Velocity Shift Research Articles

New Approach to Revise the Spatiotemporal Lightning Current Distribution Models Intended for Tall Objects

In this article, we revised the commonly known engineering return stroke models for elevated objects, by taking into account the relativistic Doppler effect of the return stroke velocity shift. This revised model is applied to calculate the electromagnetic lightning field, struck by the Peissenberg tower using the finite difference time domain method in two-dimensions method. The simulation results are both compared with the results of the experimental measurements and with those obtained from the only two theoretical extending models existing in the literature that consider the presence of towers. Results show that the vertical lightning electric field is in perfect agreement with that measured experimentally, which means that this novel model was able to eliminate the nonphysical aspect of the transmitted current wave velocity from the tower top to the lightning channel observed in the hypothesis of the other authors and to reproduce in a more refined way the experimental measured electric field. The magnetic field behavior presents a concordance in the first peak and a slight difference in the tail waveform with that measured experimentally. These new formulations approximate the reality of the lightning radiation and, thus, allow to improve protection against its harmful effects.

The Host Galaxy and Rapidly Evolving Broad-line Region in the Changing-look Active Galactic Nucleus 1ES 1927+654

Changing-look active galactic nuclei (AGNs) present an important laboratory to understand the origin and physical properties of the broad-line region (BLR). We investigate follow-up optical spectroscopy spanning ∼500 days after the outburst of the changing-look AGN 1ES 1927+654. The emission lines displayed dramatic, systematic variations in intensity, velocity width, velocity shift, and symmetry. Analysis of optical spectra and multiband images indicates that the host galaxy contains a pseudobulge and a total stellar mass of . Enhanced continuum radiation from the outburst produced an accretion disk wind, which condensed into BLR clouds in the region above and below the temporary eccentric disk. Broad Balmer lines emerged ∼100 days after the outburst, together with an unexpected, additional component of narrow-line emission. The newly formed BLR clouds then traveled along a similar eccentric orbit (e ≈ 0.6). The Balmer decrement of the BLR increased by a factor of ∼4–5 as a result of secular changes in cloud density. The drop in density at late times allowed the production of He i and He ii emission. The mass of the black hole cannot be derived from the broad emission lines because the BLR is not virialized. Instead, we use the stellar properties of the host galaxy to estimate . The nucleus reached near or above its Eddington limit during the peak of the outburst. We discuss the nature of the changing-look AGN 1ES 1927+654 in the context of other tidal disruption events.

Sensitivity Enhancement of SAW Pressure Sensor Based on the Crystalline Direction

This work presents the sensitivity enhancement of AlN based surface acoustic wave (SAW) pressure sensor fabricated on the Si (100) wafer. Based on the theoretical analysis, a novel concept is proposed to improve pressure sensitivity with crystalline direction. The effect of wave propagation along < 100> and < 110> crystalline direction on pressure sensitivity of the SAW sensor has been studied by the finite element method. The simulation results indicate that the Si (100) based SAW sensor oriented in < 110> direction shown to possess high sensitivity compared to < 100> direction. The increase in sensitivity along the < 110> direction is due to a larger <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> (velocity sensitivity to strain coefficient) value that results in increased velocity and large frequency shift. Two SAW pressure sensors, PS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{&lt; 100&gt;}$ </tex-math></inline-formula> and PS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{&lt; 110&gt;}$ </tex-math></inline-formula> with wave propagation along < 100> and < 110> directions, respectively, have been fabricated on Si (100) wafer to verify the sensitivity enhancement concept. Both sensors have been tested for the pressure range from 0–2 MPa. The measured sensitivity for the PS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{&lt; 100&gt;}$ </tex-math></inline-formula> and PS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{&lt; 110&gt;}$ </tex-math></inline-formula> are obtained as 112.68 ppm/MPa and 203.83 ppm/MPa, respectively, Which is significantly improved by 80%. Additionally, the repeatability and linearity of PS <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{&lt; 110&gt;}$ </tex-math></inline-formula> have been measured and the deviation of the measured pressure sensitivity curve from the best linear fit is very small. The obtained results show that the developed sensor design has sufficiently high sensitivity with linear response and can be used for high pressure sensing applications.

