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1

Frontal plane hip and ankle sensorimotor function, not age, predicts unipedal stance time  

PubMed Central

Introduction Changes occur in muscles and nerves with aging. This study aimed to explore the relationship between unipedal stance time (UST) and frontal plane hip and ankle sensorimotor function in subjects with diabetic neuropathy. Methods UST, quantitative measures of frontal plane ankle proprioceptive thresholds, and ankle and hip motor function were tested in forty-one persons with a spectrum of lower limb sensorimotor function, ranging from healthy to moderately severe diabetic neuropathy. Results Frontal plane hip and ankle sensorimotor function demonstrated significant relationships with UST. Multivariate analysis identified only composite hip strength, composite ankle proprioceptive threshold, and age to be significant predictors of UST (R2=0.73); they explained 46%, 24% and 3% of the variance, respectively. Discussion/Conclusions Frontal plane hip strength was the single best predictor of UST and appeared to compensate for less precise ankle proprioceptive thresholds. This finding is clinically relevant given the possibility of strengthening the hip, even in patients with significant PN. .

Allet, Lara; Kim, Hogene; Ashton-Miller, James; De Mott, Trina; Richardson, James K.

2011-01-01

2

The influence of initial bipedal stance width on the clinical measurement of unipedal balance time  

PubMed Central

Objective To determine the effect of varying initial bipedal stance width (ISW) on the clinical measurement of unipedal balance time (UBT). Design Observational, cross sectional study. Setting Academic physiatric outpatient facility. Subjects Thirty-one clinic subjects with neuromuscular and/or musculoskeletal conditions known to influence mobility, and 30 similarly-aged healthy subjects. Methods Demographic and clinical information were recorded. UBT was determined under three distinct conditions by varying bipedal inter-malleolar distance: 1) ISW of 0.3 body height; 2) ISW of 0.05 body height; and 3) ISW of 0 body height. The last was accomplished by subjects assuming unipedal balance while using the hands on a horizontal surface for stabilization. Subjects lifted the contralateral foot (or hands in the case of 0 body height condition) in response to a cadenced command to minimize variation in rate of weight transfer Main Outcome Measurements UBT under each of the three ISW conditions. Results Mean UBT increased with decreasing ISW, and the differences were significant when comparing each ISW with the next smaller. Healthy subjects demonstrated greater UBT than clinic subjects at each ISW, but the magnitude of these group differences were similar across ISW condition. A UBT > 10 seconds in the 0.3 body height ISW was the best discriminator between clinic and healthy subjects. Conclusions Because UBT varies with ISW, standardization of ISW is necessary for accurate within subject, and between subject, comparisons in UBT. Healthy subjects were best differentiated from clinic subjects by UBT > 10 sec in the 0.3 body height ISW condition.

Richardson, James K.; Tang, Chi; Nwagwu, Chijioke; Nnodim, Joseph

2012-01-01

3

Effects of ankle and hip muscle fatigue on postural sway and attentional demands during unipedal stance  

Microsoft Academic Search

The effect of muscle fatigue on quiet standing is equivocal, including its duration\\/recovery and whether it leads to an increase in attentional demands. The purpose of this study was to assess the effects of ankle and hip muscle fatigue on postural sway and simple reaction time during a unipedal task. Two groups of 14 young adults (mean age=22.50±3.23) had to

Etienne J. Bisson; Daniel McEwen; Yves Lajoie; Martin Bilodeau

2011-01-01

4

Effects of ankle and hip muscle fatigue on postural sway and attentional demands during unipedal stance.  

PubMed

The effect of muscle fatigue on quiet standing is equivocal, including its duration/recovery and whether it leads to an increase in attentional demands. The purpose of this study was to assess the effects of ankle and hip muscle fatigue on postural sway and simple reaction time during a unipedal task. Two groups of 14 young adults (mean age=22.50±3.23) had to stand on their dominant leg for 30-s trials before and after fatigue of hip or ankle flexors and extensors. Half of the unipedal trials were performed in a dual-task condition where subjects, in addition to standing, had to respond verbally to an auditory stimulus. Sway area, and sway variability and velocity in the AP and ML planes were calculated using center of pressure data obtained from a force platform. Voice reaction time was recorded seated and during the dual-task condition to assess attentional demands. A main effect of fatigue was found for AP sway variability (p=0.027), AP sway velocity (p=0.017) and ML sway velocity (p=0.004). Both groups showed increased sway velocity in both directions and in reaction time during the dual-task condition (p<0.001), but reaction time did not increase with fatigue. A group by fatigue interaction was found significant for ML sway velocity (p=0.043). Results suggest that hip and ankle fatigue affected postural control in the fatigued plane (AP) but only hip fatigue affected postural control in the non-fatigued plane (ML sway velocity). However, fatigue did not lead to an increase in attentional demands and increased AP and ML sway velocity had recovered within 30min. PMID:21050763

Bisson, Etienne J; McEwen, Daniel; Lajoie, Yves; Bilodeau, Martin

2010-11-02

5

Association of unipedal standing time and bone mineral density in community-dwelling Japanese women  

Microsoft Academic Search

Summary  Bone mineral density (BMD) and physical performance of the lower extremities decrease with age. In community-dwelling Japanese\\u000a women, unipedal standing time, timed up and go test, and age are associated with BMD while in women aged 70 years and over,\\u000a unipedal standing time is associated with BMD.\\u000a \\u000a \\u000a \\u000a Introduction  The aim of this study was to clarify whether unipedal standing time is significantly

A. Sakai; N. Toba; M. Takeda; M. Suzuki; Y. Abe; K. Aoyagi; T. Nakamura

2009-01-01

6

Shorter unipedal standing time and lower bone mineral density in women with distal radius fractures  

Microsoft Academic Search

Summary  Unipedal standing time was shorter and bone mineral density was lower in Japanese women aged 50 years and over with low-energy\\u000a distal radius fractures resulting from falls than those in age-matched community-dwelling Japanese women without distal radius\\u000a fractures.\\u000a \\u000a \\u000a \\u000a \\u000a Introduction  The aim of this study was to compare unipedal standing time and bone mineral density (BMD) of women ?50 years of age with\\u000a distal

A. Sakai; T. Oshige; Y. Zenke; Y. Yamanaka; H. Otsuka; T. Nakamura

2010-01-01

7

Do Ankle Orthoses Improve Ankle Proprioceptive Thresholds or Unipedal Balance in Older Persons with Peripheral Neuropathy?  

PubMed Central

Objective To determine whether ankle orthoses that provide medial and lateral support, and have been found to decrease gait variability in older persons with peripheral neuropathy, decrease (improve) frontal plane ankle proprioceptive thresholds or increase unipedal stance time in that same population. Design Observational study in which unipedal stance time was determined with a stopwatch, and frontal plane ankle (inversion and eversion) proprioceptive thresholds were quantified during bipedal stance with and without the ankle orthoses, in 11 older diabetic subjects with peripheral neuropathy (8 men; age 72 ± 7.1 years) using a foot cradle system which presented a series of 100 rotational stimuli. Results The subjects demonstrated no change in combined frontal plane (inversion + eversion) proprioceptive thresholds or unipedal stance time with versus without the orthoses (1.06 ± 0.56 versus 1.13 ± 0.39 degrees, respectively; p = 0.955 and 6.1 ± 6.5 versus 6.2 ± 5.4 seconds, respectively; p = 0.922). Conclusion Ankle orthoses which provide medial-lateral support do not appear to change ankle inversion/eversion proprioceptive thresholds or unipedal stance time in older persons with diabetic peripheral neuropathy. Previously identified improvements in gait variability using orthoses in this population are therefore likely related to an orthotically-induced stiffening of the ankle rather than a change in ankle afferent function.

Son, Jaebum; Ashton-Miller, James A.; Richardson, James K.

2010-01-01

8

Effect of four different starting stances on sprint time in collegiate volleyball players.  

PubMed

Starting stance plays an important role in influencing short-distance sprint speed and, therefore, the ability to reach a ball during sport play. The purpose of this study was to evaluate 4 different starting stances on sprint time. Twenty-six male and female collegiate volleyball players volunteered to participate in 1 testing session. Each subject performed 3 15-ft sprint trials at each of 4 different starting stances (P-parallel, FS-false step, S-staggered, and SFS-staggered false step) in random order. Analysis of variance revealed that there was no significant interaction of sex by stance, but there were main effects for sex (men were faster than women) and stance. The FS (1.18 ± 0.10 seconds), S (1.16 ± 0.07 seconds), and SFS (1.14 ± 0.06 seconds) stances were faster than the P (1.25 ± 0.09 seconds) stance, and the SFS stance was faster than the FS stance. This indicates that starting with a staggered stance (regardless of stepping back) produced the greatest sprinting velocity over the initial 15 feet. Although taking a staggered stance seems counterproductive, the resultant stretch-shortening cycle action and forward body lean likely increase force production of the push-off phase and place the total body center of mass ahead of the contacting foot, thereby, decreasing sprint time. PMID:20885191

Johnson, Trevor M; Brown, Lee E; Coburn, Jared W; Judelson, Daniel A; Khamoui, Andy V; Tran, Tai T; Uribe, Brandon P

2010-10-01

9

Disturbance of contralateral unipedal postural control after stimulated and voluntary contractions of the ipsilateral limb.  

PubMed

One session of sustained unilateral voluntary muscular contractions increases central fatigue and induces a cross-over of fatigue of homologous contralateral muscles. It is not known, however, how this cross-transfer affects contralateral unipedal postural control. Moreover, contralateral neurophysiological effects differ between voluntary muscular contractions and electrically stimulated contractions. The aims of this study were thus to examine the effects of muscle fatigue on contralateral unipedal postural control and to compare the effects of stimulated and voluntary contractions. Fifteen subjects took part in the protocol. Fatigue of the ipsilateral quadriceps femoris was generated either by neuromuscular electrical stimulation (NMES) or by isometric voluntary muscular contraction (VOL). Postural control on the contralateral limb was measured before (PRE condition) and after the completion of the two fatiguing exercises (POST condition) using a force platform. We analyzed body sway area and the spectral power density given by the wavelet transform. In POST condition, postural control recorded in the unipedal stance on the contralateral limb was disturbed after NMES and VOL fatiguing exercises. In addition, postural control was similarly disturbed for both exercises. These results suggest that cross-over fatigue is able to disturb postural control after both stimulated and voluntary contractions. PMID:20723569

Paillard, Thierry; Chaubet, Vincent; Maitre, Julien; Dumitrescu, Michel; Borel, Liliane

2010-08-17

10

Effects of knee and ankle muscle fatigue on postural control in the unipedal stance  

Microsoft Academic Search

The aim of this study was to compare the effects of acute muscle fatigue of the ankle and knee musculature on postural control\\u000a by immediate measures after performing fatiguing tasks (POST condition). One group of subjects (n = 8) performed a fatiguing task by voluntary contractions of the triceps surae (group TRI) and the other (n = 9) performed a fatiguing task by voluntary

Riadh Bizid; Eric Margnes; Yrieix François; Jean Louis Jully; Gerard Gonzalez; Philippe Dupui; Thierry Paillard

2009-01-01

11

Influence of ankle plantarflexor fatigue on postural sway, lower limb articular angles, and postural strategies during unipedal quiet standing.  

PubMed

The purpose of this study was to investigate the changes in postural control and in posture induced by ankle plantarflexor fatigue during a unipedal stance task. We also studied the postural strategies in the antero-posterior and medio-lateral planes used by participants to maintain balance. Thirteen young adults were asked to stand barefoot on their preferred leg as still as possible for 30s with vision or without vision. Participants performed postural trials before and after a fatigue protocol that consisted of standing on toes until exhaustion. Centre of pressure (COP) displacements were measured with a force platform and electrogoniometers were placed at the ankle, knee and hip joints of the support leg to monitor articular angles. Relationships between changes in articular angles and displacements of the COP in the antero-posterior and medio-lateral planes were tested using cross-correlations. Sway area and velocity increased with fatigue, but only without vision. A posterior shift of the mean COP position was also observed after fatigue. Ankle and hip joints were more flexed after fatigue. Moderate to good relationships between COP displacements and ankle angles were observed before and after fatigue in both planes whereas these relationships were low for hip and knee joints. Ankle plantarflexors fatigue induced impairment in postural control and changes in posture. To compensate for the effects of fatigue, participants increased the flexion of the ankle and/or the hip joints but conserved the ankle strategy as the dominant postural strategy in both planes. PMID:23102672

Boyas, Sébastien; Hajj, Maria; Bilodeau, Martin

2012-10-24

12

Arm raising in humans under loaded vs. unloaded and bipedal vs. unipedal conditions  

Microsoft Academic Search

The aim of the present experiment was to study the central organization of equilibrium control during arm raising in the frontal plane. Nine adult subjects (five seniors and four young adults) were asked to raise their right arm to a horizontal position in the frontal plane in two support conditions (bipedal vs. unipedal) and two load conditions (unloaded vs. a

S Vernazza-Martin; N Martin; M Cincera; A Pedotti; J Massion

1999-01-01

13

Disturbance of contralateral unipedal postural control after stimulated and voluntary contractions of the ipsilateral limb  

Microsoft Academic Search

One session of sustained unilateral voluntary muscular contractions increases central fatigue and induces a cross-over of fatigue of homologous contralateral muscles. It is not known, however, how this cross-transfer affects contralateral unipedal postural control. Moreover, contralateral neurophysiological effects differ between voluntary muscular contractions and electrically stimulated contractions. The aims of this study were thus to examine the effects of muscle

Thierry Paillard; Vincent Chaubet; Julien Maitre; Michel Dumitrescu; Liliane Borel

2010-01-01

14

Age-related differences in time-limit performance and force platform-based balance measures during one-leg stance.  

PubMed

Poor posture control has been associated with an increased risk of falls and mobility disability among older adults. This study was conducted to assess the test-retest reliability and sensitivity to group differences regarding the time-limit (TLimit) of one-leg standing and selected balance parameters obtained with a force platform in older and young adults. A secondary purpose was to assess the relationship between TLimit and these balance parameters. Twenty-eight healthy older adults (age: 69±5years) and thirty young adults (age: 21±4years) participated in this study. Two one-leg stance tasks were performed: (1) three trials of 30s maximum and (2) one TLimit trial. The following balance parameters were computed: center of pressure area, RMS sway amplitude, and mean velocity and mean frequency in both the anterio-posterior and medio-lateral directions. All balance parameters obtained with the force platform as well as the TLimit variable were sensitive to differences in balance performance between older and young adults. The test-retest reliability of these measures was found to be acceptable (ICC: 0.40-0.85), with better ICC scores observed for mean velocity and mean frequency in the older group. Pearson correlations coefficients (r) between balance parameters and TLimit ranged from -0.16 to -0.54. These results add to the current literature that can be used in the development of measurement tools for evaluating balance in older and young adults. PMID:23403137

da Silva, Rubens A; Bilodeau, Martin; Parreira, Rodolfo B; Teixeira, Denilson C; Amorim, César F

2013-02-10

15

"The Road to Freedom": How One Salvadoran Youth Takes an Agentive Stance to Narrate the Self across Time and Space  

ERIC Educational Resources Information Center

|In this article, we use narrative theory to analyze and discuss how one Salvadoran youth, Thomas, constructed three different yet overlapping narratives, including a digital story, on his family's movement across borders. We describe how each telling of his narratives is situated in time and space, where Thomas reveals his understandings of…

McGinnis, Theresa Ann; Garcia, Andrea

2012-01-01

16

Comparison of human and humanoid robot control of upright stance.  

PubMed

There is considerable recent interest in developing humanoid robots. An important substrate for many motor actions in both humans and biped robots is the ability to maintain a statically or dynamically stable posture. Given the success of the human design, one would expect there are lessons to be learned in formulating a postural control mechanism for robots. In this study we limit ourselves to considering the problem of maintaining upright stance. Human stance control is compared to a suggested method for robot stance control called zero moment point (ZMP) compensation. Results from experimental and modeling studies suggest there are two important subsystems that account for the low- and mid-frequency (DC to approximately 1Hz) dynamic characteristics of human stance control. These subsystems are (1) a "sensory integration" mechanism whereby orientation information from multiple sensory systems encoding body kinematics (i.e. position, velocity) is flexibly combined to provide an overall estimate of body orientation while allowing adjustments (sensory re-weighting) that compensate for changing environmental conditions and (2) an "effort control" mechanism that uses kinetic-related (i.e., force-related) sensory information to reduce the mean deviation of body orientation from upright. Functionally, ZMP compensation is directly analogous to how humans appear to use kinetic feedback to modify the main sensory integration feedback loop controlling body orientation. However, a flexible sensory integration mechanism is missing from robot control leaving the robot vulnerable to instability in conditions where humans are able to maintain stance. We suggest the addition of a simple form of sensory integration to improve robot stance control. We also investigate how the biological constraint of feedback time delay influences the human stance control design. The human system may serve as a guide for improved robot control, but should not be directly copied because the constraints on robot and human control are different. PMID:19665564

Peterka, Robert J

2009-08-07

17

Comparison of Human and Humanoid Robot Control of Upright Stance  

PubMed Central

There is considerable recent interest in developing humanoid robots. An important substrate for many motor actions in both humans and biped robots is the ability to maintain a statically or dynamically stable posture. Given the success of the human design, one would expect there are lessons to be learned in formulating a postural control mechanism for robots. In this study we limit ourselves to considering the problem of maintaining upright stance. Human stance control is compared to a suggested method for robot stance control called zero moment point (ZMP) compensation. Results from experimental and modeling studies suggest there are two important subsystems that account for the low- and mid-frequency (DC to ~1 Hz) dynamic characteristics of human stance control. These subsystems are 1) a “sensory integration” mechanism whereby orientation information from multiple sensory systems encoding body kinematics (i.e. position, velocity) is flexibly combined to provide an overall estimate of body orientation while allowing adjustments (sensory re-weighting) that compensate for changing environmental conditions, and 2) an “effort control” mechanism that uses kinetic-related (i.e., force-related) sensory information to reduce the mean deviation of body orientation from upright. Functionally, ZMP compensation is directly analogous to how humans appear to use kinetic feedback to modify the main sensory integration feedback loop controlling body orientation. However, a flexible sensory integration mechanism is missing from robot control leaving the robot vulnerable to instability in conditions were humans are able to maintain stance. We suggest the addition of a simple form of sensory integration to improve robot stance control. We also investigate how the biological constraint of feedback time delay influences the human stance control design. The human system may serve as a guide for improved robot control, but should not be directly copied because the constraints on robot and human control are different.

Peterka, Robert J.

2009-01-01

18

Changes in posture associated with postural control impairment induced by ankle plantarflexor fatigue during unipedal quiet standing.  

PubMed

The aim of the present study was to investigate changes in joint angles and limb positions accompanying postural control impairments induced by fatigue of the ankle plantarflexor muscles and vision removal. Thirteen subjects performed unipedal standing tasks with and without vision before and after isometric fatigue of the plantarflexor muscles. Results indicated that to compensate for the negative effects of fatigue and vision removal on postural control, participants increased flexion at the ankle, knee and back while the free lower limb and the pelvis moved backward and the upper limbs forward. These strategies could be performed to increase the role of non-fatigued muscles and optimize the use of all the joints implicated in unipedal standing. PMID:23680463

Boyas, Sébastien; McGown, Cory; Lajoie, Yves; Bilodeau, Martin

2013-05-13

19

Effect of hip and ankle muscle fatigue on unipedal postural control  

Microsoft Academic Search

Fatigue and deficits in postural control may predispose musculoskeletal injury. The purpose of this study was to examine the effects of fatigue at the hip and ankle during frontal plane movements on postural control during single-leg stance. Thirteen healthy volunteers completed two testing sessions 1 week apart consisting of isokinetic fatigue of the frontal plane movers of either the ankle

Phillip A. Gribble; Jay Hertel

2004-01-01

20

Using a Stance Corpus to Learn about Effective Authorial Stance-Taking: A Textlinguistic Approach  

ERIC Educational Resources Information Center

|Presenting a persuasive authorial stance is a major challenge for second language (L2) writers in writing academic research. Failure to present an effective authorial stance often results in poor evaluation, which compromises a writer's research potential. This study proposes a "textlinguistic" approach to advanced academic writing to complement…

Chang, Peichin

2012-01-01

21

Characterizing Postural Sway during Quiet Stance Based on the Intermittent Control Hypothesis  

NASA Astrophysics Data System (ADS)

This article illustrates a signal processing methodology for the time series of postural sway and accompanied electromyographs from the lower limb muscles during quiet stance. It was shown that the proposed methodology was capable of identifying the underlying postural control mechanisms. A preliminary application of the methodology provided evidence that supports the intermittent control hypothesis alternative to the conventional stiffness control hypothesis during human quiet upright stance.

Nomura, Taishin; Nakamura, Toru; Fukada, Kei; Sakoda, Saburo

2007-07-01

22

Narrative Stance in the Douglass Autobiographies.  

ERIC Educational Resources Information Center

|To consider Frederick Douglass as an autobiographer, it is useful to examine each of his three autobiographical texts with a view to drawing some conclusion about their relation to one another, and about the relation of the author to each one. It seems likely that the shifting of Douglass' narrative stance is an index of his intellectual…

Davidson, Phebe

23

Stance in Spoken and Written University Registers  

ERIC Educational Resources Information Center

Numerous studies have investigated the linguistic expression of stance and evaluation in university registers, focusing especially on academic research writing and to a lesser extent classroom teaching. The present study extends previous research in two ways: (1) it compares and contrasts the use of a wide range of lexico-grammatical features used…

Biber, Douglas

2006-01-01

24

Broad Stance Conditions Change Postural Control and Postural Sway  

Microsoft Academic Search

Intuitively, a broad stance (i.e., standing with the feet farther apart than usual) should significantly improve postural stability. However, this intuition was not confirmed in quiet stance. Hence, a motion analysis system (markers attached to the trunk and head) and a force platform were used to investigate 13 healthy, young adults who performed 8 trials in standard and broad stances.

Cédrick T. Bonnet

2012-01-01

25

Reviewer Stances and Writer Perceptions in EFL Peer Review Training  

ERIC Educational Resources Information Center

Research has shown that reviewers' stances can impact the efficacy of peer response/review and subsequent revision. The purpose of this classroom-based study was to compare reviewer stances and writer perceptions of/and attitudes toward these stances prior to and after peer review training in an EFL writing class. Eighteen intermediate EFL writers…

Min, Hui-Tzu

2008-01-01

26

Methods for exploring expressive stance  

Microsoft Academic Search

Abstract The postures a character adopts over time are a key expressive aspect of its move- ment. While IK tools help a character achieve positioning constraints, there are few tools that help an animator with the expressive aspects of a character’s poses. Three aspects are required in good pose design: achieving a set of world space constraints, finding a body

Michael Neff; Eugene Fiume

2006-01-01

27

Methods for exploring expressive stance  

Microsoft Academic Search

The postures a character adopts over time are a key expressive aspect of her movement. While IK tools help a character achieve positioning constraints, there are few tools that help an animator with the expressive aspects of a character's poses. Three aspects are combined in good pose design: achieving a set of world space constraints, finding a body shape that

Michael Neff; Eugene Fiume

2004-01-01

28

Stance controlled knee flexion improves stimulation driven walking after spinal cord injury  

PubMed Central

Background Functional neuromuscular stimulation (FNS) restores walking function after paralysis from spinal cord injury via electrical activation of muscles in a coordinated fashion. Combining FNS with a controllable orthosis to create a hybrid neuroprosthesis (HNP) has the potential to extend walking distance and time by mechanically locking the knee joint during stance to allow knee extensor muscle to rest with stimulation turned off. Recent efforts have focused on creating advanced HNPs which couple joint motion (e.g., hip and knee or knee and ankle) to improve joint coordination during swing phase while maintaining a stiff-leg during stance phase. Methods The goal of this study was to investigate the effects of incorporating stance controlled knee flexion during loading response and pre-swing phases on restored gait. Knee control in the HNP was achieved by a specially designed variable impedance knee mechanism (VIKM). One subject with a T7 level spinal cord injury was enrolled and served as his own control in examining two techniques to restore level over-ground walking: FNS-only (which retained a stiff knee during stance) and VIKM-HNP (which allowed controlled knee motion during stance). The stimulation pattern driving the walking motion remained the same for both techniques; the only difference was that knee extensor stimulation was constant during stance with FNS-only and modulated together with the VIKM to control knee motion during stance with VIKM-HNP. Results Stance phase knee angle was more natural during VIKM-HNP gait while knee hyperextension persisted during stiff-legged FNS-only walking. During loading response phase, vertical ground reaction force was less impulsive and instantaneous gait speed was increased with VIKM-HNP, suggesting that knee flexion assisted in weight transfer to the leading limb. Enhanced knee flexion during pre-swing phase also aided flexion during swing, especially when response to stimulation was compromised. Conclusions These results show the potential advantages of incorporating stance controlled knee flexion into a hybrid neuroprosthesis for walking. The addition of such control to FNS driven walking could also enable non-level walking tasks such as uneven terrain, slope navigation and stair descent where controlled knee flexion during weight bearing is critical.

2013-01-01

29

Are knee mechanics during early stance related to tibial stress fracture in runners?  

Microsoft Academic Search

BackgroundTibial stress fractures are a serious overuse injury in runners. Greater vertical loading rates and tibial shock have been found in runners with previous tibial stress fracture compared to controls. The timing of these variables occurs very early in the stance phase and suggests that conditions shortly after footstrike may be important in determining injury risk. The purpose of this

Clare E. Milner; Joseph Hamill; Irene Davis

2007-01-01

30

Do footedness and strength asymmetry relate to the dominant stance in swimming track start?  

Microsoft Academic Search

This study explored the relationship between lower limb asymmetry and stance preference in the swimming track start. Track start performances and asymmetry measures were collected from 11 male and 11 female competitive age group swimmers. The track start performance was defined as the time taken to reach the 5-m mark. Asymmetry measures included assessment of footedness using the revised version

Julie Hardt; Nat Benjanuvatra; Brian Blanksby

2009-01-01

31

Interpreting the Need for Initial Support to Perform Tandem Stance Tests of Balance  

PubMed Central

Background Geriatric rehabilitation reimbursement increasingly requires documented deficits on standardized measures. Tandem stance performance can characterize balance, but protocols are not standardized. Objective The purpose of this study was to explore the impact of: (1) initial support to stabilize in position and (2) maximum hold time on tandem stance tests of balance in older adults. Design A cross-sectional secondary analysis of observational cohort data was conducted. Methods One hundred seventeen community-dwelling older adults (71% female, 12% black) were assigned to 1 of 3 groups based on the need for initial support to perform tandem stance: (1) unable even with support, (2) able only with support, and (3) able without support. The able without support group was further stratified on hold time in seconds: (1) <10 (low), (2) 10 to 29, (medium), and (3) 30 (high). Groups were compared on primary outcomes (gait speed, Timed “Up & Go” Test performance, and balance confidence) using analysis of variance. Results Twelve participants were unable to perform tandem stance, 14 performed tandem stance only with support, and 91 performed tandem stance without support. Compared with the able without support group, the able with support group had statistically or clinically worse performance and balance confidence. No significant differences were found between the able with support group and the unable even with support group on these same measures. Extending the hold time to 30 seconds in a protocol without initial support eliminated ceiling effects for 16% of the study sample. Limitations Small comparison groups, use of a secondary analysis, and lack of generalizability of results were limitations of the study. Conclusions Requiring initial support to stabilize in tandem stance appears to reflect meaningful deficits in balance-related mobility measures, so failing to consider support may inflate balance estimates and confound hold time comparisons. Additionally, 10-second maximum hold times limit discrimination of balance in adults with a higher level of function. For community-dwelling older adults, we recommend timing for at least 30 seconds and documenting initial support for consideration when interpreting performance.

Brach, Jennifer S.; Perera, Subashan; Wert, David M.; VanSwearingen, Jessie M.; Studenski, Stephanie A.

2012-01-01

32

Stance, Navigation, and Reader Response in Expository Hypertext  

ERIC Educational Resources Information Center

|This article reports on two studies investigating reader stance, navigation, and response in expository hypertext. Subjects in the studies included 69 and 147 adult readers prompted to adopt either an efferent or aesthetic stance when reading a 36-node expository hypertext. Reading was followed by recall and essay writing tasks. Results of the…

McEneaney, John E.; Li, Ledong; Allen, Kris; Guzniczak, Lizabeth

2009-01-01

33

Green career choices: The influence of ecological stance on recruiting  

Microsoft Academic Search

Ecological issues have become a growing concern to businesses. This experimental study examined the effect of a pro-environmental stance on the recruiting efforts of a fictitious firm. Results supported the idea that a proactive company stance on the environment would be positively related to perceived company attractiveness, intentions to pursue employment with that company, and acceptance of a job offer

Talya N. Bauer; Lynda Aiman-Smith

1996-01-01

34

Stance, Navigation, and Reader Response in Expository Hypertext  

ERIC Educational Resources Information Center

This article reports on two studies investigating reader stance, navigation, and response in expository hypertext. Subjects in the studies included 69 and 147 adult readers prompted to adopt either an efferent or aesthetic stance when reading a 36-node expository hypertext. Reading was followed by recall and essay writing tasks. Results of the…

McEneaney, John E.; Li, Ledong; Allen, Kris; Guzniczak, Lizabeth

2009-01-01

35

A neurological view on reactive human stance control  

Microsoft Academic Search

During biped stance or locomotion, humans show remarkable skills in reactive balancing upon external disturbances. Mainly four types of external disturbances are relevant for stance: the field force gravity, contact forces such as a push or pull against the body, as well as body support surface rotation and translational acceleration. It is known from clinics that sensory loss severely impairs

Thomas Mergner

2010-01-01

36

Modeling sensorimotor control of human upright stance.  

PubMed

We model human postural control of upright stance during external disturbances and voluntary lean. Our focus is on how data from various sensors are combined to estimate these disturbances. Whereas most current engineering models of multisensory estimation rely on "internal observers" and complex processing, we compute our estimates by simple sensor fusion mechanisms, i.e., weighted sums of sensory signals combined with thresholds. We show with simulations that this simple device mimics human-like postural behavior in a wide range of situations and diseases. We have now embodied our mechanism in a biped humanoid robot to show that it works in the real world with complex, noisy, and imperfectly known sensors and effectors. On the other hand, we find that the more complex, internal-observer approach, when applied to bipedal posture, can also yield human-like behavior. We suggest that humans use both mechanisms: simple, fast sensor fusions with thresholding for automatic reactions (default mechanism), and more complex methods for voluntary movements. We suggest also that the fusion with thresholding mechanisms are optimized during phylogenesis but are mainly hardwired in any one organism, whereas sensorimotor learning and optimization is mainly a domain of the internal observers. PMID:17925253

Mergner, Thomas

2007-01-01

37

Bilateral labyrinthectomy in the cat: motor behaviour and quiet stance parameters.  

PubMed

The purpose of this study was to examine the effect of bilateral labyrinthectomy on quiet stance in the freely-standing cat. Since loss of the vestibular end organs produces marked deficits in motor behaviour, including ataxia and problems with balance, we hypothesized that labyrinthectomized animals would show impairment in quantitative measures of stance. Stance was quantified in terms of the ground reaction forces under each limb and the tonic electromyographic (EMG) activity of selected muscles. Animals were labyrinthectomized by drilling into the vestibule and removing the vestibular epithelium. Following lesion, animals were able to stand unsupported on the force platform within 2 days. To our surprise, the lesioned animals showed little change in stance parameters from the control, pre-lesion state. Thus, our hypothesis of changes in stance parameters was not supported. There was no change in the distribution of vertical forces under the limbs and no increase in sway, as measured by the area of excursion of the centre of pressure over time. The horizontal plane forces, which were diagonally directed prior to lesion, became more laterally directed and larger in amplitude. The change in direction persisted even after the animals had fully compensated for the lesion, but the force amplitudes returned to control values within 10-12 days. The change in horizontal force direction was similar to that observed in normal animals that were required to stand with their paws closer than preferred in the sagittal plane (unpublished observations). EMG activity changed in some muscles but not others, and usually transiently.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1893985

Thomson, D B; Inglis, J T; Schor, R H; Macpherson, J M

1991-01-01

38

Joint coordination during quiet stance: effects of vision.  

PubMed

Stabilization of the center of mass (CM) is an important goal of the postural control system. Coordination of several joints along the human "pendulum" is required to achieve this goal. We studied the coordination among body segments with respect to horizontal CM stabilization during a quiet stance task and the effects of vision on CM stability. Subjects were asked to stand quietly on a narrow wooden block supporting only the mid-foot, with either open (EO) or closed (EC) eyes on separate trials. Instant equilibrium points (IEPs) in the center of pressure (CP) trajectory were determined when the horizontal component of the ground reaction force was zero and the CP data were decomposed into their rambling and trembling components. The joint angle, CM and CP data were divided into short cycles (time-normalized to 100 data points) or longer segments (time-normalized to 1000 data points) of equal length beginning and ending in an IEP. Motor abundance with respect to patterns of joint coordination was evaluated using the uncontrolled manifold (UCM) approach. Here, a UCM is a subspace spanning all joint combinations resulting in a given CM position. All combinations of joint angles that lie within this subspace are equivalent with respect to that CM position while joint angle combinations lying in a subspace orthogonal to the UCM lead to deviation from that CM position. UCM analysis was performed on data organized either across time within longer segments or at each point in time across multiple segments or across multiple cycles. Regardless of method of analysis, most of the variance in joint space was constrained to be within the UCM, preserving the mean CM position in both the EO and EC conditions. Joint configuration variance was significantly higher in the EC than in the EO condition although this increase occurred primarily within the UCM rather than in the orthogonal subspace that would have led to variation of the CM position. These results demonstrate the ability of the control system to selectively "channel" motor variability into directions in joint space that stabilize the CM position. This effect was enhanced when the task was made more challenging in the absence of vision. There was also a significant relationship between joint variance that led to a change in the CM position and, in particular, the rambling component of the CP path, lending some support to the idea that the CNS prescribes a certain stable trajectory of the CP during quiet stance that leads to a small controlled movement of the CM. PMID:15841397

Krishnamoorthy, Vijaya; Yang, Jeng-Feng; Scholz, John P

2005-04-20

39

Light touch contribution to balance in normal bipedal stance.  

PubMed

It has previously been shown that light contact with the finger tip on a fixed surface reduces centre of pressure (CoP) fluctuations in the frontal plane when standing in an unstable posture with the feet in line (tandem Romberg stance). Positive cross-correlations between horizontal finger forces and CoP fluctuations with finger forces exhibiting a phase lead suggest the hand provides sensory input for postural stability. The present study investigates whether this is the case for normal posture. We report reduced CoP fluctuations in the sagittal plane when light touch is permitted during normal bipedal stance. Moreover, we find positive crosscorrelations between finger tip forces and CoP fluctuations which are of similar magnitude and phase lag to those observed in tandem Romberg stance. This shows the utility of hand touch input for regulation of normal upright posture as well as inherently unstable postures such as tandem Romberg. PMID:10323300

Clapp, S; Wing, A M

1999-04-01

40

A Professional Stance for Positive Discipline — Promoting Learning  

Microsoft Academic Search

This writer offers advice on establish ing a professional stance to create effective learning atmospheres and positive discipline, He describes a structure for designing staff develop ment activities that focus on preven tive strategies and positive relation ships with all students.

John J. Schmidt

1989-01-01

41

Regulation of bipedal stance: dependency on “load” receptors  

Microsoft Academic Search

According to recent observations, influence of body load has to be taken into account for the neuronal control of upright stance in addition to the systems known to be involved in this regulation (e.g. afferent input from vestibular canals, visual and muscle stretch receptors). The modulation of compensatory leg muscle electromyographic (EMG) responses observed during horizontal body posture indicates the

V. Dietz; A. Gollhofer; M. Kleiber; M. Trippel

1992-01-01

42

Effects of utmost fatigue on undisturbed upright stance control  

Microsoft Academic Search

Aim. – To assess the effects of utmost fatigue on balance control in upright quiet stance.Method. – Eleven subjects performed a postural task before and after completing a long distance triathlon. The centre of pressure (CP) displacements was recorded through a force platform and decomposed from a biomechanical relationship into two elementary motions: the horizontal motions of the centre of

C. Burdet; P. Rougier

2004-01-01

43

The artistic design stance and the interpretation of Paleolithic art.  

PubMed

The artistic design stance is an important part of art appreciation, but it remains unclear how it can be applied to artworks for which art historical context is no longer available, such as Ice Age art. We propose that some of the designer's intentions can be gathered noninferentially through direct experience with prehistoric artworks. PMID:23507094

De Smedt, Johan; De Cruz, Helen

2013-04-01

44

A push and a shove and the land is ours: Morrissey's counter-hegemonic stance(s) on social class  

Microsoft Academic Search

We explore how the singer Morrissey has represented the struggles of the proletariat in creative and provocative ways, inviting a deep textual reading that reveals a complex counter-hegemonic stance on the issue of social class. A champion of the ‘Other’ in a variety of guises, Morrissey is revealed in this article as a raconteur of the marginalized working class. We

Martin J. Power; Aileen Dillane; Eoin Devereux

2012-01-01

45

Centre of pressure sway characteristics during static one-legged stance of athletes from different sports  

Microsoft Academic Search

The frequency of one-legged stance and two-legged stance differs considerably among sports. We therefore expect the balance ability of athletes from different sports to vary. This study compared the sway characteristics during a static one-legged stance of soccer players, basketball players, swimmers, and non-athletes. The centre of pressure sway during one-legged stance of ten male participants representing each of the

Shigeki Matsuda; Shinichi Demura; Masanobu Uchiyama

2008-01-01

46

Observational Stance as a Predictor of Subjective and Genital Sexual Arousal in Men and Women.  

PubMed

Observational stance refers to the perspective a person takes while viewing a sexual stimulus, either as a passive observer (observer stance) or an active participant (participant stance). The objective of the current study was to examine the relationship between observational stance and sexual arousal (subjective and genital) across a range of sexual stimuli that do or do not correspond with a participant's sexual attraction (preferred or nonpreferred stimuli, respectively). Regression analyses revealed that, for men (n = 44), participant stance significantly predicted subjective and genital arousal. Women's (n = 47) observer and participant stance predicted subjective arousal but not genital arousal. Analysis of variance showed that participant stance was greatest under preferred sexual stimuli conditions for all groups of participants, while observer stance scores revealed a less consistent pattern of response. This was particularly true for opposite-sex-attracted women, whose ratings of observer stance were lowest for preferred stimuli. Observational stance does not appear to account for gender differences in specificity of sexual arousal; for men, however, participant stance uniquely predicted genital response after controlling for sexual attractions. Similarities in the relationships between men's and women's observational stance and sexual responses challenge previous claims of gender differences in how men and women view erotica. PMID:23514448

Bossio, Jennifer A; Spape, Jessica; Lykins, Amy D; Chivers, Meredith L

2013-03-20

47

The analyst's stance and the method of free association.  

PubMed

The concept of the analyst's stance is employed to organize a number of ideas about psychoanalytic work, past and present, especially from the viewpoint of the method of free association. Beginning with an emphasis on the intrinsic uncertainties and paradoxes of the analytic process, the author reviews the importance of words, the aim of mastering resistances (i.e., promoting freedom of association), and functional neutrality on the analyst's part. The problem of anonymity is considered from a number of angles. Two traditions of transference are described, deriving from Freud's overlapping early formulations. The distinction between old and new determinants in the two kinds of transference is useful and important in the analyst's stance. Attitudes toward insight, resistance, and conflict resolution are considered from the perspective of the distinction between divergent and convergent conflicts, with special emphasis on the role of punitive, unconscious self-criticism. PMID:2251309

Kris, A O

1990-01-01

48

Selective utilization of spatial working memory resources during stance posture.  

PubMed

While it has been shown that visual imagery tasks interfere with balance control, the neural mechanisms underlying the interference are unclear. Within a healthy young adult population, we employed a dual-task methodology to investigate the role of visual working memory in stance postural control. The employment of specific visual object and visual spatial working memory cognitive tasks facilitated the selective activation of cortically dissociated working memory resources. Challenging postural sets did not significantly impact object working memory performance, but clearly degraded performance on a spatial working memory task, suggesting that interactions between stance postural control and visual working memory are limited to the spatial domain. Results demonstrated no significant effect of the cognitive tasks upon postural stability. PMID:15858423

VanderVelde, Timothy J; Woollacott, Marjorie H; Shumway-Cook, Anne

2005-05-12

49

Taking the intentional stance at 12 months of age  

Microsoft Academic Search

This paper reports a habituation study indicating that 12-month-old infants can take the “intentional stance” in interpreting the goal-directed spatial behavior of a rational agent. First, we examine previous empirical claims suggesting that the ability to attribute intentions to others emerges during the second half of the first year. It is argued that neither the perceptual evidence (concerning the early

György Gergely; Zoltán Nádasdy; Gergely Csibra; Szilvia Bíró

1995-01-01

50

Light touch contribution to balance in normal bipedal stance  

Microsoft Academic Search

It has previously been shown that light contact with the finger tip on a fixed surface reduces centre of pressure (CoP) fluctuations\\u000a in the frontal plane when standing in an unstable posture with the feet in line (tandem Romberg stance). Positive cross-correlations\\u000a between horizontal finger forces and CoP fluctuations with finger forces exhibiting a phase lead suggest the hand provides

Sally Clapp; Alan M. Wing

1999-01-01

51

Influence of sprint acceleration stance kinetics on velocity and step kinematics in field sport athletes.  

PubMed

The interaction between step kinematics and stance kinetics determines sprint velocity. However, the influence that stance kinetics has on effective acceleration in field sport athletes requires clarification. About 25 men (age = 22.4 ± 3.2 years; mass = 82.8 ± 7.2 kg; height = 1.81 ± 0.07 m) completed twelve 10-m sprints, 6 sprints each for kinematic and kinetic assessment. Pearson's correlations (p ? 0.05) examined relationships between 0-5, 5-10, and 0-10 m velocity; step kinematics (mean step length [SL], step frequency, contact time [CT], flight time over each interval); and stance kinetics (relative vertical, horizontal, and resultant force and impulse; resultant force angle; ratio of horizontal to resultant force [RatF] for the first, second, and last contacts within the 10-m sprint). Relationships were found between 0-5, 5-10, and 0-10 m SL and 0-5 and 0-10 m velocity (r = 0.397-0.535). CT of 0-5 and 0-10 m correlated with 5-10 m velocity (r = -0.506 and -0.477, respectively). Last contact vertical force correlated with 5-10 m velocity (r = 0.405). Relationships were established between the second and last contact vertical and resultant force and CT over all intervals (r = -0.398 to 0.569). First and second contact vertical impulse correlated with 0-5 m SL (r = 0.434 and 0.442, respectively). Subjects produced resultant force angles and RatF suitable for horizontal force production. Faster acceleration in field sport athletes involved longer steps, with shorter CT. Greater vertical force production was linked with shorter CT, illustrating efficient force production. Greater SLs during acceleration were facilitated by higher vertical impulse and appropriate horizontal force. Speed training for field sport athletes should be tailored to encourage these technique adaptations. PMID:23222091

Lockie, Robert G; Murphy, Aron J; Schultz, Adrian B; Jeffriess, Matthew D; Callaghan, Samuel J

2013-09-01

52

A robotic cadaveric flatfoot analysis of stance phase.  

