In this work the improved version of an engineering model which accounts for rotational augmentation effects by means of computational fluid dynamics(CFD)calibration is explored and discussed.Based on an analysis of t...In this work the improved version of an engineering model which accounts for rotational augmentation effects by means of computational fluid dynamics(CFD)calibration is explored and discussed.Based on an analysis of the NREL Phase VI wind turbine,the novel modeling is presented,which uses as base line the formulation proposed by Chaviaropoulos and Hansen.The model is calibrated based on CFD simulations using OpenFOAM.The corresponding correction of the two dimensional polars is straightforward implemented within MoWiT,an in-house software for load calculation.The novel formulation results in improved lift and drag coefficients prediction in all considered cases,reducing the deviation with respect to the rotating CFD cases down to few percent.The optimal configuration including the correction for tip effects of Shen shows better agreements at the very tip of the blade.Furthermore the range of applicability for large wind turbine rotor blades based on a virtual 10MW rotor model is discussed.展开更多
Direct Laser Interference Patterning(DLIP)is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or...Direct Laser Interference Patterning(DLIP)is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm.The raw beam having a diameter of 3 mm@1/e^(2) is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS■-L element and cylindrical telescopes.The shaped beam is split into its diffraction orders,where the two first orders are parallelized and guided into a galvanometer scanner.The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern.The DLIP spot has a line-like interference pattern with about 15μm spatial period.Laser fluences of up to 8 J cm^(-2) were achieved using a maximum pulse energy of 0.6 mJ.Furthermore,an in-house built roll-to-roll machine was developed.Using this setup,aluminum and copper foil of 20μm and 9μm thickness,respectively,could be processed.Subsequently to current collector structuring coating of composite electrode material took place.In case of lithium nickel manganese cobalt oxide(NMC 622)cathode deposited onto textured aluminum current collector,an increased specific discharge capacity could be achieved at a C-rate of 1℃.For the silicon/graphite anode material deposited onto textured copper current collector,an improved rate capability at all C-rates between C/10 and 5℃ was achieved.The rate capability was increased up to 100%compared to reference material.At C-rates between C/2 and 2℃,the specific discharge capacity was increased to 200 mAh g^(-1),while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 m Ah g^(-1),showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.展开更多
In this study, tetrahedral amorphous carbon (ta-C) films with thicknesses between several 100 nm and several micrometers have been deposited onto polished tungsten carbide and steel substrates by pulsed laser depositi...In this study, tetrahedral amorphous carbon (ta-C) films with thicknesses between several 100 nm and several micrometers have been deposited onto polished tungsten carbide and steel substrates by pulsed laser deposition (PLD) using an excimer laser (248 nm wavelength). We investigate the optical properties (e.g. the refractive index (n) and extinction coefficient (k) in the visible and near-infrared wavelength range) of these layers in dependence of the used laser ablation fluence on the target. It is shown that n of ~2000 nm thick ta-C films can be tuned, depending on the sp3-content, between n = 2.5 and 2.8 at a wavelength of 632 nm. Besides of this k reduces with the sp3-content and is as low as 0.03 at sp3-contents of more than 75%. We proof that this gives the opportunity to prepare coating with tailored optical properties. Furthermore, it is shown that the ta-C films have low background fluorescence in the wavelengths range of 380 - 750 nm, which make this thin films attractive for certain optical, medical and biotechnological applications. We present for the first time that one possible application is the use in Lab-on-a-Chip-systems (LOC). Within these systems, the ultrasensitive detection of fluorescence markers and dyes is a challenge. In order to increase the signal-to-noise-ratio, a setup was developed, that used the specific optical properties of ta-C films produced by PLD. We used the ta-C film as an integrated reflector that combined low background fluorescence, a low reflectivity at the excitation wavelength and the high reflectivity at the emission wavelength. We prove that this setup improves the detection of fluorescence photons.展开更多
The assessment of ecological status for running waters is one of the major issues within an integrated river basin management and plays a key role with respect to the implementation of the European Water Frame- work D...The assessment of ecological status for running waters is one of the major issues within an integrated river basin management and plays a key role with respect to the implementation of the European Water Frame- work Directive (WFD).One of the tools supporting the development of sustainable river management is physi- cal habitat modeling,e.g.,for fish,because fish population are one of the most important indicators for the e- colngical integrity of rivers.Within physical habitat models hydromorphological ...展开更多
