NaAlSi: a self-doped semimetallic superconductor with free electrons and covalent holes

The layered ternary sp conductor NaAlSi, possessing the iron-pnictide "111" crystal structure, superconducts at 7 K. Using density functional methods, we show that this compound is an intrinsic (self-doped) low-carrier-density semimetal with a number of unusual features. Covalent Al-Si valence bands provide the holes, and free-electron-like Al 3s bands, which propagate in the channel between the neighboring Si layers, dip just below the Fermi level to create the electron carriers. The Fermi level (and therefore the superconducting carriers) lies in a narrow and sharp peak within a pseudogap in the density of states. The small peak arises from valence bands which are nearly of pure Si, quasi-two-dimensional, flat, and coupled to Al conduction bands. Isostructural NaAlGe, which is not superconducting above 1.6 K, has almost exactly the same band structure except for one missing piece of small Fermi surface. Certain deformation potentials induced by Si and Na displacements along the c-axis are calculated and discussed. It seems likely that the mechanism of pairing is related to that of several other lightly doped two-dimensional nonmagnetic semiconductors (TiNCl, ZrNCl, HfNCl), which is not well understood but apparently not of phonon origin.Comment: 9 pages, 7 figures, 1 tabl

IC Design for the TV Receiver

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Warm dust in the terrestrial planet zone of a sun-like Pleiad: collisions between planetary embryos?

Only a few solar-type main sequence stars are known to be orbited by warm dust particles; the most extreme is the G0 field star BD+20 307 that emits ~4% of its energy at mid-infrared wavelengths. We report the identification of a similarly dusty star HD 23514, an F6-type member of the Pleiades cluster. A strong mid-IR silicate emission feature indicates the presence of small warm dust particles, but with the primary flux density peak at the non-standard wavelength of ~9 micron. The existence of so much dust within an AU or so of these stars is not easily accounted for given the very brief lifetime in orbit of small particles. The apparent absence of very hot (>~1000 K) dust at both stars suggests the possible presence of a planet closer to the stars than the dust. The observed frequency of the BD+20 307/HD 23514 phenomenon indicates that the mass equivalent of Earth's Moon must be converted, via collisions of massive bodies, to tiny dust particles that find their way to the terrestrial planet zone during the first few hundred million years of the life of many (most?) sun-like stars. Identification of these two dusty systems among youthful nearby solar-type stars suggests that terrestrial planet formation is common.Comment: ApJ in press, 19 pages including 3 figures and 2 tables, minor changes to the tables and figure

Self-Paced Polling Increases Medical Student Engagement in Recorded Lectures and Improves Examination Performance

Research Statement/Research Question Do self-paced polling questions in recorded lectures increase preclinical medical students' engagement and academic performance? Background and relevance of the study Engaging medical students in the curriculum may promote a deep approach to learning. However, class attendance is often low, and many students prefer recorded lectures. The shift to more online classes presents further challenges for student engagement. Self-paced polling with recorded lectures could increase student engagement in online education as well as address some students’ preference for recorded lectures. Design and Methods For second-year medical students, 148 audience response questions were given in three days. Participation in live or self-paced polling was incentivized with course points. With self-paced polling, students answered at their own pace while watching recorded lectures. Students who participated actively in all three days were MA https://www.abstractscorecard.com/cfp/submit/submissions/summary/view.asp?EventKey=SXINBCDE&SubmissionID=1385661 2/3 11/1/22, 4:22 PM Preview - Call for Papers - 2023 WGEA/WGSA/WOSR Joint Regional Meeting subdivided into the Live group (2-3 days with live polling) and Self-paced (0-1 day with live polling) and compared to the Inactive group. Performance of the three groups was compared on seven examinations. Students also voluntarily answered: “How did the self-paced polling affect your experience with recorded lectures?” Results 127/165 (77.0%) students used self-paced polling. 46 students were Inactive. 60/119 active students primarily used self-paced, and 59 used live polling. The Self-paced group performed significantly better than the Inactive group only on the fourth examination after incentivized, self-paced polling was made available. 115/127 (90.6%) students made positive comments about self-paced polling, while 12 (9.4%) were negative. In the positive comments, students expressed their emotional (n=59), behavioral (n=34), or cognitive (n=39) engagement. Conclusions Self-paced polling questions in recorded lectures enhanced students' emotional, behavioral, and/or cognitive engagement with course material and improved examination performance. Significance Medical educators can use self-paced polling to enhance student engagement and academic performance. Future studies should replicate and extend findings, with a focus on the impact of self-polling on deep and strategic approaches to learning and long-term retention

Прогнозирование прочности стальных труб, поврежденных водной коррозией

Показана возможность прогноза долговечности поврежденных стальных труб. Вследствие электрохимического взаимодействия металла и воды образуются щелеобразные коррозионные дефекты, которые являются концентраторами напряжений и приводят к локальному перенапряжению материала и разрушению труб. Долговечность труб рассчитывается по скорости роста коррозионных дефектов и степени концентрации напряжений. С повышением температуры скорость электрохимической коррозии увеличивается, что приводит к снижению долговечности труб.Показана можливість прогнозування довговічності пошкоджених сталевих водопровідних труб. Внаслідок електрохімічної взаємодії металу і води виникають щілиноподібні корозійні дефекти, що є концентраторами напружень і зумовлюють локальну перенапругу матеріалу та руйнування труб. Довговічність труб розраховується по швидкості росту корозійних дефектів і ефективності концентрації напружень. Із підвищенням температури швидкість електрохімічної корозії збільшується, що призводить до зниження довговічності труб.We have demonstrated a possibility of predicting service life of damaged steel pipes. The electrochemical interaction of the metal and water causes initiation of crack-like corrosive defects, which, being stress concentrators, induce local overstressing of the material and destruction of pipes. One can calculate the durability of a pipe from the corrosion crack-growth rate and the degree of the stress concentration. An increase in temperature accelerates electrochemical corrosion, which results in the reduction of life of water pipes