536 research outputs found
Periodically Aligned Liquid Crystal: Potential application for projection displays
A nematic liquid crystal (NLC) layer with the anisotropy axis modulated at a
fixed rate q in the transverse direction is considered. If the layer locally
constitutes a half-wave plate, then the thin-screen approximation predicts 100%
-efficient diffraction of normal incident wave. The possibility of implementing
such a layer via anchoring at both surfaces of a cell with thickness L is
studied as a function of parameter qL and threshold values of this parameter
are found for a variety of cases. Distortions of the structure of director in
comparison with the preferable ideal profile are found via numerical modeling.
Freedericksz transition is studied for this configuration. Coupled-mode theory
is applied to light propagation through such cell allowing to account for
walk-off effects and effects of nematic distortion. In summary, this cell is
suggested as a means for projection display; high efficiency is predicted.Comment: 25 pages, 6 figures, 1 tabl
Empirical study of communication structures and barriers in geographically distributed teams
Conway's law asserts that communication structures of organisations constrain the design of the products they develop. This law is more explicitly observable in geographically distributed contexts because distributed teams are required to share information across different time zones and barriers. The diverse business processes and functions adopted by individual teams in geographically distributed settings create challenges for effective communication. Since the publication of Conway's law, a significant body of research has emerged in its relation to the communication structures. When it comes to software projects, the explicit observation about Conway's law has produced mixed results. The research reported in this study explores the communication structures and corresponding challenges faced by teams within a large geographically distributed software development organisation. The data was collected from relevant documents, a questionnaire and interviews with relevant stakeholders. The findings suggest that Conway's law is observable within the communication structures of globally distributed software development teams. The authors have identified the barriers and challenges of effective communications in this setting and have investigated the benefits of utilising an integrated system to overcome these challenges
Peculiar Spin Frequency and Radio Profile Evolution of PSR J11196127 Following Magnetar-like X-ray Bursts
We present the spin frequency and profile evolution of the radio pulsar
J11196127 following magnetar-like X-ray bursts from the system in 2016 July.
Using data from the Parkes radio telescope, we observe a smooth and fast
spin-down process subsequent to the X-ray bursts resulting in a net change in
the pulsar rotational frequency of \,Hz.
During the transition, a net spin-down rate increase of
\,Hz\,s is observed, followed by a
return of to its original value. In addition, the radio pulsations
disappeared after the X-ray bursts and reappeared about two weeks later with
the flux density at 1.4\,GHz increased by a factor of five. The flux density
then decreased and undershot the normal flux density followed by a slow
recovery back to normal. The pulsar's integrated profile underwent dramatic and
short-term changes in total intensity, polarization and position angle. Despite
the complex evolution, we observe correlations between the spin-down rate,
pulse profile shape and radio flux density. Strong single pulses have been
detected after the X-ray bursts with their energy distributions evolving with
time. The peculiar but smooth spin frequency evolution of PSR~J11196127
accompanied by systematic pulse profile and flux density changes are most
likely to be a result of either reconfiguration of the surface magnetic fields
or particle winds triggered by the X-ray bursts. The recovery of spin-down rate
and pulse profile to normal provides us the best case to study the connection
between high magnetic-field pulsars and magnetars.Comment: Accepted for publication in MNRAS on 2018 July 2
Asset-building payments for ecosystem services:Assessing landowner perceptions of reforestation incentives in Lebanon
Aim of study: Incentivising landowners to supply ecosystem services remains challenging, especially when this requires long-term investments such as reforestation. We investigated how landowners perceive, and would respond to, distinct types of incentives for planting diverse native trees on private lands in Lebanon. Our aim was to understand landowners’ attitudes towards hypothetical Payments for Ecosystem Services (PES) contracts options; their likely participation; and the potential additionality they would provide.Â
Area of study: Highland villages situated within eight of Lebanon’s 20 Important Plant AreasÂ
Materials and methods: Mixed-methods surveys were conducted with 34 landowners to determine past, present and future land-use strategies. Study participants were presented with three differently structured reforestation contract options (or schemes). The three schemes (results-based loan, action-based grant, and results-based payments) differed in their expected risks and benefits to landowners. Qualitative debriefing questions followed each of the schemes presented.Â
Main results: Although the results-based loan did deter uptake relative to the lower risk action-based grant, results-based payments did not significantly increase uptake or planting area, suggesting asymmetric attitudes to risk. Qualitative probing revealed economic, social (e.g. trust) and institutional factors (e.g. legal implications of planting forest trees on private land) that limited willingness to participate in the results-based contract option.Â
