R1234yf/RE170混合工质用于汽车空调的可行性

目前汽车空调常用的制冷剂四氟乙烷(R134a)存在较高的温室效应指数(GWP=1 300),会对环境造成不利的影响。将R1234yf和RE170以质量配比为70:30组成新型混合制冷剂(代号NCUR04)应用于汽车空调中,通过热力学性质、环境特性、循环性能、安全特性、润滑特性方面综合考虑替代R134a的可行性,并与潜在替代制冷剂R1234yf进行对比。研究表明:NCUR04环境性能、热力学性质较R134a和R1234yf优异;单位质量制冷量分别比R134a和R1234yf高24.7%和66.2%;单位容积制冷量比R134a低4.5%,比R1234yf高5.9%;能效比(COP)分别比R134a和R1234yf高1.4%和8.8%;排气温度比R134a低2.4℃,比R1234yf高5.5℃;与POE润滑油互溶性良好。因此,NCUR04替代R134a用于汽车空调具有可行性。     

A new formula for the decycling number of regular graphs

The decycling number $?\left(G\right)$ of a graph $G$ is the smallest number of vertices which can be removed from $G$ so that the resultant graph contains no cycle. A decycling set containing exactly $?\left(G\right)$ vertices of $G$ is called a $?$-set. For any decycling set $S$ of a $k$-regular graph $G$, we show that $\left|S\right|=\frac{\beta \left(G\right)+m\left(S\right)}{k?1}$, where $\beta \left(G\right)$ is the cycle rank of $G$, $m\left(S\right)=c+\left|E\left(S\right)\right|?1$ is the margin number of $S$, $c$ and $\left|E\left(S\right)\right|$ are, respectively, the number of components of $G?S$ and the number of edges in $G\left[S\right]$. In particular, for any $?$-set $S$ of a 3-regular graph $G$, we prove that $m\left(S\right)=\xi \left(G\right)$, where $\xi \left(G\right)$ is the Betti deficiency of $G$. This implies that the decycling number of a 3-regular graph $G$ is $\frac{\beta \left(G\right)+\xi \left(G\right)}{2}$. Hence $?\left(G\right)=?\frac{\beta \left(G\right)}{2}?$ for a 3-regular upper-embeddable graph $G$, which concludes the results in [Gao et al., 2015, Wei and Li, 2013] and solves two open problems posed by Bau and Beineke (2002). Considering an algorithm by Furst et al., (1988), there exists a polynomial time algorithm to compute $Z\left(G\right)$, the cardinality of a maximum nonseparating independent set in a $3$-regular graph $G$, which solves an open problem raised by Speckenmeyer (1988). As for a 4-regular graph $G$, we show that for any $?$-set $S$ of $G$, there exists a spanning tree $T$ of $G$ such that the elements of $S$ are simply the leaves of $T$ with at most two exceptions providing $?\left(G\right)=?\frac{\beta \left(G\right)}{3}?$. On the other hand, if $G$ is a loopless graph on $n$ vertices with maximum degree at most $4$, then

The above two upper bounds are tight, and this makes an extension of a result due to Punnim (2006).     

Constructing permutations of finite fields via linear translators

Methods for constructing large families of permutation polynomials of finite fields are introduced. For some of these permutations the cycle structure and the inverse mapping are determined. The results are applied to lift minimal blocking sets of PG(2,q) to those of PG(2,qn).     

Total chromatic number of unichord-free graphs

A unichord is an edge that is the unique chord of a cycle in a graph. The class C of unichord-free graphs — that is, graphs that do not contain, as an induced subgraph, a cycle with a unique chord — was recently studied by Trotignon and Vuškovi? (2010) [24], who proved strong structure results for these graphs and used these results to solve the recognition and vertex-colouring problems. Machado et al. (2010) [18] determined the complexity of the edge-colouring problem in the class C and in the subclass C^′ obtained from C by forbidding squares. In the present work, we prove that the total-colouring problem is NP-complete when restricted to graphs in C. For the subclass C^′, we establish the validity of the Total Colouring Conjecture by proving that every non-complete {square, unichord}-free graph of maximum degree at least 4 is Type 1.     

