Nominal Band Research Articles

Where Have All the Sulfur Atoms Gone? Polycyclic Aromatic Hydrocarbon as a Possible Sink for the Missing Sulfur in the Interstellar Medium. I. The C–S Band Strengths

Despite its biogenic and astrochemical importance, sulfur (S), the 10th most abundant element in the interstellar medium (ISM) with a total abundance of S/H ≈ 2.2 × 10−5, largely remains undetected in molecular clouds. Even in the diffuse ISM where S was previously often believed to be fully in the gas phase, in recent years, observational evidence has suggested that S may also be appreciably depleted from the gas. What might be the dominant S reservoir in the ISM remains unknown. Solid sulfides like MgS, FeS, and SiS2 are excluded as major S reservoirs due to the nondetection of their expected infrared spectral bands in the ISM. In this work, we explore the potential role of sulfurated polycyclic aromatic hydrocarbon (PAH) molecules—PAHs with sulfur heterocycles (PASHs)—as a sink for the missing S. Utilizing density function theory, we compute the vibrational spectra of 18 representative PASH molecules. It is found that these molecules exhibit a prominent C–S stretching band at ∼10 μm and two relatively weak C–S deformation bands at 15 and 25 μm that are not mixed with the nominal PAH bands at 6.2, 7.7, 8.6, 11.3, and 12.7 μm. If several parts per million of S (relative to H) are locked up in PAHs, the 10 μm C–S band would be detectable by Spitzer and the James Webb Space Telescope (JWST). To quantitatively explore the amount of S/H depleted in PASHs, a detailed comparison of the infrared emission spectra of PASHs with the Spitzer and JWST observations is needed.

Spectral band-shifting of multispectral remote-sensing reflectance products: Insights for matchup and cross-mission consistency assessments

Comparing or integrating remote-sensing reflectance, Rrsλsr−1, data from multispectral sensors is hindered by differences in their nominal bands and relative spectral-response functions. Similarly, assessing satellite-to-in situ-matchup assessments of Rrs using autonomous ground radiometers, such as the Ocean Color component of the Aerosol Robotic Network (AERONET-OC), faces the same challenges. Therefore, spectral band-shifting techniques are required to approximate Rrs in spectral bands that are mutually unavailable. We present a spectral-matching technique (SMTH) using a novel look-up-table (LUT) generated from Rrs obtained from the Hyperspectral Imager for the Coastal Ocean (HICO) sensor. This LUT consists of nearly 6.3 million unique Rrs spectra, processed from 8893 Level-2 HICO scenes. An extensive in situ hyperspectral dataset (n = 8289) was used to compare the performance of SMTH with three commonly used techniques, namely Melin and Sclep (2015) “MS-QAA” model, linear (LNR) and cubic spline (CS) interpolations. The comprehensive evaluation of eight sensors using in situ dataset revealed that the SMTH has significantly better overall accuracy with respect to spectral band-shifting than the existing approaches. The Bias was improved 7-fold, whereas the root-mean-square difference (RMSD) and mean absolute difference (MAD) were ∼ 15–60% lower. Even so, each model exhibits outstanding performance in certain bands. For instance, the LNR model excels in the 380 nm band, while the MS-QAA emerges as the optimal choice for the 400 and 412 nm bands. SMTH outperforms other models in the green-red region, notably above 600 nm, where most existing ocean-color sensors have a limited number of spectral bands. Despite this variability, all models, showcase satisfactory performance in the 443–560 nm region. Significantly, both SMTH and LNR demonstrated a 100% retrieval rate, the ratio of band-shifted samples to the input samples. In contrast, MS-QAA and CS returned invalid values for 7% and 39% of the input samples, respectively. Further evaluation of regional, global, and composite satellite data suggests that the trophic state significantly influences the model performance. The MS-QAA model exhibited the smallest differences within the oligotrophic waters, characterized by low chlorophyll-a concentrations. In contrast, the SMTH model demonstrates the lowest differences in mesotrophic/eutrophic waters and regions subject to harmful algal blooms. While HICO primarily sampled coastal waters, estuaries, and shallow regions from mid- to low latitudes, there is an opportunity to enhance the representativeness of our LUT by incorporating open-ocean and high-latitude Rrs spectra from the upcoming hyperspectral missions, such as NASA's Plankton, Aerosol, Clouds, ocean Ecosystem (PACE).

