Hot isostatic pressing of bulk magnesium diboride: Mechanical and superconducting properties

Hot isostatic pressing with glass encapsulation (pressure, 200MPa; temperature, 1000C over 200min; cooling under pressure) was used to synthesize bulk MgB 2 with diameters up to 20mm and thicknesses up to 10mm from MgB 2 powder. A sharp superconducting transition was measured at 38.5K. This method can be scaled to larger sample sizes and complex shapes. The data for density, microhardness, fracture toughness and sound speed for bulk magnesium diboride are presented. Ball milling the powder results in a more homogeneous final microstructure with a higher resistivity and with a similar superconducting transition.     

Chronic painless recording of intra-arterial blood pressure in unanesthetized dogs

A method for measuring intra-arterial blood pressure in unanesthetized dogs for as long as 12 months through the implantation of polyvinyl catheters in the abdominal aorta is described. Direct intra-aortic pressures ranged from 135 to 204 mm Hg for systolic blood pressures and 57 to 123 mm Hg for diastolic blood pressures over periods ranging from 8 to 12 months. This method provides a means for following blood pressure for a long period with minimal disturbance in the behavior of the animal. This also makes possible an additional cardiovascular measurement in the studies of the cardiac conditional reflexes.     

Sub-centimeter language organization in the human temporal lobe

The human temporal lobe is well known to be critical for language comprehension. Previous physiological research has focused mainly on non-invasive neuroimaging and electrophysiological techniques with each approach requiring averaging across many trials and subjects. The results of these studies have implicated extended anatomical regions in peri-sylvian cortex in speech perception. These non-invasive studies typically report a spatially homogenous functional pattern of activity across several centimeters of cortex. We examined the spatiotemporal dynamics of word processing using electrophysiological signals acquired from high-density electrode arrays (4 mm spacing) placed directly on the human temporal lobe. Electrocorticographic (ECoG) activity revealed a rich mosaic of language activity, which was functionally distinct at four mm separation. Cortical sites responding specifically to word and not phoneme stimuli were surrounded by sites that responded to both words and phonemes. Other sub-regions of the temporal lobe responded robustly to self-produced speech and minimally to external stimuli while surrounding sites at 4 mm distance exhibited an inverse pattern of activation. These data provide evidence for temporal lobe specificity to words as well as self-produced speech. Furthermore, the results provide evidence that cortical processing in the temporal lobe is not spatially homogenous over centimeters of cortex. Rather, language processing is supported by independent and spatially distinct functional sub-regions of cortex at a resolution of at least 4 mm.     

Foot Position Tends to be Sensed as More Medial Than the Actual Foot Position

ABSTRACT

Participants placed different parts of their foot as close as possible to a target line without stepping onto it while wearing modified goggles that obscured their view of their feet. Once they felt that their foot was appropriately placed, the distance between their foot and the target line was measured. Participants tended to step 20–30 mm over the target line when asked to place the most lateral part of their foot near the target line and tended to place their foot 20–30 mm away from the target line when asked to place the most medial part of their foot near the target line. These results indicate that the placed feet shifted more laterally than sensed, which may explain unexpected tripping during walking.     

Alterations in the thickness of motor cortical subregions after motor-skill learning and exercise

Behavioral manipulations such as housing in an enriched environment have been shown to increase brain weight and visual cortical thickness. The present study was designed to test whether skill learning or repetitive movements can alter the thickness of the motor cortex. One group of 6-mo-old Long-Evans female rats learned motor skills on an obstacle course that increased in difficulty over training and required balance and coordination. A second group ran voluntarily in exercise wheels attached to their home cage but had little opportunity for skill learning. The third group was handled daily but received no opportunity for learning or exercise. Each condition lasted 26–29 d. The skill-learning and exercise conditions had greater heart weight, and the exercise condition had greater adrenal gland weights than controls. The thickness of the motor cortex was measured in four coronal planes between −2.33 mm to −0.3 mm from bregma. Regions of interest that corresponded to published maps of forelimb and hind-limb representations were analyzed together. Rats in the skill-learning condition had significantly thicker medial cortical areas in the two anterior planes (−0.8 and −0.3 mm from bregma). These regions correspond to previously mapped hind-limb representations. The exercise group had greater thickness of the medial region at −0.8 mm from bregma. Cortical thickness in all conditions varied significantly along the medial to lateral axis. For both treatments, the effects were restricted to medial and anterior regions of interest rather than posterior or lateral regions of interest. The results indicate that robust exercise, in addition to skill learning, is capable of altering the thickness of the motor cortex, but that the effects are restricted rather than distributed within the regions studied.     

