Fictitious Field Research Articles

Infantile status epilepticus disrupts myelin development

Temporal lobe epilepsy (TLE) is the most prevalent type of epilepsy in adults; it often starts in infancy or early childhood. Although TLE is primarily considered to be a grey matter pathology, a growing body of evidence links this disease with white matter abnormalities. In this study, we explore the impact of TLE onset and progression in the immature brain on white matter integrity and development utilising the rat model of Li-pilocarpine-induced TLE at the 12th postnatal day (P). Diffusion tensor imaging (DTI) and Black-Gold II histology uncovered disruptions in major white matter tracks (corpus callosum, internal and external capsules, and deep cerebral white matter) spreading through the whole brain at P28. These abnormalities were mostly not present any longer at three months after TLE induction, with only limited abnormalities detectable in the external capsule and deep cerebral white matter. Relaxation Along a Fictitious Field in the rotating frame of rank 4 indicated that white matter changes observed at both timepoints, P28 and P72, are consistent with decreased myelin content. The animals affected by TLE-induced white matter abnormalities exhibited increased functional connectivity between the thalamus and medial prefrontal and somatosensory cortex in adulthood. Furthermore, histological analyses of additional animal groups at P15 and P18 showed only mild changes in white matter integrity, suggesting a gradual age-dependent impact of TLE progression. Taken together, TLE progression in the immature brain distorts white matter development with a peak around postnatal day 28, followed by substantial recovery in adulthood. This developmental delay might give rise to cognitive and behavioural comorbidities typical for early-onset TLE.

Whole Brain Adiabatic T1rho and Relaxation Along a Fictitious Field Imaging in Healthy Volunteers and Patients With Multiple Sclerosis: Initial Findings

BackgroundParametric maps of adiabatic T1ρADIAB (A) TRAFF2 (B) of a 37‐year‐old female are shown (contrast adapted for visualization, same scaling as Fig. 2) as well as the white matter (C) and gray matter (D) masks overlaid over T1‐weighted images BY Jambor et al. (864–877) image

Accurate measurement of the residual field in a magnetic shield using optically pumped 133Cs atoms

Determining the residual field in a magnetic shield is essential in quantum measurement. However, it faces some problems which limit the measuring accuracy. In order to overcome the main problems for the measuring method based on magnetic resonance, a method which detects the electron paramagnetic resonance frequency of 133Cs atoms is reported. By using a rotating exciting magnetic field and choosing appropriate frequency of probe light, the influences of the Bloch-Siegert effect on the measurement of the residual field is eliminated, and by extracting the sums of the residual field and the fictitious field caused by light shifts under different pump light powers and using a second-degree polynomial fitting, the influences of light shifts on the measurement of the residual field is eliminated, thus the residual field is obtained accurately. The test results demonstrate that a high measuring accuracy of 0.01 nT can be achieved for this method.

Bogoliubov-Fermi surface with inversion symmetry and electron-electron interactions: Relativistic analogies and lattice theory

We show that the general low-energy Bogoliubov-de Genness Hamiltonian in a multiband superconductor with broken time reversal and preserved inversion symmetry is a generator of real four-dimensional representation of $SO(4)$. In the particular representation such an effective Hamiltonian is a purely imaginary matrix, and it is proportional to the antisymmetric tensor of a fictitious electromagnetic field which one can define in the momentum space. The quantum time evolution of the low-energy quasiparticle state becomes this way closely related to the classical relativistic motion of a charged particle in the presence of the Lorentz force that would be derived from such an electromagnetic field configuration. The condition for the emergence of a Bogoliubov-Fermi surface can then be understood as orthogonality of the fictitious electric and magnetic fields, which would allow zero Lorentz force. The corresponding zero-energy eigenstates are identified as the physical timelike and the unphysical spacelike solutions of the Lorentz force equation. We study the looming instability of the inversion-symmetric Bogoliubov-Fermi surface in presence of electron-electron interaction by formulating a concrete interacting model on the Lieb lattice that features the requisite $SO(4)$ kinetic energy term together with nearest-neighbor two-body repulsion. The latter is shown to favor dynamical breaking of the inversion symmetry. The inversion symmetry in our lattice model indeed becomes spontaneously broken at zero temperature at infinitesimal repulsion, with the original Bogoliubov-Fermi surface deformed and reduced in size. General features of this symmetry breaking phenomenon are discussed and a comparison with other works in literature is presented.

