TY  - JOUR
A1  - Zoller, Peter
A1  - Beth, Thomas
A1  - Binosi, D.
A1  - Blatt, Rainer
A1  - Briegel, Hans J.
A1  - Bruss, D.
A1  - Calarco, Tommaso
A1  - Cirac, Juan Ignacio
A1  - Deutsch, David
A1  - Eisert, Jens
A1  - Ekert, Artur
A1  - Fabre, Claude
A1  - Gisin, Nicolas
A1  - Grangiere, P.
A1  - Grassl, Markus
A1  - Haroche, Serge
A1  - Imamoglu, Atac
A1  - Karlson, A.
A1  - Kempe, Julia
A1  - Kouwenhoven, Leo P.
A1  - Kröll, S.
A1  - Leuchs, Gerd
A1  - Lewenstein, Maciej
A1  - Loss, Daniel
A1  - Lütkenhaus, Norbert
A1  - Massar, Serge
A1  - Mooij, J. E.
A1  - Plenio, Martin Bodo
A1  - Polzik, Eugene
A1  - Popescu, Sandu
A1  - Rempe, Gerhard
A1  - Sergienko, Alexander
A1  - Suter, David
A1  - Twamley, John
A1  - Wendin, Göran
A1  - Werner, Reinhard F.
A1  - Winter, Andreas
A1  - Wrachtrup, Jörg
A1  - Zeilinger, Anton
T1  - Quantum information processing and communication : Strategic report on current status, visions and goals for research in Europe
N2  - We present an excerpt of the document "Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe", which has been recently published in electronic form at the website of FET (the Future and Emerging Technologies Unit of the Directorate General Information Society of the European Commission, http://www.cordis.lu/ist/fet/qipc-sr.htm). This document has been elaborated, following a former suggestion by FET, by a committee of QIPC scientists to provide input towards the European Commission for the preparation of the Seventh Framework Program. Besides being a document addressed to policy makers and funding agencies (both at the European and national level), the document contains a detailed scientific assessment of the state-of-the-art, main research goals, challenges, strengths, weaknesses, visions and perspectives of all the most relevant QIPC sub-fields, that we report here
Y1  - 2005
SN  - 1434-6060
ER  - 
TY  - JOUR
A1  - Zoller, Gert
A1  - Holschneider, Matthias
A1  - Ben-Zion, Yehuda
T1  - The role of heterogeneities as a tuning parameter of earthquake dynamics
N2  - We investigate the influence of spatial heterogeneities on various aspects of brittle failure and seismicity in a model of a large strike-slip fault. The model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault, static/kinetic friction laws, creep with depth-dependent coefficients, and 3-D elastic stress transfer. The dynamic rupture is approximated on a continuous time scale using a finite stress propagation velocity ("quasidynamic model''). The model produces a "brittle- ductile'' transition at a depth of about 12.5 km, realistic hypocenter distributions, and other features of seismicity compatible with observations. Previous work suggested that the range of size scales in the distribution of strength-stress heterogeneities acts as a tuning parameter of the dynamics. Here we test this hypothesis by performing a systematic parameter-space study with different forms of heterogeneities. In particular, we analyze spatial heterogeneities that can be tuned by a single parameter in two distributions: ( 1) high stress drop barriers in near- vertical directions and ( 2) spatial heterogeneities with fractal properties and variable fractal dimension. The results indicate that the first form of heterogeneities provides an effective means of tuning the behavior while the second does not. In relatively homogeneous cases, the fault self-organizes to large-scale patches and big events are associated with inward failure of individual patches and sequential failures of different patches. The frequency-size event statistics in such cases are compatible with the characteristic earthquake distribution and large events are quasi-periodic in time. In strongly heterogeneous or near-critical cases, the rupture histories are highly discontinuous and consist of complex migration patterns of slip on the fault. In such cases, the frequency-size and temporal statistics follow approximately power-law relations
Y1  - 2005
SN  - 0033-4553
ER  - 
TY  - JOUR
A1  - Zoller, Gert
A1  - Hainzl, Sebastian
A1  - Holschneider, Matthias
A1  - Ben-Zion, Yehuda
T1  - Aftershocks resulting from creeping sections in a heterogeneous fault
N2  - We show that realistic aftershock sequences with space-time characteristics compatible with observations are generated by a model consisting of brittle fault segments separated by creeping zones. The dynamics of the brittle regions is governed by static/kinetic friction, 3D elastic stress transfer and small creep deformation. The creeping parts are characterized by high ongoing creep velocities. These regions store stress during earthquake failures and then release it in the interseismic periods. The resulting postseismic deformation leads to aftershock sequences following the modified Omori law. The ratio of creep coefficients in the brittle and creeping sections determines the duration of the postseismic transients and the exponent p of the modified Omori law
Y1  - 2005
SN  - 0094-8276
ER  - 
TY  - JOUR
A1  - Zillmer, Rüdiger
A1  - Pikovskij, Arkadij
T1  - Continuous approach for the random-field Ising chain
N2  - We study the random-field Ising chain in the limit of strong exchange coupling. In order to calculate the free energy we apply a continuous Langevin-type approach. This continuous model can be solved exactly, whereupon we are able to locate the crossover between an exponential and a power-law decay of the free energy with increasing coupling strength. In terms of magnetization, this crossover restricts the validity of the linear scaling. The known analytical results for the free energy are recovered in the corresponding limits. The outcomes of numerical computations for the free energy are presented, which confirm the results of the continuous approach. We also discuss the validity of the replica method which we then utilize to investigate the sample-to-sample fluctuations of the finite size free energy
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Zhu, M. Q.
A1  - Armbruster, Dieter
A1  - Katzorke, Ines
T1  - Does synchronization of networks of chaotic maps lead to control?
