arXiv subjects

Nan Gu

Publications and source records attributed to Nan Gu.

13 recordsLinked to original sources

arXiv2026

A Pilot Kinematic Study on the Forehand Reverse Flick: Feasibility of a Novel Short Return Technique in Table Tennis

Background Following changes in table tennis ball materials, offensive returns have become more important for initiating sustained topspin offense. However, using the backhand flick (BF) to return forehand short balls often increases the difficulty of recovery and continuity, revealing a technical gap. This study preliminarily verified a novel forehand short return technique, the forehand reverse flick (FRF), and analyzed its similarities and differences with the BF. Methods Four elite athletes completed seven consecutive days of FRF specific training. Infrared motion capture and ultra-high-speed cameras were used to collect data on racket kinematics, movement duration, and ball performance. Results The success rate of the FRF increased steadily, reaching 86%. Racket trajectories of the two techniques were highly similar along the X (r = 1) and Y (r = 0.99) axes but differed along the Z (r = -0.04) axis. Racket and ball velocities were comparable between techniques, whereas the FRF showed lower resultant acceleration (approximately 265.57 m/s) and required about 0.03 s more for movement duration. Ball velocity was comparable between techniques, for the ball spin, the FRF generated lower spin (approximately 76.61 r/s) about 64% of the BF value (approximately 120.13 r/s). The highest participant mean spin rate reached 93 r/s, about 77% of the BF mean. Conclusion Overall, the FRF was found to have favorable learnability and training value, with potential for further optimization and competitive application.

physics.med-ph↗

arXiv2025

Competitive Equilibrium for Electricity Markets with Spatially Flexible Loads

Electric vehicle charging and geo-distributed datacenters introduce spatially flexible loads (FLs) that couple power, transportation, and datacenter networks. These couplings create a closed-loop feedback between locational marginal prices (LMPs) and decisions of the FL systems, challenging the foundations of conventional competitive equilibrium (CE) in electricity markets. This paper studies a notion of generalized competitive equilibrium (GCE) that aims to capture such price-demand interactions across the interconnected infrastructures. We establish structural conditions under which the GCE preserves key properties of the conventional CE, including existence, uniqueness, and efficiency, without requiring detailed knowledge of decision processes within individual FL systems. The framework generalizes to settings where the grid is coupled with multiple FL systems. Stylized examples and case studies on the New York ISO grid, coupled with the Sioux Falls transportation and distributed datacenter networks, demonstrate the use of our theoretical framework and illustrate the mutual influence among the grid and the studied FL systems.

eess.SY↗

arXiv2025

The Role of Flexible Connection in Accelerating Load Interconnection in Distribution Networks

This paper investigates the role of flexible connection in accelerating the interconnection of large loads amid rising electricity demand from data centers and electrification. Flexible connection allows new loads to defer or curtail consumption during rare, grid-constrained periods, enabling faster access without major infrastructure upgrades. To quantify how flexible connection unlocks load hosting capacity, we formulate a flexibility-aware hosting capacity analysis problem that explicitly limits the number of utility-controlled interventions per year, ensuring infrequent disruption. Efficient solution methods are developed for this nonconvex problem and applied to real load data and test feeders. Empirical results reveal that modest flexibility, i.e., few interventions with small curtailments or delays, can unlock substantial hosting capacity. Theoretical analysis further explains and generalizes these findings, highlighting the broad potential of flexible connection.

eess.SY↗

arXiv2021

An Attention Self-supervised Contrastive Learning based Three-stage Model for Hand Shape Feature Representation in Cued Speech

