2,640 research outputs found
Sound propagation over uneven ground and irregular topography
The development of theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere is discussed. Irregular topography here is understood to imply a ground surface that (1) is not idealizable as being perfectly flat or (2) that is not idealizable as having a constant specific acoustic impedance. The study focuses on circumstances where the propagation is similar to what might be expected for noise from low-altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence
Bose-Einstein condensates with attractive 1/r interaction: The case of self-trapping
Amplifying on a proposal by O'Dell et al. for the realization of
Bose-Einstein condensates of neutral atoms with attractive interaction,
we point out that the instance of self-trapping of the condensate, without
external trap potential, is physically best understood by introducing
appropriate "atomic" units. This reveals a remarkable scaling property: the
physics of the condensate depends only on the two parameters and
, where is the particle number, the scattering length,
the "Bohr" radius and the trap frequency in atomic units. We
calculate accurate numerical results for self-trapping wave functions and
potentials, for energies, sizes and peak densities, and compare with previous
variational results. As a novel feature we point out the existence of a second
solution of the extended Gross-Pitaevskii equation for negative scattering
lengths, with and without trapping potential, which is born together with the
ground state in a tangent bifurcation. This indicates the existence of an
unstable collectively excited state of the condensate for negative scattering
lengths.Comment: 7 pages, 7 figures, to appear in Phys. Rev.
Statistical physics of earthquakes: Comparison of distribution exponents for source area and potential energy and the dynamic emergence of log-periodic energy quanta
Exploring disorganized attachment style among Malay mothers in Malaysia: a study using the Attachment Style Interview
This article explores emerging themes involving disorganized attachment style among Malay Muslim mothers using the Attachment Style Interview (ASI). Analysis of the 18 mothers with disorganized attachment style (those with combined anxious and avoidant styles) utilized themes deemed important from the attachment research literature and selected based on a careful reading of the narrative cases. These include more extreme negative interpersonal experiences than found in other insecure attachment style descriptors, and included partner violence and related isolation/social exclusion. It also indicated more complex cognitive-affective disturbance including mixed or contradictory dependency patterns and both angry and fearful attitudes to others. We discuss the concept of disorganized attachment style in relation to abuse, social exclusion, and its implication for psychopathology, intervention, and treatment
Longest Common Extensions in Sublinear Space
The longest common extension problem (LCE problem) is to construct a data
structure for an input string of length that supports LCE
queries. Such a query returns the length of the longest common prefix of the
suffixes starting at positions and in . This classic problem has a
well-known solution that uses space and query time. In this paper
we show that for any trade-off parameter , the problem can
be solved in space and query time. This
significantly improves the previously best known time-space trade-offs, and
almost matches the best known time-space product lower bound.Comment: An extended abstract of this paper has been accepted to CPM 201
Symmetry breaking in crossed magnetic and electric fields
We present the first observations of cylindrical symmetry breaking in highly
excited diamagnetic hydrogen with a small crossed electric field, and we give a
semiclassical interpretation of this effect. As the small perpendicular
electric field is added, the recurrence strengths of closed orbits decrease
smoothly to a minimum, and revive again. This phenomenon, caused by
interference among the electron waves that return to the nucleus, can be
computed from the azimuthal dependence of the classical closed orbits.Comment: 4 page REVTeX file including 5 postscript files (using psfig)
Accepted for publication in Physical Review Letters. Difference from earlier
preprint: we have discovered the cause of the earlier apparent discrepancy
between experiment and theory and now achieve excellent agreemen
High frequency study of FRB 20180916B using the 100-m Effelsberg radio telescope
FRB 20180916B is a repeating fast radio burst (FRB) with an activity period
of 16.33 days. In previous observations ranging from MHz, the
activity window was found to be frequency dependent, with lower frequency
bursts occurring later. In this work, we present the highest-frequency
