Hysteresis in the pressure-saturation relation in unsaturated porous media, owing to surface tension on the liquid-gas interface, exhibits strong degeneracy in the resulting mass balance equation. As an extension of previous existence and uniqueness results, we prove that under physically admissible initial conditions and without mass exchange with the exterior, the unique global solution of the fluid diffusion problem exists and asymptotically converges as time tends to infinity to a possibly non-homogeneous mass distribution and an a priori unknown constant pressure.This article is part of the theme issue 'Non-smooth variational problems with applications in mechanics'.

• Klíčová slova
• hysteresis, long-time behaviour, porous media,
• Publikační typ
• časopisecké články MeSH

Overwintering adults of Pyrrhocoris apterus do not tolerate freezing of their body fluids and rely on a supercooling strategy and seasonal accumulation of polyols to survive at subzero body temperatures. We sampled the adults monthly in the field during the cold season 2008-2009 and found active thermal hysteresis factors (THFs) in hemolymph of winter-sampled adults. The hysteresis between the equilibrium melting and freezing points ranged from 0.18°C to 0.30°C. No signs of THFs activity were found in the autumn- and spring-sampled insects. The total free amino acid pool almost doubled during winter time. The sum concentrations of 27 free amino acids ranged between 35 and 40mM in whole body water and 40-45mM in hemolymph during December-February. Two amino acids, Pro and α-Ala most significantly contributed to the seasonal increase, while Gln showed the most dramatic seasonal decrease. Moderate levels of amino acid accumulation in overwintering P. apterus suggest that they are by-products of protein degradation and pentose pathway activity during the state of metabolic suppression imposed by diapause and low body temperature. Potential colligative effects of accumulated amino acids, extending the supercooling capacity of overwintering P. apterus, are negligible. Non-colligative effects require further study.

• MeSH
• aminokyseliny metabolismus   MeSH
• hemolymfa metabolismus   MeSH
• Heteroptera metabolismus   fyziologie   MeSH
• hmyzí proteiny metabolismus   MeSH
• kryoprotektivní proteiny metabolismus   MeSH
• osmolární koncentrace MeSH
• roční období * MeSH
• tranzitní teplota MeSH
• vodní a elektrolytová rovnováha MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• aminokyseliny MeSH
• hmyzí proteiny MeSH
• kryoprotektivní proteiny MeSH

Hysteresis is a problem in field-effect transistors (FETs) often caused by defects and charge traps inside a gate isolating (e.g., SiO2) layer. This work shows that graphene-based FETs also exhibit hysteresis due to water physisorbed on top of graphene determined by the relative humidity level, which naturally happens in biosensors and ambient operating sensors. The hysteresis effect is explained by trapping of electrons by physisorbed water, and it is shown that this hysteresis can be suppressed using short pulses of alternating gate voltages.

• Klíčová slova
• gate voltage, graphene, hysteresis, physisorption, relative humidity, sensor, water,
• MeSH
• biosenzitivní techniky * MeSH
• elektronické tranzistory MeSH
• grafit * MeSH
• oxid křemičitý MeSH
• voda MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• grafit * MeSH
• oxid křemičitý MeSH
• voda MeSH

While it is now well-understood that the extent of QT interval changes due to underlying heart rate differences (i.e., the QT/RR adaptation) needs to be distinguished from the speed with which the QT interval reacts to heart rate changes (i.e., the so-called QT/RR hysteresis), gaps still exist in the physiologic understanding of QT/RR hysteresis processes. This study was designed to address the questions of whether the speed of QT adaptation to heart rate changes is driven by time or by number of cardiac cycles; whether QT interval adaptation speed is the same when heart rate accelerates and decelerates; and whether the characteristics of QT/RR hysteresis are related to age and sex. The study evaluated 897,570 measurements of QT intervals together with their 5-min histories of preceding RR intervals, all recorded in 751 healthy volunteers (336 females) aged 34.3 ± 9.5 years. Three different QT/RR adaptation models were combined with exponential decay models that distinguished time-based and interval-based QT/RR hysteresis. In each subject and for each modelling combination, a best-fit combination of modelling parameters was obtained by seeking minimal regression residuals. The results showed that the response of QT/RR hysteresis appears to be driven by absolute time rather than by the number of cardiac cycles. The speed of QT/RR hysteresis was found decreasing with increasing age whilst the duration of individually rate corrected QTc interval was found increasing with increasing age. Contrary to the longer QTc intervals, QT/RR hysteresis speed was faster in females. QT/RR hysteresis differences between heart rate acceleration and deceleration were not found to be physiologically systematic (i.e., they differed among different healthy subjects), but on average, QT/RR hysteresis speed was found slower after heart rate acceleration than after rate deceleration.

