1,446 research outputs found
The Bulk Motion of Flat Edge-On Galaxies Based on 2MASS Photometry
We report the results of applying the 2MASS Tully-Fisher (TF) relations to
study the galaxy bulk flows. For 1141 all-sky distributed flat RFGC galaxies we
construct J, H, K_s TF relations and find that Kron magnitudes show
the smallest dispersion on the TF diagram. For the sample of 971 RFGC galaxies
with V_{3K} < 18000 km/s we find a dispersion and an
amplitude of bulk flow V= 199 +/-61 km/s, directed towards l=301 degr +/-18
degr, b=-2 degr +/-15 degr. Our determination of low-amplitude coherent flow is
in good agreement with a set of recent data derived from EFAR, PSCz, SCI/SCII
samples. The resultant two- dimensional smoothed peculiar velocity field traces
well the large-scale density variations in the galaxy distributions. The
regions of large positive peculiar velocities lie in the direction of the Great
Attractor and Shapley concentration. A significant negative peculiar velocity
is seen in the direction of Bootes and in the direction of the Local void. A
small positive peculiar velocity (100 -- 150 km/s) is seen towards the
Pisces-Perseus supercluster, as well as the Hercules - Coma - Corona Borealis
supercluster regions.Comment: 10 pages, 5 figures. A&A/2003/3582 accepted 15.05.200
Revisiting consistency conditions for quantum states of systems on closed timelike curves: an epistemic perspective
There has been considerable recent interest in the consequences of closed
timelike curves (CTCs) for the dynamics of quantum mechanical systems. A vast
majority of research into this area makes use of the dynamical equations
developed by Deutsch, which were developed from a consistency condition that
assumes that mixed quantum states uniquely describe the physical state of a
system. We criticise this choice of consistency condition from an epistemic
perspective, i.e., a perspective in which the quantum state represents a state
of knowledge about a system. We demonstrate that directly applying Deutsch's
condition when mixed states are treated as representing an observer's knowledge
of a system can conceal time travel paradoxes from the observer, rather than
resolving them. To shed further light on the appropriate dynamics for quantum
systems traversing CTCs, we make use of a toy epistemic theory with a strictly
classical ontology due to Spekkens and show that, in contrast to the results of
Deutsch, many of the traditional paradoxical effects of time travel are
present.Comment: 10 pages, 6 figures, comments welcome; v2 added references and
clarified some points; v3 published versio
Peculiar Velocities of 3000 Spiral Galaxies from the 2MFGC Catalog
The 2MFGC catalog we have used contains 18020 galaxies selected from the
extended objects in the 2MASS infrared sky survey as having apparent ratios of
the axes b/a<0.3. Most of them are spiral galaxies of later morphological types
whose disks are seen almost edge-on. The individual distances to the 2724 2MFGC
galaxies with known rotation velocities and radial velocities are determined
using a multiparameter infrared Tully-Fisher relation. A list of the distances
and peculiar velocities of these galaxies is presented. The collective motion
of the 2MFGC galaxies relative to the cosmic microwave background is
characterized by a velocity V = 199 +- 37 km/s in the direction l = 304o +-
11o, b = -8o +- 8o. Our list is currently the most representative and uniform
sample for analyzing non-Hubble motions of galaxies on a scale of ~100 Mpc.Comment: 12 pages, 5 figures, 1 table (here we present the beginning of the
table as an illustration). Astrophysics, Vol. 49, No. 4, 2006. Original
article submitted June 13, 2006. Translated from Astrofizika, Vol. 49, No. 4,
pp. 527-540 (November 2006
Can biological quantum networks solve NP-hard problems?
There is a widespread view that the human brain is so complex that it cannot
be efficiently simulated by universal Turing machines. During the last decades
the question has therefore been raised whether we need to consider quantum
effects to explain the imagined cognitive power of a conscious mind.
This paper presents a personal view of several fields of philosophy and
computational neurobiology in an attempt to suggest a realistic picture of how
the brain might work as a basis for perception, consciousness and cognition.
The purpose is to be able to identify and evaluate instances where quantum
effects might play a significant role in cognitive processes.
Not surprisingly, the conclusion is that quantum-enhanced cognition and
intelligence are very unlikely to be found in biological brains. Quantum
effects may certainly influence the functionality of various components and
signalling pathways at the molecular level in the brain network, like ion
ports, synapses, sensors, and enzymes. This might evidently influence the
functionality of some nodes and perhaps even the overall intelligence of the
brain network, but hardly give it any dramatically enhanced functionality. So,
the conclusion is that biological quantum networks can only approximately solve
small instances of NP-hard problems.
On the other hand, artificial intelligence and machine learning implemented
in complex dynamical systems based on genuine quantum networks can certainly be
expected to show enhanced performance and quantum advantage compared with
classical networks. Nevertheless, even quantum networks can only be expected to
efficiently solve NP-hard problems approximately. In the end it is a question
of precision - Nature is approximate.Comment: 38 page
Peculiar Motions in the Region of the Ursa Major Supercluster of Galaxies
We have investigated the peculiar motions of clusters of galaxies in the Ursa
Major (UMa) supercluster and its neighborhood. Based on SDSS (Sloan Digital Sky
Survey) data, we have compiled a sample of early-type galaxies and used their
fundamental plane to determine the cluster distances and peculiar velocities.
