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Biomedical subjects

F X Li

Publications and source records attributed to F X Li.

14 recordsLinked to original sources
PubMed2001

Use of 'chalk' in rock climbing: sine qua non or myth?

Magnesium carbonate, or 'chalk', is used by rock climbers to dry their hands to increase the coefficient of friction, thereby improving the grip of the holds. To date, no scientific research supports this practice; indeed, some evidence suggests that magnesium carbonate could decrease the coefficient of friction. Fifteen participants were asked to apply a force with the tip of their fingers to hold a flattened rock (normal force), while a tangential force pulled the rock away. The coefficient of friction--that is, the ratio between the tangential force (pulling the rock) and the normal force (applied by the participants)--was calculated. Coating (chalk vs no chalk), dampness (water vs no water) and rock (sandstone, granite and slate) were manipulated. The results showed that chalk decreased the coefficient of friction. Sandstone was found to be less slippery than granite and slate. Finally, water had no significant effect on the coefficient of friction. The counter-intuitive effect of chalk appears to be caused by two independent factors. First, magnesium carbonate dries the skin, decreasing its compliance and hence reducing the coefficient of friction. Secondly, magnesium carbonate creates a slippery granular layer. We conclude that, to improve the coefficient of friction in rock climbing, an effort should be made to remove all particles of chalk; alternative methods for drying the fingers are preferable.

Adult↗
PubMed2001

Prevalence of thyroid diseases in Nevada counties with respect to perchlorate in drinking water.

Perchlorate is well-known to inhibit the uptake of iodine by the thyroid and has been shown to do so at doses in the milligrams-per-day range and higher. Perchlorate has been found in the water supply of Clark County (Las Vegas), Nevada, at 4 to 24 micrograms/L (parts per billion) and may provide exposure dosages in the tens of micrograms per day. An analysis of the Medicaid database from Nevada was undertaken to determine whether an increase in the prevalence of any thyroid disease was associated with that level of perchlorate content. The prevalence of persons being seen for thyroid disease or for specific thyroid diseases (goiter, nodule, thyrotoxicosis, congenital hypothyroidism, acquired hypothyroidism, thyroiditis, and other thyroid disorders) and for thyroid cancer among the Medicaid-eligible population of each county was calculated for the 2-year period 1997 to 1998. The prevalences in Clark County were compared with those in Washoe County (i.e., Reno), the second most populous county in the state, and with those for the rest of the state. There was no evidence of an increased rate of thyroid disease (or of any specific thyroid disease) associated with perchlorate exposure. Generally, the prevalences in the metropolitan parts of the state were lower than for the rest of the state, particularly for acquired hypothyroidism. This analysis found no evidence that perchlorate-containing drinking water at the given level increased the prevalence of acquired hypothyroidism or of any other thyroid condition.

Humans↗
PubMed2001

Estimating the minimum grip force required when grasping objects under impulsive loading conditions.

As an aid to studying the efficiency of grip force scaling in the context of collisions, we present a simple cost-effective approach to estimating the slip ratio--that is, the minimum grip-to-load-force ratio needed to prevent object slippage. The grip apparatus comprises a sturdy load cell to measure grip force and two linear potentiometers to provide detailed description of finger movements. The slip ratio was estimated by plotting the magnitude of finger movement against the grip-to-load-force ratio at the time of impact. The slip ratio was dependent on the direction of loading, which stresses the importance of estimating slip ratios in a context similar to that of the experiment in which the efficiency of subjects' behavior is to be assessed.

Adult↗
PubMed2000

Neonatal thyroid-stimulating hormone level and perchlorate in drinking water.

BACKGROUND: The effect of perchlorate in drinking water on neonatal blood thyroid-stimulating hormone (thyrotropin; TSH) levels was examined for Las Vegas and Reno, Nevada. METHODS: The neonatal blood TSH levels in Las Vegas (with up to 15 microg/L (ppb) perchlorate in drinking water) and in Reno (with no perchlorate detected in the drinking water) from December 1998 to October 1999 were analyzed and compared. The study samples were from newborns in their first month of life (excluding the first day of life) with birth weights of 2, 500-4,500 g. A multivariate analysis of logarithmically transformed TSH levels was used to compare the mean TSH levels between Las Vegas and Reno newborns, with age and sex being controlled as potential confounders. RESULTS: This study of neonatal TSH levels in the first month of life found no effect from living in the areas with environmental perchlorate exposures of </=15 microg/L (P = 0.97). CONCLUSIONS: This study, which was sensitive enough to detect the effects of age and gender on neonatal blood TSH levels, detected no effect from environmental exposures to perchlorate.

Age Factors↗
PubMed2000

Neonatal thyroxine level and perchlorate in drinking water.

