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The zinc cluster proteins Upc2 and Ecm22 promote filamentation in Saccharomyces cerevisiae by sterol biosynthesis-dependent and -independent pathways.
The transition between a unicellular yeast form to multicellular filaments is crucial for budding yeast foraging and the pathogenesis of many fungal pathogens such as Candida albicans. Here, we examine the role of the related transcription factors Ecm22 and Upc2 in Saccharomyces cerevisiae filamentation. Overexpression of either ECM22 or UPC2 leads to increased filamentation, whereas cells lacking both ECM22 and UPC2 do not exhibit filamentous growth. Ecm22 and Upc2 positively control the expression of FHN1, NPR1, PRR2 and sterol biosynthesis genes. These genes all play a positive role in filamentatous growth and their expression is upregulated during filamentation in an Ecm22/Upc2-dependent manner. Furthermore ergosterol content increases during filamentous growth. UPC2 expression also increases during filamentation and is inhibited by the transcription factors Sut1 and Sut2. The expression of SUT1 and SUT2 in turn is under negative control of the transcription factor Ste12. We suggest that during filamentation Ste12 becomes activated and reduces SUT1/SUT2 expression levels. This would result in increased UPC2 levels and as a consequence to transcriptional activation of FHN1, NPR1, PRR2 and sterol biosynthesis genes. Higher ergosterol levels in combination with the proteins Fhn1, Npr1 and Prr2 would then mediate the transition to filamentous growth.The project was supported by the Deutsche Forschungsgemeinschaft (DFG) grant HO 2098/5
Advanced EVA system design requirements study
The results are presented of a study to identify specific criteria regarding space station extravehicular activity system (EVAS) hardware requirements. Key EVA design issues include maintainability, technology readiness, LSS volume vs. EVA time available, suit pressure/cabin pressure relationship and productivity effects, crew autonomy, integration of EVA as a program resource, and standardization of task interfaces. A variety of DOD EVA systems issues were taken into consideration. Recommendations include: (1) crew limitations, not hardware limitations; (2) capability to perform all of 15 generic missions; (3) 90 days on-orbit maintainability with 50 percent duty cycle as minimum; and (4) use by payload sponsors of JSC document 10615A plus a Generic Tool Kit and Specialized Tool Kit description. EVA baseline design requirements and criteria, including requirements of various subsystems, are outlined. Space station/EVA system interface requirements and EVA accommodations are discussed in the areas of atmosphere composition and pressure, communications, data management, logistics, safe haven, SS exterior and interior requirements, and SS airlock
He II recombination lines as a test of the nature of SN Ia progenitors in elliptical galaxies
To date, the question of which progenitor channel can reproduce the observed
rate of Type Ia supernovae (SNe Ia) remains unresolved, with the single and
double degenerate scenarios remaining the leading contenders. The former
implies a large population of hot accreting white dwarfs with photospheric
temperatures of T ~ 10^5-10^6 K during some part of their accretion history. We
show that in early-type galaxies, a population of accreting white dwarfs large
enough to reproduce the SN Ia rate would contribute significantly to the
ionizing UV radiation expected from the stellar population. For mean stellar
ages < ~5 Gyr, single degenerate progenitors would dominate the ionizing
background produced by stars, increasing the continuum beyond the He
II-ionizing limit more than ten-fold. This opens a new avenue for constraining
the progenitors of SNe Ia, through consideration of the spatially extended
low-ionization emission-line regions now found in many early-type galaxies.
