73 research outputs found
Learning Area Methodology 4B: Natural Sciences
Exam paper for second semester Learning Area Methodology 4B: Natural Science
Stability of wooded patches in a South African nutrient-poor grassland: do nutrients, fire or herbivores limit their expansion?
Patches of wooded vegetation in nutrient-poor grassland characteristically contain high soil moisture and nutrient availability compared with surrounding grassland. These `islands of fertilityÂż appear stable in size, suggesting that tree recruitment at the patch boundary is limited. We hypothesize that tree establishment in adjacent grassland is limited by (1) competition for resources, (2) fire or (3) herbivory. In a South African grassland, we measured moisture availability and conducted a bioassay experiment to analyse whether soil nutrient limits tree recruitment at the patch boundary. We thus measured nutrient concentrations of maize plants grown in patch, boundary and grassland soil. To investigate whether browsing or fire affected tree seedlings at the patch boundary, we burned plots including patches, and used fences to exclude browsers. Neither soil moisture nor nutrient availability at the boundary differed from inside the patches, suggesting that tree recruitment at the boundary is not resource limited. Both fire and browsing combined caused a significantly lower tree seedling growth at the patch boundary, suggesting that these two factors can impede tree recruitment. The balance between positive feedback mechanisms facilitating tree recruitment, and the negative impact of fire and browsing can explain the apparent stability of these islands of fertility
The CUORE cryostat: an infrastructure for rare event searches at millikelvin temperatures
The CUORE experiment is the world's largest bolometric experiment. The
detector consists of an array of 988 TeO2 crystals, for a total mass of 742 kg.
CUORE is presently taking data at the Laboratori Nazionali del Gran Sasso,
Italy, searching for the neutrinoless double beta decay of 130Te. A large
custom cryogen-free cryostat allows reaching and maintaining a base temperature
of about 10 mK, required for the optimal operation of the detector. This
apparatus has been designed in order to achieve a low noise environment, with
minimal contribution to the radioactive background for the experiment. In this
paper, we present an overview of the CUORE cryostat, together with a
description of all its sub-systems, focusing on the solutions identified to
satisfy the stringent requirements. We briefly illustrate the various phases of
the cryostat commissioning and highlight the relevant steps and milestones
achieved each time. Finally, we describe the successful cooldown of CUORE
Scientists' warning to humanity on insect extinctions
Here we build on the manifesto âWorld Scientistsâ Warning to Humanity, issued by the Alliance of World Scientists. As a group of conservation biologists deeply concerned about the decline of insect populations, we here review what we know about the drivers of insect extinctions, their consequences, and how extinctions can negatively impact humanity. We are causing insect extinctions by driving habitat loss, degradation, and fragmentation, use of polluting and harmful substances, the spread of invasive species, global climate change, direct overexploitation, and co-extinction of species dependent on other species. With insect extinctions, we lose much more than species. We lose abundance and biomass of insects, diversity across space and time with consequent homogenization, large parts of the tree of life, unique ecological functions and traits, and fundamental parts of extensive networks of biotic interactions. Such losses lead to the decline of key ecosystem services on which humanity depends. From pollination and decomposition, to being resources for new medicines, habitat quality indication and many others, insects provide essential and irreplaceable services. We appeal for urgent action to close key knowledge gaps and curb insect extinctions. An investment in research programs that generate local, regional and global strategies that counter this trend is essential. Solutions are available and implementable, but urgent action is needed now to match our intentions.Peer reviewe
Solutions for humanity on how to conserve insects
The fate of humans and insects intertwine, especially through the medium of plants. Global environmental change, including land transformation and contamination, is causing concerning insect diversity loss, articulated in the companion review Scientists' warning to humanity on insect extinctions. Yet, despite a sound philosophical foundation, recognized ethical values, and scientific evidence, globally we are performing poorly at instigating effective insect conservation. As insects are a major component of the tapestry of life, insect conservation would do well to integrate better with overall biodiversity conservation and climate change mitigation. This also involves popularizing insects, especially through use of iconic species, through more media coverage, and more inclusive education. Insect conservationists need to liaise better with decision makers, stakeholders, and land managers, especially at the conceptually familiar scale of the landscape. Enough evidence is now available, and synthesized here, which illustrates that multiple strategies work at local levels towards saving insects. We now need to expand these locally-crafted strategies globally. Tangible actions include ensuring maintenance of biotic complexity, especially through improving temporal and spatial heterogeneity, functional connectivity, and metapopulation dynamics, while maintaining unique habitats, across landscape mosaics, as well as instigating better communication. Key is to have more expansive sustainable agriculture and forestry, improved regulation and prevention of environmental risks, and greater recognition of protected areas alongside agro-ecology in novel landscapes. Future-proofing insect diversity is now critical, with the benefits far reaching, including continued provision of valuable ecosystem services and the conservation of a rich and impressive component of Earth's biodiversity.Peer reviewe
JUNO Conceptual Design Report
The Jiangmen Underground Neutrino Observatory (JUNO) is proposed to determine
the neutrino mass hierarchy using an underground liquid scintillator detector.
It is located 53 km away from both Yangjiang and Taishan Nuclear Power Plants
in Guangdong, China. The experimental hall, spanning more than 50 meters, is
under a granite mountain of over 700 m overburden. Within six years of running,
the detection of reactor antineutrinos can resolve the neutrino mass hierarchy
at a confidence level of 3-4, and determine neutrino oscillation
parameters , , and to
an accuracy of better than 1%. The JUNO detector can be also used to study
terrestrial and extra-terrestrial neutrinos and new physics beyond the Standard
Model. The central detector contains 20,000 tons liquid scintillator with an
acrylic sphere of 35 m in diameter. 17,000 508-mm diameter PMTs with high
quantum efficiency provide 75% optical coverage. The current choice of
the liquid scintillator is: linear alkyl benzene (LAB) as the solvent, plus PPO
as the scintillation fluor and a wavelength-shifter (Bis-MSB). The number of
detected photoelectrons per MeV is larger than 1,100 and the energy resolution
is expected to be 3% at 1 MeV. The calibration system is designed to deploy
multiple sources to cover the entire energy range of reactor antineutrinos, and
to achieve a full-volume position coverage inside the detector. The veto system
is used for muon detection, muon induced background study and reduction. It
consists of a Water Cherenkov detector and a Top Tracker system. The readout
system, the detector control system and the offline system insure efficient and
stable data acquisition and processing.Comment: 328 pages, 211 figure
International collaborative follow - up investigation of graduating high school studentsâ understandings of the nature of scientific inquiry: is progress Being made?
Understandings of the nature of scientific inquiry (NOSI), as opposed to engaging students in inquiry learning experiences, are included in science education reform documents around the world. However, little is known about what students have learned about NOSI during their pre-college school years. The purpose of this large-scale follow-up international project (i.e. 32 countries and regions, spanning six continents and including 3917 students for the high school sample) was to collect data on what exiting high school students have learned about NOSI. Additionally, the study investigated changes in 12th grade studentsâ NOSI understandings compared to seventh grade (i.e. 20 countries and regions) studentsâ understandings from a prior investigation [Lederman et al. (2019). An international collaborative investigation of beginning seventh grade studentsâ understandings of scientific inquiry: Establishing a baseline. Journal of Research in Science Teaching, 56(4), 486â515. https://doi.org/10.1002/tea.21512]. This study documents and discusses graduating high school studentsâ understandings and compares their understandings to seventh grade studentsâ understandings of the same aspects of scientific inquiry for each country. It is important to note that collecting data from each of the 130+ countries globally was not feasible. Similarly, it was not possible to collect data from every region of each country. A concerted effort was made, however, to provide a relatively representative picture of each country and the world
CUORE-0 detector: design, construction and operation
The CUORE experiment will search for neutrinoless double-beta decay ofTe with an array of 988 TeO bolometers arranged in 19 towers.CUORE-0, the first tower assembled according to the CUORE procedures, was builtand commissioned at Laboratori Nazionali del Gran Sasso, and took data fromMarch 2013 to March 2015. In this paper we describe the design, constructionand operation of the CUORE-0 experiment, with an emphasis on the improvementsmade over a predecessor experiment, Cuoricino. In particular, we demonstratewith CUORE-0 data that the design goals of CUORE are within reach
Extreme MHC class I diversity in the sedge warbler (Acrocephalus schoenobaenus); selection patterns and allelic divergence suggest that different genes have different functions
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