Flux Amplitude Research Articles

Increasing summer net CO<sub>2</sub> uptake in high northern ecosystems inferred from atmospheric inversions and comparisons to remote-sensing NDVI

Abstract. Warmer temperatures and elevated atmospheric CO2 concentrations over the last several decades have been credited with increasing vegetation activity and photosynthetic uptake of CO2 from the atmosphere in the high northern latitude ecosystems: the boreal forest and arctic tundra. At the same time, soils in the region have been warming, permafrost is melting, fire frequency and severity are increasing, and some regions of the boreal forest are showing signs of stress due to drought or insect disturbance. The recent trends in net carbon balance of these ecosystems, across heterogeneous disturbance patterns, and the future implications of these changes are unclear. Here, we examine CO2 fluxes from northern boreal and tundra regions from 1985 to 2012, estimated from two atmospheric inversions (RIGC and Jena). Both used measured atmospheric CO2 concentrations and wind fields from interannually variable climate reanalysis. In the arctic zone, the latitude region above 60° N excluding Europe (10° W–63° E), neither inversion finds a significant long-term trend in annual CO2 balance. The boreal zone, the latitude region from approximately 50–60° N, again excluding Europe, showed a trend of 8–11 Tg C yr−2 over the common period of validity from 1986 to 2006, resulting in an annual CO2 sink in 2006 that was 170–230 Tg C yr−1 larger than in 1986. This trend appears to continue through 2012 in the Jena inversion as well. In both latitudinal zones, the seasonal amplitude of monthly CO2 fluxes increased due to increased uptake in summer, and in the arctic zone also due to increased fall CO2 release. These findings suggest that the boreal zone has been maintaining and likely increasing CO2 sink strength over this period, despite browning trends in some regions and changes in fire frequency and land use. Meanwhile, the arctic zone shows that increased summer CO2 uptake, consistent with strong greening trends, is offset by increased fall CO2 release, resulting in a net neutral trend in annual fluxes. The inversion fluxes from the arctic and boreal zones covering the permafrost regions showed no indication of a large-scale positive climate–carbon feedback caused by warming temperatures on high northern latitude terrestrial CO2 fluxes from 1985 to 2012.

On the sensitivity of the diurnal cycle in the Amazon to convective intensity.

Climate and reanalysis models contain large water and energy budget errors over tropical land related to the misrepresentation of diurnally forced moist convection. Motivated by recent work suggesting that the water and energy budget is influenced by the sensitivity of the convective diurnal cycle to atmospheric state, this study investigates the relationship between convective intensity, the convective diurnal cycle, and atmospheric state in a region of frequent convection—the Amazon. Daily, 3‐hourly satellite observations of top of atmosphere (TOA) fluxes from Clouds and the Earth's Radiant Energy System Ed3a SYN1DEG and precipitation from Tropical Rainfall Measuring Mission 3B42 data sets are collocated with twice daily Integrated Global Radiosonde Archive observations from 2002 to 2012 and hourly flux tower observations. Percentiles of daily minimum outgoing longwave radiation are used to define convective intensity regimes. The results indicate a significant increase in the convective diurnal cycle amplitude with increased convective intensity. The TOA flux diurnal phase exhibits 1–3 h shifts with convective intensity, and precipitation phase is less sensitive. However, the timing of precipitation onset occurs 2–3 h earlier and the duration lasts 3–5 h longer on very convective compared to stable days. While statistically significant changes are found between morning atmospheric state and convective intensity, variations in upper and lower tropospheric humidity exhibit the strongest relationships with convective intensity and diurnal cycle characteristics. Lastly, convective available potential energy (CAPE) is found to vary with convective intensity but does not explain the variations in Amazonian convection, suggesting that a CAPE‐based convective parameterization will not capture the observed behavior without incorporating the sensitivity of convection to column humidity.

