High Pairs Research Articles

Chromosome Pairing Patterns in Interspecific Hovdeum Lechleri × H. Vulgare (Cultivated Barley) Hybrids with 2n = 21-29

Individual chromosomes or the whole genome of cultivated barley are often eliminated in interspecific Hordeum lechleri × H. vulgare crossing combinations (rarely one or a few chromosomes of H. lechleri are eliminated). This produces series of plants with chromosome numbers ranging from 2n = 21 (true trihaploids of H. lechleri and rarely aneuploids), through 2n = 22-27 (aneuploids) to 2n = 28, 29 and 30 (true hybrids and aneuploids). In such material the effect on meiotic pairing was studied for 1. influence of parental genotypes; 2. influence on pairing by chromosome number; and 3. influence on pairing by presence/absence of individual chromosomes identified by C-banding of root-tip cells. A total of 126 plants representing combinations of seven varieties of cultivated barley and ten accessions of H. lechleri were investigated. Overall there was a large variation in pairing between plants ranging from 0.12–10.09 chiasmata/cell. True trihaploids of H. lechleri (2n = 21) without barley chromosomes had a “basic pairing” ranging from 0.78–4.58 chiasmata/cell. In aneuploids and euploid hybrids the presence of individual barley chromosomes or the entire complement of barley generally resulted in higher pairing than in trihaploids. This contradicts previous proposals of a depressing effect of the H. vulgare genome in interspecific Hordeum hybrids. Some hybrid combinations showed a large difference in pairing according to parental origin. There seemed to be no clear tendencies of pairing related to different chromosomal numbers. The presence of chromosome 4H of barley had a negative effect on meiotic pairing. The greater part of the recorded pairing is assumed to reflect homoeologous pairing between the three genomes of H. lechleri whereas allosyndetic pairing between H. vulgare and H. lechleri chromosomes is considered low.

Meiotic Pairing in a Trigeneric Hybrid Triticum Tauschii-Agropyron Cristatum-Hordeum Chilense

The chromosome affinity among the P genome from Agrop-vron and the D and HCh genomes of Triticurn and Hordeum in the absence of the Ph system controlling homoeologous chromosome pairing provides information for breeding purposes. Hybrids between two accesions of the diploid barley Hordeum chilense (HchHch) and the fertile amphiploid Triticum tuuschii-Agropyron cristatum (DDPP) were made, giving rise to the trigeneric hybrid genomic combinations HChDP from which such information could be obtained. The meiotic pairing of these hybrids using fluorescence genomic in situ hybridization (FISH) on metaphase I pollen mother cells yield data on allosyndetic and autosyndetic chromosome pairing between the three genomes. The results showed that the A. cristatum tetraploid parent of the amphiploid DDPP is a segmental alloploid. A higher pairing between the D and HCh genomes than between them and the P genome from A. cristutum is observed.

The Design of a Novel Pure-Rolling Transmission to Convert Rotational into Translational Motion

The Design of a Novel Pure-Rolling Transmission to Convert Rotational into Translational Motion

Solving the Forward Kinematics of a Planar Three-Legged Platform With Holonomic Higher Pairs

A practical solution procedure for the forward kinematics problem of a fully-parallel planar three-legged platform with holonomic higher pairs is presented. Kinematic mapping is used to represent distinct planar displacements of the end-effector as discrete points in a three dimensional image space. Separate motions of each leg trace skew hyperboloids of one sheet in this space. Therefore, points of intersection of the three hyperboloids represent solutions to the forward kinematics problem. This reduces the problem to solving three simultaneous quadratics. Applications of the platform are discussed and an illustrative numerical example is given.

Formulation of a Class of Higher Pair Joints in Multibody Systems Using Joint Coordinates

This paper describes the development of general formulations of higher pair joints in multibody systems. A class of higher pair joints, described as a spatial point contact between the surfaces of two interacting bodies is formulated by means of Joint Coordinate Formulation and implemented in a general purpose multibody analysis program. The joint is formulated as remaining within the reduced open loop system according to the notation applied in the Joint Coordinate Method. This representation necessitates an evaluation of the degrees of freedom in the joint. Based on these considerations, the point contact joint is also formulated to cut a loop in the mechanical system. In this case, the appropriate constraint equations and a set of artificial variables are introduced in the analysis. The surfaces in the point contact joint are represented as parametric cubic spline patches but can also be introduced using other methods. Examples illustrating the implemented types of joints are presented at the end of the paper.

