Examining MRI contrast in three-dimensional cell culture phantoms with DNA-templated nanoparticle chains

DNA-templated nanoparticle (NP) chains were examined as potential magnetic resonance imaging (MRI) contrast agents using in vitro environments of the extracellular matrix and tissue. A 3-T clinical MRI scanner was utilized to examine and compare image contrast enhanced by dispersed NPs, DNA-templated NP chains, gold-superparamagnetic multicomponent NP chains, and polyelectrolyte encapsulated, multicomponent NP chains in both T(1)-weighted and T(2)-weighted images. In addition, the longitudinal and transverse relaxivity (r(1) and r(2)) changes were measured both in the basement membrane, using Matrigel, and in the tissue environment, using in vitro 3D cell culture scaffolds. Results suggest that MRI contrast was significantly enhanced from NP chains compared to dispersed NPs in the basement membrane and polyelectrolyte encapsulation for NP chains produced similar relaxivity to nonencapsulated NP chains due to the enhanced cell uptake of encapsulated NP chains.     

Statistical Analysis of Macromolecular Chains in the Space Filled by Nanoparticles

The paper presents a combination of worm-like chain numerical models and one with a finite set of nano-particles. The primary objective of the models was to analyze the distribution of space in a system filled by particles. Information on the distribution of space was compared to properties of chains inside the set of particles. The set of nanoparticles was constructed with a tool generating a finite set of particles that is randomly distributed in a given space. The particles have a prescribed volume fraction and uniform size. First, the proportions of chains and particles were compared. The length of chain was expressed in terms of end-to-end length. It was then compared to the size of gaps between two particles. The volume of chain was compared to the volume of space delimited by the particles. Next, a set of 10,000 random chains was generated and these were introduced into the particle set. The contact of a chain with the surface of a particle resulted in the special structural elements of the chain: a chain connecting two different particles, a loop which begins and ends at the same particle, a part of a chain which is completely adhered to the particle surface, a chain attached to a particle with one free end, as well as completely free chains. The chains were classified under three classes: chains which were not in contact with particles, chains which were in contact with one particle, and chains which were in contact with two or more particles. A statistical representation of each class is presented. The contact between chain and particle can influence macroscopic properties such as those that are elastic.     

High resolution of DL-tryptophan at high flow rates using a bovine serum albumin-multilayered porous hollow-fiber membrane

We describe a bovine serum albumin (BSA)-multilayer-adsorbed porous hollow-fiber membrane as a stationary phase that enables chiral separations at a high resolution and high rate. Epoxy-group-containing graft chains were uniformly immobilized on the surface of pores throughout a porous hollow-fiber membrane by radiation-induced graft polymerization. Subsequently, a diethylamino group as an anion-exchange moiety was introduced to the graft chains, which caused the chains to expand toward the interior of the pores due to mutual electrostatic repulsion. The expanding polymer chains provided multilayer binding sites for BSA as a chiral selector. BSA with a degree of multilayer binding of 4 specifically recognized L-tryptophan with a separation factor of 6.6 during permeation by a mobile phase (Tris-HC1 buffer) injected with a racemic solution of DL-tryptophan through the BSA-multilayered porous membrane. In addition, the separation factor was constant irrespective of flow rates of the mobile phase because of negligible diffusional mass-transfer resistance of tryptophan to BSA multilayered by the graft chains.     

Experimental study of embedded and non-embedded ordered granular chains under impulsive excitation

