Simulation d'un plan d'expérience en océanographie: Effets de la dispersion des organismes sur l'erreur d'échantillonnage

Seven spatial dispersions of organisms, reflecting some constraints of various physical and biological factors of the pelagic environment were simulated on computer. The relationships between the sampling methods (tow length, net size), the pelagic population dispersion patterns, and the sampling error were investigated by computer simulation. Two categories of dispersions were identified: 1) random or relatively uniform dispersions of organisms (including Poisson, gradient, and negative contagous dispersions), characterized by an index of dispersion $\text{s}{}^2\text{m}\text{< 1.5}$; and 2) overdispersed distributions of swarming or clustering organisms (including positive contagion and centric aggregation dispersions), characterized by a value of $\text{s}{}^2\text{m}\text{> 1.5}$.The origin and size of the sampling errors as deduced from the analysis of variance change, considerably from one group of dispersions to the other. In the first case, the net size was dominant, whereas in the second case the tow length and patch size effects are more critical. In general, the precision of estimations decreases as the over-dispersion of organisms increases. The confidence limits, for a simple estimation of abundance, vary considerably with the spatial dispersion, ranging from narrow values for the relatively uniform dispersions to very large values for the overdispersed distributions. There is an increasing imprecision in the estimate of population abundance as the dispersion coefficient $\text{s}{}^2\text{m}$ increases.Analysis of coefficients of variation indicates that more precise estimates of abundance may be obtained if a practical sampling procedure is applied to a group of specific organisms. Furthermore, it is suggested that a simulated approach, performed prior to ocean sampling, permits the establishment of the optimal sampling procedure for the species under study.     

Un nouvel heteroside nitré extrait d'Annona squamosa

A new glycoside was isolated from a 60% methanol extract of dried leaves and stems of Annona squamosa. Its chemical structure was determined as 4-(-2-nitroethyl)-1-[(6-O-β-d-xylopyranosyl-β-d-glucopyranosyl)oxy] benzene.     

Dérivés d'acides 3-(β-d-érythrofuranosyl)-pyrazolecarboxyliques

Treatment of 2,5-anhydro-1-bromo-1-deoxy-2,3-O-isopropylidene-1-p-nitrophenylhydrazono-d-ribose with methyl acetylenecarboxylate gave methyl 3-(2,3-O-isopropylidene-β-d-erythrofuranosyl)-1-p-nitrophenylpyrazole- (8) and 5-carboxylate (9). Amidification at C-5 of 8 was easier than at C-4 of 9. Similarly, dimethyl 3-(2,3-O-isopropylidene-β-d-erythrofuranosyl)- 1 - p-nitrophenylpyrazole-4,5-dicarboxylate gave specifically a 5-carbamoyl derivative, the structure of which was established by comparison of the ¹³C-n.m.r.spectrum with those of a series of glycosylpyrazoles. The correlation between the experimental values of the chemical shifts of the carbon atoms of the pyrazole ring and the values calculated by addition of the contributions of the various groups linked to the ring was better (R 0.98) than the correlations obtained by calculation by the CNDO/2 method of the total electron population (R 0.92) or of the π-electron population of each carbon atom (R 0.85).     

Synthese d'un acide gras cyclohexenique disubstitute: L'acide (propyl-2′ cyclohexen-4′ yl-1′)-9 nonanoïque

(Propyl-2′ cyclohexen-4′ yl-1′)-9 nonanoïc acid was synthesized through a succession of the following reactions: condensation, according to Kondakof, of methyl undecylenate and propionyl chloride; condensation, according to Diels Alder, between the resulting aliphatic ketone and butadiene; reduction of the disubstituted cyclohexenyl ketone, according to Hutchins.The compounds formed at each step of the synthesis were studied and characterized.     

Mise en évidence de deux types chimiques chez le Cannabis sativa originaire d'afrique du sud

Culture in a phytotron of Cannabis sativa L. originating from S. Africa revealed the presence of two chemotypes varying in concentration of tetrahy     

Alcoxyhalogénation d'acides gras éthyléniques III. Cas de l'hydroxy-12-octadecene-9-oate de methyle et de son acetate

12-Hydroxy-9-cis-methyl octadecenoate and its acetate are easily methoxybrominated.The main product of the reaction is a mixture in non equal properties of both possible methoxy bromides: the 10-bromo-9-methoxy isomer is always the most abundant ($\text{? 80\%}$).Besides by-products usually found in such reactions (unreacted substrate — αβ dibromides from bromine addition), the crude reaction product contains supplementary components: the bromohydrines mixture and the 10-methoxy-9 β 12-epoxyde, and, only in the case of non acetylated substrate, the 10-bromo-9 · 12-epoxyde.During long storage, even in very mild conditions, the importance of these new by-products increases, while the proportion of bromoethers decreases.     

