Concurrent use of two dual-combination drenches containing monepantel/abamectin and oxfendazole/levamisole in sheep: effect on marker residues 21 and 28 days after administration.

AIMS: To determine the concentration, in comparison with the maximum residue limit (MRL), of anthelmintic marker residues in the target tissues (liver and fat) of sheep treated concurrently with two oral drenches, one containing monepantel and abamectin and the other oxfendazole and levamisole. METHODS: On day 0 of the study, 12 sheep (six male and six female; 8-9-months old) were dosed according to individual body weight determined the day prior. Zolvix Plus (dual-active oral drench containing 25 g/L monepantel and 2 g/L abamectin) was administered to all animals prior to administration of Scanda (dual-active oral drench containing 80 g/L levamisole hydrochloride and 45.3 g/L oxfendazole). Six sheep (three male and three female) were slaughtered 21 and 28 days after treatment and renal fat and liver samples were collected.Using validated methods, analyses for monepantel sulfone, abamectin, levamisole and oxfendazole (expressed as total fenbendazole sulfone following conversion of the combined concentrations of oxfendazole, fenbendazole and fenbendazole sulfone) were performed on liver samples while renal fat specimens were analysed for monepantel sulfone and abamectin residues only. Detected concentrations were compared to the established MRL in sheep for each analyte determined by the Ministry for Primary Industries. RESULTS: All residues detected in samples of liver and fat collected 21 and 28 days after treatment were below the MRL for each analyte. All liver samples collected on day 21 had detectable monepantel sulfone (mean 232 (min 110, max 388) µg/kg) and oxfendazole (mean 98.7 (min 51.3, max 165) µg/kg) residues below the MRL (5,000 and 500 µg/kg, respectively). Monepantel sulfone (mean 644 (min 242, max 1,119) µg/kg; MRL 7,000 µg/kg) residues were detected in 6/6 renal fat samples. Levamisole residues were detected in 3/6 livers (mean 40.0 (min 14.3, max 78.3) µg/kg; MRL 100 µg/kg), and abamectin residues in 1/6 livers (0.795 µg/kg; MRL 25 µg/kg) and 2/6 fat samples, (mean 0.987 (min 0.514, max 1.46) µg/kg; MRL 50 µg/kg) 21 days after treatment. CONCLUSION AND CLINICAL RELEVANCE: These results suggest that concurrent administration of Zolvix Plus and Scanda to sheep is unlikely to result in an extended residue profile for any of the active ingredients, with all analytes measured being under the approved New Zealand MRL 21 days after treatment. This work was not completed in line with guidance for establishing official residue profiles, nor is it sufficient to propose a new withholding period.

Identification of Cystic Lesions by Secondary Screening of Familial Pancreatic Cancer (FPC) Kindreds Is Not Associated with the Stratified Risk of Cancer.

OBJECTIVES: Intraductal papillary mucinous neoplasms (IPMNs) are associated with risk of pancreatic ductal adenocarcinoma (PDAC). It is unclear if an IPMN in individuals at high risk of PDAC should be considered as a positive screening result or as an incidental finding. Stratified familial pancreatic cancer (FPC) populations were used to determine if IPMN risk is linked to familial risk of PDAC. METHODS: This is a cohort study of 321 individuals from 258 kindreds suspected of being FPC and undergoing secondary screening for PDAC through the European Registry of Hereditary Pancreatitis and Familial Pancreatic Cancer (EUROPAC). Computerised tomography, endoscopic ultrasound of the pancreas and magnetic resonance imaging were used. The risk of being a carrier of a dominant mutation predisposing to pancreatic cancer was stratified into three even categories (low, medium and high) based on: Mendelian probability, the number of PDAC cases and the number of people at risk in a kindred. RESULTS: There was a median (interquartile range (IQR)) follow-up of 2 (0-5) years and a median (IQR) number of investigations per participant of 4 (2-6). One PDAC, two low-grade neuroendocrine tumours and 41 cystic lesions were identified, including 23 IPMN (22 branch-duct (BD)). The PDAC case occurred in the top 10% of risk, and the BD-IPMN cases were evenly distributed amongst risk categories: low (6/107), medium (10/107) and high (6/107) (P = 0.63). CONCLUSIONS: The risk of finding BD-IPMN was independent of genetic predisposition and so they should be managed according to guidelines for incidental finding of IPMN.

