Influence of spatial structure migration of overlying strata on water storage of underground reservoir in coal mine.

Underground reservoir technology for coal mines can realize the coordinated development of coal exploitation and water protection in water-shortage-prone areas. The seepage effect of the floor seriously affects the safety of underground reservoirs under the action of mining damage and seepage pressure. Focusing on the problem of floor seepage in underground reservoirs, a spatial mechanical model of underground reservoirs was established. The main factors affecting the seepage of the surrounding rock were studied. The seepage pressure law in different stages of spatial structure evolution of overlying strata was explored. The results showed that pressure change was the main factor affecting the stability of a reservoir's surrounding rock. The pore space between the broken and fractured rock in the water-flowing fractured zone was the main water storage space, which was directly related to the development of a breaking arch. According to the spatial structure evolution process of the overlying strata, the water storage state of an underground reservoir was divided into two stages and three situations. The seepage pressure was mainly affected by the water pressure and the overlying strata weight. The water pressure was affected by the reservoir head height, and the overlying strata weight was mainly affected by the overlying strata thickness.

A Multistimuli Responsive, Flexible Luminescent Framework and Its Applicability in Anticounterfeiting.

A linear distyrylanthracene derivative (DDATAn) with two diaminotriazine (DAT) groups acting as the hydrogen bond (H-bond) units was designed and synthesized in order to construct flexible organic porous crystals. H-bonds between the DAT moieties helped the molecules to construct a double interpenetrated two-dimensional layer, and the stacking between layers provided a H-bonded organic framework (X-HOF-3) with one-dimensional solvent channels. When X-HOF-3 was placed in contact with methanol, the fluorescent colors of the HOF exhibited an apparent bathochromic shift. More interestingly, the methanol-activated HOF was able to rapidly adsorb water from the air, which was accompanied by a change in fluorescent color from yellow to red. Under heating, water was released from the HOF and the fluorescent color returned to yellow. Water molecules in the pores were also able to be released after an applied mechanical force disrupted the ordered structure of the HOF. Based on these stimuli-responsive properties, these HOFs can be used as advanced functional materials in anticounterfeiting applications.

Tunable Fluorescence in Two-Component Hydrogen-Bonded Organic Frameworks Based on Energy Transfer.

A dumbbell-shaped compound (TPAD) with four 2,4-diaminotriazine moieties as H-bond units and a benzene ring as a bridge group was found to form hydrogen-bonded organic frameworks (HOFs) with strong cyan fluorescence. An energy acceptor, 6,6',6″,6‴-(((benzo[c][1,2,5]thiadiazole-4,7-diylbis-(4,1-phenylene))bis(azanetriyl))tetrakis(benzene-4,1-diyl))tetrakis(1,3,5-triazine-2,4-diamine) (BTAD), with the same molecular skeleton as TPAD and a longer emission wavelength could homogeneously distribute within the framework of TPAD through occupying the locations of TPAD. As a result, two-component HOFs (TC-HOFs) were formed. The nonradiative energy transfer from TPAD as the donor to BTAD as the acceptor happens within frameworks owing to the efficient spectral overlap between the emission of TPAD and the absorption of BTAD. Moreover, the emission wavelengths and colors of TC-HOFs could be easily and continuously modulated by the content of the acceptor. The fluorescence color changed from cyan to orange when the content of BTAD gradually increased. This finding affirms that TC-HOFs with continuously adjustable composition can be constructed from two molecules with the same molecular skeleton, and highly efficient nonradiative energy transfer may happen in porous TC-HOFs. To the best of our knowledge, these TC-HOFs are the first example of TC-HOFs involved in energy transfer.

Guest-Regulated Luminescence and Force-Stimuli Response of a Hydrogen-Bonded Organic Framework.

Guest molecules may endow porous materials with new or enhanced properties as well as functions. Here, a porous hydrogen-bonded organic framework (HOF) constructed from a three-armed triphenylamine derivative is used to investigate how guests regulate photoluminescence and trigger force-stimuli response. It was found that guest solvents in pores might regulate HOF's luminescence. Interestingly, acetic acid as a guest endowed HOF materials with longer emission wavelengths and triggered the responses to mechanical force stimuli. Under shear force, an obvious blueshift in emission spectra was observed because of the loss of free guests and the conversion of π-stacking model. Further blue-shifted emission appeared while the bound guests were completely removed by heating. Mechanofluorochromic HOF materials could be regenerated through recrystallization and adsorbing guest. Conversely, HOFs with other guests and activated HOFs only resulted in a slight change in their fluorescence behaviors after force stimuli.

Tests of Hering- and Helmholtz-type models for saccade-vergence interactions by comparing visually guided and memory-guided movements.

