Does exercise during pregnancy impact on maternal weight gain and fetal cardiac function? A randomized controlled trial.

OBJECTIVE: To evaluate the association between physical exercise during pregnancy and maternal gestational weight gain and fetal cardiac function. METHODS: This was a randomized controlled trial of women with a singleton pregnancy managed from the first trimester at the Hospital de Torrejón, Madrid, between November 2014 and June 2015. Women were randomized to either follow a supervised physical conditioning program, consisting of a 60-min session 3 days per week for the duration of pregnancy, or not attend any exercise program (controls). The primary outcome was maternal weight gain during pregnancy. Secondary outcomes included fetal cardiac function parameters evaluated at 20, 28 and 36 weeks' gestation, Cesarean section, preterm delivery, induction of labor and birth weight. A sample size of 45 in each group was planned to detect differences in maternal weight gain of at least 1 kg, with a power of > 80% and α of 0.05. RESULTS: During the study period, 120 women were randomized into the exercise (n = 75) and control (n = 45) groups. Following exclusions, the final cohort consisted of 42 women in the exercise group and 43 in the control group. Baseline characteristics (maternal age, prepregnancy body mass index, parity, conception by in-vitro fertilization, Caucasian ethnicity, physical exercise prior to pregnancy and smoker) were similar between the two groups. No differences were found between the groups in maternal weight at 20, 28, 36 and 38 weeks' gestation or in weight gain at 38 weeks. However, the proportion of women with weight loss ≥ 9 kg at 6 weeks postpartum was higher in the exercise compared with the control group (68.2% vs 42.8%; relative risk 1.593; P = 0.02). The ductus arteriosus pulsatility index (DA-PI) at 20 weeks (2.43 ± 0.40 vs 2.26 ± 0.33, P < 0.05) and the ejection fraction (EF) at 36 weeks (0.85 ± 0.13 vs 0.81 ± 0.11, P < 0.05) were higher in the exercise compared with the control group. All other evaluated fetal cardiac function parameters were similar between the two groups. CONCLUSIONS: Performing exercise during pregnancy is not associated with a reduction in maternal weight gain but increases weight loss at 6 weeks postpartum. Physical exercise during pregnancy is associated with increased fetal DA-PI at 20 weeks and EF at 36 weeks, which could reflect adaptive mechanisms. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

BNC nanoshells: a novel structure for atomic storage.

Quantum molecular dynamics (QMD) and density functional theory are employed in this work in order to study the structural and electronic properties of carbon, boron nitride or hybrid BNC nanoshells. The studied nanoshells can be formed by stacking two zigzag graphene nanoribbons, two zigzag boron nitride nanoribbons or one zigzag graphene nanoribbon on a boron nitride nanoribbon. In all cases only one of the edges of the ribbon is passivated, while the other one is left unpassivated. Our QMD results show that these nanoribbons collapse just a few femtoseconds after the beginning of the simulation, forming a coalesced structure in the shape of a shell. Our band structure calculations revealed that this structures may be metallic or semiconductor, depending on its stoichiometry. Furthermore, a spin splitting for energies near the Fermi level is predicted for both the pure carbon and the hybrid BNC-nanoshell systems. We further show that when a transverse electric field is applied to these systems, the nanoshell structure tends to open up. This effect can lead to the application of these nanoshells for molecular storage. As a proof of concept, We investigate this storage effect for the H2 molecule.

Atypical Exciton-Phonon Interactions in WS2 and WSe2 Monolayers Revealed by Resonance Raman Spectroscopy.

Resonant Raman spectroscopy is a powerful tool for providing information about excitons and exciton-phonon coupling in two-dimensional materials. We present here resonant Raman experiments of single-layered WS2 and WSe2 using more than 25 laser lines. The Raman excitation profiles of both materials show unexpected differences. All Raman features of WS2 monolayers are enhanced by the first-optical excitations (with an asymmetric response for the spin-orbit related XA and XB excitons), whereas Raman bands of WSe2 are not enhanced at XA/B energies. Such an intriguing phenomenon is addressed by DFT calculations and by solving the Bethe-Salpeter equation. These two materials are very similar. They prefer the same crystal arrangement, and their electronic structure is akin, with comparable spin-orbit coupling. However, we reveal that WS2 and WSe2 exhibit quite different exciton-phonon interactions. In this sense, we demonstrate that the interaction between XC and XA excitons with phonons explains the different Raman responses of WS2 and WSe2, and the absence of Raman enhancement for the WSe2 modes at XA/B energies. These results reveal unusual exciton-phonon interactions and open new avenues for understanding the two-dimensional materials physics, where weak interactions play a key role coupling different degrees of freedom (spin, optic, and electronic).

