Control of a bidirectional single-phase grid interface for electric vehicles

The number of electric vehicles is expected to increase exponentially in the next decade. This represents a huge potential for grid support, such as energy storage in their batteries, with advantages for grid operators and for customers. For this purpose, flexible power interfaces are required. This paper presents a simulation of a bidirectional singlephase power interface between an electric vehicle battery and the grid. The proposed system is fully simulated and counts with features such as vehicle-to-grid, vehicle-to-home and grid-to-vehicle. All power flow and the controllers for these modes of operation are described in detail. The simulation was developed in a Software-in-the-Loop scheme to facilitate a future physical implementation with a Hardware-in-the-Loop platform. The proposed system was extensively tested via simulation, the results proving the system is stable, able to change operation modes smoothly and definition of the exchanged active and reactive powers.info:eu-repo/semantics/publishedVersio

Assessing the wind field over the continental shelf as a resource for electric power

To assess the wind power resources of a large continental shelf area, we analyze the 18-year hourly wind records from meteorological stations in the US Middle Atlantic Bight (MAB), comparing areas of coast, estuary, and open shelf. We calculate winds at turbine hub height for the sea breeze compared with synoptic winds and, for each type of site, we compare the seasonal and daily phase match to electrical load. To improve large-scale ocean power resource calculations, we derive an iterative algorithm to determine the surface roughness coefficient (z0). Our method calculates z0 for specific times and locations over the ocean, rather than the prior practice of using a generic z0 that is constant across time and space. Due to lower surface roughness of the ocean, wind speeds are notably higher at hub height, so that in the MAB we find that a representative open shelf site has three times the power content of a nearby land site. Regarding phase match to daily electric load, we find the sea breeze adjacent to the coast is a very good match to this region\u27s electric power load profile. However, the open shelf wind speeds are so much higher (10.9 m s–1 versus 5.7 m s–1 for the comparison period) that the near-coast phase advantage is obviated. We also find more consistent wind power production offshore, with single sites producing at least some power 88 to 92% of the time. By modeling electrically interconnected sites, power production improves to 96.3% with as few as three interconnected wind sites and to 99.3% with 5 interconnected sites

An HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436b

GJ 436b is a prime target for understanding warm Neptune exoplanet atmospheres and a target for multiple JWST GTO programs. Here, we report the first space-based optical transmission spectrum of the planet using two HST/STIS transit observations from 0.53-1.03 microns. We find no evidence for alkali absorption features, nor evidence of a scattering slope longward of 0.53 microns. The spectrum is indicative of moderate to high metallicity (~100-1000x solar) while moderate metallicity scenarios (~100x solar) require aerosol opacity. The optical spectrum also rules out some highly scattering haze models. We find an increase in transit depth around 0.8 microns in the transmission spectra of 3 different sub-Jovian exoplanets (GJ 436b, HAT-P-26b, and GJ 1214b). While most of the data come from STIS, data from three other instruments may indicate this is not an instrumental effect. Only the transit spectrum of GJ 1214b is well fit by a model with stellar plages on the photosphere of the host star. Our photometric monitoring of the host star reveals a stellar rotation rate of 44.1 days and an activity cycle of 7.4 years. Intriguingly, GJ 436 does not become redder as it gets dimmer, which is expected if star spots were dominating the variability. These insights into the nature of the GJ 436 system help refine our expectations for future observations in the era of JWST, whose higher precision and broader wavelength coverage will shed light on the composition and structure of GJ 436b's atmosphere.Comment: 20 pages, 11 figures, 5 tables, Accepted to AJ. A full version of table 1 is included as table1_mrt.tx

Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b

Recent results from the Kepler mission indicate that super-Earths (planets with masses between 1-10 times that of the Earth) are the most common kind of planet around nearby Sun-like stars. These planets have no direct solar system analogue, and are currently one of the least well-understood classes of extrasolar planets. Many super-Earths have average densities that are consistent with a broad range of bulk compositions, including both water-dominated worlds and rocky planets covered by a thick hydrogen and helium atmosphere. Measurements of the transmission spectra of these planets offer the opportunity to resolve this degeneracy by directly constraining the scale heights and corresponding mean molecular weights of their atmospheres. We present Hubble Space Telescope near-infrared spectroscopy of two transits of the newly discovered transiting super-Earth HD 97658b. We use the Wide Field Camera 3's scanning mode to measure the wavelength-dependent transit depth in thirty individual bandpasses. Our averaged differential transmission spectrum has a median 1 sigma uncertainty of 23 ppm in individual bins, making this the most precise observation of an exoplanetary transmission spectrum obtained with WFC3 to date. Our data are inconsistent with a cloud-free solar metallicity atmosphere at the 10 sigma level. They are consistent at the 0.4 sigma level with a flat line model, as well as effectively flat models corresponding to a metal-rich atmosphere or a solar metallicity atmosphere with a cloud or haze layer located at pressures of 10 mbar or higher.Comment: ApJ in press; revised version includes an updated orbital ephemeris for the plane

Studies of superconducting materials with muon spin rotation

The muon spin rotation/relaxation technique was found to be an exceptionally effective means of measuring the magnetic properties of superconductors, including the new high temperature superconductor materials, at the microscopic level. The technique directly measures the magnetic penetration depth (type II superconductors (SC's)) and detects the presence of magnetic ordering (antiferromagnetism or spin-glass ordering were observed in some high temperature superconductor (HTSC's) and in many closely related compounds). Extensive studies of HTSC materials were conducted by the Virginia State University - College of William and Mary - Columbia University collaboration at Brookhaven National Laboratory and TRIUMF (Vancouver). A survey of LaSrCuO and YBaCaCuO systems shows an essentially linear relationship between the transition temperature T(sub c) and the relaxation rate. This appears to be a manifestation of the proportionality between T(sub c) and the Fermi energy, which suggests a high energy scale for the SC coupling, and which is not consistent with the weak coupling of phonon-mediated SC. Studies of LaCuO and YBaCuO parent compounds show clear evidence of antiferromagnetism. YBa2Cu(3-x)CO(x)O7 shows the simultaneous presence of spin-glass magnetic ordering and superconductivity. Three-dimensional SC, (Ba, K) BiO3, unlike the layered CuO-based compounds, shows no suggestion of magnetic ordering. Experimental techniques and theoretical implications are discussed

Costs and Complications of Single Stage Fixation Versus Two-Stage Treatment of Select Bicondylar Tibial Plateau Fractures

Objectives: To determine the differences in costs and complications in patients with bicondylar tibial plateau (BTP) fractures treated with one stage definitive fixation compared to two stage fixation following initial spanning external fixation. Design: Retrospective cohort study Setting: Level one trauma center Patients/Participants: Patients with OTA 41-C (Schatzker 6) treated with open reduction internal fixation (ORIF). Intervention: Definitive treatment with ORIF either acutely (one stage) or delayed following initial spanning external fixation (two stage). Main Outcome Measures: Wound healing complications, implant costs, hospital charges, PROMIS outcome measures. Results: 105 patients were identified over a three-year period, of which 52 met inclusion criteria. There were 28 patients in the One-Stage group and 24 patients in the Two-Stage group. Mean follow-up was 21.8 months, and 87% of patients had at least 12 months follow-up. The mean number of days to definitive fixation was 1.2 in the One-Stage group and 7.8 in the Two-Stage group. There were no differences between groups with respect to wound healing or any other surgery-related complications. Functional outcomes (PROMIS) were similar between groups. Mean implant cost in the Two-Stage group was $10,821 greater than the One-Stage group, mostly due to the costs of external fixation. Median hospital inpatient charges in the Two-Stage group exceeded the One-Stage group by over$68,000 for all BTP fractures and by $61,000 for isolated BTP fractures. Conclusions: Early single stage treatment of BTP fractures is cost effective, and is not associated with a higher complication rate than two stage treatment in appropriately selected patients. Level of Evidence: Level III- Retrospective cohort stud

Locking Plate Fixation in a Series of Bicondylar Tibial Plateau Fractures Raises Treatment Costs Without Clinical Benefit

Objectives: To compare outcomes and costs between locking and nonlocking constructs in the treatment of bicondylar tibial plateau (BTP) fractures. Design: Retrospective cohort study. Setting: Level 1 academic trauma center. Patients: All patients that presented with complete articular, BTP fractures (AO/OTA 41-C and Schatzker 6) between 2013-2015 were screened (n=112). Patients treated with a mode of fixation other than plate-and-screw were excluded. 56 patients with a minimum follow-up of 12 months were included in the analysis. Intervention: Operative fixation of BTP fractures with locking (n=29) or nonlocking (n=27) implants. Main outcome measurements: Implant cost, patient reported outcomes (PROMIS physical function and pain interference), clinical, and radiographic outcomes. Results: There were no differences between the two groups with respect to demographics, injury characteristics, radiographic outcomes (change in alignment) or clinical outcomes (PROMIS, reoperation, nonunion, infection). Implant costs were significantly greater in the locking group compared to the nonlocking group (mean L $4453; mean NL$2569; p<0.01). Conclusions: This study demonstrated improved value of treatment (less cost with no difference in clinical outcome) with nonlocking implants for bicondylar tibial plateau fractures when dual plate fixation strategies are performed. Level of Evidence: Therapeutic III. See Instructions for Authors for a complete description of levels of evidence

Air Conditioner User Behavior in a Master-Metered Apartment Building

Air conditioner operation was studied in order to understand how energy consumption and peak power are determined by user behavior, equipment operation and building characteristics. In a multi-family building, thirteen room air conditioners were instrumented in eight apartments, and interviews were conducted with the residents about their operation of the units. The predominant mode of operation was to switch the unit on and off manually; only one resident consistently let it operate thermostatically, and many residents were not aware that the unit had a thermostat. Ambient temperature and time of day were observed to have major effects on the occupant's decision to turn the unit on or off. Even though residents did not pay for electricity, numerous noneconomic factors were found to limit their use of air conditioning. Across apartments, seasonal air conditioner energy consumption varies by two orders of magnitude while interior July temperature varies by 3.7°C

The neglected social dimensions to a vehicle-to-grid (V2G) transition: a critical and systematic review

Vehicle-to-grid (V2G) refers to efforts to bi-directionally link the electric power system and the transportation system in ways that can improve the sustainability and security of both. A transition to V2G could enable vehicles to simultaneously improve the efficiency (and profitability) of electricity grids, reduce greenhouse gas emissions for transport, accommodate low-carbon sources of energy, and reap cost savings for owners, drivers, and other users. To understand the recent state of this field of research, here we conduct a systematic review of 197 peer-reviewed articles published on V2G from 2015 to early 2017. We find that the majority of V2G studies in that time period focus on technical aspects of V2G, notably renewable energy storage, batteries, or load balancing to minimize electricity costs, in some cases including environmental goals as constraints. A much lower proportion of studies focus on the importance of assessing environmental and climate attributes of a V2G transition, or on the role of consumer acceptance and knowledge of V2G systems. Further, there is need for exploratory work on natural resource use and externalities, discourses and narratives as well as social justice, gender, and urban resilience considerations. These research gaps need to be addressed if V2G is to achieve the societal transition its advocates seek

Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b

The helium absorption triplet at a wavelength of 10,833 \AA\ has been proposed as a way to probe the escaping atmospheres of exoplanets. Recently this feature was detected for the first time using Hubble Space Telescope (HST) WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3 observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at the $4\sigma$ confidence level. We compare our observations to a grid of 1D models of hydrodynamic escape to constrain the thermospheric temperatures and mass loss rate. We find that our data are best fit by models with high mass loss rates of $\dot{M} \approx 10^{9}$ - $10^{11}$ g s$^{-1}$. Although we do not detect the planetary wind directly, our data are consistent with the prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape. Nevertheless, the mass loss rate is low enough that the planet has only lost up to a few percent of its mass over its history, leaving its bulk composition largely unaffected. This matches the expectation from population statistics, which indicate that close-in planets with radii greater than 2 R$_{\oplus}$ form and retain H/He-dominated atmospheres. We also confirm the independent detection of helium in HAT-P-11b obtained with the CARMENES instrument, making this the first exoplanet with the detection of the same signature of photoevaporation from both ground- and space-based facilities.Comment: 12 pages, 9 figures, accepted for publication in ApJ