detections of bursts from this FRB, using the 100-m Effelsberg Radio Telescope
at 48 GHz. We present the results from two observing campaigns. We performed
the first campaign over an entire activity period which resulted in no
detections. The second campaign was in an active window at 48 GHz which we
predicted from our modelling of chromaticity, resulting in eight burst
detections. The bursts were detected in a window of 1.35 days, 3.6 days
preceding the activity peak seen by CHIME, suggesting the chromaticity extends
to higher frequency. The detected bursts have narrower temporal widths and
larger spectral widths compared to lower frequencies. All of them have flat
polarization position angle sweeps and high polarization fractions. The bursts
also exhibit diffractive scintillation due to the Milky Way, following a
scaling, and vary significantly over time. We find that burst
rate across frequency scales as . Lastly, we examine
implications of the frequency dependency on the source models.Comment: 11 pages, 8 figures, comments welcome, submitted to MNRA
Recommended from our members
Decoupling a tandem-repeat protein: Impact of multiple loop insertions on a modular scaffold
Abstract: The simple topology and modular architecture of tandem-repeat proteins such as tetratricopeptide repeats (TPRs) and ankyrin repeats makes them straightforward to dissect and redesign. Repeat-protein stability can be manipulated in a predictable way using site-specific mutations. Here we explore a different type of modification - loop insertion - that will enable a simple route to functionalisation of this versatile scaffold. We previously showed that a single loop insertion has a dramatically different effect on stability depending on its location in the repeat array. Here we dissect this effect by a combination of multiple and alternated loop insertions to understand the origins of the context-dependent loss in stability. We find that the scaffold is remarkably robust in that its overall structure is maintained. However, adjacent repeats are now only weakly coupled, and consequently the increase in solvent protection, and thus stability, with increasing repeat number that defines the tandem-repeat protein class is lost. Our results also provide us with a rulebook with which we can apply these principles to the design of artificial repeat proteins with precisely tuned folding landscapes and functional capabilities, thereby paving the way for their exploitation as a versatile and truly modular platform in synthetic biology
Fractal Weyl law for chaotic microcavities: Fresnel's laws imply multifractal scattering
We demonstrate that the harmonic inversion technique is a powerful tool to
analyze the spectral properties of optical microcavities. As an interesting
example we study the statistical properties of complex frequencies of the fully
chaotic microstadium. We show that the conjectured fractal Weyl law for open
chaotic systems [W. T. Lu, S. Sridhar, and M. Zworski, Phys. Rev. Lett. 91,
154101 (2003)] is valid for dielectric microcavities only if the concept of the
chaotic repeller is extended to a multifractal by incorporating Fresnel's laws.Comment: 8 pages, 12 figure
Discovery and modelling of broad-scale plasma lensing in black-widow pulsar J20510827
We report on an unusually bright observation of PSR J20510827 recorded
during a regular monitoring campaign of black-widow pulsar systems with the
Effelsberg 100-m telescope. Through fortunate coincidence, a particularly
bright scintillation maximum is simultaneous with the eclipse by the companion,
enabling precise measurements of variations in the flux density, dispersion
measure (DM), and scattering strength throughout the eclipse. The flux density
is highly variable throughout the eclipse, with a peak 1.7 times the average
away from the eclipse, and yet does not significantly decrease on average. We
recover the flux density variations from the measured DM variations using
geometric optics, with a relative velocity as the only free parameter. We
measure an effective velocity of (470 10) km/s, consistent with the
relative orbital motion of the companion, suggesting that the outflow velocity
of the lensing material is low, or is directly along the line of sight. The 2
per cent uncertainty on the effective velocity is a formal error; systematics
related to our current model are likely to dominate, and we detail several
extensions to the model to be considered in a full treatment of lensing. This
is a demonstration of the causal link between DM and lensing; the flux density
variations can be predicted directly through the derivatives of DM. Going
forward, this approach can be applied to investigate the dynamics of other
eclipsing systems, and to investigate the physical nature of scintillation and
lensing in the ionized interstellar medium.Comment: 12 pages, 8 figures, typos corrected, references update
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