Fuel Efficient Control Design and Constrained Motion Analysis for Spacecraft Coulomb Formation in Elliptic Chief Orbits

The use of Coulomb force has been analyzed in recent years to provide propulsion in space for various applications. Coulomb formation can also be utilized to make close formation spacecraft missions fuel efficient. In this study, the Coulomb formation of two craft is studied in elliptic chief orbits for two formation geometries. The first formation requires both spacecraft to be aligned along the nadir (radial) direction and the second formation requires both spacecraft to maintain a constant separation distance relative to each other while each spacecraft rotates freely on the surface of a sphere with the ratio of the radii being inversely proportional to the ratio of the masses. Two nonlinear optimal feedback control techniques are implemented to stabilize the dynamics of the Coulomb formation and maintain the desired formation while minimizing the energy costs. The control accelerations are compared to the analytical constraint accelerations obtained using the Udwadia-Kalaba equations for constrained motion. Due to the effects of plasma shielding, a Debye length model is incorporated in the nonlinear dynamics as a linear function of altitude of the formation\u27s center of mass. The integrated thruster efforts are calculated for both optimal and analytical techniques and the fuel costs are determined and compared for both formations. The results demonstrated that the use of Coulomb force increases fuel efficiency for formation achievement and maintenance. The numerical analysis is performed on a) the highly eccentric Molniya orbit and b) the near-circular near-GEO orbit of the ERS-21

Investigating viscous damping using a webcam

We describe an experiment involving a mass oscillating in a viscous fluid and analyze viscous damping of harmonic motion. The mechanical oscillator is tracked using a simple webcam and an image processing algorithm records the position of the geometrical center as a function of time. Interesting information can be extracted from the displacement-time graphs, in particular for the underdamped case. For example, we use these oscillations to determine the viscosity of the fluid. Our mean value of 1.08 \pm 0.07 mPa s for distilled water is in good agreement with the accepted value at 20\circC. This experiment has been successfully employed in the freshman lab setting.Comment: 13 pages, 5 figure

Targeting cancers in the gastrointestinal tract: role of capecitabine

Capecitabine is currently the only novel, orally home-administered fluorouracil prodrug. It offers patients more freedom from hospital visits and less inconvenience and complications associated with infusion devices. The drug has been extensively studied in large clinical trials in many solid tumors, including breast cancer, colorectal cancer, gastric cancer, and many others. Furthermore, the drug compares favorably with fluorouracil in patients with such cancers, with a safe toxicity profile, consisting mainly of gastrointestinal and dermatologic adverse effects. Whereas gastrointestinal events and hand-foot syndrome occur often with capecitabine, the tolerability profile is comparatively favorable. Prompt recognition of severe adverse effects is the key to successful management of capecitabine. Ongoing and future clinical trials will continue to examine, and likely expand, the role of capecitabine as a single agent and/or in combination with other anticancer agents for the treatment of gastrointestinal as well as other solid tumors, both in the advanced palliative and adjuvant settings. The author summarizes the current data on the role of capecitabine in the management of gastrointestinal cancers

Organizational Culture and Performance: An Empirical Study of SMEs in Pakistan

This study aims to identify the prevailing type of culture and its relationship with performance in SMEs operating in Pakistan. Using competing value framework, the cultural profile and dominant characteristics of SMEs are identified and investigated to ascertain their implied relationship with organizational performance on the basis of certain self-assessment variables. For this purpose, primary data was collected form SME employees through a self-administered survey questionnaire. The results revealed that ‘hierarchy’ culture is the prevailing type of culture and a statistically significant relationship exists between organizational culture and performance among the sampled SMEs. The study concludes with certain important insinuations for theory and practice especially concerned with SMEs

Fiscal, Monetary Policies and Institutions’ Role (Political, Social and Economic) in Pakistan

