Nonlinear finite-element analysis of the role of dynamic changes inblood perfusion and optical properties in laser coagulation of tissue

A nonlinear finite-element program was developed to simulate the dynamic evolution of coagulation in tissue considering temperature and damage dependence of both the optical properties and blood perfusion rate. These dynamic parameters were derived based on the Arrhenius rate process formulation of thermal damage and kinetics of vasodilation. Using this nonlinear model, we found that the region of increased blood flow that formed at the periphery of the coagulation region significantly reduces the heat penetration. Moreover, increased scattering in the near-surface region prevents light penetration into the deeper region. Therefore, if the dynamic parameters are ignored, a relatively significant overestimation of the temperature rise occurs in a deeper area resulting in an overestimation in predicted depth of coagulation. Mathematical modeling techniques that simulate laser coagulation may not provide reliable information unless they take into account these dynamic parameters     

Use of spin echo T2 BOLD in assessment of cerebral misery perfusion at 1.5 T

Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have clinical impact in acute stroke imaging. The ability of single spin echo T₂ to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD) contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry and blood relaxation data, T₂ behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying T₂ in a rat model for cerebral misery perfusion. CBF was quantified with the H₂ clearance method. A drop of CBF from 58 ± 8 to 17 ± 3 ml/100 g min in the parieto-frontal cortex caused shortening of T₂. from 66.9 ± 0.4 to 64.6 ± 0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex with CBF of 42 ± 7 ml/100 g min showed no change in T₂. Computer simulations accurately predicted these T₂, responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by T₂ MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER.     

Control of Crystallographic Structure of Aluminum Nitride Films Prepared by Magnetron Sputtering

Aluminum nitride (AlN) films were prepared by using reactive magnetron (RMS). The substrate temperature (T_s) was varied from room temperature to 700°C, and RF power (P _w) from 100 to 250 W, and three different substrate materials (e.g. Si(100), Pt(111)/Si(100) and Al₂O₃(00·1)) were used. The mean free path of the species in the vacuum was controlled to be much shorter than the target-to-substrate distance, so that T_s and P _w have the equivalent effect in affecting the effective thermal energy of the species after landing on the substrate. With these conditions, the film structure was found to cover a broad range, varying from nearly amorphous (na-), polycrystalline (p-), (00·1) texture (t-) and epitaxial (e-) structure. The structural change is supposed to be governed the successive increase in the thermal energy of the species on the substrate. The use of substrate material having lattice matching with the AlN structure further assists the (00·1) preferential growth when the species are mobile enough at the settings of high T_s and P _w.     

Electro-Optic Properties of Heteroepitaxial Pb(Zr,Ti)O3/La0.5Sr0.5CoO3 Film Structures

Vertical ferroelectric Pb(Zr,Ti)O₃ (PZT) 1 μm thick film capacitor was fabricated by pulsed laser deposition technique (PLD) onto conducting La_0.5Sr_0.5CoO₃(LSCO) 100 nm thick bottom electrode on both side polished YAlO₃ + 1% Nd₂O₃ (Nd:YAlO₃) single crystal substrate to operate as a Pockels cell optical modulator. On top of the PZT film, semitransparent 30 nm thick Au electrode was deposited by thermal evaporation. Intensity of the chopped 670 nm polarized laser radiation transmitted through the Au/PZT/LSCO/Nd:YAlO₃ cell was measured at various temperatures and bias voltage applied. Applying 20 V (200 kV/cm) across the capacitive cell, modulation of the transmitted light as high as 3% was achieved while the voltage tunability measured at 1 kHz from C-V characteristics was about 70%. Thermo-optical measurements performed for PZT/Nd:YAlO₃ sample in the range up to 400°C showed the phenomenon of critical opalescence in the vicinity of Curie temperature at 208°C. Optical transmission through the PZT film biased with electric field was studied in the range 400 to 1000 nm. Film thickness, refraction index and absorption coefficient have been determined from the interference pattern observed in the PZT transmission spectrum. A simple model yields the dispersion relation for the electro-optic coefficient.     

