Slow magnetic dynamics and hysteresis loops of a bulk ferromagnet

Magnetic dynamics of a bulk ferromagnet, a new single crystalline compound Co7(TeO3)4Br6, was studied by ac susceptibility and the related techniques. Very large Arrhenius activation energy of 17.2 meV (201 K) and long attempt time (2x10^(-4)s) span the full spectrum of magnetic dynamics inside a convenient frequency window, offering a rare opportunity for general studies of magnetic dynamics. Within the experimental window the ac susceptibility data build almost ideally semicircular Cole-Cole plots. Comprehensive study of experimental dynamic hysteresis loops of the compound is presented and interpreted within a simple thermal-activation-assisted spin lattice relaxation model for spin reversal. Quantitative agreement between the experimental results and the model's prediction for dynamic coercive field is achieved by assuming the central physical quantity, the Debye relaxation rate, to depend on frequency, as well as on the applied field strength and sample temperature. Cross-over between minor- to major hysteresis loops is carefully analyzed. Low-frequency limitations of the model, relying on domain wall pinning effects, are experimentally detected and appropriately discussed.Comment: A paragraph on dynamical-hysteresis assymetry added, text partially revised; Accepted in Physical Review

Granular Pressure In A Liquid Fluidized Bed

The granular temperature and pressure underpins the kinetic theory of granular flows while they also playing an increasing role in other context such as modeling heat transfer, segregation, erosion, attrition and aggregation in various granular processing technologies. The validation of these theories demands experimental determination of these quantities. Diffusing wave spectroscopy (DWS) is a well established technique for measurement of granular temperature in dense granular systems. Using the dense kinetic theory expression, we derive the granular pressure from DWS data for the first time. The determined mean granular pressure variation with solid volume fraction in a liquid fluidized bed is compared with theoretical and simulation models as well as with previous experimental results. Additionally, we report axial granular pressure profiles at several solid volume fractions.Vladimir Zivkovic, Mark Biggs, Don Glasshttp://www.chemeca2010.com/abstract/341.as

Scaling of Granular Temperature in a Dense Vibrated Granular Bed

The granular temperature underpins the kinetic theory of granular flows as well as theories for heat transfer, segregation, erosion, attrition and aggregation in various granular systems. We report granular temperature data of mono-disperse glass particles in a three-dimensional dense granular bed subject to vertical sinusoidal vibrations over a wide range of vibrational conditions as measured by diffusing wave spectroscopy (DWS). The granular temperature was found to scale with the square of the peak vibrational velocity inline with a number of theoretical models and experiments, but a significant correlation was observed between the granular temperature and the acceleration at constant peak velocity. Therefore, a map of granular temperature as a function of the peak vibrational velocity (range of 30 to 55 mm/s) and acceleration (1.8 to 3.4 Γ) is presented for the first time and discussed.Vladimir Zivkovic, Mark Biggs, Don Glasshttp://www.chemeca2010.com/abstract/342.as

Addressing small-scale temperature swing adsorption challenges using intensified fluidised bed technology for carbon capture process development

\ua9 2024 The Author(s)Polyethylenimine (PEI)-based adsorbents exhibit high CO2 capacities, making them potential candidates for mitigating unavoidable industrial CO2 emissions. However, desorption of CO2 from PEI, and from adsorbents in general, has received far less attention in the literature than adsorption. Whilst Temperature Swing Adsorption (TSA) is simple to conceptualise, it is difficult to implement in small-scale experiments in practice. Here we study the desorption characteristics of a commercial branched PEI adsorbent in a small-scale swirling fluidised bed reactor (TORBED) to improve the small-scale heat transfer rates. Our experimental results show that higher desorption temperatures, higher gas flow rates, and higher CO2 concentrations during adsorption can improve the desorption efficiency (defined as the amount of CO2 removed as a fraction of the initial amount adsorbed). In terms of kinetics, we found that the fractional order kinetic model provided the best fit to the PEI adsorbent, implying that this adsorbent involves multiple simultaneous molecular interactions, physisorption processes, and chemisorption processes, that cannot be described by simpler pseudo 1st or 2nd order models. Desorption rates in the TORBED in this study were 1 order of magnitude faster than fluidised beds, and 2–3 orders of magnitude faster than packed beds

Short horizons and obesity futures: Disjunctures between public health interventions and everyday temporalities

This paper examines the spatio-temporal disjuncture between ‘the future’ in public health obesity initiatives and the embodied reality of eating. Drawing upon ethnographic fieldwork in a disadvantaged community in South Australia (August 2012–July 2014), we argue that the future oriented discourses of managing risk employed in obesity prevention programs have limited relevance to the immediacy of poverty, contingencies and survival that mark people's day to day lives. Extending Bourdieu's position that temporality is a central feature of practice, we develop the concept of short horizons to offer a theoretical framework to articulate the tensions between public health imperatives of healthy eating, and local ‘tastes of necessity’. Research undertaken at the time of Australia's largest obesity prevention program (OPAL) demonstrates that pre-emptive and risk-based approaches to health can fail to resonate when the future is not within easy reach. Considering the lack of evidence for success of obesity prevention programs, over-reliance on appeals to ‘the future’ may be a major challenge to the design, operationalisation and success of interventions. Attention to local rather than future horizons reveals a range of innovative strategies around everyday food and eating practices, and these capabilities need to be understood and supported in the delivery of obesity interventions. We argue, therefore, that public health initiatives should be located in the dynamics of a living present, tailored to the particular, localised spatio-temporal perspectives and material circumstances in which people live.Megan Warin, Tanya Zivkovic, Vivienne Moore, Paul R. Ward, Michelle Jone

