Recombination Algorithms and Jet Substructure: Pruning as a Tool for Heavy Particle Searches

We discuss jet substructure in recombination algorithms for QCD jets and single jets from heavy particle decays. We demonstrate that the jet algorithm can introduce significant systematic effects into the substructure. By characterizing these systematic effects and the substructure from QCD, splash-in, and heavy particle decays, we identify a technique, pruning, to better identify heavy particle decays into single jets and distinguish them from QCD jets. Pruning removes protojets typical of soft, wide angle radiation, improves the mass resolution of jets reconstructing a heavy particle decay, and decreases the QCD background. We show that pruning provides significant improvements over unpruned jets in identifying top quarks and W bosons and separating them from a QCD background, and may be useful in a search for heavy particles.Comment: 33 pages, 42 figure

Hydraulic Fracture

We consider a variation of Griffith's analysis of rupture, one which simulates the process of hydrofracturing, where fluid forced into a crack raises the fluid pressure until the crack begins to grow. Unlike that of Griffith, in this analysis fluid pressure drops as a hydrofracture grows. We find that growth of the fracture depends on the ratio of the compliances of the fluid and the fracture, a non-dimensional parameter called $\alpha_0$ here. The pressure needed to initiate a hydrofracture is found to be the same as that derived by Griffith. Once a fracture initiates, for relatively low values of the model parameter $\alpha_0$ ($\alpha_0 \leq 0.2$) the fracture advances spontaneously to a new radius which depends on the value of $\alpha_0$. For $\alpha_0 \leq 0.2$ further fluid injection is required to increase the fracture radius after spontaneous growth stops. For the case where $\alpha_0 > 0.2$ each increment of fracture growth requires injection of more fluid. For the extreme case where $\alpha_0 = 0$ our results are the same as Griffith's, i.e., a fracture once initiated grows without limit.Comment: 10 pages, 4 figure

Effects of Amphetamine on Striatal Dopamine Release, Open-Field Activity, and Play in Fischer 344 and Sprague–Dawley Rats

Previous work from our laboratories has shown that juvenile Fischer 344 (F344) rats are less playful than other strains and also appear to be compromised in dopamine (DA) functioning. To determine whether the dysfunctional play in this strain is associated with deficits in the handling and delivery of vesicular DA, the following experiments assessed the extent to which F344 rats are differentially sensitive to the effects of amphetamine. When exposed to amphetamine, striatal slices obtained from F344 rats showed a small increase in unstimulated DA release when compared with slices from Sprague–Dawley rats; they also showed a more rapid high K+-mediated release of DA. These data provide tentative support for the hypothesis that F344 rats have a higher concentration of cytoplasmic DA than Sprague–Dawley rats. When rats were tested for activity in an open field, F344 rats presented a pattern of results that was consistent with either an enhanced response to amphetamine (3 mg/kg) or a more rapid release of DA (10 mg/kg). Although there was some indication that amphetamine had a dose-dependent differential effect on play in the two strains, play in F344 rats was not enhanced to any degree by amphetamine. Although these results are not consistent with our working hypothesis that F344 rats are less playful because of a deficit in vesicular release of DA, they still suggest that this strain may be a useful model for better understanding the role of DA in social behavior during the juvenile period

Post-transplantation cutaneous and renal Aspergillus infection

A 68-year old renal transplant recipient suffered multiple complications following initial good graft function from a deceased-donor transplant. Late in the first week he was oliguric with haematuria; the graft failed in week 2 following development of a haematoma from rupture of a renal artery aneurysm. He had a recurrent bleed from the internal iliac graft site and subsequently developed painful dark patches on his leg, distal to where the transplant had been. Histology from the explanted graft and skin biopsies demonstrated Aspergillus flavus; this was also grown in culture of the external iliac artery tissue. Systemic aspergillosis is rare but well recognised, especially in the immunocompromised. Presentations include mycotic aneurysms and secondary cutaneous aspergillosis from haematogenous spread. Diagnosis requires confirmation by histology or direct culture, but a high beta-glucan concentration and positive galactomannan antigen can suggest invasive fungal infection in the early stages of the disease. Cases should be managed with systemic antifungals and involvement of local microbiology services; unfortunately, prognosis is poor

Absolute calibration of the intramolecular site preference of 15N fractionation in tropospheric N2O by FT-IR spectroscopy

