1,236 research outputs found
Decompositions of factor codes and embeddings between shift spaces with unequal entropies
Given a factor code between sofic shifts X and Y, there is a family of
decompositions of the original code into factor codes such that the entropies
of the intermediate subshifts arising from the decompositions are dense in the
interval from the entropy of Y to that of X. Furthermore, if X is of finite
type, we can choose those intermediate subshifts as shifts of finite type. In
the second part of the paper, given an embedding from a shift space to an
irreducible sofic shift, we characterize the set of the entropies of the
intermediate subshifts arising from the decompositions of the given embedding
into embeddings.Comment: 14pages, 2 figures; v2) minor revision. to appear in Ergodic Theory
Dynamical System
The Generalized Uncertainty Principle in (A)dS Space and the Modification of Hawking Temperature from the Minimal Length
Recently, the Heisenberg's uncertainty principle has been extended to
incorporate the existence of a large (cut-off) length scale in de Sitter or
anti-de Sitter space, and the Hawking temperatures of the Schwarzshild-(anti)
de Sitter black holes have been reproduced by using the extended uncertainty
principle. I generalize the extended uncertainty to the case with an absolute
minimum length and compute its modification to the Hawking temperature. I
obtain a general trend that the generalized uncertainty principle due to the
absolute minimum length ``always'' increases the Hawking temperature, implying
``faster'' decay, which is in conformity with the result in the asymptotically
flat space. I also revisit the ``black hole-string'' phase transition, in the
context of the generalized uncertainty principle.Comment: Accepted in Physics Letters
Restless quiescence: thermonuclear flashes between transient X-ray outbursts
For thermonuclear flashes to occur on neutron-star surfaces, fuel must have
been accreted from a donor star. However, sometimes flashes are seen from
transient binary systems when they are thought to be in their quiescent phase,
during which no accretion, or relatively little, is expected to occur. We
investigate the accretion luminosity during several such flashes, including the
first-ever and brightest detected flash from Cen X-4 in 1969. We infer from
observations and theory that immediately prior to these flashes the accretion
rate must have been between about 0.001 and 0.01 times the equivalent of the
Eddington limit, which is roughly 2 orders of magnitude less than the peak
accretion rates seen in these transients during an X-ray outburst and 3-4
orders of magnitude more than the lowest measured values in quiescence.
Furthermore, three such flashes, including the one from Cen X-4, occurred
within 2 to 7 days followed by an X-ray outburst. A long-term episode of
enhanced, but low-level, accretion is predicted near the end of the quiescent
phase by the disk-instability model, and may thus have provided the right
conditions for these flashes to occur. We discuss the possibility of whether
these flashes acted as triggers of the outbursts, signifying a dramatic
increase in the accretion rate. Although it is difficult to rule out, we find
it unlikely that the irradiance by these flashes is sufficient to change the
state of the accretion disk in such a dramatic way.Comment: 9 pages, 3 figures, accepted for publication in A&A; referee comments
included plus improved text; results unchange
Ab initio study of charge doping effect on 1D polymerization of C60
We study the interplay between charge doping and intermolecular distance in
the polymerization of C60 fullerene chains by means of density functional
theory (DFT)-based first principle calculations. The potential energy surface
analysis shows that both the equilibrium intermolecular distance of the
unpolymerized system and the polymerization energy barrier are inversely
proportional to the electron doping of the system. We analyze the origin of
this charge-induced polymerization effect by studying the behavior of the
system's wavefunctions around the Fermi level and the structural modifications
of the molecules as a function of two variables: the distance between the
centers of the molecules and the number of electrons added to the system
Point-of-care ultrasound (POCUS) practices in the helicopter emergency medical services in Europe: results of an online survey
Contains fulltext :
