Superparamagnetic relaxation in Cu_{x}Fe_{3-x}O_{4} (x=0.5 and x=1) nanoparticles

The scope of this article is to report very detailed results of the measurements of magnetic relaxation phenomena in the new Cu$_{0.5}$Fe$_{2.5}$O$_{4}$ nanoparticles and known CuFe$_{2}$O$_{4}$ nanoparticles. The size of synthesized particles is (6.5$\pm$1.5)nm. Both samples show the superparamagnetic behaviour, with the well-defined phenomena of blocking of magnetic moment. This includes the splitting of zero-field-cooled and field-cooled magnetic moment curves, dynamical hysteresis, slow quasi-logarithmic relaxation of magnetic moment below blocking temperature. The scaling of the magnetic moment relaxation data at different temperatures confirms the applicability of the simple thermal relaxation model. The two copper-ferrites with similar structures show significantly different magnetic anisotropy density and other magnetic properties. Investigated systems exhibit the consistency of all obtained results.Comment: 18 pages, 8 figure

Microwave properties of DyBa_2Cu_3O_(7-x) monodomains and related compounds in magnetic fields

We present a microwave characterization of a DyBa$_{2}$Cu$_{3}$O$_{7-x}$ single domain, grown by the top-seeded melt-textured technique. We report the (a,b) plane field-induced surface resistance, $\Delta R_s(H)$, at 48.3 GHz, measured by means of a cylindrical metal cavity in the end-wall-replacement configuration. Changes in the cavity quality factor Q against the applied magnetic field yield $\Delta R_s(H)$ at fixed temperatures. The temperature range [70 K ; T_c] was explored. The magnetic field $\mu_0 H <$ 0.8 T was applied along the c axis. The field dependence of $\Delta R_s(H)$ does not exhibit the steep, step-like increase at low fields typical of weak-links. This result indicates the single-domain character of the sample under investigation. $\Delta R_s(H)$ exhibits a nearly square-root dependence on H, as expected for fluxon motion. From the analysis of the data in terms of motion of Abrikosov vortices we estimate the temperature dependences of the London penetration depth $\lambda$ and the vortex viscosity $\eta$, and their zero-temperature values $\lambda(0)=$165 nm and $\eta(0)=$ 3 10$^{-7}$ Nsm$^{-2}$, which are found in excellent agreement with reported data in YBa$_{2}$Cu$_{3}$O$_{7-x}$ single crystals. Comparison of microwave properties with those of related samples indicate the need for reporting data as a function of T/T_c in order to obtain universal laws.Comment: 6 pages, 4 figures, LaTeX, submitted to Journal of Applied Physic

Biocompatibility and tissue regenerating capacity of crosslinked dermal sheep collagen

The biocompatibility and tissue regenerating capacity of four crosslinked dermal sheep collagens (DSC) was studied. In vitro, the four DSC versions were found to be noncytotoxic or very low in cytoxicity. After subcutaneous implantation in rats, hexamethylenediisocyanatecrcrosslinked DSC (HDSC) seldom induced an increased infiltration of neutrophils or macrophages, as compared with normal wound healing; whereas new formation of collagen was observed. DSC crosslinked with glutaraldehyde (GDSC) followed by reaction with NaBH4 shortly after implantation showed an increased infiltration of neutrophils with a deviant morphology. Furthermore, a high incidence of calcification was observed, which may explain the minor ingrowth of giant cells and fibroblasts, and the poor formation of new rat collagen. Acyl azide-crosslinked DSC (AaDSC) first induced an increased infiltration of macrophages, and then of giant cells, both with high lipid formation. AaDSC degraded at least twice as slowly as HDSC and GDSC, finally leaving a matrix of newly formed rat collagen. Samples crosslinked with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide (ENDSC) induced the same mild cellular reaction as HDSC; whereas, similar to AaDSC, the degradation rate was slow and an optimal rat collagen matrix was formed. Of the crosslinked DSC samples, ENDSC seems most promising for tissue regeneration

Synthesis, surface modification and characterisation of biocompatible magnetic iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles (MNPs) with appropriate surface chemistry exhibit many interesting properties that can be exploited in a variety of biomedical applications such as magnetic resonance imaging contrast enhancement, tissue repair, hyperthermia, drug delivery and in cell separation. These applications required that the MNPs such as iron oxide Fe 3O4 magnetic nanoparticles (Fe3O4 MNPs) having high magnetization values and particle size smaller than 100 nm. This paper reports the experimental detail for preparation of monodisperse oleic acid (OA)-coated Fe3O4 MNPs by chemical co-precipitation method to determine the optimum pH, initial temperature and stirring speed in order to obtain the MNPs with small particle size and size distribution that is needed for biomedical applications. The obtained nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence spectrometry (EDXRF), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and vibrating sample magnetometer (VSM). The results show that the particle size as well as the magnetization of the MNPs was very much dependent on pH, initial temperature of Fe2+ and Fe 3+ solutions and steering speed. The monodisperse Fe 3O4 MNPs coated with oleic acid with size of 7.8 ± 1.9 nm were successfully prepared at optimum pH 11, initial temperature of 45 °C and at stirring rate of 800 rpm. FTIR and XRD data reveal that the oleic acid molecules were adsorbed on the magnetic nanoparticles by chemisorption. Analyses of TEM show the oleic acid provided the Fe3O4 particles with better dispersibility. The synthesized Fe3O 4 nanoparticles exhibited superparamagnetic behavior and the saturation magnetization of the Fe3O4 nanoparticles increased with the particle size

Fracture toughness of rotationally moulded polyethylene and polypropylene.

