Canadian Field Soils IV: Modeling Thermal Conductivity at Dryness and Saturation

The thermal conductivity data of 40 Canadian soils at dryness \((\lambda _{\mathrm{dry}})\) and at full saturation \((\lambda _{\mathrm{sat}})\) were used to verify 13 predictive models, i.e., four mechanistic, four semi-empirical and five empirical equations. The performance of each model, for \(\lambda _{\mathrm{dry}}\) and \(\lambda _{\mathrm{sat}}\), was evaluated using a standard deviation (SD) formula. Among the mechanistic models applied to dry soils, the closest \(\lambda _{\mathrm{dry}}\) estimates were obtained by MaxRTCM \((\textit{SD} = \pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})\), followed by de Vries and a series-parallel model (\(\hbox {S-}{\vert }{\vert }\)). Among the semi-empirical equations (deVries-ave, Advanced Geometric Mean Model (A-GMM), Chaudhary and Bhandari (C–B) and Chen’s equation), the closest \(\lambda _{\mathrm{dry}}\) estimates were obtained by the C–B model \((\pm ~0.022\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})\). Among the empirical equations, the top \(\lambda _{\mathrm{dry}}\) estimates were given by CDry-40 \((\pm ~0.021\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}\) and \(\pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}\) for18-coarse and 22-fine soils, respectively). In addition, \(\lambda _{\mathrm{dry}}\) and \(\lambda _{\mathrm{sat}}\) models were applied to the \(\lambda _{\mathrm{sat}}\) database of 21 other soils. From all the models tested, only the maxRTCM and the CDry-40 models provided the closest \(\lambda _{\mathrm{dry}}\) estimates for the 40 Canadian soils as well as the 21 soils. The best \(\lambda _{\mathrm{sat}}\) estimates for the 40-Canadian soils and the 21 soils were given by the A-GMM and the \(\hbox {S-}{\vert }{\vert }\) model.     

Electrochemical impedance studies of capacity fading of electrodeposited ZnO conversion anodes in Li-ion battery

Electrodeposited ZnO coatings suffer severe capacity fading when used as conversion anodes in sealed Li cells. Capacity fading is attributed to (i) the large charge transfer resistance, \(R_{\mathrm{ct}}\) (300–700 \(\Omega \)) and (ii) the low \(\hbox {Li}^{+}\) ion diffusion coefficient, \(D_{\mathrm{Li}}^{+}\ (10^{-15}\) to \(10^{-13}\hbox { cm}^{2}\hbox { s}^{-1})\). The measured value of \(R_{\mathrm{ct}}\) is nearly 10 times higher and \(D_{\mathrm{Li}}^{+}\) 10–100 times lower than the corresponding values for \(\hbox {Cu}_{2}\hbox {O}\), which delivers a stable reversible capacity.     

Measurement of the Water Relaxation Time of $${\upvarepsilon }$$-Polylysine Aqueous Solutions

\({\upvarepsilon }\)-Polylysine is an effective food preservative. In this paper, the \({\upbeta }\)-relaxation time of \({\upvarepsilon }\)-polylysine aqueous solutions, which represents the rotational speed of a single water molecule, was measured by broadband dielectric spectroscopy at various temperatures and concentrations. The broadband dielectric spectrum of each sample containing water ranging from 35 wt% to 75 wt% at temperatures ranging from \(0\,^{\circ }\hbox {C}\) to \(25\,^{\circ }\hbox {C}\) was measured using a co-axial semirigid cable probe. The measured dielectric spectra of the samples were composed of several Debye relaxation peaks, including a shortest single molecular rotational relaxation time of water, the \({\upbeta }\)-relaxation time, longer than that of pure water. This result represents that \({\upvarepsilon }\)-polylysine suppresses the molecular kinetics of water. It is also found that the \({\upbeta }\)-relaxation time of an \({\upvarepsilon }\)-polylysine solution that contained more than 35 wt% water showed a typical Arrhenius plot in the temperature range from \(0\,^{\circ }\hbox {C}\) to \(25\,^{\circ }\hbox {C}\). The activation energy of each sample depends on the water content ratio of the sample. As indicated by its long \({\upbeta }\)-relaxation time, \({\upvarepsilon }\)-polylysine is expected to possess high abilities of suppressing freezing and ice coarsening.     

