Negative Gradient Research Articles

Plasma potential shaping using end-electrodes in the Large Plasma Device

We perform experiments in the Large Plasma Device at the University of California, Los Angeles, studying how different end-electrode biasing schemes modify the radial potential profile in the machine. We impose biasing profiles of different polarities and gradient signs on a set of five concentric electrodes placed 12 m downstream from the plasma source. We find that imposing concave-down profiles (negative potential radial gradient) on the electrodes creates radial potential profiles halfway up the plasma column that are comparable to those imposed on the electrodes and a few electron temperature in height, regardless of the biasing polarity. On the other hand, imposing concave-up profiles (positive potential radial gradient) leads to non-monotonic radial potential profiles. This observation can be explained by the current drawn through the electrodes and the parallel plasma resistivity, highlighting their important role in controlling the rotation of plasma. Concave-down plasma potential profiles, obtained by drawing electrons on the axis, are predicted to drive azimuthal drift velocities that can approach significant fractions of the ion sound speed in the central region of the plasma column.

Using contrasts in horizontal P-wave reflectivity to map the base of the continental lithosphere: Results for the central and eastern U.S.

Vertical-incidence seismic reflection profiles generated from global phases for 16 earthquakes recorded by stations of the Transportable Array (TA) show distinctive patterns of P-wave reflectivity in the uppermost mantle beneath the central and eastern United States. The overall distribution of reflections identified objectively using the sign test statistic applied to bootstrapped stacks is consistent with a westward increase in depth of the lithosphere-asthenosphere boundary (LAB) from roughly 110 to 250 km that is marked within the lower lithosphere by piecewise continuous segments of elevated horizontal P-wave reflectivity. For some profiles, the onsets of zones of increased reflectivity closely match depths corresponding to the maximum negative S-wave velocity gradients found by surface-wave tomography, suggesting that P-wave reflectivity can be used to help characterize properties of the lower lithosphere. We suggest that the vertical change in horizontal reflectivity straddles the lithosphere-asthenosphere transition, encompassing a broad zone of layering caused by increased strain in the lower lithosphere as well as drag-induced flow in the asthenosphere. Some of the lines also show waveforms that fall within the depth range of arrivals identified as midlithospheric discontinuities (MLDs) in overlapping Sp receiver-function profiles. The reflection waveforms observed in the TA lines are mostly multicyclic with a mix of polarities indicating a layered transition, consistent with previous observations and model studies that show the breakup of single Sp waveforms into a series of less prominent, shorter-period P-wave reflections as the dominant frequency of incident energy is increased.

EDIG-CHANGES

Context. The kinematic information of the extraplanar diffuse ionized gas (eDIG) around galaxies provides clues to the origin of the gas. Aims. The eDIG-CHANGES project studies the physical and kinematic properties of the eDIG around the CHANG-ES sample of nearby edge-on disk galaxies. Methods. We use a novel multi-slit narrow-band spectroscopy technique to obtain the spatial distribution of the spectral properties of the ionized gas around NGC 891, which is often regarded as an analogue of the Milky Way. We developed specific data reduction procedures for the multi-slit narrow-band spectroscopy data taken with the MDM 2.4 m telescope. The data presented in this paper cover the Hα and [N II]λλ6548, 6583 Å emission lines. Results. The eDIG traced by the Hα and [N II] lines shows an obvious asymmetric morphology, being brighter in the northeastern part of the galactic disk and extending a few kiloparsecs above and below the disk. Global variations in the [N II]/Hα line ratio suggest additional heating mechanisms for the eDIG at large heights beyond photoionization. We also construct position-velocity (PV) diagrams of the eDIG based on our optical multi-slit spectroscopy data and compare them to similar PV diagrams constructed with the H I data. The dynamics of the two gas phases are generally consistent with each other. Modelling the rotation curves at different heights from the galactic mid-plane suggests a vertical negative gradient in turnover radius and maximum rotation velocity, with magnitudes of approximately 3 kpc kpc−1 and 22 − 25 km s−1 kpc−1, respectively. Conclusions. Our measured vertical gradients of the rotation curve parameters suggest significant differential rotation of the ionized gas in the halo, often referred to as the lagging eDIG. Systematic study of the lagging eDIG, using the multi-slit narrow-band spectroscopy technique developed in our eDIG-CHANGES project, will help us to better understand the dynamics of the ionized gas in the halo.

