bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computational Methods: Heteropolyoxoanions
Authors: Poblet Josep M. , López Xavier 
Published: December 2011

Abstract

Possibly no other class of organic or inorganic compounds displays more versatility than polyoxometalates (POMs) (or polyoxoanions) with respect to electronic and molecular structures, properties, and applications. POMs attract the attention of scientists from many fields, such as catalysis, materials science, and medicine. More recently, POMs have also attracted the interest of computational chemists. This article describes some of the most relevant electronic properties for several of the most representative heteropolyoxoanions, such as the so‐called Keggin [XM
12
O
40
]

n
−

, Dawson [X
2
M
18
O
62
]

m
−

, and Preyssler [XP
5
W
30
O
110
]

q
−

anions. Density functional theory (DFT) methods have proven to be useful for the rationalization of many properties of POMs. In this article we illustrate some of them, often using the simple language of molecular orbitals.
Nuclear Magnetic Resonance (NMR) Parameters of Transition Metal Complexes: Methods and Applications
Authors: Kaupp Martin , Bühl Michael 
Published: December 2011

AbstractThis article provides an overview of first‐principle computations targeted at nuclear magnetic resonance (NMR) properties of transition‐metal complexes. Recent methodological developments and illustrative applications are highlighted, all of which are rooted in density functional theory (DFT). Special attention is called to chemical applications of such NMR computations, ranging from structure elucidation of metalloenzymes to detailed interpretation of NMR spectra of paramagnetic compounds.
Noble Gas Compounds: Reliable Computational Methods
Authors: Dixon David A. 
Published: December 2011

AbstractBecause of the general interest in the bonding in noble gas (Ng) compounds and the lack of experimental data coupled with large discrepancies, reliable theoretical calculations are very important for the prediction of their structures and thermodynamics. We describe an approach for the prediction of heats of formation to ±1 kcal mol−1(chemical accuracy) based on molecular orbital theory level using coupled cluster (CCSD(T), coupled cluster with single and double excitations plus a perturbative triples correction) theory extrapolated to the complete basis set (CBS) limit with the correlation‐consistent basis sets including relativistic effective core potentials (RECPs). Additional corrections to the valence correlation energies include core–valence (CV) correlation, molecular scalar relativistic corrections, atomic spin–orbit corrections, and zero‐point vibrational energies. Applications of this approach for the determination of the structure of XeF6, the heats of formation of the xenon fluorides and krypton fluorides, and the methyl cation affinities (MCAs) of the Ngs are described. XeF6is predicted to have C3vsymmetry only at the highest computational levels. The experimental heats of formation of XeF4and XeF6require significant revision. The predicted heats of formation for KrF4and KrF6show that it will be extremely difficult to synthesize these compounds. The calculations show that there are serious issues with the experimental MCAs of all of the Ngs except for Ne.
Spin‐Orbit Coupling: Effects in Heavy Element Chemistry
Authors: Kaltsoyannis Nikolas 
Published: December 2011

Abstract

Starting from the premise that the chemical consequences of scalar relativistic effects are by now largely understood, and may be incorporated more or less routinely into quantum chemical calculations, this contribution focuses on the historically less widely investigated part that spin‐orbit coupling plays in heavy element electronic structure. The effects of relativity are first summarized, followed by a discussion of the principal approaches to the calculation of molecular electronic structure and how relativistic effects may be incorporated into them. Two approaches for the calculation of spin‐orbit coupling effects are then presented; namely, the spin‐orbit coupled time‐dependent density functional theory technique of Wang
et al
. [Wang, F.; Ziegler, T.; van Lenthe, E.; van Gisbergen, S.; Baerends, E. J.
J. Chem. Phys.
2005
,
122
, 204103] and the spin‐orbit restricted active space state interaction method of Roos and coworkers [Roos, B. O.; Malmqvist, P. A.
Phys. Chem. Chem. Phys.
2004
,
6
, 2919]. Recent applications of both approaches to the electronic structure of p, d, and f block systems are then discussed, with emphasis on the improved understanding and agreement with experiment that these methods yield.
Computational Studies: Chemical Evolution of Metal Sites
Authors: Jensen Kasper P. 
Published: December 2011

