Ferrites have a plethora of applications in the myriad fields of technology. Ferrites are widely used in conventional electronic, electrical, and magnetic devices. For the past two decades, since the ...discovery of the superparamagnetic nature of nanostructured ferrites, their applications in biotechnology and biomedical sciences as well as in advanced electronics and microwave devices have gained immense attention. In this review, the historical development of ferrite science and technology, and the synthesis methods for ferrite nanoparticle preparation and their applications have been discussed. Various synthetic methods with typical examples, their advantages as well as limitations have been discussed in details. Traditional industrial applications of various ferrites have also been discussed citing relevant patents. Recent developments on nanoferrite research in terms of synthetic methods as well as advanced applications have been discussed elaborately.
Context. Extreme solar activity fluctuations and the occurrence of solar grand minima and maxima episodes, such as the Maunder minimum and Medieval maximum are well-established, observed features of ...the solar cycle. Nevertheless, such extreme activity fluctuations and the dynamics of the solar cycle during Maunder minima-like episodes remain ill understood. Aims. We explore the origin of such extreme solar activity fluctuations and the role of dual poloidal field sources, namely the Babcock-Leighton mechanism and the mean-field α effect in the dynamics of the solar cycle. We mainly concentrate on entry and recovery from grand minima episodes such as the Maunder minimum and the dynamics of the solar cycle, including the structure of solar butterfly diagrams during grand minima episodes. Methods. We use a kinematic solar dynamo model with a novel set-up in which stochastic perturbations force two different poloidal sources. We explore different regimes of operation of these poloidal sources with distinct operating thresholds to identify the importance of each. The perturbations are implemented independently in both hemispheres which allows the study of the level of hemispheric coupling and hemispheric asymmetry in the emergence of sunspots. Results. From the simulations performed we identify a few different ways in which the dynamo can enter a grand minima episode. While fluctuations in any of the α effects can trigger intermittency, in keeping with results from a mathematical time-delay model we find that the mean-field α effect is crucial for the recovery of the solar cycle from a grand minima episode, which a Babcock-Leighton source alone fails to achieve. Our simulations also demonstrate many types of hemispheric asymmetries, including grand minima and failed grand minima where only one hemisphere enters a quiescent state. Conclusions. We conclude that stochastic fluctuations in two interacting poloidal field sources working with distinct operating thresholds is a viable candidate for triggering episodes of extreme solar activity and that the mean-field α effect capable of working on weak, sub-equipartition fields is critical to the recovery of the solar cycle following an extended solar minimum. Based on our results, we also postulate that solar activity can exhibit significant parity shifts and hemispheric asymmetry, including phases when only one hemisphere is completely quiescent while the other remains active, to, successful grand minima like conditions in both hemispheres.
Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and ...stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (γ) on the initial structures and the competitive role of room temperature thermal energy (kT) and the change in interfacial energy (Δγ) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small kT-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (i.e. Δγ-energy, apart from the kT-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.
The structural evolution of thiol-capped Au-nanoparticle (AuNP) multilayers on a H-passivated Si substrate, formed through a Langmuir-Schaefer (LS) deposition process, has been investigated using ...complementary grazing incidence X-ray scattering techniques. The fractional coverage multilayers of AuNPs, formed through a multi-transfer process, are found to be quite unstable under ambient conditions. The thickness of these decreases with time and tends to saturate toward a near unique thickness (NUT 6 nm). Although initial low coverage and their instability create hindrance in the control and formation of desired 3D-nanostructures in the bottom-up approach, the formation of a NUT-layer, through time-evolution, is quite distinctive, thus interesting. It is clear from the evolution that the thermodynamically driven monolayer structures (of AuNPs) at the air-water interface become thermodynamically unstable when transferred sequentially onto the solid substrate. The thermal energy (
kT
) and the partial change in the substrate surface energy (Δ
γ
) create the instability and induce diffusion in the AuNPs, which in the presence of a net attractive force towards the substrate (arising from anisotropic interaction of the top AuNPs with the other AuNPs and/or hydrophobic substrate) tries to create a thermodynamically favourable and relatively stable NUT-layer through reorganization for a different duration. This happens if the number of AuNPs is less than or equal to the maximum number that can be accommodated within the NUT. The value of the NUT mainly depends on the particle size and a
kT
-energy related fluctuation of particles. Furthermore, the formation of the NUT-layer indicates that the hydrophobic-hydrophobic interaction mediated net attraction towards the substrate is long range, while the hydrophilic-hydrophobic interaction mediated repulsion and/or
kT
-energy induced fluctuations are short range.
Formation of a near unique thickness layer of nanoparticles due to a long-range hydrophobic-hydrophobic interaction mediated net attraction toward a substrate, and a short-range hydrophilic-hydrophobic interaction mediated repulsion and/or thermal energy induced fluctuation.
Two of the most widely used electronic-structure theory methods, namely, Hartree–Fock and Kohn–Sham density functional theory, require the iterative solution of a set of Schrödinger-like equations. ...The speed of convergence of such a process depends on the complexity of the system under investigation, the self-consistent-field algorithm employed, and the initial guess for the density matrix. An initial density matrix close to the ground-state matrix will effectively allow one to cut out many of the self-consistent steps necessary to achieve convergence. Here, we predict the density matrix of Kohn–Sham density functional theory by constructing a neural network that uses only the atomic positions as information. Such a neural network provides an initial guess for the density matrix far superior to that of any other recipes available. Furthermore, the quality of such a neural-network density matrix is good enough for the evaluation of interatomic forces. This allows us to run accelerated ab initio molecular dynamics with little to no self-consistent steps.
