Mössbauer spectroscopy in modern permanent magnet alloys

Intermetallic compounds involving the rare earths and a transition metal, especially iron, aroused great interest in the past twenty five years with particular attention been paid to their magnetic properties, due to the fact that these compounds have been used as a permanent magnet materials. Their study using different techniques has given new information about the mechanisms of the magnetic interactions, which are present in these compounds. Among them Mössbauer Spectroscopy (MS) has been proven to be an indispensable tool, due to the fact that information can be obtained either from the spectra of the iron sublattice or from the spectra of the rare earth sublattice. Thus information on local moments, crystal field effects, single ion anisotropy and exchange interactions can be extracted from such spectra and compared with results from other techniques. Among the best alloys for permanent magnet applications are the ones based on the Nd₂Fe₁₄B type structure. Very interesting magnetic properties are also present in the recently discovered series of RFe_12?x M _x , where M=V, Ti, Mo, Si. We will review their intrinsic and extrinsic magnetic properties, as they have been measured using (MS) and correlate them with the findings from other techniques.     

Spintronic with semiconductors

Soon afterwards the discovery of the giant magnetoresistance in metallic multilayers, researchers have attempted to integrate spintronic properties with semiconductor materials. They came up against several difficulties related to the structural and electronic properties of the ferromagnetic metal-semiconductor interface. We will report on the recent progress made in this field of spintronic with semiconductors. First of all we will explain the interfacial resistance conditions required to inject and detect efficient spin current in a semiconductor and in a second part we will show that efficient spin injection experiments have been now achieved thanks to the addition of a tunnel resistance at the interface. We will then report on the magnetoresistance experiment performed with diluted magnetic semiconductors as ferromagnetic material. This type of material can constitute an alternative road to achieving electrical control spintronic devices. Finally, we will finish by reporting on research for a highly spin-polarized source to inject spin-polarized current in a semiconductor. It will be mainly focused on tunnel magnetoresistance junctions with semiconductor barriers and hot electron transistor. To cite this article: J.-M. George et al., C. R. Physique 6 (2005).     

From space-time chaos to stochastic thermodynamics

We summarize the results of several experiments that show the evolution of some scientific interests and goals of the statistical and nonlinear physics community in the last 40 years. Specifically, we present how the ideas of extending concepts of equilibrium statistical physics to out-of-equilibrium physics have been developed to characterize various phenomena such as, for example, transition to space-time chaos and glass aging. We then discuss the applications of this out-of-equilibrium thermodynamics to microsystems driven out of equilibrium either by external forces or by temperature gradients. We show that in these systems thermal fluctuations play a role and that all thermodynamics quantities, such as work, heat, and entropy fluctuate. We recall general concepts such as fluctuation theorems and fluctuation dissipation relations used to characterize the statistical properties of these small systems. We describe experiments where all these concepts have been applied and tested with high accuracy. Finally, we show how these theoretical concepts and the experiments allowed us to improve our knowledge on the connection between information and thermodynamics.     

Critical phenomena studied via nuclear techniques

Since pioneering NMR studies of magnetic critical phenomena in MnF₂ by Heller, a range of hyperfine techniques, particularly Mössbauer effect and perturbed angular correlations, have been successfully applied to the problem. When optimally designed, these methods provide experimental approaches that are in some ways more successful than magnetic neutron scattering. Although the number of hyperfine results now number in the hundreds, only a few are sufficiently asymptotic to provide clearcut tests of theory. In this paper we outline the theoretical framework used to describe the modern theory of critical phenomena, discuss the strengths and weakness of various experimental methods, and provide a selection of the best experiments that test the theory. Whereas we emphasize hyperfine interaction studies, we also describe the principles and results of other methods where appropriate. Particular topics include: (1) static critical phenomena in chemically ordered systems studied as a function ofn andd, the spin and lattice dimensionality; (2) static critical phenomena in magnetically disordered systems studied as a function of the type of disorder; and (3) dynamic critical phenomena in chemically ordered systems.     

