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Images of ancient Egyptians wearing distinctive, cone-shaped objects on their heads have, in the absence of physical examples, long elicited scholarly debate. Did people wear these cones, or were they a purely iconographic device? What was their function and meaning? Recent excavations at the Amarna cemeteries now provide the first material examples of head cones. Spectroscopic analyses indicate that their primary constituent is a biological wax, and not fat or incense, as sometimes speculated. The authors tentatively suggest that the Amarna cones were symbols meant to enhance the rebirth or personal fertility of the deceased in the afterlife.
Photoreceptors have high energy demands and densely packed mitochondria through which light passes before phototransduction. Old world primates including humans have three cone photoreceptor types mediating color vision with short (S blue), medium (M green), and long (L red) wavelength sensitivities. However, S-cones are enigmatic. They comprise <10% of the total cone population, their responses saturate early, and they are susceptible in aging and disease. Here, we show that primate S-cones actually have few mitochondria and are fueled by glycolysis, not by mitochondrial respiration. Glycolysis has a limited ability to sustain activity, potentially explaining early S-cone saturation. Mitochondria act as optical filters showing reduced light transmission at 400–450 nm where S-cones are most sensitive (420 nm). This absorbance is likely to arise in a mitochondrial porphyrin that absorbs strongly in the Soret band. Hence, reducing mitochondria will improve S-cone sensitivity but result in increased glycolysis as an alternative energy source, potentially increasing diabetic vulnerability due to restricted glucose access. Further, glycolysis carries a price resulting in premature functional decline as seen in aged S-cones. Soret band absorption may also impact on mitochondrial rich M and L cones by reducing sensitivity at the lower end of their spectral sensitivity range resulting in increased differentiation from S-cone responses. These data add to the list of unique characteristic of S-cones and may also explain aspects of their vulnerability.
Chapter I studies the category of commutative integral monoids, especially so-called “fine monoids” which are the basic building blocks of toric and logarithmic geometry. It includes a self-contained treatment of standard results in convex geometry, including finiteness and duality and the geometry of faces and ideals, and also discusses the affine toric varieties arising from monoid algebras. In addition to these classical results, it includes a study of limits and colimits of monoids, of actions of monoids on sets, and of homomorphisms of monoids, including the key concepts of exact, integral, and saturated homomorphisms.
We compute Betti numbers for a Cohen–Macaulay tangent cone of a monomial curve in the affine
-space corresponding to a pseudo-symmetric numerical semigroup. As a byproduct, we also show that for these semigroups, being of homogeneous type and homogeneous are equivalent properties.
We study an operation, that we call lifting, creating nonisomorphic monomial curves from a single monomial curve. Our main result says that all but finitely many liftings of a monomial curve have Cohen–Macaulay tangent cones even if the tangent cone of the original curve is not Cohen–Macaulay. This implies that the Betti sequence of the tangent cone is eventually constant under this operation. Moreover, all liftings have Cohen–Macaulay tangent cones when the original monomial curve has a Cohen–Macaulay tangent cone. In this case, all the Betti sequences are just the Betti sequence of the original curve.
The distinct alignment of the Steinheim Basin and the Nördlinger Ries impact structures in SW Germany and the Central European tektite strewn field suggest ENE-directed trajectories of the Ries and Steinheim impacting bodies. From impact experiments, the asymmetry of the Steinheim crater and the arrangement of structural features therein are in good agreement with features produced during an oblique impact at 30° from the horizontal. The restriction of shatter cones to the eastern segment of the Steinheim Basin crater also suggests a west–east-directed trend of the impact direction, and supports previous models that favoured such impactor trajectory.
The ~3.8 km Steinheim Basin in SW Germany is a well-preserved complex impact structure characterized by a prominent central uplift and well-developed shatter cones that occur in different shocked target lithologies. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and electron probe microanalysis have revealed, for the first time, the occurrence of rare metals on the Steinheim shatter cone surfaces. Shatter cones produced from the Middle Jurassic (Aalenian) Opalinus Claystone (‘Opalinuston’), temporarily exposed in the central uplift in spring 2010, and shatter cones in Upper Jurassic (Oxfordian) limestones from the southeastern crater rim domain are commonly covered by faint coatings. The Opalinus Claystone shatter cone surfaces carry coatings dominated by Fe, Ca, P, S and Al, and are covered by abundant small, finely dispersed microparticles and aggregates of native gold, as well as locally elevated concentrations of Pt. On several surfaces of the claystone shatter cones, additional Fe, Ni and Co was detected. The Ca–Mn-rich coatings on the limestone shatter cone surfaces locally include patches of Fe, Ni, Co, Cu and Au in variable amounts and proportions. The intriguing coatings on the Steinheim shatter cones could either stem from the impacted Lower Jurassic to Palaeogene sedimentary target rocks; from the crystalline-metamorphic Variscan crater basement; or, alternatively, these coatings might represent altered meteoritic matter from the Steinheim impactor, possibly an iron meteorite, which may have been remobilized during post-impact hydrothermal activity. We here discuss the most plausible source for the rare metals found adherent to the shatter cone surfaces.
The permanently frozen volcanic sediment is one of the most promising geological objects for searching life on Mars. On Earth, volcanic intrusions into permafrost result in formation of the unique microbial communities. We propose several terrestrial analogues of Martian polar volcanoes, such as the permanently frozen volcanic sediments on the Kamchatka peninsula and in Antarctica. The present study shows applicability of the morphometric analysis for demonstration of the morphological similarity between the terrestrial and Martian cinder cones. In the present work, the morphometric analysis of young Martian landforms is based on the assumption that the conical structures identified on digital terrain model (DTM) are volcanic cinder cones. Morphometric analysis of the studied cones showed a range of degradation. The extent of degradation may be an indicator of age based on comparison with volcanic cinder cones on Earth. A morphometric analysis of potentially young volcanic cones in the North Polar Region of Mars was performed to estimate their relative age. The 14 potential cinder cones were identified using the DTM provided by Mars Express High Resolution Stereo Camera (HRSC), allowing for the basic morphometric calculations. The majority of the cinder cones are localized in the Chasma Boreale region within the area 79°–81°N and 261°–295°E. The calculated morphometric parameters showed that the cone average steepness varied from 3.4° to 11.8°, cone height-to-width ratio varied from 0.025 to 0.12, and the ratio between surface and basal area of the cone varied from 1.005 to 1.131. The studied cinder cones were classified with respect to the morphometric ratios assuming that larger values correspond to the younger structures. Employing the terrestrial analogy of morphometric ratios as a proxy for relative geological age, we suggest that existing microorganisms may be found in permafrost of young Martian cinder cones.
The recently discovered Agoudal impact site in Morocco is a small, eroded impact structure with well-developed shatter cones. A scanning electron microscopic study of a shatter cone surface has revealed the presence of schreibersite – a phosphide very rare on Earth but common in iron meteorites – and Fe–Ni oxides. This is the first reported evidence for primary meteoritic matter adherent to shatter cones and suggests that the Agoudal crater was formed by the impact of an iron meteorite, probably the Agoudal IIAB iron. Shatter cones from other terrestrial impact structures might also hold valuable information about the nature of the impacting projectiles.
The aim of this study was to assess the effects of hop cones (Humulus lupulus L.) from two varieties Aurora and Dana, differing in their α- and β-acid contents, on rumen microbial activity measured with in vitro gas production kinetics and short-chain fatty acids (SCFA) production. Hop cones were added to the total mixed dairy cow ration (CONT) in concentrations simulating a cow’s daily intake of 50, 100 and 200 g of hop cones – the concentrations of hop cones expressed on a substrate basis were 43, 82 and 153 mg/g of substrate. Substrates were anaerobically incubated in glass syringes, and gas production kinetic parameters were determined by fitting data with the Gompertz model. Gas produced after 24 h (Gas24), maximum fermentation rate (MFR) and time of maximum fermentation rate (TMFR) were calculated from the estimated gas production kinetic parameters. After 24 h of incubation, the fermentation liquids of each substrate were taken for the determination of SCFA. Increasing the hop cone concentration decreased the total potential gas production, Gas24, MFR and shortened TMFR. The highest hop cone concentration significantly decreased acetic and butyric acid productions and total SCFA production after 24 h of incubation, but not propionic acid production, resulting in a decreased ratio between acetic acid and propionic acid.
