170,097 research outputs found
Yapp, W.B. — Birds and woods. London, Oxford University Press, 1962
No full textFerry C. Yapp, W.B. — Birds and woods. London, Oxford University Press, 1962. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 17, n°1, 1963. pp. 122-125
Personalizing learning: Is there a shared vision?
No full textPersonalizing Learning in the 21st Century brings together contributions from a wide range of educationalists interested in the idea of personalizing learning. Although the book is intended primarily for teachers and policy makers, it will be of interest to many others, in health education, consultancy, management, research and development, and industrial training. Reading this book should be a personalized learning experience for each and every one of us. [Book abstract]
Infection outcomes in splenectomized patients with hemoglobinopathies in Australia
No full textCopyright © 2009 International Society for Infectious Diseases Published by Elsevier Ltd.Alvin R. Yapp, Robert Lindeman, Nicole Gilroy, d, Zhanhai Gao and C. Raina MacIntyr
Real time evaluation of weld quality in narrow groove pipe welding
No full textWith the growth in pipeline installations all over the world, there is a great demand for highly
productive and robust welding systems. Mechanised pipe welding has been developed over the
last 50 years and the present focus is towards development of automated pipeline welding
systems. Pipeline welding automation is aimed at reducing costs and improving the installation
quality. To attain fully automated pipe welding systems there is a need to rely on sensors and
controls systems to mimic human like capabilities, such as visual inspection, in real time. The
key aim of this work is to develop and evaluate methods of automatic assessment of weld bead
shape and quality during narrow gap GMAW of transmission pipelines. This implies that the
measured bead profile will be assessed to determine whether the bead shape will cause defects
when the subsequent pass is deposited. Different approaches have been used to conquer the
challenge that is emulating human reasoning, all with different objectives in mind. In spite of
extensive literature research performed, very little information was found concerning the real
time determination and assessment of bead shape quality and none of it was reported to be
applied successfully to the pipeline industry. Despite the continuous development of laboratory
laser vision systems commercial ones have been on the market for decades, some specifically
developed for the welding application. Laser vision sensor systems provide surface profile
information, and are the only sensors which can satisfactorily measure bead profile on a narrow
groove. In order to be able to use them to automatically assess weld bead shape and quality, a
deep understanding of their characteristics and limitations needs to be achieved. Once that
knowledge was attained it was then applied to determine the best sensor configuration for this
purpose. After that the development of human like judgment algorithms were developed to
accomplish the aim that was set. Empirical rules were obtained from an experienced welder
regarding the acceptability of bead shapes and were then applied in the developed system with
good results. To scientifically evaluate and determine the rules to use in this system, further
experiments would be required. The output of the system developed showed very accurate,
reliable and consistent results that were true to the external measurements and comparisons
performed. The developed system has numerous applications in the pipeline industry and it
could easily be implemented on commercial systems
Saturation: Race, Art, and the Circulation of Value
No full text"Controversies involving race and the art world are often discussed in terms of diversity and representation—as if having the right representative from a group or a larger plurality of embodied difference would absolve art institutions from historic forms of exclusion. This book offers another approach, taking into account not only questions of racial representation but also issues of structural change and the redistribution of resources. In essays, conversations, discussions, and artist portfolios, contributors confront in new ways questions at the intersection of art, race, and representation." -- Publisher's website
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Racing the wind. Water economy and energy expenditure in avian endurance flight
No full textEver since Ikarus, bird flight has been a fascinating miracle to man. Fragile birds cross deserts and overcome mountain ranges. They endure fasting, adverse climates, span the globe on the wing. What are the traits that make such a performance possible, what are the trade-offs, what the limitations?
This thesis is meant as a contribution to an integrated understanding of the challenges associated with avian flight, and the ways in which animals cope with them both physiologically and behaviourally. The experiments presented here deal with the different sometimes opposing demands on a bird’s energy and water budget during sustained flight periods under controlled ambient conditions in a wind tunnel.