In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current des...In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current design of axial bearing resistance of these piles leads to deviant results regarding the pile resistance when different design methods are adopted. Hence, a strong deviation regarding the required pile length must be addressed. The reliability of a design method can be evaluated based on a model error which describes the quality of the considered design method by comparing measured and predicted pile bearing resistances. However, only few pile load tests are reported with regard to the boundary conditions in the North Sea. This paper presents 6 large-scale axial pile load tests which were incorporated within a new model error approach for the current design methods used for the axial bearing resistance,namely API Main Text method and cone penetration test(CPT)-based design methods, such as simplified ICP-05, offshore UWA-05, Fugro-05 and NGI-05 methods. Based on these new model errors, a reliabilitybased study towards the safety was conducted by performing a Monte-Carlo simulation. In addition,consequences regarding the deterministic pile design in terms of quality factors were evaluated. It is shown that the current global safety factor(GSF) prescribed and the partial safety factors are only valid for the API Main Text and the offshore UWA-05 design methods; whereas for the simplified ICP-05,Fugro-05 and NGI-05 design methods, an increase in the required embedded pile length and thus in the GSF up to 2.69, 2.95 and 3.27, respectively, should be considered to satisfy the desired safety level according to DIN EN 1990 of b ? 3.8. Further, quality factors for each design method on the basis of all reliability-based design results were derived. Hence, evaluation of each design method regarding the reliability of the pile capacity prediction is possible.展开更多
The Russia–Ukraine crisis has hit hard the grain production and exports of both countries,weakening their positions on global food markets.Moreover,the crisis has resulted in a shortage of fertilizer supply and a sha...The Russia–Ukraine crisis has hit hard the grain production and exports of both countries,weakening their positions on global food markets.Moreover,the crisis has resulted in a shortage of fertilizer supply and a sharp increase in fertilizer prices.Consequently,global food production is declining,prices are hitting record highs,and market structures are shifting.Overall,global food insecurity is worsening,which,on top of several other factors,could become permanent as an aftermath of the Russia–Ukraine crisis.Therefore,food insecurity has become a topical issue in global governance.Spiking food prices and the ensuing political turbulence in vulnerable countries have altered the balance of strength between developed and developing countries,aggravating the existing imbalance between them.Furthermore,major food-producing countries are using food as a weapon to increase their influence in a fresh round of strategic competition,adding more uncertainties to the once-in-a-century changes shaping the world today.展开更多
MPW （magnetic pulse welding） is a solid state joining technology that allows for the generation of strong metallic bonds, even between dissimilar metals. Due to the absence of external heat, critical intermetallic p...MPW （magnetic pulse welding） is a solid state joining technology that allows for the generation of strong metallic bonds, even between dissimilar metals. Due to the absence of external heat, critical intermetallic phases can largely be avoided. In this process, Lorentz forces are utilized for the rapid acceleration of at least one of the two metallic joining partners leading to the controlled high velocity impact between them. The measurement of the collision conditions and their targeted manipulation are the key factors of a successful process development. Optical measuring techniques are preferred, since they are not influenced by the prevalent strong magnetic field in the vicinity of the working coil. In this paper, the characteristic high velocity impact flash during MPW was monitored and evaluated using phototransistors in order to measure the time of the impact. The results are in good accordance with the established PDV （photon Doppler velocimetry） and show a good repeatability. Furthermore, the collision front velocity was investigated using adapted part geometries within a series of tests. This velocity component is one of the key parameters in MPW; its value decreases along the weld zone. With the help of this newly introduced measurement tool, the magnetic pressure distribution or the joining geometry can be adjusted more effectively.展开更多
Poly(butylene 2,6-naphthalate)(PBN)is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit.Polymeric materials made of PBN exhibit excellent a...Poly(butylene 2,6-naphthalate)(PBN)is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit.Polymeric materials made of PBN exhibit excellent anti-abrasion and low friction properties,superior chemical resista nee,and outstanding gas barrier characteristics.Many of the properties rely on the presence of crystals and the formatio n of a semicrystalline morphology.To develop specific crystal structures and morphologies during cooling the melt,precise information about the melt-crystallization process is required.This review article summarizes the current knowledge about the temperature-controlled crystal polymorphism of PBN.At rather low supercooling of the melt,with decreasi ng crystal I izatio n temperature,0'-and a-crystals grow directly from the melt and organize in largely different spherulitic superstructures.Formation of a-crystals at high supercooling may also proceed via