Publication7

Thermotropic microenvironmental changes and the level of hydration in different microenvironments of pluronic F127 (PF127), (PEO106 PPO70 PEO106, average molar mass 13 000) in aqueous media have been studied using 1-naphthol, which is an ESPT fluorescent molecular probe. The appearance of 1-naphthol neutral form fluorescence in aqueous PF127 (10% w/v) solution indicates the ability of 1-naphthol to sense hydrophobic domains in micellar aggregations. There is a marked enhancement of the neutral form fluorescence at and above the gelation temperature (20°C), which shows that the probe can accurately sense the sol-gel transition. In the temperature range of 10-40°C, with increase in temperature there is a progressive enhancement of the neutral form fluorescence and the blue shift of the neutral and anionic form fluorescence; a decrease in the deprotonation rate constant (kpt) indicates that the water-polymer interfacial region is progressively dehydrated. Because kpt is related to the availability of proton-accepting water in the microenvironment of 1-naphthol, the reduction of kpt indicates progressive dehydration. The thermotropic response of the I1/I3 vibronic band ratio of pyrene-1-butyric acid fluorescence shows a progressive increase in the non-polarity of the interfacial domain with increasing temperature. The increase in non-polarity and the decrease of the hydration level are strongly correlated.

The 15kV /20A, 4H-SiC n-IGBT is the state-of-the-art high voltage power semiconductor device. The transformerless intelligent power substation (TIPS) [1] for 13.8kV grid interfacing is built using this device. It is proposed to use a three-phase, three-level, diode clamped topology as the front end converter (FEC) in TIPS. A modular-leg structure has been employed for FEC. In modular-leg structure, each phase-leg will have its own DC-link capacitors and a low inductance bus-bar. However, modular-leg structure adds complexity in DC bus over-load protection, which is studied in this paper. Experimental results of modular-leg converter at 3kV DC link voltage and scale down prototype of AC switch for DC bus fault protection are presented. © 2013 IEEE.

In the title compound, C30H31N3O 2S, the fused pyrrolidine ring bearing three substituents adopts an envelope conformation with the C atom bearing the benzoyl group as the flap. The other fused pyrrolidine ring adopts a twisted conformation about one of its C - C bonds. The dihedral angle between the isatin ring system and the methylthiazole ring is 25.95(8)°. An intramolecular C - H⋯O interaction closes an S(8) ring. In the crystal, molecules are linked by C - H⋯O interactions, generating C(11) chains propagating in [001]. © 2014 CrossMark.

The title compound, C22H26N2O2, crystallizes with three independent molecules, two of which are situated on inversion centers, so the asymmetric unit contains two independent half-molecules and one molecule in a general position. The two hydroxy groups in each molecule are involved in intramolecular O - H⋯N hydrogen bonds, which generate S(6) rings. In the crystal, weak intermolecular C - H⋯π interactions link the molecules into two crystallographically independent columns propagating along [001]; one column consists of molecules in general positions, while the other column is built from alternating independent centrosymmetric molecules.

In the title molecular salt, C16H10NO +·I-, the dihedral angle between the pyridinium and benzene rings is 6.61 (8)°. In the crystal, the cation is linked to the anion by a C-H⋯I interaction arising from the activated aromatic C atom adjacent to the N+cation.

Realization of increased spectral efficiency with polarization multiplexing and advanced modulation formats require performance optimization at the transmitter and the receiver, considering the laser linewidth, chromatic dispersion, polarization mode dispersion and nonlinear effects. This paper addresses the performance optimization of a 200G system using PDM-16QAM. DSP algorithms for the mitigation of the phase noise of the laser, drifts in modulator bias, frequency drifts of the transmitter and receiver lasers are discussed in detail. Frequency domain and a time domain approach is discussed to compensate for the impairments introduced due to chromatic dispersion and polarisation mode dispersion. The performance of a complete 200G system in the presence of different impairments and the associated trade-offs are discussed in detail.

Blebs are membrane protrusions that appear during several physiological processes in eukaryotic cells. The phase behavior and kinetics of blebbing in cellular membrane is investigated computationally using a particle-based model for self-assembled lipid vesicles apposed to an elastic meshwork, mimicking a cell's cytoskeleton. We found that blebbing is induced when the cytoskeleton is subjected to a localized ablation, detachment from the membrane, or a uniform contraction. These results are in good agreement with experiments.

Fine grained Cu substituted melt-spun Sm(Co0.9Cu0.1)4.8 ribbons prepared with a wheel speed of 50 m/s exhibit a high coercivity of 52.7 kOe. Detailed magnetic studies like I and II quadrant magnetization-demagnetization characteristics, minor-loop measurement with increasing field and recoil behaviour have been carried out in combination with TEM studies. Fine spots of size ∼3 nm having different crystallographic orientations within the grains have been observed, and the high coercivity of the sample is attributed to complex domain wall interactions with the fine grain (∼55 nm) microstructure containing nanoscale heterogeneities.

