scholarly journals Micromanipulation studies of chromosome movement. I. Chromosome-spindle attachment and the mechanical properties of chromosomal spindle fibers.

1979 ◽  
Vol 82 (2) ◽  
pp. 528-541 ◽  
Author(s):  
D A Begg ◽  
G W Ellis
Keyword(s):  
Mechanical Properties ◽  
Tensile Force ◽  
Metaphase Plate ◽  
Compressive Force ◽  
Preliminary Evidence ◽  
Spindle Pole ◽  
Polarization Microscopy ◽  
Similar Distance ◽  
Mechanical Attachment ◽  
Spindle Fibers

We have used micromanipulation to study the attachment of chromosomes to the spindle and the mechanical properties of the chromosomal spindle fibers. Individual chromosomes can be displaced about the periphery of the spindle, in the plane of the metaphase plate, without altering the structure of the spindle or the positions of the nonmanipulated chromosomes. From mid-prometaphase through the onset of anaphase, chromosomes resist displacement toward either spindle pole, or beyond the spindle periphery. In anaphase a chromosome can be displaced either toward its spindle pole or laterally, beyond the periphery of the spindle; however, the chromosome resists displacement away from the spindle pole. When an anaphase half-bivalent is displaced toward its spindle pole, it stops migrating until the nonmanipulated half-bivalents reach a similar distance from the pole. The manipulated half-bivalent then resumes its poleward migration at the normal anaphase rate. No evidence was found for mechanical attachments between separating half-bivalents in anaphase. Our observations demonstrate that chromosomes are individually anchored to the spindle by fibers which connect the kinetochores of the chromosomes to the spindle poles. These fibers are flexible, much less extensible than the chromosomes, and are to pivot about their attachment points. While the fibers are able to support a tensile force sufficient to stretch a chromosome, they buckle when subjected to a compressive force. Preliminary evidence suggests that the mechanical attachment fibers detected with micromanipulation correspond to the birefringent chromosomal spindle fibers observed with polarization microscopy.

Unorthodox male meiosis in Trichosia pubescens (Sciaridae). Chromosome elimination involves polar organelle degeneration and monocentric spindles in first and second division

1994 ◽  
Vol 107 (1) ◽  
pp. 299-312 ◽  
Author(s):  
H. Fuge
Keyword(s):  
Meiotic Division ◽  
Metaphase Plate ◽  
Chromosome Elimination ◽  
Spindle Pole ◽  
Male Meiosis ◽  
Early Prophase ◽  
Late Prophase ◽  
Section Electron ◽  
The One ◽  
Polar Organelle

Male meiosis in Trichosia pubescens (Sciaridae) was investigated by means of serial section electron microscopy and immunofluorescence light microscopy. From earlier studies of another sciarid fly, Sciara coprophila (Phillips (1967) J. Cell. Biol. 33, 73–92), it is known that the spindle poles in sciarid spermatogonia are characterized by pairs of ‘giant centrioles’, ring-shaped organelles composed of large numbers of singlet microtubules. In the present study spermatocytes in early prophase of Trichosia were found to possess single giant centrioles at opposite sides of the nucleus. The obvious reduction in centriole number from the spermatogonial to the spermatocyte stage is suggested to be the result of a suppression of daughter centriole formation. In late prophase, a large aster is developed around the centriole at one pole. At the opposite pole no comparable aster is formed. Instead, a number of irregular centriolar components appear in this region, a process that is understood to be a degeneration of the polar organelle. The components of the degenerate pole migrate into a cytoplasmic protrusion (‘bud’), which later is also utilized for the elimination of paternal chromosomes. The existence of only one functional polar centre is the reason for the formation of a monopolar monocentric spindle in first meiotic division, which in turn is one of the prerequisites for the elimination of paternal chromosomes. While the set of maternal and L chromosomes orientates and probably moves towards the pole, paternal chromosomes seem to be unable to contact the pole, possibly due to an inactivation of their kinetochores. Retrograde (‘away from the pole’) chromosome motion not involving kinetochores is assumed. Eventually, paternal chromosomes move into the pole-distal bud and are eliminated by casting off, together with the components of the degenerate polar organelle. Chromosome elimination can be delayed until the second meiotic division. The spindle of the second meiotic division is bipolar and monocentric. One spindle pole is marked by the polar centre of first division. The opposite spindle apex is devoid of a polar centre. It is assumed that spindle bipolarity in the second division is induced by the amphi-orientated chromosomes themselves. The maternal and L chromosome set (except the non-disjunctional X chromosome, which is found near the polar centre) congress in a metaphase plate, divide and segregate. Of the two daughter nuclei resulting from the second meiotic division, the one containing the X chromatids is retained as the nucleus of the future spermatozoon. The other nucleus becomes again eliminated within a second cytoplasmic bud.

