1,149 research outputs found
Gauge fields in (A)dS within the unfolded approach: algebraic aspects
It has recently been shown that generalized connections of the (A)dS space
symmetry algebra provide an effective geometric and algebraic framework for all
types of gauge fields in (A)dS, both for massless and partially-massless. The
equations of motion are equipped with a nilpotent operator called
whose cohomology groups correspond to the dynamically relevant quantities like
differential gauge parameters, dynamical fields, gauge invariant field
equations, Bianchi identities etc. In the paper the -cohomology is
computed for all gauge theories of this type and the field-theoretical
interpretation is discussed. In the simplest cases the -cohomology is
equivalent to the ordinary Lie algebra cohomology.Comment: 59 pages, replaced with revised verio
Ultra-structural mapping of sugarcane bagasse after oxalic acid fiber expansion (OAFEX) and ethanol production by Candida shehatae and Saccharomyces cerevisiae
Background: Diminishing supplies of fossil fuels and oil spills are rousing to explore the alternative sources of energy that can be produced from non-food/feed-based substrates. Due to its abundance, sugarcane bagasse (SB) could be a model substrate for the second-generation biofuel cellulosic ethanol. However, the efficient bioconversion of SB remains a challenge for the commercial production of cellulosic ethanol. We hypothesized that oxalic-acid-mediated thermochemical pretreatment (OAFEX) would overcome the native recalcitrance of SB by enhancing the cellulase amenability toward the embedded cellulosic microfibrils. Results: OAFEX treatment revealed the solubilization of hemicellulose releasing sugars (12.56 g/l xylose and 1.85 g/l glucose), leaving cellulignin in an accessible form for enzymatic hydrolysis. The highest hydrolytic efficiency (66.51%) of cellulignin was achieved by enzymatic hydrolysis (Celluclast 1.5 L and Novozym 188). The ultrastructure characterization of SB using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform-near infrared spectroscopy (FT-NIR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed structural differences before and after OAFEX treatment with enzymatic hydrolysis. Furthermore, fermentation mediated by C. shehatae UFMG HM52.2 and S. cerevisiae 174 showed fuel ethanol production from detoxified acid (3.2 g/l, yield 0.353 g/g; 0.52 g/l, yield, 0.246 g/g) and enzymatic hydrolysates (4.83 g/l, yield, 0.28 g/g; 6.6 g/l, yield 0.46 g/g). Conclusions: OAFEX treatment revealed marked hemicellulose degradation, improving the cellulases ability to access the cellulignin and release fermentable sugars from the pretreated substrate. The ultrastructure of SB after OAFEX and enzymatic hydrolysis of cellulignin established thorough insights at the molecular level. © 2013 Chandel et al; licensee BioMed Central Ltd
Synthesis and down conversion emission property of Eu3+ doped LaAlO3 CsAlO2 and LiLaO2 phosphors
[EN] LaAlO3:Eu3+, CsAlO2:Eu3+ and LiLaO2:Eu3+ phosphors with varying concen- trations of Eu3+ from 3 to 10 mol% were prepared by combustion synthesis method and the samples were further heated to 1,000ºC to improve the crystallinity of the materials. The structure and morphology of materials have been examined by X-ray diffraction and scan- ning electron microscopy. SEM images depicted that the morphology of crystallites have no uniform shapes and sizes. Small and coagulated particles of irregular shapes of different sizes are obtained. The characteristic emissions of Eu3+ were clearly observed at nearly 580, 592, 650, 682 to 709 (multiplet structure) nm for 5D - 7 Fn transitions where n = 0, 1, 3, 4 respectively, including the strongest emission peaks at 614 and 620 nm for 5 D0 - 7 F2 transitions in CsAlO2:Eu3+ and LiLaO2:Eu3+ host lattices. The intensity of emission peak corresponding to 5 D0 !→ 7 F1 transitions in LaAlO3 :Eu3+ material is comparable to that of 5D0 5D-7F2 transitions which is also a singlet. Photoluminescence intensity follows the order as in LiLaO2 > LaAlO3 > CsAlO2 lattices. Remarkable high photoluminescence intensity with 7 mol% doping of Eu3+ in LiLaO2 makes it a strong contender for red colored display applications.This work was supported by the European Commission through Nano CIS project (FP7-PEOPLE-2010-IRSES ref. 269279).Marí Soucase, B.; Singh, KC.; Moya Forero, MM.; Singh, I.; Om, H.; Chand, S. (2015). Synthesis and down conversion emission property of Eu3+ doped LaAlO3 CsAlO2 and LiLaO2 phosphors. Optical and Quantum Electronics. 47(7):1569-1578. https://doi.org/10.1007/s11082-014-9997-9S15691578477Abbattista, F., Vallino, M.: Remarks on the La 2 O 3 - Li 2 O binary system between 750 and 1,000 ∘ C. Ceram. 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Alloys Compd. 408, 828–830 (2006)Huang, Y., Jiang, C., Cao, Y., Shi, L., Seo, H.: Luminescence and microstructures of Eu 3 + -doped in triple phosphate Ca 8 MgR ( PO 4 ) 7 (R = La, Gd, Y) with whitlockite structure. Mater. Res. Bull. 44, 793–798 (2009)Kharbache, H., Mahiou, R., Boutinaud, P., Boyer, D., Zakaria, D., Deren, P.: Experimental evidence of Eu 3 + pairs in K 2 EuF 5 . Opt. Mater. 31, 558–561 (2009)Kijima, T., Shinbori, T., Sekita, M., Uota, M., Sakai, G.: Abnormally enhanced Eu 3 + emission in Y 2 O 2 SO 4 : Eu 3 + inherited from their precursory dodecylsulfate-templated concentric-layered nanostructure. J. Lumin. 