The Acoustophotoelectric Effect: Efficient Phonon-Photon-Electron Coupling in Zero-Voltage-Biased 2D SnS2 for Broad-Band Photodetection.

Two-dimensional (2D) layered metal dichalcogenides constitute a promising class of materials for photodetector applications due to their excellent optoelectronic properties. The most common photodetectors, which work on the principle of photoconductive or photovoltaic effects, however, require either the application of external voltage biases or built-in electric fields, which makes it challenging to simultaneously achieve high responsivities across broad-band wavelength excitation─especially beyond the material's nominal band gap─while producing low dark currents. In this work, we report the discovery of an intricate phonon-photon-electron coupling─which we term the acoustophotoelectric effect─in SnS2 that facilitates efficient photodetection through the application of 100 MHz order propagating surface acoustic waves (SAWs). This effect not only reduces the band gap of SnS2 but also provides the requisite momentum for indirect band gap transition of the photoexcited charge carriers, to enable broad-band photodetection beyond the visible light range, while maintaining pA-order dark currents─ without the need for any external voltage bias. More specifically, we show in the infrared excitation range that it is possible to achieve up to 8 orders of magnitude improvement in the material's photoresponsivity compared to that previously reported for SnS2-based photodetectors, in addition to exhibiting superior performance compared to most other 2D materials reported to date for photodetection.

Enhanced Primary Frequency Control Using Model Predictive Control in Large-Islanded Power Grids with High Penetration of DFIG-Based Wind Farm

A new primary frequency controller in power grids undergoing massive wind power penetration is the focus of this paper. The inescapable problem in a largely wind penetrated power grid is to ensure the maintenance of its frequency in the nominal band prescribed by the power system operator (PSO). However, with the massive arrival of wind farms with conventional control schemes, the operation of maintaining and restoring the frequency to the regulatory regimes remains very complicated. In order to overcome the above problem, this paper proposes a new strategy for primary frequency control in power grids using model predictive control (MPC) for a multi-cluster doubly-fed induction generator (DFIG)-based wind farm (WF), with a main objective of reducing the frequency nadir (FN), eliminating the second frequency dip (SFD), and providing the optimal support during wind speed variations. In this approach, a rolling prediction and optimization control strategy is developed based on the dynamic power system model to ideally predict the additional power to be provided. Moreover, in order to avoid second frequency dips, the wind turbines (WTs) are not allocated to extract additional power from the grid during the frequency event, the rotor speeds are not recovered to the maximum power point tracking (MPPT) operating points during the primary frequency control. The performance of the proposed controller was evaluated using a two-zone electrical system in MATLAB/Simulink®. The obtained results disclose that the frequency nadir is enhanced with more than 6.1% compared to the conventional schemes. In addition, the frequency response settling time has been improved with more than 10.51 s.

Experimental Evaluation of JANUS Fast Modes in Very High Acoustic Frequency Bands

This article presents extensive field tests of a fast-mode operation of the JANUS acoustic communication standard where the signals occupy high-frequency bands of 38 kHz spanning from 96 to 134 kHz instead of the nominal frequency band of 4.1 kHz spanning from 9.44 to 13.6 kHz specified in the standard. The fixed 32-chip preamble and the 144-chip baseline JANUS packet utilize the frequency-hopped binary frequency shift keying with 13 frequency pairs as defined in the standard while the cargo packets use the single-carrier <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary phase shift keying modulation with a center frequency of 115 kHz and a symbol rate of 23 ksps or up to 34.5 kb/s information data rate with high-order phase shift keying (PSK) and rate-1/2 forward error correction codes. The original JANUS receiver algorithm is modified to improve the frame/symbol synchronization for the fast mode and increase the decoding success rate of the baseline JANUS packet in difficult multipath channels. More than 10 experiments were conducted using a field-programmable-gate-array-based hardware platform consisting of a single transmit projector and a single receive hydrophone. The experiment results show that the JANUS fast mode worked well with both the original JANUS receiver algorithm and the modified receiver algorithm, yielding zero bit error in most of the baseline JANUS packets. The modified receiver algorithm is able to reduce 30% of error packets to zero error in the experiment experiencing difficult multipath channels where the original JANUS receiver algorithm suffers from large bit error rates (BER). Meanwhile, the cargo packets utilize the linear minimum mean-square error turbo equalizer and achieve a BER around 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> .

