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Orest Pavlosiuk, Przemysław Swatek, Piotr Wiśniewski
Very strong magnetoresistance and a resistivity plateau impeding low temperature divergence due to insulating bulk are hallmarks of topological insulators and are also present in topological semimetals where the plateau is induced by magnetic field, when time-reversal symmetry (protecting surface states in topological insulators) is broken. Similar features were observed in a simple rock-salt-structure LaSb, leading to a suggestion of the possible non-trivial topology of 2D states in this compound. We show that its sister compound YSb is also characterized by giant magnetoresistance exceeding one thousand percent and low-temperature plateau of resistivity...
December 9, 2016: Scientific Reports
An Thanh Vu, Keith Jamison, Matthew F Glasser, Stephen M Smith, Timothy Coalson, Steen Moeller, Edward J Auerbach, Kamil Ugurbil, Essa Yacoub
Whole-brain functional magnetic resonance imaging (fMRI), in conjunction with multiband acceleration, has played an important role in mapping the functional connectivity throughout the entire brain with both high temporal and spatial resolution. Ultrahigh magnetic field strengths (7T and above) allow functional imaging with even higher functional contrast-to-noise ratios for improved spatial resolution and specificity compared to traditional field strengths (1.5T and 3T). High-resolution 7T fMRI, however, has primarily been constrained to smaller brain regions given the amount of time it takes to acquire the number of slices necessary for high resolution whole brain imaging...
November 25, 2016: NeuroImage
Suhyung Park, Jaeseok Park
PURPOSE: To develop a novel, simultaneous multislice reconstruction method that exploits Hankel subspace learning (SMS-HSL) for aliasing separation in the slice direction. METHODS: An SMS signal model with the Hankel-structured matrix was proposed. To efficiently suppress interslice leakage artifacts from a signal subspace perspective, a null space was learned from the reference data combined over all slices other than a slice of interest using singular value decomposition...
November 8, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Jie Xu, Ziyi Zhao, Haochi Yu, Le Yang, Peng Gou, Jun Cao, Yuexin Zou, Jie Qian, Tianjun Shi, Qijun Ren, Zhenghua An
A triple-band perfect plasmonic metamaterial absorber based on a metal/insulator/metal (MIM) structure is designed. A new freedom through tuning the thicknesses of each ring structures is introduced to realize a quasi-three-dimensional perfect absorber at three extinction wavelengths by using the finite difference time domain method. The physical machine is explained by the time domain field analyses and the coupled mode theory. The characteristics of the absorber make our proposed strategy applicable for the design of more general multiband and broadband perfect absorbers...
October 31, 2016: Optics Express
William A Grissom, Kawin Setsompop, Samuel A Hurley, Jeffrey Tsao, Julia V Velikina, Alexey A Samsonov
PURPOSE: To advance the best solutions to two important RF pulse design problems with an open head-to-head competition. METHODS: Two sub-challenges were formulated in which contestants competed to design the shortest simultaneous multislice (SMS) refocusing pulses and slice-selective parallel transmission (pTx) excitation pulses, subject to realistic hardware and safety constraints. Short refocusing pulses are needed for spin echo SMS imaging at high multiband factors, and short slice-selective pTx pulses are needed for multislice imaging in ultra-high field MRI...
October 27, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Allison C Nugent, Bruce Luber, Frederick W Carver, Stephen E Robinson, Richard Coppola, Carlos A Zarate
Recently, independent components analysis (ICA) of resting state magnetoencephalography (MEG) recordings has revealed resting state networks (RSNs) that exhibit fluctuations of band-limited power envelopes. Most of the work in this area has concentrated on networks derived from the power envelope of beta bandpass-filtered data. Although research has demonstrated that most networks show maximal correlation in the beta band, little is known about how spatial patterns of correlations may differ across frequencies...
October 22, 2016: Human Brain Mapping
S Kasahara, T Yamashita, A Shi, R Kobayashi, Y Shimoyama, T Watashige, K Ishida, T Terashima, T Wolf, F Hardy, C Meingast, H V Löhneysen, A Levchenko, T Shibauchi, Y Matsuda
The physics of the crossover between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein condensate (BEC) limits gives a unified framework of quantum-bound (superfluid) states of interacting fermions. This crossover has been studied in the ultracold atomic systems, but is extremely difficult to be realized for electrons in solids. Recently, the superconducting semimetal FeSe with a transition temperature Tc=8.5 K has been found to be deep inside the BCS-BEC crossover regime. Here we report experimental signatures of preformed Cooper pairing in FeSe, whose energy scale is comparable to the Fermi energies...
