A Search for Vector Diquarks at the CERN LHC

Resonant production of the first generation vector diquarks at the CERN Large Hadron Collider (LHC) is investigated. It is shown that the LHC will be able to discover vector diquarks with masses up to 9 TeV for quark-diquark-quark coupling alpha_(D)=0.1 and 4 TeV for alpha_(D)=5x10^(-4).Comment: 9 pages, 4 tables, 4 figure

Effect of impurities on the mechanical and electronic properties of Au, Ag, and Cu monatomic chain nanowires

In this study, we have investigated the interaction of various different atomic and molecular species (H, C, O, H 2, and O 2) with the monatomic chains of Au, Ag, and Cu via total-energy calculations using the plane-wave pseudopotential method based on density functional theory. The stability, energetics, mechanical, and electronic properties of the clean and contaminated Au, Ag, and Cu nanowires have been presented. We have observed that the interaction of H, C, or O atoms with the monatomic chains are much stronger than the one of H 2 or O 2 molecules. The atomic impurities can easily be incorporated into these nanowires; they form stable and strong bonds with these one-dimensional structures when they are inserted in or placed close to the nanowires. Moreover, the metal-atomic impurity bond is much stronger than the metal-metal bond. Upon elongation, the nanowires contaminated with atomic impurities usually break from the remote metal-metal bond. We have observed both metallic and semiconducting contaminated nanowires depending on the type of impurity, whereas all clean monatomic chains of Au, Cu, and Ag exhibit metallic behavior. Our findings indicate that the stability and the electronic properties of these monatomic chains can be tuned by using appropriate molecular or atomic additives. © 2011 American Physical Society

Has the anomalous single production of the fourth SM family quarks decaying into light Higgs boson been observed by CDF?

Superjet events observed by the CDF Collaboration are interpreted as anomalous single production of the fourth SM family u_4 quark, decaying into a new light scalar particle. The specific predictions of the proposed mechanism are discussed.Comment: 5 pages, 1 tabl

First-principles study of thin TiOx and bulklike rutile nanowires

We have systematically investigated structural, electronic and magnetic properties of very thin TiOx (x=1,2) nanowires as well as bulklike (110) rutile nanowires by using the first-principles plane-wave pseudopotential calculations based on density functional theory. A large number of different possible structures have been searched via total-energy calculations in order to find the ground-state structures of these nanowires. Three-dimensional structures are more energetically stable than planar ones for both of the stoichiometries (i.e., x=1,2). The stability of TiOx nanowires is enhanced with its increasing radius as a result of reaching sufficient coordination number of Ti and O atoms. All stoichiometric TiO2 nanowires studied exhibit semiconducting behavior and have nonmagnetic ground state. There is a correlation between binding energy (Eb) and energy band gap (Eg) of TiO2 nanowires. In general, Eb increases with increasing Eg. In TiO nanowires, both metallic and semiconductor nanowires result. In this case, in addition to paramagnetic TiO nanowires, there are also ferromagnetic ones. We have also studied the structural and electronic properties of bulklike rutile (110) nanowires. There is a crossover in terms of energetics, and bulklike nanowires are more stable than the thin nanowires for larger radius wires after a critical diameter. These (110) rutile nanowires are all semiconductors. © 2009 The American Physical Society

Half-metallic silicon nanowires: First-principles calculations

From first-principles calculations, we predict that specific transition metal (TM) atom-adsorbed silicon nanowires have a half-metallic ground state. They are insulators for one spin direction, but show metallic properties for the opposite spin direction. At high coverage of TM atoms, ferromagnetic silicon nanowires become metallic for both spin directions with high magnetic moment and may have also significant spin polarization at the Fermi level. The spin-dependent electronic properties can be engineered by changing the type of adsorbed TM atoms, as well as the diameter of the nanowire. Present results are not only of scientific interest, but also can initiate new research on spintronic applications of silicon nanowires. © 2007 The American Physical Society

Realization of a p-n junction in a single layer boron-phosphide

Two-dimensional (2D) materials have attracted growing interest due to their potential use in the next generation of nanoelectronic and optoelectronic applications. On the basis of first-principles calculations based on density functional theory, we first investigate the electronic and mechanical properties of single layer boron phosphide (h-BP). Our calculations show that h-BP is a mechanically stable 2D material with a direct band gap of 0.9 eV at the K-point, promising for both electronic and optoelectronic applications. We next investigate the electron transport properties of a p-n junction constructed from single layer boron phosphide (h-BP) using the non-equilibrium Green's function formalism. The n- and p-type doping of BP are achieved by substitutional doping of B with C and P with Si, respectively. C(Si) substitutional doping creates donor (acceptor) states close to the conduction (valence) band edge of BP, which are essential to construct an efficient p-n junction. By modifying the structure and doping concentration, it is possible to tune the electronic and transport properties of the p-n junction which exhibits not only diode characteristics with a large current rectification but also negative differential resistance (NDR). The degree of NDR can be easily tuned via device engineering. © the Owner Societies 2015