Simulation Study of the Velocity Profile and Deflection Rate of Non-Newtonian Fluids in the Bend Part of the Pipe

As resource extraction moves deeper underground, backfill mining has received a lot of attention from the industry as a very promising mining method that can provide a safe workplace for workers. However, the safe and efficient transport of fill slurry through pipelines still needs more exploration, especially in the bend section. In order to investigate the flow characteristics and velocity evolution of the slurry in the bend section of the pipe, a three-dimensional (3D) pipe model was developed using the computational fluid dynamics software Fluent, and nine sets of two-factor, three-level simulations were performed. Furthermore, a single-factor analysis was presented to investigate the effects of the two main influencing factors on the shifting of the maximum velocity of the slurry towards the distal side in the bend section, respectively. Then, the response surface analysis method was applied to the two-factor analysis of the maximum velocity shift and the weights of the two influencing factors were specified.

The Double Detonation of a Double-degenerate System, from Type Ia Supernova Explosion to its Supernova Remnant

Type Ia supernovae (SNe) are believed to be caused by the thermonuclear explosion of a white dwarf (WD), but the nature of the progenitor system(s) is still unclear. Recent theoretical and observational developments have led to renewed interest in double-degenerate models, in particular the “helium-ignited violent merger” or “dynamically driven double-degenerate double-detonation” (D6). In this paper we take the output of an existing D6 SN model and carry it into the supernova remnant (SNR) phase up to 4000 yr after the explosion, past the time when all the ejecta have been shocked. Assuming a uniform ambient medium, we reveal specific signatures of the explosion mechanism and spatial variations intrinsic to the ejecta. The first detonation produces an ejecta tail visible at early times, while the second detonation leaves a central density peak in the ejecta that is visible at late times. The SNR shell is off-center at all times, because of an initial velocity shift due to binary motion. The companion WD produces a large conical shadow in the ejecta, visible in projection as a dark patch surrounded by a bright ring. This is a clear and long-lasting feature that is localized, and its impact on the observed morphology is dependent on the viewing angle of the SNR. These results offer a new way to diagnose the explosion mechanism and progenitor system using observations of a Type Ia SNR.

Physical properties of the molecular cloud, N4, in SS 433: Evidence for an interaction of molecular cloud with the jet from SS 433

Abstract We conducted observations and analyses of the molecular cloud, N4, which is located at ∼40 pc from SS 433 and the same line of sight as that of the radio shell, in 12CO(J = 1–0), 12CO(J = 3–2), 13CO(J = 3–2), and grand-state OH emissions. N4 has a strong gradient of the integrated intensity of 12CO(J = 1–0, 3–2) emission at the northern, eastern, and western edges. The main body of N4 also has a velocity gradient of ∼0.16 km s−1 (20″)−1. A velocity shift by up to 3 km s−1 from the systemic velocity at ∼49 km s−1 is detected at only the northwestern part of N4. The volume density of the molecular hydrogen gas and the kinematic temperature are estimated at eight local peaks of 12CO(J = 1–0) and 13CO(J = 3–2) emissions by the RADEX code. The calculated $n_{\rm (H_2)}$ is an order of 103 cm−3, and Tk ranges from ∼20 to ∼56 K. The mass of N4 is estimated to be ∼7300 M⊙. The thermal and turbulent pressures in N4 are estimated to be ∼105 K cm−3 and ∼107 K cm−3, respectively. The relation of the thermal and turbulent pressures in N4 tends to be similar to that of the molecular clouds in the Galactic plane. However, these values are higher than those in the typical molecular clouds in the Galactic plane. Several pieces of circumstantial evidence representing the physical properties of N4 and comparison with the data of infrared and X-ray radiation suggest that N4 is interacting with a jet from SS 433. However, no gamma-ray radiation is detected toward N4. Compared to the previous study, it is hard to detect the gamma-ray radiation by cosmic-ray proton origin due to the low sensitivity of the current gamma-ray observatories. No OH emission was detected toward N4 due to the low sensitivity of the observation and antenna beam dilution.

On the evolution of n-octane atomization characteristics using an air-assisted intermittent spray method

In this study, droplet size and velocity of an intermittent air-assisted n-octane spray were measured using a Phase Doppler Particle Analyzer, focusing on the effect of operating parameters on time-resolved droplet behavior and local gas flow characteristics. An electro-magnetically actuated air-assisted injector, which features internal gas-liquid premixing upstream and releasing through an annular nozzle, was used to generate intermittent sprays. The sampling time equalization method is employed to examine the time-resolved spray microscopic characteristics with various injection control parameters and spatial sampling positions. The droplet diameter range is found to be generally independent of air injection duration and sampling time while droplet velocity is correlated with these two parameters. A large air injection duration tends to accelerate droplets in the late spray period and leads to an increasing normalized gas flow velocity. Estimation of local gas flow turbulence intensity indicates a prominent radial sampling position dependence due to the rapid attenuation of the gas flow velocity away from the spray axis. A noteworthy finding for this intermittent air-assisted spray is that at 30 mm from the nozzle outlet, the zero point of droplet-gas mean slip velocity shifts toward the nozzle with sampling time. The time bin size employed to divide the sampling time has been proved to exert no influence on the statistical results of transient spray microscopic characteristics.

