Search results for "magnetism."
showing 10 items of 1879 documents
Tailoring the Exchange Interaction in Covalently Linked Basic Carboxylate Clusters through Bridging Ligand Selection
2012
We are reporting new dimeric units of basic carboxylates bearing the {Fe III 2M IIO} motif for M = Co and Ni, covalently bound through the tetradentate bridging (LL) 2,2′-azopyiridine (azpy) and 2,3-di(2-pyridyl)quinoxaline ligands (dpq). We structurally characterized the hexanuclear clusters, and their magnetic properties have been fully analyzed. DFT calculations have been performed as a supplementary tool. All results evidence a weak antiferromagnetic interaction through the bridging ligands between isolated spin ground states arising from intra-Fe 2MO core exchange couplings. Together with the pioneer 2,2′-bipyrimidine bridged systems, the new complexes reported constitute a family of c…
Magnetic excitations of a doped two-dimensional antiferromagnet
1993
Magnetic excitations of the two-dimensional (2D) t-J model are considered in the presence of a small concentration of holes c. The spin-wave approximation used implies long-range antiferromagnetic ordering from the beginning. Migdal's theorem is shown to be valid for the model considered. The energy spectrum of the magnons is determined with the help of the one-pole approximation for the hole Green's function. If the concentration of mobile holes is larger than a critical value an additional branch of overdamped magnons arises near the \ensuremath{\Gamma} and M points of the Brillouin zone. This is connected with the generation of electron-hole pairs (the Stoner excitations) by magnons. The…
Orbital Decomposition of the Carbon Chemical Shielding Tensor in Gold(I) N-Heterocyclic Carbene Complexes.
2020
The good performance of N‐heterocyclic carbenes (NHCs), in terms of versatility and selectivity, has called the attention of experimentalists and theoreticians attempting to understand their electronic properties. Analyses of the Au(I)–C bond in [(NHC)AuL]+/0 (L stands for a neutral or negatively charged ligand), through the Dewar–Chatt–Duncanson model and the charge displacement function, have revealed that NHC is not purely a σ‐donor but may have a significant π‐acceptor character. It turns out, however, that only the σ‐donation bonding component strongly correlates with one specific component of the chemical shielding tensor. Here, in extension to earlier works, a current density analysi…
Solvation of a probe molecule by fluid supercooled water in a hydrogel at 200 K
2008
By combining electron paramagnetic resonance (EPR) measurements on a nitroxide probe and differential scanning calorimetry (DSC), we demonstrate existence of liquid supercooled water in a silica hydrogel with high hydration level down to temperatures of at least 198 K. Besides the major fraction of liquid supercooled water, a minor fraction crystallizes at about 236 K during cooling and melts at 246 K during heating. The liquid domains are of sufficient size to solvate the nearly spherical paramagnetic probe molecule TEMPO with a diameter of about 6 angstrom. Analysis of EPR spectra provides the rotational correlation time of the probe that is further used to compare the viscosity of the su…
Dipolar Rings of Microscopic Ellipsoids: Magnetic Manipulation and Cell Entrapment
2016
We study the formation and dynamics of dipolar rings composed by microscopic ferromagnetic ellipsoids, which self-assemble in water by switching the direction of the applied field. We show how to manipulate these fragile structures and control their shape via application of external static and oscillating magnetic fields. We introduce a theoretical framework which describes the ring deformation under an applied field, allowing to understand the underlying physical mechanism. Our microscopic rings are finally used to capture, entrap and later release a biological cell via magnetic command, i.e. performing a simple operation which can be implemented in other microfluidic devices which make us…
Curvature increases permeability of the plasma membrane for ions, water and the anti-cancer drugs cisplatin and gemcitabine
2019
ABSTRACTIn this work the permeability of a model asymmetric plasma membrane, for ions, water and the anti-cancer drugs cisplatin and gemcitabine is studied by means of all-atom molecular dynamics simulations. It is shown that permeability of the membranes increases from one to three orders of magnitude upon membrane bending depending on the compound and the sign of curvature. Our results show that the membrane curvature is an important factor which should be considered during evaluation of drug translocation.TOC GRAPHICS
Surface Relaxivity of Cement Hydrates
2014
Numerous aspects of the physical chemistry of colloidal systems are conditioned by the solid–liquid interface, and this is also the case for hydrated cement systems. Estimating the surface area is thus essential for studying the kinetics of cement hydration and admixture adsorption. Proton nuclear magnetic resonance (NMR) relaxation techniques have already proven useful for this objective, but, for hydrating cements at early ages, it is necessary to know the surface relaxivities of all of the individual phases present to correctly interpret the relaxation data. This paper reports the results of a comparison of NMR relaxometry and Brunauer–Emmett–Teller gas adsorption measurements on various…
Some factors affecting an increase in magnetic susceptibility of cement dusts
2001
The aim of the research was to explain reasons of fluctuation in magnetic susceptibility of cement dusts and the consequences for the environment. The research comprised measurements of magnetic susceptibility and Fe content in dusts, and also in raw materials, additives, fuels, mixtures and clinkers used for cement production. The samples were taken in four cement plants located in Opole Province (southern Poland). In addition to this, the influence of two production methods (dry and wet) on magnetic susceptibility of dusts and some aspects of ferrimagnetic minerals formation in the process of clinker burning were considered. It was proven that magnetic susceptibility of dusts depends on r…
Ferrimagnetic Heisenberg chain; influence of a random exchange interaction
1985
We report on the magnetic behavior of ‘‘rigid’’ ferrimagnetic chains isolated in bimetallic complexes of the EDTA and ‘‘flexible’’ ones obtained in the amorphous variety. As shown by LAXS, the only noteworthy difference in the amorphous state is the random distribution of bond angles between nearest neighbors within chains. The ‘‘rigid’’ bimetallic chains in CoNi(EDTA)6H2O are described in terms of Heisenberg model with an exchange coupling J=−7.5 K. The behavior of the amorphous variety somewhat differs, following the law X=AT−0.8 typical of REHAC. A classical spin chain model involving a J distribution and alternating g factors allows to explain successfully the temperature dependence of …
Comparison of thermal‐ and photo‐polymerization of lauryl methacrylate monolithic columns for CEC
2009
Lauryl methacrylate-based (LMA) monolithic columns for CEC, prepared using either thermal initiation or by UV-irradiation in the presence of AIBN have been compared. Thermal polymerization was carried out at 70 degrees C for 20 h. For UV initiation, the effects of the time exposure to UV light and irradiation energy were investigated. For each initiation process, the influence of composition of porogenic solvent (1,4-butanediol/1-propanol ratio) on the physical and electrochromatographic properties of the resulting monoliths was also evaluated. Photochemically lauryl methacrylate stationary phases initiated showed higher permeabilities and better efficiencies than those prepared by thermal …