Showing papers by "James Taylor published in 2009"

Wind Power Density Forecasting Using Ensemble Predictions and Time Series Models

Abstract: Wind power is an increasingly used form of renewable energy. The uncertainty in wind generation is very large due to the inherent variability in wind speed, and this needs to be understood by operators of power systems and wind farms. To assist with the management of this risk, this paper investigates methods for predicting the probability density function of generated wind power from one to ten days ahead at five U.K. wind farm locations. These density forecasts provide a description of the expected future value and the associated uncertainty. We construct density forecasts from weather ensemble predictions, which are a relatively new type of weather forecast generated from atmospheric models. We also consider density forecasting from statistical time series models. The best results for wind power density prediction and point forecasting were produced by an approach that involves calibration and smoothing of the ensemble-based wind power density.

Effectiveness of Educational Materials Designed to Change Knowledge and Behaviors Regarding Crying and Shaken-Baby Syndrome in Mothers of Newborns: A Randomized, Controlled Trial

Abstract: BACKGROUND. Infant crying is an important precipitant for shaken-infant syndrome. OBJECTIVE. To determine if parent education materials (The Period of PURPLE Crying [PURPLE]) change maternal knowledge and behavior relevant to infant shaking. METHODS. This study was a randomized, controlled trial conducted in prenatal classes, maternity wards, and pediatric practices. There were 1374 mothers of newborns randomly assigned to the PURPLE intervention and 1364 mothers to the control group. Primary outcomes were measured by telephone 2 months after delivery. These included 2 knowledge scales about crying and the dangers of shaking; 3 scales about behavioral responses to crying generally and to unsoothable crying, and caregiver self-talk in response to unsoothable crying; and 3 questions concerning the behaviors of sharing of information with others about crying, walking away if frustrated, and the dangers of shaking. RESULTS. The mean infant crying knowledge score was greater in the intervention group (69.5) compared with controls (63.3). Mean shaking knowledge was greater for intervention subjects (84.8) compared with controls (83.5). For reported maternal behavioral responses to crying generally, responses to unsoothable crying, and for self-talk responses, mean scores for intervention mothers were similar to those for controls. For the behaviors of information sharing, more intervention mothers reported sharing information about walking away if frustrated and the dangers of shaking, but there was little difference in sharing information about infant crying. Intervention mothers also reported increased infant distress. CONCLUSIONS. Use of the PURPLE education materials seem to lead to higher scores in knowledge about early infant crying and the dangers of shaking, and in sharing of information behaviors considered to be important for the prevention of shaking. Pediatrics 2009;123:972–980

Nanosecond-pulse fiber lasers mode-locked with nanotubes

Abstract: We demonstrate that mode-locking of ytterbium fiber lasers with a carbon nanotube saturable absorber can produce pulses ranging from 20 ps to 2 ns at repetition rates between 21 MHz and 177 kHz, respectively, depending on cavity length. Nonlinear polarization evolution is not responsible for mode-locking. Even in the nanosecond regime, clean single pulses are observed and the pulse train exhibits low jitter. Combined with extremely large chirp, these properties are suited for chirped-pulse amplification systems.

Generation and direct measurement of giant chirp in a passively mode-locked laser.

Abstract: We evaluate the shape and chirp of nanosecond pulses from a fiber laser passively mode locked with a nanotube-based saturable absorber by using a synchronously scanning streak camera and a monochromator to directly measure the pulse spectrogram. We show that the stable sech2 output pulse possesses a predominantly linear chirp, with a residual quartic phase and low noise. Comparison with analytical mode-locking theory shows a good quantitative agreement with the master equation mode-locking model.

Soliton trapping of dispersive waves in tapered optical fibers.

Abstract: We show that trapping of dispersive waves by solitons is significantly enhanced in tapered optical fibers as compared with nontapered fibers. For the trapping process to occur, the soliton must be decelerating; in nontapered fiber, the cause of soliton deceleration is Raman self-scattering to spectral regions of lower group velocity. It is shown here that deceleration of the soliton due to the changing group velocities in a tapered optical fiber also enables and enhances the trapping process, independently of Raman gain. This explains the enhanced blue spectral extension observed for supercontinuum generation in tapered optical fibers. This result also indicates that trapping of dispersive waves by solitons will also be possible in fibers or waveguides made from materials with negligible Raman self-scattering.

Forecasting Intraday Time Series with Multiple Seasonal Cycles Using Parsimonious Seasonal Exponential Smoothing

Abstract: This paper concerns the forecasting of seasonal intraday time series. An extension of Holt-Winters exponential smoothing has been proposed that smoothes an intraday cycle and an intraweek cycle. A recently proposed exponential smoothing method involves smoothing a different intraday cycle for each distinct type of day of the week. Similar days are allocated identical intraday cycles. A limitation is that the method allows only whole days to be treated as identical. We introduce an exponential smoothing formulation that allows parts of different days of the week to be treated as identical. The result is a method that involves the smoothing and initialisation of fewer terms than the other two exponential smoothing methods. We evaluate forecasting up to a day ahead using two empirical studies. For electricity load data, the new method compares well with a range of alternatives. The second study involves a series of arrivals at a call centre that is open for a shorter duration at the weekends than on weekdays. By contrast with the previously proposed exponential smoothing methods, our new method can model in a straightforward way this situation, where the number of periods on each day of the week is not the same.

