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In this work we explore the interplay between superconductivity and nematicity in the framework of a Ginzburg Landau theory with a nematic order parameter coupled to the superconductor order parameter, often used in the description of superconductivity of Fe based materials. In particular, we focus on the study of the vortex-vortex interaction in order to determine the way nematicity affects its attractive or repulsive character. To do so, we use a dynamical method based on the solutions of the Time Dependent Ginzburg Landau equations in a bulk superconductor. An important contribution of our work is the implementation of a pseudo-spectral method to solve the dynamics, known to be highly efficient and of very high order in comparison to the usual finite differences/elements methods. The coupling between the superconductor and the (real) nematic order parameters is represented by two terms in the free energy: a biquadratic term and a coupling of the nematic order parameter to the covariant derivatives of the superconductor order parameter. Our results show that there is a competing effect: while the former independently of its competitive or cooperative character generates an attractive vortex-vortex interaction, the latter always generates a repulsive interaction., Comment: 37 pages; 12 figures; corrected typos; added references

The dynamics of micrometer-sized magnetic domains in ultra-thin ferromagnetic films is so dramatically slowed down by quenched disorder that the spontaneous elastic tension collapse becomes unobservable at ambient temperature. By magneto-optical imaging we show that a weak zero-bias AC magnetic field can assist such curvature-driven collapse, making the area of a bubble to reduce at a measurable rate, in spite of the negligible effect that the same curvature has on the average creep motion driven by a comparable DC field. An analytical model explains this phenomenon quantitatively., 5 pages, 3 figures. Ancillary Material included

Externally driven glassy systems may undergo nonequilibrium phase (NEPTs). In particular, ac-driven systems display special features, such as those observed in the vortex matter of NbSe2, where oscillatory drives reorganize the system into partially ordered vortex lattices. We provide experimental evidence for this dynamic reorganization and we show an unambiguous signature of its connection with an NEPT driven by ac forces. We perform a scaling analysis and we estimate critical exponents for this transition. Our results share similarities with some glass-to-viscous-liquid NEPTs and invite a search for similar physics in other elastic disordered media. Fil: Marziali Bermudez, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; Argentina Fil: Cugliandolo, L.F.. Université Pierre et Marie Curie; Francia Fil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina

The domain wall response under constant external magnetic fields reveals a complex behavior where sample disorder plays a key role. Furthermore, the response to alternating magnetic fields has only been explored in limited cases and analyzed in terms of the constant field solution. Here we unveil phenomena in the evolution of magnetic domain walls under the application of alternating magnetic fields within the creep regime, well beyond a small fluctuation limit of the domain wall position. Magnetic field pulses were applied in ultrathin ferromagnetic films with perpendicular anisotropy, and the resulting domain wall evolution was characterized by polar magneto-optical Kerr effect microscopy. Whereas the dc characterization is well predicted by the elastic interface model, striking unexpected features are observed under the application of alternating square pulses: Magneto-optical images show that after a characteristic number of cycles, domain walls evolve toward strongly distorted shapes concomitantly with a modification of domain area. The morphology of domain walls is characterized with a roughness exponent when possible and contrasted with alternative observables which are more suitable for the characterization of this transient evolution. The final stationary convergence as well as the underlying physics is discussed. Fil: Domenichini, Pablo Exequiel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Quinteros, Cynthia Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. University of Groningen; Países Bajos Fil: Granada, Mara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Collin, S.. Centre National de la Recherche Scientifique; Francia Fil: George, J. M.. Centre National de la Recherche Scientifique; Francia Fil: Curiale, Carlos Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Universidad Nacional de Cuyo; Argentina Fil: Bustingorry, Sebastian. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche | Comision Nacional de Energia Atomica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia. Unidad Ejecutora Instituto de Nanociencia y Nanotecnologia - Nodo Bariloche.; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Capeluto, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina

Evidence of nematic effects in the mixed superconducting phase of slightly underdoped $\text{Ba}(\text{Fe}_{1-x}\text{Co}_x)_2\text{As}_2$ is reported. We have found strong in-plane resistivity anisotropy for crystals in different strain conditions. For these compositions, there is no magnetic long range order, so the description may be ascribed to the interplay between the superconducting and nematic order parameters. A piezoelectric-based apparatus is used to apply tensile or compressive strain to tune nematic domain orientation in order to examine intrinsic nematicity. Measurements are done under a rotating magnetic field and the analysis of the angular dependence of physical quantities identifies the cases in which the sample is {\em detwinned}. Furthermore, the angular dependence of the data allows us to evaluate the effects of nematicity on the in-plane superconductor stiffness. Our results show that although nematicity contributes in a decisive way in the conduction properties, its contributions to the anisotropy properties of the stiffness of the superconducting order parameter is not as significant in these samples.

In type-II superconductors, the macroscopic response of vortex matter to an external perturbation depends on the local interaction of flux lines with the pinning landscape (pinscape). The (Campbell) penetration depth $\lambda_{\mathrm{\scriptscriptstyle C}}$ of an $ac$ field perturbation is often associated with a phenomenological pinning curvature. However, this basic approach is unable to capture thermal hysteresis effects observed in a variety of superconductors. The recently developed framework of strong-pinning theory has established a quantitative relationship between the microscopic pinscape and macroscopic observables. Specifically, it identifies history-dependent vortex arrangements as the primary source for thermal hysteresis in the Campbell response. In this work, we show that this interpretation is well suited to capture the experimental results of the clean superconductor $\mathrm{Nb}\mathrm{Se}_{2}$; as observed through Campbell response (linear $ac$ susceptibility) and small-angle neutron scattering measurements. Furthermore, we exploit the hysteretic Campbell response upon thermal cycling to extract the temperature dependence of microscopic pinning parameters from bulk measurements; specifically the pinning force and pinning length. This spectroscopic tool may stimulate further pinscape characterization in other superconducting systems., Comment: 7 pages, 5 figures

The fishtail magnetization observed in many type II superconductors has been investigated since the earliest nineties and associated with different phase transitions and dynamic crossovers in complex vortex matter. In systems without a sharp order-disorder phase transition, the fishtail has been related with a crossover from elastic to plastic vortex creep regimes. In this paper we perform a critical revision of this accepted picture. We show that, in slightly underdoped YBa2Cu3O7-δ single crystals, there is a clear correlation between the fishtail magnetization and the Peak Effect observed in ac experiments with the associated history effects. We propose that both features are originated in the same dynamic crossover, between two plastic creep regimes. The proposed picture can also apply to other system, as those belonging to same families of iron-based pnictides. Fil: Perez Daroca, Diego Raul. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina

We studied thermal and dynamic history effects in the vortex lattice (VL) near the order-disorder transition in clean ${\mathrm{NbSe}}_{2}$ single crystals. Comparing the evolution of the effective vortex pinning and the bulk VL structure, we observed metastable superheated and supercooled VL configurations that coexist with a hysteretic effective pinning response due to thermal cycling of the system. A novel scenario, governed by the interplay between (lower) elastic and (higher) plastic energy barriers, is proposed as an explanation for our observations: Plastic barriers, which prevent the annihilation or creation of topological defects, require dynamic assistance to be overcome and to achieve a stable VL at each temperature. Conversely, thermal hysteresis in the pining response is ascribed to low energy barriers, which inhibit rearrangement within a single VL correlation volume and are easily overcome as the relative strength of competing interactions changes with temperature.

A large amount of experimental and theoretical work has been devoted to understand memory effects (ME) in the solid vortex lattice (VL) but has remained, however, controversial until now. In the vicinity of the anomaly known as the peak effect (PE) both the VL mobility and the measured critical current density are found to be dependent of the dynamical history of the sample, in both low Tc (LTS) and high Tc (HTS) superconductors. Experiments in YBa2Cu3O7 (YBCO) crystals have shown that the mobility of the VL increases after assisting the system with a symmetric AC field (or current) of moderated amplitude. On the other hand, after an asymmetric AC field assists vortices, the VL becomes less mobile. These features indicate that ME in these samples cannot be ascribed to an equilibration process, but probably are related to the organization of the lattice after nearest neighbor re-accommodation or induced plastic VL deformation. Recently, we have shown evidence that in YBCO the PE is a dynamic anomaly observed in the non-linear response, and is absent in the Labusch constant derived from the linear Campbell regime. However, this behavior seems not to be extensive to other systems as the traditional LTS NbSe2. In this work, the AC response in the PE region of NbSe2 and YBCO samples are presented and compared. Very salient differences both in the linear and non-linear response as well as in the ME characteristics indicate that a different physics governs the PE phenomena in each case. © 2007 Elsevier B.V. All rights reserved. Fil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Luna, Diego Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Eismann, B.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Ecole Normale Supérieure; Francia Fil: Bettachini, Víctor. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Bekeris, Victoria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina

We report structural evidence of dynamic reorganization in vortex matter in clean NbSe$_2$ by joint small angle neutron scattering and ac-susceptibility measurements. The application of oscillatory forces in a transitional region near the order-disorder transition results in robust bulk vortex lattice configurations with an intermediate degree of disorder. These dynamically-originated configurations correlate with intermediate pinning responses previously observed, resolving a long standing debate regarding the origin of such responses., Comment: 9 pages, 7 figures. To be published in Physical Review Letters

Many different systemic pathogens, including viruses, affect pome and stone fruits causing diseases with adverse effects in orchards worldwide. The significance of diseases caused by these pathogens on tree health and fruit shape and quality has resulted in the imposition of control measures both nationally and internationally. Control measures depend on the identification of diseases and their etiological agents. Diagnosis is the most important aspect of controlling fruit plant viruses. Early detection of viruses in fruit trees or in the propagative material is a prerequisite for their control and to guarantee a sustainable agriculture. Many quarantine programs are in place to reduce spread of viruses among countries during international exchange of germplasm. All these phytosanitary measures are overseen by governments based on agreements produced by international organizations. Also certification schemes applied to fruit trees allow the production of planting material of known variety and plant health status for local growers by controlling the propagation of pathogen-tested mother plants. They ensure to obtain propagative material not only free of "quarantine" organisms under the national legislation but also of important "nonquarantine" pathogens. The control of insect vectors plays an important role in the systemic diseases management, but it must be used together with other control measures as eradication of infected plants and use of certified propagation material. Apart from the control of the virus vector and the use of virus-free material, the development of virus-resistant cultivars appears to be the most effective approach to achieve control of plant viruses, especially for perennial crops that are more exposed to infection during their long life span. The use of resistant or tolerant cultivars and/or rootstocks could be potentially the most important aspect of virus disease management, especially in areas in which virus infections are endemic. The conventional breeding for virus-tolerant or resistant fruit tree cultivars using available germplasm is a long-term strategy, and the development and production of these cultivars may take decades, if successful. Genetic engineering allows the introduction of specific DNA sequences offering the opportunity to obtain existing fruit tree cultivars improved for the desired resistance trait. Unfortunately, genetic transformation of pome and stone fruits is still limited to few commercial genotypes. Research carried out and the new emerging biotechnological approaches to obtain fruit tree plants resistant or tolerant to viruses are discussed.

Pendant de nombreuses annees, le Plum pox virus (PPV) etait considere comme transmissible par les semences, ce qui augmentait la crainte d'une dissemination sur de longues distances de la maladie. A la fin des annees 1970, il a ete affirme, en se basant sur la transmission biologique du virus a des plantes herbacees indicatrices et sur le developpement d'un diagnostic serologique reposant sur des anticorps polyclonaux, que le PPV etait transmis par les semences, avec un taux d'infection different selon l'espece vegetale et la partie de la semence qui etaient testees. Dans les annees 1990, le PPV a ete caracterise comme etant de quatre types differents, et des anticorps monoclonaux specifiques ont ete produits pour chacun. Ces techniques de diagnostic, nouvelles et plus sensibles, associees avec la RT-PCR avec differents ensembles d'amorces specifiques, ont ete utilisees pour approcher a nouveau le probleme de la transmission du PPV par les semences. Le virus a ete detecte dans les enveloppes des semences et les cotyledons, mais les tissus embryonnaires et les plantules obtenus a partir des graines germees n'ont jamais montre de symptomes, et ont donne des resultats negatifs pour le PPV a la fois avec les analyses ELISA et PCR. Aucun isolat du PPV n'est actuellement reconnu comme etant transmis par les semences: la transmission verticale du PPV entre les plantes-meres infectees et leur descendance ne se produit donc pas. De facon theorique, la seule possibilite de transmission par les semences pourrait provenir d'une mutation dans le cofacteur du virus, associe avec une forte sensibilite du cultivar de Prunus infecte.

