Silica from Rice as New Drug Delivery Systems

The pharmaceutical industry has seen an increased need of carriers or excipients design that allows the controlled release of a drug in the human body. The main role of an excipient is to carry the drug for its administration under therapeutic index. Among the new generation of excipients, the ordered mesoporous silica (MS) presents several advantages, such as excellent biocompatibility, good adsorption capacity, and precise control in the drug delivery. However, the high cost of synthesis of mesoporous silica restricts its use to industrial applications; therefore, a low-cost procedure is necessary for widespread use. Biogenic silica from rice husk (SiO2-rice) could be a new choice as a drug delivery system. This silica is obtained from an acid leaching of rice husk followed by calcinations processes at low temperatures; these conditions produce silica with good adsorption properties, similar to those of MS. In consequence, the excipient behavior of SiO2-rice was assessed using folic acid as the model drug, displaying an 18.5% of absorption in the SiO2-rice pores, while MS absorbed around 19%. The drug release profiles were similar for both the silicas, suggesting that SiO2-rice could be a low-cost, similar yield excipient for drugs similar to folic acid

Critical behavior of the ferromagnetic transition in GdSc(Si,Ge) intermetallic compounds

A complete study on the critical behavior of the paramagnetic to ferromagnetic transition in intermetallics GdScSi, GdScGe, GdSc(Si0.5Ge0.5) and Gd(Sc0.5Ti0.5)Ge has been carried out by means of magnetic as well as calorimetric measurements, using a high resolution ac photopyroelectric technique. The critical exponents alfa, beta, gamma, delta and the ratio of the critical coefficients A+/A- have been independently obtained for the four samples. It has been proved that the magnetic interactions are short range as the values of the critical parameters correspond to the 3D-Heisenberg class, stating an isotropic ordering of the Gd spins. In some cases, there are small deviations of some of the critical parameters from the theoretical values which have been discussed on the basis of the variation of the d states hybridization between the rare earth and the transition metal, as well as the presence of small magnetocrystalline anisotropies arising from spin-orbit coupling effects.This work has been supported by Universidad del País Vasco UPV/EHU (GIU16/93)

Laser-spot step-heating thermography to measure the thermal diffusivity of solids

In this work we show that laser-spot step-heating thermography allows measuring the thermal diffusivity of solids accurately. It consists in illuminating the sample surface with a continuous-wave focused laser spot and recording the time evolution of the surface temperature with an infrared camera. The inherent noise associated to time domain measurements is reduced by applying a very simple image processing procedure. The methodology has been tested on reference samples. Unlike laser spot lock-in (or pulsed) thermography, a step-heating thermography device can be easily put together combining a low-end laser and an entry level IR camera.This work has been supported by Ministerio de Ciencia e Innovación (PID2019-104347RB-I00, AEI/FEDER, UE), by Gobierno Vasco (PIBA 2018–15) and by Universidad del País Vasco UPV/EHU (GIU19/058)

Study of the magnetocaloric effect in intermetallics RTX (R = Nd, Gd; T = Sc, Ti ; X = Si, Ge)

A detailed study of the magnetocaloric properties of six compounds of the intermetallic family RTX (R = Nd, Gd; T = Sc, Ti ; X = Si, Ge) has been undertaken: NdScSi, NdScGe, GdScSi, GdScGe, GdSc(Si0.5Ge0.5) and Gd(Sc0.5Ti0.5)Ge. The magnetic entropy changes at the Curie temperature TC and the refrigerant capacities signal that they are competitive magnetocaloric materials, showing that an improvement can be obtained by tuning the composition, as Gd(Sc0.5Ti0.5)Ge presents the best properties. These magnetocaloric variables fulfill the scaling equations with the critical parameters corresponding to the universality classes to which the ferromagnetic transitions belong (3D-XY, 3D-Heisenberg, Mean field). For each compound, a universal curve has been found for the rescaled magnetic entropy changes obtained at different applied fields, whose behavior at temperatures below TC indicate the relevance of taking into account the demagnetization field. Finally, it has been demonstrated that the rescaled magnetic entropy changes for the compounds which share the same universality class collapse onto a single universal curve.This work has been supported by Universidad del País Vasco UPV/EHU (GIU16/93)

Determining the thermal diffusivity and the principal directions on anisotropic moving samples with laser-spot thermography

We propose a method to measure the thermal diffusivity of (an)isotropic samples moving at constant speed using laser-spot thermography with continuous illumination. The method does not require previous knowledge of the principal directions and can be applied whichever their orientation with respect to the direction of motion. We demonstrate analytically that any radial temperature profile crossing the center of the laser spot fulfills a linear relation with the distance to the laser spot, whose slope depends on the thermal diffusivity, on the sample speed and on the angle of the profile with respect the sample motion. A multi-linear fitting of the temperature profiles at several angles provides a reliable method to obtain the thermal diffusivity. Experiments performed on reference samples, both isotropic and anisotropic, con- firm the validity of the method to provide accurate and precise thermal diffusivity values and to identify the thermal principal directions.This work has been supported by Ministerio de Ciencia e Innovación (PID2019-104347RB-I00, AEI/FEDER, UE), by Gobierno Vasco (PIBA 2018-15) and by Universidad del País Vasco UPV/EHU (GIU19/058)

Characterizing the shape and heat production of open vertical cracks in burst vibrothermography experiments

