2,620 research outputs found
A geometric bound on F-term inflation
We discuss a general bound on the possibility to realise inflation in any
minimal supergravity with F-terms. The derivation crucially depends on the
sGoldstini, the scalar field directions that are singled out by spontaneous
supersymmetry breaking. The resulting bound involves both slow-roll parameters
and the geometry of the K\"ahler manifold of the chiral scalars. We analyse the
inflationary implications of this bound, and in particular discuss to what
extent the requirements of single field and slow-roll can both be met in F-term
inflation.Comment: 14 pages, improved analysis, references added, matches published
versio
Electric Field Effects on Graphene Materials
Understanding the effect of electric fields on the physical and chemical
properties of two-dimensional (2D) nanostructures is instrumental in the design
of novel electronic and optoelectronic devices. Several of those properties are
characterized in terms of the dielectric constant which play an important role
on capacitance, conductivity, screening, dielectric losses and refractive
index. Here we review our recent theoretical studies using density functional
calculations including van der Waals interactions on two types of layered
materials of similar two-dimensional molecular geometry but remarkably
different electronic structures, that is, graphene and molybdenum disulphide
(MoS). We focus on such two-dimensional crystals because of they
complementary physical and chemical properties, and the appealing interest to
incorporate them in the next generation of electronic and optoelectronic
devices. We predict that the effective dielectric constant () of
few-layer graphene and MoS is tunable by external electric fields (). We show that at low fields ( V/\AA)
assumes a nearly constant value 4 for both materials, but increases at
higher fields to values that depend on the layer thickness. The thicker the
structure the stronger is the modulation of with the electric
field. Increasing of the external field perpendicular to the layer surface
above a critical value can drive the systems to an unstable state where the
layers are weakly coupled and can be easily separated. The observed dependence
of on the external field is due to charge polarization driven by
the bias, which show several similar characteristics despite of the layer
considered.Comment: Invited book chapter on Exotic Properties of Carbon Nanomatter:
Advances in Physics and Chemistry, Springer Series on Carbon Materials.
Editors: Mihai V. Putz and Ottorino Ori (11 pages, 4 figures, 30 references
The promoter polymorphism -232C/G of the PCK1 gene is associated with type 2 diabetes in a UK-resident South Asian population
Background: The PCK1 gene, encoding cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), has previously been implicated as a candidate gene for type 2 diabetes (T2D) susceptibility. Rodent models demonstrate that over-expression of Pck1 can result in T2D development and a single nucleotide polymorphism (SNP) in the promoter region of human PCK1 (-232C/G) has exhibited significant association with the disease in several cohorts. Within the UK-resident South Asian population, T2D is 4 to 6 times more common than in indigenous white Caucasians. Despite this, few studies have reported on the genetic susceptibility to T2D in this ethnic group and none of these has investigated the possible effect of PCK1 variants. We therefore aimed to investigate the association between common variants of the PCK1 gene and T2D in a UK-resident South Asian population of Punjabi ancestry, originating predominantly from the Mirpur area of Azad Kashmir, Pakistan. \ud
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Methods: We used TaqMan assays to genotype five tagSNPs covering the PCK1 gene, including the -232C/G variant, in 903 subjects with T2D and 471 normoglycaemic controls. \ud
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Results: Of the variants studied, only the minor allele (G) of the -232C/G SNP demonstrated a significant association with T2D, displaying an OR of 1.21 (95% CI: 1.03 - 1.42, p = 0.019). \ud
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Conclusion: This study is the first to investigate the association between variants of the PCK1 gene and T2D in South Asians. Our results suggest that the -232C/G promoter polymorphism confers susceptibility to T2D in this ethnic group. \ud
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Trial registration: UKADS Trial Registration: ISRCTN38297969
Smart biomaterials - regulating cell behavior through signaling molecules
Important advances in the field of tissue engineering are arising from increased interest in novel biomaterial designs with bioactive components that directly influence cell behavior. Following the recent work of Mitchell and co-workers published in BMC Biology, we review how spatial and temporal control of signaling molecules in a matrix material regulates cellular responses for tissue-specific applications
Performance evaluation of bluetooth low energy for high data rate body area networks
Bluetooth Low Energy (BLE) is a promising wireless network technology, in the context of body area network (BAN) applications, to provide the required quality of service (QoS) support concerning the communication between sensor nodes placed on a userâs body and a personal device, such as a smartphone. Most previous BLE performance studies in the literature have focused primarily in networks with a single slave (point-to-point link) or traffic scenarios with relatively low data rate. However, many BAN sensors generate high data rate traffic, and several sensor nodes (slaves) may be actively sending data in the same BAN. Therefore, this work focuses on the evaluation of the suitability of BLE mainly under these conditions. Results show that, for the same traffic, the BLE protocol presents lower energy consumption and supports more sensor nodes than an alternative IEEE 802.15.4-based protocol. This study also identifies and characterizes some implementation constraints on the tested platforms that impose limits on the achievable performance.This work has been supported by FCT (Fundação para a CiĂȘncia e Tecnologia) in
the scope of the projects UID/EEA/04436/2013 and UID/CTM/50025/2013, and by
FEDER funds through the COMPETE 2020 Programme
Frustrated charge order and cooperative distortions in ScV6Sn6
Here we study the stability of charge order in the kagome metal ScV6Sn6.