2016: Nature Communications
An T Vu, Jeffrey S Phillips, Kendrick Kay, Matthew E Phillips, Matthew R Johnson, Svetlana V Shinkareva, Shannon Tubridy, Rachel Millin, Murray Grossman, Todd Gureckis, Rajan Bhattacharyya, Essa Yacoub
The blood-oxygen-level-dependent (BOLD) signal measured in functional magnetic resonance imaging (fMRI) experiments is generally regarded as sluggish and poorly suited for probing neural function at the rapid timescales involved in sentence comprehension. However, recent studies have shown the value of acquiring data with very short repetition times (TRs), not merely in terms of improvements in contrast to noise ratio (CNR) through averaging, but also in terms of additional fine-grained temporal information...
May 2016: Cognitive Neuropsychology
Adam M Chekroud, Geetha Anand, Jean Yong, Michael Pike, Holly Bridge
AIM: Opsoclonus-myoclonus syndrome (OMS) is a rare, poorly understood condition that can result in long-term cognitive, behavioural, and motor sequelae. Several studies have investigated structural brain changes associated with this condition, but little is known about changes in function. This study aimed to investigate changes in brain functional connectivity in patients with OMS. METHOD: Seven patients with OMS and 10 age-matched comparison participants underwent 3T magnetic resonance imaging (MRI) to acquire resting-state functional MRI data (whole-brain echo-planar images; 2mm isotropic voxels; multiband factor ×2) for a cross-sectional study...
September 23, 2016: Developmental Medicine and Child Neurology
Zhoushen Huang, Alexander V Balatsky
A sudden quantum quench of a Bloch band from one topological phase toward another has been shown to exhibit an intimate connection with the notion of a dynamical quantum phase transition (DQPT), where the returning probability of the quenched state to the initial state-i.e., the Loschmidt echo-vanishes at critical times {t^{*}}. Analytical results to date are limited to two-band models, leaving the exact relation between topology and DQPT unclear. In this Letter, we show that, for a general multiband system, a robust DQPT relies on the existence of nodes (i...
August 19, 2016: Physical Review Letters
Hyejin Ryu, Milinda Abeykoon, Emil Bozin, Yosuke Matsumoto, S Nakatsuji, C Petrovic
We report on the evidence for the multiband electronic transport in α-YbAlB4 and α-Yb0.81(2)Sr0.19(3)AlB4. Multiband transport reveals itself below 10 K in both compounds via Hall effect measurements, whereas anisotropic magnetic ground state sets in below 3 K in α-Yb0.81(2)Sr0.19(3)AlB4. Our results show that Sr(2+) substitution enhances conductivity, but does not change the quasiparticle mass of bands induced by heavy fermion hybridization.
October 26, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Huatao Zhu, Rong Wang, Tao Pu, Tao Fang, Peng Xiang, Jilin Zheng, Yeteng Tang, Dalei Chen
We propose and experimentally demonstrate an optical stealth transmission system over a 200 GHz-grid wavelength-division multiplexing (WDM) network. The stealth signal is processed by spectral broadening, temporal spreading, and power equalizing. The public signal is suppressed by multiband notch filtering at the stealth channel receiver. The interaction between the public and stealth channels is investigated in terms of public-signal-to-stealth-signal ratio, data rate, notch-filter bandwidth, and public channel number...
August 10, 2016: Applied Optics
Salvatore Vitale
With the discovery of the binary-black-hole (BBH) coalescence GW150914 the era of gravitational-wave (GW) astronomy has started. It has recently been shown that BBH with masses comparable to or higher than GW150914 would be visible in the Evolved Laser Interferometer Space Antenna (eLISA) band a few years before they finally merge in the band of ground-based detectors. This would allow for premerger electromagnetic alerts, dramatically increasing the chances of a joint detection, if BBHs are indeed luminous in the electromagnetic band...
