98 research outputs found
Non trivial critical exponents for finite temperature chiral transitions at fixed total fermion number
We analyze the finite temperature chiral restoration transition of the
-dimensional Gross-Neveu model for the case of a large number of
flavors and fixed total fermion number. This leads to the study of the model
with a nonzero imaginary chemical potential. In this formulation of the theory,
we have obtained that, in the transition region, the model is described by a
chiral conformal field theory where the concepts of dimensional reduction and
universality do apply due to a transmutation of statistics which makes fermions
act as if they were bosons, having zero energy. This result should be generic
for theories with dynamical symmetry breaking, such as Quantum Chromodynamics.Comment: 14 pages Latex, no figures, final version to be published in Phys.
Lett.
Tailoring The Interface Using Thiophene Small Molecules In Tio 2/p3ht Hybrid Solar Cells
In this paper we focus on the effect of carboxylated thiophene small molecules as interface modifiers in TiO 2/P3HT hybrid solar cells. Our results show that small differences in the chemical structure of these molecules, for example, the presence of the -CH 2- group in the 2-thiopheneacetic acid (TAA), can greatly increase the TiO 2 surface wettability, improving the TiO 2/polymer contact. This effect is important to enhance exciton splitting and charge separation. This journal is © 2012 the Owner Societies.14341199011993Huang, Y.-C., Hsu, J.-H., Liao, Y.-C., Yen, W.-C., Li, S.-S., Lin, S.-T., Chen, C.-W., Su, W.-F., (2011) J. Mater. Chem., 21, p. 4450Bouclé, J., Ravirajan, P., Nelson, J., (2007) J. Mater. Chem., 17, p. 3141Bhongale, C.J., Thelakkat, M., (2010) Sol. Energy Mater. Sol. Cells, 94, p. 817Bolognesi, M., Sánchez-Díaz, A., Ajuria, J., Pacios, R., Palomares, E., (2011) Phys. Chem. Chem. Phys., 13, p. 6105Arici, E., Meissner, D., Schaffler, F., Sariciftci, N.S., (2003) Int. J. Photoenergy, 5, p. 199Arici, E., Sariciftci, N.S., Meissner, D., (2003) Adv. Funct. Mater., 13, p. 165De Freitas, J.N., Grova, I.R., Akcelrud, L.C., Arici, E., Sariciftcic, N.S., Nogueira, A.F., (2010) J. Mater. Chem., 20, p. 4845Yella, A., Lee, H.-W., Tsao, H.N., Yi, C., Chandiran, A.K., Nazeeruddin, M.K., Diau, E.W.-G., Grätzel, M., (2011) Science, 334, p. 629Yu, Q., Wang, Y., Yi, Z., Zu, N., Zhang, J., Zhang, M., Wang, P., (2010) ACS Nano, 4, p. 6032Lin, Y.-Y., Chu, T.-H., Li, S.-S., Chuang, C.-H., Chang, C.-H., Su, W.-F., Chang, C.-P., Chen, C.-W., (2009) J. Am. Chem. Soc., 131, p. 3644Sun, Z., Li, J., Liu, C., Yang, S., Yan, F., (2011) Adv. Mater., 23, p. 3648Coakley, K.M., Srinvasan, B.S., Ziebarth, J.M., Goh, C., Liu, Y.X., McGehee, M.D., (2005) Adv. Funct. Mater., 15, p. 1927Huang, Y.-C., Yen, W.-C., Liao, Y.-C., Yu, Y.-C., Hsu, C.-C., Ho, M.-L., Chou, P.-T., Su, W.-F., (2010) Appl. Phys. Lett., 96, p. 123501Zhang, W., Zhu, R., Li, F., Wang, Q., Liu, B., (2011) J. Phys. Chem. C, 115, p. 7038Johansson, E.M.J., Scholin, R., Siegbahn, H., Hagfeldt, A., Rensmo, H., (2011) Chem. Phys. Lett., 515, p. 146Ravirajan, P., Peiró, A.M., Nazeeruddin, M.K., Grätzel, M., Bradley, D.D.C., Durrant, J.R., Nelson, J., (2006) J. Phys. Chem. B, 110, p. 7635Weickert, J., Dunbar, R.B., Hesse, H.C., Wiedemann, W., Mende, L.S., (2011) Adv. Mater., 23, p. 1810Chang, J.A., Rhee, J.H., Im, S.H., Lee, Y.H., Kim, H.