Spatiotemporal instability of a confined capillary jet

Recent experimental studies on the instability appearance of capillary jets have revealed the capabilities of linear spatiotemporal instability analysis to predict the parametrical map where steady jetting or dripping takes place. In this work, we present an extensive analytical, numerical and experimental analysis of confined capillary jets extending previous studies. We propose an extended, accurate analytic model in the limit of low Reynolds flows, and introduce a numerical scheme to predict the system response when the liquid inertia is not negligible. Theoretical predictions show a remarkable accuracy with results from the extensive experimental exploration provided.Comment: Submitted to the Physical Review E (20-March-2008

One-dimensional dynamics of nearly unstable axisymmetric liquid bridges

A general one-dimensional model is considered that describes the dynamics of slender, axisymmetric, noncylindrical liquid bridges between two equal disks. Such model depends on two adjustable parameters and includes as particular cases the standard Lee and Cosserat models. For slender liquid bridges, the model provides sufficiently accurate results and involves much easier and faster calculations than the full three-dimensional model. In particular, viscous effects are easily accounted for. The one-dimensional model is used to derive a simple weakly nonlinear description of the dynamics near the instability limit. Small perturbations of marginal instability conditions are also considered that account for volume perturbations, nonequality of the supporting disks, and axial gravity. The analysis shows that the dynamics breaks the reflection symmetry on the midplane between the supporting disks. The weakly nonlinear evolution of the amplitude of the perturbation is given by a Duffing equation, whose coefficients are calculated in terms of the slenderness as a part of the analysis and exhibit a weak dependence on the adjustable parameters of the one-dimensional model. The amplitude equation is used to make quantitative predictions of both the (first stage of) breakage for unstable configurations and the (slow) dynamics for stable configurations

Sex-specific phenotypic integration: Endocrine profiles, coloration, and behavior in fledgling boobies

The intensity of color expression in animals plays a key role in social environments as a mechanism to signal individual capacities in competitive contests. Selective pressures for resource competition differ at different stages of life and between sexes; therefore, coloration is expected to vary between juveniles and adults and between males and females. Exploring the covariance between coloration and other traits may help to understand the functional significance of color and the action of natural selection on multivariate phenotypes. Melanin-based plumage coloration was investigated in the masked booby Sula dactylatra in relation to melanin concentration, sex, hormone levels, and shy-bold behavior of chicks close to fledging. Darker brown boobies showed higher levels of both eumelanin and pheomelanin concentration and lower body mass. Males behaved bolder than females and showed on average 8% larger brown patches. Bolder females had smaller brown patches. Bolder individuals also had lower levels of circulating testosterone, but no differences in corticosterone levels were found. Stronger phenotypic integration was observed in females than males. Our study suggests that juvenile melanic coloration may reflect behavioral strategies by sex, endocrine profiles, and body mass indicating the convergence of different adaptive functions in a given phenotype, this being more evident in females. Direction of correlations differed from those predicted under the pleiotropic idea for color-related traits. These results suggest the possibility that juvenile plumage acts as a signaling system in a social context within the age class and suggest that plumage coloration may indicate different behavioral strategies. © The Author 2013.The study was supported by Spanish Ministerio de Ciencia e Innovación (CGL2009-10883-C02-01; CGL2012-40229-C02-02).Peer Reviewe

Low and high Reynolds number flows inside Taylor cones

Liquid motions inside Taylor cones exhibit interesting features which are not well understood yet. In addition to the flow rate injected through the electrified needle to which the conical meniscus is anchored, the action of the tangential electrical stress on the cone surface induces a recirculating meridional motion, towards the apex along the generatrix and away from it along the axis. Sometimes, a vigorous swirl is observed. The characteristic value of the liquid velocity is found to be highly dependent on both the electrical conductivity and the viscosity of the liquid, so that the Reynolds number of the liquid flow varies from very small values (creeping flow) for the case of highly conducting and viscous liquids to relatively large values for liquids with sufficiently low values of the liquid conductivity and viscosity. Theoretical conical flows for low and high values of the Reynolds number show qualitatively good agreement with photographs of real flows inside Taylor cones. In particular, the existence of a vigorous swirl which is observed in the electrospraying of paraffins and other poorly conducting and low viscosity liquids can be explained as bifurcation of a primarily nonswirling meridional flow when the Reynolds number reaches a critical value.Comisión Interministerial de Ciencia y Tecnología PB96-0679-C02-0

Enhancement of the stability of the flow focusing technique for low-viscosity liquids

Article number 115039We propose a modified flow focusing configuration to produce low-viscosity microjets at much smaller flow rates than those reached by the standard configuration. In the modified flow focusing device, a sharpened rod blocks the recirculation cell appearing in the tapering liquid meniscus for low flow rates, which considerably improves its stability. We measured the minimum flow rates attainable with the modified configuration and compared the results with the corresponding values for the standard technique. For moderate and large applied pressure drops, the minimum flow rate reached with the modified configuration was about five times smaller than its counterpart in the standard configuration. The Weber numbers of the jets produced with the modified flow focusing configuration were considerably smaller than those with the standard technique. Numerical simulations were conducted to show how the presence of the inner rod substantially changes the flow pattern in the liquid meniscus.Ministerio de Ciencia y Educación, Junta de Extremadura y Junta de Andalucía (España) DPI2010-21103, GR10047 y P08-TEP-0412

