511 research outputs found
The quantum correlation between the selection of the problem and that of the solution sheds light on the mechanism of the quantum speed up
In classical problem solving, there is of course correlation between the
selection of the problem on the part of Bob (the problem setter) and that of
the solution on the part of Alice (the problem solver). In quantum problem
solving, this correlation becomes quantum. This means that Alice contributes to
selecting 50% of the information that specifies the problem. As the solution is
a function of the problem, this gives to Alice advanced knowledge of 50% of the
information that specifies the solution. Both the quadratic and exponential
speed ups are explained by the fact that quantum algorithms start from this
advanced knowledge.Comment: Earlier version submitted to QIP 2011. Further clarified section 1,
"Outline of the argument", submitted to Phys Rev A, 16 page
Footprints of the Newly-Discovered Vela Supernova in Antarctic Ice Cores?
The recently-discovered, nearby young supernova remnant in the southeast
corner of the older Vela supernova remnant may have been seen in measurements
of nitrate abundances in Antarctic ice cores. Such an interpretation of this
twenty-year-old ice-core data would provide a more accurate dating of this
supernova than is possible purely using astrophysical techniques. It permits an
inference of the supernova4s Ti yield purely on an observational
basis, without reference to supernova modelling. The resulting estimates of the
supernova distance and light-arrival time are 200 pc and 700 years ago,
implying an expansion speed of 5,000 km/s for the supernova remnant. Such an
expansion speed has been argued elsewhere to imply the explosion to have been a
15 Type II supernova. This interpretation also adds new evidence to
the debate as to whether nearby supernovae can measurably affect nitrate
abundances in polar ice cores.Comment: 12 pages, TeX, 2 enclosed figures. Updated references, and more
detailed discussion of how inferences are made of supernova propertie
The fractal structure of the universe : a new field theory approach
While the universe becomes more and more homogeneous at large scales,
statistical analysis of galaxy catalogs have revealed a fractal structure at
small-scales (\lambda < 100 h^{-1} Mpc), with a fractal dimension D=1.5-2
(Sylos Labini et al 1996). We study the thermodynamics of a self-gravitating
system with the theory of critical phenomena and finite-size scaling and show
that gravity provides a dynamical mechanism to produce this fractal structure.
We develop a field theoretical approach to compute the galaxy distribution,
assuming them to be in quasi-isothermal equilibrium. Only a limited, (although
large), range of scales is involved, between a short-distance cut-off below
which other physics intervene, and a large-distance cut-off, where the thermo-
dynamic equilibrium is not satisfied. The galaxy ensemble can be considered at
critical conditions, with large density fluctuations developping at any scale.
From the theory of critical phenomena, we derive the two independent critical
exponents nu and eta and predict the fractal dimension D = 1/nu to be either
1.585 or 2, depending on whether the long-range behaviour is governed by the
Ising or the mean field fixed points, respectively. Both set of values are
compatible with present observations. In addition, we predict the scaling
behaviour of the gravitational potential to be r^{-(1 + eta)/2}. That is,
r^{-0.5} for mean field or r^{- 0.519} for the Ising fixed point. The theory
allows to compute the three and higher density correlators without any
assumption or Ansatz. We find that the N-points density scales as
r_1^{(N-1)(D-3)}, when r_1 >> r_i, 2 leq i leq N . There are no free parameters
in this theory.Comment: Latex, 20 pages, no figures, to be published in the Astrophysical
Journa
Muon-Induced Background Study for Underground Laboratories
We provide a comprehensive study of the cosmic-ray muon flux and induced
activity as a function of overburden along with a convenient parameterization
of the salient fluxes and differential distributions for a suite of underground
laboratories ranging in depth from 1 to 8 km.w.e.. Particular attention
is given to the muon-induced fast neutron activity for the underground sites
and we develop a Depth-Sensitivity-Relation to characterize the effect of such
background in experiments searching for WIMP dark matter and neutrinoless
double beta decay.Comment: 18 pages, 28 figure
Grand minima and maxima of solar activity: New observational constraints
Using a reconstruction of sunspot numbers stretching over multiple millennia,
we analyze the statistics of the occurrence of grand minima and maxima and set
new observational constraints on long-term solar and stellar dynamo models.
We present an updated reconstruction of sunspot number over multiple
millennia, from C data by means of a physics-based model, using an
updated model of the evolution of the solar open magnetic flux. A list of grand
minima and maxima of solar activity is presented for the Holocene (since 9500
BC) and the statistics of both the length of individual events as well as the
waiting time between them are analyzed.
