Conformation orientation of syndiotactic polypropylene induced by deformation at different temperatures

Two syndiotactic polypropylene (sPP) sample films (S0 and S90) with different initial structures were prepared in this paper by isothermal crystallization from the melt at 0 and 90 degrees C, respectively. The polymorphic transitions of the two samples induced by deformation at different temperatures (20, 40, and 60 degrees C) were investigated by rheo-optical FTIR spectroscopy. The results indicated that stretching leads to the transition from the helical to trans-planar conformation and improves the orientation of both helical and trans-planar conformations for the sPP films. With increasing stretching temperature, the conformational transitions for the two sPP samples are all suppressed, and the orientation behavior of the two samples appears completely different. The orientation degree of S0 decreases with increasing stretching temperature, while that of S90 increases. These results suggest that the stretching temperature and initial structure have great influence on the conformation transition and orientation behavior of the sPP sample. On the basis of the experimental results, the schematic illustration of the conformation transition and orientation behavior of sPP during stretching has been proposed.     

Linear-scaling method for calculating nuclear magnetic resonance chemical shifts using gauge-including atomic orbitals within Hartree-Fock and density-functional theory

Details of a new density matrix-based formulation for calculating nuclear magnetic resonance chemical shifts at both Hartree-Fock and density functional theory levels are presented. For systems with a nonvanishing highest occupied molecular orbital-lowest unoccupied molecular orbital gap, the method allows us to reduce the asymptotic scaling order of the computational effort from cubic to linear, so that molecular systems with 1000 and more atoms can be tackled with today's computers. The key feature is a reformulation of the coupled-perturbed self-consistent field (CPSCF) theory in terms of the one-particle density matrix (D-CPSCF), which avoids entirely the use of canonical MOs. By means of a direct solution for the required perturbed density matrices and the adaptation of linear-scaling integral contraction schemes, the overall scaling of the computational effort is reduced to linear. A particular focus of our formulation is to ensure numerical stability when sparse-algebra routines are used to obtain an overall linear-scaling behavior.     

A density matrix-based method for the linear-scaling calculation of dynamic second- and third-order properties at the Hartree-Fock and Kohn-Sham density functional theory levels

A density matrix-based time-dependent self-consistent field (D-TDSCF) method for the calculation of dynamic polarizabilities and first hyperpolarizabilities using the Hartree-Fock and Kohn-Sham density functional theory approaches is presented. The D-TDSCF method allows us to reduce the asymptotic scaling behavior of the computational effort from cubic to linear for systems with a nonvanishing band gap. The linear scaling is achieved by combining a density matrix-based reformulation of the TDSCF equations with linear-scaling schemes for the formation of Fock- or Kohn-Sham-type matrices. In our reformulation only potentially linear-scaling matrices enter the formulation and efficient sparse algebra routines can be employed. Furthermore, the corresponding formulas for the first hyperpolarizabilities are given in terms of zeroth- and first-order one-particle reduced density matrices according to Wigner's (2n+1) rule. The scaling behavior of our method is illustrated for first exemplary calculations with systems of up to 1011 atoms and 8899 basis functions.     

Water-stable biphasic nanocolloids with potential use as anisotropic imaging probes

Electrified co-jetting of two aqueous polymer solutions followed by a thermal cross-linking step was used to create water-stable biphasic nanocolloids. For this purpose, aqueous solution mixtures of poly(acrylamide-co-acrylic acid) and poly(acrylic acid) were employed as jetting solutions. When the biphasic nanocolloids created by side-by-side electrified co-jetting were thermally treated, a cross-linking reaction occurred between amide groups and carboxylic groups to form stable imide groups. Infrared spectroscopy was employed to monitor the reaction. The quality and the integrity of the resulting biphasic nanocolloids were confirmed by confocal laser scanning microscopy, flow cytometry analysis, and dynamic light scattering. Selective encapsulation of two biomolecules in each phase of the biphasic colloids was maintained even after thermal reaction and suspension in aqueous environment. Well-dispersed spherical colloids with stable dye loadings in each hemisphere were kept intact without aggregation or dissolution for several weeks. Finally, biphasic nanocolloids were selectively surface-modified with a biotin-dextran resulting in water-stable particles to ensure binding of proteins only to a single hemisphere.     

