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Glasses are often used as models for understanding the corresponding liquid melts because they are generally assumed to share similar short and intermediate-range structural characteristics. First-principles molecular dynamics calculations have been performed to investigate the structural changes in a model basaltic (Ca22Mg14Al16Si44O148) glass at 300 K and a corresponding basaltic melt at 2500 K as a function of pressure up to 25 GPa. The results show that the local structures of the melt and glass are similar over the investigated pressure range, yet there are subtle but distinct differences. The pressure trends on the average Si–O, Ca–O, Mg–O, Al–O, O–O and Si–Si distances for the glass and melt are found to be very close. At ambient pressure, both are composed primarily of Si–O and Al-O tetrahedra. As expected, the Si–O coordination increases from four to fivefold and subsequently to sixfold. However, changes in the nearest neighbor Si–O and O–O are found to behave quite differently between the glass and melt. The most significant differences are in the distributions of the Si–O–Si and O-Si–O angles, which lead to different local structures and packing of the polyhedra. However, the differences become smaller with increased pressures indicating that caution should be exercised in the use of glasses as models for probing pressure-induced structural changes in the mantle. The calculated viscosity-pressure relationship of the basaltic melt between 0 and 25 GPa is presented and compared with available experimental data. In addition, other intrinsic properties such as the bulk modulus and sound velocity are broadly similar but not identical between the basaltic glass and melt in the broad pressure range of 0–80 GPa.

Ab initio study of high-pressure phase transition and electronic structure of Fe-doped CeO2 with Fe concentrations of 3.125, 6.25, and 12.5 at% has been reported. At a constant-pressure consideration, the lattice constants and the volume of the supercell were decreased with an increasing concentration of Fe. The average bond length of Fe–O is lower than that of Ce–O. As a result, Fe doping induces the reduced volume of the cell, which is in good agreement with previous experiments. At high pressure (~ 30 GPa), it was found that the transition pressure from the fluorite to the cotunnite orthorhombic phase decreases at a higher concentration of Fe, indicating that the formation energy of the compound is induced by Fe-doping. Furthermore, compression leads to interesting electronic properties too. Under higher pressures, the bandgap increases in the cubic structure under compression and then suddenly plummets after the transition to the orthorhombic phase. The 3d states of Fe mainly induced the impurity states in the bandgap. In both the undoped and Fe-doped systems, the bandgap increased in the cubic phase at high pressure, while the gap and p-d hybridization decrease in the orthorhombic phase.

High-pressure transitions are thought to modify hydrogen molecules to a molecular metallic solid and finally to an atomic metal1, which is predicted to have exotic physical properties and the topology of a two-component (electron and proton) superconducting superfluid condensate2,3. Therefore, understanding such transitions remains an important objective in condensed matter physics4,5. However, measurements of the crystal structure of solid hydrogen, which provides crucial information about the metallization of hydrogen under compression, are lacking for most high-pressure phases, owing to the considerable technical challenges involved in X-ray and neutron diffraction measurements under extreme conditions. Here we present a single-crystal X-ray diffraction study of solid hydrogen at pressures of up to 254 gigapascals that reveals the crystallographic nature of the transitions from phase I to phases III and IV. Under compression, hydrogen molecules remain in the hexagonal close-packed (hcp) crystal lattice structure, accompanied by a monotonic increase in anisotropy. In addition, the pressure-dependent decrease of the unit cell volume exhibits a slope change when entering phase IV, suggesting a second-order isostructural phase transition. Our results indicate that the precursor to the exotic two-component atomic hydrogen may consist of electronic transitions caused by a highly distorted hcp Brillouin zone and molecular-symmetry breaking. X-ray diffraction measurements of solid hydrogen provide crystallographic information for high-pressure phases of hydrogen and transitions between them, suggesting a series of isostructural transitions under compression before band closure and metallization.

The present study measured arsenic (As) concentrations in soil, groundwater and rice grain samples in two villages, Sarapur and Chinili, under Chakdaha block, Nadia district, West Bengal, India. This study also included a survey of the two villages to understand the knowledge among villagers about the As problem. Soil and groundwater samples were collected from fields in two villages while rice grain samples were collected from villagers’ houses. The results revealed the presence of As in higher concentrations than the maximum permissible limit of As in drinking water (10 µg L−1 and 50 µg L−1 by WHO and Indian standard, respectively) in groundwater [124.50 ± 1.11 µg L−1 (Sarapur) and 138.20 ± 1.34 µg L−1 (Chinili)]. The level of As in soil was found to range from 47.7 ± 0.14 to 49.3 ± 0.19 mg Kg−1 in Sarapur and from 57.5 ± 0.25 to 62.5 ± 0.44 mg Kg−1 in Chinili which are also higher than European Union maximum acceptable limit in agricultural soil (i.e. 20 mg Kg−1). The analysis of As in rice grains of five varieties, collected from residents of two villages, showed the presence of higher than recommended safe level of As in rice by FAO/WHO (0.2 mg Kg−1). The As concentration order was Gosai (0.95 ± 0.044 mg kg−1), Satabdi (0.79 ± 0.038 mg kg−1), Banskathi (0.60 ± 0.026 mg kg−1), Kunti (0.47 ± 0.018 mg kg−1) and Ranjit (0.29 ± 0.021 mg kg−1). Importantly, Gosai and Satabdi were the most popular varieties being consumed by local people. The data of consumption of rice per day in the survey was used for the measurement of average daily dose and hazard quotient. It was seen that the As hazard was negatively correlated to the age of residents. Therefore, children and toddlers were at higher risk of As exposure than elderly people. In addition, people with skin related As toxicity symptoms were also cited in the two villages. The study emphasized the severity of As problem in remote areas of West Bengal, India where people consume As tainted rice due to lack of awareness about the As problem and associated health issues.

Borophene nanosheet has been doped with lithium, beryllium, carbon, and hydrogen atom(s). Modification of electronic properties through the splitting and shifting of the Dirac point has been explored within the framework of ab initio density functional theory (DFT). Doping the Pmmn borophene structure with lithium, beryllium, carbon, and hydrogen atoms leads to semiconductor–metallic transitions as well as absorption of light within the different parts of the electromagnetic spectrum. Indirect band-gap opening is noticed when the system is doped with one hydrogen atom. But when the doping is made double, the system becomes metallic. For lithium and beryllium doping, the split Dirac point has been observed to be situated at the conduction band (CB). However, for single-site carbon atom doping, it is seen to be situated at the valence band (VB), while, for double doping, the system becomes semiconducting with an indirect bandgap of 528 meV. Optical properties calculations show that, for parallel and perpendicular polarization, the excitations have mainly occurred within the low- and high-energy regions, respectively. The effective number of valence electrons does not show any saturation effect for all the doped systems in parallel as well as for perpendicular polarizations.

Traditionally, the surveillance component of the air traffic management system has been based on radar, which consists of two separate systems: primary radar and secondary radar, which both enable the measurement of the aircraft range and bearing to the radar station. Primary radar is based on signals emitted by a ground station simply being reflected off an object and detected by a ground-based receiver. Secondary radar also emits signals, but relies upon a transponder onboard the aircraft to emit a signal itself, modulated among others by a four-digit aircraft identity (Mode A), aircraft altitude (Mode C) and/or 24-bit unique address (Mode S). Typical accuracies of secondary radar are of the order of 0.03 NM in range and 0.07° in azimuth. However, no position integrity report is provided. Air traffic density is expected to significantly increase in the future. In order to maintain or enhance air travel efficiency, while maintaining safety, more accurate surveillance systems, with the required integrity, will be required. Automatic dependent surveillance---broadcast (ADS-B) is a new aviation surveillance system, envisioned to overcome the limitations of radar and to enhance surveillance performance and thereby increase airspace capacity. However, its high dependence on external systems such as onboard navigation and communication systems also increases the number of potential points of failure. It is important to understand and mitigate these failure modes before the system can reliably be implemented. The present study emerged as an exploratory research as part of a safety assessment framework development for the ADS-B system. It reviews the ADS-B failure modes, data collection and analysis of ADS-B and its corresponding onboard GPS data. The study identifies a set of failures common to certain aircraft models, with consistent error patterns. A key failure mode was found to be associated with the navigation data from the onboard GPS. We discuss the identified failure modes and investigate the nature and causes of these failures. The findings highlight some of the deficiencies of the current ADS-B system, which will need to be addressed before the ADS-B system can reliably be implemented.

Spatio-temporal assessment of the above ground biomass (AGB) is a cumbersome task due to the difficulties associated with the measurement of different tree parameters such as girth at breast height and height of trees. The present research was conducted in the campus of Birla Institute of Technology, Mesra, Ranchi, India, which is predominantly covered by Sal (Shorea robusta C. F. Gaertn). Two methods of regression analysis was employed to determine the potential of remote sensing parameters with the AGB measured in the field such as linear regression analysis between the AGB and the individual bands, principal components (PCs) of the bands, vegetation indices (VI), and the PCs of the VIs respectively and multiple linear regression (MLR) analysis between the AGB and all the variables in each category of data. From the linear regression analysis, it was found that only the NDVI exhibited regression coefficient value above 0.80 with the remaining parameters showing very low values. On the other hand, the MLR based analysis revealed significantly improved results as evidenced by the occurrence of very high correlation coefficient values of greater than 0.90 determined between the computed AGB from the MLR equations and field-estimated AGB thereby ascertaining their superiority in providing reliable estimates of AGB. The highest correlation coefficient of 0.99 is found with the MLR involving PCs of VIs.

Asthma is an increasing health problem worldwide, but the long-term temporal pattern of clinical symptoms is not understood and predicting asthma episodes is not generally possible. We analyse the time series of peak expiratory flows, a standard measurement of airway function that has been assessed twice daily in a large asthmatic population during a long-term crossover clinical trial. Here we introduce an approach to predict the risk of worsening airflow obstruction by calculating the conditional probability that, given the current airway condition, a severe obstruction will occur within 30 days. We find that, compared with a placebo, a regular long-acting bronchodilator (salmeterol) that is widely used to improve asthma control decreases the risk of airway obstruction. Unexpectedly, however, a regular short-acting beta2-agonist bronchodilator (albuterol) increases this risk. Furthermore, we find that the time series of peak expiratory flows show long-range correlations that change significantly with disease severity, approaching a random process with increased variability in the most severe cases. Using a nonlinear stochastic model, we show that both the increased variability and the loss of correlations augment the risk of unstable airway function. The characterization of fluctuations in airway function provides a quantitative basis for objective risk prediction of asthma episodes and for evaluating the effectiveness of therapy.

In lung diseases such as asthma, expiratory flow becomes limited, airways can collapse and the vital exchange of gases is compromised. Here we model the inflation of collapsed regions of the lung during inspiration in terms of avalanches propagating through a bifurcating network of airways, and find that the accompanying cascade of dynamic pressure instabilities -- avalanche 'shocks' -- manifests as negative elastic resistance of the lung. Our analysis of this apparent thermodynamic paradox provides a better understanding of aeration in the deep regions of the lung, which may find application in medical conditions in which gas exchange is impaired.