On the possibility of non-invasive multilayer temperature estimation using soft-computing methods

Objective and motivation

This work reports original results on the possibility of non-invasive temperature estimation (NITE) in a multilayered phantom by applying soft-computing methods. The existence of reliable non-invasive temperature estimator models would improve the security and efficacy of thermal therapies. These points would lead to a broader acceptance of this kind of therapies. Several approaches based on medical imaging technologies were proposed, magnetic resonance imaging (MRI) being appointed as the only one to achieve the acceptable temperature resolutions for hyperthermia purposes. However, MRI intrinsic characteristics (e.g., high instrumentation cost) lead us to use backscattered ultrasound (BSU). Among the different BSU features, temporal echo-shifts have received a major attention. These shifts are due to changes of speed-of-sound and expansion of the medium.

Novelty aspects

The originality of this work involves two aspects: the estimator model itself is original (based on soft-computing methods) and the application to temperature estimation in a three-layer phantom is also not reported in literature.

Materials and methods

In this work a three-layer (non-homogeneous) phantom was developed. The two external layers were composed of (in % of weight): 86.5% degassed water, 11% glycerin and 2.5% agar-agar. The intermediate layer was obtained by adding graphite powder in the amount of 2% of the water weight to the above composition. The phantom was developed to have attenuation and speed-of-sound similar to in vivo muscle, according to the literature. BSU signals were collected and cumulative temporal echo-shifts computed. These shifts and the past temperature values were then considered as possible estimators inputs. A soft-computing methodology was applied to look for appropriate multilayered temperature estimators. The methodology involves radial-basis functions neural networks (RBFNN) with structure optimized by the multi-objective genetic algorithm (MOGA). In this work 40 operating conditions were considered, i.e. five 5-mm spaced spatial points and eight therapeutic intensities (I_SATA): 0.3, 0.5, 0.7, 1.0, 1.3, 1.5, 1.7 and . Models were trained and selected to estimate temperature at only four intensities, then during the validation phase, the best-fitted models were analyzed in data collected at the eight intensities. This procedure leads to a more realistic evaluation of the generalisation level of the best-obtained structures.

Results and discussion

At the end of the identification phase, 82 (preferable) estimator models were achieved. The majority of them present an average maximum absolute error (MAE) inferior to 0.5 °C. The best-fitted estimator presents a MAE of only 0.4 °C for both the 40 operating conditions. This means that the gold-standard maximum error (0.5 °C) pointed for hyperthermia was fulfilled independently of the intensity and spatial position considered, showing the improved generalisation capacity of the identified estimator models. As the majority of the preferable estimator models, the best one presents 6 inputs and 11 neurons. In addition to the appropriate error performance, the estimator models present also a reduced computational complexity and then the possibility to be applied in real-time.

Conclusions

A non-invasive temperature estimation model, based on soft-computing technique, was proposed for a three-layered phantom. The best-achieved estimator models presented an appropriate error performance regardless of the spatial point considered (inside or at the interface of the layers) and of the intensity applied. Other methodologies published so far, estimate temperature only in homogeneous media. The main drawback of the proposed methodology is the necessity of a-priory knowledge of the temperature behavior. Data used for training and optimisation should be representative, i.e., they should cover all possible physical situations of the estimation environment.     

Magnetic properties in Fe-doped NiO synthesized by co-precipitation

The magnetic properties of 1.5 at% Fe-doped NiO bulk samples were investigated. The samples were prepared by sintering the corresponding precursor in air at temperatures between 400 and 800 °C for 6 h. The synthesis was by a chemical co-precipitation and post-thermal decomposition method. In order to allow a comparison, a NiO/0.76 at% NiFe₂O₄ mixture was also prepared. The X-ray diffraction pattern shows that the samples that were sintered at 400 and 600 °C remain single phase. As the sintering temperature increased to 800 °C, however, the sample becomes a mixture of NiO and NiFe₂O₄ ferrite phases. The samples were investigated by measuring their magnetization as a function of magnetic field. The samples sintered between 400 and 800 °C and the one mixed directly with NiFe₂O₄ nanoparticles show a coercivity value of H_c≈200, 325, 350 and 110 Oe, respectively. The magnetic properties of the samples depend strongly on the sintering temperature. Simultaneously, the field-cooling hysteresis loop shift also observed after cooling the sample sintered at 600 °C to low temperature suggests the possibility of the existence of a ferromagnetic/antiferromagnetic exchange coupling.     

