Non-perturbative determination of beta-functions and excited string states from lattices

We use lattice sum rules for the static quark potential to determine the beta-function for symmetric and asymmetric lattices non-perturbatively. We also study the colour field distributions in excited gluonic states.Comment: 9 pages, LATEX, 1 postscript figur

Postscript on Vedic jaṅgahe

Niet-projectgebonden publicaties Talen en culturen van Zuid en Centraal Azi

Two words for 'sister-in-law'? Notes on Vedic yātar- and giri-

Descriptive and Comparative Linguistic

Scotland's groundwater monitoring network : its effectiveness for monitoring nitrate

Scotland has had a national groundwater quality monitoring network since the year 2000. One of the main functions of this network is to monitor nitrate concentrations. Nitrate can be elevated in the environment due to modern agricultural practice. Initially there were 150 monitoring sites, but these have been added to, and in 2005, the number of groundwater monitoring points for nitrate was 219, comprising 139 boreholes, 51 springs and 27 wells; 67% of these sites are in agricultural areas. In order to have confidence in the interpretation of data gathered from the network it is important to know the context of the sample points, and in particular whether any sites are compromised by surface contamination or nearby point sources. Prior to this study, many of the sites had not undergone a formal risk assessment and their condition was unclear. In order to improve confidence in the network, and to help act as a baseline before improving the network, the British Geological Survey and the Macaulay Institute were commissioned by the Scottish Executive to carry out a review during the period February-July 2005. The core of the project was to undertake field assessments for 151 sites where no formal assessment had been made previously. Using criteria developed in this project, a judgement was made as to whether the monitoring point was adequate, required improvement or further assessment, or should be considered for removal. For all 219 sites on the network, a zone of influence was estimated using a semi-quantitative method. These zones were used to help focus the field surveys and also to characterise each site using national datasets; for example the monitoring site would be assigned the land use that occupied more than 60% of the zone. These data were then used to conduct an analysis of the factors controlling nitrate concentrations across the network and to help evaluate how effective the network is at monitoring nitrate in Scottish groundwater. Below is a summary of the main results from the project: 1. The fieldwork and analysis of the 151 previously unassessed sites indicated that: • 61 of the 151 sites are adequate and can continue to be monitored with no improvements. • There are serious concerns about 29 of the 151 sites (19% of the sites assessed and 13% of the total nitrate network). These sites should be considered for removal from the network. The sources found to be least reliable were shallow large diameter wells. However, there is little evidence to suggest that the data from these sources collected from 2000 – 2005 has been seriously compromised by point source pollution. • 30 sites require further assessment before being judged suitable. Most of these sites are springs and require additional work to identify the precise source. • 31 sites require improvements to the monitoring points – the improvements range from better sampling protocols to improving the headworks through simple engineering. 2. There is a clear difference between nitrate concentrations measured in the areas designated as nitrate vulnerable zones (NVZs) and other areas. Within the NVZs, the mean concentration is 25 mg-NO3 l-1 and the median 17 mg-NO3 l-1; outside the NVZs, the mean concentration is 9 mg-NO3 l-1 and the median 4.4 mg-NO3 l-1. The data from the network indicate that land use has a large influence on the nitrate concentrations measured in the monitoring network: arable areas, mixed cultivation of both arable and grassland, and areas where dairy, pigs and poultry are reared contribute to the highest nitrate concentrations, with 18% of sites in these areas exceeding 50 mg-NO3 l-1. The most significant control on nitrate concentrations in the monitoring network is the presence of dairy, pigs or poultry within the zone of influence. 4. A considerable number of monitoring sites have lower nitrate concentrations than would be expected from the nitrate pressure. This can be attributed to dilution from rainfall, mixing with older low nitrate waters, denitrification, or the presence of low permeability soil and superficial deposits which slow the movement of high nitrate water into the aquifers. 5. A “gaps” analysis which compared the current network with an idealised network based on nitrate pressures across Scotland indicated that overall the distribution of the current network is generally good. However, there are significant gaps in the improved grassland areas of the Midland Valley and Ayrshire and in the arable areas of Aberdeenshire, while Mid and East Lothian and the Borders are currently overrepresented. The following recommendations are made for the nitrate groundwater quality network in Scotland: 1. Consideration should be given to removing or replacing 29 of the 219 sites, and undertaking further assessments on 30 sites. A further 31 sites would benefit from improvements to the headworks or sampling arrangements. 2. Further statistical analysis should be undertaken to help understand the factors that control the nitrate concentrations in groundwater – particularly the environmental factors that help to reduce the measured nitrate. 3. The network should continue to be concentrated on nitrate pressured areas in Scotland, with approximately 75% of the network in high nitrate areas, and 25% used to monitor background nitrate concentrations in less pressured areas. 4. Any future sites added to the network must undergo a risk assessment similar to the one developed for this study to ensure that the network remains of good quality. 5. The network must continue to reflect the diverse hydrogeological, soil and land use conditions in Scotland. Therefore, both bedrock and superficial aquifers should be monitored in a variety of soil conditions. The network should continue to include different types of sources, although less emphasis should be given to wells, which are generally poor monitoring points. 6. In the future, the data from the network will require to be actively interpreted: an inevitable outcome from having a diverse network is that the results of the monitoring must be interpreted not only in terms of agricultural practice, but in light of the other factors such as geological and environmental conditions. In practice this could mean a regular detailed review (maybe every 2-3 years) of the data from the network. 7. The network will also need to be actively managed to account for various changes in monitoring sites, for example the land use, the condition of the headworks and the pumping rate. This will involve SEPA hydrogeologists having an overview of the network; individual sources being periodically reviewed using a simple checklist; and additional new sources being sought, possibly through the ongoing BGS/SEPA study of baseline groundwater chemistry across Scotland. 8. Wellhead measurements should be taken periodically to help identify denitrification or mixing with older waters. The limited samples taken during this study proved invaluable for interpreting apparently anomalous nitrate concentrations. To undertake this successfully, dedicated sample taps may have to be introduced. 9. A separate programme of focussed monitoring should be developed in tandem with the national groundwater monitoring network to give information on the effects of the action programmes within the NVZs. These sites should be in a controlled environment that will respond rapidly to changes in agricultural practice. The results from these studies can then be upscaled to help interpret changes in the national network as well as be used on their own to help understand the success of the Action Programmes

