Strong Inhomogeneity Research Articles

Upconversion on the Micrometer Scale: Impact of Local Heterogeneity.

The properties of perovskite/naphtho[2,3-a]pyrene (NaPy) upconversion devices are investigated by a combination of atomic force microscopy and photoluminescence mapping to understand the role of microscopic heterogeneity in the ensemble device properties. The results emphasize strong microscopic inhomogeneity across the perovskite/NaPy upconversion device due to local formation of NaPy microcrystals. NaPy shows emission from three distinct states in the solid state: S1' emission at 520 nm, excimer emission at 560 nm, and S1″ emission at 620 nm. Clear spatial differences in the emission spectrum under 405 nm excitation are found, highlighting that there is a strong microcrystal-to-microcrystal variation in the optical properties─emphasizing a need for multimodal measurements. Our results indicate that microcrystals with strong emission from the strongly coupled low-energy state S1″ (J-dimer) show much higher upconversion intensity than those with dominant emission from the high-energy S1' state (I-aggregate). Hence, our results suggest that microcrystals with strong emission from the low-energy state S1″ act as isolated hotspots for upconversion.

Lithospheric magnetic structure of cratonic regions in Central-Eastern China inferred from aeromagnetic anomalies: Insights into magnetization in the uppermost mantle

Most of the subcontinental lithospheric mantle (SCLM) beneath Proterozoic cratons consists of refertilized Archaean SCLM. Variations in SCLM composition and its physical properties significantly affect the stabilization and preservation of the ancient continents. In this paper, aeromagnetic data are analyzed to reveal the magnetic structure of the lithospheric mantle beneath two major Precambrian blocks in central-eastern China, i.e., the Upper Yangtze Block (UYB) and Ordos Block (OB). After being reduced to the pole, the Fourier power spectrum of the aeromagnetic anomalies is calculated to determine the depth to magnetic sources. Considering the lower spatial resolution of the power spectral analysis in dealing with the long-wavelength aeromagnetic anomalies, we applied the scale-normalized continuous wavelet transform (CWT) on the magnetic data to trace the magnetic sources, with special focus on deeper ones. Synthetical model of a magnetic layer and application to the profile data validate the effectiveness of this scale normalization scheme in improving the wavenumber/spatial resolution in the CWT scalogram.In order to present a detailed magnetic structure, we carried out 2.5D forward modeling work on the magnetic data of a 2280 km-long nearly N-S profile across the UYB and OB. Due to the inherent ambiguity in the modeling results, the CWT-based spectral analysis is successfully adopted to provide source depth constraints for the initial model. The constrained forward modeling results indicate strong inhomogeneities among main tectonic blocks of studied area, like humans have different fingerprints. The magnetization of OB is larger than that of UYB since its Archean to Paleoproterozoic metamorphic basement are widely exposed at the surface, while the Precambrian basement of UYB is mostly overlain by unmetamorphosed Sinian cover and weakly metamorphosed Neoproterozoic strata. The most interesting aspect is that deep-seated magnetic sources might reside in the uppermost mantle of UYB and OB, suggesting vertical layering in the SCLM in cold cratonic regions.

Hybrid-driven MRF seismic inversion for gas sand identification: A case study in the Yinggehai Basin

