212 research outputs found
Zero-Point Quantum Diffusion of Proton in Hydrogen-rich Superconductor
, as a member of hydrogen-rich superconductors, has a
superconducting critical temperature of 250 K at high pressures, which exhibits
the possibility of solving the long-term goal of room temperature
superconductivity. Considering the extreme pressure and low mass of hydrogen,
the nuclear quantum effects in should be significant and have an
impact on its various physical properties. Here, we adopt the method combines
deep-potential (DP) and quantum thermal bath (QTB), which was verified to be
able to account for quantum effects in high-accuracy large-scale molecular
dynamics simulations. Our method can actually reproduce pressure-temperature
phase diagrams of consistent with experimental and theoretical
results. After incorporating quantum effects, the quantum fluctuation driven
diffusion of proton is found even in the absence of thermal fluctuation near 0
K. The high mobility of proton is found to be compared to liquid, yet the
structure of is still rigid. These results would greatly enrich our
vision to study quantum behavior of hydrogen-rich superconductors.Comment: 7 pages, 6 figure
Catalytic reactions in a Co12 cuboctahedral cage arising from guest encapsulation and cage-based redox activation
A Co12 coordination cage with a cuboctahedral architecture, and incorporating a mixture of tritopic (face-capping) and ditopic (edge-bridging) ligands, shows strong guest binding of large aromatic fluorophores (fluorescein and its derivatives 6-carboxyfluorescein and Eosin-Y) with 1 : 1 binding constants in water in the range log K = 6.7–7.9; its large central cavity (>1000 Å3) facilitates binding of much larger guests than was possible with the smaller Co8 cage that we have reported previously. Guest binding is accompanied by catalysed reactions of bound guests because the high positive charge on the cage surface (24+) also attracts anions, allowing the organic guests and anionic reaction partners to be co-located, resulting for example in cage-catalysed hydrolysis of phosphate esters (the insecticides Me-paraoxon and Et-paraoxon) and conversion of diacetyl fluorescein to fluorescein. In addition, we demonstrate a new type of cage-based catalysis which relies on the redox activity of the Co(II)/Co(III) couple in the cage to activate the peroxymonosulfate (PMS) anion by converting it to the highly reactive SO4˙− radical ion, which bleaches cavity-bound fluorescein by complete oxidation. This is an example of an ‘advanced oxidation process’ in which the host cage not only brings the fluorescein and the PMS together via orthogonal hydrophobic and electrostatic interactions, but also provides redox activation of the PMS via a Co(II)/Co(III) couple, with the cage taking an active role in the catalytic process rather than acting simply as a passive reaction vessel
Large-scale Interactive Recommendation with Tree-structured Policy Gradient
Reinforcement learning (RL) has recently been introduced to interactive
recommender systems (IRS) because of its nature of learning from dynamic
interactions and planning for long-run performance. As IRS is always with
thousands of items to recommend (i.e., thousands of actions), most existing
RL-based methods, however, fail to handle such a large discrete action space
problem and thus become inefficient. The existing work that tries to deal with
the large discrete action space problem by utilizing the deep deterministic
policy gradient framework suffers from the inconsistency between the continuous
action representation (the output of the actor network) and the real discrete
action. To avoid such inconsistency and achieve high efficiency and
recommendation effectiveness, in this paper, we propose a Tree-structured
Policy Gradient Recommendation (TPGR) framework, where a balanced hierarchical
clustering tree is built over the items and picking an item is formulated as
seeking a path from the root to a certain leaf of the tree. Extensive
experiments on carefully-designed environments based on two real-world datasets
demonstrate that our model provides superior recommendation performance and
significant efficiency improvement over state-of-the-art methods
Experimental demonstration of an integrated on-chip p-bit core utilizing stochastic Magnetic Tunnel Junctions and 2D-MoS FETs
Probabilistic computing is a novel computing scheme that offers a more
efficient approach than conventional CMOS-based logic in a variety of
applications ranging from optimization to Bayesian inference, and invertible
Boolean logic. The probabilistic-bit (or p-bit, the base unit of probabilistic
computing) is a naturally fluctuating entity that requires tunable
stochasticity; by coupling low-barrier stochastic Magnetic Tunnel Junctions
(MTJs) with a transistor circuit, a compact implementation is achieved. In this
work, through integrating stochastic MTJs with 2D-MoS FETs, the first
on-chip realization of a key p-bit building block displaying
voltage-controllable stochasticity is demonstrated. In addition, supported by
circuit simulations, this work provides a careful analysis of the three
transistor-one magnetic tunnel junction (3T-1MTJ) p-bit design, evaluating how
the characteristics of each component influence the overall p-bit output. This
understanding of the interplay between the characteristics of the transistors
and the MTJ is vital for the construction of a fully functioning p-bit, making
the design rules presented in this article key for future experimental
implementations of scaled on-chip p-bit networks
Evolutionary Stages and Disk Properties of Young Stellar Objects in the Perseus Cloud
