Accepted to Publications of the Astronomy Society of the Pacific. 31 pages. v2: corrected typo, v3: corrected Fig. 1

Neverlast: Towards the Design and Implementation of the NVM-based Everlasting Operating System

Novel non-volatile memory (NVM) technologies allow for the efficient implementation of \u27\u27intermittently-powered\u27\u27 smart dust and edge computing systems in a previously unfamiliar way. Operating with rough environmental conditions where power-supply failures occur often requires adjustments to all parts of the system. This leads to an inevitable trade-off in the design of operating systems -- the overhead of persisting the achieved computation progress over power failures is detrimental to the possible amount of progress with the available energy budgets. It is, therefore, crucial to minimize the overhead of ensuring persistence. This paper presents the case that persistence should be provided as an operating-system service to achieve everlasting operating capabilities. Triggered by power-failure interrupts, an implicit persistence service for the processor status of a process preserves progress on the CPU-instruction level. This interrupt only triggers if necessary so that no power-state polling is needed. We outline architectures for everlasting systems and discuss their benefits and drawbacks compared to existing approaches. Thereby, the operating system provides persistence as a service at run-time to the application, with minimal overhead. Our approach enables the separation of the application from energy-supply state estimation, as well as state-preserving logic for software and hardware components

ESTCube-1 käsu- ja andmehaldussüsteemi tarkvara

Antud töö raames sai loetletud ESTCube-1 Käsu- ja Andmehaldussüsteemile ehk pardaarvutile esitatud nõuded. Vastavalt nõuetele sai arendatud pardaarvuti tark- vara, mis sisaldab FreeRTOS ajureid andmesiinide ja pardaseadmete jaoks, vea- haldust, käsuhaldurit, moodulit telemeetria salvestamiseks ning failisüsteeme jadali- idesega ferroelektriliste muutmälude ja välkmälude jaoks. Mitmed arendatud tarkvaramoodulitest on leidnud kasutust ka ESTCube-1 kaamerasüsteemi pardal. Arendatud tarkvaral on sooritatud teste kahel satelliidi maapealsel mudelil ning orbiidil lendaval satelliidil. Mõningate eranditega on orbiidil täheldatud prob- leemid edukalt reprodutseeritud maapealsetel mudelitel, ning uus parandustega versioon tarkvarast on edukalt orbiidil olevale satelliidile laetud. Orbiidil on pardaarvutil edukalt katsetatud satelliidi orientatsiooni määramise ja juhtimise tarkvara. Andurite mõõdiste eeltöötluse algoritmid on orbiidil testi- tud ning satelliidi orientatsiooni määramise algoritmi väljundit on võrreldud par- dakaamera piltidega. Kasutades satelliidi osutamise algoritmi koos pardaarvuti skriptidega, on täidetud ka osa ESTCube-1 missioonist - pildistada Eestit kos- mosest. Seni on ESTCube-1 olnud orbiidil veidi üle aasta ning kõik satelliidi süsteemid on endiselt töökorras