Physics in Riemann's mathematical papers

Riemann's mathematical papers contain many ideas that arise from physics, and some of them are motivated by problems from physics. In fact, it is not easy to separate Riemann's ideas in mathematics from those in physics. Furthermore, Riemann's philosophical ideas are often in the background of his work on science. The aim of this chapter is to give an overview of Riemann's mathematical results based on physical reasoning or motivated by physics. We also elaborate on the relation with philosophy. While we discuss some of Riemann's philosophical points of view, we review some ideas on the same subjects emitted by Riemann's predecessors, and in particular Greek philosophers, mainly the pre-socratics and Aristotle. The final version of this paper will appear in the book: From Riemann to differential geometry and relativity (L. Ji, A. Papadopoulos and S. Yamada, ed.) Berlin: Springer, 2017

Heart Valve Tissue Engineering: Concepts, Approaches, Progress, and Challenges

Potential applications of tissue engineering in regenerative medicine range from structural tissues to organs with complex function. This review focuses on the engineering of heart valve tissue, a goal which involves a unique combination of biological, engineering, and technological hurdles. We emphasize basic concepts, approaches and methods, progress made, and remaining challenges. To provide a framework for understanding the enabling scientific principles, we first examine the elements and features of normal heart valve functional structure, biomechanics, development, maturation, remodeling, and response to injury. Following a discussion of the fundamental principles of tissue engineering applicable to heart valves, we examine three approaches to achieving the goal of an engineered tissue heart valve: (1) cell seeding of biodegradable synthetic scaffolds, (2) cell seeding of processed tissue scaffolds, and (3) in-vivo repopulation by circulating endogenous cells of implanted substrates without prior in-vitro cell seeding. Lastly, we analyze challenges to the field and suggest future directions for both preclinical and translational (clinical) studies that will be needed to address key regulatory issues for safety and efficacy of the application of tissue engineering and regenerative approaches to heart valves. Although modest progress has been made toward the goal of a clinically useful tissue engineered heart valve, further success and ultimate human benefit will be dependent upon advances in biodegradable polymers and other scaffolds, cellular manipulation, strategies for rebuilding the extracellular matrix, and techniques to characterize and potentially non-invasively assess the speed and quality of tissue healing and remodeling

Plasmid macro-evolution: selection of deletions during adaptation in a nutrient-limited environment

Under conditions where plasmid-carriage is deleterious to the cell, evolutionary changes may be expected which result in an attenuation of the deleterious effect of the plasmid. During long-term growth in glucose-limited continuous culture, initiated with a single clone of Escherichia coli containing a derivative of the plasmid pBR322, a structural change arose in the plasmid and predominated in the plasmid-containing sector of the population. This variant possessed a 2.25 kb deletion encompassing the tetracycline resistance operon as well as a region of about 1.5 kb upstream from this operon. Competition experiments involving strains carrying the plasmid with the spontancous deletion, and strains carrying plasmids with artificially constructed deletions, revealed that deletion of this region of the plasmid, involving loss of tetracycline resistance, resulted in an increment in fitness of between 10 and 20%. From the magnitude of the growth advantage, we conclude that the attenuation of the deleterious effect of the plasmid was mainly due to a reduction in the plasmid mediated interference in the metabolism of the cell caused by a deletion of the tetracycline resistance gene.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42797/1/10709_2004_Article_BF00127247.pd

Improved mapping of soil erodibility (K-Factor) in the Burdekin River catchment, Queensland, to aid landscape modelling

Good-quality soil information is critical to the accuracy of models of environmental processes. In catchments that drain into Australia's Great Barrier Reef, process modelling is being used to improve understanding of the links between land-management, soil erosion, and sediment pollution of the marine environment. To underpin this modelling effort, we have been tasked with improving the available soil information for the Burdekin River catchment (the Reef catchment with the most severe land-degradation concerns) with a particular focus on those soil attributes that affect soil erodibility. We have applied geostatistical modelling techniques to the existing soil information to map K-factor of the Revised Universal Soil Loss Equation, averaged at a resolution of 1 ha.The calculation of K-factor for any mapping pixel requires soil attributes for particle size fractions, organic carbon, structure and permeability for this pixel. Data for these attributes were sourced from existing analytical and morphological soil profile description sites, and were harmonized over the 0 - 5 cm and 5 - 15 cm soil depth intervals (the first two intervals defined in the GlobalSoilMap. net project). Spatial surfaces of environmental covariates were calculated (16 terrain derivates and four gamma-ray spectroscopy covariates), and used to model and map the soil attribute data via a combination of random forest and geostatistical modelling methodology. The resultant spatial surfaces of soil attributes were mapped in rasters with a 1-ha block-averaged cell size. The modelling methods provide a probability distribution of the attribute uncertainty in each pixel. Values for attributes were then simulated and the K-factor formula applied, with this repeated to build a predictive distribution for K-factor.Compared with existing maps of K-factor derived from polygonal data for ASRIS, the K-factor map produced using our method is continuous and relatively smooth. The benefits of the resulting K-factor map are:it is spatially continuous, which agrees with our general understanding of soil variability.the new maps have an improved spatial resolution of 1 ha.the new maps can be produced at any desired percentile. This is beneficial if the K-factor is to be used as an input to further modelling, as it will enhance sensitivity analysis of the subsequent model