We compared the dynamic properties of memory-guided and visually-guided saccade-vergence movements. For memory-guided responses, convergence components were slowed proportionally more than corresponding saccadic components, compared with visually-guided responses. This result is consistent with independent saccadic and vergence systems, and supports a Hering-type model for saccade-vergence interactions.

Evaluating large saccades in patients with brain-stem or cerebellar disorders.

Clinicians conventionally test saccades at the bedside by noting the accuracy, initiation time, and speed of large movements, with the patient's head stationary. Partly for methodological reasons, laboratory analysis of saccades has mainly focused on movements of 20 degrees or less. By measuring the velocity waveform of large saccades, it is possible to examine more closely the way in which brain stem and cerebellum guide the eye to the target. Large saccades made by healthy humans show a positively skewed velocity profile. Slow saccades made by patients with brain-stem disorders show a prolonged plateau of low velocity. Some patients with cerebellar disorders may show increased acceleration and deceleration of saccades. Each of these velocity waveforms can be modeled by changing the parameters that describe medium-lead burst neuron firing. In certain other brain-stem and cerebellar disorders, transient decelerations or premature terminations of saccades occur; such velocity waveforms cannot be modeled solely by changing the parameters that describe burst neuron firing. Instead, it is necessary to postulate dysfunction of the mechanism that normally inhibits pontine omnipause neurons, thereby permitting burst neurons to discharge until the saccade is completed. Analysis of large, abnormal saccades calls for application of novel techniques to identify the beginning and end of the saccadic pulse command.

Effects of retinal image slip on modulation of visual vestibulo-ocular reflex during near viewing.

During viewing of a near target, the gain of the visually modulated vestibulo-ocular reflex (vVOR) exceeds 1.0. We investigated whether retinal image slip contributes to this gain increase by measuring responses during strobe illumination. Subjects showed greater gain values during normal versus strobe illumination of the near target, even during rotation at frequencies above 1.0 Hz, indicating that retinal image velocity information is used to optimize vVOR.

Comparison of velocity waveforms of eye and head saccades.

We compared the velocity waveforms of head and eye-in-head movements during eye-head saccades over a range 5-50 degrees. The velocity waveforms of eye-in-head saccades showed a skew ratio (acceleration period/saccade duration) that varied as a function of saccade size and duration. The velocity waveforms of head saccades showed a more constant skew of approximately 0.5 for the range of movements tested. These results suggest independent system controllers for eye and head components of eye-head saccades.

Effects of eyelid closure, blinks, and eye movements on the electroencephalogram.

OBJECTIVE: To characterize the effects of the eyeball and eyelid positions during eyeblinks on electroencephalographic (EEG) potentials. METHODS: Movements of the upper eyelids and eyes were measured in two healthy subjects using the magnetic search coil technique during horizontal and vertical eye rotations, eyeblinks, and lid closure. Corresponding signal changes were recorded simultaneously on the electroencephalogram (EEG). RESULTS: Spontaneous blinks produced small eye movements directed down and inward, whereas slow or forced blinks were associated with delayed upward eye rotations (i.e. Bell's phenomenon); both types of blinks caused positive EEG potentials with bifrontal distribution maximum at Fp1 and Fp2. CONCLUSIONS: In prior reports, these positive EEG artifacts have been attributed to upward eyeball rotation during blinks-Bell's phenomenon. By contrast, our findings indicate that movements of the eyelid contribute to a greater extent to these EEG potentials than do upward eyeball rotations. SIGNIFICANCE: Care is required in attributing EEG artifacts to movements of either eyeball or eyelid, since our findings suggest that they both contribute to these potentials.

Properties of anticipatory vergence responses.

PURPOSE: To characterize the dynamic properties of vergence eye movements made between near and far targets that were alternately illuminated with predictable timing. METHODS: Using the magnetic search coil technique, eye movements were measured in 10 normal subjects as they shifted their point of fixation between a near green LED and a distant red laser spot, both aligned on subjects' midlines. Targets were alternately illuminated every 1.25 sec. RESULTS: All subjects showed some anticipatory responses, consisting of vergence movements that preceded target jumps, accompanied by a small saccade. Group median anticipatory interval was 191 msec. Responses preceded target motion in 83% of divergence trials, and 70% of convergence trials. The velocities of both pre- and persaccadic components of anticipatory vergence responses were greater when the near target was positioned at 20-cm compared with at 36 cm. In control experiments, in which target presentation was unpredictable, vergence movements preceded stimuli in only approximately 2% of trials; for the group, vergence responses followed target presentation after a median interval of 183 msec. To determine whether anticipatory vergence movements depended on a memory of prior stimuli, trials were run in four subjects in which oddball stimuli required a different-sized vergence movement. Most responses to oddball stimuli were not significantly different from responses to the preceding stimuli. CONCLUSIONS: Anticipatory vergence movements occur commonly in response to predictable stimulus movements in depth, but uncommonly when the timing of stimulus presentation is not predictable. The speed of anticipatory vergence movements is affected by stimulus amplitude. Properties of these movements are influenced by prior vergence responses, indicating that they depend on working memory.

