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1.
The viscoelastic properties of the human arm were measured by means of short force perturbations during fast reaching movements
in two orthogonal directions. A linear spring model with time delay described the neuromuscular system of the human arm. The
obtained viscoelastic parameters ensured movement stability in spite of the time delay of 50 ms. The stiffness and viscosity
ellipses appeared to be predominantly orthogonal to the movement direction, which reduced the effect of force perturbation
in the direction orthogonal to the reaching movement. Thus, it can be argued that the viscoelastic properties of the neuromuscular
system of the human arm are adjusted to the direction of movement according to a “path preserving” strategy, which minimizes
the deviation of the movement path from a straight line, when exposed to an unexpected external force. 相似文献
2.
Closed-loop (CL) and open-loop (OL) types of motor control during human forward upper trunk bending are investigated. A two-joint
(hip and ankle) biomechanical model of the human body is used. The analysis is performed in terms of the movements along eigenvectors
of the motion equation (“eigenmovements” or “natural synergies”). Two analyzed natural synergies are called “H-synergy” (Hip)
and “A-synergy” (Ankle) according to the dominant joint in each of these synergies. Parameters of CL control were estimated
using a sudden support platform displacement applied during the movement execution. The CL gain in the H-synergy increased
and in the A-synergy decreased during the movement as compared with the quiet standing. The analysis of the time course of
OL control signal suggests that the H-synergy (responsible for the prime movement, i.e. bending per se) is controlled according
to the EP theory whereas for the associated A-synergy (responsible for posture adjustment, i.e. equilibrium maintenance) muscle
forces and gravity forces are balanced for any its final amplitude and therefore the EP theory is not applicable to its control. 相似文献
3.
In a laboratory experiment, we use a public goods game to examine the hypothesis that human subjects use an involuntary eye-detector
mechanism for evaluating the level of privacy. Half of our subjects are “watched” by images of a robot presented on their
computer screen. The robot—named Kismet and invented at MIT—is constructed from objects that are obviously not human with
the exception of its eyes. In our experiment, Kismet produces a significant difference in behavior that is not consistent
with existing economic models of preferences, either self- or other-regarding. Subjects who are “watched” by Kismet contribute
29% more to the public good than do subjects in the same setting without Kismet. 相似文献
4.
Biomechanical analysis of movement strategies in human forward trunk bending. II. Experimental study
The large mass of the human upper trunk, its elevated position during erect stance, and the small area limited by the size
of the feet, stress the importance of equilibrium control during trunk movements. The objective of the present study was to
perform a biomechanical analysis of fast forward trunk movements in order to understand the coordination between movement
and posture. The analysis is based on a comparison between experimentally observed bending and hypothetical “optimal bending”
performed on an infinitely narrow support, as presented in a companion paper. The experimental data were obtained from 16
subjects who performed fast forward bending while standing on a wide platform or on a narrow beam. The analysis is performed
by decomposition of the movement into three dynamically independent components, each representing a movement along one of
the three eigenvectors of the motion equation. The eigenmovements are termed “hip”, “ankle”, and “knee” eigenmovements, according
to the dominant joint. The experimentally observed movement is characterized mainly by the hip and ankle eigenmovements, whereas
the knee eigenmovement is negligible. Similarly to the “optimal bending” the ankle eigenmovement starts earlier and lasts
longer than the hip eigenmovement. An early forward acceleration of the center of gravity in the ankle eigenmovement is caused
by anticipatory changes in the ankle joint torque. This clarifies the role of the early tibialis anterior burst and/or soleus
inhibition usually observed in electromyographic recordings during forward bending. The results suggest that the hip and the
ankle eigenmovements can be treated as independently controlled motion units aimed at functionally different behavioral goals:
the bending per se and postural adjustment. It is proposed that the central nervous system has to control these motion units
sequentially in order to perform the movement and maintain equilibrium. It is also suggested that the hip and ankle eigenmovements
can be regarded as a biomechanical background for the hip and ankle strategies introduced by Horak and Nashner (1986) on the
basis of electromyographic recordings and kinematic patterns in response to postural perturbations.
Received: 1 July 1999 / Accepted in revised form: 23 October 2000 相似文献
5.
Indigenous knowledge is often portrayed as static and traditional, while indigenous people are considered victims of exploitation.
In the name of development and empowerment NGOs as well as scientists may run the risk of representing indigenous communities
that fit their definition of the “correct” way to be indigenous. However, for indigenous people knowledge is not necessarily
a static condition in a binary position to science or the ‘modern’ world. Rather, it is a dynamic condition that draws from
experience and adapts to a changing environment. The perspective advanced in this paper is that all forms of knowledge, including
indigenous knowledge(s), are situated and hybrid. Our argument draws from research carried out in Chiapas, Mexico, regarding
the ICBG-Maya bio-prospecting project that was initiated in the 1990s and later terminated due to accusations of bio-piracy. 相似文献
6.
