3,485 research outputs found
Investigating the differential emission measure and energetics of microflares with combined SDO/AIA and RHESSI observations
An important question in solar physics is whether solar microflares, the
smallest currently observable flare events in X-rays, possess the same
energetic properties as large flares. Recent surveys have suggested that
microflares may be less efficient particle accelerators than large flares, and
hence contribute less nonthermal energy, which may have implications for
coronal heating mechanisms. We therefore explore the energetic properties of
microflares by combining Extreme Ultraviolet (EUV) and X-ray measurements.
We present forward-fitting differential emission measure (DEM) analysis of 10
microflares. The fitting is constrained by combining, for the first time, high
temperature RHESSI observations and flux data from SDO/AIA. Two fitting models
are tested for the DEM; a Gaussian distribution and a uniform DEM profile. A
Gaussian fit proved unable to explain the observations for any of the studied
microflares. However, 8 of 10 events studied were reasonably fit by a uniform
DEM profile. Hence microflare plasma can be considered to be significantly
multi-thermal, and may not be significantly peaked or contain resolvable fine
structure, within the uncertainties of the observational instruments.
The thermal and non-thermal energy is estimated for each microflare,
comparing the energy budget with an isothermal plasma assumption. From the
multithermal fits the minimum non-thermal energy content was found to average
approximately 30% of the estimated thermal energy. By comparison, under an
isothermal model the non-thermal and thermal energy estimates were generally
comparable. Hence, multi-thermal plasma is an important consideration for solar
microflares that substantially alters their thermal and non-thermal energy
content.Comment: 13 pages, 10 Figures, 2 tables. Accepted for publication in the
Astrophysical Journa
Energy release in the solar atmosphere from a stream of infalling prominence debris
Recent high-resolution and high-cadence EUV imaging has revealed a new
phenomenon, impacting prominence debris, where prominence material from failed
or partial eruptions can impact the lower atmosphere, releasing energy. We
report a clear example of energy release and EUV brightening due to infalling
prominence debris that occurred on 2011 September 7-8. The initial eruption of
material was associated with an X1.8-class flare from AR11283, occurring at
22:30 UT on 2011 September 7. Subsequently, a semi-continuous stream of this
material returned to the solar surface with a velocity v > 150 km/s, impacting
a region remote from the original active region between 00:20 - 00:40 UT on
2011 September 8. Using SDO/AIA, the differential emission measure of the
plasma was estimated throughout this brightening event. We found that the
radiated energy of the impacted plasma was L_rad ~10^27 ergs, while the thermal
energy peaked at ~10^28 ergs. From this we were able to determine the mass
content of the debris to be in the range 2x10^14 < m < 2x10^15 g. Given typical
promimence masses, the likely debris mass is towards the lower end of this
range. This clear example of a prominence debris event shows that significant
energy release takes place during these events, and that such impacts may be
used as a novel diagnostic tool for investigating prominence material
properties.Comment: Accepted by AstroPhysical Journal Letters, 6 pages, 5 figure
Quasi-periodic pulsations in solar and stellar flares: re-evaluating their nature in the context of power-law flare Fourier spectra
The nature of quasi-periodic pulsations in solar and stellar flares remains
debated. Recent work has shown that power-law-like Fourier power spectra, also
referred to as 'red' noise processes, are an intrinsic property of solar and
stellar flare signals, a property that many previous studies of this phenomenon
have not accounted for. Hence a re-evaluation of the existing interpretations
and assumptions regarding QPP is needed. Here we adopt a Bayesian method for
investigating this phenomenon, fully considering the Fourier power law
properties of flare signals. Using data from the PROBA2/LYRA, Fermi/GBM,
Nobeyama Radioheliograph and Yohkoh/HXT instruments, we study a selection of
flares from the literature identified as QPP events. Additionally we examine
optical data from a recent stellar flare that appears to exhibit oscillatory
properties. We find that, for all but one event tested, an explicit oscillation
is not required in order to explain the observations. Instead, the flare
signals are adequately described as a manifestation of a power law in the
Fourier power spectrum, rather than a direct signature of oscillating
components or structures. However, for the flare of 1998 May 8, strong evidence
for the existence of an explicit oscillation with P ~ 14-16 s is found in the
17 GHz radio data and the 13-23 keV Yohkoh HXT data. We conclude that, most
likely, many previously analysed events in the literature may be similarly
