Indeterminacy in a Forward Looking Regime Switching Model

This paper is about the properties of Markov switching rational expectations (MSRE) models. We present a simple monetary policy model that switches between two regimes with known transition probabilities. The first regime, treated in isolation, has a unique determinate rational expectations equilibrium and the second contains a set of indeterminate sunspot equilibria. We show that the Markov switching model, which randomizes between these two regimes, may contain a continuum of indeterminate equilibria. We provide examples of stationary sunspot equilibria and bounded sunspot equilibria which exist even when the MSRE model satisfies a 'generalized Taylor principle'. Our result suggests that it may be more difficult to rule out non-fundamental equilibria in MRSE models than in the single regime case where the Taylor principle is known to guarantee local uniqueness.

Trends in Elasticity and Electronic Structure of Transition-Metal Nitrides and Carbides from First Principles

The elastic properties of the $B_1$-structured transition-metal nitrides and their carbide counterparts are studied using the {\it ab initio\} density functional perturbation theory. The linear response results of elastic constants are in excellent agreement with those obtained from numerical derivative methods, and are also consistent with measured data. We find the following trends: (1) Bulk moduli $B$ and tetragonal shear moduli $G^{\prime}=(C_{11}-C_{12})/2$, increase and lattice constants $a_{0}$ decrease rightward or downward on the Periodic Table for the metal component or if C is replaced by N; (2) The inequality $B > G^{\prime} > G > 0$ holds for $G=C_{44}$; (3) $G$ depends strongly on the number of valence electrons per unit cell ($Z_{V}$). From the fitted curve of $G$ as a function of $Z_{V}$, we can predict that MoN is unstable in $B_{1}$ structure, and transition-metal carbonitrides ($e.g.$ ZrC$_{x}$N$_{1-x}$) and di-transition-metal carbides ($e.g.$ Hf$_{x}$Ta$_{1-x}$C) have maximum $G$ at $Z_{V} \approx 8.3$.Comment: 4 pages, 2 figures, submitted to PRL. 2 typos in ref. 15 were correcte

The NMR of High Temperature Superconductors without Anti-Ferromagnetic Spin Fluctuations

A microscopic theory for the NMR anomalies of the planar Cu and O sites in superconducting La_1.85Sr_0.15CuO_4 is presented that quantitatively explains the observations without the need to invoke anit-ferromagnetic spin fluctuations on the planar Cu sites and its significant discrepancy with the observed incommensurate neutron spin fluctuations. The theory is derived from the recently published ab-initio band structure calculations that correct LDA computations tendency to overestimate the self-coulomb repulsion for the half-filled Cu d_x2-y2 orbital for these ionic systems. The new band structure leads to two bands at the Fermi level with holes in the Cu d_z2 and apical O p_z orbitals in addition to the standard Cu d_x2-y2 and planar O p_sigma orbitals. This band structure is part of a new theory for the cuprates that explains a broad range of experiments and is based upon the formation of Cooper pairs comprised of a k up spin electron from one band and a -k down spin electron from another band (Interband Pairing Model).Comment: In Press, Journal of Physical Chemistry. See also http://www.firstprinciples.com. Minor changes to references and figure readabilit

Endovascular thrombectomy time metrics in the era of COVID-19: observations from the Society of Vascular and Interventional Neurology Multicenter Collaboration

