735 research outputs found
Jet engine powers large, high-temperature wind tunnel
Wind tunnel for large component testing uses a jet engine with afterburner to provide high temperatures /1200 degrees to 2000 degrees F/ and controlled high velocity gas. This economical wind tunnel can accommodate parts ten feet by ten feet or larger, and is a useful technique for qualitative information
Mineral Occurrence Database suggestions for revision and update 2005
The Mineral Occurrence Database contains over 12000 entries from all parts of Great Britain. It
includes mineral occurrences associated with old mines and trials, unexploited more recent
discoveries and panned stream sediment concentrates (mainly gold grains). It was developed in
Oracle, using an Access interface with the user, in the mid 1990s. The database structure has
been unaltered for many years. It now requires a thorough re-examination of all the entries to
check their validity as well as a re-examination of the relationships between tables as some of the
links have become corrupted and new data entry is either difficult or impossible.
The database has an important role in the future with the increasing interest in mine waste and
environmental contamination, as well as to assist any commercial mineral exploration companies
if necessary. However, this can only be realised if the database is current, accurate and
comprehensive in both coverage and content.
The database has many problems and these are detailed in this report together with possible
solutions. In addition, a number of suggestions are made for the update of the database, with
estimates for the time required
Bubbles and denaturation in DNA
The local opening of DNA is an intriguing phenomenon from a statistical
physics point of view, but is also essential for its biological function. For
instance, the transcription and replication of our genetic code can not take
place without the unwinding of the DNA double helix. Although these biological
processes are driven by proteins, there might well be a relation between these
biological openings and the spontaneous bubble formation due to thermal
fluctuations. Mesoscopic models, like the Peyrard-Bishop-Dauxois model, have
fairly accurately reproduced some experimental denaturation curves and the
sharp phase transition in the thermodynamic limit. It is, hence, tempting to
see whether these models could be used to predict the biological activity of
DNA. In a previous study, we introduced a method that allows to obtain very
accurate results on this subject, which showed that some previous claims in
this direction, based on molecular dynamics studies, were premature. This could
either imply that the present PBD should be improved or that biological
activity can only be predicted in a more complex frame work that involves
interactions with proteins and super helical stresses. In this article, we give
detailed description of the statistical method introduced before. Moreover, for
several DNA sequences, we give a thorough analysis of the bubble-statistics as
function of position and bubble size and the so-called -denaturation curves
that can be measured experimentally. These show that some important
experimental observations are missing in the present model. We discuss how the
present model could be improved.Comment: 15 pages, 5 figures, published as Eur. Phys. J. E 20 : 421-434 AUG
200
A stitch in time: Efficient computation of genomic DNA melting bubbles
Background: It is of biological interest to make genome-wide predictions of
the locations of DNA melting bubbles using statistical mechanics models.
Computationally, this poses the challenge that a generic search through all
combinations of bubble starts and ends is quadratic.
Results: An efficient algorithm is described, which shows that the time
complexity of the task is O(NlogN) rather than quadratic. The algorithm
exploits that bubble lengths may be limited, but without a prior assumption of
a maximal bubble length. No approximations, such as windowing, have been
introduced to reduce the time complexity. More than just finding the bubbles,
the algorithm produces a stitch profile, which is a probabilistic graphical
model of bubbles and helical regions. The algorithm applies a probability peak
finding method based on a hierarchical analysis of the energy barriers in the
Poland-Scheraga model.
Conclusions: Exact and fast computation of genomic stitch profiles is thus
feasible. Sequences of several megabases have been computed, only limited by
computer memory. Possible applications are the genome-wide comparisons of
bubbles with promotors, TSS, viral integration sites, and other melting-related
regions.Comment: 16 pages, 10 figure
P5_1 ”Everybody knows the Moon is made of cheese...”: Return of the Cheddar
This Letter explores the repercussions of the Moon turning into cheddar, and finds that with the same volume and lighter mass of m = 2.49 × 1022kg, it would escape the Earth’s sphere of influence. We looked at two possible escape trajectories, prograde and retrograde, and found the new orbital distances to be between 0.73AU and 1.00AU, and between 1.00AU and 1.51AU, respectively. Thus potentially carrying the Moon very near to the orbits of Venus or Mars.
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