Superlubric Sliding of Graphene Auto-Kirigami with Interfaces Containing Self-Assembled Stripe-Pattern Adsorbates.

Van der Waals heterostructures formed by stacked 2D materials show exceptional electronic, mechanical, and optical properties. Superlubricity, a condition where atomically flat, incommensurate planes of atoms result in ultra-low friction, is a prime example enabling, for example, self-assembly of optically visible graphene nanostructures in air via a sliding auto-kirigami process. Here, it is demonstrated that a subtle but ubiquitous adsorbate stripe structure found on graphene and graphitic surfaces in ambient conditions remains stable within the interface between twisted graphene layers as they slide over each other. Despite this contamination, the interface retains an exceptional superlubricious state with an estimated upper bound frictional shear strength of 10 kPa, indicating that direct atomic incommensurate contact is not required to achieve ambient superlubricity for 2D materials. The results suggest that any phenomena depending on 2D heterostructure interfaces such as exotic electronic behavior may need to consider the presence of stripe adsorbate structures that remain intercalated.

Revision of Chaetacanthus Seidler, 1922 (Annelida, Phyllodocida, Polynoidae).

The polynoid genus Chaetacanthus Seidler, 1922 currently includes three nominal species provided with parapodial branchiae. Members of this taxon have palps with longitudinal rows of papillae, notochaetae abundant and neurochaetae spinulose. Most Chaetacanthus species were originally described as belonging to Lepidonotus Leach, 1816, and some of them were later regarded as subjective synonyms of Iphione magnifica Grube, 1876, the type species for Chaetacanthus. This species was described from the Caribbean Sea and later recorded for the tropical Eastern Pacific. After the supposed Amphi-American distribution, a revision of all available material was performed in order to clarify the generic delineation, and to improve the understanding of species systematics. Further, some non-type specimens collected in Panama allowed us to have a better understanding of the variation of elytral shape and ornamentation along the body. The type material of Polynoe brasiliensis de Quatrefages, 1866 was examined and despite its poor condition, it shows parapodial branchial filaments which were overlooked in the original description; these branchiae are also present in the holotype of I. magnifica. We identify that there are no relevant difference between both species, and they are regarded as synonyms, and Chaetacanthus brasiliensis (de Quatrefages, 1866) is newly combined and is the senior synonym. On the other hand, Chaetacanthus pilosus (Treadwell, 1937), from the Eastern Pacific, and C. pomareae (Kinberg, 1856) from the South Central Pacific are redescribed, and C. harrisae n. sp., and C. ornatus n. sp. are both newly described from the Eastern Pacific. A key to identify all species of Chaetacanthus of the World, together with an appendix for the reversal of precedence of Lepidonotus Leach, 1816 over Eumolpe Oken, 1807 are also included.

Evidence for moiré excitons in van der Waals heterostructures.

Recent advances in the isolation and stacking of monolayers of van der Waals materials have provided approaches for the preparation of quantum materials in the ultimate two-dimensional limit1,2. In van der Waals heterostructures formed by stacking two monolayer semiconductors, lattice mismatch or rotational misalignment introduces an in-plane moiré superlattice3. It is widely recognized that the moiré superlattice can modulate the electronic band structure of the material and lead to transport properties such as unconventional superconductivity4 and insulating behaviour driven by correlations5-7; however, the influence of the moiré superlattice on optical properties has not been investigated experimentally. Here we report the observation of multiple interlayer exciton resonances with either positive or negative circularly polarized emission in a molybdenum diselenide/tungsten diselenide (MoSe2/WSe2) heterobilayer with a small twist angle. We attribute these resonances to excitonic ground and excited states confined within the moiré potential. This interpretation is supported by recombination dynamics and by the dependence of these interlayer exciton resonances on twist angle and temperature. These results suggest the feasibility of engineering artificial excitonic crystals using van der Waals heterostructures for nanophotonics and quantum information applications.

Overview of pneumococcal serotypes and genotypes causing diseases in patients with chronic obstructive pulmonary disease in a Spanish hospital between 2013 and 2016.

BACKGROUND: Streptococcus pneumoniae is an important pathogen in chronic obstructive pulmonary disease (COPD). We aimed at showing the recent changes in the epidemiology of pneumococcal diseases in patients with COPD, especially after the introduction of the 13-valent pneumococcal conjugate vaccine (PCV13). METHODS: From 2013 to 2016, strains causing invasive pneumococcal disease (IPD), non-bacteremic pneumococcal pneumonia (non-BPP), and acute exacerbation of COPD (AE-COPD) were prospectively included. Antimicrobial susceptibility testing, serotyping, and genotyping were analyzed. RESULTS: We collected 345 pneumococci from 286 COPD patients (57 IPD, 78 non-BPP, and 210 AE-COPD). The most frequent serotypes were serotypes 3 (14.0%), 8 (14.0%), and 12F (8.8%) in IPD; serotypes 3 (16.7%), 11A (9%), 9L/N (7.7%), and 23A (7.7%) in non-BPP; and serotypes 11A (11%), nontypeable (11%), and 6C (10%) in AE-COPD. Resistance rates were highest among AE-COPD strains. Penicillin resistance was associated with serotypes 11A (CC156) and 19A (CC320 and CC230). Compared with previous studies, fluoroquinolone resistance in AE-COPD increased (9.5%), PCV13 serotypes decreased (31.6%, 26.9%, and 16.7% for IPD, non-BPP, and AE-COPD, respectively), and serotype 11A-CC156 in AE-COPD and serotype 8 in IPD increased. CONCLUSION: The epidemiology of pneumococcal disease in COPD changed after the introduction of PCV13 in children. Increases in the highly invasive serotype 8 among patients with IPD and in serotype 11A-CC156 among patients with AE-COPD could compromise the ability of current PCVs to prevent diseases. Vaccines with a greater coverage could improve the benefits of adult vaccination.