intermediate formation of a transient monotropic liquid crystalline structure,then yielding a non-spherulitic semicrystalline morphology.Crystallization of PBN is rather fast since its suppression requires cooling the melt at a rate higher than 6000 K-s_1.For this reason,investigation of the two-step crystallization process at low temperatu res requires application of sophisticated experimental tools.These in elude temperatureresolved X-ray scattering techniques using fast detectors and synchrotron-based X-rays and fast scanning chip calorimetry.Fast scanning chip calorimetry allows freezi ng the transie nt liquid-crystalline structure before its con version into a-crystals,by fast cooling to below its glass transition temperature.Subsequent an alysis using polarized-light optical microscopy reveals its texture and X-ray scatteri ng con firms the smectic arrangement of the mesogens.The combination of a large variety of experimental techniques allows obtaining a complete picture about crystallization of PBN in the entire range of melt-supercoolings down to the glass transition,including quantitative data about the crystallization kinetics,semicrystalline morphologies at the micrometer length scale,as well as nanoscale X-ray structure information.展开更多
Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the de...Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the deposition of tribological coatings. In this study, anti-corrosive and electrical conductive carbon-based coatings with a metallic interlayer were prepared on stainless steel substrates as surface modification for metallic bipolar plates. Hereby, the influence of the deposition temperature during the deposition of the carbon top layer was investigated. Raman spectroscopy revealed differences in the microstructure at 200°C compared to 300°C and 100°C. Measurements of the interfacial contact resistance showed that the deposited coatings significantly improve the electrical conductivity. There are only minor differences between the different carbon top layers. The corrosion resistance of the coatings was studied via potentiodynamic polarization at room temperature and 80°C. Experiments showed that the coating with a carbon top layer deposited at 200°C, considerably reduces the current density and thus corrosion of the substrate is suppressed.展开更多
In the present paper, coating systems consisting of a metallic corrosion barrier and a conductive graphitic carbon layer were deposited by a DC vacuum arc process. The coatings were developed in a batch process for ap...In the present paper, coating systems consisting of a metallic corrosion barrier and a conductive graphitic carbon layer were deposited by a DC vacuum arc process. The coatings were developed in a batch process for application in the polymer electrolyte membrane fuel cell (PEMFC), and transferred to a continuous coil process to facilitate industrial mass production. The coating samples in the coil process had to achieve comparable results to the samples produced in the batch process, to meet the requirements of the environment prevailing in the fuel cell.The transfer to roll-to-roll processes is a crucial factor for commercial upscaling of PEMFC production. The experimental results showed that the electrical conductivity and corrosion resistance of the samples in the coil process were significantly improved compared to the uncoated base material and showed comparable performance to batch coated samples. X-ray photoelectron spectroscopy (XPS) was performed to determine the depth profile and the surface composition. Additional measurements were recorded for the contact resistances using the four-wire sensing method as well as corrosion resistance using potentiodynamic methods.展开更多
Fracture toughness of disk specimens with a straight-through crack was measured under biaxial tension and uniaxial tension loads respectively. The difference between them and the reasons for the difference were discu...Fracture toughness of disk specimens with a straight-through crack was measured under biaxial tension and uniaxial tension loads respectively. The difference between them and the reasons for the difference were discussed. The influence of the stress parallel to crack on fracture of brittle material was demonstrated in theory and experiments. The results show that plane stress fracture toughness of glass is not a material constant, and that the fracture toughness measured in biaxial tension state is higher than that measured under uniaxial tension. The conventional fracture criterion upon the stress intensity factor is questioned in the case of biaxial stress problem, and the strain dependence of crack growth was discussed. (Edited author abstract) 15 Refs.展开更多
As biomarkers are important in the early diagnosis ofAlzheimer’s disease （AD）, the frst collab-orative work of recruiting early-onset familial AD （EO-FAD） families in Canada and China was initiated in 2012. The r...As biomarkers are important in the early diagnosis ofAlzheimer’s disease （AD）, the frst collab-orative work of recruiting early-onset familial AD （EO-FAD） families in Canada and China was initiated in 2012. The registration networks have collected hundreds of pedigrees, for which genetic screening, neuropsycholog-ical tests and amyloid and tau imaging was used to study diagnostic biomarkers for preclinical and mild cognitive impairment （MCI） stages of AD. Besides identifying ped-igrees with novel mutations in presenilins （PSENs）/amy-loid precursor protein （APP）, the program has benefted training of Chinese research fellows, AD clinical trials forprevention,the ethical concernsfor clinical fndings, and other collaborative projects with Chinese investiga-tors. Further research of the collaborative program may facilitate the testing and clinical use of novel treatments for EOFAD and late onset AD and contribute to dementia prevention strategies in Canada and China.展开更多
