Characterization of nanodimensional Ni-Zn ferrite prepared by mechanochemical and thermal methods.

Nickel zinc ferrite nanoparticles, Ni1−xZnxFe2O4 (x = 0, 0.2, 0.5, 0.8, 1.0), with dimensions below 10 nm have been prepared by combining chemical precipitation with high-energy ball milling. For comparison, their analogues obtained by thermal synthesis have also been studied. Mössbauer spectroscopy, X-ray diffraction, and magnetic measurements are used for the characterization of the obtained materials. X-ray diffraction shows that after 3h of mechanical treatment ferrites containing zinc are formed, while 6h of treatment is needed to obtain NiFe2O4. The magnetic properties of the samples exhibit a strong dependence on the phase composition, particle size and preparation method

Boojums in Rotating Two-Component Bose-Einstein Condensates

A boojum is a topological defect that can form only on the surface of an ordered medium such as superfluid $^3$He and liquid crystals. We study theoretically boojums appearing between two phases with different vortex structures in two-component BECs where the intracomponent interaction is repulsive in one phase and attractive in the other. The detailed structure of the boojums is revealed by investigating its density distribution, effective superflow vorticity and pseudospin texture.Comment: 4 pages, 4 figure

Conseqüències de la biodegradabilitat de la matèria orgànica en les propietats físiques i químiques dels substrats

L'ús de nous materials de naturalesa orgànica provinents de l'agricultura, de la indústria i d'unes altres activitats humanes en la preparació de substrats per al cultiu de plantes fora del sòl natural requereix el coneixement de llur bioestabilitat, ja que aquesta propietat determina la variació de les característiques físiques i químiques dels substrats en el decurs del temps. En una recerca conjunta duta a terme pels dos grups de recerca pertanyents als departaments de referència de l'INRA a França i de l'IRTA a Catalunya, s'ha estudiat la bioestabilitat de sis materials orgànics: torba d'esfagne, compost d'escorça de pi, compost de residus verds de jardineria, compost de residus de bosc, fibra de coco i compost de fems de vacum, i alhora de set barreges binàries formulades amb les matèries abans esmentades. Al mateix temps s'han estudiat els efectes de la bioestabilitat en la variació de les propietats físiques i químiques de tots els substrats.Considerant els índexs de bioestabilitat respectius, les matèries primeres s'han classificat en tres grups: han resultat materials molt estables la fibra de coco, el compost d'escorça de pi i el compost de residus de jardineria; s'ha provat que són materials estables la torba d'esfagne i el compost de residus forestals; i, finalment, el compost de fems de vacum presenta una bioestabilitat moderada. S'hi mostra que, considerant els materials estudiats, la variació relativa de certes propietats físiques, com ara l'aigua disponible i l'aigua difícilment disponible, i també la de certes propietats químiques, com la capacitat de bescanvi catiònic, es correlacionen linealment, amb significació estadística, amb l'índex de bioestabilitat dels substrats estudiats en les dues localitzacions experimentals. Considerant només les matèries primeres, la regressió lineal entre llur capacitat d'aireació i llur índex de bioestabilitat presenta un coeficient de correlació també estadísticament significatiu. Per contra, l'índex de bioestabilEl uso de nuevos materiales de naturaleza orgánica procedentes de la agricultura, de la industria y de otras actividades humanas en la preparación de sustratos para el cultivo de plantas fuera del suelo natural requiere el conocimiento de su bioestabilidad, ya que esta propiedad determina la variación de las características físicas y químicas de los sustratos en el transcurso del tiempo. En una investigación conjunta realizada por los dos grupos de investigación que pertenecen a los departamentos de referencia del INRA, en Francia, y del IRTA, en Catalunya, se ha estudiado la bioestabilidad de seis materiales orgánicos: turba de esfagno, compost de corteza de pino, compost de residuos verdes de jardinería, compost de residuos de bosque, fibra de coco y compost de estiércol de bovino. También se ha estudiado este parámetro sobre siete mezclas binarias formuladas con las primeras materias antes citadas. Igualmente, se han estudiado los efectos de la bioestabilidad en la variación de las propiedades físicas y químicas de todos los sustratos. Considerando los respectivos índices de bioestabilidad, las primeras materias se han clasificado en tres grupos: materiales muy estables han resulta-do ser la fibra de coco, el compost de corteza de pino y el compost de residuos de jardinería; materiales estables se ha probado que lo son la turba de esfagno y el compost de residuos forestales. Finalmente, el compost de estiércol de bovino presenta una bioestabilidad moderada. Se muestra que, considerando los materiales estudiados, la variación relativa de ciertas propiedades físicas, como por ejemplo el agua disponible y el agua difícilmente disponible, y también la de ciertas propiedades químicas, como la capacidad de intercambio catiónico, se correlacionan linealmente, con significación estadística, con el índice de bioestabilidad de los sustratos estudiados en las dos localizaciones experimentales. Considerando sólo las primeras materias, la regresión lineal entre su capacidad

