1,271 research outputs found
Using all-sky differential photometry to investigate how nocturnal clouds darken the night sky in rural areas
Artificial light at night has affected most of the natural nocturnal
landscapes worldwide and the subsequent light pollution has diverse effects on
flora, fauna and human well-being. To evaluate the environmental impacts of
light pollution, it is crucial to understand both the natural and artificial
components of light at night under all weather conditions. The night sky
brightness for clear skies is relatively well understood and a reference point
for a lower limit is defined. However, no such reference point exists for
cloudy skies. While some studies have examined the brightening of the night sky
by clouds in urban areas, the published data on the (natural) darkening by
clouds is very sparse. Knowledge of reference points for the illumination of
natural nocturnal environments however, is essential for experimental design
and ecological modeling to assess the impacts of light pollution. Here we use
differential all-sky photometry with a commercial digital camera to investigate
how clouds darken sky brightness at two rural sites. The spatially resolved
data enables us to identify and study the nearly unpolluted parts of the sky
and to set an upper limit on ground illumination for overcast nights at sites
without light pollution.Comment: 17 pages, 6 figure
Evaluating the summer night sky brightness at a research field site on Lake Stechlin in northeastern Germany
We report on luminance measurements of the summer night sky at a field site
on a freshwater lake in northeastern Germany (Lake Stechlin) to evaluate the
amount of artificial skyglow from nearby and distant towns in the context of a
planned study on light pollution. The site is located about 70 km north of
Berlin in a rural area possibly belonging to one of the darkest regions in
Germany. Continuous monitoring of the zenith sky luminance between June and
September 2015 was conducted utilizing a Sky Quality Meter. With this device,
typical values for clear nights in the range of 21.5-21.7
magarcsec were measured, which is on the order of the natural sky
brightness during starry nights. On overcast nights, values down to 22.84
magarcsec were obtained, which is about one third as bright as on
clear nights. The luminance measured on clear nights as well as the darkening
with the presence of clouds indicate that there is very little influence of
artificial skyglow on the zenith sky brightness at this location. Furthermore,
fish-eye lens sky imaging luminance photometry was performed with a digital
single-lens reflex camera on a clear night in the absence of moonlight. The
photographs unravel several distant towns as possible sources of light
pollution on the horizon. However, the low level of artificial skyglow makes
the field site at Lake Stechlin an excellent location to study the effects of
skyglow on a lake ecosystem in a controlled fashion.Comment: 20 pages, 8 figures, Journal of Quantitative Spectroscopy and
Radiative Transfer 201
Imaging and mapping the impact of clouds on skyglow with all-sky photometry
Artificial skyglow is constantly growing on a global scale, with potential
ecological consequences ranging up to affecting biodiversity. To understand
these consequences, worldwide mapping of skyglow for all weather conditions is
urgently required. In particular, the amplification of skyglow by clouds needs
to be studied, as clouds can extend the reach of skyglow into remote areas not
affected by light pollution on clear nights. Here we use commercial digital
single lens reflex cameras with fisheye lenses for all-sky photometry. We track
the reach of skyglow from a peri-urban into a remote area on a clear and a
partly cloudy night by performing transects from the Spanish town of Balaguer
towards Montsec Astronomical Park. From one single all-sky image, we extract
zenith luminance, horizontal and scalar illuminance. While zenith luminance
reaches near-natural levels at 5km distance from the town on the clear night,
similar levels are only reached at 27km on the partly cloudy night. Our results
show the dramatic increase of the reach of skyglow even for moderate cloud
coverage at this site. The powerful and easy-to-use method promises to be
widely applicable for studies of ecological light pollution on a global scale
also by non-specialists in photometry.Comment: 13 pages, 7 figure
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HoxA3 is an apical regulator of haemogenic endothelium.
During development, haemogenesis occurs invariably at sites of vasculogenesis. Between embryonic day (E) 9.5 and E10.5 in mice, endothelial cells in the caudal part of the dorsal aorta generate haematopoietic stem cells and are referred to as haemogenic endothelium. The mechanisms by which haematopoiesis is restricted to this domain, and how the morphological transformation from endothelial to haematopoietic is controlled are unknown. We show here that HoxA3, a gene uniquely expressed in the embryonic but not yolk sac vasculature, restrains haematopoietic differentiation of the earliest endothelial progenitors, and induces reversion of the earliest haematopoietic progenitors into CD41-negative endothelial cells. This reversible modulation of endothelial-haematopoietic state is accomplished by targeting key haematopoietic transcription factors for downregulation, including Runx1, Gata1, Gfi1B, Ikaros, and PU.1. Through loss-of-function, and gain-of-function epistasis experiments, and the identification of antipodally regulated targets, we show that among these factors, Runx1 is uniquely able to erase the endothelial program set up by HoxA3. These results suggest both why a frank endothelium does not precede haematopoiesis in the yolk sac, and why haematopoietic stem cell generation requires Runx1 expression only in endothelial cells
Measuring Light Pollution with Fisheye Lens Imagery from A Moving Boat, A Proof of Concept
Near all-sky imaging photometry was performed from a boat on the Gulf of
Aqaba to measure the night sky brightness in a coastal environment. The boat
was not anchored, and therefore drifted and rocked. The camera was mounted on a
tripod without any inertia/motion stabilization. A commercial digital single
lens reflex (DSLR) camera and fisheye lens were used with ISO setting of 6400,
with the exposure time varied between 0.5 s and 5 s. We find that despite
movement of the vessel the measurements produce quantitatively comparable
results apart from saturation effects. We discuss the potential and limitations
of this method for mapping light pollution in marine and freshwater systems.
