Twist Control Research Articles

The held out wings (how) Drosophila gene encodes a putative RNA-binding protein involved in the control of muscular and cardiac activity.

In an attempt to identify genes that are involved in Drosophila embryonic cardiac development, we have cloned and characterized a gene whose function is required late in embryogenesis to control heart rate and muscular activity. This gene has been named held out wings (how) because hypomorphic mutant alleles produce adult animals that have lost their ability to fly and that keep their wings horizontal at a 90 degree angle from the body axis. In contrast to the late phenotype observed in null mutants, the How protein is expressed early in the invaginating mesoderm and this expression is apparently under the control of twist. When the different mesodermal lineages segregate, the expression of How becomes restricted to the myogenic lineage, including the cardioblasts and probably all the myoblasts. Antibodies directed against the protein demonstrate that How is localized to the nucleus. how encodes a protein containing one KH-domain which has been implicated in binding RNA. how is highly related to the mouse quaking gene which plays a role at least in myelination and that could serve to link a signal transduction pathway to the control of mRNA metabolism. The properties of the how gene described herein suggest that this gene participates in the control of expression of as yet unidentified target mRNAs coding for proteins essential to cardiac and muscular activity.

Wind Tunnel Test of a Smart Rotor Model with Individual Blade Twist Control

The objective of this research is to develop a smart rotor with active control of blade twist using embedded piezoceramic elements as sensors and actuators to minimize rotor vibrations. A 1/8 Froude-scale (dynamically scaled) bearingless helicopter rotor model was built with banks of torsional actuators capable of manipulating blade twist at frequencies from 5 to 100 Hz. To assess the effectiveness of the torsional actuators and vibration suppression capabilities, systematic wind tunnel testing was conducted in the Glenn L. Martin Wind Tunnel. Using accelerometers embedded in the blade tip, the oscillatory blade twist response was measured. The changes in rotor vibratory loads due to piezo-induced twist were determined using a rotating hub balance located at the rotor hub. Experimental test results show that tip twist amplitudes on the order of 0.5 degrees are attainable by the current actuator configurations in forward flight. Although these amplitudes were less than the target value (I to 2 degrees for complete vibration suppression control), test results show that partial vibration reduction is possible. Using open-loop phase shift control of blade twist at the first four rotor harmonics, changes in rotor thrust of up to 9% of the steady-state values were measured.

Are Existing Seismic Torsion Provisions Achieving the Design Aims?

A simple approach to the consideration of torsional effects on the ductile seismic response of buildings is suggested. Instead of increasing torsional strength, the control of twist, which may amplify local inelastic translational deformations, is emphasised. This may be achieved when assuring in the design that some residual stiffness in ductile systems is available. To this end a classification in terms of torsional restraint is suggested. It is postulated that traditional codified techniques, based on the evaluation of torsional effects on elastic systems, are largely irrelevant to ductile structural response. The primary consideration of inelastic deformation demands rather than strength is advocated. The presentation addresses foremost concepts of torsional behaviour and their relevance to routine seismic design, rather than advancement in analytical techniques.

Seismic design for torsional response of ductile buildings


 
 
 
 A simple approach to the consideration of torsional effects in the seismic design of ductile building structures is postulated. Instead of increasing torsional strength, the control of twist, which may amplify local inelastic translational deformations, is emphasised. This may be achieved by assuring that some residual torsional stiffness of the system is available. A number of examples illustrate the simple principles involved. It is demonstrated that traditional codified techniques, based on the evaluation of torsional effects in elastic systems, are largely irrelevant to ductile structural response. It is recommended that, in accord with the philosophy of capacity design, torsional response should be controlled by elastic elements, while hysteretic damping is derived from inelastic translational mechanisms. As a general rule critical conditions for torsional response of well proportioned structures are likely to arise only when inelastic displacements are imposed in a narrow band of directions diagonal to the principal reference axes of orthogonal systems. It is suggested that in the presence of significant eccentricities the displacement ductility demand on the system should be reduced. Thereby elements with defined ductility capacity can be protected against excessive imposed inelastic deformations. The presentation addresses primarily concepts of torsional behaviour rather than advancement in analytical techniques.
 
 
 

Generating Bézier points for curves and surfaces from boundary information

This paper presents efficient methods for directly generating Bézier points of curves and surfaces explicitly from the given compatible arbitrary order boundary information of Hermite curves, Coons-Hermite Cartesian sum patches and Coons-Boolean sum patches. The explicit expressions for the generalized Hermite functions are also developed. Furthermore, a method for determining the twist control points and higher level sets of interior control points from their boundary and lower level sets of control points by using the Coons-Boolean sum schema presented. Many interesting and useful examples are also given in this paper.

