Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

An efficient approach to improve the catalytic activity of titanosilicates is introduced. The Doehlert matrix (DM) statistical model was utilized to probe the synthetic parameters of mesoporous titanosilicate microspheres (MTSM), in order to increase their catalytic activity with a minimal number of experiments. Synthesis optimization was carried out by varying two parameters simultaneously: homogenizing temperature and surfactant weight. Thirteen different MTSM samples were synthesized in two sequential ‘matrices’ according to Doehlert conditions and were used to catalyse the epoxidation of cyclohexene with 'tert'-butyl hydroperoxide. The samples (and the corresponding synthesis conditions) with superior catalytic activity in terms of product yield and selectivity were identified. In addition, this approach revealed the limiting values of each synthesis parameter, beyond which the material becomes catalytically ineffective. This study demonstrates that the DM approach can be broadly used as a powerful and time-efficient tool for investigating the optimal synthesis conditions of heterogeneous catalysts

Early holocene human burials from Fa Hien-lena and Kuragala, Sri Lanka

<p>Few human burials from Sri Lankan archaeological contexts have been described. Here we report on the analysis of two early Holocene skeletons, FH8, a young adult female skeleton excavated from Fa Hien-lena and dated to 10,640-10,139 cal BP, and BK1, a middle adult male skeleton excavated at Kuragala and dated to 7,170-6,950 cal BP.  The skeletons are both highly fragmentary, which poses challenges for their thorough analysis. However, this paper describes the archaeological context, mortuary treatment and archaeothanatology of the burials, post-mortem taphonomy of human remains, the osteobiography of both individuals, and some general observations on their morphology relative to one another and a broader range of late Pleistocene and Holocene foragers. The results demonstrate common elements of funerary treatment between these two burials, such as interment on the left side with right hands placed near or over the face. The FH8 individual died at a young age and shows some signs of early childhood stress. Both skeletons show moderate to high degrees of tooth wear for their relative ages, and no evidence for dental disease. The body size estimates of FH8 and BK1 fall in the range that would be expected of tropical or temperate forest foragers, although BK1 has a relatively low body mass relative to stature, which aligns his phenotype with populations of more arid environments. We demonstrate that much can be potentially learned about human populations and prehistoric behaviours from skeletal analyses. </p>Introduction Fa Hien-lena Kuragala Mortuary Context and Archaeothanatology Fa Hien-lena FH8 Kuragala (BK1) Common elements of each burial Skeletal and Dental Inventories and Taphonomy Osteobiographic analyses Morphology and other observations Discussio

Post-tsunami natural regeneration of coastal vegetation in the Hambantota district in south-eastern Sri Lanka

A qualitative rapid survey was conducted in 45 plots distributed in the gentle seashore vegetation andsand dunes (n = 13), coastal scrublands (n = 19), and mangroves (n = 13) along the coastline ofHambantota District, affected by the Indian Ocean tsunami. The objective of the survey was toinvestigate the natural regeneration of coastal vegetation 20 months after the tsunami disturbance21 plant species belonging to 19 families were recorded as the prominent plants regenerating inaffected mangroves, while 16 species in 15 families and 32 species in 23 families were observed asprom inent plants to regenerate in affected areas of the gentle sea-shore vegetation and coastalscrublands respectively.In tsunami affected mangrove stands Acanthus iltctfolius (in 50% of study plots), Achrosticumaureum (40%) and Lumnitzera racemosa (17%) were the dominant species establishing in openmuddy substrates, while Clerodendrum inerme (57%), Lumnitzera racemosa and Excoecariaaga//ocha (29% each) were regenerating in sand deposited in the mangrove patches.Ipomoea pes-caprae (85%), Scaevola taccada and Calotropis gigantea (23% each) were observedas the dominant species re-establishing in the gentle seashore vegetation, while Spinifex littoreusshows a slow rate of regeneration. Most of the destroyed Pandanus odoratissimus bushes facingthe beach are not regenerating. Instead a new row of Pandanus was observed regenerating immediatelybacking the original stands. Prominent species regenerating in coastal scrublands are Crotonbonplandianus and Gymnema sylvestre (37% each), Clerodendrum inerme (16%), Calotropisgigantea (10%) and Crateva adansonii (10%) and saplings of Azadirachta indica and Limoniaacidissitna .Invasive alien plants, mainly Opuntia dillennii have established well and spreading vigorously inaffected coastal scrublands (58%), some study plots of gentle seashore vegetation (31 %) as wellas on sand depositions in the affected mangroves (15%). This species was observed replacing thespaces occupied by destroyed Pandanus odoratissimus bushes and Spinifex littoreus beds.Invasive alien plants such as Prosopis juliflora and Lantana camara were also spreading intsunami disturbed coastal scrublands.

