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This chapter develops the classical equations of motion for localized magnetic moments and uses them to explain spin precession and magnetic resonance. Starting from microscopic current loops and intrinsic spin, it defines the magnetic dipole moment and its torque and energy in an external magnetic field, then derives the precession equation dS/dt = γS × B and the Larmor frequency. The dynamics of spin components are analyzed in static and time-dependent fields, including the effect of a weak transverse RF field that drives transitions between spin-up and spin-down states. Introducing a rotating reference frame leads to the resonance condition, the Rabi frequency, and an intuitive picture of how longitudinal and transverse components of the magnetization evolve. The chapter then applies the adiabatic theorem to spins in slowly varying fields, showing when a moment follows the local field direction, and develops adiabatic fast passage as a robust way to invert populations. Throughout, the connection is emphasized between these classical vector equations and the quantum two-level description underlying electron spin resonance and nuclear magnetic resonance.
The study of magnetism has driven progress in experimental science for centuries, and demonstrates how ground-breaking theoretical advances can be translated directly into essential, transformative technology. Now in an expanded second edition, this popular textbook provides comprehensive coverage of the theory and practical applications of magnetism and magnetic materials. The text has been updated throughout to address significant developments from the last decade, including new theoretical insights, advanced experimental probes, and thin film technology. A new chapter covers the important topic of transverse magnetotransport and effects of topology. The book is extensively illustrated with over 700 figures conveying important experimental data, concepts and applications, and each self-contained chapter concludes with a summary section, a list of further reading and a set of exercises. The text contains a wealth of useful information that will be of interest to graduate students and researchers in physics, materials science and engineering.
This chapter is devoted to quantum dynamics with a time-dependent Hamiltonian. The latter is written as the sum of two contributions: one stationary, the other (with the time parameter) describing the perturbation of a system by its environment and responsible for possible transitions. We thus recover the heuristic hypotheses of Bohr or Einstein on light absorption/emission. We analyse these phenomena in much more detail, for example in the case of confinement in a cavity or to describe magnetic resonance, which is at the origin of important applications. Quantum theory is essentially probabilistic, so we begin by defining the concept of transition probability. We make extensive use of the two-state system, but apply it to the situation of an initial state and a possible final state, both coupled by an explicitly time-dependent interaction. We analyse the important cases of a quasi-stationary perturbation, a harmonic perturbation and coupling to a continuum of states. The chapter ends with a more complete presentation of the theory of time-dependent perturbations according to the Heisenberg and Dirac pictures, and also examines the strong field–atom coupling in a cavity.
Welearn the key aspect of quantum mechanics – how to predict the future with Schrödinger’s equation. We learn the general recipe for solving time-dependent problems by diagonalizing the Hamiltonian to find the energy eigenvalues and eigenvectors.
Isolated central nervous system vasculitis (ICNSV) is a vasculitis limited to the central nervous system. Its etiology and pathogenesis has not been exactly elucidated yet. It is predominantly seen in the fourth to sixth decades. Neurological symptoms in ICNSV can manifest in a broad spectrum, ranging from headache to stroke. A high degree of clinical suspicion is of great importance for diagnosis. Although there is no definitive diagnostic laboratory / serological test for ICNSV; laboratory tests are performed in patients with ICNSV to exclude secondary causes. CSF analysis usually demonstrates a high protein content and lymphocytic pleocytosis. Imaging findings are quite variable, ranging from small ischemic changes to large areas of infarction, hemorrhage, white matter edema also contrast enhancement. Magnetic resonance imaging is the most commonly used imaging modality in the workup of patients with suspected ICNSV. Vessel wall imaging MR technique, which has been used frequently in recent years, can be helpful in the diagnosis of ICNSV, determination of the appropriate biopsy location and follow-up after treatment. Cerebral digital subtraction angiography is considered the most sensitive imaging modality for the diagnosis of ICNSV; but the findings are not pathognomonic. Histological confirmation obtained with cerebral and meningeal biopsy samples is the gold standard for the definitive diagnosis of ICNSV. In this chapter, we discuss the ICNSV in detail with a diagnostic algorithm in the light of modalities that can be used in diagnosis
Chapter 13 studies the dynamic spin response function measured by neutron scattering experiments. In particular, the magnetic resonance states revealed by the neutron scattering measurements for high-Tc cuprates in the superconducting state are discussed. It is argued that this spin resonance mode may arise either from a spin exciton excitation induced by an attractive residual spin interaction in the particle-hole channel or from a collective ?-resonance mode in the particle-particle channel which emerges in the neutron scattering spectrum thanks to the particle-hole mixing in the superconducting state.
