Non-local Correlation Effects in Fermionic Many-Body Systems: Overcoming the Non-causality Problem

Motivated by the intriguing physics of quasi-2d fermionic systems, such as high-temperature superconducting oxides, layered transition metal chalcogenides or surface or interface systems, the development of many-body computational methods geared at including both local and non-local electronic correlations has become a rapidly evolving field. It has been realized, however, that the success of such methods can be hampered by the emergence of noncausal features in the effective or observable quantities involved. Here, we present a new approach of extending local many-body techniques such as dynamical mean field theory (DMFT) to nonlocal correlations, which preserves causality and has a physically intuitive interpretation. Our strategy has implications for the general class of DMFT-inspired many-body methods, and can be adapted to cluster, dual boson or dual fermion techniques with minimal effort.Comment: 6 pages + 5 pages supplemental materia

Charge density functional plus UU calculation of lacunar spinel GaM4_4Se8_8 (M = Nb, Mo, Ta, and W)

Charge density functional plus $U$ calculations are carried out to examine the validity of molecular $J_\text{eff}$=1/2 and 3/2 state in lacunar spinel GaM$_4$X$_8$ (M = Nb, Mo, Ta, and W). With LDA (spin-unpolarized local density approximation)$+U$, which has recently been suggested as the more desirable choice than LSDA (local spin density approximation)$+U$, we examine the band structure in comparison with the previous prediction based on the spin-polarized version of functional and with the prototypical $J_\text{eff}$=1/2 material Sr$_2$IrO$_4$. It is found that the previously suggested $J_\text{eff}$=1/2 and 3/2 band characters remain valid still in LDA$+U$ calculations while the use of charge-only density causes some minor differences. Our result provides the further support for the novel molecular $J_\text{eff}$ state in this series of materials, which can hopefully motivate the future exploration toward its verification and the further search for new functionalities

Multiphoton imaging for morphometry of the sandwich-beam structure of the human stapedial annular ligament

Background The annular ligament of the human stapes constitutes a compliant connection between the stapes footplate and the peripheral cochlear wall at the oval window. The cross section of the human annular ligament is characterized by a three-layered structure, which resembles a sandwich-shaped composite structure. As accurate and precise descriptions of the middle-ear behavior are constrained by lack of information on the complex geometry of the annular ligament, this study aims to obtain comprehensive geometrical data of the annular ligament via multiphoton imaging. Methods The region of interest containing the stapes and annular ligament was harvested from a fresh-frozen human temporal bone of a 46-years old female. Multiphoton imaging of the unstained sample was performed by detecting the second-harmonic generation of collagen and the autofluorescence of elastin, which are constituents of the annular ligament. The multiphoton scans were conducted on the middle-ear side and cochlear side of the annular ligament to obtain accurate images of the face layers on both sides. The face layers of the annular ligament were manually segmented on both multiphoton scans, and then registered to high-resolution μCT images. Results Multiphoton scans of the annular ligament revealed 1) relatively large thickness of the core layer compared to the face layers, 2) asymmetric geometry of the face layers between the middle-ear side and cochlear side, and variation of their thickness and width along the footplate boundary, 3) divergent relative alignment of the two face layers, and 4) different fiber composition of the face layers along the boundary with a collagen-reinforcement near the anterior pole on the middle-ear side. Conclusion and outlook Multiphoton microscopy is a feasible approach to obtain the detailed three-dimensional features of the human stapedial annular ligament along its full boundary. The detailed description of the sandwich-shaped structures of the annular ligament is expected to contribute to modeling of the human middle ear for precise simulation of middle-ear behavior. Further, established methodology in this study may be applicable to imaging of other middle-ear structures. Keywords Annular ligament Stapes Multiphoton microscopy Two-photon microscopy Face layer Core laye

Performance evaluation of a novel piezoelectric subcutaneous bone conduction device

Objectives Evaluation of the transfer function efficiency of a newly-developed piezo-electric actuator for active subcutaneous bone conduction hearing aid. Methods The experiments were conducted on four Thiel embalmed whole head cadaver specimens. A novel actuator based on piezo-electric transduction (PZTA), part of a subcutaneous bone conduction hearing aid device, was sequentially implanted on three locations: 1) Immediately posterior to pinna; 2) 50–60 mm posterior to pinna, approximately the same distance as between the BAHA (bone anchored hearing aid) location and the ear canal, but the same horizontal level as location 1; 3) the traditional BAHA location. Using a single point 3-dimensional laser Doppler vibrometer (LDV) system, three types of motion measurements were performed at the cochlear promontory for each stimulation location: 1) ipsilateral side, 2) contralateral side, 3) measurements 1 and 2 were repeated after mastoidectomy on the ipsilateral side. Results On average, stimulation at locations 1 and 2 show a trend for higher promontory motion relative to location 3 (BAHA location) above 1 kHz. Stimulation at location 1 had an average improvement of 1–6 dB at 2–4 kHz, and 1–18 dB at 6–8 kHz. The spatial composition of the motion showed significant contributions from both in-plane and out-of-plane (along ear canal) motion components, with in-plane components being dominant at mid and high frequencies for locations 2 and 3. Stimulation at locations 1 and 3 produced similar transcranial attenuation at mid frequencies (0.6–4 kHz), with a potential trend of higher attenuation (seen in 3 or the 4 samples) for location 1 at higher frequencies (>4 kHz). The mastoidectomy affected negatively mostly the high frequencies (6–8 kHz) for stimulation at location 1, with no significant change for location 3. Conclusion The sound transfer function efficacy of a novel subcutaneous bone conduction device has been quantified, and the influence of stimulation location and mastoidectomy have been analyzed based on promontory motion in Thiel-preserved cadaver heads