N2  - We consider networks of chaotic maps with different network topologies. In each case, they are coupled in such a way as to generate synchronized chaotic solutions. By using the methods of control of chaos we are controlling a single map into a predetermined trajectory. We analyze the reaction of the network to such a control. Specifically we show that a line of one-dimensional logistic maps that are unidirectionally coupled can be controlled from the first oscillator whereas a ring of diffusively coupled maps cannot be controlled for more than 5 maps. We show that rings with more elements can be controlled if every third map is controlled. The dependence of unidirectionally coupled maps on noise is studied. The noise level leads to a finite synchronization lengths for which maps can be controlled by a single location. A two-dimensional lattice is also studied. (C) 2005 American Institute of Physics
Y1  - 2005
SN  - 1054-1500
ER  - 
TY  - JOUR
A1  - Zhou, Changsong
A1  - Kurths, Jürgen
T1  - Noise-sustained and controlled synchronization of stirred excitable media by external forcing
N2  - Most of the previous studies on constructive effects of noise in spatially extended systems have focused on static media, e.g., of the reaction diffusion type. Because many active chemical or biological processes occur in a fluid environment with mixing, we investigate here the interplay among noise, excitability, mixing and external forcing in excitable media advected by a chaotic flow, in a two-dimensional FitzHugh-Nagumo model described by a set of reaction- advection-diffusion equations. In the absence of external forcing, noise may generate sustained coherent oscillations of the media in a range of noise intensities and stirring rates. We find that these noise-sustained oscillations can be synchronized by external periodic signals much smaller than the threshold. Analysis of the locking regions in the parameter space of the signal period, stirring rate and noise intensity reveals that the mechanism underlying the synchronization behaviour is a matching between the time scales of the forcing signal and the noise-sustained oscillations. The results demonstrate that, in the presence of a suitable level of noise, the stirred excitable media act as self-sustained oscillatory systems and become much easier to be entrained by weak external forcing. Our results may be verified in experiments and are useful to understand the synchronization of population dynamics of oceanic ecological systems by annual cycles
Y1  - 2005
SN  - 1367-2630
ER  - 
TY  - JOUR
A1  - Zhang, B.
A1  - Henkel, Carsten
A1  - Haller, E.
A1  - Wildermuth, S.
A1  - Hofferberth, S.
A1  - Kruger, P.
A1  - Schmiedmayer, Jörg
T1  - Relevance of sub-surface chip layers for the lifetime of magnetically trapped atoms
N2  - We investigate the lifetime of magnetically trapped atoms above a planar, layered atom chip structure. Numerical calculations of the thermal magnetic noise spectrum are performed, based on the exact magnetic Green function and multi layer reflection coefficients. We have performed lifetime measurements where the center of a side guide trap is laterally shifted with respect to the current carrying wire using additional bias fields. Comparing the experiment to theory, we find a fair agreement and demonstrate that for a chip whose topmost layer is metallic, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a, much smaller conductivity; essentially the same magnetic noise would be obtained with a metallic membrane suspended in vacuum. Based on our theory we give general scaling laws of how to reduce the effect of surface magnetic noise on the trapped atoms
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Zen, Achmad
A1  - Saphiannikova, Marina
A1  - Neher, Dieter
A1  - Asawapirom, Udom
A1  - Scherf, Ullrich
T1  - Comparative study of the field-effect mobility of a copolymer and a binary blend based on poly(3- alkylthiophene)s
N2  - The performance of highly soluble regioregular poly[ (3-hexylthiophene)-co-(3-octylthiophetie)] (P3HTOT) as a semiconducting material in organic field-effect transistors (OFETs) is presented in comparison to that of the corresponding homopolymers. Transistors made from as-prepared layers of P3HTOT exhibit a mobility of ca. 7 x 10(-3) cm(2) V-1 s(-1), which is comparable to the performance of transistors made from as-prepared poly(3-hexylthiophene) (P3HT) and almost 6 times larger than the mobility of transistors prepared with poly(3-octylthiophene) (P3OT). On the other hand, the solubility parameter delta(p) of P3HTOT is close to that of the highly soluble P3OT. Moreover, compared to a physical blend of poly(3-hexylthiophene) and poly(3-octylthiophene), the mobility of P3HTOT devices is almost twice as large and the performance does not degrade upon annealing at elevated temperatures. Therefore, the copolymer approach outlined here may be one promising step toward an optimum balance between a Sufficient processability of the polymers from common organic solvents, a high solid state order, and applicable OFET performances
Y1  - 2005
SN  - 0897-4756
ER  - 
TY  - JOUR
A1  - Zen, Achmad
A1  - Neher, Dieter
A1  - Silmy, Kamel
A1  - Hollander, A.
A1  - Asawapirom, Udom
A1  - Scherf, Ullrich
T1  - Improving the performance of organic field effect transistor by optimizing the gate insulator surface
N2  - The effect of oxygen plasma treatment and/or silanization with hexamethyldisilazane (HMDS) on the surface chemistry and the morphology of the SiO2-gate insulator were studied with respect to the performance of organic field effect transistors. Using X-ray photoelectron spectroscopy (XPS), it is shown that silanization leads to the growth of a polysiloxane interfacial layer and that longer silanization times increase the thickness of this layer. Most important, silanization reduces the signal from surface contaminations such as oxidized hydrocarbon molecules. In fact, the lowest concentration of these contaminations was found after a combined oxygen plasma/silanization treatment. The results of these investigations were correlated with the characteristic device parameters of polymer field effect transistors with poly(3-hexylthiophene)s as the semiconducting layer. We found that the field effect mobility correlates with the concentration of contaminations as measured by XPS. We, finally, demonstrate that silanization significantly improves the operational stability of the device in air compared to the untreated devices
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Zeimer, Ute
A1  - Pietsch, Ullrich
A1  - Grenzer, Joerg
A1  - Fricke, J.
A1  - Knauer, A.