The peak effect (PE) in the critical current density in both low and high temperature superconductors has been the subject of a large amount of experimental and theoretical work in the last few/several years. In the case of YBCO, crucial discussions describing a, dynamic or a, static picture are not settled. In that region of field and temperature the mobility of the vortex lattice (VL) is found to be dependent on the dynamical history. Recently we reported evidence that the VL reorganizes and accesses to robust VL configurations (VLCs) with different effective pinning potential wells arising in response to different system histories. One of the keys to understand the nature of the PE is to investigate the VL behavior in the vicinity of the various VLCs in the region of the PE. The stability of these VLCs was investigated and it was found that they have distinct characteristic relaxation times, which may be related to elastic or plastic creep processes. In this paper we review some of these results and propose a scenario to describe the PE in YBCO crystals. © Indian Academy of Sciences. Fil: Pasquini, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Bekeris, Victoria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina

In the United States, yellow starthistle (Centaurea solstitialis) is an annual invasive weed with Mediterranean origins. Malformed plants displaying witches' broom, fasciations, abortion of buds and flower virescence symptoms were observed in central Italy. Attempts to transmit the causal agent from the natural yellow starthistle host to periwinkle by grafting, resulted in typical symptoms of a phytoplasma, i.e. yellowing and shortening of internodes. The detection of phytoplasmas was obtained from both symptomatic yellow starthistle and periwinkle by the specific amplification of their 16S-23S rRNA genes. PCR amplification of extracted DNA from symptomatic plant samples gave a product of expected size. Asymptomatic plants did not give positive results. An amplicon obtained by direct PCR with universal primers P1/P7 was cloned and sequenced. The homology search using CLUSTALW program showed more than 99% similarity with Illinois elm yellows (ILEY) phytoplasma from Illinois (United States) and 97% with Brinjal little leaf (BLL) phytoplasma from India. Digestion of the nested-PCR products with restriction enzymes led to restriction fragment length polymorphism patterns referable to those described for phytoplasmas belonging to the clover proliferation (16S-VI) group. Since this is a previously undescribed disease, the name Centaurea solstitialis virescence has been tentatively assigned to it. This is a new phytoplasma with closest relationships to ILEY and BLL, but distinguishable from them on the basis of 16S rDNA homology, the different associated plant hosts and their geographical origin.

A one-step reverse transcription-polymerase chain reaction (RT-PCR) protocol was developed and used for the detection of Strawberry latent ring spot virus (SLRSV) in leaves of olive trees in Italy. The protocol was used to test for infection in samples from 87 trees and to correlate infection with leaf symptoms. SLRSV was found only in olives grown in Central Italy (the Marche and Umbria regions) and was detected in c. 15% of leaf samples. Most infected plants had narrow and twisted leaves, symptoms which seemed to occur in specific cultivars. The one-step RT-PCR protocol is very rapid and sensitive and has the potential to be used on a mass scale for the diagnosis of SLRSV in olive. This virus should be considered an important pathogen in olive trees, even if its distribution in the field seems to be limited to well defined areas.