Broadband Er-Yb co-doped superfluorescent fiber source

In this paper, extensive experimental results on broad-band double cladding Er³⁺-Yb³⁺ co-doped superfluorescent fiber sources (SFSs), characterizing their output power, mean wavelength, and bandwidth (BW) stability with variations of pump power, pump wavelength, and fiber temperature, have been reported. For a 55-cm fiber, SFS power from 3.7755 (maximum BW condition of more than 80 nm) to 9.1837 mW (maximum power condition, BW is about 34 nm) has been achieved. The SFS mean wavelength dependence on pump wavelength is highly pump temperature sensitive, and can be reduced to zero in a chosen pump temperature field. The intrinsic variation of the SFS mean wavelength λ_m with fiber temperature is also measured, and a linear variation from 15 to 45 °C with a slop of −0.053 nm/°C for L_f = 100 cm and −0.04 nm/°C for L_f = 55 cm is found.     

The effects of annealing on Au/pyronine-B/MD n-InP Schottky structure

Thin film of non-polymeric organic compound pyronine-B has been fabricated on moderately doped (MD) n-InP substrate as an interfacial layer using spin coating technique for the electronic modification of Au/MD n-InP Schottky contact. The electrical characteristics have been determined at room temperature. The barrier height and the ideality factor values for Au/pyronine-B/MD n-InP Schottky diode have been obtained from the forward bias I-V characteristics at room temperature as 0.60 eV and 1.041; 0.571 and 1.253 eV after annealing at 100 and 250 °C, respectively. An increase in annealing temperature at the Au/n-InP Schottky junction is shown to increase the reverse bias leakage current by about one order of magnitude and decrease the Schottky barrier height by 0.027 eV. Furthermore, the barrier height values for the Au/pyronine-B/MD n-InP Schottky diode have also been obtained from the C-V characteristics at room temperature as 1.001 and 0.709 eV after annealing at 100 and 250 °C, respectively. Finally, it was seen that the diode parameters changed with increase in the annealing temperature.     

Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

NbN_x films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 °C, on the preferred orientation, phase, and surface properties of NbN_x films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN_x films. For a substrate temperature up to 450 °C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650−850 °C, mix of cubic δ-NbN and hexagonal phases (β-Nb₂N + δ′-NbN) were formed. Films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperature above 850 °C. The c/a ratio of β-Nb₂N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN_x films increased as the temperature was raised from 450 to 850 °C.     

Enhanced ferroelectric properties of vanadium doped bismuth titanate (BTV) thin films grown by pulsed laser ablation technique

Bi_3.99Ti_2.97V_0.03O₁₂ (BTV) thin films were grown by pulsed laser deposition at substrate temperatures ranging between 650 and 750 °C. The structural phase, and orientation of the deposited films were investigated in order to understand the effect of the deposition parameters on the properties of the BTV films. As the substrate temperature was increased to 700 °C, the films started showing a tendency of assuming a c-axis preferred orientation, while at lower temperatures polycrystalline films were formed. The Au/BTV/Pt capacitor showed an interesting dependence of the remnant polarization (P_r) as well as dc leakage current values on the growth temperature. The film deposited at 675 °C showed a very large 2P_r of 42 μC cm⁻², which is the largest for BTV thin films among the values reported so far.     

A performance analysis of echographic ultrasonic techniques for non-invasive temperature estimation in hyperthermia range using phantoms with scatterers

Optimization of efficiency in hyperthermia requires a precise and non-invasive estimation of internal distribution of temperature. Although there are several research trends for ultrasonic temperature estimation, efficient equipments for its use in the clinical practice are not still available. The main objective of this work was to research about the limitations and potential improvements of previously reported signal processing options in order to identify research efforts to facilitate their future clinical use as a thermal estimator.In this document, we have a critical analysis of potential performance of previous ultrasonic research trends for temperature estimation inside materials, using different processing techniques proposed in frequency, time and phase domains. It was carried out in phantom with scatterers, assessing at their specific applicability, linearity and limitations in hyperthermia range. Three complementary evaluation indexes: technique robustness, Mat-lab processing time and temperature resolution, with specific application protocols, were defined and employed for a comparative quantification of the behavior of the techniques. The average increment per °C and mm was identified for each technique (3 KHz/°C in the frequency analysis, 0.02 rad/°C in the phase domain, while increments in the time domain of only 1.6 ns/°C were found). Their linearity with temperature rising was measured using linear and quadratic regressions and they were correlated with the obtained data.New improvements in time and frequency signal processing in order to reveal the potential thermal and spatial resolutions of these techniques are proposed and their subsequent improved estimation results are shown for simulated and measured A-scans registers. As an example of these processing novelties, an excellent potential resolution of 0.12 °C into hyperthermia range, with near-to-linear frequency dependence, could be achieved.Specifically defined “numerical” and physical multi-scatter phantoms are described, which mimic ultrasound velocity in tissues of about 1560 m/s @ 35 °C and have a quasi-uniform internal scattering structure designed to assure standard signal patterns adequate for processing comparisons in the same time and sound velocity conditions for all the techniques analyzed, and to obtain easily repeatable multi-pulse echo-patterns.A perfect lineal dependence (100% of correlation coefficient) between the unitary average increment measured by each technique and temperature rising was observed while working with simulated A-scan registers, where all the parameters are under an accurate control. Nevertheless a very small quadratic tendency appeared in the results obtained from experimental echo registers, which are more similar to a real tissues case. It would be an interesting future work to analyze the behavior of these techniques in real tissues in order to confirm or reject this light quadratic tendency.Finally, new methods were detailed and applied in order to precisely quantify the advantages of each estimation technique; their respective intrinsic limitations were also underlined.     

Immiscibility in the NiFe2O4-NiCr2O4 spinel binary

The solid solution behavior of the Ni(Fe_1−nCr_n)₂O₄ spinel binary is investigated in the temperature range 400-1200 °C. Non-ideal solution behavior, as exhibited by non-linear changes in lattice parameter with changes in n, is observed in a series of single-phase solids air-cooled from 1200 °C. Air-annealing for 1 year at 600 °C resulted in partial phase separation in a spinel binary having n=0.5. Spinel crystals grown from NiO, Fe₂O₃ and Cr₂O₃ reactants, mixed to give NiCrFeO₄, by Ostwald ripening in a molten salt solvent, exhibited single-phase stability down to about 750 °C (the estimated consolute solution temperature, T_cs). A solvus exists below T_cs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n values of 0.2 and 0.7 at 300 °C. The extrapolated solvus is shown to be consistent with that predicted using a primitive regular solution model in which free energies of mixing are determined entirely from changes in configurational entropy at room temperature.     

The influence of substrate temperature and annealing on the properties of pulsed laser-deposited YIG films on fused quartz substrate

Yttrium iron garnet (YIG) thin films were deposited on fused quartz substrate at different substrate temperatures (T_s) varying from room temperature (RT) to 850 °C using pulsed laser deposition (PLD) technique. All the films in the as-deposited state were X-ray amorphous and non-magnetic at RT. The film deposited at RT after annealing at temperatures T_a?700 °C showed both X-ray peaks and the magnetic order. The films deposited at higher T_s (500–850 °C) and then annealed at 700 °C resulted in better-quality films with higher 4πM_s value. The highest value of magnetization was for the sample deposited at 850 °C and annealed at 700 °C, which is 68% of the bulk 4πM_s value.     

