Structure and dynamics of polymeric materials in nano-scale

The nano-palpation technique,i.e.,nanometer-scale elastic and viscoelastic measurements based on atomic force microscope,is introduced.It is demonstrated to be very useful in analyzing nanometer-scale materials properties for the surfaces and interfaces of various types of soft materials.It enables us to obtain not only structural information but also mechanical information about a material at the same place and at the same time.     

A unified approach to error bounds for structured convex optimization problems

Error bounds, which refer to inequalities that bound the distance of vectors in a test set to a given set by a residual function, have proven to be extremely useful in analyzing the convergence rates of a host of iterative methods for solving optimization problems. In this paper, we present a new framework for establishing error bounds for a class of structured convex optimization problems, in which the objective function is the sum of a smooth convex function and a general closed proper convex function. Such a class encapsulates not only fairly general constrained minimization problems but also various regularized loss minimization formulations in machine learning, signal processing, and statistics. Using our framework, we show that a number of existing error bound results can be recovered in a unified and transparent manner. To further demonstrate the power of our framework, we apply it to a class of nuclear-norm regularized loss minimization problems and establish a new error bound for this class under a strict complementarity-type regularity condition. We then complement this result by constructing an example to show that the said error bound could fail to hold without the regularity condition. We believe that our approach will find further applications in the study of error bounds for structured convex optimization problems.     

A non-linear fluid force model for vortex-induced vibration of an elastic cylinder

Even under the assumption of a sinusoidal lift and drag force at a single frequency for a stationary cylinder in a cross flow, higher harmonics that represent non-linearity in the fluid-structure interaction process are present. This fact is considered in the formulation of a non-linear fluid force model for a freely vibrating cylinder in a cross flow. The force model is developed based on an iterative process and the modal analysis approach. The fluid force components in the model can be evaluated from measured vibration data with the help of the auto-regressive moving averaging (ARMA) technique. An example is used to illustrate that non-linear (higher order) force components are present at resonance, even for a case with relatively weak fluid-structure interaction. Further analysis reveals that the fluid force components are dependent on structural damping and mass ratio. The non-linear fluid force model is further modified by taking these considerations into account and is used to predict the dynamic characteristics of a freely vibrating cylinder over a range of Reynolds numbers, mass and structural damping ratios. On comparison with measurements obtained from four different experiments and predictions made by previous single-degree-of-freedom model, good agreement is found over a wide range of these parameters.     

Electronic structure and optical absorption spectra of CdSe covered with ZnSe and ZnS epilayers

Using the first-principles methods we compute the electronic structure and the absorption spectra for a wurtzite CdSe (0001) slab covered with zincblende ZnSe and ZnS epilayers. For each structure we compute the DOS and the imaginary part of the dielectric function. We find that the semiconductor passivation shifts the ‘near Fermi-level’ states of the bare CdSe slab down to lower energy levels. The migration suggests the decrease of surface effects and energy loss. We observe the substantial reduction of the abnormal peaks in the absorption spectra of the bare CdSe slab, which seems to be a consequence of the DOS migration. This is consistent with the experimental results that a proper passivation enhance the luminescence efficiency. We also study the case that the epilayer surface is terminated with PH₃ and find the PH₃ passivation also reduces the surface state to some extent.     

Swirl effects on variable-density jet mixing in confined flows

An experimental investigation on swirl effects on inhomogeneous confined jet mixing in a combustor configuration is reported. The confined swirling flow was simulated by a swirler with a central jet mounted in a cyclindrical tube. Helium and air jets set at different velocities were injected into the confined swirling air flow. The resulting flow fields due to two vane swirlers with constant vane angles of 35° and 66° were compared. Results show that the 35° vane swirler produces a solid-body rotation core with a slope about twice that created by the 66° vane swirler. It is the behavior of this solid-body rotation core that determines jet mixing rather than the swirler vane angle. Consequently, the coaxial jet decays much faster, the mixing is more intense, and the turbulence intensities are higher for the 35° vane swirler. In view of these results, combustor designers should be more concerned with behavior of the solid-body rotation core produced by the swirler, instead of the swirler vane angle.     

