Early pottery at 20,000 years ago in Xianrendong Cave, China

The invention of pottery introduced fundamental shifts in human subsistence practices and sociosymbolic behaviors. Here, we describe the dating of the early pottery from Xianrendong Cave, Jiangxi Province, China, and the micromorphology of the stratigraphic contexts of the pottery sherds and radiocarbon samples. The radiocarbon ages of the archaeological contexts of the earliest sherds are 20,000 to 19,000 calendar years before the present, 2000 to 3000 years older than other pottery found in East Asia and elsewhere. The occupations in the cave demonstrate that pottery was produced by mobile foragers who hunted and gathered during the Late Glacial Maximum. These vessels may have served as cooking devices. The early date shows that pottery was first made and used 10 millennia or more before the emergence of agriculture.     

High-resolution protein structure determination by serial femtosecond crystallography

Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules.     

Continental-scale effects of nutrient pollution on stream ecosystem functioning

Excessive nutrient loading is a major threat to aquatic ecosystems worldwide that leads to profound changes in aquatic biodiversity and biogeochemical processes. Systematic quantitative assessment of functional ecosystem measures for river networks is, however, lacking, especially at continental scales. Here, we narrow this gap by means of a pan-European field experiment on a fundamental ecosystem process--leaf-litter breakdown--in 100 streams across a greater than 1000-fold nutrient gradient. Dramatically slowed breakdown at both extremes of the gradient indicated strong nutrient limitation in unaffected systems, potential for strong stimulation in moderately altered systems, and inhibition in highly polluted streams. This large-scale response pattern emphasizes the need to complement established structural approaches (such as water chemistry, hydrogeomorphology, and biological diversity metrics) with functional measures (such as litter-breakdown rate, whole-system metabolism, and nutrient spiraling) for assessing ecosystem health.     

Bright coherent ultrahigh harmonics in the keV x-ray regime from mid-infrared femtosecond lasers

High-harmonic generation (HHG) traditionally combines ~100 near-infrared laser photons to generate bright, phase-matched, extreme ultraviolet beams when the emission from many atoms adds constructively. Here, we show that by guiding a mid-infrared femtosecond laser in a high-pressure gas, ultrahigh harmonics can be generated, up to orders greater than 5000, that emerge as a bright supercontinuum that spans the entire electromagnetic spectrum from the ultraviolet to more than 1.6 kilo-electron volts, allowing, in principle, the generation of pulses as short as 2.5 attoseconds. The multiatmosphere gas pressures required for bright, phase-matched emission also support laser beam self-confinement, further enhancing the x-ray yield. Finally, the x-ray beam exhibits high spatial coherence, even though at high gas density the recolliding electrons responsible for HHG encounter other atoms during the emission process.     

The role of driving energy and delocalized States for charge separation in organic semiconductors

The electron-hole pair created via photon absorption in organic photoconversion systems must overcome the Coulomb attraction to achieve long-range charge separation. We show that this process is facilitated through the formation of excited, delocalized band states. In our experiments on organic photovoltaic cells, these states were accessed for a short time (<1 picosecond) via infrared (IR) optical excitation of electron-hole pairs bound at the heterojunction. Atomistic modeling showed that the IR photons promote bound charge pairs to delocalized band states, similar to those formed just after singlet exciton dissociation, which indicates that such states act as the gateway for charge separation. Our results suggest that charge separation in efficient organic photoconversion systems occurs through hot-state charge delocalization rather than energy-gradient-driven intermolecular hopping.     

Occurrence and molecular analysis of Campylobacter in wildlife on livestock farms

Wildlife harbor a variety of Campylobacter spp. and may play a significant role in the transmission of Campylobacter to livestock. Although studies have been conducted on wildlife-associated Campylobacter isolates from farms in other countries, there are little data available for livestock farms in the United States. In addition, the critical questions of whether wildlife harbor Campylobacter that is pathogenic to ruminants and/or antibiotic-resistant Campylobacter have yet to be addressed. We captured wild small mammals (n=142) and small birds (n=188) at livestock farms in central Iowa and sampled them for thermophilic Campylobacter during autumn 2009, spring 2010, and autumn 2010. Overall prevalence was 4.79%, with isolates found only in wild birds. Molecular typing revealed four multilocus sequence types (STs), three of which are novel. The remaining ST (ST-806) was found in two house sparrows and is an ST previously associated with ruminant abortion cases. Further analysis of ST-806 wild bird and ruminant abortion isolates by pulsed-field gel electrophoresis, resistance gene location, and antibiotic susceptibility tests indicated that the isolates are nearly identical. This is the first account of isolation of Campylobacter types from wild birds that are known to be pathogenic to ruminants. Furthermore, these same two wild bird isolates are resistant to the antibiotic fluoroquinolone. Our results indicate there is an overall low prevalence of Campylobacter in selected wildlife in Iowa, but suggest that wildlife may play a role in the epidemiology of pathogenic Campylobacter for domestic livestock, and may also serve as a reservoir for antibiotic-resistant Campylobacter.