Search

Optical excitation spectra of Agn and Agn@He60 (n = 2, 8) clusters are investigated in the framework of the time-dependent density functional theory (TDDFT) within the linear response regime. We have performed the ab initio calculations for two different exact exchange functionals (GGA-exact and LDA-exact). The computed spectra of Agn@He60 clusters with the GGA-exact functional accounting for exchange-correlation effects are found to be generally in a relatively good agreement with the experiment. A strategy is proposed to obtain the ground-state structures of the Agn@He60 clusters and in the initial process of the geometry optimization, the He environment is simulated with buckyballs. A redshift of the silver clusters spectra is observed in the He environment with respect to the ones of bare silver clusters. This observation is discussed and explained in terms of a contraction of the Ag-He bonding length and a consequent confinement of the s valence electrons in silver clusters. Likewise, the Mie-Gans predictions combined with our TDDFT calculations also show that the dielectric effect produced by the He matrix is considerably less important in explaining the redshifting observed in the optical spectra of Agn@He60 clusters. [ABSTRACT FROM AUTHOR]

We have performed collinear and noncollinear calculations on neutral Bi4Mn and collinear ones on ionized Bi4Mn with charges +1 and -1 to find out why theoretical calculations will not predict the magnetic state found in the experiment. We have used the density functional theory to find a fit between the theoretical prediction of the magnetic moment and the experimental value. Our calculations have consisted in a structural search of local energy minima, and the lowest energy magnetic state for each resulting isomer. The geometry optimization found three local minima whose fundamental state is the doublet spin state. These isomers could not be found in previous theoretical works, but they are higher in energy than the lowest-lying isomer by ≈1.75 eV. This magnetic state could help understand the experiment. Calculations of noncollinear magnetic states for the Bi4Mn do not lower the total magnetic moment. We conclude arguing how the three isomers with doublet state could actually be the ones measured in the experiment. [ABSTRACT FROM AUTHOR]

The ground-state properties of small silver clusters Agn (2<=n<=24) have been studied using a linear combination of atomic Gaussian-type orbitals within the density functional theory. The results show that the Ag13 clusters, due to their noticeable magnetic moment and their considerable highest occupied-lowest unoccupied molecular orbital gap, are promising candidates for the magnetic applications of nanoparticles. In particular, our study suggests that the silver nanoclusters made out of Ag13 clusters, as building blocks, are suitable for possible future applications in biomedicine, since they could improve some present-day difficulties of magnetic nanoparticles such as toxicity and opsonization. [ABSTRACT FROM AUTHOR]

The strong coupling between the crystal structure and magnetic state (ferromagnetic or helical antiferromagnetic) of FeMnP0.75Si0.25 is investigated using density functional theory in combination with atomistic spin dynamics. We find many competing energy minima for drastically different ferromagnetic and noncollinear magnetic configurations. We also find that the appearance of a helical spin-spiral magnetic structure at finite temperature is strongly related to one of the crystal structures reported for this material. Shorter Fe-Fe distances are found to lead to a destabilized ferromagnetic coupling, while out-of-plane Mn-Mn exchange interactions become negative with the shortening of the interatomic distances along the c axis, implying an antiferromagnetic coupling for the nearest-neighbor Mn-Mn interactions. The impact of the local dynamical correlations is also discussed. [ABSTRACT FROM AUTHOR]

Transport properties of very thin films have been analysed using the layered potentials calculated by means of the ab initio method represented by the density functional theory (DFT) in the planar geometry for the nFe/3Cr/nFe films, where n is the number of monoatomic Fe layers, (1 ≤ n ≤ 8). We also take into consideration the values of the relaxation time and the effective mass of an electron in terms of the considered potentials. The matching conditions have been applied at the interface and the boundary conditions at the surface in order to determine, the contributions to the giant magnetoresistance (GMR) coming from the surface, interface, and inner layers. The surface roughness is introduced by means of the specularity factor Pσ defined in the spin-dependent terms responsible for the scattering of the electrons. Thus, the electron scattering at the outer surfaces depends on both spin orientations. The main result obtained in the paper is the evaluation that the surface contribution to GMR is very small in comparison with the effect of interface. [ABSTRACT FROM AUTHOR]

