132 research outputs found
A theoretical study of population II Cepheids with periods in the range 10-20 days
No full textA theoretical study of population II variables with
periods in the range 10 - 20 days (W Virginis variables) is
presented. A modified hydrodynamic Christy code is used in
conjunction with the Carson opacities, in preference to the Los
Alamos tables, following the work of Carson, Stothers and
Vemury on the shorter period BL Herculis variables.
Twenty-five survey models are presented, along with nine other
comparison models of varying masses and opacities.
A study of the observations shows that the division of
these variables into two types by observers might be explained
by a slightly different mass for each type, thus making the
division dependent on the star's previous evolution.
The non-linear results obtained by this study show that a
mass of 0.6 M☉ is a good one to use, and that M = 0.5 M☉ makes
little difference (although M = 0.8 M☉ seems to be too high).
The results in general compare well with the observations, as
both also show the split into two types of light curve. Three good models of individual stars are presented, on a par with the models of BL Herculis published by Carson, Stothers and
Vemury. The bumps in the light and velocity curves of many of
the models seem to be real, caused by the Christy "echo".
A few of the models show some RV Tauri behaviour. One in
particular shows very strange behaviour, involving a violent
81ternation of light curve shapes. Models constructed using
the Los Alamos opacities do not produce results as consistent
with observations as those of the main survey.
The study shows that these stars can be represented by
hydrodynamic models of mass 0.6 M☉ using the Carson opacities, but also that convection may be important in the cooler stars in order to model them accurately. This indicates the
direction in which further theoretical work may lie
Development of a near-infrared spectroscopy interface able to assess oxygen recovery kinetics in the right and left sides of the pelvic floor
No full textCITATION: Macnab, A., Stothers, L. & Deegan, E. 2019. Development of a near-infrared spectroscopy interface able to assess oxygen recovery kinetics in the right and left sides of the pelvic floor.
Journal of Biomedical Optics, 24(7):075003, doi:10.1117/1.JBO.24.7.075003.The original publication is available at https://www.spiedigitallibrary.org/journals/journal-of-biomedical-opticsNear-infrared spectroscopy (NIRS) muscle oxygenation data are relied on in sports medicine. Many women with urinary incontinence (UI) have dysfunctional pelvic floor muscles (PFMs) but their evaluation lacks such measures; a transvaginal NIRS interface would enable the PFM to be interrogated. Paired miniature fiber-optic cables were configured on a rigid foam insert so their emitter detector arrays with an interoptode distance of 20 mm apposed the right and left inner sides of a disposable clear plastic vaginal speculum, and linked to a standard commercial NIRS instrument. Measurement capability was assessed through conduct of three maximum voluntary contractions (MVCs) and one sustained maximum voluntary contraction of the PFM with calculation of HbDiff (½RT), a validated muscle reoxygenation kinetic parameter. In all four asymptomatic controls, mean age 40, mean BMI 21.4, MVCs were associated with changes in PFM oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb) concentration, and their difference (HbDiff) comparable to those in voluntary muscle sports medicine studies. NIRS data during recovery (reoxygenation) allowed calculation of HbDiff (½RT). New techniques are called for to evaluate UI. This NIRS interface warrants further development as the provision of quantitative reoxygenation kinetics offers more comprehensive evaluation of patients with PFM dysfunction.https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-24/issue-07/075003/Development-of-a-near-infrared-spectroscopy-interface-able-to-assess/10.1117/1.JBO.24.7.075003.fullPublisher's versio
Photo-essays : a creative format for effective communication
No full textCITATION: Stothers, L., Mukisa, R. & Macnab, A. J. 2020. Photo-essays : a creative format for effective communication, in Macnab, A., Daar, A. & Pauw, C. 2020. Health in transition : translating developmental origins of health and disease science to improve future health in Africa. Stellenbosch: SUN PReSS, doi:10.18820/9781928357759/11.The original publication is available at https://africansunmedia.store.it.si/zaScientists and educators regularly face the challenge of effectively, concisely and
interestingly communicating their ideas and findings, and the need to engage
readers unfamiliar with the concepts or issues they want to describe.
