Central Spike Research Articles

Small heat‐shock proteins and leaf cooling capacity account for the unusual heat tolerance of the central spike leaves inAgave tequilanavar. Weber

Agaves are perennial crassulacean acid metabolism (CAM) plants distributed in tropical and subtropical arid environments, features that are attractive for studying the heat-shock response. In agaves, the stress response can be analysed easily during leaf development, as they form a spirally shaped rosette, having the meristem surrounded by folded leaves in the centre (spike) and the unfolded and more mature leaves in the periphery. Here, we report that the spike of Agave tequilana is the most thermotolerant part of the rosette withstanding shocks of up to 55 degrees C. This finding was inconsistent with the patterns of heat-shock protein (Hsp) gene expression, as maximal accumulation of Hsp transcripts was at 44 degrees C in all sectors (spike, inner, middle and outer). However, levels of small HSP (sHSP)-CI and sHSP-CII proteins were conspicuously higher in spike leaves at all temperatures correlating with their thermotolerance. In addition, spike leaves showed a higher stomatal density and abated more efficiently their temperature several degrees below that of air. We propose that the greater capacity for leaf cooling during the day in response to heat stress, and the elevated levels of sHSPs, constitute part of a set of strategies that protect the SAM and folded leaves of A. tequilana from high temperatures.

Generation of attosecond x-ray pulses with a multicycle two-color enhanced self-amplified spontaneous emission scheme

Generation of attosecond x-ray pulses is attracting much attention within the x-ray free-electron laser (FEL) user community. Several schemes using extremely short laser pulses to manipulate the electron bunches have been proposed. In this paper, we extend the attosecond two-color ESASE scheme proposed by Zholents et al. to the long optical cycle regime using a second detuned laser and a tapered undulator. Both lasers can be about ten-optical-cycles long, with the second laser frequency detuned from the first to optimize the contrast between the central and side current spikes. A tapered undulator mitigates the degradation effect of the longitudinal space charge (LSC) force in the undulator and suppresses the FEL gain of all side current peaks. Simulations using the LCLS parameters show a single attosecond x-ray spike of {approx} 110 attoseconds can be produced. The second laser can also be detuned to coherently control the number of the side x-ray spikes and the length of the radiation pulse.

Quantum-beat imaging of the nuclear dynamics inD2+: Dependence of bond softening and bond hardening on laser intensity, wavelength, and pulse duration

Based on a quantum-mechanical model, we calculate the time evolution of an initial nuclear vibrational wave packet in $\text{D}_{2}{}^{+}$ generated by the rapid ionization of ${\text{D}}_{2}$ in an ultrashort pump-laser pulse. By Fourier transformation of the nuclear probability density with respect to the time delay between the pump pulse and the instant destructive Coulomb-explosion imaging of the wave packet at the high-intensity spike of an intense probe-laser pulse, we provide two-dimensional internuclear-distance-dependent power spectra that serve as a tool for visualizing and analyzing the nuclear dynamics in $\text{D}_{2}{}^{+}$ in an intermittent external laser field. The external field models the pedestal to the central ultrashort spike of a realistic probe pulse. Variation in the intensity, wavelength, and duration of this probe-pulse pedestal (i) allows us to identify the optimal laser parameters for the observation of field-induced bond softening and bond hardening in $\text{D}_{2}{}^{+}$ and (ii) suggests a scheme for quantitatively testing the validity of the ``Floquet picture'' that is commonly used for the interpretation of short-pulse laser-molecule interactions, despite its implicit ``continuum wave'' (infinite pulse length) assumption.

Mach 3 Shock Wave Unsteadiness AlleviationUsing a Negative Corona Discharge

This paper reports experimental data obtained in ONERA M = 3 R1Ch blow-down wind tunnel. A truncated conical body with a central spike mounted on the truncated face is tested in a M = 3 airflow. Several runs have been performed, with a freestream unit Reynolds varying in the range Reu 2 [0.9 10 7 m 1 ; 2.1 10 7 m 1 ]. Depending on the spike length LS, the flow around the body is steady or unsteady. Following Kuo, 1 the model is also a pair of electrodes and is supplied with AC or DC power. Thus on-board discharges can be generated. Although different discharge regimes have been obtained on steady or unsteady flowfield, we simply report here the effect of corona discharges on an unsteady flowfield. This unsteadiness is characterized by a shock pulsation at the reduced frequency St = fc.LS/u0 = 3.10 2 . We observe a complete alleviation of the shock unsteadiness when a negative discharge is generated at the spike tip. With positive discharges, the effect is weaker. In both cases the input power is less than 1W. Discharge imaging and current measurements suggest that the negative discharge is a Trichel pulse corona discharge, whereas the positive discharge possibly involves streamers. The possible channels of interaction between the discharge and the airflow are briefly discussed.

