Search

Electrical coupling, mediated by gap junctions, contributes to signal averaging, synchronization, and noise reduction in neuronal circuits. In addition, gap junctions may also provide alternative neuronal pathways. However, because they are small and especially difficult to image, gap junctions are often ignored in large-scale 3D reconstructions. Here, we reconstruct gap junctions between photoreceptors in the mouse retina using serial blockface-scanning electron microscopy, focused ion beam-scanning electron microscopy, and confocal microscopy for the gap junction protein Cx36. An exuberant spray of fine telodendria extends from each cone pedicle (including blue cones) to contact 40-50 nearby rod spherules at sites of Cx36 labeling, with approximately 50 Cx36 clusters per cone pedicle and 2-3 per rod spherule. We were unable to detect rod/rod or cone/cone coupling. Thus, rod/cone coupling accounts for nearly all gap junctions between photoreceptors. We estimate a mean of 86 Cx36 channels per rod/cone pair, which may provide a maximum conductance of ~1200 pS, if all gap junction channels were open. This is comparable to the maximum conductance previously measured between rod/cone pairs in the presence of a dopamine antagonist to activate Cx36, suggesting that the open probability of gap junction channels can approach 100% under certain conditions.Neurons can talk to each other in two ways: they can send chemical messengers across specialized junctions between two cells, or they can directly pass electrical signals to one another. This latter process is made possible by gap junctions, a system of channel-like structures which connect neighbouring cells and let ions move between them. In most neurons, gap junction channels are made from a specialized protein called connexin 36. Gap junctions are small, difficult to observe, and therefore often ignored by researchers studying neural circuits. In response, Ishibashi et al. focused on nerve cells in the mouse retina, in particular the cones (which detect color during the day) and the rods (which are essential for night vision). Gap junctions between rods and cones allow them to communicate; for example, they enable rod signals to directly activate cones. This provides an alternative route for rod signaling known as the ‘secondary rod pathway’, which seems to be open at night and switches to closed around dawn. Both rods and cones only produce connexin 36, so Ishibashi et al. labeled these proteins with fluorescent tags to pinpoint gap junctions. This showed that each cone makes around 50 gap junctions with nearby rods; however, gap junctions were not detected between cells of the same type. In addition, 3D reconstruction helped to establish the length of each gap junction. Further experiments showed that a typical rod was connected to a cone by about 80 connexin 36 channels. Finally, calculations revealed that the gap junction channels would all need to open to account for the level of electrical activity required for the secondary rod pathway. This suggests that gap junctions may be much more active and important than previously thought. The work by Ishibashi et al. provides a new understanding of the number, size and activity of gap junctions in the retina, potentially paving the way to prevent diseases where light-sensing cells degenerate and cause blindness.

Innovations which help facilitate predictive maintenance strategies have the potential to greatly reduce costs associated with wind turbine O&M by driving efficiency and increasing wind turbine availability. This study uses multiple examples of the same generator bearing failure to provide insight into how condition monitoring systems can be used in to train machine learning algorithms with the ultimate goal of predicting failure and remaining useful life. Results show that by analysing high-frequency vibration data and extracting key features to train support vector machine algorithms, an accuracy of 67% can be achieved in successfully predicting failure 1–2 months before occurrence. This study reflects on the limitations surrounding a generalised training approach, taking advantage of all available data, showing that if too many different examples are considered of different wind turbines and operating conditions, the overall accuracy can be diminished.

This study presents a method of anomaly detection within a gearbox by way of standardising temperature data. Assessing measured parameters in isolation is not sufficient to detect faults within a wind turbine. This technique uses temperature, rotational speed, and generator torque to detect a bearing fault within the gearbox. Standardising data allows a parameter to be analysed which also takes into consideration the operating state of the wind turbine, therefore providing a more holistic view of the health of the wind turbine and component being monitored.

