Experimental and numerical investigations on acoustic damping of monoclinic crystalline wideband sound absorbing structures

In order to overcome the limitations of traditional microperforated plate with narrow sound absorption bandwidth and a single structure,two multi-cavity composite sound-absorbing materials were designed based on the shape of monoclinic crystals:uniaxial oblique structure(UOS)and biaxial oblique structure(BOS).Through finite element simulation and experimental research,the theoretical models of UOS and BOS were verified,and their sound absorption mechanisms were revealed.At the same time,the influence of multi-cavity composites on sound absorption performance was analyzed based on the theoretical model,and the influence of structural parameters on sound absorption performance was discussed.The research results show that,in the range of 100-2000 Hz,UOS has three sound absorption peaks and BOS has five sound absorption peaks.The frequency range of the half-absorption bandwidth(α>0.5)of UOS and BOS increases by 242% and 229%,respectively.Compared with traditional microperforated sound-absorbing structures,the series and parallel hybrid methods significantly increase the sound-absorbing bandwidth of the sound-absorbing structure.This research has guiding significance for noise control and has broad application prospects in the fields of transportation,construction,and mechanical design.

Effect of wire diameter compression ratio on drawing deformation of micro copper wire

A crystal plasticity finite element model was developed for the drawing deformation of pure copper micro wire,based on rate-dependent crystal plasticity theory.The impact of wire diameter compression ratio on the micro-mechanical deformation behavior during the wire drawing process was investigated.Results indicate that the internal deformation and slip of the drawn wire are unevenly distributed,forming distinct slip and non-slip zones.Additionally,horizontal strain concentration bands develop within the drawn wire.As the wire diameter compression ratio increases,the strength of the slip systems and the extent of slip zones inside the deformation zone also increase.However,the fluctuating stress state,induced by contact pressure and frictional stress,results in a rough and uneven wire surface and diminishes the stability of the drawing process.

Synthesis,crystal structures,and antibacterial activities of two zinc(Ⅱ) complexes bearing 5⁃phenyl⁃1H⁃pyrazole group

A novel compound(H_(2)L)SCN(5⁃methyl⁃3⁃phenyl⁃2H⁃pyrazol⁃1⁃ium thiocyanate)has been obtained by the reaction of thiosemicarbazide with benzoylacetone in ethanol.Two zinccomplexes[Zn(HL)_(2)(NCS)(CH_(3)COO)](1)and[Zn_(2)(L)_(2)(HL)_(2)(NCS)_(2)]_(2)·2CH_(3)OH(2)have been synthesized by the coordination reactions of Zn(OAc)_(2)·2H_(2)O or ZnCl_(2)with(H_(2)L)SCN under reflux conditions.Elemental analyses and single⁃crystal X⁃ray diffraction have con⁃firmed the structures of the synthesized compounds.The(H_(2)L)SCN ligand and complex 1 pertain to the triclinic sys⁃tem with space group P1,while complex 2 belongs to the monoclinic system with space group P2_(1)/n.Additionally,the antibacterial activities of the compounds were evaluated in vitro using the agar diffusion method against the bac⁃terial strains(Candida albicans,Staphylococcus aureus,and Escherichia coli).The results showed that the ligand exhibited relatively good antibacterial activities against the bacteria,and the complexes possessed stronger antibac⁃terial activities against the same bacteria than the free ligand.CCDC:2190252,(H2L)SCN;2190253,1;2190256,2.

Syntheses,crystal structures,and quantum chemistry calculation of two Ni(Ⅱ)coordination polymers

Two new coordination polymers,[Ni(Hpdc)(bib)(H_(2)O)]_(n)(1)and{[Ni(bib)_(3)](ClO_(4))_(2)}_(n)(2),were prepared by mixing Ni^(2+),3,5⁃pyrazoledicarboxylic acid(H3pdc)/p⁃nitrobenzoic acid and 1,4⁃bis(imidazol⁃1⁃ylmethyl)butane(bib)by a hydrothermal method,respectively.X⁃ray crystallography reveals a 2D network constructed by six⁃coordinated Ni(Ⅱ)centers,bib,and Hpdc2-ligands in complex 1,while a 2D network is built by Ni(Ⅱ)and bib ligands in 2.Furthermore,the quantum⁃chemical calculations have been performed on‘molecular fragments’extracted from the crystal structure of 1 using the PBE0/LANL2DZ method in Gaussian 16 and the VASP program.CCDC:2343794,1;2343798,2.