Experimental pulse transmission in impulsively loaded, homogeneous, and dimer granular chains, optionally embedded in a viscoelastic matrix, is studied. All tested chains are composed of spherical elastic beads of common radius. Homogeneous chains were composed of granules with equal mass, whereas dimer chains had alternating ‘heavy’ and ‘light’ granules with different masses. These media are strongly nonlinear due to Hertzian interactions between adjacent beads under compressive loads, and separations and collisions between them in the absence of compression. A series of experimental tests was performed to study primary pulse transmission in the non-embedded chains, and assess the effect of the surrounding viscoelastic matrix on pulse transmission in the embedded ones. For the case of dimer chains, the effect of mass inhomogeneity on pulse attenuation caused by scattering at the interfaces between adjacent beads is studied. In total, two embedded dimer chains, as well as an embedded homogeneous one, were manufactured and tested, and a previous theoretical model is used to compare theoretical predictions to experimental measurements. Whereas one of the non-embedded dimer chains differs from the others in that its light beads are hollow and so its experimental responses are not captured well by our theoretical model, for the other embedded and non-embedded chains, the theoretical predictions match remarkably well with the experimental measurements, despite the complexity in the acoustics induced by the surrounding matrix, and the conceptual simplicity of the theoretical model. The results of this work contribute to the development of practical acoustic metamaterials incorporating embedded granular media.     

Nature inspired supply chain solutions: definitions,analogies, and future research directions

ABSTRACT

Supply chains are becoming increasingly complex, and many companies and researchers are looking to nature for finding solutions. In this paper, we provide a narrative synthesis and systematic review to explore state-of-the-art, and identify key areas for exploration of nature inspired solutions in the supply chain area. We consider strategic, tactical, and operational decisions within supply chains and identify analogies between biological systems and supply chains to create a new research agenda. Our findings show that the majority of the research in nature inspired supply chains from the systemic perspective focuses on closed loop supply chains. In contrast, similar systemic solutions such as industrial symbiosis, circular economy, and industrial ecology have not been explored as frequently. Reducing production waste (industrial symbiosis) in addition to end-of-life product waste (closed loop supply chains), optimising raw material use and extending the life of used resources (circular economy), investigating the interactions between biosphere and technosphere (industrial ecology), and seeking solutions to industrial problems from nature (biomimicry) are all possible paths for reaching a zero-waste economy. These systemic solutions have a considerable impact on the supply chains at the strategic, tactical, and operational levels, which need to be explored to identify efficient and effective solutions.     

Polyacrylamide hydrogels and semi-interpenetrating networks (IPNs) with poly(N-isopropylacrylamide): Mechanical properties by measure of compressive elastic modulus

Semi-IPN hydrogels (based on cross-linked polyacrylamide having poly(N-isopropylacrylamide) (PN1PAAm) inside) were synthesized and their properties, such as swelling ratio and compressive elastic moduli, were studied at several temperatures. Equilibrium swelling ratios of semi-IPN markedly decreased due to the presence of less hydrophilic PNIPAAm chains. The semi-IPN presented greater elastic modulus when compared to the cross-linked PAAm hydrogel. The effect was explained as being an additional contribution of the PNIPAAm chains, which collapsed around the PAAm networks, to the elastic modulus. It was pointed out that the PAAm networks support the collapsed chains. According to the results presented in this work, semi-IPN hydrogels present better mechanical properties than the PAAm hydrogel, mainly when the PNIPAAm chains are in a collapsed state.     

Equilibrium analysis of distribution channel structures under power imbalance and asymmetric information

This paper investigates the problem of channel choice game in two power-imbalanced supply chains consisting of the leader supply chain and the follower supply chain. We assume that there exists symmetric and asymmetric cost information between the two supply chains, and that the two chains as well as the two members in each chain follow the Stackelberg game setting. We analyse four competition scenarios: both chains are decentralised, where individual members of both supply chains maximise their own profits by independently selecting their price policies; both chains are integrated, where manufacturers and retailers coordinate their decisions to maximise supply chain profits; the leader chain is decentralised and the follower integrated; the leader is integrated and the follower decentralised. The primary objective of this paper is to investigate the influence of power imbalance, information asymmetries, and the degree of product substitutability under channel choice equilibrium. We find that, in contrast to earlier literature where all manufacturers share equal or balanced decision-making power, an integrated distribution channel is the dominant strategy for the leader under symmetric and asymmetric information Stackelberg game. As the degree of product substitutability increases, the follower will gradually switch from integrated distribution channel to decentralised distribution channel; the follower can gain from constructing a decentralised distribution channel as the prediction accuracy of the leader increases.     

