Magnetic Coherence Research Articles

The association between retinal nerve fibre layer thickness and N-acetyl aspartate levels in multiple sclerosis brain normal-appearing white matter: a longitudinal study using magnetic resonance spectroscopy and optical coherence tomography.

N-acetyl aspartate (NAA) assessed using proton magnetic resonance spectroscopy (1 H MRS) has a high pathological specificity for axonal density. Retinal nerve fibre layer thickness (RNFLT) measured by using optical coherence tomography is increasingly used as a surrogate marker of neurodegeneration in multiple sclerosis (MS). Our aim was to investigate the relation between RNFLT and NAA/creatine in brain normal-appearing white matter (NAWM), their dynamics over time and the association with clinical outcome measures in relapsing MS. T2 WM lesions served as control tissue. Forty-three MS patients underwent standardized neurological examination including the Expanded Disability Status Scale (EDSS), Multiple Sclerosis Functional Composite (MSFC) score, optical coherence tomography and magnetic resonance imaging including 1 H MRS at baseline and after 1 year. At baseline, NAA/creatine level was lower in T2 WM lesions than in NAWM (1.64 ± 0.16 vs. 1.88 ± 0.24, P < 0.001). Lowest levels were found in secondary progressive MS (SPMS). Mean RNFLT was higher in clinically isolated syndrome than in the combined group of relapsing-remitting MS and SPMS (99.8 ± 12.3 μm vs. 92.4 ± 12.8 μm, P = 0.038). In all patients, mean RNFLT decreased by 1.4% during follow-up. At baseline, MSFC z-scores correlated with NAA/creatine levels both in NAWM (r = 0.42; P = 0.008) and T2 WM lesions (r = 0.52, P = 0.004). NAWM NAA/creatine variation correlated with the RNFLT change over 1 year (ρ = 0.43, P = 0.046). N-acetyl aspartate/creatine level reduction correlated with RNFLT thinning over 1 year in an EDSS stable MS cohort suggesting that these techniques might be sensitive to detect subclinical disease progression.

Management of COPD: Is there a role for quantitative imaging?

While the recent development of quantitative imaging methods have led to their increased use in the diagnosis and management of many chronic diseases, medical imaging still plays a limited role in the management of chronic obstructive pulmonary disease (COPD). In this review we highlight three pulmonary imaging modalities: computed tomography (CT), magnetic resonance imaging (MRI) and optical coherence tomography (OCT) imaging and the COPD biomarkers that may be helpful for managing COPD patients. We discussed the current role imaging plays in COPD management as well as the potential role quantitative imaging will play by identifying imaging phenotypes to enable more effective COPD management and improved outcomes.

Thickness dependence of the triplet spin-valve effect in superconductor-ferromagnet-ferromagnet heterostructures.

Background: In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature Tc, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment.Results: The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoOx an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoOx and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID) magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, dF1, of F1 and was found to decay with increasing dF1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory.Conclusion: The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance dF1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated) breakdown of the triplet spin-valve effect for dF1 smaller than 0.3 to 0.4 times the magnetic coherence length, ξF1.

Long-range supercurrents induced by the interference effect of opposite-spin triplet state in clean superconductor-ferromagnet structures

By now it is known that in an s-wave superconductor-ferromagnet-superconductor (SFS) structure the supercurrent induced by spin singlet pairs can only transmit a short distance of the order of magnetic coherence length. The long-range supercurrent, taking place on the length scale of the normal metal coherence length, will be maintained by equal-spin triplet pairs, which can be generated by magnetic inhomogeneities in the system. In this paper, we have shown an unusual long-range supercurrent, which can take place in clean junction with non-parallel orientation of magnetic moments. The mechanism behind the enhancement of Josephson current is provided by the interference of the opposite-spin triplet states deriving from and interfaces when both ferromagnetic layers have the same values of the length and exchange field. This discovery can offer a natural explanation for recent experiments (Robinson et al 2010 Phys. Rev. Lett. 104 207001; Baek et al 2014 Nat. Commun. 5 3888).

Noninvasive methods of detecting increased intracranial pressure.

