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  • 1
    Electronic Resource
    Electronic Resource
    Marketing Management: A Simple Quiz to Help Your Company Master Marketing (1994)
    Bradford : Emerald
    Journal of consumer marketing 11 (1994), S. 55-57 
    Details
    ISSN: 0736-3761
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Economics
    Notes: Technological and market changes make it increasingly difficult tomanage marketing organizations and programs. These changes have affectedhow products and services are taken to market and how marketing andsales should be organized and managed. Describes the MarketingOpportunity Quiz, which has been developed for use with top managementand marketing management of any size organization. The quiz uses 24questions to touch upon key marketing issues throughout the organizationand provides insight into areas where further investigation may beworthwhile. From this process, management can focus its efforts on howit can adapt its organization and marketing programs to today's rapidlychanging world.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/07363769410058939
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  • 2
    Electronic Resource
    Electronic Resource
    Identification of time-varying dynamics of the human triceps surae stretch reflex (1993)
    Springer
    Experimental brain research 97 (1993), S. 128-138 
    Details
    ISSN: 1432-1106
    Keywords: Triceps surae ; Stretch reflex ; Time varying ; System identification ; Ankle joint ; Ramp stretch ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We examined the time-varying dynamics of the human triceps surae stretch reflex before, during, and after a large stretch was imposed upon the ankle joint, during a constant voluntary contraction of 15% of maximum voluntary contraction. Stretch reflex dynamics were estimated by superimposing a small stochastic displacement on many such stretches and using an “ensemble-based” time-varying identification procedure to compute impulse response functions relating the perturbation to the evoked electromyogram (EMG) at each point throughout the task. We found that stretch reflex magnitude (relating joint velocity to EMG) varied directly with baseline EMG activity during steady-state conditions before and after the large imposed stretch. Following the large stretch and the reflex activity it evoked, both background EMG and stretch reflex magnitude declined for up to 100 ms; changes in the stretch reflex were substantially greater in magnitude and followed a different time course from the corresponding changes in background EMG, however, indicating that stretch reflex properties were modulated independently of motoneuron pool activation level. Based on timing and the invariance of stretch reflex dynamics across time, it is argued that this behavior is largely mediated via peripheral neural mechanisms. This peripheral modulation of the stretch reflex presumably supplements various descending influences to adjust reflex properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228823
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  • 3
    Electronic Resource
    Electronic Resource
    Identification of time-varying dynamics of the human triceps surae stretch reflex (1993)
    Springer
    Experimental brain research 97 (1993), S. 115-127 
    Details
    ISSN: 1432-1106
    Keywords: Triceps surae ; Stretch reflex ; Time-varying ; System identification ; Ankle joint ; Voluntary movement ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have examined the time variations of stretch reflex dynamics throughout rapid voluntary changes in the isometric contraction level of the human triceps surae muscles. This was achieved by superimposing a small stochastic displacement upon many such changing contractions and then identifying the time-varying relationship between the perturbation and the evoked electromyograms (EMGs). An “ensemble” time-varying system identification technique was used to estimate these input-output dynamics as a set of impulse response functions, one for each time before, during, and after the change in contraction level, with a temporal resolution equal to the data acquisition rate. Three main findings resulted. First, stretch reflex gain (relating joint velocity to EMG) was significantly modulated during changes in voluntary contraction level, increasing as the subject contracted the muscles and decreasing as the subject relaxed. Second, stretch reflex dynamics did not change with contraction level, even when its gain varied substantially. Third, the time course of the gain changes closely followed the level of the EMG, even though the subjects used rather different activation and deactivation patterns. These results suggest that, for the behavior studied (i.e., rapid changes in isometric contraction level), stretch reflex gain and motoneuron pool activation level were controlled by a common descending command rather than being independently specified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228822
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  • 4
    Electronic Resource
    Electronic Resource
    Identification of time-varying stiffness dynamics of the human ankle joint during an imposed movement (1997)
    Springer
    Experimental brain research 114 (1997), S. 71-85 
    Details
    ISSN: 1432-1106
    Keywords: Key words Joint stiffness ; Ankle joint ; System identification ; Triceps surae ; Time-varying ; Stretch reflex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The time-varying stiffness dynamics of the human ankle joint were identified during a large stretch imposed upon the active triceps surae muscles. Small stochastic position perturbations were superimposed upon many repetitions of the larger movement and an ensemble time-varying identification technique was then used to characterize the relationship between the small perturbation and the torque it evoked at each sample in time throughout the movement. This technique was found to provide an excellent description of the ankle stiffness dynamics throughout this movement, with the identified stiffness impulse response functions accounting for more than 80% of the torque variance at all times. The average low-frequency stiffness values (K low) derived from the stiffness impulse responses at each sample in time are believed to reflect primarily the instantaneous elastic properties of active crossbridges. These properties, which reflect the contractile state of the muscles more directly than force or torque measurements, have not been obtained previously from an intact muscle-joint system. We found that stiffness actually increased during the later portion of the large imposed stretch, indicating the triceps surae muscles did not yield significantly, and that the post-stretch steady-state stiffness level was approximately 60% higher than prior to the stretch. Reflex activity evoked by the large stretch did not produce a detectable change in K low, even though this activity did produce a clear twitch-like response in joint torque beginning approximately 60 ms following stretch onset. A second-order mechanical model was found to provide an adequate characterization of stiffness dynamics for steady-state periods before and well after the imposed movement, but it could not adequately describe the observed changes in stiffness dynamics during the movement itself. However, the variation of model parameters indicated that the torque evoked by the stochastic displacement was predominantly elastic in nature. The stiffness behavior during stretch observed here for the intact human ankle joint is largely consistent with previous studies performed in isolated muscle preparations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005625