Calibration of a Computational Fluid Dynamics Methodology for the Simulation of Roughness Effects on Friction and Heat Transfer in Additive Manufactured Components

Abstract It is well known from the literature that surface roughness significantly affects friction and heat transfer. This is even more evident for additive manufactured (AM) components, which are taking an increasingly important role in the gas turbine field. However, the exploitation of numerical approaches to improve their design is hindered by the lack of dedicated correlations and computational fluid dynamics (CFD) models developed for such high roughness conditions. Usually, the AM components are simulated considering the surfaces as smooth or applying an equivalent sand-grain roughness (ks) that results in a velocity shift in the boundary layer. However, determining a priori the most appropriate value of ks is challenging, as dozens of correlations are available, returning scattered and uncertain results. A previous work proved how the CFD prediction of friction and heat transfer returns significant deviations, even exploiting the ks values obtained from experimental tests on the very same test case. That work also allowed identification of a promising CFD methodology based on friction and thermal corrections proposed by Aupoix from ONERA. The aim of this work is to further the assessment and calibration activity of the model, by analyzing additional experimental data of friction factor and Nusselt number from new test cases considering different geometries and flow conditions. The new coupons consisted of straight circular channels and wavy channels. This work represents a further step in the generation of a more validated and general methodology for the high-fidelity CFD analysis of AM components.

Response of Flow and Saltating Particle Characteristics to Bed Roughness and Particle Spatial Density

AbstractWith the goal to explore the effects of natural bed roughness on bedload transport, numerical simulations of flow and particle saltation are carried out with varying bed roughness and particle spatial density. A combination of Eulerian and Lagrangian point‐particle methods is applied to solve the equations of motion of the fluid and the particles within the large‐eddy simulation framework. Flows over smooth and rough beds with four particle densities are considered. As the bed roughness increases, there is a leftward shift of the double‐averaged streamwise velocity profiles against dimensionless vertical distance, which is scaled with the bed roughness height, an upward shift of the peak values of double‐averaged Reynolds stresses, and a fragmentation and disappearance of coherent structures in the form of high‐speed and low‐speed near‐bed streaks. These observations are consistent with those of previous studies. As the bed roughness increases, the mean resting time of saltating particles increases, however the particles' saltation length, velocity, and angular velocity decrease, while their saltation height remains almost unchanged. Saltation height, saltation length, particle angular velocity, and resting time exhibit linear, gamma, normal, and exponential distributions, respectively. Further, as the bed roughness increases, the kurtosis and skewness of some particle parameters vary, and the particle velocity shifts from a symmetrical normal to an asymmetrical gamma distribution.

An Atomic Spectral Survey of WASP-76b: Resolving Chemical Gradients and Asymmetries

Abstract Ultrahot Jupiters are gas giants that orbit so close to their host star that they are tidally locked, causing a permanent hot dayside and a cooler nightside. Signatures of their nonuniform atmospheres can be observed with high-resolution transit transmission spectroscopy by resolving time-dependent velocity shifts as the planet rotates and varying areas of the evening and morning terminator are probed. These asymmetric shifts were seen for the first time in iron absorption in WASP-76b. Here, we search for other atoms/ions in the planets transmission spectrum and study the asymmetries in their signals. We detect Li i, Na i, Mg i, Ca ii, V i, Cr i, Mn i, Fe i, Ni i, and Sr ii, and tentatively detect H i, K i, and Co i, of which V, Cr, Ni, Sr ii, and Co have not been reported before. We notably do not detect Ti or Al, even though these species should be readily observable, and hypothesize this could be due to condensation or cold trapping. We find that the observed signal asymmetries in the detected species can be explained in different ways. We find a relation between the expected condensation or ionization temperatures and the strength of the observed asymmetry, which could indicate rain-out or recombination on the nightside. However, we also find a dependence on the signal broadening, which could imply a two-zoned atmospheric model, in which the lower atmosphere is dominated by a day-to-night wind, while the upper atmosphere is dominated by a vertical wind or outflow. These observations provide a new level of modeling constraint and will aid our understanding of atmospheric dynamics in highly irradiated planets.

On Coherent and Stochastic Structures in Hydrodynamic Flows with a Velocity Shift

On Coherent and Stochastic Structures in Hydrodynamic Flows with a Velocity Shift

The puzzling story of flare inactive ultra fast rotating M dwarfs. II. Searching for radial velocity variations

ABSTRACT Observations made using TESS revealed a sample of low-mass stars which show a periodic modulation on a period &amp;lt;0.2 d. Surprisingly, many of these ultra fast rotating (UFR) stars showed no evidence of flare activity which would be expected from such rapidly rotating stars. We present results from a spectroscopic survey of UFRs using the Nordic Optical Telescope to search for radial velocity variations which could reveal evidence for binarity. Our sample of 29 sources have a photometric period between 0.1–0.2 d, cover spectral classes of M0-4V, and show no evidence for flares. We detect only one source with clear radial velocity shifts, with another two having Gaia RUWE values which suggests they are binaries. Further observations reveal the former star possibly contains a brown dwarf companion with a mass of M2 &amp;gt; 58 MJup and probability P(M2 &amp;lt; 90 MJup) = 50 per cent. There is no evidence for the companion in our spectra, strengthening the case for a brown dwarf companion. We also examine the folded TESS light curves of all our targets, finding at least two are eclipsing binaries and one which has been contaminated by a spatially nearby δ Sct star. We estimate that around 1/4 of our targets may have been contaminated by short period variable stars. However, the majority of our targets are consistent with being single, low mass stars whose variability is due to starspots. We outline the possible reasons why they are not flare active despite being such rapid rotators.

APEX at the QSO MUSEUM: molecular gas reservoirs associated with z ∼ 3 quasars and their link to the extended Ly α emission

ABSTRACT Cool gas (T∼104 K) traced by hydrogen Ly α emission is now routinely detected around z ∼ 3 quasars, but little is known about their molecular gas reservoirs. Here, we present an APEX spectroscopic survey of the CO(6-5), CO(7-6), and [C i](2-1) emission lines for nine quasars from the QSO MUSEUM survey, which have similar UV luminosities, but very diverse Ly α nebulae. These observations ($\lesssim ngle ~\rm rms~\rangle =2.6$ mJy in 300 km s−1) detected three CO(6-5) lines with 3.4≤ICO(6-5) ≤5.1 Jy km s−1, 620≤FWHM≤707 km s−1, and three [C i](2-1) lines with 2.3$\le I_{\rm [C{\small I}](2-1)} \le$15.7 Jy km s−1, 329≤FWHM≤943 km s−1. For the CO and [C i] detected sources, we constrain the molecular gas reservoirs to be $\rm M_{H_{2}} = (0.4-6.9) \times 10^{11}\, M_{\odot }$, while the non-detections imply $\rm M_{H_{2}} \lt 1.1\times 10^{11}\, M_{\odot }$. We compare our observations with the extended Ly α properties to understand the link between the cool and the molecular gas phases. We find large velocity shifts between the bulk of Ly α and the molecular gas systemic redshift in five sources (from ∼−400 to ∼+1200 km s−1). The sources with the largest shifts have the largest Ly α line widths in the sample, suggesting more turbulent gas conditions and/or large-scale inflows/outflows around these quasars. We also find that the brightest ($I_{\rm [C{\small I}](2-1)}=15.7\pm 3.7~\rm Jy~km~s^{-1}$) and the widest (FWHM∼900 km s−1) lines are detected for the smallest and dimmest Ly α nebulae. From this, we speculate that host galaxy obscuration can play an important role in reducing the ionizing and Ly α photons able to escape to halo scales, and/or that these systems are hosted by more massive haloes.