Defining the molecular pathology of pancreatic body and tail adenocarcinoma.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) remains a dismal disease, with very little improvement in survival over the past 50 years. Recent large-scale genomic studies have improved understanding of the genomic and transcriptomic landscape of the disease, yet very little is known about molecular heterogeneity according to tumour location in the pancreas; body and tail PDACs especially tend to have a significantly worse prognosis. The aim was to investigate the molecular differences between PDAC of the head and those of the body and tail of the pancreas. METHODS: Detailed correlative analysis of clinicopathological variables, including tumour location, genomic and transcriptomic data, was performed using the Australian Pancreatic Cancer Genome Initiative (APGI) cohort, part of the International Cancer Genome Consortium study. RESULTS: Clinicopathological data were available for 518 patients recruited to the APGI, of whom 421 underwent genomic analyses; 179 of these patients underwent whole-genome and 96 RNA sequencing. Patients with tumours of the body and tail had significantly worse survival than those with pancreatic head tumours (12·1 versus 22·0 months; P = 0·001). Location in the body and tail was associated with the squamous subtype of PDAC. Body and tail PDACs enriched for gene programmes involved in tumour invasion and epithelial-to-mesenchymal transition, as well as features of poor antitumour immune response. Whether this is due to a molecular predisposition from the outset, or reflects a later time point on the tumour molecular clock, requires further investigation using well designed prospective studies in pancreatic cancer. CONCLUSION: PDACs of the body and tail demonstrate aggressive tumour biology that may explain worse clinical outcomes.

Serum amylase and C-reactive protein in risk stratification of pancreas-specific complications after pancreaticoduodenectomy.

BACKGROUND: Pancreas-specific complications (PSCs), comprising postoperative pancreatic fistula, haemorrhage and intra-abdominal collections, are drivers of morbidity and mortality after pancreaticoduodenectomy (PD). A serum amylase concentration of 130 units/l or more on postoperative day (POD) 0 has been shown to be an objective surrogate of pancreatic texture, a determinant of PSCs. This study evaluated serial measurements of C-reactive protein (CRP) to refine PSC risk stratification. METHODS: Consecutive patients undergoing PD between 2008 and 2014, with vascular resection if required and without preoperative chemoradiotherapy, had serum investigations from the day before operation until discharge. Receiver operating characteristic (ROC) curve analysis was used to identify a threshold value of serum CRP with clinically relevant PSCs for up to 30 days after discharge as outcome measure. RESULTS: Of 230 patients, 95 (41·3 per cent) experienced a clinically relevant PSC. A serum CRP level of 180 mg/l or higher on POD 2 was associated with PSCs, prolonged critical care stay and relaparotomy (all P < 0·050). Patients with a serum amylase concentration of 130 units/l or more on POD 0 who developed a serum CRP level of at least 180 mg/l on POD 2 had a higher incidence of morbidity. Patients were stratified into high-, intermediate- and low-risk groups using these markers. The low-risk category was associated with a negative predictive value of 86·5 per cent for development of clinically relevant PSCs. There were no deaths among 52 patients in the low-risk group, but seven deaths among 79 (9 per cent) in the high-risk group. CONCLUSION: A serum amylase level below 130 units/l on POD 0 combined with a serum CRP level under 180 mg/l on POD 2 constitutes a low-risk profile following PD, and may help identify patients suitable for early discharge.

Prospective cohort study comparing transient EUS guided elastography to EUS-FNA for the diagnosis of solid pancreatic mass lesions.

