Screw Helix Research Articles

Device dislodgement and embolization associated with a new leadless pacemaker.

Currently, there are two approved single chamber leadless pacemakers (LP) in the United States (US), Micra VR™; approved since 2016 and AVEIR VR™; approved in 2022. A potential complication of LPs is dislodgement and/or embolization (D/E) during or after implant. According to the IDE trials, there appears to be a significant difference in D/E rates between the two LPs that have different fixation mechanisms; Micra uses nitinol tines, while AVEIR uses an active screw helix. The aim of this study was to determine if the AVEIR VR LP has continued to exhibit D/E in the United States since it was approved by the Food and Drug Administration (FDA) in April 2022. The FDA Manufacturer and User Facility Device Experience (MAUDE) database was searched for US D/E reports communicated by the manufacturers of both LP devices. For AVEIR VR we reviewed reports from approval till December 2023, and for Micra VR we looked at reports from approval to April 2024. Excluded were reports based on information indirectly obtained from registries, journals, social media, or volunteers. Total number of US implants was acquired from the manufacturers' product performance reports. During a period of 21 months, 5990 AVEIR VR implants had been registered in the United States, of which 53 (0.88%) encountered D/E both during and after the procedure. More D/E (32; 60.4%) occurred during the implantation procedure, with device release problems being the most prominent procedural issue involved with these events. Within a 8-year period, 72 237 Micra VR implants have been registered in the United States, of which 211 (0.29%) showed D/E. The rate of D/E since the US approval of both devices was significantly higher for AVEIR VR compared to Micra VR (0.88% vs 0.29%; p < .0001). AVEIR VR implants may be complicated by dislodgement with or without embolization. Currently, the estimated incidence is about 0.9%, which is significantly higher than Micra VR. Fixation issues and separation problems of the device from the delivery catheter appear to be responsible for most of these D/E events.

Development and evaluation of non-contact automatic tool setting method for grinding internal screw threads

In accuracy grinding processes of screw threads, tool setting is a significant step towards avoiding thread error and ensuring machining accuracy of screw threads. It is a challenge for grinding internal screw threads due to the narrow space limitation. This paper proposes an automatic tool setting method for grinding internal screw threads with non-contact proximity switch, which can be effectively applied into realistic situation with low cost. The geometrical features of internal screw threads in the narrow space are measured by non-contact proximity switch and used to determine the initial point of screw helix. The detailed procedures of the method are presented including preliminary adjustment for tool setting, measurement of spiral centerline for internal screw threads, calculation of the initial position of threads helix, and error compensation. Moreover, the experimental platform is developed to verify the feasibility of the non-contact automatic tool setting method. Furthermore, experiments on improved induction distance of proximity switch, axial translational speed, measurement mechanism, and robustness have been carried out to improve the accuracy of the tool setting method. The results show that the measurement mechanism with double-rising-edge level jumping is relatively better on the tool setting precision. And the improved induction distance of proximity switch is basically consistent with its theoretical one, the improved axial translational speed is − 5 mm/s, and the repeat accuracy of tool setting is up to ± 0.002 mm. The results show the economical and effective method is applicable in the actual process of grinding internal screw threads.

EXTRUDER SCREW FUNCTIONAL CHARACTERISTIC CHANGING IN POLYMERIC MATERIALS REPROCESSING

&lt;p&gt;Polymeric materials reprocessing leads to modification of polymeric materials flow properties. In this paper there are summarized the correlations (obtained from previous experimental research), for several types of virgin and reprocessed polymeric materials, comparatively presented. Models and simulations were performed for the extruding polymeric materials reprocessing, the screw functional feature – with and without considering the leaks over the screw helix flight tip – to assess changes in the performances.&lt;/p&gt;

Life Threatening Perforation of Pacemaker Atrial Lead through the Right Atrium and the Right Lung

We report the case of a 65- year old female patient who was urgently admitted to our institution with hemothorax after pacemaker implantation. The bichamber pacemaker had been implanted one week before admission and the active fixation lead caused perforation of the right atrial wall and penetration of the right lung. Transthoracic echocardiography demonstrated a minimal cardiac effusion but chest X-Ray and computed Tomography (CT) visualised the atrial screw helix outside the atrial wall penetrating through the right lung middle lobe causing hemothorax. After median sternotomy and cut-off of the atrial lead screw helix, we sew the perforated area of the right atrium and the penetrated right lung, sucking away the bloody pleural effusion before closing the thorax. Three weeks later, the cut off atrial lead was extracted through the right subclavian vein and a new one was positioned and fixed again. During the hospital admission the patient was well and free of any symptoms and troubles.