Catalytic Stereoinversion of L‐Alanine to Deuterated D‐Alanine

A combination of an achiral pyridoxal analogue and a chiral base has been developed for catalytic deuteration of L ‐alanine with inversion of stereochemistry to give deuterated D ‐alanine under mild conditions (neutral pD and 25 °C) without the use of any protecting groups. This system can also be used for catalytic deuteration of D ‐alanine with retention of stereochemistry to give deuterated D ‐alanine. Thus a racemic mixture of alanine can be catalytically deuterated to give an enantiomeric excess of deuterated D ‐alanine. While catalytic deracemization of alanine is forbidden by the second law of thermodynamics, this system can be used for catalytic deracemization of alanine with deuteration. Such green and biomimetic approach to catalytic stereocontrol provides insights into efficient amino acid transformations.     

Serum exosomal microRNAs as novel biomarkers for hepatocellular carcinoma

Recent studies have shown that circulating microRNAs are a potential biomarker in various types of malignancies. The aim of this study was to investigate the feasibility of using serum exosomal microRNAs as novel serological biomarkers for hepatocellular carcinoma (HCC) in patients with chronic hepatitis B (CHB). We measured the serum exosomal microRNAs and serum circulating microRNAs in patients with CHB (n=20), liver cirrhosis (LC) (n=20) and HCC (n=20). Serum exosomal microRNA was extracted from 500 μl of serum using an Exosome RNA Isolation kit. The expression levels of microRNAs were quantified by real-time PCR. The expression levels of selected microRNAs were normalized to Caenorhabditis elegans microRNA (Cel-miR-39). The serum levels of exosomal miR-18a, miR-221, miR-222 and miR-224 were significantly higher in patients with HCC than those with CHB or LC (P<0.05). Further, the serum levels of exosomal miR-101, miR-106b, miR-122 and miR-195 were lower in patients with HCC than in patients with CHB (P=0.014, P<0.001, P<0.001 and P<0.001, respectively). There was no significant difference in the levels of miR-21 and miR-93 among the three groups. Additionally, the serum levels of circulating microRNAs showed a smaller difference between HCC and either CHB or LC. This study suggests that serum exosomal microRNAs may be used as novel serological biomarkers for HCC.     

Synthesis and antibacterial activity of versatile substrate‐coated biocidal material via catechol chemistry

We report a potential coating material showing durable and significant antimicrobial activity for preserving the surfaces of a broad range of materials. The structure of the prepared antimicrobial adhesive material features a catechol moiety of dopamine hydrochloride conjugated to 4‐bromobutanoyl chloride as an adhesive material. Antimicrobial properties against a wide range of microorganism species are achieved by quaternizing a long hydrophobic chain (N,N'‐dimethyldecylamine) onto 3,4‐dihydroxyphenylalanine (Dopa) to afford the prepared material (Dopa‐decyl). The successful formation of Dopa‐decyl is confirmed by hydrogen nuclear magnetic resonance (¹H‐NMR) and attenuated total reflectance‐infrared (ATR‐IR) measurements. The chemical composition of the quaternized adhesive material (Dopa‐decyl) is characterized by X‐ray photoelectron spectroscopy (XPS). Investigation of the antimicrobial activity of the Dopa‐decyl‐coated film against both gram‐positive Staphylococcus aureus (S. aureus) and gram‐negative Escherichia coli (E. coli) stains reveals a highly efficient antimicrobial effect under both normal and extreme stress conditions due to the biocidal effect of the quaternized amine when the materials are applied on the surface of various substrates. Copyright © 2014 John Wiley & Sons, Ltd.     

Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent-Silyliumylidene Cation

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAAC_Me] (cAAC_Me=:C(CMe₂)₂(CH₂)NAr, Ar=2,6-iPr₂C₆H₃) with H₂SiI₂ in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC_Me)₂Si:^.]⁺I⁻ ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAAC_Me−H]⁺I⁻. In addition, the reaction of the NHC–iodosilicon(I) dimer [I_Ar(I)Si:]₂ (I_Ar=:C{N(Ar)CH}₂) with 4 equiv of I_Me (:C{N(Me)CMe}₂), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I_Me)₂SiH]⁺I⁻ ( 2 ) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the C_Ar−H bond activation product [1-F-2-I_Me-C₆H₄]⁺I⁻ ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography.