7,478 research outputs found
Stretching-induced conductance variations as fingerprints of contact configurations in single-molecule junctions
Molecule-electrode contact atomic structures are a critical factor that
characterizes molecular devices, but their precise understanding and control
still remain elusive. Based on combined first-principles calculations and
single-molecule break junction experiments, we herein establish that the
conductance of alkanedithiolate junctions can both increase and decrease with
mechanical stretching and the specific trend is determined by the S-Au linkage
coordination number (CN) or the molecule-electrode contact atomic structure.
Specifically, we find that the mechanical pulling results in the conductance
increase for the junctions based on S-Au CN two and CN three contacts, while
the conductance is minimally affected by stretching for junctions with the CN
one contact and decreases upon the formation of Au monoatomic chains. Detailed
analysis unravels the mechanisms involving the competition between the
stretching-induced upshift of the highest occupied molecular orbital-related
states toward the Fermi level of electrodes and the deterioration of
molecule-electrode electronic couplings in different contact CN cases.
Moreover, we experimentally find a higher chance to observe the conductance
enhancement mode under a faster elongation speed, which is explained by ab
initio molecular dynamics simulations that reveal an important role of thermal
fluctuations in aiding deformations of contacts into low-coordination
configurations that include monoatomic Au chains. Pointing out the
insufficiency in previous notions of associating peak values in conductance
histograms with specific contact atomic structures, this work resolves the
controversy on the origins of ubiquitous multiple conductance peaks in
S-Au-based single-molecule junctions.Comment: 11 pages, 4 figures; to be published in J. Am. Chem. So
Two-gap and paramagnetic pair-breaking effects on upper critical field of SmFeAsO and SmFeAsOF single crystals
We investigated the temperature dependence of the upper critical field
[] of fluorine-free SmFeAsO and fluorine-doped
SmFeAsOF single crystals by measuring the resistive transition
in low static magnetic fields and in pulsed fields up to 60 T. Both crystals
show that 's along the c axis [] and in an -planar
direction [] exhibit a linear and a sublinear increase,
respectively, with decreasing temperature below the superconducting transition.
's in both directions deviate from the conventional one-gap
Werthamer-Helfand-Hohenberg theoretical prediction at low temperatures. A
two-gap nature and the paramagnetic pair-breaking effect are shown to be
responsible for the temperature-dependent behavior of and
, respectively.Comment: 21 pages, 8 figure
Extended π-conjugated pyrene derivatives: structural, photophysical and electrochemical properties
This article presents a set of extended π-conjugated pyrene derivatives, namely 1,3-di(arylethynyl)-7-tert-butylpyrenes, which were synthesized by a Pd-catalyzed Sonogashira coupling reaction of 1,3-dibromo-7-tert-butylpyrenes with the corresponding arylethynyl group in good yields. Despite the presence of the tert-butyl group located at the 7-position of pyrene, X-ray crystallographic analyses show that the planarity of the Y-shaped molecules still exhibits strong face-to-face π-π stacking in the solid state; all of the compounds exhibit blue or green emission with high quantum yields (QYs) in dichloromethane. DFT calculations and electrochemistry revealed that this category of compound possesses hole-transporting characteristics. In addition, with strong electron-donating (-N(CH₃)₂) or electron-withdrawing (-CHO) groups in 2 d or 2 f, these molecules displayed efficient intramolecular charge-transfer (ICT) emissions with solvatochromic shifts from blue to yellow (green) on increasing the solvent polarity. Furthermore, the compounds 2 d and 2 f possess strong CT characteristics
Breakdown of the interlayer coherence in twisted bilayer graphene
Coherent motion of the electrons in the Bloch states is one of the
fundamental concepts of the charge conduction in solid state physics. In
layered materials, however, such a condition often breaks down for the
interlayer conduction, when the interlayer coupling is significantly reduced by
e.g. large interlayer separation. We report that complete suppression of
coherent conduction is realized even in an atomic length scale of layer
separation in twisted bilayer graphene. The interlayer resistivity of twisted
bilayer graphene is much higher than the c-axis resistivity of Bernal-stacked
graphite, and exhibits strong dependence on temperature as well as on external
electric fields. These results suggest that the graphene layers are
significantly decoupled by rotation and incoherent conduction is a main
transport channel between the layers of twisted bilayer graphene.Comment: 5 pages, 3 figure
Comprehensive modeling of resistive switching in the Al/TiOx/TiO2/Al heterostructure based on space-charge-limited conduction
The reversible resistance switching (RS) effect of the Al/TiO x/TiO2/Al heterostructure is investigated in this study. This RS was attributed to space-charge-limited conduction (SCLC) as controlled by localized traps in the TiOx layer. The preexisting SCLC theory was extended to describe the abrupt resistance transition. An analytical model was developed with consideration of the ratio of free and trapped carrier density, which was extracted from the experimental data to show exponentially distributed traps in energy. The proposed model can be applicable to RS phenomena induced by interface-type traps in other material system.open231