Phyllotactic pattern is altered in the transition to flowering in the early ears of Zea mays landrace chapalote (Poaceae)

The origin of polystichy in the maize ear and central tassel spike continues to challenge our understanding of evolution in this important crop species. In this paper we tested the hypothesis that the change in phyllotaxy occurs in the region of husk leaf production before the transition to reproductive growth. Young ear or presumptive ear primordia were dissected to examine the transition from distichous husk leaves below the ear through spiral phyllotaxy to the polystichous arrangement of spikelet pair primordia in the young ear. Serial transverse sections were used to document the thickness of successive disks of insertion of lateral primordia and to reconstruct the path of procambial differentiation. The transition in phyllotaxy, though variable, typically occurs in the vegetative zone and is associated with periodic heterogeneity in the thickness of leaf bases and a delay in the development of waves of procambial differentiation into the base of the young ear.

Weighing the Quiescent Central Black Hole in an Elliptical Galaxy with X‐Ray‐Emitting Gas

We present a Chandra study of the hot interstellar medium (ISM) in the giant elliptical galaxy NGC 4649. In common with other group-centered ellipticals, its temperature profile rises with radius in the outer parts of the galaxy, from ~0.7 keV at 2 kpc to ~0.9 keV by 20 kpc. However, within the central ~2 kpc the trend reverses, and the temperature peaks at ~1.1 keV within the innermost 200 pc. Under the assumption of hydrostatic equilibrium, we demonstrate that the central temperature spike arises due to the gravitational influence of a quiescent central supermassive black hole. We constrain the black hole mass (MBH) to (3.35+ 0.67−0.95) × 109 M☉ (90% confidence), in good agreement with stellar kinematics measurements. This is the first direct measurement of MBH based on studies of hydrostatic X-ray-emitting gas, which are sensitive to the most massive black holes, and is a crucial validation of both mass-determination techniques. This agreement clearly demonstrates that the gas must be close to hydrostatic, even in the very center of the galaxy, which is consistent with the lack of morphological disturbances in the X-ray image. NGC 4649 is now one of only a handful of galaxies for which MBH has been measured by more than one method. At larger radii, we were able to decompose the gravitating mass profile into stellar and dark matter (DM) components. Unless one accounts for the DM, a standard virial analysis of the stars dramatically overestimates the stellar mass of the galaxy. We find that the measured J-band stellar mass-to-light ratio, 1.37 ± 0.10 M☉ L−1☉, is in good agreement with simple stellar population model calculations for this object.

Deterioration in Cognitive Function in Children With Benign Epilepsy of Childhood With Central Temporal Spikes Treated With Sulthiame

The purpose of this study was to determine if reduction in spike frequency in children with benign epilepsy of childhood with centrotemporal spikes treated with sulthiame correlates with improved neuropsychologic function. Six untreated children (5 boys, 1 girl) with a mean (standard deviation) age of 9.1 years (1.5 years) underwent overnight ambulatory electroencephalograph recording and neuropsychologic evaluation at baseline and after 6 months of sulthiame monotherapy. The Reliable Change Index was used to determine whether a statistically reliable change in neuropsychologic function occurred. All children continued receiving sulthiame monotherapy (dose range, 8.0-9.3 mg/kg per day) for the study period without further seizures. Although spike frequency was reduced in all 6 children (3 showing a decrease to less than 10% of baseline), they all demonstrated significant deterioration in their reading ability, 5 had significant declines in general memory, and more than half had reduction in attention skills and mathematics ability. Although sulthiame was effective at seizure control and significantly reduced spike frequency in children, it was also associated with deterioration in cognitive function.

