Artykuły w czasopismach na temat „Direction”
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Cross, R. A. "Directing direction". Nature 406, nr 6798 (sierpień 2000): 839–40. http://dx.doi.org/10.1038/35022686.
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Hiris, Eric, i Randolph Blake. "Direction repulsion in motion transparency". Visual Neuroscience 13, nr 1 (styczeń 1996): 187–97. http://dx.doi.org/10.1017/s0952523800007227.
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AbstractA series of experiments investigated perceived direction of motion and depth segregation in motion transparency displays consisting of two planes of dots moving in different directions. Direction and depth judgments were obtained from human observers viewing these "bi-directional" animation sequences with and without explicit stereoscopic depth information. We found that (1) misperception of motion direction ("direction repulsion") occurs when two spatially intermingled directions of motion are within 60 deg of each other; (2) direction repulsion is minimal at cardinal directions; (3) perception of two directions of motion always results in separate motion planes segregated in depth; and (4) stereoscopic depth information has no effect on the magnitude of direction repulsion, but it does disambiguate the depth relations between motion directions. These results are developed within the context of a two-stage model of motion transparency. On this model, motion directions are registered within units subject to inhibitory interactions that cause direction repulsion, with the outputs of these units pooled within units selective for direction and disparity.
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Kinzie, Jillian, i Lisa Wolf‐Wendel. "Announcing New Direction's New Direction". New Directions for Higher Education 2022, nr 197 (marzec 2022): 5–6. http://dx.doi.org/10.1002/he.20439.
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Gonglewski, Margaret, John Angell i Stayc DuBravac. "New Directions in Language Center Direction". IALLT Journal of Language Learning Technologies 37, nr 1 (15.04.2005): 47–50. http://dx.doi.org/10.17161/iallt.v37i1.8426.
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CAHILL, SPENCER E. "Some Rhetorical Directions of Funeral Direction". Work and Occupations 22, nr 2 (maj 1995): 115–36. http://dx.doi.org/10.1177/0730888495022002001.
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Ge, Ziwei, i Hongyan Liu. "Effects of Three-Directional Seismic Wave on Dynamic Response and Failure Behavior of High-Steep Rock Slide". Applied Sciences 12, nr 1 (21.12.2021): 20. http://dx.doi.org/10.3390/app12010020.
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The landslide triggered by earthquakes can cause severe infrastructure losses or even fatalities. The high-steep rock slide is the most common type of landslide in the earthquake area. In an earthquake, the ground moves randomly in all directions, two horizontal directions (East-West (EW) direction, North-South (NS) direction) and one vertical direction (Up-Down (UD) direction). Even though extensive studies have been carried out on the earthquake-triggered landslide, the effects of each single seismic wave and the three-directional seismic waves are not considered. This study aims to evaluate the effects of different types of the seismic waves on the dynamic response and failure behavior of the high-steep rock slide. To investigate the effects of each single seismic wave and three-directional seismic wave, this study presents a numerical model with four types of seismic waves, e.g., East-West (EW) direction, North-South (NS) direction, Up-Down (UD) direction, and three-directional wave (EW_NS_UD). The numerical results revealed that the types of the seismic waves have significantly different effects on the dynamic process, failure behavior, run-out distance, velocity, and deposition of the high-steep rock slide.
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Miyashita, Masanobu, Dae-Shik Kim i Shigeru Tanaka. "Cortical direction selectivity without directional experience". NeuroReport 8, nr 5 (marzec 1997): 1187–91. http://dx.doi.org/10.1097/00001756-199703240-00026.
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Zinberg, J. M. "Advance directive: do they provide direction?" JAMA: The Journal of the American Medical Association 263, nr 13 (4.04.1990): 1764–65. http://dx.doi.org/10.1001/jama.263.13.1764.
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Murray, Richard F., Yaniv Morgenstern i Laurence R. Harris. "How to combine direction cues optimally". Seeing and Perceiving 25 (2012): 138. http://dx.doi.org/10.1163/187847612x647702.
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Many perceptual tasks require estimating a direction in space. Often several directional cues are available, such visual and gravitational cues to the subjective vertical, or visual and auditory cues to the direction of an object. In work on the subjective vertical, researchers have developed a heuristic vector summation model that has no deep theoretical motivation, but that accounts well for the direction and reliability of observers’ direction estimates when multiple cues are available, and that can accommodate directional cues ranging over all possible directions (Mittelstaedt, 1983). In work on combining visual and auditory cues to direction, researchers have used statistically motivated cue combination models that were originally developed for linear quantities such as depth, not circular or spherical quantities such as direction, and hence work only over a limited range of cue directions (Alais and Burr, 2004). Here we present a new model of directional cue combination that combines the advantages of both previous approaches. We develop a statistical theory of cue combination based on the von Mises distribution, the analog on the circle of the normal distribution on the line. We show that this theory differs in important ways from the theory of linear cue combination, e.g., a combined direction estimate can be less certain than any of the individual cues that were used to calculate it. We also show that the vector summation model developed empirically by previous investigators is an excellent approximation to our theory, meaning that it is a nearly optimal way of combining directional cues.
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Jiang, Wanying, Xianzhi Yuan, Cong Yin i Kunlin Wei. "Visuomotor learning is dependent on direction-specific error saliency". Journal of Neurophysiology 120, nr 1 (1.07.2018): 162–70. http://dx.doi.org/10.1152/jn.00787.2017.
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People perceive better in cardinal directions compared with oblique ones. This directional effect, called oblique effect, has been documented in perception studies for a long time. However, typical motor studies do not differentiate learning in different directions. In this study we identify a significant directional effect in motor learning using visuomotor rotation paradigms. We find that adaptation to visual perturbations yields more savings when both initial learning and relearning are performed in cardinal directions than in oblique directions. We hypothesize that this directional effect arises from relatively higher error saliency in cardinal directions. Consistent with this hypothesis, we successfully increased savings in the oblique directions, which showed no saving effect before, by enhancing the error saliency with augmented visual feedback during learning. Our findings suggest that movement direction plays an important role in motor learning, especially when learning signals are direction specific. Our results also provide new insights about the role of motor errors in the formation and retrieval of motor memory and practical implications for promoting learning in motor rehabilitation and athletic training. NEW & NOTEWORTHY People perceive better when the stimulus is in cardinal directions than in oblique directions. Whether a similar directional effect exists in motor learning is unknown. Using a motor learning paradigm, we show that people relearn to compensate for a previously encountered perturbation faster when they move in cardinal directions than when they move in oblique directions. Further experimentation supports that this motor directional effect likely results from better sensory saliency of motor errors in cardinal directions.
