Structural, magnetic and electrical properties of the sol-gel prepared Li0.5Fe2.5O4 fine particles

Fine particles of lithium ferrite were synthesized by the sol-gel method. By subsequent heat treatment at different temperatures, lithium ferrites of different grain sizes were prepared. A structural characterization of all the samples was conducted by the x-ray diffraction technique. A grain size of around 12 nm was observed for Li0.5Fe2.5O4 obtained through the sol-gel method. Magnetic properties of lithium ferrite nanoparticles with grain size ranging from 12 to 32 nm were studied. Magnetization measurements showed that Li0.5Fe2.5O4 fine particles exhibit a deviation from the predicted magnetic behaviour. The as-prepared sample of lithium ferrite showed a maximum saturation magnetization of 75 emu g−1. Variation of coercivity is attributed to the transition from multi-domain to single domain nature. Dielectric permittivity and ac conductivity of all the samples were evaluated as a function of frequency, temperature and grain size. Variation of permittivity and ac conductivity with frequency reveals that the dispersion is due to the Maxwell–Wagner type interfacial polarization

Formation of carbon-encapsulated metallic nano-particles from metal acetylides by electron beam irradiation

Transition metal acetylides, MC2 (M=Fe, Co and Ni), exhibit ferromagnetic behavior of which TC is characteristic of their size and structure. CoC2 synthesized in anhydrous condition exhibited cubic structure with disordered C2− 2 orientation. Once being exposed to water (or air), the particles behave ferromagnetically due to the lengthening of the Co–Co distance by the coordination of water molecules to Co2+ cations. Heating of these particles induces segregation of metallic cores with carbon mantles. Electron beam or 193 nm laser beam can produce nanoparticles with metallic cores covered with carbon mantles

Funktion und Biogenese kleiner RNAs in Dictyostelium discoideum

RNA mediated gene silencing pathways are highly conserved among eukaryotes and they have been well investigated in animals and in plants. Longer dsRNA molecules trigger the silencing pathways: RNase III proteins and their dsRNA binding protein (dsRBP) partners recognize those molecules as a substrate and process 21 nucleotide long microRNAs (miRNAs) or small interfering RNAs (siRNAs). Some organisms encode RNA dependent RNA polymerases (RdRPs), which are able to expand the pool of existing siRNAs. Argonaute proteins are able to bind small regulatory RNAs and are subsequently recruited to target mRNAs by base complementary. This leads in turn to transcriptional or posttranscriptional silencing of respective genes. The Dictyostelium discoideum genome encodes two Dicer homologues (DrnA and DrnB), five Argonaute proteins (AgnA to AgnE) and three RdRPs (RrpA to RrpC). In addition, the amoeba is known to express miRNAs and siRNAs, while the latter derive mainly from the DIRS-1 retrotransposon. One part of this work focused on the miRNA biogenesis pathway of D. discoideum. It was shown that the dsRNA binding protein RbdB is a necessary component for miRNA processing in the amoeba. There were no mature miRNAs detectable by Northern blot analysis in rbdB- strains, which is also true for drnB mutants. Moreover, primary miRNA-transcripts (pri-miRNAs) accumulated in rbdB- and drnB- strains. Fluorescence microscopy studies showed a nuclear localization of RbdB. RbdB accumulated in distinct perinucleolar foci. These were reminiscent of plant dicing bodies that contain essential protein components for miRNA processing. It is well known that RNase III enzymes and dsRBPs work together during miRNA processing in higher eukaryotes. This work demonstrated that the same is true for members of the amoebozoa supergroup. In Arabidopsis the nuclear zinc finger protein Serrate (SE) is also necessary for miRNA processing. The D. discoideum homologue SrtA, however, is not relevant which has been shown by the analysis of the respective knockdown strain. MiRNAs are known to be differentially expressed in several RNAi knockout strains. The accumulation of miRNAs in agnA- strains and a strong decrease in rbdB- strains were criteria that could thus be successfully used (among others) to identify and validate new miRNAs candidates by Illumina®-RNA sequencing. In another part of this study, the silencing and amplification of the DIRS-1 retrotransposons was analyzed in more detail. It was already known that DIRS-1 transcripts and extrachromosomal DIRS-1 DNA molecules accumulated in agnA- strains. This phenotype was correlated with the loss of endogenous DIRS-1 siRNAs in the knockout strain. By deep sequencing analysis of small RNAs from the AX2 wild type and the agnA- strain, the strong decrease of endogenous DIRS-1 siRNAs in the mutant strain (accounting for 70 %) could be confirmed. Further analysis of the data revealed an unequal distribution of DIRS-1 derived siRNAs along the retroelement in the wild type strain, since only very few of them matched the inverted terminal repeats (ITRs) and the 5’- half of the first open reading frame (ORF). Besides, sense and antisense siRNAs were asymmetrically distributed, as well. By using different reporter constructs it was shown indirectly that AgnA is necessary for the RrpC mediated production of secondary DIRS-1 siRNAs. These analyses also demonstrated an amplification of siRNAs in 5’- and in 3’-direction. Further analysis of the agnA- strain revealed that not only DIRS-1 sense transcripts but also ORF2 and ORF3 encoded proteins were enriched. In contrast, the ORF1 encoded protein GAG was equally expressed in the mutant and the wild type. This might reflect the unequal distribution of endogenous DIRS-1 siRNAs along the retrotransposon. Southern Blot and PCR-analyses showed that extrachromosomal DIRS-1 DNA molecules are present in the cytoplasm of angA- strains and that they are complementary to sense transcripts of intact DIRS-1 elements. Thus, the extrachromosomal DIRS-1 intermediates are likely incomplete cDNA molecules generated by the DIRS-1 encoded reverse transcriptase. One could hypothesize that virus like particles (VLPs) are the places of DIRS-1 cDNA synthesis. At least, DIRS-1 GAG proteins interact and fluorescence microscopy studies showed that they localize in distinct cytoplasmic foci which accumulate in close proximity to the nuclei.

