Rational Design of Non-Centrosymmetric Hybrid Halide Perovskites.

Structural non-centrosymmetry in semiconducting organic-inorganic hybrid halide perovskites can introduce functionalities like anomalous photovoltaics and nonlinear optical properties. Here we introduce a design principle to prepare Pb- and Bi-based two- and one-dimensional hybrid perovskites with polar non-centrosymmetric space groups. The design principle relies on creating dissimilar hydrogen and halogen bonding non-covalent interactions at the organic-inorganic interface. For example, in organic cations like I-(CH2)3-NH2(CH3)+ (MIPA), -CH3 is substituted by -CH2I at one end, and -NH3+ is substituted by -NH2(CH3)+ at the other end. These substitutions of two -H atoms by -I and -CH3 reduce the rotational symmetry of MIPA at both ends, compared to an unsubstituted cation, for example, H3C-(CH2)3-NH3+. Consequently, the dissimilar hydrogen-iodine and iodine-iodine interactions at the organic-inorganic interface of (MIPA)2PbI4 2D perovskites break the local inversion symmetries of Pb-I octahedra. Owing to this non-centrosymmetry, (MIPA)2PbI4 displays visible to infrared tunable nonlinear optical properties with second and third harmonic generation susceptibility values of 5.73 pm V-1 and 3.45 × 10-18 m2 V-2, respectively. Also, the single crystal shows photocurrent on shining visible light at no external bias, exhibiting anomalous photovoltaic effect arising from the structural asymmetry. The design strategy was extended to synthesize four new non-centrosymmetric hybrid perovskite compounds. Among them, one-dimensional (H3N-(CH2)3-NH(CH3)2)BiI5 shows a second harmonic generation susceptibility of 7.3 pm V-1 and a high anomalous photovoltaic open-circuit voltage of 22.6 V.

Ultrahigh responsivity of non-van der Waals Bi2O2Se photodetector.

Bismuth oxyselenide has recently gained tremendous attention as a promising 2D material for next-generation electronic and optoelectronic devices due to its ultrahigh mobility, moderate bandgap, exceptional environmental stability, and presence of high-dielectric constant native oxide. In this study, we have synthesized single-crystalline nanosheets of Bismuth oxyselenide with thicknesses measuring below ten nanometers on Fluorophlogopite mica using an atmospheric pressure chemical vapor deposition system. We transferred as-grown samples to different substrates using a non-corrosive nail polish-assisted dry transfer method. Back-gated Bi2O2Se field effect transistors showed decent field effect mobility of 100 cm2V-1s-1. The optoelectronic property study revealed an ultrahigh responsivity of 1.16 × 106A W-1and a specific detectivity of 2.55 × 1013Jones. The samples also exhibited broadband photoresponse and gate-tunable photoresponse time. These results suggest that Bi2O2Se is an excellent candidate for future high-performance optoelectronic device applications.

Improving the optoelectronic properties of monolayer MoS2field effect transistor through dielectric engineering.

The reduced dielectric screening in atomically thin two-dimensional materials makes them very sensitive to the surrounding environment, which can be modulated to tune their optoelectronic properties. In this study, we significantly improved the optoelectronic properties of monolayer MoS2by varying the surrounding environment using different liquid dielectrics, each with a specific dielectric constant ranging from 1.89 to 18. Liquid mediums offer the possibility of environment tunability on the same device. For a back-gated field effect transistor, the field effect mobility exhibited more than two-order enhancement when exposed to a high dielectric constant medium. Further investigation into the effect of the dielectric environment on the optoelectronic properties demonstrated a variation in photoresponse relaxation time with the dielectric medium. The rise and decay times were observed to increase and decrease, respectively, with an increase in the dielectric constant of the medium. These results can be attributed to the dielectric screening provided by the surrounding medium, which strongly modifies the charged impurity scattering, the band gap, and defect levels of monolayer MoS2. These findings have important implications for the design of biological and chemical sensors, particularly those operating in a liquid environment. By leveraging the tunability of the dielectric medium, we can optimize the performance of such sensors and enhance their detection capabilities.

