Effect of mold and core preheating temperature on corrosion resistance of casting Al-12Si alloy U-shaped cooling channel

Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method.The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth.The experimental results suggest that as the preheating temperature increased from 273 K to 573 K,the roughness of the inner wall of the cooling channel reduced from 96.6μm to 77.0μm.When the preheating temperature continued to increase to 723 K,the roughness increased to 85.3μm.The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises,thereby reducing the roughness.However,with the further increase of preheating temperature,it will increase the solidification time of the Al melt.At this time,the carbon fiber and Al melt will take more time to react,which increases the roughness of the channel wall to a certain extent.The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion.The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si,which is easy to cause intergranular corrosion.Therefore,reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels.

Lumbopelvic Fixation and Sacral Decompression for U-shaped Sacral Fractures： Surgical Management and Early Outcome

U-shaped sacral fractures are rare and often difficult to diagnose primarily due to the difficulty in obtaining adequate imaging and the severe associated injuries. These fractures are highly unstable and frequently cause neurological deficits. The majority of surgeons have limited experience in management of U-shaped sacral fractures. No standard treatment protocol for U-shaped sacral fractures has been available till now. This study aimed to examine the management of U-shaped sacral fractures and the early outcomes. Clinical data of 15 consecutive patients with U-shaped sacral fracture who were admitted to our trauma center between 2009 and 2014 were retrospectively analyzed. Demographics, fracture classification, mechanism of injury and operative treatment and deformity angle were assessed. All the patients were treated with lumbopelvic fixation or （and） sacral decompression. EQ-5d score was applied to evaluate the patients＇ quality of life. Of the 15 consecutive patients with U-shaped sacral fracture, the mean age was 28.8 years （range： 15-55 years） at the time of injury. There were 6 females and 9 males. The mean follow- up time was 22.7 months （range： 9-47 months） and mean full weight-bearing time was 9.9 weeks （range： 8-14 weeks）. Ten patients received lumbopelvic fixation and sacral decompression, one lombosacral fixation, and 4 merely sacral decompression due to delayed diagnosis or surgery. The post-operation deformity angle （mean 27.87°, and range： 8°-90°） of the sacrum was smaller than that pre-operation （mean 35.67; range： 15-90） with no significance difference noted. At the latest follow-up, all patients obtained neurological recovery with different extents. Visual analogue score （VAS） was reduced from preoperative 7.07 （range： 5-9） to postoperetive 1.93 （range： 1-3）. All patients could walk without any aid after treatment. Eight patients were able to care for themselves and undertook some daily activities. Five patients had returned to work full time. In conclusion, lumbopelvic fixation is an effective method for stabilization of U-shaped sacral fractures with fewer complications developed. Effective reduction and firm fixation are the prerequisite of early mobilization and neurological recovery. Sacral decompression effectively promotes neurological recovery even in patients with old U-shaped sacral fractures.

GENERAL SOLUTION FOR U-SHAPED BELLOWS OVERALL-BENDING PROBLEMS

The formulae for stresses and angular displacements of U-shaped bellows overall bending in a meridian plane under pure bending moments are presented based on the general solution for slender ring shells proposed by Zhu Weiping, et al. and the solution for ring plates. The results evaluated in this paper are compared with those on EJMA (standards of the expansion joint manufacturers association) and of the experiment given by Li Tingxilz, et al.

Electrokinetic flow in the U-shaped micro-nanochannels

U-shaped micro-nanochannels can generate significant flow disturbance as well as locally amplified electric field, which gives itself potential to be microfluidic mixers, electrokinetic pumps,and even cell lysis process. Numerical simulation is utilized in this work to study the hidden characteristics of the U-shaped micro-nanochannel system, and the effects of key controlling parameters(the external voltage and pressure) on the device output metrics(current, maximum values of electric field, shear stress and flow velocity) were evaluated. A large portion of current flowing through the whole system goes through the nanochannels, rather than the middle part of the microchannel, with its value increasing linearly with the increase of voltage. Due to the local ion depletion near micro-nanofluidic junction, significantly enhanced electric field(as much as 15 fold at V=1 V and P_0=0) as well as strong shear stress(leading to electrokinetic flow) is generated.With increasing external pressure, both electric field and shear stress can be increased initially(due to shortening of depletion region length), but are suppressed eventually at higher pressure due to the destruction of ion depletion layer. Insights gained from this study could be useful for designing nonlinear electrokinetic pumps and other systems.