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Gizzi, M. S., E. Katz, R. A. Schumer i J. A. Movshon. "Selectivity for orientation and direction of motion of single neurons in cat striate and extrastriate visual cortex". Journal of Neurophysiology 63, nr 6 (1.06.1990): 1529–43. http://dx.doi.org/10.1152/jn.1990.63.6.1529.
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1. We consider the consequences of the orientation selectivity shown by most cortical neurons for the nature of the signals they can convey about the direction of stimulus movement. On theoretical grounds we distinguish component direction selectivity, in which cells are selective for the direction of movement of oriented components of a complex stimulus, from pattern direction selectivity, or selectivity for the overall direction of movement of a pattern irrespective of the directions of its components. We employed a novel test using grating and plaid targets to distinguish these forms of direction selectivity. 2. We studied the responses of 280 cells from the striate cortex and 107 cells from the lateral suprasylvian cortex (LS) to single sinusoidal gratings to determine their orientation preference and directional selectivity. We tested 73 of these with sinusoidal plaids, composed of two sinusoidal gratings at different orientations, to study the organization of the directional mechanisms within the receptive field. 3. When tested with single gratings, the directional tuning of 277 oriented cells in area 17 had a mean half width of 20.6 degrees, a mode near 13 degrees, and a range of 3.8-58 degrees. Simple cells were slightly more narrowly tuned than complex cells. The selectivity of LS neurons for the direction of moving gratings is not markedly different from that of neurons in area 17. The mean direction half width was 20.7 degrees. 4. We evaluated the directional selectivity of these neurons by comparing responses to stimuli moved in the optimal direction with those elicited by a stimulus moving in the opposite direction. In area 17 about two-thirds of the neurons responded less than half as well to the non-preferred direction as to the preferred direction; two-fifths of the units responded less than one-fifth as well. Complex cells showed a somewhat greater tendency to directional bias than simple cells. LS neurons tended to have stronger directional asymmetries in their response to moving gratings: 83% of LS neurons showed a significant directional asymmetry. 5. Neurons in both areas responded independently to each component of the plaid. Thus cells giving single-lobed directional-tuning curves to gratings showed bilobed plaid tuning curves, with each lobe corresponding to movement in an effective direction by one of the two component gratings within the plaid. The two best directions for the plaids were those at which one or other single grating would have produced an optimal response when presented alone.(ABSTRACT TRUNCATED AT 400 WORDS)
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Layer, Kevin, Andrew L. Johnson, Robin C. Sickles i Gary D. Ferrier. "Direction selection in stochastic directional distance functions". European Journal of Operational Research 280, nr 1 (styczeń 2020): 351–64. http://dx.doi.org/10.1016/j.ejor.2019.06.046.
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CHEN, ZHIQIANG, JIPING NING i QUN HAN. "INFLUENCE OF PUMP DIRECTION IN ALL-OPTICAL GAIN-CLAMPED FIBER RAMAN AMPLIFIER". Modern Physics Letters B 21, nr 20 (30.08.2007): 1307–12. http://dx.doi.org/10.1142/s0217984907013596.
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The influence of pump direction in all-optical gain-clamped fiber Raman amplifier using the directional couplers in feedback loop is demonstrated. The isolator direction decided the lasing direction in feedback loop. The comparison of performance in two lasing directions for both schemes is shown. It is concluded that the forward pumping configuration with forward lasing has better gain clamping performance and noise performance.
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Han, Mianzhe, Yuki Todo i Zheng Tang. "Mechanism of Motion Direction Detection Based on Barlow’s Retina Inhibitory Scheme in Direction-Selective Ganglion Cells". Electronics 10, nr 14 (13.07.2021): 1663. http://dx.doi.org/10.3390/electronics10141663.
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Previous studies have reported that directionally selective ganglion cells respond strongly in their preferred direction, but are only weakly excited by stimuli moving in the opposite null direction. Various studies have attempted to elucidate the mechanisms underlying direction selectivity with cellular basis. However, these studies have not elucidated the mechanism underlying motion direction detection. In this study, we propose the mechanism based on Barlow’s inhibitory scheme for motion direction detection. We described the local motion-sensing direction-selective neurons. Next, this model was used to construct the two-dimensional multi-directional detection neurons which detect the local motion directions. The information of local motion directions was finally used to infer the global motion direction. To verify the validity of the proposed mechanism, we conducted a series of experiments involving a dataset with a number of images. The proposed mechanism exhibited good performance in all experiments with high detection accuracy. Furthermore, we compare the performance of our proposed system and traditional Convolution Neural Network (CNN) on motion direction prediction. It is found that the performance of our system is much better than that of CNN in terms of accuracy, calculation speed and cost.
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Pierson, Charon A. "New direction—Right direction". Journal of the American Association of Nurse Practitioners 26, nr 12 (grudzień 2014): 639. http://dx.doi.org/10.1002/2327-6924.12196.
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Dai, Xianzhi, Zhang Zhang, Wang Chen, Lijun Wang, Yong Wang i Min Zheng. "A 3D multi-directional and multimodal broadband vibration energy harvester using an L-shaped bending beam". Journal of Physics: Conference Series 2527, nr 1 (1.06.2023): 012076. http://dx.doi.org/10.1088/1742-6596/2527/1/012076.
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Abstract A three-dimensional (3D), multi-directional and multimodal broadband vibration energy harvester using L-shaped curved beams is proposed in this paper. The harvester is composed of an L-shaped cylindrical bending beam and a piezoelectric beam. The free ends of the L-shaped bending beam and the piezoelectric beam are respectively fixed with a magnet. These two beams are coupled by nonlinear magnetic force introduced by the two magnets. The results show that the prototype can collect 3D multi-directional broadband vibration energies and has three natural frequencies in 3D directions. Under 5 m/s2 acceleration, the prototype obtains 42.1V, 45.0V and 66.9V peak-peak voltages in the x-direction, y-direction and z-direction respectively, and the widest 3 DB bandwidths in this three directions reach up to 6.4Hz, 6.3Hz and 4.2Hz, respectively.
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Shaki, Samuel, Martin H. Fischer i Silke M. Göbel. "Direction counts: A comparative study of spatially directional counting biases in cultures with different reading directions". Journal of Experimental Child Psychology 112, nr 2 (czerwiec 2012): 275–81. http://dx.doi.org/10.1016/j.jecp.2011.12.005.