Direct Collapse Accretion Disks within Dark Matter Halos: Saturation of the Magnetorotational Instability and the Field Expulsion

We have used high-resolution zoom-in simulations of direct collapse to supermassive black hole (SMBH) seeds within dark mater halos in the presence of magnetic fields generated during the collapse, down to 10−5 pc or 2 au. We confirm an efficient amplification of magnetic field during collapse, the formation of a geometrically thick self-gravitating accretion disk inside 0.1 pc, and damping of fragmentation in the disk by the field. This disk differs profoundly from SMBH accretion disks. We find the following: (1) The accretion disk is subject to the magnetorotational instability, which further amplifies the field to near equipartition. No artificial seeding of the disk field has been used. (2) The equipartition toroidal field changes its polarity in the midplane. (3) The nonlinear Parker instability develops, accompanied by the vertical buckling of the field lines, which injects material above the disk, leading to an increase in the disk scale height. (4) With the Coriolis force producing a coherent helicity above the disk, the vertical poloidal field has been generated and amplified. (5) We estimate that the associated outflow will be most probably squashed by accretion. The resulting configuration consists of a magnetized disk with β ≳ 0.1 and its magnetosphere with β ≪ 1, where β = P th/P B is the ratio of thermal to magnetic energy density. (6) The disk is highly variable, due to feeding by variable accretion flow, and strong vortical motions are present. (7) Finally, the negative gradient of the total vertical stress drives an equatorial outflow sandwiched by an inward accretion flow.

Untangling the Role of Assortative Mating in Educational Reproduction in Twelve European Countries

In this study, we explore how educational differences in demographic behavior – in particular, mating patterns and fertility – mediate the intergenerational reproduction of educational inequality in twelve European countries. Although this research interest itself is not new, we contribute to this debate by adopting a prospective approach and scaling it to include multiple countries and cohorts. To this end, we leverage a series of complementary datasets and the inferential method developed by Song and Mare (2015) and advanced by Skopek and Leopold (2020) to estimate the components of a stylized educational reproduction model. We then employ a simple decomposition analysis to quantify the contributions of different pathways to prospective educational reproduction rates across educational backgrounds and explore the differences across cohorts and countries. We report several findings. Most notably, (1) the intergenerational reproduction of educational inequality persists in all twelve countries and is barely offset by small (and declining) negative educational gradients in fertility, (2) educational differences in selection into partnership are small and do not account for much inequality, and (3) the role of assortative mating, where present, is ambiguous because it both reinforces inequality via its effects on resources within the family and offsets it via its effects on fertility. * This article belongs to a special issue on “Changes in Educational Homogamy and Its Consequences”.

The damping and diffusion of atoms moving in a thermal electromagnetic background

The interaction between an atom and the quantized electromagnetic field depends on the position of the atom, leading to a force which is the negative gradient of this interaction. At zero temperature, the mean of this force vanishes, but it has a nonzero value for a thermal electromagnetic background. By applying the Heisenberg equations of motion and the Born–Markov approximation, we obtain the mean and correlation of the force, which show that the center-of-mass motion of the atom is damped and diffused. This approach can be easily extended to multi-level atoms, and it is shown that the damping force and diffusion coefficients are invariant under Galilean transformations. In principle, this effect can be utilized to determine the velocity of the laboratory relative to the thermal background.