First principles study of electronic and mechanical properties of molybdenum selenide type nanowires

Using the first-principles plane-wave pseudopotential method within density functional theory, we have systematically investigated structural, electronic, and mechanical properties of M2 Y6 X6, Y6 X6 (X=Se,Te,S; Y=Mo,Cr,W; and M=Li,Na) nanowires and bulk phase of M2 Y6 X6. We found that not only Mo6 X6, but also transition metal and chalcogen atoms lying in the same columns of Mo and Se can form stable nanowires consisting of staggered triangles of Y3 X3. We have shown that all wires have nonmagnetic ground states in their equilibrium geometry. Furthermore, these structures can be either a metal or semiconductor depending on the type of chalcogen element. All Y6 X6 wires with X=Te atom are semiconductors. Mechanical stability, elastic stiffness constants, breaking point, and breaking force of these wires have been calculated in order to investigate the strength of these wires. Ab initio molecular dynamic simulations performed at 500 K suggest that overall structure remains unchanged at high temperature. Adsorption of H, O, and transition metal atoms like Cr and Ti on Mo6 Se6 have been investigated for possible functionalization. All these elements interact with Mo6 Se6 wire forming strong chemisorption bonds, and a permanent magnetic moment is induced upon the adsorption of Cr or Ti atoms. Molybdenum selenide-type nanowires can be alternative for carbon nanotubes, since the crystalline ropes consisting of one type of (M2) Y6 X6 structures can be decomposed into individual nanowires by using solvents, and an individual nanowire by itself is either a metal or semiconductor and can be functionalized. © 2006 The American Physical Society

Gate induced monolayer behavior in twisted bilayer black phosphorus

Optical and electronic properties of black phosphorus strongly depend on the number of layers and type of stacking. Using first-principles calculations within the framework of density functional theory, we investigate the electronic properties of bilayer black phosphorus with an interlayer twist angle of 90°. These calculations are complemented with a simple k p model which is able to capture most of the low energy features and is valid for arbitrary twist angles. The electronic spectrum of 90° twisted bilayer black phosphorus is found to be x-y isotropic in contrast to the monolayer. However x-y anisotropy, and a partial return to monolayer-like behavior, particularly in the valence band, can be induced by an external out-of-plane electric field. Moreover, the preferred hole effective mass can be rotated by 90° simply by changing the direction of the applied electric field. In particular, a +0.4 (-0.4) V A-1 out-of-plane electric field results in a ~60% increase in the hole effective mass along the y (x) axis and enhances the m*y /m*x (m*x /m*y) ratio as much as by a factor of 40. Our DFT and k p simulations clearly indicate that the twist angle in combination with an appropriate gate voltage is a novel way to tune the electronic and optical properties of bilayer phosphorus and it gives us a new degree of freedom to engineer the properties of black phosphorus based devices. © 2017 IOP Publishing Ltd

Multi-Risk Factors Behind the 2023 Kahramanmaraş (Türkiye) Earthquake Disaster

In the early hours of 6 February 2023, a magnitude 7.8 earthquake struck south-eastern Türkiye. Nine hours later, a magnitude 7.6 earthquake also rocked the region. The relatively shallow depth of the earthquakes, at about 10 km, resulted in severe shaking over a large area of Türkiye and Syria. As of 1 April 2023, the total death toll of over 57,000 (50,000 in Türkiye and 7,000 in Syria) makes this event the deadliest in modern Turkish history. In this presentation we discuss the state of knowledge of the seismic hazard and the social preconditioning factors that contributed to the tragic events in Türkiye and Syria. We show that the seismic hazard along the East Anatolian Fault, which hosted the earthquakes was well known, yet the devastating impacts indicate that the risks were not adequately considered. The earthquakes occurred during a winter storm with outdoor temperatures as low as -19 °C. They also triggered major aftershocks, several thousand landslides, dam bursts in Syria and flooding. We discuss how the multi-hazard context of the earthquakes exacerbated the impact in the hours to weeks after the main earthquakes. Additionally, we suggest that acute vulnerabilities arising from exposure, corruption and poverty led to a lack of seismic preparedness. We expand on the social factors and discuss how each contributed to amplifying the earthquake risk into the tragic disaster. We end by making recommendations on the ways forward to mitigate seismic risk through better integration of multi-hazard and multi-risk thinking, and management of social vulnerabilities

Non-equilibrium entangled steady state of two independent two-level systems

We determine and study the steady state of two independent two-level systems weakly coupled to a stationary non-equilibrium environment. Whereas this bipartite state is necessarily uncorrelated if the splitting energies of the two-level systems are different from each other, it can be entangled if they are equal. For identical two-level systems interacting with two bosonic heat baths at different temperatures, we discuss the influence of the baths temperatures and coupling parameters on their entanglement. Geometric properties, such as the baths dimensionalities and the distance between the two-level systems, are relevant. A regime is found where the steady state is a statistical mixture of the product ground state and of the entangled singlet state with respective weights 2/3 and 1/3