Field dependence of electronic recoil signals in a dual-phase liquid xenon time projection chamber

We present measurements of light and charge signals in a dual-phase time projection chamber at electric fields varying from 10 V/cm up to 500 V/cm and at zero field using 511 keV gamma rays from a $^{22}$Na source. We determine the drift velocity, electron lifetime, diffusion constant, and light and charge yields at 511 keV as a function of the electric field. In addition, we fit the scintillation pulse shape to an effective exponential model, showing a decay time of 43.5 ns at low field that decreases to 25 ns at high fields.Comment: 14 pages, 8 figure

On positive solutions and the Omega limit set for a class of delay differential equations

This paper studies the positive solutions of a class of delay differential equations with two delays. These equations originate from the modeling of hematopoietic cell populations. We give a sufficient condition on the initial function for $t\leq 0$ such that the solution is positive for all time $t>0$. The condition is "optimal". We also discuss the long time behavior of these positive solutions through a dynamical system on the space of continuous functions. We give a characteristic description of the $\omega$ limit set of this dynamical system, which can provide informations about the long time behavior of positive solutions of the delay differential equation.Comment: 15 pages, 2 figure

On the uniqueness of paths for spin-0 and spin-1 quantum mechanics

The uniqueness of the Bohmian particle interpretation of the Kemmer equation, which describes massive spin-0 and spin-1 particles, is discussed. Recently the same problem for spin-1/2 was dealt with by Holland. It appears that the uniqueness of boson paths can be enforced under well determined conditions. This in turn fixes the nonrelativistic particle equations of the nonrelativistic Schrodinger equation, which appear to correspond with the original definitions given by de Broglie and Bohm only in the spin-0 case. Similar to the spin-1/2 case, there appears an additional spin-dependent term in the guidance equation in the spin-1 case. We also discuss the ambiguity associated with the introduction of an electromagnetic coupling in the Kemmer theory. We argue that when the minimal coupling is correctly introduced, then the current constructed from the energy-momentum tensor is no longer conserved. Hence this current can not serve as a particle probability four-vector.Comment: 19 pages, no figures, LaTex, shortened version for Phys. Lett.

Spin-dependent Bohm trajectories for hydrogen eigenstates

The Bohm trajectories for several hydrogen atom eigenstates are determined, taking into account the additional momentum term that arises from the Pauli current. Unlike the original Bohmian result, the spin-dependent term yields nonstationary trajectories. The relationship between the trajectories and the standard visualizations of orbitals is discussed. The trajectories for a model problem that simulates a 1s-2p transition in hydrogen are also examined.Comment: 11 pages, 3 figure

Effects of memory on the shapes of simple outbreak trees

Genomic tools, including phylogenetic trees derived from sequence data, are increasingly used to understand outbreaks of infectious diseases. One challenge is to link phylogenetic trees to patterns of transmission. Particularly in bacteria that cause chronic infections, this inference is affected by variable infectious periods and infectivity over time. It is known that non-exponential infectious periods can have substantial effects on pathogens’ transmission dynamics. Here we ask how this non-Markovian nature of an outbreak process affects the branching trees describing that process, with particular focus on tree shapes. We simulate Crump-Mode-Jagers branching processes and compare different patterns of infectivity over time. We find that memory (non-Markovian-ness) in the process can have a pronounced effect on the shapes of the outbreak’s branching pattern. However, memory also has a pronounced effect on the sizes of the trees, even when the duration of the simulation is fixed. When the sizes of the trees are constrained to a constant value, memory in our processes has little direct effect on tree shapes, but can bias inference of the birth rate from trees. We compare simulated branching trees to phylogenetic trees from an outbreak of tuberculosis in Canada, and discuss the relevance of memory to this dataset

Word Order in Paraguayan Guaraní

My honors research project examines word order in Paraguayan Guaraní, i.e. the order in which the subject, object, and verb of a sentence are realized. No study of word order has been conducted on Paraguayan Guaraní, and my quantitative study brings Guaraní to bear on cross-linguistic studies of word order. The main research questions I am pursuing are: What word orders are possible in Guaraní and is there a basic word order? Do the factors of grammatical function, animacy, and discourse status affect the placement of arguments? If so, how? Knowledge of the basic word order of a language is important because it has been found to correlate with other grammatical properties of the language. For example, linguists have observed that there is a relation between basic word order and other properties like the position of adjectives relative to the noun and the type of adposition a language will have: verb-initial languages generally have prepositions, while verb-final languages generally have post-positions. Grammatical function, animacy, and discourse status have been shown in previous studies to influence the realization of word order. English word order, for example, is strongly constrained by grammatical function; the subject typically comes before the verb, while the object normally follows. In Tojolobal, a Mayan language, word order is influenced by animacy. Of the six possible word orders, there are several that are possible only if certain arguments have a certain type of animacy, such as human or animal. Discourse status, which we measure by looking at definiteness, has also been found to constrain word order. Cayuga, an Iroquoian language, has been shown to realize indefinite noun phrases before definite noun phrases. This quantitative study overall finds Subject-Verb-Object to be the basic word order of Paraguayan Guaraní, based on the criteria of frequency and disambiguation. I also find that grammatical function and discourse status affect the placement of arguments, while animacy by itself is not much of an influence. When paired together, however, discourse status and animacy do affect the realization of subjects in Paraguayan Guaraní.The Ohio State University Colleges of the Arts and Sciences Honors Committe

Internationale politieke economie: herijking van de studie naar internationale politiek

Internationale Politieke Economie (IPE) is een nieuw vakgebied dat een zekere integratie voorstaat van Internationale Betrekkingen, Internationale Economische Betrekkingen, Politicologie en Bestuurskunde. Het is een terrein dat zich goed leent om de wisselwerking van verschijnselen op subnationaal, nationaal en internationaal niveau te analyseren. Dit artikel geeft een oeverzicht van de recente ontwikkelingen op dit vakgebied en signaleert de mogelijkheden en beperkingen van IPE