360 research outputs found
Ethyl α-​phenylhydrazono-​2-​furanpropionate
The title compd. is orthorhombic, space group Pca21, with a 11.115(1)​, b 8.170(1)​, and c 15.341(1) Å; Z = 4 for dm = 1.290 and dc = 1.293. The structure was solved by direct methods and refined to an R of 0.041 for 1033 reflections. At. coordinates are given. The structure conforms to the non-​H-​bonded α form. The hydrazine moiety is planar with sp2 hybridization at the N and neighboring atoms. Intermol. N-​H...O hydrogen bonds link the mols. into chains along a
On the vacuum fluctuations, Pioneer Anomaly and Modified Newtonian Dynamics
We argue that the so-called "Pioneer Anomaly" is related to the quantum
vacuum fluctuations. Our approach is based on the hypothesis of the
gravitational repulsion between matter and antimatter, what allows considering,
the virtual particle-antiparticle pairs in the physical vacuum, as
gravitational dipoles. Our simplified calculations indicate that the anomalous
deceleration of the Pioneer spacecrafts could be a consequence of the vacuum
polarization in the gravitational field of the Sun. At the large distances, the
vacuum polarization by baryonic matter could mimic dark matter what opens
possibility that dark matter do not exist, as advocated by the Modified
Newtonian Dynamics (MOND)
Quantum vacuum and dark matter
Recently, the gravitational polarization of the quantum vacuum was proposed
as alternative to the dark matter paradigm. In the present paper we consider
four benchmark measurements: the universality of the central surface density of
galaxy dark matter haloes, the cored dark matter haloes in dwarf spheroidal
galaxies, the non-existence of dark disks in spiral galaxies and distribution
of dark matter after collision of clusters of galaxies (the Bullet cluster is a
famous example). Only some of these phenomena (but not all of them) can (in
principle) be explained by the dark matter and the theories of modified
gravity. However, we argue that the framework of the gravitational polarization
of the quantum vacuum allows the understanding of the totality of these
phenomena.Comment: Accepted for publication in Astrophysics and Space Scienc
Technically natural dark energy from Lorentz breaking
We construct a model of dark energy with a technically natural small
contribution to cosmic acceleration, i.e. this contribution does not receive
corrections from other scales in the theory. The proposed acceleration
mechanism appears generically in the low-energy limit of gravity theories with
violation of Lorentz invariance that contain a derivatively coupled scalar
field Theta. The latter may be the Goldstone field of a broken global symmetry.
The model, that we call Theta-CDM, is a valid effective field theory up to a
high cutoff just a few orders of magnitude below the Planck scale. Furthermore,
it can be ultraviolet-completed in the context of Horava gravity. We discuss
the observational predictions of the model. Even in the absence of a
cosmological constant term, the expansion history of the Universe is
essentially indistinguishable from that of Lambda-CDM. The difference between
the two theories appears at the level of cosmological perturbations. We find
that in Theta-CDM the matter power spectrum is enhanced at subhorizon scales
compared to Lambda-CDM. This property can be used to discriminate the model
from Lambda-CDM with current cosmological data.Comment: A few equations in the Appendix correcte
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Improving adherence to acute low back pain guideline recommendations with chiropractors and physiotherapists: the ALIGN cluster randomised controlled trial
Background
Acute low back pain is a common condition, has high burden, and there are evidence-to-practice gaps in the chiropractic and physiotherapy setting for imaging and giving advice to stay active. The aim of this cluster randomised trial was to estimate the effects of a theory- and evidence-based implementation intervention to increase chiropractors’ and physiotherapists’ adherence to a guideline for acute low back pain compared with the comparator (passive dissemination of the guideline). In particular, the primary aim of the intervention was to reduce inappropriate imaging referral and improve patient low back pain outcomes, and to determine whether this intervention was cost-effective.
Methods
Physiotherapy and chiropractic practices in the state of Victoria, Australia, comprising at least one practising clinician who provided care to patients with acute low back pain, were invited to participate. Patients attending these practices were included if they had acute non-specific low back pain (duration less than 3 months), were 18 years of age or older, and were able to understand and read English. Practices were randomly assigned either to a tailored, multi-faceted intervention based on the guideline (interactive educational symposium plus academic detailing) or passive dissemination of the guideline (comparator). A statistician independent of the study team undertook stratified randomisation using computer-generated random numbers; four strata were defined by professional group and the rural or metropolitan location of the practice. Investigators not involved in intervention delivery were blinded to allocation. Primary outcomes were X-ray referral self-reported by clinicians using a checklist and patient low back pain-specific disability (at 3 months).
Results
A total of 104 practices (43 chiropractors, 85 physiotherapists; 755 patients) were assigned to the intervention and 106 practices (45 chiropractors, 97 physiotherapists; 603 patients) to the comparator; 449 patients were available for the patient-level primary outcome. There was no important difference in the odds of patients being referred for X-ray (adjusted (Adj) OR: 1.40; 95% CI 0.51, 3.87; Adj risk difference (RD): 0.01; 95% CI − 0.02, 0.04) or patient low back pain-specific disability (Adj mean difference: 0.37; 95% CI − 0.48, 1.21, scale 0–24). The intervention did lead to improvement for some key secondary outcomes, including giving advice to stay active (Adj OR: 1.96; 95% CI 1.20, 3.22; Adj RD: 0.10; 95% CI 0.01, 0.19) and intending to adhere to the guideline recommendations (e.g. intention to refer for X-ray: Adj OR: 0.27; 95% CI 0.17, 0.44; intention to give advice to stay active: Adj OR: 2.37; 95% CI 1.51, 3.74).
