Self-Determination in the Western Sahara: Obstacles and Obligations

This paper aims to investigate the story of a country that was colonized by Spain, abandoned by Madrid, and subsequently claimed by Morocco. Spanish Sahara, now known as Western Sahara, is the territory in question. When Spanish Sahara was left by Spain to fend for itself in 1975, King Hassan of Morocco claimed sovereignty over it. King Hassan saw a potential “Greater Morocco”, which, in his view, encompassed Morocco-proper and the former Spanish Sahara. Since becoming recognized as a non-self-governing territory, most of Western Sahara has been occupied by Morocco and much of its native population resides in Tindouf refugee camps. These camps, in neighboring Algeria, are home to an organized government body, the Saharawi Arab Democratic Republic, alongside the Polisario Front which has militarily resisted Moroccan occupation. Despite various attempts by the U.N. to hold a referendum on the independence of Western Sahara, such a vote has never happened. Disputes over qualified voters have completely halted the process, an especially convoluted point since the Green March in 1975, in which the Moroccan government enabled hundreds of thousands of Moroccans to march into Western Saharan territory. Morocco now controls some 80 percent of the territory behind a large wall barrier constructed by Moroccan forces and reinforced by American mine technology. Ban Ki-moon, the UN Secretary General, has called Moroccan presence in Western Sahara an occupation. This raises three questions: how has Moroccan diplomacy frustrated Saharawi independence, what options are still feasible as a solution, and how should the U.S. respond to the recent developments in this longstanding conflict

The Effect of Superimposed Stress on High Temperature Degradation of Single Crystal Superalloys during Exposure to Various Sulphur and Sea Salt Environments

Alternative fuels and novel cycles are increasingly used to supply the world growing demand in energy whilst reducing the carbon emission. Such cycles include the integrated gasification combined cycle (IGCC) with carbon capture, which uses coal as fuel. In such situations however, sulphur and sodium chloride, contained in the coal, are known to form sodium sulphate that, if deposited at the root of the single crystal turbine blades, can initiate hot corrosion. Low temperature Type II corrosion consists of the formation of a fused salt melt, which interacts with the combustion gases and causes other constituents of the alloy to dissolve. The resulting melt prevents the oxide to be protective. Simultaneously, the large centrifugal stresses in the blade attachment area can cause the substrate to crack. If undetected, such cracks will grow and result in catastrophic failure. The current work consisted in the construction and commissioning of a customised test bench reproducing the environments experienced at the root of the turbine blades. The investigation compared a first-generation Ni-based superalloy with 12.2 wt% Cr (SCRY-83) commonly referred to as “Cr2O3-former” in regard to its oxide composition, to a second generation one with 6.5 wt% Cr (SCRY-4) also referred to as “Al2O3-former”. A mixture of NaCl and Na2SO4 is often used in the literature to reproduce hot corrosion. The effect of each deposits was first analysed independently. It was found that NaCl caused scale damage, via the formation of high vapor pressure compounds for the Al2O3-former, or via the transport of Cr to the gas interface for the SCRY-83. In contrast, Na2SO4 formed a liquid phase at the surface of both alloys, but initiated damage only when in contact with the Al2O3-former. Sulphur ingress was the largest on sample coated with NaCl and exposed to a mixture of air and SO2/SO3, affecting particularly the Al2O3-former. The simultaneous application of force in these environments always resulted in a larger reaction layer, and was thought to originate from the flow of liquid phases (NaCl-NiCl2 when coated with NaCl, or Ni3S2 when exposed to air+SO2/SO3, or Na2SO4-NiSO4 when coated with NaCl and exposed to air+SO2/SO3). The type II environment with applied force was the most aggressive and it initiated two cracks on the Al2O3-former, and a 40 µm thick damaged region was detected on the Cr2O3-former. Proven and novel methods of damage characterisation were assessed throughout this work, and their suitability was found to depend on the harshness of the environment. The high Cr alloy always outperform the Al2O3-former or exhibited similar depth of attack (when coated with NaCl).Solar Turbines has sponsored the PhD and has provided sample materia

The effect of manganese and silicon additions on the corrosion resistance of a polycrystalline nickel-based superalloy

The service lives of nickel superalloys are often limited by environmental degradation. The present study compares oxidation, sulfidation and hot corrosion at 750C of three variants of a polycrystalline superalloy: a baseline alloy, a variant containing 1wt% Mn and one containing 0.5wt% Si. Mn reduced the oxidation rate without changing the scale morphology. The MnCr2O4 scale formed proved more protective against sulfidation and hot corrosion, but internal sulfides extended the damage depth. Si modified the oxide morphology to a continuous Cr2O3-Al2O3 dual layer. This provided improved protection, reducing the sulfidation depth by 2/3 and the hot corrosion depth by 1/2.Comment: 21 page

Cross-validation of distance measurements in proteins by PELDOR/DEER and single-molecule FRET

