55 research outputs found
Mechanical properties of electroactive polymer microactuators with ion-implanted electrodes
We report on the use of the bulge test method to characterize the mechanical properties of miniaturized buckling mode dielectric elastomer actuators (DEA). Our actuator consists of a Polydimethylsiloxane (PDMS) membrane bonded to a silicon chip with through holes. Compliant electrodes are fabricated on both sides of the membrane by metal ion implantation. The membrane buckles when a critical voltage is applied to the electrodes. The maximum displacements as well as the efficiency of such actuators strongly depend on the mechanical parameters of the combined electrode-elastomer-electrode layer, mainly effective Young's modulus E and residual stress S. We report measured E and S obtained from bulge tests on PDMS membranes for two PDMS brands and for several different curing methods, which allows tuning the residual stress by controlling the rate of solvent evaporation. Bulge test measurements were then used to study the change in membranes' mechanical properties due to titanium ion implantation, compared to the properties obtained from depositing an 8 nm thick gold electrode. At the doses required to create a conductive layer, we find that the Ti ion implantation has a low impact on the membrane's overall rigidity (doubling of the Young's modulus and reducing the tensile stress) compared to the Au film (400% increase in E). The ion implantation method is an excellent candidate for DEAs' electrodes, which need to be compliant in order to achieve large displacements
Microstructure of 5 keV gold-implanted polydimethylsiloxane
The first high-resolution transmission electron microscopy (TEM) cross-section images of flexible electrodes fabricated by gold ion implantation at 5 keV into polydimethylsiloxane (PDMS) are presented. A TEM sample preparation method based on cryoultramicrotomy, adapted for extremely low-modulus (1 MPa) elastomers, was developed, allowing the gold nanoparticles in a PDMS matrix to be imaged. The cluster size, size distribution and implantation depth of 50 nm were determined from the images and used to calculate the Youngâs modulus of the implanted layer
Mechanical properties of electroactive polymer microactuators with ion-implanted electrodes
MosquĂ©es et centres islamiques : vers lâexpansion LâĂ©tablissement de mosquĂ©es et de centres islamiques aux Ătats-Unis remonte au dĂ©but du xxe siĂšcle. La mosquĂ©e la plus ancienne â encore en place aujourdâhui mais transformĂ©e en site historique â fut bĂątie par des Arabes en 1934 dans lâIowa. Par la suite, un certain nombre de mosquĂ©es et de centres islamiques virent le jour sur lâensemble du territoire amĂ©ricain. Ă partir des annĂ©es 1960 et 1970, durant lesquelles des immigrants qualifiĂ©s, sud..
Microactuators based on ion implanted dielectric electroactive polymer (EAP) membranes
We report on the first successfully microfabricated and tested ion-implanted dielectric electroactive polymer (EAP or DEAP) actuators. Dieletric EAP (DEAP) actuators combine exceptionally high energy-density with large amplitude displacements [1,2]. Scaling DEAPs down to the milimeter and micron scale requires patterning compliant electrodes on such a scale on the surfaces of the polymer. We used ion implantation to make the surfaces of the polymer locally conducting. Implanting the compliant electrodes solves the problem of microfabricating patterned electrodes whose elasticity is close to that of the insulating elastomer, thus avoiding the deposition of metal electrodes on the polymer which leads to significant stiffening of the membrane [3]. Several techniques based on ion implantation for chip level and wafer level fabrication are presented. Ion implanted DEAP membranes were both simulated (FEM) and characterized. We report measurements on an actuator consisting of a 30-um-thick ion implanted PDMS membrane bonded to a silicon chip into which a cavity had been etched. We measured 110 um vertical displacements for a 0.72 mm2 square membrane, achieving for the first time the same percent displacement in microscopic EAPs as in macroscopic devices. These observations show that ion implantation allows the patterning of electrodes on PDMS membranes with negligible increase in stiffness
Microactuators based on ion implanted dielectric electroactive polymer (EAP) membranes
Selection Signatures in Worldwide Sheep Populations
