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Search Results: 1 - 10 of 3304 matches for " Max Langer "
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Non-Linear Phase Tomography Based on Fréchet Derivative  [PDF]
Valentina Davidoiu, Bruno Sixou, Max Langer, Franoise Peyrin
Advances in Computed Tomography (ACT) , 2014, DOI: 10.4236/act.2014.34007
Abstract: Phase imaging coupled to micro-tomography acquisition has emerged as a powerful tool to investigate specimens in a non-destructive manner. While the intensity data can be acquired and recorded, the phase information of the signal has to be “retrieved” from the data modulus only. Phase retrieval is an ill-posed non-linear problem and regularization techniques including a priori knowledge are necessary to obtain stable solutions. Several linear phase recovery methods have been proposed and it is expected that some limitations resulting from the linearization of the direct problem will be overcome by taking into account the non-linearity of the phase problem. To achieve this goal, we propose and evaluate a non-linear algorithm for in-line phase micro-tomography based on an iterative Landweber method with an analytic calculation of the Fréchet derivative of the phase-intensity relationship and of its adjoint. The algorithm was applied in the projection space using as initialization the linear mixed solution. The efficacy of the regularization scheme was evaluated on simulated objects with a slowly and a strongly varying phase. Experimental data were also acquired at ESRF using a propagation-based X-ray imaging technique for the given pixel size 0.68 μm. Two regularization scheme were considered: first the initialization was obtained without any prior on the ratio of the real and imaginary parts of the complex refractive index and secondly a constant a priori value was assumed on \"\" . The tomographic central slices of the refractive index decrement were compared and numerical evaluation was performed. The non-linear method globally decreases the reconstruction errors compared to the linear algorithm and is achieving better reconstruction results if no prior is introduced in the initialization solution. For in-line phase micro-tomography, this non-linear approach is a new and interesting method in biomedical studies where the exact value of the a priori ratio is not known.
Mesozoic dinosaurs from Brazil and their biogeographic implications
Bittencourt, Jonathas S.;Langer, Max C.;
Anais da Academia Brasileira de Ciências , 2011, DOI: 10.1590/S0001-37652011000100003
Abstract: the record of dinosaur body-fossils in the brazilian mesozoic is restricted to the triassic of rio grande do sul and cretaceous of various parts of the country. this includes 21 named species, two of which were regarded as nomina dubia, and 19 consensually assigned to dinosauria. additional eight supraspecific taxa have been identified based on fragmentary specimens and numerous dinosaur footprints known in brazil. in fact, most brazilian specimens related to dinosaurs are composed of isolated teeth and vertebrae. despite the increase of fieldwork during the last decade, there are still no dinosaur body-fossils of jurassic age and the evidence of ornithischians in brazil is very limited. dinosaur faunas from this country are generally correlated with those from other parts of gondwana throughout the mesozoic. during the late triassic, there is a close correspondence to argentina and other south-pangaea areas. mid-cretaceous faunas of northeastern brazil resemble those of coeval deposits of north africa and argentina. southern hemisphere spinosaurids are restricted to africa and brazil, whereas abelisaurids are still unknown in the early cretaceous of the latter. late cretaceous dinosaur assemblages of south-central brazil are endemic only to genus or, more conspicuously, to species level, sharing closely related taxa with argentina, madagascar, indo-pakistan and, to a lesser degree, continental africa.
A New Baurusuchid (Crocodyliformes, Mesoeucrocodylia) from the Late Cretaceous of Brazil and the Phylogeny of Baurusuchidae
Felipe C. Montefeltro, Hans C. E. Larsson, Max C. Langer
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0021916
Abstract: Background Baurusuchidae is a group of extinct Crocodyliformes with peculiar, dog-faced skulls, hypertrophied canines, and terrestrial, cursorial limb morphologies. Their importance for crocodyliform evolution and biogeography is widely recognized, and many new taxa have been recently described. In most phylogenetic analyses of Mesoeucrocodylia, the entire clade is represented only by Baurusuchus pachecoi, and no work has attempted to study the internal relationships of the group or diagnose the clade and its members. Methodology/Principal Findings Based on a nearly complete skull and a referred partial skull and lower jaw, we describe a new baurusuchid from the Vale do Rio do Peixe Formation (Bauru Group), Late Cretaceous of Brazil. The taxon is diagnosed by a suite of characters that include: four maxillary teeth, supratemporal fenestra with equally developed medial and anterior rims, four laterally visible quadrate fenestrae, lateral Eustachian foramina larger than medial Eustachian foramen, deep depression on the dorsal surface of pterygoid wing. The new taxon was compared to all other baurusuchids and their internal relationships were examined based on the maximum parsimony analysis of a discrete morphological data matrix. Conclusion The monophyly of Baurusuchidae is supported by a large number of unique characters implying an equally large morphological gap between the clade and its immediate outgroups. A complex phylogeny of baurusuchids was recovered. The internal branch pattern suggests two main lineages, one with a relatively broad geographical range between Argentina and Brazil (Pissarrachampsinae), which includes the new taxon, and an endemic clade of the Bauru Group in Brazil (Baurusuchinae).
