Near-vertical Orientation Research Articles

Propofol Resistance of Functional Domains with Orientation and Direction Sensitivity of the Primary Visual Cortex in Rats

A method consisting of optical mapping of the intrinsic signal was used to study the activity of functional domains of the primary visual cortex at the population level in response to changes in the stimulus situation. Transient administration of propofol on the background of stable anesthesia allowed determination of the extent to which different functional domains of the cortex are stable to the systemic action of pharmacological agents. This substance was selected for the experiments because published data have demonstrated its affinity for GABAA receptors. Experiments were performed on seven adult clinically healthy cats. Analysis of the experimental data identified statistically significant differences between the responses of direction and orientation columns: signals in orientation domains were 1.6 times greater than responses in modules with directional selectivity. Analysis of changes in the structure of optical maps (i.e., the characteristic patterns of the distribution of functional columns in areas of the visual cortex) showed decreases in the level of correlation between the regions of interest by 60% for direction maps and 40% for orientation maps. Orientation columns were more stable to propofol. Additional analysis addressed the stability of the encoding of defined orientations in the cortex, which showed that the functional elements of the cortex with the greatest stability were those detecting near-vertical orientations.

Modeling a Large-Scale Historic Aquifer Test: Insight into the Hydrogeology of a Regional Fault Zone.

Faults can act as flow barriers or conduits to groundwater flow by introducing heterogeneity in permeability. We examine the hydrogeology of the Sandwich Fault Zone, a 137 km long zone of high-angle faults in northern Illinois, using a large-scale historic aquifer test. The fault zone is poorly understood at depth due to the majority of the faults being buried by glacial deposits and its near-vertical orientation which limits geologic sampling across faults. The aquifer test-perhaps one of the largest in terms of overall withdrawal in North American history-was conducted in 1942 at a facility adjacent to the fault zone. More than 34,000 m3 /day was pumped for 37 days from nine multiaquifer wells open to the stratified Cambrian-Ordovician sandstone aquifer system. We modeled the aquifer test using a transient MODFLOW-USG model and simulated pumping wells with the CLN package. We tested numerous fault core/damage zone conceptualizations and calibrated to drawdown values recorded at production and observation wells. Our analysis indicates that the fault zone is a low-permeability feature that inhibits lateral movement of groundwater and that there is at least an order of magnitude decrease in horizontal hydraulic conductivity in the fault core compared to the undeformed sandstone. Large head declines have occurred north of the fault zone (over 300 m since predevelopment conditions) and modifying fault zone parameters significantly affects calibration to regional drawdown on a decadal scale. The flow-barrier behavior of the fault zone has important implications for future groundwater availability in this highly stressed region.

Slipping Dynamics of Slender-Beam Payloads During Lay-Down Operations

When laying down a long slender beam from a near-vertical orientation, to a horizontal position on a flat surface, the payload may slip and move suddenly in unintended and unpredictable ways. This occurs during crane operations when the movements of the overhead trolley and lowering of the hoist cable are not properly coordinated. The payload's unintended sliding can potentially cause damage and injure people. This paper presents static and dynamic analyses of slender-beam payload lay-down operations that establish a structured method to predict the safe conditions for lay-down operations. Also, a new method to measure the friction coefficient of surface-to-line contact is proposed. Lay-down experiments are carried out to verify the theoretical predictions.

Evidence for tilt normalization can be explained by anisotropic orientation sensitivity.

