Screw Rotations Research Articles

EFFECT OF CYLINDER HEAD GASKET ADDITION AND VARYING OCTANE NUMBER GASOLINE TO INTERNAL COMBUSTION ENGINE PERFORMANCE

The aim of this research was to investigate the different impacts of compression pressure on power and torque outputs using gasoline RON 92, RON 95, and RON 100. The study involved experiments using a single-cylinder motorcycle engine with a capacity of 125 cm. The selection of this type of engine is based on the popularity of vehicles in Indonesia that use a single-cylinder engine with a capacity of 125 cm. To modify the compression pressure, variations in the number of gaskets were applied to the cylinder head, with quantities of 1 and 3 gaskets. Dynamometer tests were conducted to measure the engine's performance differences. Throughout the testing, the settings for the main jet, pilot jet, and the number of idle screw rotations on the carburetor remain constant. The findings indicate that the engine with the highest compression pressure of 11.8 Kg/cm, using RON 100 gasoline, produces the highest power output at 7.9 kW, with the highest torque at 10 Nm.

Process induced degradation of carbamazepine during hot melt extrusion

The aim of this studywas to evaluate hot melt extrudates of carbamazepine(CBZ) for presence of process induced degradation product iminostilbene (IMB) and quantifying using highperformance liquid chromatography (HPLC). CBZ was used as model drug. Hot-melt extrusion (HME) was performed to preparesolid dispersions. Different grades of compatible polymers were used. Drug loading,processing temperature and screw rotations per minute (RPM) showed significanteffect on degradation of CBZ The extrudates were characterized by differentialscanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared(FTIR) studies. DSC and XRD data confirmed formation of amorphous soliddispersions of CBZ. HPLC was performed to quantify percentage amount of CBZ andIMB. Process induced degradation was significantly varied depending on polymergrade and (w/w) percentage combinations. In addition, processing temperatureand RPM had direct effect on percentage of IMB formation. 

General Theory of Momentum-Space Nonsymmorphic Symmetry

As a fundamental concept of all crystals, space groups are partitioned into symmorphic groups and nonsymmorphic groups. Each nonsymmorphic group contains glide reflections or screw rotations with fractional lattice translations, which are absent in symmorphic groups. Although nonsymmorphic groups ubiquitously exist on real-space lattices, on the reciprocal lattices in momentum space, the ordinary theory only allows symmorphic groups. In this work, we develop a novel theory for momentum-space nonsymmorphic space groups ($k$-NSGs), utilizing the projective representations of space groups. The theory is quite general: Given any $k$-NSGs in any dimensions, it can identify the real-space symmorphic space groups ($r$-SSGs) and construct the corresponding projective representation of the $r$-SSG that leads to the $k$-NSG. To demonstrate the broad applicability of our theory, we show these projective representations and therefore all $k$-NSGs can be realized by gauge fluxes over real-space lattices. Our work fundamentally extends the framework of crystal symmetry, and therefore can accordingly extend any theory based on crystal symmetry, for instance, the classification crystalline topological phases.

Polyamide‐6/cellulose nanocomposites: Influence of fiber treatment and screw rotation on nanofibrillation of jute during extrusion process

The present work studied the preparation of nanocomposites of polyamide-6 (PA6) containing nanofibrillated cellulose by melt blending in a twin screw extruder at different screw rotations to verify the fibrillation of cellulose fibers. Initially, the jute fibers were purified, hydrolyzed, and modified with titanium isopropoxide and aminopropyl silane, as well as with the two chemical modifications. They were incorporated into the polymeric matrix aiming that the shear in processing further aids in fiber fibrillation. The scanning electron microscopy analysis images of the composites showed the presence of fibers with nanodiameters dispersed in the PA6 matrix. The doubly modified fibers resulted in more fibrillation during extrusion. Increasing the screw speed of the extruder improved the degree of crystallinity for the composites with the modified fibers. The thermogravimetric measurements showed that the composite containing the doubly modified fibers increased the maximum degradation temperature. The storage modulus increased for the composites with the insertion of the treated fibers, and the glass transition temperature decreased in some composites. The composites showed higher pseudoplastic behavior, especially at high shear rates.

Comparison of Shielding Material Dispersion Characteristics and Shielding Efficiency for Manufacturing Medical X-ray Shielding Barriers.

