Oscillatory stability of quantum droplets in $\text{}{ \mathcal P }{ \mathcal T }$-symmetric optical lattice

We study stability and collisions of quantum droplets (QDs) forming in a binary bosonic condensate trapped in parity-time (${ \mathcal P }{ \mathcal T }$)-symmetric optical lattices. It is found that the stability of QDs in the ${ \mathcal P }{ \mathcal T }$-symmetric system depends strongly on the values of the imaginary part W₀ of the ${ \mathcal P }{ \mathcal T }$-symmetric optical lattices, self-repulsion strength g, and the condensate norm N. As expected, the ${ \mathcal P }{ \mathcal T }$-symmetric QDs are entirely unstable in the broken ${ \mathcal P }{ \mathcal T }$-symmetric phase. However, the ${ \mathcal P }{ \mathcal T }$-symmetric QDs exhibit oscillatory stability with the increase of N and g in the unbroken ${ \mathcal P }{ \mathcal T }$-symmetric phase. Finally, collisions between ${ \mathcal P }{ \mathcal T }$-symmetric QDs are considered. The collisions of droplets with unequal norms are completely different from that in free space. Besides, a stable ${ \mathcal P }{ \mathcal T }$-symmetric QDs collides with an unstable ones tend to merge into breathers after the collision.     

Quantum droplets in two-dimensional optical lattices

We study the stability of zero-vorticity and vortex lattice quantum droplets (LQDs), which are described by a two-dimensional (2D) Gross–Pitaevskii (GP) equation with a periodic potential and Lee– Huang–Yang (LHY) term. The LQDs are divided in two types: onsite-centered and offsite-centered LQDs, the centers of which are located at the minimum and the maximum of the potential, respectively. The stability areas of these two types of LQDs with different number of sites for zero-vorticity and vorticity with S = 1 are given. We found that the μ–N relationship of the stable LQDs with a fixed number of sites can violate the Vakhitov–Kolokolov (VK) criterion, which is a necessary stability condition for nonlinear modes with an attractive interaction. Moreover, the μ–N relationship shows that two types of vortex LQDs with the same number of sites are degenerated, while the zero-vorticity LQDs are not degenerated. It is worth mentioning that the offsite-centered LQDs with zero-vorticity and vortex LQDs with S = 1 are heterogeneous.     

A visible coalescence of droplets on hydrophobic and hydrophilic fibers in water-in-oil emulsion

The droplets’ coalescence is instantaneous and rather complex in emulsion. The theoretical analysis of this process was presented by a former research, while visible experiments to verify these are still scarce. This work aims to show and analyze the visible water droplets’ coalescence on hydrophobic bamboo charcoal fibers and hydrophilic glass fibers in water-in-oil emulsion. An experimental setup with microscope and high-speed camera was designed and established to record the water droplets’ coalescence. The water droplets’ collision coalescence on bamboo charcoal fibers was observed, and the diameters of water droplets detaching from the fibers with different angles were measured. The angle between the fiber and the flow velocity can affect the diameters of water droplets detaching from the bamboo charcoal fibers, and cross-fibers can the enormously increase water diameters compared with single fiber. Meanwhile, the water droplets’ collision coalescence on glass fibers was observed and the result shows that the collision coalescence also occurred on the hydrophilic glass fibers when the droplet diameter was small. In addition, other factors, including flow velocity and droplets’ diameter for the coalescence on the hydrophilic glass fibers were investigated.     

Reduced OFF-axis haze in polymer-dispersed liquid crystals

Polymer-dispersed liquid crystals (PDLCs) are composite materials formed by micron-sized droplets of liquid crystals (LCs) dispersed in a polymer matrix, which can be turned from an opaque state to a transparent one by application of a suitable electric field. PDLCs have been proposed in applications related to the control of light transmittance on large surfaces (light shutters, displays, rear mirrors). Despite several advantages, PDLCs’ main drawback is haze, i.e. the fast decay of transmission at large viewing angles. In this paper, a method for achieving highly transparent PDLC devices over a wide range of viewing angles is proposed. The method is based on the use of PDLCs with tilted elongated LC droplets and driven by opportune electric fields, which are experimentally calculated and able to ensure an almost constant value for OFF-axis transmittance.     

