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05:24 König, Burkhard German 2014

Isolierung von Piperin aus schwarzem Pfeffer

Versuch 1022: Isolierung von Piperin aus schwarzem Pfeffer
  • Published: 2014
  • Publisher: König, Burkhard
  • Language: German
05:04 König, Burkhard German 2014

Oxidation von Anthracen zu Anthrachinon mit Kaliumpermanganat

Versuch 5026: Oxidation von Anthracen zu Anthrachinon mit Kaliumpermanganat
  • Published: 2014
  • Publisher: König, Burkhard
  • Language: German
05:10 König, Burkhard German 2014

H2O-Eliminierung aus 4-Hydroxy-4-methyl-2-pentanon

Versuch 1024: Eliminierung von Wasser aus 4-Hydroxy-4-methyl-2-pentanon
  • Published: 2014
  • Publisher: König, Burkhard
  • Language: German
05:44 König, Burkhard German 2014

Oxidation von Anthracen zu Anthrachinon mit Ammoniumcer(IV)-nitrat

Versuch 3021: Oxidation von Anthracen zu Anthrachinon mit Ammoniumcer(IV)-nitrat
  • Published: 2014
  • Publisher: König, Burkhard
  • Language: German
01:41 König, Burkhard No linguistic content; Not applicable 2014

Teaser zu den NOP-Videos

  • Published: 2014
  • Publisher: König, Burkhard
  • Language: No linguistic content; Not applicable
04:54 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2017

Anderson localization of composite excitations in disordered optomechanical arrays

Optomechanical (OMA) arrays are a promising future platform for studies of transport, many-body dynamics, quantum control and topological effects in systems of coupled photon and phonon modes. We introduce disordered OMA arrays, focusing on features of Anderson localization of hybrid photon–phonon excitations. It turns out that these represent a unique disordered system, where basic parameters can be easily controlled by varying the frequency and the amplitude of an external laser field. We show that the two-species setting leads to a non-trivial frequency dependence of the localization length for intermediate laser intensities. This could serve as a convincing evidence of localization in a non-equilibrium dissipative situation.
  • Published: 2017
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:55 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2016

Competitive annealing of multiple DNA origami: formation of chimeric origami

Scaffolded DNA origami are a robust tool for building discrete nanoscale objects at high yield. This strategy ensures, in the design process, that the desired nanostructure is the minimum free energy state for the designed set of DNA sequences. Despite aiming for the minimum free energy structure, the folding process which leads to that conformation is difficult to characterize, although it has been the subject of much research. In order to shed light on the molecular folding pathways, this study intentionally frustrates the folding process of these systems by simultaneously annealing the staple pools for multiple target or parent origami structures, forcing competition. A surprising result of these competitive, simultaneous anneals is the formation of chimeric DNA origami which inherit structural regions from both parent origami. By comparing the regions inherited from the parent origami, relative stability of substructures were compared. This allowed examination of the folding process with typical characterization techniques and materials. Anneal curves were then used as a means to rapidly generate a phase diagram of anticipated behavior as a function of staple excess and parent staple ratio. This initial study shows that competitive anneals provide an exciting way to create diverse new nanostructures and may be used to examine the relative stability of various structural motifs.
  • Published: 2016
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:43 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2016

Conceptual design of the beam source for the DEMO Neutral Beam Injectors

DEMO (DEMOnstration Fusion Power Plant) is a proposed nuclear fusion power plant that is intended to follow the ITER experimental reactor. The main goal of DEMO will be to demonstrate the possibility to produce electric energy from the fusion reaction. The injection of high energy neutral beams is one of the main tools to heat the plasma up to fusion conditions. A conceptual design of the Neutral Beam Injector (NBI) for the DEMO fusion reactor, is currently being developed by Consorzio RFX in collaboration with other European research institutes. High efficiency and low recirculating power, which are fundamental requirements for the success of DEMO, have been taken into special consideration for the DEMO NBI. Moreover, particular attention has been paid to the issues related to reliability, availability, maintainability and inspectability. A conceptual design of the beam source for the DEMO NBI is here presented featuring 20 sub-sources (two adjacent columns of 10 sub-sources each), following a modular design concept, with each sub-source featuring its radio frequency driver, capable of increasing the reliability and availability of the DEMO NBI. Copper grids with increasing size of the apertures have been adopted in the accelerator, with three main layouts of the apertures (circular apertures, slotted apertures and frame-like apertures for each sub-source). This design, permitting to significantly decrease the stripping losses in the accelerator without spoiling the beam optics, has been investigated with a self-consistent model able to study at the same time the magnetic field, the electrostatic field and the trajectory of the negative ions. Moreover, the status on the R&D carried out in Europe on the ion sources is presented.
  • Published: 2016
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:30 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2016

