1,127 research outputs found
The effect of a hub turning vane on turbulent flow and heat transfer in a four-pass channel at high rotation numbers
No full textThis paper investigates effects of rotation and a turning vane on flow field and heat transfer of a 4-pass smooth channel through CFD (Computational Fluid Dynamics) simulations. An 180° hub U-bend connecting the middle two passages (AR = 2:1) is the focus of the study. Reynolds number varies from 10,000 to 40,000 and rotation number changes from 0 to 0.4. In stationary conditions, effect of the turning vane is to reduce recirculation and non-uniformity of mainstream. In addition, pressure drop and secondary flow kinetic energy (SKE) are largely reduced by the turning vane. Heat transfer deterioration due to flow separation and recirculation is suppressed by the turning vane in Hub Turn. In rotating conditions, size of recirculation is reduced and uniformity of mainstream is increased comparing to stationary case. Velocity distribution and heat transfer exhibit different profiles on LE and TE considering the flow direction due to Coriolis. Effects of turning vane to suppress recirculation and to reduce pressure drop are not obvious. In Hub Turn and downstream 3rd pass, heat transfer enhancement due to turning vane is very weak
Tuan liu re dui liu zhong su du chang jie gou han shu he liu dong xun huan de shi yan yan jiu
No full textQi, Pengfei = 湍流熱對流中速度場結構函數和流動循環的實驗研究 / 齊鵬飛.Thesis (M.Phil.)--Chinese University of Hong Kong, 2011.Includes bibliographical references (p. 65-69).Abstracts in English and Chinese.Qi, Pengfei = Tuan liu re dui liu zhong su du chang jie gou han shu he liu dong xun huan de shi yan yan jiu / Qi Pengfei.Abstract --- p.i摘要 --- p.iiAcknowledgements --- p.iiiContents --- p.ivList of Figures --- p.viList of Tables --- p.XChapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- What is turbulence? --- p.1Chapter 1.2 --- Why study turbulence and experimentally? --- p.2Chapter 1.3 --- Turbulent Rayleigh-Benard convection --- p.4Chapter 1.4 --- Basic equations and characteristic parameters --- p.SChapter 1.4.1 --- Continuity equation --- p.5Chapter 1.4.2 --- Momentum equation (Navier-Stokes equation) --- p.5Chapter 1.4.3 --- Energy equation --- p.7Chapter 1.4.4 --- Averaged equations --- p.9Chapter 1.4.5 --- Characteristic parameters --- p.10Chapter 1.5 --- Statistical properties in small-scale turbulence --- p.13Chapter 1.5.1 --- Phenomenological description and Kolmogorov hypotheses --- p.14Chapter 1.5.2 --- Local structure of the velocity fluctuations --- p.15Chapter 1.6 --- Large-scale circulation --- p.17Chapter 1.7 --- Motivation and Organizations of this thesis --- p.19Chapter 1.7.1 --- B059 scaling --- p.19Chapter 1.7.2 --- Large-scale circulation --- p.19Chapter 1.7.3 --- Organization of the thesis --- p.20Chapter 1.8 --- Some words to my experiment and further expectation --- p.21Chapter Chapter 2 --- Experimental apparatus and techniques --- p.27Chapter 2.1 --- Rectangle cell --- p.27Chapter 2.2 --- The power supply and cooler --- p.28Chapter 2.3 --- Thermistor and multimeter --- p.29Chapter 2.4 --- Particle image velocimetry (PIV) technology --- p.30Chapter 2.4.1 --- Seeding particles --- p.31Chapter 2.4.2 --- Light source and light-sheet optics --- p.33Chapter 2.4.3 --- Imaging system --- p.34Chapter 2.4.4 --- Control system --- p.34Chapter 2.4.5 --- Analysis method --- p.35Chapter Chapter 3 --- Small-scale properties in rectangular cell --- p.37Chapter 3.1 --- Introduction --- p.37Chapter 3.2 --- Experimental condition --- p.37Chapter 3.3 --- Homogeneity --- p.39Chapter 3.4 --- Isotropy --- p.40Chapter 3.5 --- Scaling of structure function --- p.42Chapter Chapter 4 --- Large-scale circulation --- p.51Chapter 4.1 --- Introduction --- p.51Chapter 4.2 --- Experimental condition and limitation --- p.54Chapter 4.3 --- Statistical properties of large-scale circulation period --- p.56Chapter 4.4 --- Scaling of the Reynolds number --- p.59Chapter 4.5 --- Oscillation period --- p.60Chapter Chapter 5 --- Conclusion --- p.63Chapter 5.1 --- Small-scale properties in rectangular cell --- p.63Chapter 5.2 --- Large-scale circulation --- p.63Reference --- p.6
Size- and stability-dependent fracture scaling in nanoscale metallic glass
No full textExperiments show a significant size effect in the fracture modes of the metallic glass (MG) nanowires, while simulations often diverge due to differences in thermal histories caused by timescale issue of the classical molecular dynamics quenching methods. This leads to disparities between computational and experimental results. To address this, we used a hybrid molecular dynamics (MD) and Monte Carlo thermal cycling method to fabricate well-annealed MG nanowires with effective quenching rates significantly lower than those of MD-prepared samples. Our findings reveal that fracture mode transitions are strongly tied to thermal history. For high quenching rate samples, the fracture mode is only dictated by the aspect ratio (L/D) of nanowires, aligning with existing simulations. For low quenching rate samples, the critical factor determining fracture is the diameter (D), matching experimental observations. This resolves the discrepancies between simulations and experiments on size-dependent fractures in nanoscale MGs. Microscopic analysis links this variation to the intrinsic plastic zone width (delta 0), influenced by the aspect ratio in high rates but correlated solely with diameter in low rates. We propose a universal model for fracture scaling with size and thermal stability in nanostructured MGs
