Surface and interface effects on structural transformation of vapor-deposited ethylbenzene films

We have investigated how the structures of vapor-deposited glassy films change with increasing temperature by using time-of-flight secondary ion mass spectrometry and ion scattering spectroscopy. It is found that intermixing of the topmost layer of an ethylbenzene film occur at temperature (~ 80 K) considerably lower than the glass transition temperature (T_g = 118 K) when the film is deposited at 20 K. This phenomenon can be interpreted as the occurrence of a two-dimensional liquid that diffuses into pores of the film, which is evidenced from comparison with surface diffusivity measurements using a porous silicon layer. For nonporous films deposited at higher temperatures, the molecules intermix gradually prior to the abrupt film morphology change at T_g. This phenomenon can be interpreted as decoupling between translational diffusivity and viscosity in the bulk. The film thickness has no significant effects on the evolution of supercooled liquid at T_g except for the monolayer film, whereas crystallization is quenched for the films thinner than 8 monolayers. The roles of the 2D liquid on the surface and an immobilized layer formed at the interface are discussed in finite-size effects on the glass-liquid transition and crystallization.     

Electrical transport and crystallization in Cu+ ion substituted AgI–Ag2O–V2O5 glassy superionic system

A new glassy solid electrolyte system Cu_xAg_1 − xI–Ag₂O–V₂O₅ has been synthesized. The structural, thermal and electrical properties of the samples have been investigated. The glassy nature of the samples is confirmed by X-Ray diffraction and Differential Scanning Calorimetry studies. The electrical conductivity of these samples increases with CuI content and approaches a maximum value of ∼ 10⁻² Ω^− 1 cm^− 1 for x = 0.35 at room temperature. Ionic mobility measurements suggest that enhancement in the conductivity with Cu⁺ ion substitution may be attributed to increase in the mobility of Ag⁺ ions. The electrical conductivity versus temperature cycles carried out at well-controlled heating rate above T_g and T_c reveal interesting thermal properties. For lower CuI content samples conductivity exhibits anomalous rise above T_g and subsequent fall at T_c. It is also found that CuI addition into AgI–Ag₂O–V₂O₅ matrix reduces the extent of crystallization.     

Improved critical current density in Zn doped YBCO single crystals

Magnetic measurements were made using pure YBCO and Zn doped YBa₂(Cu_1?xZn_x)₃O_7?σ. Single crystals with Zn concentration of 0.5%, 1.5%, 3.0% and 4.3%. The magnetic hysteresis loops for these samples were measured in the temperature range 0.1 ? T/T_c ? 0.96 under magnetic fields of 5 T using SQUID. It was found that the critical current density J_c increased for low Zn content samples up to 3% Zn concentration compared to pure YBCO sample and decreased for the higher Zn content samples. These values varied consistently when compared at magnetic fields of 1 T and 3 T. Moreover Zn doped samples showed significant values of J_c in the temperature range of 0.7–0.9T_c, close to critical temperature compared to pure YBCO sample. The irreversibility field H_irr was also enhanced in this temperature range showing consistent decrease with increase of Zn concentration. The peak field H_p above H_c1 and irreversibility field H_irr, both show power law dependence of the form H = m₁(1 ? T/T_c)^m2 in the temperature range of 0.75–0.96T_c. The values of parameter m₂ increased from 1.44 to 1.95 for the samples up to 3% Zn content and decreased to 1.37 for higher Zn contents. The ratio H_irr/H_p was found to be 3–4 for the lower Zn content samples and was 7–8 for the sample with high Zn content indicating more disorder for higher Zn content samples. The region between peak field H_p and irreversibility field H_irr was broadened with the increase of Zn concentration. The strong effect of Zn substitution in modifying behavior of these samples even at elevated temperatures is possibly due to the changes in the anisotropy of our samples with the increase of Zn concentration and also due to the locally induced changes in magnetic moments by Zn substitution.     

XRD and EPR structural investigation of some zinc borate glasses doped with iron ions

Glasses in the system xFe₂O₃·(100?x) [45ZnO·55B₂O₃] (0≤x≤10 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The obtained samples were submitted to an additional thermal treatment at 570 °C for 12 h in order to relax the glass structure as well as to improve the local order. The as cast and heat treated samples were investigated using X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) measurements. The XRD patterns of all the studied samples show their vitreous nature. Structural modifications occurring in the heat treated samples compared to the untreated ones have been pointed out. EPR spectra of untreated and heat treated samples revealed resonance absorptions centered at g≈2.0, g≈4.3 and g≈6.4. The compositional variation of the line intensity and linewidth of the absorptions from g≈4.3 and g≈2.0 have been interpreted in terms of the variation in the concentration of the Fe³⁺ ions and the interaction between the iron ions. The EPR spectra of the untreated samples containing 5 mol% Fe₂O₃ have been studied at different temperatures (110–290 K). The line intensity of the resonance signals decreases with increase in temperature whereas the linewidth is found to be independent of temperature. It was also found that the temperature variation of reciprocal line intensity obeys the Boltzmann law.     

