Heterogeneous mass distribution of the rubble-pile asteroid (101955) Bennu.

The gravity field of a small body provides insight into its internal mass distribution. We used two approaches to measure the gravity field of the rubble-pile asteroid (101955) Bennu: (i) tracking and modeling the spacecraft in orbit about the asteroid and (ii) tracking and modeling pebble-sized particles naturally ejected from Bennu's surface into sustained orbits. These approaches yield statistically consistent results up to degree and order 3, with the particle-based field being statistically significant up to degree and order 9. Comparisons with a constant-density shape model show that Bennu has a heterogeneous mass distribution. These deviations can be modeled with lower densities at Bennu's equatorial bulge and center. The lower-density equator is consistent with recent migration and redistribution of material. The lower-density center is consistent with a past period of rapid rotation, either from a previous Yarkovsky-O'Keefe-Radzievskii-Paddack cycle or arising during Bennu's accretion following the disruption of its parent body.

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu.

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts.

A cross reactive sensor array to probe divalent metal ions.

A simple sensing ensemble was designed to discriminate structurally similar divalent metal chlorides utilizing multivariate data analysis. The system features the binding of four synthesized coumarin-enamine probes to a series of ten metal chlorides. Linear discriminant analysis (LDA) achieves what univariate data analysis alone cannot i.e., full analyte discrimination and differentiation.

Deafferentation of the olfactory bulbs of male rats reduces erection to remote cues from females.

If male rats are paired with a receptive, soliciting female rat in a setting that prevents physical contact, but permits auditory, visual, and olfactory contact, some will have erections of the penis--noncontact erections (NCE). Surgical deafferentation of the olfactory bulbs from all the known chemosensory systems of the nasal septum renders rats anosmic, decreases sexual performance in copulation tests with females, and substantially reduces the frequency of NCE. Thus, NCE appear to be primarily regulated though the olfactory perception of volatile chemosensory cues from receptive females.

Required first-year generalist clinical experience courses and their relationship to career choice: the critical effect of family medicine involvement.

BACKGROUND: This study examines the relationships among the presence of a required first-year generalist clinical experience (RFGCE) course, family medicine involvement in such courses, and the percentage of 1993 medical school graduates who chose family practice as a career upon graduation. METHODS: A prospective cohort study measured predictor variables in 1989, the presence of a required third-year family medicine clerkship in 1991, and the outcome variable in 1993. RESULTS: Data were collected from 122 US 4-year medical schools. Eighty-seven (71.3%) of 122 medical schools had RFGCE courses. In schools with courses and family medicine administrative units, family physicians were involved to some extent in most of these courses (88%). After controlling for type of medical school, the requirement of a third-year family medicine clerkship, and the involvement of a family medicine administrative unit, the presence of an RFGCE course was associated with a 3.5% increase in the number of students who selected a family practice career. This is a 28% increase on average over the mean percentage of medical students choosing a family practice career in 1993. However, in a second analysis, when all predictor variables were entered into the equation, family medicine involvement in such courses replaced the presence of such courses as a statistically significant predictor of medical students selecting family practice as a career. CONCLUSIONS: Family physicians are involved to some extent in the great majority of RFGCE courses. Such involvement is associated with an increase in the number of medical students selecting a family practice career upon graduation from medical school.

Generalist courses in US medical schools and their relationship to career choice.

We conducted a survey of required first-year generalist courses offered by US medical schools during 1980, 1985, and 1990 to see if significant growth had occurred in this curricular area and to determine if the presence of these courses was associated with an increase in the percent of graduates selecting family practice as a career option. During the 1980s, only two types of generalist courses were offered by more than 50% of US medical schools, clinical experience and human behavior/psychiatry courses, with significant growth occurring in only two types of generalist courses, ethics and medical humanities courses. The presence of a required clinical experience course in 1985 was associated with a 2% increase in the number of graduates selecting family practice as a career option in 1988.

Medical foster family care: a cost-effective solution to a community problem.

In response to the special needs of a small number of abused and neglected children who were being cared for by unnecessary extended hospitalization, a medical foster family care program was established, at much lower cost, to provide the children with a home environment and assist their parents so that family reunification was possible.

Dental machines then and now.

The earliest dentists brought instruments and techniques from Europe as well as tools used by mechanics, watch makers, jewelers and artists. This historical journey through machinery history is a study in contrast to the machines of the present.

Algorithm for model validation: theory and applications.

Validation is often defined as the process of determining the degree to which a model is an accurate representation of the real world from the perspective of its intended uses. Validation is crucial as industries and governments depend increasingly on predictions by computer models to justify their decisions. We propose to formulate the validation of a given model as an iterative construction process that mimics the often implicit process occurring in the minds of scientists. We offer a formal representation of the progressive build-up of trust in the model. Thus, we replace static claims on the impossibility of validating a given model by a dynamic process of constructive approximation. This approach is better adapted to the fuzzy, coarse-grained nature of validation. Our procedure factors in the degree of redundancy versus novelty of the experiments used for validation as well as the degree to which the model predicts the observations. We illustrate the methodology first with the maturation of quantum mechanics as the arguably best established physics theory and then with several concrete examples drawn from some of our primary scientific interests: a cellular automaton model for earthquakes, a multifractal random walk model for financial time series, an anomalous diffusion model for solar radiation transport in the cloudy atmosphere, and a computational fluid dynamics code for the Richtmyer-Meshkov instability.

Laparoscopic hernia repair in the community hospital setting.

Eighty-three patients (108 repairs) with inguinal hernias underwent laparoscopic transabdominal preperitoneal repair in the community hospital setting. The patients included 82 men and one woman, ranging in age from 15 to 82 years. Concomitant procedures included umbilical hernia repairs, lysis of adhesions, and varicocoelectomy. Ninety-four percent of these patients were discharged the same day, with only one patient requiring more than an overnight stay. Postoperative complications included five cases of urinary retention requiring overnight catherization (4.6%) and one case each of labile hypertension (0.9%), vasovagal reaction (0.9%), dizziness (0.9%), and ileus (0.9%); there were 12 cases of groin swelling with ecchymosis (11%). With follow-up of almost 2 years, there has been one known recurrence (0.9%). This study demonstrates that laparoscopic hernia repair can be performed safely and successfully in the community hospital setting and can be a sound alternative to the standard open hernia repair.