Characterization of lysozyme crystals with unusually low solvent content

Studies on the low-humidity (88%) forms of tetragonal and monoclinic lysozyme, resulting from water-mediated transformations, have provided a wealth of information on the variability in protein hydration, its structural consequences and the water structure associated with proteins, in addition to facilitating the delineation of the rigid and the flexible regions in the protein molecule and the invariant features in its hydration shell. Surprisingly, monoclinic lysozyme continues to diffract even when the environmental humidity is drastically reduced, thus permitting the structural study of the enzyme at different levels of hydration. As part of a study in this direction, three very low humidity forms, two of them occuring at a nominal relative humidity of 38% and the other at 5% relative humidity, have been characterized. These have unprecedented low solvent contents of 16.9, 17.6 and 9.4%, respectively, as determined by the Matthews method.

Escape of high mass ions due to initial thermal energy and its implications for axially symmetric RF ion trap mass analyzer design

This paper investigates the loss of high mass ions due to their initial thermal energy in ion trap mass analyzers. It provides an analytical expression for estimating the percentage loss of ions of a given mass at a particular temperature, in a trap operating under a predetermined set of conditions. The expression we developed can be used to study the loss of ions due to its initial thermal energy in traps which have nonlinear fields as well as those which have linear fields. The expression for the percentage of ions lost is shown to be a function of the temperature of the ensemble of ions, ion mass and ion escape velocity. An analytical expression for the escape velocity has also been derived in terms of the trapping field, drive frequency and ion mass. Because the trapping field is determined by trap design parameters and operating conditions, it has been possible to study the influence of these parameters on ion loss. The parameters investigated include ion temperature, magnitude of the initial potential applied to the ring electrode (which determines the low mass cut-off), trap size, dimensions of apertures in the endcap electrodes and RF drive frequency. Our studies demonstrate that ion loss due to initial thermal energy increases with increase in mass and that, in the traps investigated, ion escape occurs in the radial direction. Reduction in the loss of high mass ions is favoured by lower ion temperatures, increasing low mass cut-off, increasing trap size, and higher RF drive frequencies. However, dimensions of the apertures in the endcap electrodes do not influence ion loss in the range of aperture sizes considered. (C) 2010 Elsevier B.V. All rights reserved.

Studies on age-hardening characteristics of ceramic particle/matrix interfaces in Al-Cu-SiCp composites using ultra low-load-dynamic microhardness measurements

Ultra low-load-dynamic microhardness testing facilitates the hardness measurements in a very low volume of the material and thus is suited for characterization of the interfaces in MMC's. This paper details the studies on age-hardening behavior of the interfaces in Al-Cu-5SiC(p) composites characterized using this technique. Results of hardness studies have been further substantiated by TEM observations. In the solution-treated condition, hardness is maximum at the particle/matrix interface and decreases with increasing distance from the interface. This could be attributed to the presence of maximum dislocation density at the interface which decreases with increasing distance from the interface. In the case of composites subjected to high temperature aging, hardening at the interface is found to be faster than the bulk matrix and the aging kinetics becomes progressively slower with increasing distance from the interface. This is attributed to the dislocation density gradient at the interface, leading to enhanced nucleation and growth of precipitates at the interface compared to the bulk matrix. TEM observations reveal that the sizes of the precipitates decrease with increasing distance from the interface and thus confirms the retardation in aging kinetics with increasing distance from the interface.

X-Codes: A Low Complexity Full-Rate High-Diversity Achieving Precoder for TDD MIMO Systems

We consider a time division duplex multiple-input multiple-output (nt × nr MIMO). Using channel state information (CSI) at the transmitter, singular value decomposition (SVD) of the channel matrix is performed. This transforms the MIMO channel into parallel subchannels, but has a low overall diversity order. Hence, we propose X-Codes which achieve a higher diversity order by pairing the subchannels, prior to SVD preceding. In particular, each pair of information symbols is encoded by a fixed 2 × 2 real rotation matrix. X-Codes can be decoded using nr very low complexity two-dimensional real sphere decoders. Error probability analysis for X-Codes enables us to choose the optimal pairing and the optimal rotation angle for each pair. Finally, we show that our new scheme outperforms other low complexity precoding schemes.

