(K.A.). elusive. The use of template molecules to unambiguously dictate the diameter and chirality of the resulting nanotube 8,13-16 holds great promise in this regard, but has hitherto had only limited practical success 7,17,18 . Here we show that this bottom-up strategy can produce targeted nanotubes: we convert molecular precursors into ultrashort singly capped (6,6) 'armchair' nanotube seeds using surface-catalysed cyclodehydrogenation on a Pt(111) surface, and then elongate these during a subsequent growth phase to produce single-chirality and essentially defect-free SWCNTs with lengths up to a few hundred nanometres. We expect that our onsurface synthesis approach will provide a route to nanotube-based materials with highly Fig. 1) was designed and synthesized by multi-step organic synthesis to tackle this challenge (for details, see Methods). Upon intramolecular CDH it affords seed S1, an ultra-short singly capped (6,6) SWCNT bearing a carbon nanotube segment. The selective growth of (6,6) SWCNTs is illustrated in Fig. 1 and combines two steps: (1) formation of seed S1, and (2) subsequent epitaxial elongation. The first step is realized by depositing precursor P1 on a Pt (111) surface followed by annealing to 770 K under ultrahigh vacuum conditions to induce the surfacecatalysed CDH reaction ( Fig. 2a, b). The second step, epitaxial elongation, is achieved by the incorporation of carbon atoms originating from the surface-catalysed decomposition of a carbon feedstock gas ( Fig. 3a-c). indicates that the different topographic features observed for the adsorbed precursors can be attributed to the different adsorption geometries. Importantly, the stereoisomerism does not affect the CDH process, since all chiral centres will disappear during intramolecular cyclization. Over the last two decades, single-walled carbon nanotubes (SWCNTsAlthough P1 is designed to yield seed S1, the conformational flexibility of the peripheral biphenyl groups leads partially to undesired adsorption geometries. In contrast to the stereoisomers discussed above, these molecules will follow a different CDH pathway, ending in the formation of undesired buckybowls (Extended Data Fig. 2). A statistical analysis of more than 100 precursor monomers observed by STM revealed that more than 50% adopt the desired configurations (Extended Data Fig. 1). Most importantly, the condensation products of precursor molecules exhibiting 'wrong' conformations cannot act as seeds for the subsequent CNT growth process via epitaxial elongation, and thus will not affect the selectivity of SWCNT formation.Surface-catalysed CDH of precursors (P1) into seeds (S1) is induced by annealing at 770 K for 10 min. STM images (Fig. 2d) show that the originally quasi-planar three-fold symmetric molecules transform into dome-shaped species with a prominent increase in apparent height from 2 to 4.5 Å (Fig. 2f). Additional proof of successful dehydrogenation of P1 into S1 derives from the good agreement of high-resolution STM images and simulations of the frontier molecu...

Many enteropathogenic bacteria target the mammalian gut. The mechanisms protecting the host from infection are poorly understood. We have studied the protective functions of secretory antibodies (sIgA) and the microbiota, using a mouse model for S. typhimurium diarrhea. This pathogen is a common cause of diarrhea in humans world-wide. S. typhimurium (S. tm att, sseD) causes a self-limiting gut infection in streptomycin-treated mice. After 40 days, all animals had overcome the disease, developed a sIgA response, and most had cleared the pathogen from the gut lumen. sIgA limited pathogen access to the mucosal surface and protected from gut inflammation in challenge infections. This protection was O-antigen specific, as demonstrated with pathogens lacking the S. typhimurium O-antigen (wbaP, S. enteritidis) and sIgA-deficient mice (TCRβ−/−δ−/−, JH −/−, IgA−/−, pIgR−/−). Surprisingly, sIgA-deficiency did not affect the kinetics of pathogen clearance from the gut lumen. Instead, this was mediated by the microbiota. This was confirmed using ‘L-mice’ which harbor a low complexity gut flora, lack colonization resistance and develop a normal sIgA response, but fail to clear S. tm att from the gut lumen. In these mice, pathogen clearance was achieved by transferring a normal complex microbiota. Thus, besides colonization resistance ( = pathogen blockage by an intact microbiota), the microbiota mediates a second, novel protective function, i.e. pathogen clearance. Here, the normal microbiota re-grows from a state of depletion and disturbed composition and gradually clears even very high pathogen loads from the gut lumen, a site inaccessible to most “classical” immune effector mechanisms. In conclusion, sIgA and microbiota serve complementary protective functions. The microbiota confers colonization resistance and mediates pathogen clearance in primary infections, while sIgA protects from disease if the host re-encounters the same pathogen. This has implications for curing S. typhimurium diarrhea and for preventing transmission.

The observation of complex, Frank-Kasper (FK) particle packings in diblock polymer melts has until recently been limited to low molecular weight, conformationally asymmetric polymers. We report temperature-dependent small-angle X-ray scattering (SAXS) studies of blends of a sphere-forming poly-(styrene-block-1,4-butadiene) (SB) diblock polymer (M n = 33.3 kg/mol, Đ = M w /M n = 1.08, f B = 0.18) with two different poly(1,4butadiene) (B) homopolymer additives. When the B additive M n is the same as that of the diblock core-forming B segment, these blends remarkably form tetrahedrally close-packed FK σ and Laves C14 and C15 phases with increasing B content. However, binary blends in which the B additive M n is 60% of that of the diblock B segment form only the canonical body-centered cubic (BCC) particle packing and hexagonally-packed cylinders (HEXc). The observed phase behavior is rationalized in terms of "wet" and "dry" brush blending, whereby higher B M n drives stronger localization of the homopolymer in the particle cores while preserving the interfacial area per SB diblock chain. The consequent packing constraints in these blends destabilize the BCC packing, and FK phases emerge as optimal minimal surface solutions to filling space at constant density while maximizing local particle sphericity.

Industry 4.0 introduces modern communication and computation technologies such as cloud computing and Internet of Things to industrial manufacturing systems. As a result, many devices, machines and applications will rely on connectivity, while having different requirements to the network, ranging from high reliability and low latency to high data rates. Furthermore, these industrial networks will be highly heterogeneous as they will feature a number of diverse communication technologies. Current technologies are not well suited for this scenario, which requires that the network is managed at an abstraction level which is decoupled from the underlying technologies. In this paper, we consider network slicing as a mechanism to handle these challenges. We present methods for slicing deterministic and packet-switched industrial communication protocols which simplifies the manageability of heterogeneous networks with various application requirements. Furthermore, we show how to use network calculus to assess the end-to-end properties of the network slices.