Taro Q. P. Uyeda 《Journal of plant research》1996,109(3):231-239
Recent breakthroughs and technological improvements are rapidly generating evidence supporting the “swinging lever arm model”
for force production by myosin. Unlike previous models, this model posits that the globular domain of the myosin motor binds
to actin with a constant orientation during force generation. Movement of the neck domain of the motor is hypothesized to
occur relative to the globular domain much like a lever arm. This intramolecular conformational change drives the movement
of the bound actin. The swinging lever arm model is supported by or consistent with a large number of experimental data obtained
with skeletal muscle or slime mold myosins, all of which move actin filaments at rates between 1 and 10 μm/sin vitro. Recently myosin was purified, fromChara internodal cells.In vitro the purifiedChara myosin moves actin filaments at rates one order of magnitude faster than the “fast” skeletal muscle myosin. While this ultra
fast movement is not necessarily inconsistent with the swinging lever arm model, one or more specific facets of the motor
must be altered in theChara motor in order to accommodate such rapid movement. These characteristics are experimentally testable, thus the ultra fast
movement byChara myosin represents a powerful and compelling test of the swinging lever arm model. 相似文献
7.
Haptic interaction with virtual objects 总被引:3,自引:0,他引:3
This paper considers interaction of the human arm with “virtual” objects simulated mechanically by a planar robot. Haptic
perception of spatial properties of objects is distorted. It is reasonable to expect that it may be distorted in a geometrically
consistent way. Three experiments were performed to quantify perceptual distortion of length, angle and orientation. We found
that spatial perception is geometrically inconsistent across these perceptual tasks. Given that spatial perception is distorted,
it is plausible that motor behavior may be distorted in a way consistent with perceptual distortion. In a fourth experiment,
subjects were asked to draw circles. The results were geometrically inconsistent with those of the length perception experiment.
Interestingly, although the results were inconsistent (statistically different), this difference was not strong (the relative
distortion between the observed distributions was small). Some computational implications of this research for haptic perception
and motor planning are discussed.
Received: 12 February 1996 /Accepted in revised form: 6 May 1999 相似文献
8.
So Kanazawa 《Primates; journal of primatology》1996,37(1):25-38
Recognition of facial expressions by a Japanese monkey and two humans was studied. The monkey subject matched 20 photographs
of monkey facial expressions and 20 photographs of human facial expressions. Humans sorted the same pictures. Matching accuracy
by the monkey was about 80% correct for both human and monkey facial expressions. The confusion matrices of those facial expressions
were analyzed by a multi-dimensional scaling procedure (MDSCAL). The resulting MDS plots suggested that the important cues
in recognizing facial expressions of monkeys were “thrusting the mouth” and ‘raising the eyebrows.” Comparison of the MDS
plots by the monkey subject with those by human subjects suggested that the monkey categorized the human “happiness” faces.
This may suggest that the monkey has an ability to recognize human smile face even though it is learned. However, the monkey
did not differentiate the human “anger/disgust” faces from the human “sad” faces, while human subjects clearly did. This may
correlate with the lack of eyebrow movement in monkeys. 相似文献
9.
V. A. Namiot A. V. Batyanovskii I. V. Filatov V. G. Tumanyan N. G. Esipova 《Biophysics》2011,56(4):596-601
The process of formation of a globular structure by a long molecular chain has been examined. In this process, various regions
of the chain interact with one another. We classify the contacts thus formed as “correct” and “erroneous” ones. The correct
contacts are those characteristic of the final native globular structure. All other contacts can be treated as erroneous.
It is demonstrated that globule formation may proceed actually without formation and subsequent decay of erroneous contacts.
Our model permits avoiding examination of numerous erroneous variants inasmuch as the regions of the chain that form correct
contacts enter “long-range” interactions that at the same time can be highly selective. The existence of interactions of this
kind facilitates the mutual approach and interaction of just those regions of the chain that yield correct contacts. Based
on database analysis, it is shown that the model is valid not only for abstract structures but also for real polypeptide chains
capable of forming protein globules and helical fibrils. 相似文献
10.
