582 research outputs found
A Novel Convex Relaxation for Non-Binary Discrete Tomography
We present a novel convex relaxation and a corresponding inference algorithm
for the non-binary discrete tomography problem, that is, reconstructing
discrete-valued images from few linear measurements. In contrast to state of
the art approaches that split the problem into a continuous reconstruction
problem for the linear measurement constraints and a discrete labeling problem
to enforce discrete-valued reconstructions, we propose a joint formulation that
addresses both problems simultaneously, resulting in a tighter convex
relaxation. For this purpose a constrained graphical model is set up and
evaluated using a novel relaxation optimized by dual decomposition. We evaluate
our approach experimentally and show superior solutions both mathematically
(tighter relaxation) and experimentally in comparison to previously proposed
relaxations
Emission ratio and isotopic signatures of molecular hydrogen emissions from tropical biomass burning
In this study, we identify a biomass-burning signal in molecular hydrogen (H<sub>2</sub>) over the Amazonian tropical rainforest. To quantify this signal, we measure the mixing ratios of H<sub>2</sub> and several other species as well as the H<sub>2</sub> isotopic composition in air samples that were collected in the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) aircraft campaign during the dry season. We derive a relative H<sub>2</sub> emission ratio with respect to carbon monoxide (CO) of 0.31 ± 0.04 ppb ppb<sup>−1</sup> and an isotopic source signature of −280 ± 41‰ in the air masses influenced by tropical biomass burning. In order to retrieve a clear source signal that is not influenced by the soil uptake of H<sub>2</sub>, we exclude samples from the atmospheric boundary layer. This procedure is supported by data from a global chemistry transport model. The ΔH<sub>2</sub> / ΔCO emission ratio is significantly lower than some earlier estimates for the tropical rainforest. In addition, our results confirm the lower values of the previously conflicting estimates of the H<sub>2</sub> isotopic source signature from biomass burning. These values for the emission ratio and isotopic source signatures of H<sub>2</sub> from tropical biomass burning can be used in future bottom-up and top-down approaches aiming to constrain the strength of the biomass-burning source for H<sub>2</sub>. Hitherto, these two quantities relied only on combustion experiments or on statistical relations, since no direct signal had been obtained from in-situ observations
Morbidity and complications of bone grafting of the floor of the maxillary sinus for the placement of endosseous implants.
Placement of endosseous implants in the atrophic maxilla is often limited because of a lack of supporting bone. A technique to augment the floor of the maxillary sinus with autogenous bone graft seems to be a new reliable treatment modality. The morbidity and complication rate of augmentation of the maxillary sinus floor was studied in 75 patients. The sinus floor was augmented with iliac crest (n = 65, 128 sinuses, 276 implants), mandibular symphysis (n = 8, ten sinuses, 21 implants), or maxillary tuberosity grafts (n = 2, two sinuses, two implants). The width of the alveolar crest had to be reconstructed in 52 patients, while in the other 23 patients augmentation and implantation were performed simultaneously. Perforation of the sinus membrane occurred in 45 patients, but this did not predispose them to the development of sinusitis. Loss of bone particles and sequesters were observed in one (diabetic) patient only, in whom a mucosal dehiscence occurred. A second augmentation procedure was successful. Symptoms of transient sinusitis were observed in two of the seven patients with a predisposition for sinusitis. These symptoms were successfully treated with decongestants and antibiotics. One patient developed a purulent sinusitis which resolved after a nasal amrostomy. The bone volume was sufficient for insertion implants in all patients. Twenty of 299 patients (6.7%) in whom Brånemark implants had been inserted were lost to follow-up (mean, 32 months); no sinus pathology was observed. The patients received implant-supported overdentures (58 patients) or fixed bridges (17 patients) and experienced no complaints with regard to the grafts or implants. We conclude that the morbidity and complication rate of bone grafting of the floor of the maxillary sinus floor with autogenous bone is low.</p
The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft
More than 450 air samples that were collected in the upper troposphere – lower stratosphere (UTLS) region by the CARIBIC aircraft (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) have been analyzed for molecular hydrogen (H2) mixing ratios (χ¬(H2)) and H2 isotopic composition (deuterium content, δD).
