5,309 research outputs found
Semiclassical (Quantum Field Theory) and Quantum (String) de Sitter Regimes: New Results
We compute the quantum string entropy S_s(m, H) from the microscopic string
density of states rho_s (m,H) of mass m in de Sitter space-time. We find for
high m, a {\bf new} phase transition at the critical string temperature T_s=
(1/2 pi k_B)L c^2/alpha', higher than the flat space (Hagedorn) temperature
t_s. (L = c/H, the Hubble constant H acts at the transition as producing a
smaller string constant alpha' and thus, a higher tension). T_s is the precise
quantum dual of the semiclassical (QFT Hawking-Gibbons) de Sitter temperature
T_sem = hbar c /(2\pi k_B L). We find a new formula for the full de Sitter
entropy S_sem (H), as a function of the usual Bekenstein-Hawking entropy
S_sem^(0)(H). For L << l_{Planck}, ie. for low H << c/l_Planck,
S_{sem}^{(0)}(H) is the leading term, but for high H near c/l_Planck, a new
phase transition operates and the whole entropy S_sem (H) is drastically
different from the Bekenstein-Hawking entropy S_sem^(0)(H). We compute the
string quantum emission cross section by a black hole in de Sitter (or
asymptotically de Sitter) space-time (bhdS). For T_sem ~ bhdS << T_s, (early
evaporation stage), it shows the QFT Hawking emission with temperature T_sem ~
bhdS, (semiclassical regime). For T_sem ~ bhdS near T_{s}, it exhibits a phase
transition into a string de Sitter state of size L_s = l_s^2/L}, l_s=
\sqrt{\hbar alpha'/c), and string de Sitter temperature T_s. Instead of
featuring a single pole singularity in the temperature (Carlitz transition), it
features a square root branch point (de Vega-Sanchez transition). New bounds on
the black hole radius r_g emerge in the bhdS string regime: it can become r_g =
L_s/2, or it can reach a more quantum value, r_g = 0.365 l_s.Comment: New original materia
Warm inflationary model in loop quantum cosmology
A warm inflationary universe model in loop quantum cosmology is studied. In
general we discuss the condition of inflation in this framework. By using a
chaotic potential, , we develop a model where the
dissipation coefficient constant. We use recent astronomical
observations for constraining the parameters appearing in our model.Comment: 15 pages, 1 figure, Accepted for publication in Phys. Rev.
Semiclassical (QFT) and Quantum (String) anti - de Sitter Regimes: New Results
We compute the quantum string entropy S_s(m, H) from the microscopic string
density of states of mass m in Anti de Sitter space-time. For high m, (high Hm
-->c/\alpha'), no phase transition occurs at the Anti de Sitter string
temperature T_{s} which is higher than the flat space (Hagedorn) temperature
t_{s}. (the Hubble constant H acts as producing a smaller string constant and
thus, a higher tension). T_s is the precise quantum dual of the semiclassical
(QFT) Anti de Sitter temperature scale . We compute the quantum string emission
by a black hole in Anti de Sitter space-time (bhAdS). In the early evaporation
stage, it shows the QFT Hawking emission with temperature T_{sem~bhAdS},
(semiclassical regime). For T_{sem~bhAdS}--> T_{s}, it exhibits a phase
transition into a Anti de Sitter string state. New string bounds on the black
hole emerge in the bhAdS string regime. We find a new formula for the full
(quantum regime included) Anti de Sitter entropy S_{sem}, as a function of the
usual Bekenstein-Hawking entropy S_{sem}^(0). For low H (semiclassical regime),
S_{sem}^(0) is the leading term but for high H (quantum regime), no phase
transition operates, in contrast to de Sitter space, and the entropy S_{sem} is
very different from the Bekenstein-Hawking term S_{sem}^(0).Comment: Comments 26 pages; no figure
Semiclassical (QFT) and Quantum (String) Rotating Black Holes and their Evaporation: New Results
Combination of both quantum field theory (QFT) and string theory in curved
backgrounds in a consistent framework, the string analogue model, allows us to
provide a full picture of the Kerr-Newman black hole and its evaporation going
beyond the current picture. We compute the quantum emission cross section of
strings by a Kerr-Newmann black hole (KNbh). It shows the black hole emission
at the Hawking temperature T_{sem} in the early evaporation and the new string
emission featuring a Hagedorn transition into a string state of temperature T_
s at the last stages. New bounds on the angular momentum J and charge Q emerge
in the quantum string regime. The last state of evaporation of a semiclassical
KNbh is a string state of temperature T_s, mass M_s, J = 0 = Q, decaying as a
quantum string into all kinds of particles.(There is naturally, no loss of
information, (no paradox at all)). We compute the microscopic string entropy
S_s(m, j) of mass m and spin mode j. (Besides the usual transition at T_s), we
find for high j, (extremal string states) a new phase transition at a
temperature T_{sj} higher than T_s. We find a new formula for the Kerr black
hole entropy S_{sem}, as a function of the usual Bekenstein-Hawking entropy .