Investigation of Ni/Ta contacts on 4H silicon carbide upon thermal annealing

Nickel and Tantalum thin films with 3:5 thickness ratios were deposited in succession onto 4H-SiC substrate at room temperature. The samples were then heated in situ in vacuum at 650, 800 or 950 °C for 30 min. Glancing angle X-ray diffraction (XRD), Auger electron spectroscopy (AES) and current-voltage (I-V) technique were used for characterising the interfacial reactions and electrical properties. Amorphous Ni-Ta can be formed by solid-state reaction at 650 °C. The minor dissolved Ni in the Ta metal promotes the reaction between Ta and SiC. With increasing annealing temperature up to 950 °C, the dominant carbide changes from Ta₂C to TaC and a layer structure is developed. Electrical measurements show that ohmic contact is formed after annealing at or above 800 °C.     

Sintering temperature dependence of room temperature magnetic and dielectric properties of Co0.5Zn0.5Fe2O4 prepared using mechanically alloyed nanoparticles

Co_0.5Zn_0.5Fe₂O₄ nanoparticles were prepared using mechanical alloying (MA) and sintering. The crystallite size, coercivity, retentivity and saturation magnetization were also measured. The frequency dependence of dielectric and the magnetic parameters, namely, real permittivity ε′, loss tanget tan δ, real permeability μ′ and loss factor μ″ were measured at room temperature for samples sintered from 600 to 1000 °C, in the frequency range 10 MHz to 1.0 GHz. The results show that the crystallite size of the resulting products ranges between 16 and 67 nm for as-milled sample and the sample sintered at 1000 °C, respectively. The sample sintered at 1000 °C, measured at room temperature exhibited a saturation magnetization of 37 emu g⁻¹. The values of permittivity remain constant within the measured frequency, but vary with sintering temperature. The permeability values, on the other hand however vary with both the sintering temperature and the frequency, thus, the absolute value of the permeability decreased after the natural resonance frequency.     

Removal of chloridazon by natural and ammonium kerolite samples

The adsorption of chloridazon (5-amino-4-chloro-2-phenylpyridazin-3(2H)-one) on natural and ammonium kerolite samples from aqueous solution at 10, 25 and 40 °C has been studied by using batch experiments. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (X_m) of the samples; two straight lines were obtained, which indicates that the adsorption process takes place in two different stages. Values for X_m1 (first stage) ranged from 1.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 5.1 × 10⁻² mol kg⁻¹ for ammonium kerolite at 10 °C and the values for X_m2 (second stage) ranged from 9.1 × 10⁻² mol kg⁻¹ for natural kerolite at 40 °C up to 14 × 10⁻² mol kg⁻¹ for natural kerolite at 10 °C. The adsorption experiments showed on the one hand, that the ammonium kerolite is more effective than natural kerolite to adsorb chloridazon in the range of temperature studied and on the other hand, that the lower temperature, the more effective the adsorption of chloridazon on the adsorbents studied.     

Early-stage ordering in in-situ annealed Fe51Pt49 films

We evidenced an early-stage ordering (ESO) in Fe₅₁Pt₄₉ film before the appearance of superlattice diffraction (long-range-order, LRO) using 40-nm-thick films prepared by magnetron sputtering onto quartz substrate. The appearance of L1₀ phase for samples deposited at substrate temperatures (T_s) 400 °C and higher was verified by X-ray diffraction. Surface roughness of Fe₅₁Pt₄₉ films, obtained via X-ray specular reflectivity with computational fitting, increases from 3.8 to 11 Å as T_s is increased from 25 to 275 °C. As further increase of T_s to 375 °C, the roughness drops to 3.2 Å and then increases again to 38 Å with T_s up to 700 °C. Measurement on residual strain demonstrates that it is initially compressive at T_s<400 °C. Thereafter the strain transfers to a tensile one and increases in magnitude as increasing T_s up to 700 °C corresponding to LRO transformation. Local atomic rearrangement is observed for samples deposited at T_s>250 °C by using extended X-ray absorption fine structure. Coercivity of films increases from 10 to 460 Oe as T_s increase from 25 to 375 °C (ESO) and then from 460 to 10,700 Oe with T_s 375-700 °C (normal LRO). The worked out quantitative estimation of ESO engages with that of LRO before T_s 400 °C.     

In situ HCl etching of Si for the elaboration of locally misorientated surfaces

We have studied the in situ HCl etching of Si active areas on patterned wafers. After some in situ HCl etching at 20 Torr of Si(1 0 0), we have locally obtained 2 μm long areas with misorientation angles around 4.5° towards 〈1 1 0〉. Furthermore, we have evidenced a recess shape transition from convex (T ≤ 865 °C) to concave (T ≥ 895 °C) as the etch temperature increases, with a nearly flat surface with no facets at T = 880 °C. The morphology of the etched structures at a given time, temperature and PHCl/PH₂ ratio will be a function of the slope lengths and the pattern dimensions. Different kinds of surfaces (rounded areas, facets) were obtained in 3.5 μm × 3.5 μm Si windows after HCl etching at 850 °C during 300 s, depending on the stress within. Thermal oxidations can indeed be used to increase by 65 MPa up to 110 MPa the compressive stress in those Si windows which are bordered by SiO₂ shallow trench isolation. An increase of the misorientation angle from 4.5° up to 6° occurred after the above-mentioned HCl etch when switching from conventional to highly strained Si windows. For the shortest etching times studied here (150 s), a selective etching of 3.5 μm × 3.5 μm Si windows edges is responsible for the misorientation. The etch is then more uniform. Stress gradients might consequently be one of the main misorientation causes. We have also probed the influence of the shallow trench isolation (STI) thickness on the misorientation. A morphological difference before HCl etching has been shown to be responsible for the transition from sloped to rounded areas. A local loading effect may prevail in this case.     

On the thermal stability of Co2Z hexagonal ferrites for low-temperature ceramic cofiring technologies

Co₂Z hexaferrite Ba₃Co₂Fe₂₄O₄₁ was prepared by a mixed oxalate co-precipitation route and the standard ceramic technology. XRD studies show that at T<1300 °C different ferrite phases coexist with the M-type hexaferrite as majority phase between 1000 and 1100 °C and the Y-type ferrite at 1230 °C. The Z-type material has its stability interval between 1300 and 1350 °C. Both synthesis routes result in almost single-phase Z-type ferrites after calcination at 1330 °C, intermediate grinding and sintering at 1330 °C. The permeability of Co₂Z-type ferrite of about μ=20 is stable up to several 100 MHz, with maximum losses μ′′ around 700 MHz. Addition of 3 wt% Bi₂O₃ as sintering aid shifts the temperature of maximum shrinkage down to 950 °C and enables sintering of Z-type ferrite powders at 950 °C. However, the permeability is reduced to μ=3. It is shown here for the first time that Co₂Z ferrite is not stable under these conditions; partial thermal decomposition into other hexagonal ferrites is found by XRD studies. This is accompanied by a significant decrease of permeability. This shows that Co₂Z hexagonal ferrite is not suitable for the fabrication of multilayer inductors for high-frequency applications via the low-temperature ceramic cofiring technology since the material is not compatible with the typical process cofiring temperature of 950 °C.     

Unidirectional variation of lattice constants of Al-N-codoped ZnO films by RF magnetron sputtering

Al-N-codoped ZnO films were fabricated by RF magnetron sputtering in the ambient of N₂ and O₂ on silicon (1 0 0) and homo-buffer layer, subsequently, annealed in O₂ at low pressure. X-ray diffraction (XRD) spectra show that as-grown and 600 °C annealed films grown by codoping method are prolonged along crystal c-axis. However, they are not prolonged in (0 0 1) plane vertical to c-axis. The films annealed at 800 °C are not prolonged in any directions. Codoping makes ZnO films unidirectional variation. X-ray photoelectron spectroscopy (XPS) shows that Al content hardly varies and N escapes with increasing annealing temperature from 600 °C to 800 °C.     