Modeling re-ignition and chuffing in solid rocket motors

A nonlinear model is developed to numerically simulate dynamic combustion inside a solid rocket motor chamber. Using this model, the phenomena of re-ignition and chuffing are investigated under low-L* conditions. The model consists of two separate submodels (coupled to each other), one for unsteady burning of propellant and the other for unsteady conservation of mass and energy within the chamber. The latter yields instantaneous pressure and temperature within the chamber. The instantaneous burning rate is calculated using a one-dimensional, nonlinear, transient gas-phase model previously developed by the authors. The results presented in this paper show that the model predicts not only the critical L*, but also the various regimes of L*-instabihty. Specifically, the results exhibit (1) amplifying pressure oscillations leading to extinction, and (2) re-ignition after a dormant period following extinction. The re-ignition could be observed only when a radiation heat flux (from the combustion chamber to the propellant surface) was included. Certain high-frequency oscillations, possibly due to intrinsic instability, are observed when the pressure overshoots during re-ignition. At very low values of initial L*, successive cycles of extinction/reignition displaying typical characteristics of chuffing are predicted. Variations of the chuffing frequency and the thickness of propellant burned off during a chuff with L* are found to be qualitatively the same as that reported from experimental observations.

Starting scheme for load commutated inverter-fed wound field synchronous machine using an auxiliary low-power voltage source inverter

Conventional thyristor-based load commutated inverter (LCI)-fed wound field synchronous machine operates only above a minimum speed that is necessary to develop enough back emf to ensure commutation. The drive is started and brought up to a speed of around 10-15% by a complex `dc link current pulsing' technique. During this process, the drive have problems such as pulsating torque, insufficient average starting torque, longer starting time, etc. In this regard a simple starting and low-speed operation scheme, by employing an auxiliary low-power voltage source inverter (VSI) between the LCI and the machine terminals, is presented in this study. The drive is started and brought up to a low speed of around 15% using the VSI alone with field oriented control. The complete control is then smoothly and dynamically transferred to the conventional LCI control. After the control transfer, the VSI is turned off and physically disconnected from the main circuit. The advantages of this scheme are smooth starting, complete control of torque and flux at starting and low speeds, less starting time, stable operation, etc. The voltage rating of the required VSI is very low of the order of 10-15%, whereas the current rating is dependent on the starting torque requirement of the load. The experimental results from a 15.8 hp LCI-fed wound field synchronous machine are given to demonstrate the scheme.

Numerical Study Of Heat Transfer From Pin Fin Heat Sink Using Steady And Pulsated Impinging Jets

