795 research outputs found
Energy cascade in the Garrett-Munk spectrum of internal gravity waves
We study the spectral energy transfer due to wave-triad interactions in the
Garrett-Munk spectrum of internal gravity waves (IGWs) based on a numerical
evaluation of the collision integral in the wave kinetic equation. Our
numerical evaluation builds on the reduction of the collision integral on the
resonant manifold for a horizontally isotropic spectrum. We directly evaluate
the downscale energy flux available for ocean mixing, whose value is in close
agreement with the empirical finescale parameterization. We further decompose
the energy transfer into contributions from different mechanisms, including
local interactions and three types of nonlocal interactions, namely parametric
subharmonic instability (PSI), elastic scattering (ES) and induced diffusion
(ID). Through analysis on the role of each type of interaction, we resolve two
long-standing paradoxes regarding the mechanism for forward cascade in
frequency and zero ID flux for GM76 spectrum. In addition, our analysis
estimates the contribution of each mechanism to the energy transfer in each
spectral direction, and reveals new understanding of the importance of local
interactions and ES in the energy transfer
Two Adjacent Phenylalanines In the NMDA Receptor GluN2A Subunit M3 Domain Interactively Regulate Alcohol Sensitivity and Ion Channel Gating
The N-methyl-d-aspartate (NMDA) receptor is a key target of ethanol action in the central nervous system. Alcohol inhibition of NMDA receptor function involves small clusters of residues in the third and fourth membrane-associated (M) domains. Previous results from this laboratory have shown that two adjacent positions in the M3 domain, F636 and F637, can powerfully regulate alcohol sensitivity and ion channel gating. In this study, we report that these positions interact with one another in the regulation of both NMDA receptor gating and alcohol action. Using dual mutant cycle analysis, we detected interactions among various substitution mutants at these positions with respect to regulation of glutamate EC50, steady-state to peak current ratios (Iss:Ip), mean open time, and ethanol IC50. This interaction apparently involves a balancing of forces on the M3 helix, such that the disruption of function due to a substitution at one position can be reversed by a similar substitution at the other position. For example, tryptophan substitution at F636 or F637 increased or decreased channel mean open time, respectively, but tryptophan substitution at both positions did not alter open time. Interestingly, the effects of a number of mutations on receptor kinetics and ethanol sensitivity appeared to depend upon subtle structural differences, such as those between the isomeric amino acids leucine and isoleucine, as they could not be explained on the basis of sidechain molecular volume or hydrophilicity
THE IMPACTS OF CREDIT DEFAULT SWAPS ON DEBT PRICING, CORPORATE INVESTMENT AND DIVIDEND POLICY
A Novel Collagen Extraction Method Based on Microwave Irradiation
Content:
Microwave was used as a thermal source to extract collagen acid from the cattle hide in the present work. The effects of microwave on collagen extraction yields were studied under different microwave
temperatures, time and hide-liquid ratio. The optimal extraction process was obtained by an orthogonal experiment, and the composition, structure and properties of the extracted collagen were characterized by amino acid analysis, SDS-PAGE, FTIR, UV-Vis, CD, FL, and VP-DSC. The results showed that the extraction rate of collagen was positively correlated with temperature, time and hide-liquid ratio. Under the condition of 35 °C, 6 h and 1:30 of solid-liquid ratio, the extraction proportion of collagen extracted under microwave was the highest, reaching to 13.40 %. The extracted collagen was identified as type I collagen by Amino acid analysis, and the graphic pattern of SDS-PAGE, FTIR and UV-Vis showed that the extracted collagen was similar to the standard type I collagen. Also, the results suggest that the triple helical structure exists still in the extracted collagen. The transition from triple helix to random coil of the extracted collagen was 41 â. These results provide a scientific basis for microwave technology for the extraction of collagen.
