74 research outputs found
Minimum codimension of eigenspaces in irreducible representations of simple classical linear algebraic groups
Let k be an algebraically closed field of characteristic pâ„0, let G be a simple simply connected classical linear algebraic group of rank l and let T be a maximal torus in G with rational character group X(T). For a nonzero p-restricted dominant weight λâX(T), let V be the associated irreducible kG-module. We define ÎœG(V) as the minimum codimension of any eigenspace on V for any non-central element of G. In this paper, we determine lower-bounds for ÎœG(V) for G of type Al and dim(V)â€l32, and for G of type Bl,Cl, or Dl and dim(V)â€4l3. Moreover, we give the exact value of ÎœG(V) for G of type Al with lâ„15; for G of type Bl or Cl with lâ„14; and for G of type Dl with lâ„16
ESTIMATING THE TENDENCY AND THE VARIABILITY OF THE RAINFALL AMOUNT IN IALOMITA RIVER BASIN AND THEIR INFLUENCE UPON THE LIQUID RUN-OFF
Estimating the tendency and the variability of the rainfallamount in Ialomita river basin and their influence upon the liquid run-off.The paper focuses on an analysis of the spatial and temporal variability of rainfallamounts (meteorological parameter ) from Ialomita River Basin and also theinfluence that rainfall has upon the liquid run-off, expressed by the mean monthlydischarges (hydrologic parameter) in a common period of time (1961-2007).The study of the evolution of the above mentioned parameters has been basedupon the data recorded from 6 weather and river stations which we considered tobe representative for the studied area.For these weather stations we have used, calculated and statistically interpretedthe chronological data series of the mean monthly and annually rainfall amountswhile for the river stations we have taken into account the mean monthly andyearly liquid discharges.We have also tried to establish inter-connections between the two parameters,in order to demonstrate the tight link that is between them on both a time-spacescale and in a regional context.Any alteration of the liquid drainage is caused by alterations in the climaticsystem, mainly the rainfall patterns.In order to identify the tendencies in the dynamics of the rainfall amounts andthe mean liquid run-off and also to establish their statistic significance we haveused the Mann-Kendall test (with the help of MAKENSIS programme)
Possibility to realize spin-orbit-induced correlated physics in iridium fluorides
Recent theoretical predictions of "unprecedented proximity" of the electronic
ground state of iridium fluorides to the SU(2) symmetric
limit, relevant for superconductivity in iridates, motivated us to investigate
their crystal and electronic structure. To this aim, we performed
high-resolution x-ray powder diffraction, Ir L-edge resonant inelastic
x-ray scattering, and quantum chemical calculations on Rb[IrF] and
other iridium fluorides. Our results are consistent with the Mott insulating
scenario predicted by Birol and Haule [Phys. Rev. Lett. 114, 096403 (2015)],
but we observe a sizable deviation of the state from the
SU(2) symmetric limit. Interactions beyond the first coordination shell of
iridium are negligible, hence the iridium fluorides do not show any magnetic
ordering down to at least 20 K. A larger spin-orbit coupling in iridium
fluorides compared to oxides is ascribed to a reduction of the degree of
covalency, with consequences on the possibility to realize spin-orbit-induced
strongly correlated physics in iridium fluorides
Global occurrence, chemical properties, and ecological impacts of e-wastes (IUPAC technical report)
The waste stream of obsolete electronic equipment grows exponentially, creating a worldwide pollution and resource problem. Electrical and electronic waste (e-waste) comprises a heterogeneous mix of glass, plastics (including flame retardants and other additives), metals (including rare earth elements) and metalloids. The e-waste issue is complex and multi-faceted. In examining the different aspects of e-waste, informal recycling in developing countries has been identified as a primary concern due to widespread illegal shipments, weak environmental as well as health and safety regulations, lack of technology and inadequate waste treatment structure. For example, Nigeria, Ghana, India, Pakistan and China have all been identified as hotspots for the disposal of e-waste. This article presents a critical examination on the chemical nature of e-waste and the resulting environmental impacts on, for example, microbial biodiversity, flora and fauna in e-waste recycling sites around the world. It highlights the different types of risk assessment approaches required when evaluating the ecological impact of e-waste. Additionally, it presents examples of chemistry playing a role in potential solutions. The information presented here will be informative to relevant stakeholders to devise integrated management strategies to tackle this global environmental concern
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Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2â:6â,2ââ-terpyridine ligand: implications for actinide(III) /lanthanide(III) partitioning
The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2â:6â,2ââ-terpyridine (CyMe4-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of the 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO22+) ion were obtained by X-ray crystallographic analysis, and showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. 1H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligand
Interaction of methanol with the oxygen-evolving complex: atomistic models, channel identification, species dependence, and mechanistic implications
Methanol has long being used as a substrate analogue to probe access pathways and investigate water delivery at the oxygen-evolving complex (OEC) of photosystem-II. In this contribution we study the interaction of methanol with the OEC by assembling available spectroscopic data into a quantum mechanical treatment that takes into account the local channel architecture of the active site. The effect on the magnetic energy levels of the Mn4Ca cluster in the S2 state of the catalytic cycle can be explained equally well by two models that involve either methanol binding to the calcium ion of the cluster, or a second-sphere interaction in the vicinity of the âdanglerâ Mn4 ion. However, consideration of the latest 13C hyperfine interaction data shows that only one model is fully consistent with experiment. In contrast to previous hypotheses, methanol is not a direct ligand to the OEC, but is situated at the end-point of a water channel associated with the O4 bridge. Its effect on magnetic properties of plant PS-II results from disruption of hydrogen bonding between O4 and proximal channel water molecules, thus enhancing superexchange (antiferromagnetic coupling) between the Mn3 and Mn4 ions. The same interaction mode applies to the dark-stable S1 state and possibly to all other states of the complex. Comparison of protein sequences from cyanobacteria and plants reveals a channel-altering substitution (D1-Asn87 versus D1-Ala87) in the proximity of the methanol binding pocket, explaining the species-dependence of the methanol effect. The water channel established as the methanol access pathway is the same that delivers ammonia to the Mn4 ion, supporting the notion that this is the only directly solvent-accessible manganese site of the OEC. The results support the pivot mechanism for water binding at a component of the S3 state and would be consistent with partial inhibition of water delivery by methanol. Mechanistic implications for enzymatic regulation and catalytic progression are discussed
Comparative Theoretical Studies of the Phosphomonoester Hydrolysis Mechanism by Purple Acid Phosphatases
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