Whispering to the Deaf: Communication by a Frog without External Vocal Sac or Tympanum in Noisy Environments
Renaud Boistel, Thierry Aubin, Peter Cloetens, Max Langer, Brigitte Gillet, Patrice Josset, Nicolas Pollet, Anthony Herrel
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0022080
Abstract: Atelopus franciscus is a diurnal bufonid frog that lives in South-American tropical rain forests. As in many other frogs, males produce calls to defend their territories and attract females. However, this species is a so-called “earless” frog lacking an external tympanum and is thus anatomically deaf. Moreover, A. franciscus has no external vocal sac and lives in a sound constraining environment along river banks where it competes with other calling frogs. Despite these constraints, male A. franciscus reply acoustically to the calls of conspecifics in the field. To resolve this apparent paradox, we studied the vocal apparatus and middle-ear, analysed signal content of the calls, examined sound and signal content propagation in its natural habitat, and performed playback experiments. We show that A. franciscus males can produce only low intensity calls that propagate a short distance (<8 m) as a result of the lack of an external vocal sac. The species-specific coding of the signal is based on the pulse duration, providing a simple coding that is efficient as it allows discrimination from calls of sympatric frogs. Moreover, the signal is redundant and consequently adapted to noisy environments. As such a coding system can be efficient only at short-range, territory holders established themselves at short distances from each other. Finally, we show that the middle-ear of A. franciscus does not present any particular adaptations to compensate for the lack of an external tympanum, suggesting the existence of extra-tympanic pathways for sound propagation.
X-Ray Phase Nanotomography Resolves the 3D Human Bone Ultrastructure
Max Langer, Alexandra Pacureanu, Heikki Suhonen, Quentin Grimal, Peter Cloetens, Fran?oise Peyrin
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035691
Abstract: Bone strength and failure are increasingly thought to be due to ultrastructural properties, such as the morphology of the lacuno-canalicular network, the collagen fiber orientation and the mineralization on the nanoscale. However, these properties have not been studied in 3D so far. Here we report the investigation of the human bone ultrastructure with X-ray phase nanotomography, which now provides the required sensitivity, spatial resolution and field of view. The 3D organization of the lacuno-canalicular network is studied in detail over several cells in osteonal and interstitial tissue. Nanoscale density variations are revealed and show that the cement line separating these tissues is hypermineralized. Finally, we show that the collagen fibers are organized as a twisted plywood structure in 3D.
An Additional Baurusuchid from the Cretaceous of Brazil with Evidence of Interspecific Predation among Crocodyliformes
Pedro L. Godoy, Felipe C. Montefeltro, Mark A. Norell, Max C. Langer
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0097138
Abstract: A new Baurusuchidae (Crocodyliformes, Mesoeucrocodylia), Aplestosuchus sordidus, is described based on a nearly complete skeleton collected in deposits of the Adamantina Formation (Bauru Group, Late Cretaceous) of Brazil. The nesting of the new taxon within Baurusuchidae can be ensured based on several exclusive skull features of this clade, such as the quadrate depression, medial approximation of the prefrontals, rostral extension of palatines (not reaching the level of the rostral margin of suborbital fenestrae), cylindrical dorsal portion of palatine bar, ridge on the ectopterygoid-jugal articulation, and supraoccipital with restricted thin transversal exposure in the caudalmost part of the skull roof. A newly proposed phylogeny of Baurusuchidae encompasses A. sordidus and recently described forms, suggesting its sixter-taxon relationship to Baurusuchus albertoi, within Baurusuchinae. Additionally, the remains of a sphagesaurid crocodyliform were preserved in the abdominal cavity of the new baurusuchid. Direct fossil evidence of behavioral interaction among fossil crocodyliforms is rare and mostly restricted to bite marks resulting from predation, as well as possible conspecific male-to-male aggression. This is the first time that a direct and unmistaken evidence of predation between different taxa of this group is recorded as fossils. This discovery confirms that baurusuchids were top predators of their time, with sphagesaurids occupying a lower trophic position, possibly with a more generalist diet.
The Modernisation of Manipulative Therapy  [PDF]
Max Zusman
International Journal of Clinical Medicine (IJCM) , 2011, DOI: 10.4236/ijcm.2011.25110
Abstract: Research indicates that, despite physiotherapists’ comprehensive training in the basic sciences, manipulative (currently “musculoskeletal”) therapy is still dominated in the clinical setting by its original, now obsolete, structure-based “biomedical” model. This is further inexplicable in the light of evidence that not only the underlying “philosophy” but also several of the fundamental requirements of the clinical process itself which has the structural-mechanical model as its basis, have been shown to be flawed or at least irrelevant. The apparent inability of the profession to fully abandon outmoded “concepts” (and embrace the acknowledged science-based “best practice” biopsychosocial model) may have potentially undesirable consequences for both patients and therapists engaged in the management of (chronic) musculoskeletal pain and disability.
