On characteristic lengths used in notch fracture mechanics

In this paper, four kinds of characteristic length parameters used in a local notch fracture criterion are presented: (1) a characteristic length ${\uprho }_{\mathrm{c}}$ generally connecting to the notch radius, (2) a characteristic distance $\hbox {X}_{\mathrm{c}}$ considered as intrinsic to material and connected to the microstructure, (3) a critical distance $\hbox {d}_{0}$ considered as intrinsic to material and connected to the fracture process zone, (4) an effective distance $\hbox {X}_{\mathrm{ef}}$ considered as a characteristic of the stress distribution. Each approach is discussed. The paper ends with the author’s opinion about the different methods.     

Study of Glass-Transition Kinetics of Pb-Modified Se_{80}In_{20} System by Using Non-isothermal Differential Scanning Calorimetry

Glass-transition kinetics of $\mathrm{Se}_{80}\mathrm{In}_{20-\mathrm{x}}\mathrm{Pb}_{\mathrm{x}}$ ( $x =$ 0, 5, 10, and 15) chalcogenide glasses have been carried out at different heating rates by using differential scanning calorimeter (DSC) under the non-isothermal condition. The glass-transition temperature $T_{\mathrm{g}}$ and peak glass-transition temperature $T_{\mathrm{pg}}$ have been determined from DSC thermograms. The reduced glass temperature $T_{\mathrm{rg}}$ , total relaxation time $\tau _{T_{g}}$ thermal-stability parameters $K^{l}$ and $S$ , the activation energy of glass transition $E_{\mathrm{g}}$ , the fragility index $F_{\mathrm{i}}$ , and the average coordination number $\langle Z\rangle $ have been calculated on the basis of the experimental results. The temperature differences $(T_{\mathrm{c}}-T_{\mathrm{g}}), K_{\mathrm{gl}}, K^{l}, S$ , and $E_{\mathrm{g}}$ are found to be maxima for $\mathrm{Se}_{80}\mathrm{In}_{10}\mathrm{Pb}_{10}$ glass. This indicates that $\mathrm{Se}_{80}\mathrm{In}_{10}\mathrm{Pb}_{10}$ glass has the highest thermal stability and glass-forming ability in the investigated compositional range. These results could be explained on the basis of modification of the chemical bond formation due to incorporation of Pb in the Se–In glassy matrix.     

Molecular beam epitaxy of semipolar AlN(11\bar{2}2) and GaN(11\bar{2}2) on m-sapphire

We report on the plasma-assisted molecular-beam epitaxy of semipolar $\hbox{AlN}(11\bar{2}2)$ and GaN( $11\bar{2}2$ ) films on $(1\bar{1}00)$ m-plane sapphire. AlN deposited on m-sapphire settles into two main crystalline orientation domains, $\hbox{AlN}(11\bar{2}2)$ and $\hbox{AlN}(10\bar{1}0),$ whose ratio depends on the III/V ratio. Growth under moderate nitrogen-rich conditions enables to isolate the $(11\bar{2}2)$ orientation. The in-plane epitaxial relationships of $\hbox{AlN}(11\bar{2}2)$ on m-plane sapphire are $[11\bar{2}\bar{3}]_{\rm AlN} \vert \vert [0001]_{\rm sapphire}$ and $[1\bar{1}00]_{\rm AlN} \vert \vert [11\bar{2}0]_{\rm sapphire}.$ GaN deposited directly on m-sapphire results in ( $11\bar{2}2$ )-oriented layers with ( $10\bar{1}\bar{3}$ )-oriented inclusions. A ～100 nm-thick AlN( $11\bar{2}2$ ) buffer imposes the ( $11\bar{2}2$ )-orientation for the GaN layer grown on top. By studying the Ga-desorption on GaN( $11\bar{2}2$ ), we conclude that these optimal growth conditions corresponds to a Ga excess of one monolayer on the GaN( $11\bar{2}2$ ) surface.     