Measurement-only topological quantum computation without forced measurements

We investigate the measurement-only topological quantum computation (MOTQC) approach proposed by Bonderson et al (2008 Phys. Rev. Lett. 101 010501) where the braiding operation is shown to be equivalent to a series of topological charge 'forced measurements' of anyons. In a forced measurement, the charge measurement is forced to yield the desired outcome (e.g. charge 0) via repeatedly measuring charges in different bases. This is a probabilistic process with a certain success probability for each trial. In practice, the number of measurements needed will vary from run to run. We show that such an uncertainty associated with forced measurements can be removed by simulating the braiding operation using a fixed number of three measurements supplemented by a correction operator. Furthermore, we demonstrate that in practice we can avoid applying the correction operator in hardware by implementing it in software. Our findings greatly simplify the MOTQC proposal and only require the capability of performing charge measurements to implement topologically protected transformations generated by braiding exchanges without physically moving anyons.
  • Published: 2016
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:27 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2017

A system's wave function is uniquely determined by its underlying physical state

We address the question of whether the quantum-mechanical wave function Ψ of a system is uniquely determined by any complete description Λ of the system's physical state. We show that this is the case if the latter satisfies a notion of 'free choice'. This notion requires that certain experimental parameters—those that according to quantum theory can be chosen independently of other variables—retain this property in the presence of Λ. An implication of this result is that, among all possible descriptions Λ of a system's state compatible with free choice, the wave function } is as objective as Λ.
  • Published: 2017
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
06:27 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2015

Dielectric to pyroelectric phase transition induced by defect migration

Subjecting strontium titanate single crystals to an electric field in the order of 106 V m−1 is accompanied by a distortion of the cubic crystal structure, so that inversion symmetry vanishes and a polar phase is established. Since the polar nature of the migration-induced field-stabilized polar (MFP) phase is still unclear, the present work investigates and confirms the pyroelectric structure. We present measurements of thermally stimulated and pyroelectric currents that reveal a pyroelectric coefficient pMFP in the order of 30 μC K−1m−2. Therefore, a dielectric to pyroelectric phase transition in an originally centrosymmetric crystal structure with an inherent dipole moment is found, which is induced by defect migration. From symmetry considerations, we derive space group for the MFP phase of SrTiO3. The entire electroformation cycle yields additional information about the directed movement and defect chemistry of oxygen vacancies.
  • Published: 2015
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:03 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Does the CMB prefer a leptonic Universe?

Recent observations of the cosmic microwave background at smallest angular scales and updated abundances of primordial elements indicate an increase of the energy density and the helium-4 abundance with respect to standard big bang nucleosynthesis with three neutrino flavour. This calls for a reanalysis of the observational bounds on neutrino chemical potentials, which encode the number asymmetry between cosmic neutrinos and anti-neutrinos and thus measures the lepton asymmetry of the Universe. We compare recent data with a big bang nucleosynthesis code, assuming neutrino flavour equilibration via neutrino oscillations before the onset of big bang nucleosynthesis. We find a preference for negative neutrino chemical potentials, which would imply an excess of anti-neutrinos and thus a negative lepton number of the Universe. This lepton asymmetry could exceed the baryon asymmetry by orders of magnitude.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:10 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2014

Conductance microscopy of quantum dots weakly or strongly coupled to the conducting channel

