Multiple-reflection conical microwave antenna

Conical-Gregorian antenna concept, using conical reflector, promises excellent rf performance and offers potential advantages in areas of mechanical and structural design, surface measurement, and in furlability. Multiple reflection scheme between one or more subreflectors and main reflector is utilized. Subreflector can be reduced to as little as 0.1 the diameter of main reflector

Cohomology foundations of one-loop amplitudes in pure spinor superspace

We describe a pure spinor BRST cohomology framework to compactly represent ten-dimensional one-loop amplitudes involving any number of massless open- and closed-string states. The method of previous work to construct scalar and vectorial BRST invariants in pure spinor superspace signals the appearance of the hexagon gauge anomaly when applied to tensors. We study the systematics of the underlying BRST anomaly by defining the notion of pseudo-cohomology. This leads to a rich network of pseudo-invariant superfields of arbitrary tensor rank whose behavior under traces and contractions with external momenta is determined from cohomology manipulations. Separate papers will illustrate the virtue of the superfields in this work to represent one-loop amplitudes of the superstring and of ten-dimensional super-Yang--Mills theory.Comment: 94 pages, harvmac Te

Invariants for E_0-semigroups on II_1 factors

We introduce four new cocycle conjugacy invariants for E_0-semigroups on II_1 factors: a coupling index, a dimension for the gauge group, a super product system and a C*-semiflow. Using noncommutative It\^o integrals we show that the dimension of the gauge group can be computed from the structure of the additive cocycles. We do this for the Clifford flows and even Clifford flows on the hyperfinite II_1 factor, and for the free flows on the free group factor $L(F_\infty)$. In all cases the index is 0, which implies they have trivial gauge groups. We compute the super product systems for these families and, using this, we show they have trivial coupling index. Finally, using the C*-semiflow and the boundary representation of Powers and Alevras, we show that the families of Clifford flows and even Clifford flows contain infinitely many mutually non-cocycle-conjugate E_0-semigroups.Comment: 51 page

The origin of the spacetime metric: Bell's `Lorentzian pedagogy' and its significance in general relativity

The purpose of this paper is to evaluate the `Lorentzian pedagogy' defended by J.S. Bell in his essay ``How to teach special relativity'', and to explore its consistency with Einstein's thinking from 1905 to 1952. Some remarks are also made in this context on Weyl's philosophy of relativity and his 1918 gauge theory. Finally, it is argued that the Lorentzian pedagogy - which stresses the important connection between kinematics and dynamics - clarifies the role of rods and clocks in general relativity.Comment: To be published in ``Physics Meets Philosophy at the Planck Length'', C. Callender and N. Huggett (eds.), Cambridge University Press (1999). 22 pages, no figures, LaTeX, uses harvard.sty; 3 references added, typos corrected and minor changes to conten

Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: Effect of helium

Prominences are partially ionized, magnetized plasmas embedded in the solar corona. Damped oscillations and propagating waves are commonly observed. These oscillations have been interpreted in terms of magnetohydrodynamic (MHD) waves. Ion-neutral collisions and non-adiabatic effects (radiation losses and thermal conduction) have been proposed as damping mechanisms. We study the effect of the presence of helium on the time damping of non-adiabatic MHD waves in a plasma composed by electrons, protons, neutral hydrogen, neutral helium (He I), and singly ionized helium (He II) in the single-fluid approximation. The dispersion relation of linear non-adiabatic MHD waves in a homogeneous, unbounded, and partially ionized prominence medium is derived. The period and the damping time of Alfven, slow, fast, and thermal waves are computed. A parametric study of the ratio of the damping time to the period with respect to the helium abundance is performed. The efficiency of ion-neutral collisions as well as thermal conduction is increased by the presence of helium. However, if realistic abundances of helium in prominences (~10%) are considered, this effect has a minor influence on the wave damping. The presence of helium can be safely neglected in studies of MHD waves in partially ionized prominence plasmas.Comment: Research note submitted in A&

Non-abelian ZZ-theory: Berends-Giele recursion for the α′\alpha'-expansion of disk integrals

We present a recursive method to calculate the $\alpha'$-expansion of disk integrals arising in tree-level scattering of open strings which resembles the approach of Berends and Giele to gluon amplitudes. Following an earlier interpretation of disk integrals as doubly partial amplitudes of an effective theory of scalars dubbed as $Z$-theory, we pinpoint the equation of motion of $Z$-theory from the Berends-Giele recursion for its tree amplitudes. A computer implementation of this method including explicit results for the recursion up to order $\alpha'^7$ is made available on the website http://repo.or.cz/BGap.gitComment: 58 pages, harvmac TeX, v2: cosmetic changes, published versio

Multiparticle SYM equations of motion and pure spinor BRST blocks

In this paper a multiparticle generalization of linearized ten-dimensional super Yang--Mills superfields is proposed. Their equations of motions are shown to take the same form as in the single-particle case, supplemented by contact terms. A recursive construction of these superfields is inspired by the iterated OPEs among massless vertex operators in the pure spinor formalism. An enlarged set of BRST-covariant pure spinor blocks is then defined in a streamlined fashion and combined to multiparticle vertex operators. The latter can be used to universally describe tree-level subdiagrams in the perturbative open and closed superstring, regardless of the loop order. The inherent symmetries of the multiparticle superfields are reproduced by structure constants of the gauge group, hinting a natural appearance of the BCJ-duality between color and kinematics in the fundamentals of super Yang--Mills theory. We present one-loop applications where known scalar cohomology objects are systematically recomputed and a novel vector cohomology particularly relevant to the closed string is constructed for arbitrary multiplicity.Comment: 44 pp, 10 figures, harvmac, v2: published versio

A solution to the non-linear equations of D=10 super Yang-Mills theory

In this letter, we present a formal solution to the non-linear field equations of ten-dimensional super Yang--Mills theory. It is assembled from products of linearized superfields which have been introduced as multiparticle superfields in the context of superstring perturbation theory. Their explicit form follows recursively from the conformal field theory description of the gluon multiplet in the pure spinor superstring. Furthermore, superfields of higher mass dimensions are defined and their equations of motion spelled out.Comment: 6 pages, v2: published versio

Innovative School Counseling Approaches to Improving College and Career Readiness

School counselors are at the forefront of efforts to improve the college readiness of K-12 students. It is clear that many roadblocks exist with regard to college readiness and adequate access to college counseling. Many public schools serving minority, first-generation, low-income students have school counselors with large caseloads and numerous non-counseling duties leaving them with little time to spend on college counseling (Clinedinst, Koranteng, & Nicola, 2015). This exploratory study aimed to review promising practices that target college and career readiness for students. A deeper investigation was conducted at an urban school serving underrepresented students which revealed an innovative five-year, comprehensive, relationship-driven school counseling model that promotes equity, fosters social and emotional growth, and supports students and families through college readiness, enrollment, and degree attainment leading to a potential new framework for schools to consider