Effect of Previous Milling of Precursors on Magnetoelectric Effect in Multiferroic {\mathrm{Bi}_{5}\mathrm{Ti}_{3}\mathrm{FeO}_{15}} Ceramic

$\mathrm{Bi}_{5}\mathrm{Ti}_{3}\mathrm{FeO}_{15}$ Bi 5 Ti 3 FeO 15 magnetoelectric (ME) ceramics have been synthesized and investigated. The ME effect can be described as an induced electric polarization under an external magnetic field or an induced magnetization under an external electric field. The materials in the ME effect are called ME materials, and they are considered to be a kind of new promising materials for sensors, processors, actuators, and memory systems. Multiferroics, the materials in which both ferromagnetism and ferroelectricity can coexist, are the prospective candidates which can potentially host the gigantic ME effect. $\mathrm{Bi}_{5}\mathrm{Ti}_{3}\mathrm{FeO}_{15}$ Bi 5 Ti 3 FeO 15 , an Aurivillius compound, was synthesized by sintering a mixture of $\mathrm{Bi}_{2}\mathrm{O}_{3}, \mathrm{Fe}_{2}\mathrm{O}_{3}$ Bi 2 O 3 , Fe 2 O 3 , and $\mathrm{TiO}_{2}$ TiO 2 oxides. The precursor materials were prepared in a high-energy attritorial mill for (1, 5, and 10) h. The orthorhombic $\mathrm{Bi}_{5}\mathrm{Ti}_{3}\mathrm{FeO}_{15}$ Bi 5 Ti 3 FeO 15 ceramics were obtained by a solid-state reaction process at 1313 K. The ME voltage coefficient ( $\alpha _\mathrm{ME}$ α ME ) was measured using the dynamic lock-in method. The highest ME voltage coefficient ( $\alpha _\mathrm{ME} = 8.28\,\text{ mV }{\cdot }\text{ cm }^{-1}{\cdot }\text{ Oe }^{-1})$ α ME = 8.28 mV · cm ? 1 · Oe ? 1 ) is obtained for the sample milled for 1 h at $H_\mathrm{DC }= 4$ H DC = 4  Oe (1 Oe = 79.58  $\text{ A }{\cdot }\text{ m }^{-1})$ A · m ? 1 ) .     

Experimental Measurements of Thermophysical Properties of \mathrm{Al}_{2}\mathrm{O}_{3}– and \mathrm{TiO}_{2}–Ethylene Glycol Nanofluids

This paper presents measurements of the thermal conductivity and the dynamic viscosity of $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol and $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol (1 % to 3 % particle volume fraction) nanofluids carried out in the temperature range from $0\,^{\circ }$ 0 ° C to $50\,^{\circ }$ 50 ° C. The thermal-conductivity measurements were performed by using a transient hot-disk TPS 2500S apparatus instrumented with a 7577 probe (2.001 mm in radius) having a maximum uncertainty $(k=2)$ ( k = 2 ) lower than 5.0 % of the reading. The dynamic-viscosity measurements and the rheological analysis were carried out by a rotating disk type rheometer Haake Mars II instrumented with a single-cone probe (60 mm in diameter and $1^{\circ }$ 1 ° ) having a maximum uncertainty $(k=2)$ ( k = 2 ) lower than 5.0 % of the reading. The thermal-conductivity measurements of the tested nanofluids show a great sensitivity to particle volume fraction and a lower sensitivity to temperature: $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol and $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol nanofluids show a thermal-conductivity enhancement (with respect to pure ethylene glycol) from 1 % to 19.5 % and from 9 % to 29 %, respectively. $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol and $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol nanofluids exhibit Newtonian behavior in all the investigated temperature and particle volume fraction ranges. The relative viscosity shows a great sensitivity to the particle volume fraction and weak or no sensitivity to temperature: $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol and $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol nanofluids show a dynamic viscosity increase with respect to ethylene glycol from (4 to 5) % to 30 % and from 14 % to 50 %, respectively. Present experimental measurements were compared both with available measurements carried out by different researchers and computational models for thermophysical properties of nanofluids.     

