The relationship between viscoelasticity and elasticity.

Soft materials that are subjected to large deformations exhibit an extremely rich phenomenology, with properties lying in between those of simple fluids and those of elastic solids. In the continuum description of these systems, one typically follows either the route of solid mechanics (Lagrangian description) or the route of fluid mechanics (Eulerian description). The purpose of this review is to highlight the relationship between the theories of viscoelasticity and of elasticity, and to leverage this connection in contemporary soft matter problems. We review the principles governing models for viscoelastic liquids, for example solutions of flexible polymers. Such materials are characterized by a relaxation time λ, over which stresses relax. We recall the kinematics and elastic response of large deformations, and show which polymer models do (and which do not) correspond to a nonlinear elastic solid in the limit λ → ∞. With this insight, we split the work done by elastic stresses into reversible and dissipative parts, and establish the general form of the conservation law for the total energy. The elastic correspondence can offer an insightful tool for a broad class of problems; as an illustration, we show how the presence or absence of an elastic limit determines the fate of an elastic thread during capillary instability.

Influence of the surface viscous stress on the pinch-off of free surfaces loaded with nearly-inviscid surfactants.

We analyze the breakup of a pendant water droplet loaded with SDS. The free surface minimum radius measured in the experiments is compared with that obtained from a numerical solution of the Navier-Stokes equations for different values of the shear and dilatational surface viscosities. This comparison shows the small but measurable effect of the surface viscous stresses for sufficiently small spatiotemporal distances from the breakup point, and allows to establish upper bounds for the values of the shear and dilatational viscosities. We study numerically the distribution of Marangoni and viscous stresses over the free surface as a function of the time to the pinching, and describe how surface viscous stresses grow in the pinching region as the free surface approaches its breakup. When Marangoni and surface viscous stresses are taken into account, the surfactant is not swept away from the thread neck in the time interval analyzed. Surface viscous stresses eventually balance the driving capillary pressure in the pinching region for small enough values of the time to pinching. Based on this result, we propose a scaling law to account for the effect of the surface viscosities on the last stage of temporal evolution of the neck radius.

Viscous Effects on Inertial Drop Formation.

The breakup of low-viscosity droplets like water is a ubiquitous and rich phenomenon. Theory predicts that in the inviscid limit one observes a finite-time singularity, giving rise to a universal power law, with a prefactor that is universal for a given density and surface tension. This universality has been proposed as a powerful tool to determine the dynamic surface tension at short time scales. We combine high-resolution experiments and simulations to show that this universality is unobservable in practice: in contrast to previous studies, we show that fluid and system parameters do play a role; notably a small amount of viscosity is sufficient to alter the breakup dynamics significantly.

Cusp-Shaped Elastic Creases and Furrows.

The surfaces of growing biological tissues, swelling gels, and compressed rubbers do not remain smooth, but frequently exhibit highly localized inward folds. We reveal the morphology of this surface folding in a novel experimental setup, which permits us to deform the surface of a soft gel in a controlled fashion. The interface first forms a sharp furrow, whose tip size decreases rapidly with deformation. Above a critical deformation, the furrow bifurcates to an inward folded crease of vanishing tip size. We show experimentally and numerically that both creases and furrows exhibit a universal cusp shape, whose width scales like y^{3/2} at a distance y from the tip. We provide a similarity theory that captures the singular profiles before and after the self-folding bifurcation, and derive the length of the fold from finite deformation elasticity.

Balancing a cylinder on a thin vertical layer of viscous fluid.

We analyze recent experiments that show that a cylinder can be suspended in a stable position by placing it on a vertically moving belt that is covered by a thin layer of very viscous oil. The weight of the cylinder is supported by viscous forces in the fluid layer, and the cylinder rotates with respect to its axis in the direction of the belt motion. We propose a simple model for stable suspension of the cylinder, based on lubrication ideas.

The prognostic impact of the stroke unit care versus conventional care in treatment of patients with transient ischemic attack: a prospective population-based German study.

BACKGROUND AND PURPOSE: The risk of a stroke after a transient ischemic attack (TIA) is high in the short time following a TIA. The German Stroke Society recommends an early hospitalization of patients with TIA preferably in a stroke unit (SU). This study aims to compare the impact of SU care with conventional care (CC) in patients with TIA. METHODS: In a prospective study, during a 36-month phase (starting November 2007), patients with TIA who were admitted to the hospital within 48 h of symptom onset were enrolled. Stroke rate during hospitalization and the 90-day rates of stroke and mortality were studied. Logistic regression analyses were used to estimate the odds ratio (OR). RESULTS: Of 2,200 patients (mean age, 17.6 ± 12 years, 49% female), 1,347 (61%) treated in a SU and 853 (39%) received CC at general departments. Patients treated in SU were significantly younger than those received a CC (69.9 vs. 71.7 years; P = 0.001). TIA patients treated on SU received more ultrasound investigations of the neck arteries (98 vs. 96%; P = 0.003) and of the brain arteries (97 vs. 82%; P < 0.001) than those of CC. The primary outcomes (stroke during hospitalization, stroke after 90 days, and mortality after 90 days) did not show a difference between the SU and CC groups. In patients of male sex, the 90-day stroke rate was significantly lower in the SU group than the CC group (1.8 vs. 4.5%; P = 0.033). Using the adjusted logistic regression analysis, treatment in a SU revealed a reduction of 90-day stroke rate in patients of male sex (OR 0.38; 95% CI 0.15-0.95; P = 0.04). CONCLUSION: The impact of evaluation and treatment of patients with TIA in SU and CC appears to differ only among patients of male sex. Further randomized trials are necessary.

Stroke recurrence in patients with recently symptomatic carotid stenosis and scheduled for carotid revascularization.

BACKGROUND AND PURPOSE: Patients with symptomatic carotid stenosis (sCS) have a higher risk of stroke recurrence following the first ischaemic event. Guidelines recommend that patients undergo carotid revascularization (CR), preferably within 2 weeks of the event. We aimed to determine the rate of stroke recurrence during hospitalization in patients who were admitted to the hospital with an acute ischaemic event and who underwent CR for recently sCS. METHODS: As part of the stroke registry in Schleswig-Holstein, Germany (QugSS2; Qualitätsgemeinschaft Schlaganfallversorgung in Schleswig-Holstein), over a 4.5-year period (starting 2007) all patients (N = 15,797) who were admitted to the hospital with an acute cerebral ischaemic event were included and prospectively evaluated. RESULTS: A total of 597 (3.8%) patients (mean age, 71 ± 10 years; 30% women) underwent a CR. The median time between symptom onset and admission to hospitals was 6 h. During the mean hospitalization of 10 days, 30 patients (5%) suffered a stroke. The rates of stroke recurrence were higher, albeit non-significantly, in men compared with women (6% vs. 2.3%, respectively; P = 0.059), and in patients admitted with ischaemic stroke compared with patients admitted with transient ischaemic attack (6.1% vs. 2%, respectively; P = 0.052). The risk of stroke recurrence did not show any association with the other demographic and clinical parameters. CONCLUSION: The rate of stroke recurrence was 5% in patients with recently sCS who scheduled for CR. This suggests that CR should be performed immediately after presenting event to prevent stroke recurrence.

Delayed capillary breakup of falling viscous jets.

Thin jets of viscous fluid like honey falling from capillary nozzles can attain lengths exceeding 10 m before breaking up into droplets via the Rayleigh-Plateau (surface tension) instability. Using a combination of laboratory experiments and WKB analysis of the growth of shape perturbations on a jet being stretched by gravity, we determine how the jet's intact length l(b) depends on the flow rate Q, the viscosity η, and the surface tension coefficient γ. In the asymptotic limit of a high-viscosity jet, l(b)∼(gQ(2)η(4)/γ(4))(1/3), where g is the gravitational acceleration. The agreement between theory and experiment is good, except for very long jets.

First Report of Zebra Chip Disease and "Candidatus Liberibacter solanacearum" on Potatoes in Oregon and Washington State.

In August of 2011, potato (Solanum tuberosum) tubers grown in the lower Columbia Basin of southern Washington State and northern Oregon were observed with internal discolorations suggestive of zebra chip disease (ZC). Symptoms included brown spots, streaks, and stripes in and near the vascular tissue, typical of ZC (1). Symptoms were observed in cvs. Alturas, Russet Norkotah, Pike, Ranger Russet, Umatilla Russet, and Russet Burbank. Foliar symptoms on plants that produced symptomatic tubers included purple discoloration in upper leaves, leaf rolling, axial bud elongation, chlorosis, leaf scorch, and wilt. Tissue was taken from two symptomatic tubers each of cvs. Alturas and Russet Norkotah, three tubers of cv. Umatilla Russet, and one tuber of cv. Pike. These tubers were tested by PCR for "Candidatus Liberibacter solanacearum", an unculturable alphaproteobacterium associated with ZC (1,4). Primers specific for the 16S rDNA were CLipoF (4) and OI2c (3), and primers OMB 1482f and 2086r were specific for the outer membrane protein (2). All of these samples, except one Umatilla tuber, were positive for the bacterium. The 16S rDNA and OMB amplicons from one symptomatic tuber each of Alturas (from Washington) and Pike (from Oregon) were cloned and three clones of each were sequenced. BLAST analysis of the consensus sequences confirmed "Ca. L. solanacearum". The 16S sequences (1,071 bp) from the two tubers were identical and showed 99 to 100% identity to a number of 16S rDNA sequences of "Ca. L. solanaceaum" in GenBank (e.g., Accession Nos. HM246509 and FJ957897). The 16S rDNA sequences were deposited in GenBank as Accession Nos. JN848751 and JN848753. Consensus sequences of the two OMB clones (605 bp; deposited in GenBank as Accession Nos. JN848752 and JN848754) were identical and showed 97% identity to the two "Ca. L. solanacearum" OMB sequences in GenBank (Accession Nos. CP002371 and FJ914617). Potato psyllids (Bactericera cockerelli Sulc), the vector of "Ca. L. solanacearum", were present in ZC-affected fields in Oregon and Washington and the bacterium was confirmed by PCR in 5 to 10% of 128 adult psyllids collected from two fields. On the basis of foliar and tuber symptoms, specific PCR amplification with two primer pairs, sequence analyses, and the presence of Liberibacter-infected potato psyllids, ZC and "Ca. L. solanacearum" are present in potatoes in Oregon and Washington State. Washington and Oregon together grow ~80,000 ha of potatoes. ZC has caused significant economic damage to potatoes in Texas, Mexico, Central America, and New Zealand (1). Therefore, ZC may pose a risk to agriculture in Oregon, Washington, and neighboring states. However, the potential for development of widespread and serious disease will depend upon the arrival time and number of infective potato psyllids entering the region. References: (1) J. M. Crosslin et al. Online publication. doi:10.1094/PHP-2010-0317-01-RV, Plant Health Progress, 2010. (2) J. M. Crosslin et al. Southwest. Entomol. 36:125, 2011. (3) S. Jagoueix et al. Mol. Cell. Probes 10:43, 1996. (4) G. A. Secor. Plant Dis. 93:574, 2009.

Variation Among Phytophthora cinnamomi Isolates from Oak Forest Soils in the Eastern United States.

Phytophthora cinnamomi isolates from geographically diverse oak forest soils in the Mid-Atlantic regions were studied to determine the extent of genotypic, phenotypic, and pathogenic variation. Four microsatellite loci were targeted for genetic analysis. Phenotypic characteristics measured included sexual and asexual spore dimensions and colony growth rate and morphology. Red oak (Quercus rubra) logs were inoculated with selected isolates to determine relative pathogenicity. Microsatellite analysis showed that the genetic variability of P. cinnamomi isolates was low, with two predominant microsatellite fingerprint groups (MFG). Isolates in MFG1 (48% of the total isolates examined) were characterized by DNA fragment lengths of 120 and 122 bp at locus d39, 169 and 170 bp at locus e16, and 254 and 255 bp at locus g13. MFG2 isolates were characterized by marker sizes of 122 and 124 bp at locus d39, 161 and 163 bp at locus e16, and 247 and 248 bp at locus g13. Asexual and sexual spore dimensions varied greatly among isolates but were similar to previously published descriptions. Phenotypic differences were most pronounced when data were grouped by MFG; the most significant were colony morphology and growth rate. Neither characteristic was a reliable predictor of isolate genotype. Differences in growth rates of MFGs were observed, with MFG1 being less tolerant at higher incubation temperatures. No variation in pathogenicity was observed on red oak logs. The low level of phenotypic and genotypic variation of P. cinnamomi suggest that other factors such as climate might play a more important role in its northern distribution and the diseases it causes.

Complete basilar artery assessment by transcranial color-coded duplex sonography using the combined transforaminal and transtemporal approach.

PURPOSE: Visualization of the basilar artery (BA) by transcranial color-coded duplex sonography (TCCD) can be challenging. The detection of stenosis or occlusion of the BA often has to rely on indirect signs like a highly pulsatile flow in the vertebral arteries. In case of a distal BA occlusion, however, the flow of the VAs can even be normal. The aim of our TCCD study was to visualize a maximum length of the BA combining the customarily used transforaminal appraoch for the proximal part and the less well known transtemporal coronal approach for the distal BA segment. MATERIALS AND METHODS: TCCD was performed in 60 subjects with a good temporal bone window. Detectable extracranial or intracranial pathology was previously excluded. The BA was insonated using the transforaminal and transtemporal insonation plane and the visible length was measured. In one subject MRA was performed to substantiate our findings. RESULTS: The BA was visualized in all subjects via both approaches. The maximal detectable BA length via the transforaminal and transtemporal approach was 26 ± 8 mm and 18 ± 5 mm, respectively. Assuming a previously reported average anatomical total BA length of 33 ± 6 mm, we supposed complete vessel visualization in 44 subjects (73 %). CONCLUSION: The combined transforaminal and transtemporal insonation approach may permit total BA insonation, thus facilitating the evaluation of BA pathology.

General mechanism for the meandering instability of rivulets of Newtonian fluids.

A rivulet flowing down an inclined plane often does not follow a straight path, but starts to meander spontaneously. Here we show that this instability is the result of two key ingredients: fluid inertia and anisotropy of the friction between rivulet and substrate. Meandering only occurs if the motion normal to the instantaneous flow direction is more difficult than parallel to it. We give a quantitative criterion for the onset of meandering and confirm it by comparing to the flow of a rivulet between two glass plates which are wetted completely. Above the threshold, the rivulet follows an irregular pattern with a typical wavelength of a few cm.

[Chiari II malformation. Supportive and predictive value of brainstem reflex and EAEP recordings]. / Chiari-II-Malformation. Supportiver und prädiktiver Wert der Hirnstammreflex- und FAEP-Diagnostik.

BACKGROUND: In about 20% of patients with Chiari II malformation brainstem signs and symptoms occur. Ventilatory dysfunction is the main cause of death in these patients. The indication for craniocervical decompression is based on clinical examination because supporting electrophysiological or radiological methods were lacking. METHODS: In a prospective study the clinical courses of 106 patients were documented during a 3-year period. In addition brainstem diagnostic procedures using the masseter reflex (MR), blink reflex (BR) and early auditory evoked potentials (EAEP) were done. Based on the model of binary logistic regression the odds ratio (OR) of progression over time was calculated. RESULTS: The combination of MR and late BR components showed the highest correlation with clinical findings (OR: 23). The highest predictive value regarding clinical progression over a 3-year period was shown by the combined evaluation of MR, late BR components and EAEP interpeak latency I-V (OR: 17.6). Signs and symptoms had no predictive value. CONCLUSIONS: Combined brainstem reflex recordings (MR and late BR components) support the clinical examination. To evaluate the long-term prognosis brainstem reflexes and EAEP recordings should be used.

Superior cerebellar artery - a potential pitfall in transcranial posterior cerebral artery insonation.

PURPOSE: Transcranial color-coded duplexsonography (TCCD) of the posterior cerebral artery (PCA) is commonly performed in an axial midbrain insonation plane. The proximal PCA is easily identified as a vessel, originating from the top of the basilar artery (BA). However, the initial segment of the superior cerebellar artery (SCA) also originates from the top segment of the BA and runs in parallel. Therefore, it is possible to confuse the two vessels. The aim of our study is to anatomically differentiate the proximal PCA and SCA by means of TCCD in the coronal plane using a transtemporal approach and to analyze and compare their flow responses during a visual stimulus paradigm. MATERIALS AND METHODS: 60 subjects without a relevant vascular pathology and with a good temporal bone window were examined. The distal BA, the proximal PCA and the SCA were insonated using a coronal insonation plane and identified by their anatomical relationship. The visible length was measured and the blood flow velocities were recorded at rest and during visual stimulation. RESULTS: The identification and differentiation of both vessels was successful in 101 of 120 hemispheres (84.2 %). The PCA systolic flow velocities at rest and during visual stimulation were 58.4 +/- 11 and 71.8 +/- 13 cm/sec (23.6 % increase), while the SCA velocities were 50.7 +/- 12 and 53.5 +/- 13 cm/sec, respectively (5.8 % increase). The difference was significant (p < 0.001). CONCLUSION: Using the coronal transtemporal insonation approach, TCCD makes it possible to identify and distinguish the proximal PCA and SCA. Our study is the first to provide a systematic ultrasound assessment of the SCA and includes data on normal flow velocities and reactivity to a visual stimulus.

Numerical analysis of tips in viscous flow.

When a drop (or gas bubble) is placed in a strong viscous flow (e.g., a shear flow), it develops very sharp tips at its ends. Sharp tips are also formed when a viscous fluid is withdrawn from the neighborhood of its interface with the ambient air or with another fluid (selective withdrawal). However, it is observed frequently that there exists a critical flow strength above which the drop transitions toward a "jetting state" in which a jet comes out from the tip. In this paper, we look numerically for stationary drop shapes, both globally and close to the tip, which we study with very high resolution. To this end we use a boundary integral method to solve the axisymmetric flow equations for arbitrary viscosity ratios in the inertialess (Stokes) limit. Stationary states are solved for using Newton's method. This permits us to find both stable and unstable steady states and to investigate the nature of the jetting transition. The critical parameters for this transition are in reasonable agreement with slender-body theory. Excellent agreement is found with our earlier experiments in the selective withdrawal geometry [S. Courrech du Pont and J. Eggers, Phys. Rev. Lett. 96, 034501 (2006)], for which the viscosity of the phase inside the tip is negligible. We describe a scale invariance of the experimental interface profiles away from the tip. Then we investigate the highly curved tip region not considered previously with comparable precision. We find that the shape near the tip is universal, i.e., independent of the outer flow and of the geometry of the system (drop or selective withdrawal). While the tip curvature becomes extremely large, it always remains finite if surface tension is present.

Transcranial color-coded sonography successfully visualizes all intracranial parts of the internal carotid artery using the combined transtemporal axial and coronal approach.

BACKGROUND AND PURPOSE: Visualization of the intracranial internal carotid artery (ICA) with transcranial color-coded sonography (TCCS) by using the transtemporal coronal plane has been described previously. Because this approach is limited to the vertical running ICA segments, we investigated the feasibility of using TCCS to visualize all intracranial ICA segments by adding the transtemporal axial approach to the coronal plane. MATERIALS AND METHODS: Subjects with excellent transtemporal acoustic windows were examined by TCCS by using standardized axial and coronal planes. Identification rate, flow velocities, pulsatility and resistance indices, and length (as visible in color-coded power mode) were determined. RESULTS: A total of 120 intracranial ICAs from 60 subjects were investigated. By switching between the axial and coronal insonation planes, all intracranial segments of the ICA could be investigated in 100% of subjects-with the exception of the horizontal part of the petrosal ICA, which was identified in 96.7% of subjects. CONCLUSIONS: TCCS becomes a reliable tool in investigating all parts of the intracranial ICA by adding the transtemporal axial approach to the coronal plane.

Two-generation reproductive toxicity study of implanted depleted uranium (DU) in CD rats.

Depleted uranium (DU) munitions and armor plating have been used in several conflicts over the last 17 yr, including the Persian Gulf War and the Iraq War. Because of its effectiveness and availability, DU will continue to be used in military applications into the foreseeable future. There is much controversy over the use of DU in weapons and equipment because of its potential radiological and toxic hazards, and there is concern over the chronic adverse health effects of embedded DU shrapnel in war veterans and bystanders. This study evaluated the effects of long-term implantation of DU on the reproductive success of F0 generation adults and development and survival of subsequent F1 and F2 generations in a two-generation reproductive toxicity study. F0 generation Sprague-Dawley rats, 8 wk of age, were surgically implanted with 0, 4, 8, 12, or 20 DU pellets (1 x 2 mm). Inert implant control animals were implanted with 12 or 20 tantallum (Ta) pellets. The F0 generation was then mated at 120 d post DU implantation. In the F0 generation, when measured on postimplantation d 27 and 117, uranium was present in the urine of DU-implanted animals in a dose-dependent manner. F0 reproductive success was similar across treatment groups and the maternal retrieval test revealed no changes in maternal behavior. DU implantation exerted no effect on the survival, health, or well-being of the F0 generation. Necropsy results of F0 animals were negative with the exception of a marked inflammatory response surrounding the implanted DU pellets. For the F1 generation, measures of F1 development through postnatal day (PND) 20 were unremarkable and no gross abnormalities were observed in F1 offspring. No uranium was detected in whole-body homogenates of PND 4 or PND 20 pups. Necropsy findings of F1 PND 20 pups were negative and no instances of ribcage malformation were observed in F1 PND 20 pups. Body weight and body weight gain of F1 rats through PND 120 were similar across treatment groups. Eight of 414 F1 animals observed from PND 20 to 120 died of unknown causes; 7 were from litters of DU-implanted F0 mating pairs. F1 mating success at 10 wk of age was an overall 70% compared with 91% for F0 mating pairs. Mating success was similar between F1 animals derived from DU-implanted F0 adults and those derived from F0 implant control adults suggesting that the comparatively low mating success was not due to F1 DU exposure. The gestational index of F1 animals derived from mid-dose F0 mating pairs was found to be lower compared with F1 controls. The average gestation duration of F1 animals derived from high-dose F0 mating pairs was found to be significantly longer than F1 controls. F1 sperm motility analyses did not differ among experimental groups and no gross abnormalities were identified at necropsy among surviving F1 animals at PND 120. Histopathology of kidneys, spleen, thymus, bone marrow, ovaries, and testes of F1 high-dose animals did not differ from F1 controls. F1 high-dose females had significantly higher mean relative liver and heart weights compared with F1 controls; the biological relevance of this finding could not be determined. For the F2 generation, measures of F2 development through PND 20 were unremarkable and no gross abnormalities were observed in F2 offspring. Necropsy findings of F2 PND 20 pups were negative and no instances of ribcage malformation were observed in F2 PND 20 pups. Body weight and body weight gain of F2 rats through PND 90 were similar across treatment groups. Mean relative heart weights of males derived from high-dose F0 parents were significantly lower compared with F2 controls. Sperm motility and concentration analysis of F2 males at PND 90 were similar across F2 groups. Overall, the consistent absence of positive findings in this study seems to suggest that DU is not a significant reproductive or developmental hazard, particularly when one considers that mid- and high-dose rats were implanted with the equivalent of 0.3 and 0.5 lb of DU in a 70-kg human, respectively. However, the findings that seven of eight F1 adults that died postweaning were from DU-implanted F0 mating pairs, and that mean relative heart weights were elevated in high-dose F1 and F2 pups, suggest conservatism is warranted in characterizing the reproductive and teratogenic hazards of embedded DU until further studies are completed.

Pinch-off singularities in rotating Hele-Shaw flows at high viscosity contrast.

We study the evolution of a family of dumbbell-shaped liquid patches surrounded by air inside a rotating Hele-Shaw cell with lubrication methods and numerical simulations. Depending on initial conditions, the dumbbell either stretches to infinity, pinches off at the neck to form a droplet, or collects into a circular drop at the center of rotation. Whether or not pinch-off occurs results from a subtle interplay between centrifugal and capillary forces. In particular, rotation may delay or even prevent pinch-off from occurring owing to stretching and smoothing of the fluid neck. However, frequently rotation may have the opposite effect leading to pinch-off where the relaxation toward a circular drop would be observed in an ordinary Hele-Shaw cell.