During medical diagnoses, X-ray shielding barriers are used to protect against direct and indirect X-rays. Currently, lead is used as the primary material for shielding barriers; however, the demand for eco-friendly shielding barriers has been increasing. Conventionally, shielding barriers are manufactured using a mechanically bonded combination of lead and aluminum; however, in this study, a plastic-based injection-molded product was developed using tungsten as an eco-friendly alternative to lead. A new process technology was required for mixing tungsten—which can be difficult to process—with a polymer. Consequently, the mixing conditions within the injection molding machine and the related compounding technology factors were analyzed. The process technology considered the pre-mixing method using powdery polymer, particle dispersion method, number of screw rotations, and amount of filler input. The product’s shielding performance was then analyzed. The tungsten content of the 2-mm thick barrier manufactured using the proposed method was 90 wt%, and the lead equivalent was 0.321 mmPb. To increase the effectiveness of injection molding in the manufacturing process, specific hourly compounding conditions were proposed. Consequently, the process technology method developed in this study can be considered suitable for manufacturing various shielding barriers.

Chirality in the Solid State: Chiral Crystal Structures in Chiral and Achiral Space Groups.

Chirality depends on particular symmetries. For crystal structures it describes the absence of mirror planes and inversion centers, and in addition to translations, only rotations are allowed as symmetry elements. However, chiral space groups have additional restrictions on the allowed screw rotations as a symmetry element, because they always appear in enantiomorphous pairs. This study classifies and distinguishes the chiral structures and space groups. Chirality is quantified using Hausdorff distances and continuous chirality measures and selected crystal structures are reported. Chirality is discussed for bulk solids and their surfaces. Moreover, the band structure, and thus, the density of states, is found to be affected by the same crystal parameters as chirality. However, it is independent of handedness. The Berry curvature, as a topological measure of the electronic structure, depends on the handedness but is not proof of chirality because it responds to the inversion of a structure. For molecules, optical circular dichroism is one of the most important measures for chirality. Thus, it is proposed in this study that the circular dichroism in the angular distribution of photoelectrons in high symmetry configurations can be used to distinguish the handedness of chiral solids and their surfaces.

Numerical Modeling of the Blend Morphology Evolution in Twin‐Screw Extruders

AbstractThe blend morphology model developed by Wong et al., based on Peters et al., is used to investigate the development of the disperse polymer blend morphology in twin‐screw extruder flow. First, the model is written in a point‐wise form suitable for using in conjunction with particle tracking. Particle tracking methods are used to generate trajectories along the flow field. Macroscopic droplet populations are placed along these trajectories and the velocity gradient tensor is extracted and applied on the point‐wise blend morphology model. Very large morphology differences arise between trajectories that pass through the middle gap and those that do not. In the global distribution of (macroscopically averaged, monodisperse) droplet sizes, two distinct peaks appear due to these different trajectories. Given enough number of screw rotations, a droplet population can reach almost every position in the twin‐screw extruder and travel along both types of particle trajectories. The effect of varying the gap size is that the largest droplets are unaffected, but the smallest droplets are smaller for a smaller gap size due to the higher maximum shear rate. The effect of varying the viscosity ratio on the global droplet size distribution is found to be nonlinear and is strongly determined by the Grace curve. The effect on polydisperse droplet populations is found to be that trajectories that do not pass through the gap evolve toward a single peak, whereas trajectories that do pass through the gap lead to a split into two peaks that ultimately rejoin as one peak. It is concluded that the initial position of a population in the twin‐screw extruder has a very large effect on the developing transient blend morphology, though future work should be done on the importance of the initial position on the steady‐state blend morphology after a very large number of screw rotations.

Electron–phonon superconductivity in C-doped topological nodal-line semimetal Zr5Pt3: a muon spin rotation and relaxation (μSR) study

In the present work, we demonstrate that C-doped Zr5Pt3 is an electron–phonon superconductor (with critical temperature T C = 3.8 K) with a nonsymmorphic topological Dirac nodal-line semimetal state, which we report here for the first time. The superconducting properties of Zr5Pt3C0.5 have been investigated by means of magnetization, resistivity, specific heat, and muon spin rotation and relaxation (μSR) measurements. We find that at low temperatures, the depolarization rate is almost constant and it can be well described by a single-band s‐wave model with a superconducting gap of 2Δ(0)/k B T C = 3.84, somewhat higher than the value of BCS theory. From the transverse field μSR analysis, we estimate the London penetration depth λ L = 469 nm, superconducting carrier density n s = 1.83 × 1026 m−3, and effective mass m* = 1.428m e. The zero field μSR confirms the absence of any spontaneous magnetic field in the superconducting ground state. In order to gain additional insights into the electronic ground state of C-doped Zr5Pt3, we also performed first-principles calculations within the framework of density functional theory (DFT). The observed homogenous electronic character of the Fermi surface as well as the mutual decrease of T C and density of states at the Fermi level are consistent with the experimental findings of this study. However, the band structure reveals the presence of robust, gapless fourfold-degenerate nodal lines protected by 63 screw rotations and glide mirror planes. Therefore, Zr5Pt3 represents a novel, unprecedented condensed matter system to investigate the intricate interplay between superconductivity and topology.

Influence of Die Threading and Finishing Length in the Thread-Rolling Process Using Flat Dies: A Numerical Analysis

In this paper, a numerical analysis of the cold thread-rolling process using flat dies is presented as a function of the die geometry design. Five die geometries with different threading and finishing ratios were modelled to induce different screw deformation rates. An analytical method was proposed by the authors to design die geometries as a function of screw roll rotation. Screw geometry accuracy, induced stress, and die wear were selected to compare the tested geometries. The results showed that three screw rotations in the threading step were sufficient to guarantee good geometry accuracy. Moreover, the results highlighted that die wear is the most affected parameter among all the tested geometries. Finally, a new solution was proposed by the authors to obtain uniform wear and reduce the die length.

Chiralities of nodal points along high-symmetry lines with screw rotation symmetry

Screw rotations in nonsymmorphic space group symmetries induce the presence of hourglass and accordion-shape band structures along screw invariant lines whenever spin-orbit coupling is non-negligible. These structures induce topological enforced Weyl points on the band intersections. In this work we show that the chirality of each Weyl point is related to the representations of the cyclic group on the bands that form the intersection. To achieve this, we calculate the Picard group of isomorphism classes of complex line bundles over the two-dimensional sphere with cyclic group action, and we show how the chirality (Chern number) relates to the eigenvalues of the rotation action on the rotation invariant points. Then we write an explicit Hamiltonian endowed with a cyclic action whose eigenfunctions restricted to a sphere realize the equivariant line bundles described before. As a consequence of this relation, we determine the chiralities of the nodal points appearing on the hourglass and accordion shape structures on screw invariant lines of the nonsymmorphic materials ${\mathrm{PI}}_{3}$ (SG: $\mathrm{P}{6}_{3}$), ${\mathrm{Pd}}_{3}\mathrm{N}$ (SG: $\mathrm{P}{6}_{3}22$), ${\mathrm{AgF}}_{3}$ (SG: $\mathrm{P}{6}_{1}22$), and ${\mathrm{AuF}}_{3}$ (SG: $\mathrm{P}{6}_{1}22$), and we corroborate these results with the Berry curvature and symmetry eigenvalues calculations for the electronic wave function.

Redesign of OrthoLPPDUNS External Fixation for Bone Reconstruction Using the Function Analysis System Technique (FAST) Method

Taylor Spatial Frame (TSF) better known as an external fixation product from several types of fixation devices in the orthopedic field. The Laboratory of Product Planning and Design has manufactured TSF or called OrthoLPPDUNS external fixations. The OrthoLPPDUNS design found that frame instability forming ring-strut angles caused by strut screw rotations was feeling rough due to backlash. The purpose is how to redesign an OrthoLPPDUNS with a Function Analysis System Technique (FAST). FAST method is applied at each stage of starting from the information stage to the interpretation of the results. The OrthoLPPDUNS design with the joint system uses custom components that cause weakness in frame stability. The use of standard components in joint systems can provide solutions to external fixations, although there are still weaknesses in the ring-strut angle. The OrthoLPPDUNS redesign has a better success rate in terms of stability parameters, allowing more precise bone reconstruction.

Computer-Aided Identification of Symmetry Relating Groups of Molecules

Molecular symmetry plays an important role in many areas of chemistry, and students are generally taught to identify intramolecular symmetries at the undergraduate level. Intermolecular symmetry, the symmetry among groups of molecules, is of great importance in topics such as X-ray crystallography, but it receives substantially less attention. Even when familiar with such symmetries as translations, screw rotations, and glide reflections, students rarely obtain the same level of proficiency in identifying these symmetries via inspection as they do with the proper and improper rotations involved in point group symmetry. We describe a tool designed to scaffold the student’s ability to mentally manipulate molecules and identify the presence and nature of intermolecular symmetry. The tool consists of an algorithm that the student follows to generate centroids between atoms in putatively symmetry-related molecules. The easily recognized patterns formed by the centroids provide key information about the presence and nature of any intermolecular symmetry relating the molecules. The theoretical basis for the patterns formed by the centroids is provided along with worked examples, an example problem set, and a prescription for generating new exercises.

