Optimal Attitude Guidance for the EXACT and IMPRESS Cubesats using Graph Methods with Pruning

This work demonstrates a high-level mission planning method for maximizing data output from a pair of scientific CubeSat missions. The proposed approach identifies the optimal sequence of attitude maneuvers to perform in order to maximize total downlinked data over the mission, while considering constraints on available power. Many scientific satellite missions consist of at least three target attitudes: pointing solar panels towards the Sun for power, pointing an antenna towards a ground station to transmit data, or pointing a payload towards a point of scientific interest. While careful mechanical design of the mission may enable all three (or more) target attitudes to be achieved simultaneously in certain cases, in general a decision must be made about which target to point to at what time in order to optimally achieve mission objectives and satisfy mission constraints. In this work, we develop a mission planning method that maximizes the volume of data downlinked to the ground over the mission time horizon while respecting constraints on battery level. The optimization problem is posed as an integer program over the space of attitude trajectories and subject to battery constraints. The solution of this problem is an attitude sequence that can be used as a reference for a low-level attitude controller to track. Previous work on this problem suffered from slow solution time for complex mission scenarios which constrained the realism of simulations performed for validation, so in this work we build on our prior approach by leveraging more advanced pruning and search methods to improve optimizer efficiency. We demonstrate the proposed approach on two CubeSats: IMPRESS and EXACT, both currently in design and sharing many mechanical specifications. Both CubeSats are controlled by low-bandwidth actuators and have three main attitude targets: the Sun for power, the Crab Nebula or the Sun the scientific mission, and ground stations for communication. Using simulated orbit data, we show the effectiveness of this method in squeezing mission performance out of both CubeSats while maintaining on-board power. Additionally, the proposed method can run faster than real-time for time horizons of several orbits, enabling a high level of autonomy in orbit

Entrance of Prospective Teachers to Initial Teacher Education and Stereotypes Around the Teaching Profession: Experiences From Eritrea

The inquiry framed into an action research strategy was initiated in the College of Education (CoE) at the Eritrea Institute of Technology, a major Initial Teacher Education (ITE) center in the country. The paper tried to answer the question: How do prospective-teachers happen to attend in the CoE? The paper also sheds light on the prevailing stereotypes around the teaching profession. The methodological and analytical framework of the research lies in the premise of teaching as a reflective practice. Qualitative data were gathered through focus group discussions (FGD) and in-depth interviews involving 126 participants comprising the leadership, educators and students of the college in the academic year 2012/2013. The FGDs and interviews were audio and video recorded, transcribed and thematically analyzed. The findings reveal that learning process in the CoE is influenced by a myriad of systemic, institutional and attitudinal issues that intersect and further complicate the already problematic nature of teaching. The nature of the admission of the prospective teachers to the CoE and the stereotyped public views toward the CoE vis-à-vis the teaching profession are among the major stumbling block that affect the classroom practice at the college and beyond. As part of the researchers’ commitment to follow a collaborative action research cycle, the findings were shared with educators and learner-teachers in ITE institutions. Areas of intervention were identified and the college is engaged in a number of collaborative activities involving its staff, local and international partners in ensuring the provision of quality teacher education in the country. Keywords: admission process, teaching profession, stereotypes, collaborative action research

Rüdiger Görner, Franz Kafkas akustische Welten

Le 13 décembre 1911, en rentrant d’un concert, Kafka écrivit dans son journal : « la musique écoutée élève naturellement un mur tout autour de moi, et la seule influence musicale que je subis durablement est la suivante : ainsi enfermé, je ne suis pas le même qu’en liberté ». Le rapport que Kafka entretient avec le monde musical est donc relativement ambigu ; bien qu’il soit en mesure d’apprécier la musicalité de la langue et qu’il ait une oreille formée à la mélodie grâce à sa très bonne con..

Alternative application methods of antagonists to avocado flowers to control stem-end rot pathogens

Biological pre- and postharvest disease control strategies depend on successful colonisation and survival of the introduced antagonists on the infection court. Effective and economical applications involve targeting the antagonists where they are critically needed i.e. the infection court. Honeybee dispersal is one method of antagonist application to such specific sites. In view of this, an in vitro experiment was conducted to investigate attachment, colonisation and survival of Bacillus subtilis on avocado flowers. Scanning electron microscopy studies showed that the bacterium could attach and colonise avocado flower surfaces. It can also survive on the flowers for longer periods of time. In vivo mode of action of the antagonist against stem-end rot (SER) pathogens was also studied where results showed lysis and degradation of hyphae and conidia. However, no viable colonies were retrieved from bee antagonist dispersal under field conditions. Bee antagonist dissemination was compared with antagonist and fungicide spray applications in terms of SER control and the added effect on other diseases such as Cercospora spot and anthracnose. Spray applications of the antagonist were more effective in reducing the incidence of SER than bee dissemination. Integrated sprays of the antagonist and fungicides significantly reduced the incidence of both pre- and postharvest diseases. The identity of Dothiorella aromatica, one of the most important SER pathogens, was investigated at a molecular level. RAPD techniques using the discriminatory OPC02 primer successfully separated isolates into three groups based on banding profiles. A further study using RFLP identified the pathogen as a Botryosphaeria spp. The most dominant specie was B. parva followed by B. rhodina. Further studies should focus on assessing the distribution of these pathogens within avocado-growing regions of South Africa.Dissertation (MSc (Plant Pathology))--University of Pretoria, 2006.Microbiology and Plant Pathologyunrestricte

Double Bright Band Observations with High-Resolution Vertically Pointing Radar, Lidar, and Profiles

