Critical Tension Research Articles

Investigations on critical parameters, growth, structural and spectral studies of beta-alaninium picrate (BAP) single crystals

Beta-alaninium picrate (BAP) salt has been synthesized and the solubility of the synthesized sample in double distilled water was determined at different temperatures. Solution stability was studied by observing the metastable zone width by employing the polythermal method. Induction period values for different supersaturation ratios at room temperature were determined based on the isothermal method. The nucleation parameters such as critical radius, critical free energy change, interfacial tension, and nucleation rate have been estimated for BAP salt on the basis of the classical nucleation theory. The lattice parameters of the grown BAP crystal were determined using the x-ray diffraction (XRD) technique. The reflection planes of the sample were confirmed by the powder XRD study and diffraction peaks were indexed. Fourier transform infrared spectroscopy and Fourier transform–Raman studies were used to confirm the presence of various functional groups in the BAP crystal. The nonlinear optical property of the grown crystal was studied using the Kurtz–Perry powder technique. UV–visible spectral studies were carried out to understand optical transparency and the type of band gap of the grown BAP crystal.

A product of its environment: the epaulette shark (Hemiscyllium ocellatum) exhibits physiological tolerance to elevated environmental CO2.

Ocean acidification, resulting from increasing anthropogenic CO2 emissions, is predicted to affect the physiological performance of many marine species. Recent studies have shown substantial reductions in aerobic performance in some teleost fish species, but no change or even enhanced performance in others. Notably lacking, however, are studies on the effects of near-future CO2 conditions on larger meso and apex predators, such as elasmobranchs. The epaulette shark (Hemiscyllium ocellatum) lives on shallow coral reef flats and in lagoons, where it may frequently encounter short-term periods of environmental hypoxia and elevated CO2, especially during nocturnal low tides. Indeed, H. ocellatum is remarkably tolerant to short periods (hours) of hypoxia, and possibly hypercapnia, but nothing is known about its response to prolonged exposure. We exposed H. ocellatum individuals to control (390 µatm) or one of two near-future CO2 treatments (600 or 880 µatm) for a minimum of 60 days and then measured key aspects of their respiratory physiology, namely the resting oxygen consumption rate, which is used to estimate resting metabolic rate, and critical oxygen tension, a proxy for hypoxia sensitivity. Neither of these respiratory attributes was affected by the long-term exposure to elevated CO2. Furthermore, there was no change in citrate synthase activity, a cellular indicator of aerobic energy production. Plasma bicarbonate concentrations were significantly elevated in sharks exposed to 600 and 880 µatm CO2 treatments, indicating that acidosis was probably prevented by regulatory changes in acid-base relevant ions. Epaulette sharks may therefore possess adaptations that confer tolerance to CO2 levels projected to occur in the ocean by the end of this century. It remains uncertain whether other elasmobranchs, especially pelagic species that do not experience such diurnal fluctuations in their environment, will be equally tolerant.

The critical tension in the Cascading DGP model

We study the behaviour of weak gravitational fields in the 6D Cascading DGP model using a bulk-based approach. To deal with the ambiguity in the thin limit of branes of codimension higher than one, we consider a specific regularization of the internal structure of the branes where the 5D brane can be considered thin with respect to the 4D one. We consider the solutions corresponding to pure tension sources on the 4D brane, and study perturbations at first order around these background solutions. We adopt a 4D scalar-vector-tensor decomposition, and focus on the scalar sector of perturbations. We show that, in a suitable 4D limit, the trace part of the 4D metric perturbations obeys a decoupled equation which suggests that it is a ghost for background tensions smaller than a critical tension, while it is a healthy field otherwise. We give a geometrical interpretation of the existence of the critical tension and of the reason why the relevant field is a ghost or not depending on the background tension. We however find a value of the critical tension which is different from the one already found in the literature. Differently from the results in the literature, our analysis implies that, choosing the background tension suitably, we can construct ghost-free models for any value of the free parameters of the theory. We suggest that the difference lies in the procedure used to evaluate the pillbox integration across the codimension-2 brane. We confirm the validity of our analysis by performing numerically the integration in a particular case where the solution inside the thick cod-2 brane is known exactly. We stress that the singular structure of the perturbation fields in the nested branes set-ups is very subtle, and that great care has to be taken when deriving the codimension-2 junction conditions.

