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The early-stage ordering kinetics in C113A11 has been investigated by in situ time-resolved x-ray scattering. At temperatures above the first-order transition point, T ir , short-range order fluctuations reequilibrate in a few seconds after a quench from a high temperature. At temperatures just below T iT , the fluctuations relax to a metastable state which then decays by relatively slow nucleation and growth. At lower temperatures, the time scales of the two processes become similar. The ordering becomes continuous well above the classical spinodal temperature.PACS numbers: 64.60.Cn, 61.50.KsThe evolution of a system undergoing a homogeneous phase transition can be conceptually divided into early and late stages. During the early stage, the initial phase transforms into domains of the final phase(s), driven by a bulk free-energy difference. During the late stage, the domains of the final phase(s) coarsen, driven by interfacial free energy. The early stage of a first-order phase transition is expected to be either a nucleated process or a spinodal (continuous) process, depending upon whether the initial phase is metastable or unstable. l Few experiments have been performed with sufficient time resolution to study the range of early-stage behavior between these limiting cases. In particular, the time resolution must be smaller than the equilibration time of fluctuations in the metastable region in order to observe the early stages near the boundary of the unstable region. Furthermore, there have been no previous structural studies of the early-stage kinetics of an ordering transition. Ordering transitions may be expected to show qualitatively different behavior than clustering transitions since the order parameter is not conserved. 2 We report here on a time-resolved x-ray scattering study of the early-stage ordering kinetics in CU3AU. This study complements recent later-time experiments 3,4 on this system. The results show directly and quantitatively how nucleated ordering changes to continuous ordering with decreasing temperature. The subsecond time resolution necessary for the in situ observation of these early-stage phenomena is made possible in this study by the use of an intense synchrotron x-ray source, a fast detector system, and a method of rapidly changing the sample temperature.The experiments were performed on the IBM-MIT beam line X20C at the National Synchrotron Light Source. A high-intensity W-Si multilayer monochromator 5 was used which gave an incident flux of 10 13 photons/s at 8.0 keV. The samples were polycrystalline CU3AU ribbons (stoichiometric to within 0.5%) with -l-fim grain size, 0.5 mm wide by 20 ^m thick, produced by melt spinning. The ribbons were resistively heated in situ in a helium atmosphere while an optical pyrometer monitored the sample temperature. Since the emittance was not accurately known, an experimental value was obtained from the observed first-order transition point and the nominal 6 value of T XT =663 K. The temperature reported here are therefore relative to a transit...

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Purpose: Resistant strains of Acinetobacter baumannii (AB) that can form biofilms are resistant to polymyxin. Therefore, effective and safe polymyxin preparations against biofilm-producing AB are urgently needed. This study aims to prepare chitosan-modified polymyxin B-loaded liposomes (CLPs) and ultrasound microbubbles (USMBs) and then explore the synergistic antibacterial effects of USMBs combined with CLPs in vitro. Methods: CLPs were prepared using a modified injection method, and microbubbles were prepared using a simple mechanical vibration method. Minimal biofilm inhibitory concentration (MBIC) of CLPs against resistant biofilm-producing AB was determined. Antibacterial activities of CLPs with or without USMBs were analyzed by crystal violet staining and resazurin assays to evaluate biofilm mass and viable counts, respectively. Then, the anti-biofilm effects of CLPs with or without USMBs on biofilm-producing AB were confirmed via scanning electron microscopy (SEM) analysis. Results: We prepared CLPs that were 225.17±17.85 nm in size and carried positive charges of 12.64±1.44 mV. These CLPs, with higher encapsulation efficiency and drug loading, could exhibit a sustained release effect. We prepared microbubbles that were 2.391±0.052 µm in size and carried negative charges of −4.32±0.43 mV. The MBICs of the CLPs on the biofilmproducing AB was 8±2 µg/mL, while that of polymyxin B was 32±2 µg/mL. USMBs in combination with 2 µg/mL of polymyxin B could completely eliminate the biofilm-producing AB and achieve the maximum antimicrobial effects (P.0.05 vs sterile blank control). SEM imaging revealed some scattered bacteria without a biofilm structure in the USMB combined with the CLP group, confirming that this combination has the greatest anti-biofilm effects. Conclusion: In this research, we successfully prepared USMBs and CLPs that have a more significant antibacterial effect on biofilm-forming AB than polymyxin B alone. Experiments in vitro indicate that the synergistic antibacterial effect of combining USMBs with CLPs containing as little as 2 µg/mL of polymyxin B is sufficient to almost eliminate drug-resistant biofilm-producing AB.

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