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Dounskaia, Natalia, Jacob A. Goble i Wanyue Wang. "The role of intrinsic factors in control of arm movement direction: implications from directional preferences". Journal of Neurophysiology 105, nr 3 (marzec 2011): 999–1010. http://dx.doi.org/10.1152/jn.00630.2010.
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The role of extrinsic and intrinsic factors in control of arm movement direction remains under debate. We addressed this question by investigating preferences in selection of movement direction and whether factors causing these preferences have extrinsic or intrinsic nature. An unconstrained free-stroke drawing task was used during which participants produced straight strokes on a horizontal table, choosing the direction and the beginning and end of each stroke arbitrarily. The variation of the initial arm postures across strokes provided a possibility to distinguish between the extrinsic and intrinsic origins of directional biases. Although participants were encouraged to produce strokes equally in all directions, each participant demonstrated preferences for some directions over the others. However, the preferred directions were not consistent across participants, suggesting no directional preferences in extrinsic space. Consistent biases toward certain directions were revealed in intrinsic space representing initial arm postures. Factors contributing to the revealed preferences were analyzed within the optimal control framework. The major bias was explained by a tendency predicted by the leading joint hypothesis (LJH) to minimize active interference with interaction torque generated by shoulder motion at the elbow. Some minor biases may represent movements of minimal inertial resistance or maximal kinematic manipulability. These results support a crucial role of intrinsic factors in control of the movement direction of the arm. Based on the LJH interpretation of the major bias, we hypothesize that the dominant tendency was to minimize neural effort for control of arm intersegmental dynamics. Possible organization of neural processes underlying optimal selection of movement direction is discussed.
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Fortier-Poisson, Pascal, Jean-Sébastien Langlais i Allan M. Smith. "Correlation of fingertip shear force direction with somatosensory cortical activity in monkey". Journal of Neurophysiology 115, nr 1 (1.01.2016): 100–111. http://dx.doi.org/10.1152/jn.00749.2014.
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To examine the activity of somatosensory cortex (S1) neurons to self-generated shear forces on the index and thumb, two monkeys were trained to grasp a stationary metal tab with a key grip and exert forces without the fingers slipping in one of four orthogonal directions for 1 s. A majority (∼85%) of slowly adapting and rapidly adapting (RA) S1 neurons had activity modulated with shear force direction. The cells were recorded mainly in areas 1 and 2 of the S1, although some area 3b neurons also responded to shear direction or magnitude. The preferred shear vectors were distributed in every direction, with tuning arcs varying from 50° to 170°. Some RA neurons sensitive to dynamic shear force direction also responded to static shear force but within a narrower range, suggesting that the direction of the shear force may influence the adaptation rate. Other neurons were modulated with shear forces in diametrically opposite directions. The directional sensitivity of S1 cortical neurons is consistent with recordings from cutaneous afferents showing that shear direction, even without slip, is a powerful stimulus to S1 neurons.
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del Álamo, Juan C., Gerard N. Norwich, Yi-shuan Julie Li, Juan C. Lasheras i Shu Chien. "Anisotropic rheology and directional mechanotransduction in vascular endothelial cells". Proceedings of the National Academy of Sciences 105, nr 40 (7.10.2008): 15411–16. http://dx.doi.org/10.1073/pnas.0804573105.
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Adherent cells remodel their cytoskeleton, including its directionality, in response to directional mechanical stimuli with consequent redistribution of intracellular forces and modulation of cell function. We analyzed the temporal and spatial changes in magnitude and directionality of the cytoplasmic creep compliance (Γ) in confluent cultures of bovine aortic endothelial cells subjected to continuous laminar flow shear stresses. We extended particle tracking microrheology to determine at each point in the cytoplasm the principal directions along which Γ is maximal and minimal. Under static condition, the cells have polygonal shapes without specific alignment. Although Γ of each cell exhibits directionality with varying principal directions, Γ averaged over the whole cell population is isotropic. After continuous laminar flow shear stresses, all cells gradually elongate and the directions of maximal and minimal Γ become, respectively, parallel and perpendicular to flow direction. This mechanical alignment is accompanied by a transition of the cytoplasm to be more fluid-like along the flow direction and more solid-like along the perpendicular direction; at the same time Γ increases at the downstream part of the cells. The resulting directional anisotropy and spatial inhomogeneity of cytoplasmic rheology may play an important role in mechanotransduction in adherent cells by providing a means to sense the direction of mechanical stimuli.
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Tolhurst, D. J., i A. F. Dean. "Evaluation of a linear model of directional selectivity in simple cells of the cat's striate cortex". Visual Neuroscience 6, nr 5 (maj 1991): 421–28. http://dx.doi.org/10.1017/s0952523800001280.
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AbstractWe have compared the responses of simple cells to laterally moving sinusoidal gratings and to stationary temporally-modulated gratings. From the amplitudes and temporal phases of the responses to stationary gratings of different spatial phases, it should be possible to predict the preferred direction of movement, the amplitudes of the responses to gratings moving in the preferred and nonpreferred directions and, thence, the degree of directional preference (Reid et al., 1987). The preferred direction can be predicted reliably. However, the magnitude of the directional preference cannot be predicted, since the measured amplitude of the response in the nonpreferred direction of movement is very much less than that predicted by a linear theory. Nonlinearities in the relationship between response amplitude and contrast may contribute to the failure of the predictions, but this contribution is small. We conclude that the magnitude of the directional preference seems to be determined predominantly by nonlinear suppression of the response in the nonpreferred direction of movement.
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Shuster, Malcolm D. "Effective direction measurements for spacecraft attitude: I. Equivalent directions". Journal of the Astronautical Sciences 55, nr 4 (grudzień 2007): 463–78. http://dx.doi.org/10.1007/bf03256536.
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Shuster, Malcolm D. "Effective direction measurements for spacecraft attitude: II. Predicted directions". Journal of the Astronautical Sciences 55, nr 4 (grudzień 2007): 479–92. http://dx.doi.org/10.1007/bf03256537.
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Smyrnis, Nikolaos, Asimakis Mantas i Ioannis Evdokimidis. "“Motor Oblique Effect”: Perceptual Direction Discrimination and Pointing to Memorized Visual Targets Share the Same Preference for Cardinal Orientations". Journal of Neurophysiology 97, nr 2 (luty 2007): 1068–77. http://dx.doi.org/10.1152/jn.00515.2006.
