Engineering topics
Tang, Kun
Publications and source records attributed to Tang, Kun.
Hybrid 0D–2D black phosphorus quantum dots–graphitic carbon nitride nanosheets for efficient hydrogen evolution
As an emerging post-graphene two-dimensional (2D) nanomaterial, black phosphorus (BP) is attracting a great deal of current attention for the direct conversion of solar energy into solar fuels on account of its unique tunable direct-bandgap and high charge-carrier mobility. Herein, for the first time, we immobilize BP quantum dots (BPQDs) onto graphitic carbon nitride (g-C 3 N 4 ) nanosheets to create a 0D-2D inorganic-organic hybrid via a conventional and cost–effective sonication approach. The as-prepared BPQDs/g-C 3 N 4 hybrids display BPQD content-dependent performance in visible-light-driven hydrogen generation. 5 wt% BPQDs/g-C 3 N 4 with cyclability exhibits the greatest hydrogen evolution rate of 271 μmol h-1 g-1 that is 5.6 and 4.2 times greater than that of pristine g-C 3 N 4 and BPQDs, respectively. We demonstrate that the type-II band alignment, the formation of phosphorus–carbon bonds and the efficient interfacial charge separation between well-dispersed BPQDs and g-C 3 N 4 synergetically enhance the photoactivity and photostability. In conclusion, this study opens possibilities to create viable BP-based heterostructures for energy conversion and storage.
Exploring the Optimal Platform Configuration for Power-Constrained HPC Workflows
In high-performance computing (HPC) workflows, data analytics is typically utilized to gain insights from scientific simulations. Approaching the era of exascale, online analysis is gaining popularity due to the savings of I/O to persistent storage. As computing capability keeps growing, power consumption is becoming critical to HPC facilities. Enforcing power limits is emerging as a practical trend for power-constrained HPC facilities. However, it remains unclear how to choose the appropriate power limits for various HPC workflows and how to distribute the power limit of a workflow between simulation and analysis. In addition, given a power limit, it is unclear what the optimal scales and power capping levels are for various workflows, especially when taking reliability into account. In order to resolve these issues in power-constrained HPC, in this paper, we propose a reliability-aware model to determine the aforementioned platform configurations for HPC workflows. We also validate our model and present model-driven studies for a wide range of real-system scenarios. Our study reveals interesting insights about how platform configuration affects the performance and energy efficiency of HPC workflows under power constraints.
Effective Running of End-to-End HPC Workflows on Emerging Heterogeneous Architectures
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Toward Managing HPC Burst Buffers Effectively: Draining Strategy to Regulate Bursty I/O Behavior
HPC (high-performance computing) applications usually show bursty I/O behaviors. In order to expedite the applications, permanent storage systems are usually provisioned to serve such I/O bursts. Approaching the era of exascale computing, non-volatile RAM is introduced as burst buffers, to absorb the bursty bulk data and relax the I/O provisioning requirement of the permanent storage systems. However, without judiciously draining the burst buffers, I/O bursts are passed down to the underlying storage systems, which causes severe I/O contention issues.In order to minimize the I/O provisioning requirement and resolve the issues caused by I/O bursts, we propose a proactive draining scheme to manage the draining process of distributed node-local burst buffers. In addition, we develop an I/O provisioning model to predict the minimized I/O provisioning requirement for permanent storage systems. Evaluation results show that applying the proactive draining scheme largely relaxes the I/O provisioning requirement while preserving the I/O performance of underlying storage systems.
Proactive Draining Scheme for HPC Burst Buffers
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Making sound vortices by metasurfaces
Based on the Huygens-Fresnel principle, a metasurface structure is designed to generate a sound vortex beam in airborne environment. The metasurface is constructed by a thin planar plate perforated with a circular array of deep subwavelength resonators with desired phase and amplitude responses. The metasurface approach in making sound vortices is validated well by full-wave simulations and experimental measurements. Potential applications of such artificial spiral beams can be anticipated, as exemplified experimentally by the torque effect exerting on an absorbing disk.
Power-capping Aware Checkpointing: On the Interplay among Power-capping, Temperature, Reliability, Performance, and Energy
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Annealing in tellurium-nitrogen co-doped ZnO films: The roles of intrinsic zinc defects
In this article, the authors have conducted an extensive investigation on the roles of intrinsic zinc defects by annealing of a batch of Te-N co-doped ZnO films. The formation and annihilation of Zn interstitial (Zn{sub i}) clusters have been found in samples with different annealing temperatures. Electrical and Raman measurements have shown that the Zn{sub i} clusters are a significant compensation source to holes, and the Te co-doping has a notable effect on suppressing the Zn{sub i} clusters. Meanwhile, shallow acceptors have been identified in photoluminescence spectra. The N{sub O}-Zn-Te complex, zinc vacancy (V{sub Zn})-N{sub O} complex, and V{sub Zn} clusters are thought to be the candidates as the shallow acceptors. The evolution of shallow acceptors upon annealing temperature have been also studied. The clustering of V{sub Zn} at high annealing temperature is proposed to be a possible candidate as a stable acceptor in ZnO.
Focusing and directional beaming effects of airborne sound through a planar lens with zigzag slits
Based on the Huygens-Fresnel principle, we design a planar lens to efficiently realize the interconversion between the point-like sound source and Gaussian beam in ambient air. The lens is constructed by a planar plate perforated elaborately with a nonuniform array of zigzag slits, where the slit exits act as subwavelength-sized secondary sources carrying desired sound responses. The experiments operated at audible regime agree well with the theoretical predictions. This compact device could be useful in daily life applications, such as for medical and detection purposes.
Dynamic crystallography reveals early signalling events in ultraviolet photoreceptor UVR8
Abstract not provided