Morphogen Gradient from a Noisy Source

We investigate the effect of time-dependent noise on the shape of a morphogen gradient in a developing embryo. Perturbation theory is used to calculate the deviations from deterministic behavior in a simple reaction-diffusion model of robust gradient formation, and the results are confirmed by numerical simulation. It is shown that such deviations can disrupt robustness for sufficiently high noise levels, and the implications of these findings for more complex models of gradient-shaping pathways are discussed.Comment: Four pages, three figure

The Effect of Compliance Changes on Delivered Volumes in an Adult Patient Ventilated with High Frequency Oscillatory Ventilation: A Bench Model

Clinical concerns exist regarding the delivered tidal volume (Vt) during high-frequency oscillatory ventilation (HFOV). HFOV is increasingly being used as a lung protective mode of ventilation for patients with Adult Respiratory Distress Syndrome (ARDS), but caution must be utilized. The purpose of this study was to investigate the effect of airway compliance on Vt delivered by HFOV to the adult patient. Method: An in vitro model was used to simulate an adult passive patient with ARDS, using a high fidelity breathing simulator (ASL 5000, IngMar Medical). The simulation included independent lung ventilation with a fixed resistance and adjustable compliance for each lung. Compliances of 10, 15, 20 and 25 ml/cmH2O were used and resistance (Raw) was fixed at 15 cm H2O/L/s. The ventilator SensorMedics 3100B (Cardinal Health, Dublin, Ohio) was set to a fixed power setting of 6.0, insp-% of 33%, bias flow =30 L/min, and 50% oxygen and Hz of 5.0 (n=5) for each compliance setting. Mean airway pressure (mPaw) and amplitude (AMP) varied as the compliance changes were made. Approximately 250 breaths were recorded at each compliance setting and the data was collected via the host computer and transferred to a log to be analyzed by SPSS v. 10. Data Analysis: The data analysis was performed using SPSS v. 10 to determine the statistical significance of the delivered Vt with different compliances, different AMP and a fixed power setting. A probability of (p \u3c 0.05) was accepted as statistically significant. Results: The average delivered Vt with each compliance was 124.181 mL (range of 116.4276 mL and 132.6637 mL) and average AMP of 84.85 cm/H2O (range 82.0 cm/H2O and 88.0801 cm/H2O) n=5. There was an inverse relationship between Vt and AMP at a fixed power of 6.0. As compliance improved Vt increased and there was a corresponding decrease in AMP. The one-way ANOVA test showed that there were significant differences between the delivered tidal volume and AMP at a fixed power setting. When the post hoc Bonferroni test was used the data showed significant differences between AMP achieved with each compliance change and a fixed power of 6.0. When the post hoc Bonferroni test was used the data showed significant differences between Vt delivered with each compliance change and a fixed power setting of 6.0. Conclusion: Vt is not constant during HFOV. Compliance is one determinant of Vt in adults with ARDS during HFOV. AMP and Vt are inversely related during HFOV at a fixed power setting and improving compliance

Postglacial emergence along northern Nares Strait

During the last glaciation much of northern Nares Strait remained an ice-free corridor separating the northeast Ellesmere Island and northwest Greenland ice sheets. The disproportionate size of these ice sheets resulted in the lithosphere being differentially loaded on either side of this prominent rift valley. Postglacial emergence in this area is analyzed in order to determine whether glacio-isostatic unloading engendered any abnormal displacement along the Nares Strait fault zone. Present data suggest that synchronous shorelines dated 6000, 7000 and 8000 BP rise from north to south across northeast Ellesmere Island and northern Nares Strait towards the Greenland ice sheet. This is considered to represent the glacio-isostatic dominance of the Greenland ice sheet during the last glaciation together with earlier postglacial emergence towards northernmost Ellesmere Island which lay beyond the influence of the Greenland ice sheet. This Greenland dominance indicates that northeast Ellesmere Island lay in the depression marginal to the Greenland ice sheet. This, in turn, requires a lithospheric flexural parameter extending in an undisrupted manner across the Nares Strait rift valley. Hence, on a regional scale, it appears that the lithosphere in this area has integrated the depressions from these separated ice sheets without any observable unconformities along Nares Strait. Although postglacial faulting has followed initial glacio-isostatic unloading in other areas the present data base does not have the resolution to document similar events along Nares Strait

An Urgent Appeal to the Government of Canada to Proclaim our Northern Identity

... Looming new developments of unprecedented scale now present for Northerners both significant opportunities and challenges, especially if long-term cultural vitality and a sustainable environment are to be maintained. Northern Canada is also a key archive and bellwether for global climate change, and understandably it has become increasingly the focus of foreign researchers, whose resources vastly exceed those of Canadians. In light of this northern transformation, this article revisits Canada's ongoing unpreparedness in northern science and technology ..., contrasts Canada's inactivity with proactive steps being taken by other countries with well-structured polar agendas, and recommends recently proposed solutions as a long-awaited remedy. ..