Some data have been taken as evidence that after prolonged viewing, near-vertical orientations "normalize" to appear more vertical than they did previously. After almost a century of research, the existence of tilt normalization remains controversial. The most recent evidence for tilt normalization comes from data suggesting a measurable "perceptual drift" of near-vertical adaptors toward vertical, which can be nulled by a slight physical rotation away from vertical (Müller, Schillinger, Do, & Leopold, 2009). We argue that biases in estimates of perceptual stasis could, however, result from the anisotropic organization of orientation-selective neurons in V1, with vertically-selective cells being more narrowly tuned than obliquely-selective cells. We describe a neurophysiologically plausible model that predicts greater sensitivity to orientation displacements toward than away from vertical. We demonstrate the predicted asymmetric pattern of sensitivity in human observers by determining threshold speeds for detecting rotation direction (Experiment 1), and by determining orientation discrimination thresholds for brief static stimuli (Experiment 2). Results imply that data suggesting a perceptual drift toward vertical instead result from greater discrimination sensitivity around cardinal than oblique orientations (the oblique effect), and thus do not constitute evidence for tilt normalization.

Trajectory-Shaping Guidance with final speed and load factor constraints

This paper describes the design of a guidance law used for guiding a hypersonic gliding vehicle against a ground target from a near-vertical orientation with a specified final speed and a near-zero final load factor. The guidance law consists of two terms: one is Trajectory-Shaping Guidance (TSG) used for steering the vehicle to the target from the specified orientation; the other is Final-Speed-Control Scheme (FSCS) used for controlling the vehicle to perform lateral maneuver to adjust the final speed. Further, the generalized closed form solutions of TSG are obtained from a more general linearized engagement model, where the speed of the vehicle can be an arbitrary positive function of time. By analyzing these solutions, the stability domain of the guidance coefficients is obtained such that the final load factor is zero. This domain is not affected by the change rate of the speed. Thus, according to this analysis, the proposed guidance law can achieve a near zero final load factor by properly selecting the guidance coefficients in the stability domain.

Wing and body kinematics of takeoff and landing flight in the pigeon (Columba livia)

Takeoff and landing are critical phases in a flight. To better understand the functional importance of the kinematic adjustments birds use to execute these flight modes, we studied the wing and body movements of pigeons (Columba livia) during short-distance free-flights between two perches. The greatest accelerations were observed during the second wingbeat of takeoff. The wings were responsible for the majority of acceleration during takeoff and landing, with the legs contributing only one-quarter of the acceleration. Parameters relating to aerodynamic power output such as downstroke amplitude, wingbeat frequency and downstroke velocity were all greatest during takeoff flight and decreased with each successive takeoff wingbeat. This pattern indicates that downstroke velocity must be greater for accelerating flight to increase the amount of air accelerated by the wings. Pigeons used multiple mechanisms to adjust thrust and drag to accelerate during takeoff and decelerate during landing. Body angle, tail angle and wing plane angles all shifted from more horizontal orientations during takeoff to near-vertical orientations during landing, thereby reducing drag during takeoff and increasing drag during landing. The stroke plane was tilted steeply downward throughout takeoff (increasing from -60+/-5 deg. to -47+/-1 deg.), supporting our hypothesis that a downward-tilted stroke plane pushes more air rearward to accelerate the bird forward. Similarly, the stroke plane tilted upward during landing (increasing from -1+/-2 deg. to 17+/-7 deg.), implying that an upward-tilted stroke plane pushes more air forward to slow the bird down. Rotations of the stroke plane, wing planes and tail were all strongly correlated with rotation of the body angle, suggesting that pigeons are able to redirect aerodynamic force and shift between flight modes through modulation of body angle alone.

Pooling signals from vertically and non-vertically orientation-tuned disparity mechanisms in human stereopsis