Abstract: ab initio calculations have been performed on several ultrathin Fe/Cr/Fe trilayer systems in ferromagnetic configuration, with a fixed thickness of the spacer chromium slab of three atomic monolayers, and both iron slabs symmetrically varying in range from 1 to 6 atomic monolayers. We have calculated the magnetic structure of these trilayers, their charge distribution, and the composition of their density of states at the Fermi energy, with respect to every monolayer and to every orbital. In the spatial charge distribution, we have identified Friedel-like oscillations in the Fe slabs. [Copyright &y& Elsevier]

Abstract: Ab initio full-potential linearized augmented-plane-wave (FP-LAPW) method combined with the semiclassical Boltzmann formalism was employed to calculate the giant magnetoresistance ratio in the trilayers nFe/3Cr/nFe (). The present results emphasize the very important role of the ferromagnetic layer as well as the interfacial scattering and surface roughness on the giant magnetoresistance effect. [Copyright &y& Elsevier]

The sleep apnea syndrome (SAS) is a respiratory disorder, which is characterised by the occurrence of five or more apneic events (apnea or hypopnea) per hour of sleep. Diagnosis of the SAS is a process that is markedly heuristic by nature, in that doctors handle information that is both numerical and symbolic, and employ qualitative descriptive terminology. An expert draws up a contextualised clinical interpretation that relates a patient''s sleep process and respiratory physiology, involving a detailed analysis of the polysomnograph corresponding to a night''s sleep. This task, implying a great deal of work on the part of clinical staff and a high economic cost, can in fact be partially automated. Our paper describes a modular system based on artificial intelligence techniques that provides an individual SAS diagnosis on the basis of a patient''s polysomnograph. The main tasks of our system are the identification and classification of respiratory events, the construction of the patient''s hypnogram and the correlation of all the information obtained so as to arrive at a final diagnosis with respect to the existence of the syndrome. Finally our article presents and discusses the results obtained following a preliminary validation of the developed system. [Copyright &y& Elsevier]

Most of the articles devoted to giant magnetoresistance phenomenon take into account only the thickness variation of the spacer. Within this work, we study the magnetic behavior of the trilayer system Fe/Cr/Fe (0 0 1) after changing the thickness of the magnetic layers (Fe layers) and keeping the spacer constant (Cr layers). The calculations were done at the ab initio level by means of density functional theory, solving the Kohn–Sham equations with the full-potential linearized augmented plane wave method. These results show an oscillatory behavior of magnetic moment per atom as a function of the iron monolayers number. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]

Presents the case of a 55-year-old man with papuloerythroderma (PE), characterized by pruritic and papular erythroderma-like eruption. Sparing of the skin creases and the pressure area; Finding of peripheral eosinophilia, lymphopenia and elevated serum immunoglobulin E levels; Diseases associated with PE; Use of psoralen + ultraviolet A as treatment.

Abstract: Ab initio calculations have been performed on several ultrathin Fe/Cr/Fe trilayer systems in ferromagnetic configuration, with a fixed width of the spacer chromium slab of three atomic monolayers, and both iron slabs symmetrically varying in a range from 1 to 6 atomic monolayers. We have calculated the charge distribution of these trilayers and calculated and plotted the density of states of every one of them. We have identified Friedel-like oscillations of the charge distribution from the Mulliken population analysis in the Fe slabs. [Copyright &y& Elsevier]

Microsporum species are a frequent cause of cutaneous mycoses in humans. Atypical strains of Microsporum can sometimes be difficult to identify with conventional methods. Recently, we have obtained a Microsporum isolate with atypical morphology and special nutritional requirements ( Microsporum CHUS-126-02). As several molecular techniques have been developed for the identification of fungi, we analysed six Microsporum species ( M. canis, M. gypseum, M. gallinae, M. nanum, M. ferrugineum and M. persicolor) in order to compare them with our isolate, by using polymerase chain reaction-restriction enzyme analysis (PCR-REA). We studied the nucleotide sequence of the internal transcribed spacer regions from the nuclear DNA encoding for the ribosomal domain. Digestion with MvaI and EcoRI endonucleases obtained specific patterns for M. gypseum, M. gallinae, M. nanum and M. persicolor. Microsporum canis, M. ferrugineum and Microsporum CHUS-126-02 yielded the same patterns. Based on these results and phenotypic criteria, we classified our atypical isolate as M. canis. [ABSTRACT FROM AUTHOR]

