Adrian Patrut

A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.)

A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

PFeW11-doped polymer film modified electrodes and their electrocatalytic activity for H2O2 reduction

A study of electrochemical and electrocatalytic properties, toward H 2 O 2 reduction, of the [PFeW 11 O 39 ] -4 polyoxoanion in solution as well as immobilized in partially oxidized polypyrrole (pPy) and in polyvinyl alcohol bearing styrylpyridinium groups (PVA) films is reported. Using cyclic voltammetry at different pH values and scanning rates it was observed that: (i) the two bielectronic waves corresponding to the tungstate-oxo cage are pH-dependent ; (ii) the Fe center of the polyoxoanion has an excellent electrocatalytic effect on H 2 O 2 reduction, giving a catalytic efficiency and an electrode sensitivity, both higher when dissolved than when immobilized onto electrode surface; and (iii) the one-step method used to obtain the pPy-doped film assures a greater amount of immobilized polyoxoanion than the ionic-exchange method used for PVA films. From rotating-disk electrode (RDE) measurements, the polyoxoanion diffusion coefficient was estimated at 4. 1x10 -6 cm 2 s -1 , which agrees to that obtained by cyclic voltammetry, 3.9x10 -6 cm 2 s -1 , and the heterogeneous rate constant was found to vary between 3.5 x 10 -3 and 1.9 x10 -3 cm s -1 at a variation of the electrode potential from 30 to -30 mV vs. SCE. The best amperometric response observed for the PFeW 11 -doped pPy membrane, showed a linear response to H 2 O 2 additions up to 9 mM and a sensitivity of 4.8 mA M -1 H 2 O 2 in the first day of utilization.

Electrochemical investigation of molecular growth of the {Mo57V6} polyoxometalate cluster

Abstract The reduction of the {Mo 57 V 6 } polyoxometalate cluster which shows an interesting molecular growth process, modelling biological molybdenum uptake into a storage protein, was investigated electrochemically. The electrochemical features of the growth process were studied by using cyclic voltammetry, either as such or associated with bulk electrolysis. Resonance Raman spectroscopy was also used to identify the reduction products.

African baobabs with false inner cavities : the radiocarbon investigation of the Lebombo Eco Trail Baobab

The article reports the radiocarbon investigation results of the Lebombo Eco Trail tree, a representative African baobab from Mozambique. Several wood samples collected from the large inner cavity and from the outer part of the tree were investigated by AMS radiocarbon dating. According to dating results, the age values of all samples increase from the sampling point with the distance into the wood. For samples collected from the cavity walls, the increase of age values with the distance into the wood (up to a point of maximum age) represents a major anomaly. The only realistic explanation for this anomaly is that such inner cavities are, in fact, natural empty spaces between several fused stems disposed in a ring-shaped structure. We named them false cavities. Several important differences between normal cavities and false cavities are presented. Eventually, we dated other African baobabs with false inner cavities. We found that this new architecture enables baobabs to reach large sizes and old ages. The radiocarbon date of the oldest sample was 1425 ± 24 BP, which corresponds to a calibrated age of 1355 ± 15 yr. The dating results also show that the Lebombo baobab consists of five fused stems, with ages between 900 and 1400 years; these five stems build the complete ring. The ring and the false cavity closed 800–900 years ago. The results also indicate that the stems stopped growing toward the false cavity over the past 500 years.

Fire history of a giant African baobab evinced by radiocarbon dating

The article reports the first radiocarbon dating of a live African baobab (Adansonia digitata L.), by investigating wood samples collected from 2 inner cavities of the very large 2-stemmed Platland tree of South Africa. Some 16 segments extracted from determined positions of the samples, which correspond to a depth of up to 15-20 cm in the wood, were processed and analyzed by accelerator mass spectrometry (AMS). Calibrated ages of segments are not correlated with their positions in the stems of the tree. Dating results indicate that the segments originate from new growth layers, with a thickness of several centimeters, which cover the original old wood. Four new growth layers were dated before the reference year AD 1950 and 2 layers were dated post-AD 1950, in the post-bomb period. Formation of these layers was triggered by major damage inside the cavities. Fire episodes are the only possible explanation for such successive major wounds over large areas or over the entire area of the inner cavities of the Platland tree, able to trigger regrowth.