For high angular momentum, (extremal J = GM^2/c), a gravitational phase
transition operates and the whole entropy S_{sem} is drastically different from
the Bekenstein-Hawking entropy. This new extremal black hole transition occurs
at a temperature T_{sem J} higher than the Hawking temperature T_{sem}.Comment: New articl
Comprehensive transient-state study for CARMENES-NIR high thermal stability
CARMENES has been proposed as a next-generation instrument for the 3.5m Calar
Alto Telescope. Its objective is finding habitable exoplanets around M dwarfs
through radial velocity measurements (m/s level) in the near-infrared.
Consequently, the NIR spectrograph is highly constraint regarding
thermal/mechanical requirements. As a first approach, the thermal stability has
been limited to \pm 0.01K (within year period) over a working temperature of
243K. This can be achieved by means of several temperature-controlled rooms.
The options considered to minimise the complexity of the thermal design are
here presented, as well as the transient-state thermal analyses realised to
make the best choice
Present and future of the OTELO project
OTELO is an emission-line object survey carried out with the red tunable
filter of the instrument OSIRIS at the GTC, whose aim is to become the deepest
emission-line object survey to date. With 100% of the data of the first
pointing finally obtained in June 2014, we present here some aspects of the
processing of the data and the very first results of the OTELO survey. We also
explain the next steps to be followed in the near future.Comment: Oral contribution presented in the XI Scientific Meeting of the
Spanish Astronomical Society held on September 8-12, in Teruel, Spain (7
pages, 2 figures, 1 table). To appear in Highlights of Spanish Astrophysics
VIII, Proceedings of the XI Scientific Meeting of the Spanish Astronomical
Society. Eds. A. J. Cenarro, F. Figueras, C. Hern\'andez-Monteagudo, J.
Trujillo, L. Valdiviels
Conical refraction healing after partially blocking the input beam
In conical refraction, when a focused Gaussian beam passes along one of the
optic axes of a biaxial crystal it is transformed into a pair of concentric
bright rings at the focal plane. We demonstrate both theoretically and
experimentally that this transformation is hardly affected by partially
blocking the Gaussian input beam with an obstacle. We analyze the influence of
the size of the obstruction both on the transverse intensity pattern of the
beam and on its state of polarization, which is shown to be very robust
On the probability of reaching a barrier in an Erlang(2) risk process
HolaIn this paper the process of aggregated claims in a non-life insurance portfolio as
defined in the classical model of risk theory is modified. The Compound Poisson process is replaced with a more general renewal risk process with interoccurrence times of Erlangian type. We focus our analysis on the probability that the process of surplus reaches a certain level before ruin occurs, χ(u,b). Our main contribution is the generalization obtained in the computation of χ(u,b) for the case of interoccurrence time between claims distributed as Erlang(2, β) and the individual claim amount as Erlang
(n, γ).Peer Reviewe
Microdroplet fabrication of silver–agarose nanocomposite beads for SERS optical accumulation
Microdroplets have been used as reactors for the fabrication of agarose beads with high uniformity in shape and size, and densely loaded with silver ions, which were subsequently reduced into nanoparticles using hydrazine. The resulting nanocomposite beads not only display a high plasmonic activity, but can also trap/concentrate analytes, which can be identified by means of surface-enhanced Raman scattering (SERS) spectroscopy. The size of the beads is such that it allows the detection of a single bead under a conventional optical microscope, which is very useful to reduce the amount of material required for SERS detectio
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