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We study the temperature dependence of the magnetization switching fields of single nanoparticles with an improved micro-superconducting quantum interference device (SQUID) technique, that allows us to perform measurements independently of the critical superconducting temperature of the SQUID. A simplified Néel-Brown model that describes the magnetization reversal by thermal activation over a single anisotropy barrier is compared to measurements on a 3 nm cobalt nanoparticle embedded in a niobium matrix. [ABSTRACT FROM AUTHOR]

Frequency modulation is performed on a vortex oscillator at various modulation frequencies and powers. A global analysis of the whole set of data is proposed, so that all experimental curves are described with the same four parameters. Three of these parameters describe the dependence of the instantaneous frequency with modulating current. This dependence appears significantly different from the frequency-current dependence observed in a quasi-static experiment. The discrepancy is ascribed to the different time scales involved, compared to the relaxation time of the vortex oscillator. [ABSTRACT FROM AUTHOR]

Macroinvertebrate assemblages can vary with season as a result of changing environmental conditions and phenology of individual species. The objective of this study was to determine whether results from the South African Scoring System version 5 (SASS5) are affected by season. The standard SASS5 protocol was used to sample three sites on the Skeerpoort River, South Africa, in autumn, winter and spring 2013, and summer 2014. At each site, stream morphology was characterised and physico-chemical variables were measured. Two-way analysis of variance (ANOVA) was used to compare SASS indices in relation to site and season, and a one-way ANOVA was used to test the effect of season using both current and historical data. Macroinvertebrate assemblage similarity of sites was determined using non-metric multidimensional scaling ordination, followed by analysis of similarity. Whilst macroinvertebrate assemblages differed between seasons and sites, there was no seasonal variation in the values of SASS indices, but they did differ between sites. SASS5 appears to be robust to seasonal variation in macroinvertebrate assemblage and seems suitable for use throughout the year in a perennial river draining the South African highveld region. [ABSTRACT FROM AUTHOR]

Frequency modulation experiments were performed on a spin torque vortex oscillator for a wide range of modulation frequencies, up to 10% of the oscillator frequency. A thorough analysis of the intermodulation products shows that the key parameter that describes these experiments is the deviation sensitivity, which is the dynamical frequency-current dependence. It differs significantly from the oscillator tunability discussed so far in the context of spin-transfer oscillators. The essential difference between these two concepts is related to the response time of the vortex oscillator, driven either in quasisteady state or in a transient regime. [ABSTRACT FROM AUTHOR]

Three hymenopteran species - the ichneumonids Amblyteles armatorius and Diphyus quadripunctorius, and the proctotrupid Exallonyx longicornis - are most frequently cited from all over Europe as executing their inactive hypogean ecophase in caves. Yet, little is known about their environmental requirements during their summer quiescence and/or winter diapause; only limited data are known from Western and Eastern Europe. In this investigation, the sojourn of hymenopterans in hypogean environments is ecologically evaluated on the basis of data obtained from 63 systematically investigated caves and artificial tunnels in central and northern Slovenia, as being representative of the Central European countries. Nine environmental parameters measured at the resting sites of individuals were subjected to Principal Component Analysis (PCA). The species differ significantly from each other on ecological parameters: the euryecious A. armatorius occupies a narrow central position with respect to environmental requirements in caves; the montane D. quadripunctorius exhibits the best, and the lowland E. longicornis the feeblest adaptation to hypogean environments. In contrast to Western and Eastern Europe, in the central countries, the three hymenopteran species prefer dormancy habitats other than caves. These regional differences deserve more attention in future investigations of European hypogean fauna. [ABSTRACT FROM AUTHOR]