Cued Speech (CS) is a communication system for deaf people or hearing impaired people, in which a speaker uses it to aid a lipreader in phonetic level by clarifying potentially ambiguous mouth movements with hand shape and positions. Feature extraction of multi-modal CS is a key step in CS recognition. Recent supervised deep learning based methods suffer from noisy CS data annotations especially for hand shape modality. In this work, we first propose a self-supervised contrastive learning method to learn the feature representation of image without using labels. Secondly, a small amount of manually annotated CS data are used to fine-tune the first module. Thirdly, we present a module, which combines Bi-LSTM and self-attention networks to further learn sequential features with temporal and contextual information. Besides, to enlarge the volume and the diversity of the current limited CS datasets, we build a new British English dataset containing 5 native CS speakers. Evaluation results on both French and British English datasets show that our model achieves over 90% accuracy in hand shape recognition. Significant improvements of 8.75% (for French) and 10.09% (for British English) are achieved in CS phoneme recognition correctness compared with the state-of-the-art.

cs.MM↗

arXiv2020

Energy Storage as Public Asset

Energy storage has exhibited great potential in providing flexibility in power system to meet critical peak demand and thus reduce the overall generation cost, which in turn stabilizes the electricity prices. In this work, we exploit the opportunities for the independent system operator (ISO) to invest and manage storage as public asset, which could systematically provide benefits to the public. Assuming a quadratic generation cost structure, we apply parametric analysis to investigate the ISO's problem of economic dispatch, given variant quantities of storage investment. This investment is beneficial to users on expectation. However, it may not necessarily benefit everyone. We adopt the notion of marginal system cost impact (MCI) to measure each user's welfare and show its relationship with the conventional locational marginal price. We find interesting convergent characteristics for MCI. Furthermore, we perform $k$-means clustering to classify users for effective user profiling and conduct numerical studies on both prototype and IEEE test systems to verify our theoretical conclusions.

eess.SY↗

arXiv2019

Value of Storage for Renewable Portfolio Standard

The ambitious targets for renewable energy penetration warrant huge flexibility in the power system. Such flexibility does not come free. In this paper, we examine the possibility of utilizing storage systems for achieving high renewable energy penetration, and identify the trade-off between providing flexibility and arbitrage against real-time prices. More precisely, we investigate the relationship among the operation cost, storage capacity, and the renewable penetration level. This illustrates the value of storage as well as the true cost induced by the high renewable penetration targets.

eess.SY↗

arXiv2011

Chirality-Assisted Electronic Cloaking in Bilayer Graphene Nanostructures

We show that the strong coupling of pseudospin orientation and charge carrier motion in bilayer graphene has a drastic effect on transport properties of ballistic p-n-p junctions. Electronic states with zero momentum parallel to the barrier are confined under it for one pseudospin orientation, whereas states with the opposite pseudospin tunnel through the junction totally uninfluenced by the presence of confined states. We demonstrate that the junction acts as a cloak for confined states, making them nearly invisible to electrons in the outer regions over a range of incidence angles. This behavior is manifested in the two-terminal conductance as transmission resonances with non-Lorentzian, singular peak shapes. The response of these phenomena to a weak magnetic field or electric-field-induced interlayer gap can serve as an experimental fingerprint of electronic cloaking.

cond-mat.mes-hall↗

arXiv2010

Landau Level Collapse in Gated Graphene Structures

We describe a new regime of magnetotransport in two dimensional electron systems in the presence of a narrow potential barrier imposed by external gates. In such systems, the Landau level states, confined to the barrier region in strong magnetic fields, undergo a deconfinement transition as the field is lowered. We present transport measurements showing Shubnikov-de Haas (SdH) oscillations which, in the unipolar regime, abruptly disappear when the strength of the magnetic field is reduced below a certain critical value. This behavior is explained by a semiclassical analysis of the transformation of closed cyclotron orbits into open, deconfined trajectories. Comparison to SdH-type resonances in the local density of states is presented.

cond-mat.mes-hall↗

arXiv2008

Atomic collapse, Lorentz boosts, Klein scattering, and other quantum-relativistic phenomena in graphene

