690 research outputs found

### Explaining âcarbonâ in community sequestration projects: a key element in the creation of local carbon knowledges

The formation of local carbon knowledge is central to the meaningful participation of communities in the land-based carbon projects which have become widespread in pursuit of global emissions reductions. Through a qualitative analysis of interviews with community sensitization practitioners, this paper considers how concepts of carbon are communicated to project communities. We find that fieldworkers use peopleâs own experiences to make intangible carbon visible, but rely on scientific concepts to explain the transfer of carbon between states. However, interviews suggest that project communitiesâ knowledge and understanding of carbon is partial. This highlights the challenges of meeting the safeguarding principles of respect for local knowledge and informed consent in carbon projects. We conclude that greater attention needs to be given by planners to the role of communication in carbon projects, including the potential to draw on indigenous knowledges to advance local understanding

### Quasi Markovian behavior in mixing maps

We consider the time dependent probability distribution of a coarse grained
observable Y whose evolution is governed by a discrete time map. If the map is
mixing, the time dependent one-step transition probabilities converge in the
long time limit to yield an ergodic stochastic matrix. The stationary
distribution of this matrix is identical to the asymptotic distribution of Y
under the exact dynamics. The nth time iterate of the baker map is explicitly
computed and used to compare the time evolution of the occupation probabilities
with those of the approximating Markov chain. The convergence is found to be at
least exponentially fast for all rectangular partitions with Lebesgue measure.
In particular, uniform rectangles form a Markov partition for which we find
exact agreement.Comment: 16 pages, 1 figure, uses elsart.sty, to be published in Physica D
Special Issue on Predictability: Quantifying Uncertainty in Models of Complex
Phenomen

### A three-dimensional degree of polarization based on Rayleigh scattering

A measure of the degree of polarization for the three-dimensional
polarization matrix (coherence matrix) of an electromagnetic field is proposed,
based on Rayleigh scattering. The degree of polarization, due to dipole
scattering of the three-dimensional state of polarization, is averaged over all
scattering directions. This gives a well-defined purity measure, which, unlike
other proposed measures of the three-dimensional degree of polarization, is not
a unitary invariant of the matrix. This is demonstrated and discussed for
several examples, including a partially polarized transverse beam.Comment: 17 pages, 3 figures. OSA styl

### The governance of personal data for COVID-19 response: perspective from the access to COVID-19 tools accelerator

COVID-19 is the worldâs first digital pandemic. Digital tools and technologies have been developed to track and trace the spread of the virus, screen for infection, and the pandemic has accelerated the use of digital technology in the delivery of healthcare. The continued development of these tools and technologies, the monitoring of the virus and the development of new tests, treatments and vaccines are dependent on the collection of and access to vast amounts of personal data. This includes clinical data, epidemiological data and public health data that may be collected from laboratories, medical records, wearables and smartphone apps. Previous public health emergencies (PHEs) have demonstrated the importance in making this data available, and early in the COVID-19 pandemic, there were calls for making all kinds of data, including clinical trial data, routine surveillance data, genetic sequencing, and data on the ongoing monitoring of disease control programmes, openly and rapidly available. As part of this, personal data on age, race, sex, health, ethnic group, and socioeconomic factors have been shared. This has helped led to the rapid development of COVID-19 interventions. It has also enabled the better understanding of factors contributing to difference in infection rates and effectiveness of tests, treatments, and vaccines. However, the use of this particularly sensitive data can infringe upon individual and group privacy, increase the risks of individual and group stigma and discrimination, and it may negatively impact already vulnerable, marginalised or minority populations. [...