The impact of land use and land cover change on groundwater recharge in northwestern Bangladesh.

Groundwater recharge is affected by various anthropogenic activities, land use and land cover (LULC) change among these. The long-term temporal and seasonal changes in LULC have a substantial influence on groundwater flow dynamics. Therefore, assessment of the impacts of LULC changes on recharge is necessary for the sustainable management of groundwater resources. The objective of this study is to examine the effects of LULC changes on groundwater recharge in the northwestern part of Bangladesh. Spatially distributed monthly groundwater recharge was simulated using a semi-physically based water balance model. Long-term temporal LULC change analysis was conducted using LULC maps from 2006 to 2016, while wet and dry LULC maps were used to examine seasonal changes. The results show that the impervious built-up area has increased by 80.3%, whereas vegetated land cover has decreased by 16.4% over the study period. As a result, groundwater recharge in 2016 has decreased compared to the level seen in 2006. However, the decrease in recharge due to long-term temporal LULC changes is very small at the basin scale (2.6 mm/year), although the impact on regional level is larger (17.1 mm/year) due to urbanization. Seasonal LULC variations also affect recharge due to the higher potential for dry seasonal LULC compared to the wet seasonal LULC, a substantial difference (20.6 mm/year). The results reveal important information about the groundwater system and its response to land cover changes in northwestern Bangladesh.

Prognostic and clinicopathological insights of phosphodiesterase 9A gene as novel biomarker in human colorectal cancer.

BACKGROUND: PDE9A (Phosphodiesterase 9A) plays an important role in proliferation of cells, their differentiation and apoptosis via intracellular cGMP (cyclic guanosine monophosphate) signaling. The expression pattern of PDE9A is associated with diverse tumors and carcinomas. Therefore, PDE9A could be a prospective candidate as a therapeutic target in different types of carcinoma. The study presented here was designed to carry out the prognostic value as a biomarker of PDE9A in Colorectal cancer (CRC). The present study integrated several cancer databases with in-silico techniques to evaluate the cancer prognosis of CRC. RESULTS: The analyses suggested that the expression of PDE9A was significantly down-regulated in CRC tissues than in normal tissues. Moreover, methylation in the DNA promoter region might also manipulate PDE9A gene expression. The Kaplan-Meier curves indicated that high level of expression of PDE9A gene was associated to higher survival in OS, RFS, and DSS in CRC patients. PDE9A demonstrated the highest positive correlation for rectal cancer recurrence with a marker gene CEACAM7. Furtheremore, PDE9A shared consolidated pathways with MAPK14 to induce survival autophagy in CRC cells and showed interaction with GUCY1A2 to drive CRPC. CONCLUSIONS: Overall, the prognostic value of PDE9A gene could be used as a potential tumor biomarker for CRC.

Phase evolution of all-inorganic perovskite nanowires during its growth from quantum dots.

All-inorganic lead-halide perovskites have emerged as an exciting material owing to their excellent optoelectronic properties and high stability over hybrid organometallic perovskites. Nanowires of these materials, in particular, have shown great promise for optoelectronic applications due to their high optical absorption coefficient and low defect state density. However, the synthesis of the most promising alpha-Cesium lead iodide (α-CsPbI3) nanowires is challenging as it is metastable and spontaneously converts to a non-perovskiteδ-phase. The hot-injection method is one of the most facile, well-controlled, and commonly used approaches for synthesizing CsPbX3nanostructures. But the exact mechanism of growing these nanowires in this technique is not clear. Here, we show that the hot-injection method produces photoactive phases of quantum dots (QDs) and nanowires of CsPbBr3,and QDs of CsPbI3, but CsPbI3nanowires are grown in their non-perovskiteδ-phase. Monitoring the nanowire growth during the hot-injection technique and through detailed characterization, we establish that CsPbI3nanowires are formed in the non-perovskite phase from the beginning rather than transforming after its growth from perovskite to a non-perovskite phase. We have discussed a possible mechanism of how non-perovskite nanowires of CsPbI3grow at the expense of photoactive perovskite QDs. Our findings will help to synthesize nanostructures of all-inorganic perovskites with desired phases, which is essential for successful technological applications.