238060.pdf (Publisher’s version ) (Open Access)BACKGROUND: The extent to which Point-of-care of ultrasound (POCUS) is used in different European helicopter EMS (HEMS) is unknown. We aimed to study the availability, perception, and future aspects of POCUS in the European HEMS using an online survey. METHOD: A survey about the use of POCUS in HEMS was conducted by a multinational steering expert committee and was carried out from November 30, 2020 to December 30, 2020 via an online web portal. Invitations for participation were sent via email to the medical directors of the European HEMS organizations including two reminding notes. RESULTS: During the study period, 69 participants from 25 countries and 41 different HEMS providers took part in the survey. 96% (n = 66) completed the survey. POCUS was available in 75% (56% always when needed and 19% occasionally) of the responding HEMS organizations. 17% were planning to establish POCUS in the near future. Responders who provided POCUS used it in approximately 15% of the patients. Participants thought that POCUS is important in both trauma and non-trauma-patients (73%, n = 46). The extended focused assessment sonography for trauma (eFAST) protocol (77%) was the most common protocol used. A POCUS credentialing process including documented examinations was requested in less than one third of the HEMS organizations. CONCLUSIONS: The majority of the HEMS organizations in Europe are able to provide different POCUS protocols in their services. The most used POCUS protocols were eFAST, FATE and RUSH. Despite the enthusiasm for POCUS, comprehensive training and clear credentialing processes are not available in about two thirds of the European HEMS organizations. Due to several limitations of this survey further studies are needed to evaluate POCUS in HEMS
Right eigenvalue equation in quaternionic quantum mechanics
We study the right eigenvalue equation for quaternionic and complex linear
matrix operators defined in n-dimensional quaternionic vector spaces. For
quaternionic linear operators the eigenvalue spectrum consists of n complex
values. For these operators we give a necessary and sufficient condition for
the diagonalization of their quaternionic matrix representations. Our
discussion is also extended to complex linear operators, whose spectrum is
characterized by 2n complex eigenvalues. We show that a consistent analysis of
the eigenvalue problem for complex linear operators requires the choice of a
complex geometry in defining inner products. Finally, we introduce some
examples of the left eigenvalue equations and highlight the main difficulties
in their solution.Comment: 24 pages, AMS-Te
Critical Exponents of the N-vector model
Recently the series for two RG functions (corresponding to the anomalous
dimensions of the fields phi and phi^2) of the 3D phi^4 field theory have been
extended to next order (seven loops) by Murray and Nickel. We examine here the
influence of these additional terms on the estimates of critical exponents of
the N-vector model, using some new ideas in the context of the Borel summation
techniques. The estimates have slightly changed, but remain within errors of
the previous evaluation. Exponents like eta (related to the field anomalous
dimension), which were poorly determined in the previous evaluation of Le
Guillou--Zinn-Justin, have seen their apparent errors significantly decrease.
More importantly, perhaps, summation errors are better determined. The change
in exponents affects the recently determined ratios of amplitudes and we report
the corresponding new values. Finally, because an error has been discovered in
the last order of the published epsilon=4-d expansions (order epsilon^5), we
have also reanalyzed the determination of exponents from the epsilon-expansion.
The conclusion is that the general agreement between epsilon-expansion and 3D
series has improved with respect to Le Guillou--Zinn-Justin.Comment: TeX Files, 27 pages +2 figures; Some values are changed; references
update
Multimorbidity and its social determinants among older people in southern provinces, Vietnam
Background: Developing countries are poorly equipped for health issues related to ageing populations making multimorbidity challenging. As in Vietnam the focus tends to be on single conditions. Hence little is known about burden of multimorbidity. This study aimed to examine the prevalence and the determinants of multimorbidity among older people in Southern Vietnam. Methods: A cross-sectional study was conducted in two provinces of Southern Vietnam with a sample of 2400 people aged 60 years and older. The presence of chronic disease was ascertained by medical examination done by physicians at commune health stations. Information on social and demographic factors was collected using structured questionnaire. Univariate and multivariable logistic regression analyses were used to examine the factors associated with multimorbidity. Results: Nearly 40 % of older people had multimorbidity. Currently not working, and healthcare utilisation were associated with higher prevalence of multimorbidity. Living in urban areas and being literate were associated with lower prevalence of multimorbidity. Conclusion: The study found a high burden of multimorbidity among illiterate, especially those living in rural areas. This highlights the need for targeted community based programs aimed at reducing the burden of chronic disease
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