To understand the role that orientation-tuned disparity-sensitive mechanisms play in the perception of stereoscopic depth, we measured stereothresholds using two sets of random-dot stimuli that produce identical stimulation of disparity mechanisms tuned to vertical orientation but dissimilar stimulation of disparity mechanisms tuned to non-vertical orientations. Either 1 or 1.5 D of astigmatic blur was simulated in the random-dot images presented to both eyes, using two axis configurations. In the parallel-axis conditions, the axis of simulated astigmatic blur was same in the two eyes (0, 45 or 135 o[rientation] deg). In the orthogonal-axis conditions, the axes of astigmatic blur were orthogonal in the two eyes (LE: 180, RE: 90; LE: 90, RE: 180; LE: 45, RE: 135; and LE: 135, RE: 45). Whereas the stimulation of disparity mechanisms tuned to near-vertical orientations should be similar in the oblique parallel- and orthogonal-axis conditions, the stimulation of non-vertically tuned disparity mechanisms should be dissimilar. Measured stereothresholds were higher in the orthogonal compared to the parallel-axis condition by factors of approximately 2 and 5, for 1 and 1.5 D of simulated oblique astigmatic blur, respectively. Further, for comparable magnitudes of simulated astigmatic blur, stereothresholds in the (LE: 180, RE: 90 and LE: 90, RE: 180) conditions were similar to those in the (LE: 45, RE: 135 and LE: 135, RE: 45) conditions. These results suggest that the computation of horizontal disparity includes substantial contributions from disparity mechanisms tuned to non-vertical orientations. Simulations using a modified version of a disparity-energy model [Qian, N., & Zhu, Y. (1997). Physiological computation of binocular disparity. Vision Research, 37, 1811–1827], show (1) that pooling across disparity mechanisms tuned to vertical and non-vertical orientations is required to account for our data and (2) that this pooling can provide the spatial resolution needed to encode spatially changing horizontal disparities.

Apical control, gravitropic signaling, and the growth of lateral roots in Arabidopsis

Most research on gravity responses in plants has focused on primary roots and shoots, which typically grow in a vertical orientation. However, the patterns of lateral organ growth, which generally have large effects on overall plant architecture, are such that the organs are typically not vertical. In lateral roots of Arabidopsis, growth is initially in a nearly horizontal orientation but changes to a near-vertical orientation as the lateral root develops. Although the non-vertical lateral roots are gravitropically competent, following gravitropic reorientation of seedlings, the lateral roots on the upper flank of the primary root have different growth patterns from those on the lower side of the primary root. The differences are in part dependent on reorientation of the primary root, suggesting that gravitropic signaling from the primary root also contributes to the control of lateral root growth. The hormone auxin appears to play a role in this signaling between the primary and lateral roots, as auxin transport inhibitors applied to the primary root affect lateral root growth. Also, lateral roots of pin3 mutants, which are impaired in polar auxin transport, have altered lateral root orientations. However, other signals from the primary root tip also play an important role in regulating lateral root growth.

Fault zone fluids and seismicity in compressional and extensional environmen inferred from electrical conductivity: the New Zealand Southern Alps and U. S. Great Basin

Seismicity in both compressional and extensional settings is a function of local and regional stresses, rheological contrasts, and the distribution of fluids. The influence of these factors can be illustrated through their effects on electrical geophysical structure, since this structure reflects fluid composition, porosity, interconnection and pathways. In the compressional, amagmatic New Zealand South Island, magnetotelluric (MT) data imply a concave-upward (“U”-shaped), middle to lower crustal conductive zone beneath the west-central portion of the island due to fluids generated from prograde metamorphism within a thickening crust. Change of the conductor to near-vertical orientation at middle-upper crustal depths is interpreted to occur as fluids cross the brittle-ductile transition during uplift, and approach the surface through induced hydrofractures. The central South Island is relatively weak in seismicity compared to its more subduction-related northern and southern ends, and the production of deep crustal fluids through metamorphism may promote slip before high stresses are built up. The deep crustal conductivity is highly anisotropic, with the greater conductivity along strike, consistent with fault zone models of long-range interconnection versus degree of deformation. The central Great Basin province of the western U.S. by contrast is extensional at present although it has experienced diverse tectonic events throughout the Paleozoic. MT profiling throughout the province reveals a quasi one-dimensional conductor spanning the lower half of the crust which is interpreted to reflect high temperature fluids and perhaps melting caused ultimately by exsolution from crystallizing underplated basalts. The brittle, upper half of the crust is generally resistive, but also characterized by numerous steep, narrow conductors extending from near-surface to the middle crust where they contact the deep crustal conductive layer. These are suggested to represent fluidised/altered fault zones, with at least some fluids contributed from the deeper magmatic exsolution. The best-known faults imaged geophysically before this have been the listric normal faults bounding graben sediments as imaged by reflection seismology. However, the major damaging earthquakes of the Great Basin appear to nucleate near mid-crustal depths on near-vertical fault planes, which we suggest are being imaged with the MT transect data, and where triggering fluids from the ductile lower crust are available. In both compressional and extensional examples, the fluidised fault zones are hypothesized to act to concentrate slip, with major earthquakes resulting in asperities along the fault surface.

