10,984 research outputs found
Sulfur cycling and metabolism of phototrophic and filamentous sulfur bacteria
Phototrophic sulfur bacteria taken from different habitate (Alum Rock State Park, Palo Alto salt marsh, and Big Soda Lake) were grown on selective media, characterized by morphological and pigment analysis, and compared with bacteria maintained in pure culture. A study was made of the anaerobic reduction of intracellular sulfur globules by a phototrophic sulfur bacterium (Chromatium vinosum) and a filamentous aerobic sulfur bacterium (Beggiatoa alba). Buoyant densities of different bacteria were measured in Percoll gradients. This method was also used to separate different chlorobia in mixed cultures and to assess the relative homogeneity of cultures taken directly or enriched from natural samples (including the purple bacterial layer found at a depth of 20 meters at Big Soda Lake.) Interactions between sulfide oxidizing bacteria were studied
Shot Noise in Magnetic Tunnel Junctions: Evidence for Sequential Tunneling
We report the experimental observation of sub-Poissonian shot noise in single
magnetic tunnel junctions, indicating the importance of tunneling via impurity
levels inside the tunnel barrier. For junctions with weak zero-bias anomaly in
conductance, the Fano factor (normalized shot noise) depends on the magnetic
configuration being enhanced for antiparallel alignment of the ferromagnetic
electrodes. We propose a model of sequential tunneling through nonmagnetic and
paramagnetic impurity levels inside the tunnel barrier to qualitatively explain
the observations.Comment: 5 pages, 5 figure
The gradual extinction of transferred avoidance stimulus functions
We investigated the transfer of conditioned avoidance functions through equivalence relations, and the extinction of these functions, facilitated by verbal prompts. Nine participants acquired three 4-member stimulus equivalence classes using a matching-to-sample procedure. One class stimulus was paired, by classical conditioning, with an aversive tone, which was used in avoidance training of a distinct response. There were two groups: A established the equivalence classes before avoidance training and vice versa for B. During some avoidance trials, each stimulus presentation was followed by the request for a verbal estimation of the probability of the tone. The last trials, run in extinction, included a verbal prompt to corroborate the provided estimation. One participant in each group received no verbal prompts. To negate the necessary reliance on instructions-governed performance, an additional participant completed the experiment with minimal instructions. All participants who had the equivalence training prior to the conditioning showed within-class transfer of avoidance functions, in contrast to the others. All prompted participants who demonstrated transfer showed gradual response extinction, but with a differential gradient. Responding decreased more sharply to the indirectly related stimuli than to the directly paired stimuli. The clinical implications are discussed
Building a Sentiment Corpus of Tweets in Brazilian Portuguese
The large amount of data available in social media, forums and websites
motivates researches in several areas of Natural Language Processing, such as
sentiment analysis. The popularity of the area due to its subjective and
semantic characteristics motivates research on novel methods and approaches for
classification. Hence, there is a high demand for datasets on different domains
and different languages. This paper introduces TweetSentBR, a sentiment corpora
for Brazilian Portuguese manually annotated with 15.000 sentences on TV show
domain. The sentences were labeled in three classes (positive, neutral and
negative) by seven annotators, following literature guidelines for ensuring
reliability on the annotation. We also ran baseline experiments on polarity
classification using three machine learning methods, reaching 80.99% on
F-Measure and 82.06% on accuracy in binary classification, and 59.85% F-Measure
and 64.62% on accuracy on three point classification.Comment: Accepted for publication in 11th International Conference on Language
Resources and Evaluation (LREC 2018
Spin wave spectrum of the quantum ferromagnet on the pyrochlore lattice Lu2V2O7
Neutron inelastic scattering has been used to probe the spin dynamics of the
quantum (S=1/2) ferromagnet on the pyrochlore lattice Lu2V2O7. Well-defined
spin waves are observed at all energies and wavevectors, allowing us to
determine the parameters of the Hamiltonian of the system. The data are found
to be in excellent overall agreement with a minimal model that includes a
nearest- neighbour Heisenberg exchange J = 8:22(2) meV and a
Dzyaloshinskii-Moriya interaction (DMI) D =1:5(1) meV. The large DMI term
revealed by our study is broadly consistent with the model developed by Onose
et al. to explain the magnon Hall effect they observed in Lu2V2O7 [1], although
our ratio of D=J = 0:18(1) is roughly half of their value and three times
larger than calculated by ab initio methods [2].Comment: 5 pages, 4 figure
Medial radio-carpal arthrodesis in three cats with a 2.0 mm locking maxillofacial plate system
J Regularization Improves Imbalanced Multiclass Segmentation
We propose a new loss formulation to further advance the multiclass segmentation of cluttered cells under weakly supervised conditions. When adding a Youden's J statistic regularization term to the cross entropy loss we improve the separation of touching and immediate cells, obtaining sharp segmentation boundaries with high adequacy. This regularization intrinsically supports class imbalance thus eliminating the necessity of explicitly using weights to balance training. Simulations demonstrate this capability and show how the regularization leads to correct results by helping advancing the optimization when cross entropy stagnates. We build upon our previous work on multiclass segmentation by adding yet another training class representing gaps between adjacent cells. This addition helps the classifier identify narrow gaps as background and no longer as touching regions. We present results of our methods for 2D and 3D images, from bright field images to confocal stacks containing different types of cells, and we show that they accurately segment individual cells after training with a limited number of images, some of which are poorly annotated
Phase Diagram of the 1D Anderson Lattice
We map out the phase diagram of the one--dimensional Anderson lattice by
studying the ground state magnetization as a function of band--filling using
the density matrix renormalization group technique. For strong coupling, we
find that the quarter--filled system has an S=0 ground state with strong
antiferromagnetic correlations. As additional electrons are put in, we find
first a ferromagnetic phase, as reported by M\"{o}ller and W\"{o}lfle, and then
a phase in which the ground state has total spin . Within this
phase, we find RKKY oscillations in the spin--spin correlation functions.Comment: REVTEX manuscript with 5 Postcript figures included in uu file.
Submitted to Phys. Rev.
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