Normal state electronic structure in the heavily overdoped regime of Bi1.74Pb0.38Sr1.88CuO6+delta single-layer cuprate superconductors

We explore the electronic structure in the heavily overdoped regime of the single layer cuprate superconductor Bi1.74Pb0.38Sr1.88CuO6+delta. We found that the nodal quasiparticle behavior is dominated mostly by phonons, while the antinodal quasiparticle lineshape is dominated by spin fluctuations. Moreover, while long range spin fluctuations diminish at very high doping, the local magnetic fluctuations still dominate the quasiparticle dispersion, and the system exhibits a strange metal behavior in the entire overdoped regime.Comment: 5 pages, 4 figure

Crystal structures, elastic properties, and hardness of high-pressure synthesized CrB₂ and CrB₄

Chromium tetraboride (CrB₄), a recently proposed candidate for superhard materials, has been synthesized at high pressure and temperature by a solid-state reaction. As a byproduct, chromium diboride (CrB₂) also forms and co-exists with CrB₄ in the final product. The comparative studies of crystal structure, elastic property, and hardness of both phases have been conducted at the same sample environment conditions. The crystal structure of CrB₄ has been refined with an orthorhombic symmetry of Immm (space group no. 71) or Pnnm (space group no. 58) using X-ray diffraction data. Further simulations indicate that the structural distinction between Immm and Pnnm can be resolved by neutron diffraction, due to the high scattering cross-section of boron (11B) by neutrons. Although CrB₂ and CrB₄ have close bulk modulus at about 230 GPa, the measured asymptotic Vickers hardness yields 16 GPa for CrB₂ but 30 GPa for CrB₄, which is nearly two times that of CrB₂. The dramatic enhancement in hardness in CrB₄ is attributed to the strong three-dimensional Cr–B network, in contrast to the layered lattice structure of hexagonal CrB₂.Тетраборид хрому (CrB₄), недавно запропонований як перспективний надтвердий матеріал, був синтезований при високому тиску і температурі шляхом твердофазної реакції. Як побічний продукт, утворюється також диборид хрому (CrB₂) і співіснує з CrB₄ в кінцевому продукті. Проведено порівняльне вивчення кристалічної структури, пружних властивостей і твердості обох фаз при однакових умовах навколишнього середовища. З використанням даних дифракції рентгенівських променів кристалічна структура CrB₄ визначена як та, що має орторомбічну симетрію Immm (просторова група № 71) або Pnnm (просторова група № 58). Подальші модельні експерименти показують, що структурну відмінність між Immm і Pnnm можна визначити методом нейтронної дифракції завдяки високому перерізу розсіювання бору (11B) нейтронами. Хоча CrB₂ і CrB₄ мають близький модуль об’ємного стиску ~ 230 ГПа, асимптотично виміряна твердість за Вікерсу дорівнює 16 ГПа для CrB₂, але 30 ГПа для CrB₄, що майже в два рази більше, ніж для CrB₂. Різке підвищення твердості в CrB₄ пов’язують із сильною тривимірної сіткою Cr–B, на відміну від шаруватої структури ґратки гексагонального CrB₂.Тетраборид хрома (CrB₄), недавно предложенный как перспективный сверхтвердый материал, был синтезирован при высоком давлении и температуре путем твердофазной реакции. Как побочный продукт, образуется также диборид хрома (CrB₂) и сосуществует с CrB₄ в конечном продукте. Проведено сравнительное изучение кристаллической структуры, упругих свойств и твердости обеих фаз при одинаковых условиях окружающей среды. С использованием данных дифракции рентгеновских лучей кристаллическая структура CrB₄ определена как имеющая орторомбическую симметрию Immm (пространственная группа № 71) или Pnnm (пространственная группа № 58). Дальнейшие модельные эксперименты показывают, что структурное различие между Immm и Pnnm может быть можно определить методом нейтронной дифракции благодаря высокому сечению рассеяния бора (11B) нейтронами. Хотя CrB₂ и CrB₄ имеют близкий модуль объемного сжатия ~ 230 ГПа, асимптотически измеренная твердость по Викерсу равна 16 ГПа для CrB₂, но 30 ГПа для CrB₄, что почти в два раза больше, чем для CrB₂. Резкое повышение твердости в CrB₄ связывают с сильной трехмерной сеткой Cr–B, в отличие от слоистой структуры решетки гексагонального CrB₂

Determination of astrophysical 12N(p,g)13O reaction rate from the 2H(12N, 13O)n reaction and its astrophysical implications

The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The $^{12}$N($p$,\,$\gamma$)$^{13}$O reaction is an important branching point in the rap-processes, which are believed to be alternative paths to the slow 3$\alpha$ process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the $^2$H($^{12}$N,\,$^{13}$O)$n$ proton transfer reaction at $E_{\mathrm{c.m.}}$ = 8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of $^{13}$O$_\mathrm{g.s.}$ $\rightarrow$ $^{12}$N + $p$ was extracted to be 3.92 $\pm$ 1.47 fm$^{-1}$ from the measured angular distribution and utilized to compute the direct component in the $^{12}$N($p$,\,$\gamma$)$^{13}$O reaction. The direct astrophysical S-factor at zero energy was then found to be 0.39 $\pm$ 0.15 keV b. By considering the direct capture into the ground state of $^{13}$O, the resonant capture via the first excited state of $^{13}$O and their interference, we determined the total astrophysical S-factors and rates of the $^{12}$N($p$,\,$\gamma$)$^{13}$O reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that $^{12}$N($p,\,\gamma$)$^{13}$O will only compete successfully with the $\beta^+$ decay of $^{12}$N at higher ($\sim$two orders of magnitude) densities than initially predicted.Comment: 8 figures, 2 tables, Submitted to Physical Review

Integrative analyses of transcriptome sequencing identify novel functional lncRNAs in esophageal squamous cell carcinoma.

Long non-coding RNAs (lncRNAs) have a critical role in cancer initiation and progression, and thus may mediate oncogenic or tumor suppressing effects, as well as be a new class of cancer therapeutic targets. We performed high-throughput sequencing of RNA (RNA-seq) to investigate the expression level of lncRNAs and protein-coding genes in 30 esophageal samples, comprised of 15 esophageal squamous cell carcinoma (ESCC) samples and their 15 paired non-tumor tissues. We further developed an integrative bioinformatics method, denoted URW-LPE, to identify key functional lncRNAs that regulate expression of downstream protein-coding genes in ESCC. A number of known onco-lncRNA and many putative novel ones were effectively identified by URW-LPE. Importantly, we identified lncRNA625 as a novel regulator of ESCC cell proliferation, invasion and migration. ESCC patients with high lncRNA625 expression had significantly shorter survival time than those with low expression. LncRNA625 also showed specific prognostic value for patients with metastatic ESCC. Finally, we identified E1A-binding protein p300 (EP300) as a downstream executor of lncRNA625-induced transcriptional responses. These findings establish a catalog of novel cancer-associated functional lncRNAs, which will promote our understanding of lncRNA-mediated regulation in this malignancy