The Linear Boltzmann Equation as the Low Density Limit of a Random Schrodinger Equation

We study the evolution of a quantum particle interacting with a random potential in the low density limit (Boltzmann-Grad). The phase space density of the quantum evolution defined through the Husimi function converges weakly to a linear Boltzmann equation with collision kernel given by the full quantum scattering cross section.Comment: 74 pages, 4 figures, (Final version -- typos corrected

Broadband Tuning (170nm) of InGaAs Quantum Well Lasers

The wavelength tuning properties of strained InGaAs quantum well lasers using an external grating for feedback is reported. Tunable laser oscillation has been observed over a range of 170 nm, between 840 and 1010 nm, under pulsed current excitation. The optimal conditions for broadband tunability for the InGaAs lasers are different from GaAs lasers, which is attributed to a difference in spectral gain curves. Together with an optimised GaAs quantum well laser the entire region between 740 and 1010 nm is spanned

Assessment of shear strength of existing prestressed concrete bridge beams: Full-scale tests and numerical simulations

The obsolescence and the end of service lifetime of a big portion of our infrastructure, culmin- ated with recent catastrophic bridge collapses, determine an increasing need to implement monitoring activities and safety assessment of existing bridges and viaducts. As stated in numerous studies and experimental evi- dence, shear strength is one of the critical issues concerning existing bridges. In order to deepen the knowledge on structural shear behavior, an experimental campaign on full-scale prestressed concrete girders sampled from an existing structure has been performed in the structures laboratory of the University of Pavia (Italy). This study illustrates the results of experimental tests and numerical finite element simulations, which have been performed both to obtain a comparison with experimental data and to study the main contributing factors to the collapse of the girder for shear type failure. The failure strength obtained from experimental testing has been compared with the shear strength calculated according to different strength models presented both in design codes and in the literature; therefore the accuracy of such models will be assessed in order to define the most suitable approach to assess girder shear strength

Reducibility of Aswan Ore and Sinters with Varying Basicity Ratios

THE RESULTS of the study of the reduction kinetics of sinters of different basicity ratios (0.2-2.0) as well as of Aswan ore of definite grain size (6-10) mm. by H2 gas at a definite "Redox" potential (100 1./g. 02 /hr.) at 950°C have shown that the general shape of the reduction functions of time are unique— partly parabolic and partly topochemical in nature—and that they obey the general Jeschar equation for the overall reduction process. A specific case of the general equation has been checked among other 6 formulas by modem computing techniques using an IBM electronic computer type 1620 and found to be in good agreement with the experimental results. The equation could be derived on a theoretictd basis and considers a reduction mechanism that is controlled mainly by both diffusion and chemical reaction processes as being the slowest pertaining and hence the rate determining factors in the complex reduction mechanism. Aswan ore is far more reducible than any of the other different kinds of studied fluxed or nonfluxed sinters. Also fluxed sinters made from Aswan ore by adding incre-asing amounts of lime are far more reducible by gases at a temperature level of 950°C—normally prevailing in the shaft cf a blast furnace than nonfluxed sinters

Warning: This Is a Must Read : Participation and Disruption in Social Artifacts and Spaces

As I show in three separate case studies, content, technology, and participant relationships are key components in the design of social artifacts and spaces. One study highlights the invention and evolution of content across multiple spaces. The second shows content used as leverage for authority. The last case study examines the relationship between content and technological interfaces and how disruption may not always be successful. All of these components make up what I refer to as disruption. Disruption describes participant acts that are executed to change existing power-based structures of information sharing. Using the insights gained from this research, I develop the concept of disruption as a component of design that emphasizes the value of participant work and the ability of participants to alter existing structures of information sharing

Demonstration of astrocytes in cultured amniotic fluid cells of three cases with neural-tube defect

We have investigated the origin of rapidly adhering (RA) cells in three cases of neural tube defects (two anencephali, one encephalocele). We were able to demonstrate the presence of glial fibrillary acidic (GFA) protein in variable percentages (4–80%) of RA cells cultured for 4–6 days by use of indirect immunofluorescence with GFA antiserum. Cells cultured from amniotic fluids of normal pregnancies and fetal fibroblasts were completely GFA protein negative. GFA protein is well established as a highly specific marker for astrocytes. Demonstration of astrocytes may prove to be a criterion of high diagnostic value for neural tube defects. The percentage of astrocytes decreased with increasing culture time, while the percentage of fibronectin positive cells increased both in amniotic fluid cell cultures from neural tube defects and normal pregnancies