Showing papers by "James Taylor published in 2012"
TL;DR: In this article, the authors demonstrate mode-locking of a thulium-doped fiber laser operating at 1.94 μm, using a graphene-polymer based saturable absorber.
Abstract: We demonstrate mode-locking of a thulium-doped fiber laser operating at 1.94 μm, using a graphene-polymer based saturable absorber. The laser outputs 3.6 ps pulses, with ~0.4 nJ energy and an amplitude fluctuation ~0.5%, at 6.46 MHz. This is a simple, low-cost, stable and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics.
259 citations
TL;DR: Five recently developed exponentially weighted methods that have not previously been used for load forecasting are considered, including several exponential smoothing formulations, as well as methods using discount weighted regression, cubic splines, and singular value decomposition.
Abstract: Short-term load forecasts are needed for the efficient management of power systems. Although weather-based modeling is common, univariate models can be useful when the lead time of interest is less than one day. A class of univariate methods that has performed well with intraday data is exponential smoothing. This paper considers five recently developed exponentially weighted methods that have not previously been used for load forecasting. These methods include several exponential smoothing formulations, as well as methods using discount weighted regression, cubic splines, and singular value decomposition (SVD). In addition, this paper presents a new SVD-based exponential smoothing formulation. Using British and French half-hourly load data, these methods are compared for point forecasting up to one day ahead. Although the new SVD-based approach showed some potential, the best performing method was a previously developed exponential smoothing method. A second empirical study showed the better of the univariate methods outperforming a weather-based method up to about five hours ahead, with a combination of these methods producing the best results overall.
252 citations
TL;DR: This work demonstrates mode-locking of a thulium-doped fiber laser operating at 1.94 μm, using a graphene-polymer based saturable absorber, which is a simple, low-cost, stable and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required.
Abstract: We demonstrate mode-locking of a thulium-doped fiber laser operating at 1.94\mu m, using a graphene-based saturable absorber. The laser outputs 3.6ps pulses, with~0.4nJ energy and an amplitude fluctuation~0.5%, at 6.46MHz. This is a simple, low-cost, stable and convenient laser oscillator for applications where eye-safe and low-photon-energy light sources are required, such as sensing and biomedical diagnostics
250 citations
TL;DR: This work develops an approach to producing density forecasts for the wind power generated at individual wind farms using a VARMA-GARCH model and conditional kernel density estimation, which enables a nonparametric modeling of the conditional density of wind power.
Abstract: Of the various renewable energy resources, wind power is widely recognized as one of the most promising. The management of wind farms and electricity systems can benefit greatly from the availability of estimates of the probability distribution of wind power generation. However, most research has focused on point forecasting of wind power. In this article, we develop an approach to producing density forecasts for the wind power generated at individual wind farms. Our interest is in intraday data and prediction from 1 to 72 hours ahead. We model wind power in terms of wind speed and wind direction. In this framework, there are two key uncertainties. First, there is the inherent uncertainty in wind speed and direction, and we model this using a bivariate vector autoregressive moving average-generalized autoregressive conditional heteroscedastic (VARMA-GARCH) model, with a Student t error distribution, in the Cartesian space of wind speed and direction. Second, there is the stochastic nature of the relations...
196 citations
TL;DR: In this paper, the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth.
Abstract: We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at a distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed γ-ray emission with a jet semi-angle of 30°, we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with >99% confidence. If the event occurred in M81, then our findings support the hypothesis that GRB 051103 was due to an SGR giant flare, making it one of the most distant extragalactic magnetars observed to date.
94 citations
TL;DR: The results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs are presented in this article.
Abstract: We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole; and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10^-2 M c^2 at 150 Hz, with a median limit of 17 Mpc. For short hard GRBs we place exclusion distances on binary neutron star and neutron star-black hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.
93 citations
TL;DR: Direct observation of immunization discussions in the primary care pediatric setting is feasible and yields insight into several provider-parent immunization communication practices that are worthy of further study to determine which are effective at improving parental acceptance of immunizations.
84 citations
TL;DR: In this paper, an extension of Holt-Winters exponential smoothing has been proposed that smoothes an intraday cycle and an intraweek cycle, allowing parts of different days of the week to be treated as identical.
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.
76 citations
Journal Article•
TL;DR: A Poisson count model, with gamma distributed arrival rate, is developed, which captures the essential features of this exponential smoothing method and is confirmed by the results of a call center simulation model, which demonstrates the use of arrival rate density forecasting to support staffing decisions.
