Experiments on substratum roughness, grainsize and volume influence on the motion and spreading of rock avalanches

The main objective of the research is to link granular physics with the modelling of rock avalanches. Laboratory experiments consist to find a convenient granular material, i.e. grainsize and physical behaviour, and testing it on simple slope geometry. When the appropriate sliding material is selected, we attempted to model the debris avalanche and the spreading on a slope with different substratum to understand the relationship between the volume and the reach angle, i.e. angle of the line joining the top of the scar and the end of the deposit. For a better understanding of the mass spreading, the deposits are scanned with a laser scanner. Datasets are compared to see how the grain size and volume influence a debris avalanche. The relationship between the roughness and grainsize of the substratum shows that the spreading of the sliding mass is increased when the roughness of the substratum starts to be equivalent or greater than the grainsize of the flowing mass. The runout distance displays a more complex relationship, because a long runout distance implies that grains are less spread. This means that if the substratum is too rough the distance diminishes, as well if it is too smooth because the effect on the apparent friction decreases. Up to now our findings do not permit to validate any previous model (Melosh, 1987; Bagnold 1956).

Setting in motion the immune mechanisms underlying genetically determined resistance and susceptibility to infection with Leishmania major.

The murine model of infection with Leishmania major has allowed the demonstration of a causal relationship between, on the one hand, genetically determined resistance to infection and the development of a Th1 CD4+ cell response, and on the other hand, genetically determined susceptibility and Th2 cell maturation. Using this murine model of infection, the role of cytokines in directing the functional differentiation pathway of CD4+ T cell precursors, has been demonstrated in vivo. Thus, IL-12 and IFN-gamma have been shown to favour Th1 cell development and IL-4 is crucial for the differentiation of Th2 responses. Maturation of a Th2 response in susceptible BALB/c mice following infection with L. major is triggered by the IL-4 produced during the first two days after parasite inoculation. This IL-4 rapidly renders parasite specific CD4+ T cells precursors unresponsive to IL-12. A restricted population of CD4+ T cells expressing the V beta 4V alpha 8 TCR heterodimer and recognizing a single epitope on the LACK (Leishmania Activated C-Kinase) antigen of L. major is responsible for this rapid production of IL-4, instructing subsequent differentiation towards the Th2 phenotype of CD4+ T cells specific for several parasite antigens.

Altered vision during motion: an unusual symptom of cerebellar dysfunction, quantifiable by a simple clinical test.

PURPOSE: To report a series of patients with cerebellar dysfunction and altered vision during motion, and to quantify their visual impairment in motion with a simple clinical test. METHODS: Twenty consecutive patients suffering from cerebellar dysfunction and altered vision during motion were examined between 1994 and 2007. A control group consisted of 20 age- and sex-matched healthy people. All patients had a full neuro-ophthalmic examination. Near visual acuity (NVA) was measured at rest (static NVA) and during chair rotation (dynamic NVA). Distance visual acuity (DVA) was measured at rest (static DVA) and during rotation of the patient's head (dynamic DVA). RESULTS: Only four of the 20 patients reported altered vision during motion spontaneously. The remaining 16 patients admitted this unusual visual disturbance only when asked specifically. All patients exhibited abnormal eye movements, including saccadic smooth pursuit (20/20), dysmetric saccades (15/20), nystagmus (19/20) and impaired suppression of vestibulo-ocular reflex (VOR) (20/20). During rotation of the examination chair (dynamic NVA), the drop in NVA averaged 5.6 lines (range 1-10 lines). During rotation of the patient's head (dynamic DVA), the drop in DVA averaged only 2.5 lines (range 0-10 lines). For the control group, there was no significant drop in NVA under dynamic conditions. CONCLUSION: Patients with cerebellar dysfunction rarely complain spontaneously of altered vision during motion. However, specific questioning may bring up this unusual symptom. The use of a simple clinical test, consisting of NVA measurement during rotation of the examination chair (dynamic NVA), allows practitioners to quantify the level of visual impairment in patients presenting altered VOR modulation.

Reproducibility of acute mountain sickness in children and adults: a prospective study.

