[en] This work deals with the role of polar interactions on the viscosity and sedimentation behaviors of magnetorheological suspensions with micro-sized magnetic particles dispersed in oil carriers. The oleic acid and dimer acid were employed to make an adjustment of the hydrophobicity of iron particles, in the interest of performing a comparative evaluation of the contributions of the surface polarity. The viscosity tests show that the adsorbed surfactant layer may impose a hindrance to the movement of iron particles in the oil medium. The polar attractions between dimer acid covered particles gave rise to a considerable increase in viscosity, indicating flocculation structure developed in the suspensions. The observed plateau-like region in the vicinity of 0.1 s"−"1 for MRF containing dimer acid is possibly due to the flocculation provoked by the carboxylic polar attraction, in which the structure is stable against fragmentation. Moreover, a quick recovery of the viscosity and a higher viscosity-temperature index also suggest the existence of particle-particle polar interaction in the suspensions containing dimer acid. The sedimentation measurements reveal that the steric repulsion of oleic acid plays a limited role in the stability of suspensions only if a large quantity of surfactant was used. The sedimentation results observed in the dimer acid covered particles confirm that loose and open flocculation was formed and enhanced sedimentation stability. - Highlights: • Surfactants were employed to make adjustments of the hydrophobicity of particles. • Polar attractions between particles increased the viscosity considerably. • Loose and open flocculation was formed in CI/DA suspension. • The steric repulsion of oleic acid played a limited role in the stability.

[en] Highlights: • A novel hybrid of RGO-LDH/CuMoO₄ was synthesized by co-precipitation method. • RGO-LDH/CuMoO₄ were well-dispersed in EP matrix according to TEM observation. • RGO-LDH/CuMoO₄ has better flame retardancy and smoke suppression for epoxy resin. • The flame retardant mechanism of RGO-LDH/CuMoO₄ was studied. - Abstract: The co-precipitation method was used to synthesize a hybrid with MgAl-layered double hydroxide loaded graphene (RGO-LDH). CuMoO₄ was then introduced onto the surface of RGO-LDH to prepare a hybrid with CuMoO₄ modified RGO-LDH (RGO-LDH/CuMoO₄). The composition, structure and morphology of RGO-LDH/CuMoO₄ were characterized by X-ray diffraction, Laser raman spectroscopy and Transmission electron microscope-energy-dispersive X-ray spectroscopy. It was found that the hybrid of RGO-LDH/CuMoO₄ had been successfully prepared. The effects of flame retardancy and smoke suppression of epoxy resin were studied with added RGO-LDH/CuMoO₄. Results showed that the PHRR and THR of the EP composite with RGO-LDH/CuMoO₄ added were decreased dramatically. The char yield, LOI and UL-94 vertical burning rating of the EP composite were increased, with improved flame ratardancy. In addition, the SPR, TSP, and D_s,max of the EP composite were decreased drastically with added RGO-LDH/CuMoO₄. Its improved flame retardancy and smoke suppression performance were due mainly to the physical barrier of graphene and LDH, and the catalytic carbonization function of LDH. Meanwhile, Cu₂O and MoO₃ generated from RGO-LDH/CuMoO₄ in the combustion process helped enhance the production of char residue and raised the compactness of the char layer.

[en] Diamond-like carbon (DLC) films are deposited on quartz substrate using pure CH₄ in the surface wave plasma equipment. A direct current negative bias up to -90 V is applied to the substrate to investigate the bias effect on the film characteristics. Deposited films are characterized by Raman spectroscopy, infrared (IR) and ultraviolet-visible absorption techniques. There are two broad Raman peaks around 1340 cm^-1 and 1600 cm^-1 and the first one has a greater sp³ component with an increased bias. Infrared spectroscopy has three sp³ C-H modes at 2852 cm^-1, 2926 cm^-1 and 2962 cm^-1, respectively and also shows an intensity increase with the negative bias. Optical band gap is calculated from the ultraviolet-visible absorption spectroscopy and the increased values with negative bias and deposition time are obtained. After a thermal anneal at about 500 degree C for an hour to the film deposited under the bias of -90 V, authors get an almost unchanged Raman spectrum and a peak intensity-reduced IR signal, which indicates a reduced H-content in the film. Meanwhile the optical band gap changed from 0.85 eV to 1.5 eV. (author)

[en] The glass-forming ability (GFA) and magnetic properties of the Gd_5_0Co_5_0-based amorphous alloy with Al addition substitution for Co are investigated. It is found that the GFA and magneto-caloric effect of the Gd_5_0Co_4_5Al_5 amorphous alloy are better than Gd_5_0Co_5_0 amorphous alloy. The maximum magnetic entropy change (– Δ S_m"p"e"a"k) and the magnetic refrigerant capacity of the amorphous alloy under a field of 5T are about 6.64 J·kg"−"1 K"−"1 and 764 J·kg"−"1, respectively. The field dependence of magnetic entropy change meets the one predicted by the mean field theory, which is investigated for a better understanding of the magneto-caloric behaviors of the Gd_5_0Co_4_5Al_5 amorphous alloy. (paper)

