777 research outputs found
The Origins of Mathematical Societies and Journals
We investigate the origins of mathematical societies and journals. We argue that the origins of todayâs professional societies and journals have their roots in the informal gatherings of mathematicians in 17th century Italy, France, and England. The small gatherings in these nations began as academies and after gaining government recognition and support, they became the ancestors of the professional societies that exist today. We provide a brief background on the influences of the Renaissance and Reformation before discussing the formation of mathematical academies in each country
Influence of springtime phenology on the ratio of soil respiration to total ecosystem respiration in a mixed temperate forest
Total ecosystem (Reco) and soil (Rs) respiration are important CO2 fluxes in the carbon balance of forests. Typically Rs accounts for between 30-80% of Reco, although variation in this ratio has been shown to occur, particularly at seasonal time scales. The objective of this study was to relate changes in Rs/Reco ratio to changing springtime phenological conditions in forest ecosystems. We used one year (2003) of automated and twelve years (1995-2006) of manual chamber-based measurements of Rs. Reco was determined using tower-based eddy covariance measurements for an oak-dominated mixed temperate forest at Harvard Forest, Petersham, MA, USA. Phenological data were obtained from field observations and the JRC fAPAR remote sensing product. The automated and eddy covariance data showed that springtime phenological events do influence the ratio of soil to total ecosystem respiration. During canopy development, Reco rose strongly, mainly the aboveground component, due to the formation of an increasing amount of respiring leaf tissue. An increase in Rs was observed after most of the canopy development, which is probably the consequence of a shift in allocation of photosynthate products from above- to belowground. This hypothesized allocation shift was also confirmed by the results of the twelve year manual chamber-based measurements
Sizing Up Allometric Scaling Theory
Metabolic rate, heart rate, lifespan, and many other physiological properties vary with body mass in systematic and interrelated ways. Present empirical data suggest that these scaling relationships take the form of power laws with exponents that are simple multiples of one quarter. A compelling explanation of this observation was put forward a decade ago by West, Brown, and Enquist (WBE). Their framework elucidates the link between metabolic rate and body mass by focusing on the dynamics and structure of resource distribution networksâthe cardiovascular system in the case of mammals. Within this framework the WBE model is based on eight assumptions from which it derives the well-known observed scaling exponent of 3/4. In this paper we clarify that this result only holds in the limit of infinite network size (body mass) and that the actual exponent predicted by the model depends on the sizes of the organisms being studied. Failure to clarify and to explore the nature of this approximation has led to debates about the WBE model that were at cross purposes. We compute analytical expressions for the finite-size corrections to the 3/4 exponent, resulting in a spectrum of scaling exponents as a function of absolute network size. When accounting for these corrections over a size range spanning the eight orders of magnitude observed in mammals, the WBE model predicts a scaling exponent of 0.81, seemingly at odds with data. We then proceed to study the sensitivity of the scaling exponent with respect to variations in several assumptions that underlie the WBE model, always in the context of finite-size corrections. Here too, the trends we derive from the model seem at odds with trends detectable in empirical data. Our work illustrates the utility of the WBE framework in reasoning about allometric scaling, while at the same time suggesting that the current canonical model may need amendments to bring its predictions fully in line with available datasets.EJD acknowledges financial support from a National Institutes of Health/National Research Service Award (1F32 GM080123-01)
The Closest Damped Lyman Alpha System
A difficulty of studying damped Lyman alpha systems is that they are distant,
so one knows little about the interstellar medium of the galaxy. Here we report
upon a damped Lyman alpha system in the nearby galaxy NGC 4203, which is so
close (v_helio = 1117 km/s) and bright (B_o = 11.62) that its HI disk has been
mapped. The absorption lines are detected against Ton 1480, which lies only
1.9' (12 h_50 kpc) from the center of NGC 4203. Observations were obtained with
the Faint Object Spectrograph on HST (G270H grating) over the 2222-3277
Angstrom region with 200 km/s resolution. Low ionization lines of Fe, Mn, and
Mg were detected, leading to metallicities of -2.29, -2.4, which
are typical of other damped Lyman alpha systems, but well below the stellar
metallicity of this type of galaxy. Most notably, the velocity of the lines is
1160 +- 10 km/s, which is identical to the HI rotational velocity of 1170 km/s
at that location in NGC 4203, supporting the view that these absorption line
systems can be associated with the rotating disks of galaxies. In addition, the
line widths of the Mg lines give an upper limit to the velocity dispersion of
167 km/s, to the 99% confidence level.Comment: 4 pages LaTeX, including 1 figure and 1 table, uses emulateapj.sty.
