Current regulation plays an important role in modern power electronic AC conversion systems. The most direct strategy to regulate such currents is to use a simple closed loop proportional-integral ...(PI) regulator, which has no theoretical stability limits as the proportional and integral gains are increased, since it is only a second order system. However, pulsewidth modulation (PWM) transport and controller sampling delays limit the gain values that can be achieved in practical systems. Taking these limitations into account, this paper presents an analytical method to determine the best possible gains that can be achieved for any class of practical linear AC current controller. The analysis shows that the maximum possible proportional gain is determined by the plant series inductance, the DC bus voltage and the transport and sampling delays, while the maximum possible integral gain is determined primarily by the transport and sampling delays. The work is applicable to stationary frame PI regulators, stationary frame controllers with back electromotive force compensation, stationary frame P+ resonant (PR) controllers, and synchronous d - q frame controllers, since they all have identical proportional and integral gains that must be optimized for any particular application.
In a trial involving 304 veterans with stable PTSD, prazosin did not alleviate distressing dreams and did not improve sleep quality or overall clinical symptoms over 10 or 26 weeks. This result is in ...contrast to findings in several previous smaller or briefer trials.
To address the need for brief, reliable, valid, and standardized quality of life (QOL) assessment applicable across neurologic conditions.
Drawing from larger calibrated item banks, we developed ...short measures (8-9 items each) of 13 different QOL domains across physical, mental, and social health and evaluated their validity and reliability. Three samples were utilized during short form development: general population (Internet-based, n = 2,113); clinical panel (Internet-based, n = 553); and clinical outpatient (clinic-based, n = 581). All short forms are expressed as T scores with a mean of 50 and SD of 10.
Internal consistency (Cronbach α) of the 13 short forms ranged from 0.85 to 0.97. Correlations between short form and full-length item bank scores ranged from 0.88 to 0.99 (0.82-0.96 after removing common items from banks). Online respondents were asked whether they had any of 19 different chronic health conditions, and whether or not those reported conditions interfered with ability to function normally. All short forms, across physical, mental, and social health, were able to separate people who reported no health condition from those who reported 1-2 or 3 or more. In addition, scores on all 13 domains were worse for people who acknowledged being limited by the health conditions they reported, compared to those who reported conditions but were not limited by them.
These 13 brief measures of self-reported QOL are reliable and show preliminary evidence of concurrent validity inasmuch as they differentiate people based upon number of reported health conditions and whether those reported conditions impede normal function.
Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge density waves15 (CDW). A number of materials in the ...cuprate family, which includes the high transition-temperature (high-Tc) superconductors, show spin and charge density wave order.
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IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The application of magnetic fields to layered cuprates suppresses their high-temperature superconducting behaviour and reveals competing ground states. In widely studied underdoped YBa2Cu3O6+x ...(YBCO), the microscopic nature of field-induced electronic and structural changes at low temperatures remains unclear. Here we report an X-ray study of the high-field charge density wave (CDW) in YBCO. For hole dopings ∼0.123, we find that a field (B∼10 T) induces additional CDW correlations along the CuO chain (b-direction) only, leading to a three-dimensional (3D) ordered state along this direction at B∼15 T. The CDW signal along the a-direction is also enhanced by field, but does not develop an additional pattern of correlations. Magnetic field modifies the coupling between the CuO2 bilayers in the YBCO structure, and causes the sudden appearance of the 3D CDW order. The mirror symmetry of individual bilayers is broken by the CDW at low and high fields, allowing Fermi surface reconstruction, as recently suggested.
•Operational scale problems in hydrology require large scale models.•Data networks across large domains are inadequate for proper model calibration.•Process-based prediction is required for accurate ...extreme flow estimation.•Isotope tracers enable improved hydrologic storage simulation on long time scales.•Uptake by the community is best facilitated by increasing the accessibility of isotope-enabled models/codes.
Stable isotopes in water (oxygen-18 and deuterium) are hydrologic tracers, which have been embedded into both analytical mass balance and physically based continuous simulation models, improving hydrologic process partitioning and regional source identification, resulting in early climate change detection. Recent advances in the field of isotope hydrology have improved coordinated investment in global monitoring networks, invested in integrated modelling tools to support prediction and model evaluation, and expanded the scale of analyses possible. This review focuses on the applications of isotope tracers to large scale hydrologic modelling, its inception and evolution, and future directions for advancing this field with emphasis on the utility of isotope tracers for operational water resources prediction. The hydrologic community has begun to steer toward alternative hydrologic data due to the coinciding realities of limited data records and urgent data needs. Water resources infrastructure and management requires projections of water supply beyond the 50- to 100-year design life, with the general rule of flow frequency necessitating a 100- to 200-year assessment, however, there exist few data networks globally with records sufficient to support this kind of long-term assessment, and climate change is increasing the frequency of these extreme events. Historically, large-scale, and long time series simulation has meant less attention on process function (model fidelity) due to computational constraints, however, we argue that this may no longer be adequate under increasingly complex climate-hydrologic feedbacks, and integrated system models that incorporate human decisions, environmental health and socio-economic pressures. To expand the uptake of isotope tracers in practice, we emphasize their value for extreme quantile prediction under future projections and call for the community of practice to support data networks and accessibility, support peer review of large-domain (less data intensive) applications, and employ the FAIR (findable, accessible, interoperable, reusable) scientific principles. Though still an emerging scientific field, isotope hydrology has considerable value to the practitioner community with the proper education and training necessary to build confidence, underpinned by well developed and accessible tools for deployment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Understanding linkages between river chemistry and biological production in arctic coastal waters requires improved estimates of riverine nutrient export. Here we present the results of a synthesis ...effort focusing on relationships between watershed slope and seasonal concentrations of river-borne dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and nitrate ( NO 3 − ) around the pan-Arctic. Strong negative relationships exist between watershed slope and concentrations of DOC and DON in arctic rivers. Spring and summer concentration-slope relationships for DOC and DON are qualitatively similar, although spring concentrations are higher. Relationships for NO 3 − are more variable, but a significant positive relationship exists between summer NO 3 − concentrations and watershed slopes. These results suggest that watershed slope can serve as a master variable for estimating spring and summer DOC and DON concentrations, and to a lesser degree NO 3 − , from drainage areas where field data are lacking, thus improving our ability to develop pan-arctic estimates of watershed nutrient export.
Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray ...diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6.54 at its superconducting transition temperature ∼ 60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.
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