We consider scanning gate conductance microscopy of an open quantum dot that is connected to the conducting channel using the wave function description of the quantum transport and a finite difference approach. We discuss the information contained in conductance (G) maps. We demonstrate that the maps for a delta-like potential perturbation exactly reproduce the local density of states for a quantum dot that is weakly coupled to the channel, i.e. when the connection of the channel to the dot transmits a single transport mode only. We explain this finding in terms of the Lippmann–Schwinger perturbation theory. We demonstrate that the signature of the weak coupling conditions is the conductance, which for P subbands at the Fermi level varies between and P in units of . For stronger coupling of the quantum dot to the channel, the G maps resolve the local density of states only for very specific work points, with the Fermi energy coinciding with quasi-bound energy levels.
  • Published: 2014
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:59 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Doping dependence of the electron–phonon and electron–spin fluctuation interactions in the high-Tc superconductor Bi2Sr2CaCu2O8+δ

Using ultrafast optical techniques, we detect two types of bosons strongly coupled to electrons in the family of Bi2Sr2CaCu2O8+δ (Bi-2212) from the underdoped to overdoped regimes. The different doping dependences of the electron–boson coupling strengths enable us to identify them as phonons and spin fluctuations: electron–phonon coupling (λe−ph) peaks at optimal doping, while electron–spin fluctuation coupling (λe−sf) decreases monotonically with doping. This observation is consistent with two facts: (i) superconductivity is in close proximity with antiferromagnetism at low dopings and (ii) a pronounced lattice renormalization effect at larger dopings.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:13 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2017

Latent heat of traffic moving from rest

Contrary to traditional thinking and driver intuition, here we show that there is no benefit to ground vehicles increasing their packing density at stoppages. By systematically controlling the packing density of vehicles queued at a traffic light on a Smart Road, drone footage revealed that the benefit of an initial increase in displacement for close-packed vehicles is completely offset by the lag time inherent to changing back into a 'liquid phase' when flow resumes. This lag is analogous to the thermodynamic concept of the latent heat of fusion, as the 'temperature' (kinetic energy) of the vehicles cannot increase until the traffic 'melts' into the liquid phase. These findings suggest that in situations where gridlock is not an issue, drivers should not decrease their spacing during stoppages in order to lessen the likelihood of collisions with no loss in flow efficiency. In contrast, motion capture experiments of a line of people walking from rest showed higher flow efficiency with increased packing densities, indicating that the importance of latent heat becomes trivial for slower moving systems.
  • Published: 2017
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:09 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Quantum algorithm and circuit design solving the Poisson equation

The Poisson equation occurs in many areas of science and engineering. Here we focus on its numerical solution for an equation in d dimensions. In particular we present a quantum algorithm and a scalable quantum circuit design which approximates the solution of the Poisson equation on a grid with error ε. We assume we are given a superposition of function evaluations of the right-hand side of the Poisson equation. The algorithm produces a quantum state encoding the solution. The number of quantum operations and the number of qubits used by the circuit is almost linear in d and polylog in ε−1. We present quantum circuit modules together with performance guarantees which can also be used for other problems.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:59 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Macroscopic optical response and photonic bands

We develop a formalism for the calculation of the macroscopic dielectric response of composite systems made of particles of one material embedded periodically within a matrix of another material, each of which is characterized by a well-defined dielectric function. The nature of these dielectric functions is arbitrary, and could correspond to dielectric or conducting, transparent or opaque, absorptive and dispersive materials. The geometry of the particles and the Bravais lattice of the composite are also arbitrary. Our formalism goes beyond the long-wavelength approximation as it fully incorporates retardation effects. We test our formalism through the study of the propagation of electromagnetic waves in two-dimensional photonic crystals made of periodic arrays of cylindrical holes in a dispersionless dielectric host. Our macroscopic theory yields a spatially dispersive macroscopic response which allows the calculation of the full photonic band structure of the system, as well as the characterization of its normal modes, upon substitution into the macroscopic field equations. We can also account approximately for the spatial dispersion through a local magnetic permeability and analyze the resulting dispersion relation, obtaining a region of left handedness.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:22 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Superconducting versus semiconducting electronic ground state in chirality-specific double-wall carbon nanotubes