PubMed

The symptomatic flatfoot deformity (pes planus with peri-talar subluxation) can be a debilitating condition. Cadaveric flatfoot models have been employed to study the etiology of the deformity, as well as invasive and noninvasive surgical treatment strategies, by evaluating bone positions. Prior cadaveric flatfoot simulators, however, have not leveraged industrial robotic technologies, which provide several advantages as compared with the previously developed custom fabricated devices. Utilizing a robotic device allows the researcher to experimentally evaluate the flatfoot model at many static instants in the gait cycle, compared with most studies, which model only one to a maximum of three instances. Furthermore, the cadaveric tibia can be statically positioned with more degrees of freedom and with a greater accuracy, and then a custom device typically allows. We created a six degree of freedom robotic cadaveric simulator and used it with a flatfoot model to quantify static bone positions at ten discrete instants over the stance phase of gait. In vivo tibial gait kinematics and ground reaction forces were averaged from ten flatfoot subjects. A fresh frozen cadaveric lower limb was dissected and mounted in the robotic gait simulator (RGS). Biomechanically realistic extrinsic tendon forces, tibial kinematics, and vertical ground reaction forces were applied to the limb. In vitro bone angular position of the tibia, calcaneus, talus, navicular, medial cuneiform, and first metatarsal were recorded between 0% and 90% of stance phase at discrete 10% increments using a retroreflective six-camera motion analysis system. The foot was conditioned flat through ligament attenuation and axial cyclic loading. Post-flat testing was repeated to study the pes planus deformity. Comparison was then made between the pre-flat and post-flat conditions. The RGS was able to recreate ten gait positions of the in vivo pes planus subjects in static increments. The in vitro vertical ground reaction force was within ± 1 standard deviation (SD) of the in vivo data. The in vitro sagittal, coronal, and transverse plane tibial kinematics were almost entirely within ± 1 SD of the in vivo data. The model showed changes consistent with the flexible flatfoot pathology including the collapse of the medial arch and abduction of the forefoot, despite unexpected hindfoot inversion. Unlike previous static flatfoot models that use simplified tibial degrees of freedom to characterize only the midpoint of the stance phase or at most three gait positions, our simulator represented the stance phase of gait with ten discrete positions and with six tibial degrees of freedom. This system has the potential to replicate foot function to permit both noninvasive and surgical treatment evaluations throughout the stance phase of gait, perhaps eliciting unknown advantages or disadvantages of these treatments at other points in the gait cycle. PMID:21599096

Jackson, Lyle T; Aubin, Patrick M; Cowley, Matthew S; Sangeorzan, Bruce J; Ledoux, William R

2011-05-01

53

The effect of boundary shape and minima selection on single limb stance postural stability.  

PubMed

The effect of time-to-boundary minima selection and stability limit definition was investigated during eyes open and eyes closed condition single-limb stance postural stability. Anteroposterior and mediolateral time-to-boundary were computed using the mean and standard deviation (SD) of all time-to-boundary minima during a trial, and the mean and SD of only the 10 absolute time-to-boundary minima. Time-to-boundary with rectangular, trapezoidal, and multisegmented polygon defined stability limits were also calculated. Spearman's rank correlation coefficient test results revealed significant medium-large correlations between anteroposterior and mediolateral time-to-boundary scores calculated using both the mean and SD of the 10 absolute time-to-boundary minima and of all the time-to-boundary minima. Friedman test results revealed significant mediolateral time-to-boundary differences between boundary shape definitions. Follow-up Wilcoxon signed rank test results revealed significant differences between the rectangular boundary shape and both the trapezoidal and multisegmented polygon shapes during the eyes open and eyes closed conditions when both the mean and the SD of the time-to-boundary minima were used to represent postural stability. Significant differences were also revealed between the trapezoidal and multisegmented polygon definitions during the eyes open condition when the SD of the time-to-boundary minima was used to represent postural stability. Based on these findings, the overall results (i.e., stable versus unstable participants or groups) of studies computing postural stability using different minima selection can be compared. With respect to boundary shape, the trapezoid or multisegmented polygon shapes may be more appropriate than the rectangular shape as they more closely represent the anatomical shape of the stance foot. PMID:23193068

Cobb, Stephen C; Joshi, Mukta N; Bazett-Jones, David M; Earl-Boehm, Jennifer E

2012-11-01

54

Modelling 3D control of upright stance using an optimal control strategy.  

PubMed

A 3D balance control model of quiet upright stance is presented, based on an optimal control strategy, and evaluated in terms of its ability to simulate postural sway in both the anterior-posterior and medial-lateral directions. The human body was represented as a two-segment inverted pendulum. Several assumptions were made to linearise body dynamics, for example, that there was no transverse rotation during upright stance. The neural controller was presumed to be an optimal controller that generates ankle control torque and hip control torque according to certain performance criteria. An optimisation procedure was used to determine the values of unspecified model parameters including random disturbance gains and sensory delay times. This model was used to simulate postural sway behaviours characterised by centre-of-pressure (COP)-based measures. Confidence intervals for all normalised COP-based measures contained unity, indicating no significant differences between any of the simulated COP-based measures and corresponding experimental references. In addition, mean normalised errors for the traditional measures were < 8%, and those for most statistical mechanics measures were ?3-66%. On the basis these results, the proposed 3D balance control model appears to have the ability to accurately simulate 3D postural sway behaviours. PMID:21598131

Qu, Xingda; Nussbaum, Maury A

2011-05-23

55

Stance and swing phase costs in human walking  

PubMed Central

Leg swing in human walking has historically been viewed as a passive motion with little metabolic cost. Recent estimates of leg swing costs are equivocal, covering a range from 10 to 33 per cent of the net cost of walking. There has also been a debate as to whether the periods of double-limb support during the stance phase dominate the cost of walking. Part of this uncertainty is because of our inability to measure metabolic energy consumption in individual muscles during locomotion. Therefore, the purpose of this study was to investigate the metabolic cost of walking using a modelling approach that allowed instantaneous energy consumption rates in individual muscles to be estimated over the full gait cycle. At a typical walking speed and stride rate, leg swing represented 29 per cent of the total muscular cost. During the stance phase, the double-limb and single-limb support periods accounted for 27 and 44 per cent of the total cost, respectively. Performing step-to-step transitions, which encompasses more than just the double-support periods, represented 37 per cent of the total cost of walking. Increasing stride rate at a constant speed led to greater double-limb support costs, lower swing phase costs and no change in single-limb support costs. Together, these results provide unique insight as to how metabolic energy is expended over the human gait cycle.

Umberger, Brian R.

2010-01-01

56

Using Metrics to Describe the Participative Stances of Members Within Discussion Forums  

PubMed Central

Background Researchers using forums and online focus groups need to ensure they are safe and need tools to make best use of the data. We explored the use of metrics that would allow better forum management and more effective analysis of participant contributions. Objective To report retrospectively calculated metrics from self-harm discussion forums and to assess whether metrics add to other methods such as discourse analysis. We asked (1) which metrics are most useful to compare and manage forums, and (2) how metrics can be used to identify the participative stances of members to help manage discussion forums. Methods We studied the use of metrics in discussion forums on self-harm. SharpTalk comprised five discussion forums, all using the same software but with different forum compositions. SharpTalk forums were similar to most moderated forums but combined support and general social chat with online focus groups discussing issues on self-harm. Routinely recorded time-stamp data were used to derive metrics of episodes, time online, pages read, and postings. We compared metrics from the forums with views from discussion threads and from moderators. We identified patterns of participants’ online behavior by plotting scattergrams and identifying outliers and clusters within different metrics. Results In comparing forums, important metrics seem to be number of participants, number of active participants, total time of all participants logged on in each 24 hours, and total number of postings by all participants in 24 hours. In examining participative stances, the important metrics were individuals’ time logged per 24 hours, number of episodes, mean length of episodes, number of postings per 24 hours, and location within the forum of those postings. Metric scattergrams identified several participative stances: (1) the “caretaker,” who was “always around,” logged on for a much greater time than most other participants, posting but mainly in response to others and rarely initiating threads, (2) the “butterfly,” who “flitted in and out,” had a large number of short episodes, (3) two “discussants,” who initiated many more discussion threads than anybody else and posted proportionately less in the support room, (4) “here for you,” who posted frequently in the support room in response to other participants’ threads, and (5) seven “people in distress,” who posted many comments in the support room in comparison with their total postings and tended to post on their own threads. Conclusions Real-time metrics may be useful: (1) by offering additional ways of comparing different discussion forums helping with their management, and (2) by identifying participative stances of individuals so allowing better moderation and support of forums, and more effective use of the data collected. For this to happen, researchers need to publish metrics for their discussion forums and software developers need to offer more real-time metrics facilities.

Sharkey, Siobhan; Smithson, Janet; Ford, Tamsin; Emmens, Tobit; Hewis, Elaine; Sheaves, Bryony; Owens, Christabel

2011-01-01

57

Potential roles of force cues in human stance control.  

PubMed

Human stance is inherently unstable. A small deviation from upright body orientation is enough to yield a gravitational component in the ankle joint torque, which tends to accelerate the body further away from upright ('gravitational torque'; magnitude is related to body-space lean angle). Therefore, to maintain a given body lean position, a corresponding compensatory torque must be generated. It is well known that subjects use kinematic sensory information on body-space lean from the vestibular system for this purpose. Less is known about kinetic cues from force/torque receptors. Previous work indicated that they are involved in compensating external contact forces such as a pull or push having impact on the body. In this study, we hypothesized that they play, in addition, a role when the vestibular estimate of the gravitational torque becomes erroneous. Reasons may be sudden changes in body mass, for instance by a load, or an impairment of the vestibular system. To test this hypothesis, we mimicked load effects on the gravitational torque in normal subjects and in patients with chronic bilateral vestibular loss (VL) with eyes closed. We added/subtracted extra torque to the gravitational torque by applying an external contact force (via cable winches and a body harness). The extra torque was referenced to body-space lean, using different proportionality factors. We investigated how it affected body-space lean responses that we evoked using sinusoidal tilts of the support surface (motion platform) with different amplitudes and frequencies (normals +/-1 degrees, +/-2 degrees, and +/-4 degrees at 0.05, 0.1, 0.2, and 0.4 Hz; patients +/-1 degrees and +/-2 degrees at 0.05 and 0.1 Hz). We found that added/subtracted extra torque scales the lean response in a systematic way, leading to increase/decrease in lean excursion. Expressing the responses in terms of gain and phase curves, we compared the experimental findings to predictions obtained from a recently published sensory feedback model. For the trials in which the extra torque tended to endanger stance control, predictions in normals were better when the model included force cues than without these cues. This supports our notion that force cues provide an automatic 'gravitational load compensation' upon changes in body mass in normals. The findings in the patients support our notion that the presumed force cue mechanism provides furthermore vestibular loss compensation. Patients showed a body-space stabilization that cannot be explained by ankle angle proprioception, but must involve graviception, most likely by force cues. Our findings suggest that force cues contribute considerably to the redundancy and robustness of the human stance control system. PMID:19219426

Cnyrim, Christian; Mergner, Thomas; Maurer, Christoph

2009-02-14

58

Influence of body position on fibularis longus and soleus Hoffmann reflexes.  

PubMed

It is widely accepted that Hoffmann (H) reflex amplitudes of the soleus decrease as complexity of body positions increases, but it is not known if this same mechanism of postural control is seen in other ankle muscles such as fibularis longus (FL). Our purpose was to assess if FL H-reflex changed in different body positions and if the adaptations were correlated to soleus H-reflex modulation. Fifteen healthy subjects had their FL and soleus H-reflexes measured in three positions (prone, bipedal, unipedal). Maximal H-reflexes (H-max) and motor responses (M-max) were collected bilaterally. The average H-max and M-max were used to calculate H(max)/M(max) ratios. To control influences of background muscle activity on H-reflex measures, the ratios were normalized to their corresponding mean EMG amplitudes over a 50-ms time epoch. H-reflex amplitudes of both muscles were significantly lower in unipedal stance than other positions. Additionally, there were strong correlations (R(2)>0.7) in H-reflex modulation between the two muscles when transitioning from prone to either bipedal or unipedal stance. Down-modulation of H-reflex when transitioning to unipedal stance was present in both FL and soleus suggesting that H-reflex modulation of both muscles may play a similar role in control of upright posture. PMID:22795783

Kim, Kyung-Min; Hart, Joseph M; Hertel, Jay

2012-07-12

59

Risk Taking in Late Adolescence: Relations between Sociomoral Reasoning, Risk Stance, and Behavior  

ERIC Educational Resources Information Center

|This study explored relations among late adolescents' sociomoral reasoning about risk taking, risk stance, and behavior. One-hundred and thirty-two participants (18-20-year-olds) were surveyed about their own risk stance (Avoidant, Opportunistic, Curious, Risk Seeking) and behavior in three realms (Alcohol Use, Drug Use, Reckless Driving), and…

Shaw, Leigh A.; Amsel, Eric; Schillo, Joshua

2011-01-01

60

"This Project Has Personally Affected Me": Developing a Critical Stance in Preservice English Teachers  

ERIC Educational Resources Information Center

This study draws from a number of researchers who push for critical literacy and a critical stance to question power, inequality, and the status quo; to understand scholars' own participation in power structures; and to reframe and retheorize scholars' beliefs and understandings. In this article, the author uses the critical stance framework to…

Scherff, Lisa

2012-01-01

61

Pedagogical Stances of High School ESL Teachers: Huelgas in High School ESL Classrooms  

Microsoft Academic Search

This article presents a qualitative case study of the pedagogical stances of high school English as a Second Language (ESL) teachers, and the subsequent responses of resistance or conformity by their English Language Learners (ELLs). The participants include three high school ESL teachers and 60 high school ESL students of Mexican origin. Findings indicate that dehumanizing pedagogical stances by ESL

María del Carmen Salazar

2010-01-01

62

The duration and plantar pressure distribution during one-leg stance in Tai Chi exercise  

Microsoft Academic Search

BackgroundTai Chi exercise improved the balance control and muscle strength of the lower extremities. The aim of this study is to quantify the one-leg stance duration and plantar pressure distribution during the one-leg stance in Tai Chi and to try to elaborate on its probable effects on the ability to balance on one leg.

D. W. Mao; J. X. Li; Y. Hong

2006-01-01

63

The effect of stance width on trunk kinematics and trunk kinetics during sagitally symmetric lifting  

Microsoft Academic Search

Lifting technique can have a significant impact on spine loading during lifting. The sports biomechanics literature has documented changes in trunk and lower extremity kinematics and muscle coactivation patterns as a function of stance width during high force dead lift and squat exercises. The focus of the current study was to explore whether these lifting stance width effects might translate

Christopher J. Sorensen; Omid Haddad; Samuel Campbell; Gary A. Mirka

2011-01-01

64

Links between parents' epistemological stance and children's evidence talk.  

PubMed

Recent experimental research highlights young children's selectivity in learning from others. Little is known, however, about the patterns of information that children actually encounter in conversations with adults. This study investigated variation in parents' tendency to focus on testable evidence as a way to answer science-related questions (e.g., causes of climate change, extinction of species) and asked whether this is related to children's own use of evidence in conversation. Parents read a science-themed book with their 4- to 8-year-old children. Guided by D. Kuhn's framework of epistemological stances, we coded (a) parents' expressions of epistemology-related information (e.g., using evidence to reason about an opinion, appealing to statements of fact that do not need evidence, or pointing out that knowing for sure may not be possible) while discussing four science-related topics and (b) children's comments about evidence for two different science-related topics. We found variation in parents' expressions of epistemological information by children's age and gender for particular topics. Also, parents' expressions of evaluativist epistemology (expressing the value of reasoning with evidence) were correlated with children's talk about evidence. To the extent that children experience different conversational environments, they may seek different types of answers to questions, become familiar with different ways of thinking about "knowing," and develop different strategies for being selective about learning from the testimony of others. PMID:23244409

Luce, Megan R; Callanan, Maureen A; Smilovic, Sarah

2012-12-17

65

Influence of visual scene velocity on segmental kinematics during stance  

PubMed Central

We investigated how the velocity of anterior-posterior movement of a visual surround affected segmental kinematics during stance. Ten healthy young adults were exposed to sinusoidal oscillation of an immersive virtual scene at 5 peak velocities ranging from 1.2 to 188 cm/s at each of 4 frequencies: 0.05, 0.1, 0.2 and 0.55 Hz. Root mean square (RMS) values of head, trunk, thigh and shank angular displacements were calculated. RMS values of head-neck, hip, knee and ankle joint angles were also calculated. RMS values of head, trunk, thigh and shank displacements exhibited significant increases at a scene velocity of 188 cm/s when compared with lower scene velocities. RMS values of hip, knee and ankle joint angles exhibited significant increases at scene velocities of 125 and 188 cm/s when compared with lower scene velocities. These results suggest that visual cues continued to drive postural adjustments even during high velocity movement of the virtual scene. Significant increases in the RMS values of the lower-limb joint angles suggest that as visually-induced postural instability increased, the body was primarily controlled as a multi-segmental structure instead of a single-link inverted pendulum, with the knee playing a key role in postural stabilization.

Dokka, Kalpana; Kenyon, Robert V.; Keshner, Emily A.

2009-01-01

66

Influence of voluntary teeth clenching on the stabilization of postural stance disturbed by electrical stimulation of unilateral lower limb.  

PubMed

Studies on the relationship between dental occlusion and body balance have suggested that occlusion status contributes to the maintenance of postural balance. However, little has been reported about the effects of voluntary teeth clenching on the stabilization of postural stance in novel environments. In the present study we investigated whether teeth clenching influenced adaptation to the perturbation introduced by electrical stimulation of a unilateral lower limb. Subjects (12 adults) stood on a force plate, from which motion data were obtained in the horizontal plane with and without voluntary teeth clenching and were instructed to maintain the position throughout the experiment. We evoked a novel environment by supramaximal percutaneous electrical stimulation of the common peroneal nerve. Electromyograms (EMG) were recorded from the masseter and the peroneus longus (PL) muscles with bipolar surface cup electrodes. When the disturbed postural stance was generated by electrical stimulation, the maximum reaction force in the anterior-posterior (A/P) direction with teeth clenching (CL) was significantly smaller than that without voluntary teeth clenching (control; CO) (p<0.05) and the peak time of the ground reaction force/body mass (GRF/BM) in the A/P direction occurred earlier in the CL condition than CO (p<0.05). There were no significant differences in the peak-to-peak amplitude of GRF/BM and the peak time of GRF/BM, in the M/L direction under both CL and CO conditions. Thus, the present study showed that voluntary teeth clenching contributed to stabilization of the postural stance perturbed transiently by electrical stimulation. We concluded that voluntary teeth clenching plays an important role in rapid postural adaptation to the anterior-posterior perturbation in the upright position. PMID:19879763

Fujino, Sachiko; Takahashi, Toshiyuki; Ueno, Toshiaki

2009-10-30

67

Reading Student Writing with Anthropologists: Stance and Judgment in College Writing  

ERIC Educational Resources Information Center

This article describes how readers from a graduate program in anthropology evaluated student writing in a general education course. Readers voiced the concerns of their discipline when they focused on the stance writers assumed and how they made value judgments.

Soliday, Mary

2004-01-01

68

Task-specific Stabilization of Postural Coordination During Stance on a Beam  

Microsoft Academic Search

Surfaces shorter in extent than the feet elicit multi-joint coordination that differs from what is elicited by stance on extensive surfaces. This well-known effect arises from the mechanics of the actor-environment interaction. Multi-joint control of stance is also known to be influenced by non-mechanical aspects of a situation, including participants' task or intention. Intentional constraints do not originate in mechanics,

Olivier Oullier; Benoît G. Bardy; Thomas A. Stoffregen; Reinoud J. Bootsma

2004-01-01

69

Influence of enhanced visual feedback on postural control and spinal reflex modulation during stance  

Microsoft Academic Search

The present study assessed the influence of visual feedback on stance stability and soleus H-reflex excitability. The centre\\u000a of pressure (COP) displacement was measured in upright stance on a rigid surface (stable surface) and on a spinning top (unstable\\u000a surface) while subjects either received “normal” visual feedback (without laser pointer = WLP) or pointed with a laser pointer\\u000a on a target on

Wolfgang Taube; Christian Leukel; Albert Gollhofer

2008-01-01

70

Influence of Obesity and Gender on the Postural Stability during Upright Stance  

Microsoft Academic Search

SummaryObjective: To assess the influence of BMI group (lean\\/overweight\\/obese) and gender on the postural sway of adults and adolescents during quiet upright stance. Methods: 90 women and 90 men, aged 12 to 67 years old, accepted to participate. The center of pressure during quiet upright stance was recorded using a force platform, during 4 conditions (eyes open\\/closed on hard\\/soft surface).

Nora S. Cruz-Gómez; Georgina Plascencia; Laura A. Villanueva-Padrón; Kathrine Jáuregui-Renaud

2011-01-01

71

Development of a mechatronic platform and validation of methods for estimating ankle stiffness during the stance phase of walking.  

PubMed

The mechanical properties of human joints (i.e., impedance) are constantly modulated to precisely govern human interaction with the environment. The estimation of these properties requires the displacement of the joint from its intended motion and a subsequent analysis to determine the relationship between the imposed perturbation and the resultant joint torque. There has been much investigation into the estimation of upper-extremity joint impedance during dynamic activities, yet the estimation of ankle impedance during walking has remained a challenge. This estimation is important for understanding how the mechanical properties of the human ankle are modulated during locomotion, and how those properties can be replicated in artificial prostheses designed to restore natural movement control. Here, we introduce a mechatronic platform designed to address the challenge of estimating the stiffness component of ankle impedance during walking, where stiffness denotes the static component of impedance. The system consists of a single degree of freedom mechatronic platform that is capable of perturbing the ankle during the stance phase of walking and measuring the response torque. Additionally, we estimate the platform's intrinsic inertial impedance using parallel linear filters and present a set of methods for estimating the impedance of the ankle from walking data. The methods were validated by comparing the experimentally determined estimates for the stiffness of a prosthetic foot to those measured from an independent testing machine. The parallel filters accurately estimated the mechatronic platform's inertial impedance, accounting for 96% of the variance, when averaged across channels and trials. Furthermore, our measurement system was found to yield reliable estimates of stiffness, which had an average error of only 5.4% (standard deviation: 0.7%) when measured at three time points within the stance phase of locomotion, and compared to the independently determined stiffness values of the prosthetic foot. The mechatronic system and methods proposed in this study are capable of accurately estimating ankle stiffness during the foot-flat region of stance phase. Future work will focus on the implementation of this validated system in estimating human ankle impedance during the stance phase of walking. PMID:23719922

Rouse, Elliott J; Hargrove, Levi J; Perreault, Eric J; Peshkin, Michael A; Kuiken, Todd A

2013-08-01

72

Wavelet-based intensity analysis of mechanomyographic signals during single-legged stance following fatigue.  

PubMed

The von Tscharner (2000) "intensity analysis" describes the power of a non-stationary signal as a function of both frequency and time. The present study applied a version of this intensity analysis that utilizes Morlet wavelets as a means of gaining insight into the application of this technique as alternative to power spectral analysis for the evaluation of postural control strategy during the single-legged stance and to examine the effects of fatigue. Ten subjects (gender balanced, age: 25±3 years; height: 169.4±11.7 cm; weight: 79.0±16.9 kg) participated in two trials consisting of five 15-s dominant-leg stances. Three-uniaxial accelerometers were fixed to the surface of the dominant leg corresponding to VM, VL, SOL, and MMG was recorded at a sampling rate of 1000 Hz. Signals were later analyzed using a variation of the von Tscharner intensity analysis consisting of a filter bank of 11 Morlet wavelets (range: 2.1-131.1Hz). Two Wingate anaerobic tests (WAnT) separated by a 2-min rest were performed to introduce fatigue. Repeated measures ANOVAs showed significant effects for time, gender, trial, and wavelet (p<0.001) and significant interactions for muscle by wavelet, gender by trial, trial by wavelet, and gender by trial by wavelet (p<0.001). Peak total MMG intensity (mean±SD) was higher in males than females and higher following fatiguing exercise preWAnT (squared ms(-2)): 42.6±4.5 vs. 19.2±2.3; postWAnT (squared ms(-2)): 90.4±9.1 vs. 28.4±2.8. Peak total MMG intensity was compressed to the lower frequencies surrounding ?12 Hz, corresponding to what might be considered physiologic tremor, and a lower peak at ?42 Hz was most prominent in SOL. The intensity analysis is a useful tool in exploring postural control and in studying the effects of fatigue on the mechanical properties of skeletal muscle. PMID:21708471

Armstrong, W Jeffrey

2011-06-25

73

In vivo length patterns of the medial collateral ligament during the stance phase of gait  

PubMed Central

Purpose The function of the medial collateral ligament (MCL) during gait has not been investigated. Our objective was to measure the kinematics of the medial collateral ligament during the stance phase of gait on a treadmill using a combined dual fluoroscopic imaging system (DFIS) and MRI technique. Methods Three-dimensional models of the knee were constructed using magnetic resonance images of 7 healthy human knees. The contours of insertion areas of the superficial MCL (sMCL) and deep MCL (dMCL) on the femur and tibia were constructed using the coronal plane MR images of each knee. Both the sMCL and the dMCL were separated into 3 portions: the anterior, mid, and posterior bundles. The relative elongation of the bundles was calculated using the bundle length at heel strike (or 0% of the stance phase) as a reference. Results The lengths of the anterior bundles were positively correlated with the knee flexion angle. The mid-bundles of the sMCL and dMCL were found to function similarly in trend with the anterior bundles during the stance phase of the gait and their lengths had weak correlations with the knee flexion angles. The elongations of the posterior bundles of sMCL and dMCL were peaked at mid-stance and terminal extension/pre-swing stance phase. The lengths of the posterior bundles were negatively correlated with the knee flexion during the stance phase. Conclusion The data of this study demonstrated that the anterior and posterior bundles of the sMCL and dMCL have a reciprocal function during the stance phase of gait. This data provide insight into the function of the MCL and a normal reference for the study of physiology and pathology of the MCL. The data may be useful in designing reconstruction techniques to better reproduce the native biomechanical behavior of the MCL. Level of evidence IV.

Liu, Fang; Gadikota, Hemanth R.; Kozanek, Michal; Hosseini, Ali; Yue, Bing; Gill, Thomas J.; Rubash, Harry E.; Li, Guoan

2011-01-01

74

A markerless estimation of the ankle-foot complex 2D kinematics during stance.  

PubMed

A markerless technique is proposed and applied to estimate the two-dimensional joint kinematics of the shank and foot complex during the stance phase. Image sequences were acquired with a single camera from three healthy subjects while walking barefoot and with socks. Automatic segmentation of the shank and foot was performed to isolate the moving body from the background. A multi-rigid body model for the shank and foot complex, with the relevant segment anatomical axes, was defined and an image cross-correlation technique was applied to detect the anatomical axes locations throughout the movement. The proposed markerless technique was validated by acquiring the same trials also with a stereophotogrammetric marker-based system and a simple marker set. Differences in the joint kinematics estimates obtained with the two techniques fall in most cases within the intra-subject variability showing that, in selected applications, the markerless technique may replace more expensive and more experimental time demanding marker-based techniques. PMID:21295984

Surer, Elif; Cereatti, Andrea; Grosso, Enrico; Della Croce, Ugo

2011-02-04

75

Bone contact forces on the distal tibia during the stance phase of running.  

PubMed

Although the tibia is a common site of stress fractures in runners, the loading of the tibia during running is not well understood. An integrated experimental and modeling approach was therefore used to estimate the bone contact forces acting on the distal end of the tibia during the stance phase of running, and the contributions of external and internal sources to these forces. Motion capture and force plate data were recorded for 10 male runners as they ran at 3.5-4 m/s. From these data, the joint reaction force (JRF), muscle forces, and bone contact force on the tibia were computed at the ankle using inverse dynamics and optimization methods. The distal end of the tibia was compressed and sheared posteriorly throughout most of stance, with respective peak forces of 9.00+/-1.13 and 0.57+/-0.18 body weights occurring during mid stance. Internal muscle forces were the primary source of tibial compression, whereas the JRF was the primary source of tibial shear due to the forward inclination of the leg relative to the external ground reaction force. The muscle forces and JRF both acted to compress the tibia, but induced tibial shear forces in opposing directions during stance, magnifying tibial compression and reducing tibial shear. The superposition of the peak compressive and posterior shear forces at mid stance may contribute to stress fractures in the posterior face of the tibia. The implications are that changes in running technique could potentially reduce stress fracture risk. PMID:17662295

Sasimontonkul, Siriporn; Bay, Brian K; Pavol, Michael J

2007-07-26

76

Single stance stability and proprioceptive control in older adults living at home: gender and age differences.  

PubMed

In developed countries, falls in older people represent a rising problem. As effective prevention should start before the risk becomes evident, an early predictor is needed. Single stance instability would appear as a major risk factor. Aims of the study were to describe single stance stability, its sensory components, and their correlation with age and gender. A random sample of 597 older adults (319 men, 278 women) living at home, aged 65-84, was studied. Stability tests were performed with an electronic postural station. The single stance test showed the impairment of single stance stability in older individuals (75-84?yrs). The significant decline of stability in the older subjects may be explained by the impairment of proprioceptive control together with the decrease in compensatory visual stabilization and emergency responses. Younger subjects (65-74?yrs) exhibited better, but still inadequate, proprioceptive control with compensatory visual stabilization. Gender differences appeared in older subjects: women were significantly less stable than men. The measurement of the sensory components of single stance stability could aid in the early detection of a decay in antigravity movements many years before the risk of falling becomes evident. Adequate proprioceptive control could mitigate the effects of all other risks of falling. PMID:23984068

Riva, Dario; Mamo, Carlo; Fanì, Mara; Saccavino, Patrizia; Rocca, Flavio; Momenté, Manuel; Fratta, Marianna

2013-07-28

77

Centre of pressure sway characteristics during static one-legged stance of athletes from different sports.  

PubMed

The frequency of one-legged stance and two-legged stance differs considerably among sports. We therefore expect the balance ability of athletes from different sports to vary. This study compared the sway characteristics during a static one-legged stance of soccer players, basketball players, swimmers, and non-athletes. The centre of pressure sway during one-legged stance of ten male participants representing each of the four groups was measured using a stabilometer. Centre of pressure sway was assessed by four sway factors: sway velocity, anterior-posterior sway, horizontal sway, and high-frequency sway. None of the four groups of participants showed significant differences in body sway between standing on the dominant leg and standing on the non-dominant leg. The soccer players had more high-frequency sway and less anterior-posterior sway and horizontal sway than the basketball players, swimmers, and non-athletes. These results suggest that soccer players have superior ability to maintain a stable one-legged stance. Further study is required to determine how much of the superior balance ability in soccer players is innate and how much is developed through training, as well as to determine the relationship between balance ability and playing performance. PMID:18409108

Matsuda, Shigeki; Demura, Shinichi; Uchiyama, Masanobu

2008-05-01

78

Design and quantitative evaluation of a stance-phase controlled prosthetic knee joint for children.  

PubMed

The aims of this study were to demonstrate a theoretical basis for the design of a stance-phase controlled paediatric prosthetic knee joint, clinically test prototypes of the knee, and use a questionnaire to evaluate its efficacy. Biomechanical models were used to analyze the stance-phase control characteristics of the proposed knee, and those of three other commonly prescribed paediatric knee joint mechanisms, which were also the conventional knee joints used by the six participants of this study (mean age 10.8 years). A questionnaire pertaining to stance-phase control was designed and administered twice to each child; once for the evaluation of the prototype knee joint and once for the conventional knee joint. Stance-phase modeling results indicated decreased zones of instability for the new knee as compared to other paediatric knee joints. Questionnaire results revealed a decrease in the frequency of falls with the prototype compared to other knees, especially in highly active children. The children also reported worrying less about the knee collapsing during walking. No differences were evident for stance-phase stability during running, walking on uneven terrain, ambulating up and down stairs and inclines, fatigue, and types of activities performed. PMID:16425824

Andrysek, Jan; Naumann, Stephen; Cleghorn, William L

2005-12-01

79

Trunk's Natural Inclination Influences Stance Limb Kinetics, but Not Body Kinematics, during Gait Initiation in Able Men  

PubMed Central

The imposing mass of the trunk in relation to the whole body has an important impact on human motion. The objective of this study is to determine the influence of trunk's natural inclination - forward (FW) or backward (BW) with respect to the vertical - on body kinematics and stance limb kinetics during gait initiation. Twenty-five healthy males were divided based on their natural trunk inclination (FW or BW) during gait initiation. Instantaneous speed was calculated at the center of mass at the first heel strike. The antero-posterior impulse was calculated by integrating the antero-posterior ground reaction force in time. Ankle, knee, hip and thoraco-lumbar (L5) moments were calculated using inverse dynamics and only peaks of the joint moments were analyzed. Among all the investigated parameters, only joint moments present significant differences between the two groups. The knee extensor moment is 1.4 times higher (P<0.001) for the BW group, before the heel contact. At the hip, although the BW group displays a flexor moment 2.4 times higher (P<0.001) before the swing limb's heel-off, the FW group displays an extensor moment 3.1 times higher (P<0.01) during the swing phase. The three L5 extensor peaks after the toe-off are respectively 1.7 (P<0.001), 1.4 (P<0.001) and 1.7 (P<0.01) times higher for the FW group. The main results support the idea that the patterns described during steady-state gait are already observable during gait initiation. This study also provides reference data to further investigate stance limb kinetics in specific or pathologic populations during gait initiation. It will be of particular interest for elderly people, knowing that this population displays atypical trunk postures and present a high risk of falling during this forward stepping.

Leteneur, Sebastien; Simoneau, Emilie; Gillet, Christophe; Dessery, Yoann; Barbier, Franck

2013-01-01

80

Motor strategies used by rats spinalized at birth to maintain stance in response to imposed perturbations  

PubMed Central

Some rats spinalized P1/P2 achieve autonomous weight supported locomotion and quiet stance as adults. We used force platforms and robot applied perturbations to test such spinalized rats (n=6) which exhibited both weight supporting locomotion and stance, and also normal rats (n=8). Ground reaction forces in individual limbs, and the animals’ center of pressure were examined. In normal rats, both forelimbs and hindlimbs participated actively to control horizontal components of ground reaction forces. Rostral perturbations increased forelimb ground reaction forces, and caudal perturbations increased hindlimb ground reaction forces. Operate rats carried 60% body weight on the forelimbs and had a more rostral center of pressure placement. Normal rats pattern was to carry significantly more weight on the hindlimbs in quiet stance (~60%). Operate rats strategy of compensation for perturbations was entirely in forelimbs; as a result, the hind-limbs were largely isolated from the perturbation. Stiffness magnitude of the whole body was measured: its magnitude was hourglass shaped, with the principal axis oriented rostrocaudally. Operate rats were significantly less stiff; only 60-75% of normal rats’ stiffness. The injured rats adopt a stance strategy that isolates the hindlimbs from perturbation and may thus prevent hindlimb loadings. Such loadings could initiate reflex stepping, which we observed. This might activate lumbar pattern generators used in their locomotion. Adult spinalized rats never achieve independent hindlimb weight supported stance. The stance strategy of the P1 spinalized rats differed strongly from the behavior of intact rats and may be difficult for rats spinalized as adults to master.

Giszter, Simon F; Davies, Michelle R; Graziani, Virginia

2010-01-01

81

Public's expectation about an organization's stance in crisis communication based on perceived leadership and perceived severity of threats  

Microsoft Academic Search

Considering the importance of general public support of an organization during a crisis, this study examined how perceived leadership style influences public expectation about an organization's stance in crisis and the relationship between perceived severity of threat and the expected stance of the organization based on leadership perception. The results of the study strongly supported main effects of leadership on

Sungwook Hwang; Glen T. Cameron

2008-01-01

82

Femoral loads during passive, active, and active-resistive stance after spinal cord injury: a mathematical model  

PubMed Central

Objective The purpose of this study was to estimate the loading environment for the distal femur during a novel standing exercise paradigm for people with spinal cord injury. Design A mathematical model based on experimentally derived parameters. Background Musculoskeletal deterioration is common after spinal cord injury, often resulting in osteoporotic bone and increased risk of lower extremity fracture. Potential mechanical treatments have yet to be shown to be efficacious; however, no previous attempts have been made to quantify the lower extremity loading during passive, active, and active–resistive stance. Methods A static, 2-D model was developed to estimate the external forces; the activated quadriceps forces; and the overall bone compression and shear forces in the distal femur during passive (total support of frame), active (quadriceps activated minimally), and active–resistive (quadriceps activated against a resistance) stance. Results Passive, active, and active–resistive stance resulted in maximal distal femur compression estimates of ~45%, ~75%, and ~240% of body weight, respectively. Quadriceps force estimates peaked at 190% of body weight with active–resistive stance. The distal femur shear force estimates never exceeded 24% of body weight with any form of stance. Conclusions These results support our hypothesis that active–resistive stance induces the highest lower extremity loads of the three stance paradigms, while keeping shear to a minimum. Relevance This model allows clinicians to better understand the lower extremity forces resulting from passive, active, and active–resistive stance in individuals with spinal cord injury.

Frey Law, Laura A.; Shields, Richard K.

2013-01-01

83

Student Attachment Stances, Instructor Immediacy, and Student-Instructor Relationships as Predictors of Achievement Expectancies in College Students  

ERIC Educational Resources Information Center

In the present research, associations between student attachment stances, verbal and nonverbal instructor immediacy, student-instructor relationships, and student achievement orientations were specified. It was predicted that positive student-instructor relationships would mediate associations between student attachment stances, instructor…

Creasey, Gary; Jarvis, Patricia; Gadke, Daniel

2009-01-01

84

The effect of stance control orthoses on gait characteristics and energy expenditure in knee-ankle-foot orthosis users.  

PubMed

Stance Control knee-ankle foot orthoses (SCO) differ from their traditional locked knee counterparts by allowing free knee flexion during swing while providing stability during stance. It is widely accepted that free knee flexion during swing normalizes gait and therefore improves walking speed and reduces the energy requirements of walking. Limited research has been carried out to evaluate the benefits of SCOs when compared to locked knee-ankle foot orthoses (KAFOs). The purpose of this study was to evaluate the effectiveness of SCOs used for patients with lower limb pathology. Energy expenditure and walking velocity were measured in 10 subjects using an orthosis incorporating a Horton Stance Control knee joint. A GAITRite walkway was used to measure temporospatial gait characteristics. A Cosmed K4b2 portable metabolic system was used to measure energy expenditure and heart rate during walking. Two conditions were tested: Walking with stance control active (stance control) and walking with the knee joint locked. Ten subjects completed the GAITRite testing; nine subjects completed the Cosmed testing. Walking velocity was significantly increased in the stance control condition (p < 0.001). There was no difference in the energy cost of walking (p = 0.515) or physiological cost index (PCI) (p = 0.093) between conditions. This study supports previous evidence that stance control knee-ankle foot orthoses increase walking velocity compared to locked knee devices. Contrary to expectation, the stance control condition did not decrease energy expenditure during walking. PMID:20470059

Davis, Priya Chantal; Bach, Timothy Michael; Pereira, Darren Mark

2010-06-01

85

Three-dimensional knee joint moments during performance of the bodyweight squat: effects of stance width and foot rotation.  

PubMed

The purpose of this investigation was to assess the effects of stance width and foot rotation angle on three-dimensional knee joint moments during bodyweight squat performance. Twenty-eight participants performed 8 repetitions in 4 conditions differing in stance or foot rotation positions. Knee joint moment waveforms were subjected to principal component analysis. Results indicated that increasing stance width resulted in a larger knee flexion moment magnitude, as well as larger and phase-shifted adduction moment waveforms. The knee's internal rotation moment magnitude was significantly reduced with external foot rotation only under the wide stance condition. Moreover, squat performance with a wide stance and externally rotated feet resulted in a flattening of the internal rotation moment waveform during the middle portion of the movement. However, it is speculated that the differences observed across conditions are not of clinical relevance for young, healthy participants. PMID:23462440

Almosnino, Sivan; Kingston, David; Graham, Ryan B

2013-02-01

86

Relationships among age, sex, and lateral dominance for 3- to 6-year-old children performing unilateral stance.  

PubMed

To assess influence of age, sex, and lateral dominance on children's unilateral stance, from 6 Houston area preschools and day-care centers, 121 subjects were randomly selected and judged by teachers as normal 3- to 6-yr-old children. The children were tested for eye, hand, and foot preference and were then classified on over-all dominance. Maximal duration of unilateral stance, or up to 60 sec., was tested on each foot. Means over age groups show progressive increase in duration of unilateral stance with increasing age. No sex differences were found. A stepwise multiple correlation-regression showed stance on the nondominant foot and age as the only significant variables in stance on the dominant foot. Clinically, this study can help in evaluating children for neurodevelopmental disorders. PMID:2251093

Greenspan, K A

1990-10-01

87

Living an Inquiry Stance toward Teaching in School-University Partnerships  

ERIC Educational Resources Information Center

|The nature of partnerships and the integration of theory and practice in professional positioning is so complex that there are undoubtedly promises, potentials, and problematics. To live within this complexity, embrace tensions and challenges, and sustain this important work, the author views living an inquiry stance toward teaching as the…

Snow-Gerono, Jennifer L.

2010-01-01

88

Efferent and Aesthetic Stance: Understanding the Definition of Lois Lowry's "The Giver" as Metaphor.  

ERIC Educational Resources Information Center

Clarifies the "efferent" and "aesthetic" stance on Louise Rosenblatt's theoretical continuum by relating her model to the plot, characters, and scenes in Lois Lowry's "The Giver." Shows that Rosenblatt's view applies to the ways readers read texts and to the way characters in the texts read their text-worlds. Presents implications for aesthetic…

Menexas, Vicky

1997-01-01

89

Morphological and stance interpolations in database for simulating bipedalism of virtual humans  

Microsoft Academic Search

We present a computer tool for testing walk hypotheses for human beings. This tool aims to generate plausible walking movements according to anatomical knowledge. To this end, we introduce an interpolation method based, on one hand, on morphological data and, on the other hand, on stance hypotheses and on footprint hypotheses. We want to test these hypotheses for application to

Nicolas Pronost; Georges Dumont; Gilles Berillon; Guillaume Nicolas

2006-01-01

90

Argument or Evidence? Disciplinary Variation in the Use of the Noun "that" Pattern in Stance Construction  

ERIC Educational Resources Information Center

|This paper uses a corpus approach to investigate disciplinary variation in the construction of stance using nouns which are followed by "that" and a complement clause, "e.g. the argument that the Justices exhibit strategic behaviour..." Two corpora of theses written in English are examined: approximately 190,000 words in politics/international…

Charles, Maggie

2007-01-01

91

Stance and Engagement in Pure Mathematics Research Articles: Linking Discourse Features to Disciplinary Practices  

ERIC Educational Resources Information Center

|Recent ESP research into academic writing has shown how writers convey their stance and interact with readers across different disciplines. However, little research has been carried out into the disciplinary writing practices of the pure mathematics academic community from an ESP genre analysis perspective. This study begins to address this gap…

McGrath, Lisa; Kuteeva, Maria

2012-01-01

92

Pedagogical Stances of High School ESL Teachers: "Huelgas" in High School ESL Classrooms  

ERIC Educational Resources Information Center

|This article presents a qualitative case study of the pedagogical stances of high school English as a Second Language (ESL) teachers, and the subsequent responses of resistance or conformity by their English Language Learners (ELLs). The participants include three high school ESL teachers and 60 high school ESL students of Mexican origin.…

del Carmen Salazar, Maria

2010-01-01

93

Are stance ankle plantar flexor muscles necessary to generate propulsive force during human gait initiation?  

