No oceans on Titan from the absence of a near-infrared specular reflection.

With its substantial atmosphere of nitrogen, hydrocarbons and nitriles, Saturn's moon Titan is a unique planetary satellite. Photochemical processing of the gaseous constituents produces an extended haze that obscures the surface. Soon after the Voyager fly-bys in 1980 and 1981 photochemical models led to the conclusion that there should be enough liquid methane/ethane/nitrogen to cover the surface to a depth of several hundred metres. Recent Earth-based radar echoes imply that surface liquid may be present at a significant fraction of the locations sampled. Here we present ground-based observations (at near-infrared wavelengths) and calculations showing that there is no evidence thus far for surface liquid. Combined with the specular signatures from radar observations, we infer mechanisms that produce very flat solid surfaces, involving a substance that was liquid in the past but is not in liquid form at the locations we studied.

Photometric observations of jupiter at 2400 angstroms.

The photopolarimeter instrument on Voyager 2 was used to obtain a map of Jupiter at an effective wavelength of 2400 angstroms. Analysis of a typical north-south swath used to make this map shows strong absorption at high latitudes by a molecular or particulate constituent in the Jovian atmosphere. At 65 degrees north latitude, the absorbing constituent extends to altitudes above the 50-millibar pressure level.

Impact debris particles in Jupiter's stratosphere.

The aftermath of the impacts of periodic comet Shoemaker-Levy 9 on Jupiter was studied with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The impact debris particles may owe their dark brown color to organic material rich in sulfur and nitrogen. The total volume of aerosol 1 day after the last impact is equal to the volume of a sphere of radius 0.5 kilometer. In the optically thick core regions, the particle mean radius is between 0.15 and 0.3 micrometer, and the aerosol is spread over many scale heights, from approximately 1 millibar to 200 millibars of pressure or more. Particle coagulation can account for the evolution of particle radius and total optical depth during the month following the impacts.

Photopolarimetry from voyager 2; preliminary results on saturn, titan, and the rings.

The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 degrees N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 degrees to 154 degrees ), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.

Photometry from voyager 2: initial results from the uranian atmosphere, satellites, and rings.

The Voyager 2 photopolarimeter successfully completed the Uranus encounter, acquiring new data on the planet's atmosphere, its principal satellites, and its ring system. Spatially resolved photometry of the atmosphere at 0.27 micrometer shows no enhancement in absorption toward the pole, unlike the case for Jupiter and Saturn. Stellar occultation measurements indicate the temperature at the 1-millibar level over the north pole is near 90 kelvins. The geometric albedos of the five large satellites of Uranus were measured at 0.27 and 0.75 micrometer and indicate the presence of low albedo, spetrally flat absorbing material. Titania seems to have a fluffy surface, as indicated by its phase curve. The nine ground-based rings were detected, and their internal structure, optical depths, and positions were determined. The sharp edges of the in ring made it possible to measure its edge thickness (less than 150 meters) and particle sizes (less than 30 meters); little or no dust was detcted. New narrow rings and partial rings (arcs) were measured, and the narrow component of the eta ring was found to be discontinuous.

Photometry from voyager 2: initial results from the neptunian atmosphere, satellites, and rings.

The Voyager photopolarimeter successfully accomplished its objectives for the Neptune encounter, performing measurements on the planet, several of its satellites, and its ring system. A photometric map of Neptune at 0.26 micrometer (microm) shows the planet to be bland, with no obvious contrast features. No polar haze was observed. At 0.75 microm, contrast features are observed, with the Great Dark Spot appearing as a low-albedo region and the bright companion as being substantially brighter than its surroundings, implying it to be at a higher altitude than the Great Dark Spot. Triton's linear phase coefficients of 0.011 magnitudes per degree at 0.26 microm and 0.013 magnitudes per degree at 0.75 microm are consistent with a solid-surface object possessing high reflectivity. Preliminary geometric albedos for Triton, Nereid, and 1989N2 were obtained at 0.26 and 0.75 microm. Triton's rotational phase curve shows evidence of two major compositional units on its surface. A single stellar occultation of the Neptune ring system elucidated an internal structure in 1989N1R, in the approximately 50-kilometer region of modest optical depth. 1989N2R may have been detected. The deficiency of material in the Neptune ring system, when compared to Uranus', may imply the lack of a "recent" moon-shattering event.

Thermal maps of jupiter: spatial organization and time dependence of stratospheric temperatures, 1980 to 1990.

The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH(4) band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and mid-latitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm mid-latitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than approximately 30,000 kilometers. The amplitudes of the waves vary on a time scale of approximately 1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than +/-30 meters per second.

