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