Transport properties through hexagonal boron nitride clusters embedded in graphene nanoribbons.

First-principles calculations are employed in the study of the electronic and quantum transport properties of hexagonally shaped boron nitride (h-BN) clusters embedded in either zigzag or armchair graphene nanoribbons. Chemical doping of the h-BN cluster was taken into consideration by using carbon atoms to replace either the boron (B27N24C3) or the nitrogen (B27N24C3) sites in the central ring. While the quantum conductance of the system with zigzag edges is found to be spin-dependent, it was observed that the system with an armchair edge requires an electron imbalance in order to show a spin-dependent conductance. Furthermore, the possibility of molecular adsorption onto these doped systems is studied. The effects of the attached molecules to the quantum conductance shows the potential of these hybrid systems for molecular sensing applications.

Optoelectronic modulation by multi-wall carbon nanotubes.

We report the observation of photoconduction and a strong nonlinear optical absorptive response exhibited by multi-wall carbon nanotubes. An aerosol pyrolysis method was employed for the preparation of the samples. Measurements of the optical transmittance with 7 ns pulses at 1064 nm wavelength allowed us to identify a two-photon absorption effect as the main mechanism of third-order nonlinearity. Photoconductive experiments at 445 nm wavelength seem to confirm the possibility for generating non-resonant multi-photonic absorption processes in the multi-wall carbon nanotubes. By the optical control of the conductivity in the nanotubes, we implement an optoelectronic amplitude modulator device with potential applications for sharp selective functionalities.

ROS evaluation for a series of CNTs and their derivatives using an ESR method with DMPO.

Carbon nanotubes (CNTs) are important materials in advanced industries. It is a concern that pulmonary exposure to CNTs may induce carcinogenic responses. It has been recently reported that CNTs scavenge ROS though non-carbon fibers generate ROS. A comprehensive evaluation of ROS scavenging using various kinds of CNTs has not been demonstrated well. The present work specifically investigates ROS scavenging capabilities with a series of CNTs and their derivatives that were physically treated, and with the number of commercially available CNTs. CNT concentrations were controlled at 0.2 through 0.6 wt%. The ROS scavenging rate was measured by ESR with DMPO. Interestingly, the ROS scavenging rate was not only influenced by physical treatments, but was also dependent on individual manufacturing methods. Ratio of CNTs to DMPO/ hydrogen peroxide is a key parameter to obtain appropriate ROS quenching results for comparison of CNTs. The present results suggest that dangling bonds are not a sole factor for scavenging, and electron transfer on the CNT surface is not clearly determined to be the sole mechanism to explain ROS scavenging.

Nanotechnology: 'buckypaper' from coaxial nanotubes.

Double-walled carbon nanotubes are needed in a pure, highly crystalline form before features such as their electronic properties, thermal transport and mechanical behaviour can be investigated. Here we fabricate a paper-like material that consists of hexagonally packed bundles of clean, coaxial carbon nanotubes whose double walls vary little in diameter; it is prepared in high yields using chemical-vapour deposition with a conditioning catalyst and two-step purification. Our results will enable investigation of the physical properties of double-walled carbon nanotubes, which are predicted to be superior to those of both their single- and multiwalled relatives.

Controlling edge morphology in graphene layers using electron irradiation: from sharp atomic edges to coalesced layers forming loops.

Recent experimental reports indicate that Joule heating can atomically sharpen the edges of chemical vapor deposition grown graphitic nanoribbons. The absence or presence of loops between adjacent layers in the annealed materials is the topic of a growing debate that this Letter aims to put to rest. We offer a rationale explaining why loops do form if Joule heating is used alone, and why adjacent nanoribbon layers do not coalesce when Joule heating is applied after high-energy electrons first irradiate the sample. Our work, based on large-scale quantum molecular dynamics and electronic-transport calculations, shows that vacancies on adjacent graphene sheets, created by electron irradiation, inhibit the formation of edge loops.