Exploring the consequences of mitochondrial differences arising through hybridization of sunfish

Previous studies have shown evidence of genomic incompatibility and mitochondrial enzyme dysfunction in hybrids of bluegill (Lepomis macrochirus Rafinesque) and pumpkinseed (Lepomis gibbosus Linnaeus) sunfish (Davies et al., 2012 Physiol. Biochem. Zool. 85, 321–331). We assessed if these differences in mitochondria had an impact on metabolic processes that depend on mitochondrial function, specifically hypoxia tolerance and recovery from burst exercise. Bluegill, pumpkinseed, and their hybrids showed no difference in the critical oxygen tension (Pcrit) and no differences in tissue metabolites measured after exposure to 10% O2 for 30min. In contrast, loss of equilibrium (LOE) measurements showed that hybrids had reduced hypoxia tolerance and lacked the size-dependence in hypoxia tolerance seen in the parental species. However, we found no evidence of systematic differences in metabolite levels in fish after LOE. Furthermore, there were abundant glycogen reserves at the point of loss of equilibrium. The three genotypes did not differ in metabolite status at rest, showed an equal disruption at exhaustion, and similar metabolic profiles throughout recovery. Thus, we found no evidence of a mitochondria dysfunction in hybrids, and mitochondrial differences and oxidative metabolism did not explain the variation in hypoxia tolerance seen in the hybrid and two parental species.

Hypoxia-inducible factor-1 mediates adaptive developmental plasticity of hypoxia tolerance in zebrafish, Danio rerio.

In recent years, natural and anthropogenic factors have increased aquatic hypoxia the world over. In most organisms, the cellular response to hypoxia is mediated by the master regulator hypoxia-inducible factor-1 (HIF-1). HIF-1 also plays a critical role in the normal development of the cardiovascular system of vertebrates. We tested the hypothesis that hypoxia exposures which resulted in HIF-1 induction during embryogenesis would be associated with enhanced hypoxia tolerance in subsequent developmental stages. We exposed zebrafish (Danio rerio) embryos to just 4 h of severe hypoxia or total anoxia at 18, 24 and 36 h post-fertilization (hpf). Of these, exposure to hypoxia at 24 and 36 hpf as well as anoxia at 36 hpf activated the HIF-1 cellular pathway. Zebrafish embryos that acutely upregulated the HIF-1 pathway had an increased hypoxia tolerance as larvae. The critical window for hypoxia sensitivity and HIF-1 signalling was 24 hpf. Adult male fish had a lower critical oxygen tension (Pcrit) compared with females. Early induction of HIF-1 correlated directly with an increased proportion of males in the population. We conclude that mounting a HIF-1 response during embryogenesis is associated with long-term impacts on the phenotype of later stages which could influence both individual hypoxia tolerance and population dynamics.

Modified Theories of Gravity

The recent observational data in cosmology seem to indicate that the universe is currently expanding in an accelerated way. This unexpected conclusion can be explained assuming the presence of a non-vanishing yet extremely fine tuned cosmological constant, or invoking the existence of an exotic source of energy, dark energy, which is not observed in laboratory experiments yet seems to dominate the energy budget of the Universe. On the other hand, it may be that these observations are just signalling the fact that Einstein's General Relativity is not the correct description of gravity when we consider distances of the order of the present horizon of the universe. In order to study if the latter explanation is correct, we have to formulate new theories of the gravitational interaction, and see if they admit cosmological solutions which fit the observational data in a satisfactory way. Quite generally, modifying General Relativity introduces new degrees of freedom, which are responsible for the different large distance behaviour. On one hand, often these new degrees of freedom have negative kinetic energy, which implies that the theory is plagued by ghost instabilities. On the other hand, for a modified gravity theory to be phenomenologically viable it is necessary that the extra degrees of freedom are efficiently screened on terrestrial and astrophysical scales. One of the known mechanisms which can screen the extra degrees of freedom is the Vainshtein mechanism, which involves derivative self-interaction terms for these degrees of freedom. In this thesis, we consider two different models, the Cascading DGP and the dRGT massive gravity, which are candidates for viable models to modify gravity at very large distances. Regarding the Cascading DGP model, we consider the minimal (6D) set-up and we perform a perturbative analysis at first order of the behaviour of the gravitational field and of the branes position around background solutions where pure tension is localized on the 4D brane. We consider a specific realization of this set-up where the 5D brane can be considered thin with respect to the 4D one. We show that the thin limit of the 4D brane inside the (already thin) 5D brane is well defined, at least for the configurations that we consider, and confirm that the gravitational field on the 4D brane is finite for a general choice of the energymomentum tensor. We also confirm that there exists a critical tension which separates background configurations which possess a ghost among the perturbation modes, and background configurations which are ghost-free. We find a value for the critical tension which is different from the value which has been obtained in the literature; we comment on the difference between these two results, and perform a numeric calculation in a particular case where the exact solution is known to support the validity of our analysis. Regarding the dRGT massive gravity, we consider the static and spherically symmetric solutions of these theories, and we investigate the effectiveness of the Vainshtein screening mechanism. We focus on the branch of solutions in which the Vainshtein mechanism can occur, and we truncate the analysis to scales below the gravitational Compton wavelength, and consider the weak field limit for the gravitational potentials, while keeping all non-linearities of the mode which is involved in the screening. We determine analytically the number and properties of local solutions which exist asymptotically on large scales, and of local (inner) solutions which exist on small scales. Moreover, we analyze in detail in which cases the solutions match in an intermediate region. We show that asymptotically flat solutions connect only to inner configurations displaying the Vainshtein mechanism, while non asymptotically flat solutions can connect both with inner solutions which display the Vainshtein mechanism, or with solutions which display a self-shielding behaviour of the gravitational field. We show furthermore that there are some regions in the parameter space of the theory where global solutions do not exist, and characterize precisely in which regions the Vainshtein mechanism takes place.

