Rapid Phase Transition Research Articles

Release of liquid CO2 from the bottom of a duct

This paper presents experimental results of the rapid phase transition of liquid CO2 released from the bottom of a small rectangular duct (BR). The aim is to consider the factors influencing the phase transitions and the release rate if the rupture area is below the liquid level. The tests are initiated by rupturing the diaphragm separating the test section from an atmospheric chamber. Pressure and temperature measurements are used to analyze the phase transition. Also, a high-speed shadowgraph technique is used to visualize the waves. The results are compared with previous top-release tests (TR), where the rupture area is sited above the liquid level. Test results show that the duct’s outlet flow behavior for the BR differs from the TR tests, wherein the gas/two-phase flow is choking. In the BR tests, the shadowgraph images demonstrate that when the liquid/two-phase flows out, the liquid/vapor interface remains nearly fixed until it breaks up. This behavior indicates that the headspace vapor has little influence on the initial evaporation in the BR tests. The results from the current BR tests indicate a lower degree of superheating than in the TR tests (it decreases by 34% for LVF = 66.0%), and the evaporation rate is 1.2–1.8 times faster.Graphical abstract

Super-resolution in thin section of lacustrine shale reservoirs and its application in mineral and pore segmentation

Lacustrine shale reservoirs present intricate attributes such as the prevalence of lamination, rapid sedimentary phase transitions, and pronounced heterogeneity. These factors introduce substantial challenges in analyzing and comprehending reservoir characteristics. Thin-section imaging offers a direct medium to observe these traits, yet the intrinsic compromise between image resolution and field of view impedes the concurrent capture of comprehensive details and contextual overview. This study delves into the application of super-resolution (SR) techniques to augment the segmentation of thin-section images from lacustrine shale, an unconventional reservoir. SR application furnishes high-resolution images, facilitating a robust analysis of morphology, texture, edge properties, and target classification. Utilizing data from the lacustrine shale reservoir of the Ordos Basin, we evaluate our methodology and assess the impact of SR enhancement on segmentation. Quantitative results indicate significant improvements, with the Jaccard index for shale increasing from 0.4790 (Low-Resolution) to 0.7803 (ESRGAN) in the Y channel of the YCrCb color space after level set segmentation, exemplifying the efficacy of SR in shale gas and oil reservoirs. This research underscores the necessity to consider lacustrine shale's unique features while formulating and implementing SR techniques for improved information extraction. Furthermore, it highlights SR's potential for propelling future research and industry-specific applications.

Phase transition induced threshold resistive switching in two-dimensional VTe2 nanosheets for Boolean logic operations

Vanadium chalcogenides have been extensively studied owing to the diverse crystallographic structures with various stoichiometric ratios. The metal-to-insulator transition (MIT) widely reported in vanadium chalcogenides is a rapid reversible phase transition that requires small energy, demonstrating potential applications in memory devices. In this work, two-dimensional (2D) vanadium telluride (VTe2) nanosheets are prepared by the chemical vapor deposition method. The synthesized VTe2 nanosheets exhibit volatile threshold switching (TS) behaviors due to the MIT phase transition, which can be further confirmed by the temperature dependent TS behaviors. The TS memristor demonstrates good stability and high reliability with up to 1000 continuous and repeatable writing/erasing operations. Furthermore, based on the TS behaviors, the fabricated memristor can be utilized to implement basic Boolean logic operations of “OR,” “AND,” and “NOT.” This study not only demonstrates the TS behaviors in the 2D VTe2 nanosheets owing to the MIT phase transition but also shows the potential applications of the TS devices in Boolean logic operations.