Microsoft Academic Search

The study examined whether the generation of the forward propulsive force (PF) during gait initiation resulted mainly from the electromyogram activity of stance ankle plantar flexor muscles (APF) which ‘push’ on the ground as is generally claimed in the literature. Six unilateral above-knee amputees performed a specific gait initiation protocol, i.e. they were asked to walk as fast as possible

V. Michel

2002-01-01

94

Divergent Effects of Cognitive Load on Quiet Stance and Task-Linked Postural Coordination  

ERIC Educational Resources Information Center

Performing a cognitive task while maintaining upright stance can lead to increased or reduced body sway depending on tasks and experimental conditions. Because greater sway is commonly taken to indicate loosened postural control, and vice versa, the precise impact of cognitive load on postural stability has remained unclear. In much of the large…

Mitra, Suvobrata; Knight, Alec; Munn, Alexandra

2013-01-01

95

Faith in academia: integrating students’ faith stance into conceptions of their intellectual development  

Microsoft Academic Search

This paper explores the interaction between religious faith and academic study. It presents findings from a small-scale qualitative study of how first year theology undergraduates at Oxford experienced the relationship between academic study and their faith stance. The findings suggest varied developments in the extent to which students adapted to the learning environment, the strategies they formed in dealing with

Duna Sabri; Christopher Rowland; Jonathan Wyatt; Francesca Stavrakopoulou; Sarita Cargas; Helenann Hartley

2008-01-01

96

Situating Relational Ontology and Transformative Activist Stance within the "Everyday" Practice of Coteaching and Cogenerative Dialogue  

ERIC Educational Resources Information Center

This paper attempts to advance the thinking in Stetsenko's paper by situating the concepts of relational ontology and transformative activist stance in the context of coteaching and cogenerative dialogue. In so doing, we hope to make Stetsenko's ideas more operational in terms of access and application by researchers, teachers, policy makers and…

Murphy, Colette; Carlisle, Karen

2008-01-01

97

Embodied Discourse: Using Tableau to Explore Preservice Teachers' Reflections and Activist Stances  

ERIC Educational Resources Information Center

In the context of an arts-integration course in an elementary education program, preservice teachers used tableaux (i.e. frozen scenes) to portray field experience moments in two ways: (1) as remembered events, and (2) as projected possibilities. Using video and photographs of the tableaux, we traced the students' enactment of activist stances and…

Branscombe, Margaret; Schneider, Jenifer Jasinski

2013-01-01

98

Fixed patterns of rapid postural responses among leg muscles during stance  

Microsoft Academic Search

The aim of this study has been to present firmer evidence that during stance functionally related postural muscles in the legs are activated according to fixed patterns. The importance of fixed patterns of activation for stabilization, balance, and movement control has received considerable theoretical and experimental attention. With regard to postural adjustment in humans, however, evidence for fixed activation patterns

L. M. Nashner

1977-01-01

99

Divergent Effects of Cognitive Load on Quiet Stance and Task-Linked Postural Coordination  

ERIC Educational Resources Information Center

|Performing a cognitive task while maintaining upright stance can lead to increased or reduced body sway depending on tasks and experimental conditions. Because greater sway is commonly taken to indicate loosened postural control, and vice versa, the precise impact of cognitive load on postural stability has remained unclear. In much of the large…

Mitra, Suvobrata; Knight, Alec; Munn, Alexandra

2013-01-01

100

A Stance toward Inquiry: An Investigation of Preservice Teachers' Confidence regarding Educational Inquiry  

ERIC Educational Resources Information Center

Research suggests that effective teaching is a significant, if not the most significant, indicator of student success. However, because teaching has become an increasingly challenging profession, school reformers have advocated that educational practices be based on evidence of student learning, suggesting that teachers should develop a stance

Truxaw, Mary P.; Casa, Tutita M.; Adelson, Jill L.

2011-01-01

101

Knowledge Construction among Teachers within a Community Based on Inquiry as Stance  

ERIC Educational Resources Information Center

This study explores the process of teachers' knowledge construction within a community designed based on the concept of inquiry as stance. Through close examination of three teachers' activities, the study investigates how teachers adapt and respond to such a community, whether their inquiry actually generates knowledge, and how it relates to…

So, Kyunghee

2013-01-01

102

Balance control during an arm raising movement in bipedal stance: which biomechanical factor is controlled?  

Microsoft Academic Search

In order to obtain new insight into the control of balance during arm raising movements in bipedal stance, we performed a biomechanical analysis of kinematics and dynamical aspects of arm raising movements by combining experimental work, large-scale models of the body, and techniques simulating human behavior. A comparison between experimental and simulated joint kinematics showed that the minimum torque change

Myriam Ferry; Luc Martin; Nicolas Termoz; Julie Côté; Francois Prince

2004-01-01

103

Dynamic transitions in stance support accompanying leg flexion movements in man  

Microsoft Academic Search

The control processes underlying dynamic transitions in stance support during single leg flexion movements were investigated in human subjects as a function of the intended speed of movement, by examining the vertical and lateral horizontal components of the ground reaction forces, the frontal plane trajectory of the body center of mass (CM) recorded via motion analysis, and the electromyographic (EMG)

M. W. Rogers; Yi-Chung Pai

1990-01-01

104

Influence of an asymmetrical body weight distribution on the control of undisturbed upright stance  

Microsoft Academic Search

Postural asymmetry in humans is generally associated with different pathologies. However, its specific influence on undisturbed upright stance is poorly understood. To evaluate its separate effects on each support, the centre of pressure (CP) displacements were recorded through two force platforms. In a second step, the complex resultant centre of pressure trajectories (CPRes) were computed and decomposed into two elementary

N. Genthon; P. Rougier

2005-01-01

105

Lower extremity mechanical work during stance phase of running partially explains interindividual variability of metabolic power.  

PubMed

Recent attention given to the mechanical work of the lower extremity joints, the emerging importance of the stance phase of running, and the lack of consensus regarding the biomechanical correlates to economical running were primary justifications for this study. The purpose of this experiment was to identify the correlations between metabolic power and the positive and negative mechanical work at lower extremity joints during stance. Recreational runners (n = 16) ran on a treadmill at 3.35 m s(-1) for physiological measures and overground for biomechanical measures. Inverse dynamics were used to calculate net joint moments and powers at the ankle, knee, and hip. Joint powers were then integrated over the stance phase so that positive and negative joint mechanical work were correlated with metabolic power (r = 0.60-0.69). Positive work at the hip and ankle during stance was positively correlated to metabolic power. In addition to these results, more economical runners (lower metabolic power) exhibited greater negative work at the hip, greater positive work at the knee, and less negative work at the ankle. Between the most and least economical runners, different mechanical strategies were present at the hip and knee, whereas the kinetics of the ankle joint differed only in magnitude. PMID:21221992

Heise, Gary D; Smith, Jeremy D; Martin, Philip E

2011-01-09

106

The effect of voluntary lateral trunk bending on balance recovery following multi-directional stance perturbations.  

PubMed

Stabilising shifts of the centre of mass (COM) are observed during balance recovery when subjects simultaneously execute voluntary unilateral knee flexion or unilateral arm raising. Here, we examined whether voluntary lateral trunk bending provided more beneficial stabilising effects, and how motor programs of balance corrections are combined with those of the focal voluntary action. The upright balance of 24 healthy young subjects (19-33 years of age) was perturbed using multi-directional rotations of the support-surface. The perturbations consisted of combined pitch and roll rotations (7.5 degrees and 60 degrees/s) presented randomly in six different directions. Three conditions were tested: perturbation of stance only (PO); combined balance perturbation and cued uphill bending of the trunk (CONT); and combined perturbation and cued downhill bending of the trunk (IPS). For comparison, subjects were required to perform trunk bending alone (TO). Outcome measures were biomechanical responses and surface EMG activity of several muscles. Calculated predicted outcomes (PO + TO) were compared with combined measures (CONT or IPS). CONT trunk bending uphill showed two phases of benefit in balance recovery for laterally but, in contrast to voluntary knee bending, not for posterior directed components of the perturbations. IPS trunk bending had negative effects on balance. Early balance correcting muscle responses were marginally greater than PO responses. Prominent secondary balance correcting responses, having a similar timing as voluntary responses observed under TO conditions, were seen under CONT only in trunk muscles. These, and later stabilising, responses had amplitudes as expected from PO + TO conditions being significantly greater than PO responses. The ability with which different muscle synergies for balance corrections and voluntary trunk bending were integrated into one indicates a flexible adjustment of the CNS programs to the demands of both tasks. PMID:20204607

Küng, U M; Horlings, C G C; Honegger, F; Allum, J H J

2010-03-04

107

Ankle and Foot Kinematics Associated with Stage II PTTD During Stance  

PubMed Central

Background Subjects with stage II posterior tibial tendon dysfunction (PTTD) exhibit abnormal foot kinematics; however, how individual segment kinematics (hindfoot (HF) or first metatarsal (first MET) segments) influence global foot kinematics is unclear. The purpose of this study was to compare foot and ankle kinematics and sagittal plane HF and first MET segment kinematics between stage II PTTD and controls. Materials and Methods Thirty patients with stage II PTTD and 15 healthy controls were evaluated. Kinematic data from the tibia, calcaneus, and first MET were collected during walking using three dimensional motion analysis techniques. A threesegment foot model (HF, calcaneus; first MET, first metatarsal, and tibia) was used to calculate relative angles (ankle, HF relative to tibia; midfoot, first MET relative to HF) and segment angles (HF and first MET relative to the global). A mixed effect ANOVA model was utilized to compare angles between groups for each variable. Results Patients with PTTD showed greater ankle plantarflexion (p = 0.02) by 6.8 degrees to 8.4 degrees prior to or at 74% of stance; greater HF eversion (p < 0.01) across stance (mean difference = 4.5 degrees); and greater first MET dorsiflexion (p < 0.01) across stance (mean difference = 8.8 degrees). HF and first MET segment angles revealed greater HF dorsiflexion (p = 0.01) during early stance and greater first MET dorsiflexion (p = 0.001) across stance. Conclusion Abnormal HF and first MET segment kinematics separately influence both ankle and midfoot movement during walking in subjects with stage II PTTD. Clinical Relevance These abnormal kinematics may serve as another measure of response to clinical treatment and/or guide for clinical strategies (exercise, orthotics, and surgery) seeking to improve foot kinematics.

Houck, Jeff R.; Neville, Christopher G.; Tome, Josh; Flemister, Adolph S.

2010-01-01

108

Speaking "Common Sense" about the Soviet Threat: Reagan's Rhetorical Stance.  

ERIC Educational Resources Information Center

Although for the 15 years preceding his election as President of the United States Ronald Reagan muted his anti-Soviet rhetoric in order to achieve political power, since his election he has returned to anti-Sovietism in an effort to redirect American foreign policy against the Soviets. At the same time, however, he employs a rhetorical strategy…

Ivie, Robert L.

109

Chair rising time is longer in postmenopausal women with history of nonvertebral fracture.  

PubMed

The objective of the present study was to clarify the relationships between physical function, bone mass, biochemical markers, renal function, and a history of nonvertebral fracture in postmenopausal women with osteoporosis. In total, 143 postmenopausal women with osteoporosis (mean age: 71.2 years) and an osteoporosis treatment-naïve status were recruited. Twenty-seven women had a history of nonvertebral fracture (nonvertebral fracture group) and 116 women did not (control group). The patients' bone mass, biochemical markers, estimated glomerular filtration rate (eGFR), unipedal standing time (index of body balance), and the five-repetition chair-rising time (index of muscle power) were compared between the two groups. Age, body mass index, bone mass, serum alkaline phosphatase, creatinine, albumin, urinary cross-linked N-terminal telopeptides of type I collagen, eGFR, and the unipedal standing time did not differ significantly between the two groups. However, the chair-rising time was significantly longer (12.3 sec vs. 9.6 sec) in the nonvertebral fracture group than in the control group. The odds ratio (95% confidence intervals) for nonvertebral fractures in subjects with a chair-rising time >10.1 sec (mean value) was 4.28 (1.78, 10.30). Thus, a significant association was found between the impairment of muscle power and a history of nonvertebral fracture in postmenopausal women with osteoporosis. PMID:23989247

Iwamoto, J; Sato, Y; Matsumoto, H

2013-09-01

110

Research and Teacher Learning: Taking an Inquiry Stance  

Microsoft Academic Search

\\u000a In the United States, teacher education and teacher learning have been highly debated topics since the time that teacher preparation\\u000a first emerged as an identifiable activity in the late 1800s. The relationship of research to teacher education and the role\\u000a of research in teacher learning have been central issues in the debates almost from the beginning, particularly in disputes\\u000a about

Marilyn Cochran-Smith; Kelly Demers

111

Situating relational ontology and transformative activist stance within the `everyday' practice of coteaching and cogenerative dialogue  

NASA Astrophysics Data System (ADS)

This paper attempts to advance the thinking in Stetsenko's paper by situating the concepts of relational ontology and transformative activist stance in the context of coteaching and cogenerative dialogue. In so doing, we hope to make Stetsenko's ideas more operational in terms of access and application by researchers, teachers, policy makers and other stakeholders in education. Stetsenko argues that moving from relational ontology to a transformative activist stance can be considered as moving from participation to contribution. When this model was applied to coteaching and cogenerative dialogue, it was apparent that the coteaching and cogenerative dialogue moved further, from contribution to shared contribution, adding even greater potential for transformation. The paper also discusses the use of cultural historical activity theory in articulating the relationships, dynamics and interpretations of coteaching and cogenerative dialogue in relation to the wider context of their application.

Murphy, Colette; Carlisle, Karen

2008-07-01

112

ATAXIA OF STANCE IN DIFFERENT TYPES OF ALCOHOL DEPENDENCE — A POSTUROGRAPHIC STUDY  

Microsoft Academic Search

Abstract — The aim of this study was to assess the prevalence of ataxia of stance in different types of alcohol-dependent patients. Posturographic measurements,were,performed,in 82 abstinent alcohol- dependent,patients and 54 healthy controls in order to analyse postural control According to Lesch and co-workers, alcohol dependence was classified as total abstinence (Type I), drinking without loss of control (Type II), fluctuating

Christian Wober; Cicek Wober-bingol; Andreas Karwautz; Amanda Nimmerrichter; Henriette Walter; Luder Deecke

1998-01-01

113

Postural Asymmetries in Response to Holding Evenly and Unevenly Distributed Loads During Self-Selected Stance  

Microsoft Academic Search

The authors examined postural asymmetries during quiet stance and while holding evenly or unevenly distributed loads. Right-hand dominant subjects preferentially loaded their right lower limb when holding no load or a load evenly distributed in both hands, but no differences in center of pressure (CoP) were observed between the left and right limbs. However, longer CoP displacement was observed under

Jeffrey M. Haddad; Shirley Rietdyk; Joong Hyun Ryu; Jessica M. Seaman; Tobin A. Silver; Julia A. Kalish; Charmayne M. L. Hughes

2011-01-01

114

Human stance control beyond steady state response and inverted pendulum simplification  

Microsoft Academic Search

Systems theory analyses have suggested that human upright stance can be modelled in terms of continuous multi-sensory feedback\\u000a control. So far, these analyses have considered mainly steady-state responses to periodic stimuli and relied on a simplifying\\u000a model of the body’s mechanics in the form of an inverted pendulum. Therefore, they may have ignored relevant aspects of the\\u000a postural behaviour. To

G. Schweigart; T. Mergner

2008-01-01

115

Auditory biofeedback substitutes for loss of sensory information in maintaining stance  

Microsoft Academic Search

The importance of sensory feedback for postural control in stance is evident from the balance improvements occurring when\\u000a sensory information from the vestibular, somatosensory, and visual systems is available. However, the extent to which also\\u000a audio-biofeedback (ABF) information can improve balance has not been determined. It is also unknown why additional artificial\\u000a sensory feedback is more effective for some subjects

Marco Dozza; Fay B. Horak; Lorenzo Chiari

2007-01-01

116

A dynamic cadaver model of the stance phase of gait: performance characteristics and kinetic validation  

Microsoft Academic Search

Objective. This study was undertaken to evaluate the performance of a new dynamic laboratory model of the stance phase of gait.Design. Five cadaver feet were repetitively tested in the apparatus.Background. Typical biomechanical investigations of cadaver feet simply place a static load on the tibia. The present system was designed to better simulate the changing in-vivo loading environment of the foot

Neil A. Sharkey; Andrew J. Hamel

1998-01-01

117

Lower extremity mechanical work during stance phase of running partially explains interindividual variability of metabolic power  

Microsoft Academic Search

Recent attention given to the mechanical work of the lower extremity joints, the emerging importance of the stance phase of\\u000a running, and the lack of consensus regarding the biomechanical correlates to economical running were primary justifications\\u000a for this study. The purpose of this experiment was to identify the correlations between metabolic power and the positive and\\u000a negative mechanical work at

Gary D. Heise; Jeremy D. Smith; Philip E. Martin

118

Anteroposterior Stability of the Knee during the Stance Phase of Gait after Anterior Cruciate Ligament Deficiency  

PubMed Central

Quadriceps avoidance and higher flexion strategy have been assumed as effects of ACL deficiency on knee joint function during gait. However, the effect of ACL deficiency on anteroposterior stability of the knee during gait is not well defined. In this study, ten patients with unilateral acute ACL ruptures and the contralateral side intact performed gait on a treadmill. Flexion angles and anteroposterior translation of the ACL injured and the intact controlateral knees were measured at every 10% of the stance phase of the gait (from heel strike to toe-off) using a combined MRI and dual fluoroscopic image system (DFIS). The data indicated that during the stance phase of the gait, the ACL-deficient knees showed higher flexion angles compared to the intact contralateral side, consistent with the assumption of a higher flexion gait strategy. However, the data also revealed that the ACL-deficient knees had higher anterior tibial translation compared to the intact contralateral side during the stance phase of the gait. The higher flexion gait strategy was not shown to correlate to a reduction of the anterior tibial translation in ACL deficient knees. These data may provide indications for conservative treatment or surgical reconstruction of the ACL injured knees in restoration of the knee kinematics during daily walking activities.

Chen, CH; Li, JS; Hosseini, A; Gadikota, HR; Gill, TJ; Li, G

2011-01-01

119

Unilateral Stance Strategies of Athletes With ACL Deficiency  

PubMed Central

Aberrant movement strategies are characteristic of ACL-deficient athletes with recurrent knee instability (non-copers), and may instigate premature or accelerate joint degradation. Biomechanical evaluation of kinematic changes over time may elucidate noncopers’ responses to neuromuscular intervention and ACL reconstruction (ACLR). Forty noncopers were randomized into a perturbation group or a strength training only group. We evaluated the effects of perturbation training, and then gender on knee angle and tibial position during a unilateral standing task before and after ACLR. No statistically significant interactions were found. Before surgery, the strength training only group demonstrated knee angle asymmetry, but 6 months after ACLR, both groups presented with similar knee flexion between limbs. Aberrant and asymmetrical tibial position was found only in females following injury and ACLR. Neither treatment group showed distinct unilateral standing strategies following intervention; however, males and female noncopers appear to respond uniquely to physical therapy and surgery.

Di Stasi, Stephanie L.; Hartigan, Erin H.; Snyder-Mackler, Lynn

2013-01-01

120

Examining differences between center of pressure sway in one-legged and two-legged stances for soccer players and typical adults.  

PubMed

To examine stance during the measurement of balance ability, this study aimed to clarify the differences and relationships between balance ability in one-legged (dominant or nondominant leg) and two-legged stances in 25 typical male adults and 25 male soccer players. Balance ability was evaluated with four sway factors: sway velocity, anterior-posterior sway, lateral sway, and high-frequency sway factors. The one-legged stance was more unstable than the two-legged stance, the balance abilities related to two-legged and one-legged stances differed, and the balance abilities related to dominant-legged and nondominant-legged stances were similar. The one-legged stance, which was difficult to maintain stably, may be useful in the measurement of static balance ability in young people. PMID:20681329

Matsuda, Shigeki; Demura, Shinichi; Demura, Tomohiro

2010-06-01

121

Approximate analytic solutions to non-symmetric stance trajectories of the passive Spring-Loaded Inverted Pendulum with damping  

Microsoft Academic Search

This paper introduces an accurate yet analytically simple approximation to the stance dynamics of the Spring-Loaded Inverted\\u000a Pendulum (SLIP) model in the presence of non-negligible damping and non-symmetric stance trajectories. Since the SLIP model\\u000a has long been established as an accurate descriptive model for running behaviors, its careful analysis is instrumental in\\u000a the design of successful locomotion controllers. Unfortunately, none

Ömür Arslan; M. Mert Ankaral?; Ömer Morgül

2010-01-01

122

Developing Inquiry-as-Stance and Repertoires of Practice: Teacher Learning Across Two Settings  

NASA Astrophysics Data System (ADS)

Sixteen science educators joined a science teacher video club for one school year to collaboratively inquire into each other's classroom practice through the use of records of practice including classroom video clips and samples of student work. This group was focused on developing ambitious, equitable science teaching that capitalizes on students' ways of talking and thinking about important science ideas in order to co-construct, test, refine, and revise explanatory models. By analyzing both the teacher-to-teacher interactions taking place in the context of the video club and the on-going classroom teaching practice, this study fills important gaps in our understanding of teacher learning across settings of professional development and classroom practice. This study pursues answers to two groups of guiding questions: (1) How do teachers learn from each other in the context of collaborative inquiry groups, such as a science teacher video club? How do teachers draw upon classroom teaching experiences, re-interpret those experiences, and challenge each other's interpretations and choices made when teaching? (2) How are teachers' professional development experiences connected to and supported by teachers' on-going classroom practice? When the vision of science teaching developed in one context, such as a professional development setting, is different from the vision or teaching developed in another context, such as a local school, how do teachers wrestle with these differences to make choices about instructional practice? Using a sociocultural framework, this study traces the development of inquiry-as-stance as seen in teachers' stance-taking during collegial conversations while also tracing the development of teachers' repertoires of instructional practice. Analysis of discourse during teacher-to-teacher talk as well as during classroom interactions affords insights into the development of an inquiry stance and the evolution of instructional practice at the level of turn-by-turn talk contextualized in real school settings.

Braaten, Melissa L.

123

A shoe sole-based apparatus and method for randomly perturbing the stance phase of gait: test-retest reliability in young adults.  

PubMed

Walking on an irregular surface is associated with an elevated risk for a fall at any age. Yet, relatively little is known about how a human responds to an unexpected underfoot perturbation during gait. This is partly due to the difficulty of generating an intermittent but repeatable, unexpected, underfoot perturbation whose size and location are precisely known. So we developed a shoe sole-embedded apparatus for randomly perturbing the stance phase of gait. Medial and lateral flaps were concealed in the soles of pairs of sandals, along with their actuators. Either flap could be deployed within 400ms in the parasagittal plane under a swing foot; this altered the resulting sagittal and frontal plane orientations of the foot during the next stance phase, whereafter the flap was retracted following toe-off for the rest of that gait trial. We tested six healthy young subjects by randomly presenting a single medial or lateral perturbation in 12 of 30 gait trials. Traditional step kinematic measures were used to evaluate the test-retest reliability of the response to the stimulus at two different walking speeds in 60 randomized trials conducted 1 week apart. The method was effective in systematically inducing an alteration in gait, reproducible across visits, as evidenced by acceptable intraclass correlation coefficients for step width, time and length. We conclude that the apparatus and method has potential for measuring the ability of humans to reject one or more unexpected underfoot perturbations during gait. PMID:22633007

Kim, Hogene; Ashton-Miller, James A

2012-05-26

124

The shifting of the torsion axis of the foot during the stance phase of lateral cutting movements.  

PubMed

Previously, foot torsion has been studied with respect to peak angles during athletic movements. Athletic footwear often contains a torsion element that dictates a torsion axis of the shoe. The location of the axis of rotation of the foot is, however, unknown. Therefore, the purpose of this study was to describe the torsion axis location during the stance phase of lateral cutting movements. Thirty-nine subjects performed a barefoot lateral jab and 19 subjects performed a barefoot shuffle cut. Markers were placed on the fore- and rearfoot and their movement was quantified using a 3-D video system. The torsion axis location was determined using a modified finite helical axis approach during the stance phase while the torsion angle was calculated as the amount of rotation around the torsion axis. At the beginning of the stance phase, the axis was located on the medial aspect of the foot. During the stance phase, the axis shifted towards the lateral side of the foot before the axis moved back to the medial aspect of the foot at the end of stance. For both movements significant correlations between the axis location in the vertical and medio-lateral directions and the torsion angle were found. With larger torsion (forefoot inversion) angles the axis was in a more lateral and plantar location within the foot. With this knowledge, a shoe torsion system where the shoe torsion axis location is in agreement with the foot axis location could be developed. PMID:22959787

Graf, Eveline S; Stefanyshyn, Darren J

2012-09-07

125

Biomechanical comparison of the energy-storing capabilities of SACH and Carbon Copy II prosthetic feet during the stance phase of gait in a person with below-knee amputation.  

PubMed

In this study, the energy-storing capabilities of solid-ankle cushion heel (SACH) and Carbon Copy II prosthetic feet during the stance phase of gait were compared. A person with a unilateral below-knee amputation served as a component of the instrumentation to test the feet under dynamic loads. Ten trials per foot of bilateral stride at "free" velocity were collected with a video-based, three-dimensional data-acquisition system and two force plates. There were no differences between the prosthetic conditions in step length, single-limb support time, and swing period (analysis of variance) or in double-limb support time, cadence, and velocity (Student's t test). Angular kinematics and moments of the hip and knee were unaffected bilaterally by the type of foot. The progression of the center of pressure under the Carbon Copy II was delayed from 15% to 80% of stance as compared with the SACH foot. The Carbon Copy II showed slower unloading in late stance and a later peak propulsive force than did the SACH foot. The Carbon Copy II performed greater work in both the energy-storage (Carbon Copy II = 2.33 J, SACH = 1.16 J) and energy-return (Carbon Copy II = 1.33 J, SACH = 0.34 J) phases of stance and returned energy with 57% efficiency. Although the energy returned by the Carbon Copy II was clinically insignificant during level walking, these results confirm that it performs as an energy-storing device. PMID:1631203

Barr, A E; Siegel, K L; Danoff, J V; McGarvey, C L; Tomasko, A; Sable, I; Stanhope, S J

1992-05-01

126

Estimation of Quasi-Stiffness of the Human Knee in the Stance Phase of Walking  

PubMed Central

Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as prostheses and orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.

Shamaei, Kamran; Sawicki, Gregory S.; Dollar, Aaron M.

2013-01-01

127

Assessment of AK (Above Knee) Prosthesis with Different Ankle Assembly Using GRF Pattern in Stance Phase  

NASA Astrophysics Data System (ADS)

In this study, ground reaction force (GRF), absolute symmetry index (ASI) and coefficient of variation (CV) of fixed, single-axis and multi-axis prosthetic ankle assemblies were investigated by biomechanical evaluation of above knee amputees. In the experiments, 37 normal male volunteers, two male and two female Above Knee (AK) amputees GRF data were tested with fixed, single-axis and multi-axis prosthetic ankle assembly. A gait analysis was carried out to derive the ratio of GRF to weight as the percentage of total stance phase for ten points. The results showed that fixed-axis ankle assembly was superior to other two ankle assemblies for forwarding and braking forces. Multi-axis ankle was relatively superior to other two ankle assemblies for gait balancing and movement of the mass center. Single-axis ankle was relatively superior to the other two ankle assemblies for CV and ASI of GRF.

Kim, Sung-Min; Kim, Sung-Jae; Bae, Ha-Suk

128

Coordinated, multi-joint, fatigue-resistant feline stance produced with intrafascicular hind limb nerve stimulation.  

PubMed

The production of graceful skeletal movements requires coordinated activation of multiple muscles that produce torques around multiple joints. The work described herein is focused on one such movement, stance, that requires coordinated activation of extensor muscles acting around the hip, knee and ankle joints. The forces evoked in these muscles by external stimulation all have a complex dependence on muscle length and shortening velocities, and some of these muscles are biarticular. In order to recreate sit-to-stand maneuvers in the anesthetized feline, we excited the hind limb musculature using intrafascicular multielectrode stimulation (IFMS) of the muscular branch of the sciatic nerve, the femoral nerve and the main branch of the sciatic nerve. Stimulation was achieved with either acutely or chronically implanted Utah Slanted Electrode Arrays (USEAs) via subsets of electrodes (1) that activated motor units in the extensor muscles of the hip, knee and ankle joints, (2) that were able to evoke large extension forces and (3) that manifested minimal coactivation of the targeted motor units. Three hind limb force-generation strategies were investigated, including sequential activation of independent motor units to increase force, and interleaved or simultaneous IFMS of three sets of six or more USEA electrodes that excited the hip, knee and ankle extensors. All force-generation strategies evoked stance, but the interleaved IFMS strategy also reduced muscle fatigue produced by repeated sit-to-stand maneuvers compared with fatigue produced by simultaneous activation of different motor neuron pools. These results demonstrate the use of interleaved IFMS as a means to recreate coordinated, fatigue-resistant multi-joint muscle forces in the unilateral hind limb. This muscle activation paradigm could provide a promising neuroprosthetic approach for the restoration of sit-to-stand transitions in individuals who are paralyzed by spinal cord injury, stroke or disease. PMID:22414699

Normann, R A; Dowden, B R; Frankel, M A; Wilder, A M; Hiatt, S D; Ledbetter, N M; Warren, D A; Clark, G A

2012-03-14

129

Understanding developing country stances on post-2012 climate change negotiations: Comparative analysis of Brazil, China, India, Mexico, and South Africa  

Microsoft Academic Search

An essential issue in future climate negotiations is how to bring developing countries on board. This paper proposes and applies the two-level interest-based model to analyze the factors that affect the likely stances of the “Plus Five” countries (Brazil, China, India, Mexico, and South Africa) on international climate negotiations. This study finds mitigation capability to be a crucial factor which

Fang Rong

2010-01-01

130

Influence of voluntary teeth clenching on the stabilization of postural stance disturbed by electrical stimulation of unilateral lower limb  

Microsoft Academic Search

Studies on the relationship between dental occlusion and body balance have suggested that occlusion status contributes to the maintenance of postural balance. However, little has been reported about the effects of voluntary teeth clenching on the stabilization of postural stance in novel environments. In the present study we investigated whether teeth clenching influenced adaptation to the perturbation introduced by electrical

Sachiko Fujino; Toshiyuki Takahashi; Toshiaki Ueno

2010-01-01

131

Gait synchronized force modulation during the stance period of one limb achieved by an active partial body weight support system  

Microsoft Academic Search

Our purpose was to demonstrate the ability of an actively controlled partial body weight support (PBWS) system to provide gait synchronized support during the stance period of a single lower extremity while examining the affect of such a support condition on gait asymmetry. Using an instrumented treadmill and a motion capture system, we compared gait parameters of twelve healthy elderly

Jason R. Franz; Patrick O. Riley; Jay Dicharry; Paul E. Allaire; D. Casey Kerrigan

2008-01-01

132

Toward a Consistent Stance in Teaching for Equity: Learning To Advocate for Lesbian- and Gay-Identified Youth.  

ERIC Educational Resources Information Center

|Three education classes of mostly prospective teachers provided instruction on issues related to lesbian- and gay-identified (LG) youth in schools. Written responses of 97 students revealed lack of knowledge of LG youth prior to instruction. Though some students voiced resistance related to religiosity, the dominant stance was a strong…

Athanases, Steven Z.; Larrabee, Timothy G.

2003-01-01

133

Government Stance and Internal Diversity of Protest: A Comparative Study of Protest against the War in Iraq in Eight Countries  

ERIC Educational Resources Information Center

|This study tackles the question to what extent the composition of protest events is determined by the stance of governments. Established contextual theories do not formulate propositions on how context affects individual protesters. The article engages in empirically testing whether the macro-context affects the internal diversity of the crowds…

Walgrave, Stefaan; Verhulst, Joris

2009-01-01

134

Development of postural control in children: short-, medium-, and long latency EMG responses of leg muscles after perturbation of stance  

Microsoft Academic Search

Short (SL), medium (ML), and long (LL) latency EMG responses of leg muscles were recorded after perturbation of stance by means of a sudden toe-up tilt of a movable platform. 56 healthy children varying in age between 14 months and 15 years were investigated. All three responses were present when children were able to stand on the recording platform. The

G. Haas; H. C. Diener; M. Bacher; J. Dichgans

1986-01-01

135

Connecting Learning and Identity Development through a Transformative Activist Stance: Application in Adolescent Development in a Child Welfare Program  

ERIC Educational Resources Information Center

This paper addresses the relationship between identity and learning and how their integration in adolescence is an important part of short- and long-term developmental dynamics. We discuss how social practice theories can be expanded from a position termed "transformative activist stance" that puts emphasis on collaborative practice aimed at…

Vianna, Eduardo; Stetsenko, Anna

2011-01-01

136

Effects of Linear versus Sigmoid Coding of Visual or Audio Biofeedback for the Control of Upright Stance  

Microsoft Academic Search

Although both visual and audio biofeedback (BF) systems for postural control can reduce sway during stance, a direct comparison between the two systems has never been done. Further, comparing different coding designs of audio and visual BF may help in elucidating how BF information is integrated in the control of posture, and may improve knowledge for the design of innovative

Marco Dozza; Lorenzo Chiari; Frantisek Hlavacka; Angelo Cappello; Fay B. Horak

2006-01-01

137

Stabilizing moments of force on a prosthetic knee during stance in the first steps after gait initiation  

Microsoft Academic Search

In this study, the occurrences of stabilizing and destabilizing external moments of force on a prosthetic knee during stance, in the first steps after gait initiation, in inexperienced users were investigated. Primary aim was to identify the differences in the external moments during gait initiation with the sound leg leading and the prosthetic leg leading. A prosthetic leg simulator device,

Helco G. van Keeken; Aline H. Vrieling; At L. Hof; Klaas Postema; Bert Otten

138

Analysis of the multi-segmental postural movement strategies utilized in bipedal, tandem and one-leg stance as quantified by a principal component decomposition of marker coordinates.  

PubMed

Postural control research describes ankle-, hip-, or multi-joint strategies as mechanisms to control upright posture. The objectives of this study were, first, development of an analysis technique facilitating a direct comparison of the structure of such multi-segment postural movement patterns between subjects; second, comparison of the complexity of postural movements between three stances of different difficulty levels; and third, investigation of between-subject differences in the structure of postural movements and of factors that may contribute to these differences. Twenty-nine subjects completed 100-s trials in bipedal (BP), tandem (TA) and one-leg stance (OL). Their postural movements were recorded using 28 reflective markers distributed over all body segments. These marker coordinates were interpreted as 84-dimensional posture vectors, normalized, concatenated from all subjects, and submitted to a principal component analysis (PCA) to extract principal movement components (PMs). The PMs were characterized by determining their relative contribution to the subject's entire postural movements and the smoothness of their time series. Four, eight, and nine PM were needed to represent 90% of the total variance in BP, TA, and OL, respectively, suggesting that increased task difficulty is associated with increased complexity of the movement structure. Different subjects utilized different combinations of PMs to control their posture. In several PMs, the relative contribution of a PM to a subject's overall postural movements correlated with the smoothness of the PM's time series, suggesting that utilization of specific postural PMs may depend on the subject's ability to control the PM's temporal evolution. PMID:24021753

Federolf, Peter; Roos, Lilian; Nigg, Benno M

2013-08-27

139

Loss of large-diameter spindle afferent fibres is not detrimental to the control of body sway during upright stance: evidence from neuropathy.  

PubMed

Fifteen patients with Charcot-Marie-Tooth type 1A (CMT1A) disease and 46 normal controls were studied. In the patients, leg muscle strength, touch-pressure, vibration and joint position sense were reduced; lower limb tendon reflexes were absent in 12 or markedly decreased. Motor and sensory conduction velocity (CV) of leg nerves was either reduced or not measurable. The Neurological Disability Score and the Neuropathy Score were obtained from clinical and electrophysiological examination, respectively. Tilt of a supporting platform elicited short- (SLR) and medium-latency (MLR) responses to stretch in the foot muscle flexor digitorum brevis (FDB) in controls. In the patients, the former response was absent and the latter delayed. These findings are in keeping with the known loss of large-diameter myelinated fibres, with relative sparing of the smaller fibres. The MLR delay was fully accounted for by the slowed CV of the motor fibres. The MLR afferent time was similar to that in normal subjects. Body sway area (SA) during quiet stance was recorded with eyes open or closed, and with feet apart or together. Under all postural and visual conditions, SA was within normal range in the less severely affected patients, but was moderately increased in the patients with a more severe neuropathy score. Across all patients, no correlation was found between SA and muscle force, motor CV, touch pressure, vibration and joint position sense, considered either separately or as an aggregate. We suggest that: (1) functional integrity of the largest afferent fibres is not necessary for appropriate equilibrium control during quiet stance and (2) any unsteadiness is related to additional functional alterations in smaller fibres, most likely group II spindle afferent fibres. PMID:11131499

Nardone, A; Tarantola, J; Miscio, G; Pisano, F; Schenone, A; Schieppati, M

2000-11-01

140

Comparison of ISO Standard and TKR Patient Axial Force Profiles during the Stance Phase of Gait  

PubMed Central

Preclinical endurance testing of total knee replacements (TKRs) is performed using International Organization for Standardization (ISO) load and motion protocols. The standards are based on data from normal subjects and may not sufficiently mimic in vivo implant conditions. In this study, a mathematical model was used to calculate the axial force profile of 30 TKR patients with two current implant types, 22 with NexGen and eight with Miller-Galante II Cruciate-Retaining TKRs, and statistically compare the axial force specified by the ISO standard to the TKR patients. Significant differences were found between the axial forces of both groups of TKR patients and the ISO standard at local maxima and minima points in the first half of stance. The force impulse (area under the axial force curve, representing cumulative loading) was smaller for the ISO standard than the TKR patients, but only for those with NexGen implants. Waveform analysis using the coefficient of multiple correlation showed that the ISO and TKR patient axial force profiles were similar. The combined effect of ISO standard compressive load and motion differences from TKR patients could explain some of the differences between the wear scars on retrieved tibial components and those tested in total joint simulators.

Lundberg, Hannah J.; Ngai, Valentina; Wimmer, Markus A.

2012-01-01

141

Stimulated and voluntary fatiguing contractions of quadriceps femoris similarly disturb postural control in the bipedal stance.  

PubMed

The aim of this work was to compare the effects of fatigue of the quadriceps femoris after fatiguing voluntary contractions (VOL) and fatiguing neuromuscular electrical stimulation (ES) on bipedal postural control. Nineteen active male subjects (22.2 ± 1.7 years) completed these two fatiguing exercises. Isometric maximal voluntary contraction (MVC) and postural control were recorded using an ergometer and a force platform that registered the center of foot pressure (COP). We analyzed the COP surface, the mean COP velocity and the spectral power density given by the wavelet transform. Recordings were performed before (PRE condition) and after the completion of each fatiguing task (immediately POST condition, after a 5 min recovery POST 5 condition). In POST condition, the ES exercise affected MVC more than the VOL exercise. However, bipedal postural control was similarly deteriorated for both exercises. In POST 5 condition, for both fatiguing exercises, muscle strength and postural control did not recover their initial level. These results suggest that the postural control disturbance could not be distinguished for the two fatiguing exercises in the bipedal stance. In addition, the recovery speeds of postural control and muscle strength abilities did not differ for the ES exercise and the VOL exercise. PMID:21922258

Chaubet, Vincent; Maitre, Julien; Cormery, Bruno; Paillard, Thierry

2011-09-16

142

Identification of Neural Feedback for Upright Stance in Humans: Stabilization rather than Sway Minimization  

PubMed Central

A fundamental issue in motor control is how to determine the task goals for a given behavior. Here we address this question by separately identifying the musculoskeletal and feedback components of the human postural control loop. Eighteen subjects were perturbed by two mechanical perturbations (gentle pulling from behind at waist and shoulder levels) and one sensory perturbation (movement of a virtual visual scene). Body kinematics were described by the leg and trunk segment angles in the sagittal plane. Muscle activations were described by ankle and hip EMG signals, with each EMG signal computed as a weighted sum of rectified EMG signals from multiple muscles at the given joint. The mechanical perturbations were used to identify feedback, defined as the mapping from the two segment angles to the two EMG signals. The sensory perturbation was used to estimate parameters in a mechanistic model of the plant, defined as the mapping from the two EMG signals to the two segment angles. Using the plant model and optimal control theory, we compared identified feedback to optimal feedback for a range of cost functions. Identified feedback was similar to feedback that stabilizes upright stance with near-minimum muscle activation, but was not consistent with feedback that substantially increases muscle activation in order to reduce movements of the body's center of mass or center of pressure. The results suggest that the common assumption of reducing sway may not apply to musculoskeletal systems that are inherently unstable.

Kiemel, Tim; Zhang, Yuanfen; Jeka, John J.

2011-01-01

143

Postural stability during one-leg stance on an unstable moving platform and its relationship with each leg.  

PubMed

This study examined the laterality of the supporting leg in postural stability during a one-leg stance test on an unstable moving platform and its practice effect. 30 male university students were evaluated using the omnidirection stability index (OSI) during a one-leg stance test on an unstable moving platform (three trials). The leg used when kicking a ball was defined as the manipulation leg (ML) and the supporting leg was defined as the non-manipulation leg (NML). According to the two-way repeated measures analysis of variance (ANOVA; trials x legs), a statistically significant difference was observed only on the leg factor, and OSI values of the second and third trials were less for the ML than the NML. The correlation between both legs was statistically significant but not high. The ML was superior to NML with regard to stability, and no practice effect with trials was evident in either leg. PMID:24032330

Noguchi, Takanori; Demura, Shin-Ichi; Nakagawa, Tomoharu

2013-04-01

144

Enhancing stance phase propulsion during level walking by combining FES with a powered exoskeleton for persons with paraplegia.  

PubMed

This paper describes the design and implementation of a cooperative controller that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton to provide enhanced hip extension during the stance phase of walking in persons with paraplegia. The controller utilizes two sources of actuation: the electric motors of the powered exoskeleton and the user's machine (FSM), a set of FES. It consists of a finite-state machine (FSM), a set of proportional-derivative (PD) controllers for the exoskeleton and a cycle-to-cycle adaptive controller for muscle stimulation. Level ground walking is conducted on a single subject with complete T10 paraplegia. Results show a 34% reduction in electrical power requirements at the hip joints during the stance phase of the gait cycle with the cooperative controller compared to using electric motors alone. PMID:23365900

Ha, Kevin H; Quintero, Hugo A; Farris, Ryan J; Goldfarb, Michael

2012-01-01

145

Enhancing Stance Phase Propulsion during Level Walking by Combining FES with a Powered Exoskeleton for Persons with Paraplegia*  

PubMed Central

This paper describes the design and implementation of a cooperative controller that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton to provide enhanced hip extension during the stance phase of walking in persons with paraplegia. The controller utilizes two sources of actuation: the electric motors of the powered exoskeleton and the user’s hamstrings activated by FES. It consists of a finite-state machine (FSM), a set of proportional-derivative (PD) controllers for the exoskeleton and a cycle-to-cycle adaptive controller for muscle stimulation. Level ground walking is conducted on a single subject with complete T10 paraplegia. Results show a 34% reduction in electrical power requirements at the hip joints during the stance phase of the gait cycle with the cooperative controller compared to using electric motors alone.

