Classifier combination for in vivo magnetic resonance spectra of brain tumours

In this paper we present a multi-stage classifier for magnetic resonance spectra of human brain tumours which is being developed as part of a decision support system for radiologists. The basic idea is to decompose a complex classification scheme into a sequence of classifiers, each specialising in different classes of tumours and trying to reproducepart of the WHO classification hierarchy. Each stage uses a particular set of classification features, which are selected using a combination of classical statistical analysis, splitting performance and previous knowledge.Classifiers with different behaviour are combined using a simple voting scheme in order to extract different error patterns: LDA, decision trees and the k-NN classifier. A special label named "unknown¿ is used when the outcomes of the different classifiers disagree. Cascading is alsoused to incorporate class distances computed using LDA into decision trees. Both cascading and voting are effective tools to improve classification accuracy. Experiments also show that it is possible to extract useful information from the classification process itself in order to helpusers (clinicians and radiologists) to make more accurate predictions and reduce the number of possible classification mistakes.

Nuclear magnetic resonance investigation of structure and dynamics of some electrolyte solutions

Electrolyte solutions are of importance in a wide range of scientific contexts and as such have attracted considerable theoretical and experimental effort over many years. Nuclear Magnetic resonance provides a precise and versatile tool for investigation of electrolyte solutions, both in water and in organic solvents. Many structural and dynamic properties can be obtained through NMR experiments. The solution of aluminum chloride in water was studied. Different concentrations were taken for investigation. Independence of maximum line shift from concentration and acidity was shown. Six-coordinated structure of solvation shell was confirmed by experiments on 'H and 27A1 nuclei. Diffusion coefficients were studied. The solution of nickel chloride in methanol was studied. Lines, corresponding to coordinated and bulk methanol were found. Four-, five- and six-coordinated structures were found in different temperatures. The line for coordinated -OD group of deuterated methanol was observed on 2H spectrum for the first time. Partial deuteration of CH3 group was detected. Inability to observe coordinated -OH group was explained.

Developing of AC magnetometer and investigation of magnetic properties of LSMO

In this work AC magnetometer was developed and primary test measurements were performed for temperature range from 77 K up to 350 K in frequency range from 1 kHz up to 20 kHz. In the course of the present work dependencies of magnetization on temperature for Lao7Sr03Mni _yFeyO3 with y = 0.15, 0.20, 0.25 were obtained in DC magnetic field using SQUID magnetometer and in AC magnetic field using the developed AC magnetometer. Lai.XSrXMnO3 (LSMO) compounds belong to the class of Mn perovskites, which demonstrate very high degree of spin polarization. These materials are of great importance for nowadays applications in spintronics, where spin polarized electron transport is used. Spin glass like behavior was found as a characteristic feature of these solid solutions with the freezing temperature in the range 65 — 210 K.

Statistical Methods for Conservation and Alignment Quality in Proteins

Construction of multiple sequence alignments is a fundamental task in Bioinformatics. Multiple sequence alignments are used as a prerequisite in many Bioinformatics methods, and subsequently the quality of such methods can be critically dependent on the quality of the alignment. However, automatic construction of a multiple sequence alignment for a set of remotely related sequences does not always provide biologically relevant alignments.Therefore, there is a need for an objective approach for evaluating the quality of automatically aligned sequences. The profile hidden Markov model is a powerful approach in comparative genomics. In the profile hidden Markov model, the symbol probabilities are estimated at each conserved alignment position. This can increase the dimension of parameter space and cause an overfitting problem. These two research problems are both related to conservation. We have developed statistical measures for quantifying the conservation of multiple sequence alignments. Two types of methods are considered, those identifying conserved residues in an alignment position, and those calculating positional conservation scores. The positional conservation score was exploited in a statistical prediction model for assessing the quality of multiple sequence alignments. The residue conservation score was used as part of the emission probability estimation method proposed for profile hidden Markov models. The results of the predicted alignment quality score highly correlated with the correct alignment quality scores, indicating that our method is reliable for assessing the quality of any multiple sequence alignment. The comparison of the emission probability estimation method with the maximum likelihood method showed that the number of estimated parameters in the model was dramatically decreased, while the same level of accuracy was maintained. To conclude, we have shown that conservation can be successfully used in the statistical model for alignment quality assessment and in the estimation of emission probabilities in the profile hidden Markov models.