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In previous studies we observed a pattern of systematic directional errors when humans pointed to memorized visual target locations in two-dimensional (2-D) space. This directional error was also observed in the initial direction of slow movements toward visual targets or movements to kinesthetically defined targets in 2-D space. In this study we used a perceptual experiment where subjects decide whether an arrow points in the direction of a visual target in 2-D space and observed a systematic distortion in direction discrimination known as the “oblique effect.” More specifically, direction discrimination was better for cardinal directions than for oblique. We then used an equivalent measure of direction discrimination in a task where subjects pointed to memorized visual target locations and showed the presence of a motor oblique effect. We finally modeled the oblique effect in the perceptual and motor task using a quadratic function. The model successfully predicted the observed direction discrimination differences in both tasks and, furthermore, the parameter of the model that was related to the shape of the function was not different between the motor and the perceptual tasks. We conclude that a similarly distorted representation of target direction is present for memorized pointing movements and perceptual direction discrimination.
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Mason, A. J. S., O. J. Braddick, J. Wattam-Bell i J. Atkinson. "Directional motion asymmetry in infant VEPs — which direction?" Vision Research 41, nr 2 (styczeń 2001): 201–11. http://dx.doi.org/10.1016/s0042-6989(00)00241-8.
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Closs, Michael P. "Response to Coggins and Bricker". American Antiquity 53, nr 2 (kwiecień 1988): 402–11. http://dx.doi.org/10.2307/281030.
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Coggins and Bricker have accepted my phonetic reading of one version of the north glyph as xaman, "north." Nevertheless, they maintain that the traditional north-south axis in Maya directional symbolism pertains more properly to a zenith-nadir axis. In my response I argue against that position and provide evidence that the cardinal directions played a fundamental role in mesoamerican cosmology. These directions are interpreted in a relatively loose sense as sectors on the horizon and not as cardinal points. In particular, the north direction is viewed as a sector on the horizon centered at a point which is approximately 14 degrees east of north. The evidence includes three independent proofs of the cardinal direction hypothesis. These proofs specifically implicate the four Maya directional glyphs as symbols of the four cardinal directions.
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Gonzalo-Skok, Oliver, Thomas Dos'Santos i Chris Bishop. "Assessing Limb Dominance and Interlimb Asymmetries Over Multiple Angles During Change of Direction Speed Tests in Basketball Players". Journal of Strength and Conditioning Research 37, nr 12 (grudzień 2023): 2423–30. http://dx.doi.org/10.1519/jsc.0000000000004558.
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Abstract Gonzalo-Skok, O, Dos' Santos, T, and Bishop, C. Assessing limb dominance and interlimb asymmetries over multiple angles during change of direction speed tests in basketball players. J Strength Cond Res 37(12): 2423–2430, 2023—The aims of this study were to establish whether directional dominance is displayed during change of direction (COD) tasks across various angles, to determine the angle-variation data for the asymmetry magnitude and direction, and to analyze the relationships in COD performance (completion time and COD deficit) across tasks. Twenty-four young (U-16 to U-20), highly trained male basketball players performed a 10-m linear sprint test and four 10-m COD tests (45°, 90°, 135°, and 180°) in left and right directions. Change of direction performance was determined via total times and COD deficit, and asymmetry comparisons were made between faster and slower directions and dominant leg (DL) (i.e., first step leg in lay-up) and nondominant leg (NDL). No significant differences (p > 0.05) were found between DL and NDL for any task excluding 45° COD (p < 0.05, effect size [ES] = 0.44–0.78), but significant differences were established between faster and slower sides for all angles (p < 0.05, ES = 0.70–1.28). Levels of the agreement in directional dominance during COD tasks were generally poor to slight (k = −0.14 to 0.14), excluding a fair agreement between COD45 and COD90 (k = 0.34). Correlations between COD total times and COD deficits between angles were moderate to very large (r = 0.32 to 0.81) and moderate to large (r = −0.30 to 0.55), respectively. Players displayed superior COD performance in a particular direction across various angles. This directional dominance is not necessarily consistent between angles, thus highlighting the angle-dependent nature of COD performance. Consequently, practitioners should investigate multiple angles and directions to create a COD angle profile for their athletes.
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Li, Lin, Yanxia Li, Chang-hong Wu i Hao Fu. "Upper Limb Proprioceptive Acuity Assessment Based on Three-Dimensional Position Measurement Systems". Motor Control 24, nr 4 (1.10.2020): 605–23. http://dx.doi.org/10.1123/mc.2020-0009.
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The aim of the current work was to verify three-dimensional directional effects on the reproduction error precision of the human upper limb position. Thirty male subjects without history of upper limb pathology were recruited from Renmin University of China. A three-dimensional position reproduction task in six directions (up, down, left, right, far, and near) was performed by each subject. The results suggested that the proprioceptive sense of upper limb position depends on the direction, with smaller absolute errors in Directions 4 (right) and 5 (far) than in Directions 1 (up), 2 (down), 3 (left), and 6 (near). Proprioception near the end of the elbow joint range of motion may be more reliable and sensitive. Subjects reproduced fewer ranges in the horizontal plane (Directions 3, 5, and 6) and they overshot the target position along the z-axis (vertical direction) except for Direction 6. Overestimations of position in the z-axis may be caused by overestimations of force.
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Pettersson, Heidi, Kimmo K. Kahma i Laura Tuomi. "Wave Directions in a Narrow Bay". Journal of Physical Oceanography 40, nr 1 (1.01.2010): 155–69. http://dx.doi.org/10.1175/2009jpo4220.1.
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Abstract In slanting fetch conditions the direction of actively growing waves is strongly controlled by the fetch geometry. The effect was found to be pronounced in the long and narrow Gulf of Finland in the Baltic Sea, where it significantly modifies the directional wave climate. Three models with different assumptions on the directional coupling between the wave components were used to analyze the physics responsible for the directional behavior of the waves in the gulf. The directionally decoupled model produced the direction at the spectral peak correctly when the slanting fetch geometry was narrow but gave a weaker steering than observed when the fetch geometry was broader. The method of Donelan estimated well the direction at the spectral peak in well-defined slanting fetch conditions, but overestimated the longer fetch components during wave growth from a more complex shoreline. Neither the decoupled nor the Donelan model reproduced the observed shifting of direction with the frequency. The performance of the third-generation spectral wave model (WAM) in estimating the wave directions was strongly dependent on the grid resolution of the model. The dominant wave directions were estimated satisfactorily when the grid-step size was dropped to 5 km in the gulf, which is 70 km in its narrowest part. A mechanism based on the weakly nonlinear interactions is proposed to explain the strong steering effect in slanting fetch conditions.
