2,825 research outputs found
Short Range Interactions in the Hydrogen Atom
In calculating the energy corrections to the hydrogen levels we can identify
two different types of modifications of the Coulomb potential , with one
of them being the standard quantum electrodynamics corrections, ,
satisfying over the whole range of
the radial variable . The other possible addition to is a potential
arising due to the finite size of the atomic nucleus and as a matter of fact,
can be larger than in a very short range. We focus here on the latter
and show that the electric potential of the proton displays some undesirable
features. Among others, the energy content of the electric field associated
with this potential is very close to the threshold of pair production.
We contrast this large electric field of the Maxwell theory with one emerging
from the non-linear Euler-Heisenberg theory and show how in this theory the
short range electric field becomes smaller and is well below the pair
production threshold
Spin-Peierls Quantum Phase Transitions in Coulomb Crystals
The spin-Peierls instability describes a structural transition of a crystal
due to strong magnetic interactions. Here we demonstrate that cold Coulomb
crystals of trapped ions provide an experimental testbed in which to study this
complex many-body problem and to access extreme regimes where the instability
is triggered by quantum fluctuations alone. We present a consistent analysis
based on different analytical and numerical methods, and provide a detailed
discussion of its feasibility on the basis of ion-trap experiments. Moreover,
we identify regimes where this quantum simulation may exceed the power of
classical computers.Comment: slightly longer than the published versio
Novel Scintillating Materials Based on Phenyl-Polysiloxane for Neutron Detection and Monitoring
Neutron detectors are extensively used at many nuclear research facilities
across Europe. Their application range covers many topics in basic and applied
nuclear research: in nuclear structure and reaction dynamics (reaction
reconstruction and decay studies); in nuclear astrophysics (neutron emission
probabilities); in nuclear technology (nuclear data measurements and
in-core/off-core monitors); in nuclear medicine (radiation monitors,
dosimeters); in materials science (neutron imaging techniques); in homeland
security applications (fissile materials investigation and cargo inspection).
Liquid scintillators, widely used at present, have however some drawbacks given
by toxicity, flammability, volatility and sensitivity to oxygen that limit
their duration and quality. Even plastic scintillators are not satisfactory
because they have low radiation hardness and low thermal stability. Moreover
organic solvents may affect their optical properties due to crazing. In order
to overcome these problems, phenyl-polysiloxane based scintillators have been
recently developed at Legnaro National Laboratory. This new solution showed
very good chemical and thermal stability and high radiation hardness. The
results on the different samples performance will be presented, paying special
attention to a characterization comparison between synthesized phenyl
containing polysiloxane resins where a Pt catalyst has been used and a
scintillating material obtained by condensation reaction, where tin based
compounds are used as catalysts. Different structural arrangements as a result
of different substituents on the main chain have been investigated by High
Resolution X-Ray Diffraction, while the effect of improved optical
transmittance on the scintillation yield has been elucidated by a combination
of excitation/fluorescence measurements and scintillation yield under exposure
to alpha and {\gamma}-rays.Comment: InterM 2013 - International Multidisciplinary Microscopy Congres
A Measurement Study on the Advertisements Displayed to Web Users Coming from the Regular Web and from Tor
Online advertising is an effective way for businesses to find new customers and expand their reach to a great variety of audiences. Due to the large number of participants interacting in the process, advertising networks act as brokers between website owners and businesses facilitating the display of advertisements. Unfortunately, this system is abused by cybercriminals to perform illegal activities such as malvertising. In this paper, we perform a measurement of malvertising from the user point of view. Our goal is to collect advertisements from a regular Internet connection and using The Onion Router in an attempt to understand whether using different technologies to access the Web could influence the probability of infection. We compare the data from our experiments to find differences in the malvertising activity observed. We show that the level of maliciousness is similar between the two types of accesses. Nevertheless, there are significant differences related to the malicious landing pages delivered in each type of access. Our results provide the research community with insights into how ad traffic is treated depending on the way users access Web content