Vertical optokinetic nystagmus and saccades in normal human subjects.

PURPOSE: Optokinetic stimulation induces nystagmus that can be used to test the saccadic and visual-tracking systems in some patients with voluntary gaze palsies. The purpose of this study was to characterize vertical optokinetic nystagmus (OKN) in normal human subjects, comparing the dynamic properties of the quick phases with voluntary saccades of similar size and measuring the slow-phase responses to visual stimuli with a range of spatial and temporal frequencies. METHODS: Vertical OKN and saccades were recorded in 10 healthy adult subjects (age range, 24-54 years) using the magnetic search coil technique. The optokinetic (OK) stimulus subtended 72 degrees horizontally and 60 degrees vertically, consisted of black-and-white stripes with a spatial frequency of 0.04, 0.08, or 0.16 cyc/deg, and moved vertically at 10 to 50 deg/s. Vertical and horizontal saccades to visual targets separated by 1 degrees to 10 degrees were also elicited. RESULTS: Over 95% of quick phases were less than 10 degrees in amplitude; voluntary saccades of this amplitude range were slightly faster than quick phases of similar size. The amplitude-peak velocity relationships and amplitude-duration relationships of upward and downward fast movements (saccades or quick phases) were similar. Most vertical slow-phase OK responses showed greater gain for upward stimulus motion. OK gain decreased with increasing stimulus speed and increased spatial frequency, so that there was a general decrease in slow-phase velocity gain with increasing temporal frequency. CONCLUSIONS: In this study, the best OK responses were obtained using stripes with lower spatial frequencies and lower stripe speeds (0.4 cyc/deg at 10 deg/s). The dynamic properties of vertical quick phases of nystagmus are similar enough to those of voluntary saccades for OK stimulation to be used as a clinical test of the vertical saccadic system in individuals with voluntary gaze palsy.

Evaluating small eye movements in patients with saccadic palsies.

Slow saccades are an important diagnostic feature of a range of degenerative, metabolic, and genetic diseases of the nervous system. Many affected patients have difficulty initiating saccades, and the movements themselves may be small, making it difficult to make comparisons with control subjects. A large-field optokinetic stimulus may elicit quick phases of nystagmus in patients who cannot initiate voluntary saccades, but these movements may also be small. We show that it is still possible to compare amplitude-duration and amplitude-peak velocity relations with controls if data are fit with a power function (rather than an exponential equation). When analyzed this way, the dynamic properties of small saccades and quick phases from patients with progressive supranuclear palsy (PSP) could be differentiated from fast movements made by patients with idiopathic Parkinson's disease or controls. Normal saccades show a fairly constant ratio: peak velocity/mean velocity (Q approximately 1.6 for vertical saccades). This ratio was abnormally high (Q >3) for some larger saccades made by patients with PSP, suggesting that either these movements were not entirely saccadic or that they were composed of a series of small saccades.

Disorders of vertical optokinetic nystagmus in patients with ocular misalignment.

PURPOSE: To compare responses to vertical and horizontal optokinetic (OK) stimulation in patients with disorders of ocular alignment. METHODS: Using the magnetic search coil technique, we measured horizontal and vertical rotations of both eyes in six patients with strabismus since childhood and eight normal subjects. The OK stimulus subtended 72 degrees horizontally and 60 degrees vertically, consisted of black-and-white stripes with a spatial frequency of 0.04 cycles/degree, and moved either vertically or horizontally at 22.5 or 12 degrees/s. All patients and controls were tested with both eyes viewing and monocularly. RESULTS: Vertical OK responses were asymmetric in most normals and patients. The direction of this asymmetry varied between individuals, but upward stimuli more commonly elicited a greater response than downward stimuli. Monocular horizontal OK responses were symmetric in normals; patients showed either an asymmetry with greater responses for nasal motion, or a directional bias. During monocular and binocular viewing, vertical OK stimulation induced vertical nystagmus in normal subjects, but all patients showed diagonal responses, with horizontal components that were significantly greater than controls. The inappropriate horizontal component of the response increased at the higher stimulus speed, and was not simply due to latent nystagmus. CONCLUSIONS: Patients with disorders of ocular alignment since childhood show an inappropriate horizontal response to vertical OK stimuli, indicating directional abnormality of either motion vision pathways or the ocular motor response.