Controlled cavity collapse: scaling laws of drop formation

The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validatedRoyal Society (UF120319, URF\R\180016, and RGF\EA\180061)John Fell Oxford University Press Research Fund (0005176)EPSRC – UK (EP/P024173/1)Ministerio de Economía y Competitividad, Plan Estatal 2013–2016 Retos, project DPI2013-46485-C3-1-

Effect of molecular weight reduction by gamma irradiation on the antioxidant capacity of chitosan from lobster shells

AbstractThis study assessed the effect of molecular weight (MW) reduction by gamma irradiation on the antioxidant capacity of chitosan with potential application in the preservation of foodstuffs. Two batches of chitosan were obtained by heterogeneous chemical N-deacetylation of chitin from common lobster (Panulirus argus). Irradiation of chitosan was performed using a 60Co source and applying doses of 5, 10, 20 and 50 kGy with a dose rate of 10 kGy/h. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy was used to identify main chemical features of chitosan. The average viscosimetric MW was determined by the viscosimetric method while the deacetylation degree by a potentiometric method. Thermogravimetric analysis and differential scanning calorimetry were conducted to evaluate the thermal degradation behavior of the chitosan samples, both under nitrogen flow. The antioxidant activity of chitosan solutions at 1% (w/v) in lactic acid at 1% (v/v) and Tween 80 at 0.1% (v/v) was evaluated through the ABTS assay and scavenging of DPPH radical by chitosan. The increase of irradiation dose with 60Co until 50 kGy decreased significantly the MW of chitosan through the scission of glycosidic bonds without affecting its functional groups, while the DD (72–75 %) did not vary (p > 0.05). The AC of the chitosan solutions increased with the reduction of MW of chitosan by gamma irradiation

Imaging of skull vault tumors in adults

The skull vault, formed by the flat bones of the skull, has a limited spectrum of disease that lies between the fields of neuro- and musculoskeletal radiology. Its unique abnormalities, as well as other ubiquitous ones, present particular features in this location. Moreover, some benign entities in this region may mimic malignancy if analyzed using classical bone-tumor criteria, and proper patient management requires being familiar with these presentations. This article is structured as a practical review offering a systematic diagnostic approach to focal calvarial lesions, broadly organized into four categories: (1) pseudolesions: arachnoid granulations, meningo-/encephaloceles, vascular canals, frontal hyperostosis, parietal thinning, parietal foramina, and sinus pericrani; (2) lytic: fibrous dysplasia, epidermal inclusion and dermoid cysts, eosinophilic granuloma, hemangioma, aneurysmal bone cyst, giant cell tumor, metastasis, and myeloma; (3) sclerotic: osteomas, osteosarcoma, and metastasis; (4) transdiploic: meningioma, hemangiopericytoma, lymphoma, and metastasis, along with other less common entities. Tips on the potential usefulness of functional imaging techniques such as MR dynamic susceptibility (T2*) perfusion, MR spectroscopy, diffusion-weighted imaging, and PET imaging are provided

Increasing and decreasing droplets velocity in micro channels

This paper deals with a specific aspect of non miscible liquid-liquid systems in microfluidic. For Chemical Engineering applications, the main constraints of functioning lies in the droplets velocity and frequency. Furthermore, the material used and the composition of the fluids is often imposed by the chemistry of the system (material resistance, fluids composition) and there is no possibility of adding other compound (surfactants for example). A technique under evaluation is presented: by using secondary channels and pumps, it is possible to increase or decrease at will the droplets velocity after they have been generated. Some experimental results are presented and discussed, including the possible limits of such an approach

Heterozygosity-fitness correlations and inbreeding depression in two critically endangered mammals

The relation among inbreeding, heterozygosity, and fitness has been studied primarily among outbred populations, and little is known about these phenomena in endangered populations. Most researchers conclude that the relation between coefficient of inbreeding estimated from pedigrees and fitness traits (inbreeding-fitness correlations) better reflects inbreeding depression than the relation between marker heterozygosity and fitness traits (heterozygosity-fitness correlations). However, it has been suggested recently that heterozygosity-fitness correlations should only be expected when inbreeding generates extensive identity disequilibrium (correlations in heterozygosity and homozygosity across loci throughout the genome). We tested this hypothesis in Mohor gazelle (Gazella dama mhorr) and Iberian lynx (Lynx pardinus). For Mohor gazelle, we calculated the inbreeding coefficient and measured heterozygosity at 17 microsatellite loci. For Iberian lynx, we measured heterozygosity at 36 microsatellite loci. In both species we estimated semen quality, a phenotypic trait directly related to fitness that is controlled by many loci and is affected by inbreeding depression. Both species showed evidence of extensive identity disequilibrium, and in both species heterozygosity was associated with semen quality. In the Iberian lynx the low proportion of normal sperm associated with low levels of heterozygosity was so extreme that it is likely to limit the fertility of males. In Mohor gazelle, although heterozygosity was associated with semen quality, inbreeding coefficient was not. This result suggests that when coefficient of inbreeding is calculated on the basis of a genealogy that begins after a long history of inbreeding, the coefficient of inbreeding fails to capture previous demographic information because it is a poor estimator of accumulated individual inbreeding. We conclude that among highly endangered species with extensive identity disequilibrium, examination of heterozygosity-fitness correlations may be an effective way to detect inbreeding depression, whereas inbreeding-fitness correlations may be poor indicators of inbreeding depression if the pedigree does not accurately reflect the history of inbreeding.Peer Reviewe