July 29, 2016: Physical Review Letters
Enrico Barausse, Nicolás Yunes, Katie Chamberlain
The aLIGO detection of the black-hole binary GW150914 opens a new era for probing extreme gravity. Many gravity theories predict the emission of dipole gravitational radiation by binaries. This is excluded to high accuracy in binary pulsars, but entire classes of theories predict this effect predominantly (or only) in binaries involving black holes. Joint observations of GW150914-like systems by aLIGO and eLISA will improve bounds on dipole emission from black-hole binaries by 6 orders of magnitude relative to current constraints, provided that eLISA is not dramatically descoped...
June 17, 2016: Physical Review Letters
M Majumder, A Ghoshray, P Khuntia, C Mazumdar, A Poddar, M Baenitz, K Ghoshray
Magnetization, resistivity and (11)B, (59)Co NMR measurements have been performed on the Pauli paramagnet [Formula: see text], and the superconductors [Formula: see text] ([Formula: see text] K) and [Formula: see text] ([Formula: see text] K). The site selective NMR experiment reveals the multiband nature of the Fermi surface in these systems. The temperature independent Knight shift and 1/T 1 T clearly indicate the absence of correlated low energy magnetic spin-fluctuations in the normal state, which is in contrast to other Fe-based pnictides...
September 1, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Alberto Sesana
The black hole binary (BHB) coalescence rates inferred from the Advanced LIGO detection of GW150914 imply an unexpectedly loud gravitational-wave (GW) sky at millihertz frequencies accessible to the Evolved Laser Interferometer Space Antenna (eLISA), with several outstanding consequences. First, up to thousands of BHBs will be individually resolvable by eLISA; second, millions of nonresolvable BHBs will build a confusion noise detectable with a signal-to-noise ratio of a few to hundreds; third-and perhaps most importantly-up to hundreds of BHBs individually resolvable by eLISA will coalesce in the Advanced LIGO band within 10 y...
June 10, 2016: Physical Review Letters
Rabih Al Rahal Al Orabi, Bruno Fontaine, Regis Gautier, Patrick Gougeon, Philippe Gall, Yohan Bouyrie, Anne Dauscher, Christophe Candolfi, Bertrand Lenoir
Mo-based cluster compounds are promising materials for high-temperature thermoelectric applications due to their intrinsic, extremely low thermal conductivity values. In this study, polycrystalline cluster compounds Cs2CuxMo12Se14 were prepared for a wide range of Cu contents (0 ≤ x ≤ 2). All samples crystallize isostructurally in the trigonal space group R3̅. The position of the Cu atoms in the unit cell was determined by X-ray diffraction on a single-crystalline specimen indicating that these atoms fill the empty space between the Mo-Se clusters...
July 5, 2016: Inorganic Chemistry
Hiroshi Hayasaka, Yuki Fuseya
The ratio of the Zeeman splitting to the cyclotron energy ([Formula: see text]), which characterizes the relative strength of the spin-orbit interaction in crystals, is examined for the narrow gap IV-VI semiconductors PbTe, SnTe, and their alloy Pb1-x Sn x Te on the basis of the multiband [Formula: see text] theory. The inverse mass α, the g-factor g, and M are calculated numerically by employing the relativistic empirical tight-binding band calculation. On the other hand, a simple but exact formula of M is obtained for the six-band model based on the group theoretical analysis...
August 10, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Rasim Boyacioğlu, Jenni Schulz, David G Norris
PURPOSE: To propose the technique multiband echo-shifted (MESH) echo planar imaging (EPI), which combines the principles of echo-shifted acquisition for two-dimensional multislice EPI, with both in-plane and multiband acceleration by means of partial parallel imaging techniques. METHODS: MESH EPI is suitable for functional MRI (fMRI) in situations where there is sufficient time to insert an additional EPI readout in the dead time between slice selection and the standard EPI readout...
June 14, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
P K Nag, R Schlegel, D Baumann, H-J Grafe, R Beck, S Wurmehl, B Büchner, C Hess
A non-trivial temperature evolution of superconductivity including a temperature-induced phase transition between two superconducting phases or even a time-reversal symmetry breaking order parameter is in principle expected in multiband superconductors such as iron-pnictides. Here we present scanning tunnelling spectroscopy data of LiFeAs which reveal two distinct superconducting phases: at = 18 K a partial superconducting gap opens, evidenced by subtle, yet clear features in the tunnelling spectra, i.e...
2016: Scientific Reports
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