Nitrous oxide (N2O) plays important roles in atmospheric chemistry both as a greenhouse gas and in stratospheric ozone depletion. Isotopic measurements of N2O have provided an invaluable insight into understanding its atmospheric sources and sinks. The preference for 15N fractionation between the central and terminal positions (the “site preference”) is particularly valuable because it depends principally on the processes involved in N2O production or consumption, rather than the 15N content of the substrate from which it is formed. Despite the value of measurements of the site preference, there is no internationally recognized standard reference material of accurately known and accepted site preference, and there has been some lack of agreement in published studies aimed at providing such a standard. Previous work has been based on isotope ratio mass spectrometry (IRMS); in this work we provide an absolute calibration for the intramolecular site preference of 15N fractionation of working standard gases used in our laboratory by a completely independent technique—high-resolution Fourier transform infrared (FT-IR) spectroscopy. By reference to this absolute calibration, we determine the site preference for 25 samples of tropospheric N2O collected under clean air conditions to be 19.8‰ ± 2.1‰. This result is in agreement with that based on the earlier absolute calibration of Toyoda and Yoshida (Toyoda, S. and Yoshida, N. Anal. Chem. 1999, 71, 4711−4718) who found an average tropospheric site preference of 18.7‰ ± 2.2‰. We now recommend an interlaboratory exchange of working standard N2O gases as the next step to providing an international reference standard

Diachrony of mammalian appearance events: Implications for biochronology: Geology, v. 26

Alroy (1998) argued that there is significant diachrony in the first and last appearance events (FAE and LAE) of Cenozoic mammals in North America, and therefore individual events cannot be used for biochronology. A close examination of the data used in his paper, however, suggests that (1) most of the diachrony is largely a sampling artifact, and (2) once sampling is factored out, the remaining apparent diachrony would have little effect on the biochronological correlations that have been established for over a century. These points are demonstrated by Alroy's (1998, Any comparison between two such unequal records will inevitably yield large diachrony values, simply because of the large stratigraphic gaps in the West Coast. Alroy (personal commun.) provided me with a list of the ten "worst offenders" among FAEs. Most of these taxa (Thylacaelurus, Domnina, Pseudotrimylus, Mystipterus, Anchitheriomys, Nyctitherium, Plionictis, Mytonomys, Paramys, Leptodontomys) are small, relatively rare mammals that rarely have been important in biochronology. In addition, anyone with extensive first-hand experience in identifying the Miocene faunas of the West Coast knows they are much scrappier and less complete than those of the Midcontinent, with many erroneous or tentative identifications based on fragmentary specimens. If many of these uncertain identifications were thrown out, the apparent diachrony might diminish even further. Instead of including all available taxa, most of which are rare and subject to sampling problems and historically have not been important in North American mammalian biochronology, Alroy's point would be better demonstrated if he were to focus on mammals (such as those given by Woodburne, 1987, Fig. 10.1) which were explicitly designated as index taxa for mammalian biochronology. If this list were to show significant diachrony (greater than the available chronologic resolution), then there might be serious concern about using fossil mammals as time indicators. But comparisons based on rarely sampled taxa that were not important to the original biochronologic framework are of dubious value. I thank John Alroy for providing data, and S. L. Walsh and M. O. Woodburne for comments

Noise source characteristics in the ISO 362 vehicle pass-by noise test: literature review

Since many people are exposed to road traffic noise in urban areas, current legislation aims to limit vehicle noise emissions. In Europe, the vehicle pass-by noise test is implemented according to the international standard ISO 362. As a result of more recent investigations of urban traffic, a revision to the ISO 362 standard has been proposed that includes a constantspeed test in addition to the traditional accelerated test in order to determine the pass-by noise value. To ensure compliance with the pass-by noise test vehicle manufacturers and suppliers must quantify vehicle noise source characteristics during the design stage of the vehicle. In addition, predictive tools need to be available during the product development phase in order to estimate the final pass-by noise level. In this paper an extensive literature survey is presented of noise source characteristics in the ISO 362 vehicle pass-by noise test. Vehicle pass-by noise is analysed in the time and frequency domains and a ranking of the noise source contributions is established. The characteristics of the four major noise sources (engine, intake system, exhaust system, tyre/road system) contributing to pass-by noise as well as current prediction methods are reviewed