Spatial Interactions in Hydrogenated Perovskite Nickelate Synaptic Networks.

A key aspect of how the brain learns and enables decision-making processes is through synaptic interactions. Electrical transmission and communication in a network of synapses are modulated by extracellular fields generated by ionic chemical gradients. Emulating such spatial interactions in synthetic networks can be of potential use for neuromorphic learning and the hardware implementation of artificial intelligence. Here, we demonstrate that in a network of hydrogen-doped perovskite nickelate devices, electric bias across a single junction can tune the coupling strength between the neighboring cells. Electrical transport measurements and spatially resolved diffraction and nanoprobe X-ray and scanning microwave impedance spectroscopic studies suggest that graded proton distribution in the inhomogeneous medium of hydrogen-doped nickelate film enables this behavior. We further demonstrate signal integration through the coupling of various junctions.

Large CO2 reduction and enhanced thermal performance of agro-forestry, construction and demolition waste based fly ash bricks for sustainable construction.

The exhaust gases in production of burnt clay bricks is responsible for greenhouse gases (GHGs) emission which increase the carbon footprint in the ecosystem. Here, we report carbon emission and thermal performance based evaluation of 8 ft. × 9 ft. × 8 ft. building. The bricks used in building construction are manufactured from fly ash, agro-forestry wastes, construction & demolition wastes (C&D), ground granulated blast furnace slag (GGBFS) using NaOH as activator in order to provide compressive strength in the range of 3-6 MPa with ambient curing at 30 °C for 28 days. Life cycle analysis (LCA) reveals the total CO2 emission for fly ash and burnt clay bricks estimated to be 43.28 gCO2 and 290 gCO2 per brick, respectively. Considering the current scenario, by replacing 1-2% of brunt clay bricks with agro-forestry waste, C&D waste based fly ash bricks can potentially reduce 0.5-1.5 million tons of CO2 emission annually. The embodied energy calculation shows fly ash based bricks consumes 10-15 times less energy as compared to burnt clay bricks. Thermal paremeters viz., U-value (0.5-1.2 W/m2K), thermal conductivity (0.4-0.5 W/mK) show adequate insulation of agro-forestry waste based fly ash bricks highlighting its importance of thermal comfort, CO2 reduction along with sustainable and eco-friendly construction practices.

Picosecond carrier dynamics in InAs and GaAs revealed by ultrafast electron microscopy.

Understanding the limits of spatiotemporal carrier dynamics, especially in III-V semiconductors, is key to designing ultrafast and ultrasmall optoelectronic components. However, identifying such limits and the properties controlling them has been elusive. Here, using scanning ultrafast electron microscopy, in bulk n-GaAs and p-InAs, we simultaneously measure picosecond carrier dynamics along with three related quantities: subsurface band bending, above-surface vacuum potentials, and surface trap densities. We make two unexpected observations. First, we uncover a negative-time contrast in secondary electrons resulting from an interplay among these quantities. Second, despite dopant concentrations and surface state densities differing by many orders of magnitude between the two materials, their carrier dynamics, measured by photoexcited band bending and filling of surface states, occur at a seemingly common timescale of about 100 ps. This observation may indicate fundamental kinetic limits tied to a multitude of material and surface properties of optoelectronic III-V semiconductors and highlights the need for techniques that simultaneously measure electro-optical kinetic properties.

True random number generation using the spin crossover in LaCoO3.

While digital computers rely on software-generated pseudo-random number generators, hardware-based true random number generators (TRNGs), which employ the natural physics of the underlying hardware, provide true stochasticity, and power and area efficiency. Research into TRNGs has extensively relied on the unpredictability in phase transitions, but such phase transitions are difficult to control given their often abrupt and narrow parameter ranges (e.g., occurring in a small temperature window). Here we demonstrate a TRNG based on self-oscillations in LaCoO3 that is electrically biased within its spin crossover regime. The LaCoO3 TRNG passes all standard tests of true stochasticity and uses only half the number of components compared to prior TRNGs. Assisted by phase field modeling, we show how spin crossovers are fundamentally better in producing true stochasticity compared to traditional phase transitions. As a validation, by probabilistically solving the NP-hard max-cut problem in a memristor crossbar array using our TRNG as a source of the required stochasticity, we demonstrate solution quality exceeding that using software-generated randomness.

