Patricio Vargas

Automated discrimination and quantification of idiopathic pulmonary fibrosis from normal lung parenchyma using generalized fractal dimensions in high-resolution computed tomography images

RATIONALE AND OBJECTIVES We computed generalized fractal dimensions for high-resolution computed tomography (HRCT) images to investigate their value in the discrimination and quantification of idiopathic pulmonary fibrosis (IPF) from normal lung parenchyma. METHODS A probability distribution that was based on the pixel value in each image was used to compute capacity, information, and higher fractal dimensions for a series of 52 HRCT slices obtained from four patients. Qualitative classification of normal, mild, moderate, and severe IPF cases was achieved by computing the following parameter: DD = D0 - 2D1 + D2, where D0, D1, and D2 represents the capacity, information, and pair correlation dimensions, respectively. A multiple linear regression analysis using morphometric quantification for the set of 52 slices was tested for all possible combinations of the parameters D0, D1, D2, and D3. The generalizability of the model was tested by predicting the extent of IPF for each patient from a regression model computed with the remaining slices in the database. RESULTS The best regression results were obtained using the independent parameters D1 and D2 to quantify the extent of diseased lung parenchyma. The technique was tested with 48 slices from 12 new patients. The results indicated that the extent of IPF could be predicted within the confidence limits given by the regression analysis. CONCLUSION The extent of IPF can be predicted well within the 90% confidence interval given by the model. The width of the confidence interval decreases as the number of slices used in the linear regression model increases. This operator-independent quantitative technique may be useful in the follow-up of patients with IPF.

Simulation of hysteresis for ±J triangular lattices

Abstract We report Monte Carlo simulations of low-temperature hysteresis of ±J Ising triangular lattices. A hysteresis loop similar to the one shown by real spin glasses is found. Such loop is divided in six sectors, according to the coordination number. Average hysteresis curves, obtained over large numbers of randomly prepared samples, are discussed for different values of temperature (T): it is found that the hysteresis loop disappears for T⩾2.2J. Characteristics of the zero-temperature curve are explained by probabilistic analysis.

Hydrogen diffusion in tantalum

Abstract Using the small-polaron theory of diffusion we obtain a very good fit of the experimental data on hydrogen diffusion in tantalum between 15 and 500 K. It is shown that the phenomenon has three regimes: (a) At T > 250 K the transport occurs mainly by hydrogen tunneling between tetrahedral sites. (b) At 200 K > T > 15 K metastable states having octahedral symmetry play the main role. (c) The dominance of tetrahedral diffusion restarts at T

Unoccupied electronic states of Au(113): Theory and experiment

We present results from inverse photoemission spectroscopy in the isochromat mode, with angular resolution, from a clean Au(113) surface. To identify the origin of the different resonances, we have performed a first-principles calculation of the bulk band structure in the linear-muffin-tin-orbital formalism. We predict the dispersion of the bulk features, as a function of parallel momentum, considering energy and momentum conservation. We have been able to identify unambiguously two surface resonances and a surface state in the [{bar 1}10] and [33{bar 2}] directions, respectively, as well as various bulk-derived features.

The Electronic Structure of VH, NbH and TaH in theβ-Phase*

Calculation of the DOS (Density of States) for the three monohydrides of V Nb and Ta in the orthorhombic /3-phase were performed using the LMTO method. In all three systems the hydrogen induced states below the Fermi level split into two maxima as a consequence of the H-H interactions. This fact agrees with photoemission experiments. We report also the calculated Bulk Modulus and equilibrium lattice parameters. This is the first time that a band structure calculation is reported for the /3-VH and /3-TaH systems.

Magnetic Engine for the Single-Particle Landau Problem

We study the effect of the degeneracy factor in the energy levels of the well-known Landau problem for a magnetic engine. The scheme of the cycle is composed of two adiabatic processes and two isomagnetic processes, driven by a quasi-static modulation of external magnetic field intensity. We derive the analytical expression of the relation between the magnetic field and temperature along the adiabatic process and, in particular, reproduce the expression for the efficiency as a function of the compression ratio.