Electronic structure and magnetic properties of FeN/Cr3/FeN bcc(100) trilayers (N is the number of atomic layers) are studied on the basis of ab initio calculations performed within the framework of the density functional theory in the local spin density approximation, using the full-potential LAPW method in slab geometry. According to our calculations, the magnetic moment of a surface Fe layer increases monotonically from 2.45 μB for N = 1 to 2.92 μB for N = 3 and practically does not change at further increase of the Fe film thickness. However, the magnetic moment in the interface Fe layer changes nonmonotonically with the Fe film thickness increase and is close to the surface value at N = 5 and 7. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]

Abstract: We have studied the influence of the applied magnetic field on the blocking temperature (T B) of a fine magnetic particle system. By means of a Monte Carlo technique we have simulated zero field cooling (ZFC) curves under different applied fields, obtaining the respective T B as a function of H. We have focused our study on the limit H → HK (where HK is the anisotropy field), since the results found in the literature usually lack a detailed study of this range. The simulations were done at different sample concentration of the nanoparticles, with the purpose of observing how the magnetic dipolar interaction affects the field dependence of T B. The classical expression predicts T B to disappear for H ⩾ HK , independently of the dipolar interaction strength. Our simulations show that at strong interacting conditions T B exists even for fields H > HK . [Copyright &y& Elsevier]

Background: Superficial fungal infections are common. It is important to confirm the clinical diagnosis by mycological laboratory methods before initiating systemic antifungal treatment, especially as antifungal sensitivity and in vitro susceptibility may differ between different genera and species. For many years, the gold standard for diagnosis of superficial fungal infections has been direct fungal detection in the clinical specimen (microscopy) supplemented by culturing. Lately, newer molecular based methods for fungal identification have been developed. Objective: This study was initiated to focus on the current usage of mycological diagnostics for superficial fungal infections by dermatologists. It was designed to investigate whether it was necessary to differentiate between initial diagnostic tests and those used at treatment follow‐up in specific superficial fungal infections. Methods: An online questionnaire was distributed among members of the EADV mycology Task Force and other dermatologists with a special interest in mycology and nail disease. Results: The survey was distributed to 62 dermatologists of whom 38 (61%) completed the whole survey, 7 (11%) partially completed and 17 (27%) did not respond. Nearly, all respondents (82–100%) said that ideally they would use the result of direct microscopy (or histology) combined with a genus/species directed treatment of onychomycosis, dermatophytosis, Candida‐ and Malassezia‐related infections. The majority of the dermatologists used a combination of clinical assessment and direct microscopy for treatment assessment and the viability of the fungus was considered more important at this visit than when initiating the treatment. Molecular based methods were not available for all responders. Conclusion: The available diagnostic methods are heterogeneous and their usage differs between different practices as well as between countries. The survey confirmed that dermatologists find it important to make a mycological diagnosis, particularly prior to starting oral antifungal treatment in order to confirm the diagnose and target the therapy according to genus and species. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) in one-dimensional (1D) magnetic nanostructures is optimized for a specific value of the magnetic field H* when applied perpendicularly to the longitudinal direction of the system. Our results reveal that H* corresponds to the saturation field, slightly above the transition from a magnetically stable dipolar-coupled configuration to an unstable one. This MCE-optimizing field explicitly depends on the characteristic magnetic parameters of the system, namely, saturation magnetization (Ms) and anisotropy constant (K): H* is directly proportional to M2s, and the anisotropy contribution is equal to the anisotropy field of the particles HA = 2K/Ms. Accordingly, the MCE in 1D nanomagnets can be directly tuned by a proper choice of the characteristic Ms and K values of the materials. [ABSTRACT FROM AUTHOR]