Duchenne muscular dystrophy (DMD) is one of the most common genetic diseases in humans, affecting 1 in 3500 boys. It is characterised by progressive muscle weakness and wasting due to mutations in the dystrophin (DMD) gene resulting in absence of dystrophin protein in skeletal muscle. Although curative treatments are currently not available, genetic and pharmacological approaches are under investigation including early-phase clinical trials. Existing animal models in different species (e.g. mdx mouse, GRMD dog) have been instrumental to understand the pathophysiology of DMD, but have several limitations. Importantly, the causative point mutations (mdx mouse: nonsense mutation; GRMD dog: splice mutation) are different from the most common human mutations (out-of-frame deletion of one or several exons of the DMD gene). We used gene targeting in somatic cells and nuclear transfer to generate a genetically tailored pig model of DMD. A bacterial artificial chromosome (BAC) from the porcine DMD gene was modified by recombineering to replace exon 52, resulting in a frame shift in the transcript. Modified BAC were transfected into male neonatal kidney cells, which were screened by quantitative polymerase chain reaction for replacement of exon 52 in the X-linked DMD gene. Eight of 436 cell clones were successfully targeted and 2 of them were used for nuclear transfer. For each of the cell clones, a pregnancy was established by transfer of cloned embryos into recipient gilts. Four piglets of the first litter were live born and killed within 48 h and tissue samples were processed for histological characterisation. Two piglets of the second litter died during birth due to obstetric complications, whereas the other 2 piglets were delivered by Caesarean section and raised in an artificial feeding system. Their serum creatine kinase (CK) levels were grossly elevated. Although both piglets showed reduced mobility compared with age-matched controls, they were able to move and feed on their own. Immunofluorescence staining of dystrophin was negative in muscle fibres of DMD mutant piglets and the complete absence of dystrophin protein was confirmed by immunoblot analysis. Histological examination of biceps femoris muscle from DMD mutant pigs showed a degenerative myopathy with fibre size variation, rounded fibres, central nuclei, fibrosis and fatty replacement of muscle tissue mimicking the hallmarks of the human disease. In conclusion, we generated the first pig model for a genetic muscle disease. The DMD mutant pig appears to be a bona fide model of the human dystrophy as ascertained by absence of the dystrophin protein, elevated serum CK levels and early degenerative changes on muscle histology. Because deletion of exon 52 is one of the most frequent mutations found in human DMD, the exon 52 mutated DMD pig represents an excellent model for testing targeted genetic treatments. This study was supported by the Bayerische Forschungsstiftung. [ABSTRACT FROM AUTHOR]

The output of monitoring programs such as the National Aquatic Ecosystem Biomonitoring Program must be used in the management of aquatic ecosystems. To achieve this, collected data must, through a systematic framework, be linked to measurable management objectives. This paper demonstrates how the results obtained with biological indices and system-specific knowledge, are combined to derive semi-quantitative assessments of ecosystem condition. These assessments provide the basisfor responding to the results of a river monitoring program. [ABSTRACT FROM AUTHOR]

Biotic integrity assessment of a stream subject to acid mine drainage (AMD) indicated that a number of the expected taxa were absent. Acute and chronic toxicity assessment of water sampled in a stream subject to AMD impact indicate that even at near neutral pH the metal concentration in the water dominates the toxicity toward Daphnia pulex. Extending the observation period to the death of test cohort in an otherwise standard sub-chronic toxicity test, allowed for generating a life table for the D. pulex. The probability of population extinction was estimated from the statistical characteristics of a bootstrap estimation of the dominant eigen value of a Leslie matrix based on the life table. At the current concentration levels of metals, notably manganese and zinc, in the water, a high risk to aquatic life exists. Itis suggested that the metal content of the stream water also be addressed in an AMD water treatment plan. [ABSTRACT FROM AUTHOR]

Radiofrequency vortex spin-transfer oscillators based on magnetic tunnel junctions with very low-resistance area product were investigated. A high power of excitations has been obtained characterized by a power spectral density containing a very sharp peak at the fundamental frequency and a series of harmonics. The observed behavior is ascribed to the combined effect of spin-transfer torque and Oersted-Ampère field generated by the large applied dc current. We furthermore show that the synchronization of a vortex oscillation by applying an ac bias current is mostly efficient when the external frequency is twice the oscillator fundamental frequency. This result is interpreted in terms of a parametric oscillator. [ABSTRACT FROM AUTHOR]

Recent studies in three-dimensional spintronics propose that the Œrsted field plays a significant role in cylindrical nanowires. However, there is no direct report on its impact on magnetic textures. Here, we use time-resolved scanning transmission x-ray microscopy to image the dynamic response of magnetization in cylindrical Co30Ni70 nanowires subjected to nanosecond Œrsted field pulses. We observe the tilting of longitudinally magnetized domains toward the azimuthal Œrsted field direction and create a robust model to reproduce the differential magnetic contrasts and extract the angle of tilt. Furthermore, we report the compression and expansion, or breathing, of a Bloch-point domain wall that occurs when weak pulses with opposite signs are applied. We expect that this work lays the foundation for and provides an incentive to further studying complex and fascinating magnetization dynamics in nanowires, especially the predicted ultra-fast domain wall motion and associated spin wave emissions. [ABSTRACT FROM AUTHOR]

We present a method for fabricating Josephson junctions and superconducting quantum interference devices (SQUIDs) which is based on the local anodization of niobium strip lines 3-6.5 nm thick under the voltage-biased tip of an atomic force microscope. Microbridge junctions and SQUID loops are obtained either by partial or total oxidation of the niobium layer. Two types of weak link geometries are fabricated: lateral constriction (Dayem bridges) and variable thickness bridges. SQUIDs based on both geometries show a modulation of the maximum Josephson current with a magnetic flux periodic with respect to the superconducting flux quantum h/2e. They persist up to 4 K. The modulation shape and depth of SQUIDs based on variable thickness bridges indicate that the weak link size becomes comparable to the superconducting film coherence length ξ which is of the order of 10 nm. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Microwave-assisted switching of the magnetization is an efficient way to reduce the magnetic field required to reverse the magnetization of nanostructures. Here, the phase sensitivity of microwave-assisted switching of an individual cobalt nanoparticle is studied using a pump-probe technique. The pump microwave pulse prepares an initial state of the magnetization, and the probe pulse tests its stability against switching. Precession states are established, which are stable against switching. Their basin of attraction is measured and is in qualitative agreement with numerical macrospin calculations. The damping parameter is evaluated using the variable delay pump-probe technique. [ABSTRACT FROM AUTHOR]

