PubMed Health⌕ Search

Biomedical subjects

S Shaffer

Publications and source records attributed to S Shaffer.

At least 19 recordsLinked to original sources
PubMed2007

The lakes of Titan.

The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70 degrees north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.

Journal Article↗
PubMed2006

Titan Radar Mapper observations from Cassini's T3 fly-by.

Cassini's Titan Radar Mapper imaged the surface of Saturn's moon Titan on its February 2005 fly-by (denoted T3), collecting high-resolution synthetic-aperture radar and larger-scale radiometry and scatterometry data. These data provide the first definitive identification of impact craters on the surface of Titan, networks of fluvial channels and surficial dark streaks that may be longitudinal dunes. Here we describe this great diversity of landforms. We conclude that much of the surface thus far imaged by radar of the haze-shrouded Titan is very young, with persistent geologic activity.

Journal Article↗
PubMed2006

The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Extraterrestrial Environment↗
PubMed2005

Cassini radar views the surface of Titan.

The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of approximately 0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons.

Atmosphere↗
PubMed1999

Test-retest reliability of the ulnar F-wave minimum latency in normal adults.

BACKGROUND AND PURPOSE: The purpose of this study was to measure the test-retest reliability of the ulnar F-wave minimum latency (Fmin) in normal adults. A reliable Fmin measure allows clinicians to ascribe changes in latency to true changes in a subject and not merely random daily variation. SUBJECTS AND METHODS: Fmin in the Abductor Digiti Minimi muscle was measured bilaterally in 49 healthy adults (n = 98) with a three day separation between tests. RESULTS: The Fmin reliability estimate as measured by intraclass correlation coefficient (3,1) was 0.59 with a standard error of measurement (SEM) of 1.3 msec. A paired t-test showed no significant difference (t = 1.7, df = 97, p > 0.05) between the mean scores from the two testing sessions. DISCUSSION AND CONCLUSIONS: We found moderate reliability and relatively low precision (high SEM) in Fmin scores taken from healthy individuals on two separate days. Strict adherence to our protocol and an acceptable overall precision of measurements (as measured by mean scores) suggest the contributions of rater and instrument error were low in our study. We conclude that 1) valid clinical interpretation of minimum F-wave latency findings is questionable because the Fmin measurement appears to have only moderate reliability, and 2) the lability of the phenomenon itself is the most likely contributor to variability in the Fmin latencies. Further research is warranted before electrophysiologists may be justified in attributing small changes in the Fmin to actual changes in the subject.

Action Potentials↗
PubMed1998

Changing patterns in regionalization of perinatal care and the impact on neonatal mortality.

OBJECTIVE: Our goal was to study changing patterns of low-birth-weight outcome over the past decade as deregionalized perinatal care has occurred. STUDY DESIGN: Live births and neonatal mortality for two 5-year periods (1982 to 1986 vs 1990 to 1994) were calculated by hospital of delivery in the state of Missouri. Self-designated level of perinatal care was contrasted with number of deliveries and nursery census to evaluate outcome. Regression models were constructed to compare outcome between levels of care. RESULTS: There has been a significant shift of deliveries into self-designated level II and III perinatal centers. However, this is largely a result of redesignation of care rather than an actual increase in acuity or census. The relative risk of neonatal mortality for very-low-birth-weight infants is 2.28 in level II centers compared with level III centers, and is unchanged (2.57) from 10 years earlier. Nearly 14% of very-low-birth-weight deliveries still occur at non-level III centers. CONCLUSION: Changing patterns of perinatal regionalization have not improved outcome for inborn infants < 1500 gm except in level III centers. Attempts should be made to deliver very-low-birth-weight infants in level III centers.

Birth Weight↗
PubMed1997

Effect of human hydrosalpinx fluid on murine embryo development and implantation.

OBJECTIVE: To determine the effect of hydrosalpinx fluid-containing medium on murine embryo development and implantation. DESIGN: The development of one-, two-, and four-cell mouse embryos in medium containing 5%, 10%, and 20% of human hydrosalpinx fluid was observed. Implantation rates of mouse embryos transferred into the uterine horn with hydrosalpinx fluid-containing media were determined. SETTING: Private hospital-based fertility center and IVF program. MAIN OUTCOME MEASURE(S): Percentage of embryos continuing cell division and implantation rates after ET. RESULT(S): Hydrosalpinx fluid in culture medium affected embryo development in a dose-dependent fashion. The injection of hydrosalpinx fluid-containing medium into the uterine horn did not affect embryo implantation. CONCLUSION(S): Hydrosalpinx fluid negatively affects murine embryo development, but its presence in the uterine horn at ET did not affect implantation.

Animals↗
PubMed1996

Benign lymphoproliferative disorders.