Long-range Ising interactions mediated by fields: probing the renormalisation of sound in crystals of trapped ions
The generating functional of a self-interacting scalar quantum field theory
(QFT), which contains all the relevant information about real-time dynamics and
scattering experiments, can be mapped onto a collection of
multipartite-entangled two-level sensors via an interferometric protocol that
exploits a specific set of source functions. Although one typically focuses on
impulsive delta-like sources, as these give direct access to -point Feynman
propagators, we show in this work that using always-on harmonic sources can
simplify substantially the sensing protocol. In a specific regime, the
effective real-time dynamics of the quantum sensors can be described by a
quantum Ising model with long-range couplings, the range and strength of which
contains all the relevant information about the renormalisation of the QFT,
which can now be extracted in the absence of multi-partite entanglement. We
present a detailed analysis of how this sensing protocol can be relevant to
characterise the long-wavelength QFT that describes quantised sound waves of
trapped-ion crystals in the vicinity of a structural phase transition, opening
a new route to characterise the associated renormalisation of sound
Functional Foods Baseline and Requirements Analysis
Current spaceflight foods were evaluated to determine if their nutrient profile supports positioning as a functional food and if the stability of the bioactive compound within the food matrix over an extended shelf-life correlated with the expected storage duration during the mission. Specifically, the research aims were: Aim A. To determine the amount of each nutrient in representative spaceflight foods immediately after processing and at predetermined storage time to establish the current nutritional state. Aim B. To identify the requirements to develop foods that stabilize these nutrients such that required concentrations are maintained in the space food system throughout long duration missions (up to five years). Aim C. To coordinate collaborations with health and performance groups that may require functional foods as a countermeasure
Correlated vortex pinning in slightly orthorhombic twinned Ba(Fe1−xCox)2As2 single crystals: Possible shift of the vortex-glass/liquid transition
The interest in twin-boundary (TB) planes as a source of vortex pinning has been recently renewed with the discovery of the new iron-arsenide pnictide superconductors. In the family of compounds Ba(Fe1−xCox )2As2 a structural transition from a tetragonal to orthorhombic lattice takes place for compounds with xxcr) there is no twinning and we find good agreement with the expected scaling function under uncorrelated disorder, with small anisotropy values similar to those reported in the literature. We show that in the orthorhombic samples (xFil: Marziali Bermudez, Mariano. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; ArgentinaFil: Pasquini, Gabriela. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; ArgentinaFil: Bud´ko, S.L.. University of Iowa; Estados UnidosFil: Canfield, P.C.. University of Iowa; Estados Unido
Ecohydraulic modelling of anabranching rivers
In this paper we provide the first quantitative evidence of the spatial complexity of habitat diversity across the flow regime for locally anabranching channels, and their potential increased biodiversity value in comparison to managed single-thread rivers. Ecohydraulic modelling is used to provide evidence for the potential ecological value of anabranching channels. Hydraulic habitat (biotopes) of an anabranched reach of the River Wear at Wolsingham, UK is compared with an adjacent artificially straightened single-thread reach downstream. 2D hydraulic modelling was undertaken across the flow regime. Simulated depth and velocity data were used to calculate Froude number (Fr) index; known to be closely associated with biotope type, allowing biotope maps to be produced for each flow simulation using published Fr limits. The gross morphology of the anabranched reach appears to be controlling flow hydraulics, creating a complex and diverse biotope distribution at low and intermediate flows. This contrasts markedly with the near uniform biotope pattern modelled for the heavily modified single-thread reach. As discharge increases the pattern of biotopes altered to reflect a generally higher energy system, interestingly, however, a number of low energy biotopes were activated through the anabranched reach as new sub-channels became inundated and this process is creating valuable refugia for macroinvertebrates and fish, during times of flood. In contrast, these low energy areas were not seen in the straightened single thread reach. Model results suggest that anabranched channels have a vital role to play in regulating flood energy on river systems and in creating and maintaining hydraulic habitat diversity
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