Research highlights: This study demonstrates the importance of combining qualitative and quantitative methods to better understand landowner perceptions of incentives and risks, particularly in challenging socio-political contexts
A Shapiro delay detection in the binary system hosting the millisecond pulsar PSR J1910-5959A
PSR J1910-5959A is a binary pulsar with a helium white dwarf companion
located about 6 arcmin from the center of the globular cluster NGC6752. Based
on 12 years of observations at the Parkes radio telescope, the relativistic
Shapiro delay has been detected in this system. We obtain a companion mass Mc =
0.180+/-0.018Msun (1sigma) implying that the pulsar mass lies in the range
1.1Msun <= Mp <= 1.5Msun. We compare our results with previous optical
determinations of the companion mass, and examine prospects for using this new
measurement for calibrating the mass-radius relation for helium white dwarfs
and for investigating their evolution in a pulsar binary system. Finally we
examine the set of binary systems hosting a millisecond pulsar and a low mass
helium white dwarf for which the mass of both stars has been measured. We
confirm that the correlation between the companion mass and the orbital period
predicted by Tauris & Savonije reproduces the observed values but find that the
predicted Mp - Pb correlation over-estimates the neutron star mass by about
0.5Msun in the orbital period range covered by the observations. Moreover, a
few systems do not obey the observed Mp - Pb correlation. We discuss these
results in the framework of the mechanisms that inhibit the accretion of matter
by a neutron star during its evolution in a low-mass X-ray binary.Comment: 4 figures, 2 tables, accepted for publication in the Astrophysical
Journa
Timing of Millisecond Pulsars in NGC 6752: Evidence for a High Mass-to-Light Ratio in the Cluster Core
Using pulse timing observations we have obtained precise parameters,
including positions with about 20 mas accuracy, of five millisecond pulsars in
NGC 6752. Three of them, located relatively close to the cluster center, have
line-of-sight accelerations larger than the maximum value predicted by the
central mass density derived from optical observation, providing dynamical
evidence for a central mass-to-light ratio >~ 10, much higher than for any
other globular cluster. It is likely that the other two millisecond pulsars
have been ejected out of the core to their present locations at 1.4 and 3.3
half-mass radii, respectively, suggesting unusual non-thermal dynamics in the
cluster core.Comment: Accepted by ApJ Letter. 5 pages, 2 figures, 1 tabl
Long-term observations of the pulsars in 47 Tucanae - II. Proper motions, accelerations and jerks
This paper is the second in a series where we report the results of the
long-term timing of the millisecond pulsars (MSPs) in 47 Tucanae with the
Parkes 64-m radio telescope. We obtain improved timing parameters that provide
additional information for studies of the cluster dynamics: a) the pulsar
proper motions yield an estimate of the proper motion of the cluster as a whole
(, ) and the motion of the pulsars
relative to each other. b) We measure the second spin-period derivatives caused
by the change of the pulsar line-of-sight accelerations; 47 Tuc H, U and
possibly J are being affected by nearby objects. c) For ten binary systems we
now measure changes in the orbital period caused by their acceleration in the
gravitational field of the cluster. From all these measurements, we derive a
cluster distance no smaller than 4.69 kpc and show that the
characteristics of these MSPs are very similar to their counterparts in the
Galactic disk. We find no evidence in favour of an intermediate mass black hole
at the centre of the cluster. Finally, we describe the orbital behaviour of the
four "black widow" systems. Two of them, 47 Tuc J and O, exhibit orbital
variability similar to that observed in other such systems, while for 47 Tuc I
and R the orbits seem to be remarkably stable. It appears, therefore, that not
all "black widows" have unpredictable orbital behaviour.Comment: 21 pages in journal format, 9 figures, 4 tables, accepted for
publication in MNRAS, several clarifications made and typos fixe
Long-term observations of the pulsars in 47 Tucanae. I. A study of four elusive binary systems
For the past couple of decades, the Parkes radio telescope has been regularly
observing the millisecond pulsars in 47 Tucanae (47 Tuc). This long-term timing
program was designed to address a wide range of scientific issues related to
these pulsars and the globular cluster where they are located. In this paper,
the first of a series, we address one of these objectives: the characterization
of four previously known binary pulsars for which no precise orbital parameters
were known, namely 47 Tuc P, V, W and X (pulsars 47 Tuc R and Y are discussed
elsewhere). We determined the previously unknown orbital parameters of 47 Tuc V
and X and greatly improved those of 47 Tuc P and W. For pulsars W and X we
obtained, for the first time, full coherent timing solutions across the whole
data span, which allowed a much more detailed characterization of these
systems. 47 Tuc W, a well-known tight eclipsing binary pulsar, exhibits a large
orbital period variability, as expected for a system of its class. 47 Tuc X
turns out to be in a wide, extremely circular, 10.9-day long binary orbit and
its position is ~3.8 arcmin away from the cluster center, more than three times
the distance of any other pulsar in 47 Tuc. These characteristics make 47 Tuc X
a very different object with respect to the other pulsars of the cluster.Comment: Accepted for publication by MNRAS, 18 pages, 11 figure
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