Hironaka's characteristic polygon and effective resolution of surfaces

Hironaka's concept of characteristic polyhedron of a singularity has been one of the most powerful and fruitful ideas of the last decades in singularity theory. In fact, since then combinatorics have become a major tool in many important results. However, this seminal concept is still not enough to cope with some effective problems: for instance, giving a bound on the maximum number of blowing--ups to be performed on a surface before its multiplicity decreases. This short note shows why such a bounding is not possible, at least with the original definitions.Comment: 7 pages, 1 figur

Gravitino perturbations in Schwarzschild black holes

We consider the time evolution of massless gravitino perturbations in Schwarzschild black holes, and show that as in the case of fields of other values of spin, the evolution comes in three stages, after an initial outburst as a first stage, we observe the damped oscillations characteristic of the quasinormal ringing stage, followed by long time tails. Using the sixth order WKB method and Prony fitting of time domain data we determine the quasinormal frequencies. There is a good correspondence between the results obtained by the above two methods, and we obtain a considerable improvement with respect to the previously obtained third order WKB results. We also show that the response of a black hole depends crucially on the spin class of the perturbing field: the quality factor becomes a decreasing function of the spin for boson perturbations, whereas the opposite situation appears for fermion ones

A Silvopastoral System in the North Atlantic Zone of Costa Rica: Combining Indigenous Timber Species with Dairy Pasture Swards

The objective of this study was to design, establish and monitor a silvo pastoral experiment on a dairy farm in the northern Atlantic region of Costa Rica. Indigenous timber species, Vochysia guatemalensis and Hyeronima alchorneoides were used together with or without the tropical pasture legume, Arachis pintoi in a split plot design with a 4 x 2 x 2 factorial arrangement. First year establishment was good for the tree component (2.3 to 10 % mortality) but poor for A. pintoi (4 to 5 % of sward). Poor legume establishment was attributed to lax grazing management and excess competition from existing Brachiaria sp. A. Pintoi was reestablished in July 1996 after an adjustment of stocking rate. This experimental project is planned for a 10 year period which corresponds to the expected rotation length for harvesting the indigenous timber species

Trapping characteristics and parametric shifts in lateral GaN HEMTs with SiO₂/AlGaN gate stacks

Recovery transients following blocking-state voltage stress are analyzed for two types of AlGaN/GaN HEMTs, one set of devices with thick AlGaN barrier layers and another with recessed-gate geometry and ALD SiO₂ gate dielectric. Results show temperature-invariant emission processes are present in both devices. Recessed-gate devices with SiO₂ dielectrics are observed to exhibit simultaneous trapping and emission processes during post-stress recovery

Homophobia and heterosexism: Spanish Physical Education teachers’ perceptions

Physical education is traditionally a heteronormative environment, despite current studies highlighting the existence of positive changes in sport towards sexual diversity. In Spain, physical education teachers’ attitudes towards sexual minorities are an under-researched area. The current study identifies physical education teachers’ perceptions towards homophobia and heterosexism in their lessons, raising questions as to whether societies are hostile or more tolerant in regards to gays and lesbians in sport. This experimental and cross-sectional descriptive research involved 170 Physical Education teachers from mixed schools, using a modified version of the original questionnaire of homophobia and heterosexism perceptions by Morrow and Gill (2003). Results show heterosexist and homophobic behavior is apparent in physical education lessons, with teachers aware of these behaviours. Furthermore, it is highlighted that students use homosexually-themed language as an instrument to discriminate against gays and lesbians. This language use is not common among teachers, although when it is present, it is clearer and more frequent amongst male teachers

Microwave energy supplied by a prototype oven prevents the spread of Fusarium wilt during the propagation of melon plantlets by seed

The re-use of propagation trays in nursery greenhouses is one of the main ways in which fusarium wilt is spread in melon crops (Cucumis melo). The causal agent of the disease is the fungus Fusarium oxysporum f. sp. melonis. This paper reports that exposing these seed trays to the energy produced by a prototype microwave oven during the commercial production of melon plantlets can prevent the spread of this pathogen with only a very small increase in production costs