452 research outputs found

### Software-Architecture Recovery from Machine Code

In this paper, we present a tool, called Lego, which recovers object-oriented software architecture from stripped binaries. Lego takes a stripped binary as input, and uses information obtained from dynamic analysis to (i) group the functions in the binary into classes, and (ii) identify inheritance and composition relationships between the inferred classes. The information obtained by Lego can be used for reengineering legacy software, and for understanding the architecture of software systems that lack documentation and source code. Our experiments show that the class hierarchies recovered by Lego have a high degree of agreement---measured in terms of precision and recall---with the hierarchy defined in the source code

### Clearing Contamination in Large Networks

In this work, we study the problem of clearing contamination spreading
through a large network where we model the problem as a graph searching game.
The problem can be summarized as constructing a search strategy that will leave
the graph clear of any contamination at the end of the searching process in as
few steps as possible. We show that this problem is NP-hard even on directed
acyclic graphs and provide an efficient approximation algorithm. We
experimentally observe the performance of our approximation algorithm in
relation to the lower bound on several large online networks including
Slashdot, Epinions and Twitter. The experiments reveal that in most cases our
algorithm performs near optimally

### Counting surface-kernel epimorphisms from a co-compact Fuchsian group to a cyclic group with motivations from string theory and QFT

Graphs embedded into surfaces have many important applications, in
particular, in combinatorics, geometry, and physics. For example, ribbon graphs
and their counting is of great interest in string theory and quantum field
theory (QFT). Recently, Koch, Ramgoolam, and Wen [Nuclear Phys.\,B {\bf 870}
(2013), 530--581] gave a refined formula for counting ribbon graphs and
discussed its applications to several physics problems. An important factor in
this formula is the number of surface-kernel epimorphisms from a co-compact
Fuchsian group to a cyclic group. The aim of this paper is to give an explicit
and practical formula for the number of such epimorphisms. As a consequence, we
obtain an `equivalent' form of the famous Harvey's theorem on the cyclic groups
of automorphisms of compact Riemann surfaces. Our main tool is an explicit
formula for the number of solutions of restricted linear congruence recently
proved by Bibak et al. using properties of Ramanujan sums and of the finite
Fourier transform of arithmetic functions

### Development of a PDMS Based Micro Total Analysis System for Rapid Biomolecule Detection

The emerging field of micro total analysis system powered by microfluidics is expected to revolutionize miniaturization and automation for point-of-care-testing systems which require quick, efficient and reproducible results. In the present study, a PDMS based micro total analysis system has been developed for rapid, multi-purpose, impedance based detection of biomolecules. The major components of the micro total analysis system include a micropump, micromixer, magnetic separator and interdigitated electrodes for impedance detection. Three designs of pneumatically actuated PDMS based micropumps were fabricated and tested. Based on the performance test results, one of the micropumps was selected for integration. The experimental results of the micropump performance were confirmed by a 2D COMSOL simulation combined with an equivalent circuit analysis of the micropump. Three designs of pneumatically actuated PDMS based active micromixers were fabricated and tested. The micromixer testing involved determination of mixing efficiency based on the streptavidin-biotin conjugation reaction between biotin comjugated fluorescent microbeads and streptavidin conjugated paramagnetic microbeads, followed by fluorescence measurements. Based on the performance test results, one of the micromixers was selected for integration. The selected micropump and micromixer were integrated into a single microfluidic system. The testing of the magnetic separation scheme involved comparison of three permanent magnets and three electromagnets of different sizes and magnetic strengths, for capturing magnetic microbeads at various flow rates. Based on the test results, one of the permanent magnets was selected. The interdigitated electrodes were fabricated on a glass substrate with gold as the electrode material. The selected micropumps, micromixer and interdigitated electrodes were integrated to achieve a fully integrated microfluidic system. The fully integrated microfluidic system was first applied towards biotin conjugated fluorescent microbeads detection based on streptavidin-biotin conjugation reaction which is followed by impedance spectrum measurements. The lower detection limit for biotin conjugated fluorescent microbeads was experimentally determined to be 1.9 x 106 microbeads. The fully integrated microfluidic system was then applied towards immuno microbead based insulin detection. The lower detection limit for insulin was determined to be 10-5M. The total detection time was 20 min. An equivalent circuit analysis was performed to explain the impedance spectrum results