Synchrotron x-ray diffraction measurements reveal high-temperature, short-range
charge correlations at the wave vectors along q=(1/3,1/3,1/2) whose inter-layer
correlation lengths diverge upon cooling. At the charge order transition, this
divergence is interrupted and long-range order freezes in along
q=(1/3,1/3,1/3), as previously reported, while disorder enables the charge
correlations to persist at the q=(1/3,1/3,1/2) wave vector down to the lowest
temperatures measured. Both short-range and long-range charge correlations
seemingly arise from the same instability and both are rapidly quenched upon
the introduction of larger Y ions onto the Sc sites. Our results validate the
theoretical prediction of the primary lattice instability at q=(1/3,1/3,1/2),
and we present a heuristic picture for viewing the frustration of charge order
in this compound
Initiating head development in mouse embryos: integrating signalling and transcriptional activity
The generation of an embryonic body plan is the outcome of inductive interactions between the progenitor tissues that underpin their specification, regionalization and morphogenesis. The intercellular signalling activity driving these processes is deployed in a time- and site-specific manner, and the signal strength must be precisely controlled. Receptor and ligand functions are modulated by secreted antagonists to impose a dynamic pattern of globally controlled and locally graded signals onto the tissues of early post-implantation mouse embryo. In response to the WNT, Nodal and Bone Morphogenetic Protein (BMP) signalling cascades, the embryo acquires its body plan, which manifests as differences in the developmental fate of cells located at different positions in the anteriorâposterior body axis. The initial formation of the anterior (head) structures in the mouse embryo is critically dependent on the morphogenetic activity emanating from two signalling centres that are juxtaposed with the progenitor tissues of the head. A common property of these centres is that they are the source of antagonistic factors and the hub of transcriptional activities that negatively modulate the function of WNT, Nodal and BMP signalling cascades. These events generate the scaffold of the embryonic head by the early-somite stage of development. Beyond this, additional tissue interactions continue to support the growth, regionalization, differentiation and morphogenesis required for the elaboration of the structure recognizable as the embryonic head
MR Imaging Findings of a Primary Cardiac Osteosarcoma and Its Bone Metastasis with Histopathologic Correlation
An osteosarcoma of cardiac origin is extremely rare, and a comprehensive description of MR imaging (MRI) findings of cardiac osteosarcoma and its metastasis in the femur have not been reported in the literature. We present a case of cardiac osteosarcoma in a 47-year-old woman and its metastasis to the femur, focusing on the description of MRI findings of the cardiac and metastatic bony osteosarcoma with a histopathologic correlation
Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics
The celebrated electronic properties of graphene have opened way for
materials just one-atom-thick to be used in the post-silicon electronic era. An
important milestone was the creation of heterostructures based on graphene and
other two-dimensional (2D) crystals, which can be assembled in 3D stacks with
atomic layer precision. These layered structures have already led to a range of
fascinating physical phenomena, and also have been used in demonstrating a
prototype field effect tunnelling transistor - a candidate for post-CMOS
technology. The range of possible materials which could be incorporated into
such stacks is very large. Indeed, there are many other materials where layers
are linked by weak van der Waals forces, which can be exfoliated and combined
together to create novel highly-tailored heterostructures. Here we describe a
new generation of field effect vertical tunnelling transistors where 2D
tungsten disulphide serves as an atomically thin barrier between two layers of
either mechanically exfoliated or CVD-grown graphene. Our devices have
unprecedented current modulation exceeding one million at room temperature and
can also operate on transparent and flexible substrates
Wnt5a induces ROR1 to complex with HS1 to enhance migration of chronic lymphocytic leukemia cells.
ROR1 (receptor tyrosine kinase-like orphan receptor 1) is a conserved, oncoembryonic surface antigen expressed in chronic lymphocytic leukemia (CLL). We found that ROR1 associates with hematopoietic-lineage-cell-specific protein 1 (HS1) in freshly isolated CLL cells or in CLL cells cultured with exogenous Wnt5a. Wnt5a also induced HS1 tyrosine phosphorylation, recruitment of ARHGEF1, activation of RhoA and enhanced chemokine-directed migration; such effects could be inhibited by cirmtuzumab, a humanized anti-ROR1 mAb. We generated truncated forms of ROR1 and found its extracellular cysteine-rich domain or kringle domain was necessary for Wnt5a-induced HS1 phosphorylation. Moreover, the cytoplamic, and more specifically the proline-rich domain (PRD), of ROR1 was required for it to associate with HS1 and allow for F-actin polymerization in response to Wnt5a. Accordingly, we introduced single amino acid substitutions of proline (P) to alanine (A) in the ROR1 PRD at positions 784, 808, 826, 841 or 850 in potential SH3-binding motifs. In contrast to wild-type ROR1, or other ROR1PâïžA mutants, ROR1P(841)A had impaired capacity to recruit HS1 and ARHGEF1 to ROR1 in response to Wnt5a. Moreover, Wnt5a could not induce cells expressing ROR1P(841)A to phosphorylate HS1 or activate ARHGEF1, and was unable to enhance CLL-cell motility. Collectively, these studies indicate HS1 plays an important role in ROR1-dependent Wnt5a-enhanced chemokine-directed leukemia-cell migration
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