OBJECTIVE: Although a history of previous acute mountain sickness (AMS) is commonly used for providing advice and recommending its prophylaxis during subsequent exposure, the intraindividual reproducibility of AMS during repeated high-altitude exposure has never been examined in a prospective controlled study.METHODS: In 27 nonacclimatized children and 29 adults, AMS was assessed during the first 48 hours after rapid ascent to 3450 m on 2 consecutive occasions 9 to 12 months apart.RESULTS: During the first exposure, 18 adults (62%) and 6 children (22%) suffered from AMS; during the second exposure, 14 adults (48%) and 4 children (15%) suffered from this problem (adults versus children, P <= .01). Most importantly, the intraindividual reproducibility of AMS was very different (P < .001) between children and adults. None of the 6 children having suffered from AMS during the first exposure suffered from AMS during the second exposure, but 4 children with no AMS during the first exposure did experience this problem during the second exposure. In contrast, 14 of the 18 adults who suffered from AMS on the first occasion also presented with this problem during the second exposure, and no new case developed in those who had not experienced AMS on the first occasion.CONCLUSIONS: In adults, a history of AMS is highly predictable of the disease on subsequent exposure, whereas in children it has no predictive value. A history of AMS should not prompt practitioners to advise against reexposure to high altitude or to prescribe drugs for its prophylaxis in children. Pediatrics 2011;127:e1445-e1448

Relationship between motion of coronary arteries and diaphragm during free breathing: lessons from real-time MR imaging.

OBJECTIVE: Diaphragmatic navigators are frequently used in free-breathing coronary MR angiography, either to gate or prospectively correct slice position or both. For such approaches, a constant relationship between coronary and diaphragmatic displacement throughout the respiratory cycle is assumed. The purpose of this study was to evaluate the relationship between diaphragmatic and coronary artery motion during free breathing. SUBJECTS AND METHODS: A real-time echoplanar MR imaging sequence was used in 12 healthy volunteers to obtain 30 successive images each (one per cardiac cycle) that included the left main coronary artery and the domes of both hemidiaphragms. The coronary artery and diaphragm positions (relative to isocenter) were determined and analyzed for effective diaphragmatic gating windows of 3, 5, and 7 mm (diaphragmatic excursions of 0-3, 0-5, and 0-7 mm from the end-expiratory position, respectively). RESULTS: Although the mean slope correlating the displacement of the right diaphragm and the left main coronary artery was approximately 0.6 for all diaphragmatic gating windows, we also found great variability among individual volunteers. Linear regression slopes varied from 0.17 to 0.93, and r2 values varied from .04 to .87. CONCLUSION: Wide individual variability exists in the relationship between coronary and diaphragmatic respiratory motion during free breathing. Accordingly, coronary MR angiographic approaches that use diaphragmatic navigator position for prospective slice correction may benefit from patient-specific correction factors. Alternatively, coronary MR angiography may benefit from a more direct assessment of the respiratory displacement of the heart and coronary arteries, using left ventricular navigators.

A Motion compensated filtering approach to remove sunlight flicker in shallow water images

A common problem in video surveys in very shallow waters is the presence of strong light fluctuations, due to sun light refraction. Refracted sunlight casts fast moving patterns, which can significantly degrade the quality of the acquired data. Motivated by the growing need to improve the quality of shallow water imagery, we propose a method to remove sunlight patterns in video sequences. The method exploits the fact that video sequences allow several observations of the same area of the sea floor, over time. It is based on computing the image difference between a given reference frame and the temporal median of a registered set of neighboring images. A key observation is that this difference will have two components with separable spectral content. One is related to the illumination field (lower spatial frequencies) and the other to the registration error (higher frequencies). The illumination field, recovered by lowpass filtering, is used to correct the reference image. In addition to removing the sunflickering patterns, an important advantage of the approach is the ability to preserve the sharpness in corrected image, even in the presence of registration inaccuracies. The effectiveness of the method is illustrated in image sets acquired under strong camera motion containing non-rigid benthic structures. The results testify the good performance and generality of the approach

Trinocular System for 3D motion and Dense Stucture Estimation

The relief of the seafloor is an important source of data for many scientists. In this paper we present an optical system to deal with underwater 3D reconstruction. This system is formed by three cameras that take images synchronously in a constant frame rate scheme. We use the images taken by these cameras to compute dense 3D reconstructions. We use Bundle Adjustment to estimate the motion ofthe trinocular rig. Given the path followed by the system, we get a dense map of the observed scene by registering the different dense local reconstructions in a unique and bigger one

Three-dimensional magnetic resonance myocardial motion tracking from a single image plane.