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  • 5
    Electronic Resource
    Electronic Resource
    An Adaptive Filter to Reduce Cardiogenic Oscillations on Esophageal Pressure Signals (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 260-267 
    Details
    ISSN: 1573-9686
    Keywords: Pulmonary monitoring ; Intrinsic PEEP ; Work of breathing ; Adaptive filter ; Cardiogenic oscillations ; Esophageal pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Measurements of pressure swings in the esophagus (Pes can be used to estimate variables of clinical importance, e.g., intrinsic positive end-expiratory pressure (PEEPi. Unfortunately, cardiogenic oscillations frequently corrupt Pes and complicate further analysis. Due to significant band overlap with the respiratory component of Pes, cardiogenic oscillations cannot be suppressed adequately using standard filtering techniques. In this article, we present an adaptive filter that employs the electrocardiogram to identify and suppress the cardiogenic oscillations. This filter was tested using simulated data, where the variance accounted for relative to the simulated respiratory pressure swings increased from as low as 55% for the unfiltered Pes signal to over 95% when the adaptive filter was used. In patient data, the adaptive filter reduced the apparent cardiogenic oscillations without noticeably distorting the sharp deflections in Pes due to respiration. Furthermore, the filter suppressed peaks in the Fourier transform of Pes at integer multiples of the heart rate, while the remaining frequencies remained largely unchanged. During stable breathing, the standard deviation of PEEPi was reduced by between 44% and 71% in these four patients when the filter was used. We conclude that our filter removes a significant fraction of the cardiogenic oscillations that corrupt records of Pes. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8430Vn
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.55
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear identification of stretch reflex dynamics (1988)
    Springer
    Annals of biomedical engineering 16 (1988), S. 79-94 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The objective of this study was to use nonlinear identification techniques to study the dynamics of stretch reflexes in the human calf muscles (gastrocnemius-soleus). Stochastic perturbations of ankle position were applied while subjects maintained a constant, tonic contraction of gastrocnemius-soleus. Linear models of the relation between ankle velocity and the electromyographic (EMG) activity under these conditions typically accounted for less than 40% of the observed EMG variance. Nonlinear system identification techniques were then applied. The first- and second-order Wiener kernels were computed as the initial stage of this analysis. These did not provide an adequate description of system behavior; subsequent simulation studies showed that the major problem with the Wiener analysis was that the input spectrum was not adequately white. Nevertheless, the shape of the second-order Wiener kernel suggested that a Hammerstein structure consisting of a static nonlinearity followed by a dynamic linear system would be appropriate. Consequently, we used an iterative procedure for Hammerstein system identification to determine the form of the static nonlinearity and the associated linear dynamics. The resulting nonlinear model provided a much better description of the system's behavior than did the linear models (variance accounted for〉60%). Furthermore, they confirmed our previous empirical findings; the static nonlinearity closely resembled a half-wave rectifier while the dynamics were typified by a pure delay and a velocity filter. The application of nonlinear identification techniques thus produced a much improved, physically meaningful model of stretch reflex behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02367382
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  • 7
    Electronic Resource
    Electronic Resource
    Nonparametric Block-Structured Modeling of Lung Tissue Strip Mechanics (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 242-252 
    Details
    ISSN: 1573-9686
    Keywords: Wiener model ; Hammerstein model ; System identification ; Lung: dog ; Nonlinear dynamics ; Model: nonparametric ; Modeling ; Lung: mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Very large amplitude pseudorandom uniaxial perturbations containing frequencies between 0.125 and 12.5 Hz were applied to five dog lung tissue strips. Three different nonlinear block-structured models in nonparametric form were fit to the data. These models consisted of (1) a static nonlinear block followed by a dynamic linear block (Hammerstein model); (2) the same blocks in reverse order (Wiener model); and (3) the blocks in parallel (parallel model). Both the Hammerstein and Wiener models performed well for a given input perturbation, each accounting for greater than 99% of the measured stress signal variance. However, the Wiener and parallel model parameters showed some dependence on the strain amplitude and the mean stress. In contrast, a single Hammerstein model accounted for the data at all strain amplitudes and operating stresses. A Hammerstein model featuring a fifth-order polynomial static nonlinearity and a linear impulse response function of 1 s duration accounted for the most output variance (99.84% ± 0.13%, mean ± standard deviations for perturbations of 50% strain at 1.5 kPa stress). The static nonlinear behavior of the Hammerstein model also matched the quasistatic stress–strain behavior obtained at the same strain amplitude and operating stress. These results show that the static nonlinear behavior of the dog lung tissue strip is separable from its linear dynamic behavior. © 1998 Biomedical Engineering Society. PAC98: 8745Bp, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.119
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