Haptic detection of sine-wave gratings

We studied human haptic perception of sine-wave gratings. In the first experiment we measured the dependence of amplitude detection thresholds on the number of cycles and on the wavelength of the gratings. In haptic perception of sine-wave gratings, the results are in agreement with neural summation. The rate at which detection thresholds decrease with increasing number of cycles is much higher than can be accounted for by probability summation alone. Further, neural summation mechanisms describe the detection thresholds accurately over the whole spatial range probed in the experiment, that is wavelengths from 14 mm up to 225 mm. Earlier, we found a power-law dependence of thresholds on the spatial width of Gaussian profiles (Louw et al, 2000 Experimental Brain Research 132 369-374). The current results extend these findings; the power-law dependence holds not only for Gaussian profiles, but also for a broad range of sine-wave gratings with the number of cycles varying between 1 and 8. Haptic perception involves tactual scanning combined with an active, dynamic exploration of the environment. We measured characteristics of the velocity and force with which stimuli were scanned while performing a psychophysical task. One particularly surprising finding was that, without being instructed, participants maintained an almost constant scanning velocity during each 45-min session. A constant velocity in successive trials of the experiment might facilitate or even be necessary for discrimination. Further, a large systematic dependence of velocity on scanning length was found. An eightfold increase in scanning length resulted in about a fourfold increase in scanning velocity. A second experiment was conducted to study the influence of scanning velocity on psychophysical detection thresholds. This was done by systematically imposing specific scanning velocities to the participants while the thresholds were measured. The main result of the second experiment was that psychophysical detection thresholds are constant over a relatively broad range of scanning velocities.     

Response-contingent variation in visual recall: evidence of a dynamic memory trace

Sixty-six subjects learned responses to four ellipses (eccentrically 0.52) which varied orthogonally in area (two large: 994 mm2; two small: 671 mm2) and orientation (two with major axis vertical, two with major axis horizontal). Correct responses were contingent on either the area or the orientation of the ellipses. After learning the correct responses, subjects recalled the ellipses by drawing them. Recall was either immediately, 1 day, or 2 weeks after learning the responses. The recall drawings were measured for area and for orientation (ratio of the length of the vertical to the horizontal axis). Differences among the recall drawings increased on the dimension (area or orientation) which was associated with correct responses during the learning task. The differences on the associated dimension were large when recall was tested immediately after the response learning task, small when recall was tested 1 day after learning, and large again when recall was tested 2 weeks after learning the responses. This experiment eliminated one potential source of uncontrolled variability in earlier results. The results are consistent with previous experiments and suggest an active two-phase memory consolidation process extended over time.     

Broadening of activity with flow across neural structures

Synfire chains have long been suggested as a substrate for perception and information processing in the nervous system. However, embedding activation chains in a densely connected nervous matrix risks spread of signal that will obscure or obliterate the message. We used computer modeling and physiological measurements in rat hippocampus to assess this problem of activity broadening. We simulated a series of neural modules with feedforward propagation and random connectivity within each module and from one module to the next. We found that activity broadened as it propagated from one module to the next. This occurred over a wide array of parameters with greater broadening seen with increasing excitatory-excitatory synaptic strength. Activity broadening correlated positively with propagation velocity. Multi-electrode measurements of activity propagation in disinhibited CA1 slice demonstrated broadening of about 50% over 1 mm. Such broadening is a problem for information transfer that must be dealt with in a fully functioning nervous system.     

