Performance of slotted ALOHA satellite channels with finite buffer

The behaviour of the slotted ALOHA satellite channel with a finite buffer at each of the user terminals is studied. Approximate relationships between the queuing delay, overflow probabilities and buffer size are derived as functions of the system input parameters (i.e. the number of users, the traffic intensity, the transmission and the retransmission probabilities) for two cases found in the literature: the symmetric case (same transmission and retransmission probabilities), and the asymmetric case (transmission probability far greater than the retransmission probability). For comparison, the channel performance with an infinite buffer is also derived. Additionally, the stability condition for the system is defined in the latter case. The analysis carried out in the paper reveals that the queuing delays are quite significant, especially under high traffic conditions.

Three-dimensional corner reflector of arbitrary apex angle

A method of analysing a 3-dimensional corner reflector antenna of arbitrary apex angle is given. Expressions have been obtained for the far field of the 3-dimensional corner reflector fed by a dipole. The radiation resistance and the directive gain of the antenna have been calculated. The method described is applicable even when the feed dipole is arbitrarily oriented. It is found that the radiation along a prescribed direction can be circularly polarised (right or left) by suitably orienting the feed dipole.

Owner-driven decision support in holding-specific forest planning

Socio-economic and demographic changes among family forest owners and demands for versatile forestry decision aid motivated this study, which sought grounds for owner-driven forest planning. Finnish family forest owners’ forest-related decision making was analyzed in two interview-based qualitative studies, the main findings of which were surveyed quantitatively. Thereafter, a scheme for adaptively mixing methods in individually tailored decision support processes was constructed. The first study assessed owners’ decision-making strategies by examining varying levels of the sharing of decision-making power and the desire to learn. Five decision-making modes – trusting, learning, managing, pondering, and decisive – were discerned and discussed against conformable decision-aid approaches. The second study conceptualized smooth communication and assessed emotional, practical, and institutional boosters of and barriers to such smoothness in communicative decision support. The results emphasize the roles of trust, comprehension, and contextual services in owners’ communicative decision making. In the third study, a questionnaire tool to measure owners’ attitudes towards communicative planning was constructed by using trusting, learning, and decisive dimensions. Through a multivariate analysis of survey data, three owner groups were identified as fusions of the original decision-making modes: trusting learners (53%), decisive learners (27%), and decisive managers (20%). Differently weighted communicative services are recommended for these compound wishes. The findings of the studies above were synthesized in a form of adaptive decision analysis (ADA), which allows and encourages the decision-maker (owner) to make deliberate choices concerning the phases of a decision aid (planning) process. The ADA model relies on adaptability and feedback management, which foster smooth communication with the owner and (inter-)organizational learning of the planning institution(s). The summarized results indicate that recognizing the communication-related amenity values of family forest owners may be crucial in developing planning and extension services. It is therefore recommended that owners, root-level planners, consultation professionals, and pragmatic researchers collaboratively continue to seek stable change.

Evaluating the performance of weed containment programmes

Aim: To develop approaches to the evaluation of programmes whose strategic objectives are to halt or slow weed spread. Location: Australia. Methods: Key aspects in the evaluation of weed containment programmes are considered. These include the relevance of models that predict the effects of management intervention on spread, the detection of spread, evidence for containment failure and metrics for absolute or partial containment. Case studies documenting either near-absolute (Orobanche ramosa L., branched broomrape) or partial (Parthenium hysterophorus (L.) King and Robinson, parthenium) containment are presented. Results: While useful for informing containment strategies, predictive models cannot be employed in containment programme evaluation owing to the highly stochastic nature of realized weed spread. The quality of observations is critical to the timely detection of weed spread. Effectiveness of surveillance and monitoring activities will be improved by utilizing information on habitat suitability and identification of sites from which spread could most compromise containment. Proof of containment failure may be difficult to obtain. The default option of assuming that a new detection represents containment failure could lead to an underestimate of containment success, the magnitude of which will depend on how often this assumption is made. Main conclusions: Evaluation of weed containment programmes will be relatively straightforward if containment is either absolute or near-absolute and may be based on total containment area and direct measures of containment failure, for example, levels of dispersal, establishment and reproduction beyond (but proximal to) the containment line. Where containment is only partial, other measures of containment effectiveness will be required. These may include changes in the rates of detection of new infestations following the institution of interventions designed to reduce dispersal, the degree of compliance with such interventions, and the effectiveness of tactics intended to reduce fecundity or other demographic drivers of spread. © 2012 Blackwell Publishing Ltd.

Ordering within moral orders to manage classroom trouble

This paper demonstrates how classroom trouble warranting teacher intervention can stem from transgressions in different layers of the complex moral order regulating classroom interactions. The paper builds from Durkheim’s treatment of schooling as the institution responsible for the inculcation of a shared moral order, Bernstein’s distinction between the instructional and regulative discourses in any pedagogic setting, and the concept of verticality in the instructional discourse to illuminate how curricular knowledge might apply across different contexts. This paper proposes a similar vertical dimension of moral gravity in the regulative discourse, such that some moral expectations apply across any context, while others are highly contextualized. This paper then applies this frame to data from classroom observations conducted in prevocational pathways for 16 years olds created under Australia’s “earning or learning till 17” policy. This paper describes the variety of moral premises teachers invoked in different teacher/class combinations, according to their level of moral gravity to display the dominant use of highly contextualized moral premises seeking institutional compliance, and minimal use of broader moral frames for these students on the brink of entry to the adult world.

Continuously equivalent networks in state space

Schoeffler has derived continuously equivalent networks in the nodal-admittance domain. The letter derives a corresponding result in state space that combines the usefulness of Schoeffler's result and the power of the state-variable approach.

