Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in Ni81_{81}Fe19_{19} / α\alpha-Fe2_2O3_3

We report studies of exchange bias and coercivity in ferromagnetic Ni$_{81}$Fe$_{19}$ layers coupled to antiferromagnetic (AF) (0001), (11$\bar{2}$0), and (11$\bar{0}$2) $\alpha$-Fe$_2$O$_3$ layers. We show that AF spin configurations which permit spin-flop coupling give rise to a strong uniaxial anisotropy and hence a large coercivity, and that by annealing in magnetic fields parallel to specific directions in the AF we can control either coercivity or exchange bias. In particular, we show for the first time that a reversible temperature-induced spin reorientation in the AF can be used to control the exchange interaction.Comment: 15 pages, 5 figures, submitted to Phys. Rev. Let

Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films

We have investigated the relationship between the domain structure and the magnetic interactions in a series of FePt ferromagnetic thin films of varying thickness. As-made films grow in the magnetically soft and chemically disordered A1 phase that may have two distinct domain structures. Above a critical thickness $d_{cr}\sim 30$ nm the presence of an out of plane anisotropy induces the formation of stripes, while for $d<d_{cr}$ planar domains occur. Magnetic interactions have been characterized using the well known DCD-IRM remanence protocols, $\delta M$ plots, and magnetic viscosity measurements. We have observed a strong correlation between the domain configuration and the sign of the magnetic interactions. Planar domains are associated with positive exchange-like interactions, while stripe domains have a strong negative dipolar-like contribution. In this last case we have found a close correlation between the interaction parameter and the surface dipolar energy of the stripe domain structure. Using time dependent magnetic viscosity measurements, we have also estimated an average activation volume for magnetic reversal, $\langle V_{ac}\rangle \sim 1.37\times 10^{4}$ nm$^{3},$ which is approximately independent of the film thickness or the stripe period.Comment: 25 pages, 11 figure

Photocatalytic activity in the in-flow degradation of NO on porous TiO2 –coated glasses from hybrid inorganic–organic thin films prepared by a combined ALD/MLD deposition strategy

A combined ALD/MLD (where ALD and MLD stand for atomic and molecular layer deposition, respectively) deposition strategy using TiCl4, H2 O and HQ (hydroquinone) as precursors has been applied for the preparation of inorganic–organic thin films on soda-lime glasses. The alternate deposition of TiO2 layers, by pulsing TiCl4 /H2 O (ALD), and hybrid layers, using TiCl4 /HQ (MLD), results in the formation of thin films that are precursors for porous TiO2-coatings after removal of the HQ template by annealing. The coated-glassed show good photocatalytic activity in the degradation of NO with up to 15% reduction of NO concentration in three successive photocatalytic cycles of 5 h each. Surface Scanning Electron Microscopy (SEM) images show that the TiO2-coating is composed of large grains that are made up of finer subgrains resulting in a porous structure with an average pore size of 3–4 nm. Transmission Electron Microscopy (TEM) images show two regions, a porous columnar structure on top and a denser region over the glass substrate. Energy Dispersive X-Ray (EDX) analysis, nanocrystal electron diffraction and Raman spectroscopy confirm the presence of the anatase phase, which, together with the porosity of the material, accounts for the observed photocatalytic activity. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Control de Rhizoctonia solani con extractos de Ovidia andina

