Chiral Symmetry Restoration in the Schwinger Model with Domain Wall Fermions

Domain Wall Fermions utilize an extra space time dimension to provide a method for restoring the regularization induced chiral symmetry breaking in lattice vector gauge theories even at finite lattice spacing. The breaking is restored at an exponential rate as the size of the extra dimension increases. Before this method can be used in dynamical simulations of lattice QCD, the dependence of the restoration rate to the other parameters of the theory and, in particular, the lattice spacing must be investigated. In this paper such an investigation is carried out in the context of the two flavor lattice Schwinger model.Comment: LaTeX, 37 pages including 18 figures. Added comments regarding power law fitting in sect 7. Also, few changes were made to elucidate the content in sect. 5.1 and 5.3. To appear in Phys. Rev.

Optimal Band Selection for the Calculation of Planck Mean Absorption Coefficients

Radiative heat transfer is a major heat loss mechanism in thermal plasmas generated during arc flashes/faults in switchgear applications or during high current interruption in low voltage circuit breakers. A common way to calculate the radiation balance is by means of approximate non-gray radiation models like P1 or discrete ordinates (DOM), where the frequency dependent absorption and emission are described in a number of frequency intervals (bands) using a constant absorption coefficient in each band. Current work is focused on finding the optimal number of bands as well as band interval boundaries that provide a reasonable level of accuracy in comparison to a full spectral solution. An optimization procedure has been applied to different SF6 and copper vapor gas mixtures for an assumed temperature profile. Radiation model results using optimized band averaged absorption coefficients as well as spectral values are provided and discussed for the exemplary temperature profile

Radiative Properties and Numerical Modeling of C4F7N-CO2-O2 Thermal Plasma

C4F7N and C4F7N-CO2 mixtures are considered as alternatives to SF6 for use in medium voltage gas insulated switchgear applications (GIS), due to the low global warming potential and good dielectric properties of C4F7N. Current work is focused on the calculation of radiative properties (absorption coefficients) of C4F7N-CO2 thermal plasma and computational fluid dynamics (CFD) simulations of free burning C4F7N-CO2 arcs that are stabilized by natural convection. Absorption coefficients of C4F7N-CO2 plasma used in the CFD model are derived from spectral absorption coefficients by Planck averaging. An optimization procedure has been applied to find the optimal number of spectral bands as well as spectral band interval boundaries. Radiation and flow model results for C4F7N-CO2 in comparison to SF6 and air are provided and discussed

Domain wall fermion zero modes on classical topological backgrounds

The domain wall approach to lattice fermions employs an additional dimension, in which gauge fields are merely replicated, to separate the chiral components of a Dirac fermion. It is known that in the limit of infinite separation in this new dimension, domain wall fermions have exact zero modes, even for gauge fields which are not smooth. We explore the effects of finite extent in the fifth dimension on the zero modes for both smooth and non-smooth topological configurations and find that a fifth dimension of around ten sites is sufficient to clearly show zero mode effects. This small value for the extent of the fifth dimension indicates the practical utility of this technique for numerical simulations of QCD.Comment: Updated fig. 3-7, small changes in sect. 3, added fig. 8, added more reference

Density of states in graphene with vacancies: midgap power law and frozen multifractality

The density of states (DoS), $\varrho(E)$, of graphene is investigated numerically and within the self-consistent T-matrix approximation (SCTMA) in the presence of vacancies within the tight binding model. The focus is on compensated disorder, where the concentration of vacancies, $n_\text{A}$ and $n_\text{B}$, in both sub-lattices is the same. Formally, this model belongs to the chiral symmetry class BDI. The prediction of the non-linear sigma-model for this class is a Gade-type singularity $\varrho(E) \sim |E|^{-1}\exp(-|\log(E)|^{-1/x})$. Our numerical data is compatible with this result in a preasymptotic regime that gives way, however, at even lower energies to $\varrho(E)\sim E^{-1}|\log(E)|^{-\mathfrak{x}}$, $1\leq \mathfrak{x} < 2$. We take this finding as an evidence that similar to the case of dirty d-wave superconductors, also generic bipartite random hopping models may exhibit unconventional (strong-coupling) fixed points for certain kinds of randomly placed scatterers if these are strong enough. Our research suggests that graphene with (effective) vacancy disorder is a physical representative of such systems.Comment: References updated onl

