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Funded by Naval Postgraduate School

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Now showing 1 - 10 of 109
  • Publication
    The dynamics of intensification in a Hurricane Weather Research and Forecasting simulation of Hurricane Earl
    (2016) Smith, Roger K.; Zhang, Jun A.; Montgomery, Michael T.; Naval Postgraduate School; Meteorology
    We use a high-resolution numerical simulation of Atlantic Hurricane Earl (2010) to increase our understanding of Earl’s intensification in relatively strong vertical shear in the context of a recent paradigm for tropical cyclone intensification. The integrity of the simulation is judged by comparing analyses thereof with those of the unprecedented observational data gathered in Earl. Consistent with the classical view of spin-up, the amplification of the tangential wind field above the boundary layer is found to occur as the absolute angular momentum surfaces are drawn inwards by the aggregate heating of the rotating convective clouds in the interior of the vortex. In addition to this classical pathway, spin-up occurs within the inner-core boundary layer, where the maximum tangential winds occur. The latter is another element of the new paradigm. Despite the detrimental influence of the shear on the vortex alignment and in depressing the pseudo-equivalent potential temperature outside the developing eyewall, the combined eddy processes associated with the vortical plume structures in and around the developing eyewall region are shown to contribute to an enhanced overturning circulation and an intensifying storm. These eddy processes are distinctly agradient effects that are not features of the classical spin-up mechanism. It remains to be understood how the rotating convective updraughts combine to produce the diagnosed structures of the eddy terms themselves and how vortex Rossby waves and other eddies contribute to the alignment of the vortex during intensification.
  • Publication
    Evidence for an isovector octupole resonance at 28.4 MeV and other Giant Resonances in 238U
    (Monterey, California. Naval Postgraduate School, 1976) Houk, W.A.; Moore, R.W.; Buskirk, F.R.; Pitthan, R.; Naval Postgraduate School (U.S.); Physics and Chemistry
    The deformed, fissionable nucleus 238U was studied with inelastic scattering of 87.5 MeV electrons between 5 and 40 MeV excitation energy, at scattering angles of 45°, 60° 75° and 90°. Resonance cross sections extracted from the spectra were compared with DWBA calculations using the Tassie (Goldhaber-Teller) model. The results agree with the known positions, widths and cross sections of the two branches of the giant dipole resonance at Ex = 10.9 MeV and 14.0 MeV, thus confirming the validity of the evaluation method. In addition, isoscalar and isovector E2 resonances and an isovector EJ resonance were found at 9.9 MeV (r = 2.9), 21.5 MeV (r = 4.9) and 28.4 MeV (r = 8.1), exhausting 40%, 50% and 90% of the respective EWSR. Although isospin cannot be determined from (e,e'), ∆T assignments were based on microscopic and macroscopic considerations.
  • Publication
    Approximation of Fractional Harmonic Maps
    (ArXiv, 2021) Antil, Harbir; Zichao, Wendy Di; Khatri, Ratna; Naval Postgraduate School
    This paper addresses the approximation of fractional harmonic maps. Besides a unit-length constraint, one has to tackle the difficulty of nonlocality. We establish weak compactness results for critical points of the fractional Dirichlet energy on unit-length vector fields. We devise and analyze numerical methods for the approximation of various partial differential equations related to fractional harmonic maps. The compactness results imply the convergence of numerical approximations. Numerical examples on spin chain dynamics and point defects are presented to demonstrate the effectiveness of the proposed methods.