Effect of temperature on hypoxia tolerance and its underlying biochemical mechanism in two juvenile cyprinids exhibiting distinct hypoxia sensitivities

It is increasingly important to investigate the effect of temperature on hypoxia tolerance in fish species, as worldwide hypoxia worsens with increases in global warming. We selected the hypoxia-tolerant crucian carp (Carassius carassius) and the hypoxia-sensitive Chinese bream (Parabramis pekinensis) as model fish and investigated their hypoxia tolerance based on the critical oxygen tension of the routine metabolic rate (M˙O2rout) (Pcrit), aquatic surface respiration (ASRcrit) and loss of equilibrium (LOEcrit) after two weeks of acclimation at either 10, 20 or 30°C. We also measured the tissue substrate (glycogen and glucose of muscle and liver) and lactate levels of both normoxia- and hypoxia-treated fish (post-LOE). Crucian carp exhibited significantly lower Pcrit and LOEcrit but not ASRcrit. Crucian carp possessed higher hypoxia tolerance, partially due to a higher tissue glycogen reserve, which provides cellular fuel under severe hypoxia, as well as higher lactate tolerance and clearance ability than Chinese bream. The hypoxia tolerance was maintained in crucian carp but was decreased in Chinese bream as the temperature increased. The difference between the two species is based on the greater recruitment of tissue glycogen, resulting in an increased level of cellular fuel during hypoxia in crucian carp than in Chinese bream. In addition, crucian carp possessed the greater liver lactate clearance capacity, and the smaller increase in the M˙O2rout at higher temperatures compared to Chinese bream. Furthermore, substrate shortage and decreased lactate tolerance at high temperatures in Chinese bream might also contribute to the difference in hypoxia tolerance between the two species.

Strategic niche management from a business perspective: taking cleaner vehicle technologies from prototype to series production

Strategic niche management has been outlined as a policy approach to assist development and diffusion of cleaner new technologies. Based on a case study describing the efforts of a leading actor in the heavy vehicle industry to develop and commercially introduce hybrid-electric vehicles, this paper discusses strategic niche management from the perspective of the manufacturing firm. In particular, the paper analyses experiences from extensive field tests executed in London, tests which involved a number of different manufacturers, hybrid systems and vehicles. The scale of this technological niche added confidence and credibility to the technology and helped opening up an important niche market, which was supported by an extensive subsidy scheme. The analysis shows how the field tests and the subsidies jointly functioned as bridging policies that facilitated an important step in the market formation process. The analysis further points at a critical tension between niches and the volume-oriented business of a major vehicle manufacturer, showing how investments in new technology need to be warranted in market trends and projections of future sales and production volumes to become accepted within a vehicle manufacturer's organization.

