Toward predicting photosynthetic efficiency and biomass gain in crop genotypes over a field season.

Photosynthesis acclimates quickly to the fluctuating environment in order to optimize the absorption of sunlight energy, specifically the photosynthetic photon fluence rate (PPFR), to fuel plant growth. The conversion efficiency of intercepted PPFR to photochemical energy (ɛe) and to biomass (ɛc) are critical parameters to describe plant productivity over time. However, they mask the link of instantaneous photochemical energy uptake under specific conditions, that is, the operating efficiency of photosystem II (Fq'/Fm'), and biomass accumulation. Therefore, the identification of energy- and thus resource-efficient genotypes under changing environmental conditions is impeded. We long-term monitored Fq'/Fm' at the canopy level for 21 soybean (Glycine max (L.) Merr.) and maize (Zea mays) genotypes under greenhouse and field conditions using automated chlorophyll fluorescence and spectral scans. Fq'/Fm' derived under incident sunlight during the entire growing season was modeled based on genotypic interactions with different environmental variables. This allowed us to cumulate the photochemical energy uptake and thus estimate ɛe noninvasively. ɛe ranged from 48% to 62%, depending on the genotype, and up to 9% of photochemical energy was transduced into biomass in the most efficient C4 maize genotype. Most strikingly, ɛe correlated with shoot biomass in seven independent experiments under varying conditions with up to r = 0.68. Thus, we estimated biomass production by integrating photosynthetic response to environmental stresses over the growing season and identified energy-efficient genotypes. This has great potential to improve crop growth models and to estimate the productivity of breeding lines or whole ecosystems at any time point using autonomous measuring systems.

Si photonic-electronic monolithically integrated optical receiver with a built-in temperature-controlled wavelength filter.

We present a Si photonic-electronic integrated ring-resonator based optical receiver that contains a temperature-controlled ring-resonator filter (RRF), a Ge photodetector, and receiver circuits in a single chip. The temperature controller automatically determines the RRF temperature at which the maximum transmission of the desired WDM signal is achieved and maintains this condition against any temperature or input wavelength fluctuation. This Si photonic-electronic integrated circuit is realized with 0.25-µm photonic BiCMOS technology, and its operation is successfully confirmed with measurement.

The Nature of Chalcogen-Bonding-Type Tellurium-Nitrogen Interactions: A First Experimental Structure from the Gas Phase.

(C6 F5 )Te(CH2 )3 NMe2 (1), a perfluorophenyltellurium derivative capable of forming intramolecular N⋅⋅⋅Te interactions, was prepared and characterized. The donor-free reference substance (C6 F5 )TeMe (2) and the unsupported adduct (C6 F5 )(Me)Te⋅NMe2 Et (2 b) were studied in parallel. Molecular structures of 1, 2 and 2 b were determined by single-crystal X-ray diffraction and for 1 and 2 by gas-phase electron diffraction. The structure of 1 shows N⋅⋅⋅Te distances of 2.639(1) Š(solid) and 2.92(3) Š(gas). Ab initio plus NBO and QTAIM calculations show significant charge transfer effects within the N⋅⋅⋅Te interactions and indicate σ-hole interactions.

Molecular Mechanisms Responsible for Pharmacological Effects of Genipin on Mitochondrial Proteins.

Genipin, a natural compound from Gardenia jasminoides, is a well-known compound in Chinese medicine that is used for the treatment of cancer, inflammation, and diabetes. The use of genipin in classical medicine is hindered because of its unknown molecular mechanisms of action apart from its strong cross-linking ability. Genipin is increasingly applied as a specific inhibitor of proton transport mediated by mitochondrial uncoupling protein 2 (UCP2). However, its specificity for UCP2 is questionable, and the underlying mechanism behind its action is unknown. Here, we investigated the effect of genipin in different systems, including neuroblastoma cells, isolated mitochondria, isolated mitochondrial proteins, and planar lipid bilayer membranes reconstituted with recombinant proteins. We revealed that genipin activated dicarboxylate carrier and decreased the activity of UCP1, UCP3, and complex III of the respiratory chain alongside with UCP2 inhibition. Based on competitive inhibition experiments, the use of amino acid blockers, and site-directed mutagenesis of UCP1, we propose a mechanism of genipin's action on UCPs. At low concentrations, genipin binds to arginine residues located in the UCP funnel, which leads to a decrease in UCP's proton transporting function in the presence of long chain fatty acids. At concentrations above 200 µM, the inhibitory action of genipin on UCPs is overlaid by increased nonspecific membrane conductance due to the formation of protein-genipin aggregates. Understanding the concentration-dependent mechanism of genipin action in cells will allow its targeted application as a drug in the above-mentioned diseases.

Mechanism of Long-Chain Free Fatty Acid Protonation at the Membrane-Water Interface.

Long-chain free fatty acids (FFAs) play an important role in several physiological and pathological processes such as lipid fusion, adjustments of membrane permeability and fluidity, and the regulation of enzyme and protein activities. FFA-facilitated membrane proton transport (flip-flop) and FFA-dependent proton transport by membrane proteins (e.g., mitochondrial uncoupling proteins) are governed by the difference between FFA's intrinsic pKa value and the pH in the immediate membrane vicinity. Thus far, a quantitative understanding of the process has been hampered, because the pKa value shifts upon moving the FFA from the aqueous solution into the membrane. For the same FFA, pKa values between 5 and 10.5 were reported. Here, we systematically evaluated the dependence of pKa values on chain length and number of double bonds by measuring the ζ-potential of liposomes reconstituted with FFA at different pH values. The experimentally obtained intrinsic pKa values (6.25, 6.93, and 7.28 for DOPC membranes) increased with FFA chain length (C16, C18, and C20), indicating that the hydrophobic energy of transfer into the bilayer is an important pKa determinant. The observed pKa decrease in DOPC with increasing number of FFA double bonds (7.28, 6.49, 6.16, and 6.13 for C20:0, C20:1, C20:2, and C20:4, respectively) is in line with a decrease in transfer energy. Molecular dynamic simulations revealed that the ionized carboxylic group of the FFAs occupied a fixed position in the bilayer independent of chain length, underlining the importance of Born energy. We conclude that pKa is determined by the interplay between the energetic costs for 1) burying the charged moiety into the lipid bilayer and 2) transferring the hydrophobic protonated FFA into the bilayer.

Dimensioning of a multibeam coherent photonic beamformer fed by a phased array antenna.

The design and dimensioning of a photonic-aided payload for a multi-beam high-throughput communications satellite is a complex problem in which the antenna, RF and photonic subsystems must be considered as a whole for achieving best performance with lowest mass and power consumption. In this paper, we propose and dimension the receiving stage of a communications satellite comprising a phased array antenna (PAA) feeding a multibeam photonic beamforming system (PBS). The PBS uses a single wavelength and resorts to heterodyne detection such that the retrieved beams are frequency downconverted. End-to-end system modeling shows that the complexity of the PAA and PBS can be traded-off for signal-to-noise ratio (SNR) or power consumption without compromising the beam width. The dimensioning of a realistic scenario is presented, showing that an SNR and beam crosstalk on the order of 20 dB are achievable with a total power consumption below 1 kW for a typical number of 100 antenna elements (AEs).

Reconfigurable monitoring and control system for tunable optical delay lines.

In this Letter, we propose a monitoring and control system (MCS) for operating tunable optical delay lines (TODLs), regardless of their operation principle and implementation technology. The monitoring system resorts to two out-of-band pilot tones added to the input optical signal. The amplitude and phase difference between tones are retrieved to the control system, which calculates and applies the TODL control signals. The MCS was validated using a Mach-Zehnder delay interferometer-based TODL, implemented in three different silicon photonic integrated circuits (PICs). The three PICs resort to different kinds of phase shifters based on thermo-optic, carrier-injection, and carrier-depletion effects. The proposed MCS enabled tuning the delay within the entire range of the TODL in all tested PICs. The scalability of the MCS for large-scale photonic beamformers is discussed.

1.024 Tb/s wavelength conversion in a silicon waveguide with reverse-biased p-i-n junction.

We experimentally show an all-optical wavelength conversion of 8 × 32-GBd single-polarization 16QAM signals using a silicon nano-rib waveguide. The application of reverse biasing of the p-i-n junction of the waveguide allows a conversion efficiency of -8.5 dB with a measured 3-dB optical bandwidth of about 40 nm. Using digital coherent reception, it is shown that the receiver optical signal-to-noise ratio penalty, at a bit-error ratio of 1 × 10-3, of the wavelength-converted signals over all eight channels was less than 0.6 dB with reference to their respective back-to-back signal channels.

