Towards a modeling of the time dependence of contact area between solid bodies

I present a simple model of the time dependence of the contact area between solid bodies, assuming either a totally uncorrelated surface topography, or a self affine surface roughness. The existence of relaxation effects (that I incorporate using a recently proposed model) produces the time increase of the contact area $A(t)$ towards an asymptotic value that can be much smaller than the nominal contact area. For an uncorrelated surface topography, the time evolution of $A(t)$ is numerically found to be well fitted by expressions of the form [$A(\infty)-A(t)]\sim (t+t_0)^{-q}$, where the exponent $q$ depends on the normal load $F_N$ as $q\sim F_N^{\beta}$, with $\beta$ close to 0.5. In particular, when the contact area is much lower than the nominal area I obtain $A(t)/A(0) \sim 1+C\ln(t/t_0+1)$, i.e., a logarithmic time increase of the contact area, in accordance with experimental observations. The logarithmic increase for low loads is also obtained analytically in this case. For the more realistic case of self affine surfaces, the results are qualitatively similar.Comment: 18 pages, 9 figure

Some recent rural radio talks

Current experiments with vegetable crops - By T. WACHTEL, Agricultural Adviser, Horticultural Division Pedigree seed planting - By H. G. CARISS, B.Sc. (Agric), Regional Agricultural Adviser The Ruakura round farrowing house - By P. BECK, Field Assistant, Dairying Division How the random sample laying test could affect the poultry industry - By R. H. MORRIS, Officer-in-Charge, Poultry Branch Feeding the milking goat - By K. NEEDHAM, Dairy Cattle Husbandry Officer Fertilisers for vegetables in summer months - By J. P. FALLON, Senior Adviser (Vegetables), Horticultural Division Pastures and their carrying capacity - By H. G. ELLIOTT, Assistant Superintendent of Dairying Pollination - By J. CRIPPS, Adviser, Horticultural Division Aeroplanes and insect pest control - By P. N. FORTE, Senior Entomologist Kill those flies - By H. MASLIN, Dairy Instructor, Busselton Grazing for pigs - By P. BECK, Field Assistant, Dairying Division Feed flavours in cream - By an officer of the Dairying Division. Those old milk and cream cans - By D. C. MICKLE, Dairy Instructor, Bunbury Overrun in butter making and quality in home-made butter - By A. H. HOBBS, Dairy Produce Inspector Milk flow indicators - By G. W. SCOTT, Dairy Instructor, Head Offic

Some recent radio talks.

