Institution
University of Stuttgart
Education•Stuttgart, Germany•
About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.
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TL;DR: In this paper, the most important structural characteristic of crosslinked polymers, the crosslink density, could mostly be determined by indirect methods only, or was expressed relatively by the fraction of crosslinking monomers used in the synthesis.
Abstract: In polymer science and technology, linear, branched and crosslinked structures are usually distinguished. For crosslinked polymers, insolubility and lack of fusibility are considered as characteristic properties. However, insoluble polymers are not necessarily covalently crosslinked because insolubility and infusibility may be also caused by extremely high molecular masses,strong intermolecular interaction via secondary valency forces or by the lack of suitable solvents. For a long time, insolubility was the major obstacle for characterization of crosslinked polymers because it excluded analytical methods applicable to linear and branched macromolecules. In particular, the most important structural characteristic of crosslinked polymers, the crosslink density, could mostly be determined by indirect methods only [1],or was expressed relatively by the fraction of crosslinking monomers used in the synthesis.
236 citations
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TL;DR: In this article, a two-step post-synthesis strategy was proposed to create vacant T sites with associated silanol groups by dealumination of parent H-Beta and subsequent dry impregnation of the resulting Si-Beta with organometallic dimethyltin dichloride.
Abstract: Nanocrystalline Sn-Beta zeolites have been successfully prepared via an improved two-step postsynthesis strategy, which consists of creating vacant T sites with associated silanol groups by dealumination of parent H-Beta and subsequent dry impregnation of the resulting Si-Beta with organometallic dimethyltin dichloride. Characterization results from UV−vis, XPS, Raman, and 119 Sn solid-state MAS NMR reveal that most Sn species have been successfully incorpo- rated into the framework of Beta zeolite through the postsynthesis process and exist as isolated tetrahedral Sn(IV) in open arrangement. The creation of strong Lewis acid sites upon Sn incorporation is confirmed by FTIR spectroscopy with pyridine adsorption. The Sn-Beta Lewis acid catalysts are applied in the ring-opening hydration of epoxides to the corresponding 1,2-diols under near ambient and solvent-free conditions, and remarkable activity can be obtained. The impacts of Lewis acidity, preparation parameters, and reaction conditions on the catalytic performance of Sn-Beta zeolites are discussed in detail.
236 citations
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TL;DR: In this article, a theory is suggested which assumes a frozen dipole moment connected with the grain boundaries which induces the polar phase in the grain bulk in correlation with the bulk soft-mode frequency.
Abstract: Thorough Raman and infrared (IR) reflectivity investigations of nominally pure ${\mathrm{SrTiO}}_{3}$ ceramics in the 10--300 K range have revealed a clear presence of the polar phase whose manifestation steeply increases on cooling. The Raman strengths of the Raman-forbidden IR modes are proportional to ${\ensuremath{\omega}}_{\mathrm{TO}1}^{\ensuremath{-}\ensuremath{\alpha}}(\ensuremath{\alpha}\ensuremath{\approx}1.6)$ where ${\ensuremath{\omega}}_{\mathrm{TO}1}$ is the polar soft mode frequency. No pronounced permittivity dispersion is observed below the soft mode frequency so that, as in single crystals, the static permittivity is essentially determined by the soft mode contribution. A theory is suggested which assumes a frozen dipole moment connected with the grain boundaries which induces the polar phase in the grain bulk in correlation with the bulk soft-mode frequency. This stiffens slightly the effective soft mode response and reduces the low-temperature permittivity compared to that of single crystals. Moreover, the polar soft mode strongly couples to the ${E}_{g}$ component of the structural soft doublet showing that the polar axis is perpendicular to the tetragonal axis below the structural transition which is shifted to 132 K in our ceramics. Whereas the ${\mathrm{TiO}}_{6}$ octahedra tilt (primary order parameter) below the structural transition corresponds to that in single crystals, much smaller ${A}_{1g}\ensuremath{-}{E}_{g}$ splitting of the structural soft doublet shows that the tetragonal deformation (secondary order parameter) is nearly 10 times smaller, apparently due to the grain volume clamping in ceramics.
236 citations
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236 citations
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TL;DR: A scan-based BIST scheme is presented which guarantees complete fault coverage with very low hardware overhead, and it is shown that the output of an LFSR which feeds a scan path has to be modified only at a few bits in order to transform the random patterns into a complete test set.
Abstract: A scan-based BIST scheme is presented which guarantees complete fault coverage with very low hardware overhead. A probabilistic analysis shows that the output of an LFSR which feeds a scan path has to be modified only at a few bits in order to transform the random patterns into a complete test set. These modifications may be implemented by a bit-flipping function which has the LFSR-state as an input, and flips the value shifted into the scan path at certain times. A procedure is described for synthesizing the additional bit-flipping circuitry, and the experimental results indicate that this mixed-mode BIST scheme requires less hardware for complete fault coverage than all the other scan-based BIST approaches published so far.
235 citations
Authors
Showing all 28043 results
Name | H-index | Papers | Citations |
---|---|---|---|
Yi Chen | 217 | 4342 | 293080 |
Robert J. Lefkowitz | 214 | 860 | 147995 |
Michael Kramer | 167 | 1713 | 127224 |
Andrew G. Clark | 140 | 823 | 123333 |
Stephen D. Walter | 112 | 513 | 57012 |
Fedor Jelezko | 103 | 413 | 42616 |
Ulrich Gösele | 102 | 603 | 46223 |
Dirk Helbing | 101 | 642 | 56810 |
Ioan Pop | 101 | 1370 | 47540 |
Niyazi Serdar Sariciftci | 99 | 591 | 54055 |
Matthias Komm | 99 | 832 | 43275 |
Hans-Joachim Werner | 98 | 317 | 48508 |
Richard R. Ernst | 96 | 352 | 53100 |
Xiaoming Sun | 96 | 382 | 47153 |
Feng Chen | 95 | 2138 | 53881 |