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This study focuses on the energy-efficient separation process of styrene monomer, avoiding the formation of an azeotrope by using a vacuum distillation, derived from the pyrolysis of waste polystyrene (PS). The direct-indirect sequence, which positions the separation column of ethylbenzene and styrene monomer as the last step, exhibited a 30% reduction in the total utility consumption and a 37% reduction in the total annual cost compared to that of the direct-direct sequence that separates lighter components sequentially. A dividing wall column (DWC) configuration derived from the direct-indirect sequence showed the most significant reduction of 40% in utility consumption. However, when the feed capacity was low, the increased capital cost of DWC resulted in a total annual cost similar to that of the direct-indirect sequence. As the capacity of the entire distillation system increased, the reduction in the total operating cost of the DWC was amplified, indicating the advantages of using the DWC in high product throughputs from both energy and economic perspectives. Therefore, implementing the DWC in large-scale PS recycling processes demonstrates superior performance compared to the conventional distillation process, resulting in a more streamlined process with substantial energy savings and CO2emissions.

This paper presents a novel design and control method of an active suspension system using a linear pump control–based hydraulic system for a cost-effective application. Various active suspension systems have been proposed and applied to vehicles due to its ability to improve ride comfort and handling performance even though these active suspension systems are not popular because of their complexity, high cost, heavyweight, and low power efficiency. A new type of active suspension actuator system was designed and validated herein based on the methods of actuator sizing and modified control scheme to address the aforementioned issues. System power capability has been analyzed under various dynamics and road conditions. Active suspension actuator components have been designed based on the results. The electro-hydraulic system is powered by a battery to reduce the energy consumption of the system; hence, it is operated by torque on demand. A double-acting linear hydraulic motor pump with a dual rack and pinion has been proposed for hydraulic force control with a simple on/off switch operation. The actuator force has been controlled by continuous linear motor pump displacement control via torque control using a three-phase synchronous brushless alternative current motor. Dynamic performance evaluation of the actuator system has been conducted using AMESIM and actual rig test. Active height and roll control algorithms for the enhancement of vehicle dynamics considering actuator dynamics have also been developed and validated through the rig and real vehicle tests. The evaluation results showed that the linear motor pump–based active suspension system performs as well as the previous complicated hydraulic active suspension system. The new active system proposed in this study was able to improve the vehicle dynamics using cost-effective actuation system significantly.

ABSTRACTQuercetin is a flavonol belonging to the flavonoid group of polyphenols. Quercetin is reported to have a variety of biological functions, including antioxidant, pigment, auxin transport inhibitor and root nodulation factor. Additionally, quercetin is known to be involved in bacterial pathogen resistance in Arabidopsisthrough the transcriptional increase of pathogenesis-related(PR) genes. However, the molecular mechanisms underlying how quercetin promotes pathogen resistance remain elusive. In this study, we showed that the transcriptional increases of PRgenes were achieved by the monomerization and nuclear translocation of nonexpressor of pathogenesis-related proteins 1 (NPR1). Interestingly, salicylic acid (SA) was approximately 2-fold accumulated by the treatment with quercetin. Furthermore, we showed that the increase of SA biosynthesis by quercetin was induced by the transcriptional increases of typical SA biosynthesis-related genes. In conclusion, this study strongly suggests that quercetin induces bacterial pathogen resistance through the increase of SA biosynthesis in Arabidopsis.

•Social distancing leads to adaptive travel mobility and impacts travel experiences.•Engagement in online activity is driven by perceptions of ICT but not street crowdedness.•The modal shift from public to private transport is minimal in this transit-oriented city.•Reduced crowdedness has both direct and indirect effects on travel satisfaction.•The increased usage of rail, buses, minibuses and taxis is associated with travel satisfaction.

Recycled tire rubber is an environmentally and economically beneficial material. Ground tire rubber (GTR) as a filler in a polymer matrix was used as an ink material (composite material) for material extrusion in a 3D printing process. The maximum allowable amount of GTR incorporated into the mixture without significantly altering the rheological behavior of the ink was set. Printability investigations revealed that pressure and speed show linear and power relationships, respectively, to the line width for three different amounts of GTR. Moreover, the post-curing time of 30 min at 115 °C was set as the full-cure condition to achieve polymerization of 80% or more for the 3D printed parts. Unidirectional tensile testing demonstrated that 3D printed specimens exhibit no degradation in tensile strength when compared to molded specimens. Moreover, printability and mechanical properties of functionalized GTR were investigated to determine if this material exhibits enhanced mechanical strength. Unidirectional tensile tests show that the maximum tensile strength for specimens with functionalized GTR was 20% higher than in specimens with non-functionalized GTR. In conclusion, 3D printing of GTR composites shows promise for using recycled GTR to create 3D structures with rubber-like properties.

Nitinol structures were synthesized in a fully dense form using a laser direct deposition method. The pure elemental metal powders of nickel and titanium were used and powder ratios were controlled to arrive at the prescribed final chemical compositions of Nitinol. The transformation temperatures of synthesized Nitinol samples with different chemical composition and post heat treatment conditions were systematically analyzed and compared with those of conventional Nitinol. Compared to Nitinol parts produced by other techniques, the laser engineered net shaping (LENS) created the least amount of secondary phase, indicating the possibility of high corrosion resistance. Two step post processing of solution heat treatment and aging heat treatment was carried out to improve the homogeneity of the microstructure and to investigate its effects on phase transformation temperatures. The resultant phase transformation temperatures could be controlled by the heat treatment parameters. Compression test results showed mechanical properties of synthesized Nitinol samples are largely affected by its post heat treatment history while the effect of initial chemical composition was negligible.

In this study, two different operating strategies of gasoline and diesel dual-fuel premixed compression ignition (PCI) were investigated by using a single cylinder compression ignition engine. Verification of high thermal efficiency potential under the low load condition and the suppression of the maximum in-cylinder pressure rise rate (PRRmax) under the relatively high load condition were considered in this study. Two approaches to implement dual-fuel PCI were considered. The first approach (A-mode PCI) was an early diesel injection with very leaner overall equivalence ratio condition. In this case, a high exhaust gas recirculation (EGR) rate was not needed because lean premixed combustion promised to provide low nitrogen oxides (NOx) and particulate matter (PM) emissions. The second method (B-mode PCI) involved the use of a high EGR rate to moderate dual-fuel combustion with adjusting diesel injection timing. The first operating strategy prolonged the ignition delay via early diesel injection and lean mixture condition; in this manner, a high EGR helped to increase ignition delay. The experimental result showed that the A-mode PCI strategy promised higher gross indicated thermal efficiency (GIE) than that of the B-mode PCI. However, the B-mode PCI strategy provided a lower PRRmax than that of the first case. By applying the A-mode PCI, which was implemented by the early diesel injection with overall lean premixed combustion, a high GIE of 47.8 % could be obtained under low speed and low load condition. In addition, the dual-fuel PCI operating range could be increased using a gross indicated mean effective pressure (gIMEP) of 14 bar at 2000 r/min with a low PRRmax of 7 bar/deg (constraint 10 bar/deg) by applying the B-mode PCI strategy, which split the heat release rate (HRR) peaks to enable smooth combustion.