PIONEER, a high-resolution single-crystal polarized neutron diffractometer.

PIONEER is a high Q-resolution, single-crystal, polarized neutron diffractometer at the Second Target Station (STS), Oak Ridge National Laboratory. It will provide the unprecedented capability of measuring tiny crystals (0.001 mm3, i.e., x-ray diffraction size), ultra-thin films (10nm thickness), and weak structural and magnetic transitions. PIONEER benefits from the increased peak brightness of STS cold-neutron sources and uses advanced Montel mirrors that are able to deliver a focused beam with a high brilliance transfer, a homogeneous profile, and a low background. Monte Carlo simulations suggest that the optimized instrument has a high theoretical peak brilliance of 2.9 × 1012 n cm-2 sr-1 Å-1 s-1 at 2.5 Å at the sample position, within a 5 × 5mm2 region and a ±0.3° divergence range. The moderator-to-sample distance is 60m, providing a nominal wavelength band of 4.3 Å with a wavelength resolution better than 0.2% in the wavelength range of 1.0-6.0 Å. PIONEER is capable of characterizing large-scale periodic structures up to 200 Å. With a sample-to-detector distance of 0.8m, PIONEER accommodates various sample environments, including low/high temperature, high pressure, and high magnetic/electric field. A large cylindrical detector array (4.0 sr) with a radial collimator is planned to suppress the background scattering from sample environments. Bottom detector banks provide an additional 0.4 sr coverage or can be removed if needed to accommodate special sample environments. We present virtual experimental results to demonstrate the scientific performance of PIONEER in measuring tiny samples.

Fully Metallic Dual-Band Linear-to-Circular Polarizer for K/Ka-band

A dual-band polarizer is presented that converts linear polarization into circular polarization with orthogonal handedness in the satcom bands 19.7–20.2 GHz and 29.5–30 GHz. The polarizer consists of three identical cascaded perforated metallic screens, whose perforations are periodically repeated crosses of two sizes. Unlike previously reported dual-band polarizers, our design is fully metallic, which results in low losses and makes it suitable for space applications. A prototype of the polarizer with 20 × 20 unit cells is manufactured, and the measurement results agree well with the simulated results. In the nominal satcom bands, the measured axial ratio and the insertion loss are better than 1.7 and 0.67 dB. In the bands 18.9–20.3 GHz and 29.1–30.1 GHz, the measured axial ratio and insertion loss are below 3 and 1 dB.

Disorder-induced Anderson-like localization for bidimensional thermoelectrics optimization

Disorder-induced Anderson-like localization for bidimensional thermoelectrics optimization

Resonant metamaterial designs for a broadband mitigation of flow-induced vibrations

Resonant metamaterials have recently emerged as lightweight and performant noise and vibration solutions for the hard-to-address low-frequency ranges. These engineered materials are made by an assembly of resonant elements onto a host structure. Their interaction leads to tuneable frequency ranges, known as stop bands, in which they can outperform classical noise control measures. However, these stop bands have a limited frequency range effect. To broaden the noise and vibration performance also outside the stop band, this paper presents a design approach for a finite resonant metamaterial plate. Two regularly spaced grids of resonant elements are both added to a plate. In the first grid, the resonant elements are tuned to the same nominal frequency and stop band behaviour is achieved. In the second grid, the tuned frequency of each resonant element is found through an optimisation procedure, with the goal of minimising the dynamic response of the plate outside the stop band. To speed up the optimisation, model order reduction and a dynamic sub-structuring method are employed. The performance of this finite resonant metamaterial plate design is validated by evaluating its vibration response due to a broadband grazing flow excitation and comparing it to a plate with equivalent mass additions.

Simultaneous reactive power sharing and voltage regulation in an autonomous networked microgrid

Decentralised droop-like control method is the most favourable control system for power converter-based microgrids (MGs). In conventional V - Q droop loops, reactive power sharing is used as a means of voltage regulation to prevent currents from circulating among distributed generation units. However, since the voltage is not a global variable, reactive power sharing is not implemented precisely, and thus converters may be exposed to overcurrent conditions and the stability of the MGs is put at risk. Besides, the droop-like reactive power sharing causes voltage deviations and power quality issues. This study proposes a novel control method which is able to implement accurate reactive power sharing and voltage regulation to its nominal band in a networked MG. Both the control targets are achieved, fast and simultaneously, by only one control signal. So the requirement of a secondary controller for voltage restoration is obviated. A novel power flow-based method is proposed to estimate the voltage at the MG main bus, which is adopted as a common variable, thus making the proposed method decentralised. The presented method is fast, effective and applicable to networked MGs with arbitrary topology. Simulation results prove the effectiveness and superiority of the proposed method over existing methods.