On 11 May 2010, an elevated temperature inversion associated with an approaching warm front produced two melting layers simultaneously, which resulted in two distinct bright bands as viewed from the ER-2 Doppler radar system, a vertically pointing, coherent X band radar located in Greenbelt, MD. Due to the high temporal resolution of this radar system, an increase in altitude of the melting layer of approximately 1.2 km in the time span of 4 min was captured. The double bright band feature remained evident for approximately 17 min, until the lower atmosphere warmed enough to dissipate the lower melting layer. This case shows the relatively rapid evolution of freezing levels in response to an advancing warm front over a 2 h time period and the descent of an elevated warm air mass with time. Although observations of double bright bands are somewhat rare, the ability to identify this phenomenon is important for rainfall estimation from spaceborne sensors because algorithms employing the restriction of a radar bright band to a constant height, especially when sampling across frontal systems, will limit the ability to accurately estimate rainfall

Improvement of Raman lidar algorithm for quantifying aerosol extinction

Aerosols are particles of different composition and origin and influence the formation of clouds which are important in atmospheric radiative balance. At the present there is high uncertainty on the effect of aerosols on climate and this is mainly due to the fact that aerosol presence in the atmosphere can be highly variable in space and time. Monitoring of the aerosols in the atmosphere is necessary to better understanding many of these uncertainties. A lidar (an instrument that uses light to detect the extent of atmospheric aerosol loading) can be particularly useful to monitor aerosols in the atmosphere since it is capable to record the scattered intensity as a function of altitude from molecules and aerosols. One lidar method (the Raman lidar) makes use of the different wavelength changes that occur when light interacts with the varying chemistry and structure of atmospheric aerosols. One quantity that is indicative of aerosol presence is the aerosol extinction which quantifies the amount of attenuation (removal of photons), due to scattering, that light undergoes when propagating in the atmosphere. It can be directly measured with a Raman lidar using the wavelength dependence of the received signal. In order to calculate aerosol extinction from Raman scattering data it is necessary to evaluate the rate of change (derivative) of a Raman signal with respect to altitude. Since derivatives are defined for continuous functions, they cannot be performed directly on the experimental data which are not continuous. The most popular technique to find the functional behavior of experimental data is the least-square fit. This procedure allows finding a polynomial function which better approximate the experimental data. The typical approach in the lidar community is to make an a priori assumption about the functional behavior of the data in order to calculate the derivative. It has been shown in previous work that the use of the chi-square technique to determine the most likely functional behavior of the data prior to actually calculating the derivative eliminates the need for making a priori assumptions. We note that the a priori choice of a model itself can lead to larger uncertainties as compared to the method that is validated here. In this manuscript, the chi-square technique that determines the most likely functional behavior is validated through numerical simulation and by application to a large body of Raman lidar measurements. In general, we show that the chi-square approach to evaluate aerosol extinction yields lower extinction uncertainty than the traditional technique. We also use the technique to study the feasibility of developing a general characterization of the extinction uncertainty that could permit the uncertainty in Raman lidar aerosol extinction measurements to be estimated accurately without the use of the chi-square technique

Genotype x environment interaction and stability analysis of grain yield in QPM hybrid varieties

Maize (Zea mays L.) is a major staple cereal widely cultivated in different agro-climatic environments of Ethiopia.Maize productivity in the tropical highland region of the country is known by low average yield mainly due to thelack of high yielding and widely adapted improved cultivars. The objectives of this study were to determine G×Einteraction and yield stability of quality protein maize (QPM) experimental hybrids,to identify ideal genotype withhigh average yield depending on the differential genotypic responses to environment, and to form homogeneousgrouping of environments. The study was conducted at seven environments representing the tropical-highlandsub-humid maize growing agro-ecology of Ethiopia in 2015/2016. Thirty-three QPM hybrids and three-commercial hybridchecks were evaluated using a 4 ×9 alpha lattice design. Yield data was analyzed using AMMI and GGEbi-plot methods. Using AMMI analysis, four promising QPM hybrids designated asG31, G7, G19, G29, and G22were identified based on combined stability and average yield.GGEbi-plot displayed that variety Jibatwas closestto the ideal genotype, can be considered as best hybrid whereas G29, G22 were considered as desirably stable genotypes.GGE bi-plot also displayed Holeta as ideal environment and thus considered useful in discriminating thehybrids and representativeness as suitable environment. The GGE analysis delineated the test environments intothree mega-environments useful for targeted evaluation of genotypes. The result of this study indicated specificallyand widely adapted high yielding stable genotypes and also revealed homogeneous test environments

Rain evaporation rate estimates from dual-wavelength lidar measurements and intercomparison against a model analytical solution

Rain evaporation, while significantly contributing to moisture and heat cloud budgets, is a still poorly understood process with few measurements presently available. Multiwavelength lidars, widely employed in aerosols and clouds studies, can also provide useful information on the microphysical characteristics of light precipitation, for example, drizzle and virga. In this paper, lidar measurements of the median volume raindrop diameter and rain evaporation rate profiles are compared with a model analytical solution. The intercomparison reveals good agreement between the model and observations, with a correlation between the profiles up to 65% and a root-mean-square error up to 22% with a 5% bias. Larger discrepancies are due to radiosonde soundings different air masses and model assumptions no more valid along the profile as nonsteady atmosphere and/or appearance of collision–coalescence processes. Nevertheless, this study shares valuable information to better characterize the rain evaporation processes

The Undergraduate CubeSat Experience at the University of Minnesota

Building a satellite is a large undertaking with a lot of moving parts. Undergraduate students have complicated schedules with even more moving parts. Running a team of 60+ undergraduates toward the goal of launching a satellite is therefore quite the managerial challenge. Detailed on this poster are some specific challenges, along with strategies for mitigating them, that the UMN Small Satellite Research Lab faces in their work toward launching two small satellites