1,676 research outputs found
The Impact Of Forced Financial Restatements On The Share Prices Of JSE Listed Firms
This study investigates the effect of forced financial restatements on the share prices listed on the Johannesburg Stock Exchange (JSE). An event study methodology is used to examine the share price reaction of 34 firms that forcefully restated their results following a GAAP Monitoring Panel review. The results indicate that the equity of 79.1 per cent of the firms decreased as a result of the restatement. The average standardised abnormal returns for 55.9 per cent of these firms were also found to be negative. The study further finds that the volume of shares traded directly following the announcement increased substantially, especially five days following the announcement. The study makes a contribution to the existing literature in that is the first of its kind to focus on the share price reaction of forced financial restatements on share prices in the South African context
Lessons from the Regulation of E-scooters through the MDS Standard: Policy Lessons for Connected Vehicles
Connected vehicles generate new data streams that present promising opportunities for policymakers to monitor and learn from events and behavior. To explore what we can learn from how public entities leverage ubiquitous data streams for policy development and enforcement, we draw on a case study of the standard Mobility Data Specification (MDS) and its use by cities to regulate E-scooter operators. Our findings suggest that (1) the richness of real-time data changes the speed of policy revision, (2) data access enables moving some micro-decisions to the edge, and (3) policy will be formulated as fixed or flexible with different amendment rules
A merger in the dusty, galaxy A1689-zD1?
The gravitationally-lensed galaxy A1689-zD1 is one of the most distant
spectroscopically confirmed sources (). It is the earliest known galaxy
where the interstellar medium (ISM) has been detected; dust emission was
detected with the Atacama Large Millimetre Array (ALMA). A1689-zD1 is also
unusual among high-redshift dust emitters as it is a sub-L* galaxy and is
therefore a good prospect for the detection of gaseous ISM in a more typical
galaxy at this redshift. We observed A1689-zD1 with ALMA in bands 6 and 7 and
with the Green Bank Telescope (GBT) in band . To study the structure of
A1689-zD1, we map the mm thermal dust emission and find two spatial components
with sizes about \,kpc (lensing-corrected). The rough spatial
morphology is similar to what is observed in the near-infrared with {\it HST}
and points to a perturbed dynamical state, perhaps indicative of a major merger
or a disc in early formation. The ALMA photometry is used to constrain the
far-infrared spectral energy distribution, yielding a dust temperature (--\,K for ). We do not detect the CO(3-2) line
in the GBT data with a 95\% upper limit of 0.3\,mJy observed. We find a slight
excess emission in ALMA band~6 at 220.9\,GHz. If this excess is real, it is
likely due to emission from the [CII] 158.8\,m line at . The stringent upper limits on the [CII]/ luminosity ratio
suggest a [CII] deficit similar to several bright quasars and massive
starbursts.Comment: 9 pages, accepted to MNRAS, in pres
Extinction curve template for intrinsically reddened quasars
We analyze the near-infrared to UV data of 16 quasars with redshifts ranging
from 0.71 2.13 to investigate dust extinction properties. The
sample presented in this work is obtained from the High Quasar (HAQ)
survey. The quasar candidates were selected from the Sloan Digital Sky Survey
(SDSS) and the UKIRT Infrared Deep Sky Survey (UKIDSS), and follow-up
spectroscopy was carried out at the Nordic Optical Telescope (NOT) and the New
Technology Telescope (NTT). To study dust extinction curves intrinsic to the
quasars, from the HAQ survey we selected 16 cases where the Small Magellanic
Cloud (SMC) law could not provide a good solution to the spectral energy
distributions (SEDs). We derived the extinction curves using Fitzpatrick &
Massa 1986 (FM) law by comparing the observed SEDs to the combined quasar
template from Vanden Berk et al. 2001 and Glikman et al. 2006. The derived
extinction, , ranges from 0.2-1.0 mag. All the individual extinction
curves of our quasars are steeper (-2.7) than that of the SMC, with a
weighted mean value of . We derive an `average quasar extinction
curve' for our sample by fitting SEDs simultaneously by using the weighted mean
values of the FM law parameters and a varying . The entire sample is well
fit with a single best-fit value of . The `average quasar
extinction curve' deviates from the steepest Milky Way and SMC extinction
curves at a confidence level . Such steep extinction curves
suggest a significant population of silicates to produce small dust grains.
