Helical Rod Research Articles

Laminar Heat Transfer and Pressure Drop in Tube Fitted with Helical Louvered Rod Inserts Using CNT/Water Nanofluids

Laminar Heat Transfer and Pressure Drop in Tube Fitted with Helical Louvered Rod Inserts Using CNT/Water Nanofluids

“pH-jump” synthesis of 2D-rectangular c2mm mesoporous silica materials with helical morphology and extensive void defects

Mesoporous MMT-1 silica nanoparticles with c2mm symmetry and helical morphology were synthesized by a “pH-jump” method using sodium silicate as silica source and ethyl acetate (and other acetate esters) as a pH modifier. In the alkaline synthesis mixture containing both cationic and nonionic surfactants at low concentration, acetate esters hydrolyzed rapidly and caused drastic drop in solution pH to initiate the cooperative assembly of silicate/surfactant mesophase and the condensation of silicate species. When ethyl acetate (EA) was used, nanoparticles with ordered c2mm mesostructure and helical morphology could be formed with an EA-to-silicate ratio (x) of 4.0∼9.0. As x was increased from 4.0 to 9.0, the structural order was decreased yet the degree of silica condensation was enhanced. As a result, the materials exhibited much better hydrothermal stability than those synthesized from tetraalkoxysilanes (such as tetraethoxysilane). Moreover, the increase in x caused changes in particle morphology to long-pitch helical rods with increased length and increased extent of void defects that were irregular in shape and size. The differences in structural and textural properties of the MMT-1 materials should be associated with the pH drop rate and profile during the synthesis with varied x. In-situ small-angle X-ray scattering measurements were performed and analyzed to elucidate the formation mechanism of the materials. The results showed that the MMT-1 materials derived from the pH-jump method are promising for catalytic and other applications.

2,4,7-Triphenylbenzimidazole: the monomeric unit of supramolecular helical rod-like transmembrane transporters

Supramolecular compact helical rod as transmembrane anion transporter.

The basic keratin 10-binding domain of the virulence-associated pneumococcal serine-rich protein PsrP adopts a novel MSCRAMM fold

Streptococcus pneumoniae is a major human pathogen, and a leading cause of disease and death worldwide. Pneumococcal invasive disease is triggered by initial asymptomatic colonization of the human upper respiratory tract. The pneumococcal serine-rich repeat protein (PsrP) is a lung-specific virulence factor whose functional binding region (BR) binds to keratin-10 (KRT10) and promotes pneumococcal biofilm formation through self-oligomerization. We present the crystal structure of the KRT10-binding domain of PsrP (BR187–385) determined to 2.0 Å resolution. BR187–385 adopts a novel variant of the DEv-IgG fold, typical for microbial surface components recognizing adhesive matrix molecules adhesins, despite very low sequence identity. An extended β-sheet on one side of the compressed, two-sided barrel presents a basic groove that possibly binds to the acidic helical rod domain of KRT10. Our study also demonstrates the importance of the other side of the barrel, formed by extensive well-ordered loops and stabilized by short β-strands, for interaction with KRT10.

Issues Concerning Vibrations Reduction of the Industrial Drilling Machine in the Manufacturing Processes

The paper set the differential equations of free vibration for straight helical rods, in a general matrix form, with which determine the pulsation equation as an algebraic equation of n degree. The coefficients of this equation contain geometrical and elastic characteristics including natural degree of torsion bar and also the boundary conditions at the ends. These coefficients provide important information about the machine-tools from the mechanical industry under the action of vibrations, during execution the processing operations on the industrial products.

Intramolecular Donor Strand Complementation in the E. coli Type 1 Pilus Subunit FimA Explains the Existence of FimA Monomers As Off-Pathway Products of Pilus Assembly That Inhibit Host Cell Apoptosis