R50对-100℃三级分凝循环中后期的影响

为了确定R50对-100℃温区三级自动复叠系统中后期运行状态的影响,分别以R134a/R23/R14、R134a/R23/R14/R50为混合工质在同一台实验装置上进行两次试验,其中R134a、R23、R14组分充注量相同。通过对两组工质进行实验和对比分析,发现添加R50时第二、三级分凝器蒸发温度和冷却后温度更低,但是系统压力明显更高,设备耗能增加,达到设计温度所需时间增长,因此在-100℃温区的自动复叠系统混合组分添加R50会对系统的性能不利。     

Magnetic,spectroscopic and structural properties of a copper cyclic compound

A new compound [Cu(oda)(pmal)(H₂O)]₂·4H₂O assembled from phenylmalonic acid (H₂pmal), 4,4?-diaminodiphenyl ether (oda) and Cu(II) was synthesized under mild conditions in solution. Its structure was determined by X-ray single crystal diffraction. The structure is characteristic of neutral cyclic dimeric molecules which further aggregate through hydrogen bonds and π–π interactions to form a 3-D supramolecular network. The compound was also characterized by UV–vis, TG-DSC, XRD, ESR and magnetic susceptibility.     

Cycle frequency in standard Rock–Paper–Scissors games: Evidence from experimental economics

The Rock–Paper–Scissors (RPS) game is a widely used model system in game theory. Evolutionary game theory predicts the existence of persistent cycles in the evolutionary trajectories of the RPS game, but experimental evidence has remained to be rather weak. In this work, we performed laboratory experiments on the RPS game and analyzed the social-state evolutionary trajectories of twelve populations of N=6$N=6$ players. We found strong evidence supporting the existence of persistent cycles. The mean cycling frequency was measured to be 0.029±0.009$0.029\pm 0.009$ period per experimental round. Our experimental observations can be quantitatively explained by a simple non-equilibrium model, namely the discrete-time logit dynamical process with a noise parameter. Our work therefore favors the evolutionary game theory over the classical game theory for describing the dynamical behavior of the RPS game.     

Flow field around the flapping flag

The flapping flag is a canonical fluid–structure interaction problem that describes a cantilever plate with flow along its elastic axis. When the flapping flag loses stability it enters a large amplitude Limit Cycle Oscillation (LCO). While theoretical models can accurately predict the flutter velocity and frequency, there are still discrepancies between the experimental observations and the theoretical predictions of the post-critical LCO response. This note provides recent flow field visualizations in a single longitudinal plane for a cantilevered aluminum plate in axial flow during its LCO. Particle Image Velocimetry (PIV) techniques are used to show that the flow over the midspan of the plate is attached even during the violent LCO motion. This observation suggests that potential flow aerodynamic models may be able to capture the essential features in the flow field.     

Some Conditions for the Nonexistence of Limit Cycles in a Predator-Prey System

In this paper, we study the problem of the existence of limit cycles for a predator-prey system with a functional response. It is assumed that the functional response is positive, increasing, concave down, and its third derivative has a unique root. A necessary condition for the nonexistence of limit cycles is presented. Some conditions are given under which the necessary condition is also the sufficient condition for the nonexistence of limit cycles.     

A Haar-Fisz Algorithm for Poisson Intensity Estimation

This article introduces a new method for the estimation of the intensity of an inhomogeneous one-dimensional Poisson process. The Haar-Fisz transformation transforms a vector of binned Poisson counts to approximate normality with variance one. Hence we can use any suitable Gaussian wavelet shrinkage method to estimate the Poisson intensity. Since the Haar-Fisz operator does not commute with the shift operator we can dramatically improve accuracy by always cycle spinning before the Haar-Fisz transform as well as optionally after. Extensive simulations show that our approach usually significantly outperformed state-of-the-art competitors but was occasionally comparable. Our method is fast, simple, automatic, and easy to code. Our technique is applied to the estimation of the intensity of earthquakes in northern California. We show that our technique gives visually similar results to the current state-of-the-art.