2,213 research outputs found

    Thermodynamics of the Antiferromagnetic Heisenberg Model on the Checkerboard Lattice

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    Employing numerical linked-cluster expansions (NLCEs) along with exact diagonalizations of finite clusters with periodic boundary condition, we study the energy, specific heat, entropy, and various susceptibilities of the antiferromagnetic Heisenberg model on the checkerboard lattice. NLCEs, combined with extrapolation techniques, allow us to access temperatures much lower than those accessible to exact diagonalization and other series expansions. We find that the high-temperature peak in specific heat decreases as the frustration increases, consistent with the large amount of unquenched entropy in the region around maximum classical frustration, where the nearest-neighbor and next-nearest neighbor exchange interactions (J and J', respectively) have the same strength, and with the formation of a second peak at lower temperatures. The staggered susceptibility shows a change of character when J' increases beyond 0.75J, implying the disappearance of the long-range antiferromagnetic order at zero temperature. For J'=4J, in the limit of weakly coupled crossed chains, we find large susceptibilities for stripe and Neel order with Q=(pi/2,pi/2) at low temperatures with antiferromagnetic correlations along the chains. Other magnetic and bond orderings, such as a plaquette valence-bond solid and a crossed-dimer order suggested by previous studies, have also been investigated.Comment: 10 pages, 13 figure

    Futures Contracts in Islamic Finance: an Analytical Approach

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    Futures contracts provide a useful means of reducing risk because these are highly liquid instruments that can be entered into or liquidated at any time. However, the debate on the legitimacy or otherwise of these contracts in the Islamic commercial law continues to invoke different contentions. The paper accentuates the fact that futures contracts are at bottom a new phenomenon of this age which have no precedent or parallel in the conventional law of transactions (muamalat). Therefore their legality or otherwise should be looked into with the Islamic viewpoint of general permissibility in relation to transactions. The paper examines a number of jurisprudential and legal issues such as non-existence of the subject-matter, sale prior to taking possession, bai al-kali bil-kali, speculation and hedging, and concludes that futures contracts are allowed to benefit from. However, only hedgers can take advantage of them. These instruments can never be used for purely speculative purposes where making or taking delivery is not intended. Although it is not necessary to pay the complete price to the seller at the time of the contract yet some other precautionary measures such as a bank guarantee or a fair amount of money to be given to the seller should be taken to ensure that pure speculation is scrupulously forestalled and the delivery would certainly be made

    Short-Range Correlations and Cooling of Ultracold Fermions in the Honeycomb Lattice

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    We use determinantal quantum Monte Carlo simulations and numerical linked-cluster expansions to study thermodynamic properties and short-range spin correlations of fermions in the honeycomb lattice. We find that, at half filling and finite temperatures, nearest-neighbor spin correlations can be stronger in this lattice than in the square lattice, even in regimes where the ground state in the former is a semimetal or a spin liquid. The honeycomb lattice also exhibits a more pronounced anomalous region in the double occupancy that leads to stronger adiabatic cooling than in the square lattice. We discuss the implications of these findings for optical lattice experiments.Comment: 5 pages, 4 figure

    Sequestering atmospheric CO<sub>2</sub> inorganically:a solution for Malaysia's CO<sub>2</sub> emission

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    Malaysia is anticipating an increase of 68.86% in CO2 emission in 2020, compared with the 2000 baseline, reaching 285.73 million tonnes. A major contributor to Malaysia's CO2 emissions is coal-fired electricity power plants, responsible for 43.4% of the overall emissions. Malaysia's forest soil offers organic sequestration of 15 tonnes of CO2 ha(-1) year(-1). Unlike organic CO2 sequestration in soil, inorganic sequestration of CO2 through mineral carbonation, once formed, is considered as a permanent sink. Inorganic CO2 sequestration in Malaysia has not been extensively studied, and the country's potential for using the technique for atmospheric CO2 removal is undefined. In addition, Malaysia produces a significant amount of solid waste annually and, of that, demolition concrete waste, basalt quarry fine, and fly and bottom ashes are calcium-rich materials suitable for inorganic CO2 sequestration. This project introduces a potential solution for sequestering atmospheric CO2 inorganically for Malaysia. If lands associated to future developments in Malaysia are designed for inorganic CO2 sequestration using demolition concrete waste, basalt quarry fine, and fly and bottom ashes, 597,465 tonnes of CO2 can be captured annually adding a potential annual economic benefit of (sic)4,700,000.</p
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