Class-based storage assignments for miniload AS/RS with open-rack structure

Automated Storage and Retrieval Systems (AS/RSs) are warehousing systems that are used for the storage and retrieval of products in both distribution and production environments. This paper presents an open-rack structure with unidirectional-upward mobile loads within the rack, for miniload AS/RS, in which the stacker crane is only used for the retrieval operations, and the storage operations are carried out by separate devices namely, storage platforms. Heuristics algorithms and models are developed for load shuffling and travel time of the storage platform, respectively. The well-known ABC approach is used to classify inventory items for determination of class-based storage assignments. Then the expected travel time of the proposed AS/RS is derived. The travel time model and the performance of proposed AS/RS are validated using Monte Carlo simulation and are compared with a conventional one. The results show that the open-rack AS/RS represents a higher performance and the proposed models are reliable for the design and analysis of this kind of AS/RS

The ion-induced charge-exchange X-ray emission of the Jovian Auroras: Magnetospheric or solar wind origin?

A new and more comprehensive model of charge-exchange induced X-ray emission, due to ions precipitating into the Jovian atmosphere near the poles, has been used to analyze spectral observations made by the Chandra X-ray Observatory. The model includes for the first time carbon ions, in addition to the oxygen and sulfur ions previously considered, in order to account for possible ion origins from both the solar wind and the Jovian magnetosphere. By comparing the model spectra with newly reprocessed Chandra observations, we conclude that carbon ion emission provides a negligible contribution, suggesting that solar wind ions are not responsible for the observed polar X-rays. In addition, results of the model fits to observations support the previously estimated seeding kinetic energies of the precipitating ions (~0.7-2 MeV/u), but infer a different relative sulfur to oxygen abundance ratio for these Chandra observations.Comment: 11 pages, 2 figures, 2 tables, submitted to ApJ Lette

Surface states and Rashba-type spin polarization in antiferromagnetic MnBi2_2Te4_4

The layered van der Waals antiferromagnet MnBi$_2$Te$_4$ has been predicted to combine the band ordering of archetypical topological insulators such as Bi$_2$Te$_3$ with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of MnBi$_2$Te$_4$(0001) single crystals by use of spin- and angle-resolved photoelectron spectroscopy experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure.Comment: Revised versio

Comparative Analysis and Variability of the Jovian X‐Ray Spectra Detected by the Chandra and XMM‐Newton Observatories

Expanding upon recent work, a more comprehensive spectral model based on charge exchange induced X‐ray emission by ions precipitating into the Jovian atmosphere is used to provide new understanding of the polar auroras. In conjunction with the Xspec spectral fitting software, the model is applied to analyze observations from both Chandra and XMM‐Newton by systematically varying the initial precipitating ion parameters to obtain the best fit model for the observed spectra. In addition to the oxygen and sulfur ions considered previously, carbon is included to discriminate between solar wind and Jovian magnetospheric ion origins, enabled by the use of extensive databases of both atomic collision cross sections and radiative transitions. On the basis of fits to all the Chandra observations, we find that carbon contributes negligibly to the observed polar X‐ray emission suggesting that the highly accelerated precipitating ions are of magnetospheric origin. Most of the XMM‐Newton fits also favor this conclusion with one exception that implies a possible carbon contribution. Comparison among all the spectra from these two observatories in light of the inferred initial energies and relative abundances of precipitating ions from the modeling show that they are significantly variable in time (observation date) and space (north and south polar X‐ray auroras).Astronom

Electron-phonon effects and transport in carbon nanotubes

We calculate the electron-phonon scattering and binding in semiconducting carbon nanotubes, within a tight binding model. The mobility is derived using a multi-band Boltzmann treatment. At high fields, the dominant scattering is inter-band scattering by LO phonons corresponding to the corners K of the graphene Brillouin zone. The drift velocity saturates at approximately half the graphene Fermi velocity. The calculated mobility as a function of temperature, electric field, and nanotube chirality are well reproduced by a simple interpolation formula. Polaronic binding give a band-gap renormalization of ~70 meV, an order of magnitude larger than expected. Coherence lengths can be quite long but are strongly energy dependent.Comment: 5 pages and 4 figure

First-principles calculations of the self-trapped exciton in crystalline NaCl

The atomic and electronic structure of the lowest triplet state of the off-center (C2v symmetry) self-trapped exciton (STE) in crystalline NaCl is calculated using the local-spin-density (LSDA) approximation. In addition, the Franck-Condon broadening of the luminescence peak and the a1g -> b3u absorption peak are calculated and compared to experiment. LSDA accurately predicts transition energies if the initial and final states are both localized or delocalized, but 1 eV discrepancies with experiment occur if one state is localized and the other is delocalized.Comment: 4 pages with 4 embeddded figure

X-rays Studies of the Solar System

X-ray observatories contribute fundamental advances in Solar System studies by probing Sun-object interactions, developing planet and satellite surface composition maps, probing global magnetospheric dynamics, and tracking astrochemical reactions. Despite these crucial results, the technological limitations of current X-ray instruments hinder the overall scope and impact for broader scientific application of X-ray observations both now and in the coming decade. Implementation of modern advances in X-ray optics will provide improvements in effective area, spatial resolution, and spectral resolution for future instruments. These improvements will usher in a truly transformative era of Solar System science through the study of X-ray emission.Comment: White paper submitted to Astro2020, the Astronomy and Astrophysics Decadal Surve

Direct observation of multivalent states and charge transfer in Ce-doped yttrium iron garnet thin films

Due to their large magneto-optic responses, rare-earth-doped yttrium iron garnets, Y3Fe5O12 (YIG), are highly regarded for their potential in photonics and magnonics. Here, we consider the case of Ce-doped YIG (Ce-YIG) thin films, in which substitutional Ce3+ ions are magnetic because of their 4f1 ground state. In order to elucidate the impact of Ce substitution on the magnetization of YIG, we have carried out soft x-ray spectroscopy measurements on Ce-YIG films. In particular, we have used the element specificity of x-ray magnetic circular dichroism to extract the individual magnetization curves linked to Ce and Fe ions. Our results show that Ce doping triggers a selective charge transfer from Ce to the Fe tetrahedral sites in the YIG structure. This, in turn, causes a disruption of the electronic and magnetic properties of the parent compound, reducing the exchange coupling between the Ce and Fe magnetic moments and causing atypical magnetic behavior. Our work is relevant for understanding magnetism in rare-earth-doped YIG and, eventually, may enable a quantitative evaluation of the magneto-optical properties of rare-earth incorporation into YIG

Franck-Condon-Broadened Angle-Resolved Photoemission Spectra Predicted in LaMnO3

The sudden photohole of least energy created in the photoemission process is a vibrationally excited state of a small polaron. Therefore the photoemission spectrum in LaMnO3 is predicted to have multiple Franck-Condon vibrational sidebands. This generates an intrinsic line broadening approximately 0.5 eV. The photoemission spectral function has two peaks whose central energies disperse with band width approximately 1.2 eV. Signatures of these phenomena are predicted to appear in angle-resolved photoemission spectra.Comment: Revtex file 4 pages and 3 figure

Multi-phonon Resonant Raman Scattering Predicted in LaMnO3 from the Franck-Condon Process via Self-Trapped Excitons

Resonant behavior of the Raman process is predicted when the laser frequency is close to the orbital excitation energy of LaMnO3 at 2 eV. The incident photon creates a vibrationally excited self-trapped ``orbiton'' state from the orbitally-ordered Jahn-Teller (JT) ground state. Trapping occurs by local oxygen rearrangement. Then the Franck-Condon mechanism activates multiphonon Raman scattering. The amplitude of the $n$-phonon process is first order in the electron-phonon coupling $g$. The resonance occurs {\it via} a dipole forbidden $d$ to $d$ transition. We previously suggested that this transition (also seen in optical reflectivity) becomes allowed because of asymmetric oxygen fluctuations. Here we calculate the magnitude of the corresponding matrix element using local spin-density functional theory. This calculation agrees to better than a factor of two with our previous value extracted from experiment. This allows us to calculate the absolute value of the Raman tensor for multiphonon scattering. Observation of this effect would be a direct confirmation of the importance of the JT electron-phonon term and the presence of self-trapped orbital excitons, or ``orbitons''.Comment: 8 pages and 3 embedded figures. The earlier short version is now replaced by a more complete paper with a slightly different title. This version includes a caculation by density-functional theory of the dipole matrix element for exciting the self-trapped orbital exciton which activates the multiphonon Raman signal