High-efficiency 20 GHz traveling wave tube development for space communications

A 75 watt CW high efficiency helix TWT operating at 20 GHz was developed for satellite communication systems. The purpose was to extend the performance capabilities of helix TWTs by using recent technology developments. The TWT described is a unique design because high overall efficiency is obtained with a low perveance beam. In the past, low perveance designs resulted in low beam efficiencies. However, due to recent breakthoughs in diamond rod technology and in collector electrode materials, high efficiencies can now be achieved with low perveance beams. The advantage of a low perveance beam is a reduction in space charge within the beam which translates to more efficient collector operation. In addition, this design incorporates textured graphite electrodes which further enhance collector operation by suppressing backstreaming secondaries. The diamond supported helix circuit features low RF losses, high interaction impedance, good thermal handling capability and has been designed to compensate for the low perveance beam. One more discussed tube feature is the use of a velocity taper in the output helix that achieves low signal distortion while maintaining high efficiency

On the number of attractors in random Boolean networks

The evaluation of the number of attractors in Kauffman networks by Samuelsson and Troein is generalized to critical networks with one input per node and to networks with two inputs per node and different probability distributions for update functions. A connection is made between the terms occurring in the calculation and between the more graphic concepts of frozen, nonfrozen and relevant nodes, and relevant components. Based on this understanding, a phenomenological argument is given that reproduces the dependence of the attractor numbers on system size.Comment: 6 page

Moving Beyond the College-Preparatory High School Model to a College-Going Culture in Urban Catholic High Schools

A college-going culture has been found to improve academic outcomes for underrepresented high school students (Allen, Kimura-Walsh, & Griffin, 2009; Stanton-Salazar, 2010). The research on Catholic high schools shows their college-preparatory environment ability to produce successful outcomes for African-American and Latino students (Bryk, Lee, & Holland, 1993). This study examines two urban Catholic high schools and how they construct opportunities for low-income Latino and African-American male students. The year-long study draws from 1) ethnographic field notes; 2) interviews with students and staff; 3) survey and 4) student data. Data suggests that although both schools focused on preparing students for college, only one maintained a college-going culture through its college-going discourse which better served the needs of its underrepresented students

Brotherhood, Social Justice, and Persistent Deficit Ideologies: Latino Students’ Experiences in an All-male Catholic High School

Declining Catholic school enrollment rates coupled with increasing numbers of Latino Catholics (in the US) have prompted Catholic leaders to interrogate how they can best engage and meet the needs of the Latino community (Ospino, 2014; Notre Dame Task Force, 2009). Much of this work focuses on how Catholic schools can attract Latino students and their families, but does not situate the Latino Catholic school student experience within the historical, economic and sociopolitical context. This paper interrogates the history and experiences of Latino students at Divinity High School (pseudonym), an all male Catholic high school that has historically served a working class Latino community. The project draws its data from a one-year ethnographic study that examined Divinity High School’s school culture. Findings demonstrate how the school’s values of brotherhood and social justice facilitated Latino student engagement, while teacher deficit thinking contrasted with the mission and culture of the school. This research calls awareness to the need for critical analysis of Catholic schools focused on the education of working class Latinos. Hermandad, justicia social y persistente déficit de la ideología: experiencias de estudiantes latinos en una escuela secundaria católica masculina El declive de las tasas de matrícula en las escuelas católicas aunado al aumento de latinos católicos (en Estados Unidos) ha impulsado a que los líderes católicos se pregunten cómo pueden alcanzar y cubrir mejor las necesidades de la comunidad latina (Ospino, 2014; Notre Dame Task Force, 2009). La mayoría de este trabajo se centra en cómo las escuelas católicas pueden atraer a estudiantes latinos y a sus familias, pero no sitúa la experiencia del estudiante latino de una escuela católica en el contexto histórico, económico y sociopolítico. Este artículo interroga la historia y las experiencias de los estudiantes latinos de Divinity High School (pseudónimo), una escuela secundaria católica masculina que históricamente ha servido a la clase trabajadora de la comunidad latina. El proyecto saca los datos de un estudio etnográfico de un año que examinó la cultura de la escuela Divinity High School. Los resultados demuestran que los valores de hermandad y justicia social de la escuela facilitaron la participación de los estudiantes latinos, mientras que el déficit de la ideología del profesorado contrastó con la misión y cultura de la escuela. Esta investigación llama la atención sobre la necesidad de un análisis crítico de las escuelas católicas centrado en la educación de los latinos de clase trabajadora. Idéologies de fraternité, justice sociale et de déficit persistant : les expériences vécues par les élèves latinos dans les lycées catholiques de garçons La baisse des taux d\u27inscriptions dans les écoles catholiques associée au nombre croissant de latinos (aux États-Unis) a incité les responsables catholiques à s\u27interroger sur la meilleure manière d\u27aborder les besoins de la communauté latino-américaine et de les satisfaire (Ospino, 2014; Groupe de travail Notre Dame, 2009). La plus grande partie de ce travail porte sur la manière d\u27attirer les élèves latinos et leurs familles dans les écoles catholiques, mais elle ne situe pas ce que vivent ces élèves des écoles catholiques dans le contexte historique, économique et socio-politique. Cet article pose des questions sur l\u27histoire et l\u27expérience vécue par les élèves du lycée de la Divinité (un pseudonyme), un lycée de garçons, qui a traditionnellement desservi une communauté latino appartenant à la classe ouvrière. Les données du projet proviennent d\u27une année d\u27études ethnographiques pour examiner la culture du lycée de la Divinité. Les constatations effectuées démontrent comment les valeurs de fraternité et de justice sociale de l\u27école ont facilité la participation des élèves latinos, alors que le manque d\u27idées des professeurs contrastait avec la mission et la culture de l\u27école. Cette recherche recommande une sensibilisation à la nécessité d\u27une analyse critique des écoles catholiques centrée sur l\u27enseignement dispensé aux Latinos issus de la classe ouvrière

