Naval Postgraduate School

About: Naval Postgraduate School is a education organization based out in Monterey, California, United States. It is known for research contribution in the topics: Tropical cyclone & Nonlinear system. The organization has 5246 authors who have published 11614 publications receiving 298300 citations. The organization is also known as: NPS & U.S. Naval Postgraduate School.

Observations of the Internal Tide in Monterey Canyon

Abstract: Data from two shipboard experiments in 1994, designed to observe the semidiurnal internal tide in Monterey Canyon, reveal semidiurnal currents of about 20 cm s21, which is an order of magnitude larger than the estimated barotropic tidal currents. The kinetic and potential energy (evidenced by isopycnal displacements of about 50 m) was greatest along paths following the characteristics calculated from linear theory. These energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of Monterey Bay. Energy propagated shoreward during the April experiment (ITEX1), whereas a standing wave, that is, an internal seiche, was observed in October (ITEX2). The difference is attributed to changes in stratification between the two experiments. Higher energy levels were present during ITEX1, which took place near the spring phase of the fortnightly (14.8 days) cycle in sea level, while ITEX2 occurred close to the neap phase. Further evidence of phase-locking between the surface and internal tides comes from monthlong current and temperature records obtained near the canyon head in 1991. The measured ratio of kinetic to potential energy during both ITEX1 and ITEX2 was only half that predicted by linear theory for freely propagating internal waves, probably a result of the constraining effects of topography. Internal tidal energy dissipation rate estimates for ITEX1 range from 1.3 3 1024 to 2.3 3 1023 Wm 23, depending on assumptions made about the effect of canyon shape on dissipation. Cross-canyon measurements made during ITEX2 reveal vertical transport of denser water from within the canyon up onto the adjacent continental shelf.

Optimal PMU Placement for Power System Dynamic State Estimation by Using Empirical Observability Gramian

Abstract: In this paper, the empirical observability Gramian calculated around the operating region of a power system is used to quantify the degree of observability of the system states under specific phasor measurement unit (PMU) placement. An optimal PMU placement method for power system dynamic state estimation is further formulated as an optimization problem which maximizes the determinant of the empirical observability Gramian and is efficiently solved by the NOMAD solver, which implements the Mesh Adaptive Direct Search algorithm. The implementation, validation, and the robustness to load fluctuations and contingencies of the proposed method are carefully discussed. The proposed method is tested on WSCC 3-machine 9-bus system and NPCC 48-machine 140-bus system by performing dynamic state estimation with square-root unscented Kalman filter. The simulation results show that the determined optimal PMU placements by the proposed method can guarantee good observability of the system states, which further leads to smaller estimation errors and larger number of convergent states for dynamic state estimation compared with random PMU placements. Under optimal PMU placements an obvious observability transition can be observed. The proposed method is also validated to be very robust to both load fluctuations and contingencies.

Slot-Line Transitions (Short Papers)

Abstract: Coax-slot and microstrip-slot transitions are discussed Experimental VSWR and impedance data are presented and compared with values computed using equivalent circuits for these transitions Thick-film chip terminations are also investigated

Map usage in virtual environments: orientation issues

Abstract: Navigation tasks in large virtual environments often call for the use of a virtual map. However, all maps are not alike. Performance on navigation tasks in general has been shown to vary depending on the orientation of the map with respect to the user's frame of reference. This paper reports the results of an experiment investigating orientation issues of virtual maps for use during navigation tasks. Participants were given a virtual map in either a north-up or forward-up configuration. Performance on search tasks was measured in terms of search time and errors. Results indicate that targeted search tasks (tasks requiring only the egocentric reference frame) are best served by a forward-up alignment while primed and naive search tasks (tasks requiring information from the world reference frame) prefer a north-up alignment. Both types of maps are affected by the ability of user to perform mental rotations.

Effect of thermo-mechanically induced microstructural coarsening on the evolution of creep response of SnAg-based microelectronic solders

Abstract: The creep response of solder joints in a microelectronic package, which are subjected to aggressive thermo-mechanical cycling (TMC) during service, often limits the reliability of the entire package. Furthermore, during TMC, the microstructures of the new lead-free solders (Sn–Ag and Sn–Ag–Cu) can undergo significant in situ strain-enhanced coarsening, resulting in in-service evolution of the creep behavior. In this paper, the coarsening kinetics of Ag 3 Sn particles in SnAg-based solder are studied, and the results are correlated with impression creep data from individual microelectronic solder balls subjected to thermal aging treatments. Coarsening influences creep behavior in two ways. At low stresses, the creep rate increases proportionately with precipitate size. At high stresses, precipitate coarsening influences creep response by altering the threshold stress for particle-limited creep. Based on these observations, a microstructurally adaptive creep model for solder interconnects undergoing in situ coarsening is presented.