Microstereolithography (MSL) has been employed to create 3D microstructures for a wide range of applications. Despite the many advantages of using this process, there are still several drawbacks such as the need to use a large amount of a material compared to the volume of the microstructure to be built, oxygen inhibition, and difficulty in processing highly viscous photopolymers. To minimize the amount of material required, the use of a liquid bridge has been suggested as a modification to the existing microstereolithography process. A liquid bridge can be easily found in nature after a rainfall. Basically, a bridge can be formed between two solid bodies, where surface tension can sustain a liquid bridge against a gravitational force, which tends to destroy it. With this natural phenomenon, a photopolymer can be intentionally formed between two substrates: a transparent substrate with a low surface energy can be used as a top substrate, while another substrate with a higher surface energy can be used to hold the fabricated structure together. This process, called liquid bridge microstereolithography(LBMSL), is advantageous since it uses a relatively small amount of a material, removes oxygen inhibition due to the constraint of the material surface, and offers the possibility of utilizing a highly viscous material. In this study, a mathematical model was taken to simulate a liquid bridge with a certain volume and height. Adhesion tests were accomplished to ensure the fabricated layer detaches from the top substrate while the fabricated structure remains attached to the bottom structure. Photopolymers with different viscosities were employed in LBMSL, and the results were compared with those in the traditional MSL. Finally, various 3D microstructures were fabricated by LBMSL; these fabricated microstructures provide compelling evidence that LBMSL is advantageous over the existing process for MSL.

To better understand trip-chaining patterns and mode choice of various urban forms, this study examines the effects of land use on travel mode choice and analyzes the concept of neighborhood design in the substitution of short car trips by other transportation modes.

Multi-material 3D printing with electrically functional materials including conducting, sensing, insulating and semiconducting materials has led to the development of smart devices such as 3D structural electronics, sensors, batteries, etc. Electronically smart devices are a hot issue in 3D printing because they can certainly benefit from 3D printing technology, providing high design flexibility and customized functions. Shape-changing materials (e.g. shape memory polymers) incorporated in 3D printing have given birth to 4D printing, where 3D printed structures change in their shapes by external stimuli (temperature, light, water, etc.). The motivation of this review paper is to discuss mutual benefits from both 3D printed smart devices and 4D printed features, which can be built in a single body. It is expected that the combination of 3D printed smart devices and 4D printing would contribute to the development of high performance, adaptability to the environment and programmable 3D smart devices, which have not yet existed. This paper has reviewed the background of 3D printing, smart device fabrication using 3D printing, development into 4D printing, and future applications of 4D printing.

ABSTRACTIn Korea, the amount of greenhouse gases released due to waste materials was 14,800,000 t CO2eq in 2012, which increased from 5,000,000 t CO2eq in 2010. This included the amount released due to incineration, which has gradually increased since 2010. Incineration was found to be the biggest contributor to greenhouse gases, with 7,400,000 t CO2eq released in 2012. Therefore, with regards to the trading of greenhouse gases emissions initiated in 2015 and the writing of the national inventory report, it is important to increase the reliability of the measurements related to the incineration of waste materials.This research explored methods for estimating the biomass fraction at Korean MSW incinerator facilities and compared the biomass fractions obtained with the different biomass fraction estimation methods. The biomass fraction was estimated by the method using default values of fossil carbon fraction suggested by IPCC, the method using the solid waste composition, and the method using incinerator flue gas.The highest biomass fractions in Korean municipal solid waste incinerator facilities were estimated by the IPCC Default method, followed by the MSW analysis method and the Flue gas analysis method. Therefore, the difference in the biomass fraction estimate was the greatest between the IPCC Default and the Flue gas analysis methods. The difference between the MSW analysis and the flue gas analysis methods was smaller than the difference with IPCC Default method. This suggested that the use of the IPCC default method cannot reflect the characteristics of Korean waste incinerator facilities and Korean MSW.Implications: Incineration is one of most effective methods for disposal of municipal solid waste (MSW). This paper investigates the applicability of using biomass content to estimate the amount of CO2released, and compares the biomass contents determined by different methods in order to establish a method for estimating biomass in the MSW incinerator facilities of Korea. After analyzing the biomass contents of the collected solid waste samples and the flue gas samples, the results were compared with the Intergovernmental Panel on Climate Change (IPCC) method, and it seems that to calculate the biomass fraction it is better to use the flue gas analysis method than the IPCC method. It is valuable to design and operate a real new incineration power plant, especially for the estimation of greenhouse gas emissions.

ABSTRACTIn this study, in order to understand accurate calculation of greenhouse gas emissions of urban solid waste incineration facilities, which are major waste incineration facilities, and problems likely to occur at this time, emissions were calculated by classifying calculation methods into 3 types. For the comparison of calculation methods, the waste characteristics ratio, dry substance content by waste characteristics, carbon content in dry substance, and 12C content were analyzed; and in particular, CO2concentration in incineration gases and 12C content were analyzed together. In this study, 3 types of calculation methods were made through the assay value, and by using each calculation method, emissions of urban solid waste incineration facilities were calculated then compared. As a result of comparison, with Calculation Method A, which used the default value as presented in the IPCC guidelines, greenhouse gas emissions were calculated for the urban solid waste incineration facilities A and B at 244.43 ton CO2/day and 322.09 ton CO2/day, respectively. Hence, it showed a lot of difference from Calculation Methods B and C, which used the assay value of this study. It is determined that this was because the default value as presented in IPCC, as the world average value, could not reflect the characteristics of urban solid waste incineration facilities. Calculation Method B indicated 163.31 ton CO2/day and 230.34 ton CO2/day respectively for the urban solid waste incineration facilities A and B; also, Calculation Method C indicated 151.79 ton CO2/day and 218.99 ton CO2/day, respectively.Implications: This study intends to compare greenhouse gas emissions calculated using 12C content default value provided by the IPCC (Intergovernmental Panel on Climate Change) with greenhouse gas emissions calculated using 12C content and waste assay value that can reflect the characteristics of the target urban solid waste incineration facilities. Also, the concentration and 12C content were calculated by directly collecting incineration gases of the target urban solid waste incineration facilities, and greenhouse gas emissions of the target urban solid waste incineration facilities through this survey were compared with greenhouse gas emissions, which used the previously calculated assay value of solid waste.

