117 research outputs found
Mineralogy and Geochemistry of the Asanje Iron Ore Deposit within the Mayamaya-Hombolo Belt, Dodoma Region, Central Tanzania
This paper presents the mineralogy and chemical composition including iron ore impurities to ascertain its suitability for industrial applications. The Asanje iron ore deposit is hosted in Precambrian volcano-sedimentary rocks in the Mayamaya-Hombolo Belt in Dodoma region, within the Lake Nyanza Superterrane. Iron ores are found in two parallel ridges trending NW-SE. Ridge I occurs as vein and banded hematite-type ore and Ridge II as massive-type ore. A total of 24 ore samples were analysed for major and trace elements by XRF and petrographic studies by optical microscopy and XRD. The XRD results revealed that hematite and goethite are the main components and quartz is the gangue mineral in the iron ores. The XRF data shows the Fe2O3t content ranges from 20.8 to 87.3 wt% with an average of 52.7 wt%. The average concentrations in wt% of impurities such as SiO2, Al2O3, P2O5 and S are 37.9, 0.9, 1.2, and 0.2, respectively. By comparison, Ridge II has greater iron content (30.5â87.3 = Avg. 64.66 wt% Fe2O3t) than Ridge I (20.8â78.22 = Avg. 48.68 wt% Fe2O3t). Based on the chemical composition, the quality of iron ore is categorised as low to medium grade, and can be used in metallurgical and cement industries.
Keywords: Mineralogy, Geochemistry, Asanje Iron ore deposit, Mayamaya-Hombolo Belt, Tanzani
Total Electron Temperature Derived from Quasi-Thermal Noise Spectroscopy In the Pristine Solar Wind: Parker Solar Probe Observations
The Quasi-thermal noise (QTN) technique is a reliable tool to yield accurate
measurements of the electron parameters in the solar wind. We apply this method
on Parker Solar Probe (PSP) observations to derive the total electron
temperature () from the linear fit of the high-frequency part of the QTN
spectra acquired by the RFS/FIELDS instrument, and present a combination of
12-day period of observations around each perihelion from Encounter One (E01)
to Ten (E10) (with E08 not included) with the heliocentric distance varying
from about 13 to 60 solar radii (). We find that the total electron
temperature decreases with the distance as , which is much
slower than adiabatic. The extrapolated based on PSP observations is
consistent with the exospheric solar wind model prediction at 10
, Helios observations at 0.3 AU and Wind observations at 1 AU.
Also, , extrapolated back to 10 , is almost the same as the
strahl electron temperature (measured by SPAN-E) which is considered to
be closely related to or even almost equal to the coronal electron temperature.
Furthermore, the radial profiles in the slower solar wind (or flux tube
with larger mass flux) are steeper than those in the faster solar wind (or flux
tube with smaller mass flux). More pronounced anticorrelated - is
observed when the solar wind is slower and closer to the Sun.Comment: 10 pages, 7 figures, and Astronomy & Astrophysics Accepte
Getting the agenda right: measuring media agenda using topic models
Agenda setting is the theory of how issue salience is transferred from the media to media audience. An agenda-setting study requires one to define a set of issues and to measure their salience. We propose a semisupervised approach based on topic modeling for exploring a news corpus and measuring the media agenda by tagging news articles with issues. The approach relies on an off-the-shelf Latent Dirichlet Allocation topic model, manual labeling of topics, and topic model customization. In preliminary evaluation, the tagger achieves a micro F1-score of 0.85 and outperforms the supervised baselines, suggesting that it could be successfully used for agenda-setting studies
The Safe Use of a PTEN Inhibitor for the Activation of Dormant Mouse Primordial Follicles and Generation of Fertilizable Eggs
Primordial ovarian follicles, which are often present in the ovaries of premature ovarian failure (POF) patients or are cryopreserved from the ovaries of young cancer patients who are undergoing gonadotoxic anticancer therapies, cannot be used to generate mature oocytes for in vitro fertilization (IVF). There has been very little success in triggering growth of primordial follicles to obtain fertilizable oocytes due to the poor understanding of the biology of primordial follicle activation.We have recently reported that PTEN (phosphatase and tensin homolog deleted on chromosome ten) prevents primordial follicle activation in mice, and deletion of Pten from the oocytes of primordial follicles leads to follicular activation. Consequently, the PTEN inhibitor has been successfully used in vitro to activate primordial follicles in both mouse and human ovaries. These results suggest that PTEN inhibitors could be used in ovarian culture medium to trigger the activation of primordial follicle. To study the safety and efficacy of the use of such inhibitors, we activated primordial follicles from neonatal mouse ovaries by transient treatment with a PTEN inhibitor bpV(HOpic). These ovaries were then transplanted under the kidney capsules of recipient mice to generate mature oocytes. The mature oocytes were fertilized in vitro and progeny mice were obtained after embryo transfer.Long-term monitoring up to the second generation of progeny mice showed that the mice were reproductively active and were free from any overt signs or symptoms of chronic illnesses. Our results indicate that the use of PTEN inhibitors could be a safe and effective way of generating mature human oocytes for use in novel IVF techniques
