Abstract Aestivation and hibernation represent distinct forms of animal quiescence, characterized by physiological changes, including ion composition. Intracellular ion flows play a pivotal role in ...eliciting alterations in membrane potential and facilitating cellular communication, while outward K+ currents aid in the restitution and upkeep of the resting membrane potential. This study explores the relationship between inward and outward currents during aestivation in Achatina fulica snails. Specimens were collected near MSUBIT University in Shenzhen and divided into two groups. The first group was kept on a lattice diet, while the second one consisted of aestivating individuals, that were deprived of food and water until a cork-like structure sealed their shells. Recording of current from isolated neurons were conducted using the single-electrode voltage clamp mode with an AxoPatch 200B amplifier. Electrophysiological recordings on pedal ganglia neurons revealed significant differences in the inactivation processes of the Ia and Ikdr components. Alterations in the Ikdr component may inhibit pacemaker activity in pedal ganglion neurons, potentially contributing to locomotion cessation in aestivated animals. The KS current remains unaffected during aestivation. Changes in slow K+ current components could disrupt the resting membrane potential, possibly leading to cell depolarization and influx of Ca2+ and Na+ ions, impacting cell homeostasis. Thus, maintaining the constancy of outward K+ current is essential for cell stability.
Resumo A estivação e a hibernação representam formas distintas de quiescência animal, caracterizadas por alterações fisiológicas, incluindo a composição de íons. Os fluxos de íons intracelulares desempenham papel fundamental na provocação de alterações no potencial de membrana e na facilitação da comunicação celular, enquanto as correntes de K+ de saída ajudam na restituição e manutenção do potencial de membrana em repouso. Este estudo explora a relação entre as correntes de entrada e de saída durante a estivação em caracóis Achatina fulica. Os espécimes foram coletados perto da Universidade MSUBIT, em Shenzhen, e divididos em dois grupos. O primeiro grupo foi mantido em uma dieta de treliça, enquanto o segundo consistia em indivíduos estivados, que foram privados de alimento e água até que uma estrutura semelhante a uma rolha selasse suas conchas. O registro da corrente de neurônios isolados foi realizado usando o modo de grampo de tensão de eletrodo único com amplificador AxoPatch 200B. Os registros eletrofisiológicos nos neurônios dos gânglios pedais revelaram diferenças significativas nos processos de inativação dos componentes Ia e Ikdr. As alterações no componente Ikdr podem inibir a atividade do marcapasso nos neurônios do gânglio pedal, contribuindo potencialmente para a interrupção da locomoção em animais estivados. A corrente KS não é afetada durante a estivação. As alterações nos componentes da corrente lenta de K+ podem perturbar o potencial de membrana em repouso, possivelmente levando à despolarização celular e ao influxo de íons Ca2+ e Na+, afetando a homeostase celular. Portanto, manter a constância da corrente de K+ de saída é essencial para a estabilidade celular.
Abstract
The solution to the problem of the stress-strain state of an inhomogeneous profiled rod is based on the use of nonlinear equilibrium conditions and physical relations of a layered thermo ...elastic thin rod. A differential equation of bifurcation inhomogeneous rod stability of variable cross-section is obtained. The equation has variable functional coefficients. In the initial state, the rod is subjected to bending with the implementation of one of the asymmetric shapes. The critical state occurs under the action of a longitudinal load corresponding to one of the lowest symmetrical shapes, orthogonal to the initial shape. In the first series, numerical calculations of an inhomogeneous I-rod with a variable cross section height are performed. Shelves and wall I-rod are made of steel, aluminum and titanium alloys. The graphs of maximum deflection and normal stresses acting at the calculate points at the boundaries of the layers are plotted depending on the longitudinal load at the given levels of transverse loads and thermal field. A significant influence of the rod physical structure, the profiling its form and the factor of nonlinearity of static relations on the stress fields has been established. A homogeneous temperature field with a nominal value of 80°C creates fields of self-balanced stresses in an inhomogeneous rod. The components of normal stresses in this case reach 20-40% of the materials permissible resistance level. The presence of rod parts with a significant difference in the coefficients of thermal expansion in the composition enhances this effect. In the second, the stability analysis of an inhomogeneous I-rod with a variable width cross section was performed. The transition of the initial S-shaped bend to an unstable state is shown.
2D materials and van der Waals heterostructures Novoselov, K. S.; Mishchenko, A.; Carvalho, A. ...