CONSPECTUS:The global production of polymer products currently exceeds 400 megatons annually.To ensure effective and environmentally responsible use of this vast resource,optimizing the properties of the products is e...CONSPECTUS:The global production of polymer products currently exceeds 400 megatons annually.To ensure effective and environmentally responsible use of this vast resource,optimizing the properties of the products is essential.Achieving this requires precise control over the internal structure of the polymers.Depending on the materials used,polymers can exist in either amorphous or semicrystalline states.Processing is often performed from the melt state,and the cooling rate plays a critical role in determining whether amorphous or semicrystalline products are formed alongside other process parameters such as the pressure and shear rates.To understand the structure formation during processing,knowledge of the cooling rate dependence is therefore essential.As all of these processes are associated with thermal effects,calorimetry is universally applicable here.Achieving cooling rates that are comparable to those during processing has therefore long been a challenge for calorimetric measurement methods.With the introduction of MEMS-based chip sensors for calorimetry,significant progress has been made in reproducing conditions,such as those that occur during injection molding.These special calorimetric techniques are often summarized under the terms Fast Scanning Calorimetry(FSC)or Nanocalorimetry,alluding to nanogram samples.Investigations with controlled cooling rates of up to 1×10^(6)K/s are now possible with special chip sensors and allow the study of material properties under extreme conditions.Technological issues such as crystallization and nucleation processes under processrelevant conditions can be investigated in most cases with commercial devices that achieve cooling rates of 10^(4)K/s.The cooling rates to be considered in relation to various manufacturing processes are discussed here,and the functionality of corresponding chip calorimeters is briefly presented.Since calorimetry only provides general information on the processes taking place in the material,but not directly on the resulting structures,combinations of FSC and methods for structure elucidation,e.g.,microscopy,are also presented.The main part of this Account deals with contributions of FSC to the understanding of crystallization processes under conditions as they occur in different manufacturing processes.Not only the influence of the cooling rate during injection molding but also the multistage cooling by chill rolls during film production is considered.Thanks to the high scanning rate of FSC,needed to bypass crystallization in the low-supercooling temperature range where heterogeneous nucleation dominates,an important aspect of polymer structure formation-homogeneous crystal nucleation-has become accessible for direct observation.Homogeneous nucleation can occur not only during cooling but also during storage at temperatures close to or even below the glass transition temperature in the amorphous state.The possibilities of FSC for the generation and investigation of amorphous states are illustrated by an example.Finally,possible further developments of FSC and expected further applications of this fascinating technology are considered.展开更多
In this paper,a robust design method for current control is proposed to improve the performance of a three phase voltage source converter(VSC)with an inductorcapacitor-inductor(LCL)filter.The presence of the LCL filte...In this paper,a robust design method for current control is proposed to improve the performance of a three phase voltage source converter(VSC)with an inductorcapacitor-inductor(LCL)filter.The presence of the LCL filter complicates the dynamics of the control system and limits the achievable control bandwidth(and the overall performance),particularly when the uncertainty of the parameters is considered.To solve this problem,the advanced H?control theory is employed to design a robust current controller in stationary coordinates.Both control of the fundamental frequency current and suppression of the potential LC resonance are considered.The design procedure and the selection of the weight functions are presented in detail.A conventional proportional-resonant PR controller is also designed for comparison.Analysis showed that the proposed H∞ current controller achieved a good frequency response with explicit robustness.The conclusion was verified on a 5 kW VSC that had a LCL filter.展开更多
To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbo...To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbon coatings with varying fraction of sp^(2) and sp^(3) hybridized carbon in presence of a commercially available silicon nitride bulk ceramic,castor oil provides superlubricity although the liquid vegetable oil film in the contact is only a few nanometres thick at most.Besides a partial liquid film possibly separating surfaces in contact,local tribochemical reactions between asperities are essential to maintain superlubricity at low speeds.High local pressure activates chemical degradation of castor oil generating graphitic/graphenic-like species on top of asperities,thus helping both the chemical polishing of surface and its chemical passivation by H and OH species.Particularly,the formation of the formation of–(CH_(2)–CH_(2))n–noligomers have been evidenced to have a major role in the friction reduction.Computer simulation unveils that formation of chemical degradation products of castor oil on friction surfaces are favoured by the quantity of sp^(2)-hybridized carbon atoms in the amorphous carbon structure.Hence,tuning sp^(2)-carbon content in hydrogen-free amorphous carbon,in particular,on the top layers of the coating,provides an alternative way to control superlubricity achieved with castor oil and other selected green lubricants.展开更多