Critical-Current Degeneration Dependence on Axial Strain of Bi-based Superconducting Multi-filamentary Composite Tapes

Superconducting materials are always severely restricted in practical engineering applications due to their carrying-current degradation under mechanical loads. Based on Ekin's exponential model and Weibull's distribution function, we propose an empirical degradation model for describing the mechanical deformation influence on the critical-current of Bi-based superconducting multi-filamentary composite tapes under axial loading. The critical currents of superconducting tapes depending on the axial strain are investigated analytically. It is shown that the predictions by the developed degradation model agree with the experimental data, in the processes of axial mechanical loading and unloading on the samples. The effect of the critical tension and compression damage strains on the normalized critical currents is also discussed.

Evaporation from an Ink-Bottle Pore: Mechanisms of Adsorption and Desorption

We present a molecular simulation study of argon adsorption and desorption in ink-bottle pores in order to investigate the effects of pore width, length, and temperature on the form of the hysteresis loop, with particular emphasis on the pressure at which evaporation occurs. We show that intrinsic cavitation occurs only in an ink-bottle pore with a sufficiently long and narrow neck. The tension in the condensed fluid is characterized by the average value of the shortest distance between molecules, and when this reaches a critical value, cavitation occurs. As the neck width is increased or the neck length is decreased, the evaporation mechanism in the cavity switches from cavitation to evaporation at higher pressure than the cavitation pressure (which we call cavitation-like pore opening). For cavitation-like pore opening, the evaporation pressure is greater than the intrinsic cavitation pressure and the tensile strength just prior to evaporation is less than the critical tension. For a given temperature, the reduced pressure of cavitation, (P/P0)cav, is always lower than the cavitation-like pore opening reduced pressure, and (P/P0)cav follows a linear dependence on the temperature. The intersection between the cavitation curve and the cavitation-like pore opening curve for a given neck size is the transition temperature, Ttrans: for T < Ttrans, cavitation-like pore opening is the operating mechanism, while cavitation occurs for T > Ttrans.

Effects of stable and diel-cycling hypoxia on hypoxia tolerance, postprandial metabolic response, and growth performance in juvenile qingbo ( Spinibarbus sinensis )

Abstract To investigate the effects of hypoxia on growth performance, postprandial metabolism and hypoxia tolerance in qingbo (Spinibarbus sinensis), the feeding rate (FR), feeding efficiency (FE), specific growth rate (SGR) and body composition were quantified for fish exposed for 30 d to normoxia, stable hypoxia or diel-cycling hypoxia. In addition, three indices of hypoxia tolerance [aquatic surface respiration threshold (ASR), loss of equilibrium threshold (LOE) and critical oxygen tension (Pcrit)] were measured from fish acclimated to each of the 3 conditions. Fish exposed to diel-cycling hypoxia exhibited a higher SGR compared to those exposed to normoxia, which may reflect the higher FR. Fish exposed to stable hypoxia showed a higher weight gain, higher FE, lower routine metabolic expenditure and higher food assimilation efficiency than fish acclimated to normoxia. Fish in both hypoxia groups showed a different feeding rhythm than the normoxia group. The stable hypoxia group exhibited a lower routine M ˙ O2 and postprandial peak M ˙ O2 but a longer duration compared to the two other groups when measured in normoxic conditions. However, this difference decreased when measured in a hypoxic condition. The Pcrit, ASR and LOE were lowest in the fish acclimated to diel-cycling hypoxia and highest in the normoxia-acclimated fish. Our study suggests that moderate hypoxia is beneficial for growth performance of qingbo in aquaculture.

Dynamics of a conducting polymer jet in an electric field

The dynamics of a non-Newtonian liquid jet emanating from the Taylor cone during electrospinning of a polymer solution has been studied. The viscoelastic properties of the solution are described in terms of the finitely extensible nonlinear elastic FENE-P model. The shape of the jet has been determined, and the current and tension in the jet have been calculated. Calculations have shown the existence of a critical tension at which the jet stops stretching such that it can exhibit time-dependent behavior.

Air‐breathing fishes in aquaculture. What can we learn from physiology?