A1  - Weyers, Markus
T1  - Optimised two layer overgrowth of a lateral strain-modulated nanostructure
N2  - Recently it has been shown that lateral carrier confinement in an InGaAs quantum well (QW) embedded in GaAs can be achieved by using a laterally patterned InGaP stressor layer on top of the heterostructure. To exploit this effect in a device the structure has to be planarized by a second epitaxial step. It has been shown that the lateral strain modulation almost vanishes after overgrowth with GaAs, whereas overgrowth with a single ternary layer of opposite strain compared to the stressor layer suffers from strain induced decomposition. Here we show that the lateral carrier confinement of the initially free standing nanostructure can almost be maintained using a two step process for overgrowth, where a strained thin ternary layer is grown first followed by GaAs up to complete planarization of the patterned structure. Thickness and composition of the ternary layer are adjusted on the basis of finite element calculations of the strain distribution (FEM). The strain field achieved after overgrowth is probed by X-ray grazing- incidence diffraction (GID). (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0925-8388
ER  - 
TY  - JOUR
A1  - Zaikin, Alexei
A1  - Kurths, Jürgen
A1  - Saparin, Peter
A1  - Gowin, W.
A1  - Prohaska, Steffen
T1  - Modeling bone resorption in 2D CT and 3D mu CT images
N2  - We study several algorithms to simulate bone mass loss in two-dimensional and three-dimensional computed tomography bone images. The aim is to extrapolate and predict the bone loss, to provide test objects for newly developed structural measures, and to understand the physical mechanisms behind the bone alteration. Our bone model approach differs from those already reported in the literature by two features. First, we work with original bone images, obtained by computed tomography (CT); second, we use structural measures of complexity to evaluate bone resorption and to compare it with the data provided by CT. This gives us the possibility to test algorithms of bone resorption by comparing their results with experimentally found dependencies of structural measures of complexity, as well as to show efficiency of the complexity measures in the analysis of bone models. For two-dimensional images we suggest two algorithms, a threshold algorithm and a virtual slicing algorithm. The threshold algorithm simulates bone resorption on a boundary between bone and marrow, representing an activity of osteoclasts. The virtual slicing algorithm uses a distribution of the bone material between several virtually created slices to achieve statistically correct results, when the bone-marrow transition is not clearly defined. These algorithms have been tested for original CT 10 mm thick vertebral slices and for simulated 10 mm thick slices constructed from ten I mm thick slices. For three-dimensional data, we suggest a variation of the threshold algorithm and apply it to bone images. The results of modeling have been compared with CT images using structural measures of complexity in two- and three-dimensions. This comparison has confirmed credibility of a virtual slicing modeling algorithm for two-dimensional data and a threshold algorithm for three-dimensional data
Y1  - 2005
SN  - 0218-1274
ER  - 
TY  - JOUR
A1  - York, T.
A1  - Jackson, N.
A1  - Browne, Ian W. A.
A1  - Wucknitz, Olaf
A1  - Skelton, J. E.
T1  - The Hubble constant from the gravitational lens CLASS B0218+357 using the Advanced Camera for Surveys
N2  - We present deep optical observations of the gravitational lens system CLASS B0218 + 357, from which we derive an estimate for the Hubble constant (H-0). Extensive radio observations using the VLA, MERLIN, the VLBA and VLBI have reduced the degeneracies between H-0 and the mass model parameters in this lens to one involving only the position of the radio-quiet lensing galaxy with respect to the lensed images. B0218 + 357 has an image separation of only 334 mas, so optical observations have, up until now, been unable to resolve the lens galaxy from the bright lensed images. Using the new Advanced Camera for Surveys (ACS), installed on the Hubble Space Telescope in 2002, we have obtained deep optical images of the lens system and surrounding field. These observations have allowed us to determine the separation between the lens galaxy centre and the brightest image, and so estimate H-0. We find an optical galaxy position, and hence an H0 value, that varies depending on our approach to the spiral arms in B0218 + 357. If the most prominent spiral arms are left unmasked, we find H-0 = 70 +/- 5 km s(-1) Mpc(-1) (95 per cent confidence). If the spiral arms are masked out, we find H-0 = 61 +/- 7 km s(-1) Mpc(-1) (95 per cent confidence)
Y1  - 2005
SN  - 0035-8711
ER  - 
TY  - JOUR
A1  - Wong, J. E.
A1  - Detert, H.
A1  - Brehmer, Ludwig
A1  - Schrader, Sigurd
T1  - Green light-emitting devices based on soluble oligo(phenylenevinylenes)
N2  - In this work, we report our investigations on the film-forming properties as well as the optical and electroluminescent characterisations of a series of lateral-substituted soluble oligo(phenylenevinylenes) of various conjugation length. Preliminary investigations show that these materials are potential candidates for use in organic light-emitting devices (OLEDs). Two types of OLEDs were fabricated: single layer (SL) and single heterostructure (SHS), with poly(p-phenylenevinylene) (PPV) as hole transporting layer. Our best results were obtained with single layer device emitting green light with a luminance of 0.18 cd m(-2) and 0.24 cd m(-2) at a driving voltage of 10 V. (c) 2004 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0169-4332
ER  - 
TY  - JOUR
A1  - Wolf, M. M.
A1  - Eisert, Jens
T1  - Classical information capacity of a class of quantum channels
N2  - We consider the additivity of the minimal output entropy and the classical information capacity of a class of quantum channels. For this class of channels, the norm of the output is maximized for the output being a normalized projection. We prove the additivity of the minimal output Renyi entropies with entropic parameters alpha is an element of [ 0, 2], generalizing an argument by Alicki and Fannes, and present a number of examples in detail. In order to relate these results to the classical information capacity, we introduce a weak form of covariance of a channel. We then identify various instances of weakly covariant channels for which we can infer the additivity of the classical information capacity. Both additivity results apply to the case of an arbitrary number of different channels. Finally, we relate the obtained results to instances of bi-partite quantum states for which the entanglement cost can be calculated
Y1  - 2005
SN  - 1367-2630
ER  - 
TY  - JOUR
A1  - Witt, Annette
A1  - Schumann, A. Y.
T1  - Holocene climate variability on millennial scales recorded in Greenland ice cores
Y1  - 2005
SN  - 1023-5809
ER  - 
TY  - JOUR
A1  - Witt, Annette
A1  - Schumann, A. Y.
T1  - Holocene climate variability on millennial scales recorded in Greenland ice cores
N2  - Climate variability is triggered by several solar and orbital cycles as well as by the intern ocean dynamics. Consequently, paleoclimate proxy records are expected to vary on very different time scales ranging from subdecadal to millennial duration. We demonstrate, that Foster's (Foster, 1996) wavelet analysis technique is an appropriate tool for investigating temporarily changing spectral properties of records characterized by awkward sampling quality, which is a typical feature of climate proxy records. By applying it to the Holocene part of different glaciochemical records of Greenland ice cores we proof evidence for a significant contribution of the 1.47 kiloyears cycle over alomst the entire Holocene
Y1  - 2005
SN  - 1023-5809
ER  - 
TY  - JOUR
A1  - Wichmann, Matthias
A1  - Johst, Karin
A1  - Schwager, Monika
A1  - Jeltsch, Florian
A1  - Blasius, Bernd
T1  - Extinction risk, coloured noise and the scaling of variance
N2  - The impact of temporally correlated fluctuating environments (coloured noise) on the extinction risk of populations has become a main focus in theoretical population ecology. In this study we particularly focus on the extinction risk in strongly autocorrelated environments. Here, in contrast to moderate autocorrelation, we found the extinction risk to be highly dependent on the process of noise generation, in particular on the method of variance scaling. Such variance scaling is commonly applied to avoid variance-driven biases when comparing the extinction risk for white and coloured noise. In this study we found an often-used scaling technique to lead to high variability in the resulting variances of different time series for strong auto-correlation eventually leading to deviations in the projected extinction risk. Therefore, we present an alternative method that always delivers the target variance, even in the case of strong temporal correlation. Furthermore, in contrast to the earlier method, our very intuitive method is not bound to auto-regressive processes but can be applied to all types of coloured noises. We recommend the method introduced here to be used when the target of interest is the effect of noise colour on extinction risk not obscured by any variance effects.
Y1  - 2005
UR  - http://www.agnld.uni-potsdam.de/~bernd/papers/tpb1.pdf
ER  - 
TY  - THES
A1  - Wessel, Niels
T1  - Data analysis and modeling of the cardiovascular system
Y1  - 2005
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Wegener, Michael
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - Piezoelectric polyethylene terephthalate (PETP) foams : specifically designed and prepared ferroelectret films
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Wegener, Michael
A1  - Bergweiler, Steffen
A1  - Wirges, Werner
A1  - Pucher, Andreas
A1  - Tuncer, Enis
A1  - Gerhard, Reimund
T1  - Piezoelectric two-layer stacks of cellular polypropylene ferroelectrets : transducer response at audio and ultrasound frequencies
N2  - Piezoelectric cellular polypropylene films, so-called ferroelectrets, are assembled in a stack with two active transducer layers. The stack is characterized with respect to its linear and quadratic response in a frequency range from 1 kHz to 80 kHz. A relatively smooth frequency response in the sound-pressure level is found for the individual layers as well as for both layers driven in phase. The piezoelectric response of the two-layer stack is twice the response of an individual layer over a rather broad frequency range. Furthermore, the influence of the preparation conditions on the resonance frequency and the effect of the quadratic distortion on the radiated sound are investigated both for the individual transducer films in the stack and for the stack system as a whole
Y1  - 2005
SN  - 0885-3010
ER  - 
TY  - JOUR
A1  - von Bloh, Werner
A1  - Romano, Maria Carmen
A1  - Thiel, Marco
T1  - Long-term predictability of mean daily temperature data
N2  - We quantify the long-term predictability of global mean daily temperature data by means of the Renyi entropy of second order K-2. We are interested in the yearly amplitude fluctuations of the temperature. Hence, the data are low- pass filtered. The obtained oscillatory signal has a more or less constant frequency, depending on the geographical coordinates, but its amplitude fluctuates irregularly. Our estimate of K-2 quantifies the complexity of these amplitude fluctuations. We compare the results obtained for the CRU data set (interpolated measured temperature in the years 1901- 2003 with 0.5 degrees resolution, Mitchell et al., 2005(1)) with the ones obtained for the temperature data from a coupled ocean-atmosphere global circulation model (AOGCM, calculated at DKRZ). Furthermore, we compare the results obtained by means of K-2 with the linear variance of the temperature data
Y1  - 2005
SN  - 1023-5809
ER  - 
TY  - JOUR
A1  - Volkov, E. I.
A1  - Ullner, Ekkehard
A1  - Kurths, Jürgen
T1  - Stochastic multiresonance in the coupled relaxation oscillators
N2  - We study the noise-dependent dynamics in a chain of four very stiff excitable oscillators of the FitzHugh- Nagumo type locally coupled by inhibitor diffusion. We could demonstrate frequency- and noise-selective signal acceptance which is based on several noise-supported stochastic attractors that arise owing to slow variable diffusion between identical excitable elements. The attractors have different average periods distinct from that of an isolated oscillator and various phase relations between the elements. We explain the correspondence between the noise-supported stochastic attractors and the observed resonance peaks in the curves for the linear response versus signal frequency. (C) 2005 American Institute of Physics
Y1  - 2005
SN  - 1054-1500
ER  - 
TY  - JOUR
A1  - Viana, R. L.
A1  - Grebogi, Celso
A1  - Pinto, S. E. D.
A1  - Lopes, S. R.
A1  - Batista, A. M.
A1  - Kurths, Jürgen
T1  - Bubbling bifurcation : loss of synchronization and shadowing breakdown in complex systems
N2  - Complex dynamical systems with many degrees of freedom may exhibit a wealth of collective phenomena related to high-dimensional chaos. This paper focuses on a lattice of coupled logistic maps to investigate the relationship between the loss of chaos synchronization and the onset of shadowing breakdown via unstable dimension variability in complex systems. In the neighborhood of the critical transition to strongly non-hyperbolic behavior, the system undergoes on-off intermittency with respect to the synchronization manifold. This has been confirmed by numerical diagnostics of synchronization and non-hyperbolic behavior, the latter using the statistical properties of finite-time Lyapunov exponents. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Varykhalov, Andrei
A1  - Shikin, A. M.
