The electronic structure of some europium chalcogenides and pnictides is calculated using the {\it ab-initio} self-interaction corrected local-spin-density approximation (SIC-LSD). This approach allows both a localised description of the rare earth $f-$electrons and an itinerant description of $s$, $p$ and $d$-electrons. Localising different numbers of $f$-electrons on the rare earth atom corresponds to different nominal valencies, and the total energies can be compared, providing a first-principles description of valency. All the chalcogenides are found to be insulators in the ferromagnetic state and to have a divalent configuration. For the pnictides we find that EuN is half-metallic and the rest are normal metals. However a valence change occurs as we go down the pnictide column of the Periodic Table. EuN and EuP are trivalent, EuAs is only just trivalent and EuSb is found to be divalent. Our results suggest that these materials may find application in spintronic and spin filtering devices.

https://arxiv.org/pdf/cond-mat/0403763.pdf

The Electronic Structure of Europium Chalcogenides and Pnictides

Wheat yellow rust (WYR), caused by Puccinia striiformis f. sp. tritici (PST), is a major disease of wheat, and deployment of a single cultivar often leads to disease epidemics. Effect of inoculum level, foliar fungicide spray, and wheat cultivar mixtures were evaluated on disease development in the field and greenhouse in Nepal. Treatments were arranged in a split–split plot design with three replications in both experiments. Two inoculum levels of PST (low and high) were main plot factors; nontreated control and foliar spray of fungicides (Mancozeb and Bayleton) were subplot factors; and two-component cultivar mixtures, composed of different ratios of a susceptible (S) and a resistant (R) cultivars (90:10, 80:20, and 50:50, 100:0, and 0:100) were sub–subplot factors. WYR severity was assessed at different time intervals, and disease development was calculated as area under the disease progress curve (AUDPC). Inoculum level did not cause significant differences in AUDPC in the field but did in the greenhouse. Foliar spray of fungicides reduced the AUDPC in the greenhouse and field. In both experiments, AUDPC values were low in cultivar mixtures compared with a pure stand of a susceptible cultivar. As the proportion of resistant cultivar increased compared with the susceptible cultivar in the S:R mixture component, disease severity decreased with a consequent increase in grain yield. The greater yield obtained with cultivar mixtures compared with only the susceptible cultivar, independent of inoculum level and fungicide spray in the field, revealed a promising strategy to manage WYR in Nepal.

Effect of two-component cultivar mixtures on development of wheat yellow rust disease in the field and greenhouse in the Nepal Himalayas

Diseases in plants are important because they are the underlying causes of reduction in quality and quantity of productivity of crops, herbs, woods, and other products. While few diseases are responsible for mass destruction and endangerment of few plants, their studies are less prioritized. That is especially due to the lack of awareness, data, research, and the existing traditional practices of cultivation all over the Himalayan countries. The existence and transmission of the diseases are directly or indirectly governed by various landscape factors like properties of pathogens and host and micro-and macro- environments, but, these factors have not been elaborated in the Hindu-Kush Himalaya (HKH) region and thus, this chapter has discussed these aspects with reference to few critical diseases. In addition, field experiences along various altitudinal landscapes of the HKH region during the study of plant pathology have been included. Concluding remarks and recommendations related to further research and management have been made.

Towards a Landscape Perspective of Diseases in Plants: An Overview and Review of a Critical but Overlooked Ecology Issue in the Hindu Kush-Himalayan Region

This DFT study focuses on exploring the influence of pressure on the physical properties of RE3+N3-. We found that RE3+N3- are stable, cubic (Fm-3m) and ductile, and their structural parameters and elastic constants decrease with pressure. At low pressures, RE3+N3- show ferromagnetic half-metallic characteristic, while high pressure gives metallic nature. The FM moment is 5.0 μB (RE3+ = Sm3+), 6.0 μB (RE3+ = Eu3+) and 7.0 μB (RE3+ = Gd3+) which decrease with pressure. RE3+ = Sm3+ at ( < 20 GPa) has the largest wave velocity, and Debye and melting temperature, while at ( ≥ 20 GPa), RE3+ = Gd3+ exhibits these features. The present results conclude that pressure has the potential to enhance the optical and thermoelectric properties. RE3+N3- show p-type with ( ≈ 1.00) at low pressure and it decreases at high pressures. These tunable characteristics offer that RE3+N3- are candidates for spintronics, optoelectronics, and thermoelectronics devices. 