• Klíčová slova
• QT/RR adaptation, QT/RR hysteresis, age influence, best-fit models, healthy subjects, non-linear regression modelling, sex differences,
• Publikační typ
• časopisecké články MeSH

Mimicking the locomotive abilities of living organisms on the microscale, where the downsizing of rigid parts and circuitry presents inherent problems, is a complex feat. In nature, many soft-bodied organisms (inchworm, leech) have evolved simple, yet efficient locomotion strategies in which reciprocal actuation cycles synchronize with spatiotemporal modulation of friction between their bodies and environment. We developed microscopic (∼100 μm) hydrogel crawlers that move in aqueous environment through spatiotemporal modulation of the friction between their bodies and the substrate. Thermo-responsive poly-n-isopropyl acrylamide hydrogels loaded with gold nanoparticles shrink locally and reversibly when heated photothermally with laser light. The out-of-equilibrium collapse and reswelling of the hydrogel is responsible for asymmetric changes in the friction between the actuating section of the crawler and the substrate. This friction hysteresis, together with off-centered irradiation, results in directional motion of the crawler. We developed a model that predicts the order of magnitude of the crawler motion (within 50%) and agrees with the observed experimental trends. Crawler trajectories can be controlled enabling applications of the crawler as micromanipulator that can push small cargo along a surface.

• Klíčová slova
• PNIPAM, crawler, friction hysteresis, hydrogel, photothermal,
• MeSH
• hydrogely * chemie   MeSH
• kovové nanočástice * MeSH
• lokomoce MeSH
• tření MeSH
• zlato MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• hydrogely * MeSH
• zlato MeSH

This study investigates the origin of low-pressure hysteresis (LPH) in the adsorption and desorption of three different probe molecules: carbon dioxide, nitrogen, and argon, across various adsorption temperatures (from cryogenic to room temperature), and within five different carbon materials: synthetic carbons (pristine and one post-synthetically oxidized) and natural coal. Significant attention is dedicated to elucidating LPH in oxidized samples outgassed at various temperatures (120-350 °C). Experimental results show that insufficient outgassing temperature can lead to unreliable data due to artificial LPH and significantly underestimated textural properties, primarily caused by porosity blockage from substances like moisture. Conversely, in samples where heteroatoms have a stabilizing effect on texture, such as natural coal, careful consideration of outgassing temperature is crucial due to the risk of thermal degradation. Other factors contributing to LPH are adsorption temperature, and especially, kinetic limitations at cryogenic temperatures for cellulose-based carbons. Minor factors responsible for LPH are the physical state of the sample (monolith vs powder) and the flexibility of the porous system, both studied by carbon dioxide sorption. This study constitutes an important piece in the evaluation of LPH, providing practical recommendations and underlining the importance of experimental design, with implications for further research in this complex field.

• Klíčová slova
• artificial hysteresis, degassing, diffusion limitations, open isotherms, oxidized carbon,
• Publikační typ
• časopisecké články MeSH

Current MEMS (Micro Electro Mechanical Systems) can be modeled by state-dependent elements that exhibit hysteretic behavior. Examples include capacitors and inductors whose capacitances and inductances are dependent on the instantaneous state of the electromechanical system, resistors whose resistances exhibit temperature changes when the elements are actually heated, etc. Regardless of the physical background, such hysteresis manifestations can be studied uniformly in the broader framework of generic and extended higher-order elements, in which a classification of hysteretic loops into types I and II is established. The loop type is an important dynamical parameter of an element, having the potential to indicate, for example, its (in)volatility. Thus far, there is no reliable criterion to determine the type of steady loop from the defining relations of an element. This work reports on one special class of extended elements that produces type II loops under all circumstances. The paper presents hitherto unpublished connections between the frequency-doubling parameters of an element and the type of its hysteresis loop. The new findings are expressed by several theorems that allow the type of hysteresis to be inferred from the frequency behavior of the element parameter or state, and vice versa. These procedures are demonstrated with examples and verified by computer simulations.