Ha, Kevin H.; Quintero, Hugo A.; Farris, Ryan J.; Goldfarb, Michael

2013-01-01

146

Attachment and Marital Functioning: Comparison of Spouses With Continuous-Secure, Earned-Secure, Dismissing, and Preoccupied Attachment Stances  

Microsoft Academic Search

In a sample of 138 couples, the present study examined whether individuals' marital functioning related to both their own and their partner's attachment stance. Earned-secure wives managed their affect as well as continuous-secure wives during problem-solving discussions and better than preoccupied or dismissing wives. However, preoccupied and dismissing wives did not exhibit markedly different patterns of affect regulation in their

Blair Paley; Martha J. Cox; Margaret R. Burchinal; C. Chris Payne

1999-01-01

147

The role of knee positioning and range-of-motion on the closed-stance forehand tennis swing  

Microsoft Academic Search

This paper discusses the role of knee positioning and range-of- motion on the closed-stance forehand tennis swing. The analyses of tennis swing mechanics were performed using a computer model comprised of a full-body model of a human and an iner- tial model of a racket. The model was driven by subject fore- hand swings (16 female college-level subjects) recorded with

Steven M. Nesbit; Monika Serrano; Mike Elzinga

2008-01-01

148

Erect bipedal stance exercise partially prevents orchidectomy-induced bone loss in the lumbar vertebrae of rats  

Microsoft Academic Search

This study investigates the responses of the fourth and fifth lumbar vertebral bodies of 6-month-old male Sprague-Dawley (SD) rats to orchidectomy (orx) and to erect bipedal stance for feeding for 12 weeks in specially designed raised cages (RC) for which the heights were raised from 20 cm to 35.5 cm. A total of 30 rats were divided into groups of:

W Yao; W. S. S Jee; J Chen; C. S Tam; R. B Setterberg; H. M Frost

2000-01-01

149

Differences in preferred reference frames for postural orientation shown by after-effects of stance on an inclined surface  

Microsoft Academic Search

This study reports a postural after-effect of leaning that follows a period of stance on an inclined surface with eyes closed. This leaning after-effect maintained the body-to-surface relationship as if subjects still stood on the incline. We examined the incidence and robustness of the leaning after-effect in 51 healthy subjects. The location of the center of pressure (CoP) under the

JoAnn Kluzik; Fay B. Horak; Robert J. Peterka

2005-01-01

150

Modeling the stance leg in two-dimensional analyses of sprinting: inclusion of the MTP joint affects joint kinetics.  

PubMed

Two-dimensional analyses of sprint kinetics are commonly undertaken but often ignore the metatarsalphalangeal (MTP) joint and model the foot as a single segment. Due to the linked-segment nature of inverse dynamics analyses, the aim of this study was to investigate the effect of ignoring the MTP joint on the calculated joint kinetics at the other stance leg joints during sprinting. High-speed video and force platform data were collected from four to five trials for each of three international athletes. Resultant joint moments, powers, and net work at the stance leg joints during the first stance phase after block clearance were calculated using three different foot models. By ignoring the MTP joint, peak extensor moments at the ankle, knee, and hip were on average 35% higher (p < .05 for each athlete), 40% lower (p < .05), and 9% higher (p > .05), respectively, than those calculated with the MTP joint included. Peak ankle and knee joint powers and net work at all joints were also significantly (p < .05) different. By ignoring a genuine MTP joint plantar flexor moment, artificially high peak ankle joint moments are calculated, and these also affect the calculated joint kinetics at the knee. PMID:22723121

Bezodis, Neil E; Salo A, I T; Trewartha, Grant

2012-05-01

151

Non-linear stimulus-response behavior of the human stance control system is predicted by optimization of a system with sensory and motor noise  

Microsoft Academic Search

We developed a theory of human stance control that predicted (1) how subjects re-weight their utilization of proprioceptive\\u000a and graviceptive orientation information in experiments where eyes closed stance was perturbed by surface-tilt stimuli with\\u000a different amplitudes, (2) the experimentally observed increase in body sway variability (i.e. the “remnant” body sway that\\u000a could not be attributed to the stimulus) with increasing

Herman van der Kooij; Robert J. Peterka

2011-01-01

152

Functional fatigue of the hip and ankle musculature cause similar alterations in single leg stance postural control.  

PubMed

Isokinetic fatigue protocols have been used to determine the relative importance of lower extremity musculature to the maintenance of balance. However, these protocols are not representative of physical activity, thus the recommendations based on these findings may be inappropriate. Therefore, purpose of this investigation was to use a completely within subjects design to examine the effects of a functional ankle and hip fatigue protocol on postural control during single leg stance. All testing was completed in a health and wellness facility where 18 healthy recreationally active university students (nine female, nine male: 21.2+/-1.96 years, 72.2+/-17.8 kg, 170.4+/-10.12 cm) volunteered to participate. Testing consisted of functionally fatiguing the ankle plantar flexors and dorsiflexors as well as the hip flexors and extensors. Postural control was assessed with two pre- and post-fatigue 20s trials during single leg stance. Three measures of dynamic balance: the overall, medial/lateral, and anterior/posterior stability index were calculated using the Biodex Stability System at stability level 4. Three separate 2-way repeated measure ANOVAs indicated that fatigue of both the ankle (plantar flexors, dorsiflexors) and hip (flexors, extensors) musculature led to postural control impairments for the medial-lateral stability index (p<0.01), and anterior-posterior stability index (p<0.01). However, only ankle fatigue resulted in deficits in the overall stability index were (p<0.01). Furthermore, neither fatigue protocol impaired single leg stance postural control more than the other (p>0.05). Our results contradict previous isokinetic fatigue protocol findings, which indicate that proximal musculature fatigue results in greater postural control deficits. PMID:19342297

Reimer, Robert C; Wikstrom, Erik A

2009-04-01

153

Is the stabilization of quiet upright stance in humans driven by synchronized modulations of the activity of medial and lateral gastrocnemius muscles?  

PubMed

A matrix of 120 electromyogram (EMG) electrodes (8 rows and 15 columns) was used to investigate individual activation patterns of the medial (MG) and lateral gastrocnemius (LG) muscles during forward sways of the body in human quiet stance. This matrix was positioned on the right calf of eight subjects after identification of the MG and LG contours with ultrasound scanning. Gray-scale images were generated with the maxima and minima of the cross-correlation function between the envelope of each EMG signal and the body center of pressure (CoP) for individual forward sways. These images were automatically segmented to reduce the data set into representative and local values of EMG-CoP cross-correlation for each muscle. On average, modulations in EMG amplitude preceded the onset of forward sways with a variable timing, with both gastrocnemius muscles being similarly and synchronously modulated in 193 out of 236 sways. Variations in the timing of activation between muscles were less frequent, although consistent across subjects and significantly correlated with changes in the direction and velocity of body sways. Interestingly, the time shift between EMG and CoP traces sometimes varied consistently along different channels of the same column of electrodes, either in proximal-to-distal or distal-to-proximal direction. The variable EMG-CoP cross-correlation delay was not congruent with the delay expected for the propagation of surface potentials along muscle fibers. Comparison of surface EMGs with intramuscular EMGs recorded from six subjects demonstrated that surface potentials provide high spatial selectivity, thus supporting the notion of selective activation of motor units during quiet standing. Hence, the stabilization of the quiet standing posture likely relies on flexible rather than stereotyped mechanisms of control. PMID:19910338

Vieira, Taian M M; Windhorst, Uwe; Merletti, Roberto

2009-11-12

154

Time.  

ERIC Educational Resources Information Center

Presents brief annotations of 41 children's books that explore the concept of time from varied perspectives to elucidate some of its meanings for children. Groups books to focus on milestones in children's lives; how they enjoy spending their time; visiting the past in suspending time; recognizing different ways to mark time; celebrating special…

Matthews, Susan; Reid, Rebecca; Sylvan, Anne; Woolard, Linda; Freeman, Evelyn B.

1999-01-01

155

Age and gender moderate the effects of localized muscle fatigue on lower extremity joint torques used during quiet stance.  

PubMed

This study examined the effects of localized muscle fatigue, age, and gender on lower extremity joint torques used during quiet stance. Thirty-two participants performed exercises designed to fatigue the ankle plantarflexors, knee extensors, torso extensors, or shoulder flexors. Body kinematics and ground reaction forces were obtained both before and after the exercises, and joint torques were derived via inverse dynamics. Single joint fatigue affected torque variability at all lower extremity joints, with similar changes for both age groups. Males and females exhibited increased ankle torque variability after different tasks, with males showing more variability after ankle fatigue and females after shoulder and lumbar fatigue. Correlations between peak torques and torque variability differed between males and females and between age groups in certain cases. The results of this study suggested that both age and gender moderate the effects of fatigue on postural control and should be considered when developing strategies to prevent occupational falls. PMID:21269716

Wojcik, Laura A; Nussbaum, Maury A; Lin, Dingding; Shibata, Peggy A; Madigan, Michael L

2011-01-26

156

A systematic review of postural control during single-leg stance in patients with untreated anterior cruciate ligament injury.  

PubMed

PURPOSE: The aim of this review was to determine whether postural control is impaired in patients with anterior cruciate ligament (ACL) injury as compared to healthy controls. METHODS: The relevant papers were retrieved through electronic databases including PubMed, EMBASE, Web of Science, and Sport Discus followed by hand search and contact with the authors. Studies that evaluated static postural control during single-leg stance without applying external perturbations were included. Also, the patients should not have undergone ACL reconstruction or any surgical repair on the injured knee. RESULTS: In total, 12 studies were selected for full review. The included studies showed larger postural sway amplitudes or velocities during single-leg stance on the injured leg and the uninjured leg when compared to healthy controls with medium to large effect size. Also, no significant difference was found between the injured and uninjured legs of ACL-injured patients during eyes open condition in all studies supported by small effect size. However, the within-group difference was found to be significant during eyes closed condition, with injured leg displaying larger sway. CONCLUSIONS: The present review indicates that postural control is impaired in both legs, especially injured leg. The result of within-group difference in eyes open condition confirms bilateral deficit of postural control. However, the within-group difference during eyes closed condition indicates again that ACL injury affects the injured leg more than the uninjured leg. In designing rehabilitation protocols, clinicians should consider training postural control of not just the injured but also the uninjured leg. LEVEL OF EVIDENCE: Systematic review of Level III for prognostic studies. PMID:23644752

Negahban, Hossein; Mazaheri, Masood; Kingma, Idsart; van Dieën, Jaap H

2013-05-01

157

Balance in single-limb stance in healthy subjects – reliability of testing procedure and the effect of short-duration sub-maximal cycling  

Microsoft Academic Search

BACKGROUND: To assess balance in single-limb stance, center of pressure movements can be registered by stabilometry with force platforms. This can be used for evaluation of injuries to the lower extremities. It is important to ensure that the assessment tools we use in the clinical setting and in research have minimal measurement error. Previous studies have shown that the ability

Eva Ageberg; David Roberts; Eva Holmström; Thomas Fridén

2003-01-01

158

Wavelet-based intensity analysis of mechanomyographic signals during single-legged stance following fatigue  

Microsoft Academic Search

The von Tscharner (2000) “intensity analysis” describes the power of a non-stationary signal as a function of both frequency and time. The present study applied a version of this intensity analysis that utilizes Morlet wavelets as a means of gaining insight into the application of this technique as alternative to power spectral analysis for the evaluation of postural control strategy

W. Jeffrey Armstrong

2011-01-01

159

Identification of the Plant for Upright Stance in Humans: Multiple Movement Patterns From a Single Neural Strategy  

PubMed Central

We determined properties of the plant during human upright stance using a closed-loop system identification method originally applied to human postural control by another group. To identify the plant, which was operationally defined as the mapping from muscle activation (rectified EMG signals) to body segment angles, we rotated the visual scene about the axis through the subject's ankles using a sum-of-sines stimulus signal. Because EMG signals from ankle muscles and from hip and lower trunk muscles showed similar responses to the visual perturbation across frequency, we combined EMG signals from all recorded muscles into a single plant input. Body kinematics were described by the trunk and leg angles in the sagittal plane. The phase responses of both angles to visual scene angle were similar at low frequencies and approached a difference of ?150° at higher frequencies. Therefore we considered leg and trunk angles as separate plant outputs. We modeled the plant with a two-joint (ankle and hip) model of the body, a second-order low-pass filter from EMG activity to active joint torques, and intrinsic stiffness and damping at both joints. The results indicated that the in-phase (ankle) pattern was neurally generated, whereas the out-of-phase pattern was caused by plant dynamics. Thus a single neural strategy leads to multiple kinematic patterns. Moreover, estimated intrinsic stiffness in the model was insufficient to stabilize the plant.

Kiemel, Tim; Elahi, Alexander J.; Jeka, John J.

2008-01-01

160

Stabilizing moments of force on a prosthetic knee during stance in the first steps after gait initiation.  

PubMed

In this study, the occurrences of stabilizing and destabilizing external moments of force on a prosthetic knee during stance, in the first steps after gait initiation, in inexperienced users were investigated. Primary aim was to identify the differences in the external moments during gait initiation with the sound leg leading and the prosthetic leg leading. A prosthetic leg simulator device, with a flexible knee, was used to test able-bodied subject, with no walking aid experience. Inverse dynamics calculations were preformed to calculate the external moments. The subjects learned to control the prosthetic leg within 100 steps, without walking aids, evoking similar patterns of external moments of force during the steps after the gait initiation, either with their sound leg loading or prosthetic leg leading. Critical phases in which a sudden flexion of the knee can occur were found just after heelstrike and just before toe off, in which the external moment of force was close to the internal moment produced by a knee extension aiding spring in the opposite direction. PMID:21996358

van Keeken, Helco G; Vrieling, Aline H; Hof, At L; Postema, Klaas; Otten, Bert

2011-10-12

161

To take a stance: a developmental study of the use of pronouns and passives in spoken and written narrative and expository texts in Dutch  

Microsoft Academic Search

Discourse stance as expressed by the use of pronouns and passive-voice constructions is examined in two different text genres, narrative and expository text, produced in speech and writing by four groups of Dutch speakers: 9–10 year olds, 11–12 year olds, 15–16 year olds, and adults. In the pronoun analyses, the distribution and use of personal, impersonal, indefinite impersonal (pro)nominals, and

Janet G. van Hell; Ludo Verhoeven; Marjan Tak; Moniek van Oosterhout

2005-01-01

162

Posterior-anterior body weight shift during stance period studied by measuring sole-floor reaction forces during healthy and hemiplegic human walking  

Microsoft Academic Search

Posterior-anterior body weight shift during stance phase of human overground locomotion was investigated by recording sole-floor reaction force from five anatomically discrete points with strain gauge transducers of 14mm diameter attached firmly to the sole of bare foot. At first the subject was asked to walk straight on the laboratory floor at his\\/her preferred velocity. Then the subject was asked

Nobuyoshi Kobayashi; Tateo Warabi; Masamichi Kato; Kiichi Kiriyama; Toshikazu Yoshida; Susumu Chiba

2006-01-01

163

Effect of using poles on foot-ground kinetics during stance phase in trail running.  

PubMed

Abstract The aim of this study was to investigate the effect of using poles on foot-ground interaction during trail running with slopes of varying incline. Ten runners ran on a loop track representative of a trail running field situation with uphill (+9°), level and downhill (-6°) sections at fixed speed (3.2 m.s(-1)). Experimental conditions included running with (WP) and without (NP) the use of poles for each of the three slopes. Several quantitative and temporal foot-ground interaction parameters were calculated from plantar pressure data measured with a portable device. Using poles induced a decrease in plantar pressure intensity even when the running velocity stayed constant. However, the localisation and the magnitude of this decrease depended on the slope situations. During WP level running, regional analysis of the foot highlighted a decrease of the force time integral (FTI) for absolute (FTIabs; -12.6%; P<0.05) and relative values (FTIrel; -14.3%; P<0.05) in the medial forefoot region. FTIabs (-14.2%; P<0.05) and duration of force application (?t; -13.5%; P<0.05) also decreased in the medial heel region when WP downhill running. These results support a facilitating effect of pole use for propulsion during level running and for the absorption phase during downhill running. PMID:24050463

Daviaux, Yannick; Hintzy, Frédérique; Samozino, Pierre; Horvais, Nicolas

2012-11-13

164

Effects of lumbar extensor fatigue and surface inclination on postural control during quiet stance.  

PubMed

A number of work environments require workers to perform tasks on inclined surfaces. Such tasks, along with muscle fatigue, can impair postural control and increase falling risks. The objective of this study was to determine the effects of surface inclination angle, standing direction, and lumbar extensor fatigue on postural control during quiet standing. A group of 16 young, healthy participants were tested while standing on inclined surfaces before and after lumbar extensor fatigue (induced by repetitive isotonic exercise). Three inclination angles (0°, 18° and 26°) and three standing directions (uphill, downhill, and lateral facing) were examined. Postural control was assessed using several measures derived from center-of-pressure time series and subjectively perceived stability. Significant main and interactive effects of inclination angle and standing direction were found for all dependent measures. The adverse effects of standing on inclined surfaces were found to differ between the three standing directions. In general, dose-response relationships with inclination angle were evident, particularly in the lateral-facing direction. Fatigue-related effects differed between conditions, suggesting that the adverse effect of lumbar extensor fatigue on postural control depend on inclination angle and standing direction. These findings may facilitate the development of fall prevention interventions for work involving inclined surfaces. PMID:22405575

Lin, Dingding; Nussbaum, Maury A

2012-03-07

165

Bipedal stance exercise and prostaglandin E2 (PGE 2) and its synergistic effect in increasing bone mass and in lowering the PGE 2 dose required to prevent ovariectomized-induced cancellous bone loss in aged rats  

Microsoft Academic Search

Previous reports have shown that bone loss was partially prevented by bipedal stance “exercise” following ovariectomy (ovx), and it was well documented that prostaglandin E2 (PGE2) had an anabolic effect on the rat skeleton. The aim of this study was to determine whether lower doses of PGE2 could prevent ovx-induced cancellous bone loss with the combination of bipedal stance exercise.

A Mo; W Yao; C Li; X Tian; M Su; Y Ling; Q Zhang; R. B Setterberg; W. S. S Jee

2002-01-01

166

Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking  

PubMed Central

Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.

Shamaei, Kamran; Sawicki, Gregory S.; Dollar, Aaron M.

2013-01-01

167

The effect of low-dye taping on rearfoot motion and plantar pressure during the stance phase of gait  

PubMed Central

Background Low-dye (LD) taping is commonly used to reduce rearfoot pronation. No studies have previously investigated the effectiveness of LD taping using both plantar pressure distribution (F-Scan) and 3-D (CODA) analysis of rearfoot motion. Methods 20 healthy subjects with a navicular drop test exceeding 10 mm participated in the study. T tests were used to determine whether significant (p < 0.05) differences in plantar pressure and rearfoot motion occurred with LD taping. Results LD taping resulted in statistically significant increases in peak plantar pressure in the lateral midfoot (p = 0.000), along with significant decreases in pressure in the medial forefoot (p = 0.014), and the medial (p = 0.000) and lateral hindfoot (p = 0.007). No significant changes occurred in the medial midfoot (p = 0.794) or lateral forefoot (p = 0.654). When assessed using motion analysis, taping resulted in a statistically significant decrease in rearfoot pronation (p = 0.006), supination (p = 0.025) and total rearfoot range of motion (p = 0.000). The mean rearfoot position during stance was not significantly different however (p = 0.188). Conclusion LD taping is associated with alterations in peak plantar pressure in the midfoot and forefoot that indicate reduced pronation with LD taping. However, LD taping appears to reduce both pronation and supination in the rearfoot, rather than simply reducing pronation, when assessed using 3D motion analysis. Therefore, it would appear that LD taping does indeed reduce pronation, by restricting rearfoot motion in general, rather than pronation specifically. The degree of change observed with LD taping was however very small, and further research is needed to clarify the clinical significance of these initial findings.

O'Sullivan, Kieran; Kennedy, Norelee; O'Neill, Emer; Ni Mhainin, Una

2008-01-01

168

Changes in the relative contribution of each leg to the control of quiet two-legged stance following unilateral plantar-flexor muscles fatigue.  

PubMed

We used unilateral plantar-flexor muscles fatigue to assess the capacity of the central nervous system to adapt quiet two-legged stance control to a unilateral ankle neuromuscular perturbation. Eighteen young healthy adults stood barefoot with their eyes closed and were asked to sway as little as possible. The Experimental group (n = 9) executed this postural task in two conditions, before (pre-test) and following the completion of a fatiguing exercise designed to induce a muscular fatigue in the plantar-flexor muscles of their dominant leg (post-test). For the Control group (n = 9), this fatiguing exercise was replaced with a standing rest period corresponding to the fatiguing exercise. Results of the Experimental group showed no significant difference between the weightbearing index measured in the pre-test condition and that observed in the post-test condition. Results further revealed that unilateral plantar-flexor muscles fatigue yielded different effects on the centre of foot pressure (CoP) displacements under the non-fatigued leg and under the fatigued leg: a wider surface area of the CoP displacements was observed under the non-fatigued than under the fatigued leg, and a higher mean speed of the CoP displacements was observed under the non-fatigued leg only in the post-test relative to the pre-test condition. These findings evidenced that the contribution of each leg to the control of quiet two-legged stance is modified as a result of muscle fatigue of unilateral plantar-flexor muscles. The greater contribution of the non-fatigued leg could be viewed as a fatigue-induced adaptive change in the control of quiet two-legged stance in response to an alteration of the unilateral ankle neuromuscular function induced by unilateral plantar-flexor muscles fatigue. PMID:20390292

Vuillerme, Nicolas; Boisgontier, Matthieu

2010-09-01

169

NET CHANGE IN PERIOSTEAL STRAIN DURING STANCE SHIFT LOADING AFTER SURGERY CORRELATES TO RAPID DE NOVO BONE GENERATION IN CRITICAL SIZED DEFECTS  

PubMed Central

In an ovine femur model, proliferative woven bone fills critical sized defects enveloped by periosteum within two weeks of treatment with the one stage bone transport surgery. We hypothesize that mechanical loading modulates this process. Using high-definition optical strain measurements we determined prevailing periosteal strains for normal and surgically treated ovine femora subjected ex vivo to compressive loads simulating in vivo stance shifting (n=3 per group, normal versus treated). We determined spatial distribution of calcein green, a label for bone apposition in first the two weeks after surgery, in 15°, 30°, and 45° sectors of histological cross sections through the middle of the defect zone (n=6 bones, 3–4 sections/bone). Finally, we correlated early bone formation to either the maximal periosteal strain or the net change in maximal periosteal strain. We found that treatment with the one stage bone transport surgery profoundly changes the mechanical environment of cells within the periosteum during stance shift loading. The pattern of early bone formation is repeatable within and between animals and relates significantly to the actual strain magnitude prevailing in the periosteum during stance shift loading. Interestingly, early bone apposition after the surgery correlates more to the maximal net change in strain (above circa 2000–3000 µ?, in tension or compression) rather than strain magnitude per se, providing further evidence that changes in cell shape may drive mechanoadaptation by progenitor cells. These important insights regarding mechanobiologic factors that enhance rapid bone generation in critical sized defects can be translated to the tissue and organ scale, providing a basis for the development of best practices for clinical implementation and the definition of movement protocols to enhance the regenerative effect.

McBride, Sarah H; Dolejs, Scott; Brianza, Stefano; Knothe, Ulf; Knothe Tate, Melissa L

2013-01-01

170

Balance in single-limb stance in healthy subjects - reliability of testing procedure and the effect of short-duration sub-maximal cycling  

PubMed Central

Background To assess balance in single-limb stance, center of pressure movements can be registered by stabilometry with force platforms. This can be used for evaluation of injuries to the lower extremities. It is important to ensure that the assessment tools we use in the clinical setting and in research have minimal measurement error. Previous studies have shown that the ability to maintain standing balance is decreased by fatiguing exercise. There is, however, a need for further studies regarding possible effects of general exercise on balance in single-limb stance. The aims of this study were: 1) to assess the test-retest reliability of balance variables measured in single-limb stance on a force platform, and 2) to study the effect of exercise on balance in single-limb stance, in healthy subjects. Methods Forty-two individuals were examined for test-retest reliability, and 24 individuals were tested before (pre-exercise) and after (post-exercise) short-duration, sub-maximal cycling. Amplitude and average speed of center of pressure movements were registered in the frontal and sagittal planes. Mean difference between test and retest with 95% confidence interval, the intraclass correlation coefficient, and the Bland and Altman graphs with limits of agreement, were used as statistical methods for assessing test-retest reliability. The paired t-test was used for comparisons between pre- and post-exercise measurements. Results No difference was found between test and retest. The intraclass correlation coefficients ranged from 0.79 to 0.95 in all stabilometric variables except one. The limits of agreement revealed that small changes in an individual's performance cannot be detected. Higher values were found after cycling in three of the eight stabilometric variables. Conclusions The absence of systematic variation and the high ICC values, indicate that the test is reliable for distinguishing among groups of subjects. However, relatively large differences in an individual's balance performance would be required to confidently state that a change is real. The higher values found after cycling, indicate compensatory mechanisms intended to maintain balance, or a decreased ability to maintain balance. It is recommended that average speed and DEV 10; the variables showing the best reliability and effects of exercise, be used in future studies.

Ageberg, Eva; Roberts, David; Holmstrom, Eva; Friden, Thomas

2003-01-01

171

Frontal Plane Motion of the Pelvis and Hip during Gait Stance Discriminates Children with Diplegia Levels I and II of the GMFCS  

PubMed Central

Objective. To determine if gait waveform could discriminate children with diplegic cerebral palsy of the GMFCS levels I and II. Patients. Twenty-two children with diplegia, 11 classified as level I and 11 as level II of the GMFCS, aged 7 to 12 years. Methods. Gait kinematics included angular displacement of the pelvis and lower limb joints during the stance phase. Principal components (PCs) analyses followed by discriminant analysis were conducted. Results. PC1s of the pelvis and hip in the frontal plane differ significantly between groups and captured 80.5% and 86.1% of the variance, respectively. PC1s captured the magnitude of the pelvic obliquity and hip adduction angle during the stance phase. Children GMFCS level II walked with reduced pelvic obliquity and hip adduction angles, and these variables could discriminate the groups with a cross-validation of 95.5%. Conclusion. Reduced pelvic obliquity and hip adduction were observed between children GMFCS level II compared to level I. These results could help the classification process of mild-to-moderate children with diplegia. In addition, it highlights the importance of rehabilitation programs designed to improve pelvic and hip mobility in the frontal plane of diplegic cerebral palsy children level II of the GMFCS.

Kirkwood, Renata Noce; Franco, Rosa de Lourdes Lima Dias; Furtado, Sheyla Cavalcanti; Barela, Ana Maria Forti; Deluzio, Kevin John; Mancini, Marisa Cotta

2012-01-01

172

Time–frequency changes in electromyographic signals after hamstring lengthening surgery in children with cerebral palsy  

Microsoft Academic Search

Increased knee flexion during stance is a common gait deviation in the child with cerebral palsy (CP), with distal hamstring lengthening surgeries being an accepted course of treatment. Post-operatively, improvements in gait kinematics have been reported, however little change is noted in the patterns of muscle activity as portrayed by onset and offset timing in the surface electromyographic (sEMG) signals.

Richard T. Lauer; Brian T. Smith; Patricia A. Shewokis; James J. McCarthy; Carole A. Tucker

2007-01-01

173

The intertextual origins of public opinion: constructing Ebonics in the New York Times  

Microsoft Academic Search

In this article, I revisit the 1996 Oakland School Board (OSB) resolution on Ebonics and perform a discourse analysis of the NeW York Times coverage of the decision. Using the framework of intertextuality, I consider how reported speech allows authors to appropriate authority and construct various stances toward the OSB decision. I discuss how other framing devices work in tandem

Jennifer Sclafani

2008-01-01

174

Effects of interactive video-game based system exercise on the balance of the elderly.  

PubMed

This study evaluated the effects of interactive video-game based (IVGB) training on the balance of older adults. The participants of the study included 30 community-living persons over the age of 65. The participants were divided into 2 groups. Group A underwent IVGB training for 6 weeks and received no intervention in the following 6 weeks. Group B received no intervention during the first 6 weeks and then participated in training in the following 6 weeks. After IVGB intervention, both groups showed improved balance based on the results from the following tests: the Berg Balance Scale (BBS), Modified Falls Efficacy Scale (MFES), Timed Up and Go (TUG) test, and the Sway Velocity (SV) test (assessing bipedal stance center pressure with eyes open and closed). Results from the Sway Area (SA) test (assessing bipedal stance center pressure with eyes open and closed) revealed a significant improvement in Group B after IVGB training. Group A retained some training effects after 6 weeks without IVGB intervention. Additionally, a moderate association emerged between the Xavix measured step system stepping tests and BBS, MFES, Unipedal Stance test, and TUG test measurements. In conclusion, IVGB training improves balance after 6 weeks of implementation, and the beneficial effects partially remain after training is complete. Further investigation is required to determine if this training is superior to traditional physical therapy. PMID:23177921

Lai, Chien-Hung; Peng, Chih-Wei; Chen, Yu-Luen; Huang, Ching-Ping; Hsiao, Yu-Ling; Chen, Shih-Ching

2012-11-21

175

Philip Morris's website and television commercials use new language to mislead the public into believing it has changed its stance on smoking and disease  

PubMed Central

Objectives This paper analyses Philip Morris's evolving website and the legal strategies employed in its creation and dissemination. Methods Internal tobacco documents were searched and examined and their substance verified and triangulated using media accounts, legal and public health research papers, and visits to Philip Morris's website. Various drafts of website language, as well as informal discussion of the website's creation, were located in internal Philip Morris documents. I compared website statements pertaining to Philip Morris's stance on cigarette smoking and disease with statements made in tobacco trials. Results Philip Morris created and disseminated its website's message that it agreed that smoking causes disease and is addictive in an effort to sway public opinion, while maintaining in a litigation setting its former position that it cannot be proved that smoking causes disease or is addictive. Conclusions Philip Morris has not changed its position on smoking and health or addiction in the one arena where it has the most to lose—in the courtroom, under oath.

Friedman, Lissy C

2007-01-01

176

Age-related changes in force and power associated with balance of women in quiet bilateral stance on a firm surface.  

PubMed

Quantitative assessment of the fluctuations of the body centre of mass (CM) while in a stationary bilateral stance on a firm surface is an important criterion of the functional state of human motor-vestibular and sensory apparatus. From analysis of the literature we conclude that more objective characteristics of human balance in quiet standing may be the amount of energy used to maintain the CM in a constant position. Further analysis of the references showed that these characteristics have not been investigated in neurological practice. In this study, the displacement of CM in participants standing in a normal anatomical position was analysed. Forty-five healthy women in three age groups: 18-24, 45-55 and over 60 years participated in the experiments, which consisted of recording changes in partial body weight on the force platform (under one leg) in situations with opened and closed eyes. The specific power of oscillation of body sway and force of lateral swing of CM were calculated. Results indicated that the maximum specific power of oscillation and force of lateral swing were observed in the group of women older than 60 years, especially in the absence of vision. Minimum values occurred in the group of 18-24 years. We also found a considerable variability in all indices in all age groups. This indicates that the stability of the vertical posture in humans depends also on the individual biological characteristics of the central nervous and muscular systems. PMID:22520438

Skurvidas, A; Cesnaitiene, V J; Mickeviciene, D; Gutnik, B; Nicholson, J; Hudson, G

2012-04-19

177

The effect of subtalar inversion/eversion on the dynamic function of the tibialis anterior, soleus, and gastrocnemius during the stance phase of gait.  

PubMed

The purpose of this study was to determine how gait deviation in one plane (i.e. excessive subtalar inversion/eversion) can affect the dynamic function of the tibialis anterior, gastrocnemius, and soleus to accelerate the subtalar, ankle, knee and hip joints, as well as the body center of mass. Induced acceleration analysis was performed based on a subject-specific three-dimensional linkage model configured by stance phase gait data and driven by one unit of muscle force. Eight healthy adult subjects were examined in gait analysis. The subtalar inversion/eversion was modeled by offsetting up to 20° from the normal subtalar angle while other configurations remained unaltered. This study showed that the gastrocnemius, soleus and tibialis anterior generally functioned as their anatomical definition in normal gait, but counterintuitive function was occasionally found in the bi-articular gastrocnemius. The plantarflexors play important roles in the body support and forward progression. Excessive subtalar eversion was found to enlarge the plantarflexors and tibialis anterior's function. Induced acceleration analysis demonstrated its ability to isolate the contributions of individual muscle to a given factor, and as a means of studying effect of pathological gait on the dynamic muscle functions. PMID:21474318

Wang, Ruoli; Gutierrez-Farewik, Elena M

2011-04-06

178

A unified deformable (UD) segment model for quantifying total power of anatomical and prosthetic below-knee structures during stance in gait.  

PubMed

Anatomically-relevant (AR) biomechanical models are traditionally used to quantify joint powers and segmental energies of lower extremity structures during gait. While AR models contain a series of rigid body segments linked together via mechanical joints, prosthetic below-knee structures are often deformable objects without a definable ankle joint. Consequently, the application of AR models for the study of prosthetic limbs has been problematic. The purpose of this study was to develop and validate a unified deformable (UD) segment model for quantifying the total power of below-knee structures. Estimates of total below-knee power derived via the UD segment model were compared to those derived via an AR model during stance in gait of eleven healthy subjects. The UD segment model achieved similar results to the AR model. Differences in peak power, total positive work, and total negative work were 1.91±0.31%, 3.97±0.49%, and 1.39±0.33%, relative to the AR model estimates. The main advantage of the UD segment model is that it does not require the definition of an ankle joint or foot structures. Therefore, this technique may be valuable for facilitating direct comparisons between anatomical and disparate prosthetic below-knee structures in future studies. PMID:22939292

Takahashi, Kota Z; Kepple, Thomas M; Stanhope, Steven J

2012-08-30

179

Withdrawal reflex responses evoked by repetitive painful stimulation delivered on the sole of the foot during late stance: site, phase, and frequency modulation.  

PubMed

The modulation of the lower limb nociceptive withdrawal reflex elicited during late stance by a stimulus train with frequencies of 15 and 30 Hz delivered to the mid-forefoot, arch of the foot, and heel was investigated. Stimulation was delivered at four moments of the gait cycle between heel-off and toe-off. Stimulation at 15 Hz induced larger kinematic responses at the knee and hip. Reduced plantarflexion and increased dorsiflexion, compared to control steps, were evoked at the ankle; these kinematic responses were site dependent with minimum responses evoked by stimulation at the heel. The dorsiflexion response was largest when stimulating at toe-off and was larger for stimulation at 15 Hz than at 30 Hz. The muscle reflex responses were site modulated in tibialis anterior with largest responses evoked by stimulation at the arch of the foot and mid-forefoot, and phase and frequency modulated in soleus. This study presents a detailed assessment of the lower limb nociceptive reflex modulation and provides results, which might have application in the rehabilitation of the hemiparetic gait. PMID:19189087

Spaich, Erika G; Emborg, Jonas; Collet, Thomas; Arendt-Nielsen, Lars; Andersen, Ole Kaeseler

2009-02-03

180

Trans-tibial amputee gait: time-distance parameters and EMG activity.  

PubMed

Gait analysis of trans-tibial (TT) amputees discloses asymmetries in gait parameters between the amputated and sound legs. The present study aimed at outlining differences between both legs with regard to kinematic parameters and activity of the muscles controlling the knees. The gait of 14 traumatic TT amputees, walking at a mean speed of 74.96 m/min, was analysed by means of an electronic walkway, video camera, and portable electromyography system. Results showed differences in kinematic parameters. Step length, step time and swing time were significantly longer, while stance time and single support time were significantly shorter on the amputated side. A significant difference was also found between knee angle in both legs at heel strike. The biceps femoris/vastus medialis ratio in the amputated leg, during the first half of stance phase, was significantly higher when compared to the same muscle ratio in the sound leg. This difference was due to the higher activity of the biceps femoris, almost four times higher than the vastus medialis in the amputated leg. The observed differences in time-distance parameters are due to stiffness of the prosthesis ankle (the SACH foot) that impedes the normal forward advance of the amputated leg during the first half of stance. The higher knee flexion at heel strike is due to the necessary socket alignment. Unlike in the sound leg, the biceps femoris in the amputated leg reaches maximal activity during the first half of stance, cocontracting with the vastus medialis, to support body weight on the amputated leg. The obtained data can serve as a future reference for evaluating the influence of new prosthetic components on the quality of TT amputee's gait. PMID:11195356

Isakov, E; Keren, O; Benjuya, N

2000-12-01

181

Does sensorimotor training improve the static balance of young volleyball players?  

Microsoft Academic Search

The aim of this investigation is to assess the effectiveness of a 6-week balance training (BT) protocol, integrated in regular training sessions, on postural sway of young female volleyball players (n = 26, age 13.0 ± 0.2 years) divided into two groups (intervention and control; 13 per group). Trials were performed for bipedal and unipedal stance conditions before and after the BT protocol, using

Massimiliano Pau; Andrea Loi; Maria Cristina Pezzotta

2012-01-01

182

Does sensorimotor training improve the static balance of young volleyball players?  

Microsoft Academic Search

The aim of this investigation is to assess the effectiveness of a 6-week balance training (BT) protocol, integrated in regular training sessions, on postural sway of young female volleyball players (n = 26, age 13.0 ± 0.2 years) divided into two groups (intervention and control; 13 per group). Trials were performed for bipedal and unipedal stance conditions before and after the BT protocol, using

Massimiliano Pau; Andrea Loi; Maria Cristina Pezzotta

2011-01-01

183

A case of successful technology transfer to health care. Total quality materials management and just-in-time.  

PubMed

Describes one approach to meeting the healthcare cost reduction challenge through the hospital materials management function. Highlights the value of taking a proactive stance to meet the challenge; transferring technology across industry sectors, such as employing a just-in-time inventory management system in clinical areas of hospital materials management, and adopting a win-win managerial philosophy. Features a case study to demonstrate the ideas in practice. PMID:10166205

Heinbuch, S E

1995-01-01

184

Time After Time  

NSDL National Science Digital Library

Students use a variety of strategies and techniques to develop an understanding of telling time. They use estimation to tell time, using seconds, hours, and minutes in order to choose reasonable time estimates for given activities. Students use pictures, words, and symbols in order to read, write, and represent time to the nearest minute. Students determine elapsed time when given a start time, counting up using minutes and hours.

Service, National S.

2009-04-22

185

Fall Risk-Relevant Functional Mobility Outcomes in Dementia Following Dyadic Tai Chi Exercise  

PubMed Central

Whether persons with dementia benefit from fall prevention exercise is unclear. Applying the Positive Emotion-Motivated Tai Chi protocol, preliminary findings concerning adherence and effects of a dyadic Tai Chi exercise program on persons with Alzheimer’s disease (AD) are reported. Using pre/ posttest design, 22 community-dwelling AD-caregiver dyads participated in the program. Fall-risk-relevant functional mobility was measured using Unipedal Stance Time (UST) and Timed Up and Go (TUG) tests. Results showed that 19/22 (86.4%) AD patients completed the 16-week program and final assessment; 16/19 dyads (84.2%) completed the prescribed home program as reported by caregivers. UST adjusted mean improved from 4.0 to 5.1 (Week 4, p < .05) and 5.6 (Week 16, p < .05); TUG improved from 13.2 to 11.6 (Week 4, p < .05) and 11.6 (Week 16, p > .05) post intervention. Retaining dementia patients in an exercise intervention remains challenging. The dyadic Tai Chi approach appears to succeed in keeping AD-caregiver dyads exercising and safe.

Yao, Lan; Giordani, Bruno J.; Algase, Donna L.; You, Mei; Alexander, Neil B.

2012-01-01

186

The short version of the Activities-specific Balance Confidence (ABC) scale: its validity, reliability, and relationship to balance impairment and falls in older adults.  

PubMed

A shortened version of the ABC 16-item scale (ABC-16), the ABC-6, has been proposed as an alternative balance confidence measure. We investigated whether the ABC-6 is a valid and reliable measure of balance confidence and examined its relationship to balance impairment and falls in older adults. Thirty-five community-dwelling older adults completed the ABC-16, including the 6 questions of the ABC-6. They also completed the following clinical balance tests: unipedal stance time (UST), functional reach (FR), Timed Up and Go (TUG), and maximum step length (MSL). Participants reported 12-month falls history. Balance confidence on the ABC-6 was significantly lower than on the ABC-16, however scores were highly correlated. Fallers reported lower balance confidence than non-fallers as measured by the ABC-6 scale, but confidence did not differ between the groups with the ABC-16. The ABC-6 significantly correlated with all balance tests assessed and number of falls. The ABC-16 significantly correlated with all balance tests assessed, but not with number of falls. Test-retest reliability for the ABC-16 and ABC-6 was good to excellent. The ABC-6 is a valid and reliable measure of balance confidence in community-dwelling older adults, and shows stronger relationships to falls than does the ABC-16. The ABC-6 may be a more useful balance confidence assessment tool than the ABC-16. PMID:19615762

Schepens, Stacey; Goldberg, Allon; Wallace, Melissa

2009-07-16

187

The short version of the Activities-specific Balance Confidence (ABC) scale: Its validity, reliability, and relationship to balance impairment and falls in older adults  

PubMed Central

A shortened version of the ABC 16-item scale (ABC-16), the ABC-6, has been proposed as an alternative balance confidence measure. We investigated whether the ABC-6 is a valid and reliable measure of balance confidence and examined its relationship to balance impairment and falls in older adults. Thirty-five community-dwelling older adults completed the ABC-16, including the six questions of the ABC-6. They also completed the following clinical balance tests: unipedal stance time (UST), functional reach (FR), Timed Up and Go (TUG), and maximum step length (MSL). Participants reported twelve-month falls history. Balance confidence on the ABC-6 was significantly lower than on the ABC-16, however scores were highly correlated. Fallers reported lower balance confidence than non-fallers as measured by the ABC-6 scale, but confidence did not differ between the groups with the ABC-16. The ABC-6 significantly correlated with all balance tests assessed and number of falls. The ABC-16 significantly correlated with all balance tests assessed, but not with number of falls. Test-retest reliability for the ABC-16 and ABC-6 was good to excellent. The ABC-6 is a valid and reliable measure of balance confidence in community-dwelling older adults, and shows stronger relationships to falls than does the ABC-16. The ABC-6 may be a more useful balance confidence assessment tool than the ABC-16.

Schepens, Stacey; Goldberg, Allon; Wallace, Melissa

2009-01-01

188

Prolonged peroneal reaction time in ankle instability.  