The challenges of avian long distance migration
Powered flight as a means of locomotion is a salient characteristic of birds, and migratory endurance flight is outstanding in its high sustained metabolic demands compared to other activities in a bird’s life. The physiological mechanisms and adaptations that enable some species to cross the globe on their way from wintering to breeding grounds and back again, traversing vast inhospitable areas like deserts or oceans without eating or drinking, are part of the mystery that still waits to be solved. Three factors have been suggested as shaping the physiology and behaviour of migrants: time, energy and safety. For the flight period itself, energy is generally considered to be the most important factor of the three, due to the very high sustained metabolic rates. A fourth factor that has not received much attention but might be equally important is water. Long migratory flights may sometimes be limited by dehydration rather than by energy depletion. Energy and water management are closely interlinked and to assess the physiological challenges of long distance flights neither factor can be studied in isolation.
During their natural migratory flights, birds change their position in a three dimensional world, thereby choosing from a continuum of ambient conditions, temperature, air pressure, humidity, wind direction or speed, to name only a few. All of these have an effect on flight performance, sometimes in conflicting directions for energy metabolism or water flux: Ambient temperature is dependent on geographic location, season, time of day and flight altitude. Through its effect on thermoregulation, temperature is one of the main factors affecting evaporative water loss. While birds can in principle choose a preferred temperature during their flights by adjusting flight altitude, air pressure changes concurrently. This has effects on flight costs (negatively related with air density), but also on respiration (via decreasing oxygen partial pressure) and evaporation (via decreasing ambient humidity, which increases the driving force for evaporation). To complicate a bird’s decision even further, wind direction and wind speed are also dependent on geographic location, season and altitude. In principle, tail or head winds do not affect flight costs per se, as a bird is moving with its surrounding air, like a balloon carried by a breeze. Active flight leads to movement of the bird relative to the air, irrespective of the air’s movement. Wind conditions affect the bird’ s movement with respect to the ground. This is what matters for a migrating bird, especially if it is under time pressure to arrive at the breeding grounds in time. Therefore, a bird may choose its flight speed according to wind conditions (increase its flight speed to offset a head wind, for instance). Flight speed is a factor assumed to determine energy requirements during flight. Flight costs, migration speed, flight route and flight altitude might therefore be affected by prevalent wind conditions.
The factors affecting energy costs of flight
During flight, birds can sustain metabolic rates of more than ten times basal metabolism for several hours or even days. This is about twice the maximum sustained metabolic rate of similarly-sized running mammals. What are the physiological adaptations of birds to these high sustained metabolic demands, and which factors determine flight costs in birds? Body mass is an important factor determining energy costs of flight: Interspecific comparisons have generated allometric equations that allow an estimate of flight costs for any species based on body mass.
Intraspecifically or intraindividually, the scaling of flight costs and body mass is less clear. It appears, though, that flight costs increase less dramatically than predicted by interspecific allometry. Aerodynamic theory has led to mathematical models designed to predict mechanical costs of flight for any bird and under different ambient conditions. Following the elementary physical principles that the power to generate lift is inversely proportional to flight speed, and the power needed to generate thrust increases with the speed cubed, flight costs as the sum of both are predicted to depend on flight velocity in a U-shaped curve. This mechanical power output is only a fraction of the total metabolic power expended during flight. The major part of the metabolic energy ends up as heat and has to be dissipated. Further energy is required for respiration and circulation to supply the tissues with metabolites and oxygen, and for some basic physiological processes that are not directly involved in the generation of flight muscle work. The whole-body efficiency at which metabolic power is transformed into mechanical work remains poorly understood. We also do not know whether muscle efficiency is a fixed factor irrespective of body mass or flight velocity.