基金the German Ministry of Economy in the framework of HighRe National project(Grant O3EE2OO1)。
文摘In this work the improved version of an engineering model which accounts for rotational augmentation effects by means of computational fluid dynamics(CFD)calibration is explored and discussed.Based on an analysis of the NREL Phase VI wind turbine,the novel modeling is presented,which uses as base line the formulation proposed by Chaviaropoulos and Hansen.The model is calibrated based on CFD simulations using OpenFOAM.The corresponding correction of the two dimensional polars is straightforward implemented within MoWiT,an in-house software for load calculation.The novel formulation results in improved lift and drag coefficients prediction in all considered cases,reducing the deviation with respect to the rotating CFD cases down to few percent.The optimal configuration including the correction for tip effects of Shen shows better agreements at the very tip of the blade.Furthermore the range of applicability for large wind turbine rotor blades based on a virtual 10MW rotor model is discussed.
基金funded by the German Federal Ministry of Education and Research(BMBF),project NextGen-3DBat,Grant Number 03XP0198Fby the Fraunhofer Cluster of Excellence Advanced Photon Sources(CAPS)。
文摘Direct Laser Interference Patterning(DLIP)is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm.The raw beam having a diameter of 3 mm@1/e^(2) is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS■-L element and cylindrical telescopes.The shaped beam is split into its diffraction orders,where the two first orders are parallelized and guided into a galvanometer scanner.The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern.The DLIP spot has a line-like interference pattern with about 15μm spatial period.Laser fluences of up to 8 J cm^(-2) were achieved using a maximum pulse energy of 0.6 mJ.Furthermore,an in-house built roll-to-roll machine was developed.Using this setup,aluminum and copper foil of 20μm and 9μm thickness,respectively,could be processed.Subsequently to current collector structuring coating of composite electrode material took place.In case of lithium nickel manganese cobalt oxide(NMC 622)cathode deposited onto textured aluminum current collector,an increased specific discharge capacity could be achieved at a C-rate of 1℃.For the silicon/graphite anode material deposited onto textured copper current collector,an improved rate capability at all C-rates between C/10 and 5℃ was achieved.The rate capability was increased up to 100%compared to reference material.At C-rates between C/2 and 2℃,the specific discharge capacity was increased to 200 mAh g^(-1),while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 m Ah g^(-1),showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.
文摘In this study, tetrahedral amorphous carbon (ta-C) films with thicknesses between several 100 nm and several micrometers have been deposited onto polished tungsten carbide and steel substrates by pulsed laser deposition (PLD) using an excimer laser (248 nm wavelength). We investigate the optical properties (e.g. the refractive index (n) and extinction coefficient (k) in the visible and near-infrared wavelength range) of these layers in dependence of the used laser ablation fluence on the target. It is shown that n of ~2000 nm thick ta-C films can be tuned, depending on the sp3-content, between n = 2.5 and 2.8 at a wavelength of 632 nm. Besides of this k reduces with the sp3-content and is as low as 0.03 at sp3-contents of more than 75%. We proof that this gives the opportunity to prepare coating with tailored optical properties. Furthermore, it is shown that the ta-C films have low background fluorescence in the wavelengths range of 380 - 750 nm, which make this thin films attractive for certain optical, medical and biotechnological applications. We present for the first time that one possible application is the use in Lab-on-a-Chip-systems (LOC). Within these systems, the ultrasensitive detection of fluorescence markers and dyes is a challenge. In order to increase the signal-to-noise-ratio, a setup was developed, that used the specific optical properties of ta-C films produced by PLD. We used the ta-C film as an integrated reflector that combined low background fluorescence, a low reflectivity at the excitation wavelength and the high reflectivity at the emission wavelength. We prove that this setup improves the detection of fluorescence photons.
文摘The assessment of ecological status for running waters is one of the major issues within an integrated river basin management and plays a key role with respect to the implementation of the European Water Frame- work Directive (WFD).One of the tools supporting the development of sustainable river management is physi- cal habitat modeling,e.g.,for fish,because fish population are one of the most important indicators for the e- colngical integrity of rivers.Within physical habitat models hydromorphological ...
