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The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth's climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO 2 uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO 2 uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle–climate models.

Ambrosia Lake region in New Mexico contains the world's largest known uranium reserve, but how many Ambrosia Lakes will be needed to meet projected demands?Is there enough uranium ore in the United States to fuel the light water reactor, and does success hinge on the untried breeder? The government should halt or reduce the present program until the answers are better known

Quand NaAlMe 4 et NaAlEt 4 sont reunis dans une solution benzenique contenant de l'HMPT, des echanges des groupes alkyles se produisent conduisant a une distribution statistique des ions alkylaluminate

The crystal structures of the title compounds have been determined from diffractometer data and refined by full-matrix least squares. NaAlMe4 is orthorhombic,Cmcm,a=9.234(3),b=9.221(3),c=8.303(2) A,Z=4,D c=1.03 g cm−3,R=0.029 for 278 data. NaAlEt4 is monoclinic,P21/c (No. 14),a=13.900(2),b=13.207(2),c=14.443(1) A,β=117.43(1)°,Z=8,D c=0.94 g cm−3,R=0.056 for 2747 data. NaAl(n-Pr)4 is monoclinic,C2/c,a=9.802(5),b=15.336(4),c=21.611(10) A,β=98.34(4)°,Z=8,D c=0.92 g cm−3,R=0.072 for 899 data. Coordination of Al is essentially tetrahedral in all structures, and closest contacts to Na+ involveα-carbon atoms of alkyl groups.

The history of acquisition and maintenance of the Linnaean insect collections is briefly summarized. Curatorial details (such as kinds of label) are discussed, chiefly with reference to Hymenoptera. Some misleading opinions concerning the taxonomic value of the collections and the nature of Linnaean type-material are examined and a practical approach is recommended. The rationale governing re-curation of the collections is detailed, and the present contents of the collection of Hymenoptera are listed in order to inform interested specialists.

A detailed study of complexation of the sodium ion by HMPA2 has been made using the system[Formula: see text]where HMPA is observed to be a strong donor towards Na+ but does not complex AlEt4−. This system forms two liquid phases at low HMPA:Na+ molar ratios with the salt and the HMPA, up to a 4:1 HMPA:Na+ ratio, occurring only in the lower phase. Based on a variety of experimental techniques, reasonable proposals of the solute species in the lower phase as a function of HMPA:Na+ ratio are presented. A 2.5:1 ratio of HMPA:Na+ is observed to be particularly significant. This ratio is rationalized in terms of a bridging HMPA molecule resulting in a cationic species with the stoichiometry [2Na•5HMPA]2+. It is found that the 27Al and 1H nmr spectra are determined primarily by quadrupole relaxation of the 27Al nucleus rather than by exchange.

The linewidth of the 23Na resonance in sodium tetraethylaluminate in benzene has been measured as a function of the ratio of [donor]: [Na+] using the strong complexing agent hexamethylphosphoramide. In this system changes in the sodium linewidth arise primarily from changes in the nuclear quadrupole relaxation at the sodium nucleus which in turn arise from changes in the electric field gradient. As the ratio of hexamethylphosphoramide to sodium ion is increased up to 3: 1 the 23Na linewidth progressively decreases due to an increase in cation–anion distance in the ion pair. After a ratio of 4:1 is reached, essentially no linewidth change is noted, indicating a stable solvation number of 4 for hexamethylphosphoramide. The results of this study indicate that this is a new and promising approach to the determination of solvation numbers of the sodium ion.

The hypothesis that males of certain species of the pompilid genus Cryptocheilus Panzer are polymorphic, first proposed by H. Wolf, is examined critically in the light of modern knowledge of the mating systems of Hymenoptera and the known biology of Cryptocheilus species. Speculations are made as to the likely selection pressures operating to produce this phenomenon; nine Old World species of Cryptocheilus are identified as probable examples. The taxonomic implications of the hypothesis are considered; one new generic and nine new specific synonymies are listed, and lectotypes are designated for three nominal species. Two names are retrieved from synonymy for species here recognized as valid. A key is provided for the extreme forms of the males of these species; more detailed treatment must await full revision of Cryptocheilus.

The distinction between competence and performance models in psycholinguistics is used to analyze current theory and research strategies in the study of development. The analysis is used to argue for the construction of performance models of cognitive skills which do not reify the elements of competence models. Some suggestions are presented for a performance model which relies on Soviet notions of activity and interpsychological control. The potential theoretical and empirical benefits of the model are discussed in the context of the authors’ research on the deployment of formal operational skills.

Lithium tetra-n-butylaluminate (LiAlBu 4 ) has been prepared by reacting n-hexane solutions of n-butyllithium and tri-n-butylaluminum. The tetraalkylammonium tetra-n-butylaluminates (R 4 NAlBu 4 ; R = Me, Et, n-Pr, n-Bu) have been prepared in benzene by the addition of sodium tetra-n-butylaluminate (NaAlBu 4 ) to solutions of R 4 NBr. The significance of the syntheses of these salts for the study of ion-ion and ion-solvent interactions has been discussed. The tetra-n-butylaluminate salts have been characterized by aluminum analyses, NMR spectroscopy, solubility data, melting points, and conductance data. The similarity between the physical and chemical properties of the R 4 NAlBu 4 salts and NaAlBu 4 , which has been extensively used for ion-solvent studies, indicates the potential value of these quaternary ammonium salts in analogous investigations.

A mechanically simple magnetic balance having sufficient sensitivity to measure diamagnetic susceptibilities has been developed using a permanent magnet. Its operation is based on the twisting of a quartz or Vycor fiber in a direction such as to overcome the effects of the magnetic field. The magnetic field strength is dependent on the position of the magnet with respect to the sample and can be varied by using different magnet settings.

A new method for the determination of the inner sphere solvation number of the sodium ion is presented based on the distribution of donor between two liquid phases. The system sodium tetraethylaluminate (NaAlEt 4 -benzene (or cyclohexane)-donor forms two liquid phases with the salt in the lower phase and the distribution of donor between the two phases being strongly affected by solvation with the salt. A solvation number of six is obtained with tetrahydrofuran, pyridine, dimethoxyethane and dimethylsulfoxide.

4-year-olds made same and different judgments about pairs of stimuli requiring detailed comparison in 2 conditions: a judgment-only condition and a justification condition in which children explained the reasons for their judgments. The systematic comparison strategies revealed in the justifications indicated that all children had definite criteria for "same" and "different" although about two-thirds of the children used a criterion that differed from the adult criterion. Judgments were more accurate in the justification than in the judgment-only condition, suggesting that overt verbalizations and gestures may provide a beneficial external support for completion of a child's own visual comparison strategy.