Influence of High Pressure on Structural, Electronic, Magnetic, Optical, Mechanical and Thermoelectric Properties of Rare-Earth Nitrides Re3+N3- (Re3+ = Sm3+, Eu3+, Gd3+)

In this report, we have shown the variation of photofield emission current as a function of applied electric field, the photon energy and initial state energy of the electrons with reference to the Fermi level The photofield emission current is calculated with the help of Kronig- Penney model potential The origin of peak in photofield emission current in the valence band is explained with the help of result of density of state calculated

https://iopscience.iop.org/article/10.1088/1742-6596/765/1/012015/pdf

A theoretical study of Photofield emission in Gallium Arsenide using Kronig-Penney potential model

A broad range of applications in spintronics and spin-filtering devices are found in rare earth nitrides due to its half-metallic behaviour and high magnetic moments. We intend to study the electronic and magnetic properties of REN in the frame work of density functional theory (DFT) by using the full-potential linearized augmented plane wave (FP-LAPW) method. It was found from the computed density of states (DOS) and the band structures that the total DOS of EuN is contributed mainly by the 4f-state electrons of the Eu atom. In the case of SmN and EuN, we fill the majority spin f states and create an exchange field that is felt by the other electrons in the material whose effect is more pronounced and leads to a significant-splitting of the nitrogen p bands.

Magnetic and Electronic Structure Calculations of Rare-Earth Nitrides

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst) is an important disease of wheat (Triticum aestivum) in Nepal, which is a part of the Himalayas stretching over the North of Nepal, India, Pakistan, Bhutan and beyond. Wheat production plays a crucial role in food security of the marginal hill farmers of Nepal. Frequent epidemics of the rust have caused huge loss in farmer’s field. Periodic monitoring during 1980-2008 showed that changes in virulence occurred during this period. The objective of this study was to evaluate Pst resistance and its effective genes in wheat genotypes. For this, trap nurseries, wheat stripe rust differentials, commercial cultivars and advanced breeding lines were tested under artificial epiphytotic and natural hot spots conditions during 2005 to 2010. Four genes (Yr5, Yr10, Yr15 and YrSp) consistently showed resistance to the prevailing races. The gene Yr9 and Yr27 in combinations with Yr18 were found effective. Other lines with combination of minor genes were also found effective. The genotypes Amadina, Kukuna, Tukuru, Kakatsi and Buck Buck widely used in breeding program were resistant. The cultivation of varieties WK1204, Gautam, Gaura and Dhaulagiri have ensured genetic diversity for the rust resistance and slowed down frequent occurrence of epidemics. The findings of these studies could help in developing effective varietal resistance program in the sub-continent.

Wheat Stripe Rust Virulence and Varietal Resistance in the Foot Hill Himalayas of Nepal

In this letter, we present the calculated results of photofield emission current (PFEC) in gallium arsenide (GaAs) by using Kronig-Penney potential model of Thapa and Kar [1]. It is found that PFEC decreases from higher value towards lower value exponentially in the case of GaAs. The results of plot of PFEC against initial state energy with respect to Fermi energy showed a maximum at 2.55 eV. Occurrence of these maxima is correlated with the plot of DOS (Density of state) of GaAs obtained by using DFT (Density functional theory).

Study of Photofield Emission in GaAs Using Kronig-Penney Model

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Magnetic and Electronic Structure Calculations of Rare-Earth Nitrides

Wheat Stripe Rust Virulence and Varietal Resistance in the Foot Hill Himalayas of Nepal

Study of Photofield Emission in GaAs Using Kronig-Penney Model