2,178 research outputs found
Onset of giant planet migration before 4480 million years ago
Immediately after their formation, the terrestrial planets experienced
intense impact bombardment by comets, leftover planetesimals from primary
accretion, and asteroids. This temporal interval in solar system evolution,
termed late accretion, thermally and chemically modified solid planetary
surfaces and may have impeded the emergence of life on the Hadean Earth. The
sources and tempo of late accretion are, however, vague. Here, we present a
timeline that relates variably retentive radiometric ages from asteroidal
meteorites, to new dynamical models of late accretion that invokes giant planet
migration. Reconciliation of the geochronological data with dynamical models
shows that giant planet migration immediately leads to an intense 30 Myr influx
of comets to the entire solar system. The absence of whole-sale crustal reset
ages after 4450 Ma for the most resilient chronometers from Earth, Moon, Mars,
Vesta and various meteorite parent bodies confines the onset of giant planet
migration to no later than ca. 4480 Ma. Waning impacts from planetesimals,
asteroids (and a minor cometary component) continue to strike the inner planets
through a protracted monotonic decline in impactor flux; this is in agreement
with predictions from crater chronology. Amended global 3-D thermal analytical
bombardment models derived from our new impact mass-production functions show
that persistent niches for prebiotic chemistry on the early Hadean Earth could
endure late accretion for at least the last 4400 Myr.Comment: Main text: 46564 characters with spaces/7549 words Tables: 3
Figures:7 References: 11
Earth-like Habitats in Planetary Systems
Understanding the concept of habitability is related to an evolutionary
knowledge of the particular planet-in-question. Additional indications
so-called "systemic aspects" of the planetary system as a whole governs a
particular planet's claim on habitability. Here we focus on such systemic
aspects and discuss their relevance to the formation of an 'Earth-like'
habitable planet. We summarize our results obtained by lunar sample work and
numerical models within the framework of the Research Alliance "Planetary
Evolution and Life". We consider various scenarios which simulate the dynamical
evolution of the Solar System and discuss the likelihood of forming an
Earth-like world orbiting another star. Our model approach is constrained by
observations of the modern Solar System and the knowledge of its history.
Results suggest that the long-term presence of terrestrial planets is
jeopardized due to gravitational interactions if giant planets are present. But
habitability of inner rocky planets may be supported in those planetary systems
hosting giant planets.
Gravitational interactions within a complex multiple-body structure including
giant planets may supply terrestrial planets with materials which formed in the
colder region of the proto-planetary disk. During these processes, water, the
prime requisite for habitability, is delivered to the inner system. This may
occur either during the main accretion phase of terrestrial planets or via
impacts during a post-accretion bombardment. Results for both processes are
summarized and discussed with reference to the lunar crater record.
Starting from a scenario involving migration of the giant planets this
contribution discusses the delivery of water to Earth, the modification of
atmospheres by impacts in a planetary system context and the likelihood of the
existence of extrasolar Earth-like habitable worlds.Comment: 36 Pages, 6 figures, 2014, Special Issue in Planetary and Space
Science on the Helmholtz Research Alliance on Planetary Evolution and Lif
The cratering record of Ganymede and the origin of potential impactors: open issues
The origin of impactors on the Galilean satellites of Jupiter is an open question. In this study we present results from a mapping campaign based on reprocessed Voyager and Galileo SSI images in order to derive a thourough data base of Ganymede's crater distributions
Adjuvant radiotherapy and chemoradiation with gemcitabine after R1 resection in patients with pancreatic adenocarcinoma
Background: The purpose of the study was to evaluate the effect of radiation therapy and chemoradiation with gemcitabine (GEM) after R1 resection in patients with pancreatic adenocarcinoma (PAC). Methods: We performed a retrospective analysis of 25 patients who were treated with postoperative radiotherapy (RT) or chemoradiation (CRT) after surgery with microscopically positive resection margins for primary pancreatic cancer (PAC). Median age was 60 years (range 34 to 74 years), and there were 17 male and 8 female patients. Fractionated RT was applied with a median dose of 49.6 Gy (range 36 to 54 Gy). Eight patients received additional intraoperative radiotherapy (IORT) with a median dose of 12 Gy. Results: Median overall survival (mOS) of all treated patients was 22 months (95% confidence interval (CI) 7.9 to 36.1 months) after date of resection and 21.1 months (95% CI 7.6 to 34.6 months) after start of (C)RT. Median progression-free survival (mPFS) was 13.0 months (95% CI 0.93 to 25 months). Grading (G2 vs. G3, P = 0.005) and gender (female vs. male, P = 0.01) were significantly correlated with OS. There was a significant difference in mPFS between male and female patients (P = 0.008). A total of 11 from 25 patients experienced local tumour progression, and 19 patients were diagnosed with either locoregional or distant failure. Conclusions: We demonstrated that GEM-based CRT can be applied in analogy to neoadjuvant protocols in the adjuvant setting for PAC patients at high risk for disease recurrence after incomplete resection. Patients undergoing additive CRT have a rather good OS and PFS compared to historical control patient groups
ExoMars Raman Laser Spectrometer RLS, a tool for the potential recognition of wet target craters on Mars
In the present work, NIR, LIBS, Raman and XRD techniques have been
complementarily used to carry out a comprehensive characterization of a
terrestrial analogue selected from the Chesapeake Bay Impact Structure (CBIS).
