Search

In this work, a Model-Based Control method for a single horizontal degree of freedom shaking table is presented. The proposed approach relies on the real-time inversion of a previously identified linear state-space model of the hydraulic servoactuator which drives the table. The inputs to the model are the control command and the force exerted on servoactuator rod. The latter contains all the relevant information related to the external actions acting on the servoactuator, thus making control system performance independent from the specimen with which the table is loaded and enabling it to cope with specimen non-linear behavior and eventual external forces exerted on it. A parallel proportional integral derivative controller, which accounts for non-modeled dynamics and a feedback linearization scheme, aimed at minimizing servovalve flow non-linearity, complement the previous architecture. The effectiveness of the method has been assessed numerically. According to the simulation results, the performance of the proposed technique appears quite promising; however, several factors must be carefully considered to achieve successful actual implementation.

We define scaled skew Bessel processes and determine their Green’s functions and semi-group densities. We prove that these processes satisfy the time inversion property although the corresponding densities of the semi-groups are not, in general, twice differentiable in the density and starting point arguments. Some characterizations and semi-martingale properties are given.

We study valley polarization, spin, and valley Hall conductivity in doped monolayer MoS2 considering dopant introduced magnetic exchange field using low energy effective Hamiltonian. We found that dopant introduced magnetic exchange field breaks the time inversion symmetry and decouples the energetically degenerated valleys into nondegenerate. Moreover, the calculated result reveals that, at low temperature, in insulating regime, anomalous Hall conductivity in a single valley and the total valley Hall conductivity are quantized, whereas the total spin Hall conductivity vanishes identically. We also found that the strength of the spin-orbit coupling together with the exchange field determines the valley polarization, which in turn controls valley and spin Hall conductivity in doped monolayer MoS2 system. The spin Hall and valley Hall conductivity is dissipationless in the absence of any external magnetic field. Therefore, our results are crucial to generate low power electronics devices.

Summary To probe differences in electric conductivity around a measurement device, electromagnetic logging is a well established technique. The interpretation of electromagnetic data mostly relies on 1D inversions, because of high computational costs of 3D codes and the requirement of real time inversion results. However, the increase in computational power during the last decades, makes the step towards 2D or even 3D inversions feasible. Integral equation methods are proper for geosteering problems, because a discretization of only a small domain around the measurement device is required. Another advantage of integral equation methods is its greater suitability for inversion, because its formulation already contains the sensitivity. Our main goal of the presented work is to reduce the computational runtime of the inversion algorithm. Therefore, we investigate the applicability of different integral equation methods for geosteering problems and investigate ways to improve their performance.

We derive the precise late-time asymptotics for solutions to the wave equation on extremal Reissner-Nordstr\"om black holes and explicitly express the leading-order coefficients in terms of the initial data. Our method is based on purely physical space techniques. We derive novel weighted energy hierarchies and develop a singular time inversion theory, which allow us to uncover the subtle contribution of both the near-horizon and near-infinity regions to the precise asymptotics. We introduce a new horizon charge and provide applications pertaining to the interior dynamics of extremal black holes. Our work confirms, and in some cases extends, the numerical and heuristic analysis of Lucietti-Murata-Reall-Tanahashi, Ori-Sela and Blaksley-Burko., Comment: 87 pages, 10 figures; version accepted for publication

This study explores the quasi-real time inversion principle and precision estimation of three-dimensional coordinates of the epicenter, trigger time and magnitude of earthquakes with the aim to improve traditional methods, which are flawed due to missing information or distortion in the seismograph records. The epicenter, trigger time and magnitude from the Lushan earthquake are inverted and analyzed based on high-frequency GNSS data. The inversion results achieved a high precision, which are consistent with the data published by the China Earthquake Administration. Moreover, it has been proven that the inversion method has good theoretical value and excellent application prospects.

