323 research outputs found
Decoupling Crossover in Asymmetric Broadside Coupled Split Ring Resonators at Terahertz Frequencies
We investigate the electromagnetic response of asymmetric broadside coupled
split ring resonators (ABC-SRRs) as a function of the relative in-plane
displacement between the two component SRRs. The asymmetry is defined as the
difference in the capacitive gap widths (\Delta g) between the two resonators
comprising a coupled unit. We characterize the response of ABC-SRRs both
numerically and experimentally via terahertz time-domain spectroscopy. As with
symmetric BC-SRRs (\Delta g=0 \mu m), a large redshift in the LC resonance is
observed with increasing displacement, resulting from changes in the capacitive
and inductive coupling. However, for ABC-SRRs, in-plane shifting between the
two resonators by more than 0.375Lo (Lo=SRR sidelength) results in a transition
to a response with two resonant modes, associated with decoupling in the
ABC-SRRs. For increasing \Delta g, the decoupling transition begins at the same
relative shift (0.375Lo), though with an increase in the oscillator strength of
the new mode. This strongly contrasts with symmetric BC-SRRs which present only
one resonance for shifts up to 0.75Lo. Since all BC-SRRs are effectively
asymmetric when placed on a substrate, an understanding of ABC-SRR behavior is
essential for a complete understanding of BC-SRR based metamaterials
Soil Quality Analysis for Sustainability of Forest Ecosystem: The Case of Chilimo-Gaji Forest, West Shewa Zone, Ethiopia
The study was conducted to assess the soil quality with respect to the sustainability of Chilimo-Gaji Forest ecosystem using selected soils physicochemical parameters. Soil samples were taken through random sampling from the natural forest land under three different forest user groups (FUGs) in order to determine selected soils physicochemical properties. The result of the present study indicated that total N, available P and K, and % C were higher on the surface soil (0-20cm) than in the subsoil (20-30cm) depth indicating more nutrients are concentrated in the surface soil. The result of the study also revealed that presence of low bulk density ranges from 0.4 to 1.029 and high moisture content of soil ranging 4.89%-7.60%. The result also indicated that there is a higher per cent of carbon and organic matter across the three FUGs with Galessa recording the highest % carbon (7.69) and organic matter (13.25), followed by Gaji and Chilimo FUGs. The study also revealed that forest soil of the study area was very fertile and sustainable as the parameters analyzed indicating the forest ecosystem in the study area is sustainably managed under the new paradigm of participatory forest management. Scaling up participatory forest management to other protected forests in Ethiopia is crucial and plays a key role in the sustainability of healthy forest ecosystem. Keywords: Ethiopia; Forest user groups; physicochemical parameters; Soil organic carbon; Soil quality DOI: 10.7176/JEES/9-3-01 Publication date:March 31st 201
Three-dimensional broadband tunable terahertz metamaterials
We present optically tunable magnetic 3D metamaterials at terahertz (THz)
frequencies which exhibit a tuning range of ~30% of the resonance frequency.
This is accomplished by fabricating 3D array structures consisting of
double-split-ring resonators (DSRRs) on silicon-on-sapphire, fabricated using
multilayer electroplating. Photoexcitation of free carriers in the silicon
within the capacitive region of the DSRR results in a red-shift of the resonant
frequency from 1.74 THz to 1.16 THz. The observed frequency shift leads to a
transition from a magnetic-to-bianisotropic response as verified through
electromagnetic simulations and parameter retrieval. Our approach extends
dynamic metamaterial tuning to magnetic control, and may find applications in
switching and modulation, polarization control, or tunable perfect absorbers.Comment: 5page
FF2: A Feature Fusion Two-Stream Framework for Punctuation Restoration
To accomplish punctuation restoration, most existing methods focus on
introducing extra information (e.g., part-of-speech) or addressing the class
imbalance problem. Recently, large-scale transformer-based pre-trained language
models (PLMS) have been utilized widely and obtained remarkable success.
However, the PLMS are trained on the large dataset with marks, which may not
fit well with the small dataset without marks, causing the convergence to be
not ideal. In this study, we propose a Feature Fusion two-stream framework
(FF2) to bridge the gap. Specifically, one stream leverages a pre-trained
language model to capture the semantic feature, while another auxiliary module
captures the feature at hand. We also modify the computation of multi-head
attention to encourage communication among heads. Then, two features with
different perspectives are aggregated to fuse information and enhance context
awareness. Without additional data, the experimental results on the popular
benchmark IWSLT demonstrate that FF2 achieves new SOTA performance, which
verifies that our approach is effective.Comment: 5pages. arXiv admin note: substantial text overlap with
arXiv:2203.1248
Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs
We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at
terahertz frequencies. For SRRs on doped GaAs films, incident terahertz
radiation with peak fields of ~20 - 160 kV/cm drives intervalley scattering.
This reduces the carrier mobility and enhances the SRR LC response due to a
conductivity decrease in the doped thin film. Above ~160 kV/cm, electric field
enhancement within the SRR gaps leads to efficient impact ionization,
increasing the carrier density and the conductivity which, in turn, suppresses
the SRR resonance. We demonstrate an increase of up to 10 orders of magnitude
in the carrier density in the SRR gaps on semi-insulating GaAs substrate.
Furthermore, we show that the effective permittivity can be swept from negative
to positive values with increasing terahertz field strength in the impact
ionization regime, enabling new possibilities for nonlinear metamaterials.Comment: 5 pages, 4 figure
TLM: Token-Level Masking for Transformers
Structured dropout approaches, such as attention dropout and DropHead, have
been investigated to regularize the multi-head attention mechanism in
Transformers. In this paper, we propose a new regularization scheme based on
token-level rather than structure-level to reduce overfitting. Specifically, we
devise a novel Token-Level Masking (TLM) training strategy for Transformers to
regularize the connections of self-attention, which consists of two masking
techniques that are effective and easy to implement. The underlying idea is to
manipulate the connections between tokens in the multi-head attention via
masking, where the networks are forced to exploit partial neighbors'
information to produce a meaningful representation. The generality and
effectiveness of TLM are thoroughly evaluated via extensive experiments on 4
diversified NLP tasks across 18 datasets, including natural language
understanding benchmark GLUE, ChineseGLUE, Chinese Grammatical Error
Correction, and data-to-text generation. The results indicate that TLM can
consistently outperform attention dropout and DropHead, e.g., it increases by
0.5 points relative to DropHead with BERT-large on GLUE. Moreover, TLM can
establish a new record on the data-to-text benchmark Rotowire (18.93 BLEU). Our
code will be publicly available at https://github.com/Young1993/tlm.Comment: 13 pages. Accepted by EMNLP2023 main conferenc
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