Epitaxial Nickel Ferrocyanide Stabilizes Jahn-Teller Distortions of Manganese Ferrocyanide for Sodium-Ion Batteries

Manganese-based Prussian Blue, Na_2-δ Mn[Fe(CN)₆ ] (MnPB), is a good candidate for sodium-ion battery cathode materials due to its high capacity. However, it suffers from severe capacity decay during battery cycling due to the destabilizing Jahn-Teller distortions it undergoes as Mn²⁺ is oxidized to Mn³⁺ . Herein, the structure is stabilized by a thin epitaxial surface layer of nickel-based Prussian Blue (Na_2-δ Ni[Fe(CN)₆ ]). The one-pot synthesis relies on a chelating agent with an unequal affinity for Mn²⁺ and Ni²⁺ ions, which prevents Ni²⁺ from reacting until the Mn²⁺ is consumed. This is a new and simpler synthesis of core-shell materials, which usually needs several steps. The material has an electrochemical capacity of 93 mA h g^-1 , of which it retains 96 % after 500 charge-discharge cycles (vs. 37 % for MnPB). Its rate capability is also remarkable: at 4 A g^-1 (ca. 55 C) it can reversibly store 70 mA h g^-1 , which is also reflected in its diffusion coefficient of ca. 10^-8  cm²  s^-1 . The epitaxial outer layer appears to exert an anisotropic strain on the inner layer, preventing the Jahn-Teller distortions it normally undergoes during de-sodiation.

Multispectral LIF-Based Standoff Detection System for the Classification of CBE Hazards by Spectral and Temporal Features

Laser-induced fluorescence (LIF) is a well-established technique for monitoring chemical processes and for the standoff detection of biological substances because of its simple technical implementation and high sensitivity. Frequently, standoff LIF spectra from large molecules and bio-agents are only slightly structured and a gain of deeper information, such as classification, let alone identification, might become challenging. Improving the LIF technology by recording spectral and additionally time-resolved fluorescence emission, a significant gain of information can be achieved. This work presents results from a LIF based detection system and an analysis of the influence of time-resolved data on the classification accuracy. A multi-wavelength sub-nanosecond laser source is used to acquire spectral and time-resolved data from a standoff distance of 3.5 m. The data set contains data from seven different bacterial species and six types of oil. Classification is performed with a decision tree algorithm separately for spectral data, time-resolved data and the combination of both. The first findings show a valuable contribution of time-resolved fluorescence data to the classification of the investigated chemical and biological agents to their species level. Temporal and spectral data have been proven as partly complementary. The classification accuracy is increased from 86% for spectral data only to more than 92%.

Nickel sulfide nanocrystals on nitrogen-doped porous carbon nanotubes with high-efficiency electrocatalysis for room-temperature sodium-sulfur batteries

Polysulfide dissolution and slow electrochemical kinetics of conversion reactions lead to low utilization of sulfur cathodes that inhibits further development of room-temperature sodium-sulfur batteries. Here we report a multifunctional sulfur host, NiS₂ nanocrystals implanted in nitrogen-doped porous carbon nanotubes, which is rationally designed to achieve high polysulfide immobilization and conversion. Attributable to the synergetic effect of physical confinement and chemical bonding, the high electronic conductivity of the matrix, closed porous structure, and polarized additives of the multifunctional sulfur host effectively immobilize polysulfides. Significantly, the electrocatalytic behaviors of the Lewis base matrix and the NiS₂ component are clearly evidenced by operando synchrotron X-ray diffraction and density functional theory with strong adsorption of polysulfides and high conversion of soluble polysulfides into insoluble Na₂S₂/Na₂S. Thus, the as-obtained sulfur cathodes exhibit excellent performance in room-temperature Na/S batteries.

Room temperature rechargeable sodium sulfur batteries are promising for next-generation energy storage systems, but their development is limited by polysulfide dissolution and slow kinetics. Here the authors report a cathode that serves as a multifunctional sulfur host and imparts enhanced performance.

Precision Isotope Shift Measurements in Calcium Ions Using Quantum Logic Detection Schemes

We demonstrate an efficient high-precision optical spectroscopy technique for single trapped ions with nonclosed transitions. In a double-shelving technique, the absorption of a single photon is first amplified to several phonons of a normal motional mode shared with a cotrapped cooling ion of a different species, before being further amplified to thousands of fluorescence photons emitted by the cooling ion using the standard electron shelving technique. We employ this extension of the photon recoil spectroscopy technique to perform the first high precision absolute frequency measurement of the 2D(3/2)→2P(1/2) transition in calcium, resulting in a transition frequency of f=346 000 234 867(96)  kHz. Furthermore, we determine the isotope shift of this transition and the 2S(1/2)→2P(1/2) transition for 42Ca+, 44Ca+, and 48Ca+ ions relative to 40Ca+ with an accuracy below 100 kHz. Improved field and mass shift constants of these transitions as well as changes in mean square nuclear charge radii are extracted from this high resolution data.

Damage-free single-mode transmission of deep-UV light in hollow-core PCF

Transmission of UV light with high beam quality and pointing stability is desirable for many experiments in atomic, molecular and optical physics. In particular, laser cooling and coherent manipulation of trapped ions with transitions in the UV require stable, single-mode light delivery. Transmitting even ~2 mW CW light at 280 nm through silica solid-core fibers has previously been found to cause transmission degradation after just a few hours due to optical damage. We show that photonic crystal fiber of the kagomé type can be used for effectively single-mode transmission with acceptable loss and bending sensitivity. No transmission degradation was observed even after >100 hours of operation with 15 mW CW input power. In addition it is shown that implementation of the fiber in a trapped ion experiment increases the coherence time of the internal state transfer due to an increase in beam pointing stability.

Recent observations on schistosomiasis in Mauritius

Purpose of this study, carried out between 1967 and 1975, was to bring the existing knowledge on schistosomiasis in Mauritius up-to-date. The paper describes the distribution, the behaviour and the infection rates of Bulinus cernicus, the local intermediate snail host, and its role in human infection.