An ultra low power low noise analog front-end for ECG signal acquisition is demonstrated. Key to its performance is a multi-frequency chopping technique that helps to significantly reduce power consumption by frequency-division multiplexing of two channels in a single low noise instrumentation amplifier. A complete two-channel analog front-end, chopped at frequencies of 4 kHz and 8 kHz, is implemented in a 0.18 μm CMOS technology from UMC. A current reuse technique is employed in the first stage of the instrumentation amplifier to further improve efficiency. Simulation results show that the front-end achieves an input-referred noise voltage density of 79 nV/√Hz while consuming a current of 460 nA per channel from a 1.2 V power supply. The 1/f noise corner of the system is around 10 Hz and the CMRR of 138 dB.

This study presents the implementation of a millimeter-wave compact bandstop filter (BSF) using the standard 0.18 μm CMOS process. The topology is based on transversal signal interference technique, obtained by connecting two transmission lines with proper characteristic impedances and electrical lengths in parallel. Sharp-rejection characteristics are obtained without using any extra resonators. Moreover, BSF having single-characteristic impedance is analyzed for design simplicity. A compact thin film microstrip structure with meandered signal line is properly constructed without any post processing steps. The overall filter occupies a compact circuit area of less than 0.25 λg × 0.25 λg and exhibits a 20 dB stopband fractional bandwidth of 21% and high-rejection of about-38 dB at centre frequency of 60 GHz. A good agreement between the predicted and measured results is observed up to 110 GHz.

A new MgCl2 based molecular adduct has been synthesized with 9-fluorenemethanol (9FM) as a novel internal electron donor (IED), along with ethanol (EtOH) (MgCl2·n9FM·xEtOH). The above molecular adduct has been subjected to a variety of structural, spectroscopic and morphological characterization techniques. The results of the solid state 13C CPMAS NMR technique suggests the coordination of 9FM to MgCl 2. Observation of a low angle diffraction peak at 2θ = 5.7° (d = 15.5 Å) underscores the coordination of 9FM along the z-axis, and ethanol in the molecular adduct. Active Ziegler-Natta catalysts were prepared by two different synthesis methods; the conventional method to obtain a high surface area active catalyst, and other one with 9FM as an integral part of the active catalyst in order to study the influence of 9FM as an IED over the active sites. The active catalysts were also characterized thoroughly with different analytical tools. The XRD results show (003) facets of δ-MgCl2 (α-MgCl2) for the conventional (non-conventional) titanated catalyst. Results of the ethylene polymerization activity study reveals that the conventionally prepared highly porous active catalyst shows 1.7-2.5 times higher activity than the non-conventional prepared catalyst; however, the latter shows a low molecular weight distribution and confirms the role of the Lewis base as an IED. © the Partner Organisations 2014.

We describe a low power analog front-end for a digital hearing aid, designed and fabricated in a 0.13μm CMOS process. The IC accepts inputs from a microphone or telecoil, amplifies and digitizes it for processing by a DSP, accepts digital data from the DSP, converts it to analog form using a pulse width modulated class D amplifier, and drives the earpiece, all over a 10kHz bandwidth. The programmable gain amplifier uses current sharing in the input stage to obtain low noise with low power consumption. The single-bit continuous-time ΔΣ ADC and the closed loop class-D amplifier use assisted opamp integrators to reduce power dissipation. An on chip ring oscillator provides the clock to the digital parts of the chip and to the digital signal processor (DSP). The chip has an input referred noise of 2.1μV, a dynamic range of 106 dB, an output THD of 0.006% and a peak output SNR of 79dB. It occupies 2.3 mm2 and consumes 285μA from a 1.2V supply. © 2013 IEEE.

Monitoring the eye diagram at the output of an embedded analog adaptive equalizer used in a high speed serial link is challenging. Eye measurement using an external oscilloscope is problematic due to the bandwidth of the test setup. In this work, we describe the working principle and design details of a low cost, on-chip monitor circuit that enables the determination of the eye diagram. The eye opening monitor (EOM), implemented in a 65 nm CMOS process, occupies 0.06 mm2 and consumes 5.7 mW from a 1.2 V supply. Measurements demonstrate the efficacy of our techniques.

