Liquid Polymorphism and Density Anomaly in a Lattice Gas Model

We present a simple model for an associating liquid in which polymorphism and density anomaly are connected. Our model combines a two dimensional lattice gas with particles interacting through a soft core potential and orientational degrees of freedom represented through thermal \char`\"{}ice variables\char`\"{} . The competition between the directional attractive forces and the soft core potential leads to a phase diagram in which two liquid phases and a density anomaly are present. The coexistence line between the low density liquid and the high density liquid has a positive slope contradicting the surmise that the presence of a density anomaly implies that the high density liquid is more entropic than the low density liquid

Anomalies in a waterlike model confined between plates

Using molecular dynamic simulations we study a waterlike model confined between two fixed hydrophobic plates. The system is tested for density, diffusion and structural anomalous behavior and compared with the bulk results. Within the range of confining distances we had explored we observe that in the pressure-temperature phase diagram the temperature of maximum density (TMD line), the temperature of maximum and minimum diffusion occur at lower temperatures when compared with the bulk values. For distances between the two layers below a certain threshold ,$d\le d_c$, only two layers of particles are formed, for $d\ge d_c$ three or more layers are formed. In the case of three layers the central layer stays liquid while the contact layers crystallize. This result is in agreement with simulations for atomistic models

Vapour reactive distillation process for hydrogen production by hi decomposition from hi-i2-h2o solutions

In this contribution, a sequential and hierarchical approach for the feasibility analysis and the preliminary design of reactive distillation columns is extended to systems involving vapour phase chemical reaction and is successfully applied to the HI vapour phase decomposition to produce H2. The complex phase and physico chemical behaviour of the quaternary HI-H2-I2-H2O system is represented by the Neumann’s thermodynamic model and instantaneous vapour phase chemical equilibrium is assumed. Then, from minimal information concerning the physicochemical properties of the system, three successive steps lead to the design of the unit and the specification of its operating conditions: the feasibility analysis, the synthesis and the design step. First, the analysis of reactive condensation curve map method (rCCM), assuming infinite internal liquid and vapour flow rate and infinite reflux ratio, is used to assess the feasibility of the process. It determines the column structure and estimates the attainable compositions. These results are used as inputs data for the synthesis step. Based on the boundary value design method (BVD), considering finite internal liquid and vapour flow rate and finite reflux ratio while neglecting all thermal effects and assuming a constant heat of vaporisation, the synthesis step provides more precise information about the process configuration (minimum reflux ratio, number of theoretical stages, localisation and number of reactive plates, position of the feed plate). Finally, the BVD method results are used to initialise rigorous simulations, based on an equilibrium stage model with energy balance, to estimate the reflux ratio taking into account thermal effect on the process. The resulting design configuration consists in a single feed and entirely reactive distillation column. The column operates under a pressure of 22 bars. The feed of the reactive distillation column, coming from the Bunsen reaction section [xHI=0.10; xI2=0.39 xH2O=0.51], is at its boiling temperature. The residue consists in pure iodine. Water and produced hydrogen are recovered at the distillate. The column operates at a reflux ratio of 5 and is composed of 11 theoretical plates including the reboiler and the partial condenser with the feed at the stage 10 (counted downwards). The obtained HI dissociation yield is 99.6%

Solution of an associating lattice gas model with density anomaly on a Husimi lattice

We study a model of a lattice gas with orientational degrees of freedom which resemble the formation of hydrogen bonds between the molecules. In this model, which is the simplified version of the Henriques-Barbosa model, no distinction is made between donors and acceptors in the bonding arms. We solve the model in the grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes with a central site. The ground-state of the model, which was originally defined on the triangular lattice, is exactly reproduced by the solution on this Husimi lattice. In the phase diagram, one gas and two liquid (high density-HDL and low density-LDL) phases are present. All phase transitions (GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist at a triple point. A line of temperatures of maximum density (TMD) in the isobars is found in the metastable GAS phase, as well as another line of temperatures of minimum density (TmD) appears in the LDL phase, part of it in the stable region and another in the metastable region of this phase. These findings are at variance with simulational results for the same model on the triangular lattice, which suggested a phase diagram with two critical points. However, our results show very good quantitative agreement with the simulations, both for the coexistence loci and the densities of particles and of hydrogen bonds. We discuss the comparison of the simulations with our results.Comment: 12 pages, 5 figure