Symmetry-enforced band crossings in trigonal materials: Accordion states and Weyl nodal lines

Nonsymmoprhic symmetries, such as screw rotations or glide reflections, can enforce band crossings within high-symmetry lines or planes of the Brillouin zone. When these band degeneracies are close to the Fermi energy, they can give rise to a number of unusual phenomena: e.g., anomalous magnetoelectric responses, transverse Hall currents, and exotic surface states. In this paper, we present a comprehensive classification of such nonsymmorphic band crossings in trigonal materials with strong spin-orbit coupling. We find that in trigonal systems there are two different types of nonsymmorphic band degeneracies: (i) Weyl points protected by screw rotations with an accordion-like dispersion, and (ii) Weyl nodal lines protected by glide reflections. We report a number of existing materials, where these band crossings are realized near the Fermi energy. This includes Cu2SrSnS4 and elemental tellurium (Te), which exhibit accordion Weyl points; and the tellurium-silicon clathrate Te16Si38, which shows Weyl nodal lines. The ab-initio band structures and surface states of these materials are studied in detail, and implications for experiments are briefly discussed.

From space group to space groupoid: the partial symmetry of low-temperature E-vanillyl oxime.

The phase transition of E-vanillyl oxime {1-[(E)-(hydroxyimino)methyl]-4-hydroxy-3-methoxybenzene, C8H9NO3} has been analysed by single-crystal and powder X-ray diffraction. The high-temperature (HT) phase (P21/a, Z' = 1) transforms into the low-temperature (LT) phase (threefold superstructure, P\overline{1}, Z' = 6) at ca190 K. The point operations lost on cooling, {m[010], 2[010]}, are retained as twin operations and constitute the twin law. The screw rotations and glide reflections are retained in the LT phase as partial operations acting on a subset of Euclidean space {\bb E}^3. The full symmetry of the LT phase, including partial operations, is described by a disconnected space groupoid which is built of three connected components.

Radical scavenging activity of instant gruels enriched with cranberry fruits determined by thin-layer chromatography—DPPH test and by spectrophotometric method

Natural compounds possess multiple biological properties, among others antioxidant activity. Phenolic compounds which exhibit excellent antiradical activity may act as scavengers of free radicals or prevent their formation. The main objective of the present research was the examination of the free radical scavenging activity of instant corn gruels with 0%, 1%, 3%, 5%, and 10% addition of dried cranberry fruits. The extrusion of gruels was carried out at varying rotational speeds of the plasticising system (80, 100, and 120 rpm). The study was developed using two methods: thin-layer chromatography–2,2-diphenyl-1-picrylhydrazyl (DPPH) test and spectrophotometric analysis. The findings confirm that the use of higher screw rotations during the extrusion entailed a higher antioxidant activity of the obtained extrudates. Also, a high activity was reported for the extruded corn gruels without additives. This, in turn, demonstrates an insignificant influence of the extrusion process on the biological value of the...

Weyl points and Dirac lines protected by multiple screw rotations

In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron’s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 (P212121) and No. 198 (P213), which have three orthogonal screw rotation axes. In the case of space groups No. 61 (Pbca) and No. 205 (Pa-3) that have extra inversion symmetry, Weyl points are promoted to four-fold degenerate line nodes in glide-invariant planes. The three-fold rotation symmetry present in the space groups No. 198 and No. 205 allows Weyl and Dirac points, respectively, to appear along its rotation axes in the Brillouin zone and generates four-fold and six-fold degeneracy at the Γ point and R point, respectively.

Comparison of compressive forces caused by various cannulated cancellous screws used in arthroscopic ankle arthrodesis

BackgroundWhen performing arthroscopic ankle arthrodesis for end-stage ankle arthritis, internal fixation is performed using bone screws after appropriate preparation.However, optimal characteristics of bone screws have not been examined in terms of pressure force. Objective comparisons of bone-screw performance may provide information on procedures for arthroscopic ankle arthrodesis. The study objectives were to determine whether it was possible to measure compressive force changes using the newly developed device and to infer all screw characteristics from measurement results when used in actual surgeries. In addition, we performed experiments on cadavers to verify whether the experimental results could be applied to the joints of living subjects.MethodsThree types of screws (S1, S2, and S3) were inserted into the unique measurement device, and the changes in pressure were measured for each 45° turn. Changes in pressure and maximum pressure force were recorded after the application of the screws. After reaching the maximum pressure in the simulated bone, further screw rotations were accompanied by a gradual pressure decrease to 0 MPa. We also measured pressure changes in a similar manner by inserting a miniature pressure sensor into the talocrural joints of cadavers.ResultsThe mean maximum pressure ± standard deviation for S1, S2, and S3 were 0.832 ± 0.164 MPa, 0.434 ± 0.116 MPa, and 0.414 ± 0.127 MPa, respectively. Pressure slopes to the maximum did not significantly differ between the screws in the simulated bone, and a subsequent pressure decrease to 0 MPa was significantly more rapid for S1 than for S2 and S3. Although pressure failure after the overtightening of screws was only observed in the simulated bone, patterns of pressure vs. rotation angle were similar in simulated and cadaveric bones. The pressure profile characteristics of three different screw types were determined.ConclusionsWe were able to measure the compressive force changes using the newly developed device when the screws were inserted. On the basis of the measurement results, we were able to infer the characteristics of all screws when used in actual surgery.