The Yinggehai Basin displays anomalies characterized by heightened levels of temperature and pressure. It represents a depositional model of a submarine fan with gravity-driven flow, demonstrating significant lateral reservoir heterogeneity and intricate spatial distribution of the gas reservoir. Identifying gas formations using elastic parameters as indicators relies on stable seismic inversion results. This requires regularization to alleviate ill-posedness in the inverse problem and to construct model features of the subsurface medium. Markov Random Field (MRF)is an effective soft-constrained regularization method. It enhances the marginal features of inversion results by penalizing the objective function with the gradient of neighborhood points. However, the standard MRF method relies only on the parameter model-driven and has poor applicability in areas with strong lateral inhomogeneity or complex depositional processes. In this research paper, we propose a novel approach to seismic inversion that integrates MRF neighborhood drive and incorporates both seismic data and a parametric model. Multi-order MRF neighborhoods are constructed by using seismic data in the horizontal direction (including horizontal diagonal) and parametric model data in the vertical direction (including vertical diagonal). The model-driven results are also utilized to couple seismic data and improve the stability of the hybrid-driven MRF inversion. In addition, we select the P-impedance as the parameter for inversion due to its heightened sensitivity towards gas formation within the study region. Consequently, we utilize the inversion results to delineate the presence of sandstone in the target layer and discern any indications of gas formation. The implementation of this method in the field has demonstrated its capability to enhance the stability of inversion outcomes, effectively integrating the lateral consistency of seismic data with the vertical precision of parametric model data. This approach significantly improves reservoir heterogeneity characterization and enhances accuracy in identifying sandstone and gas.

Low-frequency propagating and evanescent waves in strongly inhomogeneous sandwich plates

The paper aims at studying dispersion of elastic waves in a sandwich plate with the parameters, characteristic of aerogel core and hard skin layers, typical for aerospace applications including optimal design of fuselage structural components. The proposed approach relies on multiparametric analysis, taking into account the effect of strong transverse inhomogeneity. It is demonstrated that both an additional low-frequency propagating wave and a slowly decaying evanescent one appear due to a high contrast in geometric and mechanical parameters of the layers. The key findings include the derivation of two-mode asymptotic expansions of the full dispersion relation at the low-frequency limit, as well as elucidation of the non-trivial link between long-wave evanescent and propagating modes. A sophisticated composite nature of the obtained expansions involving various shortened forms is investigated. The range of validity for each of these forms over frequency and wave-number domains is evaluated. Comparison of asymptotic results with the numerical solution of the full dispersion relation is presented.

A finite difference informed random walker (FDiRW) solver for strongly inhomogeneous diffusion problems

In nature, many complex multi-physics coupling problems exhibit strong diffusivity inhomogeneity. For instance, in the context of radionuclide absorption by porous wasteform materials within a flowing waste stream, the difference of species’ diffusivity in solid and liquid phases spans by 3 ∼ 8 orders of magnitude. To solve the diffusion equations with strongly inhomogeneous diffusivity, traditional discretization-based methods, such as the Finite Difference Method (FDM), require infinitesimally small-time steps (<10-10) as high spatial resolutions are employed in most microstructure evolution processes, leading to prohibitively high computational costs. This work developed an integrated numerical approach (FDiRW: Finite Difference informed Random Walk) to tackle this challenge. The idea is that utilizing the Random Walk concept, the fast diffusion is modelled as a superposition of point source’s solution for a concentration distribution while FDM is used to obtain the point source’s solution at each node. A mesh-coarsening algorithm is developed to generate an exclusive coarse mesh for FDiRW approach to maximize its efficiency. The effectiveness of the coarse mesh-based FDiRW approach is validated by benchmarking Finite Difference solutions. Numerical results demonstrated that FDiRW achieves a remarkable 1000x computational efficiency improvement over FDM while preserving desired accuracy for a medium-sized model of 192×192×192 grids. As models scale up, a floating-point operations (PLOPs) analysis of the FDiRW algorithm reveals that its computational complexity grows quadratically in terms of the number of nodes employed in computation.

Zero-echo-time sequences in highly inhomogeneous fields.

