The overlooked role of band-gap parameter in characterization of Landau levels in a gapped phase semi-Dirac system: the monolayer phosphorene case

Two-dimensional gapped semi-Dirac (GSD) materials are systems with a finite band gap that their charge carriers behave relativistically in one direction and Schr\"odinger-like in the other. In the present work, we show that besides the two well-known energy bands features (curvature and chirality), the band-gap parameter also play a crucial role in the index- and magnetic field-dependence of the Landau levels (LLs) in a GSD system. We take the monolayer phosphorene as a GSD representative example to explicitly provide physical insights into the role of this parameter in determining the index- and magnetic field-dependence of LLs. We derive an effective one-dimensional Schr\"odinger equation for charge carriers in the presence of a perpendicular magnetic field and argue that the form of its effective potential is clearly sensitive to a dimensionless band-gap that is tunable by structural parameters. The theoretical magnitude of this effective gap and its interplay with oval shape $k$-space cyclotron orbits resolve the seeming contradiction in determining the type of the quantum Hall effect in the pristine monolayer phosphorene. Our results strongly confirm that the dependence of LLs on the magnetic field in this GSD material is as conventional two-dimensional semiconductor electron gases up to a very high field regime. Using the strain-induced gap modification scheme, we show the field dependence of the LLs continuously evolves into $B^{2/3}$ behavior, which holds for a gapless semi-Dirac system. The highlighted role of the band-gap parameter may affect the consequences of the band anisotropy in the physical properties of a GSD material, including magnetotransport, optical conductivity, dielectric function, and thermoelectric performance

A comparative study of chromosome morphology among some accessions of Aegilops crassa

In this study karyotype and chromosome characteristics of the nine accessions of Aegilops crassa species obtained from gene bank of Seed and Plant Improvement Research Institute (SPII) of Iran and one accession collected by authors were inspected. Aceto-iron-hematoxilin staining method was used to stain chromosomes. For each accession, chromosome characteristics including long and short arms, chromosome lengths, arm ratio index and relative chromosome lengths were measured using micro measure 3.3 software. Results revealed that all of the studied accessions were tetraploid (2n = 4x = 28) and consisted of 13 pairs of metacentric and one pair of submetacentric chromosomes, of which two pairs were satellite chromosomes. Karyotype formula for these accessions were 13 m + 1 sm. Arm ratio index value of chromosomes ranged from 1.11 in chromosome number 6 to 1.77 in chromosome number 12. The B chromosomes were not seen in any of the accessions. Karyological characteristics of these accessions were similar to each other. However, some differences were observed between the accessions in some chromosome characteristics

Density index and length scale of Pearl Oyster Pinctada radiata in two habitats around Hendorabi Island (Iran, the Persian Gulf)

As pearling has been banned in Iran since 2006, stocks of pearl oysters has not been investigated during these years; therefore, condition of natural habitats for Pinctada radiata in its old habitats was surveyed in present research. Shallow waters around Hendorabi Island were searched with diving and two habitats namely “Sooleh” and “Sahel-e-sheni”, were considered for study. The pearl oysters had most distribution in these habitats in depth ranges of 7 to 12 m and 8 to 11 m, respectively. Total stock in Sooleh and Sahel-e-sheni was surveyed near 35700 and 12563 Pinctada radiata, respectively, of which 22% and 67% were catchable, respectively. Catch Per Unit of Area (CPUA) in Sooleh and Sahel-e-sheni habitats was estimated equal to 0.3 N/m2 in both habitats, and Catch Per Unit of Effort (CPUE) in these habitats was calculated equal to 59.5 N/hr and 50.3 N/hr, respectively. Results of this study demonstrated that area, stocks and CPUA for studied habitats were less than previous years. Despite of interdict of pearling in this region since 7 years ago, stock revival has done slowly

Factors Influencing the Concentration of Fecal Coliforms in Oysters in the River Blackwater Estuary, UK

Contamination of water systems can not only entail high risks to human health but can also result in economic losses due to closure of beaches and shellfish harvesting areas. Understanding the origin of fecal pollution at locations where shellfish are grown is essential in assessing associated health risks—as well as the determining actions necessary to remedy the problem. The aim of this work is to identify the species-specific source(s) of fecal contamination impacting waters overlying the shellfisheries in the Blackwater Estuary, East Anglia, UK. Over a twelve-month period, water samples were taken from above the oysters and from a variety of upstream points considered to be likely sources of fecal microorganism, together with oyster samples, and the number of fecal streptococci and E. coli were determined. Transition from low to high tide significantly decreased the concentration of fecal streptococci in waters overlying the oyster beds, indicative of a freshwater input of fecal pollution in oyster bed waters. In 12 months, the number of E. coli remained constant throughout, while fecal streptococci numbers were generally higher in the winter months. Analyses of upstream samples identified a sewage outfall to be the main source of E. coli to the oyster beds, with additional fecal streptococci from agricultural sources. The findings may assist in developing approaches for assessing the risks to shellfishery industries of various fecal inputs into an estuary, which could then help local governmental authorities address the problem

Effect of La³⁺ ions on the habit of KDP crystals

A few KDP (KH2PO4) and KDP: La³⁺ (LaCl₃) single crystals were grown being based on the temperature reduction method. Investigations show that the presence of three valent ions like La³⁺ could be a cause of retarded growth rate and induced crystalline lattice defects. Here the pure KDP crystals are compared with KDP: LaCl₃ before and after their exposure to gamma irradiation. Both types of crystals also were studied in aspect of other structural and optical properties

Instability of QCD ghost dark energy model

We investigate the instability of the ghost dark energy model against perturbations in different cases. To this goal we use the squared sound speed $v_s^2$ whose sign determines the stability of the model. When $v_s^2<0$ the model is unstable against perturbation. At first we discuss the noninteracting ghost dark energy model in a flat FRW universe and find out that such a model is unstable due to the negativity of the $v_s^2$ in all epoches. The interacting ghost dark energy model in both flat and non-flat universe are studied in the next parts and in both cases we find that the squared sound speed of ghost dark energy is always negative. This implies that the perfect fluid for ghost dark energy is classically unstable against perturbations. In both flat and non flat cases we find that the instability of the model increases with increasing the value of the interacting coupling parameter.Comment: 15 pages, 5 figure