Quantification of the stimuli‐responsive phase transition in polymers is topical and important for the understanding and development of novel stimuli‐responsive materials. The temperature‐induced phase transition of poly(N‐isopropylacrylamide) (PNIPAm) with one thiol end group depends on the confinement—free polymer or polymer brush—on the molecular weight and on the nature of the second end. This paper describes the synthesis of heterotelechelic PNIPAm of different molecular weights with a thiol end group—that specifically binds to gold nanorods and a hydrophilic NIPAm end group by reversible addition‐fragmentation chain‐transfer polymerization. Proton high‐resolution magic angle sample spinning NMR spectra are used as an indicator of the polymer chain conformations. The characteristics of phase transition given by the transition temperature, entropy, and width of transition are obtained by a two‐state model. The dependence of thermodynamic parameters on molecular weight is compared for hydrophilic and hydrophobic end functional‐free polymers and brushes. 相似文献
Magnetic resonance spectroscopy (MRS), as a noninvasive method for molecular structure determination and metabolite detection, has grown into a significant tool in clinical applications. However, the relatively low signal-to-noise ratio (SNR) limits its further development. Although the multichannel coil and repeated sampling are commonly used to alleviate this problem, there is still potential room for promotion. One possible improvement way is combining these two acquisition methods so that the complementary of them can be well utilized. In this paper, a novel coil-combination method, average smoothing singular value decomposition, is proposed to further improve the SNR by introducing repeatedly sampled signals into multichannel coil combination. Specifically, the sensitivity matrix of each sampling was pretreated by whitened singular value decomposition (WSVD), then the smoothing was performed along the repeated samplings’ dimension. By comparing with three existing popular methods, Brown, WSVD, and generalized least squares, the proposed method showed better performance in one phantom and 20 in vivo spectra. 相似文献
Vascular PET grafts (Dacron) have shown good performance in large vessels (≥6 mm) applications. To address the urgent unmet need for small‐diameter (2–6 mm) vascular grafts, proprietary high‐compliance nonwoven PET fiber structures were modified with various PEG concentrations using PVA as a cross‐linking agent, to fabricate non‐thrombogenic mechanically compliant vascular grafts. The blood compatibility assays measured through platelet adhesion (SEM and mepacrine dye) and platelet activation (morphological changes, P‐selectin secretion, and TXB2 production) demonstrate that functionalization using a 10% PEG solution was sufficient to significantly reduce platelet adhesion/activation close to optimal literature‐reported levels observed on carbon‐coated ePTFE.
By recourse to information-theory tools, we study aspects of the dynamics of the interaction between a single trapped ion with a laser field. Despite its simplicity the model we use exhibits a broad range of intricate physical effects that are clearly detected by information quantifiers like Wherl’s entropy and Fisher’s measure. In particular, a sensible dynamical difference between single vs. multi-photon processes is detected. 相似文献
Effects of alkyl side chains (R‐) on the electronic structural properties of aliphatic amino acids are investigated using quantum mechanical approaches. The carbon (C 1s) binding energy spectra of the aliphatic amino acids are derived from the C 1s spectrum of glycine (the parent spectrum) by the addition of spectral peaks, depending on the alkyl side chains, appearing in the lower energy region IP < 290 eV (where IP is the ionization potential). The two glycyl parent spectral peaks of the amide 291.0 eV [C(2)] and carboxylic 293.5 eV [C(1)] C atoms are shifted in the aliphatic amino acids owing to perturbations depending on the size and structure of the alkyl chains. The pattern of the N 1s and O 1s spectra in glycine is retained in the spectra of the other amino acids with small shifts to lower energy, again depending on the alkyl side chain. The Hirshfeld charge analyses confirm the observations. The alkyl effects on the valence binding energy spectra of the amino acids are concentrated in the middle valence energy region of 12–16 eV, and hence this energy region of 12–16 eV is considered as the `fingerprint' of the alkyl side chains. Selected valence orbitals, either inside or outside of the alkyl fingerprint region, are presented using both density distributions and orbital momentum distributions, in order to understand the chemical bonding of the amino acids. It is also observed that the HOMO–LUMO energy gaps of the aliphatic amino acids are reduced with the growth of the alkyl side chain. 相似文献