Research on Measurement of Ball Screw Helical Line Error Based on Electronic Generative Metrology

Aiming at the disadvantages of current error measuring instruments of ball screw helix, a new screw helical line error measuring device is developed, moreover, a new method called electronic generative metrology (EGM) is introduced. The problem of measuring head deformation has been settled down because of installation of two driving motors on the instrument, so it is easy to achieve dynamic high precision measurement. Taking the long grating and circular grating as length and angle measurement datum respectively, the torque motor and linear motor are able to form position close-loop control. The measuring head frame is installed on air flotation slider which has characters of high kinematic accuracy and stability, so it guarantees high measurement accuracy. Then, the measurement accuracy analysis of the device is given. And the last, the EGM is developed by using this new research tool. Related experimental studies are conducted to verify the feasibility of the new method.

Neptunium Thiophosphate Chemistry: Intermediate Behavior between Uranium and Plutonium

Black crystals of Np(PS(4)), Np(P(2)S(6))(2), K(11)Np(7)(PS(4))(13), and Rb(11)Np(7)(PS(4))(13) have been synthesized by the reactions of Np, P(2)S(5), and S at 1173 and 973 K; Np, K(2)S, P, and S at 773 K; and Np, Rb(2)S(3), P, and S at 823 K, respectively. The structures of these compounds have been characterized by single-crystal X-ray diffraction methods. Np(PS(4)) adopts a three-dimensional structure with Np atoms coordinated to eight S atoms from four bidentate PS(4)(3-) ligands in a distorted square antiprismatic arrangement. Np(PS(4)) is isostructural to Ln(PS(4)) (Ln = La-Nd, Sm, Gd-Er). The structure of Np(P(2)S(6))(2) is constructed from three interpenetrating diamond-type frameworks with Np atoms coordinated to eight S atoms from four bidentate P(2)S(6)(2-) ligands in a distorted square antiprismatic geometry. The centrosymmetric P(2)S(6)(2-) anion comprises two PS(2) groups connected by two bridging S centers. Np(P(2)S(6))(2) is isostructural to U(P(2)S(6))(2). A(11)Np(7)(PS(4))(13) (A = K, Rb) adopts a three-dimensional channel structure built from interlocking [Np(7)(PS(4))(13)](11-)-screw helices with A cations residing in the channels. The structure of A(11)Np(7)(PS(4))(13) includes four crystallographically independent Np atoms. Three are connected to eight S atoms in bicapped trigonal prisms. The other Np atom is connected to nine S atoms in a tricapped trigonal prism. A(11)Np(7)(PS(4))(13) is isostructural to A(11)U(7)(PS(4))(13). From Np-S bond distances and charge-balance, we infer that Np is trivalent in Np(PS(4)) and tetravalent in Np(P(2)S(6))(2) and A(11)Np(7)(PS(4))(13). Np exhibits a behavior intermediate between U and Pu in its thiophosphate chemistry.

Investigation of the scattering field under the low-frequency resonance conditions of screw helices

The frequency-selective properties of small screw helical coils are investigated. It is shown that, in a frequency band of 2–4 GHz, such coils have two resonances. The scattering patterns of helical coils are measured in the E and H planes. It is found that, at the zeroth-order resonance, a coil scatters a circularly polarized field with the maximum in the plane perpendicular to its longitudinal axis and that, at the frequency of the first resonance, the maximum of the scattered field is oriented along the longitudinal axis of the coil.

