Alternative Archaeological Representations within Virtual Worlds

Traditional VR methods allow the user to tour and view the virtual world from different perspectives. Increasingly, more interactive and adaptive worlds are being generated, potentially allowing the user to interact with and affect objects in the virtual world. We describe and compare four models of operation that allow the publisher to generate views, with the client manipulating and affecting specific objects in the world. We demonstrate these approaches through a problem in archaeological visualization

The diamond Nitrogen-Vacancy center as a probe of random fluctuations in a nuclear spin ensemble

New schemes that exploit the unique properties of Nitrogen-Vacancy (NV) centers in diamond are presently being explored as a platform for high-resolution magnetic sensing. Here we focus on the ability of a NV center to monitor an adjacent mesoscopic nuclear spin bath. For this purpose, we conduct comparative experiments where the NV spin evolves under the influence of surrounding 13C nuclei or, alternatively, in the presence of asynchronous AC fields engineered to emulate bath fluctuations. Our study reveals substantial differences that underscore the limitations of the semi-classical picture when interpreting and predicting the outcome of experiments designed to probe small nuclear spin ensembles. In particular, our study elucidates the NV center response to bath fluctuations under common pulse sequences, and explores a detection protocol designed to probe time correlations of the nuclear spin bath dynamics. Further, we show that the presence of macroscopic nuclear spin order is key to the emergence of semi-classical spin magnetometry.Comment: 30 pages, 4 figure

Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation and Experimentation

Among the many additive manufacturing (AM) processes for metallic materials, selective laser melting (SLM) is arguably the most versatile in terms of its potential to realize complex geometries along with tailored microstructure. However, the complexity of the SLM process, and the need for predictive relation of powder and process parameters to the part properties, demands further development of computational and experimental methods. This review addresses the fundamental physical phenomena of SLM, with a special emphasis on the associated thermal behavior. Simulation and experimental methods are discussed according to three primary categories. First, macroscopic approaches aim to answer questions at the component level and consider for example the determination of residual stresses or dimensional distortion effects prevalent in SLM. Second, mesoscopic approaches focus on the detection of defects such as excessive surface roughness, residual porosity or inclusions that occur at the mesoscopic length scale of individual powder particles. Third, microscopic approaches investigate the metallurgical microstructure evolution resulting from the high temperature gradients and extreme heating and cooling rates induced by the SLM process. Consideration of physical phenomena on all of these three length scales is mandatory to establish the understanding needed to realize high part quality in many applications, and to fully exploit the potential of SLM and related metal AM processes

On the Forward-Backward Asymmetry of Leptonic Decays of ttˉt\bar{t} at the Fermilab Tevatron

We report on a study of the measurement techniques used to determine the leptonic forward-backward asymmetry of top anti-top quark pairs in Tevatron experiments with a proton anti-proton initial state. Recently it was shown that a fit of the differential asymmetry as a function of $q_{l}\eta_{l}$ (where $q_{l}$ is the charge of the lepton from the cascade decay of the top quarks and $\eta_{l}$ is the final pseudorapidity of the lepton in the detector frame) to a hyperbolic tangent function can be used to extrapolate to the full leptonic asymmetry. We find this empirical method to well reproduce the results from current experiments, and present arguments as to why this is the case. We also introduce two more models, based on Gaussian functions, that better model the $q_{l}\eta_{l}$ distribution. With our better understanding, we find that the asymmetry is mainly determined by the shift of the mean of the $q_{l}\eta_{l}$ distribution, the main contribution to the inclusive asymmetry comes from the region around $|q_{l}\eta_{l}| = 1$, and the extrapolation from the detector-covered region to the inclusive asymmetry is stable via a multiplicative scale factor, giving us confidence in the previously reported experimental results.Comment: 26 pages, 12 figure

Inhibitory learning approaches to exposure therapy: A critical review and translation to obsessive-compulsive disorder

The majority of treatment research on OCD has focused on pre/post treatment efficacy of exposure-based interventions, with less attention directed towards (a) understanding mechanisms of change, and (b) maximizing long-term effectiveness. Inhibitory learning theory (ILT) provides a novel foundation for understanding how exposure therapy reduces fear. Moreover, ILT is consistent with empirical evidence that raises questions about the more traditional (i.e., habituation) explanation for exposure therapy's efficacy. Yet ILT has yet to be applied to understanding the treatment of OCD and its heterogeneity. The current review is an examination of human experimental research on ILT that seeks to translate laboratory findings on fear extinction to exposure therapy across empirically established OCD symptom dimensions. We provide an up-to-date critical review of the existing evidence for a series of strategies derived from ILT that have been proposed for the treatment of fear, discuss the limitations of existing studies, and provide suggestions for future research within this rapidly accelerating area of study. We also offer conceptual considerations for applying these principles to the treatment of OCD symptom dimensions. A common theme is the idea of introducing "desirable difficulties" into the implementation of exposure in order to foster more durable long-term learning

The Relative Contributions of Experiential Avoidance and Distress Tolerance to OC Symptoms

Background: Obsessive beliefs account for substantial (but not all) obsessive-compulsive (OC) symptoms. Intolerance of internal experiences (IIE), which encompasses the constructs of experiential avoidance (EA) and distress tolerance (DT), refers to difficulty managing unwanted thoughts, emotions, and other internal states, and might add to current explanatory models. Although IIE appears to be conceptually relevant to obsessive-compulsive (OC) symptoms, scant research has examined this relationship empirically. Aim: The present study examined the relative contributions of EA and DT as predictors of OC symptom dimensions. Method: A nonclinical sample ( n = 496) completed self-report questionnaires measuring general distress, EA, DT and OC symptom dimensions. Results: All variables of interest were significantly (all p s ≤ .001) correlated with one another, such that higher general distress, higher EA, and lower DT were associated with greater OC symptom severity for all symptom dimensions; however, only EA independently predicted obsessional symptoms, but not other OC symptom dimensions. Conclusions: One's willingness to endure (i.e. EA), rather than their ability to tolerate (i.e. DT) unpleasant internal experiences best predicts obsessional symptoms (i.e. obsessing) above and beyond general distress. Potential implications for understanding, assessing, and treating OC symptoms are discussed

Outcomes after transplantation for “failed” Fontan: A single-institution experience

ObjectiveDespite the excellent outcomes in the current era after the Fontan procedure, it continues to have an inherent risk of failure. Cardiac transplantation provides 1 option for treating these patients; however, the indications for, timing of, and outcomes after, transplantation remain undefined. We examined our own institutional experience with transplantation for failed Fontan.MethodsThe records of 155 patients transplanted for congenital heart disease at a single institution from June 1984 to September 2007 were reviewed. Of these patients, 43 had undergone a previous Fontan procedure (25 male, 15 female; median age, 14.5 years; range, 1–47; 23 classic Fontan, 13 lateral tunnel, 4 extracardiac conduit, and 3 revised to shunt). The predictors of short- and long-term survival were evaluated, and the Fontan patients were compared with all other patients with congenital heart disease (n = 129, 78 male, 51 female).ResultsThe most common indications for transplantation included protein-losing enteropathy (PLE) (39.5%), chronic heart failure (41.8%), and acute post-Fontan failure (9.3%). The transplants performed in Fontan patients were more likely to require pulmonary artery reconstruction (85.4% vs 42.9%; P < .0001) and had longer cardiopulmonary bypass times (278 vs 179 minutes; P < .0001). The 90-day mortality rate was greater in the Fontan group (35.0% vs 20.0%; P = .055). No correlation was observed between the interval from Fontan to transplantation and morality; however, renal failure was a strong predictor of early mortality (odds ratio, 10.8; 95% confidence interval, 1.5–75.7).ConclusionsTransplantation is an acceptable treatment for patients with a failed Fontan. Clinical factors (instead of the indication for transplantation) appear to have the greatest correlation with early mortality