2,323 research outputs found

    A proof of the Ryser-Brualdi-Stein conjecture for large even nn

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    A Latin square of order nn is an nn by nn grid filled using nn symbols so that each symbol appears exactly once in each row and column. A transversal in a Latin square is a collection of cells which share no symbol, row or column. The Ryser-Brualdi-Stein conjecture, with origins from 1967, states that every Latin square of order nn contains a transversal with n1n-1 cells, and a transversal with nn cells if nn is odd. Keevash, Pokrovskiy, Sudakov and Yepremyan recently improved the long-standing best known bounds towards this conjecture by showing that every Latin square of order nn has a transversal with nO(logn/loglogn)n-O(\log n/\log\log n) cells. Here, we show, for sufficiently large nn, that every Latin square of order nn has a transversal with n1n-1 cells. We also apply our methods to show that, for sufficiently large nn, every Steiner triple system of order nn has a matching containing at least (n4)/3(n-4)/3 edges. This improves a recent result of Keevash, Pokrovskiy, Sudakov and Yepremyan, who found such matchings with n/3O(logn/loglogn)n/3-O(\log n/\log\log n) edges, and proves a conjecture of Brouwer from 1981 for large nn.Comment: 71 pages, 13 figure

    Nanomaterial fate and bioavailability in freshwater environments

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    Given the widespread use of silver nanomaterials (AgNM), their accidental or intentional release into the environment is inevitable. AgNM release into riverine systems is a daily occurrence, and following their release, they will undoubtedly interact with naturally occurring organic and inorganic particulates and sediment interfaces. At this point, AgNM's long-term threat to freshwater ecosystems is unclear. We must develop our understanding of AgNM fate, toxicity, and bioavailability using testing approaches that systematically investigate AgNM environmental interaction within single-factor and multifactor systems. This body of research aimed to comprehensively examine selected AgNM particles that were tracked within parallel fate scenarios and toxicity and bioavailability studies. Results showed contrasting behavior between the two tested AgNM. Findings also demonstrated that low shear flow is a significant factor influencing the flocculation and settling rates of AgNM, which differentially regulated the persistence and residence time of aqueous phase AgNM within simulated riverine systems. Experiments with low shear flow showed a significant increase in AgNM water column removal and modulated the physicochemistry differentially compared to quiescent systems. The findings on the influence of bed sediment interactions with waterborne AgNM demonstrated that they are a vital process that increases the transfer and exchange of AgNM from the water column to the bed. Toxicity studies showed how abiotic factors could modulate toxicity differentially between aquatic species and how inorganic and organic matter can increase and decrease AgNM toxicity. Exposure studies contrasting singular and multifactor exposures with and without low shear flow demonstrated that they modulate the exposure of AgNM significantly differently. In conclusion, the proof-of-concept flume designs for testing the environmental fate and exposure of AgNM showed promise and that, with further refinement, could be further incorporated into the life-cycle testing framework of ENMs, to produce accurate semi-empirical coefficients for environmental models for the assessment of hazard

    A general approach to transversal versions of Dirac-type theorems

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    Given a collection of hypergraphs H=(H1,,Hm)\textbf{H}=(H_1,\ldots,H_m) with the same vertex set, an mm-edge graph Fi[m]HiF\subset \cup_{i\in [m]}H_i is a transversal if there is a bijection ϕ:E(F)[m]\phi:E(F)\to [m] such that eE(Hϕ(e))e\in E(H_{\phi(e)}) for each eE(F)e\in E(F). How large does the minimum degree of each HiH_i need to be so that H\textbf{H} necessarily contains a copy of FF that is a transversal? Each HiH_i in the collection could be the same hypergraph, hence the minimum degree of each HiH_i needs to be large enough to ensure that FHiF\subseteq H_i. Since its general introduction by Joos and Kim [Bull. Lond. Math. Soc., 2020, 52(3):498-504], a growing body of work has shown that in many cases this lower bound is tight. In this paper, we give a unified approach to this problem by providing a widely applicable sufficient condition for this lower bound to be asymptotically tight. This is general enough to recover many previous results in the area and obtain novel transversal variants of several classical Dirac-type results for (powers of) Hamilton cycles. For example, we derive that any collection of rnrn graphs on an nn-vertex set, each with minimum degree at least (r/(r+1)+o(1))n(r/(r+1)+o(1))n, contains a transversal copy of the rr-th power of a Hamilton cycle. This can be viewed as a rainbow version of the P\'osa-Seymour conjecture.Comment: 21 pages, 4 figures; final version as accepted for publication in the Bulletin of the London Mathematical Societ

    Food - Media - Senses: Interdisciplinary Approaches

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    Food is more than just nutrition. Its preparation, presentation and consumption is a multifold communicative practice which includes the meal's design and its whole field of experience. How is food represented in cookbooks, product packaging or in paintings? How is dining semantically charged? How is the sensuality of eating treated in different cultural contexts? In order to acknowledge the material and media-related aspects of eating as a cultural praxis, experts from media studies, art history, literary studies, philosophy, experimental psychology, anthropology, food studies, cultural studies and design studies share their specific approaches

    Properly colored subgraphs in edge-colored graphs

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    Behavior quantification as the missing link between fields: Tools for digital psychiatry and their role in the future of neurobiology

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    The great behavioral heterogeneity observed between individuals with the same psychiatric disorder and even within one individual over time complicates both clinical practice and biomedical research. However, modern technologies are an exciting opportunity to improve behavioral characterization. Existing psychiatry methods that are qualitative or unscalable, such as patient surveys or clinical interviews, can now be collected at a greater capacity and analyzed to produce new quantitative measures. Furthermore, recent capabilities for continuous collection of passive sensor streams, such as phone GPS or smartwatch accelerometer, open avenues of novel questioning that were previously entirely unrealistic. Their temporally dense nature enables a cohesive study of real-time neural and behavioral signals. To develop comprehensive neurobiological models of psychiatric disease, it will be critical to first develop strong methods for behavioral quantification. There is huge potential in what can theoretically be captured by current technologies, but this in itself presents a large computational challenge -- one that will necessitate new data processing tools, new machine learning techniques, and ultimately a shift in how interdisciplinary work is conducted. In my thesis, I detail research projects that take different perspectives on digital psychiatry, subsequently tying ideas together with a concluding discussion on the future of the field. I also provide software infrastructure where relevant, with extensive documentation. Major contributions include scientific arguments and proof of concept results for daily free-form audio journals as an underappreciated psychiatry research datatype, as well as novel stability theorems and pilot empirical success for a proposed multi-area recurrent neural network architecture.Comment: PhD thesis cop

    Studying effects of light pollution and aquacultural light regimes using the teleost model medaka (Oryzias latipes)

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    Light is the main cue in synchronizing daily circadian rhythm in most animals, in addition to synchronizing the perception of the year for some species. Due to the steady increase of light pollution around the world, and especially near water bodies, this study aims to investigate the effects of different light regimes. Those regimes include light pollution and the continuous light regime used in aquaculture, mainly to increase growth and delay sexual maturation, is also studied. Firstly, light pollution levels were measured in Oslo’s main river, and the harbor area. I found that urban light pollution is severe in some places and can reach relatively deep as I detected it at 5 meters depth in the fjord. These results suggest that aquatic animals may be exposed to light pollution in the Oslo area and thus the effects should be studied. I then investigated in a laboratory setup the effect of light pollution on the teleost model Japanese medaka (Oryzias latipes). In addition to the continuous light regime was also studied. I found several effects of the altered light regimes. The reproductive cycle was found to be desynchronized for both light regimes. The fish’s behavior was also found to be altered. Additionally, fish development was found to be affected with promoted growth and altered brain and heart morphology. The artificial light regimes were also found to affect neurochemistry and the gene expression of one pituitary gene. A clear noradrenergic response was found, with the control fish having higher noradrenergic activity. Fish exposed to light pollution had a higher serotonergic brain activity. The pituitary gonadotropin lhb was found to be decreased in the continuous light regime. All together these results demonstrate that light pollution and continuous light clearly affect the fish, having welfare implications for aquaculture production, and suggesting that light pollution indeed affects wild fish

    The mad manifesto

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    The “mad manifesto” project is a multidisciplinary mediated investigation into the circumstances by which mad (mentally ill, neurodivergent) or disabled (disclosed, undisclosed) students faced far more precarious circumstances with inadequate support models while attending North American universities during the pandemic teaching era (2020-2023). Using a combination of “emergency remote teaching” archival materials such as national student datasets, universal design for learning (UDL) training models, digital classroom teaching experiments, university budgetary releases, educational technology coursewares, and lived experience expertise, this dissertation carefully retells the story of “accessibility” as it transpired in disabling classroom containers trapped within intentionally underprepared crisis superstructures. Using rhetorical models derived from critical disability studies, mad studies, social work practice, and health humanities, it then suggests radically collaborative UDL teaching practices that may better pre-empt the dynamic needs of dis/abled students whose needs remain direly underserviced. The manifesto leaves the reader with discrete calls to action that foster more critical performances of intersectionally inclusive UDL classrooms for North American mad students, which it calls “mad-positive” facilitation techniques: 1. Seek to untie the bond that regards the digital divide and access as synonyms. 2. UDL practice requires an environment shift that prioritizes change potential. 3. Advocate against the usage of UDL as a for-all keystone of accessibility. 4. Refuse or reduce the use of technologies whose primary mandate is dataveillance. 5. Remind students and allies that university space is a non-neutral affective container. 6. Operationalize the tracking of student suicides on your home campus. 7. Seek out physical & affectual ways that your campus is harming social capital potential. 8. Revise policies and practices that are ability-adjacent imaginings of access. 9. Eliminate sanist and neuroscientific languaging from how you speak about students. 10. Vigilantly interrogate how “normal” and “belong” are socially constructed. 11. Treat lived experience expertise as a gift, not a resource to mine and to spend. 12. Create non-psychiatric routes of receiving accommodation requests in your classroom. 13. Seek out uncomfortable stories of mad exclusion and consider carceral logic’s role in it. 14. Center madness in inclusive methodologies designed to explicitly resist carceral logics. 15. Create counteraffectual classrooms that anticipate and interrupt kairotic spatial power. 16. Strive to refuse comfort and immediate intelligibility as mandatory classroom presences. 17. Create pathways that empower cozy space understandings of classroom practice. 18. Vector students wherever possible as dynamic ability constellations in assessment
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