Boron neutron capture therapy (BNCT) has been attracting interest as a new radiation modality for cancer therapy because it can selectively destroy cancer cells while maintaining the healthy state of surrounding normal cells. Many experimental trials have demonstrated significant BNCT treatment efficacy using neutron beams from research reactors. However, nuclear reactor technology cannot be scaled to sites in hospitals delivering patient treatment. Therefore, compact accelerator-based neutron sources that could be installed in many hospitals are under development or have even been commissioned at many facilities around the world. In Korea, a radio-frequency (RF) linac-based BNCT (A-BNCT) facility is under development by DawonMedax (DM). It provides the highly efficient production of an epithermal neutron beam with an optimized neutron energy spectrum range of 0.1~10 keV. With a 2-mA 10-MeV proton beam from the accelerator, the irradiation port epithermal neutron flux is higher than 1 × 109n/cm2⋅s. Comprehensive verification and validation of the system have been conducted with the measurement of both proton and neutron beam characteristics. Significant therapeutic effects from BNCT have been confirmed by DM in both in vitro and in vivo non-clinical trials. Further, during exposure to epithermal neutrons, all other unintended radiation is controlled to levels meeting International Atomic Energy Agency (IAEA) recommendations. Recently, the Korean FDA has accepted an investigational new drug (IND) and the first-in-human clinical trial of BNCT is now being prepared. This paper introduces the principles of BNCT and accelerator-based neutron sources for BNCT and reports the recent advances of DM A-BNCT facility which is the main part of this paper.

Environmental problems and climate change arising from waste incineration are taken quite seriously in the world. In Korea, the waste disposal methods are largely classified into landfill, incineration, recycling, etc. and the amount of incinerated waste has risen by 24.5% from 2002. In the analysis of CO2 emissions estimations of waste incinerators fossil carbon content are main factor by the IPCC. FCF differs depending on the characteristics of waste in each country, and a wide range of default values are proposed by the IPCC. This study conducted research on the existing classifications of the IPCC and Korean waste classification systems based on FCF for accurate greenhouse gas emissions estimation of waste incineration.The characteristics possible for sorting were classified according to FCF and form. The characteristics sorted according to fossil carbon fraction were paper, textiles, rubber, and leather. Paper was classified into pure paper and processed paper; textiles were classified into cotton and synthetic fibers; and rubber and leather were classified into artificial and natural.The analysis of FCF was implemented by collecting representative samples from each classification group, by applying the 14C method, and using AMS equipment. And the analysis values were compared with the default values proposed by the IPCC. In this study of garden and park waste and plastics, the differences were within the range of the IPCC default values or the differences were negligible. However, coated paper, synthetic textiles, natural rubber, synthetic rubber, artificial leather, and other wastes showed differences of over 10% in FCF content. IPCC is comprised of largely 9 types of qualitative classifications, in emissions estimation a great difference can occur from the combined characteristics according with the existing IPCC classification system by using the minutely classified waste characteristics as in this study.Implications: Fossil carbon fraction (FCF) differs depending on the characteristics of waste in each country; and a wide range of default values are proposed by the IPCC. This study conducted research on the existing classifications of the IPCC and Korean waste classification systems based on FCF for accurate greenhouse gas emissions estimation of waste incineration.

Rationally designed porous structures are promising as broadband electromagnetic (EM) wave absorbers for counteracting military radar signal or reducing EM interference between electronic components. However, their poor mechanical properties associated with low density limit the scalability. Here, we report a three-dimensional printed, broadband mechanical metamaterial absorber (BMMA) that implements a dual-function of EM wave absorption and reinforced relative stiffness. Based on tuning the lattice unit-cells and comprising materials, the proposed BMMAs feature a multilayered design comprising geometrically optimized octet-truss structures composed of carbon black-based backbone composites. Three-dimensionally printed BMMAs achieve > 90% absorbance (~98.66% on average) for frequencies spanning 5.8–18 GHz, while maintaining nearly constant stiffness per unit mass density of 1.37 at a low density (~200 kg/m3). This design strategy will inspire versatile metamaterials that offer multi-functions enabled by adjusting unit-cell parameters via a single structure.

This paper presents how injector nozzle distributions and the combustion chamber geometry affect the emission characteristics of diesel engines. The number of nozzle holes was increased from seven to 12 by a using double-row nozzle distribution to enhance the air–fuel mixing and the spatial distribution of the spray while avoiding spray overlap. The combustion chamber geometry was modified to have a wide shallow two-step bowl, which ensured adequate spray penetration with the double-row nozzle, to observe the influence of the spray–piston interaction on the combustion and emissions. Three hardware combinations (a seven-hole single-row nozzle with a conventional piston, a 12-hole double-row nozzle with a conventional piston, and a two-step piston) were tested in a single-cylinder direct-injection diesel engine under three boost and exhaust gas recirculation conditions. The injection timing was adjusted to result in a similar power by maintaining 50% of the total fuel mass fraction burned points for each hardware combination. For a conventional boost pressure (1.10 bar) and 30% exhaust gas recirculation, the 12-hole double-row nozzle with a conventional piston exhibited the best emission characteristics with a significant reduction in the particulate matter emissions. For a high boost pressure (1.30 bar) and 30% conventional exhaust gas recirculation, the nitrogen oxide emissions slightly increased and the particulate matter emissions decreased for the 12-hole double-row nozzle with a conventional piston compared with those for the seven-hole single-row nozzle. The two-step piston resulted in decreased particulate matter emissions but increased nitrogen oxide emissions under a high boost pressure. For 60% high exhaust gas recirculation, which is characterized by low-temperature combustion, the particulate matter emissions, the carbon monoxide emissions, and the total hydrocarbon emissions decreased simultaneously without an increase in the nitrogen oxide emissions using the 12-hole double-row nozzle with a two-step piston.

Polymerization-induced phase separation of nanoparticle-filled solution is demonstrated as a simple approach to control the structure of porous composites. These composites are subsequently demonstrated as the active component for sodium ion battery anode. To synthesize the composites, we dissolved/dispersed titanium oxide (anatase) nanoparticles (for sodium insertion) and poly(hydroxybutyl methacrylate) (PHBMA, porogen) in furfuryl alcohol (carbon precursor) containing a photoacid generator (PAG). UV exposure converts the PAG to a strong acid that catalyzes the furfuryl alcohol polymerization. This polymerization simultaneously decreases the miscibility of the PHBMA and reduces the mobility in the mixture to kinetically trap the phase separation. Carbonization of this polymer composite yields a porous nanocomposite. This nanocomposite exhibits nearly 3-fold greater gravimetric capacity in Na-ion batteries than the same titanium oxide nanoparticles that have been coated with carbon. This improved performance is attributed to the morphology as the carbon content in the composite is five times that of the coated nanoparticles. The porous composite materials exhibit stable cyclic performance. Moreover, the battery performance using materials from this polymerization-induced phase separation method is reproducible (capacity within 10% batch-to-batch). This simple fabrication methodology may be extendable to other systems and provides a facile route to generate reproducible hierarchical porous morphology that can be beneficial in energy storage applications.

In clinical practice, pregnant women have lower anesthetic requirements for general anesthesia than nonpregnant women. Although the hormonal changes such as progesterone associated with pregnancy may affect the minimum alveolar concentration of volatile anesthetics, the relationship between the anesthetic or analgesic requirements and progesterone level in full-term women has not been studied. In this study, we attempted to identify relationships between anesthetic or analgesic requirements and maternal serum concentrations of progesterone.