Abstract: The existence of enhanced or diminished interface magnetism of the trilayer structure is reported. The interfaces appearing in the structure A(n)/A c B1− c /B(p)/B1 c Ac/A(n) with n and p standing for the numbers of monoatomic layers of S A and S B spins, respectively, are considered in the form of binary alloys A c B1− c extended on two monoatomic planes mixed with an arbitrary concentration c for S A. In this structure, the temperature-dependent magnetization distribution across the trilayer we consider here leads to the non-homogeneity of the potential at the surface and interface layers, which now is different for different spin orientations. In consequence, GMR calculated by means of this local layered potential depends on the temperature. The numerical results for this dependence are presented in a particular case S A=1 and S B=1/2. [Copyright &y& Elsevier]

The transport properties of ultrathin metallic sandwich structures of Fe/Cr/Fe are studied as a function of magnetic layer thickness for the current in plane geometry (CIP). Taking into account the band structure obtained from density functional theory (DFT), we calculate basic physical properties such as Fermi energy and relaxation time for each magnetic and spacer layer. Next, using the Boltzmann formalism in its extended form, we obtain results for magnetoresistance (MR). In particular, we analyse the influence of effective mass parameterisation. [ABSTRACT FROM AUTHOR]

Abstract: Ab initio FP-APW+lo calculations were performed for the rare earth orthoferrites with , Nd, Sm, Gd, Dy, Lu using the well-known WIEN2k package. Ferromagnetic and antiferromagnetic alignments between the iron moments were studied using the GGA (PBE) functional for the exchange-correlation energy. Antiferromagnetic structures are energetically favoured in all cases. Except for SmFeO3, all antiferromagnetic configurations are insulators, while the ferromagnetic ones give metals except for LaFeO3 and LuFeO3. Hyperfine fields at the iron sites agree with experiment to within 25%. [Copyright &y& Elsevier]

Abstract: Ab initio calculations were performed in the quasi-one-dimensional BaCoO using the FP-APW+lo method as implemented in the WIEN2k package utilizing the LDA+U approach. Several magnetic configurations were studied, exploring different intra- and inter-chain couplings. The most stable configuration is the ferromagnetic low-spin state. The electronic structure of the Co ion () has an orbital degree of freedom. When an “alternating-orbital” ordering is allowed along the Co chains, the energy of the system is drastically reduced, whereas the magnetic order is a secondary effect. This orbital ordered state reproduces the experimentally found semiconducting behaviour, which is analysed studying the bandstructure of the material. [Copyright &y& Elsevier]

We discuss the magnetic properties of trilayer A(n)/AcB1-c/B(p)/AcB1-c/A′(m)-structure with two mixed–spin interfaces AcB1-c (SA=1, SB=1/2) for arbitrary concentration c of A-spins and varied partial film thickness (n,p,m). The description is obtained by means of an effective-field approach which is superior to the standard molecular-field treatment. Temperature dependent magnetisation depth profiles of trilayer structure vs. concentration c of A-atoms are presented in the whole range of reduced temperature. The existence of enhanced interface magnetism is also discussed using the phase diagrams in JAB–c plane. Depth profiles are strongly inhomogeneous in the interface region and thus they lead to complex interface potentials contributing significantly to GMR-effect. [Copyright &y& Elsevier]

A thin ferromagnetic bilayer structure with interface magnetic moment and different exchange interactions is studied in terms of a mixed Ising model. The phase diagrams of critical temperature TC vs. interface parameters and the temperature dependence of layered magnetizations are presented. In particular, the magnetization profiles across bilayer show us the existence of the interface magnetism phase and temperature reversal of magnetization profiles assigned to special domains of phase diagrams provided the interface perpendicular anisotropy is large enough. The results form the basis to extend our recent studies on the Hood–Falicov approach to the giant magneto-resistance description. [Copyright &y& Elsevier]

