89 research outputs found
Sub-optical resolution of single spins using magnetic resonance imaging at room temperature in diamond
There has been much recent interest in extending the technique of magnetic
resonance imaging (MRI) down to the level of single spins with sub-optical
wavelength resolution. However, the signal to noise ratio for images of
individual spins is usually low and this necessitates long acquisition times
and low temperatures to achieve high resolution. An exception to this is the
nitrogen-vacancy (NV) color center in diamond whose spin state can be detected
optically at room temperature. Here we apply MRI to magnetically equivalent NV
spins in order to resolve them with resolution well below the optical
wavelength of the readout light. In addition, using a microwave version of MRI
we achieved a resolution that is 1/270 size of the coplanar striplines, which
define the effective wavelength of the microwaves that were used to excite the
transition. This technique can eventually be extended to imaging of large
numbers of NVs in a confocal spot and possibly to image nearby dark spins via
their mutual magnetic interaction with the NV spin.Comment: 10 pages, 8 figures, Journal of Luminescence (Article in Press
Joint Back-pressure Power Control and Interference Cancellation in Wireless Multi-Hop Networks
Publication in the conference proceedings of EUSIPCO, Bucharest, Romania, 201
Efficient nitrogen-vacancy centers' fluorescence excitation and collection from micrometer-sized diamond by a tapered optical fiber
Efficiently excite nitrogen-vacancy (NV) centers in diamond and collect their
fluorescence significantly benefit the fiber-optic-based NV sensors. Here,
using a tapered optical fiber (TOF) tip, we significantly improve the
efficiency of the laser excitation and fluorescence collection of the NV, thus
enhance the sensitivity of the fiber-optic based micron-sized diamond magnetic
sensor. Numerical calculation shows that the TOF tip delivers a high numerical
aperture (NA) and has a high fluorescence excitation and collection efficiency.
Experiments demonstrate that using such TOF tip can obtain up to over 7-fold
the fluorescence excitation efficiency and over15-fold the fluorescence
collection efficiency of a flat-ended (non-TOF) fiber. Such fluorescence
collection enhances the sensitivity of the optical fiber-based diamond NV
magnetometer, thus extending its potential application region.Comment: 11 pages, 13 figure
Enhancing fluorescence excitation and collection from the nitrogen-vacancy center in diamond through a micro-concave mirror
We experimentally demonstrate a simple and robust optical fibers based method
to achieve simultaneously efficient excitation and fluorescence collection from
Nitrogen-Vacancy (NV) defects containing micro-crystalline diamond. We
fabricate a suitable micro-concave (MC) mirror that focuses scattered
excitation laser light into the diamond located at the focal point of the
mirror. At the same instance, the mirror also couples the fluorescence light
exiting out of the diamond crystal in the opposite direction of the optical
fiber back into the optical fiber within its light acceptance cone. This part
of fluorescence would have been otherwise lost from reaching the detector. Our
proof-of-principle demonstration achieves a 25 times improvement in
fluorescence collection compared to the case of not using any mirrors. The
increase in light collection favors getting high signal-to-noise ratio (SNR)
optically detected magnetic resonance (ODMR) signals hence offers a practical
advantage in fiber-based NV quantum sensors. Additionally, we compacted the NV
sensor system by replacing some bulky optical elements in the optical path with
a 1x2 fiber optical coupler in our optical system. This reduces the complexity
of the system and provides portability and robustness needed for applications
like magnetic endoscopy and remote-magnetic sensing.Comment: 6 pages, 8 figure
Learning Parsimonious Classification Rules from Gene Expression Data Using Bayesian Networks with Local Structure
The comprehensibility of good predictive models learned from high-dimensional gene expression data is attractive because it can lead to biomarker discovery. Several good classifiers provide comparable predictive performance but differ in their abilities to summarize the observed data. We extend a Bayesian Rule Learning (BRL-GSS) algorithm, previously shown to be a significantly better predictor than other classical approaches in this domain. It searches a space of Bayesian networks using a decision tree representation of its parameters with global constraints, and infers a set of IF-THEN rules. The number of parameters and therefore the number of rules are combinatorial in the number of predictor variables in the