By using two-loop renormalization group analysis, we explore the phase diagram with respect to the electron–phonon and Coulomb interaction strengths in the two (3,3)@(8,8) and (5,0)@(15,0) double-wall carbon nanotube systems (DWCNTs). Using estimation of the two types of coupling strengths from ab initio calculations, both systems are shown to scale to the superconducting fixed point as temperature decreases to zero. This is in contrast to the (3,3) and (5,0) single-wall carbon nanotubes, which scales to the Peierls-distorted semiconducting ground state. While the superconducting transition temperature can be quite low in the (3,3)@(8,8) system, the (5,0)@(15,0) promises observable superconducting behavior. Our result is in support of recent experimental observation of superconductivity in DWCNTs.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:10 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Controlling vortex chirality in hexagonal building blocks of artificial spin ice

We exploit dipolar coupling to control the magnetic states in assemblies of single-domain magnetic nanoislands, arranged in one, two and three adjacent hexagonal rings. On tailoring the shape anisotropy of specific islands, and thus their switching fields, we achieve particular target states with near perfect reliability, and are able to control the chirality of the vortex target states. The magnetic states are observed during magnetization reversal with x-ray photoemission electron microscopy and our results are generally in excellent agreement with a numerical model based on point dipoles and realistic values of disorder. We conclude with a quantitative discussion of how our results depend on disorder and the chosen bias in shape anisotropy.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:56 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2015

Mechanism of metallization and superconductivity suppression in YBa2(Cu0.97 Zn0.03)3 O6.92 revealed by 67Zn NQR

We measure the nuclear quadrupole resonance signal on the Zn site in nearly optimally doped YBa2Cu3O6.92, when Cu is substituted by 3% of isotopically pure 67Zn. We observe that Zn creates large insulating islands, confirming two earlier conjectures: that doping provokes an orbital transition in the CuO2 plane, which is locally reversed by Zn substitution, and that the islands are antiferromagnetic. Also, we find that the Zn impurity locally induces a breaking of the D4 symmetry. Cluster and DFT calculations show that the D4 symmetry breaking is due to the same partial lifting of degeneracy of the nearest-neighbor oxygen sites as in the LTT transition in BaxCuO4, similarly well-known to strongly suppress superconductivity (SC). These results show that in-plane oxygen 2p5 orbital configurations are principally involved in the metallicity and SC of all high-Tc cuprates, and provide a qualitative symmetry-based constraint on the SC mechanism.
  • Published: 2015
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:01 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) No linguistic content; Not applicable 2014

Communication with spatially modulated light through turbulent air across Vienna

Transverse spatial modes of light offer a large state-space with interesting physical properties. For exploiting these special modes in future long-distance experiments, the modes will have to be transmitted over turbulent free-space links. Numerous recent lab-scale experiments have found significant degradation in the mode quality after transmission through simulated turbulence and consecutive coherent detection. Here, we experimentally analyze the transmission of one prominent class of spatial modes—orbital-angular momentum (OAM) modes—through 3 km of strong turbulence over the city of Vienna. Instead of performing a coherent phase-dependent measurement, we employ an incoherent detection scheme, which relies on the unambiguous intensity patterns of the different spatial modes. We use a pattern recognition algorithm (an artificial neural network) to identify the characteristic mode patterns displayed on a screen at the receiver. We were able to distinguish between 16 different OAM mode superpositions with only a ~1.7% error rate and to use them to encode and transmit small grayscale images. Moreover, we found that the relative phase of the superposition modes is not affected by the atmosphere, establishing the feasibility for performing long-distance quantum experiments with the OAM of photons. Our detection method works for other classes of spatial modes with unambiguous intensity patterns as well, and can be further improved by modern techniques of pattern recognition.
  • Published: 2014
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: No linguistic content; Not applicable
04:03 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Electronic structure of LuRh2Si2: 'small' Fermi surface reference to YbRh2Si2

We present band structure calculations and quantum oscillation measurements on LuRh2Si2, which is an ideal reference to the intensively studied quantum critical heavy-fermion system YbRh2Si2. Our band structure calculations show a strong sensitivity of the Fermi surface on the position of the silicon atoms zSi within the unit cell. Single crystal structure refinement and comparison of predicted and observed quantum oscillation frequencies and masses yield zSi = 0.379 c in good agreement with numerical lattice relaxation.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:54 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2014

