112 research outputs found
Wafer bonding solution to epitaxial graphene - silicon integration
The development of graphene electronics requires the integration of graphene
devices with Si-CMOS technology. Most strategies involve the transfer of
graphene sheets onto silicon, with the inherent difficulties of clean transfer
and subsequent graphene nano-patterning that degrades considerably the
electronic mobility of nanopatterned graphene. Epitaxial graphene (EG) by
contrast is grown on an essentially perfect crystalline (semi-insulating)
surface, and graphene nanostructures with exceptional properties have been
realized by a selective growth process on tailored SiC surface that requires no
graphene patterning. However, the temperatures required in this structured
growth process are too high for silicon technology. Here we demonstrate a new
graphene to Si integration strategy, with a bonded and interconnected compact
double-wafer structure. Using silicon-on-insulator technology (SOI) a thin
monocrystalline silicon layer ready for CMOS processing is applied on top of
epitaxial graphene on SiC. The parallel Si and graphene platforms are
interconnected by metal vias. This method inspired by the industrial
development of 3d hyper-integration stacking thin-film electronic devices
preserves the advantages of epitaxial graphene and enables the full spectrum of
CMOS processing.Comment: 15 pages, 7 figure
The docking of synaptic vesicles on the presynaptic membrane induced by α-synuclein is modulated by lipid composition.
α-Synuclein (αS) is a presynaptic disordered protein whose aberrant aggregation is associated with Parkinson's disease. The functional role of αS is still debated, although it has been involved in the regulation of neurotransmitter release via the interaction with synaptic vesicles (SVs). We report here a detailed characterisation of the conformational properties of αS bound to the inner and outer leaflets of the presynaptic plasma membrane (PM), using small unilamellar vesicles. Our results suggest that αS preferentially binds the inner PM leaflet. On the basis of these studies we characterise in vitro a mechanism by which αS stabilises, in a concentration-dependent manner, the docking of SVs on the PM by establishing a dynamic link between the two membranes. The study then provides evidence that changes in the lipid composition of the PM, typically associated with neurodegenerative diseases, alter the modes of binding of αS, specifically in a segment of the sequence overlapping with the non-amyloid component region. Taken together, these results reveal how lipid composition modulates the interaction of αS with the PM and underlie its functional and pathological behaviours in vitro
Tissue-specific localization of β-carotene and iron in transgenic indica rice (Oryza sativa L.)
Tissue-specific distribution and localization of β-carotene and iron were characterized in transgenic rice seeds by histochemical studies. Histochemical reactions clearly revealed the accumulation of β-carotene in the endosperm of transgenic seeds in comparison with non-transgenic control where no β-carotene could be detected. A similar observation was made for iron-colour reaction in the endosperm. Since histochemical tests can be carried out easily and are fairly specific for determining particular compounds both qualitatively and to some extent quantitatively (based on the intensity of colour), this method could be used for identifying the desirable transgenic material with high β-carotene and iron content
A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems
We use the density matrix renormalization group (DMRG) method to study the
ground and low-lying excited states of three kinds of uniform and dimerized
alternating spin chains. The DMRG procedure is also employed to obtain
low-temperature thermodynamic properties of these systems. We consider a 2N
site system with spins and alternating from site to site and
interacting via a Heisenberg antiferromagnetic exchange. The three systems
studied correspond to being equal to and
; all of them have very similar properties. The ground state is found
to be ferrimagnetic with total spin . We find that there is
a gapless excitation to a state with spin , and a gapped excitation to
a state with spin . Surprisingly, the correlation length in the ground
state is found to be very small for this gapless system. The DMRG analysis
shows that the chain is susceptible to a conditional spin-Peierls instability.
