50,680 research outputs found
Long-term impacts of tropical storms and earthquakes on human population growth in Haiti and the Dominican Republic
Since the 18th century, Haiti and the Dominican Republic have experienced similar natural forces, including earthquakes and tropical storms. These countries are two of the most prone of all Latin American and Caribbean countries to natural hazards events, while Haiti seems to be more vulnerable to natural forces. This article discusses to what extent geohazards have shaped both nation's demographic developments. The data show that neither atmospheric nor seismic forces that directly hit the territory of Haiti have significantly affected the country's population growth rates and spatial population densities. Conversely, since the 1950s more people were exposed to atmospheric hazards, in particular, in regions which historically experienced higher storm frequencies
Accurate measurement of gas volumes by liquid displacement
Mariotte bottle as liquid displacement device was used to measure gas volumes at flow rates that are far below threshold of wet test gas meters. Study of factors affecting amount of liquid displaced by gas flow was completed, and equations were derived which relate different variables
The Gravitational Wave Signature of Core-Collapse Supernovae
We review the ensemble of anticipated gravitational-wave (GW) emission
processes in stellar core collapse and postbounce core-collapse supernova
evolution. We discuss recent progress in the modeling of these processes and
summarize most recent GW signal estimates. In addition, we present new results
on the GW emission from postbounce convective overturn and protoneutron star
g-mode pulsations based on axisymmetric radiation-hydrodynamic calculations.
Galactic core-collapse supernovae are very rare events, but within 3-5 Mpc from
Earth, the rate jumps to 1 in ~2 years. Using the set of currently available
theoretical gravitational waveforms, we compute upper-limit optimal
signal-to-noise ratios based on current and advanced LIGO/GEO600/VIRGO noise
curves for the recent SN 2008bk which exploded at ~3.9 Mpc. While initial LIGOs
cannot detect GWs emitted by core-collapse events at such a distance, we find
that advanced LIGO-class detectors could put significant upper limits on the GW
emission strength for such events. We study the potential occurrence of the
various GW emission processes in particular supernova explosion scenarios and
argue that the GW signatures of neutrino-driven, magneto-rotational, and
acoustically-driven core-collapse SNe may be mutually exclusive. We suggest
that even initial LIGOs could distinguish these explosion mechanisms based on
the detection (or non-detection) of GWs from a galactic core-collapse
supernova.Comment: Topical Review, accepted for publication in CQG. 51 pages, 13
figures, a version of the article with high-resolution figures is available
from http://stellarcollapse.org/papers/Ott_SN_GW_review2008.pdf. Update:
Added section on core collapse simulations and the treatment of general
relativit
Triply-Periodic Smectics
Twist-grain-boundary phases in smectics are the geometrical analogs of the
Abrikosov flux lattice in superconductors. At large twist angles, the nonlinear
elasticity is important in evaluating their energetics. We analytically
construct the height function of a pi/2 twist-grain-boundary phase in smectic-A
liquid crystals, known as Schnerk's first surface. This construction, utilizing
elliptic functions, allows us to compute the energy of the structure
analytically. By identifying a set of heretofore unknown defects along the
pitch axis of the structure, we study the necessary topological structure of
grain boundaries at other angles, concluding that there exist a set of
privileged angles and that the \pi/2 and \pi/3 grain boundary structures are
particularly simple.Comment: 13 pages, 7 figure
Space shuttle lift-off dynamic model
Previously developed dynamic models for the calculation of lift-off dynamic response of the space shuttle vehicle can handle only response of the vehicle with eight holddown arms attached or with all holddown arms detached. The new model developed in the referenced report takes into account the transition period between holddown and lift-off by giving the model the ability to vary holddown point separation as a function of vehicle flexible body and rigid body motion. This report documents a study made to verify the new model's capability to simulate vehicle response at lift-off. To do this, a finite element model of the skirt is made and coupled to the free-free modes of the vehicle and cantilevered modes calculated and compared with the previously developed model. Results indicate that the new model will be able to predict accurate vehicle loads
Effects of Anticipation in Individually Motivated Behaviour on Control and Survival in a Multi-Agent Scenario with Resource Constraints
This is an open access article distributed under the Creative Commons Attribution License CC BY 3.0 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Self-organization and survival are inextricably bound to an agent’s ability to control and anticipate its environment. Here we assess both skills when multiple agents compete for a scarce resource. Drawing on insights from psychology, microsociology and control theory, we examine how different assumptions about the behaviour of an agent’s peers in the anticipation process affect subjective control and survival strategies. To quantify control and drive behaviour, we use the recently developed information-theoretic quantity of empowerment with the principle of empowerment maximization. In two experiments involving extensive simulations, we show that agents develop risk-seeking, risk-averse and mixed strategies, which correspond to greedy, parsimonious and mixed behaviour. Although the principle of empowerment maximization is highly generic, the emerging strategies are consistent with what one would expect from rational individuals with dedicated utility models. Our results support empowerment maximization as a universal drive for guided self-organization in collective agent systemsPeer reviewedFinal Published versio
Wideband Time-Domain Digital Backpropagation via Subband Processing and Deep Learning
We propose a low-complexity sub-banded DSP architecture for digital
backpropagation where the walk-off effect is compensated using simple delay
elements. For a simulated 96-Gbaud signal and 2500 km optical link, our method
achieves a 2.8 dB SNR improvement over linear equalization.Comment: 3 pages, 3 figur
Canonical Interacting Quantum Fields on Two-Dimensional De Sitter Space
We present the model on de Sitter space in the
canonical formulation. We discuss the role of the Noether theorem and we
provide explicit expressions for the energy-stress tensor of the interacting
model.Comment: minor correction
- …