Flow and heat transfer during a single drop impact on a liquid film

ABSTRACTA two-dimensional incompressible laminar computational model was established to analyze flow and heat transfer characteristics during a single liquid drop impinging onto a liquid film, with an underneath surface of relatively low temperature. Using the coupled level set and volume of fluid method, the gas–liquid interface at different time sequences can be obtained clearly. Concerning the heat transfer process, three different factors including impact velocity, film thickness, and drop diameter were discussed. Results indicate that liquid inside the film can be classified as three zones: the impact zone, the transition zone, and the static zone, specifically according to different heat flux. Average surface heat flux can be increased by increasing impact velocity, while effects of film thickness and drop diameter are minor. Corresponding mechanisms were interpreted as well. For heat flux distribution in the impact and transition zones, both film thickness and drop diameter influence the distribution greatly. With an increment in film thickness and drop diameter, heat flux in the impact zone decreases, while heat flux in the transition zone appears to be an opposite trend. Also in the transition zone, the fluctuation amplitude of the heat flux rises as the two factors are reduced.

Optimization Design of Bearingless Permanent-Magnet Slice Motor

The parameter and distribution of air-gap flux density determined by structures and methods of permanent-magnet rotor magnetization have effects on the performance of suspension forces and torque in a bearingless permanent-magnet slice motor (BPMSM) directly. In this paper, different rotor structures and magnetization methods are analyzed for the BPMSM. Based on the finite-element analysis, the optimum length ratio of rotor magnetic yoke d r and l r is calculated in different magnetizations to get the maximum flux density. Then the radial suspension forces with maximum air-gap flux density in different structures and rotor magnetizations are compared for the BPMSM. The simulation and experiment results show that the amplitude and sinusoidal characteristic of air-gap flux density are improved with parallel magnetized ring-shaped rotor. Furthermore, the BPMSM with parallel magnetized ring-shaped rotor is easily controlled and has a good suspension and speed regulation performance.

Design of Nb3Sn Wiggler Magnets for the Compact Linear Collider and Manufacturing of a Five-Coil Prototype

To achieve the luminosity requirements of the Compact Linear Collider (CLIC) at the collision point, damping rings (DRs) equipped with superconducting wiggler magnets should be used to produce ultralow emittance with high bunch charge. Although Nb-Ti wigglers meet the specifications for CLIC DRs, the more challenging Nb3Sn technology could be used to increase the magnetic flux density amplitude in the gap and reduce the total length of wigglers in the DRs. To test the Nb3Sn technology, a small wiggler prototype is under design and will be built and tested at CERN. Magnetic calculations concerning the selection of the main wiggler's parameters are presented in this paper, which include the optimization of the main coil dimensions and the period length, in order to fulfill the normalized emittance and intrabeam scattering effect constraints, while decreasing the amount of wigglers in the DRs. Another advantage of using Nb3Sn, instead of Nb-Ti, as superconducting material is the possibility of increasing the working margin. Several scenarios well suited for CLIC damping wigglers, in which the working point is less than 80% of the magnet's current limit, are addressed in this work. In addition, the description of the manufacturing process and the current status of the Nb3Sn prototype fabrication are presented.

Field-Weakening Control for Efficiency Optimization in a DFIG Connected to a DC-Link

The field-weakening operation of a doubly fed induction generator (DFIG) connected to a dc-link is analyzed in this paper, in order to optimize the efficiency. In the considered DFIG-dc system, the stator feeds a constant-voltage dc link by a diode bridge, and the rotor current is controlled using a voltage-source inverter connected to the same dc link. Since the stator voltage amplitude is imposed by the dc-link, a variation in stator flux magnitude results in a frequency change. However, in this system, a stator frequency variation over a wide range can be accepted, if the rated flux is not exceeded. Thus, the stator flux amplitude can be adjusted through the magnetization current component by the voltage-source inverter and according to the load level, in order to reduce losses in the machine and in the inverter. This paper presents an optimization analysis and simplified formulae determining the optimal reference magnetization current in the control of the system. Conversely to field weakening in conventional drives, in this case, the enabling of field weakening control is not dependent on rotor speed, but depends on the reference torque. The proposed optimal control is validated through simulation and experimental results.

Multi-channel control circuit for real-time control of events in Aditya tokamak

Tokamak plasma is prone to many random events having potential for causing severe damages to the machine, such as disruptions, production and elimination of high-energy runaway electrons etc. These events can be mitigated by obtaining pre-cursor signal leading to these events and then taking proper measures just before their onset to avoid their happenings, like disruptions can be mitigated by massive gas injection or putting a bias voltage on an electrode placed inside the plasma, the runaways can be mitigated by gas injection and by applying specific magnetic fields. Hence for real time control of these events, the pre-cursors should be electronically recorded and the mitigation techniques should be initiated by sending triggers to their individual operational systems. To implement these methodologies of real-time controlling of events in Aditya Tokamak, a low cost multi-channel Micro-Controller based timing circuit is designed and developed in-house. This circuit first compares the precursor signals fed into it with the pre-set values and gives a trigger output whenever the signals overshoot the pre-set values. The circuit readies itself for operation along with start of the tokamak discharge and waits up to an initial pre-determined delay and then initiates a trigger at the time of overshooting of precursor signal. The circuit is fully integrated and assembled in compact enclosure with local LCD for threshold and initial trigger-delay monitoring and indicators for full stand-alone operation. The system has been successfully tested in the disruption control experiment with two different techniques viz., electrode biasing and ICRH pulse techniques in Aditya tokamak. The increase in MHD oscillation amplitude and the gas puff induced Hα intensity increase are used as a precursor for triggering the electrode bias and ICR pulse respectively in real time disruption control application. The runaway (RE) mitigation during disruption phase with local vertical field perturbation (LVF) in real time feedback mode is performed using this circuit, where runaway flux amplitude beyond pre-set threshold is used as a precursor for triggering the LVF current pulse. The detailed design features and results will be described in this paper. In addition to that the circuit is also used for single loop online plasma electron density control as well as position control.

Europa’s small impactor flux and seismic detection predictions

Europa is an attractive target for future lander missions due to its dynamic surface and potentially habitable sub-surface environment. Seismology has the potential to provide powerful new constraints on the internal structure using natural sources such as faults or meteorite impacts. Here we predict how many meteorite impacts are likely to be detected using a single seismic station on Europa to inform future mission planning efforts. To this end, we derive: (1) the current small impactor flux on Europa from Jupiter impact rate observations and models; (2) a crater diameter versus impactor energy scaling relation for icy moons by merging previous experiments and simulations; and (3) scaling relations for seismic signal amplitudes as a function of distance from the impact site for a given crater size, based on analogue explosive data obtained on Earth’s ice sheets. Finally, seismic amplitudes are compared to predicted noise levels and seismometer performance to determine detection rates. We predict detection of 0.002–20 small local impacts per year based on P-waves travelling directly through the ice crust. Larger regional and global-scale impact events, detected through mantle-refracted waves, are predicted to be extremely rare (10−8–1 detections per year), so are unlikely to be detected by a short duration mission. Estimated ranges include uncertainties from internal seismic attenuation, impactor flux, and seismic amplitude scaling. Internal attenuation is the most significant unknown and produces extreme uncertainties in the mantle-refracted P-wave amplitudes. Our nominal best-guess attenuation model predicts 0.002–5 local direct P detections and 6 × 10−6–0.2 mantle-refracted detections per year. Given that a plausible Europa landed mission will only last around 30 days, we conclude that impacts should not be relied upon for a seismic exploration of Europa. For future seismic exploration, faulting due to stresses in the rigid outer ice shell is likely to be a much more viable mechanism for probing Europa’s interior.

An Improved Design Method of High Efficiency Contactless Power Transmission in Ultrasonic Vibration System

To improve the efficiency of contactless power transmission (CPT) and the operation stability of ultrasonic vibration system, an improved design method for key parts of the contactless power transmission system was proposed and studied. By integrating both inductor model and mutual inductance model, as well as considering the fringing flux effect introduced by the air gap, this design method would be more accurate and reasonable. Considering constraint conditions, such as the operating flux density of the core, mutual inductance between primary and secondary coils, electrical signals loaded on ultrasonic vibrator, the coils and cores were designed. Simulation and experimental studies which were developed on flux density, mutual inductance and amplitude output ability of the system, verified that the key parts of CPT system could stay stable during operation and the CPT system was able to transfer ultrasonic energy efficiently.

A New Predictive Direct Torque Control Method for Improving Both Steady-State and Transient-State Operations of the PMSM

In this paper, a new predictive direct torque control (DTC) method is proposed, improving the dynamic response of the classical DTC and reducing the torque- and flux-ripples through a voltage vector with an optimal phase. In the transient state, the voltage vector phase is selected in a manner where the fastest dynamic response is achieved, while in the steady state, this phase is selected in a manner where the stator flux amplitude reaches its commanding value at the end of the control cycle. In the steady state, the selected vector is applied to the motor with an optimal time duration calculated to achieve the minimum torque ripple. The five-segment space-vector modulation is used to synthesize the voltage vector, where a fixed switching frequency is obtained. To investigate the effectiveness of the proposed method, steady-state and transient-state performances are tested in the MATLAB software and in practice. Both the simulation and experimental results confirm that the proposed method reduces the torque and flux ripples effectively while improving the dynamic response of the classical DTC method. The comparative investigation of the proposed method with the recent DTC methods indicates that the proposed method has lower ripples in the steady state and a faster dynamic response in the transient state.

High‐stability organic red‐light photodetector for narrowband applications

AbstractRed‐light photodetectors without filters are in urgent need for narrowband applications such as full‐color imaging and multi‐output visible light communication (VLC). However, their development is hindered by the lack of small‐band‐gap and narrowband response materials. Without wavelength filters, a new type of photodetector with a simple single‐layer architecture is developed, based on a stable small‐band‐gap squarylium dye and characterized by a detectivity peak at 680 nm and full width at half maximum of 80 nm. The device, which exhibits high stability in air and humid conditions, shows a significantly low dark current of ∼2 nA·cm−2 at −2 V and high specific detectivity of 3.2 × 1012 Jones. The response current ratio of the device to red, green, and blue lights with a luminous flux amplitude ratio of 3:6:1 (standard ratio for white light) is 100:12:1.1. These properties indicate that the squarylium dye red‐light photodetectors are promising for VLC and other narrowband optoelectronic applications. image

The neuroendocrine-immune regulatory network characterized as simple structure but complex function in oyster Crassostrea gigas

The characteristics of the divertor particle and heat fluxes are investigated during ELM bursts in ELMy H-mode plasmas with the lower single null (LSN) configuration in Korea Superconducting Tokamak Advanced Research (KSTAR). The particle and heat fluxes are evaluated from the electric probe measurements at the divertor region. It is found that the peak amplitude of the divertor flux during an ELM burst obtained near the outer strike point (OSP) decreases up to about 20% as the ELM frequency increases by a factor of ∼6.5 due to the ELM mitigation and the plasma shaping, which is similar to the trend of the amplitude versus the frequency of the ELM observed in other tokamaks. The ELMs are mitigated by using several methods as magnetic perturbation (MP) field, supersonic molecular beam injection (SMBI) and electron cyclotron heating (ECH) at the edge region. In addition, the particle flux, evaluated at the far scrape-off layer (SOL) region, is less than 1% of the divertor particle flux. In this work, results from the experimental investigations of particle and heat fluxes during ELM bursts from the electric probe measurements at the divertor and far SOL regions are presented.

Evaluating CMIP5 ocean biogeochemistry and Southern Ocean carbon uptake using atmospheric potential oxygen: Present‐day performance and future projection

AbstractObserved seasonal cycles in atmospheric potential oxygen (APO ~ O2 + 1.1 CO2) were used to evaluate eight ocean biogeochemistry models from the Coupled Model Intercomparison Project (CMIP5). Model APO seasonal cycles were computed from the CMIP5 air‐sea O2 and CO2 fluxes and compared to observations at three Southern Hemisphere monitoring sites. Four of the models captured either the observed APO seasonal amplitude or phasing relatively well, while the other four did not. Many models had an unrealistic seasonal phasing or amplitude of the CO2 flux, which in turn influenced APO. By 2100 under RCP8.5, the models projected little change in the O2 component of APO but large changes in the seasonality of the CO2 component associated with ocean acidification. The models with poorer performance on present‐day APO tended to project larger net carbon uptake in the Southern Ocean, both today and in 2100.

Numerical study of the spatial distribution of the M internal tides in the Strait of Sicily

The present study investigates the spatial distribution of the M internal tide in the Strait of Sicily using a three-dimensional sigma coordinate model, the Regional Ocean Modeling System. Realistic topography and stratification from existing observational data were used. The numerical simulations show that there are three distinct sites of strong M internal tide generation, namely the western sill of the Adventure Bank, northwest of Sicily and north of Pantelleria isle. The conversion rate of energy from the M surface to internal tide integrated over the whole model domain amounts to 47.5 MW, 75% of which are found to be generated over the three prominent topographic features mentioned above. The depth- integrated baroclinic energy flux depicts the propagation away from these sites, particularly toward the north and southwest. The maximum flux amplitudes are found in the three main generation sites identified, with the largest value occurring at the narrowest passage through the western sill. A comparison between the model and current-meter measurements at two stations shows reasonable agreement for different depths. The similarities in the spatial distribution of the baroclinic energy flux divergence and the barotropic forcing suggest that the generation of the M internal tide in the Strait of Sicily results primarily from barotropic tidal flow over sloping topography.

Study on divertor particle and heat fluxes from electric probe measurements during ELMy H-modes in KSTAR

The characteristics of the divertor particle and heat fluxes are investigated during ELM bursts in ELMy H-mode plasmas with the lower single null (LSN) configuration in Korea Superconducting Tokamak Advanced Research (KSTAR). The particle and heat fluxes are evaluated from the electric probe measurements at the divertor region. It is found that the peak amplitude of the divertor flux during an ELM burst obtained near the outer strike point (OSP) decreases up to about 20% as the ELM frequency increases by a factor of ∼6.5 due to the ELM mitigation and the plasma shaping, which is similar to the trend of the amplitude versus the frequency of the ELM observed in other tokamaks. The ELMs are mitigated by using several methods as magnetic perturbation (MP) field, supersonic molecular beam injection (SMBI) and electron cyclotron heating (ECH) at the edge region. In addition, the particle flux, evaluated at the far scrape-off layer (SOL) region, is less than 1% of the divertor particle flux. In this work, results from the experimental investigations of particle and heat fluxes during ELM bursts from the electric probe measurements at the divertor and far SOL regions are presented.

Transient Dynamics of a Superconducting Nonlinear Oscillator

We investigate the transient dynamics of a lumped-element oscillator based on a dc superconducting quantum interference device (SQUID). The SQUID is shunted with a capacitor forming a nonlinear oscillator with resonance frequency in the range of several GHz. The resonance frequency is varied by tuning the Josephson inductance of the SQUID with on-chip flux lines. We report measurements of decaying oscillations in the time domain following a brief excitation with a microwave pulse. The nonlinearity of the SQUID oscillator is probed by observing the ringdown response for different excitation amplitudes while the SQUID potential is varied by adjusting the flux bias. Simulations are performed on a model circuit by numerically solving the corresponding Langevin equations incorporating the SQUID potential at the experimental temperature and using parameters obtained from separate measurements characterizing the SQUID oscillator. Simulations are in good agreement with the experimental observations of the ringdowns as a function of applied magnetic flux and pulse amplitude. We observe a crossover between the occurrence of ringdowns close to resonance and adiabatic following at larger detuning from the resonance. We also discuss the occurrence of phase jumps at large amplitude drive. Finally, we briefly outline prospects for a readout scheme for superconducting flux qubits based on the discrimination between ringdown signals for different levels of magnetic flux coupled to the SQUID.

Dynamics of ion temperature gradient turbulence and transport with a static magnetic island

Understanding the interaction mechanisms between large-scale magnetohydrodynamic instabilities and small-scale drift-wave microturbulence is essential for predicting and optimizing the performance of magnetic confinement based fusion energy experiments. We report progress on understanding these interactions using both analytic theory and numerical simulations performed with the BOUT++ [Dudson et al., Comput. Phys. Commun. 180, 1467 (2009)] framework. This work focuses upon the dynamics of the ion temperature gradient instability in the presence of a background static magnetic island, using a weakly electromagnetic two-dimensional five-field fluid model. It is found that the island width must exceed a threshold size (comparable with the turbulent correlation length in the no-island limit) to significantly impact the turbulence dynamics, with the primary impact being an increase in turbulent fluctuation and heat flux amplitudes. The turbulent radial ion energy flux is shown to localize near the X-point, but does so asymmetrically in the poloidal dimension. An effective turbulent resistivity which acts upon the island outer layer is also calculated and shown to always be significantly (10×–100×) greater than the collisional resistivity used in the simulations.

Passive Study of Energy Efficiency of a Building with PCM on the Roof during Summer in Casablanca

Energy efficiency in buildings is today a prime objective for energy policy at national and international levels. Because the residential and commercial energy consumption has steadily increased reaching figures between 20% and 40%. The use of thermal insulation of the building envelope is one of the most currently requested solutions to reduce this energy consumption. Phase Change Materials (PCM) have received increased attention due to their ability to store large amounts of thermal energy within narrow temperature ranges. This property makes them ideal for storage of passive heat in the building envelopes. An experimental study was conducted to analyze the influence of PCM in the construction of exterior walls. Two test cells are constructed in the Faculty of Science Ain Chock, Casablanca. One is equipped with a 0.56 cm layer of PCM on its roof while the second is a reference cell without PCM. The results presented for the period from 8th to 10th July 2014 show that the integration of PCM layer reduces the amplitude of instantaneous heat flux through the horizontal wall. The indoor and the internal vertical wall temperatures, in the case of the cell with PCM, are relatively decreased compared to those of the reference one. For example, the maximum deviation between the indoor temperatures of the cubicles is not more than 1.5℃ while the one on the west faces reaches 3℃ by mid day. Also the inclusion of a layer of PCM shifts the time of peak load and discharge.

Virtual Signal Injection Based Direct Flux Vector Control of IPMSM Drives

This paper describes a novel virtual signal injection-based direct flux vector control for the maximum torque per ampere (MTPA) operation of the interior permanent magnet synchronous motor (IPMSM) in the constant torque region. The proposed method virtually injects a small high-frequency current angle signal for tracking the optimal flux amplitude of the MTPA operation. This control scheme is not affected by the accuracy of the flux observer and is independent of machine parameters in tracking the MTPA points and will not cause additional iron loss, copper loss, and torque ripple as a result of real signal injection. Moreover, by employing a bandpass filter with a narrow frequency range the proposed control scheme is also robust to current and voltage harmonics, and load torque disturbances. The proposed method is verified by simulations and experiments under various operating conditions on a prototype IPMSM drive system.

An evaluation of atmospheric rivers over the North Pacific in CMIP5 and their response to warming under RCP 8.5

AbstractLandfalling atmospheric rivers over the North Pacific are evaluated in historical (1980–2005) simulations from 28 models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and compared to the Modern‐Era Retrospective Analysis for Research and Applications and ERA‐Interim reanalyses. Landfalling dates are identified as having spatially elongated high wind and moisture features in physical proximity to the coastline. Model performance relative to reanalysis is found to be quite variable. The majority can resolve the spatial structure of landfalling events, but few correctly resolve the frequency distribution, interannual variability in number and amplitude of moisture flux, and median landfalling latitude. The response of a subset of high‐performing models to projected warming at the end of the 21st century is investigated using Representative Concentration Pathway (RCP) 8.5 (2070–2100) projections. Selected models show a broadening of the frequency distribution, with the largest increase in frequency occurring equatorward of peak historical frequency. While there is a robust increase in AR‐related moisture transport compared to the historical period, this increase is not linked to more extreme AR events within the context of the projected future climate. The occurrence of years with many AR dates is greater at the end of the 21st century than during the historical period. The equatorward increase in peak historical frequency is colocated with increases in the 850 and 250 hPa zonal winds. The response in moisture flux to warming is mostly thermodynamic, but equatorward of its peak distribution, it is dominated by a dynamic response.