466 research outputs found
Recommended from our members
Phasor-Based Assessment for Harmonic Sources in Distribution Networks
Phasor-based interdependencies of multiple harmonic sources, especially Distributed Energy Resources, on distribution networks are analyzed in this paper. A new index, Phasor Harmonic Index (IPH), is proposed by the authors. IPH considers both harmonic source magnitude and phase angle for different harmonic orders. Other commonly used harmonic indices are based solely on magnitude of waveforms. A very detailed model of a distribution network is used in the harmonic assessment. With the help of the detailed distribution network model, the phase couplings and the phase balancing impacts on harmonic propagation between three phases are investigated. Moreover, effects of harmonic source phase angle deviations are analyzed at both the customer side and the substation side. This paper investigates the importance of phase angles in harmonic assessment and how distribution netw
Evaluating a mesoscale atmosphere model and a satellite-based algorithm in estimating extreme rainfall events in northwestern Turkey
Quantitative precipitation estimates are obtained with more uncertainty under
the influence of changing climate variability and complex topography from
numerical weather prediction (NWP) models. On the other hand, hydrologic
model simulations depend heavily on the availability of reliable
precipitation estimates. Difficulties in estimating precipitation impose an
important limitation on the possibility and reliability of hydrologic
forecasting and early warning systems. This study examines the performance of
the Weather Research and Forecasting (WRF) model and the Multi Precipitation
Estimates (MPE) algorithm in producing the temporal and spatial
characteristics of the number of extreme precipitation events observed in the
western Black Sea region of Turkey. Precipitation derived from WRF model with
and without the three-dimensional variational (3DVAR) data assimilation scheme
and MPE algorithm at high spatial resolution (5 km) are compared with gauge
precipitation. WRF-derived precipitation showed capabilities in capturing the
timing of precipitation extremes and to some extent the spatial distribution
and magnitude of the heavy rainfall events, whereas MPE showed relatively weak
skills in these aspects. WRF skills in estimating such precipitation
characteristics are enhanced with the application of the 3DVAR scheme. Direct
impact of data assimilation on WRF precipitation reached up to 12% and at
some points there is a quantitative match for heavy rainfall events, which
are critical for hydrological forecasts
Bridging the gap between nanowires and Josephson junctions: a superconducting device based on controlled fluxon transfer across nanowires
The basis for superconducting electronics can broadly be divided between two
technologies: the Josephson junction and the superconducting nanowire. While
the Josephson junction (JJ) remains the dominant technology due to its high
speed and low power dissipation, recently proposed nanowire devices offer
improvements such as gain, high fanout, and compatibility with CMOS circuits.
Despite these benefits, nanowire-based electronics have largely been limited to
binary operations, with devices switching between the superconducting state and
a high-impedance resistive state dominated by uncontrolled hotspot dynamics.
Unlike the JJ, they cannot increment an output through successive switching,
and their operation speeds are limited by their slow thermal reset times. Thus,
there is a need for an intermediate device with the interfacing capabilities of
a nanowire but a faster, moderated response allowing for modulation of the
output. Here, we present a nanowire device based on controlled fluxon
transport. We show that the device is capable of responding proportionally to
the strength of its input, unlike other nanowire technologies. The device can
be operated to produce a multilevel output with distinguishable states, which
can be tuned by circuit parameters. Agreement between experimental results and
electrothermal circuit simulations demonstrates that the device is classical
and may be readily engineered for applications including use as a multilevel
memory
STAFFING AND THE QUALITY OF TEACHING IN UNIVERSITIES
This study sought to establish the influence of staffing on the quality of teaching in Uganda’s public universities. It was undertaken in the face of persistent stakeholder concerns regarding the declining quality of teaching and learning in these institutions that have occasionally culminated into student strikes and different kinds of protests. Basing on a mixed-methods approach, the study employed the descriptive cross-sectional survey design where both qualitative and quantitative data were collected from 14 academic managers, 111 academic staff, and 285 undergraduate university students of Kyambogo University, using survey and interview methods. The collected data from staff and students were analyzed using descriptive statistics and multiple regression techniques while content analysis technique was used to analyze qualitative data collected by interviewing purposively selected university managers. The study findings revealed that: first, staff recruitment (B=.182; p=.040), staff training (B=.340; p=.000), and development (B=.327; p=.000) have statistically significant influence on the quality of teaching. Meanwhile, staff deployment (B=.010; p=.914) has statistically insignificant influence on the quality of teaching. However, overall, the study revealed that staffing (R=.683; R2=.467; p=.000) significantly influences the quality of teaching in public universities in Uganda. Therefore, it was concluded that effective staffing would raise the quality of teaching in universities, other factors held constant. The study thus recommends that university managers and staff should stick to the prescribed recruitment policy, invest more resources in training and developing staff, and ensure that existing staff are generally well-managed
Effects of Delayed Finishing/Polishing on Surface Roughness, Hardness and Gloss of Tooth-Coloured Restorative Materials
Objectives: The aim of this study was to investigate the effect of delayed finishing/polishing on the surface roughness, hardness and gloss of tooth-coloured restorative materials. Methods: Four different tooth-coloured restoratives: a flowable resin composite- Tetric Flow, a hybrid resin composite- Venus, a nanohybrid resin composite- Grandio, and a polyacid modified resin composite- Dyract Extra were used. 30 specimens were made for each material and randomly assigned into three groups. The first group was finished/polished immediately and the second group was finished/polished after 24 hours. The remaining 10 specimens served as control. The surface roughness of each sample was recorded using a laser profilometer. Gloss measurements were performed using a small-area glossmeter. Vickers microhardness measurements were performed from three locations on each specimen surface under 100g load and 10s dwell time. Data for surface roughness and hardness were analyzed by Kruskal Wallis test and data for gloss were subjected to one-way ANOVA and Tukey test (P .05). The lowest hardness values were found under Mylar strip. Delayed finishing/polishing significantly increased the hardness of all materials. Conclusions: The effect of delayed finishing/polishing on surface roughness, gloss and hardness appears to be material dependent.PubMe
Single-Photon Single-Flux Coupled Detectors
In this work, we present a novel device that is a combination of a
superconducting nanowire single-photon detector and a superconducting
multi-level memory. We show that these devices can be used to count the number
of detections through single-photon to single-flux conversion. Electrical
characterization of the memory properties demonstrates single-flux quantum
(SFQ) separated states. Optical measurements using attenuated laser pulses with
different mean photon number, pulse energies and repetition rates are shown to
differentiate single-photon detection from other possible phenomena, such as
multi-photon detection and thermal activation. Finally, different geometries
and material stacks to improve device performance, as well as arraying methods
are discussed
Lateral and Vertical Heterostructures of h-GaN/h-AlN: Electron Confinement, Band Lineup, and Quantum Structures
Lateral and vertical heterostructures constructed of two-dimensional (2D) single-layer h-GaN and h-AlN display novel electronic and optical properties and diverse quantum structures to be utilized in 2D device applications. Lateral heterostructures formed by periodically repeating narrow h-GaN and h-AlN stripes, which are joined commensurately along their armchair edges, behave as composite semiconducting materials. Direct-indirect characters of the fundamental band gaps and their values vary with the widths of these stripes. However, for relatively wider stripes, electronic states are confined in different stripes and make a semiconductor-semiconductor junction with normal band alignment. This way one-dimensinonal multiple quantum well structures can be generated with electrons and holes confined to h-GaN stripes. Vertical heterostructures formed by thin stacks of h-GaN and h-AlN are composite semiconductors with a tunable fundamental band gap. However, depending on the stacking sequence and number of constituent sheets in the stacks, the vertical heterostructure can transform into a junction, which displays staggered band alignment with electrons and holes separated in different stacks. The weak bonds between the cations and anions in adjacent layers distinguish these heterostructures from those fabricated using thin films of GaN and AlN thin films in wurtzite structure, as well as from van der Waals solids. Despite the complexities due to confinement effects and charge transfer across the interface, the band diagram of the heterostructures in the direct space and band lineup are conveniently revealed from the electronic structure projected to the atoms or layers. Prominent features in the optical spectra of the lateral composite structures are observed within the limits of those of 2D parent constituents; however, significant deviations from pristine 2D constituents are observed for vertical heterostructures. Important dimensionality effects are revealed in the lateral and vertical heterostructures. © 2017 American Chemical Society
- …