BACKGROUND: Semiquantitative EUS-elastography has been introduced to distinguish between malignant and benign pancreatic lesions. This study investigated whether semiquantitative EUS-guided transient real time elastography increases the diagnostic accuracy for solid pancreatic lesions compared to EUS-FNA. PATIENTS AND METHODS: This single centre prospective cohort study included all patients with solitary pancreatic lesions on EUS during one year. Patients underwent EUS-FNA and semiquantitative EUS-elastography during the same session. EUS and elastography results were compared with final diagnosis which was made on the basis of tissue samples and long-term outcome. RESULTS: 91 patients were recruited of which 68 had pancreatic malignancy, 17 showed benign disease and 6 had cystic lesions and were excluded from further analysis. Strain ratios from malignant lesions were significantly higher (24.00; 8.01-43.94 95% CI vs 44.00; 32.42-55.00 95% CI) and ROC analysis indicated optimal cut-off of 24.82 with resulting sensitivity, specificity and accuracy of 77%, 65% and 73% respectively. B-mode EUS and EUS-FNA had an accuracy for the correct diagnosis of malignant lesions of 87% and 85%. When lowering the cut-off strain ratio for elastography to 10 the sensitivity rose to 96% with specificity of 43% and accuracy of 84%, resulting in the least accurate EUS-based method. This was confirmed by pairwise comparison. CONCLUSION: Semiquantitative EUS-elastography does not add substantial value to the EUS-based assessment of solid pancreatic lesions when compared to B-mode imaging.

Outcome after surgical resection for duodenal adenocarcinoma in the UK.

BACKGROUND: Factors influencing long-term outcome after surgical resection for duodenal adenocarcinoma are unclear. METHODS: A prospectively created database was reviewed for patients undergoing surgery for duodenal adenocarcinoma in six UK hepatopancreaticobiliary centres from 2000 to 2013. Factors influencing overall survival and disease-free survival (DFS) were identified by regression analysis. RESULTS: Resection with curative intent was performed in 150 (84·3 per cent) of 178 patients. The postoperative morbidity rate for these patients was 40·0 per cent and the in-hospital mortality rate was 3·3 per cent. Patients who underwent resection had a better median survival than those who had a palliative surgical procedure (84 versus 8 months; P < 0·001). The 1-, 3- and 5-year overall survival rates for patients who underwent resection were 83·9, 66·7 and 51·2 per cent respectively. Median DFS was 53 months, and 1- and 3-year DFS rates were 80·8 and 56·5 per cent respectively. Multivariable analysis revealed that node status (hazard ratio 1·73, 95 per cent c.i. 1·07 to 2·79; P = 0·006) and lymphovascular invasion (hazard ratio 3·49, 1·83 to 6·64; P = 0·003) were associated with overall survival. CONCLUSION: Resection of duodenal adenocarcinoma in specialist centres is associated with good long-term survival. Lymphovascular invasion and nodal metastases are independent prognostic indicators.

Exploiting inflammation for therapeutic gain in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy associated with <5% 5-year survival, in which standard chemotherapeutics have limited benefit. The disease is associated with significant intra- and peritumoral inflammation and failure of protective immunosurveillance. Indeed, inflammatory signals are implicated in both tumour initiation and tumour progression. The major pathways regulating PDAC-associated inflammation are now being explored. Activation of leukocytes, and upregulation of cytokine and chemokine signalling pathways, both have been shown to modulate PDAC progression. Therefore, targeting inflammatory pathways may be of benefit as part of a multi-target approach to PDAC therapy. This review explores the pathways known to modulate inflammation at different stages of tumour development, drawing conclusions on their potential as therapeutic targets in PDAC.

'Do we know if we need to reduce head impact exposure?': A mixed-methods study highlighting the varied understanding of the long-term risk and consequence of head impact exposure across all stakeholders at the highest level of rugby union.

