4,731 research outputs found
The determinants of gene order conservation in yeasts
Current intergene distance is shown to be consistently the strongest predictor of synteny conservation as expected under a simple null model, and other variables are of lesser importance
How biologically relevant are interaction-based modules in protein networks?
By applying a graph-based algorithm to yeast protein-interaction networks we have extracted modular structures and show that they can be validated using information from the phylogenetic conservation of the network components. We show that the module cores, the parts with the highest intramodular connectivity, are biologically relevant components of the networks. These constituents correlate only weakly with other levels of organization. We also discuss how such structures could be used for finding targets for antimicrobial drugs
Improving measurements of SF6 for the study of atmospheric transport and emissions
Sulfur hexafluoride (SF6) is a potent greenhouse gas and useful atmospheric tracer. Measurements of SF6 on global and regional scales are necessary to estimate emissions and to verify or examine the performance of atmospheric transport models. Typical precision for common gas chromatographic methods with electron capture detection (GC-ECD) is 1–2%. We have modified a common GC-ECD method to achieve measurement precision of 0.5% or better. Global mean SF6 measurements were used to examine changes in the growth rate of SF6 and corresponding SF6 emissions. Global emissions and mixing ratios from 2000–2008 are consistent with recently published work. More recent observations show a 10% decline in SF6 emissions in 2008–2009, which seems to coincide with a decrease in world economic output. This decline was short-lived, as the global SF6 growth rate has recently increased to near its 2007–2008 maximum value of 0.30±0.03 pmol mol−1 (ppt) yr−1 (95% C.L.)
Pulmonary Lobe Segmentation with Probabilistic Segmentation of the Fissures and a Groupwise Fissure Prior
A fully automated, unsupervised lobe segmentation algorithm is presented based on a probabilistic segmentation of the fissures and the simultaneous construction of a population model of the fissures. A two-class probabilistic segmentation segments the lung into candidate fissure voxels and the surrounding parenchyma. This was combined with anatomical information and a groupwise fissure prior to drive non-parametric surface fitting to obtain the final segmentation. The performance of our fissure segmentation was validated on 30 patients from the COPDGene cohort, achieving a high median F1-score of 0:90 and showed general insensitivity to filter parameters. We evaluated our lobe segmentation algorithm on the LOLA11 dataset, which contains 55 cases at varying levels of pathology. We achieved the highest score of 0:884 of the automated algorithms. Our method was further tested quantitatively and qualitatively on 80 patients from the COPDGene study at varying levels of functional impairment. Accurate segmentation of the lobes is shown at various degrees of fissure incompleteness for 96% of all cases. We also show the utility of including a groupwise prior in segmenting the lobes in regions of grossly incomplete fissures
A Large Area Fiber Optic Gyroscope on multiplexed fiber network
We describe a fiber optical gyroscope based on the Sagnac effect realized on a multiplexed telecom fiber network. Our loop encloses an area of 20 km2 and coexists with Internet data traffic. This Sagnac interferometer achieves a sensitivity of about (10-8 rad/s)/sqrt(Hz), thus approaching ring laser gyroscopes without using narrow linewidth laser nor sophisticated optics. The proposed gyroscope is sensitive enough for seismic applications, opening new possibilities for this kind of optical fiber sensors
Long range correlation in cosmic microwave background radiation
We investigate the statistical anisotropy and Gaussianity of temperature
fluctuations of Cosmic Microwave Background radiation (CMB) data from {\it
Wilkinson Microwave Anisotropy Probe} survey, using the multifractal detrended
fluctuation analysis, rescaled range and scaled windowed variance methods. The
multifractal detrended fluctuation analysis shows that CMB fluctuations has a
long range correlation function with a multifractal behavior. By comparing the
shuffled and surrogate series of CMB data, we conclude that the multifractality
nature of temperature fluctuation of CMB is mainly due to the long-range
correlations and the map is consistent with a Gaussian distribution.Comment: 10 pages, 7 figures, V2: Added comments, references and major
correction
Anomalous jumping in a double-well potential
Noise induced jumping between meta-stable states in a potential depends on
the structure of the noise. For an -stable noise, jumping triggered by
single extreme events contributes to the transition probability. This is also
called Levy flights and might be of importance in triggering sudden changes in
geophysical flow and perhaps even climatic changes. The steady state statistics
