Graphs with small diameter determined by their DD-spectra

Let $G$ be a connected graph with vertex set $V(G)=\{v_{1},v_{2},...,v_{n}\}$. The distance matrix $D(G)=(d_{ij})_{n\times n}$ is the matrix indexed by the vertices of $G,$ where $d_{ij}$ denotes the distance between the vertices $v_{i}$ and $v_{j}$. Suppose that $\lambda_{1}(D)\geq\lambda_{2}(D)\geq\cdots\geq\lambda_{n}(D)$ are the distance spectrum of $G$. The graph $G$ is said to be determined by its $D$-spectrum if with respect to the distance matrix $D(G)$, any graph having the same spectrum as $G$ is isomorphic to $G$. In this paper, we give the distance characteristic polynomial of some graphs with small diameter, and also prove that these graphs are determined by their $D$-spectra

China: A Tiger only in the East or a World Player in High Quality Fresh Produce Exports?

This paper examines patterns of recent change in Chinas international export trade in high quality fresh-vegetables between 2002 and 2005 since its WTO membership and some of the underlying determinants that will determine its future export opportunities. Concepts of product quality are first reviewed and the key characteristics of Chinas international trade in fresh produce are outlined based on a detailed analysis from the UN Comtrade international trade data at the 2, 4 digit and finally 6 digit levels. High quality fresh and chilled vegetables are identified through their average unit export values. In 2005, China was the 4th largest exporter of vegetables in the world with a 9.8 percent share of world trade, and almost a 6 percent share in fresh and chilled vegetables. The competitiveness of China in world trade in high value fresh produce is assessed through a trade-shares accounting and decomposition approach which enables both structural and performance effects on Chinas exports to be isolated, and the contributions its major trading partners have made to changes its share of world trade. Chinas aggregate market share rose by over 1.5 percentage points over the period, and there is evidence of an emerging orientation in its trade shares from E Asia to SE Asia, and to further progress in the Russian Federation and US markets. Chinas underlying comparative advantage in such labour-intensive products is reflected in the positive performance effect on the increase in its market share.China, vegetables, international trade., International Relations/Trade,

Exploring open-charm decay mode ΛcΛˉc\Lambda_c\bar{\Lambda}_c of charmonium-like state Y(4630)Y(4630)

The newly observed $X, Y, Z$ exotic states are definitely not in the standard $Q\bar Q'$ structures, thus their existence composes a challenge to our understanding on the fundamental principles of hadron physics. Therefore the studies on their decay patterns which are determined by the non-perturbative QCD will definitely shed light on the concerned physics. Generally the four-quark states might be in a molecular state or tetraquark or their mixture. In this work, we adopt the suggestion that $Y(4630)$ is a charmonium-like tetraquark made of a diquark and an anti-diquark. If it is true, its favorable decay mode should be $Y(4630)$ decaying into an open-charm baryon pair, since such a transition occurs via strong interaction and is super-OZI-allowed. In this work, we calculate the decay width of $Y(4630)\to\Lambda_c\bar{\Lambda}_c$ in the framework of the quark pair creation (QPC) model. Our numerical results on the partial width computed in the tetraquark configuration coincide with the Belle data within a certain error tolerance.Comment: 8 pages, 4 figures, 1 table. Accepted by Eur. Phys. J.