The obtained data clearly highlight the key role of Raman spectroscopy in the
detection of minor and trace compounds, through which inferences about
geological processes occurred in the CBIS can be extrapolated. Beside the use
of commercial systems, further Raman analyses were performed by the Raman Laser
Spectrometer (RLS) ExoMars Simulator. This instrument represents the most
reliable tool to effectively predict the scientific capabilities of the
ExoMars/Raman system that will be deployed on Mars in 2021. By emulating the
analytical procedures and operational restrictions established by the ExoMars
mission rover design, it was proved that the RLS ExoMars Simulator is able to
detect the amorphization of quartz, which constitutes an analytical clue of the
impact origin of craters. On the other hand, the detection of barite and
siderite, compounds crystallizing under hydrothermal conditions, helps to
indirectly confirm the presence of water in impact targets. Furthermore, the
RLS ExoMars Simulator capability of performing smart molecular mappings was
also evaluated. According to the obtained results, the algorithms developed for
its operation provide a great analytical advantage over most of the automatic
analysis systems employed by commercial Raman instruments, encouraging its
application for many additional scientific and commercial purposes
an island endemic forest specialist and a widespread habitat generalist
Background. The bay cat Catopuma badia is endemic to Borneo, whereas its
sister species the Asian golden cat Catopuma temminckii is distributed from
the Himalayas and southern China through Indochina, Peninsular Malaysia and
Sumatra. Based on morphological data, up to five subspecies of the Asian
golden cat have been recognized, but a taxonomic assessment, including
molecular data and morphological characters, is still lacking. Results. We
combined molecular data (whole mitochondrial genomes), morphological data
(pelage) and species distribution projections (up to the Late Pleistocene) to
infer how environmental changes may have influenced the distribution of these
sister species over the past 120 000 years. The molecular analysis was based
on sequenced mitogenomes of 3 bay cats and 40 Asian golden cats derived mainly
from archival samples. Our molecular data suggested a time of split between
the two species approximately 3.16 Ma and revealed very low nucleotide
diversity within the Asian golden cat population, which supports recent
expansion of the population. Discussion. The low nucleotide diversity
suggested a population bottleneck in the Asian golden cat, possibly caused by
the eruption of the Toba volcano in Northern Sumatra (approx. 74 kya),
followed by a continuous population expansion in the Late Pleistocene/Early
Holocene. Species distribution projections, the reconstruction of the
demographic history, a genetic isolation-by-distance pattern and a gradual
variation of pelage pattern support the hypothesis of a post-Toba population
expansion of the Asian golden cat from south China/Indochina to Peninsular
Malaysia and Sumatra. Our findings reject the current classification of five
subspecies for the Asian golden cat, but instead support either a monotypic
species or one comprising two subspecies: (i) the Sunda golden cat,
distributed south of the Isthmus of Kra: C. t. temminckii and (ii)
Indochinese, Indian, Himalayan and Chinese golden cats, occurring north of the
Isthmus: C. t. moormensis
Community Engagement newsletter, Faculty of Veterinary Science, Spring, 2011
Community engagement project at VulPro / Cassie van der Walt, Jeanine Gautschi, Werner Wentzel, Luzanne Lourens, Reinach Erasmus & Natalie Braysher - Mamelodi Animal Health Clinic (MAHC) moving forward / Cherrie Liebenberg - OP students promoting awareness of the importance of castration at Loate CVC - Spanish and South African vet students visit the Loate CVC / Stephanie Friedman (Student) & Daleen Grundlingh (SAVA CVC Coordinator) - Pets picnic in the park / Lauren DommettNews articles with colour photos about the various community engagement projects of the Faculty of Veterinary Science, University of Pretoria
Polysilsesquioxane nanoparticles for triggered release of cisplatin and effective cancer chemoradiotherapy
Chemoradiotherapy is a well-established treatment paradigm in oncology. There has been strong interest in identifying strategies to further improve its therapeutic index. An innovative strategy is to utilize nanoparticle (NP)chemotherapeutics in chemoradiation. Since the most commonly utilized chemotherapeutic with radiotherapy is cisplatin, the development of a NP cisplatin for chemoradiotherapy has the highest potential impact on this treatment. Here, we report the development of a NP comprised of polysilsesquioxane (PSQ) polymer crosslinked by a cisplatin prodrug (Cisplatin-PSQ) and its utilization in chemoradiotherapy using non-small cell lung cancer as a disease model. Cisplatin-PSQ NP has an exceptionally high loading of cisplatin. Cisplatin-PSQ NPs were evaluated in chemoradiotherapy in vitro and in vivo. They demonstrated significantly higher therapeutic efficacy when compared to cisplatin. These results suggest that the Cisplatin-PSQ NP holds potential for clinical translation in chemoradiotherapy
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