9,006 research outputs found
Symmetry of uniaxial global Landau-de Gennes minimizers in the\ud theory of nematic liquid crystals
We extend the recent radial symmetry results by Pisante [23] and Millot & Pisante [19] (who show that all entire solutions of the vector-valued Ginzburg-Landau equations in superconductivity theory, in the three-dimensional space, are comprised of the well-known class of equivariant solutions) to the Landau-de Gennes framework in the theory of nematic liquid crystals. In the low temperature limit, we obtain a characterization of global Landau-de Gennes minimizers, in the restricted class of uniaxial tensors, in terms of the well-known radial-hedgehog solution. We use this characterization to prove that global Landau-de Gennes minimizers cannot be purely uniaxial for sufficiently low temperatures
Reduced models for linearly elastic thin films allowing for fracture, debonding or delamination
This work is devoted so show the appearance of different cracking modes in
linearly elastic thin film systems by means of an asymptotic analysis as the
thickness tends to zero. By superposing two thin plates, and upon suitable
scaling law assumptions on the elasticity and fracture parameters, it is proven
that either debonding or transverse cracks can emerge in the limit. A model
coupling debonding, transverse cracks and delamination is also discussed
Sustainable Agriculture: A Way Out of Food Poverty
The most fundamental human right is the right to food (UN General Assembly, 2002). Proper nutritious food is the precondition for normal human development. Well-nourished children are more likely to succeed in learning and are less susceptible to diseases. But low-income, food-importing economies are facing increasing difficulties in accessing staple food items. Chronic food insecurity persists, especially in Sub-Saharan Africa. The recent economic crisis drove more than 100 million people into hunger in 2008 alone. Is sustainable agriculture a solution?Sustainable Agriculture: A Way Out of Food Poverty
Evolution of genome sequencing techniques
The quality and the speed for genome sequencing has advanced at the same time that technology boundaries are
stretched. This advancement has been divided so far in three generations. The first-generation methods enabled
sequencing of clonal DNA populations. The second-generation massively increased throughput by parallelizing many
reactions while the third-generation methods allow direct sequencing of single DNA molecules.
The first techniques to sequence DNA were not developed until the mid-1970s, when two distinct sequencing methods
were developed almost simultaneously, one by Alan Maxam and Walter Gilbert, and the other one by Frederick Sanger.
The first one is a chemical method to cleave DNA at specific points and the second one uses ddNTPs, which synthesizes
a copy from the DNA chain template. Nevertheless, both methods generate fragments of varying lengths that are further
electrophoresed.
Moreover, it is important to say that until the 1990s, the sequencing of DNA was relatively expensive and it was seen as
a long process. Besides, using radiolabeled nucleotides also compounded the problem through safety concerns and
prevented the automation. Some advancements within the first generation include the replacement of radioactive labels
by fluorescent labeled ddNTPs and cycle sequencing with thermostable DNA polymerase, which allows automation and
signal amplification, making the process cheaper, safer and faster. Another method is Pyrosequencing, which is based on
the âsequencing by synthesisâ principle. It differs from Sanger sequencing, in that it relies on the detection of
pyrophosphate release on nucleotide incorporation.
By the end of the last millennia, parallelization of this method started the Next Generation Sequencing (NGS) with 454 as
the first of many methods that can process multiple samples, calling it the 2Âș generation sequencing. Here
electrophoresis was completely eliminated. One of the methods that is sometimes used is SOLiD, based on sequencing
by ligation of fluorescently dye-labeled di-base probes which competes to ligate to the sequencing primer. Specificity of
the di-base probe is achieved by interrogating every 1st and 2nd base in each ligation reaction. The widely used
Solexa/Illumina method uses modified dNTPs containing so called âreversible terminatorsâ which blocks further
polymerization. The terminator also contains a fluorescent label, which can be detected by a camera.
Now, the previous step towards the third generation was in charge of Ion Torrent, who developed a technique that is
based in a method of âsequencing-by-synthesisâ. Its main feature is the detection of hydrogen ions that are released
during base incorporation.
Likewise, the third generation takes into account nanotechnology advancements for the processing of unique DNA
molecules to a real time synthesis sequencing system like PacBio; and finally, the NANOPORE, projected since 1995,
also uses Nano-sensors forming channels obtained from bacteria that conducts the sample to a sensor that allows the
detection of each nucleotide residue in the DNA strand.
The advancements in terms of technology that we have nowadays have been so quick, that it makes wonder: ÂżHow do
we imagine the next generation
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