Search for gravitational-wave bursts associated with gamma-ray bursts using data from LIGO Science Run 5 and Virgo Science Run 1

Abstract: We present the results of a search for gravitational-wave bursts associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for gravitational-wave burst signals associated with this sample of GRBs. Using simulated short-duration (<1 s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with typical limits of D ~ 15 Mpc (E_GW^iso / 0.01 M_o c^2)^1/2 for emission at frequencies around 150 Hz, where the LIGO-Virgo detector network has best sensitivity. We present astrophysical interpretations and implications of these results, and prospects for corresponding searches during future LIGO-Virgo runs.

Detection of Bocavirus in Saliva of Children with and without Respiratory Illness

Abstract: We evaluated saliva samples from 149 children 2 to 11 years old for human bocavirus (hBoV) DNA. hBoV was detected in saliva samples at asymptomatic enrollment in 3% (5/149) and during respiratory illness in 2% (2/106) of the cases. hBoV was detected in only 1/149 asymptomatic and 0/106 illness nasal samples.

Site-specific variation in wheat grain protein concentration and wheat grain yield measured on an Australian farm using harvester-mounted on-the-go sensors

Abstract: Accurately measuring and understanding the fine-scale relationship between wheat grain yield (GY) and the concomitant grain protein concentration (GPC) should provide valuable information to improve the management of nitrogen inputs. Here, GPC and GY were monitored on-harvester for three seasons across 27 paddocks on an Australian farming enterprise using two independent, on-the-go sensing systems. A Zeltex Accuharvest measured GPC (%) and a John Deere GreenStar system measured GY (t/ha). Local calibration in each season for Australian spring wheat significantly improved the prediction accuracy, precision, and bias of the Zeltex Accuharvest when compared with the initial factory calibration. Substantial variation in GPC and GY was recorded at the field scale, with the least variation recorded in both parameters in the wetter season. GY (CV = 38%) was twice as variable on average as GPC (CV = 19%) across the enterprise. At this enterprise scale, a negative correlation between GPC and GY was observed for a composite of the field data from all seasons (r = –0.48); however, at the within-field scale the relationship was shown to vary from positive (max. = +0.41) to negative (min. = –0.65). Spatial variation in GPC and GY at the within-field scale was described best in the majority of cases by an exponential semivariogram model. Within-field spatial variability in GPC is more strongly autocorrelated than GY but on average they share a similar autocorrelated range (a′ = ~190 m). This spatial variability in GPC and GY gave rise to local spatial variation in the correlation between GPC and GY, with 85% of the fields registering regions of significant negative correlations (P < 0.01) and significant positive correlations observed in 70% of fields. The spatial pattern in these regions of significantly different correlations is shown to display spatial coherence from which inferences regarding the relative availability of soil nitrogen and moisture are suggested. The results point to the suitability of these on-the-go sensors for use in more sophisticated agronomic and environmentally targeted nitrogen-use analysis.

Generalized Linear Models for Site-Specific Density Forecasting of U.K. Daily Rainfall

Abstract: Site-specific probability density rainfall forecasts are needed to price insurance premiums, contracts, and other financial products based on precipitation. The spatiotemporal correlations in U.K. daily rainfall amounts over the Thames Valley are investigated and statistical Markov chain generalized linear models (Markov GLM) of rainfall are constructed. The authors compare point and density forecasts of total rainfall amounts, and forecasts of probability of occurrence of rain from these models and from other proposed density models, including persistence, statistical climatology, Markov chain, unconditional gamma and exponential mixture models, and density forecasts from GLM regression postprocessed NCEP numerical ensembles, at up to 45-day forecast horizons. The Markov GLMs and GLM processed ensembles produced skillful 1-day-ahead and short-term point forecasts. Diagnostic checks show all models are well calibrated, but GLMs perform best under the continuous-ranked probability score. For lead times of greater than 1 day, no models were better than the GLM processed ensembles at forecasting occurrence probability. Of all models, the ensembles are best able to account for the serial correlations in rainfall amounts. In conclusion, GLMs for future site-specific density forecasting are recommended. Investigations explain this conclusion in terms of the interaction between the autocorrelation properties of the data and the structure of the models tested.

