Palaeomagnetic and synchrotron analysis of \u3e1.95 Ma fossil-bearing palaeokarst at Haasgat, South Africa

Palaeomagnetic analysis indicates that Haasgat, a fossil-bearing palaeocave in the Gauteng Province of South Africa, is dominated by reversed magnetic polarity in its oldest, deepest layers and normal polarity in the younger layers. The presence of in-situ Equus specimens suggests an age of less than ~2.3 Ma, while morphological analysis of faunal specimens from the ex-situ assemblage suggests an age greater than 1.8 Ma. Given this faunal age constraint, the older reversed polarity sections most likely date to the beginning of the Matuyama Chron (2.58–1.95 Ma), while the younger normal polarity deposits likely date to the very beginning of the Olduvai Sub-Chron (1.95–1.78 Ma). The occurrence of a magnetic reversal from reversed to normal polarity recorded in the sequence indicates the deposits of the Bridge Section date to ~1.95 Ma. All the in-situ fossil deposits that have been noted are older than the 1.95 Ma reversal, but younger than 2.3 Ma. Haasgat therefore dates to an interesting time period in South African human evolution that saw the last occurrence of two australopith species at ~2.05–2.02 Ma (Sts5 Australopithecus africanus from Sterkfontein Member 4) to ~1.98 Ma ( Australopithecus sediba from Malapa) and the first occurrence of early Homo (Sk847), Paranthropus and the Oldowan within Swartkrans Member 1 between ~2.0 Ma and ~1.8 Ma

Spin state and phase competition in TbBaCo_{2}O_{5.5} and the lanthanide series LnBaCo_{2}O_{5+\delta} (0<=\delta<=1)

A clear physics picture of TbBaCo$_{2}$O$_{5.5}$ is revealed on the basis of density functional theory calculations. An antiferromagnetic (AFM) superexchange coupling between the almost high-spin Co$^{3+}$ ions competes with a ferromagnetic (FM) interaction mediated by both p-d exchange and double exchange, being responsible for the observed AFM-FM transition. And the metal-insulator transition is accompanied by an xy/xz orbital-ordering transition. Moreover, this picture can be generalized to the whole lanthanide series, and it is predicted that a few room-temperature magnetoresistance materials could be found in LnBa$_{1-x}$A$_{x}$Co$_{2}$O$_{5+\delta}$ (Ln=Ho,Er,Tm,Yb,Lu; A=Sr,Ca,Mg).Comment: 13 pages, 2 figures; to be published in Phys. Rev. B on 1st Sept. Title and Bylines are added to the revised versio

Boeren met quotum

De contingentering van de melkproductie heeft gezorgd voor een ommezwaai in de melkveehouderij. Was het vóór 1983 nog gebruikelijk dat een inkomensverbetering mede tot stand kwam door een uitbreiding van de melkveestapel, vanaf dat moment stond de maximaal te produceren hoeveelheid melk vast. Toen later nog extra werd gekort op het melkquotum, werd duidelijk dat het op peil houden of verbeteren van de arbeidsopbrengst moest worden gerealiseerd door kwaliteitsverbetering en kostenbesparing of het uitbreiden van het bedrijf met een andere inkomensbron

Ligand-hole localization in oxides with unusual valence Fe

Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe4+ → 2Fe3+ + 2Fe5+) in CaCu3Fe4O12 and intersite charge transfer (3Cu2+ + 4Fe3.75+ → 3Cu3+ + 4Fe3+) in LaCu3Fe4O12. Here we report the synthesis of solid solutions of CaCu3Fe4O12 and LaCu3Fe4O12 and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu3Fe4O12 is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu3Fe4O12 is regarded as a Mott transition of the ligand holes

On Optimum Sculling Propulsion

Using a semilinear and two-dimensional theory, the highest possible efficiency is considered for sculling propellers consisting of two wings, the interaction of which is taken into account. The force and pitching moment acting on each wing and the power needed to move the wings are determined. The influence of the variation of a number of parameters is calculated

On Optimum Sculling Propulsion

Using a semilinear and two-dimensional theory, the highest possible efficiency is considered for sculling propellers consisting of two wings, the interaction of which is taken into account. The force and pitching moment acting on each wing and the power needed to move the wings are determined. The influence of the variation of a number of parameters is calculated