Backgroud: The Turbo Inversion Recovery Magnitude (TIRM) pulse sequence is used to examine wrist joint, especially in the coronal plane. Main parameters of inversion recovery pulse sequence are time repetition (TR), time echo (TE) and time inversion (TI) . This study aims to analyze the variation of time repetition (TR) and time inversion (TI) on anatomical information using TIRM pulse sequence on wrist joint MR imaging with 0,3 tesla. Methods: This study was a quantitave experimental study with a linear regression test. This study was conducted in Radiology Department of Banyumas hospital using twenty serial images from only one patient with 10 variation of TR (3000 ms, 3200ms, 3400 ms, 3600 ms, 3800 ms, 4000 ms, 4200 ms, 4400 ms, 4600 ms, 4800 ms) and 10 variation of TI (70 ms, 75 ms, 80 ms, 85 ms, 90 ms, 95 ms, 100 ms, 105 ms, 110 ms, 115 ms). Image assessed by only one respondent. Results: There was no significant influence of variation of TR and TI on anatomical information. Significant number was 0,240 which is bigger than p value (0,05). TR and TI variation affected just only 15,5% to anatomical information, 84,5% was influenced by other variables that unconfirmed in this study. Conclusion: There was differences of anatomical information in MRI wrist joint sequence coronal T2WI-FSE fat suppression between SPIR and SPAIR with a significance level of p value

The integration of seismic data into high-resolution geological model, provides great potential for calibrating reservoir parameters, which enables better understanding of the reservoir sweep and flow patterns. The efficacy of seismic inversion method based on the travel time of fluid saturation front using seismic onset times has been well demonstrated for integrating frequent time-lapse seismic surveys. However, due to the high cost associated with conducting seismic surveys, frequent seismic surveys are usually not commonly available. In this paper, I have generalized the onset time inversion method for infrequent seismic data using interpolated seismic onset times, making the method applicable for efficiently integrating infrequent seismic surveys. With the valuable information provided by seismic data, the uncertainty in the reservoir model parameters can be reduced through history matching. The history matched model can be used to optimize reservoir management and field development strategy. The proposed method is illustrated using synthetic and field applications.

The inversion of NMR relaxation time involves the Fredholm integral equation of the first kind. Due to its ill-posedness, numerical solutions to this type of equations are often found much less accurate and bear little resemblance to the true solution. There has been a strong interest in finding a well-posed method for this ill-posed problem since 1950s. In this paper, we prove the existence, the uniqueness, the stability and the convergence of the generalized Phillips-Twomey regularization method for solving this type of equations. Numerical simulations and core analyses arising from NMR transverse relaxation time inversion are conducted to show the effectiveness of the generalized Phillips-Twomey method. Both the simulation results and the core analyses agree well with the model and the realities.

There are significant challenges related to contamination detection and characterization within large water distribution systems. Given current sensing technology and resources, source inversion algorithms will need to rely on manual grab samples providing only a discrete positive/negative indication of the presence of contaminant. We propose an integrated real-time strategy that identifies the set of likely locations and performs additional sampling cycles to accurately identify the contamination source. We present an MILP formulation that solves the source inversion problem using discrete (positive/negative) measurements from sparse manual grab samples at limited points in time and space. The water quality model is formulated using the origin-tracking approach and is then exactly and efficiently reduced prior to the formulation of the MILP, giving a much smaller problem that is solvable in real-time settings. The formulation is tested on a water network model comprised of over 10,000 nodes and more than 150 timesteps.

We link two phenomena concerning the asymptotical behavior of stochastic processes: (i) abrupt convergence or cut-off phenomenon, and (ii) the escape behavior usually associated to exit from metastability. The former is characterized by convergence at asymptotically deterministic times, while the convergence times for the latter are exponentially distributed. We compare and study both phenomena for discrete-time birth-and-death chains on Z with drift towards zero. In particular, this includes energy-driven evolutions with energy functions in the form of a single well. Under suitable drift hypotheses, we show that there is both an abrupt convergence towards zero and escape behavior in the other direction. Furthermore, as the evolutions are reversible, the law of the final escape trajectory coincides with the time reverse of the law of cut-off paths. Thus, for evolutions defined by one-dimensional energy wells with sufficiently steep walls, cut-off and escape behavior are related by time inversion., Comment: 2 figures

I propose a reinterpretation of “Lorentz tachyonic transformations” — for |v| > c — and subsequently the fundaments of a Pseudotachyonic Relativity. We’ll see that some usually “absurd results” become comprehensible. Besides some brief reflections on issues of time inversion and causality, the main ideas and conclusions presented here are: • a tachyonic reference frame may only be detected as its “associated frame”, which has lower-than-light velocity (ˆv = c 2 /v) and in which time appears in an inverted flow; • we cannot directly detect tachyons but instead their pseudotachyonic “images”.