Take-Away:
The results showed that the extraction rate of collagen was positively correlated with temperature, time and hide-liquid ratio. Under the condition of 35 °C, 6 h and 1:30 of solid-liquid ratio, the extraction
proportion of collagen extracted under microwave was the highest, reaching to 13.40 %. The extracted collagen was identified as type I collagen by Amino acid analysis, and the graphic pattern of SDS-PAGE,
FTIR and UV-Vis showed that the extracted collagen was similar to the standard type I collagen. Also, the results suggest that the triple helical structure exists still in the extracted collagen. The transition from triple helix to random coil of the extracted collagen was 41 â. These results provide a scientific basis for microwave technology for the extraction of collagen
Positions in the NâmethylâDâaspartate Receptor GluN2C Subunit M3 and M4 Domains Regulate Alcohol Sensitivity and Receptor Kinetics
Background
Alcohol alters synaptic transmission in the brain. The NâmethylâDâaspartate (NMDA) receptor (NMDAR), a subtype of glutamateâgated ion channel, is an important synaptic target of alcohol in the brain. We and others have previously identified 4 alcoholâsensitive positions in the third and fourth membraneâassociated (M) domains, designated M31â2and M41â2, of the GluN1, GluN2A, and GluN2B NMDAR subunits. In the present study, we tested whether the corresponding positions in the GluN2C subunit also regulate alcohol sensitivity and ion channel gating. Methods
We performed alanineâ and tryptophanâscanning mutagenesis in the GluN2C subunit followed by expression in HEK 293 cells and electrophysiological patchâclamp recording. Results
Alanine substitution at the M31 (F634) and M41â2 (M821 and M823) positions did not alter ethanol (EtOH) sensitivity, whereas substitution of alanine at the M32 position (F635) yielded nonfunctional receptors. Tryptophan substitution at the M31â2 positions did not change EtOH sensitivity, whereas tryptophan substitution at the M41 position increased, and at the M42 position decreased, EtOH sensitivity. The increased EtOH sensitivity of the tryptophan mutant at M41 is in marked contrast to previous results observed in the GluN2A and GluN2B subunits. In addition, this mutant exhibited increased desensitization, but to a much lesser extent compared to the corresponding mutations in GluN2A and GluN2B. A series of mutations at M41 altered EtOH sensitivity, glutamate potency, and desensitization. Seven amino acid substitutions (of 15 tested) at this position yielded nonfunctional receptors. Among the remaining mutants at M41, EtOH sensitivity was not significantly correlated with hydrophobicity, molecular volume, or polarity of the substituent, or with glutamate EC50 values, but was correlated with maximal steadyâstateâtoâpeak current ratio, a measure of desensitization. Conclusions
The identity and characteristics of alcoholâsensitive positions in the GluN2C subunit differ from those previously reported for GluN2A and GluN2B subunits, despite the high homology among these subunits
Deep Joint Source-Channel Coding for Adaptive Image Transmission over MIMO Channels
This paper introduces a vision transformer (ViT)-based deep joint source and
channel coding (DeepJSCC) scheme for wireless image transmission over
multiple-input multiple-output (MIMO) channels, denoted as DeepJSCC-MIMO. We
consider DeepJSCC-MIMO for adaptive image transmission in both open-loop and
closed-loop MIMO systems. The novel DeepJSCC-MIMO architecture surpasses the
classical separation-based benchmarks with robustness to channel estimation
errors and showcases remarkable flexibility in adapting to diverse channel
conditions and antenna numbers without requiring retraining. Specifically, by
harnessing the self-attention mechanism of ViT, DeepJSCC-MIMO intelligently
learns feature mapping and power allocation strategies tailored to the unique
characteristics of the source image and prevailing channel conditions.
Extensive numerical experiments validate the significant improvements in
transmission quality achieved by DeepJSCC-MIMO for both open-loop and
closed-loop MIMO systems across a wide range of scenarios. Moreover,
DeepJSCC-MIMO exhibits robustness to varying channel conditions, channel
estimation errors, and different antenna numbers, making it an appealing
solution for emerging semantic communication systems.Comment: arXiv admin note: text overlap with arXiv:2210.1534
Vision Transformer for Adaptive Image Transmission over MIMO Channels
This paper presents a vision transformer (ViT) based joint source and channel
coding (JSCC) scheme for wireless image transmission over multiple-input
multiple-output (MIMO) systems, called ViT-MIMO. The proposed ViT-MIMO
architecture, in addition to outperforming separation-based benchmarks, can
flexibly adapt to different channel conditions without requiring retraining.
Specifically, exploiting the self-attention mechanism of the ViT enables the
proposed ViT-MIMO model to adaptively learn the feature mapping and power
allocation based on the source image and channel conditions. Numerical
experiments show that ViT-MIMO can significantly improve the transmission
quality cross a large variety of scenarios, including varying channel
conditions, making it an attractive solution for emerging semantic
communication systems
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