RAFF-4, Magnetization Transfer and Diffusion Tensor MRI of Lysophosphatidylcholine Induced Demyelination and Remyelination in Rats.

Remyelination is a naturally occurring response to demyelination and has a central role in the pathophysiology of multiple sclerosis and traumatic brain injury. Recently we demonstrated that a novel MRI technique entitled Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAFFn) achieved exceptional sensitivity in detecting the demyelination processes induced by lysophosphatidylcholine (LPC) in rat brain. In the present work, our aim was to test whether RAFF4, along with magnetization transfer (MT) and diffusion tensor imaging (DTI), would be capable of detecting the changes in the myelin content and microstructure caused by modifications of myelin sheets around axons or by gliosis during the remyelination phase after LPC-induced demyelination in the corpus callosum of rats. We collected MRI data with RAFF4, MT and DTI at 3 days after injection (demyelination stage) and at 38 days after injection (remyelination stage) of LPC (n = 12) or vehicle (n = 9). Cell density and myelin content were assessed by histology. All MRI metrics detected differences between LPC-injected and control groups of animals in the demyelination stage, on day 3. In the remyelination phase (day 38), RAFF4, MT parameters, fractional anisotropy, and axial diffusivity detected signs of a partial recovery consistent with the remyelination evident in histology. Radial diffusivity had undergone a further increase from day 3 to 38 and mean diffusivity revealed a complete recovery correlating with the histological assessment of cell density attributed to gliosis. The combination of RAFF4, MT and DTI has the potential to differentiate between normal, demyelinated and remyelinated axons and gliosis and thus it may be able to provide a more detailed assessment of white matter pathologies in several neurological diseases.

Docetaxel chemotherapy response in PC3 prostate cancer mouse model detected by rotating frame relaxations and water diffusion.

MRI is a common method of prostate cancer diagnosis. Several MRI-derived markers, including the apparent diffusion coefficient (ADC) based on diffusion-weighted imaging, have been shown to provide values for prostate cancer detection and characterization. The hypothesis of the study was that docetaxel chemotherapy response could be picked up earlier with rotating frame relaxation times TRAFF2 and TRAFF4 than with the continuous wave T1ρ , adiabatic T1ρ , adiabatic T2ρ , T1 , T2 or water ADC. Human PC3 prostate cancer cells expressing a red fluorescent protein were implanted in 21 male mice. Docetaxel chemotherapy was given once a week starting 1 week after cell implantation for 10 randomly selected mice, while the rest served as a control group (n = 11). The MRI consisted of relaxation along a fictitious field (RAFF) in the second (RAFF2) and fourth (RAFF4) rotating frames, T1 and T2 , continuous wave T1ρ , adiabatic T1ρ and adiabatic T2ρ relaxation time measurements and water ADC. MRI was conducted at 7 T, once a week up to 4 weeks from cell implantation. The tumor volume was monitored using T2 -weighted MRI and optical imaging. The histology was evaluated after the last imaging time point. Significantly reduced RAFFn, T1ρ, T2ρ and conventional relaxation times 4 weeks after tumor implantation were observed in the treated tumors compared with the controls. The clearest short- and long-term responses were obtained with T1 , while no clear improvement in response to treatment was detected with novel methods compared with conventional methods or with RAFFn compared with all others. The tumor volume decreased after a two-week time point for the treated group and increased significantly in the control group, which was supported by increasing red fluorescent light emission in the control tumors. Decreased relaxation times were associated with successful chemotherapy outcomes. The results indicate altered relaxation mechanisms compared with higher dose chemotherapies previously published.

