Charm-System Tests of CPT with FOCUS

We discuss a search for CPT violation in neutral charm meson oscillations. The data come from the Fermilab fixed-target experiment FOCUS. While flavor mixing in the charm sector is predicted to be small by the standard model, it is still possible to investigate CPT violation through study of the proper time dependence of the asymmetry in right-sign decay rates for D0 and D0-bar. Using present limits for D0-D0-bar mixing we infer bounds on charm CPT violation using data from FOCUS.Comment: 8 pages, invited talk at the Second Meeting on CPT and Lorentz Symmetry, Indiana University, Bloomington, August 15-18, 200

Comparative review of the effects of organic farming on biodiversity (OF0149)

This is the final report of Defra project OF0149 1. The report reviews the impact of different farming regimes and makes a comparative study of their influence on the biodiversity of arable farmland. 2. Within this review, the evaluation of impacts on biodiversity focuses on species and habitats, and includes both the number, abundance and activity of species (section 1.3). 3. Five farming regimes are defined and discussed, namely Conventional Arable, Conventional Mixed Lowland, Organic and two integrated production regimes - LEAF (Linking Environment and Farming) and IFS-Experimental regimes The main differences between the regimes in relation to the use of external inputs and other agricultural practices are discussed. The review draws on both UK and European information (section 1.4). 4. The effect of each farming regime on biodiversity is assessed according to the agricultural practices adopted and to the occurrence and management of uncropped land present. Agricultural practices are reviewed within the following categories: cultivation, crop production, crop protection and post-cropping practice (section 2.1). 5. Among the agricultural practices examined, those associated with crop protection and the artificial inputs associated with crop production were seen as the most adverse for biodiversity. Several practices were seen to benefit the biodiversity of arable land. These included set-aside, crop rotations with grass leys, spring sowing, permanent pasture, green manuring and intercropping (section 2.7). 6. Uncropped areas, such as sown grass strips (beetle banks), grass margins and conservation headlands, were seen as critical for the maintenance of biodiversity on arable farmland. Changes in the balance of cropped to uncropped land within some farming regimes, linked to increase in field size, have had a major impact on the diversity of flora and fauna associated with those regimes (section 3.4). 7. Based on the evaluation of agricultural practices used, the occurrence of uncropped land and the extent of the farming regime within England and Wales, it was concluded that Conventional Arable regimes act effectively to maintain the impoverished status of biodiversity on arable land. Extreme examples can be found of intensively managed farms that further deplete biodiversity and sympathetically managed farms that try to enhance it. Increased adoption of agricultural practices such as direct drilling, use of farmyard manure, set-aside, use of crop rotations with leys, or an increase in the incidence and sympathetic management of uncropped areas may well assist biodiversity on farms within this regime (sections 4.3 & 4.4) 8. Organic regimes were shown to have an overall benefit for biodiversity at the farm level, both in terms of the agricultural practices adopted and in the occurrence and management of uncropped areas (sections 4.3 & 4.4). 9. Conventional Mixed Lowland and LEAF regimes were both seen to have the potential for enhancing biodiversity on arable land. Here, adverse impacts associated with crop protection and crop production may be mitigated by beneficial effects associated with post-cropping practices, the occurrence of permanent pasture and uncropped land. At present, the extent to which enhancement may be achieved, may well depend on the extent, condition and management of uncropped land present within these regimes (sections 4.3 & 4.4). 10. IFS-experimental regimes were seen to have a beneficial effect on biodiversity, due to the stringent procedures used for targeting herbicides and pesticides and for establishing and managing uncropped areas. At present these regimes occupy a tiny area of the national resource of arable land and thus their impact on national biodiversity is likely to be insignificant at the present time (sections 4.3 & 4.4). 11. A number of areas are highlighted for further consideration. These include: • monitoring of biodiversity on farms pre- and post- conversion to organic farming, • comparative studies that focus on the effectiveness of different regimes or agricultural practices in enhancing biodiversity on species-impoverished intensively managed arable land, • manipulative experiments to determine the optimal balance of cropped to uncropped areas for enhancing biodiversity, • manipulative experiments to examine the separate impacts of rotational regimes and agricultural inputs on biodiversity, • an economic assessment of the costs and benefits in both production and biodiversity terms, of conversion to organic, integrated production or uptake of available agri-environment schemes

