2,205 research outputs found
The emission line near 1319 A in solar and stellar spectra
An emission line near 1319 A is one of the strongest unidentified lines in
the ultraviolet spectra of cool dwarf stars. In most line lists it is
identified as a transition in N I, although its intensity would then be
anomalous and the observed wavelength does not fit precisely that expected for
N I. The line is also observed in cool giant stars. The measured wavelength of
the line in stellar spectra is 1318.94 (+,- 0.01) A. Observations of giant
stars provide further evidence that this line is not due to N I. It is proposed
that this line is a decay from a previously unknown level in S I, which lies
above the first ionization limit. This is identified with the 3d singlet D (odd
parity) term. The previous tentative assignment of this term to the S I line at
1309.3 A then needs to be revised. The 1309.3 A line has been identified here
for the first time in an astrophysical source. The singlet D (odd parity) level
could, in principle, be populated by collisions from nearby autoionizing levels
that have large number-densities, through population by di-electronic capture.
Spin-orbit interaction with the autoionizing triplet D (odd parity) term might
also lead to di-electronic capture into the singlet D (odd parity) level. A
line at 1309.87 A observed in cool giant stars is identified as a transition in
P II, pumped by the O I resonance lines.Comment: 9 pages, 3 figures, to be published in Monthly Notices of the Royal
Astronomical Societ
THE ACUTE EFFECT OF TISSUE FLOSSING ON PAIN, FUNCTION, AND PERCEPTION OF MOVEMENT
International Journal of Exercise Science 16(3): 855-865, 2023. Tissue flossing (TF) is a novel device that has been shown to cause peripheral compression and concurrent change in joint range of motion, perception of mobility and muscular performance. However, the effect of tissue flossing on pain, perception of mobility and function at the elbow joint has not been thoroughly investigated. The purpose of this pilot study was to examine the acute effect of TF on pain and upper extremity functional performance in subjects with musculoskeletal-related complaints of pain surrounding the elbow joint. We utilized a randomized crossover design. Nine resistance trained participants (8 men/1 woman) mean age 35.6 ± 10.7 took part in this study. We measured the following outcome measures; Pain Visual Analog Scale, Short Form McGill Pain Questionnaire II, pain-pressure threshold and hand grip dynamometry (HHD) pre and post and a Likert scale for movement ability questionnaire, posttest only, following a TF and placebo condition for each participant.TF resulted in significant improvement in all test measures, except HHD, pre to post (p ≤ 0.05). All pre to post changes were associated with large effect sizes for TF compared to the placebo condition applied to the elbow improves pain quality and intensity, perception of mobility and pain-pressure threshold in resistance trained individuals with a history of musculoskeletal pain for greater than 1 month. The results of this pilot study suggest that TF may function as an adjunct to treatment in the management of musculoskeletal pathologies at the elbow joint
A study of velocity fields in the transition region of Epsilon Eri (K2 V)
Analyses of the widths and shifts of optically thin emission lines in the
ultraviolet spectrum of the active dwarf Epsilon Eri (K2 V) are presented. The
spectra were obtained using the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. The line
widths are used to find the non-thermal energy density and its variation with
temperature from the chromosphere to the upper transition region. The energy
fluxes that could be carried by Alfven and acoustic waves are investigated, to
test their possible roles in coronal heating. Acoustic waves do not appear to
be a viable means of coronal heating. There is, in principle, ample flux in
Alfven waves, but detailed calculations of wave propagation are required before
definite conclusions can be drawn about their viability. The high sensitivity
and spectral resolution of the above instruments have allowed two-component
Gaussian fits to be made to the profiles of the stronger transition region
lines. The broad and narrow components which result share some similarities
with those observed in the Sun, but in Epsilon Eri the broad component is
redshifted relative to the narrow component and contributes more to the total
line flux. The possible origins of the two components and the energy fluxes
implied are discussed. On balance our results support the conclusion of Wood,
Linsky & Ayres, that the narrow component is related to Alfven waves reaching
to the corona, but the origin of the broad component is not clear.Comment: 19 pages, 16 figures. Accepted for publication by MNRA
The corona and upper transition region of epsilon Eridani
We present analyses of observations of epsilon Eridani (K2 V) made with the
Low Energy Transmission Grating Spectrometer on Chandra and the Extreme
Ultraviolet Explorer, supplemented by observations made with the Space
Telescope Imaging Spectrograph, the Far Ultraviolet Spectroscopic Explorer and
the Reflection Grating Spectrometer on XMM-Newton. The observed emission lines
are used to find relative element abundances, to place limits on the electron
densities and pressures and to determine the mean apparent emission measure
distribution. As in the previous paper by Sim & Jordan (2003a), the mean
emitting area as a function of the electron temperature is derived by
comparisons with a theoretical emission measure distribution found from energy
balance arguments. The final model has a coronal temperature of 3.4 x 10^6 K,
an electron pressure of 1.3 x 10^16 cm^-3 K at T_e = 2 x 10^5 K and an area
filling factor of 0.14 at 3.2 x 10^5 K. We discuss a number of issues
concerning the atomic data currently available. Our analyses are based mainly
on the latest version of CHIANTI (v5.2). We conclude that the Ne/O relative
abundance is 0.30, larger than that recommended from solar studies, and that
there is no convincing evidence for enhanced coronal abundances of elements
with low first ionization potentials.Comment: accepted by MNRAS; 19 pages, five figures, 10 table
Recommended from our members
Reduced Purkinje cell number in essential tremor : a postmortem study