A1  - Gudat, Wolfgang
A1  - Moras, P.
A1  - Grazioli, C.
A1  - Carbone, C.
A1  - Rader, Oliver
T1  - Probing the ground state electronic structure of a correlated electron system by quantum well states: Ag/ Ni(111)
N2  - The ground state electronic properties of the strongly correlated transition metal Ni are usually not accessible from the excitation spectra measured in photoelectron spectroscopy. We show that the bottom of the Ni d band along [111] can be probed through the energy dependence of the phase of quantum-well states in Ag/Ni(111). Our model description of the quantum-well energies measured by angle-resolved photoemission determines the bottom of the Lambda(1) d band of Ni as 2.6 eV, in full agreement with standard local density theory and at variance with the values of 1.7-1.8 eV from direct angle-resolved photoemission experiments of Ni
Y1  - 2005
SN  - 0031-9007
ER  - 
TY  - JOUR
A1  - Varykhalov, Andrei
A1  - Rader, Oliver
A1  - Gudat, Wolfgang
T1  - Structure and quantum-size effects in a surface carbide : W(110)/C-R(15 X 3)
N2  - Results of the combined investigation of atomic and electronic structure of the W(110)/C-R(15x3) surface carbide are reported. A variety of experimental techniques has been involved such as scanning tunneling microscopy (STM), low-energy electron diffraction, x-ray photoelectron spectroscopy, and angle-resolved photoemission (ARPES). Distance-dependent STM measurements show a nontrivial geometrical behavior in the topography data, demonstrating five different patterns representing the superstructure at different values of the tip-surface separation. Atomic resolution was achieved at lower tunneling gap resistance. An unexpected spatial asymmetry in the distribution of the local density of states across the surface unit cell has been observed as well. Photoelectron spectroscopy of C1s and W4f core levels clarifies the nature of the chemical bonding in the system. The band mapping with ARPES provides information on the wave- vector dependence of the electronic states. Notable quantum size and superlattice effects were discovered in the dispersion of the valence-band states. The experimental data suggests an apparent one-dimensional character of the electronic structure. Lateral quantization and umklapp scattering are proposed as explanation. Finally, based on photoemission and STM measurements, an improved crystallographic model of the tungsten surface carbide is introduced
Y1  - 2005
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
A1  - Wegener, Michael
A1  - Gerhard, Reimund
T1  - Modeling electro-mechanical properties of layered electrets : application of the finite-element method
N2  - We present calculations on the deformation of two- and three-layer electret systems. The electrical field is coupled with the stress-strain equations by means of the Maxwell stress tensor. In the simulations, two-phase systems are considered, and intrinsic relative dielectric permittivity and Young's modulus of the phases are altered. The numerically calculated electro-mechanical activity is compared to an analytical expression. Simulations are performed on two- and three-layer systems. Various parameters in the model are systematically varied and their influence on the resulting piezoelectricity is estimated. In three-layer systems with bipolar charge, the piezoelectric coefficients exhibit a strong dependence on the elastic moduli of the phases. However, with mono-polar charge, there is no significant piezoelectric effect. A two-dimensional simulation illustrated that higher piezoelectric coefficients can be obtained for non-uniform surface charges and low Poisson's ratio of phases. Irregular structures considered exhibit low piezoelectric activity compared to two-layer structures. (C) 2004 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0304-3886
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
A1  - Wegener, Michael
A1  - Gerhard, Reimund
T1  - Distribution of relaxation times in alpha-phase polyvinylidene fluoride
N2  - In this paper, a recently developed numerical method to analyze dielectric-spectroscopy data is applied to alpha-phase polyvinylidene fluoride (PVDF). The numerical procedure is non-parametric and does not contain any of the extensively used empirical formulas mentioned in the literature. The method basically recovers the unknown distribution of relaxation times of the generalized dielectric function representation by simultaneous application of the Monte Carlo integration method and of the constrained least-squares optimization. The relaxation map constructed after the numerical analysis is compared to a-phase PVDF data presented in the literature and results of the parametric analysis with a well- known empirical formula. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0022-3093
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
A1  - Wegener, Michael
A1  - Frubing, Peter
A1  - Gerhard, Reimund
T1  - Origin of temperature dependent conductivity of alpha-polyvinylidene fluoride
N2  - The conductivity of alpha-polyvinylidene fluoride is obtained from dielectric measurements performed in the frequency domain at several temperatures. At temperatures above the glass-transition, the conductivity can be interpreted as an ionic conductivity, which confirms earlier results reported in the literature. Our investigation shows that the observed ionic conductivity is closely related to the amorphous phase of the polymer. (C) 2005 American Institute of Physics
Y1  - 2005
SN  - 0021-9606
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
A1  - Lang, Sidney B.
