J.S. Bell's Concept of Local Causality

John Stewart Bell's famous 1964 theorem is widely regarded as one of the most important developments in the foundations of physics. It has even been described as "the most profound discovery of science." Yet even as we approach the 50th anniversary of Bell's discovery, its meaning and implications remain controversial. Many textbooks and commentators report that Bell's theorem refutes the possibility (suggested especially by Einstein, Podolsky, and Rosen in 1935) of supplementing ordinary quantum theory with additional ("hidden") variables that might restore determinism and/or some notion of an observer-independent reality. On this view, Bell's theorem supports the orthodox Copenhagen interpretation. Bell's own view of his theorem, however, was quite different. He instead took the theorem as establishing an "essential conflict" between the now well-tested empirical predictions of quantum theory and relativistic \emph{local causality}. The goal of the present paper is, in general, to make Bell's own views more widely known and, in particular, to explain in detail Bell's little-known mathematical formulation of the concept of relativistic local causality on which his theorem rests. We thus collect and organize many of Bell's crucial statements on these topics, which are scattered throughout his writings, into a self-contained, pedagogical discussion including elaborations of the concepts "beable", "completeness", and "causality" which figure in the formulation. We also show how local causality (as formulated by Bell) can be used to derive an empirically testable Bell-type inequality, and how it can be used to recapitulate the EPR argument.Comment: 19 pages, 4 figure

Head CT is of limited diagnostic value in critically ill patients who remain unresponsive after discontinuation of sedation

<p>Abstract</p> <p>Background</p> <p>Prolonged sedation is common in mechanically ventilated patients and is associated with increased morbidity and mortality. We sought to determine the diagnostic value of head computed tomography (CT) in mechanically ventilated patients who remain unresponsive after discontinuation of sedation.</p> <p>Methods</p> <p>A retrospective review of adult (age >18 years of age) patients consecutively admitted to the medical intensive care unit of a tertiary care medical center. Patients requiring mechanical ventilation for management of respiratory failure for longer than 72 hours were included in the study group. A group that did not have difficulty with awakening was included as a control.</p> <p>Results</p> <p>The median time after sedation was discontinued until a head CT was performed was 2 days (interquartile range 1.375–2 days). Majority (80%) of patients underwent head CT evaluation within the first 48 hours after discontinuation of sedation. Head CT was non-diagnostic in all but one patient who had a small subarachnoid hemorrhage. Twenty-five patients (60%) had a normal head CT. Head CT findings did not alter the management of any of the patients. The control group was similar to the experimental group with respect to demographics, etiology of respiratory failure and type of sedation used. However, while 37% of subjects in the control group had daily interruption of sedation, only 19% in the patient group had daily interruption of sedation (p < 0.05).</p> <p>Conclusion</p> <p>In patients on mechanical ventilation for at least 72 hours and who remain unresponsive after sedative discontinuation and with a non-focal neurologic examination, head CT is performed early and is of very limited diagnostic utility. Routine use of daily interruption of sedation is used in a minority of patients outside of a clinical trial setting though it may decrease the frequency of unresponsiveness from prolonged sedation and the need for head CT in patients mechanically ventilated for a prolonged period.</p

Opportunistic Detection of Type 2 Diabetes Using Deep Learning From Frontal Chest Radiographs

Deep learning (DL) models can harness electronic health records (EHRs) to predict diseases and extract radiologic findings for diagnosis. With ambulatory chest radiographs (CXRs) frequently ordered, we investigated detecting type 2 diabetes (T2D) by combining radiographic and EHR data using a DL model. Our model, developed from 271,065 CXRs and 160,244 patients, was tested on a prospective dataset of 9,943 CXRs. Here we show the model effectively detected T2D with a ROC AUC of 0.84 and a 16% prevalence. The algorithm flagged 1,381 cases (14%) as suspicious for T2D. External validation at a distinct institution yielded a ROC AUC of 0.77, with 5% of patients subsequently diagnosed with T2D. Explainable AI techniques revealed correlations between specific adiposity measures and high predictivity, suggesting CXRs\u27 potential for enhanced T2D screening

Biomechanics and strain mapping in bone as related to immediately-loaded dental implants

The effects of alveolar bone socket geometry and bone-implant contact on implant biomechanics, and resulting strain distributions in bone were investigated. Following extraction of lateral incisors on a cadaver mandible, immediate implants were placed and bone-implant contact area, stability and bone strain were measured. In situ biomechanical testing coupled with micro X-ray microscope (μ-XRM) illustrated less stiff bone-implant complexes (701-822 N/mm) compared with bone-periodontal ligament (PDL)-tooth complexes (791-913 N/mm). X-ray tomograms illustrated that the cause of reduced stiffness was due to reduced and limited bone-implant contact. Heterogeneous elemental composition of bone was identified by using energy dispersive X-ray spectroscopy (EDS). The novel aspect of this study was the application of a new experimental mechanics method, that is, digital volume correlation, which allowed mapping of strains in volumes of alveolar bone in contact with a loaded implant. The identified surface and subsurface strain concentrations were a manifestation of load transferred to bone through bone-implant contact based on bone-implant geometry, quality of bone, implant placement, and implant design. 3D strain mapping indicated that strain concentrations are not exclusive to the bone-implant contact regions, but also extend into bone not directly in contact with the implant. The implications of the observed strain concentrations are discussed in the context of mechanobiology. Although a plausible explanation of surgical complications for immediate implant treatment is provided, extrapolation of results is only warranted by future systematic studies on more cadaver specimens and/or in vivo small scale animal models

A Model for Gastric Banding in the Treatment of Morbid Obesity: The Effect of Chronic Partial Gastric Outlet Obstruction on Esophageal Physiology

OBJECTIVE: This work establishes an animal model for nonadjustable gastric banding and characterizes the effect of gastric banding on esophageal physiology. SUMMARY BACKGROUND DATA: Obstruction at the esophagogastric junction (EGJ) results in esophageal dilation and aperistalsis. Although laparoscopic gastric banding as a primary treatment of morbid obesity has been widely accepted, the effects of this therapy on esophageal function remain unknown. METHODS: Twenty-five opossums were randomly divided into sham (n = 5), EGJ band (n = 5), and gastric band (n = 15) groups. Gastric and EGJ bands were surgically placed, and esophageal manometry was performed prebanding, at 2-week intervals during the banding period (up to 14 weeks), and 2 and 4 weeks after band removal. RESULTS: Manometric measures were equivalent prior to banding in all groups. There were no changes in LES or esophageal pressures during the study period in the sham group. During banding, there was a 36% decrease in baseline mean resting lower esophageal sphincter pressure in the gastric band group (P = 0.003). Mean distal esophageal peristaltic pressure decreased from baseline by 36% in gastric band animals (P < 0.001). The incidence of esophageal motility disorder during the study period for sham, EGJ band, and gastric band groups, was 2.9%, 42.1%, and 31.3%, respectively (P = 0.001, P = 0.381, pairwise comparisons of gastric band vs. sham and gastric band versus EGJ groups, respectively). Immediately prior to band removal, the probability of an abnormal peristaltic sequence with each swallow was 1%, 38%, and 16% for sham, EGJ, and gastric band groups, respectively (P < 0.005, pairwise comparisons of band groups with sham). CONCLUSIONS: Nonadjustable gastric banding results in impaired esophageal body motility, a reduction in esophageal peristaltic pressure, and a reduction in resting lower esophageal sphincter pressure. These findings suggest that gastric banding causes esophageal outlet obstruction and subsequent decompensation of peristaltic function as well as a compromise of the native antireflux mechanism