-J., Seok, S.I., Nazeeruddin, M.K., Gratzel, M., (2010) Nano Lett., 10, p. 2609Jiang, X., Karlsson, K.M., Gabrielsson, E., Johansson, E.M.J., Quintana, M., Karlsson, M., Sun, L., Hagfeldt, A., (2011) Adv. Funct. Mater., 21, p. 2944Snaith, H.J., Moule, A.J., Klein, C., Meerholz, K., Friend, R.H., Grätzel, M., (2007) Nano Lett., 7, p. 3372Weickert, J., Auras, F., Bein, T., Mende, L.S., (2011) J. Phys. Chem. C, 115, p. 15081Liu, Y., Scully, S.R., McGehee, M.D., Liu, J., Luscombe, C.K., Frechet, J.M.J., Shaheen, S.E., Ginley, D.S., (2006) J. Phys. Chem. B, 110, p. 3257Chang, Y.-M., Su, W.-F., Wang, L., (2008) Macromol. Rapid Commun., 29, p. 1303Cantu, M.L., Chafiq, A., Faissat, J., Valls, I.G., Yu, Y., (2011) Sol. Energy Mater. Sol. Cells, 95, p. 1362Jiang, K.-J., Manseki, K., Yu, Y.-H., Masaki, N., Suzuki, K., Suzuki, Y.-L., Yanagida, S., (2009) Adv. Funct. Mater., 19, p. 2481Goh, C., Scully, S.R., McGehee, M.D., (2007) J. Appl. Phys., 101, p. 114503Krüger, J., Bach, U., Grätzel, M., (2000) Adv. Mater., 12, p. 447Montanari, I., Nogueira, A.F., Nelson, J., Durrant, J.R., Winder, C., Loi, M.A., Sariciftci, N.S., Brabec, C., (2002) Appl. Phys. Lett., 81, p. 3001Nogueira, A.F., Montanari, I., Nelson, J., Brabec, C., Sariciftci, N.S., Durrant, J.R., (2003) J. Phys. Chem., 107, p. 1567Haque, S.A., Palomares, E., Cho, B.M., Green, A.N.M., Hirata, N., Klug, D.R., Durrant, J.R., (2005) J. Am. Chem. Soc., 127, p. 3456Clifford, J.N., Palomares, E., Nazeeruddin, M.K., Grätzel, M., Nelson, J., Li, X., Long, J., Durrant, J.R., (2004) J. Am. Chem. Soc., 126, p. 5225Bouclé, J., Chyla, S., Shaffer, M.S.P., Durrant, J.R., Bradley, D.D.C., Nelson, J., (2008) Adv. Funct. Mater., 18, p. 62
Critical behavior of Ginzburg-Landau model coupled to massless Dirac fermions
We point out interesting effects of additional massless Dirac fermions with
N_F colors upon the critical behavior of the Ginzburg-Landau model. For
increasing N_F, the model is driven into the type II regime of
superconductivity. The critical exponents are given as a function of N_F.Comment: RevTex4, 4 pages, 1 figure; author information and latest update to
this paper at http://www.physik.fu-berlin.de/~kleinert/institution.html;
version 2: new references and comments on chiral symmetry breaking adde
Incorporation Of Nanocrystals With Different Dimensionalities In Hybrid Tio2/p3ht Solar Cells
We investigate the effect of TiO2 nanoparticles-nanospheres and nanorods-inserted in the poly(3-hexylthiophene) (P3HT) matrix of TiO2?P3HT inverted hybrid solar cells. X-ray diffraction, high-resolution transmission electron microscopy, small-angle x-ray scattering, photoluminescence, and photoelectrochemical experiments were employed to investigate the structure, morphology, and photoactivity of TiO2 nanoparticles modified with 2-thiopheneacetic acid, mixed or not with P3HT. Both TiO2 nanospheres and TiO2 nanorods presented a good dispersion in the polymer matrix. The incorporation of TiO2 nanospheres and nanorods has improved the photocurrent generation, and devices with efficiency values up to 1.35% were obtained. Our results reveal that the nanoscale morphology enables an enhanced interfacial area for exciton dissociation. In particular, the nanospheres contribute with their high specific area, and the nanorods contribute with their high aspect ratio.51Lee, C.-K., Pao, C.-W., Chen, C.-W., Correlation of nanoscale organizations of polymer and nanocrystals in polymer/inorganic nanocrystal bulk heterojunction hybrid solar cells: Insights from multiscale molecular simulations (2013) Energy Environ. Sci., 6, pp. 307-315Huynh, W.U., Dittmer, J.J., Alivisatos, A.P., Hybrid nanorod: Polymer solar cells (2002) Science, 295, pp. 2425-2427Sian, S., Chen, C.