Prefix Codes: Equiprobable Words, Unequal Letter Costs

Describes a near-linear-time algorithm for a variant of Huffman coding, in which the letters may have non-uniform lengths (as in Morse code), but with the restriction that each word to be encoded has equal probability. [See also ``Huffman Coding with Unequal Letter Costs'' (2002).]Comment: proceedings version in ICALP (1994

Huffman Coding with Letter Costs: A Linear-Time Approximation Scheme

We give a polynomial-time approximation scheme for the generalization of Huffman Coding in which codeword letters have non-uniform costs (as in Morse code, where the dash is twice as long as the dot). The algorithm computes a (1+epsilon)-approximate solution in time O(n + f(epsilon) log^3 n), where n is the input size

On a Linear Program for Minimum-Weight Triangulation

Minimum-weight triangulation (MWT) is NP-hard. It has a polynomial-time constant-factor approximation algorithm, and a variety of effective polynomial- time heuristics that, for many instances, can find the exact MWT. Linear programs (LPs) for MWT are well-studied, but previously no connection was known between any LP and any approximation algorithm or heuristic for MWT. Here we show the first such connections: for an LP formulation due to Dantzig et al. (1985): (i) the integrality gap is bounded by a constant; (ii) given any instance, if the aforementioned heuristics find the MWT, then so does the LP.Comment: To appear in SICOMP. Extended abstract appeared in SODA 201

Chronic hepatitis C and antiviral treatment regimens: Where can psychology contribute?

To evaluate the existing literature on psychological, social, and behavioral aspects of chronic hepatitis C viral (HCV) infection and antiviral treatment; provide the state of the behavioral science in areas that currently hinder HCV-related health outcomes; and make recommendations for areas in which clinical psychology can make significant contributions

ProjectHeartforGirls.com: Development of a Web-Based HIV/STD Prevention Program for Adolescent Girls Emphasizing Sexual Communication Skills

This article describes the development of ProjectHeartforGirls.com, an interactive web-based program designed to improve sexual communication skills and reduce the risk of HIV/STDs among adolescent girls, a population at heightened risk for negative sexual health outcomes (CDC, 2013). Although sexual communication is a critical predictor of safer sex among teens, there are few online interventions that target these skills as a central program component. We developed ProjectHeartforGirls.com to fill this gap. Program development involved 1) identifying the target population (ethnically-diverse high school girls); 2) clarifying the theoretical foundation (Reasoned Action Model); 3) conducting formative qualitative research (n=25 girls); 4) drafting initial program content; 5) receiving ongoing feedback from a teen advisory board (n=5 girls); 6) programming online content; and 7) conducting usability testing (n=6 girls). These steps are described along with the final intervention product, which is currently being evaluated in a randomized controlled trial

Quantum Conductance in Semimetallic Bismuth Nanocontacts

Electronic transport properties of bismuth nanocontacts are analyzed by means of a low temperature scanning tunneling microscope. The subquantum steps observed in the conductance versus elongation curves give evidence of atomic rearrangements in the contact. The underlying quantum nature of the conductance reveals itself through peaks in the conductance histograms. The shape of the conductance curves at 77 K is well described by a simple gliding mechanism for the contact evolution during elongation. The strikingly different behaviour at 4 K suggests a charge carrier transition from light to heavy ones as the contact cross section becomes sufficiently small.Comment: 5 pages including 4 figures. Accepted for publication in Phys. Rev. Let

Sexual Communication Between Early Adolescents and Their Dating Partners, Parents, and Best Friends

This study assessed early adolescents' sexual communication with dating partners, parents, and best friends about six sexual health topics: condoms, birth control, STDs, HIV/AIDS, pregnancy, and abstinence/waiting. Using a school-based sample of 603 youth (ages = 12–15; 57% female; 46% Caucasian), we examined communication differences across demographic and developmental factors, tested whether communication with parents and best friends was associated with greater communication with partners, and examined associations between communication and condom use. Over half of participants had not discussed any sexual topics with their dating partners (54%), and many had not communicated with parents (29%) or best friends (25%). On average, communication was more frequent among adolescents who were female, African American, older, and sexually active, despite some variation in subgroups across partner, parent, and friend communication. Importantly, communication with parents and friends – and the interaction between parent and friend communication – was associated with increased communication with dating partners. Further, among sexually active youth, increased sexual communication with partners was associated with more frequent condom use. Results highlight the importance of understanding the broader family and peer context surrounding adolescent sexual decision-making and suggest a possible need to tailor sexual communication interventions

A Comparative Effectiveness Trial of Alternate Formats for Presenting Benefits and Harms Information for Low-Value Screening Services: A Randomized Clinical Trial

Healthcare overuse, the delivery of low-value services, is increasingly recognized as a critical problem. However, little is known about the comparative effectiveness of alternate formats for presenting benefits and harms information to patients as a strategy to reduce overuse. To examine the effect of different benefits and harms presentations on patients' intentions to accept low-value or potentially low-value screening services (prostate cancer screening in men ages 50-69 years; osteoporosis screening in low-risk women ages 50-64 years; or colorectal cancer screening in men and women ages 76-85 years). Randomized clinical trial of 775 individuals eligible to receive information about any 1 of the 3 screening services and scheduled for a visit with their clinician. Participants were randomized to 1 of 4 intervention arms that differed in terms of presentation format: words, numbers, numbers plus narrative, and numbers plus framed presentation. The trial was conducted from September 2012 to June 2014 at 2 family medicine and 2 internal medicine practices affiliated with the Duke Primary Care Research Consortium. The data were analyzed between May and September of 2015. One-page evidence-based decision support sheets on each of the 3 screening services, with benefits and harms information presented in 1 of 4 formats: words, numbers, numbers plus narratives, or numbers plus a framed presentation. The primary outcome was change in intention to accept screening (on a response scale from 1 to 5). Our secondary outcomes included general and disease-specific knowledge, perceived risk and consequences of disease, screening attitudes, perceived net benefit of screening, values clarity, and self-efficacy for screening. We enrolled and randomly allocated 775 individuals, aged 50 to 85 years, to 1 of 4 intervention arms: 195 to words, 192 to numbers, 196 to narrative, and 192 to framed formats. Intentions to accept screening were high before the intervention and change in intentions did not differ across intervention arms (words, -0.07; numbers, -0.05; numbers plus narrative, -0.12; numbers plus framed presentation, -0.02; P = .57 for all comparisons). Change in other outcomes also showed no difference across intervention arms. Results were similar when stratified by screening service. Single, brief, written decision support interventions, such as the ones in this study, are unlikely to be sufficient to change intentions for screening. Alternate and additional interventions are needed to reduce overused screening services. clinicaltrials.gov Identifier: NCT01694784