109 research outputs found
Overall Performance Evaluation of Tubular Scraper Conveyors Using a TOPSIS-Based Multiattribute Decision-Making Method
Properly evaluating the overall performance of tubular scraper conveyors (TSCs) can increase their overall efficiency and reduce economic investments, but such methods have rarely been studied. This study evaluated the overall performance of TSCs based on the technique for order of preference by similarity to ideal solution (TOPSIS). Three conveyors of the same type produced in the same factory were investigated. Their scraper space, material filling coefficient, and vibration coefficient of the traction components were evaluated. A mathematical model of the multiattribute decision matrix was constructed; a weighted judgment matrix was obtained using the DELPHI method. The linguistic positive-ideal solution (LPIS), the linguistic negative-ideal solution (LNIS), and the distance from each solution to the LPIS and the LNIS, that is, the approximation degrees, were calculated. The optimal solution was determined by ordering the approximation degrees for each solution. The TOPSIS-based results were compared with the measurement results provided by the manufacturer. The ordering result based on the three evaluated parameters was highly consistent with the result provided by the manufacturer. The TOPSIS-based method serves as a suitable evaluation tool for the overall performance of TSCs. It facilitates the optimal deployment of TSCs for industrial purposes
Channel Measurement and Coverage Analysis for NIRS-Aided THz Communications in Indoor Environments
Due to large reflection and diffraction losses in the THz band, it is
arguable to achieve reliable links in the none-line-of-sight (NLoS) cases.
Intelligent reflecting surfaces, although are expected to solve the blockage
problem and enhance the system connectivity, suffer from fabrication difficulty
and operation complexity. In this work, non-intelligent reflecting surfaces
(NIRS), which are simply made of costless metal foils and have no signal
configuration capability, are adopted to enhance the signal strength and
coverage in the THz band. Channel measurements are conducted in typical indoor
scenarios at 306-321 GHz and 356-371 GHz bands to validate the effectiveness of
the NIRS. Results measured with NIRS in different sizes show that large NIRS
performs much better than small NIRS. Furthermore, by invoking the NIRS, the
additional reflection loss can be reduced by more than 10~dB and the coverage
ratio is increased by up to 39 for a 10~dB signal-to-noise ratio (SNR)
threshold.Comment: 5 figures, 2 table
Channel Measurement and Characterization with Modified SAGE Algorithm in an Indoor Corridor at 300 GHz
The much higher frequencies in the Terahertz (THz) band prevent the effective
utilization of channel models dedicated for microwave or millimeter-wave
frequency bands. In this paper, a measurement campaign is conducted in an
indoor corridor scenario at 306-321 GHz with a frequency-domain Vector Network
Analyzer (VNA)-based sounder. To realize high-resolution multipath component
(MPC) extraction for the direction-scan measurement campaigns in the THz band,
a novel modified space-alternating generalized expectation-maximization (SAGE)
algorithm is further proposed. Moreover, critical channel characteristics,
including the path loss, shadow fading, K-factor, delay spread, angular
spreads, cluster parameters, and cross correlations are calculated and analyzed
in the LoS case. Besides, two contrasted measurement campaigns in the NLoS case
are conducted, with and without additional reflective foils on walls to serve
as effective scatterers. Comparison results indicate that the reflective foils
are useful to improve the channel conditions in the NLoS case by nearly 6 dB,
which is potential to be utilized as alternative of intelligent reflecting
surfaces (IRS) to enhance the coverage ability of THz communications.Comment: 12 pages, 8 figure
300 GHz Dual-Band Channel Measurement, Analysis and Modeling in an L-shaped Hallway
The Terahertz (THz) band (0.1-10 THz) has been envisioned as one of the
promising spectrum bands for sixth-generation (6G) and beyond communications.
In this paper, a dual-band angular-resolvable wideband channel measurement in
an indoor L-shaped hallway is presented and THz channel characteristics at
306-321 GHz and 356-371 GHz are analyzed. It is found that conventional
close-in and alpha-beta path loss models cannot take good care of large-scale
fading in the non-line-of-sight (NLoS) case, for which a modified alpha-beta
path loss model for the NLoS case is proposed and verified in the NLoS case for
both indoor and outdoor L-shaped scenarios. To describe both large-scale and
small-scale fading, a ray-tracing (RT)-statistical hybrid channel model is
proposed in the THz hallway scenario. Specifically in the hybrid model, the
deterministic part in hybrid channel modeling uses RT modeling of dominant
multi-path components (MPCs), i.e., LoS and multi-bounce reflected paths in the
near-NLoS region, while dominant MPCs at far-NLoS positions can be deduced
based on the developed statistical evolving model. The evolving model describes
the continuous change of arrival angle, power and delay of dominant MPCs in the
NLoS region. On the other hand, non-dominant MPCs are generated statistically.
The proposed hybrid approach reduces the computational cost and solves the
inaccuracy or even missing of dominant MPCs through RT at far-NLoS positions
300 GHz Channel Measurement and Characterization in the Atrium of a Building
With abundant bandwidth resource, the Terahertz band (0.1~THz to 10~THz) is
envisioned as a key technology to realize ultra-high data rates in the 6G and
beyond mobile communication systems. However, moving to the THz band, existing
channel models dedicated for microwave or millimeter-wave bands are
ineffective. To fill this research gap, extensive channel measurement campaigns
and characterizations are necessary. In this paper, using a frequency-domain
Vector Network Analyzer (VNA)-based sounder, a measurement campaign is
conducted in the outdoor atrium of a building in 306-321 GHz band. The measured
data are further processed to obtain the channel transfer functions (CTFs),
parameters of multipath components (MPCs), as well as clustering results. Based
on the MPC parameters, the channel characteristics, such as path loss, shadow
fading, K-factor, etc., are calculated and analyzed. The extracted channel
characteristics and numerology are helpful to study channel modeling and guide
system design for THz communications.Comment: 5 pages, 2 figures. arXiv admin note: text overlap with
arXiv:2203.16745 by other author
Terahertz Channel Measurement and Analysis on a University Campus Street
Owning abundant bandwidth resource, the Terahertz (0.1-10 THz) band is a
promising spectrum to support sixth-generation (6G) and beyond communications.
As the foundation of channel study in the spectrum, channel measurement is
ongoing in covering representative 6G communication scenarios and promising THz
frequency bands. In this paper, a wideband channel measurement in an L-shaped
university campus street is conducted at 306-321 GHz and 356-371 GHz. In
particular, ten line-of-sight (LoS) and eight non-line-of-sight (NLoS) points
are measured at the two frequency bands, respectively. In total, 6480 channel
impulse responses (CIRs) are obtained from the measurement, based on which
multi-path propagation in the L-shaped roadway in the THz band is elaborated to
identify major scatterers of walls, vehicles, etc. in the environment and their
impact on multi-path components (MPCs). Furthermore, outdoor THz channel
characteristics in the two frequency bands are analyzed, including path losses,
shadow fading, cluster parameters, delay spread and angular spread. In contrast
with the counterparts in the similar outdoor scenario at lower frequencies, the
results verify the sparsity of MPCs at THz frequencies and indicate smaller
power spreads in both temporal and spatial domains in the THz band.Comment: 6 pages, 15 figure
306-321 GHz Wideband Channel Measurement and Analysis in an Indoor Lobby
The Terahertz (0.1-10 THz) band has been envisioned as one of the promising
spectrum bands to support ultra-broadband sixth-generation (6G) and beyond
communications. In this paper, a wideband channel measurement campaign in an
indoor lobby at 306-321 GHz is presented. The measurement system consists of a
vector network analyzer (VNA)-based channel sounder, and a directional antenna
equipped at the receiver to resolve multi-path components (MPCs) in the angular
domain. In particular, 21 positions and 3780 channel impulse responses (CIRs)
are measured in the lobby, including the line-of-sight (LoS), non-line-of-sight
(NLoS) and obstructed-line-of-sight (OLoS) cases. Multi-path propagation is
elaborated in terms of clustering results, and the effect of typical scatterers
in the indoor lobby scenario in the THz band is explored. Moreover, indoor THz
channel characteristics are analyzed in depth. Specifically, best direction and
omni-directional path losses are analyzed by invoking close-in and alpha-beta
path loss models. The most clusters are observed in the OLoS case, followed by
NLoS and then LoS cases. On average, the power dispersion of MPCs is smaller in
the LoS case in both temporal and angular domains, compared with the NLoS and
OLoS counterparts.Comment: 6 pages, 15 figure
DRPT: Disentangled and Recurrent Prompt Tuning for Compositional Zero-Shot Learning
Compositional Zero-shot Learning (CZSL) aims to recognize novel concepts
composed of known knowledge without training samples. Standard CZSL either
identifies visual primitives or enhances unseen composed entities, and as a
result, entanglement between state and object primitives cannot be fully
utilized. Admittedly, vision-language models (VLMs) could naturally cope with
CZSL through tuning prompts, while uneven entanglement leads prompts to be
dragged into local optimum. In this paper, we take a further step to introduce
a novel Disentangled and Recurrent Prompt Tuning framework termed DRPT to
better tap the potential of VLMs in CZSL. Specifically, the state and object
primitives are deemed as learnable tokens of vocabulary embedded in prompts and
tuned on seen compositions. Instead of jointly tuning state and object, we
devise a disentangled and recurrent tuning strategy to suppress the traction
force caused by entanglement and gradually optimize the token parameters,
leading to a better prompt space. Notably, we develop a progressive fine-tuning
procedure that allows for incremental updates to the prompts, optimizing the
object first, then the state, and vice versa. Meanwhile, the optimization of
state and object is independent, thus clearer features can be learned to
further alleviate the issue of entangling misleading optimization. Moreover, we
quantify and analyze the entanglement in CZSL and supplement entanglement
rebalancing optimization schemes. DRPT surpasses representative
state-of-the-art methods on extensive benchmark datasets, demonstrating
superiority in both accuracy and efficiency
High-Temperature Oxidation Performance of 4Cr4Mo2NiMnSiV Hot Die Steel
A new type of hot working die steel was designed by using JMatPro, and high-temperature oxidation tests were carried out in the ambient atmosphere at 600 ℃ and 700 ℃. The heat treatment process and oxidation mechanism of the designed 4Cr4Mo2NiMnSiV steel were studied in detail. XRD, SEM and EDS were used to analyze the crystallographic phases, surface and cross-section morphologies of the oxide films. The results show that the main phases in the 4Cr4Mo2NiMnSiV steel were γ and α + δ. During the high-temperature oxidation, oxidation of the Fe outer layer and Cr inner layer occurred. After oxidation at 600℃, the surface oxidation layer comprised a monolayer with an uneven morphology. The surface oxide film had two layers after oxidation at 700℃. The outer oxide layer mainly contained Fe2O3 and Fe3O4, while the inner oxide layer mainly contained Cr2O3. The microstructure was relatively regular and had a significant effect on the protection of the metallic matrix. When oxidized, the 4Cr4Mo2NiMnSiV alloy steel easily formed protective layers, such as Cr2O3 and SiO2, so that the test steel had excellent oxidation resistance at high temperatures
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