An experimental study is performed on electromagnetic time reversal in highly scattering environments, with a particular focus on performance when environmental conditions change. In particular, we consider the case for which there is a mismatch between the Green's function used on the forward measurement and that used for time-reversal inversion. We examine the degradation in the time-reversal image with increasing media mismatch, and consider techniques that mitigate such degradation. The experimental results are also compared with theoretical predictions for time reversal in changing media, with good agreement observed

Objective To characterize MR imaging features of pure mucinous carcinoma of the breast. Materials and methods MR images obtained from 16 women (age range, 29–81; mean age, 57 years) with pure mucinous carcinoma of the breast determined at surgery were reviewed. The MR findings used were shape, margin, internal mass enhancement, kinetic curve pattern on dynamic study, signal intensity on short time inversion recovery (STIR) T2-weighted images, and non-mass-like enhancement around the main tumor. Non-mass-like enhancement was compared with the presence of extensive intraductal component (EIC) on histopathological findings. Results Eleven tumors (69%) had lobular contour, and nine tumors (56%) had smooth margin. Eight tumors (50%) showed rim enhancement and six tumors (38%) showed heterogeneous enhancement. Fourteen tumors (88%) showed a persistent enhancing pattern on kinetic curve. Fifteen tumors exhibited homogenous strongly high signal intensity on STIR T2-weighted images. In six cases with EIC, five cases had non-mass-like enhancement around the main mass. Conclusions MR findings such as lobular shape, rim or heterogeneous enhancement, persistent pattern on kinetic curve, and homogeneous strongly high signal intensity on STIR T2-weighted images may be useful in diagnosing pure mucinous carcinoma. Moreover, linear-ductal enhancement around main mass may indicate presence of EIC.

The representation analysis of magnetic structures (group theory) considers generally the group G k (symmetry elements of the space group G which keep unchanged the propagation vector k). There exists a certain confusion about the way and the usefulness of introducing time inversion, the operation which reverses the directions of the magnetic moments. We show here that we can define two ‘time inversion’ operators, one which is linear and one which is antilinear. While introducing the linear operator does not bring any new piece of information, introducing the antilinear operator brings more details on the possible magnetic structures. Because of this antilinearity, the corepresentations have to be used instead of the usual representations. The corepresentation theory had been introduced by Wigner for the operator ‘time inversion in quantum mechanics’, operator which, in quantum mechanics, must be antilinear. Finally we show that, for magnetic structures, using an antilinear operator instead of a linear operator, is connected with the reality of the magnetic moments. To cite this article: J. Schweizer, C. R. Physique 6 (2005).

The spin-statistics conection is obtained for classical point particles. The connection holds within pseudomechanics, a theory of particle motion that extends classical physics to include anticommuting Grassmann variables, and which exhibits classical analogs of both spin and statistics. Classical realizations of Lie groups can be constructed in a canonical formalism generalized to include Grassmann variables. The theory of irreducible canonical realizations of the Poincare group is developed in this framework, with particular emphasis on the rotation subgroup. The behavior of irreducible realizations under time inversion and charge conjugation is obtained. The requirement that the Lagrangian retain its form under the cominbed operation CT leads directly to the spin-statistics connection, by an adaptation of Schwinger's 1951 proof to irreducible canonical realizations of the Poincare group of spin j: Generalized spin coordinates and momenta satisfy fundamental Poisson bracket relations for 2j=even, and fundamental Poisson antibracket relations for 2j=odd., Comment: To be submitted to American Journal of Physics

Rohrlich claims that “the problem of the arrow of time in classical dynamics has been solved”. The solution he proposes is based on the equations governing the motion of extended particles. Rohrlich claims that these equations, which must take self-interaction into account, are not invariant under time reversal. I dispute this claim, on several grounds.