Liquid polymorphism and density anomaly in a three-dimensional associating lattice gas

We investigate the phase diagram of a three-dimensional associating gas $(ALG)$ model. This model combines orientational ice-like interactions and ``van der Waals'' that might be repulsive, representing, in this case, a penalty for distortion of hydrogen bonds. These interactions can be interpreted as two competing distances making the connection between this model and continuous isotropic soft-core potentials. We present Monte Carlo studies of the $ALG$ model showing the presence of two liquid phase, two critical points and A density anomaly

Convex Independence in Permutation Graphs

A set C of vertices of a graph is P_3-convex if every vertex outside C has at most one neighbor in C. The convex hull \sigma(A) of a set A is the smallest P_3-convex set that contains A. A set M is convexly independent if for every vertex x \in M, x \notin \sigma(M-x). We show that the maximal number of vertices that a convexly independent set in a permutation graph can have, can be computed in polynomial time

Avaliação da dinâmica da água no solo e da evapotranspiração, trocas gasosas, estado hídrico e produção da videira.

NO VALE DO SUBMÉDIO SÃO FRANCISCO, OS CULTIVOS DE VIDEIRA DE VINHO SÃO IRRIGADOS DURANTE TODO O ANO. NESSE CULTIVO, A IRRIGAÇÃO COM DEFICIT É UTILIZADA PARA OBTER ALGUMAS CARACTERÍSTICAS DESEJÁVEIS NA UVA PARA A VINIFICAÇÃO. ASSIM, O OBJETIVO DESSE TRABALHO FOI AVALIAR OS EFEITOS DE ESTRATÉGIAS DE IRRIGAÇÃO COM DÉFICIT NA PRODUÇÃO DE UVAS DE VINHO EM PETROLINA - PE. O EXPERIMENTO FOI INSTALADO NA EMBRAPA SEMIÁRIDO. A VIDEIRA CV. SYRAH ENXERTADA SOBRE PAULSEN 1103 FOI PLANTADA EM 30 DE ABRIL DE 2009, NO ESPAÇAMENTO DE 1 M X 3 M, E IRRIGADA POR GOTEJAMENTO EM UM ARGISSOLO VERMELHO AMARELO EUTRÓFICO LATOSSÓLICO, TEXTURA MÉDIA. OS TRATAMENTOS DE MANEJO DE IRRIGAÇÃO FORAM: 1 - IRRIGAÇÃO PLENA (IP), SEM A RESTRIÇÃO DE ÁGUA ÀS VIDEIRAS DURANTE TODO O CICLO DE PRODUÇÃO; 2 - IRRIGAÇÃO COM DÉFICIT (ID), ONDE A APLICAÇÃO DE ÁGUA FOI INTERROMPIDA DESDE A FASE DE CACHO FECHADO ATÉ A COLHEITA; 3 - A IRRIGAÇÃO COM DEFICIT CONTROLADO (IDC), ONDE A APLICAÇÃO DE ÁGUA FOI INTERROMPIDA NA FASE DE CACHO FECHADO, COM IRRIGAÇÕES EVENTUAIS CONFORME O MONITORAMENTO DA UMIDADE DO SOLO. NO SÉTIMO CICLO DE PRODUÇÃO (7 DE MAIO DE 2014 A 3 DE SETEMBRO DE 2014 - 119 DIAS), OCORREU UMA PRECIPITAÇÃO TOTAL DE 15,5 MM, SENDO 10,7 MM APÓS A INTERRUPÇÃO DA IRRIGAÇÃO. OS VALORES MÉDIOS DE EVAPOTRANSPÍRAÇÃO DE REFERÊNCIA (ETO) E EVAPOTRANSPIRAÇÃO DA CULTURA (ETC) PARA O