Mechanically robust all-hydrogel supercapacitor having seamless interfaces among components by rapid phase transition of physical gels

In a flexible energy storage device, the interface between the components not only degrades the electrochemical performance but also makes it mechanically vulnerable. Therefore, interface engineering is important to ensure device performance. Here, we propose a design strategy for the fabrication of seamless energy storage device that maximizes the structural integrity between all-components. Utilizing a rapid phase transition characteristic of agarose, a seamless device composed of carbon cloth, agarose/activated carbon electrode, and agarose electrolyte were prepared. The seamless interface improved areal capacitance and lap-shear strength by 35% (166.6 mF/cm2) and 1000% (12 kPa), respectively, compared to that of the conventional sandwich-type supercapacitor. In addition, the impedance of the seamless device was measured as 80% of that of the sandwich device demonstrating a decrease of interfacial resistance. While the areal capacitance of the seamless device was maintained even after 100 bending cycles, the device failure by interfacial slip for the sandwich device was observed. Considering that flexible electronic devices are subjected to repeated mechanical deformations, the device fabrication strategy using phase changing materials proved to be very effective which can be applied to versatile applications.

Initiator-Free Photocuring 3D-Printable PVA-Based Hydrogel with Tunable Mechanical Properties and Cell Compatibility.

Poly(vinyl alcohol) (PVA)-based hydrogels have attracted great attention and been widely used in biological tissue engineering. With the development of modern medicine, precision medicine requires the customization of medical materials. However, lacking of photocurable functional groups or the performance of rapid phase transition makes PVA-based hydrogels difficult to be customizable molded through photocuring 3D printing technique. In this research, customizable PVA-based hydrogels with high performance through 3D photocurable printing and freezing-thawing (F-T) process are obtained. The ability of 3D-printable is endowed by the introduction of polyvinyl alcohol-styrylpyridine (PVA-SBQ), which can be photo-crosslinked quickly without photoinitiator. Meanwhile, the tunable mechanical properties are achieved by adjusting the mass ratio of PVA-SBQ to PVA, and PVA can offer the physical crosslinking points through freezing-thawing (F-T) process. The hydrogels with high resolution are prepared by digital light procession 3D printing with the mass ratio 1:1 of PVA-SBQ to PVA solution. Attributed to the absence of initiator, and no small molecule residues inside the hydrogels, the hydrogels have good biocompatibility and have the potential to be applicated in the field of biological tissue engineering.

Two first-order phase transitions in hybrid compact stars: Higher-order multiplet stars, reaction modes, and intermediate conversion speeds

We study compact stars with hybrid equations of state consisting of a nuclear outer region and two nested quark phases, each separated from the lower density phase by a strong first-order phase transition. The stability of these models is determined by calculating their radial oscillation modes with different conversion rates between adjacent phases and hence junction conditions for the modes at the phase separation interface between them. In the case when the timescale of transition is faster than the period of oscillations, we recover the traditional stability criterion implying that $\ensuremath{\partial}M/\ensuremath{\partial}{\ensuremath{\rho}}_{c}>0$ on the stable branch(es), where $M$ is the mass and ${\ensuremath{\rho}}_{c}$ is the central density. In the opposite limit of slow conversion, we find stable stellar multiplets beyond triplets consisting of stars that are stable by the usual criterion plus slow-conversion (denoted by $s$) hybrid stars with $\ensuremath{\partial}M/\ensuremath{\partial}{\ensuremath{\rho}}_{c}<0$ that are stabilized due to an alternative junction condition on the fluid displacement field at the interface reflecting the slow rate of conversion. We also study the properties of the reaction mode, the radial mode that only exists for stars with rapid (abbreviated by $r$) phase transitions, in stars with either two rapid phase transitions or alternating rapid and slow phase transitions for the first time. The implications of alternative junction conditions are also examined, with these conditions generally being found to provide stability properties similar to those for a slow conversion rate.

