719 research outputs found
Universality of Sea Wave Growth and Its Physical Roots
Modern day studies of wind-driven sea waves are usually focused on wind
forcing rather than on the effect of resonant nonlinear wave interactions. The
authors assume that these effects are dominating and propose a simple
relationship between instant wave steepness and time or fetch of wave
development expressed in wave periods or lengths. This law does not contain
wind speed explicitly and relies upon this asymptotic theory. The validity of
this law is illustrated by results of numerical simulations, in situ
measurements of growing wind seas and wind wave tank experiments. The impact of
the new vision of sea wave physics is discussed in the context of conventional
approaches to wave modeling and forecasting.Comment: submitted to Journal of Fluid Mechanics 24-Sep-2014, 34 pages, 10
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An analysis of risk assessment questions based on loss-averse preference
Postprint.A variety of risk assessment questionnaires are used within the financial planning profession to assess client risk preferences. Evidence indicates that the average person overweighs losses relative to an arbitrary reference point. This paper evaluated risk assessment questions on how well they correlate with monetary loss aversion. Twenty-fine West Texas residents between the ages of 27 and 56 filled out several risk assessment questionnaires and two weeks later their coefficients of loss aversion were measured using monetary gain and loss scenarios. The individual risk assessment questions were placed into three categories: expected utility theory, prospect theory and self-assessment. Composite measures were created for within-group and between-group comparisons. Statistically significant correlations were found between monetary loss aversion and different composite measures. The results provide financial planners with a group of risk assessment questions that capture loss-averse preferences.Includes bibliographical references
RĂŽle dâune flavoprotĂ©ine dans la biogĂ©nĂšse pariĂ©tale chez le champignon phytopathogĂšne Alternaria brassicicola
Correlation between the promoter basal core and precore mutations and HBsAg quantification in French blood donors infected with hepatitis B virus
International audienceHepatitis B virus (HBV) basal core promoter (BCP) and precore (PC) mutations, HBV viral load and HBV surface antigen (HBsAg) quantitation were screened to assess correlations between these HBV markers in asymptomatic chronic hepatitis B carriers in France. From January 2006 to July 2007, 200 sera were collected from patients who were discovered to be HBsAg-positive when they volunteered to give blood. Direct sequencing of precore/core gene was used to detect A1762T/G1764A mutations in the BCP and G1896A in the PC region. HBV viral load and HBsAg were quantified with two commercials assays. The prevalence of the BCP and PC mixed/mutants were 37% and 60% respectively (Pâ=â0.0001). HBV DNA level and HBsAg titer were significantly lower in subjects harboring the mixed/mutant PC virus compared to those infected by the wild phenotype. No significant difference was observed in HBV viral loads of blood donors infected by wild or mixed/mutant BCP viruses. Mutant or mixed PC virus was associated with male gender, HBeAb-positive status and HBV/D and HBV/E genotypes. BCP mutations were associated with age, and both HBV/A-HBV/E genotypes.The genetic properties of HBV in this cohort showed that most of the blood donors had a negative HBeAg serological status and harbored the PC mutant phenotype in combination with low levels of both HBV DNA and HBsAg. As the study was conducted in healthy subjects who could be considered as asmptomatic carriers, these results suggest a possible protective effect of the G1896A mutation against severe liver lesions. J. Med. Virol. 87:529â535, 2015. © 2014 Wiley Periodicals, Inc
Alignment of Cells and Extracellular Matrix Within Tissue- Engineered Substitutes
Most of the cells in our body are in direct contact with extracellular matrix (ECM) compoâ
nents which constitute a complex network of nano-scale proteins and glycosaminoglycans.
Those cells constantly remodel the ECM by different processes. They build it by secreting difâ
ferent proteins such as collagen, proteoglycans, laminins or degrade it by producing factors
such as matrix metalloproteinase (MMP). Cells interact with the ECM via specific receptors,
the integrins [1]. They also organize this matrix, guided by different stimuli, to generate patâ
terns, essential for tissue and organ functions. Reciprocally, cells are guided by the ECM, they
modify their morphology and phenotype depending on the protein types and organization
via bidirectional integrin signaling [2-4]. In the growing field of tissue engineering [5], control
of these aspects are of the utmost importance to create constructs that closely mimic native tisâ
sues. To do so, we must take into account the composition of the scaffold (synthetic, natural,
biodegradable or not), its organization and the dimension of the structure.