We consider the transport properties in magnetic multilayers for electronic current in the plane of the surfaces. The model is based on the effective s-band construction for the multilayer consisting of the metallic spacer and two ferromagnetic layers characterized by s-d coupling. We discuss the quasielectron spectrum in its effective mass approximation, with the perturbation taken into account by the effective potential, which also includes the interface contributions. We find the energy dispersion and the Fermi level for the effective s-band common for electrons in the whole sample. The results are equivalent in fact to those obtained within the Hood-Falicov model, but they seem to us much simpler and more transparent for their extensions and applications. [ABSTRACT FROM AUTHOR]

Abstract: A superparamagnetic nanoparticle system is a good candidate for implementing the magnetocaloric effect, due to its suitable properties as a frozen ferrofluid able to follow a thermodynamic cycle. For such aim, we have concentrated on the study of the entropy dependence on both the particle size and sample concentration using a Monte Carlo simulation. We have found that for a given sample concentration there exists a particle size for the larger entropy increase, and reciprocally for a given particle volume there exists a sample concentration able to produce the larger entropy change. [Copyright &y& Elsevier]

Abstract: We study the entropy change dependence on the applied magnetic field for a dipolar interacting superparamagnetic system of fine particles. Using a Monte Carlo technique, we have obtained an enhancement of the entropy for increasing applied magnetic fields; the maximum of the entropy curves occurs at higher temperatures for larger magnetic fields. It was also observed that the blocking temperature always decreases as the magnetic field increases. [Copyright &y& Elsevier]

The quasi-one-dimensional cobalt oxide Sr6Co5O15 is studied using first-principles electronic-structure calculations and Boltzmann transport theory. We have been able to describe the electronic structure, characterized by the structural one-dimensionality and a particular type of charge ordering, with unexpected electronic structure of the different Co atoms. The origin of the large unquenched misaligned orbital angular momenta comes out naturally from a correct description of the different crystal-field environments. The evolution with the on-site Coulomb repulsion (U) of the electronic structure and the transport properties is discussed, with a best agreement with experiment found for the smallest value of U that allows to converge the correct in-chain ferrimagnetic ground state. [ABSTRACT FROM AUTHOR]

The series of V spinels [A2+] V2 O4 (A = Cd, Mn, Zn, Mg) provides an opportunity to tune the V-V distance continuously, in the frustrated pyrochlore lattice of the spinel. This system has been shown to approach the metallic state when V-V distance is reduced. The proximity to the transition leads to a dimerized structure in ZnV2 O4 caused by lattice instabilities. A different manner to tune the V - V distance of this structure is to fix the A2+ cation (in our case, Zn) and apply pressure. We have analyzed the evolution of the electronic structure of the system in the dimerized state. Such structure prevents the system to present a metallic phase at moderate pressures. We have also calculated the transport properties in a semiclassical approach based on Boltzmann transport theory. Our results support the validity of this structural distortion by providing a nice fit with experimental measurements. [ABSTRACT FROM AUTHOR]

A case of tinea faciae caused by Trichophyton equinum affecting a 5-year-old boy is described. The boy had ridden a pony a month earlier and responded to a 6-week course of treatment with oral and topical terbinafine. [ABSTRACT FROM AUTHOR]

Examines the etiology of Rubinstein-Taybi syndrome associated with ulerythema ophryogenes in children. Signs and symptoms of the disease; Presence of peculiar facies, mental retardation and broad thumbs; Diagnosis of the disease process.

We show for a simple noncollinear configuration of the atomistic spins (in particular, where one spin is rotated by a finite angle in a ferromagnetic background) that the pairwise energy variation computed in terms of multiple-scattering formalism cannot be fully mapped onto a bilinear Heisenberg spin model even in the absence of spin-orbit coupling. The non-Heisenberg terms induced by the spin-polarized host appear in leading orders in the expansion of the infinitesimal angle variations. However, an Eg-T2g symmetry analysis based on the orbital decomposition of the exchange parameters in bcc Fe leads to the conclusion that the nearest-neighbor exchange parameters related to the T2g orbitals are essentially Heisenberg-like: they do not depend on the spin configuration, and can, in this case, be mapped onto a Heisenberg spin model even in extreme noncollinear cases. [ABSTRACT FROM AUTHOR]

