Coupled symplectic maps as models for subdiffusive processes in disordered Hamiltonian lattices

Acknowledgements One of us (T. B.) acknowledges many interesting discussions on coupled maps with Professor C. Tsallis. We are also grateful to the anonymous referees for their constructive feedback that helped us improve the manuscript and to the HPCS Laboratory of the TEI of Western Greece for providing the computer facilities where all our simulations were performed. C. G. A. was partially supported by the “EPSRC EP/I032606/1” grant of the University of Aberdeen. This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES - Investing in knowledge society through the European Social Fund.

Coupled symplectic maps as models for subdiffusive processes in disordered Hamiltonian lattices

Acknowledgements One of us (T. B.) acknowledges many interesting discussions on coupled maps with Professor C. Tsallis. We are also grateful to the anonymous referees for their constructive feedback that helped us improve the manuscript and to the HPCS Laboratory of the TEI of Western Greece for providing the computer facilities where all our simulations were performed. C. G. A. was partially supported by the “EPSRC EP/I032606/1” grant of the University of Aberdeen. This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALES - Investing in knowledge society through the European Social Fund.

The Mesozoic and Cenozoic motion of Adria (central Mediterranean): a review of constraints and limitations

This paper presents kinematic analysis on the motion of Adria, which is the continental mass that bridges Africa and Europe in the central Mediterranean. Palaeomagnetic data show a general coherence between the motion of Adria and Africa since the Late Paleozoic. This mutual motion, for the period from 120 Ma and the present, is verified by comparing inferred palaeolatitudes from relatively stable parts of Adria (Apulia, Gargano, Istria, and the Southern Alps) and the Hyblean Plateau, with latitudinal changes that are calculated from the motion of Africa with respect to hotspots. Additional constraints on the motion of Adria are provided from the Late Paleozoic-Early Mesozoic passive margin of Adria in the Ionian Sea. The seismic structure of the floor of the Ionian Sea resembles the structure of the oceanic crust in marginal back-arc basins, suggesting that it formed as a small ocean basin. Furthermore, the Ionian lithosphere in the Calabrian arc has been subjected to rapid rollback, which commonly occurs only when the subducting slab is made of oceanic lithosphere. This oceanic domain marks the Pennian-Triassic to Jurassic plate boundary between Adria and Africa, suggesting that a small amount of independent motion between Adria and Africa took place at that time. Since the Jurassic, Adria and Africa have shared a relatively coherent motion path. (C) 2004 Lavoisier SAS. All rights reserved.

Calculation of electric fields induced by body and head motion in high-field MRI

In modern magnetic resonance imaging (MRI), patients are exposed to strong, nonuniform static magnetic fields outside the central imaging region, in which the movement of the body may be able to induce electric currents in tissues which could be possibly harmful. This paper presents theoretical investigations into the spatial distribution of induced electric fields and currents in the patient when moving into the MRI scanner and also for head motion at various positions in the magnet. The numerical calculations are based on an efficient, quasi-static, finite-difference scheme and an anatomically realistic, full-body, male model. 3D field profiles from an actively shielded 4T magnet system are used and the body model projected through the field profile with a range of velocities. The simulation shows that it possible to induce electric fields/currents near the level of physiological significance under some circumstances and provides insight into the spatial characteristics of the induced fields. The results are extrapolated to very high field strengths and tabulated data shows the expected induced currents and fields with both movement velocity and field strength. (C) 2003 Elsevier Science (USA). All rights reserved.

The Effect Of Induced Intraocular Straylight (cataract Simulation) On Sensitivity Measures Of Standard Automated Perimetry, Pulsar Perimetry And Moorfields Motion Displacement Test

