Spectral properties of Titan's impact craters imply chemical weathering of its surface.

We examined the spectral properties of a selection of Titan's impact craters that represent a range of degradation states. The most degraded craters have rims and ejecta blankets with spectral characteristics that suggest that they are more enriched in water ice than the rims and ejecta blankets of the freshest craters on Titan. The progression is consistent with the chemical weathering of Titan's surface. We propose an evolutionary sequence such that Titan's craters expose an intimate mixture of water ice and organic materials, and chemical weathering by methane rainfall removes the soluble organic materials, leaving the insoluble organics and water ice behind. These observations support the idea that fluvial processes are active in Titan's equatorial regions.

Rate measurements of the hydrolysis of complex organic macromolecules in cold aqueous solutions: implications for prebiotic chemistry on the early Earth and Titan.

Organic macromolecules ("complex tholins") were synthesized from a 0.95 N(2)/0.05 CH(4) atmosphere in a high-voltage AC flow discharge reactor. When placed in liquid water, specific water soluble compounds in the macromolecules demonstrated Arrhenius type first order kinetics between 273 and 313 K and produced oxygenated organic species with activation energies in the range of approximately 60+/-10 kJ mol(-1). These reactions displayed half lives between 0.3 and 17 days at 273 K. Oxygen incorporation into such materials--a necessary step toward the formation of biological molecules--is therefore fast compared to processes that occur on geologic timescales, which include the freezing of impact melt pools and possible cryovolcanic sites on Saturn's organic-rich moon Titan.

AIDS risk among students attending Seventh-day Adventist school, in North America.

In 1995, a survey was conducted among students attending 69 Seventh-day Adventist (SDA) high schools within the United States and Canada. The survey assessed the extent that these students practiced sexual and drug-use behaviors which place them at risk for contracting or transmitting the human immunodeficiency virus (HIV). A total of 1,748 respondents enrolled in grades 9 through 12 completed questionnaires similar to the instrument used in the 1993 Youth Risk Behavior Survey (YRBS). Data were collected and compared to results from the 1993 YRBS. Students who attended SDA parochial schools reported lower rates of sexual intercourse compared to YRBS school counterparts (16.3% vs. 53.1%) and lower rates of all substances measured. Furthermore, respondents were more likely to engage in substance use and sexual intercourse if they had at least one parent who used tobacco, alcohol, or marijuana, as reported by the students.

Proliferation cell nuclear antigen and soluble interleukin 2 receptor levels in cutaneous T cell lymphoma: correlation with advanced clinical diseases.

Cutaneous T-cell lymphoma and leukemias (CTCL) are malignant clonal proliferation of T lymphocytes which have a predilection to home to and proliferate in skin. There are no clinical and laboratory parameters which consistently correlate with stage of disease, which varies from patch, plaque, tumor, or erythroderma. Soluble IL-2 receptor (sIL2-R) levels are elevated both in benign and malignant diseases involving immune activation. Proliferation cell nuclear antigen (PCNA) is a marker of the G1 and G/S phases of cell cycle and can be used to quantitate proliferation. We studied 43 skin biopsies of CTCL in various clinical stages for the presence of PCNA via immunoperoxidase techniques to establish a relationship between PCNA and the stage of disease. In addition, sIL2-R levels were determined in 14 patients. PCNA reactivity was detected in the nuclei of infiltrating cells in a total of 25 patients (58%). According to clinical stage there were 2/12 patch (12%), 9/17 plaque (53%), 4/4 tumor (100%) and 9/10 erythrodermic (90%) stage patients with PCNA positive cells. Thus PCNA positivity correlated with advanced clinical stage. sIL2-R levels were elevated in 14 of 14 patients and the degree of elevation correlated with advanced clinical stage of disease and with increased numbers of PCNA positive cells. Immunohistochemical studies for PCNA and serum sIL2-R levels can be used as laboratory parameters to correlate with clinical stage of disease and enhance prognostication in CTCL.

Elevated serum soluble interleukin-2 receptor levels in subacute cutaneous lupus erythematosus.

Subacute cutaneous lupus erythematosus (SCLE) is a subset of lupus erythematosus which is characterized by unique cutaneous manifestations and immunological abnormalities. Soluble IL-2 receptor (sIL-2 R) is the shed product of membrane Il-2 R, a product of T cell activation. It is measured by enzyme-linked immunosorbent assay (ELISA) and has been found to correlate well with disease activity in systemic lupus erythematosus (SLE) patients. The objective of the present work was to determine whether there is a correlation between sIL-2 R levels and disease activity in SCLE. Serum samples were obtained from 25 SCLE patients and then measured for sIL-2 R levels of ELISA. Fifteen of 25 SCLE patients tested had normal levels of sIL-2 R, while 10 of 25 SCLE patients had elevated sIL-2 R levels. The serum sIL-2 R level in SCLE patients correlated well with disease activity and the number of American College of Rheumatology criteria for SLE. These findings indicate that sIL-2 R levels can be used as a valuable laboratory parameter in managing SCLE patients.

Antenatal ultrasound for fetal anomalies: importance of perinatal autopsy.

Sixty-one instances of congenital anomalies identified prenatally by ultrasound were reviewed to determine whether autopsy provided important additional information. An important finding was defined as one which would affect: 1) genetic counseling; 2) diagnosis of a syndrome; 3) determination of etiology or pathogenetic mechanism of the anomaly; or 4) interpretation of severity of the anomalies. In 28 cases (46%), post-mortem examination provided such information. All of these infants had multiple anomalies; correlations with oligohydramnios and poor fetal outcome were noted. Autopsy provided no additional meaningful information in 30 cases (49%), the majority (77%) of whom had isolated anomalies. In 3 cases (5%), due to tissue autolysis, autopsy provided less information than the previous ultrasound. Although most fetal anomalies are readily diagnosed by ultrasound, we found that post-mortem examination is still necessary: 1) to confirm a prenatal diagnosis; 2) to delineate multiple anomalies; 3) when the ultrasound examination is limited by oligohydramnios; and 4) to obtain tissue for microscopic examination, cytogenetic and biochemical analysis, if these studies have not been performed prenatally.