arXiv subjects

Hong Chang

Publications and source records attributed to Hong Chang.

95 records · Page 6Linked to original sources

arXiv2016

Some upper bounds for the $3$-proper index of graphs

A tree $T$ in an edge-colored graph is a {\it proper tree} if no two adjacent edges of $T$ receive the same color. Let $G$ be a connected graph of order $n$ and $k$ be a fixed integer with $2\le k\le n$. For a vertex subset $S \subseteq V(G)$ with $\left|S\right| \ge 2$, a tree containing all the vertices of $S$ in $G$ is called an $S$-tree. An edge-coloring of $G$ is called a \emph{$k$-proper coloring} if for every $k$-subset $S$ of $V(G)$, there exists a proper $S$-tree in $G$. For a connected graph $G$, the \emph{$k$-proper index} of $G$, denoted by $px_k(G)$, is the smallest number of colors that are needed in a $k$-proper coloring of $G$. In this paper, we show that for every connected graph $G$ of order $n$ and minimum degree $δ\geq 3$, $px_{3}(G)\le n\frac{\ln(δ+1)}{δ+1}(1+o_δ(1))+2$. We also prove that for every connected graph $G$ with minimum degree at least $3$, $px_{3}(G) \le px_{3}(G[D])+3$ when $D$ is a connected $3$-way dominating set of $G$ and $px_{3}(G) \le px_{3}(G[D])+1$ when $D$ is a connected $3$-dominating set of $G$. In addition, we obtain tight upper bounds of the 3-proper index for two special graph classes: threshold graphs and chain graphs. Finally, we prove that $px_3(G) \le \lfloor\frac{n}{2}\rfloor$ for any 2-connected graphs with at least four vertices.

math.CO↗

arXiv2014

Precision measurement of transverse velocity distribution of a strontium atomic beam

We measure the transverse velocity distribution in a thermal Sr atomic beam precisely by velocity-selective saturated fluorescence spectroscopy. The use of an ultrastable laser system and the narrow intercombination transition line of Sr atoms mean that the resolution of the measured velocity can reach 0.13 m/s, corresponding to 90$μK$ in energy units. The experimental results are in very good agreement with the results of theoretical calculations. Based on the spectroscopic techniques used here, the absolute frequency of the intercombination transition of $^{88}$Sr is measured using an optical-frequency comb generator referenced to the SI second through an H maser, and is given as 434 829 121 318(10) kHz.

physics.optics↗

arXiv2014

Deeply Coupled Auto-encoder Networks for Cross-view Classification

The comparison of heterogeneous samples extensively exists in many applications, especially in the task of image classification. In this paper, we propose a simple but effective coupled neural network, called Deeply Coupled Autoencoder Networks (DCAN), which seeks to build two deep neural networks, coupled with each other in every corresponding layers. In DCAN, each deep structure is developed via stacking multiple discriminative coupled auto-encoders, a denoising auto-encoder trained with maximum margin criterion consisting of intra-class compactness and inter-class penalty. This single layer component makes our model simultaneously preserve the local consistency and enhance its discriminative capability. With increasing number of layers, the coupled networks can gradually narrow the gap between the two views. Extensive experiments on cross-view image classification tasks demonstrate the superiority of our method over state-of-the-art methods.

cs.CV↗

arXiv2007

Camparison of the Hanbury Brown-Twiss effect for bosons and fermions

Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in light emitted by a chaotic source, highlighting the importance of two-photon correlations and stimulating the development of modern quantum optics . The quantum interpretation of bunching relies upon the constructive interference between amplitudes involving two indistinguishable photons, and its additive character is intimately linked to the Bose nature of photons. Advances in atom cooling and detection have led to the observation and full characterisation of the atomic analogue of the HBT effect with bosonic atoms. By contrast, fermions should reveal an antibunching effect, i.e., a tendency to avoid each other. Antibunching of fermions is associated with destructive two-particle interference and is related to the Pauli principle forbidding more than one identical fermion to occupy the same quantum state. Here we report an experimental comparison of the fermion and the boson HBT effects realised in the same apparatus with two different isotopes of helium, 3He (a fermion) and 4He (a boson). Ordinary attractive or repulsive interactions between atoms are negligible, and the contrasting bunching and antibunching behaviours can be fully attributed to the different quantum statistics. Our result shows how atom-atom correlation measurements can be used not only for revealing details in the spatial density, or momentum correlations in an atomic ensemble, but also to directly observe phase effects linked to the quantum statistics in a many body system. It may thus find applications to study more exotic situations >.

cond-mat.other↗

arXiv2006

Producing and Detecting Correlated atoms

We discuss experiments to produce and detect atom correlations in a degenerate or nearly degenerate gas of neutral atoms. First we treat the atomic analog of the celebrated Hanbury Brown Twiss experiment, in which atom correlations result simply from interference effects without any atom interactions.We have performed this experiment for both bosons and fermions. Next we show how atom interactions produce correlated atoms using the atomic analog of spontaneous four-wavemixing. Finally, we briefly mention experiments on a one dimensional gas on an atom chip in which correlation effects due to both interference and interactions have been observed.

quant-ph↗