Global orientation aftereffect in multi-attribute displays: implications for the binding problem

We investigated the binding problem (e.g. the combination of edge information across attributes), using an orientation aftereffect paradigm (OAE). Horizontal layers of vertical edges were phase-shifted to create a global near-vertical orientation. Multi-attribute displays were created by alternating the attribute defining edges (e.g. luminance, colour, texture or motion) across layers. OAE magnitude was dependent only on the attributes used in the adaptation phase, and the similarity of attributes from adaptation to testing phase had no significant effect. Moreover, compared to single-attribute conditions, the cooperation between attributes is moderate. These results favour segregation models of the binding mechanism.

Stereoscopic depth perception from oblique phase disparities

In order to understand the role of oblique retinal image disparities in the perception of stereoscopic depth, we measured the depth perceived from random dot stereograms in which phase disparities were introduced in a selected band of stimulus orientations. A band of orientation was defined by a center orientation that ranged from 7.5 (near vertical) to 82.5 o[rientation]deg and by a bandwidth that was defined as the difference between the highest and the lowest orientation in the band. The bandwidths tested were 15, 30 and 45 odeg. A constant phase disparity of 90 p[hase]deg was introduced in all of the oriented spatial frequency components within the orientation band and the perceived depth of each stimulus was matched using a small square binocular probe. For each bandwidth, perceived depth increased with an increase in the center orientation up to approximately 60 odeg. This suggests that the human stereovision system derives a large proportion of information about perceived stereoscopic depth from oblique phase disparities. Simulations using an energy model of stereoscopic depth perception indicate that oblique phase disparities are unlikely to be processed by neural mechanisms tuned to near-vertical orientations within the stimulus. Our results therefore suggest that oblique retinal disparities are initially detected as oblique phase disparities by binocular mechanisms tuned to oblique orientations. Because the perceived depth from oblique phase disparities is consistent with the trigonometrically determined equivalent horizontal disparities, we presume that the information from oblique phase disparities is included in the visual system’s computation of the horizontal retinal disparity.

Crustal Scale Controls on Gold Ore Fluid Movement and Deposition as Revealed From Electrical Resistivity Structure: Examples from Compressional and Extensional Regimes

Structurally-controlled, meso- and epithermal gold deposition in both compressional and extensional settings is a function of local and regional stresses, rheological contrasts, and thermochemical gradients. The influence of these factors can be illustrated through their effects on electrical geophysical structure, since this structure reflects fluid composition, porosity, interconnection and pathways. In the compressional, amagmatic New Zealand South Island, magnetotelluric (MT) data imply a concave-upward (``U'-shaped), middle to lower crustal conductive zone beneath the west-central portion of the island. The deep crustal conductor suggests a volume of fluids arising from prograde metamorphism and radiogenesis within a thickening crust of paleo deep-water clastic rocks. Change of the conductor to near-vertical orientation at middle-upper crustal depths is interpreted to occur as fluids cross the brittle-ductile transition during uplift, and approach the surface through induced hydrofractures. Near the brittle-ductile pressure breakthrough are deposited modern hydrothermal veining, gold mineralization, and graphite of deep crustal provenance, subsequently exposed by erosion. In Nevada, Carlin Trend deposits appear to overlie central intrusives of late Eocene age which occupy the transition from conductive paleo-abyssal pelitic sediments (potential gold source rocks) eastward to more resistive shelf carbonate/quartzite sequences along an ancient continental margin normal fault. The intrusive is flanked by conductive, apparent accommodation fault zones which may possess higher porosity as well as possible graphite flushed from sediments near the high-T system core and redeposited in the periphery. Exposed deposits are modeled to form at fluid pressure breakthroughs across permeability barriers such as organic shales or thrust planes, producing strong and favorable gradients in temperature, pressure and fluid oxidation.

