178 research outputs found
Kinetics of phase transition from lamellar to hexagonally packed cylinders for a triblock copolymer in a selective solvent
We examined the kinetics of the transformation from the lamellar (LAM) to the
hexagonally packed cylinder (HEX) phase for the triblock copolymer,
polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) in dibutyl
phthalate (DBP), a selective solvent for polystyrene (PS), using time-resolved
small angle x-ray scattering (SAXS). We observe the HEX phase with the EB block
in the cores at a lower temperature than the LAM phase due to the solvent
selectivity of DBP for the PS block. Analysis of the SAXS data for a deep
temperature quench well below the LAM-HEX transition shows that the
transformation occurs in a one-step process. We calculate the scattering using
a geometric model of rippled layers with adjacent layers totally out of phase
during the transformation. The agreement of the calculations with the data
further supports the continuous transformation mechanism from the LAM to HEX
for a deep quench. In contrast, for a shallow quench close to the OOT we find
agreement with a two-step nucleation and growth mechanism
Kinetics of HEX-BCC Transition in a Triblock Copolymer in a Selective Solvent: Time Resolved Small Angle X-ray Scattering Measurements and Model Calculations
Time-resolved small angle x-ray scattering (SAXS) was used to examine the
kinetics of the transition from HEX cylinders to BCC spheres at various
temperatures in poly(styrene-b- ethylene-co-butylene-b-styrene) (SEBS) in
mineral oil, a selective solvent for the middle EB block. Temperature-ramp SAXS
and rheology measurements show the HEX to BCC order-order transition (OOT) at
~127 oC and order-disorder transition (ODT) at ~180 oC. We also observed the
metastability limit of HEX in BCC with a spinodal temperature, Ts ~ 150 oC. The
OOT exhibits 3 stages and occurs via a nucleation and growth mechanism when the
final temperature Tf < Ts. Spinodal decomposition in a continuous ordering
system was seen when Ts< Tf < TODT. We observed that HEX cylinders transform to
disordered spheres via a transient BCC state. We develop a geometrical model of
coupled anisotropic fluctuations and calculate the scattering which shows very
good agreement with the SAXS data. The splitting of the primary peak into two
peaks when the cylinder spacing and modulation wavelength are incommensurate
predicted by the model is confirmed by analysis of the SAXS data
Survey on the Overwintering of Syrphids in Changbai Mountains and Experiments on Artificial Protection of the Overwintering Syrphid Flies
Originating text in Chinese.Citation: Gao, Junfeng, Zhang, Guangxin, Qin, Yongchun, Yu, Kai, Li, Minghai, Qin, Yi. (1993). Survey on the Overwintering of Syrphids in Changbai Mountains and Experiments on Artificial Protection of the Overwintering Syrphid Flies. Chinese Journal of Biological Control, 9(3), 142-144
Kinetics of Hexagonal Cylinders to Face-centered Cubic Spheres Transition of Triblock Copolymer in Selective Solvent: Brownian Dynamics Simulation
The kinetics of the transformation from the hexagonal packed cylinder (HEX)
phase to the face-centered-cubic (FCC) phase was simulated using Brownian
Dynamics for an ABA triblock copolymer in a selective solvent for the A block.
The kinetics was obtained by instantaneously changing either the temperature of
the system or the well-depth of the Lennard-Jones potential. Detailed analysis
showed that the transformation occurred via a rippling mechanism. The
simulation results indicated that the order-order transformation (OOT) was a
nucleation and growth process when the temperature of the system instantly
jumped from 0.8 to 0.5. The time evolution of the structure factor obtained by
Fourier Transformation showed that the peak intensities of the HEX and FCC
phases could be fit well by an Avrami equation
Complex assembly, crystallization and preliminary X-ray crystallographic studies of MHC H-2K d
PDGF induced microRNA alterations in cancer cells
Platelet derived growth factor (PDGF) regulates gene transcription by binding to specific receptors. PDGF plays a critical role in oncogenesis in brain and other tumors, regulates angiogenesis, and remodels the stroma in physiologic conditions. Here, we show by using microRNA (miR) arrays that PDGFs regulate the expression and function of miRs in glioblastoma and ovarian cancer cells. The two PDGF ligands AA and BB affect expression of several miRs in ligand-specific manner; the most robust changes consisting of let-7d repression by PDGF-AA and miR-146b induction by PDGF-BB. Induction of miR-146b by PDGF-BB is modulated via MAPK-dependent induction of c-fos. We demonstrate that PDGF regulates expression of some of its known targets (e.g. cyclin D1) through miR alterations and identify the epidermal growth factor receptor (EGFR) as a new PDGF-BB target. We show that its expression and function are repressed by PDGF-induced miR-146b and that mir-146b and EGFR correlate inversely in human glioblastomas. We propose that PDGF-regulated gene transcription involves alterations in non-coding RNAs and provide evidence for a miR-dependent feedback mechanism balancing growth factor receptor signaling in cancer cells
An Optimization of a Turbocharger Blade Based on Fluid–Structure Interaction
The structural fracture of the compressor blade is the main cause of fatigue failure. The novelty of this paper is the creative application of bent swept-back modeling to the blade of the turbocharger impeller. This paper is based on a compressor impeller satisfying the k-ε turbulence model. A simulation model was established in ANSYS software, the fluid–structure interaction was calculated in the three models before and after improvement, and the results were compared and analyzed. The optimized blade could improve the blade structure, reduce stress and deformation, and improve the pressurization ratio. In this paper, the optimization scheme of different parameters was discussed in line with the optimal solution. Based on the combination of fuzzy and grey correlation theory, it was concluded that the correlation between pressure and total deformation was higher than that of equivalent stress, and these two values reached 0.8596 and 0.8001, respectively. The results showed that the pressure and total deformation were significantly related to the flow rate. It provides a feasible scheme for further improvement of the supercharger compressor
Does top executives’ US experience matter? Evidence from US-listed Chinese firms
Foreign firms face enormous obstacles in attracting investors and analysts when issuing securities in the United States. We use US-listed Chinese firms as our research sample and find that firms that hire top executives (i.e., Chief Executive Officer [CEO] or Chief Financial Officer [CFO]) with work experience in the US or educational qualifications from the US attract more US institutional investors and analysts. Further, we find that CFOs’ US experience dominates the results. Corroborating our results, we further find that firms with US-experienced CFOs are more likely to hold conference calls and voluntarily issue management forecasts, which suggests that CFOs with a US background are better at communicating with US investors and analysts and acting in alignment with US norms compared with Chinese CFOs. Collectively, our results suggest that hiring a CFO with a US background could facilitate cross-listed foreign firms to lower US investors’ and analysts’ information disadvantage
Design and Analysis of Quartz Crystal Microbalance with a New Ring-Shaped Interdigital Electrode
In this paper, a new type of ring-shaped interdigital electrode is proposed to improve the accuracy and repeatability of quartz crystal microbalance. The influence of different types of single finger, dot finger, dot double-finger electrodes on mass sensitivity distribution as well as the optimal proportion of finger and gap width are obtained through multi-physical coupling simulation. The results show that the design criteria of interdigital electrodes will not change with the increase in the number of fingers. The gap width should obey the decrease order from central to edge and be about twice the width of finger. The width of the outermost finger and the radius of the middle dot electrode should be maintained at about 0.4 and 0.2 times of the total electrode radius. An experiment was carried out to verify that the quartz wafer with a dot double-finger electrode has high quality factors and less modal coupling, which can satisfy the engineering application well. As a conclusion, this study provides a design idea for the electrode to maintain a uniform distribution of quartz crystal microbalance mass sensitivity
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