305 research outputs found
The phase problem for cylindrically averaged diffraction patterns. Solution by isomorphous replacement and application to tobacco mosaic virus
Discrete Space-Time Volume for 3-Dimensional BF Theory and Quantum Gravity
The Turaev-Viro state sum invariant is known to give the transition amplitude
for the three dimensional BF theory with cosmological term, and its deformation
parameter hbar is related with the cosmological constant via hbar=sqrt{Lambda}.
This suggests a way to find the expectation value of the spacetime volume by
differentiating the Turaev-Viro amplitude with respect to the cosmological
constant. Using this idea, we find an explicit expression for the spacetime
volume in BF theory. According to our results, each labelled triangulation
carries a volume that depends on the labelling spins. This volume is explicitly
discrete. We also show how the Turaev-Viro model can be used to obtain the
spacetime volume for (2+1) dimensional quantum gravity.Comment: 13 pages, Revtex, figure
A limiting velocity for quarkonium propagation in a strongly coupled plasma via AdS/CFT
We study the dispersion relations of mesons in a particular hot strongly
coupled supersymmetric gauge theory plasma. We find that at large momentum k
the dispersion relations become omega = v_0 k + a + b/k + ..., where the
limiting velocity v_0 is the same for mesons with any quantum numbers and
depends only on the ratio of the temperature to the quark mass T/m_q. We
compute a and b in terms of the meson quantum numbers and T/m_q. The limiting
meson velocity v_0 becomes much smaller than the speed of light at temperatures
below but close to T_diss, the temperature above which no meson bound states at
rest in the plasma are found. From our result for v_0, we find that the
temperature above which no meson bound states with velocity v exist is
T_diss(v) \simeq (1-v^2)^(1/4) T_diss, up to few percent corrections.We thus
confirm by direct calculation of meson dispersion relations a result inferred
indirectly in previous work via analysis of the screening length between a
static quark and antiquark in a moving plasma. Although we do not do our
calculations in QCD, we argue that the qualitative features of the dispersion
relation we compute, including in particular the relation between dissociation
temperature and meson velocity, may apply to bottomonium and charmonium mesons
propagating in the strongly coupled plasma of QCD. We discuss how our results
can contribute to understanding quarkonium physics in heavy ion collisions.Comment: 57 pages, 12 figures; references adde
On the Decomposition of Clifford Algebras of Arbitrary Bilinear Form
Clifford algebras are naturally associated with quadratic forms. These
algebras are Z_2-graded by construction. However, only a Z_n-gradation induced
by a choice of a basis, or even better, by a Chevalley vector space isomorphism
Cl(V) \bigwedge V and an ordering, guarantees a multi-vector decomposition
into scalars, vectors, tensors, and so on, mandatory in physics. We show that
the Chevalley isomorphism theorem cannot be generalized to algebras if the
Z_n-grading or other structures are added, e.g., a linear form. We work with
pairs consisting of a Clifford algebra and a linear form or a Z_n-grading which
we now call 'Clifford algebras of multi-vectors' or 'quantum Clifford
algebras'. It turns out, that in this sense, all multi-vector Clifford algebras
of the same quadratic but different bilinear forms are non-isomorphic. The
usefulness of such algebras in quantum field theory and superconductivity was
shown elsewhere. Allowing for arbitrary bilinear forms however spoils their
diagonalizability which has a considerable effect on the tensor decomposition
of the Clifford algebras governed by the periodicity theorems, including the
Atiyah-Bott-Shapiro mod 8 periodicity. We consider real algebras Cl_{p,q} which
can be decomposed in the symmetric case into a tensor product Cl_{p-1,q-1}
\otimes Cl_{1,1}. The general case used in quantum field theory lacks this
feature. Theories with non-symmetric bilinear forms are however needed in the
analysis of multi-particle states in interacting theories. A connection to
q-deformed structures through nontrivial vacuum states in quantum theories is
outlined.Comment: 25 pages, 1 figure, LaTeX, {Paper presented at the 5th International
Conference on Clifford Algebras and their Applications in Mathematical
Physics, Ixtapa, Mexico, June 27 - July 4, 199
Double Counting Ambiguities in the Linear Sigma Model
We study the dynamical consequences imposed on effective chiral field
theories such as the quark-level SU(2) linear model (LM) due
to the fundamental constraints of massless Goldstone pions, the normalization
of the pion decay constant and form factor, and the pion charge radius. We
discuss quark-level double counting LM ambiguities in the context of
the Salam-Weinberg compositeness condition. Then SU(3) extensions to
the kaon are briefly considered.Comment: 23 pages To be published in Journal of Physics
Novel adaptive muting technique for packet loss concealment of ITU-T G.722 using optimized parametric shaping functions
National disability-adjusted life years(DALYs) for 257 diseases and injuries in Ethiopia, 1990–2015: findings from the global burden of disease study 2015
Background: Disability-adjusted life years (DALYs) provide a summary measure of health and can be a critical input
to guide health systems, investments, and priority-setting in Ethiopia. We aimed to determine the leading causes of
premature mortality and disability using DALYs and describe the relative burden of disease and injuries in Ethiopia.
Methods: We used results from the Global Burden of Diseases, Injuries, and Risk Factors Study 2015 (GBD 2015) for non-fatal disease burden, cause-specific mortality, and all-cause mortality to derive age-standardized DALYs by sex
for Ethiopia for each year. We calculated DALYs by summing years of life lost due to premature mortality (YLLs) and
years lived with disability (YLDs) for each age group and sex. Causes of death by age, sex, and year were measured
mainly using Causes of Death Ensemble modeling. To estimate YLDs, a Bayesian meta-regression method was used.
We reported DALY rates per 100,000 for communicable, maternal, neonatal, and nutritional (CMNN) disorders,
non-communicable diseases, and injuries, with 95% uncertainty intervals (UI) for Ethiopia.
Results: Non-communicable diseases caused 23,118.1 (95% UI, 17,124.4–30,579.6), CMNN disorders resulted in
20,200.7 (95% UI, 16,532.2–24,917.9), and injuries caused 3781 (95% UI, 2642.9–5500.6) age-standardized DALYs
per 100,000 in Ethiopia in 2015. Lower respiratory infections, diarrheal diseases, and tuberculosis were the top three leading causes of DALYs in 2015, accounting for 2998 (95% UI, 2173.7–4029), 2592.5 (95% UI, 1850.7–3495.1), and 2562.9 (95% UI, 1466.1–4220.7) DALYs per 100,000, respectively. Ischemic heart disease and cerebrovascular disease were the fourth and fifth leading causes of age-standardized DALYs, with rates of 2535.7 (95% UI, 1603.7–3843.2) and 2159.9 (95% UI, 1369.7–3216.3) per 100,000, respectively. The following causes showed a reduction of 60% or more over the last 25 years: lower respiratory infections, diarrheal diseases, tuberculosis, neonatal encephalopathy, preterm birth complications, meningitis, malaria, protein-energy malnutrition, iron-deficiency anemia, measles, war and legal intervention, and maternal hemorrhage
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