Environmental contamination of drinking water has been observed for perchlorate, a chemical able to affect thyroid function. This study examines whether that exposure affected the thyroid function of newborns. Neonatal blood thyroxine (T4) levels for days 1 to 4 of life were compared for newborns from the city of Las Vegas, Nevada, which has perchlorate in its drinking water, and those from the city of Reno, Nevada, which does not (detection limit, 4 micrograms/L [ppb]). This study is based on blood T4 analyses from more than 23,000 newborns in these two cities during the period April 1998 through June 1999. No difference was found in the mean blood T4 levels of the newborns from these two cities. Drinking water perchlorate levels measured monthly for Las Vegas ranged during this study period from non-detectable for 8 months to levels of 9 to 15 ppb for 7 months. Temporal differences in mean T4 level were noted in both cities but were unrelated to the perchlorate exposure. This study was sufficiently sensitive to detect the effects of gender, birth weight, and the day of life on which the blood sample was taken on the neonatal T4 level, but it detected no effect from environmental exposures to perchlorate that ranged up to 15 micrograms/L (ppb).

Chi-Square Distribution↗
PubMed2000

Sex differences and action scaling in overhead reaching.

Specifications of affordances is independent of the anthropometric scale of the perceiver. It is therefore predicted that sex differences disappear when perceptual performance is scaled relative to the relevant physical properties of the system formed by performer and environment in a particular action. 24 women and 30 men were compared for their ability to perceive the boundaries for overhead reaching for a ball suspended above them. Perceived and actual maximum action boundaries were measured in two height conditions, with and without wearing 15-cm high blocks under their feet. On average the men reached higher than the women; however, when perceived maximum reachable height was expressed as a ratio of actual maximum reachable height, the difference between the groups disappeared. The participants showed an identical fit between environment and performer in both height conditions. The results indicate that the specification of affordances for overhead reaching is independent of the height and the sex of the performer.

Adult↗
PubMed1999

Grip force dynamics in the approach to a collision.

This experiment investigated the prediction of load force (LF) in impulsive collisions inferred from anticipatory adjustments of grip force (GF) used to stabilise a hand-held object. Subjects used a precision grip to hold the object between thumb and index finger of their right hand and used the arm either: (1) to move the object to produce a collision by hitting the lower end of a pendulum, causing it to swing to one of three target angles, or (2) to hold the object still while receiving a collision produced by the experimenter releasing the pendulum from one of three angles. Visual feedback of the pendulum's trajectory was available in the production task only. In all conditions, subjects increased GF in advance of the collision. In receiving the collision without advance information, subjects set GF levels to the mid-range of the experienced forces. When subjects possessed knowledge about the maximum angle of pendulum swing - either because they were going to produce it or because they were verbally informed - magnitude of the anticipatory-GF magnitude response was scaled to the predicted LF magnitude. Furthermore, GF was scaled to LF with a higher gain when producing compared to receiving the collision. This suggests that updating forward models through a semantic route is not as powerful as when the updating is achieved through the more direct route of dynamic exploration.

Adolescent↗
PubMed1999

Thyroid health status of ammonium perchlorate workers: a cross-sectional occupational health study.

Since pharmaceutical exposures to perchlorate are known to suppress thyroid function in patients with hyperthyroidism, a study of employees at a perchlorate manufacturing plant was conducted to assess whether occupational exposure to perchlorate suppresses thyroid function. Exposure to perchlorate was assessed by measurement of ambient air concentrations of total and respirable perchlorate particles, and systemic absorption was assessed by measurement of urinary perchlorate excretion. Airborne exposures ranged from 0.004 to 167 mg total particulate perchlorate per day. Urinary perchlorate measurements demonstrated that exposure to the airborne particulate perchlorate resulted in systemic absorption. Workers were grouped into four exposure categories with mean absorbed perchlorate dosages of 1, 4, 11 and 34 mg perchlorate per day. Thyroid function was assessed by measurement of serum thyroid-stimulating hormone, free thyroxine index, thyroxine, triiodothyronine, thyroid hormone binding ratio, thyroid peroxidase antibodies, and by clinical examination. No differences in thyroid-function parameters were found between the four groups of workers across approximately three orders of magnitude of exposure and of dose. Thus human thyroid function was not affected by these levels of absorbed perchlorate. In addition, no clinical evidence of thyroid abnormalities was found in any exposure group. The blood-cell counts were normal in all groups, indicating no evidence of hematotoxicity in this exposure range. The absence of evidence of an effect on thyroid function or blood cells from occupational airborne perchlorate exposure at a mean absorption of 34 mg/day demonstrates a no-observed-adverse-effect-level (NOAEL) that can assist in the evaluation of human health risks from environmental perchlorate contamination.