Osteocyte pericellular and perilacunar matrices as markers of bone–implant mechanical integrity

To develop durable bone healing strategies through improved control of bone repair, it is of critical importance to understand the mechanisms of bone mechanical integrity when in contact with biomaterials and implants. Bone mechanical integrity is defined here as the adaptation of structural properties of remodeled bone in regard to an applied mechanical loading. Accordingly, the authors present why future investigations in bone repair and regeneration should emphasize on the matrix surrounding the osteocytes. Osteocytes are mechanosensitive cells considered as the orchestrators of bone remodeling, which is the biological process involved in bone homeostasis. These bone cells are trapped in an interconnected porous network, the lacunocanalicular network, which is embedded in a bone mineralized extracellular matrix. As a consequence of an applied mechanical loading, the bone deformation results in the deformation of this lacunocanalicular network inducing a shift in interstitial fluid pressure and velocity, thus resulting in osteocyte stimulation. The material environment surrounding each osteocyte, the so called perilacunar and pericellular matrices properties, define its mechanosensitivity. While this mechanical stimulation pathway is well known, the laws used to predict bone remodeling are based on strains developing at a tissue scale, suggesting that these strains are related to the shift in fluid pressure and velocity at the lacunocanalicular scale. While this relationship has been validated through observation in healthy bone, the fluid behavior at the bone-implant interface is more complex. The presence of the implant modifies fluid behavior, so that for the same strain at a tissue scale, the shift in fluid pressure and velocity will be different than in a healthy bone tissue. In that context, new markers for bone mechanical integrity, considering fluid behavior, have to be defined. The viewpoint exposed by the authors indicates that the properties of the pericellular and the perilacunar matrices have to be systematically investigated and used as structural markers of fluid behavior in the course of bone biomaterial development.

Optical and near-infrared spectroscopy of Nova V2891 Cygni: evidence for shock-induced dust formation

ABSTRACT We present multi-epoch optical and near-infrared observations of the highly reddened, Fe ii class slow Nova V2891 Cygni. The observations span 15 months since its discovery. The initial rapid brightening from quiescence, and the presence of an ∼35-d long pre-maximum halt, is well documented. The evidence that the current outburst of V2891 Cyg has undergone several distinct episodes of mass ejection is seen through time-varying P Cygni profiles of the O i 7773 Å line. A highlight is the occurrence of a dust formation event centred around approximately +273 d, which coincides with a phase of coronal line emission. The dust mass is found to be $\sim\!{0.83{-}1.25} \times 10^{-10}\ \mathrm{M}_{\odot }$. There is strong evidence to suggest that the coronal lines are created by shock heating rather than by photoionization. The simultaneous occurrence of the dust and coronal lines (with varying velocity shifts) supports the possibility that dust formation is shock induced. Such a route for dust formation has not previously been seen in a nova, although the mechanism has been proposed for dust formation in some core-collapse supernovae. Analysis of the coronal lines indicates a gas mass and temperature of 8.35–8.42 × 10−7 M⊙ and ∼(4.8–9.1) × 105 K, respectively, and an overabundance of aluminium and silicon. A Case B analysis of the hydrogen lines yields a mass of the ionized gas of (8.60 ± 1.73) × 10−5 M⊙. The reddening and distance to the nova are estimated to be E(B − V) = 2.21 ± 0.15 and d = 5.50 kpc, respectively.

EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of ϵ Eridani with Photometry and Interferometry

Abstract The distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes ≲ 10 cm s−1, but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host ϵ Eridani, we separately used ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produced an activity model that reduced the rms scatter in RVs obtained with EXPRES from 4.72 to 1.98 m s−1. We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as allow the stellar inclination and orientation with respect to the debris disk to be definitively determined. This work shows that stellar surface maps obtained with high-cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter.

Photon energy and photon behavior discussions

Photons (Solar) are the main source of energy available on Earth and provide hope of clean energy in the future, photon energy has particle characteristics, and there is an inevitable connection between the wave behavior and the particle behavior of light, in-depth understanding and exploration are required. Based on the hypothesis of the strong interaction between electrons and protons to generate photons, the energy and behaviors of photons are discussed herein. By analyzing and calculating the photon speed, the negative photon speed was found to be in excellent agreement with the existing light speed constant. The Compton effect wavelength shift was analyzed and deduced considering the interaction of positive photons and atoms, and new conclusions are drawn, proposing the reason why X-rays are positive photons. Based on existing data, the observed estimation value of the negative photon velocity shift is 0.0295 ppm. From the interaction of the spin-charged particles, the relationship between the photon wavelength and its magnetic moment was calculated. In addition, we analyzed and calculated the characteristics of photon orbits, inferred the mechanism of atomic luminescence, and qualitatively explained the phenomenon of blackbody radiation. Based on the effect of charged spin photons and the electromagnetic potential field, we explain the reason for the simultaneous existence of reflection and refraction. The relationship between the incident angle and the reflectivity was analyzed, and refractive index formulas were derived to reasonably explain the characteristics of the X-ray refractive index. As a result, edge diffraction is considered a special case of refraction. By analyzing the fluctuation of the potential field inside the atom, the diffraction phenomenon of charged particles is described, and a particle explanation of the phenomenon of light waves and beat frequencies interference is provided. It is believed that the physical model of photon charging conforms to the existing physical laws. Photon energy is kinetic energy and is derived from the potential energy of electrons or protons.

