Helical Groove Research Articles

CAD/CAM for Geometry and Process Analysis of Helical Groove Machining

Helical groove machining using disc-type tools, such as for drill flutes, helical gear teeth, threads, etc., is extremely complex due to the helical motion of the profiled tool along the helical cutting path on the workpiece. In the present paper, a mathematical analysis is presented as the basis for a CAD/CAM system for design and manufacture of components with helical grooves. The system helps the user design the profile of the tool or the helical groove, and thereafter analyze the subsequent machining process. An example is presented to illustrate how the system works and the results which can be obtained.

The origin of the rotation of one end of a cell relative to the other end during growth of Gram-positive rods

The Gram-positive rod wall elongates by an inside-to-outside mechanism of linking new peptidoglycan on the inside and the cracking, by autolysis, of old wall on the outside. During this process the peptidoglycan experiences stress in different directions in different levels of the wall. The stress that develops in a rod-shaped cell if the wall was uniform in physical properties throughout its thickness is twice as great in the hoop direction as in the axial direction. This leads to splitting in the direction of the longitudinal axis. However, the older, partially split, more peripheral wall is stressed in the direction of the elongating cell axis and thus favors circumferential cracks. It is suggested that these processes combine to form a system of helical cracks, grooves, or crevasses. The stable system of grooves would have the same handedness, fairly constant pitch and elongate as the cell grows. Their continuing development would result in the rotation of one end of the cell relative to the other even in cells with no spiral or apparent helical character. Such rotation has been experimentally observed with Bacillus subtilis. The proposed mechanism for rotation during growth may account, in part, for the formation of helical coils of bundles of filamentous organisms (macrofibers), the morphology of spirilla and vibroids, and for the shapes of some mutant and some antibiotic-treated organisms. Rotation due to generation of helical cracks as the result of the biophysics of the growth process as proposed here, is an alternative to the proposal by Mendelson (1976, Helical growth of Bacillus subtilis: a new model for cell growth. Proc. natn. Acad. Sci. U.S.A. 73, 1740-1744) that rotation is due to the laying down of nascent peptidoglycan in a helical pattern.

The Sendai virus nucleocapsid exists in at least four different helical states

Sendai virus nucleocapsids have been observed by electron microscopy to coexist in three different helical pitch conformations, 5.3, 6.8, and 37.5 nm. The 5.3- and 6.8-nm conformations are present both in uranyl acetate negatively stained preparations and in tantalum-tungsten metal-shadowed preparations, whereas the 37.5-nm conformation, which has not been previously reported, is present only in the shadowed preparations. The 5.3-nm pitch conformation appears to be a mixture of two discrete structural states, with a small difference in the twist of the structure between the two. We have used image reconstruction techniques on an averaged data set from eight negatively stained nucleocapsids to produce a three-dimensional reconstruction at 2.4-nm resolution of the structure in one of the 5.3-nm pitch states. There are 13.07 nucleocapsid protein (NP) subunits in each turn of the helix in this state. The helical repeat is 79.5 nm, containing 196 subunits in 15 turns of the left-handed 5.3-nm helix. The arrangement of subunits produces a 5.0-nm-diameter hollow core which forms an internal helical groove. The RNA accounts for about 3% of the mass of the nucleocapsid, and so its location is not conspicuous in the reconstruction. Because of the RNA remains associated with the NP subunits during mRNA transcription and genome replication, structural transitions in the nucleocapsid may determine the accessibility of the genome to polymerases. Alternatively, the large hollow core and internal helical groove we have reconstructed may allow access to the RNA even in the tightly coiled 5.3-nm pitch conformation.

Stress intensity factor for a metric fastening thread

In light of the foregoing, it would obviously be expedient to develop a new approach ensuring correct evaluation of the SIF in a fastening thread with a crack of arbitrary depth and form on the basis of known solutions of the problem of the tension of a cylindrical rod with an external annular crack. Such evaluations could be made for a range of geometries of metric thread profiles designated in accordance with the requirements of technical standards. As is known, in conformity with the requirements of GOSTs, DIN (German engineering standards), JIS (Japanese industrial standard), and JSO (international organization on standardization) and other standards on the classification of Neuber stress concentrators [8], metric threads are considered to be "fine" grooves. However, systematic studies of the effect of pitch on brittle and fatigue strength, with allowance for other parameters of the thread profile, have shown that the serviceability and safe life of a fastened joint is determined by the gradation of the thread geometry into coarse and fine classifications [6, 9, 11]. Here, the parameter D/P (D, P are the outside diameter and pitch of the thread, respectively) is changed within broad ranges up to values of 20-30 in order to obtain a greater effective cross-sectional area of the fastened part with respect to the inside diameter of the thread. The degree of refinement of the thread profile should be limited by the strength of the turns in catenary shear. Within the broad range of threads from type MI0 to type M200, having both shallow and deep helical grooves, the threads within the range MI20-M200 (used mainly for powerplant and chemical equipment under pressure) have a value of the parameter D/P which is three to five times greater than the analogous value for threads within the range MI0-M24. This fact makes it necessary to flexibly account for the "dynamics" of the stress state of the thread contour with an increase in the nominal diameter and the corresponding change in the parameters of the profile in the succession of values allowed by the standard. Thus, it is apparently necessary to solve two experimental problems in order to simplify theoretical-empirical study of the SIF for cracks in a thread.

Saccharification and Fermentation of Whole Barley Ground in the Szego Mill

AbstractBarley, after steeping in water, was ground with ease and efficiency in the Szego mill, and its starch was liquefied, saccharified and fermented to very high yields of ethanol. The Szego mill consists of vertical rollers with helical grooves which rotate within a fixed cylinder, resulting in very fine grinding and a somewhat flaky product. The steeped barley was ground to a fine paste. This was readily liquefied and saccharified by amylolytic enzymes (dual enzyme process), and the resulting sugars were fermented in 24 h by ordinary bakers' yeast Saccharomyces cerevisiae, resulting in over 450 1 ethanol/t of barley. Still shorter time, 12 h, and the same high yield were achieved when liquefied barley starch was simultaneously saccharified by glucoamylase and fermented. Fermentation to ethanol by a glucoamylase‐producing yeast S. diastaticus strain 164 A (from Labatt Brewing Company) enabled the amount of this enzyme required for saccharification to be reduced to about one‐half the normal quantity, but at some cost in slower fermentation and slightly lower ethanol yield.

The Interactions of Ruthenium Hexaammine with Z-DNA: Crystal Structure of a RU(NH3)+36Salt of d(CGCGCG) at 1.2 Å Resolution

A crystal of d(CGCGCG) in the Z-DNA lattice was soaked with ruthenium(III) hexaammine and its structure refined at 1.2 A resolution. Three unique metal complexes were found absorbed to each hexamer duplex. In addition, two symmetry-related binding sites were located, yielding a total of five ruthenium complexes bound to each d(CGCGCG) duplex. One unique site and its symmetry related site are nearly identical to the binding site of cobalt(III) hexaammine on Z-DNA. At that position, the metal complex bridges the convex surfaces of two adjacent Z-DNA strands by hydrogen bonds to the N7 and O6 functional groups of the guanine bases. The remaining three ruthenium three ruthenium(III) hexaammine binding sites are not present in the cobalt(III) hexaammine Z-DNA structure. Of these, two are related by symmetry and span the gap between the convex outer surface of one Z-DNA strand and the helical groove crevice of a neighboring strand. The third ruthenium site has no symmetry mate and involves interactions with only the deep groove. In this interaction, the metal complex hydrogen bonds to both the phosphate backbone and to a set of primary shell water molecules that extend the hydrogen bonding potential of the deep groove crevice out to the surface of the molecule. Solution studies comparing the circular dichroism spectra of low salt poly(dG-dC).poly(dG-dC) samples in the presence of ruthenium(III) and cobalt(III) hexammine show that the ruthenium complex does stabilize Z-DNA in solution, but not as effectively as the cobalt analogue. This suggests that some of the interactions available for the larger ruthenium complex may not be important for stabilization of the left-handed DNA conformation.

A STOCHASTIC CHARACTERIZATION OF THE MACHINE TOOL WORKPIECE SYSTEM IN BTA DEEP HOLE MACHINING Part II: Response Analysis and Evaluation of the Tool Tip Motion

ABSTRACT In this paper, the solutions to the stochastic differential equations, which mathematically represent the machine tool work-piece system in BTA deep hole machining are presented. The solutions to the parametric stochastic differential equations have been obtained using the well known averaging technique. The non-parametric inhomogeneous equations have been solved using the Fokker-Planck equation. Based on these solutions, the true motion of the tool tip has been described using the maximum, average and minimum deviation curves. These curves predict that helical grooves will be formed on the workpiece and such helical grooves were observed on the workpieces. Also, the maximum, average and minimum values of deviation of the tool tip which is a measure of the roundness error are established. Based on these results an upper bound for the roundness error as a function of depth of hole is derived. The measurement of roundness of the specimens reveals that the experimental values be in the zone predicte...

Planetary ball drive mechanism. Shape of scoop surface of ball and test result.

In the planetary ball drive mechanism the scoop surface for moving balls must be prepared at the ends of the groove of the carrier and the helical groove of a bolt. Moreover for the sake of circulation of the scooped balls two holes must be bored on a nut. The authors analyze the geometrical condition of the shape of the scoope surface and the position angle between two guide holes. The operation test was conducted under various loads and the results cleared the wear condition of the scoop surface.

Metals and DNA: Molecular Left-Handed Complements

Chiral metal complexes provide unique molecular probes for DNA. Chiral reagents that "recognize" different local structures along the DNA strand have been designed by a process in which the asymmetry in shape and size of the complex is matched to that of the DNA helical groove. As a result, the chiral metal complexes provide very sensitive probes for local helical structure, both left- and right-handed. Direct coordination of chiral complexes to the DNA bases adds an element of sequence selectivity to the probe design. With a suitable reactive metal center, reagents that target chemically specific sites along the strand may be developed. One such chiral reagent, which cleaves left-handed DNA sites with photoactivation, has been useful in mapping this distinct conformation and examining its biological role. The conformation-specific molecular cleaver, much like a DNA-binding enzyme, recognizes and reacts at discrete sites along the DNA strand. These site-specific chiral metal complexes provide exciting new tools for probing the local variations in DNA structure and its role in the regulation of gene expression.

Nucleotide sequence binding preferences of nogalamycin investigated by DNase I footprinting.

Four DNA restriction fragments, designated tyrT, pTyr2, pUC13, and Xbs1, have been used as substrates for footprinting studies with DNase I in the presence of the anthracycline antibiotic nogalamycin. With each fragment a distinct pattern of antibiotic-protected binding sites is observed, but no concensus sequence emerges from the data. All sites are located in regions of alternating purine-pyrimidine sequence, most commonly associated with the dinucleotide steps TpG (CpA) and GpT (ApC), suggesting that the preferred binding sites may contain all four nucleotides and/or that peculiarities of the dynamics of DNA conformation at alternating sequences may be critical for nogalamycin binding. Some concentration dependence of footprinting patterns is evident, in contrast to previous studies with a variety of sequence-specific ligands. Enhanced susceptibility to attack by DNase I is commonly observed at sequences flanking strong antibiotic-binding sites. Nogalamycin selectively inhibits cleavage of DNA at certain guanine-containing sequences by the G-specific photosensitized reaction with methylene blue. Comparison of these effects with its action on the G-specific reaction with dimethyl sulfate suggests that the amino sugar moiety of nogalamycin may be preferentially located in the minor helical groove at some binding sites but in the major groove at others.

Effect of DNA conformation on the binding of antibodies to benzo[a]pyrene diol-epoxide DNA adducts.

The effect of the helical conformation of DNA on the binding of antibodies to DNA-carcinogen adducts was evaluated. The efficiency of antibody binding to adducts produced in DNA by treatment with (+)-trans-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) was modulated by varying the winding angle of the DNA helix using heat denaturation, organic solvents, and cations. Unwinding and complete denaturation of the DNA helix increased the binding efficiency of anti-bodies to DNA-BPDE adducts 4- to 8-fold over that to BPDE adducts in the unperturbed double helical DNA. The antibody binding efficiency increased in proportion to the degree of unwinding of the double helix induced by dimethylsulfoxide, ethylene glycol, or glycerol. Conversely, winding of the double helix with monovalent cations (Na+, K+, Rb+, Li+, Cs+ and NH4+) and more effectively with divalent cations (Mg2+, Ca2+, Mn2+, Sn2+ and Ba2+) decreased antibody binding to DNA-BPDE adducts. We suggest that the molecular orientation of BPDE adducts within helical grooves modulates adduct accessibility for binding with antibody molecules. By the opening and/or unwinding of the helix, BPDE adducts (or their immunogenic sites) partially "buried" within the grooves may be exposed to varying degrees for antibody binding. Conversely, winding of the helix shielded the BPDE adducts from antibody recognition and binding.

AT base pairs are less stable than GC base pairs in Z-DNA: The crystal structure of d(m 5CGTAm 5CG)

Two hexanucleoside pentaphosphates, 5-methyl and 5-bromo cytosine derivatives of d(CpGpTp-ApCpG) have been synthesized, crystallized, and their three-dimensional structure solved. They both form left-handed Z-DNA and the methylated derivative has been refined to 1.2 Å resolution. These are the first crystal Z-DNA structures that contain AT base pairs. The overall form of the molecule is very similar to that of the unmethylated or the fully methylated (dC-dG) 3 hexamer although there are slight changes in base stacking. However, significant differences are found in the hydration of the helical groove. When GC base pairs are present, the helical groove is systematically filled with two water molecules per base pair hydrogen bonded to the bases. Both of these water molecules are not seen in the electron density map in the segments of the helix containing AT base pairs, probably because of solvent disorder. This could be one of the features that makes AT base pairs form Z-DNA less readily than GC base pairs.

DNA structural variations produced by actinomycin and distamycin as revealed by DNAase I footprinting.

The technique of DNAase I footprinting has been used to investigate preferred binding sites for actinomycin D and distamycin on a 160-base-pair DNA fragment from E. coli containing the tyr T promoter sequence. Only sites containing the dinucleotide step GpC are protected by binding of actinomycin, and all such sites are protected. Distamycin recognizes four major regions rich in A + T residues. Both antibiotics induce enhanced rates of cleavage at certain regions flanking their binding sites. These effects are not restricted to any particular base sequence since they are produced in runs of A and T by actinomycin and in GC-rich sequences by distamycin. The observed increases in susceptibility to nuclease attack are attributed to DNA structural variations induced in the vicinity of the ligand binding site, most probably involving changes in the width of the helical minor groove.

Ultrastructure of Single and Multiple Diploid Honeybee Spermatozoa

SummaryDiploid drone honeybees were reared by Woyke's method and the ultrastructure of diploid and haploid spermatozoa was investigated. The ultrastructure of diploid spermatozoa is very similar to that of the haploid ones, but the diploids are larger. The length of the aero some and the nucleus of a diploid spermatozoon are 151% and 139% respectively of those for a haploid one. The diameter of the tail of a diploid spermatozoon is 115% of that of a haploid one, A single axon e me with an arrangement of 9 + 9 + 2 fibrils is present in a diploid spermatozoon. The direction of helical grooves is the same on both mitochondrial derivatives in diploid spermatozoa, whereas it is opposite on the two derivatives in haploid spermatozoa. The volume of a diploid spermatozoon is about twice that of a haploid one.Among ordinary diploid spermatozoa were also found double ones, containing two axonemes and four mitochondrial derivatives in their tails, and triple ones, containing three axonemes and six mitochondrial deri...

Electro-optical fluorescence studies on the DNA binding of medically active drugs

By measuring the transient changes in each of the polarised components of fluorescence during the application of a pulsed electric field to a solution of macromolecules, a method has been developed for evaluating the binding characteristics of fluorescent chemotherapeutic agents to DNA. It is shown that whereas quinacrine and berberine intercalate the DNA helix, hydroxystilbamidine does not. Furthermore, measurements on both the native and the diol-epoxide forms of benzo(a)pyrene show that the former is consistent with an intercalation type of binding, whilst the latter appears to be more inclined to the major DNA axis and may possibly be associated with the external helical grooves. The significance of these findings is discussed.

Dynamic analysis of a hydrodynamic seal with helical grooves

A ring-type hydrodynamic seal with two lands, one with helical grooves and the other with a wedge, separated by a circumferential oil supply groove was studied. The dynamic performance characteristics in terms of the stiffness and damping coefficients, critical mass and critical inertia were obtained for lateral and skew motions. For the general motion of the seal, stability studies were made by obtaining the roots of the characteristic equation.

Interaction of chromosomal stains with DNA. An electrofluorescence study.

A novel fluorescence procedure has been used to study the binding characteristics of DNA with three modern fluorochromes currently used in chromosome cytochemistry. The transient changes in the polarised components of fluorescence have been recorded for dye-tagged DNA solutions when subjected to short duration electric pulses. From these data, it has been inferred that, like ethidium bromide, berberine sulphate and quinacrine mustard both intercalate the DNA structure whilst the bi-benzimidazole derivative Hoechst 33258 binds with a distinctively different geometry, probably within the helical grooves.

Analysis of a hydrodynamic seal with helical grooves

High speed turbogenerators are generally gas cooled and hydrodynamic seals are often used to prevent cooling gas leakage. The seal needs to run essentially at a low eccentricity in order to maintain an uninterrupted oil film all around the shaft. The flow of the oil towards the gas side should be minimized to avoid the contamination of oil with gas. The hydrodynamic seal studied consists of two lands, one on the gas side with helical grooves and the other exposed to ambient air with a wedge. The two lands are separated by a circumferential oil supply groove. The leakage of oil towards the gas side was investigated for different helical groove parameters such as the number of grooves, the helix angle and the groove depth. The effects of these parameters on the performance of the hydrodynamic seal in terms of load support, induced moment, attitude angle, temperature rise and friction force are reported. Equations governing the fluid flow were solved by the finite element method.

Three-dimensional reconstruction of the flagellar hook from Caulobacter crescentus

The structure of the bacterial flagellar hook produced by a mutant of Caulobacter crescentus was studied by electron microscopy, optical diffraction, and digital image processing techniques. The helical surface lattice of the hook is defined by a single, right-handed genetic helix having a pitch of about 23 Å, an axial rise per subunit of 4 Å and an azimuthal angle between subunits of 64·5 °. The lattice is also characterized by intersecting families of 5-start, 6-start and long-pitch 11-start helices. These helical parameters are remarkably similar to those determined for the flagellar filaments from several strains of gram-negative bacteria. The technique of three-dimensional image reconstruction (DeRosier & Klug, 1968) was applied to nine of the better preserved specimens and the diffraction data from five of these were correlated and averaged and used to generate an average three-dimensional model of the hook. The pattern of density modulations in the three-dimensional model is suggestive of an elongated, curved shape for the hook subunit (100 Å × 25 Å × 25 Å). The subunits are situated in the lattice of the polyhook such that their long axes are tilted about 45 ° with respect to the hook axis. The subunits appear to make contact with each other along the 6-start helices at a radius of 80 Å and also along the 11-start helices at a radius of 65 Å. Few structural features are revealed at radii between 15 å and 45 Å and, therefore, we are unable to decide to what extent the hook subunits extend into this region. The most striking characteristic of the model is the presence of deep, broad, continuous 6-start helical grooves extending from an inner radius of about 50 Å to the perimeter of the particle at 105 Å radius. Normal hooks usually appear curved in electron micrographs and sometimes so are the mutant hooks; the prominent 6-start grooves appear to allow for bending with minimal distortion of matter in the outer regions of the hook. A round stain-filled channel about 25 Å in diameter runs down the center of the polyhook. Such a channel supports a model for flagellar assembly in which flagellin subunits travel through the interior of the flagellum to the growing distal end of the filament.

Left-handed double helical DNA: variations in the backbone conformation.

Four different crystals of d(CpGpCpGpCpG) have been solved by x-ray diffraction analysis and all form similar left-handed double helical Z-DNA molecules in the crystal lattice. Two different conformations are observed for the phosphates in the GpC sequences, as the phosphates are found either facing the helical groove or rotated away from it. The latter conformation is often found when hydrated magnesium ions are complexed to a phosphate oxygen atom. These different conformations may be used when right-handed B-DNA joins left-handed Z-DNA. Atomic coordinates and torsion angles are presented for both types of Z-DNA.