Surface-emitting lasers for communications: novel metal-cavity microlasers and high-contrast-grating tunable VCSELs
No full textA comprehensive study of the theory and experiments of surface-emitting semiconductor lasers is presented. The design of novel micro and nanolasers using metal cavities for optical confinement is discussed. Theoretical modeling of quantum-well and quantum-dot emission properties, as well as experimental characterization of their coupling with optical cavities, are presented. Lasing behavior of our designed and fabricated devices is demonstrated at room temperature under continuous-wave and pulsed electrical injection with 3-μm and 1-μm cavity diameters, respectively. This work provides the research path toward dense-integrable power-efficient on-chip light sources. Surface-emitting tunable lasers for high-speed, long-haul communication are investigated. Novel laser designs using micro-electro-mechanical system controlled high-contrast gratings as tunable mirrors are presented. Rigorous, accurate, and efficient electromagnetic models for high-contrast gratings are developed. Our model enables us to design high-contrast gratings as one-dimensional or two-dimensional metastructures integrable on surface-emitting lasers. A wide range of optical functionalities such as broadband reflection, high-Q resonance, filtering, beam-steering, focusing, beam-conversion, and generation of photon orbital angular momentum are achieved. Our optical model is integrated with our laser cavity model and the rate equation model to predict the temperature-dependent voltage tunable light output intensity and spectra. Future design and experimental strategies for heterogeneously integrated tunable surface-emitting lasers are discussed.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2017-05-01The student, Pengfei Qiao, accepted the attached license on 2015-04-13 at 17:11.The student, Pengfei Qiao, submitted this Dissertation for approval on 2015-04-13 at 17:33.This Dissertation was approved for publication on 2015-04-14 at 13:35.DSpace SAF Submission Ingestion Package generated from Vireo submission #7840 on 2015-07-22 at 14:24:22Made available in DSpace on 2015-07-22T22:45:14Z (GMT). No. of bitstreams: 2
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sj-pdf-1-ajs-10.1177_03635465231208843 – Supplemental material for Fibroblast Activation Protein–Targeted PET/CT with Al18F-NODA-FAPI-04 for In Vivo Imaging of Tendon Healing in Rat Achilles Tendon Injury Models
No full textSupplemental material, sj-pdf-1-ajs-10.1177_03635465231208843 for Fibroblast Activation Protein–Targeted PET/CT with Al18F-NODA-FAPI-04 for In Vivo Imaging of Tendon Healing in Rat Achilles Tendon Injury Models by Zhenfeng Liu, Haiying Zhou, Pengfei Li, Zewei Wang, Tian Tu, Sohaib Hasan Abdullah Ezzi, Vishnu Goutham Kota, Mohamed Hasan Abdulla Hasan Abdulla, Ahmad Alhaskawi, Yanzhao Dong, Yuqiao Huang, Mengjie Dong, Xinhui Su and Hui Lu in The American Journal of Sports Medicine</p
Unsupervised Author Disambiguation using Heterogeneous Graph Convolutional Network Embedding
No full textPeople share same names in real world. When a digital library user searches for an author name, he may see a mixture of publications by different authors who have the same name. Making distinctions between them is an important prerequisite to improve the quality of services and contents in digital libraries. The general task of author disambiguation is to associate publications which belong to an identical name or names with highly similar spellings to different people entities. In recent years, many researches have been conducted to solve this challenging task. However, some works rely heavily on external knowledge bases and manually annotated data. Some unsupervised learning based works require complex feature engineering. In this paper, we propose a novel and efficient author disambiguation framework which needs no labeled data. We first construct a publication heterogeneous network for each ambiguous name. Then, we use our proposed heterogeneous graph convolutional network embedding method that encodes both graph structure and node attribute information to learn publication representations. After that, we propose a graph enhanced clustering method for name disambiguation that can greatly accelerate the clustering process and need not require the number of distinct persons. Our framework can be continually retrained and applied on incremental disambiguation task when new publications are put in. Experimental results on two datasets show that our framework clearly performs better than several state-of-the-art methods for author disambiguation
Non-adiabatic Mapping Dynamics in the Phase Space of the SU(N) Lie Group