Background: One strategy to prevent and manage concussion is to reduce head impacts, both those resulting in concussion and those that do not. Because objective data on the frequency and intensity of head impacts in rugby union (rugby) are sparse, stakeholders resort to individual perceptions to guide contact training. It is unknown whether there is a level of contact training that is protective in preparing elite players for contact during matches. Objectives: This study aimed to describe how contact training is managed in elite male rugby, and how staff and players perceive contact training load and head impact load. Methods: This was a sequential explanatory mixed-methods study. Forty-four directors of rugby, defence coaches, medical and strength/conditioning staff and 23 players across all 13 English Premiership Rugby Union clubs and the National senior team participated in semi-structured focus groups and completed two bespoke questionnaires. Results: The study identified the varied understanding of what constitutes head impact exposure across all stakeholder groups, resulting in different interpretations and a range of management strategies. The findings suggest that elite clubs conduct low levels of contact training; however, participants believe that some exposure is required to prepare players and that efforts to reduce head impact exposure must allow for individualised contact training prescription. Conclusion: There is a need for objective data, possibly from instrumented mouthguards to identify activities with a high risk for head impact and possible unintended consequences of reduced exposure to these activities. As data on head impact exposure develop, this must be accompanied with knowledge exchange within the rugby community.

Novel Antarctic yeast adapts to cold by switching energy metabolism and increasing small RNA synthesis.

The novel extremophilic yeast Rhodotorula frigidialcoholis, formerly R. JG1b, was isolated from ice-cemented permafrost in University Valley (Antarctic), one of coldest and driest environments on Earth. Phenotypic and phylogenetic analyses classified R. frigidialcoholis as a novel species. To characterize its cold-adaptive strategies, we performed mRNA and sRNA transcriptomic analyses, phenotypic profiling, and assessed ethanol production at 0 and 23 °C. Downregulation of the ETC and citrate cycle genes, overexpression of fermentation and pentose phosphate pathways genes, growth without reduction of tetrazolium dye, and our discovery of ethanol production at 0 °C indicate that R. frigidialcoholis induces a metabolic switch from respiration to ethanol fermentation as adaptation in Antarctic permafrost. This is the first report of microbial ethanol fermentation utilized as the major energy pathway in response to cold and the coldest temperature reported for natural ethanol production. R. frigidialcoholis increased its diversity and abundance of sRNAs when grown at 0 versus 23 °C. This was consistent with increase in transcription of Dicer, a key protein for sRNA processing. Our results strongly imply that post-transcriptional regulation of gene expression and mRNA silencing may be a novel evolutionary fungal adaptation in the cryosphere.

Accuracy of endoscopic ultrasound elastography used for differential diagnosis of focal pancreatic masses: a multicenter study.

BACKGROUND AND STUDY AIMS: Endoscopic ultrasound (EUS) elastography represents a new imaging procedure that might characterize the differences of hardness and strain between diseased tissue and normal tissue. The aim of this study was to assess the efficiency of EUS elastography for the differentiation of focal masses in chronic pancreatitis and pancreatic cancer. PATIENTS AND METHODS: The study group comprised 258 patients with focal pancreatic masses included prospectively at 13 participating centers. Qualitative analysis of the diagnoses made by two expert doctors using all recorded video clips was performed in order to test the interobserver variability. A post-processing software analysis was used to examine the EUS elastography videos by calculating average-hue histograms of individual elastography images. The quantitative information was used to calculate intra-observer variability and the accuracy of the method. RESULTS: Qualitative analysis of the recorded videos revealed a kappa value of 0.72. Intra-observer variability analysis revealed that the single measure intraclass correlation ranged between 0.86 and 0.94. The average-hue histogram analysis of the data indicated a sensitivity of 93.4 %, a specificity of 66.0 %, a positive predictive value of 92.5 %, a negative predictive value of 68.9 %, and an overall accuracy of 85.4 %, based on a cut-off value of 175. Area under the receiver operating characteristic curve (AUROC) was 0.854 ( P < 0.0001) with a confidence interval of 0.804 - 0.894. CONCLUSION: The value of quantitative analysis of EUS elastography recordings was proven by good reproducibility of the videos, as well as good parameters of the AUROC analysis. (Clinical Trials.gov identifier: CT00909103).

