Physical deep learning with biologically inspired training method: gradient-free approach for physical hardware.

Ever-growing demand for artificial intelligence has motivated research on unconventional computation based on physical devices. While such computation devices mimic brain-inspired analog information processing, the learning procedures still rely on methods optimized for digital processing such as backpropagation, which is not suitable for physical implementation. Here, we present physical deep learning by extending a biologically inspired training algorithm called direct feedback alignment. Unlike the original algorithm, the proposed method is based on random projection with alternative nonlinear activation. Thus, we can train a physical neural network without knowledge about the physical system and its gradient. In addition, we can emulate the computation for this training on scalable physical hardware. We demonstrate the proof-of-concept using an optoelectronic recurrent neural network called deep reservoir computer. We confirmed the potential for accelerated computation with competitive performance on benchmarks. Our results provide practical solutions for the training and acceleration of neuromorphic computation.

Neonatal isoflurane exposure disturbs granule cell migration in the rat dentate gyrus.

It has been reported that neonatal isoflurane exposure causes behavioral abnormalities following neurodegeneration in animals and gamma-aminobutyric acid type A (GABAA) receptor activation during the synaptogenesis is considered to be one possible trigger. Additionally, the inhibitory effect of excitatory GABAA receptor signaling on the granule cell (GC) migration in the neonatal rat dentate gyrus (DG) was reported in a febrile seizure model. Then, we hypothesized that neonatal isoflurane exposure, which activates GABAA receptor, causes GC migration disturbances in the neonatal rat. Rat pups were injected with 5-bromo-2'-deoxyuridine (BrdU) and divided into five treatment groups, and double immunofluorescent staining targeting BrdU and homeobox prospero-like protein 1 (Prox1) was performed to examine the localization of BrdU/Prox1 colabeled cells, and then the GC migration was assessed. As a result, we found that the ectopic migration of GC after 2% isoflurane exposure on postnatal day 7 significantly increased after P21. The number of hilar ectopic GCs was influenced by the concentration of isoflurane and the exposure day but not by carbon dioxide exposure. Our main finding is that neonatal isoflurane anesthesia disturbs the migration of GCs in the rat DG, which may be one possible mechanism underlying the neurotoxicity following neonatal isoflurane anesthesia.

Neural Schrödinger Equation: Physical Law as Deep Neural Network.

We show a new family of neural networks based on the Schrödinger equation (SE-NET). In this analogy, the trainable weights of the neural networks correspond to the physical quantities of the Schrödinger equation. These physical quantities can be trained using the complex-valued adjoint method. Since the propagation of the SE-NET can be described by the evolution of physical systems, its outputs can be computed by using a physical solver. The trained network is transferable to actual optical systems. As a demonstration, we implemented the SE-NET with the Crank-Nicolson finite difference method on Pytorch. From the results of numerical simulations, we found that the performance of the SE-NET becomes better when the SE-NET becomes wider and deeper. However, the training of the SE-NET was unstable due to gradient explosions when SE-NET becomes deeper. Therefore, we also introduced phase-only training, which only updates the phase of the potential field (refractive index) in the Schrödinger equation. This enables stable training even for the deep SE-NET model because the unitarity of the system is kept under the training. In addition, the SE-NET enables a joint optimization of physical structures and digital neural networks. As a demonstration, we performed a numerical demonstration of end-to-end machine learning (ML) with an optical frontend toward a compact spectrometer. Our results extend the application field of ML to hybrid physical-digital optimizations.

Optical frequency distribution using laser repeater stations with planar lightwave circuits.

We report a cascaded optical fiber link which connects laboratories in RIKEN, the University of Tokyo, and NTT within a 100-km region using a transfer light at 1397 nm, a subharmonic of the Sr clock frequency. The multiple cascaded link employing several laser repeater stations benefits from a wide feedback bandwidth for fiber noise compensation, which allows constructing optical lattice clock networks based on the master-slave configuration. We developed the laser repeater stations based on planar lightwave circuits to significantly reduce the interferometer noise for improved link stability. We implemented a 240-km-long cascaded link in a UTokyo-NTT-UTokyo loop using light sent from RIKEN via a 30-km-long link. In environments with large fiber noise, the link instability is 3 × 10-16 at an averaging time of 1 s and reaches 1 × 10-18 at 2,600 s.

Compound-eye metasurface optics enabling a high-sensitivity, ultra-thin polarization camera.

