Current-induced noise and damping in non-uniform ferromagnets

In the presence of spatial variation of the magnetization direction, electric current noise causes a fluctuating spin-transfer torque that increases the fluctuations of the ferromagnetic order parameter. By the fluctuation-dissipation theorem, the equilibrium fluctuations are related to the magnetization damping, which in non-uniform ferromagnets acquires a nonlocal tensor structure. In biased ferromagnets, shot noise can become the dominant contribution to the magnetization noise at low temperatures. Considering spin spirals as a simple example, we show that the current-induced noise and damping is significant.Comment: 5 pages, 1 figur

Prey consumption rates and growth of piscivorous brown trout in a subarctic watercourse

This is the peer reviewed version of the following article: Jensen, H., Amundsen, P.-A., Elliott, J.M., Bøhn, T. & Aspholm, P.E. (2006). Prey consumption rates and growth of piscivorous brown trout in a subarctic watercourse. Journal of Fish Biology, 68(3), 838-848, which has been published in final form at https://doi.org/10.1111/j.0022-1112.2006.00972.x. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Prey consumption rates of piscivorous brown trout Salmo trutta were studied in the Pasvik watercourse, which forms the border between Norway and Russia. Estimates of food consumption in the field were similar to or slightly less than maximum values from a bioenergetic model. The piscivore diet consisted mainly of vendace Coregonus albula with a smaller number of whitefish Coregonus lavaretus. Individual brown trout had an estimated mean daily intake of c. 1·5 vendace and 0·4 whitefish, and a rapid annual growth increment of 7–8 cm year−1. The total population of brown trout >25 cm total length was estimated as 8445 individuals (0·6 individuals ha−1), giving a mean ± s.e. annual consumption of 1553880 ± 405360 vendace and 439140 ± 287130 whitefish for the whole watercourse. The rapid growth in summer of brown trout >25 cm indicated a high prey consumption rate

The exceptional influence of storm ‘Xaver’ on design water levels in the German Bight

Design water levels for coastal structures are usually estimated based on extreme value statistics. Since their robustness depends heavily on the sample size of observations, regular statistical updates are needed, especially after extreme events. Here, we demonstrate the exceptional influence of such an event based on storm 'Xaver', which caused record breaking water levels for large parts of the southwestern German North Sea coastline on 6 December 2013. We show that the water level estimates for a 1 in 200 years event increased by up to 40 cm due to the update after 'Xaver', a value twice as large as the estimated regional sea level rise for the entire 20th century. However, a thorough analysis of different independent meteorological (winds and pressure) and oceanographic components (tides, surges, mean sea level (MSL) anomalies) driving the event reveals that their observed combination does not yet represent the physically possible worst case scenario. Neither tides, nor surges nor MSL anomalies were at their observational maximum, suggesting that there is a realistic risk of a storm like 'Xaver' to cause even higher extreme water levels by a few decimetres under current climate conditions. Our results question purely statistical design approaches of coastal structures, which neglect the physical boundary conditions of individual extreme events

Contemporary ocean warming and freshwater conditions contribute to delay the completion of maturation in Atlantic salmon

The completion of maturation in Atlantic salmon (Salmo salar) depends on environmental conditions that affect both feeding opportunities and growth, which would provide sufficient lipid stores for reproduction. However, if the level of energy reserves of a given fish is below a certain genetic threshold at a critical decision time further gonadal development is arrested and fully maturation postponed. This individual development pattern suggests that the proportion of fish maturing at a given sea age could vary from year to year according to the feeding opportunities in the oceanic migratory habitat, and the growth rate during freshwater residence that might be associated with growth at sea. In this study we show that sea age at maturity of adults caught in multiple Norwegian rivers has increased with increasing sea surface temperature (SST) experienced by the fish in autumn months during their first year at sea. Furthermore, freshwater conditions measured by river discharge during summer months one year ahead of seaward migration is positively related with increasing sea age at maturity. This result is discussed within the broad changes occurring in the North-east Atlantic pelagic food web mostly related with the current ocean warming, and river conditions influencing growth rates

Response of a catalytic reaction to periodic variation of the CO pressure: Increased CO_2 production and dynamic phase transition

We present a kinetic Monte Carlo study of the dynamical response of a Ziff-Gulari-Barshad model for CO oxidation with CO desorption to periodic variation of the CO presure. We use a square-wave periodic pressure variation with parameters that can be tuned to enhance the catalytic activity. We produce evidence that, below a critical value of the desorption rate, the driven system undergoes a dynamic phase transition between a CO_2 productive phase and a nonproductive one at a critical value of the period of the pressure oscillation. At the dynamic phase transition the period-averged CO_2 production rate is significantly increased and can be used as a dynamic order parameter. We perform a finite-size scaling analysis that indicates the existence of power-law singularities for the order parameter and its fluctuations, yielding estimated critical exponent ratios $\beta/\nu \approx 0.12$ and $\gamma/\nu \approx 1.77$. These exponent ratios, together with theoretical symmetry arguments and numerical data for the fourth-order cumulant associated with the transition, give reasonable support for the hypothesis that the observed nonequilibrium dynamic phase transition is in the same universality class as the two-dimensional equilibrium Ising model.Comment: 18 pages, 10 figures, accepted in Physical Review

