31,563 research outputs found
Unsupervised learning of overlapping image components using divisive input modulation
This paper demonstrates that nonnegative matrix factorisation is mathematically related to a class of neural networks that employ negative feedback as a mechanism of competition. This observation inspires a novel learning algorithm which we call Divisive Input Modulation (DIM). The proposed algorithm provides a mathematically simple and computationally efficient method for the unsupervised learning of image components, even in conditions where these elementary features overlap considerably. To test the proposed algorithm, a novel artificial task is introduced which is similar to the frequently-used bars problem but employs squares rather than bars to increase the degree of overlap between components. Using this task, we investigate how the proposed method performs on the parsing of artificial images composed of overlapping features, given the correct representation of the individual components; and secondly, we investigate how well it can learn the elementary components from artificial training images. We compare the performance of the proposed algorithm with its predecessors including variations on these algorithms that have produced state-of-the-art performance on the bars problem. The proposed algorithm is more successful than its predecessors in dealing with overlap and occlusion in the artificial task that has been used to assess performance
Exposure of ciprofloxacin-resistant Escherichia coli broiler isolates to subinhibitory concentrations of a quaternary ammonium compound does not increase antibiotic resistance gene transfer
Resistance to antibiotics threatens to become a worldwide health problem. An important attributing phenomenon in this context is that pathogens can acquire antibiotic resistance genes through conjugative transfer of plasmids. To prevent bacterial infections in agricultural settings, the use of veterinary hygiene products, such as disinfectants, has gained popularity and questions have been raised about their contribution to such spreading of antibiotic resistance. Therefore, this study investigated the effect of subinhibitory concentrations of benzalkoniumchloride (BKC), a quaternary ammonium compound (QAC), on the conjugative transfer of antibiotic resistance genes. Five Escherichia coli field strains originating from broiler chickens and with known transferable plasmid-mediated ciprofloxacin resistance were exposed to subinhibitory BKC concentrations: 1/3, 1/10 and 1/30 of the minimum bactericidal concentration. Antibiotic resistance transfer was assessed by liquid mating for 4 h at 25 degrees C using E. coli K12 MG1655 as recipient strain. The transfer ratio was calculated as the number of transconjugants divided by the number of recipients. Without exposure to BKC, the strains showed a ciprofloxacin resistance transfer ratio ranging from 10(-4) to 10(-7). No significant effect of exposure to subinhibitory concentrations of BKC was observed on this transfer ratio
Measuring gender norms about relationships in early adolescence : results from the global early adolescent study
Introduction: Gender norms are increasingly recognized as drivers of health and wellbeing. While early adolescence constitutes a critical window of development, there is limited understanding about how adolescents perceive gender relations across different cultural settings. This study used a mixed-method approach, grounded in the voices of young people around the world, to construct and test a cross-cultural scale assessing the perceptions of gender norms regulating romantic relationships between boys and girls in early adolescence.
Methods: The study draws on the Global Early Adolescent study (GEAS), a study focusing on gender norms and health related outcomes over the course of adolescence in urban poor settings worldwide. In-depth interviews were first conducted among approximately 200 adolescents between 10-14 years in seven sites across 4 continents to identify common scripts guiding romantic relations in early adolescence. These scripts were then transformed into a multidimensional scale. The scale was tested among 120 adolescents in each of 14 GEAS sites, followed by a second pilot among 75 adolescents in six sites. We evaluated the psychometric criteria of each subscale using principal component analysis, and parallel analysis, followed by exploratory factor analysis to guide the selection of a more parsimonious set of items.
Results: Results suggested a two-factor structure, consisting of an "adolescent romantic expectations" subscale and a "Sexual Double Standard" subscale. Both subscales yielded high internal validity in each site, with polychoric Cronbach alpha values above 0.70 with the exception of Kinshasa for the adolescent romantic expectations scale (0.64) and Hanoi for the sexual double standard scale (0.61).