128, 311–316 (2008)Liu, G., Hong, G., Wang, J., Dong, X.: Hydrothermal synthesis of spherical and hollow Gd 2 O 3 : Eu 3 + phosphors. J. Alloys Compd. 432, 200–204 (2007)Mączka, M., Bednarkiewicz, A., Mendoza-Mendoza, E., Fuentes, A.F., Kępiński, L.: Optical properties of Eu and Er doped LaAlO 3 nanopowders prepared by low-temperature method. J. Solid State Chem. 194, 264–269 (2012)Mao, Z., Wang, D., Lu, Q., Yu, W., Yuan, Z.: Tunable single-doped single-host full-color-emitting LaAlO 3 : Eu phosphor via valence state-controlled means. Chem. Commun. 3, 346–348 (2009)Mao, Z.Y., Wang, D.J., Liu, Y.H., Fei, Q.N., Zheng, X., Xu, S.C., Qiu, K.: Tuning the color purity of LaAlO 3 : Eu 3 + red phosphor by the cross relaxation. Opto Electron. Lett. 6, 116–119 (2010)Marí, B., Singh, K., Sahal, M., Khatkar, S., Taxak, V., Kumar, M.: Preparation and luminescence properties of Tb 3 + doped ZrO 2 and BaZrO 3 phosphors. J. Lumin. 130, 2128–2132 (2010)Marí, B., Singh, K.C., Cembrero-Coca, P., Singh, I., Singh, D., Chand, S.: Red emitting MTiO 3 (M = Ca & Sr) phosphor doped with Eu + 3 or Pr + 3 with some cations as co-dopands. Displays 34, 346–351 (2013)Ningthoujam, R., Sudarsan, V., Kulshreshtha, S.: SnO 2 : Eu nanoparticles dispersed in silica: A low-temperature synthesis and photoluminescence study. J. 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Crystal and Molecular Structure and DFT Calculations of the Steroidal Oxime 6E-Hydroximino-androst-4-ene-3,17-dione (C<sub>19</sub>H<sub>25</sub>NO<sub>3</sub>) a Molecule with Antiproliferative Activity
The single crystal X-ray structure of the novel steroid derivative, 6E-hydroximino-androst-4-ene-3,17-dione ( C19H25NO3) (code name RB-499), possessing antiproliferative activity against various cell lines is presented.
The analysis produced the following results: chemical formula C19H25NO3; Mr = 315.40; crystals are orthorhombic space group P212121 with Z = 4 molecules per unit cell with a = 6.2609(2), b = 12.5711(4), c = 20.0517(4) Å,Vc = 1578.18(7) Å3, crystal density Dc = 1.327 g/cm³. Structure determination was performed by direct methods, Fourier and full-matrix least-squares refinement. Hydrogens were located in the electron density and refined in position with isotropic thermal parameters.
The final R-index was 0.0324for 3140 reflections with I > 2σ and 308 parameters. The Absolute Structure Parameter − 0.07(5) confirms the correct allocation of the absolute configuration. The presence of the double bond C=O at position 3 in Ring A has caused a distortion from the usual chair conformation and created an unusual distorted sofa conformation folded across an approximate m-plane through C(1)–C(4). Ring B is a distorted chair, its conformation being influenced by the presence of the C(6)=N(6)–O(6)H group in position 6. Ring C is a symmetrical chair. Ring D exhibits both a distorted mirror symmetry conformation [influenced by the C(17)=O(17) group] and a distorted twofold conformation. DFT calculations indicated some degree of flexibility in rings A, C and D with ring A showing the greatest variation in torsion angles. The crystal packing is governed by H-bonds involving O(3), O(6) and O(17). DFT calculations of bond distances and angles, optimized at the B3LYP/6–31++G(d,p) level, were in good agreement with the X-ray structure
Genomic variability in Potato virus M and the development of RT-PCR and RFLP procedures for the detection of this virus in seed potatoes
Potato virus M (PVM, Carlavirus) is considered to be one of the most common potato viruses distributed worldwide. Sequences of the coat protein (CP) gene of several Canadian PVM isolates were determined. Phylogenetic analysis indicated that all known PVM isolates fell into two distinct groups and the isolates from Canada and the US clustered in the same group. The Canadian PVM isolates could be further divided into two sub-groups. Two molecular procedures, reverse transcription - polymerase chain reaction (RT-PCR) and restriction fragment length polymorphism (RFLP) were developed in this study for the detection and identification of PVM in potato tubers. RT-PCR was highly specific and only amplified PVM RNA from potato samples. PVM RNAs were easily detected in composite samples of 400 to 800 potato leaves or 200 to 400 dormant tubers. Restriction analysis of PCR amplicons with MscI was a simple method for the confirmation of PCR tests. Thus, RT-PCR followed by RFLP analysis may be a useful approach for screening potato samples on a large scale for the presence of PVM
First-Principles Study of the Electronic and Magnetic Properties of Defects in Carbon Nanostructures
Understanding the magnetic properties of graphenic nanostructures is
instrumental in future spintronics applications. These magnetic properties are
known to depend crucially on the presence of defects. Here we review our recent
theoretical studies using density functional calculations on two types of
defects in carbon nanostructures: Substitutional doping with transition metals,
and sp-type defects created by covalent functionalization with organic and
inorganic molecules. We focus on such defects because they can be used to
create and control magnetism in graphene-based materials. Our main results are
summarized as follows: i)Substitutional metal impurities are fully understood
using a model based on the hybridization between the states of the metal
