1,123 research outputs found
First-order transition in small-world networks
The small-world transition is a first-order transition at zero density of
shortcuts, whereby the normalized shortest-path distance undergoes a
discontinuity in the thermodynamic limit. On finite systems the apparent
transition is shifted by . Equivalently a ``persistence
size'' can be defined in connection with finite-size
effects. Assuming , simple rescaling arguments imply that
. We confirm this result by extensive numerical simulation in one to
four dimensions, and argue that implies that this transition is
first-order.Comment: 4 pages, 3 figures, To appear in Europhysics Letter
Catastrophic senescence and semelparity in the Penna aging model
The catastrophic senescence of the Pacific salmon is among the initial tests
used to validate the Penna aging model. Based on the mutation accumulation
theory, the sudden decrease in fitness following reproduction may be solely
attributed to the semelparity of the species. In this work, we report other
consequences of mutation accumulation. Contrary to earlier findings, such
dramatic manifestation of aging depends not only on the choice of breeding
strategy but also on the value of the reproduction age, R, and the mutation
threshold, T. Senescence is catastrophic when . As the organism's
tolerance for harmful genetic mutations increases, the aging process becomes
more gradual. We observe senescence that is threshold dependent whenever T>R.
That is, the sudden drop in survival rate occurs at age equal to the mutation
threshold value
Handcrafted and learning-based tie point features-comparison using the EuroSDR RPAS benchmark datasets
The identification of accurate and reliable image correspondences is fundamental for Structure-from-Motion (SfM) photogrammetry. Alongside handcrafted detectors and descriptors, recent machine learning-based approaches have shown promising results for tie point extraction, demonstrating matching success under strong perspective and illumination changes, and a general increase of tie point multiplicity. Recently, several methods based on convolutional neural networks (CNN) have been proposed, but few tests have yet been performed under real photogrammetric applications and, in particular, on full resolution aerial and RPAS image blocks that require rotationally invariant features. The research reported here compares two handcrafted (Metashape local features and RootSIFT) and two learning-based methods (LFNet and Key.Net) using the previously unused EuroSDR RPAS benchmark datasets. Analysis is conducted with DJI Zenmuse P1 imagery acquired at Wards Hill quarry in Northumberland, UK. The research firstly extracts keypoints using the aforementioned methods, before importing them into COLMAP for incremental reconstruction. The image coordinates of signalised ground control points (GCPs) and independent checkpoints (CPs) are automatically detected using an OpenCV algorithm, and then triangulated for comparison with accurate geometric ground-truth. The tests showed that learning-based local features are capable of outperforming traditional methods in terms of geometric accuracy, but several issues remain: few deep learning local features are trained to be rotation invariant, significant computational resources are required for large format imagery, and poor performance emerged in cases of repetitive patterns
Stimulated Raman scattering in an optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3
The evolution versus pump power of the spectrum of a singly resonant optical
parametric oscillator based on an MgO-doped periodically poled stoichiometric
lithium tantalate crystal is observed. The onset of cascade Raman lasing due to
stimulated Raman scattering in the nonlinear crystal is analyzed. Spurious
frequency doubling and sum-frequency generation phenomena are observed and
understood. A strong reduction of the intracavity Raman scattering is obtained
by a careful adjustment of the cavity losses.Comment: 6 figure
Liquid-liquid extraction in the presence of electrolytes of nisin and green fluorescent protein (GFPuv)
In the biotechnology field, it has been suggested that extractions in two-phase aqueous
complex-fluid systems can possibly be used instead of, or as complementary processes to,
the more typical chromatographic operations, to reduce the cost of the downstream
processing of many biological products (Lam et al., 2004; Mazzola et al., 2006). This method
offer attractive conditions to be applied in this study, thereby two-phase systems can be
exploited in separation science for the extraction/purification of desired biomolecules directly
on the culture medium (Mazzola et al., 2008). This study aimed to evaluate the aqueous two
phase system (ATPS) composed by a nonionic surfactant, Triton X-114 (TX), in presence or
absence of electrolytes, to separate two interesting biomolecules: nisin and recombinant
green fluorescent protein (GFP). Results indicated that nisin partitions preferentially to the
micelle rich-phase, with significant antimicrobial activity increase (up to 10-fold). GFP
partitioned evenly between the phases in TX system without electrolytes.Coordenação de Aperfeiçoamento de
Pessoal de NÃvel Superior, Brazil (CAPES)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico, Brazil (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil (FAPESP
Monte Carlo Simulations of Some Dynamical Aspects of Drop Formation
In this work we present some results from computer simulations of dynamical
aspects of drop formation in a leaky faucet. Our results, which agree very well
with the experiments, suggest that only a few elements, at the microscopic
level, would be necessary to describe the most important features of the
system. We were able to set all parameters of the model in terms of real ones.
This is an additional advantage with respect to previous theoretical works.Comment: 7 pages (Latex), 6 figures (PS) Accepted to publication in Int. J.
Mod. Phys. C Source Codes at http://www.if.uff.br/~arlim
Glassy features of a Bose Glass
We study a two-dimensional Bose-Hubbard model at a zero temperature with
random local potentials in the presence of either uniform or binary disorder.
Many low-energy metastable configurations are found with virtually the same
energy as the ground state. These are characterized by the same blotchy pattern
of the, in principle, complex nonzero local order parameter as the ground
state. Yet, unlike the ground state, each island exhibits an overall random
independent phase. The different phases in different coherent islands could
provide a further explanation for the lack of coherence observed in experiments
on Bose glasses.Comment: 14 pages, 4 figures
Optimal network topologies for local search with congestion
The problem of searchability in decentralized complex networks is of great
importance in computer science, economy and sociology. We present a formalism
that is able to cope simultaneously with the problem of search and the
congestion effects that arise when parallel searches are performed, and obtain
expressions for the average search cost--written in terms of the search
algorithm and the topological properties of the network--both in presence and
abscence of congestion. This formalism is used to obtain optimal network
structures for a system using a local search algorithm. It is found that only
two classes of networks can be optimal: star-like configurations, when the
number of parallel searches is small, and homogeneous-isotropic configurations,
when the number of parallel searches is large.Comment: 4 pages. Final version accepted in PR
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