Purpose: To investigate the effect of incremental increases in intraocular straylight on threshold measurements made by three modern forms of perimetry: Standard Automated Perimetry (SAP) using Octopus (Dynamic, G-Pattern), Pulsar Perimetry (PP) (TOP, 66 points) and the Moorfields Motion Displacement Test (MDT) (WEBS, 32 points).Methods: Four healthy young observers were recruited (mean age 26yrs [25yrs, 28yrs]), refractive correction [+2 D, -4.25D]). Five white opacity filters (WOF), each scattering light by different amounts were used to create incremental increases in intraocular straylight (IS). Resultant IS values were measured with each WOF and at baseline (no WOF) for each subject using a C-Quant Straylight Meter (Oculus, Wetzlar, Germany). A 25 yr old has an IS value of ~0.85 log(s). An increase of 40% in IS to 1.2log(s) corresponds to the physiological value of a 70yr old. Each WOFs created an increase in IS between 10-150% from baseline, ranging from effects similar to normal aging to those found with considerable cataract. Each subject underwent 6 test sessions over a 2-week period; each session consisted of the 3 perimetric tests using one of the five WOFs and baseline (both instrument and filter were randomised).Results: The reduction in sensitivity from baseline was calculated. A two-way ANOVA on mean change in threshold (where subjects were treated as rows in the block and each increment in fog filters was treated as column) was used to examine the effect of incremental increases in straylight. Both SAP (p<0.001) and Pulsar (p<0.001) were significantly affected by increases in straylight. The MDT (p=0.35) remained comparatively robust to increases in straylight.Conclusions: The Moorfields MDT measurement of threshold is robust to effects of additional straylight as compared to SAP and PP.

Examining the Agreement of Structural Loss Measured With Heidelberg Retinal Tomograhy and Functional Loss With Standard Automated Perimetry (SAP; Octopus), Pulsar Perimetry (PP), and Moorfields Motion Displacement Test (MDT) Perimetry

Purpose: To examine the relationship of functional measurements with structural measures. Methods: 146 eyes of 83 test subjects underwent Heidelberg Retinal Tomography (HRTIII) (disc area<2.43, mphsd<40), and perimetry testing with Octopus (SAP; Dynamic), Pulsar (PP; TOP) and Moorfields MDT (ESTA). Glaucoma was defined as progressive structural or functional loss (20 eyes). Perimetry test points were grouped into 6 sectors based on the estimated optic nerve head angle into which the associated nerve fiber bundle enters (Garway-Heath map). Perimetry summary measures (PSM) (MD SAP/ MD PP/ PTD MDT) were calculated from the average total deviation of each measured threshold from the normal for each sector. We calculated the 95% significance level of the sectorial PSM from the respective normative data. We calculated the percentage agreement with group1 (G1), healthy on HRT and within normal perimetric limits, and group 2 (G2), abnormal on HRT and outside normal perimetric limits. We also examined the relationship of PSM and rim area (RA) in those sectors classified as abnormal by MRA (Moorfields Regression Analysis) of HRT. Results: The mean age was 65 (range= [37, 89]). The global sensitivity versus specificity of each instrument in detecting glaucomatous eyes was: MDT 80% vs. 88%, SAP 80% vs. 80%, PP 70% vs. 89% and HRT 80% vs. 79%. Highest percentage agreement of HRT (respectively G1, G2, sector) with PSM were MDT (89%, 57%, nasal superior), SAP (83%, 74%, temporal superior), PP (74%, 63%, nasal superior). Globally percentage agreement (respectively G1, G2) was MDT (92%, 28%), SAP (87%, 40%) and PP (77%, 49%). Linear regression showed there was no significant trend globally associating RA and PSM. However, sectorally the supero-nasal sector had a statistically significant (p<0.001) trend with each instrument, the associated r2 coefficients are (MDT 0.38 SAP 0.56 and PP 0.39). Conclusions: There were no significant differences in global sensitivity or specificity between instruments. Structure-function relationships varied significantly between instruments and were consistently strongest supero-nasally. Further studies are required to investigate these relationships in detail.

Ballistic and diffusive corrections to front propagation in the presence of multiplicative noise

We study the dynamics of reaction-diffusion fronts under the influence of multiplicative noise. An approximate theoretical scheme is introduced to compute the velocity of the front and its diffusive wandering due to the presence of noise. The theoretical approach is based on a multiple scale analysis rather than on a small noise expansion and is confirmed with numerical simulations for a wide range of the noise intensity. We report on the possibility of noise sustained solutions with a continuum of possible velocities, in situations where only a single velocity is allowed without noise.