-W., Polymer-metal-oxide hybrid solar cells (2013) J. Mater. Chem. A, 1, pp. 10574-10591Das, J., A facile nonaqueous route for fabricating titania nanorods and their viability in quasi-solid-state dye-sensitized solar cells (2010) J. Mater. Chem., 20, pp. 4425-4431Cozzoli, P.D., Kornowski, A., Weller, H., Low-temperature synthesis of soluble and processable organic-capped anatase TiO2 nanorods (2003) J. Am. Chem. Soc., 125, pp. 14539-14548Zeng, T.W., A large interconnecting network within hybrid MEH-PPV/TiO2 nanorod photovoltaic devices (2006) Nanotechnology, 17, p. 5387Yang, P., TiO2 nanowire electron transport pathways inside organic photovoltaics (2013) Phys. Chem. Chem. Phys., 15, pp. 4566-4572Lin, Y., Morphology control in TiO2 nanorod/polythiophene composites for bulk heterojunction solar cells using hydrogen bonding (2012) Macromolecules, 45, pp. 8665-8673Ranjitha, A., Inverted organic solar cells based on Cd-doped TiO2 as an electron extraction layer (2014) Superlattices Microstruct., 74, pp. 114-122Bolognesi, M., The effect of selective contact electrodes on the interfacial charge recombination kinetics and device efficiency of organic polymer solar cells (2011) Phys. Chem. Chem. Phys., 13, pp. 6105-6109Mor, G.K., High efficiency double heterojunction polymer photovoltaic cells using highly ordered TiO2 nanotube arrays (2007) Appl. Phys. Lett., 91, p. 152111Planells, M., Oligothiophene interlayer effect on photocurrent generation for hybrid TiO2/P3HT solar cells (2014) Appl. Mater. Interfaces, 6, pp. 17226-17235Freitas, F.S., Tailoring the interface using thiophene small molecules in TiO2/P3HT hybrid solar cells (2012) Phys. Chem. Chem. Phys., 14, pp. 11990-11993Liu, K., Efficient hybrid plasmonic polymer solar cells with Ag nanoparticle decorated TiO2 nanorods embedded in the active layer (2014) Nanoscale, 6, pp. 6180-6186Lin, Y.-Y., Interfacial nanostructuring on the performance of polymer/TiO2 nanorod bulk heterojunction solar cells (2009) J. Am. Chem. Soc., 131, pp. 3644-3649Eom, S.H., Roles of interfacial modifiers in hybrid solar cells: Inorganic/polymer bilayer versus inorganic/polymer: Fullerene bulk heterojunction (2014) Appl. Mater. Interfaces, 6, pp. 803-810Ravirajan, P., Hybrid polymer/zinc oxide photovoltaic devices with vertically oriented ZnO nanorods and an amphiphilic molecular interface layer (2006) J. Phys. Chem. B, 110, pp. 7635-7639Abate, A., Protic ionic liquids as p-dopant for organic hole transporting materials and their application in high efficiency hybrid solar cells (2013) J. Am. Chem. Soc., 135, pp. 13538-13548Beaucage, G., Approximations leading to a unified exponential/power-law approach to small-angle scattering (1995) J. Appl. Cryst., 28, pp. 717-728Beaucage, G., Small-angle scattering from polymeric mass fractals of arbitrary mass-fractal dimension (1996) J. Appl. Cryst., 29, pp. 134-146Beaucage, G., Kammler, H.K., Pratsinis, S.E., Particle size distributions from smallangle scattering using global scattering functions (2004) J. Appl. Cryst., 37, pp. 523-535Khatri, I., Similar device architectures for inverted organic solar cell and laminated solid-state dye-sensitized solar cells (2012) ISRN Electron., 10Choi, H.C., Jung, Y.M., Kim, S.B., Size effects in the Raman spectra of TiO2 nanoparticles (2005) Vib. Spectrosc., 37, pp. 33-38Li, G., Polymer self-organization enhances photovoltaic efficiency (2005) J. Appl. Phys., 98, p. 43704Salim, T., Solvent additives and their effects on blend morphologies of bulk heterojunctions (2011) J. Mater. Chem., 21, pp. 242-250Hwang, I.W., Carrier generation and transport in bulk heterojunction films processed with 1,8-octanedithiol as a processing additive (2008) J. Appl. Phys., 104, p. 033706Nguyen, H.Q., Synthesis and characterization of a polyisoprene-b-polystyrene-b-poly (3-hexylthiophene) triblock copolymer (2013) Polym. Chem., 4, pp. 462-465Prosa, T.J., X-ray structural studies of poly(3-alkylthiophenes): An example of an inverse comb (1992) Macromolecules, 25, p. 4364De Freitas, J.N., Connecting the (quantum) dots: Towards hybrid photovoltaic devices based on chalcogenide gels (2012) Phys. Chem. Chem. Phys., 14, pp. 15180-15184Yang, P., Identifying effects of TiO2 nanowires inside bulk heterojunction organic photovoltaics on charge diffusion and recombination (2014) J. Mater. Chem. C, 2, pp. 4922-4927Grancini, G., Boosting infrared light harvesting by molecular functionalization of metal oxide/polymer interfaces in efficient hybrid solar cells (2012) Adv. Funct. Mater., 22, pp. 2160-2166Liao, H.-C., Diketopyrrolopyrrole-based oligomer modified TiO2 nanorods for airstable and all solution processed poly(3-hexylthiophene): TiO2 bulk heterojunction inverted solar cell (2012) J. Mater. Chem., 22, pp. 10589-1059
Scaling critical behavior of superconductors at zero magnetic field
We consider the scaling behavior in the critical domain of superconductors at
zero external magnetic field. The first part of the paper is concerned with the
Ginzburg-Landau model in the zero magnetic field Meissner phase. We discuss the
scaling behavior of the superfluid density and we give an alternative proof of
Josephson's relation for a charged superfluid. This proof is obtained as a
consequence of an exact renormalization group equation for the photon mass. We
obtain Josephson's relation directly in the form , that
is, we do not need to assume that the hyperscaling relation holds. Next, we
give an interpretation of a recent experiment performed in thin films of
. We argue that the measured mean field like
behavior of the penetration depth exponent is possibly associated with a
non-trivial critical behavior and we predict the exponents and
for the correlation lenght and specific heat, respectively. In the
second part of the paper we discuss the scaling behavior in the continuum dual
Ginzburg-Landau model. After reviewing lattice duality in the Ginzburg-Landau
model, we discuss the continuum dual version by considering a family of
scalings characterized by a parameter introduced such that
, where is the bare mass of the magnetic
induction field. We discuss the difficulties in identifying the renormalized
magnetic induction mass with the photon mass. We show that the only way to have
a critical regime with is having , that
is, with having the scaling behavior of the renormalized photon mass.Comment: RevTex, 15 pages, no figures; the subsection III-C has been removed
due to a mistak
Anomalous dimensions and phase transitions in superconductors
The anomalous scaling in the Ginzburg-Landau model for the superconducting
phase transition is studied. It is argued that the negative sign of the
exponent is a consequence of a special singular behavior in momentum space. The
negative sign of comes from the divergence of the critical correlation
function at finite distances. This behavior implies the existence of a Lifshitz
point in the phase diagram. The anomalous scaling of the vector potential is
also discussed. It is shown that the anomalous dimension of the vector
potential has important consequences for the critical dynamics in
superconductors. The frequency-dependent conductivity is shown to obey the
scaling . The prediction is
obtained from existing Monte Carlo data.Comment: RevTex, 20 pages, no figures; small changes; version accepted in PR
Symmetry Nonrestoration in a Gross-Neveu Model with Random Chemical Potential
We study the symmetry behavior of the Gross-Neveu model in three and two