PERÍODO DE 119 DIAS FORAM DE 5,0 MM DIA-1 E 3,6 MM DIA-1, RESPECTIVAMENTE, ENQUANTO OS MAIORES VALORES FORAM DE 9,3 MM DIA-1 (115 DIAS APÓS A PODA DE PRODUÇÃO - DAPP, 30 DE AGOSTO DE 2014) E 7,4 MM DIA-1 (80 DAPP, 26 DE JULHO DE 2014). A LÂMINA BRUTA MÉDIA FOI DE 5,6 MM DIA-1 NO TRATAMENTO IP, PARA 83 DIAS DE IRRIGAÇÃO; 5,9 MM DIA-1 NO TRATAMENTO IDC, PARA 42 DIAS DE IRRIGAÇÃO, E 6,1 MM DIA-1 NO TRATAMENTO ID, EM 37 DIAS DE IRRIGAÇÃO. APÓS O INÍCIO DA INTERRUPÇÃO DA IRRIGAÇÃO NOS TRATAMENTOS ID E IDC, A REDUÇÃO DA UMIDADE DO SOLO OCORREU ATÉ A PROFUNDIDADES DE 0,6 M, EM DECORRÊNCIA DA MAIOR PRESENÇA DO SISTEMA RADICULAR DA CULTURA NESSA CAMADA DE SOLO. NAS PROFUNDIDADES DE 0,75 M A 1,0 M, AS VARIAÇÕES NOS VALORES DE UMIDADE FORAM MENORES. OS VALORES DE POTENCIAL HÍDRICO NA ANTEMANHÃ E AO MEIO-DIA. APRESENTARAM COMPORTAMENTO SIMILAR, COM MAIORES VALORES NAS PLANTAS DE IP E MENORES NAS PLANTAS DE IDC E ID. ENTRETANTO, AS PLANTAS EM IDC E ID NÃO APRESENTAVAM SINTOMAS DE PONTO DE MURCHA PERMANENTE DURANTE A AVALIAÇÃO DE ANTEMANHÃ. OS MENORES VALORES DE POTENCIAL HÍDRICO AO MEIO-DIA EM PLANTAS DE TODOS OS TRATAMENTOS ESTÃO RELACIONADOS COM OS VALORES DA TAXA DE TRANSPIRAÇÃO, OS QUAIS TENDEM A SEREM MAIORES NESTE HORÁRIO, UMA VEZ QUE AS PLANTAS ESTAVAM PERDENDO ÁGUA PARA A ATMOSFERA VIA TRANSPIRAÇÃO. HOUVE EFEITO DOS TRATAMENTOS NA MASSA TOTAL DE CACHOS, NÚMERO DE CACHOS POR PLANTA, MASSA DE CACHOS POR PLANTA E NA PRODUTIVIDADE, COM MAIORES VALORES NO TRATAMENTO IP, SEM DIFERENÇA ESTATÍSTICA PARA O TRATAMENTO IDC. QUANTO A MASSA MÉDIA DE CACHOS, O TRATAMENTO IP APRESENTOU MAIORES VALORES

A dissemination strategy for immunizing scale-free networks

We consider the problem of distributing a vaccine for immunizing a scale-free network against a given virus or worm. We introduce a new method, based on vaccine dissemination, that seems to reflect more accurately what is expected to occur in real-world networks. Also, since the dissemination is performed using only local information, the method can be easily employed in practice. Using a random-graph framework, we analyze our method both mathematically and by means of simulations. We demonstrate its efficacy regarding the trade-off between the expected number of nodes that receive the vaccine and the network's resulting vulnerability to develop an epidemic as the virus or worm attempts to infect one of its nodes. For some scenarios, the new method is seen to render the network practically invulnerable to attacks while requiring only a small fraction of the nodes to receive the vaccine