Assessing the Glaucoma Quality of Life-15 (GCL-15) Questionnaire, Goldmann Tonometry and Moorfields Motion Displacement Test in Glaucoma Case Finding

Purpose: To compare the performance Glaucoma Quality of Life-15 (GQL-15) Questionnaire, intraocular pressure measurement (IOP Goldmann tonometry) and a measure of visual field loss using Moorfields Motion Displacement Test (MDT) in detecting glaucomatous eyes from a self referred population. Methods: The GQL-15 has been suggested to correlate with visual disability and psychophysical measures of visual function in glaucoma patients. The Moorfields MDT is a multi location perimetry test with 32 white line stimuli presented on a grey background on a standard laptop computer. Each stimulus is displaced between computer frames to give the illusion of "apparent motion". Participants (N=312, 90% older than 45 years; 20.5% family history of glaucoma) self referred to an advertised World Glaucoma Day (March 2009) Jules Gonin Eye Hospital, Lausanne Switzerland. Participants underwent a clinical exam (IOP, slit lamp, angle and disc examination by a general ophthalmologist), 90% completed a GQL-15 questionnaire and over 50% completed a MDT test in both eyes. Those who were classified as abnormal on one or more of the following (IOP >21 mmHg/ GQL-15 score >20/ MDT score >2/ clinical exam) underwent a follow up clinical examination by a glaucoma specialist including imaging and threshold perimetry. After the second examination subjects were classified as "healthy"(H), "glaucoma suspect" (GS) (ocular hypertension and/or suspicious disc, angle closure with SD) or "glaucomatous" (G). Results: One hundred and ten subjects completed all 4 initial examinations; of these 69 were referred to complete the 2nd examination and were classified as; 8 G, 24 GS, and 37 H. MDT detected 7/8 G, and 7/24 GS, with false referral rate of 3.8%. IOP detected 2/8 G and 8/24 GS, with false referral rate of 8.9%. GQL-15 detected 4/8 G, 16/24 GS with a false referral rate of 42%. Conclusions: In this sample of participants attending a self referral glaucoma detection event, the MDT performed significantly better than the GQL-15 and IOP in discriminating glaucomatous patients from healthy subjects. Further studies are required to assess the potential of the MDT as a glaucoma screening tool.

Prospective and retrospective motion correction in diffusion magnetic resonance imaging of the human brain.

Diffusion-weighting in magnetic resonance imaging (MRI) increases the sensitivity to molecular Brownian motion, providing insight in the micro-environment of the underlying tissue types and structures. At the same time, the diffusion weighting renders the scans sensitive to other motion, including bulk patient motion. Typically, several image volumes are needed to extract diffusion information, inducing also inter-volume motion susceptibility. Bulk motion is more likely during long acquisitions, as they appear in diffusion tensor, diffusion spectrum and q-ball imaging. Image registration methods are successfully used to correct for bulk motion in other MRI time series, but their performance in diffusion-weighted MRI is limited since diffusion weighting introduces strong signal and contrast changes between serial image volumes. In this work, we combine the capability of free induction decay (FID) navigators, providing information on object motion, with image registration methodology to prospectively--or optionally retrospectively--correct for motion in diffusion imaging of the human brain. Eight healthy subjects were instructed to perform small-scale voluntary head motion during clinical diffusion tensor imaging acquisitions. The implemented motion detection based on FID navigator signals is processed in real-time and provided an excellent detection performance of voluntary motion patterns even at a sub-millimetre scale (sensitivity≥92%, specificity>98%). Motion detection triggered an additional image volume acquisition with b=0 s/mm2 which was subsequently co-registered to a reference volume. In the prospective correction scenario, the calculated motion-parameters were applied to perform a real-time update of the gradient coordinate system to correct for the head movement. Quantitative analysis revealed that the motion correction implementation is capable to correct head motion in diffusion-weighted MRI to a level comparable to scans without voluntary head motion. The results indicate the potential of this method to improve image quality in diffusion-weighted MRI, a concept that can also be applied when highest diffusion weightings are performed.

The impact of spatial resolution and respiratory motion on MR imaging of atherosclerotic plaque.

PURPOSE: To examine the impact of spatial resolution and respiratory motion on the ability to accurately measure atherosclerotic plaque burden and to visually identify atherosclerotic plaque composition. MATERIALS AND METHODS: Numerical simulations of the Bloch equations and vessel wall phantom studies were performed for different spatial resolutions by incrementally increasing the field of view. In addition, respiratory motion was simulated based on a measured physiologic breathing pattern. RESULTS: While a spatial resolution of > or = 6 pixels across the wall does not result in significant errors, a resolution of < or = 4 pixels across the wall leads to an overestimation of > 20%. Using a double-inversion T2-weighted turbo spin echo sequence, a resolution of 1 pixel across equally thick tissue layers (fibrous cap, lipid, smooth muscle) and a respiratory motion correction precision (gating window) of three times the thickness of the tissue layer allow for characterization of the different coronary wall components. CONCLUSIONS: We found that measurements in low-resolution black blood images tend to overestimate vessel wall area and underestimate lumen area.