Kinematic Reasoning with Spatial Decompositions

This paper examines the application of hierarchical discrete spatial representations to the kinematic analysis and synthesis of the higher pairs. Two instances of hierarchical representation are investigated, a global decomposition in the form of quadtrees, and an object-centered, multi-level molecular decomposition. Kinematic reasoning with both representations relies upon the rapid evaluation of the single occupancy constraint. For both representations we present algorithms that allow the rapid detection of intersection between two objects, the analysis of higher pair mechanisms, and a restricted class of kinematic synthesis.

Parametric kinematic tolerance analysis of planar mechanisms

We present an efficient algorithm for worst-case and statistical kinematic tolerance analysis of mechanisms with parametric part tolerances. The algorithm derives the kinematic variation directly from the part geometry, the part degrees of freedom, and the allowable parameter variations. It first derives a geometric representation of the kinematic variation as parametric surfaces in the mechanism configuration space. It then performs sensitivity analysis on the surfaces and combines the results. In addition to traditional quantitative variations, the results reveal qualitative variations, such as play, undercutting, interference, and jamming. Our implementation handles planar mechanisms with one degree of freedom per part, including ones with higher pairs and multiple contacts. It is fast enough to be practical for full parametric models of complex mechanisms and for parametric representations of geometric tolerances, such as offsets, which typically require many parameters. The algorithm extends to linkage mechanisms when coupled with linkage analysis software. We demonstrate the implementation on a 26 parameter model of a Geneva pair and on an 82 parameter model of a camera shutter mechanism.

Kinematic analysis of certain spatial mechanisms containing higher pairs

Certain spatial mechanisms containing higher pairs are kinematically analyzed in this paper using the vector algebraic method. This method uses standardized vector expressions and operations, and specification of the relative orientation of the elements of higher pairs is not required. As a result, the analysis procedure is simpler and more direct than with other methods.

Determination of the frequency of wheat-rye chromosome pairing in wheat x rye hybrids with and without chromosome 5B

Genomic in-situ hybridization (GISH) was used to determine the amount of wheat-rye chromosome pairing in wheat (Triticum aestivum) x rye (Secale cereale) hybrids having chromosome 5B present, absent, or replaced by an extra dose of chromosome 5D. The levels of overall chromosome pairing were similar to those reported earlier but the levels of wheat-rye pairing were higher than earlier determinations using C-banding. Significant differences in chromosome pairing were found between the three genotypes studied. Both of the chromosome-5B-deficient hybrid genotypes showed much higher pairing than the euploid wheat hybrid. However, the 5B-deficient hybrid carrying an extra chromosome 5D had significantly less wheat-rye pairing than the simple 5B-deficient genotype, indicating the presence of a suppressing factor on chromosome 5D. Non-homologous/non-homoeologous chromosome pairing was observed in all three hybrid genotypes. The value of GISH for assessing the level of wheat-alien chromosome pairing in wheat/alien hybrids and the effectiveness of wheat genotypes that affect homoeologous chromosome pairing is demonstrated.

Simulation and shape synthesis of kinematic pairs via small-scale interference detection

We present a shape representation and algorithms for the simulation and shape synthesis of kinematic higher pairs. The shape of a kinematic member is represented as an arrangement of small contiguous nondirected circles, which we call “molecules”. Given the shapes of the two members, a valid initial configuration, and the motion of one of the members (known as the driver), the motion of the other member (known as the driven) is determined. This simulation is based upon finding the points of contact between the member shapes. Contact is defined by interference of the molecules. As output, the simulation produces the functional relationship between the members and a record of the molecules of each member shape that came into contact during the process. Two procedures for shape synthesis are described. Given the shape of one member and the functional kinematic relationship between the member pair, the first procedure generates the shape of the second member from a blank of material. The second procedure modifies the shapes of two interacting members in order to change their contact characteristics during a kinematic interaction. Several examples from an implementation are provided.