Plum pox virus is one of the most detrimental pathogens of stone fruit trees, largely spread in many areas throughout the world. It is included in the EPPO A2 quarantine pathogens list and must be submitted to the international and national quarantine requirements. The high importance of the harmonization of the diagnostic procedures, the contribution to greater transparency during the diagnosis of regulated pests and the need of the resolution of disputes among trading partners suggested, in the framework of the Project ARNADIA financed by the Italian Ministry of Agriculture, to set up a validated diagnostic protocol, officially approved and published at the national level. Different diagnostic methods, protocols and reagents were compared in five different laboratories, using the same target and non-target reference samples. ELISA, RT-PCR and real time RT-PCR protocols were selected and applied to determine their performance characteristics for validation under the standard ISO 17025. Sensitivity was determined performing experiments with seven serial dilutions of sample extracts for serological analysis and of total RNA extracts for molecular analysis. Specificity was determined assaying different infected samples, representative of the genomic and geographical variability of PPV, and non-target samples. Reproducibility was assessed through performance of the experiments by different laboratories. Repeatability will be established in the frame of a ring test among Italian phytosanitary laboratories. Results showed that the accuracy and sensitivity of ELISA and RT-PCR are comparable, whereas real time RT-PCR is recommended for testing symptomless samples.

Apple chlorotic leaf spot trichovirus is considered one of the most economically important viruses affecting both pome and stone fruit species. High biological and molecular variability is known to occur among ACLSV isolates of different countries. Occurrence of ACLSV on apple in Hungary is known since the age of ‘60s. Severe symptoms, not characteristic for any known virus disease of stone fruits, were observed on peach in 1974 and on wild cherry in 1982. Later it was suspected that those symptoms were caused by atypical isolates of ACLSV. Therefore the above virus isolates were studied and compared to ACLVS isolates from apple. IC-RT-PCR, Western blot analyses as well as on cloning and sequencing of PCR products were performed. On the basis of electrophoretic mobility of the coat protein, which ranged between 19.7 and 22.7 kDa, Hungarian isolates could be classified, with different percentages, into three distinct groups. Six of 12 isolates belonged to Cis, 5 belonged to Bit and one mixed infection (Cen+Bit) was found. Virus cDNA was amplified by IC-RT-PCR. Amplified fragments of two apple, one peach and two cherry isolates were cloned, sequenced and compared. Homology of the compared isolates ranged between 81-94%.

Structural properties of [BaCuO x ] 2 /[CaCuO 2 ] n superconducting superlattices with a number of Ca-CuO 2 layers ranging between 2 and 3 were investigated using synchrotron radiation, by coplanar (symmetrical and asymmetrical) X-ray diffraction and also in grazing incidence geometry. This extensive X-ray diffraction characterisation allowed to confirm the pseudomorphic growth of [Ba-CuO x ] 2 /[CaCuO 2 ] n superlattices on the SrTiO 3 (001)-oriented substrate. Reciprocal space maps in symmetrical configuration, i.e. by specular reflection, showed the effect of a slight miscut of the substrate on the inclination of the rods. Finally, the interface and surface morphology were investigated by diffuse scattering obtaining the in-plane and out-of-plane correlation properties of the interface roughness and these results were compared with the surface roughness measured by atomic force microscopy.

The structural disorder in ( Ba 2 Cu 2 O 4+x )/( CaCuO 2) n superlattices with ultrathin individual layers was investigated. Numerical simulations of x-ray spectra were carried out following a kinematical approach in a simplified model structure. The model assumes a two-dimensional layer by layer growth in which mixed composition layers can be corrugated to adjust the internal stresses due to the large mismatch between the constituent oxides. An additional random disorder is added to take into account the experimental dispersion in the amount of material deposited in each iteration. The model was successfully used to simulate x-ray spectra for samples with non integer n ranging from 2 to 16, grown in optimal conditions to obtain a superconducting behavior. The same model was used to simulate spectra of samples grown at lower pressures monitored with in-situ RHEED diagnostic. In this case, random disorder results more than one order of magnitude smaller.