Biomass pellet fueled chemical looping gasification: Reaction kinetics study with a fluidized bed - thermogravimetric analysis

Biomass pellets show the advantages of higher energy density, lower transportation and storage costs compared to powder biomass, making them attractive for future industrial applications. In this work, a fluidized bed-thermogravimetric analysis (FB-TGA) is developed. The gas-solid process for gram-scale biomass pellets under fluidization state at high temperature is characterized. The effects of gasification agents, bed material components and operating conditions on devolatilization and char gasification are investigated. The devolatilization is revealed to be a rapid phase transition process of volatiles, of which the rate is mainly affected by the intense heat and mass transfer with increasing temperature. While the char gasification is significantly slower, taking more than 600 s for all conditions, therefore be considered as the rate-control step. The hematite oxygen carrier can effectively promote the char gasification by breaking the concentration balance of gas components near the char surface. The char reaction kinetics is fitted based on the isothermal differential method. Results show that the cylindrical geometrical contraction model exhibits an excellent linear correlation. With a mass ratio of oxygen carrier/quartz sand of 1:9, the average activation energies of 130.58 kJ/mol and 104.17 kJ/mol are obtained when CO2 and steam as gasifying agents.

Rapid Phase Transitions of Thermotropic Glycolipid Quasicrystal and Frank-Kasper Mesophases: A Mechanistic Rosetta Stone.

Experimental results are presented that serve to lower the barrier for developing the science and technology of non-classical thermotropic glycolipid mesophases, which now include dodecagonal quasicrystal (DDQC) and Frank-Kasper (FK) A15 and σ mesophases that can be produced under mild conditions from a versatile class of sugar-polyolefin conjugates. By employing "alloys" comprised of mono- and disaccharide-polyolefin conjugates, and optionally with vitamin E as a small molecule phase modulator, we report the spontaneous formation of stable A15 mesophases at ambient temperature. We further document a rich thermotropic phase map that includes DDQC, A15, and σ mesophases of tunable periodicity that are connected through rapid thermotropic phase transitions as a function of increasing temperature in the order: liquid-like packing (LLP)→DDQC → A15→σ→ disorder. This first direct observation of a rapid thermotropic A15→σ phase transition provides support for a diffusionless martensitic process proceeding through strain-induced introduction of planar defects into the A15 lattice.

Rapid Phase Transitions of Thermotropic Glycolipid Quasicrystal and Frank‐Kasper Mesophases: A Mechanistic Rosetta Stone

AbstractExperimental results are presented that serve to lower the barrier for developing the science and technology of non‐classical thermotropic glycolipid mesophases, which now include dodecagonal quasicrystal (DDQC) and Frank–Kasper (FK) A15 and σ mesophases that can be produced under mild conditions from a versatile class of sugar‐polyolefin conjugates. By employing “alloys” comprised of mono‐ and disaccharide‐polyolefin conjugates, and optionally with vitamin E as a small molecule phase modulator, we report the spontaneous formation of stable A15 mesophases at ambient temperature. We further document a rich thermotropic phase map that includes DDQC, A15, and σ mesophases of tunable periodicity that are connected through rapid thermotropic phase transitions as a function of increasing temperature in the order: liquid‐like packing (LLP)→DDQC → A15→σ→ disorder. This first direct observation of a rapid thermotropic A15→σ phase transition provides support for a diffusionless martensitic process proceeding through strain‐induced introduction of planar defects into the A15 lattice.

Effect of N2 and CO2 on explosion behavior of hydrogen-air mixtures in non-premixed state

In this paper, the suppression effects of non-premixed inert gas (N2, CO2) on hydrogen-air explosion behaviors are experimentally studied. The effects of N2 and CO2 addition on flame propagation, explosion pressure and flame length are analyzed. The results show that N2 and CO2 can effectively reduce the explosion hazard in non-premixed state. The mixing process of non-premixed gases leads to the development of turbulent flame, but the suppression of inert gas on explosion exceeds the promotion of turbulent flame. Under the action of N2 and CO2, the energy of the flame decreases, and the front contour becomes blurred. When the fuel zone is only set at the ignition end, with the suppression of N2 and CO2, the maximum explosion pressure is reduced by 35.1% and 50.6%, respectively. It is worth noting that the high-frequency periodic oscillation and pressure soaring appear in the pressure histories, which are attributed to the rapid phase transition of water. Furthermore, the two inert gases can significantly reduce the chemical reaction rate and heat release rate during the explosion, which is reflected in the decrease of the maximum flame length. It is found that N2 and CO2 have different explosion suppression effects and mechanisms, but CO2 has better suppression performance on hydrogen-air explosion.

