The ability to measure optical signals with fast dynamics is of significant interest in many application fields. Usually, single-shot measurements of non-periodic signals can be enabled by time ...magnification methods. Like an optical lens in the spatial domain, a time magnifier, or a time lens, stretches a signal in the time domain. This stretched signal can then be further processed with low bandwidth photonics and electronics. For a robust and cost-effective measurement device, integrated solutions would be especially advantageous. Conventional time lenses require dispersion and nonlinear optical effects. Integration of a strong dispersion and nonlinearities is not straightforward on a silicon photonics platform and they might lead to signal distortions. Here we present a time magnifier based on an integrated silicon nitride microring resonator and frequency-time coherence optical sampling, which requires neither a dispersion, nor a nonlinearity. Sampling of signals with up to 100 GHz bandwidth with a stretching factor of more than 100 is achieved using low bandwidth measurement equipment. Nevertheless, with already demonstrated integrated 100 GHz modulators, the method enables the measurement of signals with bandwidths of up to 400 GHz. Since amplitude and phase can be sampled, a combination with the spectrum slicing method might enable integrated, cost-effective, small-footprint analog-to-digital converters, and measurement devices for the characterization of single irregular optical signals with fast dynamics and bandwidths in the THz range.
•Adaptation of EtBr fluorescence assay for estimation of efflux pump activities.•The assay was effective in both Gram negative as well as Gram positive bacteria.•The spectrum of the assay was ...extended to diverse physiologies with efflux pumps.•The assay was used for first time directly on cells harvested from natural samples.
Quick, simple and reliable assays to screen and understand active efflux pumps operative in pure bacterial cultures or mixed population in environmental samples are important. Although assays are available to monitor efflux activities in pure cultures, none has been used or tested directly on natural samples or cells harvested from them. Here, we have adapted an existing fluorescence assay using ethidium bromide (EtBr) to monitor efflux activities connected to resistance/tolerance to antibiotics (tetracycline), heavy metals (chromium), salt (NaCl) and ionic liquid (1-ethyl-3-methylimidazolium chloride) in different Gram positive and negative bacterial pure cultures. Concentration of 0.5 µg ml−1 of EtBr was found to be optimum for the assay. For all tested physiologies, 1.2–2.2 fold lower EtBr fluorescence (or higher efflux) was detected as compared to control. In addition, the assay was efficiently used for the first time to establish differences in efflux activities in microbial cells harvested from different natural environments. Similar to pure cultures, sediments with higher salinity (7%) compared to lower (3%) ones, and antibiotic contaminated hospital drain samples compared to adjoining garden soil showed up to 1.7-fold and 1.3-fold higher efflux activities respectively. Thus, EtBr fluorescence assay can be used effectively in known or novel bacterial physiologies that involve efflux activities not only in pure cultures, but also in natural environmental microbial groups.
Sampling is the first step to convert analogue into digital signals and one of the basic concepts for information handling. All practical sampling systems, however, are accompanied with errors. ...Bandwidth-limited signals can be seen as a superposition of time-shifted sinc pulses, weighted with the sampling values. Thus, due to orthogonality, bandlimited signals can be perfectly sampled by a corresponding sinc pulse with the correct time shift. But, sinc pulses are just a mathematical construct. Sinc pulse sequences, instead, can simply be generated by a rectangular, phase-locked frequency comb. For a high repetition-time to pulsewidth ratio, or a low duty cycle, the pulses of such a sequence come close to single sinc pulses, and thus, the sampling with them might lead to an almost ideal sampling. Here, we present the full-field optical sampling with a repetition-time to pulsewidth ratio of up to 153, or a duty cycle of around 0.65%. Since it enables amplitude and phase sampling, ultrahigh sampling rates should be possible.
The growing demand for bandwidth and energy efficiency requires new solutions for signal detection and processing. We demonstrate a concept for high-bandwidth signal detection with low-speed ...photodetectors and electronics. The method is based on the parallel optical sampling of a high-bandwidth signal with sinc-pulse sequences provided by a Mach-Zehnder modulator. For the electronic detection and processing this parallel sampling enables to divide the high-bandwidth optical signal with the bandwidth <inline-formula><tex-math notation="LaTeX">B</tex-math></inline-formula> into <inline-formula><tex-math notation="LaTeX">N</tex-math></inline-formula> electrical signals with the baseband bandwidth of <inline-formula><tex-math notation="LaTeX">B/(\text{2}\,N)</tex-math></inline-formula>. In proof-of-concept experiments with <inline-formula><tex-math notation="LaTeX">N=3</tex-math></inline-formula>, we present the detection of 24 GHz optical signals by detectors with a bandwidth of only 4 GHz. For ideal components, the sampling and bandwidth down-conversion does not add an excess error to the signals and even for the non-ideal components of our proof-of-concept setup, it is below 1%. Thus, the rms error for the measurement of the 24 GHz signal was reduced by a factor of about 3.4 and the effective number of bits were increased by 1.8.