According to the social brain hypothesis, the human brain includes a network designed for the processing of social information. This network includes several brain regions that elaborate social cues, interactions and contexts, i.e. prefrontal paracingulate and parietal cortices, amygdala, temporal lobes and the posterior superior temporal sulcus. While current literature suggests the importance of this network from both a psychological and evolutionary perspective, little is known about its neurobiological bases. Specifically, only a paucity of studies explored the neural underpinnings of constructs that are ascribed to the social brain network functioning, i.e. objective social isolation and perceived loneliness. As such, this review aimed to overview neuroimaging studies that investigated social isolation in healthy subjects. Social isolation correlated with both structural and functional alterations within the social brain network and in other regions that seem to support mentalising and social processes (i.e. hippocampus, insula, ventral striatum and cerebellum). However, results are mixed possibly due to the heterogeneity of methods and study design. Future neuroimaging studies with longitudinal designs are needed to measure the effect of social isolation in experimental v. control groups and to explore its relationship with perceived loneliness, ultimately helping to clarify the neural correlates of the social brain.
This review outlines the current use of magnetic resonance (MR) techniques to study digestion and highlights their potential for providing markers of digestive processes such as texture changes and nutrient breakdown. In vivo digestion research can be challenging due to practical constraints and biological complexity. Therefore, digestion is primarily studied using in vitro models. These would benefit from further in vivo validation. NMR is widely used to characterise food systems. MRI is a related technique that can be used to study both in vitro model systems and in vivo gastro-intestinal processes. MRI allows visualisation and quantification of gastric processes such as gastric emptying and coagulation. Both MRI and NMR scan sequences can be configured to be sensitive to different aspects of gastric or intestinal contents. For example, magnetisation transfer and chemical exchange saturation transfer can detect proton (1H) exchange between water and proteins. MRI techniques have the potential to provide molecular-level and quantitative information on in vivo gastric (protein) digestion. This requires careful validation in order to understand what these MR markers of digestion mean in a specific digestion context. Combined with other measures they can be used to validate and inform in vitro digestion models. This may bridge the gap between in vitro and in vivo digestion research and can aid the optimisation of food properties for different applications in health and disease.
The concepts of angular momentum, spin and magnetic moment are worked out using standard quantum mechanical formalism. The concepts of intrinsic spin of a pointlike particle is contrasted with the intrinsic angular momentum of composite particles. The Larmor frequency and the magnetic resonance of non-interacting spins are introduced. The quantum statistics of a system of spins is overviewed, before introducing the thermodynamics of a spin system in a static frame of reference. Nuclear magnetic phase transitions are briefly reviewed.
Metamaterials offer the possibility to control and manipulate electromagnetic radiation. Spoof surface plasmon metamaterials are the focus of this Element of the Metamaterials Series. The fundamentals of spoof surface plasmons are reviewed, and advances on plasmonic metamaterials based on spoof plasmons are presented. Spoof surface plasmon metamaterials on a wide range of geometries are discussed: from planar platforms to waveguides and localized modes, including cylindrical structures, grooves, wedges, dominos or conformal surface plasmons in ultrathin platforms. The Element closes with a review of recent advances and applications such as Terahertz sensing or integrated devices and circuits.
The performance of wireless power transfer (WPT) systems is a function of many parameters such as resonance matching, coil quality factor, system impedance match, and others. When designing and testing WPT systems, reliable measurement of system performance is essential. In our application, we use WPT to power biomedical implants for telemetry acquisition from small rodents, where rodent behavior data is used to study disease models. Such an application employs a large primary coil and a much smaller moving secondary coil, which can be defined as a loosely coupled WPT (LCWPT) system. This paper presents a novel wireless measurement system (WMS) that is used to collect real-time performance data from the secondary circuit (implant), while testing LCWPT systems. Presently, measuring the performance of the secondary side of LCWPT systems while they are in operation can be problematic. The literature reports various measurement errors when using voltage/current probes, or coaxial cables placed directly into the primary magnetic field. We have designed the WMS to greatly reduce such measurement errors, where the WMS measures the induced voltage (and hence received power) and relays this information by radio. Experiments were done to test the WMS, as well as comparison with cable-based measurements.
We report two cases with levoatriocardinal vein and partial anomalous pulmonary venous drainage in left-sided obstructive lesions. This association may be difficult to recognise by echocardiography. Cardiac CT and MRI were crucial to define the diagnosis and to tailor the best therapeutic option.
This article describes the use of non-invasive magnetic resonance (MR) methods for the characterization and monitoring of the pathophysiology of experimental brain injury in laboratory animals as a function of time and treatment. The impact of MR in brain research is primarily due to its non-invasive nature, thereby enabling repeated measurements in long-term studies, and due to the type of information that it provides. MR imaging (MRI) enables the measurement of the morphology/anatomy as well as the functional status of tissues under in vivo conditions. Compared to other in vivo imaging modalities, MRI has a high spatial resolution and allows for a remarkable soft tissue differentiation. MR spectroscopy (MRS) provides information on the biochemical/metabolic status of tissues. MR methods which have proven valuable in animal studies, can be readily translated to the clinical situation where MR-based diagnosis and treatment planning play a rapidly increasing role.