Polarization imaging is key for various applications ranging from biology to machine vision because it can capture valuable optical information about imaged environments, which is usually absent in intensity and spectral content. Conventional polarization cameras rely on a traditional single-eye imaging system with rotating polarizers, cascaded optics, or micropolarizer-patterned image sensors. These cameras, however, have two common issues. The first is low sensitivity resulting from the limited light utilization efficiency of absorptive polarizers or cascaded optics. The other is the difficulty in device miniaturization due to the fact that these devices require at least an optical-path length equivalent to the lens's focal length. Here, we propose a polarization imaging system based on compound-eye metasurface optics and show how it enables the creation of a high-sensitivity, ultra-thin polarization camera. Our imaging system is composed of a typical image sensor and single metasurface layer for forming a vast number of images while sorting the polarization bases. Since this system is based on a filter-free, computational imaging scheme while dramatically reducing the optical-path length required for imaging, it overcomes both efficiency and size limitations of conventional polarization cameras. As a proof of concept, we demonstrated that our system improves the amount of detected light by a factor of ∼2, while reducing device thickness to ∼1/10 that of the most prevalent polarization cameras. Such a sensitive, compact, and passive device could pave the way toward the widespread adoption of polarization imaging in applications in which available light is limited and strict size constraints exist.

Net-400-Gbps PS-PAM transmission using integrated AMUX-MZM.

Simple high-speed optical transmission technologies are desired for use in intra-and inter-datacenter networks. In this study, we demonstrate simple single-carrier intensity-modulated direct-detection (IMDD) transmissions at a net data rate of 400 Gbps (516.7 Gbps gross) over 20 km with a compact transmitter subassembly. The subassembly consists of a 2:1 analog multiplexer (AMUX) and an InP Mach-Zehnder modulator (MZM) placed close to each other and connected via wires. We employed 162-Gbaud single-carrier probabilistically shaped pulsed amplitude modulation (PS-PAM). The baseband signals with a bandwidth of around 81 GHz to drive the MZM were generated by a super-digital-to-analog converter (super-DAC) consisting of two sub-DACs and the AMUX. Digital nonlinear pre-distortion enabled us to transmit the signals with normalized generalized mutual information (NGMI) larger than the threshold of a soft-decision forward error correction (SD-FEC) code of 0.857. Truncation of the PS-PAM symbol distribution further enhanced performance. To the best of our knowledge, this is the first net-400-Gbps single-carrier IMDD transmission using a compact transmitter subassembly.

Isoflurane induces c-Fos expression in the area postrema of the rat.

INTRODUCTION: Volatile anesthetics are speculated to cause postoperative nausea and vomiting via stimulation of the chemoreceptor trigger zone (CTZ). However, the precise mechanism underlying the emetic action of these drugs is not well understood. In this study, we assessed whether isoflurane induced the expression of c-Fos, a neuronal activation marker, in the area postrema (AP), the locus of the CTZ, in rats, which do not have vomiting action. MATERIALS AND METHODS: Male rats were exposed to 1.3% isoflurane for 0-240 min, or to various concentrations of isoflurane (0, 1.3%, or 2.6%) for 120 min. Finally, the rats were exposed to 1.3% isoflurane for 120 min after ondansetron administration. After the treatments, immunohistochemistry of the rat AP was performed using c-Fos antibody staining. RESULTS: One-way analysis of variance showed that isoflurane exposure significantly increased c-Fos expression in the AP; however, the rats pretreated with 4 mg/kg ondansetron showed significantly decreased c-Fos expression. Moreover, we evaluated the effect of the anesthetic on inducing pica in the rats, and found that kaolin intake was not influenced by isoflurane exposure. CONCLUSION: Overall, these results suggest that isoflurane activates AP neurons and may be involved in the emetic mechanism of isoflurane. This study further suggests the feasibility of using rats as a model for studying emetic mechanisms of drugs, despite their lack of vomit action.

Demonstration of energy-saving membrane bioreactor (MBR) systems.

Membrane bioreactors (MBRs) have the advantages of achieving excellent effluent quality, a small footprint and smooth operation and maintenance. On the other hand, its high energy consumption remains a critical challenge for MBR application. Japan Sewage Works Agency has conducted a series of joint researches with several private companies since 2012 and developed four kinds of energy-saving MBR systems. Based on the results of long-term pilot-scale demonstrations, specific energy consumption (SEC) per unit treated effluent volume was calculated for each MBR system, resulting in all systems achieving SEC of 0.4 kWh/m3 or less. To meet an additional requirement for expanding MBR application, it is also necessary to establish the applicability of MBR systems to combined sewer systems, suffering from occasional inflow fluctuation caused by rainfall. The capability of temporary higher flux operation during and after rainy weather was also demonstrated with three of the four developed systems.

Simulating the vibrational quantum dynamics of molecules using photonics.

Advances in control techniques for vibrational quantum states in molecules present new challenges for modelling such systems, which could be amenable to quantum simulation methods. Here, by exploiting a natural mapping between vibrations in molecules and photons in waveguides, we demonstrate a reprogrammable photonic chip as a versatile simulation platform for a range of quantum dynamic behaviour in different molecules. We begin by simulating the time evolution of vibrational excitations in the harmonic approximation for several four-atom molecules, including H2CS, SO3, HNCO, HFHF, N4 and P4. We then simulate coherent and dephased energy transport in the simplest model of the peptide bond in proteins-N-methylacetamide-and simulate thermal relaxation and the effect of anharmonicities in H2O. Finally, we use multi-photon statistics with a feedback control algorithm to iteratively identify quantum states that increase a particular dissociation pathway of NH3. These methods point to powerful new simulation tools for molecular quantum dynamics and the field of femtochemistry.

Influence of nitrous oxide on granule cell migration in the dentate gyrus of the neonatal rat.

For several decades, the neurotoxicities of anesthetics to the developing brain have been reported by many researchers focusing on various phenomena such as apoptosis, neurodegeneration, electrophysiological aberrations, and behavioral abnormalities. According to these reports, signals via N-methyl-D-aspartate receptors (NMDA-r) and/or γ-aminobutyric acid type A receptors (GABAA-r) are implicated in the anesthetic neurotoxicity. On the other hand, during brain development, NMDA-r and GABAA-r are also recognized to play primary roles in neural cell migration. Therefore, anesthetics exposed in this period may influence the neural cell migration of neonates, and increase the number of hilar ectopic granule cells, which are reported to be a cause of continuous neurological deficits. To examine this hypothesis, we investigated immunohistochemically granule cell distribution in the hippocampal dentate gyrus of Wistar/ST rats after nitrous oxide (N2O) exposure. At postnatal day (P) 6, 5-bromo-2'-deoxyuridine (BrdU) was administered to label newly generated cells. Then, rats were divided into groups (n = 6 each group), exposed to 50% N2O at P7, and evaluated at P21. As a result, we found that ectopic ratios (ratio of hilar/total granule cells generated at P6) were decreased in rats at P21 compared with those at P7, and increased in N2O exposed rats for over 120 min compared with the other groups. These results suggest that 50% N2O exposure for over 120 min increases the ratios of ectopic granule cells in the rat dentate gyrus.

Plantar injection of formalin in rats reduces the expression of a potassium chroride cotransporter KCC2 in the spinal cord and a kinase inhibitor suppresses this reduction.

Brain-derived neurotrophic factor (BDNF) is released from activated microglia during neuropathic pain and is hypothesized to downregulate the expression of the potassium chloride cotransporter 2 (KCC2) via the TrkB receptor. Previous studies reported that KCC2 is downregulated 5 min after the plantar injection of formalin in rats; however, the mechanism behind this decrease in KCC2 expression during acute inflammatory pain remains unknown. In this study, we determined whether the TrkB receptor contributes to the expression of KCC2 during the acute pain. Five minutes after the plantar injection of formalin in rats, the ratio of KCC2-immunoreactive area in layer II of the spinal cord significantly decreased on the stimulated side compared to the unaffected side. On the other hand, this response was inhibited by the injection of a kinase inhibitor, K252a, in the subarachnoid space 15 min before the formalin injection. These findings suggest that in acute pain, the TrkB receptor may contribute to the decrease in the expression of KCC2.

[Comparison of the Effect of Periarticular Infiltration Analgesia versus Sciatic Nerve Block for Total Knee Arthroplasty].

BACKGROUND: Sciatic nerve block (SNB) is widely used as a supplemental analgesia after total knee arthroplasty (TKA) combined with femoral nerve block (FNB). Despite its effectiveness, SNB often causes peroneal nerve paralysis, which makes it difficult to detect peroneal nerve injury by surgical process. Recently, periarticular infiltration analgesia (PIA) is reported that it provides analgesia without peroneal nerve paralysis. We conducted a retrospective analysis to compare the effectiveness of SNB and PIA. METHODS: This study was approved by the local institutional ethics committee; 17 patients undergoing TKA under general anesthesia with continuous femoral nerve block were enrolled in the study. All patients received continuous FNB. Nine patients received sciatic nerve block successively, while 8 patients received PIA around the time of insertion of artificial joint. Primary outcome measure was the frequency of peroneal nerve paralysis when the patients woke up. Secondary outcome measures included numerical rating scale (NRS) until postoperative day 3. RESULTS: While there were 6 patients who had peroneal nerve paralysis in the SNB group, none of them had it in the PIA group (P = 0.009). There were no significant differences of the NRSs between the two groups. CONCLUSIONS: PIA provided sufficient analgesia after TKA without peroneal nerve paralysis.