Ionic liquids, such as 1-ethyl-3-methylimidazolium chloride (EmimCl), have immense applicability as solvents in different industrial settings including lignocellulosic biofuel production. However, ...these solvents are toxic to most organisms. Moderate halophiles are an established microbial group that can tolerate EmimCl by employing their general salt-tolerant mechanisms. Anticipating future exposure of EmimCl to natural environments, the present study was designed to evaluate bacterial community structure in slightly saline (20 g L
−1
or 2%) sediments of Sambhar Salt Lake, Rajasthan, India, after microcosm enrichment with EmimCl. The sediment used does not have any native EmimCl (100 mM)–tolerant bacteria. However, after a two-step enrichment of 25 days each with 0.5 M and 1.0 M EmimCl, the tolerant colonies increased to 54.9% and 93.0%, respectively. But in similar NaCl enrichment, or control incubations, such colonies were absent. Bacterial 16S rRNA gene amplicon sequence-based alpha diversity in 50 days EmimCl-enriched set was lower than the initial, control and NaCl-enriched sets (Shannon index of 6.71 vs. 8.0–8.26, respectively). Even its bacterial community structure was distinct from the remaining three sets, which clustered together. EmimCl-enriched set has almost fourfold higher abundance of
Proteobacteria
(50.36%), with
Gammaproteobacteria
(32.25%) and particularly
Enterobacteriaceae
(24.19%) members being predominant with a predicted higher abundance of membrane transporters.
Cyanobacteria
,
Actinobacteria
and
Bacteroidetes
were most sensitive groups to EmimCl enrichment
.
Although moderate halophiles can utilise their general NaCl tolerance mechanisms to resist toxicity of EmimCl, abrupt exposure of the later disturbs microbial population structure and thus demands their meticulous use avoiding environmental contamination.
Optical sinc-shaped Nyquist pulses are widely used in microwave photonics, optical signal processing, and optical telecommunications due to their numerous advantages, like rectangular shape in the ...frequency domain, the orthogonality and the consequential possibility to use these pulses to transmit data with the maximum possible symbol rate. Ideal sinc pulses with the rectangular spectrum are just a mathematical construct. However, high-quality sinc pulse sequences offer the same advantages and can be generated by a phase-locked rectangular frequency comb with mode-locked lasers, intensity modulators, and integrated devices. Nevertheless, any non-idealities in the pulse and comb generation might lead to a degradation of the system performance, especially for metrology. Here, we investigate and analyze the effect of three major non-idealities, namely, the roll-off factor, the side band suppression ratio (SSR), and the ripple of sinc-shaped reconfigurable optical Nyquist pulse sequences based on 3, 5, and 9-line optical phase-locked frequency combs. We compare these results with the existing literature for the three-line comb followed by the experimental verification of the simulation results. We illustrate that by increasing the number of comb lines, the pulse sequences have superior performance and contribute to lesser root-mean-square (r.m.s.) error. We also discuss the trade-off between the r.m.s. error and the optical power loss for increasing the SSR.
A compact device model along with simulations and an experimental analysis of a forward-biased PN junction-based silicon Mach-Zehnder modulator (MZM) with a phase-shifter length of 0.5 mm is ...presented. By placing the PN junction to a certain off-center such that 72% of the waveguide is p-doped, the refractive index swing at a given drive voltage swing is increased by 2% compared to the symmetric layout. The effects of the phase shifters' length mismatch and asymmetric splitting on the modulation efficiency and extinction ratio of the modulator are simulated and compared with experimental results. Without any pre-emphasis or post-processing, a high-speed operation up to 15 Gb/s using a non-return-to-zero modulation format is demonstrated. A modulation efficiency (<inline-formula><tex-math notation="LaTeX">{{\boldsymbol{V}}_{\boldsymbol{\pi}}}{\boldsymbol{L}}</tex-math></inline-formula>) as low as 0.07 V × cm is verified and power consumption of 0.88 mW/Gb/s is recorded while a high extinction ratio of 33 dB is experimentally demonstrated. Compared to previously reported forward-biased silicon integrated modulators, without active tuning of the power splitting ratio between the arms, the extinction ratio is 10 dB higher. This MZM along with its compact structure is also sufficiently energy-efficient due to its low power consumption. Thus, it can be suitable for applications like analog signal processing and high-order amplitude modulation transmissions.