Zero-echo-time (ZTE) sequences have proven a powerful tool for MRI of ultrashort tissues, but they fail to produce useful images in the presence of strong field inhomogeneities (14 000 ppm). Here we seek a method to correct reconstruction artifacts from non-Cartesian acquisitions in highly inhomogeneous , where the standard double-shot gradient-echo approach to field mapping fails. We present a technique based on magnetic field maps obtained from two geometric distortion-free point-wise (SPRITE) acquisitions. To this end, we employ three scanners with varying field homogeneities. These maps are used for model-based image reconstruction with iterative algebraic techniques (ART). For comparison, the same prior information is fed also to widely used Conjugate Phase (CP) algorithms. Distortions and artifacts coming from severe inhomogeneities, at the level of the encoding gradient, are largely reverted by our method, as opposed to CP reconstructions. This holds even close to the limit where intra-voxel bandwidths (determined by inhomogeneities, up to 1.2 kHz) are comparable to the encoding inter-voxel bandwidth (determined by the gradient fields, 625 Hz in this work). We have benchmarked the performance of a new method for ZTE imaging in highly inhomogeneous magnetic fields. For example, this can be exploited for dental imaging in affordable low-field MRI systems, and can be expanded for arbitrary pulse sequences and extreme magnet geometries, as in, for example, single-sided MRI.

Theoretical Procedure for Precise Evaluation of Chemical Enhancement in Molecular Surface-Enhanced Raman Scattering.

The enhancement of the molecular Raman signal in plasmon-assisted surface-enhanced Raman scattering (SERS) results from electromagnetic and chemical mechanisms, the latter determined to a large extent by the chemical interaction between the molecules and the hosting plasmonic nanoparticles. A precise quantification of the chemical mechanism in SERS based on quantum chemistry calculations is often challenging due to the interplay between the chemical and electromagnetic effects. Based on an atomistic description of the SERS signal, which includes the effect of strong field inhomogeneities, we introduce a comprehensive approach to evaluate the chemical enhancement in SERS, which conveniently removes the electromagnetic contribution inherent to any quantum calculation of the Raman polarization. Our approach uses density functional theory (DFT) and time-dependent DFT to compute the total SERS signal, together with the electromagnetic and chemical enhancement factors. We apply this framework to study the chemical enhancement of biphenyl-4,4'-dithiol embedded between two gold clusters. Although we find that for small clusters the total SERS enhancement is mainly determined by the chemical mechanism, our procedure enables removal of the electromagnetic contribution and isolation of the contribution of the bare chemical effect. This approach can be applied to reproduce and understand Raman line activation and strength in practical and challenging SERS configurations such as in plasmonic nano- and pico-cavities.

Coherence of Multidimensional Pair Production Discharges in Polar Caps of Pulsars

We report on the first self-consistent multidimensional particle-in-cell numerical simulations of nonhomogeneous pair discharges in polar caps of rotation-powered pulsars. By introducing strong inhomogeneities in the initial plasma distribution in our simulations, we analyze the degree of self-consistently emerging coherence of discharges across magnetic field lines. In 2D, we study discharge evolution for a wide range of physical parameters and boundary conditions corresponding to both the absent and free escape of charged particles from the surface of a neutron star. We also present the results of the first 3D simulations of discharges in a polar cap with a distribution of the global magnetospheric current appropriate for a pulsar with 60° inclination angle. For all parameters, we find the coherence scale of pair discharges across magnetic field lines to be of the order of the gap height. We also demonstrate that the popular “spark” model of pair discharges is incompatible with the universally adopted force-free magnetosphere model: intermittent discharges fill the entire zone of the polar cap that allows pair cascades, leaving no space for discharge-free regions. Our findings disprove the key assumption of the spark model about the existence of isolated distinct discharge columns.

Research on Phased Array Ultrasonic Imaging Method Based on Time Reversal Theory

Abstract With the wide application of additive manufacturing components and composite materials, it is of great significance to detect defects with non-destructive testing methods in the material manufacturing process and in service. Due to the strong attenuation and inhomogeneity characteristics, it is inefficient and poor imaging results to detect its internal defects by conventional ultrasonic testing methods. To improve the detection accuracy, this paper proposes an improved imaging algorithm with time reversal-total focusing method (TR-TFM) imaging technology to improve the defects detection in strongly attenuating materials. The experimental results show that the amplitude of the defect signal is increased by 8.30 dB, and compared with total focusing method (TFM), the diameter of the detected defect with TR-TFM imaging is increased from 1.20 mm to 1.60 mm, which is more adjacent to the accurate size. Meanwhile, with the sparse matrix based on FMC data, TR-TFM could obtain the same image quality with the approximate time of TFM imaging.

