Chemical modification of poly(p-phenylene) for use in ablative compositions

Development of ablative materials based on modification of polyphenylene compounds is discussed. Chemical and physical properties are analyzed for application as heat resistant materials. Synthesis of linear polyphenylenes is described. Effects of exposure to oxyacetylene flame and composition of resultant char layer are presented

Error analysis for Mariner Venus/Mercury 1973 conducted at the JPL Mesa west antenna range

Theoretical analysis and experimental data are combined to yield the errors to be used with antenna gain, antenna patterns, and RF cable insertion loss measurements for the Mariner Venus-Mercury 1973 Flight Project. These errors apply to measurements conducted at the JPL Mesa, West Antenna Range, on the high gain antenna, low gain antenna, and RF coaxial cables

Antibodies to acetylcholine receptor in parous women with myasthenia: evidence for immunization by fetal antigen

The weakness in myasthenia gravis (MG) is mediated by autoantibodies against adult muscle acetylcholine receptors (AChR) at the neuromuscular junction; most of these antibodies also bind to fetal AChR, which is present in the thymus. In rare cases, babies of mothers with MG, or even of asymptomatic mothers, develop a severe developmental condition, arthrogryposis multiplex congenita, caused by antibodies that inhibit the ion channel function of the fetal AChR while not affecting the adult AChR. Here we show that these fetal AChR inhibitory antibodies are significantly more common in females sampled after pregnancy than in those who present before pregnancy, suggesting that they may be induced by the fetus. Moreover, we were able to clone high-affinity combinatorial Fab antibodies from thymic cells of two mothers with MG who had babies with arthrogryposis multiplex congenita. These Fabs were highly specific for fetal AChR and did not bind the main immunogenic region that is common to fetal and adult AChR. The Fabs show strong biases to VH3 heavy chains and to a single Vk1 light chain in one mother. Nevertheless, they each show extensive intraclonal diversification from a highly mutated consensus sequence, consistent with antigen-driven selection in successive steps. Collectively, our results suggest that, in some cases of MG, initial immunization against fetal AChR is followed by diversification and expansion of B cells in the thymus; maternal autoimmunity will result if the immune response spreads to the main immunogenic region and other epitopes common to fetal and adult AChR

Quantum Flexoelectricity in Low Dimensional Systems

Symmetry breaking at surfaces and interfaces and the capability to support large strain gradients in nanoscale systems enable new forms of electromechanical coupling. Here we introduce the concept of quantum flexoelectricity, a phenomenon that is manifested when the mechanical deformation of non-polar quantum systems results in the emergence of net dipole moments and hence linear electromechanical coupling proportional to local curvature. The concept is illustrated in carbon systems, including polyacetylene and nano graphitic ribbons. Using density functional theory calculations for systems made of up to 400 atoms, we determine the flexoelectric coefficients to be of the order of ~ 0.1 e, in agreement with the prediction of linear theory. The implications of quantum flexoelectricity on electromechanical device applications, and physics of carbon based materials are discussed.Comment: 15 pages, 3 figure

Bifurcation and Chaos in Coupled Ratchets exhibiting Synchronized Dynamics

The bifurcation and chaotic behaviour of unidirectionally coupled deterministic ratchets is studied as a function of the driving force amplitude ($a$) and frequency ($\omega$). A classification of the various types of bifurcations likely to be encountered in this system was done by examining the stability of the steady state in linear response as well as constructing a two-parameter phase diagram in the ($a -\omega$) plane. Numerical explorations revealed varieties of bifurcation sequences including quasiperiodic route to chaos. Besides, the familiar period-doubling and crises route to chaos exhibited by the one-dimensional ratchet were also found. In addition, the coupled ratchets display symmetry-breaking, saddle-nodes and bubbles of bifurcations. Chaotic behaviour is characterized by using the sensitivity to initial condition as well as the Lyapunov exponent spectrum; while a perusal of the phase space projected in the Poincar$\acute{e}$ cross-section confirms some of the striking features.Comment: 7 pages; 8 figure

