The cleanroom case study in the Software Engineering Laboratory: Project description and early analysis

This case study analyzes the application of the cleanroom software development methodology to the development of production software at the NASA/Goddard Space Flight Center. The cleanroom methodology emphasizes human discipline in program verification to produce reliable software products that are right the first time. Preliminary analysis of the cleanroom case study shows that the method can be applied successfully in the FDD environment and may increase staff productivity and product quality. Compared to typical Software Engineering Laboratory (SEL) activities, there is evidence of lower failure rates, a more complete and consistent set of inline code documentation, a different distribution of phase effort activity, and a different growth profile in terms of lines of code developed. The major goals of the study were to: (1) assess the process used in the SEL cleanroom model with respect to team structure, team activities, and effort distribution; (2) analyze the products of the SEL cleanroom model and determine the impact on measures of interest, including reliability, productivity, overall life-cycle cost, and software quality; and (3) analyze the residual products in the application of the SEL cleanroom model, such as fault distribution, error characteristics, system growth, and computer usage

A Method for Producing Site-Specific TEM Specimens from Low Contrast Materials with Nanometer Precision

A method that enables high precision extraction of transmission electron microscope (TEM) specimens in low contrast materials has been developed. The main idea behind this work is to produce high contrast markers on both sides of and close to the area of interest. The markers are filled during the depositing of the protective layer. The marker material can be of either Pt or C depending on which one gives the highest contrast. It is thereby possible to distinguish the location of the area of interest during focused ion beam (FIB) milling and ensure that the TEM sample is extracted precisely at the desired position. This method is generally applicable and enables FIB/scanning electron microscope users to make high quality TEM specimens from small features and low contrast materials without a need for special holders. We explain the details of this method and illustrate its potential by examples from three different types of materials

Genetic Diversity in an Invasive Clonal Plant? A Historical and Contemporary Perspective

Introduced populations of Eichhornia crassipes (Pontederiaceae) possess extremely low levels of genetic diversity due to severe bottleneck events and clonal reproduction. While populations elsewhere have been well studied, North American populations of E. crassipes remain understudied. We used Amplified Fragment Length Polymorphism markers to assess genetic diversity and population structure in North American E. crassipes populations. Patterns of diversity over the past fifty years were analyzed using herbarium specimens. Furthermore, we sampled populations across the Gulf Coast of the United States throughout a year to determine contemporary genetic diversity and assess potential seasonal effects. Genetic diversity was found to be scant in the United States without population structure, agreeing with previous studies from other regions. Genetic diversity has remained consistently low over the past fifty years despite significant changes in selection pressure. However, evidence for and against population structure between seasons was found and the consequences of this are discussed

The Role of Soluble Fibrin in Lymphocyte and LAK Cell Adherence to and Migration across Vascular Endothelial Cells: Implications for Immunotherapy and Cancer

Although conventional therapies for metastatic cancers have made significant progress in recent years, they are relatively nonspecific and have many deleterious side-effects. Recently, novel therapies, including adoptive cellular immune therapies have had sporadic, but spectacular success in cancers such as malignant melanoma and renal cell carcinoma: tumors in which an immune response has been demonstrated. However, other physiological mechanisms, such as blood coagulation inhibit the immune response against cancers. Our previous work has shown that one of these coagulation proteins, soluble fibrin (sFn), inhibits unstimulated and activated lymphocyte adherence to tumor cells by blocking leukocyte integrin (CD11a/CD18) binding to tumor cell CD54, suggesting that sFn is an immunosuppressive agent in cancer. Since these receptors are also involved in lymphocyte/endothelial cell adherence and diapedesis (a necessary step in the immune response to cancer), it was hypothesized that sFn inhibits these functions, and that blockade of this inhibition using specific peptides would restore these immune responses. Fluorescently labeled lymphocytes and Interleukin-2 activated lymphocytes (LAK cells) were incubated with sFn (or its components; fibrinogen, Gly-Pro-Arg-Pro, or thrombin) in the presence or absence of specific blocking peptides. Lymphocyte and LAK cell adherence to endothelial cell monolayers was measured by perfusion at physiological shear rates in a microscope-mounted closed perfusion chamber, followed by image analysis using Image Pro Plus software. Diapedesis was measured by detection of fluorescence in 24-well microplates following immune cell incubation (18 h) with endothelial cell monolayers grown in transwells. SFn inhibited lymphocyte (54.1 + 11.3 %) and LAK cell (43.9 + 4.4 %) adherence to sFn pretreated endothelial cells, and intermediate values were obtained from sFn pre-treatment of only one cell type. Adherence was restored by peptide mediated blockade of sFn/CD54 binding, but not by CD11b blocking peptides. Diapedesis was also inhibited by sFn (lymphocyte 29.6 + 7.7 %; LAK 12.2 + 4.9 %) and restoration was observed using blocking peptides. These results confirm the stated hypotheses, and if physiologically relevant, suggest that sFn is an etiological agent in tumor growth and metastasis, and that blockade using fibrin specific peptides may enhance the effectiveness of adoptive immunotherapies

