资源环境科技发展态势分析平台

Bulk amorphous materials have been studied extensively and are widely used, yet their atomic arrangement remains an open issue. Although they are generally believed to be Zachariasen continuous random networks(1), recent experimental evidence favours the competing crystallite model in the case of amorphous silicon(2-4). In two-dimensional materials, however, the corresponding questions remain unanswered. Here we report the synthesis, by laser-assisted chemical vapour deposition(5), of centimetre-scale, free-standing, continuous and stable monolayer amorphous carbon, topologically distinct from disordered graphene. Unlike in bulk materials, the structure of monolayer amorphous carbon can be determined by atomic-resolution imaging. Extensive characterization by Raman and X-ray spectroscopy and transmission electron microscopy reveals the complete absence of long-range periodicity and a threefold-coordinated structure with a wide distribution of bond lengths, bond angles, and five-, six-, seven- and eight-member rings. The ring distribution is not a Zachariasen continuous random network, but resembles the competing (nano)crystallite model(6). We construct a corresponding model that enables density-functional-theory calculations of the properties of monolayer amorphous carbon, in accordance with observations. Direct measurements confirm that it is insulating, with resistivity values similar to those of boron nitride grown by chemical vapour deposition. Free-standing monolayer amorphous carbon is surprisingly stable and deforms to a high breaking strength, without crack propagation from the point of fracture. The excellent physical properties of this stable, free-standing monolayer amorphous carbon could prove useful for permeation and diffusion barriers in applications such as magnetic recording devices and flexible electronics.

A neuromodulator produced by commensalProvidenciabacteria that colonize the gut ofCaenorhabditis elegansmimics the functions of the cognate host molecule to manipulate a sensory decision of the host.

Animals coexist in commensal, pathogenic or mutualistic relationships with complex communities of diverse organisms, including microorganisms(1). Some bacteria produce bioactive neurotransmitters that have previously been proposed to modulate nervous system activity and behaviours of their hosts(2,3). However, the mechanistic basis of this microbiota-brain signalling and its physiological relevance are largely unknown. Here we show that inCaenorhabditis elegans, the neuromodulator tyramine produced by commensalProvidenciabacteria, which colonize the gut, bypasses the requirement for host tyramine biosynthesis and manipulates a host sensory decision. Bacterially produced tyramine is probably converted to octopamine by the host tyramine beta-hydroxylase enzyme. Octopamine, in turn, targets the OCTR-1 octopamine receptor on ASH nociceptive neurons to modulate an aversive olfactory response. We identify the genes that are required for tyramine biosynthesis inProvidencia, and show that these genes are necessary for the modulation of host behaviour. We further find thatC. eleganscolonized byProvidenciapreferentially select these bacteria in food choice assays, and that this selection bias requires bacterially produced tyramine and host octopamine signalling. Our results demonstrate that a neurotransmitter produced by gut bacteria mimics the functions of the cognate host molecule to override host control of a sensory decision, and thereby promotes fitness of both the host and the microorganism.

After taking up tumour-associated antigens, dendritic cells in mouse and human tumours upregulate a regulatory gene program that limits dendritic cell immunostimulatory function, and modulating this program can rescue antitumor immunity in mice.

The ability to communicate quantum information over long distances is of central importance in quantum science and engineering(1). Although some applications of quantum communication such as secure quantum key distribution(2,3) are already being successfully deployed(4-7), their range is currently limited by photon losses and cannot be extended using straightforward measure-and-repeat strategies without compromising unconditional security(8). Alternatively, quantum repeaters(9), which utilize intermediate quantum memory nodes and error correction techniques, can extend the range of quantum channels. However, their implementation remains an outstanding challenge(10-16), requiring a combination of efficient and high-fidelity quantum memories, gate operations, and measurements. Here we use a single solid-state spin memory integrated in a nanophotonic diamond resonator(17-19) to implement asynchronous photonic Bell-state measurements, which are a key component of quantum repeaters. In a proof-of-principle experiment, we demonstrate high-fidelity operation that effectively enables quantum communication at a rate that surpasses the ideal loss-equivalent direct-transmission method while operating at megahertz clock speeds. These results represent a crucial step towards practical quantum repeaters and large-scale quantum networks(20,21).

A solid-state spin memory is used to demonstrate quantum repeater functionality, which has the potential to overcome photon losses involved in long-distance transmission of quantum information.

Most cortical synapses are local and excitatory. Local recurrent circuits could implement amplification, allowing pattern completion and other computations(1-4). Cortical circuits contain subnetworks that consist of neurons with similar receptive fields and increased connectivity relative to the network average(5,6). Cortical neurons that encode different types of information are spatially intermingled and distributed over large brain volumes(5-7), and this complexity has hindered attempts to probe the function of these subnetworks by perturbing them individually(8). Here we use computational modelling, optical recordings and manipulations to probe the function of recurrent coupling in layer 2/3 of the mouse vibrissal somatosensory cortex during active tactile discrimination. A neural circuit model of layer 2/3 revealed that recurrent excitation enhances sensory signals by amplification, but only for subnetworks with increased connectivity. Model networks with high amplification were sensitive to damage: loss of a few members of the subnetwork degraded stimulus encoding. We tested this prediction by mapping neuronal selectivity(7) and photoablating(9,10) neurons with specific selectivity. Ablation of a small proportion of layer 2/3 neurons (10-20, less than 5% of the total) representing touch markedly reduced responses in the spared touch representation, but not in other representations. Ablations most strongly affected neurons with stimulus responses that were similar to those of the ablated population, which is also consistent with network models. Recurrence among cortical neurons with similar selectivity therefore drives input-specific amplification during behaviour.

Computational modelling, imaging and single-cell ablation in layer 2/3 of the mouse vibrissal somatosensory cortex reveals that recurrent activity in cortical neurons can drive input-specific amplification during behaviour.