Type 1 pili are filamentous organelles mediating the attachment of uropathogenic Escherichia coli to epithelial cells of host organisms. The helical pilus rod consists of up to 3000 copies of the main structural subunit FimA that interact via donor strand complementation, where the incomplete Ig-like fold of FimA is completed by insertion of the N-terminal extension (donor strand) of the following FimA subunit. Recently, it was shown that FimA also exists in a monomeric, assembly-incompetent form and that FimA monomers act as inhibitors of apoptosis in infected host cells. Here we present the NMR structure of monomeric wild-type FimA with its natural N-terminal donor strand complementing the Ig fold. Compared to FimA subunits in the assembled pilus, intramolecular self-complementation in the monomer stabilizes the FimA fold with significantly less interactions, and the natural FimA donor strand is inserted in the opposite orientation. In addition, we show that a motif of two glycine residues in the FimA donor strand, separated by five residues, is the prerequisite of the alternative, parallel donor strand insertion mechanism in the FimA monomer and that this motif is preserved in FimA homologs of many enteroinvasive pathogens. We conclude that FimA is a unique case of a protein with alternative, functionally relevant folding possibilities, with the FimA polymer forming the highly stable pilus rod and the FimA monomer promoting pathogen propagation by apoptosis suppression of infected epithelial target cells.

Homochiral Helical Metal–Organic Frameworks of Group 1 Metals

The reactions of (S)-2-(1,8-naphthalimido)propanoic acid (HL(ala)) and (S)-2-(1,8-naphthalimido)-3-hydroxypropanoic acid (HL(ser)), protonated forms of ligands that contain a carboxylate donor group, an enantiopure chiral center, and a 1,8-naphthalimide π···π stacking supramolecular tecton and in the case of HL(ser) an alcohol functional group, with the appropriate alkali metal hydroxide followed by a variety of crystallization methods leads to the formation of crystalline K(L(ala))(MeOH) (1), K(L(ala))(H2O) (2), Na(L(ala))(H2O) (3), KL(ser) (4), CsL(ser) (5), and CsL(ala) (6). Each of these new complexes has a solid state structure based on six-coordinate metals linked into homochiral helical rod secondary building unit (SBU) central cores. In addition to the bonding of the carboxylate and solvent (in the case of L(ser) the ligand alcohol) to the metals, both oxygens on the 1,8-naphthalimide act as donor groups. One naphthalimide oxygen bonds to the same helical rod SBU as the carboxylate group of that ligand forming a chelate ring. The other naphthalimide oxygen bonds to adjacent SBUs. In complexes 1-3, this inter-rod link has a square arrangement bonding four other rods forming a three-dimensional enantiopure metal-organic framework (MOF) structure, whereas in 4-6 this link has a linear arrangement bonding two other rods forming a two-dimensional, sheet structure. In the latter case, the third dimension is supported exclusively by interdigitated π···π stacking interactions of the naphthalimide supramolecular tecton, forming enantiopure supramolecular MOF solids. Compounds 1-3 lose the coordinated solvent when heating above 100 °C. For 1, the polycrystalline powder reverts to 1 only by recrystallization from methanol, whereas compounds 2 and 3 undergo gas/solid, single-crystal to single-crystal transformations to form dehydrated compounds 2* and 3*, and rehydration occurs when crystals of these new complexes are left out in air. The reversible single-crystal to single-crystal transformation of 2 involves the dissociation/coordination of a terminal water ligand, but the case of 3 is remarkable considering that the water that is lost is the only bridging ligand between the metals in the helical rod SBU and a carboxylate oxygen that is a terminal ligand in 3 moves into a bridging position in 3* to maintain the homochiral helical rods. Both 2* and 3* contain five-coordinate metals. There are no coordinated solvents in compounds 4-6, in two cases by designed ligand modification, which allows them to have high thermal stability. Compounds 1-3 did not exhibit observable Second Harmonic Generation (SHG) efficiency at an incident wavelength of 1064 nm, but compounds 4-6 did exhibit modest SHG efficiency for MOF-like compounds in the range of 30 × α-SiO2.

A facile and finely-controlled synthesis of versatile porous silica nanomaterials: Nanopods, helical nanorods and nanovesicles

A variety of mesoporous silica nanomaterials with different morphologies and pore structures have been successfully synthesized by only adjusting a single parameter in an identical approach through a basic-catalyzed silica sol–gel process with tetradecyltrimethylammonium bromide (C14TAB) and sodium perfluorooctanoate (PFONa) as co-templates. By simply increasing the amount of PFONa, the porous structure changes from ordered hexagonal mesostructure with short cylindrical shape to helical mesostructure with straight rod-like morphology, then to hollow particles with porous wall, and finally to nanovesicles. More importantly, it is found that the structural transition occurs in the middle of helical rods where the strongest micelle tension strength exists and is considered to be the most unstable area of the particle. We propose that the surface free energy and hydrophilic/hydrophobic ratio are the driving forces to induce the morphological and structural transformation. Our research provides a facile preparation method to obtain various porous silicas which opens new opportunities for the exploration of versatile practical applications for novel porous materials in future.

The Golgi puppet master: COG complex at center stage of membrane trafficking interactions

The central organelle within the secretory pathway is the Golgi apparatus, a collection of flattened membranes organized into stacks. The cisternal maturation model of intra-Golgi transport depicts Golgi cisternae that mature from cis to medial to trans by receiving resident proteins, such as glycosylation enzymes via retrograde vesicle-mediated recycling. The conserved oligomeric Golgi (COG) complex, a multi-subunit tethering complex of the complexes associated with tethering containing helical rods family, organizes vesicle targeting during intra-Golgi retrograde transport. The COG complex, both physically and functionally, interacts with all classes of molecules maintaining intra-Golgi trafficking, namely SNAREs, SNARE-interacting proteins, Rabs, coiled-coil tethers, vesicular coats, and molecular motors. In this report, we will review the current state of the COG interactome and analyze possible scenarios for the molecular mechanism of the COG orchestrated vesicle targeting, which plays a central role in maintaining glycosylation homeostasis in all eukaryotic cells.

Experimental Investigation of Hydraulics and Lateral Mixing for Helical-Cruciform Fuel Rod Assemblies

In order to significantly increase the power density of light water reactors (LWRs), the authors propose the helical-cruciform (HC) fuel rod assembly as an alternative to traditional fuel geometry. The HC fuel rod assembly is a self-supporting nuclear fuel configuration consisting of four-petalled, axially twisted fuel rods closely packed against one another in a square array. Within the LWR core, HC fuel would possess several advantages over traditional fuel, potentially allowing for operation at a higher power density. Chief among these advantages are a larger surface-to-volume ratio, improved radial mixing characteristics of the coolant, and a shorter radial heat conduction path in the fuel pellet. In adapting helical rod geometry to the LWR core, the authors identified a shortage of correlations for fluid flow in twisted geometry flow channels, causing uncertainty in modeling studies. This gap was addressed by constructing an experimental facility for the measurement of hydraulic resistance and assembly mixing within a mock bundle of HC fuel rods. The rods were manufactured and tested in 4 × 4 square arrays at twist pitches of 200, 100, and 50 cm. Hydraulic resistance was evaluated by measuring frictional pressure drop over a 1-m length of the assembly. Results showed a higher pressure drop for the HC rods in comparison to bare cylindrical rods with no spacers, at a given mass flux, but no apparent dependency on twist pitch. However, data indicated that the HC-rod effective hydraulic diameter was only 90% of the expected value given its wetted perimeter and flow area, suggesting a shift from the traditional definition of Dh for this unique shape. Mixing tests used the technique of a hot water tracer injection into the central subchannel of the assembly of room-temperature water. Downstream temperature measurements were used to judge the rate of lateral cross flow within the HC rod bundle. Over 300 tests were analyzed, yielding a best-fit correlation for use with any twist pitch, rod length, or coolant mass flux. Compared to a traditional rod bundle, this correlation implies an enhancement in the intensity of turbulent interchange of 40% brought about by the HC geometry and a 1.6% forced diversion of axial flow per subchannel, per quarter-turn along the rod length. The correlations for hydraulics and cross-flow mixing presented here should reduce the uncertainty in future analysis of this fuel type for high-power-density LWRs.

High CO2/N2 Selectivity and H2 Adsorption of a Novel Porous Yttrium Metal–Organic Framework Based on N,N′,N″-Tris(isophthalyl)-1,3,5-benzenetricarboxamide

On the basis of a new topology, a novel yttrium metal–organic framework [Y2(TPBTM)(H2O)2]·xG (TPBTM = N,N′,N″-tris(isophthalyl)-1,3,5-benzenetricarboxamide and G = guest molecule) (NJU-Bai11) has been synthesized and structurally characterized. NJU-Bai11 crystallizes in a chiral space group and in its topological net and exists left of the helical rods, which are constituted from edge-sharing pyramidal polyhedra with points of extension as carboxylic carbon atoms along the a axis. NJU-Bai11 exhibits excellent adsorption capacity for CO2 (130.0 cm3/g at 273 K, 1 bar) and H2 (160.0 cm3/g at 77 K, 1 bar). Remarkably, NJU-Bai11 possesses high H2 adsorption enthalpy (7.05 kJ/mol), which is approaching the highest value (7.3 kJ/mol) reported among rare-earth metal–organic frameworks (RE-MOFs). In addition, a high selectivity ratio of 30.2 for CO2 over N2 makes NJU-Bai11 possess a potential practical application in gas purification.

