Synthesis,Structure and Properties of a Novel Infinite Triple Helices Coordination Polymer{[Co(4,4'-bipyridine)(4,4'azobispyridine)_(2)(NCS)_(2)]·H_(2)O}_(n)

The novel complex{[Co(bipy)(azpy)_(2)(NCS)_(2)]·H_(2)O}n(where bipy=4,4′bipyridine,azpy=4,4′azobisp yridine)has been synthesized and characterized by elemental analyses,IR,UV,thermal analyses,and variable temperature magnetic susceptibility.The crystal(C_(32)H_(26)CoN_(12)OS_(2),Mr=717.70)belongs to the orthorhombic,space group Pnna,a=2.21312(16)nm,b=1.40403(10)nm,c=1.14237(8)nm,V=3.5497(4)nm^(3),Z=4,Dc=1.343g·cm^(-3),μ=0.645mm^(-1),F(000)=1476,and final R_(1)=0.0691,wR_(2)=0.1129 for 231 parameters and 1674 observed reflections[I>2.00σ(I)].The Co(Ⅱ)atom is,in a distorted octahedral geometry,coordinated by six nitrogen atoms from two bridging bipy,two monodentate azpy,and two thiocyanate groups.The bridging ligand bipy links Co(Ⅱ)atoms to form the infinite“rod"with terminal coordination azpy ligand acting as sidearms.Unprecedented three parallel interpenetrating two dimensional(4,4)networks and novel infinite triple helices are formed via hydrogen bonding interactions.CCDC:155588.

Crystal Structure of Borophosphate with 6_1 Screw Axis Helices

A brilliant purple octahedral single crystal is hydrothermally synthesized by the reaction of CoCl26H2O, H3BO3 and H3PO4 in NaOH aqueous solution of CH3(CH2)15N(CH3)3Br, and its crystal structure has been characterized by single-crystal X-ray diffraction. The compound, NaCo(H2O)2BP2O8稨2O (Mr = 336.72), belongs to hexagonal, space group P6122 with a = 9.447(5), c = 15.83(1) , V = 1223(1) 3, Dc = 2.742 g/cm3, Z = 6, F(000) = 1002 and m = 2.606 mm-1. The three-dimensional framework in the compound is built up from the linkage tetrahedral ribbons, in which the BO4 and PO4 tetrahedra alternate with CoO6 octahedra. The sodium ions and water molecules are located within the free thread of the helical ribbons.

Formation Sites and Microscopic Conformation Study on the Konjac Glucomannan Molecular Helices

In this work, the formation sites, helical parameters and hydrogen bond positions of Konjac glucomannan molecular helices were investigated using molecular dynamic simulation method. To our interest, the KGM chain is mainly composed by local left and right helix struetttres. The formation sites of KGM chain might locate at the chain-segments containing acetyl groups, and the left helix is the favorable conformation of KGM. Temperature-dependent molecule conformation study indicates that the right helix is dominant when the temperature is lower than 343 K, above which, however, the left helix is dominating （right helix disappears）. In addition, intramolecular hydrogen bonds in the left helix can be found at the -OH groups on C（2）, C（4） and C（6） of mannose residues; comparably, the intramolecular hydrogen bonds in the right helix can be mainly observed at the -OH groups on C（4） and C（6） of the mannose residues and C（3） of the glucose residues. In conclusion, molecular dynamic simulation is an efficient method for the microscopic conformation study of glucomannan molecular helices.

Primary Organicamine Templated Indium Iodate (H_2en)KIn(IO_3)_6·2(H_2O) with Hydrogen-bonded Helices

The first primary organicamine templated indium iodate with the formula （H2en）KIn（IO3）6-2（H2O） was hydrothermally synthesized via reaction at 100 ℃ for 7 d and characterized by single-crystal X-ray diffraction and thermal analysis. The compound crystallized in a triclinic system with space group P1, a=0.69803（14） nm, b=0.70863（14） nm, c=1.2091（2） nm, a=76.417（4）°,β=79.953（4）°, γ=72.206（3）°, V=0.55012（19） nm3. Structure determination indicates that it is made up of zero-dimensional units each of which consists of [In（IO3）6]3 anion, potassium, water and ethylenediamine cation. The most striking feature of the compound is that it possesses helical hydrogen bonds formed by organic amine template, water molecules and inorganic network.