Accepted for publication by Astrophysical Journal Letter
Engine Driven Pumps - Vibration Problem Resolution Using Specialized Testing Techniques
Case StudyOutline: Problem description and approach overview. Specialized testing to characterize the problem. Conclusions and recommendations based on the
test results. Implementing the solution. Lessons learned
INVESTIGATING A PUTATIVE NON STRUCTURAL PROTEIN OF THE BIRNAVIRUS DROSOPHILA-X VIRUS
Drosophila-X Virus (DXV) is the prototype virus of the Entomobirnavirus genera in the family Birnaviridae; its genome consists of two double-stranded RNA segments. DXV has two open reading frames on segment A, one encoding a polyprotein and the other capable of encoding a putative 27-kDa non structural protein (DXV-NS).
This project investigated the existence of DXV-NS since this putative protein is unique to Birnaviridae. Research into the nature of DXV-NS was furthered by the development of a number of tools: recombinant baculovirus and a stable Drosophila cell line expressing DXV-NS; an antibody against NS; a reporter construct to test a potential -1 frameshift signal. Though in the course of this research much was learned about DXV-NS, the greater question as to whether this open reading frame is expressed by DXV or is merely an artifact remains elusive
Overweight and obesity among children at risk of intellectual disability in 20 low and middle income countries
Background Children with intellectual disability (ID) in high income countries are at significantly greater risk of obesity than their non-disabled peers. We aimed to estimate the prevalence of overweight and obesity in 3 to 4-year-old children who are/are not at risk of ID in low and middle income countries. Method Secondary analysis of Round 4 and 5 UNICEF Multiple Indicator Cluster Surveys (MICS) from 20 low and middle income countries that included a total of 83â597 3 to 4-year-old children. Results Few differences in risk of overweight or obesity were apparent between 3 and 4-year-old children identified as being at risk/not at risk of ID in 20 low and middle income countries. In the two countries where statistically significant differences were observed, prevalence of overweight/obesity was lower among children at risk of ID. Conclusions These results stand in stark contrast to evidence from high income countries which suggest that children with ID are at significantly increased risk of obesity when compared to their non-intellectually disabled peers
Significant cognitive delay among 3- to 4-year old children in low- and middle-income countries:prevalence estimates and potential impact of preventative interventions
Background We sought to: (i) estimate the prevalence of significant cognitive delay (a marked delay in the development of general cognitive functioning) among nationally representative samples of young children in middle- and low-income countries; (ii) estimate the total number of children under 5âyears of age with significant cognitive delay living in low- and middle-income countries; and (iii) estimate the potential impact of five preventative interventions. Methods Secondary analysis of data collected in Rounds 4 and 5 of UNICEFâs Multiple Cluster Indicators Surveys in 51 countries involving 163 293 3- to 4-year-old children. Adjusted population-attributable fractions were used to estimate the potential impact of five interventions based on Sustainable Development Goals (SDGs). Results The prevalence of significant cognitive delay in 3- to 4-year-old children in middle- and low-income countries was 10.1% (95% confidence interval 9.7â10.4%). Prevalence was strongly inversely related to country economic wealth. The estimated total number of children under 5 with significant cognitive delay living in low- and middle-income countries was just under 55 million. This number could be reduced by over 60% if three separate SDGs were achieved; every mother had secondary-level education, every household had access to improved water and sanitation, and every child had an acceptable level of home stimulation. Conclusions Our results provide additional evidence in support of a range of specific preventative interventions in early childhood to reduce the loss of developmental potential among children in low- and middle-income countries
Prevalence of underweight, wasting and stunting among young children with a significant cognitive delay in 47 low and middle-income countries
Background Undernutrition in early childhood is associated with a range of negative outcomes across the lifespan. Little is known about the prevalence of exposure to undernutrition among young children with significant cognitive delay. Method Secondary analysis of data collected on 161 188 threeâ and fourâyearâold children in 47 lowâincome and middleâincome countries in Rounds 4â6 of UNICEF's Multiple Indicator Cluster Surveys. Of these, 12.3% (95% confidence interval 11.8â12.8%) showed evidence of significant cognitive delay. Results In both middleâincome and lowâincome countries, significant cognitive delay was associated with an increased prevalence of exposure to three indicators of undernutrition (underweight, wasting and stunting). Overall, children with significant cognitive delay were more than twice as likely than their peers to be exposed to severe underweight, severe wasting and severe stunting. Among children with significant cognitive delay (and after controlling for country economic classification group), relative household wealth was the strongest and most consistent predictor of exposure to undernutrition. Conclusions Given that undernutrition in early childhood is associated with a range of negative outcomes in later life, it is possible that undernutrition in early childhood may play an important role in accounting for health inequalities and inequities experienced by people with significant cognitive delay in lowâincome and middleâincome countries
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