Relaxation along fictitious field with rank n (RAFFn): A promising magnetic resonance imaging method to determine myocardial infarction

Purpose of this review: Cardiovascular Diseases (CVD) are the leading cause of deaths worldwide. Myocardial Infarction (MI) is one of the deadliest CVDs. MI is causing many complex cellular biological changes in the myocardium after myocardial infarction (MI). Modern magnetic resonance imaging (MRI) techniques, such as rotating frame relaxation time T1ρ, can be used to visualize and quantify the damages in the myocardium after the MI and for the detection of myocardial alternations without the use of contrast agents. However, T1ρ method suffers from high specific absorption rate i.e. tissue heating. Modern MRI technique called Relaxation Along a Fictitious Field (RAFF) in the Rotating Frame of Rank n (RAFFn) has overcome the specific absorption rate problems of T1ρ method. Additionally, RAFFn has been shown to visualize and quantify the MI in both preclinical and clinical studies. Recent findings: The RAFFn method has been used to characterize the MI in preclinical mouse MI models with promising results. The RAFFn method was implemented in standard clinical 1.5 T magnet for characterizing MI in human patients. The RAFFn has been used to determine also the fibrosis in preclinical hypertrophic cardiomyopathy mouse model and the results revealed the sensitiveness of RAFFn method to hypertrophic cardiomyopathy-related tissue changes in the myocardium. Summary: RAFFn has been used to characterize myocardial infarction in humans and in mice. RAFFn owns potential to be used in the MI diagnosis without contrast agents.

Torsional Landau levels and geometric anomalies in condensed matter Weyl systems

We consider the role of coordinate-dependent Fermi velocities, equivalent to effective tetrad (or vierbein) frame fields characterizing momentum space geometry, and torsional Landau levels (LLs) in condensed matter systems with low-energy Weyl quasiparticles. In contrast to their relativistic counterparts, they arise at finite momenta and with an explicit cutoff to the linear spectrum. Via the universal coupling of tetrads to momentum, they experience geometric chiral and axial anomalies with gravitational character. More precisely, at low energy, the fermions experience background fields corresponding to emergent anisotropic Riemann-Cartan and Newton-Cartan space-times, depending on the form of the low-energy dispersion. On these backgrounds, we show how torsion and the Nieh-Yan (NY) anomaly appear in condensed matter Weyl systems with an ultraviolet (UV) parameter with dimensions of momentum. The torsional NY anomaly arises from the spectral flow of torsional LLs and the linear Weyl description with a cutoff. We carefully review the torsional anomaly and spectral flow for relativistic fermions at zero momentum and contrast this with the spectral flow, nonzero torsional anomaly, and the appearance of the dimensionful UV-cutoff parameter in condensed matter systems at finite momentum. We apply this to chiral transport anomalies sensitive to the emergent tetrads in nonhomogeneous chiral superconductors, superfluids, and Weyl semimetals under elastic strain. This leads to previously overlooked suppression of anomalous density at nodes from momentum space geometry, as compared to (pseudo)gauge fields. We also briefly discuss torsion in anomalous thermal transport for nonrelativistic Weyl fermions, which arises via Luttinger's fictitious gravitational field corresponding to thermal gradients.

P.499 Ketamine's influence on global resting-state functional connectivity and individual variation in neuro-behavioural relationships

When viewed in a rotating frame of reference, a transverse-plane radiofrequency (RF) field manifests as a longitudinal field component called the fictitious field. By modulating the RF field and thus the fictitious field, detectable longitudinal magnetization patterns have previously been shown to be measurable. By combining fictitious-field modulation and longitudinal detection, here we demonstrate EPR spectroscopy and one-dimensional imaging in a custom-built longitudinal detection system operating at an ultra-low frequency (24 MHz) for detecting electron spins with short (~nanoseconds) relaxation times. Simultaneous transmit and receive with low transmitter leakage level (~80 dB isolation) is also demonstrated.

Ultra-low frequency EPR using longitudinal detection and fictitious-field modulation

When viewed in a rotating frame of reference, a transverse-plane radiofrequency (RF) field manifests as a longitudinal field component called the fictitious field. By modulating the RF field and thus the fictitious field, detectable longitudinal magnetization patterns have previously been shown to be measurable. By combining fictitious-field modulation and longitudinal detection, here we demonstrate EPR spectroscopy and one-dimensional imaging in a custom-built longitudinal detection system operating at an ultra-low frequency (24 MHz) for detecting electron spins with short (~nanoseconds) relaxation times. Simultaneous transmit and receive with low transmitter leakage level (~80 dB isolation) is also demonstrated.

