229 research outputs found

    Design and characterization of all-cryogenic low phase-noise sapphire K-band oscillator for sattelite communication

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    An all-cryogenic oscillator consisting of a frequency-tunable sapphire resonator, a high-temperature superconducting filter and a pseudomorphic high electron-mobility transistor amplifier was designed for the K-band frequency range and investigated. Due to the high quality factor of the resonator above 1000 000 and the low amplifier phase noise of approximately -133 dBc/Hz at a frequency offset of 1kHz from the carrier, we have achieved oscillator phase-noise values superior to quartz-stabilized oscillators at the same carrier frequency for offset frequencies higher than 100 Hz. In addition to, low phase noise, our prototype oscillator possesses mechanical and electrical frequency tunability. We have implemented a two-step electrical tuning arrangement consisting of a varactor phase shifter integrated within the amplifier circuit (fine tuning by 5'kHz) and a dielectric plunger moved by a piezomechanical transducer inside the resonator housing (course tuning by 50 kHz). This tuning range is sufficient for phase locking and for electronic compensation of temperature drifts occurring during operation of the device employing a miniaturized closed-cycle Stirling-type cryocooler

    Knowledge Distillation Applied to Optical Channel Equalization: Solving the Parallelization Problem of Recurrent Connection

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    To circumvent the non-parallelizability of recurrent neural network-based equalizers, we propose knowledge distillation to recast the RNN into a parallelizable feedforward structure. The latter shows 38\% latency decrease, while impacting the Q-factor by only 0.5dB.Comment: Paper Accepted for Oral presentation - OFC 2023 (Optical Fiber Communication Conference

    A Ca2+-activated potassium channel (BKCa) in Leydig cells is involved in testosterone production

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    Previously, we found that human steroid-producing ovarian granulosa cells express all major types of Ca2+-activated potassium channels (KCa), including BKCa, IK and SKs (Traut et al., RB&E, 2009), and that modulation of the activity of these channels resulted in alteration of steroid production. In the male gonad Leydig cells produce androgens, but whether these cells are endowed with KCas is not known. We addressed these points and focussed on BKCa, which is Ca2+-activated and the underlying channel for a prominent current. It can be manipulated, e.g. by a specific blocker, the red scorpion toxin iberiotoxin (IbTx), which binds to the outer face with high affinity and selectively inhibits the current by decreasing both the probability of opening and the open time of the channel.Fil: Siebert, S. Ludwig Maximilians Universit√§t M√ľnchen. ; AlemaniaFil: Spinnler, K. Ludwig Maximilians Universit√§t M√ľnchen. ; AlemaniaFil: Matzkin, Maria Eugenia. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Instituto de Biolog√≠a y Medicina Experimental. Fundaci√≥n de Instituto de Biolog√≠a y Medicina Experimental. Instituto de Biolog√≠a y Medicina Experimental; ArgentinaFil: Kunz, L. Ludwig Maximilians Universit√§t M√ľnchen. ; AlemaniaFil: Calandra, Ricardo Saul. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Instituto de Biolog√≠a y Medicina Experimental. Fundaci√≥n de Instituto de Biolog√≠a y Medicina Experimental. Instituto de Biolog√≠a y Medicina Experimental; ArgentinaFil: Frungieri, Monica Beatriz. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Instituto de Biolog√≠a y Medicina Experimental. Fundaci√≥n de Instituto de Biolog√≠a y Medicina Experimental. Instituto de Biolog√≠a y Medicina Experimental; ArgentinaFil: Mayerhofer, A. Ludwig Maximilians Universit√§t M√ľnchen. ; Alemania22. Jahrestagung der Deutschen Gesellschaft f√ľr Andrologie e VHamburgoAlemaniaDeutsche Gesellschaft f√ľr AndrologieConventus Congressmanagement und Marketing Gmb

    Data-aided single-carrier coherent receivers

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    Data-aided algorithms for coherent optic receivers are discussed as an extension of existing non-data aided methods. The concept presents a scalable approach with low implementation complexity and limited overhead for higher-order modulation formats

    The forebrain synaptic transcriptome is organized by clocks but its proteome is driven by sleep

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    Neurons have adapted mechanisms to traffic RNA and protein into distant dendritic and axonal arbors. Taking a biochemical approach, we reveal that forebrain synaptic transcript accumulation shows overwhelmingly daily rhythms, with two-thirds of synaptic transcripts showing time-of-day-dependent abundance independent of oscillations in the soma. These transcripts formed two sharp temporal and functional clusters, with transcripts preceding dawn related to metabolism and translation and those anticipating dusk related to synaptic transmission. Characterization of the synaptic proteome around the clock demonstrates the functional relevance of temporal gating for synaptic processes and energy homeostasis. Unexpectedly, sleep deprivation completely abolished proteome but not transcript oscillations. Altogether, the emerging picture is one of a circadian anticipation of messenger RNA needs in the synapse followed by translation as demanded by sleep-wake cycles