Kinetic Improvement of the Gel-sol Transition of Thermoresponsive Hydrogels Utilizing a High Surface Area Host

Rapid reversible phase transitions of biocompatible thermoresponsive sealants (TRS) upon cooling are required for their practical application in many sectors. The gel–sol transition rate of the TRS studied here [poly(N-isopropylacrylamide-co-butyl acrylate 95:5, number-averaged molecular weight = 7–64 kg mol–1] after being heated to 50 °C is slowed dramatically. The unheated materials return to a free-flowing sol form in a matter of minutes, while the heated materials remain in a gel or solid form for hours. The gel–sol transition of these polymers is enhanced in the presence of a high surface area host in the form of open-cell foams such as polyurethane (PUR), polyimide (PIM), hydrophilic polyurethane Aquazone (AQZ), and neoprene (NEO). An enhanced rate of sol formation on cooling and high TRS recovery (74–99%) were observed across a range of foam types and pore sizes when compared to samples stored without a host (9% recovery). Polyurethane demonstrates the greatest increase in TRS recovery (∼10-fold) after storing the TRS solution at 50 °C followed by cooling for 10 min at 0 °C, maintaining the thermally reversible gelation and mechanical strength of the TRS. Crucially, rheological measurements demonstrate that the viscosity, storage modulus, and loss modulus are not significantly affected by storage in a foam host. This work may be potentially extended to other injectable in situ forming hydrogels, which have suitable mechanical strength but less ideal phase transition times.

Пожарная опасность взрывных режимов испарения сжиженного природного газа

Introduction. The fire hazard of explosive regimes of liquefied natural gas (LNG) evaporation was analyzed on the basis of the published research findings. These regimes include the rollover and the rapid phase transition (RPT). Characteristics of explosive regimes of LNG evaporation. Rollover occurs in LNG storage tanks in case of spontaneous mixing of LNG layers having different temperatures and densities. These layers emerge when the “fresh” product is loaded into a vessel containing the residual amount of product stored there before. A rapid increase in the LNG evaporation rate accompanies a pressure rise inside the tank, which can exceed an allowable pressure of the tank. RPT occurs at a contact of LND and water in the case of a release of liquefied natural gas onto a water surface. An explosive evaporation of LNG can cause in this case a formation of a shock wave and a large-scale vapor cloud. Investigations of rollovers. It was mentioned that a stratification of LNG in a storage tank is a necessary condition of a rollover. Two layers with different temperatures and densities are formed during this stratification. A superheating of a lower layer occurs at a heat exchange between the LNG and tank walls with a decrease of a density of this layer. A preferential evaporation of light components of LNG (methane, nitrogen) takes place in the upper layer, and the density of this layer increases. When the densities of these layers are equalized a spontaneous mixing of these layers occurs with an explosive evaporation of the product in the lower superheated layer. A time delay of rollover can reach 60–70 hours after the supply of the “fresh” product into the tank with “old” product. Investigations of a rapid phase transition. An energy released at the explosive evaporation and a pressure in a shock wave depend on many factors such as a LNG release rate, a position of a source of the LNG release — over or under a water level, a product composition, water temperature etc. It was found that a pressure hazardous for buildings and structures can take place at distances 250–500 m from the point of the release. The empirical correlation was proposed connecting a water temperature at the RPT occurrence and the superheating tempe­rature of LNG at which a boiling takes place in the regime of a homogeneous nucleation. Conclusions. It was shown that a realization of the explosive regimes of the LNG evaporation increases a fire hazard of objects for a storage and a transportation of liquefied natural gas. Recommendations for a prevention of such regimes are formulated.

