Effect of cure temperature on the structure and water absorption of epoxy/amine thermosets

Dielectric and rheological measurements are reported on the effect of cure temperature on the water absorption of tris[(2,3-epoxypropoxy)phenyl] methane cured with a 1 : 1 stoichiometric ratio of 4,4′-diaminodiphenylsulphone. Analysis of the water absorption characteristics of these materials using a combination of dielectric and gravimetric measurements has indicated that water molecules can be found in two distinctly different types of environments. There are water molecules which are strongly interacting with polar groups and water molecules clustered together into sub-micro-scale cavities within the matrix structure. Changes in the final cure temperature have the effect of changing both the extent and distribution of the types of water molecules present in the matrix. Validation of the diffusion coefficients obtained from the dielectric analysis is based on a comparison with gravimetric data and the implications are discussed. Differences observed between these two different types of measurement are related to peculiarity in the dielectric method and its extreme sensitivity to interfacial phenomena.     

The antiwear and extreme pressure action mechanism of CeF3 in grease

Cerium (III) fluoride as an antiwear or extreme pressure additive has been used in grease and bonded solid film lubricant, but its action mechanism has not been clarified. In this paper, the tribological characteristics of lithium grease containing CeF₃, CaF₂, SbF₃, CeO₂ and graphite fluoride ((CF)_n) were evaluated with an SRV tester. The results show that pastes containing CaF₂ and (CF)_n give good antiwear and anti-friction performance, but do not possess extreme pressure properties. Adding CeO₂ to grease offers no benefit to the antiwear and anti-friction performance of the paste. Paste containing SbF₃ has poor lubricating properties. XPS analysis shows that the good antiwear and extreme pressure properties of paste containing CeF₃ can be attributable to the formation of a physically adherent film and a chemical reaction film on the rubbing surface. Thermogravimetry shows that CeF₃ acts as an agent for the slow release of the fluorine element.     

Carrier Planning Issues for TDMA Personal Communication System

Radio spectrum is the most valuable resource for wireless communication, thus high spectrum utilization is mostly desired to increase system economy. With an efficient frequency allocation method and an effective handoff procedure, a personal communication system can be operated with minimal number of carriers while maintaining an acceptable level of system performance, and thereby leading to a better spectrum utilization. In this paper, we study the effect of different channel selection criteria for handoff procedure on carrier planning problem with Block Oriented Network Simulator (BONeS). The results show that the C/I-based channel selection criterion leads to the best performance, and the minimal numbers of carriers required by Personal Access Communications System (PACS) are 16, 13, 10 carriers for propagation environments with path-loss exponent 2.76, 3, 4, respectively.     

InP-based micromachined Mach-Zehnder interferometer stress sensors

 In the field of III–V-based compounds, new functionalities can be reached by integrating micromechanical structures with electro-optical functions, in order to fabricate Micro Opto Electro Mechanical Systems (MOEMS). A possible application is an InP-based integrated optical stress sensor. Such a system is based on a partly suspended waveguide that can be strained under the effect of an external stress. The photoelastic effect induces a phase shift that can be converted into an intensity shift of the signal if the device is configurated as a Mach-Zehnder interferometer. This system can be integrated monolithically with the optical source and the photodetector. The mechanical, photoelastic and optical properties of this structure has been simulated in order to configurate the alloy composition of the epitaxial layers and the geometry of the device. Micromachining processes have been developed in order to realize InP-based suspended microstructures by sacrificial layer etching and bulk micromachining. Preliminary results showed that the optical behaviour of the waveguides is close to the theoretical analysis. Characterisation of the complete interferometer is underway in our group. Received: 13 December 1996/Accepted: 18 December 1996     

Growth effects of regulatory peptides and intracellular signaling routes in human pancreatic cancer cell lines

Spore germination is a defined developmental process that marks a critical point in the life cycle of Dictyostelium discoideum. Upon germination the environmental conditions must be conducive to cell growth to ensure survival of emerged amoebae. However, the signal transduction pathways controlling the various aspects of spore germination in large part remain to be elucidated. We have used degenerate PCR to identify dhkB, a two-component histidine kinase, from D. discoideum. DhkB is predicted to be a transmembrane hybrid sensor kinase. The dhkB-null cells develop with normal timing to give what seem to be mature fruiting bodies by 22 to 24 h. However, over the next several hours, the ellipsoidal and encapsulated spores proceed to swell and germinate in situ within the sorus and thus do not respond to the normal inhibitors of germination present within the sorus. The emerged amoebae dehydrate due to the high osmolarity within the sorus, and by 72 h 4% or less of the amoebae remain as spores, while most cells are now nonviable. Precocious germination is suppressed by ectopic activation of or expression of cAMP-dependent protein kinase A. Additionally, at 24 h the intracellular concentration of cAMP of dhkB- spores is 40% that of dhkB+ spores. The results indicate that DHKB regulates spore germination, and a functional DHKB sensor kinase is required for the maintenance of spore dormancy. DHKB probably acts by maintaining an active PKA that in turn is inhibitory to germination.     

A Nanostructuring Method to Decouple Electrical and Thermal Transport through the Formation of Electrically Triggered Conductive Nanofilaments

Transforming thermal energy into electric energy and vice versa needs the decoupling of electrical transport from thermal transport. An innovative strategy is proposed by forming/disrupting electrically triggered conductive nanofilaments within semiconducting thin films to switch thermoelectric properties between two states without further material modification and manufacturing processes. It can also controllably adjust the degree of decoupling, providing a potential resolution and performance adjustability for heat/coldness control or power consumption reduction on demand.     

Phase Inversion Strategy to Flexible Freestanding Electrode: Critical Coupling of Binders and Electrolytes for High Performance Li–S Battery

Development of flexible and freestanding electrode is attracting great attention in lithium–sulfur (Li–S) batteries, but the severe capacity fading caused by the lithium polysulfides (PSs) shuttle effect remains challenging. Herein, a completely new polymeric binder of polyethersulfone is introduced. Not only it enables massive production of flexible/current‐free electrode by a novel concept of “phase‐inversion” approach but also the resultant polymeric networks can effectively trap the soluble polysulfides within the electrode, owing to the higher hydrophilicity and stronger affinity properties than the routine polyvinylidene fluoride. Coupling with polysulfide‐based electrolyte, the Li–S cell shows a higher capacity of 1141 mAh g^?1, a lower polarization of 192 mV, and a more stable capacity retention with 100% Coulombic efficiency over 100 cycles at 0.25C. The advantages of favored binder and electrolyte are further demonstrated in lithium‐ion sulfur full battery with lithiated graphite anode, which demonstrates much improved performance than those previously reported. This work not only introduces a novel strategy for flexible freestanding electrodes but also enlightens the importance of coupling electrodes and electrolytes to higher performances for Li–S battery.