Retrospektive Analyse der Fruh- und Spatresultate nach chirurgischer Intervention bei supraventrikularen Arrhythmien. [Retrospective analysis of early and late results following surgical intervention in supraventricular arrhythmia]

The results of surgical procedures for treatment of supraventricular tachycardias were assessed in 65 patients undergoing operation between January, 1980 and December, 1993. Indications for intervention were WPW (59 patients), atrial fibrillation (5 patients) and atrial flutter (1 patient). All cases of WPW were refractory to medical treatment and 14 of 58 patients had one or several syncopes, 4 of whom had to be resuscitated. The surgical treatment of these patients was dissection of an accessory atrioventricular pathway. 15 of these patients underwent heart operation for a different indication at the same time. A total of 60 accessory pathways were diagnosed preoperatively, while 4 were located intraoperatively. The reoperation rate was 3% (2 patients) due to persistent WPW. Incidence of total AV block after the operation was 7% (4 patients). In the late postoperative stage, 12 patients developed supraventricular tachycardias, but none of these cases required surgical treatment. The actuarial survival rate after 10 years was 100%, and after 14 years 96%. We conclude that surgical dissection of accessory pathways offers a good alternative in cases of unsuccessful catheter ablative procedures or in cases of concomitant heart surgery. In 6 patients with mitral valve surgery, associated chronic atrial fibrillation was found. A concomitant Maze-procedure was performed for the purpose of surgically converting the atrial fibrillation to a stable sinus rhythm. The early postoperative results are promising

Tissue engineering of functional trileaflet heart valves from human marrow stromal cells

BACKGROUND: We previously demonstrated the successful tissue engineering and implantation of functioning autologous heart valves based on vascular-derived cells. Human marrow stromal cells (MSC) exhibit the potential to differentiate into multiple cell-lineages and can be easily obtained clinically. The feasibility of creating tissue engineered heart valves (TEHV) from MSC as an alternative cell source, and the impact of a biomimetic in vitro environment on tissue differentiation was investigated. METHODS AND RESULTS: Human MSC were isolated, expanded in culture, and characterized by flow-cytometry and immunohistochemistry. Trileaflet heart valves fabricated from rapidly bioabsorbable polymers were seeded with MSC and grown in vitro in a pulsatile-flow-bioreactor. Morphological characterization included histology and electron microscopy (EM). Extracellular matrix (ECM)-formation was analyzed by immunohistochemistry, ECM protein content (collagen, glycosaminoglycan) and cell proliferation (DNA) were biochemically quantified. Biomechanical evaluation was performed using Instron(TM). In all valves synchronous opening and closing was observed in the bioreactor. Flow-cytometry of MSC pre-seeding was positive for ASMA, vimentin, negative for CD 31, LDL, CD 14. Histology of the TEHV-leaflets demonstrated viable tissue and ECM formation. EM demonstrated cell elements typical of viable, secretionally active myofibroblasts (actin/myosin filaments, collagen fibrils, elastin) and confluent, homogenous tissue surfaces. Collagen types I, III, ASMA, and vimentin were detected in the TEHV-leaflets. Mechanical properties of the TEHV-leaflets were comparable to native tissue. CONCLUSION: Generation of functional TEHV from human MSC was feasible utilizing a biomimetic in vitro environment. The neo-tissue showed morphological features and mechanical properties of human native-heart-valve tissue. The human MSC demonstrated characteristics of myofibroblast differentiation

Auricall: A new device for a non-invasive, wireless, continuous monitoring of oxygen saturation and heart rate in patients with heart failure

Sleep apnoea syndrome is frequent in patients with heart failure and associated with a worse prognosis. We evaluated a new device (Auricall) for non-invasive, continuous recording of oxygen saturation (SpO(2)) and heart rate (HR) in patients with heart failure. We studied 20 patients (mean age 48.43+/-14.4 years, NYHA class II-III). All patients were requested to carry the device for at least 36 h and to write a diary during the recording time. Satisfactory recording of SpO(2) and HR was possible to obtain in 18 of 20 patients. Indeed 9 out of 18 patients showed significant periodic changes in SpO(2) during sleep. Therefore, Auricall is a useful tool to non-invasively monitor SpO(2) and HR in patients with heart failure and to detect breathing disorders in these patients