Furthermore, our studies of the magnetization, magnetic susceptibility
and specific heat show strong magnetic-field dependences. The product
shows a minimum as a function of temperature T at low magnetic fields; the
minimum vanishes at high magnetic fields. This low-field behavior is in
agreement with earlier experimental observations. The specific heat shows a
maximum as a function of temperature, and the height of the maximum increases
sharply at high magnetic fields. Although all the three systems show
qualitatively similar behavior, there are some notable quantitative differences
between the systems in which the site spin difference, , is large
and small respectively.Comment: 16 LaTeX pages, 13 postscript figure
One-Dimensional Organometallic V-Anthracene Wire and Its B-N Analogue: Efficient Half-Metallic Spin Filters
Using density functional theory, we have investigated the structural,
electronic and magnetic properties of infinitely periodic organometallic
vanadium-anthracene ([V_2Ant]_\infinity) and [V_4(BNAnt)_2]_\infinity(where
BNAnt is B-N analogue of anthracene) for their possible application in
spintronics. From our calculations, we find that one-dimensional
[V_2Ant]_\infinity and [V_4(BNAnt)_2]_\infinity wires exhibit robust
ferromagnetic half-metallic and metallic behavior, respectively. The finite
sized and clusters are also found to exhibit
efficient spin filter properties when coupled to graphene electrodes on either
side
Study of the single nucleotide polymorphism (SNP) at the palindromic sequence of hypersensitive site (HS)4 of the human β-globin locus control region (LCR) in Indian population
LCR, a genetic regulatory element, was examined in β-thalassemia patients who do not show any mutation in the β-globin genes. We sequenced LCR-HS2, HS3, and HS4 in samples from 16 such patients from the Indian population and found only one SNP A-G in the inverted repeat in HS4. A significant association was observed between the G allele and occurrence of β-thalassemia by Fisher's exact test. The AG and GG genotypes showed higher relative risk as compared to the AA genotype. We also observed linkage disequilibrium between the A/G polymorphism and the AT-rich motif of the LCR HS2 region, suggesting that the G allele could be an evolutionarily new mutation in the study population
US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report
This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in
Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference
The Effect of ACACB cis-Variants on Gene Expression and Metabolic Traits
Acetyl Coenzyme A carboxylase β (ACACB) is the rate-limiting enzyme in fatty acid oxidation, and continuous fatty acid oxidation in Acacb knock-out mice increases insulin sensitivity. Systematic human studies have not been performed to evaluate whether ACACB variants regulate gene expression and insulin sensitivity in skeletal muscle and adipose tissues. We sought to determine whether ACACB transcribed variants were associated with ACACB gene expression and insulin sensitivity in non-diabetic African American (AA) and European American (EA) adults.ACACB transcribed single nucleotide polymorphisms (SNPs) were genotyped in 105 EAs and 46 AAs whose body mass index (BMI), lipid profiles and ACACB gene expression in subcutaneous adipose and skeletal muscle had been measured. Allelic expression imbalance (AEI) was assessed in lymphoblast cell lines from heterozygous subjects in an additional EA sample (n = 95). Selected SNPs were further examined for association with insulin sensitivity in a cohort of 417 EAs and 153 AAs.ACACB transcribed SNP rs2075260 (A/G) was associated with adipose ACACB messenger RNA expression in EAs and AAs (p = 3.8×10(-5), dominant model in meta-analysis, Stouffer method), with the (A) allele representing lower gene expression in adipose and higher insulin sensitivity in EAs (p = 0.04). In EAs, adipose ACACB expression was negatively associated with age and sex-adjusted BMI (r = -0.35, p = 0.0002).Common variants within the ACACB locus appear to regulate adipose gene expression in humans. Body fat (represented by BMI) may further regulate adipose ACACB gene expression in the EA population
Genome-Wide Analyses of Recombination Prone Regions Predict Role of DNA Structural Motif in Recombination
HapMap findings reveal surprisingly asymmetric distribution of recombinogenic regions. Short recombinogenic regions (hotspots) are interspersed between large relatively non-recombinogenic regions. This raises the interesting possibility of DNA sequence and/or other cis- elements as determinants of recombination. We hypothesized the involvement of non-canonical sequences that can result in local non-B DNA structures and tested this using the G-quadruplex DNA as a model. G-quadruplex or G4 DNA is a unique form of four-stranded non-B DNA structure that engages certain G-rich sequences, presence of such motifs has been noted within telomeres. In support of this hypothesis, genome-wide computational analyses presented here reveal enrichment of potential G4 (PG4) DNA forming sequences within 25618 human hotspots relative to 9290 coldspots (p<0.0001). Furthermore, co-occurrence of PG4 DNA within several short sequence elements that are associated with recombinogenic regions was found to be significantly more than randomly expected. Interestingly, analyses of more than 50 DNA binding factors revealed that co-occurrence of PG4 DNA with target DNA binding sites of transcription factors c-Rel, NF-kappa B (p50 and p65) and Evi-1 was significantly enriched in recombination-prone regions. These observations support involvement of G4 DNA in recombination, predicting a functional model that is consistent with duplex-strand separation induced by formation of G4 motifs in supercoiled DNA and/or when assisted by other cellular factors
Transancestral mapping and genetic load in systemic lupus erythematosus
Systemic lupus erythematosus (SLE) is an autoimmune disease with marked gender and ethnic disparities. We report a large transancestral association study of SLE using Immunochip genotype data from 27,574 individuals of European (EA), African (AA) and Hispanic Amerindian (HA) ancestry. We identify 58 distinct non-HLA regions in EA, 9 in AA and 16 in HA (B50% of these regions have multiple independent associations); these include 24 novel SLE regions (Po5 10 8), refined association signals in established regions, extended associations to additional ancestries, and a disentangled complex HLA multigenic effect. The risk allele count (genetic load) exhibits an accelerating pattern of SLE risk, leading us to posit a cumulative hit hypothesis for autoimmune disease. Comparing results across the three ancestries identifies both ancestry-dependent and ancestry-independent contributions to SLE risk. Our results are consistent with the unique and complex histories of the populations sampled, and collectively help clarify the genetic architecture and ethnic disparities in SL
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