A novel true random number generator based on a stochastic diffusive memristor

The intrinsic variability of switching behavior in memristors has been a major obstacle to their adoption as the next generation universal memory. On the other hand, this natural stochasticity can be valuable for hardware security applications. Here we propose and demonstrate a novel true random number generator (TRNG) utilizing the stochastic delay time of threshold switching in a Ag:SiO2 diffusive memristor, which exhibits evident advantages in scalability, circuit complexity and power consumption. The random bits generated by the diffusive memristor TRNG passed all 15 NIST randomness tests without any post-processing, a first for memristive-switching TRNGs. Based on nanoparticle dynamic simulation and analytical estimates, we attributed the stochasticity in delay time to the probabilistic process by which Ag particles detach from a Ag reservoir. This work paves the way for memristors in hardware security applications for the era of Internet of Things (IoT)

Anatomy of Ag/Hafnia‐Based Selectors with 1010 Nonlinearity

Sneak path current is a significant remaining obstacle to the utilization of large crossbar arrays for non-volatile memories and other applications of memristors. A two-terminal selector device with an extremely large current-voltage nonlinearity and low leakage current could solve this problem. We present here a Ag/oxide-based threshold switching (TS) device with attractive features such as high current-voltage nonlinearity (~1010 ), steep turn-on slope (less than 1 mV/dec), low OFF-state leakage current (~10-14 A), fast turn ON/OFF speeds (108 cycles). The feasibility of using this selector with a typical memristor has been demonstrated by physically integrating them into a multilayered 1S1R cell. Structural analysis of the nanoscale crosspoint device suggests that elongation of a Ag nanoparticle under voltage bias followed by spontaneous reformation of a more spherical shape after power off is responsible for the observed threshold switching of the device. Such mechanism has been quantitatively verified by the Ag nanoparticle dynamics simulation based on thermal diffusion assisted by bipolar electrode effect and interfacial energy minimization

Comparison of the () human (hs), () chimpanzee (pt), () rhesus monkey (mma), () dog (cf), () mouse (mms), () rat (rn), () opossum (md), () chicken (gg), () frog (xt), and () zebrafish (dr) clusters

<p><b>Copyright information:</b></p><p>Taken from "Adaptive evolution of multiple-variable exons and structural diversity of drug-metabolizing enzymes"</p><p>http://www.biomedcentral.com/1471-2148/7/69</p><p>BMC Evolutionary Biology 2007;7():69-69.</p><p>Published online 2 May 2007</p><p>PMCID:PMC1885805.</p><p></p> Each cluster contains multiple-variable and highly-similar first exons (green boxes) arrayed in tandem and a common set of two downstream constant exons (red boxes). Exon length is indicated within each box. The approximate length of each cluster is shown below the corresponding panels

Comparison of the () human (hs), () chimpanzee (pt), () rhesus monkey (mma), () baboon (pa), () dog (cf), () chicken (gg), and () zebrafish (dr) clusters

<p><b>Copyright information:</b></p><p>Taken from "Adaptive evolution of multiple-variable exons and structural diversity of drug-metabolizing enzymes"</p><p>http://www.biomedcentral.com/1471-2148/7/69</p><p>BMC Evolutionary Biology 2007;7():69-69.</p><p>Published online 2 May 2007</p><p>PMCID:PMC1885805.</p><p></p> Each cluster contains multiple variable first exons arrayed in tandem and a common set of 4 downstream constant exons. These exons are indicated by vertical colored bars: (green) phenol-group variable exons; (orange) bilirubin-group variable exons; (blue) zebrafish variable exons; (gray) pseudogene (ψ) or relic (r); and (red) constant exons. The approximate length of each cluster is shown below the corresponding panels

Phylogenetic tree of human (h), chimpanzee (c), rhesus monkey (m), baboon (b), dog (d), chicken (gg), and zebrafish (z) clusters

<p><b>Copyright information:</b></p><p>Taken from "Adaptive evolution of multiple-variable exons and structural diversity of drug-metabolizing enzymes"</p><p>http://www.biomedcentral.com/1471-2148/7/69</p><p>BMC Evolutionary Biology 2007;7():69-69.</p><p>Published online 2 May 2007</p><p>PMCID:PMC1885805.</p><p></p> The major tree branches are labeled with the percentage support (only when >50%) for that partition based on 1,000 bootstrap replicates. The scale bar equals a distance of 0.1

Asymmetric Catalytic 1,2-Hydroperoxidation of Isatin-Derived Ketimine with Hydrogen Peroxide in the Crowding Environment of PEGs

The first enantioselective catalytic 1,2-hydroperoxidation has been achieved in the presence of PEG-600 using an acid–base bifunctional chiral squaramide as the organocatalyst, affording a range of enantioenriched α-<i>N</i>-substituted hydroperoxides bearing an oxindole moiety with excellent stereoselectivities (up to 99% ee)

