An Algorithm for Koml\'os Conjecture Matching Banaszczyk's bound

We consider the problem of finding a low discrepancy coloring for sparse set systems where each element lies in at most t sets. We give an efficient algorithm that finds a coloring with discrepancy O((t log n)^{1/2}), matching the best known non-constructive bound for the problem due to Banaszczyk. The previous algorithms only achieved an O(t^{1/2} log n) bound. The result also extends to the more general Koml\'{o}s setting and gives an algorithmic O(log^{1/2} n) bound

Linking vegetation change, carbon sequestration and biodiversity

1. Despite recent interest in linkages between above- and belowground communities and their consequences for ecosystem processes, much remains unknown about their responses to long-term ecosystem change. We synthesize multiple lines of evidence from a long-term ‘natural experiment’ to illustrate how ecosystem retrogression (the decline in ecosystem processes due to long-term absence of major disturbance) drives vegetation change, and thus aboveground and belowground carbon (C) sequestration, and communities of consumer biota. 2. Our study system involves 30 islands in Swedish boreal forest that form a 5000 year fire-driven retrogressive chronosequence. Here, retrogression leads to lower plant productivity and slower decomposition, and a community shift from plants with traits associated with resource acquisition to those linked with resource conservation. 3. We present consistent evidence that aboveground ecosystem C sequestration declines, while belowground and total C storage increases linearly for at least 5000 years following fire absence. This increase is driven primarily by changes in vegetation characteristics, impairment of decomposer organisms and absence of humus combustion. 4. Data from contrasting trophic groups show that during retrogression, biomass or abundance of plants and decomposer biota decreases, while that of aboveground invertebrates and birds increases, due to different organisms accessing resources via distinct energy channels. Meanwhile, diversity measures of vascular plants and aboveground (but not belowground) consumers respond positively to retrogression. 5. We show that taxonomic richness of plants and aboveground consumers are positively correlated with total ecosystem C storage, suggesting that conserving old growth forests simultaneously maximizes biodiversity and C sequestration. However, we find little observational or experimental evidence that plant diversity is a major driver of ecosystem C storage on the islands relative to other biotic and abiotic factors. 6. Synthesis. Our study reveals that across contrasting islands differing in exposure to a key extrinsic driver (historical disturbance regime and resulting retrogression), there are coordinated responses of soil fertility, vegetation, consumer communities, and ecosystem C sequestration, which all feed back to one another. It also highlights the value of well replicated natural experiments for tackling questions about aboveground-belowground linkages over temporal and spatial scales that are otherwise unachievable

Revisiting the empirical fundamental relationship of traffic flow for highways using a causal econometric approach

The fundamental relationship of traffic flow is empirically estimated by fitting a regression curve to a cloud of observations of traffic variables. Such estimates, however, may suffer from the confounding/endogeneity bias due to omitted variables such as driving behaviour and weather. To this end, this paper adopts a causal approach to obtain an unbiased estimate of the fundamental flow-density relationship using traffic detector data. In particular, we apply a Bayesian non-parametric spline-based regression approach with instrumental variables to adjust for the aforementioned confounding bias. The proposed approach is benchmarked against standard curve-fitting methods in estimating the flow-density relationship for three highway bottlenecks in the United States. Our empirical results suggest that the saturated (or hypercongested) regime of the estimated flow-density relationship using correlational curve fitting methods may be severely biased, which in turn leads to biased estimates of important traffic control inputs such as capacity and capacity-drop. We emphasise that our causal approach is based on the physical laws of vehicle movement in a traffic stream as opposed to a demand-supply framework adopted in the economics literature. By doing so, we also aim to conciliate the engineering and economics approaches to this empirical problem. Our results, thus, have important implications both for traffic engineers and transport economists

Radiation Induced Optic Neuritis: A Role for Steroids?

Radiation induced optic neuropathy is a devastating complication of radiotherapy to the anterior visual pathway, resulting in significant, permanent vision loss. Systemic steroids have not demonstrated a proven benefit in stabilizing or reversing vision loss. We report a case of radiation induced optic neuropathy with visual acuity improvement after initiation of high dose steroids.A 55-year-old male presented with 5 days of decreased vision in the right eye. Two years prior to presentation, he was diagnosed with squamous cell carcinoma of the skin and treated with a cumulative radiation dose of 70 Gy. ENT and oncology were monitoring the patient for a squamous cell carcinoma of the maxillary sinus without current treatment at that time. On ophthalmologic exam, his baseline visual acuity of 20/20 had decreased to counting fingers. Dilated fundus exam and fluorescein angiogram showed optic disc edema and hemorrhage. MRI orbits showed no interval increase in size of the squamous cell carcinoma with slight enhancement of the optic nerve and laboratory workup was unremarkable. The patient was diagnosed with radiation induced optic neuropathy. After risks and benefits were discussed with the patient, he agreed to a trial of high dose steroid therapy. The patient received three days of intravenous solumedrol (1 mg/kg/day), followed by a twelve day taper of oral prednisone (starting at 80 mg). Ten days after steroid initiation, the patient’s visual acuity improved to 20/40. Two months later, his visual acuity remained improved at 20/50.Acute high dose steroids may be beneficial in reversing radiation induced optic neuropathy.https://scholarlycommons.henryford.com/merf2019caserpt/1061/thumbnail.jp