On-surface Synthesis of Multiple Non-benzenoid Carbohelicenes Fused with Fluorene Unit(s)

Comprehensive Summary Carbohelicenes have garnered considerable attention for their inherent chirality and structural flexibility.Increasing multi-helicity and incorporating non-six-membered rings to substitute benzenoid rings within helicenes are effective strategies for introducing unique photoelectric properties.Despite the disclosure of numerous helicenes,the inaccessible precursors and the lack of synthetic routes pose a challenge in achieving desired helicene structures fused with non-benzenoid rings.Herein,we report the synthesis of multiple non-benzenoid carbohelicenes fused with fluorene unit(s)through intramolecular cyclodehydrogenation of 9,10-di(naphthalen-1-yl)anthracene on Au(111)surface.Two potential cyclodehydrogenation manners between naphthyl and anthracene lead to the formation of fluorene-fused[5]helicene and[4]helicene moiety.Consequently,a total of four stable products were observed.The atomic topographies of products are characterized by bond-resolving scanning tunneling microscopy.The chiral helicity of targeted products can be switched by tip manipulation.Density-functional-theory calculations unveils the reaction pathway of four products.The comparative analysis of their respective energy barriers exhibits a correlation with the experimentally determined yields.Furthermore,we synthesize the polymer chains incorporating non-benzenoid carbohelicenes via the Ullmann reaction of 2,6-dibromo-9,10-di(1-naphthyl)anthracene precursors.Our work proposes a synthetic methodology for several novel helicene-like structures fused with fluorene units and the polymer bearing helicene subunits,thus highlighting the immense potential of these compounds in the application fields of luminescent electronic devices.

Interactions between Transmembrane Helices within Monomers of the Aquaporin AtPIP2;1 Play a Crucial Role in Tetramer Formation

Aquaporin （AQP） is a water channel protein found in various subcellular membranes of both prokaryotic and eukaryotic cells. The physiological functions of AQPs have been elucidated in many organisms. However, understanding their biogenesis remains elusive, particularly regarding how they assemble into tetramers. Here, we investigated the amino acid residues involved in the tetramer formation of the Arabidopsis plasma membrane AQP AtPIP2;1 using extensive amino acid substitution mutagenesis. The mutant proteins V41A/ E44A, F51A/L52A, F87A/191A, F92A/193A, V95A/Y96A, and H216A/L217A, harboring alanine substitutions in the transmembrane （TM） helices of AtPIP2;1 polymerized into multiple oligomeric complexes with a vari- able number of subunits greater than four. Moreover, these mutant proteins failed to traffic to the plasma membrane, instead of accumulating in the endoplasmic reticulum （ER）. Structure-based modeling revealed that these residues are largely involved in interactions between TM helices within monomers. These results suggest that inter-TM interactions occurring both within and between monomers play crucial roles in tetramer formation in the AtPIP2;1 complex. Moreover, the assembly of AtPIP2;1 tetramers is critical for their trafficking from the ER to the plasma membrane, as well as water permeability.

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

Helicene-based emitters with unique inherent circularly polarized luminescence(CPL)are promising yet remain a formidable challenge for highly efficient circularly polarized organic light-emitting diodes(CP-OLEDs),ascribed to their tough synthesis,low emission efficiency,and easy racemization in the thermal deposition process.Herein,a pair of helicenebased enantiomers,namely(P)-helicene-BN and(M)-helicene-BN,were developed,which merge helical chirality and the B/N/S inserted polycyclic aromatic framework to concurrently feature CPL and narrow thermally activated delayed fluorescence(TADF)characteristics.Benefiting from the excellent thermal/photophysical/chiroptical properties,the narrowband green CP-OLEDs based on enantiomers achieved maximum external quantum efficiencies(EQE_(max))of up to 31.5%,and dissymmetry factor(|g_(EL)|)of 2.2×10^(−3).This work reveals the great potential of helicene-based emitters in CP-OLEDs.

A novel flexible nerve guidance conduit promotes nerve regeneration while providing excellent mechanical properties

Autografting is the gold standard for surgical repair of nerve defects>5 mm in length;however,autografting is associated with potential complications at the nerve donor site.As an alternative,nerve guidance conduits may be used.The ideal conduit should be flexible,resistant to kinks and lumen collapse,and provide physical cues to guide nerve regeneration.We designed a novel flexible conduit using electrospinning technology to create fibers on the innermost surface of the nerve guidance conduit and employed melt spinning to align them.Subsequently,we prepared disordered electrospun fibers outside the aligned fibers and helical melt-spun fibers on the outer wall of the electrospun fiber lumen.The presence of aligned fibers on the inner surface can promote the extension of nerve cells along the fibers.The helical melt-spun fibers on the outer surface can enhance resistance to kinking and compression and provide stability.Our novel conduit promoted nerve regeneration and functional recovery in a rat sciatic nerve defect model,suggesting that it has potential for clinical use in human nerve injuries.