Spatial Organization and Time Dependence of Jupiter's Tropospheric Temperatures, 1980-1993.

The spatial organization and time dependence of Jupiter's temperatures near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

Galileo's First Images of Jupiter and the Galilean Satellites

The first images of Jupiter, Io, Europa, and Ganymede from the Galileo spacecraft reveal new information about Jupiter's Great Red Spot (GRS) and the surfaces of the Galilean satellites. Features similar to clusters of thunderstorms were found in the GRS. Nearby wave structures suggest that the GRS may be a shallow atmospheric feature. Changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on Io. Patchy emissions were seen while Io was in eclipse by Jupiter. The outer margins of prominent linear markings (triple bands) on Europa are diffuse, suggesting that material has been vented from fractures. Numerous small circular craters indicate localized areas of relatively old surface. Pervasive brittle deformation of an ice layer appears to have formed grooves on Ganymede. Dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution.

Less absorbed solar energy and more internal heat for Jupiter.

The radiant energy budget and internal heat are fundamental properties of giant planets, but precise determination of these properties remains a challenge. Here, we report measurements of Jupiter's radiant energy budget and internal heat based on Cassini multi-instrument observations. Our findings reveal that Jupiter's Bond albedo and internal heat, 0.503 ± 0.012 and 7.485 ± 0.160 W m-2 respectively, are significantly larger than 0.343 ± 0.032 and 5.444 ± 0.425 Wm-2, the previous best estimates. The new results help constrain and improve the current evolutionary theories and models for Jupiter. Furthermore, the significant wavelength dependency of Jupiter's albedo implies that the radiant energy budgets and internal heat of the other giant planets in our solar system should be re-examined. Finally, the data sets of Jupiter's characteristics of reflective solar spectral irradiance provide an observational basis for the models of giant exoplanets.

The inferior parietal lobule is the target of output from the superior colliculus, hippocampus, and cerebellum.

The inferior parietal lobule (IPL) is a functionally and anatomically heterogeneous region that is concerned with multiple aspects of sensory processing and sensorimotor integration. Although considerable information is available about the corticocortical connections to the IPL, much less is known about the origin and importance of subcortical inputs to this cortical region. To examine this issue, we used retrograde transneuronal transport of the McIntyre-B strain of herpes simplex virus type 1 (HSV1) to identify the second-order neurons in subcortical nuclei that project to the IPL. Four monkeys (Cebus apella) received injections of HSV1 into three different subregions of the IPL. Injections into a portion of the lateral intraparietal area labeled second-order neurons primarily in the superficial (visual) layers of the superior colliculus. Injections of HSV1 into a portion of area 7a labeled many second-order neurons in the CA1 region of the hippocampus. In contrast, virus injections within a portion of area 7b labeled second-order neurons in posterior regions of the dentate nucleus of the cerebellum. These observations have some important functional implications. The IPL is known to be involved in oculomotor and attentional mechanisms, the establishment of maps of extrapersonal space, and the adaptive recalibration of eye-hand coordination. Our findings suggest that these functions are subserved by distinct subcortical systems from the superior colliculus, hippocampus, and cerebellum. Furthermore, the finding that each system appears to target a separate subregion of the IPL provides an anatomical substrate for understanding the functional heterogeneity of the IPL.

Orthodontics and orthognathic surgery: adjuncts to restorative and periodontal therapy.

Orthodontic and orthognathic surgical procedures are important adjuncts to the provision of optimum restorative and periodontal care. Dentoalveolar and skeletal abnormalities of either developmental or acquired origin can be corrected primarily, thus eliminating the necessity for compromise in prosthetic design. Dental relationships that are contributory to irreversible periodontal deterioration can be normalized to facilitate stabilization of the periodontal condition and to increase the longevity of the natural dentition. Maxillofacial surgical treatment is technically complex but is more conservative than many traditionally accepted treatment procedures. It is based on the rationale of conservation of natural structures rather than their radical ablation or their sacrifice to uncontrollable progressive disease processes. Patient participation to establishment of treatment objectives and extensive patient education are essential ingredients in such treatment. Interdisciplinary communication and coordination contribute to a mutual appreciation of treatment possibilities and limitations. Thus, orthodontic and orthognathic surgical options should be considered in planning the solution to a wide variety of periodontal and restorative treatment problems.

Rapid and extensive surface changes near Titan's equator: evidence of April showers.