Spectrally efficient modulation formats become essential for optical network scaling as the demand for routed data streams exceeds the present wavelength-division multiplexing systems’ throughput. ...However, achieving high spectral efficiency at high data rates requires complex and bandwidth-intensive electronics. In this study, we propose an all-optical aggregation scheme that combines multiple low spectral efficiency optical wavelength channels from an optical frequency comb based transmitter into fewer channels with higher spectral efficiency. Our method utilizes coherent spectral superposition and optical vector summation, eliminating the need for optical nonlinearities and relying on linear signal processing with an electro-optic modulator. By adjusting the phase of the radio frequency signal driving the modulator, we can easily achieve the required optical phase tuning for vector addition in the I-Q plane. Through experimental demonstrations, we show that the proposed approach enables the generation of 10 GBd PAM-4 and 10 GBd quadrature phase shift keying (QPSK) signals by aggregating two 10 GBd binary phase shift keying signals. Similarly, we aggregate two 10 GBd QPSK signals into one 10 GBd quadrature amplitude modulation-16 (QAM-16) signal. The experiments employ both conventional and sinc-shaped Nyquist signals. Our in-line, all-optical aggregation concept significantly enhances operational capacity while reducing complexity. It offers a promising solution for realizing flexible integrated optical transmitters for advanced modulation format signals using lower-quality electronics. Additionally, it aligns with the requirements of future dynamically reconfigurable optical networks that leverage spectral traffic aggregation. Given its reliance on linear signal processing with an electro-optic modulator, the integration of the method into any integrated photonic platform is straightforward.
Display omitted
•A Cr(VI) reducing Bacillus strain TCL isolated from derelict open-cast coalmine of Jharia, India.•TCL show multifarious morphological and biochemical stress response in ≥ Cr500.•Its ...Cr(VI) reduction activity is constitutive and facilitated by diverse mechanisms.•The strain has high bioremediation potential.
Microbial reduction of Cr(VI) to Cr(III) can mitigate environmental chromium toxicity. A chromium, cadmium and nickel tolerating strain TCL with 97% 16S rRNA gene sequence homology to Bacillus cereus was isolated from a derelict open-cast, Tasra Coalmine Lake of Jharia, India. It could tolerate up to Cr2000 2,000 mg L−1 Cr(VI) and completely reduce Cr200 within 16 h under heterotrophic condition. TCL grown in ≥ Cr500 exhibited multifarious stress responses particularly in its prolonged lag-phase, like cell aggregation, up to two-fold elongation, increased exopolysaccharide production, and stress enzyme activities. These were relieved by increasing inoculum size or nutrient content. Chromium reduction was constitutive, with maximum activities detected in loosely-bound exopolysaccharides and membrane fractions, followed by cytoplasm and spent media. Cr(VI) was efficiently reduced to Cr(III) and >90% was released in spent media. Cells also expressed Cr-induced active efflux pumps. Growing cells or its crude enzyme extracts could efficiently reduce Cr(VI) in diverse temperatures (15–45 °C), pH (5–9); and in presence of other metals (Cd, Cu, Mo, Ni, Pb), oxyanions (SO4−2, NO2−), and metabolic inhibitors (phenol, NaN3, EDTA). Growth and reduction were also detected in nutrient-limited minimal salt media, and contaminated leather industry effluent thereby making TCL a potential candidate for bioremediation.
Display omitted
•Solanum erianthum D. Don, a medicinally important plant of Solanaceae, contains steroidal alkaloid solasodine.•Genetic transfection of S. erianthum was developed with 72 % efficiency ...and fast-growing hairy rootlines were established.•The genetic transfer of rol A and rol B gene in hairy roots were confirmed using Polymerase Chain Reaction (PCR) analysis.•Transformed roots accumulated higher levels of secondary metabolites than non-transformed roots.•Enhanced solasodine produced in selected hairy rootline.
An efficient genetic transfection technique has been established using A4 strain of Agrobacterium rhizogenes for the first time in a medicinally valuable plant Solanum erianthum D. Don. The explants were randomly pricked with sterile needle, inoculated with bacterial suspension. The infected leaves were then washed and transferred to MS basal medium fortified with cefotaxime for hairy root induction. A maximum transformation efficiency of 72 % has been recorded after two days of co-cultivation period. The transfer of rolA and rolB genes from the bacterium to the plant genome has been confirmed in five transformed hairy rootlines by standard Polymerase Chain Reaction technique. On the basis of growth analysis and secondary metabolite study two potential rhizoclones (A4-HR-A and A4-HR-B) were selected. Rhizoclone A4-HR-A can produce highest amount of alkaloid, phenolic and flavonoid, whereas A4-HR-B was observed to be highest tannin producer. Alkaloid like solasodine, commercially important for steroidal drug synthesis, was quantified from leaf and A4-HR-A clone by an improved High Performance Liquid Chromatography method. This showed a sustainable increase (1.33 fold) in production of solasodine in hairy rootline.
PDF
