Size distribution of exhaled particles in the range from 0.01 to 2.0 μm

This study investigates the number size distribution of endogenously produced exhaled particles during tidal breathing and breathing with airway closure. This is the first time that the region below 0.4 μm has been investigated. The particle concentration was generally lower for tidal breathing than for airway closure, although the inter-individual variation was large. During tidal breathing, the size distribution peaks at around 0.07 μm. This peak is still present during the airway closure manoeuvre, but an additional broad and strong peak is found between 0.2 and 0.5 μm. This suggests that different mechanisms govern the generation of particles in the two cases. The particles produced from airway closure may be attributed to formation of film droplets in the distal bronchioles during inhalation. It is speculated that the very small particles are film droplets originating from the alveolar region.     

Determination of the initial heat treatment temperature in the two-step sintering of xAl–ZnO (x = 1, 2, and 3 wt.%)

The application of a two-step sintering route successfully decreased the sintering temperature of Al-doped ZnO transparent conducting oxide target. The two-step sintering consisted of initial heat treatment (IHT) at 800–1000 °C under mild (<2 MPa) external pressure, and pressureless final sintering at 1250–1350 °C in a separate furnace. The optimum IHTs for effective densification depended on the Al doping. The 800 °C IHT was effective for 1 wt.% Al doping, and the 1000 °C IHT, for 3 wt.% Al doping. As a result of the effective IHT, the volume of the micron sized pore decreased with the fragmentation into submicron pores. This suggests that cohesion of the secondary particles occurred during the effective IHT. The IHT temperature for achieving cohesion increased in the 3 wt.% Al doping. The criterion for determining the IHT in the two-step sintering was identified as the minimum temperature at which the cohesion of secondary particles can be achieved.     

Carbon nanotubes horizontal interconnects with end-bonded contacts,diameters down to 50 nm and lengths up to 20 μm

This work describes a novel approach to fabricate horizontal nanotube interconnects with dimensions comparable to state-of-the-art copper interconnects. The interconnects consist of carbon nanotubes bundles with wall density ≈10¹³ cm⁻², wire lengths of tens of micrometers and wire diameters scalable to 50 nm. The nanotubes are first grown vertically, inside vias with diameters ranging from 300 to 200 nm, and then flipped on the horizontal direction. Symmetrical contacts are made at the tips of the nanotubes in the so-called end-bonded geometry via a metallization process with a key dry-etch step. The quality of the contacts and the nanotubes is evaluated from the electrical measurements by extracting the specific contact resistivity and the carbon nanotube resistivity, respectively. The measured contact resistivity is 3.9 × 10⁻⁸ Ω cm² with Pd/Au contacts. This is the lowest value ever reported so far for nanotubes contacted in an end-bonded geometry. The nanotube resistivity is as low as 1.1 mΩ cm, a value among the best reported to date and only two decades higher than that of copper.     

Experimental and computational study of reaerosolization of 1 to 5 μm PSL microspheres using jet impingement

Chemical, biological, radiological, and explosive incidents produce immediate as well as delayed hazards as a result of reaerosolization of deposited particles from surfaces. Understanding reaerosolization mechanisms is important for hazard prediction and mitigation processes. A method to efficiently reaerosolize 1–5 µm particles (approximately the size of bacterial spores) has not been previously available; therefore, this study was conducted to test a simple and effective method to reaerosolize such particles. In this work, a high-speed vertical impinging jet was used to reaerosolize 1–5 µm polystyrene latex microspheres from a substrate, and measured removal efficiencies were compared with the performed numerical predictions. Experiments were conducted to determine the effect of location, number of pulsed air jets, particle size, aerosol generation methodology (wet and dry), and relative humidity (RH) on the amount of reaerosolization. The experimental results agreed with the numerical predictions and demonstrated that maximal reaerosolization efficiency (～90% in several cases) occurs at a few millimeters from the jet center. At the peak removal location, reaerosolization increased with increasing particle size and with increasing number of pulsed air jets. Dry deposited particles exhibited significantly higher reaerosolization compared to wet deposited particles. Equilibration of samples at low (20%) RH showed higher reaerosolization compared to the high RH conditions for dry deposited particles. This study demonstrates the effectiveness of using a single vertical impinging jet for localized reaerosolization of bacteria-sized particles from surfaces.     