The power spectra of CMB and density fluctuations seeded by local cosmic strings

We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far to evaluate the two-point functions of their stress energy tensor. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor dominate over vector and tensor components. This result has far reaching consequences. We find that cosmic strings exhibit a single Doppler peak of acceptable height at high $\ell$. They also seem to have a less severe bias problem than global defects, although the CDM power spectrum in the ``standard'' cosmology (flat geometry, zero cosmological constant, 5% baryonic component) is the wrong shape to fit large scale structure data

Strategic Leadership and Organizational Performance: A Critical Review of Literature

Effective strategic leadership is considered as a major ingredient for the successful performance of any organization operating in the ever dynamic and complex environment of the 21st century. In the context of information uncertainty and resource scarcity, strategic leadership is required to confront the reality of environmental turbulence and a continuous need for appropriate organizational change in order to achieve performance goals. Most of the conceptual and empirical studies have shown that strategic leadership actions significantly influence performance. Despite its importance, studies have demonstrated that the influence of strategic leadership on organizational performance is contingent upon situational constraints or random effects. To date, very little empirical research has analyzed the direct and indirect relationship between strategic leadership, external environment, organizational change and performance. This paper seeks to unearth this research gap by critically reviewing relevant conceptual and empirical literature to bring out the possibility that the external environment and organizational change could influence the relationship between strategic leadership and organizational performance. The paper advances the emerging postulations which anchor a conclusion that the direct effect of strategic leadership on performance is contested and hence inconclusive due to possible moderating and mediating influence of the external environment and organizational change respectively. It is hoped that the paper’s postulations would guide empirical research in various contexts to hasten addressing of the extant knowledge gaps

Recidivism Reconsidered: Preserving the Community Justice Mission of Community Corrections

In the following discussion, we describe the logical and practical problems that arise when recidivism is used as the principal outcome measure for community corrections agencies. We recognize that recidivism will always be a feature of justice policy and practice. Recidivism offers a simple and familiar outcome measure for judging the effectiveness of justice interventions. Pointing out the logical flaws of recidivism will not diminish its salience for audiences disinclined to question its utility. Our purpose in this discussion is not to end the use of recidivism as a justice system measure but to illustrate its limits and to encourage the development and use of more suitable measures — namely, positive outcomes related to the complex process of criminal desistance

Challenges of Implementing Consortium Strategy in Development Projects at ViAgroforestry, Kenya

Consortium strategy involves an arrangement in which organizations develop, utilize and amalgamate structures, cultures, and operational systems to support competitiveness in delivery of service in a dynamic environment. This study sought to investigate challenges of implementing consortium strategy and measures to mitigate the challenges at ViAgroforestry, Kenya. Through a case study design both primary and secondary data were gathered through personal interviews and analysis of relevant documents respectively. Content analysis was used to analyze data. The study established that, both internal and external factors affected effective consortium strategy implementation at ViAgroforestry. The external factors that affected strategy implementation included social-cultural, political, economic, and technological factors. The internal factor included leadership and management styles, competency of employees among the partner organizations, lack of employee commitment to consortium operation, lack of adequate financial resources, unclear implementation guidelines and inconsistency in deployment of employees to support consortium. The mitigation measures to deal with the challenges include building employee competencies and confidence, setting up and reinforcing clear guidelines for selecting, recruiting and exiting partners in the consortium, mobilization of adequate financial resources, enhanced integration of Information Communication Technology (ICT) within the operating systems, and democratic style of management among partners. It was recommended that ViAgroforestry, Kenya should align organizational structure, provide adequate resources, build employee competencies and set and reinforce clear guidelines for operations while integrating ICT in its operations for effective consortium strategy implementation. In view of the limitations of the study, further research has been suggested on evaluating performance of consortium strategy implementation at ViAgroforestry, Kenya