scholarly journals Novel Design and Position Control Strategy of a Soft Robot Arm

Robotics ◽  
2018 ◽  
Vol 7 (4) ◽  
pp. 72 ◽  
Author(s):  
Alaa Al-Ibadi ◽  
Samia Nefti-Meziani ◽  
Steve Davis ◽  
Theo Theodoridis
Keyword(s):  
Position Control ◽  
Control Strategies ◽  
Tensile Force ◽  
Compressive Force ◽  
Soft Robot ◽  
Robot Arm ◽  
Bending Actuator ◽  
Muscle Actuators ◽  
Novel Design ◽  
Bending Behaviour

This article presents a novel design of a continuum arm, which has the ability to extend and bend efficiently. Numerous designs and experiments have been done to different dimensions on both types of McKibben pneumatic muscle actuators (PMA) in order to study their performances. The contraction and extension behaviour have been illustrated with single contractor actuators and single extensor actuators, respectively. The tensile force for the contractor actuator and the compressive force for the extensor PMA are thoroughly explained and compared. Furthermore, the bending behaviour has been explained for a single extensor PMA, multi extensor actuators and multi contractor actuators. A two-section continuum arm has been implemented from both types of actuators to achieve multiple operations. Then, a novel construction is proposed to achieve efficient bending behaviour of a single contraction PMA. This novel design of a bending-actuator has been used to modify the presented continuum arm. Two different position control strategies are presented, arising from the results of the modified soft robot arm experiment. A cascaded position control is applied to control the position of the end effector of the soft arm at no load by efficiently controlling the pressure of all the actuators in the continuum arm. A new algorithm is then proposed by distributing the x, y and z-axis to the actuators and applying an effective closed-loop position control to the proposed arm at different load conditions.

scholarly journals Effect of nano-solid particles on the mechanical properties of shear thickening fluid (STF) and STF-Kevlar composite fabric

2021 ◽  
Vol 16 ◽  
pp. 155892502110448
Author(s):  
Mingmei Zhao ◽  
Jinqiu Zhang ◽  
Zhizhao Peng ◽  
Jian Zhang
Keyword(s):  
Mechanical Properties ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Tensile Force ◽  
Shear Thickening ◽  
Solid Particles ◽  
Time Range ◽  
Shear Thickening Fluid ◽  
Pull Out ◽  
Diamond Particles

To analyze the effect of nano-solid particles on the mechanical properties of shear thickening fluid (STF) and its Kevlar composite fabric. In this study, nano-silica and polyethylene glycol (PEG 200) were used as dispersed and continuous phases. Nano-graphite and nano-diamond particles were used as additives to prepare STF and Kevlar composite fabric. Study the friction characteristics and rheological characteristics of STF at different temperatures. Explore the STF’s mechanical response under transient high-speed impact conditions through the split Hopkinson pressure bar experiment. The mechanical properties of STF-Kevlar fabric are studied through yarn pull-out test and burst experiments. The experimental results show that the intermolecular repulsive force of STF is enhanced under a high-temperature environment, and shear thickening effect is reduced. Nano-diamond particles strengthen the contact coupling force and contact probability between the particle clusters, so that the maximum viscosity of the system reaches 1679 Pa s, the thickening ratio reaches 318 times, and the rheological properties of the shear thickening fluid are improved. The results of the SHPB experiment show that the STF can complete a dynamic response within a 50–75 µs time range, and the maximum stress can reach 78 MPa. The bullet’s incident kinetic energy is not only transformed into thermal energy and phase change energy of solid-liquid conversion, but also into frictional energy between particles. The mechanical experiments of STF-Kevlar composite fabrics show that the tensile force value of STF5-Kevlar is the largest (10.3 N/13.5 N), and the tensile force of neat Kevlar was the smallest (4.3 N/4.9 N). The maximum bearing capacity (0.3 kN) and absorption energy (51.8 J) of Neat Kevlar are less than those of STF1-Kevlar (3.2 kN, 116.7 J) and STF3-Kevlar (1.9 kN, 88.2 J), and STF5-Kevlar (4.7 kN, 143.3 J). Fabric’s failure mode is converted from partial yarn extraction to overall deformation and rupture of the fabric. Therefore, by changing the solid additives’ parameters, the STF and the composite fabric’s mechanical properties can be effectively controlled, which provides a reference for preparing the STF and fabric composite materials.

