Pause point spectra in DNA constant-force unzipping.

Under constant applied force, the separation of double-stranded DNA into two single strands is known to proceed through a series of pauses and jumps. Given experimental traces of constant-force unzipping, we present a method whereby the locations of pause points can be extracted in the form of a pause point spectrum. A simple theoretical model of DNA constant-force unzipping is presented, which generates theoretical pause point spectra through Monte Carlo simulation of the unzipping process. The locations of peaks in the experimental and theoretical pause point spectra are found to be nearly coincident below 6000 basepairs for unzipping the bacteriophage lambda-genome. The model only requires the sequence, temperature, and a set of empirical basepair binding and stacking energy parameters, and the good agreement with experiment suggests that pause point locations are primarily determined by the DNA sequence. The model is also used to predict pause point spectra for the bacteriophage phi X174 genome. The algorithm for extracting the pause point spectrum might also be useful for studying related systems which exhibit pausing behavior such as molecular motors.

Trends in the use of episiotomy in the United States: 1980-1998.

BACKGROUND: Despite a relative paucity of clinical evidence justifying its routine use, approximately 40 percent of all vaginal deliveries include an episiotomy. The purpose of this study is to examine trends in episiotomy in the United States from 1980 through 1998, a period during which calls increased to abandon routine episiotomy. METHODS: Data were obtained from the National Hospital Discharge Survey, which is conducted annually and based on a nationally representative sample of discharges from short-stay non-Federal hospitals. RESULTS: From 1980 through 1998 the episiotomy rate in the United States dropped by 39 percent. Rates decreased for all age and racial groups investigated, in all four geographic regions, and for all sources of payment. Significant differences remained between groups in 1998, including a higher rate for white women than for black women, and a higher rate for women with private insurance than for women with Medicaid or in the self-pay category. The incidence of first- and second-degree lacerations to the perineum increased for women without episiotomies, but the more severe third- and fourth-degree lacerations remained more frequent for women with episiotomies. Women with episiotomies were more likely to have forceps-assisted deliveries or vacuum extractions. CONCLUSIONS: Despite dramatic declines in the use of episiotomy during the last two decades, it remains one of the most frequent surgical procedures performed on women in the United States, and it continues to be performed at a higher rate for certain groups of women.

Unmet need for personal assistance with activities of daily living among older adults.

PURPOSE: This study examined the prevalence, correlates, and negative consequences of unmet need for personal assistance with activities of daily living (ADLs) among older adults. DESIGN AND METHODS: The authors analyzed cross-sectional data from the 1994 National Health Interview Survey's Supplement on Aging. Data were weighted to be representative of the noninstitutionalized population aged 70 years and older. RESULTS: Overall, 20.7% of those needing help to perform 1 or more ADLs (an estimated 629,000 persons) reported receiving inadequate assistance; for individual ADLs, the prevalence of unmet need ranged from 10.2% (eating) to 20.1% (transferring). The likelihood of having 1 or more unmet needs was associated with lower household income, multiple ADL difficulties, and living alone. Nearly half of those with unmet needs reported experiencing a negative consequence (e.g., unable to eat when hungry) as a result of their unmet need. IMPLICATIONS: Greater, targeted efforts are needed to reduce the prevalence and consequences of unmet need for ADL assistance in elderly persons.

Density fluctuations and the structure of a nonuniform hard sphere fluid.

We derive an exact equation for density changes induced by a general external field that corrects the hydrostatic approximation where the local value of the field is adsorbed into a modified chemical potential. Using linear response theory to relate density changes self-consistently in different regions of space, we arrive at an integral equation for a hard sphere fluid that is exact in the limit of a slowly varying field or at low density and reduces to the accurate Percus-Yevick equation for a hard core field. This and related equations give accurate results for a wide variety of fields.

Disability among older people: United States and Canada.

Data from two national surveys of community-dwelling people 55 years of age and over are the basis of tables presenting 25 measures of disability for each country. The report includes discussions of similarity and differences between the countries, methods used to make the data comparable, and limitations on interpretation of the data.

Van der waals picture of liquids, solids, and phase transformations.

The van der Waals picture focuses on the differing roles of the strong short-ranged repulsive intermolecular forces and the longer ranged attractions in determining the structure and dynamics of dense fluids and solids. According to this physical picture, the attractive interactions help fix the volume of the system, but the arrangements and motions of molecules within that volume are determined primarily by the local packing and steric effects produced by the repulsive forces. This very useful approach, its limitations, and its successful application to a wide variety of static and dynamic phenomena in condensed matter systems are reviewed.