Calculations of metabolic power requirements on the basis of aerodynamic modelling can be only tentative for these reasons. The application of aerodynamic theory for fixed wing aircraft, which is the basis of all available models, gets complicated further by the fact that most birds usually use flapping flight instead of gliding, thereby changing the shape of the wings continuously by stretching or flexing them. They can vary the angle of attack, wing beat frequency, and wing beat amplitude, as well as using intermittent flight and changing many other parameters that might affect flight costs. Although the predicted U-shaped power curve applies well to aircraft, experimental evidence for birds is weak and controversial. Most studies report flight costs and power-to-speed relationships only for short flights. Migratory flights differ substantially from short flights both in energetic costs and in physiological processes underlying these costs. For example, short flights are powered mainly by muscular and hepathic carbohydrate stores. Endurance flight is fuelled by the combustion of extramuscular fat reserves, accompanied by a small but important fraction of protein catabolism. Therefore, to understand the physiology of bird migration we need more studies on long duration flight under controlled environmental conditions.
The factors affecting water fluxes during flight
Water gain through metabolic water production is the only positive part in the water balance equation of a flying bird, standing against water loss through excretion and evaporation. High metabolic rates as they occur during bird flight are associated with a high production of metabolic water. The exact amount of water formed in the chemical process of fuel oxidation depends not only on the metabolic rate but also on the fuel type (carbohydrates, fat or protein) and the end product of protein metabolism: urea or, in the case of birds, uric acid. Apart from other possible physiological functions of protein catabolism, it could help to counteract dehydration during flight because it releases more water per unit energy than lipid combustion.
Water loss via excretion and evaporation is inevitable, and both processes are affected by physiological requirements other than the need to conserve water. The primary function of excretion is the elimination of metabolic waste products, which must be accompanied by water. This obligatory water loss – albeit limited by the excretion of non-soluble uric acid - and the high metabolic rate during flight could conceivably constrain the bird’s ability to reduce excretory water loss. Evaporation is a basic physical process following the water vapour pressure gradient between the bird’s body (skin and respiratory surfaces) and the environment. Still, resting birds can regulate their evaporation rates within certain limits by changing the lipid composition in the skin, thereby regulating cutaneous evaporation or by cooling the respired air below body temperature upon exhalation, thereby reducing respiratory evaporation.
During flight and its associated high levels of heat, evaporation plays an important role in thermoregulation, especially at high ambient temperatures. Although a powerful means of heat dissipation, cooling by evaporation implies the risk of dehydration. Heat balance and water fluxes during flight, both in and out, are still poorly quantified.
Experimental approaches to assess energy costs and water fluxes during flight
To assess the energetics and water economy of bird migration, studies on free flying birds under natural conditions would be desirable. There are major technical difficulties in obtaining such measurements. Furthermore the ambient conditions during natural migratory flights are hardly constant nor comparable between different locations. This limits the feasibility and value of such measurements.
To control and manipulate effects of ambient conditions on bird flight performance, we conducted experiments in a large wind tunnel.
Research questions and outline of the thesis
We chose a few key aspects of flight physiology to study in the wind tunnel, which define the scope of this thesis. We focused on the water economy of birds flying at a range of ambient temperatures, on energy metabolism - since metabolic water production is the only source of water influx during flight – and on the two main factors that determine the amount of water lost with the ventilated air: exhaled air temperature and respiratory air flow.
In chapter 2 we present energy requirements and evaporation rates of resting Rose Coloured Starlings (Sturnus roseus) as determined in a temperature-controlled metabolic chamber at temperatures between 7 °C and 30 °C. The relationship between total evaporation (TEWLr ) and ambient temperature (Tamb ) was best described by two linear regressions. At temperatures below 21.9 °C, TEWLr was on average 6.73 ± 1.07 g d-1 and increased only slightly with Tamb, following the equation TEWLr = 0.09 · Tamb + 5.28 [g d-1]. At higher temperatures (Tamb > 21.9 °C), the relationship was much steeper, following TEWLr = 0.37 · Tamb – 0.68 [g d-1].
Resting metabolic rate (RMR) was positively correlated with body mass and was therefore expressed as mass-specific metabolic rate. The relationship between RMR and Tamb was best described by two linear regressions. At temperatures above 12.9 °C mass specific RMR was constant at 0.021 ± 0.001 W g-1. At lower temperatures, RMR was negatively correlated with Tamb following RMR = 0.0011 · Tamb + 0.0366 [W g-1]. These data allow a comparison of resting energy expenditure and total evaporative water loss with flight measurements, as determined in the following chapters.