Purity speed limit of open quantum systems from magic subspaces

We introduce the concept of Magic Subspaces for the control of dissipative N- level quantum systems whose dynamics are governed by Lindblad equation. For a given purity, these subspaces can be defined as the set of density matrices for which the rate of purity change is maximum or minimum. Adding fictitious control fields to the system so that two density operators with the same purity can be connected in a very short time, we show that magic subspaces allow to derive a purity speed limit, which only depends on the relaxation rates. We emphasize the superiority of this limit with respect to established bounds and its tightness in the case of a two-level dissipative quantum system. The link between the speed limit and the corresponding time-optimal solution is discussed in the framework of this study. Explicit examples are described for two- and three- level quantum systems.

Speed of light on a rotating platform

In this paper, some analogies between the Shapiro effect in the solar gravitational field and the Sagnac phase shift have been found. Starting from Einstein equivalence principle (EEP), which states the equivalence between the gravitational force and the pseudo-force experienced by an observer in a noninertial frame of reference, we imagine an observer on a rotating platform immersed in a gravitational field. In the Shapiro effect, for example, we know that the speed of an electromagnetic signal, calculated from the Earth, is less than [Formula: see text], but, if we calculate the speed using a clock at rest in the solar gravitational field, where the photon is passing, we get that the speed of light is [Formula: see text]. Similarly, by considering the fictitious gravitational field of the rotating platform, if we look for a clock with respect to which the signal speed is [Formula: see text], we can interpret the time delay as a gravitational effect.

Unified bulk semiclassical theory for intrinsic thermal transport and magnetization currents

We reveal the unexpected role of the material inhomogeneity in unifying the formulation of intrinsic thermal and thermoelectric transport as well as magnetization currents. The smooth inhomogeneity leads to the position dependent local band dispersion and phase-space Berry curvature, enabling a general and rapid access to transport and magnetization currents displaying the momentum-space Berry curvature physics. Our theory does not invoke the boundary current, the thermodynamic approach to magnetization or any mechanical counterpart of statistical forces. By introducing a fictitious inhomogeneity, it applies to homogeneous samples as well, promoting the inhomogeneity to be a basic trick in semiclassical transport theories. Such a trick works regardless of the driving force of transport, e.g., temperature gradient, in contrast to the trick of fictitious gravitational field in quantum transport theories. We thus include more general mechanical driving forces and establish the Mott relation between the resulting transport thermal and electric currents, whereas this relation for these two currents was previously only known when an electric field is the driving force.

Grounded electrical source ground–airborne transient electromagnetic modelling with fictitious wave field methods

The finite-difference time domain (FDTD) method is widely used in ground–airborne transient electromagnetic modelling. Generally, this method offers great limitations because the calculation of the air layer is avoided and the surface assumption is flat. This study proposes a new method for ground–airborne 3D electromagnetic forward modelling that includes air layers and effectively solves the airborne TEM forward calculation of the coastal ocean and rugged terrains. The optimum selection of the air-layer resistivity and the identification ability of the long-wire source are discussed. By adding the pulse source signal to the control equation and realizing a direct calculation that includes the source, the cumbersome process of calculating the complex initial field is avoided. After establishing the mountain model and coastal ocean model, the electromagnetic response is discussed. Subsequently, the ground–airborne TEM modelling is subjected to a 3D numerical simulation of complex geological conditions. The validity of this method is verified by analytical solutions through a uniform half space. The results show that the method can achieve 3D and high-precision numerical calculations when it includes complex terrain and seawater.

