Signature of Fermi arc surface states in Andreev reflection at the WTe2_2 Weyl semimetal surface

We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe$_2$ Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe$_2$ interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.Comment: 5 pages, some misprints has been correcte

Метод визначення частоти свіп-генератора панорамного вимірювача частотних характеристик

Usage of the panoramic meters of frequency-response characteristics or frequency-response characteristic tracers significantly increases work productivity of adjusters and operators of radioelectronic and telecommunication systems. One of the main functions of the frequency-response characteristic tracer is formation of frequency-response scale, that is determining sweep generator frequency, which is a part of it. High-quality frequency-response characteristic tracers must have little error of scale bars formation in the broad frequency range, automatically and independently define their frequency of the swing band of the sweep generator. There is a basic structural scheme of the sweep generator frequency meter with a single-channel frequency-time converter, the main units of which include two reference-frequency generators and stroboscopic mixer. It is proved that usage of reference-frequency generators on quartz-crystal resonators reduces to zero the error component of frequency defining, provided by frequency instability of the generator. To compensate the deflection non-linearity influence of the sweep generator on frequency determination accuracy, the basic scheme of the meter was added with the third reference-frequency generators, as well as the operating procedure of the control and evaluation unit was changed. The evaluating formulas were received for the sweep generator frequency, on their basis the mathematical models for deflection non-linearity cases were created. As a result of the analysis it was found that in the new meter in comparison with the basic one the error component of frequency determination of the sweep generator caused by deflection non-linearity is decreased by times. Interrelation between the multiplication factor and deflection non-linearity coefficient was found, it can be used by designing of the sweep generator frequency meter and formation of the requirements to frequencies of reference-frequency generators. The developed meter with a single-channel frequency-time converter can be used in high-frequency characteristic tracers of 20 GHz and higher range. Its advantages include: simplicity, absence of fast-speed units, except for the stroboscopic mixer, transfer of measurements to great time range, that is to low frequencies.В статье на основе известного метода с двумя опорными генераторами приведена базовая структурная схема измерителя частоты СВИП-генератора с одноканальным частотно-временным преобразователем, основным узлом которого является стробоскопический смеситель. Доказано, что использование как опорных генераторов на кварцевых резонаторах существенно снижает влияние составляющей погрешности определения частоты, которая обусловлена частотной нестабильностью генераторов. Усовершенствован метод с двумя опорными генераторами, базовая структурная схема измерителя дополнена третьим опорным генератором. Установлено, что применение усовершенствованного метода уменьшает на порядок составляющую погрешности определения частоты свип-генератора, которая вызвана нелинейностью развертки,. Найдена взаимосвязь между множителем и коэффициентами нелинейности развертки свип-генератора, которая может быть использована при проектировании измерителя для формирования требований к частотам опорных генераторов.В статті на основі відомого методу з двома опорними генераторами наведено базову структурну схему вимірювача частоти СВІП-генератора з одноканальним частотно-часовим перетворювачем, основним вузлом якого є стробоскопічний змішувач. Доведено, що використання як опорних генераторів на кварцових резонаторах суттєво знижує вплив складової похибки визначення частоти, яка обумовлена частотною нестабільністю генераторів. Вдосконалено метод з двома опорними генераторами, базову структурну схему вимірювача доповнено третім опорним генератором. Встановлено, що при застосуванні вдосконаленого методу складова похибки визначення частоти свіп-генератора, яка викликана нелінійністю розгортки, зменшується на порядок. Знайдено взаємозв’язок між множником та коефіцієнтами нелінійності розгортки свіп-генератора, який може бути використаний при проектуванні вимірювача для формування вимог до частот опорних генераторів

Multiple Disguises for the Same Party: The Concepts of Morphogenesis and Phenotypic Variations in Cryptococcus neoformans†

Although morphological transitions (such as hyphae and pseudohyphae formation) are a common feature among fungi, the encapsulated pathogenic yeast Cryptococcus neoformans is found during infection as blastoconidia. However, this fungus exhibits striking variations in cellular structure and size, which have important consequences during infection. This review will summarize the main aspects related with phenotypic and morphological variations in C. neoformans, which can be divided in three classes. Two of them are related to changes in the capsule, while the third one involves changes in the whole cell. The three morphological and phenotypic variations in C. neoformans can be classified as: (1) changes in capsule structure, (2) changes in capsule size, and (3) changes in the total size of the cell, which can be achieved by the formation of cryptococcal giant/titan cells or microforms. These changes have profound consequences on the interaction with the host, involving survival, phagocytosis escape and immune evasion and dissemination. This article will summarize the main features of these changes, and highlight their importance during the interaction with the host and how they contribute to the development of the disease