Enhancing the stability of CT radiomics across different volume of interest sizes using parametric feature maps: a phantom study

Background: In radiomics studies, differences in the volume of interest (VOI) are often inevitable and may confound the extracted features. We aimed to correct this confounding effect of VOI variability by applying parametric maps with a fixed voxel size. Methods: Ten scans of a cup filled with sodium chloride solution were scanned using a multislice computed tomography (CT) unit. Sphere-shaped VOIs with different diameters (4, 8, or 16 mm) were drawn centrally into the phantom. A total of 93 features were extracted conventionally from the original images using PyRadiomics. Using a self-designed and pretested software tool, parametric maps for the same 93 features with a fixed voxel size of 4 mm3 were created. To retrieve the feature values from the maps, VOIs were copied from the original images to preserve the position. Differences in feature quantities between the VOI sizes were tested with the Mann-Whitney U-test and agreement with overall concordance correlation coefficients (OCCC). Results: Fifty-five conventionally extracted features were significantly different between the VOI sizes, and none of the features showed excellent agreement in terms of OCCCs. When read from the parametric maps, only 8 features showed significant differences, and 3 features showed an excellent OCCC (≥ 0.85). The OCCCs for 89 features substantially increased using the parametric maps. Conclusions: This phantom study shows that converting CT images into parametric maps resolves the confounding effect of VOI variability and increases feature reproducibility across VOI sizes

Cluster headache attack remission with sphenopalatine ganglion stimulation:experiences in chronic cluster headache patients through 24 months

BACKGROUND: Cluster headache (CH) is a debilitating headache disorder with severe consequences for patient quality of life. On-demand neuromodulation targeting the sphenopalatine ganglion (SPG) is effective in treating the acute pain and a subgroup of patients experience a decreased frequency of CH attacks. METHODS: We monitored self-reported attack frequency, headache disability, and medication intake in 33 patients with medically refractory, chronic CH (CCH) in an open label follow-up study of the original Pathway CH-1 study. Patients were followed for at least 24 months (average 750 ± 34 days, range 699-847) after insertion of an SPG microstimulator. Remission periods (attack-free periods exceeding one month, per the ICHD 3 (beta) definition) occurring during the 24-month study period were characterized. Attack frequency, acute effectiveness, medication usage, and questionnaire data were collected at regular clinic visits. The time point “after remission” was defined as the first visit after the end of the remission period. RESULTS: Thirty percent (10/33) of enrolled patients experienced at least one period of complete attack remission. All remission periods followed the start of SPG stimulation, with the first period beginning 134 ± 86 (range 21-272) days after initiation of stimulation. On average, each patient’s longest remission period lasted 149 ± 97 (range 62-322) days. The ability to treat acute attacks before and after remission was similar (37 % ± 25 % before, 49 % ± 32 % after; p = 0.2188). Post-remission headache disability (HIT-6) was significantly improved versus baseline (67.7 ± 6.0 before, 55.2 ± 11.4 after; p = 0.0118). Six of the 10 remission patients experienced clinical improvements in their preventive medication use. At 24 months post insertion headache disability improvements remained and patient satisfaction measures were positive in 100 % (10/10). CONCLUSIONS: In this population of 33 refractory CCH patients, in addition to providing the ability to treat acute attacks, neuromodulation of the SPG induced periods of remission from cluster attacks in a subset of these. Some patients experiencing remission were also able to reduce or stop their preventive medication and remissions were accompanied by an improvement in headache disability

Micro- and macro-habitat selection of Atlantic salmon, (Salmo salar), post-smolts in relation to marine environmental cues

Atlantic salmon is an economically and culturally important species. The species encounters several natural and man-made threats during its migration between fresh water and the ocean, which in combination may explain its ongoing decline. With the aim to better understand whether post-smolt behaviour is influenced by physical oceanographic conditions, the migratory behaviour of 173 post-smolts in a high-latitude Norwegian fjord was investigated, combining acoustic telemetry with site- and time-specific environmental variables from an oceanographic model. Most post-smolts (94%) performed a unidirectional migration out the fjord. Progression rates were relatively high (0.42–2.41 km h−1; 0.84–3.78 BL s−1) and increased with distance from the river. While post-smolts had an affinity for lower salinities in the inner fjord, statistical models failed to detect any significant relationship between the small-scale (within arrays) migratory behaviour and salinity, temperature, or coastal surface currents within the fjord. In the outer part, the post-smolts predominantly exited the fjord system through the strait with the highest surface salinities and lowest temperatures, independently of the current direction. Our findings indicate that the macro-habitat selection of the Atlantic salmon post-smolts was influenced by environmental factors: the post-smolts directed their migration towards “ocean cues.” However, this was not confirmed on the micro-habitat level.publishedVersio

Predicting the nationwide outmigration timing of Atlantic salmon (Salmo salar) smolts along 12 degrees of latitude in Norway

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