In the context of advancing the developmental origins of health and disease
(DOHaD) agenda, effective communication is essential, particularly when aiming
to engage government agencies, inform leaders in the health care professions,
and motivate organisations able to drive change in the community. Hence, it is important to consider approaches that might make key DOHaD concepts and
health promotion strategies more readily accessible to any target population.
In this chapter, we share our experience from a collaboration between the Peter Wall
Institute for Advanced Studies (PWIAS) at the University of British Columbia,
and STIAS at Stellenbosch University to explore ways to make research and global
public health issues accessible and meaningful to a broad readership; we identified
the genre of photo-essay as an established and valid format, and describe its origins
and principles.
A photo-essay effectively presents a broad range of facts and data to varied
audiences because the format principally relies on the impact visual images have.
When well-chosen images are combined with appropriate captions and a concise
explanatory text, the resulting composition can engage and inform a wide range of
readers, and in a way likely to allow even those unfamiliar with the topic to rapidly
gain an overall understanding of the information and recommendations presented.
Photographs are a powerful way to furnish evidence because they expand the scope
of the information provided and uniquely engage individual readers. The reader
cannot be made to look at the images in the presented order, nor can the time
spent on each image be indicated. So, we suggest that a photo-essay offers a very
individual, informative yet flexible format for sharing ‘what works and why”, and
how, and under what circumstances it works in the context of DOHaD.Publisher's versio
CARBON-13 ISOTOPE EFFECTS IN NUCLEOPHILIC ALIPHATIC DISPLACEMENT REACTIONS
No full textCarbon-13 isotope effects have been measured
for the solvolysis reactions of 1-brorao-l-phenylethane
in methanol and ethanol and for the bimolecular reaction
of this halide and benzyl bromide with alkoxide ion.
For the unimolecular displacements, the rate constant
has been found to be 1.006, which
corresponds to an isotope effect of 0.6 per cent. Rate
constant ratios,
observed
of 1.003 and 1.053 have been
for the reaction of 1-bromo-l-phenylethane with
ethoxide ion and of benzyl bromide with methoxide ion,
respectively. Extensive tests have been performed to
establish that the reactions wore unidirectional under
the conditions used and that the experimental procedures
were uncomplicated by exchange, rearrangement, or isotopic
fractionation. The results have been discussed in terms
of the Bigeleisen expression for the theoretical calculation of isotope effects.ThesisDoctor of Philosophy (PhD
Variable turbulent convection as the cause of the Blazhko effect - testing the Stothers model
No full textThe amplitude and phase modulation observed in a significant fraction of the RR Lyrae variables - the Blazhko effect - represents a longstanding enigma in stellar pulsation theory. No satisfactory explanation for the Blazhko effect has been proposed so far. In this paper we focus on the Stothers idea, in which modulation is caused by changes in the structure of the outer convective zone, caused by a quasi-periodically changing magnetic field. However, up to this date no quantitative estimates were made to investigate whether such a mechanism can be operational and whether it is capable of reproducing the light variation we observe in Blazhko variables. We address the latter problem. We use a simplified model, in which the variation of turbulent convection is introduced into the non-linear hydrodynamic models in an ad hoc way, neglecting interaction with the magnetic field. We study the light-curve variation through the modulation cycle and properties of the resulting frequency spectra. Our results are compared with Kepler observations of RR Lyr. We find that reproducing the light-curve variation, as is observed in RR Lyr, requires a huge modulation of the mixing length, of the order of ±50 per cent, on a relatively short time-scale of less than 40 d. Even then, we are not able to reproduce all the observed relations between modulation components present in the frequency spectrum and the relations between Fourier parameters describing the shape of the instantaneous light curves.sponsorship: [
"Funding for this Discovery mission is provided by NASA's Science Mission Directorate. The authors gratefully acknowledge the entire Kepler team, whose outstanding efforts have made these results possible.",
"Model computations presented in this paper were conducted on the psk computer cluster in the Copernicus Centre, Warsaw, Poland. We are grateful to James Nemec for comments on this manuscript. RS and KK are supported by the Austrian Science Fund (FWF projects AP 21205-N16 and T359/P19962, respectively)."