Cluster Formation in Contracting Molecular Clouds

We explore, through a simplified, semianalytic model, the formation of dense clusters containing massive stars. The parent cloud spawning the cluster is represented as an isothermal sphere. This sphere is in near-force balance between self-gravity and turbulent pressure. Self-gravity, mediated by turbulent dissipation, drives slow contraction of the cloud, eventually leading to a sharp central spike in density and the onset of dynamical instability. We suggest that, in a real cloud, this transition marks the late and rapid production of massive stars. We also offer an empirical prescription, akin to the Schmidt law, for low-mass star formation in our contracting cloud. Applying this prescription to the Orion Nebula Cluster, we are able to reproduce the accelerating star formation previously inferred from the distribution of member stars in the HR diagram. The cloud turns about 10% of its mass into low-mass stars before becoming dynamically unstable. Over a cloud free-fall time, this figure drops to 1%, consistent with the overall star formation efficiency of molecular clouds in the Galaxy.

Spin coating of non-Newtonian fluids with a moving front

We investigate axisymmetric spin coating of power law and Ellis fluids. The flow is driven by centrifugal force, gravity and surface tension. For power law and Ellis models a single equation for the fluid film height is obtained. For a Newtonian fluid the flux only involves linear derivative terms which allows the flux to be easily split for a numerical scheme. For power law and Ellis models the derivatives appear as nonlinear terms. To overcome this we develop an alternative numerical scheme to solve for the film height. Neglecting surface tension and gravity the power law model shows a central spike which is reduced by the introduction of surface tension and gravity. In certain cases the shear thinning power law model predicts slower spreading than the Newtonian model. The Ellis fluid shows no central spike, even for zero surface tension and the film always spreads further than the Newtonian fluid.

Automated identification of lava flow structures using local Fourier spectrum of digital elevation data

The rheological parameters of a lava flow can be inferred by studying structural features on the solidified lava surface. We have developed a technique using the S‐transform (a localized Fourier transform) to analyze and interpret digital elevation data. We examined structural features of a silicic lava flow, the Medicine Lake dacite flow in California. The S‐transform accurately identified and located both repeating and single‐instance structures. Several classes of structures were identified in the data, including the following: localized short wavelength features (1.3–3.6 m in wavelength) identified as large blocks and repeating medium wavelength features (5–8, 10–16, 18–26, 30–36, and 56–67 m in wavelength) identified as multiple generations of crustal folding. Fold wavelengths determined by the S‐transform and a model of compressional folding associated with near surface viscosity gradients were used to evaluate the rheology of the Medicine Lake dacite flow. The similarity of the amount of strain during folding events and the wavelength ratio of successive generations of folding suggest that the flow rheology remained relatively constant during folding of the flow surface. Repeating long wavelength features (67–70‐ and 105–140‐m wavelengths) were identified as the spacing of crease structures. Crease structures were recognized by the absence of short wavelength features at the location of their smooth flanks and by a central spike corresponding to the central trough. The limitations and applicability of this approach lie in the accuracy and resolution of the digital elevation data used.

Analysis of the generators of epileptic activity in early-onset childhood benign occipital lobe epilepsy

Objective The Panayiotopoulos type of idiopathic occipital epilepsy has peculiar and easily recognizable ictal symptoms, which are associated with complex and variable spike activity over the posterior scalp areas. These characteristics of spikes have prevented localization of the particular brain regions originating clinical manifestations. We studied spike activity in this epilepsy to determine their brain generators. Methods The EEG of 5 patients (ages 7–9) was recorded, spikes were submitted to blind decomposition in independent components (ICs) and those to source analysis (sLORETA), revealing the spike generators. Coherence analysis evaluated the dynamics of the components. Results Several ICs were recovered for posterior spikes in contrast to central spikes which originated a single one. Coherence analysis supports a model with epileptic activity originating near lateral occipital area and spreading to cortical temporal or parietal areas. Conclusions Posterior spikes demonstrate rapid spread of epileptic activity to nearby lobes, starting in the lateral occipital area. In contrast, central spikes remain localized in the rolandic fissure. Significance Rapid spread of posterior epileptic activity in the Panayitopoulos type of occipital lobe epilepsy is responsible for the variable and poorly localized spike EEG. The lateral occipital cortex is the primary generator of the epileptic activity.