Apatite-Polymer Composite Particles for Controlled Delivery of BMP-2: In Vitro Release and Cellular Response

Bone morphogenetic protein-2 (BMP-2) has the ability to induce osteoblast differentiation of undifferentiated cells, resulting in the healing of skeletal defects when delivered with a suitable carrier. We have applied a versatile delivery platform comprising a novel composite of two biomaterials with proven track records – apatite and poly(lactic-co-glycolic acid) (PLGA) – to the delivery of BMP-2. Sustained release of this growth factor was tuned with variables that affect polymer degradation and/or apatite dissolution, such as polymer molecular weight, polymer composition, apatite loading, and apatite particle size. The effect of released BMP-2 on C3H10T1/2 murine pluripotent mesenchymal cells was assessed by tracking the expression of osteoblastic makers, alkaline phosphatase (ALP) and osteocalcin. Release media collected over 100 days induced elevated ALP activity in C3H10T1/2 cells. The expression of osteocalcin was also upregulated significantly. These results demonstrated the potential of apatite-PLGA composite particles for releasing protein in bioactive form over extended periods of time.

AS - A Level physics : mechanics and materials, waves and particles.

Guía de bolsillo para la revisión de los temas clave en el área de física para alumnos de bachillerato (segundo ciclo de educación secundaria), niveles AS y A, con trescientas preguntas rápidas y sus respuestas, organizadas en secciones temáticas y con consejos de examen. Contiene: fundamentos, mecánica, radioactividad, física de partículas, electricidad, materiales sólidos, ondas y método experimental.

Algorithm for generating defective graphene sheets

An algorithm is presented for the generation of molecular models of defective graphene fragments, containing a majority of 6-membered rings with a small number of 5- and 7-membered rings as defects. The structures are generated from an initial random array of points in 2D space, which are then subject to Delaunay triangulation. The dual of the triangulation forms a Voronoi tessellation of polygons with a range of ring sizes. An iterative cycle of refinement, involving deletion and addition of points followed by further triangulation, is performed until the user-defined criteria for the number of defects are met. The array of points and connectivities are then converted to a molecular structure and subject to geometry optimization using a standard molecular modeling package to generate final atomic coordinates. On the basis of molecular mechanics with minimization, this automated method can generate structures, which conform to user-supplied criteria and avoid the potential bias associated with the manual building of structures. One application of the algorithm is the generation of structures for the evaluation of the reactivity of different defect sites. Ab initio electronic structure calculations on a representative structure indicate preferential fluorination close to 5-ring defects.

