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"Luther, R."
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Pounding imparts internal strength to rubble-piles
It is known that nearly all 0.2–10 km, thus frequent, asteroids are \"rubble-piles\". However, their internal structure remains largely uncertain, but a strength-stratification with a weaker exterior compared with the interior has been suggested for e.g., Bennu. We use projectile impact experiments to explore a possible formation mechanism for this strength stratification. High-speed video recordings show that material from crushed target boulders and projectile rapidly penetrates radially beneath the floor of the expanding cavity in a porous target. Similar features are known from terrestrial impact structures where it penetrates fractures opening in the basement. On a rubble-pile asteroid, repeated impacts over time in a coarse, porous and easily crushable material could lead to accumulation of fine-grained, and increasingly compacted, thus stronger, material at depth. Meanwhile, impact-induced seismic activity on the asteroid, causing granular convection, along with rotational centrifugal forces, could promote the segregation of finer material beneath coarser layers, potentially making this effect more pronounced at the poles.
Journal Article
Physical properties of asteroid Dimorphos as derived from the DART impact
On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, the natural satellite of the binary near-Earth asteroid (65803) Didymos. Numerical simulations of the impact provide a means to find the surface material properties and structures of the target that are consistent with the observed momentum deflection efficiency, ejecta cone geometry and ejected mass. Our simulation that best matches the observations indicates that Dimorphos is weak, with a cohesive strength of less than a few pascals, like asteroids (162173) Ryugu and (101955) Bennu. We find that the bulk density of Dimorphos
ρ
B
is lower than ~2,400 kg m
−
3
and that it has a low volume fraction of boulders (≲40 vol%) on the surface and in the shallow subsurface, which are consistent with data measured by the DART experiment. These findings suggest that Dimorphos is a rubble pile that might have formed through rotational mass shedding and reaccumulation from Didymos. Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater.
Numerical simulations of the DART impact on asteroid Didymos’s moon Dimorphos highlight its rubble-pile nature with a low bulk density and boulder volume fraction. These results indicate that Dimorphos formed from reaccumulated material shed from Didymos via rotation or impact.
Journal Article
Enhancing Seed Germination Test Classification for Pole Sitao (Vigna unguiculata (L.) Walp.) Using SSD MobileNet and Faster R-CNN Models
The classification of germinated pole sitao (Vigna unguiculata (L.) Walp.) seeds is important in seed germination tests. The automation of this process has been explored for different grain and legume seeds but is only limited to binary classification. This study aimed to develop a classifier system that can recognize three classes: normal, abnormal, and ungerminated. SSD MobileNet and Faster R-CNN models were trained to perform the classification. Both were trained using 1500 images of germinated seeds at fifth- and eighth-day observations. Each class had 500 images. The trained models were evaluated using 150 images per class. The SSD MobileNet model had an accuracy of 0.79 while the Faster R-CNN model had an accuracy of 0.75. The results showed that the average accuracies for the classes were significantly different from one another based on one-way ANOVA at a 95% confidence level with an F-critical value of 3.0159. The SSD MobileNet model outperformed the Faster R-CNN model in classifying pole sitao seeds, with improved precision in identifying abnormal and ungerminated seeds on the fifth day and normal and ungerminated seeds on the eighth day. The results confirm the potential of the SSD MobileNet model as a more reliable classifier in germination tests.
Journal Article
Free radical-producing myeloid-derived regulatory cells: potent activators and suppressors of lung inflammation and airway hyperresponsiveness
Levels of reactive free radicals are elevated in the airway during asthmatic exacerbations, but their roles in the pathophysiology of asthma remain unclear. We have identified subsets of myeloid-derived suppressor-like cells as key sources of nitric oxide and superoxide in the lungs of mice with evolving experimental allergic airway inflammation and established these cells as master regulators of the airway inflammatory response. The profiles of free radicals they produced depended on expression of inducible nitric oxide synthase (iNOS), arginase, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. These radicals controlled the pro- and anti-inflammatory potential of these cells, and also regulated the reciprocal pattern of their infiltration into the lung. The nitric oxide-producing cells were Ly-6C+Ly-6G− and they downmodulated T-cell activation, recruited Treg cells, and dramatically downregulated antigen-induced airway hyperresponsiveness. The superoxide-producing cells were Ly-6C−Ly-6G+ and they expressed proinflammatory activities, exacerbating airway hyperresponsiveness in a superoxide-dependent fashion. A smaller population of Ly-6C+Ly-6G+ cells also suppressed T-cell responses, but in an iNOS- and arginase-independent fashion. These regulatory myeloid cells represent important targets for asthma therapy.
