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See detailKinetics and thermodynamics of reversible polymerization in closed systems
Lahiri, S.; Wang, Y.; Esposito, Massimiliano UL et al

in New Journal of Physics (2015), 17(8),

Motivated by a recent study on the metabolism of carbohydrates in bacteria, we study the kinetics and thermodynamics of two classic models for reversible polymerization, one preserving the total polymer ... [more ▼]

Motivated by a recent study on the metabolism of carbohydrates in bacteria, we study the kinetics and thermodynamics of two classic models for reversible polymerization, one preserving the total polymer concentration and the other one not. The chemical kinetics is described by rate equations following the mass-action law. We consider a closed system and nonequilibrium initial conditions and show that the system dynamically evolves towards equilibrium where a detailed balance is satisfied. The entropy production during this process can be expressed as the time derivative of a Lyapunov function. When the solvent is not included in the description and the dynamics conserves the total concentration of polymer, the Lyapunov function can be expressed as a Kullback-Leibler divergence between the nonequilibrium and the equilibrium polymer length distribution. The same result holds true when the solvent is explicitly included in the description and the solution is assumed dilute, whether or not the total polymer concentration is conserved. Furthermore, in this case a consistent nonequilibrium thermodynamic formulation can be established and the out-of-equilibrium thermodynamic enthalpy, entropy and free energy can be identified. Such a framework is useful in complementing standard kinetics studies with the dynamical evolution of thermodynamic quantities during polymerization. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. [less ▲]

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See detailDouble quantum dot coupled to a quantum point contact: A stochastic thermodynamics approach
Cuetara, G. B.; Esposito, Massimiliano UL

in New Journal of Physics (2015), 17(9),

We study the nonequilibrium properties of an electronic circuit composed of a double quantum dot (DQD) channel capacitively coupled to a quantum point contact (QPC) within the framework of stochastic ... [more ▼]

We study the nonequilibrium properties of an electronic circuit composed of a double quantum dot (DQD) channel capacitively coupled to a quantum point contact (QPC) within the framework of stochastic thermodynamics. We show that the transition rates describing the dynamics satisfy a nontrivial local detailed balance and that the statistics of energy and particle currents across both channels obeys a fluctuation theorem. We analyze two regimes where the device operates as a thermodynamic machine and study its output power and efficiency fluctuations. We show that the electrons tunneling through the QPC without interacting with the DQD have a strong effect on the device efficiency. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. [less ▲]

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See detailWork statistics in stochastically driven systems
Verley, Gatien UL; Van den Broeck, Christian; Esposito, Massimiliano UL

in New Journal of Physics (2014), 16

We identify the conditions under which a stochastic driving that induces energy changes into a system coupled with a thermal bath can be treated as a work source. When these conditions are met, the work ... [more ▼]

We identify the conditions under which a stochastic driving that induces energy changes into a system coupled with a thermal bath can be treated as a work source. When these conditions are met, the work statistics satisfy the Crooks fluctuation theorem traditionally derived for deterministic drivings. We illustrate this fact by calculating and comparing the work statistics for a two-level system driven respectively by a stochastic and a deterministic piecewise constant protocol. [less ▲]

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See detailExperimental observation of magnetic poles inside bulk magnets via q \neq 0 Fourier modes of magnetostatic field
Perigo, Elio Alberto UL; Gilbert, E.P.; Metlov, K.L. et al

in New Journal of Physics (2014), 16

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See detailSingle-electron transistor strongly coupled to vibrations: counting statistics and fluctuation theorem
Schaller, Gernot; Krause, Thilo; Brandes, Tobias et al

in New Journal of Physics (2013), 033032

Using a simple quantum master equation approach, we calculate the full counting statistics of a single-electron transistor strongly coupled to vibrations. The full counting statistics contains both the ... [more ▼]

Using a simple quantum master equation approach, we calculate the full counting statistics of a single-electron transistor strongly coupled to vibrations. The full counting statistics contains both the statistics of integrated particle and energy currents associated with the transferred electrons and phonons. A universal as well as an effective fluctuation theorem are derived for the general case where the various reservoir temperatures and chemical potentials are different. The first relates to the entropy production generated in the junction, while the second reveals internal information of the system. The model recovers the Franck–Condon blockade, and potential applications to noninvasive molecular spectroscopy are discussed. [less ▲]

