27,802 research outputs found
A laser tracking dynamic robot metrology instrument
Research work over several years has resulted in the development of a laser tracking instrument capable of dynamic 3-D measurements of robot end-effector trajectories. The instrument characteristics and experiments to measure the static and dynamic performance of a robot in an industrial manufacturing environment are described. The use of this technology for space applications is examined
A Link Between the Semi-Major Axis of Extrasolar Gas Giant Planets and Stellar Metallicity
The fact that most extrasolar planets found to date are orbiting metal-rich
stars lends credence to the core accretion mechanism of gas giant planet
formation over its competitor, the disc instability mechanism. However, the
core accretion mechanism is not refined to the point of explaining orbital
parameters such as their unexpected semi-major axes and eccentricities. We
propose a model, which correlates the metallicity of the host star with the
original semi-major axis of its most massive planet, prior to migration,
considering that the core accretion scenario governs giant gas planet
formation. The model predicts that the optimum regions for planetary formation
shift inward as stellar metallicity decreases, providing an explanation for the
observed absence of long period planets in metal-poor stars. We compare our
predictions with the available data on extrasolar planets for stars with masses
similar to the mass of the Sun. A fitting procedure produces an estimate of
what we define as the Zero Age Planetary Orbit (ZAPO) curve as a function of
the metallicity of the star. The model also hints that the lack of planets
circling metal-poor stars may be partly caused by an enhanced destruction
probability during the migration process, since the planets lie initially
closer to the central stars.Comment: Nature of the replacement: According to recent simulations, the
temperature profile, T, is more adequately reproduced by beta = 1 rather than
beta = 2. We have introduced a distance scale factor that solves the very
fast drop of T for low metallicity and introduces naturally the inferior
distance limit of our ZAPO. Under this modification all the fitting process
was altere
On the Use of Historical Bathymetric Data to Determine Changes in Bathymetry: An Analysis of Errors and Application to Great Bay Estuary, NH
The depth measurements that are incorporated into bathymetric charts have associated errors with magnitudes depending on the survey circumstances and applied techniques. For this reason, combining and comparing depth measurements collected over many years with different techniques and standards is a difficult task which must be done with great caution. In this study we have developed an approach for comparing historical bathymetric surveys. Our methodology uses Monte Carlo modelling to account for the random error components inherited in the data due to positioning and depth measurement uncertainties
The final COS-B database: In-flight calibration of instrumental parameters
A method for the determination of temporal variation of sensitivity is designed to find a set of parameters which lead to maximum consistency between the intensities derived from different observation periods. This method is briefly described and the resulting sensitivity and background variations presented
Rational Trust Modeling
Trust models are widely used in various computer science disciplines. The
main purpose of a trust model is to continuously measure trustworthiness of a
set of entities based on their behaviors. In this article, the novel notion of
"rational trust modeling" is introduced by bridging trust management and game
theory. Note that trust models/reputation systems have been used in game theory
(e.g., repeated games) for a long time, however, game theory has not been
utilized in the process of trust model construction; this is where the novelty
of our approach comes from. In our proposed setting, the designer of a trust
model assumes that the players who intend to utilize the model are
rational/selfish, i.e., they decide to become trustworthy or untrustworthy
based on the utility that they can gain. In other words, the players are
incentivized (or penalized) by the model itself to act properly. The problem of
trust management can be then approached by game theoretical analyses and
solution concepts such as Nash equilibrium. Although rationality might be
built-in in some existing trust models, we intend to formalize the notion of
rational trust modeling from the designer's perspective. This approach will
result in two fascinating outcomes. First of all, the designer of a trust model
can incentivise trustworthiness in the first place by incorporating proper
parameters into the trust function, which can be later utilized among selfish
players in strategic trust-based interactions (e.g., e-commerce scenarios).
Furthermore, using a rational trust model, we can prevent many well-known
attacks on trust models. These two prominent properties also help us to predict
behavior of the players in subsequent steps by game theoretical analyses
Investigating prostate cancer tumour-stroma interactions - clinical and biological insights from an evolutionary game
BACKGROUND: Tumours are made up of a mixed population of different types of cells that include normal structures as well as ones associated with the malignancy, and there are multiple interactions between the malignant cells and the local microenvironment. These intercellular interactions, modulated by the microenvironment, effect tumour progression and represent a largely under appreciated therapeutic target. We use observations of primary tumor biology from prostate cancer to extrapolate a mathematical model: specifically; it has been observed that in prostate cancer three disparate cellular outcomes predominate: (i) the tumour remains well differentiated and clinically indolent - in this case the local stromal cells may act to restrain the growth of the cancer; (ii) early in its genesis the tumour acquires a highly malignant phenotype, growing rapidly and displacing the original stromal population (often referred to as small cell prostate cancer) - these less common aggressive tumours are relatively independent of the local microenvironment; and, (iii) the tumour co-opts the local stroma - taking on a classic stromagenic phenotype where interactions with the local microenvironment are critical to the cancer growth. METHODS: We present an evolutionary game theoretical construct that models the influence of tumour-stroma interactions in driving these outcomes. We consider three characteristic and distinct cellular populations: stromal cells, tumour cells that are self-reliant in terms of microenvironmental factors and tumour cells that depend on the environment for resources but can also co-opt stroma. 
RESULTS: Using evolutionary game theory we explore a number of different scenarios that elucidate the impact of tumour-stromal interactions on the dynamics of prostate cancer growth and progression and how different treatments in the metastatic setting can affect different types of tumors.
CONCLUSIONS: The tumour microenvironment plays a crucial role selecting the traits of the tumour cells that will determine prostate cancer progression. Equally important, treatments like hormone therapy affect the selection of these cancer phenotypes making it very important to understand how they impact prostate cancer’s somatic evolution
A new insight into the observation of spectroscopic strength reduction in atomic nuclei: implication for the physical meaning of spectroscopic factors
Experimental studies of one nucleon knockout from magic nuclei suggest that
their nucleon orbits are not fully occupied. This conflicts a commonly accepted
view of the shell closure associated with such nuclei. The conflict can be
reconciled if the overlap between initial and final nuclear states in a
knockout reaction are calculated by a non-standard method. The method employs
an inhomogeneous equation based on correlation-dependent effective
nucleon-nucleon (NN) interactions and allows the simplest wave functions, in
which all nucleons occupy only the lowest nuclear orbits, to be used. The
method also reproduces the recently established relation between reduction of
spectroscopic strength, observed in knockout reactions on other nuclei, and
nucleon binding energies. The implication of the inhomogeneous equation method
for the physical meaning of spectroscopic factors is discussed.Comment: 4 pages, accepted by Phys. Rev. Let
Study of the transition from pairing vibrational to pairing rotational regimes between magic numbers N=50 and N=82, with two-nucleon transfer
Absolute values of two-particle transfer cross sections along the Sn-isotopic
chain from closed shell to closed shell (100Sn,132Sn) are calculated taking
properly into account nuclear correlations, as well as the successive,
simultaneous and non-orthogonality contributions to the differential cross
sections. The results are compared with systematic, homogeneous bombarding
conditions (p, t) data. The observed agreement, almost within statistical
errors and without free parameters, testify to the fact that theory is able to
be quantitative in its predictions
- …