75 research outputs found
The arithmetic of genus two curves with (4,4)-split Jacobians
In this paper we study genus 2 curves whose Jacobians admit a polarized
(4,4)-isogeny to a product of elliptic curves. We consider base fields of
characteristic different from 2 and 3, which we do not assume to be
algebraically closed. We obtain a full classification of all principally
polarized abelian surfaces that can arise from gluing two elliptic curves along
their 4-torsion and we derive the relation their absolute invariants satisfy.
As an intermediate step, we give a general description of Richelot isogenies
between Jacobians of genus 2 curves, where previously only Richelot isogenies
with kernels that are pointwise defined over the base field were considered.
Our main tool is a Galois theoretic characterization of genus 2 curves
admitting multiple Richelot isogenies.Comment: 30 page
Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?
We present a new study investigating whether active galactic nuclei (AGN)
beyond the local universe are preferentially fed via large-scale bars. Our
investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the
AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disc galaxies
at 0.2 < z < 1.0. We use a novel method to robustly compare a sample of 120 AGN
host galaxies, defined to have 10^42 erg/s < L_X < 10^44 erg/s, with inactive
control galaxies matched in stellar mass, rest-frame colour, size, Sersic
index, and redshift. Using the GZH bar classifications of each sample, we
demonstrate that AGN hosts show no statistically significant enhancement in bar
fraction or average bar likelihood compared to closely-matched inactive
galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above
the control bar fraction by more than a factor of two, at 99.7% confidence. We
similarly find no significant difference in the AGN fraction among barred and
non-barred galaxies. Thus we find no compelling evidence that large-scale bars
directly fuel AGN at 0.2<z<1.0. This result, coupled with previous results at
z=0, implies that moderate-luminosity AGN have not been preferentially fed by
large-scale bars since z=1. Furthermore, given the low bar fractions at z>1,
our findings suggest that large-scale bars have likely never directly been a
dominant fueling mechanism for supermassive black hole growth.Comment: 13 pages, 5 figures, 2 tables, accepted by MNRA
Business Models for Energy Entrepreneurship in Emerging Markets
Access to electricity produces greater levels of economic value and increases the quality of life in
emerging markets across the globe. Emerging economies have surpassed developed nations in
clean energy investment and deployment1
, but based on our review of the literature, there is a lack
of high-level study on the factors that most affect the success of these businesses. The goal of this
project is to identify these success factors, and use them to inform entrepreneurs’ strategic
decision-making as well as elucidate the environments in which these ventures have a higher
probability of success. By better understanding what drives success in the renewable energy
industry, both entrepreneurs and key stakeholders such as policy makers, investors, and interested
non-governmental organizations (NGOs) can better prioritize their efforts and investments to drive
increased levels of clean energy adoption.
This project focuses on clean energy business models in two emerging economies: India and
Uganda. These countries have significant differences in levels of access to energy and
development of their entrepreneurial landscapes, and therefore, provide a broad scope for analysis.
This report presents an overview of existing empirical research on factors that hinder or increase
success of business models, identifies potential gaps in this research, and presents analysis based
on qualitative, in-country interviews conducted by our team. Based on a comparative analysis
between the literature review and interview findings, the team drew conclusions about factors that
would benefit from better coordination and investment from industry players. The team also
identified aspects of the entrepreneurial experience in developing countries that are strong
candidates for further academic research.
Throughout the project, entrepreneurs and industry experts (such as the stakeholders above)
highlighted several of the key topics identified in existing research, including the challenge of
attracting private investment, strategies for revenue collection given limited ability to pay among
customers, the effect of domestic energy policy, and the industry’s lack of institutional support,
whether it be nonexistent or ineffective small business associations, trade associations, lobbying
groups, etc. While it was reassuring to see entrepreneur and stakeholder interviews validate what
had been uncovered in the literature review, the key value created by this project was largely the
nuance the interviews provided regarding the structural issues that were inhibiting growth for the
renewable and clean energy industries, and provide context around how some of these issues were
overcome in India and Uganda. Our research questions aimed to understand how entrepreneurs
can directly improve their prospects for success and where their efforts require coordination with
other partners in the renewable energy value chain or key policymakers.
The interviews revealed a clear distinction between the factors that entrepreneurs and industry
experts found to be most relevant and important to the success of clean energy entrepreneurs.
