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.

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.

Absence of parasympathetic control of heart rate after human orthotopic cardiac transplantation.

BACKGROUND: Partial reinnervation of cardiac sympathetic nerves has been observed after heart transplantation; we hypothesized that parasympathetic control to the heart after transplantation may return as well. To test this hypothesis, we examined heart rate responses produced by two cardiovascular reflexes whose efferent limbs are subserved by vagal fibers to the heart: (1) trigeminal reflex (simulated diving reflex) and (2) arterial baroreflex with phenylephrine injection. METHODS AND RESULTS: An "early" group (n=31, <24 months after transplantation) and a "late group" (n=27, >45 months after transplantation) were studied and compared with a control group with intact cardiac innervation (n=32) and a renal transplant group with similar transplant immunosuppressive regimen (n=11). For trigeminal reflex testing, responses of the donor sinus node (DSN) (sinus node controlling heart rate) and recipient sinus node (RSN) in the innervated remnant right atrium in cardiac transplant patients were compared with heart rate responses in the control groups. For arterial baroreflex testing, baroreflex gains for the DSN and RSN in the cardiac transplant groups were compared with those of the control group. With engagement of the trigeminal reflex, the DSN rate of both transplant groups changed minimally (early, 1.2+/-1.2 bpm; late, 1.8+/-2.5 bpm) compared with the expected decrease in control subjects (-19.8+/-3.0 bpm) and renal transplant patients (-23.9+/-4.9 bpm) (P<.001 versus cardiac transplants). Changes in the RSN rate of both cardiac transplant groups (early, -13.0+/-4.0 bpm; late, -10.0+/-3.7 bpm) were similar to the control groups. Arterial baroreflex gains for the DSN were also depressed (early, 0.1+/-0.2 ms/mm Hg; late, 0.2+/-0.2 ms/mm Hg) compared with control (14.9+/-1.8 ms/mm Hg) and RSN (early, 9.9+/-1.3 ms/mm Hg; late, 10.9+/-1.3 ms/mm Hg; P<.001 versus DSN transplant). CONCLUSIONS: These data suggest that parasympathetic influences on donor heart rate are absent in the majority of patients up to 96 months after cardiac transplantation.

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.

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.

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.

Evidence against reinnervation of cardiac vagal afferents after human orthotopic cardiac transplantation.

BACKGROUND: Orthotopic cardiac transplantation results in total cardiac denervation. Recent studies in humans suggest that reinnervation of cardiac sympathetic nerves (cardiac efferents) may occur after cardiac transplantation. We hypothesized that reinnervation of cardiac afferents may occur as well. To test this hypothesis, we investigated reflex responses produced by stimulation of ventricular chemosensory endings subserved by vagal afferents (cardiac depressor reflex). METHODS AND RESULTS: Two cardiac transplant groups were studied: an "early" group (n = 18, < 24 months after transplant) and a "late" group (n = 18, > 43 months after transplant); these groups were compared with a control group with intact innervation (n = 18). The reflex response of the recipient sinus node (RSN) in the remnant right atrium, which remains innervated after transplantation, was observed during selective right coronary artery (RCA) and left coronary artery (LCA) injection of the radiographic contrast agent meglumine diatrizoate, which is known to stimulate ventricular chemosensory endings. A decrease in the rate of the RSN was expected if reinnervation of chemosensory endings had occurred and the afferent limb of the cardiac depressor reflex was intact. With injection, the RSN rate of both transplant groups did not decrease but increased (early: LCA, 7.2 +/- 1.4 beats per minute; RCA, 6.3 +/- 1.3 beats per minute; late: LCA, 5.9 +/- 1.0 beats per minute; RCA, 6.0 +/- 0.9 beats per minute) compared with the expected decrease in control patients (LCA, -20.8 +/- 2.5 beats per minute; RCA, -18.0 +/- 4.0 beats per minute; P < .001 versus transplants). Decreases in mean arterial pressure in the transplant groups (early: LCA, -11.3 +/- 1.4 mm Hg; RCA, -10.0 +/- 1.6 mm Hg; late: LCA, -13.0 +/- 1.6 mm Hg; RCA, -9.1 +/- 1.5 mm Hg) were less than those observed in the control group (LCA, -19.8 +/- 2.2 mm Hg; RCA, -18.7 +/- 4.0 mm Hg; P < .05 versus transplants). CONCLUSIONS: The results suggest that reinnervation of ventricular chemosensory endings subserved by vagal afferents in cardiac transplant patients does not occur up to 74 months after transplantation.

[Not Available]. / Cibo, lavoro e imperativi alimentari.