Magnetic properties of encapsulated nanoparticles in nitrogen-doped multiwalled cabon nanotubes embedded in SiOx matrices.

We report the production, characterization, thermal transformations (400-1000 degrees C), and magnetic properties of nanoparticles encapsulated in nitrogen-doped multiwall carbon nanotubes (CNx-MWNT), which were embedded in silicon oxide (SiOx) matrices via sol-gel techniques. The vapor chemical deposition (CVD) method with ferrocene-benzelamine mixtures was used to synthesize Fe and Fe3C nanoparticles inside CNx-MWNTs. Composites consisting of CNx-MWNTs (filler) and SiOx (matrix) were fabricated and thermally treated to different temperatures and exposure times (t). All samples were characterized using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), thermogravimetic analysis (TGA), and magnetometry (vibrating sample). We found that upon thermal treatment, the ferromagnetic nanoparticles modify their morphology, composition and aspect ratio, thus resulting in drastic changes in the magnetic and structural properties. In particular, as produced encapsulated nanoparticles mainly consisting of Fe and Fe3C phases were thermally modified into magnetite (Fe3O4). We have also observed that the hysteresis loops are very sensitive to the thermal treatment of the sample. Thus we can control the magnetic properties of the samples using thermal treatments.

Spectroscopic characterization of N-doped single-walled carbon nanotube strands: an X-ray photoelectron spectroscopy and Raman study.

We have studied in detail the carbon and nitrogen bonding environments in nitrogen-doped single-walled carbon nanotubes (SWCNTs). The samples consisting of long strands of N-doped SWCNTs were synthesized using an aerosol assisted chemical vapor deposition method involving benzylamine-ethanol-ferrocene solutions. The studied samples were produced using different benzylamine concentrations in the solutions, and exhibited a maximum concentration of ca. 0.3%at of N, determined by X-ray photoelectron spectroscopy (XPS). In general, we observed that the ratio between substitutional nitrogen and the pyridine-like bonded nitrogen varied upon the precursor composition. Moreover, we have observed that the sp2-like substitutional configuration of the C-N bond does not exceed the 50% of the total N atomic incorporation. In addition, we have characterized all these samples using Raman spectroscopy and electron microscopy.

Synthesis, electronic structure, and Raman scattering of phosphorus-doped single-wall carbon nanotubes.

Substitutional phosphorus doping in single-wall carbon nanotubes (SWNTs) is investigated by density functional theory and resonance Raman spectroscopy. Electronic structure calculations predict charge localization on the phosphorus atom, generating nondispersive valence and conduction bands close to the Fermi level. Besides confirming sustitutional doping, accurate analysis of electron and phonon renormalization effects in the double-resonance Raman process elucidates the different nature of the phosphorus donor doping (localized) when compared to nitrogen substitutional doping (nonlocalized) in SWNTs.

Metallic and ferromagnetic edges in molybdenum disulfide nanoribbons.

The magnetic and electronic properties of MoS(2) nanoribbons with zigzag and armchair edges are investigated using LSDA-DFT. We found that the properties of the nanoribbons are very different from bulk MoS(2) due to edge states. Armchair nanoribbons could be metallic and exhibit a magnetic moment; however, when passivating with hydrogen, they become semiconducting. Zigzag nanoribbons are metallic and exhibit unusual magnetic properties regardless of passivation. Our results could explain the recent evidence of ferromagnetism in flat MoS(2) clusters, and motivate the synthesis of novel MoS(2) nanosystems.

Robust water desalination membranes against degradation using high loads of carbon nanotubes.

Chlorine resistant reverse osmosis (RO) membranes were fabricated using a multi-walled carbon nanotube-polyamide (MWCNT-PA) nanocomposite. The separation performance of these membranes after chlorine exposure (4800 ppm·h) remained unchanged (99.9%) but was drastically reduced to 82% in the absence of MWCNT. It was observed that the surface roughness of the membranes changed significantly by adding MWCNT. Moreover, membranes containing MWCNT fractions above 12.5 wt.% clearly improved degradation resistance against chlorine exposure, with an increase in water flux while maintaining salt rejection performance. Molecular dynamics and quantum chemical calculations were performed in order to understand the high chemical stability of the MWCNT-PA nanocomposite membranes, and revealed that high activation energies are required for the chlorination of PA. The results presented here confirm the unique potential of carbon nanomaterials embedded in polymeric composite membranes for efficient RO water desalination technologies.

