Showing papers by "Naval Postgraduate School published in 2010"

Three Views of Entrepreneurial Opportunity

Abstract: For almost 50 years now, following the trail of issues raised by economists such as Hayek, Schumpeter, Kirzner, and Arrow, researchers have studied the economics of technological change and the problem of allocation of resources for invention (invention being the production of information). The bulk of this literature simply assumes that new technical information will either be traded as a commodity or become embodied in products and services (hereafter called “economic goods”), without addressing any specific mechanisms or processes for the transformation of new information into new economic goods or new economic entities (such as new firms and new markets). It is inside this gap that we begin our quest for the concept of an “entrepreneurial opportunity.”

Stochastic Optimization for Natural Disaster Asset Prepositioning

Abstract: A key strategic issue in pre-disaster planning for humanitarian logistics is the pre-establishment of adequate capacity and resources that enable efficient relief operations. This paper develops a two-stage stochastic optimization model to guide the allocation of budget to acquire and position relief assets, decisions that typically need to be made well in advance before a disaster strikes. The optimization focuses on minimizing the expected number of casualties, so our model includes first-stage decisions to represent the expansion of resources such as warehouses, medical facilities with personnel, ramp spaces, and shelters. Second-stage decisions concern the logistics of the problem, where allocated resources and contracted transportation assets are deployed to rescue critical population (in need of emergency evacuation), deliver required commodities to stay-back population, and transport the transfer population displaced by the disaster. Because of the uncertainty of the event's location and severity, these and other parameters are represented as scenarios. Computational results on notional test cases provide guidance on budget allocation and prove the potential benefit of using stochastic optimization.

A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer

Abstract: . An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the canonical problem of a TC in vertical wind shear on an f-plane. A suite of numerical experiments is performed with intense TCs in moderate to strong vertical shear. We employ a set of simplified model physics – a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics – to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower θe) air – "anti-fuel" for the TC power machine – can enter the core region of the TC. Strong and persistent, shear-induced downdrafts flux low θe air into the boundary layer from above, significantly depressing the θe values in the storm's inflow layer. Air with lower θe values enters the eyewall updrafts, considerably reducing eyewall θe values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is – if at all – only valid for stationary and axisymmetric TCs, a close association of the downward transport of low θe into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the boundary layer with low θe air are tied to a quasi-stationary, azimuthal wave number 1 convective asymmetry outside of the eyewall. This convective asymmetry and the associated downdraft pattern extends outwards to approximately 150 km. Downdrafts occur on the vortex scale and form when precipitation falls out from sloping updrafts and evaporates in the unsaturated air below. It is argued that, to zero order, the formation of the convective asymmetry is forced by frictional convergence associated with the azimuthal wave number 1 vortex Rossby wave structure of the outer-vortex tilt. This work points to an important connection between the thermodynamic impact in the near-core boundary layer and the asymmetric balanced dynamics governing the TC vortex evolution.

Another Look at Interannual-to-Interdecadal Variations of the East Asian Winter Monsoon: The Northern and Southern Temperature Modes

Abstract: This study investigates the causes of interannual-to-interdecadal variability of the East Asian (EA; 0°–60°N, 100°–140°E) winter monsoon (EAWM) over the past 50 yr (1957–2006). The winter mean surface air temperature variations are dominated by two distinct principal modes that together account for 74% of the total temperature variance. The two modes have notably different circulation structures and sources of variability. The northern mode, characterized by a westward shift of the EA major trough and enhanced surface pressure over central Siberia, represents a cold winter in the northern EA resulting from cold-air intrusion from central Siberia. The southern mode, on the other hand, features a deepening EA trough and increased surface pressure over Mongolia, representing a cold winter south of 40°N resulting from cold-air intrusion from western Mongolia. The cold northern mode is preceded by excessive autumn snow covers over southern Siberia–Mongolia, whereas the cold southern mode is preceded b...

