Links between topography, wind, deflation, lakes and dust: The case of the Bodélé Depression, Chad

The Bodélé Depression, Chad is the planet's largest single source of dust. Deflation from the Bodélé could be seen as a simple coincidence of two key prerequisites: strong surface winds and a large source of suitable sediment. But here we hypothesise that long term links between topography, winds, deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land-atmosphere processes with topography acting as the overall controlling agent. We use a variety of observational and numerical techniques, including a regional climate model, to show that: 1) contemporary deflation from the Bodélé is delineated by topography and a surface wind stress maximum; 2) the Tibesti and Ennedi mountains play a key role in the generation of the erosive winds in the form of the Bodélé Low Level Jet (LLJ); 3) enhanced deflation from a stronger Bodélé LLJ during drier phases, for example, the Last Glacial Maximum, was probably sufficient to create the shallow lake in which diatoms lived during wetter phases, such as the Holocene pluvial. Winds may therefore have helped to create the depression in which erodible diatom material accumulated. Instead of a simple coincidence of nature, dust from the world's largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world's largest dust source. Similar processes plausibly operate in other dust hotspots in topographic depressions

Hydrologie et géochimie isotopique

Cet ouvrage rassemble des travaux récents dans les domaines de l'hydrologie et de la géochimie isotopique. La première partie explore le cycle des eaux naturelles, depuis les précipitations jusqu'aux aquifères profonds, par l'analyse des variations de la composition isotopique de l'hydrogène, de l'oxygène et du carbone. Des types régionaux sont présentés, sous diverses latitudes : Spitzberg, Bassin parisien, bassin soudano-sahélien du Niger. L'intérêt de l'approche isotopique dans l'étude du changement global est illustrée en deuxième partie. Les variations hydro-climatiques de types régionaux, en Afrique essentiellement, sont retracées par l'analyse multidisciplinaire d'enregistrements sédimentaires, dont la géochimie isotopique constitue la clé essentielle. L'homogénéité du refroidissement, aux moyennes et basses latitudes, lors du dernier maximum glaciaire est démontrée par l'analyse isotopique des gaz nobles dans les eaux souterraines. La mise en évidence de l'origine organique du carbone de carbonates sédimentaires remet en question l'interprétation de certaines analyses isotopiques. La troisième partie fait référence aux isotopes d'origine cosmique et à la production in situ de radionucléides. Il est rappelé que la datation par 14C a contribué à la compréhension des mécanismes des changements du climat au cours du dernier maximum glaciaire et depuis lors. Les limites de cette méthode et ses progrès récents font l'objet d'une synthèse amplement documentée. Par l'apport de données isotopiques, la géochimie s'avère fonder la modélisation des conditions de stabilité du réacteur de fission nucléaire fossile d'Oklo. (Résumé d'auteur

Validation of an algorithm-based definition of treatment resistance in patients with schizophrenia

Large-scale pharmacoepidemiological research on treatment resistance relies on accurate identification of people with treatment-resistant schizophrenia (TRS) based on data that are retrievable from administrative registers. This is usually approached by operationalising clinical treatment guidelines by using prescription and hospital admission information. We examined the accuracy of an algorithm-based definition of TRS based on clozapine prescription and/or meeting algorithm-based eligibility criteria for clozapine against a gold standard definition using case notes. We additionally validated a definition entirely based on clozapine prescription. 139 schizophrenia patients aged 18–65 years were followed for a mean of 5 years after first presentation to psychiatric services in South-London, UK. The diagnostic accuracy of the algorithm-based measure against the gold standard was measured with sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). A total of 45 (32.4%) schizophrenia patients met the criteria for the gold standard definition of TRS; applying the algorithm-based definition to the same cohort led to 44 (31.7%) patients fulfilling criteria for TRS with sensitivity, specificity, PPV and NPV of 62.2%, 83.0%, 63.6% and 82.1%, respectively. The definition based on lifetime clozapine prescription had sensitivity, specificity, PPV and NPV of 40.0%, 94.7%, 78.3% and 76.7%, respectively. Although a perfect definition of TRS cannot be derived from available prescription and hospital registers, these results indicate that researchers can confidently use registries to identify individuals with TRS for research and clinical practices

Clozapine use in childhood and adolescent schizophrenia: A nationwide population-based study

Early onset schizophrenia (EOS) begins in childhood or adolescence. EOS is associated with poor treatment response and may benefit from timely use of clozapine. This study aimed to identify the predictors of clozapine use in EOS and characterize the clinical profile and outcome of clozapine-treated youths with schizophrenia. We conducted a nationwide population-based study using linked data from Danish medical registries. We examined all incident cases of EOS (i.e., cases diagnosed prior to their 18th birthday) between December 31st 1994 and December 31st 2006 and characterized their demographic, clinical and treatment profiles. We then used multivariable cox proportional hazard models to identify predictors of clozapine treatment in this patient population. We identified 662 EOS cases (1.9% of all schizophrenia cases), of whom 108 (17.6%) had commenced clozapine by December 31st 2008. Patients had on average 3 antipsychotic trials prior to clozapine initiation. The mean interval between first antipsychotic treatment and clozapine initiation was 3.2 (2.9) years. Older age at diagnosis of schizophrenia [HR=1.2, 95% CI (1.05-1.4), p=0.01], family history of schizophrenia [HR=2.1, 95% CI (1.1-3.04), p=0.02] and attempted suicide [HR=1.8, 95% CI (1.1-3.04), p=0.02] emerged as significant predictors of clozapine use. The majority of patients (n=96, 88.8%) prescribed clozapine appeared to have a favorable clinical response as indicated by continued prescription redemption and improved occupational outcomes. Our findings support current recommendations for the timely use of clozapine in EOS

Microwave Spin Control of a Tin-Vacancy Qubit in Diamond

The negatively charged tin-vacancy (SnV-) center in diamond is a promising solid-state qubit for applications in quantum networking due to its high quantum efficiency, strong zero phonon emission, and reduced sensitivity to electrical noise. The SnV- has a large spin-orbit coupling, which allows for long spin lifetimes at elevated temperatures, but unfortunately suppresses the magnetic dipole transitions desired for quantum control. Here, by use of a naturally strained center, we overcome this limitation and achieve high-fidelity microwave spin control. We demonstrate a pi-pulse fidelity of up to 99.51+/0.03%$ and a Hahn-echo coherence time of T2echo = 170.0+/-2.8 microseconds, both the highest yet reported for SnV- platform. This performance comes without compromise to optical stability, and is demonstrated at 1.7 Kelvin where ample cooling power is available to mitigate drive induced heating. These results pave the way for SnV- spins to be used as a building block for future quantum technologies

Modulation of BACE1 Activity by Chemically Modified Aptamers

A modified DNA aptamer that binds BACE1, a therapeutic target involved in Alzheimer's disease has been developed. This ssXNA not only tightly binds to BACE1 but also inhibits its protease activity in vitro in the same range as a previously described unmodified aptamer. We report the in vitro selection of functional oligonucleotides incorporating two nucleobase modifications: 5‐chlorouracil and 7‐deazaadenine. The nucleoside analogue 5‐chloro‐2′‐deoxyuridine has already been explored as a replacement for thymidine in a chemically modified genome of a bacterium. Thus, 5‐chlorouracil modification is a good candidate to support genetic transfer in vivo as well as functional activity

TWO NEW PLOCENE SPECIES OF CYCLOSTEPHANOS (BACILLARIOPHYCEAE) WITH COMMENTS ON THE CLASSIFICATION OF THE FRESHWATER THALASSIOSIRACEAE 1

Two new species of the diatom genus Cyclostephanos Round are described from Pliocene fossil deposits in western North America. Cyclostephanos undatus is distinguished from other Cyclostephanos species by its tangentially undulate valve face; Cyclostephanos fenestratus is distinguished by its extremely shallow alveoli. This paper records previously unreported morphological detail of Cyclostephanos and speculates that structure of the punctum, labiate process and strutted process may enhance diagnosis of the freshwater genera of the Thalassiosiraceae Lebour emend. Hasle. Cyclostephanos undatus is similar to several Cyclotella species, but its external costae are raised and its alveolar morphology is similar to that of Cyclostephanos dubius (Fricke) Round. Cyclostephanos fenestratus is similar in external view to Stephanodiscus Ehrenb. However, the two species described here have flat cribra covering the mantle puncta and the labiate processes appear to lack external tubes, whereas Stephanodiscus species have domed mantle cribra and external tubes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65645/1/j.1529-8817.1986.tb04154.x.pd