Although there is evidence that liquids have flowed on the surface at Titan's equator in the past, to date, liquids have only been confirmed on the surface at polar latitudes, and the vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate. We report the detection by Cassini's Imaging Science Subsystem of a large low-latitude cloud system early in Titan's northern spring and extensive surface changes (spanning more than 500,000 square kilometers) in the wake of this storm. The changes are most consistent with widespread methane rainfall reaching the surface, which suggests that the dry channels observed at Titan's low latitudes are carved by seasonal precipitation.

5q- myelodysplastic syndromes: chromosome 5q genes direct a tumor-suppression network sensing actin dynamics.

Complete loss or interstitial deletions of chromosome 5 are the most common karyotypic abnormality in myelodysplastic syndromes (MDSs). Isolated del(5q)/5q- MDS patients have a more favorable prognosis than those with additional karyotypic defects, who tend to develop myeloproliferative neoplasms (MPNs) and acute myeloid leukemia. The frequency of unbalanced chromosome 5 deletions has led to the idea that 5q harbors one or more tumor-suppressor genes that have fundamental roles in the growth control of hematopoietic stem/progenitor cells (HSCs/HPCs). Cytogenetic mapping of commonly deleted regions (CDRs) centered on 5q31 and 5q32 identified candidate tumor-suppressor genes, including the ribosomal subunit RPS14, the transcription factor Egr1/Krox20 and the cytoskeletal remodeling protein, alpha-catenin. Although each acts as a tumor suppressor, alone or in combination, no molecular mechanism accounts for how defects in individual 5q candidates may act as a lesion driving MDS or contributing to malignant progression in MPN. One candidate gene that resides between the conventional del(5q)/5q- MDS-associated CDRs is DIAPH1 (5q31.3). DIAPH1 encodes the mammalian Diaphanous-related formin, mDia1. mDia1 has critical roles in actin remodeling in cell division and in response to adhesive and migratory stimuli. This review examines evidence, with a focus on mouse gene-targeting experiments, that mDia1 acts as a node in a tumor-suppressor network that involves multiple 5q gene products. The network has the potential to sense dynamic changes in actin assembly. At the root of the network is a transcriptional response mechanism mediated by the MADS-box transcription factor, serum response factor (SRF), its actin-binding myocardin family coactivator, MAL, and the SRF-target 5q gene, EGR1, which regulate the expression of PTEN and p53-family tumor-suppressor proteins. We hypothesize that the network provides a homeostatic mechanism balancing HPC/HSC growth control and differentiation decisions in response to microenvironment and other external stimuli.

Optical properties of aggregate particles whose outer diameter is comparable to the wavelength.

I describe results of numerical calculations of the optical properties (extinction efficiency, single-scattering albedo, phase function, and linear polarization) of aggregate particles whose outer diameter is comparable with the wavelength. Results are presented for two types of particle, one composed of monomers whose radius is small compared with the wavelength and a second containing monomers with larger radii. The shape of the forward-scattered lobe of the phase function is diagnostic of the mean projected area (but differs from that for an equal-area sphere), while the linear polarization, phase function at large scattering angles, and single-scattering albedo depend on the monomer diameter. The wavelength dependence of the extinction efficiency differs markedly from that for equal-area spheres. These results can be used to infer particle properties from remotely sensed data.

Management of postoperative hemorrhage following the Le Fort I maxillary osteotomy.

The assessment and management of patients with postoperative hemorrhage following Le Fort I osteotomies is discussed. The results of a questionnaire to investigate this complication, as well as the authors' protocol for dealing with this problem, are presented. Three illustrative case histories are also presented.

Factors influencing the stability of the sagittal split osteotomy for mandibular advancement.

Relapse continues to be a potential problem with use of the sagittal split osteotomy to advance the mandible. In an effort to isolate predictive factors, the records of 235 patients were analyzed to determine the pretreatment facial morphology, the amount of advancement, the amount of relapse, and the duration of relapse. No relationship was found between any of the measures of facial morphology and relapse. However, the amount of advancement, the amount of relapse, and the duration of relapse all were found to be strongly related. It was found that all patients shared a similar facial morphology, and thus no influence of facial form on relapse would be expected from this group. The relationships between advancement and relapse could be attributed to neuromuscular adaptation, which would be more prolonged and more extensive in instances of greater advancement, and thus give rise to relapse of greater extent and duration. It is therefore suggested that mandibular advancements of greater than 10 mm be fixed more rigidly and for a greater length of time than those of lesser magnitude.

Ptosis of the chin and lip incompetence: consequences of lost mentalis muscle support.

Ptosis of the chin and lip incompetence are worrisome complications of surgery in the mandibular symphyseal region. This article relates the normal anatomy and physiology of the muscles in this region to these complications. It suggests a sequence of surgical planning that can prevent them and also offers ways of dealing with the problems should they occur.