Postglacial Isobases from Northern Ellesmere Island and Greenland: New Data

Over seventy new 14C dates on former relative sea levels from Hall Land, northwest Greenland, and Clements Markham Inlet, northern Ellesmere Island, are combined with previous data to revise the regional isobases for this area. These isobases show : 1) a centre of maximum postglacial emergence over northwest Greenland extending to; 2) an intervening cell of lower emergence over northeast Ellesmere Island which was isostatically-dominated by the Greenland Ice Sheet; in turn, extending to 3) a higher centre of emergence over the Grant Land Mountains, northernmost Ellesmere Island, associated with the independent history of local ice caps there. Radiocarbon dates from raised marine shorelines show a 2000 year lag between glacial unloading on northwest Greenland and northernmost Ellesmere Island. This lag in glacioisostatic adjustments suggests a considerable range in the glacier response times and/or glacioclimatic regimes in this area. Throughout the area the last ice limit was ca. 5-60 km beyond present ice margins. Maximum emergence at these ice limits is marked by shorelines built into a full glacial sea which range from 124 m asl in Clements Markham Inlet to 150 m asl in Hall Land. This indicates that similar emergence (120-150 m) in other areas does not necessarily require the removal of entire ice sheets although this has been commonly assumed in the literature. The geophysical implications of this warrant consideration.Plus de 70 nouvelles datations au radiocarbone effectuées sur d'anciens niveaux marins, sur la terre de Hall (nord-ouest du Groenland) et dans la baie de Clements Markham (nord de l'île d'Ellesmere), ont été associées aux données déjà recueillies et permettent de réviser les isobases de la région. Celles-ci révèlent: 1) un centre d'émersion postglaciaire maximale au nord-ouest du Groenland qui s'étend jusqu'à 2) un compartiment de faible relèvement dans le nord-est de l'île d'Ellesmere, couvert par l'inlandsis du Groenland qui s'étendait jusqu'à 3) un centre d'émersion plus importante à l'endroit des Grant Land Mountains, à l'extrême nord de l'île d'Ellesmere, associée à révolution des calottes glaciaires locales. La datation au radiocarbone de lignes de rivage soulevées révèle un décalage de 2000 ans entre le retrait glaciaire qu'a connu l'extrême nord d'Ellesmere et celui qu'a connu le nord-ouest du Groenland. Ce décalage entre les rajustements glacioisostatiques laisse entrevoir une grande variation dans le temps de réaction du glacier et dans les régimes glacioclimatiques de la région. Partout la dernière limite glaciaire se situe de 40 à 60 km au-delà des marges glaciaires actuelles. L'émersion maximale près de cette limite est marquée par des lignes de rivage construites en pleine mer glaciaire, qui vont de 124 m anm, dans la baie de Clements Markham, à 150 m anm, sur la terre de Hall. Ceci révèle qu'ailleurs une emersion de cet ordre, soit de 120 à 150 m, ne suppose pas nécessairement le retrait de toute la calotte glaciaire, bien que cette idée soit généralement acceptée. Les conséquences géophysiques qui en découlent exigent désormais qu'on en tienne compte.Ùber 70 neue 14C Daten ùberfrùhere relative Meeresspiegel von Hall Land, Nordwest-Grônland und der Clements Markham Bucht, nôrdliche Ellesmere-lnsel, werden mit schon vorhandenen Daten kombiniert, um die regionalen Isobasen fur dieses Gebiet zu revidieren. Dièse Isobasen zeigen : 1) ein Zentrum des maximalen postglazialen Auftauchens ùber Nordwest-Grônland, welches sich ausdehnt zu 2) einem dazwischenliegenden Gelàndeabschnitt mit niedrigerem Auftauchen ùber dem Nordosten der Ellesmere-lnsel, welcher isostatisch durch die Grônland Eiskappe dominiert wurde; welcher seinerseits sich zu 3) einem hôheren Auftauchzentrum ùber den Grant Land Mountains ausdehnte, im àuBersten Norden der Ellesmere-lnsel, das mit der unabhângigen Geschichte der dortigen lokalen Eiskappen in Verbindung gebracht wird. Radiokarbon-Daten der gehobenen marinen Kùstenlinien zeigen einen Zeitunterschied von 2000 Jahren zwischen dem glazialen Rùckzug im Nordwesten von Grônland und dem im àuBersten Norden der Ellesmere-lnsel. Dieser Zeitunterschied in den glazialisostatischen Anpassungen IaBt eine erhebliche Schwankung in der Reaktionszeit des Gletschers und/ oder glazialklimatischen Systemen in diesem Gebiet vermuten. In diesem ganzen Gebiet ging die âuBerste Eisgrenze etwa 40-60 km ùber die heitigen Eisgrenzen hinaus. Das maximale Auftauchen an diesen Eisgrenzen ist durch Kùstenlinien markiert, die in ein voiles glaziales Eismeer hineingebaut sind und welche von 124 m ùber dem Meeresspiegel in der Bucht von Clements Markham bis zu 150 m ùber dem Meeresspiegel in Hall Land reichen. Das zeigt, daB ein vergleichbares Auftauchen (120-150 m) in anderen Gebieten nicht unbedingt den Rùckzug der ganzen Eiskappen erfordert, auch wenn dies allge-mein in der Fachliteratur angenommen wurde