We present a quantitative characterization of the heat flux distribution generated at open vertical cracks in burstvibrothermography experiments. We use a stabilized inversion algorithm that is able to retrieve both homogeneous and inhomogeneous fluxes from surface temperature data generated by open cracks. The performance of the algorithm is checked by inverting both synthetic data with added random noise and experimental data taken on samples containing calibrated heat sources. The results show that it is possible to characterize simultaneously the geometry and the absolute value of the heat flux distribution generated at the crack and therefore, the total emitted thermal power.This work has been supported by Ministerio de Economía y Competitividad (DPI2016-77719-R, AEI/FEDER, UE), by Universidad del País Vasco UPV/EHU (GIU16/33) and by Conacyt (Beca Mixta 2017 Movilidad en el extranjero)

Critical behavior study of magnetic transitions in Dy3Co single crystals

An ac photopyroelectric calorimeter has been used to study the critical behaviour of the magnetic transitions in Dy3Co measuring thermal diffusivity, specific heat and thermal conductivity, at low temperature. There are two phase transitions, both of which present singularities in the three variables. The antiferromagnetic to paramagnetic phase transition at 42 K complies with the short range, isotropic universality class, 3D-Heisenberg (alfaexp = -0.133 for specific heat, bexp = -0.145 for thermal diffusivity, alfatheor = btheor = -0.13). In the case of the lower transition where there is a rearrangement of the antiferromagnetic spin ordering at 32 K the critical behavior shows a deviation from isotropy. These results are linked to magnetic measurements already found in literature.This work has been supported by Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU-GIU16/93) and also partially supported by FASO of Russia (themes No 01201463328 and 01201463334)

Peculiar magnetocaloric properties and critical behavior in antiferromagnetic Tb3Ni with complex magnetic structure

A study on the magnetocaloric properties of a Tb3Ni single crystal (which crystallizes in the orthorhombic Pnma space group) has been undertaken and combined with the study of the character and critical behavior of its magnetic transitions. It presents two important magnetocaloric effects in the temperature range 3–90 K due to the richness and variety of its temperature and magnetic field induced phase transitions. There is a conventional (direct) magnetocaloric effect with a maximum at 65 K and very competitive properties:  = 16.6 J/kgK, RCFWHM = 432 J/kg, with a 50 K span, for μ0ΔH = 5 T, which is due to the transition from a magnetically ordered state to the paramagnetic (PM) state with a combined antiferromagnetic to ferromagnetic (AFM-FM) metamagnetic transition. Besides, it also presents an inverse magnetocaloric effect at very low temperature for which the presence of metamagnetic transitions between AFM and FM states is responsible (=19.9 J/kgK, RCFWHM = 245 J/kg, with a 15 K span, for μ0ΔH = 5 T). At low field (<2 T), the character of the AFM-PM transition which takes place at ≈ 61 K has been well established to be second order and governed by short range order interactions, as the critical parameters α, A+/A- obtained from the specific heat at μ0H = 0 T point to the 3D-Heisenberg universality class. Conversely, the metamagnetic transitions between AFM and FM states, which appear for magnetic fields higher than 2 T, have a first order character, as proved by the magnetization behavior as a function of field and temperature. These properties make this material extremely interesting for magnetic refrigeration applications in the gas liquefaction range 4–77 K.This work has been supported by Universidad del País Vasco UPV/EHU (GIU16/93). A. Herrero thanks the Department of Education of the Basque Government as grantee of the programme “Programa Predoctoral de Formación de Personal Investigador No Doctor”. The authors thank for technical and human support provided by SGIker of UPV/EHU. This work was also supported by Russian Science Foundation (project No. 18-72-10022)

Vertical Cracks Excited in Lock-in Vibrothermography Experiments: Identification of Open and Inhomogeneous Heat Fluxes

Lock-in vibrothermography has proven to be very useful to characterizing kissing cracks producing ideal, homogeneous, and compact heat sources. Here, we approach real situations by addressing the characterization of non-compact (strip-shaped) heat sources produced by open cracks and inhomogeneous fluxes. We propose combining lock-in vibrothermography data at several modulation frequencies in order to gather penetration and precision data. The approach consists in inverting surface temperature amplitude and phase data by means of a least-squares minimization algorithm without previous knowledge of the geometry of the heat source, only assuming knowledge of the vertical plane where it is confined. We propose a methodology to solve this ill-posed inverse problem by including in the objective function penalty terms based on the expected properties of the solution. These terms are described in a comprehensive and intuitive manner. Inversions of synthetic data show that the geometry of non-compact heat sources is identified correctly and that the contours are rounded due to the penalization. Inhomogeneous smoothly varying fluxes are also qualitatively retrieved, but steep variations of the flux are hard to recover. These findings are confirmed by inversions of experimental data taken on calibrated samples. The proposed methodology is capable of identifying heat sources generated in lock-in vibrothermography experiments.This research is part of a project with grant number PID2019-104347RB-I00 funded by MCIN/AEI/10.13039/501100011033. The research was also funded by Universidad del País Vasco, UPV/EHU, grant number GIU19/058

Measuring the thermal resistance of vertical interfaces separating two different media using infrared thermography

We propose a method to measure the thermal contact resistance at the vertical interface between two materials using lock-in infrared thermography with laser spot heating. We found an analytical expression for the surface temperature of the two media when one of them is illuminated by a modulated and focused laser spot. We analyzed how the thermal conductivities of the two-media affect the sensitivity to the interface thermal resistance. We concluded that the key factor is the product of both thermal conductivities: the higher this product, the lower the thermal resistance that can be detected. The surface temperature of two media with calibrated interface thickness is measured using an infrared camera. The thermal resistance of the interface is obtained by fitting the surface temperature to its analytical expression. The good agreement between the nominal and retrieved width of the interface confirm the validity of the model.This work has been supported by Ministerio de Economía y Competitividad (DPI2016-77719-R, AEI/FEDER, UE), by Universidad del País Vasco UPV/EHU (GIU16/33) and by Conacyt (Beca Mixta 2017 Movilidad en el extranjero)