On the basis of the multiparticle theory of protonic decay, the angular distributions of protons emitted by oriented spherical and deformed nuclei in the laboratory frame and in the internal coordinate frame of deformed parent nuclei are constructed with allowance for symmetry with respect to time inversion. It is shown that, because of the deep-subbarrier character of protonic decay, the adiabatic approximation is not applicable to describing the angular distributions of protons emitted by oriented deformed nuclei and that the angular distribution of protons in the laboratory frame does not coincide with that in the internal coordinate frame. It is demonstrated that these angular distributions coincide only if the adiabatic and the semiclassical approximation are simultaneously valid.

The Ward method is used to construct initial data which correspond to two monopoles on top of each other pulled apart without any cost in potential energy. A gauge is found in which the data are real and analytic. The corresponding analytic solution near the origin is studied looking backwards and forwards in time. The solution considered breaks the combined symmetry of time inversion and 90° rotation.

It is shown that many important and still relevant results in the field of nonequilibrium statistical mechanics were derived by Bogoliubov (jointly with N.M. Krylov) early in the prewar years and were completely published in a still insufficiently known monograph of 1945. Among these findings were the concept of time hierarchy for stochastic evolution, the concept of quasi-averages that remove symmetry relative to time inversion, and the mechanism of dynamic relaxation of a physical object in a thermostat.

In this paper the transformation of the partial time inversion is discussed. For magnetic dimers it is shown that at partial time inversion the change of sign for the exchange integral takes place. This allows transforming the antiferromagnetic type of ordering into the ferromagnetic one and vice versa. Specifically, for magnetic dimers containing equivalent ions withS = 1/2, the partial time inversion transformation leads to spin level inversion. The possible 3d-3d and 4f-4f dimer clusters with antiferro- and ferromagnetic types of ordering are indicated. The electron paramagnetic resonance data for 3d-3d dimers proving the suggested statements are presented.

Let be a one-dimensional Brownian motion with constant drift µ ∈ R starting from 0. In this paper we show thatgives rise to a diffusion process and we explain how this result may be considered as an extension of the celebrated Pitman’s 2M - X theorem. We also derive the infinitesimal generator and some properties of the diffusion process and, in particular, its relation to the generalized Bessel processes.

Some new insight is obtained for the structure of the Bonhoeffer-van der Pol system. The problems of excitability and threshold are discussed for all three types of the system classified according to the existing attractors: a focus only, a limit cycle only and a limit cycle together with a focus. These problems can be treated by the T-repellers and the T-attractors of the system which are mutually reciprocal under time inversion. The threshold depends on the structure of the T-repeller (unstable part of integral manifold). This structure is then used to understand the behavior and the properties of the two different types of isochrones: Winfree isochrones (W-isochrones) and regular isochrones. Winfree's description of a W-isochrone is extended to excitable systems. Both W-isochrones and regular isochrones are calculated for the Bonhoeffer-van der Pol system in its limit cycle and excitable regimes. The important role of the T-repeller as an asymptotic limit for both types of isochrones is manifested. (c) 1999 American Institute of Physics.

Introduction: In Graves' Ophthalmopathy, it is important to distinguish active inflammatory phase, responsive to immunosuppressive treatment, from fibrotic unresponsive inactive one. The purpose of this study is, first, to identify the relevant orbital magnetic resonance imaging signal intensities before treatment, so to classify patients according to their clinical activity score (CAS), discriminating inactive (CAS3) subjects and, second, to follow post-steroid treatment disease. Methods: An observational study was executed on 32 GO consecutive patients in different phases of disease, based on clinical and orbital Magnetic Resonance Imaging parameters, compared to 32 healthy volunteers. Orbital Magnetic Resonance Imaging was performed on a 1.5 tesla Magnetic Resonance Unit by an experienced neuroradiologist blinded to the clinical examinations. Results: In pre-therapy patients, compared to controls, a medial rectus muscle statistically significant signal intensity ratio (SIR) in short-time inversion recovery (STIR) (long TR/TE) sequence was found, as well as when comparing patients before and after treatment, both medial and inferior rectus muscle SIR resulted significantly statistically different in STIR. These increased outcomes explain the inflammation oedematous phase of disease, moreover after steroid administration, compared to controls; patients presented lack of that statistically significant difference, thus suggesting treatment effectiveness. Conclusion: In our study, we proved STIR signal intensities increase in inflammation oedematous phase, confirming STIR sequence to define active phase of disease with more sensibility and reproducibility than CAS alone and to evaluate post-therapy involvement. © 2014 Springer-Verlag.