Higgs boson induced reheating and ultraviolet frozen-in dark matter

A reheating phase in the early universe is an essential part of all inflationary models during which not only the Standard Model (SM) quanta are produced but it can also shed light on the production of dark matter. In this work, we explore a class of reheating models where the reheating is induced by a cubic interaction of the inflaton ϕ to the SM Higgs boson h of the form ghϕMPlϕ|h|2 adopting the α-attractor T-model of inflation. Assuming inflaton as a background field such interaction implies a ϕ-dependent mass term of the Higgs boson and a non-trivial phase-space suppression of the reheating efficiency. As a consequence, the reheating is prolonged and the maximal temperature of the SM thermal bath is reduced. In particular, due to oscillations of the inflaton field the ϕ-dependent Higgs boson mass results in periodic transitions between phases of broken and unbroken electroweak gauge symmetry. The consequences of these rapid phase transitions have been studied in detail. A purely gravitational reheating mechanism in the presence of the inflaton background, i.e., for ghϕ = 0, has also been investigated. It turned out that even though it may account for the total production of SM radiation in the absence of ghϕ, its contribution to the reheating is subdominant for the range of ghϕ considered in this work. Approximate analytical solutions of Boltzmann equations for energy densities of the inflaton and SM radiation have been obtained. As a dark matter candidate a massive Abelian vector boson, Xμ, has been considered. Various production mechanisms of Xμ have been discussed including (i) purely gravitational production from the inflaton background, (ii) gravitational freeze-in from the SM quanta, (iii) inflaton decay through a dim-5 effective operator, and (iv) Higgs portal freeze-in and Higgs decay through a dim-6 effective operator. Parameters that properly describe the observed relic abundance have been determined.

Thermoresponsive Hydrogel-Enabled Thermostatic Photothermal Therapy for Enhanced Healing of Bacteria-Infected Wounds.

Photothermal therapy (PTT) has emerged as an attractive technique for the treatment of bacterial infections. However, the uncontrolled heat generation in conventional PTT inevitably causes thermal damages to healthy tissues and/or organs. It is thus essential to develop a smart and universal strategy to regulate the photothermal equilibrium temperature to a preset safe threshold. Herein, a thermoresponsive hydrogel-enabled thermostatic PTT system for enhanced healing of bacteria-infected wounds is reported. In this system, the near-infrared (NIR)-triggered heat generation by photothermal nanomaterials is spontaneously transferred to a thermoresponsive hydrogel with a lower critical solution temperature (LCST), leading to its rapid phase transition by forming considerable light-scattering centers to block NIR penetration. Such a dynamic and reversible process automatically regulates the photothermal equilibrium temperature to the phase-transition point of the LCST-type hydrogel. In contrast to temperature-uncontrolled conventional PTT with severe thermal damages, the thermoresponsive hydrogel-enabled thermostatic PTT provides effective protection on healthy tissues and/or organs, which remarkably accelerates wound healing by efficient bacterial eradication. This study establishes a smart, simple and universal PTT platform, holding great promise in the safe and efficient treatment of bacterial skin infections.

A switchable deep eutectic solvent for the homogeneous liquid-liquid microextraction of flavonoids from “Scutellariae Radix”

A homogeneous liquid-liquid microextraction (HLLME) was established based on a switchable deep eutectic solvent (DES) for the preconcentration and determination of six flavonoids with different polarity in “Scutellariae Radix” combined with high performance liquid chromatography (HPLC). A switchable DES composed of N,N-dimethylethanolamine (DMEA) and heptanoic acid was used as an extraction solvent in the HLLME method, which was miscible thoroughly with the aqueous sample phase initially, and then underwent rapid phase transition induced by the addition of an inorganic acid. After the extraction, the upper hydrophobic layer was recovered for HPLC analysis. Different experimental parameters were optimized, and the optimal extraction conditions were as follows: the switchable DES extraction phase, 90 µL of DMEA-heptanoic acid (1:1 mole ratio); phase-switching trigger, 100 µL of 5 mol/L HCl; 10% (w/v) of salt concentration in sample phase; extraction time, 0.3 min. Furthermore, the structures of the switchable DES and the upper hydrophobic layer were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and differential scanning calorimetry to illustrate the phase-switching mechanism of the extraction phase during the extraction process. Under the optimized conditions, the enrichment factors for six target analytes were between 0.4 and 104. The calibration curves were linear (r≥0.9866) in the range of 0.033–8.65 mg/L for scutellarin, 0.022–5.77 mg/L for baicalin, 0.0033–0.865 mg/L for scutellarein and wogonoside, and 0.0022–0.577 mg/L for baicalein and wogonin, respectively. Low detection limits (≤8.0 × 10−3 mg/L) and quantification limits (≤2.4 × 10−2 mg/L) as well as good precisions (relative standard deviations lower than 9.2%) and acceptable accuracies (spiked recoveries 89.3–114.4%) were also obtained. The proposed method is a simple, fast, and eco-friendly sample pretreatment method.

