Prediction of Maximum Lactate Concentration During an All-Out Anaerobic Test in Elite Ice Hockey Players.

The lack of specific on-ice tests to predict maximum lactate concentration limits the ability of coaches to better track and develop their ice hockey players. Thus, this study aimed to develop an equation for indirectly assessing the maximum lactate concentration produced from an all-out on-ice skating effort in elite adolescent ice hockey players. Twenty elite male ice hockey players participated in this study (age = 15.7 ± 1.0 year). The lactate anaerobic skating test (LAST) consisted of skating back and forth on an 18.2 m course at maximal speed with abrupt stops at each end for a total of 6 shuttles (total distance = 218.2 m; average time = 52.0 ± 2.0 s). The oxygen uptake was measured using a portable metabolic analyzer (Cosmed K4b2) and the maximum post-exercise lactate concentration with a Lactate Pro analyzer. The variables used to estimate lactate concentration were time, heart rate, number of skating strides in the last shuffle (6th) and the skating stride index. The average maximum lactate concentration was 14.4 mmol· L-1, which is expected in elite players. The analysis of explained common variance using T-test (r2 = 0.759) and linear regression (r2 = 0.863) demonstrates the validity of the model. Additionally, the root mean square error (RMSE = 0.60 mmol· L-1), the mean absolute error (MAE = 0.45mmol· L-1) and the standard error of estimate (SEE = 0.69 mmol· L-1) values further confirm the accuracy of the model. Thus, using simple and easy-to-measure variables (i.e., time and skating stride), coaches will be able to monitor more effectively their players' progress in an effort to optimize their individual on-ice performance.

Assessment of On-Ice Oxygen Cost of Skating Performance in Elite Youth Ice Hockey Players.

ABSTRACT: Allisse, M, Bui, HT, Desjardins, P, Léger, L, Comtois, AS, and Leone, M. Assessment of on-ice oxygen cost of skating performance in elite youth ice hockey players. J Strength Cond Res 35(12): 3466-3473, 2021-The purpose of this study was to evaluate the robustness of equations to predict the oxygen requirement during different skating circumstances commonly found in ice hockey game situations (skating forward, backward, with and without controlling a puck, during cornering and stops and starts). Twenty-four male elite ice hockey players from 3 categories (pee-wee, bantam, and midget) participated in this study. Anthropometric measurements were taken, and 4 different on-ice high-intensity and short-duration tests were performed. Execution time, heart rate, oxygen uptake, skating strides, and a skating efficiency index were measured for each test. A regression equation was calculated for each of the 4 tests providing an estimation of oxygen cost. Correlation coefficients ranged from 0.91 to 0.93, and SEE was between 4.5 and 8.4%, indicating that the precision of the regression algorithms was excellent. The results also suggest that execution time alone, which is the traditional manner to measure skating performance, is a bad estimator of oxygen uptake requirement for this kind of effort (average common variance <11%). Furthermore, age proved to be a determining factor with younger players showing an overall lower level of skating efficiency compared with older players. In addition, the introduction of a skating index also helps to better determine which factor of performance needs to be improved. Using simple and easy-to-measure variables, coaches will be able to obtain information that will allow them to intervene more precisely on the training parameters that will optimize the individual on-ice performance of their players.

Confinement of Dyes inside Boron Nitride Nanotubes: Photostable and Shifted Fluorescence down to the Near Infrared.

Fluorescence is ubiquitous in life science and used in many fields of research ranging from ecology to medicine. Among the most common fluorogenic compounds, dyes are being exploited in bioimaging for their outstanding optical properties from UV down to the near IR (NIR). However, dye molecules are often toxic to living organisms and photodegradable, which limits the time window for in vivo experiments. Here, it is demonstrated that organic dye molecules are passivated and photostable when they are encapsulated inside a boron nitride nanotube (dyes@BNNT). The results show that the BNNTs drive an aggregation of the encapsulated dyes, which induces a redshifted fluorescence from visible to NIR-II. The fluorescence remains strong and stable, exempt of bleaching and blinking, over a time scale longer than that of free dyes by more than 104 . This passivation also reduces the toxicity of the dyes and induces exceptional chemical robustness, even in harsh conditions. These properties are highlighted in bioimaging where the dyes@BNNT nanohybrids are used as fluorescent nanoprobes for in vivo monitoring of Daphnia Pulex microorganisms and for diffusion tracking on human hepatoblastoma cells with two-photon imaging.

Alignment of semiconducting graphene nanoribbons on vicinal Ge(001).

Chemical vapor deposition of CH4 on Ge(001) can enable anisotropic growth of narrow, semiconducting graphene nanoribbons with predominately smooth armchair edges and high-performance charge transport properties. However, such nanoribbons are not aligned in one direction but instead grow perpendicularly, which is not optimal for integration into high-performance electronics. Here, it is demonstrated that vicinal Ge(001) substrates can be used to synthesize armchair nanoribbons, of which ∼90% are aligned within ±1.5° perpendicular to the miscut. When the growth rate is slow, graphene crystals evolve as nanoribbons. However, as the growth rate increases, the uphill and downhill crystal edges evolve asymmetrically. This asymmetry is consistent with stronger binding between the downhill edge and the Ge surface, for example due to different edge termination as shown by density functional theory calculations. By tailoring growth rate and time, nanoribbons with sub-10 nm widths that exhibit excellent charge transport characteristics, including simultaneous high on-state conductance of 8.0 µS and a high on/off conductance ratio of 570 in field-effect transistors, are achieved. Large-area alignment of semiconducting ribbons with promising charge transport properties is an important step towards understanding the anisotropic nanoribbon growth and integrating these materials into scalable, future semiconductor technologies.

