Coverage-dependent adsorption sites for K/Cu(001) and Cs/Cu(001) determined by surface X-ray diffraction

Surface X-ray diffraction has been used to analyze in situ the room-temperature adsorption behaviour and the structure of K and Cs on Cu(100) at submonolayer coverages. Adsorption of K takes place in fourfold hollow sites up to coverages of about 0.25 monolayers (ML), where 1 ML corresponds to 1.53 × 1015 atoms/cm2. At higher coverages the formation of a quasi-hexagonal incommensurate adlayer is observed. In contrast, for Cs adsorption we observe from the very beginning the formation of the quasi-hexagonal structure up to the completion of the adlayer at about 0.30 ML. For K adsorption in the hollow sites we determine an adsorption height, d = 2.25(15) Å, corresponding to an effective K radius of reff = 1.6(1) Å close to the ionic radius of 1.33 Å. We do not observe a change in the effective radius as a function of coverage. For the quasi-hexagonal Cs structure we find an (average) adsorption height d = 2.94 Å corresponding to an effective radius of reff = 2.18 and 1.93 Å, for the limiting ca hollow- and bridge-site adsorption, respectively. The analysis of the superlattice reflections corresponding to the quasi-hexagonal incommensurate structures indicated that the K adlayer is strongly modulated. The first Fourier component of the substrate-induced modulation was determined to u01 = 1.29(3) Å. In contrast, for Cs/Cu(001) static modulation is much less important (u01 0.2 Å). Variation of the Cs adlayer density by changing the substrate temperature allows continuous expansion and contraction of the adsorbate unit cell. No commensurate-incommensurate transition has been observed

Karyotyping human chromosomes by optical and X-ray ptychography methods

Sorting and identifying chromosomes, a process known as karyotyping, is widely used to detect changes in chromosome shapes and gene positions. In a karyotype the chromosomes are identified by their size and therefore this process can be performed by measuring macroscopic structural variables. Chromosomes contain a specific number of base pairs that linearly correlate with their size; therefore it is possible to perform a karyotype on chromosomes using their mass as an identifying factor. Here, we obtain the first images of chromosomes using the novel imaging method of ptychography. We can use the images to measure the mass of chromosomes and perform a partial karyotype from the results. We also obtain high spatial resolution using this technique with synchrotron source X-rays

Wet and dry extremes reduce arthropod biomass independently of leaf phenology in the wet tropics.

Warming temperatures are increasing rainfall extremes, yet arthropod responses to climatic fluctuations remain poorly understood. Here, we used spatiotemporal variation in tropical montane climate as a natural experiment to compare the importance of biotic versus abiotic drivers in regulating arthropod biomass. We combined intensive field data on arthropods, leaf phenology and in situ weather across a 1700-3100 m elevation and rainfall gradient, along with desiccation-resistance experiments and multi-decadal modelling. We found limited support for biotic drivers with weak increases in some herbivorous taxa on shrubs with new leaves, but no landscape-scale effects of leaf phenology, which tracked light and cloud cover. Instead, rainfall explained extensive interannual variability with maximum biomass at intermediate rainfall (130 mm month-1 ) as both 3 months of high and low rainfall reduced arthropods by half. Based on 50 years of regional rainfall, our dynamic arthropod model predicted shifts in the timing of biomass maxima within cloud forests before plant communities transition to seasonally deciduous dry forests (mean annual rainfall 1000-2500 mm vs. <800 mm). Rainfall magnitude was the primary driver, but during high solar insolation, the 'drying power of air' (VPDmax ) reduced biomass within days contributing to drought related to the El Niño-Southern Oscillation (ENSO). Highlighting risks from drought, experiments demonstrated community-wide susceptibility to desiccation except for some caterpillars in which melanin-based coloration appeared to reduce the effects of evaporative drying. Overall, we provide multiple lines of evidence that several months of heavy rain or drought reduce arthropod biomass independently of deep-rooted plants with the potential to destabilize insectivore food webs

3D Ultrastructural Imaging of Chromosomes Using Serial Block-Face Scanning Electron Microscopy (SBFSEM)

To date, our understanding of how DNA is packaged in the cell nucleus, condensed from chromatin into chromosomes, and organized throughout the cell cycle remains sparse. Three dimensional (3D) ultrastructural imaging is an important tool for unravelling the organizational structure of chromosomes. For large volume 3D imaging of biological samples, serial block-face scanning electron microscopy (SBFSEM) has been applied, whereby ultrastructural information is achieved by analyzing 3D reconstructions acquired from measured data sets. In this review, we summarize the contribution of SBFSEM for obtaining 3D images of chromosomes to investigate their ultrastructure and organization in the cell and its nucleus. Furthermore, this review highlights the potential of SBFSEM for advancing 3D chromosome research

Proximity Effects and Nonequilibrium Superconductivity in Transition-Edge Sensors

We have recently shown that normal-metal/superconductor (N/S) bilayer TESs (superconducting Transition-Edge Sensors) exhibit weak-link behavior.1 Here we extend our understanding to include TESs with added noise-mitigating normal-metal structures (N structures). We find TESs with added Au structures also exhibit weak-link behavior as evidenced by exponential temperature dependence of the critical current and Josephson-like oscillations of the critical current with applied magnetic field. We explain our results in terms of an effect converse to the longitudinal proximity effect (LoPE)1, the lateral inverse proximity effect (LaiPE), for which the order parameter in the N/S bilayer is reduced due to the neighboring N structures. Resistance and critical current measurements are presented as a function of temperature and magnetic field taken on square Mo/Au bilayer TESs with lengths ranging from 8 to 130 {\mu}m with and without added N structures. We observe the inverse proximity effect on the bilayer over in-plane distances many tens of microns and find the transition shifts to lower temperatures scale approximately as the inverse square of the in- plane N-structure separation distance, without appreciable broadening of the transition width. We also present evidence for nonequilbrium superconductivity and estimate a quasiparticle lifetime of 1.8 \times 10-10 s for the bilayer. The LoPE model is also used to explain the increased conductivity at temperatures above the bilayer's steep resistive transition.Comment: 10 pages, 8 figure