Background: Clinical and functional imaging evidence suggests that cerebellar dysfunction occurs in essential tremor (ET). In recent postmortem studies, we documented increased numbers of torpedoes (Purkinje cell axonal swellings) in ET patients without Lewy bodies. Purkinje cell loss, however, has never been rigorously assessed. Objective: To quantitatively assess the number of Purkinje cells in brains of ET patients and similarly aged controls. Methods: Postmortem cerebellar tissue was available in 14 ET cases (6 with Lewy bodies and 8 without Lewy bodies) and 11 controls. Calbindin immunohistochemistry was performed on paraffin sections of the cerebellum. Images were digitally recorded and blinded measurements of the number of Purkinje cells per millimeter of cell layer (linear density) were made. Results: Purkinje cell linear density was inversely correlated with age (r=-0.53, P=.006) and number of torpedoes (r=-0.42, P=.04). Purkinje cell linear density differed by diagnosis (mean [SD], controls, 3.46 [1.27] cells/mm; ET cases with Lewy bodies, 3.33 [1.06] cells/mm; and ET cases without Lewy bodies, 2.14 [0.82] cells/mm; P=.04), with the most significant difference between ET cases without Lewy bodies and controls, where the reduction was 38.2% (P=.04). In an adjusted linear regression analysis that compared ET cases without Lewy bodies with controls, decreased linear density (outcome variable) was associated with ET (β=.56, P=.03). Conclusions: We demonstrated a reduction in Purkinje cell number in the brains of patients with ET who do not have Lewy bodies. These data further support the view that the cerebellum is anatomically, as well as functionally, abnormal in these ET cases
Crystal Structure, Electronic Structure, and Optical Properties of the Novel Li4cdge2s7, a Wide-Bandgap Quaternary Sulfide with a Polar Structure Derived from Lonsdaleite
The novel quaternary thiogermanate Li4CdGe2S7 (tetralithium cadmium digermanium heptasulfide) was discovered from a solid-state reaction at 750 °C. Single-crystal X-ray diffraction data were collected and used to solve and refine the structure. Li4CdGe2S7 is a member of the small, but growing, class of I4-II-IV2-VI7 diamond-like materials. The compound adopts the Cu5Si2S7 structure type, which is a derivative of lonsdaleite. Crystallizing in the polar space group Cc, Li4CdGe2S7 contains 14 crystallographically unique ions, all residing on general positions. Like all diamond-like structures, the compound is built of corner-sharing tetrahedral units that create a relatively dense three-dimensional assembly. The title compound is the major phase of the reaction product, as evidenced by powder X-ray diffraction and optical diffuse reflectance spectroscopy. While the compound exhibits a second-harmonic generation (SHG) response comparable to that of the AgGaS2 (AGS) reference material in the IR region, its laser-induced damage threshold (LIDT) is over an order of magnitude greater than AGS for λ = 1.064 μm and τ = 30 ps. Bond valence sums, global instability index, minimum bounding ellipsoid (MBE) analysis, and electronic structure calculations using density functional theory (DFT) were used to further evaluate the crystal structure and electronic structure of the compound and provide a comparison with the analogous I2-II-IV-VI4 diamond-like compound Li2CdGeS4. Li4CdGe2S7 appears to be a better IR nonlinear optical (NLO) candidate than Li2CdGeS4 and one of the most promising contenders to date. The exceptional LIDT is likely due, at least in part, to the wider optical bandgap of ∼3.6 eV
Detection of magnetic dipole lines of Fe XII in the ultraviolet spectrum of the dwarf star Epsilon Eri
We report observations of the dwarf star Epsilon Eri (K2 V) made with the
Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope
(HST). The high sensitivity of the STIS instrument has allowed us to detect the
magnetic dipole transitions of Fe XII at 1242.00A and 1349.38A for the first
time in a star other than the Sun. The width of the stronger line at 1242.00A
has also been measured; such measurements are not possible for the permitted
lines of Fe XII in the extreme ultraviolet. To within the accurcy of the
measurements, the N V and the Fe XII lines occur at their rest wavelengths.
Electron densities and line widths have been measured from other transition
region lines. Together, these can be used to investigate the non-thermal energy
flux in the lower and upper transition region, which is useful in constraining
possible heating processes. The Fe XII lines are also present in archival STIS
spectra of other G/K-type dwarfs.Comment: 12 pages, 4 figures, submitted to MNRAS letters (11 Jan 2001
A genealogy of hacking
Hacking is now a widely discussed and known phenomenon, but remains difficult to define and empirically identify because it has come to refer to many different, sometimes incompatible, material practices. This paper proposes genealogy as a framework for understanding hacking by briefly revisiting Foucault’s concept of genealogy and interpreting its perspectival stance through the feminist materialist concept of the situated observer. Using genealogy as a theoretical frame a history of hacking will be proposed in four phases. The first phase is the ‘pre-history’ of hacking in which four core practices were developed. The second phase is the ‘golden age of cracking’ in which hacking becomes a self-conscious identity and community and is for many identified with breaking into computers, even while non-cracking practices such as free software mature. The third phase sees hacking divide into a number of new practices even while old practices continue, including the rise of serious cybercrime, hacktivism, the division of Open Source and Free Software and hacking as an ethic of business and work. The final phase sees broad consciousness of state-sponsored hacking, the re-rise of hardware hacking in maker labs and hack spaces and the diffusion of hacking into a broad ‘clever’ practice. In conclusion it will be argued that hacking consists across all the practices surveyed of an interrogation of the rationality of information techno-cultures enacted by each hacker practice situating itself within a particular techno-culture and then using that techno-culture to change itself, both in changing potential actions that can be taken and changing the nature of the techno-culture itself
- …