Hydrogen-induced tunable remanent polarization in a perovskite nickelate.

Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential capacitance in thin film capacitors. The space-charge polarization caused by long-range movement and trapping of protons dominates when the electric field exceeds the threshold value. First-principles calculations suggest the polarization originates from the polar structure created by H doping. We find that polarization decays within ~1 second which is an interesting temporal regime for neuromorphic computing hardware design, and we implement the transient characteristics in a neural network to demonstrate unsupervised learning. These discoveries open new avenues for designing ferroelectric materials and electrets using light-ion doping.

Neuromorphic one-shot learning utilizing a phase-transition material.

Design of hardware based on biological principles of neuronal computation and plasticity in the brain is a leading approach to realizing energy- and sample-efficient AI and learning machines. An important factor in selection of the hardware building blocks is the identification of candidate materials with physical properties suitable to emulate the large dynamic ranges and varied timescales of neuronal signaling. Previous work has shown that the all-or-none spiking behavior of neurons can be mimicked by threshold switches utilizing material phase transitions. Here, we demonstrate that devices based on a prototypical metal-insulator-transition material, vanadium dioxide (VO2), can be dynamically controlled to access a continuum of intermediate resistance states. Furthermore, the timescale of their intrinsic relaxation can be configured to match a range of biologically relevant timescales from milliseconds to seconds. We exploit these device properties to emulate three aspects of neuronal analog computation: fast (~1 ms) spiking in a neuronal soma compartment, slow (~100 ms) spiking in a dendritic compartment, and ultraslow (~1 s) biochemical signaling involved in temporal credit assignment for a recently discovered biological mechanism of one-shot learning. Simulations show that an artificial neural network using properties of VO2 devices to control an agent navigating a spatial environment can learn an efficient path to a reward in up to fourfold fewer trials than standard methods. The phase relaxations described in our study may be engineered in a variety of materials and can be controlled by thermal, electrical, or optical stimuli, suggesting further opportunities to emulate biological learning in neuromorphic hardware.

Study over the clinical picture and histopathology of leukoplakia and to establish the correlation between causative factors in the patients of Garhwal hill region.

AIMS: This cross-sectional study was conducted to correlate the clinical picture, causative factors of leukoplakia with its histopathology in the patients of Garhwal hill region. MATERIALS AND METHODS: The study was carried out on indoor and outdoor patients of Department of Otorhinolaryngology, HNB Base Hospital, Srinagar, Garhwal, Uttarakhand. Patients were interviewed by a predesigned questionnaire and clinically examined. Finally, histopathological examination was done by using proper technique. STATISTICAL ANALYSIS: The data were analyzed by using SPSS version 15. RESULTS: The sample consisted of 90 patients were evaluated. Minimum age of presentation was 18 years while the maximum was 65 years. The majority of patients were in age group of 31-40 years, with male predominance. Majority of cases were of minimum dysplasia and minimum of carcinoma in situ (CIS). Buccal mucosa is the most common site for leukoplakia, while hard palate is the least common site. One case of CIS was reported in buccal mucosa, while two cases of CIS were found in specialized mucosa. Smoking and pan masala (in both types with or without tobacco mixed) had a direct relation with the histological type of leukoplakia, as the amount and duration of consumption increased, the severity of dysplasia increased. CONCLUSIONS: Majority of cases were males in age group of 31-40 years. Probably, it was due to the addiction to smoking and pan masala started early in this region. Severity of dysplasia was related to the amount and duration of exposure to smoking and pan masala. Buccal mucosa was commonly involved because of general human tendency of keeping pan masala in buccal region for a long duration.