Thermal and Nonthermal Radiation Signatures in Solar Flares: Models and Observations

The work of this thesis has been concerned with various aspects of the solar flare phenomenon, and covers a wavelength range from the optical to gamma-ray, in varying degrees of depth. The approach taken has been a combination of modelling of physical processes and the application of these models to solar observations from the Solar Maximum Mission (SMM), and in particular the Yohkoh mission. Attempts have also been made, in Chapters 3 and 5, to relate nonthermal high energy phenomena such as gamma-rays and hard X-rays to the lower energy thermal radiation signatures of soft X-ray and optical emission. Chapter 1 provides an overview to the solar flare phenomenon, with particular emphasis on the observations. Where appropriate, the mechanisms responsible for the production of radiation signatures from flares has been described, and a brief and by no means complete, description of the possible mechanisms for flare energy release and transport are described. For those radiation signatures which are considered in further detail in later chapters the emphasis is on describing recent observations, particularly those from Yohkoh. A brief description of future up and coming satellite missions is also given. Chapter 2 furnishes an introduction to the Yohkoh satellite and its instrumentation. Much of the work in later chapters involves the analysis of data from Yohkoh and it is necessary to have a basic understanding of how this data was collected, and its limitations to enable results based on it to be placed in a proper perspective. Chapter 3 discusses the hypothesis that stochastic acceleration by Alfven wave turbulence is responsible both for the acceleration of gamma-ray producing protons, and for the observed nonthermal line broadening in coronal soft X-ray lines. A general background to the subjects of nonthermal line broadening, particle acceleration and gamma-ray line production is presented and the model is described together with the results of its application to data from four flares observed by SMM and one flare observed by Yohkoh. This model is particularly interesting on the basis of its self-consistent approach to the problem of relating the thermal and nonthermal aspects of solar flares. Chapter 4 investigates the posssibility that decreasing levels of Hydrogen ionization in the deep chromosphere of solar flares could cause the return current associated with a thick target electron beam to become unstable to the generation of ion-acoustic wave turbulence. To begin with the background behind the need for a nearly co-spatial return current to exist is described, along with some observational evidence for the existence of electron beams in solar flares. A simple model is described and the results of its application to semi-empirical model solar atmospheres is described. We find that the possibility for such an instability to develop exists and that it can lead to the break up of the thick target electron beam and significant anomalous energy deposition at the level in the solar atmosphere where this occurs. Chapter 5 follows on from Chapter 4 in considering that the generation of ion-acoustic wave turbulence via a return current instability can provide sufficient heating to power the white-light flare. To begin with, the white-light flare phenomenon is described in some detail, with emphasis on the various existing theories for its production. Then the analysis of the hard X-ray and white-light emission from four white-light flares observed by the Yohkoh satellite is described. The limitations of the results in respect to the available data are also described. It is found that there is a definite correlation between the hard X-ray and white-light flare and that the hypothesis of the white-light flare being powered by anomalous ohmic heating cannot be ruled out. Chapter 6 draws together the results of the previous chapters, providing a summary of the work achieved in this thesis. It also points out some of the limitations of the approaches adopted and outlines possible improvements and new directions

Doppler Signature of a Possible Termination Shock in an Off-Limb Solar Flare

We report striking Doppler velocity gradients observed during the well-observed September 10th 2017 solar flare, and argue that they are consistent with the presence of an above-the-looptop termination shock beneath the flare current sheet. Observations from the Hinode Extreme-ultraviolet Imaging Spectrometer (EIS) measure plasma sheet Doppler shifts up to 35 km/s during the late-phase of the event. By comparing these line-of-sight flows with plane-of-sky measurements, we calculate total velocity downflows of 200+ km/s, orientated 6-10{\deg} out of the plane of sky. The observed velocities drop rapidly at the base of the hot plasma sheet seen in extreme ultraviolet, consistent with simulated velocity profiles predicted by our 2.5D magnetohydrodynamics model that features a termination shock at the same location. Finally, the striking velocity deceleration aligns spatially with the suppression of Fe XXIV non-thermal velocities, and a 35--50 keV hard X-ray looptop source observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Together, these observations are consistent with the presence of a possible termination shock within the X8.2-class solar flare.Comment: 9 pages, 5 figures; accepted for publication to MNRA