Development of a tracking error prediction system for the CyberKnife Synchrony Respiratory Tracking System with use of support vector regression.

The accuracy of the CyberKnife Synchrony Respiratory Tracking System is dependent on the breathing pattern of a patient. Therefore, the tracking error in each patient must be determined. Support vector regression (SVR) can be used to easily identify the tracking error in each patient. This study aimed to develop a system with SVR that can predict tracking error according to a patient's respiratory waveform. Datasets of the respiratory waveforms of 93 patients were obtained. The feature variables were variation in respiration amplitude, tumor velocity, and phase shift between tumor and the chest wall, and the target variable was tracking error. A learning model was evaluated with tenfold cross-validation. We documented the difference between the predicted and actual tracking errors and assessed the correlation coefficient and coefficient of determination. The average difference and maximum difference between the actual and predicted tracking errors were 0.57 ± 0.63 mm and 2.1 mm, respectively. The correlation coefficient and coefficient of determination were 0.86 and 0.74, respectively. We developed a system for obtaining tracking error by using SVR. The accuracy of such a system is clinically useful. Moreover, the system can easily evaluate tracking error. We developed a system that can be used to predict the tracking error of SRTS in the CyberKnife Robotic Radiosurgery System using machine learning. The feature variables were the breathing parameters, and the target variable was the tracking error. We used support vector regression algorithm.

Quasar clustering at redshift 6

Context. Large-scale surveys over the last years have revealed about 300 quasi-stellar objects (QSOs) at redshifts above 6. Follow-up observations have identified surprising properties, such as the very high black hole (BH) masses, spatial correlations with surrounding cold gas of the host galaxy, and high CIV-MgII Velocity shifts. In particular, the discovery of luminous high-redshift quasars suggests that at least some BHs likely have high masses at birth and grow efficiently. Aims. Our aim is to quantify quasar pairs at high redshift for a large sample of objects. This provides a new key constraint on a combination of parameters related to the origin and assembly for the most massive BHs: formation efficiency and clustering, growth efficiency, and the relative contribution of BH mergers. Methods. We observed 116 spectroscopically confirmed QSOs around redshift 6 with the simultaneous seven-channel imager Gamma-ray Burst Optical/Near-infrared Detector in order to search for companions. Applying colour-colour cuts identical to those which led to the spectroscopically confirmed QSOs, we performed Le PHARE fits to the 26 best QSO pair candidates, and obtained spectroscopic observations for 11 of them. Results. We do not find any QSO pair with a companion brighter than M1450(AB) &lt; −26 mag within our 0.1–3.3 h−1 cMpc search radius, in contrast to the serendipitous findings in the redshift range 4–5. However, a small fraction of such pairs at this luminosity and redshift is consistent with indications from present-day cosmological-scale galaxy evolution models. In turn, the incidence of L- and T-type brown dwarfs, which occupy a similar colour space to z ∼ 6 QSOs, is higher than expected, by a factor of 5 and 20, respectively.

A comparison of crack propagation theories in viscoelastic materials

Crack propagation in viscoelastic materials cannot be understood with the use of classical fracture mechanics, which predicts no dependence on the speed of propagation, unless cohesive models like Barenblatt or Dugdale are introduced, as done by Knauss & Schapery first in the 1970s. However, there is another approach, suggested qualitatively by deGennes in 1996, and quantitatively by Persson and Brener in 2005, which attempts an energy (power) balance by considering viscoelastic dissipation in the bulk of the material. Here, we revisit the main results of the two theories and show that they lead to approximately the same scaling laws not just for the standard material, but also for power law materials (which have a continuous spectrum of relaxation times). Recent findings by Schapery have concluded that the shape of the cohesive law results essentially in a shift in velocity which depends both on cohesive law shape and viscoelastic properties. Therefore, the Persson-Brener cutoff radius in the integral of dissipation can be chosen to fit approximately the cohesive model results to match the shift of the reference velocity.