After a short introduction into the principles of MR, we will illustrate the remarkable versatility of MR in research on brain injury from recent animal studies. Examples will be mainly drawn from experiments on early injury in focal cerebral ischemia and from research on mechanical brain trauma and excitotoxic lesions. The article ends with a brief description of the perspectives of MR in neuropsychiatry.
Electric vehicles (EVs) are becoming more popular due to concerns about the environment and rising gasoline prices. However, the charging infrastructure is lacking, and most people can only charge their EVs at home if they remember to plug in their cars. Using the principles of magnetic inductance and magnetic resonance, wireless charging (WC) could help significantly with these infrastructure problems by making charging secure and convenient. WC systems also have the potential to provide dynamic charging, making long road trips with EVs feasible and eliminating range anxiety. In this paper, we review the companies available in the literature that have developed electric vehicle wireless charging systems, automobile manufacturers interested in such technology, and research from universities and laboratories on the topic. While the field is still very young, there are many promising technologies available today. Some systems have already been in use for years, recharging public transit buses at bus stops. Safety and regulations are also discussed.
Sickle cell disease (SCD) is blood disorder with a high risk for cerebral vascular morbidities that impact neurocognitive functioning. Specific cognitive abilities are known to be more sensitive to neurologic effects of SCD than IQ scores, yet there is little consensus about which measures to use to assess neurocognitive functioning. We evaluated the ability of the Executive Abilities: Methods and Instruments for Neurobehavioral Evaluation and Research (EXAMINER) Battery to detect neurologic effects in SCD. Thirty-two youth with SCD and sixty demographically-matched comparison youth completed the EXAMINER Battery and selected tests from the Woodcock-Johnson Tests of Cognitive Ability, 3rd edition (WJ-III). Neurologic severity was examined via clinical history for morbidities and midsagittal corpus callosum (CC) area. Results indicated cognitive performance decreased with increasing neurologic morbidity across all cognitive measures; two of four EXAMINER factors were related to CC area. The association with clinical history and midsagittal CC area appeared at least as large for the Examiner Battery scores as for the WJ-III measures. The Examiner Battery showed sensitivity to neurologic history and white matter effects in SCD; this new measure compares favorably to established measures of disease-related neurocognitive effects, but would benefit from further development. (JINS, 2014, 1, 1–12)
This study aimed to investigate the computed tomography and magnetic resonance imaging findings of primary middle-ear carcinoma.
Methods:
In this retrospective study of 13 patients with primary middle-ear carcinoma, we collected pre- and post-contrast magnetic resonance images for all 13 cases, high-resolution computed tomography scans for 11 cases, and conventional computed tomography scans with contrast for 2 cases.
Results:
Soft-tissue masses were mainly located in the tympanum, tympanic sinus and deep within the external auditory canal, and involved the jugular fossa (9 of 13 patients), middle cranial fossa (5/13), parotid gland (2/13) and temporomandibular joint fossa (1/13). An irregular, ‘moth-eaten’ bone destruction pattern was seen on high-resolution computed tomography images, most commonly in the eustachian tube (9/13), jugular foramen (9/13) and facial nerve canal (7/13). On non-contrast magnetic resonances images, masses were isointense or slightly hypointense on T1-weighted images, and isointense or slightly hyperintense on T2-weighted images. On post-contrast images, lesions were moderately and homogeneously enhanced in seven cases and inhomogeneously enhanced in six.
Conclusion:
High-resolution computed tomography precisely detects regions of bone destruction, whereas MRI can better assess soft-tissue tumour margins, intracranial extension and vessel patency. Eustachian tube erosion is an important characteristic of primary middle-ear carcinoma.
(1) To study the prevalence and characteristics of large endolymphatic sac internal compartments on thin-section T2- and T2*-weighted magnetic resonance imaging, and to relate these to other large endolymphatic sac magnetic resonance imaging features, and (2) to correlate the compartment imaging features, endolymphatic sac size and labyrinthine anomalies with the patients' clinical and audiological data.
Method:
Magnetic resonance imaging studies for 38 patients with large endolymphatic sac anomalies were retrospectively reviewed in a tertiary referral centre. Endolymphatic sac compartment presence, morphology and imaging signal were assessed. Endolymphatic sac size and labyrinthine anomalies were also recorded. Endolymphatic sac compartments and other imaging features were correlated with clinical and audiological data.
Results:
Compartments were present in 57 per cent of the imaged endolymphatic sacs, but their presence alone did not correlate with other imaging features or clinical data. The endolymphatic sac : internal auditory meatus signal ratio was associated with a history of sudden or fluctuating hearing loss. Hearing loss correlated with opercular and extraosseous endolymphatic sac size measurements. A larger midpoint intraosseous endolymphatic sac size was associated with clear fluid loss at cochlear implantation.
Conclusion:
The magnetic resonance imaging characteristics of large endolymphatic sac compartments have been defined. The endolymphatic sac size and distal compartment signal should be recorded, as these provide prognostic information and assist the planning of appropriate interventions.