In this paper we give necessary and sufficient optimality conditions for a vector
optimization problem over cones involving support functions in objective as well as
constraints, using cone-convex and other related functions. We also associate a unified
dual to the primal problem and establish weak, strong and converse duality results. A
number of previously studied problems appear as special cases.
At certain temporal frequencies, the human cone flicker electroretinogram (ERG) contains multiple additional responses following the termination of a flicker train. The purpose of this study was to determine whether these poststimulus responses are a continuing response to the terminated flicker train or represent the oscillation of a resonant system. ERGs were recorded from 10 visually normal adults in response to full-field sinusoidally modulated flicker trains presented against a short-wavelength rod-saturating adapting field. The amplitude and timing properties of the poststimulus responses were evaluated within the context of a model of a second-order resonant system. At stimulus frequencies between 41.7 and 71.4 Hz, the majority of subjects showed at least three additional ERG responses following the termination of the flicker train. The interval between the poststimulus responses was approximately constant across stimulus frequency, with a mean of 14.4 ms, corresponding to a frequency of 69.4 Hz. The amplitude and timing characteristics of the poststimulus ERG responses were well described by an underdamped second-order system with a resonance frequency of 70.3 Hz. The observed poststimulus ERG responses may represent resonant oscillations of retinal ON bipolar cells, as has been proposed for electrophysiological recordings of poststimulus responses from retinal ganglion cells. However, further investigation is required to determine the types of retinal neurons involved in the generation of the poststimulus responses of the human flicker ERG.
Acetylcholine is present in and released from starburst amacrine cells in the inner plexiform layer (IPL), but its role in retinal function except, perhaps, in early development, is unclear. Nicotinic acetylcholine receptors are thought to be present on ganglion, amacrine, and bipolar cell processes in the IPL, and it is known that acetylcholine increases the spontaneous and light-evoked responses of retinal ganglion cells. The effects of acetylcholine on bipolar cells are not known, and here we report the effects of nicotine on the b-wave of the electroretinogram in larval zebrafish. The b-wave originates mainly from ON-bipolar cells, and the larval zebrafish retina is cone-dominated. Only small rod responses can be elicited with dim lights in wild-type larval zebrafish retinas, but rod responses can be recorded over a range of intensities in a mutant (no optokinetic response f) fish that has no cone function. We find that nicotine strongly enhances cone-driven b-wave response amplitudes but depresses rod driven b-wave response amplitudes without, however, affecting rod- or cone-driven b-wave light sensitivity.
Continuous-time discrete-state random Markov chains generated by a random linear differential equation with a random tridiagonal matrix are shown to have a random attractor consisting of singleton subsets, essentially a random path, in the simplex of probability vectors. The proof uses comparison theorems for Carathéodory random differential equations and the fact that the linear cocycle generated by the Markov chain is a uniformly contractive mapping of the positive cone into itself with respect to the Hilbert projective metric. It does not involve probabilistic properties of the sample path and is thus equally valid in the nonautonomous deterministic context of Markov chains with, say, periodically varying transition probabilities, in which case the attractor is a periodic path.
In this paper we show that any good toric contact manifold has a well-defined cylindrical contact homology, and describe how it can be combinatorially computed from the associated moment cone. As an application, we compute the cylindrical contact homology of a particularly nice family of examples that appear in the work of Gauntlett et al. on Sasaki–Einstein metrics. We show in particular that these give rise to a new infinite family of non-equivalent contact structures on S2×S3 in the unique homotopy class of almost contact structures with vanishing first Chern class.