Whistler waves generated inside magnetic dips in the young solar wind: observations of the Search-Coil Magnetometer on board Parker Solar Probe
Context. Whistler waves are electromagnetic waves produced by electron-driven
instabilities, that in turn can reshape the electron distributions via
wave-particle interactions. In the solar wind, they are one of the main
candidates for explaining the scattering of the strahl electron population into
the halo at increasing radial distances from the Sun and for subsequently
regulating the solar wind heat flux. However, it is unclear what type of
instability dominates to drive whistlers in the solar wind. Aims. Our goal is
to study whistler wave parameters in the young solar wind sampled by Parker
Solar Probe (PSP). The wave normal angle (WNA) in particular is a key parameter
to discriminate between the generation mechanisms of these waves. Methods. We
analyze the cross-spectral matrices of magnetic fieldfluctuations measured by
the Search-Coil Magnetometer (SCM) and processed by the Digital Fields Board
(DFB) from the FIELDS suite during PSP's first perihelion. Results. Among the
2701 wave packets detected in the cross spectra, namely individual bins in time
and frequency, most were quasi-parallel to the background magnetic field but a
significant part (3%) of observed waves had oblique (> 45{\deg}) WNA. The
validation analysis conducted with the time-series waveforms reveal that this
percentage is a lower limit. Moreover, we find that about 64% of the whistler
waves detected in the spectra are associated with at least one magnetic dip.
Conclusions. We conclude that magnetic dips provides favorable conditions for
the generation of whistler waves. We hypothesize that the whistlers detected in
magnetic dips are locally generated by the thermal anisotropy as quasi-parallel
and can gain obliqueness during their propagation. We finally discuss the
implication of our results for the scattering of the strahl in the solar wind.Comment: 15 pages, 14 figures, recommended for publication in A&
Analysis of LIN28A in early human ovary development and as a candidate gene for primary ovarian insufficiency
Lin28 proteins are emerging as important regulators of microRNAs in endocrine systems. Lin28a regulates primordial germ cell development and puberty timing in mice, whereas the related protein LIN28B is associated with age at menarche in genome-wide association studies in humans. Here, we studied expression of LIN28A and LIN28B in early human gonad development. LIN28A increased in the developing ovary between 6 and 9 weeks post conception, but not in the developing testis. Immunohistochemistry demonstrated LIN28A in peripheral germ cells. LIN28B was expressed at lower levels in both tissues and did not increase with time. As disruption of Lin28a affects germ cell development in mice, LIN28A was considered a candidate gene for primary ovarian insufficiency (POI) in humans. However, no significant changes were found in 50 women studied. These findings show LIN28A is strongly expressed in germ cells during early human ovary development, but disruption of LIN28A is not a common cause of POI
Proceedings from the 2018 Canadian Association for the Study of the Liver Single Topic ConferenceâDecompensated Cirrhosis : from clinic to transplant
Actes publiés dans le Canadian Liver Journal; vol. 2, no. 4, Fall 2019, p. 137-170
Electron-Driven Instabilities in the Solar Wind
The electrons are an essential particle species in the solar wind. They often exhibit non-equilibrium features in their velocity distribution function. These include temperature anisotropies, tails (kurtosis), and reflectional asymmetries (skewness), which contribute a significant heat flux to the solar wind. If these non-equilibrium features are sufficiently strong, they drive kinetic micro-instabilities. We develop a semi-graphical framework based on the equations of quasi-linear theory to describe electron-driven instabilities in the solar wind. We apply our framework to resonant instabilities driven by temperature anisotropies. These include the electron whistler anisotropy instability and the propagating electron firehose instability. We then describe resonant instabilities driven by reflectional asymmetries in the electron distribution function. These include the electron/ion-acoustic, kinetic Alfvén heat-flux, Langmuir, electron-beam, electron/ion-cyclotron, electron/electron-acoustic, whistler heat-flux, oblique fast-magnetosonic/whistler, lower-hybrid fan, and electron-deficit whistler instability. We briefly comment on non-resonant instabilities driven by electron temperature anisotropies such as the mirror-mode and the non-propagating firehose instability. We conclude our review with a list of open research topics in the field of electron-driven instabilities in the solar wind
Parker solar probe: four years of discoveries at solar cycle minimum
Launched on 12 Aug. 2018, NASAâs Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The missionâs primary science goal is to determine the structure and dynamics of the Sunâs coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-AlfvĂ©nic solar wind, which is one of the missionâs primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles
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