Anti-bacterial biofilm activity of magnesium ferrite thin film

ABSTRACT

Thin films of magnesium ferrite (MgFe₂O₄) are synthesized on the glass substrate by using thermal evaporation technique and studied their anti-bacterial biofilm activity against the gram-negative and gram-positive bacterium. The MgFe₂O₄ thin films (100 nm) were prepared at a deposition rate of 10 ± 2 Å/S, followed by annealing at 600°C. The morphological and structural study using scanning electron microscope, X-ray diffraction, and transmission electron microscope reveals crystalline structure of the magnesium ferrite. The model organisms for anti-bacterial biofilm activity were tested with E. coli (gram negative) and S. aureus (gram positive). The E. coli and S. aureus biofilms grown on the glass slides and MgFe₂O₄ coated glass slide were imaged using fluorescent microscope. It is observed that the MgFe₂O₄ coated glass slides exhibit minimum bacterial growth (both negative and positive bacteria) compared to the uncoated glass slide.     

TLM nodal state estimator: An alternative method of initializing a two‐dimensional diffusion model

The transmission line matrix (TLM) method is an established technique for modelling thermal transients in heat transfer systems. However, initial and boundary conditions have always been slightly problematic, particularly when the boundary condition is specified as a temperature (Transmission Line Matrix (TLM) Techniques for Diffusion Applications. Gordon & Breach: London, 1998), for example, when the body of interest is suddenly exposed to a different temperature on its surface. In such a case the modelled solution contains additional dynamics that are associated with the two sub‐meshes in the TLM network and the two timesteps necessary for the temperature change to be fully communicated. These initialization problems are related to the fact that the boundary temperature in merely imposed as a fixed value on the network; the fundamental information‐carrying quantity, on the other hand, is the pulse, the thermal state of the body being represented by the distribution of pulses. Here, we aim to provide an alternative initialization approach, using nodal state estimation to derive pulse distributions from boundary and initial conditions specified by temperature. Consideration is given to the accuracy of the estimator by comparison with the first timestep solution proposed by Enders (Int. J. Numer. Model. 2002; 15 :251–259). Copyright © 2008 John Wiley & Sons, Ltd.     

Wave speeds for a TLM model of moving media

In a companion paper, a transmission line matrix (TLM) scheme was presented for the solution of the 1-D equation of waves in moving media, y_tt+αy_xt+βy_xx=0, describing the superposition of two waves with direction-dependent speeds. The TLM model achieved controlled, direction-dependent wave-speed bias by means of supplementary link lines with notional ‘diodes’. Expressions for wave speed, presented without proof, were verified. Here a proof is presented using a new, time-domain approach. The apparent (direction-dependent) inductance and capacitance as seen by a single wave are first established in a generalized way from the TLM algorithm, from which two wave speeds and impedances are then derived. Copyright © 2002 John Wiley & Sons, Ltd.     

Dimensional soft tissue thermal injury analysis using transmission line matrix (TLM) method

The skin is sensitive to temperature change and the effect may not be significant while the temperature at the surface is below 44°C. However, higher surface temperatures (above 44°C) will further incur time burning and carbonization so that irreversible damage may happen. An investigation of the heating intensity and the duration of the exposure to the heating source suggested that when the surface temperature is greater than 51°C, the exposure time required to destroy the epidermis is so short that trans‐epidermal necrosis may occur. In this paper, we present one‐ and two‐dimensional numerical models based on transmission line matrix (TLM) method for a quantitative prediction of skin burn injury resulting from the exposure of the skin surface to a high temperature heat source. Transient temperatures are numerically estimated by solving the Pennes' bioheat equation, and the damage function denoting the extent of burn injury is calculated using the Arrhenius assumptions for protein damage rate. The TLM model is used to analyse the effects of exposure time and geometrical dimensions of mutlilayered skin, on the transient temperature distribution and damage extension. TLM results showed good agreement with other numerical sources, suggesting that TLM modelling can be used as a tool for an effective thermal diagnostic of burn injuries. Copyright © 2008 John Wiley & Sons, Ltd.     

Capacitor and battery charging from hot/cold air using pyroelectric ceramics

This study is an experimental investigation on thermal energy harvesting using pyroelectric ceramics. Hot and cold air sources were used for generating temperature gradient in PbZr_xTi_1?xO₃ (PZT-5H) ceramics. Four different frequencies of (heating and cooling process) 0.025, 0.05, 0.1 and 0.2 Hz were investigated for optimizing power/voltage output. Maximum output voltage of 2.51 V (across 4.7 μF and 5 MΩ) was achieved at 0.05 Hz frequency with temperature variation between 100°C and 65°C. Furthermore, maximum power density of 2.35 μW/cm³ was obtained at 0.05 Hz across 4.7 μF load capacitor and 5 MΩ load resistance. In addition to this a battery of 7 mAh capacity was charged up to 1.21 V in 55 minutes using continuous heating and cooling processes with frequency of 0.4 Hz.     

TLM for diffusion: consistent first time step. Two‐dimensional case

In initializing a transmission line matrix (TLM) diffusion model it is necessary to consider both initial concentration (temperature) and initial flow. As usual, only one of them is given; an auxiliary formula is necessary to calculate the distribution for the first time step. It has been shown that the standard formula may introduce additional numerical errors (International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1993; 6 :135; International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1993; 6 :161) and that these errors can persist over many time steps. In this paper, we show how an initial modification to the normal TLM algorithm can remove such errors, and we demonstrate the method by applying it to a two‐dimensional TLM heat diffusion model for a copper plate. Copyright © 2002 John Wiley & Sons, Ltd.     

The temperature effect of AT-cut input quartz parameters on QCM effective properties calculated with equivalent circuit models

In what follows, AT-cut quartz crystal microbalance (QCM) effective properties for two commercial QCM substrates, are calculated as a function of temperature, while varying the degree of implementation regarding the temperature dependence of input quartz parameters in the transmission line (TL) model. Results for the effective quartz viscosity, oscillation area and external capacitance, are in qualitative agreement per property, irrespective of the implemented, input quartz parameter set for the calculations. However, the effective quartz thickness accounts for the quartz thermal expansion effect, only when quartz density is temperature adjusted, whereas quantitative deviations in the effective oscillation area, are qualitatively explained in the light of literature correlations, which relate the implemented input quartz parameter set, with inherent QCM energy dissipation metrics, and the magnitude of energy trapping. Moreover, the varying degree of input quartz parameter adjustment with temperature, yields qualitative and quantitative deviations from the expected response, in terms of a QCM quality metric, the C₀/C₁ ratio. Results suggest that the precision in the determination of the static capacitance C₀ and the QCM effective properties incorporated therein, can be improved, with potential improvements in relevant, liquid or gas phase QCM applications.     

Characteristic analysis of a wideband balun transformer having a delay line element for phase compensation

The balanced‐unbalanced transformer (balun) is extensively used in radio communication and measuring instruments. In recent years, with the development of television and portable telephones, wideband transformers tend to be miniaturized. In this paper, the wideband transformer is analyzed in terms of distributed coupled‐line theory. A main result of the analysis is that the balance and unbalance transmission characteristics of the balun are markedly improved in the high‐frequency range by using a delay line element for compensation. If the connection point S_w between the coil winding and delay line is off the ground, the balance transmission band is about doubled in the low‐frequency range. If the point S_wis grounded and if the impedance ratio m² is small, a higher degree of unbalance attenuation can be obtained. Better balance transmission characteristics can be obtained when the matching factor K approaches half the optimum. In addition, we show that an in‐phase or anti‐phase transformer can be made on the basis of our isolation wideband transformer. The equivalent circuits of in‐phase and anti‐phase wideband n:1 transformers are obtained from our theoretical analysis and these can be formed by the same transformer. The transmission characteristics of in‐phase and anti‐phase wideband transformers are analyzed and improved characteristics are obtained in the high‐frequency range. The theoretical and experimental values agree well over the wide frequency range of 100 KHz to 1000 MHz. ©1998 Scripta Technica, Electr Eng Jpn, 126(2): 1–14, 1999     