PubMed

The peroneal reflex time to sudden ankle inversion and the postural control of 15 athletes with functionally instable ankles were compared with 15 stable controls. A trapdoor produced sudden ankle inversion. Surface electrodes recorded electromyographic activity of the peroneal muscles. Postural sway was expressed by a transverse sway value obtained during single limb stance on a force plate. Increased postural sway was found in subjects with functional instability (p less than 0.01). This is in accordance with previous studies. Functionally instable subjects also displayed an increased peroneal reaction time (p less than 0.01) supporting the theory that functional instability is induced by a proprioceptive reflex defect. Nine of the 15 instable subjects were unilaterally instable and showed lower peroneal reaction time and postural sway values for the stable ankle, but the difference was not significant. There was a high degree of correlation between postural sway and peroneal reaction time (Spearman's rho = .92). In ten functionally instable athletes tested with and without ankle taping, it could not be verified that a reflex enhancing effect of taping occurs through stimulation of cutaneous afferents. PMID:1889937

Konradsen, L; Ravn, J B

1991-06-01

189

Timely Time Estimates  

Microsoft Academic Search

\\u000a Estimations of execution time are essential for design and development of safety critical embedded real-time systems, such\\u000a as avionics, automotive and aerospace systems. In such systems, execution time is part of the functional specification, hence\\u000a correct behaviour requires sufficiently powerful target hardware to meet deadlines or achieve required polling rates, etc.\\u000a Yet, grossly overestimated resource usage results in excessive cost

Andreas Holzer; Visar Januzaj; Stefan Kugele; Michael Tautschnig

2010-01-01

190

The stance of stance: a critical look at ways stance is expressed and modeled in academic discourse  

Microsoft Academic Search

As work on how evaluation is expressed in academic discourse proliferates, it is easy to fall into the methodological trap of assuming that all descriptions lead in the same direction, that one need simply combine and implement existing categories and models. This paper raises a number of methodological questions about the universality of commonly applied linguistic categories by offering a

Marc Silver

2003-01-01

191

A “critical” time for HRD?  

Microsoft Academic Search

Human resource development (HRD) is a concept associated with human resource management, and, by this association, one component of the broader concept of management. Much work has examined management practices from a critical stance and this article provides a brief review. However, HRD is a more recent concept, still emerging and finding space in both academic and practitioner spheres. This

Sally Sambrook

2004-01-01

192

Realism, Instrumentalism, and the Intentional Stance  

Microsoft Academic Search

One of Dennett's principal arguments for on instrumentolistic construal of in- tentionol ottributions (e.g., ottributions of belief, etc.) is that such attributions ore environment relative. I argue that one can and should odopt a realist per- spective toword such ottributions, but accommodate their environmental rela- tivity by treoting intentional properties as relational properties. By doing so one acquires a useful

William Bechtel

1985-01-01

193

Narrative Theory and the Intentional Stance  

Microsoft Academic Search

Drawing on treatments of the problem of intentionality in fields encompassed by the umbrella discipline of cognitive science, including language theory, psychology, and the philosophy of mind, this paper explores issues underlying recent debates about the role of intentions in narrative contexts. To avoid entering the debate on the terms set by antiintentionalists, my analysis shifts the focus away from

David Herman

2008-01-01

194

Educators' Stances toward Gender Issues in Literacy.  

ERIC Educational Resources Information Center

|A study examined literacy professionals' interest in gender issues in literacy education. A total of 1,519 K-12 teachers; reading specialists; teacher educators in reading, language arts, and related fields; library media specialists; and school administrators who make policy decisions related to literacy education completed a survey. Results…

Commeyras, Michelle; And Others

195

Universal Time  

NSDL National Science Digital Library

This article explains the concept of 'Universal Time' (UT), sometimes referred to as 'Coordinated Universal Time' (UTC). Topics include how UTC is measured, who uses it, and a brief discussion of the historical context of this time standard.

196

Timing matters.  

PubMed

Cells are entities in space and time. Systems biology strives to understand their composition, structural organization as well as dynamic behavior under different conditions. Here, measures for dynamic properties such as characteristic times, time hierarchy and time-dependent response are reviewed. Using a number of examples from yeast and micro-organism systems biology, the importance of considering the timing in experimental and theoretical research is discussed. PMID:19941864

Klipp, Edda

2009-12-17

197

Sequencing Time  

NSDL National Science Digital Library

In this activity, students gain an understanding of relative and numerical time by placing events in sequence and assigning relative times to the events. This will familarize them with the methods used by scientists to develop the geologic time scale. This activity contains objectives, materials, procedure, and extensions.

2007-12-12

198

Time interpolator  

NASA Astrophysics Data System (ADS)

A time interpolator for the measurement of time difference using digital and analog techniques is described. Emitter Coupled Logic (ECL) and high frequency techniques were used. The difficulty with ECL is to keep the connections as short as possible and to properly terminate the output to avoid reflections. The digital part of the interpolator consists of a continuous clock and logic which converts the input signal into a start and stop signal. The analog part consists of a time to amplitude converter and an analog to digital convertor. The maximum measuring time is 6.4 microns with a 100 ps resolution.

Deblok, M.

1990-06-01

199

Geologic Time  

NSDL National Science Digital Library

The Earth is very old -- 4.5 billion years or more -- according to recent estimates. This vast span of time, called geologic time by earth scientists, is difficult to comprehend in the familiar time units of months and years, or even centuries. How then do scientists reckon geologic time, and why do they believe the Earth is so old? A great part of the secret of the Earth's age is locked up in its rocks, and our centuries-old search for the key led to the beginning and nourished the growth of geologic science.

Newman, William L.

1997-01-01

200

Clock Time  

NSDL National Science Digital Library

You will have practice reading the time on a clock and pairing it up with its digital or written text match. Complete this as quickly as you can in order to beat the clock! Stop the Clock 1 Stop the Clock 2 Stop the Clock 6 Each of these links varies in degree of difficulty. They progressively go up in difficulty in the time you are telling. The first starts out telling time in half hour intervals. The following activity progress to fifteen minutes. The final activity is matching up the time on the clock to ...

Greene, Miss

2010-04-26

201

Geologic time  

USGS Publications Warehouse

The Earth is very old 4 1/2 billion years or more according to recent estimates. This vast span of time, called geologic time by earth scientists, is difficult to comprehend in the familiar time units of months and years, or even centuries. How then do scientists reckon geologic time, and why do they believe the Earth is so old? A great part of the secret of the Earth's age is locked up in its rocks, and our centuries-old search for the key led to the beginning and nourished the growth of geologic science.

Newman, William L.

2000-01-01

202

Time Utilities  

NASA Astrophysics Data System (ADS)

Time Utilities are software tools that, in principal, allow one to calculate BJD to a precision of 1 ?s for any target from anywhere on Earth or from any spacecraft. As the quality and quantity of astrophysical data continue to improve, the precision with which certain astrophysical events can be timed becomes limited not by the data themselves, but by the manner, standard, and uniformity with which time itself is referenced. While some areas of astronomy (most notably pulsar studies) have required absolute time stamps with precisions of considerably better than 1 minute for many decades, recently new areas have crossed into this regime. In particular, in the exoplanet community, we have found that the (typically unspecified) time standards adopted by various groups can differ by as much as a minute. Left uncorrected, this ambiguity may be mistaken for transit timing variations and bias eccentricity measurements. We recommend using BJD_TDB, the Barycentric Julian Date in the Barycentric Dynamical Time standard for any astrophysical event. The BJD_TDB is the most practical absolute time stamp for extraterrestrial phenomena, and is ultimately limited by the properties of the target system. We compile a general summary of factors that must be considered in order to achieve timing precisions ranging from 15 minutes to 1 ?s, and provide software for download and online webapps for use.

Eastman, Jason

2012-06-01

203

Timing Nutriceuticals?  

PubMed Central

Evidence on time-dependent effects of drugs and nutrition is succinctly reviewed in order to illustrate and advocate investigations of the timing of nutriceuticals. Emphasis is placed on the merits of coordinated, individually, inferentially, statistically examined sets of N-of-1 studies.

Halberg, Franz; Cornelissen, Germaine; Singh, R.B.

2011-01-01

204

Time Management  

ERIC Educational Resources Information Center

|The time management is worthy goal of many human activities. It concerns variety problems related to goals definition, assessment of available resources, control of management policies, scheduling of decisions. This book is an attempt to illustrate the decision making process in time management for different success stories, which can be used as…

Stoilov, Todor, Ed.

2012-01-01

205

Time ephemeris  

NASA Astrophysics Data System (ADS)

The location-independent part of barycentric coordinate time and geocentric coordinate time (TCB-TCG), the difference between the two new time scales adopted by the IAU, was integrated numerically for three JPL planetary/lunar ephemerides; DE102, DE200, and DE245. The differences among these three integrations were mostly explained by the difference in the adopted constants of the ephemerides. It was shown that the post-Newtonian correction and the perturbation by asteroids are negligible except for the mean rate, LC. The comparison of these numerical integrations with the analytical formulas of Hirayama et al. (1987) and Fairhead & Bretagnon (1990) as well as their extended versions lead to the best estimate of LC as 1.480 826 845 7 x 10-8 + or - 1.0 x 10-17. Combining this with the recent value of the geoid potential in Bursa et al. (1992), we estimate the value of LB, the scale difference between TCB and terrestrial time (TT), as 1.550 519 748 x 10-8 + or - 4 x 10-17. This will be useful in converting the numerical values of some astronomical constants determined in the old IAU time scale barycentric dynamic time (TDB) to those in TCB. Also the paper will be useful when converting between TCB and TDB, i.e. the time scales themselves.

Fukushima, T.

1995-02-01

206

On Time  

NSDL National Science Digital Library

This online exhibit from a prominent American museum explores the character of time -- its impact on our daily lives and its ability to shape and reform human consciousness. The site is from the National Museum of American History and concentrates on how humans have measured time from 1700 to the present. The exhibit presents text and images describing the history of keeping time from the century immediately preceding the industrial revolution -- when sundials were still in use -- to our present age of digital access and a global village that never sleeps.

207

Creative Time  

NSDL National Science Digital Library

Creative Time curates, funds, and organizes public art projects, so their website is a reference of the form dating back to 1975. You can browse by program name, date or artist's name (the most common of these being "multiple artists.") Creative Time's roster also includes familiar names such as Marina Abramovic, Doug Aitken, Laurie Anderson, David Byrne, Paul Chan, Jenny Holzer, Gary Hume, Vik Muniz, Takashi Murakami, Shirin Neshat, Steve Powers, and Cai Guo-Qiang. For example, Creative Time worked with Cai Guo-Qiang to present Light Cycle, in 2003, to celebrate the 150th anniversary of New York City's Central Park; in 2008 David Byrne's Playing the Building transformed the Battery Maritime Building in Lower Manhattan into a massive sound sculpture that visitors could play using a keyboard; and in summer 2012 Creative Time and multiple artists hosted a sandcastle competition at Far Rockaway, possibly the start of a new New York summer tradition.

2012-08-31

208

Geologic Time  

NSDL National Science Digital Library

This site contains 24 questions on the topic of geologic time, which covers dating techniques and unconformities. This is part of the Principles of Earth Science course at the University of South Dakota. Users submit their answers and are provided immediate feedback.

Heaton, Timothy

209

Reaction Time  

NSDL National Science Digital Library

This lab is not an inquiry activity. There are some students whose reaction times will not allow them to catch a 12 inch ruler. They may use a dowel, stick, strip of cardboard, etc. Although the students are led to believe that the point of the lab is to

Horton, Michael

2009-05-30

210

Number Time  

ERIC Educational Resources Information Center

|This article features Number Time, a site developed by the British Broadcasting Corporation (BBC) for young mathematics learners, located at www.bbc.co.uk/schools/numbertime. The site uses interactive animation to help children in pre-K through grade 2 understand and practice number basics. Users will find online games, videos that tell number…

Herrera, Terese A.

2004-01-01

211

Geologic Time.  

ERIC Educational Resources Information Center

|Discusses the historical development of the concept of geologic time. Develops the topic by using the major discoveries of geologists, beginning with Steno and following through to the discovery and use of radiometric dating. An extensive reference list is provided. (JM)|

Albritton, Claude C., Jr.

1984-01-01

212

Deep Time  

NSDL National Science Digital Library

In this video a Penn State professor refers to National Park canyons carved out by water and wind as he explains “deep time” - the notion that the earth is billions of years old; another professor states how the theory of evolution is supported by evidence of an ancient Earth recorded in rocks.

Wpsu

2010-05-04

213

Gender differences exist in neuromuscular control patterns during the pre-contact and early stance phase of an unanticipated side-cut and cross-cut maneuver in 15–18 years old adolescent soccer players  

Microsoft Academic Search

Non-contact ACL injuries generally occur as the foot contacts the ground during cutting or landing maneuvers and the non-contact ACL injury rate is 2–8 times greater in females compared to males. To provide insight into the gender bias of this injury, this study set out to identify gender differences in the neuromuscular response of the quadriceps, hamstrings and gastrocnemii muscles

Scott C. Landry; Kelly A. McKean; Cheryl L. Hubley-Kozey; William D. Stanish; Kevin J. Deluzio

2009-01-01

214

Time Traveler  

NSDL National Science Digital Library

This NOVA website simulates travel to distant stars and back in a spaceship that can move at various percentages of the speed of light. You set the spaceship speed and choose your destination star, and the simulation calculates the time of travel as measured on Earth and inside the spaceship. Text describes the "twin paradox" of the theory of relativity and also the 1971 test of its prediction using airliners and atomic clocks.

2011-10-15

215

Times Square  

NSDL National Science Digital Library

This interactive online game helps students develop fluency with multiplication facts as well as strategic thinking. The goal is to claim four numbers in a row (vertically, horizontally, or diagonally) on a 6 by 6 game board displaying the products of one-digit numbers. Players take turns moving one of the two factor markers to claim a product on the board before time runs out. This game is part of NCTM's Calculation Nation project. Users may login as a guest and play against the computer, or register (free) to challenge other players online.

2010-01-01

216

Importance timing  

NASA Astrophysics Data System (ADS)

Bayesian evidence Z = ? L(x)d?(x) is defined as likelihood L integrated over prior ?, and is often computed in that form -- with nested sampling as the preferred algorithm for passing from prior to posterior in large or complicated applications. However, a user may suspect that some locations x are more useful than others, and wish to guide the computation by using a suitable weight function w(x). In conventional importance sampling, such weights are incorporated by re-writing Z as ?(L/w)(wd?), using a weighted prior w? and correspondingly de-weighted likelihood L/w. Unfortunately, w cannot be updated during a run without altering the likelihood surfaces (which nested sampling requires to be fixed). Also, the normalization ? wd? must be known if the value of Z is to be retrieved. Importance timing removes those disadvantages by preserving the likelihood unchanged. Excess prior weight w is cancelled, not through L, but by adjusting the rate of the MCMC clock which defines termination of a trial exploration. This preserves the evidence value and enables the weights to be (slowly) learned as iterations proceed.

Skilling, John

2013-08-01

217

Doing Time  

PubMed Central

Once convicted, the perpetrator of serious crime embarks upon a new journey: the challenge of adjusting to long-term imprisonment. Prisoners’ views of incarceration and the meaning of this experience may affect their later adjustment to life in the community. On the basis of brief narrative responses collected during an epidemiological survey of the psychological health of prisoners in France, this study examined the impact of incarceration on psychological state in a group of 59 inmates serving long sentences. Qualitative content analysis and computer-assisted linguistic analysis (using ALCESTE software) were performed on the textual data of open responses to three standard questions. Using a combination of these two approaches, seven categories of the subjective experience of prisoners in the sample were identified: the Outside World, Others, Punishment, Time, Affects and Impulses, Self-Concept, and Speech. Further qualitative analyses were then performed to compare the responses of Severely Mentally Ill (SMI) subjects and subjects with no psychiatric disorder. These analyses revealed contrasting attitudes towards incarceration. SMI subjects spoke in more hostile and persecutory terms about their experience in prison, attributing suffering to external circumstances, while subjects with no psychiatric disorder evoked similar themes, but with an introspective attitude. The themes evoked by mentally ill individuals in our sample suggest that their reactions to the prison environment arise in part from aspects of their psychiatric symptoms, and this may have relevance to future mental health policy and practices in criminal corrections.

Yang, Suzanne; Kadouri, Alane; Revah-Levy, Anne; Mulvey, Edward P.; Falissard, Bruno

2009-01-01

218

Cosmic Times  

NSDL National Science Digital Library

This series of curriculum support materials and classroom activities explores how our understanding of the nature of the Universe has changed during the past 100 years. Students examine the process of science through the stories of the people and the discoveries that caused our understanding to evolve from a static universe to a Universe whose expansion is accelerating. The series illustrates the nature of science by tracing the process of discovery from the confirmation of Einsteinâs theory of gravity, to Hubbleâs evidence for the expanding Universe, to the detection of the microwave background, and finally to the discovery of dark energy. The series includes six posters, each resembling the front page of a newspaper from a particular time in this history with articles describing the discoveries. Each poster is accompanied by an on-line teacher guide and 4-5 downloadable, inquiry-based lessons, which teach the science, the process of science, and skills for science literacy. Two downloadable âNewsletterâ versions of the poster are available for individual student use: one with the same text as on the poster, while the second uses text at a lower reading level.

Lochner, James

2010-02-16

219

Computation method for available response time due to tripping at minimum foot clearance.  

PubMed

Falls prevention is important for older individuals to maintain healthy lifestyles and is an essential challenge in sustaining the socioeconomic structure of many advanced nations. Tripping has been recognized as the largest cause of falls and accordingly, understanding tripping-induced anterior balance loss is necessary in reducing the overall frequency of falls among older adults. Hazardous anterior balance loss due to tripping can be attributed to the mid-swing phase event, minimum foot clearance (MFC). The mechanism of tripping-induced anterior balance loss can be described as anterior movement of the center of mass (CoM) passing the frontal boundary of the supporting base between the swing and stance toes. The first aim of the current study was to establish a computational method for determining available response time (ART) to anterior balance loss due to tripping at MFC, in other words, the time taken for CoM to reach the anterior boundary and therefore, the time limit for balance recovery. Kinematic information of CoM and both toes in addition to simulated impact force due to tripping at MFC were used to estimate ART. The second aim was to apply correlation analysis to a range of gait parameters to identify the factors influencing ART. ART for balance loss in the forward direction due to tripping was on average. 0.11s for both the dominant and non-dominant limbs' simulated tripping at MFC. Correlation analysis revealed five factors at MFC that prolong ART including: 1) greater fore-aft distance from CoM to stance toe, 2) greater sideway distance from CoM to swing toe, 3) longer distance from CoM to the frontal boundary of the supporting base, 4) slower CoM forward velocity and 5) slower horizontal toe velocity. The established ART computation method can be utilized to examine the effects of ageing and various gait tasks on the likelihood of tripping-induced anterior balance loss and associated falls. PMID:24110833

Nagano, H; Begg, R; Sparrow, W A

2013-07-01

220

Pleasure, Learning, Video Games, and Life: The Projective Stance  

ERIC Educational Resources Information Center

This article addresses three questions. First, what is the deep pleasure that humans take from video games? Second, what is the relationship between video games and real life? Third, what do the answers to these questions have to do with learning? Good commercial video games are deep technologies for recruiting learning as a form of profound…

Gee, James Paul

2005-01-01

221

SEN Students' Inclusion in Greece: Factors Influencing Greek Teachers' Stance  

ERIC Educational Resources Information Center

|The present study, based on recent research in secondary education schools in Greece, aimed at recording Greek teachers' attitudes towards inclusion and determining the factors that enhance positive attitudes or negative ones. The findings of this research confirm that Greek teachers, despite obvious infrastructural and institutional hindrances,…

Koutrouba, Konstantina; Vamvakari, Malvina; Theodoropoulos, Helen

2008-01-01

222

Conveying a Stance of Religious Pluralism in Children's Literature  

ERIC Educational Resources Information Center

Religious discrimination is a global concern, as social dissonance and devastating violence result from religious intolerance. In order to develop socially competent, global citizens and create a peaceful society, religious diversity must be explored in public school classrooms; yet it remains a controversial and seldom addressed topic. Children's…

Sanders, Jennifer; Foyil, Kris; Graff, Jennifer M.

2010-01-01

223

Morality and Foreign Policy. A Symposium on President Carter's Stance.  

ERIC Educational Resources Information Center

|This monograph contains a critical examination of President Carter's view on ethics and foreign policy as expressed in his commencement speech at Notre Dame University on May 22, 1977. The book is organized into three parts. Part 1 contains Mr. Carter's speech entitled, "Power for Humane Purposes." Part 2 contains nine responses to the speech:…

Lefever, Ernest W., Ed.

224

Effects of Operator Stance on Pushing and Pulling Tasks  

Microsoft Academic Search

A considerable amount of research has been done to determine the magnitudes of forces man can exert on loads. However, very little has been done to determine the optimum configurations an operator should assume in front of a load to be most effective. This paper presents the methodology and results of an investigation concerning these skeletal configurations and selects an

M. M. Ayoub; J. W. McDaniel

1974-01-01

225

Dialogic Teaching: Talk in Service of a Dialogic Stance  

ERIC Educational Resources Information Center

We consider what it means to be a dialogic teacher as characterized by Paulo Freire and Robin Alexander, and utilizing discourse analysis, we explicate how one elementary teacher's talk reflects these characteristics. We provide context for and analysis of a seven-minute discussion selected as a cumulative achievement the focal nine-year-olds are…

Boyd, Maureen Patricia; Markarian, William C.

2011-01-01

226

Human Genetic Engineering: A Survey of Student Value Stances  

ERIC Educational Resources Information Center

Assesses the values of high school and college students relative to human genetic engineering and recommends that biology educators explore instructional strategies merging human genetic information with value clarification techniques. (LS)

Wilson, Sara McCormack; And Others

1975-01-01

227

Pleasure, Learning, Video Games, and Life: The Projective Stance  

ERIC Educational Resources Information Center

|This article addresses three questions. First, what is the deep pleasure that humans take from video games? Second, what is the relationship between video games and real life? Third, what do the answers to these questions have to do with learning? Good commercial video games are deep technologies for recruiting learning as a form of profound…

Gee, James Paul

2005-01-01

228

Place-based education: a transformative activist stance  

NASA Astrophysics Data System (ADS)

The ethnography presented by van Eijck and Roth focuses on the activities of people involved in a government funded internship program in conservation and restoration, which was offered by a `multidisciplinary research center' through a local First Nation adult education center. The internship was designed, in partnership with a local non-profit conservation society (OceanHealth), to appeal to First Nation men and women considering career change, returning to school, or re-entering the work place. The primary aim of the internship was to `provide authentic science for diverse student populations (and their teachers), with particular attention to the needs of students from First Nations, to become scientifically literate to the extent that it prepares them for participating in public debates, community decision-making, and personal living consistent with long-term environmentally sustainable forms of life'. The authors report that at least one of the two interns was not interested in science and a WSÁNEC elder expressed dissatisfaction with the efforts to establish the nature park and its current approved uses. Van Eijck and Roth argue that the divergence between the project aims and the goals of the participants are a result of how `place' is viewed in place-based education and that disagreements like these can be resolved if place is theorized as chronotope. There are many interesting ideas raised and directions taken in the article by van Eijck and Roth. After several discussions during the review process, we decided to focus our forum response on the meaning of `place' in place-based education, the utility of theorizing place as a chronotope, the implications for teaching-learning (`education'), and musings on what remains unclear.

Coughlin, Christine A.; Kirch, Susan A.

2010-12-01

229

Illuminating a Dialectical Transformative Activist Stance in Education  

ERIC Educational Resources Information Center

In this essay I comment on Stetsenko's (2008) essay that draws together the work of Vygotsky, Piaget and Dewey, as she attempts to counter the "new" reductionist synthesis in public educational policy. While this theoretical work is helpful, it could be enhanced further by illuminating everyday practices of learners. I pose some questions that…

Ritchie, Stephen M.

2008-01-01

230

A multisensory posture control model of human upright stance  

Microsoft Academic Search

We present a multisensory postural control model based on experiments where the balance in normal subjects and vestibular loss patients was perturbed by application of external torque produced by force-controlled pull stimuli. The stimuli were applied while subjects stood on a stationary or body-sway-referenced motion platform with eyes closed and auditory cues masked. Excursions of the center of mass (COM)

T. Mergner; C. Maurer; R. J. Peterka

2003-01-01

231

Self-induced motion sickness in unperturbed stance  

Microsoft Academic Search

Motion sickness typically occurs when the body is subjected to externally imposed motions, but there are situations in which sickness occurs in the absence of imposed motion. We report a new and unanticipated instance of the latter. Subjects in a study of spontaneous standing postural sway sometimes reported dizziness and motion sickness. Reports of sickness were correlated with changes in

L. James Smart Jr; Randy J. Pagulayan; Thomas A. Stoffregen

1998-01-01

232

Human Genetic Engineering: A Survey of Student Value Stances  

ERIC Educational Resources Information Center

|Assesses the values of high school and college students relative to human genetic engineering and recommends that biology educators explore instructional strategies merging human genetic information with value clarification techniques. (LS)|

Wilson, Sara McCormack; And Others

1975-01-01

233

Place-Based Education: A Transformative Activist Stance  

ERIC Educational Resources Information Center

|The ethnography presented by van Eijck and Roth focuses on the activities of people involved in a government funded internship program in conservation and restoration, which was offered by a "multidisciplinary research center" through a local First Nation adult education center. The internship was designed, in partnership with a local non-profit…

Coughlin, Christine A.; Kirch, Susan A.

2010-01-01

234

Prenatal diagnosis yes, preimplantation genetic diagnosis no: a contradictory stance?  

Microsoft Academic Search

Preimplantation genetic diagnosis (PGD) after IVF with subsequent selection of embryos is accepted and practised in a number of European countries. In others, it is not only controversial but also forbidden by law. Since in these countries prenatal diagnosis (PND) with subsequent termination of pregnancy is legal and widely practised, a consistency problem arises. How can the discrepancy in regulation

Dieter Birnbacher

2007-01-01

235

Russia's stance against secessions: From Chechnya to Kosovo  

Microsoft Academic Search

Russia's policy towards, and interventions in, secessionist conflicts inside the state, in the immediate neighbourhood, and in Europe generally, has changed profoundly from the early 1990s. It is the fear of disintegration that is now the major factor in Moscow's policy making. Russia is set on the path of strategic retreat, which still allows for some interference, but hardly for

Pavel K. Baev

1999-01-01

236

Illuminating a dialectical transformative activist stance in education  

NASA Astrophysics Data System (ADS)

In this essay I comment on Stetsenko's (2008) essay that draws together the work of Vygotsky, Piaget and Dewey, as she attempts to counter the `new' reductionist synthesis in public educational policy. While this theoretical work is helpful, it could be enhanced further by illuminating everyday practices of learners. I pose some questions that might provoke ongoing discussions by researchers as they transform collaboratively cultural-historical activity theory.

Ritchie, Stephen M.

2008-07-01

237

An Exploration of Step Time Variability on Smooth and Irregular Surfaces in Older Persons with Neuropathy  

PubMed Central

Background Increased step time variability, particularly on an irregular surface, has been associated with impaired mobility function and a variety of diseases. However the biomechanical necessity, or advantage, of increasing step time variability has not been identified. Methods We performed a secondary analysis of gait data previously obtained on 42 subjects age 50 or older with neuropathy who walked on smooth and irregular surfaces, the latter with and without three interventions (cane, ankle orthosis and wall touch) that provided frontal plane support. Findings Step time variability on smooth and irregular surfaces was most strongly associated with reduction in step length on the irregular surface as compared to the smooth. More specifically, the greater the decrease in step length on the irregular surface the greater the step time variability on both surfaces and the greater the increase in step time variability on the irregular surface. The increase in step length on the irregular surface afforded by the interventions coincided with a decrease in step time variability. The subjects did not simultaneously demonstrate increased step time variability and step width range on the irregular surface. Interpretation Among adults age 50 and older with neuropathy, increased step time variability is strongly associated with the need to shorten step length on an irregular surface. Therefore step time variability may be a marker for instability during single limb stance which necessitates rapidly placed, shortened recovery steps. Such steps may also offer the advantage of reducing extremes in lateral foot placement of the swing limb, and so assist in maintaining frontal plane stability.

Richardson, James K.; Thies, Sibylle; Ashton-Miller, James A.

2008-01-01

238

Time uncertainty in simple reaction time  

Microsoft Academic Search

Studied the relationship between reaction time and Ss' uncertainty about the time of stimulus presentation. Reaction time increases with foreperiod variability and with mean foreperiod above an optimum value less than 1 sec. The important determiner of reaction time is not the immediate foreperiod but the distribution of foreperiods within which it is embedded.

Edmund T. Klemmer

1956-01-01

239

Value of Travel Time.  

National Technical Information Service (NTIS)

The Record includes 6 papers covering important areas of travel time value analysis, such as travel time value theory, conceptual problems in travel time value, methods of deriving travel time values, review of empirical travel time value studies, applica...

R. Gronau

1976-01-01

240

Development of energy and time parameters in the walking of healthy human infants.  

PubMed

Sixteen infants were analyzed longitudinally from the onset of independent walking to 3 years of age using time parameters, speed and energy recovery. Considerable variation and irregularities were observed in many parameters of infant walking, especially until 13 months of age when infants had difficulty in walking steadily step by step. Infant walking until 3 years of age was characterized by a small braking duration, caused mainly by the forward inclination of the trunk, a large relative stance phase duration, which maintained static balance, short stride length, due to the small range of the lower limb joint angle, and a small recovery of external energy. These characteristics were also predominantly evident until 13 months of age. The small recovery characteristic of infants was caused by flexed lower limb joints, pronounced irregularities in energy output, and in younger infants, slow speed. The maximum recovery up until 2 years of age, though smaller than in adults, appeared at about 0.45 dimensionless speed, which is about the same speed that adults in particular naturally and at which their maximum recovery appeared. The forward inclination of the trunk and the lower limb joint angle, influenced the development of many characteristics of bipedal walking. PMID:16214662

Kimura, Tasuku; Yaguramaki, Naoko; Fujita, Masaki; Ogiue-Ikeda, Mari; Nishizawa, Satoshi; Ueda, Yutaka

2004-11-19

241

Terrific Time Telling  

NSDL National Science Digital Library

Have fun learning how to tell time! First, let's telling time with Dragon. Now that you can tell time with dragon, you have to choose the time!. Time can move fast. Do you think you can keep up? Use your knowledge of time to Stop the clock!. Now that you can keep up with time, can you decide What time will it be? Finally! You have learned so much about time, ...

Triola, Ms.

2009-04-19

242

Time Domain Reflectometry in Time Variant Plasmas.  

National Technical Information Service (NTIS)

The effects of time-dependent electron density fluctuations on a synthesized time domain reflectometry response of a one-dimensional cold plasma sheath are considered. Numerical solutions of the Helmholtz wave equation, which describes the electric field ...

M. J. Scherner

1992-01-01

243

Time on Your Hands: Modeling Time  

NSDL National Science Digital Library

Building physical models relative to a concept can be an important activity to help students develop and manipulate abstract ideas and mental models that often prove difficult to grasp. One such concept is time. A method for helping students understand the cyclical nature of time involves the construction of a Time Zone Calculator through a series of physical models. This article explains how to construct a Time Zone Calculator and provides suggestions for its use.

Beaver, John; Finson, Kevin

2007-07-01

244

Neuropsychology of Timing and Time Perception  

ERIC Educational Resources Information Center

Interval timing in the range of milliseconds to minutes is affected in a variety of neurological and psychiatric populations involving disruption of the frontal cortex, hippocampus, basal ganglia, and cerebellum. Our understanding of these distortions in timing and time perception are aided by the analysis of the sources of variance attributable…

Meck, W.H.

2005-01-01

245

Being, doing, knowing, and becoming: Science and opportunities for learning in the out-of-school-time setting  

NASA Astrophysics Data System (ADS)

This dissertation addresses the question of how structured out-of-school-time settings, such as afterschool programs and summer camps, are positioned to support children's engagement and learning in science. This study addresses a gap in the research literature that does not fully specify the nature of the out-of-school-time (OST) setting and that generally does not position learning and development in relationship to one another, instead focusing on one or the other. As a result of an incomplete conceptualization of the OST setting as a site for learning and development, the OST field is becoming increasingly academicized, and its developmental qualities and benefits for children are under siege. A transformative activist stance (Stetsenko, 2008) guides my goals in undertaking this study -- to produce knowledge that can inform the design and implementation of OST science programs -- and it also guides my analysis of what constitutes learning in OST science. A transformative activist stance is a perspective on cultural-historical theory that understands individual development as occurring through agentive, goal-directed efforts to change one's self and one's world. These goals and actions are always developed and enacted in cultural-historical context. Learning, which occurs through the appropriation of cultural tools and schema to achieve one's purposes, and which leads human development, is understood broadly, as entailing processes of being, doing, knowing and becoming (see Herrenkohl & Mertl, in press). I also draw on bioecological theory (Bronfenbrenner, 1979) to analyze the proximal processes that support and sustain children's participation in the OST setting. In this study, I analyze the structural, developmental, and conceptual features of three different OST science programs to understand how they create opportunities for learning and engagement in science. The contributions of this study are to better specify the nature of the OST science program setting and to better conceptualize how learning and development relate to one another in the context of OST science. I draw on my analysis to make recommendations for ways in which OST science learning can be expanded and enriched for more children in more settings.

Bevan, Bronwyn

246

Time after Time: What is So Tricky about Time?  

ERIC Educational Resources Information Center

|As a teacher's aide this author is often asked to help children who have difficulty with mathematics. Recently she was asked to help children from three different grades with their understanding of time. Although each grade had a different activity to undertake, all of the children struggled to grasp time-concepts that adults often take for…

McGuire, Lauren

2007-01-01

247

Geological Time Scale  

NSDL National Science Digital Library

This document describes how geologic time is approached in discussions of geologic topics. The uses of relative time and absolute time are compared, and a geologic time scale is provided to represent both concepts. References are provided.

248

Elapsed Time Two  

NSDL National Science Digital Library

In this activity, students are prompted with a starting time on a clock and a certain amount of elapsed time. In âseeâ mode, students add time to the clock in order to see what time it will be after the elapsed time. In âguessâ mode, students must enter in a guess for what time it will be given a starting time and elapsed time. This activity allows students to practice reading clocks and explore elapsing time. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

2010-01-01

249

Group Time: Building Language at Group Time  

ERIC Educational Resources Information Center

|This article features energizing and surprising activities for children at group time. In the drawing activity, children are asked to give instructions on how to draw a picture using vocabulary and descriptive language. In the mailbox activity, children will be surprised to discover that they have mail at group time. Mailboxes can be used for…

Church, Ellen Booth

2004-01-01

250

Personal Time Line  

NSDL National Science Digital Library

In this activity, learners work in groups to create a time line representing significant moments in their lives. Learners use scientific suffixes and prefixes to label their time lines, modeling the Geologic Time Line (i.e. Mesozoic, Paleozoic).

Muller, Eric

2003-01-01

251

Time's Arrows Today  

NASA Astrophysics Data System (ADS)

Introduction; Part I. Cosmology and Time's Arrow: 1. Time, gravity, and quantum mechanics W. Unruh; 2. Cosmology, time's arrow, and that old double standard H. Price; Part II. Quantum Theory and Time's Arrow: 3. Time's arrow and the quantum measurement problem A. Leggett; 4. Time, decoherence, and 'reversible' measurements P. Stamp; 5. Time flows, non-locality, and measurement in quantum mechanics S. McCall; 6. Stochastically branching spacetime topology R. Douglas; Part III. Thermodynamics and Time's Arrow: 7. The elusive object of desire: in pursuit of the kinetic equations and the second law L. Sklar; 8. Time in experience and in theoretical description of the world L. Sklar; 9. When and why does entropy increase? M. Barrett and E. Sober; Part IV. Time Travel and Time's Arrow: 10. Closed causal chains P Horwich; 11. Recent work on time travel J. Earman.

Savitt, Steven F.

1997-06-01

252

Deep Time: The Geologic Time Scale  

NSDL National Science Digital Library

This page examines the issues involved in teaching students about the geologic time scale. There are suggestions for tackling troublesome issues in class as well as activities that can be used to clarify how geoscientists look at deep time. Five main concepts with which students struggle when thinking about Deep Time are addressed here: imagining or comprehending big numbers; the difference between relative and numerical age; the concept of "timescales"; the ways we know about the age of the Earth and other materials; and resolving perceived issues with religious beliefs.

2007-01-01

253

From Time to Time: Processing Time Reference Violations in Dutch  

ERIC Educational Resources Information Center

|Time reference in Indo-European languages is marked on the verb. With tensed verb forms, the speaker can refer to the past (wrote, has written), present (writes, is writing) or future (will write). Reference to the past through verb morphology has been shown to be particularly vulnerable in agrammatic aphasia and both agrammatic and…

Dragoy, Olga; Stowe, Laurie A.; Bos, Laura S.; Bastiaanse, Roelien

2012-01-01

254

History without time: Buffon's natural history as a nonmathematical physique.  

PubMed

While "natural history" is practically synonymous with the name of Buffon, the term itself has been otherwise overlooked by historians of science. This essay attempts to address this omission by investigating the meanings of "physique," "natural philosophy," and "history," among other terms, with the purpose of understanding Buffon's actual objectives. It also shows that Buffon never claimed to be a Newtonian and should not be considered as such; the goal is to provide a historical analysis that resituates Buffon's thought within his own era. This is done, primarily, by eschewing the often-studied question of time in Buffon. Instead, this study examines the nontemporal meanings of the word "history" within the naturalist's theory and method. The title of his Natural History is examined both as an indicator of the kind of science that Buffon was hoping to achieve and as a source of great misinterpretation among his peers. Unlike Buffon, many of his contemporaries actually envisioned the study of nature from a Baconian perspective where history was restricted to the mere collection of facts and where philosophy, which was the implicit and ultimate goal of studying nature, was seen, at least for the present, as unrealizable. Buffon confronts this tendency insofar as his Histoire naturelle claims to be the real physique that, along with describing nature, also sought to identify general laws and provide clear insight into what true knowledge of nature is or should be. According to Buffon, history (both natural and civil) is not analogous to mathematics; it is a nonmathematical method whose scope encompasses both nature and society. This methodological stance gives rise to the "physicization" of certain moral concepts--a gesture that was interpreted by his contemporaries as Epicurean and atheist. In addition, Buffon reduces a number of metaphysically tainted historical concepts (e.g., antediluvian monuments) to objects of physical analysis, thereby confronting the very foundation of natural theology. In Buffon, as this essay makes clear, natural history is paving the way for a new physique (science of natural beings), independent from mathematics and from God, that treats naturalia in a philosophical and "historical" manner that is not necessarily "temporal." PMID:20575489

Hoquet, Thierry

2010-03-01

255

On Time-II: Newton's Time.  

ERIC Educational Resources Information Center

A study of time in Newtonian physics is presented. Newton's laws of motion, falsifiability and physical theories, laws of motion and law of gravitation, and Laplace's demon are discussed. Short bibliographic sketches of Laplace and Karl Popper are included. (KR)

Raju, C. K.

1991-01-01

256

Capgras’ Syndrome of Time  

Microsoft Academic Search

The delusion that the usual passage of time has been changed and that time has been interfered with or is repeating itself is rare. Four patients with the delusion of warped time are presented and the significance of the symptom is discussed. The perception of the passage of time and its disorders is discussed.

V. M. Aziz; N. J. Warner

2005-01-01

257

Traveling Through Time  

NSDL National Science Digital Library

This video excerpt from NOVA’s The Fabric of the Cosmos: The Illusion of Time explains gravity’s pull on time, and how time travel may be possible in the future. However, this kind of time travel might not be exactly like Hollywood’s depiction.

Foundation, Wgbh E.

2012-02-10

258

Emerging from imaginary time  

Microsoft Academic Search

Recent models in quantum cosmology make use of the concept of imaginary time. These models all conjecture a join between regions of imaginary time and regions of real time. We examine the model of James Hartle and Stephen Hawking to argue that the various ‘no-boundary’ attempts to interpret the transition from imaginary to real time in a logically consistent and

Robert J. Deltete; Reed A. Guy

1996-01-01

259

GPS Time Steering.  

National Technical Information Service (NTIS)

The importance of the Global Positioning System (GPS) for global time transfer makes it desirable to steer GPS time as closely as possible to the UTC rate. Currently, GPS time is maintained to satisfy two system requirements. First, GPS time is steered to...

D. W. Allan H. F. Fliegel W. J. Klepczynski

1986-01-01

260

Time and Information  

Microsoft Academic Search

The relationship between 'information' and 'time' is explored in order to look for a 'solution' to the 'Problem of Time'. 'Time' is found to be the result of the conversion of energy into 'information'. The 'time' number or label we assign to 'events' can be manufactured by processing information 'flowing' from a Feynman Clock (FC), via a 'signal', to a

Scott M. Hitchcock

2000-01-01

261

Determining the preferred modality for real-time biofeedback during balance training.  

PubMed

Vestibular rehabilitation therapy has been shown to improve balance and gait stability in individuals with vestibular deficits. However, patient compliance with prescribed home exercise programs is variable. Real-time feedback of exercise performance can potentially improve exercise execution, exercise motivation, and rehabilitation outcomes. The goal of this study is to directly compare the effects of visual and vibrotactile feedback on postural performance to inform the selection of a feedback modality for inclusion in a home-based balance rehabilitation device. Eight subjects (46.6±10.6years) with peripheral vestibular deficits and eight age-matched control subjects (45.3±11.1years) participated in the study. Subjects performed eyes-open tandem Romberg stance trials with (vibrotactile, discrete visual, continuous visual, and multimodal) and without (baseline) feedback. Main outcome measures included medial-lateral (M/L) and anterior-posterior mean and standard deviation of body tilt, percent time spent within a no-feedback zone, and mean score on a comparative ranking survey. Both groups improved performance for each feedback modality compared to baseline, with no significant differences in performance observed among vibrotactile, discrete visual, or multimodal feedback for either group. Subjects with vestibular deficits performed best with continuous visual feedback and ranked it highest. Although the control subjects performed best with continuous visual feedback in terms of mean M/L tilt, they ranked it lowest. Despite the observed improvements, continuous visual feedback involves tracking a moving target, which was noted to induce dizziness in some subjects with vestibular deficits and cannot be used during exercises in which head position is actively changed or during eyes-closed conditions. PMID:23022157

Bechly, Kelli E; Carender, Wendy J; Myles, James D; Sienko, Kathleen H

2012-09-28

262

Time-Varying BRDFs  

Microsoft Academic Search

The properties of virtually all real-world materials change with time, causing their BRDFs to be time-varying. However, none of the existing BRDF models and databases take time variation into consideration; they represent the appearance of a material at a single time instance. In this work, we address the acquisition, analysis, modeling and rendering of a wide range of time-varying BRDFs.

Bo Sun; Kalyan Sunkavalli; Ravi Ramamoorthi; Peter N. Belhumeur; Shree K. Nayar

2007-01-01

263

Tempus Fugit: Time Flies  

NSDL National Science Digital Library

This online exhibit from a prominent American museum explores the character of time -- its impact on our daily lives and its ability to shape and reform human consciousness. Tempus Fugit: Time Flies is a superb exhibit from the Nelson Atkins Museum of Art that uses items from the museum to exemplify different understandings of time. The exhibit features sections on 20th Century Time, World Times, and Conservation Time. Twentieth-century time considers the changing nature of time in the technological age by examining the innovations in graphic and plastic arts inspired by an altered sense of time. The exhibit includes works by Muybridge, Edward Hopper, Salvador Dali, Kandinsky, Rothko, Roy Lichtenstein, and others. The second section, World Times, focuses on the different conceptions of time embodied in art from primitive times to the present and ranges from ancient Native American to Medieval Europe to ancestral Africa to the deeply cosmological perceptions of time in ancient Indian civilizations. Conservation Time takes visitors behind the scenes to see how conservation science can uncover the history of a work's composition and the changes wrought upon it over the course of its lifetime. The Website also offers ideas for teaching using the exhibits. In sum, this is an elegantly constructed and intelligent Website. To be sure, users will want to set aside some time for it as the graphics enforce their own meditative pace upon the viewer.

