Acoustic manipulation dynamics of levitated particle with screw-shaped reflecting surface.

Existing single-axis acoustic levitation devices with an axisymmetric reflector can manipulate particles in a variety of ways. However, the mechanism by which particles are suspended in a single-axis acoustic levitator with a non-axisymmetric reflector remains poorly understood. This work addresses this issue by proposing a novel single-axis ultrasonic levitator design that includes a flat plane emitter and a screw-plane reflector. The node positions of the standing wave formed in this levitator were predicted by calculating the Gor'kov potential according to a numerical model. The analysis results demonstrate that the nodes were distributed off-axis and their positions varied in a spiral manner when changing the distance between the emitter and reflector. Corresponding experiments based on the proposed design were also conducted, and the results indicated that the distance changes between the emitter and reflector could induce some spiral trajectories of a polyethylene-foam particle placed in the ultrasonic field. Moreover, the trajectory of the suspended particle was found to distribute along a conical surface centered on the central axis of this device. This work provides a new approach for ultrasonic particle manipulation by changing the geometry of the reflector.

[Investigation of acute poisoning event caused by carbofuran].

Objective: To analyze the epidemiological characteristics and response process of an acute poisoning event caused by carbofuran in buttered tea and provide scientific evidence for the investigation of similar events in the future. Methods: Field epidemiological survey, animal experiments and laboratory tests were conducted for an acute poisoning event occurred in Suopo township of Danba county of Sichuan province in 2018. Descriptive epidemiological method was used to analyze the epidemiological characteristics of the acute poisoning event. Results: A total of 26 poisoning cases occurred in 3 villages. The total attack rate was 41.27%. No death cases were reported. The 26 cases occurred in a few minutes after drinking buttered tea, the main symptoms were vomit, dizziness, miosis and nausea. A dog showed the same symptoms after drinking a sample of buttered tea. Carbofuran was detected in buttered tea, vomitus and zanba samples. Conclusions: The acute poisoning was caused by carbofuran in buttered tea, the transmission mode was point source spread. Effective epidemiological investigation and simple animal experiment can provide evidence for the rapid sample detection and clinical treatment of cases in emergency response. Timely case treatment and strict poisoning source control are the key measures to reduce casualty and prevent the spread of poisoning.

Dynamic evolution process of multilayer core-shell microstructures within containerlessly solidifying Fe(50)Sn(50) immiscible alloy.

Multilayer core-shell structures are frequently formed in polymers and alloys when temperature and concentration fields are well symmetrical spatially. Here we report that two- to five-layer core-shell microstructures were the dominant structural morphology of a binary Fe(50)Sn(50) immiscible alloy solidified under the containerless and microgravity states within a drop tube. Three dimensional phase field simulation reveals that both the uniformly dispersive structure and the multilayer core-shells are the various metastable and transitional states of the liquid phase separation process. Only the two-layer core-shell is the most stable microstructure with the lowest chemical potential. Because of the suppression of Stokes motion, solutal Marangoni migration becomes important to drive the evolution of core-shell structures.

The near-field acoustic levitation of high-mass rotors.

Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope.

Influence of salt on colloidal lithography of albumin.

We investigate the influence of salt on colloidal lithography of biomolecular patterns. Albumin labeled with fluorescein isothiocyanate (FITC) was adsorbed on polyelectrolyte-coated glass substrates covered by negatively charged colloids using fluorescence microscopy. After removing the colloids, a well-defined albumin pattern remains, and we study how the pattern changes upon adding salt to the protein solution. The proposed method is simple and cheap and can be used to create stable one- and two-dimensional biomolecular arrays.

Order-disorder transition in a quasi-two-dimensional colloidal system.

A 2D colloidal system governed by repulsive dipolar forces tends to form a more ordered system when the interaction strength between the particles increases. Here we report an order-disorder transition of the colloidal system followed by chain formation upon increasing the dipolar interactions and show that the critical field scales with the density of colloids. Our system can do this by changing its dimensionality and therefore exhibits novel behavior that could help us understand colloidal ordering phenomena.