Multivalued current-phase relationship in a.c. Josephson effect for a three-dimensional Weyl semimetal WTe2_2

We experimentally study electron transport between two superconducting indium leads, coupled to a single WTe$_2$ crystal, which is a three-dimensional Weyl semimetal. We demonstrate Josephson current in long 5~$\mu$m In-WTe$_2$-In junctions, as confirmed by the observation of integer (1,2,3) and fractional (1/3, 1/2, 2/3) Shapiro steps under microwave irradiation. Demonstration of fractional a.c. Josephson effect indicates multivalued character of the current-phase relationship, which we connect with Weyl topological surface states contribution to Josephson current. In contrast to topological insulators and Dirac semimetals, we do not observe $4\pi$ periodicity in a.c. Josephson effect for WTe$_2$ at different frequencies and power, which might reflect chiral character of the Fermi arc surface states in Weyl semimetal.Comment: the text is seriously corrected. arXiv admin note: text overlap with arXiv:1801.0955

Dissolution, Reactor, and Environmental Behavior of ZrO2-MgO Inert Fuel Matrix: Neutronic Evaluation of ZrO2-MgO Inert Fuels

This report presents the results of the Task 3, defined in working program as: evaluation of burnable poison designs. Adopting the basic design of a standard PWR and Pu loadings required for 18-month cycle (results of Task 2), this part of the program is aimed to estimate performance of each BP design and BP material to address challenges of Fertile-Free Fuel (FFF) Concept. Finally, an optimal BP design will be developed and an overall feasibility of FFF concept will be determined. Basically, the main challenge encountered in neutronic design for a FFF core is to develop reactivity control system which is capable to satisfy performance and safety criteria of existing PWR plants. Heavy Pu loadings combined with absence of fertile isotopes with capture resonances result in low reactivity worth of existing control mechanisms and inadequate temperature coefficients. The main solution adopted by several previous design efforts is based on increased content of BP materials with capture resonances. The BP designs proposed and analyzed in previous designs are based on such elements as: Gd, Hf, and Er, located in fuel cell, either as a homogeneous mixture or as a thin ring (IFBA-type geometry). This approach results in a large residual reactivity penalty due to an incomplete burnup of the BP material (especially Hf and Er). Description and parameters of the BP designs considered in this work are presented in section II. In this report, an extensive set of calculations was carried out to assess the potential of the main BP materials - B, Gd, Hf, and Er, utilized in three main geometrical arrangements: Wet Annular Burnable Absorber (WABA) type, Integral Fuel Burnable Absorber (IFBA) type, and Homogeneous fuel-BP mixture. Heavy loadings of BP materials in non-standard geometries combined with high Pu content in a fertile-free matrix necessitated additional verification of the calculational tools. Verification of the calculational modeling and parameters are presented in section III. A full scope of calculations is presented in section IV of this report. All cases are arranged according to geometry-type and BP material. The results and analysis of these calculations, presented and summarized in Section V, serve as a basis for a comprehensive assessment of BP potential to address challenges of the FFF concepts. Three main performance parameters of the BP designs will be evaluated: 1. Maximum critical soluble boron concentration (CBC) required during the cycle, 2. Acceptable fuel and moderator temperature coefficients (will be evaluated in Task 4), 3. Residual reactivity penalty associated with incomplete depletion of the BP materia

Multiple magnon modes in the Co3_3Sn2_2S2_2 Weyl semimetal candidate

We experimentally investigate electron transport in kagome-lattice ferromagnet Co$_3$Sn$_2$S$_2$, which is regarded as a time-reversal symmetry broken Weyl semimetal candidate. We demonstrate $dV/dI(I)$ curves with pronounced asymmetric $dV/dI$ spikes, similar to those attributed to current-induced spin-wave excitations in ferromagnetic multilayers. In contrast to multilayers, we observe several $dV/dI$ spikes' sequences at low, $\approx$10$^4$ A/cm$^2$, current densities for a thick single-crystal Co$_3$Sn$_2$S$_2$ flake in the regime of fully spin-polarized bulk. The spikes at low current densities can be attributed to novel magnon branches in magnetic Weyl semimetals, which are predicted due to the coupling between two magnetic moments mediated by Weyl fermions. Presence of spin-transfer effects at low current densities in Co$_3$Sn$_2$S$_2$ makes the material attractive for applications in spintronics.Comment: final versio

Web Workload Generation According to the UniLoG Approach

Generating synthetic loads which are suffciently close to reality represents an important and challenging task in performance and quality-of-service (QoS) evaluations of computer networks and distributed systems. Here, the load to be generated represents sequences of requests at a well-defined service interface within a network node. The paper presents a tool (UniLoG.HTTP) which can be used in a flexible manner to generate realistic and representative server and network loads, in terms of access requests to Web servers as well as creation of typical Web traffic within a communication network. The paper describes the architecture of this load generator, the critical design decisions and solution approaches which allowed us to obtain the desired flexibility

Non-autonomous reductions of the KdV equation and multi-component analogs of the Painlev\'e equations P34_{34} and P3_3

We study reductions of the Korteweg--de Vries equation corresponding to stationary equations for symmetries from the noncommutative subalgebra. An equivalent system of $n$ second-order equations is obtained, which reduces to the Painlev\'e equation P$_{34}$ for $n=1$. On the singular line $t=0$, a subclass of special solutions is described by a system of $n-1$ second-order equations, equivalent to the P$_3$ equation for $n=2$. For these systems, we obtain the isomonodromic Lax pairs and B\"acklund transformations which form the group ${\mathbb Z}^n_2\times{\mathbb Z}^n$.Comment: 11 page