Heat transfer effects in nano-aluminum combustion at high temperatures

Recent measurements of nano-aluminum combustion in which burning time and peak particle temperature are measured simultaneously have suggested that heat transfer models currently used for burning nanoparticles may significantly overestimate heat losses during combustion. By applying conventional non-continuum heat transfer correlations to burning nano-aluminum particles, the observed peak temperatures, which greatly exceed the ambient temperature, should only be observable if the burning time were very short, of the order of 1 μs, whereas the observed burning time is two orders of magnitude larger. These observations can be reconciled if the energy accommodation coefficient for these conditions is of the order of 0.005, which is the value suggested by Altman, instead of approximately unity, which is the common assumption. Experimental data obtained in the heterogeneous shock tube under a wide array of conditions are compared with basic heat transfer models, and the agreement of both peak temperature values and emission intensity traces for low energy accommodation coefficients supports the hypothesis of Altman and co-workers.     

Reactive Liners Prepared Using Powders of Aluminum and Aluminum‐Magnesium Alloys

Cylindrical reactive liners filled with powders of aluminum, aluminum‐magnesium alloys, and aluminum‐magnesium powder blends were prepared and initiated by a centrally located explosive charge. The experiments were performed in a cubic chamber. Several transient pressure measurements were taken in addition to the quasistatic pressure caused by the explosion. Results were compared against a reference case with an inert liner filled with aluminum oxide powder. For all reactive liners, an increase in both quasistatic pressure and blast wave strength were observed compared to the case of an inert liner. In experiments with mechanically alloyed Al ⋅ Mg powders, the quasistatic pressure is effectively the same as in experiments with pure aluminum. An improvement in the achieved quasistatic pressure is observed for the liners with a cast alloyed Al ⋅ Mg powder. Most interestingly, a substantial contribution to the air blast indicative of very early reaction occurring in sub‐millisecond time scale is observed for all experiments with reactive liners. The most substantial improvement in the blast characteristics is observed in experiments with mechanically alloyed Al ⋅ Mg powders. While the mechanisms of prompt reactions of metals and alloys remain largely unexplored, the present results highlight the importance of such reactions for reactive liners and other components of energetic systems.     

A planar unimorph-based actuator with large vertical displacement capability. I. Experiment

A piezoelectric actuator utilizing a planar arrangement of unimorph elements that produces displacements perpendicular to the plane of the actuator is described. The elements are connected in series mechanically so that the vertical displacement of each element adds to the vertical displacements of the other elements. Two prototype actuators were built and tested. One was stick-built from individual bars of PZT and aluminum, which were epoxied together and connected to each other with short aluminum connector bars. The other was fabricated monolithically from a single plate of PZT by bead-blasting the PZT plate through a steel shadowmask to mill out the desired actuator shape. Copper bars epoxied to the milled-out PZT bars then formed the unimorph elements. The unloaded output displacement of each actuator versus applied voltage was measured as well as the displacement versus applied force with no applied voltage. These measurements were in agreement with the predictions of an electromechanical model of the actuator that has been developed. The model predicted and measurements verified that stiffeners can be added to the basic geometry that will significantly increase the force output without affecting the displacement versus applied voltage characteristic.     

Low-Pressure Flame Deposition of Nanostructured Oxide Films

The influence of electroless nickel plating on lead-based relaxor ferroelectric multilayer ceramic capacitors (MLCs) was studied by a comparison experiment. It was found that the influence is related to reactions in the electroless plating. It is proposed that adsorbed hydrogen atoms generated in electroless plating can diffuse into the ceramic bodies of MLCs and undergo some reduction reaction with them, resulting in the failure of electroless nickel plating. The implications for the negative influence of electroplating on MLCs and for the degradation in MLCs are also included, in which much attention is paid to the reduction reaction of hydrogen atoms generated by electrolysis of water.     

High-displacement piezoelectric actuator utilizing a meander-line geometry I. Experimental characterization

The compact linear-motion piezoelectric actuator developed has relatively large displacement capabilities. It is composed of a number of parallel bars of lead zirconium titanate (PZT) connected together in a meander-line configuration so that they are mechanically in series and electrically in parallel. The polarity of the adjacent bars is arranged so that if a given bar expands under the applied voltage, the adjacent bars contract. An electromechanical model of the actuator predicted and measurements verified that stiffeners added to the basic meander line geometry significantly increased the force output without affecting the displacement versus applied voltage relationship.     

Combustion Measurements of Fuel‐Rich Aluminum and Molybdenum Oxide Nano‐Composite Mixtures

Fuel rich nano‐composite powders of aluminum and molybdenum oxide were tested for ignition and combustion behind the incident and reflected shock waves in a shock tube. The powders consisted of approximately 10 μm particles, each of which contained Al and MoO₃ mixed by mechanical alloying on the nano‐scale. These powders were aluminum rich with composition ratios of 4 : 1, 8 : 1, and 16 : 1 Al : MoO₃ by mass. Ignition tests were performed behind incident shocks for temperatures in the range of 900 to 1500 K. From these tests, ignition delay times were obtained, and some information on combustion duration was also derived. Samples were tested in air at 0.2 MPa, and compared against nano‐Al, 2.7 μm Al, and 10 μm Al baselines. Ignition results for the baseline Al cases were as expected: 10 μm Al not igniting until 2000 K, 2 μm Al igniting down to ∼1400 K, and n‐Al igniting as low as 1150 K. The thermite samples showed considerable improvement in ignition characteristics. At the lowest temperature tested (900 K), both the 8 : 1 and 4 : 1 samples ignited within 250 μs. The 16 : 1 sample (94% Al) ignited down to 1050 K – which represents an improvement of roughly 1000 K over baseline Al with only a small energetic penalty. In all cases, the ignition delay increased as the amount of MoO₃ in the composite was reduced. The 4 : 1 nano‐composite material ignited as fast or faster than the n‐Al samples. Ignition delay increased with decreasing temperature, as expected. Emission spectra and temperature data were also taken for all samples using high‐speed pyrometry and time‐integrated spectroscopy. In these cases, measurements were made behind the reflected shock using end‐wall loading, though the conditions (temperature, pressure, and gas composition) were identical to the incident shock tests. Spectroscopy showed strong AlO features in all the samples, and the spectra fit well to an equilibrium temperature. Broadband, low resolution spectra were also fit to continuum, gray body temperatures. In general, the observed temperatures were reasonably close to 3500 K, which is similar to the combustion temperatures of pure aluminum under these conditions.     