K·p theory for phosphorene: Effective g -factors, Landau levels, and excitons

Phosphorene, a single layer of black phosphorus, is a direct-band gap two-dimensional semiconductor with promising charge and spin transport properties. The electronic band structure of phosphorene is strongly affected by the structural anisotropy of the underlying crystal lattice. We describe the relevant conduction and valence bands close to the $\Gamma$ point by four- and six-band (with spin) $k \cdot p$ models, including the previously overlooked interband spin-orbit coupling which is essential for studying anisotropic crystals. All the $k \cdot p$ parameters are obtained by a robust fit to {\it ab initio} data, by taking into account the nominal band structure and the $k$-dependence of the effective mass close to $\Gamma$-point. The inclusion of interband spin-orbit coupling allows us to determine dipole transitions along both armchair and zigzag directions. The interband coupling is also key to determine the effective g-factors and Zeeman splittings of the Landau levels. We predict the electron and hole g-factor correction of $\approx 0.03$ due to the intrinsic contributions in phosphorene, which lies within the existing range of experimental data. Furthermore, we investigate excitonic effects using the $k \cdot p$ models and find exciton binding energy (0.81 eV) and exciton diameters consistent with experiments and {\it ab initio} based calculations. The proposed $k \cdot p$ Hamiltonians should be useful for investigating magnetic, spin, transport, optical properties and many-body effects in phosphorene.

Spontaneous Non-stoichiometry and Ordering in Degenerate but Gapped Transparent Conductors

Spontaneous Non-stoichiometry and Ordering in Degenerate but Gapped Transparent Conductors

The Effect of Acute Temperature Change on the Localization of Aquaporin‐3 in the Erythrocytes of the Freeze‐tolerant Cope's Gray Treefrog

Cope's gray treefrogs (Dryophytes chrysoscelis) accumulate cryoprotective glycerol (&gt;100 mM) throughout their body in response to falling temperatures, which enables them to tolerate freezing. The most likely pathway for the transmembrane transport of glycerol is through glycerol‐permeable aquaporins such as HC‐3, a homolog of Aquaporin‐3, which increases in both gene and protein expression for erythrocytes during cold acclimation. Much of the increase in immunoblot signal intensity occurs not at the nominal molecular weight of HC‐3 (~31.5 kDa), but at a higher molecular weight (~65–100 kDa) shown to be glycosylated HC‐3. We hypothesized that glycosylation of HC‐3 is involved in trafficking of the protein to the plasma membrane. To test this hypothesis, we established conditions in culture that enhance expression of HC‐3, and we assessed expression of glycosylated and un‐glycosylated HC‐3 in the plasma membrane via biotinylation and immunoblot.Erythrocytes were cultured at 20°C and 5°C over the course of 48 hours. Cell surface expression was assessed by biotinylation, which resulted in total and biotinylated (plasma membrane, PM) fractions assayed by immunoblot for HC‐3 and quantified with densitometry. Erythrocytes incubated at 20°C for 48 hours yielded total protein with 4‐fold greater glycosylated HC‐3 compared with 5°C‐incubated erythrocytes, but no change in the nominal molecular weight (unglycosylated) band. The biotinylated fraction of protein from 20°C‐incubated erythrocytes had another 4‐fold increase in glycosylated HC‐3 over the total, suggesting enrichment of glycosylated protein in HC‐3 localized to the plasma membrane. In 5°C‐incubated erythrocytes, total expression of HC‐3 was diminished compared with 20°C. In contrast to RBCs incubated at 20°C, cells at 5°C were enriched for glycosylated HC‐3 in the non‐biotinylated protein fraction compared with PM‐localized protein. Thus, while glycosylation is enhanced in the plasma membrane fraction of HC‐3 in 20°C‐incubated erythrocytes, the opposite occurs in cells incubated at 5°C, suggesting that while the glycosylation of HC‐3 isn't required for localization to the plasma membrane, its expression is variably regulated in response to environmental and humoral factors.We further hypothesized that epinephrine could induce changes in membrane localization of HC‐3 in cultured erythrocytes similar to those observed during cold acclimation. When erythrocytes incubated at 5°C for 48 hours were treated with epinephrine (1 μM) for 60 minutes, the expression of glycosylated protein in the plasma membrane fraction of HC‐3 increased &gt;10‐fold compared with 5°C‐incubated erythrocytes without epinephrine treatment; the nominal MW band was not present in the plasma membrane fraction from cells incubated with epinephrine. Our data suggest that the enhanced expression of HC‐3 observed in erythrocytes from long‐term cold‐acclimated animals is not induced by a decrease in temperature, but changes to HC‐3 expression and subsequent trafficking to the plasma membrane can be activated by epinephrine.Support or Funding InformationNSF grant (IOS‐1121457)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The correspondence between dayside long-period geomagnetic pulsations and the open-closed field line boundary