Estimating the Kinematic Viscosity of Petroleum Fractions

Kinematic viscosity correlation has been developed for liquid petroleum fractions at 37.78\(\,^{\circ }\hbox {C}\) and \(98.89\,^{\circ }\hbox {C}\) (100 and \(210^{\circ }\hbox {F})\) standard temperatures using a large variety of experimental data. The only required inputs are the specific gravity and the average boiling point temperature. The accuracy of the correlation was compared with several other correlations available in the literature. The proposed correlations proved to be more accurate in predicting the viscosity at 37.78\(\,^{\circ }\hbox {C}\) and \(98.89\,^{\circ }\hbox {C}\) with average absolute deviations of 0.39 and \(0.72\hbox { mm}^{2}/\hbox {s}\), respectively. Another objective was to develop a relation for the variation of viscosity with temperature to predict the viscosity of petroleum fraction at a certain temperature from the knowledge of the viscosity for the same liquid at two other temperatures. The newly developed correlation represents a wide array of temperatures from 20 \(^{\circ }\hbox {C}\) to 150 \(^{\circ }\hbox {C}\) and viscosities from 0.14\(\hbox { mm}^{2}/\hbox {s}\) to 343.64\(\hbox { mm}^{2}/\hbox {s}\). The results have been validated with experimental data consisting of 9558 data points, yielding an overall deviation of \(0.248\hbox { mm}^{2}/\hbox {s}\) and \(\hbox {R}^{2}\) of 0.998. In addition, new formulas were developed to interconvert the viscosity of petroleum fractions from one unit of measure to another based on finding the best fit for a set of experimental data from the literature with \(R^{2}\) as high as 1.0 for many cases. Detailed analysis showed good agreement between the predicted values and the experimental data.     

Dry Block Calibrator with Improved Temperature Field and Integrated Fixed-Point Cells

To reduce uncertainty of calibrations of contact thermometers using dry block calibrators, a concept was developed at Institute for Process Measurement and Sensor Technology of Technische Universität Ilmenau. This concept uses a multi-zone heating, heat flux sensors and a multiple fixed-point cell. The paper shows the concept and its validation on the basis of a dry block calibrator with a working temperature range of \(70\,^{\circ }\hbox {C}\) to \(430\,^{\circ }\hbox {C}\). The experimental results show a stability of \({\pm } 4\,\hbox {mK}\) for the reference temperature and axial temperature differences in the normalization block less than \({\pm }55\,\hbox {mK}\).     

Microwave dielectrics: solid solution,ordering and microwave dielectric properties of $$(1{-}x)\hbox {Ba}(\hbox {Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}{-}x\hbox {Ba(Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}$$ ceramics

The effect of Ba(\(\hbox {Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}\) phase on structure and dielectric properties of \(\hbox {Ba(Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}\) was studied by synthesizing \((1{-}x)\hbox {Ba(Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}{-}x\hbox {Ba}(\hbox {Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}\) (\(x = 0\), 0.005, 0.01 and 0.02) ceramics. Superlattice reflections due to 1:2 ordering appear as low as \(1000^{\circ }\hbox {C}\). \(\hbox {Ba}(\hbox {Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}\) forms solid solution with \(\hbox {Ba}(\hbox {Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}\) for all ‘x’ values studied until \(1350^{\circ }\hbox {C}\). Ordering was confirmed by powder X-ray diffraction pattern, Raman study and HRTEM. Ceramic pucks can be sintered to density \({>}92\%\) of theoretical density. Temperature and frequency-stable dielectric constant and nearly zero dielectric loss (tan \(\delta \)) were observed at low frequencies (20 MHz). The sintered samples exhibit dielectric constant (\(\varepsilon _{\mathrm{r}})\) between 30 and 32, high quality factor between 37000 and 74000 GHz and temperature coefficient of resonant frequency (\(\tau _{\mathrm{f}})\) between 21 and \(24\hbox { ppm }^{\circ }\hbox {C}^{-1}\).     

Thermal Conductivity of Pyroclastic Soil (<Emphasis Type="BoldItalic">Pozzolana</Emphasis>) from the Environs of Rome

