Writing Drama Today

Panel: Writing Drama Toda

Why I Write, What I Write, and How I Write It

Panel: Why I Write What I Writ

Anisotropy in s-wave Bose-Einstein condensate collisions and its relationship to superradiance

We report the experimental realization of a single-species atomic four-wave mixing process with BEC collisions for which the angular distribution of scattered atom pairs is not isotropic, despite the collisions being in the $s$-wave regime. Theoretical analysis indicates that this anomalous behavior can be explained by the anisotropic nature of the gain in the medium. There are two competing anisotropic processes: classical trajectory deflections due to the mean-field potential, and Bose enhanced scattering which bears similarity to super-radiance. We analyse the relative importance of these processes in the dynamical buildup of the anisotropic density distribution of scattered atoms, and compare to optically pumped super-radiance.Comment: 13 pages, 10 figures, added a fuller discussion of timescales, otherwise some minor changes in the text and the formatting of Figures 5-

Quantum electrodynamics of relativistic bound states with cutoffs

We consider an Hamiltonian with ultraviolet and infrared cutoffs, describing the interaction of relativistic electrons and positrons in the Coulomb potential with photons in Coulomb gauge. The interaction includes both interaction of the current density with transversal photons and the Coulomb interaction of charge density with itself. We prove that the Hamiltonian is self-adjoint and has a ground state for sufficiently small coupling constants.Comment: To appear in "Journal of Hyperbolic Differential Equation

Twisted geometries: A geometric parametrisation of SU(2) phase space

A cornerstone of the loop quantum gravity program is the fact that the phase space of general relativity on a fixed graph can be described by a product of SU(2) cotangent bundles per edge. In this paper we show how to parametrize this phase space in terms of quantities describing the intrinsic and extrinsic geometry of the triangulation dual to the graph. These are defined by the assignment to each triangle of its area, the two unit normals as seen from the two polyhedra sharing it, and an additional angle related to the extrinsic curvature. These quantities do not define a Regge geometry, since they include extrinsic data, but a looser notion of discrete geometry which is twisted in the sense that it is locally well-defined, but the local patches lack a consistent gluing among each other. We give the Poisson brackets among the new variables, and exhibit a symplectomorphism which maps them into the Poisson brackets of loop gravity. The new parametrization has the advantage of a simple description of the gauge-invariant reduced phase space, which is given by a product of phase spaces associated to edges and vertices, and it also provides an abelianisation of the SU(2) connection. The results are relevant for the construction of coherent states, and as a byproduct, contribute to clarify the connection between loop gravity and its subset corresponding to Regge geometries.Comment: 28 pages. v2 and v3 minor change

Spermatogenesis in the Siberian salamander, Salamandrella keyserlingii (Caudata: Hynobiidae)

Spermatogenic cycles of hynobiid salamanders are interesting for the study of male reproductive adaptations in amphibians living under different environmental conditions. In order to detect the main differences between spermatogenic cycles of hynobiids, we studied the spermatogenic cycle of Salamandrella keyserlingii from the suburbs of Tomsk (southeastern Western Siberia) and compared it with those in the literature of hynobiids from different regions of Asia. We histologically and histochemically examined the testes of males captured from April to September. In April, the testes of males entering breeding sites contained bundles of spermatozoa (Sz) and primary (Sg I) and secondary spermatogonia (Sg II). After spermiation and breeding, Sg II began to proliferate. Meiosis of spermatocytes occurred in late June through July. The spermiogenesis began in late July; spermatids and Sz appeared in August. In September, Sz, Sg I, and Sg II were found in testes, which was also when Sg II proliferated. There are two types of spermatogenic cycles in the studied salamanders. The first one includes one period of spermatogonial proliferation (SP) in the first half of the active season. The second type consists of two periods of SP, with one occurring at the beginning and the other at the end of the active season. To identify possible differences in hynobiid spermatogenic cycles, we tested the relation of the duration of active season (DAS), the duration of SP period in the first half of cycle (DSPP), and the number of SP periods per year (NSPPs), considering environmental (air) temperatures in these species’ habitats. We could not find a direct relationship between NSPPs and air temperatures, but DAS and DSPP were correlated with temperature. We assume that two periods of SP can play the most apparent adaptive role in S. keyserlingii in a subarctic climate and in Batrachuperus tibetanus under mountain conditions

Back To Basics: Algebraic Foundations Of The Statement Of Cash Flows

The indirect method for preparing the statement of cash flows, as described in many standard textbooks, involves an item-by-item approach, telling you to add to or subtract from the net income, the increases or decreases in the balance sheet items, such as accounts payable or accounts receivable. Many business students, especially at the undergraduate level, find these black-box-rules confusing. In recent years, several articles have appeared in the accounting literature, exploring the link between the algebraic foundations and the enumeration of items in the statement of cash flows. In this paper, an explanation is provided, through an analysis of the basic algebraic equation of the balance sheet, for the black-box-rules of the indirect method in a simple and concise manner

Oviduct, egg, and egg sac structures in the Siberian salamander, Salamandrella keyserlingii (Caudata, Hynobiidae): a histological and histochemical study

Unraveling morphological and chemical features of the eggs’ jelly layers and other clutch elements, formed by the oviduct of a female, is necessary for the understanding of reproductive adaptation in amphibians. Our study is the first microstructural and histochemical descriptions about the complexity of oviduct, ovisac, jelly layer of the ovum, and egg sac in hynobiid salamanders. We examined female Salamandrella keyserlingii in preovulatory (gravid) and ovulatory (spent) conditions using anatomical, histological, and histochemical methods. Each ovum was covered with two jelly layers. All ova from one oviduct fell into one egg sac. Inner space of the oviduct, in which ova were passed through, was filled with jelly-like substances designated as «intermediate fluids». We named the membrane-like outer layer of the egg sac as «theca». Jelly layers surrounding the ovum were formed by the oviducal tubular glands of the pars recta and pars convoluta of the oviduct, consisting of acidic and neutral glycoproteins. In the ovisac (i.e., homologous uterus), there were three glandular regions and one aglandular dilatable ovisac. Of the ovisac, glands A, B, and C secreted acidic and neutral glycoproteins for the intermediate fluids, neutral glycoproteins for the theca, and mucus-like materials with a neutral glycoprotein nature, respectively. We suggest that these mucus-like materials are essential to attaching the adhesive tips of the egg sacs to some substrates during oviposition

Spontaneous hot-electron light emission from electron-fed optical antennas

Nanoscale electronics and photonics are among the most promising research areas providing functional nano-components for data transfer and signal processing. By adopting metal-based optical antennas as a disruptive technological vehicle, we demonstrate that these two device-generating technologies can be interfaced to create an electronically-driven self-emitting unit. This nanoscale plasmonic transmitter operates by injecting electrons in a contacted tunneling antenna feedgap. Under certain operating conditions, we show that the antenna enters a highly nonlinear regime in which the energy of the emitted photons exceeds the quantum limit imposed by the applied bias. We propose a model based upon the spontaneous emission of hot electrons that correctly reproduces the experimental findings. The electron-fed optical antennas described here are critical devices for interfacing electrons and photons, enabling thus the development of optical transceivers for on-chip wireless broadcasting of information at the nanoscale