1,514 research outputs found
Topology of RNA-RNA interaction structures
The topological filtration of interacting RNA complexes is studied and the
role is analyzed of certain diagrams called irreducible shadows, which form
suitable building blocks for more general structures. We prove that for two
interacting RNAs, called interaction structures, there exist for fixed genus
only finitely many irreducible shadows. This implies that for fixed genus there
are only finitely many classes of interaction structures. In particular the
simplest case of genus zero already provides the formalism for certain types of
structures that occur in nature and are not covered by other filtrations. This
case of genus zero interaction structures is already of practical interest, is
studied here in detail and found to be expressed by a multiple context-free
grammar extending the usual one for RNA secondary structures. We show that in
time and space complexity, this grammar for genus zero
interaction structures provides not only minimum free energy solutions but also
the complete partition function and base pairing probabilities.Comment: 40 pages 15 figure
Segregated Early Weaning (SEW) of Pasture-farrowed Pigs
Segregated early weaning (SEW) works well with pasture-farrowed pigs. The SEW pasture-farrowed pigs weighed about the same as conventionally weaned pigs at 9 weeks of age with lower death losses (about 2% less). For the period 5â9 weeks of age the SEW pigs gained more rapidly and were more efficient converting feed to live gain than pigs weaned at 5 weeks of age and moved to an open-front shelter. However, costs were presumably higher for the SEW pigs because of higher labor costs from multiple feedings per day, higher-priced pig feed for early weaned pigs, higher utility costs, and the added cost of a nursery unit. Based on the results of this trial, SEW is compatible with pasture farrowing. However, pasture farrowing may not be as compatible with the mechanics of SEW. For example, because pasture farrowing is seasonal, the SEW nursery may not be kept full at all times. This would reduce the throughput, the number of pigs through the unit, which would increase the fixed building costs per pig. A new approach of putting newly weaned 2-week-old, 10-lb pigs directly into a finishing unit would partially alleviate this situation or lower fixed cost SEW nurseries are needed that then could be used on a seasonal basis. On the other hand, the technique of early weaning pasture-farrowed pigs has the potential of extending the farrowing season while reducing piglet mortality and minimizing the negative effects of weather extremes. By its nature, a one-litter pasture-farrowing system may benefit less from SEW than other more intensive or continuous pig production systems. In a one-litter system considerable age segregation of pigs occurs on the farm at all times. The sows are sold after weaning. At most times throughout the year the pigs on the farm are the same age. If the herd already has a high health status, the advantages of SEW are much less. Therefore, SEW will work for pasture farrowed pigs but herd health status and overall SEW costs need to be carefully evaluated. A cost comparison of SEW for pasture-farrowed pigs is elsewhere in this report
Power-Based Droop Control in DC Microgrids Enabling Seamless Disconnection From Upstream Grids
This paper proposes a local power-based droop controller for distributed energy resource converters in dc microgrids that are connected to upstream grids by grid-interface converters. During normal operation, the grid-interface converter imposes the microgrid bus voltage, and the proposed controller allows power flow regulation at distributed energy resource converters\u2019 output. On the other hand, during abnormal operation of the grid-interface converter (e.g., due to faults in the upstream grid), the proposed controller allows bus voltage regulation by droop control. Notably, the controller can autonomously convert from power flow control to droop control, without any need of bus voltage variation detection schemes or communication with other microgrid components, which enables seamless transitions between these two modes of operation. Considering distributed energy resource converters employing the power-based droop control, the operation modes of a single converter and of the whole microgrid are defined and investigated herein. The controller design is also introduced. Furthermore, the power sharing performance of this control approach is analyzed and compared with that of classical droop control. The experimental results from a laboratory-scale dc microgrid prototype are reported to show the final performances of the proposed power-based droop control
Size-selective nanoparticle growth on few-layer graphene films
We observe that gold atoms deposited by physical vapor deposition onto few
layer graphenes condense upon annealing to form nanoparticles with an average
diameter that is determined by the graphene film thickness. The data are well
described by a theoretical model in which the electrostatic interactions
arising from charge transfer between the graphene and the gold particle limit
the size of the growing nanoparticles. The model predicts a nanoparticle size
distribution characterized by a mean diameter D that follows a scaling law D
proportional to m^(1/3), where m is the number of carbon layers in the few
layer graphene film.Comment: 15 pages, 4 figure
The lady vanishes: what's missing from the stem cell debate
Most opponents of somatic cell nuclear transfer and embryonic stem cell technologies base their arguments on the twin assertions that the embryo is either a human being or a potential human being, and that it is wrong to destroy a human being or potential human being in order to produce stem cell lines. Proponentsâ justifications of stem cell research are more varied, but not enough to escape the charge of obsession with the status of the embryo. What unites the two warring sides in âthe stem cell warsâ is that women are equally invisible to both: âthe lady vanishesâ. Yet the only legitimate property in the body is that which women possess in their reproductive tissue and the products of their reproductive labour. By drawing on the accepted characterisation in law of property as a bundle of rights, and on a Hegelian model of contract as mutual recognition, we can lessen the impact of the tendency to regard women and their eggs as merely receptacles and womenâs reproductive labour as unimportant
Measurement of gamma p --> K+ Lambda and gamma p --> K+ Sigma0 at photon energies up to 2.6 GeV
The reactions gamma p --> K+ Lambda and gamma p --> K+ Sigma0 were measured
in the energy range from threshold up to a photon energy of 2.6 GeV. The data
were taken with the SAPHIR detector at the electron stretcher facility, ELSA.
Results on cross sections and hyperon polarizations are presented as a function
of kaon production angle and photon energy. The total cross section for Lambda
production rises steeply with energy close to threshold, whereas the Sigma0
cross section rises slowly to a maximum at about E_gamma = 1.45 GeV. Cross
sections together with their angular decompositions into Legendre polynomials
suggest contributions from resonance production for both reactions. In general,
the induced polarization of Lambda has negative values in the kaon forward
direction and positive values in the backward direction. The magnitude varies
with energy. The polarization of Sigma0 follows a similar angular and energy
dependence as that of Lambda, but with opposite sign.Comment: 21 pages, 25 figures, submitted to Eur. Phys. J.
Matrix models as solvable glass models
We present a family of solvable models of interacting particles in high
dimensionalities without quenched disorder. We show that the models have a
glassy regime with aging effects. The interaction is controlled by a parameter
. For we obtain matrix models and for `tensor' models. We
concentrate on the cases which we study analytically and numerically.Comment: 10 pages + 2 figures, Univ.Roma I, 1038/94, ROM2F/94/2
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