Reduction of green-gap effect for light-emitting diodes using InGaN-ZnGeN2-InGaN/GaN type-II MQW

In this work, the design of two multiple-quantum-wells (MQWs) green LEDs are investigated − (i) LED A with standard InGaN/GaN type I band alignment quantum wells (QWs), and (ii) LED B with InGaN-ZnGeN2-InGaN/GaN type II band alignment QWs. Using numerical program we obtain energy band diagram, carrier concentration, electric field, electroluminescence spectra and radiative-recombination-rate (RRR). Owing to presence of strong polarization field and compositional inhomogeneity in InGaN/GaN heterostructure, it is hard to obtain the high efficiency in wavelength of 500–600 nm, termed as ‘green-gap’ effect. Introduction of InGaN-ZnGeN2-InGaN QWs reduces the piezoelectric polarization field and enhances overlapping between electron-hole wave functions thereby increasing RRR. Moreover, holes are distributed uniformly in all QWs in the active region of LED that leads to improved emission efficiency. The proposed device, LED B exhibits 710 % more output optical power and less wall-plug efficiency droop is only 3.1 % in contrast to 82.4 % in LED A.

Wigner Function Method for Describing Electromagnetic Field in Plasma-Like Media with Spatial Dispersion and Resonant Dissipation

The paper gives a systematic presentation of the Wigner function method (Weyl formalism) for modeling the propagation and absorption of electromagnetic waves in anisotropic and gyrotropic dissipative media with spatial dispersion. A general kinetic equation for the Wigner function (tensor) is formulated, and its asymptotic expansion up to the second order for smoothly inhomogeneous and weakly dissipative media is constructed. As a result, a modification of the method of the kinetic equation for rays is proposed, based on the stochastic description of rays, making it possible to increase the accuracy of numerical modeling of wave problems with strong transverse inhomogeneity of the absorption coefficient without increasing the amount of calculations. The technique developed can be used to describe the propagation, absorption, and scattering of electron-cyclotron waves in high-temperature plasma of magnetic traps for controlled fusion in cases where standard modeling methods do not provide the necessary accuracy.

Magnetic skin effect in Pb(Fe _{1/2}$ Nb _{1/2}$ )O3

Relaxor-ferroelectrics display exceptional dielectric properties resulting from the underlying random dipolar fields induced by strong chemical inhomogeneity. An unusual structural aspect of relaxors is a skin-effect where the near-surface region in single crystals exhibit structures and critical phenomena that differ from the bulk. Relaxors are unique in that this skin effect extends over a macroscopic lengthscale of ∼100 μm whereas usual surface layers only extend over a few unit cells (or ∼nm). We present a muon spectroscopy study of Pb(Fe _{1/2} Nb _{1/2} )O3 (PFN) which displays ferroelectric order, including many relaxor-like dielectric properties such as a frequency broadened dielectric response, and antiferromagnetism with spatially short-range polar correlations and hence can be termed a multiferroic. In terms of the magnetic behavior determined by the Fe3+ ( S=5/2 , L ≈ 0) ions, PFN has been characterized as a unique example of a ‘cluster spin-glass’. We use variable momentum muon spectroscopy to study the depth dependence of the slow magnetic relaxations in a large 1 cm3 crystal of PFN. Zero-field positive muon spin relaxation is parameterized using a stretched exponential, indicative of a distribution of relaxation rates of the Fe3+ spins. This bandwidth of frequencies changes as a function of muon momentum, indicative of a change in the Fe3+ relaxation rates as a function of muon implantation depth in our single crystal. Using negative muon elemental analysis, we find small-to-no measurable change in the Fe3+/Nb5+ concentration with depth implying that chemical concentration alone cannot account for the change in the relaxational dynamics. PFN displays an analogous magnetic skin effect reported to exist in the structural properties of relaxor-ferroelectrics.