Moreover, another possibility could be that the large dust grains may have been
destroyed by the activity of the nearby active galactic nuclei (AGN), resulting
in steep extinction curves.Comment: 8 pages, 4 figures, 1 tabl
Helium in natal HII regions: the origin of the X-ray absorption in gamma-ray burst afterglows
Soft X-ray absorption in excess of Galactic is observed in the afterglows of
most gamma-ray bursts (GRBs), but the correct solution to its origin has not
been arrived at after more than a decade of work, preventing its use as a
powerful diagnostic tool. We resolve this long-standing problem and find that
He in the GRB's host HII region is responsible for most of the absorption. We
show that the X-ray absorbing column density (N_Hx) is correlated with both the
neutral gas column density and with the optical afterglow extinction (Av). This
correlation explains the connection between dark bursts and bursts with high
N_Hx values. From these correlations we exclude an origin of the X-ray
absorption which is not related to the host galaxy, i.e. the intergalactic
medium or intervening absorbers are not responsible. We find that the
correlation with the dust column has a strong redshift evolution, whereas the
correlation with the neutral gas does not. From this we conclude that the
column density of the X-ray absorption is correlated with the total gas column
density in the host galaxy rather than the metal column density, in spite of
the fact that X-ray absorption is typically dominated by metals. The strong
redshift evolution of N_Hx/Av is thus a reflection of the cosmic metallicity
evolution of star-forming galaxies. We conclude that the absorption of X-rays
in GRB afterglows is caused by He in the HII region hosting the GRB. While dust
is destroyed and metals are stripped of all of their electrons by the GRB to
great distances, the abundance of He saturates the He-ionising UV continuum
much closer to the GRB, allowing it to remain in the neutral or singly-ionised
state. Helium X-ray absorption explains the correlation with total gas, the
lack of strong evolution with redshift as well as the absence of dust, metal or
hydrogen absorption features in the optical-UV spectra.Comment: 10 pages, 4 figures, submitted to Ap
Ultraviolet Emission Lines in Young Low Mass Galaxies at z~2: Physical Properties and Implications for Studies at z>7
We present deep spectroscopy of 17 very low mass (M* ~ 2.0x10^6 Msun to
1.4x10^9 Msun) and low luminosity (M_UV ~ -13.7 to -19.9) gravitationally
lensed galaxies in the redshift range z~1.5-3.0. Deep rest-frame ultraviolet
spectra reveal large equivalent width emission from numerous lines (NIV],
OIII], CIV, Si III], CIII]) which are rarely seen in individual spectra of more
massive star forming galaxies. CIII] is detected in 16 of 17 low mass star
forming systems with rest-frame equivalent widths as large as 13.5 Angstroms.
Nebular CIV emission is present in the most extreme CIII] emitters, requiring
an ionizing source capable of producing a substantial component of photons with
energies in excess of 47.9 eV. Photoionization models support a picture whereby
the large equivalent widths are driven by the increased electron temperature
and enhanced ionizing output arising from metal poor gas and stars, young
stellar populations, and large ionization parameters. The young ages implied by
the emission lines and continuum SEDs indicate that the extreme line emitters
in our sample are in the midst of a significant upturn in their star formation
activity. The low stellar masses, blue UV colors, and large sSFRs of our sample
are similar to those of typical z>6 galaxies. Given the strong attenuation of
Ly-alpha in z>6 galaxies we suggest that CIII] is likely to provide our best
probe of early star forming galaxies with ground-based spectrographs and one of
the most efficient means of confirming z>10 galaxies with the James Webb Space
Telescope.Comment: 22 pages, 8 figures, accepted for publication in MNRA
Defocused imaging of UV-driven surface-bound molecular motors
Synthetic
molecular motors continue to attract great interest due
to their ability to transduce energy into nanomechanical motion, the
potential to do work and drive systems out-of-equilibrium. Of particular
interest are unidirectional rotary molecular motors driven by chemical
fuel or light. Probing the mechanistic details of their operation
at the single-molecule level is hampered by the diffraction limit,
which prevents the collection of dynamic positional information by
traditional optical methods. Here, we use defocused wide-field imaging
to examine the unidirectional rotation of individual molecular rotary
motors on a quartz surface in unprecedented detail. The sequential
occupation of nanomechanical states during the UV and heat-induced
cycle of rotation are directly imaged in real-time. The approach will
undoubtedly prove important in elucidating the mechanistic details
and assessing the utility of novel synthetic molecular motors in the
future
Guidelines by an ad hoc European committe for elective chronic peritoneal dialysis in pediatric patients
Plant-parasitic nematodes associated with the root zone of hop cultivars planted in a Florida field soil
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