model. We relax these global constraints to learn a more expressive local structure with BRL-LSS. BRL-LSS entails a more parsimonious set of rules because it does not have to generate all combinatorial rules. The search space of local structures is much richer than the space of global structures. We design the BRL-LSS with the same worst-case time-complexity as BRL-GSS while exploring a richer and more complex model space. We measure predictive performance using Area Under the ROC curve (AUC) and Accuracy. We measure model parsimony performance by noting the average number of rules and variables needed to describe the observed data. We evaluate the predictive and parsimony performance of BRL-GSS, BRL-LSS and the state-of-the-art C4.5 decision tree algorithm, across 10-fold cross-validation using ten microarray gene-expression diagnostic datasets. In these experiments, we observe that BRL-LSS is similar to BRL-GSS in terms of predictive performance, while generating a much more parsimonious set of rules to explain the same observed data. BRL-LSS also needs fewer variables than C4.5 to explain the data with similar predictive performance. We also conduct a feasibility study to demonstrate the general applicability of our BRL methods on the newer RNA sequencing gene-expression data
Studies on Distribution of Biosurfactant Producing Bacteria in Contaminated and Undisturbed Soils of Kanchipuram
Abstract: Ever increasing environmental concern about chemical surfactants triggers attention to microbial derived surface-active compounds, essentially due to their low toxicity and biodegradable nature. At present, biosurfactants are predominantly used in remediation of pollutants, in the enhanced transport of metabolites in bacteria, in enhanced oil recovery, as cosmetic additives, in biological control. However, little is known about the distribution and prevalence of biosurfactant-producing bacteria in the environment. The primary objective of this study was to determine how common culturable surfactant producing bacteria are present in contaminated and undisturbed soil samples in and around Kanchipuram (12°50'23"N 79°42'0"E), Tamilnadu, India. A series of each 5 contaminated and undisturbed soils were collected and plated on R2A agar. Totally, 155 morphologically different bacterial isolates were obtained and qualitatively screened for biosurfactant production in mineral salts medium containing 2% glucose. Out of 155 isolates, eight isolates were positive for biosurfactant production, representing most of the soils tested. Quantitative estimation of surface activity identified two potent biosurfactant producing strains Bacillus sp.BS3 and Pseudomonas sp. Maximum surface activity was observed to be 26.58 x 10 -3 nm -1 and 20.60 x 10 -3 nm -1 respectively for Bacillus sp.BS3 and Pseudomonas sp. BS5. The present study is a preliminary demonstration that the Indian soils are rich in biosurfactant producing bacteria, which can be exploited for industrial production of biosurfactants
DNA sequence information resolves taxonomic ambiguity of the common mud crab species (Genus Scylla) in Indian waters
For several years, mud crabs of genus Scylla have been misidentified owing to their high
morphological plasticity and the absence of distinct morphological diagnostic characters.
The taxonomic confusion of genus Scylla de Haan is considered to be a primary constraint
to the development of aquaculture. Although genus Scylla was revised using morphological
and genetic characteristics, taxonomy of Scylla species occurring in India is still not clear. In this
study, partial sequences of two mitochondrial genes, 16S rRNA and CO1 (Cytochrome C oxidase
subunit I) in populations of Scylla spp. obtained from eleven locations along the Indian coast
were used to differentiate and resolve taxonomical ambiguity of the mud crab species in India.
The sequences were compared with previously published sequences of Scylla spp. Both trees
generated based on 16S rRNA and CO1 indicated that all S. tranquebarica morphotypes
obtained during this study and S. tranquebarica sequences submitted previously from Indian
waters reciprocally monophyletic with reference sequence of S. serrata. Both sequence data
and morphological characters revealed that the species S. serrata (Forskal) is the most abundant
followed by S. olivacea. Further, the 16S rRNA and COI haplotypes of Indian S. tranquebarica
obtained in the study significantly differed with the known S. tranquebarica by 6.7% and 10.6%
respectively whereas it differed with known S. serrata by 0.0–0.7% only, a difference that
was not statistically significant. From these studies it is clear that ‘‘S. tranquebarica’’ commonly
reported from India should be S. serrata (Forskal)
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