Geometrical characterization of healthy red blood cells using digital holographic microscopy and parametric shape models for biophysical studies and diagnostic applications

Modeling of the red blood cell (RBC) shape is an integral part of the experimental and computer simulation investigations of light scattering by these cells for fundamental studies as well as diagnostic applications in the techniques like cytometry. In the present work, a comprehensive study of the geometrical characterization of healthy human RBCs using the digital holographic microscopy (DHM) and six frequently employed parametric shape models is reported. It is shown that the comparison of the optical phase profiles, the thickness profiles given by the models with the DHM results gives a better judgement of the appropriateness of the parametric shape models. Results of geometrical characterization of 500 healthy RBCs in terms of volume, surface area and sphericity index lead to the classification of the parametric models in two categories based on the nature of variation of these quantities with the cell diameter. In light of the variability of the healthy RBC shapes, our findings suggest that the parametric models exhibiting a negative correlation between the sphericity index and the cell diameter would provide more reliable estimates of the RBC parameters in diagnostic applications. Statistical distributions and descriptive statistics of the RBC volume, surface area and sphericity index serve as a guide for the assessment of the capability of the studied parametric models to give a reliable account of the variability of the healthy RBC shape and size.Comment: 25 pages, 17 figure

Yttrium Enhanced Glass-Forming Ability of Zr-Based Metallic Glasses

Thermodynamic behavior of Zr56-xCo28Al16Yx (0, 2, 7, 10) bulk metallic glass-forming alloys has been studied using an analytical approach where some of the key thermodynamic quantities such as ΔH, ΔS and ΔG has been estimated using a hyperbolic temperature dependence of specific heat difference ΔCp in the supercooled liquid region. The study is focused on understanding the effect of Yttrium-doping on the thermodynamics of the alloys in the supercooled region and on the glass-forming ability of these alloys. The analytical approach has been found to give estimates of ΔG in a wide supercooled liquid region in excellent agreement with the experimental results. Estimated ΔG values are found to be minimum for Y concentration of 7 and 10% which is consistent with the observed high GFA for these compositions. Fundamental elemental properties such as atomic size, electronegativity, the heat of mixing have been found to play an important role in governing the thermodynamics of the alloys in the supercooled liquid region

Yttrium Enhanced Glass-Forming Ability of Zr-Based Metallic Glasses

803-810Thermodynamic behavior of Zr56-xCo28Al16Yx (x = 0, 2, 7, 10 at. %) bulk metallic glass-forming alloys has been studied using an analytical approach where some of the key thermodynamic quantities such as ΔH, ΔS and ΔG have been estimated using a hyperbolic temperature dependence of specific heat difference ΔCp in the supercooled liquid region. The study is focused on understanding the effect of yttrium (Y) doping on the thermodynamics of the alloys in the supercooled region and on the glass-forming ability (GFA) of these alloys. The analytical approach has been found to give estimates of ΔG in a wide supercooled liquid region which is in excellent agreement with the experimental results. Estimated ΔG values are found to be minimum for Y concentration of 7% and 10% which is consistent with the observed high GFA for these compositions. Fundamental elemental properties such as atomic size, electronegativity, the heat of mixing have been found to play an important role in governing the thermodynamics of the alloys in the supercooled liquid region

Study of concentration fluctuations in liquid Li-Na alloy

810-813<span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">The concentration fluctuations in the long-wavelength limit, Scc(O), in liquid Li-Na alloy have been studied using the Bhatia-March formula, re-derived for <span style="font-size:13.0pt;mso-bidi-font-size:6.0pt;font-family: HiddenHorzOCR;mso-hansi-font-family:" times="" new="" roman";mso-bidi-font-family:="" hiddenhorzocr"="">binary <span style="font-size:15.0pt;mso-bidi-font-size: 8.0pt;font-family:" times="" new="" roman","serif""="">liquid alloys by Hoshino and Young from the first principle <span style="font-size:13.0pt;mso-bidi-font-size: 6.0pt;font-family:HiddenHorzOCR;mso-hansi-font-family:" times="" new="" roman";="" mso-bidi-font-family:hiddenhorzocr"="">calculations. <span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">The effective inter-atomic pair potentials in the binary liquid alloy are obtained in the pseudopotential formulism. Since Li possesses simple Is electronic structure, the choice of the pseudopotential is critical for it. The effect of the choice of the input parameter, namely core radius. in the Ashcroft pseudopotential and different local field correction to the dielectric function. on the effective pair potential in Li has been studied. It has been found that, the Ashcroft potential with a suitable choice of the core radius still works. The concentration dependence of S<span style="mso-bidi-font-size: 4.0pt;font-family:" arial","sans-serif""="">cc<span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">(0) shows asymmetrical behaviour in qualitative agreement with molecular dynamics results of Mori <span style="font-size:15.5pt;mso-bidi-font-size:8.5pt; font-family:" times="" new="" roman","serif""="">et al. , J Phys Soc Japan, 61 (1992) 1218. The asymmetrical behaviour <span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">indicates the phase separation tendency in the Li-Na alloy. </span

Crystallite size estimation of elemental and composite silver nano-powders using XRD principles