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See detailData pattern tomography: reconstruction with an unknown apparatus
Ignatenko, Andrew UL; Mogilevtsev, Dmitry; Maloshtan, Alexander et al

in New Journal of Physics (2013), 15

We propose a scheme for the reconstruction of the quantum state without a priori knowledge about the measurement setup. Using the data pattern approach, we develop an iterative procedure for obtaining ... [more ▼]

We propose a scheme for the reconstruction of the quantum state without a priori knowledge about the measurement setup. Using the data pattern approach, we develop an iterative procedure for obtaining information about the measurement which is sufficient for an estimation of a particular signal state. The method is illustrated with the examples of reconstruction with on/off detection and quantum homodyne tomography. [less ▲]

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See detailMicrowave-controlled coupling of Majorana bound states
Schmidt, Thomas UL; Nunnenkamp, Andreas; Bruder, Christoph

in New Journal of Physics (2013), 15

We propose microwave-controlled rotations for qubits realized as Majorana bound states. To this end, we study an inhomogeneous Kitaev chain in a microwave cavity. The chain consists of two topologically ... [more ▼]

We propose microwave-controlled rotations for qubits realized as Majorana bound states. To this end, we study an inhomogeneous Kitaev chain in a microwave cavity. The chain consists of two topologically nontrivial regions separated by a topologically trivial, gapped region. The Majorana bound states at the interfaces between the left (right) regions and the central region are coupled, and their energies are split by virtual cotunneling processes. The amplitude for these cotunneling processes decreases exponentially with the number of sites of the gapped region, and the decay length diverges as the gap of the topologically trivial region closes. We demonstrate that microwave radiation can exponentially enhance the coupling between the Majorana bound states, both for classical and quantized electric fields. By solving the appropriate Liouville equation numerically, we show that microwaves can drive Rabi oscillations in the Majorana sector. Our model emerges as an effective description of a topological semiconductor nanowire in a microwave cavity. Thus, our proposal provides an experimentally feasible way to obtain full single-qubit control necessary for universal quantum computation with Majorana qubits. [less ▲]

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See detailContribution of the buffer layer to the Raman spectrum of epitaxial graphene on SiC(0001)
Fromm, F.; Jr, M. H. Oliveira; Molina-Sanchez, Alejandro UL et al

in New Journal of Physics (2013), 15(4), 043031

We report a Raman study of the so-called buffer layer with $(6 3 6 3)R30^ $ periodicity which forms the intrinsic interface structure between epitaxial graphene and SiC(0001). We show that this interface ... [more ▼]

We report a Raman study of the so-called buffer layer with $(6 3 6 3)R30^ $ periodicity which forms the intrinsic interface structure between epitaxial graphene and SiC(0001). We show that this interface structure leads to a non-vanishing signal in the Raman spectrum at frequencies in the range of the D- and G-band of graphene and discuss its shape and intensity. Ab initio phonon calculations reveal that these features can be attributed to the vibrational density of states of the buffer layer. [less ▲]

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See detailMachine learning of molecular electronic properties in chemical compound space
Montavon, Gregoire; Rupp, Matthias; Gobre, Vivekanand et al

in NEW JOURNAL OF PHYSICS (2013), 15

The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful ... [more ▼]

The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel and predictive structure-property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning model, trained on a database of ab initio calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy polarizability, frontier orbital eigenvalues, ionization potential electron affinity and excitation energies. The machine learning model is based on a deep multi-task artificial neural network, exploiting the underlying correlations between various molecular properties. The input is identical to ab initio methods, i.e. nuclear charges and Cartesian coordinates of all atoms. For small organic molecules, the accuracy of such a `quantum machine' is similar, and sometimes superior, to modern quantum-chemical methods-at negligible computational cost. [less ▲]

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See detailStructure and energetics of benzene adsorbed on transition-metal surfaces: density-functional theory with van der Waals interactions including collective substrate response
Liu, Wei; Ruiz, Victor G.; Zhang, Guo-Xu et al

in NEW JOURNAL OF PHYSICS (2013), 15

The adsorption of benzene on metal surfaces is an important benchmark system for hybrid inorganic/organic interfaces. The reliable determination of the interface geometry and binding energy presents a ... [more ▼]