During the past decade, the culture of air-breathing fish species has increased dramatically and is now a significant global source of protein for human consumption. This development has generated a need for specific information on how to maximize growth and minimize the environmental effect of culture systems. Here, the existing data on metabolism in air-breathing fishes are reviewed, with the aim of shedding new light on the oxygen requirements of air-breathing fishes in aquaculture, reaching the conclusion that aquatic oxygenation is much more important than previously assumed. In addition, the possible effects on growth of the recurrent exposure to deep hypoxia and associated elevated concentrations of carbon dioxide, ammonia and nitrite, that occurs in the culture ponds used for air-breathing fishes, are discussed. Where data on air-breathing fishes are simply lacking, data for a few water-breathing species will be reviewed, to put the physiological effects into a growth perspective. It is argued that an understanding of air-breathing fishes' respiratory physiology, including metabolic rate, partitioning of oxygen uptake from air and water in facultative air breathers, the critical oxygen tension, can provide important input for the optimization of culture practices. Given the growing importance of air breathers in aquaculture production, there is an urgent need for further data on these issues.

A possible superhard orthorhombic carbon

Carbon is a versatile element in the periodic table because of its ability to form various stable and metastable allotropes. In the present work, an orthorhombic carbon allotrope with ‘4-membered rectangles’ is predicated by Particle Swarm Optimization method at 0 GPa. Calculations indicate that this new phase is dynamically and mechanically stable although it has a high enthalpy. Its electronic and mechanical properties such as elastic constants, hardness, ideal tensile strength and shear strength are systematically studied. The results show that it is an indirect band gap crystal with a gap of 2.68 eV; in spite of its elastic anisotropy, the theoretical hardness of 76.2 GPa still makes it a potential superhard material; the obtained ideal tensile strength and shear strength are 69.0 GPa and 75.6 GPa, respectively, confirming its superhard character. The related microscopic deformation mechanisms are also detailedly analyzed through investigating the corresponding charge density, which reveals that the bonds arranged parallel to the b-axis are responsible for the breakdown of the crystal under the critical tension and shear deformations. These studies provide important information for the potential applications of the crystal once it is synthesized.

Prediction of mechanical properties of microstructures through a nonlocal stress field theory

The gradient type of nonlocal stress field theory has been one of the most popular theoretical approaches to study some size-dependent mechanical properties of microstructures. In this work, the nonlocal elasticity field theory is employed to investigate transverse bending vibration of the microbeams subjected to a pair of initial axial tensions, and the dynamical responses of such microstructures are determined and discussed in detail. The governing equation of motion containing a small length–scale parameter is derived according to the mechanical model constructed at microscale. Subsequently, two different methods, including the method of separation of variables and the multiple-scales analysis, are applied in the equation of motion to reveal the nonlocal elastic effects in vibrational behaviors of microstructures. It shows that the results by the two methods are in good agreement. Furthermore, the critical axial tension is also obtained, and it is observed to decrease with an increase in microscale parameter, which means an increase in nonlocal elastic effects causes the critical axial tension to decrease. By comparing with the results provided by the classical continuum vibration theory, inherent frequencies of the microbeams are lower or the bending stiffness is weakened in such a nonlocal stress model presented in this article.

Micellization behavior of the ionic liquid lauryl isoquinolinium bromide in aqueous solution

The micellization behavior of the ionic liquid lauryl isoquinolinium bromide ([C12iQuin]Br) in aqueous solution has been assessed using surface tension, electrical conductivity, and 1H nuclear magnetic resonance (NMR) measurements. The results reveal that the critical micelle concentration (CMC) and constant surfactant tension (γcac) are lower than that of butyl isoquinolinium bromide ([C4iQuin]Br), octyl isoquinolinium bromide ([C8iQuin]Br, and lauryl pyridinium bromide ([C12Pyr]Br). 1H NMR spectra show the evidence of paralleled π-stacking of adjacent isoquinoline rings. To elucidate the effect of the π–π interactions on the aggregation process, thermodynamic parameters such as the standard free energy, enthalpy, and entropy of aggregation have been discussed. These parameters are evaluated from the CMC with temperature by fitting these values to expressions derived from a micellization thermodynamic model. The enthalpy–entropy compensation phenomenon has been observed in the micellization process of [C12iQuin]Br in water, and the presence of isoquinoline cations is responsible for the decrease in the ΔHmic∗, compared with [C12Pyr]Br which has the same alkyl chain and counter-ion.

