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Three-component Bose-Einstein condensates and wetting without walls
No full textFrom Gross-Pitaevskii (GP) theory for ultracold gases it is predicted that phase-segregated three-component Bose-Einstein condensates (BEC) feature a wetting phase diagram that depends only on atomic masses and scattering lengths. This is unique in theories of surface and interfacial phase transitions and provides a new opportunity for experimental observation of wetting phenomena in BEC mixtures. Previous GP theory for two-component BEC relied on an {\it ad hoc} optical wall boundary condition, on which the character and location of the wetting phase transitions depend sensitively. This boundary condition dependence is eliminated by adding a third component and treating the three phases on equal footing. An unequivocal wetting phase diagram is captured, with phase boundaries calculated analytically using an extension of the established double-parabola approximation
Social capital in academia:Measuring researchers’ collaboration habits versus preferences
No full textMany studies concerning social capital in academia have used social network theory and social network analysis as an approach. Social network analysis focuses on a boundary set of actors in a network and what it reveals as an outcome of social capital. However, social capital is also a precursor or catalyst for cooperative work. Here, we investigate researchers’ perceptions of social capital, based on the hypothesis that what academics do when they collaborate may not relate to what they actually prefer. We have piloted a questionnaire-survey to examine this, focusing on the goal-seeking behavior of publishing new research. Data were collected from 1,092 academics, across 6 faculties at the University of Copenhagen: Health and Medical Science, Science, Social Sciences, Humanities, Law, and Theology. The survey of collaboration habits first revealed significant differences at the level of gender, academic position, years active in publishing, and faculty. Collaboration preferences, interpreted from social capital theory, were also measured according to three interrelated dimensions – i.e., cognitive, relational, and structural. Survey respondents tended to prefer the cognitive-relational aspects of collaboration (i.e., reciprocity and obligation; shared understandings), over certain structural determinants (i.e., linking to networks). Few habits and preferences correlated and did not correlate strongly. Amongst the researchers that indicated a preference for bridging networks (i.e., working with people who have different types of expertise), few confirmed this as a collaboration habit, particularly with experts from organisations outside academia (i.e., the business/public sector)
The divide expand consolidate scheme for unrestricted second order Møller-Plesset perturbation theory ground state energies
No full textThe linear scaling divide-expand-consolidate (DEC) framework is expanded to include unrestricted Hartree-Fock references. By partitioning the orbital space and employing local molecular orbitals, the full molecular calculation can be performed as independent calculations on individual fragments, making the method well-suited for massively parallel implementations. This approach also incorporates error control through the fragment optimization threshold (FOT), which maintains precision and consistency throughout the calculations. A benchmark was conducted for correlation energies of open-shell systems and the relative energies of both open- and closed-shell molecules at the MP2 level of theory. The full calculation result is achieved as the FOT approaches zero. For correlation energies, an FOT of 10−3 is sufficient to recover over 98% of the full result in all cases. However, for relative energies and the electronic energy component of oxidation potentials, a tighter FOT of 10−4 is required to keep the DEC error within 10% for both open- and closed-shell molecules. This is likely due to a lack of systematic error cancellation for the molecules with vastly different chemical natures. Therefore, for accurate relative energies, the FOT should be an order of magnitude lower, and additional caution is needed, particularly for large systems. The DEC method extension to unrestricted references maintains favorable features of linear scaling and can be implemented in a massively parallel algorithm to calculate correlation energies for large open-shell systems.</p
Cluster perturbation theory. XII. Parallel implementation of variational excitation energy series for the coupled cluster singles and doubles model
No full textAn efficient implementation of the variational cluster perturbation excitation energy series through fifth order is described. The series has the coupled cluster singles excitation energies as zeroth order and targets the coupled cluster singles and doubles (CCSD) excitation energies. The implementation utilizes the resolution of the identity approximation for the two-electron integrals. The perturbation series uses the 2n + 1/2n + 2 rules to eliminate all parameters higher than second order. The computational efficiency is illustrated by performing excitation energy calculations on a single node for systems with up to 1000 basis functions and comparing with CCSD calculations. Using the hybrid parallel open multiprocessing/message-passing interface implementation with graphics processing unit offloading, fifth-order cluster perturbation excitation energies for systems with 1750 basis functions can be calculated in 8 h using 20 nodes on the Frontier supercomputer at the Oak Ridge National Laboratory. A benchmark of 131 excitation energies for a diverse set of molecules is presented. For the fourth and fifth order models, a few prominent outliers are present. We demonstrate how these cases may be identified using a simple diagnostic, with the remaining values being indistinguishable from CCSD excitation energies in practice.</p
Forward ray tracing and hot spots in Kerr spacetime
No full textHotspots, often characterized as pointlike emissions, frequently appear near black holes with significantly enhanced luminosity compared to the surrounding accretion flow. Notably, such hotspots are regularly observed near the black hole at the center of the Milky Way. Light rays emitted from these sources follow complex trajectories around the black hole before reaching distinct locations on the observer's image plane. Precisely resolving both direct emissions and their higher-order images - despite the latter's intensity suppression - is essential for extracting detailed spacetime information, including the black hole's mass, spin, and inclination angle. To improve the accuracy and efficiency of hotspot modeling, we develop a forward ray tracing method based on the analytic integral solution of Kerr geodesics, leveraging conserved quantities. Our approach traces geodesics from a given emission point near the black hole to a distant observer, effectively capturing multiple images with a tailored parametrization scheme for root-finding. By perturbing these geodesics, we map finite-size emissions to distinct regions on the image plane, enabling the quantification of image shapes and amplification rates. This method not only enhances the identification of strongly lensed photons from black holes but also enables efficient spacetime tomography and hotspot localization, leveraging observations from the Event Horizon Telescope and its upcoming next-generation upgrades.</p
Comparative genomics and phenotypes of <i>Oenococcus alcoholitolerans</i> and <i>Oenococcus oeni</i>, two sister species adapted to ethanol-rich environments
No full textFrom the genus Oenococcus, the most studied species is O. oeni due to its role in malolactic fermentation (MLF) during the winemaking process. In 2014, a new member of the genus —alongside O. kitaharae and O. sicerae— was discovered: O. alcoholitolerans. Whereas O. oeni is found in oenological matrixes, from grapes to wine, O. alcoholitolerans is found in cachaça residues and bioethanol fermentation. Though these ecological niches are different, they share the presence of high ethanol concentrations, which could be related to their evolutionary adaptation. This study provides the first sequenced and circularized genome of O. alcoholitolerans (UFRJ-M7), which was used for a comparative genomic analysis with the species O. oeni. In addition, the physiological traits of both species were compared regarding malolactic fermentation performance and survival in conditions of increasing ethanol and acid. The results showed great genetic differences in genes related to defence mechanisms, transcriptional factors, and some aspects of metabolism, such as sugar catabolism, purine/pyrimidine, coenzyme and vitamin biosynthesis. All these variations can be attributed to the specific adaptations of O. oeni and O. alcoholitolerans to their respective ecological niches. Notably, O. alcoholitolerans has not been detected in analyzed wine samples. This observation aligns with laboratory-based physiological tests, which demonstrated that the combined stress of ethanol and low pH prevented the survival of O. alcoholitolerans, despite its ability to carry out the MLF
