23,068 research outputs found
How to Run Through Walls: Dynamics of Bubble and Soliton Collisions
It has recently been shown in high resolution numerical simulations that
relativistic collisions of bubbles in the context of a multi-vacua potential
may lead to the creation of bubbles in a new vacuum. In this paper, we show
that scalar fields with only potential interactions behave like free fields
during high-speed collisions; the kick received by them in a collision can be
deduced simply by a linear superposition of the bubble wall profiles. This
process is equivalent to the scattering of solitons in 1+1 dimensions. We
deduce an expression for the field excursion (shortly after a collision), which
is related simply to the field difference between the parent and bubble vacua,
i.e. contrary to expectations, the excursion cannot be made arbitrarily large
by raising the collision energy. There is however a minimum energy threshold
for this excursion to be realized. We verify these predictions using a number
of 3+1 and 1+1 numerical simulations. A rich phenomenology follows from these
collision induced excursions - they provide a new mechanism for scanning the
landscape, they might end/begin inflation, and they might constitute our very
own big bang, leaving behind a potentially observable anisotropy.Comment: 15pgs, 14 figures, v2, thanks for the feedback
Automated knowledge capture in 2D and 3D design environments
In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured throughout its life cycle in a formal and structured manner. This will allow the information to be referred to in the future by engineers who did not work on the original design but are wanting to understand the reasons that certain design decisions were made. In the past, attempts were made to try to capture this knowledge by having the engineer record the knowledge manually during a design session. However, this is not only time-consuming but is also disruptive to the creative process. Therefore, the research presented in this paper is concerned with capturing design knowledge automatically using a traditional 2D design environment and also an immersive 3D design environment. The design knowledge is captured by continuously and non-intrusively logging the user during a design session and then storing this output in a structured eXtensible Markup Language (XML) format. Next, the XML data is analysed and the design processes that are involved can be visualised by the automatic generation of IDEF0 diagrams. Using this captured knowledge, it forms the basis of an interactive online assistance system to aid future users who are carrying out a similar design task
Vortex ring refraction at large Froude numbers
We have experimentally studied the impact of an initially planar axisymmetric
vortex ring, incident at an oblique angle, upon a gravity-induced interface
separating two fluids of differing densities. After impact, the vortex ring was
found to exhibit a variety of subsequent trajectories, which we organize
according to both the incidence angle, , and the interface strength,
defined as the ratio of the Atwood and Froude numbers, . For grazing
incidence angles ( deg.) vortices either penetrate or
reflect from the interface, depending on whether the interface is weak or
strong. In some cases, reflected vortices execute damped oscillations before
finally disintegrating. For smaller incidence angles (
deg.) vortices penetrate the interface. When there is a strong interface, these
vortices are observed to curve back up toward the interface. When there is a
weak interface, these vortices are observed to refract downward, away from the
interface. The critical interface strength below which vortex ring refraction
is observed is given by .Comment: 26 pages, 11 figures; Submitted to Physical Review
Rotating Electromagnetic Waves in Toroid-Shaped Regions
Electromagnetic waves, solving the full set of Maxwell equations in vacuum,
are numerically computed. These waves occupy a fixed bounded region of the
three dimensional space, topologically equivalent to a toroid. Thus, their
fluid dynamics analogs are vortex rings. An analysis of the shape of the
sections of the rings, depending on the angular speed of rotation and the major
diameter, is carried out. Successively, spherical electromagnetic vortex rings
of Hill's type are taken into consideration. For some interesting peculiar
configurations, explicit numerical solutions are exhibited.Comment: 27 pages, 40 figure
Numerical renormalization group calculation of near-gap peaks in spectral functions of the Anderson model with superconducting leads
We use the numerical renormalization group method (NRG) to investigate a
single-impurity Anderson model with a coupling of the impurity to a
superconducting host. Analysis of the energy flow shows, in contrast to
previous belief, that NRG iterations can be performed up to a large number of
sites, corresponding to energy differences far below the superconducting gap.
This allows us to calculate the impurity spectral function very accurately for
frequencies near the gap edge, and to resolve, in a certain parameter regime,
sharp peaks in the spectral function close to the gap edge.Comment: 18 pages, 7 figures, accepted for publication in Journal of Physics:
Condensed Matte
Calibration of <i>Herschel</i> SPIRE FTS observations at different spectral resolutions
The SPIRE Fourier Transform Spectrometer on-board the Herschel Space Observatory had two standard spectral resolution modes for science observations: high resolution (HR) and low resolution (LR), which could also be performed in sequence (H+LR). A comparison of the HR and LR resolution spectra taken in this sequential mode revealed a systematic discrepancy in the continuum level. Analysing the data at different stages during standard pipeline processing demonstrates that the telescope and instrument emission affect HR and H+LR observations in a systematically different way. The origin of this difference is found to lie in the variation of both the telescope and instrument response functions, while it is triggered by fast variation of the instrument temperatures. As it is not possible to trace the evolution of the response functions using housekeeping data from the instrument subsystems, the calibration cannot be corrected analytically. Therefore, an empirical correction for LR spectra has been developed, which removes the systematic noise introduced by the variation of the response functions
Andreev Bound States in the Kondo Quantum Dots Coupled to Superconducting Leads
We have studied the Kondo quantum dot coupled to two superconducting leads
and investigated the subgap Andreev states using the NRG method. Contrary to
the recent NCA results [Clerk and Ambegaokar, Phys. Rev. B 61, 9109 (2000);
Sellier et al., Phys. Rev. B 72, 174502 (2005)], we observe Andreev states both
below and above the Fermi level.Comment: 5 pages, 5 figure
An Assessment of Risk of Iodine Deficiency Among Pregnant Women in Sarawak, Malaysia
Previous findings from a state-wide Iodine Deficiency Disorders (IDD) study among pregnant women (PW) in Sarawak indicated that PW are at risk of IDD and further assessment is needed. This paper describes the methodology used in conducting this study for an assessment of risk of iodine deficiency among pregnant women in Sarawak, Malaysia. A total of 30 maternal child health care clinics (MCHCs) were selected using probability proportional to population size (PPS) sampling technique. The PW sample size was calculated based on 95% confidence interval (CI), relative precision of 5%, design effect of 2, anticipated IDD prevalence of 65.0% and non-response rate of 20%. Thus, the total sample size required was 750 (25 respondents per selected MCHC). The WHO Expanded Programme on Immunization (EPI) surveys approach was used to randomly select the first respondent and subsequent respondents were chosen until the required number of PW was met. The required data were obtained through: face-to-face interviews (socio-demographic and food frequency questionnaire), clinical assessments (thyroid size, and hyper/hypothyroidism) and biochemical analysis (urine and blood serum). A total of 677 PW responded in the study with a response rate of 90.2%. Majority of the PW were at second gravida, aged 25-29 years old and of Malay ethnicity. The methodology used in this study was based on International guidelines which may provide state's estimates. All the necessary steps were taken into consideration to ensure valid and reliable findings on current iodine status among PW
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