121 research outputs found
Modeling electromechanical properties of layered electrets: Application of the finite-element method
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 piezoelectricity
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.Comment: To be appaer in J Electrostatic
Innovating for and with your service customers: An assessment of the current practice of collaborative service innovation in Germany
AbstractMethods for managing innovation have been described in academia in many contexts. Service innovation processes pose particular challenges compared to those of product innovation – one of the core reasons being the lack of dedicated R&D structures in service firms or units. Collaborative innovation both with employees and with customers can be an effective means to drive innovation in services. Based on empirical evidence of a study of German innovation managers, this paper discusses findings of service innovation in organizational practice. We review the current extent and future potential of the involvement of employees and customers in the innovation process, as well implications for companies and academia
Elastic properties of highly anisotropic thin poly(propylene) foams
In this letter, elastic properties of highly anisotropic cellular
poly(propylene) films are reported. The material shows peculiar elastic
properties compared to other foams in the literature. The data is displayed as
the relative Young's modulus versus relative density .
Almost all the data from the literature are located on the region
with . The introduced material on the
other hand have lower relative Young's modulus at high relative densities,
Scale Factor Determination for the GRACE-Follow On Laser Ranging Interferometer including Thermal Coupling
The GRACE Follow-On satellites carry the very first inter-spacecraft Laser
Ranging Interferometer (LRI). After more than four years in orbit, the LRI
outperforms the sensitivity of the conventional Microwave Instrument (MWI).
However, in the current data processing scheme, the LRI product still needs the
MWI data to determine the unknown absolute laser frequency, representing the
ruler for converting the raw phase measurements into a physical displacement in
meters. In this paper, we derive formulas for precisely performing that
conversion from the phase measurement into a range, accounting for a varying
carrier frequency. Furthermore, the dominant errors due to knowledge
uncertainty of the carrier frequency as well as uncorrected time biases are
derived. In the second part, we address the dependency of the LRI on the MWI in
the currently employed cross-calibration scheme and present three different
models for the LRI laser frequency, two of which are largely independent of the
MWI. Furthermore, we analyze the contribution of thermal variations on the
scale factor estimates and the LRI-MWI residuals. A linear model called Thermal
Coupling (TC) is derived that significantly reduces the differences between LRI
and MWI to a level where the MWI observations limit the comparison.Comment: 26 pages, 15 figure
Numerical calculations of effective elastic properties of two cellular structures
Young's moduli of regular two-dimensional truss-like and eye-shape-like
structures are simulated by using the finite element method. The structures are
the idealizations of soft polymeric materials used in the electret
applications. In the simulations size of the representative smallest units are
varied, which changes the dimensions of the cell-walls in the structures. A
power-law expression with a quadratic as the exponential term is proposed for
the effective Young's moduli of the systems as a function of the solid volume
fraction. The data is divided into three regions with respect to the volume
fraction; low, intermediate and high concentrations. The parameters of the
proposed power-law expression in each region are later represented as a
function of the structural parameters, unit-cell dimensions. The presented
expression can be used to predict structure/property relationship in materials
with similar cellular structures. It is observed that the structures with
volume fractions of solid higher than 0.15 exhibit the importance of the
cell-wall thickness contribution in the elastic properties. The cell-wall
thickness is the most significant factor to predict the effective Young's
modulus of regular cellular structures at high volume fractions of solid. At
lower concentrations of solid, eye-like structure yields lower Young's modulus
than the truss-like structure with the similar anisotropy. Comparison of the
numerical results with those of experimental data of poly(propylene) show good
aggreement regarding the influence of cell-wall thickness on elastic properties
of thin cellular films.Comment: 7 figures and 2 table
Origin of temperature dependent conductivity of -polyvinylidene fluoride
The conductivity of -polyvinylidene fluoride (-PVDF) 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
Respostas e adaptações de comunidades de colêmbolos (Hexapoda: Collembola) a condições de inundação e hipoxia
Standard ecological methods (pitfall traps, trunk eclectors and soil cores) were used to evaluate collembolan community responses to different flooding intensities. Three sites of a floodplain habitat near Mainz, Germany, with different flooding regimes were investigated. The structures of collembolan communities are markedly different depending on flooding intensity. Sites more affected by flooding are dominated by hygrophilic and hygrotolerant species, whereas the hardwood floodplain is dominated by mesophilic species. The survival strategies of the hygrophilic and hygrotolerant species include egg diapause and passive drifting. The physiological adaptations to hypoxic conditions of several collembolan species were analyzed using a microcalorimeter. The activities were tested under normoxic and hypoxic/anoxic conditions as well as during post-hypoxic recovery. Lactate was increased after hypoxic intervals in the species studied, suggesting that, in addition to a massive decrease in metabolic rate, a modest glycolytic activity may be involved in the tolerance to hypoxia.Foram utilizados os métodos ecológicos padrão (armadilhas "pitfall", armadilhas de tronco e amostras de solo) para avaliar as respostas de comunidade de colêmbolos a diferentes intensidades de inundação. Foram investigados três locais de um habitat de leitos de inundação perto de Mainz, Alemanha, com diferentes regimes de inundação. As estruturas das comunidades de colêmbolos foram nitidamente diferentes conforme a intensidade das inundações. Nos locais mais afetados por inundações, as espécies higrofílicas e higrotolerantes dominaram, ao passo que as espécies mesofílicas foram dominantes nos locais de leitos de inundação com angiospermas. As estratégias de sobrevivência das espécies higrofílicas e higrotolerantes incluem a diapausa dos ovos e o deslocamento passivo. Foi testada a adaptação fisiológica a condições hipóxicas de espécies selecionadas de colêmbolos através de análises por microcalorimetria. A atividade das espécies foi testada em condições normóxicas e hipóxicas/anóxicas e durante a recuperação pós-hipoxia. Verificou-se que o lactato aumentava após condições hipóxicas nas espécies avaliadas, o que sugere que, além de um decréscimo massivo na atividade metabólica, deve haver também certa atividade glicolítica associada à tolerância à hipoxia
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