The motion, stability and breakup of a stretching liquid bridge with a receding contact line

The complex behavior of drop deposition on a hydrophobic surface is considered by looking at a model problem in which the evolution of a constant-volume liquid bridge is studied as the bridge is stretched. The bridge is pinned with a fixed diameter at the upper contact point, but the contact line at the lower attachment point is free to move on a smooth substrate. Experiments indicate that initially, as the bridge is stretched, the lower contact line slowly retreats inwards. However at a critical radius, the bridge becomes unstable, and the contact line accelerates dramatically, moving inwards very quickly. The bridge subsequently pinches off, and a small droplet is left on the substrate. A quasi-static analysis, using the Young-Laplace equation, is used to accurately predict the shape of the bridge during the initial bridge evolution, including the initial onset of the slow contact line retraction. A stability analysis is used to predict the onset of pinch-off, and a one-dimensional dynamical equation, coupled with a Tanner-law for the dynamic contact angle, is used to model the rapid pinch-off behavior. Excellent agreement between numerical predictions and experiments is found throughout the bridge evolution, and the importance of the dynamic contact line model is demonstrated.Comment: 37 pages, 12 figure

Capillary instability in a two-component Bose-Einstein condensate

Capillary instability and the resulting dynamics in an immiscible two-component Bose-Einstein condensate are investigated using the mean-field and Bogoliubov analyses. A long, cylindrical condensate surrounded by the other component is dynamically unstable against breakup into droplets due to the interfacial tension arising from the quantum pressure and interactions. A heteronuclear system confined in a cigar-shaped trap is proposed for realizing this phenomenon experimentally.Comment: 7 pages, 6 figure

The hydraulic bump: The surface signature of a plunging jet

When a falling jet of fluid strikes a horizontal fluid layer, a hydraulic jump arises downstream of the point of impact provided a critical flow rate is exceeded. We here examine a phenomenon that arises below this jump threshold, a circular deflection of relatively small amplitude on the free surface, that we call the hydraulic bump. The form of the circular bump can be simply understood in terms of the underlying vortex structure and its height simply deduced with Bernoulli arguments. As the incoming flux increases, a breaking of axial symmetry leads to polygonal hydraulic bumps. The relation between this polygonal instability and that arising in the hydraulic jump is discussed. The coexistence of hydraulic jumps and bumps can give rise to striking nested structures with polygonal jumps bound within polygonal bumps. The absence of a pronounced surface signature on the hydraulic bump indicates the dominant influence of the subsurface vorticity on its instability

Eating psychopathology in athletes: methods of identification and intervention

Background: The incidence of eating psychopathology in athletes is considerably higher than in the general population. Facilitating the early identification and successful management of eating problems in this group is therefore essential. Objectives: The thesis aimed to improve our empirical understanding of the identification and management of eating problems in athletes. Three areas were investigated. First, a measure of compulsive exercise was evaluated as a method of identification of eating psychopathology in athletes. Second, the thesis explored coach methods of identification and management of eating problems among their athletes. Finally, athlete experiences of disclosing and seeking treatment for eating disorders were explored. Main findings: The Compulsive Exercise Test was found to be a useful measure in screening for eating psychopathology in athletes. Track and field coaches relied heavily on the physical symptoms of disordered eating when identifying potential eating problems in athletes. Coaches described difficulties in identifying eating psychopathology in athletes, and in signposting athletes to appropriate support. Individual differences in the perceived value of disclosing an eating disorder were discovered among athletes currently seeking treatment. Lastly, athletes described struggling to engage with their eating disorder treatment programme, particularly where exercise was restricted or reduced. Implications: The findings suggest a need for greater support, education and resources for coaches and sports professionals in identifying and facilitating treatment access among their athletes. The Compulsive Exercise Test may be one way to assist sports professionals in identifying athletes with elevated levels of eating psychopathology. Athletes may be more willing to engage with treatment programmes when they are closely involved in goal setting and their exercise and sporting commitments are incorporated where possible