High bandwidth, high responsivity waveguide-coupled germanium p-i-n photodiode.

A novel waveguide-coupled germanium p-i-n photodiode is demonstrated which combines high responsivity with very high -3 dB bandwidth at a medium dark current. Bandwidth values are 40 GHz at zero bias and more than 70 GHz at -1 V. Responsivity at 1.55 µm wavelength ranges from 0.84 A/W at zero bias to 1 A/W at -1 V. Room temperature dark current density at -1 V is about 1 A/cm2. The high responsivity mainly results from the use of a new, low-loss contact scheme, which moreover also reduces the negative effect of photo carrier diffusion on bandwidth.

Vertical optical ring resonators fully integrated with nanophotonic waveguides on silicon-on-insulator substrates.

We demonstrate full integration of vertical optical ring resonators with silicon nanophotonic waveguides on silicon-on-insulator substrates to accomplish a significant step toward 3D photonic integration. The on-chip integration is realized by rolling up 2D differentially strained TiO(2) nanomembranes into 3D microtube cavities on a nanophotonic microchip. The integration configuration allows for out-of-plane optical coupling between the in-plane nanowaveguides and the vertical microtube cavities as a compact and mechanically stable optical unit, which could enable refined vertical light transfer in 3D stacks of multiple photonic layers. In this vertical transmission scheme, resonant filtering of optical signals at telecommunication wavelengths is demonstrated based on subwavelength thick-walled microcavities. Moreover, an array of microtube cavities is prepared, and each microtube cavity is integrated with multiple waveguides, which opens up interesting perspectives toward parallel and multi-routing through a single-cavity device as well as high-throughput optofluidic sensing schemes.

Axons giving rise to the palisade endings of feline extraocular muscles display motor features.

Palisade endings are nerve specializations found in the extraocular muscles (EOMs) of mammals, including primates. They have long been postulated to be proprioceptors. It was recently demonstrated that palisade endings are cholinergic and that in monkeys they originate from the EOM motor nuclei. Nevertheless, there is considerable difference of opinion concerning the nature of palisade ending function. Palisade endings in EOMs were examined in cats to test whether they display motor or sensory characteristics. We injected an anterograde tracer into the oculomotor or abducens nuclei and combined tracer visualization with immunohistochemistry and α-bungarotoxin staining. Employing immunohistochemistry, we performed molecular analyses of palisade endings and trigeminal ganglia to determine whether cat palisade endings are a cholinergic trigeminal projection. We confirmed that palisade endings are cholinergic and showed, for the first time, that they, like extraocular motoneurons, are also immunoreactive for calcitonin gene-related peptide. Following tracer injection into the EOM nuclei, we observed tracer-positive palisade endings that exhibited choline acetyl transferase immunoreactivity. The tracer-positive nerve fibers supplying palisade endings also established motor terminals along the muscle fibers, as demonstrated by α-bungarotoxin. Neither the trigeminal ganglion nor the ophthalmic branch of the trigeminal nerve contained cholinergic elements. This study confirms that palisade endings originate in the EOM motor nuclei and further indicates that they are extensions of the axons supplying the muscle fiber related to the palisade. The present work excludes the possibility that they receive cholinergic trigeminal projections. These findings call into doubt the proposed proprioceptive function of palisade endings.

Phase regeneration of DPSK signals in a silicon waveguide with reverse-biased p-i-n junction.

Phase regeneration of differential phase-shift keying (DPSK) signals is demonstrated using a silicon waveguide as nonlinear medium for the first time. A p-i-n junction across the waveguide enables decreasing the nonlinear losses introduced by free-carrier absorption (FCA), thus allowing phase-sensitive extinction ratios as high as 20 dB to be reached under continuous-wave (CW) pumping operation. Furthermore the regeneration properties are investigated under dynamic operation for a 10-Gb/s DPSK signal degraded by phase noise, showing receiver sensitivity improvements above 14 dB. Different phase noise frequencies and amplitudes are examined, resulting in an improvement of the performance of the regenerated signal in all the considered cases.

Optimization of fiber grating couplers on SOI using advanced search algorithms.

A one-dimensional fiber grating coupler is derived from a waveguide with random etches using implementations of particle swarm and genetic algorithms. The resulting gratings yield a theoretical coupling efficiency of up to 1.1 dB and prompt clear design rules for the layout of highly efficient fiber grating couplers.

Matching p-i-n-junctions and optical modes enables fast and ultra-small silicon modulators.