Electronic properties and stability of M2O3 (M = Al,Ga, In) and alloy (MxGa1-x)2O3 in α and β phases: A theoretical study

Ga₂O₃ is clearly emerging as an important wide band-gap semiconductor. Band-gap engineering is now highly demanded for expanding its applications. Alloying with the same group of metal oxides is a straightforward and effective way. In this work, by using hybrid density functional theory calculations, the structural, electronic properties, and phase stability of group IIIA (Al, Ga, In) metal oxides and their ternary alloys (M_xGa_1-x)₂O₃ (M = Al, In) in the corundum and monoclinic phases are systematically investigated. The lattice constants, elastic constants, modulus, formation energies, band-gaps, band-gap deformation potentials, band-edge alignments, band-gap bowing, and ternary alloy formation energies are obtained. The basic relations between the geometric structure and electronic properties are discussed. It is found that the cation ordered structure is the most stable alloy structure in the monoclinic phase, rather than the random alloy structure as is commonly thought. A phase stability diagram of the (M_xGa_1-x)₂O₃ alloys is established, showing that the stable phase of the alloy changes from the monoclinic phase to the corundum phase when the incorporation of Al₂O₃ (In₂O₃) is greater than 69% (76%). These results can be used to understand the relative experimental data and shed some light on the synthesis and device design efforts of Ga₂O₃.     

Customized casting of unstacked graphene with high surface area (>1300 m2 g−1) and its application in oxygen reduction reaction

Introducing graphene protuberances covalently bonded with the graphene sheets is a straightforward strategy to avoid the stacking of graphene layers. The as-obtained unstacked double-layer templated graphene (DTG) is expected to fully demonstrate intrinsic properties of graphene assemblies if its detailed structure and component can be well controlled. Herein, both the lateral size and graphene protuberance size and areal density of DTG were well modulated through adjusting the template morphology and casting procedures. The lateral size of the as-obtained DTG was ranging from 0.4 to 2 μm. They exhibited a very high specific surface area ranging from 1336 to 1579 m² g⁻¹ and tailorable graphene protuberances with areal density from 5.3 × 10¹⁴ to 7.8 × 10¹⁴ m⁻². DTG flakes with more hydrophilic surface and well tunable reactivity were obtained by introducing nitrogen into DTG through in-situ deposition. The as-synthesized N-doped DTG afforded significantly improved reactivity on oxygen reduction reaction (nearly 50 mV positively shifted onset potential compared with that of pristine DTG and a current preservation of 92.8% after 16,000 s test).     

Experimental measurement and modelling with Aspen Plus® of the phase behaviour of supercritical CO2 + (n-dodecane + 1-decanol + 3,7-dimethyl-1-octanol)

Experimental phase equilibrium data for the systems CO₂ + n-dodecane, CO₂ + 1-decanol and CO₂ + 3,7-dimethyl-1-octanol were used to determine values for binary interaction parameters for use in the RK-ASPEN thermodynamic model in Aspen Plus^®. Bubble and dew point data of the mixtures CO₂ + (n-dodecane + 1-decanol), CO₂ + (n-dodecane + 3,7-dimethyl-1-octanol), CO₂ + (1-decanol + 3,7-dimethyl-1-octanol) and CO₂ + (n-dodecane + 1-decanol + 3,7-dimethyl-1-octanol) were measured experimentally in a static synthetic view cell, and compared to the data predicted by the RK-ASPEN model. The model predicted the phase equilibrium data reasonably well in the low solute concentration region; significant deviation of model predictions from experimental data occurred in the mixture critical and high solute concentration regions due to the exclusion of solute–solute interaction parameters in the model. Distribution coefficients and separation factors were determined for the multi-component mixture and separation of the alkane from the alcohol mixture with a supercritical fluid extraction process was found to be possible.     