The theoretical calculation of the flow rate of granular matter from an inclined orifice

A theoretical calculation method for the flow rate of granular matter from an inclined orifice is discussed in this article and for the inclination angles at $\theta \le 90^{\circ }$ , a theoretical relation between the flow rate $Q$ and inclination angle $\theta $ is derived; and for the inclination angles at $\theta >90^{\circ }$ , a semi-theoretical relation is established. From the relations, we found that the ratio of the flow rate from a vertical orifice, $Q_{90}$ , to that from a horizontal orifice, $Q_{0}$ , is equal to the sine of the angle of repose $\theta _{\mathrm{r}}$ , i.e., $Q_{90} /Q_0 =\sin \theta _{\mathrm{r}} $ . The theoretical relations are tested by means of the experimental data and the results indicate that the theoretical calculating values are in good agreement with the experimental data over a wide range of the inclination angles. Therefore, the formula proposed in this article can be used for the theoretical calculation of the flow rate of granular matter from an inclined orifice. The relation $Q_{90} /Q_0 =\sin \theta _{\mathrm{r}}$ may be used as an alternative approach to obtaining $\theta _{\mathrm{r}}$ : measuring $Q_{90}$ and $Q_{0}$ , and then calculating $\theta _{\mathrm{r}} $ by using formula $\theta _{\mathrm{r}} =\arcsin (Q_{90} /Q_0 )$ .     

Transfer Partial Molar Isentropic Compressibilities of (l-Alanine/l-Glutamine/Glycylglycine) from Water to 0.512 {\mathrm{mol}}\!\cdot \!{\mathrm{kg}}^{-1} Aqueous {\mathrm{KNO}}_{3}/0.512\, {\mathrm{mol}}\!\cdot \! {\mathrm{kg}}^{-1} Aqueous {\mathrm{K}}_{2}{\mathrm{SO}}_{4} Solutions Between 298.15 K and 323.15 K

Speeds of sound of (l-alanine/l-glutamine/glycylglycine $\,+\, 0.512\, {\mathrm{mol}}\cdot {\mathrm{kg}}^{-1}$ + 0.512 mol · kg ? 1 aqueous ${\mathrm{KNO}}_{3}/0.512\, {\mathrm{mol}}\cdot {\mathrm{kg}}^{-1}$ KNO 3 / 0.512 mol · kg ? 1 aqueous ${\mathrm{K}}_{2}{\mathrm{SO}}_{4}$ K 2 SO 4 ) systems have been measured for several molal concentrations of amino acid/peptide at different temperatures: $T$ T = (298.15 to 323.15) K. Using the speed-of-sound and density data, the parameters, partial molar isentropic compressibilities $\phi _{\kappa }^{0}$ ? κ 0 and transfer partial molar isentropic compressibilities $\Delta _{\mathrm{tr}} \phi _{\kappa }^{0}$ Δ tr ? κ 0 , have been computed. The trends of variation of $\phi _{\kappa }^{0}$ ? κ 0 and $\Delta _{\mathrm{tr}} \phi _{\kappa }^{0}$ Δ tr ? κ 0 with changes in molal concentration of the solute and temperature have been discussed in terms of zwitterion–ion, zwitterion–water dipole, ion–water dipole, and ion–ion interactions operative in the systems.     

Magnetic Properties of Nanocrystalline Nickel–Cobalt Ferrites (\mathrm{Ni}_{1/2}{\mathrm{{Co}}}_{1/2}{\mathrm{{Fe}}}_{2}{\mathrm{O}}_{4})

In this study, the nanocrystalline nickel–cobalt ferrites $(\mathrm{Ni}_{1/2}\mathrm{Co}_{1/2}\mathrm{Fe}_{2}\mathrm{O}_{4})$ were prepared via the citrate route method at $27\,^{\circ }\mathrm{C}$ . The samples were calcined at $300\,^{\circ }\mathrm{C}$ for 3 h. The crystalline structure and the single-phase formations were confirmed by X-ray diffraction (XRD) measurements. Prepared materials showed the cubic spinel structure with m3m symmetry and Fd3m space group. The analyses of XRD patterns were carried out using POWD software. It gave an estimation of lattice constant “ $a$ ” of 8.3584 Å, which was in good agreement with the results reported in JCPDS file no. 742081. The crystal size of the prepared materials calculated by Scherer’s formula was 27.6 nm and the electrical conductivity was around $10^{-5}~\mathrm{S}\,\cdot \, \mathrm{m}^{-1}$ . The permeability component variations with frequency were realized. The magnetic properties of the prepared materials were analyzed by a vibrating sample magnetometer (VSM). It showed a saturation magnetization of $27.26\,\mathrm{emu} \cdot \mathrm{m}^{-1}$ and the behavior of a hard magnet.     

Elastic Properties of Monoclinic \hbox {ZrO}_{2} at Finite Temperatures Via First Principles

The structural and elastic properties of orthorhombic $\hbox {ZrO}_{2}\,(m\hbox {-ZrO}_{2})$ as a function of temperature are investigated by the generalized gradient approximation (GGA) correction scheme in the framework of density functional theory (DFT) and the quasi-harmonic Debye model. The thirteen independent elastic constants of $m\hbox {-ZrO}_{2}$ at temperatures to 3200 K are theoretically investigated for the first time. It is found that with increasing temperature, all elastic constants change, especially $C_{35}\hbox { and }C_{25}$ change rapidly in the temperature range of 1400 K to 1600 K and 2200 K to 2600 K, respectively. We also obtain the bulk modulus $B$ , shear modulus $G$ , Young’s moduli $E$ , as well as Poisson’s ratio $\sigma $ of $m\hbox {-ZrO}_{2}$ at high temperatures. Our work suggests that it is very important to predict the melting properties of materials via the elastic constants at temperatures.     

Surface Recombination Velocity Dependence on Morphological Properties of CdTe Thin Films Prepared by Close-Spaced Sublimation

Cadmium telluride (CdTe) thin films were prepared on glass substrates by employing the close-spaced sublimation technique. Different source ( $T_\mathrm{sou}$ ) and substrate temperatures ( $T_\mathrm{sub}$ ) were used in order to change the structural properties of layers. The ranges chosen were: $550\,^{\circ }\hbox {C} \le T_\mathrm{sou} \le 650\,^{\circ }\hbox {C}$ and $400\,^{\circ }\hbox {C} \le T_\mathrm{sub} \le 600\,^{\circ }\hbox {C}$ . The environment in the growing chamber was also changed with the purpose to study its influence on the crystalline properties of the surface and volume of the material. Three different surroundings were used: vacuum, high-purity argon, and high-purity oxygen. The surface recombination velocity (SRV) was calculated from photoacoustic (PA) measurements by employing the open PA cell configuration. The behavior of the experimental results was analyzed as a function of the structural characteristics of the films: texture and grain size. Scanning electron microscopy, optical absorption, X-ray diffraction, and dark resistivity measurements were also employed to analyze the properties of the CdTe films. The minimum value for the SRV was found for $T_\mathrm{sou} = 650\,^{\circ }\hbox {C},\, T_\mathrm{sub} = 600\,^{\circ }\hbox {C}$ in an oxygen ambient.     

Specific Heat of K_{0.71}Na_{0.29}Fe_2As_2 at Very Low Temperatures

A commercially available calorimeter has been used to investigate the specific heat of a high-quality K $_{0.71}$ Na $_{0.29}$ Fe $_2$ As $_2$ single crystal. The addenda heat capacity of the calorimeter is determined in the temperature range $0.02 \, \mathrm{K} \le T \le 0.54 \, \mathrm{K}$ . The data of the K $_{0.71}$ Na $_{0.29}$ Fe $_2$ As $_2$ crystal imply the presence of a large $T^2$ contribution to the specific heat which gives evidence of $d$ -wave order parameter symmetry in the superconducting state. To improve the measurements, a novel design for a calorimeter with a paramagnetic temperature sensor is presented. It promises a temperature resolution of $\Delta T \approx 0.1 \, \mathrm{\mu K}$ and an addenda heat capacity less than $200 \, \mathrm{pJ/K}$ at $ T < 100 \, \mathrm{mK}$ .     

