14,260 research outputs found
2-Server PIR with sub-polynomial communication
A 2-server Private Information Retrieval (PIR) scheme allows a user to
retrieve the th bit of an -bit database replicated among two servers
(which do not communicate) while not revealing any information about to
either server. In this work we construct a 1-round 2-server PIR with total
communication cost . This improves over the
currently known 2-server protocols which require communication and
matches the communication cost of known 3-server PIR schemes. Our improvement
comes from reducing the number of servers in existing protocols, based on
Matching Vector Codes, from 3 or 4 servers to 2. This is achieved by viewing
these protocols in an algebraic way (using polynomial interpolation) and
extending them using partial derivatives
Energetic particle observations of the solar-gamma ray/neutron flare events of 3 Jun 1982 and 21 June 1980 isotopic and chemical composition
Studies of the charge composition of two solar gamma ray/neutron-flare events reveal a striking enrichment of iron relative to oxygen with a smaller enrichment of intermediate nuclei. He/O is also enhanced and moderate amounts of He-3 are detected but there is no evidence for H-2 or H-3
Helios 1 energetic particle observations of the solar gamma ray flare events of 7, 21 June 1980 and 3 June 1982
The observed characteristics of the energetic particles associated with the solar gamma-ray events of 3, 21 June 1980 and 3 June 1982 differ in several important aspects from the typical solar particle increases. They have flat energy spectra, are electron rich and have small precursors increases that begin some hours before the impulsive flare increase
The variation of solar proton energy spectra size distribution with heliolongitude
A statistical study of the initial phases of 185 solar particle events was carried out using the data from cosmic ray experiments on IMP 4 and IMP 5. Special emphasis was placed on the identification of the associated solar flare, as the parent flare can be determined for 68% of the events. It appears probable that most of the unidentified increases occur on the non-visible disc of the sun. The existence of a 'preferred-connection' longitude between 20 W and 80 W was established by examining the heliolongitude of all the flare associated events. It is demonstrated that the energy spectra determined at the time of maximum particle in the 20 to 80 MeV or 4 to 20 Mev interval range give results identical to that obtained by the 'distance-travelled' method
Bending of light in axion backgrounds
In this work we examine refraction of light by computing full solutions to
axion electrodynamics. We also allow for the possibility of an additional
plasma component. We then specialise to wavelengths which are small compared to
background scales to determine if refraction can be described by geometric
optics. We also allow for the possibility of an additional plasma component. In
the absence of plasma, for small incidence angles relative to the optical axis,
axion electrodynamics and geometric optics are in good agreement, with
refraction occurring at . However, for rays
which lie far from the optical axis, the agreement with geometric optics breaks
down and the dominant refraction requires a full wave-optical treatment,
occurring at . In the presence of
sufficiently large plasma masses, the wave-like nature of light becomes
suppressed and geometric optics is in good agreement with the full theory for
all rays. Our results therefore suggest the necessity of a more comprehensive
study of lensing and ray-tracing in axion backgrounds, including a full account
of the novel wave-optical contribution to
refraction.Comment: 14 pages, 7 figures. Comments are welcom
Optical properties of dynamical axion backgrounds
We discuss spectral distortions, time delays and refraction of light in an
axion or axion-plasma background. This involves solving the full set of
geodesic equations associated to the system of Hamiltonian optics, allowing us
to self-consistently take into account the evolution of the momentum, frequency
and position of photons. We support our arguments with analytic approximations
and full numerical solutions. Remarkably, the introduction of a plasma enhances
the sensitivity to axion-induced birefringence, allowing these effects to occur
at linear order in the axion-photon coupling even when the axion background is
not present at either the emission or detection points. This suggests a general
enhancement of axion-induced birefringence when the background refractive index
is different from one.Comment: Comments are welcom
Corotating energetic particle and fast plasma streams in the inner and outer solar system: Radial dependence and energy spectra
Interplanetary acceleration processes are shown as the most plausible explanation for the observed corotating energetic particle events. The relation between the energetic particle events and the properties of the high speed solar wind streams observed at 1 AU were investigated along with the form of the energy spectrum of the corotating energetic particle streams and its variation with respect to CIR boundaries and with radial distance. It is shown that: (1) at 1 AU a correlation exists between the j particle intensity and the solar wind velocity measured during the rising part of the event, of the form I is proportional to exp (V sub sw/V sub o); and (2) the energy spectra from .5 to 20 MeV are well represented by an exponential in momentum of the form dJ/dP = C exp (-P/P sub o). This representation is found to apply from .45 AU to beyond 5 AU. The variation of P sub o with respect to the CIR boundaries was studied using a method of superposed epoch analysis. It is shown that at 1 AU the spectrum remains constant during the first two days and then progressively flattens; between 3-4AU
The radial variation of corotating energetic particle streams in the inner and outer solar system
The radial gradient of long-lived, corotating energetic particle streams was measured using observations of .9-2.2 MeV protons from Helios 1 and 2, IMP 7, Pioneer 10 and Pioneer 11. A positive gradient of approximately 350% per AU is found between .3 AU and 1 AU. Between 1 AU and some 3-5 AU, the gradient is variable with an average value of 100% per AU which is consistent with earlier statistical results. A comparison between measurements at 9 AU and approximately 4 AU shows a negative gradient which is variable from -40 to -100% per AU. Possible solar latitudinal effects on these gradient studies are also discussed. Using solar wind and magnetic field data from Helios 1 between 1 AU and .3 AU, the relation between corotating energetic particle events in the inner solar system and the interplanetary medium is examined. It is found that the energetic particles are contained inside the high speed solar wind stream in a region adjacent to the interaction region between low speed and high speed streams
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