192 research outputs found
Group expansions for impurities in superconductors
A new method is proposed for practical calculation of the effective
interaction between impurity scatterers in superconductors, based on algebraic
properties of related Nambu matrices for Green functions. In particular, we
show that the density of states within the s-wave gap can have a non-zero
contribution (impossible either in Born and in T-matrix approximation) from
non-magnetic impurities with concentration , beginning from order.Comment: 5 pages, 1 figur
Boundary friction on molecular lubricants: rolling mode?
A theoretical model is proposed for low-temperature friction between two smooth rigid solid
surfaces separated by lubricant molecules, admitting their deformations and rotations. The appearance
of different modes of energy dissipation (by «rocking» or «rolling» of lubricants) at slow relative
displacement of the surfaces is shown to be accompanied by stick-and-slip features and reveals
a nonmonotonic (mean) friction force vs external load
Impurity and vacancy effects in graphene
A Green function analysis has been developed for quasiparticle spectrum of a 2D graphene sheet in presence
of different types of substitutional disorder, including vacancies. The anomalous character of impurity effects in
this system is demonstrated, compared to those in well known doped semiconductors, and explained in terms of
conical singularities in the band spectrum of pure graphene. The criteria for appearance of localized states on
clusters of impurity scatterers and for qualitative restructuring of band spectrum are established and a possibility
for a specific metal/insulator transition at presence of vacancies is indicated
Impurity effects in quasiparticle spectrum of high-Tc superconductors
The revision is made of Green function methods that describe the dynamics of electronic quasiparticles in disordered superconducting systems with d-wave symmetry of order parameter. Various types of impurity perturbations are analyzed within the simplest T-matrix approximation. The extension of the common selfconsistent T-matrix approximation (SCTMA) to the so-called group expansions in clusters of interacting impurity centers is discussed and hence the validity criteria for SCTMA are established. A special attention is payed to the formation of impurity resonance states and localized states near the characteristic points of energy spectrum, corresponding to nodal points on the Fermi surface
5-HT2C Agonists Modulate Schizophrenia-Like Behaviors in Mice
All FDA-approved antipsychotic drugs (APDs) target primarily dopamine D2 or serotonin (5-HT2A) receptors, or both; however, these medications are not universally effective, they may produce undesirable side effects, and provide only partial amelioration of negative and cognitive symptoms. The heterogeneity of pharmacological responses in schizophrenic patients suggests that additional drug targets may be effective in improving aspects of this syndrome. Recent evidence suggests that 5-HT2C receptors may be a promising target for schizophrenia since their activation reduces mesolimbic nigrostriatal dopamine release (which conveys antipsychotic action), they are expressed almost exclusively in CNS, and have weight-loss-promoting capabilities. A difficulty in developing 5-HT2C agonists is that most ligands also possess 5-HT2B and/or 5-HT2A activities. We have developed selective 5-HT2C ligands and herein describe their preclinical effectiveness for treating schizophrenia-like behaviors. JJ-3-45, JJ-3-42, and JJ-5-34 reduced amphetamine-stimulated hyperlocomotion, restored amphetamine-disrupted prepulse inhibition, improved social behavior, and novel object recognition memory in NMDA receptor hypofunctioning NR1-knockdown mice, and were essentially devoid of catalepsy. However, they decreased motivation in a breakpoint assay and did not promote reversal learning in MK-801-treated mice. Somewhat similar effects were observed with lorcaserin, a 5-HT2C agonist with potent 5-HT2B and 5-HT2A agonist activities, which is approved for treating obesity. Microdialysis studies revealed that both JJ-3-42 and lorcaserin reduced dopamine efflux in the infralimbic cortex, while only JJ-3-42 decreased it in striatum. Collectively, these results provide additional evidence that 5-HT2C receptors are suitable drug targets with fewer side effects, greater therapeutic selectivity, and enhanced efficacy for treating schizophrenia and related disorders than current APDs. Neuropsychopharmacology advance online publication, 12 April 2017; doi:10.1038/npp.2017.52
D2 Dopamine Receptor G Protein-Biased Partial Agonists Based on Cariprazine
Functionally selective G protein-coupled receptor ligands are valuable tools for deciphering the roles of downstream signaling pathways that potentially contribute to therapeutic effects versus side effects. Recently, we discovered both Gi/o-biased and β-arrestin2-biased D2 receptor agonists based on the Food and Drug Administration (FDA)-approved drug aripiprazole. In this work, based on another FDA-approved drug, cariprazine, we conducted a structure-functional selectivity relationship study and discovered compound 38 (MS1768) as a potent partial agonist that selectively activates the Gi/o pathway over β-arrestin2. Unlike the dual D2R/D3R partial agonist cariprazine, compound 38 showed selective agonist activity for D2R over D3R. In fact, compound 38 exhibited potent antagonism of dopamine-stimulated β-arrestin2 recruitment. In our docking studies, compound 38 directly interacts with S1935.42 on TM5 but has no interactions with extracellular loop 2, which appears to be in contrast to the binding poses of D2R β-arrestin2-biased ligands. In in vivo studies, compound 38 showed high D2R receptor occupancy in mice and effectively inhibited phencyclidine-induced hyperlocomotion. © 2019 American Chemical Society
Designing Functionally Selective Noncatechol Dopamine D1 Receptor Agonists with Potent in Vivo Antiparkinsonian Activity
Dopamine receptors are important G protein-coupled receptors (GPCRs) with therapeutic opportunities for treating Parkinson's Disease (PD) motor and cognitive deficits. Biased D1 dopamine ligands that differentially activate G protein over β-arrestin recruitment pathways are valuable chemical tools for dissecting positive versus negative effects in drugs for PD. Here, we reveal an iterative approach toward modification of a D1-selective noncatechol scaffold critical for G protein-biased agonism. This approach provided enhanced understanding of the structural components critical for activity and signaling bias and led to the discovery of several novel compounds with useful pharmacological properties, including three highly GS-biased partial agonists. Administration of a potent, balanced, and brain-penetrant lead compound from this series results in robust antiparkinsonian effects in a rodent model of PD. This study suggests that the noncatechol ligands developed through this approach are valuable tools for probing D1 receptor signaling biology and biased agonism in models of neurologic disease
Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits
The WWgamma triple gauge boson coupling parameters are studied using p-pbar
-> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were
collected with the DO detector from an integrated luminosity of 162 pb^{-1}
delivered by the Fermilab Tevatron Collider. The cross section times branching
fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV
and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum)
pb. The one-dimensional 95% confidence level limits on anomalous couplings are
-0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.Comment: Submitted to Phys. Rev. D Rapid Communication
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging
We present a measurement of the top quark pair () production cross
section () in collisions at TeV
using 230 pb of data collected by the D0 experiment at the Fermilab
Tevatron Collider. We select events with one charged lepton (electron or muon),
missing transverse energy, and jets in the final state. We employ
lifetime-based b-jet identification techniques to further enhance the
purity of the selected sample. For a top quark mass of 175 GeV, we
measure pb, in
agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events
We present a measurement of the top quark pair ttbar production cross section
in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1}
of data collected by the DO detector at the Fermilab Tevatron Collider. We
select events with one charged lepton (electron or muon), large missing
transverse energy, and at least four jets, and extract the ttbar content of the
sample based on the kinematic characteristics of the events. For a top quark
mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1}
(syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let
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