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Lin, L. D., G. M. Murray i B. J. Sessle. "Functional properties of single neurons in the primate face primary somatosensory cortex. II. Relations with different directions of trained tongue protrusion". Journal of Neurophysiology 71, nr 6 (1.06.1994): 2391–400. http://dx.doi.org/10.1152/jn.1994.71.6.2391.
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1. In previous papers we have presented evidence suggesting an important role for the face primary somatosensory cortex (SI) in the fine control of tongue movements. These findings, plus our earlier evidence that many neurons in face motor cortex (MI) may exhibit firing rates related to the direction of tongue protrusion, led us to test the hypothesis that variations in the direction of a tongue-protrusion movement would be associated with variations in the activity of different face SI neurons. 2. Two monkeys were trained to perform a tongue-protrusion task in each of three directions: the task transducer was positioned at 0 degrees, 30 degrees to the left, or 30 degrees to the right from the midsagittal plane. The latter two positions were termed asymmetrical tongue-protrusion task positions. Single-neuron activity was recorded from face SI during trials of the tongue-protrusion task at each of two or three of the above positions. In addition, the mechanoreceptive field (RF) was delineated for each neuron. 3. Directional relations were found in 25 (58%) of the 43 neurons studied; this included 20 neurons showing a significant direction-by-time interaction in firing rate, i.e., the change of firing rate from the pretrial period to the task period was significantly different between different directions, and 5 showing no direction-by-time interaction but a significant difference in firing rate between different directions of the tongue-protrusion task. 4. Of the 43 neurons investigated, 21 and 20 had a RF on the tongue and lips, respectively (“tongue RF” and “lip RF” neurons), and the remaining 2 received mechanosensitive afferent inputs from other orofacial regions. There was no significant difference in the incidence of directional sensitivity between the neurons with a tongue RF and those with a lip RF (12/21 and 11/20, respectively). 5. Eight of the 25 “directional” neurons were located in area 3b and 17 in area 1. There was no significant difference in the proportion of directional neurons between areas 3b and 1. 6. The increase in discharge frequency at the preferred direction was, on the average for the 25 directional neurons, 39% over the mean discharge frequency observed during the task period for all directions of the tongue-protrusion task. Eight directional neurons showed a significant increase in firing rate during the tongue-protrusion task up to 130 ms before the onset of genioglossus electromyographic activity.(ABSTRACT TRUNCATED AT 400 WORDS)
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Wu, Wei Xia. "The Directed Transport of Elastically Coupled Brownian Motors in a Two-Dimensional Potential". Applied Mechanics and Materials 668-669 (październik 2014): 647–50. http://dx.doi.org/10.4028/www.scientific.net/amm.668-669.647.
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A model of directed transport of elastically coupled Brownian motors in a two-dimensional potential is established, in which one AC drive and a noise are acted on the non-ratchet potential direction but none is acted on the ratchet potential direction. Through numerical simulation, the position and the velocity of the coupled Brownian motors in two directions versus time are analyzed in different cases, which include that the AC drive and the noise are all moderate in the non-ratchet potential direction, no AC drive or no noise. The results show that at appropriate AC drive or the noise, there is a directional flow in the ratchet potential direction none acted.
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Rudolph, Christina, Britta Bienen i Jürgen Grabe. "Effect of variation of the loading direction on the displacement accumulation of large-diameter piles under cyclic lateral loading in sand". Canadian Geotechnical Journal 51, nr 10 (październik 2014): 1196–206. http://dx.doi.org/10.1139/cgj-2013-0438.
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Foundation piles supporting offshore structures experience cyclic lateral loading arising from waves and wind, which are not typically uni-directional over the lifetime of the structure. This paper presents results from centrifuge experiments in sand, representing a large diameter prototype tested at stress levels similar to the field subjected to cyclic lateral loading from varying directions. The results demonstrate increased deformation accumulation due to the changing loading direction, compared to the uni-directional case. Displacement accumulation is not limited to the main loading direction but includes transverse movement as well. Similar trends were observed in small-scale 1g modelling that allowed a larger number of load cycles to be applied. The centrifuge test results provide confidence of the applicability of the findings to the prototype. Current methods that neglect the effect of variation of the loading direction will provide predictions of displacement accumulation of piles that are un-conservative. Therefore, a simple approach is proposed here to estimate the augmentation of displacement accumulation due to variation in loading direction compared to the uni-directional case.
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Skottun, Bernt C., Jun Zhang i David H. Grosof. "On the directional selectivity of cells in the visual cortex to drifting dot patterns". Visual Neuroscience 11, nr 5 (wrzesień 1994): 885–97. http://dx.doi.org/10.1017/s0952523800003849.
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AbstractIt is well established that cortical neurons frequently show different preferred drift directions for random dots and gratings. Dot stimuli often produce two preferred directions which are arranged symmetrically on either side of the preferred directions for gratings. Based on their filter properties in three-dimensional (3-D) Fourier space and on the 3-D power spectra of drifting dot patterns, we estimated the optimal direction to drifting dots for ten neurons in the striate cortex of five adult cats. These estimates frequently gave two optimal directions, one on either side of the optimal direction to gratings. The angle between the two estimated peaks increases with drift speed. Predicted and actual angles were in reasonably good agreement. We conclude, therefore, that the directional selectivity of cortical neurons to drifting random dot patterns can be understood from linear filtering properties. For this reason, the directional tuning to drifting dot patterns seems to reflect the same mechanisms that mediate the responses to sinusoidal gratings and do not require a separate directional mechanism.
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Smith, Randall D., Norberto M. Grzywacz i Lyle J. Borg-Graham. "Is the input to a GABAergic synapse the sole asymmetry in turtle's retinal directional selectivity?" Visual Neuroscience 13, nr 3 (maj 1996): 423–39. http://dx.doi.org/10.1017/s0952523800008105.