In chapter 3 the metabolic costs of flight at a natural range of speeds were investigated in Rose Coloured Starlings (Sturnus roseus) using doubly labelled water. Eight birds flew repeatedly and unrestrained for bouts of six hours at speeds from 9 to 14 m s-1 in a low-turbulence wind tunnel, corresponding to travel distances between 200 and 300 km, respectively. This represents the widest speed range where we could obtain voluntarily sustained flights. From a subset of these flights data on the wing beat frequency and intermittent flight behaviour were obtained. Over the range of speeds that were tested, flight costs did not change with velocity and were on average 8.17 ± 0.64 W. Body mass was the only parameter with a significant (positive) effect on flight costs, which can be described as EEf=0.741· M 0.554. Wing beat frequency changed slightly with speed, but correlated better with body mass. Birds showed both types of intermittent flight, undulating and bounding, but their frequencies did not systematically change with flight speed.
In chapter 4 we combine data on total body water and water fluxes (derived from DLW measurements) during flight in Rose Coloured Starlings, with mass balance calculations of net water loss. These data allow the estimation of total evaporative water loss and the modelling of heat balance during flight. During all flights, the birds experienced a net water loss. Water influx was on average 0.98 g h-1 and water efflux 1.29 g h-1, irrespective of flight speed. Evaporation was related to temperature in a biphasic pattern. At temperatures below 18.2 °C net evaporation was constant at 0.36 g h-1, rising at higher temperatures with a slope of 0.11 per degree to about 1.5 g h-1 at 27 °C. We calculated the relative proportion of dry and evaporative heat loss during flight. Our data suggest that for prolonged flights Rose Coloured Starlings should adopt behavioural water saving strategies and that they can not complete their annual migration without stopover to replenish their water reserves.
In chapter 5 we present data on exhaled air temperature of flying and resting ducks. Exhaled air temperature was measured with a microbead thermistor at the nostril of the birds which was connected to a recording system via thin copper leads. A thermistor changes electrical resistance with temperature and can therefore be used as thermometer. Exhaled air temperature (Texh) has a paramount effect on respiratory water loss during flight. For migratory birds, low Texh potentially reduces water loss and increases flight range. The aim of this study was to record Texh of birds during rest and flight at a range of controlled ambient temperatures (Tamb). One wigeon and two teal flew a total of 20 times in a wind tunnel at Tamb ranging from 1 to 24 °C. Texh during flight did not differ between the two species and was strongly correlated with Tamb (Texh = 1.036 Tamb + 13.426; R2 = 0.58). In addition, body temperature had a weak positive effect on Texh. At a given Tamb, Texh was about 5 °C higher during flight than at rest. The steep slope of the relationship between Texh and Tamb during flight indicates that Texh is actively regulated and not simply the result of passive heat exchange.
