Quantized conductance coincides with state instability and excess noise in tantalum oxide memristors

Tantalum oxide memristors can switch continuously from a low-conductance semiconducting to a high-conductance metallic state. At the boundary between these two regimes are quantized conductance states, which indicate the formation of a point contact within the oxide characterized by multistable conductance fluctuations and enlarged electronic noise. Here, we observe diverse conductance-dependent noise spectra, including a transition from 1/f 2 (activated transport) to 1/f (flicker noise) as a function of the frequency f, and a large peak in the noise amplitude at the conductance quantum GQ¼2e2/h, in contrast to suppressed noise at the conductance quantum observed in other systems. We model the stochastic behaviour near the point contact regime using Molecular Dynamics–Langevin simulations and understand the observed frequency-dependent noise behaviour in terms of thermally activated atomic-scale fluctuations that make and break a quantum conductance channel. These results provide insights into switching mechanisms and guidance to device operating ranges for different applications

Magnesium and Calcium Complexes Containing Biphenyl-Based Tridentate Iminophenolate Ligands for Ring-Opening Polymerization of <i>rac</i>-Lactide

A series of racemic 2-[(2′-methoxybiphenyl-2-ylimino)­methyl]-4-R²-6-R¹-phenols (<b>L</b>^<b>1</b><b>H</b>-<b>L</b>^<b>8</b><b>H</b>) were reacted with {Mg­[N­(SiMe₃)₂]₂}₂ and Ca­[N­(SiMe₃)₂]₂·2THF (THF = tetrahydrofuran), respectively, to provide nine heteroleptic magnesium complexes <b>L</b>^{<b>1</b>–<b>8</b>}MgN­(SiMe₃)₂ [R¹ = ^<i>i</i>Pr, R² = H (<b>1a</b>); R¹ = ^<i>t</i>Bu, R² = Me (<b>2a</b> and <b>2a</b>·THF); R¹ = R² = ^<i>t</i>Bu (<b>3a</b>); R¹ = R² = CMe₂Ph (<b>4a</b>); R¹ = CPh₃, R² = ^<i>t</i>Bu (<b>5a</b>); R¹ = 1-piperidinylmethyl, R² = ^<i>t</i>Bu (<b>6a</b>); R¹ = Cl, R² = ^<i>t</i>Bu (<b>7a</b>); R¹ = Br, R² = ^<i>t</i>Bu (<b>8a</b>)], two homoleptic calcium complexes (<b>L</b>^<b>2,5</b>)₂Ca (<b>2b</b> and <b>5b</b>), and one heteroleptic calcium complex [(<b>L</b>^<b>4</b>)­CaN­(SiMe₃)₂·THF] (<b>4b</b>), which have been fully characterized. In the solid state, magnesium complexes <b>2a</b> and <b>6a</b> are isostructural, and each possesses a monomeric structure, while magnesium complexes <b>7a</b> and <b>8a</b> are dimeric, where the two metal centers are bridged by two phenolate oxygen atoms of the ligands. The coordination geometry around the magnesium center in these complexes can be best described as a distorted tetrahedral geometry. Although bearing the same iminophenoloate ligand, the molecular structures of complexes <b>2a</b> and <b>2a</b>·THF are different from each other. In complex <b>2a</b>·THF, the coordination of one molecule of THF to the magnesium atom leads to dissociation of the methoxy group of the ligand from the metal center. The homoleptic calcium complex <b>2b</b> has a six-coordinate metal core ligated by all six donor atoms of two iminophenolate ligands. The heteroleptic magnesium complexes <b>1a</b>–<b>8a</b> and calcium complex <b>4b</b> proved to be efficient initiators for the ring-opening polymerization of <i>rac</i>-lactide at ambient temperature in THF or at 70 °C in toluene, and the polymerizations were better controlled in the presence of 2-propanol. The introduction of a bulky ortho substituent on the phenoxy unit of the ligand resulted in an increase of the catalytic activity of the corresponding metal complex. Microstructure analysis of the resultant poly­(<i>rac</i>-lactide) samples via homonuclear-decoupled ¹H NMR spectroscopy revealed <i>P</i>_r values ranging from 0.60 to 0.81, which closely depended on the employed catalyst and polymerization conditions

Magnesium and Calcium Complexes Containing Biphenyl-Based Tridentate Iminophenolate Ligands for Ring-Opening Polymerization of <i>rac</i>-Lactide