Factors associated with coverage of vitamin a supplementation among Bangladeshi children: mixed modelling approach.

BACKGROUND: Vitamin A deficiency (VAD) is a prominent and widespread public health problem in developing countries, including Bangladesh. About 2% of all deaths among under-five children are attributable to VAD. Evidence-based information is required to understand the influential factors to increase vitamin A supplementation (VAS) coverage and reduce VAD. We investigated the potential factors affecting VAS coverage and its significant predictors among Bangladeshi children aged 6 to 59 months using the VAS clustered data extracted from the latest Bangladesh Demographic and Health Survey 2014. METHODS: Data were analysed using mixed logistic regression (MLR) modelling approach in the generalised linear mixed model framework. The MLR model performs better than logistic regression for analysing the clustered data because of its minimum Akaike information criterion value. The likelihood ratio test showed that the variance component was significant. Therefore, the clustering effect among children was inevitable to use. RESULTS: VAS coverage among under-five children was 63.6%, which is not optimal and below the WHO's recommendation and the country's target of 90%. Children aged 25 to 36 months (AOR = 2.07, 95% CI: 1.711 to 2.513), who had higher educated mothers (AOR = 1.37, p = 0.033, 95% CI: 1.026-1.820) and fathers (AOR = 1.32, p = 0.027, 95% CI: 1.032-1.683), whose mothers had media exposure (AOR = 1.22, p = 0.006, 95% CI: 1.059-1.408) and NGO membership (AOR = 1.24, p = 0.002, 95% CI: 1.089-1.422) were more likely to consume VAS. CONCLUSION: The relevant authorities should create proactive awareness programs for highly vulnerable local communities, specifically targeted to educate the children's mothers about the necessity and benefits of childhood nutrition.

Prevalence and transmission of COVID-19 in community and household levels of Bangladesh: Longini and Koopman epidemic modelling approach.

AIM: To estimate the prevalence of COVID-19 pandemic and its transmission rates among people in both community and household levels of Bangladesh. METHODS: We use the cross-sectional online survey data of 2080 individuals, collected from 442 households during June to September 2020 in Bangladesh. The Longini and Koopman stochastic epidemic modelling approach was adapted for analysing the data. To validate the results, a simulation study was conducted using the Markov Chain Monte Carlo (MCMC) method via the Metropolis-Hastings algorithm in the context of the Bayesian framework. RESULTS: Overall, the prevalence of COVID-19 pandemic was 15.1% (315 out of 2080) among people in Bangladesh. This proportion was higher in smaller households (size one: 40.0%, two: 35.7% and three: 25.9%) than larger (four: 15.8%, five: 13.3%, six: 14.1%, seven: 12.5% eight: 8.7%, nine: 14.8% and ten or eleven: 5.7%). The transmission rate of COVID-19 in community people was higher (12.0%, 95% CI: 10.0% to 13.0%) than household members (9.0%, 95% CI: 6.0% to 11.0%). CONCLUSION: The susceptible individuals have a higher risk of community infection than the household and the community transmission is more responsible than the household for COVID-19 pandemic in Bangladesh.

Modulating flow near substrate surface to grow clean and large-area monolayer MoS2.

Chemical vapour deposition (CVD) is one of the most promising methods to synthesize monolayers of 2D materials like transition metal dichalcogenides (TMDs) over a large area with high film quality. Among many parameters that determine the growth of 2D materials, flow of precursor near the surface is one of the most sensitive conditions. In this study, we show how subtle changes in the flow near the substrate surface can affect the quality and coverage of the MoS2 monolayer. We fine tune the flow of the carrier gas near the substrate under two extreme conditions to grow large area and clean monolayer. In the first study, we grew several centimetres long continuous monolayer under the condition, which generally produces monolayers of few tens of micrometres in size without tuning the flow on the substrate surface. In the second case, we got monolayer MoS2 under the conditions meant for the formation of bulk MoS2.We achieved this by placing blockades on the substrate surface which helped in modifying the flow near them. Through simulation, we showed how the flow is affected near these blockades and used it as a guiding rule to grow patterned continuous MoS2 monolayers. Detailed electrical and optical measurements were done to determine the quality of the as-grown samples. Our studies provide a way to obtain clean, large area monolayer of desired pattern by tuning the flow of precursor on the vicinity of the substrate surface even when the growth conditions in CVD are far from optimum.