Negative Differential Conductance & Hot-Carrier Avalanching in Monolayer WS2 FETs.

The high field phenomena of inter-valley transfer and avalanching breakdown have long been exploited in devices based on conventional semiconductors. In this Article, we demonstrate the manifestation of these effects in atomically-thin WS2 field-effect transistors. The negative differential conductance exhibits all of the features familiar from discussions of this phenomenon in bulk semiconductors, including hysteresis in the transistor characteristics and increased noise that is indicative of travelling high-field domains. It is also found to be sensitive to thermal annealing, a result that we attribute to the influence of strain on the energy separation of the different valleys involved in hot-electron transfer. This idea is supported by the results of ensemble Monte Carlo simulations, which highlight the sensitivity of the negative differential conductance to the equilibrium populations of the different valleys. At high drain currents (>10 µA/µm) avalanching breakdown is also observed, and is attributed to trap-assisted inverse Auger scattering. This mechanism is not normally relevant in conventional semiconductors, but is possible in WS2 due to the narrow width of its energy bands. The various results presented here suggest that WS2 exhibits strong potential for use in hot-electron devices, including compact high-frequency sources and photonic detectors.

Nanotube brushes: polystyrene grafted covalently on CNx nanotubes by nitroxide-mediated radical polymerization.

Polymer brushes consisting of polystyrene (PS) chains bonded covalently to N-doped multiwalled carbon nanotubes (CNx) were synthesized by a "grafting from" route using nitroxide mediated radical polymerization (NMRP).

Growth of double-walled carbon nanotubes using a conditioning catalyst.

Here we describe the effect of different synthetic conditions on the quality and purity of double-walled carbon nanotubes (DWNTs) with the aid of a conditioning catalyst. By lowering the reaction temperature down to 875 degrees C and utilizing a conditioning catalyst, increased purity and a decreased inner diameter of the DWNTs was achieved, while adverse results were observed with increasing reaction temperature. Based on detailed high-resolution transmission electron microscopy studies on the diameter distribution of the tubes, preferential growth conditions for DWNTs over single-wall carbon nanotubes are identified solely from increased carbon solubility considerations (caused by an increased portion of active carbon species by use of Mo) for the same distribution of metal particles.

Hall and field-effect mobilities in few layered p-WSe2 field-effect transistors.

Here, we present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2. Without dielectric engineering and beyond a T-dependent threshold gate-voltage, we observe maximum hole mobilities approaching 350 cm(2)/Vs at T = 300 K. The hole Hall mobility reaches a maximum value of 650 cm(2)/Vs as T is lowered below ~150 K, indicating that insofar WSe2-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. The gate capacitance, as extracted from the Hall-effect, reveals the presence of spurious charges in the channel, while the two-terminal sheet resistivity displays two-dimensional variable-range hopping behavior, indicating carrier localization induced by disorder at the interface between WSe2 and SiO2. We argue that improvements in the fabrication protocols as, for example, the use of a substrate free of dangling bonds are likely to produce WSe2-based FETs displaying higher room temperature mobilities, i.e. approaching those of p-doped Si, which would make it a suitable candidate for high performance opto-electronics.

Structure and electronic properties of MoS2 nanotubes

Structural and electronic properties as well as the stability of MoS2 nanotubes are studied using the density-functional-based tight-binding method. It is found that MoS2 zigzag ( n,0) nanotubes exhibit a narrow direct band gap and MoS2 armchair ( n,n) possess a nonzero moderate direct gap. Interestingly, the ( n,n) tubes show a small indirect gap similar to the direct gap of ( n,0) nanotubes. Simulated electron diffraction patterns confirm the existence of armchair and zigzag disulphide nanotubes. The structure of the MoS2 nanotube tips is explained by introducing topological defects which produce positive and negative curvature.

New metallic allotropes of planar and tubular carbon

We propose a new family of layered sp(2)-like carbon crystals, incorporating five-, six-, and seven-membered rings in 2D Bravais lattices. These periodic sheets can be rolled so as to generate nanotubes of different diameter and chirality. We demonstrate that these sheets and tubes are metastable and more favorable than C60, and it is also shown that their mechanical properties are similar to those of graphene. Density of states calculations of all structures revealed an intrinsic metallic behavior, independent of orientation, tube diameter, and chirality.