Mechanics of spontaneously formed nanoblisters trapped by transferred 2D crystals.

Layered systems of 2D crystals and heterostructures are widely explored for new physics and devices. In many cases, monolayer or few-layer 2D crystals are transferred to a target substrate including other 2D crystals, and nanometer-scale blisters form spontaneously between the 2D crystal and its substrate. Such nanoblisters are often recognized as an indicator of good adhesion, but there is no consensus on the contents inside the blisters. While gas-filled blisters have been modeled and measured by bulge tests, applying such models to spontaneously formed nanoblisters yielded unrealistically low adhesion energy values between the 2D crystal and its substrate. Typically, gas-filled blisters are fully deflated within hours or days. In contrast, we found that the height of the spontaneously formed nanoblisters dropped only by 20-30% after 3 mo, indicating that probably liquid instead of gas is trapped in them. We therefore developed a simple scaling law and a rigorous theoretical model for liquid-filled nanoblisters, which predicts that the interfacial work of adhesion is related to the fourth power of the aspect ratio of the nanoblister and depends on the surface tension of the liquid. Our model was verified by molecular dynamics simulations, and the adhesion energy values obtained for the measured nanoblisters are in good agreement with those reported in the literature. This model can be applied to estimate the pressure inside the nanoblisters and the work of adhesion for a variety of 2D interfaces, which provides important implications for the fabrication and deformability of 2D heterostructures and devices.

Burkholderia cepacia lipase: A versatile catalyst in synthesis reactions.

The lipase from Burkholderia cepacia, formerly known as Pseudomonas cepacia lipase, is a commercial enzyme in both soluble and immobilized forms widely recognized for its thermal resistance and tolerance to a large number of solvents and short-chain alcohols. The main applications of this lipase are in transesterification reactions and in the synthesis of drugs (because of the properties mentioned above). This review intends to show the features of this enzyme and some of the most relevant aspects of its use in different synthesis reactions. Also, different immobilization techniques together with the effect of various compounds on lipase activity are presented. This lipase shows important advantages over other lipases, especially in reaction media including solvents or reactions involving short-chain alcohols.

Interface-Governed Deformation of Nanobubbles and Nanotents Formed by Two-Dimensional Materials.

Nanoblisters such as nanobubbles and nanotents formed by two-dimensional (2D) materials have been extensively exploited for strain engineering purposes as they can produce self-sustained, nonuniform in-plane strains through out-of-plane deformation. However, deterministic measure and control of strain fields in these systems are challenging because of the atomic thinness and unconventional interface behaviors of 2D materials. Here, we experimentally characterize a simple and unified power law for the profiles of a variety of nanobubbles and nanotents formed by 2D materials such as graphene and MoS_{2} layers. Using membrane theory, we analytically unveil what sets the in-plane strains of these blisters regarding their shape and interface characteristics. Our analytical solutions are validated by Raman spectroscopy measured strain distributions in bulged graphene bubbles supported by strong and weak shear interfaces. We advocate that both the strain magnitudes and distributions can be tuned by 2D material-substrate interface adhesion and friction properties.

Microwave spectra and gas phase structural parameters for N-hydroxypyridine-2(1H)-thione.

The microwave spectrum for N-hydroxypyridine-2(1H)-thione (pyrithione) was measured in the frequency range 6-18 GHz, providing accurate rotational constants and nitrogen quadrupole coupling strengths for three isotopologues, C(5)H(4)(32)S(14)NOH, C(5)H(4)(32)S(14)NOD, and C(5)H(4)(34)S(14)NOH. Pyrithione was found to be in a higher concentration in the gas phase than the other tautomer, 2-mercaptopyridine-N-oxide (MPO). Microwave spectroscopy is best suited to determine which structure predominates in the gas phase. The measured rotational constants were used to accurately determine the coordinates of the substituted atoms and provided sufficient data to determine some of the important structural parameters for pyrithione, the only tautomer observed in the present work. The spectra were obtained using a pulsed-beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of the (14)N nuclear quadrupole hyperfine interactions. Ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The experimental rotational constants for the parent compound are A = 3212.10(1), B = 1609.328(7), and C = 1072.208(6) MHz, yielding the inertial defect Δ(0) = -0.023 amu·Å(2) for the C(5)H(4)(32)S(14)NOH isotopologue. The observed near zero inertial defect clearly indicates a planar structure. The least-squares fit structural analysis yielded the experimental bond lengths R(O-H) = 0.93(2) Å, R(C-S) = 1.66(2) Å, and angle (N-O-H) = 105(4)° for the ground state structure.