7,130 research outputs found
A matter of time: Implicit acquisition of recursive sequence structures
A dominant hypothesis in empirical research on the evolution of language is the following: the fundamental difference between animal and human communication systems is captured by the distinction between regular and more complex non-regular grammars. Studies reporting successful artificial grammar learning of nested recursive structures and imaging studies of the same have methodological shortcomings since they typically allow explicit problem solving strategies and this has been shown to account for the learning effect in subsequent behavioral studies. The present study overcomes these shortcomings by using subtle violations of agreement structure in a preference classification task. In contrast to the studies conducted so far, we use an implicit learning paradigm, allowing the time needed for both abstraction processes and consolidation to take place. Our results demonstrate robust implicit learning of recursively embedded structures (context-free grammar) and recursive structures with cross-dependencies (context-sensitive grammar) in an artificial grammar learning task spanning 9 days. Keywords: Implicit artificial grammar learning; centre embedded; cross-dependency; implicit learning; context-sensitive grammar; context-free grammar; regular grammar; non-regular gramma
Theory of Andreev reflection in a two-orbital model of iron-pnictide superconductors
A recently developed theory for the problem of Andreev reflection between a
normal metal (N) and a multiband superconductor (MBS) assumes that the incident
wave from the normal metal is coherently transmitted through several bands
inside the superconductor. Such splitting of the probability amplitude into
several channels is the analogue of a quantum waveguide. Thus, the appropriate
matching conditions for the wave function at the N/MBS interface are derived
from an extension of quantum waveguide theory. Interference effects between the
transmitted waves inside the superconductor manifest themselves in the
conductance. We provide results for a FeAs superconductor, in the framework of
a recently proposed effective two-band model and two recently proposed gap
symmetries: in the sign-reversed s-wave () scenario
resonant transmission through surface Andreev bound states (ABS) at nonzero
energy is found as well as destructive interference effects that produce zeros
in the conductance; in the extended s-wave ()
scenario no ABS at finite energy are found.Comment: 4 pages, 5 figure
Breathing synchronization in interconnected networks
Global synchronization in a complex network of oscillators emerges from the
interplay between its topology and the dynamics of the pairwise interactions
among its numerous components. When oscillators are spatially separated,
however, a time delay appears in the interaction which might obstruct
synchronization. Here we study the synchronization properties of interconnected
networks of oscillators with a time delay between networks and analyze the
dynamics as a function of the couplings and communication lag. We discover a
new breathing synchronization regime, where two groups appear in each network
synchronized at different frequencies. Each group has a counterpart in the
opposite network, one group is in phase and the other in anti-phase with their
counterpart. For strong couplings, instead, networks are internally
synchronized but a phase shift between them might occur. The implications of
our findings on several socio-technical and biological systems are discussed.Comment: 7 pages, 3 figures + 3 pages of Supplemental Materia
Two Kerr black holes with axisymmetric spins: An improved Newtonian model for the head-on collision and gravitational radiation
We present a semi-analytical approach to the interaction of two (originally)
Kerr black holes through a head-on collision process. An expression for the
rate of emission of gravitational radiation is derived from an exact solution
to the Einstein's field equations. The total amount of gravitational radiation
emitted in the process is calculated and compared to current numerical
investigations. We find that the spin-spin interaction increases the emission
of gravitational wave energy up to 0.2% of the total rest mass. We discuss also
the possibility of spin-exchange between the holes.Comment: 8 pages, RevTeX, 2 figures, psbox macro include
Efeito do sombreamento no crescimento de mudas de copaíba (Copaifera sp.).
