Vikas Kumar Singh

Compensating for Quantizer Delay in Excess of One Clock Cycle in Continuous-Time

The maximum sampling rate of a continuous-time ΔΣ modulator is limited by quantizer delay. Most conventional delay compensation techniques address less than a clock cycle of delay. A technique previously proposed for compensating quantizer delays in excess of a clock cycle in bandpass modulators involves a parallel feedback path that bypasses the quantizer. We analyze this technique for low-pass modulators and show that sampling rates hitherto not possible can be achieved. Design tradeoffs are investigated, and simulation results showing the effectiveness of the technique are given.

\Delta\Sigma

The AgNPs synthesized by green method have shown great potential in several applications such as biosensing, biomedical, catalysis, electronic etc. The present study deals with the selective colorimetric detection of Fe3+ using photoinduced green synthesized AgNPs. For the synthesis purpose, an aqueous extract of Croton bonplandianum (AEC) was used as a reducing and stabilizing agent. The biosynthesis was confirmed by UV-visible spectroscopy where an SPR band at λmax 436nm after 40s and 428nm after 30min corresponded to the existence of AgNPs. The optimum conditions for biosynthesis of AgNPs were 30min sunlight exposure time, 5.0% (v/v) AEC inoculum dose and 4mM AgNO3 concentration. The stability of synthesized AgNPs was monitored up to 9months. The size and shape of AgNPs with average size 19.4nm were determined by Field Emission Scanning Electron Microscope (FE-SEM) and High-Resolution Transmission Electron Microscope (HR-TEM). The crystallinity was determined by High-Resolution X-ray Diffractometer (HR-XRD) and Selected Area Electron Diffraction (SAED) pattern. The chemical and elemental compositions were determined by Fourier Transformed Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray Spectroscopy (EDX) respectively. The Atomic Force Microscopy (AFM) images represented the lateral and 3D topological characteristics of AgNPs. The XPS analysis confirmed the presence of two individual peaks which attributed to the Ag 3d3/2 and Ag 3d5/2 binding energies corresponding to the presence of metallic silver. The biosynthesized AgNPs showed potent antibacterial activity against both gram-positive and gram-negative bacterial strains as well as antioxidant activity. On the basis of results and facts, a probable mechanism was also proposed to explore the possible route of AgNPs synthesis, colorimetric detection of Fe3+, antibacterial and antioxidant activity.

Modulators

In the present study, a PEI cross-linked graphene oxide aerogel (GOPEI) was prepared. The interaction of GO and PEI was investigated by FT-IR and XPS analysis and after that further characterization was conducted using SEM, EDX, XRD, Raman spectroscopy and BET surface area measurement. The prepared GOPEI aerogel was utilized for the treatment of As(V) and As(III) contaminated water. The maximum uptake capacity, 4.80 ± 0.27 mg g−1 for As(V) and 4.26 ± 0.24 mg g−1 for As(III), was obtained at an initial As(V)/As(III) concentration of 3 mg L−1, GOPEI dose 0.6 g L−1, and ambient temperature (30 °C). The adsorption process was found to be pH sensitive where the optimum pH was 4 for As(V) and 7 for As(III) whereas at pH 6 significant uptake capacity was observed for both As(V) and As(III), which is close to the pH of drinking water. Therefore, GOPEI can be used for the adsorption of As(V) as well as As(III) at a common pH and ambient temperature without much changing the pH of drinking water. In order to use the GOPEI aerogel as an adsorbent in a continuous column for the treatment of arsenic contaminated water, the practicability was tested by conducting detailed kinetics, isotherm and thermodynamics studies. The adsorption, which occurs on a monolayer on the heterogeneous surface of the GOPEI aerogel, was found to be thermodynamically feasible and follows pseudo-second-order kinetics.

Photo-mediated optimized synthesis of silver nanoparticles for the selective detection of Iron(III), antibacterial and antioxidant activity

An 800MS/s CT ΔΣ ADC with 16MHz/32MHz bandwidths consumes 47.6mW from 1.8V and occupies 1mm2 in a 0.18µm CMOS process. The DR/SNR/SNDR for the two bandwidths are 75/67/65 dB and 64/57/57 dB respectively. Excess loop delay (ELD) of more than one cycle is compensated using a fast path outside the flash ADC. This and a low latency flash ADC and delay free DAC calibration result in the highest reported sampling rate in this process.

Modeling of adsorption behavior of the amine-rich GOPEI aerogel for the removal of As(III) and As(V) from aqueous media

A novel hybrid fluorophore (FHPY) has been synthesized based on a condensation reaction of two standard fluorescent hydrophobic–hydrophilic molecules, viz. pyrene and fluorescein, with an objective to tune the aggregation-induced emission (AIE) along with the morphology. Owing to the distinct photophysical properties of pyrene and fluorescein, the hybrid FHPY dramatically exhibits a fluorescence change from colourless to yellow-green via a blue colour upon varying the volume fraction of water (poor solvent) in methanol (good solvent). FHPY has exhibited not only AIE, but also an outstanding quantum yield (ΦF) of 97% at a 70% water fraction in methanol (70 : 30, v/v). We attribute the reason behind the tuning of the AIE and quantum yield to the opening of the lactam ring of fluorescein as well as to the amassing of hydrophobic pyrene at a certain water fraction. The mechanism involved in the AIE has been well supported by detailed UV-vis, fluorescence, lifetime, SEM, AFM, DFT, PXRD and 1H NMR experiments. In addition, FHPY serves as a good candidate for the live cell imaging of HeLa cells.

A 16MHz BW 75dB DR CT ΔΣ ADC compensated for more than one cycle excess loop delay

Highly fluorescent nitrogen and phosphorus-doped carbon quantum dots (N,P-CQDs) were synthesized via a one-step hydrothermal method and fully characterized via various techniques such as TEM, DLS, FT-IR, P-XRD and XPS analysis. The as-synthesized N,P-CQDs showed excellent optical properties and exhibited bright blue colour under UV-light with CIE coordinate (0.20, 0.22) along with a high quantum yield of 73%, due to which they could act as on–off fluorescent nanoprobes for the selective and sensitive detection of highly toxic Cr(VI) below its permissible limit via the inner filter effect (IFE) and static quenching mechanism. In addition, Cr(VI) could be reduced to lower valent chromium species. Therefore, the N,P-CQDs + Cr(VI) system further acted as a selective off–on sensor for reductant ascorbic acid (AA) because it reduced Cr(VI) to Cr(III) species, resulting in the elimination of IFE and recovery of fluorescence of N,P-CQDs. Notably, this system possesses excellent biocompatibility and negligible cytotoxicity; therefore, it can be potentially applied for fluorescence imaging of intracellular Cr(VI) and ascorbic acid (AA) in living cells and complex biological systems.

Pyrene–fluorescein-based colour-tunable AIE-active hybrid fluorophore material for potential live cell imaging applications

Herein, we report a green synthetic approach for the synthesis of water-soluble fluorescent CQDs via a simple one-step hydrothermal treatment using Tamarindus indica leaves for the first time. The prepared CQDs show an excitation-dependent behavior in the range from 260 to 400 nm with a high QY of approximately 46.6%. Further, the prepared CQDs serve as a very sensitive nanoprobe for the turn-off sensing of Hg2+ with a minimum LOD as low as 6 nM in the dynamic range from 0 to 0.1 μM. The attractiveness of the present sensing system is that it further acts as a turn-on sensor for GSH detection with good selectivity. The feasibility of the present sensing system is also examined using pond water samples for the detection of Hg2+. Thus, the present sensing system is reliable for sensing and several another analytical applications.

Bright-blue-emission nitrogen and phosphorus-doped carbon quantum dots as a promising nanoprobe for detection of Cr(VI) and ascorbic acid in pure aqueous solution and in living cells

Interest is growing in the development of artificial enzymes to overcome the drawbacks of natural enzymes. Herein, we have synthesized nitrogen-sulphur dual-doped carbon quantum dots (NS-CQDs) via a one-step hydrothermal method; the NS-CQDs possess excellent optical properties and a high fluorescent quantum yield (46%). Significantly, the NS-CQDs exhibited peroxidase mimetic enzyme activity without support from metals or polymeric materials and efficiently catalyzed the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue solution with an absorption maximum at 652 nm. Mechanistic studies suggest that the small size and high electron density of NS-CQDs play vital roles and accelerate the reduction of H2O2 to generate ˙OH radical, which facilitates the oxidation of TMB. The catalytic activity is based on Michaelis-Menten kinetic behavior, and steady state kinetic analysis suggests that the NS-CQDs exhibit a higher affinity for H2O2 than TMB, similar to the natural enzyme horseradish peroxidase (HRP). Moreover, the catalytic pathway follows a ping-pong mechanism. Therefore, these findings offer a worthy platform for colorimetric detection of H2O2 in a linear range of 0.02 mM to 0.1 mM with a limit of detection of 0.004 mM. Interestingly, the blue colour of oxidized TMB showed excellent selectivity over non-thiolate biological molecules, especially amino acids, and glutathione can be detected up to 0.07 μM via colorimetric and fluorimetric assays. Additionally, this system showed excellent recovery (96.0-108.3%) of GSH from human blood serum. Thus, the proposed sensing system is simple, convenient, and straightforward and can be potentially applied for real time monitoring of H2O2 and glutathione in biological samples.

Green synthesis of fluorescent carbon quantum dots for the detection of mercury(II) and glutathione

BACKGROUND: Roads and vehicles which are for making life comfortable and faster, can result in miserable life when one meet a road traffic accident. By 2020 road traffic accident is projected to become the third leading contributor to the global burden of disease in the world and 6th place as a major cause of mortality worldwide. Motor cyclists are about 25 times more risk than passenger car occupants to die because of road traffic accidents. OBJECTIVEs of the study were, to study pattern of two wheeler road traffic accidents in rural setting. Methods: The present research is a retrospective analysis of all the two-wheeler accidents victim admitted in emergency, during the period ranging from September 2015 to February 2016. Results: Among the total 2,544 patient of RTA admitted within the study period; 1,257 patients (i.e.49.41%) were due to two-wheeler accidents. Next is pedestrian (n=516, 20.2%), light motor vehicle (n=464, 18.23%), and heavy motor vehicle accidents contribute (n=307, 12.06%). Conclusions: lack of road driving sense and lack of knowledge of traffic rules. Regarding the type of vehicles involved in these accidents, the maximum number of accidents was due to two wheeler vehicles (scooter/motorcycle). Keywords: Two wheeler RTA, Stray animals, Rural RTA