Early coronary artery atherosclerosis in humans is associated with attenuated coronary retention of klotho

Abstract Background Vascular aging is a key feature of cardiovascular disease. α-klotho (klotho) is a protein inversely associated with aging and may contribute to vascular repair. Lower levels of systemic klotho have been identified in humans with features of early and advanced coronary atherosclerosis. It remains unknown if circulating klotho is present within human coronary circulation and whether cardiovascular klotho retention correlates with atherosclerosis. Purpose The current study aimed to assess the presence of klotho within coronary circulation compared to systemic circulation and hypothesized that net coronary klotho retention is attenuated in patients with early age-related features of coronary artery disease (CAD). Methods A total of 42 patients that underwent clinically indicated coronary angiogram for chest pain that had no obstructive CAD underwent intravascular ultrasound (IVUS) assessment were retrospectively examined. Virtual histology assessed coronary plaque characteristics. Blood samples simultaneously collected from the proximal aorta and coronary sinus were used for klotho detection using enzyme-linked immunosorbent assay. The net gradient of klotho across cardiovascular circulation was calculated by multiplying the arteriovenous klotho gradient by basal coronary blood flow. A net positive gradient indicated less cardiovascular klotho retention; a net negative gradient indicated greater cardiovascular klotho retention. Results Overall, participants were age 54±10 years old and 76% were female. There were overall higher levels of klotho within the coronary sinus (median 0.49 ng/mL [0.15; 1.69]) compared to systemic circulation (median 0.30 ng/mL [0.16; 1.14]). Participant groups were determined by those with positive (n = 20) or negative (n = 22) cardiovascular retention of klotho. Both groups were similar in age (56 ±2 vs. 51 ±2 years old, p = 0.080), gender (72% vs. 80% female, p = 0.580), and had similar occurrences of traditional cardiovascular comorbidities. Those with less cardiovascular klotho retention in the coronary vascular bed had significantly greater degree of non-obstructive coronary artery plaque (Gensini score 3.5 vs. 0, p < 0.001) and had higher percent plaque burden (46% [35; 53] vs. 34% [28; 46], p = 0.044) than those with greater cardiovascular klotho retention. Conclusions Patients with early coronary atherosclerosis may be characterized by attenuated retention of klotho within coronary circulation. Moreover, humans appear to have higher circulating klotho in coronary circulation than in systemic circulation. The current study may support a role for mechanism or potential therapeutic target for klotho in coronary atherosclerosis in humans.

Accelerometer-measured physical activity pattern in older patients with frailty and heart failure

Abstract Background Physical activity (PA) assessed by accelerometers represents a novel method to understand the PA profile of older patients with heart failure (HF). We hypothesized that PA level and pattern vary in HF patients across the spectrum of frailty status. Aim To report the duration, intensity and volume of PA in older patients with HF according to frailty status. Methods We recruited 150 HF patients≥65 years from a hospital-based HF clinic between March and October 2023. Frailty was assessed using the Short Physical Performance Battery (SPPB); patients with SPPB 10-12, 7-9, 4-6 and ≤3 was classified as robust, mildly, moderately and severely frail respectively. To evaluate PA profile, all patients wore a wrist accelerometer on their non-dominant hand for 7 days (24 hours/ day). PA parameters including average acceleration over 24 hours (proxy of volume of activity); time spent in inactive, light, moderate and vigorous intensity activities; intensity gradient (more negative gradient equates to poorer intensity profile) and time of most active continuous bouts of PA, were compared amongst frailty groups. Results 146 participants with good quality accelerometer data were included in the analysis; median age 80 (range 65-94 years), 65% male. Thirty-eight percent had heart failure with reduced ejection fraction (HFrEF); 21% had NYHA class III/IV symptoms; median NT-proBNP was 2040 ng/L (IQR = 1110 - 4930). Frail patients were more likely to be older with more comorbidities; they also had more severe HF symptoms and higher NT-proBNP. Frail patients had lower volume of PA compared to robust patients, evidenced by lower average acceleration (milligravity-mg) over 24 hours [20.4 (robust); 16.0 (mildly frail); 13.5 (moderately frail); 13.2 (severely frail), p<0.001]. PA intensity profile was poorer in frail patients compared to robust patients [median intensity gradient: -2.72 (robust); -2.92 (mildly frail); -3.00 (moderately frail); -3.07 (severely frail), p<0.001]. (Table 1) Frail patients spent more time inactive compared to robust patients [median time spent inactive (minutes): 654 (robust); 689 (mildly frail); 780 (moderately frail); 720 (severely frail), p<0.001]. The median time (minutes) spent in light [225 (robust); 190 (mildly frail); 164 (moderately frail); 159 (severely frail)] and moderate to vigorous activity [62 (robust), 23 (mildly frail), 15 (moderately frail) and 13 (severely frail), p<0.001] were significantly shorter in frail compared to robust patients. (Figure 1) The most active continuous bout of PA of patients across the frailty spectrum appeared to between 10 AM to 2 PM. Conclusion The duration, volume and intensity of PA was generally low in older patients with HF. Worse frailty status was associated with longer duration of physical inactivity, shorter duration of light, moderate or vigorous activity, poorer PA intensity profile and lower volume of PA.