Spintronics materials have recently been considered for radio-frequency devices such as oscillators by exploiting the transfer of spin angular momentum between a spin-polarized electrical current and the magnetic nanostructure it passes through. While previous spin-transfer oscillators (STOs) were based on in-plane magnetized structures, here we present the realization of an STO that contains a perpendicular spin current polarizer combined with an in-plane magnetized free layer. This device is characterized by high-frequency oscillations of the free-layer magnetization, consistent with out-of-plane steady-state precessions induced at the threshold current by a spin-transfer torque from perpendicularly polarized electrons. The results are summarized in static and dynamic current–field state diagrams and will be of importance for the design of STOs with enhanced output signals. [ABSTRACT FROM AUTHOR]

We report here two processes for fabricating quantum devices based on local anodization induced by Atomic Force Microscope (AFM). The first process involves ultra-thin films of doped silicon-on-insulator (SOI) passivated with hydrogen. AFM-drawn oxide lines create a chemical contrast that is used as a mask for silicon wet etch. Etching is performed down to the buried silicon oxide layer, thus leading to silicon nanowires supported on insulator. We show that this process appears well suited to obtain SOI nanostructures and investigate electrical transport though silicon wires with sub-1000 nm2 cross-section. In the second process, diffusion of oxygen species is performed through the whole layer of metallic ultra-thin films, which provides a technique for direct writing of insulating regions. This technique was applied to ultra-thin niobium films for fabricating mesoscopic structures. A superconducting quantum interferometer useful for nanomagnetism is demonstrated. [Copyright &y& Elsevier]

We present a fabrication method of superconducting quantum interference devices (SQUIDs) based on direct write lithography with an atomic force microscope (AFM). This technique involves maskless local anodization of Nb or NbN ultrathin films using the voltage biased tip of the AFM. The SQUIDs are of weak-link type, for which two geometries have been tested: Dayem and variable thickness nanobridges. The magnetic field dependence of the maximum supercurrent Ic(Φ) in resulting SQUIDs is thoroughly measured for different weak link geometries and for both tested materials. It is found that the modulation shape and depth of Ic(Φ) curves are greatly dependent on the weak link size. We analyze the results taking into account the kinetic inductance of nanobridges and using the Likharev–Yakobson model. Finally we show that the present resolution reached by this technique (20 nm) enables us to fabricate Nb weak-links which behavior approaches those of ideal Josephson junctions. [Copyright &y& Elsevier]

Abstract: The dynamic state diagram for spin current-induced magnetization dynamics is presented for an out-of-plane magnetized (perpendicular) polarizer and an in-plane magnetized (planar) free layer as obtained from macrospin simulations. The state boundaries are compared upon using a constant spin polarization factor with an angular-dependent spin polarization factor g(θ MP) as introduced by Slonczewski. While two critical boundaries remain unaffected by the angular dependence of the polarization, the transition from precession to an out-of-plane stable state is drastically shifted and shows a strong asymmetry with respect to the sign of the spin-polarized current. [Copyright &y& Elsevier]

While the usual approach to tailor the behavior of condensed matter and nanosized systems is the choice of material or finite-size or interfacial effects, topology alone may be the key. In the context of the motion of magnetic domain walls (DWs), known to suffer from dynamic instabilities with low mobilities, we report unprecedented velocities >600 m/s for DWs driven by spin-transfer torques in cylindrical nanowires made of a standard ferromagnetic material. The reason is the robust stabilization of a DW type with a specific topology by the Œrsted field associated with the current. This opens the route to the realization of predicted new physics, such as the strong coupling of DWs with spin waves above >600 m/s. [ABSTRACT FROM AUTHOR]

Domain wall propagation in modulated-diameter cylindrical nanowires is a key phenomenon to be studied with a view to designing three-dimensional magnetic memory devices. This paper presents a theoretical study of transverse domain wall behavior under the influence of a magnetic field within a cylindrical nanowire with diameter modulations. In particular, domain wall pinning close to the diameter modulation was quantified, both numerically, using finite element micromagnetic simulations, and analytically. Qualitative analytical model for gently sloping modulations resulted in a simple scaling law which may be useful to guide nanowire design when analyzing experiments. It shows that the domain wall depinning field value is proportional to the modulation slope. [ABSTRACT FROM AUTHOR]