Regime switching and monetary policy measurement

This paper applies regime-switching methods to the problem of measuring monetary policy. Policy preferences and structural factors are specified parametrically as independent Markov processes. Interaction between the structural and preference parameters in the policy rule serves to identify the two processes. The estimates uncover policy episodes that are initiated by switches to "dove regimes," shown to Granger-cause both NBER recessions and the Romer dates. These episodes imply real effects of monetary policy that are smaller than those found in previous studies.Phillips curve ; Monetary policy

Low-Degree Spanning Trees of Small Weight

The degree-d spanning tree problem asks for a minimum-weight spanning tree in which the degree of each vertex is at most d. When d=2 the problem is TSP, and in this case, the well-known Christofides algorithm provides a 1.5-approximation algorithm (assuming the edge weights satisfy the triangle inequality). In 1984, Christos Papadimitriou and Umesh Vazirani posed the challenge of finding an algorithm with performance guarantee less than 2 for Euclidean graphs (points in R^n) and d > 2. This paper gives the first answer to that challenge, presenting an algorithm to compute a degree-3 spanning tree of cost at most 5/3 times the MST. For points in the plane, the ratio improves to 3/2 and the algorithm can also find a degree-4 spanning tree of cost at most 5/4 times the MST.Comment: conference version in Symposium on Theory of Computing (1994

Approximating the Minimum Equivalent Digraph

The MEG (minimum equivalent graph) problem is, given a directed graph, to find a small subset of the edges that maintains all reachability relations between nodes. The problem is NP-hard. This paper gives an approximation algorithm with performance guarantee of pi^2/6 ~ 1.64. The algorithm and its analysis are based on the simple idea of contracting long cycles. (This result is strengthened slightly in ``On strongly connected digraphs with bounded cycle length'' (1996).) The analysis applies directly to 2-Exchange, a simple ``local improvement'' algorithm, showing that its performance guarantee is 1.75.Comment: conference version in ACM-SIAM Symposium on Discrete Algorithms (1994

Associations of Psychological Inflexibility with Exercise Self-Efficacy and Fatigue Severity among Individuals Seeking Treatment for Weight-Related Behaviors

Rates of obesity are continuing to rise, contributing to several negative health outcomes and economic burden. Past work suggests that individuals with greater body mass index (BMI) are more likely to report feeling fatigue and are less likely to follow an exercise regimen, which may lead to weight-related problems. Psychological inflexibility, a rigid thinking style in which individuals attempt to over-control psychological reactions to discomfort, may be an underrecognized explanatory factor underlying greater fatigue and lower rates of exercise among individuals with weight-related concerns. The aim of the current study was to explore the relationship between psychological inflexibility and both exercise self-efficacy and fatigue severity among adults seeking treatment for weight-related behaviors. The current study is a secondary analysis and included 162 treatment-seeking adults who attended a baseline appointment for a larger randomized-controlled trial for weight-related behaviors. Results indicated that greater psychological inflexibility was significantly related to greater fatigue severity and lower exercise self-efficacy. These results provide initial empirical evidence that psychological inflexibility may be an important individual difference factor in terms of fatigue and exercise beliefs among adults seeking treatment for weight-related behaviors

The Lazy Bureaucrat Scheduling Problem

We introduce a new class of scheduling problems in which the optimization is performed by the worker (single ``machine'') who performs the tasks. A typical worker's objective is to minimize the amount of work he does (he is ``lazy''), or more generally, to schedule as inefficiently (in some sense) as possible. The worker is subject to the constraint that he must be busy when there is work that he can do; we make this notion precise both in the preemptive and nonpreemptive settings. The resulting class of ``perverse'' scheduling problems, which we denote ``Lazy Bureaucrat Problems,'' gives rise to a rich set of new questions that explore the distinction between maximization and minimization in computing optimal schedules.Comment: 19 pages, 2 figures, Latex. To appear, Information and Computatio

Extracting dynamical equations from experimental data is NP-hard

The behavior of any physical system is governed by its underlying dynamical equations. Much of physics is concerned with discovering these dynamical equations and understanding their consequences. In this work, we show that, remarkably, identifying the underlying dynamical equation from any amount of experimental data, however precise, is a provably computationally hard problem (it is NP-hard), both for classical and quantum mechanical systems. As a by-product of this work, we give complexity-theoretic answers to both the quantum and classical embedding problems, two long-standing open problems in mathematics (the classical problem, in particular, dating back over 70 years).Comment: For mathematical details, see arXiv:0908.2128[math-ph]. v2: final version, accepted in Phys. Rev. Let

Comparison of Aquifer Sustainability Under Groundwater Administrations in Oklahoma and Texas

We compared two approaches to administration of groundwater law on a hydrologic model of the North Canadian River, an alluvial aquifer in northwestern Oklahoma. Oklahoma limits pumping rates to retain 50% aquifer saturated thickness after 20 years of groundwater use. The Texas Panhandle Groundwater Conservation District’s (GCD) rules limit pumping to a rate that consumes no more than 50% of saturated thickness in 50 years, with reevaluation and readjustment of permits every 5 years. Using a hydrologic model (MODFLOW), we simulated river-groundwater interaction and aquifer dynamics under increasing levels of ‘‘development’’ (i.e., increasing groundwater withdrawals). Oklahoma’s approach initially would limit groundwater extraction more than the GCD approach, but the GCD approach would be more protective in the long run. Under Oklahoma rules more than half of aquifer storage would be depleted when development reaches 65%. Reevaluation of permits under the Texas Panhandle GCD approach would severely limit pumping as the 50% level is approached. Both Oklahoma and Texas Panhandle GCD approaches would deplete alluvial base flow at approximately 10% development. Results suggest periodic review of permits could protect aquifer storage and river base flow. Modeling total aquifer storage is more sensitive to recharge rate and aquifer hydraulic conductivity than to specific yield, while river leakage is most sensitive to aquifer hydraulic conductivity followed by specific yield

Minimizing Unsatisfaction in Colourful Neighbourhoods

Colouring sparse graphs under various restrictions is a theoretical problem of significant practical relevance. Here we consider the problem of maximizing the number of different colours available at the nodes and their neighbourhoods, given a predetermined number of colours. In the analytical framework of a tree approximation, carried out at both zero and finite temperatures, solutions obtained by population dynamics give rise to estimates of the threshold connectivity for the incomplete to complete transition, which are consistent with those of existing algorithms. The nature of the transition as well as the validity of the tree approximation are investigated.Comment: 28 pages, 12 figures, substantially revised with additional explanatio

The Association Between Body Mass Index and Anxious Arousal, Depressive, and Insomnia Symptoms Among World Trade Center Responders

Elevations in body mass index (BMI) among World Trade Center (WTC) responders may be associated with poor mental health outcomes. The current study examined the association of BMI with anxious arousal, depressive, and insomnia symptoms among this group. Participants were 412 WTC responders (89.4% male, Mage = 55.3 years, SD = 8.66) who completed health monitoring assessments (self-report and objective) as part of the Long Island site of the WTC Health Program (LI-WTC-HP). Results suggested BMI was statistically significant only in relation to anxious arousal (sr2 = .02, p = .008), after accounting for age and sex. The current study suggests that weight management programs may aid in promoting additional benefits for WTC responders by reducing anxious arousal symptoms as a function of reduced BMI