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A poorly understood lag time of 15-20 m.y. exists between the initial Arabia-Eurasia continental collision in late Eocene to early Oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late Miocene. The late Eocene to Miocene-Pliocene clastic and shallow-marine sedimentary rocks of the Kond, Eyvanekey, and Semnan Basins in the Alborz Mountains (northern Iran) offer the possibility to track the evolution of this orogen in the framework of collision processes. A transition from volcaniclastic submarine deposits to shallow-marine evaporites and terrestrial sediments occurred shortly after 36 Ma in association with reversals in sediment provenance, strata tilting, and erosional unroofing. These events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched Arabian lithosphere. This early stage of collision produced topographic relief associated with shallow foreland basins, suggesting that shortening and tectonic loading occurred at low rates. Starting from the early Miocene (17.5 Ma), flexural subsidence in response to foreland basin initiation occurred. Fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early Miocene. We suggest that the lag time between the initiation of continental collision (36 Ma) and the acceleration of regional deformation (20-17.5 Ma) reflects a two-stage collision process, involving the "soft" collision of stretched lithosphere at first and "hard" collision following the arrival of unstretched Arabian continental litho sphere in the subduction zone.
A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d (33) coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140A degrees C keep their piezoelectric activity up to at least 120A degrees C and retain 70% of their initial d (33) even at 130A degrees C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz.
Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the "macro-dipoles" in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d (33) coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 mu m thick laminated films, consisting of one 25 mu m thick PTFE layer, two 12.5 mu m thick FEP layers, and a void of 100 mu m height, the critical voltage necessary for the build-up of the "macro-dipoles" in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d (33) coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young's moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d (33) coefficients. The thermal stability of d (33) can be further improved by pre-aging. E.g., the reduction of the d (33) value in the sample pre-aged at 150A degrees C for 5 h was less than 5% after annealing for 30 h at a temperature of 90A degrees C.
Characterization and calibration of piezoelectric polymers in situ measurements of body vibrations
(2011)
Piezoelectric polymers are known for their flexibility in applications, mainly due to their bending ability, robustness, and variable sensor geometry. It is an optimal material for minimal-invasive investigations in vibrational systems, e.g., for wood, where acoustical impedance matches particularly well. Many applications may be imagined, e. g., monitoring of buildings, vehicles, machinery, alarm systems, such that our investigations may have a large impact on technology. Longitudinal piezoelectricity converts mechanical vibrations normal to the polymer-film plane into an electrical signal, and the respective piezoelectric coefficient needs to be carefully determined in dependence on the relevant material parameters. In order to evaluate efficiency and durability for piezopolymers, we use polyvinylidene fluoride and measure the piezoelectric coefficient with respect to static pressure, amplitude of the dynamically applied force, and long-term stability. A known problem is the slow relaxation of the material towards equilibrium, if the external pressure changes; here, we demonstrate how to counter this problem with careful calibration. Since our focus is on acoustical measurements, we determine accurately the frequency response curve - for acoustics probably the most important characteristic. Eventually, we show that our piezopolymer transducers can be used as a calibrated acoustical sensors for body vibration measurements on a wooden musical instrument, where it is important to perform minimal-invasive measurements. A comparison with the simultaneously recorded airborne sound yields important insight of the mechanism of sound radiation in comparison with the sound propagating in the material. This is especially important for transient signals, where not only the long-living eigenmodes contribute to the sound radiation. Our analyses support that piezopolymer sensors can be employed as a general tool for the determination of the internal dynamics of vibrating systems.
Ether functionalities form an important cross-linking structure within the macromolecular organic matrix of lignites and coals. To obtain a deeper insight into the complex internal structure of such macromolecules and the maturation related changes of the ether compounds within the network structure, boron tribromide (BBr3) ether cleavage was applied to a series of lignite and coal samples of different maturity (R-0 0.27-0.80%) obtained from coal mines and natural outcrops from the North and South Island of New Zealand. Terminal ether-bound alcohols rapidly decrease during diagenesis and occur only in low amounts during the catagenetic stage. Comparison between ester- and ether-bound terminal alcohols indicates a parallel decreasing trend during the diagenetic stage, suggesting that the stability differences between both linkages are not large enough to be observed in maturation processes over geological time scales:Polyether compounds were detected with chain length up to five carbon atoms. After a small decrease during the diagenetic phase these compounds occur in relatively high concentrations, even in the main catagenetic stage. This suggests that these linkage structures represent important cross-linking substructures within the macromolecular matrix of lignites and coals being sterically protected within the macromolecular network during the maturation process. Additional cross-linking substructures were (poly)ether aromatics, esters and ketones.
