Energy harvesting optical modulators with sub-attojoule per bit electrical energy consumption.

The light input to a semiconductor optical modulator can constitute an electrical energy supply through the photovoltaic effect, which is unexploited in conventional modulators. In this work, we leverage this effect to demonstrate a silicon modulator with sub-aJ/bit electrical energy consumption at sub-GHz speeds, relevant for massively parallel input/output systems such as neural interfaces. We use the parasitic photovoltaic current to self-charge the modulator and a single transistor to modulate the stored charge. This way, the electrical driver only needs to charge the nano-scale gate of the transistor, with attojoule-scale energy dissipation. We implement this 'photovoltaic modulator' in a monolithic CMOS platform. This work demonstrates how close integration and co-design of electronics and photonics offers a path to optical switching with as few as 500 injected electrons and electrical energy consumption as low as 20 zJ/bit, achieved only by recovering the absorbed optical energy that is wasted in conventional modulation.

Exploring quinolone resistance-determining region in Neisseria gonorrhoeae isolates from across India.

BACKGROUND & OBJECTIVES: Antimicrobial resistance in Neisseria gonorrhoeae, the causative agent of gonorrhoea, is a subject of worldwide attention. The present study was undertaken to examine the rates of ciprofloxacin resistance, to correlate mutations in gyrA and parC genes with the level of resistance and to look for a variation in mutation pattern, if any, in isolates from across the country. METHODS: A total of 113 isolates of N. gonorrhoeae collected from sexually transmitted infection patients in six centres during November 2010 to October 2013 were investigated. Minimum inhibitory concentration (MIC) determination was done by E-test and results interpreted as per Calibrated Dichotomous Sensitivity criteria. DNA sequence analysis of gyrA and parC genes was done. RESULTS: Of the 113 isolates, only three (2.6%) were susceptible whereas eight (7.07%) were less susceptible, 32 [28.3%, 95% confidence interval (CI): 20.4-37.6%] resistant (MIC 1-3 µg/ml) and 70 (61.9%, 95% CI: 52.2-70.7%) exhibited high-level resistance (HLR) (MIC ≥4 µg/ml) to ciprofloxacin. A S91F substitution in gyrA gene was demonstrated in all ciprofloxacin non-susceptible isolates. All resistant and HLR isolates had a double mutation in gyrA gene. However, only 5.7 per cent of HLR isolates showed double mutations in parC gene. One isolate (MIC 32 µg/ml) had a previously undescribed G85D substitution in the parC gene. INTERPRETATION & CONCLUSIONS: A S91F substitution in gyrA gene was seen in all non-susceptible isolates of N. gonorrhoeae. It may be used as a marker for ciprofloxacin resistance for molecular surveillance approaches to complement the culture-based methods.

High temperature Z-meter setup for characterizing thermoelectric material under large temperature gradient.

To properly estimate a thermoelectric material's performance, one should be able to characterize a single thermoelectric (TE) element with a large temperature gradient. In this work, we present an experimental setup including a Z-meter that can heat the sample to a very high temperature of 1200 °C in vacuum. The Z-meter can simultaneously measure all three thermoelectric parameters (Seebeck coefficient, thermal conductivity, and electrical conductivity), as well as measure the generated power and the efficiency for a single TE leg. Furthermore, this measurement of power conversion efficiency is used to generate a measure of the material's ZT. An in situ metallurgical bond was used to achieve low thermal (0.05 Kcm(2)/W) and electrical (3 mΩ) contact parasitics. An integrated strain gauge ensures reproducible thermal contact. At high temperature (>600 K), radiative heat transfer is modeled and the instrument is optimized to suppress the systematic error to below 7%. The TE parameters and ZT for a bulk-sample (Bi(2)Te(3)) and a thin-film sample (ErAs:InGaAlAs) with a large temperature gradient (ΔT ∼ 200 K) have been measured and are within 3%-7% of the independently measured values.

Flexible PDMS -based dry electrodes for electro-optic acquisition of ECG signals in wearable devices.

We present a new type of flexible dry copper electrodes based on Polydimethylsiloxane (PDMS) coatings, requiring no electrical contact with the body. Tests were performed in order to evaluate the performance of these types of electrodes using electro-optic techniques, suitable for wearable devices. Conductive and insulated PDMS layers were fabricated through a spin coating process, reaching a thickness of 100µ. These layers were then deposited on top of a flexible copper sheet. In a first set of experiments PDMS-based electrodes were compared with Ag/AgCl pre-gelled electrodes, showing comparable performances and lower noise signals. In order to test the influence of electrode area into signal strength, different sizes were chosen: 10.14 cm(2), 17.55 cm(2), 25.3 cm(2) and 39 cm(2). The results have shown that the signal strength increases with electrode area. We have also tested the influence of PDMS conductivity in signal strength, by adding two types of nickel to the pre-polymer solution. PDMS conductive electrodes have shown slightly better performances, with amplitudes higher than 200mV, which is the maximum value recorded with PDMS insulated electrodes.

Semiconductor lasers without population inversion.

We propose a new scheme for lasing without population inversion that utilizes interferences in double-quantum-well intersubband transitions. In contrast to the previous inversionless laser schemes based on atomic systems, the new proposal permits us to use band-gap engineering to choose the subband energies, coupling strengths, and decay rates, as desired, and permits us to create a laser system that does not require population inversion. We present detailed calculations on a specific scheme and discuss possible extensions.