Rectangular universal cellular array

A rectangular universal cellular array consisting of cells having three inputs and one output is described. This array is based on the Reed-Muller canonical expansion of a switching function. Although the total number of external input pins required in this array is the same as that of a rectangular array proposed in the literature, the number of cells is very much less.

Active vibration suppression of non-linear beams using optimal dynamic inversion

Euler–Bernoulli beams are distributed parameter systems that are governed by a non-linear partial differential equation (PDE) of motion. This paper presents a vibration control approach for such beams that directly utilizes the non-linear PDE of motion, and hence, it is free from approximation errors (such as model reduction, linearization etc.). Two state feedback controllers are presented based on a newly developed optimal dynamic inversion technique which leads to closed-form solutions for the control variable. In one formulation a continuous controller structure is assumed in the spatial domain, whereas in the other approach it is assumed that the control force is applied through a finite number of discrete actuators located at predefined discrete locations in the spatial domain. An implicit finite difference technique with unconditional stability has been used to solve the PDE with control actions. Numerical simulation studies show that the beam vibration can effectively be decreased using either of the two formulations.

Cyrus Adler papers, undated, 1883-1937.

Primarily correspondence relating to the Dropsie College for Hebrew and Cognate Learning, the Jewish encyclopedia, the Jewish Theological Seminary of America, the Smithsonian Institution and the American Jewish Historical Society. Contains also correspondence arranged alphabetically including letters from the staff of the American Hebrew, the American Jewish Committee, Theodor Herzl, the Jewish Agricultural and Industrial Aid Society, the Jewish Publication Society of America, Max J. Kohler, Louis Marshall, Jacob H. Schiff, Oscar S. Straus, Henrietta Szold, Stephen S. Wise and Israel Zangwill. Contains also material on the structure of the Jewish calendar, correspondence relating to the publication of the Jefferson Bible, correspondence and research material concerning Jewish servicemen in the Spanish-American War (published in the American Jewish year book, 1900-1901), a list of ... of the U.S. Congress, material ... immigration, the Jews in Rus ... cript proof articles from the Jewish quarterly review, numerous published articles by and ... Adler, and a large quantity of manuscript notes and material on Jewish history in general and American Jewish history in particular. Includes also David Sulzberger's collected data pertaining to the Jewish population in the United States-1900.

Accounting for student/educator diversity: resurrecting coaction theory

This chapter challenges current approaches to defining the context and process of entrepreneurship education. In modeling our classrooms as a microcosm of the world our current and future students will enter, this chapter brings to life (and celebrates) the everpresent diversity found within. The chapter attempts to make an important (and unique) contribution to the field of enterprise education by illustrating how we can determine the success of (1) our efforts as educators, (2) our students, and (3) our various teaching methods. The chapter is based on two specific premises, the most fundamental being the assertion that the performance of student, educator and institution can only be accounted for by accepting the nature of the dialogic relationship between the student and educator and between the educator and institution. A second premise is that at any moment in time, the educator can be assessed as being either efficient or inefficient, due to the presence of observable heterogeneity in the learning environment that produces differential learning outcomes. This chapter claims that understanding and appreciating the nature of heterogeneity in our classrooms provides an avenue for improvement in all facets of learning and teaching. To explain this claim, Haskell’s (1949) theory of coaction is resurrected to provide a lens through which all manner of interaction occurring within all forms of educational contexts can be explained. Haskell (1949) asserted that coaction theory had three salient features.

The open access advantage for researchers: Reflections on experience and challenges

This paper focuses on the advantages of Open Access, (OA) particularly from the point of view of individual researchers, research centres and disciplines, and institutions. The advantage described by the phrase “OA advantage”, is multifaceted. The experience of Queensland University of Technology in Australia in pioneering OA as preferred practice in an institution with a growing research profile and energy, has seen evidence of the OA advantage develop in the experience of our researchers. The University has witnessed the development of practical evidence about improved recognition and impact, and this has occurred in the context of sector wide activity and policy where fresh approaches and leadership will result in even greater rewards for researchers whose outputs are “in the open”.

Dislocation after total hip replacement: there is no such thing as a safe zone for socket placement with the posterior approach

Introduction Malorientation of the socket contributes to instability after hip arthroplasty but the optimal orientation of the cup in relation to the pelvis has not been unequivocally described. Large radiological studies are few and problems occur with film standardisation, measurement methodology used and alternative definitions of describing acetabular orientation. Methods A cohort of 1,578 patients from a single institution is studied where all patient data was collected prospectively. Risk factors for patients undergoing surgery are analysed. Radiological data was compared between a series of non-dislocating hips and dislocating cases matched 2:1 by operation type, age and diagnosis. Results The overall dislocation rate for all 1,578 cases was 3.23% but the rate varied according to the type of surgery performed. The rate in uncomplicated primary cases was 2.4% which increased to 9.3% for second stage implantation for a two stage procedure for infection. There was no significant difference in the variability of the dislocating and non-dislocating groups for either inclination (p = 0.393) or anteversion (p = 0.661). Conclusions A “safe zone” for socket orientation to avoid dislocation could not be defined. The cause of dislocation is multifactorial, re-establishing the anatomic centre of rotation, balancing soft tissues and avoidance of impingement around the hip are important considerations.

Systematic search for optical Barker codes with minimum length

A method that yields optical Barker codes of smallest known lengths for given discrimination is described.

Multistage monostable multivibrator using load-coupled regenerative feedback

A monostable multivibrator configuration using a new technique of regenerative feedback is discussed. This circuit provides an elegant alternative in situations wherein several monostable multivibrators have to be connected in tandem.