Hydrogénolyse de 3,6,8-trioxabicyclo[3.2.1]octanes par le complexe aluminohydrure de lithium-chlorure d'aluminium

Hydrogenolysis of 3,6,8-trioxabicyclo[3.2.1]octanes by the 1:1 lithium aluminum hydride-aluminum chloride complex leads, through the specific opening of the acetal function at C-5O-6, to 1,4-dioxanes bearing a hydroxymethyl group. The stereo-chemistry of the dioxanes obtained is discussed with emphasis on the intramolecular hydrogen bond.     

'神马'菊花的离体保存及遗传稳定性

用添加不同蔗糖与甘露醇配比的培养基对切花菊品种＇神马＇（Jinba）试管苗进行离体保存,并对保存材料再生后代的遗传稳定性进行了研究.结果表明,在温度（23±2）℃、光照强度2 000～3 000 lx、光照时间12 h/d的培养条件下,MS＋0.3 mg·L^-1 6-BA＋0.1 mg·L^-1NAA培养基中分别添加10 g·L^-1蔗糖和10 g·L^-1甘露醇、10 g·L^-1蔗糖和20 g·L^-1甘露醇、20 g·L^-1蔗糖和20 g·L^-1甘露醇或30 g·L^-1蔗糖和10 g·L^-1甘露醇均能使菊花试管苗连续保存12个月,其中10 g·L^-1蔗糖和20 g·L^-1甘露醇、20 g·L^-1蔗糖和20 g·L^-1甘露醇组合处理保存12个月后成活率较高,分别达到50.00%和60.00%,且均保持最高的增殖倍数2.67.保存12个月的试管苗在增殖、生根培养基上均能正常恢复生长,且其再生后代的田间生物学性状、过氧化物酶（POD）及酯酶（EST）同工酶酶谱、ISSR扩增图谱与对照株无差异,保持了良好的遗传稳定性,说明利用上述方法保存＇神马＇种质是可行的.     

Description de Pseudolituonella? guerneti,nov. sp., nouveau foraminifere benthonique du Cenomanien d'Eubee (Grece)

A new benthonic Foraminifera: Pseudolituonella? guerneti n. sp. (Ataxophragmiidae) has been found in upper cenomanian limestones of central Eubee (Greece, pelagonian zone). It is described and illustrated in this publication.     

Who's In and Who's Out—Compositional Control of Biomolecular Condensates

Biomolecular condensates are two- and three-dimensional compartments in eukaryotic cells that concentrate specific collections of molecules without an encapsulating membrane. Many condensates behave as dynamic liquids and appear to form through liquid–liquid phase separation driven by weak, multivalent interactions between macromolecules. In this review, we discuss current models and data regarding the control of condensate composition, and we describe our current understanding of the composition of representative condensates including PML nuclear bodies, P-bodies, stress granules, the nucleolus, and two-dimensional membrane localized LAT and nephrin clusters. Specific interactions, such as interactions between modular binding domains, weaker interactions between intrinsically disorder regions and nucleic acid base pairing, and nonspecific interactions, such as electrostatic interactions and hydrophobic interactions, influence condensate composition. Understanding how specific condensate composition is determined is essential to understanding condensates as biochemical entities and ultimately discerning their cellular and organismic functions.     

Foraminifères du Lias moyenet supérieur d'Obon: Chaînes ibériques,Province de Teruel,Espagne

The Obon sections in the central Iberian ranges, thestratigraphy of which is well established, have a rich microfauna of Foraminifera from Upper Domerian and Toarcian. It is partly original (4 new species are described, and 4 are left as open nomenclature).The plentifulness of the material has allowed thestructures of some of the populations to be shown up, some of the forms to be grouped up into spectrums and precisions brought in about the notion of the Lenticulina genus and its systematics.A part of the Iberian species is also to be found in the rest of Western Europe and Morocco. The Poitou species created by J.M. Payard (1947) are the objects of critical comparison. The later appearance of the marly-calcareous facies in Poitou may explain the differences in stratigraphic repartition fairly constantly observed.     

常见绿化树种绦柳(Salix matsudana cv.'Pendula')耗水特性

于2005年5—10月,利用Granier热扩散技术对北京城市绿化树种绦柳液流速率进行连续测定,并同时监测林地光合有效辐射、风速和空气温湿度等气象因子。结果表明：绦柳液流速率具有稳定的昼夜变动规律,日变化曲线呈“宽单峰型”,且晴天比阴天的昼夜差异大;绦柳月平均液流速率从5月开始升高,8月达到最大值,为0.0050 cm·s^-1,随后逐渐下降,10月达到最小值,为0.0013 cm·s^-1;与绦柳液流速率相关性最大的环境因子是光合有效辐射和空气温度,最小的是风速;绦柳每小时的耗水量与边材面积和胸径的相关性大于与树高和树冠投影面积的相关性。     

Why don't plants fix nitrogen?

The process of biological nitrogen fixation is restricted to a small number of prokaryotic organisms and the majority of the world's crop plants depend on chemical fertilizers to achieve optimum yields. Need this always be the case or have recent advances in the genetic analysis of nitrogen fixation made the construction of nitrogen-fixing plants a realistic goal?