Ultracold neutrons are defined and their general physical properties are explained. Their relations with modern physics and how they can be produced in laboratories are discussed. Superthermal production in superfluid liquid helium, the most promising method, is presented, quoting the results of Mark 3000, a superthermal ultracold neutron generator.

The paper presents a digital method of conversion of the sensor and its hardware implementation. The method is based on excitation of oscillations in the sensitive elements of sensors, analog-digital conversion of signals and their time reversal by re-indexing of array elements, followed by Fourier transformation and determination of the initial phases of the oscillations.

In this paper we present a mixed-integer linear programming formulation for performing source inversion in drinking water systems using discrete (yes/no) measurements available from manual grab samples. Given the large size of a typical water distribution system, standard water quality models are inappropriate for use in the mixed-integer framework. In this research, we demonstrate the use of an origin-tracking approach to develop the water quality model, and show how this model can be efficiently and exactly reduced prior to the formulation of the MILP, giving rise to a much smaller MILP. Furthermore, we demonstrate that this formulation can be efficiently solved in a real-time setting on large networks with over 10,000 nodes while considering over 100 time discretizations.

Early production, as well as ultimate oil and gas recovery, from a reservoir often depend on the timeliness and the accuracy of geosteering decisions. Exiting the reservoir during drilling results in costly nonproductive intervals. Even staying within the reservoir but in a nonoptimal location eventually leads to early water breakthrough while leaving behind valuable oil. In recent years, azimuthal deep resistivity measurements have been recognized as beneficial to real-time steering decisions. Because of their deep investigation, azimuthal deep resistivity measurements anticipate exits from the reservoir well before such events occur. In addition, their azimuthal sensitivity clearly points to the direction of preferred evasive actions. Azimuthal wave resistivity measurements take on multiple embodiments with multiple characteristics and multiple depths of investigation. The best results are achieved by jointly interpreting several of these measurements according to workflows that are specific to the particular applications. In the simplest cases, the up-down resistivity curves exhibit an unexpected behavior that has proven valuable both to petrophysicists and to geosteering specialists. When approaching conductive overlaying shale, for example, the up-curve tends to read the resistivity of the reservoir and the down-curve exhibits amplified horns beneficial to reservoir navigation. Resistivity images feature bright spots whose progression with increasing depth of investigation facilitates the avoidance of unwanted boundaries. A new measurement, designated as a geosignal, features strong lateral sensitivity. The geosignal from the deepest spacing is best suited to provide an early indication of the approaching boundary, with a near-exponential dependence on the distance to boundary. Quantitative inversion based on a subset of the azimuthal resistivity logs and the use of limited local knowledge helps to quantify the distance to the reservoir boundaries and their rate of approach. This paper presents some of the most commonly used interpretation methods are demonstrated on computer models, and then applied to various wells, with applications varying from thick reservoirs to interbedded sand-shale sequences.

Eighty-three MR studies for primary bone tumors, performed with both spin echo and short time inversion recovery (STIR) sequences, were reviewed. Twenty-six patients underwent surgery within 10 days after MR imaging. Specimens were cut and directly compared with MR images. In the remainder, pathologic slides were compared in order to obtain a better understanding of MR pattern. All MR images were examined with a traditional morphologic approach and, upon comparison with surgical macroslides and with pathology samples, some MR distinctive patterns were identified: the bulky appearance of osteosarcoma surrounded by muscle edema, the multilobular high signal intensity (SI) chondroid lesions, the subtle infiltration of Ewing's sarcoma, rarely accompanied by muscle edema and prone to MR underestimation, the well defined “multiple shells” pattern of giant cell tumor, and the ill defined “storiform” appearance of malignant fibrous histocytoma are all typical MR features strictly corresponding to pathologic findings. The chondroid origin tumors may be identified based on the lobular high SI pattern whereas a benign fibrous lesion was the only one in this series to be distinguished relying on the SI. Peritumoral soft tissue edema was found by the STIR sequence only in malignant tumors (69%) of this series, and particularly in osteosarcoma (96%), chondrosarcoma (83%), and giant cell tumor (100%): this associate finding may further contribute to the diagnosis.