Reconstruction of equilibrium trajectories and joint stiffness patterns during single-joint voluntary movements under different instructions 总被引:2,自引:0,他引:2
Mark L. Latash 《Biological cybernetics》1994,71(5):441-450
A method for reconstructing joint compliant characteristics during voluntary movements was applied to the analysis of oscillatory
and unidirectional elbow flexion movements. In different series, the subjects were given one of the following instructions:
(1) do not intervene voluntarily; (2) keep the trajectory; (3) in cases of perturbations, return back to the starting position
as quickly as possible (only during unidirectional movements). Under the instruction ‘keep trajectory’, the apparent joint
stiffness increased by 50% to 250%. During oscillatory movements, this was accompanied by a decrease in the maximal difference
between the actual and equilibrium joint trajectories and, in several cases, led to a change in the phase relation between
the two trajectories. The coefficients of correlation between joint torque and angle were very high (commonly, over 0.9) under
the ‘do not intervene’ instruction. They dropped to about 0.6 under the ‘keep trajectory’ and to about 0.3 under the ‘return
back’ instructions. Under these two instructions, the low values of the coefficients of correlation did not allow reconstruction
of segments of equilibrium trajectories and joint stiffness values in all the subjects. The results provide further support
for the λ-version of the equilibrium-point hypothesis and for using the instruction ‘do not intervene voluntarily’ to obtain
reproducible time patterns of the central motor command.
Received: 14 December 1993/Accepted in revised form: 16 April 1994 相似文献
11.
Subjects made fast goal-directed arm movements towards moving targets. In some cases, the perceived direction of target motion
was manipulated by moving the background. By comparing the trajectories towards moving targets with those towards static targets,
we determined the position towards which subjects were aiming at movement onset. We showed that this position was an extrapolation
in the target’s perceived direction from its position at that moment using its perceived direction of motion. If subjects
were to continue to extrapolate in the perceived direction of target motion from the position at which they perceive the target
at each instant, the error would decrease during the movements. By analysing the differences between subjects’ arm movements
towards targets moving in different (apparent) directions with a linear second-order model, we show that the reduction in
the error that this predicts is not enough to explain how subjects compensate for their initial misjudgements.
Received: 10 February 1995/Accepted in revised form: 30 May 1995 相似文献
12.
M. H. Tixier P. Sourdille G. Charmet G. Gay C. Jaby T. Cadalen S. Bernard P. Nicolas M. Bernard 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(7):1076-1082
An intervarietal molecular-marker map was used for the detection of genomic regions influencing crossability between wheat
(Triticum aestivum L. em Thell) and rye (Secale cereale L.). Analysis of deviance and logistic marker-regression methods were conducted on data from doubled haploid lines from a
cross between “Courtot” and “Chinese Spring”. A major quantitative trait locus (QTL) involved in crossability, associated
with the marker Xfba367-5B, was detected on the short arm of chromosome 5B. An additional locus, Xwg583-5B, was indicated on the long arm of chromosome 5B. This minor QTL might correspond to Kr1 which was presumed to be the major gene controlling crossability. Another locus of the genome, Xtam51-7A on chromosome 7A, was significantly associated with this trait. Alleles of “non-crossability” were contributed by the non-crossable
cultivar “Courtot”. The three-marker model explains 65% of the difference in crossability between the two parents. The present
results are discussed in relation to those previously carried out to locate the Kr genes by using the telocentric mapping technique.
Received: 27 February 1998 / Accepted: 15 May 1998 相似文献
13.
Four Bengalese finches were trained to discriminate 2 conspecific individuals in an operant chamber. Still visual images and
contact calls were simultaneously presented to the subjects and specific (“correct”) perching response was reinforced with
food. After the birds acquired the discrimination, they received the first test in which visual cues alone, auditory cues
alone and combination of the 2 modalities were presented. Visual cues dominantly controlled the discriminative behavior of
all birds. Then the subjects received the second test in which mixtures of the visual image of 2 stimulus birds appeared under
3 different auditory conditions, namely, no call, calls of 1 bird and calls of the other bird. Two subjects used the auditory
cues when the visual stimulus was a mixture of 2 stimulus birds. These results suggest that the birds used less dominant cues
when the dominant cues gave ambiguous information. 相似文献
14.
Parasites often confront conflicting demands when evaluating and distributing themselves among host individuals, in order to attain maximum reproductive success. We tested two alternative hypotheses about host preference by fleas in relation to the age of their rodent host. The first hypothesis suggests that fleas select adult over juvenile rodents because the latter represent a better nutritional resource (the “well-fed host” hypothesis), whereas the second hypothesis suggests that fleas prefer the weaker and less resistant juveniles because they are easier to colonise and exploit (“poorly fed host” hypothesis). We sampled fleas (Synosternus cleopatrae) on the gerbil (Gerbillus andersoni) in 23 different plots in the Negev desert and found an unequal distribution of fleas between adult and juvenile hosts. Furthermore, flea distribution changed as a function of flea density—from juvenile-biased flea parasitism (the “poorly fed host” hypothesis) at low densities to adult-biased flea parasitism (the “well-fed host” hypothesis) at high densities. Other factors that influenced flea preference were soil temperature and the presence of ticks. These results suggest that host selection is not an explicit alternative choice between adults and juveniles (“well-fed host” versus “poorly fed host” hypotheses), but rather a continuum where the distribution between adults and juveniles depends on host, parasite, and environmentally related factors. 相似文献
15.
