A Conceptual Framework for Understanding the Biogeochemistry of Dry Riverbeds Through the Lens of Soil Science

Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of fluvial networks. DRBs are often overlooked because they do not strictly belong to either domain of soil or freshwater science. Due to this dual character of DRBs, we suggest that concepts and knowledge from soil science can be used to expand the understanding of IRES biogeochemistry. Based on this idea, we propose that DRBs can be conceptually understood as early stage soils exhibiting many similarities with soils through two main forces: i) time since last sediment transport event, and ii) the development status of stabilizing structures (e.g. soil crusts and/or vascular plants). Our analysis suggests that while DRBs and soils may differ in master physical attributes (e.g. soil horizons vs fluvial sedimentary facies), they become rapidly comparable in terms of microbial communities and biogeochemical processes. We further propose that drivers of DRBs biogeochemistry are similar to those of soils and, hence, concepts and methods used in soil science are transferable to DRBs research. Finally, our paper presents future research directions to advance the knowledge of DRBs and to understand their role in the biogeochemistry of intermittent fluvial networks

Optical resonant nanoprobes for the measurements of biomolecular interactions

Quantifying the interactions between biomolecules combined with discovering their structure provides better understanding of the underlying molecular mechanisms and opens the capability to accurately predict and design micromolecular structures and interactions. The ability of this approach to advancing the diagnostics and the treatment of disease is immense. In this thesis, it was demonstrated that two resonant optical nanoprobes, namely photonic crystal microcavity sensor and plasmon-coupled nanoparticle probe can be applied toward investigating biomolecular interactions. Both techniques are based on the measurements of optical resonances. Measurement of protein binding kinetics using photonic crystal microcavity sensor was demonstrated for the first time. Real-time monitoring of the resonant wavelength provides information on the strength of protein binding and concentration. The sensor performance was demonstrated with biotinylated-BSA and anti-biotin. Mass transport of molecules to the sensing surface was analyzed to explain the relatively long transition time needed to reach the binding equilibrium in time resolved experiments. Binding of small molecular species such as aromatic rings was detected. The detection limit, in terms of the mass of molecules bound to the surface, was shown to be less than 4.5fg. The small modal volume and photonic confinement inside the microcavity enable detection of attoliter samples. The calculations show that the response of the sensor to binding of a single molecule is 0.72pm. By implementing temperature control and signal processing techniques, signal-to-noise ratio can be improved to allow for single molecule detection. Plasmon coupled- nanoparticle probes were used to measure the binding strength between two DNA strands, with the idea to discern single nucleotide mismatches in the sequence. The probe consists of two streptavidin-coated gold nanoparticles interconnected with two biotinylated-DNA strands under test. An external Coulombic force was applied by lowering the ionic concentration of the solution, causing the binding strength between complementary DNA strands to be weakened. This was converted to a distance change between plasmon-coupled gold nanoparticles, causing a shift in their resonant wavelength position. This is a new approach to the measurement of the binding strength within molecular complexe

Reconfigurable parametric channelized receiver for instantaneous spectral analysis

We propose and demonstrate a photonic approach to a reconfigurable channelized radio frequency (RF) receiver for instantaneous RF spectrum monitoring and analysis. Our approach relies on the generation of high quality copies of the RF input by wavelength multicasting in a 2- pump self-seeded parametric mixer and the use of off-the-shelf filtering element such as Fabry-Perot etalon and wavelength division demultiplexers. The parametric channelizer scheme trades frequency non-degeneracy of the newly generated copies for ease of filtering design. Self seeding scheme employed to wavelength multicast the original RF signal to a large number of copies enables easy reconfigurability of the device by simple tuning of the three input waves, i.e. seed and pumps. Channelizer operation to up to 15GHz bandwidth and channel spacing of 500MHz is demonstrated. Reconfigurability is verified by tuning the receiver operating bandwidth and channel spacing

Parametric Channelized Receiver for Single-Step Spectral Analysis

We present new parametric channelized receiver for instantaneous RF spectrum characterization. Single resonant cavity filter combined with parametric wavelength multicasting achieved simultaneous channelization of 10GHz signal with 1GHz resolution and extinction ratio >;20dB

Performance of Instantaneous Microwave Analysis by Parametric Channelized Receiver Through Time Domain Monitoring

For many applications, ranging from commercial, surveillance, or defense, it is essential to analyze the frequency components of a captured microwave signal over a wide bandwidth in real time and with high resolution. Various photonic approaches have been proposed for the processing of wideband microwave signals in order to overcome limitations imposed by conventional electronic frequency measurements. Here, we present the performance analysis and characterization of a parametric channelized receiver with 275 MHz resolution defined by the Fabry-Perot 3 dB bandwidth and 1 GHz step. Our approach relies on the generation of high quality copies of the RF input by self-seeding wavelength multicasting in a two-pump parametric mixer. Periodic filtering using off-the-shelf elements is then performed on the multicast beam. Ease of filtering is thus achieved by relying on frequency nondegeneracy of the newly generated copies. In this paper, instantaneous analysis of the incoming microwave signal is demonstrated by simultaneous monitoring five of the generated parametric copies while transmitting a frequency-hopping pattern. Operating margins in terms of optical and microwave powers are studied using the five-channel data simultaneously collected on a real-time oscilloscope. Dynamic range adjustments through optical power tuning of the input signal seed are demonstrated. Finally, the effects of frequency mapping detuning are observed to determine optimal operating conditions

Demonstration of Continuous-wave four-wave mixing in AsSe Chalcogenide Microstructured Fiber

Continuous-wave four-wave mixing in a 2.5-cm long segment of AsSe Chalcogenide microstructured fiber is demonstrated. FWM products over 50nm are measured for 345mW of pump power and wavelength conversion of 4ps pulses is shown

Continuous-wave four-wave mixing in cm-long Chalcogenide microstructured fiber

We present the experimental demonstration of broadband four-wave mixing in a 2.5 cm-long segment of AsSe Chalcogenide microstructured fiber. The parametric mixing was driven by a continuous-wave pump compatible with data signal wavelength conversion. Four-wave mixing products over more than 70 nm on the anti-stoke side of the pump were measured for 345 mW of pump power and 1.5 dBm of signal power. The ultrafast signal processing capability was verified through wavelength conversion of 1.4 ps pulses at 8 GHz repetition rate. (C) 2011 Optical Society of Americ

Mid-Infrared Wavelength Conversion In Silicon Waveguides Using Ultracompact Telecom-Band-Derived Pump Source

Mid-infrared light sources are essential for applications that include free-space communication, chemical and biomolecular sensing and infrared spectroscopy1-3, but no devices comparable to those in the near-infrared regime have emerged to date. Indeed, sources operating above 1.8 μm, including optical parametric oscillators and thulium-doped fibre lasers, do not combine a large tunable range and narrow linewidth, and generally cannot be modulated to support advanced applications4,5. Widely tunable mid-infrared quantum cascade lasers are available; however, room-temperature operation in the 3g-4 μm range still presents a challenge because of material limitations6,7. Wavelength conversion in silicon offers promise for the development of an ultracompact mid-infrared source that combines wide wavelength tuning, narrow linewidth and arbitrarily complex modulation rivalling those in the telecom window. Here, we report four-wave mixing in silicon waveguides in the spectral region beyond 2 μm, using probe and pump waves derived from ultracompact telecom fibre-optic sources, achieving generation of 2,388 nm light. © 2010 Macmillan Publishers Limited. All rights reserved