Controlling the kinetic chain length of the crosslinks in photo-polymerized biodegradable networks

Biodegradable polymer networks were prepared by photo-initiated radical polymerization of methacrylate functionalized poly(d,l-lactide) oligomers. The kinetic chains formed in this radical polymerization are the multifunctional crosslinks of the networks. These chains are carbon–carbon chains that remain after degradation. If their molecular weight is too high these poly(methacrylic acid) chains can not be excreted by the kidneys. The effect of the photo-initiator concentration and the addition of 2-mercaptoethanol as a chain transfer agent on the molecular weight of the kinetic chains was investigated. It was found that both increasing the initiator concentration and adding 2-mercaptoethanol decrease the kinetic chain length. However, the effect of adding 2-mercaptoethanol was much larger. Some network properties such as the glass transition temperature and the swelling ratio in acetone are affected when the kinetic chain length is decreased.     

Self-assembly of highly ordered conjugated polymer aggregates with long-range energy transfer

Applications of conjugated polymers (CP) in organic electronic devices such as light-emitting diodes and solar cells depend critically on the nature of electronic energy transport in these materials. Single-molecule spectroscopy has revealed their fundamental properties with molecular detail, and recent reports suggest that energy transport in single CP chains can extend over extraordinarily long distances of up to 75 nm. An important question arises as to whether these characteristics are sustained when CP chains agglomerate into a neat solid. Here, we demonstrate that the electronic energy transport in aggregates composed of tens of polymer chains takes place on a similar distance scale as that in single chains. A recently developed molecular-level understanding of solvent vapour annealing has allowed us to develop a technique to control the CP agglomeration process. Aggregates with volumes of at least 45,000 nm(3) (molecular weight ≈ 21 MDa) maintain a highly ordered morphology and show pronounced fluorescence blinking behaviour, indicative of substantially long-range energy transport. Our findings provide a new lens through which the ordering of single CP chains and the evolution of their morphological and optoelectronic properties can be observed, which will ultimately enable the rational design of improved CP-based devices.     

Pricing and ordering decisions of two competing supply chains with different composite policies: a Stackelberg game-theoretic approach

In today’s global highly competitive markets, competition happens among supply chains instead of companies, as the members of supply chains. So, the partners of the chains seek to apply efficient coordinating strategies like discount, return, refund, buyback, or the other coordinating policies to abate the operation costs of the chains and subsequently increase market shares. Hence, because of the importance and application of these strategies in the current non-exclusive markets, in this study, we introduce different composite coordinating strategies to enhance the coordination of the supply chains. Here, we consider two competing supply chains where both chains launch the same product under different brands to the market by applying different composite coordinating strategies. Each supply chain comprises one manufacturer and a group of non-competing retailers where the manufacturer receives raw materials from an outside supplier and transforms them into a finished product; then, the products are sold to the retailers to satisfy the demands of market. In the first chain, a composite (QFF) policy, which is the combination of quantity and freight discount, as well as free shipping quantity policies, are considered between upstream and downstream members while in the second one, different composite polices are considered between upstream and downstream members such that the supplier offers a composite policy, as the first chain, to the manufacturer and the manufacturer proposes a composite (QPR) policy, which is the combination of quantity discount and partial-refund customer return policies, to the retailers. The main objective of the paper is to determine the optimal selling prices and the order quantities of the manufacturer and the retailers in each chain in presence of different composite coordinating strategies. A Stackelberg game-theoretic approach is employed between the members of each chain where the manufacturer is a follower and the retailers are leaders. The concavity of profit functions is proved. Finally, the applicability of the models is justified by presented numerical examples. Moreover, the effects of these strategies on the decisions of the chains’ partners are examined.     