Investigation of agro-forestry and construction demolition wastes in alkali-activated fly ash bricks as sustainable building materials.

Production of burnt clay bricks, cement and burning of agricultural/forestry wastes are responsible for major greenhouse gases emission. The present work investigate the effect of treated rice straw and forestry leaves in alkali-activated fly ash bricks with construction & demolition wastes for non-load bearing partitions walls at elevated temperature of 800 °C. 1-4 wt% incorporated agro-forestry wastes fly ash bricks with 10 and 20 wt% ground granulated blast slag (GGBFS) addition shows compressive strength ranging from 8 to 15 MPa. The thermal conductivity of the panels with 1-4 wt% agro-forestry addition varies from 0.4 to 0.5 W/m.K. The sound transmission class (STC) of 20 mm thick agro-forestry waste fly ash samples depict moderate sound insulation properties over the range of 24 to 37 dB. The wallette units of burnt clay bricks and agro-forestry based fly ash bricks show load carrying capacity of 360 kN, 273 kN and 195 kN, 110 kN at temperatures of 35 °C and 800 °C respectively. The present study shows a potential green solution toward sustainable building materials in construction sector leading to reduced depletion of fertile soil used in production of burnt clay bricks.

Performance behaviour of agro-waste based gypsum hollow blocks for partition walls.

Crop residue management is a massive problem in the agriculture sector. Agricultural waste in the form of stubble which is usually burnt in the farm fields, causes severe air pollution and poses a threat to the environment. The present study investigates the addition of agro-waste (rice straw) in gypsum hollow-core blocks for partition walls. Various compositions of agro-waste-based gypsum samples have been studied for compressive strength, thermal, sound absorption, sound transmission loss, and fire-resistant properties. The addition of rice straw in gypsum reduces the density and compressive strength of the test sample, thus making it lightweight for non-load bearing wall application. The thermal conductivity of the rice straw added gypsum samples show a decrease in thermal conductivity from 0.2 to 0.11 W/m K. Acoustic properties viz., noise reduction coefficient (NRC) increases from 25 to 45% with increase in rice straw addition and a decreasing trend in sound transmission class (STC) from 37 to 28 dB. The fire-resistant properties viz., surface spread of flame, and fire propagation index test have shown good fire-resistant properties. The agro-waste-based hollow gypsum blocks may be used as a promising material for drywall partitions owing to its thermal insulation, low density, good acoustic and fire-resistant properties.

Continuous transition from weakly localized regime to strong localization regime in Nd0.7La0.3NiO3 films.

We report an investigation of metal-insulator transition (MIT) using conductivity and magnetoconductance (MC) measurements down to 0.3 K in Nd0.7La0.3NiO3 films grown on crystalline substrates of LaAlO3 (LAO), SrTiO3 (STO), and NdGaO3 (NGO) by pulsed laser deposition. The film grown on LAO experiences a compressive strain and shows metallic behavior with the onset of a weak resistivity upturn below 2 K which is linked to the onset of weak localization contribution. Films grown on STO and NGO show a cross-over from a positive temperature coefficient (PTC) resistance regime to negative temperature coefficient (NTC) resistance regime at definite temperatures. We establish that a cross-over from PTC to NTC on cooling does not necessarily constitute a MIT because the extrapolated conductivity at zero temperature [Formula: see text] though small (<10 S cm-1) is finite, signaling the existence of a bad metallic state and absence of an activated transport. The value of [Formula: see text] for films grown on NGO is reduced by a factor of 40 compared to that for films grown on STO. We show that a combination of certain physical factors makes substituted nickelate (that are known to exhibit first-order Mott type transition), undergo a continuous transition as seen in systems undergoing disorder/composition driven Anderson transition. The MC measurement also supports the above observation and shows that at low temperatures, there exists a positive MC that arises from the quantum interference which co-exists with a spin-related negative MC that becomes progressively stronger as the electrons approach a strongly localized state in the film grown on NGO.