Siddhartha P. Duttagupta

Strain specificity in antimicrobial activity of silver and copper nanoparticles.

The antimicrobial properties of silver and copper nanoparticles were investigated using Escherichia coli (four strains), Bacillus subtilis and Staphylococcus aureus (three strains). The average sizes of the silver and copper nanoparticles were 3 nm and 9 nm, respectively, as determined through transmission electron microscopy. Energy-dispersive X-ray spectra of silver and copper nanoparticles revealed that while silver was in its pure form, an oxide layer existed on the copper nanoparticles. The bactericidal effect of silver and copper nanoparticles were compared based on diameter of inhibition zone in disk diffusion tests and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of nanoparticles dispersed in batch cultures. Bacterial sensitivity to nanoparticles was found to vary depending on the microbial species. Disk diffusion studies with E. coli and S. aureus revealed greater effectiveness of the silver nanoparticles compared to the copper nanoparticles. B. subtilis depicted the highest sensitivity to nanoparticles compared to the other strains and was more adversely affected by the copper nanoparticles. Good correlation was observed between MIC and MBC (r2=0.98) measured in liquid cultures. For copper nanoparticles a good negative correlation was observed between the inhibition zone observed in disk diffusion test and MIC/MBC determined based on liquid cultures with the various strains (r2=-0.75). Although strain-specific variation in MIC/MBC was negligible for S. aureus, some strain-specific variation was observed for E. coli.

Nanocrystalline-silicon superlattice produced by controlled recrystallization

Nanocrystalline-silicon superlattices are produced by controlled recrystallization of amorphous-Si/SiO2 multilayers. The recrystallization is performed by a two-step procedure: rapid thermal annealing at 600–1000 °C, and furnace annealing at 1050 °C. Transmission electron microscopy, Raman scattering, x-ray and electron diffraction, and photoluminescence spectroscopy show an ordered structure with Si nanocrystals confined between SiO2 layers. The size of the Si nanocrystals is limited by the thickness of the a-Si layer, the shape is nearly spherical, and the orientation is random. The luminescence from the nc-Si superlattices is demonstrated and studied.

Stable and efficient electroluminescence from a porous silicon‐based bipolar device

A complete process compatible with conventional Si technology has been developed in order to produce a bipolar light‐emitting device. This device consists of a layer of light‐emitting porous silicon annealed at high temperature (800–900 °C) sandwiched between a p‐type Si wafer and a highly doped (n+) polycrystalline Si film. The properties of the electroluminescence (EL) strongly depend on the annealing conditions. Under direct bias, EL is detected at voltages of ∼2 V and current densities J∼1 mA/cm2. The maximum EL intensity is 1 mW/cm2 and the EL can be modulated by a square wave current pulse with frequencies ν≥1 MHz. No degradation has been observed during 1 month of pulsed operation.

Body Movement Activity Recognition for Ambulatory Cardiac Monitoring

Wearable electrocardiogram (W-ECG) recorders are increasingly in use by people suffering from cardiac abnormalities who also choose to lead an active lifestyle. The challenge presently is that the ECG signal is influenced by motion artifacts induced by body movement activity (BMA) of the wearer. The usual practice is to develop effective filtering algorithms which will eliminate artifacts. Instead, our goal is to detect the motion artifacts and classify the type of BMA from the ECG signal itself. We have recorded the ECG signals during specified BMAs, e.g., sitting still, walking, movements of arms and climbing stairs, etc. with a single-lead system. The collected ECG signal during BMA is presumed to be an additive mix of signals due to cardiac activities, motion artifacts and sensor noise. A particular class of BMA is characterized by applying eigen decomposition on the corresponding ECG data. The classification accuracies range from 70% to 98% for various class combinations of BMAs depending on their uniqueness based on this technique. The above classification is also useful for analysis of P and T waves in the presence of BMA

Reconfiguration strategy for optimization of solar photovoltaic array under non-uniform illumination conditions

Performance of a solar photovoltaic (SPV) array is affected by variations in temperature, solar insolation and array configuration. At times, the SPV arrays are susceptible to non-uniform illumination due to shading caused by passing cloud, towers, trees etc. The effect of partial shading is critical; it can cause problems such as irregular P-V characteristics (multiple peaks) which makes power optimization difficult by the conventional power extraction techniques and results in significant loss of power. In most SPV systems, a DC-DC converter is connected at the SPV output to compensate for the drop in the PV output voltage. Under shaded conditions, a high gain DC-DC converter is needed to boost the low SPV voltage, which leads to additional power loss. Under such conditions, an appropriate reconfiguration scheme may prove to be beneficial as it ensures a certain minimum voltage for the next stage, obviating the need for high voltage gain, thereby reducing the power losses in the DC-DC converter. Under non-uniform illumination conditions, the P-V characteristics may exhibit multiple peaks. In the absence of reconfiguration, the conventional power optimization technique will get trapped at the local maxima and result in loss of power. While reconfiguration shows advantage in power as well as makes the P-V characteristics less irregular making the convergence to the maximum power point easier. This paper proposes a reconfiguration strategy which ensures a certain minimum deviation from the operating voltage with improvement in power. A reconfigurable 4×4 solar PV cell array is designed. The experimental results for a 4×4 cell array demonstrating the reconfiguration strategy showing improvement in power has been included. And simulation results of reconfiguration of flexible PV modules under non-uniform conditions are also provided.

