Suspending loads decreases load stability but may slightly improve body stability

Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.     

Individual admixture estimates: disease associations and individual risk of diabetes and gallbladder disease among Mexican-Americans in Starr County, Texas

The ethnic and geographic distributions of several common chronic diseases show distinct patterns that are consistent with the distribution of genes and genetic admixture. For example, diabetes and gallbladder disease occur most frequently among Amerindians, while those genetically admixed with them (such as Mexican-Americans) have intermediate rates, and lowest rates are found among Whites and Blacks. Because there will be heterogeneity from individual to individual in ancestral affinity within an admixed population, a method is developed for estimating each person's admixture probability. Results confirm that there is substantial heterogeneity of individual admixture among Mexican-Americans in Starr County, Texas, with a mean value indicating that 65% of genes in this population are Caucasian derived and 35% Amerindian derived. The individual estimates are shown to be unrelated to the probability of being diabetic and only marginally related to gallbladder disease, with those having the most Amerindian affinity being at increased risk. These results are a consequence of the independent assortment of loci and indicate that unless the markers employed are related (including linkage) to the disease of interest, the method will have limited utility. Individual admixture estimates will be useful, however, for examining aspects of population structure and will find increased utility for predicting disease and examining disease associations as more and more of the genome is represented by markers, a very probable prospect with the abundance of DNA polymorphism being identified by restriction enzymes.     

Vibration and sound communication in solitary bees and wasps

ABSTRACT. Females of solitary bees ( Colletes cunicularius L.) and of digger wasps ( Bembix rostrata L.) produce buzzing sounds and are known to secrete volatile odours when digging their way from the subterranean nests to the soil surface. The odours allow patrolling males to determine the approximate position of the digging virgin female. The buzzes are measured as substrate-borne sound (soil buzz vibrations) and as air-borne sound (soil buzz sounds). Play-back experiments suggest that the soil buzzes are used by the males as additional cues for localization. Faint buzz sounds are emitted regularly by the male during genital contact in copulation. They may serve to change the receptivity of the female. Intense and broadband buzz sounds are produced by bees of either sex, if restrained from moving, perhaps serving to deter predators.     

两种吸血水蛭对光闪烁和水扰动刺激的反应

利用自制的控温实验槽在暗室内进行医蛭科两种吸血水蛭对光闪烁和水扰动刺激的模拟个体生态实验,实验结果的统计分析表明,日本医蛭在１６℃时与照度有极好的正相关关系,而在２２℃时成负相关关系,０．２克体重的个体在两种温度对照度的敏感度均大于０．５－０．６克和１．０－１．３克体重的个体,湖北牛蛭在两种温度时与照度均成正相关关系;０．５克体重的个体在１６℃时对照度的敏感度大于１．０－３．３克体重的个体９．５－     

The vibrations of texture

The Pacinian channel has been implicated in the perception of fine textures (Hollins et al. , Somatosens Mot Res 18: 253-262, 2001a). In the present study, we investigate candidate codes for Pacinian-mediated roughness perception. We use a Hall effect transducer to record the vibrations elicited in the skin when a set of textured surfaces is passively presented to the index finger. The peak frequency of the vibrations is found to decrease systematically as spatial period increases. The power of the vibrations--weighted according to the spectral sensitivity of the Pacinian system--increases with spatial period for all but the coarsest surfaces. By varying the scanning velocity, we manipulate the temporal and intensive characteristics of the texture-induced vibrations and assess the effect of the manipulation on perceived roughness. We find that doubling the scanning velocity does not result in the substantial decrease in roughness predicted by a frequency theory of vibrotactile roughness perception. On the other hand, the effects of speed on roughness match those of speed on power. We propose that the roughness of a fine surface (spatial period<200 &#55 m) is a function of the Pacinian-weighted power of the vibrations it elicits.     

Effect of contact location on vibrotactile thresholds at the fingertip

Vibrotactile thresholds depend on the characteristics of the vibration, the location of contact with the skin, and the geometry of the contact with the skin. This experimental study investigated vibrotactile thresholds (from 8 to 250?Hz) at five locations on the distal phalanx of the finger with two contactors: (i) a 1-mm diameter circular probe (0.78-mm² area) with a 1-mm gap to a fixed circular surround (i.e., 7.1-mm² excitation area), and (ii) a 6-mm diameter circular probe (28-mm² area) with a 2-mm gap to a fixed circular surround (i.e., 79-mm² excitation area). With both contactors, especially the smaller contactor at low frequencies (i.e., 8, 16, and 31.5?Hz), thresholds decreased towards the tip of the finger, although there was little variation around the whorl. With low frequencies of vibration, and at all five locations on the finger, similar thresholds were obtained with both contactors, consistent with the NPI channel not changing in sensitivity with a change in the area of stimulation. At high frequencies (i.e., 63, 125, and 250?Hz), thresholds were lower with the larger area of stimulation at all locations, except at the extreme tip of the finger, consistent with spatial summation in the Pacinian channel. It is concluded that with a 6-mm diameter contactor, moderate variations in location around the whorl have little influence on the measured thresholds. With the 1-mm diameter contactor there were greater variations in thresholds and extreme locations, near the nail and the distal interphalangeal joint, may be unsuitable for investigating sensorineural disorders.     

