2,259 research outputs found
Superconductivity in the -carbide-type oxides Zr4Rh2Ox
We report on the synthesis and the superconductivity of ZrRhO
( = 0.4, 0.5, 0.6, 0.7, 1.0). These compounds crystallize in the
-carbide structure, which is a filled version of the complex
intermetallic TiNi structure. We find that in the system
ZrRhO, already a small amount ( 0.4) of oxygen addition
stabilizes the -carbide structure over the more common intermetallic
CuAl structure-type, in which ZrRh crystallizes. We show that
ZrRhO and ZrRhO are bulk superconductors with critical
temperatures of 2.8 K and 4.7 K in the resistivity, respectively.
Our analysis of the superconducting properties reveal both compounds to be
strongly type-II superconductors with critical fields up to (0)
8.8 mT and (0) 6.08 T. Our results support
that the -carbides are a versatile family of compounds for the
investigation of the interplay of interstitial doping on physical properties,
especially for superconductivity
Quantum Materials Discovery by Combining Chemical and Physical Design Principles
Abstract: Exploratory quantum materials discovery remains crucial to progress in material science. Due to the grand challenges that we are facing in predicting these materials and their properties from scratch, chemical design principles remain a key ingredient for the discovery of new materials. Chemical heuristics, structure, bonding, as well as global and local symmetries are at the very foundation of materials properties. In this regard, in this research, we aim to identify functional materials by composition-structure-property understanding. Materials discovery consists of a subset of methods and design principles that go hand in hand until a desired material or property is realized. However, materials synthesis is still far from a rational design approach. Rather, materials, and especially metastable materials, have to be accessed and synthesized in an exploratory, laboratory-intensive fashion. At the same time, quantum materials discovery is a vibrant highly active field of research that has seen various leaps of progress in recent years, and that holds the promise for many more in the coming years. Here, we lay out how we are discovering new materials and new materials physics in our and other chemical physics, or physical chemistry research groups, and how chemistry and chemical synthesis play a crucial role in this process.
Short-range magnetic interactions and spin-glass behavior in the quasi-2D nickelate Pr4Ni3O8
The nickelate Pr4Ni3O8 features quasi-two-dimensional layers consisting of
three stacked square-planar NiO2 planes, in a similar way to the well-known
cuprate superconductors. The mixed-valent nature of Ni and its metallic
properties makes it a candidate for potentially unconventional
superconductivity. We have synthesized Pr4Ni3O8 by topotactic reduction of
Pr4Ni3O10 in 10 percent hydrogen gas, and report on measurements of
powder-neutron diffraction, magnetization and muon-spin rotation (uSR). We find
that Pr4Ni3O8 shows complicated spin-glass behavior with a distinct magnetic
memory effect in the temperature range from 2 to 300 K and a freezing
temperature T_s ~ 68 K. Moreover, the analysis of uSR spectra indicates two
magnetic processes characterized by remarkably different relaxation rates: a
slowly-relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions,
and a fast-relaxing signal, whose relaxation rate increases substantially below
~ 70 K which can be ascribed to the presence of short-range correlated regions.
We conclude that the complex spin-freezing process in Pr4Ni3O8 is governed by
these multiple magnetic interactions. It is possible that the complex magnetism
in Pr4Ni3O8 is detrimental to the occurrence of superconductivity
Regulation of human immunodeficiency virus type 1 gene transcription by nuclear receptors in human brain cells.
Infection of cells of the central nervous system by the human immunodeficiency virus type-1 (HIV-1) leads to HIV-1-associated neuropathology. Recent studies have demonstrated the importance of long terminal repeat (LTR) binding sites in determining the pathogenicity of HIV. Here we have investigated the presence and the functional role of transcription factors that have the potential to interact, directly or indirectly, with the nuclear receptor-responsive element in the LTR of HIV-1, in different human cell lines of the brain. Cotransfection experiments showed that in oligodendroglioma TC-620 cells, the retinoic acid receptor and the retinoid X receptor activate LTR-driven transcription in the absence of ligand. Addition of all-trans- or 9-cis-retinoic acid reverses this effect. In contrast, in astrocytoma, neuronal, and microglial cells, no significant effect of the retinoid acid pathway was detected. This retinoid response is mediated by distinct molecular interactions in the lymphotropic LAI and the neurotropic JR-CSF HIV-1 strains. Moreover, retinoid receptors were found to antagonize the chicken ovalbumin upstream promoter transcription factor- as well as the c-JUN-mediated LTR transactivation. Our findings demonstrate the importance of the retinoic acid signaling pathway and of cross-coupling interactions in the repression of HIV-1 LTR gene expression.journal articleresearch support, non-u.s. gov't1996 Sep 13importe
Opening Service 9-15-68
Dr. Huegli preaches on Romans 10:8-17.https://scholar.csl.edu/opening_services/1016/thumbnail.jp
Experimental and computational analyses reveal that environmental restrictions shape HIV-1 spread in 3D cultures
Here, using an integrative experimental and computational approach, Imle et al. show how cell motility and density affect HIV cell-associated transmission in a three-dimensional tissue-like culture system of CD4+ T cells and collagen, and how different collagen matrices restrict infection by cell-free virions
Polytypism and superconductivity in the NbS2 system
We report on the phase formation and the superconducting properties in the NbS2 system. Specifically, we have performed a series of standardized solid-state syntheses in this system, which allow us to establish a comprehensive synthesis map for the formation of the two polytypes 2H-NbS2 and 3R-NbS2, respectively. We show that the identification of two polytypes by means of X-ray diffraction is not always unambiguous. Our physical property measurements on a phase-pure sample of 3R-NbS2, on a phase-pure sample of 2H-NbS2, and a mixed phase sample confirm earlier reports that 2H-NbS2 is a bulk superconductor and that 3R-NbS2 is not a superconductor above T = 1.75 K. Our results clearly show that specific heat measurements, as true bulk measurements, are crucial for the identification of superconducting materials in this and related systems. Our results indicate that for the investigation of van der Waals materials great care has to be taken on choosing the synthesis conditions for obtaining phase pure samples
Computing Topology Preservation of RBF Transformations for Landmark-Based Image Registration
In image registration, a proper transformation should be topology preserving.
Especially for landmark-based image registration, if the displacement of one
landmark is larger enough than those of neighbourhood landmarks, topology
violation will be occurred. This paper aim to analyse the topology preservation
of some Radial Basis Functions (RBFs) which are used to model deformations in
image registration. Mat\'{e}rn functions are quite common in the statistic
literature (see, e.g. \cite{Matern86,Stein99}). In this paper, we use them to
solve the landmark-based image registration problem. We present the topology
preservation properties of RBFs in one landmark and four landmarks model
respectively. Numerical results of three kinds of Mat\'{e}rn transformations
are compared with results of Gaussian, Wendland's, and Wu's functions
Editorial: The relevance of molecular mechanisms in HIV-1 latency and reactivation from latency
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