Measurement and modelling of x-direction apparent mass of the seated human body-cushioned seat system

For modelling purposes and for evaluation of driver's seat performance in the vertical direction various mechano-mathematical models of the seated human body have been developed and standardized by the ISO. No such models exist hitherto for human body sitting in an upright position in a cushioned seat upper part, used in industrial environment, where the fore-and-aft vibrations play an important role. The interaction with the steering wheel has to be taken into consideration, as well as, the position of the human body upper torso with respect to the cushioned seat back as observed in real driving conditions. This complex problem has to be simplified first to arrive at manageable simpler models, which still reflect the main problem features. In a laboratory study accelerations and forces in x-direction were measured at the seat base during whole-body vibration in the fore-and-aft direction (random signal in the frequency range between 0.3 and 30 Hz, vibration magnitudes 0.28, 0.96, and 2.03 ms(-2) unweighted rms). Thirteen male subjects with body masses between 62.2 and 103.6 kg were chosen for the tests. They sat on a cushioned driver seat with hands on a support and backrest contact in the lumbar region only. Based on these laboratory measurements a linear model of the system-seated human body and cushioned seat in the fore-and-aft direction has been developed. The model accounts for the reaction from the steering wheel. Model parameters have been identified for each subject-measured apparent mass values (modulus and phase). The developed model structure and the averaged parameters can be used for further bio-dynamical research in this field.     

Enamel ultrastructure and masticatory function in molars of the American opossum, Didelphis virginiana

Maxillary and mandibular molars of the American opossum, Didelphis virginiana L., were viewed in the scanning electron microscope (SEM) after acid-etching or after cutting and acid-etching. Observations were made on enamel prism patterns as they relate to functional properties of the tooth at a particular site. Molars at different stages of wear were also observed under a dissecting microscope; worn surfaces were correlated with function and enamel ultrastructure. Pounding surfaces of molar cusps wear more rapidly than near-vertical shearing surfaces or crushing basins (i.e. the trigon and talonid basin). Pounding surfaces are subjected to abrasion by food and arc not normally involved in tooth-tooth contact. Near-vertical shearing surfaces and basins used for crushing do experience tooth-tooth contact, but are surprisingly more resistant to wear. Prisms at pounding sites approach the occlusal surface at a near 90° angle and are surrounded with very thick interprismatic (IP) enamel parallel to the occlusal surface of the tooth. The pounding pattern is present at tips of cusps and at occlusal surfaces of ridges of the tooth. At near-vertical shearing surfaces, the prisms approach the outer surface obliquely and are surrounded with IP crystals which are perpendicular to the vertical surface. The angle between prismatic and IP enamel in these patterns is 60–90° in a cervical to occlusal direction. In basins of the tooth used principally for crushing and some shearing, IP enamel is perpendicular to the changing slope of the basin and the prisms are usually at a 55–65° angle to the IP enamel. When the pounding and shearing-crushing patterns meet at a ridge, a distinct seam is observed. Pounding forces occur parallel to the long axis of the prisms and perpendicular to the thick IP enamel (i.e. perpendicular to the long axis of the IP crystals) lying on either side of the prisms. Shearing and crushing forces occur at an oblique angle to the prism, and interprismatic enamel is more evenly distributed about the prism. A spiral pattern is found at the bottoms of the trigon and talonid basins, but not at the bottom of the trigonid which is a non-occluding basin. It is concluded that the differential rates of wear of the enamel surfaces are necessary in maintaining the sharp cutting edges and effective crushing basins of the tribosphenic molar, and the ultrastructural arrangements of the enamel prisms are of functional significance.     