Designing Electronic Structures of Multiscale Helical Converters for Tailored Ultrabroad Electromagnetic Absorption

Atomic-scale doping strategies and structure design play pivotal roles in tailoring the electronic structure and physicochemical property of electromagnetic wave absorption(EMWA)materials.However,the relationship between configuration and electromagnetic(EM)loss mechanism has remained elusive.Herein,drawing inspiration from the DNA transcription process,we report the successful synthesis of novel in situ Mn/N co-doped helical carbon nanotubes with ultrabroad EMWA capability.Theoretical calculation and EM simulation confirm that the orbital coupling and spin polarization of the Mn–N4–C configuration,along with cross polarization generated by the helical structure,endow the helical converters with enhanced EM loss.As a result,HMC-8 demonstrates outstanding EMWA performance,achieving a minimum reflection loss of−63.13 dB at an ultralow thickness of 1.29 mm.Through precise tuning of the graphite domain size,HMC-7 achieves an effective absorption bandwidth(EAB)of 6.08 GHz at 2.02 mm thickness.Furthermore,constructing macroscale gradient metamaterials enables an ultrabroadband EAB of 12.16 GHz at a thickness of only 5.00 mm,with the maximum radar cross section reduction value reaching 36.4 dB m2.This innovative approach not only advances the understanding of metal–nonmetal co-doping but also realizes broadband EMWA,thus contributing to the development of EMWA mechanisms and applications.

Tunable construction of transition metal-coordinated helicene cages

We report a facile and tailored method to prepare globally twisted chiral molecular cages through tunable coordination of bis-bipyridine-terminated helicene ligands to a series of transition metals including Fe(Ⅱ), Co(Ⅱ), Ni(Ⅱ) and Zn(Ⅱ). This system shows an efficient remote transfer of stereogenecity from the helicene core to the bipyridine-metal coordination sites and subsequently the entire cages. While the Fe(Ⅱ), Co(Ⅱ) and Ni(Ⅱ)-derived M_(2)L_(3)(M for metal and L for ligand) cages exhibit quasi-reversible redox features, the Zn(Ⅱ) analogues reveal prominent yellow circularly polarized luminescence. Interestingly,with the addition of Na_(2)SO_(4), the Zn_(2)L_(3)cages reassemble into sextuple-stranded Zn_(6)L_(6)(SO_(4))_(4)cages in which three Zn_(2)L_(2) units are bound together by four sulfates and further coalesced by offset inter-ligandπ-π interactions.

Homochiral Coordination Polymers from Single Helices to Multiple Helices Controlled by Metal Ions

Helix as essential molecular chiral phenomenon at supramolecular level offers an affective method to study chiral characteristic of homochiral coordination polymers(CPs).Herein,two homochiral CPs[Cd((R)-CBA)_(2)(3,5-DIT)]_(n)((R)-H_(2) CBA=(R)-4-(1-carboxyethoxy)benzoic acid,3,5-DIT=3,5-di(1 H-imidazol-1-yl)toluene,1-R)and[Zn((R)-CBA)(3,5-DIT)]_(n)(2-R)were synthesized under hydrothermal conditions.In complex 1-R,only a helical chain was built by chiral ligands(R)-CBA2-,ancillary ligands 3,5-DIT and Cd(Ⅱ)ions.After Cd(Ⅱ)ions were replaced by Zn(Ⅱ)ions under similar reaction system,Zn(Ⅱ),(R)-CBA^(2-)and/or 3,5-DIT formed six types of helices,resulting in complex 2-R.So,the metal ions played a key role in the construction of helical structures.Complexes 1-R and 2-R were also characterized by elemental analysis,PXRD,TGA,CD and UV-visible absorptions.In addition,complexes 1-R and 2-R exhibited different photoluminescence behaviors in solid sate compared to free ligand(R)-H_(2)CBA.

Suppression of Vortex-Induced Vibration Caused by A Terebridae-Inspired Cylinder with Different Helical Angles

Biomimetic design has recently received widespread attention.Inspired by the Terebridae structure,this paper provides a structural form for suppressing vortex-induced vibration(VIV)response.Four different structural forms are shown,including the traditional smooth cylinder(P0),and the Terebridae-inspired cylinder with the helical angle of 30°(P_(30)),60°(P_(60)),and 90°(P_(90)).Computational fluid dynamics(CFD)method is adopted to solve the flow pass the Terebridae-inspired structures,and the vibration equation is solved using the Newmark-βmethod.The results show that for P_(30),P_(60) and P_(90),the VIV responses are effectively suppressed in the lock-in region,and P_(60) showed the best VIV suppression performance.The transverse amplitude and the downstream amplitude can be reduced by 82.67%and 91.43%respectively for P_(60) compared with that for P0,and the peak of the mean-drag coefficient is suppressed by 53.33%.The Q-criterion vortices of P_(30),P_(60),and P_(90) are destroyed,with irregular vortices shedding.It is also found that the boundary layer separation is located on the Terebridae-inspired ribs.The twisted ribs cause the separation point to constantly change along the spanwise direction,resulting in the development of the boundary layer separation being completely destroyed.The strength of the wake flow is significantly weakened for the Terebridae-inspired cylinder.

Multi-physical fields distribution in billet during helical electromagnetic stirring:A numerical simulation research

Electromagnetic stirring is one of the widely applied techniques to modify the quality of casting billets.Different from conventional rotate stirring,the helical stirring is more professional in assisting multi-dimensional flow of molten metal and eliminating solidification defects.In this study,the single-winding helical stirring(SWHS)was introduced,offering advantages such as smaller volume and lower electromagnetic shielding compared to traditional helical stirring methods.Following a comprehensive numerical simulation,the stirring parameters of SWHS were adjusted to yoke inclination angle of 43°and frequency of 12 Hz.The higher electromagnetic force and flow velocity in drawing direction,as well as the lower temperature gradient induced by the SWHS,are positive factors for homogeneous solidification of billet.The experimental results on Al-8%Si alloy and 0.4%C-1.1%Mn steel demonstrate that compared to rotate stirring,the SWHS process can induce better billet quality and is more effective in accelerating the equiaxed expansion and reducing element segregation.The SWHS process can enhance the equiaxed ratio of the billet by 58.3%and reduce segregation degree of carbon element by 10.97%.Consequently,SWHS holds great promise as a potential approach for improving the quality of continuous casting billets.

Research and development of a 0.5-m-long helical superconducting undulator prototype

The helical undulator is in high demand in synchrotron radiation facilities for circular polarization generation.Owing to the higher field strength provided by the superconducting undulator compared to the conventional permanent-magnet undulator,greater research efforts should be directed toward this area.The helical superconducting undulator holds great potential in synchrotron radiation facilities,especially in low-energy storage rings that seek circularly polarized radiation with the highest possible radiation flux.Following the successful development of planar superconducting undulators,the Institute of High Energy Physics conducted research and development for the helical superconducting undulator.A 0.5-m-long Deltatype superconducting undulator prototype was developed and tested.Detailed information on the design,fabrication,and cryogenic testing of the prototype is presented and discussed.

Effect of antenna helicity on discharge characteristics of helicon plasma under a divergent magnetic field

The characteristics of the blue core phenomenon observed in a divergent magnetic field helicon plasma are investigated using two different helical antennas, namely right-handed and lefthanded helical antennas. The mode transition, discharge image, spatial profiles of plasma density and electron temperature are diagnosed using a Langmuir probe, a Nikon D90 camera,an intensified charge-coupled device camera and an optical emission spectrometer, respectively.The results demonstrated that the blue core phenomenon appeared in the upstream region of the discharge tube at a fixed magnetic field under both helical antennas. However, it is more likely to appear in a right-handed helical antenna, in which the plasma density and ionization rate of the helicon plasma are higher. The spatial profiles of the plasma density and electron temperature are also different in both axial and radial directions for these two kinds of helical antenna. The wavelength calculated based on the dispersion relation of the bounded whistler wave is consistent with the order of magnitude of plasma length. It is proved that the helicon plasma is part of the wave mode discharge mechanism.

Theoretical model of current propagation in a helical coil with varying geometry and screen tube

An analytical model of current propagation in a helical coil with varying geometry is developed.It can be used for post-acceleration and post-focusing of ions produced via laser-driven target normal sheath acceleration and generation of electromagnetic pulses.We calculate the current that propagates in a helical coil and suggest a method for improving its dispersion properties using a screening tube and with pitch and radius variation.The electromagnetic fields calculated with the analytical model are in agreement with particle-in-cell simulations.The model provides insights into the physics of current propagation in helical coils with varying geometries and enables a numerical implementation for rapid proton spectrum computations,which facilitate the design of such coils for future experiments.

