14,728 research outputs found
Latitudinal variation of the solar photospheric intensity
We have examined images from the Precision Solar Photometric Telescope (PSPT)
at the Mauna Loa Solar Observatory (MLSO) in search of latitudinal variation in
the solar photospheric intensity. Along with the expected brightening of the
solar activity belts, we have found a weak enhancement of the mean continuum
intensity at polar latitudes (continuum intensity enhancement
corresponding to a brightness temperature enhancement of ).
This appears to be thermal in origin and not due to a polar accumulation of
weak magnetic elements, with both the continuum and CaIIK intensity
distributions shifted towards higher values with little change in shape from
their mid-latitude distributions. Since the enhancement is of low spatial
frequency and of very small amplitude it is difficult to separate from
systematic instrumental and processing errors. We provide a thorough discussion
of these and conclude that the measurement captures real solar latitudinal
intensity variations.Comment: 24 pages, 8 figs, accepted in Ap
Geometry of Discrete Quantum Computing
Conventional quantum computing entails a geometry based on the description of
an n-qubit state using 2^{n} infinite precision complex numbers denoting a
vector in a Hilbert space. Such numbers are in general uncomputable using any
real-world resources, and, if we have the idea of physical law as some kind of
computational algorithm of the universe, we would be compelled to alter our
descriptions of physics to be consistent with computable numbers. Our purpose
here is to examine the geometric implications of using finite fields Fp and
finite complexified fields Fp^2 (based on primes p congruent to 3 mod{4}) as
the basis for computations in a theory of discrete quantum computing, which
would therefore become a computable theory. Because the states of a discrete
n-qubit system are in principle enumerable, we are able to determine the
proportions of entangled and unentangled states. In particular, we extend the
Hopf fibration that defines the irreducible state space of conventional
continuous n-qubit theories (which is the complex projective space CP{2^{n}-1})
to an analogous discrete geometry in which the Hopf circle for any n is found
to be a discrete set of p+1 points. The tally of unit-length n-qubit states is
given, and reduced via the generalized Hopf fibration to DCP{2^{n}-1}, the
discrete analog of the complex projective space, which has p^{2^{n}-1}
(p-1)\prod_{k=1}^{n-1} (p^{2^{k}}+1) irreducible states. Using a measure of
entanglement, the purity, we explore the entanglement features of discrete
quantum states and find that the n-qubit states based on the complexified field
Fp^2 have p^{n} (p-1)^{n} unentangled states (the product of the tally for a
single qubit) with purity 1, and they have p^{n+1}(p-1)(p+1)^{n-1} maximally
entangled states with purity zero.Comment: 24 page
Ellerman bombs and UV bursts: transient events in chromospheric current sheets
Ellerman bombs (EBs) and UV bursts are both brightenings related to flux
emergence regions and specifically to magnetic flux of opposite polarity that
meet in the photosphere. These two reconnection-related phenomena, nominally
formed far apart, occasionally occur in the same location and at the same time,
thus challenging our understanding of reconnection and heating of the lower
solar atmosphere. We consider the formation of an active region, including long
fibrils and hot and dense coronal plasma. The emergence of a untwisted magnetic
flux sheet, injected ~Mm below the photosphere, is studied as it pierces
the photosphere and interacts with the preexisting ambient field. Specifically,
we aim to study whether EBs and UV bursts are generated as a result of such
flux emergence and examine their physical relationship. The Bifrost radiative
magnetohydrodynamics code was used to model flux emerging into a model
atmosphere that contained a fairly strong ambient field, constraining the
emerging field to a limited volume wherein multiple reconnection events occur
as the field breaks through the photosphere and expands into the outer
atmosphere. Synthetic spectra of the different reconnection events were
computed using the D RH code and the fully 3D MULTI3D code. The formation
of UV bursts and EBs at intensities and with line profiles that are highly
reminiscent of observed spectra are understood to be a result of the
reconnection of emerging flux with itself in a long-lasting current sheet that
extends over several scale heights through the chromosphere. Synthetic
diagnostics suggest that there are no compelling reasons to assume that UV
bursts occur in the photosphere. Instead, EBs and UV bursts are occasionally
formed at opposite ends of a long current sheet that resides in an extended
bubble of cool gas.Comment: 10 pages, 8 figures, accepted by A&
Monopoles and the Emergence of Black Hole Entropy
One of the remarkable features of black holes is that they possess a
thermodynamic description, even though they do not appear to be statistical