Long-period pulsations in the nominal Pc5-6 band (periods about 3–15 min) have been known to be a persistent feature of dayside high latitudes. A mixture of broadband Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband P≿5 waves is often observed. The mechanism and origin of IPCL have not been firmly established yet. Magnetopause surface eigenmodes were suggested as a potential source of high-latitude ULF waves with frequencies less than 2 mHz. A ground response to these modes is expected to be beneath the ionospheric projection of the open-closed field line boundary (OCB). To unambiguously resolve a possible association of IPCL with the magnetopause surface modes, multi-instrument observation data from Svalbard have been analyzed. We examine the latitudinal structure of high-latitude pulsations in the Pc5-6 band recorded by magnetometers covering near-cusp latitudes. This structure is compared with an instant location of the equatorward boundary of the cusp aurora, assumed to be a proxy of the OCB. The optical OCB latitude has been identified by an automatic algorithm, using data from the meridian scanning photometer at Longyearbyen, Svalbard. The comparison has shown that the latitudinal maximum of the broadband IPCL maximizes about 2°–3° deeper in the magnetosphere than the OCB optical proxy. Therefore, these pulsations cannot be associated with the ground image of the magnetopause surface modes. It is likely that an essentially non-dipole geometry of field lines and a high variability of the magnetopause region may suppress the excitation efficiency. The obtained result imposes important limitations on possible mechanisms of high-latitude dayside ULF variations.

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d0 band insulator SrTiO3 when embedded within a d1 Mott SmTiO3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T*. The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

Intelligibility of bandpass filtered speech: The effect of filter types.

Many studies have examined the contribution of different spectral bands to speech intelligibility, measuring recognition scores of filtered speech stimuli. For a given filter bandwidth, the influence of filter properties on such experiments has been studied mainly with respect to transition band slopes. The objective of the present study was to determine whether nominal transition band slope is a sufficient characterization of filter properties. Several types of filters, both finite impulse response and infinite impulse response types were examined in three experiments to determine if details of the transition band behavior, as well as group delay properties, had any influence on recognition scores. The results of a total of 72 participants showed that for 1/3 octave passbands, differences between filters having the same nominal transition band slopes, but of different types, were large and statistically significant. Linearity of phase response, however, did not influence the results. Further experiments using passband widths of 1/2 and 2/3 octaves revealed that only for the latter the difference in recognition scores between filter types ceased to be significant. These results have important implications for studies which involve filtered speech as well as models that employ different types of filters to emulate peripheral auditory processing.

Modeling Electronic Trap States at Interfaces between Anatase Nanoparticles

Interfaces between crystallites in nanocrystalline anatase can give rise to localized electronic trap states, which affect the charge transport and catalytic activity of mesoporous TiO2 films and aerogels. Unlike trap states associated with point defects and surfaces, the energetic and spatial distributions of interfacial trap states are not known. We have calculated the electronic structure of attached anatase nanoparticles to search for molecular orbitals localized at the particle interfaces and to identify their energetic positions in the nominal band gap. We found that orbitals localized at the interfaces had energies near the edge of the nominal conduction band and that such trap states localized at the interface between (001) facets were lower in energy than those localized at the interface between (101) facets. The spatial distributions of the interfacial trap states were similar between different levels of theory; however, hybrid density functional theory (DFT) predicted the trap states to be deep...

