264 research outputs found
From old wars to new wars and global terrorism
Even before 9/11 there were claims that the nature of war had changed
fundamentally. The 9/11 attacks created an urgent need to understand
contemporary wars and their relationship to older conventional and terrorist
wars, both of which exhibit remarkable regularities. The frequency-intensity
distribution of fatalities in "old wars", 1816-1980, is a power-law with
exponent 1.80. Global terrorist attacks, 1968-present, also follow a power-law
with exponent 1.71 for G7 countries and 2.5 for non-G7 countries. Here we
analyze two ongoing, high-profile wars on opposite sides of the globe -
Colombia and Iraq. Our analysis uses our own unique dataset for killings and
injuries in Colombia, plus publicly available data for civilians killed in
Iraq. We show strong evidence for power-law behavior within each war. Despite
substantial differences in contexts and data coverage, the power-law
coefficients for both wars are tending toward 2.5, which is a value
characteristic of non-G7 terrorism as opposed to old wars. We propose a
plausible yet analytically-solvable model of modern insurgent warfare, which
can explain these observations.Comment: For more information, please contact [email protected] or
[email protected]
Multirelational Organization of Large-scale Social Networks in an Online World
The capacity to collect fingerprints of individuals in online media has
revolutionized the way researchers explore human society. Social systems can be
seen as a non-linear superposition of a multitude of complex social networks,
where nodes represent individuals and links capture a variety of different
social relations. Much emphasis has been put on the network topology of social
interactions, however, the multi-dimensional nature of these interactions has
largely been ignored in empirical studies, mostly because of lack of data.
Here, for the first time, we analyze a complete, multi-relational, large social
network of a society consisting of the 300,000 odd players of a massive
multiplayer online game. We extract networks of six different types of
one-to-one interactions between the players. Three of them carry a positive
connotation (friendship, communication, trade), three a negative (enmity, armed
aggression, punishment). We first analyze these types of networks as separate
entities and find that negative interactions differ from positive interactions
by their lower reciprocity, weaker clustering and fatter-tail degree
distribution. We then proceed to explore how the inter-dependence of different
network types determines the organization of the social system. In particular
we study correlations and overlap between different types of links and
demonstrate the tendency of individuals to play different roles in different
networks. As a demonstration of the power of the approach we present the first
empirical large-scale verification of the long-standing structural balance
theory, by focusing on the specific multiplex network of friendship and enmity
relations.Comment: 7 pages, 5 figures, accepted for publication in PNA
An Applied Electromagnetics Course with a Conceiving-Designing-Implementing-Operating Approach in Engineering Education
This paper describes and discusses the implementation of a project-based undergraduate course on applied electromagnetics in electronics engineering with a conceiving-designing-implementing-operating (CDIO) approach involving active project-based learning (PBL). The course, which requires a combination of mathematical and physics concepts for its completion, allows students to understand the principles of electromagnetic transmission theory in wireless communication systems. This paper presents the course proposal, its project description, and results hinting at the relationship with the CDIO process. The proposed projects allow students to engage in core concepts such as complex vectors, Maxwell’s equations, boundary conditions, Poynting\u27s theorem, uniform plane waves, reflection and transmission of waves, waveguides, cavity resonators, and computer-assisted design. The proposed methodology results suggest that students lowered their perception of the difficulty of the course, and most students recognized a better learning process of the core concepts for this course. In addition, students’ final course grades showed an average improvement of approximately 6% compared with the final grades of other groups with different methodologies
Reducing Rydberg state dc polarizability by microwave dressing
We demonstrate reduction of the dc polarizability of Cesium atom Rydberg
states in a 77 K environment utilizing microwave field dressing. In particular
we reduce the polarizability of states which have resonances at
5.35 GHz to , suitable for interfacing Rydberg atoms to
superconducting resonators in a cryogenic environment. We measure the
polarizability of the Rydberg states using Magneto-Optical-Trap (MOT) loss
spectroscopy. Using an off-resonant radio-frequency (RF) dressing field
coupling and we demonstrate a reduction in dc
polarizability of the states over 80. Experimental findings
are in good agreement with a numerical model of the atom-dressing field system
developed using the Shirley-Floquet formalism. We also demonstrate that the dc
polarizability reduction is highly anisotropic, with near total nulling
possible when the dc and dressing fields are aligned, but only a factor of two
reduction in polarizability when the fields are orthogonal. These results may
aid in stabilizing Rydberg resonances against varying dc fields present near
surfaces, enabling advancement in the development of hybrid Rydberg atom -
superconducting resonator quantum gates
Nonparallel spatial stability of shallow water flow down an inclined plane of arbitrary slope
Roll waves are known to occur in the frictional flow of a thin layer of water down an inclined solid surface. For a layer of constant depth, the formation of these waves on a solid plane with small slope angle have been explained as a hydrodynamic instability occurring above a critical Froude number by analyzing the temporal stability of the constant velocity flow. Here we analyze the linear, spatial stability of the shallow-water flow down an inclined plane of arbitrary slope including the first order effects of the gradients of both the velocity and the water depth. For constant water depth (parallel case) we reproduce previous results of the temporal stability analysis. Then we apply the nonparallel stability formulation to the kinematic wave approximation of the shallow-water flow down an inclined plane of arbitrary slope and characterize, analytically, the frequency and the wavelength of the most unstable waves as a function of the Froude number, slope angle, velocity and velocity gradient. We find important qualitative differences with respect to the parallel (constant depth) case. These stability results are used to discuss the numerical solution to the nonlinear shallow-water flow equations for the dam-break problem on an inclined surface of arbitrary slope. A good agreement between the waves resulting from the numerical simulations and the predictions of the stability analysis is found
A Universal Model of Global Civil Unrest
Civil unrest is a powerful form of collective human dynamics, which has led
to major transitions of societies in modern history. The study of collective
human dynamics, including collective aggression, has been the focus of much
discussion in the context of modeling and identification of universal patterns
of behavior. In contrast, the possibility that civil unrest activities, across
countries and over long time periods, are governed by universal mechanisms has
not been explored. Here, we analyze records of civil unrest of 170 countries
during the period 1919-2008. We demonstrate that the distributions of the
number of unrest events per year are robustly reproduced by a nonlinear,
spatially extended dynamical model, which reflects the spread of civil disorder
between geographic regions connected through social and communication networks.