Fractionalizing a Local Pair Density Wave: a Good “Recipe” for Opening a Pseudo-gap

We give a concise version of a recently proposed concept of fractionalization of an order parameter, thus generating a constraint through a fictitious gauge field. We argue that this new line of approach is key to explain the longstanding mystery of the pseudo-gap phase in cuprate superconductors. For example, the fractionalization of a finite momentum, charge two state living on latice bonds -- also called Pair Density Wave, into a particle-particle and a particle-hole pair leads to the opening of a gap in the fermionic spectrum. It induces "phase-locking" between the particle-particle and particle-hole pairs. We describe the formation of the Fermi arcs in the spectrum and give an account of recent Raman spectroscopy results from a minimal microscopic model. We relate the "phase-locking" to intriguing STM experimental observations.

Adduct under Field—A Qualitative Approach to Account for Solvent Effect on Hydrogen Bonding

The location of a mobile proton in acid-base complexes in aprotic solvents can be predicted using a simplified Adduct under Field (AuF) approach, where solute–solvent effects on the geometry of hydrogen bond are simulated using a fictitious external electric field. The parameters of the field have been estimated using experimental data on acid-base complexes in CDF3/CDClF2. With some limitations, they can be applied to the chemically similar CHCl3 and CH2Cl2. The obtained data indicate that the solute–solvent effects are critically important regardless of the type of complexes. The temperature dependences of the strength and fluctuation rate of the field explain the behavior of experimentally measured parameters.

Rotating frame MRI relaxations as markers of diffuse white matter abnormalities in multiple sclerosis

Even though MRI visualization of white matter lesions is pivotal for the diagnosis and management of multiple sclerosis (MS), the issue of detecting diffuse brain tissue damage beyond the apparent T2-hyperintense lesions continues to spark considerable interest. Motivated by the notion that rotating frame MRI methods are sensitive to slow motional regimes critical for tissue characterization, here we utilized novel imaging protocols of rotating frame MRI on a clinical 3 Tesla platform, including adiabatic longitudinal, T1ρ, and transverse, T2ρ, relaxation methods, and Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank 4 (RAFF4), in 10 relapsing-remitting multiple sclerosis patients and 10 sex- and age-matched healthy controls. T1ρ, T2ρ and RAFF4 relaxograms extracted from the whole white matter exhibited a significant shift towards longer relaxation time constants in MS patients as compared to controls. T1ρ and RAFF4 detected alterations even when considering only regions of normally appearing white matter (NAWM), while other MRI metrics such as T1w/T2w ratio and diffusion tensor imaging measures failed to find group differences. In addition, RAFF4, T2ρ and, to a lesser extent, T1ρ showed differences in subcortical grey matter structures, mainly hippocampus, whereas no functional changes in this region were detected in resting-state functional MRI metrics. We conclude that rotating frame MRI techniques are exceptionally sensitive methods for the detection of subtle abnormalities not only in NAWM, but also in deep grey matter in MS, where they surpass even highly sensitive measures of functional changes, which are often suggested to precede detectable structural alterations. Such abnormalities are consistent with a wide spectrum of different, but interconnected pathological features of MS, including the loss of neuronal cells and their axons, decreased levels of myelin even in NAWM, and altered iron content.

A locally second order symmetric method for discontinuous solution of Poisson's equation on uniform cartesian grids

A new method is proposed for numerically solving the Poisson equation for non-continuous scalar fields on a uniform Cartesian grid. The sharp discontinuity in both the magnitude and the gradient of the scalar field normal to the interface is represented by the numerical solution with second order accuracy at the interface. This is achieved by setting up a composite solution, which is a weighted average of two fictitious scalar fields that together produce the required discontinuity within each interfacial grid cell. A smooth treatment of the Poisson coefficient in a narrow band around the interface allows sharp interfacial jumps to be expressed with second order accuracy on regular grid points around the interface using a standard signed distance function. Moreover, the jump in the gradient tangent to the interface is not needed to enforce the jump in the gradient normal to the interface. The resulting linear system is symmetric and leads to second order accurate solutions on grid points adjacent to the interface. The accuracy of the new framework is compared with other methods.

P3099Lymphatic insufficiency increases cardiac edema after myocardial infarction as assessed by novel magnetic resonance TRAFFn and T2 relaxation times

Abstract Introduction The role of cardiac lymphatic system in myocardial infarction (MI) is still unclear. A new method to detect and characterize MI without contrast agent is a relaxation along a fictitious field in nth rotating frame (RAFFn). The RAFFn takes advantage of the fictitious magnetic field, which is produced by a fast sweep of an effective radio frequency field, to increase a spin locking field strength without increasing the specific absorption rate. MI is detected as increased RAFFn relaxation times and cardiac edema by an increased T2 relaxation time. We have shown earlier that MI size can be accurately measured by the RAFFn relaxation times. Purpose To study the effects of the lack of cardiac lymphatic system on MI and cardiac edema in a mouse model. Methods Transgenic (TG) mice expressing soluble decoy VEGF receptor 3 (sVEGFR3) thus blocking lymphatic vessel formation in the heart and wild type (WT) control mice were used. MI was induced in 13–17 week old TG (n=11) and WT (n=14) mice by ligating the left anterior descending coronary artery. The RAFFn (TRAFF2 and TRAFF4), a continuous wave T1ρ and a T2 relaxation times were acquired at time points 0, 3, 7 and 21 days after the MI at 9.4 T. Histological sections were stained with hematoxylin eosin and Sirius red to assess cellularity and MI area. An Area of difference (AOD) was determined by subtracting MI areas based on TRAFF2, TRAFF4 and T1ρ maps from MI area based on T2 maps. Results MI size based on the TRAFF4 and T2 relaxation time maps were larger at early time points 3 and 7 days post MI in the WT group compared to the TG group (Figure 1A-B, p<0.05). However, the MI size was significantly larger in the T2 relaxation time map in the TG group compared to the WT group at the last time point and interaction between the groups were significant as a function of time (Figure 1A-B, p<0.05). The AOD values, which reflect cardiac edema, increased in the TG group as a function of time (Figure 1C, p<0.001). TRAFF2, TRAFF4 (Figure 1D), T1ρ and T2 relaxation times increased significantly (≈50%, p<0.001) after the MI compared to remote areas in both groups. In the WT group, the lymphatic vessel network is fully functional and removes edema efficiently between days 3 and 21 after the MI, while in the TG group the MI area in T2 map is relative stable indicating insufficient edema removal, caused by the lymphatic deficiency and insufficient lymphangiogenesis in the TG group. The MIs were also verified based on Sirius red stained histology (Figure 1E). Figure 1 Conclusion Lymphatic deficiency increases cardiac edema (AOD values) 7–21 days after MI as compared to the WT group. Results support the importance of cardiac lymphatic vessels for healing after MI. Effects of the lymphatics on MI can be detected based on the MI size difference based on the TRAFFn and the T2 relaxation times. Acknowledgement/Funding Doctoral Programme of Molecular Medicine

Emergent Topological Hall Effect in La0.7Sr0.3MnO3/SrIrO3 Heterostructures.

Recently, perovskite oxide heterostructures have drawn great attention because multiple and complex coupling at the heterointerface may produce novel magnetic and electric phenomena that are not expected in homogeneous materials either in the bulk or in films. In this work, we report for the first time that an emergent giant topological Hall effect (THE), associated with a noncoplanar (NC) spin texture, can be induced in ferromagnetic (FM) La0.7Sr0.3MnO3 thin films in a wide temperature range of up to 200 K by constructing La0.7Sr0.3MnO3/SrIrO3 epitaxial heterostructures on (001) SrTiO3 substrates. This THE is not observed in La0.7Sr0.3MnO3 single-layer films or La0.7Sr0.3MnO3/SrTiO3/SrIrO3 trilayer heterostructures, indicating the relevance of the La0.7Sr0.3MnO3/SrIrO3 interface, where the Dzyaloshinskii-Moriya interaction due to strong spin-orbital coupling in SrIrO3 may play a crucial role. The fictitious field associated with THE is independent of temperature in La0.7Sr0.3MnO3/SrIrO3 heterostructures, suggesting that the NC spin texture may be magnetic skyrmions. This work demonstrates the feasibility of using SrIrO3 to generate novel magnetic and transport characteristics by interfacing with other correlated oxides, which might be useful to novel spintronic applications.