Conclusions
Intervention group clinicians were more likely to give advice to stay active and to intend to adhere to the guideline recommendations about X-ray referral. The intervention did not change the primary study outcomes, with no important differences in X-ray referral and patient disability between groups, implying that hypothesised reductions in health service utilisation and/or productivity gains are unlikely to offset the direct costs of the intervention. We report these results with the caveat that we enrolled less patients into the trial than our determined sample size. We cannot recommend this intervention as a cost-effective use of resources
Systematics of proton emission
A very simple formula is presented that relates the logarithm of the
half-life, corrected by the centrifugal barrier, with the Coulomb parameter in
proton decay processes. The corresponding experimental data lie on two straight
lines which appear as a result of a sudden change in the nuclear shape marking
two regions of deformation independently of the angular momentum of the
outgoing proton. This feature provides a powerful tool to assign experimentally
quantum numbers in proton emitters.Comment: 4 pages, 3 figure
Statistical distribution of quantum entanglement for a random bipartite state
We compute analytically the statistics of the Renyi and von Neumann entropies
(standard measures of entanglement), for a random pure state in a large
bipartite quantum system. The full probability distribution is computed by
first mapping the problem to a random matrix model and then using a Coulomb gas
method. We identify three different regimes in the entropy distribution, which
correspond to two phase transitions in the associated Coulomb gas. The two
critical points correspond to sudden changes in the shape of the Coulomb charge
density: the appearance of an integrable singularity at the origin for the
first critical point, and the detachement of the rightmost charge (largest
eigenvalue) from the sea of the other charges at the second critical point.
Analytical results are verified by Monte Carlo numerical simulations. A short
account of some of these results appeared recently in Phys. Rev. Lett. {\bf
104}, 110501 (2010).Comment: 7 figure
The problems with systematic reviews: a living systematic review
Objectives
Systematic reviews and meta-analyses are proliferating as they are an important building block to inform evidence-based guidelines and decision-making. Enforcement of best practice in clinical trials is firmly on the research agenda of good clinical practice, but there is less clarity as to how evidence syntheses that combine these studies can be influenced by bad practice. Our aim was to conduct a living systematic review of articles that highlight flaws in published systematic reviews to formally document and understand these problems.
Study Design and Setting
We conducted a comprehensive assessment of all literature examining problems, which relate to published systematic reviews.
Results
The first iteration of our living systematic review (https://systematicreviewlution.com/) has found 485 articles documenting 67 discrete problems relating to the conduct and reporting of systematic reviews which can potentially jeopardize their reliability or validity.
Conclusion
Many hundreds of articles highlight that there are many flaws in the conduct, methods, and reporting of published systematic reviews, despite the existence and frequent application of guidelines. Considering the pivotal role that systematic reviews have in medical decision-making due to having apparently transparent, objective, and replicable processes, a failure to appreciate and regulate problems with these highly cited research designs is a threat to credible science
Linking working memory and long-term memory: A computational model of the learning of new words
The nonword repetition (NWR) test has been shown to be a good predictor of children’s vocabulary size. NWR performance has been explained using phonological working memory, which is seen as a critical component in the learning of new words. However, no detailed specification of the link between phonological working memory and long-term memory (LTM) has been proposed. In this paper, we present a computational model of children’s vocabulary acquisition (EPAM-VOC) that specifies how phonological working memory and LTM interact. The model learns phoneme sequences, which are stored in LTM and mediate how much information can be held in working memory. The model’s behaviour is compared with that of children in a new study of NWR, conducted in order to ensure the same nonword stimuli and methodology across ages. EPAM-VOC shows a pattern of results similar to that of children: performance is better for shorter nonwords and for wordlike nonwords, and performance improves with age. EPAM-VOC also simulates the superior performance for single consonant nonwords over clustered consonant nonwords found in previous NWR studies. EPAM-VOC provides a simple and elegant computational account of some of the key processes involved in the learning of new words: it specifies how phonological working memory and LTM interact; makes testable predictions; and suggests that developmental changes in NWR performance may reflect differences in the amount of information that has been encoded in LTM rather than developmental changes in working memory capacity.
Keywords: EPAM, working memory, long-term memory, nonword repetition, vocabulary acquisition, developmental change
Exact Minimum Eigenvalue Distribution of an Entangled Random Pure State
A recent conjecture regarding the average of the minimum eigenvalue of the
reduced density matrix of a random complex state is proved. In fact, the full
distribution of the minimum eigenvalue is derived exactly for both the cases of
a random real and a random complex state. Our results are relevant to the
entanglement properties of eigenvectors of the orthogonal and unitary ensembles
of random matrix theory and quantum chaotic systems. They also provide a rare
exactly solvable case for the distribution of the minimum of a set of N {\em
strongly correlated} random variables for all values of N (and not just for
large N).Comment: 13 pages, 2 figures included; typos corrected; to appear in J. Stat.
Phy
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