305 research outputs found
Storage of hydrogen in nanostructured carbon materials
Recent developments focusing on novel hydrogen storage media have helped to benchmark nanostructured carbon materials as one of the ongoing strategic research areas in science and technology. In particular, certain microporous carbon powders, carbon nanomaterials, and specifically carbon nanotubes stand to deliver unparalleled performance as the next generation of base materials for storing hydrogen. Accordingly, the main goal of this report is to overview the challenges, distinguishing traits, and apparent contradictions of carbon-based hydrogen storage technologies and to emphasize recently
developed nanostructured carbon materials that show potential to store hydrogen by physisorption and/or chemisorption mechanisms. Specifically touched upon are newer material preparation methods as well as experimental and theoretical attempts to elucidate, improve or predict hydrogen storage capacities, sorption–desorption kinetics, microscopic uptake mechanisms and temperature–pressure–loading interrelations in nanostructured carbons, particularly microporous powders and carbon nanotubes
Dualisation of the Symmetric Space Sigma Model with Couplings
The first-order formulation of the G/K symmetric space sigma model of the
scalar cosets of the supergravity theories is discussed when there is coupling
of (m-1)-form matter fields. The Lie superalgebra which enables the dualized
coset formulation is constructed for a general scalar coset G/K with matter
coupling where G is a non-compact real form of a semi-simple Lie group and K is
its maximal compact subgroup.Comment: 17 page
Non-linear Realisation of the N=2, D=6 Supergravity
We have applied the method of dualisation to construct the coset realisation
of the bosonic sector of the N=2, D=6 supergravity which is coupled to a tensor
multiplet. The bosonic field equations are regained through the Cartan-Maurer
equation which the Cartan form satisfies. The first-order formulation of the
theory is also obtained as a twisted self-duality condition within the
non-linear coset construction.Comment: 11 page
Non-Linear Realisation of the Pure N=4, D=5 Supergravity
We perform the non-linear realisation or the coset formulation of the pure
N=4, D=5 supergravity. We derive the Lie superalgebra which parameterizes a
coset map whose induced Cartan-Maurer form produces the bosonic field equations
of the pure N=4, D=5 supergravity by canonically satisfying the Cartan-Maurer
equation. We also obtain the first-order field equations of the theory as a
twisted self-duality condition for the Cartan-Maurer form within the
geometrical framework of the coset construction.Comment: 12 page
On the Symmetric Space Sigma-Model Kinematics
The solvable Lie algebra parametrization of the symmetric spaces is
discussed. Based on the solvable Lie algebra gauge two equivalent formulations
of the symmetric space sigma model are studied. Their correspondence is
established by inspecting the normalization conditions and deriving the field
transformation laws.Comment: 17 page
Statistical study of thermal contact conductance
A theoretical analysis of the principles of interfacial thermal conductance between two heated metal surfaces in mutual contact is presented. It was determined that when heat flows from one metal to the other, the flow lines converge toward the actual contact points since the thermal conductivities of the metals are much greater than any intervening medium such as air or fluids. The converging lines cause contact resistance, which is usually high compared to the resistances offered to heat flow by metals. The resultant variation in resistance can produce unreliable equipment for aerospace and industrial applications unless the conductance can be determined accurately
Integrated field equations of heterotic supergravities
The first-order bosonic field equations of the D-dimensional effective low
energy theory which describes the massless background coupling of the
D-dimensional fully Higgsed heterotic string are derived.Comment: 12 page
Symmetric space sigma-model dynamics: Current formalism
After explicitly constructing the symmetric space sigma model lagrangian in
terms of the coset scalars of the solvable Lie algebra gauge in the current
formalism we derive the field equations of the theory.Comment: 10 page
The Non-Split Scalar Coset in Supergravity Theories
The general non-split scalar coset of supergravity theories is discussed.The
symmetric space sigma model is studied in two equivalent formulations and for
different coset parametrizations.The dualisation and the local first order
formulation is performed for the non-split scalar coset G/K when the rigid
symmetry group G is a real form of a non-compact semisimple Lie group (not
necessarily split) and the local symmetry group K is G's maximal compact
subgroup.A comparison with the scalar cosets arising in the
T^{10-D}-compactification of the heterotic string theory in ten dimensions is
also mentioned.Comment: 26 page
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