] (NASA's Science Mission Directorate, Austrian Science Fund (FWF)|AP 21205-N16, Austrian Science Fund (FWF)|T359/P19962, Austrian Science Fund (FWF)|P 19962, Austrian Science Fund (FWF)|P19962)status: Publishe
A study of the young cluster NGC 330 in the Small Magellanic Cloud
No full textIn this study we analyze the Colour-Magnitude Diagram (CMD) and the Luminosity Function (LF) of the SMC cluster NGC 330 on the basis of the new BV CCD photometry obtained by Vallenari et al. (1994) and the effective temperatures and bolometric magnitudes of a few supergiant stars taken from Caloi et al. (1993) and Stothers and Chin (1992a,b). The main goal of this study is to infer the kind of mixing taking place in stellar interiors. To this aim we make use of three grids of stellar tracks calculated with different schemes of mixing, namely classical semiconvection (Bressan et al. 1993), full overshoot (Bressan et al. 1993; Fagotto et al. 1994), and diffusive overshoot (Deng 1994; Deng et al. 1994). All the models are fairly homogeneous as far as the remaining input physics is concerned (opacity, nuclear reactions, mass loss rates), and are calculated with the new radiative opacities of Iglesias et al. (1992). We adopt the colour excess E(B-V) = 0.06 and the true distance modulus (m - M)(o) = 18.85. The metallicity of the cluster is highly uncertain: the observational determinations in fact go from Z = 0.0003 to Z = 0.006. The analysis of the CMD and LF is made by means of isochrones and synthetic CMDs. These latter allow us to match the CMD and the LF and to get an estimate of the slope x of the initial mass function (IMF) at the same time. With the assumed colour excess and distance modulus, NGC 330 turns out to possess a metallicity slightly lower than Z = 0.008 and an age a few 10(7) yr. However, we find that a significant spread in the age is present. The CMD is compatible with ages in the range 1 to 2.5 x 10(7) yr for semiconvective models, and 1 to 4.8 x 10(7) yr for full and diffusive overshoot models. Contrary to what claimed by Caloi et al. (1993) and Stothers and Chin (1992a,b), no clear indication arises about the mixing scheme. Indeed, neither the analysis of the integrated LF nor the location of the blue supergiant stars in the theoretical HRD are able to cast light on this point, even though there is some marginal indication that full and/or diffusive overshoot models ought to be preferred. The study of the integrated LF suggests that the slope of the IMF is about x = 2.35 for semiconvective models, about x = 2.35 for full overshoot models, and x = 2.00 for those with diffusive overshoot
Sonic visions : intertextual relations of words, music and image in Japanese nô theatre
No full textThis study on Japanese no theatre addresses questions pertaining to contemporary
concerns on text and performance: Who perceives in the no, and how is author/performer/
audience intersubjectivity achieved? How are we to discern this art form's sonically coded
intertextuality? When no plays were acquiring written form during the medieval period (1186-
1573), Japan was in the process of transition from an oral and ritual performance tradition to
the increasing predominance of written language. Thus, it is appropriate to situate these
questions at the interstices of oral, written, musical and performance texts.
The historical no audience actively remembered through snatches of lost phrases, half
forgotten songs, past stories and poetry learned by heart. Audience engagement constituted a
continuous process of calling to mind in the performative present that which had slipped into
past memory. With regards to plays by three major no playwrights (Kan'ami, Zeami, Zenchiku),
subjective intent was mirrored on the polished stage of audience collective memory.