No full textWe present the rigorous theoretical framework of the generalized spin mapping representation for non- adiabatic dynamics. This formalism is based on the generators of the su(N) Lie algebra to represent N discrete electronic states, thus preserving the size of the original Hilbert space in the state representation. The Stratonovich-Weyl transform is then used to map an operator in the Hilbert space to a continuous func- tion on the SU(N) Lie Group manifold which is a phase space of continuous variables. Wigner representation is used to describe the nuclear degrees of freedom. Using the above representations, we derived an exact expression of the time-correlation function as well as the exact quantum Liouvillian. Making the linearization approximation, this exact Liouvillian is reduced to the Liouvillian of the several recently proposed meth- ods. These expressions lead to a self-consistent trajectory-based method to simulate non-adiabatic dynamics, which is based entirely on the generalized spin mapping formalism to treat the electronic states without the necessity of converting back to the cartesian Meyer-Miller-Stock-Thoss mapping variables. We envision that the theoretical work presented in this work provides a rigorous and unified framework to formally derive non-adiabatic quantum dynamics approaches with continuous variables
Importance of initial momentum rate and air-fuel premixing on moderate or intense low oxygen dilution (MILD) combustion in a recuperative furnace
No full textCopyright © 2009 American Chemical SocietyThis paper reports an investigation on the influences of air−fuel injection momentum rate and the air−fuel premixing on the moderate or intense low oxygen dilution (MILD) combustion in a 20-kW recuperative furnace. Various patterns of partially and fully premixed reactants have proven experimentally to work extremely well in the present furnace. H2 recorded for a variety of equivalence ratios at a firing rate of 10 kW. The present numerical study suggests that there is a critical momentum rate of the inlet fuel−air mixture below which the MILD combustion cannot occur. Also, it is revealed, both experimentally and numerically, that, above the critical rate, both the inlet fuel−air mixedness and momentum rate impose insignificant influence on the stability of and emissions from the MILD combustion.Jianchun Mi, Pengfei Li, Bassam B. Dally, and Richard A. Crai
Comparing Post-Expansion Integration Policies of the Early Roman Republic and the Early Chu State from a Geopolitical Perspective
No full textUnderstanding Performance Inefficiencies In Native And Managed Languages
No full textProduction software packages have become increasingly complex with millions of lines of code, sophisticated control and data flow, and references to a hierarchy of external libraries. This complexity often introduces performance inefficiencies across software stacks, making it practically impossible for users to pinpoint them manually. Performance profiling tools (a.k.a. profilers) abound in the tools community to aid software developers in understanding program behavior. Classical profiling techniques focus on identifying hotspots. The hotspot analysis is indispensable; however, it can hardly diagnose whether a resource is being used in a productive manner that contributes to the overall efficiency of a program. Consequently, a significant burden is on developers to make a judgment call on whether there is scope to optimize a hotspot. Derived metrics, e.g., cache miss ratio, offer slightly better intuition into hotspots but are still not panaceas. Hence, there is a need for profilers that investigate resource wastage instead of usage. To overcome the critical missing pieces in prior work and complement existing profilers, we propose novel fine- and coarse-grained profilers to pinpoint varieties of performance inefficiencies and provide optimization guidance for a wide range of software covering benchmarks, enterprise applications, and large-scale parallel applications running on supercomputers and data centers. Fine-grained profilers are indispensable to understand performance inefficiencies comprehensively. We propose a whole-program profiler called LoadSpy, which works on binary executables to detect and quantify wasteful memory operations in their context and scope. Our observation, which is justified by myriad case studies, is that wasteful memory operations are often an indicator of various forms of performance inefficiencies, such as suboptimal choices of algorithms or data structures, missed compiler optimizations, and developers’ inattention to performance. Guided by LoadSpy, we are able to optimize a large number of well-known benchmarks and real-world applications, yielding significant speedups. Despite deep performance insights offered by fine-grained profilers, the high overhead keeps them away from widespread adoption, particularly in production. By contrast, coarse-grained profilers introduce low overhead at the cost of poor performance insights. Hence, another research topic is how we benefit from both, that is, the combination of deep insights of fine-grained profilers and low overhead of coarse-grained ones. The first effort to do so is proposing a lightweight profiler called JXPerf. It abandons heavyweight instrumentation by combining hardware performance monitoring units and debug registers available in commodity CPUs to detect wasteful memory operations. Compared with LoadSpy, JXPerf reduces the runtime overhead from 10x to 7% on average. The lightweight nature makes it useful in production. Another effort is proposing a lightweight profiler called FVSampler, the first nonintrusive profiler to study function execution variance.Computer ScienceDoctor of Philosophy (Ph.D.
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