黏度法研究稀溶液中高分子链尺寸的浓度依赖性

测定了不同浓度聚苯乙烯(PS)θ溶液的黏度,确定了高分子之间的流体力学相互作用参数,由此确定了良溶剂中高分子链尺寸的浓度依赖性,结果表明,在良溶剂中随着浓度的增加,高分子链的尺寸有所收缩,但是变化的程度比较小,与Wolf的理论结果以及笔者以前对此所做的理论分析并不一致,文中对出现差异的原因进行了深入的探讨。     

Micromixing with linked chains of paramagnetic particles

Paramagnetic colloidal particles aggregate into linear chains under an applied external magnetic field. These particles can be chemically linked to create chains that can be magnetically actuated to manipulate microscopic fluid flow. The flexibility of the chain can be adjusted by varying the length of the linker molecule. In this paper, we describe the use of a suspension of linked paramagnetic chains in a rotating magnetic field to perform microscale mixing. The effect of chain rotation and flexibility on the diffusion of molecules is studied by observing the mixing of an acid and base in a microchannel. We show that, as the chain rotation frequency increases, there is marked increase in the effective mixing between fluid streams; however, a maximum frequency exists and above this frequency the chains are no longer effective in mixing. More flexible chains are more effective at mixing over a larger range of frequencies.     

The influence of post-growth annealing on the optical properties of InAs quantum dot chains grown on pre-patterned GaAs(100)

We report on the effect of post-growth thermal annealing of [011]- ,[011(-)]-, and [010]-oriented quantum dot chains grown by molecular beam epitaxy on GaAs(100) substrates patterned by UV-nanoimprint lithography. We show that the quantum dot chains experience a blueshift of the photoluminescence energy, spectral narrowing, and a reduction of the intersubband energy separation during annealing. The photoluminescence blueshift is more rapid for the quantum dot chains than for self-assembled quantum dots that were used as a reference. Furthermore, we studied polarization resolved photoluminescence and observed that annealing reduces the intrinsic optical anisotropy of the quantum dot chains and the self-assembled quantum dots.     

On the solution self-assembly of nanocolloidal brushes: insights from simulations

The synthesis of novel nanoparticles with exceptional properties continues to stimulate the search for advanced applications in fields as diverse as solar energy harvesting and polymer reinforcement. It is widely recognized that to practically exploit the promised benefits it is necessary to guide the assembly of the various nanoparticles into well-defined supra-molecular structures. Towards this goal, we report Monte Carlo simulation results for the self-assembly of spherical nanoparticles in implicit solvent. The nanoparticles interact solely via dispersive interactions, modeled as square-well potentials. To control the morphology of the self-assembled aggregates, side chains are grafted on specific locations on the nanoparticle surface (i.e., on the equator, on the tropics, on the entire tropical region, or uniformly on the nanoparticle surface). The results are discussed in terms of average cluster size, probability of observing aggregates of given size, and aggregate radius of gyration and asphericity as a function of the aggregate size. The parameters of interest are the solution conditions and the nanoparticle volume fraction (always in the dilute regime). As shown in previous reports (e.g., Striolo 2007 Small 3 628), the nanoparticles form insoluble agglomerates in the absence of the side chains. When the side chains are long and uniformly distributed on the nanoparticles, these remain individually dispersed in solution. More importantly, when the side chains are grafted on selected locations on the nanoparticles, these self-assemble, yielding structures composed of up to 7-10 nanoparticles. The number of grafted side chains is the parameter that predominantly determines the average aggregate size, while the aggregate morphology can be tuned by appropriately controlling the distribution and length of the grafted side chains.     

超长侧链型聚羧酸梳形共聚物对水泥早期水化的影响

选用了一组超长侧链型聚羧酸梳形共聚物作为水泥体系的分散剂,通过水化热测定、强度试验和扫描电镜等表征手段,研究了超长侧链型聚羧酸梳形共聚物分散剂对水泥早期水化的影响.研究发现,超长侧链型聚羧酸梳形共聚物比普通聚羧酸梳形共聚物具有加速水泥水化、提高水泥基材料强度的作用.扫描电镜得到的形貌结果发现,超长侧链型聚羧酸梳形共聚物的掺入改变了水化产物的形貌,并且侧链越长,呈絮状的C-S-H凝胶和呈针状的钙矾石晶体明显增加.这说明超长侧链型聚羧酸加速了C-S-H凝胶和钙矾石晶体的形成,促进了水泥混凝土体系早期强度的形成.     