Manual discrimination of force using active finger motion.

In these experiments, two plates were grasped between the thumb and forefinger and squeezed together along a linear track. An electromechanical system presented a constant resistance force during the squeeze up to a predetermined location on the track, whereupon the force effectively went to infinity (simulating a wall) or to zero (simulating a cliff). The task of the subject was to discriminate between two alternative levels of the constant resistance force (a reference level and a reference-plus-increment level). Results of these experiments indicate a just noticeable difference of roughly 7% of the reference force using a one-interval paradigm with trial-by-trial feedback over the ranges 2.5 less than or equal to F0 less than or equal to 10.0 newtons, 5 less than or equal to D less than or equal to 30 mm, 45 less than or equal to S less than or equal to 125 mm, and 25 less than or equal to V less than or equal to 160 mm/sec, where F0 is the reference force, D is the distance squeezed, S is the initial fingerspan, and V is the mean velocity of the squeeze. These results, based on tests with 5 subjects, are consistent with a wide range of previous results, some of which are associated with other body surfaces and muscle systems and many of which were obtained with different psychophysical methods.     

Vertical disparity affects shape and size judgments across surfaces separated in depth

Vertical binocular disparity provides a useful source of information allowing three-dimensional (3-D) shape to be recovered from horizontal binocular disparity. In order to influence metric shape judgments, a large field of view is required, suggesting that vertical disparity may play a limited role in the perception of objects projecting small retinal images. This limitation could be overcome if vertical disparity information could be pooled over wide areas of 3-D space. This was investigated by assessing the effect of vertical disparity scaling of a large surround surface on the perceived size and 3-D shape of a small, central object. Observers adjusted the size and shape of a virtual, binocularly defined ellipsoid to match those of a real, hand-held tennis ball. The virtual ball was presented at three distances (200, 325, and 450 mm). Vertical disparities in a large surround surface were manipulated to be consistent with a distance of 160 mm or infinity. Both shape and size settings were influenced by this manipulation. This effect did not depend on presenting the surround and target objects at the same distance. These results suggest that the influence of vertical disparity on the perceived distance to a surface also affects the estimated distance of other visible surfaces. Vertical disparities are therefore important in the perception of metric depth, even for objects that in themselves subtend only small retinal images.     

Information entropy analysis of discrete aiming movements

Information entropy and mutual information were investigated in discrete movement aiming tasks over a wide range of spatial (20-160 mm) and temporal (250-1250 ms) constraints. Information entropy was calculated using two distinct analyses: (1) with no assumption on the nature of the data distribution; and (2) assuming the data have a normal distribution. The two analyses showed different results in the estimate of entropy that also changed as a function of task goals, indicating that the movement trajectory data were not from a normal distribution. It was also found that the information entropy of the discrete aiming movements was lower than the task defined indices of difficulty (ID) that were selected for the congruence with Fitts' law. Mutual information between time points of the trajectory was strongly influenced by the average movement velocity and the acceleration/deceleration segments of the movement. The entropy analysis revealed structure to the variability of the movement trajectory and outcome that has been masked by the traditional distributional analyses of discrete aiming movements.     

Postural leaning direction challenges the manifestation of tendon vibration responses at the ankle joint

In this study, we examined the interaction between central and peripheral proprioceptive afferent pathways by applying ankle tendon vibration during postural leaning in different directions. Twenty young participants stood for 60s over the midline of two adjacent force platforms in (a) neutral stance distributing Body Weight (BW) equally between the platforms, (b) forward leaning transferring 80% of BW to the front platform and (c) backward leaning transferring 80% of BW to the rear platform. Participants controlled the degree of leaning by receiving on-line visual feedback of BW distribution matched to a target line. Vibration (80 Hz, 1.5–1.8 mm) was applied over the Achilles or tibialis anterior tendon during the middle 20s of standing. This induced a postural shift towards the vibration side and an increase in the variability of the BW distribution that was greater in backward compared to forward leaning. EMG responses to tendon vibration were independent of the leaning direction. Antagonistic activity also increased in response to vibration, the amplitude of this increase however was direction dependent. These results favor the hypothesis about the central co-modulation of the vibration evoked proprioceptive inflow based on postural and visual feedback rather than muscle tension constraints.     