Although deriving new insights from knowledge of the scientific aspects of nutrition, a key component of health and the ability to resist disease, the cultural, social and economic factors are equally significant, but were emphasized by the mechanistic-scientific physician. Practical advice, such as counseling patients about the effect of specific foods on their health, was transferred by the mechanistic physicians to nutrition specialists or public health authorities. A variety of intrinsic and extrinsic factors contributed to the development of "high tech" medicine that minimizes or ignores the multi-dimensional dietary component of health and disease, some of which are explored here. The physician will discover that interventions made before disease strikes, especially at an age when health care costs are rising beyond society's ability to pay for them, are as important before than after the body is challenged by illness, particularly in the development of chronic diseases.

The statistical power of family practice research.

To determine the statistical power of family practice research, we conducted a survey of all family practice studies published in 3 major family practice journals in 1988. Only 5 of 86 studies calculated statistical power, although 67 (78%) reported statistically nonsignificant results. Calculations of statistical power revealed that more than 80% of family practice studies had sufficient statistical power to detect medium to large effect sizes, but not small effect sizes, which some readers might deem clinically important. We conclude that the authors of family practice research studies do not pay enough attention to the issue of statistical power when reporting statistically nonsignificant results, leaving their readers in doubt as to whether a clinically significant effect could have been detected.

Power of testing proportions in small two-sample studies when sample sizes are equal.

In planning experiments having two groups of equal but small size, investigators face the uncertainty of power calculations that rely on asymptotic methods. This paper presents a method for determining power for two-sided tests. I compare two randomization tests, Fisher's exact test (FET), and the mid-P (MID), with the uncorrected chi-square test (CHI). Results show power as a function of relative risk for these methods, and assesses their relative power and type I error rates. MID is shown to have intermediate power between CHI, which is the most powerful, and FET, the least powerful. Situations are shown in which CHI and MID occasionally exceed the nominal level of alpha.

Recurrent bacterial vaginosis: association with vaginal sponge use.

A hypothesis-generation study was conducted to examine risk factors for bacterial vaginosis recurrences among women participating in a randomized controlled trial of male sexual partner treatment. Of the 140 women enrolled in the trial, 72 had a normal vaginal gram-stained slide at the first follow-up visit and were included in this analysis. Nineteen of the 72 (26.2%) women developed a bacterial vaginosis recurrence documented by a vaginal gram-stained slide during the 6-week follow-up period. Of the 19 women, 4 of 6 sponge users (66%) developed a bacterial vaginosis recurrence (RR 2.93, 95% CI: 1.43-6.02). Logistic regression analysis supported the association between sponge use and bacterial vaginosis recurrences (adjusted RR 2.71, 95% CI: 1.06-6.99) but revealed that an apparent protective effect of diaphragm use was due to the confounding effect of sexual partner treatment. Our hypothesis is that bacterial vaginosis recurrences may be due to factors other than sexual transmission, such as sponge use. Further studies are needed to examine risk factors for bacterial vaginosis recurrences. In the interim, physicians might suggest another form of contraception to their sponge-using patient with frequent bacterial vaginosis infections.

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.

Prevalence of gastroesophageal reflux in elderly patients in a primary care setting.

Despite the aging of our population, there remains a paucity of information about gastroesophageal reflux (GER) in the elderly. To assess the prevalence and characteristics of GER within this patient population, questionnaires evaluating symptoms associated with GER were administered to 313 consecutive patients 62 yr old or older from a primary care setting. Fourteen percent of these patients reported having at least weekly heartburn. Ambulatory 24-h esophageal pH monitoring was accomplished in 54 of the 313 patients surveyed. Twenty percent (11/54) of this subgroup exhibited increased acid contact time (pH less than 4 for more than 6% of the monitoring period). Twenty-two percent (12/54) complained of heartburn, yet only six individuals (11%) exhibited both symptomatic and objective indications of acid reflux. Surprisingly, 31% (17/54) of the patients studied exhibited significant alkalinity within the distal esophagus (pH greater than 8 for greater than 1.5% of the monitoring period). Whereas 29% of these patients (5/17) reported heartburn, 40% of those reporting heartburn (2/5) had acid GER as well as excessive alkalinity. In contrast to patients with acid GER--none of whom reported pulmonary symptoms--24% (4/17) of these patients with esophageal alkalinity reported wheezing, nocturnal cough, or paroxysmal nocturnal dyspnea. Of the four patients with significant distal esophageal exposure to both acid and alkali, two reported heartburn and a third reported dysphagia. In addition to the somewhat higher prevalence of acid reflux than anticipated, a surprisingly high prevalence of esophageal alkalinity was observed.