Pulsed electron-electron double resonance spectroscopy (PELDOR/DEER) and single-molecule Förster resonance energy transfer spectroscopy (smFRET) are frequently used to determine conformational changes, structural heterogeneity, and inter probe distances in biological macromolecules. They provide qualitative information that facilitates mechanistic understanding of biochemical processes and quantitative data for structural modelling. To provide a comprehensive comparison of the accuracy of PELDOR/DEER and smFRET, we use a library of double cysteine variants of four proteins that undergo large-scale conformational changes upon ligand binding. With either method, we use established standard experimental protocols and data analysis routines to determine inter-probe distances in the presence and absence of ligands. The results are compared to distance predictions from structural models. Despite an overall satisfying and similar distance accuracy, some inconsistencies are identified, which we attribute to the use of cryoprotectants for PELDOR/DEER and label-protein interactions for smFRET. This large-scale cross-validation of PELDOR/DEER and smFRET highlights the strengths, weaknesses, and synergies of these two important and complementary tools in integrative structural biology

Long- and short-range correlations and their event-scale dependence in high-multiplicity pp collisions at 1as = 13 TeV

Two-particle angular correlations are measured in high-multiplicity proton-proton collisions at s = 13 TeV by the ALICE Collaboration. The yields of particle pairs at short-( 06\u3b7 3c 0) and long-range (1.6 < | 06\u3b7| < 1.8) in pseudorapidity are extracted on the near-side ( 06\u3c6 3c 0). They are reported as a function of transverse momentum (pT) in the range 1 < pT< 4 GeV/c. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-pT leading particles or jets for varying pT thresholds. The results demonstrate that the long-range \u201cridge\u201d yield, possibly related to the collective behavior of the system, is present in events with high-pT processes as well. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement for the pT dependency, while overestimating the event-scale dependency. [Figure not available: see fulltext.

f0(980) production in inelastic pp collisions at s = 5.02 TeV

The measurement of the production of f0(980) in inelastic pp collisions at sqrt(s) = 5.02 TeV is presented. This is the first reported measurement of inclusive f0(980) yield at LHC energies. The production is measured at midrapidity, |y| pi+pi- hadronic decay channel using the ALICE detector. The pT-differential yields are compared to those of pions, protons and ϕ mesons as well as to predictions from the HERWIG 7.2 QCD-inspired Monte Carlo event generator and calculations from a coalescence model that uses the AMPT model as an input. The ratio of the pT-integrated yield of f0(980) relative to pions is compared to measurements in e+e- and pp collisions at lower energies and predictions from statistical hadronisation models and HERWIG 7.2. A mild collision energy dependence of the f0(980) to pion production is observed in pp collisions from SPS to LHC energies. All considered models underpredict the pT-integrated 2f0(980)/(pi+ + pi-) ratio. The prediction from the canonical statistical hadronisation model assuming a zero total strangeness content of f0(980) is consistent with the data within 1.9σ and is the closest to the data. The results provide an essential reference for future measurements of the particle yield and nuclear modification in p–Pb and Pb–Pb collisions, which have been proposed to be instrumental to probe the elusive nature and quark composition of the f0(980) scalar meson

Pion-kaon femtoscopy and the lifetime of the hadronic phase in Pb-Pb collisions at root(S)(NN)=2.76 TeV

In this paper, the first femtoscopic analysis of pion-kaon correlations at the LHC is reported. The analysis was performed on the Pb-Pb collision data at root(S)(NN) = 2.76 TeV recorded with the ALICE detector. The non-identical particle correlations probe the spatio-temporal separation between sources of different particle species as well as the average source size of the emitting system. The sizes of the pion and kaon sources increase with centrality, and pions are emitted closer to the centre of the system and/or later than kaons. This is naturally expected in a system with strong radial flow and is qualitatively reproduced by hydrodynamic models. ALICE data on pion-kaon emission asymmetry are consistent with (3+1)-dimensional viscous hydrodynamics coupled to a statistical hadronisation model, resonance propagation, and decay code THERMINATOR 2 calculation, with an additional time delay between 1 and 2 fm/c for kaons. The delay can be interpreted as evidence for a significant hadronic rescattering phase in heavy-ion collisions at the LHC. (C) 2020 The Author. Published by Elsevier B.V.Peer reviewe

Elliptic and triangular flow of (anti)deuterons in Pb-Pb collisions at sNN =5.02 TeV

The measurements of the (anti)deuteron elliptic flow (v2) and the first measurements of triangular flow (v3) in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision √sNN = 5.02 TeV are presented. A mass ordering at low transverse momentum (pT) is observed when comparing these measurements with those of other identified hadrons, as expected from relativistic hydrodynamics. The measured (anti)deuteron v2 lies between the predictions from the simple coalescence and blast-wave models, which provide a good description of the data only for more peripheral and for more central collisions, respectively. The mass number scaling, which is violated for v2, is approximately valid for the (anti)deuterons v3. The measured v2 and v3 are also compared with the predictions from a coalescence approach with phase-space distributions of nucleons generated by IEBEVISHNU with AMPT initial conditions coupled with URQMD, and from a dynamical model based on relativistic hydrodynamics coupled to the hadronic afterburner SMASH. The model predictions are consistent with the data within the uncertainties in midcentral collisions, while a deviation is observed in the most central collisions