Modelling the expected emission, we show that one can constrain the
contribution of the single degenerate channel to the SN Ia rate in E/S0
galaxies from upper limits on the luminosity of He II recombination lines in
the optical and FUV. We discuss future directions, as well as possible
implications for the evolution of SNe Ia in old stellar populations.Comment: 12 pages, 13 figures, MNRA
Cultural trauma: Ron Eyerman and the founding of a new research paradigm
The field of cultural trauma has reached the status of a research paradigm. Ron Eyerman has played a central role in this development. Since he first embarked on research into cultural trauma with several colleagues in 1999, Eyerman has maintained an intensive preoccupation with the topic, resulting in the publication of numerous books and essays. In this article, I review the development of Eyerman’s approach to cultural trauma, with the broader aim of shedding light on this new research paradigm. I focus on several key themes in Eyerman’s work, including the relationship between event and representation; the significance of affect and emotion; the role of collective memory; the adoption of a dramaturgical perspective; and a multidimensional research methodology. To conclude, I discuss potential new directions in the study of cultural trauma
Balmer-Dominated Shocks Exclude Hot Progenitors for Many Type Ia Supernovae
The evolutionary mechanism underlying Type Ia supernova explosions remains
unknown. Recent efforts to constrain progenitor models based on the influence
that their high energy emission would have on the interstellar medium (ISM) of
galaxies have proven successful. For individual remnants, Balmer-dominated
shocks reveal the ionization state of hydrogen in the immediately surrounding
gas. Here we report deep upper limits on the temperature and luminosity of the
progenitors of four Type Ia remnants with associated Balmer filaments: SN 1006,
0509-67.5, 0519-69.0, and DEM L71. For SN 1006, existing observations of helium
line emission in the diffuse emission ahead of the shock provide an additional
constraint on the helium ionization state in the vicinity of the remnant. Using
the photoionization code Cloudy, we show that these constraints exclude any
hot, luminous progenitor for SN 1006, including stably hydrogen or helium
nuclear-burning white dwarfs, as well as any Chandrasekhar-mass white dwarf
accreting matter at yr via a disk. For
0509-67.5, the Balmer emission alone rules out any such white dwarf accreting
yr. For 0519-69.0 and DEM L71, the inferred
ambient ionization state of hydrogen is only weakly in tension with a recently
hot, luminous progenitor, and cannot be distinguished from e.g., a relatively
higher local Lyman continuum background, without additional line measurements.
Future deep spectroscopic observations will resolve this ambiguity, and can
either detect the influence of any luminous progenitor or rule out the same for
all resolved SN Ia remnants.Comment: 9 pages, 3 figures, 1 table. Accepted for publication in Ap
No hot and luminous progenitor for Tycho's supernova
Type Ia supernovae have proven vital to our understanding of cosmology, both
as standard candles and for their role in galactic chemical evolution; however,
their origin remains uncertain. The canonical accretion model implies a hot and
luminous progenitor which would ionize the surrounding gas out to a radius of
10--100 parsecs for 100,000 years after the explosion. Here we
report stringent upper limits on the temperature and luminosity of the
progenitor of Tycho's supernova (SN 1572), determined using the remnant itself
as a probe of its environment. Hot, luminous progenitors that would have
produced a greater hydrogen ionization fraction than that measured at the
radius of the present remnant (3 parsecs) can thus be excluded. This
conclusively rules out steadily nuclear-burning white dwarfs (supersoft X-ray
sources), as well as disk emission from a Chandrasekhar-mass white dwarf
accreting yr (recurrent novae). The lack of a
surrounding Str\"omgren sphere is consistent with the merger of a double white
dwarf binary, although other more exotic scenarios may be possible.Comment: 17 pages, 2 figures, including supplementary information. Original
accepted manuscript (before copyediting/formatting by Nature Astronomy
Upper limits on the luminosity of the progenitor of type Ia supernova SN2014J
We analysed archival data of Chandra pre-explosion observations of the
position of SN2014J in M82. No X-ray source at this position was detected in
the data, and we calculated upper limits on the luminosities of the progenitor.
These upper limits allow us to firmly rule out an unobscured supersoft X-ray
source progenitor with a photospheric radius comparable to the radius of white
dwarf near the Chandrasekhar mass (~1.38 M_sun) and mass accretion rate in the
interval where stable nuclear burning can occur. However, due to a relatively
large hydrogen column density implied by optical observations of the supernova,
we cannot exclude a supersoft source with lower temperatures, kT < 80 eV. We
find that the supernova is located in the centre of a large structure of soft
diffuse emission, about 200 pc across. The mass, ~3x10^4 M_sun and short
cooling time of the gas, tau_cool ~ 8 Myrs, suggest that it is a
supernova-inflated super-bubble, associated with the region of recent star
formation. If SN2014J is indeed located inside the bubble, it likely belongs to
the prompt population of type Ia supernovae, with a delay time as short as ~ 50
Myrs. Finally, we analysed the one existing post-supernova Chandra observation
and placed upper limit of ~ (1-2) 10^37 erg/s on the X-ray luminosity of the
supernova itself.Comment: 8 pages, 6 figure
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