Abstract

The structures of naturally occurring metal sites have evolved over hundreds of millions of years to perform complex functions under very specific biological and nonbiological constraints. Modern computational chemistry has now reached a level of accuracy that allows us to study the full significance of molecular evolution by systematically altering the components of the native metal sites and by monitoring the resulting effects on relevant computed properties. This procedure, referred to as
computational chemical evolution
, not only explains the use of certain metal ions as opposed to others in metalloproteins, but also lends promise to the design of new multifunctional metal sites that are no longer restricted by biological constraints, to be used in medicine and catalysis.
Tritium: Radionuclide
Authors: Galeriu Dan , Melintescu Anca 
Published: December 2011

AbstractTritium is the heavy isotope of hydrogen and can therefore participate directly in a wide range of biological functions. It is formed through natural processes but is also generated through human activity in nuclear reactors, fusion, and weapons. In addition, it has some commercial applications. Its occurrence, chemical and physical properties, and speciation are unique in comparison to other radionuclides. This article summarizes what is currently known about tritium with regard to the isotope's occurrence, chemistry, speciation, remediation, separation, and the analytical techniques used for its detection and quantification. The potential impact of tritium on human health is also described.
Cesium: Radionuclide
Authors: Lima Enrique 
Published: December 2011

Abstract

Radionuclides of cesium are generated mainly from nuclear fission. Many cesium radionuclides are known, but
134
Cs and
137
Cs are of the greatest concern because of their radiological properties. Cesium is present in polluted effluents of nuclear power plants. Gas, liquid, and solid wastes contaminated with cesium can be found but aqueous effluents, where cesium is present in the cationic form, are the most common. These cations can reach agricultural fields due to their high affinity for clays. Thus, cesium radionuclides can be incorporated into the food chain, and ultimately transported to human beings.
Strontium: Radionuclides
Authors: Guillén Francisco Javier , Baeza Antonio , Salas Alejandro 
Published: December 2011

AbstractStrontium has several radioactive isotopes, with90Sr being the most important in the environment. This radionuclide dispersed worldwide as a consequence of the atmospheric nuclear weapon tests in the 1960s, and is locally enhanced owing to the accidents involving radioactive material.90Sr is a pure β‐emitter and it may be detected by several detection techniques (gas‐flow proportional, liquid scintillation, Cerenkov counting, and ICP‐MS), after an appropriate radiochemical separation. The environmental behavior of radiostrontium is governed by its chemical similarities to calcium. It is usually associated with the mobile and bioavailable fractions in soils, and with the low MW fraction in aquatic ecosystems. The potential human exposure to radiostrontium is mainly due to the ingestion of food, milk and cereals being the two major sources. This exposure can be reduced to some extent by the addition of calcium fertilizers to minimize the soil‐to‐plant transfer of radiostrontium, and by increasing cattle calcium intake to decrease the90Sr content in milk.
Radium: Radionuclides
Authors: Vandenhove Hildegarde , Verrezen Freddy , Landa Edward R. 
Published: December 2011

AbstractThis article describes (1) the occurrence, chemistry, and bioavailability of radium (Ra) in terrestrial and aquatic environments, and its analysis in environmental samples, (2) the nature of naturally occurring radioactive materials (NORM) and their role in radium‐contamination scenarios, and (3) the geochemical processes and remedial measures associated with radium‐contaminated water and soil. Radium is the heaviest of the Group II, alkaline earth metals. Radium is exclusively divalent and its chemistry resembles that of barium. Radium has a limited environmental mobility due to sorption (e.g., by hydrous oxides of Fe, Mn, and Al) and coprecipitation reactions (e.g., with barite).All isotopes of radium (atomic number 88) are radioactive. The most important radium isotopes are226Ra (half life 1600 years) and228Ra (half life 5.7 years), decay products of, respectively, the238U and the232Th series. As members of natural radioactive decay series, these radium isotopes are found in uranium‐ and thorium‐bearing minerals. Concentrations of uranium and thorium in rocks can range from those of ore‐grade deposits to the trace levels typical of common rock‐forming minerals.In uncontaminated surface waters, radium content is generally low and within a narrow range (0.5–20 mBq l−1). Radium in groundwater is highly variable (<0.52–55 000 mBq l−1) and can arise from natural sources, resulting from the interaction of groundwater with radium‐bearing materials or indirectly from man's exploitation of the radioactive minerals of uranium and thorium. The major challenge associated with many NORM‐containing residues or NORM‐contaminated sites is the larger volumes of material and the relatively low specific activities.
Phosphorus: Radionuclides
Authors: Kim Kibong , Churchill David G. 
Published: December 2011