Thermal dehydration of Y(TFA)3(H2O)3: Synthesis and molecular structures of [Y(μ,η1:η1-TFA)3(THF)(H2O)]1∞ · THF and [Y4(μ3-OH)4(μ,η1:η1-TFA)6(η1-TFA)(η2-TFA)(THF)3(DMSO)(H2O)] · 6THF (TFA = trifluoroacetate)

In order to obtain a better anhydrous precursor for various applications in materials science and catalysis, thermal dehydration reactions of Y(TFA)₃(H₂O)₃ (TFA = trifluoroacetate) (A) were investigated. Thermal treatment of A at different temperatures under vacuum (5 × 10^?2 mm) for several hours failed to give totally anhydrous yttrium trifluoroacetate (as indicated by IR). Two different complexes, a partially dehydrated [Y(μ,η¹:η¹-TFA)₃(THF)(H₂O)]_1∞·THF (1) and a partially hydrolyzed [Y₄(μ₃-OH)₄(μ,η¹:η¹-TFA)₆(η¹-TFA)(η²-TFA)(THF)₃(DMSO)(H₂O)] · 6THF (2), were obtained with good and moderate yield, respectively, by crystallization of two different thermally treated batches of A from THF (or THF + DMSO) at room temperature. More efficient dehydration of A could be achieved at 200 °C in a furnace, the obtained anhydrous yttrium tris-trifluoroacetate giving Y(TFA)₃(THF)₂ (3) on crystallization from THF. All the products were characterized by elemental analyses, FT-IR and ¹H NMR spectroscopy as well as thermo-gravimetric analysis. In addition, single crystal X-ray structures are reported for 1 and 2, which show either a terminal (η¹ and η²) or bridging (μ,η¹:η¹) bonding behavior of the TFA ligand.     

Challenges to graphene growth on SiC(0 0 0 1‾): Substrate effects,hydrogen etching and growth ambient

Controlling the uniformity and morphology of graphene grown on the C-face of SiC is more difficult than on the Si-face. To improve graphene grown on the C-face, a continuous growth process was developed in a conventional tube furnace that included in situ surface preparation by annealing in H₂ followed by an Ar-mediated growth, which was done at a variety of different temperatures and pressures. Optimized H₂ etch conditions for the C-face were developed to improve the starting substrate morphology and reduce the effect of substrate defects on growth. The resulting graphene film, however, had non-uniform thickness due to intrinsic bulk defects within the SiC substrate and an interfacial oxide. Differences between substrate properties, such as polytype, are shown to have a significant effect on growth, with a 4H substrate displaying faster in-plane graphene growth than a 6H substrate. A primarily 2-domain graphene film with significant rotational disorder was found regardless of the starting substrate and growth conditions. Ultra-high vacuum desorption of the interfacial oxide caused the graphene to reorder into a single preferred rotational orientation, suggesting trace oxygen impurities in the growth chamber can play an important role in graphene growth on the C-face of SiC.     

Performance enhancement of block-copolymer solar cells through tapering the donor–acceptor interface: A multiscale study

Tapered block copolymers offer an exciting opportunity to tailor the interfacial region between different components by conserving their phase-separated mesoscale structure, which enable the generation of polymer systems with the desired spatio-dynamic properties. Here, we explore their usefulness for optimizing the photovoltaic performance of polymer bulk heterojunctions. To this end, we apply a recently developed particle-based multiscale solar-cell algorithm and investigate the effect of random tapering at the chemical junctions between the electron-donor- (D) and electron-acceptor- (A) blocks on the photovoltaic properties of various lamellar-like polyfluorene-based block-copolymer systems. Our simulation results reveal that introducing a tapered middle block with optimal length leads to a significant increase of the exciton dissociation efficiency, but deteriorates the charge transport efficiency only moderately. This results in a gain of the internal quantum efficiency from 25 up to 39% by increasing the thickness of the active layer of the solar cell from 10 up to 50 nm in direction to the DA interface.     