• Klíčová slova
• extended element, generic element, higher-order element, pinched hysteresis loop,
• Publikační typ
• časopisecké články MeSH

Three Fe-based ribbon-type samples prepared by a conventional planar flow casting process are studied from the viewpoint of the amorphous Fe80Si4B16 and partially surface crystallized Fe80Si10B10, and Fe80.5Nb6.9B12.6, microstructures. Surface magnetic properties are investigated by magneto-optical Kerr microscopy, allowing the measurement of a local hysteresis loop from a selected area on the ribbon surface, and simultaneously, a domain structure corresponding to a definite point at the loop. For an amorphous sample, the changes in the slopes of hysteresis loops are related either to the size of the selected surface area, from which the loop is measured, or to the type, width, and movement of magnetic domains through this area. In the first case, the resizing of the area simulates an effect of changing the diameter of the incident laser beam on the magneto-optical properties of the ribbon. In the latter case, the observed wide-curved and fingerprint domains are responsible for markedly different shapes of the hysteresis loops at lower magnetic fields. If the surface is crystallized, the magnetic properties are more homogenous, showing typical one-jump magnetization reversal with less dependence on the size of the surface area. The magneto-optical experiments are completed by transmission electron microscopy and magnetic force microscopy.

• Klíčová slova
• hysteresis loops, magnetic domains, magnetic force microscopy, magneto-optical Kerr microscopy, planar flow casting, ribbons, surface magnetism,
• Publikační typ
• časopisecké články MeSH

Ultrasound velocity was measured in hyaluronan solutions of various compositions at different temperatures. The velocity dependence on hyaluronan concentration at constant temperature (25 °C) was linear both in water and in 0.15 M NaCl regardless of hyaluronan molecular weight, confirming diluted-solution behavior. During cyclic heating and cooling, hysteresis on the temperature dependence of ultrasound velocity was observed in the range 30-55 °C in aqueous solutions for all molecular weights. In NaCl solutions, the hysteresis was suppressed and, in contrast to solutions in water where the velocity demonstrated a local maximum with temperature, the velocity decreased with increasing temperature. These findings were attributed to slow and hydration-linked hyaluronan conformation transitions during cooling in water, which were suppressed by the presence of salt, which makes hyaluronan's coiled conformation more compact.

• Klíčová slova
• Apparent specific compressibility, Compressibility, Hyaluronan, Hysteresis, Ultrasonic velocity, Ultrasound velocimetry,
• MeSH
• ionty MeSH
• kyselina hyaluronová chemie   MeSH
• nízká teplota * MeSH
• reologie * MeSH
• roztoky MeSH
• ultrazvuk * MeSH
• voda chemie   MeSH
• vytápění * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• ionty MeSH
• kyselina hyaluronová MeSH
• roztoky MeSH
• voda MeSH

A simple fluid, in a microscopic capillary capped at one end, is studied by means of fundamental measure density functional. The model represents a single, infinitely long nanogroove with long-range wall-fluid attractive (dispersion) forces. It is shown that the presence or absence of hysteresis in adsorption isotherms is determined by wetting properties of the wall as follows: Above wetting temperature, T(w), appropriate to a single wall of the groove, the adsorption is a continuous process corresponding to a rise of a meniscus from the capped to the open end of the groove. For a sufficiently deep capillary, the meniscus rise is shown to be a steep, yet continuous process taking place near the capillary condensation of a corresponding slit. However, for temperatures lower than T(w) the condensation exhibits a first-order transition accompanied by hysteresis of the adsorption isotherm. Finally, it is shown that hysteresis may occur even for T > T(w) as a consequence of prewetting on the side and bottom walls of the groove.

• Publikační typ
• časopisecké články MeSH