The 122 Shubnikov point groups (SPGs) are obtained from the 32 ordinary crystallographic point groups (OPGs) by taking time inversion into account. Like the OPGs, the SPGs can be grouped into 11 Laue classes. Tensors can be invariant under space inversion (s tensors), time inversion (t tensors), space–time inversion (u tensors) or all three inversions (i tensors). The restrictions imposed on the form of a property tensor by the SPG of the material under consideration depend, for i tensors, only on the Laue class of the SPG. If these restrictions are known for an i tensor, the corresponding restrictions for s, t and u tensors of the same rank and internal symmetry can be written down immediately for all the 122 SPGs and for all orientations in which the SPG under consideration appears in the corresponding holohedry. These connections provide tests for the forms of tensors given in the literature. A number of corrections and of possible simplifications are pointed out. The results are illustrated by showing how the form of the i tensor describing linear electrogyration determines the form of the piezoelectric t tensor and the piezomagnetic s tensor for all 122 SPGs. Similarly, the form of the t tensor describing quadratic electrogyration is derived explicitly from the i tensor describing the piezooptic effect.

In order to well distinguish different tissues of the human body by magnetic resonance imaging (MRI), it is of great importance to find procedures to improve the image contrast. In particular, a valuable feature is to image only specific parts of organs and/or tissues while ignoring all the others. Dedicated MRI sequences able to filter the 1 H nuclei signals based on the different longitudinal relaxation times (T1) of the tissues have been developed. Standard signal selection/attenuation sequences, such as the Short Time Inversion Recovery and Multiple Inversion Recovery, have the effect to zero the signal for a discrete number of T1 values. Parametrically Enabled Relaxation Filters with Double and multiple Inversion (PERFIDI) sequences act on a range of T1 values and behave as an electronic band-pass or high-pass or low-pass filters. PERFIDI filters are therefore primarily focused on the components that pass through, rather than on those that are blocked. These filters have been developed and tested by nuclear magnetic resonance relaxometry. Here, these sequences have been validated for MRI on phantom samples to mimic T1 distributions present in tissues. Preliminary applications show that PERFIDI filters can effectively work on a range of T1 values to give well contrasted images.

For pre-stack depth migration, a macro-velocity/depth model is required which reflects the general subsurface structure and contains the velocity distribution which correctly predicts wave propagation times. Such a macro- model can be determined by non-linear inversion of multi-offset reflection times belonging to seismic horizons picked on CDP gathers along a seismic line. In the inversion scheme, in a 2D earth model, the depths of reflecting interfaces and the laterally and vertically varying velocities within the layer above the interface are solved simultaneously. Provided accurate multi-offset reflection times, two dimensional velocity anomalies in single-layers in the shallow section (i.e. in the range 0-2000 m depending on the maximum offset available in seismic data) can be resolved. In the optimization of depth models containing macro-layers with two dimensional velocity distribution, taking the layer boundaries and vertical velocity trends from available sonic log will help in the inversion process in achieving a globally optimum solution. If a sonic log is not available, it is necessary to divide the macro-layers into thinner macro-layers with lateral velocity changes only in order to solve the velocity variation with depth.

Summary Traveltime inversion can estimate complex structures and sharp velocity changes, which may occur in the nearsurface layers. Tomostatics were recently proven to be an effective technology in difficult areas; however, the inversion quality depends to a large degree on the accuracy of traveltime picking and on the identification of related events. Identification and picking of events in pre-stack gathers, when dealing with large data sets, can become very cumbersome. Unfortunately, the constant increase of channel number in 3-D and multi-component surveys, along with their time-lapse repetition, exacerbates this problem. A criterion to compare different tomostatics approaches is their possible suitability for automation. On this basis, we compared some methods by computing tomostatics for a high-fold profile in a geologically complex area in Saudi Arabia. We found that our joint inversion of shallow reflectors and refractors yielded similar results to a multilayer up-hole time inversion, but at a cheaper cost.

