We show, by comparing observations with theoretical models, that the observed Kuiper Belt size distribution is well matched by coagulation models, which start with an initial planetesimal population ...with radii of about 1 km, and subsequent collisional evolution. We find that the observed size distribution above R ~ 30 km is primordial, i.e., it has not been modified by collisional evolution over the age of the solar system, and that the size distribution below R ~ 30 km has been modified by collisions and that its slope is well matched by collisional evolution models that use published strength laws. We find that results from recent KBO occultation surveys and the observed KBO size distribution can be best matched by an initial planetesimal population that contained about equal mass per logarithmic mass bin in bodies ranging from 0.4 km to 4 km in radius.
We present photometry of four transits of the exoplanet WASP-4b, each with a precision of approximately 500 ppm and a time sampling of 40-60 s. We have used the data to refine the estimates of the ...system parameters and ephemerides. During two of the transits we observed a short-lived, low-amplitude anomaly that we interpret as the occultation of a starspot by the planet. We also found evidence for a pair of similar anomalies in previously published photometry. The recurrence of these anomalies suggests that the stellar rotation axis is nearly aligned with the orbital axis, or else the starspot would not have remained on the transit chord. By analyzing the timings of the anomalies we find the sky-projected stellar obliquity to be Delta *l = --1+14 -- 12 degrees. This result is consistent with (and more constraining than) a recent observation of the Rossiter-McLaughlin effect. It suggests that the planet migration mechanism preserved the initially low obliquity, or else that tidal evolution has realigned the system. Future applications of this method using data from the CoRoT and Kepler missions will allow spin-orbit alignment to be probed for many other exoplanets.
Protective materials and structures found in natural organisms may inspire new armors with improved resistance to penetration, flexibility, light weight, and other interesting properties such as ...transparency and breathability. All these attributes can be found in teleost fish scales, which are the most common types of scales in modern fish species. In this work, we have studied the structure and mechanics of fish scales from striped bass (Morone saxatilis). This scale is about 200–300 µm thick and consists of a hard outer bony layer supported by a softer cross‐ply of collagen fibrils. Perforation tests with a sharp needle indicated that a single fish scale provides a high resistance to penetration which is superior to polystyrene and polycarbonate, two engineering polymers that are typically used for light transparent packaging or protective equipment. Under puncture, the scale undergoes a sequence of two distinct failure events: First, the outer bony layer cracks following a well defined cross‐like pattern which generates four “flaps” of bony material. The deflection of the flaps by the needle is resisted by the collagen layer, which in biaxial tension acts as a retaining membrane. Remarkably this second stage of the penetration process is highly stable, so that an additional 50% penetration force is required to eventually puncture the collagen layer. The combination of a hard layer that can fail in a controlled fashion with a soft and extensible backing layer is the key to the resistance to penetration of individual scales.
Fish scales provide a high‐performance light‐weight, flexible protective system. We have shown that an individual scale performs better than polycarbonate against puncture by a sharp object. The scale displays well defined puncture mechanisms where the external bony layer cracks first in a well defined “cross” pattern, while the underlying collagen acts as a retaining membrane to resist puncture.
Introduction
Multielectrode mapping catheters improve the ability to map within the heterogeneous scar. A novel Octaray catheter with eight spines and 48 electrodes may further improve the speed and ...resolution of atrial mapping. The aims of this study were to (1) establish the Octaray's baseline mapping performance and electrogram (EGM) characteristics in healthy atria and to (2) determine its utility for identifying gaps in a swine model of atrial ablation lines.
Methods and Results
The right atria of eight healthy swine were mapped with Octaray and Pentaray catheters (Biosense Webster, Irvine, CA) before and after the creation of ablation lines with intentional gaps. Baseline mapping characteristics including EGM amplitude, duration, number of EGMs, and mapping time were compared. Postablation maps were created and EGM characteristics of continuous lines and gaps were correlated with pathology. Compared with Pentaray, the Octaray collected more EGMs per map (2178 ± 637 vs 1046 ± 238; P < 0.001) at a shorter mapping duration (3.2 ± 0.79 vs 6.9 ± 2.67 minutes; P < 0.001). In healthy atria, the Octaray recorded lower bipolar voltage amplitude (1.96 ± 1.83 mV vs 2.41 ± 1.92 mV; P < 0.001) while ablation gaps were characterized by higher voltage amplitude (1.24 ± 1.12 mV vs 1.04 ± 1.27 mV; P < 0.001). Ablation gaps were similarly identified by both catheters (P = 1.0). The frequency of “false gaps,” defined as intact ablation lines with increased voltage amplitude was more common with Pentaray (6 vs 2) and resulted from erroneous annotation of far‐field EGMs.
Conclusion
The Octaray increases the mapping speed and density compared with the Pentaray catheter. It is as sensitive for identifying ablation gaps and more specific for mapping intact ablation lines.
Abstract
We introduce a general debiasing Bayesian formalism to brightness-limited surveys of solar system objects that constrains the statistical distribution of a population’s physical ...characteristics such as size, albedo, heliocentric distance, or others to account for the survey detections and measured properties such as brightness. We reanalyze the Dark Energy Camera search for main-belt asteroids of Peña et al. and fit a smooth double power-law size to its size distribution. Using only detections with reliable distances and accurate orbital information, we find no evidence for a significant difference in size distribution between the inner, middle, and outer belts for objects between 0.1 and 1 km in diameter, with
q
2
= 2.27 ± 0.05 a good fit for the small-end slope. We show that the intrinsic number density of objects is consistent between these populations and is compatible with observational biases. As spectral classes are distributed unevenly throughout the main belt, these results support the ongoing collisional reprocessing of the asteroid belt for objects smaller than 5 km.
Absolute attitude estimation sensors provide high accuracy pointing capabilities to spacecraft, but as developed thus far, they constitute a large fraction of CubeSat mission's budget. We introduce ...SPE Lab Open Star Tracker (SOST), an ultra-low-cost solution that currently provides sub-arcminute precision at a frequency of 1 to 3 estimations per minute in the Lost-In-Space scenario. Our Star Tracker development rests on open source astronomy software, the Raspberry Pi 3 B+, and its camera. We developed a new algorithm to solve the Lost-In-Space problem that works by acquiring an image and comparing it with different stellar catalog segments. We tested our algorithm using images from working satellites. The functioning of our platform was evaluated by using night-sky pictures taken from ground. We also conducted environmental tests of our platform by using a thermal-vacuum chamber. We optimized the catalog segment separation by analyzing the execution time, success rate, precision, and power consumption of the full platform. SOST delivers a mean precision below 1-arcminute for the boresight direction. With a segment separation of 10°, the attitude estimation is found in the 97.3% of the cases with processing time under 20s. The success rate improves to 99.8% by using 5° as segments separation but processing time doubles. This platform is open and freely available to CubeSat researchers interested in further development or deployment.
The article examines the way in which the State was replaced in the municipalities that are drug trafficking routes on the border between Guatemala and Mexico, by an illicit regime that represents a ...particular type of narco-governmentality, which implements bio-political practices that have repercussions on the border security. Due to the institutional and financial weakness of the Guatemalan government, it has little presence on its borders. This is taken advantage of by local and transnational organized crime dedicated to cocaine trafficking, which has replaced the State and replicated its hierarchical form of control and power over the territory and its population, in order to generate a situation of narco-governmentality. In order to maintain power, they use biopolitical practices such as the use of extreme violence against other criminal groups and government security forces, which seek to put the sovereignty of their territory at risk. In addition, they apply a state of siege in their controlled territories, all in order to avoid arrest, ensure their survival, and maintain high levels of profit. As a result, the security of some border municipalities that are routes is very fragile. In this context, improving border security requires to move from a national security approach to one of citizen security.
Since 2000, the numbers of vacant housing units have increased dramatically in many parts of Mexico. Much of this has been tied to the liberalisation of the housing market where private homebuilders ...play an important role in the production of housing and the role of public sector is limited to the support of housing finance. Public debates concerning the regulation of private sector homebuilders as well as the practices and policies of government lending agencies have hinged on housing overproduction and vacancy rates in recent years, with the latter associated with social problems in many cities. This paper explicitly examines the relationship between vacancy rate and levels of property crime (burglaries) in Ciudad Juárez, Chihuahua, Mexico. Along with data from the Population and Housing Census, the State Public Security Office data for the 2008-2009 period on property crimes (burglary), were geocoded, mapped and aggregated to the census-tract level. The ordinary least square regression results show that there are significant local variations in the relationships between the risk of property crimes and the percentage of vacant housing units, commercial and service land use and residents who are male aged 15-24. The findings strongly link housing overproduction with vacancy rates and crime, and suggest that private sector homebuilders and the mortgage allocation system should be more strongly regulated in Mexico.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Guatemala has one of the highest firearm homicide rates and gun ownership per capita in the world. This paper discusses the extent to which it stands as a case to add to the routine activity ...hypothesis versus the fear hypothesis. Using a negative binomial regression model, this study tested the relationship between firearm possession and homicide rates in its municipalities in 2018. A new dataset at the municipal level on firearm possession and ownership for 2018 was obtained from DIGECAM. The data were obtained from the National Civil Police and the 2018 Population and Housing Census. The authors found empirical evidence stating that the absence of security, justice institutions, and regional subculture of violence leads the population to use firearms due to fear or perceived risk of self-protection.
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