Universal dynamics behavior in superionic conducting glasses

The inelastic neutron scattering experiment on superionic glass system AgI-AgPO₃ have been performed in the energy and momentum transfer range from ? 5 to 15 meV and 0 to 8 Å^? 1, respectively by using a time of flight MARI instrument at Rutherford Appleton Laboratory, ISIS, UK. The E-dependence of the inelastic data show an excess intensity at low energy around 3 meV, the so-called Boson peak, which increased with the dopant salt. The Q-dependence of the elastic scattering reveals a prepeak at anomalously low Q value around 0.8 Å^? 1, which is not observed in the undoped AgPO₃ glass. The Q-dependence in the energy region from 1 to 3 meV shows clearly an excess intensity at Q ~ 2.2 Å ^? 1compared with the undoped AgPO₃. All these features correlate with the increasing mobility of Ag⁺ ions due to the expansion of the network structure caused by salt doping, which leads to the increase of ionic conductivity. Similar results have also been observed in the corresponding superionic glass system AgI-Ag₂S-AgPO₃ that was observed by both MARI and NEAT instrument at HMI, Berlin. The results show a universal dynamic behavior in silver phosphate glasses.     

Compositional modification of Se-Ge-Sb chalcogenide glasses by addition of arsenic element

The modification of structural, thermal and optical properties of Se-Ge-Sb glasses by addition of arsenic element was the goal of this study. In this regards, six different glasses of Se₆₀Ge_40-xSb₅As_x (0 ≤ x ≤ 15) were prepared by conventional melt quenching technique in quartz ampoule. The produced samples were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), UV–Vis–NIR spectrophotometer, Fourier transform infrared (FTIR) and Raman spectroscopy. The fundamental absorption edge for of the glasses was analyzed in terms of the theory proposed by Davis and Mott. Based on the obtained results, the glass transition temperature, optical energy gap and Urbach energy of prepared glasses in this alloying system were in the range of 325–380 °C, 1.43–1.64 eV and 0.03–0.3547 eV, respectively. The as prepared glasses show anomalous behavior at 5–7.5 mole% of arsenic for the glass transition temperature, transmittance, absorption edge, optical energy gap and Urbach energy. Based on the Raman spectra, the structural analysis indicates that, increasing the network connectivity upon increasing the arsenic content up to 7.5 mole% is the main reason of anomalous behavior in Se₆₀Ge_40-xSb₅As_x (0 ≤ x ≤ 15) system.     

Structure and dynamics of octamethyl-ethinyl-ferrocene: an organometallic rotator phase

The onset of dynamics and the structural changes of octamethyl–ethinyl-ferrocene around a solid–solid phase transition at 248 K have been investigated using the novel technique of quasielastic nuclear forward scattering (QNFS) in a temperature range between 61 and 257 K at a photon energy of 14.413 keV, as well as X-ray powder diffraction at various energies. A pronounced hysteresis for both the dynamical and the structural properties is observed and confirmed by differential-scanning calorimetry. We assign the observed phenomena to a first-order transition from a low-symmetry low-temperature phase to a high-symmetry high-temperature plastically crystalline phase with nearly cubic symmetry. Possible mechanisms for this transition are discussed in the light of our results.     

Magnetic and magneto-optical properties of MnSb films on various substrates

Magnetic and magneto-optical properties of MnSb films with different crystalline orientations on various semiconductors of GaAs(1 0 0), GaAs(1 1 1)A, B, and sapphire(0 0 0 1) have been measured by a vibrating sample magnetometer (VSM) and a home-made magneto-optical Kerr effect (MOKE) system. All these samples have their easy axes in the plane and show ferromagnetic properties. Among these samples, the film on GaAs(1 1 1)B has the lowest coercive force H_c and the largest squareness (SQ) value, whereas the film on GaAs(1 0 0) shows the largest H_c and the lowest SQ value. A large Kerr rotation angle of about 0.3° was observed at a wavelength of λ=632.8 nm for the film on sapphire in the field applied both parallel and perpendicular to the film plane. However, the MnSn films on other substrates do not have an observable Kerr rotation. The dynamic effect of the hysteresis was also measured using our MOKE system. As the frequency of applied magnetic field increases, the loop rounds off at the corners and the loop area increases.     