Size-independent scaling analysis for explosive percolation.

The Achlioptas process, a percolation algorithm on random network, shows a rapid second-order phase transition referred to as explosive percolation. To obtain the transition point and critical exponent β for percolations on a random network, especially for bond percolations, we propose a new scaling analysis that is independent of the system size. The transition point and critical exponent β are estimated for the product-rule (PR) and daCosta-Dorogovtsev-Goltsev-Mendes (dCDGM) (m=2) models of the Achlioptas process, as well as for the Erdős-Rényi (ER) model, which is a classical model in which the analytic values are known. The validity of the scaling analysis is confirmed, especially for the transition point. The estimations of β are also consistent with previously reported values for the ER and dCDGM(2) models, whereas the β estimation for the PR model deviates somewhat. By introducing a parameter representing the maximum cluster size, we develop an extrapolation scheme for the critical exponent β from the simulation just at the transition point in order to obtain a more accurate value. The estimated value of β is improved compared with that obtained by the scaling analysis for the ER model and is also consistent with the β value obtained for the dCDGM(2) model, whereas its deviation from the previously reported value is larger for the PR model. We discuss the accuracy of the present estimations and draw conclusions about their reliability.

Nanofiber reinforced alginate hydrogel for leak-proof delivery and higher stress loading in nucleus pulposus

Injectable hydrogels effectively remodel degenerative nucleus pulposus (NP) with a resemblance to the in vivo microenvironment. However, the pressure within the intervertebral disc requires load-bearing implants. The hydrogel must undergo a rapid phase transition upon injection to avoid leakage. In this study, an injectable sodium alginate hydrogel was reinforced with silk fibroin nanofibers with core-shell structures. The nanofiber-embedded hydrogel provided support to adjacent tissues and facilitated cell proliferation. Platelet-rich plasma (PRP) was incorporated into the core-shell nanofibers for sustained release and enhanced NP regeneration. The composite hydrogel exhibited excellent compressive strength and enabled leak-proof delivery of PRP. In rat intervertebral disc degeneration models, radiography and MRI signal intensities were significantly reduced after 8 weeks of injections with the nanofiber-reinforced hydrogel. The biomimetic fiber gel-like structure was constructed in situ, providing mechanical support for NP repair, promoting the reconstruction of the tissue microenvironment, and finally realizing the regeneration of NP.

Phase-Transitional Bismuth-Based Metals enable Rapid Embolotherapy, Hyperthermia, and Biomedical Imaging.

Embolization has been an important minimally invasive therapy for occlusion of malfunctioned vasculature and tumor treatment via target delivering embolic agents. The limitation of conventional embolic agents, such as fabrication process, precipitation time, invisibility, and lack of integrated functions often leads to insufficient embolization efficacy. To overcome these drawbacks, a multifunctional bismuth (Bi)-based liquid embolic agent for simultaneous realization of embolotherapy, thermotherapy, as well as high-contrast biomedical imaging is proposed. Benefitting from the suitable melting point, flexible nature, metallic merit, and easygoing operation via injection, the versatile embolic agent can achieve rapid liquid-solid phase transition, magnetic hyperthermia, and multimodal imaging capability. The Bi-based materials are demonstrated with excellent arteriovenous embolization efficiency and favorable biocompatibility according to in vivo investigations. Introduction of the liquid embolic agent to tumor arteries achieves evident tumor regression and rather clear imaging under computed tomography (CT), magnetic resonance imaging(MRI), and thermographs for consistently tracking the implants over the biological body. Further, the combined therapy coupled with thermotherapy exhibits improved therapeutic efficiency with formation of necrosis and total tumor eradiation at day 15after the treatment. The present innovative embolic agent and the surgical principle provide a promising modality for embolization and potential theranostic platform of tumors.