A simple paper test for isoniazid in urine

Tests for the presence of chemotherapeutic drugs or their metabolites in urine play an important part in the management of the treatment of tuberculosis (Dixon et al., 1957; Fox, 1958). A previous report from this Centre (Gangadharam et al., 1958) presented a comparison of a number of methods for detecting isoniazid in urine including the direct naphthoquinone-mercuric chloride (N-M) test (Short and Case, 1957), and also a modification of this test which employed alkaline hydrolysis to liberate isoniazid from its conjugated forms. The direct-and hydrolysis N-M tests have been employed in this Centre for the past four years to control the self-administration of isoniazid used in the domiciliary treatment of pulmonary tuberculosis. The effect of irregularity in taking isoniazid as detected by these tests on the response to treatment has been reported elsewhere (Tuberculosis Chemotherapy Centre, 1960). Since this method has the disadvantage that it requires a certain amount of equipment and trained personnel, it is not suitable for routine use in all chest clinics or under field conditions. An attempt was therefore made in this Centre to simplify the direct N-M test by incorporating the reagents in absorbent papers; Though impregnation of the paper with the pHl0 buffer and naphthoquinone reagent was successful, impregnation with the aqueous solution of the mercuric chloride was unsatisfactory. In 1960, Cattaneo, Fantoli and Belasio published details of a paper test modification of the N-M test in which this difficulty was overcome by impregnating absorbent papers with a solution of mercuric chloride in ether. Since then this modification has been adopted for the preparation of the test-paper developed in this Centre. Since a lower concentration of the naphthoquinone reagent and a shorter period of exposure was used in the preparation of the testpaper developed in this Centre than described by Cattaneo et al. (1960), both the paper tests have been compared with the direct and combined N-M tests described previously (Gangadharam et al., 1958). This paper presents the results of the comparison and of an of the specificity of the paper test

Impact of improved treatment success on the prevalence of TB in a rural community based on active surveillance.

Objective: To study the impact of improved treatment outcome of a cohort of patients treated under DOTS strategy on the prevalence of pulmonary tuberculosis (TB) in the community. Design: The data from TB register of one Tuberculosis Unit (TU) in Tiruvallur district of Tamilnadu, and two TB disease surveys conducted in the same area during 1999-2003 were analysed. The successful treatment outcome was compared to the prevalence of TB in the subsequent cohort. Results: The proportion of patients who completed treatment successfully was 75.3% in the first cohort period. This higher proportion of treatment success among patients treated under DOTS in the first cohort period (1999-2001) compared to the 51-55% reported during SCC, resulted in a lower prevalence of smear-positive cases, irrespective of culture results observed in the survey conducted during 2001-2003 compared to that in the survey conducted during 1999-2001 (252 vs. 323 per 100,000; annual decline of 9%). Similarly, a decline in culture-positive cases, irrespective of smear results, was also observed (443 vs. 605; annual decline 11%). Conclusion: The higher proportion of successful completion of treatment after DOTS implementation was associated with a substantial decline in the prevalence of TB. These findings showed that we are in the direction towards achieving the Millennium Development Goals (MDGs)

Residual Chiral Symmetry Breaking in Domain-Wall Fermions

We study the effective quark mass induced by the finite separation of the domain walls in the domain-wall formulation of chiral fermion as the function of the size of the fifth dimension ($L_s$), the gauge coupling $\beta$ and the physical volume $V$. We measure the mass by calculating the small eigenvalues of the hermitian domain-wall Dirac operator ($H_{\rm DWF}(m_0))$ in the topologically-nontrivial quenched SU(3) gauge configurations. We find that the induced quark mass is nearly independent of the physical volume, decays exponentially as a function of $L_s$, and has a strong dependence on the size of quantum fluctuations controlled by $\beta$. The effect of the choice of the lattice gluon action is also studied.Comment: 12 pages, 7 figure

Vector like gauge theories with almost massless fermions on the lattice

A truncation of the overlap (domain wall fermions) is studied and a criterion for reliability of the approximation is obtained by comparison to the exact overlap formula describing massless quarks. We also present a truncated version of regularized, pure gauge, supersymmetric models. The mechanism for generating almost masslessness is shown to be a generalized see-saw which can also be viewed as a version of Froggatt-Nielsen's method for obtaining natural large mass hierarchies. Viewed in this way the mechanism preserving the mass hierarchy naturally avoids preserving even approximately axial U(1). The new insights into the source of the mass hierarchy suggest ways to increase the efficiency of numerical simulations of QCD employing the truncated overlap.Comment: 35 pages, TeX, 4 figures using eps

Scaling and Eigenmode Tests of the Improved Fat Clover Action

We test a recently proposed improved lattice-fermion action, the fat link clover action, examining indicators of pathological small-quark-mass lattice artifacts ("exceptional configurations") on quenched lattices of spacing 0.12 fm and studying scaling properties of the light hadron spectrum for lattice spacing a=0.09 and 0.16 fm. We show that the action apparently has fewer problems with pathological lattice artifacts than the conventional nonperturbatively improved clover action and its spectrum scales just as well.Comment: 15 pp RevTeX, 5 Postscript figures, submitted to Phys. Rev. Rearranged section order and added an analysis of fluctuations of the pion correlato