A Quantitative Analysis and Guideline of Data Streaming Accelerator in Intel 4th Gen Xeon Scalable Processors
As semiconductor power density is no longer constant with the technology
process scaling down, modern CPUs are integrating capable data accelerators on
chip, aiming to improve performance and efficiency for a wide range of
applications and usages. One such accelerator is the Intel Data Streaming
Accelerator (DSA) introduced in Intel 4th Generation Xeon Scalable CPUs
(Sapphire Rapids). DSA targets data movement operations in memory that are
common sources of overhead in datacenter workloads and infrastructure. In
addition, it becomes much more versatile by supporting a wider range of
operations on streaming data, such as CRC32 calculations, delta record
creation/merging, and data integrity field (DIF) operations. This paper sets
out to introduce the latest features supported by DSA, deep-dive into its
versatility, and analyze its throughput benefits through a comprehensive
evaluation. Along with the analysis of its characteristics, and the rich
software ecosystem of DSA, we summarize several insights and guidelines for the
programmer to make the most out of DSA, and use an in-depth case study of DPDK
Vhost to demonstrate how these guidelines benefit a real application
Unleashing the full potential of Hsp90 inhibitors as cancer therapeutics through simultaneous inactivation of Hsp90, Grp94, and TRAP1
Cancer therapeutics: Extending a drug's reach A new drug that blocks heat shock proteins (HSPs), helper proteins that are co-opted by cancer cells to promote tumor growth, shows promise for cancer treatment. Several drugs have targeted HSPs, since cancer cells are known to hijack these helper proteins to shield themselves from destruction by the body. However, the drugs have had limited success. Hye-Kyung Park and Byoung Heon Kang at Ulsan National Institutes of Science and Technology in South Korea and coworkers noticed that the drugs were not absorbed into mitochondria, a key cellular compartment, and HSPs in this compartment were therefore not being blocked. They identified a new HSP inhibitor that can reach every cellular compartment and inhibit all HSPs. Testing in mice showed that this inhibitor effectively triggered death of tumor cells, and therefore shows promise for anti-cancer therapy. The Hsp90 family proteins Hsp90, Grp94, and TRAP1 are present in the cell cytoplasm, endoplasmic reticulum, and mitochondria, respectively; all play important roles in tumorigenesis by regulating protein homeostasis in response to stress. Thus, simultaneous inhibition of all Hsp90 paralogs is a reasonable strategy for cancer therapy. However, since the existing pan-Hsp90 inhibitor does not accumulate in mitochondria, the potential anticancer activity of pan-Hsp90 inhibition has not yet been fully examined in vivo. Analysis of The Cancer Genome Atlas database revealed that all Hsp90 paralogs were upregulated in prostate cancer. Inactivation of all Hsp90 paralogs induced mitochondrial dysfunction, increased cytosolic calcium, and activated calcineurin. Active calcineurin blocked prosurvival heat shock responses upon Hsp90 inhibition by preventing nuclear translocation of HSF1. The purine scaffold derivative DN401 inhibited all Hsp90 paralogs simultaneously and showed stronger anticancer activity than other Hsp90 inhibitors. Pan-Hsp90 inhibition increased cytotoxicity and suppressed mechanisms that protect cancer cells, suggesting that it is a feasible strategy for the development of potent anticancer drugs. The mitochondria-permeable drug DN401 is a newly identified in vivo pan-Hsp90 inhibitor with potent anticancer activity
Metabolic dynamics and physiological adaptation of Panax ginseng during development
Being an essential Oriental medicinal plant, ginseng (Panax ginseng Meyer) is a slow-growing perennial herb-accumulating pharmaceutically active metabolites such as ginsenosides in roots during growth. However, little is known about how ginseng plants survive in the harsh environments such as winter cold and summer heat for a longer period and accumulates those active metabolites as the plant grows. To understand the metabolic kinetics in both source and sink organs such as leaves and roots of ginseng plant, respectively, and to assess the changes in ginsenosides biosynthesis during ginseng growth, we investigated the metabolic profiles from leaves and roots of 1-, 4-, and 6-year-old field-grown ginseng plants. Using an integrated non-targeted metabolomic approach, we identified in total 348 primary and secondary metabolites, which provided us for the first time a global metabolomic assessment of ginseng during growth, and morphogenesis. Strikingly, the osmoprotectants and oxidized chemicals were highly accumulated in 4- and 6-year-old ginseng leaves suggested that ginseng develop a wide range of metabolic strategies to adapt unfavorable conditions as they mature. In 6-year-old plants, ginsenosides were decreased in leaves but increased in roots up to 1.2- to sixfold, supporting the view that there is a long-distance transport of ginsenosides from leaves to roots as ginseng plants mature. Our findings provide insights into the metabolic kinetics during the development of ginseng plant and this could complement the pharmacological importance of ginseng and its compounds according to their age
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