To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Many of the chemical and physical interactions that take place in natural soil-water systems are strongly influenced by the presence of natural organic polyelectrolytes. The most common of these organic polyelectrolytes is humic acid, which is defined as the alkali soluble, acid insoluble fraction of soil organic matter. Over a hundred years of experimental data have demonstrated that a wide variety of different materials having different physical and chemical properties fit this definition. If we are to make any progress in understanding the role of humic materials in soil-water systems, then we must have a classification system which, as far as possible, provides a unique taxonomic definition for each separate molecular species that falls into the category of humic acid.
A method is presented for the X-ray spectrometric determination of copper, tin, and uranium in a bronze heat-treating material. The method is based on the irradiation of an acid solution of the sample, to which indium and zinc have been added as internal standards. Quantitative determinations of copper and tin (each in the 40 to 60% range) are calculated from the ratios of the CuKα/ZnKα and SnKα/In Kα intensities. Uranium concentration (in the 1 to 10% range) is calculated from the ratio of the ULα/ In Kα intensities, A correction for the interference of the second-order In Kβ1,3 doublet with the first-order ULα peak is described. The over-all limits of error for single determinations at the 95% confidence level are ±0,58% copper, ±0,56% tin, and ±0,31% uranium.
Iron (Fe)-doped zinc oxide (ZnO) thin films were deposited using two techniques: (i) radio-frequency (RF) sputtering of Fe-doped ZnO targets, and (ii) co-sputtering, where ZnO was RF-sputtered and iron was direct-current (DC)-sputtered. The as-deposited films were polycrystalline, with predominant growth along the (002) direction of hexagonal ZnO, and possessed a considerable concentration of oxygen vacancies. From an optoelectronic point of view, the films were highly transparent, with a band gap of 3.25 eV, and had electrical resistivity values in the range of 100–103 Ω cm. To improve the electrical conductivity of the films, they were annealed in a vacuum and in a hydrogen atmosphere. The annealing process did not affect the optical properties of the films. However, there were substantial structural and chemical changes in the films. Moreover, the electrical conductivity of the films was enhanced drastically upon annealing in hydrogen, where the electrical resistivity was reduced to 3.2 × 10−3 Ω cm.
High-resolution optical and NIR observations are used to constrain a dynamical model of the circumnuclear star forming (SF) region in the barred galaxy M100 (NGC 4321). Small leading arms observed in our K-band image of the nuclear region have been reproduced in numerical modeling of M100, a galaxy with a double inner Lindblad resonance (ILR). We also present preliminary optical and NIR observations of NGC 6951: a barred galaxy with circumnuclear SF showing a distinctly different behavior to M100 at 2.2µm.
The Kepler space telescope has proven capable of detecting transits of objects almost as small as the Earth's Moon. Some studies suggest that moons as small as 0.2 Earth masses can be detected in the Kepler data by transit timing variations and transit duration variations of their host planets. If such massive moons exist around giant planets in the stellar habitable zone (HZ), then they could serve as habitats for extraterrestrial life. While earlier studies on exomoon habitability assumed the host planet to be in thermal equilibrium with the absorbed stellar flux, we here extend this concept by including the planetary luminosity from evolutionary shrinking. Our aim is to assess the danger of exomoons to be in a runaway greenhouse state due to extensive heating from the planet. We apply pre-computed evolution tracks for giant planets to calculate the incident planetary radiation on the moon as a function of time. Added to the stellar flux, the total illumination yields constraints on a moon's habitability. Ultimately, we include tidal heating to evaluate a moon's energy budget. We use a semi-analytical formula to parameterize the critical flux for the moon to experience a runaway greenhouse effect. Planetary illumination from a 13-Jupiter-mass planet onto an Earth-sized moon at a distance of ten Jupiter radii can drive a runaway greenhouse state on the moon for about 200 million years (Myr). When stellar illumination equivalent to that received by Earth from the Sun is added, then the runaway greenhouse holds for about 500 Myr. After 1000 Myr, the planet's habitable edge has moved inward to about six Jupiter radii. Exomoons in orbits with eccentricities of 0.1 experience strong tidal heating; they must orbit a 13-Jupiter-mass host beyond 29 or 18 Jupiter radii after 100 Myr (at the inner and outer boundaries of the stellar HZ, respectively), and beyond 13 Jupiter radii (in both cases) after 1000 Myr to be habitable. If a roughly Earth-sized, Earth-mass moon would be detected in orbit around a giant planet, and if the planet–moon duet would orbit in the stellar HZ, then it will be crucial to recover the orbital history of the moon. If, for example, such a moon around a 13-Jupiter-mass planet has been closer than 20 Jupiter radii to its host during the first few hundred million years at least, then it might have lost substantial amounts of its initial water reservoir and be uninhabitable today.
