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Xingfeng Shao, Yi Wang, Steen Moeller, Danny J J Wang
PURPOSE: To present a constrained slice-dependent (CSD) background-suppression (BS) scheme in 2D arterial spin labeling (ASL) using simultaneous multislice acquisition with blipped-CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration). METHODS: Background suppression for 2D acquisition is challenging because of the multiple nulling points required for sequential slice readout. Constrained slice-dependent BS exploits the simultaneous multislice technique to reduce the readout duration, and uses slice-dependent premodulation pulses to achieve BS across slice groups...
February 15, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Jun Geng, Weiyu Xu, Lifeng Lai
Spectrum sensing is a key technology enabling the cognitive radio system. In this paper, the problem of how to quickly and accurately find an unoccupied channel from a large amount of potential channels is considered. The cognitive radio system under consideration is equipped with a narrow band sensor, hence it can only sense those potential channels in a sequential manner. In this scenario, we propose a novel two-stage mixed-observation sensing strategy. In the first stage, which is named as scanning stage, the sensor observes a linear combination of the signals from a pair of channels...
November 15, 2016: IEEE Transactions on Signal Processing: a Publication of the IEEE Signal Processing Society
C Minot, J M Moison, S Guilet, E Cambril, A Levenson, N Belabas
Segmented strip-loaded waveguide arrays are investigated within a rigorous square lattice photonic crystal model. We derive a full multiband discrete diffraction approach for near-axial injection in the direction of a lattice vector. We obtain an effective waveguide array picture, with quasi-linear dependence on the segmentation ratio in a simplified single-band scheme. Our results are validated by beam deviation experiments. Such a diffraction framework allows for efficient shaping of the phase map in waveguide arrays and enriches the engineering toolkit of photonic crystals with the in-plane free propagation structures of discrete photonics...
February 1, 2017: Optics Letters
Zhiqiang Mu, Haochi Yu, Miao Zhang, Aimin Wu, Gongmin Qi, Paul K Chu, Zhenghua An, Zengfeng Di, Xi Wang
Besides the well-known quantum confinement effect, hot luminescence from indirect bandgap Si provides a new and promising approach to realize monolithically integrated silicon optoelectronics due to phonon-assisted light emission. In this work, multiband hot photoluminescence is generated from Si nanowire arrays by introducing trapezoid-shaped nanocavities that support hybrid photonic-plasmonic modes. By continuously adjusting the geometric parameters of the Si nanowires with trapezoidal nanocavities, the multiband hot photoluminescence can be tuned in the range from visible to near infrared independent of the excitation laser wavelength...
January 30, 2017: Nano Letters
Samy Abo Seada, Anthony N Price, Joseph V Hajnal, Shaihan J Malik
PURPOSE: Multiband pulses are characterized by highly temporally modulated waveforms. Rapid phase or frequency modulation can be extremely demanding on the performance of radiofrequency (RF) pulse generation, which can lead to errors that can be avoided if pulses are restricted to amplitude modulation (AM) only. In this work, three existing multiband pulse design techniques are modified to produce AM waveforms. THEORY AND METHODS: Multiband refocusing pulses were designed using phase optimization, time shifting, and root flipping...
January 17, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
Md Rabiul Islam, Md Molla, Masaki Nakanishi, Toshihisa Tanaka
OBJECTIVE: Recently developed effective methods for detection commands of steady-state visual evoked potential (SSVEP)-based brain-computer interface (BCI) that need calibration for visual stimuli, which cause more time and fatigue prior to the use, as the number of commands increases. This paper develops a novel unsupervised method based on canonical correlation analysis (CCA) for accurate detection of stimulus frequency. APPROACH: A novel unsupervised technique termed as binary subband CCA (BsCCA) is implemented in a multiband approach to enhance the frequency recognition performance of SSVEP...
January 10, 2017: Journal of Neural Engineering
S Maiti, T A Maier, T Böhm, R Hackl, P J Hirschfeld
In unconventional superconductors, understanding the form of the pairing interaction is the primary goal. In this regard, Raman spectroscopy is a very useful tool, as it identifies the ground state and also the subleading pairing channels by probing collective modes. Here, we propose a general theory for a multiband Raman response and identify new features in the spectrum that can provide a robust test for a pairing theory. We identify multiple Bardasis-Schrieffer type collective modes and connect the weights of these modes to the subleading gap structures within a microscopic pairing theory...
December 16, 2016: Physical Review Letters
Yun Jiang, Dan Ma, Himanshu Bhat, Huihui Ye, Stephen F Cauley, Lawrence L Wald, Kawin Setsompop, Mark A Griswold
PURPOSE: The purpose of this study is to accelerate an MR fingerprinting (MRF) acquisition by using a simultaneous multislice method. METHODS: A multiband radiofrequency (RF) pulse was designed to excite two slices with different flip angles and phases. The signals of two slices were driven to be as orthogonal as possible. The mixed and undersampled MRF signal was matched to two dictionaries to retrieve T1 and T2 maps of each slice. Quantitative results from the proposed method were validated with the gold-standard spin echo methods in a phantom...
December 26, 2016: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
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 Uğurbil, 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...
February 2017: 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
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