Mechanism of magnetism in stacked nanographite: Theoretical study

Nanographite systems, where graphene sheets of the orders of the nanometer size are stacked, show novel magnetic properties, such as, spin-glass like behaviors and the change of ESR line widths in the course of gas adsorptions. We theoretically investigate stacking effects in the zigzag nanographite sheets by using a tight binding model with the Hubbard-like onsite interactions. We find a remarkable difference in the magnetic properties between the simple A-A and A-B type stackings. For the simple stacking, there are not magnetic solutions. For the A-B stacking, we find antiferromagnetic solutions for strong onsite repulsions. The local magnetic moments tend to exist at the edge sites in each layer due to the large amplitude of wavefunctions at these sites. Relations with experiments are discussed.Comment: PACS numbers: 75.30.-m, 75.70.Cn, 75.10.Lp, 75.40.Mg; E-mail: [email protected]; http://www.etl.go.jp/~harigaya/welcome_E.htm

Validated Radiometric Mapping in 2012 of Areas in Japan Affected by the Fukushima-Daiichi Nuclear Accident.

On March 11 2011 the north-eastern region of Japan was hit by a magnitude 9 earthquake, which occurred underneath the sea-bed 70 km east of the Oshika peninsula in Tohoku. The north-eastern shore of Honshu was hit by a tsunami resulting from this earthquake. As a consequence, reactors 1-4 at the nuclear power station Fukushima-Daiichi suffered a completed loss of power and cooling causing a partial core meltdown in units 1, 2 and 3 followed by a series of explosions and the release of large quantities of radioactivity into the environment. The accident was rated level 7 (the highest level) on the International Nuclear Event Scale. While most of the emissions were driven towards the Pacific Ocean, a significant amount of radioactive material was deposited onto the Japanese land-mass, resulting in enhanced localised radiation exposure. This report covers measurements and detailed radiation maps conducted by a UK University team working with Japanese colleagues during a series of visits in 2012. They have been presented and shared locally in Japan at time of acquisition. Since then the data have been cross-validated relative to soil samples from a reference site established at the University of Fukushima, and analysed independently in the UK and in Japan. This report provides detailed descriptions of the data sets, validated radiometric maps for 134Cs, 137Cs and the overall gamma dose rates, together with a full account of the establishment of the calibration site. The work reported here demonstrates the utility of detailed radiometric maps in helping to understand the distribution of radionuclides in complex environmental systems. This information is potentially of use to help avoid unnecessary external radiation exposure in the outdoor environment, to help to visualise and target areas for remediation, to evaluate the effectiveness of clean-up and soil removal activities, to examine uptake of radioactivity from the environment through agricultural systems, and to monitor redistribution over time of the activity in the environment. The report includes full copies of digital data sets for the demonstration surveys. Radiometric methods provide means of measuring radioactivity with recognised roles in nuclear emergency response, and environmental applications. In the aftermath of nuclear accidents they are crucial to evaluate the environmental impact of the accident and guide remediation measures. The Scottish Universities Environmental Research Centre (SUERC) is a research centre attached to the University of Glasgow with extensive experience of radiometric mapping using airborne and ground based systems, conducting most of the UK post-Chernobyl radiation mapping using airborne systems and coordinating European projects to harmonise and cross-calibrate systems for nuclear emergency response purposes. In the early stages of major accidents the most pressing needs are for rapid, large scale, information. Airborne surveys of the affected area were conducted initially by a joint US/Japanese team and later on by The Ministry of Education Science and Technology (MEXT) and the Japanese Atomic Energy Agency (JAEA), eventually providing national scale radiation maps with a spatial resolution of several hundred meters. In later stages of accident recovery there are increasing needs for more detailed spatial information and increasing requirements for objective, traceable and cross validated analysis. Systems for this work need to be mobile, preferably portable, efficient, robust and well calibrated, providing detailed real time information directly on location. The SUERC Portable Gamma Spectrometry system fulfils these criteria. It provides a spatial resolution of better than 10 m for mapped data and allows a real time identification of spatial features down to 10-20 cm. In the work reported here, calibration sites have been established in Fukushima at the campus of Fukushima University and the Fukushima Prefecture Fruit Tree Research Institute to provide objective and internationally traceable validation of ground based instruments. High resolution HPGe spectrometry of soil samples conducted at laboratories at Fukushima University and SUERC was used for validation of the field instrument. Values of 137Cs activity concentration measured by the two laboratories were in full agreement to high precision. Agreement for the 134Cs activity concentration values was within 5-10%. The soil samples used in this process were analysed as a function of depth, revealing that while the majority of activity was retained in near surface layers, a small component of approximately 1% of the total activity appears to have migrated more rapidly to greater depths. This suggests complex transport behaviour in the soil columns which should be investigated further. The calibration sites are open for future use. These data establish a traceable record between local facilities and internationally acknowledged standards for future use. Deployment of the SUERC