Liquidus Temperatures and Thermodynamic Properties of the KCl–\mathrm{{KNO}}_{2}, NaCl–\mathrm{{NaNO}}_{2}, and \mathrm{{KNO}}_{2}–\mathrm {NaNO}_{2} Systems

Potassium nitrite is very sensitive to temperature, humidity, and the atmosphere, so few studies have been made in this field for the thermodynamic properties of molten salt with nitrite salt. In this article, the liquidus curves of NaCl– $\mathrm{{NaNO}}_{2}$ NaNO 2 , KCl– $\mathrm{{KNO}}_{2}$ KNO 2 , and $\mathrm {NaNO}_{2}$ NaNO 2 – $\mathrm{{KNO}}_{2}$ KNO 2 are calculated by a simple “hard-sphere” ionic interaction model. The calculated liquidus temperatures show good agreement with experimental values, which implies an ideal mixing enthalpy and entropy for the liquid binary systems. In addition to the phase equilibrium data and experimental thermochemical properties of molten salt systems, the activities of these binary systems are determined by the phase diagrams and the analytical integration of the classical Gibbs–Duhem equation.     

Vorhersage der thermischen Strahlung großer Kohlenwasserstoff- und Peroxid-Poolfeuer mit CFD Simulation

Flame temperatures (T), surface emissive powers (SEP) and irradiances (E) of large-scale JP-4 pool fires (d=2, 8, 16, 25 m) and di-tert-butyl peroxide (DTBP) pool fires (d=1.12 m, 3.4 m) are investigated experimentally and by CFD simulation. As experimental methods an infrared thermographic camera system with video-mixing unit is used for the determination of T, SEP and an ellipsoidal radiometer for the determination of E. The maximum frequency of time-averaged emission temperatures for JP-4 pool fire (d=16 m) are in a range of $ 793\,\mathrm{K} < \overline{T} < 1033$ and for DTBP pool fire (d=1.12 m) are a range of $ 1040\,\mathrm{K} < \overline{T} < 1480\,\mathrm{K}$ . For DTBP pool fire (d=1.12 m), the measurements result in $ \overline{\text{SEP}}\approx 130\,\mathrm{kW/m^{2}}$ which is up to a factor of ≈6 larger in comparison to hydrocarbon pool fires (d≈1 m). In a case of DTBP pool fire (d=3.4 m) with $ \overline{\text{SEP}} \approx 250\,\mathrm{kW/m^{2}}$ this factor is ≈5 compared to $ \overline{\text{SEP}} \approx 50\,\mathrm{kW/m^{2}}$ of LNG pool fire (d=4 m). By increasing the relative distance ?y/d from the pool rim, measured time averaged irradiances $ \overline{E}$ (?y/d) decrease and agree well with CFD predicted $ \overline{E}_{\text{CFD}}$ (?y/d). Also, there is a good agreement between the measured time averaged $ \overline{T}$ and $ \overline{\text{SEP}}$ of hydrocarbons and DTBP pool fires, with the predicted $ \overline{T}_{\text{CFD}}$ and $ \overline{\text{SEP}}_{\text{CFD}}$ values. The possibilities and nowadays limitations of CFD simulation of large pool fires are discussed. This study has shown that the risk potential of accidental pool fires referring to thermal radiation can be predicted much better than in the past.     

The Influence of Oxygen/Argon Ratio on the Structure and Surface Morphology of GaBa2Cu3O7?δ Films Deposited by RF Magnetic Sputtering

$\mathrm{GaBa}_{2}\mathrm{Cu}_{3}\mathrm{O}_{7\mbox{-}\delta}$ thin films have been grown on CeO₂ cap layer by RF magnetic sputtering with different oxygen/argon partial pressure ratio from 2:1 to 1:5. The CeO₂ cap layers were fabricated by pulse laser deposition (PLD) on YSZ/CeO₂/Ni-5%W alloy substrate and had good properties in structure and surface morphology. We study the relationship between oxygen/argon ratio and the performance of the $\mathrm{GaBa}_{2}\mathrm{Cu}_{3}\mathrm{O}_{7\mbox{-}\delta}$ film in order to find out the optimized deposition condition. The structure and surface morphology of the $\mathrm{GaBa}_{2}\mathrm{Cu}_{3}\mathrm{O}_{7\mbox{-}\delta}$ thin films were measured by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), Atomic force microscopy (AFM). It was found that the texture and surface performance of $\mathrm{GaBa}_{2}\mathrm{Cu}_{3}\mathrm{O}_{7\mbox{-}\delta}$ film, such as growth orientation, grain roughness, grain size and surface morphology, are deeply affected by the oxygen/argon ratio. And the film??s performance was the best when the oxygen/argon partial pressure ratio is 1:1.     

Fusion Diagrams in the \mathrm{BiBO}_{3}–\mathrm{YbBO}_{3} and \mathrm{Bi}_{4}\mathrm{B}_{2}\mathrm{O}_{9}–\mathrm{YbBO}_{3} Systems

A calculation model of the Gibbs energy of ternary oxide compounds from the binary components was used. Thermodynamic properties of \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2}\mathrm{O}_{3}\) – \(\mathrm{B}_{2}\mathrm{O}_{3}\) ternary systems in the condensed state were calculated. Thermodynamic data of binary and ternary compounds were used to determine the stable sections. The probability of reactions between the corresponding components in the \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) system was estimated. Fusibility diagrams of systems \(\mathrm{BiBO}_{3}\) – \(\mathrm{YbBO}_{3}\) and \(\mathrm{Bi}_{4} \mathrm{B}_{2} \mathrm{O}_{9}\) – \(\mathrm{YbBO}_{3}\) were studied by physical–chemical analysis. The isothermal section of the phase diagram of \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) at 298 K is built, as well as the projection of the liquid surface of \(\mathrm{BiBO}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) – \(\mathrm{YbBO}_{3}\) .     

A Study of Some Thermophysical Parameters in Glassy \mathrm{{Se}}_{80}\mathrm{{Te}}_{20} and \mathrm{{Se}}_{80}\mathrm{{Te}}_{10}\mathrm{{M}}_{10} (Cd, In, and Sb) Alloys

The present paper reports a comparative study of some thermophysical properties (thermal conductivity, thermal diffusivity, thermal effusivity, and specific heat per unit volume) for $\mathrm{{Se}}_{80}\mathrm{{Te}}_{20}$ Se 80 Te 20 and $\mathrm{{Se}}_{80}\mathrm{{Te}}_{10}\mathrm{{M}}_{10}$ Se 80 Te 10 M 10 (Cd, In, and Sb) alloys. The transient plane source technique is used for this purpose. The thermal conductivity is highest for $\mathrm{{Se}}_{80}\mathrm{{Te}}_{10}\mathrm{{In}}_{10}$ Se 80 Te 10 In 10 as compared to the other ternary alloys. This is explained in terms of the thermal conductivity of additive elements Cd, In, and Sb. The composition dependence of the thermal diffusivity and specific heat per unit volume is also discussed.     

Nuclear Spin Relaxation Characteristic of Submonolayer ^3He Films in Nanochannels

In order to obtain information on dynamics of helium films in the nondegenerate fluid region, we have performed a pulsed-NMR experiment at 3.29 MHz on $^3$ He films adsorbed in straight 2.4 nm channels of FSM silicates down to 0.54 K. In general, the spin-lattice and spin-spin relaxation times $T_1$ and $T_2$ were explained in terms of the two-dimensional Bloembergen–Purcell–Pound model for dipolar relaxation. Temperature dependences of $T_1$ in submonolayer $^3$ He films show a minimum, indicating that the dipolar-field correlation time $\tau _\mathrm {c}$ is about $\omega ^{-1}=4.8\times 10^{-8}$ s. The temperature $T_\mathrm {min}$ of the $T_1$ minimum monotonically lowers with increasing coverage, suggesting that $^3$ He adatoms become more mobile at higher coverages. The low-dimensional property of $^3$ He adatoms is observed as the separation of $T_1$ and $T_2$ above $T_\mathrm {min}$ where $\omega \tau _\mathrm {c}<1$ . On the other hand, several features specific to films in the nanochannel geometry were also found. Especially, the temperature dependence of $T_2$ becomes very small just below $T_\mathrm {min}$ and shows a shoulder at lower temperatures. This anomaly has not been observed in $^3$ He adsorbed in wider pores or on flat surfaces, so that it is considered to be characteristic of $^3$ He films confined in narrow channels with a diameter of a few nm.     