Manual discrimination of force using active finger motion

In these experiments, two plates were grasped between the thumb and forefinger and squeezed together along a linear track. An electromechanical system presented a constant resistance force during the squeeze up to a predetermined location on the track, whereupon the force effectively went to infinity (simulating a wall) or to zero (simulating a cliff). The task of the subject was to discriminate between two alternative levels of the constant resistance force (a reference level and a reference-plus-increment level). Results of these experiments indicate a just noticeable difference of roughly 7% of the reference force using a one-interval paradigm with trial-by-trial feedback over the ranges 2.5≤F _o≤10.0 newtons, 5≤D≤30 mm, 45≤S≤125 mm, and 25≤V≤160 mm/sec, whereF _o is the reference force,D is the distance squeezed,S is the initial finger-span, andV is the mean velocity of the squeeze. These results, based on tests with 5 subjects, are consistent with a wide range of previous results, some of which are associated with other body surfaces and muscle systems and many of which were obtained with different psychophysical methods.     

The impact of religion on men's blood pressure

Most clinical studies examining the relation between religion and blood pressure status have focused on church attendance, finding lower pressures among frequent attenders. The present study examines the effect on blood pressure status of a religious meaning variable, importance of religion, both by itself and together with frequency of church attendance. The relation between blood pressure, self-perceived importance of religion, and frequency of church attendance was examined among a rural sample of 407 white men free from hypertension or cardiovascular disease. The data confirmed an interaction between the effects of both religious variables on blood pressure status, with importance of religion having an even greater association with lower pressures than church attendance. Diastolic blood pressures of persons with high church attendance and high religious importance were significantly lower than those in the low attendance, low importance group. These differences persisted after adjusting the analyses for age, socioeconomic status, smoking, and weight-height ratio (Quetelet Index). The difference in mean diastolic pressures based on response to the religious importance variable alone was statistically and clinically significant, particularly among men aged 55 and over (6 mm) and among smokers (5 mm). These findings suggest that both religious attitudes and involvement may interact favorably in their effects on cardiovascular hemodynamics.     

Distance perception in photographic displays of natural settings

Distance perception of depicted objects was examined as a function of photographic perspective. 24 subjects viewed slides of outdoor scenes and directly estimated the distances to specified objects. Perspective was manipulated by photographing each scene with lenses of four different focal lengths: 48 mm, 28 mm, 24 mm, and 17 mm. Distance perception along the pictorial depth plane (z-axis) was systematically transformed by changing the photographic perspective: the shorter the focal length of the camera lens, the greater the perceived distance. Perceived distance between objects along the lateral plane (x-axis) was unaffected by changes in lens focal length.     

Concussion is associated with altered preparatory postural adjustments during gait initiation

Gait initiation is a useful surrogate measure of supraspinal motor control mechanisms but has never been evaluated in a cohort following concussion. The aim of this study was to quantify the preparatory postural adjustments (PPAs) of gait initiation (GI) in fifteen concussion patients (4 females, 11 males) in comparison to a group of fifteen age- and sex-matched controls. All participants completed variants of the GI task where their dominant and non-dominant limbs as the ‘stepping’ and ‘support’ limbs. Task performance was quantified using the centre of pressure (COP) trajectory of each foot (computed from a force plate) and a surrogate of the centre of mass (COM) trajectory (estimated from an inertial measurement unit placed on the sacrum).Concussed patients exhibited decreased COP excursion on their dominant foot, both when it was the stepping limb (sagittal plane: 9.71 mm [95% CI: 8.14–11.27 mm] vs 14.9 mm [95% CI: 12.31–17.49 mm]; frontal plane: 36.95 mm [95% CI: 30.87–43.03 mm] vs 54.24 mm [95% CI: 46.99–61.50 mm]) and when it was the support limb (sagittal plane: 10.43 mm [95% CI: 8.73–12.13 mm] vs 18.13 mm [95% CI: 14.92–21.35 mm]; frontal plane: 66.51 mm [95% CI: 60.45–72.57 mm] vs 88.43 mm [95% CI: 78.53–98.32 mm]). This was reflected in the trajectory of the COM, wherein concussion patients exhibited lower posterior displacement (19.67 mm [95% CI: 19.65 mm–19.7 mm]) compared with controls (23.62 mm [95% CI: 23.6–23.64]). On this basis, we conclude that individuals with concussion display deficits during a GI task which are potentially indicative of supraspinal impairments in motor control.     