Although the nasopharynx is a commonly used temperature-monitoring site during general anesthesia, it is unknown whether the position of nasopharyngeal temperature probes placed blindly by anesthesia practitioners is optimal. The purposes of this study were (1) to determine where the nasopharyngeal mucosa is in closest proximity to the internal carotid artery (ICA) and (2) to evaluate the tip position of nasopharyngeal temperature probes that were placed by anesthesiology residents and nurse anesthetists.

Although much has been written about local access to public transport, few studies have examined the role of the perceived environment in promoting transit by considering how the effects of these perceptions differ by neighborhood type. By analyzing the self-reported frequency of transit use and measured neighborhood attributes and using data from Los Angeles County, California, this study examined how the perceptions low-income people have about the walking environment affect their travel behavior. A principal component analysis was used to reduce many overlapping perceptional variables to latent factors that were used in subsequent models of transit use. Four perceptional attributes that affect regular transit use are identified: physical safety, personal safety, amenities, and perceived isolation. The results of this study show that unfavorable perceptions of environmental conditions are independently associated with decreased regular transit use; however, these effects vary among different neighborhood types. Personal safety related to crime and violence is the major concern associated with decreased transit use in mixed land use neighborhoods; in low-density neighborhoods, isolation from the street environment and physical safety concerns, including dangerous crosswalks, are the significant deterrents to public transportation use. Notably, low-income travelers view the conditions of their walking environment as problematic more often than do higher-income travelers, and it appears that transit use by lower-income travelers is more likely to be affected by safety concerns than by other urban design factors of their neighborhood. Findings suggest that safety concerns precede amenity concerns; therefore, enhancing neighborhood safety is the necessary first step to increasing the utility of transit for low-income people.

In this paper, we estimate the size of coherent activity of electromagnetic ion cyclotron (EMIC) waves using the multi‒spacecraft observations made during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. We calculate the cross‒correlations between EMIC wave powers measured by different THEMIS spacecraft, plot them over the separation distances between pairs of observing spacecraft, and determine the 1/efolding distance of the correlations as the characteristic dimension of the coherent wave activity. The characteristic radius in the direction transverse to the local magnetic field is found to lie in rather a wide range of 1500–8600 km varying from the AM to PM sectors and also from hydrogen to helium bands. However, the characteristic dimensions normalized by either gyroradius or wavelength fall into narrower ranges almost independent of the emission band and event location. Specifically, the coherent dimension is found to be 10–16 times gyroradius of 100 keV protons and 2–3 times local wavelength. The former may give a useful scale for the source dimension, and the latter suggests that the EMIC wave activity maintains coherency only up to a couple of wavelengths. First time estimation of the dimension of coherent EMIC wave activityThe typical size is found to be 10‐16 times local gyroradius of 100 keV protonsThe EMIC wave activity maintains coherency only up to 2‐3 wavelengths

Although much has been written about local access to public transport, few studies have examined the role of the perceived environment in promoting transit by considering how the effects of these perceptions differ by neighborhood type. By analyzing the self-reported frequency of transit use and measured neighborhood attributes and using data from Los Angeles County, California, this study examined how the perceptions low-income people have about the walking environment affect their travel behavior. A principal component analysis was used to reduce many overlapping perceptional variables to latent factors that were used in subsequent models of transit use. Four perceptional attributes that affect regular transit use are identified: physical safety, personal safety, amenities, and perceived isolation. The results of this study show that unfavorable perceptions of environmental conditions are independently associated with decreased regular transit use; however, these effects vary among different neighborhood types. Personal safety related to crime and violence is the major concern associated with decreased transit use in mixed land use neighborhoods; in low-density neighborhoods, isolation from the street environment and physical safety concerns, including dangerous crosswalks, are the significant deterrents to public transportation use. Notably, low-income travelers view the conditions of their walking environment as problematic more often than do higher-income travelers, and it appears that transit use by lower-income travelers is more likely to be affected by safety concerns than by other urban design factors of their neighborhood. Findings suggest that safety concerns precede amenity concerns; therefore, enhancing neighborhood safety is the necessary first step to increasing the utility of transit for low-income people.

Korea-specific GHG emissions should be estimated correctly in order to ensure effective measurement of climate change variables. The use of country-specific data that reflects fuel and technology characteristics is needed for accurate GHG emissions estimation. Oxidation factors are used to convert existing data into equivalent GHG emissions, and changes in these oxidation factors are directly related to changes in emissions. As such, the oxidation factor is one of the most important variables in using country-specific data to determine GHG emissions. In this study, the oxidation factor of bituminous coal in large scale boilers was estimated using 4,527 data points sampled from eight large-scale boilers that had been using bituminous coal for two years. The average oxidation factor was determined to be 0.997, which is lower than the oxidation factor of 1 that is recommended by the IPCC G/L for large scale boilers when estimating national GHG emissions. However, an oxidation factor less than 1 is assumed for fluidized bed boilers, internal combustion engines, and other small-scale boilers. Accordingly, studies on oxidation factor estimation should be continued to allow for accurate estimation of GHG emissions.

We present a detailed multi-wavelength analysis and interpretation of the evolution of an M7.6 flare that occurred near the southeast limb on 2003 October 24. Pre-flare images at TRACE 195 A show that the bright and complex system of coronal loops already existed at the flaring site. The X-ray observations of the flare taken from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft reveal two phases of the flare evolution. The first phase is characterized by the altitude decrease of the X-ray looptop (LT) source for [?]11 minutes. Such a long duration of the descending LT source motion is reported for the first time. The EUV loops, located below the X-ray LT source, also undergo contraction with similar speed ([?]15 km s-1) in this interval. During the second phase the two distinct hard X-ray footpoint (FP) sources are observed which correlate well with UV and Ha flare ribbons. The X-ray LT source now exhibits upward motion as anticipated from the standard flare model. The RHESSI spectra during the first phase are soft and indicative of hot thermal emission from flaring loops with temperatures T > 25 MK at the early stage. On the other hand, the spectra at high energies (e [?] 25 keV) follow hard power laws during the second phase (g = 2.6-2.8). We show that the observed motion of the LT and FP sources can be understood as a consequence of three-dimensional magnetic reconnection at a separator in the corona. During the first phase of the flare, the reconnection releases an excess of magnetic energy related to the magnetic tensions generated before a flare by the shear flows in the photosphere. The relaxation of the associated magnetic shear in the corona by the reconnection process explains the descending motion of the LT source. During the second phase, the ordinary reconnection process dominates describing the energy release in terms of the standard model of large eruptive flares with increasing FP separation and upward motion of the LT source.