Polycrystalline ZSM-5 Aggregates Induced by Seed and Catalytic Performance in Methanol to Hydrocarbon

Synthesis of ZSM-5 zeolite typically utilizes small molecule polyamines or quaternary ammonium salts as organic structure guiding agent(OSDA).By contrast,the OSDA-free hydrothermal synthesis system eliminates the use of organic templates and the subsequent calcination procedure.This not only reduces the cost of synthesis,but also prevents environmental pollution from the combustion of organic templates,representing an eco-friendly approach.Despite this,literature suggests that even so-called template-free synthesis systems often involve trace amount of organic substances like alcohol.In the present work,a calcined commercial ZSM-5 zeolite was served as seed,with sodium aluminate as aluminum source and silica sol as silicon source,ensuring an entirely template-free synthesis system.Polycrystalline ZSM-5 aggregates consisted of rod-like nanocrystals were successfully prepared in the completely OSDA-free system.Effects of the Si/Al ratio in ZSM-5 seed,dosage and crystallization conditions such as crystallization temperature and crystallization time on ZSM-5 synthesis were investigated.The results show that a highly crystallinity ZSM-5 aggregate consisting of primary nano-sized crystals less than 100 nm is produced from a gel precursor with 5.6%(in mass)seed after hydrothermal treatment for 48 h.Furthermore,the Si/Al ratio in ZSM-5 seed has little effect on the topological structure and pore structure of the synthesized samples.However,the seeds with a low Si/Al ratio facilitate faster crystallization of zeolite and enhance the acidity,especially the strong acid centers,of the catalyst.The catalytic performance of the synthesized polycrystalline ZSM-5 was evaluated during dehydration of methanol and compared with a commercial reference ZSM-5r.The results exhibit that as compared with the reference catalyst,the fabricated sample has a longer catalytic lifetime(16 h vs 8 h)attributed to its hierarchical pores derived from the loosely packed primary nanoparticles.Additionally,the prepared polycrystalline catalyst also exhibits a higher aromatics selectivity(28.1%-29.8%vs 26.5%).

Syntheses,structures,and properties of three coordination polymers based on 5⁃ethylpyridine⁃2,3⁃dicarboxylic acid and N⁃containing ligands

Three coordination polymers[Mn(epda)(2,2'⁃bipy)(H_(2)O)](1),[Mn(epda)(phen)](2),and[Co_(2)(epda)2(bpe)2(H_(2)O)_(4)]·5H_(2)O(3)(H2epda=5⁃ethyl⁃pyridine⁃2,3⁃dicarboxylic acid,2,2'⁃bipy=2,2'⁃bipyridine,phen=phenanthroline,bpe=1,2⁃bis(4⁃pyridyl)ethylene)were synthesized by solvothermal reactions and characterized by single⁃crystal X⁃ray diffraction,thermogravimetric analyses,IR spectroscopy and elemental analysis.1 displays a 1D chain struc⁃ture,and these chains are joined by O-H…O hydrogen bonding andπ⁃πstacking interactions to generate a 2D layer structure.2 displays a 2D layer structure,and adjacent layers are generated 3D architecture throughπ⁃πstacking interactions.3 displays a 1D chain structure,and adjacent chains are generated double layer structure through O-H…O hydrogen bonding.The fluorescent properties of 1 and 3 indicate that they can potentially be used as a luminescent sensor.1 was highly selective and sensitive towards o⁃nitrophenol through different detection mechanisms,however,3 was highly selective and sensitive towards 2,4,6⁃trinitrophenol.In addition,the magnetic behavior of 2 has also been investigated.CCDC:2172533,1,2355773,2,2355774,3.

Synthesis,crystal structure and photo-physical properties of tris(4-methyl-2,5-diphenylpyridine)iridium for OLED

Organic light-emitting diodes(OLEDs)have important applications in the field of next-generation displays and lighting,and phosphorescent iridium complexes are an important class of electroluminescent phosphorescent materials.In this paper,Ir(bmppy)_(3),tris(4-methyl-2,5-diphenylpyridine)iridium,was synthesized and elvaluted for photo-physical characteristics.Single crystals suitale for X-ray diffraction(XRD)were grown from a mixture solvent of dichloromethane and absolute ethanol.The composition and structur of Ir(bmppy)_(3)were determined by element analysis,NMR spectra and XRD.The complex crystallizes in the monoclinic symmetry with the space group P21/c with a slightly distorted octahedral configuration.As measured by UV-Visible and photoluminescence spectra,Ir(bmppy)_(3) displays a maximum emission at at 527 nm at ambient temperature,a typical green-emitting profile.The complex has potential for application in the OLED industry.