Any attempt to analyze Nigeria’s national oil company (NOC), the Nigerian National Petroleum Corporation (NNPC), must first confront the question of what it really is. Despite its formal organization as a vertically integrated oil company, NNPC is neither a real commercial entity nor a meaningful oil operator. It lacks control over the revenue it generates and thus is unable to set its own strategy. It relies on other firms to perform essentially all the most complex functions that are hallmarks of operating oil companies. Yet unlike some NOCs it also fails to fit the profile of a government agency: its portfolio of activities is too diverse, incoherent, and beyond the reach of government control for it to function as a government policymaking instrument.
Nigeria depends heavily on oil and gas. Hydrocarbon activities provide around 65 percent of total government revenue and 95 percent of export revenues (Nigerian Ministry of Finance and Budget Office of the Federation 2008; EIA 2010a). While Nigeria supplies some LNG to world markets and is starting to export a small amount of gas to Ghana via pipeline, the great majority of the country’s hydrocarbon earnings come from oil. In 2008, Nigeria was the fifth-largest oil exporter and tenth-largest holder of proved oil reserves in the world (EIA 2010b).
The Sociedade Nacional de Combustíveis de Angola, commonly known as Sonangol, is the dominant institution in Angola’s petroleum sector. It has guided the sector through the country’s decades-long civil war as well as during a post-conflict boom marked by massive new investments and production streams that have cemented Angola as one of the world’s most important oil centers. Growing up in the midst of a bloody and destructive contest for power and operating in a state characterized by low human capital and major physical impediments to production efficiency, Sonangol has developed into a singularly effective agent of the government’s interests. To a large degree, Sonangol’s evolution into a successful manager of state petroleum-sector policies has taken place in spite of these obstacles to a traditional national development path, as the company has had to deftly negotiate dangerous operational terrain and generate investment in an environment seen by most as extraordinarily risky. In another sense, though, Sonangol has reached the lofty position it occupies precisely because of these challenges, which have inexorably shaped the company’s outlook, competencies, and room to operate within the Angolan political system.
Since throughout most of its history the company devoted relatively little attention to field operation, its performance cannot be fully measured according to the most traditional metrics used to assess the performance of an oil company. However, I will argue that Sonangol should be viewed as a high-performing national oil company (NOC) because it is particularly skilled at providing what its political masters seek. The company’s primary responsibilities are fourfold. First, and most obviously, the state has given Sonangol primary responsibility for building a dynamic, dependable domestic oil sector. The company has achieved this primarily by establishing and managing contracts with international companies IOCs charged with the administration of technical operations and the mobilization of investments. Throughout its history, Sonangol has provided the conditions in which operational companies could make technical decisions with confidence that political interference would be minimal, which has encouraged foreign operators to make massive long-lived capital investments. This accomplishment is particularly impressive in light of the country’s broader political uncertainty. The company’s leadership in this realm was particularly crucial between its founding in 1976 and the end of the civil war in 2002. During this period, when most sophisticated economic activity in Angola was brought to a standstill by the conflict, hostility to non-oil investors, and destructive socialist policies, Sonangol managed to protect the interests of its international partners and maintain a thriving enclave oil economy. The company’s stewardship role has evolved in the late-war and postwar periods, as it has granted concessions for and managed the operations of ever more complex deep water production.
We describe the operation of lasers having active regions composed of InP self-assembled quantum dots embedded in In0.5Al0.3Ga0.2P grown on GaAs (100) substrates by MOCVD. InP quantum dots grown on In0.5Al0.3Ga0.2P have a high density on the order of about 1-2x10 cm-2 with a dominant size of about 10-15 nm for 7.5 ML growth. These In0.5Al0.3Ga0.2P/InP quantum dots have previously been characterized by atomic-force microscopy, high-resolution transmission electron microscopy, and photoluminescence. We report here the 300K operation of optically pumped red-emitting quantum dots using both double quantum-dot active regions and quantum-dot coupled with InGaP quantum-well active regions. Optically and electrically pumped 300K lasers have been obtained using this active region design; these lasers show improved operation compared to the lasers having QD-based active regions with threshold current densities as low as Jth ∼ 0.5 KA/cm2.