The Role of the Internal Audit Function in the Disclosure of Material Weaknesses

Abstract: This study investigates the role that a firm’s internal audit function (IAF) plays in the disclosure of material weaknesses reported under Section 404 of the Sarbanes-Oxley Act of 2002 (U.S. Congress 2002). Using data from 214 firms, we examine the relation between material weakness (MW) disclosures and various IAF attributes and activities. Our results indicate that MW disclosures are negatively associated with the education level of the IAF and the extent to which the IAF incorporates quality assurance techniques into fieldwork, audits activities related to financial reporting, and monitors the remediation of previously identified control problems. The timing of Section 404 work and the nature of follow-up monitoring suggests that these aspects of IAF quality help prevent MWs from occurring. We find that MW disclosures are positively associated with the IAF practice of grading audit engagements and external-internal auditor coordination, suggesting that these activities increase the effectiveness of Section 404 compliance processes.

Carbon Nanotubes: Reinforced Metal Matrix Composites

Abstract: From the Foreword, written by legendary nano pioneer M. Meyyappan, Chief Scientist for Exploration Technology NASA Ames Research Center, Moffett Field, California, USA: "…there is critical need for a book to summarize the status of the field but more importantly to lay out the principles behind the technology. This is what Professor Arvind Agarwal and his co-workers … have done here." Carbon Nanotubes: Reinforced Metal Matrix Composites reflects the authors’ desire to share the benefits of nanotechnology with the masses by developing metal matrix carbon nanotube (MM-CNT) composites for large-scale applications. Multiwall carbon nanotubes can now be produced on a large scale and at a significantly reduced cost. The book explores potential applications and applies the author’s own research to highlight critical developmental issues for different MM-CNT composites—and then outline novel solutions. With this problem-solving approach, the book explores: Advantages, limitations, and the evolution of processing techniques used for MM-CNT composites Characterization techniques unique to the study of MM-CNT composites—and the limitations of these methods Existing research on different MM-CNT composites, presented in useful tables that include composition, processing method, quality of CNT dispersion, and properties The micro-mechanical strengthening that results from adding CNT The applicability of micro-mechanics models in MM-CNT composites Significance of chemical stability for carbon nanotubes in the metal matrix as a function of processing, and its impact on CNT/metal interface and mechanical properties Computational studies that have not been sufficiently covered although they are essential to research and development The critical issue of CNT dispersion in the metal matrix, as well as a unique way to quantify CNT distribution and subsequently improve control of the processing parameters for obtaining improved properties Carbon Nanotubes: Reinforced Metal Matrix Composites paints a vivid picture of scientific and application achievements in this field. Exploring the mechanisms through which CNTs are enhancing the properties of different metal-based composites, the authors provide a roadmap to help researchers develop MM-CNT composites and choose potential materials for use in emerging areas of technology.

Humanitarian Logistics: A New Field of Research and Action

Abstract: 1. Introduction. 2. Humanitarian Logistics. 3. Design of Humanitarian Logistics. 4. Supply Chain Issues in Humanitarian Logistics. 5. Organizational Issues in Humanitarian Logistics. 6. Conclusions and Potential for Future Research. References.

Constraining the contribution of organic acids and AMS m/z 44 to the organic aerosol budget: On the importance of meteorology, aerosol hygroscopicity, and region

Abstract: Airborne measurements in regions of varying meteorology and pollution are used to quantify the contribution of organic acids and a mass spectral marker for oxygenated aerosols, m/z 44, to the total organic aerosol budget. Organic acids and m/z 44 separately are shown to exhibit their highest organic mass fractions in the vicinity of clouds. The contribution of such oxygenated species is shown to increase as a function of relative humidity, aerosol hygroscopicity (and decreasing organic mass fraction), and is typically greater off the California coast versus the continental atmospheres studied. Reasons include more efficient chemistry and partitioning of organic acid precursors with increasing water in the reaction medium, and high aqueous-phase processing times in boundary layers with higher cloud volume fractions. These results highlight the importance of secondary organic aerosol formation in both wet aerosols and cloud droplets.