described in terms of power laws in the flare Fourier power spectrum, without
the need to invoke a narrowband, oscillatory component. As a result the
prevalence of oscillatory signatures in solar and stellar flares may be less
than previously believed. The physical mechanism behind the appearance of the
observed power laws is discussed.Comment: 11 pages, 7 figures, 1 table. Accepted for publication in The
Astrophysical Journa
Microtonal procedures in 'Sailing to Byzantium'
This short paper introduces and categorises the mictrotonal writing in my composition Sailing to Byzantium for solo recorder player (1999, published Chipping Norton 2016: Composers Edition). It was delivered at UK Microsoft 1 (Riverside Arts Centre, Walton-on-Thames, 15 October 2005), with live musical excerpts performed by Rachel Barnes. (In the text version of the paper these are rendered as musical illustrations from the manuscript facsimile score). Introductory material covers sources of inspiration for the piece and the use of microtones in it, including the poetry of W B Yeats, the Sequenzas of Luciano Berio, the communicable language of Olivier Messiaen, and Tibetan chant. Three categories of microtonal procedure are then identified: those used structurally using special alternative fingerings; 'bent' pitches used colouristically; and written-out glissandi. Six examples are provided in total, covering all three categories. Pitch-divisions are generally limited to quarter-tones, but eighth-tones are also deployed on occasion. Quarter-tone fingerings are based on Michael Vetter's Blockflütencshcule (Vienna 1983: Universal Edition); eighth-tone fingerings were extrapolated from Vetter's chart via an empirical process of trial-and-error
Market-orientated accounting: Information for product-level decisions
Purpose: The paper's purpose is to explore and describe the interface between the customer component of a market orientation and the accounting information used in making product-level decisions. Design/methodology/approach: Exploratory/descriptive organisational case study of a multi-function product decision-making setting. Development of a model of the customer-accounting information requirements of a market orientation. Findings: Describes how customer-orientated product decisions are guided by managers' shared understanding of product-attributes and conceptions of a 'product' as a 'bundle of attributes, benefits or characteristics'. Describes the limited accounting function involvement in product-decisions and the use of customer-orientated and non-financial decision criteria. Practical implications: A market-orientated approach to business has been associated with increased business performance. The identification and integration of information from the management accounting discipline facilitates the understanding of the resource costs of satisfying individual customer needs and assists in operational level decisions. The authors highlight potential barriers to the integration of customer-orientated accounting information in product decisions. Originality/value: There remains a scarcity of marketing and management accounting interdisciplinary case research at the product-attribute decision-making level. The organisational study provides an insight into the decision-making information and processes at the market orientation and management accounting interface. A framework and suggestions for the further development of interfunctional product-level decision-making are provided
Biochemical Markers Predictive of Preterm Delivery
Preterm delivery is the leading cause of perinatal morbidity and mortality worldwide. Despite a great deal of research into this disease, we still do not understand its pathophysiology. Our treatments for this disease are only marginally effective. Biochemical markers were developed with the hope of giving us new tools to prevent preterm deliveries. Specifically the hope was that they could predict which patients were destined to have a preterm delivery. At the present time these markers perform only satisfactorily at predicting preterm labor. They are expensive and not convenient to use at present. Perhaps more importantly, though, these markers have given us insight into the complexities of preterm delivery. Preterm delivery can arise from many different etiologies. This will lead to research into new treatments as knowledge about preterm delivery is amassed. We know that any number of pathological processes may be involved in any given patient with preterm labor. Biochemical markers have the distinct advantage of being able to determine the specific pathophysiology in a given patient and may allow us to tailor therapy according to the specific problem. In the future it is likely that a careful search for specific pathophysiology will be the only way we can treat this disease effectively. For the present time the biochemical markers will be used only to predict preterm delivery. Ultrasound measurements of the cervix during the pregnancy are likely a faster and less expensive way to accomplish that goal
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