Hypersensitive Transition of Nd(III) Complexes in Liquids Detected by Pulsed-Laser-Induced Photoacoustic Spectroscopy

Laser-induced photoacoustic (PA) spectroscopy for the spectral measurements of extremely weak absorption such as a forbidden transition of lanthanide ions in liquids has been established. In spectroscopy, a pulsed Nd:YAG laser connected with a MOPO series optical parametric oscillator which emits a broad spectrum covering UV and visible regions is used as the excitation source, and the induced PA signals are detected by an optimized PA piezoelectric transducer. The absorption spectra of trivalent lanthanide ions ( $\text{ Pr}^{3+}, \text{ Ho}^{3+}$ , and $\text{ Nd}^{3+})$ in aqueous solutions have been obtained by the detection system with a detection-limit absorbance of $1.3\times 10^{-5}\,\text{ cm}^{-1}$ at room temperature. In addition, the effects of different binding environments on the band shapes and oscillator strengths of the hypersensitive transitions of $\text{ Nd}^{3+}$ ions, i.e., $\text{ Nd}(\text{ CH}_{3}\text{ COO})_{3}$ $\cdot $ $\text{ H}_{2}\text{ O}$ dissolved in $0.1\,{\text{ mol}} \cdot \text{ l}^{-1}$ acetic acid and $\text{ Nd(3-butanedione)}_{3}{\cdot } 2\text{ H}_{2} \text{ O}$ dissolved in triglycol compared with $\text{ NdCl}_{3}$ in $0.1\,{\text{ mol}}\cdot \text{ l}^{-1}$ hydrochloric acid, are observed. The results show that the chemical environment around the lanthanide ions has great impact on 4f–4f transitions, which is rationalized as the impact in terms of ligand (or solvent) special structures and coordination properties.     

Full-Potential Calculation of Structural, Electronic, and Thermodynamic Properties of Fluoroperovskite \text{ CsMF}_{3} (M?=?Be and Mg)

The structural and electronic properties of the cubic fluoroperoveskite $\text{ CsBeF}_{3}$ and $\text{ CsMgF}_{3}$ have been investigated using the full-potential-linearized augmented plane wave method within the density functional theory. The exchange-correlation potential was treated with the local density approximation and the generalized gradient approximation. The calculations of the electronic band structures show that $\text{ CsBeF}_{3 }$ has an indirect bandgap, whereas $\text{ CsMgF}_{3}$ has a direct bandgap. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effect of pressure $P$ and temperature $T$ on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and the heat capacity for $\text{ CsBeF}_{3}$ and $\text{ CsMgF}_{3}$ compounds are investigated for the first time.     

Influence of Magnetic Field and LO Phonon Effects on the Spin Polarization State Energy of Strong-Coupling Bipolaron in a Quantum Dot

On the basis of Lee–Low–Pines unitary transformation, the influence of magnetic field and LO phonon effects on the energy of spin polarization states of strong-coupling bipolarons in a quantum dot (QD) is studied by using the variational method of Pekar type. The variations of the ground state energy $E_0$ and the first excited state the energy $E_1$ of bipolarons in a two-dimensional QD with the confinement strength of QDs $\omega _0$ , dielectric constant ratio $\eta $ , electron–phonon coupling strength $\alpha $ and cyclotron resonance frequency of the magnetic field $\omega _{c}$ are derived when the influence of the spin and external magnetic field is taken into account. The results show that both energies of the ground and first excited states ( $E_0$ and $E_1)$ consist of four parts: the single-particle energy of electrons $E_\mathrm{e}$ , Coulomb interaction energy between two electrons $E_\mathrm{c}$ , interaction energy between the electron spin and magnetic field $E_\mathrm{S}$ and interaction energy between the electron and phonon $E_{\mathrm{e-ph}}$ ; the energy level of the first excited state $E_1$ splits into two lines as $E_1^{(1+1)}$ and $E_1^{(1-1)}$ due to the interaction between the single-particle “orbital” motion and magnetic field, and each energy level of the ground and first excited states splits into three “fine structures” caused by the interaction between the electron spin and magnetic field; the value of $E_{\mathrm{e-ph}}$ is always less than zero and its absolute value increases with increasing $\omega _0$ , $\alpha $ and $\omega _c$ ; the effect of the interaction between the electron and phonon is favorable to forming the binding bipolaron, but the existence of the confinement potential and Coulomb repulsive energy between electrons goes against that; the bipolaron with energy $E_1^{(1-1)}$ is easier and more stable in the binding state than that with $E_1^{(1+1)}$ .