ABSTRACT
We study star cluster formation at low metallicities of Z/Z⊙ = 10−4–10−1 using three-dimensional hydrodynamics simulations. Particular emphasis is put on how the stellar mass distribution is ...affected by the cosmic microwave background radiation (CMB), which sets the temperature floor to the gas. Starting from the collapse of a turbulent cloud, we follow the formation of a protostellar system resolving ∼au scale. In relatively metal-enriched cases of Z/Z⊙ ≳ 10−2, where the mass function resembles the present-day one in the absence of CMB, high-temperature CMB suppresses cloud fragmentation and reduces the number of low-mass stars, making the mass function more top-heavy than in the cases without CMB heating at z ≳ 10. In lower-metallicity cases with Z/Z⊙ ≲ 10−3, where the gas temperature is higher than the CMB value due to inefficient cooling, the CMB has only a minor impact on the mass distribution, which is top-heavy, regardless of the redshift. In cases either with a low metallicity of Z/Z⊙ ≲ 10−2 or at a high redshift z ≳ 10, the mass spectrum consists of a low-mass Salpeter-like component, peaking at 0.1 M⊙, and a top-heavy component with 10–50 M⊙, with the fraction in the latter increasing with increasing redshift. In galaxies forming at z ≳ 10, the major targets of the future instruments including JWST, CMB heating makes the stellar mass function significantly top-heavy, enhancing the number of supernova explosions by a factor of 1.4 (2.8) at z = 10 (20, respectively) compared to the prediction by Chabrier initial mass function when Z/Z⊙ = 0.1.
This qualitative study employs observation, one-on-one semi-structured interviews, and questionnaire data collection methods to focus on land use and its correlation with vitality and gender equality ...in the public park domain. The study addresses the human–environment dichotomy and seeks to provide findings that can serve as a basis for city planning and foster gender pervasiveness in our recreational milieu. The study is framed in an expanding city and the Muslim context of Afghanistan, which has been at the intersection of fundamentalism and modernity since the mid-20th century. In the capital city of Kabul, 15 out of 65 active public parks were selected based on the criteria of having essential park amenities and variety in surrounding land uses. Vitality measures such as the presence of people in a park, the diversity of activities and available amenities, and the parks' build quality and management attributes were examined and contextualized according to the various land-use zones: residential, commercial, and mixed use. Parks surrounded by residential zones were found to be more vital, foster a higher female presence compared to parks surrounded by other land-use functions, and benefit from the influence of socio-spatial bonds induced by the neighborhood unit due to the presence of people and the park's perceived safety and security. Finally, a thematic proposal that can contribute to future urban planning is presented.
Informal settlements are a widespread phenomenon in African cities. This study explores the development patterns of informal settlements in Nairobi, Kenya, with a focus on the physical patterns, ...affordability of plots and rented rooms, and characteristics of developers. The results of the study were as follows:
Spatial characteristics and conditions in informal settlements are not uniform. We identified squatter areas with iron‐sheet houses and narrow streets, planned areas with high‐rise buildings made of concrete blocks arranged in a perfect array, and intermediate conditions.
Housing plot prices are unaffordable for most residents, while room rentals are generally fixed in accordance with the area and offer low‐income residents a wide range of choices.
The owners of some structures reside in their own structure, and others are non‐residents who build and rent structures for profit. Therefore, informal settlements are not so much a place to live, but rather an attractive investment opportunity for structure owners or developers.
Informal settlements are now widespread phenomenon in African cities. This paper explores development patterns of informal settlements in Nairobi, Kenya, with a focus on physical patterns, affordability of plot and rented room, characteristics of developers.
The late heavy bombardment (LHB) hypothesis, wherein the terrestrial planets are thought to have suffered intense collisions ca. 3.9 billion years ago, is under debate. Coupled with new dynamical ...calculations, re-examination of geochronological data seem to support an earlier solar system instability and a smooth monotonic decline in impacts, as opposed to a “cataclysm.” To better understand this collisional history, records from the asteroidal meteorites are required. Here, we report a uranium–lead (U–Pb) chronological dataset for eucrite meteorites thought to originate from the asteroid 4 Vesta; this dataset indicates to a continuous history of collisions prior to 4.15 Ga. Our 207Pb⁎/206Pb⁎ model ages of apatite Ca5(PO4)3(F,Cl,OH) and merrillite Ca9NaMg(PO4)7 from three brecciated basaltic eucrites—Juvinas (4150.3 ± 11.6 million years ago (Ma); merrillite only), Camel Donga (disturbed around 4570–4370 Ma), and Stannern (4143.0 ± 12.5 Ma)—record multiple thermal metamorphic events during the period of ∼4.4–4.15 Ga. We interpret this to mean that Vesta or the vestoid cluster underwent multiple impacts and moderate high-temperature reheating during this time. The ages of ∼4.4–4.15 Ga are distinctly younger than the initial magmatic process on Vesta (>4.5 Ga) but are significantly older than a later “impact peak” based on some interpretations of 40Ar–39Ar chronologies (∼3.9–3.5 Ga). The intense collisions prior to 4.15 Ga on Vesta are at odds with the conventional LHB hypothesis but not inconsistent with the much earlier bombardment and monotonic decline scenario. Different radiometric chronologies of the asteroid likely represent the different stages of a continual collisional process. Conversely, the model 207Pb⁎/206Pb⁎ ages of apatite in the unbrecciated basaltic eucrite, Agoult, returned an age of 4524.8 ± 9.6 Ma. This may represent slow cooling from an earlier global reheating of the crust on Vesta at 4.55 Ga, as documented by other radiometric chronologies. The apatite in Juvinas recorded a coincident timing of 4516.9 ± 10.4 Ma, which could be due to either slow crustal cooling or impact.