We present a multiwavelength study of the 2005 September 13 eruption from NOAA AR 10808 that produced total four flares and two fast coronal mass ejections (CMEs) within [?]1.5 hr. Our primary attention is paid to the fact that these eruptions occurred in close succession in time, and that all of them were located along an S-shaped magnetic polarity inversion line (PIL) of the active region. In our analysis, (1) the disturbance created by the first flare propagated southward along the PIL to cause a major filament eruption that led to the first CME and the associated second flare underneath. (2) The first CME partially removed the overlying magnetic fields over the northern d spot to allow the third flare and the second CME. (3) The ribbon separation during the fourth flare would indicate reclosing of the overlying field lines opened by the second CME. It is thus concluded that these series of flares and CMEs are interrelated to each other via magnetic reconnections between the expanding magnetic structure and the nearby magnetic fields. These results complement previous works made on this event with the suggested causal relationship among the successive eruptions.

We present a morphological study of the 2004 August 18 solar eruption that occurred in the active region NOAA 10656 near the west limb using extreme-ultraviolet (EUV) data from the Transition Region and Coronal Explorer (TRACE), Ha filtergram of Big Bear Solar Observatory, white light images of Mauna Loa Solar Observatory (MLSO), hard X-ray (HXR) data of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and microwave data of the Owens Valley Solar Array. In this event, we have an excellent set of observations for tracing the early evolution of the coronal mass ejection (CME) from a flux rope emergence to its propagation into space as a well-connected series of events thanks to the coronameter's field of view (FOV) down to 1.1 solar radius in an overlap with that of the TRACE. This data set reveals continuously evolving EUV, Ha, and WL features that suggest the rise of a small, low-lying loop, its writhing motion, break of the kinked loop at its crossing point, and transformation of the ejecta to the CME. The HXR and microwave sources are found in varying locations with a complicated temporal dependence, which, we interpret, is due to two successive flares in the event. The first flare appears to be associated with the rise of the small loop, which then triggers the second flare. During the second flare a HXR coronal source is detected at the crossing point of the kinked loop, and more intriguingly, the kinked loop apparently breaks at the crossing point of the two legs, which indicates a magnetic reconnection at the X-point configuration. After the break of the kinked UV loop, a CME structure shows up in the MLSO FOV, and propagates away from the Sun. It is concluded that this CME occurred due to the kink instability.

Microwave bursts during solar flares are known to be sensitive to high-energy electrons and magnetic field, both of which are important ingredients of solar flare physics. This paper presents such information derived from the microwave bursts of the 412 flares that were measured with the Owens Valley Solar Array. We assumed that these bursts are predominantly due to gyrosynchrotron radiation by nonthermal electrons in a single power-law energy distribution to use the simplified formulae for gyrosynchrotron radiation in the data analysis. A second major assumption was that statistical properties of flare electrons derived from this microwave database should agree with an earlier result based on the hard X-ray burst spectrometer on Solar Maximum Mission. Magnetic field information was obtained in the form of a scaling law between the average magnetic field and the total source area, which turns out to be a narrow distribution around [?]400 G. The derived nonthermal electron energy is related to the peak flux, peak frequency, and spectral index, through a multistep regression fit, which can be used for a quick estimate for the nonthermal electron energy from spatially integrated microwave spectral observations.

We have investigated the variation of magnetic helicity over a span of several days around the times of 11 X-class flares which occurred in seven active regions (NOAA 9672, 10030, 10314, 10486, 10564, 10696, and 10720) using the magnetograms taken by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). As a major result we found that each of these major flares was preceded by a significant helicity accumulation, ( 1.8-16) x 1042 Mx2 over a long period (0.5 to a few days). Another finding is that the helicity accumulates at a nearly constant rate, (4.5-48) x 1040 Mx2 hr[?]1, and then becomes nearly constant before the flares. This led us to distinguish the helicity variation into two phases: a phase of monotonically increasing helicity and the following phase of relatively constant helicity. As expected, the amount of helicity accumulated shows a modest correlation with time-integrated soft X-ray flux during flares. However, the average helicity change rate in the first phase shows even stronger correlation with the time-integrated soft X-ray flux. We discuss the physical implications of this result and the possibility that this characteristic helicity variation pattern can be used as an early warning sign for solar eruptions.

This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar NOAA AR 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at the TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption, as evidenced by the multiwavelength data ranging from Ha, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether cutting to allow the flux rope to rise upward, or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Ha data show that the first scenario is relevant to this eruption. As in other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. The radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXRs. Finally, type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001.

The heterogeneous nature of aqueous heterophase polymerizations is the base for an easy route to unique block copolymers, for the development of new and more effective polymerization strategies, and the abilities to unique studies of radical polymerization kinetics. Thermo‐sensitive double hydrophilic block copolymers and micro‐ or nano‐gel particles of poly(N‐isopropyl acrylamide) as thermo‐responsible block and charged or uncharged hydrophilic polymers can easily be prepared if the polymerization of N‐isopropyl acrylamide is started with the corresponding polymeric radicals. The application of extremely fast microwave heating allows the development of highly effective pulsed thermal polymerization strategies and the production of polymers with desired molecular weight distributions over wide ranges. 2,2′‐azobisisobutyronitrile simultaneously initiates the polymerization in both the monomer and the aqueous phase and leads, even under surfactant‐free conditions, to stable latex particles.

A novel approach to fabricate polymer brushes on the surface of carbon nanotubes (CNTs) is proposed. Carboxyl groups on the surface of chemically oxidized CNTs were reacted with hexamethylene diisocyanate, followed by a reaction with methacrylamide to give terminal vinyl groups‐functionalized CNTs, so called “CNT‐mer.” The synthetic procedure was investigated step‐by‐step and the synthesized CNT‐mer was used to grow polystyrene (PS) from CNTs by a simple in situ polymerization in the presence of a thermal initiator. By employing 1H NMR, X‐ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and light scattering, the experimental results were verified. Using this approach, 45% PS with respect to CNTs are grafted on the surface of CNTs with about 4.0 nm thickness. This novel technique would provide a facile route to prepare tailor‐made polymer brushes on the surface of CNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6394–6401, 2006

We study the magnetic energy release during the 2002 September 9 flare using the high-cadence (40 ms) Ha filtergram at Big Bear Solar Observatory (BBSO), along with hard X-ray and microwave data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Owens Valley Solar Array (OVSA), respectively. We take the Poynting vector approach with the standard two-dimensional geometry of the reconnecting current sheet (RCS) but suggest a new technique to infer the area of the RCS, in order to complete the magnetic energy calculation entirely with observed quantities. We found five peaks of impulsive magnetic energy release, concentrated within 10-30 s periods, that are episodic with the peaks of the hard X-ray light curve. The maximum amount of energy released per peak reaches ~2.6 x 1030 ergs s-1, and the electron energy deposition rate derived from the RHESSI spectra falls into the range of 10%-80% of the magnetic energy release rate. We briefly discuss this result in comparison with other studies thus far made toward understanding of the magnetic reconnection in solar flares and suggest the pulsating current sheet model as the most plausible interpretation of our result.

