The effect of thermal diffusion on the formation of interface resistance on oxide-coated cathodes.

Thesis (M.A.)--Boston UniversityThe goal of this investigation is to determine many of the factors which contribute to cathode interface resistance formation in a commercial type twin triode and to analyze these factors quantitatively by well known chemical and physical methods, However, since the vacuum tube represents such a complex system it is necessary to introduce this problem by reference to early history and many of the parameters associated with vacuum tube manufacture. With reference to historical introduction, the electron theory of metals, with special emphasis on the role which work function plays, is discussed. [TRUNCATED

Systems aspects of COBE science data compression

A general approach to compression of diverse data from large scientific projects has been developed and this paper addresses the appropriate system and scientific constraints together with the algorithm development and test strategy. This framework has been implemented for the COsmic Background Explorer spacecraft (COBE) by retrofitting the existing VAS-based data management system with high-performance compression software permitting random access to the data. Algorithms which incorporate scientific knowledge and consume relatively few system resources are preferred over ad hoc methods. COBE exceeded its planned storage by a large and growing factor and the retrieval of data significantly affects the processing, delaying the availability of data for scientific usage and software test. Embedded compression software is planned to make the project tractable by reducing the data storage volume to an acceptable level during normal processing

Differential Renormalization of Massive Quantum Field Theories

We extend the method of differential renormalization to massive quantum field theories treating in particular \ph4-theory and QED. As in the massless case, the method proves to be simple and powerful, and we are able to find, in particular, compact explicit coordinate space expressions for the finite parts of two notably complicated diagrams, namely, the 2-loop 2-point function in \ph4 and the 1-loop vertex in QED.Comment: 8 pages(LaTex, no figures

Ingestive behaviour and physiology of the medicinal leech

Ingestion lasts 25 min in Hirudo medicinalis and is characterized by pharyngeal peristalsis which fills the crop. This peristalsis has an initial rate of 2.4 Hz which decays smoothly to 1.2 Hz at termination of ingestion. During ingestion, the leech body wall undergoes peristalsis which appears to aid in filling the crop diverticula. Body peristalsis begins at a rate of 10 min^(-1) and decreases linearly to 2 min^(-1) at termination. The body also undergoes dorsoventral flexions when blood flow is occluded. Blood meal size increases slightly with leech size: 8.4 g for 1-g leeches and 9.7 g for 2-g leeches. However, relative meal size decreases markedly with increasing animal size; from 8.15 times body mass for 1-g to 4.80 times for 2-g leeches. When intact leeches were exposed to micromolar concentrations of serotonin, there was an increase in the rate of pharyngeal peristalsis and the size of the blood meals. Leeches excrete the plasma from their ingested blood meals. Excretion is activated during ingestion, which increases feeding efficiency by increasing the proportion of blood cells in the ingestate. Excretion continues for 4–6 days following ingestion, removing all the remaining plasma from the ingestate. Leech ingestion comprises stereotyped muscular movements, secretion of saliva and excretion of plasma. A strikingly similar feeding physiology is seen in the blood-sucking insect Rhodnius, and we suggest that efficient sanguivory may require the convergent evolution of similar ingestive mechanisms

Pumping conductance, the intrinsic anomalous Hall effect, and statistics of topological invariants

The pumping conductance of a disordered two-dimensional Chern insulator scales with increasing size and fixed disorder strength to sharp plateau transitions at well-defined energies between ordinary and quantum Hall insulators. When the disorder strength is scaled to zero as system size increases, the "metallic" regime of fluctuating Chern numbers can extend over the whole band. A simple argument leads to a sort of weighted equipartition of Chern number over minibands in a finite system with periodic boundary conditions: even though there must be strong fluctuations between disorder realizations, the mean Chern number at a given energy is determined by the {\it clean} Berry curvature distribution expected from the intrinsic anomalous Hall effect formula for metals. This estimate is compared to numerical results using recently developed operator algebra methods, and indeed the dominant variation of average Chern number is explained by the intrinsic anomalous Hall effect. A mathematical appendix provides more precise definitions and a model for the full distribution of Chern numbers.Comment: 12 page

Holographic RG-flows and Boundary CFTs

Solutions of $(d+1)$-dimensional gravity coupled to a scalar field are obtained, which holographically realize interface and boundary CFTs. The solution utilizes a Janus-like $\mathrm{AdS}_d$ slicing ansatz and corresponds to a deformation of the CFT by a spatially-dependent coupling of a relevant operator. The BCFT solutions are singular in the bulk, but physical quantities such as the holographic entanglement entropy can be calculated.Comment: 26 pages, 11 figure

The Hidden Spatial Geometry of Non-Abelian Gauge Theories

The Gauss law constraint in the Hamiltonian form of the $SU(2)$ gauge theory of gluons is satisfied by any functional of the gauge invariant tensor variable $\phi^{ij} = B^{ia} B^{ja}$. Arguments are given that the tensor $G_{ij} = (\phi^{-1})_{ij}\,\det B$ is a more appropriate variable. When the Hamiltonian is expressed in terms of $\phi$ or $G$, the quantity $\Gamma^i_{jk}$ appears. The gauge field Bianchi and Ricci identities yield a set of partial differential equations for $\Gamma$ in terms of $G$. One can show that $\Gamma$ is a metric-compatible connection for $G$ with torsion, and that the curvature tensor of $\Gamma$ is that of an Einstein space. A curious 3-dimensional spatial geometry thus underlies the gauge-invariant configuration space of the theory, although the Hamiltonian is not invariant under spatial coordinate transformations. Spatial derivative terms in the energy density are singular when $\det G=\det B=0$. These singularities are the analogue of the centrifugal barrier of quantum mechanics, and physical wave-functionals are forced to vanish in a certain manner near $\det B=0$. It is argued that such barriers are an inevitable result of the projection on the gauge-invariant subspace of the Hilbert space, and that the barriers are a conspicuous way in which non-abelian gauge theories differ from scalar field theories.Comment: 19 pages, TeX, CTP #223

“Is that okay with you?”: Examining a simulated discussion about accommodations between university students identified as having a disability and a standardized faculty member

Postsecondary students identified as having a disability in the United States are commonly expected to discuss the use of disability-related accommodations with faculty members. Researchers have previously used surveys and interviews to examine what students report about discussing accommodations with faculty members. However, little is known about how students advocate in the moment when communicating with faculty members about accommodations. In this study, I designed a clinical simulation to examine how 15 university students identified as having a disability engaged in and reflected upon a meeting with a standardized faculty member – an actor who I trained to communicate questions and concerns that were described as common by university students and staff members. Participants engaged in a single video-recorded simulated discussion followed by a group reflection interview and an optional individual follow-up interview in which participants watched a video of the simulation. The results of this study illustrate approaches that students use to discuss accommodations with a faculty member, including how they frame the role of accommodations. The results also provide glimpses into how students respond to a standardized faculty member’s concern about an accommodation and how students advocate for their needs. Furthermore, data from follow-up interviews demonstrate an array of tactics that participants used to manage their identity with careful consideration of issues such as power, authority, and gender dynamics within the context of a student-faculty member relationship. I conclude this study by suggesting that while self-advocacy remains important for postsecondary students identified as having a disability, the voices of participants in this study illustrate the need to reform practices that place students in a stigmatized position and demand the need for students to self-advocate in the first place