Academic orientation and alcohol-related harm among adolescents

BackgroundThis study aimed to examine the social gradient in self-reported alcohol-related harm (ARH) among young alcohol consumers by including a largely overlooked group of adolescents. We also explored the extent to which such a gradient could be attributed to differential exposure or differential vulnerability to risk factors.MethodCross-sectional survey of upper-secondary students (n = 2996) in Sweden. Negative binomial regressions estimated the relationship between academic orientation (higher education preparatory; HEP, vocational; VP and introductory; IP) and ARH. To assess the contribution of explanatory factors, we estimated models that included risk factors such as heavy episodic drinking (HED).ResultsA graded association was observed between academic orientation and ARH, with more ARH among students in IP (IRR = 1.79) and VP (IRR = 1.43) than in HEP. Adjustments for risk factors attenuated the estimates by approximately half, but there was still 14% more ARH in VP and 50% more in IP than in HEP. The additive interaction test indicated a positive and significant interaction for students in VP who engaged in HED, versus students in HEP, who did not.ConclusionThe findings suggest a negative gradient in the association between academic orientation and ARH, where the students in IP experienced the highest levels of ARH. While differential exposure and vulnerability to HED account for a significant proportion of the excess risk among VP students, HED seems to be less important relative to other risk factors among IP students. More research is needed to identify the mechanisms underlying the elevated levels of ARH among the most disadvantaged group—students enrolled in IP.

Single-screw extrusion performance for LLDPE resin as a function of compression ratio

High-quality polyethylene film and sheet must be free of solid polymer fragments and degraded resin. Moreover, the products must be produced at high rates to minimize conversion costs. Thus, the extruder must produce a homogenous extrudate at the proper discharge temperature and pressure. The screw design and process operating parameters are key. A key screw design parameter is the compression ratio. This paper experimentally studies how the compression ratio affects a linear low-density polyethylene (LLDPE) resin extrusion process. A 2.8 compression ratio screw was optimal for LLDPE resin. Significant solid polymer fragments were observed in the extrudate for 2.8 to 3.6 compression ratio screws at 110 rpm and higher. For 2.0 and 2.4 compression ratio screws at less than 50 rpm, the internal pressures in the extruder were relatively low. At screw speeds 50 rpm and higher, the specific rates for all screws were higher than the calculated specific rotational rate, creating negative axial pressure gradients in the metering sections.

Impurity convection reversal caused by edge localized turbulence for generating a stationary edge radiative layer in the HL-2A tokamak

Abstract Effect of impurity on edge turbulence was investigated on the HL-2A tokamak by using Neon supersonic molecular beam injection (SMBI). For the first time, a stationary radiative layer accompanied by edge localized turbulence lasting more than 100ms is observed at the edge region ρ=0.7-0.9. This duration is much longer than the SMBI pulse length (1.2ms), indicating that the impurity diffusion is on the whole cancelled out by the impurity convection without spreading of the localized turbulence during this period. This implies that the impurity convection is reversed from positive to negative impurity density gradient region. This reversal could be explained by the parallel impurity compression mechanism. The observed turbulence is a broadband electrostatic turbulence (25-70 kHz) propagating in the electron diamagnetic drift direction with normalized poloidal wavenumber of 0.1≤ kθρs≤0.4. It has been found that the excitation of the edge localized turbulence strongly depends on the local collisionality. This feature is qualitatively predicted by the spectral multiscale gyrokinetic turbulence simulation, which suggests that the turbulence could be a dissipative trapped electron mode (DTEM). This experiment demonstrates that mutual interaction between externally injected impurity ions and edge turbulence can generate a stationary edge radiative layer and avoid impurity core accumulation. These results could provide a potential approach for the formation of a stable impurity radiative layer by impurity injection in tokamaks.

