Study on coalescence dynamics of unequal-sized microbubbles captive on solid substrate

The dynamics of bubble coalescence are of importance for a number of industrial processes, in which the size inequality of the parent bubbles plays a significant role in mass transport, topological change and overall motion. In this study, coalescence of unequal-sized microbubbles captive on a solid substrate was observed from cross-section view using synchrotron high-speed imaging technique and a microfluidic gas generation device. The bridging neck growth and surface wave propagation at the early stage of coalescence were investigated by experimental and numerical methods. The results show that theoretical half-power-law of neck growth rate is still valid when viscous effect is neglected. However, the inertial-capillary time scale is associated with the initial radius of the smaller parent microbubble. The surface wave propagation rate on the larger parent microbubble is proportional to the inertial-capillary time scale

Understanding Microbubble Coalescence Using High-Speed Imaging and Lattice Boltzmann Method Simulation

poster abstractMicrobubble coalescence is one of the important research areas of bubble dynamics. The purpose of this research is to seek deeper understanding and relative mathematical relation on microbubble coalescence. To fulfill that, we conducted both experiments and simulations. For the part of experiment, we fabricated a microfluidic gas generator with better performance leading corresponding fluidic chemical reaction. After that we utilized ultrafast synchrotron X-ray imaging facility at the Advanced Photon Source of Argonne National Laboratory to capture the gas generating and microbubble merging phenomena using high speed imaging. These experiments show how the microbubbles with the same ratio contact and merge in the reaction channel and different concentration of reactants. As for the part of simulation, we lead the simulation basing on lattice Boltzmann method to simulate microbubble coalescence in water with unequal diameter ratio. Focuses are on the effects of size inequality of parent bubbles on the coalescence geometry and time. The “coalescence preference” of coalesced bubble closer to the larger parent bubble is well captured. A power-law relation between the preferential relative distance and size inequality is consistent to the recent experimental observations. Meanwhile, the coalescence time also exhibits power-law scaling, indicating that unequal bubbles coalesce faster than equal bubbles

Spatial and Temporal Scaling of Unequal Microbubble Coalescence

We numerically study coalescence of air microbubbles in water, with density ratio 833 and viscosity ratio 50.5, using lattice Boltzmann method. The focus is on the effects of size inequality of parent bubbles on the interfacial dynamics and coalescence time. Twelve cases, varying the size ratio of large to small parent bubble from 5.33 to 1, are systematically investigated. The “coalescence preference,” coalesced bubble closer to the larger parent bubble, is well observed and the captured power-law relation between the preferential relative distance χ and size inequality γ, math formula, is consistent to the recent experimental observations. Meanwhile, the coalescence time also exhibits power-law scaling as math formula, indicating that unequal bubbles coalesce faster than equal bubbles. Such a temporal scaling of coalescence on size inequality is believed to be the first-time observation as the fast coalescence of microbubbles is generally hard to be recorded through laboratory experimentation

Spatial and Temporal Scaling of Unequal Microbubble Coalescence

poster abstractWe numerically study coalescence of air microbubble in water, with density ratio 833 and viscosity ratio 50.5, using lattice Boltzmann method (LBM). Focuses are on the effects of size inequality of parent bubbles on the coalescence geometry and time and underlying dynamics of unequal microbubble coalescence. Twelve cases, varying the size ratio of large to small parent bubble γ from 5.33 to 1, are systematically investigated. The “coalescence preference” of coalesced bubble closer to the larger parent bubble is well captured. A power-law relation between the preferential relative distance χ and size inequality γ as χ ∼ γ−2.079 is consistent to the recent experimental observations. Meanwhile, the coalescence time also exhibits power-law scaling as T ∼ γ−0.7, implying that unequal bubbles coalesce faster than equal bubbles. Such a time scaling of coalescence on size inequality is believed the first-time observation as the fast coalescence of microbubbles is generally hard to be recorded through laboratory experimentation

Nickel pyrithione induces apoptosis in chronic myeloid leukemia cells resistant to imatinib via both Bcr/Abl-dependent and Bcr/Abl-independent mechanisms

Abstract Background Acquired imatinib (IM) resistance is frequently characterized by Bcr-Abl mutations that affect IM binding and kinase inhibition in patients with chronic myelogenous leukemia (CML). Bcr-Abl-T315I mutation is the predominant mechanism of the acquired resistance to IM. Therefore, it is urgent to search for additional approaches and targeting strategies to overcome IM resistance. We recently reported that nickel pyrithione (NiPT) potently inhibits the ubiquitin proteasome system via targeting the 19S proteasome-associated deubiquitinases (UCHL5 and USP14), without effecting on the 20S proteasome. In this present study, we investigated the effect of NiPT, a novel proteasomal deubiquitinase inhibitor, on cell survival or apoptosis in CML cells bearing Bcr-Abl-T315I or wild-type Bcr-Abl. Methods Cell viability was examined by MTS assay and trypan blue exclusion staining assay in KBM5, KBM5R, K562, BaF3-p210-WT, BaF3-p210-T315I cells, and CML patients’ bone marrow samples treated with NiPT. Cell apoptosis in CML cells was detected with Annexin V-FITC/PI and rhodamine-123 staining followed by fluorescence microscopy and flow cytometry and with western blot analyses for apoptosis-associated proteins. Expression levels of Bcr-Abl in CML cells were analyzed by using western blotting and real-time PCR. The 20S proteasome peptidase activity was measured using specific fluorogenic substrate. Active-site-directed labeling of proteasomal DUBs, as well as the phosphorylation of USP14 was used for evaluating the inhibition of the DUBs activity by NiPT. Mouse xenograft models of KBM5 and KBM5R cells were analyzed, and Bcr-Abl-related proteins and protein biomarkers related to proliferation, differentiation, and adhesion in tumor tissues were detected by western blots and/or immunohistological analyses. Results NiPT induced apoptosis in CML cells and inhibited the growth of IM-resistant Bcr-Abl-T315I xenografts in nude mice. Mechanistically, NiPT induced decreases in Bcr-Abl proteins, which were associated with downregulation of Bcr-Abl transcription and with the cleavage of Bcr-Abl protein by activated caspases. NiPT-induced ubiquitin proteasome system inhibition induced caspase activation in both IM-resistant and IM-sensitive CML cells, and the caspase activation was required for NiPT-induced Bcr-Abl downregulation and apoptotic cell death. Conclusions These findings support that NiPT can overcome IM resistance through both Bcr-Abl-dependent and Bcr-Abl-independent mechanisms, providing potentially a new option for CML treatment