atom and the defect levels associated with an unreconstructed D carbon
vacancy. We identify three different regimes, associated with the occupation of
distinct hybridization levels, which determine the magnetic properties obtained
with this type of doping; ii) A spin moment of 1.0 is always induced by
chemical functionalization when a molecule chemisorbs on a graphene layer via a
single C-C (or other weakly polar) covalent bond. The magnetic coupling between
adsorbates shows a key dependence on the sublattice adsorption site. This
effect is similar to that of H adsorption, however, with universal character;
iii) The spin moment of substitutional metal impurities can be controlled using
strain. In particular, we show that although Ni substitutionals are
non-magnetic in flat and unstrained graphene, the magnetism of these defects
can be activated by applying either uniaxial strain or curvature to the
graphene layer. All these results provide key information about formation and
control of defect-induced magnetism in graphene and related materials.Comment: 40 pages, 17 Figures, 62 References; Chapter 2 in Topological
Modelling of Nanostructures and Extended Systems (2013) - Springer, edited by
A. R. Ashrafi, F. Cataldo, A. Iranmanesh, and O. Or
First order parent formulation for generic gauge field theories
We show how a generic gauge field theory described by a BRST differential can
systematically be reformulated as a first order parent system whose spacetime
part is determined by the de Rham differential. In the spirit of Vasiliev's
unfolded approach, this is done by extending the original space of fields so as
to include their derivatives as new independent fields together with associated
form fields. Through the inclusion of the antifield dependent part of the BRST
differential, the parent formulation can be used both for on and off-shell
formulations. For diffeomorphism invariant models, the parent formulation can
be reformulated as an AKSZ-type sigma model. Several examples, such as the
relativistic particle, parametrized theories, Yang-Mills theory, general
relativity and the two dimensional sigma model are worked out in details.Comment: 36 pages, additional sections and minor correction
Superfluidity of Bose-Einstein Condensate in An Optical Lattice: Landau-Zener Tunneling and Dynamical Instability
Superflow of Bose-Einstein condensate in an optical lattice is represented by
a Bloch wave, a plane wave with periodic modulation of the amplitude. We review
the theoretical results on the interaction effects in the energy dispersion of
the Bloch waves and in the linear stability of such waves. For sufficiently
strong repulsion between the atoms, the lowest Bloch band develops a loop at
the edge of the Brillouin zone, with the dramatic consequence of a finite
probability of Landau-Zener tunneling even in the limit of a vanishing external
force. Superfluidity can exist in the central region of the Brillouin zone in
the presence of a repulsive interaction, beyond which Landau instability takes
place where the system can lower its energy by making transition into states
with smaller Bloch wavenumbers. In the outer part of the region of Landau
instability, the Bloch waves are also dynamically unstable in the sense that a
small initial deviation grows exponentially in time. In the inner region of
Landau instability, a Bloch wave is dynamically stable in the absence of
persistent external perturbations. Experimental implications of our findings
will be discussed.Comment: A new section on tight-binding approximation is added with a new
figur
Spin-half paramagnetism in graphene induced by point defects
Using magnetization measurements, we show that point defects in graphene -
fluorine adatoms and irradiation defects (vacancies) - carry magnetic moments
with spin 1/2. Both types of defects lead to notable paramagnetism but no
magnetic ordering could be detected down to liquid helium temperatures. The
induced paramagnetism dominates graphene's low-temperature magnetic properties
despite the fact that maximum response we could achieve was limited to one
moment per approximately 1000 carbon atoms. This limitation is explained by
clustering of adatoms and, for the case of vacancies, by losing graphene's
structural stability.Comment: 14 pages, 14 figure
Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy
[[abstract]]This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced
graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve
defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the
GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily
reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature.
Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure
spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are
bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat
and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and
the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further
support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based
on experimental results and first-principles calculations, the variation in magnetic behavior from GO
to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-
derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with
oxygen-containing and hydroxyl groups on GO sheets.[[notice]]補正完
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