8,623 research outputs found
Parametric study on the impact of thermal bridges on the heat loss of internally insulated buildings
Internal wall insulation as energy efficiency retrofit measure could considerably help to reduce the greenhouse gas emissions of more than 6 million solid wall buildings in the UK. However during retrofit, junctions that are hard to reach are often left uninsulated, increasing heat loss and surface mould growth risk at thermal bridges. This paper presents a parametric study on the impact of thermal bridges on the total heat loss of an internally insulated mid-terrace house. Findings showed that heat flux through junctions occurred mainly at reveals and that the total heat flux at junctions per unit of exposed area was often higher than the default value used in the UK
Electron Transfer in Donor-Acceptor Systems: Many-Particle Effects and Influence of Electronic Correlations
We investigate electron transfer processes in donor-acceptor systems with a
coupling of the electronic degrees of freedom to a common bosonic bath. The
model allows to study many-particle effects and the influence of the local
Coulomb interaction U between electrons on donor and acceptor sites. Using the
non-perturbative numerical renormalization group approach we find distinct
differences between the electron transfer characteristics in the single- and
two-particle subspaces. We calculate the critical electron-boson coupling
alpha_c as a function of and show results for density-density correlation
functions in the whole parameter space. The possibility of many-particle
(bipolaronic) and Coulomb-assisted transfer is discussed.Comment: 4 pages, 4 figure
Efficient Energy Transfer in Light-Harvesting Systems, II: Quantum-Classical Comparison, Flux Network, and Robustness Analysis
Following the calculation of optimal energy transfer in thermal environment
in our first paper (Wu et al., New J. Phys., 2010, 12, 105012), full quantum
dynamics and leading-order `classical' hopping kinetics are compared in the
seven-site Fenna-Matthews-Olson (FMO) protein complex. The difference between
these two dynamic descriptions is due to higher-order quantum corrections. Two
thermal bath models, classical white noise (the Haken-Strobl-Reineker model)
and quantum Debye model, are considered. In the seven-site FMO model, we
observe that higher-order corrections lead to negligible changes in the
trapping time or in energy transfer efficiency around the optimal and
physiological conditions (2% in the HSR model and 0.1% in the quantum Debye
model for the initial site at BChl 1). However, using the concept of integrated
flux, we can identify significant differences in branching probabilities of the
energy transfer network between hopping kinetics and quantum dynamics (26% in
the HSR model and 32% in the quantum Debye model for the initial site at BChl
1). This observation indicates that the quantum coherence can significantly
change the distribution of energy transfer pathways in the flux network with
the efficiency nearly the same. The quantum-classical comparison of the average
trapping time with the removal of the bottleneck site, BChl 4, demonstrates the
robustness of the efficient energy transfer by the mechanism of multi-site
quantum coherence. To reconcile with the latest eight-site FMO model, the
quantum-classical comparison with the flux network analysis is summarized in
the appendix. The eight-site FMO model yields similar trapping time and network
structure as the seven-site FMO model but leads to a more disperse distribution
of energy transfer pathways.Comment: submitted to Journal of Chemical Physic
Andreev bound states and tunneling characteristics of a non-centrosymmetric superconductor
The tunneling characteristics of planar junctions between a normal metal and
a non-centrosymmetric superconductor like CePt3Si are examined. It is shown
that the superconducting phase with mixed parity can give rise to
characteristic zero-bias anomalies in certain junction directions. The origin
of these zero-bias anomalies are Andreev bound states at the interface. The
tunneling characteristics for different directions allow to test the structure
of the parity-mixed pairing state.Comment: 4 pages, 3 figure
Relationship between solid state structure and solution stability of copper(ii)-hydroxypyridinecarboxylate complexes
The complementary solid state/solution studies of the systematic series of bioactive ligands 3-hydroxy-
1-methyl-4-pyridinecarboxylate (L1), 3-hydroxy-1,2,6-trimethyl-4-pyridinecarboxylate (L2), 4-hydroxy-1-
methyl-3-pyridinecarboxylate (L3), 4-hydroxy-1,6-dimethyl-3-pyridinecarboxylate (L4), 4-hydroxy-1-(2-
hydroxyethyl)-6-methyl-3-pyridinecarboxylate (L5) and 4-hydroxy-1-(2-carboxyethyl)-6-methyl-3-
pyridinecarboxylate (L6) with copper(II) have been performed in order to design efficient chelating drugs
for the treatment of metal overloading conditions. Single crystals of [Cu(L1)2(H2O)]3H2O (1) (monomer) with
axial water coordination, [Cu2(L2)4]6H2O (2) and [Cu2(L3)4]4H2O (3) (cyclic dimers), where pyridinolato and
carboxylato oxygens, respectively, act as linkers between adjacent copper complexes, [Cu(L4)2]n3H2O (4) (1D
polymer) and [Cu3(L5)6]18H2O (5) (trimer), constructed using two square-pyramidal and one elongated
octahedral Cu(II) complexes have been determined by SXRD. The bidentate coordination mode of the ligands
has been found preferentially with cis arrangements in 1 and 2 and trans arrangements in 3\u20135. The solution
speciation and complex stability of aqueous solutions have been studied by pH-dependent electron
paramagnetic resonance spectroscopy resulting in the detection of solely monomeric [CuL]+ and [CuL2]
complexes. The stability order obtained for the [CuL]+ complexes could be correlated with the deprotonation
constants of their hydroxyl group (log bLH) reflecting that the higher acidity increases the complex stability in
the order L2 o L1 E L6 o L4 E L5 o L3. This stability order elucidates the different axial linkers in the
cyclic dimers 2 and 3. DFT quantum-chemical calculations support the effect of the electron distribution on
the established stability order
Localization of charge carriers in layered crystals MexTiSe 2 (Me = Cr, Mn, Cu) studied by the resonant photoemission
The probability of charge transfer in layered titanium diselenide between monolayers containing Cr, Mn, and Cu with different concentrations and host lattice TiSe2 is estimated according to the resonant photoemission data. For this purpose, the Raman-Auger contributions and narrow bands just below the Fermi energy were separated in the valence band spectra. These contributions provide the information about charge transfer. It is shown that the localization of the 3d electrons is typical for Cr and Cu atoms and strongly depends on theirs concentration. In MnxTiSe2, Mn 3d electrons are delocalized and the probability of the charge transfer is the greatest as compared with other compounds under investigation. © 2013 AIP Publishing LLC
Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters
The initial energy transfer in photosynthesis occurs between the
light-harvesting pigments and on ultrafast timescales. We analyze the
carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium
purpuratum as well as in an artificial light-harvesting dyad system by using
transient grating and two-dimensional electronic spectroscopy with 10 fs time
resolution. We find that F\"orster-type models reproduce the experimentally
observed 60 fs transfer times, but overestimate coupling constants, which leads
to a disagreement with both linear absorption and electronic 2D-spectra. We
show that a vibronic model, which treats carotenoid vibrations on both
electronic ground and excited state as part of the system's Hamiltonian,
reproduces all measured quantities. Importantly, the vibronic model presented
here can explain the fast energy transfer rates with only moderate coupling
constants, which are in agreement with structure based calculations.
Counterintuitively, the vibrational levels on the carotenoid electronic ground
state play a central role in the excited state population transfer to
bacteriochlorophyll as the resonance between the donor-acceptor energy gap and
vibrational ground state energies is the physical basis of the ultrafast energy
transfer rates in these systems
Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution
We prove that for a combined system of classical and quantum particles, it is
possible to write a dynamics for the classical particles that incorporates in a
natural way the Boltzmann equilibrium population for the quantum subsystem. In
addition, these molecular dynamics do not need to assume that the electrons
immediately follow the nuclear motion (in contrast to any adiabatic approach),
and do not present problems in the presence of crossing points between
different potential energy surfaces (conical intersections or spin-crossings).
A practical application of this molecular dynamics to study the effect of
temperature in molecular systems presenting (nearly) degenerate states - such
as the avoided crossing in the ring-closure process of ozone - is presented.Comment: published in New J. Phy
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