The Effects of an Acute Bout of Self-Myofascial Release on the Physiological Parameters of Running

International Journal of Exercise Science 13(3): 113-122, 2020. This study examined changes in the physiological parameters of running performance when self-myofascial release (SMR) was used prior to a submaximal run. A total of 16 male recreational runners, between the ages of 27 and 50 years old volunteered for the study. Participants had to complete a running event measuring a 10K or longer in the past 12 months and obtained a O2peakvalue of 45 mL·kg-lmin-1to be included in the study. Participants took part in two 40 min treadmill runs at 75% of their O2peak, one session with the use of SMR and the other with 20 min of seated rest prior to the run. Measurements of heart rate, blood lactate concentrations, ventilatory efficiency E/ O2), RPE, and running velocity were assessed. There was no statistically significant interaction or treatment effect for these variables when SMR was used prior to a 40 min treadmill run(p\u3e .05; heart rate: d = .01, E/ O2: d= .07, RPE: d= .07). Although no positive effects on running performance were found, the lack of negative effects suggests the use of SMR prior to running does not hinder performance

ALMA 1.3 Millimeter Map of the HD 95086 System

Planets and minor bodies such as asteroids, Kuiper-belt objects and comets are integral components of a planetary system. Interactions among them leave clues about the formation process of a planetary system. The signature of such interactions is most prominent through observations of its debris disk at millimeter wavelengths where emission is dominated by the population of large grains that stay close to their parent bodies. Here we present ALMA 1.3 mm observations of HD 95086, a young early-type star that hosts a directly imaged giant planet b and a massive debris disk with both asteroid- and Kuiper-belt analogs. The location of the Kuiper-belt analog is resolved for the first time. The system can be depicted as a broad ($\Delta R/R \sim$0.84), inclined (30\arcdeg$\pm$3\arcdeg) ring with millimeter emission peaked at 200$\pm$6 au from the star. The 1.3 mm disk emission is consistent with a broad disk with sharp boundaries from 106$\pm$6 to 320$\pm$20 au with a surface density distribution described by a power law with an index of --0.5$\pm$0.2. Our deep ALMA map also reveals a bright source located near the edge of the ring, whose brightness at 1.3 mm and potential spectral energy distribution are consistent with it being a luminous star-forming galaxy at high redshift. We set constraints on the orbital properties of planet b assuming co-planarity with the observed disk.Comment: accepted for publication in A

Influence of hormone therapy on the cardiovascular responses to stress of postmenopausal women

Abstract Epidemiological and psychophysiological data suggest that groups that differ in reproductive hormones and stress responses also differ in risk for cardiovascular disease. To evaluate the effects of hormone therapy on women's cardiovascular responses to laboratory stressors, 89 healthy postmenopausal women were tested twice, before and after exposure for about 8 weeks to one of the five conditions: placebo, Estratab (primarily estrone), Estratab plus Prometrium (micronized progesterone), Estratab plus Provera (synthetic progestin), and Estratest (same estrogen as in Estratab plus methyltestosterone). Results showed that women assigned to Estratab plus Prometrium and Estratest had diminished systolic blood pressure responses to stress upon retesting, whereas the other groups did not change in the level of their responses. Women assigned to Estratab plus Prometrium had diminished diastolic blood pressure responses during a speech stressor upon retesting, whereas women assigned to Estratab plus Provera increased. Our findings show that hormone therapy does affect women's stress responses, but they do not provide a simple explanation as to why groups at high and low risk for cardiovascular disease differ in reproductive hormones and stress responses.

Plasma evolution within an erupting coronal cavity

Coronal cavities have previously been observed associated with long-lived quiescent filaments and are thought to correspond to the associated magnetic flux rope. Although the standard flare model predicts a coronal cavity corresponding to the erupting flux rope, these have only been observed using broadband imaging data, restricting analysis to the plane-of-sky. We present a unique set of spectroscopic observations of an active region filament seen erupting at the solar limb in the extreme ultraviolet (EUV). The cavity erupted and expanded rapidly, with the change in rise phase contemporaneous with an increase in non-thermal electron energy flux of the associated flare. Hot and cool filamentary material was observed to rise with the erupting flux rope, disappearing suddenly as the cavity appeared. Although strongly blue-shifted plasma continued to be observed flowing from the apex of the erupting flux rope, this outflow soon ceased. These results indicate that the sudden injection of energy from the flare beneath forced the rapid eruption and expansion of the flux rope, driving strong plasma flows which resulted in the eruption of an under-dense filamentary flux rope.Comment: 11 pages, 5 figures. Accepted for publication in The Astrophysical Journa