A novel method is established for permittivity enhancement of a silicone matrix for dielectric elastomer actuators (DEAs) by molecular level modifications of the elastomer matrix. A push-pull dipole is synthesized to be compatible with the silicone crosslinking chemistry, allowing for direct grafting to the crosslinker molecules in a one-step film formation process. This method prevents agglomeration and yields elastomer films that are homogeneous down to the molecular level. The dipole-to-silicone network grafting reaction is studied by FTIR. The chemical, thermal, mechanical and electrical properties of films with dipole contents ranging from 0 wt% to 13.4 wt% were thoroughly characterized. The grafting of dipoles modifies the relative permittivity and the stiffness, resulting in the actuation strain at a given electrical field being improved by a factor of six.
Cellular polypropylene (PP) ferroelectrets combine a large piezoelectricity with mechanical flexibility and elastic compliance. Their charging process represents a series of dielectric barrier discharges (DBDs) that generate a cold plasma with numerous active species and thus modify the inner polymer surfaces of the foam cells. Both the threshold for the onset of DBDs and the piezoelectricity of ferroelectrets are sensitive to repeated DBDs in the voids. It is found that the threshold voltage is approximately halved and the charging efficiency is clearly improved after only 10(3) DBD cycles. However, plasma modification of the inner surfaces from repeated DBDs deteriorates the chargeability of the voids, leading to a significant reduction of the piezoelectricity in ferroelectrets. After a significant waiting period, the chargeability of previously fatigued voids shows a partial recovery. The plasma modification is, however, detrimental to the stability of the deposited charges and thus also of the macroscopic dipoles and of the piezoelectricity. Fatigue from only 10(3) DBD cycles already results in significantly less stable piezoelectricity in cellular PP ferroelectrets. The fatigue rate as a function of the number of voltage cycles follows a stretched exponential. Fatigue from repeated DBDs can be avoided if most of the gas molecules inside the voids are removed via a suitable evacuation process.
A simple dip-coating technique was employed to manufacture coaxial actuators with multiple layers of alternating dielectric and conducting layers. A thin rubber string was coated with an electrode-insulator-electrode structure, giving rise to a thin, fiber-like actuator with coaxial geometry. The process was repeated to achieve a compact multilayer actuator with up to three coaxial dielectric layers. Mechanical and electromechanical characterization of the actuators is presented, showing actuation strains up to 8% and proper voltage-thickness scaling behavior. Also presented is a capacitance vs. extension plot, demonstrating that these structures can be used for compact and accurate capacitive strain sensing.
The surface of polytetrafluoroethylene films was treated with titanium-tetrachloride vapor. The treatment was carried out in a flow reactor by means of molecular-layer deposition, a method from the arsenal of chemical nanotechnology. X-ray photoelectron spectroscopy reveals that such a treatment results in considerable changes in the chemical composition at and near the surface of the fluoropolymer film. Both, defluorination and oxidation of the surface were observed. At the same time, samples treated with titanium tetrachloride show a significant enhancement in the thermal stability of the positive homocharge. The thermally stimulated surface-potential-decay curves were observed to shift to higher temperatures by more than 100 degrees C.
Polymer foams and void-containing polymer-film systems with internally charged voids combine large piezoelectricity with mechanical flexibility and elastic compliance. This new class of soft materials (often called ferro-or piezoelectrets) has attracted considerable attention from science and industry. It has been found that the voids can be internally charged by means of dielectric barrier discharges (DBDs) under high electric fields. The charged voids can be considered as man-made macroscopic dipoles. Depending on the ferroelectret structure and the pressure of the internal gas, the voids may be highly compressible. Consequently, very large dipole-moment changes can be induced by mechanical or electrical stresses, leading to large piezoelectricity. DBD charging of the voids is a critical process for rendering polymer foams piezoelectric. Thus a comprehensive exploration of DBD charging is essential for the understanding and the optimization of piezoelectricity in ferroelectrets. Recent studies show that DBDs in the voids are triggered when the internal electric field reaches a threshold value according to Townsend's model of Paschen breakdown. During the DBDs, charges of opposite polarity are generated and trapped at the top and bottom internal surfaces of the gas-filled voids, respectively. The deposited charges induce an electric field opposite to the externally applied one and thus extinguish the DBDs. Back discharges may eventually be triggered when the external voltage is reduced or turned off. In order to optimize the efficiency of DBD charging, the geometry (in particular the height) of the voids, the type of gas and its pressure inside the voids are essential factors to be considered and to be optimized. In addition, the influence of the plasma treatment on the internal void surfaces during the DBDs should be taken into consideration.
Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) as the gate insulator. It is shown that the polarization states remain stable after poling with accumulation and depletion voltage. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flatband voltage expected during the sweep to accumulation voltages.
The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of > 14,000 X-ray point sources;> 9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results.
To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.
We present XMM-Newton and Chandra observations of the born-again planetary nebula A 30. These X-ray observations reveal a bright unresolved source at the position of the central star whose X-ray luminosity exceeds by far the model expectations for photospheric emission and for shocks within the stellar wind. We suggest that a “born-again hot bubble” may be responsible for this X-ray emission. Diffuse X-ray emission associated with the petal-like features and one of the H-poor knots seen in the optical is also found. The weakened emission of carbon lines in the spectrum of the diffuse emission can be interpreted as the dilution of stellar wind by mass-loading or as the detection of material ejected during a very late thermal pulse.
A key non-destructive technique for analysis, optimization and developing of new functional materials such as sensors, transducers, electro-optical and memory devices is presented. The Thermal-Pulse Tomography (TPT) provides high-resolution three-dimensional images of electric field and polarization distribution in a material. This thermal technique use a pulsed heating by means of focused laser light which is absorbed by opaque electrodes. The diffusion of the heat causes changes in the sample geometry, generating a short-circuit current or change in surface potential, which contains information about the spatial distribution of electric dipoles or space charges. Afterwards, a reconstruction of the internal electric field and polarization distribution in the material is possible via Scale Transformation or Regularization methods. In this way, the TPT was used for the first time to image the inhomogeneous ferroelectric switching in polymer ferroelectric films (candidates to memory devices). The results shows the typical pinning of electric dipoles in the ferroelectric polymer under study and support the previous hypotheses of a ferroelectric reversal at a grain level via nucleation and growth. In order to obtain more information about the impact of the lateral and depth resolution of the thermal techniques, the TPT and its counterpart called Focused Laser Intensity Modulation Method (FLIMM) were implemented in ferroelectric films with grid-shaped electrodes. The results from both techniques, after the data analysis with different regularization and scale methods, are in total agreement. It was also revealed a possible overestimated lateral resolution of the FLIMM and highlights the TPT method as the most efficient and reliable thermal technique. After an improvement in the optics, the Thermal-Pulse Tomography method was implemented in polymer-dispersed liquid crystals (PDLCs) films, which are used in electro-optical applications. The results indicated a possible electrostatic interaction between the COH group in the liquid crystals and the fluorinate atoms of the used ferroelectric matrix. The geometrical parameters of the LC droplets were partially reproduced as they were compared with Scanning Electron Microscopy (SEM) images. For further applications, it is suggested the use of a non-strong-ferroelectric polymer matrix. In an effort to develop new polymerferroelectrets and for optimizing their properties, new multilayer systems were inspected. The results of the TPT method showed the non-uniformity of the internal electric-field distribution in the shaped-macrodipoles and thus suggested the instability of the sample. Further investigation on multilayers ferroelectrets was suggested and the implementation of less conductive polymers layers too.
Soft nanocomposites with enhanced electromechanical response for dielectric elastomer actuators
(2011)
Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 % reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 % over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 % reduction of the driving electric field) as well as in the maximum actuation strain (250 %). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation.