The submarine eruption of the Bombarda volcano, Milos Island, Cyclades, Greece

The Milos volcanic field includes a well-exposed volcaniclastic succession which records a long history of submarine explosive volcanism. The Bombarda volcano, a rhyolitic monogenetic center, erupted ∼1.7 Ma at a depth <200 m below sea level. The aphyric products are represented by a volcaniclastic apron (up to 50 m thick) and a lava dome. The apron is composed of pale gray juvenile fragments and accessory lithic clasts ranging from ash to blocks. The juvenile clasts are highly vesicular to non-vesicular; the vesicles are dominantly tube vesicles. The volcaniclastic apron is made up of three fades: massive to normally graded pumice-lithic breccia, stratified pumice-lithic breccia, and laminated ash with pumice blocks. We interpret the apron beds to be the result of water-supported, volcaniclastic mass-How emplacement, derived directly from the collapse of a small-volume, subaqueous eruption column and from syn-eruptive, down-slope resedimentation of volcaniclastic debris. During this eruptive phase, the activity could have involved a complex combination of phreatomagmatic explosions and minor submarine effusion. The lava dome, emplaced later in the source area, is made up of flow-banded lava and separated from the apron by an obsidian carapace a few meters thick. The near-vertical orientation of the carapace suggests that the dome was intruded within the apron. Remobilization of pyroclastic debris could have been triggered by seismic activity and the lava dome emplacement.

The integration of orientation information in the motion correspondence problem.

We examine how differently oriented components contribute to the discrimination of motion direction along a horizontal axis. Stimuli were two-frame random-dot kinematograms that were narrowband filtered in spatial frequency. On each trial, subjects had to state whether motion was to the left or the right. For each stimulus condition, Dmax (the largest displacement supporting 80% correct direction discrimination performance) was measured. In experiment 1, Dmax was measured for orientationally narrowband stimuli as a function of their mean orientation. Dmax was found to increase as the orientation of the stimuli became closer to the axis of motion. Experiment 2 used isotropic stimuli in which some orientation bands contained a coherent motion signal, and some contained only noise. When the noise band started at vertical orientations and increased until only horizontal orientations contained a coherent motion signal, Dmax increased slightly. This suggests that near-vertical orientations interfere with motion perception at large displacements when they contain a coherent motion signal. When the noise band started at horizontal and increased until only vertical orientations contained the motion signal, Dmax decreased steadily. This implies that Dmax depends at least partly on the most horizontal motion signal in the stimulus. These results were contrasted with two models. In the first, the visual system utilises the most informative orientations (nearest horizontal). In the second, all available orientations are used equally. Results supported an intermediate interpretation, in which all orientations are used but more informative ones are weighted more heavily.

Large clockwise rotations in an extensional allochthon, Alboran Domain (southern Spain)