Collective force generated by multiple biofilaments can exceed the sum of forces due to individual ones

Collective dynamics and force generation by cytoskeletal filaments are crucial in many cellular processes. Investigating growth dynamics of a bundle of N independent cytoskeletal filaments pushing against a wall, we show that chemical switching (ATP/GTP hydrolysis) leads to a collective phenomenon that is currently unknown. Obtaining force-velocity relations for different models that capture chemical switching, we show, analytically and numerically, that the collective stall force of N filaments is greater than N times the stall force of a single filament. Employing an exactly solvable toy model, we analytically prove the above result for N = 2. We, further, numerically show the existence of this collective phenomenon, for , in realistic models (with random and sequential hydrolysis) that simulate actin and microtubule bundle growth. We make quantitative predictions for the excess forces, and argue that this collective effect is related to the non-equilibrium nature of chemical switching.
  • Published: 2014
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:39 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2016

Time-resolved x-ray imaging of a laser-induced nanoplasma and its neutral residuals

The evolution of individual, large gas-phase xenon clusters, turned into a nanoplasma by a high power infrared laser pulse, is tracked from femtoseconds up to nanoseconds after laser excitation via coherent diffractive imaging, using ultra-short soft x-ray free electron laser pulses. A decline of scattering signal at high detection angles with increasing time delay indicates a softening of the cluster surface. Here we demonstrate, for the first time a representative speckle pattern of a new stage of cluster expansion for xenon clusters after a nanosecond irradiation. The analysis of the measured average speckle size and the envelope of the intensity distribution reveals a mean cluster size and length scale of internal density fluctuations. The measured diffraction patterns were reproduced by scattering simulations which assumed that the cluster expands with pronounced internal density fluctuations hundreds of picoseconds after excitation.
  • Published: 2016
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:03 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2014

Long range triplet Josephson current and 0−π transitions in tunable domain walls

The order parameter of superconducting pairs penetrating an inhomogeneous magnetic material can acquire a long range triplet component (LRTC) with non-zero spin projection. This state has been predicted and generated in proximity systems and Josephson junctions. We show, using a realistic domain wall of an exchange spring bilayer, how the LRTC emerges and can be tuned with the twisting of the magnetization. We also introduce a new kind of Josephson current reversal, the singlet-LRTC 0–π transition, that can be observed in one and the same system either by tuning the domain wall or by varying temperature.
  • Published: 2014
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:41 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2015

Metamaterials: supra-classical dynamic homogenization*

Metamaterials are artificial composite structures designed for controlling waves or fields, and exhibit interaction phenomena that are unexpected on the basis of their chemical constituents. These phenomena are encoded in effective material parameters that can be electronic, magnetic, acoustic, or elastic, and must adequately represent the wave interaction behavior in the composite within desired frequency ranges. In some cases—for example, the low frequency regime—there exist various efficient ways by which effective material parameters for wave propagation in metamaterials may be found. However, the general problem of predicting frequency-dependent dynamic effective constants has remained unsolved. Here, we obtain novel mathematical expressions for the effective parameters of two-dimensional metamaterial systems valid at higher frequencies and wavelengths than previously possible. By way of an example, random configurations of cylindrical scatterers are considered, in various physical contexts: sound waves in a compressible fluid, anti-plane elastic waves, and electromagnetic waves. Our results point towards a paradigm shift in our understanding of these effective properties, and metamaterial designs with functionalities beyond the low-frequency regime are now open for innovation.
  • Published: 2015
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:22 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Nonlinear cross-Kerr quasiclassical dynamics

We study the quasiclassical dynamics of the cross-Kerr effect. In this approximation, the typical periodical revivals of the decorrelation between the two polarization modes disappear and remain entangled. By mapping the dynamics onto the Poincaré space, we find simple conditions for polarization squeezing. When dissipation is taken into account, the shape of the states in such a space is not considerably modified, but their size is reduced.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:10 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Bacterial biofilm mechanical properties persist upon antibiotic treatment and survive cell death

