93,606 research outputs found
Decay of Correlation for Edge Colorings When q > 3Δ
No full textWe examine various perspectives on the decay of correlation for the uniform distribution over proper q-edge colorings of graphs with maximum degree Δ.
First, we establish the coupling independence property when q ≥ 3Δ for general graphs. Together with the recent work of Chen, Feng, Guo, Zhang and Zou (2024), this result implies a fully polynomial-time approximation scheme (FPTAS) for counting the number of proper q-edge colorings.
Next, we prove the strong spatial mixing property on trees, provided that q > (3+o(1))Δ. The strong spatial mixing property is derived from the spectral independence property of a version of the weighted edge coloring distribution, which is established using the matrix trickle-down method developed in Abdolazimi, Liu and Oveis Gharan (FOCS, 2021) and Wang, Zhang and Zhang (STOC, 2024).
Finally, we show that the weak spatial mixing property holds on trees with maximum degree Δ if and only if q ≥ 2Δ-1
q-Differential equations for q-classical polynomials and q-Jacobi-Stirling numbers
No full textWe introduce, characterise and provide a combinatorial interpretation for the so-called q-Jacobi–Stirling numbers.
This study is motivated by their key role in the (reciprocal) expansion of any power of a second order
q-differential operator having the q-classical polynomials as eigenfunctions in terms of other even order operators,
which we explicitly construct in this work. The results here obtained can be viewed as the q-version of
those given by Everitt et al. and by the first author, whilst the combinatorics of this new set of numbers is a
q-version of the Jacobi–Stirling numbers given by Gelineau and the second author
Q&A with Zhentao Zhang
No full textIn this interview with Zhentao Zhang, we discuss his research focusing on the molecular mechanisms underlying the aggregation of prion-like proteins in neurodegenerative diseases and spotlight his recent work in Cell Reports that shows that a yeast prion protein interacts with tau and facilitates its aggregation
Academic Writing Q&A Series 4
No full textThe presentation describes the processes that typically follow article submission. This presentation serves as the basis for a video from the Academic Writing Q&A series that was created as a supplement to the My First Scientific Article webinar. This presentation highlights the critical issues the author needs to take into account during the writing or peer review process that are essential to publishing. The content is useful for Early Career Researchers and for everyone who is interested in scholarly communication and publishing
Accruals, Cash-Flows and Tobin’s q : An Investment Perspective on Firm Accruals
No full textFollowing Zhang (Accounting Review, 2007) we cast firm accruals in terms of short-term investment. Since many studies consider accruals as a smoothed measure of cash flows, we first adopt Zhang specification and augment the standard Jones model with a cash-flow variable. Second, if accruals are indeed a form of short-term investment they should also be influenced by firm’s performance as measured by Tobin’s q. Consequently we propose a new version of the accrual model including a proxy for Tobin’s q. Given that accounting data and Tobin’s q are generally measured with errors, we also introduce a new estimation method based on a modified version of the Hausman artificial regression, featuring an optimal weighting matrix composed of higher moments instrumental variable estimators. Our results suggest that all the key parameters of the accrual models are indeed systematically biased with measurement errors. More importantly, our findings largely qualify Zhang’s conjecture on accruals, as both cash-flows and Tobin’s q are found strongly significant regressors of firm accruals. Relatedly we find that the Tobin’s q augmented model better isolate discretionary accruals so that the residuals of the equation are particularly well-suited to forecast stock returns.Discretionary accruals; Earnings management; Investment; Measurement errors; Higher moments; Instrumental variable estimators.
A note on the Zhang omnibus test for normality based on the Q statistic
No full textA discussion about the estimators proposed by Zhang (1999) for the true standard deviation C of a normal distribution is presented. Those estimators, called by Zhang q 1 and q 2 , are functions of the expected values of the order statistics from a standard normal distribution and they were the basis of the Q statistic used in the derivation of a new test for normality proposed by Zhang. Although the type I error and the power of the test was discussed by Zhang, no study was performed to test the reliability of q 1 and q 2 as estimators of C . In this paper, it is shown that q 1 is a very poor estimator for C especially when C is large. On the other hand, the estimator q 2 has a performance very similar to the well-known sample standard deviation S. When some correlation is introduced among the sample units it can be seen that the estimator q 1 is much more affected than the estimators q 2 and S.
Electrochemical reconstruction of ZnO for selective reduction of CO2 to CO
No full textElectrocatalytic conversion of CO2 to valuable chemicals is a highly promising route to close the carbon cycle. Herein, Zn catalysts derived from electrochemical reconstruction of ZnO materials are presented as efficient CO2-to-CO catalysts. We found that ZnO precursors with different morphologies (nanowires, nanoflowers, and nanoparticles) underwent deep electro-reconstruction and formed porous structures composed of hexagonal Zn crystals, regardless of their initial properties. Using ex-situ and in operando techniques, we revealed that metallic Zn is the active phase for CO2-to-CO. Because of the large surface area and stable crystal structure resulted from the reconstruction, ZnO-derived catalysts are highly selective and stable, showing >90% selectivity to CO and more than 18 h stability. The great potential of ZnO-derived catalysts for industrial applications was demonstrated in a flow reactor, where 91.6% Faradaic efficiency for CO at a current density of 200 mA cm−2 can be achieved at –0.62 V vs. RHE
Bi-objective bi-level optimization for integrating lane-level closure and reversal in redesigning transportation networks
No full textTraditionally, traffic congestion was alleviated through significantly upgrading the infrastructure of transportation networks. However, building new roads or adding more lanes to a main road needs huge expenses. A better cost-effective approach is to redesign and fine-tune transportation networks by closing and reversing existing lanes. This paper aims at developing an optimal scheme for lane-level closure and reversal to improve the performance of existing transportation networks with a fairly tight budget. We call this new problem Lane-level Closure and Reversal Problem (LCRP). By considering the capacities of all lanes of a road, two different bi-objective bi-level programs (called the arc-based and lane-based models) are developed to formulate the LCRP. Furthermore, our proposed formulations consider the elastic traffic demand and the elimination of conflict points resulting from reversing lanes. A hybrid machine learning and bi-objective optimization (MLBO) algorithm is developed to overcome the curse of dimensionality of the bi-level programs, especially for the land-based model that is more general but with higher computational complexity. The proposed methodology is illustrated by a small-size numerical example and verified by a real-world case study from Winnipeg (i.e., a benchmark transportation network). Computational results show that the integrated lane-level closure and reversal model can achieve a 0.52% reduction in the total travel time, which is significantly better than the 0.05% reduction individually obtained by arc-level closure or the 0.10% reduction obtained by arc-level reversal. The proposed methodology is beneficial for the traffic management bureau to make a more precise decision in redesigning transportation networks in practice
Impact of crystallisation processes on depth profile formation in sol-gel PbZr(0.52)Ti(0.48)O3 thin films
No full textThis study revealed the influence of crystallisation processes on the homogeneity of the sol‐gel PbZr0·52Ti0·48O3 thin films, allowing identification and further optimisation of thin film performance. Crystallisation processes determine the optical gradient appearance, irrespective of the chemical solvents used in this work. X-ray diffraction analysis showed that a refractive index gradient was apparent in the samples which had dominant (001)/(100) orientation and significant change of lattice parameters with thickness
Dynamics Simulation of Remotely Operated Vehicle-Fiber Optic Micro Cable System
No full textLi Q, Xu H, Zhang Q, Wang X, Li ZG. Dynamics Simulation of Remotely Operated Vehicle-Fiber Optic Micro Cable System. Presented at the WCICA2008, Chongqing, China
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