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AbstractWe examined the effects of picrotoxin and pentylenetetrazol (PTZ) on the responses to motions of ON-OFF directionally selective (DS) ganglion cells of the turtle's retina. These drugs are antagonists of the inhibitory neurotransmitter GABA. For continuous motions, picrotoxin markedly reduced the overall directionality of the cells. In 21% of the cells, directional selectivity was lost regardless of speed and contrast. However, other cells maintained their preferred direction despite saturating concentrations of picrotoxin. And in most cells, loss, maintenance, or even reversal of preferred and null directions could occur as speed and contrast were modulated. In 50% of the cells, reversal of preferred and null directions occurred at some condition of visual stimuli. However, picrotoxin did not tend to alter the preferred-null axis for directional selectivity. For apparent motions, picrotoxin made motion facilitation, which normally occurs exclusively in preferred-direction responses, to become erratic and often occur during null-direction motions. Finally, PTZ had effects similar to picrotoxin but with less potency. The results in this paper indicated that models of directional selectivity based solely on a GABAergic implementation of Barlow and Levick's asymmetric-inhibition model do not apply to the turtle retina. Alternative models may comprise multiple directional mechanisms and/or a symmetric inhibitory one, but not asymmetric facilitation.
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Grigg, Peter, i Daniel R. Robichaud. "Rat Cutaneous RA Afferents Activated by Two-Dimensional Skin Stretch". Journal of Neurophysiology 92, nr 1 (lipiec 2004): 484–91. http://dx.doi.org/10.1152/jn.01011.2003.
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Skin develops biaxial stresses and strains when stretched. Rapidly adapting cutaneous mechanoreceptor neurons are known to be stretch sensitive, yet in the past, they have been studied using stretch stimuli applied along only a single direction. In this study, cutaneous rapidly adapting mechanoreceptors were studied in preparations of isolated skin in which the skin was stretched dynamically using biaxial stretch stimuli and in which loads and displacements were measured along two directions. Stretch stimuli followed a pseudo-Gaussian waveform and were applied along either one or two directions simultaneously. Associations between spikes and mechanical variables were determined using multiple logistic regression. When the skin was actuated along a single direction, holding the orthogonal axis fixed, spike responses were strongly associated with mechanical variables along the actuated direction. The variables were stress and its rate of change, the rate of change of strain, and the product of stress and its rate of change, which is proportional to strain energy density. When the skin was stretched along a single direction, spikes were very poorly associated with stress variables measured along the direction orthogonal to the stretch. Afferents showed weak directional selectivity: they were slightly more responsive to the variable stress along the circumferential direction of the hindlimb. When the skin was stretched biaxially (i.e., along both directions simultaneously) with identical pseudo-Gaussian noise stimuli, neuronal responses were associated with the same variables as above, but the associations were weaker.
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Cliet, C., i M. Dubesset. "Three‐component recordings: Interest for land seismic source study". GEOPHYSICS 52, nr 8 (sierpień 1987): 1048–59. http://dx.doi.org/10.1190/1.1442370.
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Three‐component recordings provide access to the particle trajectory due to seismic events. This three‐dimensional picture shows successions of complex phenomena. Nevertheless, this trajectory has predominant directions of polarization. A method of spatial directional filtering is described to calculate the polarization direction of parts of the trajectory. The application of this method provides means to reject trajectory parts for which the angular gap between their polarization axis and a reference direction, for example X, Y, or Z, is greater than a given threshold angle. Real data are submitted to this method, leading to a color‐coded display showing the direction of polarization of each wave train. The same noise spread, used in conjunction with two different seismic sources, was recorded with triphone groups. The two sources were an SH‐wave vibrator and Marthor®. Using spatial directional filterings with threshold angles varying from 0 to 90 degrees, the corresponding quantities of energy emitted in each principal direction X, Y, and Z were evaluated. A set of diagrams was plotted for comparing the behavior of both sources and to calculate the part of the received energies along X, Y, and Z directions as a function of (1) the emitted energies, and (2) the local propagation effects. ® SH‐wave weight‐drop source, IFP trademark.
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Imig, Thomas J., Pierre Poirier, W. Andrew Irons i Frank K. Samson. "Monaural Spectral Contrast Mechanism for Neural Sensitivity to Sound Direction in the Medial Geniculate Body of the Cat". Journal of Neurophysiology 78, nr 5 (1.11.1997): 2754–71. http://dx.doi.org/10.1152/jn.1997.78.5.2754.
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Imig, Thomas J., Pierre Poirier, W. Andrew Irons, and Frank K. Samson. Monaural spectral contrast mechanism for neural sensitivity to sound direction in the medial geniculate body of the cat. J. Neurophysiol. 78: 2754–2771, 1997. Central auditory neurons vary in sound direction sensitivity. Insensitive cells discharge well to all sound source directions, whereas sensitive cells discharge well to certain directions and poorly to others. High-frequency neurons in the latter group are differentially sensitive to binaural and monaural directional cues present in broadband noise (BBN). Binaural directional (BD) cells require binaural stimulation for directional sensitivity; monaural directional (MD) cells are sensitive to the direction of monaural stimuli. A model of MD sensitivity was tested using single-unit responses. The model assumes that MD cells derive directional sensitivity from pinna-derived spectral cues (head related transfer function, HRTF). This assumption was supported by the similarity of effects that pinna orientation produces on locations of HRTF patterns and on locations of MD cell azimuth function peaks and nulls. According to the model, MD neurons derive directional sensitivity by use of excitatory/inhibitory antagonism to compare sound pressure in excitatory and inhibitory frequency domains, and a variety of observations are consistent with this idea. 1) Frequency response areas of MD cells consist of excitatory and inhibitory domains. MD cells exhibited a higher proportion of multiple excitatory domains and narrower excitatory frequency domains than BD cells, features that may reflect specialization for spectral-dependent directional sensitivity. 2) MD sensitivity requires sound pressure in excitatory and inhibitory frequency domains. Directional sensitivity was evaluated using stimuli with frequency components confined exclusively to excitatory domains (E-only stimuli) or distributed in both excitatory and inhibitory domains (E/I stimuli). Each of 13 MD cells that were tested exhibited higher directional sensitivity to E/I than to E-only stimuli; most MD cells exhibited relatively low directional sensitivity when frequency components were confined exclusively to excitatory domains. 3) MD sensitivity derives from excitatory/inhibitory antagonism (spectral inhibition). Comparison of responses to best frequency and E/I stimuli provided strong support for spectral inhibition. Although spectral facilitation conceivably could contribute to directional sensitivity with direction-dependent increases in response, the results did not show this to be a significant factor. 4) Direction-dependent decreases in responsiveness to BBN reflect increased sound pressure in inhibitory relative to excitatory frequency domains. This idea was tested using the strength of two-tone inhibition, which is a function of stimulus levels in inhibitory relative to excitatory frequency domains. The finding that two-tone inhibition was stronger at directions where BBN responses were minimal than at directions where they were maximal supports the model.
