Optimal replacement of continuously degrading systems in partially observed environments

Motivated by wind energy applications, we consider the problem of optimally replacing a stochastically degrading component that resides and operates in a partially observable environment. The component's rate of degradation is modulated by the stochastic environment process, and the component fails when it is accumulated degradation first reaches a fixed threshold. Assuming periodic inspection of the component, the objective is to minimize the long‐run average cost per unit time of performing preventive and reactive replacements for two distinct cases. The first case examines instantaneous replacements and fixed costs, while the second considers time‐consuming replacements and revenue losses accrued during periods of unavailability. Formulated and solved are mixed state space, partially observable Markov decision process models, both of which reveal the optimality of environment‐dependent threshold policies with respect to the component's cumulative degradation level. Additionally, it is shown that for each degradation value, a threshold policy with respect to the environment belief state is optimal if the environment alternates between two states. The threshold policies are illustrated by way of numerical examples using both synthetic and real wind turbine data. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 395–415, 2015     

Spies,advisors, and grunts: Film portrayals of counterinsurgency in Vietnam

Vietnam was a complex conflict, which historians and political scientists have struggled to understand. Some of the bitterest disputes in the historiography revolve around the US approach to counterinsurgency in Vietnam. Many different facets of the war have received the attention of filmmakers, and an examination of their work suggests new ways of thinking about the conflict. This article considers film portrayals of three phases of the Vietnam War – firstly, the early period of ‘political action’, then the advisory period, and finally the Americanization of the war after 1965. It suggests that by examining the experiences of participants in each of these phases, Vietnam War cinema helps to illustrate the problems that faced various American approaches to counterinsurgency in the conflict. Combined with the importance of films in determining popular perceptions of both historical conflicts and counterinsurgency in general, it suggests that they are worthy subjects of study and critique.     

Managing Global Counterinsurgency: The Special Group (CI) 1962–1966

The contemporary American counterinsurgency discourse has emphasised a particular historical narrative of Vietnam to justify large-scale military operations in Iraq and Afghanistan. Absent from this narrative is any reference to the broader Cold War context in which Vietnam existed alongside numerous other small-scale counterinsurgencies and was therefore the exception, not the rule. This article seeks to redress this shortcoming by examining the way counterinsurgency was conceived and managed at the level of ‘grand strategy.’ Specifically, it focuses on the Special Group (Counterinsurgency) to demonstrate that senior policymakers under Presidents Kennedy and Johnson understood ‘counterinsurgency’ as involving ‘indirect’ assistance to foreign governments, rather than taking ‘direct’ military action with American ground forces.     

Varieties of Assurance

Strategies that seek to assure other states about their security have the potential to reduce international conflict and dissuade states from seeking nuclear weapons. Yet, relative to other tools of statecraft such as deterrence, assurance remains understudied. To facilitate further empirical research on assurance strategies, this article identifies variations in the terminology scholars and policymakers have used to refer to such strategies and describes the concept of assurance associated with each variant. It seeks to clarify and standardize usage and show that there is a general, overarching concept of assurance that links the different variants. It also summarizes existing bodies of empirical research that are relevant to assessing the utility of different forms of assurance.     

UNDERSTANDING CHINA'S ANTISATELLITE TEST

In discussing China's January 2007 hit-to-kill intercept of the Chinese weather satellite FengYun-1C, most American analysts sought the “message” for the United States—either by asserting that China's test was a deliberate step toward a comprehensive counterspace capability to offset U.S. conventional military superiority or an attempt to force the United States to the negotiating table on “the prevention of an arms race in outer space.” Chinese officials, after a long silence, eventually claimed the test was an “experiment” that was “not targeted at any country.” We traveled to China several times in 2007 and had a series of conversations with Chinese individuals knowledgeable about the history of this particular antisatellite program and with access to information about the decision-making process prior to and after the final test. These discussions were off the record, not for attribution, given the sensitivity of the subject. They reflected the views of some of the key institutions involved in the test from the State, the Communist Party, the People's Liberation Army, and aerospace experts involved in debris calculations. The information conveyed to us suggests that American commentators tend to place much greater importance on the United States as a driver in China's decision to develop the technology and conduct the test than do the Chinese.     

Helpless or Deliberate Bystander: American Policy towards South Vietnam's Military Coups, 1954–1975

The USA's role in fomenting and responding to military coups remains an understudied and politically contentious subject despite it being a recurring foreign policy problem exemplified most recently in both Egypt and Mali. To the extent this topic has been addressed in any depth by scholars, it is mainly limited to an examination of a small number of coups that occurred during the Cold War that the CIA was accused of sponsoring. However, this emphasis on well-known cases to the exclusion of lesser-known cases has resulted in a biased view of omnipotent US power. This limitation is reflected in the case of South Vietnam, in which the focus has been placed on the 1963 coup that overthrew President Ngo Dinh Diem, whereas the numerous other coups that occurred have received little or no attention. In this article, a more inclusive approach will be taken in which US policy will be examined with respect to all of the main coups and coup attempts that occurred during the period 1954–1975.     

Security assurances and proliferation risks in the Trump administration

Comments that Donald Trump made while campaigning to be U.S. president have raised concerns that his administration will pull back from U.S. alliance commitments and encourage countries such as Japan and South Korea to acquire nuclear arms. The new article by Frühling and O’Neil outlines an institutional framework that can be helpful in assessing the risks that Trump administration policies will lead to nuclear proliferation. An institutional perspective shows that important elements of U.S. security assurances will continue to function, and this reduces the chances that President Trump’s actions or statements will trigger proliferation by U.S. allies. The greatest risk to global non-proliferation efforts posed by a Trump administration in fact lies elsewhere, in the possibility that President Trump will seek to abrogate the Iran nuclear deal.     

The nuclear education of Donald J. Trump

During the 2016 American presidential campaign, Democrats and Republicans alike repeatedly raised concerns at the prospect of Donald Trump being in charge of America’s nuclear arsenal based on his seemingly unstable personality. Unfortunately, this emphasis on Trump’s character distracted attention from any in-depth investigation into his long-standing interest in nuclear issues. This article seeks to remedy this shortcoming by highlighting the nuclear legacy Trump will inherit from Obama, surveying his statements on nuclear issues over more than three decades, and providing an analysis of constraining factors on his administration’s nuclear agenda, particularly domestic institutions. It finds that most of Trump’s views on nuclear issues are relatively consistent with past Republican presidents. Where he is unique, however, is in his use of social media, which has potential implications on nuclear signaling.