The occurrence of grand minima/maxima is driven not by long-term cyclic
variability, but by a stochastic/chaotic process. The waiting time distribution
of the occurrence of grand minima/maxima deviates from an exponential
distribution, implying that these events tend to cluster together with long
event-free periods between the clusters. Two different types of grand minima
are observed: short (30--90 years) minima of Maunder type and long (110
years) minima of Sp\"orer type, implying that a deterministic behaviour of the
dynamo during a grand minimum defines its length. The duration of grand maxima
follows an exponential distribution, suggesting that the duration of a grand
maximum is determined by a random process.
These results set new observational constraints upon the long-term behaviour
of the solar dynamo.Comment: 10 Figure
Evolution of the solar irradiance during the Holocene
Aims. We present a physically consistent reconstruction of the total solar
irradiance for the Holocene. Methods. We extend the SATIRE models to estimate
the evolution of the total (and partly spectral) solar irradiance over the
Holocene. The basic assumption is that the variations of the solar irradiance
are due to the evolution of the dark and bright magnetic features on the solar
surface. The evolution of the decadally averaged magnetic flux is computed from
decadal values of cosmogenic isotope concentrations recorded in natural
archives employing a series of physics-based models connecting the processes
from the modulation of the cosmic ray flux in the heliosphere to their record
in natural archives. We then compute the total solar irradiance (TSI) as a
linear combination of the jth and jth + 1 decadal values of the open magnetic
flux. Results. Reconstructions of the TSI over the Holocene, each valid for a
di_erent paleomagnetic time series, are presented. Our analysis suggests that
major sources of uncertainty in the TSI in this model are the heritage of the
uncertainty of the TSI since 1610 reconstructed from sunspot data and the
uncertainty of the evolution of the Earth's magnetic dipole moment. The
analysis of the distribution functions of the reconstructed irradiance for the
last 3000 years indicates that the estimates based on the virtual axial dipole
moment are significantly lower at earlier times than the reconstructions based
on the virtual dipole moment. Conclusions. We present the first physics-based
reconstruction of the total solar irradiance over the Holocene, which will be
of interest for studies of climate change over the last 11500 years. The
reconstruction indicates that the decadally averaged total solar irradiance
ranges over approximately 1.5 W/m2 from grand maxima to grand minima
Atmospheric Muon Flux at Sea Level, Underground, and Underwater
The vertical sea-level muon spectrum at energies above 1 GeV and the
underground/underwater muon intensities at depths up to 18 km w.e. are
calculated. The results are particularly collated with a great body of the
ground-level, underground, and underwater muon data. In the hadron-cascade
calculations, the growth with energy of inelastic cross sections and pion,
kaon, and nucleon generation in pion-nucleus collisions are taken into account.
For evaluating the prompt muon contribution to the muon flux, we apply two
phenomenological approaches to the charm production problem: the recombination
quark-parton model and the quark-gluon string model. To solve the muon
transport equation at large depths of homogeneous medium, a semi-analytical
method is used. The simple fitting formulas describing our numerical results
are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially
all underground data on the muon intensity correlate with each other and with
predicted depth-intensity relation for conventional muons to within 10%.
However, the high-energy sea-level data as well as the data at large depths are
contradictory and cannot be quantitatively decribed by a single nuclear-cascade
model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data
and references added, typos correcte
Test of the CRASH experiment counters at GSI
The CRASH (Cosmic RAys and Strange Hadronic matter) balloonborne experiment is specifically designed for the detection of the Strange Quark Matter, which according to theory is probably present in the cosmic-ray radiation at
the top of the atmosphere. The detection technique is based on the measure of the AOZ ratio of the nuclei crossing the detector. The charge, the velocity and the mass of the incoming nuclei are determined using both active and passive detectors. First results of the tests of the CËerenkov and scintillation counters performed at GSI
Darmstadt with heavy ions (Ar and Ni) of different energies are reported
Cosmogenic effects in Mbale, L5/6 chondrite
Measurements of particle tracks, cosmogenic radionuclides, and rare gas isotopes in Mbale indicate that the meteoroid had a simple, one-stage exposure for 30.2 Ma in interplanetary space. On the basis of the measured track production rates and 60Co and 26Al activities, the meteoroid is estimated to be a sphere with a radius of ≈ 36 cm. The activities of several cosmogenic radionuclides (i.e., 57Co, 54Mn, 22Na, 44Ti, and 26Al) in two fragments having different shielding, as estimated by their track density and 60Co activity, provide the depth variation in their production rates. Cobalt-57, 54Mn and 22Na activities agree with the production that is expected around the maximum of the solar cycle 22 as calculated from the Sunspot numbers. The U, Th-4He and K-40Ar ages are measured to be 0.54 Ga indicating a late thermal event which is in agreement with the thermal history of some other L group chondrites. The trapped N has δ 15N of -57 ± 4%o, which is much lighter than the average L-group chondrite value; this indicates the presence of an isotopically anomalous light N component
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