Application and optimization design of non-obstructive particle damping-phononic crystal vibration isolator in viaduct structure-borne noise reduction

The problems associated with vibrations of viaducts and low-frequency structural noise radiation caused by train excitation continue to increase in importance.A new floating-slab track vibration isolator-non-obstructive particle damping-phononic crystal vibration isolator is proposed herein,which uses the particle damping vibration absorption technology and bandgap vibration control theory.The vibration reduction performance of the NOPD-PCVI was analyzed from the perspective of vibration control.The paper explores the structure-borne noise reduction performance of the NOPD-PCVIs installed on different bridge structures under varying service conditions encountered in practical engineering applications.The load transferred to the bridge is obtained from a coupled train-FST-bridge analytical model considering the different structural parameters of bridges.The vibration responses are obtained using the finite element method,while the structural noise radiation is simulated using the frequency-domain boundary element method.Using the particle swarm optimization algorithm,the parameters of the NOPD-PCVI are optimized so that its frequency bandgap matches the dominant bridge structural noise frequency range.The noise reduction performance of the NOPD-PCVIs is compared to the steel-spring isolation under different service conditions.

A new rhombohedral phase and its 48 variants inβtitanium alloy

A new rhombohedral phase(termed R′)in a solution-aging-treated titanium alloy(Ti-4.5Al-6.5Mo-2Cr-2Nb-1V-1Sn-1Zr,wt.%)was identified.Its accurate Bravais lattice parameters were determined by a novel unit cell reconstruction method based on conventional selected-area electron diffraction(SAED)technique.The orientation relationship between R'phase and BCC phase was revealed.The results show that the R′phase is found to have 48crystallographically equivalent variants,resulting in rather complicated SAED patterns with high-order reflections.A series of in-situ SAED patterns were taken along both low-and high-index zone axes,and all weak and strong reflections arising from the 48 variants were properly explained and directly assigned with self-consistent Miller indices,confirming the presence of the rhombohedral phase.Additionally,some criteria were also proposed for evaluating the indexed results,which together with the Bravais lattice reconstruction method shed light on the microstructure characterization of even unknown phases in other alloys.

Nd:Na_3La_9O_3(BO_3)_8晶体生长和性质研究

采用顶部籽晶法生长出掺杂浓度为3%的Nd:Na3La9O3(BO3)8(Nd:NLBO)晶体。X射线粉末衍射图表明Nd:NLBO与NLBO的晶体结构相同,属于六方晶系。Nd:NLBO(3%)晶体的分凝系数为1.05。测试了晶体的吸收光谱,Nd:NLBO晶体在804nm有较强的吸收,吸收截面为3.2×10-20cm2,半宽度为6.3nm。Nd:NLBO可能是一种潜在的自倍频晶体。

Regulating crystal phase of TiO_(2) to enhance catalytic activity of Ni/TiO_(2) for solar-driven dry reforming of methane

Ni/TiO_(2) catalyst is widely employed for photo-driven DRM reaction while the influence of crystal structure of TiO_(2) remains unclear.In this work,the rutile/anatase ratio in supports was successfully controlled by varying the calcination temperature of anatase-TiO_(2).Structural characterizations revealed that a distinct TiO_(x) coating on the Ni nanoparticles(NPs)was evident for Ni/TiO_(2)-700 catalyst due to strong metal-support interaction.It is observed that the TiOx overlayer gradually disappeared as the ratio of rutile/anatase increased,thereby enhancing the exposure of Ni active sites.The exposed Ni sites enhanced visible light absorption and boosted the dissociation capability of CH4,which led to the much elevated catalytic activity for Ni/TiO_(2)-950 in which rutile dominated.Therefore,the catalytic activity of solar-driven DRM reaction was significantly influenced by the rutile/anatase ratio.Ni/TiO_(2)-950,characterized by a predominant rutile phase,exhibited the highest DRM reactivity,with remarkable H_(2) and CO production rates reaching as high as 87.4 and 220.2 mmol/(g·h),respectively.These rates were approximately 257 and 130 times higher,respectively,compared to those obtained on Ni/TiO_(2)-700 with anatase.This study suggests that the optimization of crystal structure of TiO_(2) support can effectively enhance the performance of photothermal DRM reaction.