T1  - Numerical extraction of distributions of space-charge and polarization from laser intensity modulation method
N2  - The Fredholm integral equation of the laser intensity modulation method is an ill-conditioned problem with multiple solutions. An approach based on an application of the Monte Carlo technique and a least-squares solver is developed and tested on simulated data containing both Gaussian and white noise. Good agreement between the original polarization and the estimated one was found. The influences of bin size and spacing, and errors in material properties, are discussed. It is shown that the presented approach is an alternative to other data analysis techniques in the literature based on regularization algorithms. (C) 2005 American Institute of Physics
Y1  - 2005
SN  - 0003-6951
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
T1  - Extracting the spectral density function of a binary composite without a priori assumptions
N2  - The spectral representation separates the contributions of geometrical arrangement (topology) and intrinsic constituent properties in a composite. The aim of this Brief Report is to present a numerical algorithm based on the Monte Carlo integration and constrained least-squares methods to resolve the spectral density function for a given system. The numerical method is verified by testing it on the well-known Maxwell Garnett expression. Later, it is applied to a well-studied rock-and-brine system to instruct its utility. The presented method yields significant microstructural information in improving our understanding of how microstructure influences the macroscopic behavior of composites without any intricate mathematics
Y1  - 2005
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
T1  - Numerical calculations of effective elastic properties of two cellular structures
N2  - Young's moduli of regular two-dimensional truss-like and eye-shaped structures are simulated using the finite element method. The structures are idealizations of soft polymeric materials used in ferro-electret applications. In the simulations, the length scales of the smallest representative units are varied, which changes the dimensions of the cell walls in the structures. A power-law expression with a quadratic as the exponent term is proposed for the effective Young's moduli of the systems as a function of the solid volume fraction. The data are divided into three regions with respect to the volume fraction: low, intermediate and high. The parameters of the proposed power-law expression in each region are later represented as a function of the structural parameters, the unit-cell dimensions. The expression presented can be used to predict a structure/property relationship in materials with similar cellular structures. The contribution of the cell-wall thickness to the elastic properties becomes significant at concentrations > 0.15. The cell-wall thickness is the most significant factor in predicting the effective Young's modulus of regular cellular structures at high volume fractions of solid. At lower concentrations of solid, the eye-shaped structure yields a lower Young's modulus than a truss-like structure with similar anisotropy. Comparison of the numerical results with those of experimental data for poly(propylene) show good aggreement regarding the influence of cell-wall thickness on elastic properties of thin cellular films
Y1  - 2005
SN  - 0022-3727
ER  - 
TY  - JOUR
A1  - Tuncer, Enis
T1  - Structure-property relationship in dielectric mixtures: application of the spectral density theory
N2  - This paper presents numerical simulations performed on dielectric properties of two-dimensional binary composites. The influence of structural differences and intrinsic electrical properties of constituents on the composite's overall electrical properties is investigated. The structural differences are resolved by fitting the dielectric data with an empirical formula and by the spectral density representation approach. At low concentrations of inclusions (concentrations lower than the percolation threshold), the spectral density functions are delta-sequences, which corresponds to the predictions of the general Maxwell-Garnett (MG) mixture formula. At high concentrations of inclusions (close to the percolation threshold) systems exhibit non-Debye-type dielectric dispersions, and the spectral density functions differ from each other and that predicted by the MG expression. The analysis of the dielectric dispersions with an empirical formula also brings out the structural differences between the considered geometries, however, the information is not qualitative. The empirical formula can only be used to compare structures. The spectral representation method on the other hand is a concrete way of characterizing the structures of the dielectric mixtures. Therefore, as in other spectroscopic techniques, a look-up table might be useful to classify/characterize structures of composite materials. This can be achieved by generating dielectric data for known structures by using ab initio calculations, as presented and emphasized in this study. The numerical technique presented here is not based on any a priori assumption methods
Y1  - 2005
SN  - 0022-3727
ER  - 
TY  - JOUR
A1  - Talalaev, V
A1  - Tomm, JW
A1  - Elsaesser, T
A1  - Zeimer, Ute
A1  - Fricke, J
A1  - Knauer, A
A1  - Kissel, H
A1  - Weyers, Markus
A1  - Tarasov, GG
A1  - Grenzer, Jörg
A1  - Pietsch, Ullrich
T1  - Carrier dynamics in laterally strain-modulated InGaAs quantum wells
N2  - We investigate the transient recombination and transfer properties of nonequilibrium carriers in an In0.16Ga0.84As/GaAs quantum well (QW) with an additional lateral confinement implemented by a patterned stressor layer. The structure thus contains QW- and quantum-wire-like areas. At low excitation densities, photoluminescence (PL) transients from both areas are well described by a rate equation model for a three-level system with a saturable interlevel carrier transfer representing the lateral drift of carriers from the QW regions into the wires. Small-signal carrier lifetimes for QW, wires, and transfer time from QW to wire are 180, 190, and 28 ps, respectively. For high excitation densities the time constants of the observed transients increase, in agreement with the model. In addition, QW and wire PL lines merge indicating a smoothening of the potential difference, i.e., the effective carrier confinement caused by the stressor structure becomes weaker with increasing excitation. (c) 2005 American Institute of Physics
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Surovyatkina, E. D.
A1  - Kravtsov, Y. A.
A1  - Kurths, Jürgen
T1  - Fluctuation growth and saturation in nonlinear oscillators on the threshold of bifurcation of spontaneous symmetry breaking
N2  - We study prebifurcation fluctuation amplification in nonlinear oscillators subject to bifurcations of spontaneous symmetry breaking which are manifest in the doubling of stable equilibrium states. Our theoretical estimates of both the linear growth and the nonlinear saturation of the fluctuations are in good agreement with our results from numerical simulations. We show that in the saturation mode, the fluctuation variance is proportional to the standard deviation of the external noise, whereas in the linear mode, the fluctuation variance is proportional to the noise variance. It is demonstrated that the phenomenon of prebifurcation noise amplification is more pronounced in the case of a slow transition through the bifurcation point. The amplification of fluctuations in this case makes it easier to form a symmetric probability of the final equilibrium states. In contrast, for a fast transition through the bifurcation point, the effect of amplification is much less pronounced. Under backward and forward passages through the bifurcation point, a loop of noise-dependent hysteresis emerges here. We find that for a fast transition of the nonlinear oscillator through the bifurcation point, the probability symmetry of the final equilibrium states is destroyed
Y1  - 2005
SN  - 1539-3755
ER  - 
TY  - JOUR
A1  - Stiller, Burkhard
A1  - Geue, Thomas
A1  - Morawetz, Knut
A1  - Saphiannikova, Marina
T1  - Optical patterning in azobenzene polymer films
N2  - Thin azobenzene polymer films show a very unusual property, namely optically induced material transport. The underlying physics for this phenomenon has not yet been thoroughly explained. Nevertheless, this effect enables one to inscribe different patterns onto film surfaces, including one- and two-dimensional periodic structures. Typical sizes of such structures are of the order of micrometers, i.e. related to the interference pattern made by the laser used for optical excitation. In this study we have measured the mechanical properties of one- and two-dimensional gratings, with a high lateral resolution, using force-distance curves and pulse force mode of the atomic force microscope. We also report on the generation of considerably finer structures, with a typical size of 100 nm, which were inscribed onto the polymer surface by the tip of a scanning near-field optical microscope used as an optical pen. Such inscription not only opens new application possibilities but also gives deeper insight into the fundamentals physics underlying optically induced material transport
Y1  - 2005
SN  - 0022-2720
ER  - 
TY  - THES
A1  - Steuer, Ralf
T1  - Nonlinear dynamics an molecular biology : from gene expression to metabolic networks
Y1  - 2005
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Sremcevic, Miodrag
A1  - Krivov, Alexander V.