Background Unprecedented workflow shifts during the coronavirus disease 2019 (COVID-19) pandemic have contributed to delays in acute care delivery, but whether it adversely affected endovascular thrombectomy metrics in acute large vessel occlusion (LVO) is unknown. Methods We performed a retrospective review of observational data from 14 comprehensive stroke centers in nine US states with acute LVO. EVT metrics were compared between March to July 2019 against March to July 2020 (primary analysis), and between statespecific pre-peak and peak COVID-19 months (secondary analysis), with multivariable adjustment. Results Of the 1364 patients included in the primary analysis (51% female, median NIHSS 14 [IQR 7–21], and 74% of whom underwent EVT), there was no difference in the primary outcome of door-to-puncture (DTP) time between the 2019 control period and the COVID-19 period (median 71 vs 67min, P=0.10). After adjustment for variables associated with faster DTP, and clustering by site, there remained a trend toward shorter DTP during the pandemic (βadj=-73.2, 95%CI −153.8–7.4, Pp=0.07). There was no difference in DTP times according to local COVID-19 peaks vs pre-peak months in unadjusted or adjusted multivariable regression (βadj=-3.85, 95%CI −36.9–29.2, P=0.80). In this final multivariable model (secondary analysis), faster DTP times were significantly associated with transfer from an outside institution (βadj=-46.44, 95%CI −62.8 to – -30.0, P\u3c0.01) and higher NIHSS (βadj=-2.15, 95%CI −4.2to – -0.1, P=0.05). Conclusions In this multi-center study, there was no delay in EVT among patients treated for intracranial occlusion during the COVID-19 era compared with the pre-COVID era

Розробка нейромережевої інтелектуальної системи для прогнозування енергетичних центрів плямових зображень у процесах профілювання лазерного променя

Здійснено розробку нейромережевої інтелектуальної системи для прогнозування енергетичних центрів (ЕЦ) плямових зображень у процесах профілювання лазерного променя (ЛП). Обґрунтовано актуальність задачі прогнозування координат ЕЦ профілю ЛП. Розглянуто методи прогнозування та обґрунтовано доцільність застосування нейромережевої моделі. Здійснено комп’ютерне моделювання системи прогнозування, а також на основі отриманих результатів сформульовано вимоги та здійснено програмну реалізацію інтелектуальної системи.Выполнено разработку нейросетевой интеллектуальной системы для прогнозирования энергетических центров (ЭЦ) пятенных зображений в процесах профилирования лазерного луча (ЛЛ). Обоснована актуальность задачи прогнозирования координат ЭЦ профиля ЛЛ. Рассмотрены методы прогнозирования и обоснована целесообразность применения нейросетевой модели. Выполнено компьютерное моделирование системы прогнозирования, а также на основе полученных результатов сформулированы требования и выполнено программную реализацию интеллектуальной системы.The development of a neural net intellectual system for energy centers (EC) spot images forecasting in the processes of laser beam profiling (LB) is done. Actuality of the problem of coordinates forecasting of EC of laser beam profile is proved. Methods of forecasting are considered and the appropriateness of usage the neural net model is justified. Computer simulation of forecasting system is carried out and also on the basis of the obtained results the requirements are formulated and software implementation of intelligent system is performed

Model of C-Axis Resistivity of High-\Tc Cuprates

We propose a simple model which accounts for the major features and systematics of experiments on the $c$-axis resistivity, $\rho_c$, for \lsco, \ybco and \bsco . We argue that the $c$-axis resistivity can be separated into contributions from in-plane dephasing and the $c$-axis ``barrier'' scattering processes, with the low temperature semiconductor-like behavior of $\rho_c$ arising from the suppression of the in-plane density of states measured by in-plane magnetic Knight shift experiments. We report on predictions for $\rho_c$ in impurity-doped \ybco materials.Comment: 10 pages + figures, also see March Meeting J13.1

Incommensurate Charge and Spin Fluctuations in d-wave Superconductors

We show analytic results for the irreducible charge and spin susceptibilities, $\chi_0 (\omega, {\bf Q})$, where ${\bf Q}$ is the momentum transfer between the nodes in d-wave superconductors. Using the BCS theory and a circular Fermi surface, we find that the singular behavior of the irreducible charge susceptibility leads to the dynamic incommensurate charge collective modes. The peaks in the charge structure factor occur at a set of wave vectors which form an ellipse around ${\bf Q}_{\pi}=(\pi,\pi)$ and ${\bf Q}_0=(0,0)$ in momentum space with momentum dependent spectral weight. It is also found that, due to the non-singular irreducible spin susceptibility, an extremely strong interaction via random phase approximation is required to support the magnetic peaks near ${\bf Q}_{\pi}$. Under certain conditions, the peaks in the magnetic structure factor occur near ${\bf Q}=(\pi,\pi (1 \pm \delta))$ and $(\pi (1 \pm \delta),\pi)$.Comment: 5 pages, 3 figure