Molecular Dynamic Simulation of the Kv1.2 Voltage-Gated Potassium Channel in Open and Closed State Conformations

We performed 45 ns atomistic force field based molecular dynamics (MD) simulations to explore the structure and dynamics of the Kvl.2 voltage-dependent potassium ion channel in both open and closed state conformations. The Kv1.2 crystal structure (PDB 2A79) based open state model and homologically derived closed state model are embedded in a hydrated lipid membrane. We present a detailed analysis of the protein stability, the environment of the gating-charge-carrying residues, the salt bridge within the voltage sensor, S4 segment helix movement, helix interaction between S4-S5 linker and S6, interaction between subunits, and interaction between protein and lipid membrane. The four subunits of the channel lost the symmetry from the starting structure during the simulation, especially the voltage sensors. According to our comparative analysis of the open and closed state conformations, S4 in our simulation behaves more near the screw helix model except for the tilt action. The S4 segment azimuthal rotation angle difference between two conformations shifts about 60 degrees after being embedded in a membrane environment. The S4-S5 linker helix remains stable. The contact area between the S4 and S5 from the adjacent subunit increases after transition to the closed state from the open state. The current investigation provided valuable information to our understanding of the structure and dynamics of membrane-associated helices and the gating mechanism of the voltage-dependent potassium ion channel of the Kv channel.

Interlocking inorganic screw helices: synthesis, structure, and magnetism of the novel framework uranium orthothiophoshates A11U7(PS4)13 (A = K, Rb).

The novel quaternary uranium thiophosphate K11U7(PS4)13 has been synthesized by reacting uranium metal, K2S, S, and P2S5 at 700 degrees C in an evacuated silica tube. The crystal structure was determined by single crystal X-ray diffraction techniques. K11U7(PS4)13 crystallizes in the tetragonal space group I42d (a = 32.048(2) A, c = 17.321(1) A, Z = 8). The structure contains a tunnel framework composed of eight interlocking uranium U7(PS4)13 screw helices, with alkali metal cations residing inside the framework channels. The uranium atoms are coordinated in a bi- or tricapped trigonal prismatic fashion. The screw helices are built up from uranium atoms interconnected by PS4 tetrahedral units. Magnetic susceptibility measurements indicate modified Curie-Weiss-type behavior between 300 and 70 K, with an effective magnetic moment of 2.54 microB per U atom at room temperature and C = 3.78, theta = -14.54, chi 0 = 0.01. The isostructural compound Rb11U7(PS4)13 (a = 32.1641(11) A, c = 17.7244(9) A, Z = 8) was prepared by heating a mixture of the formal composition UPS5 in eutectic LiCl/RbCl melts at 700 degrees C.

Cs2CuP3S9: A Chiral Compound with Screw Helices

The reaction of Cu with a molten mixture of Cs2S/P2S5 produced the quaternary compound Cs2CuP3S9. The bright yellow crystals of Cs2CuP3S9 are stable in air and water for several weeks. The compound crystallizes in the chiral, hexagonal space group P65 (No. 170) and at 23°C: a=15.874(2) Å; c=35.100(7) Å; V=7660(3) Å3; Z=18. The [CuP3S9]2n−n chains are composed of an alternating arrangement of tetrahedral Cu+ ions and cyclic [P3S9]3− units. The structure contains parallel helical [CuP3S9]2n−n chains that run along the c-axis. The cyclic [P3S9]3− unit derives from the molecular adamantane [P4S10] unit with one [PS]3+ vertex removed. The title compound was characterized by differential thermal analysis, far-IR, Raman, and single-crystal optical transmission UV/vis spectroscopy. Positive nonlinear optical response and second harmonic generation response was observed.

Modelling the activation, opening, inactivation and reopening of the voltage-gated sodium channel.

A model of the voltage-gated sodium channel is put forward suggesting that the four S4 voltage-sensors behave as screw-helices making a series of discrete transitions that carry one elementary charge for each notch of the screw helix. After the channel has been activated by the first two steps R in equilibrium with P in equilibrium with A in all four domains, followed by a voltage-independent rearrangement, it is opened by a third cooperative step A in equilibrium with B in domains I, II and III in conjunction with hydration. Inactivation is a voltage-dependent process controlled by the third step A in equilibrium with I in sensor IVS4, and the closing of the channel is brought about its dehydration. From the inactivated steady state the channel may be reopened by a fourth step, I in equilibrium with C in sensor IVS4 and rehydration. The computed kinetics of the model are shown to conform closely with those observed experimentally.