Impact of coating particles on liquid marble lifetime: reactor engineering approach to evaporation

Liquid marbles are soft matter objects characterised by a liquid droplet enclosed within a hydrophobic particle coating, preventing wetting. This distinctive structure serves as active sites for solid-liquid-gas reactions. However, the impact the chosen coating material has on liquid marble stability, particularly regarding the number of coating layers and material wetting, remains uncertain. There is a need for a modelling approach to predict the overall lifetime considering these coating characteristics. This study reveals that for PTFE liquid marbles evaporating at ambient temperature, smaller coating particles (250 nm) extend their lifetime by forming a multilayered coating. Conversely, using larger particle sizes (200 μm) results in the formation of monolayer liquid marbles with shorter lifetimes than their equivalent naked droplets. Additionally, a higher number of particle layers and a larger contact angle generally enhance the liquid marble\u27s lifetime. For multilayered liquid marbles comprised of smaller particles (250 nm), the particle contact angle is found to have a more significant impact than the number of layers on lifetime extension, whereas the opposite holds true for larger particle sizes (20 μm). A modelling approach using the reactor engineering method for liquid marble evaporation demonstrates excellent agreement with experimental results, yielding an R2 of 0.996. The implementation of this specific model, capable of assessing lifetime across various physical modifications, will enhance our understanding of liquid marble properties before their application in biomedical, microreactor, and green technologies

Unravelling the origin of the peculiar transition in the magnetically ordered phase of the Weyl semimetal Co3Sn2S2

Recent discovery of topologically non-trivial behavior in Co3Sn2S2 stimulated a notable interest in this itinerant ferromagnet (Tc = 174 K). The exact magnetic state remains ambiguous, with several reports indicating the existence of a second transition in the range 125 -- 130 K, with antiferromagnetic and glassy phases proposed to coexist with the ferromagnetic phase. Using detailed angle-dependent DC and AC magnetization measurements on large, high-quality single crystals we reveal a highly anisotropic behavior of both static and dynamic response of Co3Sn2S2. It is established that many observations related to sharp magnetization changes when B || c are influenced by the demagnetization factor of a sample. On the other hand, a genuine transition has been found at Tp = 128 K, with the magnetic response being strictly perpendicular to the c-axis and several orders of magnitude smaller than for B || c. Calculations using density-functional theory indicate that the ground state magnetic structure consist of magnetic moments canted away from the c-axis by a small angle (~ 1.5deg). We argue that the second transition originates from a small additional canting of moments within the kagome plane, with two equivalent orientations for each spin.Comment: accepted as a Letter in PR

Intelligent dual curve-driven tool path optimization and virtual CMM inspection for sculptured surface CNC machining

This paper investigates the profitability of a dual‐curve driven surface finish tool path under the concept of optimizing crucial machining parameters such as toroidal end‐mill diameter, lead angle and tilt angle. Surface machining error as well as tool path time are treated as optimization objectives under a multi‐criteria sense, whilst a central composite design is conducted to obtain experimental outputs for examination and, finally, fit a full quadratic model considered as the fitness function for process optimization by means of a genetic algorithm. A benchmark sculptured surface given as a second‐order parametric equation was tested and simulated using a cutting‐edge manufacturing modeling software and best parameters recommended by the genetic algorithm were implemented for validation. Further assessment involves the virtual inspection to selected profile sections on the part. It was shown that the approach can produce dual‐curve driven tool trajectories capable of eliminating sharp scallop heights, maximizing machining strip widths as well as maintaining smoothness quality and machining efficiency

The role of hydrogen sulfide in homocysteine-induced cardiodynamic effects and oxidative stress markers in the isolated rat heart

This study aimed to assess the role of H2S in homocysteine-induced cardiodynamic effects in the isolated rat heart. The hearts were retrogradely perfused according to the Langendorff technique. The maximum and minimum rates of pressure in the left ventricle (dp/dt max, dp/dt min), systolic and diastolic left ventricular pressures (SLVP, DLVP), heart rate (HR), and coronary flow (CF) were measured. A spectrophotometrical method was used to measure the following oxidative stress markers: index of lipid peroxidation (thiobarbituric acid reactive substances, TBARS), nitrite level (NO2−), superoxide anion radicals (O2•−), and hydrogen peroxide (H2O2) concentrations. The administration of 10 µmol/l DL-homocysteine (DL-Hcy) alone decreased dp/dt max, SLVP, and CF but did not change any oxidative stress parameters. The administration of 10 µmol/l DL-propargylglycine (DL-PAG) decreased all cardiodynamic parameters and increased the concentration of O2•−. The co-administration of DL-Hcy and DL-PAG induced a significant decrease in all estimated cardiodynamic parameters and decreased the concentration of NO2− and O2•− but increased the levels of TBARS and H2O2. Homocysteine shows a lower pro-oxidative effect in the presence of hydrogen sulfide (H2S), which indicates a potential anti-oxidative capacity of H2S