Canada's Most Northerly Postglacial Bowhead Whales (Balaena mysticetus) : Holocene Sea-ice Conditions and Polynya Development

Rare remains of postglacial bowhead whales occur in the Norwegian Bay-Eureka Sound region. These are the northernmost remains known from the Canadian Arctic. The region is beyond the bowhead's current range because of persistent summer sea ice. We argue that the region has been beyond the bowhead's range for most of postglacial time for the same reason. With one exception, the 16 known subfossil bowheads from the region date to the last 4000 14C years. Within the region, whale bones are most common adjacent to polynyas, which connect to more southerly channels extending from Baffin Bay. This distribution suggests that the polynyas, which here occupy areas of strong currents, developed as a result of shallowing of inter-island channels due to postglacial uplift. The whale remains beyond the polynyas are seen as those of doomed strays that reached the polynyas from Baffin Bay and foraged farther along coastal leads before being trapped by freeze-up. This interpretation of Holocene sea-ice history agrees with the limited development of Holocene raised beaches in the region. However, it contradicts other interpretations of greatly ameliorated marine conditions in northernmost Canada at about 6000 14C years B.P.La région de la baie Norwegian et du détroit d'Eureka abrite un petit nombre de restes organiques de baleines boréales postglaciaires. Ce sont les restes trouvés le plus au nord de l'Arctique canadien. Cette zone est située en dehors du territoire actuel de la baleine boréale en raison de la présence constante de glace marine estivale. On soutient que la région s'est trouvée en dehors du territoire de la baleine boréale durant la plus grande partie de la période postglaciaire, et ce, pour la même raison. À une exception près, les 16 baleines boréales subfossiles qui ont été découvertes dans cette zone datent des 4000 dernières années (âge radiocarbone). Dans la région, les os de baleines se trouvent en plus grand nombre au voisinage immédiat de polynies, celles-ci étant reliées à des chenaux plus méridionaux qui sinuent depuis la baie de Baffin. Cette distribution suggère que les polynies, qui occupent ici des zones de courants forts, se sont formées à la suite d'une diminution de la profondeur des chenaux séparant les îles provoquée par un soulèvement postglaciaire. On pense que les restes de baleines qui se trouvent en dehors des polynies appartiennent à des baleines qui ont rejoint les polynies depuis la baie de Baffin et qui se sont égarées plus loin en quête de nourriture le long des passages côtiers avant d'être bloquées par les glaces. Cette interprétation de l'histoire de la glace marine de l'holocène concorde avec l'évolution restreinte des plages soulevées de la région, qui datent de l'holocène. Elle contredit toutefois d'autres interprétations de conditions marines nettement améliorées dans l'extrême nord du Canada il y a environ 6000 ans (âge radiocarbone) BP

Flow plug with length-to-hole size uniformity for use in flow conditioning and flow metering

A flow plug of varying thickness has a plurality of holes formed therethrough. The plug fits in a conduit such that a fluid flow in the conduit passes through the plug's holes. Each hole is defined by a parameter indicative of size in terms of the cross-sectional area thereof. A ratio of hole length-to-parameter is approximately the same for all of the holes