Origin of magnetic and magnetoelastic tweedlike precursor modulations in ferroic materials

Based on experimental observations of modulated magnetic patterns in a Co0.5Ni0.205Ga0.295 alloy, we propose a model to describe a (purely) magnetic tweed and a magnetoelastic tweed. The former arises above the Curie (or Nel) temperature due to magnetic disorder. The latter results from compositional fluctuations coupling to strain and then to magnetism through the magnetoelastic interaction above the structural transition temperature. We discuss the origin of purely magnetic and magnetoelastic precursor modulations and their experimental thermodynamic signatures.

CFD simulation of complex phenomena containing suspensions and flow throughporous media

There is an increasing reliance on computers to solve complex engineering problems. This is because computers, in addition to supporting the development and implementation of adequate and clear models, can especially minimize the financial support required. The ability of computers to perform complex calculations at high speed has enabled the creation of highly complex systems to model real-world phenomena. The complexity of the fluid dynamics problem makes it difficult or impossible to solve equations of an object in a flow exactly. Approximate solutions can be obtained by construction and measurement of prototypes placed in a flow, or by use of a numerical simulation. Since usage of prototypes can be prohibitively time-consuming and expensive, many have turned to simulations to provide insight during the engineering process. In this case the simulation setup and parameters can be altered much more easily than one could with a real-world experiment. The objective of this research work is to develop numerical models for different suspensions (fiber suspensions, blood flow through microvessels and branching geometries, and magnetic fluids), and also fluid flow through porous media. The models will have merit as a scientific tool and will also have practical application in industries. Most of the numerical simulations were done by the commercial software, Fluent, and user defined functions were added to apply a multiscale method and magnetic field. The results from simulation of fiber suspension can elucidate the physics behind the break up of a fiber floc, opening the possibility for developing a meaningful numerical model of the fiber flow. The simulation of blood movement from an arteriole through a venule via a capillary showed that the model based on VOF can successfully predict the deformation and flow of RBCs in an arteriole. Furthermore, the result corresponds to the experimental observation illustrates that the RBC is deformed during the movement. The concluding remarks presented, provide a correct methodology and a mathematical and numerical framework for the simulation of blood flows in branching. Analysis of ferrofluids simulations indicate that the magnetic Soret effect can be even higher than the conventional one and its strength depends on the strength of magnetic field, confirmed experimentally by Völker and Odenbach. It was also shown that when a magnetic field is perpendicular to the temperature gradient, there will be additional increase in the heat transfer compared to the cases where the magnetic field is parallel to the temperature gradient. In addition, the statistical evaluation (Taguchi technique) on magnetic fluids showed that the temperature and initial concentration of the magnetic phase exert the maximum and minimum contribution to the thermodiffusion, respectively. In the simulation of flow through porous media, dimensionless pressure drop was studied at different Reynolds numbers, based on pore permeability and interstitial fluid velocity. The obtained results agreed well with the correlation of Macdonald et al. (1979) for the range of actual flow Reynolds studied. Furthermore, calculated results for the dispersion coefficients in the cylinder geometry were found to be in agreement with those of Seymour and Callaghan.

Magnetic properties of ZnGeP2:Mn

In this work magnetic properties of ZnGeP2:Mn were investigated in DC magnetic field with SQUID magnetometer in the temperature range from 3 K up to 400 K and in AC magnetic field with AC magnetometer in the temperature range from 77 K up to 350 K in frequency range from 500 Hz up to 18 KHz. Three ZnGeP2:Mn samples were studied with Mn concentration c = 1.5 % mass, 3 % mass and 3.5 % mass.

Magnetic and transport properties of InGaAs quantum wells with Mn

In the present work structural, magnetic and transport properties of InGaAs quantum wells (QW) prepared by MBE with an remote Mn layer are investigated. By means of high-resolution X-ray diffractometry the structure of the samples is analyzed. It is shown that Mn ions penetrate into the QW. Influence of the thickness of GaAs spacer and annealing at 286 ºС on the properties of the system is shown. It is shown that annealing of the samples led to Mn activation and narrowing of the Mn layer. Substantial role of 2D holes in ferromagnetic ordering in Mn layer is shown. Evidence for that is observation of maximum at 25 – 55 K on the resistivity temperature dependence. Position of maximum, which is used for quantitative assessment of the Curie temperature, correlates with calculations of the Curie temperature for structures with indirect interaction via 2D holes’ channel. Dependence of the Curie temperature on the spacer thickness shows, that creation of applicable spintronic devices needs high-precision equipment to manufacture extra fine structures. The magnetotransport measurements show that charge carrier mobility is very low. This leads to deficiency of the anomalous Hall effect. At the same time, magnetic field dependences of the magnetization at different temperatures demonstrate that systems are ferromagnetically ordered. These facts, most probably, give evidence of presence of the ferromagnetic MnAs clusters.