Logarithmic temperature variations of the elastic constant of barium titanate near the ferroelectric phase transition

The temperature variations of the elastic constant C₁₁ and the corresponding acoustic attenuation coefficient of barium titanate single crystals grown by two different methods in the paraelectric phase were obtained in a wide temperature by means of Brillouin light scattering. Two phenomenological approaches were adopted to attempt to explain the anomalous change in C₁₁ (denoted as ΔC₁₁) in the paraelectric phase. ΔC₁₁ exhibited a logarithmic variation as log[(T ? T₀)/T₀] in a certain temperature range from T_c to about T_c + 80 °C instead of the other variation of (T ? T₀)^ζ predicted by the mean-field approach. This temperature range was almost the same as the range where precursor dynamics were theoretically predicted to set in. The fact that the logarithmic variation was proposed for uniaxial systems might indicate that the correlated deformation of precursor polar clusters is tetragonal, as was suggested from nuclear magnetic resonance study [7].     

An anomalous enhancement in the electrical conductivity of Li2O : B2O3 : Al2O3 glasses

The study of electrical conductivity of 27.5 Li₂O : (72.5 − x) B₂O₃ : x Al₂O₃ glass samples has been carried out. It has been observed that the conductivity exhibits Arrhenius behavior for all samples up to glass transition temperature T_g. Beyond T_g, an anomalous enhancement followed by decrease in conductivity has been observed. The results have been explained by dividing the temperature range into two regions. In region-I, it has been observed that the conductivity variation exhibits a maximum at 2.5 mol% Al₂O₃, which has been explained on the basis of Mixed Glass Former Effect (MGFE). An anomalous enhancement in the conductivity observed in region-II has been attributed to the nucleation in the glass. The subsequent decrease in the conductivity has been attributed to the crystallization of the glass samples.     

Ultrasound effect used as external stimulus for viscosity change of aqueous carrageenans

Ultrasound (US) serves as a stimulus to change shear viscosity of aqueous polysaccharides of ι-carrageenan, κ-carrageenan and, agar. The US effect was compared in their aqueous solutions at 60 °C for the US frequency of 23, 45, and 83 kHz. Under the US condition with 50 W at 45 kHz, the shear viscosity of each aqueous solution was decreased significantly. Subsequently, when the US was stopped, the shear viscosity returned back to the original value. In addition, the US showed different effects of the US frequency over the viscosity change in the three kinds of polysaccharides. When the US frequency was changed, the US effects were less at 83 kHz and 28 kHz for the shear viscosity change. In addition, as NaCl was present in the aqueous solution, the viscosity change decreased by the US exposure. These results suggest that the US effect on the viscosity reduction was influenced by the condition of polymer coil conformation, which was expanded or shrank by electrostatic repulsion of the SO₃^? groups. FT-IR analysis supported that the hydrogen bonds of carrageenans were broken during the US exposure. Using Fourier self-deconvolution for the FT-IR spectra without and with US exposure suggests that the US influenced the hydrogen bonds of water and the OH group of polysaccharides.     

Investigation on bulk Nd–Fe–Al amorphous/nano-crystalline alloy

Cylindrical ingots of bulk amorphous Nd₇₀Fe₂₀Al₁₀ with a diameter of 8 mm were prepared by a copper mold casting method. It was proved experimentally with X-ray diffraction, scanning electron microscopy and differential scanning calorimetry that the as-prepared alloy samples consisted mainly of the amorphous phase with a minute amount of nano-crystalline phase. The onset crystallization temperature (T_x) and the melting temperature (T_m) of the samples were 743 and 823 K, respectively, from DSC results. The temperature interval between T_x and T_m, ΔT=T_m−T_x, is 80 K and the resulting ratio of T_x/T_m is 0.90. Both a high T_x/T_m ratio and a small ΔT are considered the reasons for the good glass-forming ability. The Curie temperature (T_c) of these samples was 525 K from magneto-thermal gravimetric analysis. This measured value is higher than the highest T_c among binary Nd–Fe amorphous alloys. Annealing treatments were carried out for the as-cast samples to obtain dual-phase samples with different volume fractions of nano-crystalline phase. Magnetic measurement results indicated that the hard magnetic behavior is weakest for samples with 40% of nano-crystalline phase. The curve of the measured hysteresis loop area versus the volume fraction of nano-crystalline phase concaves upward, which agrees with what we predicated in our previous simulation results.     