The particular alignment patterns of ECM and cells observed in tissues and organs such as
the corneal stroma, vascular smooth muscle cells (SMCs), tendons, bones and skeletal musâ
cles are crucial for organ function. SMCs express contraction proteins such as alpha-smoothmuscle
(SM)-actin, desmin and myosin [6] that are essential for cell contraction [6]. To result
in vessel contraction, the cells and ECM need to be organized in such a way that most cells
are elongated in the same axis. For tubular vascular constructs, it is suitable that SMCs align
in the circumferential direction, as they do in vivo [7, 8]. Another striking example of alignâ
ment is skeletal muscle cells that form long polynuclear cells, all elongated in the same axis.
Each cell generates a weak and short contraction pulse but collectively, it results in a strong,
long and sustained contraction of the muscle and, in term, a displacement of the member. In the corneal stroma, the particular arrangement of the corneal fibroblasts (keratocytes) and
ECM is essential to keep the transparency of this tissue [9-13]. Tendons also present a pecuâ
liar matrix alignment relative to the muscle axis. It gives a substantial resistance and excepâ
tional mechanical properties to the tissue in that axis [14, 15]. Intervertebral discs [16],
cartilage [17], dental enamel [18], and basement membrane of epithelium are other examples
of tissues/organs that present peculiar cell and matrix organization. By reproducing and
controlling those alignment patterns within tissue-engineered substitutes, a more physiologâ
ical representation of human tissues could be achieved.
Taking into account the importance of cell microenvironment on the functionality of tissue engineered
organ substitutes, one can assume the importance of being able to customise the
3D structure of the biomaterial or scaffold supporting cell growth. To do so, some methods
have been developed and most of them rely on topographic or contact guidance. This is the
phenomenon by which cells elongate and migrate in the same axis as the ECM. Topographic
guidance was so termed by Curtis and Clark [19] to include cell shape, orientation and
movement in the concept of contact guidance described by Harrison [20] and implemented
by Weiss [21, 22]. Therefore, if one can achieve ECM alignment, cells will follow the same
pattern. Inversely, if cells are aligned on a patterned culture plate, the end result would be
aligned ECM deposition [23].
The specific property of tissues or materials that present a variation in their mechanical and
structural properties in different axis is called anisotropy. This property can be evaluated eiâ
ther by birefringence measurements [24, 25], mechanical testing in different axis [26], immuâ
nological staining of collagen or actin filaments [23] or direct visualisation of collagen fibrils
using their self-fluorescence around 488 nm [27, 28].
Several techniques have been recently developed to mimic the specific alignment of cells
within tissues to produce more physiologically relevant constructs. In this chapter, we will
describe five different techniques, collagen gel compaction, electromagnetic field, electroâ
spinning of nanofibers, mechanical stimulation and microstructured culture plates
So far, so good⊠Similar fitness consequences and overall energetic costs for short and long-distance migrants in a seabird
Although there is a consensus about the evolutionary drivers of animal migration, considerable work is necessary to identify the mechanisms that underlie the great variety of strategies observed in nature. The study of differential migration offers unique opportunities to identify such mechanisms and allows comparisons of the costs and benefits of migration. The purpose of this study was to compare the characteristics of short and long-distance migrations, and fitness consequences, in a long-lived seabird species. We combined demographic monitoring (survival, phenology, hatching success) of 58 Northern Gannets (Morus bassanus) breeding on Bonaventure Island (Canada) and biologging technology (Global Location Sensor or GLS loggers) to estimate activity and energy budgets during the non-breeding period for three different migration strategies: to the Gulf of Mexico (GM), southeast (SE) or northeast (NE) Atlantic coast of the U.S. Survival, timing of arrival at the colony and hatching success are similar for short (NE, SE) and long-distance (GM) migrants. Despite similar fitness consequences, we found, as expected, that the overall energetic cost of migration is higher for long-distance migrants, although the daily cost during migration was similar between strategies. In contrast, daily maintenance and thermoregulation costs were lower for GM migrants in winter, where sea-surface temperature of the GM is 4-7o C warmer than SE and NE. In addition, GM migrants tend to fly 30 min less per day in their wintering area than other migrants. Considering lower foraging effort and lower thermoregulation costs during winter for long-distance migrants, this suggests that the energetic benefits during the winter of foraging in the GM outweigh any negative consequences of the longer-distance migration. These results support the notion that the costs and benefits of short and long-distance migration is broadly equal on an annual basis, i.e. there are no apparent carry-over effects in this long-lived bird species, probably because of the favourable conditions in the furthest wintering area
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