In chapter 6 we assessed respiratory water loss in European Starlings (Sturnus vulgaris) both at rest and during steady flight in a wind tunnel over a range of ambient temperatures using respiratory air flow and exhaled air temperature data. In resting Starlings, breathing frequency (f) was constant at 1.4 ± 0.3 Hz at ambient temperatures (Tamb) between 6 °C and 25 °C. Also tidal volume (Vt, ml) was independent of Tamb with an average value of 1.9 ± SD = 0.4 ml. There was a negative correlation between Vt and f (Vt = -1.01 × f + 3.30; n = 17; p < 0.01; R2 = 0.45). Mean ventilation rate (Vmin, ml min-1), the product of f and Vt, was 156 ± 28 ml min –1 (n = 17) at all Tamb. Exhaled air temperature (Texh) during rest was strongly dependent on Tamb (Texh = 0.92 × Tamb + 12.45; n = 23; p < 0.001; R2 = 0.89). Respiratory water loss at rest (REWL) averaged 0.18 ± 0.09 ml h-1 (n = 10) and was independent of Tamb, but showed a slight positive dependence on f and Texh. In flying Starlings, f was on average 4.0 ± 0.4 Hz (n = 44) and unchanging over the range of Tamb measured. Vt during flight averaged 3.6 ± 0.4 ml (n = 25) and increased with Tamb (Vt = 0.06 × Tamb + 2.83; n = 25; p < 0.01; R2 = 0.29), as a consequence, the volume of ventilated air during flight (average Vmin = 789.9 ± 210.0 ml min-1), increased with Tamb as well. Texh during flight was 4.6 °C higher than at rest and strongly dependent on Tamb (Texh = 0.85 × Tamb + 17.29; n = 36; p < 0.001; R2 = 0.74). All factors together result in respiratory water loss during flight (average REWLf = 0.74 ± 0.22 ml h-1) significantly higher than at rest and increasing with Tamb. REWLf correlated best with the water vapour pressure deficit (VPD, hPa) in ambient air. From our measurements and data from the literature, we conclude that respiratory evaporation accounts for most water loss in flying European Starlings and increases to a higher degree than cutaneous evaporation with rising ambient temperature.
Chapter 7 synthesizes the experimental results presented in this thesis. Our data are integrated into available literature data on short and long flights. We discuss these results also in the context of field studies to draw a picture as complete as possible of the energy and water requirements during long distance flight.
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Advances in Gas Metal Arc Welding and Application to Corrosion Resistant Alloy Pipes
No full textAccording to recent estimations, the construction of pipelines will continue to increase during the next thirty years, in particular as a result of oil and gas discoveries in remote locations. Significant advances in welding technology during the last ten years have potential to provide improvements in productivity, quality and structural integrity of pipe girth welds.
In this thesis, several new processes Lincoln STT, Lincoln RapidArc, Fronius CMT, Fronius CMT-P and Kemppi FastROOT have been compared the first time to the GMAW-P to understand how these new waveforms operate for pipe welding. The process setting parameters have been analysed to understand their effect on metal transfer and arc stability control, and on bead shape characteristics. Although all waveforms present similar burn-off ratios, individual waveforms differ considerably, and especially the arc voltage waveform. This leads to considerable differences in the mechanism of metal transfer and the stability of the processes under similar experimental conditions. Understanding of these new waveforms in terms of the effect of setting parameters in the mechanism of metal transfer, process stability and melting phenomena provides a basis for assessing the potential of these processes for a range of applications, and in particular application to CRA pipe root welding
Since the arc energy is the overall energy delivered from the power source at the contact tip of the torch, and part of that energy is not absorbed by the workpiece, research was performed to measure the process efficiency associated with some of these waveforms and process setting conditions. The study led to a better understanding of the potential errors in calculating process efficiency. The results obtained show that all the short-circuiting waveforms analysed (i.e. CMT, STT and FastRoot) had a similar process efficiency of 90±3%, while pulse spray waveforms (GMAW-P, CMT-P and RapidArc) are characterized by lower process efficiency, approximately 78±3%.
The application of these waveforms to the welding a narrow groove pipe with a “J” groove design was investigated. These analyses were focused on the variation of bead shape characteristics and welding quality performance based on the analysis of the conditions that result in lack of penetration and top bead defects, such as lack of side wall fusion or undercutting. It was observed that RapidArc and CMT-P are able to satisfy the quality requirements, i.e. full penetration and absence of defects for the specific conditions described in this thesis. High welding speeds (up to 1m/min) were achieved with these processes, four times the typical speed 0.25m/min.
Finally, the shielding gas plays an important role in terms of quality and weld bead performance. This led to an optimization of the shielding gas composition used, based on mixtures of carbon dioxide, argon and helium. Statistical modelling was undertaken to optimize the shielding gas mixtures using RapidArc and CMT-P waveforms. In parallel, a new purging shielding gas device was designed to achieve a weld root free of oxidation
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