4,441 research outputs found
Solving the kilo-second QPO problem of the intermediate polar GK Persei
We detect the likely optical counterpart to previously reported X-ray QPOs in
spectrophotometry of the intermediate polar GK Persei during the 1996 dwarf
nova outburst. The characteristic timescales range between 4000--6000 s.
Although the QPOs are an order of magnitude longer than those detected in the
other dwarf novae we show that a new QPO model is not required to explain the
long timescale observed. We demonstrate that the observations are consistent
with oscillations being the result of normal-timescale QPOs beating with the
spin period of the white dwarf. We determine the spectral class of the
companion to be consistent with its quiescent classification and find no
significant evidence for irradiation over its inner face. We detect the white
dwarf spin period in line fluxes, V/R ratios and Doppler-broadened emission
profiles.Comment: 14 pages, 11 figures. Accepted for publication in MNRA
Long-Term Load Forecasting Considering Volatility Using Multiplicative Error Model
Long-term load forecasting plays a vital role for utilities and planners in
terms of grid development and expansion planning. An overestimate of long-term
electricity load will result in substantial wasted investment in the
construction of excess power facilities, while an underestimate of future load
will result in insufficient generation and unmet demand. This paper presents
first-of-its-kind approach to use multiplicative error model (MEM) in
forecasting load for long-term horizon. MEM originates from the structure of
autoregressive conditional heteroscedasticity (ARCH) model where conditional
variance is dynamically parameterized and it multiplicatively interacts with an
innovation term of time-series. Historical load data, accessed from a U.S.
regional transmission operator, and recession data for years 1993-2016 is used
in this study. The superiority of considering volatility is proven by
out-of-sample forecast results as well as directional accuracy during the great
economic recession of 2008. To incorporate future volatility, backtesting of
MEM model is performed. Two performance indicators used to assess the proposed
model are mean absolute percentage error (for both in-sample model fit and
out-of-sample forecasts) and directional accuracy.Comment: 19 pages, 11 figures, 3 table
Revealing the Archetype: The Journey of a Trecento Madonna and Child at the National Museum of Scotland
The National Museums Scotland Madonna and
Child project sought to uncover and document
the history of a fine polychrome wood carving
attributed to The Master of the Gualino St
Catherine and to prepare it for display. A new
body of knowledge has been assembled by
the interdisciplinary team. The conservation
treatment was informed by this work and led
to further discoveries: the removal of overpaint
exposing a previously hidden underdrawing.
The ethics of the treatment decisions, including
the removal of the Christ Child’s 1960s’ fingers required team dialogue and was opened up for
the public to respond to in a series of blogs.
The discovery of a rich polychromy including
gold and glazed tin has led to further plans to
produce a 3-D colour reconstruction. The collaborations
developed during this project will
facilitate future joint ventures for polychrome
sculpture in Scottish collections
On Two Complementary Types of Total Time Derivative in Classical Field Theories and Maxwell's Equations
Close insight into mathematical and conceptual structure of classical field
theories shows serious inconsistencies in their common basis. In other words,
we claim in this work to have come across two severe mathematical blunders in
the very foundations of theoretical hydrodynamics. One of the defects concerns
the traditional treatment of time derivatives in Eulerian hydrodynamic
description. The other one resides in the conventional demonstration of the
so-called Convection Theorem. Both approaches are thought to be necessary for
cross-verification of the standard differential form of continuity equation.
Any revision of these fundamental results might have important implications for
all classical field theories. Rigorous reconsideration of time derivatives in
Eulerian description shows that it evokes Minkowski metric for any flow field
domain without any previous postulation. Mathematical approach is developed
within the framework of congruences for general 4-dimensional differentiable
manifold and the final result is formulated in form of a theorem. A modified
version of the Convection Theorem provides a necessary cross-verification for a
reconsidered differential form of continuity equation. Although the approach is
developed for one-component (scalar) flow field, it can be easily generalized
to any tensor field. Some possible implications for classical electrodynamics
are also explored.Comment: no figure
Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423
CONTEXT: The induced gravitational collapse (IGC) scenario has been
introduced in order to explain the most energetic gamma ray bursts (GRBs),
Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led
to the concept of binary-driven hypernovae (BdHNe) originating in a tight
binary system composed by a FeCO core on the verge of a SN explosion and a
companion neutron star (NS). Their evolution is characterized by a rapid
sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the
farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We
compare and contrast the spectra, the luminosity evolution and the
detectability in the observations by Swift of GRB 090423 with the corresponding
ones of the best known BdHN case, GRB 090618. RESULTS: Identification of
constant slope power-law behavior in the late X-ray emission of GRB 090423 and
its overlapping with the corresponding one in GRB 090618, measured in a common
rest frame, represents the main result of this article. This result represents
a very significant step on the way to using the scaling law properties, proven
in Episode 3 of this BdHN family, as a cosmological standard candle.
CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we
can conclude that SN events, leading to NS formation, can already occur already
at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these
BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the
Population II stars after the completion and possible disappearance of
Population III stars.Comment: 9 pages, 9 figures, to appear on A&
On the thermal and double episode emissions in GRB 970828
Following the recent theoretical interpretation of GRB 090618 and GRB 101023,
we here interpret GRB 970828 in terms of a double episode emission: the first
episode, observed in the first 40 s of the emission, is interpreted as the
proto-black-hole emission; the second episode, observed after t+50 s, as a
canonical gamma ray burst. The transition between the two episodes marks the
black hole formation. The characteristics of the real GRB, in the second
episode, are an energy of erg, a
baryon load of and a bulk Lorentz factor at transparency
of . The clear analogy with GRB 090618 would require also in
GRB 970828 the presence of a possible supernova. We also infer that the GRB
exploded in an environment with a large average particle density part/cm and dense clouds characterized by typical dimensions
of cm and . Such an environment
is in line with the observed large column density absorption, which might have
darkened both the supernova emission and the GRB optical afterglow.Comment: 7 pages, 10 figures, submitted to Ap
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