The transmission of translational seat vibration to the head--II. Horizontal seat vibration

The second part of this study of the six axes of head motion caused by translational seat vibration is concerned with the effect of fore-and-aft (x-axis) and lateral (y-axis) seat vibration. Seat-to-head transmissibilities have been determined at frequencies up to 16 Hz for each of the three translational and three rotational axes of the head during exposure to random vibration of the seat. Repeatability measures within a single subject and studies of the variability across a group of twelve subjects have been conducted with two seating conditions: a rigid seat with a backrest, and the same seat with no backrest. Fore-and-aft seat motion mainly resulted in head motion within the mid-sagittal plane (x-z plane). Without the backrest, transmissibilities for the fore-and-aft, vertical and pitch axes of the head were greatest at about 2 Hz. The backrest greatly increased head vibration at frequencies above 4 Hz and caused a second peak in the transmissibility curves at about 6 to 8 Hz. Lateral seat motion mainly caused lateral head motion with a maximum transmissibility at about 2 Hz. The backrest had little effect on the transmission of lateral vibration to the head. For both axes of excitation inter-subject variability was much greater than intra-subject variability.     

Comparison of office chairs with fixed forwards or backwards inclining, or tiltable seats

Three adjustments of an office chair seat: one inclining +10 degrees (forwards), one inclining -5 degrees (backwards), and one being freely tiltable from -8 degrees to +19.5 degrees were investigated using two groups of healthy female workers in a field (n = 12), and a laboratory study (n = 10), respectively. The seat adjustments were examined with regard to effects on foot swelling, lumbar muscular load, backrest pressure and subjective acceptability. Desk-work and typing were compared according to lumbar muscular activity, seat movements (tiltable seat), and backrest pressure. Foot swelling tended to increase with increasing seat height but was not influenced by the ability to tilt the seat or not. With the different seat adjustments lumbar muscular activity did not change systematically in spite of greater backrest pressure when the seat inclined backwards. The tiltable seat was preferred to the others. Typing was associated with a more constrained and tens posture than desk work, because movements, transferred to the tiltable seat, decreased and the muscular load increased. Backrest pressure was highest during typing. A tendency towards gradually increasing restlessness (i.e. seat movements) and increasing forward inclination of the tiltable seat with time was observed.     

Electric field induced desorption of bacteria from a conditioning film covered substratum.

Desorption of three oral bacterial strains from a salivary conditioning film on an indium tin oxide electrode during application of a positive (bacterial adhesion to the anode) or a negative electric current was studied in a parallel plate flow chamber. Bacterial adhesion was from a flowing suspension of high ionic strength, after which the bacterial suspension was replaced by a low ionic strength solution without bacteria and currents ranging from -800 to +800 microA were applied. Streptococcus oralis J22 desorbed during application of a positive and negative electric current with a desorption probability that increased with increasing electric current. Two actinomyces strains, however, could not be stimulated to desorb by the electric currents applied. The desorption forces acting on adhering bacteria are electroosmotic in origin and working parallel to the electrode surface in case of a positive current, whereas they are electrophoretic and electrostatic in origin and working perpendicular to the surface in case of a negative current. By comparison of the effect of positive and negative electric currents, it can be concluded that parallel forces are more effective in stimulating bacterial desorption than perpendicular forces. The results of this study point to a new pathway of cleaning industrial and biomedical surfaces without the use of detergents or biocides.     

The transmission of translational seat vibration to the head--I. Vertical seat vibration

Vibration in the three translational (fore-and-aft, lateral and vertical) and the three rotational (roll, pitch and yaw) axes of the head has been measured during exposure to whole-body random vibration. Using an instrumented bar gripped between the teeth, the influence of variations in bite grip and bite-bar mass on movements of the head were found to be small up to a mass of 375 g. The repeatability of measures of seat-to-head transmissibility within a single subject and the variability in transmissibility across a group of twelve subjects have been determined with two seating conditions: a rigid seat with a backrest and the same seat with no backrest. Seat-to-head transmissibilities associated with vertical seat vibration are presented at frequencies up to 25 Hz for all six axes of head vibration both with and without a backrest. Head motion occurred principally in the fore-and-aft, vertical and pitch axes of the head. The backrest increased the magnitude of head vibration in most cases. Intra-subject variability was generally small compared to inter-subject variability.     

