Topological Superconductivity and Majorana Fermions in RKKY Systems

We consider quasi one-dimensional RKKY systems in proximity to an s-wave superconductor. We show that a $2k_F$-peak in the spin susceptibility of the superconductor in the one-dimensional limit supports helical order of localized magnetic moments via RKKY interaction, where $k_F$ is the Fermi wavevector. The magnetic helix is equivalent to a uniform magnetic field and very strong spin-orbit interaction (SOI) with an effective SOI length $1/2k_F$. We find the conditions to establish such a magnetic state in atomic chains and semiconducting nanowires with magnetic atoms or nuclear spins. Generically, these systems are in a topological phase with Majorana fermions. The inherent self-tuning of the helix to $2k_F$ eliminates the need to tune the chemical potential

Iran’s poultry meat export status in the Middle East region

Agriculture is literally a matter of life and death in the developing world. Ninety-six per cent of the world’s farmers – approximately 1.3 billion people – live in developing countries. In the rural areas of the developing world, close to 900 million people live on less than $1 a day.The Doha mandate encouraged the hope that dumping of subsidised exports from rich countries would finally be brought to an end, that market access for developing countries would be improved,and that developing countries would continue to be permitted to use tariffs and other border measures as part of their rural development strategies. In the Middle East,agriculture is the largest contributor to the Gross Domestic Product and foreign exchange,and is the second largest employer.Yet despite its economic importance it is largely overlooked in the development of new technologies and in the allocation of trained human resources. Agriculture in the Middle East focuses on new ways to improve food production, the challenges of a largely arid land, and managing limited agricultural resources.Agriculture is one of the oldest income sources in Iran. Close to one-third of the working population are engaged in agriculture and related industries such as poultry farming.Agriculture plays a significant role in the Iranian economy. At now agriculture account for an average of 27.8 percent of the GDP, and employ 26.1 percent of the labor force.Also agricultural products account for 47 percent of non-oil exports.Poultry species play important roles in the livelihood of human beings throughout the world both in ways that are quantifiable economically and in others that cannot and are therefore not captured in economic indices such as national GDP estimates.Poultry meat contribute directly to food security because there are no taboos against their consumption.With regard to F.A.O annual reports(2004) ,Iran has been rated 1st producer and also 1st exporter of poultry meat in the Middle East region. Capital stock in this industry consists of Breeding Farms (lines) ,Grand Parents(GP), Parent stock (PS), Broilers, Slaughter-Houses and dependant industries of governmental and private sectors is 4000 Billions Rials (5 Billions$). The current production is related to 70% of production units potential ,so with regard to remained considerable potential,it is necessary to make of them in an optimum rate. Therefore poultry products exports particularly poultry meat can be used for increasing of income and development for poultry industry. The objective of this paper was to study the dynamics on comparative advantage of Iran’s poultry meat export in the Middle East market.Poultry meat,export,Revealed comparative advantage,iran,middle east

Cd3As2 is Centrosymmetric

This is a revised version of a manuscript that was originally posted here in February of 2014. It has been accepted at the journal Inorganic Chemistry after reviews that included those of two crystallographers who made sure all the t's were crossed and the i's were dotted. The old work (from 1968) that said that Cd3As2 was noncentrosymmetric was mistaken, with the authors of that study making a type of error that in the 1980s became infamous in crystallography. As a result of the increased scrutiny of the issue of centrosymmetricity of the 1980's, there are now much better analysis tools to resolve the issue fully, and its important to understand that not just our crystals are centrosymmetric, even the old guy's crystals were centrosymmetric (and by implication everyone's are). There is no shame in having made that error back in the day and those authors would not find the current centrosymmetric result controversial; their paper is excellent in all other aspects. This manuscript describes how the structure is determined, explains the structure schematically, calculates the electronic structure based on the correct centrosymmetric crystal structure, and gives the structural details that should be used for future analysis and modeling.Comment: Accepted by ACS Inorganic Chemistr