Influence of segmental and extra-segmental conditioning stimuli on cortical potentials evoked by painful electrical stimulation

This study evaluated the effects of two different types of segmental/extra-segmental conditioning stimuli (tonic muscle pain and non-painful vibration) on the subjective experience (perceived pain intensity) and on the cortical evoked potentials to standardized test stimuli (cutaneous electrical stimuli). Twelve subjects participated in two separate sessions to investigate the effects of tonic muscle pain or cutaneous vibration on experimental test stimuli. The experimental protocol contained a baseline registration (test stimuli only), a registration with the test stimuli in combination with the conditioning stimuli, followed by a registration with the test stimuli only. In addition, the effects of the conditioning stimuli were examined at two anatomically separated locations (segmental and extra-segmental). Compared with the test stimulus alone, the perceived pain intensity and peak-to-peak amplitudes of the evoked potentials were unchanged in the presence of non-painful conditioning stimuli at either location. In contrast, a significant decrease of the perceived pain intensity and peak-to-peak amplitudes was found in the presence of painful conditioning stimuli at the extra-segmental sites. Moreover, the topographic maps of the 32-channel recordings suggested that the distribution of the scalp evoked potentials was almost symmetrical around the vertex Cz in the baseline registration. The evoked potentials were generally decreased during hypertonic saline infusion at the extra-segmental sites, but the distribution of the topographic maps did not appear to change. Vibration has previously been shown to inhibit pain, but in the present study the perceived intensity of phasic painful electrical stimuli was unchanged. The reduced perceived pain intensity and the smaller peak-to-peak amplitude of the evoked potential in the presence of extra-segmental conditioning pain are in accordance with the concept of diffuse noxious inhibitory control.     

Mechanotransduction of vocal fold fibroblasts and mesenchymal stromal cells in the context of the vocal fold mechanome

The design of cell-based therapies for vocal fold tissue engineering requires an understanding of how cells adapt to the dynamic mechanical forces found in the larynx. Our objective was to compare mechanotransductive processes in therapeutic cell candidates (mesenchymal stromal cells from adipose tissue and bone marrow, AT-MSC and BM-MSC) to native cells (vocal fold fibroblasts-VFF) in the context of vibratory strain. A bioreactor was used to expose VFF, AT-MSC, and BM-MSC to axial tensile strain and vibration at human physiological levels. Microarray, an empirical Bayes statistical approach, and geneset enrichment analysis were used to identify significant mechanotransductive pathways associated with the three cell types and three mechanical conditions. Two databases (Gene Ontology, Kyoto Encyclopedia of Genes and Genomes) were used for enrichment analyses. VFF shared more mechanotransductive pathways with BM-MSC than with AT-MSC. Gene expression that appeared to distinguish the vibratory strain condition from polystyrene condition for these two cells types related to integrin activation, focal adhesions, and lamellipodia activity, suggesting that vibratory strain may be associated with cytoarchitectural rearrangement, cell reorientation, and extracellular matrix remodeling. In response to vibration and tensile stress, BM-MSC better mimicked VFF mechanotransduction than AT-MSC, providing support for the consideration of BM-MSC as a cell therapy for vocal fold tissue engineering. Future research is needed to better understand the sorts of physical adaptations that are afforded to vocal fold tissue as a result of focal adhesions, integrins, and lamellipodia, and how these adaptations could be exploited for tissue engineering.     

The use of natural language to communicate the perception of vibrotactile stimuli

This study explores the subjective use of adjectives to verbally communicate vibrotactile stimulation across multiple frequencies. In total, nine different vibrotactile stimulus frequencies (10–300?Hz) were utilized, and subjective evaluation methods, which involved adjectives, were used to assess the sensory representations of the participants (18 healthy male participants; mean age, 22.9 years; standard deviation, 3.5). Sensory terms such as ‘slow,’ ‘protruding,’ and ‘thick’ were used as representative expressions to describe low-frequency (10–100?Hz) vibrotactile stimulations, while ‘fast,’ ‘shallow,’ and ‘tickly’ were used to describe high-frequency (225–300?Hz) vibrotactile stimulations. At the frequencies of 150 and 200?Hz, no characteristic word was found because there was no difference in subjective evaluation scores from other low or high frequencies. The results suggest that vibrotactile stimulation at different frequencies induce diverse sensory representations, owing to not only the motion and shape of the stimuli but also the subjective responses of the perceivers. The results of this study could be utilized in developing affective haptic devices in the future.     

Muscle activity reduces soft-tissue resonance at heel-strike during walking

Muscle activity has previously been suggested to minimize soft-tissue resonance which occurs at heel-strike during walking and running. If this concept were true then the greatest vibration damping would occur when the input force was closest to the resonant frequency of the soft-tissues at heel-strike. However, this idea has not been tested. The purpose of this study was to test whether muscle activity in the lower extremity is used to damp soft-tissue resonance which occurs at heel-strike during walking. Hard and soft shoe conditions were tested in a randomized block design. Ground reaction forces, soft-tissue accelerations and myoelectric activity were measured during walking for 40 subjects. Soft-tissue mass was estimated from anthropologic measurements, allowing inertial forces in the soft-tissues to be calculated. The force transfer from the ground to the tissues was compared with changes in the muscle activity. The soft condition resulted in relative frequencies (input/tissue) to be closer to resonance for the main soft-tissue groups. However, no increase in force transmission was observed. Therefore, the vibration damping in the tissues must have increased. This increase concurred with increases in the muscle activity for the biceps femoris and lateral gastrocnemius. The evidence supports the proposal that muscle activity damps soft-tissue resonance at heel-strike. Muscles generate forces which act across the joints and, therefore, shoe design may be used to modify muscle activity and thus joint loading during walking and running.