Topological charges of three-dimensional Dirac semimetals with rotation symmetry

In general, the stability of a band crossing point indicates the presence of a quantized topological number associated with it. In particular, the recent discovery of three-dimensional Dirac semimetals in Na$_{3}$Bi and Cd$_{3}$As$_{2}$ demonstrates that a Dirac point with four-fold degeneracy can be stable as long as certain crystalline symmetries are supplemented in addition to the time-reversal and inversion symmetries. However, the topological charges associated with Na$_{3}$Bi and Cd$_{3}$As$_{2}$ are not clarified yet. In this work, we identify the topological charge of three-dimensional Dirac points. It is found that although the simultaneous presence of the time-reversal and inversion symmetries forces the net chiral charge to vanish, a Dirac point can carry another quantized topological charge when an additional rotation symmetry is considered. Two different classes of Dirac semimetals are identified depending on the nature of the rotation symmetries. First, the conventional symmorphic rotational symmetry which commutes with the inversion gives rise to the class I Dirac semimetals having a pair of Dirac points on the rotation axes. Since the topological charges of each pair of Dirac points have the opposite sign, a pair-creation or a pair-annihilation is required to change the number of Dirac points in the momentum space. On the other hand, the class II Dirac semimetals possess a single isolated Dirac point at a time-reversal invariant momentum, which is protected by a screw rotation. The non-symmorphic nature of screw rotations allows the anti-commutation relation between the rotation and inversion symmetries, which enables to circumvent the doubling of the number of Dirac points and create a single Dirac point at the Brillouin zone boundary.

Twinning of three Fe-PNP pincer complexes interpreted according to order–disorder (OD) theory

The systematic twinning of three 2,6-diaminopyridine-based Fe-PNP complexes is interpreted using order-disorder (OD) theory. The monoclinic [Fe(0)(PNP(Et)-(i)Pr)(CO)2] [P112(1)/b, Z' = 4] possesses pseudo-orthorhombic metrics and crystallizes as a reflection twin by pseudo-merohedry with the twin plane (100). The structure is made up of layers with idealized p2(1)a(b) symmetry. The a glide planes of adjacent layers do not overlap, leading to OD polytypism. trans-[Fe(II)(PNP-Et)Br2(CO)] [P2(1)/n, Z' = 1] is systematically twinned via twofold rotation about [001]. It is made up of OD layers with idealized p2(1)2(1)(2) symmetry. OD polytypism is caused by the twofold rotation axes of adjacent layers which do not overlap. [Fe(II)(κ(2)P,N-PNP-(i)Pr,TAD)Cl2]·THF [P1, Z^{\prime} = 2] is systematically twinned via a twofold rotation about [010]. It is made up of layers with idealized p121(1) symmetry. OD polytypism is caused by screw rotations relating adjacent layers with an intrinsic translation along a fourth of a primitive lattice vector. In all three structures the twin individuals are a polytype with a maximum degree of order (MDO) and at the twin interface is located a fragment of the second MDO polytype.

Thermal performance evaluation of continuous khoa cooling system

Khoa is an intermediate product widely used as a base material for various indigenous milk sweets. Long duration conventional natural cooling of khoa in open trays not only increases total production time but also results to various browning reactions and microbial contamination. Thermal performance of mechanized khoa cooling system was evaluated to enhance the quality of cooled khoa . The system consisted of an enclosed jacketed tubular screw conveyor. Experiments were conducted at various combinations of 3, 6, 9 screw rotations per minute and 0°, 5°,10° inclination angle of cooling barrel. Cooling performance was evaluated in terms of overall heat transfer coefficient and cooling efficiency. The residual quantity of khoa left in the system after cooling was also determined. Optimum process parameters for maximum cooling were 9 rpm of screw speed and 10° angle of inclination. The sensory quality of mechanized cooled product was judged by an expert panel. The effect of system operational parameters on sensory attributes of khoa was insignificant.