Experimental Evidence of Density and Mechanical Properties Enhancement of Binary Alloys by Solidification Subject to Vibrations

2009 ◽  
Author(s):  
J. Vadasz ◽  
J. P. Meyer ◽  
S. Govender ◽  
M. Andrick ◽  
W. Carter ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Binary Alloys ◽  
Preliminary Evidence ◽  
Boundary Effects ◽  
Infinite Length ◽  
Vibration Source ◽  
Sound Waves

Preliminary evidence of density and mechanical properties enhancement of binary alloys by solidification subject to vibrations is presented. The frequency of vibrations was increased from 0 to 100 Hz by using sound waves as the vibration source. The latter shows that the solidified microstructure, the ultimate tensile strength, and the hardness improve as the frequency increases. The chosen alloy for this study was Pb-Sb 4.4% (lead antimony 4.4%) and was selected because of its low melting temperature. The cast chosen was of a rod shape having a diameter of 10mm and a length 500mm. This choice is consistent with assuming an infinite length and therefore ignoring boundary effects in a planned theoretical follow-up analysis. Also due to the geometry of the mould it can be assumed that the cast was cooled due to conduction alone.

Analysis of Jib Strength and Broken Jib Accident of High Pedestal Jib Crane from the Perspective of Mechanics

2012 ◽  
Vol 164 ◽  
pp. 322-325 ◽  
Author(s):  
Qing Dun Zeng ◽  
Fang Liu
Keyword(s):  
Finite Element ◽  
Working Conditions ◽  
Tensile Force ◽  
Compressive Force ◽  
Guangdong Province ◽  
Solid Model ◽  
Finite Element Software ◽  
Actual Working

According to an example of the broken jib accident of a high pedestal jib crane (HM2564) in a Shipyard Co., Ltd. in Guangdong province, this paper used a finite element software ANSYS to establish a solid model for the jib frame of the crane, calculated the stresses of jib system under various actual working conditions and checked the strengths. Simultaneously, the reasons of broken jib were quantitatively analyzed from the perspective of mechanics. The results show that the strengths of the jib system meet the requirements of safe use under all kinds of working conditions, but the related hoistman incorrectly operated the facility, cables can’t be winded normally in pulleys, thus resulting in that the tensile force of a cable was directly applied on the main jib by pulley spindle and the failure of the jib frame occurred under heavy compressive force of lifting cables.

scholarly journals Microstructure and Mechanical Properties of Fe-36Ni and 304L Dissimilar Alloy Lap Joints by Pulsed Gas Tungsten Arc Welding

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4016
Author(s):  
Qian Wang ◽  
Junqi Shen ◽  
Shengsun Hu ◽  
Guancheng Zhao ◽  
Jie Zhou
Keyword(s):  
Mechanical Properties ◽  
Arc Welding ◽  
Tensile Force ◽  
Lap Joints ◽  
Gas Tungsten Arc Welding ◽  
Lower Sheet ◽  
Gas Tungsten Arc ◽  
Microstructure And Mechanical Properties ◽  
Dissimilar Alloys ◽  
Gas Tungsten

High-quality joining of dissimilar alloys between Fe-36Ni alloy and 304L stainless steel is essential in the manufacturing of LNG tanker. In this study, lap joints of Fe-36Ni and 304L dissimilar alloys were fabricated by a pulsed gas tungsten arc welding (P-GTAW) process. The effects of low-frequency pulse on the appearance, microstructure and mechanical properties of the Fe-36Ni/304L lap joints was investigated. With the increase of frequency, the feature sizes of α (the transition angle of the upper surface of Fe-36Ni to the surface of the weld bead) and R (shortest distance between weld root and weld surface) exhibited downtrend and uptrend, respectively, while La (the maximum weld width of lower sheet) and P (the maximum weld penetration of lower sheet) changed in a smaller range. Fusion zone (FZ) is mainly composed of γ phase and M23C6 during solidification, and M23C6 particles are distributed on the grain boundaries of the cells, which reduced the mechanical properties of joint. The average hardness between 110 HV1 and 136 HV1 is lower than that of the base metals. Fractures of all joints located at the Fe-36Ni side near the weld, and a dimple fracture in all samples indicated a ductile fracture. This study found that the heat input values remain 198.86 J mm−1 and increased pulse frequency can improve the maximum tensile force. The average maximum tensile force of the lap weld is 11.95 kN when pulsed frequency is 15 Hz.