Manipulation with sound and vibration: A review on the micromanipulation system based on sub-MHz acoustic waves

Manipulation of micro-objects have been playing an essential role in biochemical analysis or clinical diagnostics. Among the diverse technologies for micromanipulation, acoustic methods show the advantages of good biocompatibility, wide tunability, a label-free and contactless manner. Thus, acoustic micromanipulations have been widely exploited in micro-analysis systems. In this article, we reviewed the acoustic micromanipulation systems that were actuated by sub-MHz acoustic waves. In contrast to the high-frequency range, the acoustic microsystems operating at sub-MHz acoustic frequency are more accessible, whose acoustic sources are at low cost and even available from daily acoustic devices (e.g. buzzers, speakers, piezoelectric plates). The broad availability, with the addition of the advantages of acoustic micromanipulation, make sub-MHz microsystems promising for a variety of biomedical applications. Here, we review recent progresses in sub-MHz acoustic micromanipulation technologies, focusing on their applications in biomedical fields. These technologies are based on the basic acoustic phenomenon, such as cavitation, acoustic radiation force, and acoustic streaming. And categorized by their applications, we introduce these systems for mixing, pumping and droplet generation, separation and enrichment, patterning, rotation, propulsion and actuation. The diverse applications of these systems hold great promise for a wide range of enhancements in biomedicines and attract increasing interest for further investigation.     

Joint reconstruction of multiecho MR images using correlated sparsity

This works addresses the problem of reconstructing multiple T1- or T2-weighted images of the same anatomical cross section from partially sampled K-space data. Previous studies in reconstructing magnetic resonance (MR) images from partial samples of the K-space used compressed sensing (CS) techniques to exploit the spatial correlation of the images (leading to sparsity in wavelet domain). Such techniques can be employed to reconstruct the individual T1- or T2-weighted images. However, in the current context, the different images are not really independent; they are images of the same cross section and, hence, are highly correlated. We exploit the correlation between the images, along with the spatial correlation within the images to achieve better reconstruction results than exploiting spatial correlation only.For individual MR images, CS-based techniques lead to a sparsity-promoting optimization problem in the wavelet domain. In this article, we show that the same framework can be extended to incorporate correlation between images leading to group/row sparsity-promoting optimization. Algorithms for solving such optimization problems have already been developed in the CS literature. We show that significant improvement in reconstruction accuracy can be achieved by considering the correlation between different T1- and T2-weighted images. If the reconstruction accuracy is considered to be constant, our proposed group sparse formulation can yield the same result with 33% less K-space samples compared with simple sparsity-promoting reconstruction. Moreover, the reconstruction time by our proposed method is about two to four times less than the previous method.     

Magnetomechanical coupling in Dy0.73Tb0.27Fe2 alloys

Dynamic and static measurements of the magnetomechanical coupling coefficient, k₃₃, have been performed on as cast random polycrystalline terfenol. The values obtained from the two techniques are consistent (k₃₃ ≈ 0.33) but are small in comparison with previously published values from similar material. Although a significant improvement could be achieved by employing refined preparation techniques to produce grain oriented material, the magnetic properties of the present material have been investigated to explore the reasons for low coupling. Data for the relative differential permeability at constant stress, μ^σ, and magnetostrictive strain coefficient, d₃₃, show that the coupling is spoiled by a low maximum permeability and an exceedingly small value for d₃₃. The difficulties in making measurements on samples which give information on material quality alone, regardless of the experimental conditions, are discussed.     

MBE and MOCVD growth and properties of self-assembling quantum dot arrays in III-V semiconductor structures

In this paper, we review our latest developments on the growth and properties of self-assembling quantum dot structures. The self-assembling growth technique which was initially developed using molecular beam epitaxy (MBE), has now been extended to metalorganic chemical vapor deposition (MOCVD). The paper first presents structural results based on atomic force and transmission electron microscopy studies of the quantum dot arrays which were obtained by MBE and MOCVD growth. From the detailed structural analysis we have observed that the formation of coherently strained dots of InAs, InAlAs, and InP dots on various cladding layer surfaces. MBE growth of InAs self-assembled dots has achieved the smallest size distribution, with dots as small as 12nm in diameter. For the MOCVD growth of InP dots we have found that the surface morphology and growth temperature of lower cladding layer growth has a profound influence on island size and density. Recent results on the optical and transport properties of the MBE grown self-assembling dot (SAD) arrays are also presented.     