New alternatives are needed to control ubiquitous soilborne fungi like Rhizoctonia solani. This work evaluates the activity of extracts from Ovidia andina on this pathogen. Powdered dried leaves and stems were extracted by maceration with dichloromethane (CH2Cl2), methanol and ethanol. An aqueous extract was obtained by decoction, and the hydrodistillation residual water was the aqueous phase after essences production. A strain of R. solani was cultivated on potato dextrose agar supplemented with the extracts, at 1:100 and 1:1000 v/v. The CH2Cl2 extract at 1:100 reduced colony growth (p&lt; 0.0001) and changed hyphal morphology. Five fractions were obtained from the CH2Cl2 extract in a glass column, and TLC analysis showed the presence of coumarins and flavonoids. The CH2Cl2 extract and fractions were diluted in CH2Cl2 or acetone. The efficiency to reduce pathogen growth of fractions 2f and 5f diluted in CH2Cl2 at 1:100 did not differ from the whole extract (p&lt;0.0001). For an in vivo test, beetroot seed balls were incubated in soil infested with R. solani and treated by immersion in the CH2Cl2 extract at 1:100 for different periods of time. As a result, pathogen colonization was diminished by immersion for 120 s and seed germination was normal (p&lt; 0.0001). Additionally, infested soil was treated with the CH2Cl2 extract, and inoculum concentration estimated using beetroot seed balls as baits diminished (p&lt; 0.0001). These results lead us to conclude that O. andina is a source of antifungal components for crop protection against R. solani.Resulta necesario generar alternativas para el control de hongos patógenos de suelo como Rhizoctonia solani. En este trabajo, se evaluó la actividad de extractos de Ovidia andina sobre una cepa del patógeno. Se realizaron extracciones a partir de hojas y tallos secos pulverizados, macerados con diclorometano (CH2Cl2), metanol y etanol. Se obtuvo un extracto acuoso por decocción y aguas residuales consistentes en la fase acuosa luego de la producción de esencias. Se cultivó una cepa de R. solani en agar papa glucosa suplementado con los extractos diluidos 1:100 o 1:1000 v/v. El extracto CH2Cl2 1:100 redujo el crecimiento de las colonias (p&lt; 0,0001) y alteró la morfología de las hifas. Se obtuvieron 5 fracciones del extracto CH2Cl2 en una columna de vidrio y mediante TLC se detectó la presencia de cumarinas y flavonoides. Posteriormente, el extracto CH2Cl2 y sus fracciones se diluyeron en CH2Cl2 o acetona. La eficiencia de las fracciones 2f y 5f diluidas CH2Cl2 1:100 para reducir el crecimiento fúngico no difirió de la del extracto completo (p&lt;0,0001). En un experimento in vivo, se incubaron glomérulos de remolacha en suelo infestado con R. solani y se sumergieron en el extracto CH2Cl2 1:100 durante tiempos variables. La colonización fúngica disminuyó mediante la inmersión durante 120 segundos, sin afectar la germinación (p&lt; 0,0001). Adicionalmente, se trató suelo infestado con el extracto CH2Cl2 y disminuyó la concentración de inóculo del patógeno estimada utilizando glomérulos de remolacha como trampas (p&lt; 0,0001). Estos resultados permiten concluir que O. andina es una fuente de componentes antifúngicos para la protección vegetal contra R. solani.Fil: Tito Mansilla, Javier. Universidad Nacional de San MartínFil: Tarcaya, Verónica P.. Universidad de Buenos AiresFil: Cufre, Ingrid M.. Universidad de Buenos AiresFil: Fabrizio, María C.. Universidad de Buenos Aires. Facultad de AgronomíaFil: Wright, Eduardo R.. Universidad de Buenos Aires. Facultad de AgronomíaFil: Broussalis, Adriana M.. Universidad de Buenos AiresFil: Rivera, Marta C.. Universidad de Buenos Aires. Facultad de Agronomí

Exact scaling in the expansion-modification system

This work is devoted to the study of the scaling, and the consequent power-law behavior, of the correlation function in a mutation-replication model known as the expansion-modification system. The latter is a biology inspired random substitution model for the genome evolution, which is defined on a binary alphabet and depends on a parameter interpreted as a \emph{mutation probability}. We prove that the time-evolution of this system is such that any initial measure converges towards a unique stationary one exhibiting decay of correlations not slower than a power-law. We then prove, for a significant range of mutation probabilities, that the decay of correlations indeed follows a power-law with scaling exponent smoothly depending on the mutation probability. Finally we put forward an argument which allows us to give a closed expression for the corresponding scaling exponent for all the values of the mutation probability. Such a scaling exponent turns out to be a piecewise smooth function of the parameter.Comment: 22 pages, 2 figure

