4,455 research outputs found
Quantum wideband traveling-wave analysis of a degenerate parametric amplifier
We develop a wideband traveling-wave formalism for analyzing quantum mechanically a degenerate parametric amplifier. The formalism is based on spatial differential equations-spatial Langevin equations-that propagate temporal Fourier components of the field operators through the nonlinear medium. In addition to the parametric nonlinearity, the Langevin equations include absorption and associated fluctuations, dispersion (phase mismatching), and pump quantum fluctuations. We analyze the dominant effects of phase mismatching and pump quantum fluctuations on the squeezing produced by a degenerate parametric amplifier
Exploratory investigation of the effect of nylon grain size on ablation of phenolic nylon
Exploratory investigation of nylon grain size effect on ablation of phenolic nylo
Numerical simulations of multiple scattering of the mode by flux tubes
We use numerial simulations to study the absorption and phase shift of
surface-gravity waves caused by groups of magnetic flux tubes. The dependence
of the scattering coefficients with the distance between the tubes and their
positions is analyzed for several cases with two or three flux tubes embedded
in a quiet Sun atmosphere. The results are compared with those obtained
neglecting completely or partially multiple scattering effects. We show that
multiple scattering has a significant impact on the absorption measurements and
tends to reduce the phase shift. We also consider more general cases of
ensembles of randomly distributed flux tubes, and we have evaluated the effects
on the scattering measurements of changing the number of tubes included in the
bundle and the average distance between flux tubes. We find that for the
longest wavelength incoming waves multiple scattering enhances the absorption,
and its efficiency increases with the number of flux tubes and the reduction of
the distance between them.Comment: Accepted for publication in The Astrophysical Journa
Physical Baryon Resonance Spectroscopy from Lattice QCD
We complement recent advances in the calculation of the masses of excited
baryons in quenched lattice QCD with finite-range regulated chiral effective
field theory enabling contact with the physical quark mass region. We examine
the P-wave contributions to the low-lying nucleon and delta resonances.Comment: Contributed paper at FB17, the 17th International Conference on
Few-Body Problems in Physics, Durham, NC, June 5-10, 2003. 3 pages, 6 figure
Evaluation of the capability of local helioseismology to discern between monolithic and spaghetti sunspot models
The helioseismic properties of the wave scattering generated by monolithic
and spaghetti sunspots are analyzed by means of numerical simulations. In these
computations, an incident f or p1 mode travels through the sunspot model, which
produces absorption and phase shift of the waves. The scattering is studied by
inspecting the wavefield, computing travel-time shifts, and performing
Fourier-Hankel analysis. The comparison between the results obtained for both
sunspot models reveals that the differences in the absorption coefficient can
be detected above noise level. The spaghetti model produces an steep increase
of the phase shift with the degree of the mode at short wavelengths, while
mode-mixing is more efficient for the monolithic model. These results provide a
clue for what to look for in solar observations to discern the constitution of
sunspots between the proposed monolithic and spaghetti models.Comment: Accepted for publication in The Astrophysical Journa
Helioseismic holography of simulated sunspots: magnetic and thermal contributions to travel times
Wave propagation through sunspots involves conversion between waves of
acoustic and magnetic character. In addition, the thermal structure of sunspots
is very different than that of the quiet Sun. As a consequence, the
interpretation of local helioseismic measurements of sunspots has long been a
challenge. With the aim of understanding these measurements, we carry out
numerical simulations of wave propagation through sunspots. Helioseismic
holography measurements made from the resulting simulated wavefields show
qualitative agreement with observations of real sunspots. We use additional
numerical experiments to determine, separately, the influence of the thermal
structure of the sunspot and the direct effect of the sunspot magnetic field.
We use the ray approximation to show that the travel-time shifts in the thermal
(non-magnetic) sunspot model are primarily produced by changes in the wave path
due to the Wilson depression rather than variations in the wave speed. This
shows that inversions for the subsurface structure of sunspots must account for
local changes in the density. In some ranges of horizontal phase speed and
frequency there is agreement (within the noise level in the simulations)
between the travel times measured in the full magnetic sunspot model and the
thermal model. If this conclusion proves to be robust for a wide range of
models, it would suggest a path towards inversions for sunspot structure.Comment: Accepted for publication in The Astrophysical Journa
Sources Of Student Engagement In Introductory Physics For Life Sciences
We explore the sources of student engagement with curricular content in an Introductory Physics for Life Science (IPLS) course at Swarthmore College. Do IPLS students find some life-science contexts more interesting than others, and, if so, what are the sources of these differences? We draw on three sources of student data to answer this question: (1) quantitative survey data illustrating how interested students were in particular contexts from the curriculum, (2) qualitative survey data in which students describe the source of their interest in these particular contexts, and (3) interview data in which students reflect on the contexts that were and were not of interest to them. We find that examples that make interdisciplinary connections with studentsâ other coursework in biology and chemistry, and examples that make connections to what students perceive to be the âreal world,â are particularly effective at fostering interest. More generally, students describe being deeply engaged with contexts that foster a sense of coherence or have personal meaning to them. We identify various âengagement pathwaysâ by which different life-science students engage with IPLS content, and suggest that a curriculum needs to be flexible enough to facilitate these different pathways
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