The similarity of shock waves generated by a cone-shaped plasma and by a solid cone in a supersonic airflow

A truncated 60° cone with a slender central spike, which protrudes to the tip location of a perfect cone, is designed as a wind tunnel model. It generates a bow shock in a supersonic airflow. This model is featured with an on-board discharge arrangement with the central spike and the truncated cone as two electrodes. When the central electrode is designated as the cathode, a dc pulsed discharge produces a hollow cone-shaped plasma that envelops the spike. The results show that this plasma has changed the original bow shock to a conical shock, equivalent to reinstating the model into a perfect cone and to generate a 70% increase in the body aspect ratio. A significant drag reduction in each discharge is inferred from the pressure measurements; at the discharge maximum, the pressure on the frontal surface of the body decreases by more than 30%, the pressure on the cone surface increases by about 5%, while the pressure on the cylinder surface remains unchanged. The energy loss due to wave drag is reduced to make up for the two-thirds of the energy consumed in the electric discharge for plasma generation. The measurements also show that the plasma effect on shock structure lasts much longer than the discharge period.

The support of pseudomeasures on

AbstractPM(E) denotes the set of pseudomeasures on $\mathbb{R}$ with support in the closed set E ⊆ $\mathbb{R}$. Then y ∈ $\mathbb{R}$ is not in E if and only if there is a neighbourhood W of y with $\lim_{N\to\infty} \int_{-N}^{N}(1-{|t|}/{N})e^{2\pi itw}\cal{F} S(t)\,dt=0$ uniformly for w ∈ W and S ∈ PM(E) with ‖S‖PM ≤ 1. This improves previous results by adding “uniformly” and its scope. The proof uses the fact that squashing the central spike of the Fejer kernel leads to A-norm convergence.

Quantitative trait loci analysis of phenotypic traits and principal components of maize tassel inflorescence architecture

Maize tassel inflorescence architecture is relevant to efficient production of F(1) seed and yield performance of F(1) hybrids. The objectives of this study were to identify genetic relationships among seven measured tassel inflorescence architecture traits and six calculated traits in a maize backcross population derived from two lines with differing tassel architectures, and identify Quantitative Trait Loci (QTL) involved in the inheritance of those tassel inflorescence architecture traits. A Principal Component (PC) analysis was performed to examine relationships among correlated traits. Traits with high loadings for PC1 were branch number and branch number density, for PC2 were spikelet density on central spike and primary branch, and for PC3 were lengths of tassel and central spike. We detected 45 QTL for individual architecture traits and eight QTL for the three PCs. For control of inflorescence architecture, important QTL were found in bins 7.02 and 9.02. The interval phi034-ramosa1 (ral) in bin 7.02 was associated with six individual architecture trait QTL and explained the largest amount of phenotypic variation (17.3%) for PC1. Interval bnlg344-phi027 in bin 9.02 explained the largest amount of phenotypic variation (14.6%) for PC2. Inflorescence architecture QTL were detected in regions with candidate genes fasciated ear2, thick tassel dwarf1, and ral. However, the vast majority of QTL mapped to regions without known candidate genes, indicating positional cloning efforts will be necessary to identify these genes.

Spike orientation may predict epileptogenic side across cerebral sulci containing the estimated equivalent dipole

Objective To evaluate whether the orientation of interictal spikes, localized in major sulci by magnetoencephalography (MEG), predicts the epileptogenic side of the sulcal wall. Methods Sixteen epilepsy patients were analyzed in whom equivalent current dipoles (ECDs) of MEG spikes were localized on the central (four patients), interhemispheric (4), or sylvian fissure (8); and the epileptogenic side across the sulci had been confirmed by seizure semiology, structural lesions, or intracranial electroencephalography (EEG). ECD was classified as epileptogenic side or normal side oriented and correlated to the scalp EEG map. Results All central ( n=50) and interhemispheric ( n=83) spike ECDs were oriented toward the epileptogenic side at peak latency. In scalp EEG, 91% of the spikes showed radial pattern of broad negativity above the sulcus whereas 9% showed tangential pattern with positive maximum above the epileptogenic side. Sylvian spikes were only found in patients with temporal lobe epilepsy (TLE). In sylvian spikes ( n=220), 73% of ECDs were oriented toward the epileptogenic side, whereas 27% were oriented toward the normal side. Conclusions In central and interhemispheric spikes, epileptogenic side cortex may be gross surface negative through the sulcal wall to the adjacent gyrus. Inconsistent orientation of the sylvian spikes suggests a complex pattern of spike propagation in TLE. Significance ECD orientation of central and interhemispheric spikes in MEG may predict the epileptogenic side.