Science (American Association for the Advancement of Science),
07/2016, Letnik:
353, Številka:
6298
Journal Article
Recenzirano
Odprti dostop
The physics of two-dimensional (2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear (for ...instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices--such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes--are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.
Indirect excitons (IXs) are explored both for studying quantum Bose gases in semiconductor materials and for the development of excitonic devices. IXs were extensively studied in III-V and II-VI ...semiconductor heterostructures where IX range of existence has been limited to low temperatures. Here, we present the observation of IXs at room temperature in van der Waals transition metal dichalcogenide (TMD) heterostructures. This is achieved in TMD heterostructures based on monolayers of MoS
separated by atomically thin hexagonal boron nitride. The IXs we realize in the TMD heterostructure have lifetimes orders of magnitude longer than lifetimes of direct excitons in single-layer TMD and their energy is gate controlled. The realization of IXs at room temperature establishes the TMD heterostructures as a material platform both for a field of high-temperature quantum Bose gases of IXs and for a field of high-temperature excitonic devices.
Topological materials may exhibit Hall-like currents flowing transversely to the applied electric field even in the absence of a magnetic field. In graphene superlattices, which have broken inversion ...symmetry, topological currents originating from graphene’s two valleys are predicted to flow in opposite directions and combine to produce long-range charge neutral flow. We observed this effect as a nonlocal voltage at zero magnetic field in a narrow energy range near Dirac points at distances as large as several micrometers away from the nominal current path. Locally, topological currents are comparable in strength with the applied current, indicating large valley-Hall angles. The long-range character of topological currents and their transistor-like control by means of gate voltage can be exploited for information processing based on valley degrees of freedom.
The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D ...crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).
The basic design relations for thermal-force spatial bending with tension, transverse shear and torsion were obtained for a spatially hospismatic rod of rectangular cross section, composed of ...quasi-homogeneous parts (phases), which were made of various structural materials. Approximations of the transverse shears functions and a membrane analogy were used for shear deformations during torsion, using the Tymoshenko hypotheses. As a sesult, obtained relations allow one to perform approximate formulations and solutions of various boundary-value direct and inverse problems, including: identifying the stress-strain state of a composite rod under thermal power, evaluating its strength and stiffness, identifying rational geometric and structural parameters of the inhomogeneous structure of the rod, and optimization problems. Expressions were obtained for the stiffness characteristics of the zeroth, first, and second orders in bending with tension, shear and tensional stiffness of the section, which allowed us to formulate the boundary value problems of spatial deformation of composite rods.
Graphene is increasingly explored as a possible platform for developing novel separation technologies. This interest has arisen because it is a maximally thin membrane that, once perforated with ...atomic accuracy, may allow ultrafast and highly selective sieving of gases, liquids, dissolved ions and other species of interest. However, a perfect graphene monolayer is impermeable to all atoms and molecules under ambient conditions: even hydrogen, the smallest of atoms, is expected to take billions of years to penetrate graphene's dense electronic cloud. Only accelerated atoms possess the kinetic energy required to do this. The same behaviour might reasonably be expected in the case of other atomically thin crystals. Here we report transport and mass spectroscopy measurements which establish that monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable to thermal protons under ambient conditions, whereas no proton transport is detected for thicker crystals such as monolayer molybdenum disulphide, bilayer graphene or multilayer hBN. Protons present an intermediate case between electrons (which can tunnel easily through atomically thin barriers) and atoms, yet our measured transport rates are unexpectedly high and raise fundamental questions about the details of the transport process. We see the highest room-temperature proton conductivity with monolayer hBN, for which we measure a resistivity to proton flow of about 10 Ω cm(2) and a low activation energy of about 0.3 electronvolts. At higher temperatures, hBN is outperformed by graphene, the resistivity of which is estimated to fall below 10(-3) Ω cm(2) above 250 degrees Celsius. Proton transport can be further enhanced by decorating the graphene and hBN membranes with catalytic metal nanoparticles. The high, selective proton conductivity and stability make one-atom-thick crystals promising candidates for use in many hydrogen-based technologies.
One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to ...separate hydrogen ion isotopes. Using electrical measurements and mass spectrometry, we found that deuterons permeate through these crystals much slower than protons, resulting in a separation factor of ≈10 at room temperature. The isotope effect is attributed to a difference of ≈60 milli–electron volts between zero-point energies of incident protons and deuterons, which translates into the equivalent difference in the activation barriers posed by two-dimensional crystals. In addition to providing insight into the proton transport mechanism, the demonstrated approach offers a competitive and scalable way for hydrogen isotope enrichment.
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