The purpose of this study is to test the fundamental relationship between fiscal, monetary policies and institutions in Pakistan from 1976 to 2008. These policies are roadmap in the progress of a country. No doubt both these policies are useful tools in the hands of the government to increase the per capita GDP of the country. Such policies depict the performance level of institutions of a country. Better institutions leads to higher level of growth. Institutions perform significant role in the progress of any country. The growth targets can be achieved through institutions. Higher the quality of institutions, higher the performance would be shown by economy. Countries can reach middle-income levels despite some corruption, but further growth requires much better institutions (Easterly, 2001, pp. 234-235, 245-248, Rodrik, 2003, pp. 16-17).Kwiatkowski et al (1992) test is used to test unit root and short run relationship is analyzed through ECM. Auto regressive distributed lags (ARDL) shows that there is long run relationship among growth policies and institutions’ role in Pakistan

Current use and potential role of bevacizumab in the treatment of gastrointestinal cancers

Angiogenesis is essential for cancer growth and metastasis. Vascular endothelial growth factor (VEGF) is a key modulator of angiogenesis. In addition, overexpression of VEGF is correlated with advanced disease and poor prognosis. Bevacizumab, a recombinant humanized anti-VEGF monoclonal antibody, is the first anti-angiogenic agent approved by Food and Drug Administration for use in treatment of human solid cancers. Although bevacizumab has received most attention for first-line treatment of advanced colorectal and nonsmall-cell lung cancer, there is a rapidly growing body of evidence for its efficacy in treatment of a number of other solid tumors. We present the current status and potential use of bevacizumab therapy in gastrointestinal cancers

USE OF DIAGRAMS AS INSTRUCTIONAL AIDS IN TEACHING OF GEOMETRICAL CONCEPTS AT SECONDARY SCHOOL LEVEL

Angle is a complex topic defined in a variety of contexts; some define angle to be as a pair of rays coming from a single point, as a rotation about a single point, or in a curve. Due to the multiple definitions of angle students get confused as to what an angle truly consists of. This study paid close attention to the misconceptions high school geometry students’ hold about the concept of angle and how to help them gain a more conceptual understanding of this essential concept with the use of different Diagrams. The main idea behind the conduction of this study is to investigate the effect of use of diagrams as instructional aids on the conceptual understanding of angles. The study hypothesizes that angle can be learned using interactive Diagrams. The results of this study showed that diagrams which based on different A.V aids was shown to be more beneficial for the students who used to clear the concept of angles

A new approach to CNC programming for accurate multi-axis face-milling of hypoid gears

A pair of hypoid gears refers to a pinion and a gear with skew axes. Hypoid gears are crucial to some power transmission systems, such as those of helicopters, power generation machines and automobiles. However, the design and manufacturing of hypoid gears are quite difficult. Currently, the major parameters of hypoid gears are calculated, but the geometries of the gears are not fully defined. To machine a hypoid gear, parameters of cutting systems are determined according to the gear design, whereas, settings of CNC machine tools with the machining parameters are also computed. The existing hypoid gears machining methods use the simplified blade model of the cutting systems, resulting in large errors in the machined gears. This new work proposes an accurate approach, to determine the parameters of the cutting system blades, for the face-milling of hypoid gears. In this work, a parametric model of the blades is established; and according to the hypoid gear parameters, the pressure angle and the cutting system radius are precisely calculated. Currently, hypoid gear engineers can use special CAD/CAM software to design the gears and to calculate machine settings. Unfortunately, these software are developed only for particular machine tools; it cannot be used for hypoid gear machine tools of different configurations. Moreover, few technical articles has been published to clearly address challenges in the CNC programming and post-processing for the multi-axis face-milling of hypoid gears, such as the parameters determination of a cutter system, its location and orientation calculation and CNC programs generation. To solve the current problems, another part of this research proposes a generic approach to CNC programming and post-processing for gear face-milling. The main contributions of this part includes (1) a new mathematical model to calculate the cutter system location and orientation and (2) a generic post-processing method to establish the machine kinematics chain and to compute the coordinates of the machine axes in face-milling. This approach provides a general and accurate methodology for the face-milling of hypoid gears on any machine tools and can be directly applied to the hypoid gear manufacturing for better quality