基金the European Union funded project Integrated Research Project Wind (IRPWind, European Union Seventh Framework Program under Grant No. 609795)
文摘In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current design of axial bearing resistance of these piles leads to deviant results regarding the pile resistance when different design methods are adopted. Hence, a strong deviation regarding the required pile length must be addressed. The reliability of a design method can be evaluated based on a model error which describes the quality of the considered design method by comparing measured and predicted pile bearing resistances. However, only few pile load tests are reported with regard to the boundary conditions in the North Sea. This paper presents 6 large-scale axial pile load tests which were incorporated within a new model error approach for the current design methods used for the axial bearing resistance,namely API Main Text method and cone penetration test(CPT)-based design methods, such as simplified ICP-05, offshore UWA-05, Fugro-05 and NGI-05 methods. Based on these new model errors, a reliabilitybased study towards the safety was conducted by performing a Monte-Carlo simulation. In addition,consequences regarding the deterministic pile design in terms of quality factors were evaluated. It is shown that the current global safety factor(GSF) prescribed and the partial safety factors are only valid for the API Main Text and the offshore UWA-05 design methods; whereas for the simplified ICP-05,Fugro-05 and NGI-05 design methods, an increase in the required embedded pile length and thus in the GSF up to 2.69, 2.95 and 3.27, respectively, should be considered to satisfy the desired safety level according to DIN EN 1990 of b ? 3.8. Further, quality factors for each design method on the basis of all reliability-based design results were derived. Hence, evaluation of each design method regarding the reliability of the pile capacity prediction is possible.
文摘The Russia–Ukraine crisis has hit hard the grain production and exports of both countries,weakening their positions on global food markets.Moreover,the crisis has resulted in a shortage of fertilizer supply and a sharp increase in fertilizer prices.Consequently,global food production is declining,prices are hitting record highs,and market structures are shifting.Overall,global food insecurity is worsening,which,on top of several other factors,could become permanent as an aftermath of the Russia–Ukraine crisis.Therefore,food insecurity has become a topical issue in global governance.Spiking food prices and the ensuing political turbulence in vulnerable countries have altered the balance of strength between developed and developing countries,aggravating the existing imbalance between them.Furthermore,major food-producing countries are using food as a weapon to increase their influence in a fresh round of strategic competition,adding more uncertainties to the once-in-a-century changes shaping the world today.
文摘MPW （magnetic pulse welding） is a solid state joining technology that allows for the generation of strong metallic bonds, even between dissimilar metals. Due to the absence of external heat, critical intermetallic phases can largely be avoided. In this process, Lorentz forces are utilized for the rapid acceleration of at least one of the two metallic joining partners leading to the controlled high velocity impact between them. The measurement of the collision conditions and their targeted manipulation are the key factors of a successful process development. Optical measuring techniques are preferred, since they are not influenced by the prevalent strong magnetic field in the vicinity of the working coil. In this paper, the characteristic high velocity impact flash during MPW was monitored and evaluated using phototransistors in order to measure the time of the impact. The results are in good accordance with the established PDV （photon Doppler velocimetry） and show a good repeatability. Furthermore, the collision front velocity was investigated using adapted part geometries within a series of tests. This velocity component is one of the key parameters in MPW; its value decreases along the weld zone. With the help of this newly introduced measurement tool, the magnetic pressure distribution or the joining geometry can be adjusted more effectively.
文摘Poly(butylene 2,6-naphthalate)(PBN)is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit.Polymeric materials made of PBN exhibit excellent anti-abrasion and low friction properties,superior chemical resista nee,and outstanding gas barrier characteristics.Many of the properties rely on the presence of crystals and the formatio n of a semicrystalline morphology.To develop specific crystal structures and morphologies during cooling the melt,precise information about the melt-crystallization process is required.This review article summarizes the current knowledge about the temperature-controlled crystal polymorphism of PBN.At rather low supercooling of the melt,with decreasi ng crystal I izatio n temperature,0'-and a-crystals grow directly from the melt and organize in largely different spherulitic superstructures.Formation of a-crystals at high supercooling may also proceed via intermediate formation of a transient monotropic liquid crystalline structure,then yielding a non-spherulitic semicrystalline morphology.Crystallization of PBN is rather fast since its suppression requires cooling the melt at a rate higher than 6000 K-s_1.For this reason,investigation of the two-step crystallization process at low temperatu res requires application of sophisticated experimental tools.These in elude temperatureresolved X-ray scattering techniques using fast detectors and synchrotron-based X-rays and fast scanning chip calorimetry.Fast scanning chip calorimetry allows freezi ng the transie nt liquid-crystalline structure before its con version into a-crystals,by fast cooling to below its glass transition temperature.Subsequent an alysis using polarized-light optical microscopy reveals its texture and X-ray scatteri ng con firms the smectic arrangement of the mesogens.The combination of a large variety of experimental techniques allows obtaining a complete picture about crystallization of PBN in the entire range of melt-supercoolings down to the glass transition,including quantitative data about the crystallization kinetics,semicrystalline morphologies at the micrometer length scale,as well as nanoscale X-ray structure information.