The work reported in this thesis is an attempt to enhance heat transfer in electronic devices with the use of impinging air jets on pin-finned heat sinks. The cooling per-formance of electronic devices has attracted increased attention owing to the demand of compact size, higher power densities and demands on system performance and re-liability. Although the technology of cooling has greatly advanced, the main cause of malfunction of the electronic devices remains overheating. The problem arises due to restriction of space and also due to high heat dissipation rates, which have increased from a fraction of a W/cm2to 100s of W /cm2. Although several researchers have at-tempted to address this at the design stage, unfortunately the speed of invention of cooling mechanism has not kept pace with the ever-increasing requirement of heat re- moval from electronic chips. As a result, efficient cooling of electronic chip remains a challenge in thermal engineering. Heat transfer can be enhanced by several ways like air cooling, liquid cooling, phase change cooling etc. However, in certain applications due to limitations on cost and weight, eg. air borne application, air cooling is imperative. The heat transfer can be increased by two ways. First, increasing the heat transfer coefficient (forced convec- tion), and second, increasing the surface area of heat transfer (finned heat sinks). From previous literature it was established that for a given volumetric air flow rate, jet im-pingement is the best option for enhancing heat transfer coefficient and for a given volume of heat sink material pin-finned heat sinks are the best option because of their high surface area to volume ratio. There are certain applications where very high jet velocities cannot be used because of limitations of noise and presence of delicate components. This process can further be improved by pulsating the jet. A steady jet often stabilizes the boundary layer on the surface to be cooled. Enhancement in the convective heat transfer can be achieved if the boundary layer is broken. Disruptions in the boundary layer can be caused by pulsating the impinging jet, i.e., making the jet unsteady. Besides, the pulsations lead to chaotic mixing, i.e., the fluid particles no more follow well defined streamlines but move unpredictably through the stagnation region. Thus the flow mimics turbulence at low Reynolds number. The pulsation should be done in such a way that the boundary layer can be disturbed periodically and yet adequate coolant is made available. So, that there is not much variation in temperature during one pulse cycle. From previous literature it was found that square waveform is most effective in enhancing heat transfer. In the present study the combined effect of pin-finned heat sink and impinging slot jet, both steady and unsteady, has been investigated for both laminar and turbulent flows. The effect of fin height and height of impingement has been studied. The jets have been pulsated in square waveform to study the effect of frequency and duty cycle. This thesis attempts to increase our understanding of the slot jet impingement on pin-finned heat sinks through numerical investigations. A systematic study is carried out using the finite-volume code FLUENT (Version 6.2) to solve the thermal and flow fields. The standard k-ε model for turbulence equations and two layer zonal model in wall function are used in the problem Pressure-velocity coupling is handled using the SIMPLE algorithm with a staggered grid. The parameters that affect the heat transfer coefficient are: height of the fins, total height of impingement, jet exit Reynolds number, frequency of the jet and duty cycle (percentage time the jet is flowing during one complete cycle of the pulse). From the studies carried out it was found that: a) beyond a certain height of the fin the rate of enhancement of heat transfer becomes very low with further increase in height, b) the heat transfer enhancement is much more sensitive to any changes at low Reynolds number than compared to high Reynolds number, c) for a given total height of impingement the use of fins and pulsated jet, increases the effective heat transfer coefficient by almost 200% for the same average Reynolds number, d) for all the cases it was observed that the optimum frequency of impingement is around 50 − 100 Hz and optimum duty cycle around 25-33.33%, e) in the case of turbulent jets the enhancement in heat transfer due to pulsations is very less compared to the enhancement in case of laminar jets.

Low-inductance axial flux BLDC motor drive for more electric aircraft

As aircraft technology is moving towards more electric architecture, use of electric motors in aircraft is increasing. Axial flux BLDC motors (brushless DC motors) are becoming popular in aero application because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. Axial flux BLDC motors, in general, and ironless axial flux BLDC motors, in particular, come with very low inductance Owing to this, they need special care to limit the magnitude of ripple current in motor winding. In most of the new more electric aircraft applications, BLDC motor needs to be driven from 300 or 600 Vdc bus. In such cases, particularly for operation from 600 Vdc bus, insulated-gate bipolar transistor (IGBT)-based inverters are used for BLDC motor drive. IGBT-based inverters have limitation on increasing the switching frequency, and hence they are not very suitable for driving BLDC motors with low winding inductance. In this study, a three-level neutral point clamped (NPC) inverter is proposed to drive axial flux BLDC motors. Operation of a BLDC motor driven from three-level NPC inverter is explained and experimental results are presented.

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

pplication of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

Application of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Low-thermal-budget solution processing of thin films of zinc ferrite and other complex oxides

Further miniaturization of magnetic and electronic devices demands thin films of advanced nanomaterials with unique properties. Spinel ferrites have been studied extensively owing to their interesting magnetic and electrical properties coupled with stability against oxidation. Being an important ferrospinel, zinc ferrite has wide applications in the biological (MRI) and electronics (RF-CMOS) arenas. The performance of an oxide like ZnFe2O4 depends on stoichiometry (defect structure), and technological applications require thin films of high density, low porosity and controlled microstructure, which depend on the preparation process. While there are many methods for the synthesis of polycrystalline ZnFe2O4 powder, few methods exist for the deposition of its thin films, where prolonged processing at elevated temperature is not required. We report a novel, microwave-assisted, low temperature (<100°C) deposition process that is conducted in the liquid medium, developed for obtaining high quality, polycrystalline ZnFe2O4 thin films on technologically important substrates like Si(100). An environment-friendly solvent (ethanol) and non-hazardous oxide precursors (β-diketonates of Zn and Fe in 1:2 molar ratio), forming a solution together, is subjected to irradiation in a domestic microwave oven (2.45 GHz) for a few minutes, leading to reactions which result in the deposition of ZnFe2O4 films on Si (100) substrates suspended in the solution. Selected surfactants added to the reactant solution in optimum concentration can be used to control film microstructure. The nominal temperature of the irradiated solution, i.e., film deposition temperature, seldom exceeds 100°C, thus sharply lowering the thermal budget. Surface roughness and uniformity of large area depositions (50x50 mm2) are controlled by tweaking the concentration of the mother solution. Thickness of the films thus grown on Si (100) within 5 min of microwave irradiation can be as high as several microns. The present process, not requiring a vacuum system, carries a very low thermal budget and, together with a proper choice of solvents, is compatible with CMOS integration. This novel solution-based process for depositing highly resistive, adherent, smooth ferrimagnetic films on Si (100) is promising to RF engineers for the fabrication of passive circuit components. It is readily extended to a wide variety of functional oxide films.