Magnetic properties of ball-milled Mn nanoparticles

Nanoparticles of Mn of sizes  < 500 Å were prepared by the ball-milling technique. The temperature dependence of the magnetic susceptibility χ showed systematic variation with particle size. Peaks observed in χ were attributed to the magnetic ordering of the oxides Mn₃O₄and MnO. Peaks found in ∂(χT) / ∂T were associated with the Neel temperature ofα -Mn. We estimated that our samples contain about 0.4% of Mn₃O₄. This low concentration of Mn₃O₄was not detected by X-ray diffraction experiments but contributed significantly to the magnetization measurements.     

Electrical,magnetic and magnetocaloric properties of polycrystalline Pr0.63A0.07Sr0.3MnO3 (A=Pr,Sm and Bi)

We studied the effects of the partial substitution (10%) of praseodymium by samarium and bismuth, on the structural, magnetic, magnetocaloric and electrical properties of the Pr_0.63A_0.07Sr_0.3MnO₃ (A=Pr, Sm and Bi) manganites prepared using the solid state reaction. Refinement of the X-ray diffraction patterns shows that all our samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Magnetic studies indicate that all the samples exhibit a ferromagnetic–paramagnetic transition with increasing temperature. Curie temperature T_C decreases by substitution. M(H) curves indicate the presence of some antiferromagnetic domains in the substituted samples testifying the phase-separated nature of these samples. The magnetic entropy curves –ΔS(T) show a maximum in vicinity of T_C. Important values of maximum of −ΔS are recorded for our compounds. For the parent compound, we found 4.59 J/kg K for an applied magnetic field of 2 T at T_C=266 K which raises the possibility of using this compound as a magnetic refrigerant. The temperature dependence of the electrical resistivity ρ(T) indicates that all compounds exhibit a metal-insulator transition with increasing temperature. Electrical study suggests the presence of a correlation between electrical and magnetic properties.     

Monitoring of laser heating temperature in laser spectroscopic measurements

During laser spectroscopic measurement, a part of laser energy will be converted into heat in the processes of excitation and light emission. Temperature monitoring can help to evaluate such nonradiative process. Upconversion luminescence of phosphor Y₂O₃:Er,Yb under laser excitation at 980 nm was investigated in this work. Point temperature of the phosphor was monitored using the fluorescent intensity ratio (FIR) technology. Laser induced temperature rising was identified by comparison with a theoretically ideal temperature calibration function: lnR = 3.1738–1167/T. The monitored temperature of laser heating rises monotonically with increasing laser power. Circumstances around heating point will modify the calibration function, but the linear slope of lnR ~ 1/T is constant.     

Giant magneto-caloric effect around room temperature at moderate low field variation in La0.7(Ca1−xSrx)0.3MnO3 perovskites

Among the perovskite manganites, a series of La_1?xCa_xMnO₃ has the largest magneto-caloric effect (MCE) (|ΔS_m|_max=3.2–6.7 J/kg K at ΔH=13.5 kOe), but the Curie temperatures, T_C, are quite low (165–270 K). The system of LaSrMnO₃ has quite high T_C but its MCE is not so large. The manganites La_0.7(Ca_1?xSr_x)_0.3MnO₃ (x=0, 0.05, 0.10, 0.15, 0.20, 0.25) have been prepared by solid state reaction technique with an expectation of large MCE at room temperature region. The samples are of single phase with orthorhombic structure. The lattice parameters as well as the volume of unit cell are continuously increased with the increase of x due to large Sr²⁺ ions substituted for smaller Ca²⁺ ions. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic measurements at low field and low temperatures indicate that there is a spin-glass like (or cluster glass) state occurred. The Curie temperature T_C increases continuously from 258 K (for x=0) to 293 K (for x=0.25). A large MCE of 5 J/kg K has been observed around 293 K at the magnetic field change ΔH=13.5 kOe for the sample x=0.25. The studied samples can be considered as giant magneto-caloric materials, which is an excellent candidate for magnetic refrigeration at room temperature region.     

