3,447 research outputs found
Upper limits on transmitter rate of extragalactic civilizations placed by Breakthrough Listen observations
The Search for Extra-Terrestrial Intelligence (SETI) has been conducted for
over sixty years, yet no technosignatures have been identified. Previous
studies have focused on stars in our galaxy, with few searches in the
extragalactic Universe despite a larger volume being available. Civilizations
capable of harvesting energy from a star or a galaxy are classified as KII or
KIII on the Kardashev scale, respectively. Technosignatures from such advanced
civilizations would be extremely luminous and detectable by current radio
telescopes, even from distant galaxies. To explore the frontier of
extragalactic SETI, we investigate the likely prevalence of extragalactic
civilizations possessing a radio transmitter, known as the transmitter rate,
based on observational results from the Breakthrough Listen (BL) observations.
We calculated the transmitter rate by considering the background galaxies in
the field of view of target stars in BL observations. We used a statistical
method to derive the total mass of stars in those background galaxies from a
galaxy stellar mass function. Our statistical method suggests that less than
one in hundreds of trillions of extragalactic civilizations within 969 Mpc
possess a radio transmitter above 7.710 W of power, assuming one
civilization per one-solar-mass stellar system. Additionally, we cross-matched
the BL survey fields with the WISESuperCOSMOS Photometric Redshift
Catalogue and compared with the statistical method. Our result sets the
strictest limits to date on the transmitter rate at such high power levels,
emphasizing the high efficiency of searching for radio transmitters in galaxies
and the rarity of technologically advanced civilizations in our Universe.Comment: 5 pages, 1 figure, accepted for publication in MNRAS. A summary video
is available:
https://www.youtube.com/watch?v=_xaRCnLMjsY&t=21s&ab_channel=NCHUAstronom
Universal scaling functions for bond percolation on planar random and square lattices with multiple percolating clusters
Percolation models with multiple percolating clusters have attracted much
attention in recent years. Here we use Monte Carlo simulations to study bond
percolation on planar random lattices, duals of random
lattices, and square lattices with free and periodic boundary conditions, in
vertical and horizontal directions, respectively, and with various aspect ratio
. We calculate the probability for the appearance of
percolating clusters, the percolating probabilities, , the average
fraction of lattice bonds (sites) in the percolating clusters,
(), and the probability distribution function for the fraction
of lattice bonds (sites), in percolating clusters of subgraphs with
percolating clusters, (). Using a small number of
nonuniversal metric factors, we find that , ,
(), and () for random lattices, duals
of random lattices, and square lattices have the same universal finite-size
scaling functions. We also find that nonuniversal metric factors are
independent of boundary conditions and aspect ratios.Comment: 15 pages, 11 figure
Particle-hole symmetry and transport properties of the flux state in underdoped cuprates
Transport properties are studied for the flux state with the gauge flux
per plaquett, which may model the underdoped cuprates, with the emphasis
on the particle-hole and parity/chiral symmetries.This model is reduced to the
Dirac fermions in (2+1)D with a mass gap introduced by the antiferromagnetic
(AF) long range order and/or the stripe formation. Without the mass gap, the
Hall constant and the thermopower obey two-parameter scaling laws,
and show the strong temperature dependence due to the recovery of the
particle-hole symmetry at high temperature. The -dependences of and (independent of ) are in a sharp
contradiction with the experiments. (Here is the hole concentration.)
Therefore there is no signature of the particle-hole symmetry or the massless
Dirac fermions in the underdoped cuprates even above the Neel temperature
. With the mass gap introduced by the AF order, there occurs the parity
anomaly for each of the Dirac fermions. However the contributions from
different valleys and spins cancel with each other to result in no spontaneous
Hall effect even if the time-reversal symmetry is broken with .
The effects of the stripes are also studied. The diagonal and vertical
(horizontal) stripes have quite different influence on the transport
properties. The suppression of occurs at low temperature only when (i)
both the AF order and the vertical (horizontal) stripe coexist, and (ii) the
average over the in-plane direction is taken. Discussions on the recent
experiments are given from the viewpoint of these theoretical results.Comment: RevTeX, 14 pages, 11 figure
Delay of Squeezing and Entanglement using Electromagnetically Induced Transparency in a Vapour Cell
We demonstrate experimentally the delay of squeezed light and entanglement
using Electromagnetically Induced Transparency (EIT) in a rubidium vapour cell.