The adsorption of benzene on metal surfaces is an important benchmark system for hybrid inorganic/organic interfaces. The reliable determination of the interface geometry and binding energy presents a significant challenge for both theory and experiment. Using the Perdew-Burke-Ernzerhof (PBE), PBE+vdW (van der Waals) and the recently developed PBE+vdW(surf) (density-functional theory with vdW interactions that include the collective electronic response of the substrate) methods, we calculated the structures and energetics for benzene on transition-metal surfaces: Cu, Ag, Au, Pd, Pt, Rh and Ir. Our calculations demonstrate that vdW interactions increase the binding energy by more than 0.70 eV for physisorbed systems (Cu, Ag and Au) and by an even larger amount for strongly bound systems (Pd, Pt, Rh and Ir). The collective response of the substrate electrons captured via the vdW(surf) method plays a significant role for most substrates shortening the equilibrium distance by 0.25 angstrom for Cu and decreasing the binding energy by 0.27 eV for Rh. The reliability of our results is assessed by comparison with calculations using the random-phase approximation including renormalized single excitations and the experimental data from temperature-programmed desorption microcalorimetry measurements and low-energy electron diffraction. [less ▲]

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See detailResolution-of-identity approach to Hartree-Fock, hybrid density functionals, RPA, MP2 and GW with numeric atom-centered orbital basis functions
Ren, Xinguo; Rinke, Patrick; Blum, Volker et al

in NEW JOURNAL OF PHYSICS (2012), 14

The efficient implementation of electronic structure methods is essential for first principles modeling of molecules and solids. We present here a particularly efficient common framework for methods ... [more ▼]

The efficient implementation of electronic structure methods is essential for first principles modeling of molecules and solids. We present here a particularly efficient common framework for methods beyond semilocal density-functional theory (DFT), including Hartree-Fock (HF), hybrid density functionals, random-phase approximation (RPA) second-order Moller-Plesset perturbation theory (MP2) and the GW method. This computational framework allows us to use compact and accurate numeric atom-centered orbitals (NAOs), popular in many implementations of semilocal DFT, as basis functions. The essence of our framework is to employ the `resolution of identity (RI)' technique to facilitate the treatment of both the two-electron Coulomb repulsion integrals (required in all these approaches) and the linear density-response function (required for RPA and GW). This is possible because these quantities can be expressed in terms of the products of single-particle basis functions, which can in turn be expanded in a set of auxiliary basis functions (ABFs). The construction of ABFs lies at the heart of the RI technique, and we propose here a simple prescription for constructing ABFs which can be applied regardless of whether the underlying radial functions have a specific analytical shape (e.g. Gaussian) or are numerically tabulated. We demonstrate the accuracy of our RI implementation for Gaussian and NAO basis functions, as well as the convergence behavior of our NAO basis sets for the above-mentioned methods. Benchmark results are presented for the ionization energies of 50 selected atoms and molecules from the G2 ion test set obtained with the GW and MP2 self-energy methods, and the G2-I atomization energies as well as the S22 molecular interaction energies obtained with the RPA method. [less ▲]

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See detailCombination of high performance refractometry and infrared spectroscopy as a probe for chemically induced gelation and vitrification of epoxies
Müller, Ulrich UL; Philipp, Martine UL; Gervais, P. C. UL et al

in New Journal of Physics (2010), 12

A combination of infrared spectroscopy and high performance refractometry was used to investigate the chemically induced sol-gel and glass transition during the polymerization of epoxies. Representations ... [more ▼]

A combination of infrared spectroscopy and high performance refractometry was used to investigate the chemically induced sol-gel and glass transition during the polymerization of epoxies. Representations of the refractive index versus chemical conversion reveal an interesting insight in the optical properties accompanying gelation and vitrification. Whereas the electronic polarizability of the liquid state of small average molecular mass and the glassy state is dominated by the mass density, an unexpected excess polarizability observed during the gelation is attributed to cooperative dipole-dipole interactions. [less ▲]

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See detailEntropy production as correlation between system and reservoir
Esposito, Massimiliano UL; Lindenberg, Katja; Van den Broeck, Christian

in New Journal of Physics (2010), 12

We derive an exact (classical and quantum) expression for the entropy production of a finite system placed in contact with one or several finite reservoirs, each of which is initially described by a ... [more ▼]

We derive an exact (classical and quantum) expression for the entropy production of a finite system placed in contact with one or several finite reservoirs, each of which is initially described by a canonical equilibrium distribution. Although the total entropy of system plus reservoirs is conserved, we show that system entropy production is always positive and is a direct measure of system–reservoir correlations and/or entanglements. Using an exactly solvable quantum model, we illustrate our novel interpretation of the Second Law in a microscopically reversible finite-size setting, with strong coupling between the system and the reservoirs. With this model, we also explicitly show the approach of our exact formulation to the standard description of irreversibility in the limit of a large reservoir. [less ▲]