  • Publication
    Hadoop MapReduce for Mobile Clouds
    (2016) George, Johnu; Chen, Chien-An; Stoleru, Radu; Xie, Geoffrey; Computer Science (CS)
    The new generations of mobile devices have high processing power and storage, but they lag behind in terms of software systems for big data storage and processing. Hadoop is a scalable platform that provides distributed storage and computational capabilities on clusters of commodity hardware. Building Hadoop on a mobile network enables the devices to run data intensive computing applications without direct knowledge of underlying distributed systems complexities. However, these applications have severe energy and reliability constraints (e.g., caused by unexpected device failures or topology changes in a dynamic network). As mobile devices are more susceptible to unauthorized access, when compared to traditional servers, security is also a concern for sensitive data. Hence, it is paramount to consider reliability, energy efficiency and security for such applications. The MDFS (Mobile Distributed File System) [1] addresses these issues for big data processing in mobile clouds. We have developed the Hadoop MapReduce framework over MDFS and have studied its performance by varying input workloads in a real heterogeneous mobile cluster. Our evaluation shows that the implementation addresses all constraints in processing large amounts of data in mobile clouds. Thus, our system is a viable solution to meet the growing demands of data processing in a mobile environment.
  • Publication
    A numerical study of time-dependent wind forcing off the west coast of Portugal, 1987-1988
    (Monterey, California. Naval Postgraduate School, 1991-06) Buss, Stephen L.; Batteen, Mary L.; Naval Postgraduate School; Oceanography; Nelson, Craig S
    A process-oriented study of time-dependent wind forcing is conducted using a ten-layer (B)-plane, positive ocean model to provide insight into mesoscale eddy generation and duration off the west coast of Portugal from 1987 to 1988. The wind forcing used was derived from synoptic surface pressure analyses off Lisbon, Portugal. Results obtained show that eddies generated during the coastal upwelling season (generally occurring during the spring and summer) decay during the winter. Only cyclonic eddies form during the 1987 and 1988 upwelling seasons. The eddies are generated through a combination of barotropic and baroclinic instability mechanisms. Since the wind forcing of the five-month long 1987 upwelling season, eddy characteristics appear to be more influenced by the characteristics (e.g., intensity, duration and frequency of occurrence) of the wind forcing than by the total length of the upwelling season. This study affirms the importance of wind stress forcing to the overall surface circulation and eddy generation in the coastal regime off the west coast of Portugal.
  • Publication
    Airflow distortion at instrument sites on the RV Knorr
    (1998) Moat, B.I.; Yelland, M.J.; University of Southampton; Southampton Oceanography Centre
    This report describes an investigation of the air flow around the RV Knorr using the Computational Fluid Dynamics software package "VECTIS" to simulate a flow of air directly over the bows of the ship. Section 2 gives a brief description of the model. This work was undertaken at the request of researchers from the Bedford Institute of Oceanography (BIO), the National Oceanic and Atmospheric Administration (NOAA) and Kiel University who had used the ship to carry meteorological instrumentation on a purpose-built mast (the "lattice tower") during an experiment in the Labrador Sea in the winter of 1997. One advantage of the VECTIS software is the ability to vary the computational mesh density; this allows regions of particular interest to be modelled using a much higher resolution than that employed elsewhere in the model. In the case of the Knorr, the highest mesh density was located around the instrument sites on the lattice tower. In Section 3 the distortion of the air flow to these instrument sites is examined, and the vertical displacement of the flow and the percentage wind speed error is calculated for each site. Section 4 describes the flow at the separate IMET instrument sites on the ship’s foremast and bowmast. The mesh resolution at the IMET sites is not as great as that around the lattice tower since data for the IMET sites were requested towards the end of the study. The results are summarised and discussed in Section 5.
  • Publication
    Surprise, Anticipation, and Sequence Effects in the Design of Experiential Services
    (2017) Dixon, Michael J.; Victorino, Liana; Kwortnik, Robert J.; Verma, Rohit
    The most salient or peak aspect of a service experience often defines customer perceptions of the service. Across two studies, using the same novel form of a scenario-based experiment, we investigate the design of peak events in a service sequence by testing how anticipated and surprised peaks influence customer perceptions. Study 1 captures the immediate reactions of participants and Study 2 surveys participants a week later. In both studies, we find a main effect for the temporal peak placement, confirming the positive influence of a strong peak ending. When assessing the peak design strategies of surprise and anticipation, we find in Study 1 that surprise and anticipation moderate the temporal peak placement (e.g., early peak vs. late peak) on overall customer perceptions, with the surprise peak at the end of an experience yielding the strongest effect. In Study 2 we see that the remembered experience of a surprise peak positively affects customer perceptions compared to an anticipated peak regardless of the temporal placement of the peak. We also find that the infusion of a surprise peak ending has a lasting effect that amplifies the peak-end effect of remembered experiences. Drawing on these findings, we discuss the role of surprise, anticipation, and sequence effects in experience design strategy.
  • Publication
    Water Masses and Circulation in the Tropical Pacific off Central Mexico and Surrounding Areas
    (American Meteorological Society, 2016) Portela, Esther; Beier, Emilio; Barton, Eric D.; Castro, Rubén; Godínez, Victor; Palacios-Hernández, Emilio; Fiedler, Paul C.; Sánchez-Velasco, Laura; Trasviña, Armando; Naval Postgraduate School
    The seasonal variations and the interactions of the water masses in the tropical Pacific off central Mexico (TPCM) and four surrounding areas were examined based on an extensive new hydrographic database. The regional water masses were redefined in terms of absolute salinity (SA) and conservative temperature (Q) according to the Thermodynamic Equation of Seawater 2010 (TEOS-10). Hydrographic data and the evapo- ration minus (precipitation 1 runoff) balance were used to investigate the origin and seasonality of two salinity minima in the area. The shallow (50–100 m) salinity minimum originates with the California Current System and becomes saltier as it extends southeastward and mixes with tropical subsurface waters while the surface salinity minimum extends farther north in the TPCM in summer and fall because of the northward advection of tropical surface waters. The interactions between water masses allow a characterization of the seasonal pattern of cir- culation of the Mexican Coastal Current (MCC), the tropical branch of the California Current, and the flows through the entrance of the Gulf of California. The seasonality of the MCC inferred from the distribution of the water masses largely coincides with the geostrophic circulation forced by an annual Rossby wave.
  • Publication
    Energy-Efficient Fault-Tolerant Data Storage and Processing in Mobile Cloud
    (2015) Chien-An Chen; Myounggyu Won; Radu Stoleru; Xie, Geoffrey G.; Computer Science (CS)
    Despite the advances in hardware for hand-held mobile devices, resource-intensive applications (e.g., video and image storage and processing or map-reduce type) still remain off bounds since they require large computation and storage capabilities. Recent research has attempted to address these issues by employing remote servers, such as clouds and peer mobile devices. For mobile devices deployed in dynamic networks (i.e., with frequent topology changes because of node failure/unavailability and mobility as in a mobile cloud), however, challenges of reliability and energy efficiency remain largely unaddressed. To the best of our knowledge, we are the first to address these challenges in an integrated manner for both data storage and processing in mobilecloud, an approach we call k-out-of-n computing. In our solution, mobile devices successfully retrieve or process data, in the most energy-efficient way, as long as k out of n remote servers are accessible. Through a real system implementation we prove the feasibility of our approach. Extensive simulations demonstrate the fault tolerance and energy efficiency performance of our framework in larger scale networks.
  • Publication
    Capillary force-driven, large-area alignment of multi-segmented nanowires
    (ACM, 2014) Zhou, Xiaozhu; Zhou, Yu; Ku, Jessie C.; Zhang, Chuan; Mirkin, Chad A.; Northwestern University; Chemistry
    We report the large-area alignment of multi-segmented nanowires in nanoscale trenches facilitated by capillary forces. Electrochemically synthesized nanowires between 120 and 250 nm in length are aligned and then etched selectively to remove one segment, resulting in arrays of nanowires with precisely controlled gaps varying between 2 and 30 nm. Crucial to this alignment process is the dispersibility of the nanowires in solution which is achieved by chemically modifying them with hexadecyltrimethylammonium bromide. We found that, even without the formation of an ordered crystalline phase at the droplet edges, the nanowires can be aligned in high yield. To illustrate the versatility of this approach as a nanofabrication technique, the aligned nanowires were used for the fabrication of arrays of gapped graphene nanoribbons and SERS substrates.