The inclined conductive column effect: a new simple model for magnetotelluric anomalous phases

SUMMARY Magnetotelluric data are sometimes accompanied by ‘anomalous’ impedance phases ($\phi $xy and $\phi $yx) in the off-diagonal components deviating from the first (0° &amp;lt; $\phi $xy &amp;lt; 90°) or third (−180° &amp;lt; $\phi $yx &amp;lt; −90°) quadrant, especially in long-period bands. This phenomenon is called the phases out-of-quadrant (POQ). The POQ poses a challenge in magnetotelluric modelling because simple 1-D or 2-D models cannot explain it. Previous studies have reported that strong inhomogeneity, anisotropy, or particular 3-D structures, such as the L-shaped or cross-shaped conductors, could explain the POQ. Aside from these models, we have discovered that a slanted columnar conductor also generates the POQ. Our systematic investigation through the synthetic forward modelling of an inclined conductive column with a varying geometry showed that the inclination angle and the column length may affect the POQ appearance. We investigated herein the behaviour of the electric currents around the inclined conductive column embedded in a resistive half-space. We found that the induced electric field in the region with the POQ tends to point in the opposite direction to the surrounding vectors. This result can reasonably explain the inverted phase in long-period bands. Furthermore, we confirmed that current is sucked into one end of the column, but discharged from the other end, suggesting that the column works as a current channel. The localized reverse vectors are associated with the current channelling along the inclined conductor, which generates the POQ. A volcanic conduit within a resistive host rock is one of the typical field examples of such an inclined channel. Our study suggests that the POQ is a helpful clue in imaging the geometry of a volcanic magma plumbing system through magnetotelluric surveys.

Turbulent structure and circulation inside different planar contractions

We study the turbulent circulation and coherent vortical structures for flow through three separate two-dimensional planar 4:1 contractions, where the turbulence is subjected to different rates of mean strain. We use four high-speed video cameras for Lagrangian particle tracking velocimetry, to measure time-resolved velocity fields in volumes inside the contractions. We identify the coherent vortical structures and quantify their alignment with the mean strain. The intermediate strain contraction shows the strongest alignment. We also compute circulations around square loops in three perpendicular planes, to form a “circulation vector,” whose instantaneous alignment mirrors that of the coherent structures, with strong inhomogeneities between circulation components at the exit of the contractions. The circulation probability density functions show extended exponential tails for the smallest loops, with more Gaussian shapes in the inertial range.

Spreading dynamics of a microgel particle-laden thermosensitive polymer drop along smooth and nanofiber surfaces

The research focuses on the influence of 300-μm microgel particles in an aqueous solution of a thermosensitive biopolymer on the spreading and deformation of 3.7-mm drops. The drops impact a smooth hydrophilic and a rough hydrophobic surface. A mass fraction of microgel particles varies in a range of 0–0.2. A universal physical model of the spreading of thermosensitive polymer drops laden with microgel particles along surfaces with significantly different roughness is proposed. It explains the strong inhomogeneity of the contact line stretching due to the deceleration of the continuous phase flow by microgel particles and the increased flow vorticity because of the addition of the surface roughness factor. The validity of the proposed physical model is proven by qualitative and quantitative assessments of the contact line deformation when spreading. An empirical expression for the maximum spreading factor is derived, taking into account the properties of liquids, wall roughness, and microgel particle concentration; it reliably predicts when Re≈110−3100, the surface roughness is 0.5–125 nm, Ca=4.5×10−7, and the number of microgel particles in drops is up to 100. The expression was successfully tested during the modeling of arbitrary surface roughness and the increased concentration of microgel particles relative to those considered in experiments during the formation of a biopolymer layer. When developing the method of additive manufacturing of a functional layer, a practical correlation was established between the volume content of microgel particles, acting as potential containers for living cells, in a drop and the area of the biopolymer layer.

Fat suppression using frequency-sweep RF saturation and iterative reconstruction.