We describe the operation of lasers having active regions composed of InP selfassembled quantum dots embedded in In0.5Al0.3Ga0.2P grown on GaAs (100) substrates by MOCVD. InP quantum dots grown on In0.5Al0.3Ga0.2P have a high density on the order of about 1–2×10 cm−2 with a dominant size of about 10–15 nm for 7.5 ML growth. These In0.5Al0.3Ga0.2P/InP quantum dots have previously been characterized by atomic-force microscopy, high-resolution transmission electron microscopy, and photoluminescence. We report here the 300K operation of optically pumped red-emitting quantum dots using both double quantum-dot active regions and quantum-dot coupled with InGaP quantum-well active regions. Optically and electrically pumped 300K lasers have been obtained using this active region design; these lasers show improved operation compared to the lasers having QD-based active regions with threshold current densities as low as Jth ∼ 0.5 KA/cm2.
Internal photoemission of both electrons and holes is used to investigate the movement of the mobility edges in high quality intrinsic, undoped hy-drogenated amorphous silicon (a-Si:H) with temperature and electrical field. The electron mobility edge is found to move up in energy by ∼40meV between 298K and 120K. On the other hand, the hole mobility edge remains essentially unchanged between 298K and 160K. The injection (and collection) of photoemitted holes is less efficient than that for electrons and in the films studied could not be measured below 160K.
The surface morphology of MBE - grown GaAs(001) has been investigated using scanning tunnelling microscopy (STM) and reflection high - energy electron diffraction (RHEED). STM shows that the missing - dimer - row structure of the (2 × 4)/c(2 × 8) reconstruction consists of rows of clusters of two As dimers separated by rows of two missing dimers, in agreement with previous reports. Layers grown on nominally flat substrates display a multi - level system of terraces elongated along  suggesting that growth occurs primarily by sticking at B - type steps. For films grown under certain growth conditions, B - type steps on vicinal substrates exhibit a dendritic step morphology, which may be an example of a step flow growth instability consistent with limited Ga diffusion over steps.
High molecular weight vinyl esters and carbonates based on oligo(ethylene glycol), oligomeric fatty acids and poly(hexamethylene carbonate), as alternatives for potentially cytotoxic acrylate based monomers have been structured by Additive Manufacturing Technologies (AMTs) like Microstereolithography (μ-SLA), Digital Light Processing (DLP) and Two-Photon Induced Photopolymerization (TPIP). With these techniques feature resolutions down to 10 μm (μ-SLA and DLP) or even 200 nm (TPIP) can be obtained.
This new class of monomers exhibits LC50 values for cytotoxicity up to two orders of magnitude lower than acrylate references. Beside a high reactivity of the resin, the shrinkage and the mechanical properties of the final part material are another essential parameter. Low molecular weight monomers are very reactive and lead to densely cross-linked materials which suffer from high shrinkage and strains within the cured material. Therefore, mixtures of high molecular weight vinyl esters/carbonates with low molecular weight crosslinkers have been evaluated regarding their photoreactivity and mechanical properties.
The accumulation of deleterious mutations in a finite diploid selfing population is investigated. It is shown that the conditions for accumulation are very similar to those for the accumulation of mutations in an asexual population by ‘Muller's ratchet’. The ratchet is likely to operate in both types of population if there is a large class of slightly deleterious mutations.
A positive effect of insulin–glucose–potassium infusion in severe bupivacaine-induced cardiovascular collapse has been described in vivo. It has been speculated that an antagonistic influence of insulin on sodium channel inhibition, transient outward potassium current, calcium-dependent adenosine triphosphatase or even improved myocardial energetics may be responsible for this effect. Using an isolated heart model, we therefore sought to further elucidate insulin effects in l-bupivacaine-induced myocardial depression.
An isolated rat heart constant-pressure perfused, non-recirculating Langendorff preparation was used. Hearts were exposed to l-bupivacaine 5 μg mL−1 and insulin 10 mIU mL−1. Heart rate, systolic pressure, the first derivative of left ventricular pressure (+dP/dt), coronary flow, double product, PR and QRS intervals were recorded. Hearts were freeze-clamped and high-performance liquid chromatography measurement of the total adenine nucleotide pool was performed.
l-Bupivacaine led to a significant decrease in heart rate, +dP/dt, systolic pressure, coronary flow and double product, and to an increase in PR and QRS. Insulin exerted a positive inotropic effect, significantly augmenting +dP/dt and systolic pressure in both l-bupivacaine-treated and control hearts. Heart rate, coronary flow, total adenine nucleotides, PR and QRS were not significantly changed by the insulin intervention.
Insulin did not have a significant effect on total adenine nucleotides in controls and in l-bupivacaine-treated hearts. However, it does exert a positive inotropic action in bupivacaine-induced myocardial depression. We conclude that the positive effect of insulin application lies in positive inotropic action and not in changes in total adenine nucleotides.