Organic thin film transistors (TFT) are an attractive option for low cost electronic applications and may be used for active matrix displays and for RFID applications. To extend the range of applications there is a need to develop and optimise the performance of non-volatile memory devices that are compatible with the solution-processing fabrication procedures used in plastic electronics. A possible candidate is an organic TFT incorporating the ferroelectric co-polymer poly(vinylidenefluoride-trifluoroethylene)(P(VDF-TrFE)) as the gate insulator. Dielectric measurements have been carried out on all-organic metal-insulator-semiconductor structures with the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) as the gate insu-lator. The capacitance spectra of MIS devices, were measured under different biases, showing the effect of charge accumulation and depletion on the Maxwell-Wagner peak. The position and height of this peak clearly indicates the lack of stable depletion behavior and the decrease of mobility when increasing the depletion zone width, i.e. upon moving into the P3HT bulk. The lack of stable depletion was further investigated with capacitance-voltage (C-V) measurements. When the structure was driven into depletion, C-V plots showed a positive flat-band voltage shift, arising from the change in polarization state of the ferroelectric insulator. When biased into accumulation, the polarization was reversed. It is shown that the two polarization states are stable i.e. no depolarization occurs below the coercive field. However, negative charge trapped at the semiconductor-insulator interface during the depletion cycle masks the negative shift in flat-band voltage expected during the sweep to accumulation voltages. The measured output characteristics of the studied ferroelectric-field-effect transistors confirmed the results of the C-V plots. Furthermore, the results indicated a trapping of electrons at the positively charged surfaces of the ferroelectrically polarized P(VDF-TrFE) crystallites near the insulator/semiconductor in-terface during the first poling cycles. The study of the MIS structure by means of thermally stimulated current (TSC) revealed further evidence for the stability of the polarization under depletion voltages. It was shown, that the lack of stable depletion behavior is caused by the compensation of the orientational polarization by fixed electrons at the interface and not by the depolarization of the insulator, as proposed in several publications. The above results suggest a performance improvement of non-volatile memory devices by the optimization of the interface.
The present thesis introduces an iterative expert-based Bayesian approach for assessing greenhouse gas (GHG) emissions from the 2030 German new vehicle fleet and quantifying the impacts of their main drivers. A first set of expert interviews has been carried out in order to identify technologies which may help to lower car GHG emissions and to quantify their emission reduction potentials. Moreover, experts were asked for their probability assessments that the different technologies will be widely adopted, as well as for important prerequisites that could foster or hamper their adoption. Drawing on the results of these expert interviews, a Bayesian Belief Network has been built which explicitly models three vehicle types: Internal Combustion Engine Vehicles (which include mild and full Hybrid Electric Vehicles), Plug-In Hybrid Electric Vehicles, and Battery Electric Vehicles. The conditional dependencies of twelve central variables within the BBN - battery energy, fuel and electricity consumption, relative costs, and sales shares of the vehicle types - have been quantified by experts from German car manufacturers in a second series of interviews. For each of the seven second-round interviews, an expert's individually specified BBN results. The BBN have been run for different hypothetical 2030 scenarios which differ, e.g., in regard to battery development, regulation, and fuel and electricity GHG intensities. The present thesis delivers results both in regard to the subject of the investigation and in regard to its method. On the subject level, it has been found that the different experts expect 2030 German new car fleet emission to be at 50 to 65% of 2008 new fleet emissions under the baseline scenario. They can be further reduced to 40 to 50% of the emissions of the 2008 fleet though a combination of a higher share of renewables in the electricity mix, a larger share of biofuels in the fuel mix, and a stricter regulation of car CO$_2$ emissions in the European Union. Technically, 2030 German new car fleet GHG emissions can be reduced to a minimum of 18 to 44% of 2008 emissions, a development which can not be triggered by any combination of measures modeled in the BBN alone but needs further commitment. Out of a wealth of existing BBN, few have been specified by individual experts through elicitation, and to my knowledge, none of them has been employed for analyzing perspectives for the future. On the level of methods, this work shows that expert-based BBN are a valuable tool for making experts' expectations for the future explicit and amenable to the analysis of different hypothetical scenarios. BBN can also be employed for quantifying the impacts of main drivers. They have been demonstrated to be a valuable tool for iterative stakeholder-based science approaches.
We have obtained spectropolarimetric observations of two Wolf-Rayet stars, WR 135 (WC8) and WR 136 (WN6), with the 6-m Russian telescope in July 2009 and July 2010. We have studied the He II 5412 angstrom line region, which contains also the C IV 5469 angstrom line (for WR 135 only). Our goals were to investigate the rapid line-profile variability (LPV) in WR star spectra and to search for magnetic fields. We find small amplitude emission peaks moving from the center of He II line to its wings during the night in spectra of both stars. These emission peaks are likely a signature of accelerating clumps in the stellar wind. We obtained upper limits of the magnetic field strength: approximate to 200G for WR 135 and approximate to 50G for WR 136. (C) 2011 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim