Steady-state Source Research Articles

Is there a simple and accessible solution to improve acute infarct core imaging? The utility of steady-state CT angiographic source images obtained from a delayed phase acquisition.

Early identification and quantification of core infarct is of importance in stroke management for treatment selection, prognostication, and complication prediction. Non-contrast computed tomography (CT) (NCCT) remains the primary tool, but it suffers from limited sensitivity and inter-rater variability; CT perfusion is inconsistently available and commonly blighted by movement artefact. We assessed the performance of a standardised form of CT angiographic source imaging (CTASI) obtained through addition of a delayed phase at 40 seconds post-contrast injection (DP40) following fast-acquisition CT angiography. Contrast resolution between ischaemic and normal grey matter (GM) was compared qualitatively and quantitatively to NCCT. Using Alberta Stroke Program Early CT Score (ASPECTS), DP40 low density was compared to NCCT and venous phase CT perfusion source images (CTPSI) and to 24-hour NCCT ASPECTS in patients with timely endovascular recanalisation (Thrombolysis In Cerebral Infarction 2C/3). Seventy-four patients with a proximal middle cerebral artery or terminal internal carotid artery occlusion were included. The mean attenuation difference between ischaemic and normal GM increased from 4.86+/-3.12 HU (NCCT) to 9.30+/-3.14 HU (DP40) (p < 0.0001). Subjective assessment by two raters revealed that DP40 improved ischaemic tissue conspicuity in 39 to 41 (78-82%) of cases (kappa 0.805, standard error 0.108, 95% confidence interval: 0.593-1.000). The correlation between ASPECTS on baseline imaging and eventual 24-hour ASPECTS improved from R = 0.7197 for NCCT to R = 0.9875 for DP40 (z = 7.89, p < 0.0001). The correlation between DP40 and venous phase CTPSI ASPECTS was 0.9681, p < 0.0001. DP40 CTASI represent a simple technique for improving detection and estimation of extent of ischaemia over NCCT and show close correlation with surrogate measures of infarct core.

Decoherence-enabled unconditional strongly sub-Poissonian squeezing

It is generally accepted that the role of quantum decoherence is to spoil the quantum superpositions and to yield the emergence of the classical behaviors from quantum mechanics. Contrary to the common knowledge of decoherence, we propose a scheme to generate a steady-state bright source of strongly sub-Poissonian squeezed light using the environmentally induced decoherence. The disappearance of the process of decoherence disables the generation of the squeezed state of the combination modes, while the presence of the decoherence results in the strongly nonclassical light source at the sub-shot-noise level and even near-perfect sub-Poissonian squeezed state of light. This excludes the use of the paradigm that the good insulation of a quantum system from its surrounding environment is highly desirable to explore its quantum property and fuel the growth of quantum information science. The interactions with the atom make no contribution to the preparation of squeezed light. These counterintuitive results are originated from the intrinsic quantum reservoir in the dressed-atom combination mode picture, which may open the door to exploring high levels of squeezing induced by the decoherence in the stationary regime. Published by the American Physical Society 2025

Measurement of sound power of steady-state sound sources: Comsol simulation study

Measurement of sound power of steady-state sound sources: Comsol simulation study

Effect of boron content of limestone on porosity coefficient measurements by neutron well logging using steadystate source

Effect of boron content of limestone on porosity coefficient measurements by neutron well logging using steadystate source

Performance enhancement in air gap membrane distillation using heat recovery configurations

Experimental investigations were conducted on an air gap membrane distillation (AGMD) unit to evaluate the impact of heat recovery on system performance. The study utilized a steady-state heat source in conjunction with a spiral air gap membrane module for water desalination. The process was implemented using two configurations aimed to minimize heat loss enhancing productivity, gain output ratio (GOR), and thermal efficiency. The experiments involved feedwater with salt concentrations ranging from 10,000 to 30,000 ppm. The measurements were recorded for inlet and outlet temperatures of the heat source, water productivity, and thermal efficiency at various coolant and water feed flow rates. These configurations effectively addressed critical technical challenges in thermal AGMD systems by optimizing heat recovery. The incorporation of heat recovery resulted in a significant increase in water productivity by 37.07 % compared to systems without heat recovery while maintaining the same initial heat input. The heat recovery in series (HRSS) and parallel (HRPS) configurations resulted in power consumption reductions of approximately 29.7 % and 23.1 %, respectively compared to the conventional configuration (CC) at a flow rate of 12 L/min. The levelized cost of water (LCOW) for the AGMD system was comprehensively evaluated and found to be $ 7.71 per cubic meter. This figure reflected the total cost of water production over the system's operational lifespan including capital expenditures, operating and maintenance costs, and energy consumption. The calculated LCOW provides a clear indicator of the system's economic viability, demonstrating the cost required to produce each cubic meter of water through the AGMD.

A novel steady-state method for measuring thermal conductivity of thermal interface materials with miniaturized thermal test chips

Thermal interface materials (TIMs) are widely used in electronic device packaging, and accurate characterization of their thermal properties is essential. However, existing TIM test platforms suffer from large size and inconsistency between copper-based test platforms and packaged silicon materials. To address these issues, this study proposes a method based on a miniaturized testing platform constructed using silicon-based thermal test chips (TTC). The thermal conductivity of several specimens was measured using steady-state heat source thermal transmission. The total thermal resistance, thermal contact resistance and thermal conductivity of several TIMs were evaluated through theoretical analysis and experimental verification. The thermal conductivity of several TIMs was tested using the proposed Back-to-Face and Back-to-Back TTC modules. The results demonstrate that this method exhibits high accuracy and can be used to characterize a wide range of TIMs.

Estimation and research of the temperature field models of large space spherical mesh shell structures under localized fire

This paper firstly investigated fire dynamics characteristics and the temperature field distributions of large space spherical mesh shell (SMS) structures under localized fire in FDS, and divided the temperature fields into plume region, smoke accumulation region and ceiling jet region. Based on the classical axisymmetric plume model, the predictive models for the steady-state and transient temperature fields in different fire regions for large space SMS structures were proposed in this paper. Thereafter, the proposed temperature models were compared with the simulated results and experimental test results by other scholars, and they were in good agreement. In order to further discover the realistic fire development progress and temperature distribution of large space fire, and validate the proposed temperature field models, this paper designed and conducted three full-scale large space fire tests (Test-1 ∼ Test-3) with different fire source powers in a large space building. Results showed that temperature fields of large space fires could be consisted of near-fire region (Flame region) and far-fire region (Plume region and Ceiling jet region). The steady-state fire source powers were tested for 443 kW, 886 kW, 1090 kW for Test-1, Test-2 and Test-3, respectively, while their maximum temperatures of the roof reached 75 °C, 105 °C and 120 °C. Based on McCaffrey plume model, we further proposed the transient temperature model in flame region for large space structures, and its accuracy was verified by the test results. Moreover, the proposed steady-state and transient temperature fields for large space SMS structures were compared with the tested temperature field data, and the tested and predicted temperature curves were generally in good agreement in plume and ceiling jet regions. Finally, the test results aimed to provide a scientific basis and reference for the fire safety and structural fire-resistant design of large space buildings.

Analysis of transient energy conversion performance improvement of thermoelectric generator with penetrating crack under pulsed heat source

To simulate the performance of a thermoelectric generator (TEG) in practical applications more accurately and comprehensively analyse the influence of transient heat source and crack on such devices, it is necessary to examine the transient performance of TEGs with cracks under periodic pulsed heat source. In this study, a three-dimensional nonlinear dynamic finite element model with thermal, electrical, and mechanical coupling was established, and the laws describing the macroscopic electrical energy output and thermal stress distribution were derived. The position of the maximum thermal stress changed as the crack size varied. When the crack field axis was increased from 0.2 mm to 1.8 mm, the total output energy increased by 14.4 %, whereas the thermal stress increased to 447 MPa. The total energy growth rate under pulsed heat source conditions reached 52.3 % (from 62.71 J to 95.52 J) compared with that of the steady-state heat source. However, the maximum thermal stress increased by 173.6 % (from 91 MPa to 249 MPa). The results show that the crack and pulsed heat source can effectively improve the electrical output performance of TEGs; however, their mechanical properties deteriorated. This study is useful in terms of predicting the performance of TEGs in practical applications more accurately.

Modelling indoor pollutant exposure from steady-state and pulse sources

Modelling indoor pollutant exposure from steady-state and pulse sources

Research on Voltage Coordinated and Stability Control of Condensers Based on Reactive Power Replacement

Abstract In this research, we investigated condenser voltage coordination and stability control systems by analyzing voltage coordinated control mode among excitation, voltage coordination and stability as well as automatic-voltage reactive power control systems. By using dynamic excitation regulation and steady-state regional voltage source control replacement, dynamic reactive power quickly output under fault condition as well as optimized regional reactive power under steady state were realized. The correctness and practicability of the proposed strategy was verified through engineering application. Adopting the reactive power displacement of voltage coordination control system to solve local voltage instability problem after UHV DC blocking. The proposed method realized multi-time scale emergency, recovery and steady-state control of the system under steady and dynamic states.

Quality assessment of the wide-angle detection option planned at the high-intensity/extended Q-range SANS diffractometer KWS-2 combining experiments and McStas simulations.

For a reliable characterization of materials and systems featuring multiple structural levels, a broad length scale from a few ångström to hundreds of nanometres must be analyzed and an extended Q range must be covered in X-ray and neutron scattering experiments. For certain samples or effects, it is advantageous to perform such characterization with a single instrument. Neutrons offer the unique advantage of contrast variation and matching by D-labeling, which is of great value in the characterization of natural or synthetic polymers. Some time-of-flight small-angle neutron scattering (TOF-SANS) instruments at neutron spallation sources can cover an extended Q range by using a broad wavelength band and a multitude of detectors. The detectors are arranged to cover a wide range of scattering angles with a resolution that allows both large-scale morphology and crystalline structure to be resolved simultaneously. However, for such analyses, the SANS instruments at steady-state sources operating in conventional monochromatic pinhole mode rely on additional wide-angle neutron scattering (WANS) detectors. The resolution must be tuned via a system of choppers and a TOF data acquisition option to reliably measure the atomic to mesoscale structures. The KWS-2 SANS diffractometer at Jülich Centre for Neutron Science allows the exploration of a wide Q range using conventional pinhole and lens focusing modes and an adjustable resolution Δλ/λ between 2 and 20%. This is achieved through the use of a versatile mechanical velocity selector combined with a variable slit opening and rotation frequency chopper. The installation of WANS detectors planned on the instrument required a detailed analysis of the quality of the data measured over a wide angular range with variable resolution. This article presents an assessment of the WANS performance by comparison with a McStas [Willendrup, Farhi & Lefmann (2004). Physica B, 350, E735-E737] simulation of ideal experimental conditions at the instrument.

Evaluation of possible network states in the future German hydrogen network 2025 and 2030

This study provides insights into possible future gas network states in the initial German hydrogen network by 2025 and 2030, as per the German transmission system operators Network Development Plan Gas 2020. Not only is the overall transport feasibility assessed, but also possible operating conditions in terms of pressures, flows and velocities. To that end, two data sets for the network topology by 2025 and 2030 were created. A heuristic, semi-random nomination generation is employed to generate 100 consistent steady-state source–sink nominations for both years, based on collected production/consumption bounds. The authors employ a so-called nomination-validation model (MILP-formulation) for the solution of the resulting transport problem(s). For the evaluation of pipeline flow velocities, the authors combine those solutions with a hypothesis on limiting flow speeds suggested in a German technical journal. The analysis exhibits feasibility among all generated nominations with respect to flows and admissible velocities.

Cavity QED systems for steady-state sources of Wigner-negative light

We present a theoretical investigation of optical cavity quantum electrodynamics (cavity QED) systems, as described by the driven, open Jaynes–Cummings model and some of its variants, as potential sources of steady-state Wigner-negative light. We consider temporal modes in the continuous output field from the cavity and demonstrate pronounced negativity in their Wigner distributions for experimentally relevant parameter regimes. We consider models of both single and collective atomic spin systems, and find a rich structure of Wigner-distribution negativity as the spin size is varied. We also demonstrate an effective realization of all of the models considered using just a single 87Rb atom and based upon combinations of laser- and laser-plus-cavity-driven Raman transitions between magnetic sublevels in a single ground hyperfine state.

Non-steady state thermometry with optical diffraction tomography.

Label-free thermometry is a pivotal tool for many disciplines. However, most current approaches are only suitable for planar heat sources in steady state, thereby restricting the range of systems that can be reliably studied. Here, we introduce pump probe-based optical diffraction tomography (ODT) as a method to map temperature precisely and accurately in three dimensions (3D) at the single-particle level. To do so, we first systematically characterize the thermal landscape in a model system consisting of gold nanorods in a microchamber and then benchmark the results against simulations and quantitative phase imaging thermometry. We then apply ODT thermometry to resolve thermal landscapes inaccessible to other label-free approaches in the form of nonplanar heat sources embedded in complex environments and freely diffusing gold nanorods in a microchamber. Last, we foresee that our approach will find many applications where routine thermal characterization of heterogeneous nanoparticles samples in 3D or in non-steady state is required.

An Improved Strategy of Grid-Forming DFIG Based on Disturbance Rejection Stator Flux Control

Grid-forming (GFM) control are promising for doubly fed induction generator-based wind turbines (DFIG -Based WTs) due to its grid-support ability and stable operation when connected to weak grid. However, GFM-DFIG might suffer from instability under symmetrical grid fault, if its electromagnetic and synchronous dynamics are poor. Therefore, an improved strategy of GFM-DFIG based on disturbance rejection stator flux control (DRSFC) is proposed in this paper. The DRSFC consists of a PI-based rotor-current loop and an active disturbance rejection control (ADRC)-based stator-flux outer loop, and both the better electromagnetic performance and the steady-state voltage source operation are achieved. Besides, impacts of DRSFC on GFM-DFIG are exposed via small-signal and large-signal analysis, and the potential inertia in the inner control loops is revealed. It is suggested that this potential inertia is reshaped by DRSFC, so the impact of inner control loop on the synchronization of GFM-DFIG can be quantitatively studied and controlled. On this basis, a pair of asymmetrical compensation are designed to improve its electromagnetic decay and synchronous dynamic. Finally, experiments are carried out to verify the effectiveness of proposed strategy.

Fast calculation of the technical shallow geothermal energy potential of large areas with a steady-state solution of the finite line source

Shallow geothermal energy systems may play a significant role in the energy transition as they can strongly reduce the carbon emissions from the residential heating and cooling sector. For urban and rural planning, policy making, and the development of regulations, regional scale estimations of the heating potential of borehole heat exchangers (BHEs) are required. For such regional estimations of the technical geothermal potential the thermal interference between BHEs is a crucial parameter to take into account as it can strongly reduce the heat extraction rate in borehole fields with a high BHE density. Here, we propose an analytical solution of the steady-state finite line source solution to calculate thermal response factors, or g-functions, within large BHE fields with variable distances between, and lengths of, boreholes. We show that the methodology can be used to rapidly calculate the thermal interference of boreholes on a regional scale and apply it to estimate the technical shallow geothermal potential of the German state of Baden-Württemberg. The results highlight areas where BHEs can offer a good alternative to fossil fuel-based heating options and will be used by municipalities within the study area for the development of local carbon neutral heating plans.

Short-term variation in Mars atmospheric methane concentrations driven by barometric pumping

Measurements of atmospheric methane by the Curiosity rover's SAM-TLS instrument are providing evidence of seasonality and diurnal variation in concentration. Given methane's short atmospheric lifetime relative to geological timescales, its presence implies a replenishing source, and the observed variation demands the proposition of a modulation mechanism. This paper focuses on the modulation mechanism on a diurnal scale, extending earlier modeling of seasonal variation. Our modeling shows that barometric pumping driven by both diurnal and seasonal variation of atmospheric pressure, along with possible adsorption and desorption of methane in the shallow subsurface driven by temperature and pressure change, can explain the variation in methane concentration. In the model, an active, continuous, steady-state deep source of methane is assumed, and carbon dioxide serves as the carrier gas for drawing methane and possible trace gaseous constituents into the atmosphere.

Energy and exergy analysis of phase change material based thermoelectric generator with pulsed heat sources

Previous studies focus on the generation capacity of phase change material based thermoelectric generator (PCM-TEG) under a steady-state heat source or single pulsed heat source, which cannot fully reflect the dynamic characteristics of TEG under a diversified actual heat source. Meanwhile, the actual heat sources have unstable characteristics of intermittence and fluctuation, resulting in troubles for TEG to maintain effective thermal management and stable generation. In this work, a three-dimensional transient numerical model of PCM-TEG is proposed to characterize its energy harvesting process under multiple pulsed heat sources, including square, triangular, linear and sinusoidal patterns. The effect principle of heat fluxes and heat source periods on PCM-TEG is sensitively performed, aiming to detect the evolution laws of the temperature field and electric field. The energy and exergy analysis of PCM-TEG is determined to indicate its transmission and conversion process. A comparison analysis of PCM-TEG and TEG is carried out to appreciate the thermal management of PCM from temperature difference and failure-free cycle times. The power generation coupling mechanism of PCM-TEG is further developed concerning the phase transition process and power generation process. The results demonstrate that the temperature difference and output power of PCM-TEG change periodically with the pulsed heat sources. The electrical energy and exergy efficiencies of PCM-TEG under square pulsed heat source are 0.10% and 0.45%, higher than other heat sources. Simultaneously, the maximum output power and the electrical energy efficiency of PCM-TEG can be improved by 173.29% and 80% respectively with the enhanced heat flux. Furthermore, although the transient power generation capacity of TEG is weakened by integrating PCM on the hot side, it can alleviate the thermal fatigue of thermoelectric device and meet its thermal management requirements. This paper is informative to understand the dynamics characteristics and power generation coupling mechanism of PCM-TEG for energy harvesting.

NGC 1068 constraints on neutrino-dark matter scattering

The IceCube collaboration has observed the first steady-state point source of high-energy neutrinos, coming from the active galaxy NGC 1068. If neutrinos interacted strongly enough with dark matter, the emitted neutrinos would have been impeded by the dense spike of dark matter surrounding the supermassive black hole at the galactic center, which powers the emission. We derive a stringent upper limit on the scattering cross section between neutrinos and dark matter based on the observed events and theoretical models of the dark matter spike. The bound can be stronger than that obtained by the single IceCube neutrino event from the blazar TXS 0506+056 for some spike models.

Selected advances in small-angle scattering and applications they serve in manufacturing, energy and climate change.

Innovations in small-angle X-ray and neutron scattering (SAXS and SANS) at major X-ray and neutron facilities offer new characterization tools for researching materials phenomena relevant to advanced applications. For SAXS, the new generation of diffraction-limited storage rings, incorporating multi-bend achromat concepts, dramatically decrease electron beam emittance and significantly increase X-ray brilliance over previous third-generation sources. This results in intense X-ray incident beams that are more compact in the horizontal plane, allowing significantly improved spatial resolution, better time resolution, and a new era for coherent-beam SAXS methods such as X-ray photon correlation spectroscopy. Elsewhere, X-ray free-electron laser sources provide extremely bright, fully coherent, X-ray pulses of <100 fs and can support SAXS studies of material processes where entire SAXS data sets are collected in a single pulse train. Meanwhile, SANS at both steady-state reactor and pulsed spallation neutron sources has significantly evolved. Developments in neutron optics and multiple detector carriages now enable data collection in a few minutes for materials characterization over nanometre-to-micrometre scale ranges, opening up real-time studies of multi-scale materials phenomena. SANS at pulsed neutron sources is becoming more integrated with neutron diffraction methods for simultaneous structure characterization of complex materials. In this paper, selected developments are highlighted and some recent state-of-the-art studies discussed, relevant to hard matter applications in advanced manufacturing, energy and climate change.