Quantitative atom probe analysis of carbides

Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti 2 AlC grains in different materials as well as on large M 2 3C 6 precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the 13 C isotope, and calculating the concentration of 12 C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) andTi 2 AlC an additional difficulty arises from the overlap between C 2 + ,C 2+ 4 and Ti 2+ at the mass-to-charge 24 Da. \ua9 2010 Elsevier B.V

NASA/DoD University Nano-Satellites for Distributed Spacecraft Control

Commonly referred to as \u27virtual platforms\u27, \u27formation flying\u27, \u27virtual spacecraft\u27, the implementation of Distributed Spacecraft Control technologies is being aggressively pursued internal and external of the National Aeronautics and Space Administration (NASA). Distributed spacecraft control architectures are characterized by interactions between spacecraft, cooperation between spacecraft, and common behavior among spacecraft within a constellation or formation. Collectively, these attributes enable a distributed network of individual spacecraft to act collaboratively as a single functional unit that exhibits a common system wide capability. Such capabilities will usher in the next generation of NASA Earth and Space science missions through the exploitation of new vantage points, the development of new sensing strategies and revolutionary measurement concepts, and the implementation of system-wide techniques which promote agility, adaptability, the ability to evolve over time, scalability, and affordability within mission concepts. A broad set of technology products is required to address the challenges presented within distributed spacecraft control architectures. Several technology development programs sponsored by NASA and the Department of Defense (DoD) have been or are now supporting efforts to develop these products. Building off the individual technology development programs and the foundations laid, DoD and NASA are teaming with one another to address common challenges, take advantage of the resources and opportunities available, and expedite the development and subsequent infusion of distributed spacecraft control technologies. The DoD University Nano-Satellite Program is serving as a focal point for such collaborative efforts

Flight dynamics software in a distributed network environment

As with all NASA facilities, the announcement of reduced budgets, reduced staffing, and the desire to implement smaller/quicker/cheaper missions has required the Agency's organizations to become more efficient in what they do. To accomplish these objectives, the FDD has initiated the development of the Flight Dynamics Distributed System (FDDS). The underlying philosophy of FDDS is to build an integrated system that breaks down the traditional barriers of attitude, mission planning, and navigation support software to provide a uniform approach to flight dynamics applications. Through the application of open systems concepts and state-of-the-art technologies, including object-oriented specification concepts, object-oriented software, and common user interface, communications, data management, and executive services, the FDD will reengineer most of its six million lines of code

Enumeration of leukocyte infiltration in solid tumors by confocal laser scanning microscopy

BACKGROUND: Leukocytes commonly infiltrate solid tumors, and have been implicated in the mechanism of spontaneous regression in some cancers. Conventional techniques for the quantitative estimation of leukocyte infiltrates in tumors rely on light microscopy of immunostained thin tissue sections, in which an arbitrary assessment (based on low, medium or high levels of infiltration) of antigen density is made by the pathologist. These estimates are relatively subjective and often require the opinion of a second pathologist. In addition, since thin tissue sections are cut, no data regarding the three-dimensional distribution of antigen can be obtained. RESULTS: To overcome these problems, we have designed a method to enumerate leukocyte infiltration into tumors, using confocal laser scanning microscopy of fluorescently immunostained leukocytes in thick tissue sections. Using image analysis software, a threshold was applied to eliminate unstained tissue and residual noise. The total antigen volume in the scanned tissue was calculated and divided by the mean cell volume (calculated by "seeding" ten individual cells) to obtain the cell count. Using this method, we compared the calculated leukocyte counts with those obtained manually by ten laboratory personnel. There was no significant difference (P > 0.05) between the cell counts obtained by either method. We then compared leukocyte infiltration into seven tumors and matched non-malignant tissue obtained from the periphery of the resected tissue. There was a significant increase in the infiltration of all leukocyte subsets into the tumors compared to minimal numbers in the non-malignant tissue. CONCLUSION: From these results we conclude that this method may be of considerable use for the enumeration of cells in tissues. Furthermore, since it can be performed by laboratory technical staff, less time input is required by the pathologist in assessing the degree of leukocyte infiltration into tumors

Rolling balls or trapping ions? How students relate models to real-world phenomena in the physics laboratory

The creation and use of models in science is of great importance for knowledge production and communication. For example, toy models are often used as idealized explanatory models in physics education. Models can be a powerful tool for exploring phenomena in ways that facilitate learning. However, careful consideration of instruction and explanations needs to be considered to guide how students relate models to real-world phenomena in subject-correct ways. A design experiment was conducted to investigate how upper secondary school students can use models for learning in the physics laboratory. The intervention used in the study was a laboratory exercise developed over three phases where students worked with a mechanical Paul trap and a simulation to understand the principle behind a real Paul trap. Each phase of the study consisted of three to five laboratory sessions. The data were analyzed using thematic analysis and the learning process was understood using the theoretical framework of variation theory. From the results, it was possible to identify patterns of variation for successful lab groups and critical aspects and features students need to discern to effectively modelize the mechanical Paul trap. The findings also indicate that having students work with models can be a meaningful clarificatory process to develop a deeper understanding of the use and limitations of models in science