We propose a new efficient permanent magnet, SmCoNiFe3, which is a development of the well-known SmCo5 prototype. More modern neodymium magnets of the Nd-Fe-B type have an advantage over SmCo5 because of their greater maximum energy products due to their iron-rich stoichiometry. Our new magnet, however, removes most of this disadvantage of SmCo5 while preserving its superior high-temperature efficiency over the neodymium magnets. We show by means of first-principles electronic-structure calculations that SmCoNiFe3 has very favorable magnetic properties and could therefore potentially replace SmCo5 or Nd-Fe-B types in various applications. [ABSTRACT FROM AUTHOR]

Temperature-dependent magnetic experiments such as pump-probe measurements generated by a pulsed laser have become a crucial technique for switching the magnetization in the picosecond time scale. Apart from having practical implications on the magnetic storage technology, the research field of ultrafast magnetization poses also fundamental physical questions. To correctly describe the time evolution of the atomic magnetic moments under the influence of a temperature-dependent laser pulse, it remains crucial to know if the magnetic material under investigation has magnetic excitation spectrum that is more or less dependent on the magnetic configuration, e.g., as reflected by the temperature dependence of the exchange interactions. In this paper, we demonstrate from first-principles theory that the magnetic excitation spectra in Co in fcc, bcc, and hcp structures are nearly identical in a wide range of noncollinear magnetic configurations. This is a curious result of a balance between the size of the magnetic moments and the strength of the Heisenberg exchange interactions, that in themselves vary with configuration, but put together in an effective spin Hamiltonian results in a configuration-independent effective model. We have used such a Hamiltonian, together with ab initio calculated damping parameters, to investigate the magnon dispersion relationship as well as ultrafast magnetization dynamics of Co and Co-rich CoMn alloys. [ABSTRACT FROM AUTHOR]

We present electronic and magnetic properties of CaMnO3 (CMO) as obtained from ab initio calculations. We identify the preferable magnetic order by means of density functional theory plus Hubbard U calculations and extract the effective exchange parameters (Jij's) using the magnetic force theorem. We find that the effects of geometrical relaxation at the surface as well as the change of crystal field are very strong and are able to influence the lower-energy magnetic configuration. In particular, our analysis reveals that the exchange interaction between the Mn atoms belonging to the surface and the subsurface layers is very sensitive to the structural changes. An earlier study [A. Filippetti and W. E. Pickett, Phys. Rev. Lett. 83, 4184 (1999)] suggested that this coupling is ferromagnetic and gives rise to the spin-flip (SF) process on the surface of CMO. In our work, we confirm their finding for an unrelaxed geometry, but once the structural relaxations are taken into account, this exchange coupling changes its sign. Thus, we suggest that the surface of CMO should have the same G-type antiferromagnetic order as in the bulk. Finally, we show that the suggested SF can be induced in the system by introducing an excess of electrons. [ABSTRACT FROM AUTHOR]

In this work we examine critically the electronic structure of the rare-earth elements by use of the so-called Hubbard I approximation. From the theoretical side all measured features of both occupied and unoccupied states are reproduced, without significant deviations between observations and theory. We also examine cohesive properties like the equilibrium volume and bulk modulus, where we find, in general, a good agreement between theory and measurements. In addition, we have reproduced the spin and orbital moments of these elements as they are reflected from measurements of the saturation moment. We have also employed the Hubbard I approximation to extract the interatomic exchange parameters of an effective spin Hamiltonian for the heavy rare earths. We show that the Hubbard I approximation gives results which are consistent with calculations where 4f electrons are treated as core states for Gd. The latter approach was also used to address the series of the heavy/late rare earths. Via Monte Carlo simulations we obtained ordering temperatures which reproduce measurements within about 20%. We have further illustrated the accuracy of these exchange parameters by comparing measured and calculated magnetic configurations for the heavy rare earths and the magnon dispersion for Gd. The Hubbard I approximation is compared to other theories of the electronic structure, and we argue that it is superior. We discuss the relevance of our results in general and how this makes it possible to treat the electronic structure of materials containing rare-earth elements, such as permanent magnets, magnetostrictive compounds, photovoltaics, optical fibers, topological insulators, and molecular magnets. [ABSTRACT FROM AUTHOR]