To introduce an alternative idea for fat suppression that is suited both for low-field applications where conventional fat-suppression approaches become ineffective due to narrow spectral separation and for applications with strong B0 homogeneities. Separation of fat and water is achieved by sweeping the frequency of RF saturation pulses during continuous radial acquisition and calculating frequency-resolved images using regularized iterative reconstruction. Voxel-wise signal-response curves are extracted that reflect tissue's response to RF saturation at different frequencies and allow the classification into fat or water. This information is then utilized to generate water-only composite images. The principle is demonstrated in free-breathing abdominal and neck examinations using stack-of-stars 3D balanced SSFP (bSSFP) and gradient-recalled echo (GRE) sequences at 0.55 and 3T. Moreover, a potential extension toward quantitative fat/water separation is described. Experiments with a proton density fat fraction (PDFF) phantom validated the reliability of fat/water separation using signal-response curves. As demonstrated for abdominal imaging at 0.55T, the approach resulted in more uniform fat suppression without loss of water signal and in improved CSF-to-fat signal ratio. Moreover, the approach provided consistent fat suppression in 3T neck exams where conventional spectrally-selective fat saturation failed due to strong local B0 inhomogeneities. The feasibility of simultaneous fat/water quantification has been demonstrated in a PDFF phantom. The proposed principle achieves reliable fat suppression in low-field applications and adapts to high-field applications with strong B0 inhomogeneity. Moreover, the principle potentially provides a basis for developing an alternative approach for PDFF quantification.

Pore structure characterization and permeability prediction of uranium-bearing sandstone based on digital core

The permeability of the ore-bearing layer is an important indicator affecting the in-situ leaching (ISL) of uranium-bearing sandstone, which is related to various factors such as pore shape, distribution, and size. In order to study the effect of pore structure on seepage in low-permeability uranium-bearing sandstone, CT scanning tests were conducted to create a 3D digital core based on scanning images and to calculate the fractal dimension using the box counting dimension method, which integrated fractal theory to define the core samples' pore structure. The permeability prediction was realized based on the porosity-permeability model and the fractal theory model. Results indicated that this type of sandstone is obviously characterized by pore connectivity, large differences in distribution, and strong microscopic inhomogeneity. The pores are dominated by micro- and nano-pores, as well as small pores, accounting for 90 %; macropores are few in number, but the diameters of their single pores are large. The distribution of pore structure in this type of sandstone exhibits a good fractal characteristic; the three-dimensional fractal dimensionality is 2.044–2.310. The porosity-permeability model was established, and permeability prediction was realized by combining the fractal theory to provide theoretical support for determining the values of well field parameters in ISL.

Direct numerical simulations of suspension of disk-shaped particles

This study investigates the dynamics of disk-shaped particles using direct numerical simulations with the smoothed profile method for rigid particles. These disk-shaped particles are formed by joining the spherical beads and are allowed to settle/sediment in a Newtonian fluid. The concentration effects of the mono-dispersed particles are studied in the Stokes regime, varying the volume fraction (ϕ) from 0.0003 to 0.1. Strong inhomogeneities in the system were noticed, producing multiple peaks in the radial distribution function caused by the orientation preference of particles, while settling. A histogram analysis of the particles' orientation angle suggests that particles prefer horizontal orientation at very low volume fractions and then start orienting vertically with subsequent increase in the volume fraction. Average settling velocity increases initially till volume fraction 0.001, creating a local maxima, and then decreases monotonically following the Richardson–Zaki law. It was also found that velocity fluctuations increased with increasing volume fraction, following the ϕ1/3 trend. These fluctuations are smaller than those of rod-like particles and larger than spherical particles, though the qualitative trend is quite similar.

Enhancing Whole-Brain Magnetic Field Homogeneity for 3D-Magnetic Resonance Spectroscopic Imaging with a Novel Unified Coil: A Preliminary Study.