The diversity of populations in domestic species offers great opportunities to study genome response to selection. The recently published Sheep HapMap dataset is a great example of characterization of the world wide genetic diversity in sheep. In this study, we re-analyzed the Sheep HapMap dataset to identify selection signatures in worldwide sheep populations. Compared to previous analyses, we made use of statistical methods that (i) take account of the hierarchical structure of sheep populations, (ii) make use of linkage disequilibrium information and (iii) focus specifically on either recent or older selection signatures. We show that this allows pinpointing several new selection signatures in the sheep genome and distinguishing those related to modern breeding objectives and to earlier post-domestication constraints. The newly identified regions, together with the ones previously identified, reveal the extensive genome response to selection on morphology, color and adaptation to new environments
The Mutational Landscape of Circulating Tumor Cells in Multiple Myeloma
The development of sensitive and non-invasive
ââliquid biopsiesââ presents new opportunities for
longitudinal monitoring of tumor dissemination and
clonal evolution. The number of circulating tumor
cells (CTCs) is prognostic in multiple myeloma
(MM), but there is little information on their genetic
features. Here, we have analyzed the genomic landscape
of CTCs from 29 MM patients, including eight
cases with matched/paired bone marrow (BM) tumor
cells. Our results show that 100% of clonal mutations
in patient BM were detected in CTCs and that 99% of
clonal mutations in CTCs were present in BM MM.
These include typical driver mutations in MM such
as in KRAS, NRAS, or BRAF. These data suggest
that BM and CTC samples have similar clonal structures,
as discordances between the two were
restricted to subclonal mutations. Accordingly, our
results pave the way for potentially less invasive
mutation screening of MM patients through characterization
of CTCs
Iran's Oil Wealth: Treasure and Trouble for the Shah's Regime - A Context-Sensitive Analysis of the Ambivalent Impact of Resource Abundance
Genetic testing for TMEM154 mutations associated with lentivirus susceptibility in sheep
Stefan Hiendleder is a member of the International Sheep Genomics ConsortiumIn sheep, small ruminant lentiviruses cause an incurable, progressive, lymphoproliferative disease that affects millions of animals worldwide. Known as ovine progressive pneumonia virus (OPPV) in the U.S., and Visna/Maedi virus (VMV) elsewhere, these viruses reduce an animalâs health, productivity, and lifespan. Genetic variation in the ovine transmembrane protein 154 gene (TMEM154) has been previously associated with OPPV infection in U.S. sheep. Sheep with the ancestral TMEM154 haplotype encoding glutamate (E) at position 35, and either form of an N70I variant, were highly-susceptible compared to sheep homozygous for the K35 missense mutation. Our current overall aim was to characterize TMEM154 in sheep from around the world to develop an efficient genetic test for reduced susceptibility. The average frequency of TMEM154 E35 among 74 breeds was 0.51 and indicated that highly-susceptible alleles were present in most breeds around the world. Analysis of whole genome sequences from an international panel of 75 sheep revealed more than 1,300 previously unreported polymorphisms in a 62 kb region containing TMEM154 and confirmed that the most susceptible haplotypes were distributed worldwide. Novel missense mutations were discovered in the signal peptide (A13V) and the extracellular domains (E31Q, I74F, and I102T) of TMEM154. A matrix-assisted laser desorption/ionizationâtime-of flight mass spectrometry (MALDI-TOF MS) assay was developed to detect these and six previously reported missense and two deletion mutations in TMEM154. In blinded trials, the call rate for the eight most common coding polymorphisms was 99.4% for 499 sheep tested and 96.0% of the animals were assigned paired TMEM154 haplotypes (i.e., diplotypes). The widespread distribution of highly-susceptible TMEM154 alleles suggests that genetic testing and selection may improve the health and productivity of infected flocks.Michael P. Heaton, Theodore S. Kalbfleisch, Dustin T. Petrik, Barry Simpson, James W. Kijas, Michael L. Clawson, Carol G. Chitko-McKown, Gregory P. Harhay, Kreg A. Leymaster, the International Sheep Genomics Consortiu
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