The detection of elevated intracranial pressure (ICP) is of paramount importance in the diagnosis and management of a number of neurologic pathologies. The current gold standard is the use of intraventricular or intraparenchymal catheters; however, this is invasive, expensive, and requires anesthesia. On the other hand, diagnosing intracranial hypertension based on clinical symptoms such as headaches, vomiting, and visual changes lacks sensitivity. As such, there exists a need for a noninvasive yet accurate and reliable method for detecting elevated ICP. In this review, we aim to cover both structural modalities such as computed tomography (CT), magnetic resonance imaging (MRI), ocular ultrasound, fundoscopy, and optical coherence tomography (OCT) as well as functional modalities such as transcranial Doppler ultrasound (TCD), visual evoked potentials (VEPs), and near-infrared spectroscopy (NIRS).

Superconductivity in Fe-Based Compound EuAFe4As4 (A = Rb and Cs)

We report the discovery of a novel Fe-based superconductor EuAFe4As4 (A = Rb, Cs) and describe its superconducting properties. EuAFe4As4 has a tetragonal unit cell with a P4/mmm (No. 123) space group, indicating that this material is an 1144-type compound. The magnetic susceptibility and electrical resistivity indicate superconducting transitions at approximately 36 and 35 K for EuRbFe4As4 and EuCsFe4As4, respectively. Moreover, an anomalous magnetic transition appears at approximately 15 K, suggesting the coexistence of superconductivity and a magnetic ordered state formed by the Eu2+ ions. The determined upper critical magnetic fields and coherence lengths are approximately 920 kOe and 1.8 nm for EuRbFe4As4 and 875 kOe and 1.9 nm for EuCsFe4As4, respectively.

Externally Delivered Focused Ultrasoundfor Renal Denervation.

The aim of this study was to assess clinical safety and efficacy outcomes of renal denervation executed by an externally delivered, completely noninvasive focused therapeutic ultrasound device. Renal denervation has emerged as a potential treatment approach for resistant hypertension. Sixty-nine subjects received renal denervation with externally delivered focused ultrasound via the KonaMedical Surround Sound System. This approach was investigated across 3 consecutive studies to optimize targeting, tracking, and dosing. In the third study, treatments were performed in a completely noninvasive way using duplex ultrasound image guidance to target the therapy. Short- and long-term safety and efficacy were evaluated through use of clinical assessments, magnetic resonance imaging scans prior to and 3 and 24 weeks after renal denervation, and, in cases in which a targeting catheter was used to facilitate targeting, fluoroscopic angiography withcontrast. All patients tolerated renal denervation using externally delivered focused ultrasound. Office blood pressure (BP) decreased by 24.6 ± 27.6/9.0 ± 15.0 mmHg (from baseline BP of 180.0 ± 18.5/97.7 ± 13.7 mmHg) in 69 patients after 6 months and 23.8 ± 24.1/10.3 ± 13.1 mmHg in 64 patients with complete 1-year follow-up. The response rate (BPdecrease >10 mmHg) was 75% after 6 months and 77% after 1 year. The most common adverse event was post-treatment back pain, which was reported in 32 of 69 patients and resolved within 72 h in most cases. No intervention-related adverse events involving motor or sensory deficits were reported. Renal function was not altered, and vascular safety was established by magnetic resonance imaging (all patients), fluoroscopic angiography (n= 48), andoptical coherence tomography (n= 5). Using externally delivered focused ultrasound and noninvasive duplex ultrasound, image-guided targeting was associated with substantial BP reduction without any major safety signals. Further randomized, sham-controlled trials will be needed to validate this unique approach.

Vortex in holographic two-band superfluid/superconductor

We construct numerically static vortex solutions in a holographic model of two-band superconductor with an interband Josephson coupling in both the superfluid and superconductor regime. We investigate the effects of the interband coupling on the order parameter of each superconducting band in the vortex solution, and we find that it is different for each of the two bands. We compute also the free energy, critical magnetic field, magnetic penetration length and coherence lengths for the two bands, and we study their dependence on the interband coupling and temperature. Interestingly, we find that the coherence lengths of the two bands are close to identical.

