611 research outputs found
N-type organic electrochemical transistors with stability in water.
Organic electrochemical transistors (OECTs) are receiving significant attention due to their ability to efficiently transduce biological signals. A major limitation of this technology is that only p-type materials have been reported, which precludes the development of complementary circuits, and limits sensor technologies. Here, we report the first ever n-type OECT, with relatively balanced ambipolar charge transport characteristics based on a polymer that supports both hole and electron transport along its backbone when doped through an aqueous electrolyte and in the presence of oxygen. This new semiconducting polymer is designed specifically to facilitate ion transport and promote electrochemical doping. Stability measurements in water show no degradation when tested for 2 h under continuous cycling. This demonstration opens the possibility to develop complementary circuits based on OECTs and to improve the sophistication of bioelectronic devices
Internal kinematics of spiral galaxies in distant clusters IV. Gas kinematics of spiral galaxies in intermediate redshift clusters and in the field
(Abridged) We trace the interaction processes of galaxies at intermediate
redshift by measuring the irregularity of their ionized gas kinematics, and
investigate these irregularities as a function of the environment (cluster
versus field) and of morphological type (spiral versus irregular). Our sample
consists of 92 distant galaxies. 16 cluster (z~0.3 and z~0.5) and 29 field
galaxies (mean z=0.44) of these have velocity fields with sufficient signal to
be analyzed. We find that the fraction of galaxies that have irregular gas
kinematics is remarkably similar in galaxy clusters and in the field at
intermediate redshifts. The distribution of the field and cluster galaxies in
(ir)regularity parameters space is also similar. On the other hand galaxies
with small central concentration of light, that we see in the field sample, are
absent in the cluster sample. We find that field galaxies at intermediate
redshifts have more irregular velocity fields as well as more clumpy and less
centrally concentrated light distributions than their local counterparts.
Comparison with a SINS sample of 11 z ~ 2 galaxies shows that these distant
galaxies have more irregular gas kinematics than our intermediate redshift
cluster and field sample. We do not find a dependence of the irregularities in
gas kinematics on morphological type. We find that two different indicators of
star formation correlate with irregularity in the gas kinematics. More
irregular gas kinematics, also more clumpy and less centrally concentrated
light distributions of spiral field galaxies at intermediate redshifts in
comparison to their local counterparts indicate that these galaxies are
probably still in the process of building their disks via mechanisms such as
accretion and mergers. On the other hand, they have less irregular gas
kinematics compared to galaxies at z ~ 2.Comment: Accepted for publication in A&A, high resolution version available at
http://www.astro.rug.nl/~kutdemir/13262/13262_hr.p
X-ray calibration of SZ scaling relations with the ACCEPT catalogue of galaxy clusters observed by Chandra
We explore the scaling relation between the flux of the Sunyaev-Zel'dovich
(SZ) effect and the total mass of galaxy clusters using already reduced Chandra
X-ray data present in the ACCEPT (Archive of Chandra Cluster Entropy Profile
Tables) catalogue. The analysis is conducted over a sample of 226 objects,
examining the relatively small scale corresponding to a cluster overdensity
equal to 2500 times the critical density of the background universe, at which
the total masses have been calculated exploiting the hydrostatic equilibrium
hypothesis. Core entropy (K0) is strongly correlated with the central cooling
time, and is therefore used to identify cooling-core (CC) objects in our
sample. Our results confirm the self-similarity of the scaling relation between
the integrated Comptonization parameter (Y) and the cluster mass, for both CC
and NCC (non-cooling-core) clusters. The consistency of our calibration with
recent ones has been checked, with further support for Y as a good mass proxy.