Surface engineering with oxidized Ti3C2Tx MXene enables efficient and stable p-i-n-structured CsPbI3 perovskite solar cells

<h2>Summary</h2> All-inorganic CsPbI₃ perovskite has a near-ideal band gap, high thermal stability, and simple material composition, thus presenting a promising option for developing perovskite/Si tandem solar cells. However, CsPbI₃ undergoes a rapid phase transition under exposure to moisture and exhibits a significant performance gap relative to other perovskite compounds, particularly in the p-i-n structure favored for perovskite/Si tandems. Here, we demonstrate highly efficient and stable p-i-n-structured CsPbI₃ perovskite solar cells by surface engineering the CsPbI₃ layer with oxidized Ti₃C₂T_x MXene (OMXene) nanoplates via spray coatings. OMXene provides a physical barrier against moisture and improves charge separation at the perovskite-electron transporting layer interface via an enhanced electric field. Consequently, we demonstrated CsPbI₃/OMXene-based p-i-n devices with efficiencies of 19.69% for 0.096-cm² cells and 14.64% for 25-cm² minimodules. The encapsulated minimodule showed good stability, retaining ∼85% of the initial efficiency under simultaneous damp heat (85°C/85% relative humidity) and 1-sun light soaking for over 1,000 h.

Effects of exercise anticipation on cardiorespiratory coherence.

In this study, we explored the role of feedforward mechanisms in triggering cardiorespiratory adjustments before the onset of exercise. To isolate the feedforward aspects, we examined the effect of exercise anticipation on cardiorespiratory coherence. Twenty‐nine healthy males (age = 18.8 [0.96] years) were subjected to bicycle (BE) and handgrip exercise (H) at two different intensities, viz., low and high. Bicycle exercise was performed in a unilateral (left‐ and right‐sided) or bilateral mode, whereas handgrip was performed only in a unilateral mode. Single‐lead ECG and respiratory rhythm, measured in the 5 min of anticipation phase before the onset of exercise, were used for analysis. Coherence was computed between ECG‐derived instantaneous heart rate and respiratory signal. Average coherence in the high‐frequency band (0.15–0.4 Hz) was used to estimate respiratory sinus arrhythmia (RSA). We found that coherence decreased with the anticipation of exercise relative to baseline (baseline = 0.54 [0.16], BE = 0.41 [0.12], H = 0.39 [0.12], p < 0.001). The decrease was greater for high intensity exercise (low = 0.42 [0.11], high = 0.37 [0.1], p < 0.001). The fall of coherence with intensity was stronger for bicycle exercise (BE: low = 0.44 [0.12], high = 0.37 [0.12], H: low = 0.4 [0.12], high = 0.37 [0.12], p = 0.00433). The expectation of bilateral exercise resulted in lower coherence compared to unilateral exercise (right‐sided = 0.45 [0.16], left‐sided = 0.4 [0.16], bilateral = 0.36 [0.15], unilateral vs. bilateral: p < 0.001), and the left‐sided exercise had lower coherence compared to that of the right (left‐sided vs. right‐sided: p = 0.00925). Handgrip exercise showed similar trend (right‐sided = 0.4 [0.15], left‐sided = 0.37 [0.14], p = 0.0056). In conclusion, feedforward RSA adjustments in anticipation of exercise covaried with subsequent exercise‐related features like intensity, muscle mass (unilateral vs. bilateral), and the exercise side (left vs. right). The left versus the right difference in coherence indicates autonomic asymmetry. Feedforward changes in RSA are like those seen during actual exercise and might facilitate the rapid phase transition between rest and exercise.