dimensions with random chemical potential. This is equivalent to a four-fermion
model with charge conjugation symmetry as well as Z_2 chiral symmetry. At high
temperature the Z_2 chiral symmetry is always restored. In three dimensions the
initially broken charge conjugation symmetry is not restored at high
temperature, irrespective of the value of the disorder strength. In two
dimensions and at zero temperature the charge conjugation symmetry undergoes a
quantum phase transition from a symmetric state (for weak disorder) to a broken
state (for strong disorder) as the disorder strength is varied. For any given
value of disorder strength, the high-temperature behavior of the charge
conjugation symmetry is the same as its zero-temperature behavior. Therefore,
in two dimensions and for strong disorder strength the charge conjugation
symmetry is not restored at high temperature.Comment: 16 pages, 3 figure
Economic analysis of an agrosilvipastoral system for a mountainous area in Zona da Mata Mineira, Brazil
The objective of this work was to evaluate the economic viability of an agrosilvipastoral system developed for Zona da Mata mountainous areas in Minas Gerais state, Brazil, as well as to compare different options for wood (Eucalyptus grandis and Acacia mangium) commercialization of the second thinning. The data were obtained from a 10 year-old agrosilvipastoral system established in four hectares at Embrapa Gado de Leite station in Coronel Pacheco, MG, Brazil. As evaluation criteria for the economic viability analysis, the adopted methods were the net present value (NPV) and the internal rate of return (IRR), both calculated at 6% interest rate. Despite the small difference, adding value to forest products increased the attractiveness of the proposed system. Considered separately, the agricultural activity was impracticable, whereas the forestry and livestock activities were independently viable. The studied system seems to be equally tolerant to price variations for forest and livestock products, as well as strongly tolerant to variations in production costs
Hamiltonian Study of Improved Lattice Gauge Theory in Three Dimensions
A comprehensive analysis of the Symanzik improved anisotropic
three-dimensional U(1) lattice gauge theory in the Hamiltonian limit is made.
Monte Carlo techniques are used to obtain numerical results for the static
potential, ratio of the renormalized and bare anisotropies, the string tension,
lowest glueball masses and the mass ratio. Evidence that rotational symmetry is
established more accurately for the Symanzik improved anisotropic action is
presented. The discretization errors in the static potential and the
renormalization of the bare anisotropy are found to be only a few percent
compared to errors of about 20-25% for the unimproved gauge action. Evidence of
scaling in the string tension, antisymmetric mass gap and the mass ratio is
observed in the weak coupling region and the behaviour is tested against
analytic and numerical results obtained in various other Hamiltonian studies of
the theory. We find that more accurate determination of the scaling
coefficients of the string tension and the antisymmetric mass gap has been
achieved, and the agreement with various other Hamiltonian studies of the
theory is excellent. The improved action is found to give faster convergence to
the continuum limit. Very clear evidence is obtained that in the continuum
limit the glueball ratio approaches exactly 2, as expected in a
theory of free, massive bosons.Comment: 13 pages, 15 figures, submitted to Phys. Rev.
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