In this article a new method is presented that allows for low loss implementation of fast carrier transport structures in diffraction limited photonic crystal resonators. We utilize a 'node-matched doping' process in which precise silicon doping results in comb-like shaped, highly-doped diode areas that are matched to the spatial field distribution of the optical modes of a Fabry-Pérot resonator. While the doping is only applied to areas with low optical field strength, the intrinsic diode region overlaps with an optical field maximum. The presented node-matched diode-modulators, combining small size, high-speed, thermal stability and energy-efficient switching could become the centerpiece for monolithically integrated transceivers.

Continuously tunable delay line based on SOI tapered Bragg gratings.

The realization of an integrated delay line using tapered Bragg gratings in a drop-filter configuration is presented. The device is fabricated on silicon-on-insulator (SOI) rib waveguides using a Deep-UV 248 nm lithography. The continuous delay tunability is achieved using the thermo-optical effect, showing experimentally that a tuning range of 450 ps can be obtained with a tuning coefficient of -51 ps/°C. Furthermore the system performance is considered, showing that an operation at a bit rate of 25 Gbit/s can be achieved, and could be extended to 80 Gbit/s with the addition of a proper dispersion compensation.

Highly efficient CW parametric conversion at 1550 nm in SOI waveguides by reverse biased p-i-n junction.

In this paper we present four-wave mixing (FWM) based parametric conversion experiments in p-i-n diode assisted silicon-on-insulator (SOI) nano-rib waveguides using continuous-wave (CW) light around 1550 nm wavelength. Using a reverse biased p-i-n waveguide diode we observe an increase of the wavelength conversion efficiency of more than 4.5 dB compared to low loss nano-rib waveguides without p-i-n junction, achieving a peak efficiency of -1 dB. Conversion efficiency improves also by more than 7 dB compared to previously reported experiments deploying 1.5 µm SOI waveguides with p-i-n structure. To the best of our knowledge, the observed peak conversion efficiency of -1dB is the highest CW efficiency in SOI reported so far.

Flexible quadrature amplitude modulation with semiconductor optical amplifier and electroabsorption modulator.

Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified.

Dual-polarization multiplexing amorphous Si:H grating couplers for silicon photonic transmitters in the photonic BiCMOS backend of line.

In this paper, we report on polarization combining two-dimensional grating couplers (2D GCs) on amorphous Si:H, fabricated in the backend of line of a photonic BiCMOS platform. The 2D GCs can be used as an interface of a hybrid silicon photonic coherent transmitter, which can be implemented on bulk Si wafers. The fabricated 2D GCs operate in the telecom C-band and show an experimental coupling efficiency of - 5 dB with a wafer variation of ± 1.2 dB. Possibilities for efficiency enhancement and improved performance stability in future design generations are outlined and extension toward O-band devices is also investigated.

Direct observation and quantitative analysis of Lck exchange between plasma membrane and cytosol in living T cells.

Palmitoylation represents a common motif for anchorage of cytosolic proteins to the plasma membrane. Being reversible, it allows for controlled exchange between cytosolic and plasma membrane-bound subpopulations. In this study, we present a live cell single molecule approach for quantifying the exchange kinetics of plasma membrane and cytosolic populations of fluorescently labeled Lck, the key Src family kinase involved in early T cell signaling. Total internal reflection (TIR) fluorescence microscopy was employed for confining the analysis to membrane-proximal molecules. Upon photobleaching Lck-YFP in TIR configuration, fluorescence recovery proceeds first via the cytosol outside of the evanescent field, so that in the early phase fluorescence signal arises predominantly from membrane-proximal cytosolic Lck. The diffusion constant of each molecule allowed us to distinguish whether the molecule has already associated with the plasma membrane or was still freely diffusing in the cytosol. From the number of molecules that inserted during the recovery time we quantified the insertion kinetics: on average, membrane-proximal molecules within the evanescent field needed approximately 400 ms to be inserted. The average lifetime of Lck in the plasma membrane was estimated at 50 s; together with the mobility of 0.26 microm(2)/s this provides sufficient time to explore the surface of the whole T cell before dissociation into the cytosol. Experiments on palmitoylation-deficient Lck mutants yielded similar on-rates, but substantially increased off-rates. We discuss our findings based on a model for the plasma membrane association and dissociation kinetics of Lck, which accounts for reversible palmitoylation on cysteine 3 and 5.