Vortex Control by an Artificial Muscle Based on the Conducting Polymer

2003 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Kazuhiro Tanaka ◽  
Shingo Sewa ◽  
Kazuo Onishi
Keyword(s):  
Mechanical Properties ◽  
Flow Control ◽  
Conducting Polymer ◽  
Electrode Potential ◽  
Tensile Force ◽  
Artificial Muscle ◽  
Running Water ◽  
Vortex Control ◽  
Scan Rate ◽  
Static Water

We have proposed the flow control by using an artificial muscle based on the conducting polymer. In order to utilize the artificial muscle for flow control, it is important to clarify the mechanical properties on the artificial muscle based on the conducting polymer. The purpose of this study is to clarify the mechanical properties on artificial muscle and possibility of flow control by using it. We have measured the tensile force generated by artificial muscle in the distilled water. Moreover, we have observed the actuation of artificial muscle based on the conducting polymer in water tunnel. The tensile force of artificial muscle increased as the electrode potential increased. The averaged maximum tensile force did not depend on the scan rate of electrode potential. It depended on the electrode potential and was almost constant. However, the time for reaching maximum tensile force depended on the scan rate. The artificial muscle performed the bending actuation sufficiently not only static water but also running water. Therefore, it can be considered that the artificial muscle will be applied to the actuator for flow control.

scholarly journals Study on Mechanical Properties of Submunition’s Ribbon Straightening Section

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Dong-ze Qin ◽  
Wei Zhang ◽  
Shu-Yun Zhang ◽  
Tian-Ji Guo ◽  
Shui-Yuan Pei ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Tensile Force ◽  
Physical Structure ◽  
Simulation Software ◽  
Tension Test ◽  
Response Characteristics ◽  
Experimental Scheme ◽  
Drop Velocity ◽  
Simulation Results

The humanitarian damage caused by the unexploded submunitions is one of the hot issues of concern to the international community at present. A portion of the submunition that did not explode was caused by a break at the connection between the ribbon riveting and the fuze. According to the physical structure of the submunition and the trajectory into which it was ejected, we analyzed the forces of the submunition in flight, deduced the related mathematical models, and clarify the key elements of the mechanics. In this paper, the commercial simulation software was used to calculate the mechanical properties of the ribbon. And the variation regularity between drop velocity and straightening force of ribbon are revealed. And the response characteristics of different material ribbon with different sizes of riveting holes and riveting joints under tensile action were simulated. The simulation results show that, in the trajectory environment with 30 m/s~55 m/s typical stream speed, the tensile force of the ribbon is less than 300 N, and the application concentration of the connecting parts of the riveting joint and the ribbon will not cause the failure of the kevlar ribbon, but it will cause the failure of the nylon ribbon. In order to verify the variation of the tension of kevlar ribbons in different trajectory environments, we designed the experimental scheme of tension test of the ribbon straightening section of submunition and conducted experiments. Experimental results and numerical simulation results revealed the same law. This paper provides effective technical support for solving the problem of unexploded submunitions.

An Analysis on the Tensile Strength of Hybridized Reinforcement Filament Yarns by Commingling Process

2007 ◽  
Vol 539-543 ◽  
pp. 974-978
Author(s):  
Chathura Nalendra Herath ◽  
Beong Bok Hwang ◽  
B.S. Ham ◽  
Jung Min Seo ◽  
Bok Choon Kang
Keyword(s):  
Mechanical Properties ◽  
Glass Matrix ◽  
High Performance ◽  
Glass Fibers ◽  
Tensile Force ◽  
Matrix Material ◽  
General Purpose ◽  
Practical Applications ◽  
Advantages And Disadvantages ◽  
Glass Matrices

Carbon, aramid and glass fibers are inherently superior to conventional textile fibers in terms of mechanical properties as well as other chemical characteristics. Because of inherent advantages and disadvantages associated with each material, it is generally better to hybridize them to fully benefit of their high performance in many practical applications. In this paper, the possibility of hybridizing Carbon/Aramid-, Carbon/Glass- and Aramid/Glass- matrices has been investigated through the commingling process. In the experiment, several process parameters were selected and they include pressure, yarn oversupply-rate and different nozzle types. As a result of experiments, it was concluded that the hybridized materials has shown better performance than individual reinforced filament yarns in terms of mechanical properties. For small tensile forces, the Carbon/Glass/matrix combination turned out to be good enough for general purpose applications. However, for high tensile applications, Carbon/Aramid or Aramid/Glass with matrix combinations was better than the other material combinations. The hybridization process was also investigated under an air pressure of 5 bar, a yarn oversupply-rate of 1.5% for reinforced filaments, and 3.5% to 6% for matrix materials, respectively. It was also shown from the experimental results that Carbon/Glass/matrix combination may be desirable for small tensile force applications and Carbon/Aramid/matrix and Glass/Aramid/matrix combinations most suitable for heavy tensile force applications, respectively. As a matrix material, polypropylene and polyester have shown better performance than polyether-ether-keeton in terms of tensile property.

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