The intelligent condition monitoring of wind turbines reduces their downtime and increases reliability. In this manuscript, a feature selection-based methodology that essentially works on regression models is used for identifying faulty scenarios. Supervisory control and data acquisition (SCADA) data with 1009 samples from one year and one month before failure are considered. Gearbox oil and bearing temperatures are treated as target variables with all the other variables used for the prediction model. Neighborhood component analysis (NCA) as a feature selection technique is employed to select the best features and prediction performance for several machine learning regression models is assessed. The results reveal that twin support vector regression (99.91%) and decision trees (98.74%) yield the highest accuracy for gearbox oil and bearing temperatures respectively. It is observed that NCA increases the accuracy and thus reliability of the condition monitoring system. Furthermore, the residuals from the class of support vector regression (SVR) models are tested from a statistical point of view. Diebold&ndash, Mariano and Durbin&ndash, Watson tests are carried out to establish the robustness of the tested models.

This paper presents a review of existing theory and practice relating to main-bearings for wind turbines. The mainbearing performs the critical role of supporting the turbine rotor, with replacements typically requiring its complete removal. The operational conditions and loading for wind turbine main-bearings deviate significantly from those of more conventional power plants and other bearings present in the wind turbine power-train, i.e. those in the gearbox and generator. This work seeks to thoroughly document current main-bearing theory in order to allow for appraisal of existing design and analysis practices, while also seeking to form a solid foundation for future research in this area. The most common main-bearing setups are presented along with standards for bearing selection and rating. Typical loads generated by a wind turbine rotor, and subsequently reacted at the main-bearing, are discussed. This is followed by the related tribological theories of lubrication, wear and associated failure mechanisms. Finally, existing techniques for bearing modeling, fault diagnosis and prognosis relevant to the main-bearing are presented.

Reducing wind turbine downtime through innovations surrounding asset management has the potential to greatly influence the levelised cost of energy (LCoE) for large wind farm developments. Focusing on generator bearing failure and vibration data, this paper presents a two-stage methodology to predict failure within 1 to 2 months of occurrence. Results are obtained by building up a database of failures and training machine learning algorithms to classify the bearing as healthy or unhealthy. This is achieved by first using clustering techniques to produce subpopulations of data based on operating conditions, which this paper demonstrates can greatly influence the ability to diagnose a fault. Secondly, this work classifies individual clusters as healthy or unhealthy from vibration-based condition monitoring systems by applying order analysis techniques to extract features. Using the methodology explained in the report, an accuracy of up to 81.6% correct failure prediction was achieved.

If households underestimate the long-run energy costs of their investments, the demand for energy efficiency will be lower. This hypothesis is explored using a randomized control trial carried out in conjunction with the website daft.ie between February and December 2018. Property advertisements were supplemented with a new property-specific energy cost (annual) label using details from the property’s Building Energy Rating (kWh and size) and the average price of energy in 2018. This label was assigned to half the counties in Ireland. Our trial is ongoing and our results should therefore be considered preliminary.

This paper details the development of a mathematical thermal model of a small wind turbine gearbox for use in condition monitoring. The model was optimised and partially validated using experimental data from a wind turbine drivetrain test rig. The model was then used to mimic bearing faults, by simulating additional heat losses at respective faulty components. The extent to which the thermal behaviour changed as a result of a fault was studied, with a view to use such an approach to detect and locate faults.

Vibration signals are widely used in wind turbine drivetrain condition monitoring with the aim of fault detection, optimization of maintenance actions and therefore reduction of operating costs. Signals are most commonly sampled by accelerometers at high frequency for a few seconds. The behavior of these signals varies significantly, even within the same turbine and depends on different parameters. The aim of this paper is to explore the effect of operational and environmental conditions on the vibration signals of wind turbine gearboxes. Parameters such as speed, power and yaw angle are taken into account and the change in vibration signals is examined. The study includes examples from real wind turbines of both normal operation and operation with known gearbox faults. The effects of varying operating conditions are removed using kalman filtering as a state observer. The findings of this paper will aid in understanding wind turbine gearbox vibration signals, making more informed decisions in the presence of faults and improving maintenance decisions.