It is shown that memoryless analog-to-digital conversion using ΔΣ modulators is possible without resetting the modulator or decimation filters by using a suitable signal transfer function for the modulator and a decimation filter which satisfies Nyquist intersymbol interference (ISI) criterion. This architecture enables memoryless operation over the entire signal bandwidth of the ΔΣ modulator which is significantly higher than the bandwidth in incremental ΔΣ architectures in which the modulator is reset. A two-channel ADC with a total effective sampling rate of fs/64 per channel is built using a third order 32× oversampled switched-capacitor ΔΣ modulator. The prototype in 0.18 μm CMOS occupies 2.1 mm2 and consumes 59.63mW. At 16MHz (64MHz) sampling rate for the DSM, the dynamic range (DR) of the standalone modulator is 86.5 dB(85.1 dB), and that in two-channel mode, with perchannel rate of 250 kHz (1MHz) is 81 dB (80.5 dB). The maximum SNR in multiplexed mode at 16MHz (64MHz) sampling rate is 80.3 dB(68.6 dB). At both sampling rates, the inter-channel crosstalk due to maximum input on the other channel is below 77.7 dB.

An optimally designed FIR feedback DAC is used in a third order, single bit continuous-time delta sigma modulator to reduce power dissipation and jitter sensitivity. The loop filter is carefully stabilized for the delay added by the FIR DAC. A current reuse two stage feedforward compensated opamp minimizes current consumption in the first integrator. The efficacy of our techniques is borne out by measurements from a 17 bit audio converter designed in a 0.18 μm CMOS technology. It achieves 103 dB dynamic range, 102 dB A-Weighted SNR and 106 dB SFDR in a 24 kHz bandwidth and dissipates 280 μW from a 1.8 V supply. © 2013 IEEE.

Conventional continuous-time delta-sigma modulator (CTDSM) architectures do not allow independent control of the shape and bandwidth of the signal transfer function (STF), since the STF is simply a by-product of NTF synthesis. This is particularly troublesome when the input to the CTDSM consists of large out-of-band interferers; handling them without saturating the quantizer needs larger inband DR, leading to increased power dissipation. A solution to this problem is to use a filter upfront to attenuate interferers. Alternatively [1], the filter can be moved into the CTDSM loop. In [1], a 1st-order RC filter was used to 'tame' the STF peak of a cascade of integrators with feedforward summation (CIFF) DSM. Apart from the limited selectivity offered by a 1st-order filter, an active feedback path was necessary to stabilize the loop. The CTDSM in our work obtains an STF with a sharper transition band and a lower cutoff frequency (normalized to the desired signal bandwidth) compared to [1], with the aim of more effectively attenuating close-in interferers. This is realized by embedding a 2nd-order active filter into the CTDSM. We show that this has the same functionality as the filter upfront, but achieves better linearity (for the same noise and power dissipation) when compared to the filter-CTDSM cascade. Further, no extra active circuitry is necessary to stabilize the loop. Measurements of a CTDSM (signal BW=2MHz), with a built-in VGA (0 to 18dB) and a 2nd-order Butterworth filter (4MHz cutoff), show that the out-of-band IIP3 improves by about 10dB when compared to the CTDSM with the filter placed upfront. The filtering CTDSM+VGA, which uses a single-bit quantizer and a 4-tap FIR DAC, achieves a DR of 92dB in a 2MHz BW while consuming 5mW in a 0.13μm CMOS process. The peak instantaneous DR/SNR/SNDR are 82/80.5/74.5dB. With the VGA, the DR is 92dB. © 2014 IEEE.

Voltage sag remains to be a serious and most common power quality problem. A definitive solution towards compensation of voltage sag with phase jump is provided by Dynamic Voltage Restorer (DVR). The conventional DVR topologies however have dc-link and two stage power conversion, which increases its size, cost and associated losses. Therefore topologies without the dc-link mitigating sag by utilizing direct ac-ac converters, are preferable over the conventional ones. As no storage device is employed, compensation by these topologies is limited only by the voltages at the point of common coupling that is feeding the converters. A direct ac-ac converter based topology fed with line voltages is proposed in this work, for the compensation of sags with phase angle jump. The capability of the topology is compared with the other existing topologies and found to have increased range of compensation. Detailed simulations have been carried out in MATLAB and the results are presented. © 2013 IEEE.

This article presents an idea to remove the inequality in maximum fillet stresses developed between pinion and gear of a step up gear drive. This uniform fillet strength of the gear drive can be achieved by using nonstandard pinion and gear with appropriate addendum modifications generated by nonstandard basic racks of respective tooth thickness not equal to 0.5πm at the pitch circle. The influence of gear parameters such as gear ratio, pressure angle, addendum factor, pinion teeth number, and addendum modifications on the maximum fillet stress on the nonstandard pinion and gears of different tooth thickness has been analyzed through finite element method and finally the optimum value of rack tooth thickness coefficients (kpc and kgc) are suggested for the given gear drive (defined by i) that improves the fillet capacity in bending. This study has been extended for various drives like Sstd, So, S+, and S- drives.