End Column Reverse Chromatography as a Novel Approach for Enhanced Separation: A Pilot Study.

Currently, the most popular technique in gas chromatography (GC) is the "temperature programming", where the temperature increases from the start of the injection. This leads to faster elution of analytes compared to isothermal methods. However, isothermal methods are considered optimal for separating compounds with similar retention times. Another interesting technique that provides higher resolution is the dynamic thermal gradient gas chromatography (TGGC), where separations are achieved as a decreasing thermal gradient. This gradually decreases the positive gas velocity. Nevertheless, it was proven that GC techniques with negative velocity gradients don't improve the resolution of compounds with nearly identical retention times. Optimizing a new GC approach to combine both the short time from positive temperature ramps programming, and the enhanced separation of the negative ramps of the TGGC, a model under the name of "end column reverse chromatography". The process simply consists of two steps, the first is a normal positive ramp from the start of the injection, the second step is a negative thermal ramp at a time that is around the retention time of the first eluting peak. This will decrease the solute velocity almost solely for the second compound leading to relatively enhanced separation. Optimized ECRC method increased the resolution of two isomers (trans and cis chlordane) from 1 (slightly overlapping) in case of temperature programming to 2.78 as shown in this study. This comes in expense of the width and intensity of the peaks, where the intensity decreased about 17% and 12% for cis and trans chlordane, and the peak width increased with 37% and 77% for the same compounds respectively. ECRC is a novel model for enhanced separation that comes with some drawbacks. It can be an alternative approach to get a fast GC method with enhanced separation for isomers.

Quasi-static and dynamic responses of gradient hexachiral auxetics: Experimental and numerical analysis

In the current paper, the mechanical responses of polymer gradient hexachiral auxetic metamaterials were experimentally and numerically investigated under quasi-static and intermediate strain rate loadings. Five gradient design strategies were explored, including uniform, positive, negative, center positive, and center negative gradients. The deformation/failure mechanism, Poisson's ratio, and energy absorption capability were experimentally analyzed, together with the effects of impact velocity and gradient distribution. Experimental results revealed that the gradient design can mitigate the shear deformation of hexachiral auxetics, which efficiently remain its negative Poisson's ratio effect under dynamic loading. Compare with the quasi-static loading, earlier failure of auxetics was observed under dynamic loads due to the strain rate and inertial effect, which diluted their negative Poisson's ratio effect and energy absorption capability. Among the designs, auxetics with negative gradient configurations showed the best energy absorption under dynamic loading. Numerical analysis further supported the experimental findings and provided insights into the influence of geometric parameters. It shows that thicker configurations and non-uniform node gradient series with coefficients of 1.15 (positive, center positive) and 0.87 (negative, center negative) provided optimal energy absorption under the dynamic loading. This work offers profound insights into enhanced performance mechanisms and provides avenues for optimizing structural design of auxetic metamaterials.

Olfactory-based powered descent guidance for Mars methane plume exploration in long-time-average wind environment

This paper investigates an olfactory-based powered descent guidance method that enable a lander to autonomously locate and target the vent source of any methane plume in long-time-average wind environment on Mars. The episodic methane plumes emanating from the Martian surface invite the possibility of direct access to the subsurface methane reservoir to acquire pristine organic materials. Constrained by the insufficient knowledge of the accurate plume vent location, Mars landers must infer the target location — the plume source — autonomously during the powered descent. However, existing powered descent guidance methods require the target location as a terminal constraint, rendering them ineffective in plume exploration missions. We propose an olfactory-based powered descent guidance method that could steer a lander to target the methane vent source by tracking the gradient of methane concentration in long-time-average wind environment, imposing sub-optimal fuel consumption. A novel olfactory navigation method based on tracking the negative logarithmic concentration gradient, and the corresponding gradient measurement method, is proposed. By implementing the negative logarithmic gradient field, gradient-dependent dynamic equations for the powered descending lander are proposed. The gradient-dependent equations provide a way to transform the original optimal guidance problem, which is non-convex and terminal-free, into a convex and terminal-fixed problem. A suboptimal guidance law, similar to E-guidance, is then derived by solving this problem. The proposed guidance could target the vent source of any methane plume in long-time-average wind environment, imposing modest fuel consumption by feeding back the concentration gradient. Numerical simulations illustrate that, in comparison to the terminal-fixed E-guidance and the open-loop fuel-optimal guidance, the lander imposes additional fuel consumption of 2.57% and 12.15% respectively, using the proposed guidance law.