A1  - Krüger, Harald
A1  - Spahn, Frank
T1  - Impact-generated dust clouds around planetary satellites : model versus Galileo
N2  - This paper focuses on tenuous dust clouds of Jupiter's Galilean moons Europa, Ganymede and Callisto. In a companion paper (Sremcevic et al., Planet. Space Sci. 51 (2003) 455-471) an analytical model of impact-generated ejecta dust clouds surrounding planetary satellites has been developed. The main aim of the model is to predict the asymmetries in the dust clouds which may arise from the orbital motion of the parent body through a field of impactors. The Galileo dust detector data from flybys at Europa, Ganymede and Callisto are compatible with the model, assuming projectiles to be interplanetary micrometeoroids. The analysis of the data suggests that two interplanetary impactor populations are most likely the source of the measured dust clouds: impactors with isotropically distributed velocities and micrometeoroids in retrograde orbits. Other impactor populations, namely those originating in the Jovian system, or interplanetary projectiles with low orbital eccentricities and inclinations, or interstellar stream particles, can be ruled out by the statistical analysis of the data. The data analysis also suggests that the mean ejecta velocity angle to the normal at the satellite surface is around 30°, which is in agreement with laboratory studies of the hypervelocity impacts. © 2004 Elsevier Ltd. All rights reserved
Y1  - 2005
SN  - 0032-0633
ER  - 
TY  - JOUR
A1  - Shabunin, A.
A1  - Astakhov, Vladimir V.
A1  - Kurths, Jürgen
T1  - Quantitative analysis of chaotic synchronization by means of coherence
N2  - We use an index of chaotic synchronization based on the averaged coherence function for the quantitative analysis of the process of the complete synchronization loss in unidirectionally coupled oscillators and maps. We demonstrate that this value manifests different stages of the synchronization breaking. It is invariant to time delay and insensitive to small noise and distortions, which can influence the accessible signals at measurements. Peculiarities of the synchronization destruction in maps and oscillators are investigated
Y1  - 2005
SN  - 1539-3755
ER  - 
TY  - JOUR
A1  - Serafini, A.
A1  - Eisert, Jens
A1  - Wolf, M. M.
T1  - Multiplicativity of maximal output purities of Gaussian channels under Gaussian inputs
N2  - We address the question of the multiplicativity of the maximal p-norm output purities of bosonic Gaussian channels under Gaussian inputs. We focus on general Gaussian channels resulting from the reduction of unitary dynamics in larger Hilbert spaces. It is shown that the maximal output purity of tensor products of single-mode channels under Gaussian inputs is multiplicative for any p is an element of (1, infinity) for products of arbitrary identical channels as well as for a large class of products of different channels. In the case of p=2, multiplicativity is shown to be true for arbitrary products of generic channels acting on any number of modes
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Seiss, Martin
A1  - Spahn, Frank
A1  - Sremcevic, Miodrag
A1  - Salo, H.
T1  - Structures induced by small moonlets in Saturn's rings : implications for the Cassini Mission
N2  - Particle simulations are carried out to study density features caused by small moonlets embedded in a dense planetary ring. The creation of a "propeller" like structure is found together with adjacent density wakes. Both features are clear indications for the existence of moonlets in the rings. We confirmed that the propeller scales with the Hill-radius in radial direction whereas its azimuthal extent is determined by the ratio between the moonlet-mass and the ring-viscosity. Our findings bear direct implications for the analysis of the Cassini imaging (ISS) and occultation (UVIS) data: (i) for the detection of embedded larger bodies (>30 m) in Saturn's rings, and (ii) for remotely probing transport properties of the rings. The existence of a moonlet population may point to a catastrophic disruption of a parent body as a formation scenario for rings
Y1  - 2005
SN  - 0094-8276
ER  - 
TY  - THES
A1  - Schwarzer, Rolf
T1  - Identification of REDDI and TRB3 as novel transcriptional targets of PI 3-kinase signalling and analysis of their involvement in growth of cancer cells
Y1  - 2005
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Schneider, M.
A1  - Teuchner, Klaus
A1  - Leupold, Dieter
T1  - Two-photon fluorescence of ocular melanomas. Studies on a new diagnostic method
N2  - Choroidal melanoma is the most frequent form of primary neoplasia among malignant ocular tumors. Since it is presumed that metastasis often occurs before the primary tumor is first diagnosed, early detection is exigent. The aim of the studies described in this report was to develop an objective, noninvasive method for the diagnosis of choroidal melanoma. The underlying new principle of fluorescence excitation is presented. This is based on the observation that melanin, due to its unique absorption characteristics, is selectively excited into fluorescence via stepwise absorption of two photons of a femtosecond laser emitting at 800 nm. In the experiment described, the fluorescence of excised tissue from healthy choroidal pigment epithelium was compared to that of excised choroidal melanoma. The fluorescence of choroidal melanomas exhibited a more reddish appearance and less intensity than that of healthy tissue. This implies that the configuration of melanin apparently changes during the process of malignant degeneration. The method described here could thus serve as an evidentiary objective diagnostic technique before initiating treatment for choroidal melanomas
Y1  - 2005
SN  - 0941-293X
ER  - 
TY  - JOUR
A1  - Schneider, J.
A1  - Fernandez, V.
A1  - Hernandez-Garcia, E.