[en] Objective: To evaluate the microstructural integrity of white matter (WM) in patients with amnestic mild cognitive impairment (aMCI) and mild Alzheimer's disease (AD) using voxel-based analysis (VBA), and investigate the relationship between WM abnormalities and gray matter (GM) atrophy. Methods: Thirty-three cases with aMCI, 32 cases with mild AD and 31 normal aging volunteers as control subjects were scanned on a 3.0 T MR system using diffusion tensor imaging (DTI) and three-dimensional spoiled gradient-recalled (3DSPGR) sequences. Fractional anisotropy (FA) maps and morphological images were preprocessed by SPM5 and voxel-based comparisons between the 2 patient groups and the control group were performed by t test. Results: Relative to the control group, patients with aMCI showed significantly reduced FA value in bilateral frontal, temporal and left occipital WM, left anterior part of cingulum, left inferior parietal lobule, and the WM adjacent to the triangular part of the right lateral ventricle (k ≥ 20 voxels). In mild AD, significantly reduced FA value was found in bilateral hippocampal, inferior parietal lobular, frontal, temporal, and occipital WM, bilateral corpus callosum, anterior part of cingulums, the WM adjacent to the triangular part of the bilateral lateral ventricles, left temporal stem, left thalamus, right precuneus (k ≥ 20 voxels). Significantly reduced GM volume was found in left hippocampus, parahippocampal gyrus, lingual gyrus and superior temporal gyrus, bilateral insulae and middle temporal gyri in aMCI group when compared with control group (k ≥ 50 voxels). In mild AD, significantly reduced GM volume was found in bilateral hippocampi, parahippocampal gyri, amygdalae, thalami, temporal, parietal, frontal, occipital cortex (k ≥ 50 voxels). The pattern of areas with reduced FA differs from that of the GM volumetric reduction. No areas with significantly reduced FA was detected in aMCI compared with mild AD. There was no significant correlation between FA value of WM in patient groups and Mini-Mental State Examination (MMSE) scores. Conclusions: Voxel-based MRI DTI analysis of whole brain white matter can objectively reveal widespread white matter abnormalities in early-stage AD. The difference between WM FA reduction pattern and GM volumetric reduction pattern indicates that the pathological WM changes in early- stage AD were caused by multiple mechanisms. FA did not vary significantly in patients progressing from aMCI to mild AD and can hardly reflect the severity of cognitive function. damage in these patients. (authors)

[en] The magneto-caloric effect (MCE) of a Gd_5_5Co_2_5Al_1_8Sn_2 bulk metallic glass (BMG) is investigated. The Gd_5_5Co_2_5Al_1_8Sn_2 as-cast rod prepared by a water-cooled copper mold suction casting method exhibits typical amorphous characteristics. The maximum magnetic entropy change (− ΔS_m"p"e"a"k) and the magnetic refrigerant capacity (R_C) of the BMG under a field of 5T are about 9.32 J·kg"−"1 ·K"−"1 and 832 J·kg"−"1, respectively, both of which are larger than the values of the Gd_5_5Co_2_5Al_2_0 BMG. The mechanism for the improved MCE by minor Sn addition is studied and the field dependence of − ΔS_m"p"e"a"k is investigated for a better understanding on the magneto-caloric behaviors of Gd_5_5Co_2_5Al_1_8Sn_2 BMG. (paper)

[en] We report the amorphization induced high magneto-caloric effect (MCE) of recently developed Gd₅₅Al₁₅Ni₃₀ bulk metallic glass (BMG). The magnetic properties of the Gd₅₅Al₁₅Ni₃₀ BMG are investigated in comparison with that of its crystalline counterpart. It is found that amorphization can increase the saturation magnetization and decrease the hysteresis of Gd₅₅ Al₁₅ Ni₃₀ alloys, which indicate the possible enhancement of MCE. The magnetic entropy changes and the refrigerant capacity of the BMG as well as the crystalline samples is calculated directly from isothermal magnetic measurements. The results show the amorphization induced high MCE of the alloy and the excellent refrigerant efficiency of Gd₅₅Al₁₅Ni₃₀ bulk metallic glass. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

[en] We investigate the kinetics and thermal stability of a simple Cu_50.3Zr_49.7 binary bulk metallic glass (BMG). The long-term thermal stability of Cu_50.3Zr_49.7 BMG is evaluated by a newly developed method from an extension of Vogel-Fulcher–Tammann analysis. The method has been proven to be valid in Cu_50.3Zr_49.7 or even other BMGs

[en] A dielectric loaded parallel plate waveguide sheet electron beam system can be taken as a reliable model for the practical dielectric loaded rectangular waveguide sheet beam system that has a transverse cross section with a large width to height ratio. By using kinetic theory, the dispersion equations for Cerenkov and cyclotron Cerenkov instabilities in the parallel plate waveguide sheet beam system have been obtained rigorously. The dependences of the growth rate of both instabilities on the electric and structural parameters have also been investigated in detail through numerical calculations. It is worthwhile to point out that adopting an electron beam with transverse velocity can evidently improve the growth rate of Cerenkov instability, which seems like the case of cyclotron Cerenkov instability.

[en] Detecting coherent phonons pose different challenges compared to coherent photons due to the much stronger interaction between phonons and matter. This is especially true for high frequency heat carrying phonons, which are intrinsic lattice vibrations experiencing many decoherence events with the environment, and are thus generally assumed to be incoherent. Two photon interference techniques, especially coherent population trapping (CPT) and electromagnetically induced transparency (EIT), have led to extremely sensitive detection, spectroscopy and metrology. Here, we propose the use of two photon interference in a three-level system to sense coherent phonons. Unlike prior works which have treated phonon coupling as damping, we account for coherent phonon coupling using a full quantum–mechanical treatment. We observe strong asymmetry in absorption spectrum in CPT and negative dispersion in EIT susceptibility in the presence of coherent phonon coupling which cannot be accounted for if only pure phonon damping is considered. Our proposal has application in sensing heat carrying coherent phonons effects and understanding coherent bosonic multi-pathway interference effects in three coupled oscillator systems. (paper)