Source-sink landscape theory and its ecological significance 总被引:2,自引:0,他引:2
Exploring the relationships between landscape pattern and ecological processes is the key topic of landscape ecology, for
which, a large number of indices as well as landscape pattern analysis model were developed. However, one problem faced by
landscape ecologists is that it is hard to link the landscape indices with a specific ecological process. Linking landscape
pattern and ecological processes has become a challenge for landscape ecologists. “Source” and “sink” are common concepts
used in air pollution research, by which the movement direction and pattern of different pollutants in air can be clearly
identified. In fact, for any ecological process, the research can be considered as a balance between the source and the sink
in space. Thus, the concepts of “source” and “sink” could be implemented to the research of landscape pattern and ecological
processes. In this paper, a theory of sourcesink landscape was proposed, which include: (1) In the research of landscape pattern
and ecological process, all landscape types can be divided into two groups, “source” landscape and “sink” landscape. “Source”
landscape contributes positively to the ecological process, while “sink” landscape is unhelpful to the ecological process.
(2) Both landscapes are recognized with regard to the specific ecological process. “Source” landscape in a target ecological
process may change into a “sink” landscape as in another ecological process. Therefore, the ecological process should be determined
before “source” or “sink” landscape were defined. (3) The key point to distinguish “source” landscape from “sink” landscape
is to quantify the effect of landscape on ecological process. The positive effect is made by “source” landscape, and the negative
effect by “sink” landscape. (4) For the same ecological process, the contribution of “source” landscapes may vary, and it
is the same to the “sink” landscapes. It is required to determine the weight of each landscape type on ecological processes.
(5) The sourcesink principle can be applied to non-point source pollution control, biologic diversity protection, urban heat
island effect mitigation, etc. However, the landscape evaluation models need to be calibrated respectively, because different
ecological processes correspond with different source-sink landscapes and evaluation models for the different study areas.
This theory is helpful to further study landscape pattern and ecological process, and offers a basis for new landscape index
design.
__________
Translated from Acta Ecologica Sinica, 2006, 26(5): 1444–1449 [译自: 生态学报] 相似文献
16.
Stroeve S 《Biological cybernetics》1999,81(5-6):475-494
The mechanical impedance of neuromusculoskeletal models of the human arm is studied in this paper. The model analysis provides
a better understanding of the contributions of possible intrinsic and reflexive components of arm impedance, makes clear the
limitations of second-order mass-viscosity-stiffness models and reveals possible task effects on the impedance. The musculoskeletal
model describes planar movements of the upper arm and forearm, which are moved by six lumped muscles with nonlinear dynamics.
The motor control system is represented by a neural network which combines feedforward and feedback control. It is optimized
for the control of movements or for posture control in the presence of external forces. The achieved impedance characteristics
depend on the conditions during the learning process. In particular, the impedance is adapted in a suitable way to the frequency
content and direction of external forces acting on the hand during an isometric task. The impedance characteristics of a model,
which is optimized for movement control, are similar to experimental data in the literature. The achieved stiffness is, to
a large extent, reflexively determined whereas the approximated viscosity is primarily due to intrinsic attributes. It is
argued that usually applied Hill-type muscle models do not properly represent intrinsic muscle stiffness.
Received: 14 October 1997 / Accepted in revised form: 18 May 1999 相似文献
17.
Tsutom Hiura 《Trees - Structure and Function》1998,12(5):274-280
Relationships between leaf or shoot size, number, and arrangement in response to light were investigated to test the hypothesis
that these characteristics are linked. In order to test this hypothesis, the divergence in allometry and shoot dynamics in
saplings of Japanese beech (Fagus crenata) obtained from four populations and having different leaf sizes were examined in a nursery under both full sun and shade
conditions. Trees with different leaf sizes also showed large differences in canopy structure, particularly when shade-grown
saplings were compared. The final leaf mass distributions of the large-leaf populations were conical or “bottom - heavy”,
while those of the small-leaf populations were planar or “top - heavy”. The slope of the allometric relations between leaf
mass and shoot and branch mass in small-leaved populations were steeper than those in large-leaf populations. The four populations
were classified into two growth types: populations producing a few large leaf and shoot modules corresponded to “stem growth
type”, and those producing many small leaf and shoot modules corresponded to “leaf growth type”. These kinds of intra-specific
variation in architecture and growth of F. crenata trees may influence the structure and dynamics of forests in accordance with differences in competitive ability or sensitivity
to disturbances such as windstorm.