Kinematics of the ultracompact helium accretor AM Canum Venaticorum

We report on the results from a five-night campaign of high-speed spectroscopy of the 17-min binary AM Canum Venaticorum (AM CVn), obtained with the 4.2-m William Herschel Telescope on La Palma. We detect a kinematic feature that appears to be entirely analogous to the 'central spike' known from the long-period, emission-line AM CVn stars GP Com, V396 Hya and SDSS J124058.03-015919.2, which has been attributed to the accreting white dwarf. Assuming that the feature indeed represents the projected velocity amplitude and phase of the accreting white dwarf, we derive a mass ratio q = 0.18 +/- 0.01 for AM CVn. This is significantly higher than the value found in previous, less direct measurements. We discuss the implications for AM CVn's evolutionary history and show that a helium star progenitor scenario is strongly favoured. We further discuss the implications for the interpretation of AM CVn's superhump behaviour, and for the detectability of its gravitational-wave signal with the Laser Interferometer Space Antenna (LISA). In addition, we demonstrate a method for measuring the circularity or eccentricity of AM CVn's accretion disc, using stroboscopic Doppler tomography. We test the predictions of an eccentric, precessing disc that are based on AM CVn's observed superhump behaviour. We limit the effective eccentricity in the outermost part of the disc, where the resonances that drive the eccentricity are thought to occur, to e = 0.04 +/- 0.01, which is smaller than previous models indicated.

Beam transformation and permanent modification in fused silica induced by femtosecond filaments

Results of an investigation of lateral beam structure by propagating femtosecond pulses in fused silica are presented. Observed spatial transformations of the beam were closely related to the onset of continuum generation. Further beam propagation was in the form of an intense central spike (filament) and surrounding rings. Increasing power led to beam splitting and the formation of a regular structure of multiple filaments. The filament was responsible for the spontaneous formation of permanent modification inside the material. Experimental results are backed by numerical simulations that include self-guided channels of a permanent change of the refractive index in a bulk medium.

Halo geometry and dark matter annihilation signal

We study the impact of the halo shape and geometry on the expected weakly interacting massive particle (WIMP) dark matter annihilation signal from the galactic center. As the halo profile in the innermost region is still poorly constrained, we focus on geometrical distortions and consider different density behaviors like flat cores, cusps, and spikes. We show that asphericity has a strong impact on the annihilation signal when the halo profile near the galactic center is flat, but becomes gradually less significant for cuspy profiles, and negligible in the presence of a central spike. However, the astrophysical factor is strongly dependent on the weakly interacting massive particle mass and annihilation cross section in the latter case.

Indirect signals from dark matter in split supersymmetry

We study the possibilities for the indirect detection of dark matter in Split Supersymmetry from gamma-rays, positrons, and antiprotons. The most promising signal is the gamma-ray line, which may be observable at the next generation of detectors. For certain halo profiles and a high mass neutralino, the line can even be visible in current experiments. The continuous gamma-ray signal may be observable, if there is a central spike in the galactic halo density. The signals are found to be similar to those in MSSM models. These indirect signals complement other experiments, being most easily observable for regions of parameter space, such as heavy wino and higgsino dominated neutralinos, which are least accessible for direct detection and accelerator searches.

SDSS J124058.03-015919.2: a new AM CVn star with a 37-min orbital period

We present high time-resolution spectroscopy with the Very Large Telescope of SDSS J124058.03−015919.2, a new helium-transferring binary star identified in the Sloan Digital Sky Survey. We measure an orbital period of 37.355 ± 0.002 min, confirming the AM CVn nature of the system. From the velocity amplitudes of the accretor and the accretion stream–disc impact, we derive a mass ratio q= 0.039 ± 0.010. Our spectral coverage extends from λλ3700–9500 A and shows the presence of helium, nitrogen, silicon and iron in the accretion disc, plus the redshifted, low-velocity 'central spikes' in the helium lines, known from the low-state AM CVn stars GP Com and CE 315. Doppler tomography of the helium and silicon emission lines reveals an unusual pattern of two bright emission sites in the tomograms, instead of the usual one emission site identified with the impact of the mass stream into the accretion disc. One of the two is preferred as the conventional stream–disc impact point in velocity space, at the 3σ confidence level. We speculate briefly on the origin of the second.