This work represents the proof of concept that all-sky photometry with a
commercial DSLR camera is a viable tool to determine light pollution in an
ecological context from a moving boat.Comment: 9 pages, 6 figures, accepted at International Journal of Sustainable
Lightin
Nebularity: The Continuing Proliferation of the Abject in Contemporary Art
This thesis investigates abject art why it has proliferated since gaining notoriety in the late 1980s/early 1990s. The exhibition, Nebularity, brings together non-traditional abject artworks in order to broaden develop abject theory for the 21st century. By employing Julia Kristeva’s theory on the abject in conjunction with Georges Bataille’s formlessness and Jean Paul Sartre’s interpretation of the hole, Nebularity argues that abject art remains current in contemporary practice because of ability to unsettle the self through the encroachment of the other. Three contemporary artists – Louis Fortier, Jesika Joy, and Kim Stanford – utilize multiple mediums to demonstrate how varied and abstract artworks can have the same type of perturbing and unsettling potential as traditionally defined abject art. By confusing boundaries, imposing intimacy, and deteriorating conventional forms, Nebularity asserts that the abject is not just another genre of art but a means to continually challenge structures of subjectivity and knowledge
Notch activation is required for downregulation of HoxA3-dependent endothelial cell phenotype during blood formation.
Hemogenic endothelium (HE) undergoes endothelial-to-hematopoietic transition (EHT) to generate blood, a process that requires progressive down-regulation of endothelial genes and induction of hematopoietic ones. Previously, we have shown that the transcription factor HoxA3 prevents blood formation by inhibiting Runx1 expression, maintaining endothelial gene expression and thus blocking EHT. In the present study, we show that HoxA3 also prevents blood formation by inhibiting Notch pathway. HoxA3 induced upregulation of Jag1 ligand in endothelial cells, which led to cis-inhibition of the Notch pathway, rendering the HE nonresponsive to Notch signals. While Notch activation alone was insufficient to promote blood formation in the presence of HoxA3, activation of Notch or downregulation of Jag1 resulted in a loss of the endothelial phenotype which is a prerequisite for EHT. Taken together, these results demonstrate that Notch pathway activation is necessary to downregulate endothelial markers during EHT
Transcripts that associate with the RNA binding protein, DEAD-END (DND1), in embryonic stem (ES) cells
BackgroundThe RNA binding protein, DEAD END (DND1), is essential for maintaining viable germ cells in vertebrates. It is also a testicular germ cell tumor susceptibility factor in mice. DND1 has been shown to interact with the 3'-untranslated region (3'-UTR) of mRNAs such as P27 and LATS2. Binding of DND1 to the 3'-UTRs of these transcripts blocks the inhibitory function of microRNAs (miRNA) from these transcripts and in this way DND1 helps maintain P27 and LATS2 protein expression. We found that DND1 is also expressed in embryonic stem (ES) cells. Because ES cells share similar gene expression patterns as germ cells, we utilized ES cells to identify additional candidate mRNAs that associate with DND1.ResultsES cells are readily amenable to genetic modification and easier to culture in vitro compared to germ cells. Therefore, for the purpose of our study, we made a genetically modified, stable, human embryonic stem (hES) cell line that expresses hemagluttinin (HA)-tagged DND1 in a doxycycline (dox) regulatable manner. This line expresses modest levels of HA-DND1 and serves as a good system to study DND1 function in vitro. We used this stable cell line to identify the transcripts that physically interact with DND1. By performing ribonucleoprotein immunoprecipitation (RIP) followed by RT-PCR, we identified that transcripts encoding pluripotency factors (OCT4, SOX2, NANOG, LIN28), cell cycle regulators (TP53, LATS2) and apoptotic factors (BCLX, BAX) are specifically associated with the HA-DND1 ribonucleoprotein complex. Surprisingly, in many cases, bioinformatics analysis of the pulled-down transcripts did not reveal the presence of known DND1 interacting motifs.ConclusionsOur results indicate that the inducible ES cell line system serves as a suitable in vitro system to identify the mRNA targets of DND1. The RIP-RT results hint at the broad spectrum of mRNA targets that interact with DND1 in ES cells. Based on what is known about DND1 function, our results suggest that DND1 may impose another level of translational regulation to modulate expression of critical factors in ES cells
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