In situ measurements of the physical characteristics of Titan's environment.

On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was mainly nitrogen, with some methane, but its temperature and pressure profiles were poorly constrained because of uncertainties in the detailed composition. The extent of atmospheric electricity ('lightning') was also hitherto unknown. Here we report the temperature and density profiles, as determined by the Huygens Atmospheric Structure Instrument (HASI), from an altitude of 1,400 km down to the surface. In the upper part of the atmosphere, the temperature and density were both higher than expected. There is a lower ionospheric layer between 140 km and 40 km, with electrical conductivity peaking near 60 km. We may also have seen the signature of lightning. At the surface, the temperature was 93.65 +/- 0.25 K, and the pressure was 1,467 +/- 1 hPa.

The reliability of the scapular posture and scapular dyskinesis tests in rugby union players.

Background: Impact forces during rugby can contribute to scapula dysfunction and shoulder pain. Reliable assessment of static and dynamic scapula position is paramount in managing athletes with, and those at risk of developing, shoulder pain. Objectives: To determine the reliability of static scapular posture (SP), clavicular tilt angle (CTA) and the scapular dyskinesis (SD) assessments by expert and student therapists. Methods: The study design was an inter-rater and intra-rater reliability study in male university level rugby union players. Four sport rehabilitation students and one experienced physiotherapist evaluated the position of the scapular and clavicle of male university-level rugby union players (inter-rater participants: session 1: n=17, session 2: n=12 and session 3: n=16; (intra-rater participants: n = 12). Participants attended 3 testing sessions, each 1 week apart. Scapular orientation and motion were assessed in five planes of movement and using the Scapular Dyskinesis Test (SDT) respectively. The inter-rater analysis included all participants from each session, while in the intra-rater analysis included only the 12 participants who attended all three testing sessions. Results: Kappa coefficient values and percentage agreement ratings for students compared to the experienced therapist were: SP=poor to fair (-0.01 to 0.33), (27% - 94%); SDT=slight (0.16; 41%); CTA=fair (0.21; 59%). Test-retest (intra-rater) agreement was fair to moderate (0.22 - 0.44; 69% - 95%), slight (0.12; 47%), and fair (0.39; 77%) for the SP, SDT, and CTA, respectively. Conclusion: Static and dynamic evaluation of the shoulder by students and an experienced therapist has poor to moderate reliability and should not be used to make clinical decisions based on observation alone.

Alternative complexes formed by the Escherichia coli clamp loader accessory protein HolC (x) with replication protein HolD (ψ) and repair protein YoaA.

Efficient and faithful replication of DNA is essential for all organisms. However, the replication fork frequently encounters barriers that need to be overcome to ensure cell survival and genetic stability. Cells must carefully balance and regulate replication vs. repair reactions. In Escherichia coli, the replisome consists of the DNA polymerase III holoenzyme, including DNA polymerase, proofreading exonuclease, processivity clamp and clamp loader, as well as a fork helicase, DnaB and primase, DnaG. We provide evidence here that one component of the clamp loader complex, HolC (or χ) plays a dual role via its ability to form 2 mutually exclusive complexes: one with HolD (or ψ) that recruits the clamp-loader and hence the DNA polymerase holoenzyme and another with helicase-like YoaA protein, a DNA-damage inducible repair protein. By yeast 2 hybrid analysis, we show that two residues of HolC, F64 and W57, at the interface in the structure with HolD, are required for interaction with HolD and for interaction with YoaA. Mutation of these residues does not interfere with HolC's interaction with single-strand DNA binding protein, SSB. In vivo, these mutations fail to complement the poor growth and sensitivity to azidothymidine, a chain-terminating replication inhibitor. In support of the notion that these are exclusive complexes, co-expression of HolC, HolD and YoaA, followed by pulldown of YoaA, yields a complex with HolC but not HolD. YoaA fails to pulldown HolC-F64A. We hypothesize that HolC, by binding with SSB, can recruit the DNA polymerase III holoenzyme through HolD, or an alternative repair complex with YoaA helicase.