Journal Article
Efficient recursive dynamics algorithms for operational-space control with application to legged locomotion
This paper presents new recursive dynamics algorithms that enable operational-space control of floating-base systems to be performed at faster rates. This type of control approach requires the computation of operational-space quantities and suffers from high computational order when these quantities are directly computed through the use of the mass matrix and Jacobian from the joint-space formulation. While many efforts have focused on efficient computation of the operational-space inertia matrix
Λ
, this paper provides a recursive algorithm to compute all quantities required for floating-base control of a tree-structure mechanism. This includes the first recursive algorithm to compute the dynamically consistent pseudoinverse of the Jacobian
J
¯
for a tree-structure system. This algorithm is extended to handle arbitrary contact constraints with the ground, which are often found in legged systems, and uses effective ground contact dynamics approximations to retain computational efficiency. The usefulness of the algorithm is demonstrated through application to control of a high-speed quadruped trot in simulation. Our contact-consistent algorithm demonstrates pitch and roll stabilization for a large dog-sized quadruped running at 3.6 m/s without any contact force sensing, and is shown to outperform a simpler Raibert-style posture controller. In addition, the operational-space control approach allows the dynamic effects of the swing legs to be effectively accounted for at this high speed.
Journal Article
Comparison of a Trial of Labor with an Elective Second Cesarean Section
In the United States and Canada, up to one quarter of all infants are delivered by cesarean section
1
–
5
; approximately half these procedures are performed only because the woman has had a previous cesarean section.
1
For years, allowing labor after a previous cesarean section was thought to be dangerous, and many clinicians recommended that any woman who had had a cesarean section should deliver all subsequent babies by cesarean section. However, others have questioned the necessity for elective cesarean section in many such cases and have considered a trial of labor after a previous cesarean section a reasonable strategy. . . .
Journal Article
Ziconotide, a new n-type calcium channel blocker, administered intrathecally for acute postoperative pain
Background and Objectives: Voltage-sensitive calcium channel conductance is essential for the nervous system to signal a painful event. However, intrathecal administration of L-type calcium channel blockers does not provide analgesia. The present investigation was designed to assess the safety and analgesic efficacy of ziconotide, a new N-type calcium channel blocker, when administered intrathecally to patients with acute postoperative pain.
Methods: This randomized, double-blind, pilot study included patients undergoing elective total abdominal hysterectomy, radical prostatectomy, or total hip replacement. After intrathecal injection of local anesthetic and before surgical incision, a continuous intrathecal infusion of either placebo or 1 of 2 doses of ziconotide (0.7 μg/h or 7.0 μg/h) was started and continued for 48 to 72 hours postoperatively. Primary and secondary efficacy variables were the mean daily patient controlled analgesia (PCA) morphine equivalent consumption and visual analog pain intensity (VASPI) scores, respectively.
Results: Thirty patients received study drug; 26 were evaluable for efficacy. Mean daily PCA morphine equivalent consumption was less in patients receiving ziconotide than in placebo-treated patients, and the difference was statistically significant between 24 and 48 hours (
P = .040). VASPI scores during the first 8 hours postoperatively were markedly lower in ziconotide-treated than in placebo-treated patients. In 4 of 6 patients receiving the high-dose of ziconotide (7 μg/h), adverse events, such as dizziness, blurred vision, nystagmus, and sedation contributed to study drug being discontinued after 24 hours. After ziconotide discontinuation, these symptoms resolved.
Conclusions: Ziconotide showed analgesic activity, as shown by decreased PCA morphine equivalent consumption and lower VASPI scores. Because of a favorable trend of decreased morphine consumption with an acceptable side-effect profile in the low-dose ziconotide group, 0.7 μg/h may be closer to the ideal dose than 7 μg/h. Large-scale studies are required to clarify this issue.
Reg Anesth Pain Med 2000;25:274–278.
Journal Article
Intelligent Control of High-Speed Turning in a Quadruped
Understanding and implementing the control mechanisms that animals use to robustly negotiate a variety of terrains at high speed remains an unsolved problem. Previous research has resulted in control of quadruped running over a range of low speeds or narrowly around a single high speed. Control over a range of both low and high speeds is difficult because a quadruped system is significantly more responsive at high speeds than at low speeds, and because the proportional-derivative style controllers used by many of the previous researchers are only effective locally around the single speed and turning rate at which the controller was tuned. This work presents a fuzzy control strategy that manages the complex coupling between the multiple system inputs and outputs to successfully execute high-speed turns over a range of speeds and turning rates. The resulting control system stabilizes a 3D quadruped trot up to 4 m/s and turning up to 30 deg/s, on a quadruped system with articulated legs and practical leg mass properties in a simulation environment with realistic friction coefficients and system losses.
Journal Article
Rapid convergence to an equilibrium state in kleptoparasitic populations
Previous papers have modelled the behaviour of populations which are subject to kleptoparasitism, and found those ecological situations in which kleptoparasitism should occur. Individuals were considered to be in one of several states, and an equilibrium distribution for the population was found. It was then assumed, for analytical purposes but without proof, that the population was actually in that equilibrium. In this paper, we show that the equilibrium is a stable one, and that it is reached in a relatively short time for all reasonable values of the ecological parameters. Thus, a population may be expected to spend most of the time in equilibrium, and this assumption of these previous works is justified.
Journal Article