IgM and IgG Immunoreactivity of SARS-CoV-2 Recombinant M Protein

Diagnostic evaluation of specific antibodies against the SARS-CoV-2 virus is mainly based on spike (S) and nucleocapsid (N) proteins. Despite the critical functions in virus infection and contribution to the pattern of immunodominance in COVID-19, exploitation of the most abundant membrane (M) protein in the SARS-CoV-2 serology tests is minimal. This study investigated the recombinant M protein’s immunoreactivity with the sera from COVID-19 convalescents. In silico designed protein was created from the outer N-terminal part (19 aa) and internal C-terminal tail (101–222 aa) of the M protein ({"type":"entrez-protein","attrs":{"text":"YP_009724393.1","term_id":"1796318601","term_text":"YP_009724393.1"}}YP_009724393.1) and was recombinantly produced and purified. The designed M protein (16,498.74 Da, pI 8.79) revealed both IgM and IgG reactivity with serum samples from COVID-19 convalescents in Western blot. In ELISA, more than 93% (28/30) of COVID-19 sera were positive for IgM detection, and more than 96% (29/30) were positive for specific IgG detection to M protein. Based on the capacity to provoke an immune response and its strong antigenic properties, as shown here, and the fact that it is also involved in the virion entry into host cells, the M protein of the SARS-CoV-2 virus as a good antigen has the potential in diagnostic purposes and vaccine design.     

TRIGA reactor spent fuel pool under severe earthquake conditions

Supplemental criticality safety analysis of a pool type storage for TRIGA spent fuel at ‘Jo ef Stefan’ Institute in Ljubljana, Slovenia, is presented. Previous results (Ravnik, M, Glumac, B., 1996. Nucl. Technol. 114, 365–371) have shown that subcriticality is not guaranteed for some postulated accidents. To mitigate this deficiency, a study was made about replacing a certain number of fuel elements in the rack with absorber rods (Glumac, B., Ravnik, M., Logar, M., 1997. Nucl. Technol. 117, 248–254.) to lower the supercriticality probability, when the pitch is decreased to contact (as a consequence of a severe earthquake) in a square arrangement. The criticality analysis for the hexagonal contact pitch is presented in this paper, following the same scenario as outlined above. The Monte Carlo computer code MCNP4B with ENDF-B/VI library and detailed three dimensional geometry was used. First, the analysis about the influence of the number of triangular fuel piles on the bottom that could appear, if the fuel rack, made of three segments, disintegrates, is presented. Next, the number of uniformly mixed absorber rods in the lattice needed to sustain the subcriticality of the storage for hexagonal contact pitch is studied. Because of supercriticality possibility due to random mixing of the absorber rods in the case of lattice compaction, a probabilistic study was made in order to sample the probability density functions for random lattice loadings of the absorber rods. The results show that reasonably low probabilities for supercriticality can be achieved even when fresh 12 wt.% standard TRIGA fuel is stored in the spent fuel pool.     

Chemical Ecology of Cave-Dwelling Millipedes: Defensive Secretions of the Typhloiulini (Diplopoda,Julida, Julidae)

Cave animals live under highly constant ecological conditions and in permanent darkness, and many evolutionary adaptations of cave-dwellers have been triggered by their specific environment. A similar “cave effect” leading to pronounced chemical interactions under such conditions may be assumed, but the chemoecology of troglobionts is mostly unknown. We investigated the defensive chemistry of a largely cave-dwelling julid group, the controversial tribe “Typhloiulini”, and we included some cave-dwelling and some endogean representatives. While chemical defense in juliform diplopods is known to be highly uniform, and mainly based on methyl- and methoxy-substituted benzoquinones, the defensive secretions of typhloiulines contained ethyl-benzoquinones and related compounds. Interestingly, ethyl-benzoquinones were found in some, but not all cave-dwelling typhloiulines, and some non-cave dwellers also contained these compounds. On the other hand, ethyl-benzoquinones were not detected in troglobiont nor in endogean typhloiuline outgroups. In order to explain the taxonomic pattern of ethyl-benzoquinone occurrence, and to unravel whether a cave-effect triggered ethyl-benzoquinone evolution, we classed the “Typhloiulini” investigated here within a phylogenetic framework of julid taxa, and traced the evolutionary history of ethyl-benzoquinones in typhloiulines in relation to cave-dwelling. The results indicated a cave-independent evolution of ethyl-substituted benzoquinones, indicating the absence of a “cave effect” on the secretions of troglobiont Typhloiulini. Ethyl-benzoquinones probably evolved early in an epi- or endogean ancestor of a clade including several, but not all Typhloiulus (basically comprising a taxonomic entity known as “Typhloiulus sensu stricto”) and Serboiulus. Ethyl-benzoquinones are proposed as novel and valuable chemical characters for julid systematics.