Reduced connectivity of the auditory cortex in patients with auditory hallucinations: a resting state functional magnetic resonance imaging study.

BACKGROUND: Previous research has reported auditory processing deficits that are specific to schizophrenia patients with a history of auditory hallucinations (AH). One explanation for these findings is that there are abnormalities in the interhemispheric connectivity of auditory cortex pathways in AH patients; as yet this explanation has not been experimentally investigated. We assessed the interhemispheric connectivity of both primary (A1) and secondary (A2) auditory cortices in n=13 AH patients, n=13 schizophrenia patients without auditory hallucinations (non-AH) and n=16 healthy controls using functional connectivity measures from functional magnetic resonance imaging (fMRI) data. METHOD: Functional connectivity was estimated from resting state fMRI data using regions of interest defined for each participant based on functional activation maps in response to passive listening to words. Additionally, stimulus-induced responses were regressed out of the stimulus data and the functional connectivity was estimated for the same regions to investigate the reliability of the estimates. RESULTS: AH patients had significantly reduced interhemispheric connectivity in both A1 and A2 when compared with non-AH patients and healthy controls. The latter two groups did not show any differences in functional connectivity. Further, this pattern of findings was similar across the two datasets, indicating the reliability of our estimates. CONCLUSIONS: These data have identified a trait deficit specific to AH patients. Since this deficit was characterized within both A1 and A2 it is expected to result in the disruption of multiple auditory functions, for example, the integration of basic auditory information between hemispheres (via A1) and higher-order language processing abilities (via A2).

Strategies used by professional rugby union clubs to manage players for artificial turf exposure.

Background: The use of artificial turf on rugby pitches is increasingly commonplace but there is limited evidence around its effects on injury, recovery, and performance. It is unclear whether this uncertainty influences player management strategies in professional clubs. Objectives: To understand how professional rugby union clubs in England approach player management for artificial turf, to explore how the beliefs of medical and strength/conditioning staff influence these decisions, and to determine whether differences exist between clubs with different levels of exposure to artificial surfaces. Methods: The study was a cross-sectional mixed methods study. Twenty-three medical and strength/conditioning staff members from 12 English Premiership Rugby Union clubs completed two bespoke questionnaires and participated in a semi-structured interview. Results: Two-thirds of the participants described formal club-level approaches to artificial turf. All participants from low-exposure clubs (<50% training and match time on artificial pitches) reported adjusting player recovery strategies following games on artificial turf to mitigate elevated muscle soreness and fatigue. Clubs with artificial surfaces at their home venues were less likely to adapt recovery than clubs with natural turf pitches. Regardless of exposure participants believed switching between surface types was a risk factor for injury. Medics reported that acute injuries associated with artificial turf exposure typically occurred at the foot or ankle, whereas abrasions and overuse injuries were more common and often affected the knees, hips and lower back. Players with compromised joints were less likely to be selected for matches on artificial surfaces. Conclusion: Player management around artificial turf is a focus for staff at professional rugby union clubs. Club practices vary by exposure and may consequently influence injury risk estimates.

The greenhouse and antigreenhouse effects on Titan.

There are many parallels between the atmospheric thermal structure of the Saturnian satellite Titan and the terrestrial greenhouse effect; these parallels provide a comparison for theories of the heat balance of Earth. Titan's atmosphere has a greenhouse effect caused primarily by pressure-induced opacity of N2, CH4, and H2. H2 is a key absorber because it is primarily responsible for the absorption in the wave number 400 to 600 cm-1 "window" region of Titan's infrared spectrum. The concentration of CH4, also an important absorber, is set by the saturation vapor pressure and hence is dependent on temperature. In this respect there is a similarity between the role of H2 and CH4 on Titan and that of CO2 and H2O on Earth. Titan also has an antigreenhouse effect that results from the presence of a high-altitude haze layer that is absorbing at solar wavelengths but transparent in the thermal infrared. The antigreenhouse effect on Titan reduces the surface temperature by 9 K whereas the greenhouse effect increases it by 21 K. The net effect is that the surface temperature (94 K) is 12 K warmer than the effective temperature (82 K). If the haze layer were removed, the antigreenhouse effect would be greatly reduced, the greenhouse effect would become even stronger, and the surface temperature would rise by over 20 K.

Biogenic methane, hydrogen escape, and the irreversible oxidation of early Earth.

The low O2 content of the Archean atmosphere implies that methane should have been present at levels approximately 10(2) to 10(3) parts per million volume (ppmv) (compared with 1.7 ppmv today) given a plausible biogenic source. CH4 is favored as the greenhouse gas that countered the lower luminosity of the early Sun. But abundant CH4 implies that hydrogen escapes to space (upward arrow space) orders of magnitude faster than today. Such reductant loss oxidizes the Earth. Photosynthesis splits water into O2 and H, and methanogenesis transfers the H into CH4. Hydrogen escape after CH4 photolysis, therefore, causes a net gain of oxygen [CO2 + 2H2O --> CH4 + 2O2 --> CO2 + O2 + 4H(upward arrow space)]. Expected irreversible oxidation (approximately 10(12) to 10(13) moles oxygen per year) may help explain how Earth's surface environment became irreversibly oxidized.

Organic synthesis in experimental impact shocks.

Laboratory simulations of shocks created with a high-energy laser demonstrate that the efficacy of organic production depends on the molecular, not just the elemental composition of the shocked gas. In a methane-rich mixture that simulates a low-temperature equilibrium mixture of cometary material, hydrogen cyanide and acetylene were produced with yields of 5 x 10(17) molecules per joule. Repeated shocking of the methane-rich mixture produced amine groups, suggesting the possible synthesis of amino acids. No organic molecules were produced in a carbon dioxide-rich mixture, which is at odds with thermodynamic equilibrium approaches to shock chemistry and has implications for the modeling of shock-produced organic molecules on early Earth.

Oxygen supersaturation in ice-covered Antarctic lakes: biological versus physical contributions.

Freezing in ice-covered lakes causes dissolved gases to become supersaturated while at the same time removing gases trapped in the ablating ice cover. Analysis of N2, O2, and Ar in bubbles from Lake Hoare ice shows that, while O2 is approximately 2.4 times supersaturated in the water below the ice, only 11% of the O2 input to this lake is due to biological activity: 89% of the O2 is derived from meltwater inflow. Trapped bubbles in a subliming ice cover provide a natural "fluxmeter" for gas exchange: in Lake Hoare as much as 70% of the total gas loss may occur by advection through the ice cover, including approximately 75% of the N2, approximately 59% of the O2, and approximately 57% of the Ar losses. The remaining gas fractions are removed by respiration at the lower boundary (O2) and by molecular exchange with the atmosphere in the peripheral summer moat around the ice.

Photochemically driven collapse of Titan's atmosphere.

Saturn's giant moon Titan has a thick (1.5 bar) nitrogen atmosphere, which has a temperature structure that is controlled by the absorption of solar and thermal radiation by methane, hydrogen, and organic aerosols into which methane is irreversibly converted by photolysis. Previous studies of Titan's climate evolution have been done with the assumption that the methane abundance was maintained against photolytic depletion throughout Titan's history, either by continuous supply from the interior or by buffering by a surface or near surface reservoir. Radiative-convective and radiative-saturated equilibrium models of Titan's atmosphere show that methane depletion may have allowed Titan's atmosphere to cool so that nitrogen, its main constituent, condenses onto the surface, collapsing Titan into a Triton-like frozen state with a thin atmosphere.