1,181 research outputs found
Ice Formation on Kaolinite: Insights from Molecular Dynamics Simulations
The formation of ice affects many aspects of our everyday life as well as
technologies such as cryotherapy and cryopreservation. Foreign substances
almost always aid water freezing through heterogeneous ice nucleation, but the
molecular details of this process remain largely unknown. In fact, insight into
the microscopic mechanism of ice formation on different substrates is difficult
to obtain even via state-of-the-art experimental techniques. At the same time,
atomistic simulations of heterogeneous ice nucleation frequently face
extraordinary challenges due to the complexity of the water-substrate
interaction and the long timescales that characterize nucleation events. Here,
we have investigated several aspects of molecular dynamics simulations of
heterogeneous ice nucleation considering as a prototypical ice nucleating
material the clay mineral kaolinite, which is of relevance in atmospheric
science. We show via seeded molecular dynamics simulations that ice nucleation
on the hydroxylated (001) face of kaolinite proceeds exclusively via the
formation of the hexagonal ice polytype. The critical nucleus size is two times
smaller than that obtained for homogeneous nucleation at the same supercooling.
Previous findings suggested that the flexibility of the kaolinite surface can
alter the time scale for ice nucleation within molecular dynamics simulations.
However, we here demonstrate that equally flexible (or non flexible) kaolinite
surfaces can lead to very different outcomes in terms of ice formation,
according to whether or not the surface relaxation of the clay is taken into
account. We show that very small structural changes upon relaxation
dramatically alter the ability of kaolinite to provide a template for the
formation of a hexagonal overlayer of water molecules at the water-kaolinite
interface, and that this relaxation therefore determines the nucleation ability
of this mineral
Anharmonic oscillation effect on the Davydov-Scott monomer in thermal bath
The dynamics of Davydov-Scott monomer in a thermal bath with higher order
amide-site's displacement leads to anharmonic oscillation effect is
investigated using full-quantum approach and the Lindblad formulation of master
equation. The specific heat is calculated based on the thermodynamic partition
function using the path integral method. The temperature dependence of the
specific heat is studied. In the model the specific heat anomaly as pointed out
in recent works by Ingold et.al is also observed. However it is found that the
anomaly occurs at high temperature region, and the anharmonic oscillation
restores the positivity of specific heat.Comment: 11 pages, 5 figure
A bolometric measurement of the antineutrino mass
High statistics calorimetric measurements of the beta spectrum of 187Re are
being performed with arrays of silver perrhenate crystals operated at low
temperature. After a modification of the experimental set-up, which allowed to
substantially reduce the background of spurious counts and therefore to
increase the sensitivity on the electron antineutrino mass, a new measurement
with 10 silver perrhenate microbolometers is running since July 2002. The
crystals have masses between 250 and 350 micrograms and their average FWHM
energy resolution, constantly monitored by means of fluorescence X-rays, is of
28.3 eV at the beta end-point. The Kurie plot collected during 4485 hours x mg
effective running time has an end-point energy of 2466.1 +/- 0.8{stat} +/- 1.5
{syst} eV, while the half lifetime of the decay is found to be 43.2 +/-
0.2{stat} +/- 0.1{syst} Gy. These values are the most precise obtained so far
for 187Re. From the fit of the Kurie plot we can deduce a value for the squared
electron antineutrino mass m(nu)^2 of 147 +/- 237{stat} +/- 90{syst} eV^2. The
corresponding 90% C.L. upper limit for m(nu) is 21.7 eV.Comment: 3 pages, 3 figures. Submitted to Phys. Rev. Let
Identificação de nematoides em abacaxizeiro no Municipio de Mari, Paraiba.
Dada a importancia da abacaxicultura no Estado da Paraiba e a pouca informação sobre a presença de nematoides associados a este cultivo, coletaram-se 10 amostras de raizes e 13 de solo da rizosfera de abacaxizeiro (Ananas comosus) cultivares Perola e Smooth Cayenne, no Municipio de Mari, para analise nematologica. Foram verificadas as especies Pratylenchus brachyurus, Meloidogyne incognita, Rotylenchulus reniformis, Helicotylenchus dinystera, Macroposthonia ornata, Tylenchorhynchus sp. e Tylenchus sp. Observaram-se altas populações de Pratylenchus brachyurus associadas a um sistema radicular reduzido e a plantas pouco desenvolvidas sendo este nematoide o principal problema nematologico do abacaxizeiro no Estado da Paraiba.bitstream/item/44150/1/ZEN.pd
Towards a catalog of usability smells
This paper presents a catalog of smells in the context of interactive applications. These so-called usability smells are indicators of poor design on an application's user interface, with the potential to hinder not only its usability but also its maintenance and evolution. To eliminate such usability smells we discuss a set of program/usability refactorings. In order to validate the presented usability smells catalog, and the associated refactorings, we present a preliminary empirical study with software developers in the context of a real open source hospital management application. Moreover, a tool that computes graphical user interface behavior models, giving the applications' source code, is used to automatically detect usability smells at the model level.This work was partially funded by the ERDF - European Regional Development Fund through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the FCT (Portuguese Foundation for Science and Technology), within projects reference FCOMP-01-0124-FEDER-020484
(J. Saraiva) and FCOMP-01-0124-FEDER-020554 (J. C. Campos)
Velocidade de embebição de sementes de soja submetidas a diferentes recobrimentos.