is also influenced by the noise structure leading to a non-Gibbs distribution
for an -stable noise.Comment: 11 pages, 7 figure
A Multi Agent Model for the Limit Order Book Dynamics
In the present work we introduce a novel multi-agent model with the aim to
reproduce the dynamics of a double auction market at microscopic time scale
through a faithful simulation of the matching mechanics in the limit order
book. The agents follow a noise decision making process where their actions are
related to a stochastic variable, "the market sentiment", which we define as a
mixture of public and private information. The model, despite making just few
basic assumptions over the trading strategies of the agents, is able to
reproduce several empirical features of the high-frequency dynamics of the
market microstructure not only related to the price movements but also to the
deposition of the orders in the book.Comment: 20 pages, 11 figures, in press European Physical Journal B (EPJB
Tropospheric water vapor profiles obtained with FTIR: comparison with balloon-borne frost point hygrometers and influence on trace gas retrievals
Retrievals of vertical profiles of key atmospheric gases provide a critical
long-term record from ground-based Fourier transform infrared (FTIR) solar
absorption measurements. However, the characterization of the retrieved
vertical profile structure can be difficult to validate, especially for gases
with large vertical gradients and spatial–temporal variability such as water
vapor. In this work, we evaluate the accuracy of the most common water vapor
isotope (H216O, hereafter WV) FTIR retrievals in the lower and upper
troposphere–lower stratosphere. Coincident high-quality vertically resolved
WV profile measurements obtained from 2010 to 2016 with balloon-borne NOAA
frost point hygrometers (FPHs) are used as reference to evaluate the
performance of the retrieved profiles at two sites: Boulder (BLD), Colorado, and at
the mountaintop observatory of Mauna Loa (MLO), Hawaii. For a meaningful
comparison, the spatial–temporal variability has been investigated. We
present results of comparisons among FTIR retrievals with unsmoothed and
smoothed FPH profiles to assess WV vertical gradients. Additionally, we
evaluate the quantitative impact of different a priori profiles in the
retrieval of WV. An orthogonal linear regression analysis shows the best
correlation among tropospheric layers using ERA-Interim (ERA-I) a priori
profiles and biases are lower for unsmoothed comparisons. In Boulder, we
found a negative bias of 0.02±1.9 % (r = 0.95) for the 1.5–3 km
layer. A larger negative bias of 11.1±3.5 % (r = 0.97) was found in
the lower free troposphere layer of 3–5 km attributed to rapid vertical
change of WV, which is not always captured by the retrievals. The bias
improves in the 5–7.5 km layer (1.0±5.3 %, r = 0.94). The bias
remains at about 13 % for layers above 7.5 km but below 13.5 km. At MLO
the spatial mismatch is significantly larger due to the launch of the sonde
being farther from the FTIR location. Nevertheless, we estimate a negative
bias of 5.9±4.6 % (r = 0.93) for the 3.5–5.5 km layer and 9.9±3.7 % (r = 0.93) for the 5.5–7.5 km layer, and we measure positive biases of
6.2±3.6 % (r = 0.95) for the 7.5–10 km layer and 12.6 % and
greater values above 10 km. The agreement for the first layer is
significantly better at BLD because the air masses are similar for both FTIR
and FPH. Furthermore, for the first time we study the influence of different
WV a priori profiles in the retrieval of selected gas profiles. Using NDACC
standard retrievals we present results for hydrogen cyanide (HCN), carbon
monoxide (CO), and ethane (C2H6) by taking NOAA FPH profiles as the
ground truth and evaluating the impact of other WV profiles. We show that the
effect is minor for C2H6 (bias < 0.5 % for all WV sources) among all
vertical layers. However, for HCN we found significant biases between 6 %
for layers close to the surface and 2 % for the upper troposphere depending
on the
WV profile source. The best results (reduced bias and precision and r values
closer to unity) are always found for pre-retrieved WV. Therefore, we
recommend first retrieving WV to use in subsequent retrieval of gases.</p
Electron affinity of Li: A state-selective measurement
We have investigated the threshold of photodetachment of Li^- leading to the
formation of the residual Li atom in the state. The excited residual
atom was selectively photoionized via an intermediate Rydberg state and the
resulting Li^+ ion was detected. A collinear laser-ion beam geometry enabled
both high resolution and sensitivity to be attained. We have demonstrated the
potential of this state selective photodetachment spectroscopic method by
improving the accuracy of Li electron affinity measurements an order of
magnitude. From a fit to the Wigner law in the threshold region, we obtained a
Li electron affinity of 0.618 049(20) eV.Comment: 5 pages,6 figures,22 reference
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