Non‐unique solutions in drift diffusion modelling of phototransistors

We report non‐unique solutions for the potential in a Drift Diffusion (DD) model of a two terminal phototransistor. These solutions are present under bias without illumination, and persist until high illumination levels. It is well known that the DD equations can yield non‐unique solutions for pn structures which contain three or more junctions and two terminals with applied biases greater than k_BT log 2 where k_BT is the thermal energy at a temperature T, but DD models of phototransistors under illumination have been less well studied. The implicit belief is that one needs to artificially impose a potential in the base of the phototransistor in order to obtain a unique solution. We show here that this is only necessary because of a weakness in the numerical methods used to solve the equations, and describe two methods which circumvent this for which we show that this problem does not occur. These methods are used to investigate the operation of GaAs and In_0·53Ga_0·47As homojunction phototransistors, including the influence of the position of the illumination region and base doping. Copyright © 2000 John Wiley & Sons, Ltd.     

Calculation of phonon spectrum and thermal properties in suspended 〈100〉 In X Ga1?X As nanowires

The phonon spectra in zinc blende InAs, GaAs and their ternary alloy nanowires (NWs) are computed using an enhanced valence force field (EVFF) model. The physical and thermal properties of these nanowires such as sound velocity, elastic constants, specific heat (C _v ), phonon density of states, phonon modes, and the ballistic thermal conductance are explored. The calculated transverse and longitudinal sound velocities in these NWs are ∼25% and 20% smaller compared to the bulk velocities, respectively. The C _v for NWs are about twice as large as the bulk values due to higher surface to volume ratio (SVR) and strong phonon confinement in the nanostructures. The temperature dependent C _v for InAs and GaAs nanowires show a cross-over at 180°K due to higher phonon density in InAs nanowires at lower temperatures. With the phonon spectra and Landauer’s model the ballistic thermal conductance is reported for these III–V NWs. The results in this work demonstrate the potential to engineer the thermal behavior of III–V NWs.     

Nanostructured TiO2-based mixed metal oxides prepared using microemulsions for carbon monoxide detection

Nanostructured powders of Nb-doped TiO₂ (TN) and SnO₂ mixed with Nb-doped TiO₂ in two different atomic ratios—10 to 1 (TSN 101) and 1 to 1 (TSN 11)—were synthesized using the reverse micelle microemulsion of a nonionic surfactant (brine solution/1-hexanol/Triton X-100/cyclohexane). The powders were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Thick films were fabricated for gas sensors and characterized by XRD analysis and field emission scanning electron microscopy (FE-SEM). The effects of the film morphology and firing temperature in the range 650–850 °C on CO sensitivity were studied. The best gas response, expressed as the ratio between the resistance in air and the resistance under gas exposure (R _air/R _gas), was measured for TSN 11 at 11 for 1,000 ppm CO exposure. All types of sensors showed good thermal stability. The electrochemical impedance spectroscopy (EIS) measurements were performed in different gas atmospheres (air, O₂, CO and NO₂) to better understand the electrical properties of the nanostructured mixed metal oxides.     