The goal of the present paper is to achieve the diagnosis of an in-service 1.5 MW wind turbine equipped with a doubly-fed induction generator through current signature and vibration analyses. Real data from operating machines have rarely been analysed in the scientific literature through current signature analysis supported by vibrations. The wind turbine under study was originally misdiagnosed by the operator, where a healthy component was replaced and the actual failure continued progressing. The chronological evolution of both the electrical current and vibration spectra is presented to conduct an in-depth tracking of the fault. The diagnosis is achieved through spectral analysis of the stator currents, where fault frequency components related to rotor mechanical unbalance are identified. This is confirmed by the vibration analysis, which provides insightful information on the health of the drive train. These results can be implemented in condition monitoring strategies, which is of great interest to optimise operation and maintenance costs of wind farms.

This paper aims to present a methodology for health monitoring wind turbine gearboxes using vibration data. Monitoring of wind turbines is a crucial aspect of maintenance optimisation that is required for wind farms to remain sustainable and profitable. The proposed methodology performs spectral line analysis and extracts health features from harmonic vibration spectra, at various time instants prior to a gear tooth failure. For this, the tachometer signal of the shaft is used to reconstruct the signal in the angular domain. The diagnosis approach is applied to detect gear faults affecting the intermediate stage of the gearbox. The health features extracted show the gradient deterioration of the gear at progressive time instants before the catastrophic failure. A classification model is trained for fault recognition and prognosis of time before failure. The effectiveness of the proposed fault diagnostic and prognostic approach has been tested with industrial data. The above will lay the groundwork of a robust framework for the early automatic detection of emerging gearbox faults. This will lead to minimisation of wind turbine downtime and increased revenue through operational enhancement.

The following paper provides an overview of a novel wind turbine concept known as the X-Rotor Offshore Wind Turbine. The X-Rotor is a new wind turbine concept that aims to reduce the cost of energy from offshore wind. Cost reductions are achieved through reduced capital costs and reduced maintenance costs. The following paper includes results from an early feasibility study completed on the concept. In the feasibility study exemplary designs were created and structural analyses were carried out. Turbine capital costs and maintenance cost of the X-Rotor concept were then roughly estimated. X-Rotor turbine costs and O&M costs were compared to four existing wind turbine types to investigate potential cost savings from the X-Rotor concept. Results show that the X-Rotor has potential to reduce O&M costs by up to 55% and capital costs by up to 32%. The combination of the capital cost and O&M cost savings show potential to reduce the CoE by up to 26%.

A new plasma flood gun (PFG) apparatus using a toroidal RF discharge has been developed producing very low energy electrons at high emission for wafer charge neutralization. The performance of the Toroidal PFG (TPFG) will be characterized and discussed under the typical implantation conditions in VIISta ion implanters. The charging performance is measured by using metal-oxide-semiconductor (MOS) capacitor antenna devices as well as the surface charge monitoring technique called surface photo voltage (SPV). The metal contamination performance of the TPFG surpasses that of the conventional cathode based PFG due to no presence of transition metals in the plasma cavity. The TPFG also provides process transparency for dose and uniformity performance. In addition, the mean time between maintenance (MTBM) has drastically increased as compared to the conventional filament PFG. The projected MTBM will exceed the filament PFG current lifetime without charging performance degradation

A well-known island of nuclear isomerism appears near A =175–180 due to the deformation alignment of single-particle orbits at high angular momentum. This sometimes results in the formation of multi-quasiparticle states with record spin that are long-lived because of “K-hindrance”, i.e. symmetry re-arrangement. Production methods and spectroscopic studies of these isomers remain a challenge for modern nuclear reaction and nuclear structure physics. In the present work, activities were produced by irradiation of 176 Yb (97.6% enriched) and nat Lu targets with 35 MeV 4 He ions from the internal beam of the U-200 cyclotron. Induced activities were analyzed by applying the methods of radiochemistry and gamma spectroscopy. Yields of the compound and nucleon-transfer reactions were measured and the isomer-to-ground state ratios were deduced. Calculated results were obtained using standard procedures to reproduce the (α, xn) cross-sections, and the systematic behavior of the nucleon-transfer yields was established. The isomer-to-ground-state ratios for direct reactions with 4 He ions were examined, resulting in a new characterization of the reaction mechanism.