Temperature‐Induced Changes to Aquaporin Localization in the Freeze‐Tolerant Cope's Gray Treefrog

Cope's gray treefrogs alter their physiology in response to cold as part of their freeze tolerance mechanism. One such change involves the accumulation, both extracellularly and intracellularly, of cryoprotective glycerol, which likely crosses cellular membranes using glycerol‐permeable channels called aquaglyceroporins (GLPs). Three GLPs (HC‐3, HC‐7, and HC‐9) have been identified in the Cope's gray treefrog, representing homologs to the mammalian AQP3, AQP7, and AQP9, respectively.Regulation of transmembrane glycerol diffusion depends on GLP expression in the plasma membrane resulting from changes to transcriptional and translational output of the GLPs and/or by changes in protein trafficking to the plasma membrane. We have previously reported that GLP mRNA and protein expression are modulated during cold acclimation and freezing; however, localization of GLP proteins in the plasma membrane has not been studied thoroughly. We hypothesized that changes in acclimation temperature would alter the localization of the GLPs HC‐3 and HC‐9 in the plasma membrane and confirmed this with immunofluorescence, plasma membrane fractionation, and biotinylation.For HC‐9 in liver, quantitation of protein expression (by immunoblot) showed a 4‐ to 6‐fold increase in the higher molecular weight band of frozen (−2.5°C for 24 hours) and thawed (5°C for 24 hours after freezing) over warm (20°C) treefrogs. In immunohistochemistry images, HC‐9 signal appeared to be localized to the plasma membrane of hepatocytes of warm‐ and cold‐acclimated animals but dispersed intracellularly in frozen treefrog hepatocytes. In preliminary studies, fractionation of cellular protein (Biovision, Milpitas, CA) indicated that between freezing and thawing, the nominal (~34 kDa) molecular weight band of HC‐9 diminishes in the plasma membrane fraction while the (putatively) glycosylated high molecular weight band of HC‐9 increases.For HC‐3 in erythrocytes, protein expression is enhanced by cold acclimation and by incubation in medium containing glycerol. We incubated erythrocytes taken from warm‐acclimated animals at 4°C for 48 hours and biotinylated the surface proteins. In immunoblots of the biotinylated fraction probed with anti‐HC‐3 primary antibody, the high molecular weight (glycosylated) band was enriched and the nominal (~32 kDa) molecular weight band was diminished. These results suggest that water and glycerol permeability during cold acclimation and freezing can be modulated by protein trafficking, which may be influenced by the post‐translational modification of glycosylation.Support or Funding InformationSupported by NSF IOS‐1121457.

Prognostic and Health Management System for Hydraulic Servoactuators for Helicopters Main and Tail Rotor

The research herein presented continues an initial work on this area performed at Politecnico di Torino in the past years and moves forward in the definition of an effective PHM system for Electro-Hydraulic Servo Actuators (EHSA). PHM of EHSAs is an area only little addressed, but of great interest for the aerospace industry and the air fleet operators. The PHM algorithm consists of three subroutines: the first subroutine extracts a set of relevant features from the data acquired by the sensors during a pre or post flight set of commands and mitigate their dependencies with environmental condition. Fault identification is then performed using mathematical data-driven techniques, three methods are presented: Nominal bands, Percentual error and Euclidean distance. Classification of a single and multiple degradations is performed by the second subroutine with the aid of two dual layer Neural Networks. Finally, the remaining useful life (RUL) is estimated by the third subroutine using a particle filter framework, where the feature evolution model is estimated online. Electro-hydraulic Servo-valves (EHSV) faults are widely addressed with the aid of a nonlinear model and the performance of the PHM algorithm is assessed using relevant metrics.

New Research in Solar Cells: Urbach Tails and Open Circuit Voltage

&lt;div class="page" title="Page 45"&gt;&lt;div class="layoutArea"&gt;&lt;div class="column"&gt;&lt;p&gt;The development of various emerging photovoltaic technologies, as classified by the National Renewable Energy Laboratory, has experienced very different rates of progress over the last five to ten years. In particular, two thin-film technologies, quantum dot solar cells and perovskite-based solar cells, have achieved drastically different values for power conversion efficiency as quantum dots have failed to keep up with perovskites. Clearly, the materials are very different, but in order to quantify the discrepancy in efficiency, we focus on measuring the tail of the absorption past the nominal band edge and therefore the Urbach energy of the two materials. We discuss a theoretical relationship between Urbach energy and open circuit voltage based on the original considerations by Shockley and Queisser on the efficiency limits of solar cells.&lt;/p&gt;&lt;/div&gt;&lt;/div&gt;&lt;/div&gt;