Abstract32P and33P are important radionuclides of phosphorus with half‐lives of 14.3 and 25.3 days, respectively, and which decay via β−emission. These isotopes (of 23 known) have anthropogenic sources and are prepared by the enrichment of sulfur. The radionuclides are used in tracer studies primarily as phosphate, or other common phosphate forms such as “phosphate rock” or ortho‐phosphoric acid. Various labeling and therapeutic studies have been performed in the fields of biology, botany, and in clinical medicine and are mentioned herein. Radioisotopes of phosphorus can be detected by liquid scintillation counting. There is, however, limited knowledge about remediation as32P and33P are short‐lived.
Thallium: Radionuclides
Authors: Wehmschulte Rudolf J. 
Published: December 2011

AbstractOf the 35 radioactive isotopes, only201Tl and204Tl with half‐lives of 73 h and 3.78 y are applied in medicine and materials analysis. Both are usually generated in situ on site in small amounts just prior to use in cyclotrons. Owing to the small amounts applied and generated, they are of minor concern as environmental radionuclides despite their high mobility under physiological and environmental conditions.
Lead: Radionuclides
Authors: Sabuti Asnor Azrin , Rahim Mohamed Che Abd 
Published: December 2011

AbstractLead (Pb) is a highly toxic and radiogenic metal. It occurs naturally in the Earth, but is not very abundant. Even so, lead isotopes have been very useful ss tracers in glaciology, limnology, oceanography, and in atmospheric studies of global (transboundary) and local pollution. The dominant radioisotope of lead is210Pb, a very ubiquitous secondary radionuclide that is formed from238U decay via222Rn.210Pb originates from the Earth's crust, through the decay of226Ra. There are many factors that complicate the behavior of210Pb in soil, air, and water. Owing to these, a great deal of effort has been devoted to the quantitative determination of lead isotopes over the past few years. The separation and counting techniques for lead need to be rapid, convenient, and precise, and utilize very small amounts of material. Humans are exposed to lead through ingestion and inhalation, and it is stored for long periods of time mainly in bone and teeth. Thus, more studies on environmental exposures to lead need to be conducted, particularly for air monitoring, dust, water, and soil sampling, and lead‐based product sampling.
Technetium: Radionuclides
Authors: Hu Qinhong 
Published: December 2011

AbstractThis article provides a review of Tc with regards to the basic chemistry, occurrence, speciation, separation, analysis, fate, and transport. Environmental99Tc originates from the nuclear fuel cycle, with most of the isotope (>90%) discharged from reprocessing plants in Europe. It has been recognized that99Tc is a very important dose contributor in risk assessment, because of its high abundance, long half‐lives, and presumably high mobility. Essentially all the technetium on the Earth has been created by human activities involving fissionable materials. Among 11 metastates of technetium,97mTc is the most stable, with a half‐life of 90.1 days. The common oxidation states of technetium include 0, +2, +4, +5, +6, and +7. Depending upon the redox conditions, Tc primarily exists in two (+7 and +4) stable oxidation states in the subsurface. Under oxidizing conditions, technetium (VII) will exist as the mobile pertechnetate ion (TcO4−) in aqueous solution. Reduction of TcO4−to Tc(IV) species (TcO2 · nH2O) will decrease Tc mobility, because Tc(IV) species are strongly retarded from mineral sorption and/or precipitation. ICP‐MS is the common analytical method used to quantify Tc levels.
Europium: Radionuclides
Authors: Wang Xiangke , Li Jiaxing 
Published: December 2011