The paper reveals the experimental procedure and thermo-physical characteristics of a coarse pyroclastic soil (Pozzolana), from the neighborhoods of Rome, Italy. The tested samples are comprised of 70.7 % sand, 25.9 % silt, and 3.4 % clay. Their mineral composition contained 38 % pyroxene, 33 % analcime, 20 % leucite, 6 % illite/muscovite, 3 % magnetite, and no quartz content was noted. The effective thermal conductivity of minerals was assessed to be about \(2.14\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\). A transient thermal probe method was applied to measure the thermal conductivity (\(\lambda \)) over a full range of the degree of saturation \((S_{\mathrm{r}})\), at two porosities (n) of 0.44 and 0.50, and at room temperature of about \(25\,^{\circ }\hbox {C}\). The \(\lambda \) data obtained were consistent between tests and showed an increasing trend with increasing \(S_{\mathrm{r}}\) and decreasing n. At full saturation (\(S_{\mathrm{r}}=1\)), a nearly quintuple \(\lambda \) increase was observed with respect to full dryness (\(S_{\mathrm{r}}=0\)). In general, the measured data closely followed the natural trend of \(\lambda \) versus \(S_{\mathrm{r}}\) exhibited by published data at room temperature for other unsaturated soils and sands. The measured \(\lambda \) data had an average root-mean-squared error (RMSE) of \(0.007\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\) and \(0.008\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\) for n of 0.50 and 0.44, respectively, as well as an average relative standard deviation of the mean at the 95 % confidence level \((\hbox {RSDM}_{0.95})\) of 2.21 % and 2.72  % for n of 0.50 and 0.44, respectively.     

Photoacoustic Study on the Structural Variation of Titania Nanomaterials Using the Pr (III) Ion as a Spectral Probe

In this work, \(\hbox {Pr}^{3+}\)-doped titania nanomaterials were prepared by a sol–gel method. The structural variations of the samples during the phase transitions were studied by using the \(\hbox {Pr}^{3+}\) ion as a photoacoustic spectral probe. The result shows that for the gel sample heated at \(80\,^{\circ }\hbox {C}\), the coordination environment of \(\hbox {Pr}^{3+}\) is similar to that of its aqueous ion. The f–f transitions of \(\hbox {Pr}^{3+}\) exhibit a continuous red shift along with the gel-to-anatase transition, indicating an increase of the ‘degree of covalency’ for the \(\hbox {Pr}^{3+}\) bonding. For the sample calcined at \(1100\,^{\circ }\hbox {C}\), however, the f–f transitions of \(\hbox {Pr}^{3+}\) show obvious blue shift. This can be attributed to the segregation of \(\hbox {Pr}^{3+}\) ions to the external surface during the anatase-to-rutile transition, forming \(\hbox {Pr}_{4}\hbox {Ti}_{9}\hbox {O}_{24}\). The stabilization effect of the doped \(\hbox {Pr}^{3+ }\)ions on the anatase phase of the samples is also discussed.     

Electrical and Thermal Characteristics of the Insulator–Metal Transition in Crystalline $$\hbox {V}_{2}\hbox {O}_{5}$$ Films

The electrical and thermal properties with respect to the crystallization in \(\hbox {V}_{2}\hbox {O}_{5}\) thin films were investigated by measuring the resistance at different temperatures and applied voltages. The changes in the crystal structure of the films at different temperatures were also explored using Raman measurements. The thermal diffusivity of the crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) film was measured by the nanosecond thermoreflectance method. The microstructures of amorphous and crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) were observed by SEM and XRD measurements. The temperature-dependent Raman spectra revealed that a structural phase transition does not occur in the crystalline film. The resistance measurements of an amorphous film indicated semiconducting behavior, whereas the resistance of the crystalline film revealed a substantial change near \(250\,{^{\circ }}\hbox {C}\), and Ohmic behavior was observed above \(380\,{^{\circ }}\hbox {C}\). This result was due to the metal–insulator transition induced by lattice distortion in the crystalline film, for which \(T_{\mathrm{c}}\) was \(260\,{^{\circ }}\hbox {C}\). \(T_{\mathrm{c}}\) of the film decreased from 260 \({^{\circ }}\hbox {C}\) to \(230\,{^{\circ }}\hbox {C}\) with increasing applied voltage from 0 V to 10 V. Furthermore, the thermal diffusivity of the crystalline film was \(1.67\times 10^{-7}\,\hbox {m}^{2}\cdot \hbox {s}^{-1}\) according to the nanosecond thermoreflectance measurements.     