Perigenual anterior cingulate morphology covaries with perceived social standing

Low socioeconomic status (SES) increases the risk for developing psychiatric and chronic medical disorders. A stress-related pathway by which low SES may affect mental and physical health is through the perception of holding a low social standing, termed low subjective social status. This proposal implicates overlapping brain regions mediating stress reactivity and socioemotional behaviors as neuroanatomical substrates that could plausibly link subjective social status to health-related outcomes. In a test of this proposal, we used a computational structural neuroimaging method (voxel-based morphometry) in a healthy community sample to examine the relationships between reports of subjective social status and regional gray matter volume. Results showed that after accounting for potential demographic confounds, subclinical depressive symptoms, dispositional forms of negative emotionality and conventional indicators of SES, self-reports of low subjective social status uniquely covaried with reduced gray matter volume in the perigenual area of the anterior cingulate cortex (pACC)—a brain region involved in experiencing emotions and regulating behavioral and physiological reactivity to psychosocial stress. The pACC may represent a neuroanatomical substrate by which perceived social standing relates to mental and physical health

Updated Parameters and a New Transmission Spectrum of HD 97658b

Recent years have seen increasing interest in the characterization of sub-Neptune-sized planets because of their prevalence in the Galaxy, contrasted with their absence in our solar system. HD 97658 is one of the brightest stars hosting a planet of this kind, and we present the transmission spectrum of this planet by combining four Hubble Space Telescope transits, 12 Spitzer/IRAC transits, and eight MOST transits of this system. Our transmission spectrum has a higher signal-to-noise ratio than those from previous works, and the result suggests that the slight increase in transit depth from wavelength 1.1–1.7 μm reported in previous works on the transmission spectrum of this planet is likely systematic. Nonetheless, our atmospheric modeling results are inconclusive, as no model provides an excellent match to our data. Nonetheless, we find that atmospheres with high C/O ratios (C/O ≳ 0.8) and metallicities of ≳100× solar metallicity are favored. We combine the mid-transit times from all of the new Spitzer and MOST observations and obtain an updated orbital period of P = 9.489295 ± 0.000005, with a best-fit transit time center at T₀ = 2456361.80690 ± 0.00038 (BJD). No transit timing variations are found in this system. We also present new measurements of the stellar rotation period (34 ± 2 days) and stellar activity cycle (9.6 yr) of the host star HD 97658. Finally, we calculate and rank the Transmission Spectroscopy Metric of all confirmed planets cooler than 1000 K and with sizes between 1 R⊕ and 4 R⊕. We find that at least a third of small planets cooler than 1000 K can be well characterized using James Webb Space Telescope, and of those, HD 97658b is ranked fifth, meaning that it remains a high-priority target for atmospheric characterization

Neck Circumference Positively Relates to Cardiovascular Risk Factors in College Students

The objective of this study was to determine the relationship between neck circumference (NC) and other anthropometric measures and examine cut-off points for males and females according to existing waist circumference cut-off levels in this age group. Across 8 universities, 1562 students underwent a physical assessment. Spearman rho correlations (ρ) were calculated to determine associations between NC and other continuous variables of health. Receiving operating characteristic curves were constructed to assess the optimal cut-off levels of NC of males and females with central obesity. Participants were predominantly Caucasian (67%), female (70%), and outside of Appalachia 2 (82%). Forty-one percent of males and 34% of females had a BMI ≥ 25 kg/m . In both sexes, significant positive correlations were seen between NC and body weight, BMI, waist circumference, hip circumference, and systolic blood pressure (all p-values \u3c 0.0001). NC ≥ 38 cm for males and ≥33.5 cm for females were the optimal cut-off values to determine subjects with central obesity. NC has been identified to closely correlate with other anthropometric measurements related to disease and could be used as a convenient, low-cost, and noninvasive measurement in large-scale studies