841 research outputs found
Feasibility of adjusting paced left ventricular activation by manipulating stimulus strength
Measurements of Charge Exchange Cross Sections for Highly Charged Tungsten Ions with Hydrogen Atoms
Interacting models for twisted bilayer graphene: a quantum chemistry approach
The nature of correlated states in twisted bilayer graphene (TBG) at the
magic angle has received intense attention in recent years. We present a
numerical study of an interacting Bistritzer-MacDonald (IBM) model of TBG using
a suite of methods in quantum chemistry, including Hartree-Fock, coupled
cluster singles, doubles (CCSD), and perturbative triples (CCSD(T)), as well as
a quantum chemistry formulation of the density matrix renormalization group
method (DMRG). Our treatment of TBG is agnostic to gauge choices, and hence we
present a new gauge-invariant formulation to detect the spontaneous symmetry
breaking in interacting models. To benchmark our approach, we focus on a
simplified spinless, valleyless IBM model. At integer filling (), all
numerical methods agree in terms of energy and symmetry
breaking. Additionally, as part of our benchmarking, we explore the impact of
different schemes for removing ``double-counting'' in the IBM model. Our
results at integer filling suggest that cross-validation of different IBM
models may be needed for future studies of the TBG system. After benchmarking
our approach at integer filling, we perform the first systematic study of the
IBM model near integer filling (for ). In this regime, we find that
the ground state can be in a metallic and symmetry
breaking phase. The ground state appears to have low entropy, and therefore can
be relatively well approximated by a single Slater determinant. Furthermore, we
observe many low entropy states with energies very close to the ground state
energy in the near integer filling regime
Constitutive dimerization of glycoprotein VI (GPVI) in resting platelets is essential for binding to collagen and activation in flowing blood
The platelet collagen receptor glycoprotein VI (GPVI) has been suggested to function as a dimer, with increased affinity for collagen. Dissociation constants (K(d)) obtained by measuring recombinant GPVI binding to collagenous substrates showed that GPVI dimers bind with high affinity to tandem GPO (Gly-Pro-Hyp) sequences in collagen, whereas the markedly lower affinity of the monomer for all substrates implies that it is not the collagen-binding form of GPVI. Dimer binding required a high density of immobilized triple-helical (GPO)(10)-containing peptide, suggesting that the dimer binds multiple, discrete peptide helices. Differential inhibition of dimer binding by dimer-specific antibodies, m-Fab-F and 204-11 Fab, suggests that m-Fab-F binds at the collagen-binding site of the dimer, and 204-11 Fab binds to a discrete site. Flow cytometric quantitation indicated that GPVI dimers account for ~29% of total GPVI in resting platelets, whereas activation by either collagen-related peptide or thrombin increases the number of dimers to ~39 and ~44%, respectively. m-Fab-F inhibits both GPVI-dependent static platelet adhesion to collagen and thrombus formation on collagen under low and high shear, indicating that pre-existing dimeric GPVI is required for the initial interaction with collagen because affinity of the monomer is too low to support binding and that interaction through the dimer is essential for platelet activation. These GPVI dimers in resting circulating platelets will enable them to bind injury-exposed subendothelial collagen to initiate platelet activation. The GPVI-specific agonist collagen-related peptide or thrombin further increases the number of dimers, thereby providing a feedback mechanism for reinforcing binding to collagen and platelet activation
Genetic and epigenetic alterations on the short arm of chromosome 11 are involved in a majority of sporadic Wilms' tumours
Wilms' tumour is one of the most common solid tumours of childhood. 11p13 (WT1 locus) and 11p15.5 (WT2 locus) are known to have genetic or epigenetic aberrations in these tumours. In Wilms' tumours, mutation of the Wilms tumour 1 (WT1) gene at the WT1 locus has been reported, and the WT2 locus, comprising the two independent imprinted domains IGF2/H19 and KIP2/LIT1, can undergo maternal deletion or alterations associated with imprinting. Although these alterations have been identified in many studies, it is still not clear how frequently combined genetic and epigenetic alterations of these loci are involved in Wilms' tumours or how these alterations occur. To answer both questions, we performed genetic and epigenetic analyses of these loci, together with an additional gene, CTNNB1, in 35 sporadic Wilms' tumours. Loss of heterozygosity of 11p15.5 and loss of imprinting of IGF2 were the most frequent genetic (29%) and epigenetic (40%) alterations in Wilms' tumours, respectively. In total, 83% of the tumours had at least one alteration at 11p15.5 and/or 11p13. One-third of the tumours had alterations at multiple loci. Our results suggest that chromosome 11p is not only genetically but also epigenetically critical for the majority of Wilms' tumours
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