19,093 research outputs found
Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites
Graphene reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), thermogravimetrical analysis (TGA) and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy (TEM). It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89% by incorporating 1 and 5 wt.% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behaviour due to the not proper exfoliation except the ash content
Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites
In this work, the study of thermal conductivity before and after in-situ
ring-opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) in presence of graphene-related materials (GRM) is
addressed, to gain insight in the modification of nanocomposites morphology
upon polymerization. Five types of GRM were used: one type of graphite
nanoplatelets, two different grades of reduced graphene oxide (rGO) and the
same rGO grades after thermal annealing for 1 hour at 1700{\deg}C under vacuum
to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and
nanoparticle organization were investigated by means of differential scanning
calorimetry, electron microscopy and rheology. Electrical and thermal
properties were investigated by means of volumetric resistivity and bulk
thermal conductivity measurement. In particular, the reduction of nanoflake
aspect ratio during ring-opening polymerization was found to have a detrimental
effect on both electrical and thermal conductivities in nanocomposites
Resonating-valence-bond structure of Gutzwiller-projected superconducting wave functions
Gutzwiller-projected (GP) wave functions have been widely used for describing
spin-liquid physics in frustrated magnets and in high-temperature
superconductors. Such wave functions are known to represent states of the
resonating-valence-bond (RVB) type. In the present work I discuss the RVB
structure of a GP singlet superconducting state with nodes in the spectrum. The
resulting state for the undoped spin system may be described in terms of the
"path integral" over loop coverings of the lattice, thus extending the known
construction for RVB states. The problem of the topological order in GP states
may be reformulated in terms of the statistical behavior of loops. The simple
example of the projected d-wave state on the square lattice demonstrates that
the statistical behavior of loops is renormalized in a nontrivial manner by the
projection.Comment: 6 pages, 4 figures, some numerical data adde
The packing of granular polymer chains
Rigid particles pack into structures, such as sand dunes on the beach, whose
overall stability is determined by the average number of contacts between
particles. However, when packing spatially extended objects with flexible
shapes, additional concepts must be invoked to understand the stability of the
resulting structure. Here we study the disordered packing of chains constructed
out of flexibly-connected hard spheres. Using X-ray tomography, we find long
chains pack into a low-density structure whose mechanical rigidity is mainly
provided by the backbone. On compaction, randomly-oriented, semi-rigid loops
form along the chain, and the packing of chains can be understood as the
jamming of these elements. Finally we uncover close similarities between the
packing of chains and the glass transition in polymers.Comment: 11 pages, 4 figure
Class I major histocompatibility complexes loaded by a periodate trigger
Class I major histocompatibility complexes (MHCs) present peptide ligands on the cell surface for recognition by appropriate cytotoxic T cells. The unstable nature of unliganded MHC necessitates the production of recombinant class I complexes through in vitro refolding reactions in the presence of an added excess of peptides. This strategy is not amenable to high-throughput production of vast collections of class I complexes. To address this issue, we recently designed photocaged MHC ligands that can be cleaved by a UV light trigger in the MHC bound state under conditions that do not affect the integrity of the MHC structure. The results obtained with photocaged MHC ligands demonstrate that conditional MHC ligands can form a generally applicable concept for the creation of defined peptideâMHCs. However, the use of UV exposure to mediate ligand exchange is unsuited for a number of applications, due to the lack of UV penetration through cell culture systems and due to the transfer of heat upon UV irradiation, which can induce evaporation. To overcome these limitations, here, we provide proof-of-concept for the generation of defined peptideâMHCs by chemical trigger-induced ligand exchange. The crystal structure of the MHC with the novel chemosensitive ligand showcases that the ligand occupies the expected binding site, in a conformation where the hydroxyl groups should be reactive to periodate. We proceed to validate this technology by producing peptideâMHCs that can be used for T cell detection. The methodology that we describe here should allow loading of MHCs with defined peptides in cell culture devices, thereby permitting antigen-specific T cell expansion and purification for cell therapy. In addition, this technology will be useful to develop miniaturized assay systems for performing high-throughput screens for natural and unnatural MHC ligands
Optimization of Mixture Parameter for Physical and Mechanical Properties of Reactive Powder Concrete under External Sulfate Attack using Taguchi Method
Reactive powder concrete (RPC) is defined as a cementitious composite material with an optimized size of granular constituents, very low water-to-binder ratio (w/b), pozzolanic materials like silica fume (SF), and discontinuous fiber reinforcement. RPC applications include bridge decks and girders, seismic columns, wind turbine towers, and pile foundations. Especially, a durable and robust RPC pile foundation with long service life is essential in building construction because continuous maintenance is impossible. Moreover, natural in-situ conditions such as water table, temperature, and sulfate concentration in soil to which the pile foundation is exposed are critical and related to deteriorating the pile foundation. Therefore, the Taguchi design of experiments (DOE) was used in this research to determine the optimal RPC mixture with beneficial characteristics against external sulfate attack (ESA). Mixture design parameters included steel fiber content (0, 1 and 2 %), w/b (0.16, 20 and 0.24), and SF content (15, 20 and 25 %). In contrast, environmental conditions of ESA exposure contained three different sodium sulfate (Na2SO4) concentrations (0.35, 1.05, and 3.15 M), cyclic and continuous exposure at normal temperature (20 °C), and continuous exposure at elevated temperatures (40 °C and 60 °C). The analytical and statistical investigation evaluated mass change, compressive strength, and modulus of rupture in RPC mixtures exposed to these conditions for 52 weeks. Test results show that cyclic exposure and increased solution temperature in ESA facilitate RPC damage. If measured after air drying, RPC mixtures subjected to cyclic ESA are especially susceptible to failure. Taguchi analysis indicated the optimum parameters\u27 level for mass change as: 0 % steel fiber, w/b = 0.16, and 20 % SF content; for the compressive strength: 2 % steel fiber, w/b = 0.24, and 20 % SF content; and, for modulus of rupture: 2 % steel fiber, w/b = 0.20, and 25 % SF content. In conclusion, RPC appears to be sustainable and durable material under different ESA exposure conditions
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