1,097 research outputs found
Index Theorem and Overlap Formalism with Naive and Minimally Doubled Fermions
We present a theoretical foundation for the Index theorem in naive and
minimally doubled lattice fermions by studying the spectral flow of a Hermitean
version of Dirac operators. We utilize the point splitting method to implement
flavored mass terms, which play an important role in constructing proper
Hermitean operators. We show the spectral flow correctly detects the index of
the would-be zero modes which is determined by gauge field topology. Using the
flavored mass terms, we present new types of overlap fermions from the naive
fermion kernels, with a number of flavors that depends on the choice of the
mass terms. We succeed to obtain a single-flavor naive overlap fermion which
maintains hypercubic symmetry.Comment: 27 pages, 17 figures; references added, version accepted in JHE
Renormalization of minimally doubled fermions
We investigate the renormalization properties of minimally doubled fermions,
at one loop in perturbation theory. Our study is based on the two particular
realizations of Borici-Creutz and Karsten-Wilczek. A common feature of both
formulations is the breaking of hyper-cubic symmetry, which requires that the
lattice actions are supplemented by suitable counterterms. We show that three
counterterms are required in each case and determine their coefficients to one
loop in perturbation theory. For both actions we compute the vacuum
polarization of the gluon. It is shown that no power divergences appear and
that all contributions which arise from the breaking of Lorentz symmetry are
cancelled by the counterterms. We also derive the conserved vector and
axial-vector currents for Karsten-Wilczek fermions. Like in the case of the
previously studied Borici-Creutz action, one obtains simple expressions,
involving only nearest-neighbour sites. We suggest methods how to fix the
coefficients of the counterterms non-perturbatively and discuss the
implications of our findings for practical simulations.Comment: 23 pages, 1 figur
A simple mathematical model of gradual Darwinian evolution: Emergence of a Gaussian trait distribution in adaptation along a fitness gradient
We consider a simple mathematical model of gradual Darwinian evolution in
continuous time and continuous trait space, due to intraspecific competition
for common resource in an asexually reproducing population in constant
environment, while far from evolutionary stable equilibrium. The model admits
exact analytical solution. In particular, Gaussian distribution of the trait
emerges from generic initial conditions.Comment: 21 pages, 2 figures, as accepted to J Math Biol 2013/03/1
Numerical properties of staggered quarks with a taste-dependent mass term
The numerical properties of staggered Dirac operators with a taste-dependent
mass term proposed by Adams [1,2] and by Hoelbling [3] are compared with those
of ordinary staggered and Wilson Dirac operators. In the free limit and on
(quenched) interacting configurations, we consider their topological
properties, their spectrum, and the resulting pion mass. Although we also
consider the spectral structure, topological properties, locality, and
computational cost of an overlap operator with a staggered kernel, we call
attention to the possibility of using the Adams and Hoelbling operators without
the overlap construction. In particular, the Hoelbling operator could be used
to simulate two degenerate flavors without additive mass renormalization, and
thus without fine-tuning in the chiral limit.Comment: 14 pages, 9 figures. V2: published version; important note added
regarding Hoelbling fermions, otherwise minor change
Revisiting symmetries of lattice fermions via spin-flavor representation
Employing the spin-flavor representation, we investigate the structures of
the doubler-mixing symmetries and the mechanisms of their spontaneous breakdown
in four types of lattice fermion formulation. We first revisit the
U(4)\timesU(4)A symmetries of the naive fermion with the vanishing bare mass
m, and re-express them in terms of the spin-flavor representation. We apply the
same method to the Wilson fermion, which possesses only the U(1) vector
symmetry for general values of m. For a special value of m, however, there
emerges an additional U(1) symmetry to be broken by pion condensation. We also
explore two types of minimally doubled fermion, and discover a similar kind of
symmetry enhancement and its spontaneous breakdown.Comment: 25 pages, no figure;v2 typos corrected;v3 Sec.2 is shortened. To
appear in JHE
Wet Granular Materials
Most studies on granular physics have focused on dry granular media, with no
liquids between the grains. However, in geology and many real world
applications (e.g., food processing, pharmaceuticals, ceramics, civil
engineering, constructions, and many industrial applications), liquid is
present between the grains. This produces inter-grain cohesion and drastically
modifies the mechanical properties of the granular media (e.g., the surface
angle can be larger than 90 degrees). Here we present a review of the
mechanical properties of wet granular media, with particular emphasis on the
effect of cohesion. We also list several open problems that might motivate
future studies in this exciting but mostly unexplored field.Comment: review article, accepted for publication in Advances in Physics;
tex-style change
Avaliação da resistência ao cisalhamento da união entre duas ligas a base de CoCr e uma cerâmica
INTRODUCTION: Based on the importance of the integrity of the metal/ceramic interface, the purpose of this work was to
evaluate the shear bond strength of the metal-ceramic union of two Co-Cr alloys (Wirobond C, Bego; Remanium 2000, Dentaurum)
combined with Omega 900 ceramic (Vita Zahnfabrik). MATERIAL and METHOD: Eleven cylindrical matrixes were made for
each alloy, and the metallic portion was obtained with the lost wax casting technique with standardized waxing of 4mm of height
and of 4mm of diameter. The ceramic was applied according to the manufacturer’s recommendations with the aid of a teflon
matrix that allowed its dimension to be standardized in the same size as the metallic portion. The specimens were submitted to
the shear bond test in an universal testing machine (EMIC), with the aid of a device developed for such intention, and constant