Observations sur l'anatomie de l'Éléphant d'Afrique (Loxodon africanus) adulte

ZOOLOGISCHER JAHRESBERICHT 1881: Verf. untersuchten einen im Zoologischen Garten in Antwerpen gestorbenen erwachsenen africanischen Elefanten , dessen Haut und Skelet an das Brüsseler Museum kam. Auge. Die knorplige Stütze der Nickhaut verlängert sich stielförmig nach hinten an der inneren Seite des Bulbus. Die Nickhaut wird durch zwei selbständig am hinteren Ende des Stiels entspringende Muskeln bewegt, welche sich vorn oben uud unten in den orbicularis palpebrarum ansetzen. Ein rectus posterior (s. choauoideus, s. retractor) fehlt. Statt der fehlenden Thränendrüse ist die, dem Stielende der Nickhaut anliegende Hardersche Drüse sehr entwickelt. Das Auge ist nicht größer als das des Pferdes, die Orbita aber viel weiter, die Muskeln viel dicker. — Das Herz ist breit , die Umrisse fast viereckig (in der schematischen Lage des menschlichen Herzens) , die breit abgerundeten unteren Enden der Ventrikel durch eine tiefe Furche getrennt (an injicirten Präparaten, ähnlich wie bei den Sirenien. Die Vorkammern sind sehr geräumig; Herzohren fehlen , statt ihrer finden sich rechts und links gewundene , stark gefurchte, solide Anhänge. Die großen Gefäße entspringen wie beim indischen Elefanten in zwei Stämmen , einem truncus anonymus für rechte Subclavia und beide Carotiden und der linken Subclavia. Während ersterer und die Aorta bis zum Abgang der Gefäße sehr kurz ist , ist die pulmonalis merkwürdig lang bis zu ihrer Theilung, was beim indischen Tapir noch auffallender ist. Es sind zwei obere Hohlvenen und eine untere vorhanden. Im Ganzen ist das Herz des africanischen Elefanten kleiner als das des indischen. — Die Milz ist platt zungenförmig, an beiden Enden verschmälert. Ihre Länge ist enorm, 1,31m, ihre größte Breite 0,28m. — In Bezug auf die Zunge sei auch nur auf das von früheren Angaben Abweichende hingewiesen. Der Wharton sehe Gang mündet auf einem 15 mm langen frei flottireuden Faden, beinahe wie beim Pferde. Papulae foliatae (Mayer'sches Organ) sind rechts 19, links 18 vorhanden (33 Forbes , 15 Mojsisovics) . Den Pharyngealsack fanden Verf. so, wie ihn Watson vom indischen Elefanten beschreibt. — Am Kehlkopf sind die oberen Stimmbänder vorhanden ; 1. Morphologie, a) Anatomie. B. Monographien einz. Abth. 9 die gegentheiligen Angaben früherer Beobachter sind wahrscheinlich darauf zurückzuführen, daß sie junge Individuen untersucht haben. — Der Magen scheint im Verhältnis größer zu sein als beim indischen Elefanten. — Die Niereu boten auf der einen Seite eine pathologische Vergrößerung , auf der anderen vielleicht eine beginnende Atrophie dar. Verf. äußern die Ansicht, daß die Lappenbildung wohl mit dem Alter verschwinde. — Die Hoden des untersuchten Thieres waren viermal größer als die von Moj sisovics gemessenen. Das veru montanum sprang stark vor, nach vorn leistenartig verlängert. Die Öffnung des Uterus war V2cni weit, der Uterus 2cm tief. Jederseits fanden sich drei Prostatagänge. Die Urethralöffnung an der Spitze des Penis war nicht Y-förmig, sondern einfach senkrecht elliptisch

Stability of viscous long liquid filaments

We study the collapse of an axisymmetric liquid filament both analytically and by means of a numerical model. The liquid filament, also known as ligament, may either collapse stably into a single droplet or break up into multiple droplets. The dynamics of the filament are governed by the viscosity and the aspect ratio, and the initial perturbations of its surface. We find that the instability of long viscous filaments can be completely explained by the Rayleigh-Plateau instability, whereas a low viscous filament can also break up due to end pinching. We analytically derive the transition between stable collapse and breakup in the Ohnesorge number versus aspect ratio phase space. Our result is confirmed by numerical simulations based on the slender jet approximation and explains recent experimental findings by Castrejon-Pita et al., PRL 108, 074506 (2012).Comment: 7 page

Instability of Compressible Drops and Jets

We revisit the classic problem of the stability of drops and jets held by surface tension, while regarding the compressibility of bulk fluids and spatial dimensions as free parameters. By mode analysis, it is shown that there exists a critical compressibility above which the drops (and disks) become unstable for a spherical perturbation. For a given value of compressibility (and those of the surface tension and density at the equilibrium), this instability criterion provides a minimal radius below which the drop cannot be a stable equilibrium. According to the existence of the above unstable mode of drop, which corresponds to a homogeneous perturbation of cylindrical jet, the dispersion relation of Rayleigh-Plateau instability for cylinders drastically changes. In particular, we identify another critical compressibility above which the homogeneous unstable mode is predominant. The analysis is done for non-relativistic and relativistic perfect fluids, of which self-gravity is ignored.Comment: 24 pages, 5 figures, 1 table; v2: typos corrected; v3: final version to appear in JF

Reoptimization in lagrangian methods for the quadratic knapsack problem

International audienceThe 0-1 quadratic knapsack problem consists in maximizing a quadratic objective function subject to a linear capacity constraint. To solve exactly large instances of this problem with a tree search algorithm (e.g. a branch and bound method), the knowledge of good lower and upper bounds is crucial for pruning the tree but also for fixing as many variables as possible in a preprocessing phase. The upper bounds used in the best known exact approaches are based on Lagrangian relaxation and decomposition. It appears that the computation of these Lagrangian dual bounds involves the resolution of numerous 0-1 linear knapsack subproblems. Thus, taking this huge number of solvings into account, we propose to embed reoptimization techniques for improving the efficiency of the preprocessing phase of the 0-1 quadratic knapsack resolution. Namely, reoptimization is introduced to accelerate each independent sequence of 0-1 linear knapsack problems induced by the Lagrangian relaxation as well as the Lagrangian decomposition. Numerous numerical experiments validate the relevance of our approach