Characterization of glycidyl methacrylate based magnetic nanocomposites

Magnetic and non-magnetic macroporous crosslinked copolymers of glycidyl methacrylate and trimethylolpropane trimethacrylate were prepared by suspension copolymerization and functionalized with diethylenetriamine. The samples were characterized by mercury porosimetry, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy analysis (FTIR-ATR), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and SQUID magnetometry. The FTIR-ATR analysis of synthesized magnetic nanocomposites confirmed the presence of magnetite and successful aminofunctionalization. Non-functionalized and amino-functionalized nanocomposites exhibited superparamagnetic behavior at 300 K, with a saturation magnetization of 5.0 emu/g and 2.9 emu/g, respectively. TEM analysis of the magnetic nanocomposite has shown that magnetic nanoparticles were homogeneously dispersed in the polymer matrix. It was demonstrated that incorporation of magnetic nanoparticles enhanced the thermal stability of the magnetic nanocomposite in comparison to the initial non-magnetic macroporous copolymer

Nonuniversal scaling behavior of Barkhausen noise

We simulate Barkhausen avalanches on fractal clusters in a two-dimensional diluted Ising ferromagnet with an effective Gaussian random field. We vary the concentration of defect sites $c$ and find a scaling region for moderate disorder, where the distribution of avalanche sizes has the form $D(s,c,L) = s^{-(1+\tau (c))}{\cal{D}}(sL^{-D_s(c)})$. The exponents $\tau (c)$ for size and $\alpha (c)$ for length distribution, and the fractal dimension of avalanches $D_s(c)$ satisfy the scaling relation $D_s(c)\tau (c) =\alpha (c)$. For fixed disorder the exponents vary with driving rate in agreement with experiments on amorphous Si-Fe alloys.Comment: 5 pages, Latex, 4 PostScript figures include

How self-organized criticality works: A unified mean-field picture

We present a unified mean-field theory, based on the single site approximation to the master-equation, for stochastic self-organized critical models. In particular, we analyze in detail the properties of sandpile and forest-fire (FF) models. In analogy with other non-equilibrium critical phenomena, we identify the order parameter with the density of ``active'' sites and the control parameters with the driving rates. Depending on the values of the control parameters, the system is shown to reach a subcritical (absorbing) or super-critical (active) stationary state. Criticality is analyzed in terms of the singularities of the zero-field susceptibility. In the limit of vanishing control parameters, the stationary state displays scaling characteristic of self-organized criticality (SOC). We show that this limit corresponds to the breakdown of space-time locality in the dynamical rules of the models. We define a complete set of critical exponents, describing the scaling of order parameter, response functions, susceptibility and correlation length in the subcritical and supercritical states. In the subcritical state, the response of the system to small perturbations takes place in avalanches. We analyze their scaling behavior in relation with branching processes. In sandpile models because of conservation laws, a critical exponents subset displays mean-field values ($\nu=1/2$ and $\gamma = 1$) in any dimensions. We treat bulk and boundary dissipation and introduce a new critical exponent relating dissipation and finite size effects. We present numerical simulations that confirm our results. In the case of the forest-fire model, our approach can distinguish between different regimes (SOC-FF and deterministic FF) studied in the literature and determine the full spectrum of critical exponents.Comment: 21 RevTex pages, 3 figures, submitted to Phys. Rev.

Bench-to-bedside review : targeting antioxidants to mitochondria in sepsis

Peer reviewedPublisher PD

Barkhausen avalanches in anisotropic ferromagnets with 180∘180^\circ domain walls

We show that Barkhausen noise in two-dimensional disordered ferromagnets with extended domain walls is characterized by the avalanche size exponent $\tau_s =1.54$ at low disorder. With increasing disorder the characteristic domain size is reduced relative to the system size due to nucleation of new domains and a dynamic phase transition occurs to the scaling behavior with $\tau_s=1.30$. The exponents decrease at finite driving rate. The results agree with recently observed behavior in amorphous Metglas and Fe-Co-B ribbons when the applied anisotropic stress is varied.Comment: Changes in the text and references, To appear in Phys. Rev.