Independent Orbiter Assessment (IOA): Assessment of instrumental subsystem FMEA/CIL

The McDonnell Douglas Astronautics Company (MDAC) was selected in June 1986 to perform an Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL). The IOA effort first completed an analysis of the Instrumentation hardware, generating draft failure modes and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The IOA results were then compared to the NASA FMEA/CIL baseline. A resolution of each discrepancy from the comparison is provided through additional analysis as required. The results of that comparison for the Orbiter Instrumentation hardware are documented. The IOA product for Instrumentation analysis consisted of 107 failure mode worksheets that resulted in 22 critical items being identified. Comparison was made to the Pre 51-L NASA baseline with 14 Post 51-L FMEAs added, which consists of 96 FMEAs and 18 CIL items. This comparison produced agreement on all but 25 FMEAs which caused differences in 5 CIL items

Nonlinear optical probe of tunable surface electrons on a topological insulator

We use ultrafast laser pulses to experimentally demonstrate that the second-order optical response of bulk single crystals of the topological insulator Bi$_2$Se$_3$ is sensitive to its surface electrons. By performing surface doping dependence measurements as a function of photon polarization and sample orientation we show that second harmonic generation can simultaneously probe both the surface crystalline structure and the surface charge of Bi$_2$Se$_3$. Furthermore, we find that second harmonic generation using circularly polarized photons reveals the time-reversal symmetry properties of the system and is surprisingly robust against surface charging, which makes it a promising tool for spectroscopic studies of topological surfaces and buried interfaces

Statistical mechanics of the multi-constraint continuous knapsack problem

We apply the replica analysis established by Gardner to the multi-constraint continuous knapsack problem,which is one of the linear programming problems and a most fundamental problem in the field of operations research (OR). For a large problem size, we analyse the space of solution and its volume, and estimate the optimal number of items to go into the knapsack as a function of the number of constraints. We study the stability of the replica symmetric (RS) solution and find that the RS calculation cannot estimate the optimal number of items in knapsack correctly if many constraints are required.In order to obtain a consistent solution in the RS region,we try the zero entropy approximation for this continuous solution space and get a stable solution within the RS ansatz.On the other hand, in replica symmetry breaking (RSB) region, the one step RSB solution is found by Parisi's scheme. It turns out that this problem is closely related to the problem of optimal storage capacity and of generalization by maximum stability rule of a spherical perceptron.Comment: Latex 13 pages using IOP style file, 5 figure

A canonical ensemble approach to graded-response perceptrons

Perceptrons with graded input-output relations and a limited output precision are studied within the Gardner-Derrida canonical ensemble approach. Soft non- negative error measures are introduced allowing for extended retrieval properties. In particular, the performance of these systems for a linear and quadratic error measure, corresponding to the perceptron respectively the adaline learning algorithm, is compared with the performance for a rigid error measure, simply counting the number of errors. Replica-symmetry-breaking effects are evaluated.Comment: 26 pages, 10 ps figure

Analytical and Numerical Study of Internal Representations in Multilayer Neural Networks with Binary Weights

We study the weight space structure of the parity machine with binary weights by deriving the distribution of volumes associated to the internal representations of the learning examples. The learning behaviour and the symmetry breaking transition are analyzed and the results are found to be in very good agreement with extended numerical simulations.Comment: revtex, 20 pages + 9 figures, to appear in Phys. Rev.

Correlations between hidden units in multilayer neural networks and replica symmetry breaking

We consider feed-forward neural networks with one hidden layer, tree architecture and a fixed hidden-to-output Boolean function. Focusing on the saturation limit of the storage problem the influence of replica symmetry breaking on the distribution of local fields at the hidden units is investigated. These field distributions determine the probability for finding a specific activation pattern of the hidden units as well as the corresponding correlation coefficients and therefore quantify the division of labor among the hidden units. We find that although modifying the storage capacity and the distribution of local fields markedly replica symmetry breaking has only a minor effect on the correlation coefficients. Detailed numerical results are provided for the PARITY, COMMITTEE and AND machines with K=3 hidden units and nonoverlapping receptive fields.Comment: 9 pages, 3 figures, RevTex, accepted for publication in Phys. Rev.