Asymptotically optimal covering designs

A (v,k,t) covering design, or covering, is a family of k-subsets, called blocks, chosen from a v-set, such that each t-subset is contained in at least one of the blocks. The number of blocks is the covering's size}, and the minimum size of such a covering is denoted by C(v,k,t). It is easy to see that a covering must contain at least (v choose t)/(k choose t) blocks, and in 1985 R\"odl [European J. Combin. 5 (1985), 69-78] proved a long-standing conjecture of Erd\H{o}s and Hanani [Publ. Math. Debrecen 10 (1963), 10-13] that for fixed k and t, coverings of size (v choose t)/(k choose t) (1+o(1)) exist (as v \to \infty). An earlier paper by the first three authors [J. Combin. Des. 3 (1995), 269-284] gave new methods for constructing good coverings, and gave tables of upper bounds on C(v,k,t) for small v, k, and t. The present paper shows that two of those constructions are asymptotically optimal: For fixed k and t, the size of the coverings constructed matches R\"odl's bound. The paper also makes the o(1) error bound explicit, and gives some evidence for a much stronger bound

Accidental Botulism Poisoning: A Case of Pickled Herring

INTRODUCTION: Botulism is a rare cause of neuromuscular weakness that presents a diagnostic challenge in the face of respiratory collapse. Pupil and bulbar paralysis aid prompt recognition and treatment, as clinical confirmation can be time intensive and limited by sample integrity. Early treatment can halt paralysis and prevent ICU and ventilator days. CASE DESCRIPTION: A 74-year-old male with hypertension and DVT presented with acute weakness and respiratory failure after three days of cough and diarrhea. Upon ICU admission for mechanical ventilation, we discovered sluggish pupils, mild ptosis, and proximal muscle weakness. Symptoms then progressed to unresponsive pupils, complete ptosis, and complete paralysis. While we suspected a neuromuscular cause, no single cause was identified despite extensive workup and neurology consultation. Our differential was narrowed after electromyogram (EMG) demonstrated a pre-synaptic defect, indicating either Lambert Eaton or Botulism as culprits. Empiric treatment with botulism anti-toxin resulted in clinical improvement of ptosis and proximal weakness. While ventilated, he wrote of recent pickeled herring ingestion, possibly left unrefrigerated for a week. He ultimately received tracheostomy and transfer to long-term assisted care, and at discharge stool and serum testing for botulism toxin was still pending. While state-run testing finally returned negative, his illness was ultimately attributed to accidental botulism poisoning. DATA: Differential and WorkupMyasthenia Gravis • CT Chest: no mediastinal/thymic mass (thymoma) • Acetylcholine Receptor Ab: negative • Striated Muscle and Titin Ab: negative Lambert Eaton • Pre-synaptic defect on EMG: low motor amplitudes that increased with sustained exercise • Voltage Gated Calcium Chanel Ab: negative • CT Chest: no nodules or masses (paraneoplastic SCLC in 50%) Demyelinating Polyneuropathy • LP: Glucose 76, protein 53, WBC 0, RBC 0, lymphocytes 67% • CSF: Ganglioside GM1 Ab negative Botulism • Stool: rejected, poor specimen quality • Serum: small sample size, Endopep-MS assay negative Central and Infectious • MRI brain and C-spine normal Infectious • Treponemal Ab negative • Lyme Ab negative Botulism Key Features Exam • Respiratory collapse • Proximal then distal paralysis, rapid progression • Preserved sensation, reflexes • Bulbar Paralysis with pupil involvement, nystagmus Workup • Botulism Neurotoxin (BoNT) of fluid, serum samples • Mouse Bioassay Treatment • Botulism equine anti-toxin, early administration can reduce ventilator and ICU days RESULTS / DISCUSSION: Yearly US incidence of botulism is 100 cases, and early treatment with equine anti-toxin reduces mortality and ventilation time1. Timely diagnosis is challenging as respiratory collapse overshadows subtle pupil and bulbar paralysis unique to botulism2. Lab diagnosis with Endopep-MS assay is not FDA approved and can be falsely negative with small samples3 while verified sacrificial mouse bioassays are rarely used2. Early suspicion should prompt anti-toxin treatment and discussion with the CDC’s botulism consultation service, who will supply anti-toxin and provide assistance with workup in conjunction with state health laboratories.https://digitalcommons.psjhealth.org/psv_internal/1012/thumbnail.jp

Vision-based guidance and control of a hovering vehicle in unknown environments

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaves 115-122).This thesis presents a methodology, architecture, hardware implementation, and results of a system capable of controlling and guiding a hovering vehicle in unknown environments, emphasizing cluttered indoor spaces. Six-axis inertial data and a low-resolution onboard camera yield sufficient information for image processing, Kalman filtering, and novel mapping algorithms to generate a, high-performance estimate of vehicle motion, as well as an accurate three-dimensional map of the environment. This combination of mapping and localization enables a quadrotor vehicle to autonomously navigate cluttered, unknown environments safely. Communication limitations are considered, and a hybrid control architecture is presented to demonstrate the feasibility of combining separated proactive offboard and reactive onboard planners simultaneously, including a detailed presentation of a novel reactive obstacle avoidance algorithm and preliminary results integrating the MIT Darpa Urban Challenge planner for high-level control. The RAVEN testbed is successfully employed as a prototyping facility for rapid development of these algorithms using emulated inertial data and offboard processing as a precursor to embedded development. An analysis of computational demand and a comparison of the emulated inertial system to an embedded sensor package demonstrates the feasibility of porting the onboard algorithms to an embedded autopilot. Finally, flight results using only the single camera and emulated inertial data for closed-loop trajectory following, environment mapping, and obstacle avoidance are presented and discussed.by Spencer Greg Ahrens.S.M

Hybrid smoothed particle hydrodynamics

We present a new algorithm for enforcing incompressibility for Smoothed Particle Hydrodynamics (SPH) by preserving uniform density across the domain. We propose a hybrid method that uses a Poisson solve on a coarse grid to enforce a divergence free velocity field, followed by a local density correction of the particles. This avoids typical grid artifacts and maintains the Lagrangian nature of SPH by directly transferring pressures onto particles. Our method can be easily integrated with existing SPH techniques such as the incompressible PCISPH method as well as weakly compressible SPH by adding an additional force term. We show that this hybrid method accelerates convergence towards uniform density and permits a significantly larger time step compared to earlier approaches while producing similar results. We demonstrate our approach in a variety of scenarios with significant pressure gradients such as splashing liquids

Walgett's Drinking Water: Yuwaya Ngarra-li Briefing Paper

This Briefing Paper documents a timeline of events in Walgett's recent history of drinking water management. It sets out the context in which drinking water is accessed, the associated risks, and the story of community advocacy pivotal to change. Its purpose is to inform efforts to improve water security and quality for residents in Walgett and the nearby Namoi and Gingie Villages, including urgent actions called for by the Dharriwaa Eldergs Group and Walgett Aboriginal Medical Service

Research Report: Prevalence and Mechanism of Atrazine Resistance in Waterhemp from Nebraska

Waterhemp is a troublesome summer annual broadleaf weed species that has evolved resistance to glyphosate and other herbicide sites of action (SOA) in Nebraska, including to groups 2 (i.e., Classic, Pursuit, FirstRate), 4 (i.e., 2, 4-D), 5(i.e., atrazine) and 27 (e.g., Callisto, Laudis). The overall objectives of this study were to Evaluate the eficay of PRE applied atrazine, metribuzin and sulfentrazone to control Nebraska waterhemp populations; Evaluate the efficacy of POST applied atrazine to control Nebraska waterhemp populations; and Determine the mechanism of atrazine resistance in Nebraska waterhemp populations

On the Vacancy-Zn Atom Binding Energy in Al

Binding energy between a vacancy and a Zn atom in Al was investigated by measurement of as-quenched resistivity in Al-0.021at % Zn and pure-Al, with the estimation of vacancy loss during quenching. The contribution of clusters to resistivity in Al-0.021at % Zn waa also investigated. Their results are summarized as follows: (1) The results of isothermal and isochronal annealing indicate that clusters in Al-0.021at % Zn cnuld not be detected beyond the experimental errors. (2) The model applied to estimate the vacancy loss in pure-Al has enough validity. The quantitative estimation of clusters ana the improvement in experimental conditions are greatly desired, which enable the more detailed, analysis of the data