Improving the numerical prediction of a cyclone in the Mediterranean by local potential vorticity modifications

This study explores the benefit that can be drawn from incorporating local potential vorticity (PV) modifications into a numerical forecast. The case under study is the severe cyclogenesis that occurred in the Western Mediterranean from 9 to 12 November 2001. This case was shown to be extremely sensitive to the upper‐level flow, which governed to a great extent the deepening of the depression and the location and intensity of its associated precipitation. Corrections of PV were guided by METEOSAT‐7 water vapour observations and restricted to the upper troposphere, mainly altering the topography of the dynamical tropopause. Using both the French operational global model ARPEGE and the non‐hydrostatic mesoscale model Meso‐NH, it is shown that carefully designed PV corrections lead to a substantial improvement in the simulation of the storm, both in terms of surface pressure, cloud cover and precipitation forecasts. Furthermore, the impact of the modifications is shown to be a maximum when they are introduced at the time corresponding to the incipient stage of cyclogenesis. Copyright © 2009 Royal Meteorological Society

Measures to assess the prognostic ability of the stratified Cox proportional hazards model

Many measures have been proposed to summarize the prognostic ability of the Cox proportional hazards (CPH) survival model, although none is universally accepted for general use. By contrast, little work has been done to summarize the prognostic ability of the stratified CPH model; such measures would be useful in analyses of individual participant data from multiple studies, data from multi‐centre studies, and in single study analysis where stratification is used to avoid making assumptions of proportional hazards. We have chosen three measures developed for the unstratified CPH model (Schemper and Henderson's , Harrell's C‐index and Royston and Sauerbrei's ), adapted them for use with the stratified CPH model and demonstrated how their values can be represented over time. Although each of these measures is promising in principle, we found the measure of explained variation very difficult to apply when data are combined from several studies with differing durations of participant follow‐up. The two other measures considered, and the C‐index, were more applicable under such circumstances. We illustrate the methods using individual participant data from several prospective epidemiological studies of chronic disease outcomes. Copyright © 2008 John Wiley & Sons, Ltd.

Systematically missing confounders in individual participant data meta‐analysis of observational cohort studies

One difficulty in performing meta‐analyses of observational cohort studies is that the availability of confounders may vary between cohorts, so that some cohorts provide fully adjusted analyses while others only provide partially adjusted analyses. Commonly, analyses of the association between an exposure and disease either are restricted to cohorts with full confounder information, or use all cohorts but do not fully adjust for confounding. We propose using a bivariate random‐effects meta‐analysis model to use information from all available cohorts while still adjusting for all the potential confounders. Our method uses both the fully adjusted and the partially adjusted estimated effects in the cohorts with full confounder information, together with an estimate of their within‐cohort correlation. The method is applied to estimate the association between fibrinogen level and coronary heart disease incidence using data from 154 012 participants in 31 cohorts. † One hundred and ninety‐nine participants from the original 154 211 withdrew their consent and have been removed from this analysis. Copyright © 2009 John Wiley & Sons, Ltd.

Effects of a cognitive stress challenge on myocardial perfusion and plasma cortisol in coronary heart disease patients with depression

Although it is well established that coronary heart disease (CHD) patients with depression exhibit increased mortality compared with equally ill cardiac patients without depression, the mechanisms mediating this effect remain obscure. Depression is characterized by vulnerability to stress and heightened stress responsiveness, and stress can theoretically act through several biological pathways to contribute to excess mortality from CHD. Mechanisms connecting stress, depression and cardiovascular mortality have not been previously explored in detail. The purpose of this study was to assess the effects of stress and depression on myocardial perfusion and plasma cortisol concentrations in CHD patients. Patients with CHD with and without depression (n = 28) underwent single photon emission computed tomography imaging of myocardial perfusion at rest and during a stressful cognitive challenge. Severity of ischaemia was measured by summing perfusion defect scores across myocardial segments and subtracting out rest from stress scores. Plasma cortisol concentrations were measured at baseline and in response to the stressful challenge. There were no differences in stress‐induced myocardial ischaemia or plasma cortisol response to stress between CHD patients with and without depression. Depressed CHD patients with a history of psychological trauma (n = 5) had an increase in stress‐induced ischaemia scores [7; standard deviation (SD) = 5] compared with CHD patients with depression without a history of psychological trauma (2 SD = 2) and CHD patients without depression or psychological trauma (1; SD = 2) (F = 8.51; degree of freedom = 2,23; p = 0.007). Eighty per cent of CHD/depression trauma‐exposed subjects had stress‐induced ischaemia as opposed to 38 per cent of CHD/depression subjects without trauma exposure and 23 per cent of subjects with CHD without depression or trauma. Self‐reported nervousness during the cognitive stressor was correlated with stress‐induced ischaemia. These preliminary findings suggest that depression with a history of prior exposure to traumatic stress is associated with increased risk for stress‐induced cardiovascular ischaemia. Copyright © 2008 John Wiley & Sons, Ltd.

