Activation gaps for the fractional quantum Hall effect: realistic treatment of transverse thickness

The activation gaps for fractional quantum Hall states at filling fractions $\nu=n/(2n+1)$ are computed for heterojunction, square quantum well, as well as parabolic quantum well geometries, using an interaction potential calculated from a self-consistent electronic structure calculation in the local density approximation. The finite thickness is estimated to make $\sim$30% correction to the gap in the heterojunction geometry for typical parameters, which accounts for roughly half of the discrepancy between the experiment and theoretical gaps computed for a pure two dimensional system. Certain model interactions are also considered. It is found that the activation energies behave qualitatively differently depending on whether the interaction is of longer or shorter range than the Coulomb interaction; there are indications that fractional Hall states close to the Fermi sea are destabilized for the latter.Comment: 32 pages, 13 figure

Microscopic origin of ferromagnetism in the trihalides CrCl3 and CrI3

Microscopic origin of the ferromagnetic (FM) exchange coupling in two Cr trihalides, CrCl3 and CrI3, their common aspects and differences, are investigated on the basis of density functional theory combined with realistic modeling approach for the analysis of interatomic exchange interactions. For these purposes, we perform a comparative study based on the pseudopotential and linear muffin-tin orbital methods by treating the effects of electron exchange and correlation in generalized gradient approximation (GGA) and local spin density approximation (LSDA), respectively. The results of ordinary band structure calculations are used in order to construct the minimal tight-binding type models describing the behavior of the magnetic Cr 3d and ligand p bands in the basis of localized Wannier functions, and evaluate the effective exchange coupling (Jeff) between two Cr sublattices employing four different technique: (i) brute force total energy calculations; (ii) the second-order Green's function perturbation theory for infinitesimal spin rotations of the LSDA (GGA) potential at the Cr sites; (iii) enforcement of the magnetic force theorem in order to treat both Cr and ligand spins on a localized footing; and (iv) constrained total-energy calculations with an external field, treated in the framework of self-consistent linear response theory. We argue that the ligand states play crucial role in the ferromagnetism of Cr trihalides, though their contribution to Jeff strongly depends on additional assumptions, which are traced back to the fundamentals of adiabatic spin dynamics. Particularly, by neglecting the ligand spins in the Green's function method, Jeff can easily become antiferromagnetic, while by treating them as localized, one can severely overestimate the FM coupling. The best considered approach is based on the constraint method, where the ligand states are allowed to relax in response to each instantaneous reorientation of the Cr spins, controlled by a constraining field. Furthermore, the differences of the electronic structure of Cr trihalides in GGA and LSDA, and their impact on the exchange coupling are discussed in details, as well as the possible roles played by the on-site Coulomb repulsion U. © 2019 American Physical Society

Сравнительное исследование структурных, функциональных и микроциркуляторных параметров в диагностике глаукомы