Fluid dynamics of rotating detonation engines with hydrogen and hydrocarbon fuels

Rotating detonation engines (RDE’s) represent a logical step from pulsed detonation engine concepts to a continuous detonation engine concept for obtaining propulsion from the high efficiency detonation cycle. The hydrogen/air and hydrogen/oxygen RDE concepts have been most extensively studied, however, being able to use hydrocarbon fuels is essential for practical RDE’s. The current paper extends our hydrogen/air model to hydrocarbon fuels with both air and pure oxygen as the oxidizer. Before beginning the RDE calculations, several detonation tube results are summarized showing the ability of the code to reproduce the correct detonation velocity and CJ properties. In addition, a calculation capturing the expected irregular detonation cell patterns of ethylene/air is also shown. To do the full range of fuels and oxidizers, we found the use of temperature-dependent thermodynamic properties to be essential, especially for hydrocarbon/oxygen mixtures. The overall results for air-breathing RDE’s with hydrocarbons ranged from 1990 to 2540 s, while in pure oxygen mode the specific impulse varied from 700 to 1070 s. These results were between 85% and 89% of the expected ideal detonation cycle results, and are in line with previous hydrogen/air estimates from our previous work. We conclude from this that hydrocarbon RDE’s are viable and that the basic flow-field patterns and behaviors are very similar to the hydrogen/air cases detailed previously.     

Raman gain in modified tellurite glasses and thin films

We report the tailoring of Raman spectra of the tellurite glass by varying molar concentrations of phosphates, fluorides in phosphate modified tellurite glasses to analyze the Raman gain. From the measured Raman spectrum, the Raman gain and gain bandwidth in these glasses were calculated and compared. The structural features that give rise to the observed spectra and its dependence on glass composition are identified and reported. Raman gain as high as 170 × 10^? 13 m/W is obtained for glass modified by zinc oxide. Glass thin films prepared by pulsed laser deposition show a Raman gain of 5.0 × 10^? 13 m/W suggesting their importance in short waveguide Raman amplifier fabrication.     

Effect of nanocrystallization on the electronic conductivity of vanadate–phosphate glasses

Electronically conducting glasses of the composition xV₂O₅·(100 − x)P₂O₅ for 60 < x < 90 were prepared. The glasses of the composition corresponding to x = 90 exhibited the highest electrical conductivity and they were studied in more detail. The effects of the annealing of the samples on their electrical conductivity, structure and other characteristics were studied by impedance spectroscopy, X-ray diffractometry, DSC and SEM microscopy. It was shown that, at temperatures close to the crystallization temperature T_c (determined from DSC), these glasses turned into nanomaterials consisting of crystalline grains of V₂O₅ (average size 25–35 nm) embedded in the glassy matrix. Their electrical conductivity was higher and the temperature stability was better than those of the starting glasses. It is postulated that the major role in this conductivity enhancement is played by the interfacial regions between crystalline and amorphous phases. The annealing at temperatures exceeding T_c led to massive crystallization and to a conductivity drop. The XRD and SEM observations have shown that the material under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after the annealing at 340 °C and to polycrystalline after the annealing at 530 °C.The obtained results are in agreement with those of our earlier studies on mixed electronic–ionic conducting glasses of the ternary Li₂O–V₂O₅–P₂O₅ system.     

Enhanced fine particle collection by the application of SMPS energisation

Over the past decade or so the health problems associated with the inhalation of sub micron particles from industrial processes has taken prominence and has lead to the stricter emission legislation, such as the US PM 2.5 approach. Generally most forms of control equipment readily handle and collect particles greater than 1 micron diameter, however, those less than 1 micron diameter are very much more difficult to collect.In the case of electrostatic precipitation, which involves both particle charging and migration under the influence of an electric field, the larger particles, generally greater than 1 micron are charged by collision with the ions and electrons present in the inter electrode area. It will be shown that the charge on these particles is proportional to the radius squared and its migration velocity proportional to the voltage squared, both reducing with particle size. The very small particles however, are charged by a diffusion processes and migrate under the influence of Brownian motion, which increases as the particle size decreases. The result of this is that a typical particle size/efficiency curve indicates a significant penetration window in the 0.8–0.2 micron diameter range, which coincides with the change from collision to diffusion charging of the particles.Because of this penetration window, should an existing precipitator operating under optimum electrical conditions, not comply with fine particle emission requirements, the conventional performance enhancement scenario, since the charging and precipitation operating conditions have been already optimised, would be to increase the precipitator's plate area, a very expensive solution. It will be shown, however, that the replacement of the conventional mains energisation system by an SMPS approach in an existing ESP will enhance the collection efficiency of particles, particularly in the penetration window, as a result of the increase in both operating field voltages and currents.The SMPS approach was applied to a 2 field ESP dealing predominately with sub micron fume, which the Client wished to enhance the performance to enable higher recycle rates, while still complying with his emission permitting. This was initially assessed using PALCPE? (Proactive Approach to Low-Cost Precipitator Enhancement), which indicated a significant reduction in the fine particle emissions was achievable by operation under SMPS Operation. An SMPS unit was subsequently fitted to the outlet field of this precipitator and the operating data will be examined in detail. With the outlet field under a mains rectification energisation system the overall emission was ～25 mg/Nm³, which after installation of the SMPS unit reduced to less than 15 mg/Nm³.     

Free-volume defects investigation of GeS2-Ga2S3-CsI chalcogenide glasses by positron annihilation spectroscopy

The transformation behavior of free-volume defect in (80GeS₂-20Ga₂S₃)_100-x (CsI)_x (x = 0, 5, 10, 15 mol%) chalcogenide glasses was studied by employing positron annihilation spectroscopic technique, which could reveal valuable information for in-depth understanding of nano-structural defects in glassy matrix. The results indicate that the structural changes caused by CsI additives can be adequately described by positron trapping modes determined with two-state model. The initial addition of CsI (x = 5 mol%) led to a void contraction, whereas, the void agglomeration occurred with the increase of CsI and the free-volume defects of the glasses were obviously reduced. The atomic density ρ is inversely proportional to the number of these defects. Meanwhile, the UV cut-off edge shifts toward short-wavelength with increasing of CsI. This study provides the valuable information of defects evolution in GeS₂-Ga₂S₃-CsI glasses.     

Influence of the selenium content on thermo-mechanical and optical properties of Ge–Ga–Sb–S chalcogenide glasses

A number of Ge₁₇Ga₄Sb₁₀S_69−xSe_x (x = 0, 15, 30, 45, 60, and 69) chalcogenide glasses have been synthesized by a melt-quenching method to investigate the effect of the Se content on thermo-mechanical and optical properties of these glasses. While it was found that the glass transition temperature (T_g) decreases from 261 to 174 °C with increasing Se contents, crystallization temperature (T_c) peak only be observed in glasses with Se content of x = 45. It was evident from the measurements of structural and physical properties that changes of the glass network bring an apparent impact on the glass properties. Also, the substitution of Se for S in Ge–Ga–Sb glasses can significantly improve the thermal stability against crystallization and broaden the infrared transmission region.     

X-ray photoelectron spectroscopy of CeO2–Na2O–SiO2 glasses

A series of (CeO₂)_x–(Na₂O)_0.3–(SiO₂)_(0.7−x) glasses, where 0.025 ≤ x ≤ 0.075, have been synthesized and investigated by mean of X-ray photoelectron spectroscopy (XPS). The Ce 3d spin-orbit doublet was curve fitted in order to quantify the proportions of each cerium oxidation state in these glasses. It was found that Ce ions are predominantly in the Ce(III) state in glasses with compositions x ≤ 0.075, while mixed Ce valences were found in the glass with composition x = 0.10. The O 1s spectra have also been curve fitted with two components, one from bridging oxygen (BO) and the other from non-bridging oxygen atoms (NBO). The measured number of NBO, based on the fact that only oxygen atoms in the site Si–O–Na⁺ contribute to the NBO peak, was found to be constant at ∼35% for all samples, in good agreement with the value calculated from the glass composition and inductively coupled plasma (ICP) suggesting that Ce ions enter the network as a glass intermediate. The thermal measurements done on these glasses agree well with the XPS findings.     