### Notes on Conformal Invisibility Devices

As a consequence of the wave nature of light, invisibility devices based on
isotropic media cannot be perfect. The principal distortions of invisibility
are due to reflections and time delays. Reflections can be made exponentially
small for devices that are large in comparison with the wavelength of light.
Time delays are unavoidable and will result in wave-front dislocations. This
paper considers invisibility devices based on optical conformal mapping. The
paper shows that the time delays do not depend on the directions and impact
parameters of incident light rays, although the refractive-index profile of any
conformal invisibility device is necessarily asymmetric. The distortions of
images are thus uniform, which reduces the risk of detection. The paper also
shows how the ideas of invisibility devices are connected to the transmutation
of force, the stereographic projection and Escheresque tilings of the plane

### Exchanging demands: Weaknesses in SSL implementations for mobile platforms

The ActiveSync protocolâs implementation on some embedded devices leaves clients vulnerable to unauthorised remote policy enforcement. This paper discusses a proof of concept attack against the implementation of ActiveSync in common Smart phones including Android devices and iOS devices. A twoâphase approach to exploiting the ActiveSync protocol is introduced. Phase 1 details the usage of a manâinâtheâmiddle attack to gain a vantage point over the client device, whilst Phase 2 involves spoofing the serverâside ActiveSync responses to initiate the unauthorised policy enforcement. These vulnerabilities are demonstrated by experiment, highlighting how the system can be exploited to perform a remote factory reset upon an Exchangeâintegrated Smart phone

### Barnett-Pegg formalism of angle operators, revivals, and flux lines

We use the Barnett-Pegg formalism of angle operators to study a rotating
particle with and without a flux line. Requiring a finite dimensional version
of the Wigner function to be well defined we find a natural time quantization
that leads to classical maps from which the arithmetical basis of quantum
revivals is seen. The flux line, that fundamentally alters the quantum
statistics, forces this time quantum to be increased by a factor of a winding
number and determines the homotopy class of the path. The value of the flux is
restricted to the rational numbers, a feature that persists in the infinite
dimensional limit.Comment: 5 pages, 0 figures, Revte

### Singular continuous spectra in a pseudo-integrable billiard

The pseudo-integrable barrier billiard invented by Hannay and McCraw [J.
Phys. A 23, 887 (1990)] -- rectangular billiard with line-segment barrier
placed on a symmetry axis -- is generalized. It is proven that the flow on
invariant surfaces of genus two exhibits a singular continuous spectral
component.Comment: 4 pages, 2 figure

### Shrunk loop theorem for the topology probabilities of closed Brownian (or Feynman) paths on the twice punctured plane

The shrunk loop theorem presented here is an integral identity which
facilitates the calculation of the relative probability (or probability
amplitude) of any given topology that a free, closed Brownian or Feynman path
of a given 'duration' might have on the twice punctured plane (the plane with
two marked points). The result is expressed as a scattering series of integrals
of increasing dimensionality based on the maximally shrunk version of the path.
Physically, this applies in different contexts: (i) the topology probability of
a closed ideal polymer chain on a plane with two impassable points, (ii) the
trace of the Schroedinger Green function, and thence spectral information, in
the presence of two Aharonov-Bohm fluxes, (iii) the same with two branch points
of a Riemann surface instead of fluxes. Our theorem starts with the Stovicek
expansion for the Green function in the presence of two Aharonov-Bohm flux
lines, which itself is based on the famous Sommerfeld one puncture point
solution of 1896 (the one puncture case has much easier topology, just one
winding number). Stovicek's expansion itself can supply the results at the
expense of choosing a base point on the loop and then integrating it away. The
shrunk loop theorem eliminates this extra two dimensional integration,
distilling the topology from the geometry.Comment: 29 pages, 5 figures (accepted by J. Phys. A: Math. Gen.

### On the semiclassical theory for universal transmission fluctuations in chaotic systems: the importance of unitarity

The standard semiclassical calculation of transmission correlation functions
for chaotic systems is severely influenced by unitarity problems. We show that
unitarity alone imposes a set of relationships between cross sections
correlation functions which go beyond the diagonal approximation. When these
relationships are properly used to supplement the semiclassical scheme we
obtain transmission correlation functions in full agreement with the exact
statistical theory and the experiment. Our approach also provides a novel
prediction for the transmission correlations in the case where time reversal
symmetry is present

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