Large Ultrathin Shelled Drops Produced via Non‐Confined Microfluidics

We present a facile approach for producing large and monodisperse core–shell drops with ultrathin shells using a single‐step process. A biphasic compound jet is introduced into a quiescent third (outer) phase that ruptures to form core–shell drops. Ultrathin shelled drops could only be produced within a certain range of surfactant concentrations and flow rates, highlighting the effect of interfacial tension in engulfing the core in a thin shell. An increase in surfactant concentrations initially resulted in drops with thinner shells. However, the drops with thinnest shells were obtained at an optimum surfactant concentration, and a further increase in the surfactant concentrations increased the shell thickness. Highly monodisperse (coefficient of variation smaller than 3 %) core–shell drops with diameter of ～200 μm–2 mm with shell thickness as small as ～2 μm were produced. The resulting drops were stable enough to undergo polymerisation and produce ultrathin shelled capsules.     

Vaporisation characteristics of methanol,ethanol and heptane droplets in opposed stagnation flow at low temperature and pressure

A computational model is developed and applied to study the vaporisation behaviour of three liquid fuels. This fundamental study is motivated by a need to understand how the performance of direct-injection-spark-ignition (DISI) engines may be affected by changes in fuel composition, especially alcohols. Currently, most DISI engines are designed for homogeneous-charge combustion, where the in-cylinder fuel injection, vaporisation and mixing is accomplished during the intake and early in the compression process. Thus the temperature and pressure are low, compared to post-compression conditions. The two-phase axisymmetric model is based upon an ideal opposed stagnation flow field. Liquid droplets are carried in one air stream that is met by an opposed air flow. Because of stagnation-flow similarity, the mathematical model can be represented as a one-dimensional boundary-value problem. Results show significant differences between methanol, ethanol and heptane fuels, which have potentially important impacts on the design and modification of fuel-injection systems for direct-injection engines with alternative fuels.     

Ionization of methane clusters in helium nanodroplets

The electron ionization of helium droplets doped with methane clusters is investigated for the first time using high-resolution mass spectrometry. The dominant ion products ejected into the gas phase are the unprotonated (CH(4))(n)(+) cluster ions along with the protonated ions, CH(5)(+)(CH(4))(n-1). The mass spectra show clear evidence for magic numbers, which are broadly consistent with icosahedral shell closings. However, unusual features were observed, including different magic numbers for CH(5)(+)(CH(4))(n-1) (n=55, 148) when compared to (CH(4))(n)(+) (n=54, 147). Possible interpretations for some of these differences are proposed. Products of the type [C(2)H(x)(CH(4))(n)](+), which result from ion-molecule chemistry, are also observed and these too show clear magic number features. Finally, we report the first observation of (CH(4))(n)(2+) dications from methane clusters. The threshold for dication survival occurs at n≥70 and is in good agreement with a liquid droplet model for fission of multiply charged ions. Furthermore, we present evidence showing that these dications are formed by an unusual two-step mechanism which is initiated by charge transfer to generate a monocation and is then followed by Penning ionization to generate a dication.     

Kinetics of freezing of an oil-in-water emulsion by pressure release. Impact on ice crystals and oil droplets

Abstract

Pressure release freezing (PRF) of an oil-in-water emulsion is studied. The characteristics of ice crystals as a function of freezing process is studied.     

凝固漂浮有机液滴-分散液液微萃取-高效液相色谱-串联质谱法测定海水中苯并三唑类紫外线过滤剂

建立了海水中7种苯并三唑类紫外线过滤剂的凝固漂浮有机液滴-分散液液微萃取-高效液相色谱-串联质谱分析方法。优化后的萃取实验条件：20 μL十二醇为萃取溶剂,400 μL甲醇为分散溶剂,NaCl质量分数为8%,pH小于6,涡旋振荡时间2 min。目标化合物经Hypersil GOLD色谱柱（150 mm×2.1 mm,5 μm）结合甲醇-水梯度洗脱分离后,用正离子多反应监测模式进行质谱分析。在较宽的线性范围内,7种化合物的线性相关系数（r²）均大于0.99;基质加标回收率为68.3%~127.5%,相对标准偏差为0.9%~15.2%,方法的检出限为0.001~0.090 μg/L,定量限为0.003~0.300 μg/L。将建立的方法用于大连8个海滨浴场海水中苯并三唑类紫外线过滤剂的测定,部分浴场海水有不同程度的检出。该方法简便、快速、环境友好、灵敏度高,可用于海水中苯并三唑类紫外线过滤剂的分析检测。     

缝隙抽吸对液膜撕裂特性影响的试验研究

本文在空气-水膜两相流动试验装置上,利用高速摄影机对空心静叶缝隙抽吸下的静叶出口边液膜撕裂特性进行了试验研究,结果表明:缝隙抽吸可以将静叶表面上的大部分流动液膜去除掉,水份在叶片出口边之前形不成完整的流动液膜,仅表现为溪状流动,静叶出口边的撕裂形式主要为丝线状撕裂,撕裂形成的水滴数目和直径将明显地减小。