14,100 research outputs found
Simple Observables from Fat Link Fermion Actions
A comparison is made of the (quenched) light hadron spectrum and of simple
matrix elements for a hypercubic fermion action (based on a fixed point action)
and the clover action, both using fat links, at a lattice spacing a= 0.18 fm.
Renormalization constants for the naive and improved vector current and the
naive axial current are computed using Ward identities. The renormalization
factors are very close to unity, and the spectroscopy of light hadrons and the
pseudoscalar and vector decay constants agree well with simulations at smaller
lattice spacings (and with experiment).Comment: 22 pages, 12 postscript figures, Revtex plus eps
Passive water control at the surface of a superhydrophobic lichen
Some lichens have a super-hydrophobic upper surface, which repels water drops, keeping the surface dry but probably preventing water uptake. Spore ejection requires water and is most efficient just after rainfall. This study was carried out to investigate how super-hydrophobic lichens manage water uptake and repellence at their fruiting bodies, or podetia. Drops of water were placed onto separate podetia of Cladonia chlorophaea and observed using optical microscopy and cryo-scanning-electron microscopy (cryo-SEM) techniques to determine the structure of podetia and to visualise their interaction with water droplets. SEM and optical microscopy studies revealed that the surface of the podetia was constructed in a three-level structural hierarchy. By cryo-SEM of water-glycerol droplets placed on the upper part of the podetium, pinning of the droplet to specific, hydrophilic spots (pycnidia/apothecia) was observed. The results suggest a mechanism for water uptake, which is highly sophisticated, using surface wettability to generate a passive response to different types of precipitation in a manner similar to the Namib Desert beetle. This mechanism is likely to be found in other organisms as it offers passive but selective water control
Potentiality in Biology
We take the potentialities that are studied in the biological sciences (e.g., totipotency) to be an important subtype of biological dispositions. The goal of this paper is twofold: first, we want to provide a detailed understanding of what biological dispositions are. We claim that two features are essential for dispositions in biology: the importance of the manifestation process and the diversity of conditions that need to be satisfied for the disposition to be manifest. Second, we demonstrate that the concept of a disposition (or potentiality) is a very useful tool for the analysis of the explanatory practice in the biological sciences. On the one hand it allows an in-depth analysis of the nature and diversity of the conditions under which biological systems display specific behaviors. On the other hand the concept of a disposition may serve a unificatory role in the philosophy of the natural sciences since it captures not only the explanatory practice of biology, but of all natural sciences. Towards the end we will briefly come back to the notion of a potentiality in biology
On the Numerical Evaluation of Loop Integrals With Mellin-Barnes Representations
An improved method is presented for the numerical evaluation of multi-loop
integrals in dimensional regularization. The technique is based on
Mellin-Barnes representations, which have been used earlier to develop
algorithms for the extraction of ultraviolet and infrared divergencies. The
coefficients of these singularities and the non-singular part can be integrated
numerically. However, the numerical integration often does not converge for
diagrams with massive propagators and physical branch cuts. In this work,
several steps are proposed which substantially improve the behavior of the
numerical integrals. The efficacy of the method is demonstrated by calculating
several two-loop examples, some of which have not been known before.Comment: 13 pp. LaTe
Uncertainty quantification of growth rates of thermoacoustic instability by an adjoint Helmholtz solver
Thermoacoustic instabilities are often calculated with Helmholtz solvers combined with a low-order model for the flame dynamics. Typically, such a formulation leads to an eigenvalue problem in which the eigenvalue appears under nonlinear terms, such as exponentials related to the time delays that result from the flame model. The objective of the present paper is to quantify uncertainties in thermoacoustic stability analysis with a Helmholtz solver and its adjoint. This approach is applied to the model of a combustion test rig with a premixed swirl burner. The nonlinear eigenvalue problem and its adjoint are solved by an in-house adjoint Helmholtz solver, based on an axisymmetric finite-volume discretization. In addition to first-order correction terms of the adjoint formulation, as they are often used in the literature, second-order terms are also taken into account. It is found that one particular second-order term has significant impact on the accuracy of the predictions. Finally, the probability density function (PDF) of the growth rate in the presence of uncertainties in the input parameters is calculated with a Monte Carlo approach. The uncertainties considered concern the gain and phase of the flame response, the outlet acoustic reflection coefficient, and the plenum geometry. It is found that the second-order adjoint method gives quantitative agreement with results based on the full nonlinear eigenvalue problem, while requiring much fewer computations.Technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems (SFB TR40), Royal Academy of Engineering Research Fellowships Schem
Uncertainty quantification of growth rates of thermoacoustic instability by an adjoint Helmholtz solver
