Wideband Balun Design with Ferrite Cores

This project explores different balun devices in order to develop a balanced to unbalanced transformer that will operate over a wide bandwidth. The balun must operate from at least 1 MHz (or below) to the highest possible frequency. It must have an insertion loss of less than 1 dB under the ideal case with an imbalance of less than 1 dB and 2.5 degrees. Three balun topologies were tested, each built for a 1:1 impedance transformation ratio. Techniques of measuring each balun topology were investigated including gathering accurate data from a three port device with two port instruments and measuring permeability of magnetic materials. The balun that showed the best results was the Guanella balun wound around 1mm diameter cores from old magnetic core memory matrices. The Guanella balun showed more stable phase difference and insertion loss compared to the other two baluns tested

Survival, extinction and approximation of discrete-time branching random walks

We consider a general discrete-time branching random walk on a countable set X. We relate local, strong local and global survival with suitable inequalities involving the first-moment matrix M of the process. In particular we prove that, while the local behavior is characterized by M, the global behavior cannot be completely described in terms of properties involving M alone. Moreover we show that locally surviving branching random walks can be approximated by sequences of spatially confined and stochastically dominated branching random walks which eventually survive locally if the (possibly finite) state space is large enough. An analogous result can be achieved by approximating a branching random walk by a sequence of multitype contact processes and allowing a sufficiently large number of particles per site. We compare these results with the ones obtained in the continuous-time case and we give some examples and counterexamples.Comment: 32 pages, a few misprints have been correcte

Field Trials to Determine the Efficacy of an Oral Plague Vaccine for Prairie Dogs

North American prairie dogs (Cynomys spp.) and black-footed ferrets (Mustela nigripes) have been severely affected by plague, an exotic zoonotic disease caused by the bacterium Yersinia pestis during the last 100 years.  Plague has contributed to population declines of prairie dogs, near extinction of black-footed ferrets, and has caused human illness and fatalities.  An oral sylvatic plague vaccine (SPV) developed and tested jointly by the U.S. Geological Survey, National Wildlife Health Center and University of Wisconsin (Madison, WI) shows great promise as an effective, pre-emptive method for controlling plague in prairie dogs.  Field trials to evaluate the efficacy of SPV were initiated in 2013 and include 4 species of prairie dogs on study areas in 7 states, including Montana.  This presentation is a status report after the second year of a planned 4 year study.  The primary objectives are to measure vaccine/bait uptake and to assess prairie dog survival rates at paired study sites, with and without vaccine application.  At the north-central Montana study site, about 8,000 baits, half with SPV and half placebos, were distributed across 5 pairs of study sites (totaling 81 ha) in 2013 and over 13,000 in 2014 on the same 5 pairs of study sites (totaling 107 ha).  In addition to ear tagging and microchip-marking each individual, flea, hair, whisker and blood samples were collected each year.  A total of 584 individual prairie dogs were marked during 929 capture events in 2013 and 814 individuals during 1,293 capture events in 2014

Nickel(II) metal-organic frameworks with N,N’-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide ligands: influence of secondary building unit geometry on dimensionality and framework dimensions

When Ni(NO3)2∙6H2O and N,N’-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide (DPNDI) are reacted, a one-dimensional coordination polymer (1) is formed. However, reaction with either terephthalic acid (2) or 2,6-naphthalenedicarboxylic acid (3) affords two-dimensional, pillared metal-organic frameworks. 2 and 3 containing rectangular voids of different dimensions which are dictated by the carboxylate ligand and the arrangement of the [M(k2-O2NO)]2(μ2-O2CR)2] secondary building unit (SBU) that forms the nodes of the framework. The role of SBU geometry, intermolecular face-to-face π–π and lone pair–π interactions involving the DPNDI ligands are discussed

Long and short paths in uniform random recursive dags

In a uniform random recursive k-dag, there is a root, 0, and each node in turn, from 1 to n, chooses k uniform random parents from among the nodes of smaller index. If S_n is the shortest path distance from node n to the root, then we determine the constant \sigma such that S_n/log(n) tends to \sigma in probability as n tends to infinity. We also show that max_{1 \le i \le n} S_i/log(n) tends to \sigma in probability.Comment: 16 page

On the identification of twinning in body-centred cubic nanoparticles

Many metals and alloys, including Fe and W, adopt body-centred cubic (BCC) crystal structures and nanoparticles of these metals are gaining significant scientific and industrial relevance. Twinning has a marked effect on catalytic activity, yet there is little evidence for or against the presence of twinning in BCC nanoparticles. Here, we explore the potential shapes of twinned BCC nanoparticles, and predict their electron microscopy and diffraction signatures. BCC single crystal and twinned shapes often appear similar and diffraction patterns along common, low-index zone axes are often indistinguishable, casting doubt on many claims of single crystallinity. We conclude by outlining how nanoparticles can be characterized to conclusively prove the presence or absence of twinning

Exact asymptotics of the freezing transition of a logarithmically correlated random energy model

We consider a logarithmically correlated random energy model, namely a model for directed polymers on a Cayley tree, which was introduced by Derrida and Spohn. We prove asymptotic properties of a generating function of the partition function of the model by studying a discrete time analogy of the KPP-equation - thus translating Bramson's work on the KPP-equation into a discrete time case. We also discuss connections to extreme value statistics of a branching random walk and a rescaled multiplicative cascade measure beyond the critical point

Decoration of plasmonic Mg nanoparticles by partial galvanic replacement.

Plasmonic structures have attracted much interest in science and engineering disciplines, exploring a myriad of potential applications owing to their strong light-matter interactions. Recently, the plasmonic concentration of energy in subwavelength volumes has been used to initiate chemical reactions, for instance by combining plasmonic materials with catalytic metals. In this work, we demonstrate that plasmonic nanoparticles of earth-abundant Mg can undergo galvanic replacement in a nonaqueous solvent to produce decorated structures. This method yields bimetallic architectures where partially oxidized 200-300 nm Mg nanoplates and nanorods support many smaller Au, Ag, Pd, or Fe nanoparticles, with potential for a stepwise process introducing multiple decoration compositions on a single Mg particle. We investigated this mechanism by electron-beam imaging and local composition mapping with energy-dispersive X-ray spectroscopy as well as, at the ensemble level, by inductively coupled plasma mass spectrometry. High-resolution scanning transmission electron microscopy further supported the bimetallic nature of the particles and provided details of the interface geometry, which includes a Mg oxide separation layer between Mg and the other metal. Depending on the composition of the metallic decorations, strong plasmonic optical signals characteristic of plasmon resonances were observed in the bulk with ultraviolet-visible spectrometry and at the single particle level with darkfield scattering. These novel bimetallic and multimetallic designs open up an exciting array of applications where one or multiple plasmonic structures could interact in the near-field of earth-abundant Mg and couple with catalytic nanoparticles for applications in sensing and plasmon-assisted catalysis.Support for this project was provided by the EU Framework Programme for Research and Innovation Horizon 2020 (Starting Grant SPECs 804523). J.A. wishes to acknowledge financial support from Natural Sciences and Engineering Research Council of Canada and “Fonds de Recherche Québec – Nature et Technologies” postdoctoral fellowships (BP and B3X programs). C.B. is thankful for funding from the Engineering and Physical Sciences Research Council (Standard Research Studentship (DTP) EP/R513180/1), and E.R.H. for support from the EPSRC NanoDTC Cambridge (EP/L015978/1). S.M.C. acknowledges support from the Henslow Research Fellowship at Girton College, Cambridge. We acknowledge access and support in the use of the electron Physical Sciences Imaging Centre (MG21980) at the Diamond Light Source, U.K

A young child with a history of wheeze

The parents of a 3-year old boy are anxious about their son who has recurring episodes of wheezing. They are frustrated that no one seems to be able to give them answers to their questions and would like a referral to a specialist. Does their son have asthma and what is the prognosis; how can the recurrent wheezing be managed and can the risk of asthma be reduced; are there lifestyle changes that could improve the environment and avoid triggers? Communication and support from the family practice team were essential. Listening to the parents' concerns, explaining the diagnostic uncertainty, being realistic about what drug treatments could achieve, and providing practical advice on inhaler use and trigger avoidance reassured the parents that there was a strategy for managing their son's wheeze. The specialist referral was postponed