The electrical transport properties of $[{\mathrm{BaCuO}}_{x}{]}_{2}/[{\mathrm{CaCuO}}_{2}{]}_{n}(\mathrm{C}\mathrm{B}\mathrm{C}\mathrm{C}\mathrm{O}\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}n)$ underdoped high-temperature superconducting superlattices grown by pulsed laser deposition have been investigated. Starting from the optimally doped $\mathrm{C}\mathrm{B}\mathrm{C}\mathrm{C}\mathrm{O}\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}2$ superlattice, having three ${\mathrm{CuO}}_{2}$ planes and ${T}_{c}$ around 80 K, we have systematically increased the number n up to 15 moving toward the underdoped region and hence decreasing ${T}_{c}.$ For $ng11$ the artificial structures are no longer superconducting, as expected, for a uniformly distributed charge carrier density inside the conducting block layer. The sheet resistance of such artificial structures $(n\ensuremath{\approx}11)$ turns out to be quite temperature independent and close to the two-dimensional quantum resistance 26 k\ensuremath{\Omega}. A further increase of the number of ${\mathrm{CuO}}_{2}$ planes results in an insulator-type dependence of $R(T)$ in the wide range of temperatures from room temperature to 1 K. The value of the sheet resistance separating the superconducting and the insulating regimes supports the fermionic scenario of the superconductor-insulator transition in these systems.

The structural disorder in $({\mathrm{Ba}}_{2}{\mathrm{Cu}}_{2}{\mathrm{O}}_{4+x})/({\mathrm{CaCuO}}_{2}{)}_{n}$ superlattices with ultrathin individual layers consisting of a noninteger number of unit cells is investigated. X-ray diffration and reflection high energy electron diffraction show that a two-dimensional layer by layer growth occurs and that layers of mixed composition are corrugated to adjust the internal stresses. On the basis of these conclusions we can outline an explanation for the behavior of ${T}_{c}$ vs n in $({\mathrm{Ba}}_{2}{\mathrm{Cu}}_{2}{\mathrm{O}}_{4+x})/({\mathrm{CaCuO}}_{2}{)}_{n}$ superlattices.

Pinning properties in 100 nm thick continuous and porous superconducting Nb films are examined by ac susceptibility and dc magnetization measurements. The Nb film was deposited on a smooth Si substrate, while the porous film, NbP, was deposited on an anodized Al oxide substrate. Pores or "antidots" 40 nm in diameter, 100 nm apart, form a triangular array. The porous film presents commensurate or matching field effects for applied magnetic fields where the magnetic flux threading each unit cell is an integer number of the flux quantum, where ac shielding capability and dc diamagnetic magnetization show an abrupt increase. The response to ac fields as a function of temperature and dc field provided a way to determine that NbP sample has higher pinning than the continuous one, and that TC suppression due to fluxoid quantization is not relevant for the investigated temperature range. © 2009 Elsevier B.V. All rights reserved. Fil: Chiliotte, Claudio Ezequiel. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Perez Daroca, Diego Raul. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Pasquini, Gabriela. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Bekeris, Victoria Isabel. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Li, C. P.. University of California at San Diego; Estados Unidos Fil: Casanova, F.. University of California at San Diego; Estados Unidos Fil: Villegas, J. E.. University of California at San Diego; Estados Unidos Fil: Schuller, I.K.. University of California at San Diego; Estados Unidos

We use ac susceptibility measurements to explore the dynamic response of vortices in YBCO single crystals pinned by aligned columnar defects at low dc fields. Using a combination of techniques for the analysis of the data, we investigate the vortex motion as a function of the amplitude and frequency of the applied ac field hac , identifying the influence of both intra- and inter-valley motion. We build up a dynamic diagram in the hac-T plane indicating the crossover lines among several regimes in the solid phase. At low hac , a linear response with very low dissipation arises from the oscillation of pinned vortices inside the tracks ~Campbell regime! .A t high hac a critical state develops. The large influence of thermal fluctuations in this limit is indicated by the frequency dependence, which allows us to obtain the current density dependence of the activation energy and the glassy exponent. We also discuss the origin of the large nonlinear transition regime observed at intermediate amplitudes. @S0163-1829~99!02613-2#

We have studied vortex pinning through ac susceptibility measurements in single crystals of YBCO with columnar defects (CDs). The CDs have 0°, 10° and 20° splay angle and average direction 10° off the c-axis. By studying the angular variation we can compensate for the anisotropy and effects of twins, etc. Using a simple expression we can obtain the angular spread when the field direction is outside the splay angle. An increase of pinning when the field direction is inside the angle defined by the CDs can be attributed to vortex entanglement due to the splay and the suppression of the sliding of double kinks.