Crack Onset at the Spherical-inclusion Matrix Interface. Application of a Coupled Stress and Energy Criterion

The problem of crack initiation at the interface of a spherical inclusion embedded in an infinite matrix subjected to a remote tension is studied by the means of the coupled criterion of the finite fracture mechanics. This allows us to predict the critical tension necessary to initiate the crack at the interface as a function of the elastic properties of the particle and matrix, the particle size and the main parameters defining the strength and fracture properties of the interface. The coupled criterion assumes that a crack of a finite length appears when the next two criteria are simultaneously fulfilled: on the one hand a stress criterion which imposes a condition over the stresses at points where the crack initiates and on the other hand the crack onset must be energetically allowed. The coupled criterion is applied with the aid of an axisymmetric boundary element method code. The numerical model shows a strong influence of the spherical-inclusion radius on the critical remote tension.

Air breathing in the Arctic: influence of temperature, hypoxia, activity and restricted air access on respiratory physiology of the Alaska blackfish Dallia pectoralis.

The Alaska blackfish (Dallia pectoralis) is an air-breathing fish native to Alaska and the Bering Sea islands, where it inhabits lakes that are ice-covered in the winter, but enters warm and hypoxic waters in the summer to forage and reproduce. To understand the respiratory physiology of this species under these conditions and the selective pressures that maintain the ability to breathe air, we acclimated fish to 5°C and 15°C and used respirometry to measure: standard oxygen uptake (Ṁ(O₂)) in normoxia (19.8 kPa P(O₂)) and hypoxia (2.5 kPa), with and without access to air; partitioning of standard Ṁ(O₂) in normoxia and hypoxia; maximum Ṁ(O₂) and partitioning after exercise; and critical oxygen tension (P(crit)). Additionally, the effects of temperature acclimation on haematocrit, haemoglobin oxygen affinity and gill morphology were assessed. Standard Ṁ(O₂) was higher, but air breathing was not increased, at 15°C or after exercise at both temperatures. Fish acclimated to 5°C or 15°C increased air breathing to compensate and fully maintain standard Ṁ(O₂) in hypoxia. Fish were able to maintain Ṁ(O₂) through aquatic respiration when air was denied in normoxia, but when air was denied in hypoxia, standard Ṁ(O₂) was reduced by ∼30-50%. P(crit) was relatively high (5 kPa) and there were no differences in P(crit), gill morphology, haematocrit or haemoglobin oxygen affinity at the two temperatures. Therefore, Alaska blackfish depends on air breathing in hypoxia and additional mechanisms must thus be utilised to survive hypoxic submergence during the winter, such as hypoxia-induced enhancement in the capacities for carrying and binding blood oxygen, behavioural avoidance of hypoxia and suppression of metabolic rate.