Ambulation Analysis in Wearable ECG

Ambulation Analysis in Wearable ECG Subhasis Chaudhuri, Tanmay Pawar, Siddhartha Duttagupta Ambulation Analysis in Wearable ECG demonstrates why, due to recent developments, the wearable ECG recorder substantiates a significant innovation in the healthcare field. About this book: Examines the viability of wearable ECG in cardiac monitoring. Includes chapters written by practitioners who have personally developed such hardware to write about the hardware details. Bridges the gap between hardware and algorithmic developments with chapters that specifically discuss the hardware aspects and their corresponding calibration issues. Presents a useful text for both practitioners and researchers in biomedical engineering and related interdisciplinary fields. Assumes basic familiarity with digital signal processing and linear algebra.

Enhancement and suppression of the formation of porous silicon

We present the results of an investigation of various means to enhance or suppress the formation of porous silicon. The first method involves a lithographic process using silicon nitride to produce sub‐0.5 μm light emitting porous silicon (LEPSi) lines adjacent to fully protected silicon regions. The second method consists of amorphizing regions of the wafer prior to anodization with high energy/high dose ion implantation, followed by anodization and annealing. In this method, LEPSi is produced in the unimplanted regions only. Using focused ion‐beam implantation ∼100 nm patterns have been obtained. The third method utilizes low energy/low dose bombardment (ion milling/reactive ion etching) with argon ions prior to anodization. Under appropriate bombardment conditions, we have observed a strong enhancement of the formation rate of LEPSi, possibly due to the generation of a large number of defects on the wafer surface. Our results demonstrate that porous silicon light emitting diodes (LEDS) and silicon elec...

Transition Detection in Body Movement Activities for Wearable ECG

It has been shown by Pawar (2007) that the motion artifacts induced by body movement activity (BMA) in a single-lead wearable electrocardiogram (ECG) signal recorder, while monitoring an ambulatory patient, can be detected and removed by using a principal component analysis (PCA)-based classification technique. However, this requires the ECG signal to be temporally segmented so that each segment comprises of artifacts due to a single type of body movement activity. In this paper, we propose a simple, recursively updated PCA-based technique to detect transitions wherever the type of body movement is changed

Microhardness of porous silicon films and composites

Microhardness measurements have been performed on porous silicon (PSi) films. The dependence of the hardness on porosity, morphology and the underlying silicon substrate has been established. A model which determines the intrinsic film hardness has been developed and experimentally validated. The load dependence of hardness was measured as an index of the disorder in porous silicon. Hardness analysis also provided information on the nature of the PSi surface. Finally, several PSi-polymer nanocomposites have been fabricated and characterized. An improvement in hardness is observed, with no apparent change in the PL characteristics.

Two-Phase Flow Pressure Drop Characteristics in Trapezoidal Silicon Microchannels

This paper focuses on experimentally studying the pressure drop characteristics for two-phase flow in microchannels of hydraulic diameter 109 mum , over a relatively large range of heat flux of (0-30 W/cm2) and mass flow rate values (44-1114 kg/m2-s). Three fluid flow regimes (single-phase, two-phase, and dryout) have been covered in this paper, with deionized water as the working fluid. For a given heat flux, the variation of average pressure drop with flow rate can be classified into three distinct regimes. In the first regime (higher flow rate), the pressure drop decreases linearly with decrease in flow rate. In the second regime (lower flow rate), pressure drop increases with decreasing flow rate and reaches a maximum (with a minimum on either side). Finally, in the very low flow rate regime, pressure drop increases rapidly with decreasing flow rate. The average pressure drop in the two-phase regime is predicted well by the annular flow model. In addition to absolute pressure drop values, we also report pressure fluctuations. The magnitude of pressure fluctuations appears to be correlated to the underlying flow regime, such as bubbly, slug, and annular regimes, which have been identified through the flow visualization. An important outcome of this study is the identification of as many as four operating points with similar pressure drop penalty. This may help to choose the right operating conditions for a microchannel-based heat sink for use in cooling electronics. These detailed experimental results are also expected to be useful for modeling two-phase flow in microchannels.