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Magnetic field

Alexander Loktyushin, Philipp Ehses, Bernhard Schölkopf, Klaus Scheffler
PURPOSE: Phase artifacts due to B0 inhomogeneity can severely degrade the quality of MR images. The artifacts are particularly prominent in long-TE scans and usually appear as ghosting and blur. We propose a retrospective phase correction method based on autofocusing. The proposed method uses raw data acquired with standard imaging sequences, and does not rely on navigators or external measures of field inhomogeneity. METHODS: We formulate and solve the optimization problem, where we seek the latent phase offsets that are associated with an optimal value of the image quality measure that is evaluated in the spatial domain...
January 19, 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Bart Ferguson, Natalia Petridou, Alessio Fracasso, Martijn P van den Heuvel, Rachel M Brouwer, Hilleke E Hulshoff Pol, René S Kahn, René C W Mandl
Studies into cortical thickness in psychiatric diseases based on T1-weighted MRI frequently report on aberrations in the cerebral cortex. Due to limitations in image resolution for studies conducted at conventional MRI field strengths (e.g. 3 Tesla (T)) this information cannot be used to establish which of the cortical layers may be implicated. Here we propose a new analysis method that computes one high-resolution average cortical profile per brain region extracting myeloarchitectural information from T1-weighted MRI scans that are routinely acquired at a conventional field strength...
January 19, 2018: Neuroinformatics
Hyung Keun Gweon, Seok Jin Yun, Sang Ho Lim
The perpendicular magnetic anisotropy (PMA) properties of Pt/Co/MgO trilayers are investigated as a function of the MgO sputtering power (PMgO) and its thickness (tMgO), both of which are important parameters affecting the degree of oxygen interpenetration into Co during sputtering. A strong PMA is achieved at small values of PMgO and tMgO, where the oxygen interpenetration into Co is expected to be small. The range of oxygen interpenetration is relatively extended in such a way that it affects both the Pt/Co and Co/MgO interfaces...
January 19, 2018: Scientific Reports
Yinlan Ruan, David A Simpson, Jan Jeske, Heike Ebendorff-Heidepriem, Desmond W M Lau, Hong Ji, Brett C Johnson, Takeshi Ohshima, Shahraam Afshar V, Lloyd Hollenberg, Andrew D Greentree, Tanya M Monro, Brant C Gibson
Traditional optical fibers are insensitive to magnetic fields, however many applications would benefit from fiber-based magnetometry devices. In this work, we demonstrate a magnetically sensitive optical fiber by doping nanodiamonds containing nitrogen vacancy centers into tellurite glass fibers. The fabrication process provides a robust and isolated sensing platform as the magnetic sensors are fixed in the tellurite glass matrix. Using optically detected magnetic resonance from the doped nanodiamonds, we demonstrate detection of local magnetic fields via side excitation and longitudinal collection...
January 19, 2018: Scientific Reports
Masaki Sekino, Akihiro Kuwahata, Tetsu Ookubo, Mikio Shiozawa, Kaichi Ohashi, Miki Kaneko, Itsuro Saito, Yusuke Inoue, Hiroyuki Ohsaki, Hiroyuki Takei, Moriaki Kusakabe
The newly developed radioisotope-free technique based on magnetic nanoparticle detection using a magnetic probe is a promising method for sentinel lymph node biopsy. In this study, a novel handheld magnetic probe with a permanent magnet and magnetic sensor is developed to detect the sentinel lymph nodes in breast cancer patients. An outstanding feature of the probe is the precise positioning of the sensor at the magnetic null point of the magnet, leading to highly sensitive measurements unaffected by the strong ambient magnetic fields of the magnet...
January 19, 2018: Scientific Reports
N A Usov, M S Nesmeyanov, V P Tarasov
Magnetic vortices existing in soft magnetic nanoparticles with sizes larger than the single-domain diameter can be efficient nano-heaters in biomedical applications. Using micromagnetic numerical simulation we prove that in the optimal range of particle diameters the magnetization reversal of the vortices in spherical iron and magnetite nanoparticles is possible for moderate amplitudes of external alternating magnetic field, H0 < 100 Oe. In contrast to the case of superparamagnetic nanoparticles, for the vortex configuration the hysteresis loop area increases as a function of frequency...
