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  • Polymer and Materials Science  (12)
  • Electromyography  (5)
  • Motor control  (5)
  • Bemisia argentifolii  (3)
  • 1
    ISSN: 1615-6102
    Keywords: Bacteria ; Bemisia tabaci ; Bemisia argentifolii ; Endosymbionts ; Microorganism ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of the endosymbionts of several populations of whitefly (Homoptera: Aleyrodidae) was examined using transmission electron microscopy. Consistent differences in morphology and relative number of endosymbionts were observed between species and biotypes of whitefly within the Bemisia taxon.Bemisia argentifolii (=B. tabaci B biotype) individuals from Hawaii, Florida, and Arizona contained two morphological types of microorganisms housed within the mycetocyte cells of immature whiteflies. In contrast, individuals from populations ofB. tabaci A biotype from Arizona and Mexico, andB. tabaci Jatropha biotype from Puerto Rico, consistently contained three distinct morphological types of microorganisms within their mycetocytes. Organisms fromB. tabaci A and Jatropha biotypes differed from each other in the relative frequency of each type of microorganism. These observations suggest that different whitefly biotypes may have variable combinations of micro-fauna, with some possibly unique to each group, and furthers the hypothesis that variation in whitefly endosymbionts may be associated with the development of biotypes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-2986
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-4927
    Keywords: Bemisia tabaci ; Bemisia argentifolii ; cotton whitefly ; squash silverleaf disorder ; sweetpotato whitefly ; tobacco whitefly ; virus vector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Esterase profiles were examined for over 40 populations of the whitefly,Bemisia tabaci, obtained from native and cultivated plant hosts worldwide. Twelve unique electromorphs were identified from distinct populations concentrated largely in Central America, Africa, and India. One electromorph, type B, has recently been proposed as a separate species,Bemisia argentifolii, and has recently spread throughout much of the world. When considered with evidence from mating studies and the ability to induce phytotoxic disorders (squash silverleaf disorder), our data suggest that the single taxonBemisia tabaci may actually represent a species complex.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-4927
    Keywords: Bemisia tabaci ; Bemisia argentifolii ; cotton whitefly ; squash silverleaf disorder ; sweetpotato whitefly ; tobacco whitefly ; virus vector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Esterase profiles were examined for over 40 populations of the whitefly,Bemisia tabaci, obtained from native and cultivated plant hosts worldwide. Twelve unique electromorphs were identified from distinct populations concentrated largely in Central America, Africa, and India. One electromorph, type B, has recently been proposed as a separate species,Bemisia argentifolii, and has recently spread throughout much of the world. When considered with evidence from mating studies and the ability to induce phytotoxic disorders (squash silverleaf disorder), our data suggest that the single taxonBemisia tabaci may actually represent a species complex.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly-1,6-diselenahexamethylene has been prepared, and some of its properties and those of its depolymerization product, 1,2-diselenane, have been studied. Depolymerization probably occurs by a free-radical mechanism. The effects of these organoselenium compounds on the thermal polymerization of styrene, methyl methacrylate, vinyl acetate, and acrylonitrile at 60°C. in the presence and absence of 2,2′-azobisisobutyronitrile and on the direct photopolymerization of these vinyl monomers at 25°C. has been examined. Various reaction mechanisms are suggested to explain the experimental results.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1439-6327
    Keywords: Motor control ; Motor skill ; Electromyography ; Inaccuracy ; Isometric
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The aim of this study was to investigate the electromyographical basis of inaccurate movement by identifying the variate and invariate characteristics of a ballistic, isometric precision-grip skill. Our results have shown that in most subjects investigated, IEMG, discharge rate and the paterns of muscle synergy were variate movement parameters while the sequence of muscle activation, the relative duration of muscle activity and the time to peak force (rise-time) remained essentially invariante. Based on these results, we can conclude that inaccurate performance of this skill, in most of the subjects investigated, was more dependant upon changes in muscle IEMG than in alterations in the temporal sequencing of muscle activity. It was apparent that from trial to trial, subjects had more difficulty in reproducing the appropriate levels of muscle contraction and synergy than in reproducing the required periods of action.