We also investigate the robustness of the constant gas fraction assumption, for
fixed overdensity, and of the Yx proxy (Kravstov et al. 2007) considering CC
and NCC clusters, again sorted on K0 from our sample. We extend our study to
implement a K0-proxy, obtained by combining SZ and X-ray observables, which is
proposed to provide a CC indicator for higher redshift objects. Finally, we
suggest that an SZ-only CC indicator could benefit from the employment of
deprojected Comptonization radial profiles.Comment: 14 pages, 10 figures, accepted in MNRA
Undergraduate Research Participation in Electrical Engineering
During the 1990-2003 summers the Electrical Engineering Department at the University of Maine will offer ten undergraduate students the opportunity to actively participate in research. Students will receive financial awards plus a subsistence allowance. The available research projects include (1) Environmental Sensors; (2) Intelligent Systems for Automation; (3) Communications Devices and Applications; (4) Motion Control; (5) Microprocessor/Instrumentation Applications; (6) Growth and Characterization of Thin Film Materials; and (7) Power Systems Applications. At least five students will come from institutions where research opportunities are limited and at least four students will be women, minorities or students with disabilities. Students chosen for the program will have displayed a high degree of initiative and independence of thought in both laboratories and course work. Student research projects are chosen to match the student\u27s interest and educational level. In addition to extensive University facilities, students will also have access to facilities at various nearby industries such as Sensor Research and Development Corporation, BIODE Corporation, Bangor Hydro Electric and Central Maine Power Companies, James River, Champion, and Scott Paper Companies, Digital Equipment Corporation, Fairchild and National Semiconductor. At the program culmination a written report and an oral seminar are required from the student. Three academic credits are awarded to the student upon satisfactory completion of the program
Mapping and sequencing of structural variation from eight human genomes
Genetic variation among individual humans occurs on many different scales, ranging from gross alterations in the human karyotype to single nucleotide changes. Here we explore variation on an intermediate scale - particularly insertions, deletions and inversions affecting from a few thousand to a few million base pairs. We employed a clone- based method to interrogate this intermediate structural variation in eight individuals of diverse geographic ancestry. Our analysis provides a comprehensive overview of the normal pattern of structural variation present in these genomes, refining the location of 1,695 structural variants. We find that 50% were seen in more than one individual and that nearly half lay outside regions of the genome previously described as structurally variant. We discover 525 new insertion sequences that are not present in the human reference genome and show that many of these are variable in copy number between individuals. Complete sequencing of 261 structural variants reveals considerable locus complexity and provides insights into the different mutational processes that have shaped the human genome. These data provide the first high- resolution sequence map of human structural variation - a standard for genotyping platforms and a prelude to future individual genome sequencing projects
Genome-Wide Profiling of H3K56 Acetylation and Transcription Factor Binding Sites in Human Adipocytes
The growing epidemic of obesity and metabolic diseases calls for a better understanding of adipocyte biology. The regulation of transcription in adipocytes is particularly important, as it is a target for several therapeutic approaches. Transcriptional outcomes are influenced by both histone modifications and transcription factor binding. Although the epigenetic states and binding sites of several important transcription factors have been profiled in the mouse 3T3-L1 cell line, such data are lacking in human adipocytes. In this study, we identified H3K56 acetylation sites in human adipocytes derived from mesenchymal stem cells. H3K56 is acetylated by CBP and p300, and deacetylated by SIRT1, all are proteins with important roles in diabetes and insulin signaling. We found that while almost half of the genome shows signs of H3K56 acetylation, the highest level of H3K56 acetylation is associated with transcription factors and proteins in the adipokine signaling and Type II Diabetes pathways. In order to discover the transcription factors that recruit acetyltransferases and deacetylases to sites of H3K56 acetylation, we analyzed DNA sequences near H3K56 acetylated regions and found that the E2F recognition sequence was enriched. Using chromatin immunoprecipitation followed by high-throughput sequencing, we confirmed that genes bound by E2F4, as well as those by HSF-1 and C/EBPα, have higher than expected levels of H3K56 acetylation, and that the transcription factor binding sites and acetylation sites are often adjacent but rarely overlap. We also discovered a significant difference between bound targets of C/EBPα in 3T3-L1 and human adipocytes, highlighting the need to construct species-specific epigenetic and transcription factor binding site maps. This is the first genome-wide profile of H3K56 acetylation, E2F4, C/EBPα and HSF-1 binding in human adipocytes, and will serve as an important resource for better understanding adipocyte transcriptional regulation.Singapore. Agency for Science, Technology and Research (National Science Scholarship )Massachusetts Institute of Technology (Eugene Bell Career Development Chair)National Science Foundation (U.S.) (Award No. DBI-0821391)Pfizer Inc
- …