24,178 research outputs found
Stereochemical properties of the OH molecule in combined electric and magnetic fields: analytic results
The stereochemical properties of the ultracold ground state OH molecule in
the presence of electric and magnetic fields are currently of considerable
interest. For example, relevant quantities such as molecular alignment and
orientation, calculated numerically by using large basis sets, have lately
appeared in the literature. In this work, based on our recent exact solution to
an effective eight-dimensional matrix Hamiltonian for the molecular ground
state, we present analytic expressions for the stereochemical properties of OH.
Our results require the solution of algebraic equations only, agree well with
the aforementioned fully numerical calculations, provide compact expressions
for simple field geometries, allow ready access to relatively unexplored
parameter space, and yield straightforwardly higher moments of the molecular
axis distribution.Comment: 8 pages, 9 figure
Online Movement Correlation of Wireless Sensor Nodes
Sensor nodes can autonomously form ad-hoc groups based on their common context. We propose a solution for grouping sensor nodes attached on the same vehicles on wheels. The nodes periodically receive the movement data from their neighbours and calculate the correlation coefficients over a time history. A high correlation coefficient implies that the nodes are moving together. We demonstrate the algorithm using two types of movement sensors: tilt switches and MEMS accelerometers. We place the nodes on two wirelessly controlled toy cars, and we observe in real-time the group membership via the LED colours of the nodes. In addition, a graphical user interface running on the base station shows the movement signals over a recent time history, the latest sampled data, the correlation between each two nodes and the group membership
Movement-based Group Awareness with Wireless Sensor Networks
We propose a method through which dynamic sensor nodes
determine that they move together, by communicating and correlating their movement information. We describe two possible solutions, one using inexpensive tilt switches, and another one using low-cost MEMS accelerometers. We implement a fast, incremental correlation algorithm,
with an execution time of 6ms, which can run on resource constrained devices. The tests with the implementation on real sensor nodes show that the method is reliable and distinguishes between joint and separate movements. In addition, we analyze the scalability from four different
perspectives: communication, energy, memory and execution speed. The solution using tilt switches proves to be simpler, cheaper and more energy efficient, while the accelerometer-based solution is more reliable, more
robust to sensor alignment problems and, potentially, more accurate by using extended features, such as speed and distance
X-ray polarization fluctuations induced by cloud eclipses in active galactic nuclei
Context: A fraction of active galactic nuclei (AGN) show dramatic X-ray
spectral changes on the day-to-week time scales associated with variation in
the line of sight of the cold absorber. Aims: We intend to model the
polarization fluctuations arising from an obscuration event, thereby offering a
method of determining whether flux variations are due to occultation or extreme
intrinsic emission variability. Methods: Undertaking 1 - 100 keV polarimetric
simulations with the Monte Carlo code STOKES, we simulated the journey of a
variety of cold gas clouds in front of an extended primary source. We varied
the hydrogen column density nH and size of the absorber, as well as the initial
polarization state of the emitting source, to cover a wide range of scenarios.
Results: For unpolarized primary fluxes, large (about 50deg) variations of the
polarization position angle psi are expected before and after an occultation
event, which is associated with very low residual polarization degrees (P lower
than 1 per cent). In the case of an emitting disk with intrinsic,
position-independent polarization, and for a given range of parameters, X-ray
eclipses significantly alter the observed polarization spectra, with most of
the variations seen in psi. Finally, non-uniformly polarized emitting regions
produce very distinctive polarization variations due to the successive covering
and uncovering of different portions of the disk. Plotted against time,
variations in P and psi form detectable P~Cygni type profiles that are
distinctive signatures of non-axisymmetric emission. Conclusions: Polarization
measurements are thus particularly adapted to distinguish between intrinsic
intensity fluctuations and external eclipsing events, constrain the geometry of
the covering medium, and test the hypothesis of non-uniformly emitting disks
predicted by general relativity.Comment: 8 pages, 5 figures. Accepted for publication in A&
Finite H2 concentrations in superfluid 4He
We have studied the solubility of molecular hydrogen in bulk liquid He at
zero temperature using the diffusion Monte Carlo method and realistic
interatomic potentials between the different species of the mixture. Around the
He equilibrium density, the H_2 molecules clusterize in liquid-like drops
blocking the existence of a uniform dilution. On the contrary, at higher
densities the cluster formation is less feasible and metastable dilute
solutions may exist.Comment: 2 pages, 2 eps figures, contribution to the LT22 Conferenc
Corporate Hierarchies and the Size of Nations: Theory and Evidence
Corporate organization varies within a country and across countries with country size. The paper starts by establishing some facts about corporate organization based on unique data of 660 Austrian and German corporations. The larger country (Germany) has larger firms with flatter more decentral corporate hierarchies compared to the smaller country (Austria). Firms in the larger country change their organization less fast than firms in the smaller country. Over time firms have been introducing less hierarchical organizations by delegating power to lower levels of the corporation. We develop a theory which explains these facts and which links these features to the trade environment that countries and firms face. We introduce firms with internal hierarchies in a Krugman (1980) model of trade. We show that international trade and the toughness of competition in international markets induce a power struggle in firms which eventually leads to decentralized corporate hierarchies. We offer econometric evidence which is consistent with the models predictions
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