The samples of early-type galaxies in the central regions (within R_200) of 12
UMa clusters of galaxies, in three main subsystems of the supercluster -- the
filamentary structures connecting the clusters, and in nine clusters from the
nearest UMa neighborhood have similar parameters. The fairly high overdensity
(3 by the galaxy number and 15 by the cluster number) suggests that the
supercluster as a whole is gravitationally bound, while no significant peculiar
motions have been found: the peculiar velocities do not exceed the measurement
errors by more than a factor of 1.5-2. The mean random peculiar velocities of
clusters and the systematic deviations from the overall Hubble expansion in the
supercluster are consistent with theoretical estimates. For the possible
approach of the three UMa subsystems to be confirmed, the measurement accuracy
must be increased by a factor of 2-3.Comment: 21 pages, 4 tables, 7 figure
Bbasic analysis of the scope of patent protection: suggestions from the transaction cost theory
The objective of this study was to evaluate the feasibility, reliability, validity and responsiveness of the HIV Overview of Problems Evaluation System (HOPES) in a Dutch sample. The HOPES was administered three times in a one-year period to a sample of 106 outpatients with a symptomatic HIV-infection (n = 23) or AIDS (n = 83). The HOPES is a self-report HIV-specific quality of life (QOL) questionnaire including five scales: physical, psycho-social and sexual functioning, medical interaction and partner relationship. QOL was also assessed with the EORTC Quality of Life Questionnaire (EORTC QLQ-C30), a 30-item self-report instrument. Clinical data included Centers for Disease Control and Prevention (CDC) stage, date of diagnosis and CD4 cell count. Patients needed approximately 20-30 minutes to complete the questionnaire. The five scales had good internal consistency reliability. Multitrait scaling analysis provided moderate support for item discriminant and convergent validity. The HOPES exhibited adequate levels of construct validity: (1) the inter-scale correlations and correlations with the EORTC QLQ-C30 were in the predicted direction; (2) it discriminated clearly between patients with AIDS and ARC and (3) it was able to document changes in QOL over time. Moreover, the HOPES was responsive to changes in clinical status over time as indicated by CD4 counts. This study provides further evidence of the reliability and validity of the HOPES and shows that this instrument is responsive to changes in CD4 cell count
Establishing the European Norm for the health-related quality of life domains of the computer-adaptive test EORTC CAT Core
OBJECTIVE: The computer-adaptive test (CAT) of the European Organisation for Research and Treatment of Cancer (EORTC), the EORTC CAT Core, assesses the same 15 domains as the EORTC QLQ-C30 health-related quality of life questionnaire but with increased precision, efficiency, measurement range and flexibility. CAT parameters for estimating scores have been established based on clinical data from cancer patients. This study aimed at establishing the European Norm for each CAT domain based on general population data.
METHODS: We collected representative general population data across 11 European Union (EU) countries, Russia, Turkey, Canada and the United States (n \u3e /= 1000/country; stratified by sex and age). We selected item subsets from each CAT domain for data collection (totalling 86 items). Differential item functioning (DIF) analyses were conducted to investigate cross-cultural measurement invariance. For each domain, means and standard deviations from the EU countries (weighted by country population, sex and age) were used to establish a T-metric with a European general population mean = 50 (standard deviation = 10).
RESULTS: A total of 15,386 respondents completed the online survey (n = 11,343 from EU countries). EORTC CAT Core norm scores for all 15 countries were calculated. DIF had negligible impact on scoring. Domain-specific T-scores differed significantly across countries with small to medium effect sizes.
CONCLUSION: This study establishes the official European Norm for the EORTC CAT Core. The European CAT Norm can be used globally and allows for meaningful interpretation of scores. Furthermore, CAT scores can be compared with sex- and age-adjusted norm scores at a national level within each of the 15 countries
Non-locality and Communication Complexity
Quantum information processing is the emerging field that defines and
realizes computing devices that make use of quantum mechanical principles, like
the superposition principle, entanglement, and interference. In this review we
study the information counterpart of computing. The abstract form of the
distributed computing setting is called communication complexity. It studies
the amount of information, in terms of bits or in our case qubits, that two
spatially separated computing devices need to exchange in order to perform some
computational task. Surprisingly, quantum mechanics can be used to obtain
dramatic advantages for such tasks.
We review the area of quantum communication complexity, and show how it
connects the foundational physics questions regarding non-locality with those
of communication complexity studied in theoretical computer science. The first
examples exhibiting the advantage of the use of qubits in distributed
information-processing tasks were based on non-locality tests. However, by now
the field has produced strong and interesting quantum protocols and algorithms
of its own that demonstrate that entanglement, although it cannot be used to
replace communication, can be used to reduce the communication exponentially.
In turn, these new advances yield a new outlook on the foundations of physics,
and could even yield new proposals for experiments that test the foundations of
physics.Comment: Survey paper, 63 pages LaTeX. A reformatted version will appear in
Reviews of Modern Physic
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