Abstract
The physicochemical behavior of europium in the environment and the speciation of europium under different experimental conditions are described. The behavior and speciation of Eu(III) in the environment are dominated by the surface properties of solid particles, presence of natural organic and inorganic materials, pH values of the systems, and other parameters. Europium can be characterized and analyzed by spectrophotometry, polarography, atomic adsorption spectrometry (AAS), atomic emission spectrometry (AES), atomic fluorescence spectrometry (AFS), atom mass spectrometry (AMS), X‐ray fluorescence spectrometry (XFS), neutron activation analysis (NAA), and liquid scintillation counting (LSC).
A
tlantic
O
cean: Radionuclides
Authors: Kershaw Peter 
Published: December 2011

Abstract
This article summarizes the main sources and the fate of radionuclides in the Atlantic Ocean, resulting primarily from human activity. This covers direct and indirect sources of artificial radionuclides due to global fallout from weapons testing, controlled releases from nuclear establishments, the deliberate disposal of radioactive waste, accidental inputs, and the presence of naturally occurring radionuclides, sometimes in enhanced quantities due to human activities. The distribution and behavior of radionuclides in seawater, sediments, and biota are described, being a consequence of both the nature of the source term and the fundamental properties of the radionuclides (chemical behavior, half‐life). Finally, the article considers the radiological consequences due to the principal sources responsible for the maximum dose to the human population: nuclear fuel reprocessing and naturally occurring radionuclides.
Mediterranean Sea: Radionuclides
Authors: Delfanti Roberta , Papucci Carlo 
Published: December 2011

AbstractThe main sources of anthropogenic radioactivity in the Mediterranean Sea are fallout from atmospheric nuclear weapon testing and from the Chernobyl accident in 1986, while the releases from the nuclear industry are small. Consequently, the present radionuclide levels in the marine environment are of no concern from the radiological point of view. However, the Mediterranean Sea is an ideal environment to show how both coastal and open‐sea processes act to redistribute radionuclides in the different compartments of the marine environment. In fact, the Mediterranean Sea is considered a miniature ocean, where all the processes characterizing the global ocean take place on smaller space and timescales. For these reasons, in the past decades it had largely been used as a “laboratory basin” for process studies. In this framework, anthropogenic and natural radionuclides were often measured to be used as tracers of water mass dynamics, transit and renewal times, particle dynamics, sediment accumulation, etc. In this article, we first briefly describe the physical and biogeochemical characteristics of the Mediterranean Sea. After reviewing and quantifying the sources of radioactivity, we mainly focus on two radionuclides: (i)137Cs: conservative in the open sea, the most abundant anthropogenic radionuclide, and, among these, the main contributor to radioactive dose to the population, and (ii) the very long‐lived239,240Pu: nonconservative and the most abundant among transuranics. We describe their distribution and time trend in seawater, sediments, and biota, define their budgets in the basin, quantify the exchanges at the Gibraltar and Turkish Straits, and indicate future trends. We also report levels and distributions of selected natural radionuclides: (i)238U, with234Th as the main tracer for particle dynamics and whose concentration in the Mediterranean slightly differs from that in the oceans, and (ii)210Po, which is efficiently accumulated by marine organisms and is the main contributor to radioactive dose to the population. Finally, we identify topics for future research, mainly related to the application of nuclear techniques to the study of oceanographic processes.
Cesium: Global Ocean Distribution
Authors: Inomata Yayoi 
Published: December 2011

