EVALUATING OCEANOGRAPHIC HYPOTHESES: THREE METHODS FOR TESTING IDEAS

The disciplines of meteorology and oceanography are both vital to understanding the earth system. Throughout most of the last half century, meteorology has largely been a prognostic discipline. Forecasts made by meteorologists have been widely used and scrutinized, allowing for countless opportunities to test and improve ideas about atmospheric circulation and physics. Since weather forecasts involve integrating numerical models and updating the model state via data assimilation, forecasting demands frequent use of the principles of Bayesian inference. This requirement essentially confronts the physics contained within numerical models at recurring intervals and can reveal systematic model bias. In contrast, prognostic applications have been less prevalent in oceanography. Oceanographic forecasts are much rarer than atmospheric forecasts and, perhaps as a consequence of this disparity, many ideas concerning oceanic circulation have not been tested to the same degree as ideas concerning atmospheric circulation. This dissertation presents three methods for testing oceanographic ideas: applying common methodologies to analogous regions of different ocean basins; creating synthetic time series to mimic the properties of oceanographic time series in order to construct null distributions for hypothesis testing; and using water mass census information to interpret the results of water mass transformation analysis

Direct Replication in Experimental Communication Science: A Conceptual and Practical Exploration

Replication is generally considered a keystone of the scientific enterprise. Unfortunately, in communication science, there is a lack of clarity on what a replication actually entails, and to what extent replicators may deviate from original studies. In order to support researchers in conducting, evaluating, and justifying the setup of replications of communication science experiments, we provide a taxonomy of replication types. We argue that researchers almost always need to adapt some elements of an original communication study to meaningfully replicate it. The extent to which deviations - ranging from mere updates to deliberate deviations and additions - are permissible, however, depends on the motivation behind conducting a replication study. We distinguish three basic motivations: verification of an original study's findings, testing the generalizability of an original study (which we further differentiate into the generalizability of study outcomes vs. theoretical claims), and extending an original study beyond the original goals. We argue that these motivations dictate what types of deviations are permissible and thereby determine the type of replication (i.e., direct, modified, and conceptual). We end with concrete recommendations for replicators: to specify the motivation to conduct a replication study and clearly label and justify any deviations from the original study for all study elements

Body Mass Index and Cognitive Decline in Mild Cognitive Impairment

This is the author's accepted manuscript.Objective To examine the relationship between body mass index (BMI) and cognitive decline in subjects diagnosed with mild cognitive impairment (MCI). Methods Neuropsychologic and clinical evaluations were conducted at baseline, 6-months, and 1-year on 286 MCI subjects enrolled in the Alzheimer’s Disease Neuroimaging Initiative. A global cognitive composite score was derived (mean Z-score) from performance on 9 neuropsychologic subtests. Height and weight were assessed at baseline and used to calculate BMI. Generalized estimating equations (linear and logistic) assessed the relationships of baseline BMI with cognitive outcomes, clinician judgment of “clinically significant decline” over 1-year, and diagnostic progression from MCI to Alzheimer disease. Results Lower baseline BMI was associated with significant declines in cognitive performance in individuals with MCI over 1 year (Mini-Mental State Examination, Alzheimer Disease Assessment Scale-Cognitive subscale, and a global cognitive composite; all P<0.05). We observed a significant protective effect of baseline BMI in reducing the risk of a clinically significant decline in Alzheimer Disease Assessment Scale-Cognitive subscale and mini-mental state examination (P<0.05). No association was found between BMI and changes in the clinical dementia rating sum of boxes or conversion to Alzheimer disease. Conclusions Lower baseline BMI is associated with more rapid cognitive decline in MCI. This relationship suggests either body composition may influence the rate of cognitive decline in MCI or factors related to MCI influence body composition

Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism

Dehydration hastens the decline in cerebral blood flow (CBF) during incremental exercise, while the cerebral metabolic rate for oxygen (CMRO2) is preserved. It remains unknown whether CMRO2 is also maintained during prolonged exercise in the heat and whether an eventual decline in CBF is coupled to fatigue. Two studies were undertaken. In study 1, ten male cyclists cycled in the heat for ~2 h with (control) and without fluid replacement (dehydration) while internal (ICA) and external (ECA) carotid artery blood flow and core and blood temperature were obtained. Arterial and internal jugular venous blood samples were assessed with dehydration to evaluate the CMRO2. In study 2 (8 males), middle cerebral artery blood velocity (MCA Vmean) was measured during prolonged exercise to exhaustion in both dehydrated and euhydrated states. After a rise at the onset of exercise, ICA flow declined to baseline with progressive dehydration (P < 0.05). However, cerebral metabolism remained stable through enhanced oxygen and glucose extraction (P < 0.05). ECA flow increased for one hour but declined prior to exhaustion. Fluid ingestion maintained cerebral and extra-cranial perfusion throughout non-fatiguing exercise. During exhaustive exercise, however, euhydration delayed but did not prevent the decline in cerebral perfusion. In conclusion, during prolonged exercise in the heat dehydration accelerates the decline in CBF without affecting CMRO2 and also restricts extra-cranial perfusion. Thus fatigue is related to reduction in CBF and extra-cranial perfusion rather than in CMRO2.The study was supported by a grant from the Gatorade Sports Science Institute, PepsiCo Inc, USA

Shear modulus of the hadron-quark mixed phase

Robust arguments predict that a hadron-quark mixed phase may exist in the cores of some "neutron" stars. Such a phase forms a crystalline lattice with a shear modulus higher than that of the crust due to the high density and charge separation, even allowing for the effects of charge screening. This may lead to strong continuous gravitational-wave emission from rapidly rotating neutron stars and gravitational-wave bursts associated with magnetar flares and pulsar glitches. We present the first detailed calculation of the shear modulus of the mixed phase. We describe the quark phase using the bag model plus first-order quantum chromodynamics corrections and the hadronic phase using relativistic mean-field models with parameters allowed by the most massive pulsar. Most of the calculation involves treating the "pasta phases" of the lattice via dimensional continuation, and we give a general method for computing dimensionally continued lattice sums including the Debye model of charge screening. We compute all the shear components of the elastic modulus tensor and angle average them to obtain the effective (scalar) shear modulus for the case where the mixed phase is a polycrystal. We include the contributions from changing the cell size, which are necessary for the stability of the lower-dimensional portions of the lattice. Stability also requires a minimum surface tension, generally tens of MeV/fm^2 depending on the equation of state. We find that the shear modulus can be a few times 10^33 erg/cm^3, two orders of magnitude higher than the first estimate, over a significant fraction of the maximum mass stable star for certain parameter choices.Comment: 22 pages, 12 figures, version accepted by Phys. Rev. D, with the corrections to the shear modulus computation and Table I given in the erratu

Cellular Structures for Computation in the Quantum Regime

We present a new cellular data processing scheme, a hybrid of existing cellular automata (CA) and gate array architectures, which is optimized for realization at the quantum scale. For conventional computing, the CA-like external clocking avoids the time-scale problems associated with ground-state relaxation schemes. For quantum computing, the architecture constitutes a novel paradigm whereby the algorithm is embedded in spatial, as opposed to temporal, structure. The architecture can be exploited to produce highly efficient algorithms: for example, a list of length N can be searched in time of order cube root N.Comment: 11 pages (LaTeX), 3 figure

Neuropsychiatric Profiles in Dementia

This is the author's accepted manuscript. The original is available at http://pt.wkhealth.com/pt/re/lwwgateway/landingpage.htm;jsessionid=Wy1M9PqrBY1LGf0bN3QqF0h42YJqr4mTnW1ZdGT87Wllb4qvTbQb!-396536289!181195628!8091!-1?sid=WKPTLP:landingpage&an=00002093-201110000-00006We compared patterns of neuropsychiatric symptom across four dementia types (AD, VAD, DLB, PDD), and two mixed groups (AD/VAD, AD/DLB) in sample of 2,963 individuals from the National Alzheimer’s Coordinating Center Uniform Data Set between September 2005 and June 2008. We used confirmatory factor analysis to compare neuropsychiatric symptom severity ratings made by collateral sources on the Neuropsychiatric Inventory (NPI-Q) for people with Clinical Dementia Rating scores of 1 or higher. A three factor model of psychiatric symptoms (mood, psychotic, and frontal) was shared across all dementia types. Between-group comparisons revealed unique neuropsychiatric profiles by dementia type. The AD group had moderate levels of mood, psychotic, and frontal symptoms while VAD exhibited the highest levels and PDD had the lowest levels. DLB and the mixed dementias had more complex symptom profiles. Depressed mood was the dominant symptom in people with mild diagnoses. Differing psychiatric symptom profiles provide useful information regarding the non-cognitive symptoms of dementia

Modulational Instability in Equations of KdV Type

It is a matter of experience that nonlinear waves in dispersive media, propagating primarily in one direction, may appear periodic in small space and time scales, but their characteristics --- amplitude, phase, wave number, etc. --- slowly vary in large space and time scales. In the 1970's, Whitham developed an asymptotic (WKB) method to study the effects of small "modulations" on nonlinear periodic wave trains. Since then, there has been a great deal of work aiming at rigorously justifying the predictions from Whitham's formal theory. We discuss recent advances in the mathematical understanding of the dynamics, in particular, the instability of slowly modulated wave trains for nonlinear dispersive equations of KdV type.Comment: 40 pages. To appear in upcoming title in Lecture Notes in Physic

First cohomology for finite groups of Lie type: simple modules with small dominant weights

Let $k$ be an algebraically closed field of characteristic $p > 0$, and let $G$ be a simple, simply connected algebraic group defined over $\mathbb{F}_p$. Given $r \geq 1$, set $q=p^r$, and let $G(\mathbb{F}_q)$ be the corresponding finite Chevalley group. In this paper we investigate the structure of the first cohomology group $H^1(G(\mathbb{F}_q),L(\lambda))$ where $L(\lambda)$ is the simple $G$-module of highest weight $\lambda$. Under certain very mild conditions on $p$ and $q$, we are able to completely describe the first cohomology group when $\lambda$ is less than or equal to a fundamental dominant weight. In particular, in the cases we consider, we show that the first cohomology group has dimension at most one. Our calculations significantly extend, and provide new proofs for, earlier results of Cline, Parshall, Scott, and Jones, who considered the special case when $\lambda$ is a minimal nonzero dominant weight.Comment: 24 pages, 5 figures, 6 tables. Typos corrected and some proofs streamlined over previous versio