Polarization-Resolved Raman Study of Bulk-like and Davydov-Induced Vibrational Modes of Exfoliated Black Phosphorus.

Owing to its crystallographic structure, black phosphorus is one of the few 2D materials expressing strongly anisotropic optical, transport, and mechanical properties. We report on the anisotropy of electron-phonon interactions through a polarization-resolved Raman study of the four vibrational modes of atomically thin black phosphorus (2D phosphane): the three bulk-like modes Ag1, B2g, and Ag2 and the Davydov-induced mode labeled Ag(B2u). The complex Raman tensor elements reveal that the relative variation in permittivity of all Ag modes is irrespective of the atomic motion involved lowest along the zigzag direction, the basal anisotropy of these variations is most pronounced for Ag2 and Ag(B2u), and interlayer interactions in multilayer samples lead to reduced anisotropy. The bulk-forbidden Ag(B2u) mode appears for n ≥ 2 and quickly subsides in thicker layers. It is assigned to a Davydov-induced IR to Raman conversion of the bulk IR mode B2u and exhibits characteristics similar to Ag2. Although this mode is expected to be weak, an electronic resonance significantly enhances its Raman efficiency such that it becomes a dominant mode in the spectrum of bilayer 2D phosphane.

Direct oriented growth of armchair graphene nanoribbons on germanium.

Graphene can be transformed from a semimetal into a semiconductor if it is confined into nanoribbons narrower than 10 nm with controlled crystallographic orientation and well-defined armchair edges. However, the scalable synthesis of nanoribbons with this precision directly on insulating or semiconducting substrates has not been possible. Here we demonstrate the synthesis of graphene nanoribbons on Ge(001) via chemical vapour deposition. The nanoribbons are self-aligning 3° from the Ge〈110〉 directions, are self-defining with predominantly smooth armchair edges, and have tunable width to <10 nm and aspect ratio to >70. In order to realize highly anisotropic ribbons, it is critical to operate in a regime in which the growth rate in the width direction is especially slow, <5 nm h(-1). This directional and anisotropic growth enables nanoribbon fabrication directly on conventional semiconductor wafer platforms and, therefore, promises to allow the integration of nanoribbons into future hybrid integrated circuits.

No Graphene Etching in Purified Hydrogen.

A systematic study has been conducted to investigate the role of hydrogen in the etching reaction of graphene films grown on copper foils. The results at 825 °C and 500 mTorr showed no evidence of graphene etching by purified ultrahigh purity (UHP)-grade hydrogen, whereas graphene films exposed to unpurified UHP-grade hydrogen were considerably etched due to the presence of oxygen or other oxidizing impurities. This finding reveals not only the major impact of oxidizing impurities in the graphene etching reaction, but also entails understanding and controlling the graphene chemical vapor deposition mechanism on copper substrates.

Fano resonances in the midinfrared spectra of single-walled carbon nanotubes.

This work revisits the physics giving rise to the carbon nanotube phonon bands in the midinfrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric line shape and that their effective cross section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that the dopant-induced intraband (not interband) continuum couples strongly to the phonon modes, and that defects created on the sidewall are scattering centers that increase the spectral amplitude of the resonance.

Probing charge transfer at surfaces using graphene transistors.

Graphene field effect transistors (FETs) are extremely sensitive to gas exposure. Charge transfer doping of graphene FETs by atmospheric gas is ubiquitous but not yet understood. We have used graphene FETs to probe minute changes in electrochemical potential during high-purity gas exposure experiments. Our study shows quantitatively that electrochemistry involving adsorbed water, graphene, and the substrate is responsible for doping. We not only identify the water/oxygen redox couple as the underlying mechanism but also capture the kinetics of this reaction. The graphene FET is highlighted here as an extremely sensitive potentiometer for probing electrochemical reactions at interfaces, arising from the unique density of states of graphene. This work establishes a fundamental basis on which new electrochemical nanoprobes and gas sensors can be developed with graphene.

Adhesion of human U937 monocytes to nitrogen-rich organic thin films: novel insights into the mechanism of cellular adhesion.

We present a two-fold study designed to elucidate the adhesion mechanism of human U937 monocytes on novel N-rich thin films deposited by plasma- and VUV photo-polymerisation, so-called "PVP:N" materials. It is shown that there exist sharply-defined ("critical") surface-chemical conditions that are necessary to induce cell adhesion. By comparing the film chemistries at the "critical" conditions, we demonstrate the dominant role of primary amines in the cell adhesion mechanism. Quantitative real-time RT-PCR experiments using U937 cells that had adhered to PVP:N materials for up to 24 h are presented. The adhesion induces a transient expression of cytokines, markers of macrophage activation, as well as a more sustained expression of PPAR gamma and ICAM-I.