A series of racemic 2-[(2′-methoxybiphenyl-2-ylimino)­methyl]-4-R²-6-R¹-phenols (<b>L</b>^<b>1</b><b>H</b>-<b>L</b>^<b>8</b><b>H</b>) were reacted with {Mg­[N­(SiMe₃)₂]₂}₂ and Ca­[N­(SiMe₃)₂]₂·2THF (THF = tetrahydrofuran), respectively, to provide nine heteroleptic magnesium complexes <b>L</b>^{<b>1</b>–<b>8</b>}MgN­(SiMe₃)₂ [R¹ = ^<i>i</i>Pr, R² = H (<b>1a</b>); R¹ = ^<i>t</i>Bu, R² = Me (<b>2a</b> and <b>2a</b>·THF); R¹ = R² = ^<i>t</i>Bu (<b>3a</b>); R¹ = R² = CMe₂Ph (<b>4a</b>); R¹ = CPh₃, R² = ^<i>t</i>Bu (<b>5a</b>); R¹ = 1-piperidinylmethyl, R² = ^<i>t</i>Bu (<b>6a</b>); R¹ = Cl, R² = ^<i>t</i>Bu (<b>7a</b>); R¹ = Br, R² = ^<i>t</i>Bu (<b>8a</b>)], two homoleptic calcium complexes (<b>L</b>^<b>2,5</b>)₂Ca (<b>2b</b> and <b>5b</b>), and one heteroleptic calcium complex [(<b>L</b>^<b>4</b>)­CaN­(SiMe₃)₂·THF] (<b>4b</b>), which have been fully characterized. In the solid state, magnesium complexes <b>2a</b> and <b>6a</b> are isostructural, and each possesses a monomeric structure, while magnesium complexes <b>7a</b> and <b>8a</b> are dimeric, where the two metal centers are bridged by two phenolate oxygen atoms of the ligands. The coordination geometry around the magnesium center in these complexes can be best described as a distorted tetrahedral geometry. Although bearing the same iminophenoloate ligand, the molecular structures of complexes <b>2a</b> and <b>2a</b>·THF are different from each other. In complex <b>2a</b>·THF, the coordination of one molecule of THF to the magnesium atom leads to dissociation of the methoxy group of the ligand from the metal center. The homoleptic calcium complex <b>2b</b> has a six-coordinate metal core ligated by all six donor atoms of two iminophenolate ligands. The heteroleptic magnesium complexes <b>1a</b>–<b>8a</b> and calcium complex <b>4b</b> proved to be efficient initiators for the ring-opening polymerization of <i>rac</i>-lactide at ambient temperature in THF or at 70 °C in toluene, and the polymerizations were better controlled in the presence of 2-propanol. The introduction of a bulky ortho substituent on the phenoxy unit of the ligand resulted in an increase of the catalytic activity of the corresponding metal complex. Microstructure analysis of the resultant poly­(<i>rac</i>-lactide) samples via homonuclear-decoupled ¹H NMR spectroscopy revealed <i>P</i>_r values ranging from 0.60 to 0.81, which closely depended on the employed catalyst and polymerization conditions

One-step synthesis of diaryloxadiazoles as potent inhibitors of BCRP

Suppl data</p

Implant devices and analysis setting in Lsdyna.

<p>(A) Umbrella-shaped femoral head support device geometric model; (B) Umbrella-shaped femoral head support device FE mesh model; (C) Material model in Lsdyna; (D) User-defined load curve in pre-step and normal step in: Lsdyna.</p

Information of four different scenarios.

<p>Information of four different scenarios.</p

Mesh Information.

<p>Mesh Information.</p

Analysis results.

<p>(A) Final shape of one typical pair of 4 opposite umbrella arm pairs in each scenario; (B) Statistical figure of maximum radius of each scenario; (C) scenario 1, without constraint; (D) scenario 2, initial position 1, Normal bone quality. H = 22.5 mm, W = 20 mm; (E) scenario 3, with osteoporosis, failure location marked with black circle line; (F) scenario 4, initial position 2; (G) Stress field distrubution inside femoral head in secnario 4; (H) Stress field distrubution of umberalle-shape device in secnario 4.</p

Regioselective Synthesis of 2,3,4-Trisubstituted Pyrroles via Pd(II)-Catalyzed Three-Component Cascade Reactions of Amines, Alkyne Esters, and Alkenes

A new, efficient, and versatile Pd­(II)-catalyzed oxidative three-component cascade reaction of diverse amines, alkyne esters, and alkenes is disclosed for the direct synthesis of diverse 2,3,4-trisubstituted pyrroles with broad functional group tolerance and in good to excellent yields. This transformation is supposed to proceed through the cascade formation of C­(sp²)–C­(sp²) and C­(sp²)–N bonds via Pd­(II)-catalyzed regioselective alkene migratory insertion, intramolecular radical addition, and oxidation sequential processes

Material parameters for 10 different sets of bone elements.

<p>Material parameters for 10 different sets of bone elements.</p