Computationally efficient expressions for the collision efficiency between electrically charged aerosol particles and cloud droplets

A multiple factor parametrization is described to permit the efficient calculation of collision efficiency (E) between electrically charged aerosol particles and neutral cloud droplets in numerical models of cloud and climate. The four-parameter representation summarizes the results obtained from a detailed microphysical model of E, which accounts for the different forces acting on the aerosol in the path of falling cloud droplets. The parametrization's range of validity is for aerosol particle radii of 0.4 to 10 mu m, aerosol particle densities of I to 2.0 g cm(-3), aerosol particle charges from neutral to 100 elementary charges and drop radii from 18.55 to 142 mu m. The parametrization yields values of E well within an order of magnitude of the detailed model's values, from a dataset of 3978 E values. Of these values 95% have modelled to parametrized ratios between 0.5 and 1.5 for aerosol particle sizes ranging between 0.4 and 2.0 mu m, and about 96% in the second size range. This parametrization speeds up the calculation of E by a factor of similar to 10(3) compared with the original microphysical model, permitting the inclusion of electric charge effects in numerical cloud and climate models.

Variation of the mixing state of Saharan dust particles with atmospheric transport

Mineral dust is an important aerosol species in the Earth’s atmosphere and has a major source within North Africa, of which the Sahara forms the major part. Aerosol Time of Flight Mass Spectrometry (ATOFMS) is first used to determine the mixing state of dust particles collected from the land surface in the Saharan region, showing low abundance of species such as nitrate and sulphate internally mixed with the dust mineral matrix. These data are then compared with the ATOFMS single particle mass spectra of Saharan dust particles detected in the marine atmosphere in the vicinity of the Cape Verde islands, which are further compared with those from particles with longer atmospheric residence sampled at a coastal station at Mace Head, Ireland. Saharan dust particles collected near the Cape Verde Islands showed increased internally mixed nitrate but no sulphate, whilst Saharan dust particles collected on the coast of Ireland showed a very high degree of internally mixed secondary species including nitrate, sulphate and methanesulphonate. This uptake of secondary species will change the pH and hygroscopic properties of the aerosol dust and thus can influence the budgets of other reactive gases, as well as influencing the radiative properties of the particles and the availability of metals for dissolution.

Dual-specificity phosphatases in the hypo-osmotic stress response of keratin-defective epithelial cell lines

Although mutations in intermediate filament proteins cause many human disorders, the detailed pathogenic mechanisms and the way these mutations affect cell metabolism are unclear. In this study, selected keratin mutations were analysed for their effect on the epidermal stress response. Expression profiles of two keratin-mutant cell lines from epidermolysis bullosa simplex patients (one severe and one mild) were compared to a control keratinocyte line before and after challenge with hypo-osmotic shock, a common physiological stress that transiently distorts cell shape. Fewer changes in gene expression were found in cells with the severely disruptive mutation (55 genes altered) than with the mild mutation (174 genes) or the wild type cells (261 genes) possibly due to stress response pre-activation in these cells. We identified 16 immediate-early genes contributing to a general cell response to hypo-osmotic shock, and 20 genes with an altered expression pattern in the mutant keratin lines only. A number of dual-specificity phosphatases (MKP-1, MKP-2, MKP-3, MKP-5 and hVH3) are differentially regulated in these cells, and their downstream targets p-ERK and p-p38 are significantly up-regulated in the mutant keratin lines. Our findings strengthen the case for the expression of mutant keratin proteins inducing physiological stress, and this intrinsic stress may affect the cell responses to secondary stresses in patients' skin.