Morphological and Magnetic Properties of Superparamagnetic Carbon-Coated Fe Nanoparticles Produced by Arc Discharge.

Spherical carbon coated iron particles of nanometric diameter in the 5-10 nm range have been produced by arc discharge at near-atmospheric pressure conditions (using 5-8·10 4 Pa of He). The particles exhibit a crystalline dense iron core with an average diameter 7.4 ± 2.0 nm surrounded by a sealed carbon shell, shown by transmission electron microscopy (TEM), selected-area diffrac- tion (SAED), energy-dispersive X-ray analysis (STEM-EDX) and electron energy loss spectroscopy (EELS). The SAED, EDX and EELS results indicate a lack of traces of core oxidized phases showing an efficient protection role of the carbon shell. The magnetic properties of the nanoparticles have been investigated in the 5-300 K temperature range using a superconducting quantum interference device (SQUID). The results reveal a superparamagnetic behaviour with an average monodomain diameter of 7.6 nm of the nanoparticles. The zero field cooled and field cooled (ZFC-FC)magnetization curves show a blocking temperature (TB)at room temperature very suitable for biomedical applications (drug delivery, magnetic resonance imaging-MRI-, hyperthermia).

Determinação da origem biossintética de ácido acético através da técnica "Site Specific Natural Isotopic Fractionation Studied by Nuclear Magnetic Resonance (SNIF-NMR)"

The main purpose of this work is to describe the use of the technique Site-Specific Natural Isotopic Fractionation of hydrogen (SNIF-NMR), using ²H and ¹H NMR spectroscopy, to investigate the biosynthetic origin of acetic acid in commercial samples of Brazilian vinegar. This method is based on the deuterium to hydrogen ratio at a specific position (methyl group) of acetic acid obtained by fermentation, through different biosynthetic mechanisms, which result in different isotopic ratios. We measured the isotopic ratio of vinegars obtained through C3, C4, and CAM biosynthetic mechanisms, blends of C3 and C4 (agrins) and synthetic acetic acid.

Observation of phonon-induced magnetic deflagration in manganites

Very fast magnetic avalanches in (La, Pr)-based manganites are the signature of a phase transition from an insulating blocked charge-ordered antiferromagnetic state to a charge-delocalized ferromagnetic (CD-FM) state. We report here the experimental observation that this transition does not occur either simultaneously or randomly in the whole sample but there is instead a spatial propagation with a velocity of the order of tens of m/s. Our results show that avalanches originate from the inside of the sample, move to the outside, and occur at values of the applied magnetic field that depend on the CD-FM fraction in the sample. Moreover, upon application of surface acoustic waves at constant magnetic fields, we are able to trigger avalanches at very well-determined values of the temperature and magnetic field. Due to the interaction with the acoustic waves, the number of isolated ferromagnetic clusters in La0.225Pr0.40Ca0.375MnO3 starts to grow across the entire sample in the same way as if it were a magnetic deflagration.

Quantum magnetic deflagration in Mn12 acetate

We report controlled ignition of magnetization reversal avalanches by surface acoustic waves in a single crystal of Mn12 acetate. Our data show that the speed of the avalanche exhibits maxima on the magnetic field at the tunneling resonances of Mn12. Combined with the evidence of magnetic deflagration in Mn12 acetate [Y. Suzuki et al., Phys. Rev. Lett. 95, 147201 (2005)], this suggests a novel physical phenomenon: deflagration assisted by quantum tunneling.

Excitation modes of vortices in submicron magnetic disks

Classical and quantum theory of spin waves in the vortex state of a mesoscopic submicron magnetic disk have been developed with account of the finite mass density of the vortex. Oscillations of the vortex core resemble oscillations of a charged string in a potential well in the presence of the magnetic field. A conventional gyrotropic frequency appears as a gap in the spectrum of spin waves of the vortex. The mass of the vortex has been computed, and the result agrees with experimental findings. The finite vortex mass generates a high-frequency branch of spin waves. The effects of an external magnetic field and dissipation have been addressed.