Spectral Analysis of Guanine and Cytosine Fluctuations of Mouse Genomic DNA

We study global fluctuations of the guanine and cytosine base content (GC%) in mouse genomic DNA using spectral analyses. Power spectra S(f) of GC% fluctuations in all nineteen autosomal and two sex chromosomes are observed to have the universal functional form S(f) \sim 1/f^alpha (alpha \approx 1) over several orders of magnitude in the frequency range 10^-7< f < 10^-5 cycle/base, corresponding to long-ranging GC% correlations at distances between 100 kb and 10 Mb. S(f) for higher frequencies (f > 10^-5 cycle/base) shows a flattened power-law function with alpha < 1 across all twenty-one chromosomes. The substitution of about 38% interspersed repeats does not affect the functional form of S(f), indicating that these are not predominantly responsible for the long-ranged multi-scale GC% fluctuations in mammalian genomes. Several biological implications of the large-scale GC% fluctuation are discussed, including neutral evolutionary history by DNA duplication, chromosomal bands, spatial distribution of transcription units (genes), replication timing, and recombination hot spots.Comment: 15 pages (figures included), 2 figure

Magnetoresistance in Fe1−x_{1-x}Gax_x thin films presenting striped magnetic pattern: the role of closure domains and domain walls

In this work we show the existence of closure domains in Fe$_{1-x}$Ga$_x$ thin films featuring a striped magnetic pattern and study the effect of the magnetic domain arrangement on the magnetotransport properties. By means of X-ray resonant magnetic scattering, we experimentally demonstrate the presence of such closure domains and estimate their sizes and relative contribution to surface magnetization. Magnetotransport experiments show that the behavior of the magnetoresistance depends on the measurement geometry as well as on the temperature. When the electric current ows perpendicular to the stripe direction, the resistivity decreases when a magnetic field is applied along the stripe direction (negative magnetoresistance) in all the studied temperature range, and the calculations indicate that the main source is the anisotropic magnetoresistance. In the case of current flowing parallel to the stripe domains, the magnetoresistance changes sign, being positive at room temperature and negative at 100 K. To explain this behavior, the contribution to magnetoresistance from the domain walls must be considered besides the anisotropic one.Comment: 8 pages, 5 figure

Protective films on complex substrates of thermoplastic and cellular elastomers:Prospective applications to rubber, nylon and cork

Deposition of thin films is an appropriate methodology to enhance the performance of a material by modification of its surface, while keeping the properties of the bulk largely unaffected. However, a practical implementation becomes less straightforward when dealing with sensitive or complex substrates, for instance, those which cannot be subjected to harsh treatments, such as cleaning and etching, or extreme deposition conditions, like high temperatures, and ion impingement et cetera. This paper concentrates on deposition processing of complex substrates. In particular, it discusses the deposition of two types of protective coatings (diamond-like carbon (DLC) films against friction and wear, and TiO2 films against UV light) on three types of thermoplastic and cellular elastomers (rubber, nylon and cork). It is demonstrated that a successful protection of thermoplastic elastomers against wear with DLC films can be attained, after a thorough adaptation of the procedure to the characteristics of the specific substrate. In addition, the paper reports the very first depositions on a cellular elastomer like cork by vapor deposition methods, including Atomic Layer Deposition (ALD)

Image Segmentation by Image Foresting Transform with Non-smooth Connectivity Functions

Abstract-In the framework of the Image Foresting Transform (IFT), there is a class of connectivity functions that were vaguely explored, which corresponds to the non-smooth connectivity functions (NSCF). These functions are more adaptive to cope with the problems of field inhomogeneity, which are common in MR images of 3 Tesla. In this work, we investigate the NSCF from the standpoint of theoretical and experimental aspects. We formally classify several non-smooth functions according to a proposed diagram representation. Then, we investigate some theoretical properties for some specific regions of the diagram. Our analysis reveals that many NSCFs are, in fact, the result of a sequence of optimizations, each of them involving a maximal set of elements, in a well-structured way. Our experimental results indicate that substantial improvements can be obtained by NSCFs in the 3D segmentation of MR images of 3 Tesla, when compared to smooth connectivity functions