Understanding the thermal degradation mechanism of perovskite solar cells via dielectric and noise measurements.

Long term stability is a major obstacle to the success of perovskite solar cell (PSC) photovoltaic technology. PSC performance deteriorates significantly in the presence of humidity, oxygen and exposure to UV light and heat. Here the change in charge transport properties of PSC with temperature and the associated significant drop in device performance at high temperature have been investigated. The latter is shown to be primarily due to an increase in charge carrier recombination, which impacts the open-circuit voltage. To understand the pathway of temperature-induced degradation, low-frequency 1/f noise characteristics, and the capacitance-frequency, as well as capacitance-voltage characteristics have been investigated under various conditions. The results show that at high operating temperature accumulation of ions and charge carriers at the interface increase the surface recombination. Aging experiments at different temperatures show high stability of PSCs up to temperature <70 °C, but a drastic, irreversible degradation occurs at higher temperature (≥80 °C). Low-frequency 1/f noise study revealed that the magnitude of normalized noise in degraded perovskite solar cells is four orders of magnitude higher than the pristine device. This study shows the power of low-frequency noise measurement technique as a highly sensitive non-invasive tool to study the degradation mechanism of PSCs.

Quantification of In Planta Zymoseptoria tritici Progression Through Different Infection Phases and Related Association with Components of Aggressiveness.

In planta growth of Zymoseptoria tritici, causal agent of Septoria tritici blotch of wheat, during the infection process has remained an understudied topic due to the long symptomless latent period before the emergence of fruiting bodies. In this study, we attempted to understand the relationship between in planta growth of Z. tritici relative to the primary components of aggressiveness, i.e., latent period and pycnidia coverage in regard to contrasting host resistance. We tested isolates collected from Ireland against the susceptible cultivar Gallant and cultivar Stigg, which has strong partial resistance. A clear isolate-host interaction effect (F = 3.018; P = 0.005, and F = 6.008; P < 0.001) for latent period and pycnidia coverage, respectively, was identified. Furthermore, during the early infection phase of latency from 5 to 11 days postinoculation (dpi), in planta growth rate of fungal biomass was significantly (F = 30.06; P < 0.001) more affected by host resistance than isolate specificity (F = 1.27; P = 0.27), indicating the importance of host resistance in the early infection phase. In planta Z. tritici growth rates in cultivar Gallant spiked between 11 and 16 dpi followed by a continuous fall onward, whereas in cultivar Stigg it was slowly progressive in nature. From correlation and regression analysis, we found that the in planta growth rate preceding the average latent period of cultivar Gallant has more influence on latency duration and pycnidia production. Likewise, correlation between component of aggressiveness and in planta growth rate of pathogen supports our understanding of aggressiveness to be driven by the pathogen's multiplication capacity within host tissue.

Extraction Methods Affect the Structure of Goji (Lycium barbarum) Polysaccharides.

Polysaccharides are considered to be the most important active substances in Goji. However, the structure of polysaccharides varies according to the extraction methods applied, and the solution used to prepare Goji polysaccharides (LBPs) were limited. Thus, it is important to clarify the connection between extraction methods and structure of Goji polysaccharide. In view of the complex composition of cell wall polysaccharides and the various forms of interaction, different extraction methods will release different parts of the cell wall. The present study compared the effects of different extraction methods, which have been used to prepare different types of plant cell wall polysaccharides based on various sources, on the structure of cell-wall polysaccharides from Goji, by the single separate use of hot water, hydrochloric acid (0.4%) and sodium hydroxide (0.6%), at both high and low temperatures. Meanwhile, in order to explore the limitations of single extraction, sequential extraction methods were applied. Structural analysis including monosaccharide analysis, GPC-MALLS, AFM and 1H-NMR suggested the persistence of more extensively branched rhamnogalacturonan I (RG-I) domains in the procedures involving low-temperature-alkali, while procedures prepared by high-temperature-acid contains more homogalacturonan (HG) regions and results in the removal of a substantial part of the side chain, specifically the arabinan. A kind of acidic heteropolysaccharide was obtained by hot water extraction. SEC-MALLS and AFM confirmed large-size polymers with branched morphologies in alkali-extracted polysaccharides. Our results provide new insight into the extraction of Goji polysaccharides, which differ from the hot water extraction used by traditional Chinese medicine.

