Thermoregulatory morphodynamics of honeybee swarm clusters

During reproductive swarming, honeybees clusters of more than 10,000 individuals that hang from structures in the environment (e.g., tree branches) are exposed to diurnal variations in ambient temperature for up to a week. Swarm clusters collectively modulate their morphology in response to these variations (i.e., expanding/contracting in response to heating/cooling) to maintain their internal temperature within a tolerable range and to avoid exhausting their honey stores prematurely. To understand the spatiotemporal aspects of thermoregulatory morphing, we measured the change in size, shape and internal temperature profiles of swarm clusters in response to dynamic temperature ramp perturbations. We see that swarm clusters show a two-fold variation in their volume/density when heated from 15°C to 30°C. However, they do not reach an equilibrium size or shape when held at 30°C for 5 hours, long after the core temperature of the cluster has stabilized. Furthermore, the changes in cluster shape and size are hysteretic, contracting in response to cooling faster than expanding in response to heating. Although the base contact diameter of the cluster increased continuously when the swarm is heated, the change in length of the swarm (base totip) over time is non-monotonic. Consequently, the aspect ratio of the swarm fluctuated continuously even when held at a constant temperature. Taken together, our results quantify the hysteretic and anisotropic morphological responses of swarm clusters to ambient temperature variations while suggesting that both mechanical constraints and heat transfer govern their thermoregulatory morphodynamics.

The Breakage of Shape-Anisotropic Particles under Normal Contact with Different Particle Shape Parameters

This paper elaborates the cone–hemispherical gypsum particle breakages under normal contact with different particle shape parameters (contact diameter d, cone angle θ and sphere diameter D) and proposes a simple quantitative approach to discriminate breakage modes. The effects of the particle shape parameters on particle breakage are investigated through analyzing breakage processes, breakage modes and force–displacement curves. Three breakage modes are formed during the breakage experiments: peeling, peeling–splitting and splitting, corresponding to three different normal force–displacement curves. The formation of a conical core is deemed as the precondition for particle splitting. The particle breakage mode transfers from peeling to splitting with the increase in contact diameter d and cone angle θ, but a decrease in sphere diameter D. The critical normal force Fcr is positively linearly related to contact diameter d and cone angle θ, but the relationship between Fcr and sphere diameter D heavily depends on the breakage mode. Furthermore, the critical contact diameter dcr described by cone angle θ and sphere diameter D is proposed to discriminate breakage modes of the cone–hemispherical gypsum particles.

Research On Non-boiling Evaporation Behavior of Fixed Droplets On Aluminum Plate Surface

In this paper, the non-boiling evaporation (30 -70?) of the fixed droplets on the Aluminum plate surface was investigated by the experiment. The effect of the plate temperature and initial volume on the contact angle, contact diameter and evaporation time were considered. The results showed that the temperature and initial volume were important for the droplets evaporation. As the heating plate temperature increased, the evaporation rate increased and the initial contact angle decreased. At the same heating plate temperature, the evaporation rate and the initial contact angle decreased with the increase of the droplets initial volume. At the constant temperature hydrophilic surface, the droplet evaporation is performed in two modes: Constant contact radius mode (CCR mode) and mix mode. The CCR mode were about 90% of the time at the droplets evaporation process and the droplet contact diameters kept constant with the increase of the evaporation time. For the mix mode, the contact angle and contact diameter decreased with the increase of the evaporation time.