Palaeomagnetic, structural and geochronological analysis of a suite of Oligocene mafic dykes intruded into the Malaguide allochthon in the Internal Zone of the Betic Cordillera demonstrate that at least 134° clockwise vertical-axis rotation of a large region occurred, probably during early Miocene thrusting onto the External Zones. Initial results from Ar/Ar whole rock analysis suggests that the dykes were probably intruded over a period of time between 23 Ma and 30 Ma. Results of demagnetization experiments demonstrate that the remanence in many of the dykes is composed of one to three components. The lowest temperature component is poorly defined. The intermediate temperature (IT) component, carried by pyrrhotite, has reversed polarity, a declination of 314° and an inclination of −48°. This component was probably acquired during cooling after greenschist-facies metamorphism. The high temperature (HT) component is carried by magnetite and was probably acquired at or shortly after intrusion. This component has both reversed and normal polarity, with an average declination of 320° and an inclination of −13°. Rotation of approximately 35° about a horizontal NNE-trending axis, in present-day coordinates, brings the inclination of the HT component into statistical agreement with both the IT component and the expected inclination for the Oligocene. This rotation leaves the dykes in a near-vertical orientation but brings the foliation in the surrounding schists to approximately horizontal. We suggest that the original regional foliation may have been sub-horizontal and related to the ductile phase of late-orogenic extension in the Betic Cordillera. The dykes were intruded sub-vertically into the schists with an original NW–SE trend. The region was then tilted and rotated clockwise by 23°±15 before acquiring the IT component after which it underwent 134°±10° of clockwise rotation about a vertical axis.

The incidence of glassy corneal striae

Glassy corneal striae (GCS) are fine colorless lines that run parallel to each other in a vertical or near-vertical orientation in the central cornea near the level of Descemet’s membrane. It is postulated that GCS “brace” the stroma, thus adding stability to the cornea. The purpose of this study was to determine the incidence of GCS in patients with “normal” corneas and to determine whether a correlation exists between the presence of GCS and gender, age, iris color, or corneal astigmatism (toricity). Modified marginal retro-illumination biomicroscopy was used to evaluate the cornea for the presence of GCS. One hundred thirteen “normal” right corneas were evaluated for the presence of GCS. A total of 85.8% (97/113) of subjects in our study sample exhibited GCS. However, we were unable to establish a statistically significant correlation between the presence of GCS and gender, age, iris color, or corneal toricity.

Early establishment of seafloor hydrothermal systems during structural extension: paleomagnetic evidence from the Troodos ophiolite, Cyprus

Paleomagnetic data from the Troodos ophiolite are used to help constrain models for the relationship between extensional normal faulting and hydrothermal alteration related to production of large-tonnage sulfide deposits at oceanic ridges. We have sampled dikes from the Troodos sheeted complex that have been subjected to variable hydrothermal alteration, from greenschist alteration typical of the low water/rock mass ratio interactions outside of hydrothermal upflow zones as well as from severely recrystallized rocks (epidosites) altered within high water/rock mass ratio hydrothermal upflow zones in the root zones beneath large sulfide ore deposits. These dikes are moderately to highly tilted from their initial near-vertical orientations due to rotations in the hangingwalls of approximately dike-parallel, oceanic normal faults. Comparison of characteristic remanence directions from these dikes with the Late Cretaceous Troodos reference direction, therefore, allows a tilt test to determine whether remanent magnetizations were acquired prior to or subsequent to tilting. Remanence directions for both greenschist and epidosite dikes show similar magnitudes of tilting due to rotational normal faulting and restore to the Late Cretaceous Troodos reference direction upon restoration of dikes to near-vertical positions about a NNW-trending, horizontal axis. These data, along with field observations of focused alteration along normal faults, suggest that epidosite alteration occurred during the early stages of extensional tilting and prior to significant rotation. This sequence of events is similar to that observed for creation of large-tonnage sulfide bodies at intermediate to slow spreading centers which form soon after cessation of magmatism and during the early stages of structural extension. We suggest that the dike-parallel normal faults were initiated as extensional fractures during this early stage of crustal extension, thus providing the necessary permeability for focused fluid flow, and that later slip along these structures during rotational-planar normal faulting caused reduction in permeability due to gouge formation.

