The influence of MWCNT and hybrid (MWCNT/nanoclay) fillers on performance of EPDM-CIIR blends in nuclear applications: Mechanical,hydrocarbon transport,and gamma-radiation aging characteristics

Blends of EPDM and chlorobutyl (CIIR) rubbers are used in nuclear plants where they have to withstand the combined effect of radiation and hydrocarbon aging. To improve their mechanical properties as well as hydrocarbon and gamma radiation resistance, the blends are reinforced with 0.5, 1, 1.5, and 2 phr of MWCNT. The increase in mechanical properties was highest for 1.5 phr MWCNT with 69% increase in tensile strength. The improvement in properties was correlated to MWCNT dispersion and filler–polymer interactions, which were confirmed by TEM and FTIR analysis. Hydrocarbon transport coefficients decreased on addition of MWCNT. The nanocomposites were exposed to 0.5, 1, and 2 MGy cumulative doses of gamma radiation. Depending on the radiation dose, crosslinking and/or chain scission occurred causes changes in physical properties. MWCNT reinforcement reduced the magnitude of changes in mechanical and transport properties after γ-irradiation. ESR and FTIR spectra provided qualitative information on free radical formation and chemical changes due to γ-rays exposure. To further enhance the properties, hybrid nanocomposites with 1.5 phr MWCNT and varying nanoclay contents (0.5, 1, 1.5, 2, and 5 phr) were prepared. Due to synergism between MWCNT and nanoclay, the hybrid composites had superior properties with hybrid containing 5 phr nanoclay giving 98% increase in tensile strength.     

Development of LTCC micro-hotplate with PTC temperature sensor for gas-sensing applications

Low temperature co-fired ceramic (LTCC) micro-hotplates show wide applications in gas sensors and micro-fluidic devices. It is easily structured in three-dimensional structures. This paper presents the low power consumption micro-hotplates which were developed with PTC (positive temperature coefficient) temperature sensor and inter-digitated electrodes. The paper presents two different structures for micro-hotplate with platinum as a heating element. The PTC temperature sensor using two different materials viz. PdAg and platinum paste are developed with micro-hotplates. The simulation has been achieved through COMSOL for LTCC and alumina micro-hotplates. The temperature variation with power consumption has been measured for the developed LTCC micro-hotplates. The change in resistance of PTC temperature sensors was measured with micro-hotplate temperature. The aim of this study was to place a temperature sensor with the gas sensor module to measure and control the temperature of micro-hotplate. A SnO₂ sensing layer is coated on LTCC micro-hotplate using screen printing and characterized for the sensing of carbon monoxide gas (CO). This study will be beneficial for designing hotplates based on LTCC technology with low power consumption and better stability of temperature for gas-sensing applications.     

Cut off frequency and transit time analysis of lightly doped drain (LDD) MOSFETs

Analytical model for the transconductance, cut off frequency, transit time and fringing capacitance of LDD MOSFETs is presented with a simple approach. The analysis is carried out considering the LDD device as a conventional MOSFET with a series resistance [Z.-H. Liu et al., Threshold voltage model for submicrometer MOSFETs. IEEE Trans Electron Devices 1993; ED-40: 86–94] and a simple closed form expressions for cut off frequency and transit time is obtained. The total gate capacitance, i.e. the geometric and fringing capacitance, is calculated for both LDD and non-LDD devices and lower fringing capacitance is reported in LDD devices. Lower cut-off frequencies and higher transit time are reported in LDD devices for the same channel length.     

The accumulation channel driven bipolar transistor (ACBT)

A new three-terminal power switch called the Accumulation Channel driven Bipolar Transistor (ACBT) is proposed and experimentally demonstrated. In the on-state, the characteristics of the ACBT have been found to approach those of a P-I-N rectifier with a MOSFET in series for regulating its current, an equivalent circuit considered to be an ideal for MOS/Bipolar power devices. Unlike previous devices, the high off-state voltage is supported by the formation of a potential barrier to the flow of electrons from the N⁺ emitter into the N-drift region within a depletion region. The absence of the P-base region within the ACBT cells eliminates the parasitic four layer PNPN thyristor which had limited the performance of previous MOS/Bipolar transistor structures. Consequently, the ACBT structure has large maximum controllable and surge current densities in addition to low on-state voltage drop and high-voltage current saturation capability     

Effects of quinine on the mechanical frequency response of the cupula in the fish lateral line

Quinine induces changes in the motion of the cupula in the lateral line canal of the African knife-fish in response to sinusoidal water movements. Two different phases in the action of quinine on the cupular frequency response can be discerned. In the first phase the best frequency, i.e., the frequency at which the cupular vibratory displacement is maximal in response to constant-amplitude sinusoidal canal fluid displacement, shifts toward higher frequencies. During this phase, lasting about 70-100 min, the best frequency increases by a factor between 1.3 and 1.5. In the second phase, during roughly the following 90 min, the best frequency decreases gradually to a value 0.3-0.5 times that observed before the application of quinine.     

HLA-B27-restricted antigen presentation in the absence of tapasin reveals polymorphism in mechanisms of HLA class I peptide loading

Tapasin is a resident ER protein believed to be critical for antigen presentation by HLA class I molecules. We demonstrate that allelic variation in MHC class I molecules influences their dependence on tapasin for peptide loading and antigen presentation. HLA-B*2705 molecules achieve high levels of surface expression and present specific viral peptides in the absence of tapasin. In contrast, HLA-B*4402 molecules are highly dependent upon human tapasin for these functions, while HLA-B8 molecules are intermediate in this regard. Significantly, HLA-B*2705 like HLA-B*4402, requires tapasin to associate efficiently with TAP (transporters associated with antigen processing). The unusual ability of HLA-B*2705 to form peptide complexes without associating with TAP or tapasin confers flexibility in the repertoire of peptides presented by this molecule. We speculate that these properties might contribute to the role of HLA-B27 in conferring susceptibility to inflammatory spondyloarthropathies.     

Hexamethyl cyclotrisiloxane–styrene block copolymers and their chemical composition

Triblock copolymers of hexamethyl cyclotrisiloxane (D₃) and styrene were synthesized by first preparing “living” species of polystyrene dianion followed by polymerization of D₃. The chain lenght of polymeric blocks could be controlled in a predictable fashion leading to a central hard block of polystyrene and the two end segments of amorphous polydimethylsiloxane having narrow molecular weight distribution, were characterized by gel permeation chromatography. The chemical composition of block copolymers was determined by silicon analysis and infrared and nuclear magnetic resonance spectra. Thermal aging of block copolymers at 150, 200, and 300°C was also discussed.