Path Following for Small Unmanned Aerial Vehicles Using L1 Adaptive Augmentation of Commercial Autopilots

Abstract: The paper presents a three-dimensional path-following control algorithm that expands the capabilities of conventional autopilots, which are normally designed to provide only guidance loops for waypoint navigation. Implementation of this algorithm broadens the range of possible applications of small unmanned aerial vehicles. The solution proposed takes explicit advantage of the fact that normally these vehicles are equipped with autopilots stabilizing the vehicles and providing angular-rate tracking capabilities. Therefore, the overall closed-loop system exhibits naturally an inner-outer (dynamics-kinematics) control loop structure. The outer-loop path-following control law developed relies on a nonlinear control strategy derived at the kinematic level, while the inner-loop consisting of the autopilot together with an L1 adaptive augmentation loop is designed to meet strict performance requirements in the presence of unmanned aerial vehicle modeling uncertainty and environmental disturbances. A rigorous proof of stability and performance of the path-following closed-loop system, including the dynamics of the unmanned aerial vehicle with its autopilot, is given. The paper bridges the gap between theory and practice and includes results of extensive flight tests performed in Camp Roberts, California, which demonstrate the benefits of the framework adopted for the control system design.

Fast software AES encryption

Abstract: This paper presents new software speed records for AES-128 encryption for architectures at both ends of the performance spectrum. On the one side we target the low-end 8-bit AVR microcontrollers and 32-bit ARM microprocessors, while on the other side of the spectrum we consider the high-performing Cell broadband engine and NVIDIA graphics processing units (GPUs). Platform specific techniques are detailed, explaining how the software speed records on these architectures are obtained. Additionally, this paper presents the first AES decryption implementation for GPU architectures.

Parametrizing turbulent exchange over summer sea ice and the marginal ice zone

Abstract: The surface of the Arctic Ocean in summer is a mix of sea ice and water in both leads and melt ponds. Here we use data collected at multiple sites during the year-long experiment to study the Surface Heat Budget of the Arctic Ocean (SHEBA) to develop a bulk turbulent flux algorithm for predicting the surface fluxes of momentum and sensible and latent heat over the Arctic Ocean during summer from readily measured or modelled quantities. The distinctive aerodynamic feature of summer sea ice is that the leads and melt ponds create vertical ice faces that the wind can push against; momentum transfer to the surface is thus enhanced through form drag. In effect, summer sea ice behaves aerodynamically like the marginal ice zone, which is another surface that consists of sea ice and water. In our bulk flux algorithm, we therefore combine our SHEBA measurements of the neutral-stability drag coefficient at a reference height of 10 m, CDN10, with similar measurements from marginal ice zones that have been reported in the literature to create a unified parametrization for CDN10 for summer sea ice and for any marginal ice zone. This parametrization predicts CDN10 from a second-order polynomial in ice concentration. Our bulk flux algorithm also includes expressions for the roughness lengths for temperature and humidity, introduces new profile stratification corrections for stable stratification, and effectively eliminates the singularities that often occur in iterative flux algorithms for very light winds. In summary, this new algorithm seems capable of estimating the friction velocity u∗ (a surrogate for the momentum flux) over summer sea ice with an absolute accuracy of 0.02 –0.03 m s −1 ; the sensible heat flux, with an accuracy of about 6 W m −2 ; and the latent heat flux, with an accuracy of 3.5 W m −2 .C opyright c � 2010 Royal Meteorological Society

Incidence of Acute Traumatic Patellar Dislocation Among Active-Duty United States Military Service Members

Abstract: BackgroundAlthough some studies have reported an increased incidence of patellar dislocations within active populations, few studies have reported incidence rates and examined risk factors for this injury.PurposeTo examine the incidence of patellar dislocation injuries and the influence of demographic and occupational risk factors associated with injury among active-duty United States (US) service members between 1998 and 2007.Study DesignCohort study; Level of evidence, 3.MethodsUsing the Defense Medical Surveillance System, a search was performed for International Classification of Disease, 9th Revision (ICD-9) code 836.3 among all US service members on active duty during the study period. Multivariable Poisson regression analysis was used to estimate the rate of patellar dislocation per 1000 person-years at risk to injury. Incidence rates (IRs) and incidence rate ratios (IRRs) for patellar dislocation along with 95% confidence intervals (CIs) were estimated by gender, age, race, branch of military serv...

Hurricane boundary-layer theory

Abstract: In the light of the plethora of definitions for the hurricane boundary layer, we advocate a dynamical definition based on the distribution of agradient flow. We seek also to clarify the fundamental role of the boundary layer in the hurricane intensification process. In particular, we contrast the differences between unsteady boundary layers that are able to facilitate the spin-up of the vortex above and steady boundary layers that cannot. If slaved to the time-dependent vortex aloft, the latter can spin up the interior vortex only indirectly by changing its thermodynamic properties through vertical advection of these from below and adjustment to thermal wind balance. These differences are highlighted by an analytical demonstration that the application of a zero-vertical-gradient condition on velocity above a steady boundary layer does not provide a direct means of allowing the boundary layer to determine the flow in the interior vortex. This result assumes that frictional forces are negligible at this boundary. Finally, echoing a few previous insights, we question the applicability of conventional boundary-layer theory at radii of strong ascent into the eyewall, where the flow is akin to that of separation in aerodynamic boundary layers. Copyright c � 2010 Royal Meteorological Society

Genesis of Pre–Hurricane Felix (2007). Part I: The Role of the Easterly Wave Critical Layer

Abstract: The formation of pre–Hurricane Felix (2007) in a tropical easterly wave is examined in a two-part study using the Weather Research and Forecasting (WRF) model with a high-resolution nested grid configuration that permits the representation of cloud system processes. The simulation commences during the wave stage of the precursor African easterly-wave disturbance. Here the simulated and observed developments are compared, while in Part II of the study various large-scale analyses, physical parameterizations, and initialization times are explored to document model sensitivities. In this first part the authors focus on the wave/vortex morphology, its interaction with the adjacent intertropical convergence zone complex, and the vorticity balance in the neighborhood of the developing storm. Analysis of the model simulation points to a bottom-up development process within the wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by Dunkerton, Montgome...

Disease and nonbattle injuries sustained by a U.S. Army Brigade Combat Team during Operation Iraqi Freedom.

Abstract: Background: A longitudinal cohort analysis of disease nonbattle injuries (DNBI) sustained by a large combat-deployed maneuver unit has not been performed. Methods: A descriptive analysis was undertaken to evaluate for DNBI casualty care statistics incurred by a U.S. Army Brigade Combat Team (BCT) during a counterinsurgency campaign of Operation Iraqi Freedom. Results: Of the 4,122 soldiers deployed, there were 1,324 DNBI with 5 (0.38%) deaths, 208 (15.7%) medical evacuations (MEDEVAC), and 1,111 (83.9%) returned to duty. The DNBI casualty rate for the BCT was 257.0/1,000 soldier combat-years. Females, compared with males, had a significantly increased incidence rate ratio for becoming a DNBI casualty 1.67 (95% CI 1.37, 2.04). Of 47 female soldiers receiving MEDEVAC 35 (74%) were for pregnancy-related issues. Musculoskeletal injuries (50.4%) and psychiatric disorders (23.3%) were the most common body systems involved with DNBI casualties. Among the BCT cohort the psychiatric DNBI casualty rate and ...

Parameterizing turbulent exchange over sea ice in winter

Abstract: The Surface Heat Budget of the Arctic Ocean (SHEBA) experiment produced 18 000 h of turbulence data from the atmospheric surface layer over sea ice while the ice camp drifted for a year in the Beaufort Gyre. Multiple sites instrumented during SHEBA suggest only two aerodynamic seasons over sea ice. In ‘‘winter’’ (October 1997 through 14 May 1998 and 15 September 1998 through the end of the SHEBA deployment in early October 1998), the ice was compact and snow covered, and the snow was dry enough to drift and blow. In ‘‘summer’’ (15 May through 14 September 1998 in this dataset), the snow melted, and melt ponds and leads appeared and covered as much as 40% of the surface with open water. This paper develops a bulk turbulent flux algorithm to explain the winter data. This algorithm predicts the surface fluxes of momentum, and sensible and latent heat from more readily measured or modeled quantities. A main result of the analysis is that the roughness length for wind speed z0 does not depend on the friction velocity u * in the drifting snow regime (u * $ 0.30 m s 21 ) but, rather, is constant in the SHEBA dataset at about 2.3 3 10 24 m. Previous analyses that found z0 to increase with u * during drifting snow may have suffered from fictitious correlation because u * also appears in z0. The present analysis mitigates this fictitious correlation by plotting measured z0 against the corresponding u * computed from the bulk flux algorithm. Such plots, created with data from six different SHEBA sites, show z0 to be independent of the bulk u * for 0.15 , u * # 0.65 m s 21 . This study also evaluates the roughness lengths for temperature zT and humidity zQ, incorporates new profile stratification corrections for stable stratification, addresses the singularities that often occur in iterative flux algorithms in very light winds, and includes an extensive analysis of whether atmospheric stratification affects z0, zT, and zQ.

Temporal observations of rip current circulation on a macro-tidal beach

Abstract: A field experiment was conducted on a high energy macro-tidal beach (Perranporth, UK) to examine rip current dynamics over a low-tide transverse bar/rip system in response to changing tide and wave conditions. Hydrodynamic data were collected using an array of in situ acoustic doppler current meters and pressure transducers, as well as 12 GPS-tracked Lagrangian surf zone drifters. Inter-tidal and subtidal morphology were measured through RTK-GPS and echo-sounder surveys. Data were collected for eight consecutive days (15 tides) over a spring-neap tidal cycle with tidal ranges of 4‐6.5m and offshore significant wave heights of 1‐2m and peak periods of 5‐12s. The hypothesis that rip current dynamics in a macro-tidal setting are controlled by the combination of variations in wave dissipation and morphological flow constriction, modulated by changes in tidal elevation was tested. During the measurement period, rip circulation was characterised by a large rotational surf zone eddy O(200m) extending offshore from the inner-surf zone to the seaward face of the inter-tidal transverse bar. During high- and mid-tide, water depth over the bars was too deep to allow wave breaking, and a strong longshore current dominated the surf zone. As the water depth decreased towards low-tide, wave breaking was concentrated over the bar crests initiating the rotational rip current eddy. Peak rip flow speeds of 1.3ms ! 1 were recorded around low-tide when the joint effects of dissipation and morphological constriction were maximised. At low tide, dissipation over the bar crests was reduced by partial bar-emergence and observations suggested that rip flows were maintained by morphological constriction and the side-drainage of water from the transverse bars.

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

Direct Method Based Control System for an Autonomous Quadrotor

Abstract: This paper proposes a real time control algorithm for autonomous operation of a quadrotor unmanned air vehicle. The quadrotor is a small agile vehicle, which as well as being a excellent test bed for advanced control techniques could also be suitable for internal surveillance, search and rescue and remote inspection. The proposed control scheme incorporates two key aspects of autonomy; trajectory planning and trajectory following. Using the differentially-flat dynamics property of the system, the trajectory optimization is posed as a non-linear constrained optimization within the output space in the virtual domain, not explicitly related to the time domain. A suitable parameterization using a virtual argument as opposed to time is applied, which ensures initial and terminal constraint satisfaction. The speed profile is optimized independently, followed by the mapping to the time domain achieved using a speed factor. Trajectory following is achieved with a standard multi-variable control technique and a digital switch is used to re-optimize the reference trajectory in the event of infeasibility or mission change. The paper includes simulations using a full dynamic model of the quadrotor demonstrating the suitability of the proposed control scheme.

Did Trade Liberalization Help Women? The Case of Mexico in the 1990s

Abstract: With the signing of the North American Free Trade Agreement (NAFTA) in 1994, Mexico entered a bilateral free trade agreement which not only lowered its own tariffs on imports but also lowered tariffs on its exports to the United States. We find that women’s relative wage increased, particularly during the period of liberalization. Both between and within-industry shifts also favored female workers. With regards to between-industry shifts, tariff reductions expanded sectors that were initially female intensive. With regards to within-industry shifts, we find a positive association between reductions in export tariffs (U.S. tariffs on Mexican goods) and hiring of women in skilled blue-collar occupations. Finally, we find suggestive evidence that household bargaining power shifted in favor of women. Expenditures shifted from goods associated with male preference, such as men’s clothing and tobacco and alcohol, to those associated with female preference such as women’s clothing and education.

The downstream impact of tropical cyclones on a developing baroclinic wave in idealized scenarios of extratropical transition

Abstract: The interaction of a tropical cyclone with a developing baroclinic wave is investigated in an idealized scenario of extratropical transition (ET). The impact of ET is examined by comparing and analyzing two numerical baroclinic-wave experiments: a traditional experiment in which baroclinic development is excited by a localized upper-level perturbation on a realistic jet profile and an experiment in which, additionally, a model tropical cyclone is inserted south of the jet at the initial time. ET occurs in a wavy upper-level flow while baroclinic surface systems are still weak. The characteristic direct impact of ET on the midlatitude flow is the formation of a distinct jet streak and the amplification of a ridge–trough couplet in the adjacent downstream region. The subsequent rapid cyclogenesis downstream is a direct consequence of these upper-level flow modifications. This faster and stronger development constitutes the amplification of the leading edge of downstream development. Both the upper-level wave pattern and the surface development are subsequently amplified in the region further downstream. The formation of the ridge adjacent to the intensified downstream cyclone is analyzed in detail to elucidate the next stage in the downstream dispersion of the ET impact. Ridge-building in the ET scenario exhibits characteristics distinct from those in the life-cycle experiment. Wave breaking, feedback from the modified low-level frontal structure and diabatic processes all contribute to the high-amplitude wave pattern downstream of ET. The downstream impact of ET is highly sensitive to the initial storm location and intensity. The considerable amplification of the leading edge found in the reference experiment is the most widespread and rapidly propagating impact. We thus speculate that this leading edge represents an optimal location of the midlatitude circulation, where ET can lead to the most significant impact on the downstream flow. Copyright © 2010 Royal Meteorological Society

Genesis of Pre–Hurricane Felix (2007). Part II: Warm Core Formation, Precipitation Evolution, and Predictability

Abstract: This is the second of a two-part study examining the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. Here several open issues are addressed concerning the formation of the storm’s warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave’s pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions. All but one of the experiments include ice microphysics as represented by one of several parameterizations, and the partition of convective versus stratiform precipitation is accomplished using a standard numerical technique based on the high-resolution control experiment. The transition to a warm-core tropical cyclone from an initially cold-core, lower tropospheric wave disturbance is analyzed first. As part of this transformation process, it is shown that deep moist convection is sustained near the pouch center. Both convecti...

Initial Maintenance of Tropical Cyclone Size in the Western North Pacific

Abstract: A tropical cyclone (TC) size parameter, which is defined here as the radius of 15 m s 21 near-surface wind speed (R15), is calculated for 145 TCs in the western North Pacific during 2000‐05 based on QuikSCAT oceanic winds. For the 73 TCs that intensified to typhoon intensity during their lifetimes, the 33% and 67% respective percentiles of R15 at tropical storm intensity and at typhoon intensity are used to categorize small, medium, and large TCs. Whereas many of the small TCs form from an easterly wave synoptic pattern, the monsoon-related formation patterns are favorable for forming medium to large TCs. Most of these 73 TCs stay in the same size category during intensification, which implies specific physical mechanisms for maintaining TC size in the basin. The 18 persistently large TCs from the tropical storm to the typhoon stage mostly havenorthwestward or north-northwestward tracks, while the 16 persistently small TCs either move westward‐ northwestward in lower latitudes or develop at higher latitudes with various track types. For the large TCs, strong low-level southwesterly winds exist in the outer core region south of the TC center throughout the intensification period. The small TCs are more influenced by the subtropical high during intensification. The conclusion is that it is the low-level environment that determines the difference between large and small size storms during the early intensification period in the western North Pacific.

Modeling dynamics in agile software development

Abstract: Changes in the business environment such as turbulent market forces, rapidly evolving system requirements, and advances in technology demand agility in the development of software systems. Though agile approaches have received wide attention, empirical research that evaluates their effectiveness and appropriateness is scarce. Further, research to-date has investigated individual practices in isolation rather than as an integrated system. Addressing these concerns, we develop a system dynamics simulation model that considers the complex interdependencies among the variety of practices used in agile development. The model is developed on the basis of an extensive review of the literature as well as quantitative and qualitative data collected from real projects in nine organizations. We present the structure of the model focusing on essential agile practices. The validity of the model is established based on extensive structural and behavioral validation tests. Insights gained from experimentation with the model answer important questions faced by development teams in implementing two unique practices used in agile development. The results suggest that due to refactoring, the cost of implementing changes to a system varies cyclically and increases during later phases of development. Delays in refactoring also increase costs and decrease development productivity. Also, the simulation shows that pair programming helps complete more tasks and at a lower cost. The systems dynamics model developed in this research can be used as a tool by IS organizations to understand and analyze the impacts of various agile development practices and project management strategies.