In adopting the methodology employed in the analyses of no literary texts and their
corresponding chanted melodies this investigation acknowledges the precision with which no
plays were created as intertextual blueprints of literary and performative affective-expression.
On the basis of a linguistic principle governing Classical Japanese called kakari musubi
Cgrammatical concord' or 'agreement'), contrastive particles as they are used in the no are
argued to be remnants of an oral tradition in the process of transition. They act as performative
links between the written and chanted texts, signalling intertextual references and coinciding
musically with an intensification of the melodic line. The procedure of mapping particles in
relation to the chanted melody of the immediate text and its intertextual source material reveals
contrastive and sometimes unexpected significations. The distinct ways in which a play's sonic
intertext is combined or juxtaposed with its visual and perceptual fields shed light on individual
stylistic differences between the three founding no playwrights receiving comparative treatment
in this investigation.Arts, Faculty ofAsian Studies, Department ofGraduat
On The Short-Period Type II Cepheid Field Stars
No full textFourier decomposition parameters for the photoelectric light curves of 20 short-period type II Cepheids in the field are compared with the models of Hodson, Cox, and King, also subjected to Fourier analysis. The hydrodynamic light curves display sequences in the Fourier phases very reminiscent of the resonance progressions among classical Population I Cepheids with periods less than 10 days. However a handful of type II models with small radii and relatively high period ratios, P2/P0, give Fourier phases which do not seem to follow the resonance sequence. Comparing the models with the type II Cepheid observations, we find very good agreement in both the phase-period and phase-phase diagrams. As in the models, there are a number of observed stars which obviously display a resonance progression and others which may not. Thus, based on the Fourier diagrams, we are led to distinguish three classes of short-period type II Cepheids with periods and period ratios as follows: type II S (1.d0 ≤ P ≤ 1.d6; P2/P0 ≥ 0.53); type II M (1. d 4 ≤ P0 ≤ 2. d0; P2/P0\u3c 0.53); and type II L (P ≥ 2.d0d; P2/P0 ≤ 0.49). An apparent resonance sequence among the II M stars leads us to propose that the resonance center (P2/P0 = 0.5) occurs near 2 days, rather than 1.6 days as suggested previously. We discuss the problems posed for theories of stellar and galactic evolution by the existence of disk, halo, and cluster pulsators with very similar light curves. Comparison of our results with the work of Carson, Stothers, and Vemury, Carson and Stothers, and Petersen and Diethelm, finds a number of points of agreement as well as some contradiction. Further calculations and additional observations, particularly CCD photometry of globular cluster Cepheids, will be necessary to resolve these problems
Spectroscopy 19 (2005) 207-212 207 IOS Press Clinical NIRS of the urinary bladder - A demonstration case report
No full textAbstract. Urinary incontinence is a common affliction among people of all ages throughout the world. There are many causes of incontinence, treatment options are determined by the cause, and current diagnostic methods require urodynamic assessment, which involves urethral and rectal catheterization, which are uncomfortable and distasteful for patients. Since clinical near infrared spectrophotometry (NIRS) is a non-invasive, rapid means of measuring tissue oxygenation status at the bedside, we examined whether NIRS could be useful as a diagnostic tool for bladder dysfunction. An adult patient attending an incontinence clinic for routine urodynamic testing also had NIRS data collection during the standard bladder filling regimen. NIRS optodes were placed on the skin of the intact abdomen over the supra pubic region. Changes in oxy and de-oxy hemoglobin concentration and changes in cytochrome c oxidase net redox status via NIRS were collected at 6 Hz. The magnitudes of change that occurred during NIRS data collection are on the order of 0.5 µmol/l and the moments of change correspond to the subject's reported sensations of bladder filling and emptying, and with conventional urodynamics. These observations suggest that NIRS may be a disruptive technology with a role to play in non-invasive evaluation of bladder dysfunction in humans
- …