Postural dynamics in maximal isometric ramp efforts

 A global biomechanical model of transient push efforts is proposed where transient efforts are taken into consideration, with the aim to examine in greater depth the postural adjustments associated with voluntary efforts. In this context, the push effort is considered as a perturbation of balance, and the other reaction forces as a counter-perturbation which is necessary for the task to be performed efficiently. The subjects were asked to exert maximal horizontal two-handed isometric pushes on a dynamometric bar, as rapidly as possible. They were seated on a custom-designed device which measured global and partitive dynamic quantities. The results showed that the horizontal reaction forces and the horizontal displacement of the centre of pressure increased quasi-proportionally with the perturbation. In addition, it was established that vertical reaction forces increased at seat level whereas they decreased at foot level, resulting in minor vertical acceleration and displacement of the centre of gravity. On the contrary, the anteroposterior reaction forces increased both at foot and at seat levels. Based on a detailed examination of the various terms of the model, it is concluded that transient muscular effort induces dynamics of the postural chain. These observations support the view that there is a postural counter-perturbation which is associated with motor activity. More generally, the model helped to specify the effect of postural dynamic phenomena. It makes it possible to stress the importance of adherence at the contact level between the subject and the seat in the course of transient efforts. Received: 1 February 2001 / Accepted in revised form: 20 February 2002     

An evaluation of a tiltable office chair with respect to seat height, backrest position and task

The amount of spontaneous movement during seated office work was estimated by analysing the tilting movements of a tiltable office chair. Both movement frequency and amplitude range were considered. The seat inclinations and subjective acceptability were also recorded. The seat was moved more frequently and with a greater range when adjusted 6 cm above popliteal level compared to 1 cm below, or when the backrest was pushed anteriorly or posteriorly compared to a middle position. The greatest acceptability occurred with the highest seat adjustment and the backrest in the middle position. Typing or desk-work influenced movement to a similar extent.     

Modeling the human body/seat system in a vibration environment

The vibration environment is a common man-made artificial surrounding with which humans have a limited tolerance to cope due to their body dynamics. This research studied the dynamic characteristics of a seated human body/seat system in a vibration environment. The main result is a multi degrees of freedom lumped parameter model that synthesizes two basic dynamics: (i) global human dynamics, the apparent mass phenomenon, including a systematic set of the model parameters for simulating various conditions like body posture, backrest, footrest, muscle tension, and vibration directions, and (ii) the local human dynamics, represented by the human pelvis/vibrating seat contact, using a cushioning interface. The model and its selected parameters successfully described the main effects of the apparent mass phenomenon compared to experimental data documented in the literature. The model provided an analytical tool for human body dynamics research. It also enabled a primary tool for seat and cushioning design. The model was further used to develop design guidelines for a composite cushion using the principle of quasi-uniform body/seat contact force distribution. In terms of evenly distributing the contact forces, the best result for the different materials and cushion geometries simulated in the current study was achieved using a two layer shaped geometry cushion built from three materials. Combining the geometry and the mechanical characteristics of a structure under large deformation into a lumped parameter model enables successful analysis of the human/seat interface system and provides practical results for body protection in dynamic environment.     

Physical and mechanical properties of European Hophornbeam (Ostrya carpinifolia Scop.) wood

The main purpose of the study was to determine some physical and mechanical properties of European Hophornbeam (Ostrya carpinifolia Scop.) wood of which is not any detailed previous research in the literature. The sample trees harvested from a mixed beech-oak-hornbeam stand in the Zonguldak Forest Enterprises, north western part of Turkey. Conventional methods followed and the test procedures were performed on small clean specimens. European Hophornbeam wood's air dry and over dry densities were determined as 890 and 853 kg m(-3); density value in volume (basic density) was determined as 671 kg m(-3); volumetric shrinkage and swelling were determined as 23.02% and 24.94%; Fiber saturation point (FSP) was found 34.21%; MOR, MOE, compression strength parallel to grain, impact bending, tensile strength parallel and perpendicular to grain, and Janka hardness values (parallel and perpendicular to grain) were determined as 131.50 N/mm2, 11501.06 N/mm2, 66.94 N/mm2, 18.66 N/mm2, 105.49 N/mm2, 7.11 N/mm2, 6.89 and 5.63 kN, respectively.     

