257 research outputs found
The Discrepancy of the Lex-Least De Bruijn Sequence
We answer the following question of R. L. Graham: What is the discrepancy of
the lexicographically-least binary de Bruijn sequence? Here, "discrepancy"
refers to the maximum (absolute) difference between the number of ones and the
number of zeros in any initial segment of the sequence. We show that the answer
is .Comment: 11 pages, 0 figure
Testing of random matrices
Let be a positive integer and be an
\linebreak \noindent sized matrix of independent random variables
having joint uniform distribution \hbox{Pr} {x_{ij} = k \hbox{for} 1 \leq k
\leq n} = \frac{1}{n} \quad (1 \leq i, j \leq n) \koz. A realization
of is called \textit{good}, if its each row and
each column contains a permutation of the numbers . We present and
analyse four typical algorithms which decide whether a given realization is
good
Testing of sequences by simulation
Let be a random integer vector, having uniform distribution
A realization of is called
\textit{good}, if its elements are different. We present algorithms
\textsc{Linear}, \textsc{Backward}, \textsc{Forward}, \textsc{Tree},
\textsc{Garbage}, \textsc{Bucket} which decide whether a given realization is
good. We analyse the number of comparisons and running time of these algorithms
using simulation gathering data on all possible inputs for small values of
and generating random inputs for large values of
Compact genome of the Antarctic midge is likely an adaptation to an extreme environment
The midge, Belgica antarctica, is the only insect endemic to Antarctica, and thus it offers a powerful model for probing responses to extreme temperatures, freeze tolerance, dehydration, osmotic stress, ultraviolet radiation and other forms of environmental stress. Here we present the first genome assembly of an extremophile, the first dipteran in the family Chironomidae, and the first Antarctic eukaryote to be sequenced. At 99 megabases, B. antarctica has the smallest insect genome sequenced thus far. Although it has a similar number of genes as other Diptera, the midge genome has very low repeat density and a reduction in intron length. Environmental extremes appear to constrain genome architecture, not gene content. The few transposable elements present are mainly ancient, inactive retroelements. An abundance of genes associated with development, regulation of metabolism and responses to external stimuli may reflect adaptations for surviving in this harsh environment
Metagenomic analysis shows the presence of bacteria related to free-living forms of sulfur-Oxidizing Chemolithoautotrophic Symbionts in the rhizosphere of the seagrass Zostera marina
Seagrasses play an important role as ecosystem engineers; they provide shelter to many animals and improve water quality by filtering out nutrients and by controlling pathogens. Moreover, their rhizosphere promotes a myriad of microbial interactions and processes, which are dominated by microorganisms involved in the sulfur cycle. This study provides a detailed insight into the metabolic sulfur pathways in the rhizobiome of the seagrass Zostera marina, a dominant seagrass species across the temperate northern hemisphere. Shotgun metagenomic sequencing revealed the relative dominance of Gamma- and Deltaproteobacteria, and comparative analysis of sulfur genes identified a higher abundance of genes related to sulfur oxidation than sulfate reduction. We retrieved four high-quality draft genomes that are closely related to the gill symbiont of the clam Solemya velum, which suggests the presence of putative free-living forms of symbiotic bacteria. These are potentially highly versatile chemolithoautotrophic bacteria, able to alternate their metabolism between parallel pathways of sulfide oxidation (via sqr and fcc), nitrate reduction (denitrification or DNRA) and carbon fixation (via CBB or TCA cycle), depending on the environmental availability of sulfide. Our results support the hypothesis that seagrass meadows might function as a source of symbionts for invertebrates that inhabit within or around seagrass meadows. While providing ideal conditions for the proliferation of these free-living forms of symbionts, seagrasses would benefit from their genetic versatility, which contributes to sulfide detoxification and ammonium production, the seagrasses' preferred nitrogen source.European Union
ERC
322551
European Science Foundation ConGenOmics program
6349
Fundacao para a Ciencia e Tecnologia (FCT)
SFRH/BPD/63/03/2009
SFRH/BPD/107878/2015info:eu-repo/semantics/publishedVersio
Computation and programmability at the nano-bio interface
PhD ThesisThe manipulation of physical reality on the molecular level and construction of devices
operating on the nanoscale has been the focal point of nanotechnology. In particular,
nanotechnology based on DNA and RNA has a potential to nd applications in the
eld of Synthetic Biology thanks to the inherent compatibility of nucleic acids with
biological systems. Sca olded DNA origami, proposed by P. Rothemund, is one of
the leading and most successful methods in which nanostructures are realised through
rational programming of short 'staple' oligomers which fold a long single-stranded
DNA called the 'sca old' strand into a variety of desired shapes. DNA origami already
has many applications; including intelligent drug delivery, miniaturisation of logic
circuits and computation in vivo. However, one of the factors that are limiting the
complexity, applicability and scalability of this approach is the source of the sca old
which commonly originates from viruses or phages. Furthermore, developing a robust
and orthogonal interface between DNA nanotechnology and biological parts remains
a signi cant challenge.
The rst part of this thesis tackles these issues by challenging the fundamental as-
sumption in the eld, namely that a viral sequence is to be used as the DNA origami
sca old. A method is introduced for de novo generation of long synthetic sequences
based on De Bruijn sequence, which has been previously proposed in combinatorics.
The thesis presents a collection of algorithms which allow the construction of custom-
made sequences that are uniquely addressable and biologically orthogonal (i.e. they
do not code for any known biological function). Synthetic sca olds generated by these
algorithms are computationally analysed and compared with their natural counter-
parts with respect to: repetition in sequence, secondary structure and thermodynamic
addressability. This also aids the design of wet lab experiments pursuing justi cation
and veri cation of this novel approach by empirical evidence.
The second part of this thesis discusses the possibility of applying evolutionary op-
timisation to synthetic DNA sequences under constraints dictated by the biological
interface. A multi-strand system is introduced based on an alternative approach to
DNA self-assembly, which relies on strand-displacement cascades, for molecular data
storage. The thesis demonstrates how a genetic algorithm can be used to generate
viable solutions to this sequence optimisation problem which favours the target self-
assembly con guration. Additionally, the kinetics of strand-displacement reactions
are analysed with existing coarse-grained DNA models (oxDNA).
This thesis is motivated by the application of scienti c computing to problems which
lie on the boundary of Computer Science and the elds of DNA Nanotechnology, DNA
Computing and Synthetic Biology, and thus I endeavour to the best of my ability to
establish this work within the context of these disciplines
The Great Umar Khayyam
The Rubáiyát by the Persian poet ‘Umar Khayyæm (1048-1131) is used in contemporary Iran as a resistance literature, symbolizing the secularist voice in cultural debates. While Islamic fundamentalists criticize Khayyæm as an atheist and materialist philosopher who questions God’s creation and the promise of reward or punishment in the hereafter, secularist intellectuals see in him an example of a scientist who scrutinizes the mysteries of the world. Others see a spiritual master, a Sufi, who guides people to the truth. This volume collects eighteen essays on the history of the reception of ‘Umar Khayyæm in various literary traditions, exploring how his philosophy of doubt, carpe diem, hedonism, and in vino veritas has inspired generations of poets, novelists, painters, musicians, calligraphers and film-makers
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