Rotating polygon instability of a swirling free surface flow.

We explain the rotating polygon instability on a swirling fluid surface [G. H. Vatistas, J. Fluid Mech. 217, 241 (1990) and Jansson et al., Phys. Rev. Lett. 96, 174502 (2006)] in terms of resonant interactions between gravity waves on the outer part of the surface and centrifugal waves on the inner part. Our model is based on potential flow theory, linearized around a potential vortex flow with a free surface for which we show that unstable resonant states appear. Limiting our attention to the lowest order mode of each type of wave and their interaction, we obtain an analytically soluble model, which, together with estimates of the circulation based on angular momentum balance, reproduces the main features of the experimental phase diagram. The generality of our arguments implies that the instability should not be limited to flows with a rotating bottom (implying singular behavior near the corners), and indeed we show that we can obtain the polygons transiently by violently stirring liquid nitrogen in a hot container.

Optimality of the Münch mechanism for translocation of sugars in plants.

Plants require effective vascular systems for the transport of water and dissolved molecules between distal regions. Their survival depends on the ability to transport sugars from the leaves where they are produced to sites of active growth; a flow driven, according to the Münch hypothesis, by osmotic gradients generated by differences in sugar concentration. The length scales over which sugars are produced (Lleaf) and over which they are transported (L(stem)), as well as the radius r of the cylindrical phloem cells through which the transport takes place, vary among species over several orders of magnitude; a major unsettled question is whether the Münch transport mechanism is effective over this wide range of sizes. Optimization of translocation speed predicts a scaling relation between radius r and the characteristic lengths as r∼(Lleaf Lstem)1/3. Direct measurements using novel in vivo techniques and biomimicking microfluidic devices support this scaling relation and provide the first quantitative support for a unified mechanism of sugar translocation in plants spanning several orders of magnitude in size. The existence of a general scaling law for phloem dimensions provides a new framework for investigating the physical principles governing the morphological diversity of plants.

Análisis de las técnicas de Anson Mcvay y Malla de Marlex en el tratamiento de Hernias Inguinales / Analysis of the Anson Mcvay and marlex techniques for Inguinal repair

OBJETIVO: analizar comparativamente los beneficios y riesgos que presenta la técnica de Anson McVay y la utilización de la Malla de Marlex en las cirugías de hernias inguinales en sus variedades directa e indirecta. MATERIAL Y MÉTODOS: se revisaron las historias clínicas correspondientes a 11 años de un universo compuesto por todos los pacientes que cumplieron con los criterios de inclusión, mediante una muestra estadísticamente significativa, y buscando indicadores prospectivos. Se trata de un estudio de terreno mediante datos secundarios y de revisión bibliográfica. En base a la totalidad de pacientes diagnosticados con hernia inguinal e intervenida por causa de esta patología durante el período del 1 de enero de 1992 al 31 de diciembre de 2002, se obtuvo una muestra estadísticamente significativa de los pacientes que fueron sometidos a cirugía en el Hospital de Clínicas durante este período. RESULTADOS: Se diagnosticaron 313 pacientes con hernia inguinal entre 01/enero/1992 y 31/diciembre/2002, 143 hospitalizados y sometidos a cirugía, la mayoría, 50 (83.3%) de sexo masculino, con un 40% mayores de 46 años. La mayoría hernias indirectas (65.0%) y del lado derecho. Se utilizó técnica de Anson McVay en 53.3% y la malla de Marlex en 23.3 %. El tiempo quirúrgico y la colocación de drenajes fue mayor utilizando la malla de Marlex. CONCLUSIONES: se encontraron diferencias estadísticamente significativas entre la relación tipo de hernia/ lado de la hernia, relación procedimiento quirúrgico/ tiempo quirúrgico, relación procedimiento quirúrgico/colocación de drenaje y relación técnica Anson McVay, Malla de Marlex/ tiempo quirúrgico.

OBJECTIVE: to compare the risks and benefits of the Anson McVay and Marlex techniques in the treatment of direct and indirect inguinal hernias MATERIAL AND METHODS: We revised the clinical data of 313 patients during January 92 to December 2002.143 were hospitalized and underwent surgical repair. 83.3% were male. 40% over 46 years of age. The majority (65%) were indirect hernias and right sided. 53.3% underwent the technique of Anson McVay and 23.3 % the Marlex technique. This last procedure has more surgical time and placing of drainages. CONCLUSIONS: there was statistic differences between the type of hernia and the location site, between the two surgical procedures, surgical time and placing of drainages.

Pattern formation of underwater sand ripples with a skewed drive.

In this paper we present an experimental study of the dynamics of underwater sand ripples when a regular pattern of ripples is subjected to a skewed oscillatory flow, i.e., one not perpendicular to the direction of the ripple crests. Striking patterns with new, superposed ripples on top of the original ones occur very quickly with a characteristic angle, which is, in general, not perpendicular to the flow. A slower, more complex transition then follows, leading to the final state where the ripples are again perpendicular to the flow. We investigate the variation of the superposed pattern as a function of the direction, amplitude, and frequency of the drive, and as a function of the viscosity (by changing the temperature). We quantify the dynamics of the entire transition process and finally study the grain motion around idealized (solid) skewed ripples. This leads to a characteristic mean path of a single particle. The path has a shape close to a parallelogram, with no apparent connection to the pattern of real, superposed ripples. On the other hand, a thin layer of sand sprinkled on the solid ripples leads to qualitatively similar patterns.

Anatomy of a bathtub vortex.

We present experiments and theory for the "bathtub vortex," which forms when a fluid drains out of a rotating cylindrical container through a small drain hole. The fast down-flow is found to be confined to a narrow and rapidly rotating "drainpipe" from the free surface down to the drain hole. Surrounding this drainpipe is a region with slow upward flow generated by the Ekman layer at the bottom of the container. This flow structure leads us to a theoretical model similar to one obtained earlier by Lundgren [J. Fluid Mech. 155, 381 (1985)]], but here including surface tension and Ekman upwelling, comparing favorably with our measurements. At the tip of the needlelike surface depression, we observe a bubble-forming instability at high rotation rates.

Stability balloon for two-dimensional vortex ripple patterns.

Patterns of vortex ripples form when a sand bed is subjected to an oscillatory fluid flow. Here we describe experiments on the response of regular vortex ripple patterns to sudden changes of the driving amplitude a or frequency f. A sufficient decrease of f leads to a "freezing" of the pattern, while a sufficient increase of f leads to a supercritical secondary "pearling" instability. Sufficient changes in the amplitude a lead to subcritical secondary "doubling" and "bulging" instabilities. Our findings are summarized in a "stability balloon" for vortex ripple pattern formation.

Breakdown of universality in transitions to spatiotemporal chaos.

We show that the transition from laminar to active behavior in extended chaotic systems can vary from a continuous transition in the universality class of directed percolation with infinitely many absorbing states to what appears as a first-order transition. The latter occurs when finite lifetime nonchaotic structures, called "solitons," dominate the dynamics. We illustrate this scenario in an extension of the deterministic Chaté-Manneville coupled map lattice model and in a soliton including variant of the stochastic Domany-Kinzel cellular automaton.

Singular Lyapunov spectra and conservation laws.

We give analytic arguments and numerical evidence to show that the presence of conservation laws can produce a singularity in the spectrum of Lyapunov exponents for extended dynamical systems of low spatial dimensionality. This phenomenon can be used, e.g., for finding hidden conservation laws. (c) 1995 American Institute of Physics.

Fibromyalgia syndrome and myofascial pain syndrome. Do they exist?

"It is in the healing business that the temptations of junk science are the strongest and the controls against it the weakest." Despite their subjective nature, these syndromes (particularly MPS) have little reliability and validity, and advocates paint them as "objective." Despite a legacy of poor-quality science, enthusiasts continue to cite small, methodologically flawed studies purporting to show biologic variables for these syndromes. Despite a wealth of traditional pain research, disciples continue to ignore the placebo effect, demonstrating a therapeutic hubris despite studies showing a dismal natural history for FS. In reviewing the literature on MPS and FS, F.M.R. Walshe's sage words come to mind that the advocates of these syndromes are "better armed with technique than with judgment." A sympathic observer might claim that labeling patients with monikers of nondiseases such as FS and MPS may not be such a bad thing. After all, there is still a stigma for psychiatric disease in our society, and even telling a sufferer that this plays only a partial role may put that patient on the defensive. Labeling may have iatrogenic consequences, however, particularly in the setting of the work place. Furthermore, review of a typical support group newsletter gives ipso facto proof of this noxious potential. The author of a flyer stuffed inside the newsletter complains that getting social security and disability benefits for "the invisible disability" can be "an uphill battle. But don't loose (sic) hope." Apparently the "seriousness of the condition" is not appreciated by the medical community at large, and "clinician bias may well be the largest threat," according to Boston epidemiologist Dr. John Mason. Sufferers are urged to trek to their local medical library and pull four particular articles claiming FS patients have more "stress," "daily hassles," and difficulty working compared with arthritis patients. If articles can't be located, patients are told to ask their lawyers for help. Although "Chronic Fatigue Syndrome" and FS are not considered by everyone to be the same malady, the "National Institute of Health (sic) has lumped these two conditions together. This could work in your favor." (A U.S. political advocacy packet is available for $8, but a list of U.S. senators with Washington, DC addresses is freely provided.) These persons see themselves as victims worthy of a star appearance on the Oprah Winfrey show. A sense of bitterness emerges; one literally bed-bound Texas homemaker writes in Parents magazine that "Some doctors may give up and tell you that you are a hypochondriac."(ABSTRACT TRUNCATED AT 400 WORDS)

Death certificates: an efficient source for ascertainment of Creutzfeldt-Jakob disease cases.

Case ascertainment for an epidemiologic study of Creutzfeldt-Jakob disease (CJD) can be difficult. This report investigates the efficiency of various sources of case ascertainment for CJD. Cases were identified utilizing neuropathologists, hospitals and death certificates from 11 targeted states. For the period of 1986-1988, 247 death certificates indicating a diagnosis of CJD were obtained. Only 26 potential cases were identified without death certificates. The proportion of neuropathologically confirmed cases identified by death certificates only, i.e., which were not identified through any other source, was 42%. Furthermore, 80% of all the neuropathologically confirmed cases were ascertained utilizing death certificates as a source. Of the remaining 20%, 7% were ascertained through neuropathologists only, 10% through hospitals only, 1.5% through a combination of hospitals and neuropathologists, and 1.5% through another source. The false-positive rate for death certificates with neuropathology (which may have been performed after the death certificate was filled out) was estimated to be 8.3%. The results indicate that death certificates were by far the most efficient source for initial ascertainment of potential CJD cases to be followed by verification of diagnosis.