Thermomechanical Properties of Polypropylene-Based Lightweight Composites Modeled on the Mesoscale

A waste-based particle polymer composite (WPPCs) made of foam glass and polypropylene was developed as a low-cost construction material. Thermomechanical properties of the composite, including creep properties of WPPC and polypropylene binder, were examined. By adding a relatively small amount of polypropylene to foam glass (about 2:8 in volume parts), the maximum bearing capacity at room temperature of the composite increased from 1.9 (pure foam glass) to 15 MPa. A significant creep strain accumulated during compressive loading of WPPC (5 MPa) in the first 2000 s at elevated temperatures (40, 60 °C). In the study, Kafka’s mesomechanical model was used to simulate creep strain changes in time for various temperatures. The applicability of Kafka’s mesomechanical model for simulating creep properties of the studied composite material was demonstrated.     

Fixed-gain CMOS differential amplifiers with no external feedback for a wide temperature range

We present original CMOS amplifiers designed for the DC to 10 MHz frequency range and operating in the 70-380 K temperature range. Aimed applications concern readout circuitry to be associated with THz bolometric pixels (either high-T_c superconducting or uncooled semiconducting), which require accuracy, low noise and low power consumption. Two designs are described that both exhibit high fixed-gain (40 dB) in a feedback-free architecture, which is based on a new low-transconductance composite transistor for an accurate control of this gain. Both amplifiers have been realized in a regular 0.35 μm CMOS process and tested in the 4.2-380 K temperature range, exhibiting good agreement between designed and measured characteristics.     

Efficiency of metal activators of accelerated sulfur vulcanization

The effects of copper, mercury, nickel, zinc, cadmium, indium, magnesium, and calcium stearates on the course of N-cyclohexyl-2-benzthiazylsulphenamide-accelerated sulfur vulcanization of natural rubber have been investigated on the basis of curemeter measurements at 145°C. The differences in the efficiencies of these metal activators of accelerated sulfur vulcanization have been discussed from the points of view of the electron configurations of the metals and their affinities to sulfur. We attempted to determine why zinc oxide is generally accepted as the best metal vulcanization activator. © 1993 John Wiley & Sons, Inc.     

Die wirtschaftlichen Transformationsgesetze und Transformatorenentwürfe bei Berücksichtigung der wahren Änderung der Eisenverluste mit der magnetischen Liniendichte

Zusammenfassung Bei der Berechnung des Transformatorenentwurfes wird die wahre Änderung der Eisenverluste mit der Liniendichte berücksichtigt. Dadurch werden im allgemeinen niedrigere optimale Werte der Liniendichte gewonnen als nach dem bisher allgemein angewandten quadratischen Näherungsgesetz. Durch Interpretation der die Kleinstwerte bestimmenden Gleichungen werden wirtschaftliche Transformationsgesetze abgeleitet, deren Fassung zum Teil neu ist, zum Teil Modifikationen schon bekannter Gesetze darstellt, die durch die Einführung der wahren Änderung der Eisenverluste mit der Liniendichte bedingt sind. Ein Berechnungsbeispiel ergänzt die Ausführungen.Zusammenstellung der verwendeten Formelzeichen a Spezifische Jahreskosten der Eisenverluste in RM/kgG^u - b spezifische Jahreskosten der Stromwärme in RM · mm⁴/kg · A² - B Säulenliniendichte in G - B _o Ausgangsliniendichte in G - C 0,25··_e·f_e·10^–3 - D Kernkreisdurchmesser in Zentimeter - f Frequenz - f _e Eisenfüllfaktor, bezogen auf den Kernkreis - f _w Fensterfüllfaktor, gemessen von Kernkreis zu Kernkreis und von Jochkante zu Jochkante - G _e Kerneisengewicht in Kilogramm - G _w Wicklungsgewicht in Kilogramm - h Verhältnis der Material- und Verlustkosten der Joche - h _e jährliche Betriebsstunden der Eisenwärme - h _w jährliche Betriebsstunden der Stromwärme - i Stromdichte in A/mm² bei Vollast - k Jochverstärkungsverhältnis - K jährliche Transformationskosten in RM - K _Ve jährliche Eisenverlustkosten, d. h. jährliche Kosten der Eisenwärme und der für sie notwendigen Kühleinrichtung in RM - K _Vw jährliche Stromwärmekosten, d. h. jährliche Kosten der Stromwärme und der für sie notwendigen Kühleinrichtung in RM - L Lagrangesche Hilfsfunktion - n _w·f_w/ _e·f_e - N Transformatorscheinleistung in kVA - P _e spezifische Jahreskosten für das Kerneisen, d. h. die auf ein Kilogramm Kerneisen entfallenden jährlichen Kapitalskosten in RM/kg - P _k spezifische Jahreskosten für die Kühleinrichtung, d. h. jährliche Kapitalskosten der auf ein kW Verluste entfallenden Kühleinrichtung in RM/kW - P _Ve Preis der kWh für die Eisenwärme in RM/kWh - P _Vw Preis der kWh für die Stromwärme in RM/kWh - P _w spezifische Jahreskosten für das Wicklungsmaterial, d. h. die auf ein Kilogramm Wicklungsmaterial entfallenden jährlichen Kapitalskosten in RM/kg - t Volumen des über den Säulen liegenden Jocheisens/Jochquerschnitt × Kernkreisdurchmesser - u Exponent der die Abhängigkeit der Eisenverluste von der magnetischen Liniendichte darstellenden Näherungsfunktion - v ₀ Eisenwärmeverlust in W/kg bei der Ausgangsliniendichte B₀ - v _w Stromwärmeverlust in W/kg bei der Stromdichtei= 1 A/mm² - V _e Kerneisenverlustleistung in kW - V _s Säuleneisenverlustleistung in kW - x relative Säulenhohe =Säulenhöhe/Kernkreisdurchmesser - y relative Fensterbreite = Fensterbreite/Kernkreisdurchmesser - _e Wichte des Eisens in kg/dm³ - _w Wichte der Wicklung in kg/dm³ - Lagrangescher Hilfsfaktor     

Effect of aerosil on the course of thiuram accelerated sulfur vulcanization

Tetramethylthiuram disulfide (TMTD)-accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 145°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. The cure curves as well as their linearized forms (dependences of the logarithm of the extent of vulcanization on the cure time) clearly show that at lower cure temperatures the course of the vulcanization differs significantly from the first-order rate law. These digressions have been removed by the addition of a highly dispersed silica gel, Aerosil, which simultaneously speeds up the course of the vulcanization up to the value corresponding to the rate of zinc dimethyldithiocarbamate (ZnDMDC)-accelerated sulfur vulcanization. These results are in accordance with our recent theory supposing that ZnDMDC is the actual accelerator in TMTD-accelerated sulfur systems. In the presence of Aerosil, the formation of ZnDMDC from TMTD is catalyzed via dispersed silica gel. Support for this view derives from the temperature dependences of vulcanization reactions. The activation energies of TMTD-accelerated sulfur vulcanizations in the absence (31 kcal/mole) and in the presence of Aerosil (23.5 kcal/mole) correspond exactly to the values calculated from the rate constants of the thiuram decrease in TMTD-accelerated vulcanization (30 kcal/mole) and from the rate constants of crosslinking in the dithiocarbamate-accelerated sulfur vulcanization (23 kcal/mole), respectively.     

Mass transfer‐limited wet oxidation of phenol

Catalytic wet oxidation carried out in a continual three‐phase trickle‐bed reactor contributes to the sustainability of chemical technology. It was found that the hydrodynamics and the mass‐transfer of reactants could have a significant impact on the performance of the trickle‐bed reactor. An aqueous phenol oxidation was tested at different temperatures and liquid feed rates and the activities of both the CuO‐supported catalyst and the extruded active carbon were compared. To avoid the impact of liquid maldistribution, a bed of catalyst particles diluted with fine glass spheres was also used. Rate‐limited conditions of both liquid‐ and gas‐phase presented reactants were determined. Under the conditions of gas component transfer limitation, a better wetting of the diluted catalyst bed can lead to a worsening in the reactor performance due to the lower overall reaction rates. © 2001 Society of Chemical Industry     

Kinetics of sulfur-free thiuram vulcanization

Sulfur-free thiuram vulcanization has been investigated at temperatures from 160° to 190°C over 0.5 to 600 min. Continuous measurements in a VUREMO curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Simultaneously the values of the network chain density were calculated from swelling measurements on the vulcanizates. The cure curves show clearly an induction period (t_i), then fast crosslinking, a partial degradation, a “long-time” crosslinking, and finally a slow, limited degradation. Apart from the induction period, the kinetic graphs are satisfactory represented by a rate equation assuming three independent first-order reactions: fast crosslinking, degradation, and slow crosslinking. The rate equation contains seven kinetic parameters. Over the temperature range studied, there is no difference between the values of activation energy for fast crosslinking, for degradation, for slow crosslinking, and for t. Due to the presence of thiourea, the values of the induction period, the rate constant, and the extent of slow crosslinking are decreased. Simultaneously the activation energies calculated from degradation and slow crosslinking are significantly increased. On the basis of the above results, the mechanism of the sulfur-free thiuram vulcanization, in which ionic and radical reactions take place, is discussed.     

The Newly Sequenced Genome of Pisum sativum Is Replete with Potential G-Quadruplex-Forming Sequences—Implications for Evolution and Biological Regulation

G-quadruplexes (G4s) have been long considered rare and physiologically unimportant in vitro curiosities, but recent methodological advances have proved their presence and functions in vivo. Moreover, in addition to their functional relevance in bacteria and animals, including humans, their importance has been recently demonstrated in evolutionarily distinct plant species. In this study, we analyzed the genome of Pisum sativum (garden pea, or the so-called green pea), a unique member of the Fabaceae family. Our results showed that this genome contained putative G4 sequences (PQSs). Interestingly, these PQSs were located nonrandomly in the nuclear genome. We also found PQSs in mitochondrial (mt) and chloroplast (cp) DNA, and we experimentally confirmed G4 formation for sequences found in these two organelles. The frequency of PQSs for nuclear DNA was 0.42 PQSs per thousand base pairs (kbp), in the same range as for cpDNA (0.53/kbp), but significantly lower than what was found for mitochondrial DNA (1.58/kbp). In the nuclear genome, PQSs were mainly associated with regulatory regions, including 5′UTRs, and upstream of the rRNA region. In contrast to genomic DNA, PQSs were located around RNA genes in cpDNA and mtDNA. Interestingly, PQSs were also associated with specific transposable elements such as TIR and LTR and around them, pointing to their role in their spreading in nuclear DNA. The nonrandom localization of PQSs uncovered their evolutionary and functional significance in the Pisum sativum genome.