2,617 research outputs found
The global symmetry in the flavor-unified theories
We study the origin of the global symmetry in a class of flavor-unified
theories with gauge groups of . In particular, we focus on
the theory which can minimally embed three-generational SM
fermions non-trivially. A reformulation of the third law for the flavor sector
proposed by Georgi is useful to manifest the underlying global symmetries. The
't Hooft anomaly matching and the generalized neutrality conditions for Higgs
fields play the key roles in defining the symmetry. Based on the global
symmetry, we count the Higgs fields that can develop the VEVs and the
massless sterile neutrinos in the theory. We also prove that a
global symmetry can always be defined in any theory
when it is spontaneously broken to the SM gauge symmetry.Comment: 34 pages, 11 table
Non-uniform Bid-scaling and Equilibria for Different Auctions: An Empirical Study
In recent years, the growing adoption of autobidding has motivated the study
of auction design with value-maximizing auto-bidders. It is known that under
mild assumptions, uniform bid-scaling is an optimal bidding strategy in
truthful auctions, e.g., Vickrey-Clarke-Groves auction (VCG), and the price of
anarchy for VCG is . However, for other auction formats like First-Price
Auction (FPA) and Generalized Second-Price auction (GSP), uniform bid-scaling
may not be an optimal bidding strategy, and bidders have incentives to deviate
to adopt strategies with non-uniform bid-scaling. Moreover, FPA can achieve
optimal welfare if restricted to uniform bid-scaling, while its price of
anarchy becomes when non-uniform bid-scaling strategies are allowed.
All these price of anarchy results have been focused on welfare approximation
in the worst-case scenarios. To complement theoretical understandings, we
empirically study how different auction formats (FPA, GSP, VCG) with different
levels of non-uniform bid-scaling perform in an autobidding world with a
synthetic dataset for auctions. Our empirical findings include:
* For both uniform bid-scaling and non-uniform bid-scaling, FPA is better
than GSP and GSP is better than VCG in terms of both welfare and profit;
* A higher level of non-uniform bid-scaling leads to lower welfare
performance in both FPA and GSP, while different levels of non-uniform
bid-scaling have no effect in VCG.
Our methodology of synthetic data generation may be of independent interest
Thermal simulation modeling of a hydrostatic machine feed platform
Hydrostatic guideways are widely applied into precision and ultra-precision machine tools. Meanwhile, the oil film heat transfer causes thermal disturbance to the machine accuracy. Therefore, it is necessary to study the mechanism of the oil film heat transfer and the heat-transfer-reducing method to improve the machine accuracy. This paper describes a comprehensive thermal finite element (FE) simulation modeling method for the hydrostatic machine feed platform to study methods of reducing machine thermal errors. First of all, the generating heat power of viscous hydraulic oil flowing between parallel planes is calculated based on the Bernoulli equation. This calculation is then employed for the simulation load calculations for the closed hydrostatic guideways, which is adopted by the hydrostatic machine feed platform. Especially, in these load calculations, the changing of oil film thickness (resulted from external loads) and the changing of oil dynamic viscosity (influenced by its temperature) are taken into account. Based on these loads, thermal FE simulation modeling of the hydrostatic machine feed platform is completed to predict and analyze its thermal characteristics. The reliability of this simulation modeling method is verified by experiments. The studies demonstrate that the hydrostatic machine thermal error degree is determined by the oil film heat transfer scale, and this scale is mainly influenced by the relative oil supply temperature to ambient temperature (quantitative comparison of oil supply temperature and ambient temperature). Furthermore, the reduction of the absolute value of this relative oil supply temperature can reduce the oil film heat transfer scale and improve the machine accuracy
A differentiated multi-loops bath recirculation system for precision machine tools
Traditional bath recirculation cooler for precision machine tools always has the uniform and open-loop cooling strategy onto different heat generating parts. This causes redundant generated heat being transferred into the machine structure, and results in unsatisfactory thermal errors of precision machine tools. For the solution of this problem, this paper presents the differentiated multi-loops bath recirculation system. The developed system can accomplish differentiated and close-loop cooling strategies onto machine heat generating parts during its operation. Specially, in order to illustrate the advantages of this system, constant supply cooling powers strategy is presented with its applications onto a certain type of built-in motorized spindle. Consequently, advantages of the proposed strategy based on the differentiated multi-loops bath recirculation system are verified experimentally in the environment within consistent temperature (TR = 20 ± 0.3°C). Compared with room temperature tracing strategy based on the traditional bath recirculation cooler, the constant supply cooling powers strategy is verified to be advantageous in spindle temperature stabilization and thermal errors decrease
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