Bacteria living on surfaces form heterogeneous three-dimensional consortia known as biofilms, where they exhibit many specific properties one of which is an increased tolerance to antibiotics. Biofilms are maintained by a polymeric network and display physical properties similar to that of complex fluids. In this work, we address the question of the impact of antibiotic treatment on the physical properties of biofilms based on recently developed tools enabling the in situ mapping of biofilm local mechanical properties at the micron scale. This approach takes into account the material heterogeneity and reveals the spatial distribution of all the small changes that may occur in the structure. With an Escherichia coli biofilm, we demonstrate using in situ fluorescent labeling that the two antibiotics ofloxacin and ticarcillin—targeting DNA replication and membrane assembly, respectively—induced no detectable alteration of the biofilm mechanical properties while they killed the vast majority of the cells. In parallel, we show that a proteolytic enzyme that cleaves extracellular proteins into short peptides, but does not alter bacterial viability in the biofilm, clearly affects the mechanical properties of the biofilm structure, inducing a significant increase of the material compliance. We conclude that conventional biofilm control strategy relying on the use of biocides targeting cells is missing a key target since biofilm structural integrity is preserved. This is expected to efficiently promote biofilm resilience, especially in the presence of persister cells. In contrast, the targeting of polymer network cross-links—among which extracellular proteins emerge as major players—offers a promising route for the development of rational multi-target strategies to fight against biofilms.
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
02:58 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2018

Quantum walk on a chimera graph

We analyse a continuous-time quantum walk on a chimera graph, which is a graph of choice for designing quantum annealers, and we discover beautiful quantum walk features such as localization that starkly distinguishes classical from quantum behaviour. Motivated by technological thrusts, we study continuous-time quantum walk on enhanced variants of the chimera graph and on diminished chimera graph with a random removal of vertices. We explain the quantum walk by constructing a generating set for a suitable subgroup of graph isomorphisms and corresponding symmetry operators that commute with the quantum walk Hamiltonian; the Hamiltonian and these symmetry operators provide a complete set of labels for the spectrum and the stationary states. Our quantum walk characterization of the chimera graph and its variants yields valuable insights into graphs used for designing quantum-annealers.
  • Published: 2018
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:14 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2015

Stückelberg interference in a superconducting qubit under periodic latching modulation

When the level separation of a qubit is modulated periodically across an avoided crossing, tunneling to the excited state—and consequently Landau–Zener–Stückelberg interference—can occur. The types of modulation studied so far correspond to a continuous change of the level separation. Here we study periodic latching modulation, in which the level separation is switched abruptly between two values and is kept constant otherwise. In this case, the conventional approach based on the asymptotic Landau–Zener formula for transition probabilities is not applicable. We develop a novel adiabatic-impulse model for the evolution of the system and derive the resonance conditions. Additionally, we derive analytical results based on the rotating-wave approximation (RWA). The adiabatic-impulse model and the RWA results are compared with those of a full numerical simulation. These theoretical predictions are tested in an experimental setup consisting of a transmon whose flux bias is modulated with a square wave form. A rich spectrum is observed, with distinctive features correspoding to two regimes: slow-modulation and fast-modulation. These experimental results are shown to be in very good agreement with the theoretical models. Also, differences with respect to the well known case of sinusoidal modulation are discussed, both theoretically and experimentally.
  • Published: 2015
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:16 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2016

Precise space–time positioning for entanglement harvesting

We explore the crucial role of relative space–time positioning between the two detectors in an operational two-party entanglement-harvesting protocol. Specifically we show that the protocol is robust if imprecision in spatial positioning and clock synchronization are much smaller than the spatial separation between the detectors and its light-crossing time thereof. This in principle guarantees robustness if the imprecision is comparable to a few times the size of the detectors, which suggests entanglement harvesting could be explored for tabletop experiments. On the other hand, keeping the effects of this imprecision under control would be demanding on astronomical scales.
  • Published: 2016
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:37 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2013

Recombination effects in soft-x-ray cluster interactions at the xenon giant resonance