Introduction to the Focus Section: The Cristo Rey Network of Schools

Introduction to the focus section

“Does Jesus Want us to be Poor?” Student Perspectives of the Religious Program at a Cristo Rey Network School

The structure of Catholic schools improves achievement by providing multiple opportunities for face-to-face interaction, the development of meaningful relationships between students, teachers, and other members of the school community, and a shared set of beliefs among all school members (Bryk, Lee, & Holland, 1993). Despite a substantiating body of research for this assertion, few empirical studies exist on how the religious program might impact the intrapersonal and interpersonal development of students. The Cristo Rey Network (CRN) of schools was developed in response to the material realities of students and families living in Chicago (Kearney, 2006). The leaders of the network, motivated by Catholic social teachings that recognize and prioritize the poor, developed the corporate work-study Catholic school model to make the Catholic school experience accessible for low-income families. This ethnographic study explored the impact of the CRN on the religious program of St. Peter High School (pseudonym) and, in turn, how the religious program used the lived experiences of Latino and African American students. Findings point to a need for teachers at CRN schools to be aware of students’ cultural and social identity and to develop an appropriate pedagogical response in religious spaces to strengthen students’ academic, social, and spiritual identities

Stable and unstable attractors in Boolean networks

Boolean networks at the critical point have been a matter of debate for many years as, e.g., scaling of number of attractor with system size. Recently it was found that this number scales superpolynomially with system size, contrary to a common earlier expectation of sublinear scaling. We here point to the fact that these results are obtained using deterministic parallel update, where a large fraction of attractors in fact are an artifact of the updating scheme. This limits the significance of these results for biological systems where noise is omnipresent. We here take a fresh look at attractors in Boolean networks with the original motivation of simplified models for biological systems in mind. We test stability of attractors w.r.t. infinitesimal deviations from synchronous update and find that most attractors found under parallel update are artifacts arising from the synchronous clocking mode. The remaining fraction of attractors are stable against fluctuating response delays. For this subset of stable attractors we observe sublinear scaling of the number of attractors with system size.Comment: extended version, additional figur

The properties of attractors of canalyzing random Boolean networks

We study critical random Boolean networks with two inputs per node that contain only canalyzing functions. We present a phenomenological theory that explains how a frozen core of nodes that are frozen on all attractors arises. This theory leads to an intuitive understanding of the system's dynamics as it demonstrates the analogy between standard random Boolean networks and networks with canalyzing functions only. It reproduces correctly the scaling of the number of nonfrozen nodes with system size. We then investigate numerically attractor lengths and numbers, and explain the findings in terms of the properties of relevant components. In particular we show that canalyzing networks can contain very long attractors, albeit they occur less often than in standard networks.Comment: 9 pages, 8 figure

Phase transition in a class of non-linear random networks

We discuss the complex dynamics of a non-linear random networks model, as a function of the connectivity k between the elements of the network. We show that this class of networks exhibit an order-chaos phase transition for a critical connectivity k = 2. Also, we show that both, pairwise correlation and complexity measures are maximized in dynamically critical networks. These results are in good agreement with the previously reported studies on random Boolean networks and random threshold networks, and show once again that critical networks provide an optimal coordination of diverse behavior.Comment: 9 pages, 3 figures, revised versio

Canalizing Kauffman networks: non-ergodicity and its effect on their critical behavior

Boolean Networks have been used to study numerous phenomena, including gene regulation, neural networks, social interactions, and biological evolution. Here, we propose a general method for determining the critical behavior of Boolean systems built from arbitrary ensembles of Boolean functions. In particular, we solve the critical condition for systems of units operating according to canalizing functions and present strong numerical evidence that our approach correctly predicts the phase transition from order to chaos in such systems.Comment: to be published in PR