Effects of electrolyte concentration and current density on the properties of electro-deposited NiFeW alloy coatings

NiWP alloy coatings were prepared by electrodeposition, and the effects of ferrous chloride (\(\hbox {FeCl}_{2})\), sodium tungstate (\(\hbox {Na}_{2}\hbox {WO}_{4})\) and current density (\(D_{\mathrm{K}}\)) on the properties of the coatings were studied. The results show that upon increasing the concentration of \(\hbox {FeCl}_{2}\), initially the Fe content of the coating increased and then tended to be stable; the deposition rate and microhardness of coating decreased when the cathodic current efficiency (\(\eta \)) initially increased and then decreased; and for a \(\hbox {FeCl}_{2}\) concentration of \(3.6\, \hbox {g\,l}^{-1}\), the cathodic current efficiency reached its maximum of 74.23%. Upon increasing the concentration of \(\hbox {Na}_{2}\hbox {WO}_{4}\), the W content and microhardness of the coatings increased; the deposition rate and the cathode current efficiency initially increased and then decreased. The cathodic current efficiency reached the maximum value of 70.33% with a \(\hbox {Na}_{2}\hbox {WO}_{4}\) concentration of 50 g \(\hbox {l}^{-1}\), whereas the deposition rate is maximum at 8.67 \(\upmu \hbox {m}\,\hbox {h}^{-1}\) with a \(\hbox {Na}_{2}\hbox {WO}_{4}\) concentration of \(40\, \hbox {g\,l}^{-1}\). Upon increasing the \(D_{\mathrm{K}}\), the deposition rate, microhardness, Fe and W content of the coatings increased, the cathodic current efficiency increases first increased and then decreased. When \(D_{\mathrm{K}}\) was 4 A dm\(^{-2}\), the current efficiency reached the maximum of 73.64%.     

Bootstrap in semi-functional partial linear regression under dependence

This paper deals with the semi-functional partial linear regression model \(Y={{\varvec{X}}}^\mathrm{T}{\varvec{\beta }}+m({\varvec{\chi }})+\varepsilon \) under \(\alpha \)-mixing conditions. \({\varvec{\beta }} \in \mathbb {R}^{p}\) and \(m(\cdot )\) denote an unknown vector and an unknown smooth real-valued operator, respectively. The covariates \({{\varvec{X}}}\) and \({\varvec{\chi }}\) are valued in \(\mathbb {R}^{p}\) and some infinite-dimensional space, respectively, and the random error \(\varepsilon \) verifies \(\mathbb {E}(\varepsilon |{{\varvec{X}}},{\varvec{\chi }})=0\). Naïve and wild bootstrap procedures are proposed to approximate the distribution of kernel-based estimators of \({\varvec{\beta }}\) and \(m(\chi )\), and their asymptotic validities are obtained. A simulation study shows the behavior (on finite sample sizes) of the proposed bootstrap methodology when applied to construct confidence intervals, while an application to real data concerning electricity market illustrates its usefulness in practice.     

Resistance-switching properties of Bi-doped $$\hbox {SrTiO}_{3}$$ films for non-volatile memory applications with different device structures

\(\hbox {SrTiO}_{3}\) and Bi-doped \(\hbox {SrTiO}_{3}\) films were fabricated with different device structures using the sol–gel method for non-volatile memory applications, and their resistance-switching behaviour, endurance and retention characteristics were investigated. \(\hbox {SrTiO}_{3}\) and \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si or Pt have the same phase structure, morphologies and grain size; however, the grain size of the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si is slightly larger than those of the \(\hbox {SrTiO}_{3}\) films grown on Si and the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Pt. The \(\hbox {SrTiO}_{3}\) or \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films grown on Si or Pt all exhibit bipolar resistive-switching behaviour and follow the same conductive mechanism; however, the \(\hbox {Ag}/\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}/\hbox {Si}\) device possesses the highest \(R_{\mathrm{HRS}}{/}R_{\mathrm{LRS}}\) of \(10^{5}\) and the best endurance and retention characteristics. The doping of Bi is conducive to enhance the \(R_{\mathrm{HRS}}{/}R_{\mathrm{LRS}}\) of the \(\hbox {SrTiO}_{3}\) films; meanwhile, the Si substrates help improve the endurance and retention characteristics of the \(\hbox {Sr}_{0.92}\hbox {Bi}_{0.08}\hbox {TiO}_{3}\) films.     

