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R Lopes

Publications and source records attributed to R Lopes.

13 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↗
PubMed2005

Survivin interacts with Smac/DIABLO in ovarian carcinoma cells but is redundant in Smac-mediated apoptosis.

Abnormalities in the control and execution of apoptosis are seen in many malignancies, including ovarian carcinoma. Many of these abnormalities involve the mitochondrial pathway of apoptosis, including overexpression of BIR-containing inhibitor of apoptosis protein (IAP) family proteins as well as dysregulated apoptosome function. We sought to stimulate the mitochondrial pathway of apoptosis by constructing a recombinant adenovirus encoding mature, processed Smac/DIABLO (Ad CMV tSmac), the second mitochondrial activator of caspases. Transfection of ovarian carcinoma cells with Ad CMV tSmac leads to increasing apoptosis in a dose-dependent manner. By contrast, transfection of IOSE397 immortalized normal ovarian surface epithelial cells does not cause apoptosis. We also show that the processed form of Smac is primarily expressed in the cytosol of ovarian carcinoma cells. Smac co-immunoprecipitates with both survivin and XIAP and stimulates survivin, but not XIAP, down-regulation. This down-regulation does not result from transcriptional changes, as determined by quantitative real-time PCR, but cycloheximide treatment indicates that survivin half-life is reduced from 6 to 2 h, which is secondary to ubiquitination and proteasomal degradation. RNA interference, however, suggests that survivin does not act to inhibit Smac-mediated apoptosis, which is confirmed by cotransfection with the phosphorylation mutant, survivin T34A. Finally, intraperitoneal delivery of Ad CMV tSmac increases median survival of mice bearing human ovarian carcinoma xenografts. We believe that expression of Smac/DIABLO can stimulate the intrinsic pathway of apoptosis in ovarian carcinoma without damaging normal ovarian tissue and therefore has therapeutic potential.

Apoptosis↗
PubMed2001

Carbohydrate metabolism in sickle cell patients using a subdermal implant containing nomegestrol acetate (Uniplant).

Uniplant, a second-generation contraceptive implant, has been demonstrated to promote a significant improvement in the overall well-being of women with sickle cell anemia. It has been suggested that the discrete increase in blood glucose levels observed in Uniplant users could be a contributory factor for clinical improvement. Ten healthy sickle cell patients were enrolled in the study. An oral glucose tolerance test was performed prior to implant insertion and at 1, 6, and 12 months of therapy. Blood glucose and insulin were measured before and at 30, 60, 120, and 180 min after a 75-g glucose load. The glucose and insulin areas under the curves were calculated. Fasting glycosylated hemoglobin was also measured. No significant changes were observed in glycosylated hemoglobin, glucose or insulin. We conclude that Uniplant is a safe contraceptive for sickle cell patients.

Adult↗
PubMed2000

Overexpression of the cat-86 gene is associated with thermosensitivity in Bacillus subtilis.

Bacillus subtilis harboring the cat-86 constitutive plasmid pPL708C2 with an ochre mutation at the 9th codon (terc 9) was sensitive to chloramphenicol (Cm(s)) and exhibited relative thermostability when heated at 47 degrees C. Reversion to chloramphenicol resistance (Cm(r)) occurred at a frequency of 5.4 x 10(-8). All of the plasmid Cm(r) revertants tested were thermosensitive. Similarly, wild-type pPL708C2 present in B. subtilis also rendered the bacterium thermosensitive. When a nonsense mutation is introduced at codon 141, however, this terc 141 variant of pPL708C2 failed to thermosensitize B. subtilis. Another variant of pPL708C2 that produces intact yet catalytically inactive CAT-86 has both His-16 and His-17 at the active site replaced by Pro. Nevertheless, cells of B. subtilis carrying this variant were thermosensitive. Plasmid-free and pPL708C2-bearing strains did not exhibit differences in major heat shock proteins. Electron micrographs revealed a threefold increase of inclusion bodies present in a strain harboring pPL708C2 when compared with those in an isogenic plasmid-free strain.

Bacillus subtilis↗
PubMed2000

Intestinal parasitic infections in an institution for the mentally retarded.

Of 550 mentally retarded patients in an Italian institution, 125 (23%) were found to be infected with intestinal parasites. The infections were most frequent in young men, those with severe mental retardation, the chronically institutionalized and those living in older wards. Ninety-four (75.2%) of the parasitised subjects were infected only with protozoa, 25 (20%) only with helminths, and six (4.8%) with protozoa and helminths. Entamoeba histolytica and E. dispar infections were detected, but at low prevalences; in-vitro culture in Robinson's medium and isoenzyme electrophoresis of the cloned amoebic isolates indicated one infection with E. histolytica (zymodeme XII) and two infections with E. dispar (zymodemes I and III). All three Entamoeba-positive subjects were asymptomatic cyst-passers. Antibodies to E. histolytica were detected in seven (1%) of the sera from the 550 patients examined; only one of these was a carrier of an E. dispar strain at the time of investigation. The low prevalences of all the parasitic infections and of the amoebic infections in particular (compared with those observed previously in institutions for the mentally retarded) reflect relatively good facilities and sanitary conditions, an adequate number of well trained staff and good control of the more susceptible subjects.

Adolescent↗
PubMedDate not supplied

Splenic abscess caused by Propionibacterium acnes.

A 59-year-old male diabetic was admitted with an acute myocardial infarction and had recurrent. Propionibacterium acnes bacteremia. Fifteen months after the initial admission a splenectomy was required for removal of a large splenic abscess caused by P. acnes. Although this organism represents part of the normal skin flora, its presence of blood cultures requires serious evaluation since it may signify clinical disease, not merely contamination of blood cultures by skin flora.

Abscess↗