Electron correlations in a C20_{20} fullerene cluster: A lattice density-functional study of the Hubbard model

The ground-state properties of C$_{20}$ fullerene clusters are determined in the framework of the Hubbard model by using lattice density-functional theory (LDFT) and scaling approximations to the interaction-energy functional. Results are given for the ground-state energy, kinetic and Coulomb energies, local magnetic moments, and charge-excitation gap, as a function of the Coulomb repulsion $U/t$ and for electron or hole doping $\delta$ close half-band filling ($|\delta| \le 1$). The role of electron correlations is analyzed by comparing the LDFT results with fully unrestricted Hartree-Fock (UHF) calculations which take into account possible noncollinear arrangements of the local spin-polarizations. The consequences of the spin-density-wave symmetry breaking, often found in UHF, and the implications of this study for more complex fullerene structures are discussed.Comment: 18 pages, 7 figures, Submitted to PR

Wannier-based calculation of the orbital magnetization in crystals

We present a first-principles scheme that allows the orbital magnetization of a magnetic crystal to be evaluated accurately and efficiently even in the presence of complex Fermi surfaces. Starting from an initial electronic-structure calculation with a coarse ab initio k-point mesh, maximally localized Wannier functions are constructed and used to interpolate the necessary k-space quantities on a fine mesh, in parallel to a previously-developed formalism for the anomalous Hall conductivity [X.Wang, J. Yates, I. Souza, and D. Vanderbilt, Phys. Rev. B 74, 195118 (2006)]. We formulate our new approach in a manifestly gauge-invariant manner, expressing the orbital magnetization in terms of traces over matrices in Wannier space. Since only a few (e.g., of the order of 20) Wannier functions are typically needed to describe the occupied and partially occupied bands, these Wannier matrices are small, which makes the interpolation itself very efficient. The method has been used to calculate the orbital magnetization of bcc Fe, hcp Co, and fcc Ni. Unlike an approximate calculation based on integrating orbital currents inside atomic spheres, our results nicely reproduce the experimentally measured ordering of the orbital magnetization in these three materials.Comment: 13 pages, 3 figures, 4 table

Sonic Quick Response Codes (SQRC) for embedding inaudible metadata in sound files

With the advent of high definition recording and playback systems, a proportion of the ultrasonic frequency spectrum can potentially be used as a container for unperceivable data and used to trigger events or to hold metadata in the form of text, ISRC (International Standard Recording Code) or a website URL. The Sonic Quick Response Code (SQRC) algorithm is proposed as a method for embedding inaudible acoustic metadata within a 96 kHz audio file in the 30-35 kHz bandwidth range. Thus any receiver that has sufficient bandwidth and decode software installed can immediately find metadata on the audio being played. SQRC data was mixed at random periods into 96 kHz music audio files and listening subjects were asked to identify if they perceived the introduction of the high frequency content. Results show that none of the subjects in this pilot study could perceive the 30-35 kHz material. As a result, it is shown that it is possible to conduct high-resolution audio testing without significant or perceptible artifacts caused by intermodulation distortion

Impact of Race and Insurance on Door-to-Appendectomy Time among Pediatric Patients

Racial and ethnic disparities in the rate of appendiceal rupture have been widely reported among the pediatric population. The main reasons for this remain largely unknown given that previous explanations pointing to signs of poor health care access have recently been shown to account for only a small percentage of the difference in perforation rates between white and minority children. Because the risk of perforation increases with time, racial disparities in time delay from emergency department presentation to OR appendectomy may help account for the higher appendiceal perforation rates observed among minority children. This is the first study dedicated to analyzing racial differences in door-to-appendectomy time. Insurance status and language barriers were also considered as variables of interest. Retrospective, observational study using admission and treatment data of 607 consecutive children less than or equal to 18 years of age with surgical confirmation of appendicitis. Patients were admitted from February 2, 2013 (start of electronic medical record use) to April 27, 2017. A significant association was found between race and perforation rate (p0.05 for all). Door-to-appendectomy times were also not significantly longer for Medicaid/uninsured patients (613 minutes) compared to private insurance patients (597 minutes) (p=0.60), nor for patients with language barriers (545 minutes) compared to patients without (612 minutes) (p=0.23). While there was a higher appendiceal perforation rate among minority children, it was not due to differences in door-to-appendectomy time. Insurance status and language barriers also did not lead to differential treatment among pediatric patients