Much of what is currently known about the visual response of retinal bipolar cells is based on studies of rod-dominant responses to flashes in the dark in the isolated retina. This minireview summarizes quantitative findings on contrast processing in the intact light-adapted retina based on intracellular recording from more than 400 cone-driven bipolar cells in the tiger salamander: 1) In the main, the contrast responses of ON and OFF cells are surprisingly similar, suggesting a need to refine the view that ON and OFF cells provide the selective substrates for processing of positive and negative contrasts, respectively. 2) Overall, the response is quite nonlinear, showing very high gain for small contrasts, some 10–15 times greater than that of cones, but then quickly approaches saturation for higher contrasts. 3) Under optimal conditions of light adaptation, both classes of bipolar cells show evidence for efficient coding with respect to the contrasts in natural images. 4) There is a marked diversity within both the ON and OFF bipolar cell populations and an absence of discrete subtypes. The dynamic ranges bracket the range of contrasts in nature. 5) For both ON and OFF cells, the receptive field organization shows a striking symmetry between center and surround for responses of the same polarity and thus opposite contrast polarities. 6) The latency difference between ON and OFF cells is about 30 ms, which seems qualitatively consistent with a delay due to the G-protein cascade in ON bipolar cells. 7) In sum, we report quantitative evidence for at least 11 transformations in signal processing that occur between the voltage response of cones and the voltage response of bipolar cells.
We study the birational geometry of irreducible holomorphic symplectic varieties arising as varieties of lines of general cubic fourfolds containing a cubic scroll. We compute the ample and moving cones, and exhibit a birational automorphism of infinite order explaining the chamber decomposition of the moving cone.
The purpose of this study was to test whether color–motion correlations carried by a pure color difference (S-cone component only) can be used to improve global motion extraction. We also examined the neural markers of color–motion correlation processing in event-related potentials. Color and motion information was dissociated using a two-colored random dot kinematogram, wherein coherent motion and motion noise differed from each other only in their S-cone component, with spatial and temporal parameters set so that global motion processing relied solely on a constant L-M component. Hence, when color and the local motion direction are correlated, more efficient segregation of coherent motion can only be brought about by the S-cone difference, and crucially, this S-cone component does not provide any effective input to a global motion mechanism but only changes the color appearance of the moving dots. The color contrasts (vector length in the S vs. L-M plane) of both the dots carrying coherent motion and the dots moving randomly were fixed at motion discrimination threshold to ensure equal effectiveness for motion extraction. In the behavioral experiment, participants were asked to discriminate between coherent and random motion, and d′ was determined for three different conditions: uncorrelated, uncued correlated, and cued correlated. In the electroencephalographic experiment, participants discriminated direction of motion for uncued correlated and cued correlated conditions. Color–motion correlations were found to improve performance. Cueing a specific color also modulated the N1 component of the event-related potential, with sources in visual area middle temporal. We conclude that S-cone signals “invisible” to the motion system can influence the analysis by direction-selective motion mechanisms through grouping of local motion signals by color. This grouping mechanism must precede motion processing and is likely to be under attentional control.
We give conditions which imply that a complete noncompact manifold with quadratic curvature decay has finite topological type. In particular, we find links between the topology of a manifold with quadratic curvature decay and some properties of the asymptotic cones of such a manifold.
Omitting a stimulus from a train of repetitive stimuli, by either interrupting or terminating the train, can elicit an electrophysiological response that occurs at the time appropriate for the omitted stimulus. This study investigated whether such an omitted stimulus response (OSR) is present in the flicker electroretinogram (ERG) of the human cone system. ERGs were recorded from 11 visually normal subjects in response to full-field sinusoidal flicker trains presented against a rod-desensitizing adapting field at frequencies ranging from 12.5 to 100 Hz. Recordings were synchronized with the onset of the stimulus trains, and the amplitude and relative delay of any additional ERG responses following the offset of the flicker train were analyzed. At stimulus frequencies below 35 Hz, the number of ERG responses always equaled the number of stimulus cycles. However, over the frequency range of 38.5 to 100 Hz, the ERG contained an extra response following flicker train offset. At stimulus frequencies from 38.5 to 62.5 Hz, there was a constant delay between the peak of the extra ERG response and the time at which the next stimulus would have occurred had the flicker train continued. This constant delay is characteristic of an OSR. In addition, an extra ERG response was apparent at these same stimulus frequencies if the flicker train was interrupted by omitting stimulus cycles from the middle of the train. The pattern of ERG findings is consistent with a recently proposed model of the OSR that attributes the phenomenon to a resonant oscillation in retinal bipolar cells.