system in vehicles has demonstrated the ability of relatively small detectors to measure regional scale deposition patterns over a wide range of radioactivity levels, varying from 10,000 Bq per square meter up to more than 10 million Bq per square meter. These activity levels are broadly consistent with the national scale airborne maps for the study areas, but the ground based maps provide very high level of local detail, which allow small scale changes to be readily observed and related to the local soils, land cover and built environment. Areas covered in two surveys in March and July 2012, respectively, cover parts of the Fukushima Prefecture including parts of the evacuation and exclusion zones as well as areas directly affected by the 2011 tsunami. Short backpack surveys in urban areas associated with the car trips were also conducted e.g. in Fukushima City (in the heart of the prefecture), Ōkuma (within 3 km of the Fukushima Daichi reactors), Minami-Daira and Kawauchi-mura (within the initial evacuation zones), demonstrate the versatility of a system which can be rapidly moved from a vehicle to backpack where further detailed information is needed. With a fully spectrometric system as used in this study, it is possible to identify specific radioactive isotopes and to quantify the activity concentrations of natural and artificial sources spanning many orders of magnitude, from less than 10 kBq m-2 to above 10 MBq m-2 for radiocaesium. This information has been used to estimate the contribution to the dose rate from different sources, so that a comparison between the contributions from naturally occurring radioactive materials (not affected by the accident) and the different radiocaesium isotopes present following the accident can be readily made. These data provide vital information to the local population and emergency services in guiding remediation efforts, and also over the course of time, in observing the extent to which weathering and radioactivity decay processed are gradually reducing the relative contributions from the accident. In the long term it is hoped that this type of representation will help put the accident contributions into perspective, and to register improvements with time which may help to establish increased confidence in affected areas. In urbanised areas backpack systems provide the means of producing detailed surveys in locations where people spend their time. Surveys conducted of Fukushima University and Fukushima Iizaka have demonstrated the ability of detailed radiometric mapping to identify locations with highly varying levels of contamination, from more highly contaminated areas around drain pipes to the relatively low levels of contamination on roads and other hard surfaces where rain and snow melt have removed deposited activity. The effectiveness of the remediation work conducted on the University campus was evident, showing the ability of radiometric surveys to demonstrate the effectiveness of remediation and to identify where remaining activity is located. The remediation methods employed resulted in a three- to fourfold reduction in dose rate compared to untreated areas. Remediation efforts in orchards or woodland are particularly challenging. Given the economic importance of agriculture in the Fukushima area and the possible pathways from contaminated produce into the human body, a precise evaluation of the local radiation risk is of prime importance. The SUERC system has been demonstrated in orchards at the Fukushima Prefecture Fruit Tree Research Institute, and at other orchards in the Prefecture. Work has also been undertaken with agricultural research institutions at Tsukuba, Ibaraki Prefecture. The comparison of measurements taken at these same sites over the time of a year show a decrease in activity following the half-life of the radioisotopes deposited, superimposed by environmental factors like precipitation, illustrating self-remediation. Ongoing work on these sites will allow an assessment of transfer of activity from to the fruit, and the impact of measures to remediate the orchards or reduce uptake of activity in the fruit, and the evaluation of external doses to workers in the orchards. The data collected during this work contain the specific activity per isotope at a given surveyed location and at a given moment in time. The data accompanying this report are transparent, open and independently validated. They are made available for reference purposes and further utilisation. The work presented here highlights many of the difficult challenges ahead in the monitoring and remediation effort in the area affected by the accident in the Fukushima Dai-ichi nuclear power plant. It demonstrates the capabilities and methods at the disposal of the international community in aiding the Japanese efforts, demonstrating the value of international collaboration in helping to address some of the difficult problems associated with recovery from a serious nuclear accident. It is hoped that these data, and the methods which they demonstrate, will contribute, together with future work, to increased understanding of the environmental impacts of the accident, and that future cooperative work involving Japanese and international teams will contribute to recovery and restoration of confidence in affected areas and communities

Magnetic Structure of Nano-Graphite Moebius Ribbon

We consider the electronic and magnetic properties of nanographite ribbon with zigzag edges under the periodic or Moebius boundary conditions. The zigzag nano-graphite ribbons possess edge localized states at the Fermi level which cause a ferrimagnetic spin polarization localized at the edge sites even in the very weak Coulomb interaction. The imposition of the Moebius boundary condition makes the system non-AB-bipartite lattice, and depress the spin polarization, resulting in the formation of a magnetic domain wall. The width of the magnetic domain depends on the Coulomb interaction and narrows with increasing U/t.Comment: 4 pages; 6 figures; published at J. Phys. Soc. Jpn. Vol. 72 No. 5 pp. 998-1001 (2003