The results also expose the similarity between global social instability and
the dynamics of natural hazards and epidemics.Comment: 8 pages, 3 figure
Mefloquine Exposure Induces Cell Cycle Delay and Reveals Stage-Specific Expression of the pfmdr1 Gene
Drug-resistant Plasmodium falciparum malaria is a major public health problem. An elevated pfmdr1 gene copy number (CN) is known to decrease parasite sensitivity to the commonly used antimalarial mefloquine (MFQ). To understand the relationship between pfmdr1 CN and mefloquine resistance, we evaluated pfmdr1 transcript levels in three P. falciparum strains with different CNs in the presence and absence of MFQ. Parasite strains with multiple pfmdr1 gene copies exhibited higher relative transcript levels than single-copy parasites, and MFQ induced pfmdr1 expression above the levels without treatment in all three strains evaluated. Concomitant morphology analyses of the sampled cultures revealed that MFQ treatment of synchronized ring-stage parasites induced a delay in parasite maturation through the intraerythrocytic cycle. pfmdr1 expression peaks in the ring stage, and MFQ could be causing increased transcription by delaying parasite maturation. However, pretreatment with mefloquine did not affect the artemisinin in vitro half-maximal inhibitory concentration (IC50). These results suggest that MFQ-induced increases in pfmdr1 expression are the direct result of the maturation delay at the ring stage but that this change in expression does not affect the antimalarial activity of artemisinin
Physical complexity to model morphological changes at a natural channel bend
This study developed a two‐dimensional (2‐D) depth‐averaged model for morphological changes at natural bends by including a secondary flow correction. The model was tested in two laboratory‐scale events. A field study was further adopted to demonstrate the capability of the model in predicting bed deformation at natural bends. Further, a series of scenarios with different setups of sediment‐related parameters were tested to explore the possibility of a 2‐D model to simulate morphological changes at a natural bend, and to investigate how much physical complexity is needed for reliable modeling. The results suggest that a 2‐D depth‐averaged model can reconstruct the hydrodynamic and morphological features at a bend reasonably provided that the model addresses a secondary flow correction, and reasonably parameterize grain‐sizes within a channel in a pragmatic way. The factors, such as sediment transport formula and roughness height, have relatively less significance on the bed change pattern at a bend. The study reveals that the secondary flow effect and grain‐size parameterization should be given a first priority among other parameters when modeling bed deformation at a natural bend using a 2‐D model
Influence of age on the occurrence of adverse events in rheumatic patients at the onset of biological treatment : Data from the BIOBADASER III register
To assess whether age, at the beginning of biologic treatment, is associated with the time a first adverse event (AE) appears in patients with rheumatoid arthritis (RA), ankylosing spondylitis (AS), or psoriatic arthritis (PsA). All patients in the BIOBADASER registry diagnosed with RA, AS, and PsA, and classified as young ( 75 years old) at start of biological treatment were included. Factors associated with the appearance of a first AE using adjusted incidence rate ratios (IRR) (Poisson regression) were analyzed. Survival to first AE was studied by Kaplan-Meier analysis and hazard ratios (HR) by Cox regression. 2483 patients were included: 1126 RA, 680 PsA, and 677 AS. Age group stratification was as follows: 63 young, 2127 adults, 237 elderly, and 56 very elderly. Regression model revealed an increased probability of suffering a first AE at age 65 years or older [IRR elderly: 1.42 (CI95% 1.13-1.77)]. Other characteristics associated with AE were female gender, the use of DMARDs, including methotrexate, the presence of comorbidities, and the time of disease duration. Factors that had the greatest impact on survival over a first AE were age > 75 years [HR 1.50 (1.01-2.24)] and female gender [HR 1.42 (1.22-1.64)]. Age at the start of treatment and female gender are key factors associated with the appearance of a first AE with biologics. Other factors related to patient status and treatment were also associated with a first AE in rheumatic patients treated with biologics
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