The next-to-next-to-leading order soft function for top quark pair production

We present the first calculation of the next-to-next-to-leading order threshold soft function for top quark pair production at hadron colliders, with full velocity dependence of the massive top quarks. Our results are fully analytic, and can be entirely written in terms of generalized polylogarithms. The scale-dependence of our result coincides with the well-known two-loop anomalous dimension matrix including the three-parton correlations, which at the two-loop order only appear when more than one massive partons are involved in the scattering process. In the boosted limit, our result exhibits the expected factorization property of mass logarithms, which leads to a consistent extraction of the soft fragmentation function. The next-to-next-to-leading order soft function obtained in this paper is an important ingredient for threshold resummation at the next-to-next-to-next-to-leading logarithmic accuracy.Comment: 34 pages, 9 figures; v2: added references, matches the published versio

Next-to-leading order corrections for gg→ZHgg \to ZH with top quark mass dependence

In this Letter, we present for the first time a calculation of the complete next-to-leading order corrections to the $gg \to ZH$ process. We use the method of small mass expansion to tackle the most challenging two-loop virtual amplitude, in which the top quark mass dependence is retained throughout the calculations. We show that our method provides reliable numeric results in all kinematic regions, and present phenomenological predictions for the total and differential cross sections at the Large Hadron Collider and its future upgrades. Our results are necessary ingredients towards reducing the theoretical uncertainties of the $pp \to ZH$ cross sections down to the percent-level, and provide important theoretical inputs for future precision experimental collider programs

Fee Policies of Higher Education and High School Students\u27College Choices in China : A Study Focusing on Perceived Fees

In China, the higher the fees, the stronger the college-going aspiration of senior high school students. This study demonstrated that this paradox didn\u27t result from the fact that the rate of economic growth and family income increase are higher thanthat of fee rise or student\u27s disability in perception of real fees, but from the fact that the expected return to higher edutcation is extremely higher than perceived fees. The perceived fees, however, gave a substantial amount of effect on senior high school students\u27college choices

Transformation of Tuition Fee System of Public Universities in China

Tuition fees of public universities are greatly increasing in recent years in China. Many researchers have made an attempt to examine the effects of rising fee on students\u27enrollment behavior. However, there is no systematic analysis of the causes of fee increase, and the causal relations between the fee rising and the expansion of higher education. This paper will focus on the following four points: (1) the history of university fees, (2) the present situation of tuition fees, (3) the mechanism responsible for the fee rising, (4) the relation between the rising of fees and the higher education expansion. The findings of this article are as follows: (1) The transformation of fee system is not from free-fee one to high-fee one directly, but through several transitive phases in which various fee policies were experimented by the central government. (2) The present standard of tuition fee is very high. Fee average is up to 5000 yuan every year. And the amount of fee collected by different institutions varies greatly according to university and department\u27s prestige. (3) Each institution of higher education played an important role in the process of fee rising. The central government changed the fee policies, which gave each institution an arbitrary power to decide its fee level and how to spend it partly. (4) Consequently, the fee rising in public universities gave an incentive to every institution and directly promoted the expansion of the higher education

A validated finite element model for predicting dynamic responses of cylinder liners in an IC engine*

Vibration of cylinder liners affects not only engine combustion performances but also tribological behaviour and noise radiations. However, it is difficult to characterize it experimentally due to multiple sources, strong background noise, and nonlinear transfer paths. Therefore, a finite element model is established in this study to predict the dynamic responses of cylinder liners under respective sources. The model takes into account both the characteristics of structural modes and nonlinearities of assembly constraints when selecting adequate elements for efficient computation of the responses under both the highly nonlinear combustion pressure excitations and subsequent piston slap impacts. The predictions are then evaluated against experimental results under different engine operating conditions. In addition, continuous wavelet analysis is employed to process the complicated responses for key response events and their frequency ranges. The results show agreeable correspondences between the numerical predictions and measured vibration signals, paving the way for investigating its effect on combustion and lubrication processes

Thermoeconomic performance optimization of an irreversible Brayton refrigeration cycle using Gd, Gd 0.95 Dy 0.05 or Gd 0.95 Er 0.05 as the working substance

Abstract(#br)An irreversible regenerative Brayton refrigerator cycle is established, in which the nonperfect regenerator, regenerative time, heat leak, and irreversible adiabatic processes are taken into account. The mathematical expressions of the refrigeration rate, coefficient of performance, and thermoeconomic function of the refrigeration cycle are derived and the thermoeconomic function is optimized. Moreover, choosing Gd, Gd 0.95 Dy 0.05 and Gd 0.95 Er 0.05 as the working substances respectively, we discussed in detail the influences of the thermoeconomic and thermodynamic parameters on the optimal thermoeconomic and thermodynamic performances. The results show that the thermoeconomic performance of the refrigeration cycle using Gd or Gd 0.95 Dy 0.05 as the working substance is better than that using Gd 0.95 Er 0.05 and the thermoeconomic performance of the refrigeration cycle using Gd 0.95 Dy 0.05 as the working substance is better than that using Gd in the situation with the lower adiabatic magnetization