Assessment of tidal volume and thoracoabdominal motion using volume and flow-oriented incentive spirometers in healthy subjects

The objective of the present study was to evaluate incentive spirometers using volume- (Coach and Voldyne) and flow-oriented (Triflo II and Respirex) devices. Sixteen healthy subjects, 24 ± 4 years, 62 ± 12 kg, were studied. Respiratory variables were obtained by respiratory inductive plethysmography, with subjects in a semi-reclined position (45º). Tidal volume, respiratory frequency, minute ventilation, inspiratory duty cycle, mean inspiratory flow, and thoracoabdominal motion were measured. Statistical analysis was performed with Kolmogorov-Smirnov test, t-test and ANOVA. Comparison between the Coach and Voldyne devices showed that larger values of tidal volume (1035 ± 268 vs 947 ± 268 ml, P = 0.02) and minute ventilation (9.07 ± 3.61 vs 7.49 ± 2.58 l/min, P = 0.01) were reached with Voldyne, whereas no significant differences in respiratory frequency were observed (7.85 ± 1.24 vs 8.57 ± 1.89 bpm). Comparison between flow-oriented devices showed larger values of inspiratory duty cycle and lower mean inspiratory flow with Triflo II (0.35 ± 0.05 vs 0.32 ± 0.05 ml/s, P = 0.00, and 531 ± 137 vs 606 ± 167 ml/s, P = 0.00, respectively). Abdominal motion was larger (P < 0.05) during the use of volume-oriented devices compared to flow-oriented devices (52 ± 11% for Coach and 50 ± 9% for Voldyne; 43 ± 13% for Triflo II and 44 ± 14% for Respirex). We observed that significantly higher tidal volume associated with low respiratory frequency was reached with Voldyne, and that there was a larger abdominal displacement with volume-oriented devices.

Breathing pattern and thoracoabdominal motion during exercise in chronic obstructive pulmonary disease

Subjects with chronic obstructive pulmonary disease (COPD) present breathing pattern and thoracoabdominal motion abnormalities that may contribute to exercise limitation. Twenty-two men with stable COPD (FEV1 = 42.6 ± 13.5% predicted; age 68 ± 8 years; mean ± SD) on usual medication and with at least 5 years of diagnosis were evaluated at rest and during an incremental cycle exercise test (10 watts/2 min). Changes in respiratory frequency, tidal volume, rib cage and abdominal motion contribution to tidal volume and the phase angle that measures the asynchrony were analyzed by inductive respiratory plethysmography at rest and during three levels of exercise (30-50, 70-80, and 100% maximal work load). Repeated measures ANOVA followed by pre-planned contrasts and Bonferroni corrections were used for analyses. As expected, the greater the exercise intensity the higher the tidal volume and respiratory frequency. Abdominal motion contributed to the tidal volume increase (rest: 49.82 ± 11.19% vs exercise: 64.15 ± 9.7%, 63.41 ± 10%, and 65.56 ± 10.2%, respectively, P < 0.001) as well as the asynchrony [phase angle: 11.95 ± 7.24° at rest vs 22.2 ± 15° (P = 0.002), 22.6 ± 9° (P < 0.001), and 22.7 ± 8° (P < 0.001), respectively, at the three levels of exercise]. In conclusion, the increase in ventilation during exercise in COPD patients was associated with the major motion of the abdominal compartment and with an increase in the asynchrony independent of exercise intensity. It suggests that cycling exercise is an effective way of enhancing ventilation in COPD patients.

Studies on function projective synchronization in chaotic and hyperchaotic systems

FPS is a more general form of synchronization. Hyperchaotic systems possessing more than one positive Lypaunov exponent exhibit highly complex behaviour and are more suitable for some applications like secure communications. In this thesis we report studies of FPS and MFPS of a few chaotic and hyperchaotic systems. When all the parameters of the system are known we show that active nonlinear control method can be efectively used to obtain FPS. Adaptive nonlinear control and OPCL control method are employed for obtaining FPS and MFPS when some or all parameters of the system are uncertain. A secure communication scheme based on MFPS is also proposed in theory. All our theoretical calculations are verified by numerical simulations.

A Model Coupling Vibrational and Rotational Motion for the DNA Molecule

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)