18 research outputs found
Making High T Higher: A Theoretical Proposal
There is considerable evidence that the highest obtainable in a
copper-oxide plane is limitted by the competition between two effects: On the
one hand, as the concentration of doped-holes, , is increased, the pairing
scale, which is related to the properties of a doped Mott insulator, decreases.
On the otherhand, the superfluid density, which controls the stiffness of the
system to phase fluctuations, vanishes as , and increases with
increasing . Optimal is obtained at a crossover from a phase ordering
dominated regime at small to a pairing dominated regime at large . If
this description is valid, then higher 's can be obtained in an array of
coupled planes with different doped hole concentrations, such that a high
pairing scale is derived from the underdoped planes and a large phase stiffness
from the optimally or overdoped ones.Comment: 6 page
Probleme bei sozialen Experimenten: Lehren aus US-amerikanischen Arbeitsmarktprogrammen
When evaluating a pilot or demonstration program, there are risks from drawing inferences from a single test. This paper reviews the experiences of replication efforts from demonstrations using randomized controlled trials in the initial evaluation and the replications. Although replications of promising programs are primarily gathered to increase sample size, replications are also used to learn if the intervention is successful for other target groups and geographic locations, and to vary some of the intervention's features. In many cases, replications fail to achieve the same success as the original evaluation, and the paper reviews reasons that have been suggested for such failures. The paper reviews what has been learned from replications where random assignment was used in six instances: income maintenance experiments, unemployment insurance bonus experiments, the Center for Employment Training program, job clubs, job search experiments, and the Quantum Opportunity Program. The paper concludes by summarizing lessons learned from the review and areas where more research is needed
Global Retinoblastoma Presentation and Analysis by National Income Level
Importance: Early diagnosis of retinoblastoma, the most common intraocular cancer, can save both a child's life and vision. However, anecdotal evidence suggests that many children across the world are diagnosed late. To our knowledge, the clinical presentation of retinoblastoma has never been assessed on a global scale. Objectives: To report the retinoblastoma stage at diagnosis in patients across the world during a single year, to investigate associations between clinical variables and national income level, and to investigate risk factors for advanced disease at diagnosis. Design, Setting, and Participants: A total of 278 retinoblastoma treatment centers were recruited from June 2017 through December 2018 to participate in a cross-sectional analysis of treatment-naive patients with retinoblastoma who were diagnosed in 2017. Main Outcomes and Measures: Age at presentation, proportion of familial history of retinoblastoma, and tumor stage and metastasis. Results: The cohort included 4351 new patients from 153 countries; the median age at diagnosis was 30.5 (interquartile range, 18.3-45.9) months, and 1976 patients (45.4) were female. Most patients (n = 3685 84.7%) were from low-and middle-income countries (LMICs). Globally, the most common indication for referral was leukocoria (n = 2638 62.8%), followed by strabismus (n = 429 10.2%) and proptosis (n = 309 7.4%). Patients from high-income countries (HICs) were diagnosed at a median age of 14.1 months, with 656 of 666 (98.5%) patients having intraocular retinoblastoma and 2 (0.3%) having metastasis. Patients from low-income countries were diagnosed at a median age of 30.5 months, with 256 of 521 (49.1%) having extraocular retinoblastoma and 94 of 498 (18.9%) having metastasis. Lower national income level was associated with older presentation age, higher proportion of locally advanced disease and distant metastasis, and smaller proportion of familial history of retinoblastoma. Advanced disease at diagnosis was more common in LMICs even after adjusting for age (odds ratio for low-income countries vs upper-middle-income countries and HICs, 17.92 95% CI, 12.94-24.80, and for lower-middle-income countries vs upper-middle-income countries and HICs, 5.74 95% CI, 4.30-7.68). Conclusions and Relevance: This study is estimated to have included more than half of all new retinoblastoma cases worldwide in 2017. Children from LMICs, where the main global retinoblastoma burden lies, presented at an older age with more advanced disease and demonstrated a smaller proportion of familial history of retinoblastoma, likely because many do not reach a childbearing age. Given that retinoblastoma is curable, these data are concerning and mandate intervention at national and international levels. Further studies are needed to investigate factors, other than age at presentation, that may be associated with advanced disease in LMICs. © 2020 American Medical Association. All rights reserved