Antifogging abilities of model nanotextures.

Nanometre-scale features with special shapes impart a broad spectrum of unique properties to the surface of insects. These properties are essential for the animal's survival, and include the low light reflectance of moth eyes, the oil repellency of springtail carapaces and the ultra-adhesive nature of palmtree bugs. Antireflective mosquito eyes and cicada wings are also known to exhibit some antifogging and self-cleaning properties. In all cases, the combination of small feature size and optimal shape provides exceptional surface properties. In this work, we investigate the underlying antifogging mechanism in model materials designed to mimic natural systems, and explain the importance of the texture's feature size and shape. While exposure to fog strongly compromises the water-repellency of hydrophobic structures, this failure can be minimized by scaling the texture down to nanosize. This undesired effect even becomes non-measurable if the hydrophobic surface consists of nanocones, which generate antifogging efficiency close to unity and water departure of droplets smaller than 2 µm.

Anomalous effect of UV light on the humidity dependence of photocurrent in perovskite solar cells.

Effect of oxygen on the humidity dependence of photocurrent in the presence of UV light has been studied for perovskite solar cells. We observed that the magnitude of photocurrent increases with decreasing humidity initially, but below a certain level, the photocurrent starts to decrease when the humidity is reduced by sending dry nitrogen gas. If we decrease the humidity by sending dry air (keeping nitrogen to oxygen ratio same), then this effect is absent. This phenomenon is related to the presence of oxygen in the environment. When humidity is decreased by flowing dry nitrogen, the oxygen present in the environment of perovskite solar cell also reduces. We found that in the reduced oxygen condition, the presence of UV light helps to remove oxygen from the surface of the mesoporous TiO2 which is responsible for the reduction of photocurrent. In the presence of white light, this effect is not observed. To understand the phenomenon we studied low-frequency noise and current-voltage characteristics, and the dielectric properties of perovskite solar cells under various conditions.

Evaluation of microbial fuel cell (MFC) for bioelectricity generation and pollutants removal from sugar beet processing wastewater (SBPW).

Bioelectricity generation from biodegradable compounds using microbial fuel cells (MFCs) offers an opportunity for simultaneous wastewater treatment. This study evaluated the synergy of electricity generation by the MFC while reducing pollutants from sugar beet processing wastewater (SBPW). A simple dual-chamber MFC was constructed with inexpensive materials without using catalysts. Raw SBPW was diluted to several concentrations (chemical oxygen demand (COD) of 505 to 5,750 mg L-1) and fed as batch-mode into the MFC without further modification. A power density of 14.9 mW m-2 as power output was observed at a COD concentration of 2,565 mg L-1. Coulombic efficiency varied from 6.21% to 0.73%, indicating diffusion of oxygen through the cation exchange membrane and other methanogenesis and fermentation processes occurring in the anode chamber. In this study, >97% of the COD and up to 100% of the total suspended solids removals were observed from MFC-treated SBPW. Scanning electron microscopy of anode indicated that a diverse community of microbial consortia was active for electricity generation and wastewater treatment. This study demonstrated that SBPW can be used as a substrate in the MFC to generate electricity as well as to treat for pollutant removal.

Measurement of critical currents of superconducting aluminum nanowires in external magnetic fields: evidence for a Weber blockade.