Support force measures of midsized men in seated positions

Two areas not well researched in the field of seating mechanics are the distribution of normal and shear forces, and how those forces change with seat position. The availability of these data would be beneficial for the design and development of office, automotive and medical seats. To increase our knowledge in the area of seating mechanics, this study sought to measure the normal and shear loads applied to segmental supports in 12 seated positions, utilizing three inclination angles and four levels of seat back articulation that were associated with automotive driving positions. Force data from six regions, including the thorax, sacral region, buttocks, thighs, feet, and hand support were gathered using multi-axis load cells. The sample contained 23 midsized subjects with an average weight of 76.7 kg and a standard deviation of 4.2 kg, and an average height of 1745 mm with a standard deviation of 19 mm. Results were examined in terms of seat back inclination and in terms of torso articulation for relationships between seat positions and support forces. Using a repeated measures analysis, significant differences (p<0.05) were identified for normal forces relative to all inclination angles except for forces occurring at the hand support. Other significant differences were observed between normal forces behind the buttocks, pelvis, and feet for torso articulations. Significant differences in the shear forces occurred under the buttocks and posterior pelvis during changes in seat back inclination. Significant differences in shear forces were also identified for torso articulations. These data suggest that as seat back inclination or torso articulation change, significant shifts in force distribution occur.     

Cimetidine suspension as adjuvant to energy restricted diet in treating obesity.

OBJECTIVE--To study the effect of cimetidine suspension compared with placebo suspension on weight loss in moderately obese patients taking a 5 MJ/day diet supplemented with dietary fibre. To determine the relation between the effectiveness of the blinding and weight loss. DESIGN--Randomised double blind study with an eight week parallel group phase and a subsequent eight week crossover or continuation phase. SETTING--Outpatient clinic. SUBJECTS--60 patients (51 women) aged 18-60. MAIN OUTCOME MEASURE--Weight loss. RESULTS--After eight weeks of treatment the mean weight loss in the cimetidine group (5.7 kg) was similar to that of the placebo group (5.9 kg; p = 0.78, 95% confidence interval -2.0 to 1.5 kg). Body mass index, waist and hip measurements, waist-hip ratio, and systolic and diastolic blood pressures decreased similarly in the two groups. No association was found between weight loss and the patients'' ability to guess if they were being given drug or placebo. Correct guesses of current drug were more prevalent than expected by chance (25/37 correct, p = 0.05 for the parallel group phase; 26/30, p = 0.0001 for the crossover phase). CONCLUSIONS--Cimetidine had no effect on weight loss in moderately obese patients. The study underlines the potential problem that blinding of patients to treatment can be compromised.     

External forces and torques generated by the brachiating white-handed gibbon (Hylobates lar)

We compared the kinetics of brachiation to bipedal walking and running. Gibbons use pectoral limbs in continuous contact with their overhead support at slow speeds, but exhibit aerial phases (or ricochetal brachiation) at faster speeds. This basic interaction between limb and support suggests some analogy to walking and running. We quantified the forces in three axes and torque about the vertical axis generated by a brachiating White-handed gibbon (Hylobates lar) and compared them with bipedal locomotion. Handholds oriented perpendicular to the direction of travel (as in ladder rungs) were spaced 0.80, 1.20, 1.60, 1.72, 1.95, and 2.25 m apart. The gibbon proportionally matched forward velocity to stride length. Handhold reaction forces resembled ground reaction forces of running humans except that the order of horizontal braking and propulsion were reversed. Peak vertical forces in brachiation increased with speed as in bipedal locomotion. In contrast to bipedalism, however, peak horizontal forces changed little with speed. Gait transition occurred within the same relative velocity range as the walk-run transition in bipeds (Froude number = 0.3-0.6). We oriented handholds parallel to the direction of travel (as in a continuous pole) at 0.80 and 1.60 m spacings. In ricochetal brachiation, the gibbon generated greater torque with handholds oriented perpendicular as opposed to parallel to the direction of travel. Handhold orientation did not affect peak forces. The similarities and differences between brachiation and bipedalism offer insight into the ubiquity of mechanical principles guiding all limbed locomotion and the distinctiveness of brachiation as a unique mode of locomotion.     

Lateral and Perpendicular Interaction Forces Involved in Mobile and Immobile Adhesion of Microorganisms on Model Solid Surfaces

Gliding and near-surface swimming of microorganisms are described as a mobile form of microbial adhesion that need not necessarily be reversible. It is argued that the reversibility of microbial adhesion depends on the depth of the secondary interaction minimum, calculated from the forces between an organism and a substratum acting in a direction perpendicular to the substratum surface. The mobility of adhering microorganisms depends on lateral interactions between the organisms. On ideally homogeneous and smooth model surfaces, only mobile adhesion occurs because the multibody, lateral interactions are weak compared with the thermal or Brownian motion energy of the organisms. Minor chemical or structural heterogeneities, which exist on all real-life surfaces, yield a lateral interaction on adhering microorganisms. This causes their immobilization, which helps to explain the physicochemical nature of microbial gliding or near-surface swimming. Moreover, these lateral interaction energies are one order of magnitude smaller than the Lifshitz-Van der Waals, electrostatic, and acid-base forces acting perpendicular to substratum surfaces that are responsible for adhesion. Received: 2 April 1998 / Accepted: 26 May 1998     

Locomotion of granulocytes on an inclined plane

The paper presents a quantitative study of the trajectories of rat granulocytes (PMNs) migrating on a glass surface inclined at various angles, i.e. under the action of gravitational force component parallel to the plane. The action of the force of the order of 5 X 10(-13) N (component parallel to the plane inclined at 80 degrees) accompanied by the decrease of a gravitational component perpendicular to the surface does not disrupt the adhesion contact of migrating PMNs with the serum coated glass surface. Under the action of the external force parallel to the surface, the PMNs exhibit a tendency to migrate in the direction of the force vector and the angles between elementary segments (steps) of cell trajectories are smaller in comparison with migration on a horizontal plane (0 degrees inclination). It has been found that the mean velocity of motion of PMNs locomoting on a steep slope (70 degrees and 80 degrees) is greater in comparison with the migration velocity on a horizontal surface. The increase of velocity concerns not only cells migrating in the downward direction, but also those which move upwards. Possible mechanisms of the influence of external force on direction and rate of migration of granulocytes are discussed, namely modification of adhesion force, stimulation of cell motile activity, individual variability of cell adhesive and migration properties, shortening of transient locomotory adhesions.     

Scanning eye movements of the stomatopod crustacean,Neogonodactylus oerstedii,in polarized light fields

ABSTRACT

Stomatopod crustaceans have highly mobile, independently moving compound eyes that are sensitive to both linearly and circularly polarized light. They rotate their eyes to predictable angles when viewing a linearly polarized target, and they scan their eyes frequently to sample the visual field. Angles of scans are roughly perpendicular to the plane of the midband (a set of specialized parallel rows of equatorial ommatidia). We investigated scanning eye movements in one Caribbean stomatopod species (Neogonodactylus oerstedii) in uniform visual fields that were vertically polarized, horizontally polarized, or depolarized. We found that mean eye rotation and scan angles differed significantly among these different treatments. Average scan angles differed by 12°, being more horizontal in a vertically polarized field than in a horizontally polarized one, and also more horizontal in a vertically polarized field than in a depolarized field. Thus, these stomatopods adjusted visual scanning to the polarization of the visual environment.     

Analytical and numerical analysis of human dental occlusal contact

The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental enamel. The development of a numerical model for analysis of the occlusal contact between two antagonistic teeth is proposed, which includes three basic steps: the characterisation of the surface roughness, its homogenisation using an assumed distribution function and the numerical determination of the resulting forces. Finite element strain results for the main different asperities are statistically combined, deriving the predicted macroscopic behaviour of the interface. Axisymmetric and 3D numerical models with an elasto-plastic constitutive law are used to simulate micro-indentations and micro-contacts, respectively. The contact is allowed to occur locally in planes not necessarily parallel to the surface's mean plane, a problem for which there is no analytical solution. The three identified parameters, homogenised surface hardness (3.68 GPa), surface yield stress (3.08 GPa) and static friction coefficient (0.23), agree with the experimental values reported in the literature.     