### The Best Answers? Think Twice: Online Detection of Commercial Campaigns in the CQA Forums

In an emerging trend, more and more Internet users search for information
from Community Question and Answer (CQA) websites, as interactive communication
in such websites provides users with a rare feeling of trust. More often than
not, end users look for instant help when they browse the CQA websites for the
best answers. Hence, it is imperative that they should be warned of any
potential commercial campaigns hidden behind the answers. However, existing
research focuses more on the quality of answers and does not meet the above
need. In this paper, we develop a system that automatically analyzes the hidden
patterns of commercial spam and raises alarms instantaneously to end users
whenever a potential commercial campaign is detected. Our detection method
integrates semantic analysis and posters' track records and utilizes the
special features of CQA websites largely different from those in other types of
forums such as microblogs or news reports. Our system is adaptive and
accommodates new evidence uncovered by the detection algorithms over time.
Validated with real-world trace data from a popular Chinese CQA website over a
period of three months, our system shows great potential towards adaptive
online detection of CQA spams.Comment: 9 pages, 10 figure

### On an almost-universal hash function family with applications to authentication and secrecy codes

Universal hashing, discovered by Carter and Wegman in 1979, has many
important applications in computer science. MMH$^*$, which was shown to be
$\Delta$-universal by Halevi and Krawczyk in 1997, is a well-known universal
hash function family. We introduce a variant of MMH$^*$, that we call GRDH,
where we use an arbitrary integer $n>1$ instead of prime $p$ and let the keys
$\mathbf{x}=\langle x_1, \ldots, x_k \rangle \in \mathbb{Z}_n^k$ satisfy the
conditions $\gcd(x_i,n)=t_i$ ($1\leq i\leq k$), where $t_1,\ldots,t_k$ are
given positive divisors of $n$. Then via connecting the universal hashing
problem to the number of solutions of restricted linear congruences, we prove
that the family GRDH is an $\varepsilon$-almost-$\Delta$-universal family of
hash functions for some $\varepsilon<1$ if and only if $n$ is odd and
$\gcd(x_i,n)=t_i=1$ $(1\leq i\leq k)$. Furthermore, if these conditions are
satisfied then GRDH is $\frac{1}{p-1}$-almost-$\Delta$-universal, where $p$ is
the smallest prime divisor of $n$. Finally, as an application of our results,
we propose an authentication code with secrecy scheme which strongly
generalizes the scheme studied by Alomair et al. [{\it J. Math. Cryptol.} {\bf
4} (2010), 121--148], and [{\it J.UCS} {\bf 15} (2009), 2937--2956].Comment: International Journal of Foundations of Computer Science, to appea

### Linear algebraic methods in communication complexity

AbstractThe notion of communication complexity seeks to capture the amount of communication between different parties that is required to find the output of a Boolean function when each party is provided with only part of the input. Different variants of the model governing the rules of this communication lead to different connections with problems in combinatorial linear algebra. In particular, problems arise in this context that concern the rank of a (0,1)-matrix and the minimum rank of a matrix meeting a given combinatorial description. This paper surveys these connections

### Restricted linear congruences

In this paper, using properties of Ramanujan sums and of the discrete Fourier
transform of arithmetic functions, we give an explicit formula for the number
of solutions of the linear congruence $a_1x_1+\cdots +a_kx_k\equiv b \pmod{n}$,
with $\gcd(x_i,n)=t_i$ ($1\leq i\leq k$), where $a_1,t_1,\ldots,a_k,t_k, b,n$
($n\geq 1$) are arbitrary integers. As a consequence, we derive necessary and
sufficient conditions under which the above restricted linear congruence has no
solutions. The number of solutions of this kind of congruence was first
considered by Rademacher in 1925 and Brauer in 1926, in the special case of
$a_i=t_i=1$ $(1\leq i \leq k)$. Since then, this problem has been studied, in
several other special cases, in many papers; in particular, Jacobson and
Williams [{\it Duke Math. J.} {\bf 39} (1972), 521--527] gave a nice explicit
formula for the number of such solutions when $(a_1,\ldots,a_k)=t_i=1$ $(1\leq
i \leq k)$. The problem is very well-motivated and has found intriguing
applications in several areas of mathematics, computer science, and physics,
and there is promise for more applications/implications in these or other
directions.Comment: Journal of Number Theory, to appea

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