Electrons in graphene, behaving as massless relativistic Dirac particles, provide a new perspective on the relation between condensed matter and high-energy physics. We discuss atomic collapse, a novel state of superheavy atoms stripped of their discrete energy levels, which are transformed into resonant states. Charge impurities in graphene provide a convenient condensed matter system in which this effect can be explored. Relativistic dynamics also manifests itself in another system, graphene p-n junctions. We show how the transport problem in the presence of magnetic field can be solved with the help of a Lorentz transformation, and use it to investigate magnetotransport in p-n junctions. Finally, we review recent proposal to use Fabry-Perot resonances in p-n-p structures as a vehicle to investigate Klein scattering, another hallmark phenomenon of relativistic dynamics.

cond-mat.mes-hall↗

arXiv2007

Transport in Graphene p-n Junctions in Magnetic Field

Ballistic transport in graphene p-n junctions in the presence of magnetic field exhibits two distinct regimes: At low fields, transport is partially suppressed by the field. When the field exceeds a certain critical value, the junction is pinched off by the Landau level formation. Transmission and conductance are found in the entire range of fields using Lorentz boost and mapping to the Landau-Zener problem. We show that perfect transmission occurs at a field-dependent collimation angle, indicating that the chiral dynamics of massless Dirac fermions persists at a finite magnetic field. A current switch, utilizing field-tunable collimation angle, is proposed. With a generalization of the developed approach we study transmission through p-n junctions in graphene bilayer.

cond-mat.mes-hall↗

arXiv2006

Energy-based Structure Prediction for d(Al70Co20Ni10)

We use energy minimization principles to predict the structure of a decagonal quasicrystal - d(AlCoNi) - in the Cobalt-rich phase. Monte Carlo methods are then used to explore configurations while relaxation and molecular dynamics are used to obtain a more realistic structure once a low energy configuration has been found. We find five-fold symmetric decagons 12.8 A in diameter as the characteristic formation of this composition, along with smaller pseudo-five-fold symmetric clusters filling the spaces between the decagons. We use our method to make comparisons with a recent experimental approximant structure model from Sugiyama et al (2002).

cond-mat.mtrl-sci↗

arXiv2006

Structure prediction for cobalt-rich decagonal AlCoNi from pair potentials

A systematic, decoration-based technique to discover the atomic structure of a decagonal quasicrystal, given pair potentials and experimentally measured lattice constants, is applied to the ``basic'' cobalt-rich decagonal Al-Co-Ni quasicrystal. First lattice-gas Monte Carlo simulations are performed, assuming the atomic sites are vertices of a rhombus tiling with edge 2.45 A. This phase is found to be dominated by 13 A diameter decagon-shaped clusters, each with a pentagon of Co atoms at the center. These, and another smaller cluster, decorate vertices of a ``binary tiling'' with rhombus edge 10.4 A. Further simulations with a restricted site list show that Al arrangements on the borders of the 13 A decagon cluster form Hexagon, Boat, and Star tiles with edge 2.45 A; they indicate specific sites for Co versus Ni atoms, and how the structure adapts to small composition changes. In the second half of the paper, relaxation (augmented by molecular dynamics annealing) is used to obtain realistic structures. The dominant new feature is a set of linear ``channels'' attractive to Al atoms and running transverse to the layers. Each is typically occupied by three atoms in four layers, implying puckering and a spontaneous period doubling to c $\approx$ 8 A. Puckering favors pentagonal long range order of the cluster orientations. Our simulation captures most features of the related $W$-AlCoNi crystal, except for its pentagonal bipyramid motif.

cond-mat.mtrl-sci↗

arXiv2005

Co-rich decagonal Al-Co-Ni: predicting structure, orientational order, and puckering

We apply systematic methods previously used by Mihalkovic et al. to predict the structure of the `basic' Co-rich modification of the decagonal Al70 Co20 Ni10 layered quasicrystal, based on known lattice constants and previously calculated pair potentials. The modelling is based on Penrose tile decoration and uses Monte Carlo annealing to discover the dominant motifs, which are converted into rules for another level of description. The result is a network of edge-sharing large decagons on a binary tiling of edge 10.5 A. A detailed analysis is given of the instability of a four-layer structure towards $c$-doubling and puckering of the atoms out of the layers, which is applied to explain the (pentagonal) orientational order.

cond-mat.mtrl-sci↗