Mechanical property of U-Shaped 65Mn steel bumpers for seismic base isolation

This study proposes a novel U-shaped 65Mn steel bumper as the displacement restraining device for base-isolated structures with laminated elastomeric rubber bearings.A series of bumpers with different geometric parameters were designed and tested under monotonic and cyclic quasi-static loading protocols.The experimental results from a total of 232 specimens were analyzed to develop an analytical model to calculate the backbone curve and the maximum elastic restoring force for U-shaped 65Mn bumpers.Thus,the analytical equations to calculate the elastic,hardening,and unloading stiffness of U-shaped 65Mn bumpers,as well as their maximum elastic restoring force,are validated by using an additional ten groups of bumpers with varying radiuses.These analytical equations can accurately predict the mechanical parameters of U-shaped 65Mn steel bumpers for a design purpose.

PROBLEMS OF U-SHAPED BELLOWS WITH NONLINEAR DEFORM TION OF LARGE AXISYMMETRICAL DEFLECTION(Ⅰ)—COUNTING NONLINEAR DEFORMATIONS OF RING SHELLS AND COMPRESSED ANGLE OF BELLOWS

This paper follows the work of [1,2]. There are some progress in dealing with moderately small rotations (the squares of rotation angles are the order of magnitude of strains) of middle surface normals of inside and outside ring shells and compressed angle of bellows. Calculation results agree with experiments well. To bellow design, the method given in this paper is of practical value and the discussion of the influence of compressed angle on characteristic relation is helpful.

ON PROBLEMS OF U-SHAPED BELLOWS WITH NONLINEAR DEFORMATION OF LARGE AXISYMMETRICAL DEFLECTION(Ⅱ)——COUNTING VARIATION OF THICKNESS DISTRIBUTION

On the basis of paper [1], assuming the logarithm of thickness at arbitrary point on a U-shaped bellows meridian is linear with the logarithm of distance between that point and axis of symmetry, perturbation solutions of the corresponding problems of large axisymmetrical deflection are given. The effects of thickness distribution variation, which result from technology factors, on stiffness of bellows are discussed.

An ultra-low specific on-resistance trench LDMOS with a U-shaped gate and accumulation layer

An ultra-low specific on-resistance （Ron,sp） oxide trench-type silicon-on-insulator （SOI） lateral double-diffusion metal-oxide semiconductor （LDMOS） with an enhanced breakdown voltage （BV） is proposed and investigated by simulation. There are two key features in the proposed device： one is a U-shaped gate around the oxide trench, which extends from source to drain （UG LDMOS）; the other is an N pillar and P pillar located in the trench sidewall. In the on-state, electrons accumulate along the U-shaped gate, providing a continuous low resistance current path from source to drain. The Ron,sp is thus greatly reduced and almost independent of the drift region doping concentration. In the off-state, the N and P pillars not only enhance the electric field （E-field） strength of the trench oxide, but also improve the E-field distribution in the drift region, leading to a significant improvement in the BV. The BV of 662 V and Ron,sp of 12.4 mΩ.cm2 are achieved for the proposed UG LDMOS. The BV is increased by 88.6% and the Ron,sp is reduced by 96.4%, compared with those of the conventional trench LDMOS （CT LDMOS）, realizing the state-of-the-art trade-off between BV and Ron,sp.

pH-dependent Synthesis of Octa-nuclear Uranyl-oxalate Network Mediated by U-shaped Linkers

In this work,we report a novel octa-nuclear uranyl(U8)motif[(UO2)8O4(μ3-OH)2(μ2-OH)2]4+embedded in a uranyl-oxalate coordination polymer(compound 1)based on a U-shaped linker with extra-long xylylene chains for stabilizing the resulting high-nuclear motif through additional cross-linking connectivity.A comparison with dimeric and monomeric uranyl compounds obtained at different pH value from the same hydrothermal system reveals that,solution pH plays a vital role in formation of this octa-nuclear uranyl motif by promoting hydrolysis of uranyl source.Since high similarity of eight uranium centers in this nearly planar U8 motif here,overlapping and broadening of signals in fluorescence,infra-red(IR)and Raman spectra can be found.