The acute effects of magnesium in atrial fibrillation and flutter with a rapid ventricular rate

Abstract: A prospective, randomised, placebo controlled, double blinded trial to assess the efficacy of intravenous magnesium sulphate (20mmol over 30 minutes) versus placebo in patients presenting to the emergency department with rapid atrial fibrillation and flutter. The end points were slowing of the ventricular rate and reversion to sinus rhythm. A total of 41 patients were enrolled. The mean decrease in heart rate 30 minutes after commencing the infusion was 24.1/min for the magnesium group compared to 11.0/min for the placebo group (different at the 95% level of significance). The mean decrease in heart rate and the reversion rate four hours after commencing the infusion were the same at the 95% level of significance for the two groups. We conclude that magnesium has a significant effect in the acute slowing of ventricular rate but no effect in achieving reversion to sinus rhythm.

Spatial Analysis of the Effect of Fruit Thinning on Apple Crop Load

Abstract: Summary There has been very little literature on the mid seasonspatial variability of fruit production in horticulturecrops published to date. Most of the existing literaturerefers to data collected post harvest. Crop load datataken prior to hand thinning and prior to harvest werecollected in 3 blocks of a commercial apple ( Malus do-mestica Borkh.) orchard in the province of Ferrara, It-aly. The purpose of the survey was to characterize thewithin field variability of crop load, using spatial sta-tistics, and assess the effectiveness of the hand-thin-ning treatment. Crop load estimations were taken at156 sites pre and post hand-thinning over a defineddistance (0.8 m) and the data used to model a vario-gram and associated spatial variation. Variation in thespatial distribution of the fruit load prior to thehand-thinning was observed, indicating a possibility tospatially differentially manage the orchard. No spatialvariation in fruit number wa s observed prior to harvest(post-thinning), indicating that thinning had removedthe previously observed spatial variation in crop load.Under the current uniform management approach thisindicates that thinning has been effectively imple-mented. However, the spatial variation observed priorto thinning may indicate that a differential crop loadmanagement strategy may be optimal for maximizingquality in the orchard.

Mode-locking fibre lasers with the E 22 transition of carbon nanotubes

Abstract: Single-walled carbon nanotubes (SWCNTs) are being widely investigated as saturable absorbers for initiating and maintaining mode-locking [1-3]. Among their advantages are low fabrication cost, a high damage threshold, sub-picosecond recovery times and a wide spectral range (1.0–2.5 µm). All mode-locked fibre laser systems based on SWCNT saturable absorbers, demonstrated to date, have used the first electronic transition of the nanotubes, known as E 11 , which corresponds to the single real gap in the electron density of states (DOS) of semiconducting nanotubes [4]. It was expected that only this transition could be used for saturable absorption. However, in a couple of recent papers [5,6], the mode-locking regime has been realized in bulk lasers at 1.06 µm with arc-synthesized nanotubes, but the authors did not pay much attention to the fact that this wavelength belongs to the second absorption band, corresponding to the E 22 pseudo-gap [4]. This means that after excitation the electron falls to the lower energy transition, corresponding to the real gap E 11 . In this work we clearly demonstrate saturable absorption on the E 22 transition by using it to mode-lock a fibre laser for the first time. This discovery should enable the use of SWCNT saturable absorbers at much shorter wavelengths, into the visible spectral region.

Low-noise microwave signals from a frequency-stabilized Yb:Tungstate optical frequency comb

Abstract: Frequency-stabilized mode-locked femtosecond lasers are a cornerstone of modern optical frequency metrology and have allowed the demonstration of many new technologies, including optical atomic clocks, novel broadband spectroscopy, and the synthesis of ultra-low phase noise optical and microwave signals. At present, optical frequency combs are predominantly based on two femtosecond laser technologies: titanium:sapphire lasers and Er and Yb:fibre lasers. Here, an alternative approach employing a 180-MHz repetition rate, diode-pumped Yb-doped tungstate (Yb:KYW) frequency comb is demonstrated. In addition to being a compact, low-cost, and efficient optical frequency comb, the Yb:KYW frequency comb has excellent noise properties. We show that when frequency-stabilized the Yb:KYW can be used to generate microwave signals having frequency stability significantly better (≫30×) than is achievable with conventional quartz or dielectric-based oscillators.

2 ns pulses from a fibre laser mode-locked by carbon nanotubes

Abstract: We demonstrate strongly chirped pulses from mode-locked Yb fibre ring lasers with cavity lengths exceeding 1 km, in the presence of very high net normal dispersion, up to −36 ps nm-1. Mode-locking was achieved using a single wall carbon nanotube saturable absorber [1–3]. The output pulse durations exceed 2 ns, which is, to the best of our knowledge, the longest pulse duration produced from a mode-locked fibre laser. The long cavities allowed us to achieve sub 200 kHz repetition rates, about an order of magnitude lower than has been reported to date [4]. In the experiments reported here, no intentional spectral filtering was employed, despite the all-normally dispersive cavity. The lasing wavelength selection is therefore a result of overlap of the gain bandwidth and spectral loss profiles of the intracavity optical components, but may also be affected by a dynamic filtering effect of the saturable absorber.