T1  - Leaking method approach to surface transport in the Mediterranean Sea from a numerical ocean model
N2  - We use Lagrangian diagnostics (the leaking and the exchange methods) to characterize surface transport out of and between selected regions in the Western Mediterranean. Velocity fields are obtained from a numerical model. Residence times of water of Atlantic origin in the Algerian subbasin, with a strong seasonal dependence, are calculated. Exchange rates between these waters and the ones occupying the northern basin are also evaluated. At surface, northward transport is dominant, and involves filamental features and eddy structures that can be identified with the Algerian eddies. The impact on these results of the presence of small scale turbulent motions is evaluated by adding Lagrangian diffusion. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0924-7963
ER  - 
TY  - JOUR
A1  - Schellnhuber, Hans Joachim
A1  - Crutzen, P. J.
A1  - Clark, W. C.
A1  - Hunt, J.
T1  - Earth system analysis for sustainability
N2  - Anthropogenic interference has resulted in climate change, ocean acidification, eutrophication and toxic pollution of the earth and it's ecosystems. The Earth System Analysis is an international research program on global environmental change to understand these processes in order to work towards global sustainability
Y1  - 2005
SN  - 0013-9157
ER  - 
TY  - JOUR
A1  - Sava, Ion
A1  - Bruma, Maria
A1  - Schulz, Burkhard
A1  - Köpnick, Thomas
T1  - Comparison of properties of silicon-containing poly(amide-imide)s
N2  - New silicon-containing poly(amide-imide)s have been synthesized by direct polycondensation of various aromatic diamines with a dicarboxylic acid containing the dimethylsilylene group and preformed in-tide cycles. These polymers are easily soluble in polar amidic solvents such as N-methylpyrrolidinone (NMP) or dimethylformamide (DMF) and can be cast into thin flexible films or coatings from such solutions. They show high thermal stability, with initial decomposition temperature being above 400 C and glass transition temperature in the range of 220-270 degrees C. Very thin polymer films deposited by spincoating technique onto silicon wafers showed a smooth, pinhole-free surface in atomic force microscopy investigations
Y1  - 2005
SN  - 0954-0083
ER  - 
TY  - JOUR
A1  - Saphiannikova, Marina
A1  - Neher, Dieter
T1  - Thermodynamic theory of light-induced material transport in amorphous azobenzene polymer films
N2  - It was discovered 10 years ago that the exposure of an initially flat layer of an azobenzene-containing polymer to an inhomogeneous light pattern leads to the formation of surface relief structures, accompanied by a mass transport over several micrometers. However, the driving force of this process is still unclear. We propose a new thermodynamic approach that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. Our basic assumption is that under homogeneous illumination, an initially isotropic sample should stretch itself along the polarization direction to compensate the entropy decrease produced by the photoinduced reorientation of azobenzene chromophores. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film. Orientational distributions of chromophores predicted by our model are compared with those deduced from Raman intensity measurements
Y1  - 2005
SN  - 1520-6106
ER  - 
TY  - JOUR
A1  - Saparin, P. I.
A1  - Thomsen, J. S.
A1  - Prohaska, Steffen
A1  - Zaikin, Alexei
A1  - Kurths, Jürgen
A1  - Hege, H. C.
A1  - Gowin, W.
T1  - Quantification of spatial structure of human proximal tibial bone biopsies using 3D measures of complexity
N2  - Changes in trabecular bone composition during development of osteoporosis are used as a model for bone loss in microgravity conditions during a space flight. Symbolic dynamics and measures of complexity are proposed and applied to assess quantitatively the structural composition of bone tissue from 3D data sets of human tibia bone biopsies acquired by a micro-CT scanner. In order to justify the newly proposed approach, the measures of complexity of the bone architecture were compared with the results of traditional 2D bone histomorphometry. The proposed technique is able to quantify the structural loss of the bone tissue and may help to diagnose and to monitor changes in bone structure of patients on Earth as well as of the space-flying personnel. © 2005 Elsevier Ltd. All rights reserved
Y1  - 2005
SN  - 0094-5765
ER  - 
TY  - THES
A1  - Saha, Subodh Kumar
T1  - The influence of an improved soil scheme on the arctic climate in a RCM
Y1  - 2005
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Romano, Maria Carmen
A1  - Thiel, M.
A1  - Kurths, Jürgen
A1  - Kiss, Istvan Z.
A1  - Hudson, J. L.
T1  - Detection of synchronization for non-phase-coherent and non-stationary data
N2  - We present a new method to detect phase as well as generalized synchronization in a wide class of complex systems. It is based on the recurrences of the system's trajectory to the neighborhood of a former state in phase space. We illustrate the applicability of the algorithm for the paradigmatic chaotic Rossler system in the funnel regime and for noisy data, where other methods to detect phase synchronization fail. Furthermore, we demonstrate for electrochemical experiments that the method can easily detect phase and generalized synchronization in non-phase- coherent and even non-stationary time series
Y1  - 2005
SN  - 0295-5075
ER  - 
TY  - JOUR
A1  - Rappich, J.
A1  - Hartig, P.
A1  - Nickel, N. H.
A1  - Sieber, I.
A1  - Schulze, S.
A1  - Dittrich, T.
T1  - Stable electrochemically passivated Si surfaces by ultra thin benzene-type layers
N2  - Ultra thin organic layers of benzene-type molecules are able to passivate Si surfaces. The organic layers were electrochemically deposited on Si surfaces from aqueous solution of diazonium compounds and show a blocking of the charge transfer from Si into the electrolyte after the deposition process. Electron microscopic images reveal a compact and homogeneous organic layer of 4-bromobenzene on the Si. The surface recombination increases only slightly with respect to a well H-passivated Si surface, so that the interface state density is about 10(11) cm(2) or slightly below. Organic layer modified Si surfaces are much longer stable in ambient air than the H-terminated surface as observed by a slower decay of the integrated photoluminescence intensity with time. Thermal desorption measurements show that the organic layer is stable up to about 200 degrees C.
Y1  - 2005
SN  - 0167-9317
ER  -