Seokjin Lee

Beamspace-Domain Multichannel Nonnegative Matrix Factorization for Audio Source Separation

In this letter, we develop a multichannel blind source separation algorithm based on a beamspace transform and the multichannel nonnegative matrix factorization (NMF) method. The conventional multichannel NMF algorithm performs well with multichannel mixing data, but there is still room for enhancement in multichannel real-world recording data. In this letter, we consider a beamspace-time-frequency domain data model for multichannel NMF method, and enhance the conventional method using a beamspace transform. Our decomposition algorithm is applied to 2-channel and 4-channel unsupervised audio source separation, using a dataset from the international Signal Separation Evaluation Campaign 2010 (SiSEC 2010). Our algorithm shows a better performance than the conventional NMF method in an evaluation results.

Dexamethasone downregulates caveolin-1 causing muscle atrophy via inhibited insulin signaling

Glucocorticoids play a major role in the development of muscle atrophy in various medical conditions, such as cancer, burn injury, and sepsis, by inhibiting insulin signaling. In this study, we report a new pathway in which glucocorticoids reduce the levels of upstream insulin signaling components by downregulating the transcription of the gene encoding caveolin-1 (CAV1), a scaffolding protein present in the caveolar membrane. Treatment with the glucocorticoid dexamethasone (DEX) decreased CAV1 protein and Cav1 mRNA expression, with a concomitant reduction in insulin receptor alpha (IRα) and IR substrate 1 (IRS1) levels in C2C12 myotubes. On the basis of the results of promoter analysis using deletion mutants and site-directed mutagenesis a negative glucocorticoid-response element in the regulatory region of the Cav1 gene was identified, confirming that Cav1 is a glucocorticoid-target gene. Cav1 knockdown using siRNA decreased the protein levels of IRα and IRS1, and overexpression of Cav1 prevented the DEX-induced decrease in IRα and IRS1 proteins, demonstrating a causal role of Cav1 in the inhibition of insulin signaling. Moreover, injection of adenovirus expressing Cav1 into the gastrocnemius muscle of mice prevented DEX-induced atrophy. These results indicate that CAV1 is a critical regulator of muscle homeostasis, linking glucocorticoid signaling to the insulin signaling pathway, thereby providing a novel target for the prevention of glucocorticoid-induced muscle atrophy.

4‐n‐butylresorcinol enhances proteolytic degradation of tyrosinase in B16F10 melanoma cells

4‐n‐butylresorcinol is a competitive inhibitor of tyrosinase and has been used as an antimelanogenic agent. However, its inhibition mechanism in intact cells is not fully understood. To elucidate the cellular mechanism, we compared in vitro and in vivo inhibitory effects of 4‐n‐butylresorcinol on tyrosinase activity.

Transglutaminase 2 mediates UV-induced skin inflammation by enhancing inflammatory cytokine production

UV irradiation elicits acute inflammation in the skin by increasing proinflammatory cytokine production in keratinocytes. However, the downstream protein target(s) that link UV radiation to the activation of signaling pathways responsible for cytokine expression have not been fully elucidated. In this study, we report a novel role of transglutaminase 2 (TG2), a member of the TG enzyme family whose activities are critical for cornified envelope formation, in mediating UV-induced inflammation. Our results showed that TG2-deficient mice exhibited reduced inflammatory responses to UV irradiation, including reduced erythema, edema, dilation of blood vessels, inflammatory cell infiltration, and levels of inflammatory cytokines. Using primary mouse keratinocytes and HaCaT cells, we found that UV irradiation-induced cytokine production by activating TG2, but not by upregulating TG2 expression, and that ER calcium release triggered by the UV-induced activation of phospholipase C was required for TG2 activation. Moreover, TG2 activity enhanced p65 phosphorylation, leading to an increase in NF-κB transcriptional activity. These results indicate that TG2 is a critical mediator of cytokine expression in the UV-induced inflammatory response of keratinocytes, and suggest that TG2 inhibition might be useful for preventing UV-related skin disorders, such as photoaging and skin cancer caused by chronic UV exposure.

