3,536 research outputs found
Self-Assembly of Monatomic Complex Crystals and Quasicrystals with a Double-Well Interaction Potential
For the study of crystal formation and dynamics we introduce a simple
two-dimensional monatomic model system with a parametrized interaction
potential. We find in molecular dynamics simulations that a surprising variety
of crystals, a decagonal and a dodecagonal quasicrystal are self-assembled. In
the case of the quasicrystals the particles reorder by phason flips at elevated
temperatures. During annealing the entropically stabilized decagonal
quasicrystal undergoes a reversible phase transition at 65% of the melting
temperature into an approximant, which is monitored by the rotation of the de
Bruijn surface in hyperspace.Comment: 4 pages, 6 figures. Physical Review Letters, in Press (April 2007
Computer-controlled mass spectrometer for on-line gas analysis
System detects gases in combustion chambers and records their levels of concentration. Simplified data recording and reduction process permits analysis rate of 9 msec per peak and recording of probe position, pressures, temperatures, and mass spectrometer data on same tape. System is applicable to air pollution control
Thomomys bottae pocket gophers of the central Rio Grande Valley, New Mexico: local differentiation, gene flow, and historical biogeography
Representatives of two strongly differentiated geographic units within Thomomys bottae come in contact along the Rio Grande south of Albuquerque, New Mexico. The two forms share an average genic similarity of only 69%, and differ in karyotype by as much as 17 pairs of uniarmed autosomes. This high level of genic and chromosomal differentiation might suggest extremely limited introgression, or perhaps none at all. However, diagnostic alleles at several strongly differentiated loci were detected in contact zone populations of the opposite group, indicating that some gene flow does oc\u3c;ur. Suitable habitat and available land area are limited in the zone of contact, and these factors, in combination with the structure of local breeding populations of pocket gophers, contribute to restriction of gene flow through the contact zone. The measured width of the contact zone corresponds reasonably well with predictions derived from a neutral diffusion cline model under current estimates of gene flow rates and time of secondary contact
Performance improvements of supermarket R744 systems by pivoting compressor arrangements
The adoption of the EU F-Gas regulation 517/2014 and the development of the Multi Ejector concept have led CO2 to take center stage as one of the preferred solutions in several applications, at the expense of synthetic refrigerants. Despite the expected significant energy saving in warm climates using the Multi Ejector, the increase in investment costs and level of complexity would hinder its spread. In this work a numerical and experimental campaign have been performed to explore the implementation of “pivoting” compressors, i.e. a technique that enables the medium temperature (MT) and parallel (IT) compressors in a booster system to be interchangeable according to cooling loads, ambient conditions and ejector capacity. The novel configuration presented in this work helps to downsize the installed compressor capacity in ejector-supported systems while maintaining all the benefits due to the ejector. The basic version of the solution is based on: i) MT and low temperature (LT) compressors, ii) high pressure controlled through a Multi Ejector both during summer and winter conditions. The tests performed in the laboratory proved how the “pivoting” solution is beneficial to attain a higher degree of flexibility with more compact systems while maintaining the efficiency and justifying economically the ejector implementation. An additional solution called LT “pivoting”, i.e. connecting LT compressors either to MT or IT compressors, proved to be particularly useful for energy saving.Performance improvements of supermarket R744 systems by pivoting compressor arrangementsacceptedVersio
Azuleno[8,8a,1,2-def]heptalene
Methyl derivatives of the still unknown hydrocarbon (1a) azuleno[8,8a,1,2-def]heptalene (dicyclohept[cd-ij]azulene) can be prepared by a simple process that has already repeatedly proved its value for preparation of polycyclic condensed non-benzenoid systems[¹]
Azuleno[8,8a,1,2-def]heptalen
Die Darstellung von Methyl-Derivaten des noch nicht bekannten Azuleno[8.8a,1,2-dej]heptalens (Dicyclohept[cd-ij]-azulen) (1a) gelingt mit Hilfe eines einfachen Syntheseprinzips, das sich mehrfach bereits bei der Herstellung polycyclisch konjugierter nichtbenzoider Systeme bewährte[¹]
Unifying Parsimonious Tree Reconciliation
Evolution is a process that is influenced by various environmental factors,
e.g. the interactions between different species, genes, and biogeographical
properties. Hence, it is interesting to study the combined evolutionary history
of multiple species, their genes, and the environment they live in. A common
approach to address this research problem is to describe each individual
evolution as a phylogenetic tree and construct a tree reconciliation which is
parsimonious with respect to a given event model. Unfortunately, most of the
previous approaches are designed only either for host-parasite systems, for
gene tree/species tree reconciliation, or biogeography. Hence, a method is
desirable, which addresses the general problem of mapping phylogenetic trees
and covering all varieties of coevolving systems, including e.g., predator-prey
and symbiotic relationships. To overcome this gap, we introduce a generalized
cophylogenetic event model considering the combinatorial complete set of local
coevolutionary events. We give a dynamic programming based heuristic for
solving the maximum parsimony reconciliation problem in time O(n^2), for two
phylogenies each with at most n leaves. Furthermore, we present an exact
branch-and-bound algorithm which uses the results from the dynamic programming
heuristic for discarding partial reconciliations. The approach has been
implemented as a Java application which is freely available from
http://pacosy.informatik.uni-leipzig.de/coresym.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013
Quantitative mass spectrometry and PAR-CLIP to identify RNA-protein interactions
Systematic analysis of the RNA-protein interactome requires robust and scalable methods. We here show the combination of two completely orthogonal, generic techniques to identify RNA-protein interactions: PAR-CLIP reveals a collection of RNAs bound to a protein whereas SILAC-based RNA pull-downs identify a group of proteins bound to an RNA. We investigated binding sites for five different proteins (IGF2BP1-3, QKI and PUM2) exhibiting different binding patterns. We report near perfect agreement between the two approaches. Nevertheless, they are non-redundant, and ideally complement each other to map the RNA-protein interaction network
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