Crystal anisotropy of AZ31 magnesium alloy under uniaxial tension and compression

To investigate the deformation twinning and the plastic anisotropy of the hexagonal-close-packed（HCP） single crystal, the crystal plastic constitutive model including slip and twinning deformation was established with finite element method based on crystal plasticity theory. The model was verified by test data. Newton-Raphson iteration method was developed with the stress components directly as the basic variables of iteration. The plastic deformation behavior of single crystal AZ31 alloy was analyzed numerically under monotonic tension and compression, respectively, in four different strain paths（i.e. along 〈2110〉, 〈 0110〉, 〈0001〉 and 〈0111〉） with this model. The stress-strain curves were obtained in the above paths. The numerical calculation results show that this crystal model is feasible to predict the activity of slip/twinning system and to describe the number of active twin variants, the types of dominant twin variants and twin intersection. Due to the polar nature of mechanical twinning in inelastic deformation of the material, the plastic behavior of the single crystal material is demonstrated to be notably anisotropic and high asymmetry.

14W X-Band AlGaN/GaN HEMT Power MMICs

The development of an AIGaN/GaN HEMT power MMIC on SI-SiC designed in microstrip technology is pres- ented. A recessed-gate and a field-plate are used in the device processing to improve the performance of the AIGaN/GaN HEMTs. S-parameter measurements show that the frequency performance of the AIGaN/GaN HEMTs depends significantly on the operating voltage. Higher operating voltage is a key to higher power gain for the AIGaN/GaN HEMTs. The developed 2-stage power MMIC delivers an output power of more than 10W with over 12dB power gain across the band of 9-11GHz at a drain bias of 30V. Peak output power inside the band reaches 14.7W with a power gain of 13.7dB and a PAE of 23%. The MMIC chip size is only 2.0mm × 1. 1mm. This work shows superiority over previously reported X-band AIGaN/GaN HEMT power MMICs in output power per millimeter gate width and output power per unit chip size.

Mineralogy and crystal chemistry of a low grade nickel laterite ore

To acquire understanding of Ni enrichment from laterite ore,the mineralogy and crystal chemistry of a low grade limonite type nickel laterite ore sample assaying 0.97% Ni from Indonesia were studied using optical microscopy,X-ray diffraction（XRD）,scanning electron microscopy（SEM） and electron probe microanalysis（EPMA）.According to EPMA results,the mineral includes 80% goethite（（Fe,Ni,Al）O（OH）） with 0.87% Ni,15% silicate minerals with lizardite（（Mg,Fe,Ni）3Si2O5（OH）） and olivine（（Mg,Fe,Ni）2SiO4）,and 1.19% Ni,and other minor phases,such as hematite,maghemite,chromite and quartz,and no Ni was detected.The mineralogy of the laterite ore indicates that due to the complicated association of the various phases and the variable distribution of Ni,this refractory laterite ore can not be upgraded by traditional physical beneficiation processes.

Anisotropic and temperature-dependent growth mechanism of S-phase precipitates in Al-Cu-Mg alloy in relation with GPB zones

By employing atomic-resolution imaging and first principles energy calculations, the growth behavior of S-phase precipitates in a high strength A1-Cu-Mg alloy was investigated. It is demonstrated that the nucleation and growth of the S-phase precipitate are rather anisotropic and temperature-dependent companying with low dimensional phase transformation. There are actually two types of Guinier-Preston （GP） zones that determine the formation mechanism of S-phase at high aging temperatures higher than 180 ℃. One is the precursors of the S-phase itself, the other is the structural units or the precursors of the well-known Guinier-Preston-Bagaryatsky （GPB） zones. At high temperatures the later GPB zone units may form around S-phase precipitate and cease its growth in the width direction, leading to the formation of rod-like S-phase crystals; whereas at low temperatures the S-phase precipitates develop without the interference with GPB zones, resulting in S-phase orecioitates with lath-like momhology.

Dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in sodium hydroxide solution under atmospheric pressure

The crystal structure, morphology, dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in Na OH solution under atmospheric pressure were systematically investigated by XRD and SEM. The results show that the size of single crystal of gibbsite in gibbsitic bauxite is smaller than that in pure gibbsite, but the interplanar distance is larger than that of pure gibbsite, which result in more defects in the crystal and less energy needed to dissolve in alkaline solution for the gibbsitic bauxite. The dissolution kinetic equations of gibbsitic bauxite and pure gibbsite were established, and the corresponding activation energies were calculated to be 99.144 and 115.149 k J/mol, respectively.