We present a multiwavelength study focusing on the large-scale activities associated with the 2003 October 29 X10 flare and a halo CME. This event was strong enough to clearly show several large-scale activities, such as remote brightenings, Moreton waves at Ha off-bands, and type II radio bursts, which offers an excellent opportunity to clarify the relationship among them. The remote brightenings were found near two coronal holes more than 2 x 105 km from the main flare in eastern and southern directions, respectively. Coronal dimmings were seen at the locus of the remote brightenings right after the flare at both EUV and soft X-ray wavelengths. The Moreton waves propagated both northeastward and southward, toward the aforementioned remote regions, at speeds of approximately 1100 and 1900 km s-1, respectively. Our analyses show that the Moreton waves, the type II radio bursts, and the CME started almost simultaneously, but were not cotemporal with the remote brightenings. The remote brightenings are rather consistent with the flare hard X-ray emissions within the active region, although they have much smaller scales. We therefore conclude that the two remote brightening regions were magnetically connected to the flaring active region, and that the remote brightenings, as well as all other activities, were due to the interaction of an erupting flux rope at the core of the flare with magnetic field overlying the region. In this scenario, the large overlying loops should open to allow the flare activity underneath them, which points to a picture similar to the magnetic break-out process in such a large scale.

The spatio-spectral maximum entropy method (SSMEM) has been developed by Komm and coworkers in 1997 for use with solar multifrequency interferometric observation. In this paper we further improve the formulation of the SSMEM to establish it as a tool for astronomical imaging spectroscopy. We maintain their original idea that spectral smoothness at neighboring frequencies can be used as an additional a priori assumption in astrophysical problems and that this can be implemented by adding a spectral entropy term to the usual maximum entropy method (MEM) formulation. We, however, address major technical difficulties in introducing the spectral entropy into the imaging problem that are not encountered in the conventional MEM. These include calculation of the spectral entropy in a generally frequency-dependent map grid, simultaneous adjustment of the temperature variables and Lagrangian multipliers in the spatial and spectral domain, and matching the solutions to the observational constraints at a large number of frequencies. We test the performance of the SSMEM in comparison with the conventional MEM.

We present results of analysis of 412 flares during 2001-2002 as detected by the Owens Valley Solar Array (OVSA). This is an in-depth study to investigate some results suggested by a previous study of solar bursts (Nita et al. 2002), which was limited to the peak time of the bursts at a few frequency bands. The new study includes the temporal dependence, at 4 s time resolution, of parameters measured at 40 frequencies in the range 1-18 GHz. We investigate distributions of burst parameters such as maximum flux density in the spectra, peak frequency, spectral slopes below and above the peak frequency (optically thick and thin slopes, respectively), and burst durations. We classify the microwave bursts according to their spectral properties and provide tables of averaged spectral parameters for each spectral type and for different frequency and intensity ranges.

In this paper we present a comprehensive case study of an X-class flare observed on 2001 April 6. The flare consists of two episodes, the first characterized by impulsive spiky bursts and the second by gradual smooth emission at hard X-ray and microwave wavelengths. Emissions in the two episodes are regarded as the impulsive and gradual components, respectively. We compare the temporal, spatial, and spectral evolution of the two components in hard X-rays and microwaves. For this event, the most important finding is that both the impulsive and gradual hard X-rays at [?]50 keV are thick-target emissions at conjugate footpoints. Evolution of hard X-rays and microwaves during the gradual phase exhibits a separation motion between two footpoint sources, which reflects progressive magnetic reconnection. Observations further reveal distinct spectral properties of the gradual component. It is most prominently observed in the high-energy (>20 keV) range, and the gradual hard X-rays have a harder and hardening spectrum compared with the impulsive component. The gradual component is also a microwave-rich event, with the microwaves lagging the hard X-rays by tens of seconds. A correlation analysis of the hard X-ray light curves shows energy-dependent time delays, with the 200 keV hard X-rays lagging the 40 keV emission by 20 s. The observations and analyses suggest that magnetic reconnection occurs during both the impulsive and gradual phases that generate nonthermal electrons, primarily precipitating at the footpoints. However, the temporal and spectral properties of the gradual component must be produced by an acceleration mechanism different from that of the impulsive phase. We propose that the "collapsing-trap" effect, as a product of progressive magnetic reconnection in bipolar magnetic fields, is a viable mechanism that continuously accelerates the gradual-phase electrons in a low-density trap before they precipitate into the footpoints.

The evolution of a GOES class X1.1 solar flare, which occurred in NOAA Active Region 8910 on 2000 March 22, is discussed using observations from the Owens Valley Solar Array (OVSA), Big Bear Solar observatory (BBSO), Transition Region and Coronal Explorer (TRACE), and the Michelson Doppler Imager (MDI) on board Solar and Heliospheric Observatory (SOHO). During the impulsive phase, a set of coronal loops are visible in the TRACE 171 A (~1 x 106 K) wavelength band, which is confined to a small volume in the center of the large bgd-type active region. This is rapidly followed by the emergence of bright Ha ribbons that coincide with the EUV emission. Radio images show a single source encompassing the Ha ribbons at 5 GHz, but at higher frequencies a double source is seen within the area bounded by the compact Ha and EUV emissions. We interpret the observation under the idea of the confined flare in contrast with the more commonly cited, eruptive flare. We use a schematic magnetic reconnection geometry based on the MDI magnetogram to suggest that the EUV loops show some parts of a separatrix, and that the radio and Ha sources coincide with the whole part of the separatrix and its footpoints, respectively. First of all, it explains why this flare lacks the separating motion of Ha ribbons, a signature for eruptive flares. Second, the very short duration of microwave bursts in spite of the large amount of soft X-ray flux is explicable under this scenario, since energy release via spontaneous reconnection in a confined magnetic structure can be very rapid. Third, the confined magnetic geometry is also considered favorable for preserving chromospheric evaporation and plasma turbulence as inferred from the OVSA microwave spectrum. In addition, a coronal mass ejection as detected in the LASCO coronagraph after this flare is briefly discussed in relation to the above flare model.

We discuss injection and transport of high-energy electrons during a GOES X-ray class M9.8 flare observed in microwaves with the Owens Valley Solar Array (OVSA) and in hard X-rays (HXRs) with the hard X-ray telescope (HXT) on board Yohkoh. Observed at 1 s timescales or better in both wavelength regimes, the event shows (1) a large difference in scale between the microwave source and the HXR source; (2) an unusually hard HXR spectrum (maximum spectral index ~-1.6), followed by rapid spectral softening; and (3) a microwave light curve containing both impulsive peaks (3 s rise time) simultaneous with those of the HXRs and a long, extended tail with a uniform decay rate (2.3 minutes). We analyze the observations within the framework of the electron trap-and-precipitation model, allowing a time-dependent injection energy spectrum. Assuming thick-target bremsstrahlung for the HXRs, we infer the electron injection function in the form Q(E, t) ~ (E/E0)-d(t), where the timescale for d(t) to change by unity is ~7 s. This injection function can account for the characteristics of the impulsive part of the microwave burst by considering the bulk of the electrons to be directly precipitating without trapping. The same injection function also accounts for the gradual part of the microwave emission by convolving the injection function with a kernel representing the trapping process, which at late times gives N(E, t) ~ e-nt(E/E0)-b. We require b ~ 1.4 and n ~ 6 x 10-3b s-1, where b is the electron speed divided by the speed of light. Therefore, the derived form of the precipitation rate n itself indicates strong pitch-angle diffusion, but the slow decay of the microwave radiation requires a small loss cone (~4deg) and a low ambient density in the coronal trap. Also, the numbers of electrons needed to account for the two components of the microwave emission differ by an order of magnitude. We estimate that the [?]100 keV number of the directly precipitating electrons is ~1033, while the trapped population requires ~1032 electrons. This leads us to a model of two interacting loops, the larger of which serves as an efficient trap while the smaller provides the impulsive source. These characteristics are consistent with the spatially resolved observations.

