Hot Spots on the Fermi Surface of Bi2212: Stripes versus Superstructure

In a recent paper Saini et al. have reported evidence for a pseudogap around (pi,0) at room temperature in the optimally doped superconductor Bi2212. This result is in contradiction with previous ARPES measurements. Furthermore they observed at certain points on the Fermi surface hot spots of high spectral intensity which they relate to the existence of stripes in the CuO planes. They also claim to have identified a new electronic band along Gamma-M1 whose one dimensional character provides further evidence for stripes. We demonstrate in this Comment that all the measured features can be simply understood by correctly considering the superstructure (umklapp) and shadow bands which occur in Bi2212.Comment: 1 page, revtex, 1 encapsulated postscript figure (color

Hierarchical approach to 'atomistic' 3-D MOSFET simulation

We present a hierarchical approach to the 'atomistic' simulation of aggressively scaled sub-0.1-μm MOSFETs. These devices are so small that their characteristics depend on the precise location of dopant atoms within them, not just on their average density. A full-scale three-dimensional drift-diffusion atomistic simulation approach is first described and used to verify more economical, but restricted, options. To reduce processor time and memory requirements at high drain voltage, we have developed a self-consistent option based on a solution of the current continuity equation restricted to a thin slab of the channel. This is coupled to the solution of the Poisson equation in the whole simulation domain in the Gummel iteration cycles. The accuracy of this approach is investigated in comparison to the full self-consistent solution. At low drain voltage, a single solution of the nonlinear Poisson equation is sufficient to extract the current with satisfactory accuracy. In this case, the current is calculated by solving the current continuity equation in a drift approximation only, also in a thin slab containing the MOSFET channel. The regions of applicability for the different components of this hierarchical approach are illustrated in example simulations covering the random dopant-induced threshold voltage fluctuations, threshold voltage lowering, threshold voltage asymmetry, and drain current fluctuations

Decolonising quantitative research methods pedagogy: teaching contemporary politics to challenge hierarchies from data

Decolonisation of the curriculum in higher education is a radical, transformative process of change that interrogates the enduring Eurocentric and racist narratives surrounding the production of academic ‘knowledge’. Our key argument is that it is essential for students of politics to understand the authorities and hierarchies exerted through quantitative data. In this paper, we show that (1) quantitative methods and data literacy can be an explicit tool in the endeavour to challenge structures of oppression, and (2) there is a need to apply decolonial principles to the teaching of quantitative methods, prioritising the historical contextualisation and anti-racist critique of the ways in which statistics amplify existing micro and macro power relations. To explain how this can be done, we begin with a commentary on the ‘state of decolonisation’ in higher education, its relevance to the sub-disciplines of politics, and its application to quantitative teaching in the UK. We then suggest some guiding principles for a decolonial approach to quantitative methods teaching, and present substantive examples from political sociology, international political economy, and international development. These suggestions and examples show how a decolonial lens advances critical and emancipatory thinking in undergraduate students of politics when it is used with quantitative methods

Bond stretching phonon softening and angle-resolved photoemission kinks in optimally doped Bi2Sr1.6La0.4Cu2O6 superconductors

We report the first measurement of the optical phonon dispersion in optimally doped single layer Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering. We found a strong softening of the Cu-O bond stretching phonon at about q=(0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates. A direct comparison with angle-resolved photoemission spectroscopy measurements taken on the same sample, revealed an excellent agreement in terms of energy and momentum between the ARPES nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63 meV kink is observed can be connected with a vector q=(xi,0,0) with xi~0.22, which corresponds exactly to the soft part of the bond stretching phonon mode. This result supports an interpretation of the ARPES kink in terms of electron-phonon coupling.Comment: submited to PR

Spring Dispersal of Some Leafhoppers and Aphids

Two species of leafhoppers and four species of cereal aphids appear to be transported to Minnesota each spring on strong winds from the south or southwest. The aster leafhopper, Macrosteles fascifrons (Stal); the English grain aphid, Macrosiphum avenae (Fabr.); the apple grain aphid, Rhopalosiphum fitchii (Sand.); and the greenbug, Schizaphis graminum (Rond.), usually arrive in Minnesota during late April or early May. Weather conditions favorable for northward movement of these insects consist of a high pressure area over the eastern states, a low pressure area over the western plains, and the resulting strong, persistent, south wind which is often called a low-level jet. The potato leafhopper, Empoasca fabae (Harris), usually arrives in southern Minnesota about May 20 and in central Minnesota about May 25. By mid-June it has usually dispersed to the northern part of the state. The corn leaf aphid, Rhopalosiphum maidis (Fitch), usually arrives during early June

