75,694 research outputs found
Around Kolmogorov complexity: basic notions and results
Algorithmic information theory studies description complexity and randomness
and is now a well known field of theoretical computer science and mathematical
logic. There are several textbooks and monographs devoted to this theory where
one can find the detailed exposition of many difficult results as well as
historical references. However, it seems that a short survey of its basic
notions and main results relating these notions to each other, is missing.
This report attempts to fill this gap and covers the basic notions of
algorithmic information theory: Kolmogorov complexity (plain, conditional,
prefix), Solomonoff universal a priori probability, notions of randomness
(Martin-L\"of randomness, Mises--Church randomness), effective Hausdorff
dimension. We prove their basic properties (symmetry of information, connection
between a priori probability and prefix complexity, criterion of randomness in
terms of complexity, complexity characterization for effective dimension) and
show some applications (incompressibility method in computational complexity
theory, incompleteness theorems). It is based on the lecture notes of a course
at Uppsala University given by the author
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Trypanosome mRNAs share a common 5' spliced leader sequence.
A 5'-terminal leader sequence of 35 nucleotides was found to be present on multiple trypanosome RNAs. Based on its representation in cDNA libraries, we estimate that many, if not all, trypanosome mRNAs contain this leader. This same leader was originally identified on mRNAs encoding the molecules responsible for antigenic variation, variant surface glycoproteins. Studies of selected cDNAs containing this leader sequence revealed that leader-containing transcripts can be stage-specific, stage-regulated, or constitutive. They can be abundant or rare, and transcribed from single or multigene families. No linkage between the genomic leader sequences and the structural gene exons was observed. Possible mechanisms by which the leader sequences are added to trypanosome mRNAs are discussed
Towards Informative Statistical Flow Inversion
This is the accepted version of 'Towards Informative Statistical Flow Inversion', archived originally at arXiv:0705.1939v1 [cs.NI] 14 May 2007.A problem which has recently attracted research attention is that of estimating the distribution of flow sizes in internet traffic. On high traffic links it is sometimes impossible to record every packet. Researchers have approached the problem of estimating flow lengths from sampled packet data in two separate ways. Firstly, different sampling methodologies can be tried to more accurately measure the desired system parameters. One such method is the sample-and-hold method where, if a packet is sampled, all subsequent packets in that flow are sampled. Secondly, statistical methods can be used to ``invert'' the sampled data and produce an estimate of flow lengths from a sample. In this paper we propose, implement and test two variants on the sample-and-hold method. In addition we show how the sample-and-hold method can be inverted to get an estimation of the genuine distribution of flow sizes. Experiments are carried out on real network traces to compare standard packet sampling with three variants of sample-and-hold. The methods are compared for their ability to reconstruct the genuine distribution of flow sizes in the traffic
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Identification of a small RNA containing the trypanosome spliced leader: a donor of shared 5' sequences of trypanosomatid mRNAs?
The 35 nucleotide spliced leader (SL) sequence is found on the 5' end of numerous trypanosome mRNAs, yet the tandemly organized reiteration units encoding this leader are not detectably linked to any of these structural genes. Here we report the presence of a class of discrete small SL RNA molecules that are derived from the genomic SL reiteration units of Trypanosoma brucei, Trypanosoma cruzi, and Leptomonas collosoma. These small SL RNAs are 135, 105, and 95 nucleotides, respectively, and contain a 5'-terminal SL or SL-like sequence. S1 nuclease analyses demonstrate that these small SL RNAs are transcribed from continuous sequence within the respective SL reiteration units. With the exception of the SL sequence and a concensus donor splice site immediately following it, these small RNAs are not well conserved. We suggest that the small SL RNAs may function as a donor of the SL sequence in an intermolecular process that places the SL at the 5' terminus of many trypanosomatid mRNAs
High phosphate content significantly increases apatite formation of fluoride-containing bioactive glasses
NOTICE: this is the author’s version of a work that was accepted for publication in Acta Biomaterialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Biomaterialia, [VOL 7, ISSUE 4, (2001)] DOI: 10.1016/j.actbio.2010.11.03
Invertibility in groupoid C*-algebras
Given a second-countable, Hausdorff, \'etale, amenable groupoid G with
compact unit space, we show that an element a in C*(G) is invertible if and
only if \lambda_x(a) is invertible for every x in the unit space of G, where
\lambda_x refers to the "regular representation" of C*(G) on l_2(G_x). We also
prove that, for every a in C*(G), there exists some x in G^{(0)} such that
||a|| = ||\lambda_x(a)||.Comment: 8 page
SYM, Chern-Simons, Wess-Zumino Couplings and their higher derivative corrections in IIA Superstring theory
We find the entire form of the amplitude of two fermion strings (with
different chirality), a massless scalar field and one closed string
Ramond-Ramond (RR) in IIA superstring theory which is different from its IIB
one. We make use of a very particular gauge fixing and explore several new
couplings in IIA. All infinite - channel scalar poles and - channel
fermion poles are also constructed. We find new form of higher derivative
corrections to two fermion two scalar couplings and show that the first simple
channel scalar pole for case can be obtained by having new
higher derivative corrections to SYM couplings at third order of . We
find that the general structure and the coefficients of higher derivative
corrections to two fermion two scalar couplings are completely different from
the derived higher derivative corrections of type IIB.Comment: 29 pages, no figure,Latex file,published version in EPJ
Dust penetrated morphology in the high redshift Universe
Images from the Hubble Deep Field (HDF) North and South show a large
percentage of dusty, high redshift galaxies whose appearance falls outside
traditional classification systems. The nature of these objects is not yet
fully understood. Since the HDF preferentially samples restframe UV light, HDF
morphologies are not dust or `mask' penetrated. The appearance of high redshift
galaxies at near-infrared restframes remains a challenge for the New
Millennium. The Next Generation Space Telescope (NGST) could routinely provide
us with such images. In this contribution, we quantitatively determine the
dust-penetrated structures of high redshift galaxies such as NGC 922 in their
near-infrared restframes. We show that such optically peculiar objects may
readily be classified using the dust penetrated z ~ 0 templates of Block and
Puerari (1999) and Buta and Block (2001).Comment: 4 pages, 2 figures. Presented at the conference "The Link between
Stars and Cosmology", 26-30 March, 2001, Puerto Vallarta, Mexico. To be
published by Kluwer, eds. M. Chavez, A. Bressan, A. Buzzoni, and D. Mayya.
High-resolution version of Figure 2 can be found at
http://www.inaoep.mx/~puerari/conf_puertovallart
The Hardness of Embedding Grids and Walls
The dichotomy conjecture for the parameterized embedding problem states that
the problem of deciding whether a given graph from some class of
"pattern graphs" can be embedded into a given graph (that is, is isomorphic
to a subgraph of ) is fixed-parameter tractable if is a class of graphs
of bounded tree width and -complete otherwise.
Towards this conjecture, we prove that the embedding problem is
-complete if is the class of all grids or the class of all walls
- …