A low-phase-noise and low-power crystal oscillator for RF tuner

A 37. 5 MHz differential complementary metal oxide semiconductor （CMOS） crystal oscillator with low power and low phase noise for the radio frequency tuner of digital radio broadcasting digital radio mondiale （DRAM） and digital audio broadcasting （DAB） systems is realized and characterized. The conventional cross-coupled n-type metal oxide semiconductor （NMOS） transistors are replaced by p-type metal oxide semiconductor （PMOS） transistors to decrease the phase noise in the core part of the crystal oscillator. A symmetry structure of the current mirror is adopted to increase the stability of direct current. The amplitude detecting circuit made up of a single- stage CMOS operational transconductance amplifier （OTA） and a simple amplitude detector is used to improve the current accuracy of the output signals. The chip is fabricated in a 0. 18- pxn CMOS process, and the total chip size is 0. 35 mm x 0. 3 mm. Under a supply voltage of 1.8 V, the measured power consumption is 3.6 mW including the output buffer for 50 testing loads. The proposed crystal oscillator exhibits a low phase noise of - 134. 7 dBc/Hz at 1-kHz offset from the center frequency of 37. 5 MHz.

Intermetallics and phase relations of Mg-Zn-Ce alloys at 400 ℃

The crystal structures,compositions and phase relations of the intermetallics of Mg-Zn-Ce system in the Mg-rich corner at 400 ℃ were identified through equilibrium alloy method.For Mg-Zn-Ce system,there is a linear ternary compound（T phase）,whose chemical formula is（Mg1-xZnx）11Ce.The range of Zn content in T phase is from 9.6% to 43.6%（molar fraction）.The crystal structure of T phase is C-centered orthorhombic lattice with lattice parameters of a=0.96-1.029 nm,b=1.115-1.204 nm,c=0.940-1.015 nm.And the lattice parameters of T phase are decreasing a little with increasing Zn content.According to the results of composition and crystal structure,the maximal solubility of Zn in Mg12Ce is about 7.8%（molar fraction）,and the chemical formula of the solid solution can be identified as（Mg1-xZnx）12Ce.The isothermal section of Mg-Zn-Ce system in Mg-rich corner at 400 ℃ was constructed.

Cooling rate dependence of polymorph selection during rapid solidification of liquid metal zinc

The polymorph selection during rapid solidification of zinc melt was investigated by molecular dynamics simulation. Several methods including g（r）, energy, CNS, basic cluster and visualization were used to analyze the results. The results reveal that the cooling rate has no observable effect on the microstructure as TTc（Tc is the onset temperature of crystallization）; and at the first stage of crystallization, although microstructures are different, the morphologies of nucleus are similar, which are composed of HCP and FCC layers; the polymorph selection of cooling rate finally takes place at the second stage of crystallization： at a high cooling rate, the rapid increase of FCC atoms leads to a FCC crystal mixed with less HCP structures; while at a low cooling rate, HCP atoms grow at the expense of FCC atoms, resulting in an almost perfect HCP phase. The results reveal that the cooling rate is one of the important factors for polymorph selection.

X-Band GaN Power HEMTs with Power Density of 2.23 W/mm Grown on Sapphire by MOCVD

The growth, fabrication, and characterization of 0. 2μm gate-length AlGaN/GaN HEMTs, with a high mobility GaN thin layer as a channel,grown on （0001） sapphire substrates by MOCVD,are described. The unintentionally doped 2.5μm thick GaN epilayers grown with the same conditions as the GaN channel have a room temperature electron mobility of 741cmz^2（V· s） at an electron concentration of 1.52 × 10^16 cm^-3. The resistivity of the thick GaN buffer layer is greater than 10^8Ω· cm at room temperature. The 50mm HEMT wafers grown on sapphire substrates show an average sheet resistance of 440.9Ω□ with uniformity better than 96%. Devices of 0.2μm× 40μm gate periphery exhibit a maximum extrinsic transconductance of 250mS/mm and a current gain cutoff frequency of 77GHz. The AlGaN/GaN HEMTs with 0.8mm gate width display a total output power of 1.78W （2.23W/mm） and a linear gain of 13.3dB at 8GHz. The power devices also show a saturated current density as high as 1.07A/mm at a gate bias of 0.5V.