Preparation of Cu-based bulk metallic glasses by suction casting

A series of Cu-Hf-Ti alloys prepared by rapid solidification of the melt and by copper mould casting were studied in the present work. Alloy ingots were prepared by arc-melting mixtures of pure metals in an argon atmosphere. An indication of the cooling rate obtained was determined using an Al-4.5 wt%Cu alloy. Cooling rates varied from 540 K/s for the centre section of a 4 mm die to 885 K/s for the outside wall section of the 2 mm die. The glass-forming ability, structure and thermal stability of Cu-Hf-Ti glassy alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Bulk glass formation was observed for the Cu64Hf36, Cu55Hf25Ti20 and Cu56Hf25Ti19 alloys, with critical diameters dc for a fully glassy structure of 1, 4 and 5 mm, respectively. The substitution of Hf by Ti increased the glassforming ability (GFA) and the thermal stability

Impact of Childhood Vaccinations Suspended Due to COVID-19

Due to the COVID-19 outbreak of 2020, a public health issue has been created that has the potential to significantly affect our view on society. Among the variety of preventative tactics to slow the spread of infection, there has been a suspension of childhood vaccination across the globe including among developing countries. The World Health Organization (WHO) has announced that governments suspend preventive vaccination programs briefly during the pandemic as of March 26th (Ray, 2020). As a result of this, there has been an impact on children\u27s health and an increase in mortality rates. The purpose of this research paper is to address the concern of decreased infant and childhood vaccination rates, and the increase on mortality rates in developing countries. In Jharkhand, India, the year-round immunization program played a crucial role in reducing children’s mortality and the death rates of those under-five in the last decade (Ray, 2020). Without the vaccinations for measles, influenza, and other viruses, this will affect children\u27s health, especially among developed countries with limited access to healthcare. It is essential to address this issue to prevent more loss in public health and for future preparation. To understand the impact and to avoid interruption of future vaccination programs during a pandemic, it is important to recognize the history of childhood vaccination in past epidemics and look at statistics of child mortality during outbreaks of the last decade

The return of the four- and five-dimensional preons

We prove the existence of 3/4-BPS preons in four- and five-dimensional gauged supergravities by explicitly constructing them as smooth quotients of the AdS_4 and AdS_5 maximally supersymmetric backgrounds, respectively. This result illustrates how the spacetime topology resurrects a fraction of supersymmetry previously ruled out by the local analysis of the Killing spinor equations.Comment: 10 pages (a minor imprecision has been corrected

The uses of Connes and Kreimer's algebraic formulation of renormalization theory

We show how, modulo the distinction between the antipode and the "twisted" or "renormalized" antipode, Connes and Kreimer's algebraic paradigm trivializes the proofs of equivalence of the (corrected) Dyson-Salam, Bogoliubov-Parasiuk-Hepp and Zimmermann procedures for renormalizing Feynman amplitudes. We discuss the outlook for a parallel simplification of computations in quantum field theory, stemming from the same algebraic approach.Comment: 15 pages, Latex. Minor changes, typos fixed, 2 references adde

Classification of IIB backgrounds with 28 supersymmetries

We show that all IIB backgrounds with strictly 28 supersymmetries are locally isometric to the plane wave solution of arXiv:hep-th/0206195. Moreover, we demonstrate that all solutions with more than 26 supersymmetries and only 5-form flux are maximally supersymmetric. The N=28 plane wave solution is a superposition of the maximally supersymmetric IIB plane wave with a heterotic string solution. We investigate the propagation of strings in this background, find the spectrum and give the string light-cone Hamiltonian.Comment: 30 pages, typos correcte

On the maximal superalgebras of supersymmetric backgrounds

In this note we give a precise definition of the notion of a maximal superalgebra of certain types of supersymmetric supergravity backgrounds, including the Freund-Rubin backgrounds, and propose a geometric construction extending the well-known construction of its Killing superalgebra. We determine the structure of maximal Lie superalgebras and show that there is a finite number of isomorphism classes, all related via contractions from an orthosymplectic Lie superalgebra. We use the structure theory to show that maximally supersymmetric waves do not possess such a maximal superalgebra, but that the maximally supersymmetric Freund-Rubin backgrounds do. We perform the explicit geometric construction of the maximal superalgebra of AdS_4 x S^7 and find that is isomorphic to osp(1|32). We propose an algebraic construction of the maximal superalgebra of any background asymptotic to AdS_4 x S^7 and we test this proposal by computing the maximal superalgebra of the M2-brane in its two maximally supersymmetric limits, finding agreement.Comment: 17 page

Entropy-energy inequalities for qudit states

We establish a procedure to find the extremal density matrices for any finite Hamiltonian of a qudit system. These extremal density matrices provide an approximate description of the energy spectra of the Hamiltonian. In the case of restricting the extremal density matrices by pure states, we show that the energy spectra of the Hamiltonian is recovered for $d=2$ and $3$. We conjecture that by means of this approach the energy spectra can be recovered for the Hamiltonian of an arbitrary finite qudit system. For a given qudit system Hamiltonian, we find new inequalities connecting the mean value of the Hamiltonian and the entropy of an arbitrary state. We demonstrate that these inequalities take place for both the considered extremal density matrices and generic ones.Comment: 12 pages, 4 figures Accepted for publication in Journal of Physics A: Mathematical and Theoretica