Assembly of 8YSZ nanoparticles into gas-tight 1-2 μm thick 8YSZ electrolyte layers using wet coating methods

The application of a thin film electrolyte layer with a thickness in the micrometer range could greatly improve current solid oxide fuel cells (SOFCs) in terms of operating temperature and power output. Since the achievable minimal layer thickness with conventional powder coating methods is limited to ∼5 μm, a variety of thin film methods have been studied, but results on regular large-scale anode substrates are still lacking in the literature. In this paper, a wet coating process is presented for fabricating gas-tight 1-2 μm thick 8YSZ electrolyte layers on a regular NiO/8YSZ substrate, with a rough surface, a high porosity and a large pore size. These layers were deposited in a similar way as conventional suspension based layers, but the essential difference includes the use of coating liquids (nano-dispersion, sol) with a considerably smaller particle size (85 nm, 60 nm, 35 nm, 6 nm). Successful deposition of such layers was accomplished by means of an innovative coating process, which involves the preparation of a hybrid polyvinyl alcohol/8YSZ membrane by dip-coating or spin-coating and subsequently burning out the polymer part at 500 °C. Results from He leak tests confirmed that the sintered layers posses a very low number of defects and with values in the range 10⁻⁴-10⁻⁶ (hPa dm³)/(s cm²) the gas-tightness of the thin film layers is satisfactory for fuel cell operation. Moreover, preliminary results have also indicated a potential reduction of the sintering temperature from 1400 °C to the range 1200-1300 °C, using the presented coating process.     

Investigation of the acousto-optical properties of Ge–As–Te–(Se) chalcogenide glasses at 10.6 μm wavelength

The acousto-optic parameters of Ge₁₀As_90−xTe_x (x = 30, 40, 50, 60, 70 mol%) and Ge₁₀As₂₀Te_70−ySe_y (y = 20, 30, 40, 50 mol%) glasses, were studied systematically to compare the pros and cons of Te-based and Se-based chalcogenide glasses in acousto-optic performance, as well as the thermomechanical properties. In the Ge₁₀As_90−xTe_x system, the acousto-optic figure of merit (M₂) increased with increased Te content, and the maximum M₂ of 2279 × 10⁻¹⁸ s³/g, which is 13 times that of commercial single-crystal Ge, obtained in Ge₁₀As₂₀Te₇₀ at 10.6 μm. However, its thermal properties and elastic modulus decreased and the acoustic attenuation (α) at different ultrasonic frequencies increased accordingly. In the Ge₁₀As₂₀Te_70−ySe_y system, the thermomechanical performance of the glasses improved with the introduction of Se element, the overall α was lower than that of Te-based chalcogenide glasses, and the minimum α was 5.29 dB/cm at 30 MHz ultrasonic frequency, although its M₂ was inferior to that of Te-based chalcogenide glasses. Additionally, the difference in the α of these glasses was smaller at low ultrasonic frequencies than at high ultrasonic frequencies. This work will promote the practical application of chalcogenide glasses as promising materials with outstanding acousto-optic properties in low ultrasonic frequency acousto-optic devices.     

Crystal structure,mixture behavior,and microwave dielectric properties of novel temperature stable (1 − x)MgMoO4 − xTiO2 composite ceramics

Novel temperature stable MgMoO₄–TiO₂ microwave dielectric ceramics were prepared by a solid state reaction process at low temperature (950 °C). As TiO₂ content increases, the relative permittivity increases while the Q × f value decreases, and the variation mechanisms are proposed, respectively. The temperature coefficient of resonant frequency (τ_f) shifts to the positive direction as TiO₂ is added. The mixture mechanisms of τ_f value for two-phase composite materials are supposed. A near-zero τ_f value (3.2 ppm/°C) is obtained when x = 0.3, with ε_r = 9.13 ± 0.03 and Q × f = 11,990 GHz. The 0.7MgMoO₄–0.3TiO₂ composites are considered to be appropriate as a low temperature co-fired ceramic material for microwave wireless communication applications.     