Xenon clusters in an intense soft-x-ray pulse are examined in detail and compared with recent experimental results by reproducing the experimental signals (Thomas et al 2009 J. Phys. B: At. Mol. Opt. Phys. 42 134018). Good agreement is found between our theoretical model and the experimental results. A detailed analysis of the experimental signals and their constituents is performed. We find that, unlike large clusters, the smaller N = 147 have a saturated electron kinetic energy distribution (Bostedt et al 2010 New J. Phys. 12 083004). We also find the highest charge states which are detected were initially on the outer shell of the cluster whereas the core ions recombine significantly and are detected as only moderately or singly charged (Hoener et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 181001). Further, we find it is the outer shell ions which obtain the highest kinetic energy upon disintegration (Trost et al 2012 Frontiers in Optics Conf. (Optical Society of America) p FW5G.5).
  • Published: 2013
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
04:41 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2016

Optimal network modification for spectral radius dependent phase transitions

The dynamics of contact processes on networks is often determined by the spectral radius of the networks adjacency matrices. A decrease of the spectral radius can prevent the outbreak of an epidemic, or impact the synchronization among systems of coupled oscillators. The spectral radius is thus tightly linked to network dynamics and function. As such, finding the minimal change in network structure necessary to reach the intended spectral radius is important theoretically and practically. Given contemporary big data resources such as large scale communication or social networks, this problem should be solved with a low runtime complexity. We introduce a novel method for the minimal decrease in weights of edges required to reach a given spectral radius. The problem is formulated as a convex optimization problem, where a global optimum is guaranteed. The method can be easily adjusted to an efficient discrete removal of edges. We introduce a variant of the method which finds optimal decrease with a focus on weights of vertices. The proposed algorithm is exceptionally scalable, solving the problem for real networks of tens of millions of edges in a short time.
  • Published: 2016
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:54 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2014

Method to enhance the resolution of x-ray coherent diffraction imaging for non-crystalline bio-samples

To circumvent the problem of radiation damage when using an x-ray coherent diffraction imaging experiment to resolve the structure of biological samples, we propose a method to add objects made of heavy atoms with the bio-samples or we load the samples on a template made of heavy atoms. This template method is shown by a numerical simulation (including shot noise) to be able to resolve the structure of a virus better than without the template. A counter-intuitive result is obtained, where heavier templates have a better resolution, even if the diffraction intensity of the bio-sample is much smaller than the noise intensity. In addition, the method also helps to greatly increase the efficiency of phase retrieval. We also provide a way to estimate the error to be expected if a particular experimental setting were chosen once the charge ratio between the sample and the template is estimated. Hence, this method will also help experiments choose the optimal setting for the best resolution with minimal radiation damage.
  • Published: 2014
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:19 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2014

The role of space charge in spin-resolved photoemission experiments

Spin-resolved photoemission is one of the most direct ways of measuring the magnetization of a ferromagnet. If all valence band electrons contribute, the measured average spin polarization is proportional to the magnetization. This is even the case if electronic excitations are present, and thus is of particular interest for studying the response of the magnetization to a pump laser pulse. Here, we demonstrate the feasibility of ultrafast spin-resolved photoemission using free electron laser (FEL) radiation and investigate the effect of space charge on the detected spin polarization. The sample is exposed to the radiation of the FEL FLASH in Hamburg. Surprisingly, the measured spin polarization depends on the fluence of the FEL radiation: a higher FEL fluence reduces the measured spin polarization. Space-charge simulations can explain this effect. These findings have consequences for future spin-polarized photoemission experiments using pulsed photon sources.
  • Published: 2014
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
03:03 Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG) English 2017

The ab initio study of unconventional superconductivity in CeCoIn5 and FeSe

The electronic structure and shape of the Fermi surface are known to be of fundamental importance for the superconducting instability in real materials. We demonstrate that such an instability may be explored by static Cooper pair susceptibility renormalized by pairing interaction and present an efficient method of its evaluation using Wannier orbitals derived from ab initio calculation. As an example, this approach is used to search for an unconventional superconducting phase of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) type in a heavy-fermion compound CeCoIn5 and an iron-based superconductor FeSe. The results suggest that the FFLO superconducting phase occurs at finite magnetic field in both materials.
  • Published: 2017
  • Publisher: Institute of Physics (IOP), Deutsche Physikalische Gesellschaft (DPG)
  • Language: English
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