Demagnetization via Nucleation of the Nonequilibrium Metastable Phase in a Model of Disorder

We study both analytically and numerically metastability and nucleation in a two-dimensional nonequilibrium Ising ferromagnet. Canonical equilibrium is dynamically impeded by a weak random perturbation which models homogeneous disorder of undetermined source. We present a simple theoretical description, in perfect agreement with Monte Carlo simulations, assuming that the decay of the nonequilibrium metastable state is due, as in equilibrium, to the competition between the surface and the bulk. This suggests one to accept a nonequilibrium "free-energy" at a mesoscopic/cluster level, and it ensues a nonequilibrium "surface tension" with some peculiar low-T behavior. We illustrate the occurrence of intriguing nonequilibrium phenomena, including: (i) Noise-enhanced stabilization of nonequilibrium metastable states; (ii) reentrance of the limit of metastability under strong nonequilibrium conditions; and (iii) resonant propagation of domain walls. The cooperative behavior of our system may also be understood in terms of a Langevin equation with additive and multiplicative noises. We also studied metastability in the case of open boundaries as it may correspond to a magnetic nanoparticle. We then observe burst-like relaxation at low T, triggered by the additional surface randomness, with scale-free avalanches which closely resemble the type of relaxation reported for many complex systems. We show that this results from the superposition of many demagnetization events, each with a well- defined scale which is determined by the curvature of the domain wall at which it originates. This is an example of (apparent) scale invariance in a nonequilibrium setting which is not to be associated with any familiar kind of criticality.Comment: 26 pages, 22 figure

Causal Network Accounts Of Ill-being: Depression & Digital Well-being

Depression is a common and devastating instance of ill-being which deserves an account. Moreover, the ill-being of depression is impacted by digital technology: some uses of digital technology increase such ill-being while other uses of digital technology increase well-being. So a good account of ill-being would explicate the antecedents of depressive symptoms and their relief, digitally and otherwise. This paper borrows a causal network account of well-being and applies it to ill-being, particularly depression. Causal networks are found to provide a principled, coherent, intuitively plausible, and empirically adequate account of cases of depression in every-day and digital contexts. Causal network accounts of ill-being also offer philosophical, scientific, and practical utility. Insofar as other accounts of ill-being cannot offer these advantages, we should prefer causal network accounts of ill-being

A PC-based radiation monitor

A low-cost high-precision system for monitoring the radioactivity level has been developed on the basis of a personal computer using the modern concept of virtual instrumentation. The proposed device has certain advantages over conventional systems: user-defined functions, open system architecture, multitask operation support, simple data sharing between different applications, convenient graphical users interface, easy network connection, full control of the system operation, complete and perfect presentation of the results of measurements, and reasonable price

Stochastyczny model dla określenia elementów cyklu produkcyjnego. Rozważania na podstawie serbskiego przemysłu tekstylnego

The paper presents an original method of determining the elements of the production cycle time by using the modified work sampling method applied to a textile factory. It is shown that the movement of the elements of time can be viewed as a process and in the mathematical sense can establish control limits of error of ± 3 SD. The mean time of the production cycle of the groups created by the number of pieces in the series – tpcu moving the hyperbolic function, which has the asymptote c, a function of the form tpcu = c + b/log n, where all groups of the production cycle in the mathematical sense do not act like strata but are function tpcu related to technology and deterministic factors of the production series.Artykuł przedstawia oryginalną metodę określania elementów trwania cyklu produkcyjnego przy zastosowaniu zmodyfikowanej metody podziału pracy w odniesieniu do przedsiębiorstwa produkującego tekstylia. Pokazano, że przemieszczanie elementów czasu cyklu produkcyjnego można rozpatrywać jako proces, w którym matematycznie ustawia się błąd ± 3s. Średni czas cyklu produkcyjnego poszczególnych grup określa się przez liczbę elementów uszeregowanych w serię. Poszczególne zależności systemu można opisać matematycznie