A comparative study on the thermal stability,textural, and structural properties of mesostructured γ-Al2O3 granules in the presence of La,Sn, and B additives

Mesoporous γ-alumina is widely used as catalyst support in various catalytic reactions of industrial interest. However, due to the instability of γ-alumina at elevated temperatures, many efforts have been reported to inhibit the α-alumina phase transition through doping with suitable metalloids, as well as transition, post-transition, or rare-earth elements. In the present study, undoped and La-, Sn-, and B-doped alumina granules were synthesized via sol-gel/oil drop method with the aim to clarify the role of the additives and their content on the porous structure as well as on the chemical, structural, and microstructural behavior of γ-alumina. XRD and DTA/TG results demonstrated that thermal stability of transition aluminas increases more than 100 °C by 3 wt% lanthanum and tin doping; however, boron doping seems to have only negligible effect on the thermal stability. On the other hand, based on nitrogen adsorption-desorption analysis, tin and boron-doped aluminas showed a higher surface area at 750 °C (between 214.74 m²/g to 245.97 m²/g) but higher loss in the surface area after calcination at 1200 °C (between 25.45 m²/g to 8.57 m²/g). On the contrary, the 3 wt% La-doped alumina sample, with a relatively high surface area at 750 °C (227.17 m²/g), exhibited the highest surface area after calcination at 1200 °C (53.07 m²/g). ²⁷Al MAS NMR and HRTEM studies indicated that the presence of 3 wt% La in alumina structure leads to thermal and mesoporous structure stability up to 1200 °C by inhibiting oxygen lattice restructuring. These results provide a comparative perspective of La, B, and Sn additives' behavior in γ-alumina.     

Crystal structure and phase formation of MgO–MoO3-based ceramics with ultralow dielectric loss: A comprehensive study

The MgO-MoO₃ system shows significant potential for applications in microwave dielectric ceramics. However, the formation mechanism, crystal structures, and microwave dielectric properties of this system have not been systematically investigated. This work aims to comprehensively study the crystal structures, phase transitions, and microwave dielectric properties of compounds in the MgO-MoO₃ system. In particular, the research delves into the unexplored transformation mechanism from β-MgMo₂O₇ to α-MgMo₂O₇ and MgMoO₄. As a result, the three compounds exhibiting favorable microwave dielectric properties have been successfully fabricated. These compounds can be effectively sintered at temperatures ranging from 685 to 900°C and exhibited dielectric constants (ε_r) ranging from 5.41 to 6.89, as well as Qf values ranging from 100 000 to 130 000 GHz. Additionally, prototype microstrip antennas are designed and fabricated using β-MgMo₂O₇ and MgMoO₄ ceramics as substrates. The obtained antenna's performance is excellent, with S₁₁ values below −30 dB and a gain exceeding 6 dB at 5.8 GHz, highlighting the potential of the developed ceramics for practical applications in microwave devices.     

Realization of pure red emission from energy transfer in the Er3+–Tm3+ system under 1550 nm excitation

NaY(WO₄)₂ is one of the excellent host materials for high-efficient upconversion luminescence, but it is still challenging to obtain red emission via lanthanide doping. In this work, pure red emission was achieved in the heavily-Er³⁺-doped NaY(WO₄)₂ by using a 1550 nm laser diode and introducing mediator Tm³⁺ ions in the lattice. On basis of the analysis of steady-state and transient-state luminescence properties related to dopant concentration and excitation wavelength, all possible red emission mechanisms were discussed. Finally, it has been demonstrated that the high-purity red emission was due to the several energy transfer processes between Er³⁺ and Tm³⁺. Our results provide a convenient pathway to investigate the upconversion luminescence mechanisms.