Ultrastructural changes and programmed cell death of trophocytes in the gonad of Isohypsibius granulifer granulifer Thulin, 1928 (Tardigrada,Eutardigrada, Isohypsibiidae)

The studies on the fates of the trophocytes, the apoptosis and autophagy in the gonad of Isohypsibius granulifer granulifer have been described using transmission electron microscope, light and fluorescent microscopes. The results presented here are the first that are connected with the cell death of nurse cells in the gonad of tardigrades. However, here we complete the results presented by Węglarska (1987).The reproductive system of I. g. granulifer contains a single sack-like hermaphroditic gonad and a single gonoduct. The gonad is composed of three parts: a germarium filled with proliferating germ cells (oogonia); a vitellarium that has clusters of female germ cells (the region of oocytes development); and a male part filled with male germ cells in which the sperm cells develop. The trophocytes (nurse cells) show distinct alterations during all of the stages of oogenesis: previtello-, vitello- and choriogenesis. During previtellogenesis the female germ cells situated in the vitellarium are connected by cytoplasmic bridges, and form clusters of cells. No ultrastructural differences appear among the germ cells in a cluster during this stage of oogenesis. In early vitellogenesis, the cells in each cluster start to grow and numerous organelles gradually accumulate in their cytoplasm. However, at the beginning of the middle of vitellogenesis, one cell in each cluster starts to grow in order to differentiate into oocyte, while the remaining cells are trophocytes. Eventually, the cytoplasmic bridges between the oocyte and trophocytes disappear. Autophagosomes also appear in the cytoplasm of nurse cells together with many degenerating organelles. The cytoplasm starts to shrink, which causes the degeneration of the cytoplasmic bridges between trophocytes. Apoptosis begins when the cytoplasm of these cells is full of autophagosomes/autolysosomes and causes their death.     

Biomolecular dynamics and binding studies in the living cell

Isolation and preparation of proteins of higher organisms often is a tedious task. In the case of success, the properties of these proteins and their interactions with other proteins can be studied in vitro. If however, these proteins are modified in the cell in order to gain or change function, this is non-trivial to correctly realise in vitro. When, furthermore, the cellular function requires the interplay of more than one or two proteins, in vitro experiments for the analysis of this situation soon become complex. Instead, we thus try to obtain information on the molecular properties of proteins in the living cell. Then, the cell takes care of correct protein folding and modification. A series of molecular techniques are, and new ones become, available which allow for measuring molecular protein properties in the living cell, offering information on concentration (FCS), dynamics (FCS, RICS, FRAP), location (PALM, STED), interactions (F3H, FCCS) and protein proximities (FRET, BRET, FLIM, BiFC). Here, these techniques are presented with their advantages and drawbacks, with examples from our current kinetochore research. The review is supposed to give orientation to researchers planning to enter the field, and inform which techniques help us to gain molecular information on a multi-protein complex. We show that the field of cellular imaging is in a phase of transition: in the future, an increasing amount of physico-chemical data can be determined in the living cell.     

The effect of time delay on Approximate & Sample Entropy calculations

Approximate and Sample Entropy are two widely used techniques to measure system complexity or regularity based on chosen parameters such as pattern length, m, and tolerance, r. In this paper, we investigate how different values of the time delay parameter, τ can be used in conjunction with standard values of m and r in the computation of Approximate and Sample Entropy. The results show that for time series generated by nonlinear dynamics that have long range correlation, a time delay equal to the first zero crossing or minimum of the autocorrelation function can provide additional information into the characteristics of the time series that may be useful in comparative analysis. With a unity delay, we demonstrate that Approximate and Sample Entropy are possibly measuring only the (linear) autocorrelation properties of the signal, and these are highly invariant under surrogate data generation methods. Hence when this occurs, the complexity measures of the surrogate and original data are not statistically different.     

Nanometric confinement: Toward new physical properties and technological developments

In numerous real life situations, molecular systems are not found in bulk but instead trapped in limited volumes of nanometric size: this is nanometric confinement. The complex interplay of the confinement topology, dimensionality (3D to 1D) and surface/volume ratio significantly affects the physical properties of the confined material. After decades of intense fundamental research, we are now entering a time when the unusual properties of fluids under confinement may be tuned to target specific technological objectives. In this paper, we highlight few situations, all related to the fields of energy production or storage, where diverse neutron scattering techniques (imaging, small angle scattering, diffraction, inelastic and quasi-elastic scattering) may help to bridge basic science and applied research.     