OBJECTIVE: To provide a review of three benign lymphoproliferative disorders commonly encountered in nursing practice: (1) infectious mononucleosis, (2) cat scratch disease, and (3) sarcoidosis. DATA SOURCES: Research studies, review articles, and book chapters pertaining to benign lymphoproliferative disorders. CONCLUSIONS: Benign lymphoproliferative disorders may be associated with infections, autoimmune disorders, hypersensitivity reactions, and unknown causes. Most of these disorders are self-limiting; however, some are associated with significant morbidity and mortality. IMPLICATIONS FOR NURSING PRACTICE: Benign as well as malignant lymphoproliferative disorders will be encountered with increasing frequency by nurses in ambulatory settings. Nurses need to have a basic knowledge of these disorders that present a diagnostic and management challenge.

Adult↗
PubMed1994

Different oligomeric forms of protein phosphatase 2A activate and inhibit simian virus 40 DNA replication.

The ability of simian virus 40 (SV40) large T antigen to catalyze the initiation of viral DNA replication is regulated by its phosphorylation state. Previous studies have identified the free catalytic subunit of protein phosphatase 2A (PP2Ac) as the cellular phosphatase which can remove inhibitory phosphoryl groups from serines 120 and 123. The catalytic C subunit exists in the cell complexed with a 65-kDa A subunit and one of several B subunits. To determine if any of the holoenzymes could activate T antigen, we tested the ability of the heterodimeric AC and two heterotrimeric ABC forms to stimulate T-antigen function in unwinding the origin of SV40 DNA replication. Only free catalytic subunit C and the heterotrimeric form with a 72-kDa B subunit (PP2A-T72) could stimulate T-antigen-dependent origin unwinding. Both the dimeric form (PP2A-D) and the heterotrimer with a 55-kDa B subunit (PP2A-T55) actively inhibited T-antigen function. We found that PP2A-T72 activated T antigen by dephosphorylating serines 120 and 123, while PP2A-D and PP2A-T55 inactivated T antigen by dephosphorylating the p34cdc2 target site, threonine 124. Thus, alterations in the subunit composition of PP2A holoenzymes have significant functional consequences for the initiation of in vitro SV40 DNA replication. The regulatory B subunits of PP2A may play a role in regulating SV40 DNA replication in infected cells as well.

Animals↗
PubMed1993

Bone marrow transplantation: critical care implications.

Bone marrow transplantation is an effective treatment for a growing list of disease processes both malignant and non-malignant. Complications associated with marrow transplantation may be related to ablative therapy, immunosuppression, graft-versus-host disease, and recurrence of the underlying disease. Survival depends upon prompt recognition of problems and timely institution of specific interventions, both medical and nursing. Nurses caring for bone marrow transplant recipients face a never-ending and ever-changing challenge to stay on top of the day-to-day problems and patient care crises that can occur.

Bone Marrow Transplantation↗
PubMed1991

Comparison of dual photon and dual energy X-ray bone densitometers in a clinic setting.

In clinical practice, decisions must be made about whether and how to convert to newer technologies. To address this issue, two separate studies were conducted. We evaluated the relationships between results of lumbar spine measurements using two dual photon absorptiometry (DPA1 and DPA2) instruments and one dual energy X-ray (DXA) instrument with the same subjects (49 volunteers), and also in 65 patients who were measured on the DPA1 and DXA machines. Second, we measured the lumbar spine and the proximal femur in three groups of 12 female volunteers three times on one instrument within 1 week. We purposely simulated a busy clinic setting with different technologists, older radioactive sources, and a heterogeneous patient group. The comparison study indicated a significant difference between the mean bone density values reported by the machines, but the results were highly correlated (R2 = 0.89-0.96). The short-term precision errors (coefficients of variation) differed among the instruments, ranging from 1.3% (DXA of the spine) to 5.1% (DPA1 of the spine), and in the femoral neck, 2.3% and 2.4% (DXA and DPA1, respectively) versus 3.5% by DPA2. This study emphasizes the differences between instruments, the potential for greater error in busy clinic environments, and the apparent superiority of dual energy X-ray absorptiometry under these less than ideal conditions.

Absorptiometry, Photon↗
PubMed1985

Beckwith-Wiedemann syndrome: prenatal ultrasound diagnosis using standard kidney to abdominal circumference ratio.

Enlarged fetal kidneys are characteristic of more than one possible diagnosis. Though infantile polycystic kidney disease is probably the most well known entity and is associated with oligohydramnios, Beckwith-Wiedemann syndrome should be considered in the differential diagnosis especially if a normal or increased amount of amniotic fluid is present. The presence of an omphalocele with a normal karyotype should also arouse suspicion. This constellation of findings carries potential morbidity including macrosomia, fetal hypoglycemia, mental retardation, microcephaly, increased risk of subsequent neoplasia, and even neonatal death. Beckwith-Wiedemann syndrome may not be obvious in the newborn period.

Beckwith-Wiedemann Syndrome↗
PubMed1984

Estimation of the slope of the acoustic attenuation coefficient.

In this paper, a theoretical framework is developed which removes the Gaussian assumption commonly used in ultrasonic attenuation estimation based on mean frequency shift. The theory is developed for general non-Gaussian spectra and for media whose attenuation coefficient is nonlinear with frequency. Then, a linear approximation in the estimation of the attenuation coefficient's slope is examined. It is shown that the error due to the linear approximation is negligibly small.

Computers↗