A systematic motion of Ha kernels during solar flares can be regarded as the chromospheric signature of progressive magnetic reconnection in the corona, in that the magnetic field lines swept through by the kernel motion are those connected to the diffusion region at the reconnection point. In this paper, we present high-cadence and high-resolution Ha-1.3 A observations of an impulsive flare that exhibits a systematic kernel motion and relate them to the reconnecting current sheet (RCS) in the corona. Through analyses of X-ray and microwave observations, we further examine the role of the macroscopic electric field inside the RCS in accelerating electrons. We measure the velocity of the kernel motion to be 20-100 km s-1. This is used together with the longitudinal magnetic field to infer an electric field as high as 90 V cm-1 at the flare maximum. This event shows a special magnetic field configuration and motion pattern of Ha kernels, in that a light bridge divides a flare kernel into two parts that move in different manners: one moving into the stronger magnetic field and the other moving along the isogauss contour of the longitudinal magnetic field. The temporal variation of the electric field inferred from the former type of kernel motion is found to be correlated with 20-85 keV hard X-ray light curves during the rise of the major impulsive phase. This would support the scenario of magnetic energy release via current dissipation inside the RCS, along with the hypothesis of the DC electric field acceleration of X-ray-emitting electrons below 100 keV. However, there is no good temporal correlation between the hard X-ray emission and the inferred electric field from the other motion pattern. Furthermore, the microwave emission, which supposedly comes from higher energy electrons, shows a time profile and electron spectrum that differs from those of the X-ray bursts. We conclude that either the two-dimensional magnetic reconnection theory related to the Ha kernel motion is applicable to only some part of the flare region due to its special magnetic geometry, or the electron acceleration is dominated by other mechanisms depending on the electron energy.

The structure and properties of a newly emerged solar active region (NOAA Active Region 7985) are discussed using the Coronal Diagnostic Spectrometer (CDS) and the Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory. CDS obtained high-resolution EUV spectra in the 308-381 A and 513-633 A wavelength ranges, while EIT recorded full-disk EUV images in the He II (304 A), Fe IX/X (171 A), Fe XII (195 A), and Fe XV (284 A) bandpasses. Electron density measurements from Si IX, Si X, Fe XII, Fe XIII, and Fe XIV line ratios indicate that the region consists of a central high-density core with peak densities of the order of 1.2 x 1010 cm-3, which decrease monotonically to ~5.0 x 108 cm-3 at the active region boundary. The derived electron densities also vary systematically with temperature. Electron pressures as a function of both active region position and temperature were estimated using the derived electron densities and ion formation temperatures, and the constant pressure assumption was found to be an unrealistic simplification. Indeed, the active region is found to have a high-pressure core (1.3 x 1016 cm-3 K) that falls to 6.0 x 1014 cm-3 K just outside the region. CDS line ratios from different ionization stages of iron, specifically Fe XVI (335.4 A) and Fe XIV (334.4 A), were used to diagnose plasma temperatures within the active region. Using this method, peak temperatures of 2.1 x 106 K were identified. This is in good agreement with electron temperatures derived using EIT filter ratios and the two-temperature model of Zhang et al. The high-temperature emission is confined to the active region core, while emission from cooler (1-1.6) x 106 K lines originates in a system of loops visible in EIT 171 and 195 A images. Finally, the three-dimensional geometry of the active region is investigated using potential field extrapolations from a Kitt Peak magnetogram. The combination of EUV and magnetic field extrapolations extends the "core-halo" picture of active region structure to one in which the core is composed of a number of compact coronal loops that confine the hot, dense, high-pressure core plasma while the halo emission emerges from a system of cooler and more extended loops.

As models for the physical properties of the corona above solar active regions grow more sophisticated, we will require better means for testing them. In this paper we discuss and apply such a test to a magnetic field model for an active region. This test is based on the expectation that the temperatures at different points on a given magnetic field line should be well correlated because of the rapid transport of heat along field lines in the corona. We use radio observations of an active region to measure the temperatures on field lines as they cross two isogauss surfaces (at 430 and 750 G) in the corona. The field lines and isogauss surfaces are derived from a coronal magnetic field model obtained via a nonlinear force-free field extrapolation of a photospheric vector magnetogram; for comparison, we also investigate a potential-field extrapolation of the same magnetogram. In a region in which strongly sheared fields are present, the nonlinear force-free field model does indeed show a good correlation between the temperatures in the two surfaces at points on the same field line, while the potential-field model does not. This diagnostic acts both as a test of the magnetic field model as well as of the interpretation of the radio data, and we show how this test can also aid in understanding the radio data.

We compare microwave images of a solar active region with state-of-the-art fully nonlinear force-free extrapolations of the photospheric fields in order to study the link between coronal currents and heating of the corona. This extrapolation fully takes into account the nonuniform distribution of electric currents observed in the photosphere and its role in the coronal magnetic structure. We carry out the comparison for AR 6615, a complex region observed with the VLA on 1991 May 7. Under the assumption that the microwave emission is dominated by optically thick gyroresonance radiation, we may use the radio images to infer the temperature of the corona at different heights and locations. This is then compared with heating models based on the observed current distribution. We are able to reproduce the radio images remarkably well with a model in which temperature is structured along magnetic field lines, depends on the current on the field line, and increases with height in a manner similar to that inferred from static heated loop models. This result implies a direct link between electric currents and coronal heating.

We made a parameter fit to the Haleakala neutron monitor counting rate during the 1991 March 22 solar flare (Pyle and Simpson, 1991) using the time profiles of ?-rays at 0.42–80 MeV obtained with the GRANAT satellite (Vilmeret al., 1994) and the microwave data from Owens Valley Radio Observatory. We use a two-component neutron injection function to find that either an impulsive injection or the ‘impulsive-plus-prolonged’ neutron injection is possible. In both cases, the number of > 300 MeV neutrons emitted towards the Earth is estimated as ˜ 2 × 1027 sr-1, which is less than that of the 1990 May 24 flare by an order of magnitude.