Conclusion: This study reveals common perceptions of gendered norms about romantic engagement in early adolescence, normative for both sexes, but socially valued for boys while devaluated for girls. The findings illustrate that social hierarchies of power in romantic relationships form early in adolescence, regardless of cultural setting
Low-power, low-penalty, flip-chip integrated, 10Gb/s ring-based 1V CMOS photonics transmitter
Modulation with 7.5dB transmitter penalty is demonstrated from a novel 1.5Vpp differential CMOS driver flip-chip integrated with a Si ring modulator, consuming 350fJ/bit from a single 1V supply at bit rates up to 10Gb/s
Comparative microbiomics of tephritid frugivorous pests (Diptera : Tephritidae) from the field : a tale of high variability across and within species
The family Tephritidae includes some of the most notorious insect pests of agricultural and horticultural crops in tropical and sub-tropical regions. Despite the interest in the study of their gut microbiome, our present knowledge is largely based on the analysis of laboratory strains. In this study, we present a first comparative analysis of the gut microbiome profiles of field populations of ten African and Mediterranean tephritid pests. For each species, third instar larvae were sampled from different locations and host fruits and compared using 16S rRNA amplicon sequencing and a multi-factorial sampling design. We observed considerable variation in gut microbiome diversity and composition both between and within fruit fly species. A "core" microbiome, shared across all targeted species, could only be identified at most at family level (Enterobacteriaceae). At genus level only a few bacterial genera (Klebsiella,Enterobacter, andBacillus) were present in most, but not all, samples, with high variability in their relative abundance. Higher relative abundances were found for seven bacterial genera in five of the fruit fly species considered. These wereErwiniainBactrocera oleae,LactococcusinB. zonata,ProvidenciainCeratitis flexuosa,Klebsiella, andRahnellainC. podocarpiandAcetobacterandSerratiainC. rosa. With the possible exception ofC. capitataandB. dorsalis(the two most polyphagous species considered) we could not detect obvious relationships between fruit fly dietary breadth and microbiome diversity or abundance patterns. Similarly, our results did not suggest straightforward differences between the microbiome profiles of species belonging to Ceratitisand the closely relatedBactrocera/Zeugodacus. These results provide a first comparative analysis of the gut microbiomes of field populations of multiple economically relevant tephritids and provide base line information for future studies that will further investigate the possible functional role of the observed associations
Wavelets: mathematics and applications
The notion of wavelets is defined. It is briefly described {\it what} are
wavelets, {\it how} to use them, {\it when} we do need them, {\it why} they are
preferred and {\it where} they have been applied. Then one proceeds to the
multiresolution analysis and fast wavelet transform as a standard procedure for
dealing with discrete wavelets. It is shown which specific features of signals
(functions) can be revealed by this analysis, but can not be found by other
methods (e.g., by the Fourier expansion). Finally, some examples of practical
application are given (in particular, to analysis of multiparticle production}.
Rigorous proofs of mathematical statements are omitted, and the reader is
referred to the corresponding literature.Comment: 16 pages, 5 figures, Latex, Phys. Atom. Nuc
Interstellar absorptions towards the LMC: Small-scale density variations in Milky Way disc gas
Observations show that the ISM contains sub-structure on scales less than 1
pc, detected in the form of spatial and temporal variations in column densities
or optical depth. Despite the number of detections, the nature and ubiquity of
the small-scale structure in the ISM is not yet fully understood. We use UV
absorption data mainly from FUSE and partly from STIS of six LMC stars
(Sk-67{\deg}111, LH54-425, Sk-67{\deg}107, Sk-67{\deg}106, Sk-67{\deg}104, and
Sk-67{\deg}101), all located within 5 arcmin of each other, and analyse the
physical properties of the Galactic disc gas in front of the LMC on sub-pc
scales. We analyse absorption lines of a number of ions within the UV spectral
range. Most importantly, interstellar molecular hydrogen, neutral oxygen, and
fine-structure levels of neutral carbon have been used in order to study
changes in the density and the physical properties of the Galactic disc gas
over small angular scales. While most species do not show any significant
variation in their column densities, we find an enhancement of almost 2 dex for
H_2 from Sk-67{\deg}111 to Sk-67{\deg}101, accompanied by only a small
variation in the OI column density. Based on the formation-dissociation
equilibrium, we trace these variations to the actual density variations in the
molecular gas. On the smallest spatial scale of < 0.08 pc, between
Sk-67{\deg}107 and LH54-425, we find a gas density variation of a factor of
1.8. The line of sight towards LH54-425 does not follow the relatively smooth
change seen from Sk-67{\deg}101 to Sk-67{\deg}111, suggesting that
sub-structure might exist on a smaller spatial scale than the linear extent of
our sight-lines. Our observations suggest that the detected H_2 in these six
lines of sight is not necessarily physically connected, but that we are
sampling molecular cloudlets with pathlengths < 0.1-1.8 pc and possibly
different densities.Comment: 17 pages, 8 figures. Accepted for publication in A&
Generic Twistless Bifurcations
We show that in the neighborhood of the tripling bifurcation of a periodic
orbit of a Hamiltonian flow or of a fixed point of an area preserving map,
there is generically a bifurcation that creates a ``twistless'' torus. At this
bifurcation, the twist, which is the derivative of the rotation number with
respect to the action, vanishes. The twistless torus moves outward after it is
created, and eventually collides with the saddle-center bifurcation that
creates the period three orbits. The existence of the twistless bifurcation is
responsible for the breakdown of the nondegeneracy condition required in the
proof of the KAM theorem for flows or the Moser twist theorem for maps. When
the twistless torus has a rational rotation number, there are typically
reconnection bifurcations of periodic orbits with that rotation number.Comment: 29 pages, 9 figure
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