Electromagnetic Form Factors of the Nucleon in a Relativistic Quark Pair Creation Model

We study the effects of the | qqq q\bar{q} > component of the hadronic wave function on the description of the electromagnetic structure of the nucleon. Starting with a qqq baryonic wave function which describes the baryonic and mesonic low energy spectrum, the extra q\bar{q} pair is generated through a relativistic version of the 3P_0 model. It is shown that this model leads to a renormalization of the quark mass that allows one to construct a conserved electromagnetic current. We conclude that these dynamical relativistic corrections play an important role in reproducing the Q2 dependence of the electromagnetic form factors at low Q^2.Comment: 15 pages, 3 figures. Minor change

A (p/E) Calculation of Strong Pionic Decays of Baryons

Strong pionic decays of baryons are studied in a non-relativistic quark model framework via a convergent (p/E) expansion of the transition operator. Results are compared to the ones obtained within a more conventional (p/m) expansion.Comment: 16 pages, LaTeX, using amssymb.st

The effect of experience and instructions on learned attentional biases

Afiliaciones: Instituto de Investigación Biomédica de Málaga (IBIMA), University of Malaga, Spain Primary Care and Public Health Sciences, King’s College London, UK School of Psychology, UNSW Australia, Sydney, AustraliaIt has been shown that selective attention is allocated to the best available predictor of an outcome, which is known as learned predictiveness. Mitchell et al. (2012) have shown that instructions about the ‘relevance’ of each stimulus can influence (and even reverse) the learned predictiveness attentional bias, suggesting that propositional reasoning plays a crucial role in this phenomenon. Our experiment further explores the effects of instructions on this learned attentional bias. As a difference with previous work, we measured attentional capture through spatial cueing effects, which have been found to rely on rapid attentional processes (Le Pelley et al., 2013). Participants responded faster to events presented in the spatial location cued by stimuli that had previously been trained as predictive through trial-by-trial learning. However, verbal instructions regarding relevance failed to speed up participants’ responses or to modulate the effect of learned predictiveness on spatial cueing. These results suggest that predictive stimuli produce an attentional bias which is not (always) under voluntary control.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Quark model description of quasi-elastic pion knockout from the proton at JLAB

The interference term between s- and t-pole contributions to the p(e,e' pi+)n cross section is evaluated on the basis of the constituent quark model. It is shown that the contribution of baryon s-poles can be modeled by a nonlocal extension of the Kroll-Rudermann contact term. This contribution is in a destructive interference with the pion t-pole that is essential to improve the description of recent JLab data at the invariant mass W=1.95 GeV. Some predictions are made for a new JLab measurement at higher values W=2.1-2.3 GeV and Q2 centered at 1.6 and 2.45 GeV2/c2.Comment: 15 pages, 4 figures, to be published in Phys. Lett.

MESSENGER Magnetic Field Observations of Upstream Ultra-Low Frequency Waves at Mercury

The region upstream from a planetary bow shock is a natural plasma laboratory containing a variety of wave particle phenomena. The study of foreshocks other than the Earth's is important for extending our understanding of collisionless shocks and foreshock physics since the bow shock strength varies with heliocentric distance from the Sun, and the sizes of the bow shocks are different at different planets. The Mercury's bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body with a predominately radial interplanetary magnetic field. Previous observations of Mercury upstream ultra-low frequency (ULF) waves came exclusively from two Mercury flybys of Mariner 10. The MESSENGER orbiter data enable us to study of upstream waves in the Mercury's foreshock in depth. This paper reports an overview of upstream ULF waves in the Mercury's foreshock using high-time resolution magnetic field data, 20 samples per second, from the MESSENGER spacecraft. The most common foreshock waves have frequencies near 2 Hz, with properties similar to the I-Hz waves in the Earth's foreshock. They are present in both the flyby data and in every orbit of the orbital data we have surveyed. The most common wave phenomenon in the Earth's foreshock is the large-amplitude 30-s waves, but similar waves at Mercury have frequencies at near 0.1 Hz and occur only sporadically with short durations (a few wave cycles). Superposed on the "30-s" waves, there are spectral peaks at near 0.6 Hz, not reported previously in Mariner 10 data. We will discuss wave properties and their occurrence characteristics in this paper

Upstream ultra‐low frequency waves in Mercury's foreshock region: MESSENGER magnetic field observations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99094/1/jgra50342.pd

The N*(1520) ---> Delta pi Amplitudes Extracted from the gamma p ---> pi+ pi- p Reaction and Comparison to Quark Models

The gamma p ---> pi+ pi- p reaction, in combination with data from the pi N ---> pi pi N reaction, allows one to obtain the s- and d-wave amplitudes for the N*(1520) decay into Delta pi with absolute sign with respect to the N*(1520) ---> N gamma helicity amplitudes. In addition one obtains the novel information on the q dependence of the amplitudes. This dependence fits exactly with the predictions of the non-relativistic constituent quark models. The absolute values provided by these models agree only qualitatively, and a discussion is done on the reasons for it and possible ways to improve.Comment: 12 pages, 1 figure, TeX, Version 3.141 [PD VMS 3.4/CERN 1.0

Clock and Power-Induced Bias Correction for UWB Time-of-Flight Measurements

Ultra-Wide Band (UWB) communication systems can be used to design low cost, power efficient and precise navigation systems for mobile robots, by measuring the Time of Flight (ToF) of messages traveling between on-board UWB transceivers to infer their locations. Theoretically, decimeter level positioning accuracy or better should be achievable, at least in benign propagation environments where Line-of-Sight (LoS) between the transceivers can be maintained. Yet, in practice, even in such favorable conditions, one often observes significant systematic errors (bias) in the ToF measurements, depending for example on the hardware configuration and relative poses between robots. This letter proposes a ToF error model that includes a standard transceiver clock offset term and an additional term that varies with the received signal power (RxP). We show experimentally that, after fine correction of the clock offset term using clock skew measurements available on modern UWB hardware, much of the remaining pose dependent error in LoS measurements can be captured by the (appropriately defined) RxP-dependent term. This leads us to propose a simple bias compensation scheme that only requires on-board measurements (clock skew and RxP) to remove most of the observed bias in LoS ToF measurements and reliably achieve cm-level ranging accuracy. Because the calibrated ToF bias model does not depend on any extrinsic information such as receiver distances or poses, it can be applied before any additional error correction scheme that requires more information about the robots and their environment

Quasi-elastic knockout of pions and kaons from nucleons by high-energy electrons and quark microscopy of "soft" meson degrees of freedom in the nucleon

Electro-production of pions and kaons at the kinematics of quasi-elastic knockout (which is well known in the physics of atomic nucleus and corresponds to the $t$-pole diagram) is proposed for obtaining their momentum distribution (MD) in various channels of virtual decay $N \to B+\pi$, $B=N$, $\Delta$, $N^*$, $N^{**}$, and $N \to Y+K$, $Y=\Lambda$, $\Sigma$. It is a powerful tool for investigation of a quark microscopic picture of the meson cloud in the nucleon. A model of scalar $q \bar{q}$ ($^3P_0$) fluctuation in the non-trivial QCD vacuum is used to calculate pion and kaon momentum distributions (MD) in these channels.Comment: 31 pages, 11 figures, submitted to Nucl.Phys.

Mathematical Modelling of Mosquito Dispersal in a Heterogeneous Environment.

Mosquito dispersal is a key behavioural factor that affects the persistence and resurgence of several vector-borne diseases. Spatial heterogeneity of mosquito resources, such as hosts and breeding sites, affects mosquito dispersal behaviour and consequently affects mosquito population structures, human exposure to vectors, and the ability to control disease transmission. In this paper, we develop and simulate a discrete-space continuous-time mathematical model to investigate the impact of dispersal and heterogeneous distribution of resources on the distribution and dynamics of mosquito populations. We build an ordinary differential equation model of the mosquito life cycle and replicate it across a hexagonal grid (multi-patch system) that represents two-dimensional space. We use the model to estimate mosquito dispersal distances and to evaluate the effect of spatial repellents as a vector control strategy. We find evidence of association between heterogeneity, dispersal, spatial distribution of resources, and mosquito population dynamics. Random distribution of repellents reduces the distance moved by mosquitoes, offering a promising strategy for disease control