CCN1, a Pro-Inflammatory Factor, Aggravates Psoriasis Skin Lesions by Promoting Keratinocyte Activation

Psoriasis is a common chronic skin disease characterized by epidermal hyperplasia and inflammation. The pathogenesis of psoriasis is multifactorial and is not fully understood. Here we demonstrate that CCN1 (also called Cyr61, which is short for cysteine-rich 61), an extracellular matrix protein that is also considered a pro-inflammatory factor, is highly expressed in the lesional skin of psoriasis patients, as well as in that of imiquimod (IMQ)- and IL-23-treated psoriasis-like mice. Then we show that blocking CCN1 function in vivo attenuates epidermal hyperplasia and inflammation in psoriasis-like mice. Further, in primary cultured normal human keratinocytes and HaCaT (human keratinocyte cell line) cells, CCN1 promotes keratinocyte activation, including the proliferation and expression of immune-related molecules. Finally, we observe that integrin α6β1 is the receptor of CCN1 in keratinocytes, and CCN1 stimulation activates the downstream phosphoinositide-3 kinase/Akt/NF-κB signaling pathway. Taken together, our findings reveal that CCN1 has a critical role in psoriasis pathogenesis. Moreover, as CCN1 is a secreted extracellular matrix (ECM) protein, our study also provides evidence that ECM, which is involved in psoriatic pathogenesis, could be a potent target for psoriasis treatment

Scalings of Inverse Energy Transfer and Energy Decay in 3-D Decaying Isotropic Turbulence with Non-rotating or Rotating Frame of Reference

Energy development of decaying isotropic turbulence in a 3-D periodic cube with non-rotating or rotating frames of reference is studied through direct numerical simulation using GPU accelerated lattice Boltzmann method. The initial turbulence is isotropic, generated in spectral space with prescribed energy spectrum E(κ)~κm in a range between κmin and κmax. The Taylor microscale Reynolds number Reλ and Rossby number Ro are introduced to characterize the inertial, viscous, and rotational attributes of the system. The focus of this study is on the scalings of early inverse energy transfer and late energy decay in the development of turbulent energy under various conditions through combinations of m, κmin, κmax, Reλ and Ro. First, we demonstrate the validity of the simulation by confirming the quantitative dependence of the decay exponent n on the initial energy spectrum exponent m, at Reλ =255 and Ro=∞, varying the values of m, κmin and κmax. Second, at relatively low Reλ, the decay exponent for different initial spectra statistically fall in respective ranges, all of which agree well with the corresponding analytical predictions. Third, we quantitatively investigate the 3-D inverse energy transfer. Our findings include (i) the exponent of inverse energy transfer spectrum E(κ)~κσ depends on the initial spectrum exponent E(κ) ~ κm: if m<4, σ=m while if m≥4, σ=4; (ii) rotation alters the inverse energy transfer rate when Reλ≤255 and Ro≥0.8; (iii) the energy increase in large scale during inverse energy transfer exhibits a bell shape, the peak of which varies with Reλ and Ro

Revisit of axis-switching in low aspect-ratio rectangular jets

poster abstractAxis switching refers to the change in the orientation of the major axis of the jet from initial spanwise to lateral direction. This phenomenon is of interest both from fundamental physics and practical application points of view. This behavior is most noticeable in square and low aspect-ratio (AR) rectangular jet flows. It has been reported computationally that square jet (AR=1) and rectangular jet (AR=1.5) switch the major axis 450 and 900 respectively [1-2]. In this work we revisit the axis-switching phenomenon through direct numerical simulation using kinetic-based lattice Boltzmann method for a square jet and 4 rectangular jets with AR =1.5, 2, 2.5, and 3 respectively at Re=200. It is observed that larger AR jet develops longer characteristic decay (CD) region where jet decay and mixing depend on the jet AR. As all rectangular jets exhibit 900 axis-switching close to the end of the CD region as expected although the location varies with ARs, 450 axis-switching is discovered in each jet before the 900 axis-switching appears downstream. Quantitative examinations of the transition from 450 to 900 in rectangular jets are conducted to reveal the physical underlying mechanism of jet development and provide physical insights for practical application