Experimental investigation of the drag flow assumption in extruder analysis

AbstractA new screw pump or extruder has been constructed with the goal of testing the drag flow analysis currently used in the evaluation of polymeric extruders. The new device has been constructed in a manner that allows the barrel, screw helix, and screw core to be rotated independently or in pairs. The experimental results of the flow produced for rotation of the barrel agree well with the theory. However, the flow produced by rotation of the screw elements does not agree with the predictions of the currently accepted theory. The experimental results indicate that the primary element that produced fluid propulsion when the screw is rotated is the screw helix. A new qualitative theory is proposed that is in agreement with the data.

Analysis of an Alternative Extruder Screw Pump Design

Abstract A new screw pump/extruder is analyzed with regard to the effect of the pump components on the pump output. The pump is constructed such that the barrel, screw core, and screw helix can all be rotated independently. Contrary to conventional wisdom, it is demonstrated that the major physical component of the pump which contributes to the output is the screw helix. A new theory is developed for pumping characteristics of this new pump and the theoretical analysis is compared with laboratory data. The theory compares quite well with the data.

Factors affecting the energy efficiency of single screw extruders

A theoretical investigation of the effect of geometrical and structural variables on the energy efficiency of single screw extruders with and without a compression section is presented. For these extruders it was concluded that efficiency increases with increasing screw helix angle, channel height and clearance height and decreases with increasing L/D ratios. Lowering the rotational velocity of the screw and raising pressure increases the energy efficiency. Increasing the feed section lenght of screw extruders with compression sections decreases their energy efficiency significantly. Changing the length of the metering section, however, has little effect. The energy efficiency of extruders with a compression section is much greater than that of single parallel extruders (generally at least double) when all other parameters remain unchanged.

Structure of β,D(1–&gt;4′)‐xylan hydrate

AbstractA structure is proposed for xylan hydrate as a result of investigations by x‐ray fiber diffraction and computer‐aided chain‐packing methods. The unit‐cell dimensions are a = b = 9.16 Å, c (fiber axis) = 14.85Å, γ = 120° and the proposed anti‐parallel chain arrangement corresponds to a space group symmetry of P3221. Left‐handed threefold screw helices are stabilized in this conformation by their interaction with chains of water molecules, so that a satisfactory hydrogen‐bonding scheme is achieved. The proposed structure provides an explanation of the changes in the x‐ray diagram with relative humidity and yields a very good structure factors agreement. An x‐ray fiber diagram corresponding to a higher hydrate (xylan dihydrate) is presented. Comments are made on the possible role of xylan in nature and in technological processes.

Stereospecific polymerization of alkyl thiolacrylates. Part II‐1. Infrared spectra of polyethyl and polypropyl thiolacrylates

AbstractThe infrared spectra of amorphous and crystalline polypropyl thiolacrylates and of amorphous polyethyl thiolacrylate were examined in the range from 3500 to 700 cm−1.A polymorphism was observed in the crystalline poly‐n‐propyl thiolacrylate. A film prepared by drying a cloroform solution of the polymer under air was transparent (Type 2), whereas, a film dried in the current of cloroform vapour was resinous and opaque (Type 1). Type 2 structure was unstable, and it turned into Type 1 structure by stretching in a stream of hot air. Type 1 polymer chains occurred as helices with three monomer units per turn. Type 2 polymer showed non three‐fold screw helices. The infrared spectrum of Type 1 polymer was different from that of Type 2 polymer in many absorption bands, viz., the methylene twisting bands in the vicinity of 1200 cm−1, the CC stretching bands near 1130 cm−1, the asymmetrical CSC stretching and methyl rocking bands in the vicinity of 960 cm−1 and the symmetrical CSC stretching bands near 730 cm−1. In these regions, the spectrum of the crystalline polyisopropyl thiolacrylate was similar to that of Type 2 polymer.