In this paper, we are primarily concerned with the solar neutron emission during the 1990 May 24 flare, utilizing the counting rate of the Climax neutron monitor and the time profiles of hard X-rays and ?-rays obtained with the GRANAT satellite (Pelaezet al., 1992; Talonet al., 1993; Terekhovet al., 1993). We compare the derived neutron injection function with macroscopic parameters of the flare region as obtained from theHa and microwave observations made at the Big Bear Solar Observatory and the Owens Valley Radio Observatory, respectively. Our results are summarized as follows: (1) to explain the neutron monitor counting rate and 57.5–110 MeV and 2.2 MeV ?-ray time profiles, we consider a two-component neutron injection function,Q(E, t), with the form $$Q(E,t) = N_f {\text{ exp[}} - E/E_f - t/T_f ] + N_s {\text{ exp[}} - E/E_s - t/T_s ],$$ whereNf(s),Ef(s), andTf(s) denote number, energy, and decay time of the fast (slow) injection component, respectively. By comparing the calculated neutron counting rate with the observations from the Climax neutron monitor we derive the best-fit parameters asTf ˜ 20 s,Ef ˜ 310 MeV,Ts ˜ 260 s,Es ˜ 80 MeV, andNf(E > 100 MeV)/Ns(E > 100 MeV) ˜ 0.2. (2) From the Ha observations, we find a relatively small loop of length ˜ 2 × 104 km, which may be regarded as the source for the fast-decaying component of ?-rays (57.5–110 MeV) and for the fast component of neutron emission. From microwave visibility and the microwave total power spectrum we postulate the presence of a rather big loop (˜ 2 × 105 km), which we regard as being responsible for the slow-decaying component of the high-energy emission. We show how the neutron and ?-ray emission data can be explained in terms of the macroscopic parameters derived from the Ha and microwave observations. (3) The Ha observations also reveal the presence of a fast mode MHD shock (the Moreton wave) which precedes the microwave peak by 20–30 s and the peak of ?-ray intensity by 40–50 s. From this relative timing and the single-pulsed time profiles of both radiations, we can attribute the whole event as due to a prompt acceleration of both electrons and protons by the shock and subsequent deceleration of the trapped particles while they propagate inside the magnetic loops.

We report peculiar spectral activity of four large microwave bursts as obtained from the Solar Arrays at the Owens Valley Radio Observatory during observations of X-class flares on 1990 May 24 and 1991 March 7, 8, and 22. Main observational points that we newly uncovered are: (1) flat flux spectra over 1–18 GHz in large amounts of flux ranging from 102 to 104 s.f.u. at the maximum phase, (2) a common evolutionary pattern in which the spectral region of dominant flux shifts from high frequencies at the initial rise to low frequencies at the decaying phase, and (3) unusual time profiles that are impulsive at high frequencies but more extended at lower frequencies.

It is well recognized that the phenomenon of depolarization (the conversion of polarized radio emission into unpolarized emission) of microwaves over solar active regions can be used to infer the coronal electron density once the coronal magnetic field is known. In this paper we explore this technique using an active region for which we have excellent radio data showing depolarization at two frequencies, and for which we have an excellent magnetic field model which has been tested against observations. We show that this technique for obtaining coronal densities is very sensitive to a number of factors. When Cohen's (1960) theory where depolarization is due to magnetic field rotation alone is used, the result is particularly sensitive to the location of the surface on which the magnetic field is orthogonal to the line of sight. Depending on whether we take into account the presence of electric currents in the photosphere or not, their extrapolation into the corona can result in very different heights being deduced for the location of the depolarization strip, and this changes the density which is then deduced from the depolarization condition. Such extreme sensitivity to the magnetic field model requires that field extrapolations be able to accurately predict the polarity of magnetic fields up to coronal heights as high as ∼ 105km in order to exploit depolarization as a density diagnostic.

Microwave emission from solar active regions at frequencies above 4 GHz is dominated by gyroresonance opacity in strong coronal magnetic fields, which allows us to use radio observations to measure coronal magnetic field strengths. In this paper we demonstrate one powerful consequence of this fact: the ability to identify coronal currents from their signatures in microwave images. Specifically, we compare potential-field (i.e., current-free) extrapolations of photospheric magnetic fields with microwave images and are able to identify regions where the potential extrapolation fails to predict the magnetic field strength required to explain the microwave images. Comparison with photospheric vector magnetic field observations indicates that the location inferred for coronal currents agrees with that implied by the presence of vertical currents in the photosphere. The location, over a neutral line exhibiting strong shear, is also apparently associated with strong heating.

We investigate the influence of seeing upon measurement of magnetic flux of photospheric fields. For this purpose we quantify seeing variation in one day's observation at Big Bear Solar Observatory in terms of the Fried function, a Modulation Transfer Function for the atmospheric seeing. The temporal variation of seeing quality is compared with that of magnetic flux measured in a quiet region with size 5′ \times 4′ near the solar disk center. A good correlation is found between the seeing change and apparent evolution of magnetic flux values, implying, as a possibility, that magnetic flux measurement might have been modulated by seeing. Based on a simple model of ensembles of Gaussian magnetic elements we argue that even the net flux as well as the total flux can change due to seeing variation if the magnetograph has a finite detection threshold and if the intrinsic fluxes in one and the other polarities are unbalanced.

We analyze the time variation of microwave spectra and hard X-ray spectra of 1989 March 18, which are obtained from the Solar Array at the Owens Valley Radio Observatory (OVRO) and the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM), respectively. From this observation, it is noted that the hard X-ray spectra gradually soften over 50–200 keV on-and-after the maximum phase while the microwaves at 1–15 GHz show neither a change in spectral shape nor as rapid a decay as hard X-rays. This leads to decoupling of hard X-rays from the microwaves in the decay phase away from their good correlation seen in the initial rise phase. To interpret this observation, we adopt a view that microwave-emitting particles and hard X-ray particles are physically separated in an inhomogeneous magnetic loop, but linked via interactions with the Whistler waves generated during flares. From this viewpoint, it is argued that the observed decoupling of microwaves from hard X-rays may be due to the different ability of each source region to maintain high energy electrons in response to the Whistler waves passing through the entire loop. To demonstrate this possibility, we solve a Fokker-Planck equation that describes evolution of electrons interacting with the Whistler waves, taking into account the variation of Fokker-Planck coefficients with physical quantities of the background medium. The numerical Fokker-Planck solutions are then used to calculate microwave spectra and hard X-ray spectra for agreement with observations. Our model results are as follows: in a stronger field region, the energy loss by electron escape due to scattering by the waves is greatly enhanced resulting in steep particle distributions that reproduce the observed hard X-ray spectra. In a region with weaker fields and lower density, this loss term is reduced allowing high energy electrons to survive longer so that microwaves can be emitted there in excess of hard X-rays during the decay phase of the flare. Our results based on spectral fitting of a flare event are discussed in comparison with previous studies of microwaves and hard X-rays based on either temporal or spatial information.