Changes in bacterial community structure in a full-scale membrane bioreactor for municipal wastewater treatment.

This study investigated changes in the structure and metabolic capabilities of the bacterial community in a full-scale membrane bioreactor (MBR) treating municipal wastewater. Microbial monitoring was also conducted for a parallel-running conventional activated sludge (CAS) process treating the same influent. The mixed-liquor suspended solid concentration in the MBR reached a steady-state on day 73 after the start-up. Then the MBR maintained higher rates of removal of organic compounds and nitrogen than the CAS process did. Terminal restriction fragment length polymorphism analysis revealed that the bacterial community structure in the MBR was similar to that in the CAS process at the start-up, but it became very different from that in the CAS process in the steady state. The bacterial community structure of the MBR continued to change dynamically even after 20 months of the steady-state operation, while that of the CAS process was maintained in a stable condition. By contrast, Biolog assay revealed that the carbon source utilization potential of the MBR resembled that of the CAS process as a whole, although it declined transiently. Overall, the results indicate that the bacterial community of the MBR has flexibility in terms of its phylogenetic structure and metabolic activity to maintain the high wastewater treatment capability.

Linearity improvement of high-speed avalanche photodiodes using thin depleted absorber operating with higher order modulation format.

We present an avalanche photodiode (APD) with high-speed, high-responsivity and high-linearity operation to cope with higher order modulation format, such as pulse-amplitude modulation (PAM). A hybrid absorber configuration with thin depleted region which we newly employed successfully eliminates the space charge effect in the APD while maintaining high responsivity and operating speed. The fabricated APD shows an improved optical-input-electrical-output linearity for an optical input power over -8 dBm, and an optical receiver with this APD achieves both an error-free operation with a KP4 FEC and a high sensitivity of -17 dBm against a 28-Gbaud PAM4 signal.

QUANTUM OPTICS. Universal linear optics.

Linear optics underpins fundamental tests of quantum mechanics and quantum technologies. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up to the size of that circuit. Our six-mode universal system consists of a cascade of 15 Mach-Zehnder interferometers with 30 thermo-optic phase shifters integrated into a single photonic chip that is electrically and optically interfaced for arbitrary setting of all phase shifters, input of up to six photons, and their measurement with a 12-single-photon detector system. We programmed this system to implement heralded quantum logic and entangling gates, boson sampling with verification tests, and six-dimensional complex Hadamards. We implemented 100 Haar random unitaries with an average fidelity of 0.999 ± 0.001. Our system can be rapidly reprogrammed to implement these and any other linear optical protocol, pointing the way to applications across fundamental science and quantum technologies.

Dexmedetomidine suppresses long-term potentiation in the hippocampal CA1 field of anesthetized rats.

PURPOSE: The aim of this study was to evaluate the effect of dexmedetomidine (DEX) on hippocampal synaptic activity in vivo. METHODS: The adult rats used for this study received a intraperitoneal bolus injection of 3, 10, 30, or 100 µg/kg of DEX or an equivalent volume of saline. Electrophysiological recording of the hippocampal CA1 region was initiated 20 min after drug administration. The results are expressed as the percentages of the population spike amplitude measured just before high-frequency stimulation (HFS). The electrophysiological data were analyzed with an area under the curve (AUC) of 10-60 min after HFS. Moreover, to investigate the sedative dose of DEX in rats, we recorded the duration of loss of spontaneous movement after the administration of each dose of DEX. RESULTS: Intraperitoneal administration of DEX at doses of 30 and 100 µg/kg induced a range of sedative effects. The AUC measurements were significantly lower in the 30 and 100 µg/kg groups than in those injected with vehicle (vehicle: 8.81 ± 0.49, n = 7; DEX 30 µg/kg: 6.02 ± 0.99, n = 6; DEX 100 µg/kg: 5.10 ± 0.43, n = 5; P < 0.05). CONCLUSION: The results of our in vivo study reveal that sedative doses of DEX impaired the induction of hippocampal long-term potentiation (LTP). These findings may signify a causal link between DEX-induced sedative action and hippocampal LTP suppression, providing a better understanding of the mechanisms underlying the DEX-induced sedative and/or amnestic effect.

[Anesthetic and perioperative management of a patient with uncontrolled thyrotoxicosis undergoing coronary artery bypass grafting surgery].