Alendronate as an effective countermeasure to disuse induced bone loss

Microgravity, similar to disuse immobilization on earth, causes rapid bone loss. This loss is believed to be an adaptive response to the reduced musculoskeletal forces in space and occurs gradually enough that changes occurring during short duration space flight are not a concern. Bone loss, however, will be a major impediment for long duration missions if effective countermeasures are not developed and implemented. Bed rest is used to simulate the reduced mechanical forces in humans and was used to test the hypothesis that oral alendronate would reduce the effects of long duration (17 weeks) inactivity on bone. Eight male subjects were given daily oral doses of alendronate during 17 weeks of horizontal bed rest and compared with 13 male control subjects not given the drug. Efficacy was evaluated based on measurements of bone markers, calcium balance and bone density performed before, during and after the bed rest. The results show that oral alendronate attenuates most of the characteristic changes in bone that are associated with long duration bed rest and presumably space flight.     

Mayfly Burrows in Firmground of Recent Rivers from the Czech Republic and Poland,with Some Comments on Ephemeropteran Burrows in General

U-shaped, pouch-like burrows with parallel limbs, covered with short scratches arranged in sets, occur in the thalweg of the Oh?e river in NW Czech Republic. Similar, but smaller burrows with rare scratches, not arranged in sets, occur in the thalweg of the Drw?ca river in N Poland. Probably, they are produced by larvae and/or nymphs of Palingenia and Polymitarcis (Ephoron), respectively. In both localities, they burrowed in firmground surfaces at shallow depths. The burrowed surfaces were emerged during low water levels. A review of recent mayfly burrows shows that they are 1) U-shaped pouches with parallel limbs and septum, which may be covered with short scratches and are oriented perpendicular to the bottom, irrespective of its inclination, or 2) wide U-shape burrows with divergent limbs, which may be branched. In the fossil record, the ichnogenera Fuersichnus, Asthenopodichnium, and Rhizocorallium are partly ascribed to mayfly burrows, but their comparison to the recent burrows shows that such interpretations are somewhat problematic. The mayfly burrows are potentially good indicators of aquatic, non-marine, well oxygenated, clean water environments.     

EPR evidence for nitric oxide production from guanidino nitrogens of L-arginine in animal tissues in vivo.

Administration of Fe(2+)-citrate complex (50 mg/kg of FeSO4 or FeCl2 plus 250 mg/kg of sodium citrate) subcutaneously in the thigh or Escherichia coli lipopolysaccharide (LPS, 1 mg/kg) intraperitoneally, (i.p.) to mice induced NO formation in the livers in vivo at the rate of 0.2-0.3 micrograms/g wet tissue per 0.5 h. The NO synthesized was specifically trapped with Fe(2+)-diethyldithiocarbamate complex (FeDETC2), formed from endogenous iron and diethyldithiocarbamate (DETC) administered i.p. 0.5 h before decapitation of the animals. NO bound with this trap resulted in the formation of a paramagnetic mononitrosyl iron complex with DETC (NO-FeDETC2), characterized by an EPR signal at g perpendicular = 2.035, g parallel = 2.02 with triplet hyperfine structure (HFS) at g perpendicular. This allowed quantification of the amount of NO formed in the livers. An inhibitor of enzymatic NO synthesis from L-arginine, NG-nitro-L-arginine (NNLA, 50 mg/kg) attenuated the NO synthesis in vivo. L-Arginine (500 mg/kg) reversed this effect. Injection of L-[guanidineimino-15N2]arginine combined with Fe(2+)-citrate or LPS led to the formation of the EPR signal of NO-FeDETC2 characterized by a doublet HFS at g perpendicular, demonstrating that the NO originates from the guanidino nitrogens of L-arginine in vivo.