•NanoSIMS U-Pb dating of phosphates in basaltic eucrites.•Unbrecciated eucrites recorded the slow cooling process of the asteroid crusts.•Brecciated eucrites reveal the presence of multiple impacts on Vesta during ∼4.4–4.15 billion years ago.•These “early collisions” may be an end tail of the earlier bombardments among the inner solar system.
Accessibility, the size of the land area, the design and build quality, and the number of parks and their correlation with population density are key elements in fostering ecological spatial equity ...within cities. This study analyzed different spatial equity attributes of existing parks in Kabul City using onsite observations, measurement analyses, and mapping and buffering of satellite imagery using computer-aided design methods. The results revealed that, presently, 309 ha of urban land is covered by parks, which accounts for 0.78% of the total land area of 394.78 km2. On average, a quarter of city residents can access a park with basic amenities within 300 to 600 m of their residence, and parks currently provide a land coverage distribution per resident of 0.69 m2. However, the majority of parks lack certain amenities like playground and sports facilities desired by different user groups. This article also explored the inequitable distribution of parks at the city scale, underlining the scarcity or concentration of parks in certain areas and stressing the importance of allocating additional land for park provision.
This study examined the role of centralized national, decentralized supranational, and multiplied Foucauldian powers in a century of urbanization and urban planning in Afghanistan's capital city. ...Centralized domestic and decentralized foreign powers are framed as vertical planning and technical rationality, whereas the multiplied Foucauldian power is framed as participatory planning and discursive rationality. Within this theoretical framework, the available urban planning literature concerning Afghanistan's urbanization process from 1919 to 2020 is surveyed. The period starting from 1919 to 1921 marks the country's independence and first major undertaking of urban development, whereas the period of 2018-2020 denotes the urban design framework preparation and tendency of its application for Kabul City. Three distinct paradigms; namely, biopower, complementary, and sporadic urban planning and development can be demonstrated by tracing the role of power and the political system in scope, method, vision, and authorization of urban plans for the country. In complementary and sporadic planning paradigms, the decentralized supranational powers guide urban development and planning, whereas the centralized domestic power guides urban development in the biopower paradigm. Within these paradigms, despite the claims and leaps of democratic political regime exercises, a few traces of participatory planning in upgrading projects of unplanned settlements occurred only recently. However, the urban planning regime has lacked discursive rationality and has not accepted meaningful citizen participation in the planning process.
18FFDG brain images acquired using the Discovery MI and Discovery PET/CT 710 with 3D-OSEM+TOF. Brain images acquired using the Discovery MI have better grey-to-white matter contrast and lower image ...noise at the slice level of the cerebellum and parietal lobe.
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•We evaluated the first commercial SiPM-based TOF PET/CT system, Discovery MI.•Discovery MI has high sensitivity and resolution.•Time-of-flight of shorter timing resolution obtains better contrast images.•Discovery MI can decrease acquisition time or injected dose.
This study aimed to determine whether the SiPM-PET/CT, Discovery MI (DMI) performs better than the PMT-PET/CT system, Discovery 710 (D710).
The physical performance of both systems was evaluated using NEMA NU 2 standards. Contrast (%), uniformity and image noise (%) are criteria proposed by the Japanese Society of Nuclear Medicine (JSNM) for phantom tests and were determined in images acquired from Hoffman and uniform phantoms using the DMI and D710. Brain and whole-body 18FFDG images were also acquired from a healthy male using the DMI and D710.
The spatial resolution at 1.0cm off-center in the DMI and D710 was 3.91 and 4.52mm, respectively. The sensitivity of the DMI and D710 was 12.62 and 7.50cps/kBq, respectively. The observed peak noise-equivalent count rates were 185.6kcps at 22.5kBq/mL and 137.0kcps at 29.0kBq/mL, and the scatter fractions were 42.1% and 37.9% in the DMI and D710, respectively. The D710 had better contrast recovery and lower background variability. Contrast, uniformity and image noise in the DMI were 61.0%, 0.0225, and 7.85%, respectively. These outcomes were better than those derived from the D710 and satisfied the JSNM criteria. Brain images acquired by the DMI had better grey-to-white matter contrast and lower image noise at the edge of axial field of view.