Normalization factors for magnetic relaxation of small particle systems in non-zero magnetic field

We critically discuss relaxation experiments in magnetic systems that can be characterized in terms of an energy barrier distribution, showing that proper normalization of the relaxation data is needed whenever curves corresponding to different temperatures are to be compared. We show how these normalization factors can be obtained from experimental data by using the $T \ln(t/\tau_0)$ scaling method without making any assumptions about the nature of the energy barrier distribution. The validity of the procedure is tested using a ferrofluid of Fe_3O_4 particles.Comment: 5 pages, 6 eps figures added in April 22, to be published in Phys. Rev. B 55 (1 April 1997

SOIL ORGANIC CARBON AS AN INDICATOR OF SOIL QUALITY: A STUDY IN SELECTED TEA PLANTATIONS IN GALLE DISTRICT

Assessment of soil quality in tea lands is important to determine the extent ofdegradation and introduce sustainable land management practices. A study wasundertaken in two stages to assess the suitability of soil organic carbon as a soil qualityindicator in tea lands. Soil samples were taken from 0-15 em tea estates in the GalleDistrict of Sri Lanka. In the first stage, soil samples were depth from selected taken from15 locations under four different field categories viz., under rehabilitation, rehabilitationcompleted, planted tea following rehabilitation and planted tea without rehabilitation.Second stage involved sampling of a tea field under rehabilitation and tea fields ofvarious ages (3, 7 and 11 year old) situated at one location. Soil samples were also takenfrom two forest sites to assess the impact of cultivation on soil organic carbon. Bulkdensity was measured at the field and soil samples were analyzed for total organiccarbon.Results revealed that land management has a significant impact on the quantity of soilcarbon in tea plantations. While rehabilitation process has increased the soil carboncontent, nearly 15% of the added carbon is lost during the initial years after planting tea.Forest soils had a soil organic carbon (in the O-15cmsoil layer) range of 3.39 to 4.42 kgm·2 compared to 3.02 to 3.18 kg m-2 observed in rehabilitated tea lands. The l l-year oldtea field has lost over 40% of its soil organic carbon since rehabilitated and planted withtea. Soil organic carbon can be considered as a robust indicator of soil quality and moreresearch is required to establish critical levels of soil carbon for tea lands in differentstages of the cultivation-rehabilitation cycle

Competition between decay and dissociation of core-excited OCS studied by X-ray scattering

We show the first evidence of dissociation during resonant inelastic soft X-ray scattering. Carbon and oxygen K-shell and sulfur L-shell resonant and non-resonant X-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur, L2,3 -> {\pi}*, {\sigma}* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast the carbon and oxygen spectra show weaker line shape variations and no atomic lines. The spectra are compared to results from ab initio calculations and the discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.Comment: 12 pages, 6 pictures, 2 tables, http://link.aps.org/doi/10.1103/PhysRevA.59.428

Effect of the GaAsP shell on optical properties of self-catalyzed GaAs nanowires grown on silicon

We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on Si substrates using molecular-beam epitaxy. Transmission electron microscopy (TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows domination of the zinc-blende phase. This is further confirmed in optics of single NWs, studied using cw and time-resolved photoluminescence (PL). A detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP capping in suppressing the non-radiative surface states: significant PL enhancement in the core-shell structures exceeding 2000 times at 10K is observed; in uncapped NWs PL is quenched at 60K whereas single core-shell GaAs/GaAsP NWs exhibit bright emission even at room temperature. From analysis of the PL temperature dependence in both types of NW we are able to determine the main carrier escape mechanisms leading to the PL quench

Breakdown of the Independent Particle Approximation in High-Energy Photoionization

The independent particle approximation is shown to break down for the photoionization of both inner and outer nℓ (ℓ\u3e0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed