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1. Progress Toward Generation of Spatially-Entangled Photon Pairs in a Few-Mode Fiber

   https://doi.org/10.1109/IPC47351.2020.9252314  

   Shamsshooli, Afshin ; Guo, Cheng ; Vasilyev, Michael ; Parmigiani, Francesca ; Li, Xiaoying ( October 2020 , IEEE Photonics Conference 2020)

   null (Ed.)

   Aiming at producing spatial-mode-entangled photon pairs in a few-mode fiber, we experimentally demonstrate generation of idler beam from a seed signal in a superposition of two fiber modes. For every signal mode superposition, we observe the indication of idler mode orthogonality to the signal mode. 

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2. An experimental study of volcanic tremor driven by magma wagging

   https://doi.org/10.1093/gji/ggab404  

   Dehghanniri, Vahid ; Jellinek, A. Mark ( November 2021 , Geophysical Journal International)

   Protracted episodes of 0.5–7 Hz pre-eruptive volcanic tremor (PVT) are common at active stratovolcanoes. Reliable links to processes related to magma movement consequently enable a potential to use properties of PVT as diagnostic eruptive precursors. A challenging feature of PVT is that generic spectral and amplitude properties of the signal evolve similarly, independent of widely varying volcano structures and conduit geometries on which most physical models rely. The ‘magma wagging’ model introduced in Jellinek & Bercovici (2011) and extended by Bercovici et al. (2013), Liao et al. and Liao & Bercovici (2018) makes progress because it depends on magma dynamics that are only weakly sensitive to volcano architecture: The flow of gas through a permeable foamy annulus of gas bubbles excites, modulates and maintains a wagging oscillation of a central magma column rising in an erupting conduit. ‘Magma wagging’ and resulting PVT are driven through an energy transfer from a ‘Bernoulli mode’ related to azimuthal variations in annular gas flow speeds. Consistent with observations, spectral and amplitude properties of PVT are predicted to evolve before an eruption as the width of the annulus decreases with increased gas fluxes. To confirm this critical Bernoulli-to-wagging energy transfer we use extensive experiments and restricted numerical simulations on wagging oscillations excited on analogue viscoelastic columns by annular air flows. We also explore sensitivities of the spatial and temporal characters of wagging to asymmetric annular air flows that are intractable in the existing magma wagging model and expected to occur in nature with spatial variations in annulus permeability. From high-resolution time-series of linear and orbital displacements of analogue column tops and time-series of axial deflections and accelerations of the column centre line, we characterize the excitation, evolution, and steady-state oscillations in unprecedented detail over a broad range of conditions. We show that the Bernoulli mode corresponds to the timescale for the buildup of axial elastic bending stresses in response to pressure variations related to air flows over the heights of columns. We identify three distinct wagging modes: (i) rotational (cf. Liao et al. 2018); (ii) mixed-mode and (iii) chaotic. Rotational modes are favoured for symmetric, high intensity forcing and a maximal delivery of mechanical energy to the fundamental magma wagging mode. Mixed-mode oscillations regimes are favoured for a symmetric, intermediate intensity forcing. Chaotic modes, involving the least efficient delivery of energy to the fundamental mode, occur for asymmetric forcing and where the intensity of imposed airflow is low. Numerical simulations also show that where forcing frequencies are comparable to a natural mode of free oscillation, power delivered by peripheral air flows is concentrated at the lowest frequency fundamental mode generally and spread among higher frequency natural modes where air pressure and column elastic forces are comparable. Our combined experimental and numerical results make qualitative predictions for the evolution of the character of volcanic tremor and its expression in seismic or infrasound arrays during natural events that is testable in field-based studies of PVT and syn-eruptive volcanic tremor.

    

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3. Demonstration of using two aperture pairs combined with multiple-mode receivers and MIMO signal processing for enhanced tolerance to turbulence and misalignment in a 10  Gbit/s QPSK FSO link

   https://doi.org/10.1364/OL.391120  

   Song, Haoqian ; Li, Long ; Pang, Kai ; Zhang, Runzhou ; Zou, Kaiheng ; Zhao, Zhe ; Du, Jing ; Song, Hao ; Liu, Cong ; Cao, Yinwen ; et al ( May 2020 , Optics Letters)

   We utilize aperture diversity combined with multiple-mode receivers and multiple-input-multiple-output (MIMO) digital signal processing (DSP) to demonstrate enhanced tolerance to atmospheric turbulence and spatial misalignment in a 10 Gbit/s quadrature-phase-shift-keyed (QPSK) free-space optical (FSO) link. Turbulence and misalignment could cause power coupling from the fundamental Gaussian mode into higher-order modes. Therefore, we detect power from multiple modes and use MIMO DSP to enhance the recovery of the original data. In our approach, (a) each of multiple transmitter apertures transmits a single fundamental Gaussian beam carrying the same data stream, (b) each of multiple receiver apertures detects the signals that are coupled from the fundamental Gaussian beams to multiple orbital angular momentum (OAM) modes, and (c) MIMO DSP is used to recover the data over multiple modes and receivers. Our simulation shows that the outage probability could be reduced from$><\#comment/>0.1$to$<<\#comment/>0.01$. Moreover, we experimentally demonstrate the scheme by transmitting two fundamental Gaussian beams carrying the same data stream and recovering the signals on OAM modes 0 and$+1$at each receiver aperture. We measure an up to$\sim <\#comment/>10\mathrm{d}\mathrm{B}$power-penalty reduction for a bit error rate (BER) at the 7% forward error correction limit for a 10 Gbit/s QPSK signal.

    

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4. Statistical Analysis of Pi2 Pulsations Observed by Van Allen Probes

   https://doi.org/10.1029/2022JA030674  

   Takahashi, Kazue ; Lysak, Robert ; Vellante, Massimo ( September 2022 , Journal of Geophysical Research: Space Physics)

   The relative importance of propagating and cavity mode waves remains an important question regarding the generation of Pi2 pulsations detected on the ground. To determine the wave mode, we statistically generate spatial maps of magnetospheric oscillations that are coherent with ground Pi2 pulsations. The magnetospheric observations were made by the two Van Allen Probes spacecraft over a 7‐year period. The amount and quality of the spacecraft data allow us to investigate the mode structure of Pi2 pulsation in ways that were not possible in previous studies. We use theHcomponent of low‐latitude ground Pi2 pulsations detected in the 22–02 magnetic local time (MLT) sector as the reference signal to generateL‐MLT and meridional maps of the coherence, amplitude, and phase of the magnetospheric electric and magnetic field components defined in magnetic field aligned coordinates. We identify low‐frequency and high‐frequency components in Pi2 power spectra, and we are able to determine the mode structure of the high‐frequency events for the first time. The maps demonstrate that the poloidal components have higher coherence than the toroidal components. For each frequency component, the maps of the poloidal components agree with those of cavity mode oscillations obtained in a numerical simulation using realistic models for the magnetospheric mass density and magnetic field. This result is conclusive evidence of the cavity mode nature of Pi2 pulsations detected in the inner magnetosphere.

    

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5. Ambulation Mode Classification of Individuals with Transfemoral Amputation through A-Mode Sonomyography and Convolutional Neural Networks

   https://doi.org/10.3390/s22239350  

   Murray, Rosemarie ; Mendez, Joel ; Gabert, Lukas ; Fey, Nicholas P. ; Liu, Honghai ; Lenzi, Tommaso ( December 2022 , Sensors)

   Many people struggle with mobility impairments due to lower limb amputations. To participate in society, they need to be able to walk on a wide variety of terrains, such as stairs, ramps, and level ground. Current lower limb powered prostheses require different control strategies for varying ambulation modes, and use data from mechanical sensors within the prosthesis to determine which ambulation mode the user is in. However, it can be challenging to distinguish between ambulation modes. Efforts have been made to improve classification accuracy by adding electromyography information, but this requires a large number of sensors, has a low signal-to-noise ratio, and cannot distinguish between superficial and deep muscle activations. An alternative sensing modality, A-mode ultrasound, can detect and distinguish between changes in superficial and deep muscles. It has also shown promising results in upper limb gesture classification. Despite these advantages, A-mode ultrasound has yet to be employed for lower limb activity classification. Here we show that A- mode ultrasound can classify ambulation mode with comparable, and in some cases, superior accuracy to mechanical sensing. In this study, seven transfemoral amputee subjects walked on an ambulation circuit while wearing A-mode ultrasound transducers, IMU sensors, and their passive prosthesis. The circuit consisted of sitting, standing, level-ground walking, ramp ascent, ramp descent, stair ascent, and stair descent, and a spatial–temporal convolutional network was trained to continuously classify these seven activities. Offline continuous classification with A-mode ultrasound alone was able to achieve an accuracy of 91.8±3.4%, compared with 93.8±3.0%, when using kinematic data alone. Combined kinematic and ultrasound produced 95.8±2.3% accuracy. This suggests that A-mode ultrasound provides additional useful information about the user’s gait beyond what is provided by mechanical sensors, and that it may be able to improve ambulation mode classification. By incorporating these sensors into powered prostheses, users may enjoy higher reliability for their prostheses, and more seamless transitions between ambulation modes. 

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