Conducting assessments to understand the effects of changing environmental conditions on polar bear (Ursus maritimus) demography has become increasingly important to inform management and ...conservation. Here, we combined physical (2005–2007) and genetic (2017–2018) mark‐recapture with harvest recovery data (2005–2018) to estimate demographic rates of the Davis Strait polar bear subpopulation and examine the possible effects of climate, dynamic ice habitat, and prey resources on survival. Large sample sizes (e.g., 2,513 marked animals) allowed us to estimate temporal variation in annual survival rates using multistate mark‐recapture‐recovery models. We did not detect statistically significant effects of climate, ice habitat, and prey during the 13‐year study. Estimated total abundance in 2006 was 2,190, credible interval (CRI) 1,954, 2,454 and 1,944, CRI 1,593, 2,366 in 2018. Geometric mean population growth rate (0.99, 95% CRI 0.97, 1.01) indicated the subpopulation may have declined slightly between 2006 and 2018. However, we did not detect a declining trend in survival or substantial change in reproductive metrics over this period. Given forecasts of major environmental change we emphasize the need to review monitoring programs for this subpopulation.
Blends of polycaprolactone (PCL) and polyethylene terephthalate (PET) - both widely used biocompatible polymers – could have applications in long-term drug delivery. To avoid PCL degradation ...characteristic of hot extrusion of this blend, we utilize phase separation of PET during electrospinning of PCL-PET blends followed by heating to 120 °C during which the PCL component eliminates porosity. The resulting crystallized PET nanofiber follows the spatial arrangement of the initially deposited electrospun PCL-PET fibers. This increased the modulus of the PCL by 38% while elongation to break and ultimate tensile strength (UTS) remain unaffected. These sintered 25:75 PET-PCL blends maintained their mechanical properties at least three months in 37 °C PBS and >3 months in 37 °C DMSO. Differential scanning calorimetry and X-ray diffraction confirm that increased brittleness is caused by increases in PCL crystallinity. Controlled phase separation to achieve directed composite formation could utilize other polymers and optimized fiber deposition to catalyze further mechanical property improvements.
Display omitted
•Novel route for PET-PCL polyblend creation without degradation or copolymerization.•25:75 PET-PCL scaffolds sintered to full density at 120 °C for 4 h under vacuum.•Self-reinforcement by crystallized PET nanofibers induced by electrospinning.•Maintained mechanical properties up to 6 m in PBS and over 3 m in DMSO at 37 °C.•Crystallinity and Tm of PCL increased versus aging time.
In this paper, the method of changing the trajectories of hazardous asteroids with orbits known for some years to be on a possible collision course with the Earth is considered. The method relies on ...the use of small asteroids (asteroid-projectiles) directed at hazardous celestial bodies by giving the projectile a sufficiently small velocity impulse ensuring the Earth gravity assist. As a result, the asteroid-projectile vector can be controllably changed over a wide range. Apophis is considered as an example of the target asteroid. The technical feasibility of this method is discussed. It is noted that despite the potential use of this elegant method, its practical implementation requires further research and development.
The human neuronal cannabinoid receptor (CB1) is a G-protein-coupled receptor (GPCR) triggered by the psychoactive ingredients in marijuana, as well as endogenous cannabinoids produced in the brain. ...As with most GPCRs, the mechanism of CB1 activation is poorly understood. In this work, we have assessed the role of cysteine residues in CB1 ligand binding and activation, and demonstrate a method for mapping key determinants in CB1 structure and function. Through mutational analysis, we find that only two cysteines, C257 and C264, are required for high-level expression and receptor function. In addition, through cysteine reactivity studies, we find that a cysteine in transmembrane helix seven, C386 (C7.42), is reactive toward methanethiosulfonate (MTS) sulfhydryl labeling agents, and is thus solvent accessible. Interestingly, steric bulk introduced at this site, either through MTS labeling or by mutation, inhibits binding of the antagonist drug SR141716A (also known as Rimonabant or Accomplia), but does not affect the binding of the agonist CP55940. Our subsequent modeling studies suggest this effect is caused by steric clash of the modified C386 residue with the piperidine ring of SR141716A and/or disruption of an aromatic microdomain in the binding pocket. On the basis of these results, we hypothesize that bound SR141716A inhibits the ability of transmembrane helix 6 to move during formation of the functionally active receptor state.
The Defense Advanced Research Projects Agency (DARPA) Air Combat Evolution (ACE) program "seeks to increase trust in combat autonomy by using human–machine collaborative dogfighting as its challenge ...problem. This also serves as an entry point into complex human–machine collaboration" (https://www.darpa.mil/program/air-combat-evolution). To set the stage for ACE, the AlphaDogfight Trials program was created to explore whether artificial intelligence (AI) agents could effectively learn basic fighter maneuvers. DARPA contracted the Johns Hopkins University Applied Physics Laboratory (APL) to create an arena to host simulated dogfights- close-range aerial battles between fighter aircraft-where autonomous agents could be trained to defeat adversary aircraft. During the dogfight trials, AI agents competed against each other and the winner competed against a human pilot. By the end of the trials, the program demonstrated that AI agents could surpass the performance of human experts. APL was critical to the success of this program: the Lab created the simulation infrastructure, developed the adversary AI agents, and evaluated the competitors' AI solutions. This article details APL's role in advancing combat autonomy through this program.
Rings of debris in near-Earth space Barmin, I. V.; Dunham, D. W.; Kulagin, V. P. ...
Solar system research,
12/2014, Letnik:
48, Številka:
7
Journal Article
Recenzirano
The formation of space debris as an accumulation of small heavenly bodies in near-Earth space is considered. How debris can arise in near-Earth space is described. The accumulation of debris is shown ...to have a ring structure. The formation and spatial distribution of debris are statistically analyzed. A hypothesis for the formation of debris rings in near-Earth space is proposed.
The atmospheric detonation of a 17 m-asteroid above Chelyabinsk, Russia on 2013 February 15 shows that even small asteroids can cause extensive damage. Earth-based telescopes have found smaller ...harmless objects, such as 2008 TC3, a 4 m-asteroid that was discovered 20h before it exploded over northeastern Sudan (Jenniskens, 2009). 2008 TC3 remains the only asteroid discovered before it hit Earth because it approached Earth from the night side, where it was observed by large telescopes searching for near-Earth objects (NEO’s). The larger object that exploded over Chelyabinsk approached Earth from the day side, from too close to the Sun to be detected from Earth. A sizeable telescope in an orbit about the Sun-Earth L1 (SE-L1) libration point could find objects like the “Chelyabinsk” asteroid approaching approximately from the line of sight to the Sun about a day before Earth closest approach. Such a system would have the astrometric accuracy needed to determine the time and impact zone for a NEO on a collision course. This would give at least several hours, and usually 2–4 days, to take protective measures, rather than the approximately two-minute interval between the flash and shock wave arrival that occurred in Chelyabinsk. A perhaps even more important reason for providing warning of these events, even smaller harmless ones that explode high in the atmosphere with the force of an atomic bomb, is to prevent mistaking such an event for a nuclear attack that could trigger a devastating nuclear war. A concept using a space telescope similar to that needed for an SE-L1 monitoring satellite, is already conceived by the B612 Foundation, whose planned Sentinel Space Telescope could find nearly all 140 m and larger NEO’s, including those in orbits mostly inside the Earth’s orbit that are hard to find with Earth-based telescopes, from a Venus-like orbit (Lu, 2013). Few modifications would be needed to the Sentinel Space Telescope to operate in a SE-L1 orbit, 0.01 AU from Earth towards the Sun, to find most asteroids larger than about 5 meters that approach the Earth from the solar direction. The spacecraft would scan 165 square degrees of the sky around the Earth every hour, finding asteroids when they are brightest (small phase angle) as they approach Earth. We will undertake Monte Carlo studies to see what fraction of asteroids 5 m and larger approaching from the Sun might be found by such a mission, and how much warning time might typically be expected. Also, we will check the overall coverage for all Earth-approaching NEO’s, including ground-based observations and observations by the recently-launched NEOSSat, which may best fill any gaps in coverage between that provided by an SE-L1 telescope and ground-based surveys. Many of the objects as large as 50 m, like the one that created Meteor Crater in Arizona, will not be found by current NEO surveys, while they would usually be seen by this possible mission even if they approached from the direction of the Sun. We should give better warning for future “Bolts out of the blue.”
The stable inheritance of genetic material depends on accurate DNA partition. Plasmids serve as tractable model systems to study DNA segregation because they require only a DNA centromere, a ...centromere-binding protein and a force-generating ATPase. The centromeres of partition (par) systems typically consist of a tandem arrangement of direct repeats. The best-characterized par system contains a centromere-binding protein called ParR and an ATPase called ParM. In the first step of segregation, multiple ParR proteins interact with the centromere repeats to form a large nucleoprotein complex of unknown structure called the segrosome, which binds ParM filaments. pSK41 ParR binds a centromere consisting of multiple 20-base-pair (bp) tandem repeats to mediate both transcription autoregulation and segregation. Here we report the structure of the pSK41 segrosome revealed in the crystal structure of a ParR-DNA complex. In the crystals, the 20-mer tandem repeats stack pseudo-continuously to generate the full-length centromere with the ribbon-helix-helix (RHH) fold of ParR binding successive DNA repeats as dimer-of-dimers. Remarkably, the dimer-of-dimers assemble in a continuous protein super-helical array, wrapping the DNA about its positive convex surface to form a large segrosome with an open, solenoid-shaped structure, suggesting a mechanism for ParM capture and subsequent plasmid segregation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A plan to use the Sun–Earth L2 libration point as the primary hub for future human space activities in the Earth's neighborhood is described. It is expected that the Sun–Earth L2 point will be the ...location of choice for a number of large astronomical observatories over the next 20 years. These observatories will probably require some level of servicing and/or repair by astronauts. To provide human access to the L2 point, the early development of a reusable vehicle called a Deep-Space Shuttle (DSS) is proposed. The DSS, based in low-Earth orbit, would be able to transport astronauts to and from the L2 point in about 35 days (including a 5-day stay time at L2). The Sun–Earth L2 point is also useful as a staging node for missions to near-Earth asteroids and Mars. For instance, a reusable interplanetary transfer vehicle (ITV) stationed at the L2 point could be used for the round-trip journey. The ITV would use lunar gravity-assists and a perigee Δ
V maneuver to enter the desired interplanetary transfer trajectory. Just prior to the Earth-escape maneuver, a DSS “taxi” would transfer the crew to the ITV. A reverse procedure would be used to return the ITV to the libration point with the crew leaving the ITV just before the Earth-capture maneuver, and returning directly to Earth via an Apollo-style re-entry capsule. Using this technique, the L2-based ITV would save approximately
6.3
km/
s
in Δ
V cost compared with an ITV stationed in low-Earth orbit.
Motions of two tethered asteroids Vil’ke, V. G.; Chumachenko, E. N.; Dunham, D. W. ...
Cosmic research,
07/2013, Letnik:
51, Številka:
4
Journal Article