Dispersal of wolves (Canis lupus) in northeastern Minnesota, 1969–1989

We examined the dispersal patterns of radio-collared wolves (Canis lupus) from 21 packs in the Superior National Forest, Minnesota, from 1969 to 1989. A total of 316 wolves (542 wolf-years) were captured, radio-collared, and followed during 21 years of radio-tracking; 75 were identified as dispersers. Both sexes dispersed equally. Of the adults, yearlings, and pups, 8, 75, and 16%, respectively, dispersed. Most dispersers left when they were 11–12 months old, only a few wolves dispersing as adults. Dispersal occurred mainly in February–April and October–November. Adults dispersed short distances into nearby territories, but yearlings and pups dispersed both short and long distances. Yearling and pup dispersal rates were highest when the wolf population was increasing or decreasing and low when the population was stable. Adults had the highest pairing and denning success. Yearlings had moderate pairing and low denning success, and pups had low pairing and denning success. Yearlings and pups that dispersed a short distance had a higher success of settling in a new territory, likely reflecting available vacancies in nearby territories. Thirty-five percent of the known-age wolves remained in their natal territory for >2 years; two wolves were known to have remained for >7 years. The relative weight of pups at capture apparently did not affect their age or success of dispersal or the tendency to disperse.

Hybrid (Symbolic-Numerical) Optimization in Mechanism Design for the Elimination of Redundant Constraints

Hybrid optimization, a new approach to design optimization employing both symbolic reasoning and algorithmic analysis, has been applied to the design of kinematic pairs in mechanisms. This hybrid design methodology provides a three-step systematic approach for (1) combining the degrees-of-freedom found in simple, lower kinematic pairs to obtain more complex but robust higher pairs, (2) judging inappropriately assigned joints for the elimination of redundant kinematic constraints and harmful mobilities, and (3) assisting nonexpert designers in applying nonlinear programming algorithms for detailed numerical design optimization of kinematic pairs. An example taken from the design of a spatial mechanism, specifically a universal joint, is presented and serves to demonstrate the utility of this procedure for detailed hybrid design optimization of kinematic pairs in mechanisms.

Simple explanation of the linget al. experiment on the clapping mode frequency

Recent precise measurements of the clapping (cl) mode frequency in He3-A (Refs. 1 and 2) show a discrepancy with an ordinary kinetic-equation theory3: a 6% difference between experimental data and theory remains even after taking the higher pairing and Fermi-liquid corrections into account. The Brusov-Popov path-integration theory4 is in much better agreement with the data of Refs. 1 and 2. The difference is less than 2% even without taking the above-mentioned corrections into account.

Segregation in the pollen of F2 rye (Secale cereale) plants for induction of homoeologous chromosome pairing in hybrids with wheat (Triticum aestivum)

An attempt was made to determine the inheritance of the rye genes which induce high chiasma frequency in hybrids with wheat and to study if the ability of rye to induce partial amphiploidy in hybrids with wheat was heritable. Five to eight F2 pollen plants were derived from seeds taken from each of three F1 plants that had given high chiasma frequency in hybrids with 'Chinese Spring' wheat in earlier studies. Similarly, six to seven F2 pollen plants were derived from each of three F1 plants that had given partial amphiploids in hybrids with 'Chinese Spring' wheat in earlier studies. Chiasma frequency was studied in 127 hybrids with 'Chinese Spring' wheat. In the present study, significant differences in chiasma frequency were observed (i) among the 38 families represented by 127 plants, and (ii) between two groups of three sets each, one known for inducing high pairing and the other known for inducing partial amphiploidy associated with low pairing in wheat × F1 rye plants. Significant variation was also observed between families within sets (each originated from one F1 rye plant) suggesting that F2 rye plants derived from the same F1 plants also differed genetically for inducing heterogenetic (homoeologous) pairing in wheat × rye hybrids. One of the six sets particularly showed significantly higher pairing with a mean of 2.13 per cell (individual hybrids gave a chiasma frequency as high as a mean of 6.07 per cell) as against a range of 0.96 to 1.18 in the remaining five sets, suggesting accumulation of genes in F2 rye plants for inducing pairing in wheat × rye hybrids. It is expected that by intermating the segregating rye plants, it should be possible to accumulate genes and eventually to isolate homozygous lines inducing high pairing in hybrids with wheat. Contrary to expectation, no partial amphiploids were obtained in a study of 127 wheat × F2 rye hybrids, although three of the six F1 rye plants had earlier given partial amphiploids in wheat × F1 rye hybrids. Key words: intergeneric hybrids, wheat, rye, genetic control, chromosome pairing.