The Cortical Processing of Sensorimotor Sequences is Disrupted in Writer's Cramp.

Evidence for pre-existing abnormalities in the sensory and motor systems has been previously reported in writer's cramp (WC). However, the processing of somatosensory information during motor planning has received little attention. We hypothesized that sensorimotor integration processes might be impaired partly due to a disruption in the parieto-premotor network. To test this assumption, we designed 2 nonwriting motor tasks in which subjects had to perform a 4-finger motor sequence either on the basis of sensory stimuli previously memorized (SM task) or freely generated (SG task). Brain activity was measured by combining event-related functional magnetic resonance imaging and coherency electroencephalography in 15 WC patients and 15 normal controls. The bold signal was decreased in patients in both tasks during sensory stimulation but not during movement execution. However, the EEG study showed that coherency was decreased in patients compared with controls, during the delay of the SM task and during the execution of the SG task, on both the whole network and for specific couples of electrodes. Overall, these results demonstrate an endophenotypic impairment in the synchronization of cortical areas within the parieto-premotor network during somatosensory processing and motor planning in WC patients.

INTERPLAY AMONG COOLING, AGN FEEDBACK, AND ANISOTROPIC CONDUCTION IN THE COOL CORES OF GALAXY CLUSTERS

ABSTRACT Feedback from the active galactic nuclei (AGNs) is one of the most promising heating mechanisms to circumvent the cooling-flow problem in galaxy clusters. However, the role of thermal conduction remains unclear. Previous studies have shown that anisotropic thermal conduction in cluster cool cores (CCs) could drive the heat-flux-driven buoyancy instabilities (HBIs) that reorient the field lines in the azimuthal directions and isolate the cores from conductive heating from the outskirts. However, how the AGN interacts with the HBI is still unknown. To understand these interwined processes, we perform the first 3D magnetohydrodynamic simulations of isolated CC clusters that include anisotropic conduction, radiative cooling, and AGN feedback. We find the following: (1) For realistic magnetic field strengths in clusters, magnetic tension can suppress a significant portion of HBI-unstable modes, and thus the HBI is either completely inhibited or significantly impaired, depending on the unknown magnetic field coherence length. (2) Turbulence driven by AGN jets can effectively randomize magnetic field lines and sustain conductivity at ∼1/3 of the Spitzer value; however, the AGN-driven turbulence is not volume filling. (3) Conductive heating within the cores could contribute to ∼10% of the radiative losses in Perseus-like clusters and up to ∼50% for clusters twice the mass of Perseus. (4) Thermal conduction has various impacts on the AGN activity and intracluster medium properties for the hottest clusters, which may be searched by future observations to constrain the level of conductivity in clusters. The distribution of cold gas and the implications are also discussed.

Unusual Case of an Orbital Lymphangioma Presenting as Chorioretinal Folds with Macular Involvement in an Elderly Patient

We report a case of 75-year-old elderly male who presented with diminution and distortion of vision, swelling, pain and upward and nasal deviation of eyes. Computed tomography (CT) scan and magnetic resonance imaging (MRI), fundus photography and optical coherence tomography (OCT) were performed. A multilocular intraconal cystic mass lesion causing chorioretinal folds was seen. A presumptive diagnosis of orbital lymphangioma with chorioretinal folds was made and was confirmed by histopathology. This case is being reported because of its unusual presentation in an elderly patient (chorioretinal folds with macular involvement).

Structural Characterization of the Lignins from the Green and Yellow Bamboo of Bamboo Culm (Phyllostachys pubescens)

Milled wood lignins were isolated from green and yellow bamboo (Phyllostachys pubescens), termed MWLg and MWLy, respectively. The structural features of the lignin preparations and the remaining LCC were characterized by quantitative 13C nuclear magnetic resonance (13C NMR) spectroscopy and two-dimensional heteronuclear signal quantum coherence NMR (2D HSQC NMR) spectroscopy. The results indicated that the main substructures in MWLg and MWLy were β-O-4 alkyl-aryl ether, resinol, phenylcoumaran, spirodienone, and α,β-diaryl ether, and their abundances per 100 Ar units were 38.2 and 39.8, 6.9 and 6.3, 3.8 and 2.9, 1.7 and 2.1, 0.4 and 0.3, respectively. The S:G:H ratios of MWLg and MWLy were estimated to be 40:54:6 and 51:44:5, respectively. The γ-acylation of green bamboo lignin was 17.22%, lower than that of yellow bamboo lignin (21.12%). Moreover, a flavonoid compound (tricin) was also detected in the MWLg and MWLy. Some carbohydrates remained in the purified MWL preparations, which were considered as the lignin-carbohydrate complexes (LCC).