Micropatterned Fiber Scaffolds for Spatially Controlled Cell Adhesion

Because the local microstructure plays a pivotal role for many biological functions, a wide range of methods have been developed to design precisely engineered substrates for both fundamental biological studies and biotechnological applications. However, these techniques have been by‐and‐large limited to flat surfaces. Herein, we use electrohydrodynamic co‐spinning to prepare biodegradable three‐dimensional fiber scaffolds with precisely engineered, micrometre‐scale patterns, wherein each fiber is comprised of two distinguishable compartments. When bicompartmental fiber scaffolds are modified via spatially controlled peptide immobilization, highly selective cell guidance at spatial resolutions (<10 µm), so far exclusively reserved for flat substrates, is achieved. Microstructured fiber scaffolds may have utility for a range of biotechnological applications including tissue engineering or cell‐based assays.

     

STM manipulation of a subphthalocyanine double-wheel molecule on Au(111)

A new class of double-wheel molecules is manipulated on a Au(111) surface by the tip of a scanning tunneling microscope (STM) at low temperature. The double-wheel molecule consists of two subphthalocyanine wheels connected by a central rotation carbon axis. Each of the subphthalocyanine wheels has a nitrogen tag to monitor its intramolecular rolling during an STM manipulation sequence. The position of the tag can be followed by STM, allowing us to distinguish between the different lateral movements of the molecule on the surface when manipulated by the STM tip.     

Acoustic Radiation Force Impulse-Imaging for the evaluation of the thyroid gland: a limited patient feasibility study

Purpose

Real-time tissue elastography, a qualitative elastography method, has shown promising results in the diagnostic work up of thyroid nodules. However, to our knowledge no study has evaluated a quantitative elastography method in the thyroid gland. The present study is a feasibility study evaluating Acoustic Radiation Force Impulse-Imaging, a novel quantitative elastography method in the thyroid gland.

Methods

ARFI-imaging involves the mechanical excitation of tissue using short-duration acoustic pulses to generate localized displacements in tissue. The displacements induce a lateral shear-wave propagation which is tracked using multiple laterally positioned ultrasound “tracking“ beams. Inclusion criteria were: thyroid nodules ?1 cm, non-functioning or hypo-functioning on radionuclide scanning, and cytological/histological assessment of thyroid nodule as reference method. All patients received conventional ultrasound, and examination of the thyroid gland including Power Doppler Ultrasound using a 9 MHz linear transducer, in addition real-time elastography (RTE) was performed at 9 MHz frequency and ARFI-imaging was performed at 4 MHz using Siemens (ACUSON S2000) B-mode-ARFI combination transducer.

Results

Sixty nodules in 55 patients were analyzed. Three nodules were papillary carcinoma. The stiffer the tissue the faster the shear wave propagates. The results obtained indicated that the shear wave velocity in thyroid lobes ranged between 0.5 and 4.9 m/s. The median velocity of ARFI-imaging in the healthy nodule-free thyroid gland, as well as in benign and malignant thyroid nodules was 1.98 m/s (range: 1.20-3.63 m/s), 2.02 m/s (range: 0.92-3.97 m/s), and 4.30 m/s (range: 2.40-4.50 m/s), respectively. While no significant difference in median velocity was found between healthy thyroid tissue and benign thyroid nodules, a significant difference was found between malignant thyroid nodules on the one hand and healthy thyroid tissue (p = 0.018) or benign thyroid nodules (p = 0.014) on the other hand. Specificity of ARFI-imaging for the differentiation of benign and malignant thyroid nodules was comparable with RTE (91-95%).

Conclusions

ARFI can be performed in the thyroid tissue with reliable results.