Degenerative Changes in the Reproductive Organs of Female Schistosomes during Maintenance In vitro

Degenerative alteration of the reproductive organs of female schistosomes in correlation with the change in egg-laying rate of schistosome pairs in vitro was studied by electron microscopy. The production of normal eggs by adult S. japonicum pairs decreased after 4 days in vitro followed by an increase of abnormal egg laying up to day 8. In S. mansoni, the yield of both normal and abnormal eggs decreased gradually from the start of maintenance in vitro in spite of a much higher pairing rate than in S. japonicum. The vitelline gland of 14-day in vitro-maintained S. japonicum stained with Fast red B, while that of S. mansoni did not. The ovary of both species exhibited regressive features after 14 days of maintenance in vitro. Ultrastructural examination showed that the vitelline cells and oocytes of S. japonicum and S. mansoni had already lost their structural integrity after 2 days in vitro and continued to exhibit signs of structural degeneration throughout the 14-day in vitro maintenance period. The regressive changes in reproductive potential of female S. mansoni maintained in vitro for 4 days could be reversed by surgically implanting the parasites into mouse mesenteric veins.

Model of complex structural unit in condensed media

In the theory of petroleum disperse systems, the concept of the complex structural unit (CSU) establishes the layer-by-layer differentiation of components around the core. Molecules with the highest pair interaction potential (PIP) form the core of the CSU and molecules with lower PIP form the interfacial layer. To support the proposed CSU model, experimental data were analyzed on the heats of mixing of compounds of different classes (paraffins, naphthenes, aromatics) present in crude oils, and the mixing heats were correlated with intermolecular interaction energies. The change in the mixing heat values from an exothermic effect to an endothermic effect corresponded to a change to weaker intermolecular interactions. Two series of hydrocarbons with decreasing interaction strength were established.

C-banding pattern and meiotic pairing in five rye chromosomes of hexaploid triticale

The meiotic behaviour of rye chromosomes 1R, 2R, 3R, 6R and 7R/4R of hexaploid triticale 'Cachirulo' is analyzed using the C-banding technique. These chromosomes show different C-banding patterns and present different pairing levels at metaphase I. A decreasing effect of large telomeric heterochromatin bands on pairing is deduced from the following two main facts: i) The chromosome 7R/4R shows the highest pairing associated with the smallest amount of heterochromatin, ii) pairing levels of 2 R short arm and 3 R long arm which carry large telomeric bands are less than their respective long and short arms lacking telomeric heterochromatin. Possible desynaptic effects of heterochromatin are discussed although an asynaptic effect cannot be rejected.

Curvature Analysis of Surfaces in Higher Pair Contact—Part 1: An Analytical Investigation

In this paper, the analytical investigation is done to evaluate the normal and principal curvatures of contacting surfaces in higher pair contact. The velocity ratio of the members connected with the higher-pair-contact surfaces is assumed to be variable. The principal curvatures of the generated or driven surface are expressed in terms of those of the generating or driving surface.

Curvature Analysis of Surfaces in Higher Pair Contact—Part 2: Application to Spatial Cam Mechanisms

In this paper curvature analysis is performed for different three-dimensional cam mechanisms. In every case the expressions for principal curvatures of the cam surface are given in closed forms for ready use. A numerical example is given to show the usefulness of the proposed procedure.

A Generalized Symbolic Notation for Mechanisms

Revisions of the Denavit-Hartenberg symbolic notation are proposed which extend its use to the entire domain of rigid link mechanisms. The extended notation provides a clear separation of the pair variables and the invariant parameters of a mechanism and thus provides a framework in which higher pairs can be systematically modeled. The new symbolism can be used directly with the existing matrix methods of kinematic analysis, and a numerical scheme is presented to reduce the task of data collection for these methods.