Theory of monolayers with boundaries: Exact results and Perturbative analysis

Domains and bubbles in tilted phases of Langmuir monolayers contain a class of textures knows as boojums. The boundaries of such domains and bubbles may display either cusp-like features or indentations. We derive analytic expressions for the textures within domains and surrounding bubbles, and for the shapes of the boundaries of these regions. The derivation is perturbative in the deviation of the bounding curve from a circle. This method is not expected to be accurate when the boundary suffers large distortions, but it does provide important clues with regard to the influence of various energetic terms on the order-parameter texture and the shape of the domain or bubble bounding curve. We also look into the effects of thermal fluctuations, which include a sample-size-dependent effective line tension.Comment: replaced with published version, 21 pages, 16 figures include

Co-factor-free aggregation of tau into seeding-competent RNA-sequestering amyloid fibrils

Pathological aggregation of the protein tau into insoluble aggregates is a hallmark of neurodegenerative diseases. The emergence of disease-specific tau aggregate structures termed tau strains, however, remains elusive. Here we show that full-length tau protein can be aggregated in the absence of co-factors into seeding-competent amyloid fibrils that sequester RNA. Using a combination of solid-state NMR spectroscopy and biochemical experiments we demonstrate that the co-factor-free amyloid fibrils of tau have a rigid core that is similar in size and location to the rigid core of tau fibrils purified from the brain of patients with corticobasal degeneration. In addition, we demonstrate that the N-terminal 30 residues of tau are immobilized during fibril formation, in agreement with the presence of an N-terminal epitope that is specifically detected by antibodies in pathological tau. Experiments in vitro and in biosensor cells further established that co-factor-free tau fibrils efficiently seed tau aggregation, while binding studies with different RNAs show that the co-factor-free tau fibrils strongly sequester RNA. Taken together the study provides a critical advance to reveal the molecular factors that guide aggregation towards disease-specific tau strains

The A-shell star φ Leo revisited: its photospheric and circumstellar spectra

Context. We previously suggested that variable red- and blueshifted absorption features observed in the Ca I

Resolved Sideband Cooling of a Micromechanical Oscillator

Micro- and nanoscale opto-mechanical systems provide radiation pressure coupling of optical and mechanical degree of freedom and are actively pursued for their ability to explore quantum mechanical phenomena of macroscopic objects. Many of these investigations require preparation of the mechanical system in or close to its quantum ground state. Remarkable progress in ground state cooling has been achieved for trapped ions and atoms confined in optical lattices. Imperative to this progress has been the technique of resolved sideband cooling, which allows overcoming the inherent temperature limit of Doppler cooling and necessitates a harmonic trapping frequency which exceeds the atomic species' transition rate. The recent advent of cavity back-action cooling of mechanical oscillators by radiation pressure has followed a similar path with Doppler-type cooling being demonstrated, but lacking inherently the ability to attain ground state cooling as recently predicted. Here we demonstrate for the first time resolved sideband cooling of a mechanical oscillator. By pumping the first lower sideband of an optical microcavity, whose decay rate is more than twenty times smaller than the eigen-frequency of the associated mechanical oscillator, cooling rates above 1.5 MHz are attained. Direct spectroscopy of the motional sidebands reveals 40-fold suppression of motional increasing processes, which could enable reaching phonon occupancies well below unity (<0.03). Elemental demonstration of resolved sideband cooling as reported here should find widespread use in opto-mechanical cooling experiments. Apart from ground state cooling, this regime allows realization of motion measurement with an accuracy exceeding the standard quantum limit.Comment: 13 pages, 5 figure