Adult↗
PubMed1999

A role for E2F1 in the induction of ARF, p53, and apoptosis during thymic negative selection.

E2F transcriptional activity controls the expression of many of the genes required for G1 to S phase progression. E2F1, one member of the E2F family, plays an important role in the induction of apoptosis. We have examined the role of the E2F1 transcription factor in apoptosis during T-cell maturation in the thymus. We show that E2F1 is required for the apoptosis of autoimmune immature T cells during thymic negative selection in vivo. This T-cell receptor-mediated apoptosis coincides with the E2F1-dependent increase of p19-ARF mRNA and p53 protein levels. In contrast, E2F1 is not required for the induction of apoptosis by glucocorticoids or DNA damage. These results demonstrate a specific role for E2F1, which triggers a pathway leading to ARF and p53 induction, in a physiological apoptosis pathway that is uncoupled from a normal proliferative event.

Animals↗
PubMed1997

Expertise and the regulation of gait in the approach phase of the long jump.

In the approach phase of the long jump, athletes attempt to strike the take-off board accurately with minimum loss of speed, and in an optimum body position for take-off. Previous research has shown that skilled long jumpers demonstrate an ascending-descending trend of variability rather than a consistent pattern of foot placement over trials. The present study examined whether non-long jumpers showed a similar pattern of variability in footfall placement between trials to skilled long jumpers. Consistency of foot placement over trials for non-long jumpers (n = 11) was determined using a panned video camera. Digitization of the foot position provided toe-board distances during the run-up phase. Our results showed that non-long jumpers have a similar pattern of descending variability near to the take-off board to expert long jumpers, suggesting the use of visual regulation. However, in comparison to more skilled subjects, non-long jumpers accumulated a considerably larger maximum mean standard deviation in footfall placement between trials (58 cm). Since non-long jumpers had no previous task-specific training, these data extend our current understanding of the regulation of goal-directed gait.

Adult↗
PubMed1997

[Separation and identification of the llungianin A and B from the root of Pimpinella thellungiana Wolff].

Two compounds were isolated from the roots of Pimpinella thellungiana wolff. On the basis of spectral analysis (UV, IR, MS, 1HNMR, 1H-1H COSY, 13CNMR, 1H-13C COSY, DEPT), they were identified as 2-(1-ethoxy-2-hydroxy) propyl-4-methoxyphenol(I); 2-(1-ethoxy-2-hydroxy) propyl-4-methoxyphenyl-2-methyl-butyrate (II). They are new compounds named the llungianin A and B. Pharmacological tests showed that they have some hypotensive effects.

Antihypertensive Agents↗
PubMed1997

[Comparative study of applying tiaoxue yisui recipe and SSL regimen in treating infantile chronic aplastic anemia and analysis of its therapeutical mechanism].

OBJECTIVE: To explore the effective method in treating infantile chronic aplastic anemia (ICAA) by using traditional Chinese medicine (TCM). METHODS: Seventy-eight cases of ICAA were observed, 48 of them were treated with Tiaoxue Yisui recipe (treated group), 30 cases were treated with SSL regimen (control group). RESULTS: The remission rate and total effective rate in treated group were 52.08% and 81.25% respectively, they were higher than those in control group (P < 0.05). After one year treatment the ratio of hemopoietic and non-hemopoietic cells in treated group was higher than that in control group (P < 0.05). The number of megakaryocyte in treated group was more than those in control group (P < 0.05). CONCLUSION: Tiaoxue Yisui recipe could improve the quality of the patient's life. The therapeutical mechanism of the Tiaoxue Yisui recipe might promote the proliferation of hemopoietic stem cells and regulate the immune function.

Adolescent↗
PubMed1995

Occlusion rate of ball texture as a source of velocity information.

When a ball is rolling on the ground toward an observer, its elements of texture are successively occluded. The number of the elements of texture occluded per unit of time determines the occlusion rate. The aim of this study was to examine the role of the occlusion rate of ball texture and the velocity of the ball in the perception of the time remaining before the arrival. If the occlusion rate is used to perceive the time to arrival, then timing the initiation of movement should depend on occlusion rate. On the other hand, if the optical variable tau is exclusively used, then no variation is expected. 20 subjects were required to avoid balls rolling directly toward them. Three different ball textures and five ball velocities were used, leading to 10 different occlusion rates. The results showed that the timing of the initiation of the movement was not modified by variations of occlusion rate. However, the velocity of the avoidance movement increased with occlusion rate. The role of timing initiation and movement velocity in the control of the action are discussed, and it is suggested that occlusion rate is perceived and taken into account in the control of avoidance movements.

Acceleration↗