Sub-harmonic resonant excitation of confined acoustic modes at GHz frequencies with a high-repetition-rate femtosecond laser

We propose sub-harmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a sub-harmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution

DNA sequencing by a single molecule detection of labeled nucleotides sequentially cleaved from a single strand of DNA

We are developing a laser-based technique for the rapid sequencing of large DNA fragments (several kb in size) at a rate of 100 to 1000 bases per second. Our approach relies on fluorescent labeling of the bases in a single fragment of DNA, attachment of this labeled DNA fragment to a support, movement of the supported DNA into a flowing sample stream, sequential cleavage of the end nucleotide from the DNA fragment with an exonuclease, and detection of the individual fluorescently labeled bases by laser-induced fluorescence

The rapid DNA sequencing project

Under Task 24, the RAE Team provided Quality Assurance support to the Special Recovery Line (SRL) and the Advanced Recovery and Integrated Extraction System (ARIES) projects of NMT-6. Support was provided through ESH-14. Monthly reports of work performed under this task were provided to NMT-6 and ESH-14. Copies of these reports are in RAE's project files. The procedures and assessment reports required by the task are on file only at NMT-6 because of the sensitive nature of the information. In March 1999, our subcontractor, General Physics, informed us that the two individuals working on the task were resigning effective April 2, 1999. RAE notified Gary Cort, ESH-14 technical representative for the task, and offered to replace the two individuals so that we could complete our obligations under the task (e-mail attached). No reply was ever received from Mr. Cert. We then reiterated our concern and offer of replacement with Mr. Cort's deputy, Spencer Hill (e-mail attached). No reply was received from Mr. Hill either. We subsequently learned the two General Physics employees were hired by another contractor and that the remaining work under the task was given to that contractor. We assumed our obligations under the task were completed at that point and notified the contracting officer to that effect

NEAR-NEIGHBOR DEFECT CONTRIBUTION TO THE HYPERFINE FIELD OF Fe IN Fe

The hyperfine fields of isomeric 54Fe nuclei have been measured in Fe at 85 K and 293 K by observing the spin precession following recoil-implantation. A unique defect structure has been detected by its well-resolved different magnetic hyperfine field at 85 K. It is tentatively assigned to a vacancy in the next neighborhood of the probe atom

Konstruktive Schutzmassnahmen sowie Rueckhalte- und Auffangsysteme fuer gefaehrliche chemische Reaktionsablaeufe Statusbericht

Available from TIB Hannover: F98B1147+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Identifying students’ mental models of sound propagation: the role of conceptual blending in understanding conceptual change

We investigated introductory physics students’ mental models of sound propagation. We used a phenomenographic method to analyze the data in the study. In addition to the scientifically accepted Wave model, students used the “Entity” model to describe the propagation of sound. In this latter model sound is a self-standing entity, different from the medium through which it propagates. All other observed alternative models contain elements of both Entity and Wave models, but at the same time are distinct from each of the constituent models. We called these models “hybrid” or “blend” models. We discuss how students use these models in various contexts before and after instruction and how our findings contribute to the understanding of conceptual change. Implications of our findings for teaching are summarized