Study of $$\upbeta $$-phase development in spin-coated PVDF thick films

A study was conducted to ascertain the effect of variation in spin speed and baking temperature on \(\upbeta \)-phase content in the spin-coated poly(vinylidene fluoride) (PVDF) thick films (\({\sim }4{-}25\,\upmu \hbox {m}\)). Development of \(\upbeta \)-phase is dependent on film stretching and crystallization temperature. Therefore, to study the development of \(\upbeta \)-phase in films, stretching is achieved by spinning and crystallization temperature is adjusted by means of baking. PVDF films are characterized using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. It is observed that crystallization temperature lower than \(60^{\circ }\hbox {C}\) and increase in spin speed increases the \(\upbeta \)-phase content in PVDF films. Crystallization temperature above \(60^{\circ }\hbox {C}\) reduces \(\upbeta \)-phase content and increases \(\upalpha \)-phase content. It was also observed that viscosity of the PVDF solution affects the \(\upbeta \)-phase development in films at a particular spin speed.     

Rectifying resistance-switching behaviour of Ag/SBTO/STMO/$$\hbox {p}^{+}$$-Si heterostructure films

The \(\hbox {Sr}_{0.88}\hbox {Bi}_{0.12}\hbox {TiO}_{3}/\hbox {SrTi}_{0.92}\hbox {Mg}_{0.08}\hbox {O}_{3}\) (SBTO/STMO) heterostructure films were prepared on \(\hbox {p}^{+}\hbox {-Si}\) substrates by sol–gel spin-coating technique, and the films had good crystallinity and uniform grain distribution. The heterostructure films with a structure of Ag/SBTO/STMO/\(\hbox {p}^{+}\hbox {-Si}\) exhibited a bipolar, remarkable resistance-switching characteristic, and \(R_{\mathrm{HRS}}/R_{\mathrm{LRS}}\,\,{\sim }10^{4}\). More importantly, the heterostructure films showed rectifying characteristic in the low resistance state (LRS), and the rectification ratio can reach \(10^{2 }\) at \(\pm 1\hbox { V}\). The dominant resistive-switching conduction mechanism of high resistance state (HRS) was Ohmic behaviour, and the LRS changed to space charge-limited current (SCLC).     

Facile synthesis and characterization of rough surface $$\mathrm{V}_{2}\hbox {O}_{5}$$ nanomaterials for pseudo-supercapacitor electrode material with high capacitance

\(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials with rough surface were synthesized using commercial \(\hbox {V}_{2}\hbox {O}_{5}\), ethanol (EtOH) and \(\hbox {H}_{2}\hbox {O}\) as the starting materials by a simple hydrothermal route and combination of calcination. The electrochemical properties of \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials as electrodes in a supercapacitor device were measured using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) method. \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials exhibit the specific capacitance of 423 F \(\hbox {g}^{-1}\) at the current density of 0.5 A \(\hbox {g}^{-1}\) and retain 327 F \(\hbox {g}^{-1}\) even at the high current density of 10 A \(\hbox {g}^{-1}\). The influence of the ratio of \(\hbox {EtOH/H}_{2}\hbox {O}\), the calcined time and temperature on the morphology, purity and electrochemical property of the products is discussed in detail. The results revealed that the ratio of \(\hbox {EtOH}\hbox {/}\hbox {H}_{2}\hbox {O}= 10\hbox {/}25\) and calcination at \(400{^{\circ }}\hbox {C}\) for 2–4 h are favourable for preparing \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials and they exhibited the best electrochemical property. The novel morphology and high specific surface area are the main factors that contribute to high electrochemical performance of \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials during the charge–discharge processes. It turns out that \(\hbox {V}_{2}\hbox {O}_{5}\) nanomaterials with rough surface is an ideal material for supercapacitor electrode in the present work.     

Measurement of Out-of-Plane Thermal Conductivity of Epitaxial $$\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-{\delta }}$$ Thin Films in the Temperature Range from 10 K to 300 K by Photothermal Reflectance

We measured the out-of-plane (c-axis) thermal conductivity of epitaxially grown \(\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-{\delta }}\) (YBCO) thin films (250 nm, 500 nm and 1000 nm) in the temperature range from 10 K to 300 K using the photothermal reflectance technique. The technique enables us to determine the thermal conductivity perpendicular to a thin film on a substrate by curve fitting analysis of the phase lag between the thermoreflectance signal and modulated heating laser beam in the frequency range from \(10^{2}\,\hbox {Hz}\) to \(10^{6}\,\hbox {Hz}\). The uncertainties of measured thermal conductivity of all samples were estimated to be within \({\pm }9\,\%\) at 300 K, \({\pm }12\,\%\) at 180 K, \({\pm }16\,\%\) at 90 K and \({\pm }20\,\%\) below 50 K. The experimental results show that the thermal conductivity is dependent on the thickness of the thin films across the entire temperature range. We also observed that the thermal conductivity of the present YBCO thin films showed \(T^{1.4}\) to \(T^{1.6}\) glass-like dependence below 50 K, even though the films are crystalline solids. In order to explain the reason for this temperature dependence, we attempted to analyze our results using phonon relaxation times for possible phonon scattering models, including stacking faults, grain boundary and tunneling states scattering models.     