A multiscale approach for network intrusion detection based on variance–covariance subspace distance and EQL v2

As an important network defense approach, network intrusion detection is mainly used to identify anomaly traffic behavior. However, dominant network intrusion detection approaches are now struggling to identify the complex and variable means of attack, leading to high false alarm rate. Additionally, the feature redundancy and class imbalance problem in the intrusion detection dataset also constrain the performance of detection methods. This paper proposes a multiscale intrusion detection approach based on variance–covariance subspace distance and Equalization Loss v2 (EQL v2). Firstly, the variance–covariance subspace distance is used for feature selection on the preprocessed dataset to determine a set of representative feature subsets that can effectively approximate the original feature space. Secondly, the loss function, EQL v2, is adopted to balance the positive and negative gradients, addressing the class imbalance problem. Finally, a pyramid depthwise separable convolution model is proposed to capture the multiscale information of the traffic, and the convolutional layer in the depthwise convolution is replaced with self-supervised predictive convolutional attention block to compensate for the performance loss caused by the parameter reduction. Extensive experiments demonstrated that the proposed approach exhibits better performance on the three datasets of NSL-KDD, UNSW_NB15, and CIC-IDS-2017, with accuracy rates of 99.19%, 97.81%, and 99.83%, respectively, effectively improve the intrusion detection performance.

Direct measurements of sediment geoacoustic properties in the New England Mud Patch and shelf breaka).

This paper reports on an original set of direct sound speed measurements collected with the acoustic coring system in the New England Mud Patch (NEMP) and shelf break area to the south. Cores collected within the NEMP show range-dependence of the mud with slower sound speed and lower attenuation on the west side. In the shelf break region, the highest sound speeds are observed between the 200- and 350-m isobaths. The depth-dependence of the mud layer in the NEMP includes a surficial layer with a negative sound speed gradient of 28 s-1. The remainder of the mud column has a weak positive sound speed gradient of 6.2 s-1 over an isovelocity layer. Comparison between in situ and ex situ sound speed measurements provides an assessment of the effects of sediment disturbance from gravity coring operations. Small differences in the upper 2.5 m were attributed to the changes in the geoacoustic properties caused by disturbance from the coring process. Below 2.5 m, the average difference is close to zero, suggesting that these sediments were minimally disturbed. Finally, an in situ measurement of shear speed was obtained near the depth of maximum penetration. The shear speed was well correlated with sound speed from approximately the same depth interval.

Relationships Between Upper-Plate Structure, Mantle Wedge Melting, and Fore-Arc Sliver Transport in the Nicaraguan Subduction Zone

Abstract This study images the base of the upper-plate lithosphere in the Nicaraguan subduction zone using common conversion point stacking of Sp phases and explores the relationships between deep upper-plate structure, subduction zone melting processes, and the arc-parallel transport of the Central American fore-arc sliver. We observe the negative velocity gradient associated with the upper-plate lithosphere–asthenosphere boundary in the Nicaraguan back-arc at depths of 60–80 km. However, the amplitude of the lithosphere–asthenosphere velocity gradient diminishes beneath the arc, consistent with a reduction in the shear-wave velocity of the deep upper-plate lithosphere. This zone lies above mantle wedge velocity anomalies which indicate upward-migrating partial melt, suggesting that ascending melt has altered and weakened the lithospheric mantle of the upper plate. In northwestern Nicaragua, the boundary of the Central American fore-arc sliver and the Caribbean plate, which is marked by a northeast decrease in geodetically measured arc-parallel surface velocities, lies above the northeast increase in the amplitude and localization of the lithosphere–asthenosphere velocity gradient. This correlation indicates that the kinematic margin of the Central American fore-arc sliver corresponds to a structural boundary that extends throughout the upper plate, and that is influenced by melt ascending from the mantle wedge.