An improved competitive inhibition enzymatic immunoassay method for tetrodotoxin quantification

Quantifying tetrodotoxin (TTX) has been a challenge in both ecological and medical research due to the cost, time and training required of most quantification techniques. Here we present a modified Competitive Inhibition Enzymatic Immunoassay for the quantification of TTX, and to aid researchers in the optimization of this technique for widespread use with a high degree of accuracy and repeatability

Paralytic shellfish poisoning (PSP) toxin binders for optical biosensor technology: problems and possibilities for the future: a review

This review examines the developments in optical biosensor technology, which uses the phenomenon of surface plasmon resonance, for the detection of paralytic shellfish poisoning (PSP) toxins. Optical biosensor technology measures the competitive biomolecular interaction of a specific biological recognition element or binder with a target toxin immobilised onto a sensor chip surface against toxin in a sample. Different binders such as receptors and antibodies previously employed in functional and immunological assays have been assessed. Highlighted are the difficulties in detecting this range of low molecular weight toxins, with analogues differing at four chemical substitution sites, using a single binder. The complications that arise with the toxicity factors of each toxin relative to the parent compound, saxitoxin, for the measurement of total toxicity relative to the mouse bioassay are also considered. For antibodies, the cross-reactivity profile does not always correlate to toxic potency, but rather to the toxin structure to which it was produced. Restrictions and availability of the toxins makes alternative chemical strategies for the synthesis of protein conjugate derivatives for antibody production a difficult task. However, when two antibodies with different cross-reactivity profiles are employed, with a toxin chip surface generic to both antibodies, it was demonstrated that the cross-reactivity profile of each could be combined into a single-assay format. Difficulties with receptors for optical biosensor analysis of low molecular weight compounds are discussed, as are the potential of alternative non-antibody-based binders for future assay development in this area

Does dietary tocopherol level affect fatty acid metabolism in fish?

Fish are a rich source of the n-3 polyunsaturated fatty acids (PUFA), particularly the highly unsaturated fatty acids (HUFA), eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids, which are vital constituents for cell membrane structure and function, but which are also highly susceptible to attack by oxygen and other organic radicals. Resultant damage to PUFA in membrane phospholipids can have serious consequences for cell membrane structure and function, with potential pathological effects on cells and tissues. Physiological antioxidant protection involves both endogenous components, such as free radical scavenging enzymes, and exogenous dietary micronutrients including tocopherols and tocotrienols, the vitamin E-type compounds, widely regarded as the primary lipid soluble antioxidants. The antioxidant activities of tocopherols are imparted by their ability to donate their phenolic hydrogen atoms to lipid (fatty acid) free radicals resulting in the stabilisation of the latter and the termination of the lipid peroxidation chain reaction. However, tocopherols can also prevent PUFA peroxidation by acting as quenchers of singlet oxygen. Recent studies on marine fish have shown correlations between dietary and tissue PUFA/tocopherol ratios and incidence of lipid peroxidation as indicated by the levels of TBARS and isoprostanes. These studies also showed that feeding diets containing oxidised oil significantly affected the activities of liver antioxidant defence enzymes and that dietary tocopherol partially attenuated these effects. However, there is evidence that dietary tocopherols can affect fatty acid metabolism in other ways. An increase in membrane PUFA was observed in rats deficient in vitamin E. This was suggested to be due to over production of PUFA arising from increased activity of the desaturation/elongation mechanisms responsible for the synthesis of PUFA. Consistent with this, increased desaturation of 18:3n-3 and 20:5n-3 in hepatocytes from salmon fed diets deficient in tocopherol and/or astaxanthin has been observed. Although the mechanism is unclear, tocopherols may influence biosynthesis of n-3PUFA through alteration of cellular oxidation potential or “peroxide tone”

Exciton/Charge-transfer Electronic Couplings in Organic Semiconductors

Charge transfer (CT) states and excitons are important in energy conversion processes that occur in organic light emitting devices (OLEDS) and organic solar cells. An ab initio density functional theory (DFT) method for obtaining CT−exciton electronic couplings between CT states and excitons is presented. This method is applied to two organic heterodimers to obtain their CT−exciton coupling and adiabatic energy surfaces near their CT−exciton diabatic surface crossings. The results show that the new method provides a new window into the role of CT states in exciton−exciton transitions within organic semiconductors.United States. Dept. of Energy (DEFG02- 07ER46474)David & Lucile Packard Foundation (Fellowship