文摘Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the deposition of tribological coatings. In this study, anti-corrosive and electrical conductive carbon-based coatings with a metallic interlayer were prepared on stainless steel substrates as surface modification for metallic bipolar plates. Hereby, the influence of the deposition temperature during the deposition of the carbon top layer was investigated. Raman spectroscopy revealed differences in the microstructure at 200°C compared to 300°C and 100°C. Measurements of the interfacial contact resistance showed that the deposited coatings significantly improve the electrical conductivity. There are only minor differences between the different carbon top layers. The corrosion resistance of the coatings was studied via potentiodynamic polarization at room temperature and 80°C. Experiments showed that the coating with a carbon top layer deposited at 200°C, considerably reduces the current density and thus corrosion of the substrate is suppressed.
文摘In the present paper, coating systems consisting of a metallic corrosion barrier and a conductive graphitic carbon layer were deposited by a DC vacuum arc process. The coatings were developed in a batch process for application in the polymer electrolyte membrane fuel cell (PEMFC), and transferred to a continuous coil process to facilitate industrial mass production. The coating samples in the coil process had to achieve comparable results to the samples produced in the batch process, to meet the requirements of the environment prevailing in the fuel cell.The transfer to roll-to-roll processes is a crucial factor for commercial upscaling of PEMFC production. The experimental results showed that the electrical conductivity and corrosion resistance of the samples in the coil process were significantly improved compared to the uncoated base material and showed comparable performance to batch coated samples. X-ray photoelectron spectroscopy (XPS) was performed to determine the depth profile and the surface composition. Additional measurements were recorded for the contact resistances using the four-wire sensing method as well as corrosion resistance using potentiodynamic methods.
文摘Fracture toughness of disk specimens with a straight-through crack was measured under biaxial tension and uniaxial tension loads respectively. The difference between them and the reasons for the difference were discussed. The influence of the stress parallel to crack on fracture of brittle material was demonstrated in theory and experiments. The results show that plane stress fracture toughness of glass is not a material constant, and that the fracture toughness measured in biaxial tension state is higher than that measured under uniaxial tension. The conventional fracture criterion upon the stress intensity factor is questioned in the case of biaxial stress problem, and the strain dependence of crack growth was discussed. (Edited author abstract) 15 Refs.
文摘As biomarkers are important in the early diagnosis ofAlzheimer’s disease （AD）, the frst collab-orative work of recruiting early-onset familial AD （EO-FAD） families in Canada and China was initiated in 2012. The registration networks have collected hundreds of pedigrees, for which genetic screening, neuropsycholog-ical tests and amyloid and tau imaging was used to study diagnostic biomarkers for preclinical and mild cognitive impairment （MCI） stages of AD. Besides identifying ped-igrees with novel mutations in presenilins （PSENs）/amy-loid precursor protein （APP）, the program has benefted training of Chinese research fellows, AD clinical trials forprevention,the ethical concernsfor clinical fndings, and other collaborative projects with Chinese investiga-tors. Further research of the collaborative program may facilitate the testing and clinical use of novel treatments for EOFAD and late onset AD and contribute to dementia prevention strategies in Canada and China.
基金support by Wenzhou City’s key R&D project,“Unveiling the List and Assigning the Leader”(ZG2023044)Anhui Provence key R&D project(202304a05020081)the DFG SPP2122 project ZH 662/3−2 and Open Research Fund of the State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences.