Multichannel fiber laser Doppler vibrometer studies of low momentum and hypervelocity impacts

A multichannel optical fiber laser Doppler vibrometer was demonstrated with the capability of making simultaneous non-contact measurements of impacts at 3 different locations. Two sets of measurements were performed, firstly using small ball bearings (1 mm–5.5 mm) falling under gravity and secondly using small projectiles (1 mm) fired from an extremely high velocity light gas gun (LGG) with speeds in the range 1 km/s–8 km/s. Determination of impact damage is important for industries such as aerospace, military and rail, where the effect of an impact on the structure can result in a major structural damage. To our knowledge the research reported here demonstrates the first trials of a multichannel fiber laser Doppler vibrometer being used to detect hypervelocity impacts.     

Anomalous strain effect on the thermal conductivity of borophene: a reactive molecular dynamics study

Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, has been recently synthesized. Here we investigate mechanical properties and lattice thermal conductivity of borophene using reactive molecular dynamics simulations. We performed uniaxial tensile strain simulations at room temperature along in-plane directions, and found 2D elastic moduli of 188 N m⁻¹ and 403 N m⁻¹ along zigzag and armchair directions, respectively. This anisotropy is attributed to the buckling of the borophene structure along the zigzag direction. We also performed non-equilibrium molecular dynamics to calculate the lattice thermal conductivity. Considering its size-dependence, we predict room-temperature lattice thermal conductivities of 75.9 ± 5.0 W m⁻¹ K⁻¹ and 147 ± 7.3 W m⁻¹ K⁻¹, respectively, and estimate effective phonon mean free paths of 16.7 ± 1.7 nm and 21.4 ± 1.0 nm for the zigzag and armchair directions. In this case, the anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. We also observe that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. For a strain of 8% along the armchair direction the thermal conductivity increases by a factor of 3.5 (250%), whereas for the same amount of strain along the zigzag direction the increase is only by a factor of 1.2 (20%). Our predictions are in agreement with recent first principles results, at a fraction of the computational cost. The simulations shall serve as a guide for experiments concerning mechanical and thermal properties of borophene and related 2D materials.     

Clustered and integrated fluorescence spectra from single atmospheric aerosol particles excited by a 263- and 351-nm laser at New Haven,CT, and Adelphi,MD

Fluorescence spectra from individual micron-sized atmospheric aerosol particles were measured by a Dual-wavelength-excitation Particle Fluorescence Spectrometer (DPFS). Particles were drawn into our laboratory at Adelphi, MD, an urban site in the Washington, DC, metroplex and within the Yale University campus at New Haven, CT. Two fluorescence spectra were obtained for every individual particle as it was moving through the DPFS system and excited sequentially by single laser pulses at 263 and 351 nm. There were around ten to a few hundred particles detected per second and up to a few million per day within the 1–10 μm particle size range. The majority of the particles have weak fluorescence, but 10–50% of the particles have fluorescence signals above the noise level at both sites at different time period. For the first time, these Ultra Violet laser-induced-fluorescence (UV-LIF) spectra from individual particles were integrated every 10 min, which forms a group of about a few thousand to a few tens of thousand particles, to provide the averaged background atmospheric fluorescence spectral profiles which may be helpful in the development of bioaerosol detection systems, particularly those systems based on integrated fluorescence from a group of aerosol particles, such as Light Detection And Rangeing (LIDAR) remotor biosensor and the point sensor based on collected particles on substrate. These integrated spectral profiles had small variations from time to time and were distinguishable from that of the bacterial simulant B. subtilis. Also for the first time, the individual spectra excited by a 351 nm laser were grouped using unstructured hierarchical cluster analysis, with parameters chosen so that spectra clustered into 8 main categories. They showed less spectral variations than that excited by a 263-nm laser. Over 98% of the spectra were able to be grouped into 8 clusters, and over 90% of the fluorescent particles were in clusters 3–5 with a fluorescence emission peak around 420–470 nm; these were mostly from biological and organic carbon-containing compounds. Integrated fluorescence spectral profiles and averaged spectra for each cluster show high similarity between New Haven, CT and Adelphi, MD.     

