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.

Estimating the Reliability of Systems Subject to Imperfect Repair

Abstract: This study of statistical inference for repairable systems focuses on the development of estimation procedures for the life distribution F of a new system based on data on system lifetimes between consecutive repairs The Brown—Proschan imperfect-repair model postulates that at failure the system is repaired to a condition as good as new with probability p, and is otherwise repaired to the condition just prior to failure In treating issues of statistical inference for this model, the article first points out the lack of identifiability of the pair (p, F) as an index of the distribution of interfailure times T 1, T 2, … It is then shown that data pairs (Ti, Zi ) (i = 1, 2, …) render the parameter pair (p, F) identifiable, where Zi is a Bernoulli variable that records the mode of repair (perfect or imperfect) following the ith failure Under the assumption that data of the form {(Ti, Zi )} are drawn via inverse sampling until the occurrence of the mth perfect repair, the problem of estimating the

Tropical cyclone and extreme rainfall trends in East Asian summer monsoon since mid‐20th century

Abstract: [1] Proper interpretations of extreme rainfall trends in the Asian monsoon regions are complicated by tropical cyclones (TCs) from tropical oceans, whose rainfall trend may be different from the local monsoon (non-TC) rain. Here we show that the trends over the China summer monsoon region have been distorted by western North Pacific typhoons, which bring rainfall with decreasing frequency and increasing intensity. Typically the latter is not sufficient to overcome the former, so TC-related extreme rainfall trend is smaller than monsoon-related extreme rainfall. The net impact underestimates the increasing trend and overestimates the decreasing trend in monsoon extreme rainfall over most areas. The effect is minimal in the Meiyu rain belt region, but reaches 30% in northeastern and southern China. The largest distortions occur on offshore islands in the main TC paths that underwent significant decadal variations. In Hainan, the −3%/decade trend becomes +7%/decade if typhoon rainfall is removed. An opposite case occurs in Taiwan, where the extreme rainfall trend is hugely inflated by local increases in TC rainfall. These opposite effects emphasize the importance of considering the different mechanisms of rainfall systems in order to avoid mis-attribution of regional effects on extreme rainfall to thermodynamic consequences of global warming.

Verifying secrets and relative secrecy

Abstract: Systems that authenticate a user based on a shared secret (such as a password or PIN) normally allow anyone to query whether the secret is a given value. For example, an ATM machine allows one to ask whether a string is the secret PIN of a (lost or stolen) ATM card. Yet such queries are prohibited in any model whose programs satisfy an information-flow property like Noninterference. But there is complexity-based justification for allowing these queries. A type system is given that provides the access control needed to prove that no well-typed program can leak secrets in polynomial time, or even leak them with nonnegligible probability if secrets are of sufficient length and randomly chosen. However, there are well-typed deterministic programs in a synchronous concurrent model capable of leaking secrets in linear time.

Sensitivity of tropical-cyclone models to the surface drag coefficient

Abstract: Motivated by recent developments in tropical-cyclone dynamics, this paper reexamines a basic aspect of tropical-cyclone behaviour, namely, the sensitivity of tropical-cyclone models to the surface drag coefficient. Previous theoretical and numerical studies of the sensitivity in axisymmetric models have found that the intensity decreases markedly with increasing drag coefficient. Here we present a series of three-dimensional convection-permitting numerical experiments in which the intensification rate and intensity of the vortex increase with increasing surface drag coefficient until a certain threshold value is attained and then decrease. In particular, tropical depression-strength vortices intensify to major hurricane intensity for values of CK/CD as small as 0.1, significantly smaller than the critical threshold value of about 0.75 for major hurricane development predicted by Emanuel using an axisymmetric balance model. Moreover, when the drag coefficient is set to zero, no system-scale intensification occurs, despite persistent sea-to-air fluxes of moisture that maintain deep convective activity. This result is opposite to that found in a prior axisymmetric study by Craig and Gray. The findings are interpreted using recent insights obtained on tropical-cyclone intensification, which highlight the intrinsically unbalanced dynamics of the tropicalcyclone boundary layer. The reasons for the differences from earlier axisymmetric studies and some potential ramifications of our findings are discussed. The relative insensitivity of the intensification rate and intensity found for drag coefficients typical of high wind speeds over the ocean calls into question the need for coupled ocean wave–atmospheric models to accurately forecast tropical-cyclone intensity. Copyright c � 2010 Royal Meteorological Society

Assessment of Technology In Organizations: Closed versus Open Systems Approach

Abstract: Technology is a multiphasic, multilevel input/output mechanism that is interdependent with its environment. Past research suggests that inconsistent assessments of technology may be attributed to examining different phases of the same transformation process. Past research has generally ignored input and output activities as well as critical energy exchanges between the technology and the environment. Technology can be assessed at several levels (individual job, subunit, and organization), which are interdependent, yet may reflect qualitatively different activities. A framework for assessing technology is derived from these multiple levels. This framework can be used to aid integration of research, to encourage more thorough assessment of technology, and to investigate the relations between the environment and technology.