A Fast Radio Burst Search Method for VLBI Observation

We introduce the cross spectrum based FRB (Fast Radio Burst) search method for VLBI observation. This method optimizes the fringe fitting scheme in geodetic VLBI data post processing, which fully utilizes the cross spectrum fringe phase information and therefore maximizes the power of single pulse signals. Working with cross spectrum greatly reduces the effect of radio frequency interference (RFI) compared with using auto spectrum. Single pulse detection confidence increases by cross identifying detections from multiple baselines. By combining the power of multiple baselines, we may improve the detection sensitivity. Our method is similar to that of coherent beam forming, but without the computational expense to form a great number of beams to cover the whole field of view of our telescopes. The data processing pipeline designed for this method is easy to implement and parallelize, which can be deployed in various kinds of VLBI observations. In particular, we point out that VGOS observations are very suitable for FRB search.Comment: Accepted for publication in A

Eulerian superpath approach to correct sequencing error in shotgun assembly

This work describes an error correction method based on the Euler Superpath problem. Sequence data is mapped to an Euler Superpath dynamically by Merging Transformation. With restriction and guiding rules, data consistency is maintained and error paths are separated from correct data: Error edges are mapped to the correct ones and after substitution (of error edges with right paths), corresponding errors in the sequencing data are eliminated.<br /

A parallel DNA fragment assembly algorithm based on eulerian superpath approach

Fragments assembly is among the core problems in the research of Genome. Although many assembly tools based on the &quot;overlap-layout-consensus&quot; paradigm are widely used such as in the Human Genome Project currently, they still can not resolve the &quot;repeats problem&quot; in the DNA sequencing. For the purpose of resolving such problem, Pevzner et al. put forward a new Euler Superpath assembly algorithm. But it needs a big and complex de Bruijin graph which consumes large amounts of memories i.e. becomes the bottleneck of the performance. We present a parallel DNA fragment assembly algorithm based on the Eularian Superpath theory and solve the bottleneck in the current assembly program. The experimental results demonstrate that our approach has a good scalability, and can be used in DNA assembly of middle and large size of eukaryote genome

Shanghai VLBI Correlator

This report summarizes the activities of the Shanghai VLBI Correlator during 2012

Errors of linear multistep methods and Runge-Kutta methods for singular perturbation problems with delays

AbstractThis paper is concerned with the error analysis of linear multistep methods and Runge-Kutta methods applied to some classes of one-parameter stiff singularly perturbed problems with delays. We derive the global error estimates of A(α)-stable linear multistep methods and algebraically and diagonally stable Runge-Kutta methods with Lagrange interpolation procedure. Numerical experiments confirm our theoretical analysis

Twins: Scalable 2-Hop Structured Overlay Network

In this paper we propose a new structured overlay network, which is more efficient and scalable than previous ones. We call it Twins, because its routing table consists of two parts, one containing nodes with common prefix and the other containing nodes with common suffix. Twins routes messages to their destinations in just 2 hops even in a very large scale and the overhead is very low. When deployed in a peer-to-peer system with 5 000 000 nodes, each node receives only 6 messages per second for routing table maintenance. This cost, as well as routing table size, varies as a O(sqrt N) function to the overlay scale, so Twins can also run well in an even larger environment

MVNC: A Multiview Network Computer Architecture

In this paper, MVNC, a multiview network computer system for a high usability thin-client computing environment, is introduced. MVNC uses a revised SBC model to offer a new framework for thin client computing. MVNC can be used as a full functional Windows machine, or used as a Linux workstation, or a~graphic terminal. Its multiview work style is achieved by the attempts on GUI seamless integration technology, device integration technology and local video playback support. MVNC is implemented in an embedded Linux environment using a MIPS-4KC microprocessor. Test results on video application show that MVNC system uses its client hardware more efficiently and the load of MVNC server is lightened

The localization of single pulse in VLBI observation

In our previous work, we propose a cross spectrum based method to extract single pulse signals from RFI contaminated data, which is originated from geodetic VLBI postprocessing. This method fully utilizes fringe phase information of the cross spectrum and hence maximizes signal power, however the localization was not discussed in that work yet. As the continuation of that work, in this paper, we further study how to localize single pulses using astrometric solving method. Assuming that the burst is a point source, we derive the burst position by solving a set of linear equations given the relation between residual delay and offset to a priori position. We find that the single pulse localization results given by both astrometric solving and radio imaging are consistent within 3 sigma level. Therefore we claim that it is possible to derive the position of a single pulse with reasonable precision based on only 3 or even 2 baselines with 4 milliseconds integration. The combination of cross spectrum based detection and the localization proposed in this work then provide a thorough solution for searching single pulse in VLBI observation. According to our calculation, our pipeline gives comparable accuracy as radio imaging pipeline. Moreover, the computational cost of our pipeline is much smaller, which makes it more practical for FRB search in regular VLBI observation. The pipeline is now publicly available and we name it as "VOLKS", which is the acronym of "VLBI Observation for frb Localization Keen Searcher".Comment: 11 pages, 4 figures, 3 tables, accepted for publication in A

Attention-Enhancing Backdoor Attacks Against BERT-based Models

Recent studies have revealed that \textit{Backdoor Attacks} can threaten the safety of natural language processing (NLP) models. Investigating the strategies of backdoor attacks will help to understand the model's vulnerability. Most existing textual backdoor attacks focus on generating stealthy triggers or modifying model weights. In this paper, we directly target the interior structure of neural networks and the backdoor mechanism. We propose a novel Trojan Attention Loss (TAL), which enhances the Trojan behavior by directly manipulating the attention patterns. Our loss can be applied to different attacking methods to boost their attack efficacy in terms of attack successful rates and poisoning rates. It applies to not only traditional dirty-label attacks, but also the more challenging clean-label attacks. We validate our method on different backbone models (BERT, RoBERTa, and DistilBERT) and various tasks (Sentiment Analysis, Toxic Detection, and Topic Classification).Comment: Findings of EMNLP 202