A copaíba é uma árvore com grande potencial medicinal, pela produção de seu óleo-resina indicado para o controle de inflamações em geral, como antisséptico e cicatrizante. Estudos sobre a produção de mudas dessa espécie são escassos. O presente estudo objetivou avaliar a influência de diferentes níveis de sombreamento no desenvolvimento inicial de mudas de copaíba (Copaífera sp). O experimento foi conduzido no viveiro do Campo experimental da Embrapa Acre. Os tratamentos foram compostos por cinco níveis de sombreamento (pleno sol, 20%, 30%, 50% e 75%), obtidos com telas sombrite com as referidas capacidades de retenção da radiação solar. O delineamento experimental utilizado foi de blocos ao acaso, com seis repetições e oito plantas por unidade amostral. Aos 10 meses após a semeadura, foram avaliadas as seguintes variáveis: diâmetro do coleto, diâmetro da copa, altura e matéria seca total das plantas. Observou-se diferença significativa para todas as variáveis analisadas. O crescimento das mudas de copaíba foi modificado pela intensidade de sombreamento. Todas as variáveis avaliadas foram afetadas significativamente (p<0,05) pelo nível de sombreamento incidente nas plantas. Tanto o excesso de sombreamento como o de radiação solar foram prejudiciais ao crescimento das plantas. Sombreamentos em torno de 43 a 53% proporcionaram os melhores resultados paras as variáveis estudadas (diâmetro do coleto, massa seca da parte aérea e massa seca total. Pelos resultados obtidos, conclui-se que mudas de copaíba (Copaifera sp.) necessitam de sombra, sendo um sombreamento de 50% o recomendado para a produção de mudas desta espécie, em função da disponibilidade no mercado de tela sombrite com essa retenção de luminosidade
Watersheds are Schramm-Loewner Evolution curves
We show that in the continuum limit watersheds dividing drainage basins are
Schramm-Loewner Evolution (SLE) curves, being described by one single parameter
. Several numerical evaluations are applied to ascertain this. All
calculations are consistent with SLE, with ,
being the only known physical example of an SLE with . This lies
outside the well-known duality conjecture, bringing up new questions regarding
the existence and reversibility of dual models. Furthermore it constitutes a
strong indication for conformal invariance in random landscapes and suggests
that watersheds likely correspond to a logarithmic Conformal Field Theory (CFT)
with central charge .Comment: 5 pages and 4 figure
Magnetic and superconducting instabilities in the periodic Anderson model: an RPA stud
We study the magnetic and superconducting instabilities of the periodic
Anderson model with infinite Coulomb repulsion U in the random phase
approximation. The Neel temperature and the superconducting critical
temperature are obtained as functions of electronic density (chemical pressure)
and hybridization V (pressure). It is found that close to the region where the
system exhibits magnetic order the critical temperature T_c is much smaller
than the Neel temperature, in qualitative agreement with some T_N/T_c ratios
found for some heavy-fermion materials. In our study, all the magnetic and
superconducting physical behaviour of the system has its origin in the
fluctuating boson fields implementing the infinite on-site Coulomb repulsion
among the f-electrons.Comment: 9 pages, 2 figure
Oscillatory behavior of light in the composite Goos-Hanchen shift
Sem informaçãoFor incidence in the critical region, the propagation of Gaussian lasers through dielectric blocks is characterized by the joint action of angular deviations and lateral displacements. This mixed effect, known as the composite Goos-Hanchen shift, produces a lateral displacement that is dependent on the axial coordinate, recently confirmed by a weak measurement experiment. We discuss under which conditions this axial lateral displacement, which only exists for the composite Goos-Hanchen shift, presents an oscillatory behavior. This oscillation phenomenon shows a peculiar behavior of light for critical incidence and, if experimentally tested, could stimulate further theoretical studies and lead to interesting optical applications.95519Sem informaçãoSem informaçãoSem informaçã
Produção de morango no Distrito Federal.
O morangueiro no Distrito Federal; Perfil dos produtores; Práticas culturais; Controle fitossanitário; Comercialização; Dificuldades e desafios.bitstream/item/109187/1/CNPH-PROD.-DE-MORAN.-DO-DF.-09.pd
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