More than 120 of the analyzed samples contained air from the lowermost stratosphere (LMS). These show that ¬ χ(H2) does not vary appreciably with O3-derived height above the thermal tropopause (TP), whereas δD does increase with height. The isotope enrichment is caused by H2 production and destruction processes that enrich the stratospheric H2 reservoir in deuterium (D); the exact shapes of the profiles are mainly determined by mixing of stratospheric with tropospheric air. Tight negative correlations are found between δD and the mixing ratios of methane (¬ χ(CH4)) and nitrous oxide (χ-(N2O)), as a result of the relatively long lifetimes of these three species. The correlations are described by δD[‰] = −0.35 · ¬χ(CH4)[ppb]+768 and δD[‰] = −1.90 · χ(N2O)[ppb]+745. These correlations are similar to previously published results and likely hold globally for the LMS.
Samples that were collected from the Indian subcontinentup to 40° N before, during and after the summer monsoon season show no significant seasonal change in χ¬(H2), but δD is up to 12.3‰ lower in the July, August and September monsoon samples. This δD decrease is correlated with the χ¬(CH4) increase in these samples. The significant correlation with χ¬(CH4) and the absence of a perceptible χ-(H2) increase that accompanies the δD decrease indicates that microbial production of very D-depleted H2 in the wet season may contribute to this phenomenon.
Some of the samples have very high χ¬(H2) and very low δD values, which indicates a pollution effect. Aircraft engine exhaust plumes are a suspected cause, since the effect mostly occurs in samples collected close to airports, but no similar signals are found in other chemical tracers to support this. The isotopic source signature of the H2 pollution seems to be on the low end of the signature for fossil fuel burning
A parametric level-set method for partially discrete tomography
This paper introduces a parametric level-set method for tomographic
reconstruction of partially discrete images. Such images consist of a
continuously varying background and an anomaly with a constant (known)
grey-value. We represent the geometry of the anomaly using a level-set
function, which we represent using radial basis functions. We pose the
reconstruction problem as a bi-level optimization problem in terms of the
background and coefficients for the level-set function. To constrain the
background reconstruction we impose smoothness through Tikhonov regularization.
The bi-level optimization problem is solved in an alternating fashion; in each
iteration we first reconstruct the background and consequently update the
level-set function. We test our method on numerical phantoms and show that we
can successfully reconstruct the geometry of the anomaly, even from limited
data. On these phantoms, our method outperforms Total Variation reconstruction,
DART and P-DART.Comment: Paper submitted to 20th International Conference on Discrete Geometry
for Computer Imager
Analyzing Empowerment Processes Among Cancer Patients in an Online Community: A Text Mining Approach
Алгоритм функціонування системи захисту
Детально розглянуті алгоритми виявлення атак у середовищі мереж зв'язку.In detail the algorithms of exposure of attacks are considered in the environment of communication network
Colouring triangle-free graphs with local list sizes
We prove two distinct and natural refinements of a recent breakthrough result
of Molloy (and a follow-up work of Bernshteyn) on the (list) chromatic number
of triangle-free graphs. In both our results, we permit the amount of colour
made available to vertices of lower degree to be accordingly lower. One result
concerns list colouring and correspondence colouring, while the other concerns
fractional colouring. Our proof of the second illustrates the use of the
hard-core model to prove a Johansson-type result, which may be of independent
interest.Comment: 16 pages; v2 includes minor corrections after review; to appear in
Random Structures & Algorithm
PseudoBase++: an extension of PseudoBase for easy searching, formatting and visualization of pseudoknots
Pseudoknots have been recognized to be an important type of RNA secondary structures responsible for many biological functions. PseudoBase, a widely used database of pseudoknot secondary structures developed at Leiden University, contains over 250 records of pseudoknots obtained in the past 25 years through crystallography, NMR, mutational experiments and sequence comparisons. To promptly address the growing analysis requests of the researchers on RNA structures and bring together information from multiple sources across the Internet to a single platform, we designed and implemented PseudoBase++, an extension of PseudoBase for easy searching, formatting and visualization of pseudoknots. PseudoBase++ (http://pseudobaseplusplus.utep.edu) maps the PseudoBase dataset into a searchable relational database including additional functionalities such as pseudoknot type. PseudoBase++ links each pseudoknot in PseudoBase to the GenBank record of the corresponding nucleotide sequence and allows scientists to automatically visualize RNA secondary structures with PseudoViewer. It also includes the capabilities of fine-grained reference searching and collecting new pseudoknot information
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