WATER DROPLET EVAPORATION IN A CHAMBER ISOLATED FROM THE EXTERNAL ENVIRONMENT

With an increase in the productivity of power equipment and the miniaturization of its components, the use of traditional thermal management systems becomes insufficient. There is a need to develop drip heat removal systems, based on phase transition effects. Cooling with small volumes of liquids is a promising technology for microfluidic devices or evaporation chambers, which are self-regulating systems isolated from the external environment. However, the heat removal during evaporation of droplets into a limited volume is a difficult task due to the temperature difference in the cooling device and the concentration of water vapor that is unsteady in time depending on the mass of the evaporated liquid. This paper presents the results of an experimental study of the distilled water microdrops’ (5-25 μl) evaporation on an aluminum alloy AMg6 with the temperatures of 298-353 K in an isolated chamber (70 × 70 × 30 mm3) in the presence of heat supply to its lower part. Based on the analysis of shadow images, the changes in the geometric dimensions of evaporating drops were established. They included the increase in the contact diameter, engagement of the contact line due to nano roughening and chemical composition inhomogeneous on the surface (90-95% of the total evaporation time) of the alloy and a decrease in the contact diameter. The surface temperature and droplet volume did not affect the sequence of changes in the geometric dimensions of the droplets. It was found that the droplet volume has a significant effect on the evaporation time at relatively low substrate temperatures. The results of the analysis of droplet evaporation rates and hygrometer readings have shown that reservoirs with salt solutions can be used in isolated chambers to control the concentration of water vapor. The water droplets evaporation time was determined. The analysis of the time dependences of the evaporation rate has revealed that upon the evaporation of droplets in an isolated chamber under the conditions of the present experiment, the air was not saturated with water vapor. The latter did not affect the evaporation rate.

MORPHOLOGICAL FEATURES AND WETTABILITY OF POLYTETRAFLUOROETHYLENE SURFACE TEXTURED BY LASER ABLATION

In this paper, the morphological features of textures with non-uniform wettability created using femtosecond laser ablation of polytetrafluoroethylene substrates have been studied. Covering the surface of polytetrafluoroethylene with microcraters in accordance with a proper design a texture in the form of periodically located microcollets could be created. The period of the location of the columns is the same over the entire surface and is selected in the range from 15 to 100 microns. In the case when the period lies within 30–100 µm, the diameter of the bars is ~ 20 µm. If in the range of 15–20 µm, then this diameter decreases accordingly to ~ 10 µm. Depending on the pulse energy, the height of the pillars could be smoothly changed from 0 to 60 μm. However, to create a superhydrophobic concentrator, textures with the greatest depth were used so that the height of the columns does not limit the stability of the superhydrophobic state by the sagging mechanism. It was established that on the surface of each pillar during the process of laser ablation, a relief with a two-modal roughness in the form of short drop-shaped projections of the material covered with spherical globules is additionally formed. Thus, in one stage of laser micromachining, it is possible to create a surface with a three-modal roughness – microcolumns, drop-shaped projections and spherical globules. The process of droplet evaporation is represented by two main modes of constant contact angle and constant contact diameter, when the latter ceases to decrease and remains constant until the complete evaporation of the drop. As a result, a precipitate of the substance dissolved in a drop is formed on the substrate. It has been established that in the interval 0 <τ <0.9, evaporation occurs in the constant contact angle mode.

Verification and Calibration of Instrumented Indentation Testing Machines

The frame compliance is calibrated by experimental and calculation methods for an instrumented indentation equipment. The indentation depth and contact diameter with single cycle test is determined by confocal laser scanning microscopy directly. The alternative method is to calculate the contact depth and the contact radius from the load-depth curves. The observed and calculated frame compliances are obtained respectively according to EN ISO 14577-4 Annex Methods 2.

Transient Interface Shape and Deposition Profile Left by Desiccation of Colloidal Droplets on Multiple Surfaces

Control of deposition patterns left by desiccated colloidal droplets is valuable in applications ranging from medical diagnostics to inkjet printing. This investigation presents an experimental method to monitor the transient interface shape of a colloidal droplet during desiccation and to quantify the deposition pattern left by the colloidal material optically. Transient image profiles and particle deposition patterns are examined for droplets containing fluorescent particles that were desiccated on glass and on the photoresist SU-8 3005. Contact line pinning was more prevalent on glass, where the contact diameter remained approximately constant throughout the process and the contact angle decreased with time. On SU-8, the contact diameter was initially constant, but decreased after the contact angle was reduced. The initial contact diameter on glass was similar to the diameter of the deposition pattern. The diameter of the deposition pattern on SU-8 was approximately half of the initial contact diameter. The deposition on SU-8 was also observed to be more uniform than that left on glass. These results suggest that selection of an appropriate substrate is an important consideration for colloidal deposition. The method presented will be used to in future investigations to characterize the effectiveness of coffee stain suppression through the application of external electric fields.