    Implementing Neural Network-Based Equalizers in a Coherent Optical Transmission System Using Field-Programmable Gate Arrays

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    In this work, we demonstrate the offline FPGA realization of both recurrent and feedforward neural network (NN)-based equalizers for nonlinearity compensation in coherent optical transmission systems. First, we present a realization pipeline showing the conversion of the models from Python libraries to the FPGA chip synthesis and implementation. Then, we review the main alternatives for the hardware implementation of nonlinear activation functions. The main results are divided into three parts: a performance comparison, an analysis of how activation functions are implemented, and a report on the complexity of the hardware. The performance in Q-factor is presented for the cases of bidirectional long-short-term memory coupled with convolutional NN (biLSTM + CNN) equalizer, CNN equalizer, and standard 1-StpS digital back-propagation (DBP) for the simulation and experiment propagation of a single channel dual-polarization (SC-DP) 16QAM at 34 GBd along 17x70km of LEAF. The biLSTM+CNN equalizer provides a similar result to DBP and a 1.7 dB Q-factor gain compared with the chromatic dispersion compensation baseline in the experimental dataset. After that, we assess the Q-factor and the impact of hardware utilization when approximating the activation functions of NN using Taylor series, piecewise linear, and look-up table (LUT) approximations. We also show how to mitigate the approximation errors with extra training and provide some insights into possible gradient problems in the LUT approximation. Finally, to evaluate the complexity of hardware implementation to achieve 400G throughput, fixed-point NN-based equalizers with approximated activation functions are developed and implemented in an FPGA.Comment: Invited paper at Journal of Lightwave Technology - IEE

    DSP for Coherent Single-Carrier Receivers

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    Parallelization of Recurrent Neural Network-Based Equalizer for Coherent Optical Systems via Knowledge Distillation

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    The recurrent neural network (RNN)-based equalizers, especially the bidirectional long-short-term memory (biLSTM) structure, have already been proven to outperform the feed-forward NNs in nonlinear mitigation in coherent optical systems. However, the recurrent connections still prevent the computation from being fully parallelizable. To circumvent the non-parallelizability of recurrent-based equalizers, we propose, for the first time, knowledge distillation (KD) to recast the biLSTM into a parallelizable feed-forward 1D-convolutional NN structure. In this work, we applied KD to the cross-architecture regression problem, which is still in its infancy. We highlight how the KD helps the student's learning from the teacher in the regression problem. Additionally, we provide a comparative study of the performance of the NN-based equalizers for both the teacher and the students with different NN architectures. The performance comparison was carried out in terms of the Q-factor, inference speed, and computational complexity. The equalization performance was evaluated using both simulated and experimental data. The 1D-CNN outperformed other NN types as a student model with respect to the Q-factor. The proposed 1D-CNN showed a significant reduction in the inference time compared to the biLSTM while maintaining comparable performance in the experimental data and experiencing only a slight degradation in the Q-factor in the simulated data

    Computational Complexity Optimization of Neural Network-Based Equalizers in Digital Signal Processing: A Comprehensive Approach

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    Experimental results based on offline processing reported at optical conferences increasingly rely on neural network-based equalizers for accurate data recovery. However, achieving low-complexity implementations that are efficient for real-time digital signal processing remains a challenge. This paper addresses this critical need by proposing a systematic approach to designing and evaluating low-complexity neural network equalizers. Our approach focuses on three key phases: training, inference, and hardware synthesis. We provide a comprehensive review of existing methods for reducing complexity in each phase, enabling informed choices during design. For the training and inference phases, we introduce a novel methodology for quantifying complexity. This includes new metrics that bridge software-to-hardware considerations, revealing the relationship between complexity and specific neural network architectures and hyperparameters. We guide the calculation of these metrics for both feed-forward and recurrent layers, highlighting the appropriate choice depending on the application's focus (software or hardware). Finally, to demonstrate the practical benefits of our approach, we showcase how the computational complexity of neural network equalizers can be significantly reduced and measured for both teacher (biLSTM+CNN) and student (1D-CNN) architectures in different scenarios. This work aims to standardize the estimation and optimization of computational complexity for neural networks applied to real-time digital signal processing, paving the way for more efficient and deployable optical communication systems
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