Tests of models for saccade-vergence interaction using novel stimulus conditions.

During natural activities, two types of eye movements - saccades and vergence - are used in concert to point the fovea of each eye at features of interest. Some electrophysiological studies support the concept of independent neurobiological substrates for saccades and vergence, namely saccadic and vergence burst neurons. Discerning the interaction of these two components is complicated by the near-synchronous occurrence of saccadic and vergence components. However, by positioning the far target below the near target, it is possible to induce responses in which the peak velocity of the vertical saccadic component precedes the peak velocity of the horizontal vergence component by approximately 75 ms. When saccade-vergence responses are temporally dissociated in this way, the vergence velocity waveform changes, becoming less skewed. We excluded the possibility that such change in skewing was due to visual feedback by showing that similar behavior occurred in darkness. We then tested a saccade-related vergence burst neuron (SVBN) model proposed by Zee et al. in J Neurophysiol 68:1624-1641 (1992), in which omnipause neurons remove inhibition from both saccadic and vergence burst neurons. The technique of parameter estimation was used to calculate optimal values for responses from human subjects in which saccadic and convergence components of response were either nearly synchronized or temporally dissociated. Although the SVBN model could account for convergence waveforms when saccadic and vergence components were nearly synchronized, it could not when the components were temporally dissociated. We modified the model so that the saccadic pulse changed the parameter values of the convergence burst units if both components were synchronized. The modified model accounted for velocity waveforms of both synchronous and dissociated convergence movements. We conclude that both the saccadic pulse and omnipause neuron inhibition influence the generation of vergence movements when they are made synchronously with saccades.

Directional asymmetry during combined saccade-vergence movements.

We investigated relationships between saccadic and vergence components of gaze shifts as 10 human subjects switched visual fixation between targets aligned in the midsagittal plane that lay in different vertical directions and at different distances. When fixation was shifted between a higher distant target and a lower near target, peak convergence velocity followed peak vertical saccadic velocity by a median interval of 12 ms. However, when fixation was shifted between a lower distant target and a higher near target, peak convergence velocity followed peak vertical saccadic velocity by a median interval of 76 ms. For the 2 stimulus arrangements, the median intervals by which peak divergence velocity followed the peak vertical saccadic velocity were 4 and 20 ms, respectively. The dissociation interval between the peak velocities of convergence and upward saccades increased with vertical saccade size, required convergence angle, and elevation of the endpoint of the movement. Velocity waveforms of vergence responses were more skewed when peak velocity was closely associated with saccadic peak velocity than when the vergence responses were delayed. Convergence peak velocities did not vary in any consistent pattern, but divergence peak velocities were generally smaller with responses that were delayed. Vergence movements were accompanied by small, high-frequency conjugate oscillations, suggesting that omnipause neurons were inhibited for both types of responses. In conclusion, the present findings indicate that the dynamic properties of horizontal vergence movements depend on the direction and timing of vertical saccades; these findings suggest experimental tests for current models of saccade-vergence interaction.

Vestibular and non-vestibular contributions to eye movements that compensate for head rotations during viewing of near targets.

Geometry dictates that when subjects view a near target during head rotation the eyes must rotate more than the head. The relative contribution to this compensatory response by adjustment of the vestibulo-ocular reflex gain (Gvor), visual tracking mechanisms including prediction, and convergence is debated. We studied horizontal eye movements induced by sinusoidal 0.2-2.8 Hz, en-bloc yaw rotation as ten normal humans viewed a near target that was either earth-fixed (EFT) or head-fixed (HFT). For EFT, group median gain was 1.49 at 0.2 Hz declining to 1.08 at 2.8 Hz. For HFT, group median gain was 0.03 at 0.2 Hz increasing to 0.71 at 2.8 Hz. By applying transient head perturbations (peak acceleration >1,000 degrees s(-2)) during sinusoidal rotation, we determined that Gvor was similar during either EFT or HFT conditions, and contributed only approximately 75% to the compensatory response. We confirmed that retinal image slip contributed to the compensatory response by demonstrating reduced gain during EFT viewing under strobe illumination. Gain also declined during sum-of-sines head rotations, confirming the contribution of predictive mechanisms. The gain of compensatory eye movements was similar during monocular or binocular viewing, although vergence angle was greater during binocular viewing. Comparison with previous studies indicates that mechanisms for generation of eye rotations during near viewing depend on head stimulus type (rotation or translation), waveform (transient or sinusoidal), and the species being tested.