Factors such as positioning/strategy, company structure, ability to collect revenue, and business
model flexibility were by far more relevant for entrepreneurs than industry experts. This
understanding of which factors are more directly in entrepreneurs’ control can allow them to
prioritize which factors to focus their attention and resources on. In contrast, industry experts
regularly mentioned factors that were not top of mind for entrepreneurs in interviews such as
domestic energy policy, customer financial resources, and distribution and utility infrastructure.
Despite the relative dichotomy between entrepreneurs and industry experts, there was some
overlap among what factors the two groups found to be the most important. These factors include
talent attraction and retention, accessibility of private investment, competitive landscape,
consumer education and strategic partnerships. The overlapping factors indicate the significance
of these challenges, and highlights the potential areas where strategic partnerships would be the
most beneficial to foster a healthier entrepreneurial ecosystem.
Overall, the interviews raised new issues that were not discussed as in-depth in the literature. For
example, the conclusion that there is a lack of product awareness and trust among most consumers,
and that regulatory uncertainty of even the most well-intentioned policies can be extremely
detrimental. In India, there were difficulties retaining employees. In Uganda, there appears to be a
weak pipeline of educated, local talent. These issues demand comprehensive solutions that can
only be realized by greater cooperation and coordination between entrepreneurs, industry experts,
and policy makers. In sum, the hope is that this research will inform market players of key factors
of entrepreneurial success and act as a catalyst for future research. In particular, what factors do
entrepreneurs and industry experts see affecting success, where do they see greater opportunities
for coordination, and how are the Indian and Ugandan experiences representative of other
emerging markets?Master of ScienceSchool for Environment and SustainabilityUniversity of Michiganhttps://deepblue.lib.umich.edu/bitstream/2027.42/148815/1/Business Models for Energy Entrepreneurship in Emerging Markets_P46.pd
Combining Rainwater Harvesting and Grass Reseeding to Revegetate Denuded African Semi-arid Landscapes
In African drylands, perennial grasses preferred by grazing livestock are disappearing at an alarming rate. This has led to recurrent livestock feed shortages threatening pastoralist’s livelihoods. Combining native grass reseeding and rainwater harvesting offers a viable and innovative solution to reverse this trend. However, studies to determine how biomass yields are affected by soil moisture availability attributed to in situ rainwater harvesting in African drylands are limited. We investigated how biomass yields of three grasses native to Africa, i.e., Enteropogon macrostachyus (Bush rye grass), Cenchrus ciliaris (African foxtail grass), and Eragrostis superba (Maasai love grass), are affected by soil moisture content in a typical semi-arid landscape. Rainwater harvesting structures included trenches, micro-catchments and furrows. Additionally, rain runoff was diverted from an adjacent road used as a catchment area. Soil moisture was measured between November 2018 and August 2019 using PlantCare Mini-Logger sensors installed at 40 and 50 cm depths and 0, 1, 5 and 15 m away from the trench. Quadrat method was used to determine biomass yields in August 2019. Peaks in soil moisture were observed after rainfall events. Soil moisture content gradually decreased after the rainy season, but was higher closer to the trench. This is attributed to the prolonged rainwater retention in the trenches. Biomass yields were in the order Eragrostis superba > Cenchrus ciliaris > Enteropogon macrostachyus. Biomass production was higher near the trenches for all the studied species. Sensitivity to soil moisture demonstrated by the magnitude to yield reduction during the growing season was in the order Eragrostis superba > Cenchrus ciliaris > Enteropogon macrostachyus. These results suggest that Eragrostis superba is more sensitive to drought stress than Enteropogon macrostachyus that is adapted to a wide range of soil moisture conditions. We demonstrated that in situ rainwater harvesting structures enhanced soil moisture availability and displayed great potential for revegetating denuded natural rangelands in semi-arid African landscapes. Thus, combining rainwater harvesting and reseeding techniques can produce measurable improvements in pastoral livelihoods and should be incorporated in dryland development policies in the region. Ultimately, incorporating such innovative strategies can strengthen the effectiveness of ecological restoration in African drylands to meet the objectives of the UN Decade on Ecosystem Restoration and achieving the UN Sustainable Development Goals.Peer reviewe
Plant Morphoecological Traits, Grass-Weed Interactions and Water Use Efficiencies of Grasses Used for Restoration of African Rangelands