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  • 8
    ISSN: 1439-6327
    Keywords: Motor control ; Electromyography ; Motor skill ; Triphasic electromyogram ; Muscle contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of this investigation was to determine how the triphasic electromyogram (EMG) pattern of muscle activation developed from the agonist muscle only pattern as movement time (t mov) decreased. Six adult women produced a series of 30° elbow extension movements in the horizontal plane at speeds ranging from ballistic (〈 400-ms t mov) to very slow (〉 800-ms t mov). Surface EMG from triceps brachii (agonist) and biceps brachii (antagonist) muscles were recorded, together with elbow angle, on a microcomputer. The results showed that triphasic EMG patterns developed systematically as t mov decreased from 1000 ms to 〈 200 ms. In trials with very long t mov, many elbow extension movements were produced by a single continuous activation of the agonist triceps brachii muscle. As t mov decreased however, agonist activation became predominantly burst-like and other components of the triphasic EMG pattern [activation of the antagonist (Ant) and second agonist activation (Ag2)] began to appear. At the fastest movement speeds, triphasic EMG patterns (Ag1-Ant-Ag2, Ag1 being first activation of agonist muscle) were always present. This data indicated that the triphasic pattern of muscle activation was not switched on when a particular t mov was achieved. Rather, each component systematically developed until all were present, as distinctive bursts of activity, in most trials with t mov less than 400 ms.
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  • 9
    ISSN: 1439-6327
    Keywords: Aging ; Electromyography ; Reaction time ; Motor control ; Muscle contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this investigation was to determine whether age-related changes in the dynamics of muscle activation were, in part, responsible for longer reaction times (RT) in the elderly. A group of 12 young (mean age, 20.6 years) and 12 elderly (mean age, 64.3 years) women performed a series of ballistic forearm supination movements in response to an auditory stimulus while using a simple reaction time test. Surface electromyographic waveforms from biceps brachii (agonist) and pronator teres (antagonist) muscles were recorded, together with the angle-time curves representing the motion of the forearm, on to an IBM compatible microcomputer. The results showed that an age-related increase (P〈0.05) in motor reaction time (MRT) contributed to longer RT in the elderly. In addition, the longer (P〈0.05) MRTs in the elderly were associated with a significantly slower rate (P〈0.05) of biceps brachii muscle activation and a significantly increased proportion (P〈0.05) of the initial biceps brachii muscle burst required to initiate the movement. This data suggested that an important part of the slowing of motor behaviour, commonly observed with increasing age, may be due to either decreases in the ability of aged skeletal muscle to rapidly generate tension or to a reduction in motor drive.
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  • 10
    ISSN: 1439-6327
    Keywords: Key words Functional differentiation ; Electromyography ; Deltoid ; Motor control ; Muscle function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this investigation was to anatomically identify, and then determine the function of, individual segments within the human deltoid muscle. The anatomical structure of the deltoid was determined through dissection and/or observation of the shoulder girdles of 11 male cadavers (aged 65–84 years). These results indicate that the deltoid consists of seven anatomical segments (D1–D7) based upon the distinctive arrangement of each segment's origin and insertion. Radiographic analysis of a cadaveric shoulder joint suggested that only the postero-medial segment D7 has a line of action directed below the shoulder joint's axis of rotation. The functional role of each individual segment was then determined utilising an electromyographic (EMG) technique. Seven miniature (1 mm active plate; 7 mm interelectrode distance) bipolar surface electrodes were positioned over the proximal portion of each segment's muscle belly in 18 male and female subjects (18–30 years). EMG waveforms were then recorded during the production of rapid isometric shoulder abduction and adduction force impulses with the shoulder joint in 40 degrees of abduction in the plane of the scapula. Each subject randomly performed 15 abduction and 15 adduction isometric force impulses following a short familiarisation period. All subjects received visual feed back on the duration and amplitude of each isometric force impulse produced via a visual force-time display which compared subject performance to a criterion force-time curve. Movement time was 400 ms (time-to-peak isometric force) at an intensity level of 50% maximal voluntary contraction. Temporal and intensity analyses of the EMG waveforms, as well as temporal analysis of the isometric force impulses, revealed the neuromotor control strategies utilised by the CNS to control the activity of each muscle segment. The results showed that segmental neuromotor control strategies differ across the breadth of the muscle and that individual segments of the deltoid can be identified as having either “prime mover”, “synergist”, “stabiliser” or “antagonist” functions; functional classifications normally associated with whole muscle function. Therefore, it was concluded that the CNS can “fine tune” the activity of at least six discrete segments within the human deltoid muscle to efficiently meet the demands of the imposed motor task.
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