Новая взвешенная гибридная система рекомендаций с использованием коэффициента Шарпа для прибыльного диверсифицированного инвестиционного портфеля

Identifying where to invest and how much to invest can be very challenging for common people who have limited knowledge in the domain. Portfolio managers are financial professionals who spend a lot of time and effort to help investors in investing funds and implementing investment strategies, but not all can afford to consult them. The study aims to develop a weighted hybrid recommendation system that recommends an optimized investment portfolio based on the investor’s preferences regarding risk and return. Generally, investors usually ask investment for advice from friends or relatives with similar risk preferences or if they are interested in a particular item, the investors ask for the experience of someone who already has invested in the same item. Therefore, the methodology considers the investor’s past behavior and the past behavior of the nearest neighbor investors with similar risk preferences. Using user-based collaborative filtering the number of stocks is recommended using Pearson correlation based on the investor’s income, then using another user-based collaborative filtering the number of stocks is recommended based on the investor’s age. Weights are assigned to the recommended number of stocks generated based on income and age and their weighted average is finally considered. Finally, the feasibility of the proposed system was assessed through various experiments. Based on the received results, the authors conclude that the proposed weighted hybrid approach is robust enough for implementation in the real world. The novelty of the paper lies in the fact that none of the existing approaches make use of more than one type of weighted recommendation algorithm. Additionally, the final results obtained this way have been never further fortified with the highest Sharpe ratio and minimum risk for the investor. This combination of hybrid and Sharpe ratios has never been explored before.Выбор того, куда и сколько инвестировать, может быть очень сложной задачей для обычных людей, которые имеют ограниченные знания в этой области. Портфолио-менеджеры — это финансовые профессионалы, которые тратят много времени и усилий, чтобы помочь инвесторам в размещении средств и реализации финансовых стратегий, но не все могут позволить себе обратиться к ним за консультацией. Цель исследования — разработать взвешенную систему гибридных рекомендаций оптимизированного инвестиционного портфеля на основе предпочтений инвестора относительно риска и доходности. Как правило, инвесторы спрашивают совета по инвестициям у друзей или родственников со схожими предпочтениями в отношении риска, или, если их интересует конкретный товар, у того, кто уже инвестировал в тот же товар. Поэтому методология учитывает прошлое поведение инвестора и его ближайших соседей-инвесторов со схожими предпочтениями риска. С помощью коллаборативной фильтрации на основе интересов пользователя авторы рекомендуют выбрать определенное количество акций, используя метод корреляции Пирсона на основе дохода инвестора. Затем с помощью другой коллаборативной фильтрации на основе интересов пользователя рекомендуется определенное количество акций на основе возраста инвестора. Рекомендованному количеству акций, сгенерированному на основе дохода и возраста инвестора, присваиваются веса, и в итоге считается их средневзвешенное значение. В заключение проведена оценка реализуемости предложенной системы с помощью различных экспериментов. На основании полученных результатов авторы делают вывод, что предложенный взвешенный гибридный подход достаточно надежен для реализации в реальных условиях. Новизна работы заключается в том, что ни один из существующих подходов не использует более одного типа алгоритма взвешенных рекомендаций. Кроме того, конечные результаты, полученные таким образом, также никогда не отличались максимальным коэффициентом Шарпа и минимальным риском для инвестора. Такая комбинация гибридной фильтрации и коэффициента Шарпа никогда ранее не исследовалась

Free circular introns with an unusual branchpoint in neuronal projections

The polarized structure of axons and dendrites in neuronal cells depends in part on RNA localization. Previous studies have looked at which polyadenylated RNAs are enriched in neuronal projections or at synapses, but less is known about the distribution of non-adenylated RNAs. By physically dissecting projections from cell bodies of primary rat hippocampal neurons and sequencing total RNA, we found an unexpected set of free circular introns with a non-canonical branchpoint enriched in neuronal projections. These introns appear to be tailless lariats that escape debranching. They lack ribosome occupancy, sequence conservation, and known localization signals, and their function, if any, is not known. Nonetheless, their enrichment in projections has important implications for our understanding of the mechanisms by which RNAs reach distal compartments of asymmetric cells

Metallic phase in stoichiometric CeOBiS 2 revealed by space-resolved ARPES

Recently CeOBiS2 system without any fluorine doping is found to show superconductivity posing question on its origin. Using space resolved ARPES we have found a metallic phase embedded in the morphological defects and at the sample edges of stoichiometric CeOBiS2. While bulk of the sample is semiconducting, the embedded metallic phase is characterized by the usual electron pocket at X point, similar to the Fermi surface of doped BiS2-based superconductors. Typical size of the observed metallic domain is larger than the superconducting correlation length of the system suggesting that the observed superconductivity in undoped CeOBiS2 might be due to this embedded metallic phase at the defects. The results also suggest a possible way to develop new systems by manipulation of the defects in these chalcogenides with structural instability

Atlantic water inflow to Labrador Sea and its interaction with ice sheet dynamics during the Holocene

The hydrodynamics of the Labrador Sea, controlled by the complex interplay of oceanographic, atmospheric and ice-sheet processes, play a crucial role for the Atlantic Meridional Overturning Circulation (AMOC). An improved understanding of the hydrodynamics and its forcing in the past could therefore hold a key to understanding its future behaviour. At present, there is a remarkable temporal mismatch, in that the largely microfossil-based reconstructions of Holocene Atlantic-water inflow/influence in the Labrador Sea and Baffin Bay appear to lag grain size-based current strength reconstructions from the adjacent North Atlantic by > 2ka. Here, we present the first current strength record from the West Greenland shelf off Nuuk to reconstruct Atlantic Water (AW)-inflow to the Labrador Sea via the West Greenland Current. Our data show that the Holocene AW-inflow into Labrador Sea is well aligned with the Holocene Speed Maximum documented in the North Atlantic (McCave and Andrews, 2019; Quat. Sci. Rev. 223), suggesting a close coupling with the AMOC. The observed lag between the microfossil-based records and the Holocene Speed Maximum can be explained when considering the presence of an extended meltwater lens that prevented the shoaling of the inflowing Atlantic waters. Once the meltwater discharge waned after the cessation of large-scale melting of the surrounding ice sheets, the AW could influence the surface waters, independently of the strength of its inflow. Only then was an effective ocean-atmosphere heat transfer enabled, triggering the comparably late onset of the regional Holocene Thermal Maximum. Furthermore, sediment geochemical analyses show that short term cooling events, such as the 8.2 ka event related to the final drainage of glacial Lake Agassiz, lead to glacier advances of the Greenland Ice Sheet. Since the grain size data show that these events had no influence on the AW-inflow to the north eastern Labrador Sea, these advances must have been caused by atmospheric cooling. Consequently, we argue that (i) in this region, surface water-based proxies register AW influence rather than inflow (ii) the AW inflow into the Labrador Sea is controlled by the AMOC, but (iii) its impact on an effective ocean-atmosphere heat transfer was hindered by a prevailing meltwater lens in the early Holocene, i.e. until the cessation of large-scale melting of the surrounding ice sheets

Density functional electronic spectrum of the CuO−6−10Cu O_{-6}^{-10} cluster and possible local Jahn-Teller distorsions in the La-Ba-Cu-O superconductor

We present a density functional theory (DFT) calculation in the generalized gradient approximation to study the possibility for the existence of Jahn-Teller (JT) or pseudo Jahn-Teller (PJT) type local distortions in the La-Ba-Cu-O superconducting system. We performed the calculation and correspondingly group theory classification of the electronic ground state of the CuO${_{6}}^{-10}$ elongated octahedra cluster, immersed in a background simulating the superconductor. Part of the motivation to do this study is that the origin of the apical deformation of the CuO${_{6}}^{-10}$ cluster is not due to a pure JT effect, having therefore a non {\it a priori} condition to remove the degeneracy of the electronic ground state of the parent regular octahedron. We present a comparative analysis of the symmetry classified electron spectrum with previously reported results using unrestricted Hartree-Fock calculations (UHF). Both the DFT and UHF calculations produced a non degenerate electronic ground state, not having therefore the necessary condition for a pure JT effect. However, the appearance of a degenerate E$_{g}$ state near to the highest occupied molecular orbital in the DFT calculation, suggests the possibility for a PJT effect responsible for a local distortion of the oxidized CuO$_{6}^{-9}$ cluster.Comment: 12 pages, 3 figures, submitted to International Journal of Modern Physics B (IJMPB