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See detailInterphases, gelation, vitrication, porous glasses and the generalized Cauchy relation: epoxy/silica nanocomposites
Philipp, Martine UL; Müller, Ulrich UL; Jiménez Riobóo, R. J. et al

in New Journal of Physics (2009), 11(2), 023015

The generalized Cauchy relation (gCR) of epoxy/silica nanocomposites does not show either the chemically induced sol–gel transition or the chemically induced glass transition in the course of ... [more ▼]

The generalized Cauchy relation (gCR) of epoxy/silica nanocomposites does not show either the chemically induced sol–gel transition or the chemically induced glass transition in the course of polymerization. Astonishingly, by varying the silica nanoparticles’ concentration between 0 and 25 vol%in the composites, the Cauchy parameter A of the gCR remains universal and can be determined from the pure epoxy’s elastic moduli. Air-filled porous silica glasses are considered as models for percolated silica particles. A longitudinal modulus versus density representation evidences the aforementioned transition phenomena during polymerization of the epoxy/silica nanocomposites. The existence of optically and mechanically relevant interphases is discussed. [less ▲]

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See detailAcoustic Profilometry Of Interphases In An Epoxy Due To Segregation and Diffusion Using Brillouin Microscopy.
Müller, Ulrich UL; Bactavatchalou, R.; Baller, Jörg UL et al

in New Journal of Physics (2008), 10(2), 023-031

Reactive network forming polymer systems like epoxies are of huge technological interest because of their adhesive properties based on specific interactions with a large variety of materials. These ... [more ▼]

Reactive network forming polymer systems like epoxies are of huge technological interest because of their adhesive properties based on specific interactions with a large variety of materials. These specific interactions alter the morphology of the epoxy within areas determined by the correlation length of these interactions. The changed morphology leads to interphases with altered (mechanical) properties. Besides these surface-induced interphases, bulk interphases do occur due to segregation, crystallization, diffusion, etc. A new experimental technique to characterize such mechanical interphases is μ-Brillouin spectroscopy (μ-BS). With μ-BS, we studied interphases and their formation in epoxies due to segregation of the constituent components and due to selective diffusion of one component. In the latter case, we will demonstrate the influence of changing the boundary conditions of the diffusion process on the shape of the interphase. [less ▲]

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See detailOrganization versus frustration: low temperature transitions in a gelatine-based gel
Philipp, Martine UL; Müller, Ulrich UL; Sanctuary, Roland UL et al

in New Journal of Physics (2008), 10

A commercial physical gel composed of gelatine, water and glycerol shows a sol–gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not ... [more ▼]

A commercial physical gel composed of gelatine, water and glycerol shows a sol–gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not observable in the longitudinal acoustic mode measured at hypersonic frequencies with Brillouin spectroscopy. Depending on the thermal treatment of the investigated material during the sol–gel transition and within the gel state, Brillouin spectroscopy reflects tremendously different hypersonic dynamics. These distinct dynamics are responsible for the formation of different glassy states at low temperatures including that of a glass-ceramic. The large variety of super-cooled and glassy states is attributed to distinct distributions of the gel's constituents within the samples. Surprisingly, the same gel state can be produced either by annealing the gel over months or by the non-equilibrium effect of thermo-diffusion (Soret effect) in the course of some minutes. [less ▲]

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See detailDifferent glassy states, as indicated by a violation of the generalized Cauchy relation.
Krüger, Jan-Kristian UL; Britz, Th; le Coutre, A. et al

in New Journal of Physics (2003), 5(80), 1-11

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus can be measured in addition to the longitudinal modulus already well above the thermal glass ... [more ▼]

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus can be measured in addition to the longitudinal modulus already well above the thermal glass transition. On slow cooling of the liquid through the thermal glass transition temperature Tg, both moduli show a kink-like behaviour and the function follows a generalized Cauchy relation (gCR) defined by the linear relation , which completely hides the glass transition. In this work we show experimentally that on fast cooling this linear transformation becomes violated within the glassy state, but that thermal ageing drives the elastic coefficients towards the gCR, i.e. towards a unique glassy state. [less ▲]

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