Size‐Dependent Cytotoxicity of Monodisperse Silica Nanoparticles in Human Endothelial Cells

The effect that monodisperse amorphous spherical silica particles of different sizes have on the viability of endothelial cells (EAHY926 cell line) is investigated. The results indicate that exposure to silica nanoparticles causes cytotoxic damage (as indicated by lactate dehydrogenase (LDH) release) and a decrease in cell survival (as determined by the tetrazolium reduction, MTT, assay) in the EAHY926 cell line in a dose‐related manner. Concentrations leading to a 50% reduction in cell viability ( TC 50 ) for the smallest particles tested (14‐, 15‐, and 16‐nm diameter) ranging from 33 to 47 µg cm −2 of cell culture differ significantly from values assessed for the bigger nanoparticles: 89 and 254 µg cm −2 (diameter of 19 and 60 nm, respectively). Two fine silica particles with diameters of 104 and 335 nm show very low cytotoxic response compared to nanometer‐sized particles with TC 50 values of 1095 and 1087 µg cm −2 , respectively. The smaller particles also appear to affect the exposed cells faster with cell death (by necrosis) being observed within just a few hours. The surface area of the tested particles is an important parameter in determining the toxicity of monodisperse amorphous silica nanoparticles.

Second‐Harmonic Generation from a Single Core/Shell Quantum Dot

Nanoparticles emitting two‐photon luminescence are broadly used as photostable emitters for nonlinear microscopy. Second‐harmonic generation (SHG) as another two‐photon mechanism offers complementary optical properties but the reported sizes of nanoparticles are still large, of a few tens of nanometers. Herein, coherent SHG from single core/shell CdTe/CdS nanocrystals with a diameter of 10 to 15 nm is reported. The nanocrystal excitation spectrum reveals resonances in the nonlinear efficiency with an overall maximum at about 970 nm. Polarization analysis of the second‐harmonic emission confirms the expected zinc blende symmetry, and allows extraction of the three‐dimensional nanocrystal orientation. The small size of these nonlinearly active quantum dots, together with the intrinsic coherence and orientation sensitivity of the SHG process, are well adapted for ultrafast probing of optical near‐fields with high resolution as well as for orientation tracking for bioimaging applications.

Screening of Starch Quality Traits in Cassava ( Manihot esculenta Crantz)

Cassava ( Manihot esculenta Crantz) is one of the most important sources of starch in the tropics. There is limited and contradictory information regarding cassava starch characteristics. The International Center for Tropical Agriculture (CIAT) holds in trust FAO's cassava germplasm collection. Starches from 3272 landraces (including 12 wild relatives) and 772 improved clones were extracted and analyzed over a period of several years. In most cases only one starch sample per genotype was analyzed. Average cyanogenic potential was 327 ppm but considerably higher in the landraces (340 ppm) than in improved clones (267 ppm). Average total and reducing sugars were slightly higher in improved clones (4.06 and 1.56%, respectively) than in landraces (3.68 and 1.25%, respectively). Amylose content was similar in both types of germplasm with an average of 20.7%. Average pasting temperature was 65.3°C. Maximum viscosity was 777.5 mPa s, breakdown was 298.1 mPa s, consistency was 155.8 mPa s and setback was ‐144.5 mPa s. The large sample of starches analyzed provides very robust information regarding the actual characteristics of cassava starch.

Screening of Starch Quality Traits in Cassava ( Manihot esculenta Crantz)

Gfi‐1B Promoter Remains Associated with Active Chromatin Marks Throughout Erythroid Differentiation of Human Primary Progenitor Cells

Growth Factor Independent‐1B (Gfi‐1B) is a transcriptional repressor that plays critical roles in the control of erythropoiesis and megakaryopoiesis. Gfi‐1B expression was described to be repressed by an autoregulatory feedback control loop. Here, we show that Gfi‐1 transcription is positively regulated early after induction of erythroid differentiation and remains highly active to late erythroblasts. Using chromatin immunoprecipitation assays in CD34 + cells from human cord blood, we found that Gfi‐1 and GATA‐2 in immature progenitors and then Gfi‐1B and GATA‐1 in erythroblasts are bound to the Gfi‐1B promoter as well as to the promoter of c‐myc , a known Gfi‐1B target gene. Surprisingly, this Gfi‐1/GATA‐2–Gfi‐1B/GATA‐1 switch observed at erythroblast stages is associated to an increase in the Gfi‐1B transcription whereas it triggers repression of c‐myc transcription. Accordingly, analysis of chromatin modification patterns shows that HDAC, CoREST, and LSD1 are recruited to the c‐myc promoter leading to appearance of repressive chromatin marks. In contrast, the Gfi‐1B promoter remains associated with a transcriptionally active chromatin configuration as highlighted by an increase in histone H3 acetylation and concomitant release of the LSD1 and CoREST corepressors. The repressive function of Gfi‐1B therefore depends on the nature of the proteins recruited to the target gene promoters and on chromatin modifications. We conclude that Gfi‐1B behaves as a lineage‐affiliated gene with an open chromatin configuration in multipotent progenitors and sustained activation as cells progress throughout erythroid differentiation. STEM CELLS 2009;27:2153–2162

Structural Characterization and Theoretical Calculations of cis ‐Dioxo(N‐salicylidene‐2‐aminophenolato)(ethanol)molybdenum(VI) Complexes MoO 2 (SAP)(EtOH) (SAP = N‐salicylidene‐2 aminophenolato)

The crystal structure of MoO 2 (SAP)(EtOH) is reported for the first time. The compound crystallizes in the monoclinic crystallographic system ( P 2 1 / n , a = 11.0923(3) Å, b = 6.9590(2) Å, c = 19.4499(5) Å, β = 94.458(1)°, V = 1496.82(7) Å 3 , Z = 4). The molybdenum atom adopts a distorted octahedral arrangement with cis Mo=O bonds, typical for cis ‐dioxomolybdenum(VI) complexes. The ethanol ligand is situated trans to one oxido ligand. Theoretical calculations in the gas phase were performed to examine the relative stability of MoO 2 (L)(EtOH) and the [MoO 2 (L)] 2 dimeric form (L = SAP, SAE).