Ultralow Specific on-Resistance Trench MOSFET with a U-Shaped Extended Gate

An ultralow specific on-resistance （Ron,sp） trench metal-oxide-semiconductor field effect transistor （MOSFET） with an improved off-state breakdown voltage （BV） is proposed. It features a U-shaped gate around the drift region and an oxide trench inserted in the drift region （UG MOSFET）. In the on-state, the U-shaped gate induces a high density electron accumulation layer along its sidewall, which provides a low-resistance current path from the source to the drain, realizing an ultralow Ron,sp. The value of Ron,sp is almost independent of the drift doping concentration, and thus the UG MOSFET breaks through the contradiction relationship between R p and the off-state BV. Moreover, the oxide trench folds the drift region, enabling the UG MOSFET to support a high BV with a shortened cell pitch. The UG MOSFET achieves an Ron,sp of 2 mΩ·cm^2 and an improved BV of 216 V, superior to the best existing state-of-the-art transistors at the same BV level

Numerical Simulation of U-Shaped Metal Rings in a Wind-Sand Environment

The interaction of U-shaped rings used for power transmission hardware with a wind-sand field is simulated numerically.A standard k
turbulence model is used in synergy with an Eulerian-Lagrangian approach.The results show that the wind pressure on the windward side of the U-shaped ring is the highest,a negative pressure zone appears on both sides of the U-shaped ring,while a Kármán Vortex Street is created on its leeward side.There are three possible regimes of motion for the sand grains in the wind field.Sand grains with size below 0.125 mm can follow the airflow directly into the contact area of two U-shaped rings.When the sand size is about 0.1 mm,the number of sand grains that are blown into the contact area attains a maximum.Through the simulation of U-shaped rings in the wind-sand field,the dynamics of such processes are explained in detail,thereby providing relevant information for the subsequent protection and design of connecting hardware used for power transmission.

Discussion on Standardization and Automatic Flow Measurement of U-shaped Channel Water

In human life,water resources are inseparable.In recent years,China’s population growth has accelerated,and the industrial level has been continuously improved,resulting in the rapid use and waste of water resources.The protection and rational distribution of water resources are the most pressing issue in China’s water resources.At present,the water measuring facilities of the U-shaped channel mainly include a straight wall measuring pool,a parabolic throat measuring pool,and a long throat measuring pool.In view of the problems in irrigation measurement,the empirical water measurement of basic open-channel and automatic flow measurement system in irrigation district is summarized to improve the accuracy,fairness,and rationality of water measurement,and promote irrigation district management to a higher level.

Double U-Shaped Slots Loaded Stacked Patch Antenna for Multiband Operation

The design of a seven-band stacked patch antenna for the C, X and Ku band is presented. The antenna consists of an H-slot loaded fed patch, stacked with dual U-slot loaded rectangular patch to generate the seven frequency bands. The total size of the antenna is 39.25 × 29.25 mm2. The multiband stacked patch antenna is studied and designed using IE3D simulator. For verification of simulation results, the antenna is analyzed by circuit theory concept. The simulated return loss, radiation pattern and gain are presented. Simulated results show that the antenna can be designed to cover the frequency bands from (4.24 GHz to 4.50 GHz, 5.02 GHz to 5.25 GHz) in C-band application, (7.84 GHz to 8.23 GHz) in X-band and (12.16 GHz to 12.35 GHz, 14.25 GHz to 14.76 GHz, 15.25 GHz to 15.51 GHz, 17.52 GHz to 17.86 GHz) in Ku band applications. The bandwidths of each band of the proposed antenna are 5.9%, 4.5%, 4.83%, 2.36%, 3.53%, 1.68% and 1.91%. Similarly the gains of the proposed band are 2.80 dBi, 4.39 dBi, 4.54 dBi, 10.26 dBi, 8.36 dBi and 9.91 dBi, respectively.

