Ab-initio analysis of superstructures revealed by STM on bilayer graphene

In this work we performed density functional theory calculations for a twisted bilayer graphene (BLG). Several conmensurable rotation angles were analyzed and for each one a constant height mode STM image was obtained. These STM images, calculated under the Tersoff-Hamman theory, reproduce the main features experimentally observed, paticularly superstructures and giant corrugations. In this way we confirm that STM characterization of twisted BLG can produce superstructures whose tunneling current intensity maxima occur over regions with $AA$ stacking. Additionally we give new evidence in favour of an electronic origin for the superstructures instead another physical grounds

Ladders for Wilson Loops Beyond Leading Order

We set up a general scheme to resum ladder diagrams for the quark-anti-quark potential in N=4 super-Yang-Mills theory, and do explicit calculations at the next-to-leading order. The results perfectly agree with string theory in AdS(5)xS(5) when continued to strong coupling, in spite of a potential order-of-limits problem.Comment: 18 pages, 5 figure

Negative-energy perturbations in cylindrical equilibria with a radial electric field

The impact of an equilibrium radial electric field $E$ on negative-energy perturbations (NEPs) (which are potentially dangerous because they can lead to either linear or nonlinear explosive instabilities) in cylindrical equilibria of magnetically confined plasmas is investigated within the framework of Maxwell-drift kinetic theory. It turns out that for wave vectors with a non-vanishing component parallel to the magnetic field the conditions for the existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D. Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for the existence of perpendicular NEPs, which are found to be the most important perturbations, is modified. For $|e_i\phi|\approx T_i$ ($\phi$ is the electrostatic potential) and $T_i/T_e > \beta_c\approx P/(B^2/8\pi)$ ($P$ is the total plasma pressure), a case which is of operational interest in magnetic confinement systems, the existence of perpendicular NEPs depends on $e_\nu E$, where $e_\nu$ is the charge of the particle species $\nu$. In this case the electric field can reduce the NEPs activity in the edge region of tokamaklike and stellaratorlike equilibria with identical parabolic pressure profiles, the reduction of electron NEPs being more pronounced than that of ion NEPs.Comment: 30 pages, late

The Resonance Overlap and Hill Stability Criteria Revisited

We review the orbital stability of the planar circular restricted three-body problem, in the case of massless particles initially located between both massive bodies. We present new estimates of the resonance overlap criterion and the Hill stability limit, and compare their predictions with detailed dynamical maps constructed with N-body simulations. We show that the boundary between (Hill) stable and unstable orbits is not smooth but characterized by a rich structure generated by the superposition of different mean-motion resonances which does not allow for a simple global expression for stability. We propose that, for a given perturbing mass $m_1$ and initial eccentricity $e$, there are actually two critical values of the semimajor axis. All values $a a_{\rm unstable}$ are unstable in the Hill sense. The first limit is given by the Hill-stability criterion and is a function of the eccentricity. The second limit is virtually insensitive to the initial eccentricity, and closely resembles a new resonance overlap condition (for circular orbits) developed in terms of the intersection between first and second-order mean-motion resonances.Comment: 33 pages, 14 figures, accepte

MAMA: An Algebraic Map for the Secular Dynamics of Planetesimals in Tight Binary Systems

We present an algebraic map (MAMA) for the dynamical and collisional evolution of a planetesimal swarm orbiting the main star of a tight binary system (TBS). The orbital evolution of each planetesimal is dictated by the secular perturbations of the secondary star and gas drag due to interactions with a protoplanetary disk. The gas disk is assumed eccentric with a constant precession rate. Gravitational interactions between the planetesimals are ignored. All bodies are assumed coplanar. A comparison with full N-body simulations shows that the map is of the order of 100 times faster, while preserving all the main characteristics of the full system. In a second part of the work, we apply MAMA to the \gamma-Cephei, searching for friendly scenarios that may explain the formation of the giant planet detected in this system. For low-mass protoplanetary disks, we find that a low-eccentricity static disk aligned with the binary yields impact velocities between planetesimals below the disruption threshold. All other scenarios appear hostile to planetary formation

Caracteristicas fisicas de um Latossolo Amarelo muito argiloso (Typic Acrorthox) do Estado do Amazonas, sob diferentes metodos de preparo de solo.

Foi avaliado o efeito de tres metodos de preparo de solo (convencional, direto e rotavator) sobre a permeabilidade e porosidade de um Latossolo Amarelo (Typic Acrorthox) muito argiloso, localizado na EMBRAPA/UEPAE de Manaus. Observou-se uma significativa influencia dos metodos, quando comparados com a area de floresta virgem sem uso, reduzindo a macroporosidade do solo na profundidade compreendida entre 0 cm - 20 cm. Consequentemente, a condutividade hidraulica e a infiltracao basica desses tratamentos foram sensivelmente alteradas. O plantio direto, entretanto, foi o que mais contribuiu para a reducao da permeabilidade: apresentou maior tendencia para compactar a camada superficial do solo

O uso correto de fertilizantes orgânicos para produção de forragens.

Projeto: 01.09.01.004

Recovering Yemen's Cultural Heritage: The Stookey Microfilms

In 1973, recent PhD and newly-affiliated Research Associate at the University of Texas at Austin, Robert W. Stookey, made microfilm copies of a number of Arabic manuscripts in Yemen on a variety of subjects. Stookey was not himself a manuscripts expert, but was instead invested in preserving and making available for research the intellectual tradition of Yemen, a country in which he had spent considerable time as a researcher and member of the Foreign Service. Stookey’s microfilms were accessioned to the UT Libraries’ Middle East collection in 1980, and digitized starting in 2014. This article discusses the importance of the Stookey microfilms as an early post-custodial arrangement for preserving, making accessible, and ultimately recovering the intellectual heritage of Zaydism in Yemen. Through their inclusion in the Zaydi Manuscript Tradition portal, these microfilms will be made freely and openly available for anyone to discover and study on the Internet. While the destruction of life, property, and cultural memory continues in Yemen, this is an example of a way for North American library collections to help to recover Yemen’s precious heritage.Author's OriginalUT Librarie