264

GNSS times and UTC  

NASA Astrophysics Data System (ADS)

Global Navigation Satellite Systems (GNSSs) use internal reference time scales: GPS Time, GLONASS Time, Galileo System Time and BeiDou System Time. Constructed from a clock ensemble, they are designed for internal system synchronization, necessary to produce a navigation solution. They are usually steered to an external stable reference time scale, for example UTC(USNO), modulo 1 s, for GPS time. To achieve safe operation of a GNSS, a system time should preferably be a uniform time scale not affected by the leap seconds of Coordinated Universal Time (UTC). But this is not compatible with international recommendations that radio broadcast time signals should conform as closely as possible to UTC. This paper describes the various approaches chosen by GNSS providers and the relation between GNSS system times and UTC in terms of numbering of seconds. Different solutions for numbering seconds do not help the GNSS interoperability. This paper also explains why, on some occasions, GNSS system times play a role of alternative time scales with the consequent risk of confusion.

Lewandowski, W.; Arias, E. F.

2011-08-01

265

Effect of a vocal choice reaction time task on the kinematics of the first recovery step after a sudden underfoot perturbation during gait.  

PubMed

Thirty-two healthy young adults (15 women) were tested for their ability to maintain their comfortable step pattern following an unpredictable underfoot perturbation in the presence and absence of a concurrent vocal choice reaction time task. Custom instrumented shoes were used to randomly deliver an unexpected medial or lateral forefoot perturbation that inverted the mid-foot an average of 10° or everted the midfoot an average of 9° during one stance phase of a gait trial. Medial and lateral perturbations were randomized between left and right feet in 12 of 30 gait trials. The results of the repeated measures analyses of variance show that, compared to the step parameters of unperturbed gait, the administration of the unexpected underfoot perturbation did not significantly lead to alterations in the step length or width of the first recovery step. In addition, the simultaneous administration of a vocal choice reaction time task with the underfoot perturbation did not significantly affect the kinematics of the first recovery step. We conclude that in young healthy adults an unexpected 9-10° underfoot perturbation, with or without a vocal reaction time task, will not affect their recovery step kinematics when walking at a comfortable gait speed. PMID:22795474

Nnodim, Joseph O; Kim, Hogene; Ashton-Miller, James A

2012-07-12

266

Physiologic time: a hypothesis.  

PubMed

The scaling of respiratory metabolism with body size in animals is considered by many to be a fundamental law of nature. One apparent consequence of this law is the scaling of physiologic time with body size, implying that physiologic time is separate and distinct from clock time. Physiologic time is manifest in allometry relations for lifespans, cardiac cycles, blood volume circulation, respiratory cycle, along with a number of other physiologic phenomena. Herein we present a theory of physiologic time that explains the allometry relation between time and total body mass averages as entailed by the hypothesis that the fluctuations in the total body mass are described by a scaling probability density. PMID:23659904

West, Damien; West, Bruce J

2013-04-22

267

Late Time Containment Research.  

National Technical Information Service (NTIS)

This summary of Late-Time Containment Research describes the various tasks undertaken during 1981. Cavity conditions were estimated for Red Hot as a function of time, and consideration of connecting tunnel conditions suggested that venting from the cavity...

J.R. Barthel K. Lie N. Rimer R.E. Duff W.J. Proffer

1982-01-01

268

Lead Time Study.  

National Technical Information Service (NTIS)

Lead times for the procurement of ammunition items are usually established during the latter part of the development phase, which is approximately two years before the initial production buy. Typical procurement lead time forecasts have been 15 months for...

J. Chu

1982-01-01

269

Screen time and children  

MedlinePLUS

... helpful when kids are using them to do schoolwork. But surfing the internet, spending time on Facebook, ... healthier. Ways to decrease screen time: Remove the television or computer from your child’s bedroom. Do not ...

270

Time and Relativity  

NSDL National Science Digital Library

This video from the American Museum of Natural History illustrates Einstein's special theory of relativity and the relationship between time and the motion of objects, including the concept of time dilation.

Foundation, Wgbh E.

2007-08-09

271

Late Time Containment.  

National Technical Information Service (NTIS)

Major contributions in the Late Time Containment research effort are summarized. Test design activity showed that cavity venting into a tunnel could effectively lower cavity pressure on a fast time scale and that a reasonable, fast-turn-around horizontal ...

J. R. Barthel R. E. Duff

1980-01-01

272

It's about Time.  

ERIC Educational Resources Information Center

|A realistic production schedule helps deliver college publications on time. This requires team effort and a spirit of cooperation, specific task scheduling, using tickler systems to keep staff on track, not allowing procrastination, and setting aside planning time. (MSE)|

Bieberle, Gordon F.

1993-01-01

273

Bounded time-stamps  

Microsoft Academic Search

Time-stamps are labels which a system adds to its data items. These labels enable the system to keep track of the temporal precedence relations among its data elements. Many distributed protocols and some applications use the natural numbers as time-stamps. The natural numbers however are not useful for bounded protocols. In this paper we develop a theory ofbounded time-stamps. Time-stamp

Amos Israeli; Ming Li

1993-01-01

274

Bounded time-stamps  

Microsoft Academic Search

Time-stamps are numerical labels which enable a system to keep track of temporal precedence relation among its data elements. Traditionally time-stamps are used as unbounded numbers and inevitable overflows cause a loss of this precedence relation. In this paper we develop a complete theory of bounded time-stamps. Time-stamp systems are defined and the complexity of their implementation is fully analyzed.

Amos Israeli; Ming Li

1987-01-01

275

Geologic Time: Online Edition  

NSDL National Science Digital Library

Offered by the United States Geological Survey (USGS) as a general interest publication, this site is an online edition of a text by the same name, offering a concise overview of the concepts associated with the age of the Earth. The online edition was revised in October of 1997 to reflect current thinking on this topic. Section headers are Geologic Time, Relative Time Scale, Major Divisions of Geologic Time, Index Fossils, Radiometric Time Scale, and Age of the Earth.

1997-10-09

276

Time and Information  

Microsoft Academic Search

The relationship between 'information' and 'time' is explored in order to\\u000alook for a 'solution' to the 'Problem of Time'. 'Time' is found to be the\\u000aresult of the conversion of energy into 'information'. The 'time' number or\\u000alabel we assign to 'events' can be manufactured by processing information\\u000a'flowing' from a Feynman Clock (FC), via a 'signal', to a

Scott M. Hitchcock

2000-01-01

277

Picosecond time-lenses  

Microsoft Academic Search

There is an interesting analogy between the spatial problem of Fresnel diffraction and the temporal problem of first-order dispersion. This space-time analogy was recently extended to propose a time-domain analog to spatial imaging that allows for the distortionless expansion or compression of optical waveforms in time. This process is called temporal imaging. The extension includes the idea of a time-lens

Asif A. Godil; B. A. Auld; David M. Bloom

1994-01-01

278

Picosecond time-lenses  

Microsoft Academic Search

There is an interesting analogy between the spatial problem of Fresnel diffraction and the temporal problem of first-order dispersion. This space-time analogy was recently extended to propose a time-domain analog to spatial imaging that allows for the distortionless expansion of compression of optical waveforms in time. This process is called temporal imaging. The extension includes the idea of a time-lens

Asif A. Godil; B. A. Auld; David M. Bloom

1994-01-01

279

Event time recorder  

NASA Astrophysics Data System (ADS)

Accurate timing of sounding rocket payload events is critical for successful missions. The payload event timers used must be checked numerous times to verify proper settings. A cost-effective time event recorder was developed which will store up to 32 time events and provide a hard copy printout. The event recorder consists of an AIM 65 microcomputer with a custom hardware interface and assembly language software. The 32 input lines can be triggered by voltage changes or current sensing.

Stuchlik, D. W.

1986-10-01

280

Filling the Time  

NSDL National Science Digital Library

Build time sense into the schedule by asking learners to predict what can happen in a certain amount of time: We have 20 minutes before outdoor time. What can you get done? Everyone makes a prediction, for instance, how many rounds of a card game theyâll play or how many origami cranes they can make. Then, stop part-way through the time period and ask if anyone wants to revise their predictions. Available as a web page or downloadable pdf.

Terc

2010-01-01

281

Calculus for Timed Automata.  

National Technical Information Service (NTIS)

A language for representing timed automata is introduced. Its semantics is defined in terms of timed automata. This language is complete in the sense that any timed automation can be represented by a term in the language. The authors also define a direct ...

P. R. D'Argenio E. Brinksma

1996-01-01

282

Time warp operating system  

Microsoft Academic Search

This paper describes the Time Warp Operating System, under development for three years at the Jet Propulsion Laboratory for the Caltech Mark III Hypercube multi-processor. Its primary goal is concurrent execution of large, irregular discrete event simulations at maximum speed. It also supports any other distributed applications that are synchronized by virtual time.The Time Warp Operating System includes a complete

David Jefferson; Brian Beckman; Fred Wieland; Leo Blume; Mike DiLoreto

1987-01-01

283

The Myth of Time.  

ERIC Educational Resources Information Center

|This paper offers a variety of approaches to teaching the concept of time. Many social studies courses traditionally emphasize time as measured by clocks and as useful for recording when events occur in relation to each other. In addition to this approach, the author suggests that students should reflect upon four other modes of time. These are…

Hantula, James

284

Managing Time and Stress.  

ERIC Educational Resources Information Center

|Chapter 10 in a volume on school leadership, this chapter lists practical suggestions from many diverse sources for managing time and reducing stress. The author begins by noting attitudes and concepts that block or facilitate time or stress management. A number of time management strategies are suggested, including goal-setting, using a daily…

Huffstutter, Sandra

285

Time Is Money  

ERIC Educational Resources Information Center

|One has heard it before: time is money, especially when it comes to adding time for instruction to the school day. When budgets are tight and relief is nowhere in sight, how can schools afford to implement a reform as costly as adding instructional time? It's a daunting task, yet current federal educational priorities tied to federal funding…

Oxley, Diana; Baete, Glenn

2012-01-01

286

Ultrasonic Time Reversal Mirrors  

Microsoft Academic Search

For more than ten years, time reversal techniques have been developed in many different fields of applications including detection of defects in solids, underwater acoustics, room acoustics and also ultrasound medical imaging and therapy. The essential property that makes time reversed acoustics possible is that the underlying physical process of wave propagation would be unchanged if time were reversed. In

Mathias Fink; Gabriel Montaldo; Mickael Tanter

2004-01-01

287

Managing Time and Stress.  

ERIC Educational Resources Information Center

Chapter 10 in a volume on school leadership, this chapter lists practical suggestions from many diverse sources for managing time and reducing stress. The author begins by noting attitudes and concepts that block or facilitate time or stress management. A number of time management strategies are suggested, including goal-setting, using a daily…

Huffstutter, Sandra

288

Time for Class  

ERIC Educational Resources Information Center

One of the most abstract concepts that teachers will introduce to students is the concept of time. Usually introduced at the beginning of the school year, the concept of time is taught along with measurements and scientific units such as length, mass, and volume (NRC 1996). However, unlike length, mass, and volume, time can be a very confusing…

Christmann, Edwin P.

2004-01-01

289

Time Management for Educators.  

ERIC Educational Resources Information Center

Time management principles can help teachers become more aware of ways in which time can be used to the greatest advantage. An exploration of personal time perspectives is a step toward establishing effective patterns of behavior. Productivity may be high in the morning and low in the late afternoon, for example, and organizing some activities to…

Burden, Paul R.

290

International atomic time and time transfer  

NASA Astrophysics Data System (ADS)

Global Navigation Satellite Systems (GNSS) keep a central role in the international timekeeping. American Global Positioning System (GPS) is a navigation system that has proven itself to be a reliable source of positioning for both the military community and the civilian community. But, little known by many, is the fact that GPS has proven itself to be an important and valuabe utility to the timekeeping community (Lewandowski et al. 1999). GPS is a versatile and global tool which can be used to both distribute time to an arbitrary number of users and synchronise clocks over large distances with a high degree of precision and accuracy. Similar performance can be obtained with Russian Global Navigation Satellite System (GLONASS). It is expected in the near future satellites of a new European navigation system GALILEO might bring some important opportunities for international timekeeping. This paper after a brief introduction to international timekeeping focuses on the description of recent progress in time transfer techniques using GNSS satellites.

Lewandowski, Wlodzimierz

291

Modeling Geologic Time  

NSDL National Science Digital Library

In this activity students convert major events in Earth history from years before present into scale distances. After a list of events and their scale distances have been formulated, students construct a geologic time scale on 5 meters of adding machine paper, beginning with the formation of the Earth. Students will investigate change through geologic time; design, construct and interpret a model of geologic time; relate major events in Earth history to the geologic time scale; and compare and relate the span of Earth history to events of historical time and of the human lifetime. Some sample events and their approximate relative ages are included.

Firebaugh, James

292

Big Time Tour  

NSDL National Science Digital Library

In this activity (on pages 16-21), learners get a sense of geological time by understanding how big a million is. Part One of the activity is the "Million Appreciation Lesson," which puts a million seconds, names in a phone book, and hiked steps into more familiar units. Part Two is "Investigating All Time," where learners make a time line for the history of the Earth using the length of their own arm to represent the total 4.5 billion year long scale. They mark major time zones, such as the age of the dinosaurs, at appropriate lengths along the time line.

Museum, University O.; Nebraska Cooperative Extension 4-H Youth Development

2002-01-01

293

SNS TIMING SYSTEM.  

SciTech Connect

A modern physics facility must synchronize the operation of equipment over a wide area. The primary purpose of the site wide SNS synchronization and timing system is to synchronize the operation of the LINAC, accumulator ring and neutron choppers and to distribute appropriate timing signals to accelerator systems, including the Injector, LINAC, Accumulator Ring and Experimental Facilities. Signals to be distributed include the ring RF clock, real-time timing triggers, machine mode and other informational events. Timing triggers and clocks from the SNS synchronization and timing system are used to synchronize hardware operations including the MEBT beam chopper, RF turn on, synchronous equipment state changes, as well as data acquisition for power supplies and beam diagnostics equipment. This paper will describe the timing equipment being designed for the SNS facility and discuss the tradeoffs between conflicting demands of the accelerator and neutron chopper performance due to AC power grid frequency fluctuations.

NELSON,J.R.; OERTER,B.; SHEA,T.; SIBLEY,C.

2001-11-27

294

Influence of pole plant time on the performance of a special jump and plant exercise in the pole vault.  

PubMed

The purpose of this study was to examine the effect of the timing of the pole plant during the stance phase of the jump on the energy level of the vaulter/pole system at take-off for a special pole vault take-off exercise (Jagodin). We hypothesised that an earlier pole plant would increase the pole energy at take-off compared to the energy decrease of the vaulter during the jump and plant complex and so lead to a higher total energy of the vaulter/pole system at take-off. Six male pole vaulters experienced three Jagodins each with different pole plant time building three groups of vaults (early, intermediate, late pole plant). Kinematic data of vaulter and pole were recorded, as were ground reaction forces measured at the end of the pole under the planting box and under the take-off foot. These measurements allowed the energy exchange between the vaulter and pole to be determined. We found neither statistical significant differences in the mechanical energy level of the vaulter/pole system during take-off between the three groups nor a relationship between the timing of the pole plant and the energy level of the vaulter-pole system during take-off. We conclude that although the timing of the pole plant influences the interactions between the vaulter, the pole, and the ground, it does not affect the athlete's performance. Although a late pole plant decreases the loss of energy by the vaulter during the take-off, this is counterbalanced by a decrease in the energy stored in the pole at take-off. PMID:22534564

Schade, Falk; Arampatzis, Adamantios

2012-04-24

295

Medial patellar taping changes the peak plantar force location and timing of female basketball players.  

PubMed

Subtle changes in patellofemoral joint biomechanics may influence lower extremity function. The McConnell method of patellar taping has become an increasingly popular method of managing patients with various patellofemoral joint disorders. The purpose of this order effect controlled study was to assess medial patellar taping (McConnell Method) for changes in peak plantar force location and timing while running and dribbling a basketball prior to the performance of a basketball lay-up. Sixteen non-impaired, right hand dominant members of a female junior varsity basketball team (age=14.6 +/- 2 years) participated in this study. Subject bodyweight and height were 607.8 +/- 99 N and 1.67 +/- 0.10 m, respectively. All data were collected from the preferred stance limb. A series of two way analysis of variance (ANOVA) (condition, trial) were used to determine statistical significance (P < or = 0.05). During medial patellar taping, subjects displayed a more forefoot directed peak plantar force location 89.9 +/- 18 versus 81.3 +/- 21 mm and delayed peak plantar force onset 141 +/ - 23 versus 130 +/- 29 ms following initial ground contact. Medial-lateral peak plantar force location and peak plantar force magnitude did not differ between conditions, however, medial-lateral peak plantar force location displayed significant trial sequence influences with the latter trials displaying more lateral center of plantar force locations (30.4 +/- 2 vs. 32.5 +/- 3 mm). The results of this study suggest that medial patellar taping influences distal lower extremity function by shifting peak plantar force location toward the forefoot, and delaying its onset. These changes with consideration for known synergistic ankle plantar flexor-subtalar joint invertor and knee extensor function during weight bearing suggest the presence of increased muscular stiffness acting through a more rigid foot to improve the impact force attenuating capability of the lower extremity. PMID:11869908

Nyland, J A; Ullery, L R; Caborn, David N M

2002-04-01

296

Space-time gestures  

Microsoft Academic Search

A method for learning, tracking, and recognizing human gestures using a view-based approach to model articulated objects is presented. Objects are represented using sets of view models, rather than single templates. Stereotypical space-time patterns, i.e., gestures, are then matched to stored gesture patterns using dynamic time warping. Real-time performance is achieved by using special purpose correlation hardware and view prediction

Trevor Darrell; Alex Pentland

1993-01-01

297

Modelling Financial Time Series  

Microsoft Academic Search

Financial time series, in general, exhibit average behaviour at “long” time scales and stochastic behaviour at ‘short” time\\u000a scales. As in statistical physics, the two have to be modelled using different approaches — deterministic for trends and probabilistic\\u000a for fluctuations about the trend. In this talk, we will describe a new wavelet based approach to separate the trend from the

P. Manimaran; J. C. Parikh; P. K. Panigrahi; S. Basu; C. M. Kishtawal; M. B. Porecha

298

Time Functions as Utilities  

Microsoft Academic Search

Every time function on spacetime gives a (continuous) total preordering of the spacetime events which respects the notion\\u000a of causal precedence. The problem of the existence of a (semi-)time function on spacetime and the problem of recovering the\\u000a causal structure starting from the set of time functions are studied. It is pointed out that these problems have an analog\\u000a in

E. Minguzzi

2010-01-01

299

Itâs About Time  

NSDL National Science Digital Library

In past times, ocean navigators tossed a piece of wood over the side of their ships and noted how long until the ship passed the wood. They used this time measurement and the length of the ship to calculate their speed and estimate how far they had traveled. In this activity, students act the part of a GPS signal traveling to the receiver to learn how travel time is converted to distance.

Integrated Teaching And Learning Program

300

Making Time for Feedback  

ERIC Educational Resources Information Center

|Ask any teacher what he or she needs more of, and it is a good bet that time will top the list. Anything that promises to recoup a little bit of their workday time is sure to be a best seller. One overlooked time-saver is in how they use feedback. Teachers know that feedback is important for teaching and learning. Unfortunately, most secondary…

Fisher, Douglas; Frey, Nancy

2012-01-01

301

The effect of activity history and current activity on static and dynamic postural balance in older adults.  

PubMed

The purpose of this study was to investigate the effects of former athleticism and current activity status on static and dynamic postural balance in older adults. Fifty-six subjects participated in four study groups including former athletes, currently active (AA; n = 15; 69.1+/-4.4 years.; 77.8+/-9.8 kg), former athletes, currently inactive (AI; n = 12; 66.7 years.; 87.2+/-15.1 kg), controls currently active (CA; n = 14; 68.6 +/- 4.5 years.; 73.9+/-15 kg), and controls currently inactive (CI; n = 15; 72.8+/-4.8 years; 81.1+/-14.8). All subjects were tested for height, weight, flexibility, thigh circumference, and static (sharpened Romberg/unipedal stance), and dynamic (step length and width) balance tests. The sharpened Romberg (eyes open) test showed that AA (60.0+/-0 s) and CA (59.4+/- 0.5 s) balanced significantly longer than AI (41.5+/-7.2 s), and CI (41.8+/-6.1 s) (p<0.05). The unipedal (eyes open) test balance scores for AA, CA, AI, and CI were respectively 40.0+/-4.5, 55.1+/- 3.4, 33.0+/-7.1, and 27.5+/-6.1 s, with CA significantly better than CI (p<0.05). In dynamic balance AA and CA (746.1+/-28.0 and 724.6+/-24.3 mm) showed significantly longer step lengths (p<0.05) than CI (643.7+/-26.5 mm). The eyes closed test results for relative group comparisons were similar. Overall, two-way analysis of variance showed a significant activity main effect for all dependent variables measured (p<0.05). The results indicated that current activity status plays a key role on balance performance in older adults. Furthermore, former athletic activity history provides no protection for the age related onset of postural imbalance. PMID:11006430

Bulbulian, R; Hargan, M L

302

Fields of Time  

NSDL National Science Digital Library

This outdoor exercise shows students the great expanse of time that has elapsed between the formation of Earth and the emergence of living creatures, particularly humans. The great length of the football field helps reinforce the idea of the vast amounts of time that have passed. Starting on one goal line, they will mark off distances representing the times of various events, rocks, fossils, or geologic eras. The teacher can calculate the distances needed, or students can do it themselves in the classroom. A table is provided to help convert distances in yards to time in millions of years, and links to additional information are included.

Greb, Stephen

303

Tour of Geologic Time  

NSDL National Science Digital Library

This online tour offers users a 'journey' through the history of the Earth, with stops at particular points in time to examine the fossil record and stratigraphy. Clicking on an interactive time scale allows access to information on the geologc eras, from the Hadean (4.5- 3.8 billion years ago) to the Cenozoic (65 billion years ago to the present). Or, users can explore specific time periods by selecting the appropriate link, or study the history of the gelogic time scale.

304

What is Geologic Time?  

NSDL National Science Digital Library

This webpage of the National Park Service (NPS) and United States Geological Survey (USGS) discusses geologic time and what it represents. Beginning about 4.6 billion years ago and ending in the present day, this site exhibits (to scale) the various eras, periods, eons, and epochs of Earth's history with a downloadable geologic time scale available. Links provide maps of what the Earth looked like at various times in its history, as well as a description of how scientists developed the time scale and how they know the age of the Earth.

305

Time Functions as Utilities  

NASA Astrophysics Data System (ADS)

Every time function on spacetime gives a (continuous) total preordering of the spacetime events which respects the notion of causal precedence. The problem of the existence of a (semi-)time function on spacetime and the problem of recovering the causal structure starting from the set of time functions are studied. It is pointed out that these problems have an analog in the field of microeconomics known as utility theory. In a chronological spacetime the semi-time functions correspond to the utilities for the chronological relation, while in a K-causal (stably causal) spacetime the time functions correspond to the utilities for the K + relation (Seifert’s relation). By exploiting this analogy, we are able to import some mathematical results, most notably Peleg’s and Levin’s theorems, to the spacetime framework. As a consequence, we prove that a K-causal (i.e. stably causal) spacetime admits a time function and that the time or temporal functions can be used to recover the K + (or Seifert) relation which indeed turns out to be the intersection of the time or temporal orderings. This result tells us in which circumstances it is possible to recover the chronological or causal relation starting from the set of time or temporal functions allowed by the spacetime. Moreover, it is proved that a chronological spacetime in which the closure of the causal relation is transitive (for instance a reflective spacetime) admits a semi-time function. Along the way a new proof avoiding smoothing techniques is given that the existence of a time function implies stable causality, and a new short proof of the equivalence between K-causality and stable causality is given which takes advantage of Levin’s theorem and smoothing techniques.

Minguzzi, E.

2010-09-01

306

Times Tables Grid Game  

NSDL National Science Digital Library

This Flash applet provides targeted practice of multiplication facts. After a player selects which group(s) of multiples to practice, the applet displays products one at a time, and the player locates a cell on a blank grid that identifies a possible factor pair. Users may choose to play timed or untimed, and must complete a round with no more than 5 errors.

2013-01-01

307

Deciding branching time logic  

Microsoft Academic Search

In this paper we study the full branching time logic (CTL*) in which a path quantifier, either A (“for all paths-&-rdquo;) or E (-&-ldquo;for some path”), prefixes an assertion composed of arbitrary combinations of the usual linear time operators F (“sometime”), G (“always”), X (“nexttime”), and U (“until”). We show that the problem of determining if a CTL* formula is

E. Allen Emerson; A. Prasad Sistla

1984-01-01

308

ZERO-TIME INDICATOR  

DOEpatents

The travel time of a nuclear shock wave from its point of origin to a location can be determined accurately by an apparatus for noting and comparably recording both zerotime, as indicated by the electromagnetic transient associated with the nuclear detonation, and shock wave arrival time.

Sander, H.H.

1960-08-30

309

Telling Time Worksheet  

NSDL National Science Digital Library

This site allows teachers to create worksheets to give students practice telling time. Worksheets have several options: 1) Students write time, draw hands, or both; 2) hour, half hour, 15 minutes, 5 minutes, or minute; 3) small, medium, or large clock faces; 4) and answer key options.

Cafe, Math F.

2009-03-16

310

Tips for Taming Time  

ERIC Educational Resources Information Center

|This article shares seven easy ideas to help teachers tame their time-management problems. To reduce the amount of mail that makes it to one's desk, the author suggests using the "Chicken Pox" technique to limit the number of times a piece of mail is handled. With this technique, it is not necessary to make an immediate decision regarding the…

LaBelle, Sandy

2006-01-01

311

Time and Teaching  

NASA Astrophysics Data System (ADS)

Time management is an important issue for teachers and students. This article discusses teachers' use of time from the perspective of curriculum and instruction. Average high school students spend fewer than 5 hours per week in outside-of-class study; average college students spend about 20 hours. Procrastination, often viewed in a negative light by teachers, usually pays off so well for college students that seniors become better at it than freshmen. Three suggestions for designing instruction are: test early and often; do not waste the best students' time in an effort to improve overall performance; and use engaging activities that motivate students to give of their time. The impact of computers on curricula is a double-edged sword. Time must be devoted to teaching the use of applications, but the programs reduce busywork. Will this turn out to be a simple tradeoff, or will the programs make us much more efficient so that less time is required? Will computer programs ultimately lead to an expanded criterion for expertise, thus demanding even more time to become an expert? These issues are described and suggestions for controlling time during instruction are provided.

Zielinski, Theresa Julia; Brooks, David W.; Crippen, Kent J.; March, Joe L.

2001-06-01

312

Time and Teaching  

Microsoft Academic Search

Time management is an important issue for teachers and students. This article discusses teachers' use of time from the perspective of curriculum and instruction. Average high school students spend fewer than 5 hours per week in outside-of-class study; average college students spend about 20 hours. Procrastination, often viewed in a negative light by teachers, usually pays off so well for

Theresa Julia Zielinski; David W. Brooks; Kent J. Crippen; Joe L. March

2001-01-01

313

Timed CSP: A Retrospective  

Microsoft Academic Search

We review the development of the process algebra Timed CSP, from its inception nearly twenty years ago to very recent semantical and algorithmic developments. Rather than aim at exhaustiveness, this paper retraces some of the milestones in the development of Timed CSP, and records some of its interesting features. Reed and Roscoe's original model ( 25) was predicated on complete

Joël Ouaknine; Steve Schneider

2006-01-01

314

Timely Warning Update  

ERIC Educational Resources Information Center

|A complaint received by the Department of Education alleged that Virginia Tech violated the "timely warning" requirements of the Clery Act on April 16, 2007, by not issuing specific campus-wide alerts once senior officials knew of the immediate threat to health and safety. The complaint also alleged that the University's timely warning policy, as…

Stafford, Dolores

2011-01-01

315

Prime Time School Television.  

National Technical Information Service (NTIS)

The complete text and pictures of a slide/tape and videotape presentation explain Prime Time School Television (PTST), a non-profit organization, with emphasis on the active role of participants in utilizing prime time programs in everday teaching-learnin...

J. C. Ittelson

1977-01-01

316

Managing Time and Stress.  

ERIC Educational Resources Information Center

Chapter 14 of a revised volume on school leadership, this chapter offers many practical suggestions for managing time and reducing stress. The primary challenge is to unblock the route to effective time/stress management by recognizing unproductive values and attitudes (such as overreliance on the Protestant work ethic or the appearance of…

Huffstutter, Sandra; Smith, Stuart C.

317

Constructing augmented time compactors  

Microsoft Academic Search

In this paper, a procedure for constructing time compactors based on a new 3-dimensional augmented product code is presented. Accordingly, augmented time compactors are constructed by assigning a unique triplet <;x, y, z> to each scan chain and calculating at least four sets of parity check bits. Each set of parity check bits is attached to one or more multi-input

Emil Gizdarski

2010-01-01

318

The metrology of time.  

PubMed

Measuring time is a continuous activity, an international and restless enterprise hidden in time laboratories spread all over the planet. The Bureau International des Poids et Mesures is charged with coordinating activities for international timekeeping and it makes use of the world's capacity to produce a remarkably stable and accurate reference time-scale. Commercial atomic clocks beating the second in national laboratories can reach a stability of one part in 10(14) over a 5 day averaging time, compelling us to research the most highly performing methods of remote clock comparison. The unit of the international time-scale is the second of the International System of Units, realized with an uncertainty of the order 10(-15) by caesium fountains. Physicists in a few time laboratories are making efforts to gain one order of magnitude in the uncertainty of the realization of the second, and more refined techniques of time and frequency transfer are in development to accompany this progress. Femtosecond comb technology will most probably contribute in the near future to enhance the definition of the second with the incorporation of optical clocks. We will explain the evolution of the measuring of time, current state-of-the-art measures and future challenges. PMID:16147510

Arias, Elisa Felicitas

2005-09-15

319

Quantum Measurement of Time.  

National Technical Information Service (NTIS)

Traditionally, in non-relativistic Quantum Mechanics, time is considered to be a parameter, rather than an observable quantity like space. In relativistic Quantum Field Theory, space and time are treated equally by reducing space to also be a parameter. H...

S. R. Shepard

1994-01-01

320

Quantum time crystals.  

PubMed

Some subtleties and apparent difficulties associated with the notion of spontaneous breaking of time-translation symmetry in quantum mechanics are identified and resolved. A model exhibiting that phenomenon is displayed. The possibility and significance of breaking of imaginary time-translation symmetry is discussed. PMID:23215056

Wilczek, Frank

2012-10-15

321

Modelling Reaction Times  

Microsoft Academic Search

We discuss the simulation of reaction times in connectionist systems. The obvious way to do this involves thinking in terms of neural activations building up towards some threshold in cascaded systems, but it has also been suggested that the output activation error scores in standard back-propagation networks should also be correlated with response times. The idea is that in the

John A. Bullinaria

322

Time Series Data Library  

NSDL National Science Digital Library

This is a collection of time series datasets covering many application areas, but are all for time series analysis. Some of the topics covered are: agriculture, chemistry, crime, demography, ecology, finance, health, hydrology, industry, labor market, macroeconomics, physics, production, sales, sport, transportation, tourism, tree rings and utilities. The data are in text format, thus they can be used without any additional software.

Hyndman, Robert

2009-08-13

323

Estimating Distance and Time  

NSDL National Science Digital Library

Students learn to estimate the time it takes to travel different distances based on an estimation of the time it takes to travel a part of the whole route. This reinforces basic fractional/ratio thinking, as well as early multiplication as repeated addition.

Wnet

2008-08-22

324

GR Schwarzschild Time Program  

NSDL National Science Digital Library

The GR Schwarzschild Time uses the Schwarzschild metric to show the local time at points near a black hole in comparison to the time measured by a faraway observer. It also shows sinusoidal signals emitted from nearby points as recorded by a local (shell) observer. The default configuration is three observers near a black hole. GR Schwarzschild Time is part of a suite of Open Source Physics programs that model aspects of General Relativity. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the gr_schwarzschild_time.jar file will run the program if Java is installed. Other programs provide additional visualizations. They can be found by searching ComPADRE for Open Source Physics, OSP, or General Relativity.

Christian, Wolfgang; Belloni, Mario; Cox, Anne

2008-05-23

325

Timing in telecommunications networks  

NASA Astrophysics Data System (ADS)

I describe the statistical considerations used to design systems whose clocks are compared by the use of dial-up telephone lines or the Internet to exchange timing information. The comparison is usually used to synchronize the time of a client system to the time of a server, which is, in turn, synchronized to the time scale of a national timing laboratory. The design includes a dynamic estimate of the system performance and a comparison between the performance and a parameter that specifies the required stability based on external considerations. The algorithm adjusts the polling interval and other parameters of the algorithm to realize the specified performance at minimal cost, where the cost is taken to be proportional to the inverse of the interval between message exchanges using either the Internet or dial-up telephone calls.

Levine, Judah

2011-08-01

326

Modelling bursty time series  

NASA Astrophysics Data System (ADS)

Many human-related activities show power-law decaying interevent time distribution with exponents usually varying between 1 and 2. We study a simple task-queuing model, which produces bursty time series due to the non-trivial dynamics of the task list. The model is characterized by a priority distribution as an input parameter, which describes the choice procedure from the list. We give exact results on the asymptotic behaviour of the model and we show that the interevent time distribution is power-law decaying for any kind of input distributions that remain normalizable in the infinite list limit, with exponents tunable between 1 and 2. The model satisfies a scaling law between the exponents of interevent time distribution (?) and autocorrelation function (?): ? + ? = 2. This law is general for renewal processes with power-law decaying interevent time distribution. We conclude that slowly decaying autocorrelation function indicates long-range dependence only if the scaling law is violated.

Vajna, Szabolcs; Tóth, Bálint; Kertész, János

2013-10-01

327

Picosecond time-lenses  

NASA Astrophysics Data System (ADS)

There is an interesting analogy between the spatial problem of Fresnel diffraction and the temporal problem of first-order dispersion. This space-time analogy was recently extended to propose a time-domain analog to spatial imaging that allows for the distortionless expansion or compression of optical waveforms in time. This process is called temporal imaging. The extension includes the idea of a time-lens as a dual of a spatial lens (regular lens). The time-lens is simply a quadratic optical phase modulator in time, which is approximated by a portion of a sinusoidal phase modulator. Thus, by using phase modulators as lenses and grating pairs as dispersive elements, complete temporal imaging systems can be constructed in exact duality with spatial imaging systems. However, for practically useful time-lenses, considerable modulation is required at fairly high frequencies. The main body of the paper is the detailed design and development of a practical time-lens. This is addressed in Section II, where a resonant microwave modulator is developed based on a LiNbO3 loaded waveguide. Multiple passes are obtained through the modulator using an off-axis path in a stable optical resonator. At 5.2 GHz operation, 44 radians of phase modulation is obtained at 1.06 micron wavelength for 13 W of microwave power. This corresponds to a time-lens with 31 ps aperture and 1.9 ps resolution. This was confirmed by demonstrating temporal focusing of 45 ps pulses to 1.9 ps. By optimizing the design of the time-lens and better thermal engineering, it may be possible to obtain subpicosecond resolution.

Godil, Asif A.; Auld, B. A.; Bloom, David M.

1994-03-01

328

Prescribing antidepressants for depression: time to be dimensional and inclusive.  

PubMed

The article by Middleton and Moncrieff questions the role of antidepressants in treating depression on both philosophical and practical grounds; namely that depression isn't a brain disease to be treated by a drug and that antidepressants are ineffective except as placebos. We argue that their stance is unhelpful and factually incorrect and that a more dimensional and integrative approach is needed in order to be able to best tailor treatment to individual needs. This involves a personalised assessment of the likely benefits and risks of both psychological and drug approaches when recommending treatment for someone with depression. PMID:21401994

Anderson, Ian M; Haddad, Peter M

2011-01-01

329

Time Asymmetric Quantum Mechanics  

NASA Astrophysics Data System (ADS)

The meaning of time asymmetry in quantum physics is discussed. On the basis of a mathematical theorem, the Stone-von Neumann theorem, the solutions of the dynamical equations, the Schrödinger equation (1) for states or the Heisenberg equation (6a) for observables are given by a unitary group. Dirac kets require the concept of a RHS (rigged Hilbert space) of Schwartz functions; for this kind of RHS a mathematical theorem also leads to time symmetric group evolution. Scattering theory suggests to distinguish mathematically between states (defined by a preparation apparatus) and observables (defined by a registration apparatus (detector)). If one requires that scattering resonances of width ? and exponentially decaying states of lifetime ?=h/? should be the same physical entities (for which there is sufficient evidence) one is led to a pair of RHS's of Hardy functions and connected with it, to a semigroup time evolution t0?ttime, just like the big bang time for the universe, when it was a quantum system. The decay of quasi-stable particles is used to illustrate this quantum mechanical time asymmetry. From the analysis of these processes, we show that the properties of rigged Hilbert spaces of Hardy functions are suitable for a formulation of time asymmetry in quantum mechanics.

Bohm, Arno R.; Gadella, Manuel; Kielanowski, Piotr

2011-09-01

330

True time delay beamforming  

NASA Astrophysics Data System (ADS)

Wide aperture arrays for transmitting and receiving wideband signals suffer beam broadening when steered away from the array normal using phase delays between the array elements. This beam dispersion is eliminated if time delays instead of phase shifts are used between antenna array elements. This report represents the results of a project to demonstrate the proof-of-principle of an acousto-optic signal processing concept that generates and controls, with a single tone, the set of time delays required for linear antenna array beamforming. This acousto-optic concept allows an array to scan a beam rapidly over a continuum of angles. In the approach described in this report, the time delays between elements are generated by using an acousto-optic Bragg cell as a continuous delay line, and indirectly tapping selected points in the Bragg cell to the output. This optical tapping is controlled with a second Bragg cell and other standard passive optical elements. Included in this concept is a passive optical element to ensure that the phase shifts of the carrier of the time delayed signals will be correct at the RF of the array. The time-delay controller also provides the proper relative phases between the carriers of the time delayed signals at the RF of the antenna array. A proof-of-principle breadboard of the time delay controller was assembled. Results of the demonstration of the breadboard are described.

Gesell, Leslie H.; Feinleib, Richard E.

1994-08-01

331

Digital time delay  

SciTech Connect

Method and apparatus are provided for generating an output pulse following a trigger pulse at a time delay interval preset with a resolution which is high relative to a low resolution available from supplied clock pulses. A first lumped constant delay provides a first output signal at predetermined interpolation intervals corresponding to the desired high resolution time interval. Latching circuits latch the high resolution data to form a first synchronizing data set. A selected time interval has been preset to internal counters and corrected for circuit propagation delay times having the same order of magnitude as the desired high resolution. Internal system clock pulses count down the counters to generate an internal pulse delayed by an internal which is functionally related to the preset time interval. A second LCD corrects the internal signal with the high resolution time delay. A second internal pulse is then applied to a third LCD to generate a second set of synchronizing data which is complementary with the first set of synchronizing data for presentation to logic circuits. The logic circuits further delay the internal output signal with the internal pulses. The final delayed output signal thereafter enables the output pulse generator to produce the desired output pulse at the preset time delay interval following input of the trigger pulse.

Martin, A.D.

1986-05-09

332

The Time Series Toolbox  

NASA Astrophysics Data System (ADS)

Many applications commonly used in sensor service networks operate on the same type of data repeatedly over time. This kind of data is most naturally represented in the form of "time series". In its simplest form, a time series may consist of a single floating point number (e.g. temperature), that is recorded at regular intervals. More complex forms of time series include time series of complex observations (e.g. aggregations of related measurements, spectra, 2D coverages/images, ...), and time series recorded at irregular intervals. In addition, the time series may contain meta-information describing e.g. the provenance, uncertainty, and reliability of observations. The Time Series Toolbox (TS Toolbox) provides a set of software components and application programming interfaces that simplify recording, storage, processing and publishing of time series. This includes (1) "data connector" components implementing access to data using various protocols and data formats; (2) core components interfacing with the connector components and providing specific additional functionalities like data processing or caching; and (3) front-end components implementing interface functionality (user interfaces or software interfaces). The functionalities implemented by TS Toolbox components provide application developers with higher-level building blocks than typical general purpose libraries, and allow rapid development of fully fledged applications. The TS Toolbox also includes example applications that can be either used as they are, or as a basis for developing more complex applications. The TS-Toolbox, which was initially developed by the Austrian Institute of Technology in the scope of SANY "Sensors Anywhere", is written in Java, published under the terms of the GPL, and available for download on the SANY web site.

Boži?, Bojan; Havlik, Denis

2010-05-01

333

Asia Times Online  

NSDL National Science Digital Library

As the world's news flows increasingly from Asian nations, those people looking for a credible online source that concentrates on this region will find it in Asia Times Online. The site's front page features top stories from Asia Times journalists as well as from other online dailies and reports, including the South China Morning Post, Business Times Online, and the Australian Financial Review. The site offers separate sections for China, Southeast Asia, Japan, the Koreas, India/ Pakistan, Central Asia, and Oceania as well as departments devoted to Business Briefs, Global Economy, and Media and Industrial Technology. The entire site, including archives, is searchable.

334

VARIABLE TIME DELAY MEANS  

DOEpatents

An electrically variable time delay line is described which may be readily controlled simuitaneously with variable impedance matching means coupied thereto such that reflections are prevented. Broadly, the delay line includes a signal winding about a magnetic core whose permeability is electrically variable. Inasmuch as the inductance of the line varies directly with the permeability, the time delay and characteristic impedance of the line both vary as the square root of the permeability. Consequently, impedance matching means may be varied similariy and simultaneously w:th the electrically variable permeability to match the line impedance over the entire range of time delay whereby reflections are prevented.

Clemensen, R.E.

1959-11-01

335

Understanding Geological Time  

NSDL National Science Digital Library

In this classroom activity, middle school students gain an understanding of geologic time. The activity opens with background information for teachers about carbon and radiometric dating. In a classroom discussion, students share what they know about geologic time. Then, working in small groups responsible for different eras, students create a timeline for their assigned era by conducting library and Internet research. The activity concludes by having students review all the timelines to compare how long humans have been on the Earth to the length of time dinosaurs inhabited the planet.

336

Observations on Time 2012  

NASA Astrophysics Data System (ADS)

The main purpose of this paper is to present the authorâ??s observations on time to you, the world. Time has been a major subject of religion, philosophy, and science but defining it in a non-controversial manner applicable to all fields of study has consistently eluded the greatest scholars. Therefore, the goal of this paper is to define time in a new way that has never been presented before. The potential bombshell in the paper is the unification of thermodynamics with general relativity.

Prahlad K, Sai

2012-06-01

337

Time Projection Spectrometer.  

National Technical Information Service (NTIS)

The time projection chamber (TPC) is discussed. Its advantage is its ability to collect a great deal of information on multiparticle reactions from high-energy colliding beam experiments. The TPC makes it possible to reconstruct all the charged particles ...