Objective:
This study was designed to establish the reliability of neurologic examination, neuron‐specific enolase (NSE), and median nerve somatosensory‐evoked potentials (SEPs) to predict poor ...outcome in patients treated with mild hypothermia after cardiopulmonary resuscitation (CPR).
Methods:
This multicenter prospective cohort study included adult comatose patients admitted to the intensive care unit (ICU) after CPR and treated with hypothermia (32–34°C). False‐positive rates (FPRs 1 − specificity) with their 95% confidence intervals (CIs) were calculated for pupillary light responses, corneal reflexes, and motor scores 72 hours after CPR; NSE levels at admission, 12 hours after reaching target temperature, and 36 hours and 48 hours after collapse; and SEPs during hypothermia and after rewarming. The primary outcome was poor outcome, defined as death, vegetative state, or severe disability (Glasgow Outcome Scale 1–3) after 6 months.
Results:
Of 391 patients included, 53% had a poor outcome. Absent pupillary light responses (FPR 1; 95% CI, 0–7) or absent corneal reflexes (FPR 4; 95% CI, 1–13) 72 hours after CPR, and absent SEPs during hypothermia (FPR 3; 95% CI, 1–7) and after rewarming (FPR 0; 95% CI, 0–18) were reliable predictors. Motor scores 72 hours after CPR (FPR 10; 95% CI, 6–16) and NSE levels were not.
Interpretation:
In patients with persisting coma after CPR and therapeutic hypothermia, use of motor score or NSE, as recommended in current guidelines, could possibly lead to inappropriate withdrawal of treatment. Poor outcomes can reliably be predicted by testing brainstem reflexes 72 hours after CPR and performing SEP. ANN NEUROL 2012;71:206–212
•Carbon black-ethylene glycol (CB-EG) nanofluids were investigated.•Extinction coefficient increased linearly with CB concentration within 450–820 nm.•An enhancement of overall photo-thermal ...efficiency of 27.43% was obtained.•Local photo-thermal efficiency improves with concentration and depth of fluid.
Direct absorption solar collector (DASC) is a promising method of harvesting solar energy. Present work considers carbon black-ethylene glycol (CB-EG) based nanofluids as the working fluids for DASC applications. Nanofluids were synthesized by the two-step method. Various studies carried out in this work include long time homogeneity, energy absorption characteristic and transient temperature profiles as functions of fluid thickness, light exposure time and concentration of the nanoparticles. Improved absorption characteristics, compared with those of the base fluid, towards incident irradiance were observed in all cases. About 27.90% increment in overall photo-thermal conversion efficiency over that of the ethylene glycol (EG) alone is observed for the case of 15 ppm carbon black (CB) concentration with an exposure time of 1200 s. Measured data show increasing trends in local photo-thermal efficiency with the thickness of the liquid layer as well as with the concentration of the suspended nanoparticles. These studies confirm that CB-EG based nanofluids can be used as potential working fluids for DASCs.
The influence of poor solvent and thermal annealing, and their specific roles, in the crystalline ordering of poly(3-dodecylthiophene) P3DDT films, which are of immense importance in their ...performance as semiconducting materials, were investigated using complementary techniques. Edge-on oriented crystallites (Form-II like) are enhanced in the as-cast films prepared after addition of a poor solvent. However, the coil-to-rod-like conformational transition is more prevalent compared to the crystallites, suggesting that a poor solvent predominantly helps to overcome the unfavorable conformational transition. A very large enhancement in the amount of the crystallites (Form-I-like) is observed for the films annealed above the melting temperature of the alkyl side chains, suggesting thermal annealing essentially helps to promote the diffusion of rod-like chains and to overcome the hindrance of the π–π stacking. Perfectly edge-on oriented crystallites, which are enhanced with increasing annealing temperature, start to deteriorate when the melting temperature of the polymer backbone is reached. The domain-like morphology of the as-cast film, however, remains almost unchanged upon thermal annealing suggesting the spontaneous organization of π-stacked layers through alkyl side chains to form crystallites is essentially within the small domains. The best edge-on oriented crystallites are found for the P3DDT films prepared from a solution containing a large amount of poor solvent and subsequently annealing the film at around 130 °C.
Direct absorption using a nanofluid is an efficient way of harnessing solar energy. Present works aim to investigate hexagonal boron nitride-ethylene glycol (BN-EG) nanofluids and BN mixed with ...carbon black (CB) in EG (BN/CB-EG) hybrid nanofluids for applications in direct absorption solar collectors (DASCs). Nanofluids were prepared by using the two-step method. Stability and homogeneity were inspected photographically after storage of one month. The optical properties of the nanofluids were measured and computed under varying concentration mixing ratios (CMRs). An absorbed energy fraction of 98.92% was obtained in a 2.0 cm height of 90 ppm/15 ppm BN/CB nanofluid. Photo-thermal conversion performances of the nanofluids were investigated using a small in-house built experimental collector. Temperature-rises in the working fluids were measured under varying durations of exposure to a fixed irradiance, fluid height, and CMRs of the nanoparticles. An enhancement of 34.55% photo-thermal conversion efficiency over that of EG alone was obtained in the 90 ppm/15 ppm BN/CB nanofluid after 1200 s exposure to 437 W/m2 incident irradiance. Some basic approaches for designing a DASC in an optimized manner are also discussed. It is concluded that BN/CB-EG hybrid nanofluids can be the prospective working fluids in DASCs.
•Optical and photo-thermal conversion characteristics were experimentally studied•Absorbed energy fraction of 90 ppm BN-EG is 38.75 times of that of EG•Energy storage efficiency increases by 16.23% using 90 ppm BN-EG nanofluid•Using 20 mm 90 ppm/15 ppm BN/CB-EG nanofluid 98.92% energy is absorbed•Energy storage efficiency increases by 34.55% using 90 ppm/15 ppm BN/CB-EG
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