A clinical study of the evolution of the space resolved near infrared reflectance with the subcutaneous layers thickness, at rest, on the vastus lateralis, is used to determine convenient sets of muscle and fat optical coefficients at 850 nm and 780 nm. These coefficients are then used to establish pre-calculated 3 layers MC simulations tables of the reflectance as a function of the fat thickness. Real time inversion during effort is then performed to determine the absolute muscle oxygenation.

The aim was to compare fast short time inversion recovery (FSTIR) images and fat suppression, contrast enhanced T(1) weighted (FSCE T1W) spin echo images in the diagnosis of nasopharyngeal carcinoma (NPC). 102 MR studies were obtained with a 1.0 T or a 1.5 T system in 28 patients with NPC. The MR studies comprised both FSTIR and FSCE T1W images. FSTIR and FSCE T1W images were compared for detection of NPC by means of a receiver operating characteristic (ROC) analysis. The areas under the ROC curves of FSTIR and FSCE T1W images showed no statistical difference (0.87 vs 0.87). There was also no statistical difference in the sensitivity, specificity and accuracy of each sequence (0.74 vs 0.77, 0.81 vs 0.77 and 0.79 vs 0.77, respectively). Both sequences had the same performance for detection of NPC. FSTIR is as useful as FSCE T1W images, especially in the detection of recurrent tumours, but without the cost of contrast medium.

A clinical study of the evolution of the space resolved reflectance with the subcutaneous layers thickness, at rest, on the vastus lateralis, is used to determine convenient sets of muscle and fat optical coefficients at 850 nm. The results are compared to the data available in the literature. When the same study will be completed at 780 nm, these coefficients will be used in 3 layers MC simulations to establish pre-calculated tables of the reflectance as a function of the fat thickness and of the muscle absorption coefficient. The goal of this study is eventually to perform real time inversion during effort in order to determine the muscle oxygenation with this very simple technique (part 2).

A “bewildering” array of pulse sequences is available for magnetic resonance imaging.1 Slight variations on these sequences have led to various acronyms. Some pulse sequences are nearly synonymous with or identical to others but have been given different names by different authors. Spin-echo (SE), inversion recovery (IR), short time inversion recovery (STIR), gradient recalled acquisition in the steady state (GRASS), steady-state free precession (SSFP), Carr-Purcell-Meiboom-Gill (CPMG) are but a few in the current literature. On top of that, with each new pulse sequence modified by variations of gradients and acquisition times, equipment manufacturers have coined acronyms for their own particular usage (Appendix A).

The aim of my lecture is to give an exact definition of time inversion. The set of time inversions constitute a four dimensional manifold. The subgroup generated by the time inversions is described.

In 82 asymptomatic subjects aged 8–62 years we evaluated the menisci by magnetic resonance imaging [MRI; L0 tesla; spin-echo (SE 700/20), PS (partial saturation: 500/10), STIR (short time inversion recovery sequence: 1600/130/30)]. For grading the degeneration of the meniscus we used a standard classification (grades 0–4). MR findings were correlated with the patients' age, weight, profession, and athletic activity. Statistic analysis revealed a correlation between athletic activity and meniscal degeneration of both anterior horns and the posterior horn of the lateral meniscus. Especially the anterior horn of the lateral meniscus seems to be loaded during athletic activities. Correlation of meniscus degeneration with subjects' age showed an increase in grade 3 and grade 4 lesions with advancing age. Among subjects older than 50 years, grade 3 and 4 lesions were present in the SE sequence in 28.5% of cases, in PS sequences in 40.7% of cases, and in STIR sequences in 25% of cases.Clinical relevance: Athletic activity seems to load the anterior knee compartments, especially the lateral compartment. MRI shows meniscal lesions in a significant number of asymptomatic subjects, especially those older than 50 years.