NW Pacific slab rheology, the seismicity cutoff, and the olivine to spinel phase change

Along the Kamchatka-Kuril-Japan-Izu-Bonin-Mariana subduction zones, the old age of the subducting Pacific Plate and the rapid subduction rate together suggest that earthquakes should occur to the bottom of the transition zone. However, the seismicity cutoff varies in depth between 350 km and 650 km. Along these subduction zones, the largest deep-focus earthquakes invariably occur near the depth of the local seismicity cutoff regardless of its depth. The events near the seismicity cutoffs also have systematically different focal mechanisms than shallower events. Furthermore, data from S660P arrivals, residual sphere analysis, and tomographic studies all show that the slab dip consistently steepens to a near-vertical orientation at the seismicity cutoff. This change in slab dip indicates a strength loss in the slab. We hypothesize the following causal connection among all these observations: The cold temperatures in the slab kinetically hinder the olivine to spinel phase change and allow the olivine to persist metastably to depths well below its equilibrium pressure. When the phase transition occurs, it nucleates very fine-grained spinel which acts as a lubricant, allowing the initiation of earthquake faulting at high confining pressures which further nucleates additional fine-grained spinel. The cold anomaly of the slab severely inhibits the growth of the nucleated spinel crystals. The presence of the fine-grained spinel crystals reduces the strength of the coldest part of the slab by several orders of magnitude, allowing high slab deformation rates. Additionally, the phase change, by increasing the density, provides a negative buoyancy force. Combined, these processes reduce the slab membrane strength and allow the slab to descend at a steeper dip.

Assembly of Amphiphilic Phenylacetylene Macrocycles at the Air−Water Interface and on Solid Surfaces

The assembly of amphiphilic phenylacetylene macrocycles (PAMs), with molecular structures that vary in terms of the nature and orientation of their pendant functional groups, has been studied on a Langmuir−Blodgett trough and after transfer onto solid substrates. These monolayer films are of interest as two-dimensional host matrices and shape selective membranes whose two-dimensional organization should bring together shape selective compartments. The disk-like PAMs can, in principle, adopt orientations in which the plane of the macrocycle can range from perpendicular (edge-on) to parallel (face-on) at the interface. PAMs functionalized with six hydrophilic groups around the periphery do not prefer the face-on orientation and are most likely tilted, perhaps in a poorly organized state. PAMs that have spatially segregated hydrophilic and hydrophobic groups adopt the edge-on orientation when the hydrophilic moieties are carboxylate groups. In contrast, PAMs appended with acid moieties do not lead to stable monolayers, most likely because they engage in strong intermolecular hydrogen bonding interactions as evidenced by 1H NMR and vapor pressure osmometry of the solutions. Monolayers of the dicarboxylate PAMs were transferred onto fused silica and Si(100) surfaces and these were in turn characterized by contact angle, ellipsometry, absorption FTIR, and angle-resolved X-ray photoelectron spectroscopies. Taken together these characterization experiments strongly support the hypothesis that the dicarboxylate PAMs form a well-ordered and stable two-dimensional array and that they adopt the edge-on configuration with near-vertical orientation of the macrocycle plane.

Binocular attributes of length summation and end stopping in cat striate cortex

Length selectivity for each eye was compared as response increment-decrement to optimal sine-wave grating patches, in strongly binocular, striate cortical neurons in adult cats. Neurons were characterized as simple, or as standard, intermediate or special complex, on criteria that included length summation. Length summation was characterized for stimulus length, incremented symmetrically about the receptive field, up to optimal response levels. Many neurons additionally showed end stopping: response decrement to supra-optimal lengths. Optimal length and/or end stopping for each eye differed in most neurons, although the distributions of optimal length or percentage end stopping for each eye were comparable for the overall sample and for each neuronal subclass. However, paired comparisons of length and end-stopping data for each neuron revealed a marked tendency for receptive fields to be relatively smaller on average, but more strongly end stopped, for contralateral input. On the Wilcoxon signed rank test, these differences were statistically significant for standard complex neurons. There was also a tendency for differences in end stopping to be greater and more widely scattered for neurons with near-horizontal than near-vertical orientation preferences. Although the functional value of skew in the distributions of interocular differences in optimal length and end stopping remains conjectural, the scatter and balanced distribution of these differences in length specificity across the neuronal population may provide a basis for encoding visual perspective cues.