Abstract: A key input to the call center staffing process is a forecast for the number of calls arriving. Density forecasts of arrival rates are needed for analytical call center models, which assume Poisson arrivals with a stochastic arrival rate. Density forecasts of call volumes can be used in simulation models and are also important for the analysis of outsourcing contracts. A forecasting method, which has previously shown strong potential, is Holt--Winters exponential smoothing adapted for modeling the intraday and intraweek cycles in intraday data. To enable density forecasting of the arrival volume and rate, we develop a Poisson count model, with gamma distributed arrival rate, which captures the essential features of this exponential smoothing method. The apparent stationary level in our data leads us to develop versions of the new model for series with stationary levels. We evaluate forecast accuracy up to two weeks ahead using data from three organizations. We find that the stationary level models improve prediction beyond approximately two days ahead, and that these models perform well in comparison with sophisticated benchmarks. This is confirmed by the results of a call center simulation model, which demonstrates the use of arrival rate density forecasting to support staffing decisions.
This paper was accepted by Yossi Aviv, operations management.
68 citations
TL;DR: In this paper, the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetic determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth, were presented.
Abstract: We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.
61 citations
TL;DR: In this paper, the authors developed a Poisson count model with gamma distributed arrival rate, which captures the essential features of the Holt-Winters exponential smoothing method, and evaluated forecast accuracy up to two weeks ahead using data from three organizations.
Abstract: A key input to the call center staffing process is a forecast for the number of calls arriving. Density forecasts of arrival rates are needed for analytical call center models, which assume Poisson arrivals with a stochastic arrival rate. Density forecasts of call volumes can be used in simulation models and are also important for the analysis of outsourcing contracts. A forecasting method, which has previously shown strong potential, is Holt--Winters exponential smoothing adapted for modeling the intraday and intraweek cycles in intraday data. To enable density forecasting of the arrival volume and rate, we develop a Poisson count model, with gamma distributed arrival rate, which captures the essential features of this exponential smoothing method. The apparent stationary level in our data leads us to develop versions of the new model for series with stationary levels. We evaluate forecast accuracy up to two weeks ahead using data from three organizations. We find that the stationary level models improve prediction beyond approximately two days ahead, and that these models perform well in comparison with sophisticated benchmarks. This is confirmed by the results of a call center simulation model, which demonstrates the use of arrival rate density forecasting to support staffing decisions.
This paper was accepted by Yossi Aviv, operations management.
TL;DR: In this article, an optical-electronic approach to generate microwave signals with high spectral purity was presented. And they demonstrated 10 GHz signals with an absolute timing jitter for a single hybrid oscillator of 420 attoseconds (1Hz - 5 GHz).
Abstract: We present an optical-electronic approach to generating microwave signals with high spectral purity. By circumventing shot noise and operating near fundamental thermal limits, we demonstrate 10 GHz signals with an absolute timing jitter for a single hybrid oscillator of 420 attoseconds (1Hz - 5 GHz).
TL;DR: In this article, an omission in the Collaboration author list of S. S. Dwyer has been identified. But the list is incorrect in the printed version of the journal.
Abstract: This paper was published online on 1 February 2011 with an omission in the Collaboration author list. S. Dwyer has been added as of 12 April 2012. The Collaboration author list is incorrect in the printed version of the journal.
TL;DR: In this article, the efficiency of supercontinua in optical fiber driven by modulation instability of a continuous-wave (CW) pump source has been investigated, and it is shown that the degree of pump coherence has a dramatic effect on the resulting spectral expansion.
Abstract: We report in detail, both experimentally and using numerical simulation, the efficiency of generation of supercontinua in optical fiber driven by modulation instability of a continuous-wave (CW) pump source. It is shown that the degree of pump coherence has a dramatic effect on the resulting spectral expansion and it is discussed how this can be explained by having the proper conditions for efficient modulation instability to break the CW pump light into a train of fundamental solitons that subsequently undergo self-Raman shift to longer wavelengths. It is proposed that an optimal pump bandwidth exists corresponding to the optimal degree of pump incoherence, defined as a function of the modulation instability period.
TL;DR: It is calculated that the risk of early-onset sepsis in a hypothetical infant born at term to a mother with chorioamnionitis, who has a normal physical examination at birth, is likely substantially <1% if the mother’s screen for Group B Streptococcus was negative, calling into question current guidelines recommending treatment of all newborns with intravenous antibiotics for 48 hours pending the results of a blood culture.
Abstract: The management of a newborn born to a mother with chorioamnionitis is controversial. By using data collected on neonates born in the era of routine maternal screening for Group B Streptococcus , we calculate that the risk of early-onset sepsis in a hypothetical infant born at term to a mother with chorioamnionitis, who has a normal physical examination at birth, is likely substantially <1% if the mother’s screen for Group B Streptococcus was negative. This low rate of sepsis calls into question current guidelines recommending treatment of all such newborns with intravenous antibiotics for 48 hours pending the results of a blood culture. Current guidelines for the management of infants born to mothers with chorioamnionitis also raise an important ethical issue; the recommendation to treat these infants with intravenous antibiotics is, in essence, a de facto determination of what constitutes unacceptable risk to the newborn. We argue that this determination is ultimately value-based and therefore requires broader deliberation than that which frequently occurs among medical experts who develop medical guidelines.
* Abbreviations:
CBC — : complete blood cell count
CDC — : Centers for Disease Control and Prevention
GBS — : group B Streptococcus IV — : intravenous
TL;DR: In this paper, an all-fiber passively mode-locked Ra-man laser using graphene as a saturable absorber was presented. Butt et al. used a different length of a highly non-linear fiber presenting normal disper- sion at both pump and signal wavelengths to provide Raman amplification.
Abstract: W e present an all-fiber passively mode-locked Ra- man laser using graphene as a saturable absorber. Different lengths of a highly non-linear fiber presenting normal disper- sion at both pump and signal wavelengths are used in the cav- ity to provide Raman amplification. The cavity is pumped by a continuous wave Raman laser at 1450 nm, and generates short pulses around 1550 nm, which depending on polarization and filtering parameters can be either at the repetition rate of the cavity or at higher harmonics of it.
TL;DR: It is demonstrated that deletion of STEP can enhance experience-induced neuroplasticity and memory formation and identifies STEP as a target for pharmacological treatment aimed at improving the formation of long-term memories.
TL;DR: In this article, a stratified, randomised, replicated "small strip" experimental design is proposed for use in commercial-scale cropping systems that employ a management class approach.
TL;DR: A compact, tunable synchronously pumped photonic crystal fiber (PCF)-based optical parametric oscillator (FOPO) that produces anti-Stokes pulses at wavelengths between 757 and 773 nm, with durations of 150 ps at average output powers exceeding 290 mW is reported.
Abstract: We report the development of a compact, tunable synchronously pumped photonic crystal fiber (PCF)-based optical parametric oscillator (FOPO). The oscillator is pumped using a gain-switched laser diode producing 220 ps pulses around 1062 nm, amplified in a ytterbium doped amplifier to peak powers of 3.5 kW. The FOPO produces anti-Stokes pulses at wavelengths between 757 and 773 nm, with durations of 150 ps at average output powers exceeding 290 mW. The output slope efficiency of the device varies with output wavelength from 1.9 to 6.0%.
TL;DR: In this paper, a sampling scheme based on 23 random interpost samples (3-vine sampling) is suggested as a good compromise to minimize the time associated with sampling and to maximize the accuracy of measurement and the value of the information.
Abstract: Pruning weights are a useful indication for growers of vine size within their production systems. However, pruning weights are rarely collected in commercial situations, as there is little information to help growers determine how many samples to measure. An intensive study of individual vine pruning weights was undertaken over three years in a Concord (Vitis lambruscana Bailey) block at the Lake Erie Research and Extension Laboratory, New York. The population variances associated with individual and aggregated neighboring vine measurements were used to determine random sampling schemes to assist growers. A sampling scheme based on 23 random interpost samples (3-vine sampling) is suggested as a good compromise to minimize the time associated with sampling and to maximize the accuracy of measurement and the value of the information. A spatial analysis of the variance indicates that the same sampling scheme could be extrapolated to block sizes larger than the survey area (0.93 ha), provided that the management and environmental conditions can be considered uniform over the larger block.
TL;DR: It is reported the development of a 10 GHz repetition rate all-fiber integrated femtosecond source tunable around 1.55 μm, and similar performance was achieved over a 20 nm bandwidth.
Abstract: We report the development of a 10 GHz repetition rate all-fiber integrated femtosecond source tunable around 1.55 μm. A phase modulator and sharp spectral filter are used to convert the output of a tunable CW diode to a 10 GHz pulse train. These pulses are compressed using Raman soliton adiabatic compression in a 21 km long length of fiber to generate sub-300-fs duration pulses at a 10 GHz repetition rate. By tuning the wavelength of the diode and appropriate filtering, similar performance was achieved over a 20 nm bandwidth.
Journal Article•
TL;DR: Abadie et al. as mentioned in this paper search for gravitational waves from binary black hole inspiral, merger, and ringdown, Phys. Rev. D 83, 122005 (2011).
Abstract: Original Article: J. Abadie et al. (LIGO Scientific Collaboration, Virgo Collaboration), Search for gravitational waves from binary black hole inspiral, merger, and ringdown, Phys. Rev. D 83, 122005 (2011).
TL;DR: In this paper, a stepwise linear regression model was developed to predict the mean predawn leaf water potential of a vineyard block at a given date from climatic variables and time.
Abstract: Aims: Climate-based indices exist for viticulture, particularly for modelling phenological events, but not for vine water status. In this work, climatic variables are linked to the temporal evolution of the water status of the vineMethods and Results: Within-season time-series of predawn leaf water potential from previous studies across 8 seasons in the south of France were collated. Meteorological data were also collected at each site. A stepwise linear regression model was developed to predict the mean predawn leaf water potential of a vineyard block at a given date from climatic variables and time. Variables selected were growing degree days, short-term humidity and temperature effects. Application of the stepwise model to an independent data set, collected at the other two research sites, produced a linear response but required a local calibration at each site.Conclusion: The analysis demonstrated that climatic variables can be used for predicting the temporal evolution of vine water stress in non-irrigated vineyards.Significance and impact of study: The modelling can assist with within-season crop management and future vineyard planning/development in non-irrigated regions. In irrigated vineyards the application is more restricted but it may be used to identify when to start irrigation.
22 Oct 2012
TL;DR: It is shown through statistical analysis that the hourly prediction error distributions are nearly Gaussian in nature, which appears to show that the statistics of the wind-speed prediction error do not increase significantly as time increases, which is in contrast to other researchers' arguments that the error increases over time.
Abstract: Wind energy utilities use wind speed modeling and prediction to forecast their power production in order to participate in electricity markets. Time-series models which are indirectly based on a Weibull Distribution (WD) are used extensively to predict wind speed. The WD is converted into an approximately Gaussian distribution, as there are no rigorously developed time-series models for random variables possessing a WD. This conversion is performed using the parameters of the WD, a procedure that may negatively impact the accuracy of the forecast - research has demonstrated that WDs under- or over-fit the lower and upper ranges of wind speed histograms.
TL;DR: In this article, the authors demonstrate gain-guided dissipative soliton operation of a linearly polarized Yb-doped fiber laser, mode-locked by carbon nanotubes.
Abstract: We demonstrate gain-guided dissipative soliton operation of a linearly polarized Yb-doped fiber laser, mode-locked by carbon nanotubes. In the regime of low nonlinear phase shift per cavity roundtrip, a dissipative soliton pulse can be supported by the finite gain bandwidth, without the need for strong spectral selection. The gain-guiding dynamics are confirmed by simulations.
TL;DR: In this article, an omission in the Collaboration author list of S. S. Dwyer has been corrected. But the list is incorrect in the printed version of the journal.
Abstract: This paper was published online on 5 May 2010 with an omission in the Collaboration author list. S. Dwyer has been added as of 12 April 2012. The Collaboration author list is incorrect in the printed version of the journal
01 Oct 2012
TL;DR: This proposed framework represents a synthesis of two formerly separate bodies of research, one primarily focussed on communication requirements for safety and security and the other on safe and reliable controls, that addresses safety, reliability and security in two primary aspects: communication and control.
Abstract: Wireless technology has gained much interest in industrial automation due to its flexibility, mobility, ease of installation, and lower cost. Wireless systems, in general, require additional and different engineering and maintenance tasks, for example cryptographic key management for security. The pace of application in process control has been impeded, however, by concern about the risks involved in incorporating wireless paths in feedback loops and making the accommodations necessary for reliable control. The issue is that there are conflicts between maintaining control loop performance and the usual objectives in managing a wireless sensor network. In this paper, we take a holistic approach that addresses safety, reliability and security in two primary aspects: communication and control; thus we hope to contribute a more complete roadmap for developing safe and secure wireless networked control systems. This proposed framework represents a synthesis of two formerly separate bodies of research, one primarily focussed on communication requirements for safety and security and the other on safe and reliable controls.
10 Jan 2012
TL;DR: In this article, the authors developed an approach to produce density forecasts for the wind power generated at individual wind farms by using conditional kernel density (CKD) estimation, which enables a nonparametric modeling of the conditional density of wind power.
Abstract: Of the various renewable energy resources, wind power is widely recognized as one of the most promising The management of wind farms and electricity systems can benefit greatly from the availability of estimates of the probability distribution of wind power generation However, most research has focused on point forecasting of wind power In this paper, we develop an approach to producing density forecasts for the wind power generated at individual wind farms Our interest is in intraday data and prediction from 1 to 72 hours ahead We model wind power in terms of wind speed and wind direction In this framework, there are two key uncertainties First, there is the inherent uncertainty in wind speed and direction, and we model this using a bivariate VARMA-GARCH model, with a Student t distribution, in the Cartesian space of wind speed and direction Second, there is the stochastic nature of the relationship of wind power to wind speed (described by the power curve), and to wind direction We model this using conditional kernel density (CKD) estimation, which enables a nonparametric modeling of the conditional density of wind power Using Monte Carlo simulation of the VARMA-GARCH model and CKD estimation, density forecasts of wind speed and direction are converted to wind power density forecasts Our work is novel in several respects: previous wind power studies have not modeled a stochastic power curve; to accommodate time evolution in the power curve, we incorporate a time decay factor within the CKD method; and the CKD method is conditional on a density, rather than a single value The new approach is evaluated using datasets from four Greek wind farms