Conclusions The change in molecular weight characteristics and in viscosimetric data during the synthesis process of an aromatic copolyamide has been analyzed. It has been found that, with rise in the degree of completion of the reaction, at definite molecular weight values the dynamic viscosity rises sharply, which indicates the presence of a significant structural component of this system.The effect of polymer molecular weight on fibre physicomechanical properties has been shown. An increase in fibre strength has been noted on increase in molecular weight from 5400 to 7300. The impairment in physicomechanical properties on further increase in polymer molecular weight is connected with difficulties in processing the strongly structured spinning solutions. Processing polymer with a high molecular weight, and, as a consequence, with an elevated dynamic viscosity requires new approaches both to spinning conditions and, possibly, also to synthesis conditions.Translated from Khimicheskie Volokna, No. 2, pp. 29–30, March–April, 1989. 相似文献
Conclusions -- A dependence of the second moment of the NMR line on the angle between the fibre axis and the magnetic field has been given; the structural coefficient C0, C2, and C4 have been calculated for fibres based on poly-p-phenyleneterephthalamide and poly-p-benzamide at temperatures of –196 and +20°C and for Kevlar-49, from –196 to +400°C.-- The intramolecular structural coefficients C0im, C2im, and C4im have been calculated theoretically, and the orientation parameters
and
and the acoustic orientation factor f have been obtained, values for which indicate a high degree of orientation of the macromolecules in fibres.-- The smaller values of the second moment of the NMR line for PABI as compared with fibres based on PPTA in the temperature region 250–380°C indicate a more mobile structure for the PABI.-- In the range from –196 to +20°C thermal action leads to a more important change in the coefficient C0 for Kevlar-29 and Kevlar-49 as compared with PABI; this is apparently connected with thermal expansion in planes having a predominant concentration of van der Waals bonds for Kevlar-29 and Kevlar-49.Translated from Khimicheskie Volokna, No. 4, pp. 23–26, July–August, 1990. 相似文献
For the purpose of developing collaborative support in design studio environments, we have carried out ethnographic fieldwork in professional and academic product design studios. Our intention was to understand design practices beyond the productivity point of view and take into account the experiential, inspirational and aesthetical aspects of design practices. Using examples from our fieldwork, we develop our results around three broad themes by which design professionals support communication and collaboration: (1) use of artefacts, (2) use of space and (3) designerly practices. We use the results of our fieldwork for drawing implications for designing technologies for the design studio culture. 相似文献
Organizations are increasingly delegating customer inquiries to speech dialog systems (SDSs) to save personnel resources. However, customers often report frustration when interacting with SDSs due to poorly designed solutions. Despite these issues, design knowledge for SDSs in customer service remains elusive. To address this research gap, we employ the design science approach and devise a design theory for SDSs in customer service. The design theory, including 14 requirements and five design principles, draws on the principles of dialog theory and undergoes validation in three iterations using five hypotheses. A summative evaluation comprising a two-phase experiment with 205 participants yields positive results regarding the user experience of the artifact. This study contributes to design knowledge for SDSs in customer service and supports practitioners striving to implement similar systems in their organizations.
Light management and electrical isolation are essential for the majority of optoelectronic nanowire (NW) devices.Here,we present a cost-effective technique,based on vapor-phase deposition of parylene-C and subsequent annealing,that provides conformal encapsulation,anti-reflective coating,improved optical properties,and electrical insulation for GaAs nanowires.The process presented allows facile encapsulation and insulation that is suitable for any nanowire structure.In particular,the parylene-C encapsulation functions as an efficient antireflection coating for the nanowires,with reflectivity down to <1% in the visible spectrum.Furthermore,the parylene-C coating increases photoluminescence intensity,suggesting improved light guiding to the NWs.Finally,based on this process,a NW LED was fabricated,which showed good diode performance and a clear electroluminescence signal.We believe the process can expand the fabrication possibilities and improve the performance of optoelectronic nanowire devices. 相似文献
A device is described in which a biological specimen is periodically accelerated for a short period. Each event is followed by a variable period of free fall. Assuming that the g-dose (expressed g s) has to surpass a certain minimal value to be perceived by cells, and in addition, there is a minimal time threshold for sensing a change in gravity, it is conceivable that conditions are created in which cells do not detect the periodic acceleration, and only experience the periodic free-fall movement as a long-term weightlessness condition. Using the cell-cycle progression of the unicellular green alga Chlamydomonas as an example, it is shown that with this device effects can be generated which are similar to those observed in satellite flights. 相似文献
This paper describes the influence of a chip scale MEMS package (CSMP) on the acoustic behaviour of a silicon microphone.
The influence was calculated using an electro-mechanical–acoustical equivalent circuit. Standard packaging of microphones
using die bonding and wire bonding leads to a large front volume which acts as a Helmholtz resonator. This can dramatically
influence the frequency response of the microphone system by adding a second resonance. In the worst case this second resonance
is in the acoustic frequency range, thus degrading its performance in an unacceptable way. In case of the CSMP only a small
front volume is generated between the substrate and the flip-chipped microphone chip. Thus the resonance step-up is very small
compared to standard packages. Furthermore the frequency response can be flattened by optimizing the geometry of the small
sound holes in the substrate. By choosing an appropriate geometry of these sound holes the package can act as a low pass filter
where the cut-off frequency can be placed to the desired value of the acoustic spectrum. 相似文献