Generation of cluster capsules (Ih) from decomposition products of a smaller cluster (Keggin-Td) while surviving ones get encapsulated: species with core–shell topology formed by a fundamental symmetry-driven reaction

A novel and fundamental reaction system of matter following a type of ‘supramolecular Darwinism’ leads to the formation of giant spherical nano-sized cluster capsules as kinetically controlled destination having the highest possible symmetry (Ih) and formed directly from the decomposition products of the well known but less symmetrical Keggin anions (Td) in aqueous medium in the presence of FeIII–acting as a type of environmental influence–under conditions where Keggin anions are known to be extremely stable; remarkably the remaining non-decomposed Keggin anions finally get (non-covalently) encapsulated protected by the formed spherical capsules of the new supramolecular compound [PMo12O40 ⊂ {(MoVI)MoVI5}12 FeIII30O252- (H2O)102(MeCO2)15]· xH2O 1 1a ·xH2O (x ≈ 120).

Age and Growth Rate Dynamics of an Old African Baobab Determined by Radiocarbon Dating

In 2008, a large African baobab (Adansonia digitata L.) from Makulu Makete, South Africa, split vertically into 2 sections, revealing a large enclosed cavity. Several wood samples collected from the cavity were processed and radiocarbon dated by accelerator mass spectrometry (AMS) for determining the age and growth rate dynamics of the tree. The 14C date of the oldest sample was found to be of 1016 ± 22 BP, which corresponds to a calibrated age of 1000 ± 15 yr. Thus, the Makulu Makete tree, which eventually collapsed to the ground and died, becomes the second oldest African baobab dated accurately to at least 1000 yr. The conventional growth rate of the trunk, estimated by the radial increase, declined gradually over its life cycle. However, the growth rate expressed more adequately by the cross-sectional area increase and by the volume increase accelerated up to the age of 650 yr and remained almost constant over the past 450 yr.

A Regional Stable Carbon Isotope Dendro-Climatology from the South African Summer Rainfall Area.

Carbon isotope analysis of four baobab (Adansonia digitata L.) trees from the Pafuri region of South Africa yielded a 1000-year proxy rainfall record. The Pafuri record age model was based on 17 radiocarbon dates, cross correlation of the climate record, and ring structures that were presumed to be annual for two of the trees. Here we present the analysis of five additional baobabs from the Mapungubwe region, approximately 200km west of Pafuri. The Mapungubwe chronology demonstrates that ring structures are not necessarily annually formed, and accordingly the Pafuri chronology is revised. Changes in intrinsic water-use efficiency indicate an active response by the trees to elevated atmospheric CO2, but this has little effect on the environmental signal. The revised Pafuri record, and the new Mapungubwe record correlate significantly with local rainfall. Both records confirm that the Medieval Warm Period was substantially wetter than present, and the Little Ice Age was the driest period in the last 1000 years. Although Mapungubwe is generally drier than Pafuri, both regions experience elevated rainfall peaking between AD 1570 and AD 1620 after which dry conditions persist in the Mapungubwe area until about AD 1840. Differences between the two records correlate with Agulhas Current sea-surface temperature variations suggesting east/west displacement of the temperate tropical trough system as an underlying mechanism. The Pafuri and Mapungubwe records are combined to provide a regional climate proxy record for the northern summer rainfall area of southern Africa.

Nonobatteries: Decreasing Size Power Sources for Growing Technologies

Increasing need for portable nanoelectronic devices triggers the development of dimensionally small batteries. Nanobatteries are being designed for specific applications, including computer chips, micro-electromechanical systems (such as micro-actuators, micro-instruments, or micro-robots), or nanostructured medical devices. As the size of power source should be commensurate with the device it powers, battery miniaturization is an important design challenge faced by the battery community. Further advantages of such minute batteries include the long shelf life and a quick ramp up to full power. Hence, design may enable the nanobattery to stay dormant for several years, and then getting reactivated, so that it can provide immediately a burst of high energy.

Searching for the Oldest Baobab of Madagascar: Radiocarbon Investigation of Large Adansonia rubrostipa Trees

We extended our research on the architecture, growth and age of trees belonging to the genus Adansonia, by starting to investigate large individuals of the most widespread Malagasy species. Our research also intends to identify the oldest baobabs of Madagascar. Here we present results of the radiocarbon investigation of the two most representative Adansonia rubrostipa (fony baobab) specimens, which are located in south-western Madagascar, in the Tsimanampetsotse National Park. We found that the fony baobab called “Grandmother” consists of 3 perfectly fused stems of different ages. The radiocarbon date of the oldest sample was found to be 1136 ± 16 BP. We estimated that the oldest part of this tree, which is mainly hollow, has an age close to 1,600 yr. This value is comparable to the age of the oldest Adansonia digitata (African baobab) specimens. By its age, the Grandmother is a major candidate for the oldest baobab of Madagascar. The second investigated specimen, called the “polygamous baobab”, consists of 6 partially fused stems of different ages. According to dating results, this fony baobab is 1,000 yr old. This research is the first investigation of the structure and age of Malagasy baobabs.