Thermal stability of permafrost under U-shaped crushed rock embankment of the Qinghai-Tibet Railway

The U-shaped crushed rock embankment(UCRE),of which widely utilized in the permafrost regions along the Qinghai-Tibet Railway,has the capability to rapidly reduce the ground temperature of the underlying permafrost.However,there remains uncertainty regarding the adaptation of UCRE to climate change and its long-term cooling trend.This study focuses on nine UCRE monitoring sites along the Qinghai-Tibet Railway to analyze the dynamic variations of the ground temperature underlying permafrost from 2006 to 2020.The efficiency of UCRE in stabilizing permafrost temperature in different permafrost zones is evaluated by considering the permafrost table,ground temperature,and MAGT,as well as the temperature difference between the top and bottom of the crushed rock layer and the ground temperature variation index(GTVI).The results show that UCRE is suitable for application in extremely unstable warm permafrost regions where the MAGT is higher than-0.5℃.Moreover,UCRE effectively diminishes the disparity in permafrost thermal stability between the sunny and shaded shoulders of the embankment.The short-term and long-term effect of cooling permafrost is experiencing a change related with permafrost stability.Notably,in stable cold permafrost regions with MAGT lower than-1.5℃,the long-term cooling effect of UCRE on permafrost seems to gradually di-minishes,but UCRE continues to fulfill the role of stabilizing the underlying permafrost thermal state over the long-term.These results show that UCRE can quickly restore and stabilize the thermal state of permafrost in the early stages of construction,and adapt to the influence of future climate change.The findings provide important guidance for understanding the variations of permafrost thermal stability beneath the embankment in permafrost regions,as well as for improving the embankment stability and operational safety of the Qinghai-Tibet Railway.

A U-Shaped Network-Based Grid Tagging Model for Chinese Named Entity Recognition

Chinese named entity recognition(CNER)has received widespread attention as an important task of Chinese information extraction.Most previous research has focused on individually studying flat CNER,overlapped CNER,or discontinuous CNER.However,a unified CNER is often needed in real-world scenarios.Recent studies have shown that grid tagging-based methods based on character-pair relationship classification hold great potential for achieving unified NER.Nevertheless,how to enrich Chinese character-pair grid representations and capture deeper dependencies between character pairs to improve entity recognition performance remains an unresolved challenge.In this study,we enhance the character-pair grid representation by incorporating both local and global information.Significantly,we introduce a new approach by considering the character-pair grid representation matrix as a specialized image,converting the classification of character-pair relationships into a pixel-level semantic segmentation task.We devise a U-shaped network to extract multi-scale and deeper semantic information from the grid image,allowing for a more comprehensive understanding of associative features between character pairs.This approach leads to improved accuracy in predicting their relationships,ultimately enhancing entity recognition performance.We conducted experiments on two public CNER datasets in the biomedical domain,namely CMeEE-V2 and Diakg.The results demonstrate the effectiveness of our approach,which achieves F1-score improvements of 7.29 percentage points and 1.64 percentage points compared to the current state-of-the-art(SOTA)models,respectively.

Deformation behaviors of four-layered U-shaped metallic bellows in hydroforming

Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming,the stress concentration and defects such as wrinkling and fracture may easily occur.It is a key to reveal the deformation behaviors in order to obtain a sound product.Based on the ABAQUS platform,a 3 D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment.The stress and strain distributions,wall thickness variations and bellow profiles of each layer in the whole process,including bulging,folding and springback stages,are studied.Then deformation behaviors of bellows under different forming conditions are discussed.It is found that the wall thinning degrees of different layer vary after hydroforming,and is the largest for the inner layer and smallest for the outer layer.At folding stage,the wall thinning degree of the crown point increases lineally,and the difference among layers increases as the process going.The displacements of the crown point decrease from the inner layer to the outer layer.After springback,the U-shaped cross section changes to a tongue shape,the change of convolution pitch is much larger than the change of convolution height,and the springback values of the inner layer are smaller than the outer layer.An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase.With changing of process parameters,bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback.This research is helpful for precision forming of multi-layered bellows.