AbstractSince the 1950s Cesium‐137(137Cs) concentrations in the surface waters of the global ocean have been extensively measured in numerous studies. This article, based on the analysis of the137Cs concentrations in the HAM‐global database, summarizes the results of spatial and temporal variations in137Cs concentrations in the surface waters (0–10 m) of the global ocean for the period 1957 to 2005.137Cs in the surface waters of the North Pacific Ocean and North Atlantic Ocean has mainly originated from the nuclear weapon testing global fallout in the late 1950s and early 1960s. In the 1970s and 1980s, the discharge from the nuclear fuel reprocessing plants was the dominant source for the North Atlantic Ocean and its northeast marginal seas. The seas that were largely affected by the fallout of the Chernobyl accident in 1986 were the Baltic, the Black, and the Mediterranean Seas. In the 1990s and 2000s, the137Cs concentrations were decreasing in the global ocean. During this time, the difference in concentrations in the various seas reduced when compared with those in the 1960s and 1970s. In 2005, the most anthropogenic137Cs contaminated area of the global ocean was Baltic Sea, whereas the most undisturbed area was the Antarctic Ocean.137Cs in the surface water had an almost homogeneous distribution in the North Pacific, the equatorial region in the Pacific, and the Indian Ocean. The fact that the apparent‐half residence time (the decreasing rate of137Cs concentration) is almost equal in these regions suggests that the137Cs injected into the western North Pacific Ocean by global fallout was transported to the subtropics and tropics through oceanographic processes. Part of137Cs was recirculated in the Pacific Ocean, and the rest was transported into the Indian Ocean via the Indonesian through flow.
Hydrogen Production from Renewables
Authors: Navarro Rufino M. , Sanchez‐Sanchez M. Cruz , Alvarez‐Galvan M. Consuelo , Fierro Jose Luis G. , Al‐Zaharani Saeed M. 
Published: December 2011

AbstractHydrogen is considered to be critical for energy and environmental sustainability. However, as hydrogen is currently produced from fossil fuels, it emits large amounts of carbon dioxide along the reforming steps. The technical challenges to achieve a stable hydrogen economy include improving process efficiencies, lowering the cost of production, and harnessing renewable sources for hydrogen production. Lignocellulosic biomass is one of the most abundant forms of renewable resources. When this precursor is used, virtually no net greenhouse gas emissions result because a natural cycle is maintained, in which carbon is extracted from the atmosphere during plant growth and is released during hydrogen production. This article focuses on recent developments in biomass and biomass‐derived product conversion to H2. The second option explored here is the conversion of solar energy into hydrogen via water‐splitting processes assisted by two‐step metal‐oxide thermochemical cycles or by photosemiconductor catalysts. The conversion of solar energy into a clean fuel (H2) is the most promising technology for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. Undoubtedly, the conversion of solar energy into H2is one of the greatest challenges scientists are facing in the twenty first century. A survey is presented of the advances made in the development of metal oxide redox pairs since the pioneering work by Nakamura in 1977 and in the development of photocatalysts for water splitting under visible light since the first work of Fujishima and Honda in 1972. The very high thermal reduction temperature used for the metal oxide redox pairs developed until now leads to severe sintering, melting, and vaporization of materials, decreasing the efficiency and durability in the cyclic operation. Consequently, the application of material science and engineering to the development of materials with lower reduction temperature and high water‐splitting ability is still a challenge in this scientific area and an overview of the progress is provided in this article. On the other hand, there are still major challenges in the development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy. An overview is provided in this article of research strategies and approaches adopted in the search for photocatalysts for water splitting under visible light (new photocatalyst materials and the control of the synthesis of materials for customizing the crystallinity, electronic structure, and morphology of catalysts at nanometric scale).
Fuel Cells: Intermediate Temperature Solid Oxides
Authors: Atkinson Alan , Kilner John , Skinner Stephen , Brandon Nigel P. , Brett Dan J. L. 
Published: December 2011

Abstract
Fuel cells are electrochemical energy conversion devices that convert chemical energy in fuels directly into electrical energy, without the process of combustion. As a result, they are not constrained by the same thermodynamic limitations as those of heat engines and therefore have the potential to achieve higher efficiencies. High‐temperature solid oxide fuel cells (HT‐SOFCs) operate up to 1000 °C. These fuel cells achieve very high system efficiencies when integrated with gas turbines for large‐scale stationary applications. However, operation at such high temperatures means that the components of the stack need to be predominantly ceramic, in addition to expensive high‐temperature metal alloys. For smaller scale applications, there is a trend to move to lower operating temperatures, into the so‐called intermediate‐temperature (IT) range of 500–750 °C. In doing so, a wider range of construction materials can be used, offering reduced system cost and, in principle, improved performance durability. In this article, we introduce the IT‐SOFC and explain their main operational advantages. We also focus on the combination of inorganic materials and processing routes that go to make reduced temperature SOFC operation possible.