January 19, 2018: Scientific Reports
Manikandan Krishnan, Rukshana Pervin, Kalai Selvan Ganesan, Kannan Murugesan, Govindaraj Lingannan, Akshay Kumar Verma, Parasharam M Shirage, Arumugam Sonachalam
The impact of hydrostatic pressure (P) up to 1 GPa on T c , J c and the nature of the pinning mechanism in FexNbSe2 single crystals have been investigated within the framework of the collective theory. We found that the pressure can induce a transition from the regime where pinning is controlled by spatial variation in the critical transition temperature (δT c ) to the regime controlled by spatial variation in the mean free path (δℓ). Furthermore, T c and low field J c are slightly induced, although the J c drops more rapidly at high fields than at ambient P...
January 19, 2018: Scientific Reports
Anna S Huang, Jameson A Mitchell, Suzanne N Haber, Nelly Alia-Klein, Rita Z Goldstein
Impairments in response inhibition and salience attribution (iRISA) have been proposed to underlie the clinical symptoms of drug addiction as mediated by cortico-striatal-thalamo-cortical networks. The bulk of evidence supporting the iRISA model comes from neuroimaging research that has focused on cortical and striatal influences with less emphasis on the role of the thalamus. Here, we highlight the importance of the thalamus in drug addiction, focusing on animal literature findings on thalamic nuclei in the context of drug-seeking, structural and functional changes of the thalamus as measured by imaging studies in human drug addiction, particularly during drug cue and non-drug reward processing, and response inhibition tasks...
March 19, 2018: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Zikuan Chen, Jennifer Robinson, Vince Calhoun
PURPOSE: To computationally separate dynamic brain functional BOLD responses from static background in a brain functional activity for forward fMRI signal analysis and inverse mapping. METHODS: A brain functional activity is represented in terms of magnetic source by a perturbation model: χ = χ0 +δχ, with δχ for BOLD magnetic perturbations and χ0 for background. A brain fMRI experiment produces a timeseries of complex-valued images (T2* images), whereby we extract the BOLD phase signals (denoted by δP) by a complex division...
2018: PloS One
Shima Ghasemi-Roudsari, Abbas Al-Shimary, Benjamin Varcoe, Rowena Byrom, Lorraine Kearney, Mark Kearney
BACKGROUND: Magnetocardiography (MCG) is a non-invasive technique used to measure and map cardiac magnetic fields. We describe the predictive performance of a portable prototype magnetometer designed for use in acute and routine clinical settings. We assessed the predictive ability of the measurements derived from the magnetometer for the ruling-out of healthy subjects and patients whose chest pain has a non-ischemic origin from those with ischemic heart disease (IHD). METHODS: MCG data were analyzed from a technical performance study, a pilot clinical study, and a young healthy reference group...
2018: PloS One
Jonathan Kohler, Justin A Gerber, Emma Dowd, Dan M Stamper-Kurn
We realize a spin-orbit interaction between the collective spin precession and center-of-mass motion of a trapped ultracold atomic gas, mediated by spin- and position-dependent dispersive coupling to a driven optical cavity. The collective spin, precessing near its highest-energy state in an applied magnetic field, can be approximated as a negative-mass harmonic oscillator. When the Larmor precession and mechanical motion are nearly resonant, cavity mediated coupling leads to a negative-mass instability, driving exponential growth of a correlated mode of the hybrid system...
January 5, 2018: Physical Review Letters
Krzysztof Jachymski, Tomasz Wasak, Zbigniew Idziaszek, Paul S Julienne, Antonio Negretti, Tommaso Calarco
Feshbach resonances, which allow for tuning the interactions of ultracold atoms with an external magnetic field, have been widely used to control the properties of quantum gases. We propose a scheme for using scattering resonances as a probe for external fields, showing that by carefully tuning the parameters it is possible to reach a 10^{-5}  G (or nT) level of precision with a single pair of atoms. We show that, for our collisional setup, it is possible to saturate the quantum precision bound with a simple measurement protocol...
January 5, 2018: Physical Review Letters
A A Burkov
We demonstrate that, apart from the chiral anomaly, Dirac semimetals possess another quantum anomaly, which we call the mirror anomaly and which manifests in a singular response of the Dirac semimetal to an applied magnetic field. Namely, the anomalous Hall conductivity exhibits step-function singularities when the field is rotated. We show that this phenomenon is closely analogous to the parity anomaly of (2+1)-dimensional Dirac fermions, but with mirror symmetry, which we demonstrate emerges near any Dirac point at a time reversal invariant momentum, replacing the parity symmetry...
January 5, 2018: Physical Review Letters
Insun Jo, Hao Deng, Yang Liu, L N Pfeiffer, K W West, K W Baldwin, M Shayegan
We study a bilayer GaAs hole system that hosts two distinct many-body phases at low temperatures and high perpendicular magnetic fields. The higher-density (top) layer develops a Fermi sea of composite fermions (CFs) in its half-filled lowest Landau level, while the lower-density (bottom) layer forms a Wigner crystal (WC) as its filling becomes very small. Owing to the interlayer interaction, the CFs in the top layer feel the periodic Coulomb potential of the WC in the bottom layer. We measure the magnetoresistance of the top layer while changing the bottom-layer density...
January 5, 2018: Physical Review Letters
S L Zuo, Y Zhang, L C Peng, X Zhao, R Li, H Li, J F Xiong, M He, T Y Zhao, J R Sun, F X Hu, B G Shen
The evolution of topological magnetic domains microscopically correlates the dynamic behavior of memory units in spintronic application. Nanometric bubbles with variation of spin configurations have been directly observed in a centrosymmetric hexagonal magnet (Mn0.5Ni0.5)65(Ga1-yYy)35 (y = 0.01) using Lorentz transmission electron microscopy. Magnetic bubbles instead of biskyrmions are generated due to the enhancement of quality factor Q caused by the substitution of rare-earth element Y. Furthermore, the bubble density and diversified spin configurations are systematically manipulated via combining the electric current with perpendicular magnetic fields...
January 19, 2018: Nanoscale
Marina Carotti, Vittoria Galeazzi, Francesca Catucci, Marcello Zappia, Francesco Arrigoni, Antonio Barile, Andrea Giovagnoni
With the introduction of new biologics such as anti-TNF-alpha antibodies and other therapies in the treatment of inflammatory arthritis, capable of halting joint destruction and functional disability, there are new pressures on diagnostic and prognostic imaging. Early demonstration of pre-erosive inflammatory features and monitoring of the long-term effects of treatment are becoming increasingly important. Early detection of synovitis offers advantages in terms of allowing early instigation of therapy and may allow the identification of those patients displaying more aggressive disease who might benefit from early intervention with expensive DMARD therapy...
January 19, 2018: Acta Bio-medica: Atenei Parmensis
Anke Huss, Susan Peters, Roel Vermeulen
We performed a meta-analysis to examine associations of occupational exposure to extremely-low frequency magnetic fields (ELF-MF) with amyotrophic lateral sclerosis (ALS). Epidemiologic studies were identified in EMBASE and MEDLINE, in reference lists and a specialist database. We included studies that reported risk estimates of ALS in association with occupational ELF-MF exposure. Summary relative risks (RR) or odds ratios (OR) were obtained with random effect meta-analysis, and analyses were stratified by type of exposure assessment...
January 19, 2018: Bioelectromagnetics
Antoine Delmas, Lamia Belguerras, Nicolas Weber, Freddy Odille, Cédric Pasquier, Jacques Felblinger, Pierre-André Vuissoz
A Magnetic Resonance Imaging (MRI) scanner uses three different electromagnetic fields (EMF) to produce body images: a static permanent magnetic field (MF), several pulsed magnetic gradients, and a radiofrequency pulse. As a result, any occupation that includes an MRI exposes workers to a strong MF. The World Health Organization has now given the monitoring of occupational EMF exposure a high priority. One design for a low-cost, compact MF exposure monitor (« MR exposimeter ») uses a set of three orthogonally assembled Hall sensors...
January 19, 2018: Bioelectromagnetics
Davide Bertelli, Virginia Brighenti, Lucia Marchetti, Anna Reik, Federica Pellati
Humulus lupulus L. (hop) represents one of the most cultivated crops, it being a key ingredient in the brewing process. Many health-related properties have been described for hop extracts, making this plant gain more interest in the field of pharmaceutical and nutraceutical research. Among the analytical tools available for the phytochemical characterization of plant extracts, quantitative nuclear magnetic resonance (qNMR) represents a new and powerful technique. In this ambit, the present study was aimed at the development of a new, simple, and efficient qNMR method for the metabolite fingerprinting of bioactive compounds in hop cones, taking advantage of the novel ERETIC 2 tool...
January 19, 2018: Analytical and Bioanalytical Chemistry
Lisa Rödling, Esther Magano Volz, Annamarija Raic, Katharina Brändle, Matthias Franzreb, Cornelia Lee-Thedieck
There is an urgent need for 3D cell culture systems that avoid the oversimplifications and artifacts of conventional culture in 2D. However, 3D culture within the cavities of porous biomaterials or large 3D structures harboring high cell numbers is limited by the needs to nurture cells and to remove growth-limiting metabolites. To overcome the diffusion-limited transport of such soluble factors in 3D culture, mixing can be improved by pumping, stirring or shaking, but this in turn can lead to other problems...
January 19, 2018: Advanced Healthcare Materials
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