H. L. Anderson

1979-01-01

338

Real Time Holographic Interferometry.  

National Technical Information Service (NTIS)

The thesis presents an introduction into holographic interferometry with its history and applications. Problems involved with recording, developing, and reconstructing real time holographic interferograms are presented. Reconstruction was accomplished usi...

J. W. Somers

1974-01-01

339

Web Geologic Time Scale  

NSDL National Science Digital Library

The University of California-Berkeley Museum of Paleontology (last mentioned in the June 16, 1995 Scout Report) has recently updated its Web Geologic Time Scale, an online feature that helps users learn about the geologic timeline and explore related museum exhibits. The familiar geologic timeline appears on the main page of the Web site, with hypertext links for each division of time. Every page of the Web Geologic Time Machine site is liberally sprinkled with links to related UCMP Web pages; think of it as a portal to all online information available from the museum. Altogether, this Web site provides a well-organized and comprehensive resource for learning how the planet has changed over time, and would be a great addition to earth or life sciences classroom material for a broad range of grades.

1994-01-01

340

Comprehending Geologic Time  

NSDL National Science Digital Library

This online calculator helps students understand the classic analogy of relating the geologic time scale to a yard stick. It will help reinforce the concept of the briefness of human history relative to the age of the Earth.

341

The Grand Time Game  

NSDL National Science Digital Library

The Grand Time Game is a collection of activities that teach students about geologic time. The game elements consist of a tabletop model that demonstrates the geologic history of the Grand Canyon, a script in which students report selected events along the geologic time scale as the instructor operates the model, and a set of overhead transparencies that the instructor shows to illustrate the story. The materials also include an activity sheet for students to record important events as they progress, and a card game about fossils and geologic time, played in groups of three or four students after the script reading (the cards can also be pasted onto a calendar or timeline). Instructions for building the model are provided.

342

GSA Geologic Time Scale  

NSDL National Science Digital Library

This Geological Society of America (GSA) site contains a detailed geologic time scale as an educational resource. It may be downloaded to a larger size, and includes all Eras, Eons, Periods, Epochs and ages as well as magnetic polarity information.

1999-01-01

343

True Time Delay Beamforming.  

National Technical Information Service (NTIS)

Wide aperture arrays for transmitting and receiving wideband signals suffer beam broadening when steered away from the array normal using phase delays between the array elements. This beam dispersion is eliminated if time delays instead of phase shifts ar...

L. H. Gesell R. E. Feinleib

1994-01-01

344

Fathering: The First Time.  

ERIC Educational Resources Information Center

Describes a group called "Fathering: The First Time" formed to help new fathers cope with stress and to share support and information. Discusses the therapists' role and group process from euphoria to competency. (JAC)

Klein, Bruce

1985-01-01

345

Music in Galileo's Time  

Microsoft Academic Search

Claudio Monteverdi appears as the key personality of the music in Galileo's time. His revolution in format and function of the musical language-from an essentially edonistic creation of purely sonorous images to a musical language consciously \\

P. Petrobelli

2011-01-01

346

Tsunami Travel Time Approximation  

NSDL National Science Digital Library

Eric Grosfils, Pomona College Summary Students are asked to calculate approximate tsunami travel times across the Pacific basin. The assignment builds off of a lab introducing students to Spatial Analyst, and ...

Grosfils, Eric

347

Telemetry Time Integration.  

National Technical Information Service (NTIS)

A new systems hardware and software architecture is presented. Time- tagging is accomplished on multiple packets of information flowing concurrently at extremely high data rates. In the telemetry field to date, there has been a serious problem with the in...

E. L. Davis

1985-01-01

348

Timing of breastfeeding  

MedlinePLUS

... together to make sure there is enough milk. Resist supplementing your baby's diet with formula feedings for ... are more tired by this time of day. Resist giving the baby a bottle of formula. This ...

349

Global Temperature Time Series  

NSDL National Science Digital Library

The phenomenon is the rising and falling of temperatures on the Earth's surface. Click to choose a city on a regional map, showing graphs of the daily maximum, minimum, and mean temperatures for a 365 day time period.

350

Drug Retention Times  

SciTech Connect

The purpose of this monograph is to provide information on drug retention times in the human body. The information provided is based on plausible illegal drug use activities that might be engaged in by a recreational drug user.

Center for Human Reliability Studies

2007-05-01

351

Drug Retention Times  

SciTech Connect

The purpose of this monograph is to provide information on drug retention times in the human body. The information provided is based on plausible illegal drug use activities that might be engaged in by a recreational drug user

Center for Human Reliability Studies

2007-05-01

352

Stopping Times and Tightness  

Microsoft Academic Search

A sufficient condition for the tightness of a sequence of stochastic processes is given in terms of their behavior after stopping times. As an application, the conditions for McLeish's invariance principle for martingales are weakened.

David Aldous

1978-01-01

353

Time Dependent Magnetic Perturbations.  

National Technical Information Service (NTIS)

An introductory review is given of time dependent magnetic perturbations, with emphasis upon their utility in nuclear magnetic resonance experiments designed to determine the nature and rate of dynamic processes in solids and fluids. The types of magnetic...

H. S. Gutowsky

1974-01-01

354

Integration on time scales  

Microsoft Academic Search

In this paper we study the process of Riemann and Lebesgue integration on time scales. The relationship of the Riemann and Lebesgue integrals is considered and a criterion for Riemann integrability is established.

Gusein Sh. Guseinov

2003-01-01

355

Timed multitasking for real-time embedded software  

Microsoft Academic Search

An event-triggered programming model, timed multitasking, is introduced that also takes a time-centric approach to real-time programming but controls timing properties through deadlines and events rather than time triggers.

Jie Liu; E.A. Lee

2003-01-01

356

A Mesozoic time scale  

Microsoft Academic Search

We present an integrated geomagnetic polarity and stratigraphic time scale for the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era, with age estimates and uncertainty limits for stage boundaries. The time scale uses a suite of 324 radiometric dates, including high-resolution Ar-40\\/Ar-39 age estimates. This framework involves the observed ties between (1) radiometric dates, biozones, and stage boundaries, and

Felix M. Gradstein; Frits P. Agterberg; James G. Ogg; Jan Hardenbol; Paul van Veen; Jacques Thierry; Zehui Huang

1994-01-01

357

Time Value of Money  

NSDL National Science Digital Library

This PowerPoint presentation from University of Tennessee's Suzan Murphy gives an excellent tutorial for the Time Value of Money, which is the concept that "money received sooner rather than later allows one to use the funds for investment or consumption purposes." The presentation focuses on methods of using a calculator (specifically Hewlett Packard 17B II calculator) to solve problems of Time Value. This easy-to-understand tutorial presents basic concepts, story problems, and solutions to the story problems.

358

Superoscillations and tunneling times  

NASA Astrophysics Data System (ADS)

It is proposed that superoscillations play an important role in the interferences that give rise to superluminal effects. To exemplify that, we consider a toy model that a wave packet to travel in zero time and negligible distortion, a distance arbitrarily larger than the width of the wave packet. The peak is shown to result from a superoscillatory superposition at the tail. Similar reasoning applies to the dwell time.

Aharonov, Yakir; Erez, Noam; Reznik, Benni

2002-05-01

359

Gamma rate versus time  

Microsoft Academic Search

Initial- and residual-gamma rates were measured as a function of time at various distances from high-yield thermonuclear detonations. Initial gamma rate versus time was measured at fixed distances from ground zero. In particular, measurements were made of the effect on initial-gamma rate caused by the passage of the shock front from ground zero through the detector station. Residual-gamma rate versus

P. Brown; G. Carp

1954-01-01

360

Time, Quantum and Information  

Microsoft Academic Search

Time, Quantum and Information, a paean to Professor Carl Friedrich von Weizsäcker, commemorates his 90th birthday. The range of Professor Weizsäcker's endeavours is an exhilarating example of what can be accomplished by one freely-soaring human spirit, who is at the same time a physicist, a philosopher, and a humanitarian.The editors, Lutz Castell and Otfried Ischebeck, have assembled an admirable collection

Leaf Turner

2004-01-01

361

TechKnow Times  

NSDL National Science Digital Library

TechKnow Times(tm) specializes in selecting and synthesizing information about Internet resources. Its goal is to make information access as simple and as quick as possible. It covers news related to Internet and online marketing, World Wide Web sites and design, and online technology and culture, all drawn from a wide range of print and electronic sources. TechKnow Times(tm) is giving online entrepreneurs the information they need to accomplish their goals.

1996-01-01

362

The Los Angeles Times  

NSDL National Science Digital Library

The Los Angeles Times debuts its Internet edition April 8. It is slated to include daily news and features, coverage of movies and entertainment, a computers and technology section, a special section devoted to Southern California sights and events, classified advertising, and chat boards. The site will be free. A fee based site will also be available, with access to Times' archives, as well as educational and research services. http://www.latimes.com

363

Timing using temporal context  

PubMed Central

We present a memory model that explicitly constructs and stores the temporal information about when a stimulus was encountered in the past. The temporal information is constructed from a set of temporal context vectors adapted from the temporal context model (TCM). These vectors are leaky integrators that could be constructed from a population of persistently-firing cells. An array of temporal context vectors with different decay rates calculates the Laplace transform of real time events. Simple bands of feedforward excitatory and inhibitory connections from these temporal context vectors enable another population of cells, timing cells. These timing cells approximately reconstruct the entire temporal history of past events. The temporal representation of events farther in the past is less accurate than for more recent events. This history-reconstruction procedure, which we refer to as timing from inverse Laplace transform (TILT), displays a scalar property with respect to the accuracy of reconstruction. When incorporated into a simple associative memory framework, we show that TILT predicts well-timed peak responses and the Weber law property, like that observed in interval timing tasks and classical conditioning experiments.

Shankar, Karthik H.; Howard, Marc W.

2010-01-01

364

Timing using temporal context.  

PubMed

We present a memory model that explicitly constructs and stores the temporal information about when a stimulus was encountered in the past. The temporal information is constructed from a set of temporal context vectors adapted from the temporal context model (TCM). These vectors are leaky integrators that could be constructed from a population of persistently firing cells. An array of temporal context vectors with different decay rates calculates the Laplace transform of real time events. Simple bands of feedforward excitatory and inhibitory connections from these temporal context vectors enable another population of cells, timing cells. These timing cells approximately reconstruct the entire temporal history of past events. The temporal representation of events farther in the past is less accurate than for more recent events. This history-reconstruction procedure, which we refer to as timing from inverse Laplace transform (TILT), displays a scalar property with respect to the accuracy of reconstruction. When incorporated into a simple associative memory framework, we show that TILT predicts well-timed peak responses and the Weber law property, like that observed in interval timing tasks and classical conditioning experiments. PMID:20654587

Shankar, Karthik H; Howard, Marc W

2010-07-21

365

Characteristic time model validation  

NASA Astrophysics Data System (ADS)

An experimental program for validation of the semi-empirical Characteristic Time Model (CTM) is described. A two-dimensional turbulent shear layer is generated in the experimental test section using a two-stream, vertically downflowing wind tunnel with a flat pre-filming airblast atomizer fitted along its centerline. This facility simulates the shear layer around the recirculation zone found in the primary zone of a gas turbine combustor. Experimental results are used to investigate CTM parameters for turbulent mixing and droplet lifetime and to examine current finite difference modeling techniques. Global mixing times evaluated at the origin of the shear layer and defined in terms of geometric macroscale and a reference velocity are compared with the locally measured values of turbulent mixing time. The results demonstrate that these global times, as defined for the CTM, do in fact accurately represent the events occurring on a local scale, as hypothesized. Modifications to the mixing time parameter to improve existing correlations are proposed. Due to restrictions imposed by the facility and instrumentation, validation of the droplet lifetime parameter was not possible. Measurements were restricted to mean spray diameters. These data and others demonstrate that current correlations for Sauter mean diameter do not adequately account for changes in atomizer geometry or liquid properties.

Tallio, K. V.; Prior, J. C., Jr.; Mellor, A. M.

1988-09-01

366

Timing is everything  

PubMed Central

Environmental influence on developmental plasticity impacts a wide diversity of animal life from insects to humans. We now understand the epigenetic basis for many of these altered phenotypes. The five environmental factors of nutrition, behavior, stress, toxins and stochasticity work individually and in concert to affect the developing epigenome. During early embryogenesis, epigenetic marks, such as DNA methylation, are reset at specific times. Two waves of global demethylation and reestablishment of methylation frame the sensitive times for early environmental influences and will be the focus of this review. Gene transcription, translation and post-translational modification of chromatin remodeling complexes are three mechanisms affected by developmental exposure to environmental factors. To illustrate how changes in the early environment profoundly affect these mechanisms, we provide examples throughout the animal kingdom. Herein we review the history, time points and mechanisms of epigenetic gene-environment interaction.

Faulk, Christopher

2011-01-01

367

Kinesthetic Astronomy: Sky Time  

NSDL National Science Digital Library

This lesson teaches basic astronomical concepts such as the astronomical meaning of the day, year, and seasons through choreographed bodily movements and positions that provide educational sensory experiences. Through a series of simple body movements, students gain insight into the relationship between time and astronomical motions of Earth (rotation about its axis, and orbit around the Sun), and also about how these motions influence what we see in the sky at various times of the day and year. The lesson can be applied to understand the times of day and year on other planets (e.g. Mars). The lesson provides a set-up for understanding seasons and can be taught with or without an emphasis thereon.

Morrow, Cherilynn; Zawaski, Michael

368

Accurate measurement of time  

NASA Astrophysics Data System (ADS)

The paper discusses current methods for accurate measurements of time by conventional atomic clocks, with particular attention given to the principles of operation of atomic-beam frequency standards, atomic hydrogen masers, and atomic fountain and to the potential use of strings of trapped mercury ions as a time device more stable than conventional atomic clocks. The areas of application of the ultraprecise and ultrastable time-measuring devices that tax the capacity of modern atomic clocks include radio astronomy and tests of relativity. The paper also discusses practical applications of ultraprecise clocks, such as navigation of space vehicles and pinpointing the exact position of ships and other objects on earth using the GPS.

Itano, Wayne M.; Ramsey, Norman F.

1993-07-01

369

The Earth Times  

NSDL National Science Digital Library

The Earth Times is an "independent, international, nonpartisan newspaper focusing on environment and sustainable development, and such interrelated concerns of the international system as population, human rights, trade, and women's and children's rights." It is specifically aimed at opinion and policy makers, community and business leaders, nongovernmental organizations, and students and teachers. It was founded in 1991 by Pranay Gupte, a columnist for Newsweek International and a former foreign correspondent for The New York Times. The newspaper form of the Earth Times is available by subscription. Students and teachers in the US can receive it free upon request. The website offers two feature articles from the current issue and all articles from back issues. Articles can be searched for keywords; however, the web version only includes issues going back to June of 1996.

370

Activated clotting time (ACT).  

PubMed

The standard assay for monitoring anticoagulation during extracorporeal life support (ECLS) is the activated clotting time (ACT) test, with celite, kaolin, and glass beads being the most commonly used activators to initiate contact activation. The point-of-care ACT test has been the preferred test in catheterization labs and cardiac theatres because it has a number of advantages over laboratory tests (Spinler et al., Ann Pharmacother 39(7-8):1275-1285, 2005): Shorter time between sampling and results. Smaller blood sample size. Availability to have test performed by non-lab personnel. Reduced errors associated with sample mislabeling/mishandling. Decreased risk of sample degradation with time. There are other coagulation monitoring tests available; however these are usually specific and do not take into account the global picture of the entire clotting system. The standard coagulation tests (prothrombin time (PT), activated partial thromboplastin time, thrombin time (TT), and fibrinogen level) are plasma tests measuring plasma haemostasis and not patient haemostasis. The ACT measurement uses whole blood, thereby incorporating the importance of platelets and phospholipids in the role of coagulation. Many of the problems with the haemostatic system during ECLS are caused by the activation of platelets, which are not detected by standard tests. Because an ACT test is nonspecific there are many variables such as hypothermia, platelets, aprotinin, GP IIb/IIIa antagonists, haemodilution, etc. that can alter its results. For this reason it is important to gain an understanding as to how these variables interact for meaningful interpretation of the ACT test result. PMID:23546712

Horton, Stephen; Augustin, Simon

2013-01-01

371

The Geologic Time Scale  

NSDL National Science Digital Library

This site contains a large, easy to read, detailed geologic time scale for the Phanerozoic Eon (544 million years ago - Present). This is the period of time, also known as an eon, between the end of the Precambrian and today. The Phanerozoic begins with the start of the Cambrian period, 544 million years ago. It encompasses the period of abundant, complex life on Earth. The chart includes the Era, Period or System, and the Epoch or Series and features a brief description of each.

372

Thrombin clotting time.  

PubMed

Thrombin clotting time (TCT) is a coagulation assay used to diagnose congenital and acquired fibrinogen deficiency (Adcock et al., Coagulation handbook, Esoterix Coagulation, Austin, TX, 2002), as well as to identify contamination by heparin, prior to performing additional coagulation assays. This test is based on the principle that in citrated plasma, the addition of Thrombin allows for formation of a stable clot. The time required for the formation of a stable clot is recorded in seconds and represents the actual TCT result. PMID:23546710

Ignjatovic, Vera

2013-01-01

373

Nonlinear Time Series Analysis  

NASA Astrophysics Data System (ADS)

The time variability of many natural and social phenomena is not well described by standard methods of data analysis. However, nonlinear time series analysis uses chaos theory and nonlinear dynamics to understand seemingly unpredictable behavior. The results are applied to real data from physics, biology, medicine, and engineering in this volume. Researchers from all experimental disciplines, including physics, the life sciences, and the economy, will find the work helpful in the analysis of real world systems. First Edition Hb (1997): 0-521-55144-7 First Edition Pb (1997): 0-521-65387-8

Kantz, Holger; Schreiber, Thomas

2004-01-01

374

Time as an Illusion  

NASA Astrophysics Data System (ADS)

We review the idea, due to Einstein, Eddington, Hoyle and Ballard, that time is a subjective label, whose primary purpose is to order events, perhaps in a higher-dimensional universe. In this approach, all moments in time exist simultaneously, but they are ordered to create the illusion of an unfolding experience by some physical mechanism. This, in the language of relativity, may be connected to a hypersurface in a world that extends beyond spacetime. Death in such a scenario may be merely a phase change.

Wesson, Paul S.

375

Sky Time: Kinesthetic Astronomy  

NSDL National Science Digital Library

Through a series of simple body movements, learners gain insight into the relationship between time and astronomical motions of Earth (rotation about its axis, and orbit around the Sun), and also about how these motions influence what we see in the sky at various times of the day and year. This activity can be used to introduce seasons on Earth and other planets. Learners will especially enjoy finding their birthdays in the orbit and using a zodiac diagram. This comprehensive lesson plan includes detailed background information, common misconceptions, extensions, teacher tips, references/resources, and FAQs.

Morrow, Cherilynn A.; Zawaski, Michael

2004-01-01

376

Systematically Controlling for the Influence of Age, Sex, Hertz and Time Post-Whole-Body Vibration Exposure on Four Measures of Physical Performance in Community-Dwelling Older Adults: A Randomized Cross-Over Study  

PubMed Central

Though popular, there is little agreement on what whole-body vibration (WBV) parameters will optimize performance. This study aimed to clarify the effects of age, sex, hertz and time on four physical function indicators in community-dwelling older adults (N = 32). Participants were exposed to 2?min WBV per session at either 2?Hz or 26?Hz and outcome measures were recorded at 2, 20 and 40?min post-WBV. Timed get up-and-go and chair sit-and-reach performances improved post-WBV for both sexes, were significantly different between 2?Hz and 26?Hz treatments (P ? 0.05) and showed statistically significant interactions between age and gender (P ? 0.01). Counter movement jump and timed one-legged stance performances showed a similar but non-significant response to 2?Hz and 26?Hz treatments, though male subjects showed a distinct trended response. Age and gender should be statistically controlled and both 2?Hz and 26?Hz exert a treatment effect.

Merriman, Harold L.; Brahler, C. Jayne; Jackson, Kurt

2011-01-01

377

Branching time temporal logic  

Microsoft Academic Search

Many important parallel computer programs exhibit ongoing behaviour that is characterized naturally in terms of infinite execution traces, which can be organized into branching trees, and which reflect the high degree of nondeterminism inherent in parallel computation. In this paper, we give a systematic account of Branching Time Temporal Logics, which provide a formal system for describing and reasoning about

E. Allen Emerson; Jai Srinivasan

1988-01-01

378

Times of Albert Einstein.  

National Technical Information Service (NTIS)

''The life of Albert Einstein has a dramatic quality that does not rest exclusively on his theory of relativity. The extravagant timing of history linked him with three shattering developments of the twentieth century: the rise and fall of Nazi Germany, t...

S. M. W. Ahmad

1990-01-01

379

This Time It's Personal  

ERIC Educational Resources Information Center

Educators have known for some time now that a one-size-fits-all approach to learning does not lead to the level of student engagement and academic success that schools strive to achieve. In their search for a more customized approach to delivering instruction, they've explored project-based learning, addressed different learning styles, and…

Demski, Jennifer

2012-01-01

380

The First Time  

ERIC Educational Resources Information Center

|In this article, the author narrates her experience of meeting a Montessori kid for the first time and shares the characteristics she observed in Montessori students. The author was working as director of academic resources in university housing at the University of Wisconsin-Madison and met Jason, a pre-med sophomore who was the resident…

Black, Beth

2011-01-01

381

TIMED Solar EUV experiment  

Microsoft Academic Search

The Solar EUV Experiment (SEE) selected for the NASA Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) mission will measure the solar vacuum ultraviolet (VUV) spectral irradiance from 0.1 to 200 nm. To cover this wide spectral range two different types of instruments are used: a grating spectrograph for spectra above 25 nm and a set of silicon soft x-ray

Thomas N. Woods; Scott Bailey; Frank Eparvier; George Lawrence; Judith Lean; Bill McClintock; Raymond Roble; Gary J. Rottman; Stanley C. Solomon; W. Kent Tobiska

2000-01-01

382

Timing of Fatherhood.  

National Technical Information Service (NTIS)

Basic qualitative data on the adult child-father relationship from the child's perspective, with attention to sources of diversity among families, was collected. The effects of family timing on adult children was also assessed. In addition, work on a life...

C. N. Nydegger

1983-01-01

383

Timing driven placement  

Microsoft Academic Search

The authors address the problem of incorporating timing constraints into the physical design of integrated circuits. First they formulate the problem and discuss graph models suitable for its analysis. Next, they describe algorithms resulting in placements of improved performance in comparison to placements whose objective is to minimize the summation of wire lengths on the chip. Finally, the authors show

Malgorzara Marek-Sadowska; Shen P. Lin

1989-01-01

384

Timing of seasonal sales  

Microsoft Academic Search

We present a model of timing of seasonal sales where stores choose several designs at the beginning of the season without knowing wich one, if any, will be fashionable. Fashionable designs have a chance to fetch high prices in fashion markets while non-fashionable ones must be sold in a discount market. In the beginning of the season, stores charge high

Pascal Courty

1998-01-01

385

Time in perspective.  

PubMed

Perceptions of time and space are subject to strong contextual effects. Like their physical counterparts, they appear to be bound together. The perceived spatial extent of a constant retinal extent increases with its perceived distance from the observer. The perceived duration of a moving object increases with its covered angular trajectory. It follows that the perceived duration of moving objects covering identical angular trajectories should also increase with distance. Using three-dimensionally rendered balls rolling for 600 ms, 900 ms, and 1,200 ms and covering 5.5°, 11°, and 22° trajectories in fronto-parallel planes of a linear-perspective scene, we showed that perceived duration dilates by up to 50% as the fronto-parallel plane of the rolling ball recedes from the observer. Such time dilation is mostly contributed to by the smaller size of the distant ball. As in a three-dimensional world, objects' sizes and their covered trajectories per time unit decrease with distance, and as the two factors lead to opposite perceived-duration effects, the results suggest a form of time constancy in a three-dimensional world. PMID:23774463

Gorea, Andrei; Hau, Janice

2013-06-17

386

It's Time to Reassess.  

ERIC Educational Resources Information Center

|In light of recent changes in social and cultural values and the effects these changes have had on higher education, community college leaders must take the time to reassess the mission and function of the California community colleges. Shifts away from traditional values toward an increased emphasis on personal needs and aspirations may explain…

Van Groningen, Tom

387

Real-time sonography  

Microsoft Academic Search

This textbook acquaints the reader with normal and pathologic anatomy as depicted on dynamic or real-time scanning. Chapters are organized by specialty, such as abdominal, urologic, or pediatric. The text is illustrated with still-frame images and line drawings. The drawings show important areas of interest and provide graphic notation as to where and in what orientation the scan was obtained.

A. C. Fleischey; A. E. Jr. James

1984-01-01

388

Finding similar time series  

Microsoft Academic Search

Similarity of objects is one of the crucial concepts in several applications, including data mining. For complex objects, similarity is nontrivial to define. In this paper we present an intuitive model for measuring the similarity between two time series. The model takes into account outliers, different scaling functions, and variable sampling rates. Using methods from computational geometry, we show that

Gautam Das; Dimitrios Gunopulos; Heikki Mannila

389

Gossiping in Minimal Time  

Microsoft Academic Search

The gossip problem involves communicating a unique item fromeach node in a graph to every other node. We study the minimumtime required to do this under the weakest model of parallel communicationwhich allows each node to participate in just one communicationat a time as either sender or receiver. We study a number of topologiesincluding the complete graph, grids, hypercubes and

David W. Krumme; George Cybenko; K. N. Venkataraman

1992-01-01

390

Medication timing device  

US Patent & Trademark Office Database

A medication regime control device employs a plurality of liquid crystal displays controlled by a preprogrammed electronic circuit to display to a patient the number of doses of selected identified medications to be consumed at the time of display and any special instructions with respect thereto. The device acts as a watch and personal identifier between displays of the need to take medication.

1998-02-17

391

Fluid Time Gate.  

National Technical Information Service (NTIS)

The pure fluid time gate is capable of gating fluid input signals without the use of moving mechanical parts. The output passage of a pure fluid oscillator of the sonic or relaxation type is coupled to the power nozzle of an AND or OR-NOR pure fluid logic...

R. W. Warren

1965-01-01

392

Pulsar Searching and Timing  

NASA Astrophysics Data System (ADS)

More than 2000 pulsars are now known. These pulsars may be divided into a number of different classes according to their period, period derivative, binary properties, emission characteristics and so on. Some important classes have relatively few members, e.g. double-neutron-star binary systems, and so continued searches for currently unknown pulsars are important. Such searches are being undertaken at various observatories around the world. Somewhat unexpectedly, the Fermi Gamma-ray Observatory, has proved to be an efficient pulsar detector, especially for millisecond pulsars (MSPs). The great stability of pulsar periods, especially for MSPs, leads to a number of important applications of pulsar timing. The detection and study of relativistic orbit perturbations in double-neutron-star systems has proved to be a powerful tool with measurements of the original binary pulsar, PSR B1913+16, and more recently the double pulsar, PSR J0737-3039A/B, showing that Einstein's general theory of relativity accurately describes these gravitational interactions. Direct detection of gravitational waves using pulsar timing is close to being achieved with the development of pulsar timing arrays (PTAs) in Europe, North America and Australia. Combining data from these PTAs to form the International Pulsar Timing Array (IPTA) will lead to improved significance of such a detection. Ultimately, detailed study of gravitational-wave sources will be possible using future large radio telescopes such as FAST and the SKA.

Manchester, R. N.

2013-01-01

393

Swing in Time  

NSDL National Science Digital Library

Students examine the motion of pendulums and come to understand that the longer the string of the pendulum, the fewer the number of swings in a given time interval. They see that changing the weight on the pendulum does not have an effect on the period. They also observe that changing the angle of release of the pendulum has negligible effect upon the period.

Integrated Teaching And Learning Program

394

Time reversal communication system  

SciTech Connect

A system of transmitting a signal through a channel medium comprises digitizing the signal, time-reversing the digitized signal, and transmitting the signal through the channel medium. The channel medium may be air, earth, water, tissue, metal, and/or non-metal.

Candy, James V. (Danville, CA); Meyer, Alan W. (Danville, CA)

2008-12-02

395

Video time encoding machines.  

PubMed

We investigate architectures for time encoding and time decoding of visual stimuli such as natural and synthetic video streams (movies, animation). The architecture for time encoding is akin to models of the early visual system. It consists of a bank of filters in cascade with single-input multi-output neural circuits. Neuron firing is based on either a threshold-and-fire or an integrate-and-fire spiking mechanism with feedback. We show that analog information is represented by the neural circuits as projections on a set of band-limited functions determined by the spike sequence. Under Nyquist-type and frame conditions, the encoded signal can be recovered from these projections with arbitrary precision. For the video time encoding machine architecture, we demonstrate that band-limited video streams of finite energy can be faithfully recovered from the spike trains and provide a stable algorithm for perfect recovery. The key condition for recovery calls for the number of neurons in the population to be above a threshold value. PMID:21296708

Lazar, Aurel A; Pnevmatikakis, Eftychios A

2011-02-04

396

Distance Rate Time  

NSDL National Science Digital Library

Measurement is one of the core NCTM Principals and Standards for School Mathematics content standards, and rate is central to its practical application. While most middle school students know the distance-rate-time formula, they may still benefit from a closer study of the relationship through these online resources.

National Science Digital Library (NSDL) Middle School Portal Staff

2008-03-10

397

Distance-Time Graphs  

NSDL National Science Digital Library

This site describes a distance-time graph, how it compares to the equation for a line, and uses equations to calculate speed and slope. The steps and relationships are clear and specific, and the problems are solved using both graphic and computational methods.

2000-01-01

398

Choice Over Time  

Microsoft Academic Search

In the last twenty years a growing body of experimental evidence has posed a challenge to the standard Exponential Discounting Model of choice over time. Attention has focused on some specific ‘anomalies’, notably preference reversal and declining discount rates, leading to the formulation of the model of hyperbolic discounting which is finding increasing favour in the literature. In this paper

Paola Manzini; Marco Mariotti

2007-01-01

399

Decay Time of Cathodoluminescence  

ERIC Educational Resources Information Center

|Simple measurements of the decay time of cathodoluminescence are described. Cathodoluminescence is used in many devices, including computer monitors, oscilloscopes, radar displays and television tubes. The experimental setup is simple and easy to build. Two oscilloscopes, a function generator, and a fast photodiode are needed for the experiments.…

Kraftmakher, Yaakov

2009-01-01

400

Time Dependent Fluids  

ERIC Educational Resources Information Center

|Discusses the flow characteristics of thixotropic and negative thixotropic fluids; various theories underlying the thixotropic behavior; and thixotropic phenomena exhibited in drilling muds, commercial paints, pastes, and greases. Inconsistencies in the terminology used to label time dependent effects are revealed. (CC)|

Collyer, A. A.

1974-01-01

401

Timing subsystem development  

Microsoft Academic Search

In the predominately digital DCS, a requirement exists to coordinate clocks at geographically distinct nodes to handle switched digital traffic and provide a general system timing capability. Aside from the characteristics of the clocks, medium, and link equipment, the synchronization technique itself is an important aspect in considering overall network performance. This document presents the findings of a program in

K. R. Backe

1982-01-01

402

Time Adaptive Wavelet Denoising  

Microsoft Academic Search

this paper we address shrinking wavelet coefficients by taking into considerationthe "time" behavior of data. Our approach is Bayesian. We test the hypotheses that thesignal parts of the wavelet coefficients are zero (H0 ) against general alternatives. The priorprobabilities of the hypotheses H0 are assumed dependent on the coarsest level of details. Theachieved shrinkage is of "hard-thresholding" type. Both 1D

Brani Vidakovic; Concha Bielza

1998-01-01

403

Timing of Seasonal Sales  

Microsoft Academic Search

We present a model of timing of seasonal sales in which stores choose several designs before the season without knowing which, if any, is fashionable. Stores begin by charging high prices to capture the fashion market. As the season approaches the end with goods still unsold, stores have sales to capture the discount market. More designs and greater price competition

Pascal Courty; Hao Li

1999-01-01

404

Particulate residence times  

Microsoft Academic Search

Examination of suspended particulate concentration data from a year-long, regional air-quality study of a portion of the Great Lakes area revealed that depletion of particulates occurred during extended periods of travel over water surfaces. Based on particulate concentrations and meteorological measurements, residence times of background regional particulate matter were found to be between 5 and 16 h in the region.

D. M. Whelpdale

1974-01-01

405

Seismic Travel Time Study.  

National Technical Information Service (NTIS)

The report consists of an introduction in which is given a list of published papers on the travel times of body waves together with brief comments on the results. The main body of the report describes a new determination of the velocity distribution in th...

A. L. Hales

1971-01-01

406

Borrowed Traits, Borrowed Time  

Microsoft Academic Search

Every time you look into the mirror, you see history in its purest form. The curve of the nose, the shape of the eye, the hair on the head—everything represents a path that has been traveled and a choice that has been made. But this choice was not made by you, but by those infinitesimal strands of mate- rial that

JADE TAKAKUWA

407

Budgeting in Hard Times.  

ERIC Educational Resources Information Center

|Interviews with school board members and administrators produced a list of suggestions for balancing a budget in hard times. Among these are changing calendars and schedules to reduce heating and cooling costs; sharing personnel; rescheduling some extracurricular activities; and forming cooperative agreements with other districts. (MLF)|

Parrino, Frank M.

2003-01-01

408

Early Time STARFISH Calculations.  

National Technical Information Service (NTIS)

In this report, we present results from recent CMHD (Collisionless Magnetohydrodynamics) code calculations of the early time (0 to 1 sec.) evolution of the STARFISH event. The emphasis of this report is on the velocity spectrum of the energy going to the ...

F. E. Fajen R. W. Kilb

1982-01-01

409

Decay Time of Cathodoluminescence  

ERIC Educational Resources Information Center

Simple measurements of the decay time of cathodoluminescence are described. Cathodoluminescence is used in many devices, including computer monitors, oscilloscopes, radar displays and television tubes. The experimental setup is simple and easy to build. Two oscilloscopes, a function generator, and a fast photodiode are needed for the experiments.…

Kraftmakher, Yaakov

2009-01-01

410

HAWC Timing Calibration  

NASA Astrophysics Data System (ADS)

The High-Altitude Water Cherenkov (HAWC) Experiment is a second-generation high sensitivity gamma-ray and cosmic-ray detector that builds on the experience and technology of the Milagro observatory. HAWC utilizes the water Cherenkov technique to measure extensive air showers. Instead of a pond filled with water (as in Milagro), an array of closely packed water tanks with 3 PMTs each is used. The cosmic ray's direction will be reconstructed using the times when the PMTs in each tank are triggered. Therefore, the timing calibration will be crucial for reaching an angular resolution as low as 0.1 degrees. We propose to use a laser calibration system, patterned after the calibration system in Milagro. The HAWC optical calibration system uses less than 1 ns laser light pulses, directed into two optical fiber networks. Each network will use optical fan-outs and switches to direct light to specific tanks. The first network is used to measure the light transit time out to each pair of tanks, and the second network sends light to each tank, calibrating each tank's 3 PMTs. Time slewing corrections will be made using neutral density filters to control the light intensity over 4 orders of magnitude. This system is envisioned to run both continuously at a low rate, or at a high rate with many intensity levels. In this presentation, we present the design of the calibration system and first measurements of its performance.

Kelley-Hoskins, Nathan; Huentemeyer, Petra; Matthews, John; Dingus, Brenda

2011-04-01

411

Sound Image of Time  

Microsoft Academic Search

It is said that music begins where words fail. Music's vague messages awaken cloud-like feeling—idiosyncratic, and yet direct and precise in its animalistic power. The delicate beauty of the art of music would wither long time ago if not the mighty physiological element that the sound flow of music elicits from us, s haking, making shivers, affecting heartbeat, and giving

J. L. Borges

2007-01-01

412

The fire next time  

Microsoft Academic Search

Rodney King's beating by Los Angeles Police Department officers, and their subsequent acquittal by an all White jury sparked the first “multicultural riot” in Los Angeles in 1992. Twenty years since the time of the uprising, the vigilante murder of teenager Trayvon Martin in a gated community in Florida brought thousands across the country into the streets to protest the

Jenna M. Loyd

2012-01-01

413

Video Time Encoding Machines  

PubMed Central

We investigate architectures for time encoding and time decoding of visual stimuli such as natural and synthetic video streams (movies, animation). The architecture for time encoding is akin to models of the early visual system. It consists of a bank of filters in cascade with single-input multi-output neural circuits. Neuron firing is based on either a threshold-and-fire or an integrate-and-fire spiking mechanism with feedback. We show that analog information is represented by the neural circuits as projections on a set of band-limited functions determined by the spike sequence. Under Nyquist-type and frame conditions, the encoded signal can be recovered from these projections with arbitrary precision. For the video time encoding machine architecture, we demonstrate that band-limited video streams of finite energy can be faithfully recovered from the spike trains and provide a stable algorithm for perfect recovery. The key condition for recovery calls for the number of neurons in the population to be above a threshold value.

Lazar, Aurel A.; Pnevmatikakis, Eftychios A.

2013-01-01

414

Reaction Time Sound Explanation  

NSDL National Science Digital Library

This experiment presents auditory stimuli and requires the participant to respond after hearing target stimuli under different conditions. This experiment gives students the opportunity to determine whether their reaction times are reliably different for tasks that require slightly different decisions. This page provides guidance for faculty who wish to incorporate this activity into their classroom.

415

Time at the Beginning.  

National Technical Information Service (NTIS)

Age consistency for the Universe today has been an important cosmological test. Even more powerful consistency tests at times as early as 10(sup -32) sec lie ahead in the precision era of cosmology. I outline tests based upon cosmic microwave background (...

M. S. Turner

2002-01-01

416

Knowledge, Belief and Time  

Microsoft Academic Search

In the conclusion of [HM2] Halpern and Moses expressed their interest in a logical system in which one could talk about knowledge and belief (and belief about knowledge, knowledge about belief and so on). We investigate such systems. In the first part of the paper knowledge and belief, without time, are considered. Common knowledge and common belief are defined and

Sarit Kraus; Daniel J. Lehmann

1986-01-01

417

Take Time to Dream  

Microsoft Academic Search

College librarians have the unique opportunity of implementing plans somewhat more quickly than their larger academic partners. There is less opportunity for bureaucracy to come between an idea, its plan and its implementation. Take time to dream. It could start you on the road to excellence.

Alice Harrison Bahr

1999-01-01

418

Real Time Marathon Bonds  

Microsoft Academic Search

Marathons have gained increasing popularity in recent years for both athletic competitors and those with fitness goals. Major marathon events attract at least 20,000 race participants and even more spectators making it a formidable task to locate one's friends and family. Supporters have an even more difficult time getting updates on the location of race participants since sections of the

Michelle Chang

419

Time and Learning. ERIC Digest.  

ERIC Educational Resources Information Center

The use of time in school is undergoing close scrutiny. Over the years, educators have sought to enhance learning time through such reforms as block scheduling and year-round schools. School time can be conceived as an inverted pyramid, in which allocated time (total time in the school day or year) forms the top tier, engaged time (time-on-task)…

Metzker, Bill

420

Biomechanical evaluation of the relationship between postural control and body mass index.  

PubMed

Postural stability is crucial in maintaining body balance during quiet standing, locomotion, and any activities that require a high degree of balance performance, such as participating in sports and dancing. Research has shown that there is a relationship between stability and body mass. The aims of this study were to examine the impact that two variables had on static postural control: body mass index (BMI) and gender. Eighty healthy young adults (age=21.7±1.8 yr; height=1.65±0.09 m; mass=67.5±19.0 kg) participated in the study and the static postural control was assessed using the Biodex Balance System, with a 20 Hz sampling rate in the bipedic stance (BLS) and unipedic stance (ULS) for 30s. Five test evaluations were performed for each balance test. Postural control was found to be negatively correlated with increased adiposity, as the obese BMI group performed significantly poorer than the underweight, normal weight and overweight groups during BLS and ULS tests. The underweight, normal weight and overweight groups exhibited greater anterior-posterior stability in postural control during quiet stance. In addition, female displayed a trend of having a greater postural sway than male young adults, although it was evidenced in only some BMI groups. This study revealed that BMI do have an impact on postural control during both BLS and ULS. As such, BMI and gender-specific effects should be taken into consideration when selecting individuals for different types of sporting activities, especially those that require quiet standing. PMID:22507349

Ku, P X; Abu Osman, N A; Yusof, A; Wan Abas, W A B

2012-04-14

421

Time Dependent Volcano Deformation  

NASA Astrophysics Data System (ADS)

Time varying deformation can arise due to changes in magma pressure, evolution of the source geometry (e.g., dike propagation), or time dependent response of the surrounding crust. It is important to understand the signatures of these processes in order to distinguish between them. Here I explore time dependent surface deformation due to viscoelastic and poroelastic relaxation of the crust surrounding simplified magma chambers. Viscoelastic deformation is considered in a shell surrounding a spherical magma chamber in a half-space (as analyzed numerically by Newman et al, 2001). The full space solution for a Maxwell rheology was given by Dragoni and Magnanensi (PEPI, 1989). An approximate half-space solution is simply constructed following the approach of McTigue (JGR, 1987) as long as the outer radius R2 is small compared to the depth d. The surface displacements are scaled, time-dependent versions of the Mogi solution in an elastic half-space. For a step increase in magma pressure (other source histories are also simply constructed) uz (?, z=0, t) = (1 - ?) p0 R13 / ? d2 [ e-t/tR + R23 / R13 ( 1 - e-t/tR ) ] 1 / (1 + ?2)3/2 where R1 is the magma chamber radius, ? is the normalized radial distance from the center of the source, and the characteristic relaxation time is tR = (3?/?)(1-?)/(1+?)(R2/R1)3, where ? is viscosity and ? is shear modulus. The post-intrusion displacements scale with (R2/R1)3 - 1 and can be significant. For example, a viscoelastic shell of only 20% the radius of the magma chamber leads to time dependent displacements that are 70% of the instantaneous elastic displacements. An approximate fully time-dependent solution for a cylindrical (plane strain) magma chamber in a homogeneous poro-elastic half-space is constructed as the superposition of the solution due to an expanding chamber in a full plane, and distributed shear and normal loads on a poroelastic half-space. The full-space solution is pure shear and thus induces no change in pore pressure. Consequently, the distributed loads necessary to cancel the imposed tractions on the free surface are time invariant. The surface displacements due to the applied surface loads are found using displacement potentials in the Fourier-Laplace domain; the Laplace transforms are inverted analytically. The vertical velocity resulting from the instantaneous inflation of the magma chamber is 2 ? vz(z=0,t) = ? (1-?) [ N? - i sgn(k) T? ] ? c/? t e- c k2 t - c k ?1-? e-? c k2 terfc( ?c (1-?) k2 t) where k is horizontal wavenumber, c is hydraulic diffusivity, ?{1-?} = 1-2?2, ?2 = ?u - ?/1-? , ?u is the undrained Poisson's ratio, and N? and T? are the Fourier transformed normal N and shear T tractions acting on the plane z = 0, N = (? ? V/? ) (x2- d2) /(d2 + x2)2, T = (2? ? V/ ? )dx/(d2 + x2)2. The displacement immediately above the source increases monotonically, however the flanking regions subside for some time following the initial elastic uplift before further uplifting. This arises because pore fluid flows from the flanking region to the center of uplift. The final uplift is identical to the initial elastic uplift but increased by a factor of ?u-?.