We perform quadrature amplitude measurements of the probe field and find no
appreciable excess noise from the EIT process. From an input squeezing of 3.1
dB at low sideband frequencies, we observed the survival of 2 dB of squeezing
at the EIT output. By splitting the squeezed light on a beam-splitter, we
generated biased entanglement between two beams. We transmit one of the
entangled beams through the EIT cell and correlate the quantum statistics of
this beam with its entangled counterpart. We experimentally observed a 2 s
delay of the biased entanglement and obtained a preserved degree of
wavefunction inseparability of 0.71, below the unity value for separable
states.Comment: 8 pages, 5 figure
Axionic D3-D7 Inflation
We study the motion of a D3 brane moving within a Type IIB string vacuum
compactified to 4D on K3 x T_2/Z_2 in the presence of D7 and O7 planes. We work
within the effective 4D supergravity describing how the mobile D3 interacts
with the lightest bulk moduli of the compactification, including the effects of
modulus-stabilizing fluxes. We seek inflationary solutions to the resulting
equations, performing our search numerically in order to avoid resorting to
approximate parameterizations of the low-energy potential. We consider
uplifting from D-terms and from the supersymmetry-breaking effects of anti-D3
branes. We find examples of slow-roll inflation (with anti-brane uplifting)
with the mobile D3 moving along the toroidal directions, falling towards a
D7-O7 stack starting from the antipodal point. The inflaton turns out to be a
linear combination of the brane position and the axionic partner of the K3
volume modulus, and the similarity of the potential along the inflaton
direction with that of racetrack inflation leads to the prediction n_s \le 0.95
for the spectral index. The slow roll is insensitive to most of the features of
the effective superpotential, and requires a one-in-10^4 tuning to ensure that
the torus is close to square in shape. We also consider D-term inflation with
the D3 close to the attractive D7, but find that for a broad (but not
exhaustive) class of parameters the conditions for slow roll tend to
destabilize the bulk moduli. In contrast to the axionic case, the best
inflationary example of this kind requires the delicate adjustment of potential
parameters (much more than the part-per-mille level), and gives inflation only
at an inflection point of the potential (and so suffers from additional
fine-tuning of initial conditions to avoid an overshoot problem).Comment: 29 pages, 5 figure
Self-similar Approximants of the Permeability in Heterogeneous Porous Media from Moment Equation Expansions
We use a mathematical technique, the self-similar functional renormalization,
to construct formulas for the average conductivity that apply for large
heterogeneity, based on perturbative expansions in powers of a small parameter,
usually the log-variance of the local conductivity. Using
perturbation expansions up to third order and fourth order in
obtained from the moment equation approach, we construct the general functional
dependence of the transport variables in the regime where is of
order 1 and larger than 1. Comparison with available numerical simulations give
encouraging results and show that the proposed method provides significant
improvements over available expansions.Comment: Latex, 14 pages + 5 ps figure
Weekly gemcitabine plus 24-h infusion of high-dose 5-fluorouracil/leucovorin for locally advanced or metastatic carcinoma of the biliary tract
[[abstract]]Both gemcitabine and weekly 24-h infusion of high-dose 5-fluorouracil/leucovorin (HDFL) have shown promising antitumour activity for patients with locally advanced or metastatic carcinoma of the biliary tract (CBT). From April 1999 through December 2002, 30 patients with inoperable CBT were treated with gemcitabine 800 mg m(-2), intravenous infusion for 30 min, followed by 5-FU, 2000 mg m(-2) and leucovorin, 300 mg m(-2), intravenous infusion for 24 h, on day 1, 8 and 15, every 4 weeks. A total of 166 cycles were given (median of four cycles per patient, range 1-24 cycles). Response was evaluable in 28 patients and toxicity in 29 patients. Partial response was obtained in six patients, stable disease in 13, while progressive disease occurred in nine. The objective response rate was 21.4% (95% CI: 5.2-37.6%). The most common grade 3 or 4 toxicity was infection (nine patients). Other types of grade 3 or 4 toxicity included leucopenia (four patients), thrombocytopenia (three patients), anaemia (three patients), nausea/vomiting (two patients) and elevation of liver transaminases (three patients). As of 30 September 2003, the median progression-free survival was 3.7 months (95% CI: 2.8-4.6 months) and the median overall survival was 4.7 months (95% CI: 0.8-8.6 months). Our data suggest that weekly gemcitabine plus HDFL is modestly active with acceptable treatment-related toxicity for patients with advanced CBT
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