1,039 research outputs found
Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors
We present the first study of codoped iron-arsenide superconductors of the
122 family (Sr/Ba)_(1-x)K_xFe_(2-y)Co_yAs_2 with the purpose to increase the
upper critical field H_c2 compared to single doped (Sr/Ba)Fe_2As_2 materials.
H_c2 was investigated by measuring the magnetoresistance in high pulsed
magnetic fields up to 64 T. We find, that H_c2 extrapolated to T = 0 is indeed
enhanced significantly to ~ 90 T for polycrystalline samples of
Ba_0.55K_0.45Fe_1.95Co_0.05As_2 compared to ~75 T for Ba_0.55K_0.45Fe_2As_2 and
BaFe_1.8Co_0.2As_2 single crystals. Codoping thus is a promising way for the
systematic optimization of iron-arsenic based superconductors for
magnetic-field and high-current applications.Comment: 7 pages, 5 figures, submitted to Journal of Applied Physic
Quantifying the improvement of surrogate indices of hepatic insulin resistance using complex measurement techniques
We evaluated the ability of simple and complex surrogate-indices to identify individuals from an overweight/obese cohort with hepatic insulin-resistance (HEP-IR). Five indices, one previously defined and four newly generated through step-wise linear regression, were created against a single-cohort sample of 77 extensively characterised participants with the metabolic syndrome (age 55.6±1.0 years, BMI 31.5±0.4 kg/m2; 30 males). HEP-IR was defined by measuring endogenous-glucose-production (EGP) with [6–62H2] glucose during fasting and euglycemic-hyperinsulinemic clamps and expressed as EGP*fasting plasma insulin. Complex measures were incorporated into the model, including various non-standard biomarkers and the measurement of body-fat distribution and liver-fat, to further improve the predictive capability of the index. Validation was performed against a data set of the same subjects after an isoenergetic dietary intervention (4 arms, diets varying in protein and fiber content versus control). All five indices produced comparable prediction of HEP-IR, explaining 39–56% of the variance, depending on regression variable combination. The validation of the regression equations showed little variation between the different proposed indices (r2 = 27–32%) on a matched dataset. New complex indices encompassing advanced measurement techniques offered an improved correlation (r = 0.75, P<0.001). However, when validated against the alternative dataset all indices performed comparably with the standard homeostasis model assessment for insulin resistance (HOMA-IR) (r = 0.54, P<0.001). Thus, simple estimates of HEP-IR performed comparable to more complex indices and could be an efficient and cost effective approach in large epidemiological investigations
Nonlinear Diffusion on the 2D Euclidean Motion Group
Linear and nonlinear diffusion equations are usually considered on an image, which is in fact a function on the translation group. In this paper we study diffusion on orientation scores, i.e. on functions on the Euclidean motion group SE(2). An orientation score is obtained from an image by a linear invertible transformation. The goal is to enhance elongated structures by applying nonlinear left-invariant diffusion on the orientation score of the image. For this purpose we describe how we can use Gaussian derivatives to obtain regularized left-invariant derivatives that obey the non-commutative structure of the Lie algebra of SE(2). The Hessian constructed with these derivatives is used to estimate local curvature and orientation strength and the diffusion is made nonlinearly dependent on these measures. We propose an explicit finite difference scheme to apply the nonlinear diffusion on orientation scores. The experiments show that preservation of crossing structures is the main advantage compared to approaches such as coherence enhancing diffusion
Huge First-Order Metamagnetic Transition in the Paramagnetic Heavy-Fermion System CeTiGe
We report on the observation of large, step-like anomalies in the
magnetization (\,/Ce), in the magnetostriction
(), and in the magnetoresistance in
polycrystals of the paramagnetic heavy-fermion system CeTiGe at a critical
magnetic field 12.5\,T at low temperatures. The size of
these anomalies is much larger than those reported for the prototypical
heavy-fermion metamagnet CeRuSi. Furthermore, hysteresis between
increasing and decreasing field data indicate a real thermodynamic, first-order
type of phase transition, in contrast to the crossover reported for
CeRuSi. Analysis of the resistivity data shows a pronounced decrease of
the electronic quasiparticle mass across . These results establish CeTiGe
as a new metamagnetic Kondo-lattice system, with an exceptionally large,