O tratamento de sementes de soja é uma prática utilizada para aumentar o desempenho das sementes, especialmente durante as fases iniciais do ciclo. A utilização do tratamento de sementes com polímeros tem sido uma alternativa para os agricultores por permitir melhor fi xação dos princípios ativos utilizados no tratamento químico. Entretanto, esses produtos não devem afetar as propriedades fisiológicas e físicas das sementes, como a velocidade de embebição. Assim, o objetivo do trabalho foi estudar o efeito de diferentes recobrimentos na velocidade de embebição das sementes de soja. Foram utilizados dois lotes de sementes de soja das cultivares SYN1263 RR e BMX Potência RR, as quais foram submetidas a seis diferentes recobrimentos: 1: Testemunha (ausência de fungicida, inseticida e polímero); 2: Fungicida + Inseticida; 3: Fungicida + Inseticida + Polímero A; 4: Fungicida + Inseticida + Polímero B; 5: Polímero A; 6: Polímero B. O fungicida e o inseticida utilizados foram Derosal Plus (carbendazim + thiram) e Cropstar FloRite 1197 (Nitral Urbana (imidacloprido + tiodicarbe), respectivamente, e os polímeros ) (A) e Laborsan (Laborsan) (B). Para a determinação da velocidade de embebição, as sementes foram dispostas sobre papel germitest umedecido 2,25 vezes o peso do papel seco e incubadas àtemperatura de 20°C, mensurando-se a massa das sementes em intervalos regularesde 1h, durante um período de 24h. De acordo com os resultados, o recobrimento das sementes de soja com os polímeros FloRite1197 (Nitral Urbana) e Laborsan (Laborsan) isolados ou em associação com o fungicida e inseticida não retardam a velocidade de absorção de água
Near-brane SU(6) origin Higgs in Scherk-Schwarz breaking of five-dimensional SU(6) GUT
The symmetry breaking of five-dimensional SU(6) GUT is realized by
Scherk-Schwarz mechanisms through trivial and pseudo nontrivial orbifold S1/Z2
breakings to produce dimensional deconstruction 5D SU(6) \rightarrow4D SU(6).
The latter also induces near-brane weakly-coupled SU(6) Baby Higgs to further
break the symmetry into SU(3)C \otimes SU(3)H \otimes U(1)C. The model
successfully provides a scenario of the origin of (Little) Higgs from GUT
scale, produces the (intermediate and light) Higgs boson with the most
preferred range and establishes coupling unification and compactification scale
correctly.Comment: 23 pages, 5 figure
Desempenho agronômico e rendimento da cultura do milho a partir de sementes tratadas com biorreguladores.
Edição Especial contendo os Anais do XVIII Congresso Brasileiro de Sementes, Florianópolis, set. 2013
TurboRVB: A many-body toolkit for ab initio electronic simulations by quantum Monte Carlo
TurboRVB is a computational package for ab initio Quantum Monte Carlo (QMC) simulations of both molecular and bulk electronic systems. The code implements two types of well established QMC algorithms: Variational Monte Carlo (VMC) and diffusion Monte Carlo in its robust and efficient lattice regularized variant. A key feature of the code is the possibility of using strongly correlated many-body wave functions (WFs), capable of describing several materials with very high accuracy, even when standard mean-field approaches [e.g., density functional theory (DFT)] fail. The electronic WF is obtained by applying a Jastrow factor, which takes into account dynamical correlations, to the most general mean-field ground state, written either as an antisymmetrized geminal power with spin-singlet pairing or as a Pfaffian, including both singlet and triplet correlations. This WF can be viewed as an efficient implementation of the so-called resonating valence bond (RVB) Ansatz, first proposed by Pauling and Anderson in quantum chemistry [L. Pauling, The Nature of the Chemical Bond (Cornell University Press, 1960)] and condensed matter physics [P.W. Anderson, Mat. Res. Bull 8, 153 (1973)], respectively. The RVB Ansatz implemented in TurboRVB has a large variational freedom, including the Jastrow correlated Slater determinant as its simplest, but nontrivial case. Moreover, it has the remarkable advantage of remaining with an affordable computational cost, proportional to the one spent for the evaluation of a single Slater determinant. Therefore, its application to large systems is computationally feasible. The WF is expanded in a localized basis set. Several basis set functions are implemented, such as Gaussian, Slater, and mixed types, with no restriction on the choice of their contraction. The code implements the adjoint algorithmic differentiation that enables a very efficient evaluation of energy derivatives, comprising the ionic forces. Thus, one can perform structural optimizations and molecular dynamics in the canonical NVT ensemble at the VMC level. For the electronic part, a full WF optimization (Jastrow and antisymmetric parts together) is made possible, thanks to state-of-the-art stochastic algorithms for energy minimization. In the optimization procedure, the first guess can be obtained at the mean-field level by a built-in DFT driver. The code has been efficiently parallelized by using a hybrid MPI-OpenMP protocol, which is also an ideal environment for exploiting the computational power of modern Graphics Processing Unit accelerators
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