B1 field-insensitive transformers for RF-safe transmission lines

Objective: Integration of transformers into transmission lines suppresses radiofrequency (RF)-induced heating. New figure-of-eight-shaped transformer coils are compared to conventional loop transformer coils to assess their signal transmission properties and safety profile. Materials and methods: The transmission properties of figure-of-eight-shaped transformers were measured and compared to transformers with loop coils. Experiments to quantify the effect of decoupling from the B₁ field of the MR system were conducted. Temperature measurements were performed to demonstrate the effective reduction of RF-induced heating. The transformers were investigated during active tracking experiments. Results: Coupling to the B₁ field was reduced by 18 dB over conventional loop-shaped transformer coils. MR images showed a significantly reduced artifact for the figure-of-eight- shaped coils generated by local flip-angle amplification. Comparable transmission properties were seen for both transformer types. Temperature measurements showed a maximal temperature increase of 30K/3.5 K for an unsegmented/ segmented cable. With a segmented transmission line a robotic assistance system could be successfully localized using active tracking. Conclusion: The figure-of-eight-shaped transformer design reduces both RF field coupling with the MR system and artifact sizes. Anatomical structure close to the figure-of-eight-shaped transformer may be less obscured as with loop-shaped transformers if these transformers are integrated into e.g. intravascular catheters.     

Use of lossless transmission‐line segments and shunt resistors for TLM diffusion modelling

In diffusion modelling by means of the transmission‐line matrix (TLM) method, a nodal arrangement of using lossless transmission‐line segments and series resistors is almost exclusively adopted and is currently considered as a standard approach. In this paper, the use of shunt resistors instead of series resistors is shown to represent an equally valid configuration. As a starting point, we have derived the telegrapher's equation in its most general form for TLM modelling of diffusion processes. A general algorithm based on the shunt‐resistor TLM model for implementing a numerical solution of the diffusion equation in multiple dimensions is given. Fundamental analysis and calculated examples confirm that the alternative shunt‐resistor configuration does not exhibit the unwanted absorption effects suggested by a recent paper (Internat. J. Numerical Model.: Electronic Networks, Devices and Fields 2002; 15 :261). Copyright © 2003 John Wiley & Sons, Ltd.     

Dispersive TLM Z‐transform model of left‐handed metamaterials

In this paper, a numerical model of electromagnetic left‐handed metamaterials is proposed. The dispersive properties of these materials are accounted for in the time domain by using the transmission‐line matrix method based on Z‐transforms. The close agreements obtained between the analytic and numerical results verify the validity, accuracy and stability of the approach. Copyright © 2013 John Wiley & Sons, Ltd.     

Fabrication of conductive oxide polycrystalline BaPbO3 films by chemical solution deposition and their electrical resistivity

BaPbO₃ films were fabricated by a chemical solution deposition on the SiO₂/Si(100) and MgO(100) substrates followed by a post-deposition annealing at the temperatures between 673 and 1073 K under oxygen flow. Polycrystalline BaPbO₃ films were formed together with secondary phases such as PbO and Pb₃O₄ onto MgO(100) substrates at around 750 K, and the films were crystallized into single phase of BaPbO₃ above 823 K. Endothermic peak in differential thermal analysis due to crystallization of BaPbO₃ was observed at 750 K, which is consistent with crystallization temperature of BaPbO₃ estimated from X-ray diffraction. The electrical resistivity depended on the annealing temperature even in the single phase BaPbO₃ films, the lowest resistivity of 3?×?10^?6 μΩ·m which was comparable to that of bulk BaPbO₃ was achieved at the annealing temperature of 873 K.     

A wave‐front‐time dependent corona model for transmission‐line surge calculations

For transmission‐line surge studies, the inclusion of corona discharge due to high voltage surges is important as well as the inclusion of frequency‐dependent effects. Because the charge‐voltage (q‐v) curve of a lightning surge is different from that of a switching surge, a corona model should reproduce different q‐v curves for different wave‐front times. The present paper proposes a wave‐front time dependent corona model which can express the dependence by a simple calculation procedure as accurately as a rigorous finite‐difference method which requires an enormous calculation time. The simplicity enhances the incorporation of the corona model into a line model, because a large number of models are to be inserted into the line model by discretization. The q‐v curves calculated by the proposed method agrees well with field tests. This paper also proposes an efficient method to deal with nonlinear corona branches in distributed‐parameter line model using the trapezoidal rule of integration and the predictor‐corrector method. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 29–38, 1999