157-161Studies on nanocrystalline materials require an accurate determination of crystallite size as well as the microstrains induced in the material. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are the two well-known techniques for this purpose. Based on XRD principles, numerous approaches such as use of Scherrer equation, integral breath analysis, single-line approximation, Hall-Williamson method, etc have been developed for estimation of crystallite size. Present work deals with a systematic application of Hall-Williamson method for crystallite size estimation of high-energy milled elemental silver and silver-metal oxide (AgMeO) type composite powders and its comparison with Scherrer equation that does not take into account the peak broadening due to strain. The effect of second phase particles on the crystallite size of silver matrix in AgMeO composite is also investigated

Thermodynamic properties of magnetic liquid metals in undercooled region

371-374The experimental study of the thermodynamic properties of liquid metals has been confined usually to the stable liquid range of temperature and pressure. Nevertheless, there is a significant range between the melting point and the glass transition over which the liquid state can exist in a metastable equilibrium provided that crystallization can be avoided. The specific heat of undercooled liquid metals is a very important thermodynamic parameter. Appropriate knowledge of ΔCp¹⁻x i.e. the difference of specific heats of undercooled liquid and the corresponding crystalline solid can be utilized to derive accurate results for the parameters like ΔG, ΔS and ΔH. However, the experimental determination of Cp in undercooled system is difficult due to its metastable nature. Still, it is possible to arrive at an expression for the ΔCp¹⁻x, if the value of ΔCpm i.e. specific heat difference at melting point and the nature of variation of ΔCp¹⁻x in undercooled region can be estimated. In the present paper, ΔG for pure liquid Co and Ni have been estimated using linear temperature dependence of ΔCp in the undercooled region. Further, a general expression has been used which is valid in a large temperature range. The calculated results for ΔG are in excellent agreement with experimental data. Other thermodynamic parameters like ΔS and ΔH are also evaluated

Gibbs free energy difference in bulk metallic glass forming alloys

The Gibbs Free Energy Difference between the solid and liquid phases (DG) is related to nucleation frequency and has played an important role in predicting the glass forming ability (GFA) of multicomponent metallic alloys. This is due to the fact that the maximum energy for nucleus formation i.e. the activation barrier for nucleation has an inverse square relation with DG. The Gibbs Free Energy Difference of three multi-component bulk metallic glasses namely Mg65Cu25Y10, Zr57Cu15.4Ni12.6Al10Nb5 and Zr52.5Cu17.9Ni14.6Al10Ti5 have been evaluated using two new expressions. The results show that the DG values calculated assuming DCp to be constant lie closer to the experimental values for the Mg based system while in the case of two Zr based systems, DG computed using the hyperbolic variation of DCp show improved agreement with the experimental data

Kinetic analysis of crystallization processes in amorphous 2826A (Ni₃₆Fe₃₂Cr₁₄P₁₂ B₆) metallic glass

390-393The crystallization processes of 2826A (Ni₃₆Fe₃₂Cr₁₄P₁₂B₆) metallic glass were investigated using differential scanning calorimetry (DSC) at various heating rates. The thermograms at all scanning rates show two exothermic events. Different methods of kinetic analysis were employed at non-isothermal condition to derive important kinetic parameters namely activation energy of crystallization (E), frequency factor (A) and Avrami exponent (n) for the two exothermic peaks. The obtained values of E for peaks 1 and 2 are 298 and 457 (kJ/mol), respectively. The obtained Avrami exponent values 2.2(peak1) and 1.6(peak2) indicate one-dimensional and surface crystallization, respectively

Isokinetic and isoconversional study of crystallization kinetics of a Zr-based metallic glass

The crystallization kinetics of Zr<SUB>69.5</SUB>Cu<SUB>12</SUB>Ni<SUB>11</SUB>Al<SUB>7.5</SUB> metallic glass is studied under non-isothermal condition using differential scanning calorimetry (DSC). The kinetic parameters, viz. the activation energy (E) and the Avrami exponent (n), for the primary (first) crystallization peak are obtained using the isokinetic and the isoconversional methods. The so-obtained E and n are utilized to derive theoretical normalized heat flow curves through the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The comparison of the experimental and theoretical normalized heat flow curves at different heating rates demonstrates that the completely isokinetic description of the crystallization process is not suitable. On the other hand, the isoconversional methods in combination with the KJMA equation provide better understanding of the kinetics of the crystallization process

Microstructural and thermo analytical investigations of nano-phase formation in Ti<SUB>20</SUB>Zr<SUB>20</SUB>Cu<SUB>60</SUB> alloy

The kinetics of crystallization of Ti20Zr20Cu60 amorphous alloy has been investigated from room temperature to 773 K using differential scanning calorimetry (DSC). The thermogram exhibits two-stage crystallization in this alloy. The values of activation energy of crystallization for the two steps using Kissinger equation are 423.8 and 314.7 kJ/mol respectively. On annealing the specimen to a temperature just before the glass transition temperature, primary crystallization is observed to occur with Cu2Ti orthorhombic and CuZr cubic metastable phases. Further, annealing the specimen to a temperature just below the onset of crystallization obtained from DSC thermogram, tetragonal CuTi3 and cubic Cu5Zr equilibrium phases were found to form as observed from the selected area electron diffraction (SAED) pattern in TEM. Presence of some unidentified d-lines indicated the formation of a metastable Laves phase namely Zr2TiCu3