Bombyx mori U-shaped regulates the melanization cascade and immune response via binding with the Lozenge protein

Zinc finger protein,an important transcription factor,regulates gene expression associated with various physiological and pathological processes.U-shaped,belong to the Friend of GATA(FOG)transcription factor,plays a crucial role in hematopoiesis by interacting with the GATA transcription factor as a co-factor.However,little is known about its functions in insects.In the present study,a U-shaped cDNA was identified and characterized from the silkworm Bombyx mori and its potential roles in innate immunity investigated.The predicted silkworm U-shaped amino acid sequence contained a classical nuclear localization signal(NLS)motif“GESSPKRRRR”at position 45CU459,and arginine residues at position 456 and 478 are the critical sites of the NLS.U-shaped mRNA was detected in all tested tissues of the B.mori;however,the highest levels were found in the hemocytes.U-shaped mRNA expression levels were upregulated in the hemocyte after the Escherichia coli and Staphylococcus aureus challenge.Furthermore,U-shaped knockdown significantly reduced the melanization process and suppressed the expression of melanization-associated genes,including PPO1,PPO2,PPAE and BAEE.In addition,U-shaped interacts with Lozenge protein to regulate the innate immune response of the insect.Our results revealed that U-shaped binds directly to Lozenge protein to modulate the melanization process and innate immune responses in silkworm.

Galerkin finite element analysis of magneto-hydrodynamic natural convection of Cu-water nanoliquid in a baffled U-shaped enclosure

In this paper,single-phase homogeneous nanofluid model is proposed to investigate the natural convection of magneto-hydrodynamic(MIID)flow of Newtonian Cu—H20 nanoli­quid in a baffled U-shaped enclosure.The Brinkman model and Wasp model are considered to measure the effective dynamic viscosity and effective thermal conductivity of the nanoliquid coreespondingly.Nanoliquid's effective properties such as specific heat,density and thermal expansion coefficient are modeled using mixture theory.The complicated PDS(partial differ­ential system)is treated for numeric solutions via the Galerkin finite element method.The perti­nent parameters Hartmann number(1≤Ha≤60),Rayleigh number(10^(3)≤Ra≤10^(6))and nanoparticles volume fraction (0% ≤Ф≤4%) are taken for the parametric analysis, and it is conducted via streamlines and isotherms. Excellent agreement between numerical results and open literature. It is ascertained that heat transfer rate enhances with Rayleigh number Ra and volume fraction 0, however it is diminished for laiger Hartmann number Ha.

U-shaped micro-groove fiber based on femtosecond laser processing for humidity sensing

A novel optical fiber sensor with a U-shaped micro-groove structure ablated by femtosecond laser on single-mode fiber for measuring air relative humidity(RH)is reported in this paper.In order to improve the accuracy of sensor,a graphene oxide(GO)/polyvinyl alcohol(PVA)composite film is coated on the surface of micro-groove structure.In the U-shaped micro-groove structure,the remaining core and micro-cavity in the micro-groove make up two major optical propagation paths,forming a Mach-Zehnder interferometer(MZI).The sensor has a good linear response within the RH range of 30%—85%,and the maximum sensitivity can reach 0.638 1 nm/%RH.The effect of temperature on the overall performance of the humidity sensor is also investigated.As a new type of all-fiber device,the sensor shows excellent sensitivity and stability.

Effect of Guide Vane on Pressure Loss and Heat Transfer Characteristics of Supercritical CO_(2)in U-Shaped Channel

U-shaped channel is a common unit structure in heat exchanger.The pressure loss and heat transfer characteristics of U-shaped channel have important influence on the comprehensive performance of heat exchanger.In this paper,combined with the thermo-physical property of supercritical CO_(2)(SCO_(2)),the influence of the guide vanes on the pressure loss and heat transfer characteristics of SCO_(2)in U-shaped channel was studied numerically.The four different guide vanes included integral guide vane,two-stage symmetric guide vane,two-stage asymmetric guide vane and discrete guide vane.CO_(2)Real Gas Property file(RGP)was imported into ANSYS CFX commercial software for calculation,and the turbulence model was SST k-ω.At the same time,the influence of different inlet Reynolds numbers and heating conditions of channel wall were also studied.