生境不完全重叠的两种鲤科鱼类耐低氧及运动能力的比较

PDF HTML阅读 XML下载 导出引用 引用提醒 生境不完全重叠的两种鲤科鱼类耐低氧及运动能力比较 DOI: 10.5846/stxb201301230130 作者: 作者单位: 重庆师范大学 进化生理与行为学实验室 动物生物学重庆市重点实验室,重庆师范大学 进化生理与行为学实验室 动物生物学重庆市重点实验室,重庆师范大学 进化生理与行为学实验室 动物生物学重庆市重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31172096）；重庆科技创新能力建设项目（CSTC2010CA1010） Comparison of hypoxia tolerance and locomotor performance in two cyprinids with incompletely overlapped habitat Author: Affiliation: Laboratory of Ecolutionary Physiology and Behaviour,Chongqing Key Laboratory of Animal Biology,Chongqing Normal University,Laboratory of Ecolutionary Physiology and Behaviour,Chongqing Key Laboratory of Animal Biology,Chongqing Normal University,Laboratory of Ecolutionary Physiology and Behaviour,Chongqing Key Laboratory of Animal Biology,Chongqing Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以乌江流域亲缘关系近，但分布并不完全重叠的马口鱼（Opsariichthys bidens）和宽鳍鱲（Zacco platypus）作为实验对象，分别考察这两种实验鱼的低氧耐受及游泳运动能力。将野外采回的实验鱼置于（25±1）℃条件下，分别测定两种鱼的临界氧分压（Pcrit）、水面呼吸（ASR）、失去平衡点（LOE）以及在不同溶氧水平（8.0、4.0和2.0 mg/L）下的临界游泳速度（Ucrit）和活跃耗氧率（MO2active）。研究发现：马口鱼的Pcrit（2.44±0.20）mg/L 显著高于宽鳍鱲（1.86±0.10）mg/L（P=0.031）。但马口鱼的50% ASR（1.23±0.16）mg/L显著低于宽鳍鱲（1.97±0.11）mg/L（P=0.023）；马口鱼的50% LOE（0.84±0.01）mg/L 同样显著低于宽鳍鱲（0.97±0.02）mg/L（P=0.004）。宽鳍鱲在8.0和4.0 mg/L下的游泳能力显著高于马口鱼，然而马口鱼和宽鳍鱲的Ucrit均随测定溶氧水平的下降而显著降低（P < 0.01）；宽鳍鱲和马口鱼的运动耗氧率均随水流速度的增加而呈现指数增加，但随测定溶氧水平的降低运动耗氧曲线变得相对平缓，尤其是在溶氧为4.0 mg/L时马口鱼的运动耗氧曲线与宽鳍鱲相比越发平缓；两种实验鱼的MO2active随溶氧水平下降的变化趋势与Ucrit相似（P < 0.001）。结果表明：两种野外生存的实验鱼不仅在低氧耐受能力方面存在显著差异，而且两者的游泳运动能力也有不同表现，这很有可能与其遗传特征、生存环境及生态习性相关。 Abstract:Two genetic closely related cyprinids-hook snout carp (Opsariichthys bidens) and pale chub (Zacco platypus) with incompletely overlapped habitats in Wu River-were selected as experimental models to investigated the difference of hypoxia tolerance and locomotor performance between two fish species and whether the possible exist difference be related with the distributed habitats. We first measured the critical oxygen tension (Pcrit), aquatic surface respiration (ASR) and loss of equilibrium (LOE) as the hypoxia indicators. Then we measured the critical swimming speed (Ucrit) and active oxygen consumption rate (MO2active) at different dissolved oxygen level (8.0, 4.0 and 2.0 mg/L, respectively) at (25.0±1.0) ℃. The Pcrit of hook snout carp (2.44±0.20) mg/L were significantly higher than that of pale chub (1.86±0.10) mg/L (P=0.031). However, the dissolved oxygen level at which 50% fish performing ASR (P=0.023) and LOE (P=0.004) in hook snout carp (ASR: (1.23±0.16) mg/L; LOE: (0.84±0.01) mg/L) were significantly lower than those in pale chub (ASR: (1.97±0.11) mg/L; LOE: (0.97±0.02) mg/L). Both the Ucrit and MO2active of hook snout carp and pale chub reduced significantly with the decreased dissolved oxygen level (P=0.008 and P=0.002, respectively); The swimming oxygen consumption rate of hook snout carp and pale chub increased exponentially with increasing swimming speed. However, the swimming speed-oxygen consumption curve became relatively flat at lower testing dissolved oxygen levels. The swimming speed-oxygen consumption curve of hook snout carp was more gently compared with that of pale chub at the dissolved oxygen level of 4.0 mg/L. The present study demonstrated that there were significant differences in both hypoxia tolerance and swimming performance between hook snout carp and pale chub which may be crucial to its survival in the field. The difference may be due to the difference of ecological habit and hence different preferred habitats of two fish species. 参考文献 相似文献 引证文献

Actin polymerization or myosin contraction: two ways to build up cortical tension for symmetry breaking

Cells use complex biochemical pathways to drive shape changes for polarization and movement. One of these pathways is the self-assembly of actin filaments and myosin motors that together produce the forces and tensions that drive cell shape changes. Whereas the role of actin and myosin motors in cell polarization is clear, the exact mechanism of how the cortex, a thin shell of actin that is underneath the plasma membrane, can drive cell shape changes is still an open question. Here, we address this issue using biomimetic systems: the actin cortex is reconstituted on liposome membranes, in an 'outside geometry'. The actin shell is either grown from an activator of actin polymerization immobilized at the membrane by a biotin-streptavidin link, or built by simple adsorption of biotinylated actin filaments to the membrane, in the presence or absence of myosin motors. We show that tension in the actin network can be induced either by active actin polymerization on the membrane via the Arp2/3 complex or by myosin II filament pulling activity. Symmetry breaking and spontaneous polarization occur above a critical tension that opens up a crack in the actin shell. We show that this critical tension is reached by growing branched networks, nucleated by the Arp2/3 complex, in a concentration window of capping protein that limits actin filament growth and by a sufficient number of motors that pull on actin filaments. Our study provides the groundwork to understanding the physical mechanisms at work during polarization prior to cell shape modifications.