Three-dimensional imaging for the quantification of myocardial motion is a key step in the evaluation of cardiac disease. A tagged magnetic resonance imaging method that automatically tracks myocardial displacement in three dimensions is presented. Unlike other techniques, this method tracks both in-plane and through-plane motion from a single image plane without affecting the duration of image acquisition. A small z-encoding gradient is subsequently added to the refocusing lobe of the slice-selection gradient pulse in a slice following CSPAMM acquisition. An opposite polarity z-encoding gradient is added to the orthogonal tag direction. The additional z-gradients encode the instantaneous through plane position of the slice. The vertical and horizontal tags are used to resolve in-plane motion, while the added z-gradients is used to resolve through-plane motion. Postprocessing automatically decodes the acquired data and tracks the three-dimensional displacement of every material point within the image plane for each cine frame. Experiments include both a phantom and in vivo human validation. These studies demonstrate that the simultaneous extraction of both in-plane and through-plane displacements and pathlines from tagged images is achievable. This capability should open up new avenues for the automatic quantification of cardiac motion and strain for scientific and clinical purposes.

UBVRI photoelectric photometry of high proper motion stars

UBVRI photoelectric photometry is presented for 269 late spectral type, high proper motion stars belonging to the 'Lowell Proper Motion Survey' and included in the present version of the Hipparcos Input Catalogue. The observations and data reduction are described. The external errors obtained by comparison of the results with those obtained in other studies are presented.

Reduction in range of cervical motion on serial long-term follow-up in patients undergoing oblique corpectomy for cervical spondylotic myelopathy.

PURPOSE: To determine whether motion preservation following oblique cervical corpectomy (OCC) for cervical spondylotic myelopathy (CSM) persists with serial follow-up. METHODS: We included 28 patients with preoperative and at least two serial follow-up neutral and dynamic cervical spine radiographs who underwent OCC for CSM. Patients with an ossified posterior longitudinal ligament (OPLL) were excluded. Changes in sagittal curvature, segmental and whole spine range of motion (ROM) were measured. Nathan's system graded anterior osteophyte formation. Neurological function was measured by Nurick's grade and modified Japanese Orthopedic Association (JOA) scores. RESULTS: The majority (23 patients) had a single or 2-level corpectomy. The average duration of follow-up was 45 months. The Nurick's grade and the JOA scores showed statistically significant improvements after surgery (p < 0.001). 17% of patients with preoperative lordotic spines had a loss of lordosis at last follow-up, but with no clinical worsening. 77% of the whole spine ROM and 62% of segmental ROM was preserved at last follow-up. The whole spine and segmental ROM decreased by 11.2° and 10.9°, respectively (p ≤ 0.001). Patients with a greater range of segmental movement preoperatively had a statistically greater range of movement at follow-up. The analysis of serial radiographs indicated that the range of movement of the whole spine and the range of movement at the segmental spine levels significantly reduced during the follow-up period. Nathan's grade showed increase in osteophytosis in more than two-thirds of the patients (p ≤ 0.01). The whole spine range of movement at follow-up significantly correlated with Nathan's grade. CONCLUSIONS: Although the OCC preserves segmental and whole spine ROM, serial measurements show a progressive decrease in ROM albeit without clinical worsening. The reduction in this ROM is probably related to degenerative ossification of spinal ligaments.

Exaggerated exercise-induced pulmonary hypertension causes lung water accumulation and right ventricular dysfunction in patients with chronic mountain sickness

Background: Chronic mountain sickness (CMS) is characterized by exaggerated exercise-induced pulmonary hypertension. Evidences suggests that exercise may cause lung fluid accumulation at high altitude. We hypothesized that, in patients with CMS, exercise causes lung fluid accumulation.Methods: In 21 male CMS patients and 20 matched healthy controls born and permanently living in La Paz (Bolivia, 3600m) we assessed with echocardiogram, pulmonary artery pressure (PASP), right and left ventricular function and ultrasoundlung comets (ULCs, a marker of lung fluid accumulation) at rest and during mild bicycle exercise (10 min at 50W).Results: CMS patients presented a more than 2-fold greater exercise-induced increase in pulmonary artery pressure than controls (17.1±8.3 vs 7.2±7.9 mmHg, P=0.003). This exaggerated PASP response to exercise was associated with a roughly 3-fold greater increase in UCLs in patients with CMS than in controls (6.3±5.1 vs. 2.1±5.3, p<0.05), and there existed a significant relationship between PASP and UCLs (r=0.44, p<0.001). Finally, TDI on lateral tricuspid annulus decreased during exercise in patients with CMS (from 13.2±3.2 to 11.5±2.1 cm s-1, p=0.03), but increased in controls (from 13.1±2.9 to 14.9±2.6 cm s-1 , p=0.04). Left ventricular function remained unaltered in the 2 groups.Conclusions: we provide the first direct evidence in CMS patients that exaggerated exercise-induced pulmonary hypertension causes rapid lung fluid accumulation and right ventricular dysfunction. We speculate that in patients with CMS these two phenomena contribute to reduced exercise performances and Figure 1 increased cardiovascular morbidity and mortality that characterise these subjects.