We have studied the critical current as a function of magnetic field in short and narrow superconducting aluminum nanowires. In the range of magnetic fields in which vortices can enter a nanowire in a single row, we find regular oscillations of the critical current as a function of magnetic field, with each oscillation corresponding to adding a single vortex to the nanowire. In this regime, the nanowires behave as quantum dots for vortices. As a function of current and magnetic field, we find diamond-shaped regions in which the resistance is zero and the number of vortices is fixed.

Quantum noise and asymmetric scattering of electrons and holes in graphene.

We present measurements of quantum interference noise in double-gated single layer graphene devices at low temperatures. The noise characteristics show a nonmonotonic dependence on carrier density, which is related to the interplay between charge inhomogeneity and different scattering mechanisms. Linearly increasing 1/f noise at low carrier densities coincides with the observation of weak localization, suggesting the importance of short-range disorder in this regime. Using perpendicular and parallel p-n junctions, we find that the observed asymmetry of the noise with respect to the Dirac point can be related to asymmetric scattering of electrons and holes on the disorder potential.

BODIPY directed one-dimensional self-assembly of gold nanorods.

The assembly of anisotropic nanomaterials into ordered structures is challenging. Nevertheless, such self-assembled systems are known to have novel physicochemical properties and the presence of a chromophore within the nanoparticle ensemble can enhance the optical properties through plasmon-molecule electronic coupling. Here, we report the end-to-end assembly of gold nanorods into micrometer-long chains using a linear diamino BODIPY derivative. The preferential binding affinity of the amino group and the steric bulkiness of BODIPY directed the longitudinal assembly of gold nanorods. As a result of the linear assembly, the BODIPY chromophores positioned themselves in the plasmonic hotspots, which resulted in efficient plasmon-molecule coupling, thereby imparting photothermal properties to the assembled nanorods. This work thus demonstrates a new approach for the linear assembly of gold nanorods resulting in a plasmon-molecule coupled system, and the synergy between self-assembly and electronic coupling resulted in an efficient system having potential biomedical applications.

C646 degrades Exportin-1 to modulate p300 chromatin occupancy and function.

Molecular glues can induce proximity between a target protein and ubiquitin ligases to induce target degradation, but strategies for their discovery remain limited. We screened 3,200 bioactive small molecules and identified that C646 requires neddylation-dependent protein degradation to induce cytotoxicity. Although the histone acetyltransferase p300 is the canonical target of C646, we provide extensive evidence that C646 directly targets and degrades Exportin-1 (XPO1). Multiple cellular phenotypes induced by C646 were abrogated in cells expressing the known XPO1C528S drug-resistance allele. While XPO1 catalyzes nuclear-to-cytoplasmic transport of many cargo proteins, it also directly binds chromatin. We demonstrate that p300 and XPO1 co-occupy hundreds of chromatin loci. Degrading XPO1 using C646 or the known XPO1 modulator S109 diminishes the chromatin occupancy of both XPO1 and p300, enabling direct targeting of XPO1 to phenocopy p300 inhibition. This work highlights the utility of drug-resistant alleles and further validates XPO1 as a targetable regulator of chromatin state.

Combining π-Conjugation and Cation-π Interaction for Water-Stable and Photoconductive One-Dimensional Hybrid Lead Bromide.

Hybrid lead halide perovskites and their derivatives are important optoelectronic materials but suffer from water instability. Combining both the optoelectronics and the water stability of such systems is a major challenge in material design today. To address this issue, we employ the well-known π-conjugation and cation-π interaction concepts in designing a hybrid lead halide perovskite derivative system. (4,4'-VDP)Pb2Br6 (VDP = vinylenedipyridinium) single crystals are prepared. They have a one-dimensional (1D) arrangement of inorganic Pb-Br sublattices connected via the 4,4'-VDP organic sublattice. The π-conjugation in the 4,4'-VDP sublattice allows electronic communication between the 1D Pb-Br units, reducing the band gap and improving the photoconductivity. Importantly, N+ of one 4,4'-VDP molecular ion interacts with the π-electron cloud of the adjacent one. This intermolecular cation-π interaction extends throughout the organic sublattice, making the hybrid crystal stable when stored under water for more than a year without requiring any encapsulations.