We explore the AC magnetic susceptibility of YBa 2 Cu 3 O 7 single crystals with columnar defects. For vortices parallel to the defects the linear response is mainly determined by the Campbell penetration depth with a field independent Labusch parameter indicating that vortices are individually pinned. The small dissipation in this limit is likely to arise from thermal fluctuations of vortex segments between pairs of metastable states (two-level systems) in the Bose glass phase. Tilting vortices away from the tracks results in a reduction of the Bose glass temperature and an increase of the dissipation due to the reduction of the pinning forces. We discuss the onset of nonlinear response as the AC field increases.

The interest in twin-boundary (TB) planes as a source of vortex pinning has been recently renewed with the discovery of the new iron-arsenide pnictide superconductors. In the family of compounds Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ a structural transition from a tetragonal to orthorhombic lattice takes place for compounds with $xl{x}_{\mathrm{cr}}\ensuremath{\sim}0.065$. Approaching the critical doping, domain structure shrinks with sizes ultimately becoming comparable to vortex cores. In this work we investigate the changes in anisotropy produced by subtle differences in the Co doping level, in the neighborhood of the structural transition, in good-quality single crystals. Using a scaling approach we are able to determine the angular regions where correlated or uncorrelated disorder prevails. In the tetragonal samples ($xg{x}_{\mathrm{cr}}$) there is no twinning and we find good agreement with the expected scaling function under uncorrelated disorder, with small anisotropy values similar to those reported in the literature. We show that in the orthorhombic samples ($xl{x}_{\mathrm{cr}}$), TBs act as correlated disorder in a broad angular range. We propose that the observed angular dependence could be due to an increase in the vortex liquid-glass transition temperature.

Artichoke latent virus (ArLV) is one of the most economically important and widely distributed viruses of artichoke in the Mediterranean area. The availability of a sensitive and reliable diagnostic method is a prerequisite for evaluating the sanitary status of globe artichoke plants. We report here two molecular methods for the detection of ArLV. The first consists of RNA extraction from infected leaf tissue using a commercial kit, followed by a one-step reverse transcription polymerase chain reaction (RT-PCR) protocol, using primers designed in this investigation. The second is based on the tissue imprint hybridization technique, using a denatured digoxigenin-labelled ArLV DNA probe. Both methods were effective in detecting ArLV in late globe artichoke plant samples.

Purpose: To improve quality of newborn screening by tandem mass spectrometry with a novel approach made possible by the collaboration of 154 laboratories in 49 countries. Methods: A database of 767,464 results from 12,721 cases affected with 60 conditions was used to build multivariate pattern recognition software that generates tools integrating multiple clinically significant results into a single score. This score is determined by the overlap between normal and disease ranges, penetration within the disease range, differences between conditions, and weighted correction factors. Results: Ninety tools target either a single condition or the differential diagnosis between multiple conditions. Scores are expressed as the percentile rank among all cases with the same condition and are compared to interpretation guidelines. Retrospective evaluation of past cases suggests that these tools could have avoided at least half of 279 false-positive outcomes caused by carrier status for fatty-acid oxidation disorders and could have prevented 88% of known false-negative events. Conclusion: Application of this computational approach to raw data is independent from single analyte cutoff values. In Minnesota, the tools have been a major contributing factor to the sustained achievement of a false-positive rate below 0.1% and a positive predictive value above 60%. © 2012 American College of Medical Genetics and Genomics.

We study experimentally and theoretically, the reorganization of superconducting vortices driven by oscillatory forces near the plastic depinning transition. We show that the system can be taken to configurations that are tagged by the shaking parameters but keep no trace of the initial conditions. In experiments performed in $NbSe_2$ crystals, the periodic drive is induced by ac magnetic shaking fields and the overall order of the resulting configuration is determined by non invasive ac susceptibility measurements. With a model of interacting particles driven over random landscapes, we perform molecular dynamics simulations that reveal the nature of the shaking dynamics as fluctuating states similar to those predicted for other interacting particle systems., Comment: 5 pages, 4 figures