Degradation characterized by depleted vegetation cover is a serious environmental problem in African rangelands. It poses a serious threat to millions of pastoralists and agropastoralists who depend on livestock as a source of livelihood. Consequently, there has been a growing global interest to consolidate efforts to restore degraded ecosystems. For example, the UN decade of Ecosystem Restoration initiative aims at uniting the world behind a common goal of preventing, halting and reversing the degradation of ecosystems. Grass reseeding using native perennial species has been identified as one of the practical ecological strategies for restoring degraded African rangelands, enhancing vegetation cover and forage production. Knowledge of the multifaceted performance of African rangeland grasses in terms of morphoecological traits, interaction with weeds and water use efficiencies is however largely limited and often elusive. Perennial grasses indigenous to African rangelands Cenchrus ciliaris L. (African foxtail grass), Enteropogon macrostachyus (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass) and Eragrostis superba Peyr. (Maasai love grass), were established in an African semi-arid rangeland under natural conditions to fill this knowledge gap. Morphoecological plant traits: aboveground biomass (shoot, leaf and stem) production, plant densities, basal cover, tiller densities and plant height were measured 9 months after establishment. Interaction between the target grass species and weeds and water use efficiencies (WUE) were also determined. Enteropogon macrostachyus displayed significantly higher values for plant densities, tiller densities and basal cover, indices commonly used to estimate the potential of grasses for ecological restoration. Eragrostis superba produced the highest shoot biomass and water use efficiencies. This is attributed to its higher leafy biomass fraction. Higher aboveground biomass production of E. superba demonstrate its suitability for enhancing rangeland productivity. Cenchrus ciliaris suppressed the weeds. This is linked to its aggressive and allelopathic nature. In conclusion, the three perennial grasses displayed distinct morphoecological traits. In order to achieve successful seed-based restoration of degraded African rangelands using native perennial grasses, careful selection species to maximize on their unique traits is recommended. Ultimately, this selection process should match the desired restoration outcomes and subsequent use of the rangeland.Peer reviewe
Galaxy Zoo: Are bars responsible for the feeding of active galactic nuclei at 0.2<z<1.0?
We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS (All-wavelength Extended Groth strip International Survey), COSMOS (Cosmological Evolution Survey), and (Great Observatories Origins Deep Survey-South) GOODS-S surveys to create samples of face-on, disc galaxies at 0.21, our findings suggest that large-scale bars have likely never directly been a dominant fuelling mechanism for supermassive black hole growt
Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 \u3c \u3cem\u3ez\u3c/em\u3e \u3c 1.0?
We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS (All-wavelength Extended Groth strip International Survey), COSMOS (Cosmological Evolution Survey), and (Great Observatories Origins Deep Survey-South) GOODS-S surveys to create samples of face-on, disc galaxies at 0.2 \u3c z \u3c 1.0. We use a novel method to robustly compare a sample of 120 AGN host galaxies, defined to have 1042 erg s−1 \u3c LX \u3c 1044 erg s−1, with inactive control galaxies matched in stellar mass, rest-frame colour, size, Sérsic index, and redshift. Using the GZH bar classifications of each sample, we demonstrate that AGN hosts show no statistically significant enhancement in bar fraction or average bar likelihood compared to closely-matched inactive galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above the control bar fraction by more than a factor of 2, at 99.7 per cent confidence. We similarly find no significant difference in the AGN fraction among barred and non-barred galaxies. Thus we find no compelling evidence that large-scale bars directly fuel AGN at 0.2 \u3c z \u3c 1.0. This result, coupled with previous results at z = 0, implies that moderate-luminosity AGN have not been preferentially fed by large-scale bars since z = 1. Furthermore, given the low bar fractions at z \u3e 1, our findings suggest that large-scale bars have likely never directly been a dominant fuelling mechanism for supermassive black hole growth
Morphoecological characteristics of grasses used to restore degraded semi-arid African rangelands
Progressive loss of productivity and plant diversity is a concern in global rangelands. In African rangelands, this process is partly attributed to heavy and uncontrolled grazing by livestock and wildlife, leading to land degradation. Therefore, restoring such degraded rangelands is critical for enhancing ecosystem health and securing the livelihoods of millions of people. Active restoration strategies, for example, reseeding using indigenous perennial grasses, have been identified as a viable ecological solution for restoring degraded African rangelands. Grass species indigenous to African rangelands Cenchrus ciliaris L. (African foxtail grass), Eragrostis superba Peyr. (Maasai love grass), Enteropogon macrostachyus (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass), Chloris roxburghiana Schult. (Horsetail grass) and Chloris gayana Kunth. cv