Advancing high-speed train gearbox durability:enhanced bearing load and contact stress through transition from helical to herringbone gears

High-speed trains typically utilize helical gear transmissions,which significantly impact the bearing load capacity and fatigue service performance of the gearbox bearings.This paper focuses on the gearbox bearings,establishing dynamic models for both helical gear and herringbone gear transmissions in high-speed trains.The modeling particularly emphasizes the precision of the bearings at the gearbox's pinion and gear wheels.Using this model,a comparative analysis is conducted on the bearing loads and contact stresses of the gearbox bearings under uniform-speed operation between the two gear transmissions.The findings reveal that the helical gear transmission generates axial forces leading to severe load imbalance on the bearings at both sides of the large gear,and this imbalance intensifies with the increase in train speed.Consequently,this results in a significant increase in contact stress on the bearings on one side.The adoption of herringbone gear transmission effectively suppresses axial forces,resolving the load imbalance issue and substantially reducing the contact stress on the originally biased side of the bearings.The study demonstrates that employing herringbone gear transmission can significantly enhance the service performance of high-speed train gearbox bearings,thereby extending their service life.

Numerical Studies on Thermal and Hydrodynamic Characteristics of LNG in Helically Coiled Tube-in-Tube Heat Exchangers

As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natural gas(LNG)as the working fluid inHCTT heat exchangers is rarely reported.In this paper,the characteristics of HCTT heat exchangers,in which LNG flows in the inner tube and ethylene glycol-water solution flows in the outer tube,are studied by numerical simulations.The influences of heat transfer characteristics and pressure drops of the HCTT heat transfers are studied by changing the initial flow velocity,the helical middle diameter,and the helical pitch.The results indicate that different initial flow velocities in the inner tube and the outer tube of the HCTT heat exchanger have little influence on the secondary flow of the fluid in the helical tubes,and the overall flow characteristics tend to be stable.The smaller helical middle diameter of the HCTT heat exchanger leads to the shorter fluid flow length,the smaller resistance along the tubes and the increase of initial pressure under the condition of constant inlet velocity,which promotes the occurrence of secondary flow.The axial flow of fluid promotes the destruction of heat transfer boundary layer and gains strength of the turbulence and heat transfer efficiency.With the increase of the helical pitch of the HCTT heat exchanger,the turbulent intensity and the heat transfer efficiency are also increased.Moreover,the improvement of the flow state of the HCTT exchanger in a longer helical pitch also enhances the heat exchange efficiency.

Numerical Simulation of Liquified Natural Gas Boiling Heat Transfer Characteristics in Helically Coiled Tube-in-Tube Heat Exchangers

Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified natural gas(LNG)use and cold energy recovery.The heat transfer characteristics,pressure distribution,and degree of vaporization of LNG in HCTT heat exchangers are numerically investigated.By comparing the simulation results of the computational model with existing experimental results,the effectiveness of the computational model is verified.The numerical simulation results show the vapor volume fraction of the HCTT heat exchanger is related to the inlet Reynolds number,inner tube diameters,and helix diameter.The vapor volume fraction increases rapidly from the fourth to the seventh equal division points of the helix tube length.On condition that the inlet Reynolds number is greater than 33500,the pressure drop rate gradually increases.When the magnitude of the vapor volume fraction is below 0.2,the heat transfer coefficient increase rate is greater than that when the vapor volume fraction is above 0.2.The heat exchange efficiency of HCTT heat exchangers increases with the decrease of the ratio of helix diameter to inner tube diameter.

Mathematical Modelling and Design of Helical Coil Heat Exchanger for Production of Hot Air for Fluidized Bed Dryer

In global industrialization, efforts have been made to increase the rate of heat transfer in heat exchanger, minimizing the size of heat exchanger to reduce cost as well as increasing the effectiveness. Helical coil heat exchanger (HCHE) has been proven to be effective in improving heat transfer due to its large surface area. In this study, HCHE was designed to provide hot air needed for fluidized bed drying processes. The HCHE design model was fabricated and evaluated to study the efficiency of the hot air output for a laboratory fluidized bed dryer. The mathematical model for estimation of the final (output) temperature of air, Taf, passing through the HCHE was developed and validated experimentally. The drying of bitter kola particulates was carried out with a drying temperature of 50C 3C and a bed height-to-bed diameter ratio (H/D) of 1.5. The time taken to dry bitter kola particulates to 0.4% moisture content was 1 hour 45 minutes. Hence, HCHE is recommended for use in the production of hot for laboratory-scale fluidized bed dryers.