Mapping the wavefunction of transition metal acceptor states in the GaAs surface

We utilize a single atom substitution technique with spectroscopic imaging in a scanning tunneling microscope (STM) to visualize the anisotropic spatial structure of magnetic and non-magnetic transition metal acceptor states in the GaAs (110) surface. The character of the defect states play a critical role in the properties of the semiconductor, the localization of the states influencing such things as the onset of the metal-insulator transition, and in dilute magnetic semiconductors the mechanism and strength of magnetic interactions that lead to the emergence of ferromagnetism. We study these states in the GaAs surface finding remarkable similarities between the shape of the acceptor state wavefunction for Mn, Fe, Co and Zn dopants, which is determined by the GaAs host and is generally reproduced by tight binding calculations of Mn in bulk GaAs [Tang, J.M. & Flatte, M.E., Phys. Rev. Lett. 92, 047201 (2004)]. The similarities originate from the antibonding nature of the acceptor states that arise from the hybridization of the impurity d-levels with the host. A second deeper in-gap state is also observed for Fe and Co that can be explained by the symmetry breaking of the surface.Comment: 19 pages, 6 figure

The Majorana spin in magnetic atomic chain systems

In this paper, we establish that Majorana zero modes emerging from a topological band structure of a chain of magnetic atoms embedded in a superconductor can be distinguished from trivial localized zero energy states that may accidentally form in this system using spin resolved measurements. To demonstrate this key Majorana diagnostics, we study the spin composition of magnetic impurity induced in-gap Shiba states in a superconductor using a quantum impurity model (at the mean-field level). By examining the spin and spectral densities in the context of the Bogoliubov-de Gennes (BdG) particle-hole symmetry, we derive a sum rule that relates the spin densities of localized Shiba states with those in the normal state without superconductivity. Extending our investigations to ferromagnetic chain of magnetic impurities, we identify key features of the spin properties of the extended Shiba state bands, as well as those associated with a localized Majorana end mode when the effect of spin-orbit interaction is included. We then formulate a phenomenological theory for the measurement of the local spin densities with spin-polarized scanning tunneling microscopy (STM) techniques. By combining the calculated spin densities and the measurement theory, we show that spin-polarized STM measurements can reveal a sharp contrast in spin polarization between an accidentally-zero-energy trivial Shiba state and a Majorana zero mode in a topological superconducting phase in atomic chains. We further confirm our results with numerical simulations that address generic parameter settings.Comment: 22 pages, 12 figures (references updated

Pair Density Wave in the Pseudogap State of High Temperature Superconductors

Recent scanning tunneling microscopy (STM) experiments of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ have shown evidence of real-space organization of electronic states at low energies in the pseudogap state. We argue based on symmetry considerations as well as model calculations that the experimentally observed modulations are due to a density wave of d-wave Cooper-pairs without global phase coherence. We show that STM measurements can distinguish a pair-density-wave from more typical electronic modulations such as those due to charge density wave ordering or scattering from an onsite periodic potential.Comment: 4 pages, 4 figures. Final version. PRL 93, 187002 (2004

Effects of Withania coagulans extract and morphine on spermatogenesis in rats

Purpose: To investigate the comparative effects of Withania coagolans extract and morphine on spermatogenesis in rats Methods: W. coagolans was collected from Sistan and Baluchestan, Iran and 50 and 100 mg/kg body weight doses of methanol extract and 5, 10 and 15 mg/kg body weight doses of morphine were administered parenterally to the rats which were divided into groups. Blood samples were collected and the levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone were assayed. The testicular tissue was isolated for histopathological examination. Results: No significant changes were observed in levels of LH, FSH and testosterone in treated groups (p < 0.05). However, there was significant difference between the treated groups for extract plus morphine groups, in terms of the number of spermatogonium, spermatocytes and spermatide variation. Moreover, the results indicate tissue disorders in all groups relative to control. The extract caused more disturbances in spermatogenesis compared to morphine, and appears to improve parameters related to spermatogenesis. Conclusion: The results show that the higher dose of Withania coagolans extract (100 mg/kg) exerts varying effects on reproductive parameters. Moreover, the lower dose of Withania coagolans extract (50 mg/kg) enhanced spermatogenesis while also protecting against the damaging effects of morphine

The study of the role of professional ethics in accounting

Economic entities that operate in a competitive environment based on risk and profit are their goal. Meanwhile, the majority of property management companies are here and it is because the investors are concerned about the possibility of a conflict of interest, which may result in questioning the reliability of accounting information. This makes auditing seem necessary. Therefore, from the perspective of users, there is an accredited role. Undoubtedly, the rules and regulations are essential for professional accountants. One of these rules is necessary to comply with the code of professional conduct. Since the accountants in organizations play the vital role in financial management, risk management is in financial consulting role, too. Therefore, information and reports are provided so that they can influence the decisions of the organization. Professional ethics in the business environment do not have damaging effects on those who have trusted them to leave