Segall, P.

2006-12-01

422

Funding Full-Time Study through Part-Time Work  

ERIC Educational Resources Information Center

Full-time students engaged in part-time studies have been a subject of increasing academic attention. This study extends work in this area by examining: the extent to which full-time undergraduate students undertake part-time employment, the reasons for working whilst studying full-time and the extent to which students relate their part-time

Richardson, Mark; Evans, Carl; Gbadamosi, Gbolahan

2009-01-01

423

space and time in ergodic gemorphology  

NASA Astrophysics Data System (ADS)

Epistemological perspectives rank among the main factors contributing to word coinage in scientific literature. New words come into existence as new epistemological fields evolve (Sack1992). Each field, however, tends to impose its own interpretation on the words associated with it. To illustrate the point, certain words retain formal structure and relate to the same subject area, but can nonetheless be employed in totally different epistemological fields. The semantic content undergoes a drastic change in each case. Granted that numerous theoretical stances can be identified within the discipline of geomorphology, acquaintance with the semantic content of certain words should help toward a more realistic understanding of what the theorists and practitioners in this field have in mind. This paper, which is based on an analysis of these three theoretical positions aims to highlight the importance of the semantic content of the term equilibrium as utilized in ergodic geomorphology, and the ways in which it is construed from different viewpoints. For this purpose, the authors have of necessity availed themselves of dated sources, rather than up-to-date ones. The paper also argues that familiarity with concepts such as these will ensure a better grasp of the paradigms in question.

Seyed Ebrahimi, S.

2009-04-01

424

Tracking change over time  

USGS Publications Warehouse

Landsat satellites capture images of Earth from space-and have since 1972! These images provide a long-term record of natural and human-induced changes on the global landscape. Comparing images from multiple years reveals slow and subtle changes as well as rapid and devastating ones. Landsat images are available over the Internet at no charge. Using the free software MultiSpec, students can track changes to the landscape over time-just like remote sensing scientists do! The objective of the Tracking Change Over Time lesson plan is to get students excited about studying the changing Earth. Intended for students in grades 5-8, the lesson plan is flexible and may be used as a student self-guided tutorial or as a teacher-led class lesson. Enhance students' learning of geography, map reading, earth science, and problem solving by seeing landscape changes from space.

U.S. Geological Survey

2011-01-01

425

Kaolin clotting time.  

PubMed

The kaolin clotting time (KCT) is a sensitive test used in the laboratory detection of lupus anticoagulants (LA) (Derksen and de Groot, Thromb Res 114:521-526, 2004). It is essentially an activated partial thromboplastin time (APTT) test with no added phospholipid. Kaolin acts as the activator in the KCT. In the absence of additional phospholipid reagent, the quality of the test sample is extremely important since the generation of thrombin completely depends on the presence of residual cell membranes and plasma lipids (Derksen and de Groot, Thromb Res 114:521-526, 2004). Since the test contains no exogenous phospholipid, a confirmatory test using excess phospholipid is required to confirm the presence of lupus anticoagulant in the sample (Court, Br J Biomed Sci 54:287-298, 1997). PMID:23546725

Radhakrishnan, Kottayam

2013-01-01

426

Realism in real time  

Microsoft Academic Search

Abstract With the continuous improvement in ray tracing and radiosity algorithms, image synthesis quality has reached the level of photo realism. However, efforts to achieve real-time performances by implementing ray tracing and radiosity algorithms on parallel processors and dedicated hardware have not been very successful so far. Increasing the number,of processors introduces a corresponding growth in inter-processor communication. Caching could

F. W. Jansen; A. Chalmers

1993-01-01

427

A Journey Through Time  

NSDL National Science Digital Library

This activity has students create a travel brochure of a geologic period. Links are provided to research questions about the dominant life forms, position of the continents, and climate of the period. Questions in the conclusion section are for students to consider the duration of human existence compared to geologic time, why dinosaurs and humans never fought, and whether they would want to travel to their chosen geologic period.

Schneider, Amy

428

Bath Time with Archimedes  

NSDL National Science Digital Library

This algebra lesson helps students make the connection between functions and their graphs. The model of the level of water in a bathtub is used. Students will watch the graph and a chart of the depth of the water at different time increments. They are then asked to identify the events that caused each change in the graph. A student worksheet is available for download here in a Word Document.

2010-12-14

429

Differential entropy and time  

Microsoft Academic Search

We give a detailed analysis of the Gibbs-type entropy notion and its dynamical behavior in case of time-dependent continuous probability distributions of varied origins: related to classical and quantum systems. The purpose-dependent usage of conditional Kullback-Leibler and Gibbs (Shannon) entropies is explained in case of non-equilibrium Smoluchowski processes. A very different temporal behavior of Gibbs and Kullback entropies is confronted.

Piotr Garbaczewski

2005-01-01

430

Making Time to Write?  

PubMed Central

Clinicians are busy people who must develop strategies for making time to write. With many obligations, their first strategy may be to try to clear the decks to make way for the current project. When writing takes on a more constant challenge, medical writers find themselves wedging writing in between myriad other tasks and commitments. Ultimately, committed writers, with effort and help, find a way to schedule writing as another essential activity in their lives.

Candib, Lucy M.

2005-01-01

431

Reaction Time 2: Zap!  

NSDL National Science Digital Library

This Science NetLinks lesson is the second of a two-part series that encourages students to think about their own learning and the strategies that best help them learn new skills and ideas. In this lesson, students build upon what they have already learned by participating in another online reaction-time activity--this one testing their visual and auditory abilities, both separately and together.

Science Netlinks;

2003-06-19

432

Real time interferogram simulation  

Microsoft Academic Search

An electronic analog device has been constructed which displays synthesized interferograms on a cathode-ray tube (CRT) for real-time viewing. First- and third-order aberrations are generated individually or in combination. The exact amount of each aberration (in waves) appearing in the simulated interferogram is also displayed. A radial line cursor adjustable over 360 deg in the artificial exit pupil provides profile

J. M. Geary; D. Holmes

1979-01-01

433

The Best of Times  

NSDL National Science Digital Library

This interactive Flash book of poems by Greg Tang and pictures by Harry Briggs helps children master their times tables through a deeper, more intuitive understanding of multiplication instead of memorization. Students use partial products to multiply larger numbers, first breaking them into smaller, more manageable parts. After reading the poem and examples, learners can test themselves by applying the strategies to a series of 3-5 challenges.

Tang, Greg

2013-06-01

434

Circadian Time Perception  

Microsoft Academic Search

The variability of anticipating a meal was investigated. Sprague-Dawley rats earned food by inspecting a food source during a 3-hr interval. Food was not available at other times. In Experiment 1, the meal started 3 or 7 hr after light offset in a 12-hr light–dark cycle. Experiment 2 was conducted in constant darkness with 14-, 22-, 22.5-, 24-, 25.5-, 26-,

Jonathon D. Crystal

2001-01-01

435

TIMED Spacecraft Model  

NSDL National Science Digital Library

This is a model for students to assemble, aimed at enhancing their knowledge of NASA spacecraft and scientific facts. The cover of this four-color tri-fold contains background information about the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) mission as well as two language arts activities to reinforce space science vocabulary and concepts. This product is available in hardcopy and electronic formats.

2001-06-01

436

Real Time Baseball Database  

NASA Astrophysics Data System (ADS)

The author describes the system outline, features and operations of "Nikkan Sports Realtime Basaball Database" which was developed and operated by Nikkan Sports Shimbun, K. K. The system enables to input numerical data of professional baseball games as they proceed simultaneously, and execute data updating at realtime, just-in-time. Other than serving as supporting tool for prepareing newspapers it is also available for broadcasting media, general users through NTT dial Q2 and others.

Fukue, Yasuhiro

437

Gravity, Time, and Lagrangians  

ERIC Educational Resources Information Center

|Feynman mentioned to us that he understood a topic in physics if he could explain it to a college freshman, a high school student, or a dinner guest. Here we will discuss two topics that took us a while to get to that level. One is the relationship between gravity and time. The other is the minus sign that appears in the Lagrangian. (Why would…

Huggins, Elisha

2010-01-01

438

Time warp football  

Microsoft Academic Search

We describe a system called Time Warp Football (TWF) which puts fans in control of the game watching experience. TWF uses annotated video streams to enable instantaneous forward and backward play-by-play navigation and on-demand switching between multiple camera angles. These features allow fans to easily watch and re-watch plays they are interested in from any camera angle. The annotations also

Stephen G. Lynn; Brett G. Partridge

2009-01-01

439

Telescopes as Time Machines  

NSDL National Science Digital Library

This fun, nighttime hands-on astronomy activity lets learners explore how long it takes for light from different objects in the universe to reach Earth. The activity shows participants the difference among three distance categories: within our Solar System, within the Milky Way, and within the rest of the universe. The PDF contains step-by-step instructions, photos, presentation tips, ready-to-print "Passport through Time" activity handout, and links to background information.

Pacific, Astronomical S.

2008-01-01

440

Telescope Time Allocation Tool  

Microsoft Academic Search

TaToo is ESO's new Time Allocation Tool. This software scheduler is a combination of a user-friendly graphical user interface and an intelligent constraint-programming engine fine-tuned to ESO's scheduling problem. TaToo is able to produce a high quality and reliable schedule taking into consideration all constraints of the recommended programs for all telescopes in about 15 minutes. This performance allows schedulers

J. Alves

2005-01-01

441

ANOXIA THROUGH TIME  

Microsoft Academic Search

The rock record provides unequivocal evidence for multiple times in Earth history during which the entire global ocean or\\u000a parts of it were characterized by severe oxygen-deficiency. Evidence includes geological and paleontological observations\\u000a but also diverse geochemical fingerprints such as trace element abundances, organic geochemical markers or various isotope\\u000a records, all of which are diagnostic for water column anoxia. The

Harald Strauss

442

Time scales in fragmentation  

SciTech Connect

The problem of fragmentation of excited finite systems is explored in the frame of classical molecular dynamics experiments of two-dimensional Lennard-Jones drops. The main objective of this work is to get information about the relative value of the relevant characteristic time scales (CTS) for this kind of process. We investigate the CTS for fragment formation, the stabilization of the radial flux, and the internal {open_quotes}temperature.{close_quotes} It is found that the asymptotic fragments are realized early in phase space, when the system is still dense, by the time the radial flux attains its asymptotic value. It is also shown that the temperature of the system during the breakup is quite homogenous with respect to the expected profile if local thermal equilibration takes place. Special emphasis is put on the investigation of the time scale of stabilization of the statistical properties of the mass spectrum, which is related to the kind of information carried by the asymptotic fragments. {copyright} {ital 1997} {ital The American Physical Society}

Strachan, A.; Dorso, C.O. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Nunez 1428, Buenos Aires (Argentina)

1997-02-01

443

Residence time distribution  

SciTech Connect

Slurry phase residence time in the SRC-II dissolver is a major process variable affecting the extent of conversion to distillate products. Kinetic studies have shown that overall conversion of vacuum bottoms to lighter hydrocarbons is a zero order process with respect to vacuum bottoms. This implies that although the extent of backmixing is not a critical process variable, slurry phase mean residence time is. Experimental results from the P-99 PDU supported this. Radioactive tracers were injected into the Ft. Lewis dissolver during normal operation to study the residence time distribution of the gas and slurry phases. Results from gas phase radiotracers showed the gas phase to approach plug flow behavior, but with much larger than expected gas holdup. Gas holdup appeared to be 20% of the reactor volume, rather than the 10 to 12% predicted by standard holdup correlations. Slurry phase radiotracer results indicated that the slurry phase was well-backmixed. Experiments with a downcomer designed to enhance direct slurry flow from the top to the bottom of the dissolver showed this to be a viable and controllable device. The high level of gas holdup at Ft. Lewis suggest that standard holdup correlations must be modified to be used with confidence in the design of coal liquefaction reactors. Additional programs to define holdup relationships in high temperature, high pressure coal liquefaction reactors are recommended. 11 references, 6 figures, 6 tables.

Not Available

1984-02-01

444

Time Reversal Violation  

SciTech Connect

This talk briefly reviews three types of time-asymmetry in physics, which I classify as universal, macroscopic and microscopic. Most of the talk is focused on the latter, namely the violation of T-reversal invariance in particle physics theories. In sum tests of microscopic T-invariance, or observations of its violation, are limited by the fact that, while we can measure many processes, only in very few cases can we construct a matched pair of process and inverse process and observe it with sufficient sensitivity to make a test. In both the cases discussed here we can achieve an observable T violation making use of flavor tagging, and in the second case also using the quantum properties of an antisymmetric coherent state of two B mesons to construct a CP-tag. Both these tagging properties depend only on very general properties of the flavor and/or CP quantum numbers and so provide model independent tests for T-invariance violations. The microscopic laws of physics are very close to T-symmetric. There are small effects that give CP- and T-violating processes in three-generation-probing weak decays. Where a T-violating observable can be constructed we see the relationships between T-violation and CP-violation expected in a CPT conserving theory. These microscopic effects are unrelated to the 'arrow of time' that is defined by increasing entropy, or in the time direction defined by the expansion of our Universe.

Quinn, H; /SLAC

2009-01-27

445

Hippocampus, time, and memory.  

PubMed

Five experiments were conducted to determine the effects of hippocampal damage on timing and the memory for temporal events. In Experiments 1-3, rats were trained to discriminate between auditory signals that differed in both duration (2 or 8 s) and rate (2 or 16 cycles/s). Half of the rats were trained to discriminate duration, and half were trained to discriminate rate. After rats acquired the relevant discrimination, signals with intermediate durations and rates were presented to obtain psychophysical functions that related signal duration and/or rate to response choice. Rats then received either lesions of the fimbria-fornix or control operations. Postoperatively, the accuracy of duration and rate discriminations as measured by the difference limen (DL) was unaffected by the lesion, but the point of subjective equality (PSE) was shifted to a shorter duration and a slower rate by the lesion in Experiment 1. Both rats with lesions and rats with control operations showed cross-modal transfer of duration and rate from the auditory signals used in training to visual signals used in testing in Experiment 2. A 5-s delay was imposed between the end of a signal and the opportunity to respond in Experiment 3. The delay served as a retention interval for the rats trained in the rate discrimination, and the rats with fimbria-fornix lesions were selectively impaired by the addition of the delay as measured by an increase in the DL. The delay did not serve as a retention interval for rats trained in the duration discrimination because they were able to continue timing through the delay. A peak procedure was employed in Experiment 4. The maximum response rate of control rats was approximately at the time of scheduled reinforcement (20 s), but the maximum response rate of rats with fimbria-fornix lesions was reliably earlier than the time of scheduled reinforcement. When a 5-s gap was imposed in the signal, control rats summed the signal durations before and after the gap, whereas rats with fimbria-fornix lesions showed no retention of the signal duration prior to the gap. Experiment 5 continued the testing of the rats used in Experiments 1-4 and showed that rats with lesions had an impairment in a test of spatial working memory in an eight-arm radial maze. Taken together, these results demonstrate that a fimbria-fornix lesion interferes with temporal and spatial working memory, reduces the remembered time of reinforcement stored in reference memory, and has no effect on the animal's sensitivity to stimulus duration. (PsycINFO Database Record (c) 2013 APA, all rights reserved). PMID:24128355

Meck, Warren H; Church, Russell M; Olton, David S

2013-10-01

446

Commission 31: Time  

NASA Astrophysics Data System (ADS)

The most intensely discussed and controversial issue in time keeping has been the proposal before the International Telecommunications Union (ITU) to redefine Coordinated Universal Time (UTC) so as to replace leap seconds by leap hours. Should this proposal be adopted, the practice of inserting leap seconds would cease after a specific date. Should the Earth's rotation continue to de-accelerate at its historical rate, the next discontinuity in UTC would be an hour inserted several centuries from now. Advocates of this proposal cite the need to synchronize satellite and other systems, such as GPS, Galileo, and GLONASS, which did not exist and were not envisioned when the current system was adopted. They note that leap second insertions can be and have been incorrectly implemented or accounted for. Such errors have to date had localized impact, but they could cause serious mishaps involving loss of life. For example, some GPS receivers have been known to fail simply because there was no leap second after a long enough interval, other GPS receivers failed because the leap second information was broadcast more than three months in advance, and some commercial software used for internet time-transfer Network Time Protocol (NTP) could either discard all data received after a leap second or interpret it as a frequency change. The ambiguity associated with the extra second could also disrupt financial accounting and certain forms of encryption. Those opposed to the proposal question the need for a change, and also point out the costs of adjusting to the proposed change and its inconvenience to amateur astronomers and others who rely upon astronomical calculations published in advance. Reports have been circulated that the cost of checking and correcting software to accommodate the new definition of UTC would be many millions of dollars for some systems. In October 2005 American Astronomical Society asked the ITU for a year's time to study the issue. This commission has supported the efforts of the IAU' s Committee on the Leap Second to make an informed recommendation, and anticipates considerable discussion at the IAU's 26th General Assembly in 2006.

Matsakis, Demetrios; Defraigne, Pascale; Hosokawa, M.; Leschiutta, S.; Petit, G.; Zhai, Z.-C.

2007-03-01

447

Are animals stuck in time?  

Microsoft Academic Search

People can time travel cognitively because they can remember events having occurred at particular times in the past (episodic memory) and because they can anticipate new events occurring at particular times in the future. The ability to assign points in time to events arises from human development of a sense of time and its accompanying time-keeping technology. The hypothesis is

William A. Roberts

2002-01-01

448

QUADRENNIAL MCNP TIMING STUDY  

SciTech Connect

The Los Alamos National Laboratory Monte Carlo N-Particle radiation transport code, MCNP, is widely used around the world for many radiation protection and shielding applications. As a well-known standard it is also an excellent vehicle for assessing the relative performance of scientific computing platforms. Every three-to-four years a new version of MCNP is released internationally by the Radiation Safety Information Computational Center (RSICC) in Oak Ridge, Tennessee. For each of the past few releases, we have also done a timing study to assess the progress of scientific computing platforms and software. These quadrennial timing studies are valuable to the radiation protection and shielding community because (a) they are performed by a recognized scientific team, not a computer vendor, (b) they use an internationally recognized code for radiation protection and shielding calculations, (c) they are eminently reproducible since the code and the test problems are internationally distributed. Further, if one has a computer platform, operating system, or compiler not presented in our results, its performance is directly comparable to the ones we report because it can use the same code, data, and test problems as we used. Our results, using a single processor per platform, indicate that hardware advances during the past three years have improved performance by less than a factor of two and software improvements have had a marginal effect on performance. The most significant impacts on performance have resulted from developments in multiprocessing and multitasking. The other most significant advance in the last three years has been the accelerated improvements in personal computers. In the last timing study, the tested personal computer was approximately a factor of four slower that the fastest machine tested, a DEC Alphastation 500. In the present study, the fastest PC tested was less than a factor of two slower than the fastest platform, which is a Compaq (previously DEC) Alpha XP1000.

E. C. SELCOW; B. D. LANSRUD

2000-09-01

449

Pulsar Timing Arrays  

NASA Astrophysics Data System (ADS)

In the last decade, the use of an ensemble of radio pulsars to constrain the characteristic strain caused by a stochastic gravitational wave background has advanced the cause of detection of very low frequency gravitational waves (GWs) significantly. This electromagnetic means of GW detection, called Pulsar Timing Array (PTA), is reviewed in this paper. The principle of operation of PTA, the current operating PTAs and their status are presented along with a discussion of the main challenges in the detection of GWs using PTA.

Joshi, Bhal Chandra

2013-01-01

450

Time Dilation Equation  

NSDL National Science Digital Library

This online article is from the Museum's Seminars on Science, a series of distance-learning courses designed to help educators meet the new national science standards. The article, which offers a simple demonstration of Einstein's Time Dilation Equation, is part of the Frontiers in Physical Science seminar. It uses the example of a light beam bouncing between two mirrors in a rocket to illustrate the theory, and includes a step-by-step look at the math involved in calculating the quantitative solution.

451

Time-Series Analysis  

Microsoft Academic Search

\\u000a Time-series analysis aims to investigate the temporal behavior of one of several variables x(t). Examples include the investigation of long-term records of mountain uplift , sea-level fluctuations, orbitally-induced\\u000a insolation variations and their influence on the ice-age cycles, millenium-scale variations in the atmosphere-ocean system,\\u000a the effect of the El Niño\\/Southern Oscillation on tropical rainfall and sedimentation (Fig. 5.1) and tidal influences

Martin H. Trauth

452

Hope in Hard Times  

PubMed Central

In the face of challenging times, advocates for women and their families in maternal-child health care continue to promote evidence-based and mother-/baby-friendly care. What qualities allow childbirth educators, doulas, nurses, and perinatal care providers to keep going even when the health-care practices around them often do not match their values? This editorial explores the impact of recent trends in which increasing utilization of elective technology in maternity care may affect the individual commitment of childbirth advocates. Borrowing from research on successful advocates in other fields, the author speculates on both why and how childbirth advocates sustain commitment and how “we will prevail.”

Leslie, Mayri Sagady

2008-01-01

453

Time for geriatric jurisprudence.  

PubMed

Geriatrics and law may not be natural bedfellows. Moreover, law and lawyers were not part of the professions that were the 'founding fathers' of the field of geriatrics. In this short viewpoint we invite the readers to consider a new inter-disciplinary research approach that attempts to combine jurisprudence with geriatrics. Geriatric jurisprudence is a special and timely opportunity for doctors and lawyers to come together in a new, different and more united way to jointly conceptualize a medico-legal theory of aging to better serve our shared community: older and aging persons. PMID:22538767

Doron, Israel; Meenan, Helen

2012-01-18

454

Memory on time.  

PubMed

Considerable recent work has shown that the hippocampus is critical for remembering the order of events in distinct experiences, a defining feature of episodic memory. Correspondingly, hippocampal neuronal activity can 'replay' sequential events in memories and hippocampal neuronal ensembles represent a gradually changing temporal context signal. Most strikingly, single hippocampal neurons - called time cells - encode moments in temporally structured experiences much as the well-known place cells encode locations in spatially structured experiences. These observations bridge largely disconnected literatures on the role of the hippocampus in episodic memory and spatial mapping, and suggest that the fundamental function of the hippocampus is to establish spatio-temporal frameworks for organizing memories. PMID:23318095

Eichenbaum, Howard

2013-01-12

455

Telescope Time Allocation Tool  

NASA Astrophysics Data System (ADS)

TaToo is ESO's new Time Allocation Tool. This software scheduler is a combination of a user-friendly graphical user interface and an intelligent constraint-programming engine fine-tuned to ESO's scheduling problem. TaToo is able to produce a high quality and reliable schedule taking into consideration all constraints of the recommended programs for all telescopes in about 15 minutes. This performance allows schedulers at ESO-VISAS to simulate and evaluate different scenarios, optimize the scheduling of engineering activities at the observatories, and in the end construct the most science efficient schedule possible.

Alves, J.

2005-03-01

456

Space-time qubits  

SciTech Connect

We construct a qubit algebra from field creation and annihilation operators acting on a global vacuum state. Particles to be used as qubits are created from the vacuum by a near-deterministic single-particle source. Our formulation makes the space-time dependence of the qubits explicit, preparing the way for quantum computation within a field framework. The method can be generalized to deal with interacting qubits whose wave packets are not perfectly matched to each other. We give an example of how to calculate the Heisenberg evolution of a simple two-qubit circuit, taking expectation values in the field vacuum state.

Pienaar, J. L.; Myers, C. R.; Ralph, T. C. [Centre for Quantum Computation and Communication Technology, School of Mathematics and Physics, University of Queensland, Brisbane 4072, Queensland (Australia)

2011-08-15

457

Timing is Everything  

NSDL National Science Digital Library

Kids today are growing up with televisions, movies, videos, and DVDs, so it's logical to assume that this type of media could be motivating and used to great effect in the classroom. But at what point should film and other visual media be used? Are there times in the inquiry process when showing a film or incorporating other visual media is more effective? One teacher tackles these questions by assessing video use among her upper-elementary students in a small rural Northeastern Missouri school district.

Drury, Debra

2006-07-01

458

The public rhetorics of policing in times of war and violence: countering apocalyptic visions  

Microsoft Academic Search

Public debate about post 9\\/11 policing presumes for the most part that the world changed fundamentally at that point and that\\u000a policing powers and tactics have altered in response. For some people, largely defenders of the necessity of a strong security\\u000a stance, the changes have been possibly not enough. For others, opponents of the security state, the changes represent a

Mark Finnane

2008-01-01

459

Remapping time across space.  

PubMed

Multiple lines of evidence indicate that visual attention's temporal properties differ between the left and right visual fields (LVF and RVF). Notably, recent electroencephalograph recordings indicate that event-related potentials peak earlier for LVF than for RVF targets on bilateral-stream rapid serial visual presentation (RSVP) identification tasks. Might this hastened neural response render LVF targets perceptually available sooner than RVF targets? If so, how might the visual system reconcile these timing differences to estimate simultaneity across the LVF and RVF? We approached these questions by presenting bilateral-stream RSVP displays that contained opposite-hemifield targets and requiring participants to judge both the targets' temporal order and simultaneity. The temporal order judgments (TOJs) revealed that participants perceived LVF targets ?134 ms sooner than RVF targets. This LVF hastening approximates a full cycle of visual attention's canonical ?10 Hz (?100 ms) temporal resolution. In contrast, performance on the simultaneity task did not exhibit the LVF hastening observed on the TOJ task, despite identical retinal stimulation across the two tasks. This finding rules out a stimulus-driven "bottom-up" explanation for the task-specific behavior. Moreover, error patterns across the two tasks revealed that, within the decision stage of simultaneity judgments, participants remapped LVF targets, but not RVF targets, to a later time in the RSVP sequence. Such hemifield-specific remapping would effectively compensate for the cross-hemifield asymmetries in neural response latencies that could otherwise impair simultaneity estimates. PMID:23818678

Matthews, Nestor; Welch, Leslie; Festa, Elena; Clement, Andrew

2013-07-01

460

DNA Replication Timing.  

PubMed

Patterns of replication within eukaryotic genomes correlate with gene expression, chromatin structure, and genome evolution. Recent advances in genome-scale mapping of replication kinetics have allowed these correlations to be explored in many species, cell types, and growth conditions, and these large data sets have allowed quantitative and computational analyses. One striking new correlation to emerge from these analyses is between replication timing and the three-dimensional structure of chromosomes. This correlation, which is significantly stronger than with any single histone modification or chromosome-binding protein, suggests that replication timing is controlled at the level of chromosomal domains. This conclusion dove tails with parallel work on the heterogeneity of origin firing and the competition between origins for limiting activators to suggest a model in which the stochastic probability of individual origin firing is modulated by chromosomal domain structure to produce patterns of replication. Whether these patterns have inherent biological functions or simply reflect higher-order genome structure is an open question. PMID:23984435

Rhind, Nicholas; Gilbert, David M

2013-07-01

461

Moments in Time  

PubMed Central

It has been suggested that perception and action can be understood as evolving in temporal epochs or sequential processing units. Successive events are fused into units forming a unitary experience or “psychological present.” Studies have identified several temporal integration levels on different time scales which are fundamental for our understanding of behavior and subjective experience. In recent literature concerning the philosophy and neuroscience of consciousness these separate temporal processing levels are not always precisely distinguished. Therefore, empirical evidence from psychophysics and neuropsychology on these distinct temporal processing levels is presented and discussed within philosophical conceptualizations of time experience. On an elementary level, one can identify a functional moment, a basic temporal building block of perception in the range of milliseconds that defines simultaneity and succession. Below a certain threshold temporal order is not perceived, individual events are processed as co-temporal. On a second level, an experienced moment, which is based on temporal integration of up to a few seconds, has been reported in many qualitatively different experiments in perception and action. It has been suggested that this segmental processing mechanism creates temporal windows that provide a logistical basis for conscious representation and the experience of nowness. On a third level of integration, continuity of experience is enabled by working memory in the range of multiple seconds allowing the maintenance of cognitive operations and emotional feelings, leading to mental presence, a temporal window of an individual’s experienced presence.

Wittmann, Marc

2011-01-01

462

Moments in time.  

PubMed

It has been suggested that perception and action can be understood as evolving in temporal epochs or sequential processing units. Successive events are fused into units forming a unitary experience or "psychological present." Studies have identified several temporal integration levels on different time scales which are fundamental for our understanding of behavior and subjective experience. In recent literature concerning the philosophy and neuroscience of consciousness these separate temporal processing levels are not always precisely distinguished. Therefore, empirical evidence from psychophysics and neuropsychology on these distinct temporal processing levels is presented and discussed within philosophical conceptualizations of time experience. On an elementary level, one can identify a functional moment, a basic temporal building block of perception in the range of milliseconds that defines simultaneity and succession. Below a certain threshold temporal order is not perceived, individual events are processed as co-temporal. On a second level, an experienced moment, which is based on temporal integration of up to a few seconds, has been reported in many qualitatively different experiments in perception and action. It has been suggested that this segmental processing mechanism creates temporal windows that provide a logistical basis for conscious representation and the experience of nowness. On a third level of integration, continuity of experience is enabled by working memory in the range of multiple seconds allowing the maintenance of cognitive operations and emotional feelings, leading to mental presence, a temporal window of an individual's experienced presence. PMID:22022310

Wittmann, Marc

2011-10-18

463

The Sun in Time  

NASA Astrophysics Data System (ADS)

The Sun varies in time over at least twenty orders of magnitude. In this highly selective look at a vast subject, the focus is on solar variations related to the magnetic field structure of the heliosphere since these changes affect the propagation of cosmic rays in the heliosphere. The root of the changes is the magnetic field pattern near the solar surface. Some key aspects of the behavior of this pattern are reviewed. Recent solar activity has been unlike any experienced in living memory and several of the observed oddities are noted. Included here is a first attempt to directly compare three decades of magnetic field measurements in coronal holes with the heliospheric magnetic field at 1 AU. Results support the idea that nearly all the open magnetic flux from the Sun originates in coronal holes (including those close to active regions).

Harvey, J. W.

2013-06-01

464

Real time automated inspection  

DOEpatents

A method and apparatus relating to the real time automatic detection and classification of characteristic type surface imperfections occurring on the surfaces of material of interest such as moving hot metal slabs produced by a continuous steel caster. A data camera transversely scans continuous lines of such a surface to sense light intensities of scanned pixels and generates corresponding voltage values. The voltage values are converted to corresponding digital values to form a digital image of the surface which is subsequently processed to form an edge-enhanced image having scan lines characterized by intervals corresponding to the edges of the image. The edge-enhanced image is thresholded to segment out the edges and objects formed by the edges are segmented out by interval matching and bin tracking. Features of the objects are derived and such features are utilized to classify the objects into characteristic type surface imperfections.

Fant, Karl M. (Minneapolis, MN); Fundakowski, Richard A. (Saint Paul, MN); Levitt, Tod S. (Minneapolis, MN); Overland, John E. (Plymouth, MN); Suresh, Bindinganavle R. (New Brighton, MN); Ulrich, Franz W. (Minneapolis, MN)

1985-01-01

465

Jazz Old Time Online  

NSDL National Science Digital Library

For fans of jazz, the Jazz Old Time site will be a fun way to listen to few well-known chestnuts from the early days of this musical idiom. Of course, those who don't know much about jazz will appreciate listening to a few new artists as well. The site features over 18,000 songs in the public domain, and visitors can browse through the selections by artists or take a look at a few sample playlists. As one might suspect, artists like King Oliver, Meade Lux Lewis, and Louis Armstrong are featured prominently, though early recordings from later artists, such as Stan Getz, are also available. The site might also be recommended to students in a music appreciation course.

466

Teaching Time Savers  

NSDL National Science Digital Library

The Mathematical Association of America (MAA) has a number of online materials designed for math educators, and their "Teaching Time Savers" feature is quite a pip. This series is edited by Professor Michael E. Orrison of Harvey Mudd College, and the articles are "designed to share easy-to-implement activities for streamlining the day-to-day tasks of faculty members everywhere." The feature started in 2006, and visitors to the site can look over the twenty or so pieces here. Some of the pieces featured here include "The List of Grievances and Special Requests", "Working for a Week", "Keeping Homework at Home", and "Activities That Make Every Minute Count". Faculty members are also encouraged to submit their own entries for possible inclusion, and details about getting in touch with Professor Orrison are made available here.

467

A Journey Through Time  

NSDL National Science Digital Library

Noted photographer Frans Lanting opens the website dedicated to his most recent ambitious project with these words: "Seven years ago I stood at the tide line of an estuary and began a personal journey through time.� Auspicious words indeed, and this lovely exploration of what he found on this journey takes visitors on a "lyrical interpretation of life on Earth from its earliest beginnings to its present diversity.� As visitors click on the words "Start Journey" they will be taken through eighty six photographs which document the various physical landforms and processes from the Hawaiian Islands to the heights of the Himalayas. After clicking on each photo, visitors will be presented with an interactive timeline that locates the photo within a timeline of geologic history. Interested parties can also peruse the "More about LIFE" section to learn more about the equipment Lanting uses in his work, and how the project came to life.

Lanting, Frans

468

Cell complexes through time  

NASA Astrophysics Data System (ADS)

The history of cell complexes is closely related to the birth and development of topology in general. Johann Benedict Listing (1802 - 1882) introduced the term 'topology' into mathematics in a paper published in 1847, and he also defined cell complexes for the first time in a paper published in 1862. Carl Friedrich Gauss (1777 - 1855) is often cited as the one who initiated these ideas, but he did not publish either on topology or on cell complexes. The pioneering work of Leonhard Euler (1707 - 1783) on graphs is also often cited as the birth of topology, and Euler's work was cited by Listing in 1862 as a stimulus for his research on cell complexes. There are different branches in topology which have little in common: point set topology, algebraic topology, differential topology etc. Confusion may arise if just 'topology' is specified, without clarifying the used concept. Topological subjects in mathematics are often related to continuous models, and therefore quite irrelevant to computer based solutions in image analysis. Compared to this, only a minority of topology publications in mathematics addresses discrete spaces which are appropriate for computer-based image analysis. In these cases, often the notion of a cell complex plays a crucial role. This paper briefly reports on a few of these publications. This paper is not intended to cover the very lively progress in cell complex studies within the context of image analysis during the last two decades. Basically it stops its historic review at the time when this subject in image analysis research gained speed in 1980 - 1990. As a general point of view, the paper indicates that image analysis contributes to a fusion of topological concepts, the geometric and the abstract cell structure approach and point set topology, which may lead towards new problems for the study of topologies defined on geometric or abstract cell complexes.

Klette, Reinhard

2000-10-01

469

Timing of tracheostomy.  

PubMed

Currently, tracheostomy represents an established procedure for airway management in critically ill patients who require long-term respiratory support, and it is one of the most frequently performed surgical procedures in critically ill patients. It offers a number of practical and theoretical advantages when compared to conventional translaryngeal oro- or nasotracheal intubation, but is also associated with a number of serious complications. In the last 20 years, several retrospective studies, randomized prospective trials, and meta-analyses have been published to determine the best timing for tracheostomy. However, these studies presented conflicting results. All studies performed so far in a prospective randomized fashion were relatively small and underpowered. Currently, several large controlled randomized studies are underway that will hopefully help physicians make better evidence-based decisions on the timing of tracheostomy. Based on our current knowledge, the following recommendations might be made on a low level of evidence: on day 2 or 3 after onset of mechanical ventilation (>48 h of mechanical ventilation or need for an artificial airway) tracheostomy should be seriously considered. Before decisions are made, several questions should be answered: Is the situation suitable for tracheostomy? Are there relevant contraindications for the performance of a tracheostomy? What is the most likely course of the underlying respiratory insufficiency? What is the likelihood the patient will stay in need of invasive mechanical ventilation for more than a week, either because of an ongoing impairment of oxygenation, weaning failure, upper airway obstruction, coma or a swallowing disorder? If no relevant contraindication is present and if the need for invasive mechanical ventilation can be expected to last for more than one week, tracheostomy should be planned and performed within the next 2 days. PMID:18946428

Quintel, M; Bräuer, A

2008-10-23

470

Time Life Pictures  

NSDL National Science Digital Library

Although this is a commercial site with pictures and images for sale, users can nonetheless view and appreciate one of "the most extraordinary collections of pictures in the world" at The Picture Collection from Time, Inc. An initial free registration is required, and after that users need only log on to gain access to over 22 million images, including illustrations, prints, and photographs. Archival materials from many popular magazines are available here, including images from Time, Life, Sports Illustrated, People, and Entertainment Weekly, as well as material from the recently acquired Mansell Collection. "Mansell photographs date from the beginnings of the medium in the 1840s through World War II [and] depict a vast range of scenics, important news events, and historical personalities, with a special emphasis on art and architecture. In addition, the new Mansell Collection includes extraordinary holdings of engraved illustrations, lithographs, and drawings predating the advent of photographic imaging." In addition to a key word search function, The Picture Collection offers a special searching and licensing program that lets you search for and store materials in "Lightboxes" of your own creation for later use; these are similar to folders that one might use in a conventional software setting. The program also calculates licensing fees for images based on what type of usage is intended (newspaper, magazine, Website, etc.). Research help is available for those users who would like someone else to do the searching, with one half-hour of free research offered initially. After that, a fee of 85 dollars an hour is charged; some or all of this fee may be waived if one or more images are licensed. An excellent help section rounds out this site and makes perusing this amazing (if somewhat overwhelming) collection even more pleasurable.

471

Time Constraints in Workflow Systems  

Microsoft Academic Search

Time management is a critical component of workflow-based process management. Important aspects of time management include planning of workflow process execution in time, estimating workflow execution duration, avoiding deadline violations, and satisfying all external time constraints such as fixed-date constraints and upper and lower bounds for time intervals between activities. In this paper, we present a framework for computing activity

Johann Eder; Euthimios Panagos; Michael Rabinovich

1999-01-01

472

Time Estimation Predicts Mathematical Intelligence  

Microsoft Academic Search

BackgroundPerforming mental subtractions affects time (duration) estimates, and making time estimates disrupts mental subtractions. This interaction has been attributed to the concurrent involvement of time estimation and arithmetic with general intelligence and working memory. Given the extant evidence of a relationship between time and number, here we test the stronger hypothesis that time estimation correlates specifically with mathematical intelligence, and

Peter Kramer; Paola Bressan; Massimo Grassi

2011-01-01

473

Real time polarimetric dehazing.  

PubMed

Remote sensing is a rich topic due to its utility in gathering detailed accurate information from locations that are not economically feasible traveling destinations or are physically inaccessible. However, poor visibility over long path lengths is problematic for a variety of reasons. Haze induced by light scatter is one cause for poor visibility and is the focus of this article. Image haze comes about as a result of light scattering off particles and into the imaging path causing a haziness to appear on the image. Image processing using polarimetric information of light scatter can be used to mitigate image haze. An imaging polarimeter which provides the Stokes values in real time combined with a "dehazing" algorithm can automate image haze removal for instant applications. Example uses are to improve visual display providing on-the-spot detection or imbedding in an active control loop to improve viewing and tracking while on a moving platform. In addition, removing haze in this manner allows the trade space for a system operational waveband to be opened up to bands which are object matched and not necessarily restricted by scatter effects. PMID:23518739

Mudge, Jason; Virgen, Miguel

2013-03-20

474

Timing Neurogenesis and Differentiation  

PubMed Central

The cerebellum is an excellent model system to study how developmental programs give rise to exquisite neuronal circuits in the adult brain. Here, we describe our findings regarding granule cell neurogenesis and differentiation using the MADM method (mosaic analysis with double markers) in mice. By following the development of individual granule cell clones, we show that (1) granule cell precursors (GCPs) undergo predominantly symmetric division during postnatal development; (2) clonally related granule cells (GCs) exit the cell cycle within a narrow time window and stack their axons in the molecular layer in chronological order from deep to superficial sublayers; and (3) whereas the average GCP proliferation in the external granular layer is progressively slower as development proceeds, there is a rapid expansion of GCPs shortly before clonally related GCs exit the cell cycle. These properties produce GC clones that are distinct, each having a restricted axonal projection, but that are on average similar in cell number. We discuss possible developmental mechanisms and functional implications of these findings.

Espinosa, J. Sebastian; Luo, Liqun

2008-01-01

475

Towards time dependent DSD  

NASA Astrophysics Data System (ADS)

DSD makes it possible to calculate propagation of expanding detonation shocks without a need to evaluate the flow field behind them. DSD is a quasi steady state model calibrated from detonation breakout curves of steady detonations, usually in sticks. Once calibrated (D (k)), it is applied to non steady expanding detonation shocks with slowly varying shapes. Time dependent D(k) relations were introduced in the past in forms like D(k,dk/dt) or k(D,dD/dt), but were not calibrated or applied to realistic detonation situations. In this paper we check predictions of DSD in a spherical outgoing detonation, which is non-steady, by comparing them to reactive flow calculations. From the results we conclude that: 1) for each initial state (in D(R) plane, say) we get a different shock path. All shock paths converge for large R; 2) detonation acceleration dD/dt depends on detonation velocity through: dD/dt=A(Dcj-D), where A depends on the initial radius; 3) the various detonation shock paths do not coincide with the D(k) relation obtained by solving the eigen value problem of quasi steady detonation in spherical symmetry.

Partom, Yehuda

2009-06-01

476

METAS Time & Frequency Metrology Report.  

National Technical Information Service (NTIS)

METAS is the Swiss Federal Office of Metrology and Accreditation. The METAS Time & Frequency Laboratory (T&F Lab) operates a cesium primary standard, maintains the Swiss national time scales, disseminates precise time and performs calibrations for custome...

C. Schlunegger G. Dudle L. Bernier

2005-01-01

477

It's about Time: Difficulties in Developing Time Concepts  

ERIC Educational Resources Information Center

For years, students have become frustrated with the task of learning to tell time, and teachers have become frustrated at not fully understanding why this task is such a difficult one . The concepts of time include point of time ("measured" or labelled by clocks, and calendars), and durations (measuring elapsed time)--abstract ideas about the…

Harris, Sally

2008-01-01

478

Group Time: Taking a "Humor Break" at Group Time  

ERIC Educational Resources Information Center

|January is a perfect time to insert a strong dose of humor into group time gatherings. Oftentimes, children have tired of the predictable pattern of group meetings and need some change. Humor-filled group time activities can be the best secret remedy. Not only will children become more interested in the group time meetings (and therefore listen…

Church, Ellen Booth

2005-01-01

479

On ‘arriving on time’, but what is ‘on time’?  

Microsoft Academic Search

The time-geographical concept of coupling constraints, which define when, where and for how long individuals have to join other individuals and material objects, can be useful to ‘time squeeze’ studies. Geographers have typically operationalised the ‘when’ dimension of coupling constrains through arrival times at locations in physical space or the starting time of specific activities. This paper questions this approach

Tim Schwanen

2006-01-01

480

How Reaction Time, Update Time, and Adaptation Time Influence the Stability of Traffic Flow  

Microsoft Academic Search

When modeling the acceleration and decel- eration of drivers, there are three characteristic time con- stants that influence the dynamics and stability of traffic flow: The reaction time of the drivers, the velocity adap- tation time needed to accelerate to a new desired velocity, and the numerical update time. By means of numerical simulations with a time-continuous car-following model, we

Arne Kesting; Martin Treiber

2008-01-01