Spin glass like transition in a highly concentrated Fe-C nanoparticle system

A highly concentrated (17 vol.%) Fe-C nano-particle system, with a narrow size distribution $d = 5.4\pm 0.4$ nm, has been investigated using magnetic ac susceptibility measurements covering a wide range of frequencies (17 mHz - 170 Hz). A dynamic scaling analysis gives evidence for a phase transition to a low temperature spin-glass-like phase. The critical exponents associated with the transition are $z\nu = 10.5 \pm 2$ and $\beta = 1.1 \pm 0.2$. The reason why the scaling analysis works for this sample, while it may not work for other samples exhibiting collective behavior as evidenced by aging phenomena, is that the single particle contribution to $\chi''$ is vanishingly small for $T>T_g$ and hence all slow dynamics is due to collective behavior. This criterion can only be fulfilled for a highly concentrated nano-particle sample with a narrow size distribution.Comment: 2 pages, 3 figures, Proceeding for ICM200

Equation of State for Parallel Rigid Spherocylinders

The pair distribution function of monodisperse rigid spherocylinders is calculated by Shinomoto's method, which was originally proposed for hard spheres. The equation of state is derived by two different routes: Shinomoto's original route, in which a hard wall is introduced to estimate the pressure exerted on it, and the virial route. The pressure from Shinomoto's original route is valid only when the length-to-width ratio is less than or equal to 0.25 (i.e., when the spherocylinders are nearly spherical). The virial equation of state is shown to agree very well with the results of numerical simulations of spherocylinders with length-to-width ratio greater than or equal to 2

Phosphorus status of calcareous and sodic soils treated with cheese whey

Acid cheese whey, made using phosphoric acid, contains up to 1200 mg total P kg-1 whey, and cultured cheese or sweet wheys contain up to 500 mg total P kg-1 whey. Much of the 32 x 106 m3 of whey produced in the United States each year is applied to soil. Whey P mobility has not been documented for calcareous or sodic soils. This study was conducted to determine the ratio between ortho- and the more soluble organic P forms in freshly produced cheese whey, and to determine ortho- and organic P concentrations by depth within calcareous and sodic soils within one to two years of different whey rates and time of the year applications. Applications of up to 1050 kg P ha-1 in acid whey were applied to a sodic soil (in green house lysimeters) and up to 750 kg P ha-1 in sweet whey were applied to calcareous soils (field plots). Bicarbonate-extractable ortho-P did not move below 0.3 m in the sodic Freedom silt loam (fine-silty, mixed, mesic, Xerollic Calciorthid) soil by the end of one growing season. Neither bicarbonate-extractable nor saturation extract ortho- or organic P moved below 0.6 m in the calcareous Portneuf silt loam (coarse-silty, mixed, mesic, Durixerollic Calciorthid) soil after three growing seasons or below 0.3 m in the calcareous Nibley silty clay loam (fine, mixed, mesic Aquic Argiustolls) soil after two growing seasons. Even though the wheys contained up to 42% organic P, these soils retained the applied ortho- and organic P against leaching. The winter-applied whey-P did not move deeper into the soil than that applied during the growing season

Extractable Potassium and Soluble Calcium, Magnesium, Sodium, and Potassium in Two-Whey-Treated Calcareous Soils

Cheese whey contains 1.0 to 1.4 g K kg-1 and 5.0 to 10.0 g total salts kg-1 (electrical conductivity [EC] of 7 to 15 dS m-1) and has a pH of 3.3 to 4.6. Much of the 38 x 10^9 L of whey produced in the USA each year is applied to soils. Whey application effect on the K and salinity status of irrigated calcareous soils has not been documented. Objectives of this study were to measure soil pH, sodium adsorption ratio (SAR), saturation paste extract (EC,), and extractable Ca, Mg, Na, and K changes due to whey application to irrigated calcareous soils at different whey rates and different times of the year. Whey was applied to two calcareous Portneuf silt loam (coarse-silty, mixed, mesic, Durixerollic Calciorthids) soils and a calcareous Nibley silty clay loam (fine, mixes, mesic Aquic Argiustolls) soil at rates up to 2200 m3 ha-1 These treatments added up to 1050 kg Ca, 200 kg Mg, 790 kg Na, and 2200 kg K ha-1 during winter-time, growing season, or year-round whey application. Soil bicarbonate-extractable K increased to more than 500 mg K kg-1 in the surface 0.3 m at the highest whey rates and may induce grass tetany in livestock grazed on high whey-treated pastures. Soil K did not increase below 0.6 m in any treatment. Soil pH and SAR were not affected sufficiently to be of concern under these conditions. The EC, increased to nearly 2.0 dS m-1 in the surface 0.3 m under the highest whey rates and would likely affect salt-sensitive crop yields. After a 1-yr whey application rest period under irrigated alfalfa (Medicago saliva L.), the EC, levels returned to background levels

BIMP: A real-time biological model of multi-scale keypoint detection in V1

We present an improved, biologically inspired and multiscale keypoint operator. Models of single- and double-stopped hypercomplex cells in area V1 of the mammalian visual cortex are used to detect stable points of high complexity at multiple scales. Keypoints represent line and edge crossings, junctions and terminations at fine scales, and blobs at coarse scales. They are detected by applying first and second derivatives to responses of complex cells in combination with two inhibition schemes to suppress responses along lines and edges. A number of optimisations make our new algorithm much faster than previous biologically inspired models, achieving real-time performance on modern GPUs and competitive speeds on CPUs. In this paper we show that the keypoints exhibit state-of-the-art repeatability in standardised benchmarks, often yielding best-in-class performance. This makes them interesting both in biological models and as a useful detector in practice. We also show that keypoints can be used as a data selection step, significantly reducing the complexity in state-of-the-art object categorisation. (C) 2014 Elsevier B.V. All rights reserved

Anisotropic Superparamagnetism of Monodispersive Cobalt-Platinum Nanocrystals

Based on the high-temperature organometallic route (Sun et al. Science 287, 1989 (2000)), we have synthesized powders containing CoPt_3 single crystals with mean diameters of 3.3(2) nm and 6.0(2) nm and small log-normal widths sigma=0.15(1). In the entire temperature range from 5 K to 400 K, the zero-field cooled susceptibility chi(T) displays significant deviations from ideal superparamagnetism. Approaching the Curie temperature of 450(10) K, the deviations arise from the (mean-field) type reduction of the ferromagnetic moments, while below the blocking temperature T_b, chi(T) is suppressed by the presence of energy barriers, the distributions of which scale with the particle volumes obtained from transmission electron microscopy (TEM). This indication for volume anisotropy is supported by scaling analyses of the shape of the magnetic absorption chi''(T,omega) which reveal distribution functions for the barriers being also consistent with the volume distributions observed by TEM. Above 200 K, the magnetization isotherms M(H,T) display Langevin behavior providing 2.5(1) mu_B per CoPt_3 in agreement with reports on bulk and thin film CoPt_3. The non-Langevin shape of the magnetization curves at lower temperatures is for the first time interpreted as anisotropic superparamagnetism by taking into account an anisotropy energy of the nanoparticles E_A(T). Using the magnitude and temperature variation of E_A(T), the mean energy barriers and 'unphysical' small switching times of the particles obtained from the analyses of chi''(T,omega) are explained. Below T_b hysteresis loops appear and are quantitatively described by a blocking model, which also ignores particle interactions, but takes the size distributions from TEM and the conventional field dependence of E_A into account.Comment: 12 pages with 10 figures and 1 table. Version accepted for publication in Phys. Rev. B . Two-column layou

Scaling behavior of the dipole coupling energy in two-dimensional disordered magnetic nanostructures

Numerical calculations of the average dipole-coupling energy $\bar E_\mathrm{dip}$ in two-dimensional disordered magnetic nanostructures are performed as function of the particle coverage $C$. We observe that $\bar E_\mathrm{dip}$ scales as $\bar E_\mathrm{dip}\propto C^{\alpha^*}$ with an unusually small exponent $\alpha^*\simeq 0.8$--1.0 for coverages $C\lesssim20$. This behavior is shown to be primarly given by the contributions of particle pairs at short distances, which is intrinsically related to the presence of an appreciable degree of disorder. The value of $\alpha^*$ is found to be sensitive to the magnetic arrangement within the nanostructure and to the degree of disorder. For large coverages $C\gtrsim20$ we obtain $\bar E_\mathrm{dip}\propto C^\alpha$ with $\alpha=3/2$, in agreement with the straighforward scaling of the dipole coupling as in a periodic particle setup. Taking into account the effect of single-particle anisotropies, we show that the scaling exponent can be used as a criterion to distinguish between weakly interacting ($\alpha^* \simeq 1.0$) and strongly interacting ($\alpha^* \simeq 0.8$) particle ensembles as function of coverage.Comment: accepted for publication in Phys.Rev.