15,192 research outputs found
Relativistic Hydrodynamic Cosmological Perturbations
Relativistic cosmological perturbation analyses can be made based on several
different fundamental gauge conditions. In the pressureless limit the variables
in certain gauge conditions show the correct Newtonian behaviors. Considering
the general curvature () and the cosmological constant () in the
background medium, the perturbed density in the comoving gauge, and the
perturbed velocity and the perturbed potential in the zero-shear gauge show the
same behavior as the Newtonian ones in general scales. In the first part, we
elaborate these Newtonian correspondences. In the second part, using the
identified gauge-invariant variables with correct Newtonian correspondences, we
present the relativistic results with general pressures in the background and
perturbation. We present the general super-sound-horizon scale solutions of the
above mentioned variables valid for general , , and generally
evolving equation of state. We show that, for vanishing , the
super-sound-horizon scale evolution is characterised by a conserved variable
which is the perturbed three-space curvature in the comoving gauge. We also
present equations for the multi-component hydrodynamic situation and for the
rotation and gravitational wave.Comment: 16 pages, no figure, To appear in Gen. Rel. Gra
A strategic study of energy efficient and hybrid energy system options for a multi-family building in Korea
This study is to identify performance of energy efficiency measures and to match low-carbon and renewable energy (RE) systems supplies to demands in the context of multi-family residential buildings in Korea. An approach to the evaluation of the hybrid energy systems was investigated, including consideration of heat and power demand profiles, energy system combinations, building design options and strategies for matching supply to demand. The approach is encapsulated within an integrated software environment. Building energy simulation technology was exploited to make virtual energy use data. Low-carbon and RE system modelling techniques were used to predict energy supply profiles. A series of demand/supply matching-based analyses were made to identify the effect of energy efficient demand measures (e.g. roof-top gardens, innovative underfloor heating system) and evaluate the capacity utilisation factor from the hybrid energy systems. On the basis of performance information obtained at the conceptual design stage, the design team can pinpoint the most energy efficient demand/supply combination, and consequently, maximise the impact of hybrid energy systems adoption
String theoretic axion coupling and the evolution of cosmic structures
We examine the effects of the axion coupling to on the evolution
of cosmic structures. It is shown that the evolutions of the scalar- and
vector-type perturbations are not affected by this axion coupling. However the
axion coupling causes an asymmetric evolution of the two polarization states of
the tensor-type perturbation, which may lead to a sizable polarization
asymmetry in the cosmological gravitational wave if inflation involves a period
in which the axion coupling is important. The polarization asymmetry produced
during inflation are conserved over the subsequent evolution as long as the
scales remain in the large-scale limit, and thus this may lead to an observable
trace in the cosmic microwave background radiation.Comment: 10 pages, REVte
Singularities in scalar-tensor gravity
The analysis of certain singularities in scalar-tensor gravity contained in a
recent paper is completed, and situations are pointed out in which these
singularities cannot occur.Comment: 6 pages, LaTe
Cosmological Gravitational Wave in a Gravity with Quadratic Order Curvature Couplings
We present a set of equations describing the cosmological gravitational wave
in a gravity theory with quadratic order gravitational coupling terms which
naturally arise in quantum correction procedures. It is known that the
gravitational wave equation in the gravity theories with a general term
in the action leads to a second order differential equation with the only
correction factor appearing in the damping term. The case for a
term is completely different. The gravitational wave is described by a fourth
order differential equation both in time and space. However, curiously, we find
that the contributions to the background evolution are qualitatively the same
for both terms.Comment: 4 pages, revtex, no figure
Optical Self Energy in Graphene due to Correlations
In highly correlated systems one can define an optical self energy in analogy
to its quasiparticle (QP) self energy counterpart. This quantity provides
useful information on the nature of the excitations involved in inelastic
scattering processes. Here we calculate the self energy of the intraband
optical transitions in graphene originating in the electron-electron
interaction (EEI) as well as electron-phonon interaction (EPI). Although optics
involves an average over all momenta () of the charge carriers, the
structure in the optical self energy is nevertheless found to mirror mainly
that of the corresponding quasiparticles for equal to or near the Fermi
momentum . Consequently plasmaronic structures which are associated with
momenta near the Dirac point at are not important in the intraband
optical response. While the structure of the electron-phonon interaction (EPI)
reflects the sharp peaks of the phonon density of states, the excitation
spectrum associated with the electron-electron interaction is in comparison
structureless and flat and extends over an energy range which scales linearly
with the value of the chemical potential. Modulations seen on the edge of the
interband optical conductivity as it rises towards its universal background
value are traced to structure in the quasiparticle self energies around
of the lower Dirac cone associated with the occupied states.Comment: 30 pages, 10 figure
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