RESUMEN
When the OSIRIS-REx spacecraft pressed its sample collection mechanism into the surface of Bennu, it provided a direct test of the poorly understood near-subsurface physical properties of rubble-pile asteroids, which consist of rock fragments at rest in microgravity. Here, we find that the forces measured by the spacecraft are best modeled as a granular bed with near-zero cohesion that is half as dense as the bulk asteroid. The low gravity of a small rubble-pile asteroid such as Bennu effectively weakens its near subsurface by not compressing the upper layers, thereby minimizing the influence of interparticle cohesion on surface geology. The underdensity and weak near subsurface should be global properties of Bennu and not localized to the contact point.
RESUMEN
Spin off events and impacts can eject boulders from an asteroid surface and rubble pile asteroids can accumulate from debris following a collision between large asteroids. These processes produce a population of gravitational bound objects in orbit that can impact an asteroid surface at low velocity and with a distribution of impact angles. We present laboratory experiments of low velocity spherical projectiles into a fine granular medium, sand. We delineate velocity and impact angles giving ricochets, those giving projectiles that roll-out from the impact crater and those that stop within their impact crater. With high speed camera images and fluorescent markers on the projectiles we track spin and projectile trajectories during impact. We find that the projectile only reaches a rolling without slipping condition well after the marble has reached peak penetration depth. The required friction coefficient during the penetration phase of impact is 4-5 times lower than that of the sand suggesting that the sand is fluidized near the projectile surface during penetration. We find that the critical grazing impact critical angle dividing ricochets from roll-outs, increases with increasing impact velocity. The critical angles for ricochet and for roll-out as a function of velocity can be matched by an empirical model during the rebound phase that balances a lift force against gravity. We estimate constraints on projectile radius, velocity and impact angle that would allow projectiles on asteroids to ricochet or roll away from impact, finally coming to rest distant from their initial impact sites.
RESUMEN
CONTEXT: Dietary supplement manufacturers claim cutaneous anti-aging properties for their products; however, research supporting these claims remains sparse. OBJECTIVES: The study intended to determine if a correlation existed between the effects of a collagen dietary supplement and changes associated with skin aging. DESIGN: The study was a 12-week, double-blind, placebo-controlled trial. SETTING: The study took place at a clinical facility specializing in dermatological testing that could perform biophysical, instrumental analysis on the effects of proprietary supplement on human skin. PARTICIPANTS: Participants were 128 females, aged 39-59 (50.57 ± 5.55). INTERVENTION: Participants were randomly assigned to an intervention or a placebo. The intervention consisted of twice daily oral administration of a supplement containing 500 mg BioCell Collagen, a chicken sternal cartilage derived dietary ingredient composed of a naturally-occurring matrix of hydrolyzed collagen type-II (≥300 mg), chondroitin sulfate (≥100 mg), hyaluronic acid (≥50 mg). OUTCOME MEASURES: The primary parameters included transepidermal water loss, viscoelasticity, hydration, (indirect) collagen content, chromophore (melanin) content and hemoglobin level, and photographic analysis. An expert visually graded participants' skin to determine the intervention's efficacy, measuring facial lines and wrinkles, crow's feet lines and wrinkles, skin texture and smoothness, and skin tone. The presence of erythema and/or dryness determined tolerance. Secondary outcome measures were tolerance and incidence of adverse events, and the participant's perception of the supplement's value. RESULTS: For the 113 participants completing the study, the dietary supplementation compared to a placebo: (1) significantly reduced facial lines and wrinkles (P = .019) and crow's feet lines and wrinkles (P = .05), (2) increased skin elasticity (P = .008) and cutaneous collagen content (P < .001) by 12%, (3) improved indicators associated with a more youthful skin appearance based on visual grading and wrinkle width (P = .046), and (4) decreased skin dryness and erythema. No difference existed between the supplement and the placebo for skin-surface water content or retention. The supplement was well tolerated, with no reported adverse reactions. CONCLUSIONS: Dietary supplementation with chicken, sternal cartilage extract supports the accumulation of types-I/III collagen in skin to promote increased elasticity and reduced skin wrinkling.
Asunto(s)
Pollos , Colágeno Tipo II/administración & dosificación , Cartílago Costal/química , Epidermis/efectos de los fármacos , Envejecimiento de la Piel/efectos de los fármacos , Esternón/química , Adulto , Animales , Colágeno Tipo II/farmacología , Método Doble Ciego , Cara/irrigación sanguínea , Femenino , Humanos , Persona de Mediana Edad , Resultado del TratamientoRESUMEN
We consider an impact on an asteroid that is energetic enough to cause resurfacing by seismic reverberation and just below the catastrophic disruption threshold, assuming that seismic waves are not rapidly attenuated. In asteroids with diameter less than 1 km we identify a regime where rare energetic impactors can excite seismic waves with frequencies near those of the asteroid's slowest normal modes. In this regime, the distribution of seismic reverberation is not evenly distributed across the body surface. With mass-spring model elastic simulations, we model impact excitation of seismic waves with a force pulse exerted on the surface and using three different asteroid shape models. The simulations exhibit antipodal focusing and normal mode excitation. If the impulse excited vibrational energy is long lasting, vibrations are highest at impact point, its antipode and at high surface elevations such as an equatorial ridge. A near equatorial impact launches a seismic impulse on a non-spherical body that can be focused on two additional points on an the equatorial ridge. We explore simple flow models for the morphology of vibration induced surface slumping. We find that the initial seismic pulse is unlikely to cause large shape changes. Long lasting seismic reverberation on Bennu caused by a near equatorial impact could have raised the height of its equatorial ridge by a few meters and raised two peaks on it, one near impact site and the other near its antipode.
RESUMEN
Skin aging and its clinical manifestation is associated with altered molecular metabolism in the extracellular matrix of the dermis. In a pilot open-label study, we investigated the effect of a dietary supplement, BioCell Collagen(®) (BCC), which contains a naturally occurring matrix of hydrolyzed collagen type II and low-molecular-weight hyaluronic acid and chondroitin sulfate, in 26 healthy females who displayed visible signs of natural and photoaging in the face. Daily supplementation with 1 g of BCC for 12 weeks led to a significant reduction of skin dryness/scaling (76%, P = 0.002) and global lines/wrinkles (13.2%, P = 0.028) as measured by visual/tactile score. Additionally, a significant increase in the content of hemoglobin (17.7%, P = 0.018) and collagen (6.3%, P = 0.002) in the skin dermis was observed after 6 weeks of supplementation. At the end of the study, the increase in hemoglobin remained significant (15%, P = 0.008), while the increase in collagen content was maintained, but the difference from baseline was not significant (3.5%, P = 0.134). This study provides preliminary data suggesting that dietary supplementation with BCC elicits several physiological events which can be harnessed to counteract natural photoaging processes to reduce visible aging signs in the human face. A controlled study is necessary to verify these observations.