The spectral quality of magnetic resonance spectroscopic imaging (MRSI) can be affected by strong magnetic field inhomogeneities, posing a challenge for 3D-MRSI's widespread clinical use with standard scanner-equipped 2nd-order shim coils. To overcome this, we designed an empirical unified shim-RF head coil (32-ch RF receive and 51-ch shim) for 3D-MRSI improvement. We compared its shimming performance and 3D-MRSI brain coverages against the standard scanner shim (2nd-order spherical harmonic (SH) shim coils) and integrated parallel reception, excitation, and shimming (iPRES) 32-ch AC/DC head coil. We also simulated a theoretical 3rd-, 4th-, and 5th-order SH shim as a benchmark to assess the UNIfied shim-RF coil (UNIC) improvements. In this preliminary study, the whole-brain coverage was simulated by using B0 field maps of twenty-four healthy human subjects (n = 24). Our results demonstrated that UNIC substantially improves brain field homogeneity, reducing whole-brain frequency standard deviations by 27% compared to the standard 2nd-order scanner shim and 17% compared to the iPRES shim. Moreover, UNIC enhances whole-brain coverage of 3D-MRSI by up to 34% compared to the standard 2nd-order scanner shim and up to 13% compared to the iPRES shim. UNIC markedly increases coverage in the prefrontal cortex by 147% and 47% and in the medial temporal lobe and temporal pole by 29% and 13%, respectively, at voxel resolutions of 1.4 cc and 0.09 cc for 3D-MRSI. Furthermore, UNIC effectively reduces variations in shim quality and brain coverage among different subjects compared to scanner shim and iPRES shim. Anticipated advancements in higher-order shimming (beyond 6th order) are expected via optimized designs using dimensionality reduction methods.

Thermal stimulus task fMRI in the cervical spinal cord at 7 Tesla.

Although functional magnetic resonance imaging (fMRI) is widely applied in the brain, fMRI of the spinal cord is more technically demanding. Proximity to the vertebral column and lungs results in strong spatial inhomogeneity and temporal fluctuations in B0 . Increasing field strength enables higher spatial resolution and improved sensitivity to blood oxygenation level-dependent (BOLD) signal, but amplifies the effects of B0 inhomogeneity. In this work, we present the first task fMRI in the spinal cord at 7 T. Further, we compare the performance of single-shot and multi-shot 2D echo-planar imaging (EPI) protocols, which differ in sensitivity to spatial and temporal B0 inhomogeneity. The cervical spinal cords of 11 healthy volunteers were scanned at 7 T using single-shot 2D EPI at 0.75 mm in-plane resolution and multi-shot 2D EPI at 0.75 and 0.6 mm in-plane resolutions. All protocols used 3 mm slice thickness. For each protocol, the BOLD response to 13 10-s noxious thermal stimuli applied to the right thumb was acquired in a 10-min fMRI run. Image quality, temporal signal to noise ratio (SNR), and BOLD activation (percent signal change and z-stat) at both individual- and group-level were evaluated between the protocols. Temporal SNR was highest in single-shot and multi-shot 0.75 mm protocols. In group-level analyses, activation clusters appeared in all protocols in the ipsilateral dorsal quadrant at the expected C6 neurological level. In individual-level analyses, activation clusters at the expected level were detected in some, but not all subjects and protocols. Single-shot 0.75 mm generally produced the highest mean z-statistic, while multi-shot 0.60 mm produced the best-localized activation clusters and the least geometric distortion. Larger than expected within-subject segmental variation of BOLD activation along the cord was observed. Group-level sensory task fMRI of the cervical spinal cord is feasible at 7 T with single-shot or multi-shot EPI. The best choice of protocol will likely depend on the relative importance of sensitivity to activation versus spatial localization of activation for a given experiment. PRACTITIONER POINTS: First stimulus task fMRI results in the spinal cord at 7 T. Single-shot 0.75 mm 2D EPI produced the highest mean z-statistic. Multi-shot 0.60 mm 2D EPI provided the best-localized activation and least distortion.