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Han, Minglei, Xu Yang i Shimin Guo. "Research on the Directional Adaptability of a Self-Adaptive Energy Harvester". Sensors 23, nr 11 (26.05.2023): 5106. http://dx.doi.org/10.3390/s23115106.
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With the continuous development of wireless sensor networks (WSNs), multi-directional energy harvesting technology has received widespread attention from scholars. In order to evaluate the performance of multi-directional energy harvesters, this paper uses a directional self-adaptive piezoelectric energy harvester (DSPEH) as an example, defines the direction of the excitation in three-dimensional space, and studies the influence of excitations on the key parameters of the DSPEH. The rolling angle and pitch angle are used to define complex excitations in three-dimensional space, and the dynamic response of the excitation changes in a single direction and multiple directions is discussed. It is noteworthy that this work presents the concept of “Energy Harvesting Workspace” to describe the working ability of a multi-directional energy harvesting system. The workspace is expressed by the excitation angle and voltage amplitude, and energy harvesting performance is evaluated by the volume-wrapping method and area-covering method. The DSPEH exhibits good directional adaptability in two-dimensional space (rolling direction); in particular, when the mass eccentricity coefficient is r = 0 mm, 100% of the workspace in two-dimensional space is obtained. The total workspace in three-dimensional space depends entirely on the energy output in the pitch direction.
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Ding, Chenxi, Hong Su, Haitao Yang i Chenglong Xiao. "Fracture and Damage of Slit Charge Blasting in the Layered Rock Mass". Applied Sciences 14, nr 13 (4.07.2024): 5840. http://dx.doi.org/10.3390/app14135840.
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Directional fracture blasting technology of the slit charge has broad application prospects in the drilling and blasting construction of the layered rock mass. In this paper, the method of model experiment and numerical simulation is used to preliminarily explore the fracture damage characteristics of slit charge blasting in the layered rock mass. The results show that the blasting effect of the slit charge in the layered rock mass is significantly different from that of the unlayered rock mass, and the pressure relief of the blasting gas at the layer is the main factor affecting the blasting effect. The length of directional cracks in the slit direction is significantly larger than that in other directions, and the directional fracture effect of the slit charge in the layered rock mass can still be played well. However, both the directional crack length and the damage range of rock mass in the slit direction gradually decrease along the detonation direction. In addition, the damage value of a single-layer rock mass also decreases gradually along the detonation direction. In engineering practice, the directional fracture effect of the layered rock mass can be improved by detonating at both ends of the slit charge at the same time.
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Lyu, Anqi, Larry Abel i Allen M. Y. Cheong. "Effect of habitual reading direction on saccadic eye movements: A pilot study". PLOS ONE 18, nr 6 (2.06.2023): e0286801. http://dx.doi.org/10.1371/journal.pone.0286801.
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Cognitive processes can influence the characteristics of saccadic eye movements. Reading habits, including habitual reading direction, also affect cognitive and visuospatial processes, favouring attention to the side where reading begins. Few studies have investigated the effect of habitual reading direction on saccade directionality of low-cognitive-demand stimuli (such as dots). The current study examined horizontal prosaccade, antisaccade, and self-paced saccade in subjects with two primary habitual reading directions. We hypothesised that saccades responding to the stimuli in subject’s habitual reading direction would show a longer prosaccade latency and lower antisaccade error rate (errors being a reflexive glance to a sudden-appearing target, rather than a saccade away from it). Sixteen young Chinese participants with primary habitual reading direction from left to right and sixteen young Arabic and Persian participants with primary habitual reading direction from right to left were recruited. All subjects spoke/read English as their second language. Subjects needed to look towards a 5°/10° target in the prosaccade task or look towards the mirror image location of the target in the antisaccade task and look between two 10° targets in the self-paced saccade task. Only Arabic and Persian participants showed a shorter and directional prosaccade latency towards 5° stimuli against their habitual reading direction. No significant effect of reading direction on antisaccade latency towards the correct directions was found. Chinese readers were found to generate significantly shorter prosaccade latencies and higher antisaccade directional errors compared with Arabic and Persian readers for stimuli appearing at their habitual reading side. The present pilot study provides insights into the effect of reading habits on saccadic eye movements of low-cognitive-demand stimuli and offers a platform for future studies to investigate the relationship between reading habits and eye movement behaviours.
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Zeng, Qilin, Wenwei Chen, Hua Du, Wentao Zhang, Xianming Xiong, Zhengyi Zhao, Fangjun Zhou, Xin Guo i Le Xu. "Real-Time Direction Judgment System for Dual-Frequency Laser Interferometer". Sensors 24, nr 7 (22.03.2024): 2030. http://dx.doi.org/10.3390/s24072030.
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Current real-time direction judgment systems are inaccurate and insensitive, as well as limited by the sampling rate of analog-to-digital converters. To address this problem, we propose a dynamic real-time direction judgment system based on an integral dual-frequency laser interferometer and field-programmable gate array technology. The optoelectronic signals resulting from the introduction of a phase subdivision method based on the amplitude resolution of the laser interferometer when measuring displacement are analyzed. The proposed system integrates the optoelectronic signals to increase the accuracy of its direction judgments and ensures these direction judgments are made in real time by dynamically controlling the integration time. Several experiments were conducted to verify the performance of the proposed system. The results show that, compared with current real-time direction judgment systems, the proposed system makes accurate judgements during low-speed motions and can update directions within 0.125 cycles of the phase difference change at different speeds. Moreover, a sweep frequency experiment confirmed the system’s ability to effectively judge dynamic directions. The proposed system is capable of accurate and real-time directional judgment during low-speed movements of a table in motion.
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Wu, Zhao-Jun. "T-Direction and Borel Direction of Algebroid Functions of Finite and Positive Order". gmj 16, nr 3 (wrzesień 2009): 583–96. http://dx.doi.org/10.1515/gmj.2009.583.
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Abstract In the present paper, the connection between a T-direction and Borel direction of algebroid functions is investigated. Two algebroid functions (not meromorphic) are obtained to prove that T-directions and Borel directions are two different classes of singular directions for algebroid functions. The existence of an algebroid function (not meromorphic) with a given Borel direction is proved.
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Takikawa, Yoriko, Reiko Kawagoe i Okihide Hikosaka. "Reward-Dependent Spatial Selectivity of Anticipatory Activity in Monkey Caudate Neurons". Journal of Neurophysiology 87, nr 1 (1.01.2002): 508–15. http://dx.doi.org/10.1152/jn.00288.2001.
