The Cyprus Institute

About: The Cyprus Institute is a other organization based out in Nicosia, Cyprus. It is known for research contribution in the topics: Aerosol & Environmental science. The organization has 418 authors who have published 1252 publications receiving 32586 citations.

Nucleon and pion structure with lattice QCD simulations at physical value of the pion mass

Abstract: We present results on the nucleon scalar, axial, and tensor charges as well as on the momentum fraction and the helicity and transversity moments. The pion momentum fraction is also presented. The computation of these key observables is carried out using lattice QCD simulations at a physical value of the pion mass. The evaluation is based on gauge configurations generated with two degenerate sea quarks of twisted mass fermions with a clover term. We investigate excited state contributions with the nucleon quantum numbers by analyzing three sink-source time separations. We find that, for the scalar charge, excited states contribute significantly and, to a lesser degree, for the nucleon momentum fraction and the helicity moment. Our result for the nucleon axial charge agrees with the experimental value. Furthermore, we predict a value of 1.027(62) in the $\overline{\mathrm{MS}}$ scheme at 2 GeV for the isovector nucleon tensor charge directly at the physical point. The pion momentum fraction is found to be $⟨x{⟩}_{u\ensuremath{-}d}^{{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}}=0.214(15){(}_{\ensuremath{-}9}^{+12})$ in the $\overline{\mathrm{MS}}$ at 2 GeV.

Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations.

Abstract: We determine within lattice QCD the nucleon spin carried by valence and sea quarks and gluons. The calculation is performed using an ensemble of gauge configurations with two degenerate light quarks with mass fixed to approximately reproduce the physical pion mass. We find that the total angular momentum carried by the quarks in the nucleon is ${J}_{u+d+s}=0.408(61{)}_{\text{stat}}(48{)}_{\text{syst}}$ and the gluon contribution is ${J}_{g}=0.133(11{)}_{\text{stat}}(14{)}_{\text{syst}}$, giving a total of ${J}_{N}=0.54(6{)}_{\text{stat}}(5{)}_{\text{syst}}$ that is consistent with the spin sum. For the quark intrinsic spin contribution, we obtain $\frac{1}{2}\mathrm{\ensuremath{\Delta}}{\mathrm{\ensuremath{\Sigma}}}_{u+d+s}=0.201(17{)}_{\text{stat}}(5{)}_{\text{syst}}$. All quantities are given in the modified minimal subtraction scheme at 2 GeV. The quark and gluon momentum fractions are also computed and add up to $⟨x{⟩}_{u+d+s}+⟨x{⟩}_{g}=0.804(121{)}_{\text{stat}}(95{)}_{\text{syst}}+0.267(12{)}_{\text{stat}}(10{)}_{\text{syst}}=1.07(12{)}_{\text{stat}}(10{)}_{\text{syst}}$, thus satisfying the momentum sum.

The summer circulation over the eastern Mediterranean and the Middle East: influence of the South Asian monsoon

Abstract: The summer circulation over the eastern Mediterranean and the Middle East (EMME) is dominated by persistent northerly winds (Etesians) whose ventilating effect counteracts the adiabatic warming induced by large scale subsidence. The ERA40 dataset is used to study the vertical distribution of these circulation features, which both appear to be reconciled manifestations of the South Asian monsoon influence. As predicted by past idealized modeling studies, in late spring a westward expanding upper level warm structure and subsidence areas are associated with Rossby waves excited by the monsoon convection. Steep sloping isentropes that develop over the EMME facilitate further subsidence on the western and northern periphery of the warm structure, which is exposed to the midlatitude westerlies. The northerly flow and descent over the eastern Mediterranean have maxima in July that are strikingly synchronous to the monsoon convection over northern India, where the weaker easterly jet favors a stronger Rossby wave response and consequent impact on the EMME circulation. The pronounced EMME topography modifies the monsoon induced structure, firstly, by inducing orographically locked summer anticyclones. These enhance the mid and low level northwesterly flow at their eastern flanks, leading to distinct subsidence maxima over the eastern Mediterranean and Iran. Secondly, topography amplifies the subsidence and the northerly flow over the Aegean, Red Sea, the Iraq—Gulf region and to the east of the Caspian Sea.

Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods.

Abstract: We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation double- and single-ended transition-state optimization algorithms—the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several single-molecule systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only “known” reaction pathways, manually detected in the previous studies, but also new, previously “unknown”, reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes.