COMMUNICATIONof particular interest as their physical properties can be temporarily or permanently altered with light, thus giving the opportunity to provide similar conditions to propagating optical signals that exists for biochemical and electrical signal transduction in the brain. [18][19][20][21] The "photonic axon and synapse" proposed here is based on the gallium lanthanum oxysulphide (GLSO) fi ber. Here, photodarkening manifests itself as a volatile (transient) and nonvolatile (metastable) broadband reduction of transmissivity of the fi ber resulting from a fl ash of illumination at a subbandgap optical frequency. While the transient changes rapidly decay upon switching off the illumination, metastable photodarkening is permanent, but is reversible by annealing. [22][23][24][25][26] To emulate functions of the chemical synapse, the fi ber is illuminated from the side at a sub-bandgap wavelength of λ = 532 nm. Such a fl ash of light is analogous of the prespike that acts within a living neuron. The fl ash of illumination forms the "photonic synapse" at the exposure point (Figure 1 B). Conversely, the postspike function is delivered by light at λ = 650 nm, which is guided through the fi ber (in principle this wavelength could be anywhere within the transparency range of the fi ber). In this confi guration, the GLSO fi ber perfectly replicates, in the photonic regime, the data transmission characteristics of the biological axon, as well as its ability to be depolarized or hyperpolarized at any point across the membrane to form a synaptic junction. Unlimited photonic synapses could be created along the length of the fi ber, allowing changes induced in the transmission of the fi ber at any of the synaptic junctions to propagate to the next synaptic junction, or eventually power the analogue of a biological actuator.GLSO microfi bers are drawn using conventional fi ber fabrication techniques on a special adapted fi ber drawing tower, from a premelted polished glass preform (see Experimental Section). Their photodarkening characteristics are determined under sub-bandgap green illumination ( Figure 2 A,B). Broadband attenuation (depression) upon illumination of the fi ber is the sum of transient and metastable photodarkening phenomena. [ 22 ] As shown in thin fi lms, the attenuation can be modulated (depressed or potentiated) via transient photodarkening upon successive cycling of illumination. [ 25,26 ] In the GLSO fi ber, as much as 35% change in transmission is observed by subbandgap optical excitation (Figure 2 A).Transient and metastable changes occur for short illumination times and, in the absence of thermal annealing, the metastable changes are cumulative upon successive illumination. The transient photodarkening effect observed during illumination of chalcogenide glasses are time and intensity dependent ( Figure S2, Supporting Information), a phenomenon that involves nonradiative recombination of photoexcited charge carriers and defects, while metastable effects arise from The human brain, with all its co...

Articles you may be interested inPhase change behaviors of Zn-doped Ge2Sb2Te5 films Appl.

Flexible thermoelectric generators (TEGs) can provide uninterrupted, green energy from body-heat, overcoming bulky battery configurations that limit the wearable-technologies market today. High-throughput production of flexible TEGs is currently dominated by printing techniques, limiting material choices and performance. This work investigates the compatibility of physical vapour deposition (PVD) techniques with a flexible commercial process, roll-to-roll (R2R), for thermoelectric applications. We demonstrate, on a flexible polyimide substrate, a sputtered Bi2Te3/GeTe TEG with Seebeck coefficient (S) of 140 μV/K per pair and output power (P) of 0.4 nW per pair for a 20 °C temperature difference. For the first time, thermoelectric properties of R2R sputtered Bi2Te3 films are reported and we demonstrate the ability to tune the power factor by lowering run times, lending itself to a high-speed low-cost process. To further illustrate this high-rate PVD/R2R compatibility, we fabricate a TEG using Virtual Cathode Deposition (VCD), a novel high deposition rate PVD tool, for the first time. This Bi2Te3/Bi0.5Sb1.5Te3 TEG exhibits S = 250 μV/K per pair and P = 0.2 nW per pair for a 20 °C temperature difference.

Optical axons and photonic synapses implemented using chalcogenide microfibers allow the generation and propagation of photonic action potentials which give rise to the demonstration of various neuromorphic concepts. Thus far, inorganic scalable neuromorphic systems and devices have been demonstrated using software and electronic configurations. However, as compared to biological systems based on organic axons and synapses, today's programmable inorganic computers are 6 to 9 orders of magnitude less efficient in complex environments. Simulating 5 seconds of brain activity takes 500 seconds and needs 1.4 MW of power [1,2,3,4]. Inspired by the emerging neuromorphic electronic systems and motivated by the potential of an all-optical cognitive platform, here we investigate and propose the use of amorphous chalcogenide microfibers as all-optical axons and synapses that exhibit brain-like functionality in the form of plasticity and data transmission in one scalable configuration.Optical fibers provide a mature mass manufacturable technology that has given rise to the complex network of interconnected nodes transferring information around the planet. They have been realized in a range of functional optical and electronic materials including amorphous, crystalline and semiconducting compounds [5,6,7]. In this work we realise an optical axon and photonic synapse based on neuromorphic chalcogenide microfibers of the alloy gallium lanthanum oxysulphide (GLSO) with an outer diameter of 150 µm, with a transmission window from 550 nm to 7 µm (Fig. 1). As a proof-of-concept, we demonstrate a variety of neurophysiological phenomena in the optical regime mimicking communication protocols in the mammalian central nervous system, including temporal and spatial summation, excitatory and inhibitory post synaptic potentials, and short and long term plasticity. Chalcogenide alloys are amorphous semiconducting media whose physical properties can be temporarily or permanently altered with light. Thanks to this, chalcogenide microfibers present an inorganic analogue of a biological neuron where signal propagation and processing is realised by optical confinement of light waves and photomodulation of their transmission properties, rather than by biochemical and electrical signal transduction. To implement an all-optical neuron in amorphous chalcogenide microfibers, we use photodarkening, which is a temperature dependent phenomenon that manifests itself in the form of a volatile (transient) and non-volatile (metastable) broadband attenuation in transparency and optical bandgap, brought about as a result of illumination with near or sub-bandgap light (Fig. 2). While the transient changes decay upon switching off the illumination, metastable photodarkening is non-volatile and reversible by annealing [8,9,10,11,12] providing the basis for short term and long term plasticity.

Alcohol-induced liver injury (ALI) has been associated with, among other molecular changes, abnormal hepatic methionine metabolism, resulting in decreased levels of S-adenosylmethionine (SAM). Dietary methyl donor supplements such as SAM and betaine mitigate ALI in animal models; however, the mechanisms of protection remain elusive. It has been suggested that methyl donors may act via attenuation of alcohol-induced oxidative stress. We hypothesized that the protective action of methyl donors is mediated by an effect on the oxidative metabolism of alcohol in the liver. Male C57BL/6J mice were administered a control high-fat diet or diet enriched in methyl donors with or without alcohol for 4 weeks using the enteral alcohol feeding model. As expected, attenuation of ALI and an increase in reduced glutathione:oxidized glutathione ratio were achieved with methyl donor supplementation. Interestingly, methyl donors led to a 35% increase in blood alcohol elimination rate, and while there was no effect on alcohol metabolism in the stomach, a profound effect on liver alcohol metabolism was observed. The catalase-dependent pathway of alcohol metabolism was induced, yet the increase in CYP2E1 activity by alcohol was blunted, which may be mitigating production of oxidants. Additional factors contributing to the protective effects of methyl donors in ALI were increased activity of low- and high-K(m) aldehyde dehydrogenases leading to lower hepatic acetaldehyde, maintenance of the efficient mitochondrial energy metabolism, and promotion of peroxisomal beta-oxidation. Profound changes in alcohol metabolism represent additional important mechanism of the protective effect of methyl donors in ALI.