Microwave hydrothermal synthesis and upconversion luminescence properties of $$\hbox {Yb}^{3+}$$/$$\hbox {Tm}^{3+}$$Tm3+ co-doped $$\hbox {NaY}(\hbox {MoO}_{4})_{2}$$NaY(MoO4)2 phosphor

Tetragonal \(\text {NaY}(\text {MoO}_{4})_{2}\) (NYM) phosphors co-doped with \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) ions were synthesized through microwave hydrothermal method followed by calcining treatment. Powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence spectra were used to characterize the properties of as-prepared samples. The results show that \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM displayed bright blue emission near 472 and 476 nm (\(^{1}\hbox {G}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition), strong near-infrared upconversion (UC) emission around 795 nm (\(^{3}\hbox {H}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition). The optimum doping concentrations of \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) for the most intense UC luminescence were obtained, and the related UC mechanism of \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM depending on pump power was studied in detail.     

Effect of CTAB coating on structural,magnetic and peroxidase mimic activity of ferric oxide nanoparticles

In the present work, pristine and cetyl trimethyl ammonium bromide (CTAB)-coated ferric oxide nanoparticles \((\hbox {CTAB@Fe}_{2}\hbox {O}_{3} \hbox { NPs})\) were synthesized and studied as enzyme mimics. The w/w ratio of \(\hbox {Fe}_{2}\hbox {O}_{3}\) to CTAB was varied as 1:1 and 1:2. Transmission electron microscopic analysis revealed that pristine NPs had an average size of 50 nm, whereas the presence of CTAB resulted in the formation of nanorods with length of 130 nm. BET studies confirmed enhancement of surface area on CTAB coating, which was maximum for w/w ratio 1:1. The synthesized pristine NPs and CTAB-coated NPs were evaluated for their peroxidase mimic activity using o-dianisidine dihydrochloride as substrate. Optimum pH, temperature, substrate and NPs concentration for the reaction were 1, \(25^{\circ }{\mathrm{C}}\), \(0.16~\hbox {mg}~\hbox {ml}^{-1}\) and \(1~\hbox {mg}~\hbox {ml}^{-1}\), respectively. Peroxidase mimic activity of \(\hbox {CTAB@Fe}_{2}\hbox {O}_{3}\hbox { NPs}\) (w/w 1:1) was higher than that of pristine NPs. However, further increase in CTAB coating (w/w 1:2) resulted in lowering of peroxidase mimic activity. Kinetic analysis was carried out at optimized conditions; maximum velocity (\(V_{\mathrm{max}})\) and Michaelis constant (\(K_{\mathrm{m}})\) value of \(\hbox {CTAB@Fe}_{2}\hbox {O}_{3}\hbox { NPs}\) at 1:1 w/w ratio were 7.69 mM and \(1.12~\upmu \hbox {mol}~\hbox {s}^{-1}\), respectively.     

Characterization and optical properties of $$\hbox {Pr}_{2}\hbox {O}_{3}$$-doped molybdenum lead-borate glasses

\(\hbox {Pr}^{3+}\) doped molybdenum lead-borate glasses with the chemical composition 75PbO?[25–(x \(+\) y)\(\hbox {B}_{2}\hbox {O}_{3}]\)–\(y\hbox {MoO}_{3}\)–\(x\hbox {Pr}_{2}\hbox {O}_{3}\) (where \(x = 0.5\) and 1.0 mol% and \(y = 0\) and 5 mol%) were prepared by conventional melt-quenching technique. Thermal, optical and structural analyses are carried out using DSC, UV and FTIR spectra. The physical parameters, like glass transition \((T_{\mathrm{g}})\), stability factor \((\Delta T)\), optical energy band gap \((E_{\mathrm{gopt}})\), of these glasses have been determined as a function of dopant concentration. The \({T}_{\mathrm{g}}\) and optical energy gaps of these glasses were found to be in the range of 290–350\({^{\circ }}\hbox {C}\) and 2.45–2.7 eV, respectively. Stability of the glass doped with \(\hbox {Pr}^{3+}\) is found to be moderate (\(\sim \)40). The results are discussed using the structural model of Mo–lead-borate glass.