Light land development in the South - By A. S. WILD, Assistant Superintendent of Wheat Farming, Department of Agriculture. It is only since World War II ended that successful large scale development of light land near the south coast of this State has been undertaken, although the many millions of acres of treeless plain country throughout the agricultural areas have, for many years, presented a challenge to the pioneering ability of Western Australians. The use of hormones in viticulture - By L. T. JONES, Senior Plant Research Officer The discovery and proper use of plant hormones, or as they are more accurately termed, growth-regulating: substances, probably represents the greatest contribution which science has made to agriculture in the past few decades. It was the discovery by Kogl in 1934 that indole acetic acid was an active growth substance which led rapidly to the preparation and testing of large numbers of compounds of similar chemical structure and among these were found many substances which were very potent and also comparatively cheap to produce. Recent trends in viticulture in Western Australia - By W. R. JAMIESON, Viticulturist, Department of Agriculture, Perth Today I want to talk very briefly about some of the more recent trends in viticulture in this State. The commercial production of grapevines is centred mainly around the Swan Valley and as most of the suitable vineyard land in this area has been planted, growers are exploring avenues to increase the returns per acre. Methods of irrigation - By G. GAUNTLETT, Assistant Officer-in-Charge, Irrigation The success of an irrigation scheme depends on several factors. Important among these is the choice and design of the method to be adopted. There are two methods of irrigation, viz., surface and spray irrigation. Canker disease of Red-flowered gum - By W. P. CASS SMITH, B.Sc. (Agric), Government Plant Pathologist Of the many beautiful native plants in Western Australia, few are esteemed more than the red-flowered gum known botanically as Eucalyptus flcifolia. This shapely tree commences blossoming about Christmas time—and provides a magnificent display for several weeks—the blossom shades varying from dark red to pink. Why many beans grow crooked - By M. HARDIE, Vegetable Instructor Sometimes in the process of growing a crop, bean growers find a number of pods which, instead of being long and straight and suitable for marketing, are crooked or bent and quite unsuitable for sale unless beans are in very short supply. It is not unusual for a small number of pods to be affected in this way, generally at the tail-end of the crop, but occasionally the percentage may be high. When this happens the grower is often at a loss to account for his failure to grow a marketable crop. To the best of his ability he has followed methods which normally return a crop of first-grade pods and yet for some reason, his crop is an unpayable one and he is anxious to ascertain the cause. Salt land programme for Autumn - By T. C. STONEMAN, Adviser, Soil Conservation Service Now that summer is over and winter approaches, the time has come to decide what you\u27ll do with that salt problem on your farm. What you SHOULD do, will depend on how severely the area is affected. To make quite clear how the recommendations made by the Department of Agriculture can be applied I will deal with each degree of severity in turn. Orchard cover crops - By J. CRIPPS, Horticultural Adviser The sowing of a cover crop is one of those routine operations which the orchardist often undertakes without much thought, but it is an operation worthy of consideration. Lupin seed - By B. J. QUINLIVAN, B.Sc. (Agric), Botanist, Weeds and Seeds Branch The three types of lupins which we grow in this State are the New Zealand, the W.A. blue, and the yellow lupin. The first two types are very common, the New Zealand lupin being grown mainly in the South-West, while the W.A. lupin is grown over extensive areas of the central and northern wheatbelt, particularly on the sandier types of soil. Cereal rye will grow on wind-eroded areas - By G. H. BURVILL, Chief Plant Research Officer. Travelling around the wheatbelt, one often sees areas of sandy soil quite bare, A due to wind erosion. Surface soil blown from these patches has built up against fences, or as mounds in the nearby scrub. Many of the eroded places are quite small— perhaps less than an acre or only a few acres. But some are large, with one to three hundred acres of bare yellow sand. As much as two feet of soil has been blown from big areas. Autumn-winter feeding for the fat lamb flock - By N. DAVENPORT, Senior Adviser, Meat Production The autumn-winter period is the most important part of the year for the fat lamb crop from a feed point of view. It is important not only from the aspect of the wellbeing of the sheep, but also of the pasture. Pasture plants are living things, too, and they also require consideration and care for their development. When a new season pasture is kept hard grazed in those critical first few weeks of growth it cannot carry as many sheep over the season as one which is lightly stocked during that time. Plant diseases in the home garden - By W. P. CASS-SMITH, B.Sc. (Agric), Government Plant Pathologist Recently many home-gardeners have complained that plantings of vegetables or ornamentals are making unthrifty growth, in spite of liberal waterings and fertilisation. These symptoms are commonly caused by root-knot eelworm, a pest which has unfortunately become very widespread in the sandy soils adjacent to Perth, and in many other parts of this State. This eelworm parasite attacks the roots of many kinds of plants causing them to rot and to develop bead-like swellings or galls. As a result, the intake of plant food and water is restricted and stunting of the above-ground parts occurs. Principles of commercial beekeeping - By R. S. COLEMAN, R.D.A., Government Apiculturist We have many queries from small beekeepers, and from people who have never opened a hive, on how to break into full-time beekeeping. So it was thought that you would like to know just what are the principles of successful bee farming. Grasshoppers and locusts - By C. F. H. JENKINS, M.A., Government Entomologist Grasshoppers and locusts are among the most ancient enemies of mankind for they figured prominently in Biblical times, and periodically throughout the ages have devastated crops in all parts of the world. Acetonaemia in dairy cattle - By P. M. A. HARWOOD, M.R.C.V.S., Veterinary Officer Acetonaemia, more correctly known as ketosis is a metabolic disease. Unlike infectious diseases such as tuberculosis or mastitis, which are caused by microbes, metabolic diseases result from an upset in the normal bodily processes. Molybdenum for subterranean clover - By T. C. DUNNE, B.Sc. (Agric), Ph.D. (Calif.), Chief Plant Nutrition and Research Officer Subterranean clover is undoubtedly the most important pasture species in this State. Because it is a legume, it can make excellent growth on soils with a low nitrogen content. The nitrogen it needs is, of course, provided by bacteria which inhabit the nodules found on its roots. These bacteria provide nitrogen by taking it from the air and converting it to a form which can be used by the clover. However, it is now known that the bacteria can use the nitrogen of the air only if enough molybdenum is available to them. Cobalt deficiency in sheep and cattle - By C. R. TOOP, B.V.SC, Chief Veterinary Officer With the establishment of group settlements at Denmark after the first world war, it was observed that young cattle, although running on lush pastures, developed systems of unthriftness and wasting and usually died. Research conducted of Filmer and Underwood later revealed that this condition was caused by a deficiency of cobalt and that it could be cured and prevented by addition of this mineral to the diet. Cobalt deficiency has since been met with other parts of the State and was recently diagnosed in sheep at Mount Manypeaks

The LAGUNA design study- towards giant liquid based underground detectors for neutrino physics and astrophysics and proton decay searches

The feasibility of a next generation neutrino observatory in Europe is being considered within the LAGUNA design study. To accommodate giant neutrino detectors and shield them from cosmic rays, a new very large underground infrastructure is required. Seven potential candidate sites in different parts of Europe and at several distances from CERN are being studied: Boulby (UK), Canfranc (Spain), Fr\'ejus (France/Italy), Pyh\"asalmi (Finland), Polkowice-Sieroszowice (Poland), Slanic (Romania) and Umbria (Italy). The design study aims at the comprehensive and coordinated technical assessment of each site, at a coherent cost estimation, and at a prioritization of the sites within the summer 2010.Comment: 5 pages, contribution to the Workshop "European Strategy for Future Neutrino Physics", CERN, Oct. 200

Constructing non-stationary Dynamic Bayesian Networks with a flexible lag choosing mechanism

<p>Abstract</p> <p>Background</p> <p>Dynamic Bayesian Networks (DBNs) are widely used in regulatory network structure inference with gene expression data. Current methods assumed that the underlying stochastic processes that generate the gene expression data are stationary. The assumption is not realistic in certain applications where the intrinsic regulatory networks are subject to changes for adapting to internal or external stimuli.</p> <p>Results</p> <p>In this paper we investigate a novel non-stationary DBNs method with a potential regulator detection technique and a flexible lag choosing mechanism. We apply the approach for the gene regulatory network inference on three non-stationary time series data. For the Macrophages and Arabidopsis data sets with the reference networks, our method shows better network structure prediction accuracy. For the Drosophila data set, our approach converges faster and shows a better prediction accuracy on transition times. In addition, our reconstructed regulatory networks on the Drosophila data not only share a lot of similarities with the predictions of the work of other researchers but also provide many new structural information for further investigation.</p> <p>Conclusions</p> <p>Compared with recent proposed non-stationary DBNs methods, our approach has better structure prediction accuracy By detecting potential regulators, our method reduces the size of the search space, hence may speed up the convergence of MCMC sampling.</p

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV

A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 inverse picobarns collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets

Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version includes a minor typo correction that will be submitted as an erratu

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO