Fluid pinch-off in superfluid and normal 4He.

We present frames from high-speed videos of the pinch-off of liquid 4He droplets. The temperature of the fluid droplets ranged from 1.33 K to 4.8 K, and the size of the drops was proportional to the temperature-dependent capillary length. We observed no qualitative difference between pinch-off in the normal and superfluid states. In both cases, the shape of the fluid in the final stages of pinch-off resembles a cone piercing a sphere, which is typical of other low-viscosity fluids. The evolution of the minimum neck radius rmin can be characterized by power laws rmin proportional, taun, where tau is the time remaining until pinch-off occurs. In the regime near pinch-off, the data from image analysis are consistent with n=2/3. The data at the beginning of the pinch process when the neck is of the order of the capillary length are also described by n=2/3, but with a different proportionality factor. There is an intermediate crossover regime characterized by n=2/5.

Predictors of congestive heart failure in the elderly: the Cardiovascular Health Study.

OBJECTIVES: We sought to characterize the predictors of incident congestive heart failure (CHF), as determined by central adjudication, in a community-based elderly population. BACKGROUND: The elderly constitute a growing proportion of patients admitted to the hospital with CHF, and CHF is a leading source of morbidity and mortality in this group. Elderly patients differ from younger individuals diagnosed with CHF in terms of biologic characteristics. METHODS: We analyzed data from the Cardiovascular Health Study, a prospective population-based study of 5,888 elderly people >65 years old (average 73 +/- 5, range 65 to 100) at four locations. Multiple laboratory measures of cardiovascular structure and function, blood chemistries and functional assessments were obtained. RESULTS: During an average follow-up of 5.5 years (median 6.3), 597 participants developed incident CHF (rate 19.3/1,000 person-years). The incidence of CHF increased progressively across age groups and was greater in men than in women. On multivariate analysis, other independent predictors included prevalent coronary heart disease, stroke or transient ischemic attack at baseline, diabetes, systolic blood pressure (BP), forced expiratory volume 1 s, creatinine >1.4 mg/dl, C-reactive protein, ankle-arm index <0.9, atrial fibrillation, electrocardiographic (ECG) left ventricular (LV) mass, ECG ST-T segment abnormality, internal carotid artery wall thickness and decreased LV systolic function. Population-attributable risk, determined from predictors of risk and prevalence, was relatively high for prevalent coronary heart disease (13.1%), systolic BP > or =140 mm Hg (12.8%) and a high level of C-reactive protein (9.7%), but was low for subnormal LV function (4.1%) and atrial fibrillation (2.2%). CONCLUSIONS: The incidence of CHF is high in the elderly and is related mainly to age, gender, clinical and subclinical coronary heart disease, systolic BP and inflammation. Despite the high relative risk of subnormal systolic LV function and atrial fibrillation, the actual population risk of these for CHF is small because of their relatively low prevalence in community-dwelling elderly people.

Fluid pinch-off dynamics at nanometer length scales.

The breakup of a drop of inviscid fluid into two smaller drops is determined by a competition between surface and inertial forces. This process forms a thin filament of fluid with a connecting neck that shrinks to zero diameter at a finite time singularity. We present measurements of the electrical resistance of a liquid bridge of mercury as it undergoes pinch off. The electrical measurements allow us to probe the region of the singularity down to nanosecond times and nanometer lengths. Near pinch off, the resistance of the liquid bridge diverges as t(-2/3), as expected for inviscid flow.