Theoretical Study of Structure, Stability, and the Hydrolysis Reactions of Small Iridium Oxide Nanoclusters

The geometric structures and relative stabilities of small iridium oxide nanoclusters, Ir_<i>m</i>O_<i>n</i> (<i>m</i> = 1–5 and <i>n</i> = 1–2<i>m</i>), have been systematically investigated using density functional theory (DFT) calculations at the B3LYP level. Our results show that the lowest-energy structures of these clusters can be obtained by the sequential oxidation of small “core” iridium clusters. The iridium-monoxide-like clusters have relatively higher stability because of their relatively high binding energy and second difference in energies. On the basis of the optimized lowest-energy structures of neutral and cationic (IrO₂)_<i>n</i> (<i>n</i> = 1–5), DFT has been used to study the hydrolysis reaction of these clusters with water molecules. The calculated results show that the addition of water molecules to the cationic species is much easier than the neutral ones. The overall hydrolysis reaction energies are more exothermic for the cationic clusters than for the neutral clusters. Our calculations indicate that H₂O can be more easily split on the cationic iridium oxide clusters than on the neutral clusters

Methanol Steam Reforming for Hydrogen Production over CuZnZrOx: Promotion Effect of Cu

Mixed metal oxides catalyze steam reforming of methanol (SRM) usually at reaction temperatures of >400 °C, leading to high energy consumption. Herein, we report that a small amount of Cu doping can greatly promote the activity of ZnZrOx in the SRM at low temperatures. The 2%CuZnZrOx can efficiently catalyze the SRM at temperatures as low as 300 °C to give 95.3% methanol conversion, but ZnZrOx only shows low methanol conversion (23.6%) under similar reaction conditions. Structural characterizations show that CuZnZrOx catalysts are ternary solid solutions rich in Ov, which is favorable for water activation. CuZnZrOx with low-valence Cuδ+ shows faster kinetics for the generation and decomposition of HCOOH intermediate than ZnZrOx. The co-presence of Cuδ+ and Ov contributes to the excellent performance of CuZnZrOx. These findings provide an efficient strategy for promoting the catalytic performance of metal oxides toward SRM

Significance of Crystal Morphology Controlling in Semiconductor-Based Photocatalysis: A Case Study on BiVO₄ Photocatalyst

Precise control of the morphology and crystalline structure of semiconductor-based photocatalyst is crucial for improving the efficiency of solar energy conversion system. In this work, taking BiVO₄ semiconductor photocatalyst as an example, we investigated the formation process for the regular decahedron BiVO₄ crystals prepared by a convenient hydrothermal method and found that the synthesis is undergoing a dissolution–recrystallization process, concomitantly, the phase was transformed from tetragonal zircon type to monoclinic sheelite-type. By controlling the kinetics of crystal growth for BiVO₄ through regulating acidity of the reaction solution, we rationally tune the morphology of monoclinic BiVO₄ from regular decahedron crystals to short rod-like particles, particularly precisely modulate the proportion of {010}/{011} facets for the decahedron BiVO₄. By tuning the crystalline phase and morphologies of BiVO₄ crystal, we found that the photocatalytic water oxidation activity for the well-defined BiVO₄ crystal with specific configuration of {010} and {011} exposed facets can be 50 times of tetragonal BiVO₄ particles. Our work shows a convenient strategy for precise control of the growth process of semiconductor-based photocatalyst, based on the understanding of the crystal morphology evolution mechanism, which will be instructive for constructing semiconductor-based photocatalysts for solar energy conversion

Crucial Roles of Electron–Proton Transport Relay in the Photosystem II-Photocatalytic Hybrid System for Overall Water Splitting

Redox shuttle reaction plays a crucial role in electron and proton transfer process of natural and artificial photosynthesis for the solar-to-chemical energy conversion. In nature, photosynthetic electron transfer is delivered efficiently by the elaborated redox cofactors for generation of the reducing equivalents. However, efficient electron/proton transport is still a challenge to couple the natural and artificial photosynthetic system. Herein, we demonstrate a hybrid photosystem in conjugation of plant photosystem II (PSII) and inorganic Ru/SrTiO₃:Rh (Rh-doped) photocatalyst with quinone–ferricyanide relay for overall water splitting reaction under visible light irradiation. Electrons and protons from natural PSII to artificial photocatalyst by a quinone molecule are transported at the bioinorganic interface. Furthermore, the quinone–ferricyanide transport relay is found to be much more efficient in enhancement of the water splitting activity. This work makes it possible to construct the hybrid photosynthetic system by taking the advantages of both natural and artificial systems