Novel digital imaging techniques to assess the outcome in oral rehabilitation with dental implants: a narrative review.

To examine the literature on novel digital imaging techniques for the assessment of outcomes in oral rehabilitation with dental implants. An electronic search of Medline and Embase databases including studies published prior to 28th December 2014 was performed and supplemented by a manual search. A synthesis of the publications was presented describing the use of computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography, optical scanning, spectrophotometry or optical coherence tomography (OCT) related to the outcome measures in implant therapy. Most of the digital imaging techniques have not yet sufficiently been validated to be used for outcome measures in implant dentistry. In clinical research, cone beam CT (CBCT) is increasingly being used for 3D assessment of bone and soft tissue following augmentation procedures and implant placement. Currently, there are no effective methods for the reduction of artifacts around implants in CBCT. Optical scanning is being used for the 3D assessment of changes in the soft tissue contour. The combination of optical scan with pre-operative CBCT allows the determination of the implant position and its spatial relation to anatomical structures. Spectrophotometry is the method most commonly used to objectively assess the color match of reconstructions and peri-implant mucosa to natural dentition and gingiva. New optical imaging techniques may be considered possible approaches for monitoring peri-implant soft tissue health. MRI and ultrasonography appear promising non-ionizing radiation imaging modalities for the assessment of soft tissue and bone defect morphologies. Optical scanners and OCT may represent efficient clinical methods for accurate assessment of the misfit between the reconstructions and the implants.

Generalized formalisms of the radio interferometer measurement equation

The Radio Interferometer Measurement Equation (RIME) is a matrix-based mathematical model that describes the response of a radio interferometer. The Jones calculus it employs is not suitable for describing the analogue components of a telescope. This is because it does not consider the effect of impedance mismatches between components. This paper aims to highlight the limitations of Jones calculus, and suggests some alternative methods that are more applicable. We reformulate the RIME with a different basis that includes magnetic and mixed coherency statistics. We present a microwave network inspired 2N-port version of the RIME, and a tensor formalism based upon the electromagnetic tensor from special relativity. We elucidate the limitations of the Jones-matrix-based RIME for describing analogue components. We show how measured scattering parameters of analogue components can be used in a 2N-port version of the RIME. In addition, we show how motion at relativistic speed affects the observed flux. We present reformulations of the RIME that correctly account for magnetic field coherency. These reformulations extend the standard formulation, highlight its limitations, and may have applications in space-based interferometry and precise absolute calibration experiments.

The critical current reaction on hydrostatic pressure of a superconductor–semimetal composite

The transport characteristics of a composite consisting of microparticles of a superconductor MgB2 and nanopowder of a ferromagnetic half-metal La0.7Ca0.3MnO3 (LCMO) were investigated under hydrostatic compression. It was observed that as the concentration of the LCMO manganite is increased above the percolation threshold of MgB2, the superconducting current flows through the superconductor–ferromagnet–superconductor chains with the LCMO thickness exceeding the magnetic coherence length ξM in the half-metal (ξM ≤ 10 Å) by an order of magnitude. This behavior can be attributed to the presence of triplet superconducting correlations in the half-metal, which arise due to the spin-active surface of LCMO nanograins. An increase in pressure led to an increase in the critical current of the MgB2–LCMO composite, while the critical current and the transition temperature of pure MgB2 decreased under pressure.