The DMI offers better sensitivity, performance under conditions of high count rates and image quality than the conventional PMT-PET/CT system, D710.
Urbanization and informal settlements are a prevalent phenomenon in most African regions; they play an important role in the real estate market and the housing supply. This study examines the process ...and mechanism of land acquisition and land tenure security in informal settlements in Nairobi. We found that pseudo‐customary and pseudo‐formal systems work together in land acquisition and land tenure security. The former system derives from land acquisition and land tenure security under the authority of a traditional chief in rural areas, whereas the latter refers to the modern land registration procedure and urban planning standards. To ensure land acquisition and land tenure security, people use each of these systems and sometimes combine them. Moreover this study demonstrates that these land‐related systems are closely connected to the governance structure and site layout planning.
Urbanization and informal settlements are a prevalent phenomenon in most African regions; they play an important role in the real estate market and the housing supply. This study examines the process and mechanism of land acquisition and land tenure security in informal settlements in Nairobi. We found that pseudo‐customary and pseudo‐formal systems work together in land acquisition and land tenure security: the former system derives from land acquisition and land tenure security under the authority of a traditional chief in rural areas, whereas the latter refers to the modern land registration procedure and urban planning standards.
Silica mineral is present in different stable polymorphs depending on the temperature and pressure conditions of crystallization. We suggest using silica mineral phases to constrain the thermal ...history of eucrites. We focused on silica minerals in basaltic clasts of nine non‐cumulate eucrites to compare with previously studied cumulate eucrites. Our observations indicate an apparent relationship between thermal metamorphic degrees and silica phase texture in basaltic clasts of non‐cumulate eucrites. To reveal complex transformation relations between silica polymorphs in eucrites, we performed cooling experiments (cooling rate: 1 and 0.1 °C h−1) and heating experiments (heating 500 °C for 168 h and 800 °C for 96 h) using eucrites. The cooling experiments show that cristobalite is an initial silica phase crystallized from eucritic magma and transforms to quartz at the cooling rate between 0.1 and 1 °C h−1. Based on the cooling experiments and observations of eucrites, we suggest that a combination of silica minerals varies depending mainly on cooling rates. According to the heating experiments, monoclinic tridymite hardly transforms to other phases at low temperature by short reheating events such as brecciation. Monoclinic tridymite can partially transform to quartz with a “hackle” fracture. We conclude that a reheating event partially transformed monoclinic tridymite to quartz to form aggregates of monoclinic tridymite and quartz with the hackle fracture in eucrites. We suggested that some basaltic clasts in non‐cumulate eucrites experienced two‐stage thermal metamorphism in the eucritic crust. The first metamorphic event has resulted from burial under lava produced by successive eruptions. Igneous intrusions into the preformed crust may have caused the second metamorphic event. The intrusions heated the deep eucritic crust and induced the transformation from monoclinic tridymite to quartz.
Basaltic rocks occur widely on the terrestrial planets and differentiated asteroids, including the asteroid 4 Vesta. We conducted a shock recovery experiment with decaying compressive pulses on a ...terrestrial basalt at the Chiba Institute of Technology, Japan. The sample recorded a range of pressures, and shock physics modeling was conducted to add a pressure scale to the observed shock features. The shocked sample was examined by optical and electron microscopy, electron back‐scattered diffractometry, and Raman spectroscopy. We found that localized melting occurs at a lower pressure (∼10 GPa) than previously thought (>20 GPa). The shocked basalt near the epicenter represents “shock degree C” of a recently proposed classification scheme for basaltic eucrites and, as such, our results provide a pressure scale for the classification scheme. Finally, we estimated the total fraction of the basaltic eucrites classified as shock degree C to be ∼15% by assuming the impact velocity distribution onto Vesta.
Plain Language Summary
Basaltic rocks occur on numerous planetary bodies, including Mars, the Moon, and the asteroid Vesta. Shock metamorphic features in meteorites from such bodies are the ancient imprints of past impact events. We can extract information about the bombardment histories experienced by such bodies if we have an accurate method to link the degree of metamorphism to the impact conditions. Although two such methods for basaltic rocks have been published, one of these does not have a scale that relates the shock features and peak pressures. In this study, we designed an impact experiment with a terrestrial basalt sample to add a pressure scale to one of these methods. We found that basaltic materials are more easily melted than previously expected. The shock features of our shocked sample match “shock degree C.” The required pressure for producing the materials classified into this shock degree is 1–2 × 105 times greater than atmospheric pressure. Our results may provide insights into impact processes on Vesta. We estimate that the total fraction of meteorites from Vesta classified into shock degree C is ∼15%.
Key Points
We investigated the shock effects in basaltic rocks with impact experiments and shock physics modeling
We added a pressure scale to the shock degree classification for basaltic eucrites, allowing us to link our results with the Stöffler table
Localized melting occurs from 10 GPa rather than 20 GPa as previously thought
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