Uncontrolled hyperthyroidism is a risk factor of perioperative thyrotoxic crisis. We report a case of a 61-year-old woman with thyrotoxicosis diagnosed with unstable angina pectoris. She needed to have an early scheduled coronay artery bypass grafting surgery, because percutaneous intervention for the left main coronary artery in support of intra-aortic balloon pumping (IABP) resulted in failure. Tachycardia and hyperthermia were observed at admission to the ICU, and hemodynamic parameters suggested high-output heart failure. Preoperative management using antithyroid drug, inorganic iodine, corticosteroid and propranolol stabilized her hemodynamic condition, and then CABG was performed on ICU day 3. Intraoperative and postoperative use of landiolol, a short acting beta blocker, was useful for maintaining hemodynamic stability. Surgery was uneventfully completed and she was extubated on postoperative day 1 following IABP withdrawal. Appropriate preoperative management and perioperative use of the short acting beta blocker were useful for management of the patient with uncontrolled hyperthyroid state.

Neonatal exposure to sevoflurane causes significant suppression of hippocampal long-term potentiation in postgrowth rats.

BACKGROUND: The inhaled anesthetic sevoflurane is commonly used for neonates in the clinical setting. Recent studies have indicated that exposure of neonatal rodents to sevoflurane causes acute widespread neurodegeneration and long-lasting neurocognitive dysfunction. Although acute toxic effects of sevoflurane on cellular viability in the hippocampus have been reported in some studies, little is known about the effects of neonatal sevoflurane exposure on long-term hippocampal synaptic plasticity, which has been implicated in the processes of learning and memory formation. Our study is the first to examine the long-term electrophysiological impact of neonatal exposure to a clinically relevant concentration of sevoflurane. METHODS: On postnatal day 7, rats were exposed to sevoflurane (1% or 2% for 2 hours) with oxygen. To eliminate the influence of blood gas abnormalities caused by sevoflurane-induced respiratory suppression, a group of rats were exposed to a high concentration of carbon dioxide (8% for 2 hours) to duplicate respiratory disturbances caused by 2% sevoflurane exposure. RESULTS: Exposure of neonatal rats to 2% sevoflurane for 2 hours caused significant suppression of long-term potentiation (LTP) induction in the postgrowth period. There was no significant difference between the control group and the CO2-exposed group in LTP induction, indicating that sevoflurane-induced LTP suppression was not caused by blood gas abnormalities. CONCLUSION: Our present findings indicate that neonatal exposure to sevoflurane at a higher concentration can cause alterations in the hippocampal synaptic plasticity that persists into adulthood.

Neonatal exposure to high concentration of carbon dioxide produces persistent learning deficits with impaired hippocampal synaptic plasticity.

Although respiratory complications with blood gas abnormalities contribute significantly to neurodevelopment in the immature brain, little is known about the mechanisms via which blood gas abnormalities, such as hypoxic hypercapnia, impair neurocognitive outcomes. To investigate the possible long-term consequences of neonatal exposure to hypoxic hypercapnia regarding learning ability, we investigated the effect of neonatal hypoxic hypercapnia on later functions in the hippocampus, which is a structure that has been implicated in many learning and memory processes. Neonatal rat pups (postnatal day 7; P7) were exposed to a high concentration of carbon dioxide (CO2; 13%) for 2 or 4h. Exposure to CO2 in P7 rat pups caused blood gas abnormalities, including hypercapnia, hypoxia, and acidosis, and disrupted later learning acquisition, as assessed in 10-week-old adult rats subjected to a Morris water maze test. Induction of long-term potentiation (LTP) in the synapses of the hippocampal CA1 area was also impaired, whereas the paired-pulse responses of population spikes exhibited a significant increase, in CO2-exposed rats, suggesting decreased recurrent inhibition in the hippocampus. Such long-lasting modifications in hippocampal synaptic plasticity may contribute to the learning impairments associated with perinatal hypoxic hypercapnia and acidosis.

Silica-based, compact and variable-optical-attenuator integrated coherent receiver with stable optoelectronic coupling system.

We demonstrate a compact and variable-optical-attenuator (VOA) integrated coherent receiver with a silica-based planar lightwave circuit (PLC). To realize the compact receiver, we integrate a VOA in a single PLC chip with polarization beam splitters and optical 90-degree hybrids, and employ a stable optoelectronic coupling system consisting of micro lens arrays and photodiode (PD) subcarriers with high-speed right-angled signal lines. We integrate a VOA and a coherent receiver in a 27x40x6 mm package, and successfully demodulate a 128-Gbit/s polarization division multiplexed (PDM) quadrature phase shift keying (QPSK) signal with a VOA-assisted wide dynamic range of more than 30 dB.