The host of GRB 171205A in 3D

Long GRB hosts at z < 1 are usually low-mass, low-metallicity star-forming galaxies. Here we present the most detailed, spatially resolved study of the host of GRB 171205A so far, a grand-design barred spiral galaxy at z = 0.036. Our analysis includes MUSE integral field spectroscopy complemented with high-spatial-resolution UV/VIS HST imaging and CO(1−0) and H I 21 cm data. The GRB is located in a small star-forming region in a spiral arm of the galaxy at a deprojected distance of ∼8 kpc from the center. The galaxy shows a smooth negative metallicity gradient and the metallicity at the GRB site is half solar, slightly below the mean metallicity at the corresponding distance from the center. Star formation in this galaxy is concentrated in a few H II regions between 5 and 7 kpc from the center and at the end of the bar, inwards from the GRB region; however the H II region hosting the GRB is in the top 10% of the regions with the highest specific star-formation rate. The stellar population at the GRB site has a very young component (< 5 Myr) that contributes a significant part of the light. Ionized and molecular gas show only minor deviations at the end of the bar. A parallel study found an asymmetric H I distribution and some additional gas near the position of the GRB, which might explain the star-forming region of the GRB site. Our study shows that long GRBs can occur in many types of star-forming galaxies; however the actual GRB sites have consistently low metallicity, high star formation rates, and a young population. Furthermore, gas inflow or interactions triggering the star formation producing the GRB progenitor might not be evident in ionized or even molecular gas but only in H I.

Characterizing and predicting the partial slip subjected to variable gradients of velocity and pressure in eccentric micro-scale Taylor–Couette flows

In the context of eccentric micro-scale Taylor–Couette flow, variations in localized flow scales result in a non-uniform fluid–solid interface slip state, distinct from the typically studied uniform slip velocity distribution. This study introduces a boundary condition definition method aimed at characterizing partial slip states, complemented by a coupled iterative analysis system tailored to address this complexity. Key contributions include the development of a method for calculating the limiting shear stress, which considers local velocity gradients and pressures. Validation demonstrates that the locally derived slip state aligns more closely with Knudsen number distributions of local flow scales compared to traditional uniform slip models, and exhibits greater consistency with experimentally measured pressure distributions. Additionally, the study reveals that eccentric Taylor–Couette flow, characterized by significant variations in local flow scales and strong self-induced pressure effects, leads to complex distributions of local pressure, velocity gradients, and differences in local slip velocities. Specifically, the non-uniform distribution of local pressure gradients due to eccentricity results in partial slip occurring predominantly on the rotor in regions with positive pressure gradients, and on the stator in regions with negative pressure gradients. Furthermore, the variation in gap height exerts a greater influence on local slip compared to rotational speed and eccentricity ratio. Under certain conditions influenced by pressure gradients, the slip velocity on the rotor may exceed its tangential speed.

Diffusion model conditioning on gaussian mixture model and negative gaussian mixture gradient

Diffusion models (DMs) are a type of generative model that has had a significant impact on image synthesis and beyond.They can incorporate a wide variety of conditioning inputs—such as text or bounding boxes—to guide generation. In this work, we introduce a novel conditioning mechanism that applies Gaussian mixture models (GMMs) for feature conditioning, which helps steer the denoising process in DMs. Drawing on set theory, our comprehensive theoretical analysis reveals that the conditional latent distribution based on features differs markedly from that based on classes. Consequently, feature-based conditioning tends to generate fewer defects than class-based conditioning. Experiments are designed and carried out and the experimental results support our theoretical findings as well as effectiveness of proposed feature conditioning mechanism. Additionally, we propose a new gradient function named the Negative Gaussian Mixture Gradient (NGMG) and incorporate it into the training of diffusion models alongside an auxiliary classifier. We theoretically demonstrate that NGMG offers comparable advantages to the Wasserstein distance, serving as a more effective cost function when learning distributions supported by low-dimensional manifolds, especially in contrast to many likelihood-based cost functions, such as KL divergences.