Terahertz spectroscopy of quantum phase transitions and the temperature-frequency scaling

In the last few decades, significant progress has been achieved in the development of generators and detectors of terahertz radiation (at frequencies in the range from ≈300 GHz to ≈3 THz). Different terahertz spectroscopic techniques have been widely used now in investigating semiconductors, superconductors, molecular magnets, multiferroics, metamaterials, and other promising objects. It has been demonstrated that terahertz spectroscopy offers wide but not completely realized possibilities for studying quantum phase transitions in electron-correlated systems.     

Power-law behavior in complex organizational communication networks during crisis

Communication networks can be described as patterns of contacts which are created due to the flow of messages and information shared among participating actors. Contemporary organizations are now commonly viewed as dynamic systems of adaptation and evolution containing several parts, which interact with one another both in internal and in external environment. Although there is limited consensus among researchers on the precise definition of organizational crisis, there is evidence of shared meaning: crisis produces individual crisis, crisis can be associated with positive or negative conditions, crises can be situations having been precipitated quickly or suddenly or situations that have developed over time and are predictable etc. In this research, we study the power-law behavior of an organizational email communication network during crisis from complexity perspective. Power law simply describes that, the probability that a randomly selected node has k links (i.e. degree k) follows P(k)∼k^−γ, where γ is the degree exponent. We used social network analysis tools and techniques to analyze the email communication dataset. We tested two propositions: (1) as organization goes through crisis, a few actors, who are prominent or more active, will become central, and (2) the daily communication network as well as the actors in the communication network exhibit power-law behavior. Our preliminary results support these two propositions. The outcome of this study may provide significant advancement in exploring organizational communication network behavior during crisis.     

Solution of the reduced occupation-number equation for a fermion system

Using the thin target — thin catchers techniques, masses, mean recoil energies and angular distributions of target residues have been measured for 86 MeV/nucleon¹²C induced reactions. Several different nuclear reaction processes, from peripheral to central collisions have been observed. Experimental results are partly reproduced by intranuclear cascade+evaporation calculations. Up to now, the production of the lightest masses (44<A<71) recoiling with high kinetic energies is not correctly understood by theoretical models. More exclusive experiments are needful to check if the formation of a highly excited quasi-compound nucleus could be a possible explanation of the phenomena.     

Spatial coherence properties of azimuthally polarized laser modes

Understanding of coherence properties of optical fields is of basic importance both in classical optics and in quantum physics. Coherence properties of electromagnetic laser modes are only now beginning to be explored and have not yet been tested experimentally, except in the simplest cases. In this paper, we first study theoretically the coherence properties of azimuthally polarized laser modes and we clarify the distinction between coherence and correlations in stochastic electromagnetic fields, a distinction which has up to now not been fully understood and has, in fact, been a subject of controversy. Our analysis clearly illustrates the distinction between these two concepts. After elucidating theoretically the coherence properties of radially polarized laser modes, we describe an experimental study of their properties, made by the use of a recently introduced reversed-wavefront Young’s interferometer. A good agreement between theory and experiment has been found.     

Physical implications of Fisher-information’s scaling symmetry

We study the scaling properties of Fisher’s information measure (FIM) and show that from these one can straightforwardly deduce significant quantum-mechanical results. Specifically, we investigate the scaling properties of Fisher’s measure I and encounter that, from the concomitant operating rules, several interesting, albeit known, results can be derived. This entails that such results can be regarded as pre-configured by the conjunction of scaling and information theory. The central notion to be arrived at is that scaling entails that I must obey a certain partial differential equation (PDE). These PDE-solutions have properties that enable the application of a Legendre-transform (LT). The conjunction PDE+LT leads one to obtain several quantum results without recourse to the Schrödinger’s equation.     