On-Line Nonnegative Matrix Factorization for Music Signal Separation

Nonnegative matrix factorization (NMF) is widely used in audio source analysis and audio signal separation systems. However, conventional NMF algorithms cannot be used on-line because they process all available data at once. On-line NMF algorithms have been developed recently, but most of them cannot be applied to audio systems. In this paper, an on-line NMF algorithm, based on multiple normal equations and recursive solutions, is developed, and the developed algorithm is extended to more enhanced algorithm and more simplified algorithm. An on-line monaural ambient signal separation system is presented to demonstrate the applicability of the proposed algorithm.

Context-Based Arithmetic Coding Scheme for Parametric Stereo in Enhanced aacPlus *

Enhanced aacPlus is an audio codec which is composed of advanced audio coding (AAC), spectral band replication (SBR), and parametric stereo (PS) for efficient audio coding at low bit rates. We propose a new coding scheme for lossless bit rate reduction of PS in enhanced aacPlus. We first determine the optimal contexts for context-based coding of quantized stereo parameter indexes in PS. Then we propose a coding scheme which is based on context-based coding using the determined optimal contexts in conjunction with arithmetic coding. The proposed scheme has normal and memory-reduced versions, both of which are shown to guarantee significant and consistent lossless bit rate reduction of PS. The saved bits by the proposed scheme can be used for the other modules of enhanced aacPlus, AAC and SBR.

Audio Source Separation Method Based on Beamspace-domain Multichannel Non-negative Matrix Factorization, Part I: Beamspace-domain Multichannel Non-negative Matrix Factorization system

In this paper, we develop a multichannel blind source separation algorithm based on a beamspace transform and the multichannel non-negative matrix factorization (NMF) method. The NMF algorithm is a famous algorithm which is used to solve the source separation problems. In this paper, we consider a beamspace-time-frequency domain data model for multichannel NMF method, and enhance the conventional method using a beamspace transform. Our decomposition algorithm is applied to audio source separation, using a dataset from the international Signal Separation Evaluation Campaign 2010 (SiSEC 2010) for evaluation.

Audio Source Separation Method based on Beamspace-domain Multichannel Non-negative Matrix Factorization, Part II: A Study on the Beamspace Transform Algorithms

Beamspace transform algorithm transforms spatial-domain data - such as x, y, z dimension - into incidence-angle-domain data, which is called beamspace-domain data. The beamspace transform method is generally used in source localization and tracking, and adaptive beamforming problem. When the beamspace transform method is used in multichannel audio source separation, the inverse beamspace transform is also important because the source image have to be reconstructed. This paper studies the beamspace transform and inverse transform algorithms for multichannel audio source separation system, especially for the beamspace-domain multichannel NMF algorithm.

Optimizing the sound pressure levels at low frequency limits of electrodynamic loudspeakers

This paper focuses on reproducible low frequency ranges of electrodynamic loudspeaker drivers. The research findings lead to a guide that allows the optimal driver to be selected at the early stages of the design when the consumer electronic products such as home theater systems, digital TVs or PC speakers are being considered. The suggested frequency ranges are based on the acoustics and estimated from statistical data from 1,473 loudspeaker drivers of various sizes. In particular, the lower frequency limit is discussed together with the peak volume displacement which is closely related to the maximum reproducible sound pressure in a loudspeaker.

A study on the adaptive design of loudspeaker driver parameters for a given enclosure

In the conventional methods of electro‐dynamic loudspeaker design, driver units are selected first and then the enclosures are designed for the best compensation of frequency responses of the given drivers. However, in the industry of nowadays, these conventional methods are not appropriate; the enclosure design is determined first, and after that, a proper driver unit is selected by trial and error. In this paper, an adaptive design method of loudspeaker driver parameters for a given enclosure is studied. We estimated loudspeaker parameters such as diaphragm size, acoustic compliance, acoustic resistance, etc., to obtain an optimal alignment or desired response curve for a given enclosure. In the proposed method, the target frequency response curve in low‐frequency range is determined first. Second, the optimal size of driver is calculated. The other driver parameters, such as driver suspension, Q of driver, etc., are designed lastly. Easier and faster design can be achieved by the proposed design method...