1,326 research outputs found
Observation and Numerical Simulation of Terrain-Induced Windshear at the Hong Kong International Airport in a Planetary Boundary Layer without Temperature Inversions
Terrain-induced windshear at Hong Kong International Airport (HKIA) could be hazardous to the landing and departing aircraft. Such windshear occurring in a planetary boundary layer without temperature inversions is studied in this paper by using the data from the Terminal Doppler Weather Radar and Light Detection and Ranging systems. A high resolution numerical model, called aviation model (AVM), is also employed to find out its capability to forecast the occurrence of such windshear. The model is found to have skills in capturing the terrain-induced windshear, including the terrain-induced microburst due to the mountains of Lantau Island. Moreover, the windshear detection algorithm as applied to the AVM output, called AVM-GLYGA, is able to give advance alert for the occurrence of low-level windshear. The model also offers new dataset, such as vertical velocity and vertical cross sections across the windshear feature, to study the terrain-induced windshear phenomena with new insights. The AVM is found to have good skills in depicting the terrain-disrupted airflow at the airport area, and more comprehensive study would be conducted to study the skills of AVM-GLYGA as compared with pilot windshear report as sky truth
Succinct Dictionary Matching With No Slowdown
The problem of dictionary matching is a classical problem in string matching:
given a set S of d strings of total length n characters over an (not
necessarily constant) alphabet of size sigma, build a data structure so that we
can match in a any text T all occurrences of strings belonging to S. The
classical solution for this problem is the Aho-Corasick automaton which finds
all occ occurrences in a text T in time O(|T| + occ) using a data structure
that occupies O(m log m) bits of space where m <= n + 1 is the number of states
in the automaton. In this paper we show that the Aho-Corasick automaton can be
represented in just m(log sigma + O(1)) + O(d log(n/d)) bits of space while
still maintaining the ability to answer to queries in O(|T| + occ) time. To the
best of our knowledge, the currently fastest succinct data structure for the
dictionary matching problem uses space O(n log sigma) while answering queries
in O(|T|log log n + occ) time. In this paper we also show how the space
occupancy can be reduced to m(H0 + O(1)) + O(d log(n/d)) where H0 is the
empirical entropy of the characters appearing in the trie representation of the
set S, provided that sigma < m^epsilon for any constant 0 < epsilon < 1. The
query time remains unchanged.Comment: Corrected typos and other minor error
Compressed Data Structures for Dynamic Sequences
We consider the problem of storing a dynamic string over an alphabet
in compressed form. Our representation
supports insertions and deletions of symbols and answers three fundamental
queries: returns the -th symbol in ,
counts how many times a symbol occurs among the
first positions in , and finds the position
where a symbol occurs for the -th time. We present the first
fully-dynamic data structure for arbitrarily large alphabets that achieves
optimal query times for all three operations and supports updates with
worst-case time guarantees. Ours is also the first fully-dynamic data structure
that needs only bits, where is the -th order
entropy and is the string length. Moreover our representation supports
extraction of a substring in optimal time
Periodically-Poled Silicon [Updated]
We propose a new class of photonic devices based on periodic stress fields in
silicon that enable second-order nonlinearity as well as quasi-phase matching.
Periodically-poled silicon (PePSi) adds the periodic poling capability to
silicon photonics, and allows the excellent crystal quality and advanced
manufacturing capabilities of silicon to be harnessed for devices based on
second-order nonlinear effects. As an example of the utility of the PePSi
technology, we present simulations showing that mid-wave infrared radiation can
be efficiently generated through difference frequency generation from
near-infrared with a conversion efficiency of 50%. This technology can also be
implemented with piezoelectric material, which offers the capability to
dynamically control the X(2) nonlinearity.Comment: 11 pages, 4 figure
Large-vocabulary speaker-independent continuous speech recognition with semi-continuous hidden Markov models
A semi-continuous hidden Markov model based on the muluple vector quantization codebooks is used here for large.vocabulary speaker-independent continuous speech recognition in the techn,ques employed here. the semi-continuous output probab~hty densHy function for each codebook is represented by a comhinat,on of the corre,~ponding discrete output probablhttes of the hidden Markov model end the continuous Gauss,an den. stay functions of each individual codebook. Parameters of vec. tor qusnttzation codebook and hidden Markov model are mutuully optimized to achJeve an optimal model'codebook comb,nation under a untried probab,hshc framework Another advantages of thts approach is the enhanced robustness of the semi. continuous output probability by the combination of multiple codewords and multtple codebooks For a 1000.word speakermdependen
An Efficient Alignment Algorithm for Searching Simple Pseudoknots over Long Genomic Sequence
published_or_final_versio
Low Space External Memory Construction of the Succinct Permuted Longest Common Prefix Array
The longest common prefix (LCP) array is a versatile auxiliary data structure
in indexed string matching. It can be used to speed up searching using the
suffix array (SA) and provides an implicit representation of the topology of an
underlying suffix tree. The LCP array of a string of length can be
represented as an array of length words, or, in the presence of the SA, as
a bit vector of bits plus asymptotically negligible support data
structures. External memory construction algorithms for the LCP array have been
proposed, but those proposed so far have a space requirement of words
(i.e. bits) in external memory. This space requirement is in some
practical cases prohibitively expensive. We present an external memory
algorithm for constructing the bit version of the LCP array which uses
bits of additional space in external memory when given a
(compressed) BWT with alphabet size and a sampled inverse suffix array
at sampling rate . This is often a significant space gain in
practice where is usually much smaller than or even constant. We
also consider the case of computing succinct LCP arrays for circular strings
Efficient Representation of Multidimensional Data over Hierarchical Domains
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-46049-9_19[Abstract] We consider the problem of representing multidimensional data where the domain of each dimension is organized hierarchically, and the queries require summary information at a different node in the hierarchy of each dimension. This is the typical case of OLAP databases. A basic approach is to represent each hierarchy as a one-dimensional line and recast the queries as multidimensional range queries. This approach can be implemented compactly by generalizing to more dimensions the k2k2 -treap, a compact representation of two-dimensional points that allows for efficient summarization queries along generic ranges. Instead, we propose a more flexible generalization, which instead of a generic quadtree-like partition of the space, follows the domain hierarchies across each dimension to organize the partitioning. The resulting structure is much more efficient than a generic multidimensional structure, since queries are resolved by aggregating much fewer nodes of the tree.Ministerio de Economía, Industria y Competitividad; TIN2013-46238-C4-3-RMinisterio de Economía, Industria y Competitividad; IDI-20141259Ministerio de Economía, Industria y Competitividad; ITC-20151305Ministerio de Economía y Competitividad; ITC-20151247Xunta de Galicia; GRC2013/053Chile.Fondo Nacional de Desarrollo Científico y Tecnológico; 1-140796COST. IC130
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