1,667 research outputs found
A Tensor-Based Dictionary Learning Approach to Tomographic Image Reconstruction
We consider tomographic reconstruction using priors in the form of a
dictionary learned from training images. The reconstruction has two stages:
first we construct a tensor dictionary prior from our training data, and then
we pose the reconstruction problem in terms of recovering the expansion
coefficients in that dictionary. Our approach differs from past approaches in
that a) we use a third-order tensor representation for our images and b) we
recast the reconstruction problem using the tensor formulation. The dictionary
learning problem is presented as a non-negative tensor factorization problem
with sparsity constraints. The reconstruction problem is formulated in a convex
optimization framework by looking for a solution with a sparse representation
in the tensor dictionary. Numerical results show that our tensor formulation
leads to very sparse representations of both the training images and the
reconstructions due to the ability of representing repeated features compactly
in the dictionary.Comment: 29 page
BN Nanotube Serving as a Gas Chemical Sensor for NâO by Parallel Electric Field
Density functional theory calculations were performed to understand the electronic properties of Cââ, BââNââ, BââPââ, and (6, 0) BNNT interacted with NâO molecule in the presence and absence of an external electric field using the B3LYP method and 6-31G** basis set. The adsorption of NâO from O-side on the surface of (6, 0) BNNT has high sensitivity in comparison with BââNââ nano-cage. The adsorption energy of NâO (O-side) on the sidewalls of BââNââ and BNNT in the presence of an electric field are â21.01 and â15.48 kJ molâ»Âč, respectively. Our results suggest that in the presence of an electric field, the BââNââ nano-cage is the more energetically notable upon the NâO adsorption than (6, 0) BNNT, Cââ, and BââPââ. Whereas, our results indicate that the electronic property of BNNT is more sensitive to NâO molecule at the presence of an electric field than BââNââ nano-cage. It is anticipated that BNNT could be a favorable gas sensor for the detection of NâO molecule. © 2016, Springer Science+Business Media New York
A DFT study of 5-fluorouracil adsorption on the pure and doped BN nanotubes
Abstract The electronic and adsorption properties of the pristine, Al-, Ga-, and Ge-doped BN nanotubes interacted with 5-fluorouracil molecule (5-FU) were theoretically investigated in the gas phase using the B3LYP density functional theory (DFT) calculations. It was found that the adsorption behavior of 5FU molecule on the pristine (8, 0) and (5, 5) BNNTs are electrostatic in nature. In contrast, the 5FU molecule (O-side) implies strong adsorption on the metal-doped BNNTs. Our results indicate that the Ga-doped presents high sensitivity and strong adsorption with the 5-FU molecule than the Al- and Ge-doped BNNTs. Therefore, it can be introduced as a carrier for drug delivery applications. © 2015 Elsevier Ltd
Binding energy of localized biexcitons in quantum wells
A variational calculation of the ground state energy of a biexciton in a
GaAs/AlGaAs quantum well is presented. The well width fluctuations leading to
trapping of the biexcitons are modeled by a parabolic potential. The results
obtained for different well widths are compared with recent experimental data.
Good agreement is obtained both for the biexciton binding energy and for the
Haynes factor. We find that the structure of a biexciton is similar to the one
of the H_2 molecule.Comment: 9 pages, 4 figure
Isolation, spectroscopic characterization, X-ray, theoretical studies as well as in vitro cytotoxicity of Samarcandin
Samarcandin 1, a natural sesquiterpene-coumarin, was isolated as well as elucidated from F. assa-foetida which has significant effect in Iranian traditional medicine because of its medicinal attitudes. The crystal structure of samarcandin was determined by single-crystal X-ray structure analysis. It is orthorhombic, with unit cell parameters a = 10.8204 (5) Ă
, b = 12.9894 (7) Ă
, c = 15.2467 (9) Ă
, V = 2142.9 (2) Ă
3, space group P212121 and four symmetry equivalent molecules in the unit cell. Samarcandin was isolated in order to study for its theoretical studies as well as its cellular toxicity as anti-cancer drug against two cancerous cells. In comparison with controls, our microscopic and MTT assay data showed that samarcandin suppresses cancer cell proliferation in a dose-dependent manner with IC50 = 11 ÎŒM and 13 for AGS and WEHI-164 cell lines, respectively. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) of the structure was computed by three functional methods and 6-311++Gââ standard basis set. The optimized molecular geometry and theoretical analysis agree closely to that obtained from the single crystal X-ray crystallography. To sum up, the good correlations between experimental and theoretical studies by UV, NMR, and IR spectra were found. © 2016 Elsevier Inc. All rights reserved
The effect of gut microbiota and probiotics on metabolism in fish and shrimp
The present paper presents an overview of the effects of gut microbiota and probiotics on lipid-, carbohydrate-, protein- and amino acid metabolism in fish and shrimp. In probiotic fish studies, the zebrafish (Danio rerio) model is the most frequently used, and probiotic administration reveals the effect on glucose homeostasis, anti-lipidemic effects and increasing short-chain fatty acids, and increased expressions of genes related to carbohydrate metabolism and innate immunity, along with down-regulation of oxidative stress-related genes. Further, improved length of the intestinal villi and expression of nutrient transporters in fish owing to probiotics exposure have been documented. The present review will present an appraisal of the effect of intestinal microbiota and probiotic administration on the metabolism of nutrients and metabolites related to stress and immunity in diverse fish- and shrimp species. Furthermore, to give the reader satisfactory information on the topics discussed, some information from endothermic animals is also presented
Socio-demographic and built environment determinants of car use among older adults in Iran
Internationally, an age-friendly built environment, including safe, affordable, and convenient transportation, has been identified as crucial in enhancing the quality of life for increasingly large numbers of elderly people. This study presents data on the urban travel and mobility patterns of older adults in Shiraz, Iran â a country where the population is ageing faster than the average of western societies. The relationship between car use and socio-demographic and built environment variables is investigated through Ordinary Least Squares and Geographically Weighted Regression models. These models show that the main determinants of car use among older adults are: employment status; household size; car ownership rate; trip purpose; property prices; and mixed land-uses. Also, the study reveals that car dependency is significant and more pronounced among wealthier individuals, who tend to be clustered in the northern section of the city. The population density and road network design characteristics do not affect car use among older adults, while a mix of land-uses tends to attenuate car dependency. Gender gaps in car use are much wider than in the West, and some level of spatial mismatch between travel needs and car access is observed in the southern section of the city. Clearly, Iranian cities must move away from the current car-centric development model
Multibody expansion of the local integrals of motion: How many pairs of particle-hole do we really need to describe the quasiparticles in the many-body localized phase?
The emergent integrability in a many-body localized (MBL) system can be well
characterized by the existence of the complete set of local integrals of motion
(LIOMs). Such exactly conserved and exponentially localized operators are often
understood as quasiparticle operators which can be expanded in terms of
single-particle operators dressed with different numbers of particle-hole
pairs. Here, we consider a one-dimensional XXZ spin- Heisenberg chain
in the presence of a random field and try to quantify the corrections needed to
be considered in the picture of quasiparticles associated with LIOMs due to the
presence of particle-hole excitations. To this end, we explicitly present the
multibody expansion of LIOM creation operators of the system in the MBL regime.
We analytically obtain the coefficients of this expansion and discuss the
effect of higher-order corrections associated with different numbers of
particle-hole excitations. Our analysis shows that depending on the
localization length of the system, there exist a regime in which the
contributions that come from higher-order terms can break down the effective
one-particle description of the LIOMs and such quasiparticles become
essentially many-body-like
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