文摘CONSPECTUS:The global production of polymer products currently exceeds 400 megatons annually.To ensure effective and environmentally responsible use of this vast resource,optimizing the properties of the products is essential.Achieving this requires precise control over the internal structure of the polymers.Depending on the materials used,polymers can exist in either amorphous or semicrystalline states.Processing is often performed from the melt state,and the cooling rate plays a critical role in determining whether amorphous or semicrystalline products are formed alongside other process parameters such as the pressure and shear rates.To understand the structure formation during processing,knowledge of the cooling rate dependence is therefore essential.As all of these processes are associated with thermal effects,calorimetry is universally applicable here.Achieving cooling rates that are comparable to those during processing has therefore long been a challenge for calorimetric measurement methods.With the introduction of MEMS-based chip sensors for calorimetry,significant progress has been made in reproducing conditions,such as those that occur during injection molding.These special calorimetric techniques are often summarized under the terms Fast Scanning Calorimetry(FSC)or Nanocalorimetry,alluding to nanogram samples.Investigations with controlled cooling rates of up to 1×10^(6)K/s are now possible with special chip sensors and allow the study of material properties under extreme conditions.Technological issues such as crystallization and nucleation processes under processrelevant conditions can be investigated in most cases with commercial devices that achieve cooling rates of 10^(4)K/s.The cooling rates to be considered in relation to various manufacturing processes are discussed here,and the functionality of corresponding chip calorimeters is briefly presented.Since calorimetry only provides general information on the processes taking place in the material,but not directly on the resulting structures,combinations of FSC and methods for structure elucidation,e.g.,microscopy,are also presented.The main part of this Account deals with contributions of FSC to the understanding of crystallization processes under conditions as they occur in different manufacturing processes.Not only the influence of the cooling rate during injection molding but also the multistage cooling by chill rolls during film production is considered.Thanks to the high scanning rate of FSC,needed to bypass crystallization in the low-supercooling temperature range where heterogeneous nucleation dominates,an important aspect of polymer structure formation-homogeneous crystal nucleation-has become accessible for direct observation.Homogeneous nucleation can occur not only during cooling but also during storage at temperatures close to or even below the glass transition temperature in the amorphous state.The possibilities of FSC for the generation and investigation of amorphous states are illustrated by an example.Finally,possible further developments of FSC and expected further applications of this fascinating technology are considered.
基金This research was supported by the CAS Fraunhofer Joint Doctoral Promotion Program(DPP)and the National High Technology Research and Development Program of China(863 program)(No.2011AA050204).
文摘In this paper,a robust design method for current control is proposed to improve the performance of a three phase voltage source converter(VSC)with an inductorcapacitor-inductor(LCL)filter.The presence of the LCL filter complicates the dynamics of the control system and limits the achievable control bandwidth(and the overall performance),particularly when the uncertainty of the parameters is considered.To solve this problem,the advanced H?control theory is employed to design a robust current controller in stationary coordinates.Both control of the fundamental frequency current and suppression of the potential LC resonance are considered.The design procedure and the selection of the weight functions are presented in detail.A conventional proportional-resonant PR controller is also designed for comparison.Analysis showed that the proposed H∞ current controller achieved a good frequency response with explicit robustness.The conclusion was verified on a 5 kW VSC that had a LCL filter.
基金This research is supported by TOTAL,Solaize Research Center and Federal Ministry of Economic Affairs and Energy Germany(BMWi)within project CHEOPS3(Funding number 03ET1286B).
文摘To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is proposed.By coupling different hydrogen-free amorphous carbon coatings with varying fraction of sp^(2) and sp^(3) hybridized carbon in presence of a commercially available silicon nitride bulk ceramic,castor oil provides superlubricity although the liquid vegetable oil film in the contact is only a few nanometres thick at most.Besides a partial liquid film possibly separating surfaces in contact,local tribochemical reactions between asperities are essential to maintain superlubricity at low speeds.High local pressure activates chemical degradation of castor oil generating graphitic/graphenic-like species on top of asperities,thus helping both the chemical polishing of surface and its chemical passivation by H and OH species.Particularly,the formation of the formation of–(CH_(2)–CH_(2))n–noligomers have been evidenced to have a major role in the friction reduction.Computer simulation unveils that formation of chemical degradation products of castor oil on friction surfaces are favoured by the quantity of sp^(2)-hybridized carbon atoms in the amorphous carbon structure.Hence,tuning sp^(2)-carbon content in hydrogen-free amorphous carbon,in particular,on the top layers of the coating,provides an alternative way to control superlubricity achieved with castor oil and other selected green lubricants.
