Jun Han

Jun Han
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Jun Han

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Computer Science - Software Engineering (4)
Statistics - Machine Learning (2)
Solar and Stellar Astrophysics (2)
High Energy Astrophysical Phenomena (2)
Physics - Materials Science (1)
Computer Science - Cryptography and Security (1)
Computer Science - Artificial Intelligence (1)
Computer Science - Learning (1)

Publications Authored By Jun Han

We propose a novel adaptive importance sampling algorithm which incorporates Stein variational gradient decent algorithm (SVGD) with importance sampling (IS). Our algorithm leverages the nonparametric transforms in SVGD to iteratively decrease the KL divergence between our importance proposal and the target distribution. The advantages of this algorithm are twofold: first, our algorithm turns SVGD into a standard IS algorithm, allowing us to use standard diagnostic and analytic tools of IS to evaluate and interpret the results; second, we do not restrict the choice of our importance proposal to predefined distribution families like traditional (adaptive) IS methods. Read More

We determine spectral indices of 228 pulsars by using Parkes pulsar data observed at 1.4 GHz, among which 200 spectra are newly determined. The indices are distributed in the range from -4. Read More

In today's dynamic ICT environments, the ability to control users' access to resources becomes ever important. On the one hand, it should adapt to the users' changing needs; on the other hand, it should not be compromised. Therefore, it is essential to have a flexible access control model, incorporating dynamically changing context information. Read More

In distributed, or privacy-preserving learning, we are often given a set of probabilistic models estimated from different local repositories, and asked to combine them into a single model that gives efficient statistical estimation. A simple method is to linearly average the parameters of the local models, which, however, tends to be degenerate or not applicable on non-convex models, or models with different parameter dimensions. One more practical strategy is to generate bootstrap samples from the local models, and then learn a joint model based on the combined bootstrap set. Read More

Service virtualisation is a supporting tool for DevOps to generate interactive service models of dependency systems on which a system-under-test relies. These service models allow applications under development to be continuously tested against production-like conditions. Generating these virtual service models requires expert knowledge of the service protocol, which may not always be available. Read More

Large enterprise software systems make many complex interactions with other services in their environment. Developing and testing for production-like conditions is therefore a very challenging task. Current approaches include emulation of dependent services using either explicit modelling or record-and-replay approaches. Read More

Constructing testbeds for systems which are interconnected with large networks of other software services is a challenging task. It is particularly difficult to create testbeds facilitating evaluation of the non-functional qualities of a system, such as scalability, that can be expected in production deployments. Software service emulation is an approach for creating such testbeds where service behaviour is defined by emulate-able models executed in an emulation runtime environment. Read More

PSR B0919+06 generally radiates radio pulses in a normal phase range. It has been known for its occasional perplexing abnormal emission events wherein individual pulses come to an earlier phase range for a few tens of periods and then returns to its usual phase. Heretofore, only a few such events have been available for study. Read More

Enterprise software systems make complex interactions with other services in their environment. Developing and testing for production-like conditions is therefore a challenging task. Prior approaches include emulations of the dependency services using either explicit modelling or record-and-replay approaches. Read More

The photoelectric properties of complex oxides have prompted interest in materials with a tunable band gap, because the absorption The substitution of iron atoms in La-modified bismuth titanate (BLT) can lead to dramatic improvements in the band gap, however, the substitution of iron atoms in BLT without forming a BiFeO3 secondary phase is quite challenging. Therefore, a series of Fe-doped BLT (Fe-BLT) samples were characterized using a solid reaction at various calcination temperatures (300~900{\deg}C) to remove the secondary phase. The structural and optical properties were analyzed by X-ray diffraction and ultraviolet-visible absorption spectroscopy. Read More