Received: 18 March 1997 / Accepted: 21 October 1997 相似文献
18.
Ernesto Trucco 《Bulletin of mathematical biology》1963,25(3):303-323
This paper, consisting of two parts, gives all the mathematical details that were omitted in a previous work by G. A. Sacher
and E. Trucco (“The Stochastic Theory of Mortality.”Ann. N. Y. Acad. Sci.,96, 985–1007, cited here as ST). We assume that the reader is familiar with ST, where the stochastic theory of mortality, originally
proposed by Sacher, is discussed at length. We recall that the basic model presented there refers to an ensemble of particles
performing Brownian motion in one dimension, with the added constraint of two absorbing barriers. These two points, collectively,
are designated as the “lethal bound.” Part I (section 1 to 4) deals with the special case in which the two absorbing barriers
are symmetrically located at a finite distance from the origin. The solution of the Fokker-Planck equation is obtained from
the theory of eigenvalue problems. Quite generally, the eigenfunctions functions belong to the family of Kummer's confluent
hypergeometric functions, but the symmetry condition imposed here results in considerable simplification and makes it possible
to estimate the first few eigenvalues by a graphical procedure. In section 3 we show how perturbation theory can be applied
in the limiting case of “weak homeostasis,” and section 4 deals with the opposite extreme of “strong homeostasis.” A rigorous
proof is given for the result corresponding to equation (28) of ST (asymptotic or quasi-static approximation for the “force
of mortality”).
This work was performed under the auspices of the U.S. Atomic Energy Commission. 相似文献
19.
Two behavioral goals are achieved simultaneously during forward trunk bending in humans: the bending movement per se and
equilibrium maintenance. The objective of the present study was to understand how the two goals are achieved by using a biomechanical
model of this task. Since keeping the center of pressure inside the support area is a crucial condition for equilibrium maintenance
during the movement, we decided to model an extreme case, called “optimal bending”, in which the movement is performed without
any center of pressure displacement at all, as if standing on an extremely narrow support. The “optimal bending” is used as
a reference in the analysis of experimental data in a companion paper. The study is based on a three-joint (ankle, knee, and
hip) model of the human body and is performed in terms of “eigenmovements”, i.e., the movements along eigenvectors of the
motion equation. They are termed “ankle”, “hip”, and “knee” eigenmovements according to the dominant joint that provides the
largest contribution to the corresponding eigenmovement. The advantage of the eigenmovement approach is the presentation of
the coupled system of dynamic equations in the form of three independent motion equations. Each of these equations is equivalent
to the motion equation for an inverted pendulum. Optimal bending is constructed as a superposition of two (hip and ankle)
eigenmovements. The hip eigenmovement contributes the most to the movement kinematics, whereas the contributions of both eigenmovements
into the movement dynamics are comparable. The ankle eigenmovement moves the center of gravity forward and compensates for
the backward center of gravity shift that is provoked by trunk bending as a result of dynamic interactions between body segments.
An important characteristic of the optimal bending is the timing of the onset of each eigenmovement: the ankle eigenmovement
onset precedes that of the hip eigenmovement. Without an earlier onset of the ankle eigenmovement, forward bending on the
extremely narrow support results in falling backward. This modeling approach suggests that during trunk bending, two motion
units – the hip and ankle eigenmovements – are responsible for the movement and for equilibrium maintenance, respectively.
Received: 1 July 1999 / Accepted in revised form: 23 October 2000 相似文献
20.
Wavelet entropy in event-related potentials: a new method shows ordering of EEG oscillations 总被引:3,自引:0,他引:3
In this work we show the application of a measure of entropy defined from the wavelet transform, namely the wavelet entropy
(WS), to the study of event-related potentials (ERPs). WS was computed for ERPs recorded from nine healthy subjects with three
different types of stimuli, among them target stimuli in a cognitive task. A significant decrease of entropy was correlated
with the responses to target stimuli (P300), thus showing that these responses correspond to a more “ordered” state than the
spontaneous EEG. Furthermore, we propose the WS as a quantitative measure for such transitions between EEG (“disordered state”)
and ERP (“ordered state”).
Received: 12 April 2000 / Accepted in revised form: 11 September 2000 相似文献