On the Existence of Subharmonic Screech in Choked Circular Jets from a Sharp-Edged Orifice  [PDF]
Max Kandula
Open Journal of Acoustics (OJA) , 2014, DOI: 10.4236/oja.2014.41003
Abstract: Experiments are performed in choked circular hot and cold nitrogen jets issuing from a 2.44 cm diameter sharp-edged orifice at a fully expanded jet Mach number of 1.85 in an effort to investigate the character of screech phenomenon. The stagnation temperature of the cold and the hot jets are 299 K and 319 K respectively. The axial distribution of the centerline Mach number was obtained with a pitot tube, while the screech data (frequency and amplitude) at different axial and radial stations were measured with the aid of microphones. The fundamental screech frequency of the hot jet is slightly increased relative to that of the cold jet. It is concluded that temperature effects on the screech amplitude are manifested with regard to the fundamental and the subharmonic even at relatively small temperature range considered.
Alterations of Mass Density and 3D Osteocyte Lacunar Properties in Bisphosphonate-Related Osteonecrotic Human Jaw Bone, a Synchrotron μCT Study
Bernhard Hesse, Max Langer, Peter Varga, Alexandra Pacureanu, Pei Dong, Susanne Schrof, Nils M?nnicke, Heikki Suhonen, Cecile Olivier, Peter Maurer, Galateia J. Kazakia, Kay Raum, Francoise Peyrin
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088481
Abstract: Osteonecrosis of the jaw, in association with bisphosphonates (BRONJ) used for treating osteoporosis or cancer, is a severe and most often irreversible side effect whose underlying pathophysiological mechanisms remain largely unknown. Osteocytes are involved in bone remodeling and mineralization where they orchestrate the delicate equilibrium between osteoclast and osteoblast activity and through the active process called osteocytic osteolysis. Here, we hypothesized that (i) changes of the mineralized tissue matrix play a substantial role in the pathogenesis of BRONJ, and (ii) the osteocyte lacunar morphology is altered in BRONJ. Synchrotron μCT with phase contrast is an appropriate tool for assessing both the 3D morphology of the osteocyte lacunae and the bone matrix mass density. Here, we used this technique to investigate the mass density distribution and 3D osteocyte lacunar properties at the sub-micrometer scale in human bone samples from the jaw, femur and tibia. First, we compared healthy human jaw bone to human tibia and femur in order to assess the specific differences and address potential explanations of why the jaw bone is exclusively targeted by the necrosis as a side effect of BP treatment. Second, we investigated the differences between BRONJ and control jaw bone samples to detect potential differences which could aid an improved understanding of the course of BRONJ. We found that the apparent mass density of jaw bone was significantly smaller compared to that of tibia, consistent with a higher bone turnover in the jaw bone. The variance of the lacunar volume distribution was significantly different depending on the anatomical site. The comparison between BRONJ and control jaw specimens revealed no significant increase in mineralization after BP. We found a significant decrease in osteocyte-lacunar density in the BRONJ group compared to the control jaw. Interestingly, the osteocyte-lacunar volume distribution was not altered after BP treatment.
A systematic review of PET and PET/CT in oncology: A way to personalize cancer treatment in a cost-effective manner?
Astrid Langer
BMC Health Services Research , 2010, DOI: 10.1186/1472-6963-10-283
Abstract: Eight electronic databases were searched from 2005 until February 2010 to identify economic evaluation studies not included in previous Health Technology Assessment (HTA) reports. Only full health economic evaluations in English, French, or German were considered for inclusion. Economic evaluations were appraised using published quality criteria for assessing the quality of decision-analytic models. Given the variety of methods used in the health economic evaluations, the economic evidence has been summarized in qualitative form.From this new search, 14 publications were identified that met the inclusion criteria. All publications were decision-analytic models and evaluated PET using Fluorodeoxyglucose F18 (FDG-PET). Eight publications were cost-effectiveness analyses; six were cost-utility analyses. The studies were from Australia, Belgium, Canada, France, Italy, Taiwan, Japan, the Netherlands, the United Kingdom, and the United States. In the base case analyses of these studies, cost-effectiveness results ranged from dominated to dominant. The methodology of the economic evaluations was of varying quality. Cost-effectiveness was primarily influenced by the cost of PET, the specificity of PET, and the risk of malignancy.Owing to improved care and less exposure to ineffective treatments, personalized medicine using PET may be cost-effective. However, the strongest evidence for the cost-effectiveness of PET is still in the staging of non-small cell lung cancer. Management decisions relating to the assessment of treatment response or radiotherapy treatment planning require further research to show the impact of PET on patient management and its cost-effectiveness. Because of the potential for increased patient throughput and the possible greater accuracy, the cost-effectiveness of PET/CT may be superior to that of PET. Only four studies of the cost-effectiveness of PET/CT were found in this review, and this is clearly an area for future research.Positron emission tomo
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