Ferromagnetic Half-Semiconductor (HSC) gaps in co-doped CdS: Ab-initio study

In this work we have used the density functional theory (DFT) to study structural, magnetic and electronic properties of Co doped CdS in the zinc-blende (ZB) phase. Three approximations have been used to treat the exchange-correlation potential: the (PBE) GGA, (PBE) GGA+U and the model of Tran–Blaha modified Becke–Johnson potential (TB-mBJ). The on–site Coulomb interaction correction given by the Hubbard U has been calculated by the local density approximation constraint for the Co electronic orbitals. The theoretical results show that all the properties under study are affected by the doping of Co atom. Co doped CdS becomes a Ferromagnetic Half-Semiconductors (HSC). The total magnetic moment increases with increasing Co concentration; reaching the value of 9 (in the units of Bohr magneton) at high concentration (x = 18.75 %). The total magnetic moment value is an integer in the GGA+U and TB-mBJ approximations. Furthermore, to validate the effects resulting from the exchange splitting process, we have calculated the values of the spin-exchange constants N_0α and N_0β, respectively. All these changes make CdS:Co extremely interesting system for the spintronic applications.     

Use of hydrodynamic cavitation in (waste)water treatment

The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed.In the first part of this paper a general overview of techniques that employ hydrodynamic cavitation for cleaning of water and wastewater is presented.In the second part of the paper the focus is on our own most recent work using hydrodynamic cavitation for removal of pharmaceuticals (clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac, carbamazepine), toxic cyanobacteria (Microcystis aeruginosa), green microalgae (Chlorella vulgaris), bacteria (Legionella pneumophila) and viruses (Rotavirus) from water and wastewater.As will be shown, hydrodynamic cavitation, like acoustic, can manifest itself in many different forms each having its own distinctive properties and mechanisms. This was until now neglected, which eventually led to poor performance of the technique. We will show that a different type of hydrodynamic cavitation (different removal mechanism) is required for successful removal of different pollutants.The path to use hydrodynamic cavitation as a routine water cleaning method is still long, but recent results have already shown great potential for optimisation, which could lead to a low energy tool for water and wastewater cleaning.     

Percy W. Bridgman's second century

Percy Williams Bridgman's impact on science began in 1909 with his first three experimental papers. These publications on high pressure calibration, techniques, and compressibility, together with the many articles that followed, established his influence on the course of modern high pressure research. Grounded in classical thermodynamics and practical mechanics, his developments showed how the variable of pressure leads to myriad transformations in materials. Studies carried out under a broader range of conditions now provide unprecedented insights into chemical and physical properties at multimegabar pressures and temperatures from millikelvins to thousands of degrees, where novel electronic, magnetic, and superconducting phases are now being discovered. With careful attention to experimental techniques and material performance, Bridgman extended the available pressure range that could be achieved in the laboratory with the development of new devices. We are now witness to continued refinement of static and dynamic compression methods and in situ measurement techniques, including the marriage of high pressure methods with large facilities such as synchrotron, neutron, and laser sources. Bridgman showed the broad range of implications of this work; the modern field of high pressure research now spans physics and chemistry, geosciences and planetary science, materials science and technology, and biology. Selected examples illustrate Bridgman's impact and legacy in this, his second century. For dense hydrogen, new insights have been obtained from high P–T measurements as well as studies of alloys and compounds of hydrogen, leading to the creation of new metallic and superconducting phases. Studies of other hydrogen-rich systems provide both tests of fundamental theory and potentially useful materials for hydrogen storage. High pressure studies of oxides have led to new ferroelectric and multiferroic materials and phases with remarkable properties that guide the design and fabrication of new devices. With the discovery of super-Earths outside our solar system, the high pressure properties of silicates, oxides, volatiles, and the full complement of planetary materials are now problems of cosmic importance well beyond the conditions found on and within the Earth. Developments in high pressure biology are addressing the question of the depth of the biosphere, the processes and reservoirs of carbon in our planet, and new insights into the origins of life as we know it, as well as the possibility of extraterrestrial life. Improved materials that can withstand high P–T conditions and other extreme environments include new forms of diamond, which are advancing experimental methods and finding numerous applications in advanced technology. These developments dovetail with synergetic advances in a broad spectrum of radiation techniques including coherent X-ray, intense neutron, and ultrabright laser sources.