metamagnetic transition of first-order type at a moderate field.Comment: 5 pages, 4 figure
Anisotropic osmosis filtering for shadow removal in images
We present an anisotropic extension of the isotropic osmosis model that has
been introduced by Weickert et al.~(Weickert, 2013) for visual computing
applications, and we adapt it specifically to shadow removal applications. We
show that in the integrable setting, linear anisotropic osmosis minimises an
energy that involves a suitable quadratic form which models local directional
structures. In our shadow removal applications we estimate the local structure
via a modified tensor voting approach (Moreno, 2012) and use this information
within an anisotropic diffusion inpainting that resembles edge-enhancing
anisotropic diffusion inpainting (Weickert, 2006, Gali\'c, 2008). Our numerical
scheme combines the nonnegativity preserving stencil of Fehrenbach and Mirebeau
(Fehrenbach, 2014) with an exact time stepping based on highly accurate
polynomial approximations of the matrix exponential. The resulting anisotropic
model is tested on several synthetic and natural images corrupted by constant
shadows. We show that it outperforms isotropic osmosis, since it does not
suffer from blurring artefacts at the shadow boundaries
Антиутопия как диагноз будущему
Материалы XIV Междунар. науч. конф. студентов, магистрантов, аспирантов и молодых ученых, Гомель, 13–14 мая 2021 г
The application of KAZE features to the classification echocardiogram videos
In the computer vision field, both approaches of SIFT and SURF are prevalent in the extraction of scale-invariant points and have demonstrated a number of advantages. However, when they are applied to medical images with relevant low contrast between target structures and surrounding regions, these approaches lack the ability to distinguish salient features. Therefore, this research proposes a different approach by extracting feature points using the emerging method of KAZE. As such, to categorise a collection of video images of echocardiograms, KAZE feature points, coupled with three popular representation methods, are addressed in this paper, which includes the bag of words (BOW), sparse coding, and Fisher vector (FV). In comparison with the SIFT features represented using Sparse coding approach that gives 72% overall performance on the classification of eight viewpoints, KAZE feature integrated with either BOW, sparse coding or FV improves the performance significantly with the accuracy being 81.09%, 78.85% and 80.8% respectively. When it comes to distinguish only three primary view locations, 97.44% accuracy can be achieved when employing the approach of KAZE whereas 90% accuracy is realised while applying SIFT features
Bridging frustrated-spin-chain and spin-ladder physics: quasi-one-dimensional magnetism of BiCu2PO6
We derive and investigate the microscopic model of the quantum magnet
BiCu2PO6 using band structure calculations, magnetic susceptibility and
high-field magnetization measurements, as well as ED and DMRG techniques. The
resulting quasi-one-dimensional spin model is a two-leg AFM ladder with
frustrating next-nearest-neighbor couplings along the legs. The individual
couplings are estimated from band structure calculations and by fitting the
magnetic susceptibility with theoretical predictions, obtained using ED. The
nearest-neighbor leg coupling J1, the rung coupling J4, and one of the
next-nearest-neighbor couplings J2 amount to 120-150 K, while the second
next-nearest-neighbor coupling is J2'~J2/2. The spin ladders do not match the
structural chains, and although the next-nearest-neighbor interactions J2 and
J2' have very similar superexchange pathways, they differ substantially in
magnitude due to a tiny difference in the O-O distances and in the arrangement
of non-magnetic PO4 tetrahedra. An extensive ED study of the proposed model
provides the low-energy excitation spectrum and shows that the system is in the
strong rung coupling regime. The strong frustration by the
next-nearest-neighbor couplings leads to a triplon branch with an
incommensurate minimum. This is further corroborated by a strong-coupling
expansion up to second order in the inter-rung coupling. Based on high-field
magnetization measurements, we estimate the spin gap of 32 K and suggest the
likely presence of antisymmetric DM anisotropy and inter-ladder coupling J3. We
also provide a tentative description of the physics of BiCu2PO6 in magnetic
field, in the light of the low-energy excitation spectra and numerical
calculations based on ED and DMRG. In particular, we raise the possibility for
a rich interplay between one- and two-component Luttinger liquid phases and a
magnetization plateau at 1/2 of the saturation value
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