Visual field size necessary for length comparison

Influence of visual field size upon acuity for comparing lengths of two lines was investigated. The visual field was effectively narrowed to any desired size by use of a TV display system. The TV screen presented a portion of the test stimulus, the position of which was controlled by the subject’s eye movement so that his fixation point always coincided with the center of the portion. The test stimulus was composed of two lines arranged horizontally, one of which had a length of 81 mm and the other a slightly different value. Sizes of the narrowed visual field were 20, 40, 70, 100, 150, and 340 mm wide. The comparison acuity dropped rapidly as the visual field was narrowed to and below 70 mm which was about the same extent as one of the two lines. The implication is that our excellent ability for length comparison is only possible when we can observe the whole line at one time.     

Ocular vergence-induced accommodation and its relation to dark focus

Two experiments were conducted in an attempt to develop an open-loop technique for assessing the influence of ocular vergence on accommodation changes. Past research had shown that a small point of light (1.2 mm in diameter) induces relatively small changes in monocular accommodation at viewing distances greater than 50 cm. However, Experiment 1 (using seven male and six female undergraduates as subjects) demonstrated that, even with a smaller light spot (.29 mm), subjects could accommodate to the stimulus at distances closer than 50 cm. It was only with a very impoverished target (.08 mm diameter), as used in Experiment 2 (in which five male and five female undergraduates served as subjects), that it was possible to present a stimulus that could induce ocular vergence without being a direct stimulus in itself for accommodation. It was also shown that ocular vergence can drive accommodation and that ocular vergence can vary systematically under conditions in which illumination is greatly reduced. In addition, both experiments showed significant relationships among dark focus and both monocular and binocular accommodation.     

Pencil lead diameter affects response sheet completion time

The effect of pencil lead diameter on the completion time of a multiple-choice response sheet was examined. Participants used three pencil lead diameters (.5 mm, .9 mm, and a standard No. 2 pencil) to fill in "bubbles" on response sheets in one experiment; a .7-mm pencil was substituted for the No. 2 pencil in Exp. 2. Participants using a .5-mm pencil completed response sheets more slowly than when using a .7-mm, .9-mm, or a No. 2 pencil.     

Contest experience and body size affect different types of contest decisions

This study examined the relative importance of contest experience and size differences to behavioral decisions over the course of contests. Using a mangrove rivulus fish, Kryptolebias marmoratus, we showed that although contest experience and size differences jointly determined contest outcomes, they affected contestants’ interactions at different stages of contests. Contest experience affected behavioral decisions at earlier stages of contests, including the tendency and latency to launch attacks, the tendency to escalate contests into mutual attacks and the outcome of non-escalated contests. Once contests were escalated into mutual attacks, the degree of size difference affected the fish’s persistence in escalation and chance of winning, but contest experience did not. These results support the hypothesis that contest experience modifies individuals’ estimation of their fighting ability rather than their actual strength. Furthermore, (1) in contests between two naïve contestants, more than 60 % of fish that were 2–3 mm smaller than their opponent escalated the contest to physical fights, even though their larger opponents eventually won 92 % of escalated fights and (2) fish with a losing experience were very likely to retreat in the face of an opponent 2–3 mm smaller than them without escalating. The result that a 2–3 mm size advantage could not offset the influence of a losing experience on the tendency to escalate suggests that, as well as depending on body size, the fish’s physical strength is influenced by other factors which require further investigation.