Strength and stiffness analysis of Z-shape bladed shaft of a dual-shaft mixer

A procedure for analysis of the strength and stiffness of a dual-bladed Z-shape mixer shaft, which is a three-dimensional structure with curvilinear rods, is proposed; the structure is uniformly loaded along one of the helical rods. An example is cited for analysis of a plant version of the bladed Z-shape shaft of a mixer.

Gas-puff liner implosion in the configuration with helical current return rods

Results of experiments with double-shell gas-puff liners carried out on a high-current MIG generator (2 MA, 80 ns) are presented. To stabilize the process of liner implosion and increase the efficiency of energy transfer from the generator to the liner plasma, a current return in the form of a multifilar helix was used. The effect of the configuration of the current return on the parameters of the generated pulses of argon and neon K-shell radiation (with photon energies of 3–5 and 0.9–1.5 keV, respectively) and the neutron yield from a deuterium liner were studied.

Construction and Characterization of Molecular Nonwoven Fabrics Consisting of Cross-Linked Poly(γ-methyl-l-glutamate)

Molecular nonwoven fabrics in the form of ultrathin layer-by-layer (LbL) helical polymer films with covalent cross-linking were assembled on substrates by an alternate ester-amide exchange reaction between poly(γ-methyl L-glutamate) (PMLG) and cross-linking agent ethylene diamine or 4,4'-diamino azobenzene. The regular growth of helical monolayers without excessive adsorption and the formation of amide bonds were confirmed by ultraviolet-visible (UV-vis) spectrophotometry, quartz crystal microbalance (QCM), ellipsometry, and infrared reflection-absorption spectroscopy (IR-RAS) measurements. Nanostructures with high uniformity and ultrathin films with few defects formed by helical rod segments of PMLG were characterized by atomic force microscopy (AFM) and Kelvin probe force microscopy (KFM).

Molecular Dynamics Study of Phosphorylation Mediated Structural Changes in Neurofilament Medium (NF-M) Subunit

Neurofilaments (NFs) are essential building blocks of axonal architecture. Abnormal behavior of these cytostructural elements has been associated with several neuromuscular disorders such as Amyotropic Lateral Sclerosis (ALS). NFs are assembled from three subunits: Low (NFL), Medium (NFM) and Heavy (NFH). These subunits are characterized by a common alpha helical rod domain and carboxyl terminal domains of different lengths specific to each subunit. The tails project from the core of the filament and contain a number of KSP repeat motifs that belongs to the sites for phosphorylation. Especially, the C-terminal tails of NFM and NFH that have relatively longer lengths and higher number of KSP repeats were found to be the key participants of the sidearm-mediated interfilament interactions that regulate the axonal diameter. Though it has been established that that the sidearms play a key functional role, little is known about the roles of individual subunits and the effect of phosphorylation on their behavior. Initially, it was believed that the NFH sidearms play a more integral role in determining axonal structure due to the presence of longer polypeptides and relatively higher KSP repeat units. However, recent studies showed that deleting NFH from neurofilaments does not affect axonal diameter, suggesting that NFM may in fact be the key player. In view of this, it is essential to have an understanding of the morphological behavior of the NFM sidearm in response to physiological conditions. In the present study we carried out MD simulations of human and mouse NFM C terminals under different phosphorylation and ionic conditions. The results from these studies provide useful molecular level insight into the structural changes of NFM sidearms in response to phosphorylation, ionic concentrations. The present study reveals sidearm-mediated regulation mechanism of axonal caliber.

CAPS and Munc13: CATCHRs that SNARE Vesicles

CAPS (Calcium-dependent Activator Protein for Secretion, aka CADPS) and Munc13 (Mammalian Unc-13) proteins function to prime vesicles for Ca2+-triggered exocytosis in neurons and neuroendocrine cells. CAPS and Munc13 proteins contain conserved C-terminal domains that promote the assembly of SNARE complexes for vesicle priming. Similarities of the C-terminal domains of CAPS/Munc13 proteins with Complex Associated with Tethering Containing Helical Rods domains in multi-subunit tethering complexes (MTCs) have been reported. MTCs coordinate multiple interactions for SNARE complex assembly at constitutive membrane fusion steps. We review aspects of these diverse tethering and priming factors to identify common operating principles.

Cone Penetrometer with a Helical-Type Outer Screw Rod for Evaluation of the Subgrade Condition

AbstractA weak railway subgrade may lead to instability of the railway track system. The condition of a railway subgrade is typically evaluated using trial pit excavation and a portable ballast sampler, which may severely disturb the ballast layer. Also, nondestructive geophysical techniques, such as ground penetrating radar (GPR), are used to investigate the condition of the ballast and subgrade along the track. The objective of this study is the development and application of a cone penetrometer with a helical-type outer screw rod (CPH) that minimizes the disturbance of the ballast layer for the evaluation of the subgrade condition by measuring the resistance of the cone tip. The CPH consists of a helical-type outer screw rod (helical rod) and a mini cone penetrometer inside the rod. The design concerns include easy installation of the helical rod into the ballast layer, the reaction force of the mini cone penetrometer, installation of the strain gauge, and calculation of the cone tip resistance. The he...

The DSL1 Complex: The Smallest but Not the Least CATCHR

The DSL1 complex is a conserved tethering complex at the endoplasmic reticulum that recognizes Golgi-derived COPI vesicles and hands them over to the fusion machinery. The DSL1 complex is the simplest tethering complex of the complexes associated with tethering containing helical rods (CATCHR) family. CATCHR tethering complexes play a role at compartments along the exocytic and endocytic pathways. In this review, different functions of the DSL1 complex are discussed, some open questions with the seemingly straightforward picture are pointed out and alternative functions of the DSL1 complex members are mentioned.

Motor-driven bacterial flagella and buckling instabilities

Many types of bacteria swim by rotating a bundle of helical filaments also called flagella. Each filament is driven by a rotary motor and a very flexible hook transmits the motor torque to the filament. We model it by discretizing Kirchhoff's elastic-rod theory and develop a coarse-grained approach for driving the helical filament by a motor torque. A rotating flagellum generates a thrust force, which pushes the cell body forward and which increases with the motor torque. We fix the rotating flagellum in space and show that it buckles under the thrust force at a critical motor torque. Buckling becomes visible as a supercritical Hopf bifurcation in the thrust force. A second buckling transition occurs at an even higher motor torque. We attach the flagellum to a spherical cell body and also observe the first buckling transition during locomotion. By changing the size of the cell body, we vary the necessary thrust force and thereby obtain a characteristic relation between the critical thrust force and motor torque. We present a elaborate analytical model for the buckling transition based on a helical rod which quantitatively reproduces the critical force-torque relation. Real values for motor torque, cell body size, and the geometry of the helical filament suggest that buckling should occur in single bacterial flagella. We also find that the orientation of pulling flagella along the driving torque is not stable and comment on the biological relevance for marine bacteria.

Structure, Folding and Stability of FimA, the Main Structural Subunit of Type 1 Pili from Uropathogenic Escherichia coli Strains

Filamentous type 1 pili are responsible for attachment of uropathogenic Escherichia coli strains to host cells. They consist of a linear tip fibrillum and a helical rod formed by up to 3000 copies of the main structural pilus subunit FimA. The subunits in the pilus interact via donor strand complementation, where the incomplete, immunoglobulin-like fold of each subunit is complemented by an N-terminal donor strand of the subsequent subunit. Here, we show that folding of FimA occurs at an extremely slow rate (half-life: 1.6 h) and is catalyzed more than 400-fold by the pilus chaperone FimC. Moreover, FimA is capable of intramolecular self-complementation via its own donor strand, as evidenced by the loss of folding competence upon donor strand deletion. Folded FimA is an assembly-incompetent monomer of low thermodynamic stability (−10.1 kJ mol−1) that can be rescued for pilus assembly at 37 °C because FimC selectively pulls the fraction of unfolded FimA molecules from the FimA folding equilibrium and allows FimA refolding on its surface. Elongation of FimA at the C-terminus by its own donor strand generated a self-complemented variant (FimAa) with alternative folding possibilities that spontaneously adopts the more stable conformation (−85.0 kJ mol−1) in which the C-terminal donor strand is inserted in the opposite orientation relative to that in FimA. The solved NMR structure of FimAa revealed extensive β-sheet hydrogen bonding between the FimA pilin domain and the C-terminal donor strand and provides the basis for reconstruction of an atomic model of the pilus rod.