We investigated the evolutionary stages and disk properties of 211 Young
stellar objects (YSOs) across the Perseus cloud by modeling the broadband
optical to mid-infrared (IR) spectral energy distribution (SED). By exploring
the relationships among the turnoff wave bands lambda_turnoff (longward of
which significant IR excesses above the stellar photosphere are observed), the
excess spectral index alpha_excess at lambda <~ 24 microns, and the disk inner
radius R_in (from SED modeling) for YSOs of different evolutionary stages, we
found that the median and standard deviation of alpha_excess of YSOs with
optically thick disks tend to increase with lambda_turnoff, especially at
lambda_turnoff >= 5.8 microns, whereas the median fractional dust luminosities
L_dust/L_star tend to decrease with lambda_turnoff. This points to an
inside-out disk clearing of small dust grains. Moreover, a positive correlation
between alpha_excess and R_in was found at alpha_excess > ~0 and R_in > ~10
the dust sublimation radius R_sub, irrespective of lambda_turnoff,
L_dust/L_star and disk flaring. This suggests that the outer disk flaring
either does not evolve synchronously with the inside-out disk clearing or has
little influence on alpha_excess shortward of 24 microns. About 23% of our YSO
disks are classified as transitional disks, which have lambda_turnoff >= 5.8
microns and L_dust/L_star >10^(-3). The transitional disks and full disks
occupy distinctly different regions on the L_dust/L_star vs. alpha_excess
diagram. Taking L_dust/L_star as an approximate discriminator of disks with
(>0.1) and without (<0.1) considerable accretion activity, we found that 65%
and 35% of the transitional disks may be consistent with being dominantly
cleared by photoevaporation and dynamical interaction respectively. [abridged]Comment: 31 pages, 13 figures, 2 tables. To appear in a special issue of RAA
on LAMOST science
Improved reliability of planar power interconnect with ceramic-based structure
This paper proposes an advanced Si3N4 ceramic-based structure with through vias designed and filled with brazing alloy as a reliable interconnect solution in planar power modules. Finite element (FE) modeling and simulation were first used to predict the potential of using the proposed Si3N4 ceramic-based structure to improve the heat dissipation and reliability of planar interconnects. Power cycling tests and non-destructive microstructural characterization were then performed on Si3N4 ceramic-based structures, flexible printed circuit boards (PCB) and conventional Al wire interconnect samples to evaluate the FE predictions. Both the FE simulations and experimental tests were carried out on single Si diode samples where both the ceramic-based structures and flexible PCBs were bonded on the top sides of Si diodes with eutectic Sn-3.5Ag solder joints. The results obtained demonstrate that Si3N4 ceramic-based structures can significantly improve the reliability of planar interconnects. The experimental average lifetimes and FE simulated maximum creep strain accumulations for the ceramic-based structure and flexible PCB interconnect samples can reasonably be fitted to existing lifetime models for Sn-3.5Ag solder joints. Discrepancies between the models and experimental results can be attributed to defects and poor filling of the brazing alloy in the vias through the Si3N4 ceramic
Distribution and health risk evaluation of heavy metal lead in the main production area of rice in Heilongjiang Province
Abstract In order to explore the distribution and transfer of lead elements in soil and rice in the five regions of Chahayang, Wuchang, Fangzheng, Xiangshui and Jiansanjiang in Heilongjiang Province, and analyze the impact of rice intake on human health, the samples were tested by ICP-MS. Modeling the lead-element transfer in the soil-rice system, using the Nemero comprehensive pollution index method and the health risk assessment model to evaluate the lead pollution status of rice in the study area and its health risks to adults and children. The results showed that the average content of lead in rice in the study area was Chahayang 0.02 mg/kg, Wuchang 0.03 mg/kg, Fangzheng 0.017 mg/kg, Xiangshui 0.023 mg/kg and Jiansanjiang. 0.024 mg/kg did not exceed the lead content limit specified by China's National Food Hygiene Standard (0.2 mg/kg); Based on the prediction model of heavy metal lead content, pH value, and organic matter in the soil, the transfer of lead elements in the soil-rice system of Chahayang, Fangzheng, Xiangshui, and Jiansanjiang rice fields can be significantly described, with R2 values ranging from 0.224 to 0.419; Both the pollution index and the comprehensive pollution index in the study area were less than 1, which belong to the non-pollution category. The health risk index of heavy metal lead for adults and children in all five regions is lower than the maximum acceptable risk level recommended by USEPA, and there is no risk of causing cancer
Lanthanide Complexes that Respond to Changes in Cyanide Concentration in Water
Cyanide ions are shown to interact with lanthanide complexes of phenacylDO3A derivatives in aqueous solution, giving rise to changes in the luminescence and NMR spectra. These changes are the consequence of cyanohydrin formation, which is favored by the coordination of the phenacyl carbonyl group to the lanthanide center. These complexes display minimal affinity for fluoride and can detect cyanide at concentrations less than 1 μm. By contrast, lanthanide complexes with DOTAM derivatives display no affinity for cyanide in water, but respond to changes in fluoride concentration
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