Although they are based on the same fundamental electromechanical principles, the design rotating electrical machines to convert mechanical to electrical power in wind turbines is different to that found in more conventional power plants. Because of the differences in the rest of the wind farm, the design priorities of generators for offshore wind tend to be different to those for onshore wind: there is an emphasis on high efficiency, higher power rating and high reliability. The search for a generator type that delivers lowest cost of energy continues, with a number of technologies in development.

The 242m Am isomer, a well-known candidate for photodepopulation research, has been studied in this first ever Coulomb excitation of a nearly pure (≈98%) isomer target. Thirty new states, including a new rotational band built on a K π = 6− state, have been identified. Strong K-mixing results in nearly equal populations of the K π=5− and 6− states. Newly identified states have been assigned to the K π=3− rotational band, the lowest states of which are known to decay into the ground-state band. Implications regarding K-mixing and Coulomb excitation paths to the ground state are discussed.

High-productivity methods are required for the accumulation of long-lived isomers in amounts that are sufficient for the creation of experimental targets. A tantalum sample was activated with the Yerevan synchrotron using 4.5-GeV bremsstrahlung and the presence of 178m2Hf was detected with good statistical accuracy by γ-activity measurements. The integrated and mean cross-section values were deduced from the experiment. The isomer-to-ground-state ratio was then estimated and compared with that known for the p+ Ta reaction studied at 660 MeV. In the present experiment, both converter and target were relatively thin for better definition of the experimental conditions. However, an assembly designed for high-productivity irradiations should be thick and then the converter can also serve as the target sample when irradiated with a high-energy electron beam. The optimization of the isomer production was solved analytically and the largest estimated yield was determined as calibrated to the experimental yield. The maximum yield of 178m2Hf was found to be of about 3×109 nuclei/s using an electron beam current of 100 μA. This is lower than the yield achieved with proton beams, although for a practical comparison the total cost and radiation safety conditions should be considered. The present results provide a basis for numerical estimations.

The study of triggered depopulation of nuclear isomers, with accompanying gamma emission, is a rapidly-changing field that is only now attaining some degree of maturity. Because isomer decays via electromagnetic transitions are strongly inhibited, the interaction of these levels with externally-produced photons provides an important probe of nuclear structure. Also, since some isomers may store large amounts of energy for long times, a number of applications have been proposed, including the creation of a gamma-ray laser. Early experiments conclusively demonstrated triggering of the 1015-year isomer of 180Ta, but even a partial correlation of the effect with known levels could only be obtained recently. Investigations of triggering for the 31-year isomer of 178Hf were initially guided just by systematics and experiments are characterized by considerable controversy. Against this background, the field of triggered gamma emission is entering a new phase in which improved level data allow targeting of specific potentially-useful transitions. This paper summarizes the current state-of-the-art and discusses the changing nature of the field.

Ireland has a long history of philanthropy, rooted in a strong religious tradition. In the late 1700s, Protestant philanthropy helped to alleviate the physical and medical needs of the impoverished working classes (Kelly & Powell, 2010). Beginning in 1770, the incremental waning of the Penal laws1 enabled the growth of Catholic charities (Raughter, 1997). Following Catholic emancipation in 1829, greater Catholic clergy involvement in charitable activity emerged with religious involvement in philanthropy becoming more formalized in Irish society. The introduction of the Poor Laws to Ireland in 1838, which brought into existence a statutory relief system for the destitute, however, led to a fall off in charitable donations and resulted in some charities ceasing to operate thereafter (Cousins, 2008). The Irish famine in the 1840s had a further chilling effect on charitable institutions. Nevertheless, given the Poor Laws’ strict eligibility requirements for receiving relief, religious orders once more found their way to the forefront of philanthropy, providing voluntary hospitals and assisting those in need (Donoghue, Prizeman, O’Regan, & Noel, 2006).

Preliminary survey experiments have been performed to examine the triggering of gamma emission from the 31-year Hf-178m2 isomer using intense monochromatic synchrotron radiation from the X15A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. Initial studies were performed to probe incident photon energies over the L 1, L 2, and L 3 X-ray edges of Hf and the 12–13 keV range. Resonances larger than the experimental minimum detectable level of 10−25 cm2 keV were not observed.

