540 research outputs found
Energy performance assessment of HVAC systems by inspection and monitoring
The paper discusses the collection and processing of energy performance data as part of the
inspection of HVAC systems, aimed at identifying technically feasible and cost-effective
Energy Conservation Opportunities (ECO), as required by EPBD. Case studies developed by
the HARMONAC project have shown that low-cost or no-cost ECO’s - mostly related to
system operation and management - can be identified with an effective system monitoring.
Building Management Systems (BMS) may be a powerful tool for this task, provided their
HW and SW architecture is designed with adequate attention to energy monitoring. Dedicated
instrumentation – such as electricity meters and temperature loggers – may also be employed
as an alternative / integration to BMS monitoring. The paper also discusses the application of
data analysis tools – such as “carpet plots” and “energy signatures” – to the identification of
component malfunctioning, control problems, inadequate maintenance, or system schedule
optimization, and to the evaluation of achieved energy savings
Photochemical Energy Conversion with Artificial Molecular Machines
The exploitation of sunlight as a clean, renewable, and distributed energy source is key to facing the energetic demand of modern society in a sustainable and affordable fashion. In the past few decades, chemists have learned to make molecular machines, that is, synthetic chemical systems in which energy inputs cause controlled movements of molecular components that could be used to perform a task. A variety of artificial molecular machines operated by light have been constructed by implementing photochemical processes within appropriately designed (supra)molecular assemblies. These studies could open up new routes for the realization of nanostructured devices and materials capable to harness, convert, and store light energy
The Structure of the [Zn_In - V_P] Defect Complex in Zn Doped InP
We study the structure, the formation and binding energies and the transfer
levels of the zinc-phosphorus vacancy complex [Zn_In - V_P] in Zn doped p-type
InP, as a function of the charge, using plane wave ab initio DFT-LDA
calculations in a 64 atom supercell. We find a binding energy of 0.39 eV for
the complex, which is neutral in p-type material, the 0/-1 transfer level lying
0.50 eV above the valence band edge, all in agreement with recent positron
annihilation experiments. This indicates that, whilst the formation of
phosphorus vacancies (V_P) may be involved in carrier compensation in heavily
Zn doped material, the formation of Zn-vacancy complexes is not.
Regarding the structure: for charge states Q=+6 to -4 the Zn atom is in an
sp^2 bonded DX position and electrons added/removed go to/come from the
remaining dangling bonds on the triangle of In atoms. This reduces the
effective vacancy volume monatonically as electrons are added to the complex,
also in agreement with experiment. The reduction occurs through a combination
of increased In-In bonding and increased Zn-In electrostatic attraction. In
addition, for certain charge states we find complex Jahn-Teller behaviour in
which up to three different structures, (with the In triangle dimerised,
antidimerised or symmetric) are stable and are close to degenerate. We are able
to predict and successfully explain the structural behaviour of this complex
using a simple tight binding model.Comment: 10 pages text (postscript) plus 8 figures (jpeg). Submitted to Phys.
Rev.
Critical properties of homogeneous binary trees
Many-body states whose wave-function admits a representation in terms of a
uniform binary-tree tensor decomposition are shown to obey to power-law
two-body correlations functions. Any such state can be associated with the
ground state of a translational invariant Hamiltonian which, depending on the
dimension of the systems sites, involve at most couplings between
third-neighboring sites. A detailed analysis of their spectra shows that they
admit an exponentially large ground space.Comment: 6 pages, 2 figure
A positive tensor network approach for simulating open quantum many-body systems
Open many-body quantum systems play an important role in quantum optics and
condensed-matter physics, and capture phenomena like transport, interplay
between Hamiltonian and incoherent dynamics, and topological order generated by
dissipation. We introduce a versatile and practical method to numerically
simulate one-dimensional open quantum many-body dynamics using tensor networks.
It is based on representing mixed quantum states in a locally purified form,
which guarantees that positivity is preserved at all times. Moreover, the
approximation error is controlled with respect to the trace norm. Hence, this
scheme overcomes various obstacles of the known numerical open-system evolution
schemes. To exemplify the functioning of the approach, we study both stationary
states and transient dissipative behaviour, for various open quantum systems
ranging from few to many bodies.Comment: 13 pages, 7 figures, significant material on error bounds adde
A Master equation approach to modeling an artificial protein motor
Linear bio-molecular motors move unidirectionally along a track by
coordinating several different processes, such as fuel (ATP) capture,
hydrolysis, conformational changes, binding and unbinding from a track, and
center-of-mass diffusion. A better understanding of the interdependencies
between these processes, which take place over a wide range of different time
scales, would help elucidate the general operational principles of molecular
motors. Artificial molecular motors present a unique opportunity for such a
study because motor structure and function are a priori known. Here we describe
use of a Master equation approach, integrated with input from Langevin and
molecular dynamics modeling, to stochastically model a molecular motor across
many time scales. We apply this approach to a specific concept for an
artificial protein motor, the Tumbleweed.Comment: Submitted to Chemical Physics; 9 pages, 7 figure
Ground-state properties of rutile: electron-correlation effects
Electron-correlation effects on cohesive energy, lattice constant and bulk
compressibility of rutile are calculated using an ab-initio scheme. A
competition between the two groups of partially covalent Ti-O bonds is the
reason that the correlation energy does not change linearly with deviations
from the equilibrium geometry, but is dominated by quadratic terms instead. As
a consequence, the Hartree-Fock lattice constants are close to the experimental
ones, while the compressibility is strongly renormalized by electronic
correlations.Comment: 1 figure to appear in Phys. Rev.
Ground states of unfrustrated spin Hamiltonians satisfy an area law
We show that ground states of unfrustrated quantum spin-1/2 systems on
general lattices satisfy an entanglement area law, provided that the
Hamiltonian can be decomposed into nearest-neighbor interaction terms which
have entangled excited states. The ground state manifold can be efficiently
described as the image of a low-dimensional subspace of low Schmidt measure,
under an efficiently contractible tree-tensor network. This structure gives
rise to the possibility of efficiently simulating the complete ground space
(which is in general degenerate). We briefly discuss "non-generic" cases,
including highly degenerate interactions with product eigenbases, using a
relationship to percolation theory. We finally assess the possibility of using
such tree tensor networks to simulate almost frustration-free spin models.Comment: 14 pages, 4 figures, small corrections, added a referenc
Dynamics of gravity driven three-dimensional thin films on hydrophilic-hydrophobic patterned substrates
We investigate numerically the dynamics of unstable gravity driven
three-dimensional thin liquid films on hydrophilic-hydrophobic patterned
substrates of longitudinal stripes and checkerboard arrangements. The thin film
can be guided preferentially on hydrophilic longitudinal stripes, while fingers
develop on adjacent hydrophobic stripes if their width is large enough. On
checkerboard patterns, the film fingering occurs on hydrophobic domains, while
lateral spreading is favoured on hydrophilic domains, providing a mechanism to
tune the growth rate of the film. By means of kinematical arguments, we
quantitatively predict the growth rate of the contact line on checkerboard
arrangements, providing a first step towards potential techniques that control
thin film growth in experimental setups.Comment: 30 pages, 12 figure
- …