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Many neurons show anticipatory activity in learned tasks. This phenomenon appears to reflect the brain's ability to predict future events. However, what actually is predicted is unknown. Using a memory-guided saccade task, in which only one out of four directions was rewarded in each block of trials, we found that a group of neurons in the monkey caudate nucleus (CD) showed activity before presentation of an instruction cue stimulus. Among 329 CD neurons that were related to memory-guided saccade tasks, 156 showed the precue activity and 91 of them were examined fully. Remarkably, the magnitude of the precue activity varied across the four blocks of the one-direction-rewarded (1DR) condition, depending on which direction was rewarded. A majority of neurons with precue activity (83/91, 91%) showed significant directional preference. The best and worst directions were usually in the contralateral and ipsilateral directions, respectively. Within a block, the precue activity increased rapidly for the best direction in 1DR and decreased gradually for the worst direction in 1DR and all-directions-rewarded (ADR) condition. The precue activity was weak in ADR. The precue activity did not reflect the likelihood of a particular cue stimulus, because the probability of the cue appearing in each direction was the same regardless of the rewarded direction. These results suggest that each CD neuron indicates a particular position–reward association prospectively, usually with contralateral preference. Assuming that the CD neurons have access to saccadic motor outputs, the precue activity would create a motivational bias toward the contralateral space, even before an instruction is given by the cue stimulus.
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Wu, Gengkun, Chuanxi Liu i Yongquan Liang. "Comparative Study on Numerical Calculation of 2-D Random Sea Surface Based on Fractal Method and Monte Carlo Method". Water 12, nr 7 (30.06.2020): 1871. http://dx.doi.org/10.3390/w12071871.
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Based on fifty one groups of data on direction distribution measured from buoy sites, several important spectrum parameters including distribution characteristics of the measured data’s spectrum, the Wen’s direction spectrum and the Donelan function are analyzed from the perspectives of standard deviation of directional distribution function and statistical results. Then, a numeric calculation model based on the Monte Carlo method is proposed in this work. At the same time—based on Weierstrass self-affine fractal function—numeric simulation of random sea surface is conducted by modifying the bilateral power law. The analysis of the numeric calculation results under different wind directions, speeds and fetches proves that both methods can be adopted for different water directional distributions and target spectrum models. In addition, this study compares the characteristic wave within different distribution frequency domains in the main wave direction and in its orthogonal direction. It is proved that the fractal method cannot fully reflect the anisotropy of gravity wave and tension wave in the superposition direction, however, it can maintain the similarity of overall energy part with the rough length of the waves. Moreover, there are still limitations of the fractal method in the numeric modeling of undeveloped sea surface.
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Starbuck, Kathryn. "Direction". Antioch Review 63, nr 3 (2005): 532. http://dx.doi.org/10.2307/4614855.
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Gregory, Alex. "Changing Direction on Direction of Fit". Ethical Theory and Moral Practice 15, nr 5 (29.03.2012): 603–14. http://dx.doi.org/10.1007/s10677-012-9355-6.
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Miller, Jeffrey D. "Direction-direction correlations of oriented polymers". Journal of Statistical Physics 63, nr 1-2 (kwiecień 1991): 89–113. http://dx.doi.org/10.1007/bf01026594.
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Abdullah, Amnah, i Robert Francis Peters. "Malaysia’s Post-PISA2012 Direction". International Journal of Culture and History (EJournal) 1, nr 1 (2015): 15–20. http://dx.doi.org/10.18178/ijch.2015.1.1.003.
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Wang, Jiangtao, Longlong Qian, Songwei Wang, Li Shi i Zhizhong Wang. "Directional Preference in Avian Midbrain Saliency Computing Nucleus Reflects a Well-Designed Receptive Field Structure". Animals 12, nr 9 (28.04.2022): 1143. http://dx.doi.org/10.3390/ani12091143.
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Neurons responding sensitively to motions in several rather than all directions have been identified in many sensory systems. Although this directional preference has been demonstrated by previous studies to exist in the isthmi pars magnocellularis (Imc) of pigeon (Columba livia), which plays a key role in the midbrain saliency computing network, the dynamic response characteristics and the physiological basis underlying this phenomenon are unclear. Herein, dots moving in 16 directions and a biologically plausible computational model were used. We found that pigeon Imc’s significant responses for objects moving in preferred directions benefit the long response duration and high instantaneous firing rate. Furthermore, the receptive field structures predicted by a computational model, which captures the actual directional tuning curves, agree with the real data collected from population Imc units. These results suggested that directional preference in Imc may be internally prebuilt by elongating the vertical axis of the receptive field, making predators attack from the dorsal-ventral direction and conspecifics flying away in the ventral-dorsal direction, more salient for avians, which is of great ecological and physiological significance for survival.
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Helbig, Klaus. "Longitudinal directions in media of arbitrary anisotropy". GEOPHYSICS 58, nr 5 (maj 1993): 680–91. http://dx.doi.org/10.1190/1.1443452.
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A longitudinal direction is one in which three pure modes can propagate. It is known that every medium has at least three longitudinal directions. Every axis of symmetry is such a “bound” longitudinal direction, but in most media there are additional “free” longitudinal directions which do not coincide with symmetry directions. In particular, there are longitudinal directions even in triclinic media that possess no symmetry except the point symmetry. The maximum number of distinct longitudinal directions is thirteen. In a longitudinal direction the wave propagation is particularly simple: for the longitudinal mode, wave normal, displacement direction, and ray direction are identical, while for the two transverse modes the deviation of the ray direction from that of the wave normal depends on the type of longitudinal direction and the relative magnitude of a few stiffnesses expressed in a coordinate system aligned with the longitudinal direction. Similarly, the polarization pattern in the vicinity of a longitudinal direction depends strongly on the type of the longitudinal direction and on the relative magnitude of some off‐diagonal stiffnesses. Since the polarization pattern can be observed in suitable vertical seismic profiling (VSP) surveys, it might be inverted to obtain information on elastic parameters that is difficult to obtain by other means. For orthorhombic symmetry, there are always the three bound longitudinal directions coinciding with the axes. In each plane of symmetry a pair of free longitudinal directions can exist, and there can be four symmetrically disposed free longitudinal directions outside the planes of symmetry. Existence and direction of these free directions follows from simple expressions in the elastic stiffnesses.