In this work, the fracture toughness of rotationally moulded Polyethylene (PE) and Polypropylene (PP) was measured using J integral methods at static loading rates and at room temperature. Two different commercially available rotational moulding grades PE and PP were tested in this study which have been used in various rotationally moulded products such as small leisure craft, water storage tanks etc. Scanning Electron Microscope (SEM), Optical Microscope, Differential Scanning Calorimetry (DSC), Solid-state Nuclear Magnetic Resonance (solid-state NMR) and X-ray scattering were used to investigate the microstructure, fracture surfaces and compare toughness properties of these materials. In PE, higher molecular weight and broader molecular weight distribution, larger amorphous and crystal region thicknesses are found to be related to higher toughness values. High molecular weight favours higher number of entanglements that improve fracture energy and broader distribution increases long chain branching of higher molecular weight fractions which creates higher entanglements at the branch sites. Larger amorphous regions promote micro-voiding more easily compared to thinner amorphous regions, leading to greater plastic deformation and energy absorption. Higher crystal thickness also contributes to micro-voiding in the amorphous region. For PP, greater plastic deformation observed in the fracture surfaces is related to higher fracture toughness values

Orangerie – One Unique Museum in Paris

Located right in the heart of Paris in the Tuileries Gardens and renovated in 2006, the Musée de l'Orangerie offers the visitor a poetic and artistic presentation of two prestigious collections. This article will present only the collection of Claude Monet’s paintings Water Lilies (Les Nymphéas). Both monumental and intimate, Water Lilies are the ultimate expression of Claude Monet's artistic ideas, an incredible project by a painter who wanted to explore all the variations of light in his garden at Giverny. The paintings are housed in two elliptical halls, and encourage the visitor to gaze in endless contemplation. After the horror of the First World War, Monet wanted his work to take on this aesthetic and poetic dimension, and provide a haven for peaceful meditation

The Rise and Development of Art Museums

Most of the people associate the term „museum“ with the Louvre, the Hermitage, the Prado, i.e. art museums. This seems to be so natural because the mentioned museums are emblematic for the museum work all over the world. The brilliant exhibitions of these „temples“ of art annually attract millions of visitors from near and far. In front of museum visitors are revealed the artistic achievements of the human civilization from ancient times till modernity. Thus the art museums continue to be schools of humanism and aestheticism. The numerous experts in these museums: curators, restorers, conservators, researchers provide systematic care for the protection, preservation and exhibition of the movable cultural heritage worldwide. The study is chronological history of the emergence and development of the major art museums in Europe. The term „muzeyon“ originates from ancient Greece. The first antique museum is created in the famous library of Alexandria. It was known in antiquity as „muzeyon“ and was the first purposely built antique museum. By this time there were some beginnings of museum activity. It was in Ancient Greece where the first art galleries known as the Pinacotec and sculpture collections - Gliptotek. During the Italian Renaissance emerged and gradually formed a new cultural institution - the art museum, which acquired popularity of the unique Italian name - gallery. Florence is the city that creates the most favorable conditions for the flourishing of Italian Renaissance. There occurred the world-famous galleries Uffizi and Pitti. Until German unification in 1870, it is divided into small independent states. Their rulers are seeking to emulate the kings of European empires and create rich art collections located in special rooms for this purpose called in German - Kunstkamera. 62 These cabinets of art are most widespread in the seventeenth and eighteenth centuries. They do not differ from the Italian galleries. They kept mostly private collections of paintings and sculptures, as well as some examples of applied arts. The Kunstkamera was widely spread among the various German states and in neighboring countries. Following this model, Peter the Great created his famous Kunstkamera in St. Petersburg. The absolutist monarchies in the seventeenth and eighteenth centuries are among the traditional patrons of artists. The nobility collections are filled with orders, purchases, and often through conquest wars, the most striking evidence of this is the Napoleonic wars. Gradually they grew into the largest art museums in the world. The Louvre is a result of the French Revolution. By decision of the Covenant the largest art museum is opened to all citizens of the French Republic. Different is the history of the emergence of the largest museum in Russia - the Hermitage. Another museum that is created on the basis of regal collections in Russia is the Armory Chamber. Similar is the story of emergence of the Prado Museum. It is created on the basis of the Spanish royal collections in 1819. The Habsburg dynasty (Austrian branch) is the longest ruling in Europe - whole 693 years. These collections are the basis for the History and Art Museum in Vienna. By the late nineteenth century the largest and richest art museums in Europe and worldwide were created. Their story is the story of conservation, preservation and presentation of the greatest achievements of human civilization in the arts. The digitization of works of art is the modern way for their documentation and preservation. Publication in virtual museums on the World Wide Web helps for further promotion, especially among young people. Thus the art museums have become more popular in the virtual world. By most valuable and attractive exhibits they attend many websites as emblems of art museums

Effect of the molecular structure of the polymer and nucleation on the optical properties of polypropylene homo- and copolymers.

Two soluble nucleating agents were used to modify the optical properties of nine PP homo- and random copolymers. The ethylene content of the polymers changed between 0 and 5.3 wt%. Chain regularity was characterized by the stepwise isothermal segregation technique (SIST), while optical properties by the measurement of the haze of injection molded samples. Crystallization and melting characteristics were determined by differential scanning calorimetry (DSC). The analysis of the results proved that lamella thickness and change in crystallinity influence haze only slightly. A model was introduced which describes quantitatively the dependence of nucleation efficiency and haze on the concentration of the nucleating agent. The model assumes that the same factors influence the peak temperature of crystallization and optical properties. The analysis of the results proved that the assumption is valid under the same crystallization conditions. The parameters of the model depend on the molecular architecture of the polymer. Chain regularity determines supermolecular structure and thus the dependence of optical properties on nucleation