Thermoacoustic instabilities are often calculated with Helmholtz solvers combined with a low-order model for the flame dynamics. Typically, such a formulation leads to an eigenvalue problem in which the eigenvalue appears under nonlinear terms, such as exponentials related to the time delays that result from the flame model. The objective of the present paper is to quantify uncertainties in thermoacoustic stability analysis with a Helmholtz solver and its adjoint. This approach is applied to the model of a combustion test rig with a premixed swirl burner. The nonlinear eigenvalue problem and its adjoint are solved by an in-house adjoint Helmholtz solver, based on an axisymmetric finite-volume discretization. In addition to first-order correction terms of the adjoint formulation, as they are often used in the literature, second-order terms are also taken into account. It is found that one particular second-order term has significant impact on the accuracy of the predictions. Finally, the probability density function (PDF) of the growth rate in the presence of uncertainties in the input parameters is calculated with a Monte Carlo approach. The uncertainties considered concern the gain and phase of the flame response, the outlet acoustic reflection coefficient, and the plenum geometry. It is found that the second-order adjoint method gives quantitative agreement with results based on the full nonlinear eigenvalue problem, while requiring much fewer computations.Technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems (SFB TR40), Royal Academy of Engineering Research Fellowships Schem
Probing High Reheating Temperature Scenarios at the LHC with Long-Lived Staus
We investigate the possibility of probing high reheating temperature
scenarios at the LHC, in supersymmetric models where the gravitino is the
lightest supersymmetric particle, and the stau is the next-to-lightest
supersymmetric particle. In such scenarios, the big-bang nucleosynthesis and
the gravitino abundance give a severe upper bound on the gluino mass. We find
that, if the reheating temperature is \sim 10^8 GeV or higher, the scenarios
can be tested at the LHC with an integrated luminosity of O(1 fb^{-1}) at
\sqrt{s}=7 TeV in most of the parameter space.Comment: 17 pages, 5 figures, minor modification
Feynman Rules for the Rational Part of the Standard Model One-loop Amplitudes in the 't Hooft-Veltman Scheme
We study Feynman rules for the rational part of the Standard Model
amplitudes at one-loop level in the 't Hooft-Veltman scheme.
Comparing our results for quantum chromodynamics and electroweak 1-loop
amplitudes with that obtained based on the Kreimer-Korner-Schilcher (KKS)
scheme, we find the latter result can be recovered when our
scheme becomes identical (by setting in our expressions)
with the KKS scheme. As an independent check, we also calculate Feynman rules
obtained in the KKS scheme, finding our results in complete agreement with
formulae presented in the literature. Our results, which are studied in two
different schemes, may be useful for clarifying the
problem in dimensional regularization. They are helpful to eliminate or find
ambiguities arising from different dimensional regularization schemes.Comment: Version published in JHEP, presentation improved, 41 pages, 10
figure
Bi-allelic mutations in uncoordinated mutant number-45 myosin chaperone B are a cause for congenital myopathy
Congenital myopathies (CM) form a genetically heterogeneous group of disorders characterized by perinatal muscle weakness. Here, we report an 11-year old male offspring of consanguineous parents of Lebanese origin. He presented with proximal weakness including Gower's sign, and skeletal muscle biopsy revealed myopathic changes with core-like structures. Whole exome sequencing of this index patient lead to the discovery of a novel genetically defined CM subtype based on bi-allelic mutations in the uncoordinated mutant number-45 myosin chaperone B (UNC45B) NM_173167:c.2261G > A, p.Arg754Gln. The mutation is conserved in evolution and co-segregates within the pedigree with the phenotype, and located in the myosin binding armadillo repeat domain 3 (ARM3), and has a CADD Score of 35. On a multimeric level, UNC45B aggregates to a chain which serves as an assembly line and functions as a template defining the geometry, regularity, and periodicity of myosin arranged into muscle thick filaments. Our discovery is in line with the previously described myopathological phenotypes in C. elegans and in vertebrate mutants and knockdown-models. In conclusion, we here report for the first time a patient with an UNC45B mutation causing a novel genetically defined congenital myopathy disease entity
Scattering AMplitudes from Unitarity-based Reduction Algorithm at the Integrand-level
SAMURAI is a tool for the automated numerical evaluation of one-loop
corrections to any scattering amplitudes within the dimensional-regularization
scheme. It is based on the decomposition of the integrand according to the
OPP-approach, extended to accommodate an implementation of the generalized
d-dimensional unitarity-cuts technique, and uses a polynomial interpolation
exploiting the Discrete Fourier Transform. SAMURAI can process integrands
written either as numerator of Feynman diagrams or as product of tree-level
amplitudes. We discuss some applications, among which the 6- and 8-photon
scattering in QED, and the 6-quark scattering in QCD. SAMURAI has been
implemented as a Fortran90 library, publicly available, and it could be a
useful module for the systematic evaluation of the virtual corrections oriented
towards automating next-to-leading order calculations relevant for the LHC
phenomenology.Comment: 35 pages, 7 figure
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