Effects of thermo-hygro-mechanical densification on the surface characteristics of trembling aspen and hybrid poplar wood veneers

The effect of thermo-hygro-mechanical (THM) densification temperature on the surface color, roughness, wettability, and chemical composition of trembling aspen (Populus tremuloides) and hybrid poplar (Populus maximowiczii × P. balsamifera) veneers was investigated. Veneers were subjected to four THM densification temperatures (160 °C, 180 °C, 200 °C, and 220 °C). Veneer color darkened with increasing THM densification temperature. Surface roughness decreased between 160 °C and 200 °C. Wettability decreased after THM densification, but no significant difference was found between treated specimens. ATR-FTIR and XPS results confirmed that THM densification caused major chemical changes in veneer surfaces, and more pronounced at temperatures higher than 160 °C.     

Synthesis and magnetic study on Mg-substituted Li-Mn spinel oxides

LiMn_2−xMg_xO₄ (X<0.5) cubic spinel oxide was synthesized by the sol-gel technique using Li-nitrate, Mn-acetate and Mg-acetate salts. The gel precursors were decomposed at 300 °C in air and then annealed at temperatures ranging from 500 to 850 °C in an oxygen flow. For a fixed annealing temperature of 700 °C, the lattice constant decreased with an increase in the substitution degree X and a discontinuity was found around X=0.3. With a further increase in X>0.3, the space group of the crystal structure was converted from Fd3m to P4₃32 by the cation ordering in the octahedral site. The low-temperature magnetization increased with X, and the Weiss constant moved in the positive direction and changed its sign from negative to positive around X=0.3. In the case of X=0.5, all the specimens showed P4₃32 structure and ferromagnetic character. The maximum Curie temperature (T_c=23 K) and the maximum magnetization (M_s=4.68 μ_B per the chemical formula unit) were attained simultaneously for the specimen obtained around 700 °C. The Mn valence state was sensitive not only to the substitution but also to the preparation conditions. Hence, it was possible to explain these variations by considering the magnetic interactions between transition metal ions.     

Intermediate-temperature polymorphic phase transition in KH2PO4: A synchrotron X-ray diffraction study

We have used synchrotron X-ray diffraction to investigate the structural and chemical changes undergone by polycrystalline KH₂PO₄ (KDP) upon heating within the 30-250 °C temperature interval. Our data show evidence of a polymorphic transition at T∼190 °C from the room-temperature tetragonal KDP phase to a new intermediate-temperature monoclinic KDP modification (spacegroup P2₁/m and lattice parameters a=7.590, b=6.209, c=4.530 Å, and β=107.36°). The monoclinic RDP polymorph remains stable upon further heating to 235 °C, and is isomorphic to its RbH₂PO₄ and CsH₂PO₄ counterparts.     

Comparison of annealing effects on Zn-doped GaMnAs and undoped GaMnAs epilayers

To compare the annealing effects on GaMnAs-doped with Zn (GaMnAs:Zn) and undoped GaMnAs (u-GaMnAs) epilayers, we grew GaMnAs thin films at 200 °C by molecular beam epitaxy (MBE) on GaAs substrates, and they were annealed at temperatures ranging from 220 °C to 380 °C for 100 min in air. These epilayers were characterized by high-resolution X-ray diffraction (XRD), electrical, and magnetic measurements. A maximum resistivity at temperatures T_m close to the Curie temperatures T_c was observed from the measurement of the temperature-dependent resistivity ρ(T) for both the GaMnAs:Zn and the u-GaMnAs samples. We found, however, that the maximum temperature T_m observed for GaMnAs:Zn epilayers increased with increasing annealing temperature, which was different from the result with the u-GaMnAs epilayers. The formation of GaAs:Zn and MnAs or Mn-Zn-As complexes with increasing annealing temperature is most likely responsible for the differences in appearance.