A unique strategy towards high dielectric constant and low loss with multiwall carbon nanotubes anchored onto graphene oxide sheets

Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C-C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT-GO hybrid was then melt mixed with 50/50 polyamide6-maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6-mABS) blend to design materials with high dielectric constant (30) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT-GO hybrid was selectively localized in the PA6 phase of the blend. The 30 scales with the concentration of MWNT-GO in the blends, which interestingly showed a very low dielectric loss (< 0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT-GO in the blends, demonstrating their reinforcing capability as well.

Effect of mass loading on ionic polymer metal composite actuators and sensors

Ionic polymer metal composites (IPMC) actuator for flapping insect scale wing is advantageous due to its low mass, high deflection and simple actuation mechanism. Some of the factors that affect the actuation of IPMC are the amount of hydration in the polymer membrane and the environmental conditions such as temperature, humidity etc. In structural design, the attachment of wing on the IPMC actuators is an important concern as the attached wing increases the mass of actuators thereby affecting the parameters like displacement, stiffness and resonant frequencies. Such IPMC actuators have to produce sufficient actuation force and frequency to lift and flap the attached wing. Therefore, it is relevant to study the influence of attachment of wing on the actuator parameters (displacement, resonant frequency, block force and stiffness) and performance of the actuators. This paper is divided into two parts; the first part deals with the modeling of the IPMC actuators for its effect on the level of water uptake and temperature using energy based method. The modeling method adapted is validated with the experimental procedure used to actuate the IPMC. The second part deals with the experimental analysis of IPMC actuation at dry, wet and in water conditions. The effect of end mass loading on the performance of 20 Hz, high frequency actuator (HFA) and 8.7 Hz, low frequency IPMC actuators (LFA) and sensors is studied. The IPMC actuators are attached with IPMC flapping wing at its free end and performance analysis on the attached wing is also carried out.

Optimal Power Allocation Policies for Low Powered Wireless Communication Systems

We consider optimal average power allocation policies in a wireless channel in the presence of individual delay constraints on the transmitted packets. Power is consumed in transmission of data only. We consider the case when the power used in transmission is a linear function of the data transmitted. The transmission channel may experience multipath fading. We have developed a computationally efficient online algorithm, when there is same hard delay constraint for all packets. Later on, we generalize it to the case when there are multiple real time streams with different hard deadline constraints. Our algorithm uses linear programming and has very low complexity.

Properties of a-C:H films deposited from a methane electron cyclotron wave resonant plasma

An electron cyclotron wave resonant methane plasma discharge was used for the high rate deposition of hydrogenated amorphous carbon (a-C:H). Deposition rates of up to ∼400 Å/min were obtained over substrates up to 2.5 in. in diameter with a film thickness uniformity of ∼±10%. The deposited films were characterised in terms of their mass density, sp3 and hydrogen contents, C-H bonding, intrinsic stress, scratch resistance and friction properties. The deposited films possessed an average sp3 content, mass density and refractive index of ∼58%, 1.76 g/cm3 and 2.035 respectively.Mechanical characterisation indicated that the films possessed very low steady-state coefficients of friction (ca. 0.06) and a moderate shear strength of ∼141 MPa. Nano-indentation measurements also indicated a hardness and elastic modulus of ∼16.1 and 160 GPa respectively. The critical loads required to induce coating failure were also observed to increase with ion energy as a consequence of the increase in degree of ion mixing at the interface. Furthermore, coating failure under scratch test conditions was observed to take place via fracture within the silicon substrate itself, rather than either in the coating or at the film/substrate interface. © 2003 Elsevier B.V. All rights reserved.