The Hidden College: Noncredit Education in the United States

Provides an overview of the growing enrollment in noncredit programs, and outlines the need to incorporate them better with credit-bearing courses to offer new options for learning, as well as to include them in discussions about higher education policy

A regularized solution to edge detection

AbstractWe assume that edge detection is the task of measuring and localizing changes of light intensity in the image. As discussed by V. Torre and T. Poggio (1984), “On Edge Detection,” AI Memo 768, MIT AI Lab), edge detection, when defined in this way, is λ problem of numerical differentiation, which is ill posed. This paper shows that simple regularization methods lead to filtering the image prior to an appropriate differentiation operation. In particular, we prove (1) that the variational formulation of Tikhonov regularization leads to λ convolution filter, (2) that the form of this filter is similar to the Gaussian filter, and (3) that the regularizing parameter λ in the variational principle effectively controls the scale of the filter

A Study of Snippet Length and Informativeness: Behaviour, Performance and User Experience

The design and presentation of a Search Engine Results Page (SERP) has been subject to much research. With many contemporary aspects of the SERP now under scrutiny, work still remains in investigating more traditional SERP components, such as the result summary. Prior studies have examined a variety of different aspects of result summaries, but in this paper we investigate the influence of result summary length on search behaviour, performance and user experience. To this end, we designed and conducted a within-subjects experiment using the TREC AQUAINT news collection with 53 participants. Using Kullback-Leibler distance as a measure of information gain, we examined result summaries of different lengths and selected four conditions where the change in information gain was the greatest: (i) title only; (ii) title plus one snippet; (iii) title plus two snippets; and (iv) title plus four snippets. Findings show that participants broadly preferred longer result summaries, as they were perceived to be more informative. However, their performance in terms of correctly identifying relevant documents was similar across all four conditions. Furthermore, while the participants felt that longer summaries were more informative, empirical observations suggest otherwise; while participants were more likely to click on relevant items given longer summaries, they also were more likely to click on non-relevant items. This shows that longer is not necessarily better, though participants perceived that to be the case - and second, they reveal a positive relationship between the length and informativeness of summaries and their attractiveness (i.e. clickthrough rates). These findings show that there are tensions between perception and performance when designing result summaries that need to be taken into account

Intrapulmonary Epinephrine During Prolonged Cardipulmonary Resuscitation: Improved Regional Blood Flow and Resuscitation in Dogs

Blood flow to vital organs was measured at five-minute intervals during 20 minutes of cardiopulmonary resuscitation (CPR) and ventricular fibrillation in two groups of anesthetized dogs (n = 15 per group). The relationship between organ blood flow and restoration of circulation after 20 minutes was assessed with no additional treatment in Group I and with intrapulmonary epinephrine in Group II. Cardiac output and organ blood flow did not vary significantly in Group I. In Group II, intrapulmonary epinephrine significantly improved blood flow to the myocardium, the brain, and the adrenal glands. A mean myocardial blood flow of less than 0.13 mL/min/g resulted in no survival, while a flow of greater than 0.16 mL/min/g resulted in survival. These studies show that a critical level of myocardial blood flow is required to restore ability of the heart to function as a pump after prolonged CPR, and that a drug that increases flow improves resuscitation efforts

Regional Blood Flow during Cardiopulmonary Resuscitation with Abdominal Counterpulsation in Dogs

The addition of abdominal counterpulsation to standard cardiopulmonary resuscitation (IAC-CPR) during ventricular fibrillation has been shown to improve cardiac output, oxygen uptake, and central arterial blood pressure in dogs. The present study was performed to determine the effect of IAC-CPR on regional blood flow. Regional blood flow was measured with radioactively labeled microspheres during sinus rhythm and during alternate periods of IAC-CPR and standard CPR (STD-CPR) in nine dogs anesthetized with pentobarbital. Blood pressures and oxygen uptake were measured continuously. As in previous studies, diastolic arterial pressure was higher (30.8%) during IAC-CPR than during STD-CPR, as were cardiac output (24.5%) and oxygen uptake (37.5%). Whole brain and myocardial blood flow increased 12.0% and 22.7%, respectively, during IAC-CPR. Blood flow to abdominal organs was not changed appreciably in response to abdominal compression, and postmortem examination revealed no gross trauma to the abdominal viscera. The IAC-CPR technique is simple and is easily added to present basic life support procedures. In light of the improvements observed in myocardial and cerebral blood flow, IAC-CPR could significantly improve the outcome of CPR attempts

Assessor Differences and User Preferences in Tweet Timeline Generation

In information retrieval evaluation, when presented with an effectiveness difference between two systems, there are three relevant questions one might ask. First, are the differences statistically significant? Second, is the comparison stable with respect to assessor differences? Finally, is the differ-ence actually meaningful to a user? This paper tackles the last two questions about assessor differences and user prefer-ences in the context of the newly-introduced tweet timeline generation task in the TREC 2014 Microblog track, where the system’s goal is to construct an informative summary of non-redundant tweets that addresses the user’s informa-tion need. Central to the evaluation methodology is human-generated semantic clusters of tweets that contain substan-tively similar information. We show that the evaluation is stable with respect to assessor differences in clustering and that user preferences generally correlate with effectiveness metrics even though users are not explicitly aware of the semantic clustering being performed by the systems. Al-though our analyses are limited to this particular task, we believe that lessons learned could generalize to other eval-uations based on establishing semantic equivalence between information units, such as nugget-based evaluations in ques-tion answering and temporal summarization

Structure of the Mammalian Ribosome-Sec61 Complex to 3.4 Å Resolution

Cotranslational protein translocation is a universally conserved process for secretory and membrane protein biosynthesis. Nascent polypeptides emerging from a translating ribosome are either transported across or inserted into the membrane via the ribosome-bound Sec61 channel. Here, we report structures of a mammalian ribosome-Sec61 complex in both idle and translating states, determined to 3.4 and 3.9 Å resolution. The data sets permit building of a near-complete atomic model of the mammalian ribosome, visualization of A/P and P/E hybrid-state tRNAs, and analysis of a nascent polypeptide in the exit tunnel. Unprecedented chemical detail is observed for both the ribosome-Sec61 interaction and the conformational state of Sec61 upon ribosome binding. Comparison of the maps from idle and translating complexes suggests how conformational changes to the Sec61 channel could facilitate translocation of a secreted polypeptide. The high-resolution structure of the mammalian ribosome-Sec61 complex provides a valuable reference for future functional and structural studies

Controlling crystal symmetries in phase-field crystal models

We investigate the possibility to control the symmetry of ordered states in phase-field crystal models by tuning nonlinear resonances. In two dimensions, we find that a state of square symmetry as well as coexistence between squares and hexagons can be easily obtained. In contrast, it is delicate to obtain coexistence of squares and liquid. We develop a general method for constructing free energy functionals that exhibit solid-liquid coexistence with desired crystal symmetries. As an example, we develop a free energy functional for square-liquid coexistence in two dimensions. A systematic analysis for determining the parameters of the necessary nonlinear terms is provided. The implications of our findings for simulations of materials with simple cubic symmetry are discussed.Comment: 19 pages, 6 figure