Giant magnetic refrigerant capacity in Ho3Al2 compound

Magnetic properties and magnetocaloric effects (MCEs) of the intermetallic Ho₃Al₂ compound are investigated by magnetization and heat capacity measurements. Two successive magnetic transitions, a spin-reorientation (SR) transition at T_SR=31 K followed by a ferromagnetic (FM) to paramagnetic (PM) transition at T_C=40 K, are observed. Both magnetic transitions contribute to the MCE and result in a large magnetic entropy change (ΔS_M) in a wide temperature range. The maximum values of ?ΔS_M and adiabatic temperature change (ΔT_ad) reach 18.7 J/kg K and 4.8 K for the field changes of 0–5 T, respectively. In particular, a giant value of refrigerant capacity (RC) is estimated to be 704 J/kg for a field change of 5 T, which is much higher than those of many potential refrigerant materials with similar transition temperatures.     

Thermal boundary between normal conductivity and fluctuation superconductivity in YBa2Cu3O7 − δ

The absence of a linear behaviour of the dependence of the resistance() over a temperature interval 77–300 K was observed for ceramic superconductors YBa₂Cu₃O_7 − δand thick polycrystallin films of the same composition with the addition of silver. A comparative analysis of the excess conductivity for HTSC and metal samples, characterizing the deviationR(T) from a linear dependence, allows one to determine the onset temperature of fluctuation superconductivity: within 105–110 K. The analysis of fluctuation superconductivity is performed using the Aslamazov–Larkin model. A smooth transition from the one-dimensional to the two- and three-dimensional nature of superconducting fluctuations in the order parameter was observed for ceramic samples as the temperature decreased.     

Surface electromigration of In on vicinal Si(0 0 1)

Surface mass transport of In film on vicinal Si(0 0 1) has been systematically investigated by a scanning Auger electron microscopy (SAM), low energy electron diffraction (LEED) and atomic force microscopy (AFM). It was observed that the temperature dependence of the mass transport shows the critical phenomenon. Above a critical temperature T_c, surface electromigration of the In film toward the cathode side dominated the surface mass transport on the vicinal Si(0 0 1) surface. The LEED and AFM observations revealed that the In film surface on the vicinal Si(0 0 1) consists of 3×4 terraces and (3 1 0) facets. The area ratio of the facet to the terrace exhibited abrupt an increase at T_c. It is believed that the change of the mass transport is related to the abrupt change of the area ratio of the facet to the terrace. Both the critical temperature T_c and the spread due to the surface electromigration of the In film depended on the configuration of the DC current direction and the step edge.     

Transverse relaxation of cerebrospinal fluid depends on glucose concentration

PurposeTo evaluate the biophysical processes that generate specific T₂ values and their relationship to specific cerebrospinal fluid (CSF) content.Materials and methodsCSF T_2s were measured ex vivo (14.1 T) from isolated CSF collected from human, rat and non-human primate. CSF T_2s were also measured in vivo at different field strength in human (3 and 7 T) and rodent (1, 4.7, 9,4 and 11.7 T) using different pulse sequences. Then, relaxivities of CSF constituents were measured, in vitro, to determine the major molecule responsible for shortening CSF T₂ (2 s) compared to saline T₂ (3 s). The impact of this major molecule on CSF T₂ was then validated in rodent, in vivo, by the simultaneous measurement of the major molecule concentration and CSF T₂.ResultsEx vivo CSF T₂ was about 2.0 s at 14.1 T for all species. In vivo human CSF T₂ approached ex vivo values at 3 T (2.0 s) but was significantly shorter at 7 T (0.9 s). In vivo rodent CSF T₂ decreased with increasing magnetic field and T₂ values similar to the in vitro ones were reached at 1 T (1.6 s). Glucose had the largest contribution of shortening CSF T₂ in vitro. This result was validated in rodent in vivo, showing that an acute change in CSF glucose by infusion of glucose into the blood, can be monitored via changes in CSF T₂ values.ConclusionThis study opens the possibility of monitoring glucose regulation of CSF at the resolution of MRI by quantitating T₂.     

Effects of Zn on magnetic properties and pseudogap of optimally doped La2−xSrxCuO4

The effects of Zn substitution on the uniform (q = 0) magnetic susceptibility, χ(T), of optimally doped (x = 0.15) La_2?xSr_xCu_1?yZn_yO₄ sintered samples were investigated over a wide range of Zn contents (y). Non-magnetic Zn was found to enhance χ(T) systematically and depress T_c very effectively. We have extracted the characteristic pseudogap energy scale, ε_g, from the analysis of χ(T) data. Unlike T_c, ε_g was found to be fairly insensitive to the level of Zn substitution. This supports the scenario where the pseudogap phenomenon has non-superconducting origin. We have also analyzed the Zn-induced Curie-like enhancement of the χ(T) data using different models and discussed the various possible implications.     

Internal evaluation of impregnation treatment of waterlogged wood; relation between concentration of internal materials and relaxation time using magnetic resonance imaging

The purpose of this study is to clarify the degree of impregnation resulting from treatment of internal waterlogged wood samples using MRI. On a 1.5 T MR scanner, T₁ and T₂ measurements were performed using inversion recovery and spin-echo sequences, respectively. The samples were cut waterlogged pieces of wood treated with various impregnation techniques which were divided into different concentrations of trehalose (C₁₂H₂₂O₁₁) and polyethylene glycol (PEG; HO-(C₂H₄O)_n-H) solutions. Then these samples underwent impregnation treatment every two weeks. From the results, we found that the slope of the T₁-concentration curve using linear fitting showed the value of the internal area for PEG to be higher than the external area; internal, − 2.73 ms/wt% (R² = 0.880); external, − 1.50 ms/wt% (R² = 0.887). Furthermore, the slope of the T₁-concentration curve using linear fitting showed the values for trehalose to have almost no difference when comparing the internal and the external areas; internal, − 2.79 ms/wt% (R² = 0.759); external, − 3.02 ms/wt% (R² = 0.795). However, the slope of the T₂-concentration curve using linear fitting for PEG showed that there was only a slight change between the internal and the external areas; internal, 0.26 ms/wt% (R² = 0.642); external, 0.18 ms/wt% (R² = 0.920). The slope of the T₂-concentration curve did not show a change in linear relationship between the internal and the external areas; internal, 0.06 ms/wt% (R² = 0.175); external, − 0.14 ms/wt% (R² = 0.043). In conclusion, using visualization of relaxation time T₁, it is possible to obtain more detail information noninvasively concerning the state of impregnation treatment of internal waterlogged wood.     

Effects of pulsed ultrasound on rheological and structural properties of chicken myofibrillar protein

The effects of pulsed ultrasound (PUS) (power: 240 w) with varying time (0, 3, 6, 9, 12 and 15 min) on rheological and structural properties of chicken myofibrillar protein (CMP) were examined. PUS treatment significantly caused a decrease in the viscosity coefficients (k) but an increase in the flow index (n) value of CMP solutions within short time (0–6 min), while had no significant effect for longer time (9–15 min). Besides, at 6 min, the solubility and microstructure of CMP samples were optimum. The primary structure of CMP was not altered by PUS treatment. However, Raman spectroscopy revealed a decrease in the α-helix and β-sheets proportion and an increase in the β-turn of CMP following PUS treatment. Random coil reached a maximum at 6 min. The changes in tertiary and quaternary structure of CMP by PUS treatment also occurred. As PUS time extended, S₀-ANS for CMP increased measured by ANS fluorescence probe method. However, the normalized intensity of 760 cm⁻¹ increased from 0 min to 6 min, and then decreased to 15 min by Raman test. Moreover, the reactive sulphur (SH) contents and disulfide bonds (S-S) of samples increased while the total SH contents decreased within 0–6 min. At 9 min and above, the contents of reactive SH groups were almost equal to the contents of total SH groups. Differential scanning calorimetry (DSC) of CMP showed that peak temperature (T_d2) for myosin and peak temperature (T_d3) for actin were both reduced in the first 6 min, while T_d3 was not observed from 9 min following PUS treatment. Therefore, 6 min was the optimum PUS time to obtain better CMP rheological and structural properties.     

Magnetic properties of RPdIn (R=Gd–Er) compounds

AC susceptibility and DC magnetization measurements were performed for the RPdIn (R=Gd–Er) compounds both in the paramagnetic and in the ordered state. In opposite to GdPdIn, which is a ferromagnet (T_c=102 K), the other samples show a complex ferrimagnetic behavior with the additional transition at T_t<T_c. In the high-temperature phase (for T_t<T<T_c), a ferromagnetic interaction dominates, while in the low-temperature phase (for T⩽T_t) antiferromagnetic interactions with the magnetocrystalline anisotropy, especially strong for TbPdIn, come into play. The ordering temperatures are T_c=70, 34, 25 and 12.3 K for Tb-, Dy-, Ho- and ErPdIn respectively, while transition temperatures are T_t=6, 14 and 6 K for Tb-, Dy- and HoPdIn respectively. TbPdIn reveals an additional transition at 27 K connected with the intermediate ferrimagnetic phase. The critical fields for the magnetization process of the low-temperature phase are high (52 and 150 kOe for TbPdIn and 32 kOe for DyPdIn at T=4.2 K) yet these values decrease remarkably with increasing temperature. Results of the study are compared with magnetic and neutron diffraction data hitherto available. We state that irreversibility of the zero-field cooled–field cooled magnetization is not connected with the spin-glass phase claimed elsewhere.