Ionic conductivities of various GeS2-based oxy-sulfide amorphous materials prepared by melt-quenching and mechanical milling methods

We have previously explored the Li₂S + GeS₂ + GeO₂ system to determine the specific effect of added GeO₂ to a base 0.5Li₂S + 0.5GeS₂ glass composition. In this new study, we report the conductivities of these Li₂S + GeS₂ + GeO₂ glasses over their full glass forming range to more fully optimize the ionic conductivity. In addition to this study of bulk glasses, we have also studied the effect of creating powders of the bulk glasses and compared the conductivities of the bulk glasses to those of compacted powders. This latter study is relevant due to the fact that in most battery applications powders are the form of choice in forming battery stacks. Since we used the mechanical milling technique to produce the powders, we further extended this study to determine the extent to which the amorphous range could be expanded using the mechanical milling technique. Having access to these extended compositional range materials, we were able to extend all examinations of the role of composition, powder size, and compaction of the sample on the conductivity and we compared these results to those of the bulk glass samples.     

Magnetostructural study of iron sucrose

Magnetic and structural analyses have been performed on an iron sucrose complex used as a haematinic agent. The system contains two-line ferrihydrite particles of about 5 nm that are superparamagnetic above approximately 50 K. The observed low-temperature magnetic dynamics of this compound is closer to simple models than in the case of other iron-containing drugs for intravenous use like iron dextran.     

Effect of CuI on the formation and properties of Te-based far infrared transmitting chalcogenide glasses

A series of Ge–Te–CuI far infrared transmitting chalcohalide glasses were prepared by traditional melt-quenching method and the glass-forming region was determined. Properties measurements include density, DTA, XRD, SEM, Vis–NIR and infrared (IR) transmission spectra. The results show that with the addition of CuI, the glass-forming ability is improved and nearly 30 mol% CuI can be dissolved into the Ge₂₀Te_80?x(CuI)_x glass system. The density and glass transition temperature of Ge–Te–CuI chalcohalide glasses are within the range 5.459–5.960 g cm^?3 and 150–184 °C, respectively. These glasses all have wide optical transmission window from 1.8 to 25 μm and offer an alternative solution for far infrared transmitting materials.     

Synthesis and electrochemical properties of Li2S–B2S3–Li4SiO4

New Li⁺ ion-conductive glasses Li₂S–B₂S₃–Li₄SiO₄ were synthesized by rapid quenching, and they were transformed into glass ceramics by heat treatment. The heat treatment increased the ionic conductivities of the Li₄SiO₄-doped glasses, and the highest ionic conductivity observed in the system was 1.0 × 10^− 3 S cm^− 1 at room temperature. The glass ceramics were highly stable against electrochemical oxidation with a wide electrochemical window of 10 V.     

Structural and electrical properties of tellurovanadate glasses containing Li2O

Glassy materials are promising intercalation compounds, due to their open network structure and absence of grain boundaries. Some glasses containing alkali ions and a high concentration of transition metal ions can present mixed ionic-electronic conductivity and are therefore potential candidates for application as cathode material in Li-ion batteries. The present work is devoted to the ternary system xLi₂O–(1 − x)[0.3V₂O₅–0.7TeO₂] with 0 ≤ x ≤ 0.4. These compounds were prepared by heat treatment in air at 800 °C followed by traditional quenching. Raman spectroscopy and ⁵¹V nuclear magnetic resonance measurements were performed in order to highlight the structural short range order modifications induced by the introduction of the Li₂O network modifier. These structural effects can be related to the electrical behaviour, as studied by complex impedance spectroscopy measurements.     

Spiral MR fingerprinting at 7 T with simultaneous B1 estimation

Magnetic resonance fingerprinting is an efficient, new approach for quantitative imaging with MR. We aimed to extend this technique to cases with B1 + inhomogeneities within the imaging volume.Previous approaches have used abrupt changes in flip angles to estimate the B1 + field simultaneously with T1 and T2, using a Cartesian approach in a small-animal scanner at 4.7 T. Here, we evaluated whether a similar approach would be suitable for imaging human brains using spiral readouts with a 7 T scanner.We found that our modified scheme could significantly reduce the adverse effects of B1 + inhomogeneities even in extreme cases, reducing both the bias and the variance in T2 estimations by an order of magnitude when compared to literature methods. Acquisitions used less than 1.5 W/kg SAR and could be performed in 12 s per slice.In conclusion, our approach can be used to perform quantitative imaging of the brain at 7 T in a short time, simultaneously estimating the B1 + profile.