Automated determination of left ventricular volume curves from bi-plane digital angiography without explicit use of edge detection algorithms

Automated computation of left ventricular (LV) global and regional function using contrast angiography has not yet become a routine procedure with the advent of digital cardiac imaging systems. We describe a new technique to compute LV volume curves which does not require the use of manual or semi-automated detection of endocardial borders and provides on-line implementation of volumetric curves and computation of pressure volume loops during catheterization. The approach uses the concepts of variableentropy (orinformation) of left ventricular images throughout the cardiac cycle. LV volume curves are computed with an interpolation scheme using those LV volume curves of a patient data base which are associated with the closest variation in entropy in the RAO projection to the analyzed patient data according to a simple metric. Computed LV volume curves were correlated with those obtained with manual tracing. Left ventricular ejection fraction (LVEF), time to end systole (TES) and angiographic cardiac output (CO) were compared to those obtained with the manual method. Results using a data base of 365 patients revealed excellent correlation (r=0.97) between manually derived volume curves and volume curves computed with the automated technique within a large range of LVEFs. In 87% of all cases the computed LVEF values were found within ± 10% of the value obtained with thegold standard method. The systolic phase of the volume curves showed that 81% of all cases had the same accuracy. The TES showed much more variation due to undersampling of the cardiac cycle in time (r=0.71).

Computation of left ventricular volume curves from gated blood pool studies without explicit use of edge detection algorithms: concise communication

A new technique has been developed to compute left ventricular (LV) time activity curves from gated blood pool (GBP) studies without the use of manual, semiautomated or fully automated edge detection algorithms. The method utilizes the correlation of entropy calculated from the counts of a fixed region of interest covering the left ventricle during a cardiac cycle to compute the LV volume curve for a new patient. The new LV volume curve is obtained through interpolation of those volume curves of a data base which are associated with the closest variations in normalized entropy to the new one. The computed LV time activity curves agree with those obtained from manual or fully automated outlines of the left ventricle within 9 percent for the selected set of 67 patients demonstrating the potential of the method. The accuracy of calculated LV volume curves can be improved theoretically to any degree by increasing the number of cases in the data base of known statistical feature vectors associated with the LV images and LV volume curves. The new method for computation of LV curves is very efficient and robust when compared to traditional techniques.

Thermodynamics of Small Magnetic Particles

In the present paper, we discuss the interpretation of some of the results of the thermodynamics in the case of very small systems. Most of the usual statistical physics is done for systems with a huge number of elements in what is called the thermodynamic limit, but not all of the approximations done for those conditions can be extended to all properties in the case of objects with less than a thousand elements. The starting point is the Ising model in two dimensions (2D) where an analytic solution exits, which allows validating the numerical techniques used in the present article. From there on, we introduce several variations bearing in mind the small systems such as the nanoscopic or even subnanoscopic particles, which are nowadays produced for several applications. Magnetization is the main property investigated aimed for two singular possible devices. The size of the systems (number of magnetic sites) is decreased so as to appreciate the departure from the results valid in the thermodynamic limit; periodic boundary conditions are eliminated to approach the reality of small particles; 1D, 2D and 3D systems are examined to appreciate the differences established by dimensionality is this small world; upon diluting the lattices, the effect of coordination number (bonding) is also explored; since the 2D Ising model is equivalent to the clock model with q = 2 degrees of freedom, we combine previous results with the supplementary degrees of freedom coming from the variation of q up to q = 20 . Most of the previous results are numeric; however, for the case of a very small system, we obtain the exact partition function to compare with the conclusions coming from our numerical results. Conclusions can be summarized in the following way: the laws of thermodynamics remain the same, but the interpretation of the results, averages and numerical treatments need special care for systems with less than about a thousand constituents, and this might need to be adapted for different properties or devices.

Quantum diffusion in transition metals

Abstract The functions governing the temperature dependence of small-polaron diffusion are calculated by using the phonon dispersion relations with high accuracy for octahedral interstitial sites in copper, palladium, nickel and platinum f.c.c. hosts, as well as for tetrahedral and octahedral sites in tantalum, niobium and vanadium hosts. The current experimental data on the diffusion coefficient for hydrogen in b.c.c. tantalum and niobium and for positive muons in copper are very well reproduced for all temperature ranges. By comparison with exact calculation, very accurate results are also obtained by using an approximate universal function calculated within the Debye approximation, for which we give a closed analytical formula. This allows manual calculations of the diffusion coefficient for light interstitial impurities in transition metals within the small-polaron model.