Boma (Rhodes grass) were established in a semi-arid rangeland in Africa under natural conditions to compare their morphoecological characteristics and suitability for use in ecological restoration. Biomass dry matter yields, plant densities, basal cover, seed production, tiller densities and plant height were measured. Chloris gayana cv Boma and E. superba produced significantly higher dry matter biomass yields and attained higher seed production than other species. High biomass and seed production indicate their suitability to support livestock production and replenish depleted soil seed banks, respectively. Enteropogon macrostachyus and C. ciliaris displayed significantly higher values for components of establishment and ecological restoration success, that is, plant densities, tiller densities and basal cover. Overall, C. roxburghiana ranked lowest in the measured morphoecological characteristics. Successful restoration of degraded African semi-arid rangelands using indigenous grass reseeding can best be achieved through careful selection of grasses to take advantage of their specific morphoecological characteristics. This selection should primarily be informed by the intended use of the rangeland and the specific challenges of restoring each site
Multi‐stakeholder participation for successful implementation of applied research projects in Africa
Rainwater harvesting from Roads For Indigenous Pasture production and improved rural livelihoods in Kitui, Kenya (ROFIP) is an applied research project. It assessed the potential of combining multiple sustainable land management practices, for example native grass reseeding, rainwater harvesting from roads and in situ microcatchments to enhance vegetation cover in a semi-arid dryland in Kenya. Rural earth roads were used as a catchment. Runoff generated from rainfall events was diverted into reseeded pastures with trenches established at intervals, across a slope. The ROFIP project also integrated microcatchments created using ox-driven ploughs, a traditional practice for seedbed preparation and harnessing in situ rainwater harvesting in African drylands. Combining the diversion of runoff from roads and harvesting rainwater in situ improves and prolongs soil moisture availability in reseeded pastures. Consequently, this translated to higher biomass yields (i.e. forage for livestock) and vegetation cover (land degradation mitigation and enhanced soil health). This project clearly showed that combining rainwater harvesting and native pasture reseeding improves water retention and soil health, thus improving sustainable pasture production. However, for this to be achieved, it is prudent to involve practitioners to co-design practical solutions that are socially, economically and environmentally sustainable. Multi-stakeholder engagement, effective knowledge sharing, and community involvement can be major enablers in the pursuit of environmental and socioeconomic relevant benefits in applied research projects in Africa. This approach enhances a sense of shared purpose among practitioners and empowers them to become points of reference to their peers
Kinome capture sequencing of high-grade serous ovarian carcinoma reveals novel mutations in the JAK3 gene.
High-grade serous ovarian carcinoma (HGSOC) remains the deadliest form of epithelial ovarian cancer and despite major efforts little improvement in overall survival has been achieved. Identification of recurring "driver" genetic lesions has the potential to enable design of novel therapies for cancer. Here, we report on a study to find such new therapeutic targets for HGSOC using exome-capture sequencing approach targeting all kinase genes in 127 patient samples. Consistent with previous reports, the most frequently mutated gene was TP53 (97% mutation frequency) followed by BRCA1 (10% mutation frequency). The average mutation frequency of the kinase genes mutated from our panel was 1.5%. Intriguingly, after BRCA1, JAK3 was the most frequently mutated gene (4% mutation frequency). We tested the transforming properties of JAK3 mutants using the Ba/F3 cell-based in vitro functional assay and identified a novel gain-of-function mutation in the kinase domain of JAK3 (p.T1022I). Importantly, p.T1022I JAK3 mutants displayed higher sensitivity to the JAK3-selective inhibitor Tofacitinib compared to controls. For independent validation, we re-sequenced the entire JAK3 coding sequence using tagged amplicon sequencing (TAm-Seq) in 463 HGSOCs resulting in an overall somatic mutation frequency of 1%. TAm-Seq screening of CDK12 in the same population revealed a 7% mutation frequency. Our data confirms that the frequency of mutations in kinase genes in HGSOC is low and provides accurate estimates for the frequency of JAK3 and CDK12 mutations in a large well characterized cohort. Although p.T1022I JAK3 mutations are rare, our functional validation shows that if detected they should be considered as potentially actionable for therapy. The observation of CDK12 mutations in 7% of HGSOC cases provides a strong rationale for routine somatic testing, although more functional and clinical characterization is required to understand which nonsynonymous mutations alterations are associated with homologous recombination deficiency
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