Solution landscapes in nematic microfluidics

We study the static equilibria of a simplified Leslie–Ericksen model for a unidirectional uniaxial nematic flow in a prototype microfluidic channel, as a function of the pressure gradient G and inverse anchoring strength, B. We numerically find multiple static equilibria for admissible pairs (G,B) and classify them according to their winding numbers and stability. The case G=0 is analytically tractable and we numerically study how the solution landscape is transformed as G increases. We study the one-dimensional dynamical model, the sensitivity of the dynamic solutions to initial conditions and the rate of change of G and B. We provide a physically interesting example of how the time delay between the applications of G and B can determine the selection of the final steady state

Decoherence and wave function collapse

The possibility of consistency between the basic quantum principles of quantum mechanics and wave function collapse is reexamined. A specific interpretation of environment is proposed for this aim and applied to decoherence. When the organization of a measuring apparatus is taken into account, this approach leads also to an interpretation of wave function collapse, which would result in principle from the same interactions with environment as decoherence. This proposal is shown consistent with the non-separable character of quantum mechanics

Hybrid meson decay from the lattice

We discuss the allowed decays of a hybrid meson in the heavy quark limit. We deduce that an important decay will be into a heavy quark non-hybrid state and a light quark meson, in other words, the de-excitation of an excited gluonic string by emission of a light quark-antiquark pair. We discuss the study of hadronic decays from the lattice in the heavy quark limit and apply this approach to explore the transitions from a spin-exotic hybrid to $\chi_b \eta$ and $\chi_b S$ where $S$ is a scalar meson. We obtain a signal for the transition emitting a scalar meson and we discuss the phenomenological implications.Comment: 18 pages, LATEX, 3 ps figure

Crossover and self-averaging in the two-dimensional site-diluted Ising model

Using the newly proposed probability-changing cluster (PCC) Monte Carlo algorithm, we simulate the two-dimensional (2D) site-diluted Ising model. Since we can tune the critical point of each random sample automatically with the PCC algorithm, we succeed in studying the sample-dependent $T_c(L)$ and the sample average of physical quantities at each $T_c(L)$ systematically. Using the finite-size scaling (FSS) analysis for $T_c(L)$, we discuss the importance of corrections to FSS both in the strong-dilution and weak-dilution regions. The critical phenomena of the 2D site-diluted Ising model are shown to be controlled by the pure fixed point. The crossover from the percolation fixed point to the pure Ising fixed point with the system size is explicitly demonstrated by the study of the Binder parameter. We also study the distribution of critical temperature $T_c(L)$. Its variance shows the power-law $L$ dependence, $L^{-n}$, and the estimate of the exponent $n$ is consistent with the prediction of Aharony and Harris [Phys. Rev. Lett. {\bf 77}, 3700 (1996)]. Calculating the relative variance of critical magnetization at the sample-dependent $T_c(L)$, we show that the 2D site-diluted Ising model exhibits weak self-averaging.Comment: 6 pages including 6 eps figures, RevTeX, to appear in Phys. Rev.

The Hitchin functionals and the topological B-model at one loop

The quantization in quadratic order of the Hitchin functional, which defines by critical points a Calabi-Yau structure on a six-dimensional manifold, is performed. The conjectured relation between the topological B-model and the Hitchin functional is studied at one loop. It is found that the genus one free energy of the topological B-model disagrees with the one-loop free energy of the minimal Hitchin functional. However, the topological B-model does agree at one-loop order with the extended Hitchin functional, which also defines by critical points a generalized Calabi-Yau structure. The dependence of the one-loop result on a background metric is studied, and a gravitational anomaly is found for both the B-model and the extended Hitchin model. The anomaly reduces to a volume-dependent factor if one computes for only Ricci-flat Kahler metrics.Comment: 33 pages, LaTe

Antiferromagnetic Zigzag Spin Chain in Magnetic Fields at Finite Temperatures

We study thermodynamic behaviors of the antiferromagnetic zigzag spin chain in magnetic fields, using the density-matrix renormalization group method for the quantum transfer matrix. We focus on the thermodynamics of the system near the critical fields in the ground-state magnetization process($M$-$H$ curve): the saturation field, the lower critical field associated with excitation gap, and the field at the middle-field cusp singularity. We calculate magnetization, susceptibility and specific heat of the zigzag chain in magnetic fields at finite temperatures, and then discuss how the calculated quantities reflect the low-lying excitations of the system related with the critical behaviors in the $M$-$H$ curve.Comment: accepted for publication in Physical Review