Demonstration of an elastically coupled twist control concept for tilt rotor blade application

The purpose of this Note is to present results from an analytic/experimental study that investigated the potential for passively changing blade twist through the use of extension-twist coupling. A set of composite model rotor blades was manufactured from existing blade molds for a low-twist metal helicopter rotor blade, with a view toward establishing a preliminary proof concept for extension-twist-coupled rotor blades. Data were obtained in hover for both a ballasted and unballasted blade configuration in sea-level atmospheric conditions. Test data were compared with results obtained from a geometrically nonlinear analysis of a detailed finite element model of the rotor blade developed in MSC/NASTRAN.

Mechanisms of early Drosophila mesoderm formation

Several morphogenetic processes occur simultaneously during Drosophila gastrulation, including ventral furrow invagination to form the mesoderm, anterior and posterior midgut invagination to create the endoderm, and germ band extension. Mutations changing the behaviour of different parts of the embryo can be used to test the roles of different cell populations in gastrulation. Posterior midgut morphogenesis and germ band extension are partly independent, and neither depends on mesoderm formation, nor mesoderm formation on them. The invagination of the ventral furrow is caused by forces from within the prospective mesoderm (i.e. the invaginating cells) without any necessary contribution from other parts of the embryo. The events that lead to the cell shape changes mediating ventral furrow formation require the transcription of zygotic genes under the control of twist and snail. Such genes can be isolated by molecular and genetic screens.

Static Aeroelastic Control Using Strain Actuated Adaptive Structures

In this study, the feasibility of using representative box wing adaptive structures for static aeroelastic control is examined. A deformable typical section is uti lized to derive the optimal and suboptimal relations for induced strain actuated adaptive wings, and the relations developed are used to design representative adaptive lifting sur faces which are assessed in trade studies. The optimal relations developed showed that op timal adaptive airfoil designs are possible for some realistic configurations, and effective sub-optimal designs can be achieved for others. In addition, the important parameters associated with inducing curvature and twist, thereby altering the lifting forces on the air foil, are determined. The most important of which were found to be the airfoil thickness ratio, the actuation strain produced by the induced strain actuators, and the relative stiff ness ratio of the actuator to the wing skin for both camber and twist control. The stiffness coupling parameter and the wing aspect ratio were also found to be important for twist control. The potential benefits of using adaptive airfoils for aeroelastic control, rather than conventional articulated control surfaces, is demonstrated in trade studies. It was found that greater control authority along with a lower weight penalty is achievable using adap tive aeroelastic structures for a variety of wing designs. Thus, strain actuated adaptive wings may be used rather than conventional lifting surfaces to increase performance while reducing weight, decreasing loads in critical areas, improving the radar cross section, and maximizing the lift-to-drag ratio for many flight conditions.

Computer analysis of the effects of asymmetries of a two-conductor bundle upon its aeolian vibration

A brief description of VIBEOL, a new computer model for the analysis of aeolian vibrations of bundled conductors, is given. Its main characteristics include the capability to treat, in the same span, different spacer-dampers, subconductors, and dampers and a calculation scheme based on the random behavior of aeolian vibrations. In addition, the model can take into account the flexural rigidity of the conductor, thus yielding more accurate estimates of conductor strains and allowing for the moments of inertia and angular stiffness of spacers, dampers and other special types of line equipment. The model has been used to investigate the effects of asymmetries of a twin ASCR conductor bundle equipped with Hydro-Quebec spacer-dampers. While differences in the rigidity of the spacer-damper articulation did not affect the control of aeolian vibration, tension differentials and bundle twist were shown to have a large influence on the reduction of vibration levels. >

Special Bézier quartics in three dimensional curve design and interpolation

The use of special Bezier quartics for three dimensional curve design and interpolation is proposed. These quartics form an extension of parametric cubics and allow the designer one additional local control parameter. The suggested parameters yield control of position and twist of the resulting curve. Using the quartics as interpolating curve segments allows flexible curves for avoiding obstructions (in robotic path design) or for adjusting curvature at the shoulder point of curve segments.

80—CONTROL OF DRAFTING BY TWIST

A yarn may be drafted from a large mass of fibres by using twist to supply the nip force to select fibre leading ends. An account is given of an experimental machine using this principle in which withdrawal tension in the yarn was used to control the amount of twist being inserted. The coefficients of variation of the mass per unit length of a series of yarns produced by this machine are compared with a minimum value calculated assuming perfect operation. Some possible reasons for the shortcomings in levelness are discussed. Experiments in which the forces necessary to extract single fibres and groups of fibres from large masses are described and their relevance to tension control of twist is discussed.