Polymer-grafted-nanoparticle surfactants

We have studied the surface behavior of nanoparticles, which are lightly grafted with polymer chains, when they are mixed with matrix chains of the same architecture as the grafts. We consider the particular case where the nanoparticle core and the grafted polymer chains energetically dislike each other and show that the extent of surface segregation of these "hairy" nanoparticles and their self-assembly into a variety of structures can be tuned by varying the number and the length of the grafted chains and the matrix chain length. These results unequivocally show that grafted nanoparticles in polymer matrices behave akin to block copolymers (or amphiphiles) in selective solvents, with readily controllable surface behavior.     

Preparation of polyurethane with zwitterionic side chains and their protein resistance

Polyurethane (PU) with zwitterionic side chains has been prepared to resist nonspecific adsorption of proteins. First, dihydroxy-terminated poly(2-(dimethylamino)ethyl methacrylate) (PDEM(OH)(2)) is synthesized by free radical polymerization with 3-mercapto-1,2-propanediol as the chain transfer agent, which polyadds with diisocyanate to yield a PU with PDEM side chains. Such side chains are zwitterionized by 1,3-propane sultone. Proton nuclear magnetic resonance spectroscopy ((1)H NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) show that the zwitterionic side chains are incorporated into the PU. Thermal analysis demonstrates the thermal stability is greatly affected by the content of the side chains. By use of quartz crystal microbalance with dissipation (QCM-D), we have investigated the adsorption of fibrinogen, bovine serum albumin, and lysozyme on a surface constructed by such a PU. It shows the PU has a controllable protein resistance depending on the content of the zwitterionic side chains.     

In situ organization of gold nanorods on mixed self-assembled-monolayer substrates

A method is described for assembling gold nanorods, end-to-end, into long chains attached on top of a mixed self-assembled monolayer that has been functionalized with streptavidin. Methods to prepare chains of nanorods in colloidal suspension have been reported by others, but our protocol offers a way to directly form such structures on a substrate. The rods are spaced approximately 5 nm apart in the resulting chains, which extend for over a micrometer in length. The assembly and morphology of the nanorod structures were characterized by surface plasmon resonance spectroscopy, as well as by scanning electron microscopy and scanning probe microscopy. Structures of this type could conceivably serve as plasmonic waveguides in future nanodevices.     

Characterization of polyubiquitin chain structure by middle-down mass spectrometry

Ubiquitin (Ub) is a 76 amino acid polypeptide that modifies a wide range of proteins in the types of monomer or polymers, and functional consequence of ubiquitination is modulated by the length and topologies of polyUb chains. Whereas polyUb chains are usually analyzed by fully trypsin digestion and mass spectrometry (MS), we present here a middle-down strategy to characterize the structure of polyUb chains by high-resolution mass spectrometry (MS). Under optimized condition, native folded polyUb is partially trypsinized exclusively at the R74 residue, generating a large Ub fragment (1-74 residues termed UbR74) and its ubiquitinated form with a diglycine tag (UbR74-GG). The molar ratio between UbR74 and UbR74-GG reflects the length of homogeneous polyUb chains (i.e., 1:1 for the dimer, 1:2 for the trimer, 1:3 for the tetramer, and so on). Moreover, lysine residues in ubiquitin used for chain linkages are detectable by MS/MS and MS/MS/MS of large GG-tagged Ub fragments. The strategy was validated using a number of ubiquitin polymers, including K48-linked human di-Ub, K63-linked human tetra-Ub, as well as His-tagged polyUb chains purified from yeast under native condition. The potential of this strategy to analyze polyUb chains with mixed linkages (e.g., forked chains) is also discussed. Together, this middle-down MS strategy provides a novel complementary method for studying the length and linkages of complex polyUb chain structures.     

基于MAS的供应链管理及其IT技术方案

提出将供应链管理作为一种跨组织系统，结合多代理人系统(MAS)模型，通过运用CORBA这种中间技术，为供应链的运作提供了一种可行的IT方案。研究结果表明：适当的IT技术的应用可以减少供应链系统的不确定性，降低交易成本。