 PURPOSE: To conduct a comparative analysis of clinical and functional parameters in patients with primary openangle glaucoma (POAG), pseudoexfoliation glaucoma (PEG) and pseudoexfoliation syndrome (PES), to justify angio-OCT expedience in diagnostics and monitoring.METHODS: The study included 121 patients (121 eyes). Group 1 consisted of 29 patients (29 eyes) diagnosed with stage I PEG. Group 2 included 32 patients (32 eyes) diagnosed with stage I POAG. Group 3 consisted of 31 patients (31 eyes) with pseudoexfoliative syndrome signs. Group 4 (control) consisted of 28 people (28 eyes) without significant ophthalmopathology. Patients underwent standard ophthalmologic examination, tonography, gonioscopy, pachymetry, tonometry, perimetry, optical coherent angiography of the optic disc. All patients underwent 3 examinations: at baseline, 6 and 12 months after.RESULTS: Angio-OCT data comparison showed that morphometric parameters of the optic disc and microhemodynamics indices differed significantly between all the studied groups. Patients’ examination a year after revealed a negative dynamics of the optic disc parameters in some patients, with the most significant changes observed in PEG patients. To identify the diagnostic significance of the optic disc morphological parameters, the parameters of the peripapillary zone and the macular area, a comparative study of angioOCT data was conducted. Scatterplots with regression equations were also constructed based on data obtained during the second and the third follow-up examinations.CONCLUSION: The study results showed that morphometric indices and optic disc perfusion indices differ significantly both in healthy patients as compared to POAG patients, and in patients with different types of glaucoma. The conducted correlation analysis showed that morphometric indices dynamics correlate with microcirculation indicators in glaucoma patients. Retinal ganglion cells apoptosis and optic nerve fiber degradation was most prominent in PEG patients. Correlation analysis showed that the optic disc microcirculation indicators, specifically the perfusion density and vascular density, were the most significant criteria indicating the pathological process progression. Therefore they may be used as reliable markers  of the pathological process.ЦЕЛЬ. Провести сравнительный анализ клинико-функциональных показателей у пациентов с первичной открытоугольной глаукомой (ПОУГ), псевдоэксфолиативной глаукомой (ПЭГ) и псевдоэксфолиативным синдромом (ПЭС), обосновать целесообразность использования метода ангио-ОКТ в их диагностике и мониторинге.МЕТОДЫ. В исследование был включен 121 пациент (121 глаз). Группу 1 составили 29 больных (29 глаз) с диагнозом «ПЭГ I стадии». В группу 2 были включены 32 пациента (32 глаза) с диагнозом «ПОУГ I стадии». Группу 3 составил 31 пациент (31 глаз) с признаками ПЭС. Группу 4 (контрольную) составили 28 человек (28 глаз) без значимой офтальмопатологии. Пациентам проводили стандартное офтальмологическое обследование, тонографию, гониоскопию, пахиметрию, тонометрию, периметрию, оптическую когерентную ангио-томографию диска зрительного нерва (ДЗН). Всем пациентам проводили 3 обследования: первичное обследование, второе через 6 месяцев и третье — через 12 месяцев. РЕЗУЛЬТАТЫ.Результаты сравнения данных ангио- ОКТ у пациентов различных групп показали, что имеются значимые отличия морфометрических показателей ДЗН, показателей микрогемодинамики между всеми исследуемыми группами. Обследование пациентов через 1 год выявило отрицательную динамику параметров ДЗН у больных ПЭГ, ПОУГ и ПЭС, наиболее значимые изменения наблюдались при ПЭГ. Для выявления диагностической значимости морфологических параметров ДЗН, параметров перипапиллярной зоны и макулярной области было проведено сравнительное исследование данных ангио-ОКТ. На основании полученных данных после повторного и третьего приема также были построены диаграммы рассеяния с уравнениями регрессии.ЗАКЛЮЧЕНИЕ. Результаты исследования показали, что морфометрические показатели и показатели перфузии ДЗН значимо отличаются не только у здоровых пациентов в сравнении с пациентами с ПОУГ, но также у пациентов с разными видами глаукомы. Проведенный анализ показал, что динамика состояния морфометрических показателей коррелирует с изменением показателей микроциркуляции у больных глаукомой. Апоптоз ганглиозных клеток сетчатки и распад нервных волокон ДЗН более выражен у больных ПЭГ. Статистический анализ показал, что наиболее значимыми критериями, указывающими на прогрессирование патологического процесса, являются показатели микроциркуляции ДЗН – плотность перфузии и плотность сосудов, в связи с чем их можно рассматривать как маркеры патологического процесса

Clonal Evolution and Heterogeneity of Osimertinib Acquired Resistance Mechanisms in EGFR Mutant Lung Cancer

Clonal evolution of osimertinib-resistance mechanisms in EGFR mutant lung adenocarcinoma is poorly understood. Using multi-region whole-exome and RNA sequencing of prospectively collected pre- and post-osimertinib-resistant tumors, including at rapid autopsies, we identify a likely mechanism driving osimertinib resistance in all patients analyzed. The majority of patients acquire two or more resistance mechanisms either concurrently or in temporal sequence. Focal copy-number amplifications occur subclonally and are spatially and temporally separated from common resistance mutations such as EGFR C797S. MET amplification occurs in 66% (n = 6/9) of first-line osimertinib-treated patients, albeit spatially heterogeneous, often co-occurs with additional acquired focal copy-number amplifications and is associated with early progression. Noteworthy osimertinib-resistance mechanisms discovered include neuroendocrine differentiation without histologic transformation, PD-L1, KRAS amplification, and ESR1-AKAP12, MKRN1-BRAF fusions. The subclonal co-occurrence of acquired genomic alterations upon osimertinib resistance will likely require targeting multiple resistance mechanisms by combination therapies