A γ-ray laser would stimulate the emission of radiation of wavelengths below 1 Å from excited states of nuclei. However, the anticipation of a need for high pump powers tended to discourage early research and the difficulties in demonstrating a device were first assumed to be insurmountable. Over the past decade, advances in pulsed-power technology have changed these perceptions and studies have built a strong momentum. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and concepts has shown the γ-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals modeled. The greatest positive impact upon feasibility has come from the discovery of giant resonances for pumping nuclei that greatly reduce the levels of pump power needed.

The major goal of this project is to make a proof of principle experiment demonstrating the influence of laser radiation on the Mossbauer spectrum of $^?151!$Eu$^?2+!$:CaS.

This paper reviews the experimental research accomplished to date relating to catastrophic electromagnetic breakdown in certain media that are interesting for high voltage, short temporal pulse width pulsers. The authors begin with the classic work of Felsenthal and Proud and follow experimental results into the present day. The paper considers not only the experimental results of short pulse radio frequency breakdown but also the relationship with long pulse RF breakdown. The paper presents some recent measurements as well as reviewing the previous work performed in our laboratories and elsewhere.

Recent advances in theoretical and experimental research concerned with the feasibility of the gamma-ray laser are reviewed. The discussion covers the principal concepts, pump calibration, giant pumping resonances, and the development of a laser model. A quantitative model based on new data and concepts demonstrates the feasibility of the gamma-ray laser.

A gamma-ray laser would stimulate the emission of radiation at wavelengths below 1 A from excited states of nuclei. However, the difficulties in realizing such a device were considered insurmountable when the first cycle of study ended in 1981. Nevertheless, research on the feasibility of a gamma-ray laser has taken a completely new character since then. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and concepts of this decade shows the gamma-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals modeled.

Efforts to demonstrate the feasibility of a gamma-ray laser scored major advances in 1988 and 1989. Culminating with the discovery of giant pumping resonances below 4 MeV for dumping isomeric populations, priority issues were brought into better focus by the lessons learned from a wealth of new results. Perceptions were advanced so greatly that we must reassess the critical issues for the 1990’s. Only the bottom line remains the same. A gamma-ray laser is feasible if the right combination of energy levels occurs in some real material. The likelihood of this favorable arrangement has been markedly increased by the experimental results to date.

Efforts to demonstrate the feasibility of a gamma-ray laser scored major advances in 1987. Culminating with the successes in optically pumping the first of the 29 actual candidate isomers, priority issues were brought into better focus by the lessons learned from a wealth of new results. Perceptions were advanced so greatly that we must reassess the critical issues for 1988. Only the bottom line remains the same. A gamma-ray laser is feasible if the right combination of energy levels occurs in some real material. The likelihood of this favorable arrangement has been markedly increased by the experimental results to date.

The current lightweight camouflage screening system (LOSS) used by U.S. military forces consists of a color coated polymer containing radar scattering dipoles (flat stock material) attached to a fish-net type substrate. As a general purpose radar scattering camouflage system, the screen is designed to be reflective enough to reduce the radar return from a covered target, but not so reflective that the screen itself becomes a significant target. The screen is produced to specified transmission parameters. In order to evaluate the effectiveness of the production specifications, screens with different transmission properties were compared using tactical and instrumentation radar systems.

A REPLY TO DR. AGRAMONTE. Washington, D. C., June 26, 1903. To the Editor: —In connection with my paper published inThe Journalof May 23 several statements made by my esteemed colleague, Dr. Aristides Agramonte, in his letter published in theJournalof June 13, call for reply, and I beg to be permitted to submit the following necessary explanations: With manifest feeling Dr. Agramonte takes exception to the omission of his name in the early part of my paper—and naturally too, in view of his lack of knowledge of the facts—and proceeds to show that I was in error in my statement that the decision to put the mosquito theory to a practical test was arrived at during a consultation between Drs. Reed, Lazear and myself. He then makes certain statements in regard to our late colleague, Dr. Lazear, with which, with one exception, I heartily agree, and