systems. We use self-gravitating magnetic monopole solutions as tools for
understanding the emergence of this description as one goes from an ordinary
spacetime to one containing a black hole. We describe how causally distinct
regions emerge as a monopole solution develops a horizon. We define an entropy
that is naturally associated with these regions and that has a clear connection
with the Hawking-Bekenstein entropy in the critical black hole limit.Comment: 6 pages, one figure RevTe
First observations and magnitude measurement of Starlink's Darksat
Measure the Sloan g' magnitudes of the Starlink's STARLINK-1130 (Darksat) and
1113 LEO communication satellites and determine the effectiveness of the
Darksat darkening treatment at 475.4\,nm. Two observations of the Starlink's
Darksat LEO communication satellite were conducted on 2020/02/08 and 2020/03/06
using a Sloan r' and g' filter respectively. While a second satellite,
STARLINK-1113 was observed on 2020/03/06 using a Sloan g' filter. The initial
observation on 2020/02/08 was a test observation when Darksat was still
manoeuvring to its nominal orbit and orientation. Based on the successful test
observation, the first main observation was conducted on 2020/03/06 along with
an observation of the second Starlink satellite. The calibration, image
processing and analysis of the Darksat Sloan g' image gives an estimated Sloan
g' magnitude of at a range of 976.50\,km. For STARLINK-1113 an
estimated Sloan g' magnitude of at a range of 941.62\,km was
found. When scaled to a range of 550\,km and corrected for the solar and
observer phase angles, a reduction by a factor of two is seen in the reflected
solar flux between Darksat and STARLINK-1113. The data and results presented in
this work, show that the special darkening coating used by Starlink for Darksat
has darkened the Sloan g' magnitude by \,mag, when the range is
equal to a nominal orbital height (550\,km). This result will serve members of
the astronomical community modelling the satellite mega-constellations, to
ascertain their true impact on both the amateur and professional astronomical
communities. Concurrent and further observations are planned to cover the full
optical and NIR spectrum, from an ensemble of instruments, telescopes and
observatories.Comment: Accepted for publication in A&A Letters. 5 pages, 2 figures and 4
table
Hierarchical mean-field approach to the - Heisenberg model on a square lattice
We study the quantum phase diagram and excitation spectrum of the frustrated
- spin-1/2 Heisenberg Hamiltonian. A hierarchical mean-field
approach, at the heart of which lies the idea of identifying {\it relevant}
degrees of freedom, is developed. Thus, by performing educated, manifestly
symmetry preserving mean-field approximations, we unveil fundamental properties
of the system. We then compare various coverings of the square lattice with
plaquettes, dimers and other degrees of freedom, and show that only the {\it
symmetric plaquette} covering, which reproduces the original Bravais lattice,
leads to the known phase diagram. The intermediate quantum paramagnetic phase
is shown to be a (singlet) {\it plaquette crystal}, connected with the
neighboring N\'eel phase by a continuous phase transition. We also introduce
fluctuations around the hierarchical mean-field solutions, and demonstrate that
in the paramagnetic phase the ground and first excited states are separated by
a finite gap, which closes in the N\'eel and columnar phases. Our results
suggest that the quantum phase transition between N\'eel and paramagnetic
phases can be properly described within the Ginzburg-Landau-Wilson paradigm.Comment: LaTeX 2e, 14 pages, 17 figure
Conceptual design of the enhanced coolant purification systems for the European HCLL and HCPB test blanket modules
The Coolant Purification Systems (CPSs) is one of the most relevant ancillary systems of European Helium Cooled Lead Lithium (HCLL) and Helium Cooled Pebble Bed (HCPB) Test Blanket Modules (TBMs) which are currently in the preliminary design phase in view of their installation and operation in ITER. The CPS implements mainly two functions: the extraction and concentration of the tritium permeated from the TBM modules into the primary cooling circuit and the chemistry control of helium primary coolant. During the HCLL and HCPB-TBSs (Test Blanket Systems) Conceptual Design Review (CDR) in 2015 it was recognized the need of reducing the tritium permeation into the Port Cell #16 of ITER. To achieve this and, then, to lower the tritium partial pressure in the Helium Cooling Systems in normal operation, the helium flow-rate treated by each CPS has been increased of almost one order of magnitude. In 2017, to satisfy the CDR outcomes and the new design requirements requested by Fusion for Energy (F4E, the European Domestic Agency for ITER), ENEA performed a preliminary design of the “enhanced” CPSs. This paper presents the current design of the “enhanced” CPSs, focusing on design requirements, assumptions, selection of technologies and preliminary components sizing
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