Improvement of the intergranular pinning energy in the Na-doped Bi-2212 superconductors

In the present study, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1−x Na x Cu2O8+y superconductor with x = 0.0, 0.05, 0.075, 0.10, 0.15, and 0.20 has been studied by change of flux pinning mechanism. Samples have been prepared using a polymer solution technique with polyethyleneimine. The effects of Na substitution for Ca on the activation energies, irreversibility field, upper critical magnetic field and coherence length have been studied. The magnetoresistance of samples has been measured at applied magnetic fields between 0 and 9 T. Broadening of superconducting transition has been observed under magnetic field, explained on the basis of Thermally Activated Flux Flow (TAFF) model. The upper critical magnetic field H C2 (0) and the coherence length (ζ(0)) at T = 0 K were calculated using the resistivity data and H C2(0), respectively. H C2 (0) and ξ(0) values have been calculated as 186.4, 195.5, 321.0, 296.0, 292.5, 280.9 T, and 13.29, 12.98, 10.13, 10.55, 10.61, 10.69 Å for the 0.0, 0.05, 0.075, 0.10, 0.15, and 0.20 Na-doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1−xNaxCu2O8+y where x = 0.075 determined to be 0.019 eV for 9 T and 0.239 eV for 0 T.

INVERSE CASCADE OF NONHELICAL MAGNETIC TURBULENCE IN A RELATIVISTIC FLUID

The free decay of non-helical relativistic magnetohydrodynamic turbulence is studied numerically, and found to exhibit cascading of magnetic energy toward large scales. Evolution of the magnetic energy spectrum $P_M(k,t)$ is self-similar in time and well modeled by a broken power law with sub-inertial and inertial range indices very close to $7/2$ and $-2$ respectively. The magnetic coherence scale is found to grow in time as $t^{2/5}$, much too slow to account for optical polarization of gamma-ray burst afterglow emission if magnetic energy is to be supplied only at microphysical length scales. No bursty or explosive energy loss is observed in relativistic MHD turbulence having modest magnetization, which constrains magnetic reconnection models for rapid time variability of GRB prompt emission, blazars and the Crab nebula.

Electric and magnetic field-assisted orientational transitions in the ensembles of domains in a nematic liquid crystal on the polymer surface.

Using electro- and magneto-optical techniques, we investigated orientational transitions in the ensembles of domains in a nematic liquid crystal on the polycarbonate film surface under the conditions of competing surface forces that favor radial and uniform planar alignment of nematic molecules. Having analyzed field dependences of the intensity of light passed through a sample, we established the threshold character of the orientational effects, plotted the calculated intensity versus magnetic coherence length, and compared the latter with the equilibrium length that characterizes the balance of forces on the polymer surface.

The Effect of K Substitution on Magnetoresistivity and Activation Energy of Bi-2212 System

In the present work, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1−x K x Cu2 O 8+y superconductor with x=0.0,0.05,0.075, and 0.1 has been studied by change of flux pinning mechanism, using magnetoresistivity measurements. The samples were prepared using a polymer solution technique. The effects of K substitution for Ca on the irreversibility field, upper critical magnetic field, coherence length, and activation energies have been investigated. The magnetoresistivity of the samples has been measured under applied magnetic fields ranging from 0 to 9 T. Broadening of superconducting transition is observed under magnetic field, explained on the basis of thermally activated flux flow (TAFF) model. The upper critical magnetic field H C2(0) and the coherence length (ζ(0)) at T = 0 K were calculated using the resistivity data and from H C2(0) ,respectively. H C2(0) and ξ(0) values have been calculated as 62, 72, 75, and 53 T and 23, 21, 20, and 25 A for the 0.0, 0.05, 0.075, and 0.10 K doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1−x K x Cu2 O 8+y where x = 0.075 are calculated as 0.0147 eV for 9 T and 0.29 eV for 0 T.

Polarization phenomena in the transparency and adsorption effects induced by the field of counterpropagating waves

The physical processes that form the resonances of saturated absorption and magnetic scanning in the field of counterpropagating waves of an arbitrary intensity when their polarizations change are numerically simulated. The atomic transition with level moment J = 1 is used as an example to show that the anomalies in the experimental saturated absorption spectra are determined by the degree of opening of the atomic transition. In the case of magnetic scanning, the anomalies are caused by the magnetic coherence induced by the wave fields at the levels of the lower state rather than by its transfer from the excited states, as was proposed earlier.