speed of 0.5mm/min. RESULTS and CONCLUSIONS: The mean resistance was 48.387MPa for Wirobond C alloy, with standard
deviation of 17.718, and 55.956MPa for Remanium 2000, with standard deviation of 17.198. No statistically significant difference
was observed between the shear strength of the two metal-ceramic alloys. ______________________________________________________________________________________________________________ RESUMOINTRODUÇÃO: Baseados na importância da integridade da interface metal-cerâmica, este trabalho tem como objetivo
avaliar a resistência ao cisalhamento da união metal-cerâmica de duas ligas de Co-Cr (Wirobond C, Bego; Remanium 2000,
Dentaurum) combinadas com a cerâmica Omega 900 (Vita Zahnfabrik). MATERIAIS E MÉTODOS: Foram confeccionados 11
corpos-de-prova cilíndricos para cada liga utilizada, sendo que a porção metálica foi obtida por fundição pela técnica da cera
perdida, através de enceramentos padronizados com 4mm de altura por 4mm de diâmetro. A aplicação da cerâmica foi realizada
segundo recomendações do fabricante, com auxílio de uma matriz de teflon que permitia sua padronização com as mesmas
dimensões da porção metálica. Os corpos-de-prova foram submetidos ao ensaio de resistência ao cisalhamento em máquina de
ensaios universal (EMIC), com auxílio de dispositivo desenvolvido para tal propósito, sob velocidade constante de 0,5mm/
min. RESULTADOS E CONCLUSÕES: As médias de resistência obtidas foram 48,387 MPa para a liga Wirobond C, com desvio
padrão de 17,718, e 55,956 MPa para a Remanium 2000, com desvio padrão de 17,198. Após análise de variância foi possível
observar que não há diferença estatisticamente significante entre os valores de resistência ao cisalhamento das duas ligas
metalocerâmicas
On the complexity of the Saccharomyces bayanus taxon: hybridization and potential hybrid speciation
Although the genus Saccharomyces has been thoroughly studied, some species in the genus has not yet been accurately resolved; an example is S. bayanus, a taxon that includes genetically diverse lineages of pure and hybrid strains. This diversity makes the assignation and classification of strains belonging to this species unclear and controversial. They have been subdivided by some authors into two varieties (bayanus and uvarum), which have been raised to the species level by others. In this work, we evaluate the complexity of 46 different strains included in the S. bayanus taxon by means of PCR-RFLP analysis and by sequencing of 34 gene regions and one mitochondrial gene. Using the sequence data, and based on the S. bayanus var. bayanus reference strain NBRC 1948, a hypothetical pure S. bayanus was reconstructed for these genes that showed alleles with similarity values lower than 97% with the S. bayanus var. uvarum strain CBS 7001, and of 99¿100% with the non S. cerevisiae portion in S. pastorianus Weihenstephan 34/70 and with the new species S. eubayanus. Among the S. bayanus strains under study, different levels of homozygosity, hybridization and introgression were found; however, no pure S. bayanus var. bayanus strain was identified. These S. bayanus hybrids can be classified into two types: homozygous (type I) and heterozygous hybrids (type II), indicating that they have been originated by different hybridization processes. Therefore, a putative evolutionary scenario involving two different hybridization events between a S. bayanus var. uvarum and unknown European S. eubayanus-like strains can be postulated to explain the genomic diversity observed in our S. bayanus var. bayanus strains
Ultrasonographic median nerve cross-section areas measured by 8-point "inching test" for idiopathic carpal tunnel syndrome: a correlation of nerve conduction study severity and duration of clinical symptoms
<p>Abstract</p> <p>Background</p> <p>Incremental palmar stimulation of the median nerve sensory conduction at the wrist, the "inching test", provides an assessment with reference to segments proximal and distal to the entrapment. This study used high-resolution ultrasonography (US) to measure the median nerve's cross-section areas (CSAs) like the "inching test" and to correlate with the nerve conduction study (NCS) severity and duration of carpal tunnel syndrome (CTS).</p> <p>Methods</p> <p>Two hundred and twelve (212) "CTS-hands" from 135 CTS patients and 50 asymptomatic hands ("A-hands") from 25 control individuals were enrolled. The median nerve CSAs were measured at the 8-point marked as <it>i</it>4, <it>i</it>3, <it>i</it>2, <it>i</it>1, <it>w</it>, <it>o</it>1, <it>o</it>2, and <it>0</it>3 in inching test. The NCS severities were classified into six groups based on motor and sensory responses (i.e., negative, minimal, mild, moderate, severe, and extreme). Results of US studies were compared in terms of NCS severity and duration of clinical CTS symptoms.</p> <p>Results</p> <p>There was significantly larger CSA of the NCS negative group of "CTS-hands" than of "A-hands". The cut-off values of the CSAs of the NCS negative CTS group were 12.5 mm<sup>2</sup>, 11.5 mm<sup>2 </sup>and 10.1 mm<sup>2 </sup>at the inlet, wrist crease, and outlet, respectively. Of the 212 "CTS-hands", 32 were NCS negative while 40 had minimal, 43 mild, 85 moderate, 10 severe, and two extreme NCS severities. The CSAs of "CTS-hands" positively correlated with different NCS severities and with the duration of CTS symptoms. By duration of clinical symptoms, 12 of the 212 "CTS-hands" were in the 1 month group; 82 in >1 month and ≤12 months group, and 118 in >12 months group. In "inching test", segments <it>i</it>4-<it>i</it>3 and <it>i</it>3-<it>i</it>2 were the most common "positive-site". The corresponding CSAs measured at <it>i</it>4 and <it>i</it>3, but not at <it>i</it>2, were significantly larger than those measured at points that were not "positive-site".</p> <p>Conclusions</p> <p>Using the 8-point measurement of the median nerve CSA from inlet to outlet similar to the "inching test" has positive correlations with NCS severity and duration of CTS clinical symptoms, and can provide more information on anatomic changes. Combined NCS and US studies using the 8-point measurement may have a higher positive rate than NCS alone for diagnosing CTS.</p
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